U.S. patent application number 14/738559 was filed with the patent office on 2015-12-17 for hydrothermal carbonization of algal feedstocks and fuels produced thereby.
This patent application is currently assigned to BOARD OF REGENTS OF THE NEVADA SYSTEM OF HIGHER EDUCATION, ON BEHALF OF THE DESERT RESEARCH INSTIT. The applicant listed for this patent is BOARD OF REGENTS OF THE NEVADA SYSTEM OF HIGHER EDUCATION, ON BEHALF OF THE DESERT RESEARCH INSTIT. Invention is credited to Amber Lea Broch, S. Kent Hoekman, Umakanta Jena.
Application Number | 20150361371 14/738559 |
Document ID | / |
Family ID | 54835638 |
Filed Date | 2015-12-17 |
United States Patent
Application |
20150361371 |
Kind Code |
A1 |
Hoekman; S. Kent ; et
al. |
December 17, 2015 |
HYDROTHERMAL CARBONIZATION OF ALGAL FEEDSTOCKS AND FUELS PRODUCED
THEREBY
Abstract
In one embodiment, the present disclosure provides a method for
producing a solid fuel. A feedstock that includes algae or
delipidized algal residue and a liquid carrier is heated to a
suitable temperature, at a suitable pressure, and for a suitable
amount of time to form a desired amount of solid hydrochar. The
hydrochar is collected and compressed into a compressed solid.
Inventors: |
Hoekman; S. Kent; (Reno,
NV) ; Broch; Amber Lea; (Reno, NV) ; Jena;
Umakanta; (Reno, NV) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BOARD OF REGENTS OF THE NEVADA SYSTEM OF HIGHER EDUCATION, ON
BEHALF OF THE DESERT RESEARCH INSTIT |
Reno |
NV |
US |
|
|
Assignee: |
BOARD OF REGENTS OF THE NEVADA
SYSTEM OF HIGHER EDUCATION, ON BEHALF OF THE DESERT RESEARCH
INSTIT
RENO
NV
|
Family ID: |
54835638 |
Appl. No.: |
14/738559 |
Filed: |
June 12, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62011793 |
Jun 13, 2014 |
|
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|
Current U.S.
Class: |
44/589 |
Current CPC
Class: |
C10L 2200/0469 20130101;
C10L 5/363 20130101; C10L 2290/06 20130101; Y02E 50/10 20130101;
C10L 5/10 20130101; C10L 9/08 20130101; C10L 2290/30 20130101; C10L
2290/24 20130101; Y02E 50/30 20130101; C10L 5/08 20130101; C10L
9/086 20130101; C10L 5/447 20130101 |
International
Class: |
C10L 5/44 20060101
C10L005/44; C10L 5/10 20060101 C10L005/10; C10L 5/08 20060101
C10L005/08 |
Claims
1. A method for producing solid fuel comprising: providing a
feedstock comprising algae or delipidized algal residue and a
liquid carrier; heating the feedstock at a temperature of between
about 120.degree. C. and about 250.degree. C., and a pressure of
between about 2 bar and about 40 bar for a period of between about
5 minutes and about 16 hours, thereby forming an amount of a solid
hydrochar; collecting the hydrochar; and compressing the hydrochar
into a compressed solid.
2. The method of claim 1, wherein the feedstock comprises between
about 2% and about 10% by weight algae or delipidized algal
residue.
3. The method of claim 1, wherein the feedstock comprises less than
about 20% by weight of algae or delipidized algal residue.
4. The method of claim 1, wherein the hydrochar is compressed at a
temperature of between about 25.degree. C. and about 200.degree.
C.
5. The method of claim 1, wherein the hydrochar is compressed at a
temperature of between about 100.degree. C. and about 160.degree.
C.
6. The method of claim 1, wherein the hydrochar is compressed at a
temperature of between about 120.degree. C. and about 180.degree.
C.
7. The method of claim 1, wherein the hydrochar is compressed at a
temperature of between about 140.degree. C. and about 160.degree.
C.
8. The method of claim 1, wherein the hydrochar is compressed at a
temperature of less than about 200.degree. C.
9. The method of claim 1, wherein the hydrochar is compressed at a
temperature less than a temperature typically used to compress
hydrochar produced from the hydrothermal carbonization of
lignocellulosic biomass.
10. The method of claim 1, wherein the hydrochar is compressed
without the addition of an external binder.
11. The method of claim 1, wherein the hydrochar is capable of
being compressed without the addition of an external binder.
12. The method of claim 1, wherein the hydrochar is compressed
essentially without the addition of an external binder.
13. The method of claim 1, wherein the hydrochar is compressed with
less than about 10% by weight of an external binder.
14. The method of claim 1, wherein the hydrochar is compressed with
less than about 5% by weight of an external binder.
15. The method of claim 1, wherein the hydrochar is mixed with
hydrochar produced from hydrothermal carbonization of a
lignocellulosic feedstock and the mixture is compressed.
16. The method of claim 1, wherein the temperature is between about
150.degree. C. and about 250.degree. C. and the pressure is between
about 5 bar and about 40 bar, and the reaction time is between
about 5 minutes and about 2 hours.
17. The method of claim 1, wherein the temperature is between about
180.degree. C. and about 250.degree. C., the pressure is between
about 5 bar and about 40 bar, and the reaction time is between
about 5 minutes and about 1 hour.
18. The method of claim 1, wherein the feedstock comprises
delipidized algal residue.
19. The method of claim 1, wherein the feedstock comprises whole
algae.
20. The method of claim 1, wherein the feedstock consists
essentially of delipidized algal residue and/or algae and the
liquid carrier.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of, and incorporates by
reference, U.S. Provisional Patent Application Ser. No. 62/011,793,
filed Jun. 13, 2014.
[0002] This disclosure relates generally to the hydrothermal
carbonization of feedstocks that include algae or an algal
component, and fuels produced therefrom. In particular embodiments,
the hydrochar produced from the hydrothermal carbonization reaction
is compressed, such as being formed into pellets.
SUMMARY
[0003] In one embodiment, the present disclosure provides a method
for producing a solid fuel from a feedstock that includes algae or
delipidized algal residence and a liquid carrier. In particular
implementations, the feedstock include algae, delipidized algal
residue, or a mixture of algae and delipidized algal residue. The
feedstock optionally can include additional components, such as
other types of biomass. In some aspects of the present disclosure,
the feedstock includes less than about 20% by weight of algae or
delipidized algal residue, such as between about 2% and about 10%
by weight of algae or delipidized algal residue.
[0004] The feedstock is heated at a suitable temperature and
pressure, and for a suitable period of time, to form solid
hydrochar. The temperature, in particular implementations, is
between about 120.degree. C. and about 250.degree. C., between
about 150.degree. C. and about 250.degree. C., or between about
180.degree. C. and about 250.degree. C. The pressure is between
about 2 bar and about 40 bar, such as between about 5 bar and about
40 bar, in a particular example. In a particular implementation,
the reaction is carried out for a period of between about 5 minutes
and about 16 hours. In various examples, the reaction is carried
about for between about 5 minutes and about 2 hours, such as
between about 5 minutes and about 1 hour.
[0005] In a specific implementation, after reaction, the solid
hydrochar is collected and compressed into a compressed solid. For
example, the compressed solid may be pellets or briquettes. In some
implementations, the solid hydrochar is compressed, or capable of
being compressed, without the addition of an external binder. In
some implementations where an external binder is used, the binder
is less than about 10% by weight of the material to be compressed,
such as less than about 5% by weight. In additional aspects of the
present disclosure, the hydrochar formed from the method is
combined with hydrochar produced from a lignocellulosic feedstock
and then compressed to a solid.
[0006] In another implementation, the hydrochar is subjected to an
extrusion process. In one example, the hydrochar is formed and then
subjected to an extrusion process. In another example, the
hydrothermal carbonization reaction is carried out as part of the
extrusion process. For example, the extrusion process may generate
sufficient heat and pressure to carry out the hydrothermal
carbonization reaction.
[0007] In yet another implementation, the hydrochar is collected
but not compressed, or is not specifically collected. For example,
the hydrochar may be subjected to another reaction or process.
[0008] In some aspects of the disclosed method, the hydrochar is
compressed at a temperature of between about 25.degree. C. and
about 200.degree. C., such as between about 100.degree. C. and
about 160.degree. C., between about 120.degree. C. and about
180.degree. C., between about 140.degree. C. and 160.degree. C., or
less than about 200.degree. C. In another aspect of the disclosed
method, the hydrochar is compressed at a temperature less than a
temperature typically used to compress hydrochar produced from the
hydrothermal carbonization of lignocellulosic biomass.
[0009] In another embodiment, the present disclosure provides a
method for producing a solid fuel using a feedstock that includes
delipidized algal residue and a liquid carrier. In particular
examples, the feedstock consists of, or consists essentially of,
delipidized algal residue and the liquid carrier. The liquid
carrier, in particular implementations, is water.
