EP2804950A1

EP2804950A1 - Method for pretreating lignocellulosic biomass with a hydrated inorganic salt to obtain a cellulosic fraction and a hemicellulosic fraction

Info

Publication number: EP2804950A1
Application number: EP12819075.8A
Authority: EP
Inventors: Christophe Vallee; Didier Bernard; Caroline Aymard; Hélène Olivier-Bourbigou
Original assignee: IFP Energies Nouvelles IFPEN
Current assignee: IFP Energies Nouvelles IFPEN
Priority date: 2012-01-18
Filing date: 2012-12-11
Publication date: 2014-11-26
Also published as: FR2985736A1; FR2985736B1; BR112014017603A2; BR112014017603A8; WO2013107947A1; US20150031092A1

Abstract

The present invention describes a method for pretreating lignocellulosic biomass comprising: a) a step of acid hydrolysis of the biomass with an acid solution resulting in a liquid fraction and a solid fraction, b) a step of separating the solid fraction and the liquid fraction, c) a step of drying the solid fraction, d) a step of firing the dried solid fraction in a medium comprising at least one hydrated inorganic salt to obtain a solid fraction and a liquid fraction, e) a step of separating the solid fraction and the liquid fraction obtained in step d) f) optionally, a step of treating said solid fraction obtained in step e), g) a step of enzymatic hydrolysis of said solid fraction obtained in step e) and/or f), and wherein at least a portion of the liquid fraction obtained in step b) is used to grow microorganisms which produce the enzymes necessary for the enzymatic hydrolysis of step g).

Description

PROCESS FOR PRETREATMENT OF LIGNOCELLULOSIC BIOMASS WITH A MOISTURIZED INORGANIC SALT FOR OBTAINING A CELLULOSIC FRACTION AND A HEMICELLULOSIC FRACTION

Field of the invention

The present invention is part of the pretreatment processes of lignocellulosic biomass. It is more specifically part of a pretreatment process for lignocellulosic biomass for the production of so-called "second generation" alcohol. Prior art

Faced with the increase in pollution and global warming, many studies are currently being conducted to use and optimize renewable bio-resources, such as lignocellulosic biomass.

Lignocellulosic biomass is composed of three main constituents: cellulose (35 to 50%), hemicellulose (23 to 32%) which is a polysaccharide essentially consisting of pentoses and hexoses and lignin (15 to 25%) which is a macromolecule of complex structure and high molecular weight, derived from the copolymerization of phenylpropenoic alcohols. These different molecules are responsible for the intrinsic properties of the plant wall and are organized in a complex entanglement.

Cellulose, the majority of this biomass, is thus the most abundant polymer on Earth and the one with the greatest potential for forming materials and biofuels. However, the potential of cellulose and its derivatives has not, for the moment, been fully exploited, mainly because of the difficulty of extracting cellulose. Indeed, this step is made difficult by the very structure of the plants. The technological barriers identified in the extraction and processing of cellulose include its accessibility, its crystallinity, its degree of polymerization, the presence of hemicellulose and lignin. It is therefore essential to develop new methods of pretreatment of the lignocellulosic biomass for easier access to cellulose and its transformation.

In particular, biofuel production is an application requiring pretreatment of biomass. Indeed, the second generation of biofuel uses as load vegetable or agricultural waste, such as wood, straw, or plantations with high growth potential such as miscanthus. This raw material is perceived as an alternative, sustainable solution with little or no impact on the environment and its low cost and high availability make it a solid candidate for biofuel production.

The production of chemical intermediates by biotechnological processes, which use in particular one or more fermentation stages, also requires a pretreatment of the biomass to use a lignocellulosic raw material whose use does not compete with food.

The principle of the process of converting lignocellulosic biomass by biotechnological methods uses a step of enzymatic hydrolysis of the cellulose contained in plant material to produce glucose. The glucose obtained can then be fermented into various products such as alcohols (ethanol, 1,3-propanediol, 1-butanol, 1,4-butanediol, etc.) or acids (acetic acid, lactic acid, 3- hydroxypropionic acid, fumaric acid, succinic acid, etc.). For biofuel production, glucose is usually fermented to ethanol. However, the cellulose contained in the lignocellulosic biomass is particularly refractory to enzymatic hydrolysis, especially since the cellulose is not directly accessible to the enzymes. To overcome this refractory nature, a pretreatment step upstream of the enzymatic hydrolysis is necessary. There are many methods of chemical, enzymatic, microbiological treatment of cellulose-rich materials to enhance the subsequent stage of enzymatic hydrolysis. These methods are for example: steam explosion, organosolv process, dilute or concentrated acid hydrolysis or AFEX ("Ammonia Fiber Explosion") process. These techniques can still be improved and suffer in particular from costs that are still too high, problems of corrosion, low yields and difficulties of extrapolation at the industrial level (F. Talebnia, D. Karakashev, I. Angelidaki Biores, Technol 2010, 101 , 4744-4753).

