A process for producing alcohols using a support on which microorganisms are immobilized.

Abstract

The present invention relates to a process for producing alcohols, in 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. The supports comprise structured packings or packings arranged in bulk within the reaction section. These packings are such that they offer an accessible surface area of ​​between 50 and 1000 m² / m³ of the effective volume of the reaction section; they have an overall void ratio of at least 70%; and they are made of metal, glass, ceramic, or polymer(s) capable of withstanding temperatures up to at least 80°C. Figure for the abstract: Fig. 6

Description

Title of the invention: Process for producing alcohols with a support on which microorganisms are immobilized. Technical field

[0001] The present invention relates to a process for producing alcohols by fermentation of a sugary fluid. Previous technique

[0002] In order to meet the challenges of the energy transition, much research is being carried out to develop so-called "green" processes, allowing access to chemical intermediates in an alternative way to oil refining and / or petrochemicals.

[0003] Alcohols produced by 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 extensively studied. More recently, IBE (Isopropanol-Butanol-Ethanol) fermentation, which produces a mixture of isopropanol, butanol, and ethanol and is also carried out by microorganisms belonging to the genus Clostridium, has been the subject of numerous studies.

[0004] 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 observed for this type of process, in the range of 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 16, Bioalcohol Production: Biochemical Conversion of Lignocellulosic Biomass, 2010). However, these productivities remain too low to consider an economically viable industrial process.

[0005] A continuous process with cells suspended in a homogeneous reactor can also be considered. However, productivity is also quite low and can hardly be increased significantly. A technical problem is the concentration of cells in the fermentation medium, mainly controlled by the dilution rate applied in the process. This rate cannot be high enough to avoid cell washout in the fermenter. For these reasons, in recent years, considerable interest has been shown in methods aimed at high retention of microbial biomass. Two means Existing methods include "cell immobilization" and cell "recycling" with retention using filter membranes. The present invention will focus primarily on the cell immobilization technique.

[0006] In the first case of adsorption onto a solid support, the physical adsorption of microorganisms onto a solid surface occurs through electrostatic forces, van der Waals forces, or 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" according to Anglo-Saxon 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 synthèses, Trends in biotechnol., 30 (9), 453-465). .

[0007] Several solid supports have been tested and found to be promising 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).However, such solid supports are not synthetic and can generate reproducibility problems for fermentation processes.

[0008] 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 to the external environment, while allowing the transfer of matter for the support and nutrients, as well as for the reaction products. Examples of supports using the confinement technique by encapsulation include alginate beads (see, for example, 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 beads (see, for example, Godia F., Howard I., Scott D., Davison BH, 1990, Use of immobilized microbial membrane fragments to remove oxygen and favor the acetone-butanol fermentation, Biotechnol. Prog., 1990, 210-213).

[0009] Furthermore, patent FR-3 086 670 proposed a process in which at least a portion of the bacterial biomass is fixed in the fermentation reactor by adsorption in the form of a biofilm onto 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 desired biofilms to immobilize them. This material has proven particularly effective, enabling a continuous fermentation process, as the foam allows for sufficient fixation of the bacteria, i.e., beyond the dilution rate that causes cell washing. This material opens a new avenue for the production of IBEA-type mixtures, also providing access to continuous production through the immobilization of bacterial biomass.

[0010] However, its use is not without certain drawbacks. For example, its high porosity makes thorough cleaning complex when the material's pores are saturated / clogged by biofilms, even though an effective cleaning method has been proposed, notably in French patent FR-3 086 553. Furthermore, the low density of these foams compared to the essentially aqueous reaction liquid with which they are mixed in the reactor means that the foam blocks introduced into the reactor tend to "float," rising to the top of the reactor's usable volume. It is generally necessary to provide mechanical means of retention within the reactor to ensure that these foam blocks are evenly distributed throughout the reactor's usable volume and remain properly / fully immersed in the reaction liquid. These means may include 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 need to be replaced, in whole or in part, regularly.

