Note: Descriptions are shown in the official language in which they were submitted.
CA 02565433 2006-10-25
INORGANIC SALT RECOVERY DURING PROCESSING OF LIGNOCELLULOSIC
FEEDSTOCKS
FIELD OF INVENTION
[0001] The present invention relates to a method for processing
lignocellulosic
feedstocks. More specifically, the present invention provides a method for
recovering
inorganic salt during the processing of lignocellulosic feedstocks.
BACKGROUND OF THE INVENTION
[0002] Fuel ethanol is currently made from feedstocks such as corn starch,
sugar cane,
and sugar beets. The production of ethanol from these sources cannot grow much
further,
as most of the farmland suitable for the production of these crops is in use.
In addition,
these feedstocks can be costly since they compete with the human and animal
food chain.
Finally, the use of fossil fuels, with the associated release of carbon
dioxide and other
products, for the conversion process is a negative environmental impact of the
use of
these feedstocks.
[0003] The production of fuel ethanol from cellulosic feedstocks provides an
attractive
alternative to the fuel ethanol feedstocks used to date. Cellulose is the most
abundant
natural polymer, so there is an enormous untapped potential for its use as a
source of
ethanol. Cellulosic feedstocks are also inexpensive, as they do not have many
other uses.
Another advantage of producing ethanol from cellulosic feedstocks is that
lignin, which is
a byproduct of the cellulose conversion process, can be used as a fuel to
power the
conversion process, thereby avoiding the use of fossil fuels. Several studies
have
concluded that, when the entire cycle is taken into account, the use of
ethanol produced
from cellulose generates close to nil greenhouse gases.
[0004] The cellulosic feedstocks that are the most promising for ethanol
production
include (1) agricultural wastes such as corn stover, wheat straw, barley
straw, canola
straw, rice straw, and soybean stover; (2) grasses such as switch grass,
miscanthus, cord
grass, and reed canary grass, (3) forestry wastes such as aspen wood and
sawdust, and (4)
sugar processing residues such as bagasse and beet pulp.
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[0005] Regardless of the feedstock used, the first step involves handling and
size
reduction of the material. The feedstock must be conveyed into the plant. This
is
contemplated to be carried out by trucks, followed by placing the feedstock on
conveyor
belts to be conveyed into the plant. The feedstock particles must then be
reduced to the
desired size to be suitable for handling in the subsequent processing steps.
[0006] The first process step is a chemical treatment, which generally
involves the use of
steam or heated water along with acid or alkali to break down the fibrous
material. The
chemical treatment is carried out either as a direct conversion process- acid
hydrolysis or
alkali hydrolysis-or as a pretreatment prior to enzymatic hydrolysis.
[0007] In the acid hydrolysis process, the feedstock is subjected to steam and
sulfuric
acid at a temperature, acid concentration, and length of time that are
sufficient to
hydrolyze the cellulose to glucose and hemicellulose to xylose and arabinose.
The
sulfuric acid can be concentrated (25-90% w/w) or dilute (3-8% w/w). The
glucose,
xylose and arabinose are then fermented to ethanol using yeast, and the
ethanol is
recovered and purified by distillation. A problem with concentrated acid
hydrolysis is
that the high levels of concentrated acid required necessitate the recovery
and re-use of
over 99% of the acid in the process. The recovery of this high proportion of
acid is
especially difficult due to the high viscosity and corrosivity of concentrated
acid.
[0008] In the alkali hydrolysis process, the feedstock is subjected to steam
and sodium
hydroxide or potassium hydroxide at a temperature, concentration, and length
of time that
are sufficient to hydrolyze the cellulose to glucose and hemicellulose to
xylose and
arabinose. The alkali is concentrated (15-50% w/w). The glucose, xylose and
arabinose
are then fermented to ethanol using yeast, and the ethanol is recovered and
purified by
distillation. A problem with alkali hydrolysis is that the high levels of
alkali required
necessitate the recovery and re-use of over 99% of the alkali in the process.
The recovery
of this high proportion of alkali is especially difficult due to the high
viscosity of
concentrated alkali.
[0009] In the enzymatic hydrolysis process, the feedstock is first pretreated
with acid or
base under milder conditions than that in the acid or alkali hydrolysis
processes such that
the exposed cellulose surface area is greatly increased as the fibrous
feedstock is
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converted to a muddy texture. During acid pretreatment, much of the
hemicellulose is
hydrolyzed, but there is little conversion of the cellulose to glucose. The
cellulose is
hydrolyzed to glucose in a subsequent step that uses cellulase enzymes, and
the
steam/acid treatment in this case is known as pretreatment. The acids used in
pretreatment typically include sulfuric acid in steam explosion and batch and
continuous
flow pretreatments and also sulfurous acid and phosphoric acid.
[0010] Some alkali pretreatment methods disclosed in the prior art, such as
those
involving concentrated ammonia, do not hydrolyze hemicellulose, but rather the
base
reacts with acidic groups present on the hemicellulose to open up the surface
of the
substrate. In addition, the concentrated ammonia alters the crystal structure
of the
cellulose so that it is more amenable to hydrolysis. Examples of such bases
typically used
in pretreatment include ammonia or ammonium hydroxide. The cellulose is
hydrolyzed
to glucose in a subsequent step that uses cellulase enzymes, although it is
also possible to
hydrolyze the cellulose, in addition to the hemicellulose, using acid
hydrolysis after
alkaline pretreatment.
[0011] The hydrolysis of the cellulose, whether by acid or alkali hydrolysis
or by
cellulase enzymes after pretreatment with acid or base, is followed by the
fermentation of
the sugar to ethanol. The ethanol is then recovered by distillation.
[0012] There are several problems that must be overcome in order for the
conversion of
cellulosic biomass to sugar or ethanol to be commercially viable. In
particular, there is a
large amount of inorganic salt present in the feedstock. Furthermore,
inorganic salt is
generated in the process, in particular, during the neutralization of the acid
or alkali used
in the pretreatment or hydrolysis. The inorganic salt has an adverse impact on
the
enzymatic hydrolysis and yeast fermentation processes. In addition, the
purchase of the
acid and the alkali and the disposal of the salt are costly.
[0013] If the pretreated feedstock is subjected to enzymatic hydrolysis by
cellulase
enzymes, the pH of the pretreated feedstock is typically between about 4-6.
Cellulase
enzymes produced by the fungus Trichoderma, which are the leading sources of
cellulase
for cellulose conversion, exhibit optimum activity at pH 4.5 to 5Ø These
enzymes
exhibit little activity below pH 3 or above pH 6. Microbes that ferment the
sugar include
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yeast and Zymomonas bacteria. The yeast are active at pH 4-5 while the
Zymomonas are
active at pH 5-6. An acidic chemical treatment is often carried out at a pH of
about 0.8 to
2.0, so a significant amount of alkali must be added to increase the pH to the
range that is
required for microbial fermentation and enzymatic hydrolysis. An alkaline
pretreatment
is often carried out at a pH of 9.5 to 12, so a significant amount of acid
must be added to
decrease the pH to the range that is required for enzymatic hydrolysis and
microbial
fermentation.
[0014] When an acidic pretreatment is carried out, the alkaline that is
usually used for
neutralization of the acid is sodium hydroxide, but potassium hydroxide and
ammonium
hydroxide have also been reported. The high levels of these compounds that are
required
increase the cost of the process.
[0015] Although the neutralized slurry is at a pH range that is compatible
with yeast or
fermenting bacteria or cellulase enzymes, the inorganic salt concentration is
high enough
to be inhibitory to the microbes or enzymes. The inorganic salt can also cause
a
degradation of the sugar, particularly the xylose, in evaporation and
distillation processes
that are carried out downstream of the hydrolysis.
[0016] One known pretreatment method utilizing a base is known as Ammonia
Freeze
Explosion, and more recently as the Ammonia Fiber Explosion or "AFEX" process.
The
process involves contacting lignocellulosic feedstock with liquid ammonia in a
pressure
vessel. The contact is maintained for a sufficient time to enable the ammonia
to swell
(i.e., decrystallize) the cellulose fibers, and the pressure is then rapidly
reduced which
causes the ammonia to flash or boil and explode the cellulose fiber structure.
(See U.S.
Patent Nos. 5,171,592, 5,037,663, 4,600,590, 6,106,888, 4,356,196, 5,939,544,
6,176,176, 5,037,663 and 5,171,592).
[0017] The AFEX process typically requires the addition of ammonia at high
concentrations. Due to the high cost of ammonia, AFEX pretreatment methods
involve
recovery of the flashed ammonia, which, in turn, is recycled to the
pretreatment step.
However, the ammonia recovery process does not remove all of the ammonia from
the
pretreated feedstock. The inability to recover this residual ammonia decreases
the
economics of the process.
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[0018] U.S. Patent No. 4,644,060 discloses a pretreatment method involving
contacting
lignocellulosic materials with ammonia. This is followed by flashing to
recover and re-
use the ammonia. The pretreated material is then subjected to enzyme
hydrolysis with
cellulases. Prior to enzyme hydrolysis, the pH of the pretreated feedstock is
neutralized
by addition of hydrochloric acid. As a result of the cellulase treatment, most
of the
available cellulose was hydrolyzed to glucose and 78% of the available xylan
was
hydrolyzed to xylobiose and xylose. However, a disadvantage of this method is
that the
ammonia recovery process does not remove all of the ammonia from the
pretreated
feedstock, which limits the economic viability of the method..
[0019] Alkali that is used during processing of the lignocellulosic feedstock
can be either
soluble or insoluble. An example of an insoluble alkali is lime, which is
typically used to
neutralize acids and precipitate inhibitors of cellulase enzymes arising from
the
pretreatment. It is also known to pretreat lignocellulosic feedstocks with
hydrated lime
(calcium hydroxide). However, there are numerous problems associated with
using lime
including (1) disposal of the lime; (2) calcium precipitation which leads to
downstream
scaling; (3) the expense of the lime; and (4) its ineffectiveness at
completely removing
inhibitors of enzymes and yeast.
[0020] Holtzapple (U.S. Patent No. 5,865,898) discloses an alkaline
pretreatment using
insoluble hydrated lime (calcium hydroxide). After the alkali pretreatment,
the pH is
reduced to a pH amenable for enzymatic hydrolysis using acetic acid. The
pretreated
biomass is digested and useful products such as alcohols, organic acids,
sugars, ketones,
starches, fatty acids, are separated from the remaining or residual mixture.
Calcium
hydroxide is recovered by reacting the pretreated material with carbon dioxide
to convert
it to calcium carbonate. The residual insoluble solids, comprising lignin and
calcium
carbonate, are heated in a lime kiln to convert the calcium carbonate into
calcium
hydroxide. However, this is a very expensive and time consuming process that
involves
handling and processing a large amount of insoluble salts. It has therefore
not been
possible, to date, for this process to be economically viable.
