Method for treating an aqueous-phase mixture of compounds comprising sugars containing 5 and 6 carbon atoms

Abstract

The invention relates to a method for treating a mixture M in the aqueous phase of compounds comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons, said C5 sugars and / or said C6 sugars being partly in monomeric form and partly in oligomeric form, such that said mixture is heated, in the presence of acid(s), at a temperature T of at least 60°C so as to obtain a mixture M' enriched in C5 sugars in monomeric form and / or in C6 sugars in monomeric form and depleted in C5 sugars in oligomeric form and / or in C6 sugars in oligomeric form.

Description

[0001] PROCESS FOR TREATING AN AQUEOUS PHASE MIXTURE OF COMPOUNDS COMPRISING SUGARS WITH 5 AND 6 CARBON ATOMS.

[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.), particularly as substitutes for petrochemical derivatives. These are called bio-sourced compounds.

[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, we obtain so-called second generation (2G) sweet juices by a biochemical transformation process which generally includes a pretreatment step and an enzymatic hydrolysis step by an enzymatic cocktail. The pretreatment most often includes an impregnation step with a liquor, in particular acidic or basic or oxidizing, then cooking of the impregnated biomass which is possibly accompanied by a steam explosion.

[0009] The sugary juices resulting from hydrolysis can then be further processed, for example by fermentation to convert them into alcohol, and the conversion process also includes separation and / or purification steps.

[0010] These sweet juices can also come from a mixture of sweet juices from different types of biomass. 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] A solid / liquid separation can then be carried out on the pretreated biomass, so as to recover a liquid fraction which is a sweet juice in the aqueous phase, and a solid fraction, which is a pretreated marc also called cake. Patent FR 3 083 126 thus describes a liquid / solid separation operation on the pretreated biomass obtained at the end of the pretreatment step or at the end of an additional step of said pretreated biomass, this separation step comprising two successive sub-steps:

[0018] - an upstream sub-step b1 of contacting the solid / liquid mixture implemented by a continuous mixer using a mixing fluid,

[0019] - and a downstream extraction / washing sub-step b2 implemented by a continuous filter, in particular of the belt filter type, using a washing fluid, to obtain a solid phase enriched in solid and a plurality of liquid phases enriched in liquid, with operation of the filter preferably in counter-current between the circulation of the solid / liquid mixture to be separated and the extraction / washing fluid, and at least partial recycling of a liquid phase extracted from the belt filter at the inlet of the mixer as a mixing fluid.

[0020] 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.

[0021] Particularly in the case of type 2G sweet juices resulting from the pretreatment of lignocellulosic biomass, for the majority of lignocellulosic biomasses, a proportion of C5 sugars in the sweet juice is observed to be higher than that of C6 sugars. By sweet juice, we mean that sugars are released by a treatment carried out on the biomass, in particular a pretreatment in the known sense of the term in the field of biomass conversion, and that they can be solubilized by mixing the pretreated biomass with water for example.

[0022] The sugars in sweet juice, as seen above, are mainly, or even exclusively, C5 and C6 sugars. In fact, they can be found in three different forms: - in a polymeric form, with a high degree of polymerization, greater than 6, that is to say that they have not been converted, they are insoluble in water, this is the case of cellulose,

[0023] - in monomeric form, they are soluble in water

[0024] - in an oligomeric form, that is, the sugars are in a polymeric form, but with a low degree of polymerization, between 2 and 6, they are also soluble in water.

[0025] This means that, after pretreatment of the biomass, and after having carried out a solid / liquid separation of the biomass thus treated, the liquid fraction obtained is a sweet juice with sugars in monomeric and oligomeric form, the sugars in polymeric form, insoluble, being found in the solid fraction.

[0026] The proportion of C5 sugars compared to C6 sugars, and the proportion, for each of these types of sugars, of the oligomeric form compared to the monomeric form are variable, notably depending on the nature of the biomass (straw, wood, etc.), depending on the type and severity of the pretreatment, depending on the washing conditions when there is washing, etc. But in most cases, there is indeed a significant content of sugars in oligomeric form in the sweet juices.

