Method for producing alcohols using a support on which microorganisms are immobilized

Abstract

The present invention relates to a method for producing alcohols, according to which a sugary fluid is introduced into a reaction section comprising supports on which microorganisms are immobilized, in order to produce, by fermentation, an alcohol-enriched must under the action of said microorganisms, wherein said supports comprise structured packings or packings arranged randomly in the reaction section, wherein said packings - offer an accessible surface area of between 50 and 1000 m2 / m3 of working volume of the reaction section, - have an overall void fraction of at least 70%, - are made of metal, glass, ceramic, or based on polymer(s) withstanding temperatures up to at least 80°C.

Description

[0001] Process for producing alcohols with a support on which microorganisms are immobilized

[0002] Technical field

[0003] The present invention relates to a process for producing alcohols by fermentation of a sugar fluid.

[0004] Prior art

[0005] In order to meet the challenges of the energy transition, a great deal of research is being carried out to develop so-called "green" processes, providing access to chemical intermediates as an alternative to oil refining and / or petrochemicals.

[0006] Alcohols derived from fermentation processes (e.g., isopropanol and n-butanol) are among the most promising substitutes for petrochemical derivatives. ABE (Acetone-Butanol-Ethanol) fermentation, carried out by microorganisms belonging to the genus Clostridium, is one of the oldest fermentations to have been industrialized and has since been widely studied. More recently, IBE (Isopropanol-Butanol-Ethanol) fermentation, producing a mixture of isopropanol, butanol, and ethanol and also carried out by microorganisms belonging to the genus Clostridium, has been the subject of numerous studies.

[0007] Regarding the fermentation method used in this type of process, batch production remains the conventional method for ABE and IBE fermentations, despite the low productivity shown for this type of process, in the range 0.1-0.7 g / Lh (see, for example, Jones DT, Woods DR, 1986, Acetone-Butanol Fermentation Revisited. Microbiol. Rew., 50 (4), 484-524 or Table 16.6 Lopez-contreras A. et al chapter book 16, Bioalcohol Production: Biochemical Conversion of Lignocellulosic Biomass, 2010). But these productivities remain too low to consider an economically viable industrial process.

[0008] A continuous process with cells suspended in a homogeneous reactor can also be considered. However, productivity is also quite low and can hardly be significantly increased. A technical problem is the concentration of cells in the fermentation medium, mainly controlled by the dilution rate applied in the process. This cannot be high to avoid cell washout in the fermenter. For these reasons, in recent years, there has been a strong interest in methods aimed at high retention of microbial biomass. Two methods exist: "cell immobilization" and cell "recycling" with retention by means of filter membranes. The present invention will mainly focus on the cell immobilization technique.

[0009] In the first case of adsorption on solid support, the physical adsorption of microorganisms onto a solid surface occurs by electrostatic forces, van der Waals forces, or by covalent bonding between the bacterial cell membrane and the support. Since there is no physical barrier between the microbial biofilm and the fermentation solution, different equilibria between the rates of adsorption, cell detachment and recolonization of the solid support can be achieved depending on the solid support, the implementation and the operating conditions. It should be noted that immobilized cells are typically surrounded by polysaccharides excreted by the microorganisms (EPS: "Extracellular Polymeric Substances" in English terminology), and exhibit different growth and bioactivity regimes than those obtained when the cells are in suspension (see, for example, Halan B., Buehler K., Schmid A., 2012, Biofilms as living catalysts in continuous chemical syntheses, Trends in biotechnol., 30 (9), 453-465).

