NZ750869B2 - Process for the production of an organic acid from a lignocellulosic feedstock - Google Patents
Process for the production of an organic acid from a lignocellulosic feedstock Download PDFInfo
- Publication number
- NZ750869B2 NZ750869B2 NZ750869A NZ75086917A NZ750869B2 NZ 750869 B2 NZ750869 B2 NZ 750869B2 NZ 750869 A NZ750869 A NZ 750869A NZ 75086917 A NZ75086917 A NZ 75086917A NZ 750869 B2 NZ750869 B2 NZ 750869B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- pulp mill
- acid
- obtaining
- liquor
- organic acid
- Prior art date
Links
- 238000000034 method Methods 0.000 title claims abstract description 104
- 150000007524 organic acids Chemical class 0.000 title claims abstract description 101
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 58
- ODINCKMPIJJUCX-UHFFFAOYSA-N calcium monoxide Chemical compound [Ca]=O ODINCKMPIJJUCX-UHFFFAOYSA-N 0.000 claims abstract description 50
- 229920005610 lignin Polymers 0.000 claims abstract description 49
- 239000000126 substance Substances 0.000 claims abstract description 46
- 238000000855 fermentation Methods 0.000 claims abstract description 40
- 230000004151 fermentation Effects 0.000 claims abstract description 40
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 claims abstract description 39
- 238000011084 recovery Methods 0.000 claims abstract description 27
- 239000000292 calcium oxide Substances 0.000 claims abstract description 25
- 229910052602 gypsum Inorganic materials 0.000 claims abstract description 25
- 239000010440 gypsum Substances 0.000 claims abstract description 25
- -1 organic acid calcium salt Chemical class 0.000 claims abstract description 10
- 150000001720 carbohydrates Chemical class 0.000 claims abstract description 9
- 239000003795 chemical substances by application Substances 0.000 claims abstract description 5
- 238000006047 enzymatic hydrolysis reaction Methods 0.000 claims abstract description 5
- 230000000813 microbial Effects 0.000 claims abstract description 5
- 230000001264 neutralization Effects 0.000 claims abstract description 4
- QTBSBXVTEAMEQO-UHFFFAOYSA-N acetic acid Chemical compound CC(O)=O QTBSBXVTEAMEQO-UHFFFAOYSA-N 0.000 claims description 42
- 239000000047 product Substances 0.000 claims description 34
- BVKZGUZCCUSVTD-UHFFFAOYSA-N Carbonic acid Chemical compound OC(O)=O BVKZGUZCCUSVTD-UHFFFAOYSA-N 0.000 claims description 30
- 229920002488 Hemicellulose Polymers 0.000 claims description 28
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 claims description 27
- 239000004310 lactic acid Substances 0.000 claims description 27
- 235000014655 lactic acid Nutrition 0.000 claims description 27
- 238000006460 hydrolysis reaction Methods 0.000 claims description 22
- 239000000463 material Substances 0.000 claims description 21
- 239000000428 dust Substances 0.000 claims description 20
- 239000000203 mixture Substances 0.000 claims description 20
- 239000000413 hydrolysate Substances 0.000 claims description 19
- 235000011054 acetic acid Nutrition 0.000 claims description 14
- 238000007792 addition Methods 0.000 claims description 14
- 239000002023 wood Substances 0.000 claims description 13
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 11
- 239000011734 sodium Substances 0.000 claims description 10
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- 235000015450 Tilia cordata Nutrition 0.000 claims description 9
- 235000011941 Tilia x europaea Nutrition 0.000 claims description 9
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 9
- 238000005868 electrolysis reaction Methods 0.000 claims description 9
- 239000004571 lime Substances 0.000 claims description 9
- XBDQKXXYIPTUBI-UHFFFAOYSA-N propionic acid Chemical compound CCC(O)=O XBDQKXXYIPTUBI-UHFFFAOYSA-N 0.000 claims description 9
- 230000008929 regeneration Effects 0.000 claims description 9
- 238000011069 regeneration method Methods 0.000 claims description 9
- VZCYOOQTPOCHFL-OWOJBTEDSA-N (E)-but-2-enedioate;hydron Chemical compound OC(=O)\C=C\C(O)=O VZCYOOQTPOCHFL-OWOJBTEDSA-N 0.000 claims description 6
- FERIUCNNQQJTOY-UHFFFAOYSA-N Butanoic acid Chemical compound CCCC(O)=O FERIUCNNQQJTOY-UHFFFAOYSA-N 0.000 claims description 6
- RGHNJXZEOKUKBD-SQOUGZDYSA-N Gluconic acid Chemical compound OC[C@@H](O)[C@@H](O)[C@H](O)[C@@H](O)C(O)=O RGHNJXZEOKUKBD-SQOUGZDYSA-N 0.000 claims description 6
- KDYFGRWQOYBRFD-UHFFFAOYSA-N Succinic acid Chemical compound OC(=O)CCC(O)=O KDYFGRWQOYBRFD-UHFFFAOYSA-N 0.000 claims description 6
- SRBFZHDQGSBBOR-SQOUGZDYSA-N Xylose Natural products O[C@@H]1CO[C@@H](O)[C@@H](O)[C@@H]1O SRBFZHDQGSBBOR-SQOUGZDYSA-N 0.000 claims description 6
- AEMRFAOFKBGASW-UHFFFAOYSA-N glycolic acid Chemical compound OCC(O)=O AEMRFAOFKBGASW-UHFFFAOYSA-N 0.000 claims description 6
- 229910052760 oxygen Inorganic materials 0.000 claims description 6
- MYMOFIZGZYHOMD-UHFFFAOYSA-N oxygen Chemical compound O=O MYMOFIZGZYHOMD-UHFFFAOYSA-N 0.000 claims description 6
- 239000001301 oxygen Substances 0.000 claims description 6
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- 241000196324 Embryophyta Species 0.000 claims description 5
- 239000010905 bagasse Substances 0.000 claims description 5
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- 238000000066 reactive distillation Methods 0.000 claims description 5
- 239000010902 straw Substances 0.000 claims description 5
- 240000000218 Cannabis sativa Species 0.000 claims description 4
- 239000000706 filtrate Substances 0.000 claims description 4
- 229910052708 sodium Inorganic materials 0.000 claims description 4
- HYBBIBNJHNGZAN-UHFFFAOYSA-N Furfural Chemical compound O=CC1=CC=CO1 HYBBIBNJHNGZAN-UHFFFAOYSA-N 0.000 claims description 3
- 229960002989 Glutamic Acid Drugs 0.000 claims description 3
- LVHBHZANLOWSRM-UHFFFAOYSA-N Itaconic acid Chemical compound OC(=O)CC(=C)C(O)=O LVHBHZANLOWSRM-UHFFFAOYSA-N 0.000 claims description 3
- WHUUTDBJXJRKMK-VKHMYHEASA-N L-glutamic acid Chemical compound OC(=O)[C@@H](N)CCC(O)=O WHUUTDBJXJRKMK-VKHMYHEASA-N 0.000 claims description 3
- BJEPYKJPYRNKOW-UHFFFAOYSA-N Malic acid Chemical compound OC(=O)C(O)CC(O)=O BJEPYKJPYRNKOW-UHFFFAOYSA-N 0.000 claims description 3
- 229960003487 Xylose Drugs 0.000 claims description 3
- 235000015165 citric acid Nutrition 0.000 claims description 3
- VZCYOOQTPOCHFL-UHFFFAOYSA-N fumaric acid Chemical compound OC(=O)C=CC(O)=O VZCYOOQTPOCHFL-UHFFFAOYSA-N 0.000 claims description 3
- 239000001530 fumaric acid Substances 0.000 claims description 3
- 239000000174 gluconic acid Substances 0.000 claims description 3
- 235000012208 gluconic acid Nutrition 0.000 claims description 3
- 229950006191 gluconic acid Drugs 0.000 claims description 3
- 235000013922 glutamic acid Nutrition 0.000 claims description 3
- 239000004220 glutamic acid Substances 0.000 claims description 3
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- KEAYESYHFKHZAL-UHFFFAOYSA-N sodium Chemical compound [Na] KEAYESYHFKHZAL-UHFFFAOYSA-N 0.000 claims description 3
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- 150000004823 xylans Chemical class 0.000 claims description 3
- 230000005591 charge neutralization Effects 0.000 claims description 2
- 238000006386 neutralization reaction Methods 0.000 claims description 2
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- 150000003568 thioethers Chemical class 0.000 claims 1
- HEMHJVSKTPXQMS-UHFFFAOYSA-M sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 42
- 238000002203 pretreatment Methods 0.000 description 39
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- 235000005985 organic acids Nutrition 0.000 description 13
- 229910052717 sulfur Inorganic materials 0.000 description 13
- 238000010411 cooking Methods 0.000 description 12
