Process for treating lignocellulosic biomass

Abstract

The present invention relates to a process for treating previously pretreated lignocellulosic biomass (1), said process comprising the extraction of free sugars from said pretreated biomass by an alcoholic or hydro-alcoholic extraction solution (2), so as to obtain a liquid phase enriched in free sugars, called juice (3), and a solid phase depleted in free sugars, called pomace (4). Figure for the abstract: Fig 1

Description

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

[0001] 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 by chemical or biochemical / fermentation means (for example, alcohols such as ethanol, butanol or other molecules, for example solvents such as acetone, furfural, xylitol, and other biosourced molecules, etc.). Prior art

[0002] 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, rice straw, corn cobs, bagasse, etc.) or even paper industries, etc. Lignocellulosic biomass is composed of three main polymers: cellulose (35 to 50%), which is a crystalline polysaccharide essentially composed of glucose; hemicellulose (20 to 30%), which is an amorphous polysaccharide mainly composed of xylose, galactose, arabinose, mannose, glucose; and lignin (15 to 25%), which is a polymer with a complex structure and high molecular weight, composed of different phenolic monomers linked by ether bonds.These different polymers 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 so-called second generation (2G) sugar juices and 2G ethanol. It should be noted that the composition of hemicelluloses varies depending on the nature of the lignocellulosic biomass considered.

[0003] There are many processes for the recovery of lignocellulosic biomass into 2G sugars or 2G ethanol, which differ in the operating conditions applied and the nature of the reagents used to release the sugars. However, the processes for the recovery of lignocellulosic biomass into 2G sugars most developed on an industrial scale have in common a pretreatment step and an enzymatic hydrolysis step using an enzyme cocktail. The pretreatment step allows the native biomass to be destructured, and generally a portion of the hemicellulose polymer is depolymerized at this step. Enzymatic hydrolysis mainly targets cellulose, and residual hemicelluloses, the polymers are depolymerized under the action of a cocktail of enzymes.

[0004] These 2G sugar juices can be used / recovered for example in a fermentation or chemical process, as is or possibly be treated further. Most often, the overall process includes intermediate separation steps and / or a purification step of the final product(s).

[0005] Pretreatment makes it possible to modify the physicochemical properties of lignocellulosic biomass in order to make the cellulose accessible to enzymes and achieve good reactivity in enzymatic hydrolysis. Many pretreatment technologies exist and allow the biomass to be heated under various chemical conditions. Pretreatment can be carried out with or without the addition of acidic or basic products. It can also be carried out in a solvent such as water or an organic product such as, for example, alcohol (so-called organosolv process) but also in a slightly diluting medium such as steam. This pretreatment can also include a physical step such as defibration or explosive expansion in the context of a steam explosion. This pretreatment can also have several steps to optimize the overall process, such as, for example, acid cooking followed by a steam explosion or two consecutive steam explosions.The pretreatments below grouped under the generic term "cooking" concern heat treatments, with temperatures above 100°C. For technological reasons, particularly mixing and pumpability, cooking is carried out in so-called dilute conditions with cooking liquid / biomass mass ratios greater than 2. Cooking generally combines a thermal effect with a chemical effect obtained by low or, on the contrary, high pH and / or the use of solvents. This cooking term includes, for example, acid cooking, alkaline cooking, and "organosolv" cooking. This last process concerns a pretreatment in the presence of one or more organic solvents and generally water. The solvent may be, but is not limited to, 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, and 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 part of the lignin and part of the solubilized hemicelluloses. There is generally a solvent regeneration step which allows a solid lignin stream to be extracted. In certain pretreatments, called "organosolv pulping" (notably with ethanol), the action of the organic solvent is improved by the addition of a strong acid (such as H2SO4). It is then possible to envisage contacting the biomass with the solvent via an impregnation reactor before the cooking phase and / or to have contact. biomass with the acid catalyst before carrying out “organosolv pulping”.

[0006] A technological solution is well known to those skilled in the art to overcome the technological problems of cooking: Reactors using explosive expansion as the mode of exit of the pretreated biomass (also called steam explosion or Steam gun or Steam explosion according to Anglo-Saxon terminology), make it possible to overcome the problems of pumpability at the end of cooking. Steam explosion type pretreatment makes it possible to work with mass ratios of liquid / biomass lower than 2, the biomass is thus subjected to a proportionally low quantity of water vapor. Part of the water vapor used to entrain the solid during the explosive expansion can then be separated from the medium.Explosive expansion thus makes it possible to produce pre-treated marc that does not contain a continuous liquid phase; it can be described as "dry" as opposed to marc produced by conventional cooking, although its water content is generally greater than 30% by weight. Most often, steam explosion under acidic conditions is preferred, as it allows a good compromise between the acid hydrolysis of hemicellulose and the reactivity of cellulose in enzymatic hydrolysis, with almost total 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) (grinding, impregnation, cooking, etc.).

[0007] It is noted that this type of pretreatment, cooking or steam explosion, requires a transformation of the raw biomass into a reactive pretreated substrate, before starting the following steps of conversion of cellulose, which is the most refractory polymer. After this pretreatment, sugars (C5 and C6 sugars) are released in monomeric or oligomeric form soluble in water. The extraction of these free sugars in a juice is interesting for recovery in the rest of the biomass transformation process or in another process (in parallel) or for marketing as is the sweet juice. There is therefore an interest in extracting these free sugar juices from the pretreated substrate, before the pretreated marc in question, which will then be enriched in solid matter and depleted in sugars, undergoes the following cellulose conversion treatments.With this in mind, in the case of a cooking-type pretreatment, the liquid fraction and the solid fraction of the pretreated biomass are separated, then the solid fraction is optionally washed with water to recover more sugars. On the other hand, in the case of a steam explosion-type pretreatment, at the end of the pretreatment, a marc with a high dry matter content (typically greater than 40% by weight) is recovered. The extraction of free sugars requires a prior step called "repulping" of the marc in water as described in patent EP-3 587 583, before separating the liquid fraction and the fraction. solid, then carry out a possible water wash of the solid fraction to recover more free sugars.

