Method for treating lignocellulosic biomass

Abstract

The invention relates to a method for treating lignocellulosic biomass, which method comprises - a) a step (2) of pretreating the biomass to obtain pretreated biomass (3) - b) a first solid / liquid separation step of separating the solids / liquids of all or a portion (3a) of the pretreated biomass (3) into a first solid fraction (7) and a first liquid fraction (6) comprising a mixture of sugars - c) a step (14) of performing enzymatic hydrolysis on the first solid fraction (7) of the pretreated biomass to obtain a hydrolysate (15) in the form of one or more sugars - d) a step (24) of purifying the first liquid fraction by bringing the first liquid fraction (6) into contact with microorganisms that consume only C6 sugars in order to obtain a purified liquid fraction (26) - e) a second solid / liquid separation step (27) of separating the solid / liquids of the purified liquid fraction (26).

Description

[0001] PROCESS FOR TREATING LIGNOCELLULOSIC BIOMASS

[0002] Technical field

[0003] The present invention relates to the treatment of sweet juices, in particular those known as second generation (2G), which can be obtained from lignocellulosic biomass.

[0004] These sugary juices can be used to produce other products by chemical or biochemical means (for example alcohols such as ethanol, butanol, or other molecules, for example solvents such as acetone, intermediate products used in the chemical industry, etc.), in particular as substitutes for petrochemical derivatives.

[0005] Prior art

[0006] 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 industries, such as the food industry, paper, etc.

[0007] Different types of processes exist for converting lignocellulosic biomass into sugary juices depending on the type of biomass. In the case of sacchariferous plants (sugar beet, sugar cane) or starchy plants (corn and wheat), so-called first-generation (1G) sugary juices are obtained, for example through extraction operations.

[0008] If it is biomass of the agricultural, forestry or paper residue type, so-called second generation (2G) sweet juices are obtained by a biochemical transformation process which generally includes a pretreatment step and an enzymatic hydrolysis step using an enzymatic cocktail. The pretreatment most often includes an impregnation step using an acidic, basic or oxidizing liquor, then cooking of the impregnated biomass which is possibly accompanied by a steam explosion. The sweet juices resulting from the hydrolysis can then be further treated, for example by fermentation to convert them into alcohol, and the process also includes separation and / or purification steps.

[0009] These sweet juices can also come from a mixture of sweet juices from different types of biomass.

[0010] 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 30% by weight), which is a polysaccharide most often consisting mainly of pentoses; and lignin (15 to 25% 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.

[0011] Among the three basic polymers that integrate lignocellulosic biomass, cellulose and hemicellulose are those that allow the production of 2G sweet juices.

[0012] Most often, hemicellulose is mainly broken down into sugars during pretreatment, and the cellulose is converted into glucose by enzymatic hydrolysis. However, access to raw cellulose remains difficult for enzymes, hence the need for the pretreatment mentioned above. 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.

[0013] 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.

[0014] Different configurations are reported for example in the document “Production of bioethanol from lignocellulosic materials via the biochemical pathway: A review”, M. Balat, Energy Conversion and Management 52 (2011) 858-875, or in the document “Bioethanol production from agricultural wastes: an overview”, N. Sarkar, S. Kumar Ghosh, S. Bannerjee, K. Aikat, Renewable Energy 37 (2012) 19-27.

[0015] 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).

[0016] Thus, the pretreatment can generally comprise three stages which are the preparation of liquor, the impregnation of the biomass with this liquor and the pretreatment of the impregnated biomass, for example by cooking possibly coupled with a steam explosion: Patent FR 3 075 203 describes a process with impregnation of the biomass with an acid liquor, then cooking and steam explosion of the impregnated biomass, with an adjustment of the acidity of the acid liquor and a recycling of the latter. Patent FR 3 075 201 also describes a process for pretreatment of the biomass by acid impregnation then steam explosion, with in addition a washing of the means of feeding the reactors and recycling of the washing water in the process.

[0017] The sweet juices thus obtained from lignocellulosic biomass, in particular after its pretreatment or after enzymatic hydrolysis in the case of so-called 2G sugars, are in the form of a mixture of sugars in the aqueous phase, where we find so-called C5 sugars (i.e. with 5 carbons), such as xylose and arabinose, and so-called C6 sugars (i.e. with 6 carbons), such as glucose, mannose and galactose.

[0018] Particularly in the case of type 2G sweet juices resulting from the pretreatment of lignocellulosic biomass, we observe for the majority of lignocellulosic biomasses, in the sweet juice, a proportion of C5 sugars significantly higher than that of C6 sugars. By sweet juice, we mean that sugars are released by the pretreatment, and that they can be solubilized by mixing the pretreated biomass with water for example.

[0019] However, there are outlets for juices sweetened with C5 specifically (for example to convert xylose into xylitol).

[0020] To a lesser extent, these sweet juices may also contain furfural or furfural derivatives, sugar degradation products, carboxylic alcohols, furanic compounds, which are fermentation inhibitors, which is detrimental when one wants to continue the conversion of sweet juices into alcohols by fermentation using microorganisms such as yeasts or bacteria.

[0021] For example, the publication "Removal of the Fermentation Inhibitor, Furfural, Using Activated Carbon in Cellulosic-Ethanol Production" by Kuang Zhang et al. (Industrial & Engineering Chemistry Research 2011, 50, 14055-14060) demonstrates the inhibitory character of furfural at a content of 4 g / L for the bacterium Zymomonas mobiliz A3 during fermentations.

[0022] There is therefore a need to separate or purify C5 sugars from other sugars, in particular C6 sugars, and possibly other undesirable compounds, in order to obtain pure C5 sugar juices, or at least with an increased content of C5 sugars compared to other sugars in the sugar juice, and this particularly in the context of production of sugars or alcohol from 2G lignocellulosic biomass.

[0023] Different purification / separation techniques have already been considered.

[0024] Thus, patent application WO 2022 / 023686 describes a biomass treatment comprising pretreatment and then enzymatic hydrolysis to obtain a sweet juice comprising glucose, which is then clarified and purified by filtration through activated carbon, in order to remove suspended matter and capture certain soluble contaminants. This is a simple technique, but it does not allow the separation of C5 sugars from C6 sugars.

[0025] The publication “Removal of furfural and HMF from monosaccharides by nanofiltration and reverse osmosis membranes” by Tielin Wang et al. (Journal of the Energy Institute 91 (2018) 473-480) proposes to remove furfural and its derivative from a sugar juice to increase the yield of sugar juice fermentation, using nanofiltration and reverse osmosis membrane techniques. This is a complex and expensive technique, and it does not allow the separation of C5 sugars from both C6 sugars and furfural derivatives, unless multiple membrane filtration operations are performed.

[0026] US patent application 2013 / 0149761 proposes to precipitate non-sugar compounds using barium or calcium hydroxide, in order to obtain a juice that contains only sugars such as glucose, xylose and other sugars. This technique therefore does not allow for the selective separation of sugars, but simply for the removal of minority compounds from the sugary juice that are by-products of the biomass pretreatment.

[0027] Patent EP3990464 describes the separation of glucose from a mixture of C5 and C6 sugars by adsorption of glucose onto a FAU-type zeolite adsorbent. This is an interesting method, which does not, however, allow for optimal separation of glucose, which has selectivity that can be improved.

[0028] Patent EP3990668 describes the separation of xylose from a mixture of C5 sugars and C6 sugars, also by adsorption, here of xylose, on a FAU type zeolite adsorbent, with the same limit in terms of selectivity in the separation carried out.

[0029] However, in one case (separation of glucose) as in the other (separation of xylose), it may be necessary, depending on the intended applications, to obtain extremely pure separated sugars.

[0030] The invention therefore aims to overcome the aforementioned drawbacks. Its aim is to improve the techniques for selectively separating sugars in a sweet juice comprising different sugars, in particular C5 sugars and C6 sugars, with the aim in particular of obtaining juice enriched in C5 sugars. (By "enriched" juice, it is meant that the sweet juice obtained by the invention has a ratio of C5 / C6 sugars higher than the ratio of the sweet juice obtained without the invention).

[0031] The invention also aims to integrate this separation into a production line for sugar or alcohol from lignocellulosic biomass in order to improve its operation or performance, in particular so as to obtain a higher quality of sweet juice in the case of sugar production, and / or so as to obtain a higher conversion rate into alcohol in the case of alcohol production. Summary of the invention

[0032] The invention firstly relates to a method for treating lignocellulosic biomass, said method comprising

[0033] - a) a biomass pretreatment step, comprising cooking the biomass, possibly accompanied by a steam explosion, to obtain a pretreated biomass,

[0034] - b) a first step of solid / liquid separation of all or part (3a) of the pretreated biomass (3) obtained in step a) into a first solid fraction (7) of pretreated biomass and a first liquid fraction (6) comprising a mixture of compounds, in particular in aqueous phase, comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons and the content by weight of C5 sugars of which is greater than the content by weight of C6 sugars,

[0035] - c) a step of enzymatic hydrolysis (14) of the first solid fraction (7) of pretreated biomass obtained in step b), to obtain a hydrolysate (15) in the form of sugar(s), including C6 sugars with 6 carbons,

[0036] - d) a step of purifying said first liquid fraction by bringing said first liquid fraction into contact with first microorganisms consuming, among the sugars of said fraction, essentially only C6 sugars, in order to obtain a purified liquid fraction, containing C5 sugars and depleted in C6 sugars,

[0037] - e) a second step of solid / liquid separation of the purified liquid fraction containing C5 sugars and depleted in C6 sugars obtained in step d) to obtain a second solid fraction comprising the first microorganisms and a second liquid fraction containing C5 sugars and depleted in C6 sugars.

[0038] In this text, "essentially only C6 sugars" means that the microorganism does not consume the other sugar(s), particularly C5 sugars, present in the mixture, or only in such a small proportion that it is negligible / not measurable.