[0010] In particular aspects of the present disclosure, the
feedstock used in the method includes a biomass component, and the
delipidized algal residue comprises at least about 25% of the
biomass component, such as at least about 50% or at least about
75%. The feedstock optionally can include additional components,
such as other types of biomass. In implementations of the method
where an additional biomass component is used, in a particular
example, the additional biomass includes algae.
[0011] The feedstock is heated at a suitable temperature and
pressure, and for a suitable period of time, to form solid
hydrochar. The temperature, in particular implementations, is
between about 120.degree. C. and about 250.degree. C., between
about 150.degree. C. and about 250.degree. C., or between about
180.degree. C. and about 250.degree. C. The pressure is between
about 2 bar and about 40 bar, such as between about 5 bar and about
40 bar, in a particular example. In a particular implementation,
the reaction is carried out for a period of between about 5 minutes
and about 16 hours. In various examples, the reaction is carried
about for between about 5 minutes and about 2 hours, such as
between about 5 minutes and about 1 hour.
[0012] After reaction, the hydrochar is typically collected.
Optionally, the hydrochar may be compressed into a compressed
solid. For example, the compressed solid may be pellets or
briquettes. In some implementations, the solid hydrochar is
compressed, or capable of being compressed, without the addition of
an external binder. In some implementations where an external
binder is used, the binder is less than about 10% by weight of the
hydrochar material to be compressed, such as less than about 5% by
weight. In additional aspects of the present disclosure, the
hydrochar formed from the method is combined with hydrochar
produced from a lignocellulosic feedstock and then compressed to a
solid.
[0013] In some aspects of the disclosed method, the hydrochar is
compressed at a temperature of between about 25.degree. C. and
about 200.degree. C., such as between about 100.degree. C. and
about 160.degree. C., between about 120.degree. C. and about
180.degree. C., between about 140.degree. C. and 160.degree. C., or
less than about 200.degree. C. In another aspect of the disclosed
method, the hydrochar is compressed at a temperature less than a
temperature typically used to compress hydrochar produced from the
hydrothermal carbonization of lignocellulosic biomass.
[0014] In some cases, the hydrochar is not specifically collected.
For example, the hydrochar may be subjected to another reaction or
process.
[0015] In a particular implementation, the hydrochar is subjected
to an extrusion process. In one example, the hydrochar is formed
and then extruded. In another example, the extrusion process is
part of the hydrothermal carbonization process. An extrusion
process may, for example, generate the desired heat and pressure
conditions for a hydrothermal carbonization reaction.
[0016] The disclosed method can provide greater energy
densification between the feedstock and the hydrochar than
comparable hydrothermal carbonization of lignocellulosic
feedstocks. In one particular example, when the hydrothermal
carbonization reaction is carried about between about 120.degree.
C. and about 215.degree. C., such as between about 120.degree. C.
and about 200.degree. C. or between about 120.degree. C. and about
175.degree. C., the energy densification may be at least about
1.1
[0017] In another aspect, the disclosed method can allow for lower
temperatures and pressures to be used than in hydrothermal
carbonization of lignocellulosic feedstocks. In another aspect, the
energy content of the hydrochar is significantly higher than the
energy content of hydrochar produced from lignocellulosic biomass
under the same reaction conditions. In yet another aspect, the
method produces hydrochar having an energy content that is at least
about equivalent to the energy content of lignocellulosic hydrochar
produced at a reaction temperature that is at least about
30.degree. C. higher, such as at least about 50.degree. C. higher
or at least about 60.degree. C. higher, than that used to produce
the hydrochar from the feedstock including biomass from an algal
source, such as whole algae or delipidized algae.
[0018] In another aspect, the present disclosure provides a solid
fuel comprising hydrochar formed from the hydrothermal
carbonization of algae, delipidized algal residue, or a mixture
thereof. The solid fuel may be, for example, pellets or briquettes.
In another example, the solid fuel is an extruded material.
[0019] In one implementation, the solid fuel comprises at least
about 5% of biomass of algal origin treated via hydrothermal
carbonization, or "algal hydrochar," according to a method of the
present disclosure. For example, the solid fuel may be at least
about 10%, about 25%, about 50%, about 75%, about 85%, about 90, or
about 95% of algal origin/algal hydrochar. In one example, being of
algal origin means being algae, delipidized algal residue, or a
mixture thereof. In a more specific example, being of algal origin
means being whole (non-delipidized) algae. In another specific
example, being of algal origin means being delipidized algal
residue.
[0020] In some examples, the solid fuel, such as briquettes or
pellets, including solid fuels from the previously described
implementation, include less than about 10% by weight of an
external binder, such as less than about 5%, 4%, 2%, or 1%. In
another example, the solid fuel does not include an external
binder.
[0021] In another implementation, the present disclosure provides
solid fuels from hydrothermal carbonization of algal sources that
have higher energy densities than solid fuels produced from
hydrothermal carbonization of lignocellulosic sources. For example,
the solid fuel may have an energy density of 1.1 or higher.
[0022] Some aspects of the present disclosure provide solid fuels,
such as compressed solids or extruded materials, that demonstrate
improved stability. In one example, the fuel, after being immersed
in water for 60 minutes, exhibits a stability of at least about
55%, such as at least about 60%, about 65%, about 70%, about 75%,
about 80%, about 90%, or about 95%. In a specific example,
stability is defined as the pellet weight after tumbling divided by
the pellet weight before tumbling, multiplied by one hundred. For
example, the stability may be the pellet of an immersed pellet
after tumbling, divided by the weight of the immersed pellet before
tumbling, multiplied by one hundred. In a yet more specific
example, the immersion test is the immersion test described
herein.
[0023] In some implementations, the fuels with enhanced stability
include less than about 10% by weight of an external binder, such
as less than about 5, about 4%, about 2%, or about 1%. In a
specific example, the solid fuel does not include an external
binder, or is substantially free of external binders. In further
implementations, including examples with the previously described
limits on external binders, the fuel includes at least about 10%,
about 25%, about 50%, about 75%, about 85%, about 90, or about 95%
hydrochar of algal origin, such as algae or delipidized algal
residue
[0024] There are additional features and advantages of the various
embodiments of the present disclosure. They will become evident
from the following disclosure.
[0025] In this regard, it is to be understood that this is a
summary of the various embodiments described herein. Any given
embodiment of the present disclosure need not provide all features
noted above, nor must it solve all problems or address all issues
in the prior art noted above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Various embodiments are shown and described in connection
with the following drawings in which:
[0027] FIG. 1 is a schematic diagram illustrating an embodiment
according to the present disclosure of processing an
algae-containing feedstock using hydrothermal carbonization.
[0028] FIG. 2 is a schematic diagram providing a flowchart for a
process for assessing the durability of pelletized materials.
[0029] FIG. 3 is table summarizing water immersion pellet
durability tests of pellets made from whole Spirulina.
[0030] FIG. 4 is table summarizing water immersion pellet
durability tests of pellets made from lipid-extracted
Spirulina.
[0031] FIG. 5 is table summarizing water immersion pellet
durability tests of pellets made from whole Spirulina treated via
HTC at 175.degree. C.
[0032] FIG. 6 is table summarizing water immersion pellet
durability tests of pellets made from lipid-extracted Spirulina
treated via HTC at 175.degree. C.
[0033] FIG. 7 is a graph of mass recoveries, elemental analyses,
aqueous coproducts ("ACP"), and gasses produced from HTC treatment
of lipid-extracted algae ("LEA") and whole Spirulina compared with
loblolly pine and sugarcane bagasse (the balance of the solids is
equal to 100%).
[0034] FIG. 8 is photographs of raw Spirulina (A), hydrochar
produced from Spirulina feedstock (B), and hydrochar produced from
loblolly pine feedstock (C).
[0035] FIG. 9 is a table showing hydrochar recoveries and
compositions for various biomass feedstocks, including feedstocks
according to various implementations of an embodiment of the
present disclosure.
[0036] FIG. 10 is a graph illustrating the energy density of algal
feedstocks (stars) compared with various lignocellulosic feedstocks
(squares) at various HTC reaction temperatures and a 30 minute hold
time.
[0037] FIG. 11 is a graph showing inorganic elemental analysis by
X-ray fluorescence of feedstocks and hydrochars produced therefrom,
according to an embodiment of the present disclosure, expressed as
a percentage of starting dry mass (not including C, H, N, and
O).
[0038] FIG. 12 is a table listing value added chemicals that may be
produced from biomass.
[0039] FIG. 13 is a table showing the compositions of aqueous
co-products formed during HTC of various algal-containing
feedstocks according to an embodiment of the present disclosure,
and various lignocellulosic feedstocks.
[0040] FIG. 14A is a graph showing the results of GC/MS analysis of
polar compounds in aqueous products resulting from HTC treatment of
whole and LEA Spirulina at 175.degree. C. according to an
embodiment of the present disclosure.
[0041] FIG. 14B is a graph showing the results of GC/MS analysis of
sugars and sugar alcohols in aqueous products resulting from HTC
treatment of whole and LEA Spirulina at 175.degree. C. according to
an embodiment of the present disclosure; species that are
identified as high value chemicals are outlined.
