Optimized IBE fermentation process for acetone upgrading

Abstract

The present invention relates to a method for producing alcohol, comprising: a. a step of IBE fermentation in at least one bioreactor (R1) in the presence of microorganisms of a natural strain, feeding at least an aqueous solution of C5 and / or C6 sugars (1) and a recycled acetone stream (3) thereto, resulting in a fermentation gas and a fermentation must containing fermentation products; b. a step of recovering the fermentation products to obtain a fermentation product stream (2); c. a step of treating the fermentation product stream from step b), comprising a section for separating acetone, to produce at least one acetone effluent (3) and an aqueous alcohol effluent (4); and d. a step of recycling at least a portion of the acetone effluent (3) from step c) to step a).

Description

[Technical Field]

[0001] The present invention relates to a method for producing alcohol, which comprises IBE fermentation of an aqueous solution containing C5 and / or C6 sugars in the presence of naturally occurring microorganisms, and which allows maximizing the yield of alcohol, in particular isopropanol. [Background technology]

[0002] To meet the challenges of the energy transition, considerable research is being conducted to develop "green" processes that allow access to chemical intermediates in alternative ways to petroleum refining and / or petrochemicals.

[0003] Fermentation-derived alcohols (ethanol, n-butanol (hereafter referred to as butanol), and isopropanol) are the most promising substitutes for petrochemical derivatives. ABE (acetone-butanol-ethanol) fermentation is one of the oldest industrialized fermentations (early 20th century) and has been widely studied since then (see Non-Patent Document 1). There is also IBE (isopropanol-butanol-ethanol) fermentation, which produces a mixture of isopropanol, butanol, and ethanol (see Non-Patent Document 2). These two types of fermentation are carried out under strict anaerobic conditions by fermenting microorganisms, generally belonging to the genus Clostridium.

[0004] These "solvent-producing," non-pathogenic strains of Clostridium used in biotechnology have the ability to naturally convert a wide variety of sugars to desired chemical species, particularly to produce a mixture of acetone, butanol, and ethanol during ABE fermentation (Non-Patent Document 3). Some can themselves produce a mixture of isopropanol, butanol, and ethanol during IBE fermentation (Non-Patent Documents 4 and 5).

[0005] Only a few specific solventogenic strains of Clostridium can naturally produce isopropanol as a nearly complete replacement for acetone during the fermentation process, in particular certain strains of Clostridium, such as Clostridium beijerinckii (or C. beijerinckii), e.g., strain DSM 6423. Other strains produce an acetone / butanol / ethanol (A / B / E) mixture.

[0006] Thus, during the IBE fermentation process leading to the isopropanol / butanol / ethanol (I / B / E) alcohol mixture, acetone is an intermediate product in the fermentation pathway for isopropanol production (Non-Patent Documents 6 and 7). However, at the end of IBE fermentation, such as that carried out by the DSM6423 strain, the resulting fermentation broth systematically contains acetone, often at low concentrations (generally about 2% of the mass of the resulting solvent). However, the presence of this acetone in the product of the IBE fermentation process is characteristic of the yield of alcohols, particularly isopropanol, and may be incomplete.

[0007] Therefore, it would be useful to optimize the conventional IBE fermentation process by converting the co-produced acetone into alcohols, especially isopropanol, to make large-scale fermentative production of I / B / E alcohols economically viable, thereby limiting the accumulation of this acetone by-product in the process. Recovery and conversion of acetone also allows for upgrading, particularly to improve the yield of sugar-to-alcohol conversion.

[0008] Industrial processes exist for converting acetone into isopropanol by chemical means. These are conventional catalytic hydrogenation processes under pressure. For example, the literature (Patent Documents 1 and 2) describes a process for producing isopropanol by reacting acetone with hydrogen in the presence of a hydrogenation metal, in particular a Raney nickel-based catalyst, at temperatures between 20°C and 200°C and pressures between 1 and 80 bar (see Patent Document 1). Patent Document 2 specifies that the selectivity of isopropanol is improved in the presence of water. Patent Document 3 itself describes a process for hydrogenating acetone to isopropanol in several reaction stages to produce high-purity isopropanol with improved selectivity.

[0009] At the same time, enzymatic pathways for converting acetone are investigated. For example, the reduction of acetone to isopropanol using certain strains of Clostridium, particularly Clostridium ragsdalei, has been described in a fermentation system that is significantly different from IBE or ABE fermentation because it consists of the fermentation of a gaseous substrate resulting from gasification, also called syngas, which contains a gaseous mixture of nitrogen (N), hydrogen (H), carbon dioxide (CO), and carbon monoxide (CO) (Non-Patent Document 8). In this method, acetone is added to the fermentation medium at concentrations ranging up to 2 g / L without affecting the growth of the microorganisms.

[0010] Another study proposed optimizing acetone-isopropanol-butanol fermentation in the presence of the native Clostridium strain NJP7 by specifically introducing exogenous acids (acetic acid or butyric acid) or precursors of certain enzymes into a glucose-containing medium to improve butanol or butanol-isopropanol production (Non-Patent Document 9). This same study showed that the butanol and isopropanol titers and productivity of Clostridium strain NJP7 could be further improved during fed-batch fermentation with in situ extraction using biodiesel.

