U.S. patent application number 14/546146 was filed with the patent office on 2015-05-21 for methods of washing cellulose-rich solids from biomass fractionation to reduce lignin and ash content.
The applicant listed for this patent is API Intellectual Property Holdings, LLC. Invention is credited to Zheng DANG, Vesa PYLKKANEN, Mehmet Sefik TUNC, Ziyu WANG.
Application Number | 20150136345 14/546146 |
Document ID | / |
Family ID | 53172101 |
Filed Date | 2015-05-21 |
United States Patent
Application |
20150136345 |
Kind Code |
A1 |
TUNC; Mehmet Sefik ; et
al. |
May 21, 2015 |
METHODS OF WASHING CELLULOSE-RICH SOLIDS FROM BIOMASS FRACTIONATION
TO REDUCE LIGNIN AND ASH CONTENT
Abstract
The present invention provides a process for fractionating
lignocellulosic biomass, comprising: digesting a biomass feedstock
in the presence of a solvent for lignin, an acid, and water, to
produce cellulose-rich solids; separating and washing the
cellulose-rich solids with a wash solvent; washing the
cellulose-rich solids with water, to generate washed cellulose-rich
solids and a wash liquor comprising fines, wherein the wash liquor
is introduced to or in contact with a classifier to remove the
fines; and separating the fines and recycling the remaining water.
The classifier may include a screen with mesh size in the range of
10 to 500, such as 200. The washed cellulose-rich solids will
typically have a lower Kappa number (lignin content) and ash
content compared to cellulose-rich solids from a process without a
classifier that removes fines.
Inventors: |
TUNC; Mehmet Sefik;
(Thomaston, GA) ; DANG; Zheng; (Lilburn, GA)
; WANG; Ziyu; (Newnan, GA) ; PYLKKANEN; Vesa;
(Atlanta, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
API Intellectual Property Holdings, LLC |
Atlanta |
GA |
US |
|
|
Family ID: |
53172101 |
Appl. No.: |
14/546146 |
Filed: |
November 18, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61905938 |
Nov 19, 2013 |
|
|
|
Current U.S.
Class: |
162/16 ;
162/14 |
Current CPC
Class: |
D21C 3/04 20130101; Y02P
40/44 20151101; D21C 3/20 20130101; D21C 11/0007 20130101; Y02P
40/40 20151101; D21C 9/02 20130101 |
Class at
Publication: |
162/16 ;
162/14 |
International
Class: |
D21C 11/00 20060101
D21C011/00; D21C 9/02 20060101 D21C009/02 |
Claims
1. A process for fractionating lignocellulosic biomass, said
process comprising: (a) digesting a lignocellulosic biomass
feedstock under effective conditions in the presence of a solvent
for lignin, an acid or acid precursor, and water, to produce
cellulose-rich solids in a digestor liquor; (b) separating said
cellulose-rich solids from said digestor liquor and washing said
cellulose-rich solids with a first wash liquid comprising a wash
solvent for lignin, to generate first washed cellulose-rich solids;
(c) washing said first washed cellulose-rich solids with a second
wash liquid comprising water, to generate second washed
cellulose-rich solids and a wash liquor comprising fines, wherein
said wash liquor is introduced to or in contact with a classifier
to remove at least a portion of said fines in a liquid
fines-containing stream; (d) recovering said second washed
cellulose-rich solids; and (e) optionally separating said fines
from said fines-containing stream and recycling water contained in
said fines-containing stream back to step (c).
2. The process of claim 1, wherein said lignocellulosic biomass
feedstock is a hardwood.
3. The process of claim 1, wherein said lignocellulosic biomass
feedstock is an annual plant or agricultural residue.
4. The process of claim 1, wherein said solvent for lignin is
ethanol.
5. The process of claim 1, wherein said solvent for lignin is the
same as said wash solvent for lignin.
6. The process of claim 1, wherein said acid or acid precursor is
sulfur dioxide.
7. The process of claim 1, wherein said classifier comprises a
screen with mesh size in the range of 10 to 500.
8. The process of claim 7, wherein said classifier comprises a
screen with mesh size in the range of 150 to 250.
9. The process of claim 1, wherein during step (b) and/or step (c),
a disperser is utilized to liberate said fines from said second
washed cellulose-rich solids.
10. The process of claim 1, wherein during step (c), at least 95%
of said fines contained in said wash liquor are removed into said
liquid fines-containing stream.
11. The process of claim 1, wherein during step (b) and/or step
(c), one or more additives are introduced to remove minerals
remaining in said first washed cellulose-rich solids and/or said
second washed cellulose-rich solids.
12. The process of claim 1, wherein said second washed
cellulose-rich solids have a lower Kappa number compared to
cellulose-rich solids from an otherwise-identical process without a
classifier to remove at least a portion of said fines.
13. The process of claim 1, wherein said second washed
cellulose-rich solids have a lower ash content compared to
cellulose-rich solids from an otherwise-identical process without a
classifier to remove at least a portion of said fines.
14. The process of claim 1, wherein said second washed
cellulose-rich solids have a lower hemicellulose content compared
to cellulose-rich solids from an otherwise-identical process
without a classifier to remove at least a portion of said
fines.
15. The process of claim 1, wherein said second washed
cellulose-rich solids contain about 75% or more cellulose, about 7
wt % or less lignin, about 5 wt % or less hemicellulose, and about
10 wt % or less ash.
16. The process of claim 15, wherein said second washed
cellulose-rich solids contain about 80% or more cellulose, about 3
wt % or less lignin, about 5 wt % or less hemicellulose, and about
8 wt % or less ash.
17. The process claim 1, wherein steps (a)-(c) are conducted
countercurrently.
18. The process of claim 1, wherein said process is batch or
semi-continuous, wherein step (b) and/or step (c) is conducted in
simulated countercurrent fashion, and wherein multiple wash streams
are generated.
19. A method of separating fines from cellulose-rich solids, said
method comprising: (a) obtaining a biomass digestor liquor
comprising cellulose-rich solids; (b) separating said
cellulose-rich solids from said digestor liquor and washing said
cellulose-rich solids with a first wash liquid, to generate first
washed cellulose-rich solids; (c) washing said first washed
cellulose-rich solids with a second wash liquid, to generate second
washed cellulose-rich solids and a wash liquor comprising fines,
wherein said wash liquor is introduced to or in contact with a
classifier to remove at least a portion of said fines in a liquid
fines-containing stream; (d) recovering said second washed
cellulose-rich solids; and (e) optionally separating said fines
from said fines-containing stream and recycling water contained in
said fines-containing stream back to step (c).
20. A method of separating fines from cellulose-rich solids, said
method comprising: (a) obtaining a biomass digestor liquor
comprising cellulose-rich solids; (b) separating said
cellulose-rich solids from said digestor liquor and washing said
cellulose-rich solids with a wash liquid, to generate washed
cellulose-rich solids and a wash liquor comprising fines, wherein
said wash liquor is introduced to or in contact with a classifier
to remove at least a portion of said fines in a liquid
fines-containing stream; (c) recovering said second washed
cellulose-rich solids; and (d) optionally separating said fines
from said fines-containing stream and recycling water contained in
said fines-containing stream back to step (b).
Description
PRIORITY DATA
[0001] This patent application is a non-provisional application
claiming priority to U.S. Provisional Patent App. No. 61/905,938,
filed Nov. 19, 2013, which is hereby incorporated by reference
herein.
FIELD
[0002] The present invention generally relates to fractionation
processes for converting biomass into fermentable sugars,
cellulose, and lignin, and for processes and apparatus to recover
the lignin.
BACKGROUND
[0003] Biomass refining (or biorefining) is becoming more prevalent
in industry. Cellulose fibers and sugars, hemicellulose sugars,
lignin, syngas, and derivatives of these intermediates are being
used by many companies for chemical and fuel production. Indeed, we
now are observing the commercialization of integrated biorefineries
that are capable of processing incoming biomass much the same as
petroleum refineries now process crude oil. Underutilized
lignocellulosic biomass feedstocks have the potential to be much
cheaper than petroleum, on a carbon basis, as well as much better
from an environmental life-cycle standpoint.
