Classifications

• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
  • C12P7/06—Ethanol, i.e. non-beverage
  • C12P7/14—Multiple stages of fermentation; Multiple types of microorganisms or re-use of microorganisms
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
  • C12P7/06—Ethanol, i.e. non-beverage
  • C12P7/08—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate
  • C12P7/10—Ethanol, i.e. non-beverage produced as by-product or from waste or cellulosic material substrate substrate containing cellulosic material
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/02—Preparation of oxygen-containing organic compounds containing a hydroxy group
  • C12P7/04—Preparation of oxygen-containing organic compounds containing a hydroxy group acyclic
  • C12P7/16—Butanols
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P7/00—Preparation of oxygen-containing organic compounds
  • C12P7/24—Preparation of oxygen-containing organic compounds containing a carbonyl group
  • C12P7/26—Ketones
  • C12P7/28—Acetone-containing products
• • C—CHEMISTRY; METALLURGY
  • C12—BIOCHEMISTRY; BEER; SPIRITS; WINE; VINEGAR; MICROBIOLOGY; ENZYMOLOGY; MUTATION OR GENETIC ENGINEERING
  • C12P—FERMENTATION OR ENZYME-USING PROCESSES TO SYNTHESISE A DESIRED CHEMICAL COMPOUND OR COMPOSITION OR TO SEPARATE OPTICAL ISOMERS FROM A RACEMIC MIXTURE
  • C12P2201/00—Pretreatment of cellulosic or lignocellulosic material for subsequent enzymatic treatment or hydrolysis
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E50/00—Technologies for the production of fuel of non-fossil origin
  • Y02E50/10—Biofuels, e.g. bio-diesel
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P20/00—Technologies relating to chemical industry
  • Y02P20/50—Improvements relating to the production of bulk chemicals
  • Y02P20/582—Recycling of unreacted starting or intermediate materials

Definitions

• the present invention is part of a process for producing alcohol and / or so-called "second generation" solvent from lignocellulosic biomass. It relates more particularly to a process for producing ethanol and / or an acetone-butanol-ethanol mixture (also called ABE mixture).
• Lignocellulosic biomass is one of the most abundant renewable resources on earth.
• the substrates considered are very varied, since they concern both woody substrates (hardwood and softwood), agricultural by-products (straw) or lignocellulosic waste-generating industries (agro-food industries, paper mills).
• Lignocellulosic biomass is composed of three main polymers: cellulose (35 to 50%), hemicellulose (20 to 30%) which is a polysaccharide essentially consisting of pentoses and hexoses and lignin (15 to 25%) which is a polymer of complex structure and high molecular weight, composed of aromatic alcohols connected by ether bonds.
• Cellulose and possibly hemicelluloses are targets for enzymatic hydrolysis but are not directly accessible to enzymes. This is the reason why these substrates must undergo a pretreatment preceding the enzymatic hydrolysis step.
• the purpose of the pretreatment is to modify the physical and physicochemical properties of the lignocellulosic material, with a view to improving the accessibility of the cellulose trapped within the lignin and hemicellulose matrix.
• the effectiveness of the pretreatment is measured both by the material balance after pretreatment (recovery rate of sugars in monomeric or soluble oligomeric form or insoluble polymers) and also by the susceptibility to enzymatic hydrolysis of cellulosic residues and hemicellulose.
• Processes for producing alcohols and / or solvents from lignocellulosic biomass comprise at least the following steps:
• the insoluble dry matter subjected to the enzymatic hydrolysis can vary from 5 to 40%, and generally from 10 to 25%. According to the publication by Kristensen et al. Biotechnology for biofuels, 2009 (2) 11, in order to obtain an identical hydrolysis yield, the enzymatic consumption must be higher in the case of a high insoluble solids load, in particular because of the inactivation of the enzyme. by products of enzymatic hydrolysis (glucose, cellobiose).
• the solution which consists in carrying out a dilution at the level of the enzymatic hydrolysis step is however limited since it will have important consequences on the energy expenditure related to the separation of the alcohol carried out by distillation. In the specific case of the manufacture of ethanol, an alcoholic concentration of the wort of fermentation with 23-25g / L of minimum ethanol (alcoholic strength of 3) is necessary for a reasonable expense of the distillation station.
