U.S. patent application number 14/606442 was filed with the patent office on 2015-08-20 for lignin-coated cellulose fibers from lignocellulosic biomass.
The applicant listed for this patent is API Intellectual Property Holdings, LLC. Invention is credited to Vesa PYLKKANEN, Theodora RETSINA, Mehmet Sefik TUNC.
Application Number | 20150233057 14/606442 |
Document ID | / |
Family ID | 53797605 |
Filed Date | 2015-08-20 |
United States Patent
Application |
20150233057 |
Kind Code |
A1 |
TUNC; Mehmet Sefik ; et
al. |
August 20, 2015 |
LIGNIN-COATED CELLULOSE FIBERS FROM LIGNOCELLULOSIC BIOMASS
Abstract
A process is provided for producing a lignin-coated cellulose
material, comprising: pre-extracting a lignocellulosic biomass
feedstock in the presence of steam or hot water, depositing lignin
from the liquid onto a surface of solids to generate a
lignin-coated intermediate material; optionally drying the
intermediate material; digesting the lignin-coated intermediate
material in the presence of an acid, a solvent for lignin, and
water, wherein the rate of delignification of surface lignin is
lower than the rate of delignification of bulk lignin; and
recovering a hydrophobic lignin-coated cellulose material. In some
variations, part of the overall process is a combination of Green
Power+.RTM. and AVAP.RTM. technologies. A cellulose-rich
composition is provided, containing about 5 wt % to about 15 wt %
total lignin, with particles having a higher average surface
concentration of lignin compared to an average bulk (internal)
concentration of lignin.
Inventors: |
TUNC; Mehmet Sefik;
(Thomaston, GA) ; PYLKKANEN; Vesa; (Atlanta,
GA) ; RETSINA; Theodora; (Atlanta, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
API Intellectual Property Holdings, LLC |
Atlanta |
GA |
US |
|
|
Family ID: |
53797605 |
Appl. No.: |
14/606442 |
Filed: |
January 27, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61941215 |
Feb 18, 2014 |
|
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|
Current U.S.
Class: |
162/16 |
Current CPC
Class: |
D21H 11/12 20130101;
D21C 3/04 20130101; Y02P 40/44 20151101; D21C 1/02 20130101; D21C
11/0007 20130101; D21C 11/12 20130101; Y02P 40/40 20151101 |
International
Class: |
D21H 11/12 20060101
D21H011/12; D21C 1/02 20060101 D21C001/02; D21C 11/00 20060101
D21C011/00 |
Claims
1. A process for producing a lignin-coated cellulose material, said
process comprising: (a) providing a lignocellulosic biomass
feedstock; (b) pre-extracting said feedstock in the presence of
steam or hot water, thereby generating a first solids stream and a
first liquid stream, wherein said first liquid stream contains
hemicelluloses and lignin; (c) depositing at least some of said
lignin, from said first liquid stream, onto a surface of said first
solids stream to generate a lignin-coated intermediate material
comprising cellulose-rich particles with a lignin coating; (d)
optionally drying said lignin-coated intermediate material; (e)
digesting said lignin-coated intermediate material in the presence
of an acid, a solvent for lignin, and water, to generate a second
solids stream and a second liquid stream, wherein during said
digesting, the rate of delignification of surface lignin deposited
from step (c) is lower than the rate of delignification of bulk
lignin, thereby retaining at least a portion of said lignin
coating; and (f) recovering said second solids stream as a
lignin-coated cellulose material, wherein said lignin-coated
cellulose material is at least partially hydrophobic.
2. The process of claim 1, wherein step (b) further includes
introducing an acid catalyst to enhance lignin deposition.
3. The process of claim 2, wherein said acid catalyst includes an
acid selected from the group consisting of acetic acid, formic
acid, uronic acids, levulinic acid, sulfur dioxide, sulfurous acid,
sulfuric acid, lignosulfonic acid, carbon dioxide, carbonic acid,
and combinations thereof.
4. The process of claim 1, wherein said drying is conducted in step
(d).
5. The process of claim 1, wherein said acid in step (e) is
selected from the group consisting of sulfur dioxide, sulfurous
acid, sulfur trioxide, sulfuric acid, lignosulfonic acid, and
combinations thereof.
6. The process of claim 5, wherein said acid is sulfur dioxide.
7. The process of claim 1, said process further comprising
hydrolyzing said hemicelluloses to produce monomeric sugars.
8. The process of claim 1, wherein said second liquid stream
contains hemicellulose oligomers; said process further comprising
hydrolyzing said hemicellulose oligomers to monomers.
9. The process of claim 8, wherein said hemicellulose oligomers and
said hemicelluloses from step (b) are combined and hydrolyzed in a
single reactor.
10. The process of claim 1, wherein said lignin-coated cellulose
material includes one or more materials selected from the group
consisting of pulp, dissolving pulp, fibrillated cellulose,
microcrystalline cellulose, and nanocellulose.
11. The process of claim 1, wherein said lignin-coated cellulose
material is combusted as a lignin-rich cellulosic fuel.
12. The process of claim 1, said process further comprising
recovering, combusting, or further treating said lignin that does
not deposit during step (c).
13. The process of claim 1, wherein said lignin-coated cellulose
material contains, on a dry basis, about 3 wt % or less
hemicellulose content.
14. A cellulose-rich composition comprising from about 70 wt % to
about 90 wt % cellulose and about 5 wt % to about 15 wt % total
lignin, wherein said cellulose-rich composition includes particles
with a higher average surface concentration of lignin compared to
an average bulk (internal) concentration of lignin.
15. The cellulose-rich composition of claim 14, wherein said
composition comprises from about 75 wt % to about 87 wt %
cellulose.
16. The cellulose-rich composition of claim 14, wherein said
composition comprises from about 7 wt % to about 12 wt %
lignin.
17. The cellulose-rich composition of claim 14, wherein said
composition comprises about 3 wt % or less hemicellulose.
18. The cellulose-rich composition of claim 17, wherein said
composition comprises about 2 wt % or less hemicellulose.