[0042] FIG. 15 is a graph of the results of HPLC-RI analysis of
sugar in aqueous products from HTC treatment of various feedstocks
(including according to an embodiment of the present disclosure),
expressed as a percent of starting dry mass; sugars noted as high
value chemicals are outlined.
[0043] FIG. 16 is a graph showing high value chemicals, as a
percentage of starting dry feedstock, identified from HPLC and
GC/MS analysis of sugars in the aqueous fraction from HTC of
Spirulina at 175.degree. C. for 30 minutes, according to an
embodiment of the present disclosure.
[0044] FIG. 17 is a schematic diagram of a HTC process, and product
collection, according to a particular example of an embodiment of
the present disclosure.
DETAILED DESCRIPTION
[0045] Unless otherwise explained, 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 disclosure belongs.
The singular terms "a," "an," and "the" include plural referents
unless the context clearly indicates otherwise. Similarly, the word
"or" is intended to include "and" unless the context clearly
indicates otherwise. The term "includes" means "comprises." The
terms "solvent," "a solvent" and "the solvent" include one or more
than one individual solvent compound unless indicated otherwise.
Mixing solvents that include more than one individual solvent
compound with other materials can include mixing the individual
solvent compounds simultaneously or serially unless indicated
otherwise. The separations and extractions described herein can be
partial, substantial or complete separations unless indicated
otherwise. All percentages recited herein are weight percentages
unless indicated otherwise. All numerical ranges given herein
include all values, including end values (unless specifically
excluded) and intermediate ranges.
[0046] FIG. 1 illustrates a general method 100 for converting algae
to biofuel. In step 105, algae is harvested or otherwise obtained.
The algae may be from any suitable strain or combination of
strains. Strain selection may take various factors into account,
including ease of growth and processing, lipid content, and
reaction products and byproducts. For example, hydrothermal
carbonization (HTC) typically produces hydrochar and an aqueous
phase that includes various reaction products/byproducts, such as
high value organic compounds and sugars.
[0047] After harvesting, algae is typically dewatered in step 110.
Dewatering may be carried out through mechanical, thermal, or
chemical means. Initial dewatering techniques can include
centrifuges, decanters, filters, hydrocyclones, mechanical presses,
and flocculation, including polymer flocculation. If a greater
degree of drying is desired, drying can include direct heat drying,
fluidized bed dryers, microwave dryers, or steam drying. In some
implementations, the algae is dried to a biomass (algae)
concentration of 98% or less by weight, such as less than about
95%, about 90%, about 50%, about 30%, about 25%, about 20%, about
15%, about 10%, about 7%, about 5%, or about 2%. In other
implementations, the algae is dried to a biomass concentration of
between about 1% and about 30% by weight, such as between about 2%
and about 25%, between about 1% and about 10%, between about 2% and
about 7%, between about 2% and about 15%, or between about 7% and
about 15%. In other implementations, the dewatering or drying
process is omitted.
[0048] An advantage of at least certain implementations of the
present disclosure is that that the HTC process may employ slurries
of algae, which may not require extensive dewatering or drying. In
at least one example, a slurry is feedstock having about 2% to
about 20% by weight of biomass, such as algae or delipidized algal
residue, in a liquid carrier, such as water. In a more specific
example, the slurry has a biomass content (such as algae or
delipidized algal residue) of between about 2% and about 7% or
between about 5% and about 20% by weight. In another
implementation, the present disclosure uses feedstocks that contain
a higher percentage of biomass, such as feedstocks in the form of
wet pastes.
[0049] After harvesting, and optionally drying, the algae, lipids
are optionally extracted from the algae in step 115. Suitable
methods of removing lipids from the algae include, without
limitation, expellers, presses, solvent extraction, supercritical
carbon dioxide extraction, enzyme extraction, and
ultrasonication.
[0050] The extracted lipids can be optionally processed in step
120. For example, the lipids may be converted to a biofuel product,
such as biodiesel, as is known for lipids obtained from other
sources. One suitable method of converting lipids to a biofuel
product is transesterification.
[0051] The feedstock for the method 100 is typically a mixture of
solids and a liquid carrier, typically water, for reaction. In a
specific example, the mixture is a slurry. The components of the
feedstock can be modified prior to reaction in step 125. For
example, water or another carrier can be added to produce a desired
amount of solids in the slurry. Additional feedstocks 130, such as
from other biomass sources, may be added to the slurry. Additional
components may be added, such as to influence the reaction rate or
reaction products. For example, acid, such as acetic acid, can be
added, which may assist in suppressing gas formation and favoring
solid products.
[0052] In some implementations, the biomass component of the
feedstock consists essentially of algae with the lipids still
present. In other implementations, the biomass component of the
feedstock consists essentially of delipidized algae. The biomass
component, in a further implementation, consists essentially of a
mixture of algae and delipidized algal residue.
[0053] In some examples, a biomass component "consisting
essentially of" a particular component, or mixture of components,
means that the feedstock does not include a significant portion of
biomass other than from the recited sources. In a particular
example, biomass from other sources is less than about 10% by
weight of the biomass component of the feedstock. In another
example, biomass from other sources is less than about 5% by weight
of the biomass component of the feedstock. In yet another example,
biomass from other sources is than about 1% by weight of the
biomass component of the feedstock.
[0054] In a further example, which may, but is not required to, be
combined with the preceding examples, the feedstock can include
additional components, such as salts, solvents, pH modifiers, and
similar components that affect the process parameters of the HTC
reaction or the products produced therefrom.
[0055] In further implementations, the biomass component of the
feedstock is at least about 5% by weight of algal origin (algae or
delipidized algal residue), such as being at least about 10%, about
25%, about 50%, about 75%, about 85%, about 90%, or about 95% of
algal origin.
[0056] In some examples, the amount of feedstock (the algal
feedstock combined with any other feedstock) in the aqueous slurry
is between about 1% and about 50% by weight solids, such as between
about 2% and about 20% solids, between about 2% and about 15%
solids, between about 2% and about 10% solids, between about 2% and
about 7% solids, between about 5% and about 40% by solids, between
about 10% and about 30% solids, and about 15% and about 20% solids.
In further examples, the solids are at least about 1% by weight of
the slurry, such as at least about 2%, about 5%, about 10%, about
15%, about 20%, about 25%, about 30%, about 40%, or about 50%
solids. In other examples, the solids are less than about 50% by
weight of the slurry, such as being less than about 40%, about 30%,
about 20%, about 10%, or about 5% of the slurry.
[0057] The algae, or lipid-extracted algal residues, are subjected
to a hydrothermal carbonization reaction in step 135. Hydrothermal
carbonization reactions typically take place at elevated
temperatures and pressures. In one implementation, in various
examples, suitable temperatures are between about 120.degree. C.
and about 295.degree. C., between about 120.degree. C. and about
250.degree. C., between about 155.degree. C. and about 295.degree.
C., between about 150.degree. C. and about 250.degree. C., between
about 180.degree. C. and about 300.degree. C., between about
180.degree. C. and about 250.degree. C., between about 220.degree.
C. and about 250.degree. C., between about 225.degree. C. and about
250.degree. C., between about 190.degree. C. and about 240.degree.
C., or between about 200.degree. C. and about 220.degree. C. In
other examples, the temperature is less than about 250.degree. C.,
such as less than about 240.degree. C., about 230.degree. C., about
220.degree. C., about 210.degree. C., about 200.degree. C., about
190.degree. C., about 180.degree. C., about 170.degree. C., about
160.degree. C., or about 150.degree. C.
[0058] Suitable pressures are typically between about 2 bar and
about 175 bar, such as between about 2 bar and about 100 bar,
between about 5 bar and about 85 bar, between about 5 bar and about
40 bar, between about 10 bar and about 85 bar, between about 10 bar
and about 40 bar, and between about 20 and about 30 bar. In further
examples, the pressure is less than about 85 bar, such as less than
about 40 bar, about 30 bar, about 20 bar, or about 10 bar. In some
implementations, the pressure is sufficient to maintain water in
the reactor in a condensed state, such as a pressure that is at
least equal to the saturated vapor pressure of water at the
reaction temperature.
[0059] In some cases, the temperature of the reaction mixture is
controlled, while the pressure is the autogenous pressure produced
by the reaction mixture at that temperature. In other cases, the
temperature and pressure are independently controlled. For example,
the reaction may be carried out in an overpressure environment.
[0060] In further implementations, the HTC process is carried out
at a temperature of between about 150.degree. C. and about
250.degree. C., such as between about 175.degree. C. and about
225.degree. C. In these implementations, the pressure is at least
about the saturated steam pressure at the temperature. In one
example, the pressure is about the saturated steam pressure at the
temperature.
[0061] In some cases, the HTC reaction is carried out in an ambient
atmosphere. In other cases, the atmosphere is reduced in oxygen or
another component. For example, the atmosphere, such as prior to
reaction, may be fully or partially purged with an inert gas, or
otherwise unreactive gas, such as nitrogen, helium, argon, or
mixtures thereof.