[0039] For the sake of brevity, in this text, sugars with 5 carbons will be referred to as C5 sugars, and sugars with 6 carbons as C6 sugars.

[0040] Preferably, the first liquid fraction contains sugars derived mainly, in particular entirely, from the depolymerization of the hemicelluloses present in the lignocellulosic biomass. This first fraction is a sweet juice obtained without the addition of enzymes, and obtained at the end of the pretreatment of a lignocellulosic biomass. The invention has thus developed a new technique for separating C5 and C6 sugars in a sweet juice resulting from the pretreatment of lignocellulosic biomass: the invention has selected in step d) called purification a microorganism which will selectively consume the sugar, here the C6 sugar, which is to be removed from the first liquid fraction which is a sweet juice, in order to obtain a liquid fraction said to be purified in C5 sugars, which can be recovered as such in the chemical industry in particular, or which can be used in an alcohol production line, in particular ethanol.

[0041] It is a separation by biochemical means, rather than by physical or chemical means, which is very interesting: it is both simpler to implement than known filtration techniques, and significantly more efficient and selective.

[0042] For the purposes of the invention, the microorganism may be a single type of microorganism or a combination of different microorganisms.

[0043] For the purposes of the invention, the term “mixture in aqueous phase of compounds comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons” may also be designated, for the sake of brevity, under the term “sweet juice”.

[0044] For the purposes of the invention, the term “sugars” means sugars in their monomeric form (and not in an oligomeric / polymeric form).

[0045] For the purposes of the invention, “juice” is equivalent to a mixture of compounds in aqueous phase: the juice is aqueous, the same is true for the first and second liquid fractions of the treatment method according to the invention described above.

[0046] Generally in this text, unless expressly stated otherwise, all liquid fractions are aqueous.

[0047] In this purification step d), the microorganism will consume the C6 sugar from the first liquid fraction at least for its own maintenance / metabolism or growth: the C6 sugar can thus disappear, in its entirety or almost entirely, by appropriately dosing the quantity / activity of the microorganism according to the quantity / concentration of C6 sugars in the first liquid fraction to be purified.

[0048] The microorganism can also, depending on the quantity of C6 sugars present in the liquid fraction, depending on the operating conditions used (for example pH, temperature, aeration, etc.) and depending on the quantity and type of microorganism chosen, convert the sugar into another usable compound. (Note, however, that the microorganism can also consume a very small quantity of C5 sugar such as xylose, but it remains essentially a consumer of C6 sugars). Thus, advantageously, the microorganism can convert at least a portion, notably the majority, of the C6 sugars into alcohol, notably ethanol. The conversion into alcohol is not necessarily complete, because the microorganism can use some sugars for non-alcohol by-products or for its metabolism.We therefore understand here by "the majority" the fact that the microorganism can convert at least half of the C6 sugars into ethanol (in particular more than half, for example at least two thirds of said C6 sugars, or even almost all of them).

[0049] Ethanol is a highly recoverable product: it can be easily separated from the first purified liquid fraction. For example, ethanol can be separated from an aqueous mixture by distillation or by stripping. It can also be preserved, in whole or in part, in a mixture with C5 sugars, in particular to exploit its antimicrobial properties.

[0050] The microorganism used in purification step d), particularly when it is yeast, is in solid suspension in the first separated liquid fraction. In most cases, therefore, it is planned to separate these solid microorganisms, in order to be able to recover the purified sweet juice free of solid suspension. This separation, provided for in solid / liquid separation step e) of the process according to the invention, can use any device known to those skilled in the art, such as a filtration, centrifugation, decantation, sieve, cyclone device, or the combination of several of these devices for example.

[0051] It could be optional in the case where the purified liquid fraction is used, as is or after separation of the alcohol it contains, for example for propagation of microorganisms such as yeast or fermentation.

[0052] The invention therefore "intercalates" into a biomass treatment process aimed at converting it into sugars and then possibly into alcohol, and which provides, in a known manner, a pretreatment of the biomass then its enzymatic hydrolysis, then its possible fermentation, a stage of purification of the sugary juice obtained at the end of the pretreatment, which opens the way to a quantity of new possibilities for valorization, product quality and biomass conversion yield, as detailed below.

[0053] Advantageously, only a first part of the pretreated biomass obtained in step a) is conducted to the first step b) of solid / liquid separation and a second part (or the remainder) of the pretreated biomass is conducted directly to step c) of enzymatic hydrolysis. The enzymatic hydrolysis can then be carried out on the two types of streams at the same time, one coming directly from the pretreatment, the other having passed through a solid / liquid separation step, the relative proportion of the stream from the impregnated biomass which goes to the solid / liquid separation and of the stream from the impregnated biomass which goes directly to the enzymatic hydrolysis is adjustable, for example between a relative proportion of 90 / 10 to 10 / 90 by weight.

[0054] We can thus jointly operate the enzymatic hydrolysis at the same time

[0055] - on the solid residue resulting from the solid / liquid separation b), because this residue still contains compounds convertible into sugars by enzymatic hydrolysis,

[0056] - and on pretreated biomass resulting directly from the pretreatment, which makes it possible to maintain a high conversion yield by enzymatic hydrolysis compared to the initial quantity of biomass, despite the removal of a portion of pretreated biomass to recover the soluble sugars.

[0057] Step b) of solid / liquid separation may, according to a preferred embodiment, comprise a first step of contact between the pretreated lignocellulosic biomass and water, then a second step of filtration, and optionally washing.

[0058] When step b) of solid / liquid separation comprises a step of contacting the pretreated biomass with a fluid and then a washing step, this can be carried out in co-current or counter-current mode, in particular using part of the recovered liquid fraction as washing and / or contacting fluid.

[0059] Step b) of solid / liquid separation can, according to a preferred embodiment, be carried out on a filtration unit, in particular a belt filter or a filter press, by centrifugation or by decantation.

[0060] The process according to the invention may also comprise a step f) of fermentation by third microorganisms of the hydrolyzate in the form of sugar(s) obtained in step c), in order to obtain a fermented biomass comprising at least one alcohol, in particular ethanol. This is then a process for producing ethanol-type alcohol which can be used as biofuel.

[0061] And in this case, according to a preferred embodiment, the enzymatic hydrolysis steps b) and fermentation f) can be carried out simultaneously. This is called SSCF for "Simultaneous Saccharification and Co-Fermentation" in English.

[0062] Preferably, at least a portion of the second solid fraction comprising the first microorganisms obtained in step e) is recycled in purification step d). Indeed, the microorganisms retain a certain activity for a certain time for a certain concentration of sugars, here in C6 sugars, activity which goes beyond a single production when the purification is carried out, for example, discontinuously, in batch in a dedicated reactor: it is thus possible to recover the microorganisms from the purified liquid fraction and reintroduce them into the reactor where the purification takes place, for the following n productions with the possible addition of additional microorganisms if necessary, as their activity decreases.

[0063] Advantageously, the second liquid fraction containing C5 sugars and depleted in C6 sugars obtained in step e) contains alcohol, in particular ethanol, obtained by conversion of all or part of the C6 sugars under the action of the first microorganisms, as seen above. It is then possible, according to the invention, to separate in a step g), in particular by evaporation or stripping, said second liquid fraction into a third liquid fraction enriched in sugars and a fourth liquid fraction enriched in alcohol. This separation between sugar(s) and alcohol can in fact have different advantages depending on the product(s) that one wishes to valorize.

[0064] Thus, if we want to recover a very pure liquid fraction of C5 sugars, it may be necessary, in order to respect a given purity level, to remove the alcohol it contains. We can also remove only a part of it, so that a residual alcohol content in the sugar solution guarantees an anti-microbial effect.

[0065] Furthermore, ethanol is in itself a recoverable product, in two ways: either directly as a recoverable product, or by reintegrating it into the process of the invention, if it aims at a conversion of biomass into alcohol (ethanol): it is thus possible, for example, to add it to the ethanol obtained in the process by enzymatic hydrolysis / fermentation, then distillation (to dehydrate it): the two ethanol streams can be mixed either upstream or downstream of the dehydration device such as the distillation column of the installation. It is thus possible to increase the conversion efficiency of the biomass into ethanol in the process.

[0066] Advantageously, it is also possible to send all or part of the fourth liquid fraction containing the alcohol obtained in step g) to the fermentation step f), or, as detailed above, to mix all or part of said fourth liquid fraction with the fermented biomass comprising at least one alcohol obtained at the end of the fermentation step f).

[0067] The method according to the invention may also comprise a step h) of producing enzymes from second microorganisms, in particular fungi, in order to use said enzymes to ensure the enzymatic hydrolysis of step c). And in this case, all or part of the second liquid fraction containing C5 sugars and depleted in C6 sugars obtained in step e) or of the third liquid fraction enriched in sugars obtained in step g) may be sent to said step h) as a substrate for the growth of the second microorganisms and / or for the production of enzymes by said microorganisms. This is the case where the method integrates in situ production of enzymes to carry out the enzymatic hydrolysis of the pretreated biomass (the other alternative being to bring enzymes produced on another site to the production site).And in this case, the liquid fractions (in whole or in part) obtained according to the invention due to the introduction of the purification step, and which contain C5 sugars, are particularly suitable for the growth of fungi and for the production of enzymes.

[0068] It should be noted that it is also possible, or alternatively, to send all or part of the hydrolysate obtained at the end of the enzymatic hydrolysis and containing sugars, in particular glucose, to step h) of enzyme production as a substrate for the growth of the second microorganisms, or for the production of enzymes by them.

