WO2018130776A1 - Biomass treatment method - Google Patents

Abstract

The invention relates to a biomass treatment method, said method comprising at least (a) bringing the biomass into contact with subcritical water in the presence of at least one hydrophilic ionic liquid.

Description

 PROCESS FOR TREATING BIOMASS

The present invention relates to a new process for treating biomass, intended in particular to allow the valorisation of lignocellulosic biomass, this process comprising a treatment of biomass with subcritical water in the presence of an ionic liquid.

State of the art

 Lignocellulosic biomass represents a strong potential for developing the bioconversion of previously undeveloped plant wastes into high value-added bio-products (Tamaru and Lôpez-Contreras, 2013). In addition, fuels and organic chemicals from lignocellulosic biomass can help reduce greenhouse gas emissions, improve energy security and improve solid waste management (Tamaru and Lôpez-Contreras, 2013). ). Oleaginous plants are grown to extract the fat fraction from their seeds or fruits for food, energy or industrial use. These crops are currently characterized by the low value of co-products containing lignocellulose such as, among others, straw, leaves, stems, shells, cakes. These co-products from these crops represent an important source of lignocellulosic biomass. It is the same for other waste from the plant world, such as sawdust, bagasse sugar cane etc.

 Effective fractionation of lignocellulosic biomass would allow the replacement of some fossil fuels with biosourced carbohydrates, thus reducing the dependence of the chemical industry on oil.

An important limitation to the transformation and recovery of lignocellulosic biomass is its resistance to enzymatic conversion to sugar-type compounds. The resilient nature of biomass, due in particular to its complex structure and resistance to hydrolysis of the polymers that make up lignocellulose, is a major obstacle to efficient low-cost fractionation of lignocellulosic biomass. The treatment of the biomass directly by enzymatic hydrolysis is not effective, and different pretreatments that fracture the lignocellulosic structure are necessary to make the biomass accessible to hydrolysis by enzymes. Similarly, the chemical treatment of biomass requires drastic conditions which lead to a low yield of sugars and produce derivatives such as for example the furfural inhibitor of fermentation enzymes.

 Currently, the pretreatment stage of lignocellulosic biomass constitutes a technological lock for its transformation into valuable products. Several variants of pretreatments have been studied. The main chemical pretreatment processes are as follows:

 • Pretreatment with dilute acid (100 ° C to 200 ° C, 0.3 to 2% aqueous sulfuric acid, for up to 20 minutes),

 "Pretreatment under alkaline conditions (8-12% NaOH aqueous solution, at 80-120 ° C, for 30-60 minutes), and

 • The Organosolv process which consists of extracting lignin and hemicellulose with organic solvents (ethanol, acetone) at 150-200 ° C under acidic conditions.

 Some conventional pretreatments are effective, but they have a high environmental impact, which is incompatible with sustainable development. Therefore, the search for environmentally friendly pretreatments has been the subject of many developments.

 These pretreatments produce, in particular, simple sugars and polymers sensitive to hydrolysis, but they also form other reaction products which are capable of inhibiting the hydrolysis reaction. In such a case, the yields of the enzymatic hydrolysis of the biomass have low values and the economic viability of the whole recovery process is low.

 Fractionation of biomass by hydrophilic ionic liquids (IL) or by subcritical water (SCW) are two ecological pretreatments that have been the subject of numerous studies and have been revealed as promising processes.

Ionic liquids, such as imidazolium with a carbon chain length of less than or equal to 4 C, are low melting point salts (below 100 ° C), and compared to other solvents, they are more respectful of the environment for those with imidazolium cations substituted with acylated chains of length less than or equal to 4 carbons (Garcia-Lorenzo, A. et al., Green Chem., 2008, 10, 508-516, Egorova, KS et al, ChemSuschem 2014, 7, 336-360). Their use in the fractionation of lignocellulosic biomass showed a gain considerable attention in recent years, as they have several advantages, including high thermal stability, minimal corrosion (Hasib-ur-Rahman, M. et al., Ind. Eng Chem. Res 51, 8711-8718) and low volatility which is advantageous for recycling. These properties distinguish them from conventional organic solvents (unstable and toxic) which must be used under severe conditions. The first results confirmed that the use of ionic liquids is an effective method, more advantageous compared to conventional pretreatment methods.

Up to now, 1-ethyl-3-methylimidazolium acetate, designated [C ₂ mim] ⁺ [CH3COO] ^" , appears to be the most suitable ionic liquid for pretreatment of lignocellulosic biomass: it has been found that it induced the dissolution of biomass polymers (lignin and cellulose) (Auxenfans et al, 2012, Husson et al., 2011, Sant'Ana da Silva et al, 2011) and allowed its subsequent hydrolysis by enzymes.

 The treatment of lignocellulosic biomass by ionic liquids alone is characterized by a low degradation of the hemicellulose solubilized in the liquid fraction, and a loss of mass, which depends on the duration and temperature, and is at most order of 30%. Pre-treatment residues of lignocellulosic biomass by ionic liquids have a moderate sensitivity to enzymatic hydrolysis, this sensitivity being variable as a function of the ionic liquid used and pretreatment conditions (temperature, duration, biomass loading). Finally, such treatment uses large amounts of ionic liquids, which is not totally satisfactory from an economic point of view.

Water is the most abundant molecule on Earth and it has many advantages: it is non-toxic, safe for health, non-flammable. When using water as an extraction solvent, its dielectric constant, which can be changed by temperature, is the most important factor. It decreases from 80 to room temperature, at 27 to 250 ⁰ C, a value substantially equal to that of ethanol at room temperature.

Subcritical water is defined as water brought to temperatures between 100 and 374 ⁰ C (critical temperature of the water around 374 ⁰ C) under high pressure which maintain the water in the liquid state (the pressure critical of the water is approximately equal to 221 bars). The water is then in a particular state that confers properties, in particular of density, diffusivity and viscosity, intermediate between those which it presents in the liquid state and in the gaseous state.

 Subcritical water has been widely used for the hydrolysis of organic compounds, and recently it has been used in pretreatment of biomass. Subcritical water has been used to convert carbohydrates into useful components by hydrolysis and fractionation of lignocellulose (Ahmed et al, 2013, Kruse and Gawlik, 2003, Sasaki et al., 1998). In the literature concerning the pretreatment of biomass with subcritical water, we find two main operational conditions applied: either a high-pressure treatment for a very short time (250-350 ° C, between 1-300 sec) (Cheng et al 2009, Kumar et al., 2010); or moderate pressure for a longer period (100-180 ° C, between 10-90 min) (Ahmed et al, 2013, King et al, 2012, Tsigie et al, 2013a, 2013b, 2012).

