Method for treating a lignocellulosic biomass

Abstract

The invention relates to a method for treating a lignocellulosic biomass, the method comprising: - a) a step of impregnating the biomass with a liquor to obtain an impregnated biomass; - b) a step of cooking the impregnated biomass, optionally accompanied by a steam explosion, to obtain a pretreated biomass; - c) a step of enzyme hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass in the form of one or more sugars; - d) a step of solid / liquid separation of the hydrolyzed biomass in the form of one or more sugars or of the hydrolyzed biomass in the form of one or more sugars which is then treated in one or more other steps subsequent to enzyme hydrolysis step c), so as to obtain a separated juice and an unconverted solid residue; - e) a step of recirculating at least some of the unconverted solid residue back to impregnation step a) and / or to cooking step b).

Description

[0001] PROCESS FOR TREATING LIGNOCELLULOSIC BIOMASS

[0002] Technical field

[0003] The invention relates to a method for treating lignocellulosic biomass to produce so-called second generation (2G) sweet juices. These sweet juices can be used to produce other products biochemically, in particular by fermentation (for example alcohols such as ethanol, butanol), or other molecules, for example solvents such as acetone, etc.).

[0004] Prior art

[0005] Lignocellulosic biomass represents one of the most abundant renewable resources on Earth. The substrates considered are very varied, they concern both woody substrates such as different woods (hardwoods and softwoods), co-products from agriculture (wheat straw, corn cobs, etc.) or other agri-food industries, paper mills, lignocellulosic waste, etc.

[0006] The lignocellulosic biomass treatment process generally comprises - 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, - enzymatic hydrolysis, leading to the production of sweet juices, generally based on C5 and C6 sugars (i.e. sugars with 5 or 6 carbons),

[0007] - and possibly fermentation of these sugars by yeast, to convert them into alcohol of the ethanol type. The process also includes steps of separation and / or purification of the final product (sugar, alcohol, solvent, etc.).

[0008] Lignocellulosic biomass is composed of three main polymers: cellulose (35 to 50% by weight), which is a polysaccharide consisting mainly of hexoses; hemicellulose (20 to 40% by weight), which is a polysaccharide consisting mainly of pentoses; and lignin (10 to 30% by weight), which is a polymer with a complex structure and high molecular weight, composed of aromatic alcohols linked by ether bonds. These different molecules are responsible for the intrinsic properties of the plant wall and are organized into a complex tangle. Among the three basic polymers that integrate lignocellulosic biomass, cellulose and hemicellulose are those that allow the production of 2G sugar juices.

[0009] Most often, hemicellulose is mainly broken down into sugar during pretreatment, and the cellulose is converted into sugar (glucose) by enzymatic hydrolysis. However, access to raw cellulose remains difficult for enzymes, hence the need for pretreatment. This pretreatment makes it possible to modify the physicochemical properties of lignocellulosic biomass in order to improve the accessibility of cellulose to enzymes and its reactivity to enzymatic hydrolysis.

[0010] Many technologies of interest to the invention for carrying out this pretreatment exist, which will be grouped hereinafter under the generic term of "cooking": acid cooking, alkaline cooking, cooking by auto-hydrolysis, steam explosion, processes called "organosolv pulping" according to the known English term (or treatment with organo-solvent in French). This last process concerns a 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, formic acid, or even acetone. The "organosolv pulping" processes lead to at least partial solubilization of the lignin, partial solubilization of the hemicelluloses. There are then two output streams: the pretreated substrate with residual cellulose, hemicellulose and lignin and the solvent phase which contains the solubilized lignin and a portion of the hemicelluloses.There is generally a solvent regeneration step that allows a lignin stream to be extracted. Some "organosolv pulping" treatments (particularly with 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 carrying out "organosolv pulping" cooking.

[0011] 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 (201 1) 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.

[0012] One of the most effective pretreatments is steam explosion, especially under acidic conditions, which allows 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).

[0013] Patents US-8057639 and US-8512512 propose a process comprising a first step of hydrolysis of 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 possibly in the presence of weak acid. After this step, washing is carried out to extract and recover the sugar juices from the hemicellulose (generally C5 sugars and C6 sugars, the relative proportion of which depends, in particular, on the nature of the biomass) before sending the remaining biomass, enriched in cellulose and lignin, to a second step (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 which causes a sudden expansion of the biomass (steam explosion).

[0014] Whenever a treatment requires a pressure step (impregnation, pretreatment such as cooking or other), it is necessary to use means for introducing solid biomass 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.

[0015] Patent FR 3 075 203 describes a process involving impregnation of the biomass with an acid liquor, followed by cooking and steam explosion of the impregnated biomass, with adjustment of the acidity of the acid liquor and recycling thereof. Patent FR 3 075 201 also describes a process for pre-treating the biomass by acid impregnation followed by steam explosion, with, in addition, washing of the reactor feed means and recycling of the wash water in the process.

[0016] 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 will be called in this text "unconverted solid residue" or "lignin cake", are rich in lignin, which does not react or reacts little to the action of the enzymes used for the hydrolysis of biomass and which are generally cellulases and hemicellulases. These woody residues can be used, in particular as fuel, or be integrated as a filler in resin or bitumen-based products for example. However, these unconverted residues are not made up (apart from a certain quantity of water) only of lignin: they can also contain hemicellulose and / or cellulose which have not reacted to hydrolysis.And removing these residues from the biomass conversion process means losing these unreacted polymeric sugar fractions, which impacts the conversion efficiency of biomass into sugar (or alcohol).

