U.S. patent application number 15/276834 was filed with the patent office on 2017-07-20 for methods and systems for enzymatic hydrolysis of pretreated biomass at high solids concentrations.
The applicant listed for this patent is API Intellectual Property Holdings, LLC. Invention is credited to Theodora RETSINA, Ryan ZEBROSKI.
Application Number | 20170204440 15/276834 |
Document ID | / |
Family ID | 59314944 |
Filed Date | 2017-07-20 |
United States Patent
Application |
20170204440 |
Kind Code |
A1 |
RETSINA; Theodora ; et
al. |
July 20, 2017 |
METHODS AND SYSTEMS FOR ENZYMATIC HYDROLYSIS OF PRETREATED BIOMASS
AT HIGH SOLIDS CONCENTRATIONS
Abstract
A method of enzymatically hydrolyzing pretreated lignocellulosic
biomass at high solids concentration includes introducing
pretreated biomass to a hydrolysis reactor, to hydrolyze the
cellulose to glucose monomer and glucose oligomers, and circulating
a liquid stream, from which glucose is removed to reduce glucose
inhibition of cellulose hydrolysis. A surfactant may be added to
the hydrolysis reactor. Heat and/or acid treatment of the glucose
oligomers may be used to generate additional glucose monomer. Some
variations introduce pretreated biomass to a hydrolysis reactor to
hydrolyze cellulose to glucose monomer and glucose oligomers,
followed by conveying a portion of the solid phase to a mechanical
refiner and/or a unit under reduced pressure, to generate a refined
and/or exploded solid phase; and recycling the refined and/or
exploded solid phase, optionally reheated, back to an input of the
hydrolysis reactor.
Inventors: |
RETSINA; Theodora; (Atlanta,
GA) ; ZEBROSKI; Ryan; (Fayetteville, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
API Intellectual Property Holdings, LLC |
Atlanta |
GA |
US |
|
|
Family ID: |
59314944 |
Appl. No.: |
15/276834 |
Filed: |
September 27, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62234415 |
Sep 29, 2015 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C12P 19/02 20130101;
C12P 19/14 20130101; C12P 2203/00 20130101 |
International
Class: |
C12P 19/02 20060101
C12P019/02 |
Claims
1. A method of enzymatically hydrolyzing pretreated lignocellulosic
biomass at high solids concentration, said method comprising: (a)
providing pretreated lignocellulosic biomass containing cellulose;
(b) introducing said pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze said
cellulose to glucose monomer and glucose oligomers; and (c)
circulating a liquid stream in a circulation line configured from
an output of said reactor back to an input of said hydrolysis
reactor, wherein at least a portion of said glucose monomer is
removed from said circulation line to reduce glucose inhibition of
cellulose hydrolysis, wherein said method further comprises a
glucose oligomer hydrolysis step to generate additional glucose
monomer from said glucose oligomers.
2. The method of claim 1, wherein said glucose oligomer hydrolysis
step is integrated with step (b).
3. The method of claim 1, wherein said glucose oligomer hydrolysis
step is integrated with step (c).
4. The method of claim 1, wherein at least a portion of said
glucose oligomers is also removed from said circulation line to
reduce glucose oligomer inhibition of cellulose hydrolysis.
5. The method of claim 1, wherein additional cellulase enzymes are
introduced to said circulation line, to convert said glucose
oligomers to said additional glucose monomer.
6. The method of claim 1, wherein said method further comprises
introducing a surfactant to said hydrolysis reactor during step (b)
or step (c).
7. The method of claim 6, wherein said surfactant includes
lignin.
8. A method of enzymatically hydrolyzing pretreated lignocellulosic
biomass at high solids concentration, said method comprising: (a)
providing pretreated lignocellulosic biomass containing cellulose;
(b) introducing said pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
said cellulose to glucose monomer and glucose oligomers present in
a liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase; and (c) conveying a portion of said solid phase to a
mechanical refiner, to generate a refined solid phase; and (d)
recycling said refined solid phase back to an input of said
hydrolysis reactor.
9. A method of enzymatically hydrolyzing pretreated lignocellulosic
biomass at high solids concentration, said method comprising: (a)
providing pretreated lignocellulosic biomass containing cellulose;
(b) introducing said pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
said cellulose to glucose monomer and glucose oligomers present in
a liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase; (c) feeding a portion of said solid phase to a unit under
reduced pressure, to generate an exploded solid phase; and (d)
recycling said exploded solid phase, optionally reheated, back to
an input of said hydrolysis reactor.
10. The method of either one of claim 8 or 9, wherein said method
further comprises an oligomer hydrolysis step of said glucose
oligomers to generate additional glucose monomer.
11. The method of either one of claim 8 or 9, wherein said method
further comprises introducing a surfactant to said hydrolysis
reactor.
12. The method of either one of claim 8 or 9, wherein said
pretreated lignocellulosic biomass is a pulp material, derived from
wood or lignocellulosic biomass, selected from the group consisting
of kraft pulp, sulfite pulp, soda pulp, mechanical pulp,
thermomechanical pulp, chemimechanical pulp, and combinations
thereof.
13. The method of either one of claim 8 or 9, wherein said
pretreated lignocellulosic biomass is obtained from steam or
hot-water extraction of lignocellulosic biomass.
14. The method of either one of claim 8 or 9, wherein said
pretreated lignocellulosic biomass is present in said hydrolysis
reactor at a solids concentration of about 20 wt % or more.
15. The method of either one of claim 8 or 9, wherein a first
amount of enzymes is introduced at a first solids concentration,
wherein a second amount of enzymes is introduced at a second solids
concentration, and wherein said second solids concentration is
higher than said first solids concentration.
Description
PRIORITY DATA
[0001] This non-provisional patent application claims priority to
U.S. Provisional Patent App. No. 62/234,415, filed on Sep. 29,
2016, which is incorporated by reference herein.
FIELD OF THE INVENTION
[0002] The present invention generally relates to methods and
systems for preparing fermentable sugars from lignocellulosic
biomass.
BACKGROUND OF THE INVENTION
[0003] Enzymatic hydrolysis is a key process for a biorefinery
based on production of sugars. The rate of enzymatic hydrolysis,
final carbohydrate conversion, and concentration all critically
affect the technoeconomic feasibility of commercial operations.
Enzymatic hydrolysis performed at high solids loading offers
several advantages over low solids loading, because of higher sugar
and bioproduct concentrations, smaller equipment, less energy for
heating and cooling of the slurry, and lower hydraulic loads.
Therefore, enzymatic hydrolysis at high solids loadings is highly
desirable to develop an economically viable process. See Geng et
al., "Strategies to achieve high-solids enzymatic hydrolysis of
dilute-acid pretreated corn stover," Bioresource Technology 187
(2015) 43-48.
[0004] However, hydrolysis at high insoluble solids introduces a
lack of available water in the reactor. Water is essential to the
hydrolysis and conversion of lignocellulosic biomass since it is
the key medium for enzymes to diffuse in and for products to
diffuse away from reaction sites. Water also reduces the viscosity
of the slurry by increasing the lubricity of the particles, which
decreases the required shear stress necessary to produce a given
shear rate, allowing lower power input for mixing during
hydrolysis. Therefore, high-solids hydrolysis can create
rheological challenges, cause insufficient mixing, reduce mass- and
heat-transfer efficiency, and increase the concentration of enzymes
inhibitors in the system, resulting in low conversion of
carbohydrates into fermentable sugars.
[0005] To overcome the challenges of enzymatic hydrolysis at high
solids and make the overall conversion process more economically
viable, several approaches have been developed, including
fed-batch, splitting/thickening, and clarifier processes.