• the improvement of the economic balance sheet of ethanol or EBA production can be obtained by recycling different streams or products.
• the patent application WO 94/29475 proposes a process for the improved conversion of cellulosic biomass to ethanol in which part of the effluents from the fermentor is recycled at the inlet of the same fermenter as a source of nutrients for the microorganism used during of fermentation.
• the present invention describes an improved process for the production of alcohols and / or solvents backed by a papermaking pulp production unit using an alkaline chemical pretreatment.
• the present invention relates to a process for the production of alcohols and / or so-called second-generation solvents, in which the lignocellulosic or cellulosic biomass is subjected to an alkaline pretreatment based on sodium sulphate, of the Kraft pretreatment type, in which intensive recycling is carried out. non-hydrolysed pasta enzymatically is operated.
• Figure 1 is a schematic representation of a device implementing a process for producing alcohols and / or solvents from paper pulps, comprising a step of recycling solid residues, according to the present invention.
• the present invention describes a process for producing alcohols and / or solvents from cellulosic or lignocellulosic biomass comprising at least the following steps:
• step d) microorganism fermentation of the hydrolyzate from step c) and obtaining a fermentation broth containing at least one alcohol and / or solvent;
• step f) wherein at least a portion of the cake obtained in step f) is recycled upstream of the pretreatment step a), and / or upstream of the washing step b).
• the method allows to use more than 80% by weight, and preferably more than 90% by weight of the cellulose contained in the plant for its future alcoholic conversion and / or mixture ABE.
• unhydrolyzed cellulose also called recalcitrant cellulose
• recalcitrant cellulose partially rediscovers its susceptibility to enzymatic hydrolysis.
• the term "recalcitrant cellulose” is intended to mean unhydrolyzed cellulose during step c) of enzymatic hydrolysis and which has, without specific treatment, a poor susceptibility to enzymatic hydrolysis.
• the recycling is carried out upstream of the pretreatment step a).
• the alkaline treatment thus applied identical to that carried out during the pretreatment step a) allows the swelling of the fibers of the pulp and regenerates the susceptibility of the substrate thus pretreated to the enzymatic hydrolysis (mercerization), without causing accumulation of the lignin.
• the recycling of at least one fraction of the cake is carried out upstream of the washing step b): the unhydrolyzed recalcitrant cellulose is not subjected to heat treatment and the energy expended is negligible.
• Simple alkaline recycling before the washing step substantially increases the susceptibility to enzymatic hydrolysis. This treatment, however, remains less effective than that described above.
• the recycling of at least one fraction of the cake is carried out upstream of the pretreatment step a) and upstream of the washing step b).
• the method according to the present invention makes it possible to limit the amount of enzymes to be used to achieve an overall hydrolysis greater than 90% of the cellulose of the initial pretreated substrate. In fine, the enzyme only encounters a substrate "highly susceptible to enzymatic hydrolysis" and no longer encounters recalcitrant cellulose due to recycling thereof.
• Stage a) of alkaline chemical pretreatment of the cellulosic or lignocellulosic substrate uses a process known as sodium sulphate process or Kraft process based on the use of sodium hydroxide and sodium sulphate. This is a proven and economically validated process as it is commonly used in paper processes
• the substrate used is chosen from the most varied biomasses, but more particularly from resinous tree species (softwood species such as spruce or pine) or hardwood species (hardwood such as eucalyptus) or agricultural lignocellulosic waste (wheat straw, rice, etc.).
• resinous tree species softwood species such as spruce or pine
• hardwood species hardwood such as eucalyptus
• agricultural lignocellulosic waste wheat straw, rice, etc.
• the biomass 1 is introduced into the cooking reactor or else designated hereinafter as a digester 2.
• An alkaline solution based on sodium sulphate 3 is introduced into the digester 2
• the alkaline chemical treatment of the biomass is at 150-180 ° C for a period of 2 to 5 hours depending on the substrate used. It is thus partially delignified by means of high temperature cooking and in the presence of soda.