[0021] US Patent No. 6,043,392 (Holtzapple et al.) employs a pretreatment step
with
lime prior to producing volatile fatty acids during the fermentation of
lignocellulosic
biomass by anaerobic or thermophilic bacteria. After the lime treatment, lime
is removed
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by draining the lime-containing water from the biomass, followed by
fermentation with
anaerobic bacteria. The anaerobic organisms then convert the biomass to
organic acids
such as acetic acid, proprionic and butyric acids. The organic acids produced
by these
fermentation processes can be concentrated and converted to ketones by
pyrolysis in a
thermal converter. Calcium salts can be precipitated by evaporation, dried and
pyrolyzed
to produce solid calcium carbonate. The calcium carbonate may be sent to a
lime kiln to
regenerate lime which may then be mixed with water to produce a dissolved lime
stream
and insolubles. Minerals may be recovered from a side stream of calcium
carbonate or
from the insolubles and sold as fertilizer. Alternatively, the organic acids
are treated with
a tertiary amine and carbon dioxide to produce an acid/amine complex that
decomposes
to form an acid and an amine with different volatilities. The acid can then be
separated
from the amine by distillation and precipitated minerals that accumulate in
the bottoms of
the distillation column can be recovered. Although Holtzapple et al. describe
an effective
method for the isolation of organic acids produced during fermentation using
an alkaline
pretreatment, the method involves pretreatment with insoluble lime, which is
subject to
the disadvantages described above.
[0022] Alkali treatment of lignocellulosic feedstocks has also been employed
to produce
animal feed. In this case, the treatment with alkali increases the feed value
of the
feedstock by making cellulose more accessible to digestion by ruminants. U.S.
Patent
No. 4,048,341 discloses such a process for producing animal fodder. After
alkali
chemical treatment, the lignocellulosic material is treated with acid to
neutralize the
fodder. However, the process is limited to the production of animal fodder and
there is
no disclosure of producing a sugar stream.
[0023] Wooley et al. (In Lignocellulosic Biomass to Ethanol Process Design and
Economics Utilizing Co-Current Dilute Acid Prehydrolysis and Enzyme Hydrolysis
Current and Future Scenarios, (1999) Technical Report, National Renewable
Energy
Laboratory pp. 16-17) describe a process of treating lignocellulosic material
utilizing
over-liming following acid pretreatment. Milled wood chips are first
pretreated with
dilute sulfuric acid followed by enzyme hydrolysis and fermentation. Following
pretreatment, the resulting liquid and solids are flash cooled to vapourize a
large amount
of water and inhibitors of the downstream fermentation reaction. After ion
exchange to
remove acetic acid, the material is over-limed by adding lime to raise the pH
to 10. The
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liquid is then adjusted to pH 4.5 which results in the formation of gypsum
crystals
(CaSO4). These crystals can be removed from the liquid by hydrocyclone and
rotary
drum filtration in series. Although the process describes the removal of
gypsum after
acid treatment, the investigators do not address the problems associated with
removal of
insoluble calcium salt.
[0024] U.S. Patent No. 6,478,965 (Holtzapple et al.) discloses a method for
isolating
carboxylate salts formed as a product during the fermentation of
lignocellulosic biomass
by anaerobic bacteria. A fermentation broth, which contains dilute carboxylate
salt in
aqueous solution, is contacted with a low molecular weight secondary or
tertiary amine
which has a high affinity for water and a low affinity for the carboxylate
salt. This allows
the water to be selectively extracted while the carboxylate salt remains in
the
fermentation broth and becomes concentrated so that it can be easily
recovered. The
carboxylate salt may be further concentrated by evaporation, dried or
converted to a more
concentrated carboxylic acid solution. While Holtzapple et al. describe an
effective
method for the isolation of carboxylate fermentation products, they do not
address the
recovery of inorganic salts from the feedstock itself or inorganic salts
arising from the
acids and bases used during the processing of the lignocellulosic feedstocks.
[0025] U.S. Patent No. 5,124,004 (Grethlein et al.) discloses a method for
concentrating
an ethanol solution by distillation. The method first involves partially
concentrating the
ethanol solution by distillation and withdrawing a vapour stream. Next, the
condensation
temperature of the vapour is raised above the evaporation temperature of a re-
boiler
liquid used in the process (a heat-sink liquid). The vapour stream is then
used to heat the
re-boiler liquid and partially enriched vapour is then removed and condensed.
The
condensed stream is introduced to an extractive distillation column and
concentrated in
the presence of an added salt to increase the volatility of the ethanol. The
method
provides the benefit that the heat requirement of distillation is reduced
since vapour
required to heat the system does not need to be provided by an external
source. However,
there is no discussion of recovering and removing the salts added during the
final
distillation step.
[0026] U.S. Patent No. 5,177,008 (Kampen) discloses the recovery of
fermentation by-
products, namely glycerol, betaine, L-pyroglutamic acid, succinic acid, lactic
acid and
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potassium sulfate, produced during the manufacture of ethanol from sugar
beets. The
process involves fermenting the raw material, collecting the ethanol by
distillation and
then recovering the by-products in the remaining still bottoms. The by-
products are
isolated by first centrifuging the still bottoms and performing
microfiltration to further
clarify the solution. The resulting permeate is then concentrated to a solids
concentration
of 50-75%. The concentrated solution is first subjected to a crystallization
step to recover
potassium sulfate and then passed to a chromatographic separation step for the
subsequent recovery of glycerol, betaine, succinic acid, L-pyroglutamic acid
or lactic
acid. The potassium sulfate is present in the raw material and its
concentration is
increased by cooling the solution and/or by the addition of sulfuric acid as
part of the
crystallization. The process of Kampen has several advantages such as energy
and water
savings and high solids concentrations. However, there is no discussion of a
chemical
pretreatment of lignocellulosic material with acid or alkali or an acid or
alkali
neutralization step prior to enzymatic hydrolysis and fermentation and the
associated
problems with the presence of sodium and magnesium salts arising from such a
pretreatment. Furthermore, since Kampen et al. used sugar beets, they were
able to
crystallize potassium sulfate directly from the still bottoms, and they do not
address the
recovery from still bottoms of salt mixtures with high levels of impurities
that do not
crystallize. Acid pretreatment of lignocellulosic feedstocks results in
mixtures of
inorganic salts in the still bottoms that cannot be directly crystallized.
[0027] U.S. Patent Nos. 5,620,877 and 5,782,982 (Farone et al.) disclose a
method for
producing sugars from rice straw using concentrated acid hydrolysis which, as
set out
above, is not a preferred pretreatment method. The method results in the
production of
quantitative yields of potassium silicate. In this method, the rice straw is
treated with
concentrated sulfuric acid at a concentration of between 25% and 90%. The
resulting
mixture is then heated to a temperature to effect acid hydrolysis of the rice
straw.
Subsequently, the mixture is separated from the remaining solids by pressing.
The
pressed solids can then be treated with 5% to 10% sodium hydroxide to extract
silicic
acid. Following the treatment with sodium hydroxide, the solids are heated and
then
pressed and washed with water to extract a liquid. The extracted liquid is
then treated
with an acid, which results in the formation of a precipitate that can be
separated by
filtration. The filtered material is then treated with bleach to produce
silica gel that can
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be further treated to produce sodium silicate, potassium silicate or other
useful materials.
The method also employs a neutralization step using lime to precipitate
soluble inorganic
salts present in a sugar stream produced during fermentation. Lime is an
insoluble base
that can build up on process equipment downstream of its point of addition and
decrease
the efficiency of the process.
[0028] WO 02/070753 (Griffin et al.) discloses a leaching process to remove
alkali from
lignocellulosic feedstocks thereby decreasing the acid requirement for
chemical
treatment. The process includes milling the feedstock, followed by
preconditioning it
with steam and then contacting the feedstock with water to leach out the
salts, protein,
and other impurities. The water containing these soluble compounds is then
removed
from the feedstock. This process decreases the acid requirements in the
subsequent
pretreatment process, which increases the yield of xylose after pretreatment.
However,
the costs and problems associated with the salt arising from the acid or
alkali added for
chemical treatment and the alkali or acid added after chemical treatment for
adjustment of
the pH are not addressed.
[0029] U.S. Patent No. 4,321,360 (Blount) discloses the preparation of ethanol
from
lignocellulosic feedstocks; however, there is no discussion of salt processing
or recovery
arising during this process. U.S. Patent No. 6,608,184 (Blount) describes the
production
of ethanol, salt, and several other organic products from sewer sludge
comprising
sewered cellulose waste material (rather than a lignin-cellulose material).
This process
involves mixing sewer sludge with water and sodium hydroxide, or an acid
(sulfuric or
hydrochloric acid). The slurry containing acid or alkali is then heated to
hydrolyze the
cellulose in the sludge, and an excess of water is added to dissolve the
organic
compounds. The aqueous material is then separated from the insolubles and
evaporated
to concentrate the solution and crystallize out the carbohydrates. The
carbohydrates are
filtered off, slurried in water, and fermented to ethanol using yeast. The
aqueous solution
containing ammonium sulfate and other compounds may then be used as a
fertilizer.
Alternatively, the salt is separated from the sugar by membrane filtration and
then the salt
is evaporated and dried.
[0030] U.S. Patent No. 6,709,527 (Fechter et al.) discloses a process of
treating an
impure cane-derived sugar juice to produce white sugar and white strap
molasses. The
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process involves subjecting the sugar juice to microfiltration/ultrafiltration
to decrease the
levels of suspended solids, organic non-sugar impurities and/or colour. The
sugar juice is
next subjected to ion exchange with a strong acid cation exchange resin in the
hydrogen
form and then to ion exchange with an anion ion exchange resin in the
hydroxide form.
Potassium-based fertilizer components can be obtained by regenerating the
strong acid
cation exchange resin with a strong acid such as hydrochloric acid or nitric
acid to
produce an acid stream rich in potassium salt. Ammonium-based fertilizer
components
can be obtained by regenerating the anion ion exchange resin with a strong or
weak base
such as sodium or potassium hydroxide and ammonium hydroxide to obtain an
alkaline
stream which is rich in nitrogen. After ion exchange, the resulting sugar
solution is
concentrated to produce a syrup, which is crystallized twice to produce impure
crystallized sugar and white strap molasses. Although the process involves the
production of potassium and ammonium-based fertilizer components from an
impure
sugar cane juice, there is no disclosure of producing a sugar stream by
hydrolysis of a
lignocellulosic feedstock.
[0031] U.S. Patent No. 4,101,338 (Rapaport et al.) disclose the separation of
sucrose
from impurities in sugar cane molasses. Rapaport et al. teach the pretreatment
of a
molasses stream to remove a significant amount of organic non-carbohydrate
impurities
and colour. The pretreatment can be carried out by precipitation with iron
salts, such as
ferric chloride or ferric sulfate. The insoluble flocculants are then removed
from the
molasses stream and the soluble iron salts are removed by the addition of lime
and
phosphoric acid or phosphate salts. The pretreatment may also be carried out
by other
processes which include: centrifilgation, with removal of the cake;
precipitation by
adding ethanol to the molasses stream; and filtering the molasses across a
membrane of
cellulose acetate. Regardless of the pretreatment process, the purpose is to
decrease the
amount of organic non-carbohydrate impurities so that a subsequent step of ion
exclusion
chromatography will separate the carbohydrate fraction from the dissolved
impurities.
Rapaport et al. report that the pretreatment decreased the ash content to 10%
and the
organic non-sugar content to 16.3% of the solids present.
[0032] Organic non-carbohydrate impurities, within a lignocellulosic system,
cannot be
removed by the methods of U.S. Patent No. 4,101,338 (Rapaport et al.)
According to
Rapaport's method, the amount of solids precipitated by iron salts or ethanol
is modest
CA 02565433 2006-10-25
and no solids are removed by centrifugation. By contrast, the sugar streams
produced
during the processing of lignocellulosic feedstock have a much higher level of
organic
non-carbohydrate impurities and inorganic salts. Rapaport et al. do not
address the
processing of such concentrated streams. Furthermore, the use of cellulose
acetate
membranes in a lignocellulosic system may not be feasible since such membranes
could
be destroyed by cellulase enzymes.