[0027] However, the presence of these sugars in oligomeric form can be detrimental, regardless of the intended application for these sweet juices. Indeed, when the aim is to convert these sweet juices into other compounds, whether by chemical or biochemical conversion (fermentation for example), sugars in monomeric form are more reactive than sugars in oligomeric form. And while there are outlets for sweet juices as is, without further conversion, these must generally meet data specifications, including a high monomeric sugar content.

[0028] There is therefore a need to improve the quality of these sweet juices, and in particular to increase their sugar content in monomeric form or reduce their sugar content in oligomeric form.

[0029] Summary of the invention

[0030] The invention firstly relates to a process for treating an initial mixture M in aqueous phase of compounds comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons, said C5 sugars and / or said C6 sugars being partly in monomeric form and partly in oligomeric form. This treatment process is such that said mixture is heated, in the presence of acid(s), to a temperature T of at least 60°C in order to obtain a treated mixture M' enriched in C5 sugars in monomeric form and / or in C6 sugars in monomeric form and depleted in C5 sugars in oligomeric form and / or in C6 sugars in oligomeric form.

[0031] The acid or acids present may come from the own acidity of the juice to be treated, in particular when the juice is obtained by acid pretreatment of biomass and / or the addition of acid(s) to the juice.

[0032] 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 “initial sugar juice” or “initial mixture M”.

[0033] For the purposes of the invention, the term "mixture M' enriched in C5 sugars in monomeric form and / or in C6 sugars in monomeric form and depleted in C5 sugars in oligomeric form and / or in C6 sugars in oligomeric form" may also be designated, for the sake of brevity, under the term "treated sweet juice" or "treated mixture M'".

[0034] For the purposes of the invention, "depleted" means that the concentration (or content) of the sugar in question in the mixture decreases due to the treatment and "enriched", conversely, means that the concentration of sugar in the mixture increases due to the treatment.

[0035] For the purposes of the invention, the term “sugars” means sugars in their monomeric form and in their oligomeric form, unless otherwise specified.

[0036] For the purposes of the invention, “juice” is equivalent to a mixture of compounds in aqueous phase: the juice is aqueous, and the sugars it contains are soluble in water.

[0037] To give an order of magnitude, the initial sweet juice preferably has a sugar concentration of at least 20 g / kg. Its concentration can thus be between 20 and 80 g / kg, in particular between 30 and 70 g / kg, for example between 40 and 60 g / kg. And the dry matter content (DM) (defined below) of the initial sweet juice can typically be between 2 and 20%, in particular between 5 and 15%.

[0038] It can therefore be seen that, preferably, the treatment according to the invention is carried out on a sweet juice with a low dry matter content / with a low sugar concentration, even if the invention can also be applied to higher dry matter levels / concentrations.

[0039] The invention has therefore developed a treatment which will transform at least part of the sugars in oligomeric form into sugars in monomeric form, by a hot acid treatment, which will in fact cause a hydrolysis of all or part of the oligomers into monomers. What is very advantageous is that we thus succeed in reducing / eliminating the undesirable compounds, namely the sugars in oligomeric form, to convert them into sugars in monomeric form, which are the desired products: it is not simply a matter of removing them from the initial sugary juice, but of converting them to the desired form.

[0040] The conversion efficiency of oligomers into monomers obtained with the treatment according to the invention can in fact reach up to 50% and more.

[0041] The conditions of this hydrolysis, in particular the acidity of the medium and the temperature, are adjusted according to, in particular, the nature of the biomass, the type of pretreatment it has had when the sugar juice comes from a treatment / pretreatment of lignocellulosic biomass, which determine the oligomer content of the mixture, or even the monomeric sugar purity specifications if it is used as is. It is thus possible to modulate the severity of the treatment according to the sugar juice to be treated and the monomeric sugar purity to be achieved, by modulating temperature, acidity and treatment duration, or even modulating one of the parameters according to the other two.

