U.S. patent application number 13/462569 was filed with the patent office on 2012-08-23 for methods of sequestering co2.
Invention is credited to Allen J. Bard, BRENT R. CONSTANTZ, Robert Danziger, Valentin Decker, Kasra Farsad, Miguel Fernandez, Ryan J. Gilliam, Donald W. Kirk, Sidney Omelon, Cecily Ryan, Philip Brian Tuet, J. Douglas Way, Andrew Youngs.
Application Number | 20120213688 13/462569 |
Document ID | / |
Family ID | 43009564 |
Filed Date | 2012-08-23 |
United States Patent
Application |
20120213688 |
Kind Code |
A1 |
CONSTANTZ; BRENT R. ; et
al. |
August 23, 2012 |
METHODS OF SEQUESTERING CO2
Abstract
Methods of sequestering carbon dioxide (CO.sub.2) are provided.
Aspects of the methods include precipitating a storage stable
carbon dioxide sequestering product from an
alkaline-earth-metal-containing water and then disposing of the
product, e.g., by placing the product in a disposal location or
using the product as a component of a manufactured composition.
Also provided are systems for practicing methods of the
invention.
Inventors: |
CONSTANTZ; BRENT R.;
(Portola Valley, CA) ; Youngs; Andrew; (Antelope,
CA) ; Tuet; Philip Brian; (Milpitas, CA) ;
Omelon; Sidney; (Willowdale, CA) ; Farsad; Kasra;
(San Jose, CA) ; Gilliam; Ryan J.; (San Jose,
CA) ; Decker; Valentin; (San Jose, CA) ; Kirk;
Donald W.; (Caledon, CA) ; Way; J. Douglas;
(Boulder, CO) ; Bard; Allen J.; (San Jose, CA)
; Danziger; Robert; (Carmel, CA) ; Fernandez;
Miguel; (San Jose, CA) ; Ryan; Cecily; (San
Jose, CA) |
Family ID: |
43009564 |
Appl. No.: |
13/462569 |
Filed: |
May 2, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12698741 |
Feb 2, 2010 |
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13462569 |
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12344019 |
Dec 24, 2008 |
7887694 |
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12698741 |
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PCT/US08/88242 |
Dec 23, 2008 |
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12344019 |
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PCT/US08/88246 |
Dec 23, 2008 |
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PCT/US08/88242 |
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61017405 |
Dec 28, 2007 |
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61057173 |
May 29, 2008 |
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61073319 |
Jun 17, 2008 |
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61082766 |
Jul 22, 2008 |
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61088340 |
Aug 12, 2008 |
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61088347 |
Aug 13, 2008 |
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61101626 |
Sep 30, 2008 |
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61121872 |
Dec 11, 2008 |
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Current U.S.
Class: |
423/419.1 ;
252/182.32; 264/299 |
Current CPC
Class: |
C01F 5/24 20130101; Y02W
10/37 20150501; B01D 2251/402 20130101; B01D 2257/404 20130101;
C02F 1/683 20130101; C02F 1/66 20130101; Y02W 10/33 20150501; C04B
7/367 20130101; Y02C 20/40 20200801; B01D 2251/404 20130101; B01D
2257/302 20130101; C01B 32/60 20170801; B01D 53/1493 20130101; Y02C
10/04 20130101; Y02P 20/151 20151101; Y02E 60/36 20130101; Y02P
20/133 20151101; B01D 2257/504 20130101; B01D 2257/602 20130101;
C01F 11/18 20130101; Y02C 10/06 20130101; B01D 53/62 20130101; Y02E
60/366 20130101; Y02P 40/18 20151101; B01D 53/1425 20130101; Y02P
20/152 20151101; B01D 53/1475 20130101; C01P 2004/03 20130101; B01D
53/77 20130101 |
Class at
Publication: |
423/419.1 ;
252/182.32; 264/299 |
International
Class: |
C01B 31/00 20060101
C01B031/00; C09K 3/00 20060101 C09K003/00; B29C 39/00 20060101
B29C039/00; C01B 31/24 20060101 C01B031/24 |
Claims
1-20. (canceled)
21. A method of making artificial reef structure, comprising:
treating at least a portion of flue gas from an industrial plant,
wherein said flue gas comprises carbon dioxide, with a proton
removing agent to produce a solution comprising carbonate ions;
treating said solution with alkaline-earth-metal-ions to produce a
precipitate comprising carbonate wherein said carbonate comprises
metastable carbonate; and using said precipitate to make artificial
reef structure.
22. The method of claim 21, further comprising dewatering said
precipitate to produce a slurry comprising said precipitate.
23. The method of claim 22, further comprising pouring said slurry
into a mold and allowing said slurry to solidify into the shape of
the mold.
24. The method of claim 23, further comprising depositing said mold
in a suitable ocean location to produce an artificial reef.
25. The method of claim 21, wherein said precipitate comprises
calcium carbonate, magnesium carbonate, calcium magnesium
carbonate, or combination thereof.
26. The method of claim 21, wherein said precipitate comprises
strontium in an amount ranging from 3 to 10,000 ppm.
27. The method of claim 21, wherein said alkaline-earth-metal-ions
comprise saltwater or fresh water.
28. The method of claim 27, wherein said saltwater is brackish
water, sea water, or brine.
29. The method of claim 21, wherein said alkaline-earth-metal-ions
are obtained from a mineral selected from the group consisting of
serpentine, olivine, and combination thereof.
30. The method of claim 21, wherein said alkaline-earth-metal-ions
comprise calcium ions, magnesium ions, silica ions, or combination
thereof.
31. The method of claim 21, wherein said solution further comprises
bicarbonate ions.
32. The method of claim 21, wherein said proton removing agent
raises a pH of said solution to 9.5 or higher.
33. The method of claim 21, wherein said proton removing agent is
selected from the group consisting of oxide, hydroxide, carbonate,
mineral, ash, natural body of alkaline water, slag, and combination
thereof.
34. The method of claim 33, wherein said hydroxide is made using an
electrochemical process.
35. The method of claim 21, wherein said industrial plant is
selected from the group consisting of power plants, chemical
processing plants, mechanical processing plants, refineries, cement
plants, steel plants, other industrial plants that produce CO.sub.2
as a byproduct of fuel combustion or other processing step, and
combination thereof.
36. The method of claim 21, wherein said artificial reef structure
has a negative carbon footprint.
37. The method of claim 21, wherein about 10 to 100% of the carbon
present in the artificial reef structure is from the carbon dioxide
source.
38. The method of claim 21, wherein said metastable carbonate
comprises vaterite.
39. The method of claim 21, wherein said precipitate is dried
before making the artificial reef structure.
40. An artificial reef structure formed by the method of claim 21.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] Pursuant to 35 U.S.C. .sctn.119 (e), this application claims
priority to the filing dates of: U.S. Provisional Patent
Application Ser. No. 61/017,405 filed on Dec. 28, 2007; U.S.
Provisional Patent Application Ser. No. 61/057,173 filed on May 29,
2008; U.S. Provisional Patent Application 61/073,319 filed on Jun.
17, 2008; U.S. Provisional Patent Application 61/082,766 filed on
Jul. 22, 2008; U.S. Provisional Patent Application Ser. No.
61/088,340 filed on Aug. 12, 2008; U.S. Provisional Patent
Application Ser. No. 61/088,347 filed on Aug. 13, 2008; U.S.
Provisional Patent Application Ser. No. 61/101,626 filed on Sep.
30, 2008; and U.S. Provisional Patent Application No. 61/121,872
filed on Dec. 11 ,2008; and Pursuant to 35 U.S.C. .sctn.120, this
application claims priority to the filing dates of PCT Application
No. PCT/US08/88242 entitled "Low-Energy Electrochemical Hydroxide
System and Method," filed on Dec. 23, 2008, and PCT Application
No.PCT/US08/88246 entitled "Low-Energy Electrochemical Proton
Transfer System and Method," filed on Dec. 23, 2008; the
disclosures of which applications are herein incorporated by
reference.
INTRODUCTION
[0002] Carbon dioxide (CO.sub.2) emissions have been identified as
a major contributor to the phenomenon of global warming and ocean
acidification. CO.sub.2 is a by-product of combustion and it
creates operational, economic, and environmental problems. It is
expected that elevated atmospheric concentrations of CO.sub.2 and
other greenhouse gases will facilitate greater storage of heat
within the atmosphere leading to enhanced surface temperatures and
rapid climate change. CO.sub.2 has also been interacting with the
oceans driving down the pH toward 8.0 from 8.2. CO.sub.2 monitoring
has shown atmospheric CO.sub.2 has risen from approximately 280 ppm
in the 1950s to approximately 380 ppm today, and is expect to
exceed 400 ppm in the next decade. The impact of climate change
will likely be economically expensive and environmentally
hazardous. Reducing potential risks of climate change will require
sequestration of atmospheric CO.sub.2.
[0003] Many types of industrial plants (such as cement refineries,
steel mills and power plants) combust various carbon-based fuels,
such as fossil fuels and syngases. Fossil fuels that are employed
include coal, natural gas, oil, used tires, municipal waste,
petroleum coke and biofuels. Fuels are also derived from tar sands,
oil shale, coal liquids, and coal gasification and biofuels that
are made via syngas. CO.sub.2 concentrations in the exhaust gases
of various fuels vary from a few % to nearly pure CO.sub.2. Cement
plants are a major source of CO.sub.2 emissions, from both the
burning of fossil fuels and the CO.sub.2 released from calcination
which changes limestone, shale and other ingredients to Portland
cement. Similarly, power plants which utilize combustion of
carbon-based fuels to generate electricity are also a major source
of CO.sub.2 emissions. Many industrial plants also produce several
other pollutants including NOx, SOx, VOCx, particulates and
mercury, in addition to wasted heat. Furthermore, many industrial
plants can produce materials such as cement kiln dust from a cement
production plant or ash from coal-fired power plants, that must
sometimes be disposed in hazardous material landfill sites.
[0004] Methods proposed to separate CO.sub.2 from flue gas, contain
it and store CO.sub.2 include storage in geological formations,
injection into the deep-ocean, and uptake by phytoplankton via
fertilization of the ocean. The limited capacity and duration,
expense, and environmental outcomes of these methods are largely
unresolved and may prohibit their utility.
SUMMARY
[0005] Methods of sequestering carbon dioxide (CO.sub.2) are
provided. Aspects of the methods include precipitating a storage
stable carbon dioxide sequestering product from an
alkaline-earth-metal-containing water and then disposing of the
product, e.g., by placing the product in a disposal location or
using the product as a component of a manufactured item, such as a
building material. Also provided are systems for practicing methods
of the invention.
BRIEF DESCRIPTION OF THE FIGURES
[0006] FIG. 1 provides a schematic diagram of a CO.sub.2
sequestration method according to one embodiment of the
invention.
[0007] FIG. 2 provides a schematic diagram of a CO.sub.2
sequestration system according to another embodiment of the
invention.
[0008] FIG. 3 provides a schematic diagram of power plant that is
integrated with a CO.sub.2 sequestration system according to an
embodiment of the invention.
[0009] FIG. 4 provides a schematic diagram of a portland cement
plant.
[0010] FIG. 5 provides a schematic diagram of a cement plant
co-located with a precipitation plant according to one embodiment
of the invention
[0011] FIG. 6 provides a schematic of a cement plant which does not
require a mined limestone feedstock according to one embodiment of
the invention
[0012] FIG. 7A provides a diagram of one embodiment of a
bi-electrode apparatus for removing protons form solutions
electrochemically.
[0013] FIG. 7B provides a diagram of one embodiment of a
bi-electrode apparatus for removing protons form solutions
electrochemically.
[0014] FIG. 8 provides a diagram of one embodiment of a low-voltage
apparatus for producing hydroxide electrochemically.
[0015] FIG. 9 provides a diagram of another embodiment of a
low-voltage apparatus for producing hydroxide
electrochemically.
[0016] FIG. 10 provides a diagram of another embodiment of a
low-voltage apparatus for producing hydroxide
electrochemically.
[0017] FIG. 11 provides a schematic of a system according to one
embodiment of the invention.
[0018] FIGS. 12A, 12B and 12C provide schematics of a system
according to one embodiment of the invention.
[0019] FIGS. 13A and 13B provide pictures of precipitate of the
invention.
[0020] FIG. 14 provides a picture of amorphous precipitate of the
invention.
[0021] FIG. 15 provides graphical results of a CO.sub.2 absorption
experiment reported in the Experimental Section, below.
RELEVANT CHEMICAL REACTIONS
[0022] The methods and systems of the invention utilize processes
summarized by the following chemical reactions: [0023] (1)
Combustion of a carbon-containing fuel source in liquid, gas, or
solid phase forms gaseous carbon dioxide:
[0023] C+O.sub.2(g).fwdarw.CO.sub.2(g) [0024] (2) Contacting the
source of carbon dioxide with a water source solvates the carbon
dioxide to give an aqueous solution of carbon dioxide:
[0024] CO.sub.2(g).fwdarw.CO.sub.2(aq) [0025] (3) Carbon dioxide
dissolved in water establishes equilibrium with aqueous carbonic
acid:
[0025] CO.sub.2(aq)+H.sub.2OH.sub.2CO.sub.3(aq) [0026] (4) Carbonic
acid is a weak acid which dissociates in two steps, where the
equilibrium balance is determined in part by the pH of the
solution, with, generally, pHs below 8-9 favoring bicarbonate
formation and pHs above 9-10 favoring carbonate formation. In the
second step, a hydroxide source may be added to increase
alkalinity:
[0026] H.sub.2CO.sub.3+2
H.sub.2OH.sub.3O.sup.+(aq)+HCO.sub.3.sup.-(aq)
HCO.sub.3.sup.-(aq)+OH.sup.-(aq)H.sub.2O+CO.sub.3.sup.2-(aq)
[0027] Reaction of elemental metal cations from Group IIA with the
carbonate anion forms a metal carbonate precipitate:
mX(aq)+nCO.sub.3.sup.2-X.sub.m(CO.sub.3).sub.n(s) [0028] wherein X
is any element or combination of elements that can chemically bond
with a carbonate group or its multiple and m and n are
stoichiometric positive integers.
DETAILED DESCRIPTION
[0029] Methods of sequestering carbon dioxide (CO.sub.2) are
provided. Aspects of the methods include precipitating a storage
stable carbon dioxide sequestering product from an
alkaline-earth-metal-containing water and then disposing of the
product, e.g., by placing the product in a disposal location or
using the product as a component of a manufactured item, such as a
building material. Also provided are systems for practicing methods
of the invention.
[0030] Before the present invention is described in greater detail,
it is to be understood that this invention is not limited to
particular embodiments described, as such may, of course, vary. It
is also to be understood that the terminology used herein is for
the purpose of describing particular embodiments only, and is not
intended to be limiting, since the scope of the present invention
will be limited only by the appended claims.
[0031] Where a range of values is provided, it is understood that
each intervening value, to the tenth of the unit of the lower limit
unless the context clearly dictates otherwise, between the upper
and lower limit of that range and any other stated or intervening
value in that stated range, is encompassed within the invention.
The upper and lower limits of these smaller ranges may
independently be included in the smaller ranges and are also
encompassed within the invention, subject to any specifically
excluded limit in the stated range. Where the stated range includes
one or both of the limits, ranges excluding either or both of those
included limits are also included in the invention.
[0032] Certain ranges are presented herein with numerical values
being preceded by the term "about." The term "about" is used herein
to provide literal support for the exact number that it precedes,
as well as a number that is near to or approximately the number
that the term precedes. In determining whether a number is near to
or approximately a specifically recited number, the near or
approximating unrecited number may be a number which, in the
context in which it is presented, provides the substantial
equivalent of the specifically recited number.
[0033] Unless defined otherwise, all technical and scientific terms
used herein have the same meaning as commonly understood by one of
ordinary skill in the art to which this invention belongs. Although
any methods and materials similar or equivalent to those described
herein can also be used in the practice or testing of the present
invention, representative illustrative methods and materials are
now described.
[0034] All publications and patents cited in this specification are
herein incorporated by reference as if each individual publication
or patent were specifically and individually indicated to be
incorporated by reference and are incorporated herein by reference
to disclose and describe the methods and/or materials in connection
with which the publications are cited. The citation of any
publication is for its disclosure prior to the filing date and
should not be construed as an admission that the present invention
is not entitled to antedate such publication by virtue of prior
invention. Further, the dates of publication provided may be
different from the actual publication dates which may need to be
independently confirmed.
[0035] It is noted that, as used herein and in the appended claims,
the singular forms "a", "an", and "the" include plural referents
unless the context clearly dictates otherwise. It is further noted
that the claims may be drafted to exclude any optional element. As
such, this statement is intended to serve as antecedent basis for
use of such exclusive terminology as "solely," "only" and the like
in connection with the recitation of claim elements, or use of a
"negative" limitation.
[0036] As will be apparent to those of skill in the art upon
reading this disclosure, each of the individual embodiments
described and illustrated herein has discrete components and
features which may be readily separated from or combined with the
features of any of the other several embodiments without departing
from the scope or spirit of the present invention. Any recited
method can be carried out in the order of events recited or in any
other order which is logically possible.
[0037] In further describing the subject invention, the methods of
CO.sub.2 sequestration according to embodiments of the invention
are described first in greater detail. Next systems that find use
in practicing various embodiments of the methods of the invention
are reviewed.
Methods of CO.sub.2 Sequestration
[0038] As reviewed above, the invention provides methods of
CO.sub.2 sequestration. By "CO.sub.2 sequestration" is meant the
removal or segregation of an amount of CO.sub.2 from an
environment, such as the Earth's atmosphere or a gaseous waste
stream produced by an industrial plant, so that some or all of the
CO.sub.2 is no longer present in the environment from which it has
been removed. CO.sub.2 sequestering methods of the invention
sequester CO.sub.2 producing a storage stable carbon dioxide
sequestering product from an amount of CO.sub.2, such that the
CO.sub.2 from which the product is produced is then sequestered in
that product. The storage stable CO.sub.2 sequestering product is a
storage stable composition that incorporates an amount of CO.sub.2
into a storage stable form, such as an above-ground storage or
underwater storage stable form, so that the CO.sub.2 is no longer
present as, or available to be, a gas in the atmosphere. As such,
sequestering of CO.sub.2 according to methods of the invention
results in prevention of CO.sub.2 gas from entering the atmosphere
and allows for long term storage of CO.sub.2 in a manner such that
CO.sub.2 does not become part of the atmosphere.
[0039] Embodiments of methods of the invention are negative carbon
footprint methods. By "negative carbon footprint" is meant that the
amount by weight of CO.sub.2 that is sequestered (e.g., through
conversion of CO.sub.2 to carbonate) by practice of the methods is
greater that the amount of CO.sub.2 that is generated (e.g.,
through power production, base production, etc) to practice the
methods. In some instances, the amount by weight of CO.sub.2 that
is sequestered by practicing the methods exceeds the amount by
weight of CO.sub.2 that is generated in practicing the methods by 1
to 100%, such as 5 to 100%, including 10 to 95%, 10 to 90%, 10 to
80%, 10 to 70%, 10 to 60%, 10 to 50%, 10 to 40%, 10 to 30%, 10 to
20%, 20 to 95%, 20 to 90%, 20 to 80%, 20 to 70%, 20 to 60%, 20 to
50%, 20 to 40%, 20 to 30%, 30 to 95%, 30 to 90%, 30 to 80%, 30 to
70%, 30 to 60%, 30 to 50%, 30 to 40%, 40 to 95%, 40 to 90%, 40 to
80%, 40 to 70%, 40 to 60%, 40 to 50%, 50 to 95%, 50 to 90%, 50 to
80%, 50 to 70%, 50 to 60%, 60 to 95%, 60 to 90%, 60 to 80%, 60 to
70%, 70 to 95%, 70 to 90%, 70 to 80%, 80 to 95%, 80 to 90%, and 90
to 95%, In some instances, the amount by weight of CO.sub.2 that is
sequestered by practicing the methods exceeds the amount by weight
of CO.sub.2 that is generated in practicing the methods by 5% or
more, by 10% or more, by 15% or more, by 20% or more, by 30% or
more, by 40% or more, by 50% or more, by 60% or more, by 70% or
more, by 80% or more, by 90% or more, by 95% or more.
[0040] As summarized above, the methods of invention produce a
precipitated storage stable carbon dioxide sequestering product,
such that the carbon dioxide is sequestered in a "storage stable
form". By "storage stable form" is meant a form of matter that can
be stored, for example above ground or underwater, under exposed
conditions (for example, open to the atmosphere, underwater
environment, etc.), without significant, if any, degradation for
extended durations, e.g., 1 year or longer, 5 years or longer, 10
years or longer, 25 years or longer, 50 years or longer, 100 years
or longer, 250 years or longer, 1000 years or longer, 10,000 years
or longer, 1,000,000 years or longer, or 100,000,000 years or
longer, or 1,000,000,000 years or longer. As the storage stable
form undergoes little if any degradation while stored above ground
under normal rain water pH, the amount of degradation if any as
measured in terms of CO.sub.2 gas release from the product will not
exceed 5%/year, and in certain embodiments will not exceed 1%/year
or 0.001% per year. The above-ground storage stable forms are
storage stable under a variety of different environment conditions,
e.g., from temperatures ranging from -100.degree. to 600.degree.
C., humidity ranging from 0% to 100% where the conditions may be
calm, windy or stormy. In some instances, the storage stable
product is employed as a component of a manufactured item, such as
a building material, e.g., component of a cement or concrete. In
these embodiments, the product is still a storage stable CO.sub.2
sequestering product, as use of the product in the manufactured
item (such as building material) does not result in release of
CO.sub.2 from the product. In certain embodiments, the carbonate
compounds of the precipitate when combined with portland cement may
dissolve and combine with compounds of the portland cement, without
releasing CO.sub.2.
[0041] The amount of carbon present in storage stable carbon
dioxide sequestering products produced by methods of the invention
may vary. In some instances, the amount of carbon that is present
in the precipitated product (as determined by using protocols
described in greater detail below, such as isotopic analysis, e.g.,
.sup.13C isotopic analysis) in the product ranges from 1% to 15%
(w/w), such as 5 to 15% (w/w), and including 5 to 14% (w/w), 5 to
13% (w/w), 6 to 14% (w/w), 6 to 12% (w/w), and 7 to 12% (w/w).
Where the method employed to produce the precipitated product
includes contacting a water with a source of CO.sub.2 (for example
as described in greater detail below), a substantial amount of the
carbon may be carbon that originated (as determined by protocols
described in greater detail below) in the source of CO.sub.2. By
substantial amount is meant that 10 to 100%, such as 50 to 100% and
including 90 to 100% of the carbon present in the storage stable
carbon dioxide sequestering product is from the carbon dioxide
source (such as a carbon dioxide containing gaseous stream). In
some instances, the amount of carbon present in the product that is
traceable to the carbon dioxide source is 50% or more, 60% or more,
70% or more, 80% or more, 90% or more, 95% or more, 99% or more,
including 100%.
[0042] In certain embodiments, the CO.sub.2 sequestering product
can store about 50 tons or more of CO.sub.2, such as about 100 tons
or more of CO.sub.2, including 150 tons or more of CO.sub.2, for
instance about 200 tons or more of CO.sub.2, such as about 250 tons
or more of CO.sub.2, including about 300 tons or more of CO.sub.2,
such as about 350 tons or more of CO.sub.2, including 400 tons or
more of CO.sub.2, for instance about 450 tons or more of CO.sub.2,
such as about 500 tons or more of CO.sub.2, including about 550
tons or more of CO.sub.2, such as about 600 tons or more of
CO.sub.2, including 650 tons or more of CO.sub.2, for instance
about 700 tons or more of CO.sub.2, for every 1000 tons of CO.sub.2
sequestering product, e.g., a material to be used in the built
environment such as cement or aggregate, produced. Thus, in certain
embodiments, the CO.sub.2 sequestering product comprises about 5%
or more of CO.sub.2, such as about 10% or more of CO.sub.2,
including about 25% or more of CO.sub.2, for instance about 50% or
more of CO.sub.2, such as about 75% or more of CO.sub.2, including
about 90% or more of CO.sub.2.
[0043] Storage stable CO.sub.2 sequestering products produced by
methods of the invention may include carbonate compounds that, upon
combination with fresh water, dissolve and produce different
minerals that are more stable in fresh water than compounds of the
initial precipitate product composition. (Although the compounds of
the initial precipitate product composition may dissolve upon
combination with freshwater and then produce different components,
CO.sub.2 gas is not liberated in significant amounts, or in some
cases at all, in any such reaction). The compounds of the initial
precipitate product composition may be ones that are more stable in
salt water than they are in freshwater, such that they may be
viewed as saltwater metastable compounds. The amount of carbonate
in the product, as determined by coulometry using the protocol
described in coulometric titration, is 40% or higher, such as 70%
or higher, including 80% or higher.
[0044] The storage stable precipitated product may include one or
more different carbonate compounds, such as two or more different
carbonate compounds, e.g., three or more different carbonate
compounds, five or more different carbonate compounds, etc.,
including non-distinct, amorphous carbonate compounds. Carbonate
compounds of precipitated products of the invention may be
compounds having a molecular formulation X.sub.m(CO.sub.3).sub.n
where X is any element or combination of elements that can
chemically bond with a carbonate group or its multiple, wherein X
is in certain embodiments an alkaline earth metal (elements found
in column IIA of the periodic table of elements) and not an alkali
metal (elements found in column IA of the periodic table of
elements); wherein m and n are stoichiometric positive integers.
These carbonate compounds may have a molecular formula of
X.sub.m(CO.sub.3).sub.n.H.sub.2O, where there are one or more
structural waters in the molecular formula.
[0045] The carbonate compounds may be amorphous or crystalline. The
particular mineral profile, i.e., the identity of the different
types of different carbonate minerals and the amounts of each, in
the carbonate compound composition may vary and will be dependent
on the particular nature of the water source from which it is
derived, as well as the particular conditions employed to derive
it.
[0046] As indicated above, in some embodiments of the invention,
the carbonate compounds of the compositions are metastable
carbonate compounds that are more stable in saltwater than in
freshwater, such that upon contact with fresh water of any pH they
dissolve and reprecipitate into other fresh water stable minerals.
