Process for treating lignocellulosic biomass

Abstract

The invention relates to a process for treating lignocellulosic biomass, comprising - a) a step of impregnating the biomass with a liquor to obtain impregnated biomass - b) a step of cooking the impregnated biomass, optionally accompanied by a steam explosion, to obtain pre-treated biomass - c) a step of enzymatic hydrolysis of the pre-treated biomass, to obtain hydrolyzed biomass in the form of sugar(s) - d) a solid / liquid separation step of the hydrolyzed biomass in the form of sugar(s) or of the hydrolyzed biomass in the form of sugar(s) and then treated in one or more further steps subsequent to step c) of enzymatic hydrolysis, in order to obtain a separated juice and an unconverted solid residue, - e) a step of recycling at least a part of said unconverted solid residue from step a) of impregnation and / or step b) of cooking. Figure for the abridged version: Fig. 1

Description

Title of the invention: Process for treating lignocellulosic biomass technical field

[0001] The invention relates to a process for treating lignocellulosic biomass to produce so-called second-generation (2G) sugar juices. These sugar juices can be used to produce other products by biochemical means, in particular by fermentation (for example, alcohols such as ethanol, butanol), or other molecules, for example, solvents such as acetone, etc. Previous technique

[0002] Lignocellulosic biomass represents one of the most abundant renewable resources on Earth. The substrates considered are very varied, including woody substrates such as different types of wood (hardwood and softwood), by-products from agriculture (wheat straw, corn cobs, etc.) or other agri-food and paper industries, lignocellulosic waste, etc.

[0003] The lignocellulosic biomass treatment process generally comprises - a pretreatment of the biomass by cooking, possibly coupled with a steam explosion, and generally preceded by impregnation of the biomass with an acidic, basic, neutral or oxidizing liquor, - an enzymatic hydrolysis, leading to the production of sugary juices, generally based on C5 and C6 sugars (i.e. sugars with 5 or 6 carbons), - and possibly a fermentation of these sugars by a yeast, to convert them into alcohol of the ethanol type. The process also includes steps for separating and / or purifying the target final product (sugar, alcohol, solvent...).

[0004] Lignocellulosic biomass is composed of three main polymers: cellulose (35 to 50% by weight), which is a polysaccharide essentially made up of hexoses; hemicellulose (20 to 40% by weight), which is a polysaccharide essentially made up of pentoses; and lignin (10 to 30% by weight), which is a complex, high molecular weight polymer composed of aromatic alcohols linked by ether bonds. These different molecules are responsible for the intrinsic properties of the plant cell wall and are organized into a complex network. Of the three basic polymers that incorporate lignocellulosic biomass, cellulose and hemicellulose are those that enable the production of 2G sugar juices.

[0005] Most often, hemicellulose is mostly decomposed into sugar during pretreatment, and cellulose is converted into sugar (glucose) by hydrolysis enzymatic. However, access to raw cellulose remains difficult for enzymes, hence the need for pretreatment. This pretreatment modifies the physicochemical properties of lignocellulosic biomass to improve cellulose accessibility to enzymes and its reactivity to enzymatic hydrolysis.

[0006] Numerous technologies relevant to the invention exist for carrying out this pretreatment, which will hereafter be grouped under the generic term "cooking": acid cooking, alkaline cooking, autohydrolysis cooking, steam explosion, and so-called "organosolv pulping" processes (or organo-solvent treatment in French). This last process involves pretreatment in the presence of one or more organic solvents and generally water. The solvent can be an alcohol (ethanol), an acid such as acetic acid or formic acid, or even acetone. Organosolv pulping processes lead to at least partial solubilization of the lignin and partial solubilization of the hemicelluloses. Two output streams are then produced: the substrate pretreated with residual cellulose, hemicellulose, and lignin, and the solvent phase containing the solubilized lignin and some of the hemicelluloses.There is generally a solvent regeneration step that allows for the extraction of a lignin stream. Some organosolv pulping treatments (particularly those using ethanol) are coupled with the addition of a strong acid (such as H2SO4). It is also possible to consider contacting the biomass with the solvent via an impregnation reactor before the cooking phase, or contacting the biomass with the acid catalyst before performing organosolv pulping.

[0007] Different configurations are reported for example in the document “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 document “Bioethanol production from agricultural wastes: an overview”, N. Sarkar, S. Kumar Ghosh, S. Bannerjee, K. Aikat, Renewable Energy 37 (2012) 19-27.

[0008] One of the most effective pretreatments is steam blasting, particularly under acidic conditions, which allows for almost complete hydrolysis of hemicellulose and a significant improvement in the accessibility and reactivity of cellulose to enzymes. This pretreatment may be preceded by other treatment(s).

[0009] US patents 8057639 and 8512512 describe a process comprising a first step of hydrolyzing hemicellulose into C5 sugars under mild conditions, thus preserving them from degradation. This step is carried out in a first reactor under a pressure of 1.5 bar (0.15 MPa) or more, by steam injection, at a temperature of 110°C or more, and optionally in the presence of a weak acid. After this step, a washing process is performed to extract and recover the sugar juices from the hemicellulose (generally C5 and C6 sugars, the proportion of which is (relative depends, in particular, on the nature of the biomass) before sending the remaining biomass, enriched in cellulose and lignin, to a second stage (second reactor) where the steam explosion takes place. This second reactor operates at a higher pressure than the first reactor with a high-pressure steam injection that causes a sudden expansion of the biomass (steam explosion).

[0010] Whenever a treatment requires a pressure step (impregnation, pretreatment such as cooking, or other), it is necessary to use means of introducing solid biomass that are compatible with these pressure steps. This is the case, for example, with compression screws, one embodiment of which is described in US patent 4,599,138.

[0011] French patent FR 3 075 203 describes a process involving impregnating biomass with an acidic liquor, followed by cooking and steam explosion of the impregnated biomass, with adjustment of the acidity of the acidic liquor and its recycling. French patent FR 3 075 201 also describes a process for pretreating biomass by acid impregnation followed by steam explosion, further involving washing the reactor feed means and recycling the wash water into the process.

[0012] These different types of process, starting from lignocellulosic biomass, generate solid residues based on lignin, in particular after enzymatic hydrolysis, and / or after fermentation if the conversion of sugars into alcohol is continued in particular. These solid residues, which we will refer to in this text as "unconverted solid residue" or "lignin cake," are rich in lignin, which reacts little or not at all to the enzymes used for biomass hydrolysis, generally cellulases and hemicellulases. These woody residues can be used, notably as fuel, or incorporated as filler in resin- or bitumen-based products, for example. However, these unconverted residues are not composed solely of lignin (besides a certain amount of water): they can also contain hemicellulose and / or cellulose that did not react with hydrolysis. Removing these residues from the biomass conversion process means losing these unreacted polymeric sugar fractions, which impacts the biomass conversion yield into sugar (or alcohol).

