U.S. patent application number 12/534509 was filed with the patent office on 2009-12-31 for methods of manufacturing bentonite polution control sorbents.
This patent application is currently assigned to BASF Catalysts LLC. Invention is credited to Ronald T. Mentz, Lawrence Shore, Barry K. Speronello, Pascaline H. Tran, Xiaolin D. Yang.
Application Number | 20090320680 12/534509 |
Document ID | / |
Family ID | 38086160 |
Filed Date | 2009-12-31 |
United States Patent
Application |
20090320680 |
Kind Code |
A1 |
Yang; Xiaolin D. ; et
al. |
December 31, 2009 |
Methods of Manufacturing Bentonite Polution Control Sorbents
Abstract
Methods of manufacturing bentonite sorbents for removal of
pollutants including mercury from gas streams, such as a flue gas
stream from coal-fired utility plants are disclosed. The methods
include mixing bentonite sorbent particles with a sulfide salt and
a metal salt to form a metal sulfide on the outer surface of the
bentonite sorbent particles.
Inventors: |
Yang; Xiaolin D.; (Edison,
NJ) ; Tran; Pascaline H.; (Holmdel, NJ) ;
Shore; Lawrence; (Edison, NJ) ; Speronello; Barry
K.; (Belle Meade, NJ) ; Mentz; Ronald T.;
(Erie, PA) |
Correspondence
Address: |
BASF CATALYSTS LLC
100 CAMPUS DRIVE
FLORHAM PARK
NJ
07932
US
|
Assignee: |
BASF Catalysts LLC
Florham Park
NJ
|
Family ID: |
38086160 |
Appl. No.: |
12/534509 |
Filed: |
August 3, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11291091 |
Nov 30, 2005 |
7578869 |
|
|
12534509 |
|
|
|
|
Current U.S.
Class: |
95/107 |
Current CPC
Class: |
B01J 20/0214 20130101;
B01J 20/0296 20130101; B01D 53/10 20130101; B01J 20/3204 20130101;
B01J 20/0207 20130101; B01J 20/12 20130101; B01J 20/3021 20130101;
B01J 20/0285 20130101; B01J 20/0218 20130101; B01J 20/0288
20130101; B01D 53/02 20130101; B01J 20/024 20130101; B01J 20/0251
20130101; B01J 20/045 20130101; B01J 20/3078 20130101; B01J 20/0229
20130101; B01J 20/0222 20130101; B01J 20/3236 20130101; B01J
20/3293 20130101; B01D 53/83 20130101; B01J 20/0211 20130101; B01J
20/0244 20130101; B01J 20/0248 20130101; B01J 20/0281 20130101;
B01D 53/64 20130101; B01D 2257/602 20130101; B01J 20/0237
20130101 |
Class at
Publication: |
95/107 |
International
Class: |
B01D 53/06 20060101
B01D053/06 |
Claims
1. A method of removing pollutants from a flue gas stream
comprising injecting a sorbent into a coal-fired boiler flue gas
stream, the sorbent comprising bentonite particles having a metal
sulfide dispersed on the surface of the particles by a grinding,
milling or incipient wetness process.
2. The method of claim 1, wherein the pollutants include
mercury.
3. The method of claim 1, wherein the metal sulfide is the reaction
product of a metal salt and a sulfide salt.
4. The method of claim 3, wherein the reaction product is an in
situ reaction product.
5. The method of claim 1, wherein the bentonite particles have an
average size less than about 80 .mu.m.
6. The method of claim 3, wherein the metal salts are salts
selected from the group consisting of alkaline, alkaline earth
metals and metals having an atomic number in the range of 21 to 30,
38 to 50 and 56 to 79, and combinations thereof.
7. The method of claim 6, wherein the metal salt includes a metal
selected from the group consisting of copper, titanium, tin, iron,
manganese and mixtures thereof.
8. The method of claim 6, wherein the metal salt is selected from
the group consisting of nitrate, chloride, sulfate, acetate salts
and mixtures thereof.
9. The method of claim 1, wherein the loading level of the metal
sulfide is in the range of about 1 to about 20 weight percent.
10. The method of claim 3, wherein the sulfide salt is a sulfide
precursor that forms a S.sup.2- anion.
11. The method of claim 10, wherein the sulfide salt is selected
from the group consisting of Na.sub.2S and (NH.sub.4).sub.2S.
12. The method of claim 1, wherein the metal sulfide is selected
from the group consisting of copper sulfides, tin sulfides,
manganese sulfides, titanium sulfides and iron sulfides.
13. A method of removing pollutants from a flue gas stream
comprising: preparing sorbent particles by mixing a solid metal
salt with bentonite particles, adding a sulfide salt into the
mixture using a grinding process, milling process or an incipient
wetness process so that the metal salt and sulfide salt react to
form a metal sulfide on the surface of the bentonite particles, and
drying the mixture; and injecting the sorbent particles into a
coal-fired boiler flue gas stream.
14. The method of claim 13, wherein the method does not utilize ion
exchange to form the metal sulfide on the surface of the
particles.
15. The method of claim 13, wherein the metal sulfide forms in situ
on the particles.
16. The method of claim 13, wherein the metal salts are salts
selected from the group consisting of alkaline, alkaline earth
metals and metals having an atomic number in the range of 21 to 30,
38 to 50 and 56 to 79, and combinations thereof.
17. The method of claim 13, wherein the sulfide salt is a sulfide
precursor that forms a S.sup.2- anion.