 However, subcritical water treatment is characterized by a higher mass loss than pretreatment with ionic liquids. The pre-treatment residues of lignocellulosic biomass by subcritical water have a very low sensitivity to enzymatic hydrolysis, which is a major drawback to the use of this pretreatment method in the recovery of biomass.

 WO2012 / 174459 has described the pretreatment of lignocellulosic biomass by an ionic liquid under pressure, which makes it possible to improve the kinetics of the reaction and to increase the glucose yield during subsequent hydrolysis. This treatment can be carried out in the presence of a co-solvent such as water. However, it is not taught in this document to implement a treatment method using water in subcritical state. Neither is the synergistic action of treatment with subcritical water and ionic liquid taught. Moreover, the ionic liquid content used in this process is high and therefore expensive.

WO2014 / 138100 discloses methods for (a) dissolving biomass in ionic liquids, (b) deconstructing cellulose, hemicellulose and / or lignin derivatives thereof, (c) separating biomass derivatives from ionic liquid , and (d) converting biomass derivatives into fuels or useful chemicals. These processes involve the use of ionic liquids and possibly co-solvents such as water. The treatment can be performed under pressure, however, it is not taught in this document to implement a treatment method using water in subcritical state. Neither is the synergistic action of treatment with subcritical water and ionic liquid taught. In such a process, if the water is not in the subcritical state, there is a high risk of cellulose precipitation and therefore limited efficiency in terms of fractionation and disruption of lignocellulosic matrix and cellulose. itself, which hinders enzymatic degradation.

 WO 2013/036863 describes various processes using ionic liquids. This document notably describes a process for separating one or more compounds derived from biomass from an ionic liquid by contacting the composition comprising the compound (s) derived from the biomass and the ionic liquid with a fluid.

 Surprisingly, the inventors have found that a treatment of lignocellulosic biomass with subcritical water in the presence of at least one ionic liquid makes it possible to overcome the disadvantages of the processes of the prior art.

Summary of the invention

 A first subject of the invention consists of a process for treating a biomass, this process comprising at least (a) bringing the biomass into contact with a water in the subcritical state in the presence of at least one ionic liquid hydrophilic.

According to a preferred embodiment, the amount of biomass is from 1 to 30% by weight relative to the total volume of liquid.

According to a still preferred embodiment, the amount of biomass is from 1 to 15% by weight relative to the total volume of liquid, more preferably from 2 to 10%.

According to a preferred embodiment, the amount of hydrophilic ionic liquid is 1 to 10% by volume relative to the total volume of water.

According to a still preferred embodiment, the amount of hydrophilic ionic liquid is 2 to 7% by volume relative to the total volume of water, more preferably 3 to 5%. According to a preferred embodiment, the biomass is a lignocellulosic biomass. According to a still preferred embodiment, the biomass is chosen from biomasses of oleaginous origin, such as sunflower hulls, rapeseed straw.

According to a preferred embodiment, the hydrophilic ionic liquid is chosen from those whose cation is an imidazolium optionally substituted with one or more alkyl groups.

According to a further preferred embodiment, the hydrophilic ionic liquid is chosen from those whose cation is an imidazolium substituted with one or more C 1 -C 4 alkyl groups.

According to a very advantageous embodiment, the hydrophilic ionic liquid is chosen from the organic salts of 1-ethyl-3-methylimidazolium, even more preferentially from 1-ethyl-3-methylimidazolium acetate and 1-ethylethylphosphonate. 3-methylimidazolium.

Preferably, the hydrophilic ionic liquid is 1-ethyl-3-methylimidazolium acetate.

According to a preferred embodiment, in step (a) the reaction medium is subjected to a temperature ranging from 160 to 240 ° C.

According to a still more preferred embodiment, in step (a) the reaction medium is subjected to a temperature ranging from 160 to 240 ° C. for a duration ranging from 15 minutes to six hours, preferably from 30 minutes to four hours, even more preferably from 30 minutes to two hours. According to a preferred embodiment, step (a) is preceded by mechanical treatment to obtain a biomass in the form of controlled-size particles, in particular a grinding of the biomass. According to a preferred embodiment, step (a) is followed by a step (b) filtration and washing to obtain: firstly a solid fraction of pre-treated biomass, on the other hand a liquid fraction comprising water and ionic liquid as well as lignin. According to a preferred embodiment, step (b) is followed by a step (c) of enzymatic treatment of the solid pre-treated biomass.

According to a still more preferred embodiment, step (c) comprises treatment with cellulases, for example treatment with cellulases derived from Trichoderma reesei.

According to a still preferred embodiment, step (c) is followed by at least one fermentation step. According to a preferred embodiment, the process further comprises at the end of step (b) a step (d) of removing the solvents, advantageously a step (d) of removing water from the fraction liquid.

According to a still preferred embodiment, step (d) is followed by a step (e) of dialysis and enzymatic treatment to recover: on the one hand a lignin fraction and on the other hand a mixture comprising water and the ionic liquid.

According to a still more preferred embodiment, step (e) comprises treatment with cellulases, such as, for example, treatment with cellulases derived from Trichoderma reesei. According to a still more preferred embodiment, step (e) comprises a treatment with xylanases, such as, for example, treatment with xylanases derived from Trichoderma viride. According to a preferred embodiment, the ionic liquid obtained at the end of step (d) and optionally of step (e) is reused in step (a) of a new treatment cycle of a biomass.

In the lignocellulosic biomass pretreatment process of the invention, the ionic liquid acts as a catalyst or as a synergistic component in pretreatment with subcritical water. At the end of this process, a very significant improvement in the solid mass recovery efficiency was observed, compared to each of the processes of the prior art taken in isolation (treatment with ionic liquids and treatment with subcritical water). It has also been found that the method of the invention makes it possible to access a pre-treated biomass which exhibits an increased sensitivity to enzymatic hydrolysis, compared with each of the processes of the prior art, in particular compared to treatment with the prior art. subcritical water alone. Thus, this pre-treatment method provides access to a fraction that can be efficiently converted into fermentable sugars by subsequent enzymatic bioconversion treatment. The method of the invention allows for selective degradation of hemicellulose compared to ionic liquid treatment processes, without significant degradation of the cellulosic fraction. This degradation of hemicellulose leads to the formation of C ₅ sugars in the recovered liquid fraction. Also obtained by the process of the invention are pre-treated biomass fractions having a lower lignin content compared to the pre-treatment method with subcritical water alone. Indeed, the lignin is partially extracted in the liquid fraction obtained at the end of steps a) and b). The method of the invention thus provides access to compositions of matter different from those obtained by the processes of the prior art and whose recovery can be facilitated by the low hemicellulose content. Moreover, this process allows the recovery of lignin as a co-product and its recovery independently of the other fractions of material obtained. This process also makes it possible to recover simple sugars, in particular C ₅ sugars, resulting from the degradation. hemicellulose. The process of the invention leads to a fraction containing cellulose whose crystallinity index is higher than that of the starting biomass, which allows its valuation in the polymer industry for the production of composites. The process can be carried out with relatively high concentrations of biomass (up to 10% by mass of biomass per volume of solvent). The reproducibility of this process is satisfactory. The ionic liquids used in this process are implemented in a much smaller quantity than in pre-treatment processes with ionic liquids alone, which represents a gain both in terms of economy and environmental impact. These ionic liquids can be recycled and the process performance has been maintained after several cycles of reuse of the ionic liquids.

detailed description

 The biomass

 Biomasses that can be used in the process of the present invention include, but are not limited to, cellulose biomass, hemicellulose biomass, lignocellulosic biomass, and mixtures thereof. In a preferred embodiment, the biomass is a lignocellulosic biomass.