[0013] It has already been proposed to reuse these types of solid residues in the biomass treatment process: patent EP 2 516 661 proposes a biomass treatment process with pretreatment of the biomass in an alkaline medium, enzymatic hydrolysis, fermentation of the resulting hydrolysate to obtain a fermentation mash containing an alcohol, separation / purification of the alcohol, and separation of a residue cake. This residue cake is sent to a separate cellulose regeneration reactor where the cake is mixed with an alkaline solution and heated before being recycled downstream of the pretreatment. This solution is interesting, Because it chooses to recover the remaining cellulose contained in this woody cake, to reintegrate it into the process, in order to increase the overall biomass conversion yield. However, it requires separate treatment of this cake, with an additional dedicated reactor that will perform an alkaline cooking of the cake before recycling it, which increases the installation and operating costs of the entire process, and increases the complexity of its implementation.

[0014] Another solution was proposed in patent EP 2 430 171, quite close to the previous one, but providing for an acidic rather than alkaline cooking of the woody residue, with the same disadvantages.

[0015] The invention aims to overcome these drawbacks. The invention aims to improve the processing of lignocellulosic biomass. More specifically, it aims to increase biomass conversion yields, particularly in a more efficient manner than with prior solutions. Summary of the invention

[0016] The invention relates firstly to a process for treating lignocellulosic biomass, said process comprising - a) a step of impregnating the biomass with a liquor, in particular an acidic one, to obtain impregnated biomass - b) a cooking stage of the impregnated biomass, possibly accompanied by a steam explosion, to obtain pre-treated biomass - c) an enzymatic hydrolysis step of the pretreated biomass, to obtain hydrolyzed biomass in the form of sugar(s); said process also includes - d) a solid / liquid separation step of the biomass hydrolyzed in the form of sugar(s) or of the biomass hydrolyzed in the form of sugar(s) and then treated in one or more further steps subsequent to step c) of enzymatic hydrolysis, in order to obtain a separated juice and an unconverted solid residue, - e) a recycling step of at least part of said solid residue not converted in step a) of impregnation and / or step b) of cooking.

[0017] For the purposes of the present invention, the term "unconverted solid" residue means a residue comprising at least 20% by weight of solids, in particular at least 30% or 35% by weight of solids. The solids content can be measured by its dry matter (DM) content, which is measured according to ASTM E1756-08(2015) "Standard Test Method for Determination of Total Solids in Biomass". The DM content of the unconverted solid residue according to the invention is preferably at least 20%, 30%, or 35%.

[0018] The impregnation liquor may comprise a chemical compound such as an acid, a base or an oxidizing agent or a water-based liquor, with autohydrolysis of the biomass naturally releasing an acid, in particular acetic acid.

[0019] The invention therefore chooses to recycle the unconverted solid residue which is obtained by solid liquid separation, either after enzymatic hydrolysis (separation on sugar juice), or after fermentation (separation on alcoholic juice), by reintroducing it into the impregnation step or into the cooking step constituting the pretreatment of the biomass before its enzymatic hydrolysis. What is specific to the present invention is that the unconverted solid residue can be directly reintroduced into a pretreatment step, without a specific operation such as dedicated impregnation / cooking for this residue: thus, a significant increase in yield (in sugar or alcohol) is obtained, without having to invest in additional energy-intensive equipment such as a cooking reactor.

[0020] It was thus found, surprisingly, that reintroducing this residue into the impregnation or cooking device, along with the biomass being processed, made it possible to extract from this residue at least some of the cellulose and / or hemicellulose retained therein, the enzymatic hydrolysis reaction not allowing the total conversion of these compounds, - and to convert them at least in part by making them follow again the path of "fresh" biomass in its pretreatment and then enzymatic hydrolysis stages, which, in fact, ultimately increases the production of sugars (or alcohol) from the process. What is also surprising is that the addition of this residue to the rest of the biomass being processed did not in fact raise any problems in the operation of the pretreatment tools: whether this residue was added to the biomass in the impregnation stage or in the cooking stage, it did not complicate the proper functioning of the devices used, whereas one might have feared that the addition of this residue with a texture very different from that of the biomass would lead to problems of fouling of the devices, problems of the residue being carried from one device to another or within a device etc... This was not the case.

[0021] Another highly advantageous effect of the invention is that the ultimate unconverted residue obtained at the end of production is depleted in cellulose / hemicellulose and enriched in lignin compared to a residue that has not undergone recycling according to the invention: this ultimate residue thus has a higher calorific value, making it more efficient as a fuel for generating heat via a combustion step. The heat produced can be used in the process in one or more steps requiring the heating of a fluid (liquefaction). impregnation), a reactor (cooking during pretreatment) or reboiler of a distillation column (to purify alcohol obtained by fermentation...).

[0022] According to one embodiment, the process according to the invention aims at the production of sugar juice only, the separation step d) being carried out on the sugar juice at the exit of the enzymatic hydrolysis.

[0023] According to another embodiment, the process aims to transform all or part of the sugar juice obtained by enzymatic hydrolysis. It may then also include: - a step f) of fermenting the hydrolyzed biomass in the form of sugar(s), in order to obtain a fermented biomass comprising at least one alcohol, the step d) of solid / liquid separation being carried out on said fermented biomass.

[0024] In this latter mode, according to the invention, it is possible to recycle both the unconverted residue at the end of enzymatic hydrolysis and at the end of fermentation:

[0025] The enzymatic hydrolysis steps c) and fermentation steps f) can be carried out simultaneously on the pretreated biomass; this is then referred to as SSF, for the acronym of the English term "Simultaneous Saccharification and Fermentation," or SSCF, for the acronym of the English term "Simultaneous Saccharification and Co-Fermentation." They can also be carried out one after the other, in separate reactors, for example.

[0026] The method according to the invention may also include: - a step g) of separation or purification, in particular distillation, of the fermented biomass, the step d) of solid / liquid separation being carried out before or after said step g) of separation or purification. Performing separation d) before step g), when step g) is a distillation, is advantageous because it avoids introducing a liquid phase containing this residue, which could clog the column or at least impair its operation. However, it can also be beneficial to perform separation d) according to the invention after the separation / purification of the fermented biomass, since the solid residue may contain an alcohol fraction, and passing it through the separation / purification step can allow the extraction of at least some of this alcohol fraction trapped in the solid residue.

[0027] As mentioned above, the process according to the invention may also include: - a step h) of combustion of the ultimate unconverted solid residue obtained at the end of the biomass treatment, the heat produced of which is used in a step of said process requiring heating, in particular the heating of a fluid, in particular in the step d) of cooking or a step g) of separation by distillation. The ultimate residue obtained with the invention has an improved calorific value, due to a lower content of cellulose / hemicellulose, which are polymeric sugars with low calorific value, unlike lignin.