[0004] Lignocellulosic biomass is the most abundant renewable
material on the planet and has long been recognized as a potential
feedstock for producing chemicals, fuels, and materials.
Lignocellulosic biomass normally comprises primarily cellulose,
hemicellulose, and lignin. Cellulose and hemicellulose are natural
polymers of sugars, and lignin is an aromatic/aliphatic hydrocarbon
polymer reinforcing the entire biomass network. Some forms of
biomass (e.g., recycled materials) do not contain
hemicellulose.
[0005] There are many reasons why it would be beneficial to process
biomass in a way that effectively separates the major fractions
(cellulose, hemicellulose, and lignin) from each other. Cellulose
from biomass can be used in industrial cellulose applications
directly, such as to make paper or other pulp-derived products. The
cellulose can also be subjected to further processing to either
modify the cellulose in some way or convert it into glucose.
Hemicellulose sugars can be fermented to a variety of products,
such as ethanol, or converted to other chemicals. Lignin from
biomass has value as a solid fuel and also as an energy feedstock
to produce liquid fuels, synthesis gas, or hydrogen; and as an
intermediate to make a variety of polymeric compounds.
Additionally, minor components such as proteins or rare sugars can
be extracted and purified for specialty applications.
[0006] In light of this objective, a major shortcoming of previous
process technologies is that one or two of the major components can
be economically recovered in high yields, but not all three. Either
the third component is sacrificially degraded in an effort to
produce the other two components, or incomplete fractionation is
accomplished. An important example is traditional biomass pulping
(to produce paper and related goods). Cellulose is recovered in
high yields, but lignin is primarily consumed by oxidation and
hemicellulose sugars are mostly degraded. Approximately half of the
starting biomass is essentially wasted in this manufacturing
process. State-of-the-art biomass-pretreatment approaches typically
can produce high yields of hemicellulose sugars but suffer from
moderate cellulose and lignin yields.
[0007] There are several possible pathways to convert biomass into
intermediates. One thermochemical pathway converts the feedstock
into syngas (CO and H.sub.2) through gasification or partial
oxidation. Another thermochemical pathway converts biomass into
liquid bio-oils through pyrolysis and separation. These are both
high-temperature processes that intentionally destroy sugars in
biomass.
[0008] Sugars (e.g., glucose and xylose) are desirable platform
molecules because they can be fermented to a wide variety of fuels
and chemicals, used to grow organisms or produce enzymes, converted
catalytically to chemicals, or recovered and sold to the market. To
recover sugars from biomass, the cellulose and/or the hemicellulose
in the biomass must be hydrolyzed into sugars. This is a difficult
task because lignin and hemicelluloses are bound to each other by
covalent bonds, and the three components are arranged inside the
fiber wall in a complex manner. This recalcitrance explains the
natural resistance of woody biomass to decomposition, and explains
the difficulty to convert biomass to sugars at high yields.
[0009] Fractionation of biomass into its principle components
(cellulose, hemicellulose, and lignin) has several advantages.
Fractionation of lignocellulosics leads to release of cellulosic
fibers and opens the cell wall structure by dissolution of lignin
and hemicellulose between the cellulose microfibrils. The fibers
become more accessible for hydrolysis by enzymes. When the sugars
in lignocellulosics are used as feedstock for fermentation, the
process to open up the cell wall structure is often called
"pretreatment." Pretreatment can significantly impact the
production cost of lignocellulosic ethanol.
[0010] One of the most challenging technical obstacles for
cellulose has been its recalcitrance towards hydrolysis for glucose
production. Because of the high quantity of enzymes typically
required, the enzyme cost can be a tremendous burden on the overall
cost to turn cellulose into glucose for fermentation. Cellulose can
be made to be reactive by subjecting biomass to severe chemistry,
but that would jeopardize not only its integrity for other
potential uses but also the yields of hemicellulose and lignin.
[0011] Many types of pretreatment have been studied. A common
chemical pretreatment process employs a dilute acid, usually
sulfuric acid, to hydrolyze and extract hemicellulose sugars and
some lignin. A common physical pretreatment process employs steam
explosion to mechanically disrupt the cellulose fibers and promote
some separation of hemicellulose and lignin. Combinations of
chemical and physical pretreatments are possible, such as acid
pretreatment coupled with mechanical refining. It is difficult to
avoid degradation of sugars. In some cases, severe pretreatments
(i.e., high temperature and/or low pH) intentionally dehydrate
sugars to furfural, levulinic acid, and related chemicals. Also, in
common acidic pretreatment approaches, lignin handling is very
problematic because acid-condensed lignin precipitates and forms
deposits on surfaces throughout the process.
[0012] One type of pretreatment that can overcome many of these
disadvantages is called "organosolv" pretreatment. Organosolv
refers to the presence of an organic solvent for lignin, which
allows the lignin to remain soluble for better lignin handling.
Traditionally, organosolv pretreatment or pulping has employed
ethanol-water solutions to extract most of the lignin but leave
much of the hemicellulose attached to the cellulose. For some
market pulps, it is acceptable or desirable to have high
hemicellulose content in the pulp. When high sugar yields are
desired, however, there is a problem. Traditional ethanol/water
pulping cannot give high yields of hemicellulose sugars because the
timescale for sufficient hydrolysis of hemicellulose to monomers
causes soluble-lignin polymerization and then precipitation back
onto cellulose, which negatively impacts both pulp quality as well
as cellulose enzymatic digestibility.
[0013] An acid catalyst can be introduced into organosolv
pretreatment to hydrolyze hemicellulose into monomers while still
obtaining the solvent benefit. Conventional organosolv wisdom
dictates that high delignification can be achieved, but that a
substantial fraction of hemicellulose must be left in the solids
because any catalyst added to hydrolyze the hemicellulose will
necessarily degrade the sugars (e.g., to furfural) during
extraction of residual lignin.
[0014] Solvent cooking chemicals have been attempted as an
alternative to Kraft or sulfite pulping. The original solvent
process is described in U.S. Pat. No. 1,856,567 by Kleinert et al.
Groombridge et al. in U.S. Pat. No. 2,060,068 showed that an
aqueous solvent with sulfur dioxide is a potent delignifying system
to produce cellulose from lignocellulosic material. Three
demonstration facilities for ethanol-water (Alcell), alkaline
sulfite with anthraquinone and methanol (ASAM), and
ethanol-water-sodium hydroxide (Organocell) were operated briefly
in the 1990s.
[0015] Contrary to conventional wisdom, it has been found that
fractionation with a solution of ethanol (or another solvent for
lignin), water, and sulfur dioxide (SO.sub.2) can simultaneously
achieve several important objectives. The fractionation can be
achieved at modest temperatures (e.g., 120-160.degree. C.). The
SO.sub.2 can be easily recovered and reused. This process is able
to effectively fractionation many biomass species, including
softwoods, hardwoods, agricultural residues, and waste biomass. The
SO.sub.2 hydrolyzes the hemicelluloses and reduces or eliminates
troublesome lignin-based precipitates. The presence of ethanol
leads to rapid impregnation of the biomass, so that neither a
separate impregnation stage nor size reduction smaller than wood
chips are needed, thereby avoiding electricity-consuming sizing
operations. The dissolved hemicelluloses are neither dehydrated nor
oxidized (Iakovlev, "SO.sub.2-ethanol-water fractionation of
lignocellulosics," Ph.D. Thesis, Aalto Univ., Espoo, Finland,
2011). Cellulose is fully retained in the solid phase and can
subsequently be hydrolyzed to glucose. The mixture of hemicellulose
monomer sugars and cellulose-derived glucose may be used for
production of biofuels and chemicals.
[0016] In view of the state of the art, what is desired is to
efficiently fractionate any lignocellulosic-based biomass
(including, in particular, softwoods) into its primary components
so that each can be used in potentially distinct processes. While
not all commercial products require pure forms of cellulose,
hemicellulose, or lignin, a platform biorefinery technology that
enables processing flexibility in downstream optimization of
product mix, is particularly desirable. An especially flexible
fractionation technique would not only separate most of the
hemicellulose and lignin from the cellulose, but also render the
cellulose highly reactive to cellulase enzymes for the manufacture
of fermentable glucose.