[0017] 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 hydrolyzate obtained to obtain a fermentation must 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 efficiency.On the other hand, it requires separate treatment of this cake, with an additional reactor dedicated to it and which will carry out alkaline cooking of the cake before recycling it, which increases the installation and operating costs of the process as a whole, and which increases the complexity of its implementation.

[0018] Another solution was proposed in patent EP 2 430 171, quite close to the previous one, but providing for cooking of the woody residue not alkaline but acidic, with the same drawbacks.

[0019] The invention then aims to remedy these drawbacks. The invention aims to improve the treatment of lignocellulosic biomass. More specifically, it aims to increase biomass conversion yields, particularly more efficiently than in previous solutions.

[0020] Summary of the invention

[0021] The invention firstly relates to a method for treating lignocellulosic biomass, said method comprising

[0022] - a) a step of impregnating the biomass with a liquor, in particular acid, to obtain an impregnated biomass

[0023] - b) a step of cooking the impregnated biomass, possibly accompanied by a steam explosion, to obtain a pretreated biomass

[0024] - c) a step of enzymatic hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass in the form of sugar(s) said process also comprises

[0025] - 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) then treated in one or more other steps subsequent to step c) of enzymatic hydrolysis, in order to obtain a separated juice and an unconverted solid residue,

[0026] - e) a step of recycling at least part of said solid residue not converted in step a) of impregnation and / or in step b) of cooking.

[0027] For the purposes of the present invention, the term “unconverted solid” residue” means a residue which comprises at least 20% by weight of solid, in particular at least 30 or 35% by weight of solid. The solid content can be measured by its Dry Matter (acronym “DM”) content, which is measured according to the ASTM E1756 - 08(2015) “Standard Test Method for Determination of Total Solids in Biomass” standard. The DM of the unconverted “solid” residue according to the invention is preferably at least 20, 30 or 35%.

[0028] The impregnation liquor may comprise a chemical compound such as an acid, a base or an oxidizing agent or by a water-based liquor, with autohydrolysis of the biomass naturally releasing an acid, in particular acetic acid.

[0029] 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 stage or into the cooking stage constituting the pretreatment of the biomass before its enzymatic hydrolysis.

[0030] What is specific to the present invention is that the unconverted solid residue can be reintroduced directly into a pretreatment stage, without a specific operation such as dedicated impregnation / cooking dedicated to this residue: thus an increase in yield (in sugar or alcohol) is obtained which is not negligible, without having to invest in additional energy-consuming equipment such as a cooking reactor.

[0031] It thus turned out, surprisingly, that reintroducing this residue into the impregnation or cooking device, with the biomass being treated, made it possible

[0032] - to extract from this residue at least part of the cellulose and / or hemicellulose which were retained there, the enzymatic hydrolysis reaction not allowing the total conversion of these compounds,

[0033] - and to convert them at least in part by making them follow the path of the "fresh" biomass again in its pretreatment and then enzymatic hydrolysis stages, which, in fact, ultimately increases the sugar (or alcohol) production of the process. What is also surprising is that the addition of this residue to the rest of the biomass during treatment 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 smooth operation of the devices used, whereas one might have feared that the addition of this residue, of a texture very different from that of the biomass, would lead to problems of fouling of the devices, problems of carrying the residue from one device to another or within a device, etc. This did not happen.

[0034] Another very 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 of this ultimate residue. The heat produced can be used in the process in one or more steps requiring heating of a fluid (impregnation liquor), a reactor (cooking during pretreatment) or reboiler of a distillation column (to purify an alcohol obtained by fermentation, etc.).

[0035] According to one embodiment, the method according to the invention aims at the production of sweet juice only, the separation step d) being carried out on the sweet juice at the outlet of the enzymatic hydrolysis.

[0036] According to another embodiment, the method aims to transform all or part of the sugar juice obtained by enzymatic hydrolysis. It can then also comprise: - 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, step d) of solid / liquid separation being carried out on said fermented biomass.

[0037] In this latter mode, it is possible, according to the invention, to recycle both the unconverted residue at the end of the enzymatic hydrolysis and at the end of the fermentation:

[0038] The enzymatic hydrolysis steps c) and fermentation f) can be carried out simultaneously on the pretreated biomass, in which case we speak of 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 in particular.

[0039] The method according to the invention may also comprise: - 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. Carrying out separation d) before step g), when step g) is a distillation, is advantageous, because this avoids introducing a liquid phase containing this residue, which is likely to foul the column or at least to hinder its operation. But it may also prove advantageous to carry out separation d) according to the invention after the separation / purification of the fermented biomass, because the solid residue may contain a fraction of alcohol, and passing it into the separation / purification step may make it possible to extract at least a portion of this fraction of alcohol trapped in the solid residue.

[0040] As mentioned above, the method according to the invention may also comprise: - a step h) of combustion of the ultimate unconverted solid residue obtained at the end of the treatment of the biomass, the heat produced from which is used in a step of said method requiring heating, in particular the heating of a fluid, in particular in 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 a low calorific value, unlike lignin.