In certain embodiments, the carbonate compounds are present as
small particles, e.g., with particle sizes ranging from 0.1 microns
to 100 microns, e.g., 1 to 100 microns, or 10 to 100 microns, or 50
to 100 microns, in some embodiments 0.5 to 10 microns, as
determined by Scanning electron microscopy. In some embodiments,
the particle sizes exhibit a bimodal or multi-modal distribution.
In certain embodiments, the particles have a high surface are,
e.g., ranging from 0.5 to 100 m.sup.2/gm, 0.5 to 50 m.sup.2/gm,
such as from 0.5 to 2.0 m.sup.2/gm, as determined by Brauner,
Emmit, & Teller (BET) Surface Area Analysis. In some
embodiments, the CO.sub.2 sequestering products produced by methods
of the invention may include rod-shaped crystals and amorphous
solids. The rod-shaped crystals may vary in structure, and in
certain embodiments have length to diameter ratio ranging from 500
to 1, such as 10 to 1. In certain embodiments, the length of the
crystals ranges from 0.5 .mu.m to 500 .mu.m, such as from 5 .mu.m
to 100 .mu.m. In yet other embodiments, substantially completely
amorphous solids are produced.
[0047] The carbonate compounds of the precipitated products may
include a number of different cations, such as but not limited to:
calcium, magnesium, sodium, potassium, sulfur, boron, silicon,
strontium, and combinations thereof. Of interest are carbonate
compounds of divalent metal cations, such as calcium and magnesium
carbonate compounds. Specific carbonate compounds of interest
include, but are not limited to: calcium carbonate minerals,
magnesium carbonate minerals and calcium magnesium carbonate
minerals. Calcium carbonate minerals of interest include, but are
not limited to: calcite (CaCO.sub.3), aragonite (Ca CO.sub.3),
vaterite (Ca CO.sub.3), ikaite (Ca CO.sub.3.6H.sub.2O), and
amorphous calcium carbonate (CaCO.sub.3.nH.sub.2O). Magnesium
carbonate minerals of interest include, but are not limited to
magnesite (Mg CO.sub.3), barringtonite (Mg CO.sub.3.2H.sub.2O),
nesquehonite (Mg CO.sub.3.3H.sub.2O), lanfordite (Mg
CO.sub.3.5H.sub.2O), hydromagnisite, and amorphous magnesium
calcium carbonate (MgCO.sub.3.nH.sub.2O). Calcium magnesium
carbonate minerals of interest include, but are not limited to
dolomite (CaMg CO.sub.3), huntitte (CaMg (CO.sub.3).sub.4) and
sergeevite (Ca.sub.2Mg.sub.11(CO.sub.3).sub.13.H.sub.2O). The
carbon compounds of the product may include one or more waters of
hydration, or may be anhydrous.
[0048] In some instances, the amount by weight of magnesium
carbonate compounds in the precipitate exceeds the amount by weight
of calcium carbonate compounds in the precipitate. For example, the
amount by weight of magnesium carbonate compounds in the
precipitate may exceed the amount by weight calcium carbonate
compounds in the precipitate by 5% or more, such as 10% or more,
15% or more, 20% or more, 25% or more, 30% or more. In some
instances, the weight ratio of magnesium carbonate compounds to
calcium carbonate compounds in the precipitate ranges from 1.5-5 to
1, such as 2-4 to 1 including 2-3 to 1.
[0049] In some instances, the precipitated product may include
hydroxides, such as divalent metal ion hydroxides, e.g., calcium
and/or magnesium hydroxides. The principal calcium hydroxide
mineral of interest is portlandite Ca(OH).sub.2, and amorphous
hydrated analogs thereof. The principal magnesium hydroxide mineral
of interest is brucite Mg(OH).sub.2, and amorphous hydrated analogs
thereof.
[0050] As the precipitated products are derived from an
alkaline-earth-metal-ion-containing water source, they will include
one or more components that are present in the water source from
which they are precipitated and identify the compositions that come
from the water source, where these identifying components and the
amounts thereof are collectively referred to herein as a water
source identifier. For example, if the water source is sea water,
identifying compounds that may be present in carbonate compound
compositions include, but are not limited to: chloride, sodium,
sulfur, potassium, bromide, silicon, strontium and the like. Any
such source-identifying or "marker" elements are generally present
in small amounts, e.g., in amounts of 20,000 ppm or less, such as
amounts of 2000 ppm or less. In certain embodiments, the "marker"
compound is strontium, which may be present in the precipitate
incorporated into the aragonite lattice, and make up 10,000 ppm or
less, ranging in certain embodiments from 3 to 10,000 ppm, such as
from 5 to 5000 ppm, including 5 to 1000 ppm, e.g., 5 to 500 ppm,
including 5 to 100 ppm. Another "marker" compound of interest is
magnesium, which may be present in amounts of up to 20% mole
substitution for calcium in carbonate compounds. The water source
identifier of the compositions may vary depending on the particular
water source, e.g., saltwater employed to produce the water-derived
carbonate composition. In certain embodiments, the calcium
carbonate content of the precipitate is 25% w/w or higher, such as
40% w/w or higher, and including 50% w/w or higher, e.g., 60% w/w.
The carbonate compound composition has, in certain embodiments, a
calcium/magnesium ratio that is influenced by, and therefore
reflects, the water source from which it has been precipitated. In
certain embodiments, the calcium/magnesium molar ratio ranges from
10/1 to 1/5 Ca/Mg, such as 5/1 to 1/3 Ca/Mg. In certain
embodiments, the carbonate composition is characterized by having a
water source identifying carbonate to hydroxide compound ratio,
where in certain embodiments this ratio ranges from 100 to 1, such
as 10 to 1 and including 1 to 1.
[0051] In methods of the invention, an
alkaline-earth-metal-ion-containing water is subjected to carbonate
compound precipitation conditions to produce the precipitated
storage stable carbon dioxide sequestering product. The
alkaline-earth-metal-ion-containing water may vary depending on the
particular method of sequestration that is to be performed. One
type of water of interest is saltwater. The term "saltwater" is
employed in its conventional sense to refer a number of different
types of aqueous fluids other than fresh water, where the term
"saltwater" includes brackish water, sea water and brine (including
man-made brines, such as geothermal plant wastewaters, desalination
waste waters, etc, as well as natural brines such as surface brines
found in bodies of water on the surface of the earth and deep
brines, found underneath the earth), as well as other salines
having a salinity that is greater than that of freshwater. The term
"brine" refers to water saturated or nearly saturated with salt and
has a salinity that is 50 ppt (parts per thousand) or greater.
Brackish water is water that is saltier than fresh water, but not
as salty as seawater, having a salinity ranging from 0.5 to 35 ppt.
Seawater is water from a sea or ocean and has a salinity ranging
from 35 to 50 ppt. The saltwater source from which the carbonate
mineral composition of the cements of the invention is derived may
be a naturally occurring source, such as a sea, ocean, lake, swamp,
estuary, lagoon, deep brine, alkaline lakes, inland seas, etc., or
a man-made source.
[0052] Another type of water that may be employed in methods of the
invention is freshwater. Any suitable freshwater source may be
used, including sources ranging from relatively free of minerals to
sources rich in minerals. Freshwater sources of interest include
mineral rich freshwater sources. Mineral rich freshwater sources of
interest may be naturally occurring, such as hard waters or lakes
or inland seas, for example alkaline lakes or inland seas (such as
Lake Van in Turkey) which may provide a source of alkalinity for
removal of protons and/or pH shift and/or a source of minerals to
be precipitated with the CO.sub.2; such lakes are described further
elsewhere herein. Mineral rich freshwater sources of interest may
also be man-made, e.g., by producing a mineral rich water from a
soft water. For example, a mineral poor (soft) water may be
contacted with a source of desired ions, such as a calcium and/or
magnesium ion source, to produce a mineral rich water that is
suitable for use methods of the invention.
[0053] As indicated above, the alkaline-earth-metal-containing
water employed in methods of the invention may be a water that is
obtained from naturally occurring sources. Alternatively, the water
may be one that prepared from an initial water, for example by
adding one or more minerals to the water. As such, some methods
include preparing the alkaline-earth-metal containing water from an
initial water by adding to the initial water a source of one or
more divalent metal ions, such as magnesium, calcium, etc. Sources
of magnesium ions include, but are not limited, magnesium
hydroxides, magnesium oxides, etc. sources of calcium ions include,
but are not limited to, calcium hydroxides, calcium oxides, etc.
Both naturally occurring and man-made sources of such ions may be
employed. Specific naturally occurring sources of such ions
include, but are not limited to: mafic minerals, such as olivine,
serpentine, periodotite, talc, etc., and the like. Addition of
supplementary magnesium (Mg) ions to the source water, e.g.,
seawater, prior to precipitation increases yields of precipitate as
well as affects the composition of precipitate, providing a means
for increasing CO.sub.2 sequestration by utilizing minerals such
as, but not limited to, Olivine, Serpentine and Mg(OH).sub.2
(Brucite). The particular Mg ion source may be naturally occurring
or man-made sources, and may be pure with respect to the Mg mineral
or impure, e.g., be a composition made up of the Mg mineral of
interest and other minerals and components.
[0054] In some methods of the invention, the water (such as salt
water or mineral rich water) is not contacted with a source of
CO.sub.2 prior to subjecting the water to precipitation conditions.
In these methods, the water will have an amount of CO.sub.2
associated with it, e.g., in the form of bicarbonate ion, which has
been obtained from the environment to which the water has been
exposed prior to practice of the method. Subjecting the water to
precipitate conditions of the invention results in conversion of
this CO.sub.2 into a storage stable precipitate, and therefore
sequestration of the CO.sub.2. When the water subject to processes
of the invention is again exposed to its natural environment, such
as the atmosphere, more CO.sub.2 from the atmosphere will be taken
up by the water resulting in a net removal of CO.sub.2 from the
atmosphere and incorporation of a corresponding amount of CO.sub.2
into a storage stable product, where the mineral rich freshwater
source may be contacted with a source of CO.sub.2, e.g., as
described in greater detail below. Embodiments of these methods may
be viewed as methods of sequestering CO.sub.2 gas directly from the
Earth's atmosphere. Embodiments of the methods are efficient for
the removal of CO.sub.2 from the Earth's atmosphere. For example,
embodiments of the methods are configured to remove CO.sub.2 from
saltwater at a rate of 0.025 M or more, such as 0.05 M or more,
including 0.1 M or more per gallon of saltwater.
[0055] It will be appreciated by those of skill in the art that,
although industrial waste gas offers a relatively concentrated
source of CO.sub.2, the methods and systems of the invention are
also applicable to removing CO.sub.2 from less concentrated
sources, e.g., atmospheric air, which contains a much lower
concentration of CO.sub.2 than, e.g., flue gas. Thus, in some
embodiments the methods and systems of the invention encompass
decreasing the concentration of CO.sub.2 in atmospheric air by
producing a stable precipitate, using the procedures outlined
herein. In these cases the concentration of CO.sub.2 in the
atmospheric air may be decreased by 10% or more, 20% or more, 30%
or more, 40% or more, 50% or more, 60% or more, 70% or more, 80% or
more, 90% or more, 95% or more, 99% or more, 99.9% or more, or
99.99%. Such decreases in atmospheric CO.sub.2 may be accomplished
with yields as described herein, or with lower yields, and may be
accomplished in one precipitation step or in a series of
precipitation steps.
[0056] In some embodiments, a source of CO.sub.2 is contacted with
an alkaline-earth-metal containing water at some point during the
method, such as before, during or even after the water has been
subjected to precipitation conditions of the invention. The source
of CO.sub.2 that is contacted with the alkaline-earth-metal-ion
containing water in these embodiments may be any convenient
CO.sub.2 source. The CO.sub.2 source may be a liquid, solid (e.g.,
dry ice), a supercritical fluid, or gaseous CO.sub.2 source.
[0057] In certain embodiments, the CO.sub.2 source is a gaseous
CO.sub.2 source. This gaseous CO.sub.2 source is, in certain
instances, a waste feed from an industrial plant. The nature of the
industrial plant may vary in these embodiments, where industrial
plants of interest include power plants, chemical processing
plants, mechanical processing plants, refineries, cement plants,
steel plants, and other industrial plants that produce CO.sub.2 as
a byproduct of fuel combustion or other processing step (such as
calcination by a cement plant). By waste feed is meant a stream of
gas (or analogous stream) that is produced as a byproduct of an
active process of the industrial plant. The gaseous stream may be
substantially pure CO.sub.2 or a multi-component gaseous stream
that includes CO.sub.2 and one or more additional gases.
Multi-component gaseous streams (containing CO.sub.2) that may be
employed as a CO.sub.2 source in embodiments of the subject methods
include both reducing, e.g., syngas, shifted syngas, natural gas,
and hydrogen and the like, and oxidizing condition streams, e.g.,
flue gases from combustion. Particular multi-component gaseous
streams of interest that may be treated according to the subject
invention include: oxygen containing combustion industrial plant
flue gas, turbo charged boiler product gas, coal gasification
product gas, shifted coal gasification product gas, anaerobic
digester product gas, wellhead natural gas stream, reformed natural
gas or methane hydrates and the like.
[0058] A variety of different gaseous waste streams may be treated
according to methods of the invention in order to sequester
CO.sub.2. Gaseous waste streams of interest have, in certain
embodiments, CO.sub.2 present in amounts of 200 ppm to 1,000,000
ppm, such as 200,000 ppm to 1000 ppm and including 200,000 ppm to
2000 ppm, for example 130,000 ppm to 2000 ppm. The waste streams
may include one or more additional components, e.g., water, NOx
(mononitrogen oxides; NO and NO.sub.2), SOx (monosulfur oxides; SO,
SO.sub.2 and SO.sub.3), VOC (Volatile organic compounds), mercury
and particulates (particulate matter, particles of solid or liquid
suspended in a gas).
[0059] The waste streams may be produced from a variety of
different types of industrial plants. Of interest in certain
embodiments are waste streams produced by industrial plants that
combust fossil fuels, e.g., coal, oil, natural gas, as well as
man-made fuel products of naturally occurring organic fuel
deposits, such as but not limited to tar sands, heavy oil, oil
shale, etc. In certain embodiments, power plants are pulverized
coal power plants, supercritical coal power plants, mass burn coal
power plants, fluidized bed coal power plants, gas or oil-fired
boiler and steam turbine power plants, gas or oil-fired boiler
simple cycle gas turbine power plants, and gas or oil-fired boiler
combined cycle gas turbine power plants. Of interest in certain
embodiments are waste streams produced by power plants that combust
syngas, i.e., gas that is produced by the gasification of organic
matter, e.g., coal, biomass, etc., where in certain embodiments
such plants are integrated gasification combined cycle (IGCC)
plants. Of interest in certain embodiments are waste streams
produced by Heat Recovery Steam Generator (HRSG) plants.
[0060] In some embodiments of the invention substantially 100% of
the CO.sub.2 contained in a flue gas from a power plant is
sequestered as a stable mineral; this may be done in a single
precipitation step or in multiple precipitation steps, and may
further involve other processes for sequestering CO.sub.2, e.g., as
the concentration of CO.sub.2 is decreased in the flue gas, more
energy-intensive processes that be prohibitive in energy
consumption for removing all of the original CO.sub.2 in the gas
may become practical in removing the final CO.sub.2 in the gas.
Thus, in some embodiments, the gas entering the power plant
(ordinary atmospheric air) may contain a concentration of CO.sub.2
that is greater than the concentration of CO.sub.2 in the flue gas
exiting the plant that has been treated by the processes and
systems of the invention. Hence, in some embodiments, the methods
and systems of the invention encompass a method comprising
supplying a gas, e.g., atmospheric air, to a power plant, where the
gas comprises CO.sub.2; treating the gas in the power plant, e.g.,
by combustion of fossil fuel to consume O.sub.2 and to produce
CO.sub.2 then treating exhaust gas to remove CO.sub.2; and
releasing gas from the power plant, where the gas released from the
power plant has a lower CO.sub.2 content than the gas supplied to
the power plant. In some embodiments, the gas released from the
power plant contains at least 10% less CO.sub.2, or at least 20%
less CO.sub.2, or at least 30% less CO.sub.2, or at least 40% less
CO.sub.2, or at least 50% less CO.sub.2, or at least 60% less
CO.sub.2, or at least 70% less CO.sub.2, or at least 80% less
CO.sub.2, or at least 90% less CO.sub.2, or at least 95% less
CO.sub.2, or at least 99% less CO.sub.2, or at least 99.5% less
CO.sub.2, or at least 99.9% less CO.sub.2, than the gas entering
the power plant; in some embodiments the gas entering the power
plant is atmospheric air and the gas exiting the power plant is
treated flue gas.
[0061] Waste streams of interest also include waste streams
produced by cement plants. Cement plants whose waste streams may be
employed in methods of the invention include both wet process and
dry process plants, which plants may employ shaft kilns or rotary
kilns, and may include pre-calciners. Each of these types of
industrial plants may burn a single fuel, or may burn two or more
fuels sequentially or simultaneously.
[0062] A waste stream of interest is industrial plant exhaust gas,
e.g., a flue gas. By "flue gas" is meant a gas that is obtained
from the products of combustion from burning a fossil or biomass
fuel that are then directed to the smokestack, also known as the
flue of an industrial plant. In addition to CO.sub.2 generated by
the burning of fuels, CO.sub.2 can also be released as a result of
other industrial processing (e.g., calcination of minerals in a
cement plant). The composition of the flue gas may vary. In certain
embodiments, the amount of CO.sub.2 in the flue gas may range from
350 ppm to 400,000 ppm, such as 2000 ppm to 200,000 ppm and
including 2000 ppm to 180,000 ppm. Other components may also be
present in the flue gas, e.g., water, NOx, SOx, VOC, mercury and
particulates. The temperature of the flue gas may vary, e.g., from
0.degree. C. to 2000.degree. C., such as from 60.degree. C. to
7000.degree. C. and including 100.degree. C. to 400.degree. C.
[0063] The gaseous waste stream employed in methods of the
invention may be provided from the industrial plant to the site of
precipitation in any convenient manner that conveys the gaseous
waste stream from the industrial plant to the precipitation plant.
In certain embodiments, the waste stream is provided with a gas
conveyer, e.g., a duct, which runs from a site of the industrial
plant, e.g., a flue of the industrial plant, to one or more
locations of the precipitation site. The source of the gaseous
waste stream may be a distal location relative to the site of
precipitation, such that the source of the gaseous waste stream is
a location that is 1 mile or more, such as 10 miles or more,
including 100 miles or more, from the precipitation location. For
example, the gaseous waste stream may have been transported to the
site of precipitation from a remote industrial plant via a CO.sub.2
gas conveyance system, e.g., a pipeline. The industrial plant
generated CO.sub.2 containing gas may or may not be processed,
e.g., remove other components, etc., before it reaches the
precipitation site (i.e., a carbonate compound precipitation
plant). In yet other instances, source of the gaseous waste stream
is proximal to the precipitation site, where such instances may
include instances where the precipitation site is integrated with
the source of the gaseous waste stream, such as a power plant that
integrates a carbonate compound precipitation reactor.
[0064] Where desired, a portion of but less than the entire gaseous
waste stream from the industrial plant may be employed in
precipitation reaction. In these embodiments, the portion of the
gaseous waste stream that is employed in precipitation may be 75%
or less, such as 60% or less and including 50% and less.
[0065] In yet other embodiments, substantially all of the gaseous
waste stream produced by the industrial plant, e.g., substantially
all of the flue gas produced by the industrial plant, is employed
in precipitation. In these embodiments, 80% or more, such as 90% or
more, including 95% or more, up to 100% of the gaseous waste stream
(e.g., flue gas) generated by the source may be employed during
precipitation.
[0066] As indicated above, the gaseous waste stream may be one that
is obtained from a flue or analogous structure of an industrial
plant. In these embodiments, a line, e.g., duct, is connected to
the flue so that gas leaves the flue through the line and is
conveyed to the appropriate location(s) of a precipitation system
(described in greater detail below). Depending on the particular
configuration of the portion of the precipitation system at which
the gaseous waste stream is employed, the location of the source
from which the gaseous waste stream is obtained may vary, e.g., to
provide a waste stream that has the appropriate or desired
temperature. As such, in certain embodiments where a gaseous waste
stream having a temperature ranging for 0.degree. C. to
1800.degree. C., such as 60.degree. C. to 700.degree. C. is
desired, the flue gas may be obtained at the exit point of the
boiler or gas turbine, the kiln, or at any point through the power
plant or stack, that provides the desired temperature. Where
desired, the flue gas is maintained at a temperature above the dew
point, e.g., 125.degree. C., in order to avoid condensation and
related complications. Where such is not possible, steps may be
taken to reduce the adverse impact of condensation, e.g., employing
ducting that is stainless steel, fluorocarbon (such as
poly(tetrafluoroethylene)) lined, diluted with water and pH
controlled, etc., so the duct does not rapidly deteriorate.
[0067] To provide for efficiencies, the industrial plant that
generates the gaseous waste stream may be co-located with the
precipitation system. By "co-located" is meant that the distances
between the industrial plant and precipitation system range from 10
to 500 yards, such as 25 to 400 yards, including 30 to 350 yards.
Where desired, the precipitation and industrial plants may be
configured relative to each other to minimize temperature loss and
avoid condensation, as well as minimize ducting costs, e.g., where
the precipitation plant is located within 40 yards of the
industrial plant.
[0068] Also of interest in certain embodiments is a fully
integrated plant that includes an industrial function (such as
power generation, cement production, etc.) and a precipitation
system of the invention. In such integrated plants, conventional
industrial plants and precipitation system, such as described
below, are modified to provide for the desired integrated plant.
Modifications include, but are not limited to: coordination of
stacks, pumping, controls, instrumentation, monitoring, use of
plant energy, e.g., steam turbine energy to run portions of the
precipitation component, e.g., mechanical press, pumps,
compressors, use of heat from cement and/or power plant obtained
from steam or heat from air to air heat exchanger, etc.
[0069] The pH of the water that is contacted with the CO.sub.2
source may vary. In some instances, the pH of the water that is
contacted with the CO.sub.2 source is acidic, such that the pH is
lower than 7, such as 6.5 or lower, 6 or lower, 5.5 or lower, 5 or
lower, 4.5 or lower, 4 or lower. In yet other embodiments, the pH
of the water may be neutral to slightly basic, by which is meant
that the pH of the water may range from 7 to 9, such as 7 to 8.5,
including 7.5 to 8.5
[0070] In some instances, the water, such as
alkaline-earth-metal-ion-containing water (including alkaline
solutions or natural saline alkaline waters), is basic when
contacted with the CO.sub.2 source, such as a carbon dioxide
containing gaseous stream. In these instances, while being basic
the pH of the water is insufficient to cause precipitation of the
storage stable carbon dioxide sequestering product. As such, the pH
may be 9.5 or lower, such as 9.3 or lower, including 9 or
lower.
[0071] In some instances, the pH as described above may be
maintained at a substantially constant value during contact with
the carbon dioxide containing gaseous stream, or the pH may be
manipulated to maximize CO.sub.2 absorption while minimizing base
consumption or other means of removing protons, such as by starting
at a certain pH and gradually causing the pH to rise as CO.sub.2
continues to be introduced. In embodiments where the pH is
maintained substantially constant, where by "substantially
constant" is meant that the magnitude of change in pH during some
phase of contact with the carbon dioxide source is 0.75 or less,
such as 0.50 or less, including 0.25 or less, such as 0.10 or less.
The pH may be maintained at substantially constant value, or
manipulated to maximize CO.sub.2 absorption but prevent hydroxide
precipitation without precipitation, using any convenient approach.
In some instances, the pH is maintained at substantially constant
value, or manipulated to maximize CO.sub.2 absorption without
precipitation, during CO.sub.2 charging of the water by adding a
sufficient amount of base to the water in a manner that provides
the substantially constant pH. Any convenient base or combination
of bases may be adding, including but not limited to oxides and
hydroxides, such as magnesium hydroxide, where further examples of
suitable bases are reviewed below. In yet other instances, the pH
may be maintained at substantially constant value, or manipulated
to maximize CO.sub.2 absorption, through use of electrochemical
protocols, such as the protocols described below, so that the pH of
the water is electrochemically maintained at the substantially
constant value. Surprisingly, as shown in Example IV, it has been
found that it is possible to absorb, e.g., more than 50% of the
CO.sub.2 contained in a gas comprising about 20% CO.sub.2 through
simple sparging of seawater with addition of base (removal of
protons).
[0072] In some embodiments, the methods and systems of the
invention are capable of absorbing 5% or more, 10% or more, 15% or
more, 20% or more, 25% or more 30% or more, 35% or more, 40% or
more, 45% or more, 50% or more, 55% or more, 60% or more, 65% or
more, 70% or more, 75% or more, 80% or more, 85% or more, 90% or
more, 95% or more, or 99% or more of the CO.sub.2 in a gaseous
source of CO.sub.2, such as an industrial source of CO.sub.2, e.g.,
flue gas from a power plant or waste gas from a cement plant. In
some embodiments, the methods and systems of the invention are
capable of absorbing 50% or more of the CO.sub.2 in a gaseous
source of CO.sub.2, such as an industrial source of CO.sub.2, e.g.,
flue gas from a power plant or waste gas from a cement plant.
[0073] In addition to charging the initial water with CO.sub.2,
e.g., as described above, some embodiments of the methods include
adding a magnesium ion source to the initial water in a manner
sufficient to produce a magnesium to calcium ratio in the water of
3 or higher, e.g., 4 or higher, such as 5 or higher, for example 6
or higher, including 7 or higher. In certain embodiments, the
desired magnesium to calcium ion ratio ranges from 3 to 10, such as
4 to 8. Any convenient magnesium ion source may be added to the
water to provide the desired magnesium to calcium ion ratio, where
specific magnesium ion sources of interest include, but are not
limited to: Mg(OH).sub.2, serpentine, olivine, mafic minerals, and
ultramafic minerals. The amount of magnesium ion source that is
added to the water may vary, e.g., depending on the specific
magnesium ion source and the initial water from which the CO.sub.2
charged water is produced. In certain embodiments, the amount of
magnesium ion that is added to the water ranges from 0.01 to 100.0
grams/liter, such as from 1 to 100 grams/liter of water, including
from 5 to 100 grams/liter of water, for example from 5 to 80
grams/liter of water, including from 5 to 50 grams/liter of water.