[0010] Several solid supports have been tested and found to be interesting according to the literature for ABE-type fermentation, including charcoal (see, for example, Qureshi N., Maddox IS, 1987, Continuous solvent production from whey permeate using cells of Clostridium acetobutylicum immobilized by adsorption onto bonechar, Enzyme Microb. Technol., (9), 668-371), bricks (see, for example, Qureshi N., Schripsema J., Lienhardt J., Blaschek HP, 2000, Continuous solvent production by Clostridium beijerinckii BA101 immobilized by adsorption onto brick, World Journal of Microbiology & Biotechnology, (16), 377-382), and paper pulp (see, for example, Survase SA, van Heiningen A., Granstrôm T., 2012, Continuous bio-catalytic conversion of sugar mixture to acetone-butanol-ethanol by immobilized Clostridium acetobutylicum DSM 792, Appl. Microbiol. Biotechnol., (93), 2309-2316).But such solid supports are not synthetic, and can generate reproducibility problems for fermentation processes.

[0011] In the second case, that of immobilization by confinement, of the encapsulation type, the microorganisms are introduced inside a porous matrix, so as to prevent their diffusion towards the external environment, while allowing the transfer of material for the support and nutrients, as well as for the reaction products. Examples of supports using the encapsulation confinement technique include alginate beads (see, e.g., Mollah AH, Stuckey DC, 1993, Maximizing the production of acetone-butanol in alginate bead fluidized bed reactor using Clostridium acetobutylicum, J. Chem. Tech. Biotechnol., (56), 83-89), and k-carrageenan (see, e.g., Godia F., Howard I., Scott D., Davison BH, 1990, Use of immobilized microbial membrane fragments to remove oxygen and promote the acetone-butanol fermentation, Biotechnol. Prog., 1990, 210-213).Furthermore, patent FR-3 086670 has proposed a process in which at least part of the bacterial biomass is fixed in the fermentation reactor by adsorption in the form of a biofilm on a porous material based on polymeric foam, such as polyurethane foam. This high porosity provides a very large accessible surface area for microorganisms, and greatly promotes the formation of the biofilms sought to immobilize them. This material has proven particularly effective, allowing a continuous fermentation process, the foam allowing the bacteria to be fixed sufficiently, i.e. beyond the dilution rate causing cell washing. This material opens a new avenue for the production of IBEA-type mixtures, also providing access to continuous production by immobilizing the bacterial biomass.

[0012] However, its use is not without certain drawbacks. Thus, this high porosity makes its thorough cleaning complex, when the pores of the material are saturated / clogged by biofilms, even if an effective cleaning method has been proposed, in particular in patent FR- 3 086 553. In addition, the low density of these foams compared to the reaction liquid, essentially aqueous, with which it is present in the reactor, means that the foam blocks introduced into the reactor tend to "float", to rise in the upper part of the useful volume of the reactor: it is generally necessary to provide mechanical holding means in the reactor so that these foam blocks are well distributed throughout the useful volume of the reactor and remain correctly / entirely immersed in the reaction liquid. These may in particular be rigid or semi-rigid nets, grids, etc.to be fixed inside the reactor, which complicates the installation and removal of the foam blocks, even though the supports must be replaced, in whole or in part, regularly.

[0013] The invention then aims to improve continuous fermentation processes, of the type producing ABE or IBE alcohol mixtures, in particular to improve / simplify their implementation without sacrificing their performance or productivity.

[0014] Summary of the invention

[0015] The invention firstly relates to a process for producing alcohols, according to which a sugary fluid is introduced into a reaction section comprising supports on which microorganisms are immobilized, in order to produce by fermentation a must enriched in alcohols under the action of said microorganisms. According to this process, said supports comprise packings

[0016] - arranged loosely (preferably non-porous)

[0017] - or arranged in a structured manner (preferably porous or non-porous), called structured packings in the reaction section, said packings being such

[0018] - that they offer an accessible surface area of ​​between 50 and 1000 m 2 / m 3 useful volume of the reaction section,

[0019] - that they have an overall void rate of at least 70%,

[0020] - that they are made of metal, glass, ceramic, or based on polymer(s) capable of withstanding temperatures up to at least 80°C, or up to at least 100°C.