[0033] A method for the processing of lignocellulosic feedstock to produce a
sugar
stream is required that addresses the problems associated with high inorganic
salt
concentrations. The development of such a method would represent a significant
step
forward in the commercialization of, for example, ethanol production from
lignocellulosic biomass.
SUMMARY OF THE INVENTION
[0034] The present invention relates to a method for processing
lignocellulosic
feedstocks. More specifically, the present invention provides a method for
recovering
inorganic salt during the processing of lignocellulosic feedstocks.
[0035] It is an object of the invention to provide a method for recovery of
inorganic salt
during processing of lignocellulosic feedstocks.
[0036] According to the present invention, there is provided a method (A) for
processing
a lignocellulosic feedstock and obtaining an inorganic salt, the method
comprising:
a. pretreating the lignocellulosic feedstock by adding one or more than one
soluble base to the lignocellulosic feedstock to produce a pretreated
lignocellulosic
feedstock;
b. adding one or more than one acid to the pretreated lignocellulosic
feedstock to
adjust the pH of the pretreated lignocellulosic feedstock produce a
neutralized feedstock;
c. hydrolyzing the neutralized feedstock to produce a sugar stream and a
hydrolyzed feedstock; and
d. recovering the inorganic salt from a stream obtained from the neutralized
feedstock, the sugar stream, or a combination thereof.
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[0037] Preferably, the inorganic salt is soluble.
[0038] The lignocellulosic feedstock used in the method as described above may
be
selected from the group consisting of corn stover, wheat straw, barley straw,
canola straw,
rice straw, oat straw, soybean stover, grass, switch grass, miscanthus, cord
grass, and reed
canary grass, aspen wood, sawdust, bagasse and beet pulp.
[0039] The present invention also pertains to the method (A) described above,
wherein
the inorganic salt comprises ammonium sulfate salts, ammonium phosphate salts,
potassium phosphate salts, ammonium carbonate salts, ammonium chloride salts,
ammonium sulfite salts, potassium sulfate salts, potassium chloride salts or a
mixture
thereof. Preferably, the salt comprises ammonium sulfate salts, ammonium
phosphate
salts, ammonium chloride salts, or a mixture thereof. Ammonium carbonate salts
maybe
decomposed to form ammonia and carbon dioxide, followed by recovery of the
ammonia.
[0040] The present invention also relates to the method (A) described above,
wherein, in
the step of recovering (step d.), the inorganic salt is recovered by ion
exclusion. The step
of recovering may be followed by crystallization of the inorganic salt,
electrodialysis,
drying, or agglomeration and granulation. Alternatively, the inorganic salt
may be
concentrated by evaporation, membrane filtration, or a combination thereof,
prior to
recovery to produce a concentrated solution comprising the inorganic salt. The
concentrated solution may be clarified by membrane filtration, plate and frame
filtration,
or centrifugation prior to recovery.
[0041] Moreover, the present invention pertains to the method (A) described
above,
wherein the one or more than one soluble base is selected from the group
consisting of
ammonia, ammonium hydroxide, potassium hydroxide and sodium hydroxide.
Preferably, the soluble base is ammonium hydroxide or ammonia. When ammonium
hydroxide or ammonia is employed, the pretreatment may be performed at a
temperature
from about 20 C to about 200 C, at a pH from about 9.5 to about 12 and/or for
a time
period of from about 2 to about 20 minutes.
[0042] Furthermore, the present invention relates to the method (A) described
above,
wherein the one or more than one acid is selected from the group consisting of
sulfuric
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acid, sulfurous acid, sulfur dioxide, phosphoric acid, carbonic acid, carbon
dioxide,
hydrochloric acid and a combination thereof. Preferably, the acid is sulfuric
acid.
[0043] The present invention also pertains to the method (A) as described
above,
wherein, in the step of hydrolyzing (step c.), one or more than one cellulse
enzyme is
added to the neutralized feedstock so that at least a portion of the cellulose
in the
neutralized feedstock is hydrolyzed to produce glucose. Alternatively, the
step of
hydrolyzing, the neutralized feedstock is treated with one or more than one
acid so that at
least a portion of cellulose and hemicellulose in the neutralized feedstock is
hydrolyzed to
produce a sugar stream comprising glucose, xylose, arabinose, mannose and
galactose.
[0044] In addition, the present invention pertains to the method (A) as
described above,
wherein, after the step of hydrolyzing (step c.), the sugar stream is
separated from the
hydrolyzed feedstock to form a solid residue and a sugar hydrolyzate stream.
The
inorganic salt may then concentrated prior to recovery by evaporation,
membrane
filtration, or a combination thereof.
[0045] The present invention also relates to the method (A) as described
above, wherein
the inorganic salt is for use as a fertilizer. Inorganic salts suitable for
use as a fertilizer
include ammonium sulfate, ammonium phosphate, potassium phosphate, ammonium
chloride, potassium sulfate, potassium chloride or a combination thereof.
[0046] Furthermore, the present invention pertains to the method (A) described
above
further comprising the steps of:
e. fermenting the sugar stream to produce a fermentation broth comprising
ethanol;
and
f. distilling the fermentation broth to produce concentrated ethanol and
still bottoms.
[0047] Optionally, the inorganic salt is recovered from the still bottoms
followed by
purifying the inorganic salt. Prior to the step of recovering the inorganic
salt from the
still bottoms, the concentration of the still bottoms may be increased by
evaporation,
membrane filtration, or a combination thereof, to produce concentrated still
bottoms,
followed by a step of ion exclusion chromatography using a simulated moving
bed
(SMB) process. The concentrated still bottoms may be clarified by
microfiltration, plate
13
CA 02565433 2006-10-25
and frame filtration or centrifugation prior to the step of ion exclusion
chromatography.
The step of purifying the inorganic salt may comprise crystallization of the
inorganic salt
or electrodialysis, drying or agglomeration and granulation.
[0048] The present invention also pertains to a method (B) for processing of a
lignocellulosic feedstock and obtaining an inorganic salt which comprises:
a. pretreating the lignocellulosic feedstock by adding one or more than
soluble
base to the lignocellulosic feedstock to produce a pretreated lignocellulosic
feedstock;
b. adding one or more than one acid to the pretreated lignocellulosic
feedstock to
adjust the pH of the pretreated lignocellulosic feedstock to produce a
neutralized
feedstock;
c. hydrolyzing the neutralized feedstock to produce a sugar stream and a
hydrolyzed feedstock;
d. fermenting the sugar stream to produce a fermentation broth comprising
ethanol or butanol;
e. separating ethanol or butanol from the fermentation broth by distillation,
membrane filtration, liquid-liquid extraction or gas stripping to produce
concentrated
ethanol or butanol and an aqueous stream comprising the inorganic salt; and
f. recovering the inorganic salt from the aqueous stream to produce a
recovered
inorganic salt.
[0049] The present invention also pertains to the method (B) described above
further
comprising the steps of purifying the recovered inorganic salt to obtain a
purified
inorganic salt and producing a product comprising the purified inorganic salt.
The step of
purifying may comprise performing ion exclusion chromatography, followed by
electrodialysis, drying, agglomeration and granulation, or crystallization.
[0050] The present invention also provides a method (C) for processing a
lignocellulosic
feedstock and obtaining an inorganic salt, the method comprising:
a. pretreating the lignocellulosic feedstock by adding one or more than one
soluble base comprising ammonia or ammonium hydroxide, or a combination
thereof, to
the lignocellulosic feedstock to produce a pretreated lignocellulosic
feedstock;
14
CA 02565433 2006-10-25
=
b. adding one or more than one acid comprising sulfuric acid to the pretreated
lignocellulosic feedstock to adjust the pH of pretreated lignocellulosic
feedstock produce
a neutralized feedstock and an inorganic salt comprising ammonium sulfate; and
c. recovering the inorganic salt from a stream obtained from the neutralized
feedstock, the sugar stream, or a combination thereof.
[0051] Preferably, the ammonium sulfate is for use as a fertilizer.
[0052] The present invention also relates to the method (C) as described
above, wherein
the step of pretreating (step a.) is performed at a temperature from about 20
C to about
200 C, at a pH from about pH 9.5 to about 12 and for a time period of from
about 2 to
about 20 minutes.
[0053] The present invention also relates to the method (C) as described
above, wherein,
in the step of recovering (step c.), the inorganic salt is recovered by ion
exclusion. The
step of recovering (step c.) may be followed by crystallization of the
inorganic salt,
electrodialysis, drying, or agglomeration and granulation.
[0054] The present invention also provides a method (D) for processing a
lignocellulosic
feedstock and obtaining an inorganic salt, the method comprising:
a. pretreating the lignocellulosic feedstock by adding one or more than one
soluble base to produce a pretreated lignocellulosic feedstock;
b. washing the pretreated lignocellulosic feedstock to produce a wash stream
and
a washed feedstock;
c. neutralizing the wash stream by treatment with one or more than one acid to
produce a neutralized wash stream comprising an inorganic salt; and
d. recovering a salt comprising the inorganic salt from the neutralized wash
stream.
[0055] Preferably, the inorganic salt is for use as a fertilizer.
[0056] The present invention also pertains to the method (D) as defined above,
wherein,
in the step of recovering (step d.), the inorganic salt comprises ammonium
sulfate salts,
ammonium phosphate salts, potassium phosphate salts, ammonium carbonate salts,
ammonium chloride salts, ammonium sulfite salts, potassium sulfate salts,
potassium
CA 02565433 2006-10-25
chloride salts, or a mixture thereof. Preferably, the salt comprises ammonium
sulfate
salts, ammonium phosphate, ammonium chloride salts, or a mixture thereof. The
ammonium carbonate salts may be decomposed to form ammonia and carbon dioxide
and
the ammonia may then be recovered.
[0057] The present invention also pertains to the method (D) as described
above,
wherein, in the step of neutralizing (step c.), the one or more than one acid
is selected
from the group consisting of sulfuric acid, sulfurous acid, sulfur dioxide,
phosphoric acid,
carbonic acid, carbon dioxide, hydrochloric acid and a combination thereof
[0058] Furthermore, the present invention pertains to the method (D) as
defined above,
wherein the wash stream is neutralized by treatment with a strong acid cation
exchange
resin.
[0059] The process of the present invention overcomes several disadvantages of
the prior
art by taking into account the difficulties in the conversion of
lignocellulosic feedstocks
to sugar and then ethanol. By removing inorganic salt during the processing of
lignocellulosic feedstock, several of the steps operate more efficiently, for
example
enzymatic hydrolysis, or fermentation of sugar to ethanol, as the inhibitory
effect of the
salt is reduced. Furthermore, the inorganic salts recovered during this
process and the
value generated from these salts help offset the cost associated with the use
of these salts.
The present invention offers significant advances in the production of sugar,
ethanol, and
other products from lignocellulosic feedstocks.
[0060] This summary of the invention does not necessarily describe all
features of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0061] These and other features of the invention will become more apparent
from the
following description in which reference is made to the appended drawings
wherein:
[0062] FIGURE 1 shows a schematic outline of the process of the present
invention, and
indicates several stages where inorganic salt may be removed and recovered
(indicated as
stages 1-4).