[0017] The AVAP.RTM. fractionation process developed by American
Process, Inc. and its affiliates is able to economically accomplish
these objectives. Improvements are still desired in the area of
washing of pulp to reduce lignin and ash content.
SUMMARY
[0018] The present invention addresses the aforementioned needs in
the art.
[0019] In some variations, the invention provides a process for
fractionating lignocellulosic biomass, the process comprising:
[0020] (a) digesting a lignocellulosic biomass feedstock under
effective conditions in the presence of a solvent for lignin, an
acid or acid precursor, and water, to produce cellulose-rich solids
in a digestor liquor;
[0021] (b) separating the cellulose-rich solids from the digestor
liquor and washing the cellulose-rich solids with a first wash
liquid comprising a wash solvent for lignin, to generate first
washed cellulose-rich solids;
[0022] (c) washing the first washed cellulose-rich solids with a
second wash liquid comprising water, to generate second washed
cellulose-rich solids and a wash liquor comprising fines, wherein
the wash liquor is introduced to or in contact with a classifier to
remove at least a portion of the fines in a liquid fines-containing
stream;
[0023] (d) recovering the second washed cellulose-rich solids;
and
[0024] (e) optionally separating the fines from the
fines-containing stream and recycling water contained in the
fines-containing stream back to step (c).
[0025] The lignocellulosic biomass feedstock is a hardwood or an
annual plant or agricultural residue, in some embodiments. The
solvent for lignin may be ethanol, and the wash solvent for lignin
may be the same (e.g., ethanol) or different. The acid or acid
precursor is preferably sulfur dioxide.
[0026] In some embodiments, the classifier comprises a screen with
mesh size in the range of 10 to 500, such as a range of 100 to 325
or 150 to 250. In certain embodiments, the classifier comprises a
screen with mesh size of 200. The classifier may also comprise a
centrifuge or other separation device.
[0027] In some embodiments, during step (b) and/or step (c), a
disperser is utilized to liberate the fines from the second washed
cellulose-rich solids. During step (c), a portion of the fines
contained in the wash liquor are removed into the liquid
fines-containing stream. The portion of fines removed may be at
least 50%, at least 75%, or at least 95% of the fines contained in
the wash liquor removed into the liquid fines-containing
stream.
[0028] In some embodiments, during step (b) and/or step (c), one or
more additives are introduced to remove minerals remaining in the
first washed cellulose-rich solids and/or the second washed
cellulose-rich solids.
[0029] The second washed cellulose-rich solids will typically have
a lower Kappa number compared to cellulose-rich solids from an
otherwise-identical process without a classifier to remove at least
a portion of the fines. In some embodiments, the second washed
cellulose-rich solids have a lower ash content compared to
cellulose-rich solids from an otherwise-identical process without a
classifier to remove at least a portion of the fines. In some of
these embodiments, the second washed cellulose-rich solids have a
lower hemicellulose content compared to cellulose-rich solids from
an otherwise-identical process without a classifier to remove at
least a portion of the fines.
[0030] For example, the second washed cellulose-rich solids may
contain about 75% or more cellulose, about 7 wt % or less lignin,
about 5 wt % or less hemicellulose, and about 10 wt % or less ash.
In certain embodiments, the second washed cellulose-rich solids
contain about 80% or more cellulose, about 3 wt % or less lignin,
about 5 wt % or less hemicellulose, and about 8 wt % or less
ash.
[0031] The process may be continuous or semi-continuous, or batch.
In some embodiments, steps (a) and (b) are conducted
countercurrently. In some embodiments, steps (a)-(c) are conducted
countercurrently. In certain embodiments, the process is batch or
semi-continuous, wherein step (b) and/or step (c) is conducted in
simulated countercurrent fashion, and wherein multiple wash streams
are generated.
[0032] In some embodiments, the process further comprises
hydrolyzing the second washed cellulose-rich solids to produce
glucose. In some embodiments, the process further comprises feeding
the second washed cellulose-rich solids to a pulping operation.
[0033] The process may further include separating and recycling
unreacted acid or acid precursor from the digestor liquor. In some
embodiments, the process further comprises further treating the
digestor liquor to generate fermentable sugars.
[0034] Some variations provide a method of separating fines from
cellulose-rich solids, the method comprising:
[0035] (a) obtaining a biomass digestor liquor comprising
cellulose-rich solids;
[0036] (b) separating the cellulose-rich solids from the digestor
liquor and washing the cellulose-rich solids with a first wash
liquid, to generate first washed cellulose-rich solids;
[0037] (c) washing the first washed cellulose-rich solids with a
second wash liquid, to generate second washed cellulose-rich solids
and a wash liquor comprising fines, wherein the wash liquor is
introduced to or in contact with a classifier to remove at least a
portion of the fines in a liquid fines-containing stream;
[0038] (d) recovering the second washed cellulose-rich solids;
and
[0039] (e) optionally separating the fines from the
fines-containing stream and recycling water contained in the
fines-containing stream back to step (c).
[0040] Some variations provide a method of separating fines from
cellulose-rich solids, the method comprising:
[0041] (a) obtaining a biomass digestor liquor comprising
cellulose-rich solids;
[0042] (b) separating the cellulose-rich solids from the digestor
liquor and washing the cellulose-rich solids with a wash liquid, to
generate washed cellulose-rich solids and a wash liquor comprising
fines, wherein the wash liquor is introduced to or in contact with
a classifier to remove at least a portion of the fines in a liquid
fines-containing stream;
[0043] (c) recovering the second washed cellulose-rich solids;
and
[0044] (d) optionally separating the fines from the
fines-containing stream and recycling water contained in the
fines-containing stream back to step (b).
[0045] In some embodiments, the classifier comprises a screen with
mesh size in the range of 10 to 500, such as 100 to 325 or 150 to
250 (e.g., 200). In some embodiments, a disperser is utilized to
liberate the fines from the washed cellulose-rich solids. At least
50%, 75%, or 95% of the fines contained in the wash liquor may be
removed into the liquid fines-containing stream.
[0046] Optionally, one or more additives are introduced to remove
minerals remaining in the washed cellulose-rich solids.
[0047] In some embodiments, the washed cellulose-rich solids have a
lower Kappa number compared to cellulose-rich solids from an
otherwise-identical process without a classifier to remove at least
a portion of the fines. In some embodiments, the second washed
cellulose-rich solids have a lower ash content compared to
cellulose-rich solids from an otherwise-identical process without a
classifier to remove at least a portion of the fines. In some
embodiments, the second washed cellulose-rich solids have a lower
hemicellulose content compared to cellulose-rich solids from an
otherwise-identical process without a classifier to remove at least
a portion of the fines.
BRIEF DESCRIPTION OF THE DRAWINGS
[0048] FIG. 1 depicts a process of fractionating lignocellulosic
biomass, in some embodiments of the invention.
[0049] FIG. 2 shows photographs of fibers and fines isolated from
the pulp with a Britt jar assembly, in some embodiments.
[0050] FIG. 3 summarizes an isolation process of fines from washing
water, according to certain embodiments of the invention.
[0051] FIG. 4 shows exemplary SEM images of pulp produced from
sugarcane straw by AVAP.RTM. technology.
[0052] FIG. 5 shows exemplary SEM images of fines isolated from the
pulp (shown in FIG. 4) during a water-washing stage, according to
some embodiments.
[0053] FIG. 6 is a schematic representation of certain improved
washing procedures, in preferred embodiments.
[0054] These drawings are exemplary in nature and should not be
construed to limit the invention in any way.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
[0055] 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.
[0056] 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. For example, reference to
"unit" also includes a plurality of units (e.g., reactors or
vessels). 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.
[0057] Unless otherwise indicated, all numbers expressing
parameters, reaction conditions, 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.
[0058] 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.
[0059] As used herein, the phase "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 phase "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.
[0060] 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."