 Lignocellulosic biomass can be defined as woody plant material. It includes, but is not limited to, wood and green residues, straw, sugarcane bagasse, fodder, some crop waste such as stems, leaves, hulls, husks and groynes. plants or leaves, branches. Lignocellulose biomass may also include, but is not limited to, herbaceous material, agricultural residues, forest residues, paper waste, and pulp mill residues. Lignocellulosic biomass is generally characterized by the presence of cellulose, hemicellulose and lignin, varying in content depending on the origin of the biomass. Lignocellulosic biomass may also contain proteins, ashes, lipids and other organic compounds. All these examples of biomasses can be implemented in the process of the invention.

Preferably, the process of the invention applies to lignocellulosic biomasses in which the compound composed of cellulose, hemicellulose and the lignin represents at least 50% by mass relative to the totality of the mass of the biomass.

 It is understood that the lignocellulosic biomass may be in the form of a plant cell wall material containing lignin, cellulose and hemicellulose in a mixed matrix.

 Among the known lignocellulosic biomasses that can be used preferentially in the process of the invention, mention may be made of: sunflower hulls, cereal straw, such as wheat straw, rapeseed straw, miscanthus straw, rice straw, wood chips, such as oak, pine, spruce, poplar or birch, wheat straw, corn stover, corn fiber, rice bark, wheat bran, bagasse, paper, waste processing paper pulp or mixtures of these materials. Preferably, the process of the invention is applicable to lignocellulosic biomasses chosen from biomasses of oleaginous origin, for example: sunflower hulls, rapeseed straw, whose crops cover large cultivable areas, in particular in France.

 In fact, oilseed crops are characterized by the large proportion of non-recoverable waste by the processes of the prior art. This is particularly the case for sunflower hulls which are considered waste. This is also the case for rapeseed straw, which may, however, initially be left in the fields as fertilizer.

 Preferably, before it is used in the process of the invention, the biomass is subjected to a mechanical treatment step making it possible to give it the shape of particles of substantially homogeneous size. Such a mechanical pretreatment makes it possible to facilitate the pretreatment of the biomass of step (a) and to obtain a product of substantially homogeneous composition. The mechanical pre-treatment also allows improved reproducibility of step (a). Such pre-mechanical treatment is advantageously carried out in a known manner, by grinding, or by hashing, the biomass into particles. - Pretreatment of biomass:

According to the invention, the method for treating biomass comprises at least one pre-treatment step (a) comprising contacting the biomass with a water in the subcritical state in the presence of at least one hydrophilic ionic liquid . Subcritical water treatment is known to those skilled in the art. The components of the reaction medium (biomass, ionic liquid and water) are introduced into the reactor. In order to achieve subcritical conditions, the pressure is increased in increments of temperature and reduced by the purge of steam from the reactor. It is impossible to define a fixed pressure for the implementation of this step, but this parameter is controlled, in a manner known to those skilled in the art, in order to remain in subcritical conditions.

 Advantageously, step (a) has been carried out at a temperature ranging from 160 ° C to 240 ° C. Below 160 ° C were found less interesting results, in particular a lower sensitivity to enzymatic hydrolysis downstream. Above 240 ° C the hydrophilic ionic liquids have less stability.

 The biomass is brought into contact with the ionic liquid for a time sufficient to increase the accessibility and hydrolysis of the carbohydrate constituents present in the biomass. The contacting may comprise agitation or mixing of the reaction medium. In general, the biomass is contacted with water in the subcritical state in the presence of at least one hydrophilic ionic liquid for a period of time ranging from about 15 minutes to about 6 hours. Preferably, the biomass is contacted with water in the subcritical state in the presence of at least one hydrophilic ionic liquid for a period of time ranging from about 0.5 to about 4 hours. More preferably, the biomass is contacted with water in the subcritical state in the presence of at least one hydrophilic ionic liquid for about 0.5 to 2 hours.

 The method of the invention makes it possible to obtain a pre-treated biomass sensitive to hydrolysis, with high recovery yields, in a relatively short time, which gives this process a certain economic advantage.

 The pre-treatment is carried out in the presence of ionic liquid in the reactor. Ionic liquids are salts that are liquid rather than crystalline at ambient temperatures. Many ionic liquids can be used in the pretreatment process of the present invention.

Preferably, the ionic liquid is chosen for its compatibility with the treatment (b) of enzymatic hydrolysis of cellulose. In fact, small amounts of residues of certain ionic liquids in the pretreated biomass can adversely affect the effectiveness of the enzymatic treatment of step (b). An ionic liquid which is compatible with a subsequent treatment with a thermostable cellulase is preferably chosen.

 The ionic liquids used are preferably hydrophilic, which means that they are miscible in all proportions with water. Preferably, the hydrophilic ionic liquid is chosen from those whose cation is an imidazolium optionally substituted with one or more alkyl groups.

 Such ionic liquids are well known to those skilled in the art, mention may be made in particular, in a nonlimiting manner: alkanoates of 1-alkyl-3-alkylimidazolium, alkylphosphonates of 1-alkyl-3-alkylimidazolium, alkyl sulphates of -alkyl-3-alkylimidazolium, 1-alkyl-3-alkylimidazolium methylsulfonates, 1-alkyl-3-alkylimidazolium hydrogensulfates, 1-alkyl-3-alkylimidazolium thiocyanates, and 1-alkyl-3-halogenides alkylimidazolium, wherein the term "alkyl" refers to an alkyl group having 1 to 6 carbon atoms, and an "alkanoate" is an alkanoate comprising 1 to 10 carbon atoms. Preferentially, the term "alkyl" denotes an alkyl group comprising from 1 to 4 carbon atoms, for example a methyl group, an ethyl group, a propyl group or a butyl group.