[0011] The invention then aims to improve continuous fermentation processes, from type of those producing ABE or IBE alcohol mixtures, in particular to improve / simplify their implementation without sacrificing their performance or productivity. Summary of the invention

[0012] The invention relates firstly 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 fillings - arranged loose (preferably non-porous) - or arranged in a structured manner (preferably porous or non-porous), known as structured fillings

[0013] in the reaction section, said packings being such - that they offer an accessible surface area of ​​between 50 and 1000 m2 / m3 of usable volume of the reaction section, - that they have an overall emptiness rate of at least 70%, - that they are made of metal, glass, ceramic, or polymer(s) that can withstand temperatures up to at least 80°C, or up to at least 100°C.

[0014] Preferably, the packings according to the invention have an accessible surface area of ​​between 60 and 900 m2 / m3, in particular between 70 and 800 m2 / m3, or even between 100 and 700 m2 / m3 of useful volume of the reaction section,

[0015] For the purposes of this invention, "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 fluidic connection means. It is of course possible to operate a plurality of reactors in parallel in this way, and potentially to pool the collection and processing of the fermenting 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, and optionally at least one spare reactor. The support is then distributed among the n reactors in the form of n support portions.

[0016] It should also be noted that the supports according to the invention may also have coatings 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 promote the adhesion of microorganisms.

[0017] Structured packing materials are also of interest and can, if necessary, be cleaned between production runs. Examples of structured packing materials known for distillation column applications are described in patent EP2134463. Structured packing materials are commercially available, notably from SULZER CHEMTECH.

[0018] 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).

[0019] Surprisingly, it turned out that choosing immobilization supports of this type, rather than bulk polymer block foams as previously recommended, whether in bulk or structured form, gave very good results in several respects: - On the one hand, the productivity of the microorganisms thus immobilized is at least as good, or even better, than with very porous bulk supports such as foam, even though the surface area of ​​these supports is much smaller than that of the mosses - on the other hand, because these supports do not "float" (density close to or greater than that of the reaction medium, especially water-based), it is much easier to maintain them in the desired position in the reaction section without having to provide mechanical means of fixing, without having to mechanically constrain them to be completely immersed.

[0020] Finally, in the case of bulk-type supports, 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 at the outlet of the reactor or the pipes in question) - Finally, the fact that they are in bulk makes them very easy to use, as they can adapt to any shape and size of the reaction section, you just need to adjust the quantity.

[0021] According to a first embodiment, the supports comprise (or are made of) structured fillings, porous or non-porous. These may be monoliths, also called single blocks, whose dimensions (in particular the cross-section) approach those of the reactor they are to equip, possibly by stacking several of them to obtain the required height. They may be monoliths of porous material, such as metallic foam, or monoliths of structured non-porous material, for example, ceramic or polymer-based.

[0022] According to a second embodiment, the supports comprise non-porous loose fillings, which may in particular be polymer-based, metallic or ceramic in nature.

[0023] Advantageously, particularly in the case of bulk packings of the reaction section, they can be unloaded from the reaction section by gravity, at the end of production or during production, to replace them in whole or in part.

[0024] The packings are preferably without mechanical means of retention in the reaction section: their implementation is simpler than that of foams, without the need for a grid to keep them immersed or meshes / nets to distribute them over the entire height of the useful volume of the reaction section.

[0025] Advantageously, the packings may have a geometric shape comprising fins, in particular flat or spiral, grids, tubes or portions of tubes, rings or portions of rings, solid or perforated. This geometric shape preferably develops a hollow structure delimited by solid or perforated walls, which offers both a large surface area accessible to microorganisms and easy flow of any fluid between and through the packings.

[0026] According to one embodiment of the invention, these packings have an annular or tubular shape, and are in particular selected from Raschig-type rings, of type Ralu or Pall type. These fillings are commercially available from RASCHIG GmbH and JAEGER PRODUCTS, Inc.

[0027] 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.

[0028] Microorganisms are preferably immobilized on the supports at least partly in the form of biofilms.