[0006] For the fed-batch process, substrates and/or enzymes are
introduced into a hydrolysis reactor successively. The fed-batch
system allows time for the slurry to liquefy before adding
additional solids and a low initial insoluble solids content can be
kept. In order to maintain high rates of carbohydrate conversion of
hydrolysis, it is important to find an optimal point to add solids
into the system, which is highly dependent on substrate
characteristics and enzyme dosage/type.
[0007] For the splitting/thickening process, pretreated substrate
is mixed with part of the enzymes at a lower solids loading and
then filtered to obtain the desired solids loading. Using split
addition, the solids content can be increased to 20% while
maintaining the enzymatic hydrolysis conversion efficiency
comparable to that with 5% total solids.
[0008] For the clarifier process, a gravity clarifier separates the
partially hydrolyzed stream into a sugar stream and unhydrolyzed
solids, and the sugar stream is used to dilute the initial
insoluble solids content. This process can reduce the initial
viscosity without decreasing the final sugar concentration because
of the high sugar concentration of the sugar stream.
[0009] Improvements are still desired to reach high solids
concentrations in enzymatic hydrolysis of pretreated biomass.
SUMMARY OF THE INVENTION
[0010] The present invention addresses the aforementioned needs in
the art.
[0011] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0012] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0013] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze the
cellulose to glucose monomer and glucose oligomers; and
[0014] (c) circulating a liquid stream in a circulation line
configured from an output of the reactor back to an input of the
hydrolysis reactor, wherein at least a portion of the glucose is
removed from the circulation line to reduce glucose inhibition of
cellulose hydrolysis.
[0015] In some embodiments, the method further comprises
introducing a surfactant to the hydrolysis reactor during step (b)
or step (c). The surfactant may include lignin, such as hardwood
lignin, for example.
[0016] In some embodiments, the method further comprises an
oligomer hydrolysis step comprising heat treatment and/or acid
treatment of the glucose oligomers to generate additional glucose
monomer. The oligomer hydrolysis step may be integrated with step
(b) and/or step (c). Additional enzymes may be introduced to the
circulation line or at another location.
[0017] Optionally, at least a portion of the glucose oligomers may
be removed from the circulation line to reduce glucose oligomer
inhibition of cellulose hydrolysis. The removal of glucose
oligomers may target cellobiose, which is a relatively high enzyme
inhibition effect, compared to larger oligomers.
[0018] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0019] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0020] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
the cellulose to glucose monomer and glucose oligomers present in a
liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase; and
[0021] (c) conveying a portion of the solid phase to a mechanical
refiner, to generate a refined solid phase; and
[0022] (d) recycling the refined solid phase back to an input of
the hydrolysis reactor.
[0023] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0024] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0025] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
the cellulose to glucose monomer and glucose oligomers present in a
liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase;
[0026] (c) feeding a portion of the solid phase to a unit under
reduced pressure, to generate an exploded solid phase; and
[0027] (d) recycling the exploded solid phase, optionally reheated,
back to an input of the hydrolysis reactor.
[0028] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0029] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0030] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
the cellulose to glucose monomer and glucose oligomers present in a
liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase;
[0031] (c) conveying a portion of the solid phase to a mechanical
refiner, to generate a refined solid phase;
[0032] (d) feeding the refined solid phase to a unit under reduced
pressure, to generate an exploded and refined solid phase; and
[0033] (e) recycling the exploded and refined solid phase,
optionally reheated, back to an input of the hydrolysis
reactor.
[0034] In some embodiments, the method further comprises
introducing a surfactant to the hydrolysis reactor. In some
embodiments, the method further comprises an oligomer hydrolysis
step comprising heat treatment and/or acid treatment of the glucose
oligomers to generate additional glucose monomer.
[0035] In various embodiments, the pretreated lignocellulosic
biomass is chemically pretreated (e.g., with an acid or base),
physically pretreated (e.g., refined or exploded), or a combination
thereof. The pretreated lignocellulosic biomass may be a pulp
material, derived from wood or lignocellulosic biomass, selected
from the group consisting of kraft pulp, sulfite pulp, soda pulp,
mechanical pulp, thermomechanical pulp, chemimechanical pulp, and
combinations thereof.
[0036] In certain embodiments, the pretreated lignocellulosic
biomass is GP3+.RTM. pulp derived from wood or lignocellulosic
biomass. The pretreated lignocellulosic biomass may be obtained
from steam or hot-water extraction of lignocellulosic biomass.
[0037] In certain embodiments, the pretreated lignocellulosic
biomass is AVAP.RTM. pulp derived from wood or lignocellulosic
biomass. The pretreated lignocellulosic biomass may be obtained
from fractionation of lignocellulosic biomass in the presence of
water, an acid catalyst, and a solvent for lignin.
[0038] In preferred embodiments, the pretreated lignocellulosic
biomass is present in the hydrolysis reactor at a solids
concentration of about 15 wt % or more, about 20 wt % or more,
about 25 wt % or more, or about 30 wt % or more.
[0039] Enzymes may be introduced to the pretreated lignocellulosic
biomass at multiple times and/or locations. The concept of split
addition of enzymes may be applied. In some embodiments, a first
amount of enzymes is introduced at a first solids concentration, a
second amount of enzymes is introduced at a second solids
concentration, the second solids concentration being higher than
the first solids concentration.
[0040] Also provided is a system configured for carrying out a
method as described.
[0041] Also provided is a sugar product produced by a process
comprising a method as described. A fermentation product (e.g.,
ethanol) may be derived from the sugar product.
BRIEF DESCRIPTION OF THE FIGURES
[0042] FIG. 1 is a simplified block-flow diagram depicting the
process of some embodiments of the present invention.
[0043] FIG. 2 is a simplified block-flow diagram depicting the
process of some embodiments of the present invention.
[0044] FIG. 3 is a simplified block-flow diagram depicting the
process of some embodiments of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0045] This description will enable one skilled in the art to make
and use the invention, and it describes several embodiments,
adaptations, variations, alternatives, and uses of the invention.
These and other embodiments, features, and advantages of the
present invention will become more apparent to those skilled in the
art when taken with reference to the following detailed description
of the invention in conjunction with any accompanying drawings.
[0046] As used in this specification and the appended claims, the
singular forms "a," "an," and "the" include plural referents unless
the context clearly indicates otherwise. Unless defined otherwise,
all technical and scientific terms used herein have the same
meaning as is commonly understood by one of ordinary skill in the
art to which this invention belongs. All composition numbers and
ranges based on percentages are weight percentages, unless
indicated otherwise. All ranges of numbers or conditions are meant
to encompass any specific value contained within the range, rounded
to any suitable decimal point.
[0047] Unless otherwise indicated, all numbers expressing reaction
conditions, stoichiometries, concentrations of components, and so
forth used in the specification and claims are to be understood as
being modified in all instances by the term "about." Accordingly,
unless indicated to the contrary, the numerical parameters set
forth in the following specification and attached claims are
approximations that may vary depending at least upon a specific
analytical technique.
[0048] The term "comprising," which is synonymous with "including,"
"containing," or "characterized by" is inclusive or open-ended and
does not exclude additional, unrecited elements or method steps.
"Comprising" is a term of art used in claim language which means
that the named claim elements are essential, but other claim
elements may be added and still form a construct within the scope
of the claim.
[0049] As used herein, the phrase "consisting of" excludes any
element, step, or ingredient not specified in the claim. When the
phrase "consists of" (or variations thereof) appears in a clause of
the body of a claim, rather than immediately following the
preamble, it limits only the element set forth in that clause;
other elements are not excluded from the claim as a whole. As used
herein, the phrase "consisting essentially of" limits the scope of
a claim to the specified elements or method steps, plus those that
do not materially affect the basis and novel characteristic(s) of
the claimed subject matter.