Acidic hydrolysis of hemicellulose is easier than that of cellulose, and hydrolysis of hemicellulose may be the first step in treating lignocellulosic biomass (Mâki-Arvela, T. Salmi, B. Holmbom S. Willfer and D. Yu Murzin, Chem: Rev. 2011, 111, 5638-5666). Consequently, the implementation of an acid pretreatment, such as hydrolysis by dilute or concentrated acid or else by steam explosion, leads to the production of a pretreated substrate (solid fraction, containing in particular the fraction cellulosic) and a sugar solution containing the sugars resulting from the partial or total acid hydrolysis of the hemicelluloses (in the form of soluble monomers and / or oligomers). This fractionation is interesting insofar as it makes it possible to separately value fractions derived from cellulose and hemicellulose. However, pretreatments under acidic conditions are penalized by their tendency to form degradation products. Among these degradation products, it is possible to mention the furfural resulting from the degradation of pentoses, 5-HMF, formic acid or levulinic acid resulting from the degradation of hexoses; as well as phenolic aldehydes or alcohols resulting from acid degradations of the partially solubilized lignin. These degradation products can, depending on their concentration, inhibit fermentative organisms. The formation of these degradation products increases with the severity of the pretreatment (temperature, reaction time, acidity). Thus, acid pretreatment performed under severe conditions will make it possible to obtain a pretreated substrate (solid fraction containing cellulose) having a good susceptibility to enzymatic hydrolysis, but the associated liquid fraction will contain sugars resulting from hydrolysis of the "polluted" hemicelluloses. By the presence of degradation products. On the contrary, if the acid pretreatment is achieved under less severe conditions, the recovery of the hemicellulosic fraction will not be penalized by the presence of degradation products but the susceptibility of the solid substrate to enzymatic hydrolysis will be poor. Applications WO2011 / 027220 and WO2011 / 027223 describe a pretreatment process of lignocellulosic biomass employing hydrated inorganic salts preceded by a demineralization step with an aqueous solution of acid or base. These requests are not interested in a valuation of hemicellulose.

A process for converting lignocellulosic biomass into fermentable sugars with excellent yields has recently been described in the FR10 / 03092, FR10 / 03093 and FR11 / 02730 applications of the applicant. This process involves the firing of biomass in inexpensive, widely available and recyclable hydrated inorganic salts. This technology is simple to implement and makes it easy to envisage an extrapolation at the industrial level.

However, the compositional analyzes performed on the solid fraction resulting from this pretreatment show that the hemicellulose contained in the biomass is hydrolysed during cooking. The products resulting from this hydrolysis are therefore found in the liquid fraction consisting of the anti-solvent and the hydrated inorganic salt. The recovery of these hydrolysis products of hemicellulose proves difficult because of the high salt concentration of this solution and requires a complex and expensive process. In addition, the recycling of the inorganic salt is made more complex and requires a high purge rate in order to limit the accumulation of hemicellulose hydrolysis products during recycling.

The object of the present invention is to provide a pretreatment process for optimized recovery of cellulosic and hemicellulosic fractions. The pretreatment process according to the invention consists in combining acid hydrolysis under mild conditions with pretreatment with hydrated inorganic salts and upgrading sugars resulting from acid hydrolysis to the growth of enzyme-producing microorganisms for enzymatic hydrolysis.

Description of the Figures

FIG. 1 is a schematic representation of the process according to the invention comprising an acid hydrolysis step, a separation step, a drying step, a step of cooking the dried solid fraction, a step of separating the solid fraction, a step of treating said solid fraction and an enzymatic hydrolysis step.

Detailed description of the invention

The pretreatment method of the lignocellulosic biomass according to the present invention comprises the following steps:

a) a step of acid hydrolysis of the biomass by an acid solution leading to a liquid fraction containing most of the hemicellulose in the form of hydrolysis products and the acid, and to a solid fraction containing the major part cellulose and lignin,

b) a step of separating the solid fraction and the liquid fraction obtained in step a),

c) a step of drying the solid fraction obtained in step b),

d) a step of firing the dried solid fraction obtained in step c) in the presence or absence of an organic solvent, in a medium comprising at least one hydrated inorganic salt of formula (I):

ΜΧ _η .ηΉ ₂ 0

in which

M a metal selected from groups 1 to 13 of the Periodic Table, X is an anion and

n is an integer between 1 and 6 and

n being between 0.5 and 12,

to obtain a solid fraction and a liquid fraction containing the hydrated inorganic salt, e) a step of separating the solid fraction and the liquid fraction obtained in step d),

f) optionally a step of treating the solid fraction obtained in step e),

g) a step of enzymatic hydrolysis of said solid fraction obtained in step e) and / or f),

and wherein at least a portion of the liquid fraction obtained in step b) is used for the growth of the microorganism producing the enzymes necessary for the enzymatic hydrolysis of step g).

The acid hydrolysis step with an acidic solution leads to a liquid fraction containing most of the hemicellulose in the form of hydrolysis products and the acid, and to a solid fraction containing most of the cellulose and lignin. This step thus makes it possible to solubilize selectively the hemicellulose contained in the cellulosic biomass.