[0029] Advantageously, the microorganisms belong to the genus Clostridium, in particular to species selected 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.

[0030] According to one embodiment of the invention, the fermenting must is enriched with respect to the sugary fluid in at least one of the following alcohols: isopropanol, butanol, ethanol and optionally in a solvent, in particular acetone.

[0031] The invention also relates to a fermentation reactor comprising microorganisms for producing, from a sugary juice by fermentation, a must enriched in alcohols under the action of said microorganisms, said microorganisms being immobilized at least partially in the form of biofilms on supports comprising fillings - arranged loose (preferably in non-porous material) - or arranged in a structured manner (preferably in porous or non-porous material), known as structured fillings

[0032] in the reaction section, said packings being such - that they offer an accessible surface area of ​​between 50 and 1000 m2 / m3 of usable reactor volume, - that they have an overall emptiness rate of at least 70%, - that they are made of metal, glass, ceramic or plastic material(s) capable of withstanding temperatures up to at least 80°C, or up to at least 100°C, - that they are immersed in a liquid reaction medium contained in the reactor without mechanical means of retention in said reactor.

[0033] Advantageously, this fermentation reactor is a fixed bed or fluidized bed reactor, preferably operating continuously. List of figures

[0034] [Fig.1] Figure 1 represents a first series of fillings usable in the installation work of invention. [Fig.2] Figure [Fig. 2] represents a second series of fillings that can be used in the implementation of the invention. [Fig.3] Figure 3 represents a third series of fillings that can be used in the implementation of the invention. [Fig.4] Figure 4 represents a fourth series of fillings that can be used in the implementation of the invention. [Fig. 5] Figure 5 represents a graph of the evolution of the volumetric productivity as a function of time of a fermentation reactor according to comparative examples and according to the invention, with time in hours on the abscissa and volumetric productivity expressed in kg solvents produced / m3 of reactor / hour on the ordinate. [Fig.6] Figure 6 represents a top view of a filling according to an example described later, Figure 6a represents it before use, and Figure 6b after use and biofilm deposition. [Fig.7] Figure 7 represents a top view of a filling according to an example described later, figure 7a showing it before use, and figure 7b after use and biofilm deposition. Description of the implementation methods

[0035] The invention will be described in more detail with the aid of non-limiting examples. It proposes the selection of biofilm supports in bioreactors, which are packings or internals, that were previously used for other purposes, particularly in distillation columns. They are characterized by an accessible surface area of ​​between 50 and 2000 m² / m³ of the effective volume of the reaction section, an overall void ratio of at least 70%, and by a constituent material made of metal, glass, ceramic, or polymer(s) that can withstand temperatures of at least 100°C.

[0036] These fillings / internals have proven effective, although not porous like a foam structure: they meet a number of criteria that lead to the appropriate growth of microbial biofilms. Specifically: - they promote cell adhesion to their surface, and they are not toxic to microorganisms. - they exhibit good mechanical resistance to hydrodynamic stresses namics - they are available, usable (and reusable) on an industrial scale at a reasonable cost compared to the value of the products formed.

[0037] They were tested in a fermentation reactor fed with a sugary fluid and from which a flow of fermenting wort is drawn off. In one variant, the reactor is fed into the upper part of the reactor, and the wort is extracted from the lower part of the reactor: the flow in the reactor is said to be downward ("downflow"). In another variant, it is the opposite, and this is referred to as upward ("upflow") in the reactor.

[0038] The sugar fluid comprises C5 (i.e., containing 5 carbons) and / or C6 (i.e., containing 6 carbons) sugars in the aqueous phase. The fermenting must (which can also be called fermenting juice, wine, or fermenting products) is enriched in isopropanol, butanol, ethanol, and acetone compared to the sugar fluid by the conversion of 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.