19. The cellulose-rich composition of claim 14, wherein said
composition comprises from about 1 wt % to about 2 wt % uronic acid
groups.
20. The cellulose-rich composition of claim 14, wherein said
composition comprises about 2 wt % or less ash.
21. The cellulose-rich composition of claim 14, wherein said
composition is characterized by a ratio H/(C+H) of about 0.03 to
about 0.04, wherein H is total hemicellulose and C is total
cellulose.
22. The cellulose-rich composition of claim 14, wherein said
composition is produced by a process comprising: (a) providing a
lignocellulosic biomass feedstock; (b) pre-extracting said
feedstock in the presence of steam or hot water, thereby generating
a first solids stream and a first liquid stream, wherein said first
liquid stream contains hemicelluloses and lignin; (c) depositing at
least some of said lignin, from said first liquid stream, onto a
surface of said first solids stream to generate a lignin-coated
intermediate material comprising cellulose-rich particles with a
lignin coating; (d) optionally drying said lignin-coated
intermediate material; (e) digesting said lignin-coated
intermediate material in the presence of an acid, a solvent for
lignin, and water, to generate a second solids stream and a second
liquid stream, wherein during said digesting, the rate of
delignification of surface lignin deposited from step (c) is lower
than the rate of delignification of bulk lignin, thereby retaining
at least a portion of said lignin coating; and (f) recovering said
second solids stream as a lignin-coated cellulose-rich composition,
wherein said lignin-coated cellulose-rich composition is at least
partially hydrophobic.
23. A cellulose-containing product comprising the cellulose-rich
composition of claim 14.
24. The cellulose-containing product of claim 23, wherein said
cellulose-containing product is selected from the group consisting
of a structural object, a foam, an aerogel, a polymer composite, a
carbon composite, a film, a coating, a coating precursor, a current
or voltage carrier, a filter, a membrane, a catalyst, a catalyst
substrate, a coating additive, a paint additive, an adhesive
additive, a cement additive, a paper coating, a thickening agent, a
rheological modifier, an additive for a drilling fluid, and
combinations or derivatives thereof.
Description
PRIORITY DATA
[0001] This patent application is a non-provisional application
with priority to U.S. Provisional Patent App. No. 61/941,215, filed
Feb. 18, 2014, 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.
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 attempt 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] Contrary to the 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.
[0015] Commercial sulfite pulping has been practiced since 1874.
The focus of sulfite pulping is the preservation of cellulose. In
an effort to do that, industrial variants of sulfite pulping take
6-10 hours to dissolve hemicelluloses and lignin, producing a low
yield of fermentable sugars. Stronger acidic cooking conditions
that hydrolyze the hemicellulose to produce a high yield of
fermentable sugars also hydrolyze the cellulose, and therefore the
cellulose is not preserved.
[0016] The dominant pulping process today is the Kraft process.
Kraft pulping does not fractionate lignocellulosic material into
its primary components. Instead, hemicellulose is degraded in a
strong solution of sodium hydroxide with or without sodium sulfide.
The cellulose pulp produced by the Kraft process is high quality,
essentially at the expense of both hemicellulose and lignin.
[0017] Sulfite pulping produces spent cooking liquor termed sulfite
liquor. Fermentation of sulfite liquor to hemicellulosic ethanol
has been practiced primarily to reduce the environmental impact of
the discharges from sulfite mills since 1909. However, ethanol
yields do not exceed one-third of the original hemicellulose
component. Ethanol yield is low due to the incomplete hydrolysis of
the hemicelluloses to fermentable sugars and further compounded by
sulfite pulping side products, such as furfural, methanol, acetic
acid, and others fermentation inhibitors.
[0018] 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.
[0019] 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.
[0020] Cellulose or cellulose derivatives can be used in a wide
variety of applications such as polymer reinforcement,
anti-microbial films, biodegradable food packaging, printing
papers, pigments and inks, paper and board packaging, barrier
films, adhesives, biocomposites, wound healing, pharmaceuticals and
drug delivery, textiles, water-soluble polymers, construction
materials, recyclable interior and structural components for the
transportation industry, rheology modifiers, low-calorie food
additives, cosmetics thickeners, pharmaceutical tablet binders,
bioactive paper, pickering stabilizers for emulsion and particle
stabilized foams, paint formulations, films for optical switching,
and detergents.
[0021] For some cellulose applications, is would be beneficial to
increase the hydrophobicity of the cellulose. Therefore, improved
processes are needed in the art.
SUMMARY
[0022] The present invention addresses the aforementioned needs in
the art.
[0023] In some variations, the invention provides a process for
producing a lignin-coated cellulose material, the process
comprising:
[0024] (a) providing a lignocellulosic biomass feedstock;
[0025] (b) pre-extracting the feedstock in the presence of steam or
hot water, thereby generating a first solids stream and a first
liquid stream, wherein the first liquid stream contains
hemicelluloses and lignin;
[0026] (c) depositing at least some of the lignin, from the first
liquid stream, onto a surface of the first solids stream to
generate a lignin-coated intermediate material comprising
cellulose-rich particles with a lignin coating;
[0027] (d) optionally drying the lignin-coated intermediate
material;
[0028] (e) digesting the lignin-coated intermediate material in the
presence of an acid, a solvent for lignin, and water, to generate a
second solids stream and a second liquid stream, wherein during the
digesting, the rate of delignification of surface lignin deposited
from step (c) is lower than the rate of delignification of bulk
lignin, thereby retaining at least a portion of the lignin coating;
and
[0029] (f) recovering the second solids stream as a lignin-coated
cellulose material, wherein the lignin-coated cellulose material is
at least partially hydrophobic.
[0030] In some embodiments, step (b) further includes introducing
an acid catalyst to enhance lignin deposition. Such an acid
catalyst may be selected from the group consisting of acetic acid,
formic acid, uronic acids, levulinic acid, sulfur dioxide,
sulfurous acid, sulfuric acid, lignosulfonic acid, carbon dioxide,
carbonic acid, and combinations thereof.