The process according to the present invention makes it possible to recover, with a good yield, the sugars resulting from the hemicellulosic fraction of the biomass. The use of mild conditions for acid hydrolysis minimizes the formation of degradation products of sugars. The liquid fraction containing the sugars resulting from the hemicellulosic fraction of the biomass therefore does not have an inhibitory effect for recovery by a biotechnological process, in particular for its use for the growth of the microorganism producing the enzymes necessary for the enzymatic hydrolysis. of step g). This fraction can in addition be used in other biotechnological processes described later.

The solid fraction containing most of the cellulose and lignin is then separated from the liquid fraction. It should be noted that the cellulose contained in the solid fraction after acid hydrolysis is not reactive in enzymatic hydrolysis.

The solid fraction containing most of the cellulose and the separated lignin is then dried. It should be noted that the drying step is an essential step in the success of the pretreatment process. In fact, without an intermediate drying step, the cooking step does not lead to a reactive cellulose in enzymatic hydrolysis.

The step of firing with hydrated inorganic salts is then carried out on the dried solid fraction containing most of the cellulose and lignin (but without the hemicellulose which has been solubilized during the acid hydrolysis step).

This makes it possible to obtain, after a solid / liquid separation step, a solid fraction and a liquid fraction. This solid fraction contains most of the cellulose present in the lignocellulosic biomass. This cellulose has the property of being particularly reactive in enzymatic hydrolysis.

Due to the elimination of hemicellulose by preliminary acid hydrolysis, the liquid fraction obtained after the baking step contains the hydrated inorganic salts in good purity. Indeed, the liquid fraction containing hydrated inorganic salts is no longer "polluted" by hydrolysis products of hemicellulose as is the case without acid hydrolysis step.

This low organic content in the liquid fraction facilitates the recycling of salts in the cooking step and reduces the purge rate of this recycling.

According to a preferred variant, the acid solution used in the acid hydrolysis step is chemically identical to the hydrated inorganic salt of the cooking step diluted in water. In this case, at least a portion of the liquid fraction containing the hydrated inorganic salts obtained in the separation step e) can be used, optionally with addition of additional water, as the acid solution in the acid hydrolysis step. The method according to the present invention makes it possible to efficiently transform various types of native lignocellulosic biomass into a pretreated biomass by retaining most of the cellulose present in the starting substrate. It also has the advantage of using inexpensive, widely available reagents and recyclable, thus obtaining a low pretreatment cost. This technology is also simple to implement and makes it easy to envisage an extrapolation at the industrial level.

The lignocellulosic biomass, or lignocellulosic materials used in the process according to the invention is obtained from wood (hardwood and softwood), raw or treated, by agricultural products such as straw, plant fibers, cultures. forestry, residues of alcoholic, sugar and cereal plants, residues of the paper industry, marine biomass (eg, cellulosic macroalgae) or transformation products of cellulosic or lignocellulosic materials. The lignocellulosic materials can also be biopolymers and are preferably rich in cellulose.

Preferably the lignocellulosic biomass used is wood, wheat straw, wood pulp, miscanthus, rice straw or corn stalks.

According to the process of the present invention, the different types of lignocellulosic biomass can be used alone or in mixture.

The various steps of the process will be described in detail below.

Acid hydrolysis (step a)

The acid hydrolysis step makes it possible to solubilize selectively the hemicellulose contained in the lignocellulosic biomass.

Acid hydrolysis of hemicellulose can be catalyzed by inorganic acids or by organic acids. Among the acids that can be used for the hydrolysis of hemicellulose, mention may be made of sulfuric acid, hydrochloric acid, nitric acid, ferric chloride, zinc chloride, phosphoric acid, acid and the like. formic acid, acetic acid, oxalic acid, trifluoroacetic acid and maleic acid, alone or as a mixture.

The concentration of the acid is generally between 0.001 mol / L and 1 mol / L. The concentration of the acid is preferably between 0.01 mol / L and 0.4 mol / L. The acidic hydrolysis of hemicellulose can be carried out at a temperature between room temperature and 150 ° C, preferably between 50 ° C and 130 ° C.

The duration of the acid hydrolysis is between 10 minutes and 24 hours, preferably between 30 minutes and 6 hours.

The mass concentration of the biomass (expressed as dry matter) in the acid hydrolysis step is between 1% and 30%. The acid hydrolysis of hemicellulose is carried out under so-called mild conditions, ie the sugars solubilized in the liquid fraction undergo little degradation reactions (such as the dehydration of xylose in furfural) and that this step does not occur. does not allow to obtain a reactive cellulose in enzymatic hydrolysis. Those skilled in the art will readily be able to choose the conditions of temperature, pH and reaction time to obtain an acid hydrolysis under the so-called mild conditions.

Acidic hydrolysis provides a liquid fraction containing most of the hemicellulose, in the form of hydrolysis products (sugars or oligomers of sugars), and the acid, and a solid fraction containing the major part of the cellulose and lignin. At least a portion of the liquid fraction is used for growth of enzyme-producing microorganisms for enzymatic hydrolysis.