[0039] The supports are packings / intemes that act as a moving bed in the reactor, in the form of elements arranged loose within the reactor. The reactor defines a usable volume, which is the maximum volume that can contain the reaction medium. The packings / intemes fill at least 50% of this usable volume and are preferably intended to be fully immersed during the production period. They have a density greater than that of the reaction medium and are placed in the reactor (and unloaded from it) by gravity, removed at the end of the test, or cleaned in place. In the case of loose packing, they can be loaded into the upper part of the reactor and unloaded into the lower part.

[0040] 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 fermenting must includes products of the IBEA type fermentation reaction, for example isopropanol, which is then removed from the reactor.

[0041] Next, the fermenting must is processed, notably with one or more successive separation steps (not detailed here): for example, it is introduced into a separation unit that separates and extracts the compounds of interest from the fermenting must, which are then removed for further processing or valorization as is. The residues from the separation, commonly called vinasse, are removed from the separation unit; they generally consist of water as well as any liquid or solid product not converted or extracted during the preceding steps. The separation unit may implement one or more distillations, and possibly a separation of solid and / or suspended matter, for example by centrifugation, de- cantation and / or filtration.

[0042] Returning to the fermentation reactor: the supports serve to immobilize the microorganisms (hereinafter also referred to as bacteria or bacterial biomass) and to promote their growth by adsorption onto these supports in the fermentation reactor. This immobilization / adsorption step can also be carried out indirectly, in an optional secondary reservoir, operating, for example, in "in-stream" mode with respect to the fermentation reactor: The solid supports, once loaded with bacterial biomass, can then be introduced into the fermentation reactor.

[0043] The following is a more detailed description of the sugary fluid, the biomass fixed on the supports, and on the supports themselves, and the operating conditions of the fermentation reaction:

[0044] The sugary fluid In one or more embodiments, the sugar fluid comprises an aqueous solution of C5 and / or C6 lignocellulose sugars, and / or sugars from sugar-producing plants (e.g., glucose, fructose, and sucrose), and / or sugars from starchy plants (e.g., dextrins, maltose, and other oligomers, or even starch). In one or more embodiments, the aqueous solution of C5 and / or C6 sugars is derived from the processing of a renewable source. In one or more embodiments, the renewable source is of the lignocellulosic biomass type, which may include, in particular, woody substrates (e.g., hardwoods and softwoods), agricultural by-products (e.g., straw), or by-products from industries that generate lignocellulosic waste (from the food processing and paper industries).The renewable source can also come from sugar crops, such as sugar beets and sugar cane, or from starchy crops like corn and wheat. The aqueous solution of C5 and / or C6 sugars can also come from a mixture of different renewable sources.

[0045] The biomass produced by the strain belonging to the genus Clostridium Bacterial biomass is primarily adsorbed as a biofilm onto 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 are naturally isopropanol-producing, and / or genetically modified Clostridium strains that are naturally acetone-producing and are made to produce isopropanol. In the following examples, the bacteria used are Clostridium beijerinckii DSM 6423.

[0046] The solid support - According to comparative example 1, the solid support is in the form of a polyurethane (PU) foam. It has: - volumetric cavities (i.e., pores or cells) with an equivalent sphere diameter 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 - an apparent density (Le., 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. This PU foam comes in the form of small, loose parallelepipeds measuring 20 mm x 20 mm x 7 mm. These blocks are secured by a net, a container with a mesh forming a cylinder whose diameter is less than or approximately equal to the internal diameter of the fermentation reactor. Gas emissions may cause the foam blocks to rise; therefore, at least a perforated plate, a simple net, or at least a grid in the upper part of the reactor's usable volume is sufficient to keep them submerged in the fermentation reactor.