[0050] With respect to the terms "comprising," "consisting of," and
"consisting essentially of," where one of these three terms is used
herein, the presently disclosed and claimed subject matter may
include the use of either of the other two terms. Thus in some
embodiments not otherwise explicitly recited, any instance of
"comprising" may be replaced by "consisting of" or, alternatively,
by "consisting essentially of."
[0051] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0052] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0053] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze the
cellulose to glucose monomer and glucose oligomers; and
[0054] (c) circulating a liquid stream in a circulation line
configured from an output of the reactor back to an input of the
hydrolysis reactor, wherein at least a portion of the glucose is
removed from the circulation line to reduce glucose inhibition of
cellulose hydrolysis.
[0055] For example, see FIG. 1 for an illustration of some
embodiments.
[0056] In some embodiments, the method further comprises
introducing a surfactant to the hydrolysis reactor during step (b)
or step (c). The surfactant may include lignin, such as hardwood
lignin, for example.
[0057] In some embodiments, the method further comprises an
oligomer hydrolysis step comprising heat treatment and/or acid
treatment of the glucose oligomers to generate additional glucose
monomer. The oligomer hydrolysis step may be integrated with step
(b) and/or step (c). Additional enzymes may be introduced to the
circulation line or at another location.
[0058] Optionally, at least a portion of the glucose oligomers may
be removed from the circulation line to reduce glucose oligomer
inhibition of cellulose hydrolysis. The removal of glucose
oligomers may target cellobiose, which is a relatively high enzyme
inhibition effect, compared to larger oligomers.
[0059] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0060] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0061] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
the cellulose to glucose monomer and glucose oligomers present in a
liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase; and
[0062] (c) conveying a portion of the solid phase to a mechanical
refiner, to generate a refined solid phase; and
[0063] (d) recycling the refined solid phase back to an input of
the hydrolysis reactor.
[0064] For example, see FIG. 2 for an illustration of some
embodiments.
[0065] The mechanical refiner can be configured to cause cellulose
chain end-opening action, for enhanced enzyme accessibility.
[0066] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0067] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0068] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
the cellulose to glucose monomer and glucose oligomers present in a
liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase;
[0069] (c) feeding a portion of the solid phase to a unit under
reduced pressure, to generate an exploded solid phase; and
[0070] (d) recycling the exploded solid phase, optionally reheated,
back to an input of the hydrolysis reactor.
[0071] For example, see FIG. 3 for an illustration of some
embodiments.
[0072] The unit under reduced pressure (e.g., vacuum) can be
configured to cause cellulose fiber expansion, for enhanced enzyme
accessibility.
[0073] Some variations provide a method of enzymatically
hydrolyzing pretreated lignocellulosic biomass at high solids
concentration, the method comprising:
[0074] (a) providing pretreated lignocellulosic biomass containing
cellulose;
[0075] (b) introducing the pretreated lignocellulosic biomass to a
hydrolysis reactor under effective hydrolysis conditions and in the
presence of enzymes including cellulases, to hydrolyze a portion of
the cellulose to glucose monomer and glucose oligomers present in a
liquid phase, wherein non-hydrolyzed cellulose remains in a solid
phase;
[0076] (c) conveying a portion of the solid phase to a mechanical
refiner, to generate a refined solid phase;
[0077] (d) feeding the refined solid phase to a unit under reduced
pressure, to generate an exploded and refined solid phase; and
[0078] (e) recycling the exploded and refined solid phase,
optionally reheated, back to an input of the hydrolysis
reactor.
[0079] In some embodiments, the method further comprises
introducing a surfactant to the hydrolysis reactor. In some
embodiments, the method further comprises an oligomer hydrolysis
step comprising heat treatment and/or acid treatment of the glucose
oligomers to generate additional glucose monomer.
[0080] In various embodiments, the pretreated lignocellulosic
biomass is chemically pretreated (e.g., with an acid or base),
physically pretreated (e.g., refined or exploded), or a combination
thereof. The pretreated lignocellulosic biomass may be a pulp
material, derived from wood or lignocellulosic biomass, selected
from the group consisting of kraft pulp, sulfite pulp, soda pulp,
mechanical pulp, thermomechanical pulp, chemimechanical pulp, and
combinations thereof.
[0081] In certain embodiments, the pretreated lignocellulosic
biomass is GP3+.RTM. pulp derived from wood or lignocellulosic
biomass. The pretreated lignocellulosic biomass may be obtained
from steam or hot-water extraction of lignocellulosic biomass.
[0082] In certain embodiments, the pretreated lignocellulosic
biomass is AVAP.RTM. pulp derived from wood or lignocellulosic
biomass. The pretreated lignocellulosic biomass may be obtained
from fractionation of lignocellulosic biomass in the presence of
water, an acid catalyst, and a solvent for lignin.
[0083] In preferred embodiments, the pretreated lignocellulosic
biomass is present in the hydrolysis reactor at a solids
concentration of about 15 wt % or more, about 20 wt % or more,
about 25 wt % or more, or about 30 wt % or more.
[0084] Enzymes may be introduced to the pretreated lignocellulosic
biomass at multiple times and/or locations. The concept of split
addition of enzymes may be applied. In some embodiments, a first
amount of enzymes is introduced at a first solids concentration, a
second amount of enzymes is introduced at a second solids
concentration, the second solids concentration being higher than
the first solids concentration.
[0085] Also provided is a system configured for carrying out a
method as described.
[0086] Also provided is a sugar product produced by a process
comprising a method as described. A fermentation product (e.g.,
ethanol) may be derived from the sugar product.
[0087] Some variations are premised on the discovery of a
surprisingly simple process for converting lignocellulosic biomass
into fermentable sugars. Biomass may be subjected to a steam or
hot-water soak to dissolved hemicelluloses, with or without acetic
acid recycle. This step is followed by mechanical refining, such as
in a hot-blow refiner, of the cellulose-rich (and lignin-rich)
solids. The refined solids are then enzymatically hydrolyzed to
generate sugars. A stripping step for removing fermentation
inhibitors in the hydrolysate may be included.
[0088] Certain exemplary embodiments of the invention will now be
described. These embodiments are not intended to limit the scope of
the invention as claimed. The order of steps may be varied, some
steps may be omitted, and/or other steps may be added. Reference
herein to first step, second step, etc. is for illustration
purposes only.
[0089] Some variations provide a process for producing fermentable
sugars from cellulosic biomass, the process comprising:
[0090] (a) providing a feedstock comprising cellulosic biomass;
[0091] (b) digesting the feedstock with a reaction solution
including steam and/or hot water in a digestor under effective
reaction conditions to produce a digested stream containing
cellulose-rich solids, hemicellulose oligomers, and lignin;
[0092] (c) conveying the digested stream through a mechanical
refiner, thereby generating a refined stream with reduced average
particle size of the cellulose-rich solids;
[0093] (d) separating a vapor from the refined stream;
[0094] (e) introducing the refined stream to an enzymatic
hydrolysis unit under effective hydrolysis conditions to produce
sugars from the cellulose-rich solids and optionally from the
hemicellulose oligomers; and
[0095] (f) recovering or further processing at least some of the
sugars as fermentable sugars.
[0096] In some embodiments, the reaction solution comprises steam
in saturated, superheated, or supersaturated form. In some
embodiments, the reaction solution comprises pressurized hot
water.
[0097] In some embodiments, the reaction solution further comprises
an acid, such as a sulfur-containing acid (e.g., sulfuric acid,
sulfurous acid, or sulfur dioxide), acetic acid, formic acid, or
others. The acid may include acetic acid recovered from the
digested stream.