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- 238000002360 preparation method Methods 0.000 description 11
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- WQZGKKKJIJFFOK-GASJEMHNSA-N D-Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 description 9
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- GRVFOGOEDUUMBP-UHFFFAOYSA-N Sodium sulfide Chemical compound [Na+].[Na+].[S-2] GRVFOGOEDUUMBP-UHFFFAOYSA-N 0.000 description 6
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- 239000003513 alkali Substances 0.000 description 4
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- CURLTUGMZLYLDI-UHFFFAOYSA-N carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 3
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- CZMRCDWAGMRECN-UGDNZRGBSA-N D-sucrose Chemical compound O[C@H]1[C@H](O)[C@@H](CO)O[C@@]1(CO)O[C@@H]1[C@H](O)[C@@H](O)[C@H](O)[C@@H](CO)O1 CZMRCDWAGMRECN-UGDNZRGBSA-N 0.000 description 2
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Abstract
The present invention relates to a process for the production of an organic acid from a lignocellulosic feedstock. The process is integrated with a pulp mill and comprises the steps: a) providing a lignocellulosic feedstock; b) obtaining an alkaline liquor from the pulp mill; c) pre-treating the lignocellulosic feedstock with the alkaline liquor, thereby obtaining a pretreated cellulosic feed and a black liquor; d) obtaining calcium oxide from the pulp mill; e) subjecting the pretreated cellulosic feed from step c) to enzymatic hydrolysis, thereby obtaining a saccharide feed; f) subjecting the saccharide feed from step e) to microbial fermentation using the calcium oxide from step d) as a neutralising agent, thereby obtaining an organic acid calcium salt; g) treating the organic acid calcium salt with sulfuric acid, thereby obtaining gypsum and the organic acid; h) optionally isolating lignin from the black liquor obtained in step c), thereby obtaining lignin and weak black liquor; and i) returning the black liquor obtained in step c) and/or the weak black liquor obtained in step h) to the pulp mill for integration with the pulp mill chemical recovery process; wherein steps e) and f) are performed either sequentially or simultaneously. nocellulosic feedstock with the alkaline liquor, thereby obtaining a pretreated cellulosic feed and a black liquor; d) obtaining calcium oxide from the pulp mill; e) subjecting the pretreated cellulosic feed from step c) to enzymatic hydrolysis, thereby obtaining a saccharide feed; f) subjecting the saccharide feed from step e) to microbial fermentation using the calcium oxide from step d) as a neutralising agent, thereby obtaining an organic acid calcium salt; g) treating the organic acid calcium salt with sulfuric acid, thereby obtaining gypsum and the organic acid; h) optionally isolating lignin from the black liquor obtained in step c), thereby obtaining lignin and weak black liquor; and i) returning the black liquor obtained in step c) and/or the weak black liquor obtained in step h) to the pulp mill for integration with the pulp mill chemical recovery process; wherein steps e) and f) are performed either sequentially or simultaneously.
Description
Process for the production of an organic acid from a lignocellulosic feedstock
TECHNICAL FIELD
The present disclosure relates to the field of biomass valorisation and more specifically to the
production of organic acids from biomass by saccharification and fermentation.
BACKGROUND ART
In order to achieve a sustainable society it is in the long-term necessary to replace fossil-based
materials, such as fuels, commodity- and speciality chemicals, with materials from renewable
sources. This has resulted in an increasing focus on, and prevalence of, bio-based production
of chemicals.
Organic acids such as lactic acid are among chemicals already commonly produced from
renewable sources. Today, large-scale production of lactic acid is performed by microbial
fermentation of feedstocks comprising oligosaccharides or starches, such as corn, beet sugar
or cane sugar. Lactic acid is a platform chemical that can be used to produce products such as
polylactic acid (PLA), an increasingly prevalent biodegradable thermoplastic polymer.
The use of starchy feedstocks requires diverting the use of cropland and therefore competes
with food production. Therefore, there is a general desire in the field of bio-based materials to
develop next generation methods which utilize non-food biomass such as forestry materials,
grasses or waste materials from food processing as raw materials.
describes a method for the production of an organic acid as a fermentation
product from lignocellulosic biomass. The method comprises the steps of pretreatment of the
lignocellulosic biomass with an alkaline agent; simultaneous saccharification and fermentation
(SSF) of the pretreated lignocellulosic biomass; and optionally recovery of the fermentation
product. The lignocellulosic biomass is selected from the group consisting of grass, wood,
bagasse, straw, paper, plant material, and combinations thereof.
US 2009/0226979 discloses a method for hydrolyzing cellulosic material into sugars using the
spent liquor media from a pulping process or from another cellulosic biomass process.
There remains a need for improved processes for producing organic acids, such as lactic acid
or acetic acid, from lignocellulosic feedstocks.
SUMMARY OF THE INVENTION
The inventors of the present invention have identified a number of deficiencies associated
with prior art methods for the production of organic acids such as lactic acid and acetic acid
from lignocellulosic feedstocks. In order to obtain a suitable yield of product organic acids, a
pretreatment step is required, but this pretreatment requires the use of substantial amounts
of alkaline liquor. Such a pretreatment is expensive, making prior-art methods commercially
less viable. Moreover, the process for producing organic acids generates large amounts of
waste products that require disposal.
It is thus an object of the present invention to provide a process for the production of an
organic acid from a lignocellulosic feedstock, the said process having a greater economic
viability and a more benign environmental impact as compared to prior art methods and/or to
at least provide the public with a useful choice.
This object is achieved by a process for the production of an organic acid from a lignocellulosic
feedstock according to the appended claims. The process is integrated with a pulp mill and
comprises the steps:
a) providing a lignocellulosic feedstock;
b) obtaining an alkaline liquor from the pulp mill;
c) pre-treating the lignocellulosic feedstock with the alkaline liquor, thereby
obtaining a pretreated cellulosic feed and a black liquor;
d) obtaining calcium oxide from the pulp mill;
e) subjecting the pretreated cellulosic feed from step c) to enzymatic hydrolysis,
thereby obtaining a saccharide feed;
f) subjecting the saccharide feed from step e) to microbial fermentation using the
calcium oxide from step d) as a neutralising agent, thereby obtaining an organic acid calcium
salt;
g) treating the organic acid calcium salt with sulfuric acid, thereby obtaining
gypsum and the organic acid;
h) optionally isolating lignin from the black liquor obtained in step c), thereby
obtaining lignin and weak black liquor; and
i) returning the black liquor obtained in step c) and/or the weak black liquor
obtained in step h) to the pulp mill for integration with the pulp mill chemical recovery
process;
wherein steps e) and f) are performed either sequentially or simultaneously.