[0042] This treatment is very advantageous, because the treated sweet juice sees its content of sugars in monomeric form increase and its content of sugars in oligomeric form decrease or even disappear: it has been shown that it is thus possible to easily achieve the purity specifications required for the recovery of these juices. And when these juices are intended to be converted by chemical or biochemical processes, it has also been verified that their reactivity is improved, and therefore that their conversion yield is higher than that of untreated sweet juice according to the invention.

[0043] Advantageously, the temperature T of the treatment may be at least 70°C, in particular at least 75°C, or at least 80°C, or at least 90°C, or at least 100°C.

[0044] Advantageously, the treatment temperature T can be at most 140°C, in particular at most 130°C. Indeed, it is useful not to raise the temperature of the juice too much, in order to avoid any parasitic reaction of the Maillard type which would degrade the sugars.

[0045] Advantageously, the duration of the treatment may be at least 5 minutes, in particular at least 10 minutes, in particular at least 30 minutes, and preferably at most 3 hours, in particular at most 2 hours. Just as for the treatment temperature, it is indeed preferable not to extend the treatment duration too much in order to avoid unwanted reactions such as the Maillard reaction. The temperature / duration pair is therefore chosen for this objective. As mentioned above, the severity of the treatment of the invention can be modulated by adjusting the parameters of its implementation, for example by choosing a temperature that is not too high, but coupled with high acidity and / or a long treatment duration, or, on the contrary, choosing a higher temperature coupled with lower acidity and / or a shorter treatment duration. As already mentioned, this severity is adapted to the type of initial sweet juice and its content of sugars in oligomeric form.

[0046] Advantageously, the treatment of the initial mixture M in acidic conditions can be carried out so that there is at least 0.1% by weight of acid in the total mixture M (sugars + water), in particular between 0.2 and 2.8% by weight of acid in said mixture. This acid content in the total mixture M (sugars + water) corresponds to an addition of acid to the initial sweetened juice. The acid is preferably added in the form of a solution of acid diluted in water. The acid content indicated above takes into account this water supply by taking into account the juice and the aqueous acid solution added to the initial mixture M.

[0047] Note that the initial mixture itself may already be acidic, for example when it comes from pretreatment in an acid medium of lignocellulosic biomass: in this case, it may already be at a pH of, for example, 0.5 to 2.5, the addition of additional acid allowing, if necessary, to adjust the pH to the desired value. If the pretreatment is rather basic, it is then necessary to add acid in appropriate quantities to achieve the same acidity.

[0048] Advantageously, the acid is chosen from at least one of the following strong acids: sulfuric acid, hydrochloric acid and / or at least one of the following organic acids: acetic acid, oxalic acid, formic acid, etc.

[0049] Advantageously, the treatment of the initial mixture M in the presence of acid(s) according to the invention is carried out at a pH of at most 4.5, in particular at most 4 or at most 3.5 or at most 3. It is preferably chosen between 0.5 and 2.5.

[0050] The treatment according to the invention can be carried out continuously, or in batches, in particular in a stirred or piston-type reactor.

[0051] Preferably, the initial sugar juice is mainly derived from the depolymerization of the hemicelluloses present in the lignocellulosic biomass. Preferably, the initial sugar juice contains more C5 sugars than C6 sugars by weight. Preferably, the initial sugar juice is obtained without the addition of enzymes or microorganisms such as bacteria. Finally, preferably, the initial sugar juice is mainly derived from the pretreatment of a lignocellulosic biomass. Here, the term "mainly derived" means that at least half of the initial sugar juice in question comes from the depolymerization in question (in particular all of it).

[0052] According to one embodiment of the invention, the initial mixture M comes from the treatment of biomass, in particular lignocellulosic, 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).