18. The method of claim 13, further comprising reducing the average
particle of the particles to less than about 80 .mu.m.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/291,091, filed on Nov. 30, 2005, the content of which
is hereby incorporated by reference in its entirety.
TECHNICAL FIELD
[0002] Embodiments of the invention relate methods for the
manufacture of bentonite pollution control sorbents.
BACKGROUND ART
[0003] Emission of pollutants, for example, mercury, from sources
such as coal-fired and oil-fired boilers has become a major
environmental concern. Mercury (Hg) is a potent neurotoxin that can
affect human health at very low concentrations. The largest source
of mercury emission in the United States is coal-fired electric
power plants. Coal-fired power plants account for between one-third
and one-half of total mercury emissions in the United States.
Mercury is found predominantly in the vapor-phase in coal-fired
boiler flue gas. Mercury can also be bound to fly ash in the flue
gas.
[0004] On Dec. 15, 2003, the Environmental Protection Agency (EPA)
proposed standards for emissions of mercury from coal-fired
electric power plants, under the authority of Sections 111 and 112
of the Clean Air Act. In their first phase, the standards could
require a 29% reduction in emissions by 2008 or 2010, depending on
the regulatory option chosen by the government. In addition to
EPA's regulatory effort, in the United States Congress, numerous
bills recently have been introduced to regulate these emissions.
These regulatory and legislative initiatives to reduce mercury
emissions indicate a need for improvements in mercury emission
technology.
[0005] There are three basic forms of Hg in the flue gas from a
coal-fired electric utility boiler: elemental Hg (referred to
herein by the symbol Hg.sup.0); compounds of oxidized Hg (referred
to herein by the symbol Hg.sup.2+); and particle-bound mercury.
Oxidized mercury compounds in the flue gas from a coal-fired
electric utility boiler may include mercury chloride (HgCl.sub.2),
mercury oxide (HgO), and mercury sulfate (HgSO.sub.4). Oxidized
mercury compounds are sometimes referred to collectively as ionic
mercury. This is because, while oxidized mercury compounds may not
exist as mercuric ions in the boiler flue gas, these compounds are
measured as ionic mercury by the speciation test method used to
measure oxidized Hg. The term speciation is used to denote the
relative amounts of these three forms of Hg in the flue gas of the
boiler. High temperatures generated by combustion in a coal boiler
furnace vaporize Hg in the coal. The resulting gaseous Hg.sup.0
exiting the furnace combustion zone can undergo subsequent
oxidation in the flue gas by several mechanisms. The predominant
oxidized Hg species in boiler flue gases is believed to be
HgCl.sub.2. Other possible oxidized species may include HgO,
HgSO.sub.4, and mercuric nitrate monohydrate
(Hg(NO.sub.3).sub.2.H.sub.2O).
[0006] Gaseous Hg (both Hg.sup.0 and Hg.sup.2+) can be adsorbed by
the solid particles in boiler flue gas. Adsorption refers to the
phenomenon where a vapor molecule in a gas stream contacts the
surface of a solid particle and is held there by attractive forces
between the vapor molecule and the solid. Solid particles are
present in all coal-fired electric utility boiler flue gas as a
result of the ash that is generated during combustion of the coal.
Ash that exits the furnace with the flue gas is called fly ash.
Other types of solid particles, called sorbents, may be introduced
into the flue gas stream (e.g., lime, powdered activated carbon)
for pollutant emission control. Both types of particles may adsorb
gaseous Hg in the boiler flue gas.
[0007] Sorbents used to capture mercury and other pollutants in
flue gas are characterized by their physical and chemical
properties. The most common physical characterization is surface
area. The interior of certain sorbent particles are highly porous.
The surface area of sorbents may be determined using the Brunauer,
Emmett, and Teller (BET) method of N.sub.2 adsorption. Surface
areas of currently used sorbents range from 5 m.sup.2/g for
Ca-based sorbents to over 2000 m.sup.2/g for highly porous
activated carbons. EPA Report, Control of Mercury Emissions From
Coal-Fired Electric Utility Boilers, Interim Report,
EPA-600/R-01-109, April 2002. For most sorbents, mercury capture
often increases with increasing surface area of the sorbent.
[0008] Mercury and other pollutants can be captured and removed
from a flue gas stream by injection of a sorbent into the exhaust
stream with subsequent collection in a particulate matter control
device such as an electrostatic precipitator or a fabric filter.
Adsorptive capture of Hg from flue gas is a complex process that
involves many variables. These variables include the temperature
and composition of the flue gas, the concentration of Hg in the
exhaust stream, and the physical and chemical characteristics of
the sorbent. Of the known Hg sorbents, activated carbon and
calcium-based sorbents have been the most actively studied.
[0009] Currently, the most commonly used method for mercury
emission reduction is the injection of powdered activated carbon
into the flue stream of coal-fired and oil-fired plants. Currently,
there is no available control method that efficiently collects all
mercury species present in the flue gas stream. Coal-fired
combustion flue gas streams are of particular concern because their
composition includes trace amounts of acid gases, including
SO.sub.2 and SO.sub.3, NO and NO.sub.2, and HCl. These acid gases
have been shown to degrade the performance of activated carbon.
Though powdered activated carbon is effective to capture oxidized
mercury species such as Hg.sup.+2, powdered activated carbon (PAC)
is not as effective for elemental mercury which constitutes a major
Hg species in flue gas, especially for subbituminous coals and
lignite. There have been efforts to enhance the Hg.sup.0 trapping
efficiency of PAC by incorporating bromine species. This, however,
not only introduces significantly higher cost, but a disadvantage
to this approach is that bromine itself is a potential
environmental hazard. Furthermore, the presence of PAC hinders the
use of the fly ash for cement industry and other applications due
to its color and other properties.