[0062] The HTC process is typically carried out for a period of
time for a sufficient level of conversion to take place. The
duration of the HTC process may be influenced by a number of
factors, including the nature of the algal feedstock (including
whether the algae is present with lipids intact or as delipidized
residue), the temperature selected for the reaction, and the
pressure selected for the reaction. The temperature can be selected
to provide a desired reaction rate. The relationship can be
evaluated according to the "severity factor", given by:
Severity Factor=Log10 (time*exp[(Temp.-100)/14.75]) (1)
The Severity factor is further described in Overend, et al.,
Fractionation of Lignocellulosics by Steam-Aqueous Pretreatments.
Phil. Trans. R. Soc. Lond., A 321, 523-536. 1987, incorporated by
reference herein to the extent not inconsistent with the present
disclosure. Generally, higher temperatures require shorter
processing times to achieve a similar level of conversion.
[0063] The HTC process parameters, including, temperature,
pressure, and reaction time, may also be selected based on process
efficiency for a desired output, as well as the nature of the
desired output. For example, the process conditions may be adjusted
to favor the production of hydrochar or certain components present
in the liquid carrier after the reaction. The presence of
co-feedstocks may also influence processing conditions and
times.
[0064] In some examples, the reaction is carried out for between
about 5 minutes and about sixteen hours, such as between about 5
minutes and about six hours, between about 5 minutes and about four
hours, between about 5 minutes and about 3 hours, or between about
4 hours and about 16 hours. In further examples, the reaction is
carried out for between about 5 minutes and about 180 minutes,
between about 15 minutes and about 120 minutes, between about 30
minutes and about 90 minutes, between about 5 minutes and about 50
minutes, or between about 5 minutes and about 30 minutes. In other
examples, the reaction is carried about for at least about 5
minutes, such as at least about 10 minutes, about 15 minutes, about
30 minutes, about 45 minutes, about 60 minutes, about 90 minutes,
about 120 minutes, or about 180 minutes. In yet further examples,
the reaction is carried out for less than about 240 minutes, such
as less than about 180 minutes, about 120 minutes, about 90
minutes, about 60 minutes, about 45 minutes, about 30 minutes,
about 15 minutes, or about 10 minutes. In other examples, the
reaction is carried out for a different amount of time.
[0065] For example, when the reaction is carried out in an
extrusion system, the reaction may be carried out in less than
about thirty minutes, such as less than about 20 minutes, less than
about 10 minutes, less than about 5 minutes, less than about 2
minutes, or less than about a minute. In more specific examples,
the reaction may be carried out in less than about 60 seconds, such
as less than about 45 seconds, less than about 30 seconds, less
than about 20 seconds, or less than about 10 seconds.
[0066] After the reaction has reached a desired level of
completion, the formed hydrochar is typically collected in step
140. Suitable methods of collection include decantation,
filtration, and centrifugation.
[0067] In some implementations, the hydrochar is converted to a
compressed solid, such as being pelletized or formed into a
briquette, in step 145, which may aid in using or transporting the
fuel. Surprisingly, it has been found that hydrochar formed from
algae, whether the feedstock includes or does not include lipids,
is capable of forming compressed solids, such as pellets or
briquettes, without added binder. Typically, when hydrochar is
formed from lignocellulosic biomass, lignin present in the
hydrochar can serve as a binder for the compressed solid. However,
algae lacks lignin, and thus would have been expected to require an
added binder. However, a binder can be included in some
implementations, if desired.
[0068] Prior to conversion to a compressed solid, the hydrochar may
be processed to aid in the compression process. For example, the
hydrochar may be ground or chipped to a more uniform size or size
range. Typically, the particles are reduced to a size that is less
than the thickness of the compressed solid that will be produced.
In a specific example, the material used to create a compressed
solid has an average cross-sectional width of less than about 3 mm.
In another example, the material to be pelletized is in the form of
a powder, such as a powder having an average cross-sectional width
of less than about 1 mm, such as less than about 0.75 mm, less than
about 0.5 mm, or less than about 0.25 mm.
[0069] In some implementations, the compressed solid is a pellet.
In various examples, the pellets have an average cross sectional
width of between about 3 mm and about 24 mm, such as between about
6 mm and about 8 mm, between about 10 mm and about 12 mm, or
between about 6 mm and about 10 mm. In a specific example, the
pellets have an average cross sectional width of about 13 mm.
[0070] In further implementations, the compressed solid is a
briquette. In a particular example, the briquettes have an average
cross sectional width of at least about 25 mm.
[0071] In some aspects of the disclosed method, the hydrochar is
compressed into a form other than pellets or briquettes, or is not
compressed.
[0072] The hydrochar may also be cleaned, such as by rinsing with
solvents or by screening, to remove contaminants or aid in
processing. The hydrochar may also be treated, such as with water
or steam at varying temperatures. The hydrochar may also be dried
prior to pelletization (or other uses). In some examples, the
hydrochar is dried to less than about 10% moisture by weight. In
other examples, the hydrochar has a moisture content of less than
about 15% by weight, such as less than about 12% by weight, less
than about 10% by weight, less than about 7% by weight, or less
than about 5% by weight. In further examples, the hydrochar is
dried to a moisture content of between about 1% and about 10% by
weight, such as between about 2% and about 8% by weight, between
about 3% and about 7% by weight, between about 7% and about 9% by
weight or between about 8% and about 12% by weight. In some aspects
of the disclosed method, the hydrochar is not dried.
[0073] In some implementations, the temperature of the hydrochar
feed, the pelletization apparatus, or the environment of the
pelletization apparatus is selected to influence the pelletization
process or pellet properties. For example, the die through which
the hydrochar is extruded may be heated or cooled. In a specific
example, the die is operatively associated with an induction
heater, such as a band heater. In another specific example, a
coolant, such as water, is applied to the die.
[0074] In certain examples, the extrusion/pelletization mechanism
is operated at a temperature of between about 0.degree. C. and
about 200.degree. C., such as between about 0.degree. C. and about
180.degree. C., between about 0.degree. C. and about 50.degree. C.,
between about 25.degree. C. and about 180.degree. C., between about
25.degree. C. and about 150.degree. C., between about 75.degree. C.
and about 150.degree. C., between about 75.degree. C. and about
125.degree. C., between about 75.degree. C. and about 100.degree.
C., or between about 100.degree. C. and about 150.degree. C. In
further examples, the temperature is less than about 200.degree.
C., such as less than about 180.degree. C., about 150.degree. C.,
about 125.degree. C., about 100.degree. C., about 75.degree. C., or
about 50.degree. C. In a specific example, the pelletization
temperature is selected to be less than that typically required for
pelletization of hydrochar produced from lignocellulosic biomass
sources.
[0075] The force applied to the hydrochar during pelletization may
also affect the properties of the pellets, in addition to altering
the pelletization conditions. The pressure is typically selected to
be in a range that produces pellets of a desired hardness; being
sufficient to bind particles together, but not so great as to shear
the bound particles apart. In certain implementations, a pellet
press, such as the Carver bench top laboratory hydraulic press,
Model M (available from Carver, Inc., of Wabash, IN) is set to a
pressure of between about 0.5 MPa and about 250 MPa, such as
between about 5 MPa and about 250 MPa, between about 5 MPa and
about 50 MPa, between about 10 MPa and about 50 MPa, between about
15 MPa and about 40 MPa, such as between about 50 MPa and about 200
MPa, between about 75 MPa and about 175 MPa, or between about 100
MPa and about 150 MPa. In other implementations, the pressure is
less than about 250 MPa, such as less than about 225 MPa, about 200
MPa, about 175 MPa, or about 150 MPa. In further aspects of the
disclosed method, other pressures are used.
[0076] In another aspect of the invention, the pressure applied to
the surface of the pellet-in-formation is between about 30 MPa and
about 750 MPa, such as between about 60 MPa and about 500 MPa,
between about 100 and about 400 MPa, or between about 150 MPa and
about 250 MPa. In other examples, other pressures are used.
[0077] The duration the pellet-in-formation is subjected to
compression may also influence pellet properties and pelletization
times, with increased times generally resulting in harder pellets
and longer production times/lower throughput. The hold time is
typically selected to provide the appropriate balance of hardness
and throughput, as desired by an operator. In one implementation,
the hold time is between about 1 second and about 600 seconds, such
as between about 1 second and about 60 seconds, between about 5
seconds and about 60 seconds, between about 15 seconds and about 60
seconds, or between about 30 seconds and about 45 seconds. In other
examples, the hold time is less than about 600 seconds, such as
less than about 180 seconds, less than about 90 seconds, less than
about 60 seconds, less than about 45 seconds, or less than about 30
seconds. In other aspects of the disclosed method, other hold time
are used.
[0078] In some implementations, the algae hydrochar, whether or not
from delipidized, or algae/co-feed hydrochar, is processed into
pellets without the addition of external binders. In other
examples, a binder is added to the hydrochar prior to
pelletization. Suitable binders include lignin, paraffin oils,
starches, fats, proteins, sugars, or mixtures thereof. In specific
examples, the amount of binder is less than about 10% by weight of
the material to be pelletized, such as less than about 5%, about
4%, about 2%, or about 1%. In a particular example, the amount of
binder is between about 2% and about 4% by weight of the material
to be pelletized. In further aspects of the disclosed method, other
binder percentages are used.