[0061] This disclosure describes processes and apparatus to
efficiently fractionate any lignocellulosic-based biomass into its
primary major components (cellulose, lignin, and if present,
hemicellulose) so that each can be used in potentially distinct
processes. An advantage of the process is that it produces
cellulose-rich solids while concurrently producing a liquid phase
containing a high yield of both hemicellulose sugars and lignin,
and low quantities of lignin and hemicellulose degradation
products. The flexible fractionation technique enables multiple
uses for the products. The washed cellulose is highly reactive to
cellulase enzymes for the manufacture of glucose. Other uses for
celluloses can be adjusted based on market conditions.
[0062] 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.
[0063] In order to produce cellulose fiber (or pulp) from
lignocellulosic biomass, the biomass along with cooking liquor is
first cooked in a digestor and then liquid and solid phases are
separated. The liquid phase, also called "spent liquor," mainly
includes dissolved biomass substances such as lignin,
hemicellulosic and cellulosic sugars in oligomeric and monomeric
form, as well as organic acids (acetic acid, uronic acids, formic
acid, levulinic acid, lactic acid, etc.), and sugar-degradation
products (furfural, hydroxymethylfurfural (HMF), etc.). The spent
liquor is typically sent to downstream processes to recover heat
value, cooking chemicals and other dissolved products such as
organic acids, sugars, furfural, levulinic acid, formic acid,
lactic acid, and HMF. The solid phase is subjected to subsequent
washing and disintegration to free solid from spent liquor and
produce cellulose fibers.
[0064] A schematic representation of a cooking process (or
fractionation process) of lignocellulosic biomass is shown in FIG.
1. The biomass is cooked in a digestor (reactor), and then it is
subsequently washed with washing liquors as shown in FIG. 1.
Cellulose fibers are prepared after defibrillation, disintegration,
and screening of the cooked biomass. FIG. 1 also shows other
streams of the cooking/fractionation process. The spent liquor
mostly contains hemicellulose and lignin, while the washing liquor
mainly contains lignin and some hemicellulose as well as "fines"
that are suspended or dissolved in the liquid phase.
[0065] As used herein in some variations, "fines" are defined as
small particles passing through 200 mesh (or 76 .mu.m in diameter)
screen, according to Tappi 261 cm-10, which is incorporated by
reference herein. These particles may include both cellulosic and
non-cellulosic materials. The fines from annual plants are mostly
originated from different small vessel elements such as tracheids,
parenchyma cells, etc. and called "primary fines." The fines
generated during chemical pulping of wood are mostly as a result of
refining and are called "secondary fines." Therefore the fines
generated during a cooking/fractionation process (such as that
depicted in FIG. 1) may be either (or both) cellulosic or
non-cellulosic in origin. Generally speaking, fine components may
include (but are not limited to) cellulose, hemicellulose, lignin,
ash, dirt, dust, metals, and foreign materials (i.e. materials that
were not in the original biomass).
[0066] Interestingly, it has been found that the lignin and mineral
content of cellulose fibers decreases when the amount of washing
water used is increased during the washing procedure. In order to
further investigate this behavior, the amount of washing water used
during water washing cycle following lignin washing cycle was
altered as shown in Table 1.
[0067] Four identical cooks with sugarcane straw were conducted in
a digestor. The subsequent washing procedure is almost the same for
all four cooks, the only difference being the amount of washing
water used in the final washing stage. Chemical composition of
straw used for cooks is summarized in Table 2. Chemical composition
of cellulose fibers obtained following washing procedure suggested
in Table 1 is summarized in Table 3.
[0068] According to Table 3, the water washing cycle following
lignin washing cycle has a significant effect on the fiber yield
and lignin content (Kappa number) as well as on cellulose and
hemicellulose content. A high yield of 51% (Experiment #1) was
obtained without water washing cycle, while the lowest yield
(Experiment #4) of 34% is measured after extensive water washing
cycle. The material loss during extensive water washing step is
most likely due to loss of small particles with wash water. It
should be noted that during washing procedure, filtering bags with
200 mesh were used to separate solid and liquid phases by
filtration. The particles smaller than 200 mesh can go through
filtering bags.
[0069] The fines content of pulp produced from sugarcane straws
with washing procedure described by Experiment #3 in Table 1 can be
quantified by Tappi method 261 cm-90 with Britt jar assembly. The
Britt Jar is a single screen classifier with 200 mesh screen or a
round hole of 76 .mu.m in diameter. Fibers are retained while fines
pass through the 200 mesh screen. The fibers and fines isolated
from the pulp are shown in FIG. 2. The fines content of pulp based
on o.d. (oven dried) pulp is around 23%. The amount of fines (23%)
determined by Britt Jar is reasonable when compared with pulp
produced from hardwoods and other annual plants. The Britt jar
fines reported for variety of pulp produced from hardwoods is
between 5% and 21%, depending on wood species and operation
conditions (Nanko et al., 2005). Sadovnik et al. (2007) reported
that the pulp produced from sugarcane bagasse has high content of
fines from 35 to 40%. It is also reported that bleachable-grade
wheat straw pulp produced by soda pulping process in continuous
Pandia digestor has 21.4% of fines (Casey, 1980).
[0070] It is clear from Table 3 that increased amount of water used
during water washing cycle (as seen in Table 1) decreases lignin
and ash content of cellulose fiber while increases cellulose
content of fiber. Without being limited by any particular
hypothesis, this reduction in lignin and ash content may be
attributed to removal of fines which have high lignin and ash
content and relatively low cellulose content compared to cellulose
fiber during washing procedure. Fines were separated during water
washing stage and chemical characterization of fines was
determined. As shown in FIG. 3, the fines were allowed to pass
through 200 mesh filtering bag into washing water and then they
were isolated from washing water by filtering or freeze drying
following centrifugation. The fines isolated by filtration and
freeze-drying are shown in FIG. 3.
TABLE-US-00001 TABLE 1 Effect of water washing procedure on fiber
yield and kappa number. Water Exp. # Water washing procedure
following lignin wash Amount 1 No water washing following EtOH
washing after of cooking washing 2 Just rinsed with little water
following EtOH water after cooking 3 Washed with some water
following EtOH washing after cooking 4 Washed with plenty of water
following EtOH washing after cooking
TABLE-US-00002 TABLE 2 The chemical composition of sugarcane straws
based on o.d. straws. Component % Arabinan 2.8 .+-. 0.0 Galactan
1.1 .+-. 0.0 Glucan 37.1 .+-. 0.5 Xylan 20.0 .+-. 0.2 Mannan 0.6
.+-. 0.0 Acetyl Groups 1.1 .+-. 0.0 Uronic Acid Groups 2.2 .+-. 0.3
Lignin 23.7 .+-. 0.2 Ash 6.8 .+-. 0.4 Extractives 2.6 .+-. 0.0
Total 98.0 .+-. 1.6
TABLE-US-00003 TABLE 3 Effect of water washing procedure on fiber
composition. % on straw % on fiber Exp.# Yield Cellulose
Hemicellulose Lignin Ash Kappa # 1 50.9 73.8 5.2 7.9 11.4 52.1 2
43.3 78.8 4.4 5.9 9.3 39.2 3 38.9 81.3 4.4 3.7 8.4 25.0 4 34.4 83.5
4.6 2.8 7.4 19.5
[0071] The chemical composition of freeze-dried fines was
determined and is summarized in Table 4. It is apparent from Table
4 that fines isolated during water washing stage mostly contain
cellulose, lignin, and ash. Lignin, ash, and hemicellulose content
of fines are each higher than the corresponding content in the
fiber (see Table 3, Experiments 2, 3 and 4) while the opposite is
true for cellulose. Therefore, it can be concluded that depending
on the amount of fines removed during the washing stage, the
cellulose content of fibers can be increased while hemicellulose,
lignin, and ash content of the fiber can be reduced.