[0053] In this case, the initial mixture M is preferably derived

[0054] - a biomass washing operation,

[0055] - or pretreatment of the biomass including in particular impregnation of the biomass with a liquor, of neutral, acidic or basic pH or of an oxidizing nature, preferably with an acidic liquor, followed by cooking of the impregnated biomass, in particular cooking with steam explosion, possibly followed by a washing operation of the pretreated biomass,

[0056] - then a solid / liquid separation of said washed or pretreated biomass.

[0057] The method according to the invention may, moreover, comprise at least one operation subsequent to the treatment. This subsequent operation may comprise bringing said mixture in aqueous phase into contact with a microorganism consuming, among the sugars in the mixture, essentially only the C6 sugars, in order to obtain a mixture also depleted in C6 sugars (in monomeric and oligomeric form). The microorganism may be chosen from yeasts in the genus Saccharomyces, in particular the species Saccharomyces cerevisae or, among bacteria, in the genus Corynebacterium, and is capable of converting C6 sugars into alcohol, but also of converting certain undesirable impurities such as furfural or 5-HMF. For further details, reference may be made to patent application FR2212406 filed on November 28, 2022.

[0058] Another type of operation subsequent to the treatment according to the invention may be any purification operation in the broad sense, for example to remove acid.

[0059] The invention also relates to a mixture M' of compounds in aqueous solution, comprising C5 sugars and / or C6 sugars, in particular treated according to the process described above, and which has the following characteristics:

[0060] - an S1 content of C5 sugars and / or C6 sugars of between 10 and 100 g / kg of solution

[0061] - including a ratio P1 of C5 sugars and / or C6 sugars in oligomeric form to C5 and / or monomeric C6 sugars of at most 40% by weight, in particular at most 30% by weight or at most 20% by weight. Note that, in the initial mixture before treatment, this ratio can be up to 50% by weight (and preferably at least 10% by weight).

[0062] With the treatment of the invention, this ratio can be reduced by at least 5, 10 or 15% by weight.

[0063] The invention also relates to a mixture M' of compounds in aqueous solution, comprising C5 sugars and / or C6 sugars, obtained from an initial mixture M in aqueous phase of compounds comprising C5 sugars with 5 carbons and / or C6 sugars with 6 carbons and treated according to the process described above.

[0064] The invention also relates to the use of the mixture M' described above as a sweet juice with a high sugar content in monomeric form, which can be recovered as such, or as an intermediate product for a subsequent chemical or biochemical conversion, which can be preceded by prior treatments such as concentration, purification or even dilution, for example. It is thus possible to target the production of biofuel (ethanol and other alcohols obtained by fermentation of sugars), of intermediates for chemistry known as biosourced compounds, or that of sweet juices (the concentration, water content or other minor compounds of which can be modified according to the imposed specifications).

[0065] It should also be noted that the initial sweet juices (and the juices treated according to the invention) may also contain other minor compounds, in addition to sugars, including, for example, mineral salts, sugar degradation products, carboxylic alcohols, or furan compounds. They may thus comprise furfural, and / or 5-hydroxymethyl furfural (5-HMF), in particular when the initial sweet juice comes from the pretreatment of lignocellulosic biomass under acidic conditions. It is then possible that these are also converted by the treatment according to the invention, for example into formic or levulinic acid.

[0066] The invention will be described below in more detail, using non-limiting examples and the following figures:

[0067] List of figures

[0068] Figure 1 is a very schematic representation of a process for treating lignocellulosic biomass to obtain the initial sugary juice which will be treated according to the invention.

[0069] Description of the embodiments

[0070] The invention therefore seeks, starting from a sweet juice containing C5 sugars and / or C6 sugars (and preferably only these two types of sugars), to obtain a so-called treated sweet juice where the content of sugars in oligomeric form has been reduced, or even eliminated, in favor of the monomeric form of said sugars.

[0071] The invention can be applied to all kinds of sweet juices, as long as the juice contains at least one type of sugar in liquid phase, in particular aqueous phase, which is present both in monomeric form and in oligomeric form.