[0008] The cooking and / or steam explosion step is often preceded by an impregnation step. It is often followed by a step of enzymatic hydrolysis of the cellulose using a dedicated enzymatic cocktail. This enzymatic cocktail is a solution containing enzymes having cellulolytic and / or hemicellulolytic activities which will selectively hydrolyze the cellulose polymer and possibly the residual hemicellulose polymers. Due to the targeted action of the enzymes, the residual lignin is little affected by the enzymatic hydrolysis. The enzymatic hydrolysis is carried out under mild temperature and pH conditions. Typically, at a temperature of 30°C to 55°C, and a pH between 3 and 7. The enzymatic hydrolysis reaction of sugar polymers into monomers requires the addition of water molecules, the hydrolysis being favored by the presence of a continuous liquid medium. There are multiple reactor technologies that allow its implementation.Enzymatic hydrolysis can be carried out directly on pretreated biomass and / or on pretreated biomass from which soluble sugars have been extracted, for example.

[0009] In some cases, the enzymatic hydrolysis step of cellulose is followed by a fermentation step, e.g. ethanolic, of the released sugars and a purification step of the fermentation products. In certain configurations of the process flowsheet, the enzymatic hydrolysis and fermentation steps can take place in the same reactor, in a fermentation configuration called SSF (Simultaneous Saccharification and Fermentation). When these two process steps are separated, this is referred to as a SHF (Separated Hydrolysis and Fermentation) type flowsheet. Examples are given in the document "Ethanol from lignocellulosics: A review of the economy", M. von Silvers and G. Zacchi, Bioresource Technology 56 (1996) 131-140.

[0010] It is then necessary to extract the free sugars present after the pretreatment step for use in a subsequent step sensitive to the presence of solids, for example in the case of sensitivity of the fermentative microorganism used in a subsequent fermentation step, or in the case of recycling of the microorganism around this fermentation step or to facilitate the operation of purification and / or separation of the sugars or fermentation products that could be obtained from these sugars. With this in mind, the liquid fraction and the solid fraction are separated. The solid fraction is in the form of a cake, in which a part of the liquid fraction remains trapped due to the limitations of the solid / liquid separation tools and the characteristics of the lignocellulosic biomass.

[0011] We therefore see that at different stages of the biomass treatment processes, we are dealing with products in the form of solid / liquid mixtures, and that there may be an interest in extracting at least part of the liquid phase from the solid phase with a view to enhance it and optimize the overall process, and possibly carry out washing of the solid phase to maximize the recovery of soluble sugars.

[0012] Patent WO 2014 / 135755 proposes a method for treating biomass with the following succession of steps: a- a pretreatment step is carried out by contacting and heating the biomass feedstock with water and an acidic or basic compound, so as to obtain a pretreated substrate, b- the pretreated substrate is brought into contact with cellulase enzymes and with a liquid stream enriched in fermentation products obtained in step e) so as to obtain a hydrolysate comprising a solid residue and a liquid phase containing sugars, c- an alcoholic fermentation of the hydrolysate is carried out by means of an alcohol-producing microorganism so as to produce a fermentation wine comprising a solid matter and a liquid phase containing fermentation products, d- at least a portion of the solid matter contained in the fermentation wine is extracted so as to obtain a stream enriched in solid matter and a fermentation wine depleted in solid matter,e- the solid-enriched stream is washed with a liquid stream so as to obtain said liquid stream enriched with fermentation products, the liquid stream enriched with fermentation products being recycled to step b), f- a step of separating the fermentation wine depleted in solid matter is carried out so as to obtain at least one purified stream comprising an alcohol or a solvent and at least one vinasse stream.

[0013] This patent thus proposes to carry out the separation of lignin and other possible inert solids after the fermentation step. The solid matter composed mainly of lignin is then subjected to washing with water to recover the trapped fermentation products, in particular alcohols and solvents. The liquid resulting from the washing is then recycled into the enzymatic hydrolysis unit, which may be the same unit as the fermentation unit or which may be separate from the fermentation unit so as not to dilute the existing flows.

[0014] Patent EP- 2 774 992 proposes to carry out, in a process comprising a pretreatment step, an enzymatic hydrolysis step and then a fermentation step, to extract at least a portion of the solid residue contained in the hydrolysate so as to obtain a solid residue stream comprising lignin and a hydrolysate depleted in solid residue, then the solid residue stream is washed with a liquid stream such as water so as to recover a liquid phase enriched in sugars, which can be recycled to the enzymatic hydrolysis step to be able to recover the sugars without diluting the streams in the process.

[0015] Patent EP-3 587 583 describes a process for extracting free sugars in two stages on a pretreated biomass obtained by a steam explosion type pretreatment: a first stage called “repulping” which consists of bringing dry marc and a mixing fluid into contact by a continuous mixer, then a second extraction / washing step implemented by a continuous filter, using a washing fluid to obtain a solid phase enriched in solid and depleted in free sugars and a plurality of liquid phases enriched in sugars, with at least partial recycling of a liquid phase extracted from the filter at the inlet of the mixer as a mixing fluid. Partial recycling of another liquid phase extracted from the filter is carried out to use it as a washing fluid.

[0016] These different biomass treatments therefore involve an extraction of free sugars or their fermentation products from a biomass which may have already been treated / converted at least in part to extract free sugars in a recoverable liquid phase.

[0017] To increase the efficiency of this washing, which can also be expressed as the extraction yield of free sugars, it is possible, at the same quantity of mixing water and washing water, to increase the number of theoretical stages of the operation, and to adopt counter-current or cross-current operation rather than co-current operation. Furthermore, an increase in the quantity of washing (and / or mixing) water at the same configuration will result in an improvement in the extraction yield, but also in an increased dilution of the free sugars in the extracted juice. However, to recover the recoverable sugars from the juice, juice concentration operations are usually carried out, in particular by heating / evaporation, and the more diluted the juice, the greater the energy consumption will be to concentrate it.

[0018] The invention then aims to improve the way of carrying out an operation of extracting free sugars from lignocellulosic biomass after one or more treatments, in particular by reducing the energy consumption / costs of their subsequent treatment / recovery. Summary of the invention

[0019] The invention firstly relates to a method for treating a previously pretreated lignocellulosic biomass, said method comprising the extraction of free sugars from said pretreated biomass by an alcoholic or hydro-alcoholic extraction solution, so as to obtain a liquid phase enriched in free sugars, called juice, and a solid phase depleted in free sugars, called marc.

[0020] It has been demonstrated, with the invention, that extracting free sugars from lignocellulosic biomass pretreated with an alcoholic or hydroalcoholic solution would make it possible to reduce the costs associated with the concentration of the extracted sugar juices, and this without degrading the efficiency of sugar extraction. However, this is a completely surprising result, insofar as alcohols are rather poor solvents for sugars (solubility of sugars less than 1% by weight in the case of ethanol, which is moreover rather known for facilitating the crystallization of sugars, that is to say the complete opposite of what is sought in the context of the present invention).

