Process for treating lignocellulosic biomass

Abstract

The invention relates to a method for treating lignocellulosic biomass, comprising: a) a step of impregnating the biomass with a liquid to obtain an impregnated biomass, b) a step of cooking the impregnated biomass, optionally with steam explosion, to obtain a pretreated biomass, c) enzymatic hydrolysis of the pretreated biomass, a step of enzymatically hydrolyzing biomass in one or more sugar forms to obtain hydrolyzed biomass in one or more sugar forms, d) solid / liquid separation of the hydrolyzed biomass in one or more sugar forms or of the hydrolyzed biomass in one or more sugar forms subsequently treated in one or more other steps after the enzymatic hydrolysis step c), a step of separating the mash to obtain separated mash and unconverted solid residue, e) a step of recycling at least a portion of the unconverted solid residue to the step of steeping step a) and / or cooking step b).

Description

Technical Field

[0001] The present invention relates to a method for processing lignocellulosic biomass to produce "second generation" (2G) sugar juices. These sugar juices can be used to produce other products via biochemical pathways, especially by fermentation (e.g., alcohols such as ethanol and butanol, or other molecules such as solvents, such as acetone, etc.). Prior art

[0002] Lignocellulosic biomass represents one of the most abundant renewable resources on Earth. The substrates considered are very diverse and they involve wood substrates such as various woods (hardwood and softwood), by-products derived from agriculture (wheat straw, corn cobs, etc.) or other agricultural products, papermaking, lignocellulosic waste, etc.

[0003] Methods for processing lignocellulosic biomass generally include:

[0004] - pretreatment of the biomass by cooking, optionally coupled with steam explosion, and usually preceded by impregnation of the biomass with an acidic, alkaline, neutral or oxidizing liquor,

[0005] - enzymatic hydrolysis, resulting in the production of sugar juice, usually based on C5 and C6 sugars (i.e. sugars with 5 or 6 carbons),

[0006] - and optionally fermenting these sugars by yeast to convert them into ethanol-type alcohols. The method also includes a step of isolating and / or purifying the target end product (sugar, alcohol, solvent, etc.).

[0007] Lignocellulosic biomass is composed of three major polymers: cellulose (35% to 50% by weight), a polysaccharide consisting essentially of hexoses; hemicellulose (20% to 40% by weight), a polysaccharide consisting essentially of pentoses; and lignin (10% to 30% by weight), a complex polymer of high molecular weight consisting of aromatic alcohols linked via ether bonds. These different molecules are responsible for the intrinsic properties of plant walls and are organized into complex entanglements. Of the three basic polymers that make up lignocellulosic biomass, cellulose and hemicellulose are those that are capable of producing 2G juice.

[0008] Typically, hemicellulose is mainly broken down into sugars during pretreatment, while cellulose is converted into sugars (glucose) by enzymatic hydrolysis. However, crude cellulose is still difficult to be accessible to enzymes, so pretreatment is required. This pretreatment makes it possible to change the physicochemical properties of lignocellulosic biomass, thereby improving the accessibility of cellulose to enzymes and its reactivity to enzymatic hydrolysis.

[0009] There are many advantageous techniques for carrying out this pretreatment, which will be combined below under the general term "cooking": acid cooking, alkaline cooking, cooking by autohydrolysis, steam explosion and "organosolv pulping" processes. The latter process involves pretreatment in the presence of one or more organic solvents and usually water. The solvent can be an alcohol (ethanol), an acid (such as acetic acid or formic acid) or acetone. The "organosolv pulping" process results in at least partial dissolution of the lignin and partial dissolution of the hemicellulose. Thus, there are two outlet streams: a pretreated matrix with residual cellulose, hemicellulose and lignin, and a solvent phase containing dissolved lignin and part of the hemicellulose. There is usually a step of solvent regeneration, which makes it possible to extract the lignin stream. Certain "organosolv pulping" treatments (especially with ethanol) are combined with the addition of strong acids (such as H2SO4). It is also conceivable to contact the biomass with a solvent via an impregnation reactor before the cooking stage, or to contact the biomass with an acid catalyst before carrying out the "organosolv pulping" cooking.

[0010] Various configurations are reported, for example, in the publication “Production of bioethanol from lignocellulosic materials via the biochemical pathway: A review”, M. Balat, Energy Conversion and Management 52 (2011) 858–875 or in the publication “Bioethanol production from agricultural wastes: An overview”, N. Sarkar, S. Kumar Ghosh, S. Bannerjee, K. Aikat, Renewable Energy 37 (2012) 19-27.

[0011] One of the most effective pretreatments is steam explosion, especially under acidic conditions, which enables almost complete hydrolysis of hemicellulose and significantly improves the accessibility and reactivity of cellulose to enzymes. This pretreatment may be preceded by other treatment(s).

[0012] Patents US-8057639 and US-8512512 propose a method comprising a first step of hydrolyzing hemicellulose to C5 sugars under mild conditions to protect them from degradation. This step is carried out in a first reactor at a pressure of 1.5 bar (0.15 MPa) or higher by injecting steam, at a temperature of 110°C or higher and optionally in the presence of a weak acid. After this step, washing is performed to extract and recover the juice obtained from the hemicellulose (usually juice of C5 sugars and C6 sugars, the relative proportion of which depends in particular on the nature of the biomass), and then the residual biomass rich in cellulose and lignin is sent to a second step (second reactor), where steam explosion occurs. The second reactor is operated at a higher pressure than the first reactor, where high-pressure steam is injected, which causes the biomass to suddenly expand (steam explosion).

[0013] When the treatment requires a pressure step (impregnation, cooking type pretreatment, etc.), a solid biomass introduction device compatible with these pressure steps must be used. For example, this is the case with compression screws, one embodiment of which is described in patent US 4,599,138.

[0014] Patent FR 3075203 describes a process involving impregnation of biomass with an acid solution, followed by cooking and steam explosion of the impregnated biomass, wherein the acidity of the acid solution is adjusted and recycled. Patent FR 3075201 also describes a process for pre-treating biomass by acid impregnation followed by steam explosion, as well as washing the reactor feed and recycling the washing water to the process.

[0015] These different types of methods start from lignocellulosic biomass, particularly after enzymatic hydrolysis and / or particularly after fermentation, continue to convert sugar into alcohol and produce residues based on solid lignin. These solid residues rich in lignin are referred to as "unconverted solid residues" or "lignin cakes" in this article, and these lignins will not or hardly react to the action of the enzyme for hydrolyzing biomass, and these enzymes are cellulases and hemicellulases typically. These wood residues can be used as fuel in particular, or can be incorporated into products based on resin or based on asphalt as fillers, for example. However, these unconverted residues (except a certain amount of water) are not only composed of lignin: they may also contain hemicellulose and / or cellulose that do not react in hydrolysis. And removing these residues from biomass conversion process means losing these unreacted polymeric sugar fractions, which affects the conversion efficiency of biomass to sugar (or alcohol).