[0031] In some embodiments, some amount of drying is conducted in
step (d). In these or alternative embodiments, water is removed by
membranes, molecular sieves, centrifuges, or other means.
[0032] In some embodiments, the acid in step (e) is selected from
the group consisting of sulfur dioxide, sulfurous acid, sulfur
trioxide, sulfuric acid, lignosulfonic acid, and combinations
thereof. The acid is sulfur dioxide, in particular embodiments.
[0033] The process may further comprise hydrolyzing the
hemicelluloses (in the first liquid stream) to produce monomeric
sugars. The second liquid stream also typically contains
hemicellulose oligomers; the process may further comprise
hydrolyzing the hemicellulose oligomers to monomers. Optionally,
the hemicellulose oligomers and the hemicelluloses from step (b)
are combined and hydrolyzed in a single reactor. The lignin-coated
cellulose material contains, on a dry basis, about 3 wt % or less
hemicellulose content.
[0034] The lignin-coated cellulose material may include one or more
materials selected from the group consisting of pulp, dissolving
pulp, fibrillated cellulose, microcrystalline cellulose, and
nanocellulose. The lignin-coated cellulose material may be
combusted as a lignin-rich cellulosic fuel. In some embodiments,
the process further comprises recovering, combusting, or further
treating the lignin that does not deposit during step (c).
[0035] Variations of the invention provide a cellulose-rich
composition comprising from about 70 wt % to about 90 wt %
cellulose and about 5 wt % to about 15 wt % total lignin, wherein
the cellulose-rich composition includes particles with a higher
average surface concentration of lignin compared to an average bulk
(internal) concentration of lignin.
[0036] In some embodiments, the composition comprises from about 75
wt % to about 87 wt % cellulose. In certain embodiments, the
composition comprises from about 77 wt % to about 86 wt %
cellulose.
[0037] In some embodiments, the cellulose-rich composition
comprises from about 7 wt % to about 12 wt % lignin. In certain
embodiments, the composition comprises from about 8 wt % to about
11 wt % lignin.
[0038] In some embodiments, the cellulose-rich composition
comprises about 3 wt % or less hemicellulose. In certain
embodiments, the composition comprises about 2 wt % or less
hemicellulose.
[0039] In some embodiments, the composition comprises from about
1.0 wt % to about 2.0 wt % uronic acid groups. In some embodiments,
the composition comprises about 2 wt % or less ash.
[0040] The cellulose-rich composition may be characterized by an
elemental ratio H/(C+H) of about 0.03 to about 0.04, such as about
0.031 to about 0.034, in certain embodiments, where H is total
hemicellulose and C is total cellulose.
[0041] Various cellulose-containing products may include the
cellulose-rich compositions disclosed herein. In various
embodiments, the cellulose-containing product is selected from the
group consisting of a structural object, a foam, an aerogel, a
polymer composite, a carbon composite, a film, a coating, a coating
precursor, a current or voltage carrier, a filter, a membrane, a
catalyst, a catalyst substrate, a coating additive, a paint
additive, an adhesive additive, a cement additive, a paper coating,
a thickening agent, a rheological modifier, an additive for a
drilling fluid, and combinations or derivatives thereof.
BRIEF DESCRIPTION OF THE FIGURES
[0042] FIG. 1 is an exemplary block-flow diagram of some
embodiments of the invention to fractionate biomass into cellulose,
hemicellulose, and lignin, comprising hot-water extraction followed
by digestion with an acid and solvent for lignin.
[0043] FIG. 2 is an exemplary block-flow diagram depicting a Green
Power+.RTM. process followed by an AVAP.RTM. process to produce
lignin-coated cellulose fibers.
[0044] FIG. 3 shows photographs of (a) pre-extracted sugarcane
straw and (b) lignin-coated cellulose fibers produced, according to
some embodiments.
[0045] FIG. 4 is a graph of experimental Kappa number versus
ethanol concentration in cooking liquor.
DETAILED DESCRIPTION OF SOME EMBODIMENTS
[0046] 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.
[0047] 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.
[0048] 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.
[0049] 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.
[0050] 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.
[0051] 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".
[0052] The present invention, in some variations, is premised on
the realization that aspects of Green Power+.RTM. and AVAP.RTM.
technologies may be combined and improved in certain ways to
realize various benefits (as described herein).
[0053] 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 cellulose is highly reactive to
cellulase enzymes for the manufacture of glucose. Other uses for
celluloses can be adjusted based on market conditions.
[0054] 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.
[0055] In some variations, the invention provides a process for
producing a lignin-coated cellulose material, the process
comprising:
[0056] (a) providing a lignocellulosic biomass feedstock;
[0057] (b) pre-extracting the feedstock in the presence of steam or
hot water, thereby generating a first solids stream and a first
liquid stream, wherein the first liquid stream contains
hemicelluloses and lignin;
[0058] (c) depositing at least some of the lignin, from the first
liquid stream, onto a surface of the first solids stream to
generate a lignin-coated intermediate material comprising
cellulose-rich particles with a lignin coating;
[0059] (d) optionally drying the lignin-coated intermediate
material;
[0060] (e) digesting the lignin-coated intermediate material in the
presence of an acid, a solvent for lignin, and water, to generate a
second solids stream and a second liquid stream, wherein during the
digesting, the rate of delignification of surface lignin deposited
from step (c) is lower than the rate of delignification of bulk
lignin, thereby retaining at least a portion of the lignin coating;
and
[0061] (f) recovering the second solids stream as a lignin-coated
cellulose material, wherein the lignin-coated cellulose material is
at least partially hydrophobic.
[0062] In some embodiments, step (b) further includes introducing
an acid catalyst to enhance lignin deposition (such as by
catalyzing precipitation reactions). Such an acid catalyst may be
selected from the group consisting of acetic acid, formic acid,
uronic acids, levulinic acid, sulfur dioxide, sulfurous acid,
sulfuric acid, lignosulfonic acid, carbon dioxide, carbonic acid,
and combinations thereof.