[0069] The method according to the invention may also comprise a step i) of propagation of third fermentation microorganisms, in order to use said microorganisms, in particular yeasts, to ensure the fermentation of step f) when it is planned. This is the case where the microorganisms are propagated in situ, on the biomass treatment site. And in this case, all or part of the second liquid fraction containing C5 sugars and depleted in C6 sugars obtained in step e) or the third liquid fraction enriched in sugars obtained in step g) may be sent to said step i) as a substrate for propagation of said third microorganisms. Here again, these fractions (in whole or in part) are particularly suitable for helping to propagate yeast-type microorganisms used for the fermentation of hydrolyzed biomass, also called hydrolyzate.

[0070] According to the process of the invention, all or part of the second liquid fraction containing C5 sugars and depleted in C6 sugars obtained in step e) or the third liquid fraction enriched in sugars obtained in step g) can also be sent to fermentation step f). In this case, when the aim is to produce alcohol, the C5 sugars contained in this or these fractions continue their conversion into alcohol with the hydrolysate from the biomass.

[0071] It can thus be seen that one, the other or both of the liquid fractions (or at least a part of one or the other of these fractions) containing C5 sugars and obtained as a result of the purification provided for by the invention, can be used according to at least three different modes, each of these modes being able to be operated alternatively or cumulatively with the other two. The choice will be made, in particular, according to whether the fermentation and enzyme-producing microorganisms are produced in situ or not, according to whether the final product targeted is a solution of C5 sugar juice or alcohol (ethanol) or even both, and even according to the type of biomass, because the relative content of C6 sugars of the 1 ère liquid fraction before purification varies depending on the biomass chosen.

[0072] The first liquid fraction obtained in step b) may also comprise furfural. This is particularly the case when the liquid fraction to be purified comes from biomass pretreated under acidic conditions. And the first microorganisms can also advantageously consume furfural, in particular at least in part by converting furfural into alcohol, in particular furfuryl alcohol. Here again, this consumption is very interesting, insofar as furfural is known to be an inhibitor of fermentation reactions (using yeasts): this improves the productivity and yields of any biochemical conversions planned for the purified juice. It has also been observed that furfural can also be an inhibitor of the growth of microorganisms producing enzymes, in particular the fungus Trichoderma Reesei.

[0073] The first liquid fraction obtained in step b) may also comprise 5-hydroxymethyl furfural 5-HMF. This is particularly the case when the liquid fraction to be purified comes from biomass pretreated under acidic conditions. And the first microorganisms can also advantageously consume 5-hydroxymethyl furfural, in particular at least in part by conversion of 5-hydroxymethyl furfural into 5-hydroxymethyl furfuryl alcohol.

[0074] Here again, this consumption is very interesting, insofar as 5-HMF is also known to be an inhibitor of fermentation reactions: this improves the yields of possible biochemical conversions planned for the purified juice.

[0075] The first liquid fraction to be purified comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons may also comprise other compounds from the degradation of C5 or C6 sugars, in particular furanic compounds, organic acids, high molecular weight compounds, in particular when it comes from the pretreatment of lignocellulosic biomass at high temperature or by solvent.

[0076] What is advantageous, and surprising, in the process according to the invention, is that the biochemical purification according to the invention of this first liquid fraction remains efficient, even when the liquid fraction contains this type of compound, whereas one could have feared that they would potentially play a role of inhibitor(s) with regard to the conversion of C6 sugars during the purification according to the invention.

[0077] The first liquid fraction to be purified may also include mineral salts.

[0078] The first liquid fraction to be purified may also comprise sugars in oligomeric form. Preferably, the first and third microorganisms are chosen from yeasts, bacteria, fungi, and in particular from yeasts in the genus Saccharomyces, in particular the species Saccharomyces cerevisae or, among bacteria, in the genus Corynebacterium, in particular the species Corynebacterium, Zymomonas mobilis. The choice of Saccharomyces cerevisae, in particular, is interesting, because the wild strain naturally consumes C6 sugars, but not C5 sugars, and work has been carried out to genetically modify it so that it is precisely capable of consuming both types of sugars: the invention thus recommends returning to the non-genetically modified version of this yeast / the native version, in particular for the first microorganism, precisely to exploit its selectivity with respect to sugars, hitherto perceived as a disadvantage.

[0079] Preferably, the second microorganisms are chosen from fungi, in particular filamentous fungi, preferably those of the genus Trichoderma, in particular Trichoderma reesei.

[0080] According to a preferred embodiment of the invention, the pretreatment according to step a) of the biomass comprises

[0081] - a1) a sub-step of impregnation of the biomass with a liquor, in particular acidic, to obtain an impregnated biomass (alternatively, the liquor can be basic or oxidizing or be only water)

[0082] - a2) a sub-step of cooking the impregnated biomass, possibly accompanied by a steam explosion, to obtain a pre-treated biomass.

[0083] The process according to the invention may also comprise a step j) of separation, in particular by distillation, of the fermented biomass in the form of alcohol obtained in step f), with an optional step k) of solid / liquid separation of the fermented biomass before or after said separation step j).

[0084] Step j) in particular allows the alcohol to be dehydrated, and its preferred embodiment uses a beer column to carry out distillation, allowing the ethanol to be recovered at the top of the column, and vinasse at the bottom of the column.

[0085] The possible step k) is preferably carried out before the separation step j), to avoid any risk of traces of solid residue in the distillation column, when step j) is carried out by distillation.

[0086] Preferably, the purification d) of the first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons with the microorganism is carried out at a temperature between 20 and 60°C, in particular between 25 and 40°C, in particular between 30 and 35°C. The treatment temperature is to be adapted according to the microorganism chosen, each microorganism having a temperature range where its activity is maximum.

[0087] Advantageously, the purification d) of the first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons with the microorganism has a duration of between 5 minutes and 15 hours, in particular between 10 minutes and 8 hours.

[0088] Advantageously, the purification d) of the first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons with the microorganism can be carried out in batch, in fed-batch of said liquid fraction, or continuously.

[0089] The selected microorganism which will selectively consume the C6 sugar according to the invention, i.e. the first microorganism, can be added in one go directly with the first liquid fraction, or according to a sequential feeding, independently or not of the feeding of the first liquid fraction.

[0090] The duration of purification step d) is to be adjusted according to the type and quantity of microorganism used, according to the quantity of C6 sugars in the liquid fraction to be purified, according to the quantity of compounds known as inhibitors of the microorganism (furanic compounds such as furfural or 5-hydroxymethyl furfural, carboxylic acids such as acetic acid or formic acid, or phenolic compounds) for the Saccharomyces Cerevisae yeast, and according to the final acceptable content of C6 sugars in the purified juice, or, expressed differently, according to the desired degree of purity of C5 sugars.

[0091] Advantageously, the purification d) of the first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons with the microorganism can be carried out at a pH between 2 and 10, in particular between 4 and 6, in particular between 4.5 and 5.5.

[0092] Advantageously, the purification d) of the first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons with the microorganism can be carried out under aerobic or anaerobic conditions, depending on the microorganism chosen and the desired product (alcohol, growth of the microorganism, etc.) from the consumption of the sugars.

[0093] Advantageously, the concentration of microorganisms in the first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons is between 1 and 200 g / kg of C6 sugars, in particular between 10 and 30 g / kg of C6 sugars. The biomass from which the first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons is derived is of the lignocellulosic type, originating in particular from forestry and / or agricultural and / or paper residues, and / or sacchariferous plants and / or starchy plants and / or Fermentable Fractions of Household Waste (FFOM).

[0094] The pretreatment of biomass from which the first liquid fraction is obtained may be hydrolysis (without enzyme) or pretreatment of the biomass including in particular impregnation of the biomass with an acidic or basic or oxidizing liquor followed by cooking of the impregnated biomass, in particular cooking with steam explosion.

[0095] The first liquid fraction comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons is preferably obtained, according to the invention, after a solid / liquid separation step b) preferably using a biomass pretreated by steam explosion, optionally repulped with a solvent (water in particular) and optionally washed with a solvent (water in particular).

[0096] The invention also relates to the first purified liquid fraction obtained in step d) or the second liquid fraction obtained in step e) according to the process of the invention (i.e. the “purified juice” according to the invention, before or after separation from the microorganisms by solid / liquid separation): it thus relates to a liquid comprising a mixture of compounds in aqueous solution, which comprises C5 sugars and conversion products of the C6 sugars and possibly other minority compounds present in the juice to be purified.

[0097] For example, these conversion products of C6 sugars and other minor compounds are alcohols such as ethanol, 5-hydroxymethylfurfuryl alcohol and furfuryl alcohol, especially in the following concentrations;

[0098] - C5 sugars: between 10 and 100 g / kg of solution, in particular between 20 and 60 g / kg of solution

[0099] - ethanol: between 1 and 12 g / kg of solution, in particular between 2 and 7 g / kg of solution

[0100] - 5-hydroxymethylfurfuryl alcohol: between 0.1 and 9 g / kg of solution, in particular between 0.2 and 4 g / kg of solution

[0101] - furfuryl alcohol: between 0.05 and 9 g / kg of solution, in particular between 0.1 and 3.8 g / kg, in particular between 0.1 and 1.8 g / kg of solution

[0102] The first purified liquid fraction obtained in step d) or the second liquid fraction obtained in step e) according to the process of the invention may thus contain alcohols, in particular an alcohol which results from the conversion of C6 sugars under the action of the microorganism, for example ethanol, butanol or isopropanol, and alcohols resulting in particular from the conversion of the two inhibitors (furfural and 5-HMF), also under the action of the microorganism.

[0103] The conversion products of C6 sugars can also be microorganisms themselves, in particular yeasts, in the case where the treatment according to the invention is carried out under aerobic conditions. The C6 sugars are in fact consumed by the microorganism for its own growth or maintenance.

