METHOD FOR EXTRACTING ALCOHOLS FROM AN ALCOHOL-CONTAINING STARTING MIXTURE IN AQUEOUS PHASE

Description

Technical field

[0001] The present invention relates to a process for extracting, in particular, alcohols from a mixture comprising these alcohols in aqueous phase. It can be applied to the recovery of alcohols as products of a must obtained at the end of the fermentation of an aqueous solution of C5 and / or C6 sugars, as is known from the fermentation processes known as IBE type (Isopropanol / Butanol / Ethanol) or IBEA type (Isopropanol / Butanol / Ethanol / Acetone) carried out by “solventogenic” strains of the type Clostridium. Fermentation must is understood to mean an aqueous medium in which fermentation has taken place. C5 and / or C6 sugars are understood to mean oses having 5 or 6 carbons. The invention aims more specifically to extract isopropanol and butanol as the majority of valuable compounds. Prior art

[0002] 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.

[0003] 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 fermentation (Isopropanol - Butanol - Ethanol) producing a mixture of isopropanol, butanol and ethanol and also carried out by microorganisms belonging to the genus Clostridiumhas been the subject of fairly recent studies (Dos Santos Vieira et al Bioresour Technol; 2019 287:121425. doi:10.1016 / j.biortech.2019.121425 Acetone-free biobutanol production: Past and recent advances in the Isopropanol-Butanol-Ethanol (IBE) fermentation).

[0004] Regarding the fermentation method used in this type of process, batch production has been studied for ABE and IBE fermentations (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).

[0005] Continuous processes were also studied, initially with cells suspended in a homogeneous reactor. Improvements to continuous processes were then proposed by increasing the retention of microbial biomass in the bioreactor, in particular by using cells immobilized on a substrate, and / or by using cell recycling with retention by means of filter membranes (Vieira et al. 2019 Acetone-free biobutanol production: past and recent advances in the Isopropanol-Butanol-Ethanol (IBE) fermentation Biores. Technol., 287; 121425).

[0006] One of the obstacles encountered in the development of fermentation processes is the recovery step of highly diluted products in the fermentation must. This is a determining parameter in terms of the economic cost of these types of processes. In order to make this fermentation production process economically viable on a large scale, we first seek to optimize fermentation performance by maximizing the final titer as well as the volumetric productivity in the bioreactor where the fermentation is carried out. But once the fermentation conditions are optimized, for a given concentration of the molecules of interest in the water, it is economically important to seek to improve the energy consumption linked to the extraction phase of the molecules of interest from the fermentation must.

[0007] Several techniques exist to carry out this extraction, the most conventional uses one or more distillation columns in series, such as FR3053357, even if other techniques, such as stripping the must by a gas flow, have also been explored, for example in patent WO2018 / 001628.

[0008] The invention concerns extraction by distillation(s). Its aim is to improve this extraction. It seeks, more particularly, for a given concentration of the fermentation must, to reduce the energy consumption and / or the investment in equipment required for this extraction. Summary of the invention

[0009] The invention firstly relates to a process for extracting alcohols from an initial mixture comprising alcohols, including at least isopropanol and butanol, and optionally ethanol and / or acetone, in aqueous phase, said process comprising a series of separation operations, including: a separation by distillation carried out by at least one distillation column called isopropanol-butanol and aimed at separating said initial mixture or a mixture derived from said initial mixture at the top into a water-isopropanol azeotrope flow and at the bottom into a water-butanol azeotrope flow, a separation by distillation aimed at separating the water-butanol azeotrope flow into water and butanol, carried out by a hetero-azeotropic distillation system comprising at least one column called a water column recovering the water and at least one column called a butanol column recovering the butanol.

[0010] According to the invention, heat is transferred from the water-isopropanol azeotrope flow entering the condenser of the isopropanol-butanol distillation column to the flow entering the reboiler of the butanol column.

[0011] For the purposes of the invention, the expression "a mixture derived from said initial mixture" means a mixture which comes from the initial mixture, in particular after at least one separation treatment of the distillation type.