[0011] Yet another study proposed genetically modifying Clostridium acetobutylicum ATCC 824, which naturally produces an acetone-butanol-ethanol mixture, to produce isopropanol instead of acetone. However, despite the presence of an alcohol dehydrogenase enzyme produced by the genetically modified microorganism that can effectively convert acetone, residual acetone production was still observed (Non-Patent Documents 10 and 11).

[0012] None of these documents proposes a method for producing alcohols by enzymatic conversion of C5 and / or C6 sugars that allows for the direct upgrading of acetone, in particular acetone co-produced with alcohol. Furthermore, none of these documents proposes a relatively simple process scheme that allows for a substantial improvement in the sugar-to-alcohol conversion rate and thus in the yield of the resulting alcohol, in particular isopropanol, which would represent a significant economic saving. [Prior art documents] [Patent documents]

[0013] [Patent Document 1] European Patent Application Publication No. 0379323 (JP Patent Publication No. 2-270829) [Patent Document 2] US Patent Application Publication No. 2011 / 0218367 [Patent Document 3] U.S. Patent No. 6,930,213 [Non-patent literature]

[0014] [Non-Patent Document 1] Moon et al., “One hundred years of clostridial butanol fermentation.” FEMS Microbiol Lett., February 2016, 363, 3

Non-licensed Document 2

Non-licensed Document 4

Non-licensed Document 5

Non-licensed Document 6

Non-licensed Document 7

[0015] (Summary of the Invention) Therefore, the present invention relates to a method for producing alcohol, the method comprising the steps of: a) a fermentation process using a reaction section comprising at least one bioreactor in which an IBE-type fermentation is carried out in the presence of a Clostridium strain, in particular an industrially important Clostridium strain, to which at least an aqueous solution of C5 and / or C6 sugars and a recycled acetone stream are fed to produce a fermentation gas and a fermentation broth containing fermentation products comprising butanol, ethanol, isopropanol and acetone; b) recovering the fermentation product to obtain a fermentation product stream; c) treating the fermentation product stream from step b) with an acetone separation section to produce at least an acetone effluent and an aqueous alcohol effluent; d) recycling acetone using at least one transfer section to recycle at least a portion of the acetone effluent from step c) to step a), said at least a portion of the transferred acetone effluent constituting the recycled acetone stream fed to the reaction section of step a).

[0016] Surprisingly, the applicant discovered that, according to a simple scheme, it was possible to reintroduce acetone co-produced with alcohol by natural microorganisms into the fermentation medium without any specific purification and convert it to isopropanol using these same natural microorganisms. This re-assimilation and conversion of the co-products into alcohol, especially isopropanol, allows for a substantial improvement in the sugar-to-alcohol yield, which represents a significant economic saving. The applicant discovered that, in fact, acetone co-produced during IBE fermentation by natural microorganisms can be easily recycled and almost completely re-assimilated and converted into isopropanol by the same microorganisms.

[0017] Therefore, the method according to the invention makes it possible to increase the isopropanol yield by 4 to 6% by weight compared to the prior art method using the same strain and the same amount of natural microorganisms, in particular by using a simple system for recycling the co-produced acetone. The improved performance obtained by the method according to the invention appears possible with limited investment and operating costs.

[0018] Another advantage of the present invention is the possibility of upgrading the co-produced acetone, but also of converting exogenous acetone, which may be defined as biocompatible acetone derived from fermentation or chemical processes external to the method of the present invention. Indeed, even at high concentrations of acetone in the fermentation medium, acetone appears to be very well converted to isopropanol, with conversion rates of up to 90%, by microorganisms that naturally produce a mixture of isopropanol, butanol, and ethanol. DETAILED DESCRIPTION OF THE INVENTION

[0019] (Description of the embodiment) According to the present invention, IBE-type fermentation or IBE fermentation is a fermentation using microorganisms that allows the conversion of sugars containing five carbon atoms (C5) and / or six carbon atoms (C6) solubilized in an aqueous solution into a fermentation product containing a solvent consisting mainly of an alcohol mixture of isopropanol, butanol, and ethanol. During this IBE fermentation, acetone is co-produced; this solvent represents about 2% by weight of the solvent produced. Generally, the fermentation also produces fermentation gases, in particular carbon dioxide (CO2) and hydrogen.

[0020] According to the present invention, the microorganisms, also called bacteria, used in the fermentation system are strains from the Clostridium species, particularly those of industrial importance, that are naturally, i.e., in the wild, capable of producing primarily the alcohols isopropanol, n-butanol (hereinafter referred to as butanol), and ethanol from sugars containing five carbons (C5) or six carbons (C6). The term "predominantly" here means preferably at least 60% by weight, preferentially at least 80% by weight, and preferably at least 90% by weight of the solvent obtained by fermentation. These strains are also called "IBE strains" or "wild-type IBE strains."