• the cooking is carried out in a vertical reactor, where the biomass chips are lowered by gravity and meet the various cooking liquors.
• Sodium sulphide is prepared directly from sodium sulphate by combustion. During cooking, sodium sulphide is hydrolyzed to sodium hydroxide, NaHS and H 2 S. The various sulfur compounds present react with lignin to give thiolignins more easily soluble.
• the Kraft process includes a chemical reagent recycling loop used. Most of the chemicals (soda and sodium sulphide) are recovered from the residual cooking liquors.
• the lignin contained in the biomass is partially solubilized and is evacuated with the spent alkaline solution 4, also called black liquor. This delignification is controlled by the operating parameters of the digesters. Black liquor 4 may contain hemicelluloses and very little cellulose.
• the pretreated substrate is obtained in the form of a pulp (also called "pulp") enriched in cellulose.
• step b) of washing the pretreated substrate this paste 5 is washed in the reactor 6.
• One or more washing liquids 7 are introduced into said washing reactor 6. Further delignification can be carried out during the washing. washing step performed in the reactor 6.
• a separation tool such as a centrifugal press or decanter can be installed to remove the alkalinity.
• the used washing liquid (s) 8 are withdrawn at the outlet of the reactor 6.
• the washed pulp or pulp 9 which is extracted from the washing reactor 6 contains between 1% and 40% solids, preferably between 7% and 40%, and more preferably between 10% and 25%.
• a neutralization of the paste can be carried out before the enzymatic hydrolysis step by addition of acids. It is indeed necessary that the enzymatic hydrolysis be carried out at a pH of between 4 and 5.5.
• the pretreated and washed pulp is then sent to the conversion process into alcohols and / or solvents schematically represented by the rectangle 10, where steps c) to e), corresponding to the conversion steps, are carried out properly. say.
• These conversion steps can be two to eight. Preferably, there are between three and five.
• These conversion steps comprise at least steps c) and d) respectively corresponding to enzymatic hydrolysis and fermentation of the pulp. These steps may optionally be coupled in the same reactor. This is known as SSF (Simultaneous Saccharification and Fermentation).
• Step c) of enzymatic hydrolysis is carried out using cellulase and / or hemicellulase type enzymes produced by a microorganism.
• the microorganism used is a fungus belonging to the genera Trichoderma, Aspergillus, Penicillium or Schizophyllum, or an anaerobic bacterium belonging to the genus Clostridium.
• the microorganism used is Trichoderma reesei. It is produced in an independent production line that can be done on-site or off-site.
• the susceptibility to enzymatic hydrolysis is excellent and the polymers of cellulose and hemicellulose are converted into sugars called “very firm nescibles” (glucose, mannose), “poorly fermentable” (galactose), “hardly fermentable “, (xylose and arabinose).
• the conditions of the enzymatic hydrolysis mainly the solids content of the mixture to be hydrolysed and the amount of enzymes used, are chosen so that at the end of step c) a conversion between 20% and 90 % of the cellulose of the pulp circulating in line 9 in glucose is obtained, and more particularly between 30% and 80%.
• the alcoholic fermentation carried out in step d) is provided by yeasts or other microorganisms.
• step e the alcohols and / or solvents produced in step d) of which purified and separated.
• the step f) of separating the cake can be carried out downstream of steps c), d) and / or e) and can optionally be coupled to a washing of the cake.
• a product stream 11 is obtained, possibly separated by any means known to those skilled in the art, a liquid residue 12 (called vinasses) containing non-sugar fermented and a solid cake 13 containing solid material from the initial substrate (solid residue) and a liquid fraction.
• the solid residue is partly composed of cellulose which has not been hydrolysed, which represents between 10% and 100% of this residue, and preferably between 30% and 70%.
• the stream 13 corresponding to the cake is divided into 3 fractions 13-1, 13-2 and 13-3.
• the fraction 13-1 is returned to the top of the digester 2 with the initial plant 1, which corresponds to the recycling upstream of the pre-treatment stage a). It represents between 0 and 100% of the cake13, and preferably between 20 and 100%
• the fraction 13-2 is returned downstream of the digester 6, thus upstream of the washing step b) to simply be mixed cold with the dough 5. It represents between 0 and 95% of the cake 13, and preferably between 0 and 80%.