[0041] Optionally, combustion step h) may be preceded by a step i) of drying the residue, in particular so that the residue reaches a water content lower than a given threshold, for example less than or equal to 40% by weight, in particular less than or equal to 30% by weight.

[0042] Step d) of solid / liquid separation 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, wringer device or a combination of different devices.

[0043] 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 feed 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 feed device(s).

[0044] At least one of the feeding devices may thus be a feeding screw, in particular at least partly conical, comprising a fairing provided with a cage provided with openings which 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" according to English terminology), in a known manner, creates a hermetic plug of biomass in the downstream portion of the screw, which creates a compression on the biomass resulting in a pressure difference between the inlet of the biomass and the outlet of the biomass from the screw. But any other known device may be used. For the impregnation step, a reactor operating continuously or in batch mode may be used, or other means than a dedicated reactor, in particular a conveyor belt which is sprayed with liquor, etc.

[0045] The unconverted solid residue obtained in step d) of solid / liquid separation contains, in addition to water, a majority compound in the form of lignin, and minority compounds among 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 fermentation step f).

[0046] The unconverted solid residue obtained in step d) of solid / liquid separation may contain, for example, between 40 and 70% by weight of water, in particular between 50 and 60% by weight of water, between 2 and 35% by weight of cellulose, in particular between 5 and 20% by weight of cellulose, and between 0 and 15% by weight of hemicellulose, in particular between 1 and 10% by weight of hemicellulose. It may also comprise other minor compounds, such as ash. The different contents of lignin, cellulose and hemicellulose may indeed vary, in particular depending on the type of biomass used and its reactivity during enzymatic hydrolysis in particular.

[0047] 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 efficiency and for the thermal integration of the process.

[0048] The dry basis composition of the ultimate solid residue obtained at the end of biomass processing generally comprises mainly lignin, and less than 20% DM of cellulose and less than 8% DM of hemicellulose.

[0049] The treatment method of 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.

[0050] The invention also relates to any installation implementing the method described above.

[0051] The invention also relates to an installation, in particular for implementing the method described above and which comprises:

[0052] - a) a device for impregnating, in particular an impregnation reactor, the biomass with a liquor, in particular acid, to obtain an impregnated biomass

[0053] - b) a reactor for cooking the impregnated biomass, possibly accompanied by a steam explosion, to obtain a pretreated biomass

[0054] - c) a reactor for enzymatic hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass, said installation also comprising

[0055] - d) a device for solid / liquid separation of the hydrolyzed biomass or of the hydrolyzed biomass then treated in one or more other reactors or devices arranged downstream of the enzymatic hydrolysis reactor c), in order to obtain an unconverted solid residue, - e) means for recycling at least part of said unconverted solid residue in the impregnation reactor a) and / or in the cooking reactor b). The means for recycling the unconverted solid residue are conventional, and may comprise any suitable conveying system (for example by conveyor, screw, hopper or belt).

[0056] The installation according to the invention advantageously comprises reactors a) for impregnation and b) for cooking, which are provided with feed devices, and the recycling means comprise means of fluidic connection between the solid / liquid separation device and at least one of said feed devices for conveying the unconverted solid residue from the separation device to the or at least one of the feed devices. The introduction of the unconverted solid residue and that of the biomass being treated in the feed device (or directly in the reactor concerned) can be done jointly or via different introduction points, or not simultaneously.

[0057] The invention also relates to the use of the method or installation described above for the treatment of lignocellulosic biomasses, such as wood, straw, agricultural residues, paper residues, and all dedicated energy crops, in particular annual or multi-annual plants such as miscanthus, with a view to producing sugars, alcohol-type biofuels or bio-sourced molecules.

[0058] The invention will be described in detail below, using figures and non-limiting examples.

[0059] List of figures

[0060] Figure 1 is a schematic representation of a first variant of a lignocellulosic biomass conversion plant where the method according to the invention can be applied.

[0061] Figure 2 is a schematic representation of a second variant of a lignocellulosic biomass conversion plant where the method according to the invention can be applied.

[0062] Figure 3 is a schematic representation of a third variant of a lignocellulosic biomass conversion plant where the method according to the invention can be applied.

[0063] Figure 4 is a schematic representation of a lignocellulosic biomass conversion plant applying the invention.

[0064] Note that the same references concern the same flow, the same device, from one figure to another.

[0065] The description of the references is presented below: 1: Water inlet into the liquor preparation tank

[0066] 2: Acid entry into the liquor preparation tank

[0067] 3: Tool (tank) for preparing the liqueur

[0068] 4: Acid liquor to impregnation tool (reactor)

[0069] 5: Crushed biomass

[0070] 6: Impregnation tool feeding device

[0071] 7: Wash water from the plug-screw feeder of the impregnation tool

[0072] 8: Washing liquid outlet from the “plug screw feeder” 6 of the impregnation tool

[0073] 9: Impregnation tool (reactor)

[0074] 10: Impregnated and drained biomass

[0075] 11: Pretreatment tool feed device

[0076] 12: Wash water from the “plug screw feeder” of the pretreatment tool

[0077] 13: Pressing the “plug screw feeder” of the pre-treatment tool

[0078] 14: Pretreatment cooking tool (explosion reactor)