[0016] It has been proposed to reuse these types of solid residues in biomass treatment methods: Patent EP2516661 proposes a biomass treatment method, which pre-treats the biomass in an alkaline medium, enzymatically hydrolyzes, ferments the hydrolyzate obtained to obtain a fermentation must containing alcohol, separates / purifies the alcohol, and separates the residue cake. The residue cake is sent to a separate cellulose regeneration reactor, in which the cake is mixed with an alkaline solution and heated, and then recycled downstream of the pretreatment. This solution is advantageous because it chooses to recover the residual cellulose contained in the wood cake and reincorporates it into the method to improve the overall biomass conversion efficiency. However, it requires a separate treatment of the cake and an additional reactor dedicated to the treatment, and the reactor will be alkaline cooked before the cake is recycled, which increases the installation and operating costs of the entire method and increases the complexity of its implementation.

[0017] Another solution has been proposed in patent EP 2430171, which is very similar to the previous one but provides an acidic rather than alkaline cooking of wood residues, with the same drawbacks.

[0018] The object of the present invention is therefore to overcome these disadvantages. The object of the present invention is to improve the processing of lignocellulosic biomass. More specifically the object of the present invention is to increase the biomass conversion rate, in particular to increase the biomass conversion rate in a more efficient way than previous solutions. Summary of the invention

[0019] The subject of the present invention is firstly a method for treating lignocellulosic biomass, said method comprising:

[0020] a) a step of impregnating the biomass with a liquid, in particular an acidic liquid, to obtain an impregnated biomass,

[0021] -b) a step of cooking the impregnated biomass, optionally accompanied by steam explosion, to obtain a pretreated biomass,

[0022] -c) enzymatically hydrolyzing the pretreated biomass to obtain hydrolyzed biomass in the form of (one or more) sugars, the method further comprising

[0023] -d) a step of solid / liquid separation of the hydrolyzed biomass in the form of sugar(s) or of the hydrolyzed biomass in the form of sugar(s) subsequently treated in one or more further steps after the enzymatic hydrolysis step c) to obtain a separated juice and an unconverted solid residue,

[0024] -e) a step of recycling at least part of said unconverted solid residue to the impregnation step a) and / or the cooking step b).

[0025] For the purposes of the present invention, an unconverted "solid" residue is understood to mean a residue comprising at least 20% by weight of solids, in particular a residue of at least 30% by weight or 35% by weight of solids. The solid content can be measured by its dry matter (DM) content, which is measured according to standard ASTM E1756-08 (2015) "Standard Test Method for Determination of Total Solids in Biomass". According to the present invention, the DM of the unconverted "solid" residue is preferably at least 20%, 30% or 35%.

[0026] The impregnation liquid may include chemical compounds such as acids, bases or oxidants, or consist of a water-based liquid, where autohydrolysis of the biomass naturally releases acids, especially acetic acid.

[0027] The invention thus chooses to recycle the unconverted solid residue obtained by solid / liquid separation, after enzymatic hydrolysis (separation from sugar juice) or fermentation (separation from alcoholic juice), by reintroducing it into an impregnation step or a cooking step which constitutes a pretreatment of the biomass prior to enzymatic hydrolysis. The particularity of the invention is that the unconverted solid residue can be directly reintroduced into the pretreatment step without having to carry out an impregnation / cooking operation specifically for this residue: thus, a yield (sugar or alcohol) is obtained which can be scaled up without having to invest in additional energy-consuming equipment of the cooking reactor type.

[0028] Surprisingly, it has thus turned out that reintroduction of these residues into the impregnation or cooking plant, together with the biomass to be treated, makes it possible to:

[0029] - extracting from the residue at least some of the cellulose and / or hemicellulose remaining therein, the enzymatic hydrolysis reaction not being able to completely convert these compounds,

[0030] - and at least partially convert them by making them follow the path of "fresh" biomass again in the pretreatment and subsequent enzymatic hydrolysis steps, which actually ends up increasing the yield of sugars (or alcohols) in the process.

[0031] It is also surprising that the addition of this residue to the remaining biomass to be treated does not in fact cause any problems for the operation of the pretreatment means: whether this residue is added to the biomass during the impregnation step or during the cooking step, it does not complicate the proper functioning of the equipment used, whereas the fear that the addition of this residue, which has a texture very different from that of the biomass, would cause problems with fouling of the equipment, problems with the carryover of the residue from one equipment to another or inside the equipment, etc., is not the case.

[0032] Another very advantageous effect of the invention is that the final unconverted residue obtained at the end of the production is reduced in cellulose / hemicellulose and enriched in lignin compared to the residue not recycled according to the invention: this final residue therefore has a higher calorific value, making it more efficient as a fuel for the generation of heat via the step of burning this final residue. The heat generated can be used in the process in one or more steps requiring the heating of fluids (impregnation liquor), reactors (cooking during pretreatment) or reboilers of distillation columns (to purify the alcohol obtained by fermentation, etc.).

[0033] According to one embodiment, the method according to the invention is directed solely to the production of sugar juice, wherein the sugar juice is subjected to a separation step d) at the outlet of the enzymatic hydrolysis.

[0034] According to another embodiment, the method aims at converting all or part of the sugar juice obtained by enzymatic hydrolysis. It may then also comprise: - a step f) of fermenting the hydrolyzed biomass in the form of (one or more) sugars to obtain a fermented biomass comprising at least one alcohol, a solid / liquid separation step d) being performed on said fermented biomass.

[0035] In the latter mode, the invention makes it possible to recycle the unconverted residue at the end of the enzymatic hydrolysis and at the end of the fermentation:

[0036] The enzymatic hydrolysis step c) and the fermentation step f) can be carried out simultaneously on the pretreated biomass, which is then called SFF, simultaneous saccharification and fermentation, or SSCF, simultaneous saccharification and co-fermentation. They can also be carried out one after the other, in particular in separate reactors.

[0037] The method according to the invention may also comprise: a separation or purification step g) of the fermented biomass, in particular a distillation step, wherein a solid / liquid separation step d) is carried out before or after said separation or purification step g). When step g) is a distillation, it is advantageous to carry out the separation d) before step g), since the introduction of a liquid phase containing the residue, which could foul the column or at least hamper its operation, is thereby avoided. However, it may also prove advantageous to carry out the separation d) according to the invention after the separation / purification of the fermented biomass, since the solid residue may contain an alcohol fraction and subjecting the solid residue to a separation / purification step makes it possible to extract at least a portion of the alcohol fraction trapped in the solid residue.

[0038] As mentioned above, the method according to the invention may also comprise: - a step h) of burning the final unconverted solid residue obtained at the end of the biomass treatment, the heat thus generated being used in the steps of the method requiring heating, in particular heating of fluids, in particular in the cooking step d) or in the separation step g) by distillation. The final residue obtained according to the invention has an improved calorific value, due to the lower content of cellulose / hemicellulose, which, unlike lignin, are polymeric sugars with a low calorific value.

[0039] Optionally, the combustion step h) may be preceded by a step i) of drying the residue, in particular to bring the moisture content of the residue below a given threshold, for example less than or equal to 40% by weight, in particular less than or equal to 30% by weight.

[0040] The solid / liquid separation step d) can be carried out by filtration, in particular using a pressure or drainage device, such as a filter press or vacuum filter, a belt filter, a belt press or a centrifugal, decanting or dewatering device or a combination of various devices.

[0041] Advantageously, step a) of impregnating the biomass with a liquid and step b) of cooking the impregnated biomass can be carried out by means of reactors each equipped with at least one biomass feeding device, and step e) of recycling the unconverted solid residue is then carried out by introducing said residue into said feeding device(s) together with the biomass to be treated.