[0104] Advantageously, the purified liquid fraction obtained in step d) or the second liquid fraction obtained in step e) according to the process of the invention contains less than 0.5 g / kg of C6 sugar solution, and preferably no C6 sugar, less than 0.1 g / kg of furfural solution, in particular no furfural, and less than 0.1 g / kg of 5-hydroxymethyl furfural solution, in particular no 5-hydroxymethyl furfural.

[0105] With the invention, we can therefore go so far as to completely eliminate (by consumption or conversion) all the C6 sugar from the initial sweet juice, and the same is true for the two furan derivatives: depending on the constraints of the degree of purity of the juice purified in C5 sugars, we can therefore eliminate the C6 sugar, or at least maintain it at a very low content, at the level of an acceptable content of impurities for example.

[0106] Advantageously, the purified liquid fraction obtained in step d) or the second liquid fraction obtained in step e) according to the process of the invention contains the following compounds:

[0107] - glucose: between 0 and 0.3 g / kg of solution

[0108] - xylose: between 9 and 91 g / kg of solution

[0109] - arabinose: between 1 and 9 g / kg of solution

[0110] - galactose: between 0 and 0.1 g / kg of solution

[0111] - mannose: between 0 and 0.1 g / kg of solution

[0112] - 5-hydroxymethylfurfuryl alcohol: between 0.1 and 9 g / kg of solution

[0113] - furfuryl alcohol: between 0.05 and 3.8 g / kg of solution

[0114] - ethanol: between 0 and 7 g / kg

[0115] The first purified liquid fraction obtained in step d) or the second liquid fraction obtained in step e) according to the process of the invention may also contain carboxylic alcohols, such as acetic acid, formic acid or levullinic acid. Advantageously, the first purified liquid fraction obtained in step d) or the second liquid fraction obtained in step e) according to the process of the invention ("purified juice" before or after separation from the microorganisms by solid / liquid separation) contains less than 8 g / kg of acetic acid, preferably less than 5 g / kg of acetic acid. The purified juice according to the invention may also contain sugars in oligomeric form, for example arabinoxylan compounds, pentose and hexose oligomers.

[0116] Advantageously, the purified juice according to the invention contains between 0% and 100% of oligomeric sugars relative to the monomeric sugars, preferably between 0.1% and 50%, in particular between 0.1% and 20% of oligomeric sugars relative to the monomeric sugars.

[0117] The invention also relates to the use of the purified juice described above, which is therefore a sweet juice with a very high content of C5 sugars (compared to its content of C6 sugars), to convert the C5 sugars chemically, in particular to convert xylose into xylitol, or biochemically, in particular to serve as a carbon substrate for the propagation of yeasts or for the induction of fungi for the production of enzymes.

[0118] Xylose is considered a platform molecule, and many recovery routes are possible (xylitol, monoethylene glycol, propanol, butanol, lactic acid, succinic acid, etc.).

[0119] The invention also relates to any installation for treating lignocellulosic biomass using the biomass treatment method described above.

[0120] The invention also relates to an installation for treating lignocellulosic biomass, said installation comprising

[0121] - a) a biomass pretreatment unit, comprising a biomass cooking device, possibly accompanied by a steam explosion, to obtain pretreated biomass

[0122] - b) a first solid / liquid separation unit (4), comprising in particular a filtration device, of all or part (3a) of the pretreated biomass (3) obtained in unit a) into a first solid fraction (7) of pretreated biomass and a first liquid fraction (6) comprising a mixture of compounds, in particular in aqueous phase, comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons and the content by weight of C5 sugars of which is greater than the content by weight of C6 sugars

[0123] - c) an enzymatic hydrolysis unit (14) of the first solid fraction (7) of pretreated biomass obtained in step b), to obtain a hydrolysate (15) in the form of sugar(s), including C6 sugars with 6 carbons,

[0124] - a unit d) for purifying said first liquid fraction with contacting said first liquid fraction with first microorganisms consuming, among the sugars of said fraction, essentially only C6 sugars, in order to obtain a purified liquid fraction, containing C5 sugars and depleted in C6 sugars

[0125] - a second unit e) for solid / liquid separation, comprising in particular at least one filtration or centrifugation device, of the purified liquid fraction containing C5 sugars and depleted in C6 sugars obtained in unit d) to obtain a second solid fraction comprising the first microorganisms and a second liquid fraction containing C5 sugars and depleted in C6 sugars.

[0126] Advantageously, according to a variant, only a first part (3a) of the pretreated biomass (3) obtained in the pretreatment unit a) is conducted to the first solid / liquid separation unit b), and a second part of the pretreated biomass (all the rest of the pretreated biomass flow, preferably) is conducted directly to the enzymatic hydrolysis unit c).

[0127] The solid / liquid separation unit b) may, according to a preferred embodiment, comprise a first contacting device between the pretreated lignocellulosic biomass and water, then a second filtration device, and optionally a washing device (the same device may be used with two functions, or two separate devices).

[0128] Advantageously, in this installation, the second liquid fraction containing C5 sugars and depleted in C6 sugars obtained in unit e) contains alcohol, in particular ethanol, obtained by conversion of all or part of the C6 sugars under the action of the first microorganisms, and said installation comprises a unit g) for separating said second liquid fraction into a third liquid fraction enriched in sugars and a fourth liquid fraction enriched in alcohol, said separation unit g) comprising at least one evaporation or stripping device.

[0129] The invention will be described below in more detail, using non-limiting examples and the following figures:

[0130] List of figures

[0131] Figure 1 is a very schematic representation of a reactor implementing step d) of purification of the treatment process according to the invention, and representing the compounds of interest entering and leaving the reactor.

[0132] Figure 2 is a graph representing on the abscissa the duration of step d) of purification of the process according to the invention (in hours) and on the ordinate the evolution of the concentrations of compounds of a mixture of sugars treated according to the invention, in g / kg of reaction medium. The abbreviations in Figure 2 mean: glu: glucose xyl: xylose ara: arabinose gal: galactose man: mannose

[0133] Figure 3 is a very schematic representation of a reactor implementing step d) of purification of the treatment method according to the invention, and representing the compounds of interest entering and leaving the reactor under aerobic conditions, to propagate the microorganisms (yeasts).

[0134] Figure 4 represents in the form of a block diagram a process for treating lignocellulosic biomass with a view to converting it into alcohol (ethanol), without carrying out the purification according to the invention.

[0135] Figure 5 represents in the form of a block diagram a process for treating lignocellulosic biomass with a view to converting it into alcohol (ethanol), which modifies the process of Figure 4 to implement the purification according to the invention.

[0136] Figure 6 represents in the form of a block diagram a process for treating lignocellulosic biomass with a view to converting it into sugar(s), without carrying out the purification according to the invention.

[0137] Figure 7 represents in the form of a block diagram a process for treating lignocellulosic biomass with a view to converting it into sugar(s), which modifies the process of Figure 6 to implement the purification according to the invention.

[0138] Figure 8 represents in the form of a block diagram a process for treating lignocellulosic biomass with a view to converting it partly into sugar(s), partly into alcohol (ethanol), without carrying out the purification according to the invention.

[0139] Figure 9 represents in the form of a block diagram a process for treating lignocellulosic biomass with a view to converting it partly into sugar(s) and partly into alcohol (ethanol), which modifies the process of Figure 8 to implement the purification according to the invention.

[0140] Figure 10 is a graph representing on the abscissa the time, expressed in hours, and on the ordinate, along the vertical axis on the left the concentrations of furfural and 5 HMF expressed in g / l, and along the vertical axis on the right the concentration of ethanol in g / l, during the realization of a simultaneous enzymatic hydrolysis and fermentation (SSCF) of a pretreated biomass, with a purification according to the invention.

[0141] Figure 11 is a graph representing on the abscissa the ethanol concentration (in % weight) of the aqueous reaction medium obtained at the end of treatment by enzymatic hydrolysis and fermentation of the pretreated biomass, and on the ordinate the energy consumption (in MJ per kg of ethanol) to separate by distillation the ethanol from the aqueous phase from said aqueous reaction medium.

[0142] Figures 1 and 3 are extremely schematic to facilitate understanding, and the reactor shown is therefore a symbolic representation, which is not to scale, which does not predict its dimensions and shape, and does not show all the equipment necessary for its operation.

[0143] Figures 4 to 9 representing process block diagrams are also highly simplified to facilitate understanding. They do not necessarily represent all the steps / equipment necessary for the processes described, focusing on the most significant steps / equipment / flows in view of the invention.

[0144] The references keep the same meaning from one figure to another.

[0145] Description of the embodiments

[0146] The invention integrates into a process for converting biomass, of the lignocellulosic type, into sugar(s) or alcohol, a biochemical purification treatment of sugary juices containing C5 sugars, and, in a lower content / proportion, C6 sugars, so as to reduce or even eliminate the C6 sugar content of these juices and thus obtain juices "purified" in C5 sugars, to benefit therefrom, in particular either to increase the biomass conversion yield (into alcohol more particularly), or to obtain sugars of higher quality / purity.

[0147] Indeed, in the biomass treatment process, the invention focuses on processes with pretreatment of the biomass before enzymatic hydrolysis, pretreatment which results in the production of sweet juices mixing C5 sugars and C6 sugars.

[0148] We will therefore describe:

[0149] - firstly, and using figures 1 to 3, the stage of purification of the sugary juices,

[0150] - then, in a second step, and using the following figures, the process of converting lignocellulosic biomass producing these sugary juices and integrating this purification step to benefit from them.

[0151] Purification stage of sweet juices

[0152] This biochemical purification treatment involves bringing the juice sweetened with C5 and C6 sugars, juice obtained by processing lignocellulosic biomass-based material and comprising mainly C5 sugar, into contact with a microorganism that selectively consumes the C6 sugars: the C5 sugars are not modified, remaining almost intact in the juice, while the C6 sugars will gradually be consumed by the microorganism for its own growth and / or to be converted into another compound, for example in the form of alcohol in the case of fermentation.