[0098] The mechanical refiner may be selected from the group
consisting of a hot-blow refiner, a hot-stock refiner, a blow-line
refiner, a disk refiner, a conical refiner, a cylindrical refiner,
an in-line defibrator, a homogenizer, and combinations thereof. In
some embodiments, the mechanical refiner is a blow-line refiner.
Other mechanical refiners may be employed, and chemical refining
aids may be introduced.
[0099] Mechanically treating (refining) may employ one or more
known techniques such as, but by no means limited to, milling,
grinding, beating, sonicating, or any other means to reduce
cellulose particle size. Such refiners are well-known in the
industry and include, without limitation, Valley beaters, single
disk refiners, double disk refiners, conical refiners, including
both wide angle and narrow angle, cylindrical refiners,
homogenizers, microfluidizers, and other similar milling or
grinding apparatus. See, for example, Smook, Handbook for Pulp
& Paper Technologists, Tappi Press, 1992.
[0100] A blow tank may be situated downstream of the mechanical
refiner, so that the mechanical refiner operates under pressure.
The pressure of the mechanical refiner may be the same as the
digestor pressure, or it may be different. In some embodiments, the
mechanical refiner is operated at a refining pressure selected from
about 30 psig to about 300 psig, such as about 40, 50, 60, 70, 80,
90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210,
220, 230, 240, 250, 260, 270, 280, or 290 psig.
[0101] A blow tank may be situated upstream of the mechanical
refiner, so that the mechanical refiner operates under reduced
pressure or atmospheric pressure. In some embodiments, the
mechanical refiner is operated a refining pressure of less than
about 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 psig, or at or about
atmospheric pressure (0 psig).
[0102] In certain embodiments of the invention, a first blow tank
is situated upstream of the mechanical refiner and a second blow
tank is situated downstream of the mechanical refiner. In this
scenario, the pressure is reduced somewhat between the digestor and
the refiner, which operates above atmospheric pressure. Following
the refining, the pressure is released in the second blow tank. In
some embodiments, the mechanical refiner is operated at a refining
pressure selected from about 10 psig to about 150 psig, such as
about 20 psig to about 100 psig, or about 25, 30, 35, 40, 45, 50,
55, 60, 65, 70, or 75 psig.
[0103] A pressurized refiner may operate at the same pressure as
the digestor, or at a different pressure. In some embodiments, both
the digestor and the refiner operate in a pressure range
corresponding to equilibrium steam saturation temperatures from
about 170.degree. C. to about 210.degree. C., such as about
180.degree. C. to about 200.degree. C. In some embodiments, a
pressurized refiner is fed by a screw between the digestor and the
refiner.
[0104] In principle, the pressure in the refiner could be higher
than the digestor pressure, due to mechanical energy input. For
example, a high-pressure screw feeder could be utilized to increase
pressure, if desired, in refining. Also, it will be recognized that
localized pressures (forces) may be higher than the vapor pressure,
due to the presence of mechanical surface force (e.g., plates)
impacting the solid material or slurry.
[0105] In some embodiments, the vapor is separated from a blow
tank, and heat is recovered from at least some of the vapor. At
least some of the vapor may be compressed and returned to the
digestor. Some of the vapor may be purged from the process.
[0106] The enzymes introduced or present in the enzymatic
hydrolysis unit may include cellulases and optionally
hemicellulases. The enzymes may include endoglucanases and
exoglucanases.
[0107] The process may further include removal of one or more
fermentation inhibitors by stripping, conducted for example
following step (e).
[0108] The process may further include a step of fermenting the
fermentable sugars to a fermentation product; and concentrating and
purifying the fermentation product. In various embodiments, the
fermentation product may be selected from ethanol, n-butanol,
1,4-butanediol, succinic acid, lactic acid, or combinations
thereof.
[0109] Some embodiments further include comprising removing a solid
stream containing lignin following step (e) but prior to
fermentation of the fermentable sugars. In these or other
embodiments, the process may further include removing a solid
stream containing lignin following fermentation of the fermentable
sugars. The lignin may be combusted or use for other purposes.
[0110] Other variations of the invention provide a process for
producing fermentable sugars from cellulosic biomass, the process
comprising:
[0111] (a) providing a feedstock comprising cellulosic biomass;
[0112] (b) digesting the feedstock with a reaction solution
including steam and/or hot water in a digestor under effective
reaction conditions to produce a digested stream containing
cellulose-rich solids, hemicellulose oligomers, and lignin;
[0113] (c) conveying the digested stream through a mechanical
refiner, thereby generating a refined stream with reduced average
particle size of the cellulose-rich solids;
[0114] (d) introducing enzymes to the mechanical refiner and
maintaining effective hydrolysis conditions to produce sugars from
the cellulose-rich solids and optionally from the hemicellulose
oligomers, optionally simultaneously with step (c); and
[0115] (e) recovering or further processing at least some of the
sugars as fermentable sugars.
[0116] In some embodiments, the enzymes are introduced directly to
the mechanical refiner. In these or other embodiments, the enzymes
are introduced to the digested stream, upstream of the mechanical
refiner. The enzymes may include cellulases (e.g., endoglucanases
and exoglucanases) and hemicellulases.
[0117] The effective hydrolysis conditions may include a maximum
temperature of 75.degree. C. or less, preferably 65.degree. C. or
less, within the mechanical refiner. In some embodiments, the
effective hydrolysis conditions include a hydrolysis temperature of
about 30, 35, 40, 45, 50, 55, 60, 65, or 70.degree. C. within the
mechanical refiner. These are average temperatures within the
refining zone. Local hot spots may be present within the refiner,
such as in regions of high-shear contact between cellulose-rich
solids and metal plates.
[0118] The reaction solution may comprise hot water or steam in
saturated, superheated, or supersaturated form. In some
embodiments, the reaction solution further comprises an acid, such
as a sulfur-containing acid. In some embodiments, the reaction
solution further comprises acetic acid, which may be (at least in
part) acetic acid recovered from the digested stream.
[0119] The mechanical refiner may be selected from the group
consisting of a hot-blow refiner, a hot-stock refiner, a blow-line
refiner, a disk refiner, a conical refiner, a cylindrical refiner,
an in-line defibrator, a homogenizer, and combinations thereof. In
certain embodiments, the mechanical refiner is one or more
blow-line refiners.
[0120] In some embodiments, a blow tank is situated upstream of the
mechanical refiner. The mechanical refiner is preferably operated
at or about atmospheric pressure, due to the presence of
enzymes.
[0121] In some embodiments, vapor is separated from a blow tank,
and heat is recovered from at least some of the vapor. Some or all
of the vapor may be compressed and returned to the digestor. Some
of the vapor may be purged from the process.
[0122] The process may also include removal of one or more
fermentation inhibitors by stripping. The stripping may be
conducted following step (e), prior to fermentation. One
fermentation inhibitor is acetic acid, which may be recycled to the
digestor, i.e. step (b).
[0123] The process may further include a step of fermenting the
fermentable sugars to a fermentation product, such as ethanol,
n-butanol, 1,4-butanediol, succinic acid, lactic acid, or
combinations thereof. The fermentation product may be concentrated
and purified.
[0124] The process may further include a solid stream containing
lignin (i) following step (d) but prior to fermentation of the
fermentable sugars and/or (ii) following fermentation of the
fermentable sugars. The lignin may be recovered for various uses,
such as combustion (energy).
[0125] In some embodiments, a blow tank is situated downstream of
the mechanical refiner. In other embodiments, a blow tank is
situated upstream of the mechanical refiner. In certain
embodiments, a first blow tank is situated downstream of the
mechanical refiner and a second blow tank is situated upstream of
the mechanical refiner. The vapor separated in step (d) may be
separated from a blow tank.