[0063] The acid for either step (b), if employed, or step (e) may
be derived and recycled from operations downstream. For example,
acetic acid may be recycled from evaporator condensate. In some
embodiments, a sulfur-containing acid contained in or derived from
a liquid stream is recycled to step (b) and/or step (e).
[0064] Without being limited by theory, it is believed that the
surface lignin, deposited back into the cellulose particles or
fibers during pre-extraction, will be chemically more recalcitrant
than the native lignin that is present in the bulk, internal
portion of the cellulose particles or fibers. It is believed that
the surface lignin will experience a slower rate of delignification
in the digestion step, and possibly no net delignification,
compared to the delignification rate of the bulk lignin. It should
be noted that the surface lignin layer is not regarded as an
impenetrable layer since bulk lignin and hemicellulose need to
diffuse through the layer to enter solution in the digesting step.
During digesting, additional lignin may precipitate as well.
[0065] In some embodiments, some amount of drying is conducted in
step (d). In these or alternative embodiments, water is removed by
membranes, molecular sieves, centrifuges, or other means. Drying or
other treatment between pre-extraction and digestion may modify the
surface lignin so that it is less susceptible to delignification
during the digesting step, for example.
[0066] In some embodiments, the acid in step (e) is selected from
the group consisting of sulfur dioxide, sulfurous acid, sulfur
trioxide, sulfuric acid, lignosulfonic acid, and combinations
thereof. The acid is sulfur dioxide, in particular embodiments.
[0067] The process may further comprise hydrolyzing the
hemicelluloses (in the first liquid stream) to produce monomeric
sugars. The second liquid stream also typically contains
hemicellulose oligomers; the process may further comprise
hydrolyzing the hemicellulose oligomers to monomers. Optionally,
the hemicellulose oligomers and the hemicelluloses from step (b)
are combined and hydrolyzed in a single reactor. The lignin-coated
cellulose material contains, on a dry basis, about 3 wt % or less
hemicellulose content.
[0068] The lignin-coated cellulose material may include one or more
materials selected from the group consisting of pulp, dissolving
pulp, fibrillated cellulose, microcrystalline cellulose, and
nanocellulose. The lignin-coated cellulose material may be
combusted as a lignin-rich cellulosic fuel. In some embodiments,
the process further comprises recovering, combusting, or further
treating the lignin that does not deposit during step (c).
[0069] Variations of the invention provide a cellulose-rich
composition comprising from about 70 wt % to about 90 wt %
cellulose and about 5 wt % to about 15 wt % total lignin, wherein
the cellulose-rich composition includes particles with a higher
average surface concentration of lignin compared to an average bulk
(internal) concentration of lignin.
[0070] In some embodiments, the composition comprises from about 75
wt % to about 87 wt % cellulose. In certain embodiments, the
composition comprises from about 77 wt % to about 86 wt %
cellulose.
[0071] In some embodiments, the cellulose-rich composition
comprises from about 7 wt % to about 12 wt % lignin. In certain
embodiments, the composition comprises from about 8 wt % to about
11 wt % lignin.
[0072] In some embodiments, the cellulose-rich composition
comprises about 3 wt % or less hemicellulose. In certain
embodiments, the composition comprises about 2 wt % or less
hemicellulose.
[0073] In some embodiments, the composition comprises from about
1.0 wt % to about 2.0 wt % uronic acid groups. In some embodiments,
the composition comprises about 2 wt % or less ash.
[0074] The cellulose-rich composition may be characterized by an
elemental ratio H/(C+H) of about 0.03 to about 0.04, such as about
0.031 to about 0.034, in certain embodiments, where H is total
hemicellulose and C is total cellulose.
[0075] Various cellulose-containing products may include the
cellulose-rich compositions disclosed herein. In various
embodiments, the cellulose-containing product is selected from the
group consisting of a structural object, a foam, an aerogel, a
polymer composite, a carbon composite, a film, a coating, a coating
precursor, a current or voltage carrier, a filter, a membrane, a
catalyst, a catalyst substrate, a coating additive, a paint
additive, an adhesive additive, a cement additive, a paper coating,
a thickening agent, a rheological modifier, an additive for a
drilling fluid, and combinations or derivatives thereof.
[0076] The second liquid stream typically (although not
necessarily) contains hemicellulose oligomers. In some embodiments,
the process further comprises hydrolyzing the hemicellulose
oligomers to monomers in the presence of heat and optionally a
second hydrolysis catalyst. The second hydrolysis catalyst may
include an acid selected from the group consisting of acetic acid,
formic acid, uronic acids, levulinic acid, sulfur dioxide,
sulfurous acid, sulfuric acid, lignosulfonic acid, carbon dioxide,
carbonic acid, and combinations thereof.
[0077] There are many opportunities for mass and energy
integration. In some embodiments, the hemicelluloses from step (e)
and the hemicellulose oligomers from step (b) are combined and
hydrolyzed in a single reactor (or a series of reactors, tanks, or
other units).
[0078] In certain embodiments, step (b) is conducted at a first
location and step (e) is conducted at a second location that is not
co-located at a single site. In these embodiments, the first solids
stream is transported (e.g., by truck, rail, barge, or other means)
from the first location to the second location, which may be for
example 5, 25, 50, 100, 500, 1000 miles away or more.
[0079] 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.
[0080] 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.).
[0081] 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.
[0082] 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; U.S.
Pat. No. 8,585,863, issued Nov. 19, 2013; and U.S. patent
application Ser. Nos. 12/234,286; 13/585,710; 13/626,220;
12/854,869; 12/250,734; 12/397,284; 12/304,046; 13/500,916;
13/626,220; 12/854,869; 14/048,068; 14/005,382; 61/732,047;
61/735,738; 61/747,010; 61/747,105; 61/747,376; 61/747,379;
61/747,382; 61/747,408; 61/747,566; 61/747,771; 61/827,827;
61/845,298; 61/845,046; 61/732,047; 61/739,343; 61/770,130;
61/836,014; and 61/747,631. 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.