[0010] As noted above, alternatives to PAC sorbents have been
utilized to reduce mercury emissions from coal-fired boilers.
Examples of sorbents that have been used for mercury removal
include those disclosed in United States Patent Application
Publication No. 2003/0103882 and in U.S. Pat. No. 6,719,828. In
United States Patent Application Publication No. 2003/0103882,
calcium carbonate and kaolin from paper mill waste sludge were
calcined and used for Hg removal at high temperatures above
170.degree. C., preferably 500.degree. C. U.S. Pat. No. 6,719,828
teaches the preparation of layered sorbents such as clays with
metal sulfide between the clay layers and methods for their
preparation. The method used to prepare the layered sorbents is
based on an ion exchange process, which limits the selection of
substrates to only those having high ion exchange capacity. In
addition, ion exchange is time-consuming and involves several wet
process steps, which significantly impairs the reproducibility,
performance, scalability, equipment requirements, and cost of the
sorbent. For example, a sorbent made in accordance with the
teachings of U.S. Pat. No. 6,719,828 involves swelling a clay in an
acidified solution, introducing a metal salt solution to exchange
metal ions between the layers of the clay, filtering the ion
exchanged clay, re-dispersing the clay in solution, sulfidation of
the clay by adding another sulfide solution, and finally the
product is filtered and dried. Another shortcoming of the process
disclosed in U.S. Pat. No. 6,719,828 is that the by-products of the
ion exchange process, i.e., the waste solutions of metal ions and
hydrogen sulfide generated from the acidic solution, are an
environmental liability.
[0011] There is an ongoing need to provide improved pollution
control sorbents and methods of their manufacture. It would be
desirable to provide sorbents containing metal sulfides on the
sorbent substrate that can be manufactured easily and
inexpensively. In this regard, simple and environmentally friendly
methods that effectively disperse metal sulfide on readily
available substrates, which do not require the numerous steps
involved in an ion exchange process are needed.
SUMMARY
[0012] Aspects of the invention include methods of manufacturing
bentonite sorbents for removal of pollutants such as heavy metals
from gas streams. The sorbents are useful for, but not limited to,
the removal of mercury from flue gas streams generated by the
combustion of coal.
[0013] In a first aspect, a method of making sorbent particles for
the removal of mercury from a gaseous stream is provided. The
method comprises mixing a metal salt with bentonite particles by
grinding or milling; mixing a sulfide salt with the bentonite
particles and the metal salt; and drying the mixture. In certain
embodiments, the method may further include reducing the particle
size of the particles.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is graph showing mercury removal versus copper
loading on a copper weight percent basis; and
[0015] FIG. 2 is a graph showing the effect of the addition of
chloride salts on mercury removal.
DETAILED DESCRIPTION
[0016] Before describing several exemplary embodiments of the
invention, it is to be understood that the invention is not limited
to the details of construction or process steps set forth in the
following description. The invention is capable of other
embodiments and of being practiced or being carried out in various
ways.
[0017] One aspect of the present invention relates to methods of
manufacturing bentonite sorbents. Bentonite is an aluminum
phyllosilicate clay consisting mostly of montmorillonite,
(Na,Ca).sub.0.33(Al,Mg).sub.2Si.sub.4O.sub.10(OH).sub.2.nH.sub.2O,
which may also be referred to as Fuller's earth or montmorillonite.
Applicants have determined that an ion exchange process such as the
type disclosed in U.S. Pat. No. 6,719,828, is not necessary for
mercury capture by the bentonite sorbent material.
[0018] According to one or more embodiments, incipient wetness or
solid-state reactive grinding processes are used to disperse metal
sulfide salts on the surface of bentonite sorbent particles. The
incipient wetness or solid-state reactive grinding methods
disclosed herein do not require excessive liquids associated with
wet processes, thus eliminating problems associated with wet
processes. These problems may include disposal of waste of metal
ions solution or hydrogen sulfide. In addition, certain embodiments
of the present invention provide accurate control of the amount of
metal sulfide on the surface of the sorbent. Further, the processes
according to certain embodiments are much faster and significantly
reduce the equipment and resources required for the large-scale
production. Moreover, the highly dispersed metal sulfide on the
surface of the sorbent provides better contact between Hg and metal
sulfide when used for mercury removal, as evidenced by the higher
and faster mercury capture than those obtained by the ion exchange
process when measured by an in-flight test with simulated flue
gases.
[0019] Another embodiment of the invention pertains to the addition
of at least one halogen-containing salt to the sorbent. The
presence of chloride significantly promotes the Hg-capture,
possibly due to the formation of mercury chloride complexes.
[0020] According to one embodiment of the invention, the steps for
making surface-dispersed metal sulfide include: mixing a metal salt
with a bentonite substrate particle by grinding or milling; adding
and mixing, preferably by grinding, a sulfide salt with the metal
salt and substrate particle mixture; and drying the mixture. In
certain embodiments, the resultant material is optionally milled to
the desired particle size. For low metal sulfide loading, the
sulfide can be added by incipient wetness as described below. For
high metal sulfide loading, the sulfide can be added by solid-state
grinding.