[0079] In another example, the hydrochar from the HTC reaction is
combined with hydrochar produced from HTC of lignocellulosic
feedstock. The lignocellulosic hydrochar can assist in pelletizing
the algal-sourced hydrochar. In yet another example, the hydrochar
produced from an embodiment of the present disclosure is used as a
binder for raw lignocellulosic biomass, torrefied or pyrolyzed
biomass, or hydrochar from biomass sources other than from an
embodiment of the present disclosure.
[0080] As shown in step 150, the method 100, in some
implementations, includes adding additional feedstocks to the
material to be compressed. The feedstocks can include, for example,
raw biomass, such as unprocessed lignocellulosic biomass, torrefied
or pyrolyzed biomass (such as lignocellulosic biomass), or
hydrochar produced through hydrothermal carbonization of a
different source than the particular feedstock 125 used in the
example. In another aspect, the additional feedstock 150 includes
coal fines or pulverized coal. The additional feedstock 150, in one
example, is another feedstock produced according to an embodiment
of the present disclosure. In another example, the feedstock 150 is
a feedstock produced other than through an embodiment according to
the present disclosure. Mixtures of additional feedstocks 150,
including both those produced according to a method of the present
disclosure and those not so produced, are used in yet another
example.
[0081] The pellet mill, extruder, or other pelletization apparatus
may be set to produce pellets of a desired size, hardness, and
quality, including by selecting a suitable pellet die thickness,
processing speed, temperature, and pressure. The exact nature of
the pellets and processing conditions may be affected by the
desired use. For example, softer, less robust, but more quickly
processed pellets may suffice when the pellets are to be used
quickly. Harder pellets may be indicated when the pellets are to be
transported or stored for long periods of time, or when the
environment to which the pellets will be exposed warrants harder
pellets. For example, environment having higher humidity may
benefit from harder pellets.
[0082] Suitable pellet mills include those available from Farm Feed
Systems Ltd. of Gloucestershire UK, Pellet Pros of Dubuque, Iowa,
Andritz AG of Graz, Austria, California Pellet Mill of
Crawfordsville, Ind., and Amandus Kahl GmbH & Co. KG, of
Reinbek, Germany. Pellet mills types include, without limitation,
flat die pellet mills and ring die pellet mills.
[0083] After the pelletization process, the pellets are typically
cooled. The pellets may also be screened, such as to remove
residual fines. A drying process, with or without heat, may also be
carried out. In a specific example, air is blown through the
pellets to achieve a final moisture content of less than about 10%,
such as less than about 8%, less than about 6%, less than about 4%,
or less than about 2%. In another example, the moisture content is
between about 2% and about 15%, such as between about 4% and about
10% or between about 4% and about 8%.
[0084] In other embodiments, in step 155, the hydrochar from
reaction 125, such as that collected in step 140, is directly
gasified, liquefied, or otherwise processed, such as without prior
pelletization.
[0085] In some implementations of the present disclosure, rather
than being compressed into a solid, the hydrochar is extruded. In
one example, the hydrochar is extruded after being formed. In
another example, the hydrochar is formed and extruded in a common
process. For example, the extrusion process may generate sufficient
temperatures and pressures to carry out hydrothermal carbonization
of the feedstock prior to be being extruded. One suitable extrusion
apparatus and method is described in U.S. Patent Publication US
2014/0262727, incorporated by reference herein to the extent not
inconsistent with the present disclosure.
EXAMPLE 1
[0086] Pelletization of HTC Hydrochar from Algal Feedstocks
[0087] In some cases, production of satisfactory pellets is
assisted when the solid material is heated while being compressed.
Heating can assist the binder (either natural or added) in becoming
fluidized, causing more effective adhesion of the particles. In
this Example, a heated die system was used. The system included a
13-mm diameter, hardened steel heated die (Across International,
Berkeley Heights, N.J.), along with an Omega bench top temperature
controller (Model CSC32J) and Omega thermocouple (type J
iron-constantan).
[0088] The heated die system used to create pellets consisted of a
13 mm diameter die with an electric heating element, support plate,
core dies, thermal insulator plate, push rod, and pellet ejector.
Schematics of this die system are available at the website of
Across International, including, for example,
http://www.acrossinternational.com/13mm-1-2-Diameter-ID-250C-Heated-Die-w-
-Digital-Controller-SDS13H.htm, and are incorporated by reference
herein. To produce a pellet, the die is first heated to the desired
temperature (such as, in one example, 140.degree. C.). The die is
then placed on its support plate and a steel core die is inserted
from the top. Approximately 1 g of hydrochar (or other material to
be pelletized) is added on top of the core die. The push rod is
inserted and the die assembly is placed on the press.
[0089] A Carver bench top laboratory press Model M (Menomonee
Falls, Wis.) was used to produce pellets from raw and hydrotreated
biomass materials. The pressure gauge (Wika Instruments Model
232.34, 0-5000 psi) enabled accurate determinations of hydraulic
pressure, thus improving the uniformity of produced pellets. The
handle of the press was manually depressed while watching the
pressure gauge. A hydraulic pressure of 20 MPa (equivalent to about
295 MPa at the surface of the pellet-in-formation) was attained and
held for 60-seconds. The pressure was then released and the die
assembly removed from the press. The die body was removed from the
support plate base and placed on the pellet ejector base. This
assembly was then placed back on the press, and gentle pressure
applied to the push rod until the pellet ejected out the
bottom.
[0090] Pellet lengths were measured with a set of Vernier calipers.
Assuming a diameter of 13 mm, these measurements were used to
calculate the volume of an individual pellet. Knowing the pellet
volume enables calculation of both mass density (kg/m.sup.3) and
energy density (GJ/m.sup.3) of individual pellets.
[0091] Pellet Durability Testing
[0092] Several standard (and non-standard) tests are commonly
employed to evaluate the quality of biomass pellets. These tests
address properties such as mass density, energy density,
compressive strength, durability, modulus of elasticity,
equilibrium moisture content, and others.
[0093] A series of tests were carried out to systematically explore
the water tolerance behavior of pellets. The aim was to develop
standard tests that could be utilized to quantify water tolerance,
thereby enabling meaningful comparisons among different types of
pellets--including pellets produced from blends of hydrochar with
other materials such as raw biomass, torrefied biomass, and
coal.
[0094] The approach followed is summarized in the schematic of FIG.
2. A traditional tumbler test was used to define pellet durability,
both before and after immersion in water for varying lengths of
time. The apparatus used was a Thumbler' s Model A-R1 rotary
tumbler, with a 41/2-in. rubber barrel. In the standard test, 40
pellets were placed in the barrel and rotated for 3000 revolutions
at a speed of approximately 38 rpm (typically over a period of
approximte 90-min. of tumbling).
[0095] Durability was defined as the ratio of pellet weight after
tumbling to the initial pellet weight. Weight determinations were
made using an Acculab Model ALC80.4 analytical balance, with a
sensitivity of +/-0.0001 g.
[0096] Water immersion test results show a high degree of
repeatability, and provide a means for readily distinguishing among
pellets that exhibit different water-immersion behaviors. The water
immersion and tumbling process is an extremely severe test of
pellet durability, and only very robust pellets can maintain their
integrity when exposed to these conditions. In cases where the
pellets are very robust, 3 test pellets and 37 round wood filler
pellets may be used in a single tumbler test, and to determine the
individual weight loss from each pellet. However, low-stability
pellets often lose a significant fraction of their weight, due to
attrition of large fragments, making it difficult to identify the
same pellet before and after tumbling if multiple pellets are used
in a single tumbler test. Thus, for these weaker pellets, tumbler
testing of a single pellet along with 39 filler pellets may be
used.
[0097] Tests were carried out to determine whether reliable
durability results could be obtained using a smaller number of
pellets. In these tests, spherical objects were substituted as
"filler" for most of the 40-pellets, and only a small number of
actual test pellets were used. Three different filler materials
were investigated -1/2 in. diameter solid balls of maple wood,
low-carbon steel, and plastic (HDPE) (all three of these filler
types were obtained from McMaster-Carr).
[0098] Hydrochar pellets were severely damaged when steel balls
were used in the tumbler test, resulting in low values of pellet
durability. The wood and plastic filler materials behaved
similarly, and resulted in much less pellet damage. Because the
wood balls are more similar to hydrochar pellets in material
composition and density, wood fillers were used in subsequent
tumbler tests.
[0099] Pellets were made from whole Spirulina feedstock,
lipid-extracted Spirulina feedstock, whole Spirulina treated via
HTC at 175.degree. C., and lipid-extracted Spirulina treated via
HTC at 175.degree. C. Pellets were immersed for 0 minutes (control
sample) and 60 minutes. These tests were conducted in triplicate.
Before immersion, each pellet was weighed and its dimensions were
measured. From these measurements, pellet densities were
calculated, expressed as kg/m3. After water immersion, the pellets
were allowed to air dry for twenty-four hours, and were then
re-measured for weight and length. In addition, each pellet
underwent a tumbler durability test, along with 39 round wood
filler pellets as described above. Results of these tests are
summarized in tabular form in FIGS. 3-6.