In certain embodiments, the amount of magnesium ion added to the
water is sufficient to produce water with a hardness reading of
about 0.06 grams/liter or more, such as about 0.08 grams/liter or
more, including about 0.1 grams/liter or more as determined a
Metrohm Titrator (Metrohm AG, Switzerland) according to
manufacturer's instructions. The magnesium ion source may be
combined with the water using any convenient protocol, e.g. with
agitation, mixing, etc.
[0074] In embodiments where a source of magnesium, calcium, or a
combination of magnesium and calcium is added to the water, the
source may be in solid form e.g., in the form of large, hard, and
often crystalline particles or agglomerations of particles that are
difficult to get into solution. For example, Mg(OH).sub.2 as
brucite can be in such a form, as are many minerals useful in
embodiments of the invention, such as serpentine, olivine, and
other magnesium silicate minerals, as well as cement waste and the
like. Any suitable method may be used to introduce divalent cations
such as magnesium from such sources into aqueous solution in a form
suitable for reaction with carbonate to form carbonates of divalent
cations. Increasing surface area by reducing particle size is one
such method, which can be done by means well known in the art such
as ball grinding and jet milling. Jet milling has the further
advantage of destroying much of the crystal structure of the
substance, enhancing solubility. Also of interest is sonochemistry,
where intense sonication may be employed to increase reaction rates
by a desired amount, e.g., 10.sup.6.times. or more. The particles,
with or without size reduction, may be exposed to conditions which
promote aqueous solution, such as exposure to an acid such as HCl,
H.sub.2SO.sub.4, or the like; a weak acid or a base may also be
used in some embodiments. See, e.g., U.S. Patent Publication Nos.
2005/0022847; 2004/0213705; 2005/0018910; 2008/0031801; and
2007/0217981; European Patent Nos. EP1379469; and EP1554031; and
PCT Publication Nos. WO 07/016,271 and WO 08/061,305, all of which
are incorporated by reference herein in their entirety.
[0075] In some embodiments the methods and systems of the invention
utilize serpentine as a mineral source. Serpentine is an abundant
mineral that occurs naturally and may be generally described by the
formula of X.sub.2-3Si.sub.2O.sub.5(OH).sub.4, wherein X is
selected from the following: Mg, Ca, Fe.sup.2+, Fe.sup.3+, Ni, Al,
Zn, and Mn, the serpentine material being a heterogeneous mixture
consisting primarily of magnesium hydroxide and silica. In some
embodiments of the invention, serpentine is used not only as a
source of magnesium, but also as a source of hydroxide. Thus in
some embodiments of the invention, hydroxide is provided for
removal of protons from water and/or adjustment of pH by dissolving
serpentine; in these embodiments an acid dissolution is not ideal
to accelerate dissolution, and other means are used, such as jet
milling and/or sonication. It will be appreciated that in a batch
or continuous process, the length of time to dissolve the
serpentine or other mineral is not critical, as once the process is
started at the desired scale, and sufficient time has passed for
appropriate levels of dissolution, a continuous stream of dissolved
material may be maintained indefinitely. Thus, even if dissolution
to the desired level takes days, weeks, months, or even years, once
the process has reached the first time point at which desired
dissolution has occurred, it may be maintained indefinitely. Prior
to the timepoint at which desired dissolution has occurred, other
processes may be used to provide some or all of the magnesium
and/or hydroxide to the process. Serpentine is also a source of
iron, which is a useful component of precipitates that are used
for, e.g., cements, where iron components are often desired.
[0076] Other examples of silicate-based minerals useful in the
invention include, but are not limited to olivine, a natural
magnesium-iron silicate ((Mg, Fe).sub.2SiO.sub.4), which can also
be generally described by the formula X.sub.2(SiO.sub.4).sub.n,
wherein X is selected from Mg, Ca, Fe.sup.2+, Fe.sup.3+, Ni, Al,
Zn, and Mn, and n=2 or 3; and a calcium silicate, such as
wollastonite. The minerals may be used individually or in
combination with each other. Additionally, the materials may be
found in nature or may be manufactured. Examples of industrial
by-products include but are not limited to waste cement and
calcium-rich fly ash.
[0077] In embodiments in which an electrochemical process is used
to remove protons and/or to produce base, often an acid stream,
such as an HCl stream, is also generated, and this stream, alone or
any other convenient source of acid, or a combination thereof, may
be used to enhance dissolution of, e.g., magnesium-bearing minerals
such as olivine or serpentine, or sources of calcium such as cement
waste. Dissolution may be further enhanced by sonication methods,
which can produce localized pockets of extreme temperature and
pressure, enhancing reaction rates by one hundred to over one
million-fold. Such methods are known in the art.
[0078] In some embodiments the methods of the invention allow large
amounts of magnesium and, in some cases, calcium, to be added to
the water used in some embodiments of the invention, increasing the
amount of precipitate that may be formed per unit of water in a
single precipitation step, allowing surprisingly high yields of
carbonate-containing precipitate when combined with methods of
dissolution of CO.sub.2 from an industrial source in water, e.g.,
seawater or other saltwater source. In some embodiments, the
methods of the invention include a method of removing CO.sub.2 from
a gaseous source, e.g., an industrial gaseous source of CO.sub.2
such as flue gas from a power plant, or such as exhaust gas from a
cement plant, by performing a precipitation step on water into
which CO.sub.2 has been dissolved from the gaseous source of
CO.sub.2, where the precipitation step provides precipitate in an
amount of 10 g/L or more in a single precipitation step, 15 g/L or
more in a single precipitation step, 20 g/L or more in a single
precipitation step, 25 g/L or more in a single precipitation step,
30 g/L or more in a single precipitation step, 40 g/L or more in a
single precipitation step, 50 g/L or more in a single precipitation
step, 60 g/L or more in a single precipitation step, 70 g/L or more
in a single precipitation step, 80 g/L or more in a single
precipitation step, 90 g/L or more in a single precipitation step,
100 g/L or more in a single precipitation step, 125 g/L or more in
a single precipitation step, or 150 g/L or more in a single
precipitation step, In some embodiments the precipitate comprises
magnesium carbonate; in some embodiments the preciptate comprises
calcium carbonate; in some embodiments, the precipitate comprises
magnesium and calcium, and/or magnesium/calcium carbonates. In some
embodiments the ratio of magnesium to calcium in the precipitated
material produced in a single precipitation step is at least 0.5:1,
or at least 1:1, or at least 2:1, or at least 3:1, or at least 4:1,
or at least 5:1, or at least 6:1, or at least 7:1, or at least 8:1,
or at least 9:1, or at least 10:1. In some embodiments the ratio of
magnesium to calcium in the precipitated material produced in a
single precipitation step is at least 2:1. In some embodiments the
ratio of magnesium to calcium in the precipitated material produced
in a single precipitation step is at least 4:1. In some embodiments
the ratio of magnesium to calcium in the precipitated material
produced in a single precipitation step is at least 6:1. In some
embodiments, the precipitate contains calcium and magnesium
carbonates, and contains components that allow at least a portion
of the carbon in the carbonate to be traced back to a fossil fuel
origin.
[0079] As reviewed above, methods of the invention include
subjecting water (which may or may have been charged with CO.sub.2,
as described above) to precipitation conditions sufficient to
produce a storage stable precipitated carbon dioxide sequestering
product. Any convenient precipitation conditions may be employed,
which conditions result in the production of the desired
sequestering product.
[0080] Precipitation conditions of interest include those that
modulate the physical environment of the water to produce the
desired precipitate product. For example, the temperature of the
water may be raised to an amount suitable for precipitation of the
desired product to occur. In such embodiments, the temperature of
the water may be raised to a value from 5 to 70.degree. C., such as
from 20 to 50.degree. C. and including from 25 to 45.degree. C. As
such, while a given set of precipitation conditions may have a
temperature ranging from 0 to 100.degree. C., the temperature may
be raised in certain embodiments to produce the desired
precipitate. The temperature of the water may be raised using any
convenient protocol. In some instances, the temperature is raised
using energy generated from low or zero carbon dioxide emission
sources, e.g., solar energy sources, wind energy sources,
hydroelectric energy sources, geothermal energy sources, from the
waste heat of the flue gas which can range up to 500.degree. C.,
etc.
[0081] While the pH of the water may range from 7 to 14 during a
given precipitation process, in some instances the pH is raised to
alkaline levels in order to produce the desired precipitation
product. In these embodiments, the pH is raised to a level
sufficient to cause precipitation of the desired CO.sub.2
sequestering product, as described above. As such, the pH may be
raised to 9.5 or higher, such as 10 or higher, including 10.5 or
higher. Where desired, the pH may be raised to a level which
minimizes if not eliminates CO.sub.2 production during
precipitation. For example, the pH may be raised to a value of 10
or higher, such as a value of 11 or higher. In certain embodiments,
the pH is raised to between 7 and 11, such as between 8 and 11,
including between 9 and 11, for example between 10 and 11. In this
step, the pH may be raised to and maintained at the desired
alkaline level, such that the pH is maintained at a constant
alkaline level, or the pH may be transitioned or cycled between two
or more different alkaline levels, as desired.
[0082] The pH of the water may be raised using any convenient
approach. Approaches of interest include, but are not limited to:
use of a pH raising agent, electrochemical approaches, using
naturally alkaline water such as from an alkaline lake, etc. In
some instances, a pH raising agent may be employed, where examples
of such agents include oxides (such as calcium oxide, magnesium
oxide, etc.), hydroxides (such as sodium hydroxide, potassium
hydroxide, and magnesium hydroxide), carbonates (such as sodium
carbonate) and the like. The amount of pH elevating agent which is
added to the water will depend on the particular nature of the
agent and the volume of water being modified, and will be
sufficient to raise the pH of the water to the desired value.
[0083] In some embodiments, a source of an agent for removal of
protons, during dissolution of CO2 and/or during the precipitation
step in which pH is raised, may be a naturally-occurring source.
For example, in some embodiments the agent may comprise serpentine
dissolved into aqueous solution, as described above. In other
embodiments the agent may comprise a natural body of highly
alkaline water. Such bodies of water are well-known and are sources
of large amounts of alkalinity, e.g., Lake Van in Turkey has an
average pH of 9.7-9.8. In addition, flyash, slag, cement waste, and
other industrial wastes can provide sufficient alkalinity to remove
at least a portion of the protons and/or provide a sufficient pH
change for precipitation.
[0084] In addition or as an alternative, protons may be removed
from the water, e.g. while CO.sub.2 is dissolved and/or at the
precipitation step, using electrochemical approaches, which may
remove protons without production of hydroxide (e.g., if proton
production from CO.sub.2 dissolution matches or exceeds proton
removal by an electrochemical process) or with production of
hydroxide. For example, electrodes (cathode and anode) may be
provided in the reactor which holds the water source, where the
electrodes may be separated by a selective barrier, such as a
membrane, as desired. Where desired, byproducts of the hydrolysis
product, e.g., H.sub.2, sodium metal, etc. may be harvested and
employed for other purposes, as desired. Additional electrochemical
approaches of interest include, but are not limited, those
described in U.S. Provisional Application Ser. Nos. 61/081,299 and
61/091,729; the disclosures of which are herein incorporated by
reference.
[0085] In some instances, low-voltage electrochemical protocols are
employed remove protons from the water, e.g. while CO.sub.2 is
dissolved and at the precipitation step. By "low-voltage" is meant
that the employed electrochemical protocol operates at an average
voltage of 2, 1.9, 1.8, 1.7, or 1.6 V or less, such as 1.5, 1.4,
1.3, 1.2, 1.1 V or less, such as 1V or less, including 0.9V or
less, 0.8V or less, 0.7V or less, 0.6V or less, 0.5V or less, 0.4V
or less, 0.3V or less, 0.2V or less, or 0.1V or less. Of interest
are electrochemical protocols that do not generate chlorine gas.
Also of interest are electrochemical protocols that do not generate
oxygen gas. Also of interest are electrochemical protocols that do
not generate hydrogen gas. In some instances, the electrochemical
protocol is one that does not generate any gaseous
by-byproduct.
[0086] Described below are two electrochemical processes and
systems that may be used in embodiments of the invention. The first
makes use of a hydrogen transfer member that can act as both a
cathode and an anode (i.e., a bielectrode). The second makes use of
one or more ion-selective membranes (a low-voltage system for
producing hydroxide). These processes and systems are further
described in PCT Application No. PCT/US08/88242 entitled
"Low-Energy Electrochemical Hydroxide System and Method," filed on
Dec. 23, 2008, and PCT Application No. PCT/US08/88246 entitled
"Low-Energy Electrochemical Proton Transfer System and Method,"
filed on Dec. 23, 2008; the disclosures of which are herein
incorporated by reference.
Bielectrode Methods and System
[0087] In various embodiments, the present method and system
provides a low energy source of a deprotonated solution by
positioning a hydrogen transfer member in an electrolytic cell
wherein: on biasing a voltage on a first electrode positive
relative to the hydrogen transfer member, and a second electrode in
the cell negative relative to the hydrogen transfer member, a first
electrolyte, in contact with the hydrogen transfer member and the
first electrode, is deprotonated without forming oxygen or chlorine
gas at the first electrode.
[0088] In one embodiment, the method comprises: positioning a
conductive hydrogen transfer member to isolate a first electrolyte
from a second electrolyte, the first electrolyte contacting a first
electrode and the second electrolyte contacting a second electrode;
and biasing a voltage on the first electrode positive relative to
the hydrogen transfer member, and a voltage on the second electrode
negative relative to the hydrogen transfer member to establish a
current in the electrodes.
[0089] In an another embodiment, the method comprises: utilizing a
hydrogen transfer member to isolate a first electrolyte from a
second electrolyte; and biasing a voltage on a first electrode
contacting the first electrolyte positive relative to the hydrogen
transfer member; and biasing a voltage on the second electrode
contacting the second electrolyte negative relative to the hydrogen
transfer member wherein, whereby protons are removed from the first
electrolyte and introduced into the second electrolyte.
[0090] In another embodiment, the system comprises: a first
electrode contacting a first electrolyte; a second electrode
contacting in a second electrolyte; a hydrogen transfer member
isolating the first electrolyte from the second electrolyte; and a
voltage regulator operable for biasing a voltage on the first
electrode positive relative to the hydrogen transfer member, and
biasing a voltage on the second electrode negative relative to the
hydrogen transfer member.
[0091] In another embodiment, the system comprises: a first
electrolytic cell comprising a first electrode contacting a first
electrolyte; a second electrolytic cell comprising a second
electrolyte contacting a second electrolyte; a hydrogen transfer
member positioned to isolate the first electrolyte from the second
electrolyte; a first conduit positioned for supplying positive ions
to the first electrolyte; a second conduit positioned for supplying
negative ions into the second electrolyte; and a voltage regulator
operable to establish a current through the electrodes by biasing a
voltage on the first electrode positive relative to the hydrogen
transfer member, and a voltage on the second electrode negative
relative to the hydrogen transfer member.
[0092] In another embodiment, the method comprises forming a
carbonate-ion enriched solution from a first electrolyte by
contacting the first electrolyte with CO.sub.2 while transferring
hydrogen ions from the first electrolyte to a second electrolyte
solution utilizing a hydrogen transfer member. In accordance with
the method, a voltage regulator is operable to establish a current
through the electrodes by biasing a voltage on the first electrode
positive relative to the hydrogen transfer member, and a voltage on
the second electrode negative relative to the hydrogen transfer
member.
[0093] By the present system and method, protons are removed from
the first electrolyte in contact with a first electrode, while
protons are introduced into another solution in contact with the
second electrode (i.e., in some embodiments the PH of the first
electrolyte in increased and the pH of the other solution is
decreased) without forming chlorine or oxygen gas on the first
electrode. In one embodiment, the solution comprising removed
protons has a decreased H.sup.+ concentration, corresponding to an
increase OH.sup.- concentration, and is useable in sequestering
CO.sub.2 by precipitating calcium and magnesium carbonates and
bicarbonates from a solution containing dissolved salts of these
alkali metals, as described further herein. Further, the solution
comprising the increase in H.sup.+ concentration is useable in
preparing the alkali solutions herein, and/or other industrial
applications.
[0094] The bielectrode described herein is directed to
electrochemical systems and methods for transferring H+ from one
electrolyte solution to another. Thus, by transferring H.sup.+
between aqueous electrolytic solutions, the concentration of
H.sup.+ in one solution may decrease, i.e. the solution becomes
more basic, while the concentration of H.sup.+ in the other
solution also increases i.e., the solution become more acidic.
Alternatively, if one solution contains a proton source or a proton
sink, the pH my not change, or may change more slowly, or even
change in the opposite direction from that predicted by proton
removal or addition.
[0095] In various embodiments, the methods and apparatus produce a
basic solution and an acidic solution. In various embodiments, the
basic solution is useable to sequester CO.sub.2, and the acidic
solution is useable to dissolve calcium and magnesium bearing
minerals to provide a calcium and magnesium ions for sequestering
CO.sub.2, as described further herein. In various embodiments, a
hydrogen transfer material, such as palladium, separates the
solutions and serve as a hydrogen transfer medium. Also, in various
embodiments the hydrogen transfer material functions as a central
electrode between an anode and a cathode in a bi-electrode
configuration.
[0096] FIGS. 7A-7B illustrate various embodiments of the present
system. These embodiments are illustrative only and in no way limit
the methods or apparatuses. The system is adaptable for batch and
continuous processes as described herein. Referring to FIG. 7A,
system in one embodiment comprises a first electrode 702 contacting
a first electrolyte 704; a second electrode 706 contacting a second
electrolyte 708; a hydrogen transfer member 770 contacting and
isolating first electrolyte 704 from second electrolyte 708; and
voltage regulators 724A and 724B operable for biasing a voltage on
first electrode 702 positive relative to hydrogen transfer member
770, and biasing a voltage on second electrode 706 negative
relative to the hydrogen transfer member. In various embodiments,
the voltage regulator is set to a voltage such that a gas, e.g.,
oxygen or chlorine gas does not form at the first electrode.
[0097] In the embodiment illustrated in FIG. 7A, first electrode
702 and first electrolyte 704 are contained in a first electrolytic
chamber or cell 772; and second electrode 706 and second
electrolyte 708 are contained in a second electrolytic chamber or
cell 714. First electrolyte cell 712 and second electrolytic cell
714 are defined by positioning hydrogen transfer member 710 to
isolate first electrolyte 704 from second electrolyte 708. In
various embodiments, first and second electrolytic cells 712, 714
are comprised of a reservoir 716 such as a tank, a vessel, a
chamber, bag or a conduit. As is illustrated in FIGS. 7A-7B,
hydrogen transfer member 710 member may constitute an entire
barrier 718 between electrolytes 704, 708, or a portion thereof. In
embodiments where hydrogen transfer member 710 constitutes only a
portion of barrier 718, the remainder of the barrier comprises an
insulating material.
[0098] In various embodiments, hydrogen transfer material 710
comprises a noble metal, a transition metal, a platinum group
metal, a metal of Groups IVB, VB, VIB, or VIII of the periodic
table of elements, alloys of these metals, oxides of these metals,
or combinations of any of the foregoing. Other exemplary materials
include palladium, platinum, iridium, rhodium, ruthenium, titanium,
zirconium, chromium, iron, cobalt, nickel, palladium-silver alloys,
palladium-copper alloys or amorphous alloys comprising one or more
of these metals. In various embodiments, the hydrogen transfer
member also comprises a non-porous materials from the titanium and
vanadium groups, or comprise complex hydrides of group one, two,
and three light elements of the Periodic Table such as Li, Mg, B,
and Al. In other embodiments, a non-conductive or poorly conductive
material can be made conductive as needed to function as a hydrogen
transfer member, e.g. with a thin metal coating that can be applied
by sputter deposition. In various embodiments, the hydrogen storage
material 710 comprise a supported film or foil. In some
embodiments, the hydrogen storage material 710 comprises
palladium.
[0099] In operation, first electrode 702 is disposed at least
partially in first electrolyte solution 704 and in contact
therewith, and second electrode 706 is likewise disposed at least
partially in second electrolyte solution 708 and in contact
therewith.
[0100] In various embodiments the electrolyte solution in first
electrolytic cell 712 comprises a conductive aqueous such as fresh
water or a salt water including seawater, brine, or brackish fresh
water. Similarly, in second cell 714, the electrolyte comprises a
conductive aqueous such as fresh water or a salt water including
seawater, brine, or brackish fresh water as described herein. In
either cell, the solution may be obtained form a natural source, or
artificially created, or a combination of a natural source that has
been modified for operation in the process and/or apparatus of the
invention as described herein.
[0101] In an embodiment illustrated in FIGS. 7A-7B, first
electrolytic solution 704 is enriched with cations ions obtained,
for example, by selectively di-ionizing salt water. Similarly,
electrolytic solution 708 is enriched with anions ions obtained,
for example, by selectively di-ionizing salt water. As is
illustrated in FIG. 7A by adding positive ions, e.g., sodium ions
to first electrolytic solution 704, and suitably biasing first 702
and second 706 electrodes as described herein, protons are removed
from the first solution; if protons are not replenished, or are
replenished more slowly than they are removed, then the system
provides a deprotonated first electrolyte 704. Further, by
surrounding first electrode 702 with a porous material 720 to
prevent mixing of cations from first electrode 702 with other ions
in first electrolytic cell solution 704, these electrode cations
can be recovered at second electrode 706 in the second electrolytic
cell by surrounding second electrode 706 with recovered cations and
adjusting the voltages in the system to preferentially plate out
cations on second electrode 706. Although tin is the electrode
material illustrated in FIG. 7A, it will be appreciated that any
suitable material may be used. Similarly by introducing chloride
ions in second electrolyte 708 wherein the proton concentration
increases, an acid solution e.g., hydrochloric acid is obtained in
second electrolytic cell 714. It will be appreciated that any
suitable cationic and anionic species may be used, and that
selection of species will depend on operating requirements of the
system, the acid desired in second electrolyte 708, and the like.
In some embodiments, the cation is sodium and the anion is
chloride, as illustrated in FIG. 7A.
[0102] In various embodiments first electrode 702 comprises an
anode, and second electrode 706 comprises a cathode. In various
embodiments, first electrode 702 comprises a sacrificial anode
comprising a material comprising iron, tin, magnesium, calcium or
combinations thereof and a mineral. Other exemplary materials
include a mineral, such as a mafic mineral e.g., olivine or
serpentine that provides cations. Where a mineral is used as a part
of first electrode 702 and functions as a source of cations, the
mineral is positioned on a chemically inert conductive carrier such
as stainless steel or platinum. Any suitable mineral may be used
and selection of the mineral is based on the cation or cations
desired for release, availability, cost and the like.
[0103] The system also comprises a voltage regulator and/or power
supply 724A, 724B configured to bias first electrode 702 positive
relative to hydrogen transfer member 710, and configured to bias
second electrode 706 negative to hydrogen transfer member 710. In
various embodiments, power supply comprises two separate power
supplies 724A, 724B as illustrated in FIGS. 7-8, one configured to
bias the first electrode positively relative to the membrane, and
another configured to bias the second electrode negative relative
to the hydrogen transfer member 710.
[0104] In operation, power supply 724A, 724B drives an
electrochemical reaction in which, without intending to be bound by
any theory, it is believed that hydrogen ions in first electrolyte
solution 704 are reduced to atomic hydrogen and adsorb on a surface
of hydrogen transfer member 710 in contact with first electrolyte
702. At least a portion of the adsorbed hydrogen is absorbed in the
body of hydrogen transfer member 710 and desorbs on a surface of
hydrogen transfer member 710 into second electrolyte 708 in contact
with hydrogen transfer member 710 as hydrogen ions. Regardless of
mechanism, the result of the electrochemical reaction is removal of
proton from first electrolyte 704, and introduction of a proton
into second electrolyte 708. In embodiments wherein first electrode
702 comprises an oxidizable material e.g. iron, electrode 702 is
oxidized to release iron ions (e.g., Fe.sup.+2 and/or Fe.sup.+3)
into first electrolyte solution 704 to balance the reduction of the
hydrogen ions in first electrolyte 704.
[0105] In the present system, voltages on electrodes 702, 706 are
biased relative to hydrogen transfer member 710 such that a gas
does not form on first electrode 702. Hence, wherein first
electrolyte 704 comprises water, oxygen does not form on first
electrode 702. Similarly, wherein the first electrolyte comprises
chloride ions, e.g., an electrolyte comprising salt water, chlorine
gas does not form on the first electrode.
[0106] Without being bound to any theory as to a mechanism for
proton transfer from first electrolyte 704 to second electrolyte
708, it is believed that hydrogen ions present in first electrolyte
704 are reduced to atomic hydrogen and adsorbs on the surface of
hydrogen transfer member 710 in contact the first electrolyte. In
the system, power supply 724B drives another reaction at the
opposing surface of membrane 710 in contact with second electrolyte
708 such that hydrogen absorbed in the body of hydrogen transfer
member 710 is oxidized back to hydrogen ions and are released into
second electrolyte solution 708 as hydrogen ions. To balance the
reaction in which the atomic hydrogen is oxidized back to hydrogen
ions, electrons are taken up at second electrode 706, for instance,
by reducing a cation in second electrolytic solution 708. For
example, where second electrolytic solution 708 comprises seawater,
then depending upon the applied voltage some or all of sodium,
calcium, magnesium, and other ions can be reduced at second
electrode 706 to form a coating thereon.
[0107] In various embodiments as illustrated in FIGS. 7A-7B, the
system comprises a source of CO.sub.2 726 coupled to a gas
injection system 728 disposed in first cell 712. The gas injection
system mixes a gas including CO.sub.2 supplied by the source of
CO.sub.2 into first electrolyte solution 704. Exemplary sources of
CO.sub.2 are described herein, and can include flue gas from
burning fossil fuel burning at power plants, or waste gas from an
industrial process e.g., cement manufacture or steel manufacture,
for example. In various embodiments, gas injection system 728 can
comprise a sparger or injection nozzle; however, any suitable
mechanism and apparatus for introducing CO.sub.2 into an aqueous
solution, as known in the art, may be used.
[0108] Referring to FIGS. 7A and 7B, the system in an alternative
embodiment further comprises a conduit 730A positioned to supply a
solution of positive ions to first electrolyte 704, and conduit
730B positioned to supply negative ions to second electrolyte 708.