[0021] While embodiments of the present invention should not be
limited by a particular theory of operation or scientific
principle, it is believed that the metal salt (e.g., CuCl.sub.2)
reacts with sulfide (e.g., Na.sub.2S) in situ to form a metal
sulfide (for example, CuS) on the surface of the substrate,
particles (for example, kaolin clay). The formation of the metal
sulfide can occur either by contact via incipient wetness of the
reaction or said solid-state reactive grinding. Since most metal
salts and sulfides are crystal hydrates, for high metal sulfide
loading, the water released from the chemicals during mixing is
sufficient to moisten the mixture. As an example, the following
reaction,
CuCl.sub.2.2H.sub.2O+Na.sub.2S.9H.sub.2O.fwdarw.CuS+2NaCl+11H.sub.2O,
demonstrates that no additional water is required to disperse CuS
in the mixture.
[0022] The metal salts used according to method embodiments include
any metal salt that can release a metal ion with any oxidation
states when the salt contacts a sulfide salt and thereafter forms
water insoluble metal sulfide on the surface of a substrate. The
metal includes alkaline earth metals and the metals that have an
atomic number of between 21 and 30, between 38 and 50, and between
56 and 79 and combinations thereof. Examples of metals include
copper, titanium, tin, iron, and manganese. A presently preferred
metal ion is Cu.sup.+2 and presently preferred salts are nitrate,
chloride, sulfate, and acetate and combinations thereof. The
loading level of metal is between about 0 and 100 weight percent,
preferably between about 1 and 50 weight percent, and most
preferably between about 1 and 20 weight percent.
[0023] Any sulfide precursor that forms the S.sup.-2 anion can be
used in accordance with embodiments of the invention. This
includes, but is not limited to, Na.sub.2S and (NH.sub.4).sub.2S.
In a specific embodiment, the sulfide precursor is Na.sub.2S.
Sulfide loading level can be stoichiometric (1:1 atomic ratio) or
different than that of the metal ion.
[0024] Dispersion of the metal sulfide can be accomplished by any
method as long as the metal sulfide is well dispersed on the
surface of the substrate. Such methods include, but are not limited
to, incipient wetness, solid-state mixing, spray-drying, sprinkling
of solution on the solid, precipitation, co-precipitation, etc.
Detailed embodiments use solid-state reactive grinding for high
metal sulfide loading, incipient wetness for low metal sulfide
loading, or a combination of grinding and incipient wetness. The
order of adding the metal salts and sulfide salts can be altered,
e.g., the sulfide salt can be added to the substrate first followed
by addition of the metal salt. The metal sulfide can be added to
the substrate one salt at a time (e.g., add CuCl.sub.2 first,
followed by adding Na.sub.2S), two salts at the same time (e.g.,
co-precipitation), or directly mixing a fine metal sulfide powder
with the substrate.
[0025] Additional steps according to embodiments of the invention
may include drying and milling the sorbent. Drying may be
accomplished by any means such as static, spray-drying, microwave
drying, or on a moving belt at a temperature in the range of about
25.degree. and 200.degree. C. for 0 to 15 hours. In detailed
embodiments, drying occurs within the temperature range of about
60.degree. and 150.degree. C. In further detailed embodiments,
drying occurs in the range of about 90.degree. and 140.degree. C.
The sorbent can optionally be milled to an average particle size
below about 80 .mu.m, preferably below about 40 .mu.m.
[0026] Without intending to limit the invention in any manner, the
present invention will be more fully described by the following
examples.
EXAMPLES
[0027] Several samples were prepared in accordance with the methods
for manufacturing sorbent substrates described above. Table 1 lists
the sample number, the sulfide salt formed on the surface of the
sorbent (D), the sorbent substrate (A), the metal salt (B), and the
precursor sulfide salt (C). The last column of Table 1 indicates
the order of mixing of each of the ingredients. For example, A-B-C
indicates that the metal salt (B) was added to the substrate (A)
first, and then precursor sulfide salt (C) was added to the
mixture.
[0028] For example, sample ECS22, 1.18 g of CuCl.sub.2.2H.sub.2O
was mixed with 10.0 g of bentonite by a thorough solid-state
grinding. Then 1.67 g of Na.sub.2S.9H.sub.2O was dissolved in
de-ionized water and added to the solid mixture by what is termed
herein as an incipient wetness process, in which the solution was
added drop-wise to the solid mixture which was stirred rigorously.
The resultant moistened solid was wet enough to completely disperse
CuS on the bentonite, but dry enough so that the paste did not
flow. The moistened paste was then dried at 105.degree. C. in air
overnight and milled to a particle size of D.sub.90<10
.mu.m.
[0029] For sample ECS24, 2.44 g of CuCl.sub.2.2H.sub.2O was mixed
with 10.0 g of bentonite by a thorough solid-state grinding Then,
2.91 g of Na.sub.2S.9H.sub.2O powder was added in by another
thorough solid-state grinding. The moistened paste was then dried
at 105.degree. C. in air overnight and milled to a particle size of
D.sub.90<10 .mu.m.
[0030] The remaining samples were prepared in a very similar way as
the above two samples. The source and purity of the raw chemicals
are listed in Table 2, and the main characteristic properties of
the sorbent substrates are listed in Table 3.