• the non-recycled fraction 13-3 is directly removed outside the process. It represents between 0 and 80% of the cake 13, and preferably less than 15%, and more preferably less than 10%.
• FPu Filter Paper unit, or filter paper unit, which is a measure of enzymatic activity.
• the FPu - weight match is a characteristic of the enzymatic cocktail.
• Example 1 Material balance - without recycling (not in accordance with the invention)
• a process for the production of ethanol from paper pulp resulting from an alkaline Kraft process is considered.
• the process processes 80 tons / hour of native plant.
• the plant is spruce (softwood), containing 55% weight of dry matter consisting of: cellulose 42%
• Hemicelluloses are half mannan.
• Kraft cooking is carried out at 175 ° C for 5 hours. This pretreatment and the washing processes carried out in steps a) and b) respectively are conducted in such a way that the paper pulp contains 15% dry matter, and retains: cellulose 97%
• the ethanol conversion process consists of an enzymatic hydrolysis of the pulp (step c)), followed by an alcoholic fermentation in ethanol (step d)), a separation of suspended solids to form a solid residue or cake of the distillation and dehydration of ethanol at 99.7% by weight (step e)).
• the enzymatic hydrolysis is carried out under conditions such that the hydrolysis of 75% of the cellulose and 55% of the hemicelluloses is observed. FPu / g of cellulose entering the hydrolysis reactor is consumed.
• Fermentation makes it possible to transform 90% of the previously formed glucose and mannose into ethanol.
• the other sugars resulting from hemicelluloses (xylose, arabinose, etc.) are not fermented by the strain of Saccharomyces cerevisae used.
• the solid residue Prior to the distillation step, the solid residue is separated and washed to limit the loss of ethanol with the cake.
• the process conditions are such that the output streams are:
• solid cake 22.96 tons / hour to 36% of solid matter.
• the solid part is for 54.1% of the unhydrolyzed cellulose.
• the ethanol yield of this process is therefore 15.8% by weight on the native plant (dry matter basis).
• the specific enzyme consumption is 51,540 FPu / kg of ethanol produced.
• the ethanol yield of this process is therefore 18.0% by weight on the native plant (dry matter basis), an improvement of 2.2 points compared to the base case. Nevertheless, this improvement in the mass balance is to the detriment of the specific consumption of enzymes which is then 61 740 FPu / kg of ethanol produced (+ 20%), and requires a larger reaction volume: + 56% for l enzymatic hydrolysis, an increase in the specific volume (relative to production) of 36%.
• the improvement of the mass balance makes it possible to reduce the contribution of the cost of the raw material in the final cost of production of ethanol, but the expenditure items "enzymes” and “investments” are increased significantly.
• Example 3 Material balance - with recycling of the solid residue at the top of the digester (according to the invention)
• the conditions of hydrolysis and fermentation are preserved.
• the hydrolysis of the native plant has the same yield. Because of the substantial swelling of recycled cellulose fibers in alkaline medium and in the absence of lignin surrounding these fibers at their entry into the digester for chemical alkaline pretreatment, cellulose regains all its susceptibility to enzymatic hydrolysis and therefore has a yield of hydrolysis equal to that of the cellulose derived from the native plant (75%). Hemicelluloses also recover 55%.
• the conditions of alcoholic fermentation and separation are maintained.
• the process according to the invention thus provides fluxes at the output of the process:
• the ethanol yield of this process is therefore 19.1% by weight on the native plant (dry matter basis), ie 3.3 points more than Example 1 and 1.1 percentage point more than Example 2.
• the specific consumption of enzymes has only slightly increased and is 51 870 FPu / kg of ethanol produced, only 0.6% increase.
• the reaction volume involved is 20% higher than Example 1, and therefore the specific volume is the same as for Example 1.
• 8.7 tons of solids are sent to Kraft treatment in addition to the 44 tonnes of native plant solids, an increase of 20%, proportional to the increase in production.