[0083] Some embodiments employ conditions described in U.S. Pat.
No. 8,211,680, issued Jul. 3, 2012; U.S. Pat. No. 8,518,672, issued
Aug. 27, 2013; U.S. Pat. No. 8,518,213, issued Aug. 27, 2013; and
U.S. patent application Ser. Nos. 13/950,289; 13/929,858;
12/397,284; 13/471,662; 13/026,273; 13/026,280; 13/500,917;
13/929,858; 13/968,892; 13/829,237; 13/829,355; 13/874,761;
13/959,705; 14/017,286; 14/044,784; 14/044,790; 61/810,767;
61/839,912; and 61/878,421. 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
Green Power+.RTM. process technology which is commonly owned with
the assignee of this patent application.
[0084] Some variations may be understood with reference to FIGS. 1
and 2. Dotted lines denote optional streams. Various embodiments
will now be further described, without limitation as to the scope
of the invention. These embodiments are exemplary in nature.
[0085] In some variations associated with FIG. 1, the invention
provides a process for fractionating lignocellulosic biomass, the
process comprising:
[0086] (a) providing a feedstock comprising lignocellulosic
biomass;
[0087] (b) extracting hemicelluloses from the feedstock in the
presence of steam or hot water, and optionally a first hydrolysis
catalyst, thereby generating a first solids stream (with
lignin-coated cellulose) and a first liquid stream;
[0088] (c) contacting the first solids stream with an acid or acid
precursor, water, and a solvent for lignin, to produce a second
liquid stream containing lignin-coated cellulose-rich solids and
lignin;
[0089] (d) recovering the lignin-coated cellulose-rich solids from
the second liquid stream;
[0090] (e) hydrolyzing the hemicelluloses to produce monomeric
sugars; and
[0091] (f) recovering the monomeric sugars.
[0092] In preferred embodiments, the process further comprises
recovering or further treating the lignin-coated cellulose-rich
solids as pulp, a cellulose product, or a cellulose derivative. In
some embodiments, the process further comprises hydrolyzing the
lignin-coated cellulose-rich solids using an acid catalyst or
cellulase enzymes to produce glucose.
[0093] The lignocellulosic material following pre-extraction may be
processed in a solution (cooking liquor) of aliphatic alcohol,
water, and sulfur dioxide. The cooking liquor preferably contains
at least 10 wt %, such as about 20 wt %, 30 wt %, 35 wt % 40 wt %,
or 50 wt % of a solvent for lignin. For example, the cooking liquor
may contain about 10-70 wt % solvent, such as about 30 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.
[0094] 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.
[0095] The cooking liquor for the digestor contains an effective
amount of an acid or acid precursor. Acids may be sulfur-containing
acids (e.g. SO.sub.2 or lignosulfonic acid), nitrogen-containing
acids (e.g. nitric acid), phosphorus-containing acids (e.g.
phosphoric acid), carbon-containing acids (e.g. carbonic acid), and
so on. An "acid precursor" is any compound that, at least in part,
forms or releases an acid in the digestor. Sulfur dioxide may be
considered an acid precursor since SO.sub.2 is not itself a
Bronsted acid, although SO.sub.2 is a Lewis acid.
[0096] 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.
[0097] 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.
[0098] In some embodiments, an additive may be included in amounts
of about 0.1 wt % to 10 wt % or more to increase cellulose
viscosity. Exemplary additives include ammonia, ammonia hydroxide,
urea, anthraquinone, magnesium oxide, magnesium hydroxide, sodium
hydroxide, and their derivatives.
[0099] 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.
[0100] 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.
[0101] 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.
[0102] 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, bisulfate ions, combinations thereof, or a salt of
any of the foregoing. Excess sulfur dioxide, following hydrolysis,
may be recovered and reused.
[0103] 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.
[0104] 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.
[0105] 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.).
[0106] 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.
[0107] 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. Recycle streams, such as from
solvent-recovery operations, may be used to wash the solids.
[0108] 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.
[0109] 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.
[0110] 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.
[0111] 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.
[0112] 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.
[0113] 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.
[0114] 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.
[0115] 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.
[0116] 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.
[0117] 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.
[0118] 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.
[0119] When the fermentation will employ bacteria, such as
Clostridia bacteria, it is preferable to further 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 or other means) 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.
[0120] In some embodiments, the process further comprises
recovering the lignin as a co-product. The sulfonated lignin may
also be recovered as a co-product. 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.
[0121] The process lignin separation step is for the separation of
lignin from the hydrolysate and can be located before or after the
final reaction step and evaporation. If located after, then lignin
will precipitate from the hydrolysate since alcohol has been
removed in the evaporation step. 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 combined
lignin and lignosulfonate precipitate may be filtered. The lignin
and 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.
[0122] 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).
[0123] In some embodiments, the soluble lignin precipitates from
the hydrolysate after solvent has been removed in the evaporation
step. In some embodiments, reactive lignosulfonates are selectively
precipitated from hydrolysate using excess lime (or other base,
such as ammonia) in the presence of aliphatic alcohol. In some
embodiments, hydrated lime is used to precipitate lignosulfonates.
In some embodiments, part of the lignin is precipitated in reactive
form and the remaining lignin is sulfonated in water-soluble
form.
[0124] 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.
[0125] 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,
hydroxymethylfurfural (HMF), methanol, acetic acid, and
lignin-derived compounds, for example.
[0126] 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.
[0127] 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, may be converted into
xylitol.
[0128] A lignin product can be readily obtained from a liquid phase
using one or more of several methods. One simple technique is to
evaporate off all liquid, resulting in a solid lignin-rich residue.
This technique would be especially advantageous if the solvent for
lignin is water-immiscible. Another method is to cause the lignin
to precipitate out of solution. Some of the ways to precipitate the
lignin include (1) removing the solvent for lignin from the liquid
phase, but not the water, such as by selectively evaporating the
solvent from the liquid phase until the lignin is no longer
soluble; (2) diluting the liquid phase with water until the lignin
is no longer soluble; and (3) adjusting the temperature and/or pH
of the liquid phase. Methods such as centrifugation can then be
utilized to capture the lignin. Yet another technique for removing
the lignin is continuous liquid-liquid extraction to selectively
remove the lignin from the liquid phase, followed by removal of the
extraction solvent to recover relatively pure lignin.