[0100] As shown in FIG. 3, pellets of whole Spirulina, with lipids
intact, exhibit nominal weight changes before water immersion and
after 60 minutes of water immersion. Pellet length exhibited a
minor increase. However, while unimmersed pellets generally exhibit
high durability, typically exceeding 90%, water-immersed pellets
lost structural integrity during the tumbling process, resulting in
the tumbled pellets having signficantly lower weights than before
tumbling. The pellet durablity for the immersed pellets was
typically less than 60%, such as being less than 55%.
[0101] Referring to FIG. 4, pellets of deplipidized Spirulina
residue exhibited minor changes in weight and length before and
after water immersion for 60 minutes. Like the pellets formed from
whole Spirulina, pellets from delipidized Spirulina residue were
very stable in the tumble test, pre-immersion. After 60 minutes of
water immersion, the tumbled pellets again exbhibited significant
degradation and weight loss. The pellet stability for pellets from
delipidized Sprirulina residue was typically less than about 60%,
such as less than about 55%.
[0102] FIGS. 5 and 6 present the results of immersion test for
whole Spirulina and delipidized Spirulina residue, respectivly,
treated via HTC at 175.degree. C. Like the unprocessed source
materials, the hydrochar material exhibited only minor changes in
weight and length before and after water immersion. However, the
hydrochar pellets were substantially more stable, even after water
immersion, than pellets from the unproccessed source material.
Pellets formed from HTC of whole Spirulina exhibited greater than
75% stability even after water immersion, with stabilities
typically being around 80%. Even pellets formed from HTC of
delipidized Spirulina residue exhibited enhanced stabilities of
greater than 65%, even after water immersion, with typically
stabilities being between about 70-80%.
EXAMPLE 2
[0103] Hydrothermal Carbonization of Algal Feedstocks
[0104] HTC processes were conducted at 175.degree. C. using both
whole and LEA Spirulina, and at 215.degree. C. for whole Spirulina.
Results of these processes were compared with results from
treatment of lignocellulosic feedstocks, using examples of loblolly
pine and sugarcane bagasse.
[0105] A mass balance of each HTC experiment was computed by
determining the mass of each recovered product and comparing the
sum of all products recovered to the total dry starting mass. The
recovered products include the solid hydrochar, gases (mainly
CO.sub.2 with small amounts of CO), aqueous co-products (ACP), and
produced water. Very little water is typically produced under the
low process temperature conditions used in this Example 2.
[0106] The mass recoveries from Spirulina experiments are shown in
FIG. 7, along with recoveries from loblolly pine and sugarcane
bagasse feedstocks for comparison. The composition of the feedstock
was normalized to 100%, and the three product bars (hydrochar, ACP
and gas shown as the offset bars) show the percentage mass recovery
of each so that the sum of the three show the total mass recovery
of the starting dry feedstock. The relative composition in terms of
C, H, N, S, O, and ash are illustrated for both the starting dry
feedstock and the recovered hydrochar by the shaded, stacked bars.
The balance of mass is shown when the compositional elements do not
add up to 100% (Note that oxygen is measured directly). The total
mass that was recovered in the aqueous co-product (ACP) and gaseous
phases are represented by the offset bars.
[0107] FIG. 7 illustrates that much lower mass fractions were
recovered as hydrochar from the algae experiments as compared to
the lignocellulosic feedstocks, and that much greater mass was
recovered in the ACP. At 175.degree. C., less than 50% of the
starting mass was recovered as hydrochar from both LEA and whole
Spirulina, while hydrochar recoveries from lignocellulosic
feedstocks were greater than 70%. Hydrochar recovery was further
reduced with increasing temperatures, with a larger effect seen for
algae compared to the lignocellulosic feedstocks.
[0108] FIG. 7 also shows that much less of the carbon in the
starting feedstock was recovered in the algae hydrochar in
comparison with the lignocellulosic hydrochars. About 50% of the
carbon is retained in the solid hydrochar from algae at 175.degree.
C., while 80%-90% is retained after HTC treatment of
lignocellulosic feedstocks. Note also that the oxygen contents of
the algae hydrochar were reduced significantly, similar to the
lignocellulosic hydrochar. In addition, much of the ash
constituents in the algal feedstocks were solubilized in the water,
and are significantly reduced in the resulting hydrochar. Taken
together, these compositional changes result in an energy densified
solid, as discussed in the next section.
[0109] Much of the starting algal mass was recovered as
non-volatile residue (NVR) after HTC treatment, which was measured
through oven drying of the ACP. The ash fraction of the solid
feedstock that was washed into the aqueous phase contributes to
this NVR, along with other nitrogen-containing Maillard-type
heterocyclic compounds and piperazinediones. In a similar trend to
the lignocellulosic feedstocks, the mass recovered as NVR was
reduced as treatment temperature increased. This is primarily due
to increases in the production of volatile compounds such as formic
acid, acetic acid and furfural. Note that the only portion of ACP
included in FIG. 7 is the NVR; other volatiles that may be lost
through oven drying are not included. Similar to treatment of
lignocellulosic feedstocks, only a small amount of gas (primarily
CO.sub.2) is produced at low HTC treatment temperatures.
[0110] At an HTC treatment temperature of 175.degree. C., nearly
all of the starting algal mass is accounted for by the three
recovered products. However, as the treatment temperature is
increased to 215.degree. C., only 85% of the starting mass is
accounted for. This could be due to higher amounts of water being
produced (note the reduction in hydrogen), or from greater
production of volatiles that were not measured, such as
ammonia.
[0111] Hydrochar Products
[0112] HTC of algal feedstocks produces a hydrophobic char that is
easily dried and pelletized. Photographs of the Spirulina feedstock
and resulting hydrochar products are shown in FIG. 8, along with a
photo of loblolly pine hydrochar. Results from characterization of
the feedstocks and hydrochars are given in FIG. 9. Energy
densification is defined as the energy content of the hydrochar
divided by that of the starting feedstock (both on a dry basis).
Energy yield is then the mass yield multiplied by the energy
densification.
[0113] The energy content of the raw algae was similar or even
higher than that of woody feedstocks treated previously (e.g.,
loblolly pine). In addition, the energy densification seen, even at
these low temperatures, is much higher than for comparable
treatment temperatures of lignocellulosic feedstocks. In earlier
studies, very little energy densification of lignocellulosic
hydrochar was seen at treatment temperatures less than 200.degree.
C. For algal feedstocks, however, energy densification of around
1.1 occurred at 175.degree. C., while densification of 1.3 was
observed at 215.degree. C. The energy densification of Spirulina at
215.degree. C. is equivalent to that observed from lignocellulosic
feedstocks at temperatures of 255.degree. C. or higher. Thus it
appears that these algal materials can be converted to hydrochars
under considerably milder HTC process conditions than required for
treatment of lignocellulosic feedstocks. This is attributed in part
to the lack of cellulose and lignin structures in algae (which are
difficult to break down), and to the presence of high energy
lipids. However, because of the low hydrochar mass recovery from
algae, the overall energy yield in algal hydrochar is much lower
than in lignocellulosic hydrochar.
[0114] The elemental compositions of the biomass feedstocks and
hydrochar products are given in FIG. 9. The algal feedstocks have
much lower oxygen contents than the lignocellulosic feedstocks.
Consequently, the atomic O/C ratio for algae is approximately 0.4,
as compared to 0.7 for lignocellulosic biomass. HTC treatment of
whole Spirulina at 215.degree. C. produced a hydrochar having an
O/C ratio of 0.22, which approaches that typically associated with
lignite or bituminous coal.
[0115] The energy contents of the biomass feedstocks and resulting
hydrochars are shown in FIG. 10 for treatment of both whole and LEA
Spirulina, along with results obtained from HTC treatment of
lignocellulosic biomass. The algal feedstocks treated here have
slightly higher starting energy contents than the lignocellulosic
feedstocks. However, substantial energy densification of the algal
hydrochars was observed at much milder process conditions than
typically required when treating lignocellulosic feedstocks.
[0116] Elemental analysis was performed using X-ray fluorescence
(XRF) (PANalytical, Westborough, Mass., USA) on the feedstock and
hydrochar from each HTC experiment to evaluate the fate of the
inorganic fraction in the algal feedstock. The results are
expressed as a percentage of starting dry mass and shown in FIG.
11. Much of the ash constituents that are present in the starting
feedstock are not seen in the solid product, indicating that the
HTC process is effective in extracting some of them into the
aqueous phase. At 175.degree. C., 80% of the inorganic fraction is
removed from both whole and LEA Spirulina, while at 215.degree. C.,
92% is removed.