16
CA 02565433 2006-10-25,
DETAILED DESCRIPTION
[0063] The present invention relates to a method for processing
lignocellulosic
feedstocks. More specifically, the present invention provides a method for
recovering
inorganic salt during the processing of lignocellulosic feedstocks.
[0064] The following description is of a preferred embodiment.
[0065] The present invention provides a process for the recovery of inorganic
salt during
the conversion of a lignocellulosic feedstock to sugar. The inorganic salt may
be used as
fertilizer or for other purposes as desired.
[0066] The feedstock for the process is a lignocellulosic material. By the
term
"lignocellulosic feedstock", it is meant any type of plant biomass such as but
not limited
to non-woody plant biomass, cultivated crops such as, but not limited to
gasses, for
example but not limited to C4 grasses, such as switch grass, cord grass, rye
grass,
miscanthus, reed canary grass, or a combination thereof, or sugar processing
residues
such as baggase, or beet pulp, agricultural residues, for example, soybean
stover, corn
stover, rice straw, rice hulls, barley straw, corn cobs, wheat straw, canola
straw, rice
straw, oat straw, oat hulls, corn fiber, recycled wood pulp fiber, sawdust,
hardwood, for
example aspen wood and sawdust, softwood, or a combination thereof Further,
the
lignocellulosic feedstock may comprise cellulosic waste material such as, but
not limited
to newsprint, cardboard, sawdust and the like. Lignocellulosic feedstock may
comprise
one species of fiber or alternatively, lignocellulosic feedstock may comprise
a mixture of
fibers that originate from different lignocellulosic feedstocks. Furthermore,
the
lignocellulosic feedstock may comprise fresh lignocellulosic feedstock,
partially dried
lignocellulosic feedstock, fully dried lignocellulosic feedstock or a
combination thereof.
[0067] Lignocellulosic feedstocks comprise cellulose in an amount greater than
about
20%, more preferably greater than about 30%, still more preferably greater
than about
40% (w/w). The lignocellulosic feedstock also comprises lignin in an amount
greater
than about 10%, or, more typically, in an amount greater than about 15% (w/w).
The
lignocellulosic feedstock also comprises a combined amount of sucrose,
fructose and
starch in an amount less than about 20%, generally less than about 10% (w/w).
17
CA 02565433 2006-10-25
=
[0068] By the term "inorganic salt", it is meant salts that do not contain
either a cation or
an anion with carbon-hydrogen bonds. This term is meant to exclude salts
containing
acetate anions, oxalate anions and other organic anions. These salts, and
other salts
containing an anion with a carbon-hydrogen bond, are "organic salts".
[0069] Preferably, the inorganic salt is soluble. By the term "soluble
inorganic salt", it is
meant that the inorganic salt has a solubility in water that is at least 0.1 M
at 20 C.
Calcium hydroxide, lime and calcium sulfate are examples of insoluble
inorganic salts.
[0070] The presence of inorganic salts within the processing of the
lignocellulosic
feedstock can lead to the degradation of xylose. Degradation of xylose results
in reduced
yields of sugar, ethanol or a combination thereof. Furthermore, the inorganic
salt has an
adverse impact on the enzymatic hydrolysis and yeast fermentation processes.
[0071] The processes described herein recover the inorganic salt from the
product
streams. The inorganic salts are recovered by, for example, ion exclusion, ion
exchange
or electrodialysis. . The removal of salts produces a stream with greater
xylose stability.
Any inorganic salt, for example potassium sulfate or ammonium sulfate, that is
recovered
as a by-product during the processing of lignocellulosic feedstocks may be
used for a
variety of purposes, for example within a fertilizer. Moreover, since acid and
alkali are
costly, the recovery of inorganic salts resulting from the neutralization
improves the
economic viability of the process.
[0072] By the term "ion-exchange", it is meant a separation technique that
employs a
chemical reaction in which an ion from solution is exchanged for a similarly
charged ion
attached to an immobile solid particle. The ion exchange resins may be cation
exchangers that have positively charged mobile ions available for exchange, or
anion
exchangers, whose exchangeable ions are negatively charged. The solid ion
exchange
particles may be either naturally occurring inorganic zeolites or
synthetically produced
organic resins.
[0073] By the term "ion exclusion", it is meant a separation technique that
separates ionic
species in solution from non-ionic species, or weakly ionic species from
strongly ionic
species, by employing a resin having a structure that allows the non-ionic
species or
18
CA 02565433 2006-10-25
weakly ionic species to diffuse into it while preventing more ionic species
from entering
the resin. The species with less ionic character then elutes after the more
ionic species.
[0074] As used herein, the term "membrane filtration" refers to any process of
filtering a
solution with a membrane that is suitable for concentrating a solution.
Included in this
definition are micro filtration, which employs membranes of a pore size of
0.05-1 microns
for the removal of particulate matter; ultrafiltration, which employs
membranes with a
cut-off of 500-50,000 mw for removing large soluble molecules; and reverse
osmosis
using nanofiltration membranes to separate small molecules from water. The
term
"reverse osmosis" refers to the separation of solutions having different
solute
concentrations with a semi-permeable membrane by applying sufficient pressure
to the
more concentrated liquid to reverse the direction of osmosis across the
membrane. The
term "nanofiltration" refers to processes that separate solutions of differing
solute
concentrations using reverse osmosis, but that employ membranes which
generally have a
larger pore size than those used in reverse osmosis. For the purposes of this
specification,
the term "membrane filtration" also encompasses "pervaporation". Pervaporation
refers
to a method for the separation of mixtures of liquids by partial vaporization
through a
membrane.
[0075] In addition to concentrating a solution, microfiltration may be used
for
clarification.
[0076] Separation by ion exclusion may employ Simulated Moving Bed (SMB)
technology. As used herein, the term "Simulated Moving Bed" or "SMB" refers to
an ion
exclusion chromatographic separation process that utilizes a set of columns
interconnected in series in which liquid circulates in the unit by
simultaneous shifting of
the columns in the opposite direction. As used herein, this term encompasses
Improved
Simulated Moving Bed (ISMB) systems. A non-limiting example of an ISMB system
is
provided in Example 1. SMB is a preferred separation method for ion exclusion
chromatography since solvent use is minimized, thereby leading to a greatly
reduced cost
of operation when compared to traditional batch chromatography methods.
[0077] Prior to separation by ion exclusion, the inorganic salt solution may
be
concentrated and clarified. Concentration may be carried out by evaporation or
by
19
CA 02565433 2006-10-25
microfiltration (0.14 microns) to remove particles, ultrafiltration (500-2000
mw cut off)
to remove soluble lignin and other large molecules and reverse osmosis to
increase solids
to a concentration of about 12 to about 20%, or any amount therebetween,
followed by
evaporation. Following concentration, the solution may be clarified by
microfiltration,
plate and frame filtration or centrifugation.
[0078] After separation from the product stream, the inorganic salt may be
crystallized,
dried or subjected to electrodialysis or agglomeration and granulation, and
used as
desired, for example, as a solid fertilizer. Alternatively, the inorganic salt
may be
concentrated as a wet slurry and used in a liquid form, for example as a
liquid fertilizer.
The remaining components within the product streams, for example sugar, maybe
further
processed or collected, as desired.
[0079] By the term "electrodialysis", it is meant a separation process in
which ions are
transported across a semi-permeable membrane under the influence of an
electric
potential. The membrane may be either cation or anion selective to allow for
the
separation of cations or anions, respectively.
[0080] By the term "crystallization", it is meant any process for the
formation of solid
particles or crystals of a solute from a saturated solution. This can be
carried out by
concentration, cooling (under vacuum or with a heat exchanger), reaction
displacement or
equilibrium displacement.
[0081] By the term "agglomeration and granulation", it is meant process steps
to modify
particle size, for example, to improve bulk properties. Non-limiting examples
of bulk
properties that can be improved include, but are not limited to, dissolving
behavior, form
and stability of the granulated product and storage stability.
[0082] By the term "drying", it is meant any process for removing water,
volatile
components or other liquids from a solid material, to reduce the content of
residual liquid
to an acceptable low value. This includes, but is not limited to, direct and
indirect drying.
Direct drying refers to using direct contact of hot gases to drive off some,
or all of the
water, and indirect drying refers to contact with a heated surface as opposed
to hot gas.
CA 02565433 2006-10-25
[0083] The inorganic salts in the product stream result from the
lignocellulosic feedstock
itself, and from the acids and bases used during the processing of the
lignocellulosic
feedstock. For example, the inorganic salt mixtures that arise from sulfuric
acid include
mixtures of sulfuric acid, sodium bisulfate, and disodium sulfate, depending
on the pH of
the system and on the total ionic concentration. For this discussion, these
salt mixtures
will be referred to as "sodium sulfate salts". Other salt mixtures may also be
present in
the product streams for example, but not limited to, ammonium sulfate salts
(sulfuric
acid, ammonium bisulfate, and diammonium sulfate); sodium sulfite salts,
(sulfurous
acid, sodium bisulfite, and disodium sulfite); ammonium sulfite salts
(sulfuric acid,
ammonium bisulfite, and diammonium sulfite), sodium phosphate salts
(phosphoric acid,
sodium dihydrogen phosphate, and disodium hydrogen phosphate), ammonium
phosphate
salts (phosphoric acid, diammonium hydrogen phosphate, and ammonium dihydrogen
phosphate), potassium sulfate salts (sulfuric acid, potassium bisulfate, and
dipotassium
sulfate), potassium sulfite salts (sulfuric acid, potassium bisulfite, and
dipotassium
sulfite), and potassium phosphate salts (phosphoric acid, potassium dihydrogen
phosphate, and dipotassium hydrogen phosphate).
[0084] The inorganic salts recovered from the process as described herein have
value as a
fertilizer; however, additional uses of the recovered salts may be exploited
as desired. In
the case of fertilizer, ammonium, potassium, sulfate, and phosphate salts are
typically of
value. Other compounds present, including inorganic salts of sodium and
sulfite salts,
may be of less value in fertilizer. However, these inorganic salts can be
converted to
forms of higher value. For example, which is not to be considered limiting,
sodium salts
can be converted to potassium salts by the use of ion exchange. In this
example, sodium
hydroxide may be used for some or all of the neutralization of sulfuric acid
during the
processing of a lignocellulosic feedstock and the sodium ion exchanged with
potassium
using a cation exchange resin. The resulting potassium salt may then be of
more value as
a fertilizer.
[0085] Additionally, sulfite salts can be converted to sulfate salts by
oxidation with air or
with oxidizing agents. For example, sulfurous acid or sulfur dioxide present
in
pretreatment may be used to oxidize the sulfite salts to sulfate for use in
fertilizer.
21
CA 02565433 2013-02-19
[0086] The step of pretreatment increases the susceptibility of the
lignocellulosic
feedstock to hydrolysis by cellulase enzymes. In the case of acid
pretreatment,
hemicellulose, or a portion thereof, that is present in the lignocellulosic
feedstock is
hydrolyzed to monomeric sugars, for example xylose, arabinose, mannose,
galactose, or a
combination thereof. Preferably, the acid pretreatment is designed to carry
out almost
complete hydrolysis of the hemicellulose and a small amount of conversion of
cellulose
to glucose. The cellulose is hydrolyzed to glucose in a subsequent step that
uses cellulase
enzymes. Typically a dilute acid, from about 0.02%(w/v) to about 1%(w/v), or
any
amount therebetween, is used for the acidic pretreatment of the
lignocellulosic feedstock.