By obtaining the alkaline liquor from the pulp mill in step b) and returning the spent alkaline
liquor to the pulp mill chemical recovery process in step i), the liquor can be regenerated and
reused in either the pulp mill processes and/or the organic acid production process. Therefore,
the cost of alkaline pretreatment and the amount of waste produced during the production of
organic acid is substantially reduced, making the process for the production of organic acids
more viable from a commercial and environmental standpoint.
Steps e) and f) may be performed simultaneously, i.e. as a simultaneous saccharification and
fermentation step. This simplifies the process, reducing the number of operations and
requirement for equipment, and may potentially increase the yield of the organic acid
product.
The organic acid produced by the process may be lactic acid, acetic acid, citric acid, itaconic
acid, succinic acid, fumaric acid, glycolic acid, pyruvic acid, acetic acid, glutamic acid, malic
acid, maleic acid, propionic acid, butyric acid, gluconic acid or combinations thereof. Any of
these acids may be produced by saccharificaton and fermentation of a lignocellulosic
feedstock by appropriate selection of the fermentation microorganisms. The organic acid
produced by the process is preferably lactic acid or acetic acid, even more preferably lactic
acid.
The alkaline liquor used in the pre-treatment step c) may comprise or consist of pulp mill
white liquor and/or soda liquor. White liquor is abundantly available in kraft pulp mills and is
highly suitable for the fractionation and pretreatment of lignocellulosic feedstocks. Soda liquor
is readily available as the pulping liquor in soda pulp mills, as NaOH make-up in Kraft pulp
mills, or by electrolysis of electrostatic precipitator dust.
The alkaline liquor used in the pre-treatment step c) may be in part derived from electrolysis
of pulp mill electrostatic precipitator (EP) dust. The sulfuric acid used in step g) may also be
derived from electrolysis of pulp mill electrostatic precipitator dust. By utilising EP dust, a pulp
mill waste product is converted to two process chemicals necessary for the production of the
organic acid. This reduces the amount of waste produced by the integrated process and also
reduces the quantities of “make-up” chemicals required for the pulp mill and organic acid
production processes.
The alkaline liquor may be essentially free from sodium sulfide. Such an alkaline liquor may be
obtained by the electrolysis of pulp mill electrostatic precipitator (EP) dust as described above.
By using liquor free from sodium sulfide in the pre-treatment step, lignin that is essentially
free from sulfur may be obtained from the resulting hydrolysate (black liquor).
The black liquor obtained in step c) may be combined with pulp mill black liquor prior to
isolating lignin in step h). By isolating lignin from the black liquor of the organic acid
production process, the pulp mill process, or both, a number of advantages are obtained. A
potentially valuable product, lignin, is obtained from a waste stream, and at the same time the
mass of waste being provided to the pulp mill recovery boiler is reduced, thus increasing the
capacity of the pulp mill and/or organic acid production process.
At least a portion of the gypsum obtained in step g) may be returned to the pulp mill for
integration with a pulp mill lime regeneration process. By regenerating calcium oxide from the
gypsum by-product the amount of waste produced by the organic acid production process is
reduced and the amount of calcium oxide make-up required by the pulp mill and/or organic
acid production process is also reduced. This favourably improves the overall process
economics.
The lignocellulosic feedstock from step a) may be subjected to an aqueous prehydrolysis step
prior to step b), thereby obtaining a prehydrolysed lignocellulosic feedstock and a
hemicellulose hydrolysate. This allows a relatively pure hemicellulose-rich fraction to be
obtained directly. A hemicellulose, such as xylan, or a product derived from hemicellulose,
such as xylose or furfural, may be isolated from the hemicellulose hydrolysate. This enables
further valorisation of the hemicellulose component of the lignocellulosic feedstock.
The organic acid obtained in step g) may be purified by reactive distillation with an alcohol to
provide an ester, followed by hydrolysis of the ester to provide a purified organic acid. Since
the alcohol can be easily recycled, the reactive distillation is a simple, resource-effective
means of obtaining a purified organic acid.
The pretreated cellulosic feed from step c) may be subjected to an oxygen delignification step
prior to step e). In some cases this may increase the yield of the organic acid and/or reduce
the need for further purification of the organic acid obtained by saccharification and
fermentation.
At least part of the pretreated cellulosic feed from step c) may be subjected to neutralisation
by addition of sulfuric acid prior to step e). This allows the saccharification and fermentation
steps to be performed at an optimal pH, increasing the rate and yield of product formation.
The lignocellulosic feedstock may be selected from the group consisting of wood, grass,
bagasse, straw, plant material, paper, and combinations thereof. Such materials include, but
are not limited to, pulpwood, forestry residues, energy cane, and mixtures thereof.
The pretreated cellulosic feed obtained in step c) may comprise or consist of pulp stock
obtained from the regular pulping process stream of a pulp mill; i.e. steps a) to c) may be
performed as part of the usual pulp mill operation using the usual pulp mill feedstock. Such a
process integration may for example be used to reduce expenditure on capital equipment
upon setting up production of an organic acid.
The pretreated cellulosic feed obtained in step c) may comprise or consist of material
produced entirely separately from the regular pulping process stream of a pulp mill; i.e. steps
a) to c) are performed separately from the usual pulp mill operation using a separate
feedstock. This allows a greater flexibility in the choice of lignocellulosic feedstock and may for
example allow the use of a cheaper feedstock. For example, the lignocellulosic feedstock may
comprise or consist of material that has been or would be rejected as feedstock in the normal
pulp mill operation, such as for example forestry residues and energy cane. This may reduce
the cost of the lignocellulosic feedstock, may reduce the load on the pulp mill bark boiler, and
may provide a use for materials that otherwise may be of limited use in chemical production.
The pretreated lignocellulosic feedstock may comprise or consist of mixtures of pulp mill pulp
stock and material produced entirely separately from the pulping process stream of a pulp
mill.
All filtrates and residues from the organic acid production process may be returned to the pulp
mill and integrated with the pulp mill chemical and/ energy recovery processes. Thus, the
organic acid production process may be fully integrated with pre-existing pulp mill processes.
Since a modern pulp mill is essentially a closed-loop system, this makes highly efficient use of
the input materials to the organic acid production process, since nearly all materials are
utilised in chemical regeneration or energy generation.
The pulp mill may be an alkaline pulp mill, preferably a kraft pulp mill or soda pulp mill, even
more preferably a kraft pulp mill. Kraft pulping if the predominant form of pulping in use, and
therefore the organic acid production process is readily integrated with the majority of paper
mills in operation.
Further aspects, objects and advantages are defined in the detailed description below with
reference to the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
For the understanding of the present invention and further objects and advantages of it, the
detailed description set out below can be read together with the accompanying drawings, in
which the same reference notations denote similar items in the various diagrams, and in
which:
Fig 1 schematically illustrates the pretreatment steps for the lignocellulosic feedstock
according to the present invention.
Fig 2 is a chart providing a comparison between eucalyptus pulpwood hydrolysate and
a glucose reference medium as a fermentation medium for the production of
lactic acid.