[0021] Bacteria capable of producing isopropanol in the wild, particularly bacteria capable of IBE fermentation in the wild, include, for example, C. beijerinckii bacteria, C. The bacteria may be selected from C. diolis bacteria, C. puniceum bacteria, C. Aurantibutyricum bacteria, C. butyricum bacteria, C. saccharoperbutylacetonicum bacteria, C. botulinum bacteria, C. drakei bacteria, C. scatologenes bacteria, C. perfringens bacteria and C. tunisiense bacteria, preferably selected from C. beijerinckii bacteria, C. diolis bacteria, C. puniceum bacteria, C. aurantibutyricum bacteria and C. saccharoperbutylacetonicum bacteria. Preferably, the bacterium capable of naturally producing isopropanol, particularly the bacterium capable of IBE fermentation in the wild, is a C. beijerinckii bacterium, preferably a subclade of C. beijerinckii selected from DSM 6423, LMG 7814, LMG 7815, NRRL B-593, NCCB 27006, C. aurantibutyricum DSZM 793 or ATCC 17777 bacterium, or a subclade of C. beijerinckii or C. aurantibutyricum having at least 90%, 95%, 96%, 97%, 98%, or 99% identity to the DSM 6423 strain (see https: / / www.ebi.ac.uk / ena / data / view / GCA_900010805.1). C. beijerinckii bacteria of the DSM 6423 subclass are particularly preferred.

[0022] Advantageously, the microorganisms used naturally synthesize, during fermentation, a specific enzyme called secondary alcohol dehydrogenase (sadh), which is capable of converting acetone into isopropanol in the presence of a cofactor, more particularly NADPH (nicotinamide adenine dinucleotide phosphate), which is produced by the same microorganism, in particular in the presence of glucose. According to the invention, these microorganisms are interchangeably referred to as "microorganisms", "natural strain microorganisms", "strains derived from Clostridium species" or "natural strains" or even "wild strains".

[0023] However, wild-type strains can naturally undergo point mutations within their genetic material (i.e., within their DNA) without affecting their fermentation performance.

[0024] According to the present invention, a "bioreactor", also called a "fermenter", is an item of equipment for propagating fermenting microorganisms capable of producing molecules of interest (solvents or other organic compounds). Fermentation in a bioreactor therefore allows the growth of the microorganisms used and the production of the solvent of interest in the presence of C5 and / or C6 sugars, while controlling key parameters such as pH, agitation and temperature of the fermentation (or fermentable) medium, also called reaction medium.

[0025] Thus, the fermentation process according to the present invention comprises growing a microorganism and recovering a reaction effluent comprising a fermentation broth containing an aqueous solution comprising a mixture of isopropanol, n-butanol and ethanol.

[0026] According to the invention, the volume of a bioreactor corresponds to the working volume of said bioreactor.

[0027] According to the present invention, the term "solvent" refers to all alcohol and ketone compounds produced by fermentation. More specifically, the term "solvent" refers to the mixture of isopropanol, butanol, ethanol and acetone produced during the IBE fermentation carried out in the method according to the present invention.

[0028] According to the present invention, the expression "between A and B" means that both limits of the interval are included in the range of values ​​stated. If this is not the case and if both limits are not included in the range stated, a statement to that effect will be introduced by the present invention.

[0029] For purposes of the present invention, various ranges of parameters for a given process, such as pressure and temperature ranges, may be used alone or in combination, e.g., a range of preferred pressure values ​​may be combined with a range of more preferred temperature values ​​within the meaning of the present invention.

[0030] In the following text, specific and / or preferred embodiments of the present invention may be described, which may be implemented individually or in combination together, without limitation of combination, where this is technically feasible.

[0031] Therefore, the present invention relates to a method for producing alcohol, comprising, preferably consisting of, the following steps: a) a process for IBE-type fermentation using a reaction section comprising at least one bioreactor containing microorganisms of a natural strain, feeding the reaction section with at least an aqueous solution of C5 and / or C6 sugars and a recycled acetone stream to produce a fermentation gas and a fermentation broth containing fermentation products comprising butanol, ethanol, isopropanol and acetone; b) recovering the fermentation product to obtain a fermentation product stream; c) treating the fermentation product stream from step b) with an acetone separation section to produce at least an acetone effluent and an aqueous alcohol effluent; d) recycling acetone using at least one transfer section, wherein at least a portion of the acetone effluent from step c) is recycled to step a), said at least a portion of the transferred acetone effluent constituting the recycled acetone stream fed to the reaction section.

[0032] (Feed material) According to the invention, the process is fed with an aqueous solution of C5 and / or C6 sugars.

[0033] The aqueous solution of C5 and / or C6 sugars can have various origins. It advantageously comes from the processing of renewable resources. This renewable resource can be of the lignocellulosic biomass type, including in particular woody substrates (deciduous and coniferous plants), agricultural by-products (straw) or by-products from industries that generate lignocellulosic waste (agri-food or paper industries). The aqueous sugar solution can also be obtained from sugar-producing plants, such as sugar beets and sugar cane, or from starchy plants, such as corn or wheat.

[0034] Any C5 sugar naturally occurring in the various lignocellulosic biomass (monocotyledonous or dicotyledonous plants) used in biological biofuel production can be fermented by the method according to the invention. Preferably, the C5 sugar is selected from xylose and arabinose.

[0035] Any C6 sugar can be fermented by the method according to the present invention. Preferably, the C6 sugar is selected from glucose, mannose, and galactose. More preferably, the C6 sugar is glucose.

[0036] Advantageously, C5 and / or C6 sugars are solubilized in the aqueous sugar solution, which has a concentration of C5 and / or C6 sugars of 1 to 900 g / L, preferably 10 to 600 g / L, preferentially 20 to 500 g / L, and highly preferably 25 to 150 g / L. Preferably, the aqueous solution of C5 and / or C6 sugars is a liquid solution.