[0042] Thus, at least one of the feeding devices may be a feeding screw, which is in particular at least partially conical, comprising a cover provided with a cage provided with an opening which allows the extraction of solid-liquid residues from the biomass and the circulation of the washing fluid. As is well known, such a compression screw (also referred to as a "plug screw") forms a sealing plug of the biomass in the downstream part of the screw, which compresses the biomass, which is reflected in the pressure difference between the biomass inlet and the biomass outlet of the screw. However, any other known device may be used. For the impregnation step, a reactor operating continuously or in batch mode, or a device other than a dedicated reactor, in particular a conveyor belt for spraying liquid, etc. may be used.

[0043] When solid / liquid separation d) is carried out after fermentation step f), the unconverted solid residue obtained in solid / liquid separation step d) contains, besides water, primary compounds in the form of lignin and secondary compounds comprising cellulose and / or hemicellulose and optionally one or more alcohols of the ethanol type.

[0044] The unconverted solid residue obtained in the solid / liquid separation step d) may contain, for example, 40% to 70% by weight of water, in particular 50% to 60% by weight of water, 2% to 35% DM of cellulose, in particular 5% to 20% DM of cellulose, and 0% to 15% DM of hemicellulose, in particular 1% to 10% DM of hemicellulose. It may also include other minor compounds, such as ash. The various lignin, cellulose and hemicellulose contents may vary, in particular depending on the type of biomass used and in particular on its reactivity during enzymatic hydrolysis.

[0045] Step e) of recycling the unconverted solid residue reduces the content of at least one of cellulose and hemicellulose secondary compounds in the final solid residue obtained at the end of biomass treatment and increases its calorific value, which is beneficial to the biomass conversion efficiency and heat integration of the process.

[0046] The dry composition of the final solid residue obtained at the end of biomass processing generally comprises mainly lignin, as well as less than 20% DM of cellulose and less than 8% DM of hemicellulose.

[0047] The present invention is directed to a treatment process that can convert lignocellulosic biomass into juice, especially C5 and C6 juice, after enzymatic hydrolysis, or into alcohol(s), especially ethanol, after fermentation of the juice.

[0048] The invention also relates to any device for implementing the above method.

[0049] Another subject of the invention is a device, in particular a device for implementing the above method, and comprising:

[0050] a) an apparatus, in particular a reactor, for impregnating biomass with a liquid, in particular an acidic liquid, to obtain impregnated biomass,

[0051] - b) a reactor for cooking the impregnated biomass, optionally with steam explosion, to obtain pretreated biomass,

[0052] -c) a reactor for enzymatically hydrolyzing the pretreated biomass to obtain hydrolyzed biomass, the device further comprising:

[0053] -d) means for solid / liquid separation of the hydrolyzed biomass or of the hydrolyzed biomass subsequently treated in one or more further reactors or means located downstream of the enzymatic hydrolysis reactor c) in order to obtain an unconverted solid residue,

[0054] - e) means for recycling at least part of the unconverted solid residue to the impregnation reactor a) and / or the digestion reactor b).

[0055] The means for recycling the unconverted solid residue is conventional and may include any suitable conveying system (eg, by conveyor, screw, hopper or conveyor belt).

[0056] The device according to the invention advantageously comprises an impregnation reactor a) and a cooking reactor b), which are provided with a feed device and a recirculation device, the recirculation device comprising a fluid connection device between the solid / liquid separation device and at least one of the feed devices for conveying the unconverted solid residue from the separation device to the feed device or to at least one of the feed devices. The unconverted solid residue and the biomass to be treated can be introduced into the feed device (or directly into the relevant reactor) jointly or through different feed points, or not simultaneously.

[0057] Another subject of the invention is the use of the above-described method or device for processing lignocellulosic biomass such as wood, straw, agricultural residues, paper residues and all dedicated energy crops, in particular annual or perennial plants such as miscanthus, in order to produce sugar, alcohol biofuels or bio-based molecules.

[0058] The invention will be described in more detail below with the aid of the accompanying drawings and non-limiting examples.

[0059] List of Figures

[0060] Figure 1 is a schematic diagram of a first variant of an apparatus for converting lignocellulosic biomass in which the method according to the invention can be applied.

[0061] Figure 2is a schematic diagram of a second variant of a plant for converting lignocellulosic biomass in which the method according to the invention can be applied.

[0062] Figure 3 is a schematic diagram of a third variant of an apparatus for converting lignocellulosic biomass in which the method according to the invention can be applied.

[0063] Figure 4 is a schematic diagram of an apparatus for converting lignocellulosic biomass using the present invention.

[0064] It should be noted that from one figure to another, the same reference numerals relate to the same streams or the same devices.

[0065] A description of the reference numerals is presented below:

[0066] 1: Water enters the liquor preparation tank

[0067] 2: Acid enters the liquid preparation tank

[0068] 3: Liquid preparation tool (tank)

[0069] 4: Acid to impregnation tool (reactor)

[0070] 5: Ground biomass

[0071] 6: Dipping tool feeding device

[0072] 7: Water for washing the plug screw feeder of the dipping tool

[0073] 8: Washing liquid outlet of the plug screw feeder 6 of the impregnation tool

[0074] 9: Impregnation tool (reactor)

[0075] 10: Soaked and drained biomass

[0076] 11: Pre-treatment tool feeding device

[0077] 12: Water for washing the screw feeder of the pre-treatment tool

[0078] 13: Pressate from the plug screw feeder of the pre-treatment tool

[0079] 14: Pretreatment cooking tool (explosion reactor)

[0080] 15: Inject steam for pretreatment

[0081] 16: Pretreated biomass and steam

[0082] 17: Tools for separating steam and pre-treated biomass (cyclone separator)

[0083] 18: Steam

[0084] 19: Pretreated biomass

[0085] 20: Enzyme hydrolysis reactor

[0086] 21: Sugary hydrolysate

[0087] 22: Alcohol (ethanol) fermentation reactor

[0088] 23: Fermented fruit wine containing ethanol (alcohol)

[0089] 24: Ethanol recovery unit, such as (one or more) distillation columns

[0090] 25: Concentrated alcohol

[0091] 27: Solid (lignin) / liquid separation, such as filter press

[0092] 28: Liquid residue (vinasse)

[0093] 29: Unconverted solid residue (lignin cake)

[0094] 30: Clarified (solids-free) fermented wine

[0095] 31: Clear (no solids) hydrolyzate

[0096] Description of the implementation plan

[0097] The present invention proposes to recycle the unconverted solid residue of the process of converting lignocellulosic biomass into sugars or alcohols. This residue consists mainly of lignin, a compound that was not converted during the process. This residue is usually separated out in order to be burned in traditional biorefineries, and lignin can also be used as a target compound for special products (resins, pitch, etc.). The present invention proposes to recycle this compound upstream of the process, because the extracted lignin is not pure: it contains a part of unconverted polymeric sugars (cellulose and / or hemicellulose). Recycling these sugar polymers makes it possible to increase the yield of the process.

[0098] The present invention relates to the recycling of at least part of the solid residue, referred to herein as "lignin cake" or "unconverted solid residue". This solid is advantageously recycled to a step of pre-treatment of the lignocellulosic biomass under normal (e.g. acidic) conditions, in order to increase its reactivity in a downstream enzymatic hydrolysis step. Recycling it directly to a step such as enzymatic hydrolysis or SSCF is technically less relevant, since the accessibility of the enzymes to the cellulose will not be improved, or not sufficiently to significantly improve the biomass conversion efficiency and / or the calorific value of the final residue will be significantly improved compared to no recycling, or at least much lower than the present invention.