Fig 3 schematically illustrates the integration of the pulp mill process with the process
for the production of an organic acid.
Fig 4 schematically illustrates a potential mass balance of the integrated pulp mill and
organic acid production processes when soda liquor is used as the alkaline pre-
treatment liquor.
Fig 5 schematically illustrates a potential mass balance of the integrated pulp mill and
organic acid production processes when white liquor is used as the alkaline pre-
treatment liquor.
DETAILED DESCRIPTION
The process according to the present invention is performed in close integration with a pulp
mill, preferably an alkaline pulp mill, such as a kraft pulp mill or soda pulp mill, and even more
preferably a kraft pulp mill. The chemicals required for the process of the invention are readily
available or obtainable from the pulp mill, and the waste and residue streams can be returned
to the pulp mill for regeneration of the required chemicals.
Rising wood and energy costs make it increasingly urgent for the forest-based industry to find
by-product uses with higher market value. Pulp mills have unique prerequisites to make large
volumes of value-added bio-based materials and chemicals in parallel with pulp production. A
modern kraft pulp mill produces considerable amounts of organic by-products in the cooking
liquors, often in quantities exceeding the amount of pulp produced. This broad spectrum of
organic compounds may potentially be processed to valuable chemical products within pulp
mill biorefineries, utilising the energy surplus of the pulp production for the manufacture.
Kraft pulp mills typically operate by pulping chipped lignocellulosic material using white liquor,
an aqueous solution comprising sodium hydroxide and sodium sulfide. The white liquor
removes lignin and hemicellulose from the lignocellulosic material, giving a cellulose pulp and
black liquor comprising the white liquor components plus leached lignin and hemicellulose.
The black liquor is concentrated and tall oil soap is skimmed. After further concentration and
optional removal of a lignin fraction, the black liquor is combusted in the pulp mill recovery
boiler, producing energy in the form of steam and electricity, as well as a slag comprising
sodium carbonate and sodium sulfide. This slag is dissolved in process fluids to give a solution
comprising sodium carbonate and sodium sulfide, known as green liquor. The green liquor is
treated with calcium oxide (quicklime), regenerating a white liquor and giving a calcium
carbonate precipitate (lime mud). The lime mud is calcined in lime kilns to regenerate
quicklime. Thus, the overall mill process theoretically represents a closed cycle with respect to
sodium, sulfur and calcium, although in practice some losses are obtained and the addition of
make-up chemicals is required. Make-up chemicals are chemicals added to any stage of the
pulping cycle in order to replenish and/or rebalance the chemical composition of the pulping
chemicals. Typical make-up chemicals include sodium sulfate, sodium hydroxide or sodium
carbonate.
Soda pulp mills operate by a similar closed cycle principle, although the recovery cycle differs
somewhat. The main difference between soda pulping and kraft pulping is the pulping liquor:
in a soda mill, soda liquor (aqueous sodium hydroxide) is used, which lacks sodium sulfide. The
soda pulping process degrades the cellulose to a greater degree giving a weaker pulp.
Therefore, kraft mills are the predominant form of pulp production.
The process of the present invention for producing organic acids may be integrated with a
kraft mill or a soda mill. The process will now be described in further detail.
Process Overview
The process for producing an organic acid from a lignocellulosic feestock comprises a number
of steps. The process is integrated with pre-existing pulp mill processes in order to recycle
process streams, thus reducing chemical utilization, reducing waste, increasing energy
production, and making the process for producing an organic acid from a lignocellulosic
feedstock more economically viable and environmentally benign.
The process comprises the following steps: optional pre-hydrolysis of the lignocellulosic
feedstock; alkaline pre-treatment of the lignocellulosic feedstock; optional oxidative
delignification of the cellulose stream; saccharification and fermentation of the cellulose
stream, either sequentially or simultaneously; and work-up and optional purification of the
organic acid product. The streams derived from pre-hydrolysis and alkaline pre-treatment may
optionally be processed to provide products derived from hemicellulose and lignin
respectively. At least the spent alkaline pretreatment liquor is returned to the pulp mill for
regeneration of alkaline liquor and energy generation. However, a number of further means of
integration with pre-existing pulp mill processes are also feasible, as is made apparent in the
following detailed process description.
Feedstock
Any lignocellulosic feedstock known in the art may be used. Such lignocellulosic feedstocks
include, but are not limited to, wood, grass, bagasse, straw, plant material, paper, and
combinations thereof. Suitable woods include both softwoods and hardwoods. The softwood
tree species can be for example, but are not limited to: spruce, pine, fir, larch, cedar, and
hemlock. Examples of hardwood species include, but are not limited to: birch, oak, poplar,
beech, eucalyptus, acacia, maple, alder, aspen, gum trees and gmelina. The feedstock may
comprise a mixture of different softwoods, e.g. pine and spruce. The feedstock may also
comprise a non-wood raw material, such as bamboo, sugar beet pulp, wheat straw, soy hulls
and bagasse. The raw material may also be a mixture of at least two of softwood, hardwood
and/or non-wood.
Since the process is performed in close integration with a paper mill, feedstocks obtainable in
proximity to, or in conjunction with, a paper mill may be preferable. Such feedstocks include
pulpwood and forestry residues.
Forestry residues may be screened to reject fractions not suitable for further processing to
organic acids. Such non-suitable forestry residue fractions, such as pins and sticks, may be
combusted in the bark boiler of the pulp mill to provide steam and electricity.
The feedstock may be chipped to a suitable size prior to further processing.
Pre-treatment
The goals of the pretreatment steps are to fractionate the lignocellulose feedstock into
process streams suitable for further upgrading, and to provide a cellulose feed that can readily
be converted to organic acids by the saccharification and fermentation steps.
Lignocellulosic feedstocks comprise significant quantities of hemicellulose. The presence of
hemicellulose in the saccharification and fermentation feed means that enzymes capable of
breaking down hemicellulose and microorganisms capable of fermenting the resulting C5
sugars are required if significant quantities of unprocessed hemicellulose are not to be
obtained in the product organic acid stream. This means that microorganisms developed for
use in current commercial methods utilizing starchy feedstocks may need to be replaced or
supplemented. Moreover, the presence of hemicellulose or hemicellulose byproducts in the
fermentation step may inhibit the production of organic acids from cellulose, thus lowering
the product yield and/or purity. A high purity product stream is essential for commercial
viability, in order to limit the costs for further purification of the organic acid products.
An initial pre-hydrolysis step may be performed on the lignocellulosic feedstock in order to
substantially remove the hemicellulose fraction. No pre-hydrolysis is necessary however, and
an alkaline pretreatment step may be performed directly on the raw lignocellulosic feedstock.
Pre-hydrolysis may be performed by cooking the lignocellulosic feedstock in aqueous solution.
The pre-hydrolysis solution may have a regulated ionic strength by addition of alkali metal
carbonate to the solution, for example at a [CO ] concentration of 0.1 mol/l. The cooking
temperature may be from 140 °C to 200 °C, preferably between 160-180 °C, and the cooking
time may be from 30 minutes up to 2 hours. The temperature may be slowly ramped up to the
cooking temperature after an impregnation period that may last up to 1 hour. After the pre-
hydrolysis, the pre-hydrolysate is removed prior to the alkaline pre-treatment step. The pre-
hydrolysate contains hemicellulose and C5 sugars that may be subjected to further
valorisation steps.