[0072] In the non-limiting example of implementation of the invention described below, the initial sweet juice is entirely derived from an acid pretreatment of a lignocellulosic biomass. This pretreatment is described below using Figure 1.

[0073] The references in the figure represent the following flows / devices / steps:

[0074] 1: Biomass

[0075] 2: Conditioning and pretreatment

[0076] 3: Pretreated biomass

[0077] 3a: Pretreated biomass towards the filtration tool

[0078] 3b: Pretreated biomass towards enzymatic hydrolysis (optional stream)

[0079] 4: Solid / liquid separation (a belt filter or a filter press for example) to extract a sweet juice, with an optional washing step

[0080] 5: Water as contact and / or washing fluid

[0081] 6: Sweet juice containing mainly C5 sugars (C5 and / or C6 sugars in monomeric and oligomeric form)

[0082] 6a: Sweet juice comprising mainly C5 sugars for the production of enzymes 6b: Sweet juice comprising mainly C5 sugars which will be treated according to the invention

[0083] 7: Pretreated and washed biomass

[0084] 8: Enzyme production reactor

[0085] 9: Mushroom inoculum (Trichoderma Reese / for example) for enzyme production

[0086] 10: Enzyme cocktail (mixture of one or more enzymes, including cellulases, beta glucosidases, xylanases, etc.)

[0087] 14: Enzymatic hydrolysis reactor.

[0088] 15: Hydrolyzate

[0089] 18: Solid / liquid separation with an optional step (not shown) of washing the solid residue with a solvent (e.g. water)

[0090] 19: Solid residue (composed mainly of lignin)

[0091] 20: Liquid product of filtration, here the filtered hydrolyzate (sugars mainly C6) Throughout this text, and in particular in the description of the figure, 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 filtration, solid / liquid separation, etc. type tools (for the sake of brevity).

[0092] If we take the process sequence according to figure 1: Biomass 1 undergoes conditioning / pretreatment in unit 2 (possible mechanical crushing, 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).

[0093] A portion of this pretreated biomass, the stream 3a, goes to a solid / liquid filtration and separation tool 4, said tool also being supplied with water 5 as contact water and / or washing water for the pretreated biomass. Firstly, the pretreated biomass is contacted with water to improve its filterability. The mixture is then filtered on a belt filter and washed with water.

[0094] Another part of the pretreated biomass, stream 3b, can go to the enzymatic hydrolysis reactor 14.

[0095] At the outlet of the separation tool 4, the liquid fraction 6 is an aqueous sugary juice comprising mainly C5 sugars, but also, to a lesser extent, C6 sugars, the C5 and / or C6 sugars being partly in monomeric form and partly in oligomeric form. 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 the microorganisms of the Trichoderma reese type which produce this mixture of enzymes 10. The remainder of the flow 6, the flow 6b (or which constitutes the entire flow 6 if this flow is not used for the production of enzymes) is the sugary juice which will be treated according to the invention.

[0096] At the outlet of the separation tool 4, the solid fraction 7 which contains unconverted cellulose, and also unconverted residual hemicelluloses, feeds the enzymatic hydrolysis reactor 14.

[0097] 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 solid and soluble compounds in a sample of the product 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”. The enzymatic hydrolysis reactor 14 is fed by stream 3b, and also by stream 7 which is the solid fraction resulting from filtration in unit 4, which is therefore the solid washed pretreated biomass.

[0098] 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.

[0099] At the outlet of reactor 14, there is a flow 15 of hydrolyzate (sugars), which then feeds a solid / liquid separation device 18 of the filter press type for example, with an optional step of washing the solid residue with a solvent (for example water). From this device 18 emerge a liquid fraction 19, in the form of a sugary juice with mainly C6 sugars, and a solid fraction 20 which is a woody solid residue.

[0100] It should also be noted that enzyme production can be done on the biomass processing site, as shown in Figure 1. But it can also be done ex situ: ready-to-use enzymes 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 depending on the needs), or be used only for the production of enzymes (flow 6a) or only to be used as such (flow 6b).