[0028] Optionally, step h) of combustion may be preceded by a step i) of drying the residue, in particular so that the residue reaches a water content below a given threshold, for example less than or equal to 40% by weight, in particular less than or equal to 30% by weight.

[0029] The solid / liquid separation step d) can be 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 centrifugation, decantation, spin dryer device or a combination of different devices.

[0030] Advantageously, step a) of impregnating the biomass with a liquor and step b) of cooking the impregnated biomass can be carried out by 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 with the biomass being treated into said feeding device(s).

[0031] At least one of the feeding devices can thus be a feed screw, in particular at least partially conical, comprising a casing with a cage having openings that allow the extraction of the solid-liquid residue from the biomass and possibly the circulation of a washing fluid. This compression screw (also called a "plug screw" in Anglo-Saxon terminology), in a known manner, creates a hermetic plug of biomass in the downstream portion of the screw, which creates compression on the biomass resulting in a pressure difference between the biomass inlet and outlet of the screw. However, any other known device can be used. For the impregnation step, a reactor operating continuously or in batches can be used, or other means than a dedicated reactor, in particular a conveyor belt that is sprayed with liquor, etc.

[0032] The unconverted solid residue obtained in step d) of solid / liquid separation contains, in addition to water, a major compound in the form of lignin, and minor compounds including cellulose and / or hemicellulose and possibly one or more alcohols of the ethanol type when the solid / liquid separation d) is carried out after a step f) of fermentation.

[0033] The unconverted solid residue obtained in step d) of solid / liquid separation may contain, for example, between 40 and 70 wt% water, in particular between 50 and 60 wt% water, between 2 and 35 wt% cellulose, in particular between 5 and 20 wt% cellulose, and between 0 and 15 wt% hemicellulose, in particular between 1 and 10 wt% hemicellulose. It may also include other minor compounds, such as ash. The different levels of lignin, cellulose and hemicellulose can indeed vary, particularly depending on the type of biomass used and its reactivity during enzymatic hydrolysis.

[0034] Step e) of recycling the unconverted solid residue reduces the content of at least one of its minor compounds, cellulose and hemicellulose, in the final solid residue obtained at the end of the biomass treatment, and increases its calorific value, which is beneficial both for the biomass conversion yield and for the thermal integration of the process.

[0035] The dry basis composition of the ultimate solid residue obtained at the end of biomass processing generally comprises mostly lignin, and less than 20% DM of cellulose and less than 8% DM of hemicellulose.

[0036] The treatment process referred to in the invention can convert lignocellulosic biomass into sugar juice, in particular C5 and C6 juices, after enzymatic hydrolysis, or into alcohol(s), in particular ethanol, after fermentation of said sugar juice.

[0037] The invention also relates to any installation implementing the process described above.

[0038] The invention also relates to an installation, in particular for implementing the process described above, which comprises: - a) an impregnation device, in particular an impregnation reactor, for the biomass using a liquor, in particular an acidic liquor, to obtain impregnated biomass; - b) a reactor for cooking the impregnated biomass, possibly accompanied by a steam explosion, to obtain pre-treated biomass - c) an enzymatic hydrolysis reactor for pre-treated biomass, to obtain hydrolyzed biomass said installation including also - d) a solid / liquid separation device for hydrolyzed biomass or for biomass that is hydrolyzed and then treated in one or more other reactors or devices located downstream of reactor c) for enzymatic hydrolysis, in order to obtain an unconverted solid residue, - e) means of recycling at least part of said unconverted solid residue in reactor a) impregnation and / or in reactor b) cooking.

[0039] The means of recycling the unconverted solid residue are conventional, and may include any suitable conveying system (for example by conveyor, screw, hopper or belt).

[0040] The installation according to the invention advantageously comprises reactors a) for impregnation and b) for cooking, which are equipped with feeding devices, and the recycling means comprise fluidic connection means between the a solid / liquid separation device and at least one of said feeding devices to convey the unconverted solid residue from the separation device to the feeding device(s). The introduction of the unconverted solid residue and that of the biomass being processed into the feeding device (or directly into the reactor concerned) may be carried out jointly or via different introduction points, or not simultaneously.

[0041] The invention also relates to the use of the process or installation described above for the treatment of 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 sugars, alcohol-type biofuels or bio-based molecules.

[0042] The invention will be described in detail below, with the aid of figures and non-limiting examples.

[0043] List of figures [Fig. 1] Figure 1 is a schematic representation of a first variant of a lignocellulosic biomass conversion plant where the process according to the invention can be applied. [Fig.2] Figure 2 is a schematic representation of a second variant of a lignocellulosic biomass conversion plant where the process according to the invention can be applied. [Fig.3] Figure 3 is a schematic representation of a third variant of a lignocellulosic biomass conversion plant where the process according to the invention can be applied. [Fig.4] Figure 4 is a schematic representation of a lignocellulosic biomass conversion plant applying the invention. Note that the same references concern the same flow, the same device, from one figure to the other. The description of the references is presented below: 1: Water enters the liquor preparation tank 2: Acid enters the liquor preparation tank 3: Tool (tank) for preparing the liquor 4: Acidic liquid to impregnation tool (reactor) 5: Crushed biomass 6: Impregnation tool feeding device 7: Wash water from the plug-screw feeder of the impregnation tool 8: Wash liquid outlet from the "plug screw feeder" 6 of the impregnation tool 9: Impregnation tool (reactor) 10: Impregnated and drained biomass 11: Pretreatment tool feeding device 12: Wash water from the "plug screw feeder" of the pretreatment tool 13: Pressing the "plug screw feeder" of the pretreatment tool 14: Pretreatment cooking tool (explosion reactor) 15: Steam injection for pretreatment 16: Pre-treated biomass and steam 17: Steam and pre-treated biomass separation tool (cyclone) 18: Steam 19: Pre-treated biomass 20: Enzymatic hydrolysis reactor 21: Hydrolysate containing sugars 22: Alcoholic (ethanolic) fermentation reactor 23: Fermented wine containing ethanol (alcohol) 24: Ethanol recovery device, for example, distillation column(s) 25: Concentrated alcohol 27: Solid (lignin) / liquid separation, for example a filter press 28: Liquid residue (vinasse) 29: Unconverted solid residue (lignin cake) 30: Clarified fermentation wine (without solids) 31: Clarified hydrolysate (without solids) Description of the implementation methods

[0044] The invention proposes recycling the unconverted solid residue from the process of converting lignocellulosic biomass into sugars or alcohols. This residue is composed mainly of lignin, a compound not converted during the process. This residue is generally separated for incineration in conventional biorefineries; lignin can also be used as a compound of interest for specialty products (resins, bitumen, etc.). The invention proposes recycling this compound upstream in the process, because the extracted lignin is not pure: it contains a fraction of unconverted polymeric sugars (cellulose and / or hemicellulose). Recycling these sugar polymers then makes it possible to increase the process yield.