[0021] The extraction of free sugars according to the invention has also proven advantageous in at least two other aspects:

[0022] On the one hand, it has been found that the extraction according to the invention of the free sugars present in the solid / liquid mixture obtained after pretreatment of the lignocellulosic biomass made it possible to improve the stages of purification of the sugars before their concentration. The pretreated lignocellulosic biomass generally contains, in fact, a significant quantity of mineral salts, and in particular sulfate anions SO4 2 when the biomass has been pretreated with sulfuric acid. An effective means for eliminating them known to those skilled in the art is to carry out a liming stage commonly practiced on sugar juices obtained from first generation IG biomass, that is to say the addition of a milk of lime containing calcium hydroxide. This treatment makes it possible to precipitate, among other things, the sulfate anions in the form of calcium sulfate.It turned out that carrying out liming on a sugar juice obtained according to the invention with extraction of free sugars by an alcoholic or hydro-alcoholic solution, made it possible to eliminate more sulfates, thus reducing the cost of subsequent treatment operations.

[0023] On the other hand, it turns out that the biomass thus treated retains a (small) portion of the washing solution, therefore a (small) portion of alcohol according to the invention. And the extracted sweetened juices also contain a certain proportion of alcohol. In both cases, this presence of alcohol is favorable because it tends to limit the microbial contamination of the marc and the sweetened juice. Microbial contamination is in fact a problem frequently encountered industrially, and the presence of alcohol can avoid having to resort to antimicrobial treatments, in particular by adding antibiotics or other compounds.

[0024] Advantageously, the biomass is pretreated beforehand by impregnation with an acidic, basic or oxidizing aqueous solution, then cooking or steam explosion. This is a known pretreatment, an example of which is described in patent EP 3728408.

[0025] Preferably, the extraction of the sugars is carried out on a pretreated biomass which has an insoluble dry matter MSI content of at least 20%, in particular at least 25% or at least 30%, and preferably at most 70 or 65%, in particular between 25% and 65%.

[0026] The insoluble dry matter rate MSI can be determined as follows: the sample is vacuum filtered by carrying out successive rinses with osmosis water with a mass ratio between 40 and 100 and then the sample is dried at 105°C until a constant mass is obtained. The mass lost during washing, filtration and drying corresponds to the mass of water (liquid) initially present in the sample as well as the soluble materials contained in the liquid fraction, the remaining mass corresponds to the insoluble dry materials MSI.

[0027] Preferably, the extraction of the sugars is carried out on a pretreated biomass which has a dry matter MS content of at least 25%, in particular at least 30% or at least 35%, and preferably at most 70 or 65%, in particular between 30% and 65%.

[0028] The dry matter content, MS, is determined according to ASTM E1756-01, which consists of measuring the mass loss of the liquid fraction by drying at 105°C until a constant mass of residue is obtained. The mass lost during drying corresponds to the mass of water (liquid) initially present in the sample, and the remaining mass corresponds to the solid and soluble matter contained in the liquid fraction.

[0029] According to a variant, it is possible to provide for preceding the extraction of the sugars by a step of adjusting the dry matter MS content of the pretreated biomass, in particular by a prior solid / liquid separation operation, preferably of the filtration or centrifugation type.

[0030] Preferably, the extraction of sugars from the pretreated biomass according to the invention comprises contacting said pretreated biomass with the alcoholic or hydro-alcoholic extraction solution, in particular suspending it in said solution, then solid / liquid separation.

[0031] Optionally, the extraction of the sugars according to the invention may comprise, after the solid / liquid separation, washing of the solid phase obtained by said separation with an alcoholic or hydro-alcoholic washing solution. The washing is then preferably carried out continuously, in co-current or counter-current.

[0032] The extraction solution and the washing solution, when washing is planned, may be of the same composition, with the same alcohol(s), or have one or more different alcohols. In the case of hydro-alcoholic solutions, their alcohol contents relative to water may also be identical or different. Thus, in the case where the extraction of sugars and the washing of the solid phase obtained at the end of the solid / liquid separation is staged, different proportions of alcohol may be used. Carrying out a final washing of the solid phase with an aqueous solution not containing alcohol is also possible.

[0033] In the context of the present invention, when a solid / liquid separation is carried out, the separated "solid phase" is to be understood as containing the solid phase itself and the liquid phase trapped in said solid phase.

[0034] The contacting of the pretreated biomass with the alcoholic or hydroalcoholic solution can be carried out by a mixer continuously (as described in the aforementioned patent EP-3 587 583) or discontinuously, in one or more steps / stages.

[0035] The solid / liquid separation can be carried out discontinuously or continuously, in particular by a filter press or a belt filter (as described in the aforementioned patent EP-3 587 583). Advantageously, the extraction solution and / or the washing solution when washing is planned, comprises at least one alcohol chosen from: methanol, ethanol, isopropanol, n-butanol, isobutanol. The preferred alcohol is ethanol.

[0036] Preferably, the extraction solution and / or the washing solution when washing is planned, is a hydro-alcoholic solution containing at least 5% by weight of alcohol, in particular at least 10% by weight, preferably between 5% by weight and 96% by weight, or between 10% by weight and 85% by weight, or between 15% by weight and 50 or 70% by weight of alcohol. With this proportion of alcohol in the water, we have a solution which provides the desired effect without reaching too high a level of alcohol consumption which would not be economically advantageous.

[0037] Very preferably, the alcohol content is between 15 and 50% by weight, so as to increase the flash point of the hydro-alcoholic solution to overcome certain industrial constraints, and to limit alcohol losses by evaporation. It should also be noted that a hydro-alcoholic solution is easier to handle and store in an industrial installation than pure alcohol.

[0038] In fact, the choice of the proportion of alcohol in the extraction solution (and / or washing when there is washing) depends in particular on the water content in the pretreated biomass before extraction, which can vary widely from one type of biomass to another. (To stabilize / modify this content, the invention can, as already indicated above, adjust the DM level of the pretreated biomass before extraction).

[0039] One solution consists of adjusting the alcohol content of the hydroalcoholic extraction solution, and also the ratio of the mass flow rate of said solution to the mass flow rate of biomass so that the alcohol content in the juice obtained is at most 70% by weight excluding solute, preferably at most 50% by weight excluding solute, and preferably at least 10% by weight excluding solute.