 Preferably, the alkanoate is an acetate. Preferably, the alkylphosphonate is methylphosphonate.

Examples of ionic liquids that can be used in the process of the invention include: 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium methylphosphonate, 1-ethyl-3-chloride methylimidazolium, 1-ethyl-3-methylimidazolium hydrogen sulfate, 1-ethyl-3-methylimidazolium methylsulfate, 1-ethyl-3-methylimidazolium methanesulfonate, 1-ethyl-3-methylimidazolium ethylsulfate, tetrachloroaluminate 1-ethyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium chloride, 1-butylformate 3-methylimidazolium, 1-allyl-3-methylimidazolium formate, 1-allyl-3-methylimidazolium chloride, 1-allyl-2,3-dimethylimidazolium bromide, 1-butyl-3-methylimidazolium hydrogen sulfate 1-butyl-3-methylimidazolium methanesulfonate, 1-butyl-3-methylimidazolium methylsulfate 1-butyl-3-methylimidazolium achloroaluminate, 1-butyl-3-methylimidazolium thiocyanate, 1-ethyl-2,3-dimethylimidazolium ethylsulfate, tris (2-hydroxyethyl) methylammonium methylsulfate, 1-methylimidazolium chloride, 1-ethylimidazolium chloride, 1-methylimidazolium hydrogen sulfate, 1,2,4-trimethylpyrazolium methylsulfate, tributylmethylammonium methylsulfate, methylphosphonate 1-ethyl-3-methylimidazolium, 1-ethyl-3-methylimidazolium dimethylphosphonate, 1-ethyl-3-methylimidazolium diethylphosphate, 1-ethyl-3-methylimidazolium dimethylphosphate, choline acetate, salicylate choline, and mixtures thereof.

Preferred ionic liquids for the implementation of the invention are:

 1-ethyl-3-methylimidazolium acetate (EmimAc)

le méthylphosphonate de l-éthyl-3 -méthylimidazolium (E:

1-ethyl-3-methylimidazolium methylphosphonate (E:

Advantageously, using an ionic liquid or a mixture of ionic liquids having a purity greater than or equal to 95% by weight relative to the total mass of ionic liquid, more preferably a purity greater than or equal to 98%.

 In step (a), advantageously, the amount of biomass is from 1 to 30% by weight relative to the total volume of liquid. According to a still preferred embodiment, the amount of biomass is from 1 to 15% by weight relative to the total volume of liquid, more preferably from 2 to 10%. A high amount of biomass in the reactor allows a better economic viability of the process.

In step (a), advantageously, the amount of hydrophilic ionic liquid is 1 to 10% by volume relative to the total volume of water. According to a still preferred embodiment, the quantity of hydrophilic ionic liquid is from 2 to 7% by volume relative to the total volume of water, more preferably from 3 to 5%. The method of the invention has made it possible to obtain a synergistic effect between the ionic liquid and the subcritical water, even in the presence of very small amounts of ionic liquid, which represents an economic and ecological advantage.

 The pretreatment of step (a) can be carried out in the presence of a polar co-solvent and miscible with ionic liquids, such as, for example, ethanol, methanol, acetone or a mixture of these solvents. Preferentially, the pretreatment of step (a) is carried out in a medium composed of ionic liquid and water.

The medium obtained at the end of step (a) comprises a solid part, essentially composed of precipitated biomass, and a liquid part. Advantageously, step (a) is followed by a step (b) of filtration and washing to obtain: on the one hand a solid fraction of pre-treated biomass, on the other hand a liquid fraction comprising: water and the ionic liquid as well as a part of the lignin and sugars resulting mainly from the hemicellulose initially present in the biomass. These sugars are essentially simple sugars, in particular C ₅ sugars, such as, for example: xylose, mannose, arabinose but also C ₆ sugars derived from hemicellulose, such as, for example: arabinose, galactose, glucose. Glucose can also come from a slight partial degradation of the cellulose as evidenced by the presence of cellobiose. The solid fraction of pre-treated biomass is obtained at the end of step (b) with a high mass yield relative to the total mass of the biomass engaged in step (a). It can be stored as is or engaged in an enzymatic treatment process aimed at reducing hydrocarbon chains to small sugars. The pre-treated biomass is characterized, compared to the biomass involved in step (a), by a very significantly reduced hemicellulose content. This was transformed during step (a) into smaller carbohydrate residues.

Enzymatic treatments

Advantageously, step (b) is followed by a step (c) of enzymatic treatment of the solid pre-treated biomass, so as to reduce the hydrocarbon chains to small sugars. This enzymatic treatment is carried out in a manner known to those skilled in the art by means of a treatment with a cellulase, a protease, a pectate, a xylanase, a lyase, a ferulic acid esterase and mannanase or a combination of such enzymes.

 Advantageously, the enzymatic treatment comprises at least treatment with cellulases, such as, for example, treatment with cellulases derived from Trichoderma reesei or Aspergillus niger.

 After the enzymatic hydrolysis, the sugars present in the hydrolyzed biomass can be fermented using one or more fermentation organisms, for example yeasts, capable of fermenting certain sugars such as glucose, xylose, mannose and galactose. The fermentation conditions depend on the desired fermentation product and are well known to those skilled in the art. The fermentation can be carried out in order to produce ethanol that can be used as a biofuel.

Lignin recovery and recycling:

 Advantageously, the liquid fraction recovered at the end of step (b), which comprises the ionic liquid, water, part of the lignin involved in step (a) and sugars mainly derived from hemicellulose , is treated to remove solvents, during a step (d). During step (d), most of the water and the ionic liquid are separated so as to recover a fraction essentially composed of lignin and sugars mainly from hemicellulose. Advantageously, the water, and optionally the co-solvents, is first evaporated, then the ionic liquid thus recovered can be reused directly as such in a new treatment cycle, or else subjected to step e).

The biomass fraction containing the lignin recovered in step (d) is at this stage solubilized in the ionic liquid. Advantageously, the fraction of biomass containing the lignin, recovered in step (d), is subjected to a step (e) of dialysis and enzymatic treatment to recover: on the one hand a fraction of lignin and secondly a mixture of water and ionic liquid and sugars mainly from hemicellulose, that is to say mainly simple C ₅ sugars.

This mixture of water and ionic liquid can be further heat-treated to evaporate the water and recover a second fraction of ionic liquid that can be reused directly in a new treatment cycle. Advantageously, the enzymatic treatment of step (e) comprises treatment with cellulases, such as, for example, treatment with cellulases derived from Trichoderma reesei or Aspergillus niger.

 Advantageously, the enzymatic treatment of step (e) comprises treatment with xylanases, for example treatment with xylanases from Trichoderma viride.