[0012] The condenser of the isopropanol-butanol distillation column and the reboiler of the butanol column can advantageously be integrated into the same (and unique) equipment.

[0013] The extraction according to the invention therefore comprises a succession of distillations, each distillation column used requiring an energy-intensive heat input. It is known that the columns are generally equipped with a reboiler at the bottom, which will be heated, generally by external steam, to raise the temperature of the liquid from the bottom of the column to the desired temperature and vaporize a portion of it, and thus generate a circulation of gas ("steam traffic") in the column, and a condenser at the top to lower the temperature of the top effluent and return it to the liquid phase, and thus generate the liquid traffic in the column. In the case of a succession of columns, as in the present case, the choice of the invention was to thermally integrate two distillation columns, by selecting those which were capable of doing so, namely: on the one hand the isopropanol-butanol column, whose head effluent comprising isopropanol could have a sufficient temperature to transfer heat, even if it meant modifying the operating conditions of its operation to reach this temperature, on the other hand the butanol column, needing a sufficient heat input to raise the load to a temperature appropriate for distillation, even if, again, it means adjusting it to allow this heat transfer, knowing that a heat transfer is technically only possible if the difference in temperatures to be reached between the "hot" effluent on the one hand and the "cold" load on the other hand is at least 5, and preferably at least 10°C.

[0014] And this heat transfer has proven to be very effective in reducing the energy consumption of the process as a whole, since the butanol column reboiler is heated at least partially, or even completely, by the condensation heat of the isopropanol-butanol column: the steam consumption previously required to heat the butanol column reboiler can be reduced or even eliminated. In terms of equipment, the gain is also significant, since the furnace-type heating means required to produce the steam needed to heat the reboiler can be undersized or even eliminated.

[0015] Preferably, the isopropanol-butanol distillation column is equipped at the top with a condenser, the butanol column is equipped with a reboiler, and the heat transfer is carried out by a heat exchanger common to both columns, integrating said condenser and said reboiler, which is particularly efficient and economical in terms of equipment resources.

[0016] As indicated above, the thermal integration proposed by the invention can lead to modifying the operation, the operating conditions (temperature, pressure) of the isopropanol-butanol distillation column, so that the water-isopropanol effluent has a sufficient temperature at the column outlet to be able to carry out the transfer.

[0017] It is thus possible to modify, in particular to increase, the operating pressure of the column. Advantageously, the pressure of the isopropanol-butanol distillation column can be adjusted to a value of at least 3 bars absolute, in particular at least 4 bars absolute, preferably at most 10 bars absolute, in particular at most 7 bars absolute, in particular between 4.5 and 6.5 bars absolute.

[0018] The isopropanol-butanol distillation column and the butanol column are preferably operated at temperatures chosen so that the water-isopropanol azeotrope stream at the top of the isopropanol-butanol distillation column (the "top" stream of this column corresponds to the stream entering the condenser of said column) is at a temperature T1 at least 8°C, in particular at least 10°C higher than the temperature T2 of the stream leaving the bottom of the butanol column.

[0019] Thus, preferably, the isopropanol-butanol distillation column and the butanol column are operated at temperatures chosen so that the water-isopropanol azeotrope stream at the top of the isopropanol-butanol distillation column is at a temperature T1 of at least 120°C, in particular at most 140°C.

[0020] The operation of the isopropanol-butanol distillation column can be adjusted to maintain a two-phase liquid / gas mixture in the column, in particular by imposing the temperature / pressure conditions mentioned above, such as a temperature of the water-isopropanol stream leaving the column head of at least 120°C and / or a pressure in the column of at least 3 bars absolute.

[0021] It was in fact noticed that modifying the operating conditions of this column (operating more usually at lower pressure, notably at atmospheric pressure, and at lower temperature) made it possible at the same time to obtain another advantage than a reduction in energy cost: at higher pressure / temperature, the column which tended to operate in a three-phase liquid / liquid / gas medium switches to a two-phase liquid / gas medium only, the demixing zone disappears, which makes it possible to operate the column with usual / conventional internals / packings and not with specific trays adapted to the operation of three-phase columns, therefore with a lower investment in equipment and easier control of the column.