[0021] Preferably, the fillings according to the invention have an accessible surface area of ​​between 60 and 900 m 2 / m 3 , especially between 70 and 800 m 2 / m 3 , or between 100 and 700 m 2 / m 3 useful volume of the reaction section,

[0022] For the purposes of the invention, the term "reaction section" means a reactor or a set of reactors connected in parallel or in series. They may in particular be connected in series, by providing fluid connection means. It is of course possible to operate a plurality of reactors in parallel, and possibly to share the collection and treatment of the fermentation musts from each of the reactors. According to another embodiment of the invention, the reaction section comprises a series of n reactors fluidically connected in series with each other, and possibly at least one spare reactor. The support is then distributed between the n reactors in the form of n support portions.

[0023] It should also be noted that the supports according to the invention may also have coatings made of a different material (ceramic coating on metal or vice versa, for example). They may also have a particular surface treatment (roughness, channels, scratches, etc.) so as to encourage the attachment of microorganisms.

[0024] Structured-type supports are also of interest and can, if necessary, be cleaned between two production campaigns. Examples of known structured packings for applications in distillation columns are described in patent EP2134463. Structured packings are commercially available, notably from the company SULZER CHEMTECH.

[0025] For the sake of brevity, in the remainder of this text, the term reactor may be used, without specifying the number or configuration of the reactor(s).

[0026] Surprisingly, it turned out that choosing immobilization supports of this type, and not loose block polymer foams as previously recommended, and in bulk or in a structured manner, gave very good results, in several respects:

[0027] - on the one hand, the productivity of the micro-organisms thus immobilized is at least as good, or even better, than with very porous bulk supports of the foam type, even though the developed surface of these supports is much less than that of foams

[0028] - on the other hand, because these supports do not "float" (density close to or greater than that of the reaction medium, particularly water-based), it is much easier to maintain them in the desired position in the reaction section without having to provide mechanical fixing means, without having to mechanically constrain them to be completely immersed.

[0029] Finally, in the case of bulk media, it is possible to unload them easily, under the effect of gravity from the reactor to the outside by means of evacuation such as pipes, without risk of blockage / clogging at the bottom of the reactor or the outlet of the reactor or the pipes in question)

[0030] - finally, the fact that they are in bulk makes their use very easy, because they can adapt to any shape and size of the reaction section, you just have to adjust the quantity.

[0031] According to a first embodiment, the supports comprise (or are made of) structured, porous or non-porous linings. These may be single-pieces, also called monoliths, the dimensions of which (in particular the section) approach those of the reactor which they are to equip, possibly by superimposing several of them to have the required height. These may be monoliths of porous material, a metal foam for example, or monoliths of structured non-porous material, for example based on ceramic or polymer(s).

[0032] According to a second embodiment, the supports comprise non-porous loose fillings, which may in particular be based on polymer(s), be metallic or ceramic in nature.

[0033] Advantageously, in particular in the case of bulk packings from the reaction section, they can be discharged from the reaction section by gravity, at the end of production or during production, to replace them in whole or in part.

[0034] The packings are preferably devoid of mechanical means of support in the reaction section: their implementation is simpler than that of foams, without the need for a grid to keep them immersed or mesh / nets to distribute them over the entire height of the useful volume of the reaction section.

[0035] Advantageously, the packings may have a geometric shape comprising fins, in particular flat or spiral, grids, tubes or tube portions, rings or ring portions, solid or openwork. This geometric shape preferably develops a hollow structure delimited by solid or openwork walls, which offers both a large surface area accessible to microorganisms and easy flow of any fluid between the packings and through the packings.

[0036] According to one embodiment of the invention, these packings have an annular or tubular shape, and are in particular chosen from Raschig type, Ralu type or Pali type rings. These packings are commercially available from the companies RASCHIG GmbH and JAEGER PRODUCTS, Inc.

[0037] Preferably, the reaction section is filled with a volume VI of liquid and in that the packings and / or internals are immersed in at least 50%, in particular at least 60% or at least 70 or 80% of said volume VI.

[0038] The microorganisms are preferably immobilized on the supports at least partly in the form of biofilms.