[0126] Note that "blow tank" should be broadly construed to include
not only a tank but any other apparatus or equipment capable of
allowing a pressure reduction in the process stream. Thus a blow
tank may be a tank, vessel, section of pipe, valve, separation
device, or other unit.
[0127] In some embodiments, following a digestor to remove
hemicellulose, an intermediate blow is performed to, for example,
about 40 psig. The material is sent to a blowline refiner, and then
to a final blow to atmospheric pressure.
[0128] In some embodiments, a cold blow discharger is utilized to
feed a pressurized refiner. In some embodiments, a transfer
conveyor is utilized to feed a pressurized refiner.
[0129] The refining may be conducted at a wide range of solids
concentrations (consistency), including from about 2% to about 50%
consistency, such as about 4%, 6%, 8%, 10%, 15%, 20%, 30%, 35%, or
40% consistency.
[0130] In some embodiments, heat is recovered from at least some of
the vapor, using the principles of heat integration. At least some
of the vapor may be compressed and returned to the digestor. Some
of the vapor may be purged from the process.
[0131] In some embodiments, enzymes introduced or present in the
enzymatic hydrolysis unit may include not only cellulases but also
hemicellulases. In certain embodiments, enzymes introduced or
present in the enzymatic hydrolysis unit include endoglucanases and
exoglucanases.
[0132] The reaction solution optionally includes an acid catalyst,
to assist in extraction of hemicelluloses from the starting
material, and possibly to catalyze some hydrolysis. In some
embodiments, the acid is a sulfur-containing acid (e.g., sulfur
dioxide). In some embodiments, the acid is acetic acid, which may
be recovered from the digested stream (i.e., from downstream
operations).
[0133] The starting feedstock may include sucrose, such as in the
case of energy cane. A majority of the sucrose may be recovered as
part of the fermentable sugars.
[0134] The process may include cleaning the starting feedstock, by
wet or dry cleaning. The process may include size reduction,
hot-water soaking, dewatering, steaming, or other operations,
upstream of the digestor.
[0135] The process may further include removal of one or more
fermentation inhibitors (such as acetic acid or furfural) by
stripping. This stripping may be conducted following step (e), i.e.
treating the hydrolyzed cellulose stream, prior to fermentation.
Alternatively, or additionally, the stripping may be conducted on a
stream following digestion, such as in the blow line, or as part of
an acetic acid recycle system.
[0136] The process may further include a step of fermenting the
fermentable sugars to a fermentation product. Typically the process
will further include concentration and purification of the
fermentation product. The fermentation product may be selected from
ethanol, n-butanol, 1,4-butanediol, succinic acid, lactic acid, or
combinations thereof, for example. The lignin may be combusted for
energy production, for example.
[0137] Some variations provide a process for producing fermentable
sugars from cellulosic biomass, the process comprising:
[0138] (a) providing a feedstock comprising cellulosic biomass;
[0139] (b) digesting the feedstock with a reaction solution
including steam and/or hot water in a digestor under effective
reaction conditions to produce a digested stream containing
cellulose-rich solids, hemicellulose oligomers, and lignin;
[0140] (c) conveying the digested stream through a mechanical
refiner, thereby generating a refined stream with reduced average
particle size of the cellulose-rich solids;
[0141] (d) separating a vapor from the refined stream;
[0142] (e) introducing the refined stream to an acid hydrolysis
unit under effective hydrolysis conditions to produce sugars from
the cellulose-rich solids and optionally from the hemicellulose
oligomers;
[0143] (f) recovering or further processing at least some of the
sugars as fermentable sugars.
[0144] Certain embodiments provide a process for producing ethanol
from cellulosic biomass, the process comprising:
[0145] (a) providing a feedstock comprising cellulosic biomass;
[0146] (b) digesting the feedstock with a reaction solution
including steam and/or hot water in a digestor under effective
reaction conditions to produce a digested stream containing
cellulose-rich solids, hemicellulose oligomers, and lignin;
[0147] (c) conveying the digested stream through a blow-line
refiner, thereby generating a refined stream with reduced average
particle size of the cellulose-rich solids;
[0148] (d) separating a vapor from the refined stream;
[0149] (e) introducing the refined stream to an enzymatic
hydrolysis unit under effective hydrolysis conditions to produce
sugars from the cellulose-rich solids and from the hemicellulose
oligomers;
[0150] (f) fermenting the sugars to produce ethanol in dilute
solution; and
[0151] (g) concentrating the dilute solution to produce an ethanol
product.
[0152] In some embodiments, the extraction solution comprises steam
in saturated, superheated, or supersaturated form. In some
embodiments, the extraction solution comprises hot water. Additives
may be present, such as acid or base catalysts, or other compounds
present in recycled streams. The fraction of starting hemicellulose
that is extracted into solution may be from about 60% to about 95%,
such as about 75%, 80%, 85%, or 90%.
[0153] In some embodiments, the process includes washing the
cellulose-rich solids using an aqueous wash solution, to produce a
wash filtrate; and optionally combining at least some of the wash
filtrate with the extract liquor. In some of these embodiments, the
process further includes pressing the cellulose-rich solids to
produce the washed cellulose-rich solids and a press filtrate; and
optionally combining at least some of the press filtrate with the
extract liquor.
[0154] The process may include countercurrent washing, such as in
two, three, four, or more washing stages. The separation/washing
may be combined with the application of enzymes, in various
ways.
[0155] In some embodiments, a refiner is configured to cause at
least some liquefaction as a result of enzymatic action on the
cellulose-rich solids. "Liquefaction" means partial hydrolysis of
cellulose to form glucose oligomers (i.e. glucan) that dissolve
into solution, but not total hydrolysis of cellulose to glucose
monomers (saccharification). Various fractions of cellulose may be
hydrolyzed during liquefaction. In some embodiments, the fraction
of cellulose hydrolyzed may be from about 5% to about 90%, such as
about 10% to about 75% (e.g. about 15%, 20%, 25%, 30%, 35%, 40%,
45%, 50%, 55%, 60%, 65%, or 70%). In certain embodiments, there is
no separate liquefaction tank or reactor; liquefaction and
hydrolysis occur in the same vessel (e.g., refiner or hydrolysis
reactor).
[0156] A "liquefaction-focused blend of enzymes" means a mixture of
enzymes that includes at least one enzyme capable of hydrolyzing
cellulose to form soluble oligomers. In some embodiments, a
liquefaction-focused blend of enzymes includes both endoglucanases
and exoglucanases. Endoglucanases are cellulases that attack
low-crystallinity regions in the cellulose fibers by endoaction,
creating free chain-ends. Exoglucanases or cellobiohydrolases are
cellulases that hydrolyze the 1,4-glycocidyl linkages in
cellobiose.
[0157] Various cellulase enzymes may be utilized in the
liquefaction-focused blend of enzymes, such as one or more enzymes
recited in Verardi et al., "Hydrolysis of Lignocellulosic Biomass:
Current Status of Processes and Technologies and Future
Perspectives," Bioethanol, Prof. Marco Aurelio Pinheiro Lima (Ed.),
ISBN: 978-953-51-0008-9, InTech (2012), which is hereby
incorporated by reference.
[0158] Some embodiments employ thermotolerant enzymes obtained from
thermophilic microrganisms. The thermophilic microrganisms can be
grouped in thermophiles (growth up to 60.degree. C.), extreme
thermophiles (65-80.degree. C.) and hyperthermophiles
(85-110.degree. C.). The unique stability of the enzymes produced
by these microrganisms at elevated temperatures, extreme pH and
high pressure (up to 1000 bar) makes them valuable for processes at
harsh conditions. Also, thermophilic enzymes have an increased
resistance to many denaturing conditions such as the use of
detergents which can be an efficient means to obviate the
irreversible adsorption of cellulases on the substrates.