[0079] 15: Steam injection for pretreatment

[0080] 16: Pretreated biomass and steam

[0081] 17: Tool (cyclone) for separating steam and pretreated biomass

[0082] 18: Steam

[0083] 19: Pretreated biomass

[0084] 20: Enzymatic hydrolysis reactor

[0085] 21: Hydrolyzate containing sugars

[0086] 22: Alcoholic (ethanolic) fermentation reactor

[0087] 23: Fermentation wine containing ethanol (alcohol)

[0088] 24: Ethanol recovery device, for example a distillation column(s)

[0089] 25: Concentrated alcohol

[0090] 27: Solid (lignin) / liquid separation, e.g. filter press

[0091] 28: Liquid residue (vinasses)

[0092] 29: Unconverted solid residue (lignin cake)

[0093] 30: Clarified fermentation wine (without solids)

[0094] 31: Clarified hydrolyzate (without solids) Description of the embodiments

[0095] The invention proposes to recycle the unconverted solid residue from the process of converting lignocellulosic biomass into sugars or alcohols. This residue is mainly composed of lignin, a compound not converted during the process. This residue is generally separated to be burned in conventional biorefineries; lignin can also be used as a compound of interest for specialty products (resins, bitumen, etc.). The invention proposes to recycle 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). The recycling of these sugar polymers then makes it possible to increase the yield of the process.

[0096] The invention relates to the recycling of at least a portion of a solid residue, referred to as "lignin cake" or "unconverted solid residue" in the present text. This solid is advantageously recycled in the pretreatment step under normal conditions (for example acid) of the lignocellulosic biomass, to increase its reactivity in the downstream enzymatic hydrolysis step. Its direct recycling in a step such as enzymatic hydrolysis or SSCF is less technically relevant, because the access of the enzymes to the cellulose will not be improved, or not sufficiently so that the biomass conversion yield is significantly improved and / or the ultimate residue has a calorific value that is significantly improved compared to no recycling, or at least much less than with the invention.

[0097] Lignin is one of the major components of lignocellulosic biomass (up to 30% DM). In a lignocellulosic biomass conversion process that uses sugars (cellulose and hemicellulose), the lignin cake is a co-product of the process that is composed of water (water can represent 50% to 60% by weight of the cake) and solids from the biomass that are not converted during the process, namely mainly lignin but also cellulose and hemicellulose.

[0098] 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: [Table 1] And Table 2 below indicates, for the same biomass and the same lignin cake, their flow rates and composition of solid compounds, expressed here in dry matter content MS: [Table 2]

[0099] It can be seen from these tables that two unconverted sugar polymers (cellulose and hemicellulose) are present in the lignin cake, for a total of 11% by weight (or 28% by mass). The invention recycles at least part of the lignin cake (unconverted solid) to convert these polymers and thus increase the efficiency of the process, since 11% of the polymeric sugars in the biomass are found in the unconverted solid, without adding a treatment step dedicated to this lignin cake. In addition, the calorific value of the lignin cake (measured by the value of the Higher Calorific Value PCS of the unconverted solid residue) increases if the sugar polymers it contains are converted. Indeed, the sugar polymers contain oxygen molecules which reduce the average PCS of the solid.

[0100] Below are briefly examples of operating conditions for the key stages of biomass processing:

[0101] The process

[0102] Below is a more detailed description of the various key stages 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).

[0103] Lignocellulosic biomass conditioning stage

[0104] The treatment process comprises in its first step, a step of conditioning the lignocellulosic biomass with at least one grinding so as to obtain biomass particles having a size of at most 300 mm. It is of course possible to carry out several successive grinding steps in order to reach the target particle size. Generally, the ground biomass has a particle size (the largest size) of at most 300 mm, most often at least 1 mm, and often between 2 and 200 mm. Any method known to those skilled in the art can be implemented to carry out this step. Most often, the grinding of straw is done with screens of 5 to 100 mm. As for the wood, it is generally shredded into parallelepiped plates with a length between 20 and 160 mm, a width between 10 and 100 mm and a thickness between 2 and 20 mm.The crushed lignocellulosic biomass is brought to the next stage by any means known to those skilled in the art, in particular a transfer screw.

[0105] Impregnation step with an acidic liquor

[0106] The treatment method according to the invention comprises a step a) of impregnating the lignocellulosic substrate with an acid liquor so as to obtain an impregnated lignocellulosic substrate whose pH is between 0.1 and 3. This step aims to prepare the lignocellulosic substrate for the pretreatment step.

[0107] 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. The impregnation reactor or impregnator is equipped with one or more screws which transfer(s) the lignocellulosic substrate from its inlet to the outlet opening. The impregnator is also equipped with one or more pipes for supplying the acid liquor and, if necessary, one or more pipes for withdrawing acid liquor. Said acid liquor inlet and outlet pipes are generally installed so as to operate in co-current or counter-current recycling.

[0108] 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.

[0109] Solid / liquid separation step on the lignocellulosic substrate impregnated with acid liquor The lignocellulosic substrate impregnated with acid liquor is subjected to a solid / liquid separation step in order to obtain a lignocellulosic substrate having a dry matter content of between 15% and 70% by weight and a spent acid liquor. Preferably, the lignocellulosic substrate impregnated with acid liquor is first drained in order to extract at least a portion of the free acid liquor before being treated by solid / liquid separation.