[0099] Lignin is one of the main compounds of lignocellulosic biomass (up to 30% DM). During the conversion of lignocellulosic biomass to upgraded sugars (cellulose and hemicellulose), a lignin cake is a byproduct of the process consisting of water (water can account for 50 to 60 wt% of the cake) and biomass solids that were not converted during the process, i.e., mainly lignin, but also cellulose and hemicellulose.

[0100] Table 1 below therefore shows the flow rates into the process and the composition of a typical example of the biomass to be treated (wheat straw) and the lignin cake obtained after separation at the end of the alcohol production line:

[0101] [Table 1]

[0102] Biomass Unconverted solid Flow rate kg / h 100 67 water weight% 10 60 Cellulose weight% 34 8 Hemicellulose weight% 27 3 Lignin weight% 15 22 other weight% 14 7

[0103] And the following Table 2 shows, for the same biomass and the same lignin cake, their flow rates and the composition of the solid compounds, here expressed as dry matter content DM:

[0104] [Table 2]

[0105]

[0106]

[0107] As can be seen from these tables, there are two unconverted sugar polymers (cellulose and hemicellulose) in the lignin cake, totaling 11 mass % (or 28% DM). The present invention recycles at least a portion of the lignin cake (unconverted solids) to convert these polymers, thereby increasing the yield of the process, since 11% of the polymeric sugars in the biomass are present in the unconverted solids, without the need to add a treatment step specifically for the lignin cake.

[0108] Furthermore, if the sugar polymers contained in the lignin cake are converted, their calorific value (measured by the higher heating value HHV of the unconverted solid residue) increases. Specifically, the sugar polymers contain oxygen molecules that reduce the average HHV of the solid.

[0109] Examples of operating conditions for key steps in biomass processing are briefly summarized as follows:

[0110] method

[0111] The following describes in more detail the various key steps of the biomass conversion method using such equipment, and the present invention can be advantageously applied to these steps: (This is an embodiment, and the present invention is not limited thereto).

[0112] Steps for conditioning lignocellulosic biomass

[0113] The treatment method comprises in its first step conditioning lignocellulosic biomass with at least one grinding to obtain the step of biomass particles with a size of up to 300mm. Of course, multiple continuous grinding steps can be carried out to reach the target particle size. Usually, the ground biomass has a particle size (maximum size) of up to 300mm, usually at least 1mm, and usually 2 to 200mm. Any method known to those skilled in the art can be used to carry out this step. Usually, the stalk is ground with a screen of 5 to 100mm. For wood, it is usually cut into parallelepiped fragments of 20 to 160mm in length, 10 to 100mm in width, and 2 to 20mm in thickness. The ground lignocellulosic biomass is sent to the next step by any means known to those skilled in the art, particularly a screw conveyor.

[0114] Steps of acid impregnation

[0115] The treatment method according to the invention comprises a step a) of impregnating the lignocellulosic substrate with an acid solution to obtain an impregnated lignocellulosic substrate, the pH of which is between 0.1 and 3. This step is intended to prepare the lignocellulosic substrate for a pretreatment step.

[0116] The impregnation is carried out in an impregnation reactor at a temperature of 10° C. to 90° C. and preferably at atmospheric pressure. The residence time of the lignocellulosic substrate in the impregnation reactor is generally 10 seconds to 180 minutes, preferably 30 seconds to 60 minutes, and still more preferably 30 seconds to 15 minutes. Preferably, the impregnation step is carried out in a single step.

[0117] The impregnation reactor or impregnator is equipped with one or more screws for conveying the lignocellulosic substrate from its inlet to its outlet. In addition, the impregnator is also equipped with one or more pipelines for conveying acid solution and, if necessary, one or more pipelines for extracting acid solution. The acid solution inlet and outlet pipelines are usually installed to function by co-current or counter-current recirculation.

[0118] The acid solution is an aqueous solution of a strong acid, for example, the strong acid is selected from sulfuric acid, hydrochloric acid and nitric acid, for example, the acid content is 0.5 wt % to 4 wt %.

[0119] Steps for solid / liquid separation on a lignocellulosic substrate impregnated with an acid solution

[0120] The lignocellulosic substrate impregnated with the acid solution is subjected to a solid / liquid separation step to obtain a lignocellulosic substrate having a dry matter content of 15 wt % to 70 wt % and a used acid solution. Preferably, before the solid / liquid separation treatment, the lignocellulosic substrate impregnated with the acid solution is first drained to extract at least a portion of the free acid solution.

[0121] The solid / liquid separation step may employ any technique known to a person skilled in the art, which may be, for example, decantation, centrifugation or pressing.

[0122] Preferably, the pressing of the lignocellulosic substrate is carried out simultaneously with its transfer to the pretreatment step, which is then subjected to the steam explosion method described below. This method of carrying out this step is carried out, for example, by means of a compression screw called a "plug screw feeder", the operation of which has been described above. The formation of a plug of the pressed lignocellulosic substrate ensures the pressure tightness of the steam explosion reactor, thereby preventing a dangerous escape of steam. The screw conveyor is also provided with one or more lines for extracting the waste liquid separated during the pressing, called pressate. The pressate can be recycled to the impregnation step and / or to the step of washing with a washing liquid 12 passed through the feed screw 11.

[0123] The wet biomass obtained at the end of the solid / liquid separation step, which may be indicated by the term "washed and acidified lignocellulosic substrate", preferably has a dry matter content ranging from 15% to 70% by weight and more preferably ranging from 40% to 65% by weight.

[0124] Steps for pre-treating washed and acidified lignocellulosic substrates

[0125] The washed and acidified lignocellulosic substrate undergoes a pretreatment step.

[0126] The cellulose (and optionally hemicellulose) that is the target of the enzymatic hydrolysis is not directly accessible to the enzymes. This is why the biomass is subjected to a pretreatment prior to the enzymatic hydrolysis step. The pretreatment is especially intended to modify the physical and physicochemical properties of the cellulose fraction, such as its degree of polymerization and its crystalline state.

[0127] The person skilled in the art is aware of various types of pretreatment which combine chemical and thermal treatments. Mention may in particular be made of acidic or alkaline cooking, organosolv processes, ionic liquid treatments and steam explosion processes.

[0128] The preferred pretreatment method is steam explosion (or "SteamEx") in an acidic medium. This method rapidly raises the lignocellulosic substrate to a high temperature by injecting pressurized steam. The treatment is stopped by a sudden reduction of the pressure.

[0129] The operating conditions of the steam explosion process are as follows: steam is injected directly into the reactor; the temperature of the reactor is generally between 150°C and 220°C, preferably between 170°C and 210°C; the pressure is between 5 and 25 bar (0.5 and 2.5 MPa) absolute pressure, more preferably between 8 and 19 bar (0.8 and 1.9 MPa) absolute pressure; the residence time before the expansion stage is between 10 seconds and 50 minutes, and preferably between 3 minutes and 30 or 40 minutes.

[0130] Steam explosion can be performed in batch or continuous mode, and the decompression step allowing destructuring of the biomass can be performed in one or more steps.