Furthermore, the utilization of high operation temperatures, which
cause a decrease in viscosity and an increase in the diffusion
coefficients of substrates, have a significant influence on the
cellulose solubilization. It is worth noting that most thermophilic
cellulases do not show inhibition at high level of reaction
products (e.g. cellobiose and glucose). As consequence, higher
reaction rates and higher process yields are expected. The high
process temperature also reduces contamination. See Table 6,
"Thermostable cellulases" in Verardi et al., cited previously, for
exemplary thermotolerant enzymes that may be used in the
liquefaction-focused blend of enzymes.
[0159] In some embodiments, an enzyme is selected such that at a
high temperature, the enzyme is able to catalyze liquefaction
(partial hydrolysis) but not saccharification (total hydrolysis).
When the temperature is reduced, the same enzyme is able to
catalyze saccharification to produce glucose.
[0160] When the hydrolysis process employs enzymes, these enzymes
will typically contain cellulases and hemicellulases. The
cellulases here may include .beta.-glucosidases that convert
cellooligosaccharides and disaccharide cellobiose into glucose.
There are a number of enzymes that can attack hemicelluloses, such
as glucoronide, acetylesterase, xylanase, .beta.-xylosidase,
galactomannase and glucomannase. Exemplary acid catalysts include
sulfuric acid, sulfur dioxide, hydrochloric acid, phosphoric acid,
and nitric acid.
[0161] In some embodiments, non-acid and non-enzyme catalysts may
be employed for co-hydrolyzing the glucose oligomers and the
hemicellulose oligomers. For example, base catalysts, solid
catalysts, ionic liquids, or other effective materials may be
employed.
[0162] The process further comprises a step of fermenting the
fermentable sugars to a fermentation product (such as ethanol), in
some embodiments.
[0163] Other variations provide a process for producing fermentable
sugars from cellulosic biomass, the process comprising:
[0164] (a) providing a feedstock comprising cellulosic biomass;
[0165] (b) extracting the feedstock with steam and/or hot water
under effective extraction conditions to produce an extract liquor
containing hemicellulose oligomers, dissolved lignin, and
cellulose-rich solids;
[0166] (c) separating at least a portion of the cellulose-rich
solids from the extract liquor, to produce washed cellulose-rich
solids;
[0167] (d) removing a portion of glucan contained in the washed
cellulose-rich solids by contacting the washed cellulose-rich
solids with a liquefaction-focused blend of enzymes, to release
glucose oligomers;
[0168] (e) hydrolyzing the glucose oligomers with a first
hydrolysis catalyst, to produce glucose;
[0169] (f) hydrolyzing the hemicellulose oligomers with a second
hydrolysis catalyst, to produce hemicellulose monomers; and
[0170] (g) recovering the glucose and hemicellulose monomers,
individually or in combination, as fermentable sugars.
[0171] In some embodiments, the first hydrolysis catalyst includes
cellulases. In some embodiments, the second hydrolysis catalyst
includes hemicellulases. In other embodiments, the first hydrolysis
catalyst and the second hydrolysis catalyst are acid catalysts,
base catalysts, ionic liquids, solid catalysts, or other effective
materials. The first hydrolysis catalyst may be the same as, or
different than, the second hydrolysis catalyst.
[0172] In some embodiments, the glucose is recovered in a separate
stream from the hemicellulose monomers. In other embodiments, the
glucose and the hemicellulose monomers are recovered in the same
stream. The process may include fermentation of the glucose and/or
the fermentable hemicellulose sugars to a fermentation product.
[0173] The biomass feedstock may be selected from hardwoods,
softwoods, forest residues, agricultural residues (such as
sugarcane bagasse), industrial wastes, consumer wastes, or
combinations thereof. In any of these processes, the feedstock may
include sucrose. In some embodiments with sucrose present in the
feedstock, a majority of the sucrose is recovered as part of the
fermentable sugars. In order to preserve sucrose (when present), it
is preferred to utilize enzymes rather than acid catalysts for
cellulose hydrolysis.
[0174] In some embodiments, the process starts as biomass is
received or reduced to approximately 1/4'' thickness. In a first
step of the process, the biomass is fed (e.g., from a bin) to a
pressurized extraction vessel operating continuously or in batch
mode. The biomass may first be steamed or water-washed to remove
dirt and entrained air. The biomass may be immersed with aqueous
liquor or saturated vapor and heated to a temperature between about
100.degree. C. to about 250.degree. C., for example 150.degree. C.,
160.degree. C., 170.degree. C., 180.degree. C., 190.degree. C.,
200.degree. C., or 210.degree. C. Preferably, the biomass is heated
to about 180.degree. C. to 210.degree. C.
[0175] The pressure in the pressurized vessel may be adjusted to
maintain the aqueous liquor as a liquid, a vapor, or a combination
thereof. Exemplary pressures are about 1 atm to about 30 atm, such
as about 3 atm, 5 atm, 10 atm, or 15 atm.
[0176] The solid-phase residence time for the digestor (pressurized
extraction vessel) may vary from about 2 minutes to about 4 hours,
such as about 5 minutes to about 1 hour. In certain embodiments,
the digestor residence time is controlled to be about 5 to 15
minutes, such as 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or 15 minutes.
The liquid-phase residence time for the digestor may vary from
about 2 minutes to about 4 hours, such as about 5 minutes to about
1 hour. The vapor-phase residence time for the digestor may vary
from about 1 minute to about 2 hours, for example, such as about 3
minutes to about 30 minutes. The solid-phase, liquid-phase, and
vapor-phase residence times may all be about the same, or they may
be independently controlled according to reactor-engineering
principles (e.g., recycling and internal recirculation
strategies).
[0177] The aqueous liquor may contain acidifying compounds, such as
(but not limited to) sulfuric acid, sulfurous acid, sulfur dioxide,
acetic acid, formic acid, or oxalic acid, or combinations thereof.
The dilute acid concentration can range from 0.01% to 10% as
necessary to improve solubility of particular minerals, such as
potassium, sodium, or silica. Preferably, the acid concentration is
selected from about 0.01% to 4%, such as 0.1%, 0.5%, 1%, 1.5%, 2%,
2.5%, 3%, or 3.5%.
[0178] A second step may include depressurization of the extracted
chips into a blow tank or other tank or unit. The vapor can be used
for heating the incoming woodchips or cooking liquor, directly or
indirectly. The volatilized organic acids (e.g., acetic acid),
which are generated or included in the cooking step, may be
recycled back to the cooking.
[0179] A third step may include mechanically refining the extracted
chips. This step (using, for example, a blow-line refiner) may be
done before or after depressurization. Optionally, refined solids
may be washed. The washing may be accomplished with water, recycled
condensates, recycled permeate, or combination thereof. Washing
typically removes most of the dissolved material, including
hemicelluloses and minerals. The final consistency of the dewatered
cellulose-rich solids may be increased to 30% or more, preferably
to 50% or more, using a mechanical pressing device. The mechanical
pressing device may be integrated with the mechanical refiner, to
accomplish combined refining and washing.
[0180] A fourth step may include hydrolyzing the extracted chips
with enzymes to convert some of the cellulose to glucose. When
enzymes are employed for the cellulose hydrolysis, the enzymes
preferably include cellulase enzymes. Enzymes may be introduced to
the extracted chips along with water, recycled condensates,
recycled permeate, additives to adjust pH, additives to enhance
hydrolysis (such as lignosulfonates), or combinations thereof.