[0129] 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.
[0130] 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,
analyzed (including on-line or off-line analysis), and/or marketed
or sold.
[0131] 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.
[0132] 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.
[0133] 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.
[0134] 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.
Examples
Production of Lignin-Coated Cellulose Fibers by Implementation of
AVAP Process Following Hot Water Pre-Extraction of Lignocellulosic
Biomass by Green Power+ Process
[0135] Green Power+ pre-extraction of sugarcane straws with water
was performed at 180.degree. C. for 2.5 and 10 min at L/W ratio of
4:1. The extraction yields of 2.5 and 10 min hot water
pre-treatments were 28 and 35% respectively. Hemicellulose and
mineral removal of the straws were promoted with hot water
pretreatment by Green Power+ process addition prior to AVAP
process; lignin condensation on cellulose fibers took place which
hindered delignification during AVAP cooking. Therefore,
lignin-coated cellulose fibers with low hemicellulose and lignin
contents can be produced by AVAP process following the hot water
pre-extraction of lignocellulosic biomass by Green Power+.
Material and Methods
[0136] Sugar cane straws were used as lignocellulosic feedstock for
the experiments. Green Power+ pre-treatment and AVAP cooking of the
straws were conducted in mini-reactors of multi digester oil bath
(MDOB). Subsequent fiber washing with 40% ethanol following the
AVAP process was conducted and cellulose fibers were prepared after
defibrillation, disintegration and screening processes.
Subsequent Fiber Washing Procedure Following AVAP Process
[0137] The mini-reactors were rapidly removed from the oil bath at
the end of AVAP cooking and they were placed in an ice-water bath.
The bombs were opened after about 10 min of cooling. The cooking
mixture (the fibers and liquor) was separated using a nylon washing
bag by squeezing. The nylon bag was then put into a plastic bag and
50 ml of washing liquid (40% (w/w) ethanol) was added into the
plastic bag. The EtOH washing was conducted in a water bath at
60.degree. C. for 5 min. Liquor is squeezed out after the 1.sup.st
EtOH washing. The washing step was repeated one more time for more
complete washing. The nylon bag was placed into a 1 L beaker and it
was washed with 500 ml of water at 20.degree. C. for 5 min. The
water washing step was repeated one more time. Finally, the
cellulose fibers were mixed with about 500 ml of water and stirred
about 5 min with a mechanical stirrer and filtered through the
Whatman filter paper to produce the fiber pad (cellulose
fiber).
Composition Analysis of Straws and Fibers
[0138] Sugar cane straws and cellulose fibers were air dried and
ground to less than 0.1 mm using a Wiley Mill and the moisture
content of the milled particles was determined using a convection
oven at 100.+-.5.degree. C. overnight. The ash content of the
samples was determined according to Tappi standard method T211
om-85. The extractives content of air dried ground particles was
determined by the Soxhlet extraction method with acetone. The acid
insoluble lignin content, or Klason lignin, was determined
according to the method by Effland (1977), while the acid soluble
lignin content was determined by Tappi Method 250. The uronic
anhydride content was determined using the chromophoric group
analysis method developed by Scott (1979). The milled straw
particles were first acid hydrolyzed with 72% H.sub.2SO.sub.4 in a
water bath at 30.+-.1.degree. C. for 2 hours and then exposed to
secondary acid hydrolysis at 4% H.sub.2SO.sub.4 in an autoclave at
120.+-.1.degree. C. and 2 hours for monosugar content analysis
(Davis, 1998). A High Performance Anion Exchange Chromatography
with Pulse Amperometric Detection (HPAEC-PAD) was used for
separation of the monosugars. Acetic acid in the hydrolysate was
determined by High Performance Liquid Chromatography (HPLC) using a
refractive index detector and BIO-RAD Aminex HPX-87H column. The
mobile phase used was 0.6 mL/min 5 mM H.sub.2SO.sub.4, and the oven
temperature was 60.degree. C. The Kappa number of the fibers was
analyzed by Tappi method T236 om-99.
Results and Discussion
[0139] The chemical composition of the original sugar cane straw
used for the pre-extraction experiments is summarized in Table 1.
The cellulose and hemicellulose contents are 34.9.+-.0.6 and
23.9.+-.0.8% respectively based on oven dried (od) straw.
TABLE-US-00001 TABLE 1 The chemical composition of sugar cane
straws based on od straw Component % Component % Arabinan 3.0 .+-.
0.6 OAc.sup.a 0.9 .+-. 0.0 Galactan 1.1 .+-. 0.0 UAG.sup.b 1.4 .+-.
0.0 Glucan 35.3 .+-. 0.7 Lignin 20.5 .+-. 0.4 Xylan 18.6 .+-. 0.5
Extractives 3.1 .+-. 0.0 Mannan 0.7 .+-. 0.5 Ash 3.1 .+-. 0.0
.sup.aAcetyl groups, .sup.bUronic acid groups
[0140] Hot water pre-extraction of sugar cane straws by Green
Power+ was performed in the mini reactors of MDOB at 180.degree. C.
for 2.5 and 10 min. The liquid to wood ratio of the pre-extraction
was 4:1. The sugar cane straws subjected to hot water
pre-extraction were washed in total with about 950 ml of water.
First the straws were rinsed with 9 times with 50 ml of water
(collecting 450 ml of rinsing water identified as 1.sup.st wash),
and then the straws were washed with 500 ml water (2.sup.nd wash)
for about 30 min with occasional stirring. The extraction yields
following 2.5 and 10 min of pre-extraction were 28 and 35%
respectively. Solid phases following hot water pre-extractions were
dried in a convection oven overnight at 100.+-.5.degree. C. and
oven dried solids were subjected to AVAP cooking at 155.degree. C.
for 58 min with 12% SO.sub.2 in 50% (w/w) EtOH at L/W ratio of 4:1
as illustrated in FIG. 2.