After the optional pre-hydrolysis step, the lignocellulosic feedstock is subjected to an alkaline
pre-treatment in order to provide a substantially pure cellulose stream suitable for further
conversion into the desired organic acid; i.e. lignin and any hemicellulose not removed by a
pre-hydrolysis step is removed at the pre-treatment stage.
The alkaline pre-treatment step is performed by cooking the lignocellulosic feedstock in an
alkaline liquor from the pulp mill, otherwise termed an alkaline pre-treatment liquor. The
most suitable alkaline liquor for use depends on a number of factors including the nature of
the lignocellulosic feedstock, whether the lignin stream from the pre-treatment step is to be
subject to further valorisation, and if so, whether low-sulfur lignin is desired.
Soda liquor (aqueous NaOH) may be used as the alkaline pre-treatment liquor. Soda liquor has
the advantage that it is substantially free from sulfur and therefore the lignin obtainable after
the pre-treatment is also substantially free from sulfur. The soda liquor may be obtained from
a number of pulp-mill related sources.
In a soda pulp mill, soda liquor is the pulping liquor and is therefore readily available in vast
quantities.
In a kraft pulp mill, soda liquor is obtainable by electrolysis of dust from the electrostatic
precipitator of the pulp mill recovery boiler (ESP-dust). ESP-dust comprises mostly Na SO ,
which can be converted to NaOH and H2SO4 by electrolysis. Other anions such as chloride and
carbonate, or cations such as potassium, may be removed from the ESP-dust prior to
electrolysis. Methods of purification of ESP-dust, such as pulse filtration and ion exchange, are
known in the art. By using ESP-dust as the source of the soda liquor, several advantages are
obtained. A substance that is normally purged from the pulp mill process (ESP-dust) can
instead be used to provide not only the soda liquor required in the alkaline pre-treatment, but
also sulfuric acid which is used in subsequent process steps. The Na/S ratio of the pulp mill
white liquor must be controlled carefully. By purging a portion of the gypsum (CaSO ) formed
during the manufacture of an organic acid, while returning the sodium to the pulp mill
recovery process, the Na/S ratio is rebalanced, reducing the need for expensive NaOH makeup
to the pulp mill.
The NaOH make-up normally added to the kraft pulp mill white liquor may also be used as the
soda liquor in the pre-treatment process. However, the quantity of NaOH make-up normally
added to the white liquor in a typical pulp mill may in some cases be insufficient by itself to
support production of an organic acid on a commercially viable scale.
White liquor from the kraft pulp mill may be utilized as the alkaline pre-treatment liquor. This
has the advantage that white liquor is already abundant at the pulp mill and therefore no new
processes need be implemented for production of the alkaline pre-treatment liquor. Pre-
treatment with white liquor is milder than treatment with soda liquor and therefore may
provide greater yields of a cellulose feed suitable for saccharification and fermentation in
some instances, depending on feedstock. However, pre-treatment using white liquor results in
a sulfur-containing lignin stream. In many circumstances the presence of sulfur in the lignin is
non-problematic, but if sulfur-free lignin is desired, a pretreatment liquor comprising less
sulfur should be used. Such a liquor may be soda liquor, or alternatively, white liquor may be
oxidised by known methods in order to avoid sulfur in the lignin product. Use of white liquor
as the alkaline pre-treatment liquor may lead to a somewhat greater demand for NaOH make-
up in the pulp mill.
The alkaline pre-treatment liquor may be a combination of liquors from a variety of sources.
For example, a blend of white liquor and soda liquor may be used. The soda liquor may itself
comprise a blend of NaOH make-up liquor and liquor derived from electrolysis of ESP-dust. A
proportion of black liquor from the pulp mill or pretreatment step may also be used in the
alkaline pre-treatment liquor.
The alkaline pre-treatment step may be performed by cooking the lignocellulosic feedstock in
the alkaline liquor. The cooking temperature may be from 140 °C to 190 °C, preferably from
150 °C to 180 °C. The cooking time may be from 30 minutes up to four hours. After alkaline
pre-treatment, the process stream is separated into a pretreated cellulosic feed and a black
liquor stream.
The pretreated cellulosic feed may optionally be subjected to an oxygen delignification step
prior to undergoing saccharification and fermentation. The oxygen delignification may be
performed in a single stage or as two-stages. The temperature for delignification may be from
80 °C to 110 °C and the time required may be from 30 minutes to three hours. The use of an
oxygen delignification step may in some cases provide a purer feed to the saccharification and
fermentation steps, resulting in a lesser need for purification of the organic acid product and
therefore an improved overall process economy.
Saccharification and fermentation
The saccharification (hydrolysis) and fermentation of the cellulosic feed converts cellulose,
and possibly any hemicelluloses present in the feed, to the desired organic acid in two stages.
The first stage is the enzymatically catalysed hydrolysis of cellulose to fermentable sugars,
primarily glucose. Depending on the enzyme preparation used, any hemicelluloses present in
the reaction mixture may also be hydrolysed to sugars, primarily a mixture of C5 and C6
sugars.
Suitable enzyme preparations include, but are not limited to, cellulase preparations,
hemicellulase preparations, cellobiase preparations, xylanase preparations, amylase
preparations, pectinase preparations, or enzyme preparations comprising a mixture of such
enzymes. Preparations intended for the saccharification of lignocellulose feeds and comprising
a mixture of cellulases and hemicellulases are commercially available. One such preparation is
for example marketed by Novozymes under the name Cellic® CTec3.
The second stage is the fermentation of the sugars by one or more suitable microorganisms to
provide the desired organic acid product. The obtained organic acid depends on the
microorganism(s) used.
Organic acids that may be obtained by the saccharification and fermentation process include,
but are not limited to, lactic acid, acetic acid, citric acid, itaconic acid, succinic acid, fumaric
acid, glycolic acid, pyruvic acid, acetic acid, glutamic acid, malic acid, maleic acid, propionic
acid, butyric acid, gluconic acid and combinations thereof. The saccharification and
fermentation product is preferably lactic acid or acetic acid, even more preferably lactic acid.
The microorganism used in the fermentation may be a bacterium, a fungus, a yeast, an
archaea or an algae. The microorganism is preferably a bacterium of the genus lactobacillus if
lactic acid is to be produced, or a bacterium of the genus acetobacterium if acetic acid is the
desired product.
The saccharification and fermentation may be performed sequentially (SHF) or simultaneously
(SSF). If performed sequentially, each stage may be performed in a separate reactor, with
optional further processing of the obtained saccharide feed between stages. Alternatively, the
stages can be performed sequentially but in a single reactor, by addition of a microorganism to
the enzymatic hydrolysis reaction mixture.
Preferably, the saccharification and fermentation are performed simultaneously, as a
simultaneous saccharification and fermentation (SSF). SSF has the advantages of a less capitial
equipment required as compared to two-reactor methods, and a reduced risk of product
inhibition of enzyme activity.
The SSF step may be performed by stirring a slurry of the cellulosic stream together with a
suitable enzyme preparation and microorganism as described above. Suitable concentrations
and conditions depend on a number of parameters including the nature of the feedstock, pre-
treatment, enzyme and microorganism used. The pH of the cellulosic feed may be adjusted
prior to the SSF step in order to optimise the rate of organic acid formation. This can for
example be performed by addition of suitable quantities of sulfuric acid. During fermentation
the pH of the reaction mixture is lowered by formation of the organic acid, leading to
inhibition of the microorganism. This is countered by addition of calcium oxide obtained from
the pulp mill in order to maintain the pH of the mixture within the optimal pH operating
window. Addition of calcium oxide gives the calcium salt of the organic acid, e.g. calcium
lactate or calcium acetate.