[0153] For example, the native yeast Saccharomyces Cerevisae consumes C6 sugars primarily to multiply under aerobic conditions, and consumes C6 sugars primarily to produce ethanol under anaerobic conditions.

[0154] The operating conditions of the treatment are adapted according to the initial content of C6 sugars and the final content of C6 sugars which is acceptable (no more C6 sugars at all, or a content lower than a given value): temperature, pH, duration, aeration, choice and concentration of the microorganism.

[0155] Examples of sweet juice purification

[0156] Example 1 (comparative)

[0157] We start with an initial sweet juice JO from biomass pretreated by acid impregnation of the biomass then steam explosion, in accordance with the teaching of the aforementioned patent FR 3 083 126, to which we refer for more details.

[0158] Briefly, this pretreatment is an operation of impregnation of lignocellulosic biomass with an acid liquor, followed by a steam explosion operation of the impregnated biomass. At least part of the pretreated biomass undergoes a liquid / solid separation operation at the end of the pretreatment step, this liquid / solid separation step comprising a contacting step between the pretreated lignocellulosic biomass and water, and a filtration and optionally washing step. To obtain the JO juice, 550 kg of pretreated biomass are mixed with 1010 kg of water, then filtered and pressed. After filtration and pressing, 885 kg of an JO juice, also called C5 hydrolysate, is obtained. The pretreatment takes place under acidic conditions, this juice has a pH of 2.

[0159] The concentration of compounds of interest in this JO juice is given in Table 1 below, with concentrations expressed in g per kg of juice. Note that it is possible that the composition contains other impurities, which we have not sought to analyze, for example of the salt (mineral) or acid type, in very low levels.

[0160] [Table 1]

[0161] We see that 82% of the sugars in JO juice are C5 sugars, that 18% of the sugars are C6 sugars, and that 5-HMF and furfural are also present, in much lower levels than sugars, known to inhibit biochemical reactions that can be considered to operate on the sugars subsequently (for example for ethanolic fermentations with yeasts).

[0162] Sugar juices from pre-treated biomass generally contain a much higher quantity of C5 sugars than C6 sugars, and there is a need, in order to recover them, to separate the C5 sugars from the C6 sugars. However, the techniques currently available are unsatisfactory (membrane filtration in particular), because they are complex to implement and generally do not allow the desired level of purity of C5 sugars to be achieved in the juice separated from C5 sugars.

[0163] For example, the publication “Removal of furfural and HMF from monosaccharides by nanofiltration and reverse osmosis membranes” by Tielin Wang et al. (Journal of the Energy Institute 91 (2018) 473-480) concludes that the most efficient membranes for separating 5-HMF and furfural from a sugary juice are the Desal-5 DK and Alfa Laval-NF membranes (less than 2% retention for 5-HMF and furfural) but that they lead to too high a loss of sugars (2 to 8% for glucose and 10 to 20% for xylose).

[0164] The publication "Removal of the Fermentation Inhibitor, Furfural, Using Activated Carbon in Cellulosic-Ethanol Production" by Kuang Zhang et al. (Industrial & Engineering Chemistry Research 2011, 50, 14055-14060) concludes that the commercial activated carbon Norit_1240 from Norit Company can selectively reduce the furfural concentration of a model sugar juice solution from 4 g / L to 0 g / L, but C6 sugars (here glucose) are not selectively separated from C5 sugars (here xylose).

[0165] Example 2 (according to the invention)

[0166] We start with the sweet juice J0 defined in example 1. We carry out fermentation of the juice J0 with a microorganism, the yeast Saccharomyces cerevisae, in a native version, not genetically modified, and which has the particularity of selectively consuming C6 sugars, and not C5 sugars.

[0167] The yeast is inoculated at 0.5 g of yeast per kg of solution, or 60 g yeast per kg of C6 sugars. The experiment was conducted in a bioreactor for 6 hours, at 33°C and pH 5.3. The treatment was carried out under anaerobic conditions to maximize ethanol production from C6 sugars by fermentation, and not biomass production. This reaction can be carried out in batch, fed-batch or continuous. They can then be separated for separate processing / recovery.

[0168] The reactions resulting from the action of yeast are shown schematically in Figure 1, which represents bioreactor 1, with the following inputs:

[0169] 2: yeast

[0170] 3: a base (to regulate the pH and maintain the reaction medium in the conditions necessary for the activity of the chosen yeast), such as NH4OH, KOH or NaOH for example

[0171] 4: Nutrients for yeast

[0172] 5: JO juice, which contains in the aqueous phase C5 sugars 51, C6 sugars 52, 5-HMF 53 and furfural 54, and with the outgoing products:

[0173] 6: emission of CO2 in gaseous phase, evacuated in the upper part of the bioreactor, indicator of yeast activity,

[0174] 5': drawing off a juice J1, from the juice JO after action of the yeast on the juice JO, and which contains yeast 2, sugars C5 51, 5-hydroxymethylfurfuryl alcohol 55, furfuryl alcohol 56, ethanol 57 and yeasts 2.

[0175] The quantities of inputs (in addition to the concentrations indicated above) are specified below: In an agitated tank, 985 kg of JO juice are mixed with:

[0176] - 0.4 kg of urea (for nitrogen requirements)

[0177] - 0.5 kg of dry yeast S. Cerevisae

[0178] - 5 kg of yeast extract (nutrients)

[0179] - 9.1 kg of a 50% wt. KOH solution to adjust the pH to 5.3

[0180] The concentration of compounds of interest in the mixture in the initial state is given in Table 2 below, with concentrations expressed in g per kg of juice. Note that it is possible that the composition contains other impurities, which we have not sought to analyze, such as salt or acid, in very low levels.

[0181] [Table 2]

[0182] At the start of the reaction, the reaction medium contains:

[0183] - 8.3 kg of C6 sugars (glucose + galactose + mannose)

[0184] - 37.3 kg of C5 sugars (xylose + arabinose)

[0185] - 0.4 kg of 5-HMF

[0186] - 0.2 kg of furfural

[0187] The fermentation process is detailed below:

[0188] Fermentation lasted 6 hours and shows that glucose, galactose, and mannose (C6 sugars, dotted lines) are completely consumed. Arabinose and xylose (C5 sugars) are not consumed. Furfural and 5-HMF were consumed by the yeast, which detoxified its environment, to produce furfuryl alcohol and 5-hydroxymethyl furfuryl alcohol (also called 2,5-Bis(hydroxy methyl)furan), which do not inhibit the yeast.

[0189] It was therefore found that the initial juice JO, composed of 45.6 kg of monomeric sugars (18% C6 sugars / 82% C5 sugars) is purified in a few hours into a juice J1 composed of 37.3 kg of monomeric sugars (0% C6 sugars and 100% C5 sugars).

[0190] Under anaerobic conditions, at 33°C and pH 5.3, yeasts consume C6 sugars (mainly to produce ethanol) and inhibitors (5-HMF and furfural) within six hours.

[0191] At the end of the reaction, the medium contains a juice J1 whose composition is given in table 2 below, with concentrations expressed in g per kg of medium: [Table 3]

[0192] So after 6 hours of reaction we have:

[0193] - 0 kg of C6 sugars (glucose + galactose + mannose), i.e. a consumption of 100% of C6 sugars - 37.3 kg of C5 sugars (xylose + arabinose), i.e. a consumption of only 1.6% of C5 sugars

[0194] - 0 kg of 5-HMF, i.e. a consumption of 100% of 5-HMF - 0 kg of furfural, i.e. a consumption of 100% of furfural

[0195] - 0.4 kg of 5-hydroxymethylfurfurlic alcohol

[0196] - 0.2 kg of furfuryl alcohol

[0197] - 2.9 kg of ethanol, i.e. an ethanol / C6 sugar yield of 0.35 kg ethanol / kg C6 sugars

[0198] The data in Table 2 and the graph in Figure 2 confirm that the yeast has no effect on the C5 sugars, the content of which remains constant. On the other hand, the yeast has completely consumed both the C6 sugars and the two inhibitors, converting them at least in part into alcohols (another part can be consumed by the yeast for its own growth). The yeast treatment therefore gives spectacular results, with a juice purified of C5 sugars which no longer contains any C6 sugars and from which the inhibitors have also been, simultaneously, completely eliminated.

[0199] The fact that at least part of the C6 sugars has been transformed into ethanol is also very advantageous, because ethanol is a highly valuable product and can be produced in processes dealing with lignocellulosic biomass.

[0200] We also observe from the data in the graph of Figure 2 that the fermentation time for the C6 sugars to be completely consumed is 6 hours, which is a reasonable time, which can be further reduced by varying, in particular, the quantity of yeast added, or if lower but not zero levels of C6 sugars are acceptable. Experiments have thus been successfully carried out with much shorter fermentation times, in particular from 30 minutes to 2 hours, for example a duration of approximately 1 hour.

[0201] Figure 3 represents a variant of Figure 2: starting from the same juice J0 as in Figure 1 and as in Example 1, fermentation is carried out this time under aerobic conditions of the juice J0 with the same microorganism as in Example 2, the yeast Saccharomyces cerevisae, in a native version, not genetically modified, and which has the particularity of selectively consuming C6 sugars, and not C5 sugars.

[0202] The reactions resulting from the action of yeast are shown schematically in Figure 3, which represents bioreactor 1, with the following inputs:

[0203] 2: yeast

[0204] 3: a base (to regulate the pH and maintain the reaction medium in the conditions necessary for the activity of the chosen yeast), such as NH4OH, KOH or NaOH for example

[0205] 4: Nutrients for yeast

[0206] 5: juice J0, which contains in the aqueous phase C5 sugars 51, C6 sugars 52, 5-HMF 53, furfural 54, and acetic acid 60 and with the outgoing products:

[0207] 6: emission of CO2 in gaseous phase, evacuated in the upper part of the bioreactor, indicator of yeast activity,

[0208] 5': drawing off a juice J1, from the juice JO after action of the yeast on the juice JO, and which contains the propagated yeast 2, sugars C5 51, 5-hydroxymethylfurfuryl alcohol 55 and furfuryl alcohol 56.