In various embodiments, conduits 730A, 730B are adaptable for batch
or continuous flow. As illustrated in FIGS. 7A and 7B, the system
comprises a first electrolytic cell 712 comprising a first
electrode 702 contacting a first electrolyte 704; a second
electrolytic cell 714 comprising a second electrode 706 contacting
a second electrolyte 708; a hydrogen transfer member 710 positioned
to isolate the first electrolyte from the second electrolyte; a
first conduit 730A positioned for supplying positive ions to the
first electrolyte; a second conduit 730B positioned for supplying
negative ions into the second electrolyte; and voltage regulators
724A, 724B operable to establish a current through electrodes 702,
706 by biasing a voltage on first electrode 702 positive relative
to the hydrogen transfer member 710, and a voltage on the second
electrode 706 negative relative to the hydrogen transfer
member.
[0109] As will be appreciated by one skilled in the art, protons
are removed from electrolyte solution 704 and introduced in to
electrolyte solution 708. In some embodiments, electrolyte solution
704 further includes a source of protons as illustrated in FIGS. 7A
and 7B. In some embodiments, CO.sub.2 gas may be introduced into
electrolyte solution 704 and through well known chemistry, react
with water to form a carbonic acid that can dissociate to form a
bicarbonate ion and a proton; and the bicarbonate ion may further
dissociate to form a carbonate ion and another proton.
[0110] Thus, in some embodiments, e.g., where CO.sub.2 is
introduced, proton are both removed and introduced into electrolyte
solution 704, and the net result--net removal, no change, or net
introduction of protons--will depend on the relative rates of
protons removal by the electrochemical process and introduction by
e.g., CO.sub.2 introduction. Similarly, in electrolyte solution
708, if there is a process that removes protons e.g., dissolution
of a basic substance, then the net result in electrolyte solution
708 may be introduction of, no change in, or removal of
protons.
[0111] In some embodiments, there is a net removal of protons
(coupled with introduction of cations) in electrolyte solution 704,
and/or a net introduction of protons (couple with introduction of
anions, e.g., chloride) in electrolyte solution 708. Thus, in some
embodiments, a cationic hydroxide, e.g. sodium hydroxide will be
formed in first electrolyte solution 704 and/or hydrogen anion
solution, e.g., hydrochloric acid will be formed in second solution
708. Either or both of cationic hydroxide e.g., sodium hydroxide,
or the hydrogen anionic solution e.g. hydrochloric acid can be
withdrawn and used elsewhere, e.g., in the sequestration of carbon
dioxide as describe above, and in other industrial
applications.
[0112] The voltage across the electrodes used to remove protons
from solution may be low. In various embodiments, the voltage
across the electrodes may be less than about 0.1, 0.2, 0.3, 0.4,
0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7,
1.8, 1.9, 2.0, 2.1, or 2.2 V. In some embodiments, the voltage
across the electrodes is less than about 2.0V. In some embodiments,
the voltage across the electrodes is less than about 1.5V. In some
embodiments, the voltage across the electrodes is less than about
1.0V. In some embodiments, the voltage across the electrodes is
less than about 0.8V. In some embodiments, the voltage across the
electrodes is less than about 0.6V. In some embodiments, the
voltage across the electrodes is less than about 0.4V.
[0113] Exemplary results achieved in accordance with the present
system are summarized in Table 1 below.
TABLE-US-00001 TABLE 1 Low Energy Electrochemical Method and System
(Bi-electrode) Volt across Time Initial pH End pH Initial pH End pH
at Electrodes (min) Anode at Anode at Cathode Cathode 0.45 V 30
4.994 5.204 7.801 10. 7.431 [0.15 V across the deprotonated
solution; and 0.30 V across the protonated solution]
Low Voltage System for Production of Hydroxide
[0114] A second set of methods and systems for removing protons
from aqueous solution/producing hydroxide pertains to a low energy
process for electrochemically preparing an ionic solution utilizing
an ion exchange membrane in an electrochemical cell. In one
embodiment, the system comprises an electrochemical system wherein
an ion exchange membrane separates a first electrolyte from a
second electrolyte, the first electrolyte contacting an anode and
the second electrolyte contacting a cathode. In the system, on
applying a voltage across the anode and cathode, hydroxide ions
form at the cathode and a gas does not form at the anode.
[0115] In an another embodiment, the system comprises an
electrochemical system comprising a first electrolytic cell
including an anode contacting a first electrolyte, and an anion
exchange membrane separating the first electrolyte from a third
electrolyte; and a second electrolytic cell including a second
electrolyte contacting a cathode and a cation exchange membrane
separating the first electrolyte from the third electrolyte;
wherein on applying a voltage across the anode and cathode,
hydroxide ions form at the cathode and a gas does not form at the
anode.
[0116] In one embodiment the method comprises placing an ion
exchange membrane between a first electrolyte and a second
electrolyte, the first electrolyte contacting an anode and the
second electrolyte contacting a cathode; and migrating ions across
the ion exchange membrane by applying a voltage across the anode
and cathode to form hydroxide ions at the cathode without forming a
gas at the anode.
[0117] In another embodiment the method comprises placing a third
electrolyte between an anion exchange membrane and a cation
exchange membrane; a first electrolyte between the anion exchange
and an anode; and second electrolyte between the cation exchange
membrane and a cathode; and migrating ions across the cation
exchange membrane and the anion exchange membrane by applying a
voltage to the anode and cathode to form hydroxide ions at the
cathode without forming a gas at the anode.
[0118] By the present methods and systems, ionic species from one
solution are transferred to another solution in an low voltage
electrochemical manner, thereby providing anionic solutions for
various applications, including preparing a solution of sodium
hydroxide for use in sequestration carbon dioxide as described
herein. In one embodiment, a solution comprising OH.sup.- is
obtained from salt water and used in sequestering CO.sub.2 by
precipitating calcium and magnesium carbonates and bicarbonates
from a salt solution comprising alkaline earth metal ions as
described herein.
[0119] The methods and systems in various embodiments are directed
to a low voltage electrochemical system and method for generating a
solution of sodium hydroxide in an aqueous solution utilizing one
or more ion exchange membranes wherein, a gas is not formed at the
anode and wherein hydroxyl ions are formed at the cathode. Thus, in
some embodiments, hydroxide ions are formed in an electrochemical
process without the formation of oxygen or chlorine gas. In some
embodiments, hydroxide ions are formed in an electrochemical
process where the voltage applied across the anode and cathode is
less than 2.8, 2.7, 2.5, 2.4, 2.3, 2.2, 2.1, 2.0, 1.9, 1.8, 1.7,
1.6, 1.5, 1.4, 1.3, 1.2, 1.1, 1.0, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4,
0.3, 0.2, or 0.1 V. In various embodiments, an ionic membrane is
utilized to separate a salt water in contact with the anode, from a
solution of e.g., sodium chloride in contact with the cathode. On
applying a low voltage across the cathode and anode, a solution of
e.g., sodium hydroxide is formed in the solution around the
cathode; concurrently, an acidified solution comprising
hydrochloric acid is formed in the solution around the anode. In
various embodiments, a gas such as chorine or oxygen does not form
at the anode.
[0120] In various embodiments, the sodium hydroxide solution is
useable to sequester CO.sub.2 as described herein, and the acidic
solution is useable to dissolve calcium and magnesium bearing
minerals to provide a calcium and magnesium ions for sequestering
CO.sub.2, also as described herein.
[0121] Turning to FIGS. 8-10, in various embodiments the system is
adaptable for batch and continuous processes as described herein.
Referring to FIGS. 8-9, in one embodiment the system includes an
electrochemical cell wherein an ion exchange membrane (802, 824) is
positioned to separate a first electrolyte (804) from a second
electrolyte (806), the first electrolyte contacting an anode (808)
and the second electrolyte contacting a cathode (810). As
illustrated in FIG. 8, an anion exchange membrane (802) is
utilized; in FIG. 9, a cation exchange membrane (824) is
utilized.
[0122] In various embodiments as illustrated in FIGS. 8 and 9,
first electrolyte (804) comprises an aqueous salt solution
comprising seawater, freshwater, brine, or brackish water or the
like; and second electrolyte comprises a solution substantially of
sodium chloride. In various embodiments, second (806) electrolyte
may comprise seawater or a concentrated solution of sodium
chloride. In various embodiments anion exchange membrane (802) and
cation exchange membrane (824) comprise a conventional ion exchange
membranes suitable for use in an acidic and/or basic solution at
operating temperatures in an aqueous solution up to about
100.degree. C. As illustrated in FIGS. 8 and 9, first and second
electrolytes are in contact with the anode and cathode to complete
an electrical circuit that includes voltage or current regulator
(812). The current/voltage regulator is adaptable to increase or
decrease the current or voltage across the cathode and anode in the
system as desired.
[0123] With reference to FIGS. 8 and 9, in various embodiments, the
electrochemical cell includes first electrolyte inlet port (814)
adaptable for inputting first electrolyte (804) into the system and
in contact with anode (808). Similarly, the cell includes second
electrolyte inlet port (816) for inputting second electrolyte (806)
into the system and in contact with cathode (810). Additionally,
the cell includes outlet port (818) for draining first electrolyte
from the cell, and outlet port (820) for draining second
electrolyte from the cell. As will be appreciated by one ordinarily
skilled, the inlet and outlet ports are adaptable for various flow
protocols including batch flow, semi-batch flow, or continuous
flow. In alternative embodiments, the system includes a duct (822)
for directing gas to the anode; in various embodiments the gas
comprises hydrogen formed at the cathode (810).
[0124] With reference to FIG. 8 where an anion membrane (802) is
utilized, upon applying a low voltage across the cathode (810) and
anode (808), hydroxide ions form at the cathode (810) and a gas
does not form at the anode (808). Further, where second electrolyte
(806) comprises sodium chloride, chloride ions migrate into the
first electrolyte (804) from the second electrolyte (806) through
the anion exchange membrane (802); protons form at the anode (808);
and hydrogen gas forms at the cathode (810). As noted above, a gas
e.g., oxygen or chlorine does not form at the anode (808).
[0125] With reference to FIG. 9 where a cation membrane (824) is
utilized, upon applying a low voltage across the cathode (810) and
anode (808), hydroxide ions form at the cathode (810) and a gas
does not form at the anode (808). In various embodiments cation
exchange membrane (824) comprises a conventional cation exchange
membrane suitable for use with an acidic and basic solution at
operating temperatures in an aqueous solution up to about
100.degree. C. As illustrated in FIG. 9, first and second
electrolytes are in contact with the anode and cathode to complete
an electrical circuit that includes voltage and/or current
regulator (812). The voltage/current regulator is adaptable to
increase or decrease the current or voltage across the cathode and
anode in the system as desired. In the system as illustrated in
FIG. 9 wherein second electrolyte (806) comprises sodium chloride,
sodium ions migrate into the second electrolyte (806) from the
first electrolyte (804) through the cation exchange membrane (824);
protons form at the anode (808); and hydrogen gas forms at the
cathode (810). As noted above, a gas e.g., oxygen or chlorine does
not form at the anode (808).
[0126] As can be appreciated by one ordinarily skilled in the art,
and with reference to FIG. 8 in second electrolyte (806) as
hydroxide ions from the anode (810) and enter in to the second
electrolyte (806) concurrent with migration of chloride ions from
the second electrolyte, an aqueous solution of sodium hydroxide
will form in second electrolyte (806). Consequently, depending on
the voltage applied across the system and the flow rate of the
second electrolyte (806) through the system, the pH of the second
electrolyte is adjusted. In one embodiment, when a potential of
about 0.1 V or less, 0.2 V or less, 0.3 V or less, 0.4 V or less,
0.5 V or less, 0.6 V or less, 0.7 V or less, 0.8 V or less, 0.9 V
or less, 1.0 V or less, 1.1 V or less, 1.2 V or less, 1.3 V or
less, 01.4 V or less, 1.5 V or less, 1.6 V or less, 1.7 V or less,
1.8 V or less, 1.9 V or less, or 2.0 V or less, is applied across
the anode and cathode, the pH of the second electrolyte solution
increased; in another embodiment, when a volt of about 0.1 to 2.0 V
is applied across the anode and cathode the pH of the second
electrolyte increased; in yet another embodiment, when a voltage of
about 0.1 to 1 V is applied across the anode and cathode the pH of
the second electrolyte solution increased. Similar results are
achievable with voltages of 0.1 to 0.8 V; 0.1 to 0.7 V; 0.1 to 0.6
V; 0.1 to 0.5 V; 0.1 to 0.4 V; and 0.1 to 0.3 V across the
electrodes. Exemplary results achieved in accordance with the
present system are summarized in Table 2.
TABLE-US-00002 TABLE 2 Low Energy Electrochemical Method and System
Volt across Initial pH at End pH at Initial pH at End pH at
Electrodes Time (sec) Anode Anode Cathode Cathode 0.6 2000 6.7 3.8
6.8 10.8 1.0 2000 6.6 3.5 6.8 11.1
[0127] In this example, both the anode and the cathode comprise
platinum, and the first and second electrolytes comprise a solution
of sodium chloride.
[0128] Similarly, with reference to FIG. 9, in second electrolyte
(806) as hydroxide ions from the anode (810) enter into the
solution concurrent with migration of sodium ions from the first
electrolyte to the second electrolyte, increasingly an aqueous
solution of sodium hydroxide will form in second electrolyte (806).
Depending on the voltage applied across the system and the flow
rate of the second electrolyte through the system, the pH of the
solution will be adjusted. In one embodiment, when a volt of about
0.1 V or less, 0.2 V or less, 0.3 V or less, 0.4 V or less, 0.5 V
or less, 0.6 V or less, 0.7 V or less, 0.8 V or less, 0.9 V or
less, 1.0 V or less, 1.1 V or less, 1.2 V or less, 1.3 V or less,
01.4 V or less, 1.5 V or less, 1.6 V or less, 1.7 V or less, 1.8 V
or less, 1.9 V or less, or 2.0 V or less is applied across the
anode and cathode, the pH of the second electrolyte solution
increased; in another embodiment, when a volt of about 0.1 to 2.0 V
is applied across the anode and cathode the pH of the second
electrolyte increased; in yet another embodiment, when a voltage of
about 0.1.0 to 1 V is applied across the anode and cathode the pH
of the second electrolyte solution increased. Similar results are
achievable with voltages of 0.1 to 0.8 V; 0.1 to 0.7 V; 0.1 to 0.6
V; 0.1 to 0.5 V; 0.1 to 0.4 V; and 0.1 to 0.3 V across the
electrodes. In one embodiment, a volt of about 0.6 volt or less is
applied across the anode and cathode; in another embodiment, a volt
of about 0.1 to 0.6 volt or less is applied across the anode and
cathode; in yet another embodiment, a voltage of about 0.1 to 1
volt or less is applied across the anode and cathode.
[0129] In various embodiments and with reference to FIGS. 8-10,
hydrogen gas formed at the cathode (810) is directed to the anode
(808) where, without being bound to any theory, it is believed that
the gas is adsorbed and/or absorbed into the anode and subsequently
forms protons at the anode. Accordingly, as can be appreciated,
with the formation of protons at the anode and migration of e.g.,
chloride ions into the first electrolyte (804) as in FIG. 8, or
migration of e.g., sodium ions from the first electrolyte as in
FIG. 10, an acidic solution comprising e.g., hydrochloric acid is
obtained in the first electrolyte (804).
[0130] In another embodiment as illustrated in FIG. 10, the system
in accordance with the present invention comprises an
electrochemical cell including anode (808) contacting first
electrolyte (804) and an anion exchange membrane (802) separating
the first electrolyte from a third electrolyte (830); and a second
electrolytic cell comprising a second electrolyte (806) contacting
a cathode (880) and a cation exchange membrane (824) separating the
first electrolyte from the third electrolyte, wherein on applying a
voltage across the anode and cathode, hydrogen ions form at the
cathode without a gas forming at the anode. As with the system of
FIGS. 8 and 9, the system of FIG. 10 is adaptable for batch and
continuous processes.
[0131] In various embodiments as illustrated in FIG. 10, first
electrolyte (804) and second electrolyte (806) comprise an aqueous
salt solution comprising seawater, freshwater, brine, or brackish
water or the like; and second electrolyte comprises a solution
substantially of sodium chloride. In various embodiments, first
(804) and second (806) electrolytes may comprise seawater. In the
embodiment illustrated in FIG. 10, the third electrolyte (830)
comprises substantially sodium chloride solution.
[0132] In various embodiments anion exchange membrane (802)
comprises any suitable anion exchange membrane suitable for use
with an acidic and basic solution at operating temperatures in an
aqueous solution up to about 100.degree. C. Similarly, cation
exchange membrane (824) comprises any suitable cation exchange
membrane suitable for use with an acidic and basic solution at
operating temperatures in an aqueous solution up to about
100.degree. C.
[0133] As illustrated in FIG. 10, in various embodiments first
electrolyte (804) is in contact with the anode (808) and second
electrolyte (806) is in contact with the cathode (810). The third
electrolyte (830), in contact with the anion and cation exchange
membrane, completes an electrical circuit that includes voltage or
current regulator (812). The current/voltage regulator is adaptable
to increase or decrease the current or voltage across the cathode
and anode in the system as desired.
[0134] With reference to FIG. 10, in various embodiments, the
electrochemical cell includes first electrolyte inlet port (814)
adaptable for inputting first electrolyte 804 into the system;
second electrolyte inlet port (816) for inputting second
electrolyte (806) into the system; and third inlet port (826) for
inputting third electrolyte into the system. Additionally, the cell
includes outlet port (818) for draining first electrolyte; outlet
port (820) for draining second electrolyte; and outlet port (828)
for draining third electrolyte. As will be appreciated by one
ordinarily skilled, the inlet and outlet ports are adaptable for
various flow protocols including batch flow, semi-batch flow, or
continuous flow. In alternative embodiments, the system includes a
duct (822) for directing gas to the anode; in various embodiments
the gas is hydrogen formed at the cathode (810).
[0135] With reference to FIG. 10, upon applying a low voltage
across the cathode (810) and anode (808), hydroxide ions form at
the cathode (810) and a gas does not form at the anode (808).
Further, where third electrolyte (830) comprises sodium chloride,
chloride ions migrate into the first electrolyte (804) from the
third electrolyte (830) through the anion exchange membrane (802);
sodium ions migrate to the second electrolyte (806) from the third
electrolyte (830); protons form at the anode; and hydrogen gas
forms at the cathode. As noted previously, a gas e.g., oxygen or
chlorine does not form at the anode (808).
[0136] As can be appreciated by one ordinarily skilled in the art,
and with reference to FIG. 10 in second electrolyte (806) as
hydroxide ions from the cathode (810) enter into the solution
concurrent with migration of sodium ions from the third
electrolyte, increasingly an aqueous solution of sodium hydroxide
will form in second electrolyte (806). Depending on the voltage
applied across the system and the flow rate of the second
electrolyte through the system, the pH of the solution will be
adjusted. In one embodiment, when a volt of about 0.1 V or less,
0.2 V or less, 0.3 V or less, 0.4 V or less, 0.5 V or less, 0.6 V
or less, 0.7 V or less, 0.8 V or less, 0.9 V or less, 1.0 V or
less, 1.1 V or less, 1.2 V or less, 1.3 V or less, 01.4 V or less,
1.5 V or less, 1.6 V or less, 1.7 V or less, 1.8 V or less, 1.9 V
or less, or 2.0 V or less or less is applied across the anode and
cathode, the pH of the second electrolyte solution increased; in
another embodiment, when a volt of about 0.1 to 2.0 V is applied
across the anode and cathode the pH of the second electrolyte
increased; in yet another embodiment, when a voltage of about 0.1.0
to 1 V is applied across the anode and cathode the pH of the second
electrolyte solution increased. Similar results are achievable with
voltages of 0.1 to 0.8 V; 0.1 to 0.7 V; 0.1 to 0.6 V; 0.1 to 0.5 V;
0.1 to 0.4 V; and 0.1 to 0.3 V across the electrodes. In one
embodiment, a volt of about 0.6 volt or less is applied across the
anode and cathode; in another embodiment, a volt of about 0.1 to
0.6 volt or less is applied across the anode and cathode; in yet
another embodiment, a voltage of about 0.1 to 1 volt or less is
applied across the anode and cathode.
[0137] Similarly, with reference to FIG. 10, in first electrolyte
(804) as proton form at the anode (808) and enter into the solution
concurrent with migration of chloride ions from the third
electrolyte to the first electrolyte, increasingly an acidic
solution will form in first electrolyte (804). Depending on the
voltage applied across the system and the flow rate of the second
electrolyte through the system, the pH of the solution will be
adjusted. In one embodiment, when a volt of about 0.1 V or less,
0.2 V or less, 0.3 V or less, 0.4 V or less, 0.5 V or less, 0.6 V
or less, 0.7 V or less, 0.8 V or less, 0.9 V or less, 1.0 V or
less, 1.1 V or less, 1.2 V or less, 1.3 V or less, 01.4 V or less,
1.5 V or less, 1.6 V or less, 1.7 V or less, 1.8 V or less, 1.9 V
or less, or 2.0 V or less is applied across the anode and cathode,
the pH of the second electrolyte solution increased; in another
embodiment, when a volt of about 0.1 to 2.0 V is applied across the
anode and cathode the pH of the second electrolyte increased; in
yet another embodiment, when a voltage of about 0.1.0 to 1 V is
applied across the anode and cathode the pH of the second
electrolyte solution increased. Similar results are achievable with
voltages of 0.1 to 0.8 V; 0.1 to 0.7 V; 0.1 to 0.6 V; 0.1 to 0.5 V;
0.1 to 0.4 V; and 0.1 to 0.3 V across the electrodes. In one
embodiment, a volt of about 0.6 volt or less is applied across the
anode and cathode; in another embodiment, a volt of about 0.1 to
0.6 volt or less is applied across the anode and cathode; in yet
another embodiment, a voltage of about 0.1 to 1 volt or less is
applied across the anode and cathode as indicated in Table 2.
[0138] As illustrated in FIG. 10, hydrogen gas formed at the
cathode (810) is directed to the anode (808) where, without being
bound to any theory, it is believed that hydrogen gas is adsorbed
and/or absorbed into the anode and subsequently forms protons at
the anode and enters the first electrolyte (804). Also, in various
embodiments as illustrated in FIGS. 8-10, a gas such as oxygen or
chlorine does not form at the anode (808). Accordingly, as can be
appreciated, with the formation of protons at the anode and
migration of chlorine into the first electrolyte, hydrochloric acid
is obtained in the first electrolyte (804).
[0139] As described with reference to FIGS. 8-9, as hydroxide ions
from the anode (810) and enter in to the second electrolyte (806)
concurrent with migration of chloride ions from the second
electrolyte, an aqueous solution of sodium hydroxide will form in
second electrolyte (806). Consequently, depending on the voltage
applied across the system and the flow rate of the second
electrolyte (806) through the system, the pH of the second
electrolyte is adjusted. In one embodiment, when a volt of about
0.1 V or less, 0.2 V or less, 0.3 V or less, 0.4 V or less, 0.5 V
or less, 0.6 V or less, 0.7 V or less, 0.8 V or less, 0.9 V or
less, 1.0 V or less, 1.1 V or less, 1.2 V or less, 1.3 V or less,
01.4 V or less, 1.5 V or less, 1.6 V or less, 1.7 V or less, 1.8 V
or less, 1.9 V or less, or 2.0 V or less is applied across the
anode and cathode, the pH of the second electrolyte solution
increased; in another embodiment, when a volt of about 0.1 to 2.0 V
is applied across the anode and cathode the pH of the second
electrolyte increased; in yet another embodiment, when a voltage of
about 0.1.0 to 1 V is applied across the anode and cathode the pH
of the second electrolyte solution increased. Similar results are
achievable with voltages of 0.1 to 0.8 V; 0.1 to 0.7 V; 0.1 to 0.6
V; 0.1 to 0.5 V; 0.1 to 0.4 V; and 0.1 to 0.3 V across the
electrodes. In one embodiment, when a volt of about 0.6 volt or
less is applied across the anode and cathode, the pH of the second
electrolyte solution increased; in another embodiment, when a volt
of about 0.1 to 0.6 volt or less is applied across the anode and
cathode the pH of the second electrolyte increased; in yet another
embodiment, when a voltage of about 0.1 to 1 volt or less is
applied across the anode and cathode the pH of the second
electrolyte solution increased.
[0140] Optionally, a gas including CO.sub.2 is dissolve into the
second electrolyte solution by bubbling the gas into the first
electrolyte solution 804 as describe above. In an optional step the
resulting second electrolyte solution is used to precipitate a
carbonate and/or bicarbonate compounds such as calcium carbonate or
magnesium carbonate and or their bicarbonates, as described herein.
The precipitated carbonate compound can be used as cements and
build material as described herein.
[0141] In another optional step, acidified second electrolyte
solution 804 is utilized to dissolve a calcium and/or magnesium
rich mineral, such as mafic mineral including serpentine or olivine
for use as the solution for precipitating carbonates and
bicarbonates as described herein. In various embodiments, the
resulting solution can be used as the second electrolyte solution.
Similarly, in embodiments where hydrochloric acid is produced in
second electrolyte 806, the hydrochloric acid can be used in place
of, or in addition to, the acidified second electrolyte
solution.
[0142] Embodiments described above produce electrolyte solutions
enriched in bicarbonate ions and carbonate ions, or combinations
thereof as well as an acidified stream. The acidified stream can
also find application in various chemical processes. For example,
the acidified stream can be employed to dissolve calcium and/or
magnesium rich minerals such as serpentine and olivine to create
the electrolyte solution used in the reservoir 816. Such an
electrolyte solution can be charged with bicarbonate ions and then
made sufficiently basic so as to precipitate carbonate compounds as
described herein.