[0131] At the end of the steam explosion pretreatment step, a pretreated lignocellulosic substrate having a high dry matter content (typically 20 to 70% by weight) and a condensable vapour phase is obtained.

[0132] After steam explosion under acidic conditions, the pH of the pretreated lignocellulosic substrate is generally below a pH compatible with the enzymatic hydrolysis medium. Therefore, the lignocellulosic substrate is subjected to a neutralization step in order to bring its pH to a value between 4 and 6.

[0133] For the neutralization step, an aqueous solution containing a neutralizing agent is used, which can be selected from all weak or strong bases known to the person skilled in the art. The term "base" means any chemical species which, when added to water, produces an aqueous solution with a pH greater than 7. Preferably, the neutralizing agent is selected from potassium hydroxide, sodium hydroxide, ammonia and lime. Still more preferably, the neutralizing agent is selected from potassium hydroxide and ammonia, alone or in combination with each other. Preferably, the neutralizing agent is used in the form of an aqueous solution, wherein the weight concentration is from 2% to 75%, and still more preferably from 20% to 70%.

[0134] Neutralization is carried out at a temperature of 15° C. to 95° C., preferably 20° C. to 70° C. Typically, the temperature of the neutralization step is not precisely controlled but is simply controlled by the heat released by the acid-base neutralization reaction.

[0135] The neutralization step can be performed continuously, in batch mode or in fed-batch mode.

[0136] It is worth noting that all or part of the pretreated lignocellulosic substrate may be subjected to an optional washing step before or after the neutralization step.

[0137] If washing is applied, the liquid stream is contacted with the pretreated lignocellulosic substrate and the liquid is then separated from the solid. The washing step can be carried out by diafiltration, by continuous mixing and liquid / solid separation operations, by washing on a belt filter or by any other technique known to those skilled in the art. The washing liquid used can be water or a process stream. The weight ratio of the added washing liquid to the liquid contained in the substrate to be washed is typically 0.5 to 4. The washing step produces a sugar wash containing a portion of the hemicellulose solubilized during pretreatment. The washing liquor can, for example, be used as a carbon source for the production of biocatalysts (enzymes and / or microorganisms). The washing step is typically carried out at a temperature of 10° C. to 95° C.

[0138] Enzymatic hydrolysis step

[0139] The pretreated lignocellulosic substrate (optionally neutralized and washed) is sent to the enzymatic hydrolysis step of the process.

[0140] The dry matter content of the pretreated lignocellulosic substrate fed to the enzymatic hydrolysis step is typically between 15 and 70 wt%.

[0141] The purpose of enzymatic hydrolysis is to hydrolyze (depolymerize) hemicellulose and cellulose into fermentable sugars, preferably glucose, by means of biocatalysts.

[0142] The enzymatic hydrolysis step is carried out under mild conditions at a temperature of about 40° C. and 55° C., preferably 45° C. to 50° C. and a pH of 4.0 to 5.5, and still more preferably 4.5 to 5.2. The dry matter content of the enzymatic hydrolysis medium is from 2% to 45% by weight, preferably from 10% to 30% by weight. It is carried out by means of enzymes produced by microorganisms. Natural or genetically modified microorganisms, such as fungi of the genera Trichoderma, Aspergillus, Penicillium or Schizophyllum, or anaerobic bacteria, such as Clostridium, produce enzyme mixtures, in particular containing cellulases and hemicellulases, suitable for extensive hydrolysis of cellulose and hemicellulose.

[0143] The enzymatic hydrolysis can be carried out continuously or in batch mode or in fed-batch mode in one or more reactors. The residence time is from 5 hours to 200 hours, and preferably from 24 hours to 120 hours, and still more preferably from 48 hours to 120 hours.

[0144] At the end of the step, a hydrolysate containing fermentable sugars is recovered from the bioreactor and is then processed in a fermentation step.

[0145] It is worth noting that, before the fermentation step, the hydrolysate obtained may optionally undergo one or more treatment steps. For example, these treatment steps may be restoration of pH, partial purification in order to limit the content of inhibitor compounds of the fermenting microorganisms, or at least partial separation of the solid residues contained in the hydrolysate (thus obtaining the unconverted solid residues to be treated according to the invention).

[0146] When it is desired to continue converting the obtained sugars into alcohol(s), the step of fermenting the hydrolysate

[0147] According to the steps of the process for producing solvents and / or alcohols, the optionally treated hydrolyzate is sent to a fermentation step, making it possible to convert the fermentable sugars into the target solvent and / or alcohol with the aid of one or more microorganisms of different genera. Fermentation methods are well known to those skilled in the art and are described in particular in document US 8,456,633.

[0148] The term "solvent" is intended to mean organic compounds other than alcohols, for example organic compounds having a ketone functionality, such as acetone.

[0149] The term "alcohol" denotes in particular ethanol, propanol, isopropanol and butanol.

[0150] The natural or genetically modified microorganism can be selected from, for example, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Saccharomyces vitis, Saccharomyces diastaticus, Kluyveromyces fragilis, Candida shehatae, Pichia stipitis, Pachysolen tanninophilus or the bacterium Zymomonas mobilis, Clostridium acetobutylicum, Escherichia coli.

[0151] In the context of the present invention, the fermentation step makes it possible, for example, to produce ethanol alone or in mixture with butanol, propanol, isopropanol and / or acetone. For example, the fermenting microorganism may be able to produce an "ABE (acetone-butanol-ethanol)" mixture or an "IBE (isopropanol-butanol-ethanol)" mixture.

[0152] Preferably, the microorganism selected is a native or genetically modified Saccharomyces yeast capable of producing ethanol.

[0153] At the end of the step, the fermentation mash is recovered diluted in the target product.

[0154] According to one embodiment of the method, the hydrolysis and fermentation steps can be carried out simultaneously in at least one same bioreactor, so that enzymatic hydrolysis and fermentation are carried out simultaneously according to the method represented by the term "simultaneous saccharification and fermentation (SSF)". When the hydrolysis step is combined with the fermentation step, the operating conditions, in particular the temperature conditions, can be adjusted to be compatible with the tolerance of the fermenting microorganism. For example, when fermentation is carried out using yeast of the genus Saccharomyces, the temperature can be reduced to 28°C to 45°C, and preferably 30°C to 35°C. The pH is preferably adjusted to 5 to 5.5 in order to promote the performance of the yeast.

[0155] In addition to the equipment already described, the production unit for carrying out the method according to the invention may also comprise a unit for the in situ production of enzymes and / or yeasts.

[0156] Step of separating solvent and / or alcohol from fermented mash

[0157] The method according to the invention finally comprises a step of separating the target product(s) from the fermented mash, which step may be preceded or followed by a solid / liquid separation step to remove at least part of the solid matter contained in the fermented mash and produce an unconverted solid residue to be treated according to the invention.

[0158] Preferably, the step of separating (one or more) target products (eg, ethanol) adopts one or more distillations, which is a technique well known to those skilled in the art.

[0159] Raw material: lignocellulosic biomass. According to the invention, the raw material for the process can be a single biomass or as a mixture. The amount of water contained in the raw raw material is generally at least 10% by weight, in particular 10% to 70% by weight.