[0110] The solid / liquid separation step can use any technique known to those skilled in the art, which can be, for example, decantation, centrifugation or pressing.

[0111] Preferably, the lignocellulosic substrate is pressed concomitantly with its transfer to the pretreatment step when the latter uses the steam explosion method described below. This method of conducting the step is, for example, ensured by a compression screw called a "plug screw feeder" whose 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 provided with one or more lines for withdrawing the used liquor (called pressate) separated during pressing. The pressate can be recycled to the impregnation step and / or to the washing step by the washing liquid 12 passing through the feed screw 11.

[0112] 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.

[0113] Pretreatment stage of washed and acidified lignocellulosic substrate

[0114] The washed and acidified lignocellulosic substrate undergoes a pretreatment step.

[0115] 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 cellulose fraction, such as its degree of polymerization and its state of crystallinity.

[0116] Various types of pretreatment are known to those skilled in the art, combining chemical and thermal treatment. Examples include acid or basic cooking, the Organosolv process, ionic liquid treatments, and the steam explosion process.

[0117] The preferred pretreatment process is steam explosion ("SteamEx" or "Steam Explosion" in English terminology) carried out in an acidic environment. This is a process in which the lignocellulosic substrate is rapidly brought to a high temperature by injecting pressurized steam. The treatment is stopped by abrupt decompression.

[0118] The operating conditions of the steam explosion process are as follows: the steam is injected directly into the reactor; the temperature of the reactor is generally between 150 and 220°C, preferably between 170°C and 210°C, the pressure is between 5 and 25 bars absolute (0.5 and 2.5 MPa), more preferably between 8 and 19 bars 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

[0119] Steam explosion can be carried out in batch or continuous mode, and the depressurization step which allows the biomass to be deconstructed can take place in one or more stages.

[0120] At the end of the steam explosion pretreatment stage, a pretreated lignocellulosic substrate with a high dry matter content, generally between 20 and 70% by weight, and a vapor phase which can be condensed is obtained.

[0121] Following steam explosion under acidic conditions, the pretreated lignocellulosic substrate generally has a pH lower than that compatible with the medium for enzymatic hydrolysis. Thus, the lignocellulosic substrate is subjected to a neutralization step to bring its pH to a value between 4 and 6.

[0122] For the neutralization step, an aqueous solution containing a neutralizing agent is used which 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 which, 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, lime. Even more preferably, the neutralizing agent is chosen from potassium hydroxide and ammonia, alone or in combination with each other. Preferably, the neutralizing agent is used in aqueous solution, with a mass concentration of between 2% and 75%, and even more preferably between 20% and 70%.

[0123] 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.

[0124] The neutralization step can be carried out continuously, batchwise or fed-batch.

[0125] It should be noted that a possible washing step can be carried out before or after the neutralization step, on all or part of the pretreated lignocellulosic substrate.

[0126] If washing is applied, a liquid stream is brought into contact with the pretreated lignocellulosic substrate, then the liquid is separated from the solid. The washing step can be carried out by percolation, by successive mixing operations and liquid / solid separation, 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 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 washing juice containing a portion of the hemicelluloses solubilized during the pretreatment. This washing juice 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.

[0127] Enzymatic hydrolysis step

[0128] The pretreated lignocellulosic substrate, optionally neutralized and washed, is sent to the enzymatic hydrolysis stage of the process.

[0129] The pretreated lignocellulosic substrate which is sent to the enzymatic hydrolysis stage has a dry matter content generally between 15% and 70% by weight.

[0130] The objective of enzymatic hydrolysis is to hydrolyze (depolymerize), by means of biocatalysts, hemicelluloses and cellulose into fermentable sugars, preferably glucose.

[0131] The enzymatic hydrolysis step is carried out under mild conditions, at a temperature of the order of 40°C and 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 carried out 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, suitable for extensive hydrolysis of cellulose and hemicelluloses.

[0132] Enzymatic hydrolysis can be carried out in continuous or batch mode, or in fed continuous mode, in one or more reactors. The residence time is between 5 hours and 200 hours and preferably between 24 hours and 120 hours and even more preferably between 48 hours and 120 hours.

[0133] At the end of this stage, a hydrolysate containing fermentable sugars is recovered from the bioreactor and is then treated in the fermentation stage.

[0134] It should be noted that the hydrolyzate obtained may optionally undergo one or more treatment steps before the fermentation step. For example, this may involve a pH adjustment, a partial purification in order to limit the content of inhibitory compound for the fermentative microorganism, or at least a partial separation of the solid residues contained in the hydrolyzate (and thus obtain the unconverted solid residue to be treated according to the invention).

[0135] Fermentation stage of the hydrolyzate, when we want to continue the conversion of the sugars obtained into alcohol(s)

[0136] Depending on the step of the process for producing solvents and / or alcohols, the optionally treated hydrolyzate is sent to the fermentation step allowing the conversion by means of one or more microorganisms of different genera of the fermentable sugars into solvent and / or alcohols of interest. The fermentation methods are known to those skilled in the art and are described in particular in document US 8,456,633.

[0137] The term "solvent" means organic compounds other than alcohols, for example organic compounds having a ketone function such as acetone.

[0138] The term "alcohol" includes, in particular, ethanol, propanol, isopropanol and butanol.