TABLE-US-00001 TABLE 1 Summary of the Hg-removal sorbent
composition and preparation methods Example Metal Sulfide (D)
Substrate (A) Metal Salt (B) Precursor Sulfide (C) Prep ECS01 CuS
(10% Cu basis) 10 g Na-bentonite 2.95 g CuCl.sub.2.cndot.2H.sub.2O
4.16 g Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding
solid-state grinding ECS02 CuS (10% Cu basis) 10 g Na-bentonite
4.32 g CuSO.sub.4.cndot.5H.sub.2O 4.16 g Na.sub.2S.cndot.9H.sub.2O
A-B-C solid-state grinding solid-state grinding ECS03 CuS (20% Cu
basis) 10 g Na-bentonite 5.9 g CuCl.sub.2.cndot.2H.sub.2O 8.33 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding solid-state
grinding ECS04 Fe.sub.2S.sub.3 (6% Fe basis) 10 g Na-bentonite 3.12
g FeCl.sub.3.cndot.6H.sub.2O 16 g Na.sub.2S.cndot.9H.sub.2O A-B-C
solid-state grinding solid-state grinding ECS06 CuS (20% Cu basis)
+ 10 g Na-bentonite 5.9 g CuCl.sub.2.cndot.2H.sub.2O 2.70 g
Na.sub.2S.cndot.9H.sub.2O A-B-C CuCl.sub.2, solid-state grinding
solid-state grinding ECS07 CuS (10% Cu basis) + 10 g Na bentonite
2.95 g CuCl.sub.2.cndot.2H.sub.2O 0.56 g sulfur powder A-B-C sulfur
powder solid state grinding heated to 150.degree. C. for 0.5 hr
ECS08 MnS (4% Mn basis) 10 g Na-bentonite 1.71 g
MnCl.sub.2.cndot.4H.sub.2O 4.16 g Na.sub.2S.cndot.9H.sub.2O A-B-C
solid-state grinding solid-state grinding ECS09 S (10% S basis) 10
g Na-bentonite 0 1.11 g sulfur powder A-B ECS10 none 10 g
Na-bentonite 0 0 A ECS11 MnS.sub.2 (3% Mn basis) 10 g Na-bentonite
1.37 g KMnO.sub.4 8.33 g Na.sub.2S.cndot.9H.sub.2O A-B-C
solid-state grinding solid-state grinding ECS12 KMnO.sub.4 (4% Mn
basis) 10 g Na-bentonite 1.37 g KMnO.sub.4 solid-state grinding A-B
solid-state grinding ECS13 AgNO.sub.3 (1% Ag basis) 10 g
Na-bentonite 0.159 g AgNO.sub.3 0 A-B ECS15 CuS (20% Cu basis) 10 g
Na-bentonite 1.48 g CuCl.sub.2.cndot.2H.sub.2O 2.08 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding solid-state
grinding ECS20 CuS (15% Cu basis) 10 g bentonite 4.43 g
CuCl.sub.2.cndot.2H.sub.2O 6.25 g Na.sub.2S.cndot.9H.sub.2O A-B-C
solid-state grinding solid-state grinding ECS21 CuS (10% Cu basis)
20 g bentonite 0.90 g CuCl.sub.2.cndot.2H.sub.2O 8.33 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding solid-state
grinding (food processor blending) ECS22 CuS (4% Cu basis) 10 g
bentonite 1.18 g CuCl.sub.2.cndot.2H.sub.2O 1.67 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding incipient
wetness ECS23 CuS (4% Cu basis) 10 g bentonite 1.72 g
CuSO.sub.4.cndot.5H.sub.2O 1.67 g Na.sub.2S.cndot.9H.sub.2O A-B-C
solid-state grinding incipient wetness ECS24 CuS (7% Cu basis) 10 g
bentonite 2.44 g CuCl.sub.2.cndot.2H.sub.2O 2.91 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding solid-state
grinding ECS25 CuS (7% Cu basis) 10 g bentonite 3.01 g
CuSO.sub.4.cndot.5H.sub.2O 2.91 g Na.sub.2S.cndot.9H.sub.2O A-B-C
solid-state grinding solid-state grinding ECS26 CuS (10% Cu basis)
20 g bentonite 5.9 g CuCl.sub.2.cndot.2H.sub.2O 8.33 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding blending by
blender ECS27 CuS (10% Cu basis) + 10 g bentonite 4.32 g
CuSO.sub.4.cndot.5H.sub.2O + 4.161 g Na.sub.2S.cndot.9H.sub.2O
A-B-C MgCl.sub.2 1.00 g MgCl.sub.2 solid-state grinding solid-state
grinding ECS28 CuS (10% Cu basis) + 10 g bentonite 4.32 g
CuSO.sub.4.cndot.5H.sub.2O + 4.16 g Na.sub.2S.cndot.9H.sub.2O A-B-C
MgCl.sub.2 2.00 g MgCl.sub.2 solid-state grinding solid-state
grinding ECS29 CuS (10% Cu basis) + 10 g bentonite + 4.32 g
CuSO.sub.4.cndot.5H.sub.2O + 4.16 g Na.sub.2S.cndot.9H.sub.2O A-B-C
MgCl.sub.2 5.00 g MgCl.sub.2 solid-state grinding solid-state
grinding ECS30 CuS (10% Cu basis) 10 g bentonite 2.16 g
CuSO.sub.4.cndot.5H.sub.2O + 4.16 g Na.sub.2S.cndot.9H.sub.2O A-B-C
1.48 g CCl.sub.2.cndot.2H.sub.2O solid-state grinding solid-state