[0039] Advantageously, the microorganisms belong to the genus Clostridium, in particular to the species chosen from Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium saccharobutylicum, Clostridium tyrobutyricum, Clostridium saccharoperbutylacetonicum, Clostridium butylicum, genetically modified or not, and in particular to the species Clostridium beijerinckii naturally producing isopropanol and / or Clostridium acetobutylicum genetically modified for the production of isopropanol.

[0040] According to one embodiment of the invention, the fermentation must is enriched relative to the sugar fluid in at least one of the following alcohols: isopropanol, butanol, ethanol and optionally in a solvent, in particular acetone.

[0041] The invention also relates to a fermentation reactor comprising microorganisms in order to produce from a sweet juice by fermentation a must enriched in alcohols under the action of said microorganisms, said microorganisms being immobilized at least in part in the form of biofilms on supports comprising linings

[0042] - arranged loosely (preferably in non-porous material)

[0043] - or arranged in a structured manner (preferably in porous or non-porous material), called structured packings in the reaction section, said packings being such that - they offer an accessible surface area of ​​between 50 and 1000 m 2 / m 3of useful volume of the reactor,

[0044] - that they have an overall void rate of at least 70%,

[0045] - that they are made of metal, glass, ceramic or plastic material(s) capable of withstanding temperatures of at least 80°C, or at least 100°C,

[0046] - that they are immersed in a liquid reaction medium contained in the reactor without mechanical means of holding them in said reactor.

[0047] Advantageously, this fermentation reactor is a fixed bed or fluidized bed reactor, preferably operating continuously.

[0048] List of figures

[0049] [Fig 1]

[0050] Figure 1 represents a first series of fillings that can be used in the implementation of the invention.

[0051] [Fig 2]

[0052] Figure 2 represents a second series of fillings that can be used in the implementation of the invention.

[0053] [Fig 3]

[0054] Figure 3 represents a third series of fillings that can be used in the implementation of the invention.

[0055] [Fig 4]

[0056] Figure 4 represents a fourth series of fillings usable in the implementation of the invention.

[0057] [Fig 5]

[0058] Figure 5 represents a graph of the evolution of the volume productivity as a function of time of a fermentation reactor according to comparative examples and according to the invention, with the time in hours on the abscissa, and the volume productivity expressed in kg of solvents produced / m on the ordinate. 3 of reactor / hour.

[0059] [Fig 6] Figure 6 represents a packing in top view according to an example described later, Figure 6.a represents it before use, and Figure 6b after use and deposition of biofilm.

[0060] [Fig 7]

[0061] Figure 7 represents a packing in top view according to an example described later, Figure 7a representing it before use, and Figure 7b after use and deposition of biofilm.

[0062] Description of the embodiments

[0063] The invention will be described in more detail using non-limiting examples. It recommends choosing biofilm supports in bioreactors, which are packings or internals, which were previously used for other purposes, in particular in distillation columns. They are characterized by an accessible surface area of ​​between 50 and 2000 m 2 / m 3 useful volume of the reaction section, an overall void rate of at least 70%, and by a constituent material made of metal, glass, ceramic, or based on polymer(s) capable of withstanding temperatures of at least 100°C.

[0064] These fillings / internals have proven to be effective, although not porous like a foam structure: they in fact meet a certain number of criteria which lead to appropriate growth of micro-organism biofilms. Indeed:

[0065] - they promote the adhesion of cells to their surface, they are not toxic to microorganisms,

[0066] - they have good mechanical resistance to hydrodynamic constraints

[0067] - they are available for use (and re-use) on an industrial scale at a reasonable cost compared to the value of the products formed.

[0068] They were tested in a fermentation reactor fed by a sugar fluid and from which a flow of fermentation must is drawn. In one variant, the reactor is fed from the top of the reactor, and the must is drawn from the bottom of the reactor: the flow in the reactor is called descending ("downflow" in English). In another variant, it is the opposite, we then speak of rising flow ("upflow" in English) in the reactor.