[0139] 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.

[0140] In the context of the invention, the fermentation step makes it possible, for example, to produce 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)".

[0141] Preferably, the chosen microorganism is a natural or genetically modified yeast of the genus Saccharomyces capable of producing ethanol.

[0142] At the end of the stage, a fermentation must diluted in products of interest is recovered.

[0143] According to one embodiment of the method, the hydrolysis and fermentation steps can be carried out at the same time in at least one bioreactor so that the enzymatic hydrolysis and the fermentation are carried out simultaneously according to a method designated by the term "Simultaneous Saccharification and Fermentation (SSF)". When the hydrolysis step is combined with the fermentation step, the operating conditions, in particular temperature, can be adapted to adapt to the tolerances of the fermentation 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 to between 5 and 5.5 in order to promote the performance of the yeasts.

[0144] The production unit implementing the method according to the invention may comprise, in addition to the installations already described, in situ production units for enzymes and / or yeasts.

[0145] Stage of separation of solvents and / or alcohols from the fermentation must.

[0146] The method 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 eliminate 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.

[0147] Preferably, the step of separating the product(s) of interest, for example ethanol, uses one or more distillations which is a technology well known to those skilled in the art.

[0148] The feedstock: lignocellulosic biomassAccording to the invention, the feedstock of the process may be a biomass alone or in a mixture. The quantity of water contained in the raw feedstock is generally at least 10%, in particular between 10 and 70% by mass. The raw biomass is chosen from any type of biomass, preferably solid biomass, and in particular lignocellulosic biomass. Non-limiting examples of types of biomass concern, for example, agricultural residues (in particular straw, corn cobs), forestry residues, forestry products, sawmill residues, dedicated crops, for example short-rotation coppices. Preferably, the raw biomass, also called native biomass, is lignocellulosic biomass. It essentially comprises three natural constituents present in variable quantities depending on its origin: cellulose, hemicellulose and lignin.The lignocellulosic biomass feedstock is preferably used in its raw form, i.e. in all three constituents: cellulose, hemicellulose and lignin.

[0149] 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. The impregnation fluid: The optional fluid, injected for impregnation, is an aqueous liquid solution containing or not 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, preferably between 0.3 and 2. According to a preferred embodiment, the liquor used is an acid-catalyzed liquor, and the pH of the liquor is adjusted between 0.1 and 4, in particular between 0.3 and 2.As an acid, it is possible, for example, to use at least one acid chosen from sulfuric acid, hydrochloric acid, nitric acid, oxalic acid. Their content, in the aqueous phase, is preferably between 0.2 and 8% by weight.

[0150] The invention applies similarly to different processes and installations, in particular to: - installations which only aim at the production of sugars, and which therefore do not provide for alcoholic fermentation, - installations which provide for pre-treatment by cooking without prior impregnation with a liquor (auto-hydrolysis for example), - installations which provide for pre-treatment by cooking with prior impregnation with a non-acidic liquor.

[0151] Figure 1 very schematically represents a non-limiting variant of a lignocellulosic biomass conversion plant in which the invention can be applied, an installation which provides for pretreatment of the biomass including impregnation with an acid liquor then cooking / explosion with steam, then enzymatic hydrolysis followed by alcoholic fermentation, to transform the biomass into ethanol.

[0152] Figure 1 therefore represents a biomass conversion carried out in the following way: the crushed biomass 5 (impregnated or not with a catalytic liquor) is introduced into an impregnation reactor 9 by a feed device 6. This may be a pressurized feed 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 drainage grid, a wash water inlet 7 and a wash water outlet 8. A hermetic biomass plug 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 part of the liquid contained in the biomass, in particular when the MS of the biomass is less than 80% before it enters the pressurized feed means 6. The liquid thus extracted mixes with the washing water and is withdrawn with the used washing water 8. The impregnation reactor is also supplied with acid liquor 4 (water with added sulfuric acid) coming from a liquor preparation tank 3, itself supplied with acid 2 and water 1. The impregnated and drained biomass 10 leaves the reactor 9 to feed a steam explosion cooking reactor 14 via another feed device 11, for example of the compression type, such as the feed device 6. In the device 11, due to the compression exerted on the biomass, a liquid 13 resulting from this pressing, also called pressate, is recovered, which is composed of water and acid.The device 11 is washed, using a dedicated inlet, by a washing liquid 12 (water and / or a recycled liquid, as seen below), which is then evacuated through the outlet through which the press 13 is also evacuated.

[0153] The reactor 14 is also supplied with steam 15. At the outlet of the reactor 14, the biomass-steam mixture passes into a tool 17 for separating the biomass 19 and the steam 18. The biomass 19 is then treated in an enzymatic hydrolysis reactor 20, then once hydrolyzed into sugars, the hydrolyzed biomass 21 (also called hydrolysis must) passes into an alcoholic fermentation reactor 22. The biomass fermented into alcohol 23, also called fermentation must) is then brought into one or more distillation columns 24 to obtain concentrated alcohol 25 and crude vinasses 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 device 27 of the filter press type, and a liquid residue 28 (the vinasses) and a residue 29 are obtained at the outlet. 29 which is the lignin cake of interest to the invention.