[0181] Some or all of the enzymes may be added to the blow line
before or at the blow-line refiner, for example, to assist in
enzyme contact with fibers. In some embodiments, at least a portion
of enzymes are recycled in a batch or continuous process.
[0182] When an acid is employed for the cellulose hydrolysis, the
acid may be selected from sulfuric acid, sulfurous acid, sulfur
dioxide, formic acid, acetic acid, oxalic acid, or combinations
thereof. Acids may be added to the extracted chips before or after
mechanical refining. In some embodiments, dilute acidic conditions
are used at temperatures between about 100.degree. C. and
190.degree. C., for example about 120.degree. C., 130.degree. C.,
140.degree. C., 150.degree. C., 160.degree. C., or 170.degree. C.,
and preferably from 120.degree. C. to 150.degree. C. In some
embodiments, at least a portion of the acid is recycled in a batch
or continuous process.
[0183] The acid may be selected from sulfuric acid, sulfurous acid,
or sulfur dioxide. Alternatively, or additionally, the acid may
include formic acid, acetic acid, or oxalic acid from the cooking
liquor or recycled from previous hydrolysis.
[0184] A fifth step may include conditioning of hydrolysate to
remove some or most of the volatile acids and other fermentation
inhibitors. The evaporation may include flashing or stripping to
remove sulfur dioxide, if present, prior to removal of volatile
acids. The evaporation step is preferably performed below the
acetic acid dissociation pH of 4.8, and most preferably a pH
selected from about 1 to about 2.5. In some embodiments, additional
evaporation steps may be employed. These additional evaporation
steps may be conducted at different conditions (e.g., temperature,
pressure, and pH) relative to the first evaporation step.
[0185] In some embodiments, some or all of the organic acids
evaporated may be recycled, as vapor or condensate, to the first
step (cooking step) to assist in the removal of hemicelluloses or
minerals from the biomass. This recycle of organic acids, such as
acetic acid, may be optimized along with process conditions that
may vary depending on the amount recycled, to improve the cooking
effectiveness.
[0186] A sixth step may include recovering fermentable sugars,
which may be stored, transported, or processed. A sixth step may
include fermenting the fermentable sugars to a product, as further
discussed below.
[0187] A seventh step may include preparing the solid residuals
(containing lignin) for combustion. This step may include refining,
milling, fluidizing, compacting, and/or pelletizing the dried,
extracted biomass. The solid residuals may be fed to a boiler in
the form of fine powder, loose fiber, pellets, briquettes,
extrudates, or any other suitable form. Using known equipment,
solid residuals may be extruded through a pressurized chamber to
form uniformly sized pellets or briquettes.
[0188] Some embodiments of the invention enable processing of
"agricultural residues," which for present purposes is meant to
include lignocellulosic biomass associated with food crops, annual
grasses, energy crops, or other annually renewable feedstocks.
Exemplary agricultural residues include, but are not limited to,
corn stover, corn fiber, wheat straw, sugarcane bagasse, rice
straw, oat straw, barley straw, miscanthus, energy cane, or
combinations thereof. In certain embodiments, the agricultural
residue is sugarcane bagasse.
[0189] In some embodiments, the fermentable sugars are recovered
from solution, in purified form. In some embodiments, the
fermentable sugars are fermented to produce of biochemicals or
biofuels such as (but by no means limited to) ethanol, 1-butanol,
isobutanol, acetic acid, lactic acid, or any other fermentation
products. A purified fermentation product may be produced by
distilling the fermentation product, which will also generate a
distillation bottoms stream containing residual solids. A bottoms
evaporation stage may be used, to produce residual solids.
[0190] Following fermentation, residual solids (such as
distillation bottoms) may be recovered, or burned in solid or
slurry form, or recycled to be combined into the biomass pellets.
Use of the fermentation residual solids may require further removal
of minerals. Generally, any leftover solids may be used for
burning, after concentration of the distillation bottoms.
[0191] Alternatively, or additionally, the process may include
recovering the residual solids as a fermentation co-product in
solid, liquid, or slurry form. The fermentation co-product may be
used as a fertilizer or fertilizer component, since it will
typically be rich in potassium, nitrogen, and/or phosphorous.
[0192] In certain embodiments, the process further comprises
combining, at a pH of about 4.8 to 10 or higher, a portion of
vaporized acetic acid with an alkali oxide, alkali hydroxide,
alkali carbonate, and/or alkali bicarbonate, wherein the alkali is
selected from the group consisting of potassium, sodium, magnesium,
calcium, and combinations thereof, to convert the portion of the
vaporized acetic acid to an alkaline acetate. The alkaline acetate
may be recovered. If desired, purified acetic acid may be generated
from the alkaline acetate.
[0193] In some variations, the invention provides a process for
separating fermentation inhibitors from a biomass-derived
hydrolysate, the process comprising:
[0194] (a) providing a biomass-derived liquid hydrolysate stream
comprising a fermentation inhibitor;
[0195] (b) introducing the liquid hydrolysate stream to a stripping
column;
[0196] (c) introducing a steam-rich vapor stream to the stripping
column to strip at least a portion of the fermentation inhibitor
from the liquid hydrolysate stream;
[0197] (d) recovering, from the stripping column, a stripped liquid
stream and a stripper vapor output stream, wherein the stripped
liquid stream has lower fermentation inhibitor concentration than
the liquid hydrolysate stream;
[0198] (e) compressing the stripper vapor output stream to generate
a compressed vapor stream;
[0199] (f) introducing the compressed vapor stream, and a
water-rich liquid stream, to an evaporator;
[0200] (g) recovering, from the evaporator, an evaporated liquid
stream and an evaporator output vapor stream; and
[0201] (h) recycling at least a portion of the evaporator output
vapor stream to the stripping column as the steam-rich vapor
stream, or a portion thereof.
[0202] The biomass-derived hydrolysate may be the product of acidic
or enzymatic hydrolysis, or it may be the extracted solution from
the digestor, for example. In some embodiments, the fermentation
inhibitor is selected from the group consisting of acetic acid,
formic acid, formaldehyde, acetaldehyde, lactic acid, furfural,
5-hydroxymethylfurfural, furans, uronic acids, phenolic compounds,
sulfur-containing compounds, and combinations or derivatives
thereof.
[0203] In certain embodiments, the fermentation inhibitor is acetic
acid. The stripped liquid stream preferably has less than 10 g/L
acetic acid concentration, such as less than 5 g/L acetic acid
concentration.
[0204] In some embodiments, the water-rich liquid stream contains
biomass solids that are concentrated in the evaporator. These
biomass solids may be derived from the same biomass feedstock as is
the biomass-derived liquid hydrolysate, in an integrated
process.
[0205] Optionally, the fermentation inhibitor is recycled to a
previous unit operation (e.g., digestor or reactor) for generating
the biomass-derived liquid hydrolysate stream, to assist with
hydrolysis or pretreatment of a biomass feedstock or component
thereof. For example, acetic acid may be recycled for this purpose,
to aid in removal of hemicelluloses from biomass and/or in oligomer
hydrolysis to monomer sugars.
[0206] Some variations provide a process for separating
fermentation inhibitors from a biomass-derived hydrolysate, the
process comprising:
[0207] (a) providing a biomass-derived liquid hydrolysate stream
comprising a fermentation inhibitor;
[0208] (b) introducing the liquid hydrolysate stream to a stripping
column;
[0209] (c) introducing a steam-rich vapor stream to the stripping
column to strip at least a portion of the fermentation inhibitor
from the liquid hydrolysate stream;
[0210] (d) recovering, from the stripping column, a stripped liquid
stream and a stripper vapor output stream, wherein the stripped
liquid stream has lower fermentation inhibitor concentration than
the liquid hydrolysate stream;
[0211] (e) introducing the stripper vapor output stream, and a
water-rich liquid stream, to an evaporator;
[0212] (f) recovering, from the evaporator, an evaporated liquid
stream and an evaporator output vapor stream;
[0213] (g) compressing the evaporator output vapor stream to
generate a compressed vapor stream; and
[0214] (h) recycling at least a portion of the compressed vapor
stream to the stripping column as the steam-rich vapor stream, or a
portion thereof.