 Preferably, step (e) comprises treatment with at least two enzymes belonging to two distinct families, such as a cellulase and a xylanase. Figures:

 Figure 1: Figure 1 schematically illustrates the steps of the method of the invention described above and illustrated in the experimental part.

Figure 2: FTIR spectra of sunflower seed shell biomass before and after pretreatments. The transmittance (%) is represented on the ordinate and the number of waves on the abscissa (cm ¹ ). The upper curve corresponds to sunflower seed shells that have not been pretreated. The lower curves correspond to the biomass of sunflower seed hulls after pretreatment.

Figure 3: FTIR spectra of rapeseed biomass before and after pretreatments. The transmittance (%) is represented on the ordinate and the number of waves on the abscissa (cm ¹ ). The upper curve corresponds to untreated rapeseed straw. The lower curves correspond to the biomass of rapeseed straw after pretreatment.

 FIG. 4: graphical representation of the glucose yield (%) after enzymatic hydrolysis of the sunflower seed shell biomass before and after the pretreatments. The left column corresponds to the biomass of sunflower seed hulls that have not been pretreated.

 FIG. 5: graphical representation of the glucose yield (%) after enzymatic hydrolysis of the rapeseed biomass before and after the pretreatments. The left column corresponds to the biomass of unprocessed rapeseed straw.

Figures 6A and 6B: graphical representation of the concentration of lignin in the ionic liquid fractions after pretreatment and separation of the solid mass. The concentration is in the ordinate in g / liter. On the abscissa the indices R0, R1, Rn denote the treatment cycle: RO = first treatment, R1 = first recycle, Rn = nth recycle ionic liquid.

 The results corresponding to the shells of sunflower seeds are represented by points: (·), the results corresponding to rapeseed straw are represented by squares: (■)

Experimental part :

 The study was conducted using by-products and oleaginous waste: rapeseed straw and sunflower shells. The objective of the process is to break down the complex and well-organized structure of the lignocellulosic matrix and to study the fractionation, composition and structure modification (determined by enzymatic hydrolysis) observed after pretreatment. In order to reduce the cost of pre-treatment, the process was completed with a recycling study. 1. Material and Methods:

 1.1 Hardware

 Rapeseed straw and sunflower seed husks were used as raw materials. Both biomasses come from the vegetable oil industry. The size of the biomass particles was reduced using a FORPLEX POITTEMILL FNG1 mill equipped with a hammer rotor with a 500 micron grid. The powders obtained were stored at 5 ° C. until use.

 The ionic liquids used for pretreatment are:

 1-ethyl-3-methylimidazolium acetate ([EmimAc]) with a purity greater than 98% marketed by Solvonic SA, Verniole, France;

 1-ethyl-3-methylimidazolium methylphosphonate ([EmimPh]) with a purity greater than 98% marketed by Solvonic SA, Verniole, France.

The enzymatic hydrolyses were carried out using anhydrous sodium acetate (99%) marketed by the company Sigma-Aldrich Steinheim, Germany, acetic acid (99%) marketed by the company Cari Roth, Lauterbourg, France and the cellulases of Trichoderma reesei (EC 3.2.1.4), sold by Sigma-Aldrich (Steinheim, Germany), with an activity of 5 U / mg. The reagents used for the quantification of fibers by the Van Soest technique are: ADF solutions for "Acid Detergent Fiber" or "acid detergent fiber" in French, marketed by the company VWR International Haasrode, Belgium; decahydronaphthalene sold by the company VWR International, Briare France; sulfuric acid (95%) marketed by Fisher Scientific, Loughborough, United Kingdom; acetone (99%) marketed by Fisher Scientific, Loughborough, United Kingdom and finally sodium sulphite (98%) supplied by Aldrich Sternheim, Germany 1.2 Physicochemical characterization

The physicochemical characterization was performed on the samples before and / or after the treatment of the invention. Proteins were quantified by a micro-Kjeldahl technique (based on the quantitative analysis of nitrogen), applying a conversion factor N (gN) X 6.25 (gproteins.gN ^-1 ) (AOAC International, 1990). The water content was measured by the loss of mass after drying the samples in an oven at 105 ° C. The ash content was obtained by incineration of the sample in a muffle furnace with a temperature program at 550 ° C. The materials extractable with water and ethanol were determined using the technique described by NREL (NREL, 2012): the sample is boiled in water for 8 hours, then at room temperature. ethanol reflux for 12 hours using a Soxhlet apparatus. Quantification of the fibers was performed using the Van Soest technique (Goering and Soest, 1970), which requires about one gram to determine the amount of cellulose, hemicellulose and lignin. Pretreatment with ionic liquids is a limiting step because of the high cost of ionic liquids (laboratory grade), so this method shows the best results for a small sample. Extractable lipids were evaluated according to the Soxhlet extraction method, using a 1: 1 (v: v) mixture of diethyl ether-petroleum ether as the solvent. The mass of the biomass sample was 5g. The solvent-oil mixture was distilled using a rotary vacuum evaporator (R Buchi Rotavapor-200 with a thermostatic bath B-490 Buchi, Rugins, France) for 5 hours at 40 ° C and 40 rpm, the content in lipids was calculated by the difference in mass in the flask. 1.3. Pretreatment of biomass

 For this step, the biomass has been pretreated by three methods:

 the treatment of the biomass with an ionic liquid,

 - extraction by water in subcritical state,

 a combination of these two methods consisting of extraction by water in subcritical state in the presence of a small amount of ionic liquid.

1.3.1. Pretreatment with ionic liquid (IL) and solvent recycling:

 Pretreatment with the ionic liquid was done according to the protocol described by Auxenfans et al, 2012 Husson et al, 2011 with some modifications: two hundred milligrams of biomass were weighed, then 10 ml of ionic liquid were added. The suspension was incubated in an oil bath at 110 ° C for 40 minutes with magnetic stirring. After this period, the reaction was stopped with 10 ml of ultrapure water (demineralized with a resistivity of 13.3 MQ cm, obtained from BarnstedEasy pure RF water), and the reactor was placed in a ice bath with magnetic stirring for 30 minutes, to increase the polarity of the medium. After this time, the liquid fraction was filtered (45 microns). After filtration of the liquid fraction, the solid was washed with 20 ml of ultrapure water. Finally, the two fractions were dried: the solid fraction by lyophilization (Christ Alpha Scientific Biobock Fisher 1-2, Amueblados Osterode, Germany), and the liquid fraction by rotary evaporation (R Buchi Rotavapor-200 with a thermostatic bath B-490 Buchi, Rougins, France) Both fractions were stored at 5 ° C until use. 1.3.2. Classic pre-treatment with subcritical water

 The high pressure reactor used in this study was purchased from Autoclaves France. The reactor has a capacity of 560 ml. Agitation and temperature are controlled by an automatic system. The subcritical water is prepared in a second reactor and then injected into the first reactor containing the biomass.