[0160] The raw biomass is selected from any type of biomass, preferably solid type of biomass, and in particular lignocellulose type of biomass. Non-limiting examples of biomass types relate to, for example, agricultural residues (especially straw, corn cobs), forestry management residues, forestry management products, lumber mill residues and special crops, such as short rotation coppice. Preferably, raw biomass, also referred to as natural biomass, is lignocellulose biomass. It substantially comprises three natural components, which exist in variable amounts depending on their source: cellulose, hemicellulose and lignin.

[0161] The lignocellulosic biomass feedstock is preferably used in its crude form, ie containing all three components of cellulose, hemicellulose and lignin.

[0162] In a preferred embodiment of the present invention, the lignocellulosic biomass is selected from grass biomass, agricultural residues (such as straw waste, corn cobs, bagasse), forestry management residues or lumber mill residues (such as wood chips) or any other type of woody residues.

[0163] Impregnation fluid: The optional fluid injected for impregnation is an aqueous liquid solution optionally containing an acid at a temperature of 10° C. to 95° C. and at atmospheric pressure. The pH of the chemical solution is 0.1 to 12.0, preferably 0.1 to 7, preferably 0.3 to 2. According to a preferred embodiment, the liquid used is an acid-catalyzed liquid, and the pH of the liquid is adjusted to 0.1 to 4, especially 0.3 to 2. Examples of acids that can be used include at least one acid selected from sulfuric acid, hydrochloric acid, nitric acid and oxalic acid. Their content in the aqueous phase is preferably 0.2% to 8% by weight.

[0164] The invention is applicable in an analogous manner to different processes and plants, in particular: - plants intended only for the production of sugars and which therefore do not provide for alcoholic fermentation, - plants providing pretreatment by cooking without prior impregnation with a liquid (e.g. autohydrolysis), - plants providing pretreatment by cooking with prior impregnation with a non-acidic liquid.

[0165] Figure 1 Very schematically represented are non-limiting variants of the apparatus for converting lignocellulosic biomass to which the invention may be applied, the apparatus being used for pre-treatment of the biomass comprising acid impregnation, followed by cooking / steam explosion, then enzymatic hydrolysis and subsequent alcohol fermentation to convert the biomass into ethanol.

[0166] therefore, Figure 1 Represents the conversion of biomass in the following manner: ground biomass 5 (optionally impregnated with catalytic liquid) is introduced into an impregnation reactor 9 via a feed device 6. This can be a pressurized feed device, such as a screw, also called a plug screw feeder, which is conical at the end, has a fairing with a draining screen, a wash water inlet 7 and a wash water outlet 8. A sealing plug of biomass is formed in the downstream part of the screw, which produces a compression on the biomass, which is reflected in the pressure difference of at least 0.05 MPa between the biomass inlet and the biomass outlet of the screw. The compression applied to the biomass may lead to the discharge of part of the liquid contained in the biomass, especially when the DM of the biomass is less than 80% before entering the pressurized feed device 6. The liquid thus extracted is mixed with the wash water and discharged together with the used wash water 8. The impregnation reactor is also supplied with acid 4 (water supplemented with sulfuric acid) originating from a liquid preparation tank 3, which is itself supplied with acid 2 and water 1. The impregnated and drained biomass 10 leaves the reactor 9 in order to be fed to a steam explosion cooking reactor 14 via another feeding device 11 (e.g. a compression type feeding device, such as the feeding device 6). In this device 11, as a result of the compression applied to the biomass, a liquid 13 resulting from this pressurization, also called a pressate, is recovered, which consists of water and acid. A dedicated inlet is used to wash the device 11 with a wash liquid 12 (water and / or a recycle liquid, as shown below), which is then discharged via an outlet, through which the pressate 13 is also discharged.

[0167] The reactor 14 is also supplied with steam 15. After leaving the reactor 14, the biomass-steam mixture enters means 17 for separating biomass 19 and steam 18. The biomass 19 is then treated in an enzymatic hydrolysis reactor 20, and once hydrolyzed into sugars, the hydrolyzed biomass 21 (also called hydrolyzed mash) then enters an alcohol fermentation reactor 22. The biomass fermented into alcohol 23 (also called fermented mash) is then conveyed to one or more distillation columns 24 to obtain concentrated alcohol 25 and crude stillage 26, which is a solid / liquid residue, separated as a mixture or depending on the arrangement of the columns 24. The solid / liquid separation is carried out by a filter press type device 27, obtaining at the outlet a liquid residue 28 (stillage) and a residue 29, i.e. the lignin cake targeted by the present invention.

[0168] This is only one example of an apparatus, and there are also many variations of the apparatus. Thus, enzymatic hydrolysis and fermentation can be carried out together in the same reactor, which is then called SSCF (simultaneous saccharification and co-fermentation).

[0169] Figure 2 is based on Figure 1 A variant of the method shown, in which, all other conditions being equal, the fermented wine 23 is subjected to solid / liquid separation by means of a filter press 27 before entering the distillation column(s) 24: the lignin cake 29 is extracted and the liquid residue (i.e. the fermented wine 30 without solid residue) is then conveyed to the distillation column(s) 24.

[0170] Figure 3 is based on Figure 2 A variant of the method shown, in which, under all other conditions being the same, a filter press type solid / liquid separator 27 is arranged between the enzyme hydrolysis reactor 20 and the fermentation reactor 22: here, the unfermented hydrolysate 21 is separated, and then the liquid part (sugar juice) 31 of the hydrolysate enters the fermentation reactor 22. Figure 3 In a variant of the method shown (not shown), only the production of sugar juice 31 is targeted, without the conversion of the sugar juice continuing by fermentation in the same production line.

[0171] In all these variants, the object of the invention is to treat a lignin cake 29 which is ultimately intended to be burned to produce energy.

[0172] Figure 4 Two alternative or cumulative embodiments of the invention are shown, from Figure 1Starting with a variant: - the lignin cake 29 is at least partially (stream 29') recycled to the feed device 6 of the impregnation reactor 9. This recycling before impregnation is advantageous since the lignin cake 29 will come into contact with the (acidic) impregnation liquid in the reactor 9, which will help extract the residual polymeric sugars contained in the cake and subsequently make them more reactive during the enzymatic hydrolysis. One might fear that the lignin cake would break up and settle at the bottom of the reactor 9 and not be transported with the biomass, but surprisingly this is not the case even when the biomass is transported from its injection point to its exit point by means of a screw inside the reactor;

[0173] - the lignin cake is at least partially recycled (stream 29″) to the feed device 11 of the cooking / steam explosion reactor 14. In this case, the lignin cake is no longer impregnated with liquid, but is entrained with the impregnated biomass;

[0174] - Optionally, part of the lignin cake (stream 29'") is not recycled: the lignin cake may only be partially recycled. At the end of production, the non-recycled cake (and the final residue) is stored for use as fuel, either on the production line or for other uses outside the production line, as fuel or incorporated into various products.

[0175] according to Figure 1 and Figure 3 The same type of recycling applies to the lignin cake as shown. Example

[0176] Example 1 (Comparative) This example is not in accordance with the present invention, as the unconverted solids 29 are separated and not recycled. Biomass 5 is a lignocellulosic biomass, wheat straw. Its composition is as follows

[0177] As shown in Table 3: [Table 3]

[0178] Cellulose 34％ By weight Hemicellulose 27％ By weight Lignin 15％ By weight water 10％ By weight other 14％ By weight

[0179] Biomass according to Figure 2 The method shown in the figure is used for processing. After hydrolysis, cellulose is converted into glucose or glucose oligomers, and hemicellulose is converted into xylose or xylose oligomers. For this reason, the flow rate of cellulose or hemicellulose is expressed as potential glucose or potential xylose.