Solid / liquid separation (step b)

At the end of the acid hydrolysis, a separation of the liquid fraction and the solid fraction is carried out. This separation step can be carried out by the usual solid-liquid separation techniques, for example by decantation, by filtration or by centrifugation. Drying (step c)

The solid fraction containing most of the cellulose and the separated lignin is then dried. The drying step is an essential step in the success of the pretreatment process. In fact, without an intermediate drying step, the cooking step does not lead to a reactive cellulose in enzymatic hydrolysis.

The drying step can be carried out by any method known to those skilled in the art, for example by evaporation. Known technologies for evaporative drying are for example the rotary furnace, the moving bed, the fluidized bed, the heated worm, the contact with metal balls providing the heat. These technologies may optionally use a gas flowing at co or countercurrent such as nitrogen or any other gas inert under the conditions of the reaction.

The drying step is carried out at a temperature greater than or equal to 50 ° C. At the end of the drying step, the residual water content is less than 30%, preferably less than 20% and more preferably less than 10%.

Baking in a medium comprising at least one hydrated inorganic salt (step d)

The step of cooking with hydrated inorganic salts makes it possible to obtain a solid fraction which contains most of the cellulose present in the lignocellulosic biomass. This cellulose has the property of being particularly reactive in enzymatic hydrolysis. A liquid fraction containing the hydrated inorganic salt (s) is also obtained. The firing of the dried solid fraction is carried out in the presence of a hydrated inorganic salt of formula (I): MX _n .n'H ₂ O

in which

M a metal selected from groups 1 to 13 of the Periodic Table, X is an anion and

n is an integer between 1 and 6 and

n being between 0.5 and 12.

A mixture of hydrated inorganic salts can be used for cooking the dried solid fraction. Anion X can be a monovalent, divalent or trivalent anion. Preferably, the anion X is a halide anion chosen from Cl ^" , F ^" , Br ^' and Γ, a perchlorate anion (ClO ₄ ^" ), a thiocyanate anion (SCN), a nitrate anion (NO3 ^" ), a anion para-methylbenzene sulfonate (CH3-C6H4-SO3 ^"), an acetate anion ^(CH3COO"), a sulfate anion (S0 ₄ ^2), oxalate anion (C2O4 ^{2 ")} or a phosphate anion (P0 ₄ ^3). From even more preferably, the anion X is a chloride.

Preferably, the metal M in the formula (I) is chosen from lithium, iron, zinc or aluminum.

In a particularly preferred manner, the hydrated inorganic salt is chosen from: UCI.H ₂ O, LiCl ₂ .H ₂ O, ZnCl ₂ .2.5H ₂ O, ZnCl ₂ .4H ₂ O and FeCl ₃ .6H ₂ O.

Preferably, the firing temperature is between -20 ° C and 250 ° C, preferably between 20 and 60 ° C.

When the metal M of the hydrated inorganic salt is chosen from groups 1 and 2 of the periodic table, the firing temperature is preferably between 100 ° C. and 160 ° C.

When the metal M of the hydrated inorganic salt is chosen from groups 3 to 13 of the periodic table, the firing temperature is preferably between 20 ° C. and 100 ° C.

The duration of the cooking is between 0.5 minutes and 168 hours, preferably between 5 minutes and 24 hours and even more preferably between 20 minutes and 12 hours.

According to the method of the present invention, several successive firing steps can be performed.

The firing step can be carried out in the presence of one or more organic solvents, chosen from alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol or tert-butanol, diols and polyols such as ethanediol, propanediol or glycerol, amino alcohols such as ethanolamine, diethanolamine or triethanolamine, ketones such as acetone or methyl ethyl ketone, carboxylic acids such as that formic acid or acid acetic acid, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, aromatic solvents such as benzene, toluene, xylenes, alkanes. According to another embodiment, the firing step can be carried out in the absence of an organic solvent.

In the firing step, the dried solid fraction is present in an amount of between 4% and 40% by weight, based on the dry weight of the total mass of the solid fraction / hydrated inorganic salt mixture, preferably in a quantity of between 5% and 30% by weight. % weight

Solid / liquid separation (step e)

At the end of the firing step, a mixture of a solid fraction containing the pretreated cellulosic substrate and a liquid fraction containing the hydrated inorganic salt or salts and optionally an organic solvent are obtained. This mixture is sent in a solid / liquid separation step.

This separation can be carried out directly on the mixture resulting from the cooking step or after addition of at least one anti-solvent promoting the precipitation of the solid fraction.

Preferably, the separation is carried out after addition of at least one antisolvent promoting the precipitation of the solid fraction. The separation of a solid fraction and a liquid fraction containing the hydrated inorganic salt and optionally the anti-solvent may be carried out by the usual solid-liquid separation techniques, for example by decantation, by filtration or by centrifugation. The anti-solvent used is a solvent or a mixture of solvents chosen from water, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol or tert-butanol, diols and polyols such as ethanediol, propanediol or glycerol, amino alcohols such as ethanolamine, diethanolamine or triethanolamine, ketones such as acetone or methyl ethyl ketone, carboxylic acids such as formic acid or acetic acid, esters such as ethyl acetate or isopropyl acetate dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile.

Preferably, the anti-solvent is selected from water, methanol or ethanol.