For pretreatment, the solid feedstock of biomass introduced into the reactor is 2% (10 g per 500 ml of water), using the maximum volume capacity of the reactor (500 ml). The temperature conditions are defined in the system of control (160, 200, 240 or 280 ° C). In order to achieve subcritical conditions, the pressure was increased in increments of temperature and reduced by the purge of steam from the reactor. It is impossible to set a fixed pressure, but this parameter has been controlled to remain in subcritical conditions. Actual temperatures and operating pressures were recorded. Once the treatment time has passed (30min or 2h), the depressurization is carried out by discharging the steam from the reactor. The reactor was allowed to cool to room temperature. Then the pretreated biomass was collected by filtration. The solid fraction was dried using the lyophilizer described above, the samples were stored at 4 ° C until use.

1.3.3. Combination of ionic liquids and subcritical water

 The combination of pre-treatments (ionic liquid and subcritical water) was done in batches, using ionic liquids introduced into the reactor. 2% of the biomass (approximately 10 g) was immersed directly in 20 ml of ionic liquid (approximately 4% of the reactor volume, v / v), followed by the same procedure as for batch pretreatment classic (addition of 500 ml of subcritical water). As illustrated in FIG. 1, the lignocellulosic biomass and the ionic liquid are introduced into a subcritical water pressurized reactor. At the end of the treatment (160 ° C / 120 min or 200 ° C / 120 min) the solid biomass is extracted, filtered and washed, it can be used in a subsequent process of enzymatic saccharification and possibly fermentation. The liquid fraction is recovered, the water is evaporated, the recovered ionic liquid is subjected to dialysis and enzymatic treatment by T. reesei cellulases and T. viride xylanases. This treatment makes it possible to recover, on the one hand, a lignin fraction and, on the other hand, a mixture of water and ionic liquid and sugars mainly derived from Γ-hemicellulose. The water is evaporated from this fraction and the ionic liquid recycled.

1.4. Enzymatic hydrolysis of cellulose

 Enzymatic hydrolysis is a good indicator of polymer conversion

(mainly cellulose) in glucose (Auxenfans et al, 2012, Husson et al, 2011), reflecting the accessibility of enzymes in the lignocellulosic matrix, and thus the degree of complexity and organizational structure. The conversion efficiency of cellulose in glucose after enzymatic hydrolysis was determined after each pretreatment in the solid fraction.

 Cellulase catalyzed biomass hydrolysis (before and after pretreatment) was performed in 1.5 ml Eppendorf tubes. In a typical hydrolysis reaction, 20 mg of sample are added to 0.9 ml of a buffer solution (acetate / sodium acid, acetic acid, 50 mM, pH 4.8) and incubated in a Thermomixer 5436 (Eppendorf Netheler-Hinz, Hamburg, Germany) for 30 minutes at 40 ° C with shaking at 1400 rpm. During the waiting time, a buffer solution of 60 cellulase units / ml was prepared (10 or 12 mg / ml depending on the enzymatic activity of 5 units or 6 respectively). After preincubation, 0.1 ml of the enzyme solution was added to start the hydrolysis. The final concentrations of the biomass and the enzyme in the reaction medium were 2% by weight by volume and 1 mg / ml, respectively. After 48 hours, 400 microliters of supernatant was decanted and incubated in an oil bath at 90 ° C for 20 min. This action helps to denature the enzyme and stop the enzymatic hydrolysis. Each enzymatic hydrolysis was carried out in triplicate. Then, the sample was diluted with ultrapure water and then filtered with a 0.2 micron syringe filter, before analysis by high performance anion exchange chromatography (HPAEC-PAD). HPAEC-PAD analysis was performed using a Dionex DX-500 instrument (Sunnyvale, CA, USA) with an AS50 autosampler, a GP50 gradient pump and an ED50 electrochemical detector implemented in the method. Amperometric pulsed for the detection of carbohydrates. The column was an analytical CarboPac PA-20 (150 mm X 3 mm 6 μιη) (Dionex, Sunnyvale, CA, USA) equipped with a guard column, operating at 25 ° C with a gradient of the mobile phase (solvent A and B: 2 and 200 mM NaOH, respectively, and the solvent C: 200 mM NaOH and 250 mM sodium acetate) at a flow rate of 1 mL / min.

 The calculation of the glucose yield after the enzymatic hydrolysis was carried out with the following formulas:

 Yglucose (%) = Glucose (g) x Correction Factor / Initial Cellulose (g) x 100

Correction Factor = Free Glu Molar Mass / Molar Mass GluPS = 162/180 = 0.9 1.5. Fourier Transform Infrared Spectroscopy (FTIR)

 The apparatus used is an infrared Fourier transform spectroscope

(Shimadzu 8400S, ATROOS FTIR) equipped with a diamond ATR reflection cell (total attenuated reflection) with a DTGS detector (deuterated triglycine sulfate). Absorption spectra were collected over a spectral range of wave number between 600 and 4000 cm ^-1 using a resolution of 4 cm ^-1 with 200 scans. A mass of about 3-5 mg of freeze-dried biomass fines was applied to the crystal surface and then pressed onto the crystal head. Two analyzes were performed. Ambient air analysis and background correction were done before each analysis. The scans were recorded using spectroscopic software (version 10. PerkinElmer, Germany). Ethanol and acetone were used to clean the ATR diamond tip between two runs.

1.6. Crystallinity Index (ICR) by Nuclear Magnetic Resonance (NMR)

 Crystallinity indices (ICR) were determined by the deconvolution of 13 C NMR spectra from the crystalline (86-92 ppm) and amorphous (79-86 ppm) C4 regions of glucose (Auxenfans et al, 2012a, Husson et al. 2011). ICRs were given at ± 5%. Cross-polarization spectroscopy with nuclear magnetic resonance angle spinning (CP-MAS 13C) was performed on a Bruker DRX-500 spectrometer equipped with a 4 mm probe operating at 125.7452 MHz (channel 13C) and 500.0800 MHz (channel 1H).

Cd {%} = -4gs-S2ppi _T i / {-? S-8 & ppiH -f Ags_92m) x 100

The rotational speed of the rotor containing the sample is 5 kHz. Calibration of ¹³ C NMR spectra was performed using ethylbenzene as a reference.

1.7. Scanning electron microscopy (SEM)

Biomass particle micrographs before and after pretreatment were obtained using a Quanta 200 FEG high resolution scanning microscope (FEI Company, USA). Samples were observed without low vacuum metallization (partial water pressure in vacuum) using the secondary electron mode to allow the contrast of the topography produced by the differences in the chemical composition of the components. The observation conditions were as follows: acceleration voltage between 10 and 20 kV, the working distance between 5 and 9 mm, and a pressure between 0.5 and 2 mbar.