[0143] In some embodiments, a first electrochemical process may be
used to remove protons from solution to facilitate CO.sub.2
absorption, without concomitant production of hydroxide, while a
second electrochemical process may be used to produce hydroxide in
order to further remove protons to shift equilibrium toward
carbonate and cause precipitation of carbonates. The two processes
may have different voltage requirements, e.g., the first process
may require lower voltage than the second, thus minimizing total
overall voltage used in the process. For example, the first process
may be a bielectrode process as described above, operating at 1.0V
or less, or 0.9V or less, or 0.8V or less, or 0.7V or less, or 0.6V
or less, or 0.5V or less, or 0.4V or less, or 0.3V or less, or 0.2V
or less, or 0.1V or less, while the second process may be a
low-voltage hydroxide producing process as described above,
operating at 1.5 V or less, or 1.4V or less, or 1.3V or less, or
1.2V or less, or 1.1 V or less, 1.0V or less, or 0.9V or less, or
0.8V or less, or 0.7V or less, or 0.6V or less, or 0.5V or less, or
0.4V or less, or 0.3V or less, or 0.2V or less, or 0.1V or less.
For example, in some embodiments the first process is a bielectrode
process operating at 0.6 V or less and the second process is a
low-voltage hydroxide producing process operating at 1.2V or
less.
[0144] Also of interest are the electrochemical approaches
described in published United States Application Publication Nos.
20060185985 and 20080248350, as well as published PCT Application
Publication No. WO 2008/018928; the disclosures of which are hereby
incorporated by reference.
[0145] Stoichiometry dictates that the production of a carbonate to
be precipitated in order to sequester CO.sub.2 from a source of
CO.sub.2 requires the removal of two protons from the initial
carbonic acid that is formed when CO.sub.2 is dissolved in water
(see equations 1-5, above). Removal of the first proton produces
bicarbonate and removal of the second produces carbonate, which may
be precipitated as, e.g., a carbonate of a divalent cation, such as
magnesium carbonate or calcium carbonate. The removal of the two
protons requires some process or combination of processes which
typically require energy. For example, if the protons are removed
through the addition of sodium hydroxide, the source of renewable
sodium hydroxide is typically the chloralkali process, which uses
an electrochemical process requiring at least 2.8 V and a fixed
amount of electrons per mole of sodium hydroxide. That energy
requirement may be expressed in terms of a carbon footprint, i.e.,
amount of carbon produced to provide the energy to drive the
process.
[0146] A convenient way of expressing the carbon footprint for a
given process of proton removal is as a percentage of the CO.sub.2
removed from the source of CO.sub.2. That is, the energy required
for the removal of the protons may be expressed in terms of
CO.sub.2 emission of a conventional method of power generation to
produce that energy, which may in turn be expressed as a percent of
the CO.sub.2 removed from the source of CO.sub.2. For convenience,
and as a definition in this aspect of the invention, the "CO.sub.2
produced" in such a process will be considered the CO.sub.2 that
would be produced in a conventional coal/steam power plant to
provide sufficient energy to remove two protons. Data are publicly
available for such power plants for the last several years that
show tons of CO.sub.2 produced per total MWh of energy produced.
See, e.g., the website having the address produced by combining
"http://carma." with "org/api/". For purposes of definition here, a
value of 1 ton CO.sub.2 per MWh will be used, which corresponds
closely to typical coal-fired power plants; for example, the WA
Parish plant produced 18,200,000 MWh of energy in 2000 while
producing approximately 19,500,000 tons of CO.sub.2 and at present
produces 21,300,00 MWh of energy while producing 20,900,000 tons of
CO.sub.2, which average out very close to the definitional 1 ton
CO.sub.2 per MWh that will be used herein. These numbers can then
be used to calculate the CO.sub.2 production necessary to remove
sufficient protons to remove CO.sub.2 from a gas stream, and
compare it to the CO.sub.2 removed. For example, in a process
utilizing the chloralkali process operating at 2.8 V to provide
base, and used to sequester CO.sub.2 from a coal/stem power plant,
the amount of CO.sub.2 produced by the power plant to supply the
energy to create base by the chloralkali process to remove two
protons, using the 1 ton CO.sub.2/1 MWh ratio, would be well above
200% of the amount of CO.sub.2 sequestered by the removal of the
two protons and precipitation of the CO.sub.2 in stable form. As a
further condition of the definition of "CO.sub.2 produced" in this
aspect of the invention, no theoretical or actual calculations of
reduction of the energy load due to, e.g., reuse of byproducts of
the process for removing the protons (e.g., in the case of the
chloralkali process, use of hydrogen produced in the process in a
fuel cell or by direct combustion to produce energy) are included
in the total of "CO.sub.2 produced." In addition, no theoretical or
actual supplementation of the power supplied by the power plant
with renewable sources of energy is considered, e.g., sources of
energy that produce little or no carbon dioxide, such as wind,
solar, tide, hydroelectric, and the like. If the process of
removing protons includes the use of a hydroxide or other base,
including a naturally-occurring or stockpiled base, the amount of
CO.sub.2 produced would be the amount that may be
stoichiometrically calculated based on the process by which the
base is produced, e.g., for industrially produced base, the
standard chloralkali process or other process by which the base is
produced, and for natural base, the best theoretical model for the
natural production of the base.
[0147] Using this definition of "CO.sub.2 produced," in some
embodiments the invention includes forming a stable
CO.sub.2-containing precipitate from a human-produced gaseous
source of CO.sub.2, wherein the formation of the precipitate
utilizes a process for removing protons from an aqueous solution in
which a portion or all of the CO.sub.2 of the gaseous source of
CO.sub.2 is dissolved, and wherein the CO.sub.2 produced by the
process of removing protons is less than 100, 90, 80, 70, 65, 60,
55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5% of the CO.sub.2
removed from the gaseous source of CO.sub.2 by said formation of
precipitate. In some embodiments, the invention includes forming a
stable CO.sub.2-containing precipitate from a human-produced
gaseous source of CO.sub.2, wherein the formation of the
precipitate utilizes a process for removing protons from an aqueous
solution in which a portion or all of the CO.sub.2 of the gaseous
source of CO.sub.2 is dissolved, and wherein the CO.sub.2 produced
by the process of removing protons is less than 70% of the CO.sub.2
removed from the gaseous source of CO.sub.2 by the formation of
precipitate. In some embodiments the invention includes forming a
stable CO2-containing precipitate from a human-produced gaseous
source of CO.sub.2, wherein the formation of the precipitate
utilizes a process for removing protons from an aqueous solution in
which a portion or all of the CO.sub.2 of the gaseous source of
CO.sub.2 is dissolved, and wherein the CO.sub.2 produced by the
process of removing protons is less than 50% of the CO.sub.2
removed from the gaseous source of CO.sub.2 by the formation of
precipitate. In some embodiments the invention includes forming a
stable CO2-containing precipitate from a human-produced gaseous
source of CO.sub.2, wherein the formation of the precipitate
utilizes a process for removing protons from an aqueous solution in
which a portion or all of the CO.sub.2 of the gaseous source of
CO.sub.2 is dissolved, and wherein the CO.sub.2 produced by the
process of removing protons is less than 30% of the CO.sub.2
removed from the gaseous source of CO.sub.2 by the formation of
precipitate. In some embodiments, the process of removing protons
is a process, such as an electrochemical process as described
herein, that removes protons without producing a base, e.g.,
hydroxide. In some embodiments, the process of removing protons is
a process, such as an electrochemical process as described herein,
that removes protons by producing a base, e.g., hydroxide. In some
embodiments, the process is a combination of a process, such as an
electrochemical process as described herein, that removes protons
without producing a base, e.g., hydroxide, and a process, such as
an electrochemical process as described herein, that removes
protons by producing a base, e.g., hydroxide. In some embodiments,
the process of proton removal comprises an electrochemical process,
either removes protons directly (e.g., direct removal of protons)
or indirectly (e.g., production of hydroxide). In some embodiments
a combination of processes, e.g., electrochemical processes is
used, where a first process, e.g., electrochemical process, removes
protons directly and a second process, e.g., electrochemical
process, removes protons indirectly (e.g., by production of
hydroxide).
[0148] In some instances, precipitation of the desired product
following CO.sub.2 charging (e.g., as described above) occurs
without addition of a source divalent metal ions. As such, after
the water is charged with CO.sub.2, the water is not then contacted
with a source of divalent metal ions, such as one or more divalent
metal ion salts, e.g., calcium chloride, magnesium chloride, sea
salts, etc.
[0149] In one embodiment of the invention, a carbonate
precipitation process may be employed to selectively precipitate
calcium carbonate materials from the solution in order to provide
the desired ratio of magnesium to calcium, followed by additional
CO.sub.2 charging, and in some embodiments additional Mg ion
charging, and a final carbonate precipitation step. This embodiment
is useful in utilizing concentrated waters such as desalination
brine, wherein the cation content is sufficiently high that
addition of more Mg ions is difficult. This embodiment is also
useful in solutions of any concentration where two different
products are desired to be produced--a primarily calcium carbonate
material, and then a magnesium carbonate dominated material.
[0150] The yield of product from a given precipitation reaction may
vary depending on a number of factors, including the specific type
of water employed, whether or not the water is supplemented with
divalent metal ions, the particular precipitation protocol
employed, etc. In some instances, the precipitate protocols
employed to precipitate the product are high yield precipitation
protocols. In these instances, the amount of product produced from
a single precipitation reaction (by which is meant a single time
that that the water is subjected to precipitation conditions, such
as increasing the pH to a value of 9.5 or higher, such as 10 or
higher as reviewed above in greater detail) may be 5 g or more,
such as 10 g or more, 15 g or more, 20 g or more, 25 g or more, 30
g or more, 35 g or more, 40 g or more, 45 g or more, 50 g or more,
60 g or more, 70 g or more, 80 g or more, 90 g or more, 100 g or
more, 120 g or more, 140 g or more, 160 g or more, 180 g or more,
200 g or more of the storage stable carbon dioxide sequestering
product for every liter of water. In some instances, the amount of
product produced for every liter of water ranges from 5 to 200 g,
such as 10 to 100 g, including 20 to 100 g. In instances where the
divalent metal ion content of the water is not supplemented prior
to subjecting the water to precipitate conditions (for example
where the water is seawater and the seawater is not supplemented
with a source of divalent metal ion or ions), the yield of product
may range from 5 to 20 g product per liter of water, such as 5 to
10, e.g., 6 to 8, g product per liter of water. In other instances
where the water is supplemental with a source of divalent metal
ions, such as magnesium and/or calcium ions, the yield of product
may be higher, 2-fold higher, 3-fold higher, 5-fold higher, 10-fold
higher, 20-fold higher or more, such that the yield of such
processes may range in some embodiments from 10 to 200, such as 50
to 200 including 100 to 200 g product for every liter of water
subjected to precipitation conditions.
[0151] In certain embodiments, a multi-step process is employed. In
these embodiments, a carbonate precipitation process may be
employed to selectively precipitate calcium carbonate materials
from the solution, followed by additional steps of CO.sub.2
charging and subsequent carbonate precipitation. The steps of
additional CO.sub.2 charging and carbonate precipitation can in
some cases be repeated one, two, three, four, five, six, seven,
eight, nine, ten, or more times, precipitating additional amounts
of carbonate material with each cycle. In some cases, the final pH
ranges from about 8 to 10, such as from about 9 to 10, including
from about 9.5 to 10, for example, from about 9.6 to 9.8.
[0152] In certain embodiments, two or more reactors may be used to
carry out the methods described herein. In these embodiments, the
method may include a first reactor and a second reactor. In these
cases, the first reactor is used for contacting the initial water
with a magnesium ion source and for charging the initial water with
CO.sub.2, as described above. The water may be agitated to
facilitate the dissolution of the magnesium ion source and to
facilitate contact of the initial water with the CO.sub.2. In some
cases, before the CO.sub.2 charged water is transferred to the
second reactor, agitation of the CO.sub.2 charged water is stopped,
such that undissolved solids may settle by gravity. The CO.sub.2
charged water is then transferred from the first reactor to the
second reactor. After transferring the CO.sub.2 charged water to
the second reactor, the step of carbonate precipitation may be
performed, as described herein.
[0153] In certain embodiments, a multi-step process, as described
above, employing two or more reactors, as described above, can be
used to carry out the methods described herein. In these
embodiments, a first reactor is used for contacting the initial
water with a magnesium ion source and for charging the initial
water with CO.sub.2, as described above. Subsequently, the CO.sub.2
charged water is transferred from the first reactor to a second
reactor for the carbonate precipitation reaction. In certain
embodiments, one or more additional steps of CO.sub.2 charging and
subsequent carbonate precipitation may be performed in the second
reactor, as described above.
[0154] In certain embodiments, precipitation conditions can be used
that favor the formation of particular morphologies of carbonate
compound precipitates. For instance, precipitation conditions can
be used that favor the formation of amorphous carbonate compound
precipitates over the formation of crystalline carbonate compound
precipitates. In these cases, in addition to contacting the initial
water with a magnesium ion source and charging the initial water
with CO.sub.2, as described above, a precipitation facilitator may
be added. In these cases, the precipitation facilitator facilitates
the formation of carbonate compound precipitates at lower pH's
sufficient for nucleation, but insufficient for crystal formation
and growth. Examples of precipitation facilitators include, but are
not limited to, aluminum sulfate (Al.sub.2SO.sub.4).sub.3. In
certain embodiments, the amount of precipitation facilitator added
ranges from about 1 ppm to about 1000 ppm, such as from about 1 ppm
to about 500, including from about 10 ppm to about 200 ppm, for
example from about 25 ppm to about 75 ppm. Additionally, the pH of
the water can be maintained between about 6 and 8, such as between
about 7 and 8, during carbonate compound precipitation formation by
alternating CO.sub.2 charging and subsequent carbonate
precipitation, as described above.
[0155] Alternatively, in yet other embodiments, precipitation
conditions can be used that favor the formation of crystalline
carbonate compound precipitates over the formation of amorphous
carbonate compound precipitates.
[0156] Further details regarding specific precipitation protocols
employed in certain embodiments of the invention are provided below
with respect to the description of the figures of the
application.
[0157] Following production of the precipitate product from the
water, a composition is produced which includes precipitated
product and a mother liquor (i.e., the remaining liquid from which
the precipitated product was produced). This composition may be a
slurry of the precipitate and mother liquor.
[0158] As summarized above, in sequestering carbon dioxide, the
precipitated product is disposed of in some manner following its
production. The phrase "disposed of" means that the product is
either placed at a storage site or employed for a further use in
another product, i.e., a manufactured or man-made item, where it is
stored in that other product at least for the expected lifetime of
that other product. In some instances, this disposal step includes
forwarding the slurry composition described above to a long term
storage site. The storage site could be an above ground site, a
below ground site or an underwater site. In these embodiments,
following placement of the slurry at the storage site, the mother
liquor component of the slurry may naturally separate from the
precipitate, e.g., via evaporation, dispersal, etc.
[0159] Where desired, the resultant precipitated product may be
separated from the resultant mother liquor. Separation of the
precipitate can be achieved using any convenient approach. For
example, separation may be achieved by drying the precipitated
product to produce a dried precipitated product. Drying protocols
of interest include filtering the precipitate from the mother
liquor to produce a filtrate and then air drying the filtrate.
Where the filtrate is air dried, air drying may be at a temperature
ranging from -70 to 120.degree. C., as desired. In some instances,
drying may include placing the slurry at a drying site, such as a
tailings pond, and allowing the liquid component of the precipitate
to evaporate and leave behind the desired dried product. Also of
interest are freeze-drying (i.e., lyophilization) protocols, where
the precipitate is frozen, the surrounding pressure is reduced and
enough heat is added to allow the frozen water in the material to
sublime directly from the frozen precipitate phase to gas. Yet
another drying protocol of interest is spray drying, where the
liquid containing the precipitate is dried by feeding it through a
hot gas, e.g., where the liquid feed is pumped through an atomiser
into a main drying chamber and a hot gas is passed as a co-current
or counter-current to the atomiser direction.
[0160] Where the precipitated product is separated from the mother
liquor, the resultant precipitate may be disposed of in a variety
of different ways, as further elaborated below. For example, the
precipitate may be employed as a component of a building material,
as reviewed in greater detail below. Alternatively, the precipitate
may be placed at a long term storage site (sometimes referred to in
the art as a carbon bank), where the site may be above ground site,
a below ground site or an underwater site. Further details
regarding disposal protocols of interest are provided below.
[0161] The resultant mother liquor may also be processed as
desired. For example, the mother liquor may be returned to the
source of the water, e.g., ocean, or to another location. In
certain embodiments, the mother liquor may be contacted with a
source of CO.sub.2, e.g., as described above, to sequester further
CO.sub.2. For example, where the mother liquor is to be returned to
the ocean, the mother liquor may be contacted with a gaseous source
of CO.sub.2 in a manner sufficient to increase the concentration of
carbonate ion present in the mother liquor. Contact may be
conducted using any convenient protocol, such as those described
above. In certain embodiments, the mother liquor has an alkaline
pH, and contact with the CO.sub.2 source is carried out in a manner
sufficient to reduce the pH to a range between 5 and 9, e.g., 6 and
8.5, including 7.5 to 8.2.
[0162] The methods of the invention may be carried out at land or
sea, e.g., at a land location where a suitable water is present at
or is transported to the location, or in the ocean or other body of
alkali-earth-metal-containing water, be that body naturally
occurring or manmade. In certain embodiments, a system is employed
to perform the above methods, where such systems include those
described below in greater detail.
[0163] The above portion of this application provides an overview
of various aspects of the methods of the invention. Certain
embodiments of the invention are now reviewed further in greater
detail in terms of the certain figures of the invention.
[0164] FIG. 1 provides a schematic flow diagram of a carbon dioxide
sequestration process that may be implemented in a system, where
the system may be manifested as a stand-alone plant or as an
integrated part of another type of plant, such as a power
generation plant, a cement production plant, etc. In FIG. 1, water
10 is delivered to a precipitation reactor 20, e.g., via a pipeline
or other convenient manner, and subjected to carbonate mineral
precipitation conditions. The water employed in the process
illustrated in FIG. 1 is one that includes one or more alkaline
earth metals, e.g., calcium, magnesium etc., such that it may be
viewed as an alkaline-earth-metal-ion-containing water, as reviewed
above. In certain embodiments of the invention, the water of
interest is one that includes calcium in amounts ranging from 50
ppm to 20,000 ppm, such as 200 ppm to 5000 ppm and including 400
ppm to 1000 ppm. Also of interest are waters that include magnesium
in amounts ranging from 50 ppm to 40,000 ppm, such as 100 ppm to
10,000 ppm and including 500 ppm to 2500 ppm. In embodiments of the
invention, the alkaline-earth-metal-ion-containing water is a
saltwater. As reviewed above, saltwaters of interest include a
number of different types of aqueous fluids other than fresh water,
such as brackish water, sea water and brine (including man-made
brines, for example geothermal plant wastewaters, desalination
waste waters, etc., as well as naturally occurring brines as
described herein), as well as other salines having a salinity that
is greater than that of freshwater. Brine is water saturated or
nearly saturated with salt and has a salinity that is 50 ppt (parts
per thousand) or greater. Brackish water is water that is saltier
than fresh water, but not as salty as seawater, having a salinity
ranging from 0.5 to 35 ppt. Seawater is water from a sea or ocean
and has a salinity ranging from 35 to 50 ppt. Freshwater is water
which has a salinity of less than 5 ppt dissolved salts. Saltwaters
of interest may be obtained from a naturally occurring source, such
as a sea, ocean, lake, swamp, estuary, lagoon, etc., or a man-made
source, as desired.
[0165] As reviewed above, waters of interest also include
freshwaters. In certain embodiments, the water employed in the
invention may be a mineral rich, e.g., calcium and/or magnesium
rich, freshwater source. In some embodiments, freshwaters, such as
calcium rich waters may be combined with magnesium silicate
minerals, such as olivine or serpentine, in a solution that has
become acidic due to the addition of carbon dioxide from carbonic
acid, which dissolves the magnesium silicate, leading to the
formation of calcium magnesium silicate carbonate compounds. In
certain embodiments, the water source can be freshwater wherein
metal-ions, e.g., sodium, potassium, calcium, magnesium, etc. are
added. Metal-ions can be added to the freshwater source using any
convenient protocol, e.g., as a solid, aqueous solution, suspension
etc.
[0166] In certain embodiments, the water may be obtained from the
industrial plant that is also providing the gaseous waste stream.
For example, in water cooled industrial plants, such as seawater
cooled industrial plants, water that has been employed by the
industrial plant may then be sent to the precipitation system and
employed as the water in the precipitation reaction. Where desired,
the water may be cooled prior to entering the precipitation
reactor. Such approaches may be employed, e.g., with once-through
cooling systems. For example, a city or agricultural water supply
may be employed as a once-through cooling system for an industrial
plant. The water from the industrial plant may then be employed in
the precipitation protocol, where output water has a reduced
hardness and greater purity. Where desired, such systems may be
modified to include security measures, e.g., to detect tampering
(such as addition of poisons) and coordinated with governmental
agencies, e.g., Homeland Security or other agencies. Additional
tampering or attack safeguards may be employed in such
embodiments.
[0167] As shown in FIG. 1, an industrial plant gaseous waste stream
30 is contacted with the water at precipitation step 20 to produce
a CO.sub.2 charged water. By CO.sub.2 charged water is meant water
that has had CO.sub.2 gas contacted with it, where CO.sub.2
molecules have combined with water molecules to produce, e.g.,
carbonic acid, bicarbonate and carbonate ion. Charging water in
this step results in an increase in the "CO.sub.2 content" of the
water, e.g., in the form of carbonic acid, bicarbonate and
carbonate ion, and a concomitant decrease in the amount of CO.sub.2
of the waste stream that is contacted with the water. The CO.sub.2
charged water is acidic in some embodiments, having a pH of 6.0 or
less, such as 4.0 or less and including 3.0 and less. In certain
embodiments, the amount of CO.sub.2 of the gas that is used to
charge the water decreases by 85% or more, such as 99% or more as a
result of this contact step, such that the methods remove 50% or
more, such as 75% or more, e.g., 85% or more, including 99% or more
of the CO.sub.2 originally present in the gaseous waste stream that
is contacted with the water. Contact protocols of interest include,
but are not limited to: direct contacting protocols, e.g., bubbling
the gas through the volume of water, concurrent contacting means,
i.e., contact between unidirectionally flowing gaseous and liquid
phase streams, countercurrent means, i.e., contact between
oppositely flowing gaseous and liquid phase streams, and the like.
The gaseous stream may contact the water source vertically,
horizontally, or at some other angle. The CO.sub.2 may be contacted
with the water source from one or more of the following positions:
below, above, or at the surface level of the
alkaline-earth-metal-ion-containing water. Contact may be
accomplished through the use of infusers, bubblers, fluidic Venturi
reactor, sparger, gas filter, spray, tray, catalytic bubble column
reactors, draft-tube type reactors or packed column reactors, and
the like, as may be convenient. Where desired, two or more
different CO.sub.2 charging reactors (such as columns or other
types of reactor configurations) may be employed, e.g., in series,
such as three or more, four or more, etc. In certain embodiments,
various means, e.g., mechanical stirring, electromagnetic stirring,
spinners, shakers, vibrators, blowers, ultrasonication, to agitate
or stir the reaction solution are used to increase the contact
between CO.sub.2 and the water source.
[0168] As reviewed above, the gas from the industrial plant 30 may
be processed before being used to charge the water. For example,
the gas may be subjected to oxidation conditions, e.g., to convert
CO to CO.sub.2, NO to NO.sub.2, and SO.sub.2 to SO.sub.3, where
desired.
[0169] At step 20, the storage stable product is precipitated at
precipitation step 20. Precipitation conditions of interest include
those that modulate the physical environment of the water to
produce the desired precipitate product. For example, the
temperature of the water may be raised to an amount suitable for
precipitation of the desired carbonate mineral to occur. In such
embodiments, the temperature of the water may be raised to a value
from 5 to 70.degree. C., such as from 20 to 50.degree. C. and
including 25 to 45.degree. C. As such, while a given set of
precipitation conditions may have a temperature ranging from 0 to
100.degree. C., the temperature may be raised in certain
embodiments to produce the desired precipitate. In certain
embodiments, the temperature is raised using energy generated from
low- or zero-carbon dioxide emission sources, e.g., solar energy
source, wind energy source, hydroelectric energy source, etc. In
certain embodiments, excess and/or process heat from the industrial
plant carried in the gaseous waste stream is employed to raise the
temperature of the water during precipitation either as hot gases
or steam. In certain embodiments, contact of the water with the
gaseous waste stream may have raised the water to the desired
temperature, where in other embodiments, the water may need to be
cooled to the desired temperature.
[0170] In normal sea water, 93% of the dissolved CO.sub.2 is in the
form of bicarbonate ions (HCO.sub.3.sup.-) and 6% is in the form of
carbonate ions (CO.sub.3.sup.-2). When calcium carbonate
precipitates from normal sea water, CO.sub.2 is released. In fresh
water, above pH 10.33, greater than 90% of the carbonate is in the
form of carbonate ion, and no CO.sub.2 is released during the
precipitation of calcium carbonate. In sea water this transition
occurs at a slightly lower pH, closer to a pH of 9.7. While the pH
of the water employed in methods may range from 5 to 14 during a
given precipitation process, in certain embodiments the pH is
raised to alkaline levels in order to drive the precipitation of
carbonate compounds, as well as other compounds, e.g., hydroxide
compounds, as desired. In certain of these embodiments, the pH is
raised to a level which minimizes if not eliminates CO.sub.2
production during precipitation, causing dissolved CO.sub.2, e.g.,
in the form of carbonate and bicarbonate, to be trapped in the
carbonate compound precipitate. In these embodiments, the pH may be
raised to 9 or higher, such as 10 or higher, including 11 or
higher.
[0171] As summarized above, the pH of the
alkaline-earth-metal-ion-containing source is raised using any
convenient approach. In certain embodiments, a pH raising agent may
be employed, where examples of such agents include oxides (calcium
oxide, magnesium oxide), hydroxides (e.g., potassium hydroxide,
sodium hydroxide, brucite (Mg(OH).sub.2, etc.), carbonates (e.g.,
sodium carbonate) and the like.
[0172] In embodiments of the invention, ash is employed as a pH
modifying agent, e.g., to increase the pH of the CO.sub.2 charged
water. The ash may be used as a as the sole pH modifier or in
conjunction with one or more additional pH modifiers. Of interest
in certain embodiments is use of a coal ash as the ash. The coal
ash as employed in this invention refers to the residue produced in
power plant boilers or coal burning furnaces, for example, chain
grate boilers, cyclone boilers and fluidized bed boilers, from
burning pulverized anthracite, lignite, bituminous or
sub-bituminous coal. Such coal ash includes fly ash which is the
finely divided coal ash carried from the furnace by exhaust or flue
gases; and bottom ash which collects at the base of the furnace as
agglomerates.