TABLE-US-00004 TABLE 4 Sugar and lignin contents of "fines"
isolated during water washing process following AVAP .RTM. cooking
of the straws and ethanol washing stage. Component % on od "fines"
Arabinan 0.7 Galactan 0.2 Glucan 57.8 Xylan 6.0 Mannan 0.2 Lignin
15.6 Ash 19.0 Total 99.5
[0072] As explained earlier, lignin content of fines is much higher
than that of final pulp. This high lignin content of cellulosic
fines may be a result of lignin precipitation on fines during
cooking process or subsequent washing process due to higher
mobility and surface area of fines in comparison to fibers (Gess,
1998). For this reason, in order to investigate the precipitation
of lignin, scanning electron microscopy (SEM) images of both pulp
and fines were taken and are displayed in FIGS. 4 and 5
respectively. More lignin precipitation on cellulosic fines can be
observed and also it appears that pulp fibers are smoother than
fines.
[0073] A schematic representation of an improved washing procedure
to produce cellulose fibers (pulp) with low Kappa number and ash
content, along while high cellulose content, following cooking of
hardwood and/or annual plants is shown in FIG. 6. Since fines have
high lignin and ash content, Kappa number (lignin content) and ash
content of cellulose fibers can be lowered based on how much fines
are removed during the washing procedure.
[0074] Some variations provide a process for fractionating
lignocellulosic biomass, the process comprising:
[0075] (a) digesting a lignocellulosic biomass feedstock under
effective conditions in the presence of a solvent for lignin, an
acid or acid precursor, and water, to produce cellulose-rich solids
in a digestor liquor;
[0076] (b) separating the cellulose-rich solids from the digestor
liquor and washing the cellulose-rich solids with a first wash
liquid comprising a wash solvent for lignin, to generate first
washed cellulose-rich solids;
[0077] (c) washing the first washed cellulose-rich solids with a
second wash liquid comprising water, to generate second washed
cellulose-rich solids and a wash liquid comprising fines, wherein
the wash liquid is introduced to or in contact with a classifier to
remove at least a portion of the fines in a liquid fines-containing
stream;
[0078] (d) recovering the second washed cellulose-rich solids;
and
[0079] (e) optionally separating the fines from the
fines-containing stream and recycling water to step (c).
[0080] In some embodiments, the classifier comprises a screen with
mesh size in the range of 10 to 500. In certain embodiments, the
classifier comprises a screen with mesh size in the range of 100 to
325, such as 150 to 250. In a particular embodiment, the classifier
comprises a screen with mesh size of 200. Other screen sizes may be
employed.
[0081] In some embodiments, the classifier is a batch or continuous
centrifuge or hydrocyclone operated to remove fines within one or
more selected size ranges. In certain embodiments, both a
centrifuge and screen(s) may be used, such as screening the liquid
discharge of a decanting centrifuge. Screen centrifuges, wherein
the centrifugal acceleration allows the liquid to pass through a
screen, include screen/scroll centrifuges, pusher centrifuges,
peeler centrifuges, and decanter centrifuges, in which there is no
physical separation between the solid and liquid phase, rather an
accelerated settling due to centrifugal acceleration. Solid bowl
centrifuges or conical plate centrifuges may also be employed.
[0082] Dispersers may also be added to liberate more fines if
necessary. During step (b) and/or step (c), a disperser may be
utilized to liberate fines from the second washed cellulose-rich
solids. A disperser may liberate additional fines that would not
have otherwise been released. In some embodiments, a disperser is a
simple mixing tank, i.e. a stirred tank or vessel. Dispersers may
also be in-line (static) mixers, high-shear mixers, centrifuges, or
other equipment. In some embodiments, the disperser is integrated
with the classifier; for example, a centrifuge may be adapted to
both disperse fines from solids as well as classify the fines as
described above.
[0083] Instead of a disperser, or in addition, other reagents may
also be used to liberate more fines and/or remove minerals
remaining in the pulp at this stage, depending on targeted quality
of product. During step (b) and/or step (c), one or more additives
may be introduced to remove minerals remaining in the first washed
cellulose-rich solids and/or the second washed cellulose-rich
solids. Additives include, but are not limited to, acids, bases,
salts, carbon (such as activated carbon or carbon foams), metal
foams, silica, alumina, or other compounds.
[0084] Cellulose fibers may also be bleached to remove remaining
lignin from the fiber. Any known bleaching sequence may be
utilized.
[0085] The process may be continuous, semi-continuous, or batch. In
some embodiments, one or more steps are conducted countercurrently.
In certain embodiments, the process is batch or semi-continuous,
washing is conducted in simulated countercurrent fashion, and
multiple wash streams (such as two, three, or more wash streams)
are generated.
[0086] In some embodiments, the solvent for lignin includes an
aliphatic alcohol, such as ethanol. Preferably, the process further
comprises recycling the solvent for lignin back to the digestor.
Also, the process preferably comprises recycling the unreacted acid
or acid precursor to the digestor.
[0087] In some embodiments, the acid catalyst (or acid precursor)
is a sulfur-containing compound or a derivative thereof. For
example the sulfur-containing compound may be selected from the
group consisting of sulfur dioxide, sulfur trioxide, sulfurous
acid, sulfuric acid, sulfonic acids, lignosulfonic acids, elemental
sulfur, and combinations thereof.
[0088] In some embodiments, the acid catalyst is a
nitrogen-containing compound (e.g., HNO.sub.3) or a derivative
thereof. In some embodiments, the acid catalyst is a
phosphorous-containing compound (e.g., H.sub.3PO.sub.4) or a
derivative thereof. In some embodiments, the acid catalyst is one
or more hydrogen halides (e.g., HBr or HCl).
[0089] Removal of SO.sub.2 may be conducted in a sulfur dioxide
separation unit selected from the group consisting of a flash
vessel, a stripping column, a distillation column, and combinations
thereof, operated under vacuum or pressure. In some embodiments,
the sulfur dioxide separation unit is a stripping column employing
steam for stripping the unreacted sulfur dioxide.
[0090] The process may further include dilution with liquid water
during one or more steps. As intended here, dilution with liquid
water may occur via injection of a liquid-phase stream comprising
water, which may be fresh water or recycled water (e.g., process
condensate); alternatively, or additionally, dilution with liquid
water may occur via injection of steam which condenses to form
liquid water that dilutes a process stream. Dilution with liquid
water may assist in the precipitating at least some of the lignin
in a lignin-containing stream.
[0091] In some embodiments, the process further comprises pH
adjustment during one or more steps. The pH adjustment may assist
in controlling lignin precipitation in the lignin-containing
stream. For example, raising pH may increase lignin solubility in
aqueous solution, while lowering pH may reduce lignin solubility in
aqueous solution, in some embodiments.
[0092] In embodiments employing SO.sub.2 during fractionation, some
amount of lignin sulfonation typically occurs. In some embodiments,
the process comprises further lignin sulfonation during one or more
steps. Lignin sulfonation generally increases lignin solubility in
aqueous solution. Lignin sulfonation may be accomplished by
reaction of soluble lignin or suspended lignin with SO.sub.2 or
another sulfur-containing compound.
[0093] The lignin-containing stream may be in various forms and
phases, including multiple phases (two, three, or more). For
example, the lignin-containing stream may be in the form of a
slurry. In certain embodiments, lignin-containing stream or product
contains lignin in substantially solid form, such as lignin solids
recovered periodically from a semi-continuous process or lignin
solids that form a filter cake.
[0094] In some embodiments, the lignin-containing stream contains
colloids of lignin dispersed in the continuous phase (liquor).
Colloids of lignin may be removed by filtration or centrifugation,
for example. To enhance the removal of lignin colloids from
suspension, it may be desirable to adjust the pH of the suspension
either during or after dilution with water. Also, additives may be
introduced to change kinetics or thermodynamics of colloid phase
formation. In some embodiments, the lignin/lignosulfonate ratio is
optimized during digestion or downstream, to adjust the properties
of the colloidal suspension.
[0095] The hemicelluloses may be recovered for fermentation or for
further processing. In some embodiments, the process further
comprises a step of hemicellulose hydrolysis with an acid or
enzymes. The acid for hemicellulose hydrolysis may include
lignosulfonic acids that are derived from the initial fractionation
step.
[0096] The cellulose-rich solids may be recovered as a pulp
product. Alternatively, or additionally, the cellulose-rich solids
may be hydrolyzed to produce glucose.