grinding ECS31 CuS (10% Cu basis) 10 g bentonite 3.24 g
CuSO.sub.4.cndot.5H.sub.2O + 0.74 g Na.sub.2S.cndot.9H.sub.2O A-B-C
1.48 g CCl.sub.2.cndot.2H.sub.2O solid-state grinding solid-state
grinding ECS32 CuS (10% Cu basis) 10 g bentonite 3.45 g
Cu(acetate).sub.2.cndot.H.sub.2O 16 g Na.sub.2S.cndot.9H.sub.2O
A-B-C solid-state grinding solid-state grinding ECS33 CuS (7% Cu
basis) 10 g bentonite 2.42 g Cu(acetate).sub.2.cndot.H.sub.2O 2.91
g Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding solid-state
grinding ECS34 CuS (4% Cu basis) 10 g bentonite 1.38 g
Cu(acetate).sub.2.cndot.H.sub.2O 1.66 g Na.sub.2S.cndot.9H.sub.2O
A-B-C solid-state grinding incipient wetness ECS35 CuS (100% Cu
basis) 10 g bentonite 4.02 g Cu(NO.sub.3).sub.2.cndot. 5/2H.sub.2O
16 g Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding
solid-state grinding ECS36 CuS (7% Cu basis) 10 g bentonite 2.82 g
Cu(NO.sub.3).sub.2.cndot. 5/2H.sub.2O 2.91 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding solid-state
grinding ECS37 CuS (4% Cu basis) 10 g bentonite 1.61 g
Cu(NO.sub.3).sub.2.cndot. 5/2H.sub.2O 1.66 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding incipient
wetness ECS38 CuS (10% Cu basis) 5 g bentonite 0.83 g CuS -- A-B
solid-state mixing ECS39 CuS (20% Cu basis) 5 g bentonite 1.66 g
CuS -- A-B solid-state mixing ECS40 CuS (1% Cu basis) 10 g
Bentonite 0.295 g CuCl.sub.2.cndot.2H.sub.2O 0.416 g
Na.sub.2S.cndot.9H.sub.2O A-C-B incipient wetness solid-state
grinding ECS41 CuS (2% Cu basis) 10 g Bentonite 0.59
CuCl.sub.2.cndot.2H.sub.2O 0.832 g Na.sub.2S.cndot.9H.sub.2O A-C-B
incipient wetness solid-state grinding ECS42 CuS (3% Cu basis) 10 g
Bentonite 0.885 g CuCl.sub.2.cndot.2H.sub.2O 1.248 g
Na.sub.2S.cndot.9H.sub.2O A-C-B incipient wetness solid-state
grinding ECS43 CuS (1% Cu basis) 10 g Bentonite 0.433 g
CuSO.sub.4.cndot.5H.sub.2O 0.416 g Na.sub.2S.cndot.9H.sub.2O A-C-B
incipient wetness solid-state grinding ECS44 CuS (2% Cu basis) 10 g
Bentonite 0.866 g CuSO.sub.4.cndot.5H.sub.2O 0.833 g
Na.sub.2S.cndot.9H.sub.2O A-C-B incipient wetness solid-state
grinding ECS45 CuS (3% Cu basis) 10 g Bentonite 1.299 g
CuSO.sub.4.cndot.5H.sub.2O 1.248 g Na.sub.2S.cndot.9H.sub.2O A-C-B
incipient wetness solid-state grinding ECS46 CuS (4% Cu basis) + 10
g Bentonite 1.732 g CuSO.sub.4.cndot.5H.sub.2O 1.664 g
Na.sub.2S.cndot.9H.sub.2O A-B-C MgCl.sub.2 0.100 g MgCl.sub.2
incipient wetness solid-state grinding ECS47 CuS (3% Cu basis) + 10
g Bentonite 1.299 g CuSO.sub.4.cndot.5H.sub.2O 1.248 g
Na.sub.2S.cndot.9H.sub.2O A-B-C MgCl.sub.2 0.100 g MgCl.sub.2
incipient wetness solid-state grinding ECS48 CuS (3% Cu basis) + 10
g Bentonite 1.299 g CuSO.sub.4.cndot.5H.sub.2O 1.248 g
Na.sub.2S.cndot.9H.sub.2O A-B-C MgCl.sub.2 0.200 g MgCl.sub.2
incipient wetness solid-state grinding ECS49 CuS (3% Cu basis) + 10
g Bentonite 1.299 g CuSO.sub.4.cndot.5H.sub.2O 1.248 g
Na.sub.2S.cndot.9H.sub.2O A-B-C MgCl.sub.2 0.500 g MgCl.sub.2
incipient wetness solid-state grinding ECS50 CuS (3% Cu basis) + 10
g Bentonite 1.299 g CuSO.sub.4.cndot.5H.sub.2O 1.248 g
Na.sub.2S.cndot.9H.sub.2O A-B-C NaCl 0.100 g NaCl.sub.2 incipient
wetness solid-state grinding ECS51 CuS (3% Cu basis) + 10 g
Bentonite 1.299 g CuSO.sub.4.cndot.5H.sub.2O 1.248 g
Na.sub.2S.cndot.9H.sub.2O A-B-C NaCl 0.200 g NaCl.sub.2 incipient
wetness solid-state grinding ECS52 CuS (3% Cu basis) + 10 g
Bentonite 1.299 g CuSO.sub.4.cndot.5H.sub.2O 1.248 g
Na.sub.2S.cndot.9H.sub.2O A-B-C NaCl 0.500 g NaCl.sub.2 incipient
wetness solid-state grinding ECS57 Fe.sub.2S.sub.3 (10.0% S basis)
10 g Na-bentonite 6.24 g FeCl.sub.3.cndot.6H.sub.2O 8.33 g
Na.sub.2S.cndot.9H.sub.2O A-B-C solid-state grinding solid-state
grinding ECS58 CuS (5.0% S basis) 10 g bentonite 4.33 g