[0101] The treatment according to the invention can advantageously be applied to the flow of sweet juice 6 or 6b.

[0102] We recall the reaction path which leads, during the pretreatment carried out in steps 2-3-4, to obtaining a sweet juice (flow 6): we start from a lignocellulosic biomass which includes cellulose and hemicelluloses. After pretreatment, at the end of step 2, we obtain an acidic pretreated marc where:

[0103] - cellulose is at least partly converted into monomers and oligomers of C6 sugars, such as glucose,

[0104] - hemicelluloses, namely, galactan, mannan, arabinan, xylan are at least partly converted into monomers and oligomers of C5 and C6 sugars, such as galactose, mannose, arabinose and xylose.

[0105] The recovered sugar juice 6 at the outlet of the separation device contains these C5 and C6 sugars which are in monomeric form, but also, to a smaller extent, in oligomeric form. It may also contain very minor compounds, as already mentioned, such as 5-HMF and furfural. It does not contain sugars in polymeric form, which are insoluble and which therefore remain in the solid fraction 7 at the outlet of the separation device 4.

[0106] The composition of sweet juice 6 may vary depending on the biomass, the type of pretreatment, the pretreatment conditions, the washing conditions of the pretreated biomass.

[0107] For example, the sweet juice to be treated according to the invention may have the following composition:

[0108] - between 0.5 and 30 g of glucose per kg of juice, in particular between 5 and 15 g / kg of glucose

[0109] - between 10 and 100 g of xylose per kg of juice, in particular between 20 and 60 g / kg of xylose

[0110] - between 0.5 and 36 g / kg of potential glucose, in particular between 5.5 and 20 g / kg of potential glucose, or between 0.1 and 35 g / kg of oligomeric glucose, in particular between 0.5 and 30 g / kg of oligomeric glucose, in particular between 0.5 and 10 g / kg of oligomeric glucose

[0111] - between 10 and 130 g / kg of potential xylose, in particular between 22 and 75 g / kg of potential xylose, or between 0.1 and 30 g / kg of oligomeric xylose, in particular between 2 and 20 g / kg of oligomeric xylose with the following conventions:

[0112] - Glucose concentration is understood in the sense of monomeric glucose.

[0113] - The xylose concentration is understood in the sense of monomeric xylose.

[0114] - These concentrations can be analyzed for example by high performance liquid chromatography (HPLC) methods

[0115] - The potential sugar concentration is the measurement of the concentration of monomeric sugars after acid hydrolysis on the initial sugar juice at 120°C for 1 hour in the presence of a large excess of dilute acid: to 0.3 grams of DM of the initial juice are added 4.92 grams of 72% sulfuric acid and water, the quantity of which is calculated to obtain a mixture of 90 g.

[0116] - The concentration of oligomeric sugars corresponds to the difference between the concentration of potential sugars and the concentration of monomeric sugars.

[0117] The invention consists of treating this type of sweet juice hot and under acidic conditions, in order to hydrolyze the sugars in oligomeric form into sugars in monomeric form, while preserving the monomeric sugars already present in the initial sweet juice.

[0118] The following non-limiting examples illustrate its implementation and use a biomass pretreated under acidic conditions, which means that the sweet juices to be treated according to the invention and which are derived therefrom can be / are already under acidic conditions. The invention applies equally well to juices resulting from the treatment / pretreatment of biomass under non-acidic conditions (in particular neutral or basic conditions).

[0119] Examples

[0120] Example 1 (comparative)

[0121] We start with an initial sweet juice M from biomass pretreated by acid impregnation of the biomass followed by steam explosion, pretreated biomass which is then washed and separated into liquid fraction (the sweet juice) and solid fraction in accordance with the teaching of the aforementioned patent FR 3 083 126, to which we will refer for more details. This is the juice from stream 6 described above.