[0209] 7: an air supply to be in aerobic condition

[0210] It was verified that the yeast therefore has no action on the C5 sugars, the content of which remains constant. On the other hand, the yeast has completely consumed both the C6 sugars and the two inhibitors (5-HMF and furfural) as well as the acetic acid, to convert them at least in part into alcohols (another part can be consumed by the yeast for its own growth). The treatment with yeast therefore gives spectacular results, with a juice purified in C5 sugars which no longer contains any C6 sugars, whose inhibitors have, simultaneously, also been completely eliminated, while multiplying the yeast.

[0211] In conclusion on this purification step, we see that we manage to purify sugar mixtures to obtain juices containing the type of sugars that we want to preserve (C5 sugars), by choosing a selective microorganism, which can also, optionally, consume / eliminate undesirable compounds / impurities in the sugar mixtures, and in particular inhibitors of biochemical reactions such as furan derivatives. Its implementation is simple, in one aerobic fermentation step, and its efficiency is formidable, with possibly complete eliminations of the compounds that we want to remove from the sugar juices.

[0212] It allows the production of very pure C5 sugar juices, with no or very low C6 sugar content, with a purity which had not previously been achieved by separation methods, such as selective adsorption on zeolites, as described in the patents cited in the preamble to this application.

[0213] It is also very interesting, in that it does not really lead to a separation between two types of sugars, but to obtaining a very pure type of sugar, and to converting the other sugar (C6 sugar) into a recoverable product such as ethanol. With the combination of C5 sugars and ethanol from the conversion of C6 sugars obtained with the process according to the invention, several possibilities are available, in particular depending on the recovery routes envisaged and the proportion between the two types of sugars in the initial sugar juice. Thus, it is then possible to separate the C5 sugars from the ethanol, and to obtain on the one hand very pure C5 sugars and on the other hand ethanol, recoverable / usable separately. It is also possible to keep them together for common recovery. It is still possible to keep a low ethanol content with the C5 sugars, to benefit from the preservative / antimicrobial effect of alcohol on the sugars.Processes for converting liqnocellulosic biomass producing sugary juices and integrating the step of purifying said sugary juices and previously described.

[0214] Three conversion processes are described below:

[0215] - a process A for conversion into alcohol (ethanol)

[0216] - a process B of conversion into sugar(s), and

[0217] - a so-called “hybrid” process C aimed at obtaining both an alcohol and sugar(s)

[0218] Process A for converting biomass into ethanol

[0219] It is illustrated using figures 4 and 5.

[0220] Figure 4 depicts a conversion process without the purification step described above. The figure references represent the following flows / devices / steps:

[0221] 1: Biomass

[0222] 2: Conditioning and pretreatment

[0223] 3: Pretreated biomass

[0224] 3a: Pretreated biomass towards the filtration tool

[0225] 3b: Pretreated biomass towards enzymatic hydrolysis (optional)

[0226] 4: Solid / liquid separation (a belt filter or a filter press for example) to extract a sweet juice, with an optional washing step

[0227] 5: Water as contact and / or washing fluid

[0228] 6: Sweet juice containing mainly C5 sugars

[0229] 6a: Sweet juice comprising mainly C5 sugars for the production of enzymes

[0230] 6b: Sweet juice comprising mainly C5 sugars towards the propagation of yeasts

[0231] 7: Pretreated and washed biomass

[0232] 8: Enzyme production reactor

[0233] 9: Mushroom inoculum (Trichoderma Reese / for example) for enzyme production

[0234] 10: Enzyme cocktail (mixture of one or more enzymes, including cellulases, beta glucosidases, xylanases, etc.)

[0235] 11: Yeast propagation reactor

[0236] 12: Yeasts

[0237] 13: Propagated yeasts

[0238] 14: Enzymatic hydrolysis reactor.

[0239] 15: Hydrolyzate

[0240] 16: Fermentation reactor

[0241] 17: Fermentation must (wine)

[0242] 18: Solid / liquid separation (a filter press for example) with an optional step of washing the solid residue with a solvent (for example water) 19: Solid residue (composed mainly of lignin)

[0243] 20: Liquid product of filtration, here filtered wine

[0244] 21: Separation of ethanol and water (distillation column, sieve for example)

[0245] 22: Liquid residue (vinasses)

[0246] 23: Purified ethanol

[0247] Throughout this text, and in particular in the description of the figures, the term reactor does not require that there be only one, and can be understood as a unit comprising at least one reactor. The same applies to all other devices, in particular tools such as filtration, solid / liquid separation, distillation column, etc. (for the sake of brevity).

[0248] If we take the process sequence according to Figure 4: Biomass 1 undergoes conditioning / pretreatment in unit 2 (possible mechanical grinding, dust removal, removal of any metal parts, then, here as an example, impregnation with an acid liquor and cooking / steam explosion of the pretreated biomass 3). Part of this pretreated biomass, flow 3a, goes to a solid / liquid filtration tool 4, said tool also being supplied with water 5 as contact and / or washing water. Initially, the pretreated biomass is contacted with water to improve its filterability. The mixture is then filtered on a belt filter, and washed with water. Another part of the pretreated biomass, stream 3b, can go to the enzymatic hydrolysis reactor 14. This reactor 14 is also fed by stream 7 which is the solid fraction resulting from filtration in unit 4, which is therefore the solid washed pretreated biomass.

[0249] Please note that throughout this text, “solid” is to be understood in opposition to “liquid”, but that any solid fraction may still contain a certain proportion of liquid (and vice versa). This proportion of liquid in a solid fraction can be assessed by measuring its Dry Matter (acronym “DM”) content, which is measured according to ASTM E1756 - 08(2015) “Standard Test Method for Determination of Total Solids in Biomass”.

[0250] At the outlet of reactor 14, there is a flow 15 of hydrolyzate (sugars), which then feeds a fermentation reactor 16 to be converted into ethanol: at the outlet of fermentation reactor 16, a fermentation must is obtained, also called wine, which contains ethanol in water. A solid / liquid separation tool 18 separates a ligneous solid residue 19 from a liquid fraction 20, the filtered wine. This filtered wine is conducted into a separation tool 21 (distillation column) to obtain ethanol 23 and an aqueous liquid residue (called vinasse).

[0251] At the outlet of the separation tool 4, the liquid fraction 6 is an aqueous sugary juice comprising mainly C5 sugars. All or part of this fraction, the flow 6a, can go to the enzyme production reactor 8, which produces an enzymatic cocktail 10 to feed the enzymatic hydrolysis reactor 14: this flow can thus constitute a growth and / or production substrate for microorganisms of the Trichoderma reesei type which produce this mixture of enzymes 10. All or part of this flow 6, the flow 6b, can also go to the reactor 11 for propagation of the yeasts 13 which feed the fermentation reactor 16. Here again, the sugary juice 6b will be able to serve as a propagation substrate for yeasts, for example Saccharomyces, in particular the species Saccharomyces cerevisae.

[0252] It should also be noted that the enzymatic hydrolysis operation 14 is preferably carried out in 2 stages: liquefaction with a fed-batch of substrate then enzymatic hydrolysis in batch, (possibly with two reactors in series, or in the same reactor), to work at the highest possible DM content and to convert lignocellulosic substrates whose rheology can be complex. Neutralization of the medium can be carried out before the enzymatic hydrolysis, for example by adding a basic solution in the case where the pretreatment is carried out under acidic conditions.

[0253] It should also be noted that enzymatic hydrolysis and fermentation can be done simultaneously (SSCF). When they are done one after the other, an adjustment of the pH of the medium between units 14 and 16 can be achieved.

[0254] It should also be noted that enzyme production and / or yeast propagation can be carried out on the biomass processing site, as shown in Figure 4. But one or the other can also be carried out ex situ: ready-to-use enzymes or yeasts can thus be brought to the site. This explains why, depending on the choices made on this subject, the flow can be divided into two flows 6a, 6b (with a distribution between the two flows which can be equal or not according to the needs), or be used only for yeast propagation or only for enzyme production.

[0255] Figure 5 shows the method of Figure 4, but with the modifications according to the invention, and the following additional references:

[0256] 6a': Sweet juice comprising only C5 sugars towards enzyme production 6b': Sweet juice comprising only C5 sugars towards yeast propagation 6c': Sweet juice comprising only C5 sugars towards fermentation

[0257] 24: Biochemical purification reactor

[0258] 25: Yeasts consuming C6 sugars

[0259] 26: Sweet juice comprising only C5 sugars, yeasts and ethanol

[0260] 27: Solid / liquid separation (a centrifuge, a filter or an ultrafiltration unit for example) 28: Yeasts consuming C6 sugars, recycled

[0261] 29: Sweet juice comprising only C5 sugars and possibly ethanol

[0262] 30: Separation of ethanol and C5 sugar juice (a stripper or an evaporator for example), optional step

[0263] 31: stripped ethanol stream

[0264] 32: Sweet juice containing only C5 sugars

[0265] Note that the pretreated biomass flow 3 is divided in Figure 5 into two flows: flow 3a which goes to tool 4 and flow 3b which goes directly to the enzymatic hydrolysis reactor 14. But here, as in the case of the processes represented in the following Figures 7 and 9, the relative proportion between flows 3a and 3b is variable.