[0045] The invention relates to the recycling of at least part of a solid residue, referred to as "lignin cake" or "unconverted solid residue" in this text. This solid is advantageously recycled in the pretreatment stage under normal conditions (e.g. acid) of lignocellulosic biomass, to increase its reactivity in the downstream enzymatic hydrolysis stage. Its direct recycling in a step such as enzymatic hydrolysis or SSCF is less technically relevant, because the access of enzymes to cellulose will not be improved, or not enough for the biomass conversion yield to be significantly improved and / or for the ultimate residue to have a calorific value that is significantly improved compared to no recycling, or at least much less so than with the invention.

[0046] Lignin is one of the major compounds of lignocellulosic biomass (up to 30% DM). In a lignocellulosic biomass conversion process that recovers sugars (cellulose and hemicellulose), the lignin cake is a co-product of the process which is composed of water (water can represent 50% to 60% wt of the cake) and solids from the biomass and not converted during the process, namely mainly lignin but also cellulose and hemicellulose.

[0047] Thus, Table 1 below indicates the flow rate entering the process and the composition of a typical example of biomass (wheat straw) to be treated and of a lignin cake obtained after separation at the end of the alcohol production line:

[0048] [Tables 1] Solid unconverted biomass Flow rate kg / h 100 67 Water %wt 10 60 Cellulose %wt 34 8 Hemicellulose %wt 27 3 Lignin %wt 15 22 Other %wt 14 7

[0049] And Table 2 below indicates, for the same biomass and the same lignin cake, their flow rates and composition of solid compounds, expressed here as dry matter content (DM): [Tables 2] Solid Unconverted Biomass Flow Rate kg / h 100 67 DM %wt 90 40 Cellulose %DM 38 20 Hemicellulose %DM 30 8 Lignin %DM 17 55 Other %DM 16 17

[0050] These tables show that two unconverted sugar polymers (cellulose and hemicellulose) are present in the lignin cake, totaling 1 1% wt% (or 28% DM). The invention recycles at least a portion of the lignin cake (unconverted solid) to convert these polymers and thus increase the process yield, since 11% of the polymer sugars from the biomass are found in the unconverted solid, without adding a dedicated processing step for this lignin cake.

[0051] Furthermore, the calorific value of the lignin cake (measured by the Higher Heating Value (HHV) of the unconverted solid residue) increases if the sugar polymers it contains are converted. This is because sugar polymers contain oxygen molecules that decrease the average HHV of the solid.

[0052] Examples of operating conditions for key stages of biomass processing are briefly recalled below:

[0053] The process Below is a more detailed description of the different key steps of a biomass conversion process using such an installation and to which the invention can advantageously be applied: (this is an example to which the invention is not limited).

[0054] Conditioning step of lignocellulosic biomass The treatment process begins with a conditioning stage for the lignocellulosic biomass, involving at least one grinding to obtain biomass particles no larger than 300 mm. Several successive grinding stages are, of course, possible to achieve the desired particle size. Generally, the ground biomass has a particle size (the largest size) of no more than 300 mm, most often at least 1 mm, and frequently between 2 and 200 mm. Any method known to those skilled in the art can be used to carry out this stage. Straw is usually ground using screens with a mesh size of 5 to 100 mm. Wood is generally chipped into parallelepiped-shaped pieces with a length between 20 and 160 mm, a width between 10 and 100 mm, and a thickness between 2 mm and 10 mm. and 20 mm. The ground lignocellulosic biomass is brought to the next stage by any means known to those skilled in the art, in particular a transfer screw.

[0055] Impregnation step with an acidic liquid

[0056] The treatment process according to the invention includes a step a) of impregnating the lignocellulosic substrate with an acidic liquor so as to obtain an impregnated lignocellulosic substrate having a pH between 0.1 and 3. This step aims to prepare the lignocellulosic substrate for the pretreatment step.

[0057] The impregnation is carried out in an impregnation reactor at a temperature between 10 and 90°C and preferably at atmospheric pressure. The residence time of the lignocellulosic substrate in the impregnation reactor is usually from 10 seconds to 180 minutes, preferably between 30 seconds and 60 minutes, and even more preferably between 30 seconds and 15 minutes. Preferably, the impregnation step is carried out in a single step.

[0058] The impregnation reactor or impregnator is equipped with one or more screws that transfer the lignocellulosic substrate from its inlet to the outlet. The impregnator is also equipped with one or more lines for supplying the acidic liquor and, if necessary, one or more lines for withdrawing the acidic liquor. These inlet and outlet lines for the acidic liquor are generally installed to operate in co-current or counter-current recirculation.

[0059] The acid liquor is an aqueous solution of a strong acid, which is for example chosen from sulfuric acid, hydrochloric acid, nitric acid, for example at an acid content of between 0.5 and 4% by weight.

[0060] Solid / liquid separation step on the lignocellulosic substrate impregnated with acidic liquor The lignocellulosic substrate impregnated with acid liquor is subjected to a solid / liquid separation step to obtain a lignocellulosic substrate with a dry matter content between 15% and 70% by weight and a spent acid liquor. Preferably, the lignocellulosic substrate impregnated with acid liquor is first drained to remove at least some of the free acid liquor before being treated by solid / liquid separation.

[0061] The solid / liquid separation step can implement any technique known to those skilled in the art, which may be, for example, decantation, centrifugation or pressing.

[0062] Preferably, the lignocellulosic substrate is pressed concurrently with its transfer to the pretreatment step when the latter employs the steam explosion process described below. This method of conducting the step is, for example, ensured by a compression screw called a "plug screw feeder" of which The operation has already been described above. The formation of a plug of pressed lignocellulosic substrate ensures the pressure-tightness of the steam explosion reactor, thus preventing dangerous steam leaks. The transfer screw is also equipped with one or more withdrawal lines for the spent liquor (called pressate) separated during pressing. The pressate can be recycled during the impregnation and / or washing stages by the washing liquid 12 passing through the feed screw 11.

[0063] The wet biomass obtained at the end of the solid / liquid separation step, which can be designated by the term "washed and acidified lignocellulosic substrate", has a dry matter content preferably between 15% and 70% by weight, and more preferably between 40% and 65% by weight.

[0064] Pretreatment step of the washed and acidified lignocellulosic substrate

[0065] The washed and acidified lignocellulosic substrate undergoes a pretreatment step.

[0066] Cellulose (and possibly hemicelluloses), which are the targets of enzymatic hydrolysis, are not directly accessible to enzymes. This is why a pretreatment of the biomass is carried out before the enzymatic hydrolysis step. The pretreatment aims in particular to modify the physical and physicochemical properties of the cellulosic fraction, such as its degree of polymerization and its state of crystallinity.