[0040] It is thus possible to adjust the alcohol level (alcohol / water + alcohol) in the extraction solution according to the desired alcohol level (alcohol / water + alcohol) -excluding sugars - in the juice obtained.

[0041] Operating parameters for the contacting step between the pretreated biomass and the extraction solution can be selected so that, ultimately, the desired MSI rate is obtained for separation and then possible washing, in particular depending on the type of equipment chosen for separation and the target separation efficiency.

[0042] Preferably, the contacting of the pretreated biomass (and / or the washing when it is provided) is carried out at moderate temperature, and even at ambient temperature, in particular at a temperature less than or equal to 100°C, in particular between between 10 and 80°C, preferably between 20 and 60°C. The temperature in question is understood as the temperature of the mixture in the step of contacting the biomass with an alcoholic or hydro-alcoholic solution. Preferably in this configuration, the regulation of the temperature of the mixture is done by regulating mainly the temperature of the alcoholic or hydro-alcoholic extraction solution. (The temperature is understood as the temperature of the alcoholic or hydro-alcoholic washing solution in the washing step if it is provided).

[0043] The juice obtained can be treated in different ways to recover the extracted sugars: - the free sugars in the juice can be converted into furfural, in particular by dehydration using acid catalysis, - or the free sugars in the juice can be converted into xylitol and / or sorbitol, in particular by hydrogenation using metal catalysis, - or they can be converted into alcohol, in particular by alcoholic fermentation.

[0044] The juice obtained can be treated to deplete it of mineral salts, in particular by liming and / or by contacting it with one or more active substrates of the ion exchange resin(s) type and / or by electrodialysis.

[0045] Optionally, the juice can be treated with other substrates, such as activated carbon for example, to deplete it of other compounds, the activated carbon thus being able to capture colored compounds contained in the juice.

[0046] Advantageously, the free sugar juices can therefore be treated by liming. A liming operation consists of adding to the extracted free sugar juice a solution of quicklime milk, i.e. a saturated aqueous solution of calcium hydroxide Ca(OH)2. The concentration of the added lime milk solution is between 5 and 40% by weight, in particular between 10 and 20% by weight. The mixing of the lime milk and the sugar juice is carried out at a temperature between 20 and 80°C. The pH of the mixture obtained is between 8 and 11.5, preferably between 9 and 10.5. The hydroxyl anions HO allow the neutralization of the acid pH induced by the protons H+, and induce the formation of water. The calcium cations Ca2+ induce a partial precipitation of the sulfate ions SO42, in the form of calcium sulfate. The precipitate formed can be removed by filtration, decantation or centrifugation.The liming operation can also eliminate various contaminants, mainly inorganic, but also organic.

[0047] Liming on a sugar juice produced according to the invention, i.e. a hydro-alcoholic solution of sugars, is significantly more effective than liming on an aqueous solution of sugars. However, it does not always allow the concentration of salts to be reduced to very low levels. In this case, liming can be supplemented or replaced by an operation aimed at further / totally removing mineral salts, especially in the case where the sugar juice is subsequently concentrated.

[0048] For very effective salt removal, an ion exchange resin can be used: the juice (possibly previously limed) is passed through anion exchange resins in hydroxide form, then through cation exchange resins in protonated form. The anions and cations present in the aqueous solution of free sugars are retained on the anion and cation exchange resins respectively, and release hydroxide anions and protons respectively. These react together completely to form water. The saturated resins can then be regenerated.

[0049] It is also possible to use the electrodialysis technique, which works on the same principle as ion exchange resins, but the exchange of ions takes place through selective membranes, under the effect of an electric current producing the necessary hydroxide anions and protons.

[0050] When an ion exchange resin and / or electrodialysis is used on a sugar juice solution produced by the present invention, this can be carried out on the solution produced by the invention, on the solution produced by the invention which has undergone prior liming, on the solution produced by the invention from which the solvent (ethanol, etc.) has been removed by evaporation and / or distillation in addition or not to the liming.

[0051] The juice obtained can also be concentrated in sugars, in particular by evaporation, optionally after and / or before a treatment to deplete the mineral salts of said juice. The step of concentrating the sugar juice produced by the present invention can be carried out using any technique known to those skilled in the art, for example by multi-effect evaporation or with mechanical compression of the vapor.

[0052] The concentration can be carried out with recovery of the alcohol and / or water to constitute all or part of the alcohol and / or water of the alcoholic or hydro-alcoholic extraction solution used and / or for the washing solution when washing is planned: The concentration of the juice can be carried out by evaporation and it is then possible to recover alcohol and / or water to constitute all or part of the alcohol or hydro-alcoholic solution necessary for carrying out the invention (extraction and / or possible washing): it is thus possible to recycle, at least in part, the constituent(s) of the alcoholic or hydro-alcoholic solution. The condensates obtained after concentration of the sugar juice according to the invention, mainly consisting of alcohol and water, can be distilled in a distillation column to separate all or part of the alcohol from the water.

[0053] According to one embodiment, the juice obtained can be treated to deplete it of mineral salts (at high concentrations when hot), then concentrated, and finally crystallized (cold) on this juice depleted of mineral salts and concentrated in sugars.

[0054] The invention also relates to a process as described above and which comprises an enzymatic hydrolysis of the marc obtained after extraction, which is followed by, or is concomitant with, an alcoholic fermentation, then a distillation of the liquid fraction obtained after fermentation. Thus, part of the alcohol and / or all or part of the water recovered during the distillation can be used to constitute all or part of the alcoholic or hydro-alcoholic extraction solution (and / or the washing solution when washing is planned).

[0055] The invention also relates to a method for treating lignocellulosic biomass which comprises the following successive steps: - impregnation of the biomass with an acidic, basic or oxidizing aqueous solution, to obtain an impregnated biomass, - pretreatment of the impregnated biomass by cooking or steam explosion, to obtain a pretreated biomass, - enzymatic hydrolysis of the pretreated biomass, to obtain a hydrolyzed biomass, - possibly alcoholic fermentation of the hydrolyzed biomass, and such that an extraction of free sugars is carried out using an alcoholic or hydro-alcoholic extraction solution on all or part of the pre-treated biomass before its enzymatic hydrolysis.

[0056] According to the invention, it is thus possible to provide for extracting the sugars from all of the pretreated biomass, or only from part of it.

[0057] In this latter case, it is preferably provided that the entire part of the pretreated biomass having undergone the extraction of sugars and the part which has not undergone it is treated by enzymatic hydrolysis.