[0037] (Step a)) According to the present invention, the method for producing alcohol comprises a fermentation step a) using a reaction section which itself comprises at least one bioreactor in which an IBE fermentation is carried out in the presence of naturally occurring microorganisms.

[0038] Said naturally occurring microorganisms are strains of Clostridium that are naturally capable of producing the alcohols isopropanol, n-butanol (also referred to as butanol according to the present invention) and ethanol from C5 and / or C6 sugars.

[0039] According to one or more embodiments, the fermentation system, also referred to as bacterial biomass, belongs to the genus Clostridium and is capable of producing isopropanol in the wild, in particular capable of carrying out IBE fermentation in the wild, and advantageously comprises bacteria such as C. beijerinckii, C. diolis, C. puniceum, C. aurantibutyricum, C. butyricum, C. saccharoperbutylacetonicum, C. botulinum, C. drakei, C. scatologenes, C. perfringens, and C. tunisiense bacteria, preferably C. beijerinckii bacteria, C. diolis bacteria, C. puniceum bacteria, C. aurantibutyricum bacteria and C. saccharoperbutyricum bacteria, or at least produced by (and / or comprising) a microorganism or bacteria selected from C. beijerinckii bacteria, C. diolis bacteria, C. puniceum bacteria, C. aurantibutyricum bacteria and C. saccharoperbutyricum bacteria. Preferably, the microorganism used is a C. beijerinckii bacterium, preferably a subclade of C. beijerinckii selected from DSM 6423, LMG 7814, LMG 7815, NRRL B-593, NCCB 27006, C. aurantibutyricum DSZM 793 or ATCC 17777 bacterium, or a subclade of C. beijerinckii or C. aurantibutyricum bacteria having at least 90%, 95%, 96%, 97%, 98% or 99% identity to the DSM 6423 strain (see https: / / www.ebi.ac.uk / ena / data / view / GCA_900010805.1).

[0040] The reaction section may comprise one or more bioreactors, preferably at least two bioreactors, preferentially at least five bioreactors. Advantageously, the reaction section comprises up to 30 bioreactors, preferably up to 20 bioreactors, preferentially up to 10 bioreactors. Each bioreactor comprises said naturally occurring microorganisms. When the reaction section comprises several bioreactors, the bioreactors are operated in parallel.

[0041] The reaction section is fed with an aqueous solution of C5 and / or C6 sugars. Advantageously, the aqueous solution is in liquid form. If the reaction section comprises several bioreactors, the aqueous solution of C5 and / or C6 sugars may be split into as many aqueous sugar solution feed streams as there are bioreactors in the reaction section.

[0042] The reaction section is also advantageously fed with a recycled acetone stream, advantageously from step d) of the process according to the invention. Advantageously, the recycled acetone stream is in liquid form. The recycled acetone stream can be introduced directly into the bioreactor(s) or into a mixer placed upstream of the bioreactor, where it is mixed with the aqueous solution of C5 and / or C6 sugars before being introduced into the bioreactor(s). If the reaction section comprises several bioreactors, the recycled acetone stream can be directly split into as many recycled acetone feed streams as there are bioreactors in the reaction section.

[0043] The reaction section may optionally also be fed with an exogenous acetone stream. Advantageously, the exogenous acetone stream optionally fed to the reaction section is in liquid form. The exogenous acetone stream may be introduced into the bioreactor(s) or fed to the bioreactor(s) after being mixed with a recycled acetone stream C6.

[0044] The exogenous acetone stream optionally fed to the reaction section is a biocompatible acetone stream, which originates from at least one process other than the process according to the invention. The exogenous acetone stream may originate, at least in part, from another fermentation process, for example one which performs ABE fermentation, or from a "chemical" process, i.e. a process which does not perform fermentation at all. In the latter case, the acetone produced by the chemical process is directly biocompatible, i.e. does not contain any poisons for the microorganisms used in step a) of the process according to the invention, or has been treated to make it biocompatible before being introduced into the reaction section of step a).

[0045] Advantageously, the reaction section of step a) is fed with said recycled acetone stream and optionally said exogenous acetone stream, the flow rates being adjusted so that the concentration of acetone fed to the reaction section of step a), relative to all of the liquid streams fed to the reaction section of step a), i.e. relative to the aqueous C5 and / or C6 sugar solution, the recycled acetone stream and the optional exogenous acetone stream, is at most 10 g / L, preferably at most 5 g / L, preferentially at most 2 g / L, and preferably strictly greater than 0, preferentially at least 0.01 g / L, preferably at least 0.1 g / L. The concentration of acetone fed to the reaction section of step a) is defined as the weight of the total acetone entering the reaction section of step a), i.e. provided by the recycled acetone stream and the optional exogenous acetone stream, relative to the total volume of the streams feeding the reaction section of step a), i.e. relative to the sum, expressed by volume, of the liquid streams consisting of the aqueous sugar solution stream, the recycled acetone stream and the optional exogenous acetone stream.

[0046] Advantageously, the fermentation carried out in the reaction section is carried out at a temperature between 25° C. and 40° C., preferably between 30° C. and 37° C., preferably at 34° C. Preferably, the fermentation is carried out at a pH between 4.0 and 7.0, preferably between 4.5 and 6.0. Advantageously, the reaction section of step a) is operated at atmospheric pressure.