[0122] Briefly, this pretreatment is an operation of impregnation of lignocellulosic biomass (wheat straw) with an acid liquor, followed by a steam explosion operation of the impregnated biomass. 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 initial sweet juice M to be treated according to the invention, 550 kg of pretreated biomass are mixed with 1010 kg of water, then filtered and then pressed. After filtration and pressing, 885 kg of a juice M, also called C5 hydrolysate, is obtained. The pretreatment taking place under acidic conditions, this juice has a pH of 1.5.

[0123] The concentration of compounds of interest in this initial sweet juice M 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. The dry matter content of the initial sweet juice M is 8% by weight. Juice M contains 49.5 g / kg of glucose and xylose sugars. The concentrations of minority sugars, such as arabinose, galactose and mannose for this biomass, are not indicated.

[0124] [Table 1]

[0125] This juice is the control juice, which will be treated according to the invention in the following examples.

[0126] Example 2 (according to the invention)

[0127] We start with the sweet juice M defined in example 1. It is treated according to the invention with the following operating conditions: The juice is treated in a stirred batch reactor for 1 hour at 120°C. The pH of the juice is already acidic (pH of approximately 1.5), no acid is added to the juice.

[0128] Example 3 (according to the invention)

[0129] We start with the sweet juice M defined in example 1. It is treated according to the invention with the following operating conditions: The juice is treated in a stirred batch reactor for 1 hour at 120°C. 72% sulfuric acid in water is added to the initial sweet juice M so that the final concentration of pure sulfuric acid added to the total mixture is 1% by weight.

[0130] Example 4 (according to the invention)

[0131] We start with the sweet juice M defined in example 1. It is treated according to the invention with the following operating conditions: The juice is treated in a stirred batch reactor for 1 hour at 120°C. 72% sulfuric acid in water is added to the initial sweet juice M so that the final concentration of pure sulfuric acid added to the total mixture is 2%. weight

[0132] Example 5 (comparative)

[0133] We start with the sweet juice M defined in example 1. It is treated according to the invention with the following operating conditions: The juice is treated in a stirred batch reactor for 1 hour at 120°C. 72% sulfuric acid in water is added to the initial sweet juice M so that the final concentration of pure sulfuric acid added to the total mixture is 3% by weight.

[0134] Example 6 (comparative)

[0135] We start with the sweet juice M defined in example 1. It is treated according to the invention with the following operating conditions: The juice is treated in a stirred batch reactor for 1 hour at 120°C. 72% sulfuric acid in water is added to the initial sweet juice M so that the final concentration of pure sulfuric acid added to the total mixture is 4% by weight.

[0136] Table 2 below groups together the sugar concentrations in the sweet juices of the examples once hydrolyzed according to the invention.

[0137] C is the concentration of glucose and xylose sugars analyzed by HPLC in g / kg, and R is the change in the yield of monomeric sugars.

[0138] [Table 2]

[0139] The first line tO corresponds to the concentrations of juice M before starting the treatment according to the invention. Note that the sugar concentration decreases when acid is added, due to the dilution caused by this addition of acid in aqueous solution: the more acid is added, the more the concentration decreases.

[0140] The theoretical potential sugar concentration at tO + 1 hour corresponds to the total potential glucose and xylose of the juice M: it is the sugar concentration after acid hydrolysis in the presence of excess acid under dilute conditions. Thus the maximum change in the yield of monomeric sugars is 15.5%.

[0141] From the data in Table 2, we see that without adding acid (example 2), since the juice is already at an acidic pH, a certain amount of oligomers is converted into monomers by the heat treatment. By adding 1% (example 3) and 2% acid (example 4), this is also the case, with an increased yield.

[0142] On the other hand, by adding 3% (example 5) or 4% of acid (example 6), there is no longer a favorable change in yield: the conversion of oligomers into monomers is thwarted by the degradation of the monomers.

[0143] In conclusion, it can be seen that the acid hydrolysis of the juices according to the invention is favorable for obtaining juices with higher monomeric sugar contents and a lower oligomeric sugar content. However, the treatment must be adjusted, particularly in terms of acidity, because too high an acidity (and / or too high a treatment temperature) can lead to degradation of the monomeric sugars, which can tend to cause the loss of all or part of the benefit of the invention.