Very preferably, the anti-solvent is water alone or as a mixture, and preferably alone. At the end of the separation step e), a so-called solid fraction and a liquid fraction containing the hydrated inorganic salt (s) are obtained.

The solid fraction is composed of solid matter, between 5% and 60%, and preferably between 5% and 45%, and a liquid phase. The presence of liquid in this fraction is related to the limitations of liquid / solid separation devices. The solid material contains most of the cellulose of the initial substrate, between 60% and 100%, and preferably between 75% and 99% of the cellulose initially introduced.

The liquid fraction contains the hydrated inorganic salt or salts used during the baking step, and optionally the antisolvent. Due to the elimination of hemicellulose by acid hydrolysis, this fraction contains very little hemicellulose (or products derived from hemicellulose). It may contain lignin.

Additional treatments (step f)

The solid fraction obtained in step e) may optionally be subjected to additional treatments (step f). These additional treatments may in particular be intended to eliminate the traces of hydrated inorganic salts in this solid fraction. Step f) of treatment of the solid fraction obtained in step e) can be carried out by one or more washes, neutralization, pressing, and / or drying.

The washes can be carried out with antisolvent or with water. The washes may also be made with a stream from a processing unit of products from the pretreatment process of the present invention.

By way of example, when the process according to the present invention is used as pretreatment upstream of a cellulosic ethanol production unit, the washes can be carried out with a stream coming from this cellulosic ethanol production unit.

The neutralization can be carried out by suspending the solid fraction obtained in step e) in water and adding a base. By the term base, we refer to any chemical species which, when added to water, gives an aqueous solution of pH greater than 7. The neutralization can be carried out by an organic or inorganic base. Among the bases that can be used for the neutralization, mention may be made of soda, potassium hydroxide and ammonia.

The solid fraction obtained at the end of the separation step may optionally be dried or pressed to increase the percentage of dry matter contained in the solid.

Enzymatic hydrolysis (step g)

The treated solid fraction is then sent to an enzymatic hydrolysis step to convert the polysaccharides to monosaccharides. The actual enzymatic hydrolysis step is carried out under mild conditions, at a temperature of between 40 and 60 ° C., preferably between 45 and 50 ° C. and a pH of 4.5 to 5.5, and preferentially between 4.8 and 5.2. It is performed using enzymes produced by a microorganism. The enzymatic solution added to the pretreated substrate contains enzymes that break down cellulose into glucose. Microorganisms, such as fungi belonging to the genera Trichoderma, Aspergillus, Penicillium or Schizophyllum, or anaerobic bacteria belonging for example to the genus Clostridium, produce these enzymes, notably containing cellulases and hemicellulases, suitable for the extensive hydrolysis of the cellulose and hemicelluloses.

Very preferably, the microorganism used is Trichoderma reesei.

The monosaccharides thus obtained can be transformed by fermentation. The fermentation products may be alcohols (ethanol, 1,3-propanediol, 1-butanol, 1,4-butanediol, etc.) or acids (acetic acid, lactic acid, 3-hydroxypropionic acid, fumaric acid, acid succinic, ...) or any other fermentation product. For example, monosaccharides can easily be converted to alcohol by fermentation with yeasts such as, for example, Saccharomyces cerevisiae. The fermentation must obtained is then distilled to separate the vinasses and the alcohol produced. This distillation step may be thermally integrated with the drying step c) and / or with the purification step h) of the inorganic salt described hereinafter.

Concomitantly, enzymatic hydrolysis and fermentation can be carried out in what is commonly referred to as SSF (Simultaneous Saccharification and Fermentation).

Valuation of the liquid fraction obtained in step b)

At least a portion of the liquid fraction obtained in step b) is used for the growth of the microorganism producing the enzymes necessary for the enzymatic hydrolysis of step g). Preferably, the liquid fraction obtained in step b) is neutralized before use for the growth of the microorganism. This neutralization can be carried out by adding an organic base or an inorganic base. Among the bases that can be used for the neutralization, mention may be made of soda, potassium hydroxide and ammonia.

The use of mild conditions for acid hydrolysis makes it possible to minimize the formation of inhibitory products. The liquid fraction containing the sugars from the The hemicellulosic fraction of the biomass therefore has no inhibitory effect for such a valuation.

The strains used for the production of cellulolytic and / or hemicellulolytic enzymes are strains of fungi belonging to the genera Trichoderma, Aspergillus, Penicillium, Fusarium, Chrysosporium or Schizophyllum, preferably belonging to the species Trichoderma reesei. The presence of an inducing substrate is essential for the expression of cellulytic and / or hemicellulolytic enzymes. The most effective industrial strains are the strains belonging to the species Trichoderma reesei, modified to improve the cellulolytic and / or hemicellulolytic enzymes by mutation-selection methods, for example the strain IFP CL847 (FR2555803); strains improved by genetic recombination techniques can also be used. These strains are cultured in agitated and aerated fermenters under conditions compatible with their growth and the production of enzymes. Depending on the nature, the carbon substrate chosen for obtaining the biomass is introduced into the fermentor before sterilization or is sterilized separately and introduced into the fermentor after sterilization of the latter to have an initial concentration of 20 to 35 g / L; the inducing source may not be added in this phase. An aqueous solution containing the substrate selected for the production of the enzymes is prepared, preferably at a concentration of 200 to 250 g / L; this solution must contain the inductive substrate. It is injected after depletion of the initial substrate so as to provide an optimized amount, for example between 35 and 45 mg / g of cells ("fed batch") for Trichoderma reesei. The residual concentration of sugar in the culture medium is preferably less than 1 g / l during this "fed batch" phase so as to promote the production of the enzymes.