[0097] The present invention includes apparatus and systems to
carry out the processes described herein. The present invention
also includes products produced by the processes described herein.
Such products include biomass-derived sugars, cellulose materials,
lignin, lignosulfonates, and other co-products.
[0098] As used herein, "lignocellulosic biomass" means any material
containing cellulose and lignin. Lignocellulosic biomass may also
contain hemicellulose. Mixtures of one or more types of biomass can
be used. In some embodiments, the biomass feedstock comprises both
a lignocellulosic component (such as one described above) in
addition to a sucrose-containing component (e.g., sugarcane or
energy cane) and/or a starch component (e.g., corn, wheat, rice,
etc.).
[0099] The biomass feedstock may be selected from hardwoods,
softwoods, forest residues, industrial wastes, pulp and paper
wastes, consumer wastes, or combinations thereof. Some embodiments
utilize agricultural residues, which 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, sugarcane straw, rice straw, oat
straw, barley straw, miscanthus, energy cane straw/residue, or
combinations thereof. In some embodiments, the biomass feedstock is
not softwood.
[0100] Various moisture levels may be associated with the starting
biomass. The biomass feedstock need not be, but may be, relatively
dry. In general, the biomass is in the form of a particulate or
chip, but particle size is not critical in this invention.
[0101] Reaction conditions and operation sequences may vary widely.
Some embodiments employ conditions described in U.S. Pat. No.
8,030,039, issued Oct. 4, 2011; U.S. Pat. No. 8,038,842, issued
Oct. 11, 2011; U.S. Pat. No. 8,268,125, issued Sep. 18, 2012; and
U.S. patent application Ser. Nos. 13/004,431; 12/234,286;
13/585,710; 12/250,734; 12/397,284; 12/304,046; 13/500,916;
13/626,220; 12/854,869; 61/732,047; 61/735,738; 61/739,343;
61/747,010; 61/747,105; 61/747,376; 61/747,379; 61/747,382; and
61/747,408 including the prosecution histories thereof. Each of
these commonly owned patent applications is hereby incorporated by
reference herein in its entirety. In some embodiments, the process
is a variation of the AVAP.RTM. process technology which is
commonly owned with the assignee of this patent application.
[0102] In some embodiments, a first process step is "cooking"
(equivalently, "digesting") which fractionates the three
lignocellulosic material components (cellulose, hemicellulose, and
lignin) to allow easy downstream removal. Specifically,
hemicelluloses are dissolved and over 50% are completely
hydrolyzed; cellulose is separated but remains resistant to
hydrolysis; and part of the lignin is sulfonated into water-soluble
lignosulfonates.
[0103] The lignocellulosic material is processed in a solution
(cooking liquor) of solvent, water, and sulfur dioxide. The cooking
liquor preferably contains at least 10 wt %, such as at least 20 wt
%, 30 wt %, 40 wt %, or 50 wt % of a solvent for lignin. By
"solvent for lignin," it is meant a chemical that is capable of
dissolving at least some lignin, in native (non-sulfonated) form,
at the conditions of digestion.
[0104] For example, the cooking liquor may contain about 30-70 wt %
solvent, such as about 50 wt % solvent. The solvent for lignin may
be an aliphatic alcohol, such as methanol, ethanol, 1-propanol,
2-propanol, 1-butanol, 2-butanol, isobutanol, 1-pentanol,
1-hexanol, or cyclohexanol. The solvent for lignin may be an
aromatic alcohol, such as phenol or cresol. Other lignin solvents
are possible, such as (but not limited to) glycerol, methyl ethyl
ketone, or diethyl ether. Combinations of more than one solvent may
be employed.
[0105] Preferably, enough solvent is included in the extractant
mixture to dissolve the lignin present in the starting material.
The solvent for lignin may be completely miscible, partially
miscible, or immiscible with water, so that there may be more than
one liquid phase. Potential process advantages arise when the
solvent is miscible with water, and also when the solvent is
immiscible with water. When the solvent is water-miscible, a single
liquid phase forms, so mass transfer of lignin and hemicellulose
extraction is enhanced, and the downstream process must only deal
with one liquid stream. When the solvent is immiscible in water,
the extractant mixture readily separates to form liquid phases, so
a distinct separation step can be avoided or simplified. This can
be advantageous if one liquid phase contains most of the lignin and
the other contains most of the hemicellulose sugars, as this
facilitates recovering the lignin from the hemicellulose
sugars.
[0106] The cooking liquor preferably contains sulfur dioxide and/or
sulfurous acid (H.sub.2SO.sub.3). The cooking liquor preferably
contains SO.sub.2, in dissolved or reacted form, in a concentration
of at least 3 wt %, preferably at least 6 wt %, more preferably at
least 8 wt %, such as about 9 wt %, 10 wt %, 11 wt %, 12 wt %, 13
wt %, 14 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt % or higher. The
cooking liquor may also contain one or more species, separately
from SO.sub.2, to adjust the pH. The pH of the cooking liquor is
typically about 4 or less.
[0107] Sulfur dioxide is a preferred acid catalyst, because it can
be recovered easily from solution after hydrolysis. The majority of
the SO.sub.2 from the hydrolysate may be stripped and recycled back
to the reactor. Recovery and recycling translates to less lime
required compared to neutralization of comparable sulfuric acid,
less solids to dispose of, and less separation equipment. The
increased efficiency owing to the inherent properties of sulfur
dioxide mean that less total acid or other catalysts may be
required. This has cost advantages, since sulfuric acid can be
expensive. Additionally, and quite significantly, less acid usage
also will translate into lower costs for a base (e.g., lime) to
increase the pH following hydrolysis, for downstream operations.
Furthermore, less acid and less base will also mean substantially
less generation of waste salts (e.g., gypsum) that may otherwise
require disposal.
[0108] The cooking is performed in one or more stages using batch
or continuous digestors. Solid and liquid may flow cocurrently or
countercurrently, or in any other flow pattern that achieves the
desired fractionation. The cooking reactor may be internally
agitated, if desired.
[0109] Depending on the lignocellulosic material to be processed,
the cooking conditions are varied, with temperatures from about
65.degree. C. to 175.degree. C., for example 75.degree. C.,
85.degree. C., 95.degree. C., 105.degree. C., 115.degree. C.,
125.degree. C., 130.degree. C., 135.degree. C., 140.degree. C.,
145.degree. C., 150.degree. C., 155.degree. C., 165.degree. C. or
170.degree. C., and corresponding pressures from about 1 atmosphere
to about 15 atmospheres in the liquid or vapor phase. The cooking
time of one or more stages may be selected from about 15 minutes to
about 720 minutes, such as about 30, 45, 60, 90, 120, 140, 160,
180, 250, 300, 360, 450, 550, 600, or 700 minutes. Generally, there
is an inverse relationship between the temperature used during the
digestion step and the time needed to obtain good fractionation of
the biomass into its constituent parts.
[0110] The cooking liquor to lignocellulosic material ratio may be
selected from about 1 to about 10, such as about 2, 3, 4, 5, or 6.
In some embodiments, biomass is digested in a pressurized vessel
with low liquor volume (low ratio of cooking liquor to
lignocellulosic material), so that the cooking space is filled with
ethanol and sulfur dioxide vapor in equilibrium with moisture. The
cooked biomass is washed in alcohol-rich solution to recover lignin
and dissolved hemicelluloses, while the remaining pulp is further
processed. In some embodiments, the process of fractionating
lignocellulosic material comprises vapor-phase cooking of
lignocellulosic material with aliphatic alcohol (or other solvent
for lignin), water, and sulfur dioxide. See, for example, U.S. Pat.
Nos. 8,038,842 and 8,268,125 which are incorporated by reference
herein.
[0111] A portion or all of the sulfur dioxide may be present as
sulfurous acid in the extract liquor. In certain embodiments,
sulfur dioxide is generated in situ by introducing sulfurous acid,
sulfite ions, bisulfite ions, combinations thereof, or a salt of
any of the foregoing. Excess sulfur dioxide, following hydrolysis,
may be recovered and reused.