2. Results and discussion

 2.1. Composition of raw materials

 The content of hemicellulose, cellulose, lignin, proteins, lipids and ashes was determined for the hulls of sunflower seeds and rapeseed straw (Table 1).

 A similar composition of hemicellulose and cellulose was observed in both samples, while lignin content was higher in sunflower cockle seeds (17%) than in rapeseed straw (9%). A higher amount of non-lignocellulosic components (proteins, lipids, ash) was observed in rapeseed straw. The effect of lignin on the accessibility of other cell wall components is considered a largely physical effect, with lignin molecules reducing the available surface area for penetration and enzymatic activity. Therefore, these results suggest a stronger resistance of sunflower seed shells to enzymatic treatment than canola straw.

 Table 1

 (*) Extractable with water and ethanol (proteins, lipids and ashes)

2.2. pretreatment

 Pretreatments applied to both biomasses were:

 Dissolution of the lignocellulosic hydrophilic polymers by an imidazolium-based ionic liquid ([Emim Ac] or ([Emim Ph]) at 110 ° C. for 40 min.

- Subcritical water extraction (HPSW) in a high pressure reactor. Moderate temperatures during long-term pre-treatments have were studied (200 ° C for 120 min). According to the literature, these conditions would allow the fractionation of the main components (cellulose, hemicellulose and lignin), while taking into account the performance of the reactor.

 - Addition of ionic liquid based on imidazolium ([Emim Ac] or [Emim Ph]) as a catalyst for extraction with water under subcritical conditions. Pretreatment combining subcritical water and the ionic liquid (4% by volume relative to the volume of water) at 160 or 200 ° C for 120 minutes was carried out.

2.2.1. Effect of pre-treatments on the composition of biomass

 The loss of mass after the different pretreatments of the two biomasses was determined and the results are presented in Table 2.

Table 2 A lower mass loss was observed for sunflower seed shells, confirming their high strength properties. The composition of the insoluble fibers (in percentages by mass of hemicellulose, cellulose and lignin relative to the total mass of the biomass recovered) before and after the pretreatment of sunflower seed hulls and rapeseed straw are summarized in Tables 3 and 4 respectively.

 Table 3: Component content of sunflower seed shell biomass before and after pretreatments

Pretreatment Hemicellulose Cellulose Lignine

 None 20.8 ± 1.2 41.6 ± 1.2 9.0 ± 1.2

EmimAc 110 ° C / 40min 22.6 ± 1.6 35.2 ± 2.6 5.5 ± 0.4

EmimPh 110 ° C / 40min 22.3 ± 0.8 34.2 ± 1.2 6.2 ± 0.8

HPSW 200 ° C / 120min 3.5 ± 1.0 35.9 ± 0.7 11.9 ± 0.4

HPSW

 2.1 ± 0.2 24.2 ± 2.1 11.4 ± 3.8 240 ° C / 30min

 HPSW- EmimAc 4%

 5.8 ± 0.7 38.5 ± 1.6 9.3 ± 0.9 160 ° C / 120min

 HPSW- EmimAc 4%

 2.8 ± 0.4 36.4 ± 1.1 9.5 ± 0.3 200 ° C / 120min

 HPSW- EmimPh 4%

 7.2 ± 0.3 46.5 ± 6.8 10 ± 3.2 160 ° C / 120min

 HPSW- EmimPh 4%

6.8 ± 0.3 32.7 ± 3.8 19.4 ± 2.4 200 ° C / 120min Table 4: Component content of rapeseed biomass before and after pretreatments

Pre-treatment with ionic liquid alone for a short time (40 min) induces the dissolution of a fraction of lignin and cellulose, while hemicelluloses are not dissolved.

 Similarly, pre-treatment with subcritical water (HPSW) at 200 ° C / 120 min led to a strong dissolution of hemicelluloses, while cellulose and lignin were not dissolved. At 240 ° C / 30 min, the cellulose and hemicellulose are dissolved but not the lignin, which has been preserved.

 From the results, sub-critical water pretreatment can be considered as a suitable method for selectively breaking up cellulose or lignin from oilseed biomasses. Indeed, at high temperature (> 240 ° C) for a short time (30min) hemicelluloses and cellulose dissolve, which allows the recovery of a lignin-rich fraction. In contrast, a lower temperature (200 ° C) for a longer time (120 min) induces the solubility of hemicelluloses allowing the recovery of the cellulose-rich fraction.

 The combination of the two methods (HPSW - 4% EmimAc) makes it possible to observe a catalytic effect with the production of a fraction rich in cellulose and a very low content of hemicelluloses.

2.2.2. Effect of Γ EmimAc on the structure of the polymers studied by FTIR and

The FTIR spectra of sunflower seed and rapeseed hull shells are shown in Figures 2 and 3, respectively. The spectra show bands centered on 3700 and 730 cm ^-1 .The dominant peaks at 3346 cm ^-1 (lengthening of the bonds OH) and 2892 cm ^-1 (elongation of CH bonds) attributed to aliphatic groups of three polymers (cellulose, lignin and hemicellulose) are not shown in the spectra because the main changes were observed between 600 and 200 cm ^-1 . The peak at 1730 cm ^-1 in biomass is attributed to the stretching vibration of C = O of acetyl groups in hemicelluloses.The characteristic peaks of lignin are observed at 1591-1505 cm- ¹ (stretching vibration) , 1256 cm- ¹ (asymmetrical deformation of C¾) and 1251 cm- ¹ attributed to the stretching of aromatic cycles (CO vibration of the syringyl nucleus). The absorption bands at 1093 and 896 cm ^-1 respectively correspond to the CO stretching vibration in cellulose / hemicellulose and the CH deformation vibration in cellulose, the latter peak (896 cm ^-1 ) being characteristic amorphous regions of cellulose.

The FTIR spectra of sunflower seed hulls and crude rapeseed straw are similar except for the characteristic peak of 1505 cm ^-1 lignin corresponding to the stretching vibration which is well defined on the rapeseed straw spectra.

 The main impacts of HPSW-EmimAc pretreatment on sunflower seed shells (Figure 2) and on rapeseed straw (Figure 3) are:

 - the disappearance of the characteristic band of hemicellulose (according to the chemical composition);

 - an effect on the lignin fraction of partial delignification or structural changes;

 an impact on the cellulose fraction of decreasing the intensity of the bands bound to amorphous regions.