[0154] This is just one example of a plant, which can also have many variations. For example, enzymatic hydrolysis and fermentation can be carried out jointly in the same reactor; this is known as SSCF, which stands for "Simultaneous Saccharification and Co-Fermentation."

[0155] Figure 2 is a variant of the method according to Figure 1, where, all other things being equal, the solid / liquid separation by the filter press 27 is carried out on the fermentation 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.

[0156] Figure 3 is a variant of the process according to Figure 2, where, all other things being equal, the solid / liquid separation device of the filter press type 27 is arranged between the enzymatic hydrolysis reactor 20 and the fermentation reactor 22: here the separation is carried out on the still unfermented hydrolysate 21, and the liquid part of the hydrolysate (sweet juice) 31 then goes into the fermentation reactor 22. In a variant not shown of the process according to Figure 3, only the production of sweet juice 31 is targeted, the conversion of which by fermentation is not continued on the same production line.

[0157] 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. 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 (flow 29') in the feed device 6 of the impregnation reactor 9. This recycling before impregnation is advantageous, because the lignin cake 29 will be brought back into contact with the impregnation liquor (acid) in the reactor 9, which will help to extract the residual polymeric sugars contained in the cake and subsequently make them react more easily during the enzymatic hydrolysis.It might have been feared that the lignin cake would crumble and settle at the bottom of reactor 9, without being able to be carried along with the biomass, but this was surprisingly not the case, even when the biomass was carried into the reactor from its injection point to its exit point by screws inside the reactor.

[0158] - the lignin cake is recycled at least in part (stream 29”) in the feed device 1 1 of the steam cooking / explosion reactor 14. In this case, the lignin cake is not impregnated with liquor again, but is carried along by the biomass which is impregnated

[0159] - 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 non-recycled cake (and the final residue) is stored to be used as fuel, either on the production line or for another use outside the production line, as fuel or to be incorporated into various products.

[0160] The same types of recycling apply analogously to lignin cakes according to the processes in Figures 1 and 3.

[0161] Examples of achievements

[0162] Example 1 (comparative) This example, which does not conform to the invention, separates the unconverted solid 29 without recycling it. Biomass 5 is a lignocellulosic biomass, wheat straw. Its composition is indicated in Table 3 below: [Table 3]

[0163] Biomass is processed according to the process shown in Figure 2. After hydrolysis, cellulose is converted into glucose or glucose oligomers, and hemicellulose is converted into xylose or xylose oligomers. For this, the cellulose or hemicellulose flow rates are expressed as potential glucose or potential xylose.

[0164] The term "potential sugar" (e.g. xylose, glucose) used below defines the addition 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 polymer (e.g. cellulose or hemicellulose), and some of the sugars are in the form of sugar monomer (e.g. glucose or xylose). This measurement can be carried out using ASTM £1758-01 (2020) "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 (e.g. cellulose), the water of hydrolysis must be subtracted from this quantity.

[0165] The operating mode is as follows: 642 kg / h of this crushed biomass 5 to 50 mm 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. The process being intended to produce ethanol by fermentation, these potential sugar flows 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 flow 8 of 203.8 kg / h leaves the process, in this flow there is 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 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, a second solid / liquid flow 13 of 5099.9 kg / h leaves the zone 11. In this flow 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 steam flow 15 of 3471.1 kg / h. At the outlet of this reactor 14, the pretreated biomass flow 16 of 4803.2 kg / h leaves, comprising 237.8 kg / h of potential glucose, 155.2 kg / h of xylose and 94.7 kg / h of lignin.

[0166] This stream 16 is separated into a gas stream 18 of 3039.8 kg / h comprising essentially 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 potential polymeric glucose, 198.9 kg / h of glucose, 15.4 kg / h of potential polymeric 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.

[0167] After fermentation, stream 23 comprises 38.9 kg / h of potential polymer glucose, 15.4 kg / h of potential polymer xylose, 94.7 kg / h of lignin and 157.8 kg / h of ethanol. Stream 23 then undergoes solid-liquid separation in a separation tool 27 (a filter press for example).

[0168] The solid stream resulting from separation 27 is stream 29, defined as the unconverted solid, comprising 38.9 kg / h of potential polymer glucose, 15.4 kg / h of potential polymer xylose, 94.7 kg / h of lignin and 2.2 kg / h of ethanol (loss of ethanol 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, the final stream 25 then comprises 154.1 kg / h of ethanol. Reduced to the ethanol potential of the biomass of 224.6 kg / h, the process has a yield of 68.6%.

[0169] Example 2 (according to the invention) This example in accordance with the invention proposes recycling the unconverted solid 29 at the inlet 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 biomass ground 5 to 50 mm 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. The process being intended to produce ethanol by fermentation, these potential sugar flow rates correspond to 224.6 kg / h of potential ethanol.

[0170] 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 flow 8 of 203.8 kg / h leaves the process, in this flow there is 1.3 kg / h of potential glucose, 1.1 kg / h of potential xylose and 0.5 kg / h of lignin.

[0171] 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 preparation tank 3 and constitute the impregnation liquid 4.

[0172] At the inlet of the cooking reactor 14, the transfer zone 11 is fed with the impregnated biomass 10 and with the flow 29” corresponding to 80% of the unconverted solid, and which is recycled from the solid / liquid separation 27. 20% of the unconverted solid is removed from the process.