[0117] This includes elements such as chlorine (10%-20%), magnesium
(5%-50%) and calcium (25%-40% reduction), which have adverse
effects during combustion. HTC may also result in a reduction in
inorganics from lignocellulosic feedstocks, ranging from 50% to 75%
at temperatures of 200.degree. C. Lower concentrations of silicon
in Spirulina (about 0.3%) in comparison to lignocellulosic
feedstocks (1.1%-3.6%), which is largely not removed by HTC,
contribute to a larger reduction in the inorganic fraction seen
here. This reduction in inorganic fraction also contributes to the
energy densification of the hydrochar. FIG. 11 also suggests that
some ash constituents were removed during the lipid extraction
process. In particular, comparing the two feedstock bars indicates
that significant fractions of sodium and magnesium were removed by
extraction. However, it should be noted that the XRF method of
evaluation for inorganics applied here is semi-quantitative for
sodium and magnesium.
[0118] Aqueous Co-Products
[0119] To identify potential high-value chemicals in the ACP as
shown in FIG. 12, a series of laboratory analyses were completed. A
summary of these results is shown in FIG. 13 in comparison to
similar results from HTC treatment of loblolly and sugarcane
bagasse. Although much of the mass is recovered in the ACP as a
non-volatile residue (NVR), only a small fraction of the mass is
identified through multiple analyses applied. An analysis of the
total organic carbon (TOC) of the ACP shown in FIG. 13, taken with
the carbon content of the solids FIG. 9 and the total gases
produced gives a carbon balance within 85%-90%. This suggests that
the elemental analysis of the solids is useful to evaluate the
nutrient content in the ACP. The reduction in nitrogen content of
the solid hydrochar therefore indicates that much of the mass in
the NVR is a result of other nitrogen-containing Maillard-type
heterocyclic compounds and piperazinediones.
[0120] The pH of the aqueous co-products (ACP) was measured after
each experiment and was found to be approximately 5.8, as shown in
FIG. 13. This is considerably higher than the pH values of 3.0-3.5
that were seen from lignocellulosic feedstocks. Other volatiles,
such as acetic and formic acid, were not measured in this study but
are shown in FIG. 13 for comparison from lignocellulosic
feedstocks. Higher pH may be related to the elevated N content of
the algae feedstocks.
[0121] A gas chromatography/mass spectrometer (GC/MS) (Varian,
Inc., Walnut Creek, Calif., USA) analysis was performed on the
aqueous product streams from whole and LEA Spirulina treated at
175.degree. C. to identify polar compounds and sugars or sugar
alcohols. The polars results are shown in FIG. 14A; sugars/sugar
alcohols are shown in FIG. 14B. In both cases, the results are
expressed as a percentage of starting dry algal mass.
[0122] Using the analysis of polar compounds, malonic, succinic,
and glutaric acids were detected in high concentrations relative to
all species identified. However, less than 1% of the starting dry
algal mass was converted into these identified species. From the
sugars analysis, relatively large amounts of lactic acid were
observed, with lesser amounts of trehalose and very small amounts
of other sugar-related species. Although the high value sugars make
up approximately 50% of the total sugars identified through this
method, they are still a very small fraction of the starting dry
feedstock. It is possible, however, that higher treatment
temperatures would produce a greater amount of desirable chemicals.
For example, maximum recovery of sugars from treatment of
lignocellulosic feedstocks occurred around 230.degree. C., while
increasing amounts of acids (such as acetic and formic acid) were
produced with increasing temperatures up to 295.degree. C.
[0123] Interestingly, higher amounts of polar compounds were
observed from HTC treatment of the whole algae, while approximately
equivalent amounts of sugars were seen from HTC of whole and LEA
Spirulina. This may be because the sugars are produced from
degradation of carbohydrates (which are not removed by the
extraction process used to obtain the LEA), while at least some of
the polar compounds result from degradation of lipids (which are
removed by extraction).
[0124] An HPLC-RI analysis (Waters Corporation, Milford, Mass.,
USA) was also applied to identify and quantify sugars in the
aqueous products from HTC treatment of algae. The results are shown
in FIG. 15, where they are compared with results from HTC treatment
of woody and herbaceous feedstocks. Sugars that are identified as
high-value chemicals are outlined in this figure (note that some of
these sugars co-elute using this HPLC method). For experiments
using these lignocellulosic feedstocks, treatment temperatures were
varied from 175.degree. C. to 295 .degree. C., although only
temperatures of 235.degree. C. and below are shown here, as they
correspond more closely to the algal treatment temperatures. For
the lignocellulosic feedstocks, produced sugars increased with
treatment temperatures up to 235.degree. C., and declined at higher
temperatures. Sugars produced at low temperatures (175.degree. C.)
were primarily sucrose/trehalose, galactose/xylose/mannose, and
fructose/inositol/arabinose. As temperatures increased, more
glucose/pinitol, 5-HMF, and furfural were produced. 5-HMF and
furfural are secondary products of cellulose degradation at these
high temperatures. High value chemicals were produced in yields of
3%-4%, relative to the starting lignocellulosic feedstock mass.
However, since several of the sugars co-elute, particularly those
that dominate at low temperature conditions (e.g., fructose
co-elutes with inositol and arabinose, and glycerol with mannitol),
these yields of high-value chemicals may be slightly
over-estimated.
[0125] Also shown in FIG. 15 are results from HTC studies with
another algae, Scenedesmus Dimorphus. Although, not explored in
detail, HPLC analyses of sugars from HTC treatment of Scenedesmus
at three temperatures were performed. These results are shown in
FIG. 15 for comparison with the Spirulina results. Clearly, these
two algae materials produced different concentrations and types of
sugars, although it should be noted that most of the HTC treatments
of Scenedesmus were conducted at higher temperatures than those
used for Spirulina. HTC of Scenedesmus produced higher yields of
high-value sugars, primarily levoglucosan, arabitol, glycerol
(which co-elutes with mannitol), and fructose (which co-elutes with
inositol and arabinose). Similar high-value chemicals were produced
by treatment of Spirulina at 215.degree. C., although in lower
yields. The low process temperature of 175.degree. C. used in this
Example 2 resulted in very low recovery of sugars from both whole
and LEA Spirulina algae. The total mass of sugars recovered from
both algae was much lower than that produced from the woody and
herbaceous feedstocks. The products of cellulose degradation
(furfural and 5-HMF) which dominate the total sugars from
lignocellulosic feedstocks are largely absent from the algae
products.
[0126] A compilation of results of identified high value chemicals
from each of the methods described above is shown in FIG. 16. This
illustrates that only a small fraction of the starting dry algae
mass is converted to high value chemicals at these low process
temperatures. Due to higher concentrations of malonic acid, HTC
treatment of whole Spirulina resulted in nearly twice the amount of
total valuable products as did treatment of LEA Spirulina. The
amounts of other high-value products identified are similar from
both algal feedstocks. The primary valuable products are
glycerol/mannitol, arabitol, levoglucosan, lactic acid, malonic
acid, and succinic acid.
[0127] Feedstock Preparation
[0128] Spirulina maxima was purchased in powdered form as a health
supplement to evaluate for this Example 2. Spirulina typically
contains 6%-13% lipids, 64%-74% proteins, and 15%-20%
carbohydrates.
[0129] To obtain the LEA fraction, samples of whole, oven-dried
algae were extracted using dichloromethane and hexane in an
accelerated solvent extraction (ASE) instrument. 10.0% of the dry
mass of the Spirulina was extracted through this process. The
residues after lipid extraction are referred to as LEA.
[0130] The Scenedesmus Dimorphus that was evaluated previously was
grown in outdoor ponds in Reno, (NV, USA). After harvesting, it was
dewatered and frozen. The frozen wet algae were thawed at room
temperature before use in the HTC process. Due to their growing
conditions, the algae accumulated high concentrations of ash
resulting from fertilizer use and dust contamination.
[0131] Hydrothermal Carbonization Reactor
[0132] Reactions were conducted in a 2-L Parr stirred pressure
reactor (Model 4522, Parr Instruments, Moline, Ill., USA), as shown
in FIG. 17. The reactor was charged with 50-60 grams of air-dried
algal feedstock material, and 500-600 grams of distilled water in a
10:1 water to biomass ratio to ensure that all algae was thoroughly
mixed with water to create a thin paste.
[0133] The vessel was first sealed, de-oxygenated (by flushing with
helium), and then heated to the desired temperature while stirring.
The reactor temperature was controlled with a National Instruments
(Austin, Tex., USA) LabView data acquisition system. At the end of
the reaction period, the reactor vessel was cooled by immersion in
an ice bath, and the three product streams (gases, ACP, and solids)
were isolated.
[0134] A vacuum filtration process is typically used to separate
the solids from the ACP as illustrated in FIG. 17. However, because
of the algae product's very small particle size, the filter paper
quickly plugged up and slowed the vacuum filtration process.
Therefore, a centrifuge process was used in which the solids and
ACP were first separated at 6000 rpm for 30 min. Subsequent vacuum
filtration was performed on the aqueous product to separate the
fine particles.
[0135] Reaction Conditions
[0136] Effective carbonization of algae typically occurs at fairly
mild temperatures. Maximum recovery of sugars often occurs at
temperatures around 215-235.degree. C. for a 30 minute reaction
time. In an effort to maximize both high value chemicals and solid
product recovery, a treatment temperature of 215.degree. C. was
initially selected with a 30 minute hold time. An initial run of
whole Spirulina at 215.degree. C. resulted in very low hydrochar
recovery. Therefore, additional studies on whole and LEA Spirulina
were completed with a target temperature of 175.degree. C. to
increase the recovery of the solid product.