The preferred acid for pretreatment is sulfuric acid. Acid pretreatment is
familiar to
those skilled in the art, see for example U.S. Patent No. 5,536,325 (Brink);
U.S. Patent
No. 4,237,226 (Grethlein). Other methods that are known within the art may be
used as
required for preparation of a pretreated feedstock, for example, but not
limited to, those
disclosed in U.S. Patent No. 4,556,430 (Converse).
[0087] Preferably, the step of reacting the acidified feedstock is performed
at a
temperature between about 100 C to about 280 C, or any amount therebetween,
for
example a temperature of 100, 120, 140, 160, 180, 200, 22,0, 240, 260, 280 C,
or any
amount therebetween, at a pH from about pH 0.4 to about pH 2.5 or any amount
therebetween, for example, a pH of 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8,
2.0, 2.2, 2.4, 2.5,
or any amount therebetween, for about 5 seconds to about 60 minutes, or any
amount
therebetween, for example, for 5, 10, 20, 30, 40, 50 60 seconds, or for 1.5,
2, 4, 6, 8, 10,
15, 20, 25, 30, 35, 40, 45, 50, 55, 60 minutes, and any amount therebetween.
It is
understood by those skilled in the art that the feedstock temperature is that
of the
feedstock itself, which might differ from the temperature measured outside the
reaction
chamber. Devices used to carry out this pretreatment include, but are not
limited to
sealed batch reactors, continuous extruders and steam guns.
[0088] An example of a suitable acidic pretreatment, without intending to be
limiting, is
steam explosion described in US 4,416,648 (Foody). A typical set of
pretreatment
conditions for processing lignocellulosic feedstocks is a temperature of about
170 C to
about 260 C, for a period of about 0.1 to about 30 minutes and/or at a pH of
about 0.4 to
about
2Ø
22
CA 02565433 2013-02-19
[0089] It is also within the scope of the present invention that a two-stage
acid
pretreatment process may be used, whereby the first stage improves the
cellulose
hydrolysis somewhat while solubilizing primarily the hemicellulose but little
cellulose.
The second stage then completes a full pretreatment. Using this method, the
first stage
reaction is run at a temperature of less than about 180 C while the second
stage reaction
is run at a temperature of greater than about 180 C. Preferably, the first
stage of the
reaction is carried out at a temperature of about 60 C to about 140 C, or an
amount
therebetween, for 0.25 to 24 hours, or any amount therebetween, and at a pH
from about
pH 0.5 to about pH 2.5, or any amount therebetween. More preferably, the first
stage of
pretreatment is carried out at a temperature of 100 C to 130 C for 0.5 to 3
hours at pH
0.5 to 2.5. While the second stage of reaction may be carried out at a
temperature of
180 C to 270 C, at pH 0.5 to 2.5 for a period of 5 seconds to 120 seconds. The
two-stage
pretreatment provides separate recovery of the soluble monomers from
hemicellulose for
downstream processing.
[0090] Furthermore, the lignocellulosic feedstock may be processed using the
methods
disclosed in WO 02/070753 (Griffin et al.). A pretreatment process using flow-
through
hydrolysis is disclosed in US 4,237,226 (Grethlein et al.).
[0091] Any acid can be used to adjust the pH of the lignocellulosic feedstock
during acid
pretreatment. However, preferred acids are sulfuric acid, sulfurous acid,
sulfur dioxide,
and phosphoric acid, due to their low cost, effectiveness in pretreatment,
and, in the case
of sulfate and phosphate salts, their further use within a fertilizer. A
suitable alternative
to sulfuric acid is phosphoric acid.
[0092] Alternatively, the pretreatment involves the addition of alkali to
produce an alkali
pretreated feedstock. Without wishing to be bound by theory, alkali
pretreatment
typically does not hydrolyze hemicellulose, but rather the base reacts with
acidic groups
present on the hemicellulose to open up the surface of the substrate. In
addition, the base
may alter the crystal structure of the cellulose so that it is more amenable
to hydrolysis.
[0093] Bases that may be used in the pretreatment include ammonia, ammonium
hydroxide, potassium hydroxide, and sodium hydroxide. The base used in the
23
CA 02565433 2013-02-19
pretreatment is preferably soluble in water, which excludes lime or magnesium
hydroxide. Lime pretreatment is subject to the disadvantages described
previously.
[0094] An example of a suitable alkali pretreatment is Ammonia Freeze
Explosion, or
Ammonia Fiber Explosion ("AFEX" process). According to this process, the
lignocellulosic feedstock is contacted with ammonia or ammonium hydroxide in a
pressure vessel. The contact is maintained for a sufficient time to enable the
ammonia or
ammonium hydroxide to swell (i.e., decrystallize) the cellulose fibers. The
pressure is
then rapidly reduced which allows the ammonia to flash or boil and explode the
cellulose
fiber structure. (See U.S. Patent Nos. 5,171,592, 5,037,663, 4,600,590,
6,106,888,
4,356,196, 5,939,544, 6,176,176, 5,037,663 and 5,171,592). The flashed ammonia
may
then be recovered according to known processes. However, this only removes a
portion
of the ammonia and any remaining ammonia may be neutralized with acid to
produce an
inorganic salt. The inorganic salt, in turn, is recovered using the processes
described
herein. Alternatively, the ammonia is not recovered by flashing, in which
case, all or a
portion of the ammonia is neutralized with acid.
[0095] The step of reacting the feedstock with ammonia or ammonium hydroxide
may be
performed at a temperature between about 20 C to about 200 C, or any
temperature
therebetween. For example, the temperature may be 20, 40, 60, 80, 100, 120,
140, 160,
180, or 200 C. The pH is typically from about pH 9.5 to about pH 12, or any pH
therebetween. For example, the pH of the feedstock may be 9.5, 9.8, 10.0,
10.2, 10.4,
10.6, 10.8, 11.0, 11.2, 11.4, 11.6, 11.8 or 12Ø The treatment time may be
from 2
minutes to about 20 minutes, or any amount of time therebetween. For example,
the
duration of the pretreatment may be 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13,
14, 15, 16, 17, 18,
19 or 20 minutes. The moisture content of the feedstock may be between 50% and
70%,
or any range therebetween; for example, the moisture content may be 50, 52,
54, 56, 58,
60, 62, 64, 66, 68 or 70%. The ammonia or ammonium hydroxide is added to
achieve a
concentration which is generally about 0.5 to about 2.5 times the mass of the
feedstock on
a dry basis, or any amount therebetween. For example, the ammonia
concentration may
be about 0.5, 0.7, 0.8, 0.9, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0, 2.2, 2.4 or 2.5
times the mass of the
feedstock on a dry basis.
24
CA 02565433 2006-10-25
[0096] If the feedstock is pretreated with sodium hydroxide or potassium
hydroxide, the
temperature may be between about 120 C to about 220 C, or any temperature
range
therebetween. For example, the temperature may be 120, 130, 140, 150, 160,
170, 180,
190, 200, 210 or 220 C. The pH is typically between about 10 to about 13, or
any pH
range therebetween. For example, the pH may be 10.0, 10.5, 11.0, 11.5, 12.0,
12.5 or
13Ø The treatment time may be from about 15 minutes to about 120 minutes, or
any
range therebetween. The treatment time may be 15, 20, 30, 40, 50, 60, 70, 80,
90, 100,
110 or 120 minutes.
[0097] The pretreated feedstock may be washed to remove the sugar-acid mixture
or
sugar-base mixture, depending on the pretreatment, from the solids portion.
The
separated acid stream or alkaline stream may then be neutralized and inorganic
salt
recovered from this stream. After salt removal from the neutralized wash
stream, the
feedstock solids remaining may be neutralized and processed for sugar
fermentation or
enzymatic or acid hydrolysis, as described below. The inorganic salt recovered
from the
wash stream obtained from the pretreated lignocellulosic feedstock may be
concentrated,
or dried as described herein.
[0098] The pretreated lignocellulosic feedstock is highly acidic or alkali,
depending on
the chemical used in pretreatment. It is neutralized prior to enzymatic
hydrolysis and
sugar fermentation. Cellulase enzymes are active over a range of pH of about 3
to about
7, or any range therebetween, preferably, the pH is from about 4.0 to about
6.0, or any
range therebetween, and more preferably the pH is from about 4.5 to about 5.0,
or any
range therebetween. For example, the pH is 3.0, 3.5, 3.7,4.0, 4.2, 4.5, 4.7,
5.0, 5.2, 5.5,
6.0, 6.5, 7.0, or any amount therebetween. Yeast and Zymomonas bacteria are
typically
used for sugar fermentation. The optimum pH for yeast is from about pH 4 to
about pH
5, while the optimum pH for Zymomonas is from about pH 5 to about pH 6.
[0099] In principle, any soluble base can be used to adjust the pH of acidic
material.
However, it is preferred that the base used for pH adjustment of acid material
is ammonia
gas or ammonia dissolved in water for example, ammonium hydroxide. Sodium
hydroxide or potassium hydroxide may also be used. These compounds are
inexpensive,
effective, and, in the case of ammonium and potassium salts, of high value if
the
inorganic salt is to be used in fertilizer.
CA 02565433 2006-10-25
[00100] By the term "soluble base", it is meant a base that has a solubility
in water that is
at least 0.1 M at 20 C. This term is meant to exclude salts that are slightly
soluble or
insoluble. Examples of bases that are excluded are CaCO3 and Ca(OH)2.
Insoluble bases
cannot be recovered according to the methods of the present invention. The
term "base"
is meant to encompass any species that, when dissolved in water, gives a
solution with a
pH that is more than 7.
[00101] If an alkaline pretreatment is carried out, an acid is used to
neutralize the
pretreated feedstock. Non-limiting examples of acids that may be used in the
neutralization step are sulfuric acid, sulfurous acid, sulfur dioxide,
phosphoric acid,
carbonic acid, carbon dioxide, hydrochloric acid, or a combination thereof. In
the case of
a pretreatment carried out with ammonia or ammonium hydroxide, the pH may be
adjusted with sulfuric acid, phosphoric acid, hydrochloric acid, carbon
dioxide/carbonic
acid or sulfurous acid which produces the inorganic salts ammonium sulfate,
ammonium
phosphate, ammonium chloride, ammonium carbonate or ammonium sulfite,
respectively. If potassium hydroxide is used in the pretreatment, the
feedstock may be
neutralized with phosphoric acid to produce potassium phosphate. These
inorganic salts
may be used directly as a fertilizer or, in the case of ammonium sulfate or
ammonium
carbonate, subjected to degradation reactions to produce ammonia, which, in
turn, may be
recovered and/or recycled in the process.
[00102] For example, ammonium carbonate may be decomposed to produce ammonia
and carbon dioxide. The decomposition may involve thermal treatment to
liberate the
ammonia and carbon dioxide. The ammonia and/or the carbon dioxide may then be
recovered, for example by distillation, stripping or evaporation. The
recovered ammonia
may, in turn, be recycled to the alkaline pretreatment step.
[00103] Preferably, the alkali pretreatment comprises addition of ammonia or
ammonium
hydroxide, followed by neutralization with sulfuric acid to produce ammonium
sulfate. It
will be understood by those of skill in the art that the ammonia may be
provided in
anhydrous form. The ammonium sulfate produced during the neutralization may be
used
directly as a fertilizer, or, alternatively, may be subjected to thermal
decomposition
according to the method of a co-pending U.S. application entitled "Process for
Producing
26
CA 02565433 2006-10-25
Ammonia and Sulfuric Acid from a Stream Comprising Ammonium Sulfate" (Curren
et
al.) to produce sulfuric acid and sulfate salts, such as ammonium sulfate.