[0067] Various types of pretreatment are known to those skilled in the art; they combine chemical and thermal treatments. Examples include acid or basic baking, the organosolv process, ionic liquid treatments, and the steam explosion process.

[0068] The preferred pretreatment process is steam explosion (or "SteamEx" or "Steam Explosion" in Anglo-Saxon terminology) carried out in an acidic medium. This process involves rapidly heating the lignocellulosic substrate to a high temperature by injecting pressurized steam. The treatment is stopped by abrupt decompression.

[0069] The operating conditions of the steam explosion process are as follows: the steam is injected directly into the reactor; The reactor temperature is generally between 150 and 220°C, preferably between 170°C and 210°C. The pressure is between 5 and 25 bar absolute (0.5 and 2.5 MPa), more preferably between 8 and 19 bar absolute (0.8 to 1.9 MPa), the residence time before the expansion phase varies from 10 seconds to 50 minutes, and preferably between 3 minutes and 30 or 40 minutes.

[0070] The steam explosion can be carried out in batch or continuous operation, and the depressurization step which allows the biomass to be broken down can take place in one or more steps.

[0071] At the end of the pretreatment step by steam explosion, a pretreated lignocellulosic substrate with a high dry matter content, generally between 20 and 70% by weight, and a vapor phase that can be condensed are obtained.

[0072] Following steam explosion under acidic conditions, the pretreated lignocellulosic substrate generally has a pH lower than that compatible with the medium for enzymatic hydrolysis. Therefore, the lignocellulosic substrate is subjected to a neutralization step to bring its pH to a value between 4 and 6.

[0073] For the neutralization step, an aqueous solution containing a neutralizing agent is used. This neutralizing agent can be chosen from any weak or strong base known to those skilled in the art. By the term "base," we mean any chemical species that, when added to water, gives an aqueous solution with a pH greater than 7. Preferably, the neutralizing agent is chosen from potassium hydroxide, sodium hydroxide, ammonia, or lime. Even more preferably, the neutralizing agent is chosen from potassium hydroxide and ammonia, alone or in combination. Preferably, the neutralizing agent is used in aqueous solution, with a mass concentration between 2% and 75%, and even more preferably between 20% and 70%.

[0074] Neutralization is carried out at a temperature between 15°C and 95°C, and preferably between 20°C and 70°C. In general, the temperature of the neutralization step is not precisely controlled and is simply governed by the heat released by the acid-base neutralization reaction.

[0075] The neutralization step can be carried out continuously, discontinuously or in fed-batch mode.

[0076] It should be noted that an optional washing step may be carried out before or after the neutralization step, on all or part of the pre-treated lignocellulosic substrate.

[0077] If a wash is applied, a liquid stream is brought into contact with the pretreated lignocellulosic substrate, and then the liquid is separated from the solid. The washing step can be carried out by percolation, by successive liquid / solid mixing and separation operations, by belt filter washing, or by any other technique known to those skilled in the art. The washing liquid used can be water or a process stream. The mass ratio between the added washing liquid and the liquid contained in the substrate to be washed is generally between 0.5 and 4. The washing step generates a sugary wash liquid containing some of the hemicelluloses solubilized during the pretreatment. This wash liquid can, for example, be used as a carbon source for the production of biocatalysts (enzymes and / or microorganisms). The washing step is generally carried out at a temperature between 10°C and 95°C.

[0078] Enzymatic hydrolysis step

[0079] The pre-treated lignocellulosic substrate, optionally neutralized and washed, is sent to the enzymatic hydrolysis step of the process.

[0080] The pre-treated lignocellulosic substrate which is sent to the enzymatic hydrolysis step has a dry matter content generally between 15% and 70% by weight.

[0081] The objective of enzymatic hydrolysis is to hydrolyze (depolymerize), by means of biocatalysts, hemicelluloses and cellulose into fermentable sugars, preferably glucose.

[0082] The enzymatic hydrolysis step is carried out under mild conditions, at a temperature of approximately 40°C to 55°C, preferably between 45°C and 50°C, and at a pH of 4.0 to 5.5, and even more preferably between 4.5 and 5.2. The dry matter content of the enzymatic hydrolysis medium is between 2 and 45% by weight, preferably between 10 and 30% by weight. It is performed using enzymes produced by a microorganism. Natural or genetically modified microorganisms, such as fungi belonging to the genera Trichoderma, Aspergillus, Penicillium, or Schizophyllum, or anaerobic bacteria belonging, for example, to the genus Clostridium, produce a cocktail of enzymes containing, in particular, cellulases and hemicellulases, adapted to the extensive hydrolysis of cellulose and hemicelluloses.

[0083] Enzymatic hydrolysis can be carried out in continuous or batch mode, or in continuous-feed mode, in one or more reactors. The residence time is between 5 and 200 hours, and preferably between 24 and 120 hours, and even more preferably between 48 and 120 hours.

[0084] At the end of the step, a hydrolysate containing fermentable sugars is recovered from the bioreactor and is then treated in the fermentation step.

[0085] It should be noted that the hydrolysate obtained may optionally undergo one or more treatment steps before the fermentation step. For example, this may involve pH adjustment, partial purification to limit the content of the compound that inhibits the fermenting microorganism, or at least partial separation of the solid residues contained in the hydrolysate (and thus obtain the unconverted solid residue to be treated according to the invention).

[0086] Fermentation stage of the hydrolysate, when one wants to continue the conversion of the sugars obtained into alcohol(s)

[0087] Depending on the stage of the solvent and / or alcohol production process, the hydrolysate, if treated, is sent to the fermentation stage, which allows the conversion of fermentable sugars into the solvent and / or alcohols of interest by means of one or more microorganisms of different kinds. Fermentation methods are known to those skilled in the art and are described in particular in document US 8,456,633.

[0088] The term "solvent" is meant to designate organic compounds other than alcohols, for example organic compounds having a ketone function such as acetone.

[0089] The term "alcohol" refers in particular to ethanol, propanol, isopropanol and butanol.

[0090] Natural or genetically modified microorganisms can be chosen for example from Saccharomyces cerevisiae, Schizosaccharomyces pombe, Saccharomyces uvarum, Saccharomyces diastaticus, Kluyveromyces fragilis, Candida shehatae, Pichia stipitis, Pachysolen tannophilis or the bacteria Zymomonas mobilis, Clostridium acetobutylicum, Escherichia coli.

[0091] In the context of the invention, the fermentation step allows, for example, the production of ethanol alone or in a mixture with butanol, propanol, isopropanol and / or acetone. For example, the fermentative microorganism may be capable of producing a mixture called "ABE (acetone-butanol-ethanol)" or "IBE (isopropanol-butanol-ethanol)".