[0137] Product Characterization
[0138] A variety of laboratory analyses were conducted on the HTC
products to compute mass balance, carbon balance, and energy
densification, as well as identify high value chemicals and other
product species.
[0139] Hydrochar and Feedstock
[0140] Similar analyses were performed on the solid hydrochar and
the feedstocks. The energy content of oven-dried samples was
measured using a Parr 6200 calorimeter. Ultimate analysis (C, H, N,
S, O) was performed using a Flash EA 1112 automatic elemental
analyzer (ThermoElectron, Delft, The Netherlands). In order to
directly measure the O content, two methods are used with two
different injections, one to measure C, H, N and S, and the other
to measure O.
[0141] To determine the amount of ash, proximate analysis was
performed on the solid samples using a thermal gravimetric analyzer
(Mettler Toledo TGA/DSC 1, Columbus, Ohio, USA). First, the samples
were homogenized in an analytical mill (IKA ALL Basic, Wilmington,
N.C., USA) for two minutes per sample. The homogenized samples were
stored in capped glass vials at room temperature until analysis.
The proximate analysis was then carried out according to ASTM
standard D7582-12 with two differences; the volatile matter
analysis was done at 700.degree. C. instead of 950.degree. C., and
the sample size was limited to milligram amounts because the TGA
instrument was equipped with small (70 .mu.L) alumina crucibles.
Two crucible blanks were analyzed for equilibration and subtraction
of buoyance effects. Succeeding crucibles containing homogenized
biomass samples were half filled to reduce surface area effects on
pyrolysis. Each sample was analyzed in triplicate with every nine
runs having an intermittent performance working standard (Vanguard
Solutions VS6-006, Ashland, Ky., USA).
[0142] To perform the elemental analyses, solid particles were
first re-suspended onto filters. In the re-suspension process,
materials are first homogenized and then sieved to <38 .mu.m
diameter (400 mesh screen), then re-suspended using a high velocity
air stream, blown into a large chamber for mixing and dispersion,
and collected onto filters using a modified Parallel Impactor
Sampling Device (PISD, OMNI Environmental, Portland, Oreg., USA).
The filter samples are then analyzed using a PANalytical Epsilon 5
energy dispersive X-ray fluorescence (ED-XRF) instrument
(PANalytical, Westborough, Mass., USA). The analyzer emits X-rays,
which are focused on secondary targets and in turn emit polarized
X-rays which excite a sample. Subsequent emissions of X-ray photons
are integrated over time to give quantitative measurements of
elements ranging from aluminum through uranium, and
semi-quantitative measurements of sodium and magnesium.
[0143] Aqueous Co-Products
[0144] The pH and non-volatile residue (NVR) content of the ACP
were measured immediately following completion of the reaction and
separation of the products. The pH of the ACP was measured using a
portable Hanna Instruments HI 8424 digital pH and temperature meter
(Hanna Instruments, Smithfield, R.I., USA). The NVR content was
measured by weighing triplicate samples of the ACP into drying tins
which were then placed in a convective oven at 105.degree. C.
overnight (approximately 18-20 h) to obtain an oven-dried weight.
The remaining residue represents the NVR content of the ACP.
[0145] The total organic carbon (TOC) and other sugars and polars
were measured on a batch of samples once all experiments were
completed. The ACP solutions were stored in a laboratory
refrigerator until all samples were collected. The TOC was measured
using a Shimadzu TOC-VCSH instrument (Columbia, Md., USA) which
catalytically oxidizes all organic compounds into CO.sub.2, which
is then measured by nondispersive infrared detection (NDIR). Sugars
were measured using a previously developed high-performance liquid
chromatography (HPLC) method. Using a Waters Alliance 2695 HPLC
(Waters Corporation, Milford, Mass., USA) equipped with a Waters
2414 Refractive Index Detector and Waters Sugar-Pak.TM. HPLC
column, several sugars and sugar alcohols can be quantified,
several of which are included in the United States Department of
Energy's high value chemical list provided in FIG. 12. The
high-value sugars identified through this method include furfural,
levoglucosan and arabitol. Fructose and glycerol are also
identified, although they co-elute with other sugars and are
reported together.
[0146] Additional high-value chemicals were identified using GC/MS
with two different analytical protocols: one called polars analysis
and the other called sugars/sugar alcohols analysis. In both cases,
the compounds of interest are extracted from the whole algae, LEA,
and NVR fraction of the aqueous products from HTC treatment using
the ASE instrument with dichloromethane, followed by acetone. After
drying, the extracted materials are derivatized using BSTFA
[N,O-bis-(trimethylsilyl) trifluoroacetamide] with 1% TMCS
(trimethylchlorosilane). The derivatized samples are analyzed by an
electron impact GC/MS technique using a Varian 3400 GC with a model
CP-8400 autosampler and interfaced to a Saturn 2000 ion trap
spectrometer (Varian, Inc., Walnut Creek, Calif., USA). A 30-m,
DB-5 capillary column (0.25 mm ID; 0.25 .mu.m thickness) was used
for both analyses. For the sugars protocol, a set of calibration
standards was used that consisted of numerous sugars,
anhydrosugars, and sugar alcohols. For the polars protocol, a set
of calibration standards was used that consisted of organic acids,
lignin monomers, and other anhydrosugars.
[0147] Gases
[0148] The composition of produced gases was analyzed with an SRI
8610C gas chromatograph (GC, SRI Instruments, Torrance, Calif.,
USA), equipped with a thermal conductivity detector using a method
for measurement of H.sub.2, CO, CO.sub.2, and C.sub.1-C.sub.3. The
gases are comprised mainly of CO.sub.2, and are not discussed in
detail.
CONCLUSIONS
[0149] Hydrothermal carbonization (HTC) was applied to algae and
lipid-extracted algae (LEA) residue to produce an energy-dense
solid hydrochar that is similar in energy content to low-grade
coals. Algal feedstocks behave differently in HTC treatment as
compared to lignocellulosic feedstocks, and can benefit from milder
conditions (treatment temperatures less than 200.degree. C.) for
acceptable levels of carbonization. These lower process temperature
requirements result from the lack of lignin and cellulose
structures in algae, which typically require higher process
temperatures to break down in lignocellulosic feedstocks. However,
a lower amount of the starting algal feedstock is recovered as a
solid hydrochar, while more of the mass is recovered in the aqueous
phase products. In part, the reduction of solid mass recovery and
increase in aqueous products is due the removal of ash constituents
which are dissolved into the aqueous co-product. This ash reduction
also contributes to increased energy content of the hydrochar,
which results in higher energy densification of algal hydrochars
relative to hydrochars produced from treatment of lignocellulosic
feedstocks at comparable temperatures.
[0150] The aqueous co-products (ACP) from HTC of whole algae and
LEA algae were also evaluated to identify high-value chemicals.
Although there was a very large amount of non-volatile residue
(NVR) in the aqueous phase from treatment of the algal materials as
compared to treatment of lignocellulosic feedstocks, only a small
fraction of the ACP was identified through the various methods
used. Using three different methods to characterize ACP,
approximately 1% of the starting dry mass was identified as high
value chemicals from the treatment of Spirulina. The total organic
carbon in the ACP accounts for less than half of the dissolved
mass, but the elemental balance of the solids indicates that much
of the unidentified dissolved solids are nitrogen-containing
compounds. Results from earlier, studies with Scenedesmus Dimorphus
showed that different amounts and types of sugars are produced from
HTC treatment of a different strain of algae. Overall, higher
concentrations of high-value chemicals were identified in the ACP
from Scenedesmus. However, it should be noted that the two algae
treated by HTC came from two different sources: the Spirulina was
purchased from a health food supplier while the Scenedesmus was
grown in local ponds. The different processing and handling
histories of the two algae could contribute to the observed
differences in their behaviors.
[0151] Despite the lipid extraction, the sugar-related products
from HTC treatment of LEA and whole algae were quite similar.
Energy densification of the hydrochars was also similar. However, a
lower fraction of high-value chemicals was observed in the ACP from
LEA, as compared to whole algae. Overall, the results of this
Example 2 indicate that HTC can produce both an energy-dense
hydrochar at much milder conditions than those required for
lignocellulosic feedstocks, as well as a valuable aqueous product
stream from whole and lipid-extracted algae. Relatively mild
treatment temperatures were applied, and it is possible that
additional high value chemicals could be produced as treatment
temperatures are increased.
[0152] It is to be understood that the above discussion provides a
detailed description of various embodiments. The above descriptions
will enable those skilled in the art to make many departures from
the particular examples described above to provide apparatuses
constructed in accordance with the present disclosure. The
embodiments are illustrative, and not intended to limit the scope
of the present disclosure. The scope of the present disclosure is
rather to be determined by the scope of the claims as issued and
equivalents thereto.
* * * * *
References