[0112] In some embodiments, sulfur dioxide is saturated in water
(or aqueous solution, optionally with an alcohol) at a first
temperature, and the hydrolysis is then carried out at a second,
generally higher, temperature. In some embodiments, sulfur dioxide
is sub-saturated. In some embodiments, sulfur dioxide is
super-saturated. In some embodiments, sulfur dioxide concentration
is selected to achieve a certain degree of lignin sulfonation, such
as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10% sulfur content.
SO.sub.2 reacts chemically with lignin to form stable lignosulfonic
acids which may be present both in the solid and liquid phases.
[0113] The concentration of sulfur dioxide, additives, and
aliphatic alcohol (or other solvent) in the solution and the time
of cook may be varied to control the yield of cellulose and
hemicellulose in the pulp. The concentration of sulfur dioxide and
the time of cook may be varied to control the yield of lignin
versus lignosulfonates in the hydrolysate. In some embodiments, the
concentration of sulfur dioxide, temperature, and the time of cook
may be varied to control the yield of fermentable sugars.
[0114] Once the desired amount of fractionation of both
hemicellulose and lignin from the solid phase is achieved, the
liquid and solid phases are separated. Conditions for the
separation may be selected to minimize the reprecipitation of the
extracted lignin on the solid phase. This is favored by conducting
separation or washing at a temperature of at least the
glass-transition temperature of lignin (about 120.degree. C.).
[0115] The physical separation can be accomplished either by
transferring the entire mixture to a device that can carry out the
separation and washing, or by removing only one of the phases from
the reactor while keeping the other phase in place. The solid phase
can be physically retained by appropriately sized screens through
which liquid can pass. The solid is retained on the screens and can
be kept there for successive solid-wash cycles. Alternately, the
liquid may be retained and solid phase forced out of the reaction
zone, with centrifugal or other forces that can effectively
transfer the solids out of the slurry. In a continuous system,
countercurrent flow of solids and liquid can accomplish the
physical separation.
[0116] The recovered solids normally will contain a quantity of
lignin and sugars, some of which can be removed easily by washing.
The washing-liquid composition can be the same as or different than
the liquor composition used during fractionation. Multiple washes
may be performed to increase effectiveness. Preferably, one or more
washes are performed with a composition including a solvent for
lignin, to remove additional lignin from the solids, followed by
one or more washes with water to displace residual solvent and
sugars from the solids, as well as release fines from the fibers as
disclosed in detail herein. Recycle streams, such as from
solvent-recovery operations, may be used to wash the solids.
[0117] After separation and washing as described, a solid phase and
at least one liquid phase are obtained. The solid phase contains
substantially undigested cellulose. A single liquid phase is
usually obtained when the solvent and the water are miscible in the
relative proportions that are present. In that case, the liquid
phase contains, in dissolved form, most of the lignin originally in
the starting lignocellulosic material, as well as soluble monomeric
and oligomeric sugars formed in the hydrolysis of any hemicellulose
that may have been present. Multiple liquid phases tend to form
when the solvent and water are wholly or partially immiscible. The
lignin tends to be contained in the liquid phase that contains most
of the solvent. Hemicellulose hydrolysis products tend to be
present in the liquid phase that contains most of the water.
[0118] In some embodiments, hydrolysate from the cooking step is
subjected to pressure reduction. Pressure reduction may be done at
the end of a cook in a batch digestor, or in an external flash tank
after extraction from a continuous digestor, for example. The flash
vapor from the pressure reduction may be collected into a cooking
liquor make-up vessel. The flash vapor contains substantially all
the unreacted sulfur dioxide which may be directly dissolved into
new cooking liquor. The cellulose is then removed to be washed and
further treated as desired.
[0119] A process washing step recovers the hydrolysate from the
cellulose. The washed cellulose is pulp that may be used for
various purposes (e.g., paper or nanocellulose production). The
weak hydrolysate from the washer continues to the final reaction
step; in a continuous digestor this weak hydrolysate may be
combined with the extracted hydrolysate from the external flash
tank. In some embodiments, washing and/or separation of hydrolysate
and cellulose-rich solids is conducted at a temperature of at least
about 100.degree. C., 110.degree. C., or 120.degree. C. The washed
cellulose may also be used for glucose production via cellulose
hydrolysis with enzymes or acids.
[0120] In another reaction step, the hydrolysate may be further
treated in one or multiple steps to hydrolyze the oligomers into
monomers. This step may be conducted before, during, or after the
removal of solvent and sulfur dioxide. The solution may or may not
contain residual solvent (e.g. alcohol). In some embodiments,
sulfur dioxide is added or allowed to pass through to this step, to
assist hydrolysis. In these or other embodiments, an acid such as
sulfurous acid or sulfuric acid is introduced to assist with
hydrolysis. In some embodiments, the hydrolysate is autohydrolyzed
by heating under pressure. In some embodiments, no additional acid
is introduced, but lignosulfonic acids produced during the initial
cooking are effective to catalyze hydrolysis of hemicellulose
oligomers to monomers. In various embodiments, this step utilizes
sulfur dioxide, sulfurous acid, sulfuric acid at a concentration of
about 0.01 wt % to 30 wt %, such as about 0.05 wt %, 0.1 wt %, 0.2
wt %, 0.5 wt %, 1 wt %, 2 wt %, 5 wt %, 10 wt %, or 20 wt %. This
step may be carried out at a temperature from about 100.degree. C.
to 220.degree. C., such as about 110.degree. C., 120.degree. C.,
130.degree. C., 140.degree. C., 150.degree. C., 160.degree. C.,
170.degree. C., 180.degree. C., 190.degree. C., 200.degree. C., or
210.degree. C. Heating may be direct or indirect to reach the
selected temperature.
[0121] The reaction step produces fermentable sugars which can then
be concentrated by evaporation to a fermentation feedstock.
Concentration by evaporation may be accomplished before, during, or
after the treatment to hydrolyze oligomers. The final reaction step
may optionally be followed by steam stripping of the resulting
hydrolysate to remove and recover sulfur dioxide and alcohol, and
for removal of potential fermentation-inhibiting side products. The
evaporation process may be under vacuum or pressure, from about
-0.1 atmospheres to about 10 atmospheres, such as about 0.1 atm,
0.3 atm, 0.5 atm, 1.0 atm, 1.5 atm, 2 atm, 4 atm, 6 atm, or 8
atm.
[0122] Recovering and recycling the sulfur dioxide may utilize
separations such as, but not limited to, vapor-liquid disengagement
(e.g. flashing), steam stripping, extraction, or combinations or
multiple stages thereof. Various recycle ratios may be practiced,
such as about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.95, or
more. In some embodiments, about 90-99% of initially charged
SO.sub.2 is readily recovered by distillation from the liquid
phase, with the remaining 1-10% (e.g., about 3-5%) of the SO.sub.2
primarily bound to dissolved lignin in the form of
lignosulfonates.
[0123] In a preferred embodiment, the evaporation step utilizes an
integrated alcohol stripper and evaporator. Evaporated vapor
streams may be segregated so as to have different concentrations of
organic compounds in different streams. Evaporator condensate
streams may be segregated so as to have different concentrations of
organic compounds in different streams. Alcohol may be recovered
from the evaporation process by condensing the exhaust vapor and
returning to the cooking liquor make-up vessel in the cooking step.
Clean condensate from the evaporation process may be used in the
washing step.
[0124] In some embodiments, an integrated alcohol stripper and
evaporator system is employed, wherein aliphatic alcohol is removed
by vapor stripping, the resulting stripper product stream is
concentrated by evaporating water from the stream, and evaporated
vapor is compressed using vapor compression and is reused to
provide thermal energy.
[0125] The hydrolysate from the evaporation and final reaction step
contains mainly fermentable sugars but may also contain lignin
depending on the location of lignin separation in the overall
process configuration. The hydrolysate may be concentrated to a
concentration of about 5 wt % to about 60 wt % solids, such as
about 10 wt %, 15 wt %, 20 wt %, 25 wt %, 30 wt %, 35 wt %, 40 wt
%, 45 wt %, 50 wt % or 55 wt % solids. The hydrolysate contains
fermentable sugars.