[0180] The term "potential sugar" (e.g., xylose, glucose) used below defines the addition of various sugars, regardless of their form: monomeric sugars or polymeric sugars. Specifically, after pretreatment by cooking, a portion of the sugars still exist in the form of sugar polymers (e.g., cellulose or hemicellulose), while a portion of the sugars exist in the form of sugar monomers (e.g., glucose or xylose). This measurement can be performed using the standard ASTM E1758-01 (2020) "Standard Test Method for Determination of Carbohydrates in Biomass by High Performance Liquid Chromatography". As defined in the standard, in order to express the amount of the sugar in polymer form (e.g., cellulose), the hydrolysis water must be subtracted from the amount.

[0181] The operating procedure is as follows: 642 kg / h of this 50 mm ground biomass 5 enters the process, i.e. 242.5 kg / h of potential glucose, 197 kg / h of potential xylose and 96.3 kg / h of lignin. Since the process is intended to produce ethanol by fermentation, these potential sugar flow rates correspond to 224.6 kg / h of potential ethanol. The ground biomass 5 enters the feed screw 6 and is washed with wash water 7 at a flow rate of 200 kg / h. A first solid / liquid stream 8 of 203.8 kg / leaves the process, in which there are 1.3 kg / h of potential glucose, 1.1 kg / h of potential xylose and 0.5 kg / h of lignin. In the impregnation step (reactor 9), 1622.6 kg / h of water and 84.2 kg / h of sulfuric acid are added to the reactor from the preparation tank 3 and constitute the impregnation liquid 4. At the inlet of the cooking reactor 14, the impregnated biomass 10 is fed to the transfer zone 11. The transfer zone 11 (compression screw) is washed with 4087.0 kg / h of water 12, and a second solid / liquid stream 13 of 5099.9 kg / h leaves the zone 11. In this stream 13, there are 2.7 kg / h of potential glucose, 2.2 kg / h of potential xylose and 1.1 kg / h of lignin. The cooking reactor 14 is heated by a 3471.1 kg / h steam stream 15. At the outlet of this reactor 14, a pretreated biomass stream 16 of 4803.2 kg / h leaves, which contains 237.8 kg / h of potential glucose, 155.2 kg / h of xylose and 94.7 kg / h of lignin.

[0182] The material stream 16 is separated into a gaseous material stream 18 of 3039.8 kg / h, which mainly comprises steam, and a solid / liquid material stream 19 of 1763.4 kg / h, which comprises 237.8 kg / h of potential glucose, 155.2 kg / h of potential xylose and 94.7 kg / h of lignin. Then, the material stream 19 undergoes an enzymatic hydrolysis step in an enzymatic hydrolysis reactor 20. After the enzymatic hydrolysis, the material stream 21 comprises 38.9 kg / h of potential polymerized glucose, 198.9 kg / h of glucose, 15.4 kg / h of potential polymerized xylose, 139.8 kg / h of xylose and 94.7 kg / h of lignin. Then, the material stream 21 undergoes a fermentation step in a fermentation reactor 22.

[0183] After fermentation, stream 23 comprises 38.9 kg / h of potentially polymerized glucose, 15.4 kg / h of potentially polymerized xylose, 94.7 kg / h of lignin and 157.8 kg / h of ethanol. Stream 23 subsequently undergoes solid / liquid separation in a separation means 27 (eg a filter press).

[0184] The solid stream resulting from separation 27 is stream 29, defined as unconverted solids, which contains 38.9 kg / h of potentially polymerized glucose, 15.4 kg / h of potentially polymerized xylose, 94.7 kg / h of lignin, and 2.2 kg / h of ethanol (loss of ethanol in the solids). The liquid stream resulting from separation 27 is stream 30, which contains 155.7 kg / h of ethanol. Stream 30 is then distilled in distillation column 24, when final stream 25 contains 154.1 kg / h of ethanol. Compared to the biomass ethanol potential of 224.6 kg / h, the yield of the process is 68.6%.

[0185] Example 2 (according to the invention) This example according to the invention proposes to recycle the unconverted solids 29 to the inlet of the digestion reactor 14 via the feed screw 11. The biomass used in this example is the same as in Example 1. 642 kg / h of this 50 mm ground biomass 5 enters the process, i.e. 242.5 kg / h of potential glucose, 197 kg / h of potential xylose and 96.3 kg / h of lignin. Since the process is intended to produce ethanol by fermentation, these potential sugar flow rates correspond to 224.6 kg / h of potential ethanol.

[0186] The ground biomass 5 enters the feed screw 6 and is washed with 200 kg / h of wash water 7. A first solid / liquid stream 8 of 203.8 kg / h leaves the process, including 1.3 kg / h of potential glucose, 1.1 kg / h of potential xylose and 0.5 kg / h of lignin in this stream.

[0187] In the impregnation step (reactor 9 ), 1622.6 kg / h of water and 84.2 kg / h of sulfuric acid were added to the reactor from the preparation tank 3 , and the impregnation liquid 4 was formed.

[0188] At the inlet of the cooking reactor 14, the transfer zone 11 is fed with the impregnated biomass 10 and a stream 29" corresponding to 80% of the unconverted solids, which is recycled from the solid / liquid separation 27. 20% of the unconverted solids are removed from the process.

[0189] This is because preferably not 100%, but only a portion of the unconverted solids is recycled, for example at least 1 wt%, 5 wt%, 10 wt%, 20 wt%, 30 wt%, 40 wt%, 50 wt% or even at least 60 wt% or at least 70 wt% or 80 wt% of the residue, so that the lignin compounds can be discharged from the biomass conversion pipeline. Even if this recycling rate is not very high, the present invention is also advantageous, and very high recycling rates may lead to the necessary increase in the size of the equipment, which may be undesirable.

[0190] The maximum amount of final solid residue actually corresponds to the amount of lignin in the biomass.

[0191] The recycle stream 29″ contains 31.1 kg / h of potential glucose, 12.3 kg / h of potential xylose, 75.8 kg / h of lignin and 1.7 kg / h of ethanol. The transfer zone 11 (compression screw) is rinsed with 4087.0 kg / h of water 12, and a second solid / liquid stream 13 of 5099.9 kg / h leaves the zone 11. In this stream 13, there is 2.5 kg / h of potential glucose (compared to 2.7 kg / h in Example 1), 1.9 kg / h of potential xylose (compared to 2.2 kg / h in Example 1), and 1.6 kg / h of lignin (compared to 1.1 kg / h in Example 1). kg / h), that is, in terms of the crude flow rate, this solid loss is comparable to that of Example 1, but its latent sugar content is lower than that of Example 1. Specifically, the solids contained in the stream 13 must pass through the holes of the cage of the spiral 11, which determine the solid flow rate of the stream 13, rather than the solid flow rate in the spiral inlet stream. The cooking reactor 14 is heated by a steam stream 15 of 3471.1 kg / h. At the outlet of this reactor 14, 4982.9 kg / h of pretreated biomass stream 16 flows out, which contains 268.9 kg / h of latent glucose, 165.1 kg / h of xylose and 170.5 kg / h of lignin.