CuSO.sub.4.cndot.5H.sub.2O 4.16 g Na.sub.2S.cndot.9H.sub.2O A-B-C
co-precipitation co-precipitation
TABLE-US-00002 TABLE 2 Source and purity of the raw chemicals Raw
Chemical Supplier or Source Purity CuCl.sub.2.cndot.2H.sub.2O
Alfa-Aesar 99+% CuSO.sub.4.cndot.5H.sub.2O Alfa-Aesar 98.0-102.0%
Cu(Acetate).sub.2.cndot.H.sub.2O Aldrich 98+%
Cu(NO.sub.3).sub.2.cndot.5H.sub.2O Aldrich 98%
Na.sub.2S.cndot.9H.sub.2O Alfa-Aesar 98.0-103.0%
FeCl.sub.3.cndot.6H.sub.2O Aldrich 98+% MnCl.sub.2.cndot.4H.sub.2O
Aldrich 98+% MgCl.sub.2 Alfa-Aesar 99% KMnO.sub.4 Alfa-Aesar
99.0%
TABLE-US-00003 TABLE 3 Source Treatment and Propeties of Bentonite
Substrate Supplier or Source Black Hill Bento Pre-treatment Milled
to a particle size of D.sub.90 <10 .mu.m N.sub.2 Surface Area
35.4 m.sup.2/g N.sub.2 Pore Volume 0.11 cc/g XRD Crystallinity
Crystalline Structure Layered - Interlayer accessible Pore Diameter
12.2 nm Main Chemical Composition (%) SiO.sub.2 Al.sub.2O.sub.3
Fe.sub.2O.sub.3 K.sub.2O MgO Na.sub.2O TiO.sub.2 CaO 67.50 20.20
3.20 0.51 2.06 2.64 0.23 2.42
[0031] The formation of metal sulfide (CuS) on the substrate
particles is evidenced by the darkening of the paste and the heat
release due to the following process:
CuCl.sub.2.2H.sub.2O+Na.sub.2S.9H.sub.2O.fwdarw.CuS+2NaCl+11H.sub.2O
[0032] Spectroscopic data also supports this observation of CuS
formation on the substrate. Infrared (IR) spectra of
bentonite-supported chemical CuCl.sub.2, Na.sub.2S, CuS, NaCl, and
three sorbents that were prepared from the solid-state grinding of
CuCl.sub.2.2H.sub.2O, Na.sub.2S.9H.sub.2O and bentonite, as
described above, confirmed that the three sorbents (2.5, 5.0 and
10.0% S basis) contain predominantly CuS and NaCl and very little
CuCl.sub.2 and Na.sub.2S precursors. X-ray powder diffraction
provided similar evidence of the formation of CuS. X-ray elemental
microprobe also showed that the space distribution of Cu on the
surface of substrate particles is identical to that of sulfur,
indicating again the formation of CuS on the substrate surface.
Mercury Removal Evaluation
[0033] The Hg-removal performance of the sorbents described above
was evaluated by an in-flight test, which is a commonly used fast
screening method used to rank sorbents. The measurement includes
the total mercury removal from simulated flue gas
(Hg].sub.injection start-[Hg].sub.injection
stop)/[Hg].sub.injection start*100%) and the kinetics, or rate, of
the Hg-capture (-d(Hg %)/dt). Both parameters are important since
the former measures the total Hg-capture while the latter is
directly related to the strength of adsorption sites on the sorbent
material. Thus, good sorption may be characterized by both high and
fast Hg removal at fixed sorbent injection rate.
[0034] Mercury concentration at the outlet of the sorbent injection
chamber was measured using an Ohio Lumex cold vapor atomic
absorption instrument. The simulated flue gas consisted of 1600 ppm
SO.sub.2, 400 ppm NOx, 12% CO.sub.2, 6% oxygen, 2% water, and
balanced by nitrogen. The flow rate was 944 sccm, sorption pressure
12 psia, and sorption temperature 140.5.degree. C.
[0035] Table 4 summarizes the in-flight test results of metal
sulfide/substrate sorbents from Table 1. All of the sorb ent
samples were sieved through a 325 mesh sieve prior to the
injection. In-flight test results were compared to samples made in
accordance with the ion exchange methods disclosed in U.S. Pat. No.
6,719,828, which demonstrated a total Hg removal between 70 to 90%
(injection rate 6-10 lb/MMacf).
[0036] The data in Table 4 shows that the CuS/bentonite samples
prepared by incipient wetness or solid-state grinding has the same
or better Hg-removal than sorbents made by ion exchange
methods.