In order to reduce the quantities of calcium oxide required, the SSF step may be initiated using
only a partial quantity of the cellulosic feed, adjusted to a suitable pH. As organic acid is
formed during the SSF step, the corresponding lowering of the pH may be countered by
periodic or continuous addition of cellulosic feed having basic pH, i.e cellulosic feed that is
non-pH adjusted.
Gypsum precipitation
After the production of the organic acid, the product stream must be purified. The initial step
in purification is addition of sulfuric acid in quantities sufficient to retrieve the free organic
acid from the calcium salt. The resulting calcium sulfate (gypsum) is substantially insoluble in
the aqueous medium and precipitates. The gypsum precipitate is removed, for example by
filtration or centrifugation, thus providing a relatively pure aqueous solution of organic acid. In
some cases the product may be sufficiently pure and concentrated for the intended purpose,
otherwise further purification and concentration as described below may be necessary.
The gypsum isolated by precipitation may be returned to the pulp mill where it is integrated
with the chemical recovery cycle for regeneration to calcium oxide. This may for example be
performed by adding the gypsum to the pulp mill green liquor. The green liquor is then
recausticized by addition of calcium oxide to provide white liquor and lime mud (calcium
carbonate). The lime mud is then calcined in the lime kiln to regenerate the calcium oxide.
Thus, the pulp mill recovery process is essentially a closed cycle for Na, Ca and S, although
some losses do occur and make-up chemicals must therefore be added as required.
If the sulfuric acid used to precipitate gypsum is intrinsic to the pulp mill, i.e. is derived from
the pulp mill process chemicals such as ESP-dust, then returning the gypsum to the pulp mill
recovery cycle will have a negligible impact on the pulp mill Na/S ratio. However, if extrinsic
sulfuric acid (i.e. sulfuric acid not deriving from the pulp mill process chemicals) is used to
form and precipitate the gypsum, integration of the gypsum in the pulp mill recovery cycle will
affect the Na/S balance of the pulp mill process. In some cases this may be desirable, and
reduces the need for addition of other sulfur make-up chemicals such as elemental sulfur or
salt cake to the pulp mill processes. In other cases, the Na/S balance may be negatively
affected by the return of gypsum, meaning that additional NaOH make-up may be required to
rebalance the Na/S ratio.
Purification and concentration
If the dilute organic acid obtained after precipitation of gypsum is insufficiently pure or
concentrated, further purification steps may be performed.
The dilute organic acid may for example be purified by reactive distillation with a simple
alcohol such as methanol or ethanol in order to provide the organic acid alcohol ester, e.g.
methyl acetate or methyl lactate. The isolated ester may then be subjected to hydrolysis to
provide the original organic acid in a purer, more concentrated form. The alcohol recovered
may be re-used in the reactive distillation, and therefore the process is overall a closed cycle
with regard to the alcohol. Other operations such as filtration, extraction, electrodialysis and
evaporation may be performed as required in order to obtain a product with the desired
properties.
Lignin recovery
If desired, lignin may be recovered from the spent pre-treatment (black) liquor. The market for
lignin is expanding, and extensive research regarding valorisation of lignin product streams is
ongoing. Moreover, if the capacity of a pulp mill is limited by the throughput capacity of its
recovery boiler, then removal of lignin from black liquor can reduce the load on the recovery
boiler, thereby increasing the overall capacity of the plant. The isolated lignin may be sold or
used to replace fossil fuel when firing the pulp mill lime kilns.
The black liquor from the pretreatment may be combined with black liquor from the pulp mill
and processed together with the pulp mill black liquor. This is particularly suitable if the
pretreatment is performed using white liquor, since the resulting lignin is essentially
indistinguishable from regular kraft lignin. Alternatively, the black liquor from the
pretreatment may be processed in isolation. This is especially suitable if pre-treatment is
performed using soda liquor and it is desired to isolate the resulting sulfur-free lignin. Sulfur-
free lignin may potentially command a premium price in applications where the presence of
sulfur in the lignin is considered problematic. Such applications may include use as solid fuel
(where no flue scrubbing is available), as a food additive, or as a precursor to carbon fiber.
Lignin may be recovered from black liquor using any method known in the art. Such methods
include, but are not limited to the Lignoboost process, the Lignoforce process, the SLRP
(Sequential Liquid-Lignin Recovery and Purification) process, and membrane filtration
methods. In short, the Lignoboost process involves taking a stream of concentrated black
liquor from the black liquor evaporators. Lignin is precipitated from the concentrated black
liquor by acidification, preferably using carbon dioxide. The precipitated lignin is isolated by
filtration, re-dispersed and the dispersion is acidified. The resulting slurry is then filtered and
washed.
Tall oil soap may be skimmed from the black liquor prior to precipitation of lignin. Other
known means and methods for isolating kraft lignin may alternatively be used.
After optional lignin removal the black liquor is conveyed to the recovery boiler of the pulp
mill, providing steam, electricity and recovering the pulping/pretreatment white liquor by the
pulp mill recovery cycle. The pulp mill may use alternative chemical recovery technologies,
such as black liquor gasification, to recover the pulping chemicals.
Hemicellulose utilisation
If the lignocellulosic feed is subjected to a pre-hydrolysis step, a pre-hydrolysate rich in
hemicellulose and C5 sugars is obtained. This pre-hydrolysate may be subjected to treatment
in order to recover potentially valuable product fractions such as xylose and furfural. Such
treatments may include membrane filtration and/or hydrolysis of hemicelluloses.
The process described herein may be performed in a fully integrated manner with pre-existing
pulp mill processes, meaning that all process streams and resides are returned to the pulp mill
for chemical and energy generation. Thus, the process is essentially closed-cycle with regard
to process chemicals such as calcium oxide and alkaline liquor. The biomass feedstock is
processed to valorised products, and all residues may be used to generate energy in the form
of steam and electricity production. Thus, the process herein described, by being integrated
with pulp mill processes, provides an economically viable and green method of obtaining
organic acids from abundant renewable lignocellulosic feedstocks.
EXAMPLES
Feedstocks tested in the examples were eucalyptus pulpwood (E. urograndis), short-rotation
eucalyptus, Scots pine forestry residues, and energy cane. The feedstocks were chipped to a
suitable size prior to processing.
Pre-treatment
Figure 1 illustrates schematically the pretreatment steps for the lignocellulosic feedstock. The
feedstock 1 is first subject to an optional pre-hydrolysis step 3 using water 5 as the pre-
hydrolysis liquor and obtaining a pre-hydrolysate 7. The lignocellulosic feedstock then
undergoes a pretreatment step 9 with an alkaline pretreatment liquor 11. This gives a black
liquor 13 and a pretreated cellulose feed. The pretreated cellulose feed is subjected to an
optional oxygen delignification step 15 using an alkaline liquor 17, giving a spent liquor 19 and
a cellulosic feed 21 suitable for further processing.
Tested pre-hydrolysis conditions for a range of feedstocks are outlined in Table 1.
Table 1
Type of biomass Eucalyptus urograndis Pine Forest Residues Energy Cane
Amount charged 1.25 2.5 46 0.25 2.0 0.1
biomass, dry weight
(kg100)
Type of digester Forced circulation Autoclave Forced Autoclave
circulation
Liquor-to- 6 5.3 6 6 14
wood/material ratio
(L/kg)
Time to temperature 64 50 63 53 64
(min)
Temperature (°C) 160 180 175 160
Time (min) 60 0-60 30-40 0-90 90 45
Table 2 outlines the tested pre-treatment conditions and the results of the pre-treatment for
the eucalyptus feedstocks. It can be seen that using partially oxidised white liquor allows a
substantial reduction in cooking time.