[0192] This stream 16 is separated into a gaseous stream 18 of 3039.8 kg / h comprising mainly steam and a solid / liquid stream 19 of 2005.3 kg / h comprising 269.1 kg / h of potential glucose, 165.4 kg / h of potential xylose and 170.0 kg / h of lignin. Stream 19 then undergoes an enzymatic hydrolysis step in an enzymatic hydrolysis reactor 20. After enzymatic hydrolysis, stream 21 comprises 63.9 kg / h of potential polymerized glucose, 205.2 kg / h of glucose, 17.5 kg / h of potential polymerized xylose, 147.9 kg / h of xylose and 170 kg / h of lignin.

[0193] Stream 21 then undergoes a fermentation step in a fermentation reactor 22. After fermentation, stream 23 comprises 63.9 kg / h of potentially polymerized glucose, 17.5 kg / h of potentially polymerized xylose, 170 kg / h of lignin and 164.6 kg / h of ethanol. Stream 23 then undergoes solid / liquid separation in a separation means 27 (e.g., a filter press). 80% of the solid stream resulting from separation 27 is recycled as described above (stream 29"), and 20% leaves the process (stream 29'"), which comprises 32.8 kg / h of potentially polymerized glucose, 5.1 kg / h of potentially polymerized xylose, 94.2 kg / h of lignin and 0.5 kg / h of ethanol. The liquid stream resulting from separation 27 is stream 30, which comprises 162.3 kg / h of ethanol. Stream 30 is then distilled in a distillation column 24, when the final stream 25 comprises 160.7 kg / h of ethanol.

[0194] Compared to the biomass ethanol potential of 224.6 kg / h, the process yield was 71.5%, an increase of 2.9 points in yield.

[0195] The HHV of the solid residue itself increased by 2.7% (from 20.9 MJ / kg DM lignin to 21.5 MJ / kg DM lignin). HHV is the abbreviation for higher heating value and corresponds to the total heat released at a constant volume when 1 kg or 1 Nm3 of fuel is burned at standard atmospheric pressure, the water formed during combustion will return to the liquid state, and the other products will return to the gaseous state.

[0196] In summary, compared with the prior art, the present invention has the following advantages:

[0197] - The overall sugar / ethanol yield of the process is improved by recycling unconverted polymeric sugars (cellulose and hemicellulose). After recycling to the pretreatment, these polymeric sugars are partially converted to monomeric sugars or are more easily taken up by the enzymes used in the enzymatic hydrolysis step;

[0198] - The quality of the lignin is improved because the conversion of sugars makes the lignin purer / richer, so the HHV of the solid increases, since the HHV of polymerized sugars is lower than that of lignin.

Claims

1. A method for treating lignocellulosic biomass, the method comprising: a) a step of impregnating the biomass with a liquid, in particular an acidic liquid, to obtain an impregnated biomass, -b) a step of cooking the impregnated biomass, optionally accompanied by steam explosion, to obtain a pretreated biomass, -c) a step of enzymatically hydrolyzing the pretreated biomass to obtain hydrolyzed biomass in the form of (one or more) sugars, characterized in that the method further comprises: -d) a step of solid / liquid separation of the hydrolyzed biomass in the form of sugars (one or more) or of the hydrolyzed biomass in the form of sugars (one or more) subsequently treated in one or more further steps after the enzymatic hydrolysis step c) to obtain a separated juice and an unconverted solid residue, -e) a step of recycling at least part of said unconverted solid residue to the impregnation step a) and / or the cooking step b), - h) a step of burning the unconverted solid residue obtained at the end of the biomass treatment, called final solid residue, which generates heat for use in the steps of the process requiring heating.

2. A method as claimed in the preceding claims, characterized in that It also includes: - step f) of fermenting said hydrolyzed biomass in the form of sugar(s) to obtain a fermented biomass comprising at least one alcohol, and wherein step d) of solid / liquid separation is performed on said fermented biomass.

3. A method as claimed in the preceding claims, characterized in that Enzymatic hydrolysis step c) and fermentation step f) are performed simultaneously on said pretreated biomass.

4. The method as claimed in claim 2 or 3, characterized in that It also includes: - a step g) of separating or purifying, in particular distilling, the fermented biomass, and wherein a solid / liquid separation step d) is carried out before or after the separation or purification step g).

5. A method as claimed in any one of the preceding claims, characterized in that The steps in the process requiring heating, in particular heating of a fluid, are the cooking step d) or the separation step g) by distillation, said step h) being optionally carried out before the step i) of drying the residue.

6. A method as claimed in any one of the preceding claims, characterized in that The solid / liquid separation step d) is carried out by filtration, in particular using a pressing or draining device, such as a filter press or a vacuum filter, a belt filter, a belt press or a centrifugal, decanting or dewatering device or a combination of various devices.

7. A method as claimed in any one of the preceding claims, characterized in that Step a) of impregnating the biomass with a liquid and step b) of cooking the impregnated biomass are carried out by means of reactors each provided with at least one biomass feeding device, and step e) of recycling the unconverted solid residue is carried out by introducing said residue with the biomass to be treated into said feeding device(s).

8. A method as claimed in any one of the preceding claims, characterised in that The unconverted solid residue obtained in the solid / liquid separation step d) contains 40 to 70 wt.-% water, in particular 50 to 60 wt.-% water, 2 to 35 wt.-% DM of cellulose, in particular 5 to 20 wt.-% DM of cellulose, and 0 to 15 wt.-% DM of hemicellulose, in particular 1 to 10 wt.-% DM of hemicellulose.

9. A method as claimed in any one of the preceding claims, characterized in that The treatment converts the lignocellulosic biomass into sugar juice, in particular C5 and C6 sugar juice, after enzymatic hydrolysis, or into alcohol after fermentation of the sugar juice.

10. A device for implementing the method as claimed in any one of the preceding claims, characterized in that It includes: a) an apparatus, in particular a reactor, for impregnating biomass with a liquid, in particular an acidic liquid, to obtain impregnated biomass, -b) a reactor for cooking said impregnated biomass, optionally with steam explosion, to obtain a pretreated biomass, -c) a reactor for enzymatically hydrolyzing the pretreated biomass to obtain hydrolyzed biomass, characterized in that the device further comprises: -d) means for solid / liquid separation of the hydrolyzed biomass or of the hydrolyzed biomass subsequently treated in one or more other reactors or means located downstream of the enzymatic hydrolysis reactor c) to obtain an unconverted solid residue, -e) means for recycling at least part of the unconverted solid residue to the impregnation reactor a) and / or the digestion reactor b), - h) A reactor for burning the unconverted solid residue obtained at the end of the biomass treatment, called final solid residue, which generates heat for use in the steps of the process requiring heating.

11. A device as claimed in the preceding claim, characterised in that The impregnation reactor a) and the cooking reactor b) are provided with a feed device, and wherein the recirculation device comprises a fluid connection device between the solid / liquid separation device and at least one of the feed devices for conveying the unconverted solid residue from the separation device to the feed device or at least one of the feed devices.

12. Use of a process as claimed in any one of claims 1 to 9 for the treatment of lignocellulosic biomass such as wood, straw, agricultural residues, papermaking residues and all dedicated energy crops, in particular annual or perennial plants such as Miscanthus, to produce sugars, alcohol biofuels or bio-based molecules.

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