The liquid fraction obtained in step b) containing the sugars may also be recovered in other biotechnological processes for converting sugars. Preferably, the liquid fraction obtained in step b) is neutralized before use in other biotechnological processes for converting sugars. Biotechnological processes for converting sugars are any process for converting sugars using a living microorganism or an agent derived from a living micro-organism for the conversion of these sugars into products of interest, and for example:

fermentation of the C 6 sugars in ethanol by a yeast, for example a yeast belonging to the genus Saccharomyces (S. cerevisiae, S. carlsbergensis, S. bayanus, S. uvarum), Schizosaccharomyces (S. pombe) or Kluyveromyces (K. fragilis);

fermentation by solvents such as acetone or butanol by a bacterium, such as for example that of the genus Clostridium,

- Ethanol fermentation of C6 and C5 sugars by a yeast such as for example Pichia Stipitis or Candida Sheatae or Pachysolen tannophilus; or by a bacterium such as for example Zymomonas mobilis; or by yeast genetically modified to use C5;

- production of filamentous fungi, for example T. reesei.

The method will be described with reference to FIG.

The lignocellulosic biomass is introduced via line 1 into reactor 2 in which the acid hydrolysis step takes place. The acid solution is introduced via line 3. At the end of the acid hydrolysis step, line 4 draws a mixture of a liquid fraction containing most of the hemicellulose in the form of hydrolysis products (sugars or oligomers of sugars) and acid, and a solid fraction containing most of the cellulose and lignin. This mixture is sent to the liquid / solid separation device 5 in which the separation step b) takes place. At the end of the separation step b), a so-called solid fraction 6 and a liquid fraction 7 are obtained.

The solid fraction 6 is then sent in a drying step 8.

The dried solid fraction is then introduced via line 9 into the cooking reactor 10 in which the cooking step takes place. The cooking medium comprising one or more hydrated inorganic salts and optionally an organic solvent is introduced via line 11. At the end of the firing step, the line 12 draws a mixture containing the pretreated lignocellulosic substrate, the hydrated inorganic salt or salts and optionally an organic solvent. This mixture is sent into the liquid / solid separation device 13 in which the separation step e) takes place. The optional anti-solvent is added through line 14.

At the end of the separation step e), a so-called solid fraction 15 and a liquid fraction 16 containing the hydrated inorganic salt (s) are obtained.

The solid fraction (15) may optionally be subjected to additional treatments (step f) carried out in the device (17). The agents possibly necessary for the treatment (s) carried out in the chamber 17 are introduced via line 18.

Any residues of this treatment (s) are withdrawn via line 19. The treated solid fraction is withdrawn via line 20 and is sent to an enzymatic hydrolysis step in reactor 30 to convert polysaccharides to monosaccharides. .

The liquid fraction 7 obtained in the separation step b) and containing the sugars resulting from the hemicellulose is at least partly (7a) sent into a chamber 28 for the growth of the microorganism producing the enzymes necessary for the hydrolysis Enzymatic in the chamber 30. Preferably, the liquid fraction 7 is previously neutralized by the injection of a base 32.

The enzymes thus produced are introduced via line 29 into enclosure 30.

Alternatively, another portion (7b) of the liquid fraction 7 may be used in other methods using a living microorganism or an agent derived from a living microorganism to convert these sugars into 'interest. According to an embodiment not shown, the separation step e) is carried out with the addition of an anti-solvent, and the additional treatment carried out in the chamber 17 (step f)) consists of one or more washes carried out with the anti-solvent introduced via line 18. The liquid after washing mainly contains the anti-solvent and contains hydrated inorganic salt. This effluent is used in the separation step e). This embodiment allows a better recovery rate of the hydrated inorganic salt, a better purity of the solid fraction while limiting the consumption of the anti-solvent. In this embodiment, the anti-solvent is preferably water.

According to a preferred embodiment, the inorganic salt contained in different liquid fractions obtained during the process can be recycled.

According to a first variant, at least a portion of the liquid fraction obtained in step e) (16a) is sent to a purification step (21), called step h), making it possible to concentrate the inorganic salt contained in the fraction liquid and to obtain a liquid fraction containing the concentrated inorganic salt (23a) and another liquid fraction depleted in inorganic salt (25), said liquid fraction containing the concentrated inorganic salt (23a) being then at least partially recycled in the cooking step d).

The purification step h) may in particular be a separation step of the inorganic salt and the anti-solvent. This separation can be carried out by any method known to those skilled in the art, such as, for example, evaporation, precipitation, extraction, passage over ion exchange resin, electrodialysis, chromatographic methods, solidification. hydrated inorganic salt by lowering the temperature or adding a third body, reverse osmosis.