Table 2
Cook type Oxidised Soda Soda Soda
White liquor
Feedstock Pulpwood Pulpwood Short rotation Pulpwood
Alkali charge, EA % 20.5 21.5 21.5 22.5
Initial HS-, mol/L 0.02 0 0 0
Cooking time, min 85 190 190 190-195
Residual alkali, g/L 6.9 6.3 8.2 8.1 +/- 1.7
Alkali consumption, 177.3 190 182.4 190 +/- 10
kg/ton
Kappa number 15.3 14.5 10.6 10 +/- 0.5
Reject, % on wood 0.1 0.2 0.1 0.1
Total yield, % on wood 44.1 42.1 43.0 39.4
Dry Solids hydrolysate 1.4 1.4 2.0 1.95
(wt%)
End-pH hydrolysate 3.9 3.2 3.3 3.1
Dry Solids Black Liquor 16 14.4 14.1 13.9
(wt%)
Table 3 outlines the tested pre-treatment methods and results for the pine forestry residue
feedstock. It can be seen that pre-treatment with white liquor provides a greater total yield
and that a greater proportion of hemicellulose is retained in the pulp.
Table 3
Pretreatment method White liquor Soda
Xylan % on pulp 12 2.2
Glucomannan % on pulp 6.6 0.7
Cellulose % on pulp 75 91
Acid-insoluble lignin % on pulp 4.4 4.3
Acid-soluble lignin % on pulp 0.7 0.4
Extractives % on pulp 0.5 1.1
Ash content % on pulp 0.7 0.5
Total yield after cooking % on wood 37.6 24.1
Table 4 outlines the tested pre-treatment methods for energy cane feedstock.
Table 4
Pretreatment method Soda Soda + O2
delignification
Kappa number 13.1 5.5
Total yield 45.6 n.d
Alkali consumption, 200
kg/ton
Ash content, % 2.7 ~2
Lignin, % on pulp 2.7 n.d.
Thus, it can be seen that a range of pre-treatment methods using pulp mill chemicals can be
applied to the lignocellulosic feedstocks.
Hydrolysis and Fermentation
Pulps from Eucalyptus urograndis and Scandinavian softwood were evaluated as the substrate
and Lactobacillus bacteria were selected as the fermenting microorganisms. Cellic® CTec3
from Novozymes was used as the hydrolytic enzyme preparation.
Separate hydrolysis and fermentation (SHF) experiments were initially performed on
laboratory scale.
The pretreated eucalyptus was readily enzymatically hydrolysed into high concentrations of
glucose which in turn enabled high concentrations of lactic acid. High product titer and “clean”
or noncomplex substrates is a key aspect for downstream processing. Using relatively pure
and noncomplex feedstock with high cellulose content, such as pulp, could therefore be
advantageous compared to using more complex feedstock such as dilute-acid pre-treated or
steam exploded lignocellulosic material.
In the fermentation step, very high titers of lactic acid (143 g/L) and good yields (0.98 g lactic
acid/g consumed glucose) were achieved using a Lactobacillus mixed culture. The Lactobacillus
bacteria performed better when grown on the pulp hydrolysate compared to a glucose-based
reference medium.
Figure 2 shows a comparison between eucalyptus pulpwood hydrolysate and a glucose
reference as the fermentation medium. It can be seen that production of lactic acid from the
eucalyptus hydrolysate (line 201) proceeds at a greater rate as compared to lactic acid
production from the glucose reference medium (line 203). A greater final lactic acid
concentration is obtained from the eucalyptus hydrolysate. Looking at the glucose
concentration, it can be seen that the eucalyptus hydrolysate is more-or-less fully converted
(line 205), whereas a significant proportion of the glucose reference remains unconverted (line
207).
A simultaneous saccharification and fermentation (SSF) experiment on a 50 litre pilot
bioreactor scale resulted in a concentration of 107 g/L lactic acid after 98 h using a pretreated
eucalyptus feed concentration of 15% dry solids and an enzyme concentration of 6% (g
CTec3/dry solids). The addition of 2% additional enzyme at 98 h did not result in a large
increase in lactic acid production. The final lactic acid concentration was 114 g/L after 123 h,
the yield was 0.76 g lactic acid per g feed and the productivity was 0.91 g/L/h. In this pilot
scale test, pH was adjusted during cultivation using NH OH (25 wt%) and H SO (2M). The
4 2 4
consumption of NH OH and H SO for pH adjustment during cultivation was 3.75 litre and 50
4 2 4
mL, respectively.
Both the SHF (separate hydrolysis and fermentation) and SSF (simultaneous saccharification
and fermentation) experiments resulted in a mixture of D- and L- lactic acid.
Integrated process
Figure 3 shows a schematic overview of the process for producing an organic acid integrated
with a pulp mill process. A pulp mill 301 has a first lignocellulosic feedstock 303 as an input
and produces pulp 305 and electricity 307. The organic acid production process runs parallel
to the pulp mill process. A second lignocellulosic feedstock 309 is provided to an alkaline
pretreatment step 311. An alkaline liquor 313 is obtained from the pulp mill as a process
chemical in the pretreatment step. The alkaline liquor 313 may be selected from liquors
including, but not limited to, white liquor, soda liquor, or mixtures therefore. Following the
alkaline pretreatment step 311, the pretreated feedstock 315 is transferred to a SSF step 317,
optionally being neutralised by the addition of an acid 319 prior to commencement of the SSF
stage. Further inputs to the SSF stage 315 are saccharification enzymes 321, fermentation
microorganisms 323, and calcium oxide 324 obtained from the pulp mill. After the SSF stage
317 the obtained raw product 325 is transferred to a purification stage 327, including the
steps of precipitation and esterification. Inputs to the purification stage 327 are sulfuric acid
329, optionally obtained from the pulp mill ESP dust, and alcohol 331. Outputs from the
purification stage are, besides the esterified acid 333, organic residues 335 including lignin and
biomass which are transferred to the pulp mill for energy recovery, and precipitated gypsum
337. A portion 339 of the precipitated gypsum stream is purged, whereas a further portion
341 of the gypsum steam is returned to the chemical recovery cycle of the pulp mill in order to
recover calcium oxide. The esterified acid 333 is hydrolysed in a final step 343 to provide pure
acid product 345 and recover alcohol 331 for use in the purification stage.
The hydrolysate 347 from the alkaline pretreatment stage 311 is transferred to an evaporation
stage 349. Here it may optionally be combined with black liquor 351 from the pulp mill. Lignin
353 is then recovered from the evaporation product in an lignin precipitation stage 355.
Residues 357 from this stage are returned to the pulp mill 301 for chemical and energy
recovery.
Figure 4 shows a schematic mass balance for a pulp mill and integrated organic acid
production line using soda liquor and sulfuric acid derived from ESP dust as process chemicals
in the organic acid production line.
The pulp mill 401 is shown with a regular wood chip input 403 and pulp output 405.