• the implementation of the process according to the invention makes it possible to greatly improve the mass balance and therefore to reduce the contribution of the cost of the raw material to the final cost of producing ethanol. Recycling upstream of the pretreatment step makes it possible to control the level of lignin in the process, and thus to recycle a larger quantity than Example 2, while keeping a correct level of solids in fermentation, which leads to an even better material yield.
• the invention makes it possible to maintain the contribution of the items of expenditure "enzymes” and "investments” at the case level without recycle. Nevertheless, an increase in the pre-treatment expenditure item will be noted, due to the increase of the material to be processed.
• Example 4 Material balance - with recycling partly upstream of the digester 2 and partly upstream of the washing reactor 6 (in accordance with the invention)
• the cellulose recycled at the inlet of the washing reactor is also subjected to an alkaline medium but of lower basicity and at much more moderate temperatures (40 ° C.). as a result, the swelling of the fibers is more limited than during the Kraft leaching, but nevertheless present, which makes it possible to obtain an increase in the hydrolysis yield of two thirds with respect to the recalcitrant cellulose of the cake (ie 50%).
• the washing makes it possible to preserve 99% of the cake solids and some of the solubles present in the liquid part of the cake (50%).
• the conditions of alcoholic fermentation are maintained.
• the ethanol yield of this process is therefore 20.3% by weight on the native plant (dry matter base), ie 4.5 points more than Example 1 and 2.3 points more that example 2.
• the specific consumption of enzymes increased to 54 750 FPu / kg of ethanol produced, 6.2% increase compared to Example 1, but is still well below the example 2.
• the reaction volume involved is 52% higher than Example 1, which corresponds to an increase in the specific volume of 18.4% relative to Example 1, and is still well below the example 2.
• pretreatment only 3.9 tons of solids are sent to Kraft processing in addition to 44 tons of native plant solids, an increase of 9%, which is much lower than the increase in production.
• the implementation of the process according to the variant of the invention has made it possible to greatly improve the mass balance and thus to reduce the contribution of the cost of the raw material to the final cost of producing ethanol.
• the recycling according to the invention makes it possible to control the level of lignin in the process, and thus makes it possible to recycle a larger quantity than Example 2, while keeping a correct level of solids in fermentation, which leads to a material yield. even better.
• this variant of the process of the invention makes it possible to improve the material balance while limiting the quantity of solids sent to the Kraft pre-treatment and therefore represents a lower cost of reprocessing than that mentioned in the example. 3 where the recycling is done entirely at the preprocessing stage. However, in return, the positions "enzymes" and "investments" are increased.
• the economic optimum of an installation depends on the relative cost of the items of expenditure, and mainly the cost of the raw material, pre-treatment, investments and enzymes used.
• This embodiment of the invention makes it possible to greatly improve the material balance of the process, with limited or no impact on the other stations. According to the economic data of an installation, this embodiment will be used to greatly improve the profitability of the process.
• Example 5 Material balance - without recycling (not in accordance with the invention)
• a process for producing an acetone-butanol-ethanol (ABE) mixture from paper pulp resulting from an alkaline Kraft process is considered.
• the process processes 150 tons / hour of native plant.
• the plant is eucalyptus (hardwood), containing 50% weight of dry matter consisting of: cellulose 45%
• Hemicelluloses consist of C5 sugars (xylans and arabinans).
• Kraft cooking takes place at 165 ° C for 2.5 hours.
• This pretreatment and the washing processes carried out in steps a) and b) respectively are conducted in such a way that the paper pulp contains 10% dry matter, and retains: cellulose 98.5%
• the ethanol conversion process consists of enzymatic hydrolysis of the pulp (step c), separation of the suspended solids to form a cake with a wash to maximize the recovery of sugars, followed by fermentation with ABE of the liquid phase containing the sugars (step d)), the distillation of ⁇ (step e). It should be noted that fermentation in ABE uses both 6-carbon and 5-carbon sugars (glucose and xylose).
• the enzymatic hydrolysis is carried out under conditions such that the hydrolysis of 85% of the cellulose and 65% of the hemicelluloses is observed. FPu / g of cellulose entering the hydrolysis reactor is consumed.