With respect to the characteristic peaks of cellulose, considered in both biomasses, the peaks of the crystalline regions (1093 cm- ¹ ) showed a higher intensity after HPSW + ionic liquid pretreatment and suggest a confirmed cellulose-enriched fraction. by the results of the compositions (Table 3) In addition, the peaks of the amorphous regions (893 cm ^-1 ) show a clear increase in the samples after pretreatment with the ionic liquid in the two biomasses, as well as after pretreatment with water subcritical at 200 ° C / 120 min in the hulls of sunflower seeds and 240 ° C / 30 min in rapeseed straw. In the case of samples pretreated with HPSW-EmimAc 4%, the peaks of the crystalline region show a significant increase in intensity, whereas the peaks of the amorphous regions are absent in the two biomasses (hulls of sunflower seeds and rapeseed straw ).

To complete, the Crystallinity Index (ICR%) was determined by NMR and is reported in Table 4 for both biomasses. Considering that pretreatment with ionic liquid resulted in a decrease in ICR% in both samples, HPSW and HPSW-EmimAc 4% pretreatments significantly increased this index. Finally, the pre-treatment of the two samples with ionic liquid does not lead to modifications on the characteristic peaks (730cm ¹ ) of the hemicelluloses. The HPSW and HPSW-EmimAc 4% pretreatments lead to the disappearance of the characteristic peaks of the hemicelluloses, which can be explained by a complete dissolution of the hemicelluloses, this hypothesis was confirmed by analysis of the composition (Table 3).

 The results of the compositional analyzes confirm the dissolution of the lignin in the ionic liquid, in fact the concentration of lignin of the solid fraction decreases in the hulls of sunflower seeds of 17-14 g / 100 g, as well as in the straw of rapeseed 9-5 g / 100g. The same effect is observed for cellulose whose concentration decreases in sunflower seed shells of 42-31 g / 100g and in rapeseed straw 42-33 g / 100g.

2.2.3. Glucose yield after enzymatic hydrolysis

 The effect of pretreatments on glucose yield (after enzymatic hydrolysis) is shown in Figures 4 and 5 respectively for sunflower seed hulls and rapeseed straw.

 It is found that the combination of pretreatments compared to individual pretreatments with subcritical water (HPSW) leads to an improvement in the enzymatic digestibility of the cellulose fraction and to obtaining saccharification performance similar to that of treatment with an ionic liquid. alone.

2.2.4. Crystallinity index

 The results of the analyzes are reported in Table 5 below

Table 5 The values of the crystallinity indices reported in Table 5 are given at ± 5%.

 There is an increase in crystallinity induced by a subcritical water treatment which is preserved in the presence of ionic liquid.

2.3. Influence of the biomass load:

 Unless otherwise indicated, the tests were carried out with a load of 2% by mass of biomass with respect to the volume of liquid.

 Trials at 5 and 10% were also performed to evaluate the feasibility of treatment at a higher concentration. The pre-treatment carried out was HPSW-EmimAc 4% 200 ° C / 120min.

 The biomass recovery yield and the composition of the insoluble fiber (in percentages by mass of hemicellulose, cellulose and lignin in relation to the total mass of biomass recovered) before and after the pretreatment of sunflower seed hulls and rapeseed straw is summarized in Table 6.

 Table 6

2.4. Ionic liquid recycling:

It has been observed a maintenance of the performances of the process on the enzymatic degradation in glucose obtained after several recycling of the ionic liquid implemented in accordance with the diagram represented in FIG. 1 and under the same operating conditions as reported in § 1.3.3 above ( up to 7 cycles). 2.5. Recovery of lignin in the ionic liquid fraction:

 FIGS. 6A and 6B show a lower delignification with HPSW-EmimAc 4% 200 ° C / 120 min pretreatment (FIG. 6B) compared to treatment with the ionic liquid alone (EmirnAc 110 ° C./40 min) (FIG. 6A). ).

 Statistical analysis of recycling was performed by variance analysis and the difference between pre-treatments was evaluated by the Tukey HSD method.

Bibliographical references

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Claims

A method of treating a biomass, said method comprising at least (a) contacting the biomass with water in the subcritical state in the presence of at least one hydrophilic ionic liquid. 2. Method according to claim 1, wherein the amount of biomass is from 1 to 30%, preferably from 1 to 15%, even more preferably from 2 to 10% by weight relative to the total volume of liquid. 3. Method according to claim 1 or claim 2, wherein the amount of hydrophilic ionic liquid is from 1 to 10%, preferably from 2 to 7%, even more preferably from 3 to 5% by volume relative to the total volume. of water. 4. Method according to any one of the preceding claims, wherein the biomass is a lignocellulosic biomass, preferably selected from biomasses of oleaginous origin, such as sunflower hulls, rapeseed straw. 5. Process according to any one of the preceding claims, in which the hydrophilic ionic liquid is chosen from those whose cation is an imidazolium, optionally substituted with one or more alkyl groups, preferably C1-C4 alkyls. 6. Process according to claim 5, in which the hydrophilic ionic liquid is chosen from organic salts of 1-ethyl-3-methylimidazolium, even more preferentially from 1-ethyl-3-methylimidazolium acetate and methylphosphonate. ethyl-3-methylimidazolium. 7. Method according to any one of the preceding claims, wherein in step (a) the reaction medium is subjected to a temperature ranging from 160 to 240 ° C. 8. The process as claimed in claim 7, wherein in step (a) the reaction medium is subjected to a temperature ranging from 160 to 240 ° C. for a duration of from minutes to six hours, preferably from 30 minutes to four hours, even more preferably from 30 minutes to two hours. 9. Method according to any one of the preceding claims, wherein step (a) is preceded by a mechanical treatment to obtain a biomass in the form of controlled size particles, including a grinding of the biomass. 10. A method according to any one of the preceding claims, wherein step (a) is followed by a step (b) of filtration and washing to obtain: on the one hand a solid fraction of biomass pre- treated, on the other hand a liquid fraction comprising water and the ionic liquid as well as lignin. 11. The method of claim 10, wherein step (b) is followed by a step (c) of enzymatic treatment of the solid pre-treated biomass, in particular treatment with cellulases, such as for example cellulases from Trichoderma reesei. The process of claim 11, wherein step (c) is followed by at least one fermentation step. 13. The method of claim 10, which further comprises at the end of step (b) a step (d) of removing solvents, advantageously a step (d) of removing water from the fraction liquid. 14. The method of claim 13 wherein step (d) is followed by a step (e) of dialysis and enzymatic treatment to recover: on the one hand a lignin fraction and on the other hand a mixture comprising water and ionic liquid. 15. The method of claim 13 or claim 14 wherein the ionic liquid obtained at the end of step (d) and optionally of step (e) is reused in step (a) of a new cycle of treatment of a biomass.