[0141] Yield and Kappa number of fibers produced from AVAP cooking
of hot-water pre-extracted sugar cane straws are summarized in
Table 3. It is apparent from Table 3 that the fiber yield increases
with addition of hot water pre-extraction. The Kappa number is also
increased with hot water pre-extraction. The longer the hot water
pre-extraction, the higher the yield and Kappa number. The reason
for such high a Kappa number with hot water pre-extraction addition
is believed to be that the lignin remaining after hot water
pre-extraction is more condensed (Iakovlev, 2011) and that
dissolved lignin is re-deposited (Xu et al., 2007) on cellulose
fibers due to condensation reactions. Indirect evidence for
condensation of lignin is the dark brown color of the hot water
pre-extracted straws and cellulose fibers produced from hot water
pre-extracted straws with AVAP cooking as shown in FIG. 3. The
lignin-free yields as a result of 2.5 min and 10 min hot water
addition are around 36 and 37% respectively. The lignin-free yield
without any hot water extraction is around 35%.
TABLE-US-00002 TABLE 3 Results of AVAP cooking following hot water
pre-extraction of straws Pre-extraction with Pre-extraction with No
GP.sup.+ process (2.5 min) GP.sup.+ process (10 min) Pre-extraction
Yield (%) 44.3 47.6 38.5 Kappa # 56.1 68.8 23.8 pH ~0.76 ~0.76
~1.0
[0142] FIG. 3 shows a picture of the (a) pre-extracted sugar cane
straws and (b) cellulose fiber produced by the AVAP process
(starting with the pre-extracted sugar cane straws).
[0143] The composition of the cellulose fibers produced from hot
water pre-extracted sugar cane straws by the AVAP process at
155.degree. C. for 58 min at L/W ratio of 4:1 with 12% SO.sub.2 in
50% EtOH is summarized in Table 4. It is clear from Table 4 that
the hemicellulose content of fibers produced with the AVAP process
may be reduced by addition of the hot water pre-treatment as well
as that the hemicellulose content to relative cellulose and
hemicellulose content can be improved with hot water pre-extraction
at 180.degree. C. for 2.5 and 10 min. As was discussed earlier,
condensation of lignin takes place during hot water pre-extraction
and hinders delignification during AVAP process (see Table 4).
Although all acetyl groups are removed during AVAP cooking of sugar
cane straws with or without addition of the Green Power+ process,
the cellulose fibers produced from hot water pre-treated straws
still have higher uronic acid groups. Somehow hot water
pre-extraction addition obstructs dissolution of uronic acid groups
of sugar cane straws during AVAP process. It is clear from Table 4
that hot water pre-treatment helps removal of minerals from sugar
cane straw that might diminish the acid neutralization power of
minerals in the straws during AVAP cooking. Indirect evidence of
this is the lower pH of the extract generated during AVAP cooking
of hot water pre-extracted straws (see Table 3).
TABLE-US-00003 TABLE 4 Composition of cellulose fibers produced by
AVAP process following hot water pre-extraction of the straws
GP.sup.+ Process Cell Hemi Lignin OAc UAG Ash H/(C + H), % 2.5 min
84.1 .+-. 1.5 2.9 .+-. 0.1 8.5 0.0 1.7 .+-. 0.1 1.6 .+-. 0.1 3.3 10
min 78.6 .+-. 1.1 2.6 .+-. 0.1 10.5 0.0 1.4 .+-. 0.1 1.5 .+-. 0.1
3.2 None 88.1 .+-. 0.1 3.7 .+-. 0.1 3.2 0.0 0.8 .+-. 0.2 2.9 .+-.
0.4 4.2 C: Cellulose; H: Hemicellulose; OAc: Acetyl Groups; UAG:
Uronic Acid Groups
Conclusions
[0144] Hot water pre-extraction of sugarcane straws was performed
in the MDOB at 180.degree. C. for 2.5 and 10 min at a L/W ratio of
4:1 and the extraction yields were 28 and 35% for 2.5 and 10 min
respectively. Although hemicellulose and mineral removal from sugar
cane straws were promoted with hot water pretreatment prior to AVAP
cooking, condensation of lignin takes place during pre-treatment
and hinders subsequent delignification during AVAP process. These
combined process can be implemented for production of novel
lignin-coated cellulose fibers.
Effect of Ethanol (EtOH) Concentration on AVAP Cooking of Sugar
Cane Straws
[0145] AVAP cooking of sugar cane straws conducted with lower EtOH
concentration (35% (w/w)) in MDOB was compared with previously
conducted AVAP cooking at higher EtOH concentration (50% (w/w)).
Both cooks were performed at 155.degree. C. for 58 minutes with 12%
SO.sub.2 at L/W ratio of 4 L/Kg and results are summarized in Table
5.
[0146] It is apparent from Table 5 that the fiber yield as a result
of AVAP cooking with 35% EtOH is higher than that of with 50% EtOH
because more lignin dissolved at higher EtOH content as can easily
be inferred from lower Kappa number of the cellulose fibers
produced at 50% EtOH cooking.
[0147] As was expected and shown in Table 4, the extract generated
as a result of AVAP cooking at 35% EtOH has a higher acidity (lower
pH) due to the lower EtOH concentration. The relatively high Kappa
number produced at lower EtOH (35%) concentration is probably due
to both low EtOH concentration and higher acidity (see Table 5). It
is well known that ethanol is a much better solvent for lignin and
lignosulfonates than water (Primakov et al. 1979), and higher
acidity can cause condensation of lignin during AVAP cooking
(Iakovlev, 2011; Sierra-Alvarez and Tjeerdsma, 1995; Eliashberg et
al., 1960; Primakov 1961a).