[0058] The extraction of free sugars according to the invention may comprise at least partial recycling of a liquid phase extracted from the filter-type device carrying out the solid / liquid separation to the inlet of the mixer-type device carrying out the contacting. This recycling makes it possible to reduce the consumption of alcoholic or hydroalcoholic solution, and has surprisingly proven to allow both more efficient mixing at the mixer and extraction of liquid phase(s) at the filter with a higher sugar concentration.

[0059] These various possible recycling methods make it possible to reduce alcohol and water consumption in the washing process, and / or to reduce energy consumption. They can be carried out individually or in a complementary manner. Thermal integration between the various optional stages is possible, and even recommended.

[0060] In terms of pressure conditions used during extraction: the operating pressure depends on the step considered (contacting, solid / liquid separation and possible washing), the technology chosen and the measurement point. In many technologies, pressure is the driving force for circulating the liquid phase allowing extraction and / or washing. Generally speaking, the technologies all have a fluid at atmospheric pressure and a pressure differential between 0.2 and 25 bars between the incoming and outgoing fluids, and even more preferably, between 0.4 and 20 bars. This pressure differential can be negative during solid / liquid separation. This pressure differential can also be obtained by applying external pressure to the solid / liquid mixture as in the case of a belt press, or when using an optional press on a belt filter.

[0061] For example, in the case of using a filter press for solid / liquid separation, the fluid extracted from the filter is at atmospheric pressure and the incoming fluid is at a higher pressure. This pressure is variable depending on the operating phase. During filtration, the pressure of the fluid to be filtered increases between atmospheric pressure and a maximum pressure dependent on the equipment, generally between 5 and 15 bars. During the possible washing step, the pressure of the washing fluid is constant, and generally higher than the pressure at the end of filtration and generally between 6 and 20 bars.

[0062] For example, when using a belt filter for solid / liquid separation, the mixture is deposited on the filter and a vacuum is applied under the filter: the liquid is thus drawn from the "cake" deposited on the filter and passes through the filter before being collected in tanks. The vacuum applied is generally between 0.2 and 2 bars, preferably between 0.4 and 1 bar. The operation is sequential, the belt moves according to a defined time sequence, during the movement of the belt, there is no vacuum applied. Optionally, a press can be added in order to increase the pressure applied to the mixture deposited on the belt and increase the liquid extraction. List of figures

[0063] [Fig.l]

[0064] [Fig.l] represents a block diagram of a sugar extraction operation according to a first embodiment of the invention. [Fig.2]

[0065] [Fig.2] represents a block diagram of a sugar extraction operation according to a second embodiment of the invention. [Fig.3]

[0066] [Fig. 3] represents a block diagram of a sugar extraction operation according to a third embodiment of the invention.

[0067] Description of the embodiments The invention will be detailed below using non-limiting examples illustrated by figures 1, 2 and 3. The same references correspond to the same components / fluids / products in all the figures. The figures are extremely schematic.

[0068] It has been discovered, with the present invention, that it is possible and very advantageous to carry out an extraction of free sugars from the biomass pretreated with an alcohol or a hydro-alcoholic mixture. Preferably, the alcohol used is ethanol, which at first glance appears to be a choice that goes against the desired goal, which is to extract the free sugars from the biomass, because ethanol is rather a poor solvent for sugars (solubility of sugars less than 1% by weight). Ethanol is known to be an “anti-solvent” for sugars, used to facilitate their crystallization.

[0069] Advantageously, the alcohol or hydro-alcoholic mixture used for the extraction of free sugars can be produced by a fermentation step of all or part of the free sugars recovered in the washing step of the pretreated biomass.

[0070] Advantageously, the alcohol or hydro-alcoholic mixture used for the extraction of free sugars from the pre-treated biomass can be produced by enzymatic hydrolysis and fermentation of the extracted pre-treated biomass called washed marc.

[0071] It is thus possible to integrate the process of extracting free sugars into the complete process of converting biomass in an industrial installation for the production of ethanol, or for the production of ethanol and sugars.

[0072] The use of an alcohol or a hydro-alcoholic mixture to extract the free sugars from the biomass makes it possible to obtain extraction yields of the free sugars at least equivalent to the use of water as a solvent, all other things being equal (flow rates, performance and operating mode of the liquid-solid separation tool).

[0073] On the other hand, the use of an alcohol or a hydro-alcoholic mixture to extract the free sugars from the biomass makes it possible to obtain additional advantages compared to a purely aqueous washing solution: reduction of the energy consumption associated with the concentration of the extracted free sugars in the juice; reduction of the costs associated with the elimination of salts; limitation of the risks of microbial contamination of the washed marc and of the solution of free sugars extracted from the biomass.

[0074] Preferably, the mass ratio of alcoholic or hydro-alcoholic solution to the mass of biomass (on an insoluble dry matter basis) used in the present invention is between 0.1 and 100. Preferably, the mass ratio of alcoholic or hydro-alcoholic solution to the mass of biomass is between 1 and 10. The mass ratio can be based on the ratio of the flow rates mass when the operation is continuous feed, or on the ratio of masses used in a cycle when the operation is a batch operation.

[0075] The biomass produced in the pretreatment step contains a quantity of water which may vary, depending on the type and conditions of the pretreatment. The extraction of the free sugars may comprise a step of contacting with an alcoholic or hydro-alcoholic solution. The extraction of the free sugars comprises at least one liquid-solid separation step. The extraction of the free sugars may comprise a step of washing the solid obtained after separation of the solid / liquid mixture with an alcoholic or hydro-alcoholic solution.

[0076] Preferably, the alcohol content in the hydro-alcoholic solution and the ratio of mass of hydro-alcoholic solution to mass of biomass are adjusted so that the alcohol content in the extracted free sugar juice is less than 70% by weight (excluding solute), preferably less than 50% by weight (excluding solute).

[0077] Preferably, the alcohol content in the hydro-alcoholic solution and the mass ratio of hydro-alcoholic solution to the mass of pre-treated biomass are adjusted so that the alcohol content in the extracted free sugar juice is greater than 10% by weight (excluding solute).

[0078] The operation of washing the solid obtained after possibly bringing the pretreated biomass into contact with an alcoholic or hydroalcoholic solution and after liquid / solid separation is carried out at a pressure depending on the technology chosen, preferably with a pressure differential between the inlet of the washing solution and the outlet of the sugary juice of between 0.2 and 25 bars, and preferably between 0.4 and 20 bars. Preferably, at least one liquid inlet or at least one liquid outlet is at atmospheric pressure.