[0266] And according to an embodiment of the invention, it is also provided that the entire pretreated biomass flow 3 first passes into the tool 4 before separation and sending of the solid portion to the hydrolysis reactor 14: there is only one flow 3 / 3a entering in its entirety into the tool 4, and the flow 3b is zero: the reactor 14 is no longer supplied with flow 3b. This embodiment is more particularly recommended in the case of the production of sugar (figure 7), more than in the case of the production of alcohol (figure 5) or sugar and alcohol (figure 9).

[0267] This zero 3b flow scenario is therefore also part of the invention, whether it is a process for producing alcohol, sugar or a hybrid alcohol / sugar process.

[0268] The ethanol-rich stream 31 may be introduced separately or mixed with the filtered wine at the inlet of the ethanol and water separation section 20, or into the fermenter 16. The operating conditions of the stripper may be adjusted to produce a stream rich in C5 sugars and a stream rich in ethanol.

[0269] The ethanol produced 31 can also be recycled to the pretreatment step 2 or to the biomass filtration and washing step 4.

[0270] The 32 sweet juice stream comprising only C5 sugars can be used as a substrate for enzyme production, yeast propagation or in fermentation.

[0271] Here, the stream 6 containing more C5 sugars than C6 sugars is purified in the following way: it is brought into a biochemical purification reactor 24, which may include a preliminary step of neutralizing the juice 6, for example with a basic solution of sodium or potassium hydroxide, in the case where the pretreatment of the biomass was carried out under acidic conditions. The reactor 24 is also supplied with microorganisms 25 (yeasts in particular) which have the particularity of consuming C6 sugars only. At the outlet of the reactor 24, there is a stream 26 of sweet juice depleted in C6 sugars. The solid / liquid separation tool 27 makes it possible to recover a solid fraction 28, which comprises the insoluble yeasts which will be able, in whole or in part, to be recycled into the reactor 24.The separated liquid fraction 29 is therefore a C5 sugar juice, without microorganisms and with less / no C6 sugars and possibly ethanol, which is a product of conversion of C6 sugars by yeasts. This fraction 29 is sent to a separation tool 30 which separates the sugars from the ethanol when there is ethanol in the fraction 29 in a measurable content. Then the separated sugar juice 32 can be used in different ways: all or part in the form of a stream 6a' towards the production 8 of enzymes, all or part of a stream 6b' towards the propagation of yeasts for the fermentation 11 of the biomass (as in the process of figure 4), and all or part of a stream 6c' can be sent to the fermentation reactor 16. The ethanol stream 31 can be sent to the fermentation reactor 16 (either during fermentation, or added to the stream leaving the reactor 16, or added to the stream 20 at the inlet of the ethanol separation device 21.The relative proportion of the streams 6a', 6b', 6c' is adjustable, in particular if the propagation of the yeasts and / or the production of enzymes are carried out in situ or ex situ (in this case the streams 6a' and / or 6b' do not exist). In all cases, an additional proportion of ethanol 6c' is added to the production of ethanol leaving the fermenter 16, at the level of the fermenter 16 or downstream thereof (the terms "upstream" and "downstream" are understood in this text according to the general direction of the biomass through the installation).

[0272] Integrating the biochemical purification of the sugar mixture 6 ultimately allows for an increase in the quantity of ethanol produced for a given quantity of biomass, and therefore for an increase in its conversion yield.

[0273] Process B for converting biomass into sugars.

[0274] It is illustrated by Figures 6 and 7.

[0275] Figure 6 represents the process without purification according to the invention. This involves stopping the conversion of the biomass at the sugar production stage, therefore without fermentation. Compared to Figure 4, the sugar juice 20, mainly consisting of C6 sugars, is therefore the first final product that is recovered, the stream 6a can be used to serve as a substrate for the growth and / or production of enzymes in the reactor 8 (if in situ enzyme production), and the stream 6b is the second final product that can be recovered, a juice of sugars mainly in C5, but which still contains C6 sugars.

[0276] Figure 7 is a process which integrates the purification of sugar juice according to the invention into the process of Figure 6: It shows the reactors / tools 24, 27 and 30 of the process of Figure 5, which are operated in the same way. Here, the sugar juice 6 containing mainly C5 sugars is, after purification and separation of the yeasts, purified into a juice 32, which is divided partly into a stream 6a' of C5 sugars to serve as a substrate for the growth / production of enzymes in the reactor 8 if the production of enzymes is done in situ, and partly or entirely into a stream 6d', which is a purified C5 sugar juice which can be used as such. This juice of C5 sugars referenced 6d' is very pure, purer than the juice of stream 6b of the process of Figure 6, it can therefore be used as is.

[0277] “Hybrid” process C for converting biomass into ethanol and sugar(s)

[0278] It is illustrated by Figures 8 and 9.

[0279] The process according to Figure 8 does not use the purification according to the invention. Here, the aim is to produce sugars and ethanol in parallel. Compared to the process of Figure 4, which aims to produce ethanol, here we have both:

[0280] - ethanol production, which is stream 23 obtained as in the process of fig 4, and

[0281] - a production of sugars mainly in C5: this is flow 6d, from flow 6 as in the process of figure 4. This flow 6d can be a part of flow 6, or the whole of this flow (if ex situ production of enzymes, and / or ex situ propagation of yeasts, or if we prefer to use other, external sources, for the growth / propagation of microorganisms / production of enzymes).

[0282] The process of Figure 9 integrates, in the process of Figure 8, the purification according to the invention: We find the reactors / tools 24, 27 and 30 previously described, the obtaining of a purified flow 32 in C5 sugars, and that of a flow 6d' which constitutes all or part of the juice 32 and which constitutes a sweet juice purified in C5 sugars which can be used as is, in parallel with the production of ethanol 23. The flow of ethanol 31 resulting from the separation 30 can, as in the case of the process of Figure 5, be reinjected into the fermenter 16, or downstream of it, in a mixture with the flow leaving the fermenter 16 or upstream of the device 21 (distillation column) separating the ethanol from the water. So we have a double win here, with both an improved ethanol yield and improved C5 sugar juice quality / purity.

[0283] From these different implementations of the invention, we see all the advantages: The lignocellulosic sugar hydrolyzate composed of a mixture of sugars with 6 and 5 carbon atoms is purified into a hydrolyzate containing only sugars with 5 carbon atoms:

[0284] The use of this "pure" mixture of C5 sugars is beneficial for many chemical conversion applications (conversion of xylose into xylitol by catalysis) or biochemical applications (propagation of yeasts, induction of fungi for the production of enzymes for example).

[0285] The complex and costly physical separation of C5 and C6 sugars (e.g. by nanofiltration, membranes, ion exchange resins, zeolites, etc.) is thus avoided. The lignocellulosic sugar hydrolysate composed of a mixture of sugars with 6 and 5 carbon atoms is purified into a hydrolysate containing only sugars with 5 carbon atoms but also containing less / more compounds called inhibitors such as furfural or 5-hydroxymethylfurfural (5-HMF): These two compounds are, for example, inhibitors for fermentation reactions.

[0286] In the case of using S. Cerevisae yeast and under anaerobic conditions to carry out the biochemical purification of the sugar mixture, the consumption of C6 sugars produces ethanol which can be recovered and integrated into the biomass conversion process.

[0287] In the case of using S. Cerevisae yeast and under aerobic conditions to carry out the biochemical purification of the sugar mixture, the consumption of C6 sugars produces additional microorganisms (yeast multiplication) that can be recovered and integrated into the biomass conversion process.

[0288] Under aerobic conditions, the yeast S. Cerevisae can also consume acetic acid from the medium, which also inhibits fermentation reactions or the growth of the fungus T. Reesei.

[0289] Biochemical purification is carried out on a clear medium, it is easy to separate microorganisms by solid / liquid separation, for example centrifugation or ultrafiltration membranes, to remove and recycle the microorganisms.

[0290] The ethanol produced can be advantageously used in the 2G sugar production process:

[0291] - A fraction of the ethanol can be used in pretreatment 2,

[0292] - A fraction of the ethanol can also or alternatively be used as a washing fluid for filtration step 4.

[0293] - A fraction of the ethanol can also or alternatively be used as a washing fluid for the unconverted residual solid residue. This makes it possible to increase the PCI (acronym for Lower Calorific Value) of the solid residue which can be burned in a cogeneration boiler for the production of electricity and steam, or to extract a soluble fraction for better recovery (fuel base, or for bioproducts)

[0294] - A fraction of the ethanol can also or alternatively be incorporated into the reaction medium of the enzymatic hydrolysis reactor 14, which makes it possible to limit the risks of contamination.

[0295] The separation step 30 of the purified sugars and ethanol is carried out in such a way as to concentrate the sugars to a content of, for example, 50 g / kg, which is all the more advantageous since this sugar juice is used for the production of enzymes and propagation of yeasts. The purification steps are therefore perfectly integrated into the production of ethanol and / or 2G sugars. Examples using a biomass conversion process

[0296] Example 3 according to process A for converting biomass into ethanol

[0297] It is operated according to the method of Figure 5, in comparison with that of Figure 4.

[0298] In this example, the reactions are carried out in SSCF, steps 14 (enzymatic hydrolysis) and 16 (ethanolic fermentation) are carried out in the same reactor and are conducted at a temperature of 33°C and pH 5.3 under anaerobic conditions. In this example according to the invention, step 30 of separation of ethanol from the C5 juice is not carried out. In the scheme according to the invention, the purification in step 24 makes it possible to reduce the concentration of 5-HMF (from 2.80 to 0.56 g / L) and furfural (from 1.60 to 0.32 g / L) present at the start of the reaction. This purification also produces ethanol, from the C6 sugars (2.84 g / L).

[0299] Since these compounds are inhibitors for the yeast Saccharomyces Cerevisae, the production of ethanol undergoes a latency or even an inhibition of the fermentation activity in the process of figure 4 without the purification of the sugars: concretely, the duration of the fermentation reaction is extended, or the yeasts may not even ferment.