TABLE-US-00004 TABLE 4 Selected In-Flight Test Results Rate
Injection Hg d Sample Rate removal (Hg %)/ # Sorbent* (lb/MMacf)
(%) dt ECS-01 CuS/bentonite 8.4 93 0.133 10% Cu basis ECS-02
CuS/bentonite 8.4 93 0.133 10% Cu basis CuSO.sub.4 precursor ECS-03
Cu/bentonite 9.9 89 0.264 20% Cu basis ECS-04
Fe.sub.2S.sub.3/bentonite 7.4 17 0.044 10% S basis ECS-06 (CuS +
CuCl.sub.2)/bentonite 8.2 62 0.067 20% Cu basis; Cu:S = 2:1 ECS-07
(CuS + S)/bentonite 9.0 90 0.406 10% Cu basis; Cu:S = 1:2 ECS-08
MnS/bentonite 5.9 73 0.030 5% S basis ECS-09 Sulfur/bentonite 5.5
32 2.5 10% S basis ECS-10 Bentonite, As-is 5.0 27 0.021 ECS-11
MnS.sub.2/bentonite 8.6 47 0.086 10% S basis ECS-12
KMnO.sub.4/bentonite 9.3 9 2.8 6% Mn basis ECS-15 CuS/bentonite
11.6 90 68.3 20% Cu basis dried at 150.degree. C. ECS-21
CuS/bentonite 8.2 92 29.1 10% Cu Basis ECS-22 CuS/bentonite 6.2 93
43.0 4% Cu basis ECS-23 CuS/bentonite 7.2 76 24.6 4% Cu basis,
CuSO.sub.4 ECS-24 CuS/bentonite 8.8 89 22.3 7% Cu basis ECS-25
CuS/bentonite 7.3 62 22.0 7% Cu basis, CuSO.sub.4 ECS-26
CuS/bentonite 5.7 94 30.8 10% Cu basis (blender scale-up) ECS-27
CuS/bentonite 7.7 94 47.4 10% Cu + 10 g MgCl.sub.2 ECS-28
CuS/bentonite 10.3 94 20.5 10% Cu + 2.0 g MgCl.sub.2 ECS-29
CuS/bentonite 7.8 36 6.2 10% Cu + 5.0 g MgCl.sub.2 ECS-30
CuS/bentonite 7.5 93 47.4 10% Cu, CuSO.sub.4/CuCl.sub.2 = 1.5
ECS-31 CuS/bentonite 7.0 91 39.5 10% Cu, CuSO.sub.4/CuCl.sub.2 =
2.2 ECS-32 CuS/bentonite 9.9 31 28.5 10% Cu, Cu acetate ECS-33
CuS/bentonite 7.8 59 24.6 7% Cu, Cu acetate ECS-34 CuS/bentonite
11.5 23 18.9 4% Cu, Cu acetate ECS-35 CuS/bentonite 4.5 58 24.0 10%
Cu, Cu nitrate ECS-36 CuS/bentonite 6.3 54 14.6 7% Cu, Cu nitrate
ECS-37 CuS/bentonite 5.3 55 19.6 4% Cu, Cu nitrate ECS-38
CuS/bentonite 3.2 19 10.0 10% Cu, CuS ECS-39 CuS/bentonite 3.6 32
14.1 2% Cu, CuS ECS-40 CuS/bentonite 6.1 93 31.9 1% Cu, incipient
wet ECS-41 CuS/bentonite 6.0 93 31.0 2% Cu, incipient wet ECS-42
CuS/bentonite 7.0 98 28.0 3% Cu, incipient wet ECS-43 CuS/bentonite
5.9 36 12.3 1% Cu, CuSO.sub.4, incipient wet ECS-44 CuS/bentonite
6.9 31 12.0 2% Cu, CuSO.sub.4, incipient wet ECS-45 CuS/bentonite
75. 40 118.4 3% Cu, CuSO.sub.4, incipient wet ECS-46 CuS/bentonite
7.3 87 27.9 4% Cu, CuSO.sub.4 + 0.1 gMgCl.sub.2 ECS-47
CuS/bentonite 7.7 83 31.1 3% Cu, CuSO.sub.4 + 0.1 gMgCl.sub.2
ECS-48 CuS/bentonite 7.5 80 33.5 3% Cu, CuSO.sub.4 + 0.2
gMgCl.sub.2 ECS-49 CuS/bentonite 6.2 81 27.1 3% Cu, CuSO.sub.4 +
0.5 gMgCl.sub.2 ECS-50 CuS/bentonite 6.4 87 30.5 3% Cu, CuSO.sub.4
+ 0.1 gNaCl ECS-51 CuS/bentonite 6.7 83 27.4 3% Cu, CuSO.sub.4 +
0.2 gNaCl ECS-52 CuS/bentonite 5.6 89 18.1 (*unless stated
otherwise, CuCl.sub.2.cndot.2H.sub.2O and Na.sub.2S.cndot.9H.sub.2O
precursors were used)
[0037] FIGS. 1 and 2 further demonstrate the optimized copper
loading and importance of the presence of chloride anion in the
sorbent. As shown in FIG. 1, at the Cu loading of 4 wt %, the
Hg-removal seems to have reached the maximum level. Samples were
prepared by the incipient wetness and solid state grinding
techniques described using the bentonite substrate and the
precursors noted in Table 1. The copper loading level was varied
between 0 and 10% and the Hg removal was measured as described
above. Different metal precursors exhibited different Hg-removal
efficiency. For the results shown in FIG. 1, only the sorbents made
using a CuCl.sub.2 precursor provided Hg-removal of above 80%. The
highest Hg removal was 98% at 3% Cu loading level, which is not
shown in the Figures.
[0038] Adding a small amount of chloride, such as NaCl or
MgCl.sub.2, to copper sulfate significantly increases its Hg
removal, shown in FIG. 2 where all sorbents have 3% Cu loading
level on bentonite substrate loaded with copper sulfate precursors
as described above and prepared by incipient wetness. FIG. 2
demonstrates that adding a small amount of chloride in the sorbents
effectively enhances Hg-removal. This also has practical
importance. For example, the use of pure chloride salt precursor
can lead to corrosion of stainless steel reaction vessels.
Therefore, the addition of mixed salts not only enhances mercury
removal but reduces corrosion of equipment.
[0039] It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit or scope of the invention. For
example, while the sorbents disclosed herein are particularly
useful for removal of mercury from the flue gas of coal-fired
boilers, the sorbents can be used to remove heavy metals such as
mercury from other gas streams, including the flue gas of municipal
waste combustors, medical waste incinerators, and other Hg-emission
sources. Thus, it is intended that the present invention cover
modifications and variations of this invention provided they come
within the scope of the appended claims and their equivalents.
* * * * *