[0079] The operation of extracting free sugars from the biomass can be carried out by any liquid-solid extraction techniques known to those skilled in the art. This liquid-solid extraction can be carried out in one or more contact stages. If several contact stages are used, the hydro-alcoholic solution or solutions can be used in cross-currents, co-currents or counter-currents to the biomass.

[0080] The operation of extracting free sugars can be discontinuous or continuous. In the case of a cross-current operation, the hydro-alcoholic solutions successively brought into contact with the biomass can have different alcohol contents.

[0081] In a non-limiting manner, the extraction of free sugars can be carried out by prior dispersion of the biomass in a hydro-alcoholic solution, then liquid-solid separation using equipment such as a filter press or a belt filter.

[0082] Advantageously, the hydro-alcoholic solution is produced on site, by fermentation of a fraction of the sugars of the lignocellulosic biomass into alcohol.

[0083] In one embodiment, the biomass pretreated and freed from its free sugars by the process according to the invention, called washed marc, can then be treated in a hydrolysis and fermentation step with the aim of producing ethanol. In a non-limiting manner, the must obtained at the end of fermentation, containing approximately between 4% by weight and 10% by weight of ethanol, can be filtered to remove the residual solid, and then be used as for carrying out the invention. In a non-limiting manner, the must obtained at the end of fermentation, containing approximately between 4% by weight and 10% by weight of ethanol, can be filtered to remove the biomass and the lignin or any other residual solid, and then distilled according to any technique known to those skilled in the art, in a distillation column or beer column.By a lateral withdrawal from the column, it is possible to obtain a water-ethanol mixture having an alcohol content of between 10% by weight and 96% by weight, and which can be used to reconstitute a hydro-alcoholic solution necessary for carrying out the invention.

[0084] In one embodiment, a fraction of the free sugars present in the juice obtained by carrying out the invention undergoes a treatment (pH adjustment in particular) so as to be able to be treated by alcoholic fermentation. By way of illustration, this fermentation can be an ethanolic fermentation (in the presence of yeast) or a fermentation in an acetone / butanol / ethanol mixture or even a fermentation in an isopropanol / butanol / ethanol mixture. The fermentation must can be distilled to recover solutions of water and alcohol(s) or water + alcohol mixtures, which can be used to carry out the invention.

[0085] The invention can be applied to any type of pretreated lignocellulosic biomass, for example from biomass such as forest residues, fast-growing coppices, Miscanthus, agricultural residues, such as cereal residues such as straw (wheat) or corn residues. Before pretreatment, the biomass may, in a known manner, be conditioned, in particular with mechanical treatment (crushing) so as to obtain biomass particles preferably having a size of at most 300 mm. Generally, the conditioned 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.

[0086] A non-limiting example of implementation of the invention consists of carrying out: a- an explosive pretreatment step, such as for example a pretreatment by steam explosion of the lignocellulosic biomass after its impregnation with an acid solution; b- a step of extracting free sugars from the pretreated biomass obtained in step a- using a hydro-alcoholic solution with contacting the pretreated biomass and hydro-alcoholic solution, solid / liquid separation and possibly washing of the solid with the hydro-alcoholic solution, in order to recover in a juice the sugars released by the biomass during its pre-treatment and a marc (washed); c- a step of valorizing the sugars from the juice recovered in step bd- a possible step of valorizing the marc (washed) obtained in step b-

[0087] A non-limiting example of implementation of step c) consists of carrying out: cl- a liming step c2- a first stage of concentration c3- a demineralization step by resin or electrodialysis c4- a second concentration step c5- a crystallization step

[0088] A non-limiting example of implementation of step d- consists of carrying out: dl- a step of dissolving the (washed) marc d2- an enzymatic hydrolysis of the cellulosic fraction of the marc d3- a step of ethanolic fermentation of the sugars released by step d2-, possibly coupled with d2-d4- a step of distillation of the fermentation must, making it possible to produce ethanol, water, and the hydro-alcoholic solution necessary for carrying out step b-,

[0089] Description of the figures With reference to [Fig.l], a pretreated biomass 1 obtained by pretreatment of lignocellulosic biomass undergoes an operation of extraction of free sugars L by a hydro-alcoholic solution 2 of the water-ethanol type. It produces a washed marc 4 and a juice 3 composed of a hydro-alcoholic solution of extracted free sugars.

[0090] [Fig. 2] represents an extraction of sugars according to the invention which comprises an operation of contacting the pretreated biomass with an alcoholic or hydro-alcoholic solution, then a solid / liquid separation, and a washing of the solid phase obtained after separation with an alcoholic or hydro-alcoholic washing solution. With reference to [Fig. 2], a pre-treated biomass 1 obtained by pre-treatment of the lignocellulosic biomass is brought into contact in a mixer M with a hydro-alcoholic solution 2 of the water-ethanol type. The solid / liquid mixture 21 then undergoes a solid / liquid separation S. It produces a liquid phase 22 composed of a hydro-alcoholic solution of extracted free sugars and a solid phase 23 depleted in free sugars.

[0091] The solid phase 23 undergoes a washing operation W with a hydroalcoholic solution 24 to produce a washed marc 4 more depleted in free sugars than the solid phase 23, and a washing filtrate 25 composed of a hydroalcoholic solution of free sugars. This solution 24 can be of the same composition as the extraction solution 2, or be of a different composition.

[0092] The liquid phase 22 obtained by solid / liquid separation and the washing filtrate 25 can be mixed to constitute the juice 3 of free sugars in a hydroalcoholic solution.

[0093] The succession of contacting, solid / liquid separation and washing steps makes it possible to increase the recovery of free sugars in the juice.

[0094] It should be noted that the invention may provide for recycling of fluids, in particular, for example, of solution 25 to supplement or replace extraction solution 2.

[0095] With reference to [Fig.3], a biomass obtained by pretreatment of lignocellulosic biomass 1 undergoes an operation of extraction of free sugars L by a hydro-alcoholic solution 2 of the ethanol + water type. It produces a washed marc 4 and a hydro-ethanolic solution of extracted free sugars: the juice 3. The operation of extraction of free sugars L comprises contacting the pretreated biomass 1 with the water-ethanol mixture 2, then a solid / liquid separation and optionally a washing step (as with flow 24 of [Fig.2]) of the solid phase obtained by separation with the water-ethanol mixture 2.