[0173] Fly ashes are generally highly heterogeneous, and include of
a mixture of glassy particles with various identifiable crystalline
phases such as quartz, mullite, and various iron oxides. Fly ashes
of interest include Type F and Type C fly ash. The Type F and Type
C flyashes referred to above are defined by CSA Standard A23.5 and
ASTM C618. The chief difference between these classes is the amount
of calcium, silica, alumina, and iron content in the ash. The
chemical properties of the fly ash are largely influenced by the
chemical content of the coal burned (i.e., anthracite, bituminous,
and lignite). Fly ashes of interest include substantial amounts of
silica (silicon dioxide, SiO.sub.2) (both amorphous and
crystalline) and lime (calcium oxide, CaO, magnesium oxide,
MgO).
[0174] Table 3 below provides the chemical makeup of various types
of fly ash that find use in embodiments of the invention.
TABLE-US-00003 TABLE 3 Component Bituminous Subbituminous Lignite
SiO.sub.2 (%) 20-60 40-60 15-45 Al.sub.2O.sub.3 (%) 5-35 20-30
20-25 Fe.sub.2O.sub.3 (%) 10-40 4-10 4-15 CaO (%) 1-12 5-30
15-40
[0175] The burning of harder, older anthracite and bituminous coal
typically produces Class F fly ash. Class F fly ash is pozzolanic
in nature, and contains less than 10% lime (CaO). Fly ash produced
from the burning of younger lignite or subbituminous coal, in
addition to having pozzolanic properties, also has some
self-cementing properties. In the presence of water, Class C fly
ash will harden and gain strength over time. Class C fly ash
generally contains more than 20% lime (CaO). Alkali and sulfate
(SO.sub.4) contents are generally higher in Class C fly ashes.
[0176] Fly ash material solidifies while suspended in exhaust gases
and is collected using various approaches, e.g., by electrostatic
precipitators or filter bags. Since the particles solidify while
suspended in the exhaust gases, fly ash particles are generally
spherical in shape and range in size from 0.5 .mu.m to 100 .mu.m.
Flyashes of interest include those in which at least about 80%, by
weight comprises particles of less than 45 microns. Also of
interest in certain embodiments of the invention is the use of
highly alkaline fluidized bed combustor (FBC) fly ash.
[0177] Also of interest in embodiments of the invention is the use
of bottom ash. Bottom ash is formed as agglomerates in coal
combustion boilers from the combustion of coal. Such combustion
boilers may be wet bottom boilers or dry bottom boilers. When
produced in a wet or dry bottom boiler, the bottom ash is quenched
in water. The quenching results in agglomerates having a size in
which 90% fall within the particle size range of 0.1 mm to 20 mm,
where the bottom ash agglomerates have a wide distribution of
agglomerate size within this range. The main chemical components of
a bottom ash are silica and alumina with lesser amounts of oxides
of Fe, Ca, Mg, Mn, Na and K, as well as sulphur and carbon.
[0178] Also of interest in certain embodiments is the use of
volcanic ash as the ash. Volcanic ash is made up of small tephra,
i.e., bits of pulverized rock and glass created by volcanic
eruptions, less than 2 millimetres (0.079 in) in diameter.
[0179] In one embodiment of the invention, cement kiln dust (CKD)
is added to the reaction vessel as a means of modifying pH. The
nature of the fuel from which the ash and/or CKD were produced, and
the means of combustion of said fuel, will influence the chemical
composition of the resultant ash and/or CKD. Thus ash and/or CKD
may be used as a portion of the means for adjusting pH, or the sole
means, and a variety of other components may be utilized with
specific ashes and/or CKDs, based on chemical composition of the
ash and/or CKD.
[0180] In embodiments of the invention, ash is added to the
reaction as one source of these additional reactants, to produce
carbonate mineral precipitates which contain one or more components
such as amorphous silica, crystalline silica, calcium silicates,
calcium alumina silicates, or any other moiety which may result
from the reaction of ash in the carbonate mineral precipitation
process.
[0181] The ash employed in the invention may be contacted with the
water to achieve the desired pH modification using any convenient
protocol, e.g., by placing an amount of ash into the reactor
holding the water, where the amount of ash added is sufficient to
raise the pH to the desired level, by flowing the water through an
amount of the ash, e.g., in the form of a column or bed, etc.
[0182] In certain embodiments where the pH is not raised to a level
of 12 or higher, the fly ash employed in the method, e.g., as
described below, may not dissolve but instead will remain as a
particulate composition. This un-dissolved ash may be separated
from the remainder of the reaction product, e.g., filtered out, for
a subsequent use. Alternatively, the water may be flowed through an
amount of ash that is provided in an immobilized configuration,
e.g., in a column or analogous structure, which provides for flow
through of a liquid through the ash but does not allow ash solid to
flow out of the structure with the liquid. This embodiment does not
require separation of un-dissolved ash from the product liquid. In
yet other embodiments where the pH exceeds 12, the ash dissolved
and provides for pozzolanic products, e.g., as described in greater
detail elsewhere.
[0183] In embodiments of the invention where ash is utilized in the
precipitation process, the ash may first be removed from the flue
gas by means such as electrostatic precipitation, or may be
utilized directly via the flue gas. The use of ash in embodiments
of the invention may provide reactants such as alumina or silica in
addition to raising the pH.
[0184] In certain embodiments of the invention, slag is employed as
a pH modifying agent, e.g., to increase the pH of the CO.sub.2
charged water. The slag may be used as a as the sole pH modifier or
in conjunction with one or more additional pH modifiers, e.g.,
ashes, etc. Slag is generated from the processing of metals, and
may contain calcium and magnesium oxides as well as iron, silicon
and aluminum compounds. In certain embodiments, the use of slag as
a pH modifying material provides additional benefits via the
introduction of reactive silicon and alumina to the precipitated
product. Slags of interest include, but are not limited to, blast
furnace slag from iron smelting, slag from electric-arc or blast
furnace processing of steel, copper slag, nickel slag and
phosphorus slag.
[0185] As indicated above, ash (or slag in certain embodiments) is
employed in certain embodiments as the sole way to modify the pH of
the water to the desired level. In yet other embodiments, one or
more additional pH modifying protocols is employed in conjunction
with the use of ash.
[0186] Alternatively or in conjunction with the use of a pH
elevating agent (such as described above), the pH of the
alkaline-earth-metal-ion-containing water source can be raised to
the desired level by electrolysis of the water using an
electrolytic or electrochemical protocol. Electrochemical protocols
of interest include, but are not limited, those described above as
well as those described in U.S. Provisional Application Ser. Nos.
61/081,299 and 61/091,729; the disclosures of which are herein
incorporated by reference. Also of interest are the electrolytic
approaches described in published United States Application
Publication Nos. 20060185985 and 20080248350, as well as published
PCT Application Publication No. WO 2008/018928; the disclosures of
which are hereby incorporated by reference.
[0187] Where desired, additives other than pH elevating agents may
also be introduced into the water in order to influence the nature
of the precipitate that is produced. As such, certain embodiments
of the methods include providing an additive in the water before or
during the time when the water is subjected to the precipitation
conditions. Certain calcium carbonate polymorphs can be favored by
trace amounts of certain additives. For example, vaterite, a highly
unstable polymorph of CaCO.sub.3 which precipitates in a variety of
different morphologies and converts rapidly to calcite, can be
obtained at very high yields by including trace amounts of
lanthanum as lanthanum chloride in a supersaturated solution of
calcium carbonate. Other additives besides lanthanum that are of
interest include, but are not limited to transition metals and the
like. For instance, the addition of ferrous or ferric iron is known
to favor the formation of disordered dolomite (protodolomite) where
it would not form otherwise.
[0188] The nature of the precipitate can also be influenced by
selection of appropriate major ion ratios. Major ion ratios also
have considerable influence of polymorph formation. For example, as
the magnesium:calcium ratio in the water increases, aragonite
becomes the favored polymorph of calcium carbonate over
low-magnesium calcite. At low magnesium:calcium ratios,
low-magnesium calcite is the preferred polymorph.
[0189] Rate of precipitation also has a large effect on compound
phase formation. The most rapid precipitation can be achieved by
seeding the solution with a desired phase. Without seeding, rapid
precipitation can be achieved by rapidly increasing the pH of the
sea water, which results in more amorphous constituents. When
silica is present, the more rapid the reaction rate, the more
silica is incorporated with the carbonate precipitate. The higher
the pH is, the more rapid the precipitation is and the more
amorphous the precipitate is.
[0190] Accordingly, a set of precipitation conditions to produce a
desired precipitate from a water include, in certain embodiments,
the water's temperature and pH, and in some instances the
concentrations of additives and ionic species in the water.
Precipitation conditions may also include factors such as mixing
rate, forms of agitation such as ultrasonics, and the presence of
seed crystals, catalysts, membranes, or substrates. In some
embodiments, precipitation conditions include supersaturated
conditions, temperature, pH, and/or concentration gradients, or
cycling or changing any of these parameters. The protocols employed
to prepare carbonate compound precipitates according to the
invention may be batch or continuous protocols. It will be
appreciated that precipitation conditions may be different to
produce a given precipitate in a continuous flow system compared to
a batch system.
[0191] In certain embodiments, contact between the
alkaline-earth-metal-ion containing water and CO.sub.2 may be
accomplished using any convenient protocol, (e.g., spray gun,
segmented flow-tube reactor) to control the range of sizes of
precipitate particles. One or more additives may be added to the
metal-ion containing water source, e.g., flocculents, dispersants,
surfactants, antiscalants, crystal growth retarders, sequestration
agents etc, in the methods and systems of the claimed invention in
order to control the range of sizes of precipitate particles.
[0192] In the embodiment depicted in FIG. 1, the water from the
alkaline-earth-metal-ion-containing water source 10 is first
charged with CO.sub.2 to produce CO.sub.2 charged water, which
CO.sub.2 is then subjected to carbonate mineral precipitation
conditions. As depicted in FIG. 1, a CO.sub.2 gaseous stream 30 is
contacted with the water at precipitation step 20. The provided
gaseous stream 30 is contacted with a suitable water at
precipitation step 20 to produce a CO.sub.2 charged water. By
CO.sub.2 charged water is meant water that has had CO.sub.2 gas
contacted with it, where CO.sub.2 molecules have combined with
water molecules to produce, e.g., carbonic acid, bicarbonate and
carbonate ion. Charging water in this step results in an increase
in the "CO.sub.2 content" of the water, e.g., in the form of
carbonic acid, bicarbonate and carbonate ion, and a concomitant
decrease in the pCO.sub.2 of the waste stream that is contacted
with the water. The CO.sub.2 charged water can be acidic, having a
pH of 6 or less, such as 5 or less and including 4 or less. In some
embodiments, the CO.sub.2 charged water is not acidic, e.g., having
a pH of 7 or more, such as a pH of 7-10, or 7-9, or 7.5-9.5, or
8-10, or 8-9.5, or 8-9. In certain embodiments, the concentration
of CO.sub.2 of the gas that is used to charge the water is 10% or
higher, 25% or higher, including 50% or higher, such as 75% or
higher.
[0193] CO.sub.2 charging and carbonate mineral precipitation may
occur in the same or different reactors of the system. As such,
charging and precipitation may occur in the same reactor of a
system, e.g., as illustrated in FIG. 1 at step 20, according to
certain embodiments of the invention. In yet other embodiments of
the invention, these two steps may occur in separate reactors, such
that the water is first charged with CO.sub.2 in a charging reactor
and the resultant CO.sub.2 charged water is then subjected to
precipitation conditions in a separate reactor. Further reactors
may be used to, e.g., charge the water with desired minerals.
[0194] Contact of the water with the source CO.sub.2 may occur
before and/or during the time when the water is subjected to
CO.sub.2 precipitation conditions. Accordingly, embodiments of the
invention include methods in which the volume of water is contacted
with a source of CO.sub.2 prior to subjecting the volume of
alkaline-earth-metal-ion-containing water to mineral precipitation
conditions. Embodiments of the invention also include methods in
which the volume of water is contacted with a source of CO.sub.2
while the volume of water is being subjected to carbonate compound
precipitation conditions. Embodiments of the invention include
methods in which the volume of water is contacted with a source of
a CO.sub.2 both prior to subjecting the volume of
alkaline-earth-metal-ion-containing water to carbonate compound
precipitation conditions and while the volume of water is being
subjected to carbonate compound precipitation conditions. In some
embodiments, the same water may be cycled more than once, wherein a
first cycle of precipitation removes primarily calcium carbonate
and magnesium carbonate minerals, and leaves remaining
alkaline-earth-metal-ion-containing water to which other
alkaline-earth-metal-ion sources may be added, that can have more
CO.sub.2 cycled through it, precipitating more carbonate
compounds.
[0195] Regardless of when the CO.sub.2 is contacted with the water,
in some instances when the CO.sub.2 is contacted with the water,
the water is not exceedingly alkaline, such that the water
contacted with the CO.sub.2 may have a pH of 10 or lower, such as
9.5 or lower, including 9 or lower and even 8 or lower. In some
embodiments, the water that is contacted with the CO.sub.2 is not a
water that has first been made basic from an electrochemical
protocol. In some embodiments, the water that is contacted with the
CO.sub.2 is not a water that has been made basic by addition of
hydroxides, such as sodium hydroxide. In some embodiment, the water
is one that has been made only slightly alkaline, such as by
addition of an amount of an oxide, such as calcium oxide or
magnesium oxide.
[0196] The carbonate mineral precipitation station 20 (i.e.,
reactor) may include any of a number of different components, such
as temperature control components (e.g., configured to heat the
water to a desired temperature), chemical additive components,
e.g., for introducing chemical pH elevating agents (such as KOH,
NaOH) into the water, electrolysis components, e.g.,
cathodes/anodes, etc, gas charging components, pressurization
components (for example where operating the protocol under
pressurized conditions, such as from 50-800 psi, or 100-800 psi, or
400 to 800 psi, or any other suitable pressure range, is desired)
etc, mechanical agitation and physical stirring components and
components to re-circulate industrial plant flue gas through the
precipitation plant. The precipitation station 20 may contain
components that allow for the monitoring of one or more parameters
such as internal reactor pressure, pH, precipitate particle size,
metal-ion concentration, conductivity and alkalinity of the aqueous
solution, and pCO.sub.2. Monitoring conditions during the carbonate
precipitation process can allow for corrective adjustments to be
made during processing, or if desired, to increase or decrease
carbonate compound precipitation production.
[0197] Following production of the storage stable precipitated
CO.sub.2 product from the water, the resultant precipitated product
may be separated from the mother liquor to produce separated
precipitate product, as illustrated at step 40 of FIG. 1. In some
embodiments the precipitate is not separated, or is only partially
separated, from the mother liquor. In such embodiments, the mother
liquor including some or all of the precipitate may be disposed of
by any suitable means. In some embodiments, the mother liquor
including some or all of the precipitate is transported to a land
or water location and placed at the location, e.g., the mother
liquor including some or all of the precipitate may be transported
to the ocean; this is especially useful in embodiments wherein the
source of water is seawater. It will be appreciated that the carbon
footprint, amount of energy used, and/or amount of CO.sub.2
produced for sequestering a given amount of CO.sub.2 from an
industrial exhaust gas is minimized in a process where no further
processing beyond disposal occurs with the precipitate. Separation
of the precipitate can be achieved using any convenient approach,
including a mechanical approach, e.g., where bulk excess water is
drained from the precipitate, e.g., either by gravity alone or with
the addition of vacuum, mechanical pressing (where energy for
mechanical pressing can be obtained from the industrial plant by
connecting to the steam turbine, from crushing equipment used to
make pulverized coal, etc.) by filtering the precipitate from the
mother liquor to produce a filtrate, etc. Separation can also be
achieved by centrifugation or by gravitational sedimentation of the
precipitated product followed by drainage of the mother liquor.
Separation of bulk water produces a wet dewatered precipitate.
[0198] In the embodiment illustrated in FIG. 1, the resultant
dewatered precipitate is then dried to produce a product, as
illustrated at step 60 of FIG. 1. Drying can be achieved by air
drying the filtrate. Where the filtrate is air dried, air drying
may be at room or elevated temperature. In certain embodiments, the
elevated temperature is provided by the industrial plant gaseous
waste stream, as illustrated at step 70 of FIG. 2. In these
embodiments, the gaseous waste stream (e.g., flue gas) from the
power plant may be first used in the drying step, where the gaseous
waste stream may have a temperature ranging from 30 to 700.degree.
C., such as 75 to 300.degree. C. The gaseous waste stream may be
contacted directly with the wet precipitate in the drying stage, or
used to indirectly heat gases (such as air) in the drying stage.
The desired temperature may be provided in the gaseous waste stream
by having the gas conveyer, e.g., duct, from the industrial plant
originate at a suitable location, e.g., at a location a certain
distance in the HRSG or up the flue, as determined based on the
specifics of the exhaust gas and configuration of the industrial
plant. In yet another embodiment, the precipitate is spray dried to
dry the precipitate, where the liquid containing the precipitate is
dried by feeding it through a hot gas (such as the gaseous waste
stream from the industrial plant), e.g., where the liquid feed is
pumped through an atomizer into a main drying chamber and hot gas
is passed as a co-current or counter-current to the atomizer
direction. In certain embodiments, drying is achieved by
freeze-drying (i.e., lyophilization), where the precipitate is
frozen, the surrounding pressure is reduced and enough heat is
added to allow the frozen water in the material to sublime directly
from the frozen precipitate phase to gas. Depending on the
particular drying protocol of the system, the drying station may
include a filtration element, freeze drying structure, spray drying
structure, etc.
[0199] Where desired, the dewatered precipitate product from the
separation reactor 40 may be washed before drying, as illustrated
at optional step 50 of FIG. 1. The precipitate may be washed with
freshwater, e.g., to remove salts (such as NaCl) from the dewatered
precipitate. Used wash water may be disposed of as convenient,
e.g., disposing of it in a tailings pond, etc.
[0200] In certain embodiments of the invention, the precipitate can
be separated, washed, and dried in the same station for all
processes, or in different stations for all processes or any other
possible combination. For example, in one embodiment, the
precipitation and separation may occur in precipitation reactor 20,
but drying and washing occur in different reactors. In yet another
embodiment, precipitation, separation, and drying may occur all in
the precipitation reactor 20 and washing occurring in a different
reactor.
[0201] Following separation of the precipitate from the mother
liquor, e.g., as described above, the separated precipitate may be
further processed as desired. In certain embodiments, the
precipitate may then be transported to a location for long term
storage, effectively sequestering CO.sub.2. For example, the
precipitate may be transported and placed at long term storage
sites, e.g., above ground, below ground, in the deep ocean, etc. as
desired.
[0202] The dried product may be disposed of in a number of
different ways. In certain embodiments, the precipitate product is
transported to a location for long term storage, effectively
sequestering CO.sub.2 in a stable precipitated product, e.g., as a
storage stable above ground CO.sub.2 sequestering material. For
example, the precipitate may be stored at a long term storage site
adjacent to the industrial plant and precipitation system. In yet
other embodiments, the precipitate may be transported and placed at
long term storage sites, e.g., above ground, below ground, etc. as
desired, where the long term storage site is distal to the power
plant (which may be desirable in embodiments where real estate is
scarce in the vicinity of the power plant). In these embodiments
where the precipitate is transported to a long term storage site,
it may be transported in empty conveyance vehicles (e.g., barges,
train cars, trucks, etc.) that were employed to transport the fuel
or other materials to the industrial plant and/or precipitation
plant. In this manner, conveyance vehicles used to bring fuel to
the industrial plant, materials to the precipitation plant (e.g.,
alkali sources) may be employed to transport precipitated product,
and therefore sequester CO.sub.2 from the industrial plant.
[0203] In certain embodiments, the composition is disposed of in an
underwater location. Underwater locations may vary depending on a
particular application. While the underwater location may be an
inland underwater location, e.g., in a lake, including a freshwater
lake, or interest in certain embodiments are ocean or sea
underwater locations. The composition may be still in the mother
liquor, without separation or without complete separation, or the
composition may have been separated from the mother liquor. The
underwater location may be shallow or deep. Shallow locations are
locations which are 200 feet or less, such as 150 feet or less,
including 1000 feet or less. Deep locations are those which are 200
feet or more, e.g., 500 feet or more, 1000 feet or more, 2000 feet
or more, including 5000 feet or more.
[0204] Where desired, the compositions made up of the precipitate
and the mother liquor may be stored for a period of time following
precipitation and prior to disposal. For example, the composition
may be stored for a period of time ranging from 1 to 1000 days or
longer, such as 1 to 10 days or longer, at a temperature ranging
from 1 to 40.degree. C., such as 20 to 25.degree. C.
[0205] Any convenient protocol for transporting the composition to
the site of disposal may be employed, and will necessarily vary
depending on the locations of the precipitation reactor and site of
disposal relative to each other, where the site of disposal is an
above ground or below ground site disposal, etc. In certain
embodiments, a pipeline or analogous slurry conveyance structure is
employed, where these approaches may include active pumping,
gravitational mediated flow, etc., as desired.
[0206] While in certain embodiments the precipitate is directly
disposed at the disposal site without further processing following
precipitation, in yet other embodiments the composition may be
further processed prior to disposal. For example, in certain
embodiments solid physical shapes may be produced from the
composition, where the resultant shapes are then disposed of at the
disposal site of interest. One example of this embodiment is where
artificial reef structures are produced from the carbonate compound
compositions, e.g., by placing the flowable composition in a
suitable mold structure and allowing the composition to solidify
over time into the desired shape. The resultant solid reef
structures may then be deposited in a suitable ocean location,
e.g., a shallow underwater locations, to produce an artificial
reef, as desired.
[0207] In certain embodiments, the precipitate produced by the
methods of the invention is disposed of by employing it in an
article of manufacture. In other words, the product is employed to
make a man-made item, i.e., a manufactured item. The product may be
employed by itself or combined with one or more additional
materials, such that it is a component of the manufactured items.
Manufactured items of interest may vary, where examples of
manufactured items of interest include building materials and
non-building materials, such as non-cementitious manufactured
items. Building materials of interest include components of
concrete, such as cement, aggregate (both fine and coarse),
supplementary cementitious materials, etc. Building materials of
interest also include pre-formed building materials.
[0208] Where the product is disposed of by incorporating the
product in a building material, the CO.sub.2 from the gaseous waste
stream of the industrial plant is effectively sequestered in the
built environment. Examples of using the product in a building
material include instances where the product is employed as a
construction material for some type of manmade structure, e.g.,
buildings (both commercial and residential), roads, bridges,
levees, dams, and other manmade structures etc. The building
material may be employed as a structure or nonstructural component
of such structures. In such embodiments, the precipitation plant
may be co-located with a building products factory.
[0209] In certain embodiments, the precipitate product is refined
(i.e., processed) in some manner prior to subsequent use.
Refinement as illustrated in step 80 of FIG. 1 may include a
variety of different protocols. In certain embodiments, the product
is subjected to mechanical refinement, e.g., grinding, in order to
obtain a product with desired physical properties, e.g., particle
size, etc. In certain embodiments, the precipitate is combined with
a hydraulic cement, e.g., as a supplemental cementitious material,
as a sand, a gravel, as an aggregate, etc. In certain embodiments,
one or more components may be added to the precipitate, e.g., where
the precipitate is to be employed as a cement, e.g., one or more
additives, sands, aggregates, supplemental cementitious materials,
etc. to produce final product, e.g., concrete or mortar, 90.
[0210] In certain embodiments, the carbonate compound precipitate
is utilized to produce aggregates. Such aggregates, methods for
their manufacture and use are described in co-pending United State
Application Ser. No. 61/056,972 filed May 29, 2008, the disclosure
of which is herein incorporated by reference.
[0211] In certain embodiments, the carbonate compound precipitate
is employed as a component of hydraulic cement. The term "hydraulic
cement" is employed in its conventional sense to refer to a
composition which sets and hardens after combining with water.
Setting and hardening of the product produced by combination of the
cements of the invention with an aqueous fluid result from the
production of hydrates that are formed from the cement upon
reaction with water, where the hydrates are essentially insoluble
in water. Such carbonate compound component hydraulic cements,
methods for their manufacture and use are described in co-pending
U.S. application Ser. No. 12/126,776 filed on May 23, 2008; the
disclosure of which application is herein incorporated by
reference.
[0212] Also of interest are formed building materials. The formed
building materials of the invention may vary greatly. By "formed"
is meant shaped, e.g., molded, cast, cut or otherwise produced,
into a man-made structure defined physical shape, i.e.,
configuration. Formed building materials are distinct from
amorphous building materials, e.g., particulate (such as powder)
compositions that do not have a defined and stable shape, but
instead conform to the container in which they are held, e.g., a
bag or other container. Illustrative formed building materials
include, but are not limited to: bricks; boards; conduits; beams;
basins; columns; drywalls etc. Further examples and details
regarding formed building materials include those described in U.S.
Provisional Patent Application Ser. No. 61/110,489 filed on Oct.
31, 2008; the disclosure of which is herein incorporated by
reference.
[0213] Also of interest are non-cementitious manufactured items
that include the product of the invention as a component.
Non-cementitious manufactured items of the invention may vary
greatly. By non-cementitious is meant that the compositions are not
hydraulic cements. As such, the compositions are not dried
compositions that, when combined with a setting fluid, such as
water, set to produce a stable product. Illustrative compositions
include, but are not limited to: paper products; polymeric
products; lubricants; asphalt products; paints; personal care
products, such as cosmetics, toothpastes, deodorants, soaps and
shampoos; human ingestible products, including both liquids and
solids; agricultural products, such as soil amendment products and
animal feeds; etc. Further examples and details non-cementitious
manufactured items include those described in U.S. Provisional
Patent Application Ser. No. 61/110,495 filed on Oct. 31, 2008; the
disclosure of which is herein incorporated by reference.