[0300] After 144 hours of reaction, the ethanolic content of the ethanol produced according to the process of Figure 5 according to the invention is 52.4 g / L compared to 49.3 g / L for the process of Figure 4. The difference in ethanolic content is even greater before 50 hours of reaction. For example, after 42 hours of fermentation, the invention makes it possible to go from 33.8 to 45.9 g / L of ethanol. This can be observed from the graph in Figure 10, which represents the changes in concentration in g / l of different compounds during the SSCF reaction (simultaneous enzymatic hydrolysis and fermentation):

[0301] - curve C10: evolution of the 5-HMF content by applying the process of figure 4 (without purification)

[0302] - curve C11: evolution of the 5-HMF content by applying the process of figure 5 (with purification)

[0303] - curve C20: evolution of the furfural content by applying the process of figure 4 (without purification)

[0304] - curve C21: evolution of the furfural content by applying the process of figure 5 (with purification)

[0305] - curve C30: evolution of the ethanol content by applying the process of figure 4 (without purification)

[0306] - curve C31: evolution of the ethanol content by applying the process of figure 5 (with purification) We see from this graph that at t = 0, the purification of the C5 sugars made it possible to reduce the inhibitor load: furfural, 5-HMF and that after 50 hours of reaction, the ethanol productivity is much higher with the purification according to the invention. At the end of the reaction, the quantity of ethanol produced is greater.

[0307] In addition, this increase in the ethanol concentration makes it possible to reduce the energy consumption required for the distillation step in column 21, to separate the ethanol from the water.

[0308] When a reaction time of 144 hours is chosen, the energy gain is 4.5%. When a reaction time of 42 hours is chosen, the energy gain is 21%. This is shown in Figure 11, which represents the energy required (in MJ) per kg of ethanol present in the distillation column feedstock as a function of the ethanol concentration of the solution to be separated to recover a rich stream at 94% by weight of ethanol at the top of the distillation and a stream containing 0.02% by weight of ethanol at the bottom of the column, and which is taken from the VANE, LM publication “Separation technologies for the recovery and dehydration of alcohols from fermentation broths. Biofuels, Bioproducts and Biorefining”, Society of Chemical Industry, London, Uk, 2(6):553-588, (2008).

Claims

Claims 1. Method for treating a lignocellulosic biomass, said method comprising - a) a pretreatment step (2) of the biomass, comprising cooking the biomass, possibly accompanied by a steam explosion, to obtain a pretreated biomass (3) - b) a first step of solid / liquid separation of all or part (3a) of the pretreated biomass (3) obtained in step a) into a first solid fraction (7) of pretreated biomass and a first liquid fraction (6) comprising a mixture of compounds, in particular in aqueous phase, comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons and the content by weight of C5 sugars of which is greater than the content by weight of C6 sugars - c) a step of enzymatic hydrolysis (14) of the first solid fraction (7) of pretreated biomass obtained in step b), to obtain a hydrolysate (15) in the form of sugar(s), including C6 sugars with 6 carbons, - d) a step of purification (24) of said first liquid fraction obtained in step b) by bringing said first liquid fraction (6) into contact with first microorganisms consuming, among the sugars of said fraction, essentially only C6 sugars, in order to obtain a purified liquid fraction (26), containing C5 sugars and depleted in C6 sugars - e) a second step e) of solid / liquid separation (27) of the purified liquid fraction (26) containing C5 sugars and depleted in C6 sugars obtained in step d) to obtain a second solid fraction (28) comprising the first microorganisms and a second liquid fraction (29) containing C5 sugars and depleted in C6 sugars.

2. Method according to the preceding claim, characterized in that only a first part (3a) of the pretreated biomass (3) obtained in step a) is conducted to the first step b) of solid / liquid separation, and in that a second part (3b) of the pretreated biomass (3) is conducted directly to step c) of enzymatic hydrolysis.

3. Method according to one of the preceding claims, characterized in that it also comprises a step f) of fermentation (16) by third microorganisms of the hydrolyzate in the form of sugar(s) obtained in step c), in order to obtain a fermented biomass (17) comprising at least one alcohol, in particular ethanol.

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

5. Method according to one of the preceding claims, characterized in that at least a part of the second solid fraction (28) comprising the first microorganisms obtained in step e) is recycled in the purification step d) (24).

6. Method according to one of the preceding claims, characterized in that the second liquid fraction (29) containing C5 sugars and depleted in C6 sugars obtained in step e) contains alcohol, in particular ethanol, obtained by conversion of all or part of the C6 sugars under the action of the first microorganisms, and in that said second liquid fraction is separated (30) in a step g), in particular by evaporation or stripping, into a third liquid fraction (32) enriched in sugars and a fourth liquid fraction (31) enriched in alcohol.

7. Method according to claim 3 and the preceding claim, characterized in that all or part of the fourth liquid fraction (31) containing the alcohol obtained in step g) is sent to the fermentation step f) (16) or in that all or part of said fourth liquid fraction is mixed with the fermented biomass (17) comprising at least one alcohol obtained at the end of the fermentation step f).

8. Method according to one of the preceding claims, characterized in that it comprises a step h) of producing enzymes (8) from second microorganisms, in particular fungi, in order to use said enzymes to ensure the enzymatic hydrolysis of step c), and in that all or part (6a') of the second liquid fraction (29) containing C5 sugars and depleted in C6 sugars obtained in step e) or the third liquid fraction (32) enriched in sugars obtained in step g) is sent to said step h) as a substrate for growth of the second microorganisms and / or production of the enzymes.

9. Method according to one of claims 3 or 4, characterized in that it comprises a step i) of propagation (11) of third fermentation microorganisms, in order to use said microorganisms, in particular yeasts, to ensure the fermentation of step f), and in that all or part (6b') of the second liquid fraction (29) containing C5 sugars and depleted in C6 sugars obtained in step e) or the third liquid fraction (32) enriched in sugars obtained in step g) is sent to said step i) as a substrate for propagation of said third microorganisms.

10. Method according to one of the preceding claims, characterized in that all or part (6c') of the second liquid fraction (29) containing C5 sugars and depleted in C6 sugars obtained in step e) or the third liquid fraction (32) enriched in sugars obtained in step g) is sent to the fermentation step f) (16).

11. Method according to one of the preceding claims, characterized in that the first liquid fraction (6) obtained in step b) also comprises furfural, and in that the first microorganisms also consume furfural, in particular at least in part by conversion of furfural into alcohol, in particular into furfuryl alcohol.

12. Method according to one of the preceding claims, characterized in that the first liquid fraction (6) obtained in step b) also comprises 5-hydroxymethyl furfural 5-HMF, and in that the first microorganisms also consume 5-hydroxymethyl furfural, in particular at least in part by conversion of 5-hydroxymethyl furfural into 5-hydroxymethylfurfuryl alcohol.

13. Method according to one of the preceding claims, characterized in that the first microorganisms used in step d) and optionally the third microorganisms used in step i) are chosen from yeasts, bacteria, fungi, and preferably from yeasts in the genus Saccharomyces, in particular the species Saccharomyces cerevisae or, among bacteria, in the genus Corynebacterium.

14. Method according to claim 8, characterized in that the second microorganisms are chosen from fungi, in particular filamentous fungi, preferably those of the genus Trichoderma, in particular Trichoderma reesei.

15. Method according to one of the preceding claims, characterized in that the pretreatment (2) according to step a) of the biomass comprises - a1) a sub-step of impregnation of the biomass (1) with a liquor, in particular acid, to obtain an impregnated biomass - a2) a sub-step of cooking the impregnated biomass, possibly accompanied by a steam explosion, to obtain a pre-treated biomass (3).

16. Method according to claim 3 or 4, characterized in that it also comprises: - a step j) of separation, in particular by distillation (21), of the fermented biomass in the form of alcohol (20) obtained in step f), with a possible step k) of solid / liquid separation of the fermented biomass before or after said separation step j).

17. Installation for processing lignocellulosic biomass, said installation comprising - a) a biomass pretreatment unit (2), comprising a biomass cooking device, possibly accompanied by a steam explosion, to obtain a pretreated biomass - b) a first solid / liquid separation unit (4), comprising in particular a filtration device, of all or part (3a) of the pretreated biomass (3) obtained in unit a) in a first solid fraction (7) of pretreated biomass and a first liquid fraction (6) comprising a mixture of compounds, in particular in aqueous phase, comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons and the weight content of C5 sugars of which is greater than the weight content of C6 sugars - c) an enzymatic hydrolysis unit (14) of the first solid fraction (7) of pretreated biomass obtained in step b), to obtain a hydrolysate (15) in the form of sugar(s), including C6 sugars with 6 carbons, - a unit d) for purifying (24) said first liquid fraction (6) with contacting said first liquid fraction with first microorganisms consuming, among the sugars of said fraction, essentially only C6 sugars, in order to obtain a purified liquid fraction (26), containing C5 sugars and depleted in C6 sugars - a second unit e) for solid / liquid separation (27), comprising in particular at least one filtration or centrifugation device, of the purified liquid fraction (26) containing C5 sugars and depleted in C6 sugars obtained in unit d) to obtain a second solid fraction (28) comprising the first microorganisms and a second liquid fraction (29) containing C5 sugars and depleted in C6 sugars.

18. Installation according to claim 17, characterized in that the second liquid fraction (29) containing C5 sugars and depleted in C6 sugars obtained in unit e) contains alcohol, in particular ethanol, obtained by conversion of all or part of the C6 sugars under the action of the first microorganisms, and in that said installation comprises a unit g) for separating (30) said second liquid fraction into a third liquid fraction (32) enriched in sugars and a fourth liquid fraction (31) enriched in alcohol, said separation unit g) comprising at least one evaporation or stripping device.

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