[0096] Note that the extraction L can be carried out in one step as in [Fig. 1] or in several steps as in [Fig. 2].

[0097] The washed marc 4 then undergoes an HF enzymatic hydrolysis operation and an alcoholic fermentation operation, dissociated / successive or simultaneous, with the aim of producing an aqueous ethanol solution 6. To this end, the washed marc is brought into contact with one or more aqueous solutions 5 containing the enzymes and yeasts necessary for this transformation. The aqueous ethanol solution 6 thus produced then undergoes a DI distillation operation to produce ethanol 7 and vinasses 8. The ethanol stream 7, in a known manner, is not necessarily pure and may still contain water.

[0098] A hydro-alcoholic solution 2 is withdrawn from the distillation column DI in order to feed the extraction operation L.

[0099] The hydro-ethanolic solution of extracted free sugars (juice) 3 undergoes one or more optional purification steps, here in the form of liming (i.e. depleted in certain mineral salts of the sulfate type). Stream 9 represents the separation agent(s) (calcium hydroxide, resins, etc.) intended to deplete the juice 3 of its mineral salts, in particular of the sulfate type originating from the sulfuric acid used to pretreat the biomass. This stream 9 is brought into contact with the hydro-ethanolic solution of extracted free sugars 3. Stream 10 represents the separation agent(s) which have captured the mineral salts (calcium sulfate, saturated resins, etc.), which are then replaced or regenerated.

[0100] The hydro-ethanolic solution of purified free sugars (juice depleted in salts) 11 undergoes a concentration operation by evaporation D2 with the aim of producing an aqueous solution of concentrated purified free sugars 13 and a hydro-alcoholic solution 12. This hydro-alcoholic solution 12 can advantageously be directly recycled to the step of extracting the free sugars from the marc L (dotted line in the figure), or indirectly recycled by feeding the distillation column D1. Examples

[0101] A lignocellulosic biomass, wheat straw, containing 30% by weight of hemicellulose with a dry matter content of 90% by weight and an insoluble dry matter content of 80% by weight undergoes a pretreatment which consists of: - impregnation with an aqueous solution of sulfuric acid: the impregnation is carried out in the presence of acid liquor heated to 80°C and a residence time of 2 minutes. The acid concentration in the liquor is 2.5% by weight (expressed as % by weight of H2SO4). The dry matter content of the impregnated biomass is 25% by weight. - the introduction of this impregnated biomass into a pressurized reactor heated to 180°C with steam injection, for a residence time of 5 min, allowing a conversion yield of hemicellulose to monomeric xylose of 70% by weight; - an atmospheric pressure expansion releasing steam and a pre-treated biomass having a dry matter content of 50% by weight and an insoluble dry matter content of 40% by weight.

[0102] The pretreated biomass thus produced is used to produce examples 1 and 2 (non-compliant), and 3 and 4 (compliant with the invention).

[0103] The extraction of the free sugars present in the pretreated biomass, according to the invention and for the four examples, is done in two stages. 1 / The pretreated biomass is first repulped, at room temperature at a dry matter content MS of 20% by weight and an insoluble dry matter content MSI of 16% by weight, with an aqueous mixing solution having ethanol contents between 0 and 70% by weight, at a rate of 1.3 g of mixing solution per gram of pretreated biomass. “Repulping” means the operation consisting of bringing the pretreated biomass into contact with the hydroalcoholic solution by suspending the biomass in the solution. 2 / The repulped biomass feeds a filter press to carry out a solid / liquid separation with the production of sugar juice and washed marc: The repulped biomass is first filtered under pressure at a temperature of 50°C, then the solid phase retained by the filter cloth in the filtration chambers of the filter press is compacted into injecting air to press. The insoluble dry matter content in the washed marc after liquid-solid separation is approximately 45% by weight for the different examples. The sugar content in the different juices is determined by HPLC (high performance liquid chromatography), and makes it possible to determine a sugar extraction yield defined as the ratio between the quantity of sugars extracted in the juice and the quantity of sugars present in the pretreated biomass of the order of 75% for all examples. The sugar content (glucose and xylose in particular) in the juice obtained is 56 g / kg. The H2SO4 content in the juice obtained is of the order of 1.1% by weight determined by ion chromatography. Optionally, the solid phase retained by the filter cloth in the filtration chambers of the filter press before compaction is washed with the hydro-alcoholic solution. This washing produces a washing filtrate.This optional washing step takes place at a constant flow rate of the washing solution. The pressure is slightly lower than the filtration pressure. The sugar juices are then limed at 50°C, as follows to achieve a pH of 10: The concentration of the added milk of lime solution is equal to 15% by weight. The mixture of milk of lime and juice is left stirring for 30 to 60 minutes. Once the milk is mixed with the sugar juice, the lime reacts immediately with the non-sugar components thanks to the presence of calcium ions and hydroxide ions. Calcium ions help in the dissociation of certain organic acids by forming calcium salts which precipitate: oxalic, citric, tartaric, and phosphoric acid salts. Calcium also induces coagulation reactions of coloring compounds. Hydroxide ions neutralize acids and lead to the precipitation of magnesium or iron hydroxides.The ion concentration is determined by ion chromatography, before and after liming, for the different examples. It allows the determination of a rate of elimination of sulfate ions, which is given in Table 1 below. A loss of sugars of 10% is observed after liming.

[0104] The sugar juices are then concentrated using a rotary evaporator operated under vacuum, to a concentration level of approximately 300 g sugars / kg water.

[0105] Furthermore, an analysis is carried out by gas chromatography to determine the ethanol content (and by difference the water content) in the evaporated solvent. On this basis, a calculation is made of the enthalpy of vaporization corresponding to the energy to be provided to concentrate the sugars, compared to the reference case (i.e. in the absence of ethanol in the extraction solution) which is example 1. The energy gains are reported in the table below.

[0106] [Tables 1] Example %wt Ethano 1 in the extraction solution %wt Ethanol in the juice before liming and evaporation Sulfate removal rate (%) Concentration at 300 g / kg water Reduction in enthalpy of vaporization (%) compared to Example 1 1 0 0 86.4 Precipitation of salts 0.0 2 15 10 95.9 Precipitation of salts 11.3 3 30 20 98.2 - 22.6 4 50 33 99.7 - 37.7 5 70 47 99.9 - 52.8

[0107] For comparative examples 1 and 2, where the salt removal rates are lower, precipitation of the salts is observed, which is not desirable (fouling of the equipment).