[0047] According to one particular embodiment of the invention, the fermentation may be carried out batchwise, i.e. with an initial feed and without intermediate feed and / or without continuous feed, in particular without continuous feed of the aqueous sugar solution, said recycled acetone stream, optionally one or more preceding batches, and optionally an exogenous acetone stream. In other words, in this embodiment, the fermentation is carried out in bioreactor(s), which are advantageously closed to the liquid phase (but open to the exiting gas phase), for a period of 30 to 150 hours, which advantageously corresponds to the duration of the batch. Preferably, the working volume of the bioreactor(s) is between 10 and 500 m 3 An aqueous solution of C5 and / or C6 sugars is initially introduced into the bioreactor (or into each bioreactor) at a concentration of preferably 1 to 900 g / L, preferably 10 to 600 g / L, preferably 20 to 500 g / L, even more preferably 30 g / L to 90 g / L, in particular 40 g / L to 60 g / L, this amount corresponding to half the working volume of the bioreactor considered and advantageously to the fermentation medium of said bioreactor. The amount of microorganisms introduced per batch and per bioreactor corresponds to the volume of the cell (or bacterial) culture medium at maximum growth rate, such that said volume of culture medium is 2% to 10% of the volume of the fermentation medium (or reaction volume). Continuous stirring is maintained to homogenize the reaction medium.

[0048] According to a second particular embodiment of the invention, the fermentation may be carried out in "semi-continuous" or "fed-batch" mode. In this embodiment, the aqueous sugar solution, and advantageously the acetone stream, is advantageously introduced into the bioreactor(s) in part at the beginning of the batch and in another part added to the bioreactor(s) during the course of the batch. Batch, according to the knowledge of the skilled person, advantageously means the time for carrying out the fermentation between two emptyings of the bioreactor(s) and the operations carried out during this time. The batch preferably lasts from 20 to 200 hours, preferably from 30 to 150 hours. Preferably, the working volume of the bioreactor(s) is from 10 to 500 m3 Preferably, the bioreactor (or each bioreactor) is initially fed with an aqueous solution of C5 and / or C6 sugars, preferably with a sugar concentration of 30 g / L to 90 g / L, preferably 40 g / L to 60 g / L, the amount of aqueous sugar solution corresponding to a volume preferably equal to half the working volume of the bioreactor (or each bioreactor). During fermentation, each bioreactor is advantageously fed, either continuously or in pulses, with an aqueous solution of C5 and / or C6 sugars, preferably with a sugar concentration of 500 to 800 g / L, at a flow rate advantageously of 10 to 5000 L / h, preferably 20 to 2500 L / h. The amount of microorganisms introduced per batch and per bioreactor corresponds to the volume of the culture medium of the cells (or bacteria) at maximum growth rate, said volume of culture medium being 2% to 10% of the fermentation medium (or reaction volume). Continuous stirring is maintained in each bioreactor to homogenize the reaction medium. The butanol produced is then extracted in liquid or gas form in each bioreactor, either continuously or in a pulsed manner. The purpose of this technique is to remove butanol, which is toxic to microorganisms and is produced by the strain. This technique is called ISPR (In Situ Product Recovery) and is well known to those skilled in the art (see Outram V. et al. "A comparison of the energy use of in situ product recovery techniques for the acetone butanol ethanol fermentation", Bioresource Technology, 2016, 220, 590-600).

[0049] When fermentation is carried out in batch or semi-continuous (or fed-batch) mode, the term "flow" refers to the amount introduced into or exiting the bioreactor(s) per batch.

[0050] According to a third particular embodiment of the invention, the fermentation can be carried out in a "simple continuous" mode, also called continuous mode with free cells. The bioreactor(s) are then continuously fed with an aqueous sugar solution and a recycled acetone stream, and optionally an exogenous acetone stream. The feed flow rate of said aqueous solution of C5 and / or C6 sugars is preferably at a concentration of advantageously between 1 and 900 g / L, preferentially between 10 and 600 g / L, preferably between 20 and 500 g / L, and highly preferably between 25 and 150 g / L, and is preferably between 10 and 600 g / L and more preferably between 10 and 600 g / L. -1 The dilution rate in the bioreactor(s) is between 0.01 and 0.05 h -1 , preferably 0.0125 to 0.033 h -1 This dilution rate corresponds to the inverse of the residence time (i.e. the flow rate of said aqueous solution of C5 and / or C6 sugars divided by the volume of the bioreactor, i.e. the working volume), as is well known to those skilled in the art. The feed rates of said recycled acetone stream and optionally said exogenous acetone stream are adjusted, as described above, so that the concentration of acetone fed to the bioreactor relative to the sum of the liquid streams fed to the bioreactor (i.e. the aqueous sugar solution, the recycled acetone stream and the optional exogenous acetone stream) is not more than 10 g / L, preferably not more than 5 g / L, preferentially not more than 2 g / L, and preferably strictly greater than 0, preferentially not less than 0.01 g / L, preferably not less than 0.1 g / L. Advantageously, when fermentation is carried out in simple continuous mode, the concentration of microorganisms in the reaction medium, also called fermentation medium, is greater than 10 8 ~10 11 cells / mL reaction medium, preferably 10 9 ~10 10 cells / mL reaction medium. Continuous stirring of the reaction medium in the bioreactor(s) is advantageously maintained to homogenize the reaction medium. In this embodiment, the microorganisms and the formed products are withdrawn from the bioreactor(s) continuously or in a pulsed manner. The ISPR technique described above can also be applied to remove butanol, which is toxic to bacteria.