[0047] - According to non-limiting embodiments of the invention, they are chosen particularly among those shown in figures 1 to 3: - From left to right, the first series (figures 1a to 1g) represents a Raschig ring, a PA11 type metal ring, a PA11 type plastic ring, a VSP (internal arc ring) metal ring, a VSP plastic ring and a Top-Pak type metal element, - From left to right, the second series (figures 2a to 2g) represents a Bialecki metal ring, a NorPac (NSW) plastic ring, another NorPak (dhh) plastic ring, a Tellerette metal collar, a Dtnpac plastic ring, another Dtnpac plastic ring, an Rpac ceramic ring and a McPac metal ring, - From left to right, the third series (figures 3a to 3g) represents a portion of a perforated ring made of Hilflow saddle plastic, another portion of a solid ring made of Intalox plastic, a portion of a solid ring made of Italox ceramic, another portion of a ring called "Super saddle", a portion of a metal ring called Intalox saddle, a Ralu plastic ring, and a Ralu-flow plastic ring. - 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-shaped element, an Envipac plastic spherical cage-shaped element, a Raschig Super metal ring. These fillings are notably available commercially from the aforementioned companies.

[0048] It can be seen that these fillings all share a common shape delimited by solid or perforated walls. Thus, we have hollow fillings with an outer casing closed or open, substantially at least partially cylindrical or toroidal, or at least partially spherical, or even in the shape of a crown or radial fins, which offer a large accessible surface area and a large capacity for fluid flow through them. They may take the form of cages with bars, have ribs and possibly solid or perforated internal partitions, crossbars for example, which both increase the accessible surface area and stiffen the lining.

[0049] They can be made of metal, plastic or ceramic.

[0050] Their dimensions can generally range between 0.5 and 5 cm.

[0051] The materials, particularly plastics, should preferably be thermally sterilizable, meaning they must be able to withstand temperatures of at least 80 or 100°C without degrading (for example, during the cleaning process between two production runs). They should also be non-porous, unlike the porosity of the PU foam used in the comparative examples.

[0052] The preferred operating conditions according to the invention, and used in the examples - The temperature in the reactor(s) is between 28°C and 40°C, preferably between 30°C and 37°C, specifically 36°C in this case. - The pressure in the reactor(s) is approximately atmospheric pressure (plus the height of water in the reactor(s)) - The concentration of sugary fluid is between 90 and 35 g / L, preferably between 30 and 70 g / L, and in particular here of 44 g / L (aqueous medium) - The reactor is operated continuously, with imposed dilution rates, it has a recirculation loop and / or means of agitation. - The target fermentation yield is between 0.28 and 0.34 g of IBEA product / g of sugar used, and in particular here of 0.31 g of IBEA product / g of sugar used. - The microorganism is Clostridium beijerinckii DSM 6423 - The porous support in the comparative examples is PU foam in the form of small loose parallelepipeds measuring 20 mm x 20 mm x 7 mm, whose porosity is defined as follows: an "open" porosity (so that the liquid of the reaction medium can pass through it) of 40 PPI (pores per inch), a specific density of 40 kg / m3, an accessible surface area of ​​around 4000 m2 / m3 and a void ratio greater than 90%, commercial reference "ISP 4452 PHH (ISP GmbH & Co) - For all the following examples, we consider a fermentation reactor defining a useful volume of 200 to 250 mL each. Examples

[0053] Comparative example 1 It is made using the PU foam blocks mentioned above as a support. The blocks are arranged loosely in the reactor, so as to fill 50% of its usable volume. They are kept immersed in the reaction medium in a metal cage.

[0054] Example 2 It is constructed using a monolithic structure 3D-printed from polylactic acid (reference UNIV1126, commercially available from VOLUMIC ULTRA). The support consists of a stack of several monoliths arranged within the reactor to fill approximately 80% of the volume (excluding channels). Unlike the PU blocks in the comparative examples, these supports do not float; therefore, no mechanical means such as cages or grids are used to keep them submerged. This is a structured packing, one monolith of which is shown in Figures 6a and 6b: it is a cylindrical shell material with internal cross-bracing that divides the cylindrical section into cylindrical cells with a square cross-section.

[0055] Example 3 It is constructed using metallic foam discs as a support, the diameter of which is close to that of the reactor, so that the liquid flows preferentially through the metallic foam. The support consists of a stack of metallic foam discs. Unlike the PU blocks in the comparative examples, these supports do not float; therefore, no mechanical means such as cages or grids are used to keep them submerged. This is a structured packing. The metallic foam discs are made of a nickel-chromium alloy. Their part number is RCM-NC1116.20, commercially available from Recemat BV. The monolith is positioned to fill approximately 56% of the reactor volume (not including pores).