[0069] The sugar fluid comprises C5 (i.e. comprising 5 carbons) and / or C6 (i.e. comprising 6 carbons) sugars in the aqueous phase. The fermentation must (which can also be called fermentation juice or wine or fermentation products) is enriched in isopropanol, butanol, ethanol and acetone compared to the sugar fluid by conversion of the sugars into alcohol / solvent under the action of a microorganism deposited on the solid supports contained in the reactor. The microorganism colonizing the support is of the Clostridium type. The supports are packings / internals which play the role of a moving bed in the reactor in the form of elements arranged in bulk in the reactor: the reactor delimits a useful volume, which is the maximum volume which can contain the reaction medium. The packings / internals fill at least 50% of the useful volume in question, and are intended to be preferably entirely submerged during the production period.They have a density greater than that of the reaction medium, and are placed in the reactor (and discharged from it) by gravity or removed at the end of the test or cleaned in place. For the bulk case, they can be loaded in the upper part of the reactor and discharged in the lower part of the reactor.

[0070] The fermentation step in the fermentation reactor can be carried out at a temperature between 28°C and 40°C, preferably between 30°C and 37°C, so that the fermentation must includes products of the IBEA type fermentation reaction, for example isopropanol, which is then discharged from the reactor.

[0071] Then, the fermentation must is treated, in particular with one or more successive stages of separation type (not detailed here): it is for example introduced into a separation unit allowing the separation and extraction of the compounds of interest from the fermentation must, the latter being evacuated to be transformed or recovered as is. The residues from the separation, commonly called vinasse, are evacuated from the separation unit, they are generally composed of water as well as any liquid or solid product not converted or not extracted during the previous stages. The separation unit can implement one or more distillations, and possibly a separation of solid and / or suspended matter for example by centrifugation, decantation and / or filtration.

[0072] Let's return to the fermentation reactor: the supports are therefore used to immobilize the microorganisms (hereinafter also referred to as bacteria or bacterial biomass), and to promote their growth by adsorption on these supports in the fermentation reactor. This immobilization / adsorption step can also be carried out indirectly, in an optional secondary tank, operating for example in "in stream" mode relative to the fermentation reactor: The solid supports, once loaded with bacterial biomass, can then be introduced into the fermentation reactor.

[0073] Below is a more detailed description of the sugar fluid, the biomass fixed on the supports, and on the supports themselves and the operating conditions of the fermentation reaction:

[0074] The sweet fluid

[0075] According to one or more embodiments, the sugar fluid comprises an aqueous solution of sugars derived from C5 and / or C6 lignocellulose, and / or sugars derived from sacchariferous plants (for example glucose, fructose and sucrose), and / or sugars derived from starchy plants (for example dextrins, maltose and other oligomers, or even starch). According to one or more embodiments, the aqueous solution of C5 and / or C6 sugars comes from the processing of a renewable source. According to one or more embodiments, the renewable source is of the lignocellulosic biomass type which may in particular comprise woody substrates (for example hardwoods and softwoods), agricultural by-products (for example straw) or those from industries generating lignocellulosic waste (from agri-food industries, paper mills).The renewable source can also come from sugar plants, such as sugar beet and sugar cane, or starchy plants such as corn and wheat. The aqueous solution of C5 and / or C6 sugars can also come from a mixture of different renewable sources.

[0076] The biomass produced by the strain belonging to the genus Clostridium

[0077] The bacterial biomass is mainly adsorbed in the form of a biofilm on a solid support. Preferably, the bacteria are strains belonging to the species Clostridium beijerinckii and / or Clostridium acetobutylicum. The bacteria used in the process may be genetically modified or non-genetically modified strains that naturally produce isopropanol and / or naturally acetone-producing Clostridium strains that have been genetically modified to produce isopropanol. In the following examples, it is Clostridium beijerinckii DSM 6423.

[0078] The solid support

[0079] - According to comparative example 1, the solid support is in the form of a PU polyurethane foam. It has:

[0080] - volume cavities (i.e., pores or cells) whose equivalent sphere diameter is between 0.1 and 5 mm, preferably between 0.25 mm and 1.1 mm, preferably between 0.55 and 0.99 mm, and / or

[0081] - an apparent density (i.e., mass over apparent volume) measured in air of between 10 and 90 g / L, preferably between 10 and 80 g / L, preferably between 15 and 45 g / L, such as between 20 and 45 g / L or between 25 and 45 g / L.