The additives that may be necessary for this step are introduced via the pipe (22) into the chamber (21). At the outlet of the chamber (21), a liquid fraction containing the concentrated inorganic salt (23a) is obtained, which is advantageously recycled at least in part to the cooking reactor (10) (step d). Possibly, water can be added at the flow (23a) through the pipe (24) to adjust the water stoichiometry and obtain a hydrated inorganic salt composition identical to that introduced by the pipe (11). Preferably, the concentrated inorganic salt obtained has the same composition as that introduced by the pipe (11). Optionally, the liquid fraction (23a) may contain all or part of the organic solvent.

The inorganic salt-depleted liquid fraction (25) may contain the anti-solvent, the organic solvent, residues of products derived from biomass, inorganic salt. Preferably, the inorganic salt-depleted liquid fraction (25) contains less than 50% of the hydrated inorganic salt initially contained in fraction (16). Even more preferably, the inorganic salt-depleted liquid fraction (25) contains less than 25% of the hydrated inorganic salt initially contained in fraction (16).

The inorganic salt-depleted liquid fraction (25) obtained in the enclosure (21) may also be a partial purge (25a).

When step e) is carried out with the addition of an antisolvent, the antisolvent is recovered mainly in the liquid fraction depleted in inorganic salt (25) and can be recycled (not shown) to step e) after any reprocessing, or to step f).

According to another variant, the f) treatment step of the solid fraction obtained in step e) is performed by one or more washes to obtain a treated solid fraction (20) and a liquid fraction (19), said liquid fraction being at least partly (19a) sent to a purification step (21) to concentrate the inorganic salt contained in the liquid fraction and to obtain a liquid fraction containing the concentrated inorganic salt (23a) and another fraction a liquid depleted of inorganic salt (25), said liquid fraction containing the concentrated inorganic salt (23a) being then at least partly recycled in the baking step d).

When step f) is carried out with the addition of an antisolvent, any residues of this treatment (s) are withdrawn by the pipe (19), then either purged (19c) or sent to the enclosure (21) via the pipe (19a). According to one embodiment (not shown), the antisolvent (8) added in step f) is separated during the purification step (25) and recycled in step f).

The process according to the invention makes it possible, by the acid hydrolysis step, to selectively separate hemicellulose, which results in a significant drop in products derived from biomass in the liquid fraction obtained after the firing step d). According to one embodiment not shown, and when necessary, the very small amount of products derived from biomass still contained in the liquid fraction can be separated before or after the separation of the inorganic salt hydrate and the solvent. The products derived from biomass may for example be extracted by addition of an immiscible solvent with the hydrated inorganic salt or with the hydrated inorganic salt-anti-solvent mixture. Products derived from biomass can also be precipitated by changing conditions (temperature, pH, etc.) or by adding a third body. Products derived from biomass can also be adsorbed on a solid.

Special case: chemical identity of the acid solution and the hydrated inorganic salt diluted in water

According to a preferred variant, the acid solution used in step a) is chemically identical to the hydrated inorganic salt of formula (I) of step d) diluted in water.

In this case, the inorganic salt is preferably selected from ferric chloride and / or zinc chloride, and the acidic solution used for step a) is a dilute aqueous solution of ferric chloride and / or zinc chloride.

The liquid fraction after the firing step is, thanks to the prior acid hydrolysis step, highly concentrated in hydrated inorganic salts without being enriched by a significant portion of hydrolysis products of hemicellulose. When the salt diluted in water and the acid solution are chemically identical, the recycling of this composition in each of the steps (acid hydrolysis and baking) then becomes possible. In addition, this makes it possible to obtain an even lower pretreatment cost since only one chemical compound is used in the two pretreatment stages. In this case, at least a portion of the acidic solution used in step a) originates from at least a portion of the liquid fraction obtained in step e) and / or step f), with or without passing through a purification step for concentrating the inorganic salt contained in the liquid fraction (s) and obtaining a liquid fraction containing the concentrated inorganic salt and another liquid fraction depleted in inorganic salt, and or from at least part of the liquid fraction depleted of inorganic salt resulting from the purification step h).

This case is represented in Figure 1 by dotted arrows. Referring to Figure 1, a portion of the liquid fraction (16b) obtained in step e) can be recycled (without purification step) into the acid hydrolysis chamber (2). Another part of the liquid fraction (16a) can be sent to a purification stage implemented in the chamber (21) as described above. A liquid fraction containing the concentrated inorganic salt (23a) and (23b) and another inorganic salt-depleted liquid fraction (25), a portion of said liquid fraction containing the inorganic salt, are obtained at the outlet of the enclosure (21). concentrate (23b) which can then be recycled in the acid hydrolysis (2), another part of said liquid fraction containing the concentrated inorganic salt (23a) can then be recycled in the cooking step d).

Optionally, water may be added to the stream (23b) through line (26) to adjust the amount of water to an acidic solution of the same composition as that introduced by line (3).

According to another mode not shown, another part of the liquid fraction (16) obtained in step e) can be recycled directly (without purification step) in the cooking step d).