[0215] In some embodiments, the evaporator is a boiler, the
water-rich liquid stream comprises boiler feed water, and the
evaporated liquid stream comprises boiler condensate.
[0216] The process may be continuous, semi-continuous, or batch.
When continuous or semi-continuous, the stripping column may be
operated countercurrently, cocurrently, or a combination
thereof.
[0217] In certain variations of the present invention, a process
for separating and recovering a fermentation inhibitor from a
biomass-derived hydrolysate comprises:
[0218] (a) providing a biomass-derived liquid hydrolysate stream
comprising a fermentation inhibitor;
[0219] (b) introducing the liquid hydrolysate stream to a stripping
column;
[0220] (c) introducing a steam-rich vapor stream to the stripping
column to strip at least a portion of the fermentation inhibitor
from the liquid hydrolysate stream;
[0221] (d) recovering, from the stripping column, a stripped liquid
stream and a stripper vapor output stream, wherein the stripped
liquid stream has lower fermentation inhibitor concentration than
the liquid hydrolysate stream;
[0222] (e) introducing the stripper vapor output stream, and a
water-rich liquid stream, to a rectification column;
[0223] (f) recovering, from the rectification column, a rectified
liquid stream and a rectification column vapor stream, wherein the
rectified liquid stream has higher fermentation inhibitor
concentration than the liquid hydrolysate stream; and
[0224] (g) recycling at least a portion of the rectification column
vapor stream to the stripping column as the steam-rich vapor
stream, or a portion thereof.
[0225] The fermentation inhibitor may be selected from the group
consisting of acetic acid, formic acid, formaldehyde, acetaldehyde,
lactic acid, furfural, 5-hydroxymethylfurfural, furans, uronic
acids, phenolic compounds, sulfur-containing compounds, and
combinations or derivatives thereof. In some embodiments, the
fermentation inhibitor comprises or consists essentially of acetic
acid.
[0226] In the case of acetic acid, the stripped liquid stream
preferably has less than 10 g/L acetic acid concentration, such as
less than 5 g/L acetic acid concentration. The rectification column
vapor stream preferably has less than 0.5 g/L acetic acid
concentration, such as less than 0.1 g/L acetic acid concentration.
The rectified liquid stream preferably has at least 25 g/L acetic
acid concentration, such as about 40 g/L or more acetic acid. In
some embodiments, the rectified liquid stream has at least 10 times
higher concentration of acetic acid compared to the stripped liquid
stream. In certain embodiments, the process further comprises
recovering the acetic acid contained in the rectified liquid stream
using liquid-vapor extraction or liquid-liquid extraction.
[0227] In some embodiments, the water-rich liquid stream includes
evaporator condensate. The evaporator condensate may be derived
from an evaporator in which biomass solids are concentrated, and
the biomass solids may be derived from the same biomass feedstock
as the biomass-derived liquid hydrolysate, in an integrated
process.
[0228] Optionally, the fermentation inhibitor (e.g., acetic acid)
is recycled to a previous unit operation for generating the
biomass-derived liquid hydrolysate stream, to assist with
hydrolysis or pretreatment of a biomass feedstock or component
thereof.
[0229] The process may be continuous, semi-continuous, or batch.
When continuous or semi-continuous, the stripping column may be
operated countercurrently, cocurrently, or a combination thereof.
The rectification column may be operated continuous,
semi-continuous, or batch.
[0230] In various embodiments, step (g) comprises compressing
and/or conveying the rectification column vapor stream using a
device selected from the group consisting of a mechanical
centrifugal vapor compressor, a mechanical axial vapor compressor,
a thermocompressor, an ejector, a diffusion pump, a turbomolecular
pump, and combinations thereof.
[0231] If desired, a base or other additive may be included in the
water-rich liquid stream, or separately introduced to the
rectification column, to produce salts or other reaction products
derived from fermentation inhibitors. In some embodiments, the
water-rich liquid stream includes one or more additives capable of
reacting with the fermentation inhibitor. In certain embodiments,
the fermentation inhibitor includes acetic acid, and the one or
more additives include a base. An acetate salt may then be
generated within the rectification column, or in a unit coupled to
the rectification column. Optionally, the acetate salt may be
separated and recovered using liquid-vapor extraction or
liquid-liquid extraction.
[0232] This patent application hereby incorporates by reference
herein the following commonly owned patents: "PROCESS FOR OBTAINING
BIOCHEMICALS IN A ZERO LIQUID DISCHARGE PLANT," U.S. Pat. No.
8,211,680; "PROCESS FOR PRODUCING HEMICELLULOSE SUGARS AND ENERGY
FROM BIOMASS," U.S. Pat. No. 8,518,672; "PROCESS FOR PRODUCING
ALCOHOL AND OTHER BIOPRODUCTS FROM BIOMASS EXTRACTS IN A KRAFT PULP
MILL," U.S. Pat. No. 8,518,213; "DEICER COMPOSITIONS AND PROCESSES
FOR MAKING DEICERS," U.S. Pat. No. 8,679,364; "CORROSION-INHIBITING
DEICERS DERIVED FROM BIOMASS," U.S. Pat. No. 8,845,923; "PROCESSES
FOR PRODUCING FERMENTABLE SUGARS AND LOW-ASH BIOMASS FOR COMBUSTION
OR PELLETS," U.S. Pat. No. 8,685,685; "PROCESS FOR OBTAINING
BIOCHEMICALS IN A ZERO LIQUID DISCHARGE PLANT," U.S. Pat. No.
8,785,155; "PROCESSES FOR PRODUCING FERMENTABLE SUGARS AND
ENERGY-DENSE BIOMASS FOR COMBUSTION," U.S. Pat. No. 8,906,657;
"STEPWISE ENZYMATIC HYDROLYSIS PROCESS FOR CONVERTING CELLULOSE TO
GLUCOSE," U.S. Pat. No. 9,139,857; and "PROCESSES FOR PRODUCING
CELLULOSE PULP, SUGARS, AND CO-PRODUCTS FROM LIGNOCELLULOSIC
BIOMASS," U.S. Pat. No. 9,347,176.
[0233] In this detailed description, reference has been made to
multiple embodiments of the invention and non-limiting examples
relating to how the invention can be understood and practiced.
Other embodiments that do not provide all of the features and
advantages set forth herein may be utilized, without departing from
the spirit and scope of the present invention. This invention
incorporates routine experimentation and optimization of the
methods and systems described herein. Such modifications and
variations are considered to be within the scope of the invention
defined by the claims.
[0234] All publications, patents, and patent applications cited in
this specification are herein incorporated by reference in their
entirety as if each publication, patent, or patent application were
specifically and individually put forth herein.
[0235] Where methods and steps described above indicate certain
events occurring in certain order, those of ordinary skill in the
art will recognize that the ordering of certain steps may be
modified and that such modifications are in accordance with the
variations of the invention. Additionally, certain of the steps may
be performed concurrently in a parallel process when possible, as
well as performed sequentially.
[0236] Therefore, to the extent there are variations of the
invention, which are within the spirit of the disclosure or
equivalent to the inventions found in the appended claims, it is
the intent that this patent will cover those variations as well.
The present invention shall only be limited by what is claimed.
* * * * *