[0214] The resultant mother liquor may also be processed as
desired. For example, the mother liquor may be returned to the
source of the water, e.g., ocean, or to another location. In
certain embodiments, the mother liquor may be contacted with a
source of CO.sub.2, e.g., as described above, to sequester further
CO.sub.2. For example, where the mother liquor is to be returned to
the ocean, the mother liquor may be contacted with a gaseous source
of CO.sub.2 in a manner sufficient to increase the concentration of
carbonate ion present in the mother liquor. Contact may be
conducted using any convenient protocol, such as those described
above. In certain embodiments, the mother liquor has an alkaline
pH, and contact with the CO.sub.2 source is carried out in a manner
sufficient to reduce the pH to a range between 5 and 9, e.g., 6 and
8.5, including 7.5 to 8.2. Accordingly, the resultant mother liquor
of the reaction, e.g., mineral carbonate depleted water, may be
disposed of using any convenient protocol. In certain embodiments,
it may be sent to a tailings pond for disposal. In certain
embodiments, it may be disposed of in a naturally occurring body of
water, e.g., ocean, sea, lake or river. In certain embodiments, it
may be employed as a coolant for the industrial plant, e.g., by a
line running between the precipitation system and the industrial
plant. In certain embodiments, it may be employed as grey water, as
water input for desalination and subsequent use as fresh water,
e.g., in irrigation, for human and animal consumption, etc.
Accordingly, of interest are configurations where the precipitation
plant is co-located with a desalination plant, such that output
water from the precipitation plant is employed as input water for
the desalination plant.
[0215] As mentioned above, in certain embodiments the mother liquor
produced by the precipitation process may be employed to cool the
power plant, e.g., in a once through cooling system. In such
embodiments, heat picked up in the process may then be recycled
back to precipitation plant for further use, as desired. In such
embodiments, the initial water source may come from the industrial
plant. Such embodiments may be modified to employ pumping capacity
provided by the industrial plant, e.g., to increase overall
efficiencies.
[0216] Where desired and subsequent to the production of a CO.sub.2
sequestering product, e.g., as described above, the amount of
CO.sub.2 sequestered in the product is quantified. By "quantified"
is meant determining an amount, e.g., in the form of a numeric
value, of CO.sub.2 that has been sequestered (i.e., fixed) in the
CO.sub.2 sequestering product. The determination may be an absolute
quantification of the product where desired, or it may be an
approximate quantification, i.e., not exact. In some embodiments,
the quantification is adequate to give a market-acceptable measure
of the amount of CO.sub.2 sequestered.
[0217] The amount of CO.sub.2 in the CO.sub.2 sequestering product
may be quantified using any convenient method. In certain
embodiments the quantification may be done by actual measurement of
the composition. A variety of different methods may be employed in
these embodiments. For example, the mass or volume of the
composition is measured. In certain embodiments, such measurement
can be taken while the precipitate is in the mother liquor. In
these cases, additional methods such as x-ray diffraction may be
used to quantify the product. In other embodiments, the measurement
is taken after the precipitate has been washed and/or dried. The
measurement is then used to quantify the amount of CO.sub.2
sequestered in the product, for example, by mathematical
calculation. For example, a Coulometer may be used to obtain a
reading of the amount of carbon in the precipitated sequestration
product. This Coulometer reading may be used to determine the
amount of alkaline carbonate in the precipitate, which may then be
converted into CO.sub.2 sequestered by stoichiometry based on
several factors, such as the initial alkaline metal ion content of
the water, the limiting reagent of the chemical reaction, the
theoretical yield of the starting materials of the reaction, waters
of hydration of the precipitated products, etc. In some
embodiments, contaminants may be present in the product, and other
determinations of the purity of the product, e.g., elemental
analysis, may be necessary to determine the amount of CO.sub.2
sequestered.
[0218] In yet other embodiments, an isotopic method is employed to
determine the carbon content of the product. The ratio of carbon
isotopes in fossil fuels is substantially different than the ratio
of such isotopes in geologic sources such as limestone.
Accordingly, the source or ratio of sources of carbon in a sample
is readily elucidated via mass spectrometry that quantitatively
measures isotopic mass. So even if limestone aggregate is used in
concrete (which will increase total carbon determined via
coulometry), the utilization of mass spectrometry for isotopic
analysis will allow elucidation of the amount of the carbon
attributable to captured CO.sub.2 from fossil fuel combustion. In
this manner, the amount of carbon sequestered in the precipitate or
even a downstream product that incorporates the precipitate, e.g.,
concrete, may be determined, particularly where the CO.sub.2 gas
employed to make the precipitate is obtained from combustion of
fossil fuels, e.g., coal. Benefits of this isotopic approach
include the ability to determine carbon content of pure precipitate
as well as precipitate that has been incorporated into another
product, e.g., as an aggregate or sand in a concrete, etc.
[0219] In other embodiments, the quantification may be done by
making a theoretical determination of the amount of CO.sub.2
sequestered, such as by calculating the amount of CO.sub.2
sequestered. The amount of CO.sub.2 sequestered may be calculated
by using a known yield of the above described method, such as where
the yield is known from previous experimentation. The known yield
may vary according to a number of factors, including one or more of
the input of gas (e.g. CO.sub.2) and water, the concentration of
alkaline-earth-metal ions in the water, pH, salinity, temperature,
the rate of the gaseous stream, the embodiment of the method
selected, etc., as reviewed above. Standard information, e.g., a
predetermined amount of CO.sub.2 sequestered per amount of product
produced by a given reference process, may be used to readily
determine the quantity of CO.sub.2 sequestered in a given process
that is the same or approximately similar to the reference process,
e.g., by determining the amount produced and then calculating the
amount of CO.sub.2 that must be sequestered therein.
Systems of CO.sub.2 Sequestration
[0220] Aspects of the invention further include systems, e.g.,
processing plants or factories, for sequestering CO.sub.2, e.g., by
practicing methods as described above. Systems of the invention may
have any configuration which enables practice of the particular
production method of interest.
[0221] FIG. 2 provides a schematic of a system according to one
embodiment of the invention. In FIG. 2, system 100 includes water
source 110. In certain embodiments, water source 110 includes a
structure having an input for alkaline-earth-metal-ion-containing
water, such as a pipe or conduit from an ocean, etc. Where the
alkaline-earth-metal-ion water source that is processed by the
system to produce the precipitate is seawater, the input is in
fluid communication with a source of sea water, e.g., such as where
the input is a pipe line or feed from ocean water to a land based
system or a inlet port in the hull of ship, e.g., where the system
is part of a ship, e.g., in an ocean based system.
[0222] Also shown in FIG. 2, is CO.sub.2 source 130. This system
also includes a pipe, duct, or conduit which directs CO.sub.2 to
system 100. The water source 110 and the CO.sub.2 gaseous stream
source 130 are connected to a CO.sub.2 charger in precipitation
reactor 120. The precipitation reactor 120 may include any of a
number of different design features, such as temperature regulators
(e.g., configured to heat the water to a desired temperature),
chemical additive components, e.g., for introducing chemical pH
elevating agents (such as hydroxides, metal oxides, or fly ash)
into the water, electrochemical components, e.g., cathodes/anodes,
mechanical agitation and physical stirring mechanisms and
components to re-circulate industrial plant flue gas through the
precipitation plant. Precipitation reactor 120 may also contain
design features that allow for the monitoring of one or more
parameters such as internal reactor pressure, pH, precipitate
particle size, metal-ion concentration, conductivity and alkalinity
of the aqueous solution, and pCO.sub.2. This reactor 120 may
operate as a batch process or a continuous process.
[0223] Precipitation reactor 120, further includes an output
conveyance for mother liquor. In some embodiments, the output
conveyance may be configured to transport the mother liquor to a
tailings pond for disposal or in a naturally occurring body of
water, e.g., ocean, sea, lake, or river. In other embodiments, the
systems may be configured to allow for the mother liquor to be
employed as a coolant for an industrial plant by a line running
between the precipitation system and the industrial plant. In
certain embodiments, the precipitation plant may be co-located with
a desalination plant, such that output water from the precipitation
plant is employed as input water for the desalination plant. The
systems may include a conveyance (i.e., duct) where the output
water (e.g., mother liquor) may be directly pumped into the
desalination plant.
[0224] The system illustrated in FIG. 2 further includes a
separator 140 for separating a precipitated carbonate mineral
composition from a mother liquor. In certain embodiments, the
separator may achieve separation of a precipitated carbonate
mineral composition from a mother liquor by a mechanical approach,
e.g., where bulk excess water is drained from the precipitate by
gravity or with the addition of a vacuum, mechanical pressing,
filtering the precipitate from the mother liquor to produce a
filtrate, centrifugation or by gravitational sedimentation of the
precipitate and drainage of the mother liquor.
[0225] The system also includes a washing station, 150, where bulk
dewatered precipitate from separation station, 140 is washed, e.g.,
to remove salts and other solutes from the precipitate, prior to
drying at the drying station.
[0226] The system further includes a drying station 160 for drying
the precipitated carbonate mineral composition produced by the
carbonate mineral precipitation station. Depending on the
particular drying protocol of the system, the drying station may
include a filtration element, freeze drying structure, spray drying
structure, etc as described more fully above. The system may
include a conveyer, e.g., duct, from the industrial plant that is
connected to the dryer so that a gaseous waste stream (i.e.,
industrial plant flue gas) may be contacted directly with the wet
precipitate in the drying stage.
[0227] The dried precipitate may undergo further processing, e.g.,
grinding, milling, in refining station, 180, in order to obtain
desired physical properties. One or more components may be added to
the precipitate where the precipitate is used as a building
material.
[0228] The system further includes outlet conveyers, e.g., conveyer
belt, slurry pump, that allow for the removal of precipitate from
one or more of the following: the reactor, drying station, washing
station or from the refining station. The product of the
precipitation reaction may be disposed of in a number of different
ways. The precipitate may be transported to a long term storage
site in empty conveyance vehicles, e.g., barges, train cars,
trucks, etc., that may include both above ground and underground
storage facilities. In other embodiments, the precipitate may be
disposed of in an underwater location. Any convenient protocol for
transporting the composition to the site of disposal may be
employed. In certain embodiments, a pipeline or analogous slurry
conveyance structure may be employed, where these approaches may
include active pumping, gravitational mediated flow, etc.
[0229] In certain embodiments, the system will further include a
station for preparing a building material, such as cement, from the
precipitate. This station can be configured to produce a variety of
cements, aggregates, or cementitious materials from the
precipitate, e.g., as described in co-pending U.S. application Ser.
No. 12/126,776; the disclosure of which application is herein
incorporated by reference.
[0230] As indicated above, the system may be present on land or
sea. For example, the system may be a land based system that is in
a coastal region, e.g., close to a source of sea water, or even an
interior location, where water is piped into the system from a salt
water source, e.g., ocean. Alternatively, the system may be a water
based system, i.e., a system that is present on or in water. Such a
system may be present on a boat, ocean based platform etc., as
desired. In certain embodiments, the system may be co-located with
an industrial plant at any convenient location. The precipitation
plant may be a land-based plant that is co-located with the
land-based industrial plant, e.g., in a coastal region, such as
close to a source of an alkaline-earth-metal-ion-containing water,
e.g., seawater. Also of interest are interior locations, where
water is piped into the system directly from a water source, e.g.,
the industrial plant, a distal lake, a distal ocean. Alternatively,
the precipitation plant may be present on water, e.g., on a barge,
boat, ocean based platform etc., as desired, for example where
real-estate next to a industrial plant is scarce. In certain
embodiments, the precipitation plant may be a mobile plant, such
that it is readily co-located with an industrial plant.
[0231] Systems of the invention that are co-located with an
industrial plant, such as a power plant, may be configured to allow
for synchronizing the activities of the industrial plant and
precipitation plant. In certain instances, the activity of one
plant may not be matched to the activity of the other. For example,
the precipitation plant may need to reduce or stop its acceptance
of the gaseous waste stream but the industrial plant may need to
keep operating. Conversely, situations may arise where the
industrial plant reduces or ceases operation and the precipitation
plant does not. To address situations where either the
precipitation plant or industrial plant may need to reduce or stop
its activities, design features that provide for continued
operation of one of the co-located plants while the other reduces
or ceases operation may be employed, as described in detail above.
For example, the systems of the invention may include in certain
embodiments, blowers, fans, and/or compressors at various points
along the connecting line between the industrial plant and the
precipitation plant in order to control the occurrence of
backpressure in the ducts that connect the industrial plant to the
precipitation plant. In certain embodiments, a gas storage facility
may be present between the industrial plant and the precipitation
plant. Where desired, the precipitation plant may include emissions
monitors to evaluate any gaseous emissions produced by the
precipitation plant as required by Air Quality Agencies.
[0232] Aspects of the invention include the use of a CO.sub.2
containing industrial plant gaseous waste stream, e.g., an
industrial plant flue gas, at one or more stages of a process in
which a storage stable CO.sub.2 containing product is precipitated.
As such, the CO.sub.2 containing industrial plant gaseous waste
stream is employed in a precipitation process. In embodiments of
the invention, the gaseous waste stream is employed at one or more
steps of the precipitation process, such as in a precipitation
step, e.g., where it is employed to charge water with CO.sub.2, or
during a precipitate drying step, e.g., where precipitated
carbonate compound is dried, etc. Where desired, the flue gas from
the industrial plant can be re-circulated through the precipitation
plant until total adsorption of the remnant CO.sub.2 approaches
100%, or a point of diminishing returns is achieved such that the
remaining flue gas can be processed using alternative protocols
and/or released into the atmosphere.
[0233] As reviewed above, precipitation systems of the invention
may be co-located with an industrial plant. An example of such a
system is illustrated in FIG. 2. In FIG. 2, flue gas outlet 170
from power plant 200 is used in both the precipitation reactor 120
as the source of CO.sub.2 130 and the dryer 160 and the source of
heat. Where desired, backpressure controls are employed to at least
reduce, if not eliminate, the occurrence of backpressure which
could arise from directing a portion of, if not all of, the
industrial plant gaseous waste stream to the precipitation plant
100. Any convenient manner of controlling backpressure occurrence
may be employed. In certain embodiments, blowers, fans and/or
compressors are provided at some point along the connecting line
between the industrial plant and precipitation plant. In certain
embodiments, the blowers are installed to pull the flue gas into
ducts that port the flue gas to the precipitation plant. The
blowers employed in these embodiments may be electrically or
mechanically driven blowers. In these embodiments, if present at
all, backpressure is reduced to a level of 5 inches or less, such
as one inch or less. In certain embodiments, a gas storage facility
may be present between the industrial plant and the precipitation
plant. When present, the gas storage facility may be employed as a
surge, shutdown and smoothing system so that there is an even flow
of flue gases to the precipitation plant.
[0234] Aspects of the invention include synchronizing the
activities of the industrial plant and precipitation plant. In
certain instances, the activity of one plant may not be matched to
the activity of the other. For example, the precipitation plant may
need to reduce or stop its acceptance of the gaseous waste stream
but the industrial plant may need to keep operating. Conversely,
situations may arise where the industrial plant reduces or ceases
operation and yet the precipitation plant does not. To address such
situations, the plants may be configured to provide for continued
operation of one of the co-located plants while the other reduces
or ceases operation may be employed. For example, to address the
situation where the precipitation plant has to reduce or eliminate
the amount of gaseous waste stream it accepts from the industrial
plant, the system may be configured so that the blowers and ducts
conveying waste stream to the precipitation plant shut off in a
controlled sequence to minimize pressure swings and the industrial
plant flue acts as a bypass stack for discharge of the gaseous
waste stream. Similarly, if the industrial plant reduces or
eliminates its production of gaseous waste stream, e.g., the
industrial plant is dispatched wholly or partially down, or there
is curtailment of industrial plant output under some pre-agreed
level, the system may be configured to allow the precipitation
plant to continue operation, e.g., by providing an alternate source
of CO.sub.2, by providing for alternate heating protocols in the
dryer, etc.
[0235] Where desired, the precipitation plant may include emissions
monitors to evaluate any gaseous emissions produced by the
precipitation plant and to make required reports to regulatory
agencies, both electronic (typically every 15 minutes), daily,
weekly, monthly, quarterly, and annually. In certain embodiments,
gaseous handling at the precipitation plant is sufficiently closed
that exhaust air from the precipitation plant which contains
essentially all of the unused flue gas from the industrial plant is
directed to a stack so that required Continuous Emissions
Monitoring Systems can be installed in accordance with the
statutory and regulatory requirements of the Country, province,
state city or other political jurisdiction.
[0236] In certain embodiments, the gaseous waste stream generated
by the industrial plant and conveyed to the precipitation plant has
been treated as required by Air Quality Agencies, so the flue gas
delivered to the precipitation plan already meets Air Quality
requirements. In these embodiments, the precipitation plant may or
may not have alternative treatment systems in place in the event of
a shutdown of the precipitation plant. However, if the flue gas
delivered to has been only partially treated or not treated at all,
the precipitation plant may include air pollution control devices
to meet regulatory requirements, or seek regulatory authority to
emit partially-treated flue gas for short periods of time. In yet
other embodiments, the flue gas is delivered to precipitation plant
for all processing. In such embodiments, the system may include a
safeguard for the situation where the precipitation plant cannot
accept the waste stream, e.g., by ensuring that the pollution
controls installed in the industrial plant turn on and control
emissions as required by the Air Quality Agencies.
[0237] The precipitation plant that is co-located with the
industrial plant may be present at any convenient location, be that
on land or water. For example, the precipitation plant may be a
land-based plant that is co-located with the land-based industrial
plant, e.g., in a coastal region, such as close to a source of sea
water. Also of interest are interior locations, where water is
piped into the system directly from a water source, e.g., the
industrial plant, a distal lake, a distal ocean. Alternatively, the
precipitation plant may be present on water, e.g., on a barge,
boat, ocean based platform etc., as desired, for example where
real-estate next to a industrial plant is scarce. In certain
embodiments, the precipitation plant may be a mobile plant, such
that it is readily co-located with a industrial plant.
[0238] As indicated above, of interest in certain embodiments are
waste streams produced by integrated gasification combined cycle
(IGCC) plants. In these types of plants, the initial fuel, e.g.,
coal, biomass, etc., is first subjected to a gasification process
to produce syngas, which may be shifted, generating amounts of
CO.sub.2, CO and H.sub.2. The product of the gasification protocol
may be conveyed to the precipitation plant to first remove
CO.sub.2, with the resultant CO.sub.2 scrubbed product being
returned to a power plant for use as fuel. In such embodiments, a
line from the gasification unit of a power plant may be present
between a power plant and precipitation plant, and a second return
line may be present between the precipitation plant and a power
plant to convey scrubbed syngas back to a power plant.
[0239] In certain embodiments, the co-located industrial plant and
precipitation plant (or integrated plant) is operated with
additional CO.sub.2 emission reduction approaches. For example,
material handling, vehicles and earthmoving equipment, locomotives,
may be configured to use biofuels in lieu of fossil fuels. In such
embodiments, the site may include fuel tanks to store the
biofuels
[0240] In addition to sequestering CO.sub.2, embodiments of the
invention also sequester other components of industrial plant
generated gaseous waste streams. For example, embodiments of the
invention results in sequestration of at least a portion of one or
more of NOx, SOx, VOC, Mercury and particulates that may be present
in the waste stream, such that one or more of these products are
fixed in the solid precipitate product.
[0241] In FIG. 2, precipitation system 100 is co-located with
industrial plant 200. However, precipitation system 100 is not
integrated with the industrial plant 200. Of further interest in
certain embodiments therefore is an integrated facility which, in
addition to an industrial plant, includes power generation, water
treatment (seawater desalinization or mineral rich freshwater
treatment) and precipitation components' as described in U.S.
patent application Ser. No. 12/163,205, the disclosure of which is
herein incorporated by reference. The water source for the
precipitation plant may be derived from the waste streams of the
water treatment plant. The resultant mother liquor from the
carbonate precipitation plant may be used as the feedstock for the
water treatment plant. The resultant integrated facility
essentially uses fuel, minerals and untreated water as inputs, and
outputs energy, a processed industrial product, e.g., cement, clean
water, clean air and carbon-sequestering building materials.
[0242] FIG. 3 provides an example of where a precipitation system
100 is integrated with an industrial plant, in this case a coal
fired power plant 300. In power plant 300, coal 310 fuels steam
boiler 315 to produce steam which in turn runs a turbine (not
shown) to produce power. Steam boiler 315 also produces bottom ash
or boiler slag 325 and flue gas 320. Flue gas 320 contains fly ash,
CO.sub.2 and sulfates. Flue gas 320 and bottom ash 325 are combined
with water from water source 330 in reactor 340 and subjected to
precipitation reactions, as described above. Pump 350 facilitates
transport of precipitated product from reactor 340 to spray dryer
360, which employs flue gas 320 to spray dry the precipitated
product for subsequent disposal, e.g., by placement in a landfill
or use in a building product. Treated flue gas 370 exits spray
dryer 360 and then is discharged to the atmosphere in stack 380.
Treated flue gas 370 is gas in which the fly ash, sulfur, and
CO.sub.2 content has been substantially reduced, if not completely
removed, as compared to flue gas 320. As an example of the system
shown in FIG. 3, the CO.sub.2 source may be flue gas from coal or
other fuel combustion, which is contacted with the volume of
saltwater with little or no pretreatment of the flue gas. In these
embodiments, the use of fuels such as high-sulfur coal,
sub-bituminous coal, lignite and the like, which are often
inexpensive and considered low quality, is practical due to the
ability of the process to remove the SOx and other pollutants as
well as removing CO.sub.2. These fuels may also provide higher
levels of co-reactants such as alumina and silica in fly ash
carried by the flue gas, producing modified carbonate mineral
precipitates with beneficial properties.
[0243] When co-located with a power plant, methods of the invention
provide sequestration of substantial amounts of CO.sub.2 from the
gaseous waste stream produced by the power plant with a limited
parasitic energy requirement. In some instances, the methods
provide for removal of 5% or more, 10% or more, 25% or more, 50% or
more, 75% or more of the CO.sub.2 from the gaseous waste stream
with a parasitic energy requirement of 50% or less, such as 30% or
less, including 25% or less. The parasitic energy requirement is
the amount of energy generated by the power plant that is required
to operate the carbon dioxide sequestration process. In some
instances the above levels of CO.sub.2 removal are achieve with a
parasitic energy requirement of 20% or less, 15% or less, 10% or
less.
[0244] Another type of industrial plant which may be co-located
with a precipitation plant of the invention is a cement plant, such
as a portland cement production plant. FIG. 4 provides a schematic
of an exemplary portland cement production facility. In FIG. 4,
limestone 400 along with shales and other additives 410 are milled
to appropriate size and moved through precalciner 500, which uses
waste heat from flue gas 430 to preheat the mixture, utilizing
waste heat from kiln 510 to improve operational efficiency. The
preheated mixture enters kiln 510 where it is further heated by
burning coal 420. The resultant clinker 480 is collected and stored
in silos 570, where it is blended with additives 571 such as
gypsum, limestone, etc. and ground to desired size in ball mill
580. The product which exits the ball mill is portland cement 490
which is stored in cement silo 590 prior to shipment to
customers.
[0245] The flue gas 430 which comes from kiln 510 contains both
gaseous and particulate contaminants. The particulate contaminants
are known as kiln dust 440, and are removed from the flue gas via
electrostatic precipitators or baghouses 520. The kiln dust so
removed is commonly sent to landfill 600, though occasionally kiln
dust is recycled into the kiln, or sold as a supplementary
cementitious material. The flue gas is then pulled by fan 540 into
wet scrubber 550, where the sulfur oxides in the flue gas are
removed by reaction with a calcined lime slurry, producing a
calcium sulfite (e.g., gypsum) slurry 480 which is normally
dewatered in reclaim tank 572 and disposed of in landfill 600. The
flue gas 430 exits wet scrubber 430 and is released to the
atmosphere via stack 560. The flue gas so released has a high
concentration of CO.sub.2, which is released both by the burning of
coal and via the calcination required to oxidize limestone to
portland cement.
[0246] FIG. 5 shows a schematic of an exemplary co-located cement
plant and precipitation plant according to one embodiment of the
invention. The process in this example is the same as that in FIG.
4, except that a carbonate precipitation plant replaces the flue
gas treatment system of FIG. 4. Once the flue gas exits the
precalciner 500, it is pulled by fan 540 to reactor 630, wherein a
precipitation reaction is initiated utilizing seawater 620 and
alkali 625. The resultant slurry 631 is pumped via pump 640 to
drying station 650, where water 651 is discharged and dried
cementitious material 660 is stored for shipment to customers. Flue
gas 430 is emitted from stack 670 with a portion if not all of the
contaminants removed, including mercury, SO.sub.x, particulates,
and CO.sub.2.
[0247] FIG. 5 shows a schematic of an exemplary cement plant which
does not require a limestone quarry, according to one embodiment of
the invention. In this embodiment, the product of reactor 630 may
take the form of a relatively pure calcium carbonate during
portions of time during its operation, and other forms of building
materials during other portions of time. In this example, rather
than mined limestone, the precalciner 500 and kiln 510 is charged
with a mixture of shale and other ingredients 410 blended with a
relatively pure precipitated calcium carbonate 670. Previously
mentioned and incorporated by reference U.S. patent application
Ser. No. 12/126,776 details protocols of precipitating an aragonite
calcium carbonate from seawater using flue gas. By using the
product of the flue gas treatment reactor as a feedstock, the
cement plant draws its calcium ion from the sea via the
precipitated product, and only requires mined limestone in the
first short period of operation until sufficient precipitated
calcium carbonate is generated to charge the kiln.
[0248] In embodiments of the invention, the carbonate precipitation
is performed in two stages. The first stage selectively
precipitates calcium carbonate, which can then be used as a
feedstock for the cement plant as illustrated in FIG. 6. The second
precipitation stage can produce a number of different materials,
including cements, aggregates, above ground carbon sequestering
materials, and the like.
[0249] Portland cement is 60-70% by mass CaO, which is produced by
heating CaCO.sub.3, requiring heat and releasing one molecule of
CO.sub.2 for every molecule of CaO released. Because of the
additional CO.sub.2 released from the burning of fuel, the output
of precipitated CaCO.sub.3 from the precipitation plant will exceed
the amount required to provide feedstock for the cement plant. In
this instance a portion of the time of operation of the
precipitation plant may be devoted to production of other
cementitious materials 660 such as those described in U.S.
application Ser. No. 12/126,776; the disclosures of which are
herein incorporated by reference.