[0051] According to another particular embodiment of the present invention, the fermentation can be carried out in a "supported continuous" mode, also called a confined continuous mode or a continuous mode using immobilized cells. The microorganisms then form a film, or biofilm, on a solid support, for example a solid support made of a porous inorganic material, such as clay, metal foam, polymer foam, in particular polyurethane foam, with polyurethane foam being preferred (see FR 3 086 670). Advantageously, when carrying out the fermentation in a supported continuous mode, the concentration of the microorganisms is 10 7 ~10 10 cells / cm 3 Solid support, preferably 10 8 ~10 9 cells / cm 3 The inoculated solid support, i.e., the solid support containing the microbial biofilm, preferably an inoculated polyurethane foam, is then placed in the bioreactor or bioreactors so that the volume of the inoculated solid support occupies preferably 1% to 50%, preferably 5% to 30%, of the working volume of the bioreactor. The bioreactor(s) are then continuously fed with an aqueous solution of C5 and / or C6 sugars at a concentration advantageously between 1 and 900 g / L, preferentially between 10 and 600 g / L, preferably between 20 and 500 g / L, and highly preferably between 25 and 150 g / L, and a recycled acetone stream, and optionally an exogenous acetone stream. The flow rate at which said aqueous solution of C5 and / or C6 sugars is fed to the bioreactor(s) is preferably between 1 and 900 g / L, preferentially between 10 and 600 g / L, preferably between 20 and 500 g / L, and highly preferably between 25 and 150 g / L ... -1 The dilution rate is 0.01 to 0.40 h -1 , preferably 0.015 to 0.30 h -1 , preferably 0.02 to 0.20 h -1This dilution rate corresponds to the inverse of the residence time (i.e., the flow rate of the aqueous solution of C5 and / or C6 sugars divided by the volume of the bioreactor, i.e., the working volume), as is well known to those skilled in the art. The feed rates of the recycled acetone stream and, optionally, the exogenous acetone stream, are adjusted so that the concentration of acetone fed to the bioreactor relative to the total of the liquid streams feeding the bioreactor (i.e., the aqueous sugar solution, the recycled acetone stream, and the optional exogenous acetone stream), as described above, is not more than 10 g / L, preferably not more than 5 g / L, preferentially not more than 2 g / L, and preferably strictly greater than 0, preferentially not less than 0.01 g / L, preferably not less than 0.1 g / L. Continuous stirring of the reaction medium in the bioreactor(s) is advantageously maintained in order to homogenize the reaction medium. In this embodiment, the microorganisms and the products formed are withdrawn from the bioreactor(s) continuously or in a pulsed manner. ISPR technology can also be applied to remove butanol, which is harmful to bacteria, as described above.

[0052] Preferably, the fermentation is carried out in simple continuous mode or in continuous mode with cell immobilization, preferentially in continuous mode with cell immobilization.

[0053] Said step a) allows the production of a fermentation broth containing fermentation gases, in particular comprising carbon dioxide (CO2) and hydrogen, and fermentation products comprising butanol, ethanol, isopropanol and acetone.

[0054] (Step b)) According to the present invention, the method for producing alcohol comprises a step b) of recovering the fermentation product produced in step a) to obtain a fermentation product stream.

[0055] This step advantageously consists at least in separating the fermentation products, in particular the fermentation products comprising butanol, ethanol, isopropanol and acetone in admixture with water, from the fermentation broth and fermentation gas.

[0056] This separation can be carried out by any method known to those skilled in the art, for example the method for recovering alcohol in a fermenter described in WO 2018 / 001628 can be used in particular in this step b).

[0057] Said stream of fermentation product obtained at the end of step b) comprises in particular isopropanol, n-butanol, ethanol and acetone in a mixture with water.

[0058] (Step c)) According to the present invention, the method for producing alcohol comprises step c) of treating the fermentation product stream resulting from step b), said step c) using at least one acetone separation section to produce at least an acetone effluent and an aqueous alcohol effluent, said aqueous alcohol effluent comprising, inter alia, butanol, ethanol and isopropanol.

[0059] The separation of acetone from the fermentation product stream can be carried out by any method known to those skilled in the art, for example by distillation(s), fractional distillation(s), etc. It can in particular be carried out as a series of distillations. Thus, in a particular embodiment of the present invention, step c) comprises, in said acetone separation section: c-1) distillation of the fermentation product stream from step b) in a beer column; obtaining a water stream at the bottom of the beer column and an aqueous mixture of solvents at the top of the beer column; c-2) Distillation of an aqueous mixture of solvents in a distillation column; obtaining the acetone effluent at the top of the column and the aqueous alcohol effluent at the bottom of the column.

[0060] The aqueous mixture of solvents extracted at the top of the beer column in step c-1) of this particular embodiment comprises water, butanol, in particular n-butanol, ethanol, isopropanol and acetone. The beer column in step c-1) may advantageously be equipped with a reboiling system, preferably by recompression of the overhead vapors. It may also include a reflux recycle system.

[0061] The aqueous mixture of solvents extracted at the top of the beer column in step c-1) in a particular embodiment is then sent to a distillation column, also called an "acetone column". The role of the acetone column in step c-2) is to separate acetone from the alcohol stream (acetone is extracted at the top of the column) and to produce an aqueous alcohol effluent, advantageously concentrated in isopropanol-butanol-ethanol, which is withdrawn at the bottom of the acetone column.