[00104] As described previously, after alkali pretreatment, the aqueous phase
may be
separated from the pretreated feedstock solids to produce a wash stream.
Neutralization
may be carried out by direct addition of acid to the alkaline wash stream or
may involve
treatment of the wash stream with a strong acid cation exchange resin. This
may involve
passage of the wash stream through a column packed with a sulfonated
polystyrene resin
cross-linked with divinyl benzenes in an alkali/alkaline earth metal form.
After
neutralization, recovery of the inorganic salt from the neutralized wash
stream may be
carried out using the methods described herein.
[00105] Following neutralization of the pretreated lignocellulosic feedstock
by the
addition of the soluble base or the acid, depending on the pretreatment,
enzymatic
hydrolysis may be carried out. Typically, the enzymes used for hydrolysis are
cellulase
enzymes that hydrolyze the cellulose to glucose. Any cellulase may be used;
however,
preferred cellulase enzymes are those made by the fungus Trichoderma.
Preferably, the
enzyme treatment is carried out between about 40 C to about 60 C, or any
temperature
range therebetween, or between about 45 C and about 55 C, or any temperature
range
therebetween. For example, the enzyme treatment may be carried out at 40, 42,
44, 46,
48, 50, 52, 54, 56, 58, 60 C, or any amount therebetween. The treatment may be
performed for a time period of about 1 to about 10 days, or any time interval
therebetween, or for a time period of about 3 to about 7 days, or any time
interval
therebetween. For example, the treatment may be performed for a time period of
1, 2, 3,
4, 5, 6, 7, 8, 9 or 10 days, or any time period therebetween.
[00106] Following enzymatic hydrolysis, the aqueous phase containing the
sugar,
inorganic salts, and other soluble compounds may be separated from the
insoluble, un-
hydrolyzed solids phase to produce a soluble sugar stream (also referred to as
the wash
stream). The un-hydrolyzed solids are primarily lignin and cellulose, and, to
a lesser
extent, silica, insoluble salts and other compounds. The sugar stream can be
pumped,
mixed, and controlled more easily than a slurry containing liquids and
insoluble solids.
The insoluble solids are separated from the sugar stream by any suitable
method, for
27
CA 02565433 2013-02-19
= =
example but not limited to plate and frame filtration, crossflow filtration,
centrifugation,
or other methods known to one of skill in the art.
[00107] As an alternative to enzyme hydrolysis, the pretreated feedstock may
be
subjected to acid hydrolysis. This may involve hydrolyzing the pretreated
feedstock with
steam and sulfuric acid at a temperature, acid concentration, and length of
time that are
sufficient to hydrolyze the cellulose to glucose and hemicellulose to xylose
and arabinose.
The sulfuric acid can be concentrated (25-90% w/w) or dilute (3-8% w/w).
[00108] Sugars present in the sugar stream, for example glucose, xylose,
arabinose,
mannose, galactose, or mixtures thereof, may be fermented by microbes. The
fermentation products can include any desired products that generate value to
the
fermentation plant. The preferred fermentation products are ethanol, butanol
or lactic
acid, which have large markets and are made efficiently by many microbes. For
ethanol
production, fermentation can be carried out by one or more than one microbe
that is able
to ferment the sugars to ethanol. For example, the fermentation may be carried
out by
recombinant Saccharomyces yeast that has been engineered to ferment glucose,
mannose,
galactose and xylose to ethanol, or glucose, mannose, galactose, xylose, and
arabinose to
ethanol. Recombinant yeasts that can ferment xylose to ethanol are described
in US
5,789,210. The yeast produces a fermentation broth comprising ethanol in an
aqueous
solution. For lactic acid production, the fermentation can be carried out by
one or more
than one microbe that ferments the sugars to lactic acid. Butanol production
may involve
the addition of one or more than one microbe to a sugar stream to convert
sugars to
butanol. An example of a suitable microbe for fermenting sugars to butanol is
Clostridium acetobutylicum.
[00109] If ethanol or butanol is the product, the alcohol may then be
recovered from the
fermentation broth. For example, the ethanol may be recovered by distillation
of the
fermentation broth. After recovery of the ethanol, for example by
distillation, further
ethanol purification may be carried out by adsorption or other methods
familiar to one of
skill in the art. The aqueous stream after distillation is still and contains
yeast cells,
inorganic salts, unfermented sugars, organic salts and other impurities.
Butanol is
preferably recovered from the fermentation broth by membrane filtration,
liquid-liquid
extraction or gas stripping to produce concentrated butanol.
28
CA 02565433 2013-02-19
[00110] Inorganic salts present in the still bottoms may also be recovered
using any
suitable method known to one of skill in the art, for example, but not limited
to ion
exclusion. These processes can be followed by crystallization,
electrodialysis, drying, or
agglomeration and granulation. A preferred method for recovering the inorganic
salt
from the still bottoms is increasing the concentration of the still bottoms by
evaporation,
membrane filtration, or a combination thereof, followed by clarification by
microfiltration, plate and frame filtration and centrifugation. This is
followed by ion
exclusion chromatography using a simulated moving bed (SMB) process and then
crystallization, electrodialysis, drying, or agglomeration and granulation.
[00111] Inorganic salts may also be removed from the lignocellulosic feedstock
prior to
pretreatment by washing, leaching, or a combination thereof to produce a
liquid stream or
"leachate". An example of a leaching process is described in WO 02/070753
(Griffin et
al.). This process involves contacting the lignocellulosic feedstock with
water for two
minutes or longer, and then separating the solids from the aqueous phase. This
decreases
the acid requirement for pretreatment, and decreases costs, and degradation of
xylose, in
the pretreatment process.
[00112] After leaching, the aqueous solution containing salts (the "leachate")
contains
potassium and other salts and trace elements that may be of value for
subsequent use, for
example within a fertilizer. The leachate may be concentrated by evaporation
or filtered
through a reverse osmosis membrane to remove the water or subjected to reverse
osmosis
and evaporation. The leachate may be subsequently clarified by
microfiltration, plate and
frame filtration or centrifugation. Leachate salts can be separated from
organics by ion
exclusion chromatography using a simulated moving bed (SMB) process to produce
a
product that is useable as a fertilizer. Either the liquid or the solid salt
streams obtained
from the leachate can be combined with other salt streams produced as
described herein.
[00113] With reference to Figure 1, there is shown an outline of an embodiment
of the
method of the present invention for the processing of lignocellulosic
feedstock (100) to
sugar (300, 400) and ethanol (600), through the successive processes of
pretreatment
(200), enzymatic hydrolysis (300), sugar fermentation (400), and ethanol
recovery (500).
As indicated in this figure, there are several steps leading to the production
of ethanol
where inorganic salt may be removed. For example, which is not to be
considered
29
CA 02565433 2006-10-25
limiting, inorganic salt may be removed at the stages indicated as 1, 2, 3,
and 4 (150, 250,
350 and 550, respectively) in Figure 1.
[00114] Following pretreatment with acid (200; Figure 1), the lignocellulosic
feedstock
may be washed with water (250) to remove the inorganic salts at step 1. Prior
to
pretreatment, the acid, for example sulfuric acid, sulfurous acid, sulfur
dioxide, or
phosphoric acid, is added to the lignocellulosic feedstock to adjust the pH,
for example,
to about 0.4 to about 2.0, as described above. After pretreatment (200), the
lignocellulosic feedstock is neutralized to a pH, for example, of about 4 to
about 6 for
example using ammonia or other alkali, as described above. The resulting
inorganic salt
can then be removed from the lignocellulosic feedstock at step 2 (250). The
separation is
carried out optionally by adding water to the pretreated lignocellulosic
feedstock (200)
and then separating the aqueous phase from the solids using a filter press,
centrifuge or
other suitable equipment. The aqueous stream (soluble stream) at this point is
known as
the pentose washings. The solids concentration in the pentose washings can be
increased
by evaporation, membrane filtration or a combination thereof
[00115] The pentose washings containing ammonium sulfate and other inorganic
salts
can not be crystallized without further processing to remove the organic
impurities. Ion
exclusion by SMB chromatography can be used to separate the inorganic salts
from the
organic impurities. The inorganic salts can then be purified by
crystallization or
electrodialysis, drying, or agglomeration and granulation. The salt stream can
then be
used as a liquid fertilizer, or alternately dried and used as a solid
fertilizer.
[00116] The resulting salt stream obtained following pretreatment of the
lignocellulosic
feedstock, either comprising sugars, or following removal of sugars, can be
sold
separately or combined with other salt streams obtained in the process
described herein.
For example, either the liquid or the solid salt streams obtained from the
pentose
washings can be combined with the salts from the leachate, indicated as step 1
in Figure 1
(150), described above.
[00117] Preferably, the desalted sugar streams (pentose washings) are
fermented to
ethanol, since the desalted streams are easier to ferment than the streams
containing salt.
CA 02565433 2006-10-25
[00118] The present invention also contemplates separating the aqueous salt
and sugar
stream from the un-hydrolyzed, insoluble solids following the enzymatic
hydrolysis (300)
at step 3 (350). The process for recovery of inorganic salts following
enzymatic
hydrolysis (300) at step 3 (350) is analogous to the process of salt recovery
described
above for pretreatment (200), at step 1 (150). For example, the wash stream
obtained at
step 3 (350) may be concentrated, or the sugars present in the wash stream
obtained at
step 3 removed and the remaining salt stream concentrated, and the sugar
stream
collected, or further processed at 400 (sugar fermentation) to produce
ethanol.
[00119] The hydrolyzate stream produced following enzymatic hydrolysis (300),
and
containing salt and sugars is sent to fermentation (400), where yeast or other
suitable
microbes ferment the sugar to ethanol (600) or other products. If ethanol is
made, it is
recovered by distillation or other suitable means (500). The remaining slurry
is the still
bottoms (700) and contains unfermented sugars, inorganic salts, organic salts,
yeast cells,
and other compounds. The inorganic salts can be recovered from the still
bottoms by
means described above, and then used as desired, for example as a fertilizer.
[00120] Also shown in Figure 1, is the removal of inorganic salts from the
lignocellulosic
feedstock prior to pretreatment (100) at step 1 (150). This may be carried out
by leaching
or other process, as described above.
[00121] An alkaline pretreatment followed by recovery of salt may be carried
out as
follows. This as an example of how the present invention can be practiced, and
is not
meant to be limiting in any manner.
[00122] Wheat straw is received in bales and chopped into pieces of size 20
mesh and
smaller. The chopped straw is slurried in water to reach a moisture content of
70%. The
wet straw is added to a reactor with pressurized ammonia slurry heated to 120
C to reach
a pressure of 300 psia. The mass of ammonia equal the mass of straw on a dry
basis. The
temperature is maintained for 20 minutes, after which the pressure is released
quickly,
which flashes off about 99% of the ammonia. The flash cools the reactor
contents down
to ambient temperature. The slurry is then adjusted to about pH 5.0 with
concentrated
sulfuric acid.
31
CA 02565433 2006-10-25
=
[00123] Upon acid addition, the soluble salt of ammonium sulfate is formed.
The
insoluble salt, calcium sulfate, is also formed.