[0082] This PU foam comes in the form of small loose parallelepipeds measuring 20 mm x 20 mm x 7 mm. These blocks are fixed by a net, a container with mesh forming a cylinder whose diameter is less than or substantially equal to the internal diameter of the fermentation reactor. It is possible that gas releases may tend to make the foam blocks rise: we therefore provide at least one perforated plate, a simple net or at least a grid in the upper part of the useful volume of the reactor may be sufficient to keep them immersed in the fermentation reactor.

[0083] - According to non-limiting embodiments of the invention, they are chosen in particular from those shown in Figures 1 to 3:

[0084] - from left to right, the first series (figures 1a to 1g) represents a Raschig ring, a PAH type metal ring, a PAU type plastic ring, a metal VSP ring (internal arc ring), a plastic VSP ring and a Top-Pak type metal element,

[0085] - from left to right, the second series (figures 2a to 2g) represents a Bialecki metal ring, a plastic NorPac (NSW) ring, another plastic NorPak (dhh) ring, a Tellerette metal collar, a Dtnpac plastic ring, another Dtnpac plastic ring, a Rpac ceramic ring and a McPac metal ring,

[0086] - from left to right, the third series (figures 3a to 3g) represents a portion of an openwork ring in Hilflow saddle plastic, another portion of a solid ring in Intalox plastic, a portion of a solid ring in Italox ceramic, another portion of a ring portion called Super saddle, a portion of a metal ring called Intalox saddle, a Ralu plastic ring, a Ralu-flow plastic ring

[0087] - from left to right, the fourth series (figures 4a to 4g) represents a Hilflow plastic ring, a Hilflow ceramic ring, a Hilflow metal ring, a Hilflow Super plastic ring, a Hackette plastic cage element, an Envipac plastic spherical cage element, a Raschig Super metal ring. These packings are commercially available from the above-mentioned companies.

[0088] We see that these packings all have in common a shape delimited by solid or open walls. We thus have hollow packings, with a closed or open outer envelope, substantially at least partially cylindrical or toric, or at least partially spherical, or in the form of a crown or radial fins, which offer a large accessible surface and a large capacity for fluid flow through them. They can take the form of cages with bars, have ribs and possibly solid or openwork internal partitions, crosspieces for example, which make it possible both to increase the accessible surface and to stiffen the packing.

[0089] They can be made of metal, plastic or ceramic. Their dimensions can generally range between 0.5 and 5 cm.

[0090] Materials, especially plastic ones, should preferably be thermally sterilizable, i.e. able to withstand temperatures of at least 80 or 100°C without degrading (in the cleaning process between two production runs, for example). We also see that they are not porous, unrelated to the porosity of the PU foam used in the comparative examples.

[0091] The preferred operating conditions according to the invention, and used in the examples

[0092] - The temperature in the reactor(s) is between 28°C and 40°C, preferably between 30°C and 37°C, in particular here 36°C

[0093] - The pressure in the reactor(s) is approximately atmospheric pressure (plus the height of water in the reactor(s))

[0094] - The concentration of sugar fluid is between 90 and 35 g / L, preferably between 30 and 70 g / L, and in particular here 44 g / L (aqueous medium)

[0095] - The reactor is operated continuously, with imposed dilution rates, it has a recirculation loop and / or stirring means.

[0096] - The targeted fermentation yield is between 0.28 and 0.34 g of IBEA product / g of sugar used, and in particular here 0.31 g of IBEA product / g of sugar used.