[0062] Advantageously, the acetone effluent obtained at the end of step c) has an acetone concentration of at least 95% by weight, preferably at least 98% by weight, preferably at least 99.5% by weight, relative to the weight of said acetone effluent. The hydroalcoholic effluent itself comprises water and a mixture of alcohols, advantageously those produced during the IBE fermentation, in particular n-butanol (also called butanol), ethanol and isopropanol.

[0063] Step c) may optionally further comprise an alcohol separation section, which comprises a distillation column and is fed with the aqueous alcohol effluent from the acetone separation section, thereby enabling separation of at least one butanol effluent and at least one aqueous-alcohol effluent containing ethanol and isopropanol.

[0064] (Step d)) According to the present invention, the process for producing alcohols comprises a step d) of recycling acetone, which uses at least one transfer section to recycle at least a portion of the acetone effluent from step c) to step a), said portion of the acetone effluent recycled to step a) constituting a recycled acetone stream fed to the reaction section of step a) of the process according to the present invention.

[0065] The process according to the invention can be operated in a continuous, batch or semi-continuous mode, as described above. Preferably, the process is operated in a continuous mode, preferably a confined continuous mode.

[0066] The method according to the invention therefore allows for the reintegration of acetone co-produced in the fermentation medium into the bioreactor, where it is reassimilated by the microorganisms and converted to isopropanol. Because acetone reassimilation is virtually complete, the isopropanol yield is improved, with a gain of 4% to 6% by weight, depending on the Clostridium strain used, compared to a method using the same strain and the same number of native microorganisms but without a system for recycling and reassimilation of the co-produced acetone. Therefore, the method according to the invention allows for an increase in the overall yield of sugars to alcohol conversion compared to an IBE fermentation method without upgrading the acetone co-product.

[0067] The process according to the invention also makes it possible to upgrade acetone exogenous to the process by converting it into isopropanol, in particular at low pressures compared to conventional processes using chemical means.

[0068] The figures incorporated herein and the following examples are presented as non-limiting illustrations of the method according to the present invention.

[0069] According to the present invention, and particularly in the examples, the unit of weight "ton" is denoted as "t", the unit of weight "gram" is denoted as "g", and the unit of time "hour" is denoted as "h".

[0070] (List of drawings) (Figure 1) Figure 1 shows a schematic diagram of a specific configuration of the process according to the invention. An aqueous solution of C5 and / or C6 sugars (1) is fed to a reaction section (R1) containing at least one bioreactor. The bioreactor contains microorganisms that naturally convert the sugars to alcohols such as isopropanol, butanol, and ethanol. The fermentation product (2) obtained after IBE fermentation of the sugars is recovered and introduced into an acetone separation section (C), which separates an acetone effluent (3) and an aqueous alcohol effluent (4), the acetone effluent (3) being completely recycled to the reaction section (R1) and the aqueous alcohol effluent (4) containing isopropanol, butanol, and ethanol.

[0071] (Figure 2) Figure 2 shows another specific configuration of the process according to the invention. The process shown in Figure 2, in comparison with the process shown in Figure 1, further comprises an exogenous acetone feed (5) so that the total concentration of acetone fed to section (R1), relative to the total of the streams fed to said section (R1), is less than or equal to 10 g / L, preferably less than or equal to 5 g / L, preferably less than or equal to 2 g / L, and preferably strictly greater than 0, preferentially greater than or equal to 0.01 g / L, preferably greater than or equal to 0.1 g / L.

[0072] (Example) The following examples are based on the results of laboratory tests carried out with microorganisms of the genus Clostridium, in particular with strain DSM 6423, which naturally produce solvents from C5 and / or C6 sugars with a distribution expressed in weight percentages as follows: isopropanol / butanol / ethanol / acetone: 36% / 60% / 2% / 2%.

[0073] (Example 1: Not in accordance with the present invention) Example 1 illustrates an IBE fermentation process in the presence of Clostridium beijerinckii strain DSM 6423 without a system for recycling the co-produced acetone, which is a prior art process.

[0074] The fermentation production unit uses a fermentation unit containing four fermenters that process an aqueous solution of 62.5 g / L of glucose (C6 sugar). The total working volume of the fermenters in the fermentation unit is 14,000 m 3 The sugar consumption of the plant is about 125,000 t / year of glucose, and the flow rate of the glucose solution is 250,000 L / h, i.e., the dilution rate is 0.022 h -1 The fermenter is operated at 37°C, atmospheric pressure, and pH 4.5-6. The unit is operated in a simple continuous mode. The number of microorganisms is 10 9 ~10 10 cells / mL reaction medium.

[0075] The production unit also includes a unit for treating the solvent produced, in particular an acetone separation unit, which comprises a beer column followed by an acetone column, in which the acetone produced is separated from the alcohol.

[0076] The production unit will produce 40,000 tonnes of solvent per year.

[0077] Table 1 summarizes the amounts of the various solvents produced.

[0078] [Table 1]

[0079] The overall yield of glucose to solvent (acetone + ethanol + isopropanol + butanol) is 0.320 kg / kg (i.e., kg of solvent produced per kg of glucose consumed), and the conversion of glucose to alcohol (ethanol + isopropanol + butanol) is 0.314 kg / kg.