[00124] The neutralized, cooled pretreated slurry is then added to a
hydrolysis reactor and
the reactor is mixed. The slurry consists of 4.5% undissolved solids, and the
undissolved
solids consist of 35% cellulose. Once the pretreated slurry is added to the
hydrolysis
reactor, cellulase and hemicellulase enzyme from Trichoderma reesei are added.
The
enzyme dosage is 35 mg protein per gram cellulose, which corresponded to a
cellulase
activity of 35.6 Filter Paper Units (FPU) per gram of cellulose and a xylanase
activity of
275 xylanase units per gram of solids.
[00125] The hydrolysis runs for 2 days, at which point over 90% of the
cellulose is
converted to glucose and over 90% of the xylan is converted to xylose. The
final glucose
concentration is 6.0 to 8.0 g/L, with an average of 7.5 g/L. The hydrolysis
slurry is
filtered by using a vacuum filter to separate the unhydrolyzed solid residue
from the
aqueous stream. The unhydrolyzed solid residue contains primarily lignin,
unhydrolyzed
cellulose and silica, but also the insoluble salts such as calcium sulfate.
The filtrate is
essentially free of insoluble particles and contains glucose, xylose, and
arabinose sugar;
the soluble salts ammonium sulfate, potassium sulfate, magnesium sulfate and a
small
amount of dissolved calcium sulfate, and acetic acid, soluble lignin, and
other dissolved
organics.
[00126] The process stream is evaporated to increase the solids concentration
ten-fold.
The glucose concentration in the evaporated stream is 62 g/L, the xylose is 20
g/L, and
the acetic acid is 2.0 g/L.
[00127] The evaporated stream is added to a fermentor to carry out sugar
fermentation
with yeast. The yeast strain is LNHST from Purdue University and has been
genetically
modified to enable it to ferment xylose, as well as glucose to ethanol. The
strain is grown
by propagation as described in U.S. Patent No. 5,789,210. The fermentation is
fed over a
period of 7 hours and then run as a batch for 48 hours.
[00128] At the conclusion of the fermentation, the yeast cells are removed by
centrifugation. The dilute beer is distilled to recover the ethanol from the
aqueous
solution, leaving still bottoms behind.
32
CA 02565433 2006-10-25
[00129] The ammonium sulfate salt is recovered from the still bottoms by
evaporating the
water to concentrate the salt and then crystallizing the salt.
[00130] The present invention may be illustrated in the following examples.
However, it
is to be understood that these examples are for illustrative purposes only,
and should not
be used to limit the scope of the present invention in any manner.
Examples:
EXAMPLE 1: Recovery of soluble inorganic salt from a hydrolyzate sugar stream
[00131] A sugar hydrolyzate stream containing sodium sulfate and other soluble
inorganic salts was prepared as follows.
Feedstock preparation
[90132] Wheat straw was received in bales measuring 3 feet by 3 feet by 4
feet. The
wheat straw consisted of 60.3% carbohydrates, 18.7% lignin, 3.6% protein, 3.1%
silica,
and 4.9% non-silica inorganic salts. The inorganic salts included the cationic
salt ions
potassium (1.2%), calcium (0.57%), sodium (0.04%) and magnesium (0.15%), and
the
anionic ions chloride (0.22%) and phosphate (0.04%). The organic salt oxalate
was also
present at a concentration of 0.51%.
[00133] Two batches of 15 tonnes of the straw were hammer-milled to an average
size of
1/8" and slurried in water at a ratio of 10 parts water to 1 part solids. The
slurry was
pumped through piping heated by direct injection with 350 psig steam to reach
a
temperature of 185 C. Once at this temperature, 10% sulfuric acid was added to
reach a
level of 0.9% acid on solids (w/w). The heated, acidified stock was held at
this condition
for 2 minutes as it passed through a pipe of 8 inches diameter. Upon exiting
the pipe, the
slurry was flashed through a series of three cyclones to drop the temperature
to 70 C and
adjusted to pH 5.0 with 30% concentrated sodium hydroxide. The slurry was
finally
cooled to 50 C by passing it through a heat exchanger cooled with cold water.
[00134] Upon acid addition, the soluble inorganic salts of potassium sulfate,
sodium
sulfate, and magnesium sulfate were formed. The insoluble salt, calcium
sulfate, was
also formed. Upon neutralization with sodium hydroxide, which is soluble, the
33
CA 02565433 2006-10-25
concentration of sodium sulfate in the slurry increased markedly. The calcium
sulfate
concentration was above the solubility limit and a portion of it precipitated
and deposited
on the cyclones and related piping. A portion of the organic salt calcium
oxalate also
deposited on the equipment.
Hydrolysis
[00135] The neutralized, cooled pretreated slurry was then pumped into three
hydrolysis
tanks, each of working volume of about 130,000 liters. The tanks are equipped
with
bottom-mounted eductors to mix the slurry; one of the three tanks has two side-
mounted
agitators. The slurry consisted of 4.5% undissolved solids, and the
undissolved solids
consisted of 55% cellulose. Once the hydrolysis tanks were filled or the
pretreated slurry
was exhausted, cellulase enzyme from Trichoderma reesei was added. The enzyme
dosage was 25 mg protein per gram cellulose, which corresponded to a cellulase
activity
of 25.4 Filter Paper Units (FPU) per gram of cellulose.
[00136] The hydrolyses ran for 5 days, at which point over 90% of the
cellulose was
converted to glucose. The final glucose concentration was 26.0 to 28.0 g/L,
with an
average of 27.5 g/L. The hydrolysis slurries were pumped to a Lasta plate and
frame
filter press to separate the un-hydrolyzed solid residue from the aqueous
stream. A
polymeric flocculent was added in line at a level of 1-3 kg polymer/t solids
to improve
the rate of filtration. The filter cake was 45% solids. The un-hydrolyzed
solid residue
contains primarily lignin and un-hydrolyzed cellulose, but also the insoluble
salts such as
calcium sulfate. The aqueous process stream is essentially free of insoluble
particles and
contains glucose, xylose, and arabinose sugar; the soluble salts sodium
sulfate, potassium
sulfate, magnesium sulfate, and a small amount of dissolved calcium sulfate;
and acetic
acid and other dissolved organics.
[00137] The process stream was evaporated under vacuum using a four-effect
evaporator
at 90 C, 80 C, 70 C and 45 C, respectively, to a volume of 81,700 liters with
a solids
concentration of 34%. Some of the acetic acid evaporated with the water, and
some
solids precipitated upon evaporation. The pH of the evaporated slurry was
adjusted to pH
6.5 with 50% sodium hydroxide solution, and this caused more precipitation.
The
concentrated, pH-adjusted stream was sent to the Lasta plate and frame filter
press a
34
CA 02565433 2006-10-25
second time, with a Perlite filter aid, to remove the precipitated solids. The
clear,
evaporated process stream had inorganic salt concentrations of 105 g/L sodium
sulfate,
40 g/L potassium sulfate, and 5 g/L magnesium sulfate. In addition, organic
compounds
present included 153 g/L glucose, 49 g/L xylose, 7.3 g/L arabinose, 3.4 g/L
furfural, 3.5
g/L hydroxymethyl furfural, and 9.1 g/L acetate salt, an organic salt that was
measured as
acetic acid, and various trace metals (including trace quantities of calcium),
and a
significant amount of unidentified impurities.
Ion exclusion chromatography
[00138] The inorganic, soluble salts sodium sulfate, potassium sulfate, and
magnesium
sulfate were recovered from the concentrated process stream by ion exclusion
chromatography, as follows.
[00139] The ion exclusion chromatography separation was carried out over a 15-
day
period with continuous operation except for periodic shutdowns for filter
changes and
one complete cycle of water flushing. The separation was carried out on an
Improved
Simulated Moving Bed (ISMB) system (Eurodia Industrie S.A. of Wissous, France,
available through Ameridia, Somerset, New Jersey) of volume 6700 liters,
packed with
cation exchange resin from Mitsubishi Chemical, resin #UBK530. The ISMB system
consists of 4 columns with 4 bed shifts per cycle and was operated with the
feed stream at
pH 5.8 to 6.5. The system was maintained at 70 C as was the process feed and
the
dilution water. The process stream was fed at an average rate of 262 liters
per hour and
dilution water was added at a rate of 969 L/hr, which is an average ratio of
3.7:1 with the
process feed. Salt raffinate and sugar product streams were collected at
average flow
rates of 760 and 461 liters/hr, respectively.
[00140] The salt raffinate stream contained over 99% of the salt. The
inorganic salt
concentrations were 35.6 g/L sodium sulfate, 14.4 g/L potassium sulfate, 1.9
g/L
magnesium sulfate. In addition, the organic salt acetate was present at a
concentration of
3.3 g/L, measured as acetic acid. A very small fraction of the organic
compounds were
present in this stream at concentrations of 1.2 g/L glucose, 0.5 g/L xylose,
0.2 g/L
arabinose, 0.3 g/L furfural and 0.6 g/L hydroxymethyl furfural.
CA 02565433 2006-10-25
[00141] The sugar product stream contained the vast majority of the organic
compounds
and tiny amounts of salt. The concentrations of this stream were 1.2 g/L
sodium sulfate,
0.4 g/L potassium sulfate, 66 g/L glucose, 22 g/L xylose, 3.3 g/L arabinose,
and 0.09 g/L
acetic acid, measured as acetate salt.
[00142] The salt raffinate stream is evaporated to 40% solids, then sent to an
evaporator-
crystallizer to produce granulates for use as fertilizer.
EXAMPLE 2: Recovery of soluble inorganic salt from wheat straw leachate
[00143] Wheat straw was received in bales measuring 3 feet by 3 feet by 4
feet. The
wheat straw consisted of 15.9% moisture. The composition of the straw, on a
dry basis,
was 60.1% carbohydrates, 19.7% lignin, 3.36% protein, 3.0% silica, and 4.5%
non-silica
salts. The inorganic cationic salt ions included 1.28% potassium, 0.45%
calcium, 0.04%
sodium, and 0.15% magnesium. The inorganic anions were chloride at 0.22% and
0.04%
phosphate. The organic salt oxalate was present at a concentration of 0.55%. A
weight
of 1199 kg wet straw was hammer-milled to 1/8 inch.
[00144] The hammer-milled straw was slurried in 49,590 liters of 65 C water.
The slurry
was gravity fed into a mixed tank, where it was mixed overnight for 18 hours
and
rnaintained at 65 C. The pH was 6.4 throughout the leaching process. The
slurry was
then flowed through screened baskets by gravity to separate the solids from
the liquid
leachate stream. The screened baskets produced a cake of 21.1% solids content.
[00145] The leachate contained 9.9% of the initial fiber solids. This was at a
concentration of 2010 mg/L total dissolved solids, which included 127 mg/L
protein, 262
mg/L potassium, 1.5 mg/L calcium, 36 mg/L magnesium, 55 mg/L chloride and a
majority of 1530 mg/L unidentified. Other than calcium, which was not removed
to a
significant degree, the salts were removed from the straw by leaching at a
yield of 87% to
93%. The protein yield in the leachate was 14%.
[00146] The leachate stream was evaporated to increase the solids
concentration
approximately 100-fold, to a solids concentration of 19.9% and a volume of 464
liters. A
significant amount of protein precipitated and was removed by filtration. A
preliminary
evaluation of drying and crystallizing the filtrate indicated that the
inorganic salts
36
CA 02565433 2006-10-25
constituted much too small a proportion of the total solids for
crystallization of the salts
to be possible.