• the solid residue Prior to the fermentation step, the solid residue is separated and washed to limit the loss of sugars with the cake.
• Fermentation transforms the previously formed glucose and xylose into an ABE mixture, producing 0.3 g ABE per gram of sugar present.
• the process conditions are such that the output streams are:
• the ABE yield of this process is therefore 14.9% by weight on the native plant (dry matter basis).
• the specific enzyme consumption is 74,470 FPu / kg of ABE produced.
• the so-called "recalcitrant" cellulose which is present in the cake, has a hydrolysis yield (under the conditions of the above process), and with the same enzyme load which will be only 25%.
• Example 6 Material balance - with recycling of the solid residue at the level of the enzymatic hydrolysis (not in accordance with the invention)
• the ABE yield of this process is therefore 17.1% by weight on the native plant (dry matter basis), an improvement of 2.2 points compared to the base case.
• this improvement in the mass balance is to the detriment of the specific consumption of enzymes which is then 91 590 FPu / kg of ABE produced (+ 23%), and requires a reaction volume which has more than doubled: +113 % for enzymatic hydrolysis, an increase of the specific volume (relative to production) of + 85%.
• the improvement of the mass balance makes it possible to reduce the contribution of the cost of the raw material in the final production cost of ⁇ , but the expenditure items "enzymes” and especially “investments” are increased significantly.
• Example 7 Material balance - with recycling of the solid residue at the top of the digester
• the conditions of hydrolysis and fermentation are preserved.
• the hydrolysis of the native plant has the same yield. Due to the substantial swelling of the recycled cellulose fibers in alkaline medium and in the absence of lignin surrounding these fibers at their entry into the digester for the chemical alkaline pretreatment, the cellulose found all its susceptibility to enzymatic hydrolysis and therefore has a yield of hydrolysis equal to that of the cellulose derived from the native plant (85%). Hemicelluloses also recover 65%.
• the separation and fermentation conditions ABE are maintained.
• the process according to the invention thus provides fluxes at the output of the process:
• the yield of ABE of this process is therefore 17.0% by weight on the native plant (dry matter basis), ie 2.1 points more than Example 5 and 0.1 point less than Example 6.
• the specific consumption of enzymes has slightly decreased and is 73 835 FPu / kg of ABE product, or 0.8% reduction.
• the reaction volume involved is 14.3% greater than Example 5, and therefore the specific volume is the same as for Example 5.
• 11.6 tonnes of solids are sent to Kraft treatment in addition 75 tonnes of native plant solids, an increase of 15.5%, slightly higher than the increase in production.
• the implementation of the process according to the invention has made it possible to greatly improve the mass balance and thus to reduce the contribution of the cost of the raw material to the final cost of production of ⁇ .
• the recycling according to the invention makes it possible to control the level of lignin in the process, and thus makes it possible to limit the volume necessary for hydrolysis with respect to Example 6. r.
• Example 8 Material balance - with recycling partly upstream of the digester 2 and partly upstream of the washing reactor 6 (in accordance with the invention)
• the yield of ABE of this process is therefore 17.1% by weight on the native plant (dry matter basis), ie 2.2 points more than Example 5 and the same as Example 6.
• the reaction volume involved is 35.7% higher than Example 5, which corresponds to an increase in the specific volume of 18% compared to Example 5, and is still much lower than example 6.
• For pretreatment only 6.5 tons of solids are sent to Kraft processing in addition to 75 tons of native plant solids, an increase of 8.7%, which is much lower than the increase in production.
• the implementation of the method according to this variant has made it possible to greatly improve the mass balance and thus to reduce the contribution of the cost of the raw material in the final cost of producing the ABE.
• the recycling according to the invention makes it possible to control the level of lignin in the process, and thus makes it possible to limit the volume necessary for the hydrolysis compared with Example 6. Compared to Example 7, this mode of realization makes it possible to improve the material balance while limiting the quantity of solids sent to the Kraft pretreatment and thus makes it possible to reduce the cost of reprocessing. . However, in return, the positions "enzymes” and “investments” are increased, but still lower than in the case of a "direct” recycling.

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