In the same way, at least a portion of the liquid fraction (19b) obtained in step f) can be recycled (without purification step) into the acid hydrolysis chamber (2). Another part of the liquid fraction (19a) can be sent to a purification stage implemented in the chamber (21) as described above. An liquid fraction containing the concentrated inorganic salt (23a) and (23b) and another salt-depleted liquid fraction are obtained at the outlet of the chamber (21). inorganic (25), a part of said liquid fraction containing the concentrated inorganic salt (23b) which can then be recycled in the acid hydrolysis (2), another part of said liquid fraction containing the concentrated inorganic salt (23a) being then recycled in the cooking step d).

It is also possible to recycle in the acid hydrolysis step at least a portion of the inorganic salt-depleted liquid fraction (25b) resulting from the purification step h).

Claims

A pretreatment process for lignocellulosic biomass comprising the following steps:

c) a step of drying the solid fraction obtained in step b),

MX _n .n'H ₂ 0

in which

M a metal selected from groups 1 to 13 of the Periodic Table, X is an anion and

n is an integer between 1 and 6 and

n being between 0.5 and 12,

to obtain a solid fraction and a liquid fraction containing the hydrated inorganic salt,

e) a step of separating the solid fraction and the liquid fraction obtained in step d),

f) optionally a step of treating the solid fraction obtained in step e),

2. Method according to the preceding claim wherein the acid of step a) is selected from sulfuric acid, hydrochloric acid, nitric acid, ferric chloride, zinc chloride, phosphoric acid, formic acid, acetic acid, oxalic acid, trifluoroacetic acid and maleic acid, alone or as a mixture.

3. Method according to one of the preceding claims wherein the concentration of the acid of step a) is between 0.001 mol / L and 1 mol / L.

4. Method according to one of the preceding claims wherein step a) is carried out between room temperature and 150 ° C.

5. Method according to one of the preceding claims wherein the drying step is carried out at a temperature greater than or equal to 50 ° C.

6. Method according to one of the preceding claims wherein the anion X of the hydrated inorganic salt of formula (I) is a halide anion selected from CI ^" , F ^" , Br ^" , Γ, a perchlorate anion, a thiocyanate anion, a nitrate anion, an acetate anion, a para-methylbenzene sulphonate anion, a sulphate anion, an oxalate anion or a phosphate anion and in which the metal M in the formula (I) is chosen from lithium, iron, zinc or aluminum.

7. Method according to one of the preceding claims wherein the firing step d) is carried out at a temperature between -20 and 250 ° C, preferably between 20 and 160 ° C.

8. Method according to one of the preceding claims wherein the firing step d) is carried out in the presence of one or more organic solvents, selected from alcohols such as methanol, ethanol, n-propanol isopropanol, n-butanol, isobutanol or tert-butanol, diols and polyols such as ethanediol, propanediol or glycerol, amino alcohols such as ethanolamine, diethanolamine or triethanolamine, ketones such as acetone or methyl ethyl ketone, carboxylic acids such as formic acid or acetic acid, dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, aromatic solvents such as benzene, toluene, xylenes , the alkanes.

9. Method according to one of the preceding claims wherein the separation step e) of the solid fraction is carried out by precipitation by adding at least one anti-solvent which is a solvent or a mixture of solvents chosen from water, alcohols such as methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol or tert-butanol, diols and polyols such as ethanediol, propanediol or glycerol, amino alcohols such as ethanolamine, diethanolamine or triethanolamine, ketones such as acetone or methyl ethyl ketone, carboxylic acids such as formic acid or acetic acid, esters such as ethyl acetate or isopropyl acetate dimethylformamide, dimethylacetamide, dimethylsulfoxide, acetonitrile, and preferably the anti-solvent is water alone or in mixture.

10. Method according to one of the preceding claims wherein the f) treatment step of the solid fraction obtained in step e) is carried out by one or more washings, neutralization, pressing, and / or drying.

11. Method according to one of the preceding claims wherein the enzymatic hydrolysis g) is carried out at a temperature between 40 and 60 ° C and at a pH between 4.5 and 5.5.

12. Method according to one of the preceding claims wherein at least a portion of the liquid fraction obtained in step b) is neutralized before being used for the growth of the enzyme-producing microorganism.

13. Method according to one of the preceding claims wherein at least a portion of the liquid fraction obtained in step b) is used in biotechnological processes for converting sugars chosen from:

the ethanol fermentation of C6 sugars by a yeast,

the fermentation in solvents by a bacterium,

the ethanol fermentation of the C6 and C5 sugars by a yeast, by a bacterium or by a genetically modified yeast,

- the production of filamentous fungi.

14. Method according to one of claims wherein at least a portion of the liquid fraction obtained in step e) is sent to a purification step, called step h), for concentrating the inorganic salt contained in the fraction liquid and to obtain a liquid fraction containing the concentrated inorganic salt and another liquid fraction depleted of inorganic salt, said liquid fraction containing the concentrated inorganic salt being then at least partially recycled in the cooking step d).

15. Method according to one of the preceding claims wherein the acid solution used in step a) is chemically identical to the hydrated inorganic salt of formula (I) diluted in water.