[00147] An aliquot of the leachate stream is fed to a laboratory ion exclusion
chromatography system to separate the salts from the organics. The ion
exclusion
chromatography separation is carried out on a fixed bed of volume 127 mL,
packed with
cation exchange resin from Mitsubishi Chemical, resin #UBK530. The bed is
operated
with the feed stream at pH 6.8. The column is maintained at 70 C as is the
feed and the
elution water. Prior to carrying out the separation, the column is conditioned
with three
bed volumes of the process stream. The process stream is fed in a pulse of 5
mL and
elution water is then added at a rate of 4 mL/minute. Salt raffinate and sugar
product
streams are collected as the conductivity of the effluent indicates the
presence and
absence of salt, respectively.
[00148] The salt raffinate stream contains most of the inorganic salts, which
are primarily
potassium chloride and magnesium chloride and a small amount of organic
impurities.
The inorganic salt concentrations are high enough to permit crystallization to
recover the
salts.
EXAMPLE 3: Recovery of soluble inorganic salts from wheat straw leachate
[00149] Wheat straw was received in bales measuring 3 feet by 3 feet by 4
feet. The
wheat straw consisted of 6.4% moisture. The composition of the straw, on a dry
basis,
was 60.3% carbohydrates, 18.7% lignin, 3.6% protein, 3.1% silica, and 4.9% non-
silica
salts. The inorganic cationic salt ions present included 1.22% potassium,
0.57% calcium,
0.04% sodium, and 0.15% magnesium. The inorganic anions were chloride at
0.10%,
0.16% phosphate and 0.08% sulfate. A weight of 3,363 kg of moist straw was
hammer-
milled to 1/8 inch pieces. The hammer-milled straw was slurried in 70,626
liters of 65 C
water. The slurry was gravity fed into a mixed tank, where it was mixed
overnight for 18
hours and maintained at 65 C. The pH was 4.9 throughout the leaching process.
The
slurry was then flowed through a centrifuge to separate the solids from the
liquid leachate
stream. The centrifuge produced a cake of 29.6% solids content.
[00150] The leachate contained 10.6% of the initial fiber solids. This was at
a
concentration of 4090 mg/L total dissolved solids, which included 1138 mg/L
protein,
37
CA 02565433 2006-10-25
494 mg/L potassium, 67 mg/L calcium, 36 mg/L magnesium, 67 mg/L chloride, 80
mg/L
of sulfate, 45 mg/L of phosphate, 27 mg/L of sodium, 163 mg/L of silica, 2010
mg/L of
soluble phenolics and about 600 mg/L unidentified. Other than calcium and
silica, which
were not removed to a significant degree, the salts were removed from the
straw by
leaching at a yield of 50% to 93%. The protein yield in the leachate was 72%.
[00151] The leachate stream is evaporated to increase the solids concentration
approximately 40-fold, to a solids concentration of 19.6% and a volume of 1770
liters. A
significant amount of protein precipitates and is removed by filtration.
[00152] An aliquot of the leachate stream is fed to a laboratory ion exclusion
chromatography system to separate the salts from the organics. The ion
exclusion
chromatography separation is carried out on a fixed bed of volume 127 mL,
packed with
cation exchange resin from Mitsubishi Chemical, resin #UBK530. The bed is
operated
with the feed stream at pH 6.8. The column is maintained at 70 C as is the
feed and the
elution water. Prior to carrying out the separation, the column is conditioned
with three
bed volumes of the process stream. The process stream is fed in a pulse of 5
mL and
elution water is then added at a rate of 4 mL/minute. Salt raffinate and sugar
product
streams are collected as the conductivity of the effluent indicates the
presence of salt and
water, respectively.
[00153] The salt raffinate stream contains most of the inorganic salts, which
are primarily
potassium chloride and magnesium chloride, and a small amount of organic
impurities.
The inorganic salt concentrations are high enough to permit crystallization to
recover the
salts.
EXAMPLE 4: Recovery of soluble inorganic salts during conversion of wheat
straw
to ethanol
[00154] A sugar hydrolyzate stream containing ammonium sulfate and other
soluble
inorganic salts was prepared as follows.
[00155] Wheat straw was received in bales measuring 3 feet by 3 feet by 4 feet
and
chopped and leached according to the procedures of Example 3. The leached
wheat straw
consisted of 57.1% carbohydrates, 36.6% lignin, 1.75% protein, 3.9% silica,
and 0.8%
38
CA 02565433 2006-10-25
non-silica salts. The salts included 0.2% potassium, 0.17% calcium, 0.05%
sodium,
0.03% magnesium, <0.01% phosphate, 0.014% chloride and 0.023% sulfate. The
leached straw was slurried in water at a ratio of 8 parts water to 1 part
solids. The slurry
was pumped through piping heated by direct injection with 350 psig steam to
reach a
temperature of 185 C. Once at this temperature, 10% concentrated sulfuric acid
was
added at a level of 0.9% acid on solids (w/w). The heated, acidified stock was
held at this
condition for 2 minutes as it passed through a pipe of 8 inches diameter. Upon
exiting
the pipe, the slurry was flashed through a series of three cyclones to drop
the temperature
o 75 C and then cooled to 50 C by using heat exchange with cool water. The
slurry was
then adjusted to pH 5.0 with concentrated ammonium hydroxide.
[00156] Upon acid addition, the soluble salts of potassium sulfate, sodium
sulfate, and
magnesium sulfate were formed. The insoluble salt, calcium sulfate, was also
formed.
Upon neutralization with ammonium hydroxide, which is soluble, the
concentration of
ammonium sulfate in the slurry increased markedly. The calcium sulfate
concentration
was above the solubility limit and a portion of it precipitated and deposited
on the
cyclones and related piping.
[00157] The neutralized, cooled pretreated slurry was then pumped into a
hydrolysis tank
at a volume of about 100,000 liters. The tank is equipped with side-mounted
eductors to
mix the slurry. The slurry consisted of 4.5% undissolved solids, and the
undissolved
solids consisted of 55% cellulose. Once the pretreated slurry was added to the
hydrolysis
tank, cellulase enzyme from Trichoderma reesei was added. The enzyme dosage
was 35
mg protein per gam cellulose, which corresponded to a cellulase activity of
35.6 Filter
Paper Units (FPU) per gram of cellulose.
[00158] The hydrolysis ran for 2 days, at which point over 90% of the
cellulose was
converted to glucose. The final glucose concentration was 26.0 to 28.0 g/L,
with an
average of 27.5 g/L. The hydrolysis slurry was pumped to a Lasta plate and
frame filter
press to separate the unhydrolyzed solid residue from the aqueous stream. A
polyacrylamide flocculent was added at a level of 1-3 kg/t solids to aid in
the filtration.
The unhydrolyzed solid residue contains primarily lignin, unhydrolyzed
cellulose and
sand, but also the insoluble salts such as calcium sulfate. The aqueous
process stream is
essentially free of insoluble particles and contains glucose, xylose, and
arabinose sugar;
39
CA 02565433 2006-10-25
the soluble salts ammonium sulfate, potassium sulfate, magnesium sulfate and a
small
amount of dissolved calcium sulfate, and acetic acid, soluble lignin, and
other dissolved
organics.
[00159] The process stream was evaporated to increase the solids concentration
three-fold
by using a 4-effect falling film evaporator. The glucose concentration in the
evaporated
stream was 62 g/L, the xylose was 20 g/L, and the acetic acid was 2.0 g/L. The
evaporated stream was filtered across the Lasta press with a Perlite filter
aid to remove
particulates.
[00160] The evaporated stream was pumped to a fermentor to carry out sugar
fermentation with yeast. The yeast strain was LNHST from Purdue University and
has
been genetically modified to enable it to ferment xylose, as well as glucose,
to ethanol.
The strain was grown by propagation through successive fermentors, as
described in US
5,789,210. The fermentation was fed over a period of 7 hours and then run as a
batch for
48 hours at a volume of 65,000 liters.
[00161] At the conclusion of the fermentation, the yeast cells were removed by
centrifugation. The dilute beer was distilled to separate the ethanol from the
aqueous
solution. The distillation was carried out using a beer column and a
rectifying column.
The still bottoms were collected as a liquid stream from the bottom of the
beer column
with a volume of 87,000 liters.
[00162] The still bottoms were evaporated under vacuum at 80 C to a volume of
18,000
liters with a solids concentration of 13%. Some of the solids precipitated
upon
evaporation. The pH of the evaporated slurry was adjusted to pH 7.0 with 30%
ammonium hydroxide solution, and this caused more precipitation. The
concentrated,
pH-adjusted stream was sent to the Lasta press with a diatomaceous earth body
feed to
remove the precipitated solids. The clear, evaporated process stream had
inorganic salt
concentrations of 55 g/L ammonium sulfate, 20 g/L potassium sulfate, and 2.5
g/L
magnesium sulfate. In addition, organic compounds present included 24 g/L
xylose, 3.3
g/L arabinose, 3.4 g/L furfural, 3.5 g/L hydroxymethyl furfural, and 9.1 g/L
acetate salt,
an organic salt that was measured as acetic acid, and various trace metals
(including trace
quantities of calcium), and a significant amount of unidentified impurities.
CA 02565433 2013-02-19
[00163] The inorganic, soluble salts ammonium sulfate, potassium sulfate, and
magnesium sulfate were recovered from the concentrated process stream by ion
exclusion
chromatography, as follows.
[00164] The ion exclusion chromatography separation is carried out over a 2.5-
day period
with continuous operation except for periodic shutdowns for filter changes and
one
complete cycle of water flushing. The separation is carried out on an Improved
Simulated Moving Bed (ISMB) system (Eurodia Industrie S.A. of Wissous, France,
available through Ameridia, Somerset, New Jersey) of volume 6700 liters,
packed with
cation exchange resin from Mitsubishi Chemical, resin #UBK530. The ISMB system
consists of 4 columns with 4 bed shifts per cycle and is operated with the
feed stream at
pH 6.0 to 7.5. The system is maintained at 65 C as was the process feed and
the dilution
water. The process stream is fed at an average rate of 320 liters per hour and
dilution
water was added at a rate of 960 L/hr, which is an average ratio of 3.0:1 with
the process
feed. Salt raffinate and sugar product streams are each collected at average
flow rates of
640 liters/hr.
[00165] The salt raffinate stream contains over 99% of the salt. The inorganic
salt
concentrations are 15.6 g/L ammonium sulfate, 4.4 g/L potassium sulfate, and
1.9 g/L
magnesium sulfate. In addition, the organic salt acetate is present at a
concentration of 0.9
g/L, measured as acetic acid. A very small fraction of the organic compounds
were in
this stream at concentrations of 0.5 g/L xylose, 0.2 g/L arabinose, 0.3 g/L
furfural, and 0.6
g/L hydroxymethyl ftirfural.
[00166] The sugar product stream contained the vast majority of the organic
compounds
and very small amounts of salt. The concentrations of this stream were 1.2 g/L
ammonium sulfate, 0.4 g/L potassium sulfate, 14 g/L xylose, 2.3 g/L arabinose,
and 0.09
g/L acetic acid, measured as acetate salt.
[00167] The salt raffinate stream is evaporated to 40% solids, then sent to an
evaporator-
crystallizer to produce granulates for use as fertilizer.
[00168] The present invention has been described with regard to one or more
embodiments. However, it will be apparent to persons skilled in the art that a
number of
41
CA 02565433 2013-02-19
variations and modifications can be made without departing from the scope of
the
invention as described in the claims.
42