[0092] Preferably, the chosen microorganism is a natural or genetically modified yeast of the genus Saccharomyces capable of producing ethanol.

[0093] At the end of the step, a fermentation broth diluted in products of interest is recovered.

[0094] According to one embodiment of the process, the hydrolysis and fermentation steps can be carried out simultaneously in at least one bioreactor so that enzymatic hydrolysis and fermentation are conducted simultaneously according to a process designated by the term "Simultaneous Saccharification and Fermentation (SSF)". When the hydrolysis step is combined with the fermentation step, the operating conditions, particularly temperature, can be adapted to suit the tolerances of the fermenting microorganism. For example, the temperature can be lowered to between 28°C and 45°C, and preferably between 30°C and 35°C when the fermentation is carried out with a yeast of the genus Saccharomyces.The pH is preferably adjusted between 5 and 5.5 to promote yeast performance.

[0095] The production unit implementing the process according to the invention may include, in addition to the installations already described, in situ production units for enzymes and / or yeasts.

[0096] Step of separating solvents and / or alcohols from the fermentation must.

[0097] The process according to the invention finally comprises a step of separating the product(s) of interest from the fermentation must, which is preceded or followed by a solid / liquid separation step in order to remove at least a fraction of the solid matter contained in the fermentation must, and to produce the unconverted solid residue which will be treated according to the invention.

[0098] Preferably the step of separating the product(s) of interest, for example ethanol, implements one or more distillations which is a technology well known to those skilled in the art.

[0099] The load: lignocellulosic biomass According to the invention, the process feed can be biomass alone or in mixtures. The amount of water contained in the raw feed is generally at least 10%, in particular between 10 and 70% by mass. Raw biomass is selected from all types of biomass, preferably solid biomass, and in particular lignocellulosic biomass. Non-limiting examples of biomass types include agricultural residues (notably straw, corn cobs), forestry residues, forestry products, sawmill residues, and dedicated crops such as short-rotation coppice. Preferably, raw biomass, also called native biomass, is lignocellulosic biomass. It essentially comprises three natural constituents present in varying quantities depending on its origin: cellulose, hemicellulose and lignin. Lignocellulosic biomass feedstock is preferably used in its raw form, that is to say in the entirety of its three constituents: cellulose, hemicellulose and lignin.

[0100] In a preferred embodiment of the invention, the lignocellulosic biomass is chosen from grass biomass, agricultural residues such as straw waste, corn cobs, sugar cane bagasse, forestry or sawmill residues such as wood chips or any other type of woody residue.

[0101] The impregnation fluid: The optional fluid injected for impregnation is an aqueous liquid solution, with or without acid, at a temperature between 10 and 95°C and at atmospheric pressure. The pH of this chemical solution is between 0.1 and 12.0, preferably between 0.1 and 7, and more preferably between 0.3 and 2. In a preferred embodiment, the solution used is an acid-catalyzed solution, and its pH is set between 0.1 and 4, in particular between 0.3 and 2. For example, at least one acid may be used, selected from sulfuric acid, hydrochloric acid, nitric acid, or oxalic acid. Their concentration in the aqueous phase is preferably between 0.2 and 8% by weight.

[0102] The invention applies similarly to different processes and installations, in particular to: - facilities that are solely intended for sugar production, and therefore do not involve alcoholic fermentation, - installations that provide for pretreatment by cooking without prior impregnation with a liquid (auto-hydrolysis for example), - installations which provide for pretreatment by cooking with prior impregnation by a non-acidic liquor.

[0103] Fig. 1 represents in a very schematic way a non-limiting variant of a lignocellulosic biomass conversion plant in which the invention can be applied, plant which provides for a pretreatment of the biomass including impregnation with an acidic liquor then steam cooking / explosion, then enzymatic hydrolysis followed by alcoholic fermentation, to transform the biomass into ethanol.

[0104] Fig. 1 therefore represents a biomass conversion carried out as follows: the crushed biomass 5 (impregnated or not with a catalytic liquor) is introduced into an impregnation reactor 9 by a feeding device 6. This can be a pressurized feeding means, for example a screw, also called in English "Plug Screw Feeder", the terminal portion of which is conical, which has a fairing with a draining grid, a wash water inlet 7 and a wash water outlet 8. A hermetic plug of biomass is created in the downstream portion of the screw, which creates a compression on the biomass resulting in a pressure difference between the biomass inlet and the biomass outlet of the screw of at least 0.05 MPa.The compression applied to the biomass can lead to the expulsion of some of the liquid contained in the biomass, particularly when the dry matter of the biomass is less than 80% before it enters the pressurized feeding means 6. The liquid thus extracted mixes with the wash water and is drawn off with the waste wash water 8. The impregnation reactor is also supplied with acid liquor 4 (water with added sulfuric acid) from a liquor preparation tank 3, itself supplied with acid 2 and water 1. The impregnated and drained biomass 10 exits reactor 9 to feed a steam explosion reactor 14 via another feeding device 11, for example, a compression type, like feeding device 6. In device 11, due to the compression exerted on the biomass, a liquid 13 resulting from this pressing, also called pressate, is recovered; this liquid is composed of water and acid. Device 11 is washed, using a dedicated inlet, by a washing liquid 12 (water and / or a recycled liquid, as seen later), which is then discharged through the outlet through which the pressate 13 is also discharged.

[0105] Reactor 14 is also supplied with steam 15. At the outlet of reactor 14, the biomass-steam mixture passes through a biomass 19 / steam 18 separation unit 17. The biomass 19 is then treated in an enzymatic hydrolysis reactor 20, and once hydrolyzed into sugars, the hydrolyzed biomass 21 (also called hydrolysis mash) passes into an alcoholic fermentation reactor 22. The biomass fermented into alcohol 23 (also called fermentation mash) is then fed into one or more distillation columns 24 to obtain concentrated alcohol 25 and crude vinasse 26, which are solid / liquid residues, mixed or separated depending on the arrangement of the columns 24. A solid / liquid separation is carried out by a filter-press type device 27, and a liquid residue 28 (the vinasse) is obtained at the outlet. a residue 29 which is the lignin cake of interest to the invention. This is just one example of an installation, which can also have many variations. For example, enzymatic hydrolysis and fermentation can be carried out simultaneously in the same reactor; this is then called SSCF for "Simultaneous Saccharification and Co-Fermentation" in English.

[0106] Fig. 2 is a variant of the process according to Fig. 1, where, all other things being equal, the solid / liquid separation by the filter press 27 is carried out on the fermenting wine 23 before the distillation column(s) 24: the lignin cake 29 is extracted, and the liquid residue, i.e. the fermented wine without solid residue, 30 is then brought into the distillation column(s) 24.