[0097] - The microorganism is Clostridium beijerinckii DSM 6423

[0098] - The porous support of the comparative examples is PU foam in the form of small bulk parallelepipeds with dimensions of 20 mm x 20 mm x 7 mm, the porosity of which is defined as follows: a so-called "open" porosity (so that the liquid of the reaction medium can pass through it) of 40 PPI (pore per inch), a specific density of 40 kg / m 3 , an accessible surface area of ​​around 4000 m2 / m3 and a void rate greater than 90%, commercial reference “ISP 4452 PHH (ISP GmbH & Co)

[0099] - For all the following examples, we consider a fermentation reactor defining a useful volume of 200 to 250 mL each.

[0100] Examples

[0101] Comparative example 1 It is made with the PU foam blocks mentioned above as support. The blocks are arranged loosely in the reactor, so as to fill 50% of its useful volume. They are kept immersed in the reaction medium in a metal cage.

[0102] Example 2

[0103] It is made with a 3D printed monolithic structure as support from polylactic acid (reference UNIV1126 commercially available from the company VOLUMIC ULTRA). The support consists of a stack of several monoliths arranged in the reactor so as to fill approximately 80% of the volume (without taking into account the channels). These supports do not float, unlike the PU blocks of the comparative examples, so no mechanical means such as cages or grids are provided to keep them submerged. This is a structured type packing, a monolith of which is shown in Figures 6a and 6b: it is in the form of a cylindrical envelope material and equipped with internal crosspieces which partition the cylindrical section into cylindrical cells of square section here.

[0104] Example 3

[0105] It is made with metal foam discs as support whose diameter is close to the diameter of the reactor so that the liquid flows preferentially through the metal foam. The support consists of a stack of metal foam discs. These supports do not float, unlike the PU blocks of the comparative examples, so no mechanical means such as cages or grids are provided to keep them submerged. It is a structured type packing. The metal foam discs are made of Nickel-Chromium alloy. Its reference is RCM-NC1116.20, commercially available from the company Recemat BV. The monolith is arranged so as to fill approximately 56% of the reactor volume (without taking into account the pores).

[0106] Example 4

[0107] It is made with a bulk-type support comprising plastic objects (non-porous) measuring 12 x 7 mm. These supports have a density close to that of water. Depending on the conditions, less than 30% of the volume of the supports floats on the liquid surface. Therefore, no mechanical means such as cages or grids are provided to keep them submerged. The bulk supports are arranged so as to fill approximately 85% of the reactor volume (without taking into account the holes in the support).

[0108] One of these supports is shown in Figure 1h: it is a ring with a serrated exterior surface and two internal partitions which cross perpendicularly to each other in the center of the ring, to define four cells, each defining a quarter of a cylinder.

[0109] The table below compares examples 1 to 4, once the tests have been launched, all in the same type of reactor and under the same operating conditions: Vu designates the useful volume of the reactor, P the productivity

[0110] Table 1

[0111] The Support Surface / Seen (m 2 / m 3 of reactor) actual in the Vu indicated in this table corresponds to the accessible surface in m 2 / m 3 of useful volume of the reaction section mentioned above.

[0112] It can be deduced from this table that examples 2, 3, 4 according to the invention, using structured and loose type fillings, make it possible to obtain results at least as good, or very close to those obtained with the comparative example which uses loose PU foam blocks nevertheless having an accessible surface in m 2 / m 3useful volume of the reaction section) much higher, which is surprising and goes against what one could expect.

[0113] Thus, the time to reach a productivity P threshold of 1 kg / m 3 / h is of the same type, which means that the ramp-up of the process is not extended, or not significantly extended, with the invention, which is important.

[0114] Furthermore, the volume productivity (average plateau production) after 500 hours of fermentation of the examples according to the invention is very close to, or even better than, that of the examples according to the invention: once a stable production regime has been obtained, the production yields with the supports according to the invention are similar to those with the supports of the comparative examples.

[0115] This means that abandoning bulk polymer foam block supports in favor of structured filling type supports (porous or non-porous) or non-porous bulk filling type supports, allows the process to maintain all its performance, and therefore that these supports promote the formation of biofilms in the same way as bulk polymer foams, which was not a given.