[0148] Lignin-free yields of fiber produced with 35 and 50% EtOH
are 38 and 35% respectively. This is interesting since acidity
during 35% EtOH cooking is higher than that of 50% EtOH cooking
(see Table 7); higher dissolution yield of non-lignin straw
components is expected during 35% EtOH cooking. The possible
explanation is that hemicelluloses are dissolved along with lignin
as lignin carbohydrate complexes (Fengel and Wegener, 1984) during
50% EtOH cooking since more lignin dissolved during the higher EtOH
AVAP cook as mentioned earlier.
TABLE-US-00004 TABLE 5 Results of AVAP cooking of the straw with 35
and 50% EtOH 35% EtOH 50% EtOH Yield (%) 44.1 .+-. 1.2 38.5 .+-.
0.6 Kappa # 31.6 .+-. 0.9 23.8 .+-. 1.7 Highest Kappa 32.5 25.0
Lowest Kappa 31.3 22.5 pH ~0.60 ~1.0 Number of cooks 2 2
[0149] The composition of cellulose fibers produced by AVAP cooking
of sugar cane straws at 155.degree. C. for 58 minutes at L/W ratio
of 4 L/Kg with 12% SO.sub.2 in 35 and 50% EtOH are summarized in
Table 6. It is clear from Table 6 that the hemicellulose content of
fibers produced with AVAP cooking could be reduced with decreasing
EtOH concentration of the AVAP cooking liquor. Higher acidity of
AVAP cooking as a result of lower EtOH concentration promotes
hemicellulose removal (Iakovlev, 2011). However the selectivity of
hemicellulose removal relative to total carbohydrate (cellulose and
hemicellulose) is only slightly improved by reducing the EtOH
concentration since the cellulose content of the fibers produced at
higher EtOH concentration is higher than that for the lower EtOH
concentration cook. Both fibers produced during AVAP cooking of
sugar cane straws with 35 and 50% EtOH are completely deacetylated,
while also the uronic acid groups and ash content of these two
fibers are the same.
TABLE-US-00005 TABLE 6 Composition of cellulose fibers produced by
the AVAP process with different EtOH concentration ID Cell Hemi
Lignin AcG UAG Ash Hemicellulose 35% EtOH 78.0 .+-. 0.8 3.9 .+-.
0.2 4.8 .+-. 0.1 0.0 1.5 .+-. 0.3 8.5 .+-. 0.4 4.7 50% EtOH 82.3
.+-. 1.3 4.5 .+-. 0.1 3.5 .+-. 0.3 0.0 1.6 .+-. 0.3 8.4 .+-. 0.1
5.2 C: Cellulose; H: Hemicellulose; AcG: Acetyl Groups; UAG: Uronic
Acid Groups
[0150] Similarly, AVAP cooking of sugar cane straws were conducted
at 155 for 58 min with 12% SO.sub.2 at the L/W ratio of 4. Fibers
were subjected to subsequent fiber washing twice with 50 g of 60%
ethanol at 60 C for 30 min following the AVAP cooks. FIG. 4 shows
the Kappa number of straw pulp produced by AVAP versus ethanol
ratio (percentage) of AVAP cooking liquor. It is clear from FIG. 4
that lignin content of pulp decreases with increasing ethanol
concentration up to 30%, then stays constant in the range of
study.
Effect of Liquid to Wood Ratio on AVAP Cooking of Sugar Cane
Straws
[0151] Sugar cane straws were subjected to AVAP cooking in the
Multi Digester Oil Bath (MDOB) at 155.degree. C. for 58 minutes
with 12% SO.sub.2 dissolved in 50% (w/w) EtOH solution at different
L/W ratios (from 3 to 6). Cellulose fibers without any rejects were
produced during AVAP cooking of sugarcane straws at the conditions
summarized above. Cellulose fiber yield was calculated after AVAP
cooking of the straw and the Kappa number of the fibers produced
was determined and summarized in Table 7. The pH values of AVAP
extracts were recorded and are also listed in Table 7. It is
apparent from Table 7 that Kappa number of pulp (cellulose fiber)
produced with lower L/W ratio (3) is higher than with that of
higher L/W ratio (6).
TABLE-US-00006 TABLE 7 Results of AVAP cooking of the straw at LW
ratio of 3 and 6 L/W = 3:1 L/W = 6:1 Yield (%) 41.6 .+-. 1.0 39.9
.+-. 0.1 Kappa # 33.9 .+-. 3.9 23.9 .+-. 0.5 Highest Kappa 39.1
24.4 Lowest Kappa 29.9 23.5 pH ~0.80 ~0.74 Number of cooks 4 3
[0152] The chemical composition of the fibers produced with the
AVAP process at two different L/W ratios is summarized in Table 8.
Table 8 shows that dissolution of hemicellulose and lignin
increases with increasing L/W ratio. Although both fibers produced
with AVAP process at L/W ratio of 3 and 6 contain about 1% uronic
acid groups, they are completely deacetylated--indicative of that
the covalent bond between uronic acid groups and hemicelluloses are
more resistant than that of acetyl groups and hemicellulose against
acid hydrolysis (acidity arising mostly from lignosulfonic acids
formed during SO.sub.2-EtOH cooking). It is clear from Table 8 that
selectivity of cellulose content of fiber relative to total
carbohydrates (cellulose and hemicellulose) is improved with
increasing L/W ratio during AVAP cooking of sugar cane straws at
155.degree. C. for 58 minutes with 12% SO.sub.2 in 50% (w/w)
EtOH.
TABLE-US-00007 TABLE 8 Composition of cellulose fibers produced by
the AVAP process at different L/W ratio ID Cell Hemi Lignin AcG UAG
Ash Hemicellulose L/W:3:1 73.6 .+-. 0.7 7.5 .+-. 0.3 5.1 .+-. 0.6
0.0 1.1 .+-. 0.2 7.1 .+-. 0.2 9.2 L/W:6:1 75.5 .+-. 0.7 5.2 .+-.
0.5 3.5 .+-. 0.1 0.0 1.2 .+-. 0.1 7.5 .+-. 0.3 6.5 C: Cellulose; H:
Hemicellulose; AcG: Acetyl Groups; UAG: Uronic Acid Groups
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