[0126] Fermentable sugars are defined as hydrolysis products of
cellulose, galactoglucomannan, glucomannan, arabinoglucuronoxylans,
arabinogalactan, and glucuronoxylans into their respective
short-chained oligomers and monomer products, i.e., glucose,
mannose, galactose, xylose, and arabinose. The fermentable sugars
may be recovered in purified form, as a sugar slurry or dry sugar
solids, for example. Any known technique may be employed to recover
a slurry of sugars or to dry the solution to produce dry sugar
solids.
[0127] In some embodiments, the fermentable sugars are fermented to
produce biochemicals or biofuels such as (but by no means limited
to) ethanol, isopropanol, acetone, 1-butanol, isobutanol, lactic
acid, succinic acid, or any other fermentation products. Some
amount of the fermentation product may be a microorganism or
enzymes, which may be recovered if desired.
[0128] When the fermentation will employ bacteria, such as
Clostridia bacteria, it is preferable to further process and
condition the hydrolysate to raise pH and remove residual SO.sub.2
and other fermentation inhibitors. The residual SO.sub.2 (i.e.,
following removal of most of it by stripping) may be catalytically
oxidized to convert residual sulfite ions to sulfate ions by
oxidation. This oxidation may be accomplished by adding an
oxidation catalyst, such as FeSO4.7H.sub.2O, that oxidizes sulfite
ions to sulfate ions. Preferably, the residual SO.sub.2 is reduced
to less than about 100 ppm, 50 ppm, 25 ppm, 10 ppm, 5 ppm, or 1
ppm.
[0129] The process fermentation and distillation steps are intended
for the production of fermentation products, such as alcohols or
organic acids. After removal of cooking chemicals and lignin, and
further treatment (oligomer hydrolysis), the hydrolysate contains
mainly fermentable sugars in water solution from which any
fermentation inhibitors have been preferably removed or
neutralized. The hydrolysate is fermented to produce dilute alcohol
or organic acids, from 1 wt % to 20 wt % concentration. The dilute
product is distilled or otherwise purified as is known in the
art.
[0130] When alcohol is produced, such as ethanol, some of it may be
used for cooking liquor makeup in the process cooking step. Also,
in some embodiments, a distillation column stream, such as the
bottoms, with or without evaporator condensate, may be reused to
wash cellulose. In some embodiments, lime may be used to dehydrate
product alcohol. Side products may be removed and recovered from
the hydrolysate. These side products may be isolated by processing
the vent from the final reaction step and/or the condensate from
the evaporation step. Side products include furfural, hydroxymethyl
furfural (HMF), methanol, acetic acid, and lignin-derived
compounds, for example.
[0131] The cellulose-rich material is highly reactive in the
presence of industrial cellulase enzymes that efficiently break the
cellulose down to glucose monomers. It has been found
experimentally that the cellulose-rich material, which generally
speaking is highly delignified, rapidly hydrolyzes to glucose with
relatively low quantities of enzymes. For example, the
cellulose-rich solids may be converted to glucose with at least 80%
yield within 24 hours at 50.degree. C. and 2 wt % solids, in the
presence of a cellulase enzyme mixture in an amount of no more than
15 filter paper units (FPU) per g of the solids. In some
embodiments, this same conversion requires no more than 5 FPU per g
of the solids.
[0132] The glucose may be fermented to an alcohol, an organic acid,
or another fermentation product. The glucose may be used as a
sweetener or isomerized to enrich its fructose content. The glucose
may be used to produce baker's yeast. The glucose may be
catalytically or thermally converted to various organic acids and
other materials.
[0133] In some embodiments, the cellulose-rich material is further
processed into one more cellulose products. Cellulose products
include market pulp, dissolving pulp (also known as
.alpha.-cellulose), fluff pulp, purified cellulose, paper, paper
products, and so on. Further processing may include bleaching, if
desired. Further processing may include modification of fiber
length or particle size, such as when producing nanocellulose or
nanofibrillated or microfibrillated cellulose. It is believed that
the cellulose produced by this process is highly amenable to
derivatization chemistry for cellulose derivatives and
cellulose-based materials such as polymers.
[0134] When hemicellulose is present in the starting biomass, all
or a portion of the liquid phase contains hemicellulose sugars and
soluble oligomers. It is preferred to remove most of the lignin
from the liquid, as described above, to produce a fermentation
broth which will contain water, possibly some of the solvent for
lignin, hemicellulose sugars, and various minor components from the
digestion process. This fermentation broth can be used directly,
combined with one or more other fermentation streams, or further
treated. Further treatment can include sugar concentration by
evaporation; addition of glucose or other sugars (optionally as
obtained from cellulose saccharification); addition of various
nutrients such as salts, vitamins, or trace elements; pH
adjustment; and removal of fermentation inhibitors such as acetic
acid and phenolic compounds. The choice of conditioning steps
should be specific to the target product(s) and microorganism(s)
employed.
[0135] In some embodiments, hemicellulose sugars are not fermented
but rather are recovered and purified, stored, sold, or converted
to a specialty product. Xylose, for example, can be converted into
xylitol.
[0136] Lignin produced in accordance with the invention can be used
as a fuel. As a solid fuel, lignin is similar in energy content to
coal. Lignin can act as an oxygenated component in liquid fuels, to
enhance octane while meeting standards as a renewable fuel. The
lignin produced herein can also be used as polymeric material, and
as a chemical precursor for producing lignin derivatives. The
sulfonated lignin may be sold as a lignosulfonate product, or
burned for fuel value. In certain embodiments, the process further
comprises combusting or gasifying the sulfonated lignin, recovering
sulfur contained in the sulfonated lignin in a gas stream
comprising reclaimed sulfur dioxide, and then recycling the
reclaimed sulfur dioxide for reuse.
[0137] Native (non-sulfonated) lignin is hydrophobic, while
lignosulfonates are hydrophilic. Hydrophilic lignosulfonates may
have less propensity to clump, agglomerate, and stick to surfaces.
Even lignosulfonates that do undergo some condensation and increase
of molecular weight, will still have an HSO.sub.3 group that will
contribute some solubility (hydrophilic). After the evaporative
precipitation or other method to remove water-insoluble lignin, the
remaining water-soluble lignosulfonates may be precipitated by
converting the hydrolysate to an alkaline condition (pH higher than
7) using, for example, an alkaline earth oxide, preferably calcium
oxide (lime). The lignosulfonate precipitate may be filtered. The
lignosulfonate filter cake may be dried as a co-product or burned
or gasified for energy production. The hydrolysate from filtering
may be recovered and sold as a concentrated sugar solution product
or further processed in a subsequent fermentation or other reaction
step.
[0138] Lignin with specific property ranges may be obtained by
doing a multiple-effect evaporative crystallization to purposely
create lignin precipitates with various properties. Thus in some
embodiments, several types of non-sulfonated lignin or lignin with
low levels of sulfur may be obtained, in addition to one or more
sulfonated lignins.
[0139] The present invention also provides systems configured for
carrying out the disclosed processes, and compositions produced
therefrom. Any stream generated by the disclosed processes may be
partially or completed recovered, purified or further treated,
and/or marketed or sold.
[0140] 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.
[0141] 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.
[0142] 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.
[0143] 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.
REFERENCES
[0144] Casey, J. P. Pulp and paper, chemistry and chemical
technology. 3rd edition, vol. 1, John Wily and Sons, Inc., USA,
1980. [0145] Gess, J. M. Retention of fines and fillers during
papermaking, Tappi Press. Atlanta, Ga. (1998). [0146] Nanko, H.,
Button, A., Hillman, D. The world of market Pulp, Appleton, Wis.,
WOMP LLC (2005). [0147] Sadovnik, J. C, Betancourt, L. A, Ramos,
J., and Alban, F., "Fines Study in the Bleached Pulp from the Sugar
Cane Bagasse," Tappi 2007 Engineering, Pulping & Environmental
Conference (2007). [0148] Tappi standard T 261 cm-90 "Fines
fraction of paper stock by wet screening," Tappi press, Atlanta,
Ga., USA (1992).
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