[0056] Example 4 It is constructed using a bulk support system comprised of 12 x 7 mm non-porous plastic objects. These objects 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 planned to keep them submerged. The bulk supports are arranged to fill approximately 85% of the reactor volume (not including the holes in the support).

[0057] One of these supports is shown in figure Ih: it is a ring with serrations on its outer surface and having two internal partitions which cross each other perpendicularly at the center of the ring, to define four alveoli each defining a quarter of a cylinder.

[0058] 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 denotes the useful volume of the reactor, P the productivity

[0059] [Tables 1] Examples Comparative Ex. 1 Cl Ex. 2 C2 Ex. 3 C3 Ex. 4 C4 Support Type PU-L Monolithic 3D Loose Metallic Foam Time to reach P = 1 kg / m³ / h 432 480 430 506 Average production plateau (kg / m³ / h) after 500h 1.27 1.30 1.41 1.18 Maximum production time (hours) 839 935 820 554 Specific surface area of ​​support (m² / m³ of support) 3000-5000 60-100 500-1000 900 Actual support surface area / Vu (m² / m³ of reactor) in the Vu 1300-2200 60-100 200-450 700

[0060] The actual support surface / Vu (m2 / m3 of reactor) in the Vu indicated in this table corresponds to the accessible surface in m2 / m3 of useful volume of the reaction section mentioned above.

[0061] It can be deduced from this table that examples 2, 3, 4 according to the invention, using gar Structured and bulk-type mixtures allow us to obtain results at least as good, or very close to those obtained with the comparative example which uses bulk PU foam blocks, yet has a much larger accessible surface area (in m2 / m3 of useful volume of the reaction section), which is surprising and goes against what one could expect.

[0062] Thus, the time to reach a threshold productivity P of 1 kg / m3 / h is of the same type, which means that the ramp-up of the process is not lengthened, or not significantly lengthened, with the invention, which is important.

[0063] In addition, the volumetric productivity (average plateau production) after 500h 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 is obtained, the production yields with the supports according to the invention are analogous to those with the supports of the comparative examples.

[0064] This means that abandoning bulk polymer foam block supports in favor of structured packing type supports (porous or non-porous) or non-porous bulk packing type supports allows the process to retain 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.

[0065] Fig. 5 confirms the conclusions drawn from Table 1: The graph represents on the x-axis the production time in hours and on the y-axis the volumetric productivity in kg / m3 / hour for the 4 examples, the curves Cl to C4 corresponding respectively to examples 1 to 4.

[0066] These supports according to the invention also have the advantage of being easier to design, to maintain in place within the reactor, and to unload (by gravity), and easier to clean between two production runs with regard to non-porous packing materials (the lack of porosity makes cleaning easier / faster). With regard to structured porous materials, cleaning can be carried out at the end of the production run 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 packings structured or arranged in bulk in the reaction section, said packings being such that - they offer an accessible surface area of ​​between 50 and 1000 m2 / m3 of useful volume of the reaction section, - they have an overall void rate of at least 70%, - they are made of metal, glass, ceramic, or based on polymer(s) 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. A method according to claim 1, characterized in that the supports comprise non-porous loose packings.

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 Pall type rings.

8. Method according to one of the preceding claims, characterized in that the packings offer an accessible surface area of ​​between 60 and 900 m2 / m3, in particular between 70 and 800 m2 / m3, or between 100 and 700 m2 / m3 of 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 m2 / m3 of useful volume of the reactor, - they have an overall void rate of at least 70%, - they are made of metal, glass, ceramic or based on plastic material(s) withstanding temperatures up to at least 80°C, or up to at least 100°C, - they are immersed in a liquid reaction medium contained in said reactor, without mechanical means of maintenance 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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