[0116] Figure 5 confirms the conclusions drawn from Table 1: The graph represents on the abscissa the production time in hours and on the ordinate the volume productivity in kg / m3 / hour for the 4 examples, curves C1 to C4 corresponding respectively to examples 1 to 4. These supports according to the invention also have the advantage of being easier to design, to maintain in palace in the reactor and to unload (by gravity), and easier to clean between two production campaigns for non-porous packing materials (no porosity makes cleaning easier / faster). For structured porous materials, cleaning can be done at the end of the production campaign once the materials have been unloaded.

Claims

Claims 1 Process for the production of alcohols, according to which a sugary fluid is introduced into a reaction section comprising supports on which microorganisms are immobilized, in order to produce by fermentation a must enriched in alcohols under the action of said microorganisms, characterized in that said supports comprise structured packings or packings arranged in bulk in the reaction section, said packings being such - that they offer an accessible surface area of ​​between 50 and 1000 m 2 / m 3 useful volume of the reaction section, that they have an overall void rate of at least 70%, - that they are made of metal, glass, ceramic, or based on polymer(s) capable of withstanding temperatures up to at least 80°C, or up to at least 100°C. 2 Method according to the preceding claim, characterized in that the supports comprise structured, porous or non-porous fillings.

3. Method according to claim 1, characterized in that the supports comprise non-porous loose fillings.

4. Method according to one of the preceding claims, characterized in that the packings are unloaded from the reaction section by gravity, at the end of production or during production, to replace them in whole or in part.

5. Method according to one of the preceding claims, characterized in that the packings are devoid of mechanical holding means in the reaction section.

6. Method according to one of the preceding claims, characterized in that the packings have a geometric shape comprising fins, in particular flat or spiral, grids, tubes or tube portions, rings or ring portions.

7. Method according to one of the preceding claims, characterized in that the packings have an annular or tubular shape, and are in particular chosen from Raschig type, Ralu type or Pali type rings.

8. Method according to one of the preceding claims, characterized in that the fillings offer an accessible surface area of ​​between 60 and 900 m 2 / m 3 , especially between 70 and 800 m 2 / m 3 , or between 100 and 700 m 2 / m 3 useful volume of the reaction section, 9. Method according to one of the preceding claims, characterized in that the reaction section is filled with a volume VI of liquid and in that the packings are immersed in at least 50%, in particular at least 60% or at least 70 or 80% of said volume VI.

10. Method according to one of the preceding claims, characterized in that the microorganisms are immobilized on the supports at least partly in the form of biofilms.

11. Method according to one of the preceding claims, characterized in that the microorganisms belong to the genus Clostridium, in particular to the species chosen from Clostridium acetobutylicum, Clostridium beijerinckii, Clostridium saccharobutylicum, Clostridium tyrobutyricum, Clostridium saccharoperbutylacetonicum, Clostridium butylicum, genetically modified or not, and in particular to the species Clostridium beijerinckii naturally producing isopropanol and / or Clostridium acetobutylicum genetically modified for the production of isopropanol.

12. Method according to one of the preceding claims, characterized in that the fermentation must is enriched relative to the sugar fluid in at least one of the following alcohols: isopropanol, butanol, ethanol and optionally in a solvent, in particular acetone.

13. Fermentation reactor comprising microorganisms in order to produce from a sweet juice by fermentation a must enriched in alcohols under the action of said microorganisms, said microorganisms being immobilized at least in part in the form of biofilms on supports comprising structured packings or arranged in bulk in said reactor, said packings being such - that they offer an accessible surface area of ​​between 50 and 1000 m 2 / m 3 of useful volume of the reactor, - that they have an overall void rate of at least 70%, - that they are made of metal, glass, ceramic or plastic material(s) capable of withstanding temperatures of at least 80°C, or at least 100°C, - that they are immersed in a liquid reaction medium contained in said reactor, without mechanical means of holding them in said reactor.

14. Fermentation reactor according to the preceding claim, characterized in that it is a fixed bed or fluidized bed reactor, operating continuously.

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