[0108] It can be seen that this precipitation is correlated with the ethanol content in the juice, itself correlated with the ethanol content of the extraction solution and the characteristics of the biomass used here (its initial water content before extraction). The preferred minimum value of ethanol in the juice is here at least 15% by weight, preferably at least 18 or 20% by weight, which amounts to preferably choosing an ethanol content in the extraction solution greater than 15% by weight, in particular at least 18% or at least 20% or at least 25% by weight.

[0109] It should be noted that depending on the implementation of the extraction, in particular depending on the choice of the composition (of the alcohol(s)) of the extraction solution and depending on the nature of the biomass, the minimum alcohol content of the extraction solution may be less than or equal to 15% by weight, for example between 5 and 15% or between 5 and 10% by weight, and already bring about a positive effect according to the invention (energy gain and no / little fouling by precipitation of salts). The invention brings about a gain, depending on the case, as soon as the extraction solution comprises a non-negligible alcohol content, in particular of at least 5% by weight.

[0110] It can be seen from these results that the examples according to the invention 3 to 5 with a repulping of the biomass pretreated with a hydro-alcoholic solution allow, at a similar sugar extraction yield in the juice, (extraction yield of 75.6% by weight for the examples according to the invention) a much more effective treatment of depletion of mineral salts from the juice, moving to an elimination of sulfates of more than 95% and even more than 98%, which is remarkable.

[0111] In addition, a strong reduction in the enthalpy of vaporization is observed, all the greater as the alcohol content of the extraction solution is high, resulting in a reduction in the energy cost of extraction, the evaporation of a water-alcohol mixture being less energy-consuming than the evaporation of an entirely aqueous phase. A favorable impact on equipment costs can also be expected.

Claims

Claims

1. A method for treating a previously pretreated lignocellulosic biomass (1), characterized in that the biomass is pretreated by impregnation with an acidic, basic or oxidizing aqueous solution, then cooking or steam explosion so as to obtain said pretreated biomass (1) in the form of a solid / liquid mixture, and in that said method comprises the extraction of free sugars from said pretreated biomass by a hydro-alcoholic extraction solution (2) containing between 15% by weight and 50 or 70% by weight of alcohol, at a temperature less than or equal to 100°C, so as to obtain a liquid phase enriched in free sugars, called juice (3), and a solid phase depleted in free sugars, called marc (4), characterized in that the extraction of free sugars from the pretreated biomass (1) comprises contacting said pretreated biomass (1) with the hydro-alcoholic extraction solution (2), then a solid / liquid separation.

2. Method according to one of the preceding claims, characterized in that the extraction of the sugars is carried out on the pretreated biomass (1) having a dry matter MS content of at least 25%, in particular at least 30% or at least 35%, and preferably at most 70 or 65%, in particular between 30% and 65%.

3. Method according to one of the preceding claims, characterized in that the extraction of free sugars from the pretreated biomass (1) comprises suspending said biomass in said hydro-alcoholic extraction solution (2).

4. Method according to one of the preceding claims, characterized in that the extraction of the free sugars comprises, after the solid / liquid separation, washing of the solid phase (23) obtained by said separation with an alcoholic or hydroalcoholic washing solution (24), the washing preferably being carried out continuously in co-current or counter-current.

5. Method according to one of the preceding claims, characterized in that the contacting of the pretreated biomass (1) with the hydro-alcoholic extraction solution (2) is carried out by a mixer continuously or discontinuously, in one or more steps / stages.

6. Method according to one of the preceding claims, characterized in that the solid / liquid separation is carried out discontinuously or continuously, in particular by a filter press or a belt filter.

7. Method according to one of the preceding claims, characterized in that the extraction solution (2) and / or the washing solution (24) when washing is planned, comprises at least one alcohol chosen from: methanol, ethanol, isopropanol, n-butanol, isobutanol.

8. Method according to one of claims 4 to 7, characterized in that the washing solution (24) when washing is planned, is a hydro-alcoholic solution containing at least 5% by weight of alcohol, in particular at least 10% by weight, preferably between 5% by weight and 96% by weight, or between 10% by weight and 85% by weight, or between 15% by weight and 50 or 70% by weight of alcohol.

9. Method according to one of the preceding claims, characterized in that the alcohol content of the hydroalcoholic extraction solution (2) and the ratio of the mass flow rate of said solution to the mass flow rate of pretreated biomass (1) are adjusted so that the alcohol content in the juice is at most 70% by weight excluding solute, preferably at most 50% by weight excluding solute, and preferably at least 10% by weight excluding solute.

10. Method according to one of the preceding claims, characterized in that the juice (3) obtained is treated to deplete it of mineral salts, in particular by liming and / or by contacting with one or more active substrates of the ion exchange resin(s) type and / or by electrodialysis.

11. Method according to one of the preceding claims, characterized in that the juice (3) obtained is concentrated in sugars, in particular by evaporation, optionally after and / or before a treatment to reduce the mineral salts in said juice.

12. Method according to the preceding claim, characterized in that the concentration is carried out by evaporation, with recovery of the alcohol and / or water to constitute all or part of the alcohol and / or water of the hydro-alcoholic extraction solution used (2) and / or for the washing solution (24) when washing is planned.

13. Method according to one of the preceding claims, characterized in that it comprises an enzymatic hydrolysis of the marc (4) obtained after extraction, which is followed by, or concomitant with, an alcoholic fermentation, then a distillation of the liquid fraction obtained after fermentation, and in that part of the alcohol (7) and / or all or part of the water (8) recovered during the distillation is / are used to constitute all or part of the hydroalcoholic extraction solution (2).

14. Process for treating a lignocellulosic biomass, said process comprising the following successive steps: - impregnation of the biomass with an acidic, basic or oxidizing aqueous solution, to obtain an impregnated biomass, - pretreatment of the impregnated biomass by cooking or steam explosion, to obtain a pretreated biomass (1) in the form of a solid / liquid mixture, - enzymatic hydrolysis of the pretreated biomass (1), to obtain a hydrolyzed biomass, - optionally alcoholic fermentation of the hydrolyzed biomass, characterized in that an extraction at a temperature lower than or equal to 100°C of the free sugars of at least a portion of the pretreated biomass (1) is carried out using a hydroalcoholic extraction solution (2) containing between 15% by weight and 50 or 70% by weight of alcohol, before its enzymatic hydrolysis,said extraction of free sugars from the pretreated biomass (1) comprising contacting said biomass with the hydro-alcoholic extraction solution (2), then a solid / liquid separation.,

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