[0080] (Example 2: Consistent with the present invention) Example 2 illustrates a method according to the present invention. Example 2 specifically illustrates an IBE fermentation process with a system for recycling co-produced acetone in the presence of Clostridium beijerinckii strain DSM 6423.

[0081] The process parameters and operating conditions described in Example 1 are used. The production unit further comprises a system for recycling the acetone co-produced and separated in a dedicated separation unit. An acetone flow of about 100,000 g / h is thus generated and continuously recycled to the fermenter. The separated acetone effluent is entirely recycled to the fermentation unit.

[0082] The acetone concentration in all streams feeding the bioreactor is 0.4 g / L throughout the production.

[0083] Table 2 shows the amounts of various solvents produced by the method described in Example 2.

[0084] [Table 2]

[0085] The overall yield of glucose from glucose to solvent (acetone + ethanol + isopropanol + butanol) is still 0.320 kg of solvent per kg of glucose, but the conversion of glucose to alcohol (ethanol + isopropanol + butanol) is 0.319 kg / kg by the method of Example 2 instead of 0.314 kg / kg obtained by the method of Example 1, which is not in accordance with the invention.

[0086] The Clostridium beijerinckii DSM6423 strain present in the fermenter of the fermentation unit absorbed the reintroduced acetone and converted it to isopropanol, with a yield of 90% by weight from acetone to isopropanol (90% = 100 × (15120-14400) / 800).

[0087] The increase in isopropanol production is about 5.0 wt. % (5.0% = (15120 - 14400) / 14400) compared to the process described in Example 1, which does not include a system for upgrading acetone (not in accordance with the present invention). [Brief explanation of the drawings]

[0088] [Figure 1] 1 shows a schematic representation of a particular arrangement of the method according to the invention; [Figure 2] 2 represents another particular arrangement of the method according to the invention.

Claims

1. 1. A method for producing alcohol, comprising the steps of: a) a fermentation process using a reaction section comprising at least one bioreactor in which an IBE-type fermentation is carried out in the presence of a Clostridium strain, and feeding at least an aqueous solution of C5 and / or C6 sugars and a recycled acetone stream to the reaction section to produce a fermentation gas and a fermentation broth containing fermentation products comprising butanol, ethanol, isopropanol and acetone; b) recovering the fermentation product to obtain a fermentation product stream; c) treating the fermentation product stream from step b) with an acetone separation section to produce at least an acetone effluent and an aqueous alcohol effluent; d) recycling acetone, using at least one transfer section to recycle at least a portion of the acetone effluent from step c) to step a), said at least a portion of the transferred acetone effluent constituting the recycled acetone stream fed to the reaction section of step a).

2. 2. The process of claim 1, wherein the reaction section of step a) is further fed with an exogenous acetone stream.

3. 3. The method according to claim 1 or 2, wherein the recycled acetone stream and the optional exogenous acetone stream are fed to the reaction section of step a) at flow rates adjusted in such a way that the concentration of acetone in all of the liquid streams fed to the reaction section of step a), consisting of the aqueous solution of C5 and / or C6 sugars, the recycled acetone stream and the optional exogenous acetone stream, is at most 10 g / L, preferably at most 5 g / L, preferentially at most 2 g / L.

4. The method according to any one of claims 1 to 3, wherein the temperature at which the fermentation takes place in the reaction section of step a) is between 25°C and 40°C, preferably between 30°C and 37°C, preferably 34°C.

5. The method according to any one of claims 1 to 4, wherein the pH during the fermentation carried out in the reaction section of step a) is between 4 and 7, preferably between 4.5 and 6.

6. 6. The process according to claim 1, wherein the reaction section of step a) is operated at atmospheric pressure.

7. 7. The method according to any one of claims 1 to 6, wherein the reaction section comprises at least 2 bioreactors, preferentially at least 5 bioreactors, and advantageously up to 30 bioreactors, preferably up to 20 bioreactors, preferentially up to 10 bioreactors.

8. 8. The method according to any one of claims 1 to 7, wherein the fermentation is carried out in batch mode over a period of 30 to 150 hours.

9. A method according to any one of claims 1 to 7, wherein the fermentation is carried out in semi-continuous mode for a period of between 20 and 200 hours, preferentially between 30 and 150 hours.

10. Fermentation was carried out in a simple continuous mode, and the concentration of the clostridial strain in the reaction medium was 10 ８ ~10 １１ cells / mL reaction medium, preferably 10 ９ ~10 １０ The method of any one of claims 1 to 7, wherein the reaction medium is cells / mL.

11. Fermentation is carried out in a supported continuous mode, the clostridium strains are in the form of a biofilm on a solid support, and the concentration of the clostridium strains in the reaction medium is 10 ７ ~10 １０ cells / cm ３ Solid support, preferably 10 ８ ~10 ９ cells / cm ３ The method according to any one of claims 1 to 7, which is a solid support.

12. The method according to any one of claims 1 to 11, wherein step c) comprises performing in the acetone separation section: c-1) Distillation of the fermentation product stream from step b) in a first distillation column; obtaining a water stream at the bottom of said first distillation column and an aqueous mixture of solvents at the top of said first distillation column; c-2) Distillation of the aqueous mixture of solvents obtained from c-1) in a second distillation column; obtaining said acetone effluent at the top of the second column and said aqueous alcohol effluent at the bottom of the second column.

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