[0173] In fact, it is preferable to recycle not 100% but only a fraction of the unconverted solid, for example at least 1%, 5%, 10%, 20%, 30%, 40%, 50%, or even at least 60% or at least 70 or 80% by weight of the residue, so that the lignin compound can be removed from the biomass conversion line. The invention is of interest even when this recycling is low, and a very high recycling rate may lead to having to enlarge the size of the equipment, which may not be desirable.

[0174] The maximum quantity of ultimate solid residue actually corresponds to the quantity of lignin in the biomass. This recycled stream 29” includes 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 stream 13 of 5099.9 kg / h leaves the zone 11. In this stream 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 loss of solid 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 flow 13 must pass through the holes in the cage of screw 11, it is these holes which fix the flow rate of solid in 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, there exits the pretreated biomass flow 16 of 4982.9 kg / h, 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 comprising essentially 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. 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 polymer glucose, 205.2 kg / h of glucose, 17.5 kg / h of potential polymer xylose, 147.9 kg / h of xylose and 170 kg / h of lignin.

[0175] Stream 21 then undergoes a fermentation step in a fermentation reactor 22. After fermentation, stream 23 comprises 63.9 kg / h of potential polymer glucose, 17.5 kg / h of potential polymer xylose, 170 kg / h of lignin and 164.6 kg / h of ethanol. Stream 23 then undergoes a solid-liquid separation in a separation tool 27 (a filter press for example). The solid stream resulting from separation 27 is recycled at 80% as described previously (stream 29”) and leaves the process at 20% (stream 29'”) comprising 32.8 kg / h of potential polymer glucose, 5.1 kg / h of potential polymer xylose, 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 comprises 160.7 kg / h of ethanol.

[0176] Reduced to the ethanol potential of the biomass of 224.6 kg / h, the process has a yield of 71.5%, an increase of 2.9 yield points.

[0177] 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 Calorific Value, which corresponds to the total quantity 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. In conclusion, compared to the state of the art, the present invention leads to the following advantages:

[0178] - 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 partly converted into monomeric sugars or are made more accessible to the enzymes used in the enzymatic hydrolysis step,

[0179] - The quality of lignin is improved since the conversion of sugars has made it purer / richer in lignin, the PCS of the solid is therefore increased since polymeric sugars have a lower PCS than lignin.

Claims

Claims 1. A method of treating a lignocellulosic biomass, said method comprising - a) a step of impregnating the biomass with a liquor, in particular acid, to obtain an impregnated biomass - b) a step of cooking the impregnated biomass, possibly accompanied by a steam explosion, to obtain a pretreated biomass - c) a step of enzymatic hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass in the form of sugar(s) characterized in that said process also comprises- 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) then treated in one or more other 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 part of said solid residue not converted in step a) of impregnation and / or in step b) of cooking, -h) a step of combustion of the unconverted solid residue known as the ultimate residue obtained at the end of the treatment of the biomass, the heat of which is used in a step of said process requiring heating.

2. Method 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 step d) of solid / liquid separation is carried out on said fermented biomass.

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

4. Method 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 step d) of solid / liquid separation is carried out before or after said step g) of separation or purification.

5. Method according to one of the preceding claims, characterized in that the step of said method 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. Method according to one of the preceding claims, characterized in that step d) of solid / liquid separation is carried out by filtration, in particular using a pressing device or drainage, such as a filter press or vacuum filter, a belt filter, a belt press, a centrifuging, decanting or dewatering device or a combination of different devices.

7. Method according to 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 feed 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 feed device(s).

8. Method according to 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% by weight of water, in particular between 50 and 60% by weight of water, between 2 and 35% DM of cellulose, in particular between 5 and 20% DM of cellulose, and between 0 and 15% DM of hemicellulose, in particular between 1 and 10% DM of hemicellulose.

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

10. Installation for implementing the method according to one of the preceding claims, characterized in that it comprises: - a) an impregnation device, in particular an impregnation reactor, of the biomass with a liquor, in particular acid, to obtain an impregnated biomass - b) a reactor for cooking the impregnated biomass, possibly accompanied by a steam explosion, to obtain a pretreated biomass - c) a reactor for enzymatic hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass characterized in that said installation also comprises - d) a device for solid / liquid separation of the hydrolyzed biomass or of the hydrolyzed biomass then treated in one or more other reactors or devices arranged downstream of the enzymatic hydrolysis reactor c), in order to obtain an unconverted solid residue, - e) means for recycling at least part of said unconverted solid residue in the impregnation reactor a) and / or in the cooking reactor b). -h) a combustion reactor for the unconverted solid residue known as the ultimate residue obtained at the end of the treatment of the biomass, the heat of which is used in a stage of said process requiring heating.

11. Installation according to the preceding claim, characterized in that the impregnation reactors a) and b) for cooking are provided with feed devices, and in that the recycling means comprise fluid connection means between the solid / liquid separation device and at least one of said feed devices for conveying the unconverted solid residue from the separation device to the or at least one of the feed devices.

12. Use of the method according to one of claims 1 to 9 for the treatment of lignocellulosic biomasses, such as wood, straw, agricultural residues, paper residues, and all dedicated energy crops, in particular annual or multi-annual plants such as miscanthus, with a view to producing sugars, alcohol-type biofuels or bio-sourced molecules.

Images