[0250] The portland cement 490 produced as shown in FIG. 6 is
carbon neutral as the CO.sub.2 from its manufacture is sequestered
into precipitated carbonate mineral 670 and cementitious materials
660. The portland cement 490 may be sold as is, or blended or
interground with cementitious material 660 to produce a blended
cement.
[0251] An example of a continuous feed system of interest is
depicted in FIG. 11. In FIG. 11, system 1100 includes water source
(e.g., pipe from ocean to provide seawater) 1101 which is in fluid
communication with reactor 1110. Also present in reactor 1110 is
Ca/Mg/OH ion sources and catalysts 1111, which have been added in
amounts sufficient to raise the Mg/Ca ion ratio in water present in
reactor 1110 to 3 or more. Reactor 1110 may configured as a packed
bed column, and configured from bicarbonate charging, if desired.
CO.sub.2 containing gas, e.g., flue gas 1112, is combined with
water in reactor 1110 by sparger/bubbler 1113. The Mg ion source
and CO.sub.2 are combined with the water in reactor 1110 to produce
CO.sub.2 charged acidic water, which flows out of reactor 1110 at a
pH of between 4.8 and 7.5. Next, the CO.sub.2 charged acidic water
flows through conduit 1120 where it is cycled with mixing through
different levels of alkalinity, e.g., 8.5 and 9.8, with the use of
various CO.sub.2 gas injectors 1121, OH- modulators 1123 (such as
introduces of pH elevating agents, electrodes, etc.) and static
mixers 1122 positioned at various locations along conduit 1120. The
flow rate through conduit 1120 may be controlled as desired, e.g.,
to be between 1 GPM and 1,000,000 GPM, such as 30 GPM and 100,000
GPM and including 4,000 GPM and 60,000 GPM. The length of conduit
1120 may vary, ranging from 100 ft to 20,000 ft, such as 1000 ft to
7000 ft. At the end of conduit 1120, as slurry product 1130 is
obtained, which slurry product includes the precipitated CO.sub.2
sequestering product and mother liquor. The resultant slurry is
then forwarded to a water/solids separator or settling tank, as
illustrated at 1140.
[0252] In certain embodiments, two or more reactors may be used to
carry out the methods described herein. A schematic of an
embodiment using two reactors is shown in FIGS. 12A, 12B, and 12C.
In this embodiment, the method may include a first reactor 1210 and
a second reactor 1220. In these cases, the first reactor 1210 is
used for contacting the initial water, e.g. fresh seawater 1230,
with a magnesium ion source 1240 and for charging the initial water
with CO.sub.2 containing gas, e.g. flue gas 1250 (where this step
is also referred to as bicarbonate charging). The flue gas 1250 may
be contacted with the water in the first reactor 1210 through a
sparger/bubbler 1280. The water is agitated with agitator 1260 to
facilitate the dissolution of the magnesium ion source and to
facilitate contact of the initial water with the CO.sub.2
containing gas. In some cases, before the CO.sub.2 charged acidic
water is transferred to the second reactor 1220, agitation of the
CO.sub.2 charged acidic water is stopped, such that undissolved
solids may settle by gravity. The CO.sub.2 charged acidic water is
then transferred through conduit 1270 from the first reactor 1210
to the second reactor 1220.
[0253] After transferring the CO.sub.2 charged acidic water to the
second reactor 1220, the step of carbonate precipitation may be
performed. In some cases, a pH raising agent 1290 is contacted with
the water in the second reactor 1220 to facilitate formation of the
carbonate containing precipitate. The contents of the second
reactor 1220 may be agitated with agitator 1295. In certain
embodiments, one or more additional steps of CO.sub.2 charging and
subsequent carbonate precipitation may be performed in the second
reactor, as described above. In these cases, additional CO.sub.2
containing gas, e.g. flue gas 1255, is contacted with the water in
the second reactor 520 through sparger/bubbler 1285. The resulting
slurry product includes the precipitated CO.sub.2 sequestering
product and mother liquor, which is then forwarded to a
water/solids separator or settling tank, as described above.
[0254] The following examples are put forth so as to provide those
of ordinary skill in the art with a complete disclosure and
description of how to make and use the present invention, and are
not intended to limit the scope of what the inventors regard as
their invention nor are they intended to represent that the
experiments below are all or the only experiments performed.
Efforts have been made to ensure accuracy with respect to numbers
used (e.g. amounts, temperature, etc.) but some experimental errors
and deviations should be accounted for. Unless indicated otherwise,
parts are parts by weight, molecular weight is weight average
molecular weight, temperature is in degrees Centigrade, and
pressure is at or near atmospheric.
EXPERIMENTAL
Example I
Precipitation of P00099
A. P00099 Precipitation Process
[0255] The following protocol was used to produce the P00099
precipitate. 380 L of filtered seawater was pumped into a
cylindrical polyethylene 60.degree.-cone bottom graduated tank.
This reaction tank was an open system, left exposed to the ambient
atmosphere. The reaction tank was constantly stirred using an
overhead mixer. pH, room temperature, and water temperature were
constantly monitored throughout the reaction.
[0256] 25 g of granulated (Ca,Mg)O (a.k.a., dolime or calcined
dolomite) was mixed into the seawater. Dolime that settled to the
bottom of the tank was manually re-circulated from the bottom of
the tank through the top again, in order to facilitate adequate
mixing and dissolution of reactants. A second addition of 25 g of
dolime was performed in an identical manner, including a manual
recirculation of settled reactant. When the pH of the water reached
9.2, a gas mixture of 10% CO.sub.2 (and 90% compressed air) was
slowly diffused through a ceramic airstone into solution. When the
pH of the solution fell to 9.0, another 25 g addition of dolime was
added to the reaction tank, which caused the pH to rise again. The
additions of dolime were repeated whenever the pH of the solution
dropped to 9.0 (or below), until a total of 225 g were added. A
manual recirculation of settled reactant was performed in between
each dolime addition.
[0257] After the final addition of dolime, the continuous diffusion
of gas through the solution was stopped. The reaction was stirred
for an additional 2 hours. During this time, the pH continued to
rise. To maintain a pH between 9.0 and 9.2, additional gas was
diffused through the reaction when the pH rose above 9.2 until it
reached 9.0. Manual re-circulations of settled reactant were also
performed 4 times throughout this 2 hour period.
[0258] 2 hours after the final addition of dolime, stirring, gas
diffusion and recirculation of settled reactant was stopped. The
reaction tank was left undisturbed for 15 hours (open to the
atmosphere).
[0259] After the 15 hour period, supernatant was removed through
the top of the reaction tank using a submersible pump. The
remaining mixture was removed through the bottom of the tank. The
collected mixture was allowed to settle for 2 hours. After
settling, the supernatant was decanted. The remaining slurry was
vacuum filtered through 11 .mu.m pore size filter paper, in a
Buchner funnel. The collected filter cake was placed into a Pyrex
dish and baked at 110.degree. C. for 24 hours.
[0260] The dried product was ground in a ball mix and fractioned by
size through a series of sieves to produce the P00099
precipitate.
B. Materials Analysis
[0261] Of the different sieve fractions collected, only the
fraction containing particles retained on the 38 .mu.m-opening
sieve and passing through the 75 .mu.m-opening sieve was used.
1. Chemical Characteristics
[0262] The P00099 precipitate used for the blend were analyzed for
elemental composition using XRF. Results for the main elements are
reported for the QUIKRETE.TM. type I/II Portland cement used in
this blend as well as for the P00099 precipitate. In Table 4,
below.
TABLE-US-00004 TABLE 4 P.sub.2O.sub.5 Sr CO.sub.3 % Sample
Na.sub.2O % MgO % Al.sub.2O.sub.3 % SiO.sub.2 % ppm SO.sub.3 % Cl %
K.sub.2O % CaO % Fe.sub.2O.sub.3 % ppm diff. OPC1 2.15 1.95 4.32
20.31 2336 2.54 0.072 0.36 62.88 3.88 1099 0.002 P00099 1.36 3.44
0.14 0.083 462 0.65 1.123 0.04 45.75 0.12 3589 46.82 Table 4: XRF
analysis of the type I/II portland cement and P00099-002 used in
this blend
The XRD analysis of this precipitate indicates the presence of
aragonite and magnesium calcite (composition close to
Mg.sub.0.1Ca.sub.0.9CO.sub.3) and in minor amounts, brucite and
halite (Table 5). The FT-IR analysis of the P00099 precipitate
confirmed the presence of aragonite, calcite and brucite.
TABLE-US-00005 TABLE 5 Magnesium Sample Aragonite Calcite Brucite
Halite P00099 79.9 17.1 2.8 0.2
The total inorganic carbon content measured by coulometry is in
fair agreement with the same value derived from the XRD Rietveld
estimated composition coupled with XRF elemental composition. Table
6 provides a coulometric analysis of P00099 compared to % C derived
from XRD/XRF data
TABLE-US-00006 TABLE 6 Total C derived from Total C from coulometry
other analytical data 10.93 .+-. 0.16% 11.5%
2. Physical Characteristics
[0263] SEM observations on the precipitate confirmed the dominance
of aragonite (needle-like) as well as the size of the particle
agglomerates. The determined BET specific surface areas ("SSA") of
the Portland cement and the P00099 precipitate are given in Table
7.
TABLE-US-00007 TABLE 7 Type I/II Quikrete Portland cement P00099
1.18 .+-. 0.04 m.sup.2/g 8.31 .+-. 0.04 m.sup.2/g
[0264] The particle size distribution was determined after 2 min of
pre-sonication to dissociate the agglomerated particles.
Example II
Use of Fly Ash as an Alakali Source
A. Methods
[0265] 500 mL of seawater (initial pH=8.01) was continuously
stirred in a glass beaker using a magnetic stir bar. The pH and
temperature of the reaction was continuously monitored. Class F fly
ash (.about.10% CaO) was incrementally added as a powder, allowing
the pH to equilibrate in between additions.
B. Results and Observations
[0266] (Amounts of fly ash listed are the cumulative totals, i.e.
the total amount added at that point in the experiment.)
[0267] After the additions of 5.00 g of fly ash the pH reached
9.00.
34.14 g->9.50 168.89 g->9.76 219.47 g->10.94 254.13
g->11.20 300.87 g->11.28 Much more fly ash was needed to
raise the pH of the seawater than distilled water. The initial pH
raise (8 to 9) required much less fly ash than the further raises.
The pH remained fairly stable around 9.7 for much of the reaction.
The rate of rate of pH increase went up after .about.10. Also of
note was an initial drop in pH when the fly ash was added. This
drop in pH is quickly overcome by the effects of the calcium
hydroxide. SEM images of vacuum dried slurry from the reaction
showed some spheres of the fly ash that had partially dissolved.
The remaining spheres also seemed to be embedded in a possibly
cementitious material.
C. Conclusions
[0268] In fresh (distilled) water, it was found that small amounts
of class F fly ash (<1 g/L) immediately raised the pH from 7
(neutral) to .about.11. The small amount necessary to raise the pH
is most likely due to the unbuffered nature of nature of distilled
water. Seawater is highly buffered by the carbonate system, and
thus it took much more fly ash to raise the pH to similar
levels.
Example III
Production of High Yields
A. Process 1
[0269] A 20% CO.sub.2/80% Air gas mixture was sparged into 1 L of
seawater until a pH <5 was reached. Once reached, 1.0 g of
Mg(OH).sub.2 was added to the 1 L of carbonic acid/seawater
solution. The 20/80 gas mixture continued to be sparged for 20
minutes to ensure maximal dissolution of the Mg(OH).sub.2 and
gases. After dissolution, sparging was stopped and 2M NaOH was
added until a pH of 9.8 was reached. Sparging of the 20/80 gas was
resumed until a pH of 8.5 was reached. 2M NaOH and
counter-additions of the 20/80 gas were continued maintaining a pH
range between 8.5 and 9.8 until a total of 200 ml of 2M NaOH was
added. A yield of 6.91 g was observed having a Coulometer reading
of 10.6% carbon (.about.80% carbonate).
B. Process 2
[0270] A 20% CO.sub.2/80% Air gas mixture was sparged into 1 L of
seawater until a pH <5 was reached. Once reached, 2.69 g of
Mg(OH).sub.2 was added to the 1 L of carbonic acid/seawater
solution. The 20/80 gas mixture continued to be sparged for 20
minutes to ensure maximal dissolution of the Mg(OH).sub.2 and
gases. After dissolution, sparging was stopped and 2M NaOH was
added until a pH of 9.8 was reached. Sparging of the 20/80 gas was
resumed until a pH of 8.5 was reached. 2M NaOH and
counter-additions of the 20/80 gas were continued maintaining a pH
range between 8.5 and 9.8 until a total of 200 ml of 2M NaOH was
added. A yield of 10.24 g was observed having a Coulometer reading
of 9.7% carbon (.about.75% carbonate).
[0271] SEM, EDS, and X-Ray Diffraction of the precipitated
carbonates showed amorphous and crystalline Ca and Mg carbonates,
and also the presence of Ca/Mg carbonates. Pictures of the
precipitates are provided in FIGS. 13A and 13B.
C. Process 3
[0272] CO.sub.2 was sparged into 1 L seawater until a pH 7 or lower
was reached. 0 to 5.0 g Mg ion supplement referred to as "Moss Mag"
and obtained from Calera Corporation's Moss Landing site (which is
the former site of the Kaiser Aluminum & Chemical Corporation
and National Refractorie in Moss Landing Calif., where the
supplement is Mg rich waste product found in tailings ponds of the
site) was added while mixing and continuing to sparge CO.sub.2. 0.1
75 ppm Al.sub.2(SO.sub.4).sub.3 was added. CO.sub.2 was continued
to be sparged and base was added while maintaining a pH between 7
and 8 ending at a pH of 7. Sparging of CO.sub.2 was stopped and
base was added until a pH between 9.0 and 10.4 was reached. As
shown in FIG. 14, the above reaction conditions favour the
formation of amorphous carbonate compound precipitates. The
resultant amorphous precipitate product is readily spray dried to
produce a dry product.
D. Process 4
[0273] As shown in FIGS. 12A, 12B and 12C, in certain embodiments,
a multi-step, multi-reactor process is used to carry out the
methods disclosed herein. In the first reactor, a magnesium ion
source obtained from a Moss Landing, Calif. site (hereinafter
referred to as Moss Mag), was put into solution using carbonic acid
and agitation. The pH of the seawater in the first reactor was
maintained a pH of 7.0 or less during Moss Mag dissolution. In
certain embodiments, 1.0 gram of 50-150 .mu.m Moss Mag was
dissolved into solution per 1 L of seawater. A pH of 6.2-6.6 or a
hardness reading >0.08 grams/liter indicated that the
appropriate amount of Moss Mag was dissolved in solution. A source
of CO.sub.2, e.g. flue gas, was sparged into the water in the first
reactor. About 40-50% of the total flue gas consumed during the
entire reaction is dissolved into the seawater in this step. Flue
gas was sparged until the pH no longer responded to flue gas
dissolution which took approximately 30-60 minutes. Agitation was
stopped to allow unreacted Moss Mag, sand or other large particles
to gravity settle before transferring the CO.sub.2 charged acidic
water from the first reactor to the second reactor.
[0274] The CO.sub.2 charged acidic water was then transferred from
the first reactor to the second reactor. The second reactor was
used for both nucleation site generation and crystal growth. After
transferring the solution from the first reactor to the second
reactor, the following steps were performed: [0275] 1.50% NaOH was
added until a pH of 9.5 was reached. For example, for a 1000 gallon
reaction, about 20-25 kg of 50% NaOH was added using a dosing pump
capable of pumping 5-25 ml/sec of 50% NaOH. After reaching a pH of
9.5, the addition of 50% NaOH was stopped. [0276] 2. A CO.sub.2
source including a mixture of 20% CO.sub.2/80% compressed air was
sparged into the second reactor until a pH of 8.5 was reached.
After reaching a pH of 8.5, the sparging of the CO.sub.2 was
stopped. [0277] 3. Alternating steps of adding 50% NaOH into the
reactor to raise the pH and sparging CO.sub.2 to lower the pH were
performed. The pH was maintained between 8.5-9.8 during the
alternate addition of the 50% NaOH and sparging of CO.sub.2.
Alternate dosing of 50% NaOH and sparging of CO.sub.2 was continued
until a total of 90 kg (i.e., 65-70 kg in this step +20-25 kg from
the first step) of 50% NaOH was added to the reactor. [0278] 4. The
final pH after the last addition of 50% NaOH was between 9.6-9.8.
[0279] 5. Agitation was stopped and the precipitate was allowed to
gravity settle overnight and then water/solids separation was
performed. Alternatively, after agitation was stopped, the
precipitate was allowed to gravity settle for 15 minutes and then
accelerated water/solids separation was performed. Precipitate was
maintained at a temperature below 50.degree. C.
[0280] Resulting yields ranged from 30-50 lbs of precipitate per
1000 gallon reactor and depended on Mg ion dissolution and total
hardness prior to precipitation.
Example IV
CO.sub.2 Absorption
A. Process 1
[0281] In this example, absorption of carbon dioxide on the
laboratory-scale is described. 4.00 L of seawater was magnetically
stirred while 100% CO.sub.2 was heavily sparged through the
solution for 19 minutes where the pH reached a minimum of 4.89. To
this solution, 32.00 g of jet milled Mg(OH).sub.2 was added over a
period of 2 minutes. Simultaneously, CO.sub.2 was continuously
added for a total of 18 minutes to maintain a pH between 7.90 and
8.00 as Mg(OH).sub.2 dissolved. Next, 100.00 mL of 2 M NaOH was
added over a period of 5 minutes while the pH was maintained
between 8.00 and 8.10 by addition of CO.sub.2. To facilitate
precipitation, 275 mL of 2 M NaOH was added over a period of 5
minutes and the resultant solution was stirred for an additional 52
minutes. The slurry was vacuum filtered and dried in an oven at
50.degree. C. for 22 hours to recover 19.5 g of calcium and
magnesium carbonates (primarily aragonite and nesquehonite,
respectively) per 1 L of initial seawater solution.
B. Process 2
[0282] In this example, absorption of carbon dioxide on the
laboratory-scale is described. A 100-gallon cone-bottomed plastic
reaction vessel was filled with 100 gallons (380 L) of seawater,
which was stirred throughout the entire process with an overhead
stirrer (Portable Mixer w/Shaft, 2-4'' SS Propeller Blades (1-push,
1-pull), and Mounting Frame). The first step was to sparge the
solution with CO.sub.2 concentrated at 20% CO.sub.2 and 80%
Compressed Air, with a flow rate of 25 scfh. Equilibrium was
determined by the stabilization of the solution pH. The second step
was to add 2.70 g/L of Mg(OH).sub.2 (1.02 kg) with heavy mixing. To
further facilitate the dissolution of Mg(OH).sub.2, CO.sub.2 was
sparged through the solution. The third step was to add a solution
of 50 wt % NaOH until a pH of 9.8 was reached, followed by
additional CO.sub.2 sparging to lower the pH to 8.0. These last two
steps of an addition of 50 wt % NaOH to a pH of 9.8 and CO.sub.2
sparging to a pH of 8.0 was repeated until a total of 16.0 kg of 50
wt % NaOH had been added to the solution, where the final addition
of NaOH was used to reach a pH of 10.0. The precipitate was
separated and collected from the solution in a yield of 10.24 g/L
of calcium carbonate and magnesium carbonate hydrates.
C. Process 3
[0283] In this example, absorption of carbon dioxide on the
laboratory-scale is described. A 100-gallon cone-bottomed plastic
reaction vessel was filled with 100 gallons (380 L) of seawater,
which was stirred throughout the entire process with an overhead
stirrer. The first step was to sparge the solution with CO.sub.2
concentrated at 20% by volume at a flow rate of 100 scfm (standard
cubic feet per minute). Equilibrium was determined when the
concentration of CO.sub.2 in the vessel headspace approached that
of the inlet gas. The calculated absorption of CO.sub.2 during this
step was understandably low. The second step was to slowly add 379
g of Mg(OH).sub.2 to avoid a sharp increase in pH which would favor
the undesired carbonate precipitation. To further facilitate the
dissolution of Mg(OH).sub.2, CO.sub.2 was sparged through the
solution to an end pH of 6.3. The final step was to continuously
capture CO.sub.2 in the solution. Over the course of 3.5 hours, 4.9
kg of NaOH was added to balance the pH at 7.9 while CO.sub.2 was
sparged and reacted to form bicarbonate ions. The calculated
absorption of CO.sub.2 during this step was between 68% and 70%.
Results are provided in FIG. 15 which shows the evolution of pH and
CO.sub.2 absorption (instantaneous and cumulative). Artifacts at
point 1 in the pH plot were from removal of the pH probe to add
Mg(OH).sub.2.
D Process 4
[0284] In this example, absorption of carbon dioxide on the
industrial-scale is described. A 1000-gallon reaction vessel was
filled with 900 gallons (3400 L) of seawater, which was stirred
throughout the entire process. The first step was to load the
solution with 3.3 kg Mg(OH).sub.2, which increases both the pH and
the magnesium content. Next, 10% by volume CO.sub.2 was sparged and
the pH of 7.9 was maintained by a continuous addition of NaOH up to
30 kg. The total duration of these steps was 5-6 hours. A final
charge of 38 kg NaOH was added to increase the pH so that
carbonates would form and precipitate. The duration of this step
was 10-20 minutes. The solution was stirred for 1 hour more to
allow further precipitation. The reaction was allowed to settle
overnight. The solution was decanted and the solid product was
recovered by either filter press or vacuum filtration.
Additionally, the solution could be rinsed after the decant
process; whereby water was added and the sample was filter pressed.
Alternatively, water was added after initial vacuum filtration,
stirred, and filtered again. Finally, the product was spray dried.
The overall yield was 5-7 g/L of the original solution.
Example V
High Yield Dissolution of Mafic Mineral in HCl
[0285] In this example, the dissolution of olivine and subsequent
use to precipitate CO.sub.2 is described. A solution of 10% HCl
(475.66 g) was used to dissolve olivine (10.01 g, particle size
.about.5.8 .mu.m) at 50.degree. C. After the solution was stirred
for 10 hours and allowed to sit for 9 hours to provide a
Mg.sup.2+.sub.(aq) concentration of 0.2491 mol/L, it was vacuum
filtered hot to recover 404.52 g filtrate. Over the period of 1
hour, 15.01 g NaOH.sub.(s) and 5.23 g NaOH.sub.(aq) (in a 50 wt %
solution) were used to neutralize the solution. Simultaneously,
100% CO.sub.2 was heavily sparged through the mixture to provide a
final pH of 8.9 where precipitate formed. The slurry was vacuum
filtered and dried at 50.degree. C. for 17 hours to yield 19.26 g
which contained MgCO.sub.3.H.sub.2O, NaCl, an Fe-based compound and
a Si-based compound.
Example VI
Electrochemistry
[0286] Exemplary results achieved in accordance with the present
bi-electrode system are summarized in Table 8 below.
TABLE-US-00008 TABLE 8 Low Energy Electrochemical Bi-electrode
Method and System V across Time Initial pH at End pH at Initial pH
at End pH at Electrodes (min) Anode Anode Cathode Cathode 0.45 V 30
4.994 5.204 7.801 7.431 0.30 V in the 1.sup.st, and 0.15 V in the
2.sup.nd compartment
[0287] In this example, an electrochemistry system for
de-protonating seawater that has been charged with CO.sub.2 is
described. The cell that was used consisted of two 1-liter
compartments separated by a palladium foil. The first compartment
was charged with CO.sub.2 until a pH of 4.994 was achieved. A
sacrificial tin anode was placed into the first compartment, and
the tin electrode and palladium membrane were held under
galvanostatic control at 100 nA/cm.sup.2, which represented a
voltage of 0.30V. The second compartment consisted of a tin
electrode and SnCl.sub.2 dissolved in seawater. The palladium
membrane and tin electrode in the second compartment where held at
0.15V. The system was run for 30 minutes and as set forth in Table
8, the system showed an increase in pH in the first electrolyte,
and a decrease in pH in the second electrolyte.
[0288] Exemplary results achieved in accordance with the present
ionic membrane system are summarized in Table 9 below.
TABLE-US-00009 TABLE 9 Low Energy Electrochemical Ion Exchange
System and Method Volt across Time Initial pH at End pH at Initial
pH at End pH at Electrodes (sec) Anode Anode Cathode Cathode 0.6 V
2000 6.7 3.8 6.8 10.8 1.0 V 2000 6.6 3.5 6.8 11.1
In this example, an electrochemical cell for producing NaOH and HCl
at a low operating voltage utilizing an ion exchange membrane
positioned between an anode and a cathode is described. The cell
that was used consisted of two 250 mL compartments that were
separated by an anionic exchange membrane (PC-SA-250-250 (PCT GmbH
of Germany)). In both compartments 0.5M NaCl in a 18M.OMEGA.
aqueous solution was used. Both the anode and cathode were
constructed from a 10 cm.times.5 cm, 45 mesh Pt gauze. The anode
compartment had H.sub.2 gas sparged under the Pt electrode, and the
two electrodes were held at a bias of 0.6 V and 1.0 V for 2000
seconds. As set forth in Table 9, the two tests achieved a
significant increase in the pH in the cathode compartment, and a
decrease pH in the anode compartment.
[0289] Although the foregoing invention has been described in some
detail by way of illustration and example for purposes of clarity
of understanding, it is readily apparent to those of ordinary skill
in the art in light of the teachings of this invention that certain
changes and modifications may be made thereto without departing
from the spirit or scope of the appended claims.
[0290] Accordingly, the preceding merely illustrates the principles
of the invention. It will be appreciated that those skilled in the
art will be able to devise various arrangements which, although not
explicitly described or shown herein, embody the principles of the
invention and are included within its spirit and scope.
Furthermore, all examples and conditional language recited herein
are principally intended to aid the reader in understanding the
principles of the invention and the concepts contributed by the
inventors to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions. Moreover, all statements herein reciting principles,
aspects, and embodiments of the invention as well as specific
examples thereof, are intended to encompass both structural and
functional equivalents thereof. Additionally, it is intended that
such equivalents include both currently known equivalents and
equivalents developed in the future, i.e., any design features
developed that perform the same function, regardless of structure.
The scope of the present invention, therefore, is not intended to
be limited to the exemplary embodiments shown and described herein.
Rather, the scope and spirit of present invention is embodied by
the appended claims.
* * * * *
References