Claims

Claims 1. Process for treating an initial mixture M in aqueous phase of compounds comprising C5 sugars with 5 carbons and C6 sugars with 6 carbons, said C5 sugars and / or said C6 sugars being partly in monomeric form and partly in oligomeric form, characterized in that said mixture is heated, in the presence of acid(s), to a temperature T of at least 60°C in order to obtain a treated mixture M' enriched in C5 sugars in monomeric form and / or in C6 sugars in monomeric form and depleted in C5 sugars in oligomeric form and / or in C6 sugars in oligomeric form.

2. Method according to the preceding claim, characterized in that the temperature T of the treatment is at least 70°C, in particular at least 75°C, or at least 80°C, or at least 90°C, or at least 100°C.

3. Method according to one of the preceding claims, characterized in that the temperature T of the treatment is at most 140°C, in particular at most 130°C.

4. Method according to one of the preceding claims, characterized in that the duration of the treatment is at least 5 minutes, in particular at least 10 minutes, in particular at least 30 minutes, and preferably at most 3 hours, in particular at most 2 hours.

5. Method according to one of the preceding claims, characterized in that the treatment of the initial mixture M in acidic conditions is carried out with at least 0.1% by weight of acid added to the mixture, in particular between 0.2 and 2.8% by weight of acid in said mixture.

6. Method according to one of the preceding claims, characterized in that the acid is chosen from at least one of the following strong acids: sulfuric acid, hydrochloric acid and / or at least from at least one of the following organic acids: acetic acid, oxalic acid, formic acid.

7. Method according to one of the preceding claims, characterized in that the treatment of the initial mixture M in the presence of acid(s) is carried out at a pH of at most 4.5, and preferably between 0.5 and 2.

5.

8. Method according to one of the preceding claims, characterized in that the treatment is carried out continuously or in batches, in particular in a stirred or piston-type reactor.

9. Method according to one of the preceding claims, characterized in that the initial mixture M comes from the treatment of biomass, in particular lignocellulosic, originating in particular forest and / or agricultural and / or paper residues, and / or sacchariferous plants and / or starchy plants and / or Fermentable Fractions of Household Waste (FFOM).

10. Method according to the preceding claim, characterized in that the initial mixture M comes from - a biomass washing operation, - or pretreatment of the biomass including in particular impregnation of the biomass with a liquor, of neutral, acidic or basic pH or of an oxidizing nature, preferably with an acidic liquor, followed by cooking of the impregnated biomass, in particular cooking with steam explosion, possibly followed by a washing operation of the pretreated biomass, - then a solid / liquid separation of said washed or pretreated biomass.

11. Method according to one of the preceding claims, characterized in that it comprises an operation subsequent to the treatment by heating in the presence of acid of the initial mixture M, said subsequent operation comprising bringing said mixture in aqueous phase into contact with a microorganism consuming, among the sugars of the mixture, essentially only the C6 sugars, in order to obtain a mixture depleted in C6 sugars.

12. Mixture M' of compounds in aqueous solution, comprising C5 sugars and / or C6 sugars; - with an S1 content of C5 sugars and / or C6 sugars of between 10 and 100 g / kg of solution - including a ratio P1 of C5 sugars and / or C6 sugars in oligomeric form to monomeric C5 and / or C6 sugars of at most 40% by weight, in particular at most 30% by weight or at most 20% by weight.

13. Mixture M' of compounds in aqueous solution, comprising C5 sugars and / or C6 sugars, characterized in that it is obtained from an initial mixture M in aqueous phase of compounds comprising C5 sugars with 5 carbons and / or C6 sugars with 6 carbons treated according to the process according to one of claims 1 to 11.

14. Use of the mixture M' according to one of claims 12 or 13 as a sweet juice with a high sugar content in monomeric form, which can be recovered as such, or as an intermediate product for subsequent chemical or biochemical conversion.

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