Integration with the organic acid production line 407 means that the need for purging of ESP
dust 413 is greatly reduced. The requirement for NaOH make-up 408 to the mill is also greatly
reduced or avoided completely. Instead, the pulp mill ESP dust can be converted to sodium
hydroxide 409 and sulfuric acid 411 that are provided as inputs to the organic acid (OA) line
407. Calcium oxide 415 is also taken from the pulp mill 401 for use in the OA line 407. Thus,
the majority of the process chemicals required for the OA line are obtained from the pulp mill.
Lignocellulosic feedstock 417 is provided to the OA line. This lignocellulosic feedstock 417 may
be pulpwood, but may also comprise rejects from the pulp mill or forestry residues not
suitable for conventional pulp production. Further inputs to the OA line 407 are enzymes 419,
carbon dioxide 421, and sulfuric acid make-up 423.
With regard to process outputs, end products of the OA line are the organic acid 429, such as
lactic acid or acetic acid, and sulfur-free lignin 431. By-products of the organic acid production
process are mostly returned to the pulp mill for recycling or energy generation. A first portion
425 of the gypsum produced in the OA line is returned to the pulp mill 401 for integration with
the mill regeneration cycle, whereas a second portion 426 of the gypsum produced is purged.
The purged portion 426 is typically less than the recycled portion 325. Filtrates and residues
427 from the OA line are also returned to the pulp mill for regeneration of
pulping/pretreatment chemicals and energy generation. It can be seen from the schematic
mass balance that very little excess chemical input is required for the OA production line and
very little non-regenerable waste is produced.
Figure 5 shows a schematic mass balance for a pulp mill and integrated organic acid
production line using white liquor as the pretreatment liquor for the organic acid (OA) line.
The pulp mill 501 is shown with a regular wood chip input 503 and pulp output 505. White
liquor 509 and calcium oxide 515 are provided to the organic acid production line 507 as
process chemicals. This results in an increased requirement for NaOH make up 508 and CaO
make up 516 to the pulp mill.
Lignocellulosic feedstock 517 is provided to the OA line 507. This lignocellulosic feedstock 517
may be pulpwood, but may also comprise rejects from the pulp mill or forestry residues not
suitable for conventional pulp production. Forestry residues not suitable for use in the OA line
may be diverted to the bark boiler of the pulp mill in order to further increase electricity
production. Further inputs to the OA line 507 are enzymes 519, carbon dioxide 521, and
sulfuric acid 523.
With regard to process outputs, end products of the OA line are the organic acid 529, such as
lactic acid or acetic acid, and lignin 531. In order to maintain the sulfur balance of the pulp
mill, gypsum 526 produced during the organic acid production is purged. However, further
filtrates and residues 527 from the OA line are returned to the pulp mill for regeneration of
pulping/pretreatment chemicals and energy generation. This results in a somewhat increased
production of ESP dust 513 in the pulp mill, but provides much increased electricity production
514. Again, it can be seen from the schematic mass balance that relatively little non-
regenerable waste is produced.
The term “comprising” as used in this specification and claims means “consisting at least in
part of”. When interpreting statements in this specification and claims which include the term
“comprising”, other features besides the features prefaced by this term in each statement can
also be present. Related terms such as “comprise” and “comprises” are to be interpreted in
similar manner.
In this specification where reference has been made to patent specifications, other external
documents, or other sources of information, this is generally for the purpose of providing a
context for discussing the features of the invention. Unless specifically stated otherwise,
reference to such external documents is not to be construed as an admission that such
documents, or such sources of information, in any jurisdiction, are prior art, or form part of
the common general knowledge in the art.
Claims (15)
1. Process for the production of an organic acid from a lignocellulosic feedstock, wherein the process is integrated with a pulp mill and comprises the steps: a) providing a lignocellulosic feedstock; 5 b) obtaining an alkaline liquor from the pulp mill; c) pre-treating the lignocellulosic feedstock with the alkaline liquor, thereby obtaining a pretreated cellulosic feed and a black liquor; d) obtaining calcium oxide from the pulp mill; e) subjecting the pretreated cellulosic feed from step c) to enzymatic hydrolysis, 10 thereby obtaining a saccharide feed; f) subjecting the saccharide feed from step e) to microbial fermentation using the calcium oxide from step d) as a neutralising agent, thereby obtaining an organic acid calcium salt; g) treating the organic acid calcium salt with sulfuric acid, thereby obtaining gypsum 15 and the organic acid; h) optionally isolating lignin from the black liquor obtained in step c), thereby obtaining lignin and weak black liquor; and i) returning the black liquor obtained in step c) and/or the weak black liquor obtained in step h) to the pulp mill for integration with the pulp mill chemical recovery 20 process; wherein steps e) and f) are performed either sequentially or simultaneously.
2. Process according to claim 1 wherein steps e) and f) are performed simultaneously.
3. Process according to any one of claims 1-2, wherein the organic acid is lactic acid, acetic acid, citric acid, itaconic acid, succinic acid, fumaric acid, glycolic acid, pyruvic 25 acid, acetic acid, glutamic acid, malic acid, maleic acid, propionic acid, butyric acid, gluconic acid or combinations thereof, preferably lactic acid or acetic acid, even more preferably lactic acid.
4. Process according to any one of the preceding claims, wherein the alkaline liquor comprises pulp mill white liquor and/or soda liquor.
5. Process according to any one of the preceding claims, wherein the alkaline liquor and the sulfuric acid are at least in part derived from electrolysis of pulp mill electrostatic precipitator dust.
6. Process according to claim 5, wherein the alkaline liquor is essentially free from sodium 5 sulfide.
7. Process according to any one of the preceding claims, wherein the black liquor obtained in step c) is combined with pulp mill black liquor prior to isolating lignin in step h).
8. Process according to any one of the preceding claims, wherein at least a portion of the 10 gypsum obtained in step g) is returned to the pulp mill for integration with a pulp mill lime regeneration process.
9. Process according to any one of the preceding claims, wherein the lignocellulosic feedstock from step a) is subjected to an aqueous prehydrolysis step prior to step b), thereby obtaining a prehydrolysed lignocellulosic feedstock and a hemicellulose 15 hydrolysate.
10. Process according to claim 9, wherein a hemicellulose, such as xylan, or a product derived from hemicellulose, such as xylose or furfural, is isolated from the hemicellulose hydrolysate.
11. Process according to any one of the preceding claims, wherein the organic acid 20 obtained in step g) is purified by reactive distillation with an alcohol to provide an ester, followed by hydrolysis of the ester to provide a purified organic acid.
12. Process according to any one of the preceding claims, wherein the pretreated cellulosic feed from step c) is subjected to an oxygen delignification step prior to step e).
13. Process according to any one of the preceding claims, wherein at least part of the 25 pretreated cellulosic feed from step c) is subjected to neutralisation by addition of sulfuric acid prior to step e).
14. Process according to any one of the preceding claims, wherein the lignocellulosic feedstock is selected from the group consisting of wood, grass, bagasse, straw, plant material, paper, and combinations thereof. 30
15. Process according to any one of the preceding claims, wherein all filtrates and residues from the process are returned to the pulp mill and integrated with the pulp mill chemical and/ energy recovery processes.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP16188531.4 | 2016-09-13 | ||
EP16188531.4A EP3293268B1 (en) | 2016-09-13 | 2016-09-13 | Process for the production of an organic acid from a lignocellulosic feedstock |
PCT/SE2017/050883 WO2018052359A1 (en) | 2016-09-13 | 2017-09-06 | Process for the production of an organic acid from a lignocellulosic feedstock |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ750869A NZ750869A (en) | 2021-03-26 |
NZ750869B2 true NZ750869B2 (en) | 2021-06-29 |
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