[0107] Fig. 3 is a variant of the process according to Fig. 2, where, all other things being equal, the filter-press type solid / liquid separation device 27 is arranged between the enzymatic hydrolysis reactor 20 and the fermentation reactor 22: here the separation is carried out on the hydrolysate 21 still unfermented, and the liquid part of the hydrolysate (sugar juice) 31 then goes into the fermentation reactor 22. In an unrepresented variant of the process according to [Fig.3], only the production of sweet juice 31 is targeted, the conversion of which by fermentation is not continued on the same production line.

[0108] In all these variants, the object of the invention is to treat the lignin cake 29, which is ultimately intended to be burned to produce energy.

[0109] Figure 4 represents two alternative or cumulative implementations of the invention, starting from the variant of Figure 1: - The lignin cake 29 is recycled at least in part (stream 29') into the feed device 6 of the impregnation reactor 9. This recycling before impregnation is advantageous, because the lignin cake 29 will be re-contacted with the impregnation liquor (acid) in reactor 9, which will help to extract the sugars residual polymers contained in the cake and subsequently make them react more easily during enzymatic hydrolysis. It might have been feared that the lignin cake would crumble and settle at the bottom of reactor 9, failing to be carried along with the biomass, but surprisingly this was not the case, even when the biomass was carried through the reactor from its injection point to its exit point by internal screws. - The lignin cake is recycled at least partially (stream 29”) into the feed device 11 of the steam-fired reactor 14. In this case, the lignin cake is not re-impregnated with liquor, but is carried along by the impregnated biomass - possibly part of the lignin cake (29'' stream) is not recycled: The lignin cake may only be partially recycled. At the end of production, the unrecycled cake (and ultimate residue) is stored to serve as fuel, either on the production line, or for other use off the production line, as fuel or to be incorporated into various products.

[0110] The same types of recycling apply analogously to lignin cakes according to the processes of Figures 1 and 3. Examples of completed projects [YES] Example 1 (comparative) This example, which is not in accordance with the invention, separates the unconverted solid 29 without recycling it. The biomass 5 is a lignocellulosic biomass, wheat straw. Its composition is shown in Table 3 below: [Tables 3] Cellulose 34% by weight, Hemicellulose 27% by weight, Lignin 15% by weight, Water 10% by weight, Other 14% by weight

[0112] The biomass is treated according to the process shown in [Fig. 2]. After hydrolysis, the cellulose is converted into glucose or glucose oligomers, and the hemicellulose is converted into xylose or xylose oligomers. The cellulose or hemicellulose yields are expressed as potential glucose or potential xylose.

[0113] The term "potential sugar" (xylose, glucose, for example) used later defines the sum of different sugars, regardless of their form: monomeric or polymeric sugar. Indeed, after pretreatment by cooking, some of the sugars remain in the form of sugar polymers (cellulose or hemicellulose, for example), and some of the sugars are in the form of sugar monomers (glucose or xylose, for example). This measurement can be performed using the ASTM E1758-01(2020) standard, "Standard Test Method for Determination of Carbohydrates in Biomass by High Performance Liquid Chromatography." As defined in the standard, to express this quantity of sugars in polymer form (cellulose, for example), the water from hydrolysis must be subtracted from this quantity.

[0114] The operating procedure is as follows: 642 kg / h of this biomass, ground to a size of 5 to 50 mm, enters the process, yielding 242.5 kg / h of potential glucose, 197 kg / h of potential xylose, and 96.3 kg / h of lignin. Since the process is designed to produce ethanol by fermentation, these potential sugar yields correspond to 224.6 kg / h of potential ethanol. The crushed biomass 5 enters the feed screw 6 which is washed with a flow rate of 200 kg / h of wash water 7. A first solid / liquid stream 8 of 203.8 kg / h exits the process, in this stream 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 stage (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 transfer zone 11 is fed with the impregnated biomass 10. 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 exits zone 11. This stream 13 contains 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 steam stream 15 of 3471.1 kg / h. At the outlet of this reactor 14, the pre-treated biomass stream 16 of 4803.2 kg / h emerges, comprising 237.8 kg / h of potential glucose, 155.2 kg / h of xylose and 94.7 kg / h of lignin.

[0115] This stream 16 is separated into a gaseous stream 18 of 3039.8 kg / h consisting essentially of water vapor and a solid / liquid stream 19 of 1763.4 kg / h, comprising 237.8 kg / h of potential glucose, 155.2 kg / h of potential xylose, and 94.7 kg / h of lignin. The stream 19 then undergoes an enzymatic hydrolysis step in an enzymatic hydrolysis reactor 20. After enzymatic hydrolysis, the stream 21 comprises 38.9 kg / h of polymeric potential glucose, 198.9 kg / h of glucose, 15.4 kg / h of polymeric potential xylose, 139.8 kg / h of xylose, and 94.7 kg / h of lignin. The stream 21 then undergoes a fermentation step in a fermentation reactor 22. After fermentation, the stream 23 comprises 38.9 kg / h of polymeric potential glucose, 15.4 kg / h of polymeric potential xylose, 94.7 kg / h of lignin and 157.8 kg / h of ethanol. The stream 23 then undergoes solid-liquid separation in a separation tool 27 (a filter press for example). The solid stream resulting from separation 27 is stream 29, defined as the unconverted solid, comprising 38.9 kg / h of glucose with polymeric potential, 15.4 kg / h of xylose with polymeric potential, 94.7 kg / h of lignin, and 2.2 kg / h of ethanol (ethanol loss in the solid). The liquid stream resulting from separation 27 is stream 30, comprising 155.7 kg / h of ethanol. Stream 30 is then distilled in a distillation column 24, and the final stream 25 comprises 154.1 kg / h of ethanol. Based on the biomass ethanol potential of 224.6 kg / h, the process has a yield of 68.6%.

[0116] Example 2 (according to the invention) This example according to the invention proposes to recycle the unconverted solid 29 into the input of the cooking reactor 14 via the feed screw 11. The biomass used for this example is the same as for example 1. 642 kg / h of this 5-50 mm ground biomass enters the process, yielding 242.5 kg / h of potential glucose, 197 kg / h of potential xylose, and 96.3 kg / h of lignin. Since the process is designed to produce ethanol by fermentation, these potential sugar yields correspond to 224.6 kg / h of potential ethanol. The crushed biomass 5 enters the feed screw 6 which is washed with a flow rate of 200 kg / h of wash water 7. A first solid / liquid stream 8 of 203.8 kg / h exits the process, in this stream 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 stage (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.

[0117] At the inlet of the cooking reactor 14, the transfer zone 11 is fed with the impregnated biomass 10 and with the stream 29” corresponding to 80% of the unconverted solid, which is recycled from the solid / liquid separation 27. 20% of the unconverted solid is removed from the process.

[0118] Preferably, not 100% but only a fraction of the unconverted solid is recycled, for example, at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, or even at least 60%, 70%, or 80% by weight of the residue, so that the lignin compound can be removed from the biomass conversion line. The invention is advantageous even when this recycling rate is low, and a very high recycling rate may necessitate larger equipment, which may not be desirable.

[0119] The maximum quantity of ultimate solid residue corresponds in fact to the quantity of lignin in the biomass. This recycled 29” stream comprises 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 washed with 4087.0 kg / h of water 12, a second solid / liquid flow 13 of 5099.9 kg / h exits the zone 11. In this flow 13, there are 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), that is to say that this solid loss is equivalent to example 1 in terms of gross flow rate, but that it is less rich in potential sugars than for example 1. Indeed, the solid included in the flow 13 must pass through the holes in the cage of the screw 11; it is these holes that fix the flow rate of solid in the flow 13, and not the flow rate of solid in the inlet flow of the screw. The cooking reactor 14 is heated by a steam flow 15 of 3471.1 kg / h. At the outlet of this reactor 14, the pre-treated biomass stream 16 of 4982.9 kg / h emerges, comprising 268.9 kg / h of potential glucose, 165.1 kg / h of xylose and 170.5 kg / h of lignin. This flow 16 is separated into a gaseous flow 18 of 3039.8 kg / h consisting essentially of water vapor and a solid / liquid flow 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. The stream 19 then undergoes an enzymatic hydrolysis step in an enzymatic hydrolysis reactor 20. After enzymatic hydrolysis, the stream 21 comprises 63.9 kg / h of glucose polymer potential, 205.2 kg / h of glucose, 17.5 kg / h of xylose polymer potential, 147.9 kg / h of xylose and 170 kg / h of lignin. The stream 21 then undergoes a fermentation step in a fermentation reactor 22. After fermentation, the stream 23 comprises 63.9 kg / h of polymeric potential glucose, 17.5 kg / h of polymeric potential xylose, 170 kg / h of lignin and 164.6 kg / h of ethanol. The stream 23 then undergoes solid-liquid separation in a separation tool 27 (a filter press, for example). The solid stream resulting from the separation 27 is recycled at 80% as described previously (stream 29”) and exits the process at 20% (stream 29'”) comprising 32.8 kg / h of glucose with polymeric potential, 5.1 kg / h of xylose with polymeric potential, 94.2 kg / h of lignin and 0.5 kg / h of ethanol. The liquid stream resulting from separation 27 is stream 30, comprising 162.3 kg / h of ethanol. Stream 30 is then distilled in a distillation column 24, the final stream 25 then comprising 160.7 kg / h of ethanol. When compared to the biomass ethanol potential of 224.6 kg / h, the process has a yield of 71.5%, representing an increase of 2.9 points in yield.

[0120] The PCS of the solid residue increased by 2.7% (from 20.9 MJ / kg DM of lignin to 21.5 MJ / kg DM of lignin). “PCS” is the acronym for Higher Specific Gravity. Higher Calorific Value, which corresponds to the total amount of heat released at constant volume by the combustion of one kg or one Nm3 of a fuel under standard atmospheric pressure, the water formed during combustion being returned to the liquid state and the other products to the gaseous state.

[0121] In conclusion, compared to the prior art, the present invention leads to the following advantages: - The overall sugar / ethanol yield of the process is improved by recycling unconverted polymeric sugars (cellulose and hemicellulose). After recycling in the pretreatment, these polymeric sugars are partially converted into monomeric sugars or made more accessible to the enzymes used in the enzymatic hydrolysis step. - The quality of the lignin is improved since the conversion of sugars has made it purer / richer in lignin, the PCS of the solid is therefore increased since polymer sugars have a lower PCS than lignin.

Claims

Demands

1. A process for treating lignocellulosic biomass, said process comprising: a) a step of impregnating the biomass with a liquor, in particular an acidic liquor, to obtain impregnated biomass; b) a step of cooking the impregnated biomass, optionally accompanied by a steam explosion, to obtain pre-treated biomass; c) a step of enzymatic hydrolysis of the pre-treated biomass, to obtain hydrolyzed biomass in the form of sugar(s), characterized in that said process also comprises: d) a solid / liquid separation step of the biomass hydrolyzed in the form of sugar(s) or of the biomass hydrolyzed in the form of sugar(s), and then processing it in one or more further steps subsequent to step c) of enzymatic hydrolysis, in order to obtain a separated juice and an unconverted solid residue; e) a step of recycling at least a portion of said unconverted solid residue from step a) of impregnation and / or to step b) of cooking,-h) a combustion step of the unconverted solid residue, referred to as the ultimate residue, obtained at the end of biomass processing, the heat from which is used in a heating step of said process.

2. A process according to the preceding claim, characterized in that it also comprises: - a step f) of fermentation of the hydrolyzed biomass in the form of sugar(s), in order to obtain a fermented biomass comprising at least one alcohol, and in that the step d) of solid / liquid separation is carried out on said fermented biomass.

3. A process according to the preceding claim, characterized in that the enzymatic hydrolysis steps c) and fermentation steps f) are carried out simultaneously on the pretreated biomass.

4. A process according to claim 2 or 3, characterized in that it also comprises: - a step g) of separation or purification, in particular distillation, of the fermented biomass, and in that the step d) of solid / liquid separation is carried out before or after said step g) of separation or purification.

5. A process according to any one of the preceding claims, characterized in that the step of said process requiring heating, in particular the heating of a fluid, is step d) of cooking or a step g) of separation by distillation, said step h) being optionally preceded by a step i) of drying said residue.

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

7. A process according to any one of the preceding claims, characterized in that step a) of impregnating the biomass with a liquor and step b) of cooking the impregnated biomass are carried out by reactors each equipped with at least one biomass feeding device, and in that step e) of recycling the unconverted solid residue is carried out by introducing said residue with the biomass being treated into said feeding device(s).

8. A process according to any one of the preceding claims, characterized in that the unconverted solid residue obtained in step d) of solid / liquid separation contains between 40 and 70 wt% water, in particular between 50 and 60 wt% water, between 2 and 35 wt% cellulose, in particular between 5 and 20 wt% cellulose, and between 0 and 15 wt% hemicellulose, in particular between 1 and 10 wt% hemicellulose.

9. A process according to any one of the preceding claims, characterized in that the treatment converts lignocellulosic biomass into sugar juice, in particular C5 and C6 juices, after enzymatic hydrolysis, or into alcohol after fermentation of said sugar juice.

10. Use of the process according to any one of claims 1 to 9 for the treatment of lignocellulosic biomass, such as wood, straw, agricultural residues, paper residues, and all dedicated energy crops, in particular annual or perennial plants such as miscanthus, with a view to producing sugars, alcohol-type biofuels or bio-based molecules.

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