[0022] It should be emphasized that the additional energy cost, if any, due to a possible increase in pressure / temperature in the isopropanol-butanol column remains much lower than the energy gain obtained for the butanol column, making the invention very attractive. It should also be emphasized that this increase in pressure / temperature in the isopropanol-butanol column, which remains controlled, is in no way detrimental to the quality, efficiency or operability of the distillation carried out in the isopropanol-butanol column in question.

[0023] The mixture to be treated according to the invention may also contain another alcohol, in particular ethanol, generally in a minority quantity compared to that of isopropanol and butanol.

[0024] For example, the initial mixture to be treated may correspond to a fermentation must in aqueous phase comprising two major compounds, namely isopropanol I and butanol B, and minor compounds, in particular two minor compounds such as acetone A and ethanol E, which have the following characteristics: total concentration of isopropanol I and butanol B: 8 to 30 g / L mass ratio I / B (majority products isopropanol / butanol): 0.25-0.5 / 0.75-0.5 total concentration of minority products if the must contains them (for example acetone A and ethanol E): 0.1 g / l to 2 g / l.

[0025] In the case where the initial mixture also includes ethanol, the separation by distillation carried out by at least the so-called isopropanol-butanol distillation column aims to separate said mixture or a mixture derived from said initial mixture at the top into a water-isopropanol-ethanol azeotrope flow and at the bottom into a water-butanol azeotrope flow. The heat transfer according to the invention then uses the heat of condensation of the water-isopropanol-ethanol mixture.

[0026] According to a preferred embodiment, the heat transfer to the flow entering the reboiler of the butanol column provides all the heat required for the operation of said column. In this case, the furnace generating the steam to heat the reboiler of the butanol column can therefore be eliminated.

[0027] According to another embodiment, the heat transfer to the flow entering the reboiler of the butanol column provides a portion of the heat required for the flow entering the butanol column for the operation of said column, the additional heat being provided by another heat source, in particular by an external source of water vapor. In this case, another heat supply is therefore required, either available elsewhere in the installation, or by means of a steam-generating furnace, but then of smaller capacity, of lower energy consumption than without the heat transfer according to the invention.

[0028] According to another embodiment, the heat transfer to the flow entering the butanol column provides more heat than that required for the flow entering the reboiler of the butanol column for the operation of said column, and in this case a cooler is added to remove the excess heat. A cooler is understood to mean any known technical means, for example of the condenser(s) type.

[0029] An example of a process according to the invention comprises the following series of operations for separating the mixture comprising alcohols including at least isopropanol and butanol, and optionally ethanol, as well as acetone, in the aqueous phase: (a) a separation of said mixture, by distillation carried out in a beer column aimed at removing at least a portion of the water from the aqueous phase to obtain a concentrated mixture, (b) a separation of the concentrated mixture in step (a), by distillation carried out in a so-called acetone column aimed at separating the acetone from said concentrated mixture to obtain a concentrated mixture depleted in acetone, (c) a separation by distillation carried out by at least one so-called isopropanol-butanol distillation column and aimed at separating the concentrated mixture depleted in acetone obtained in step (b) at the top into a water-isopropanol or water-isopropanol-ethanol azeotrope stream and at the bottom into a water-butanol azeotrope stream, (d) a separation by distillation aimed at separating the water-butanol azeotrope stream obtained in step (c) into water and butanol,operated by a heteroazeotropic distillation system comprising at least one column called a water column recovering the water and at least one column called a butanol column recovering the butanol.

[0030] Advantageously, the initial mixture comprising alcohols, including at least isopropanol and butanol, and optionally ethanol and / or acetone, in the aqueous phase is a must obtained by fermentation of sugary juices, in particular derived from lignocellulosic biomass, under the action of microorganisms, in particular derived from a solventogenic strain, preferably chosen from at least one of the following microorganisms: bacteria, in particular of the genus Clostridium (like C. tyrobutyricum or C. cellulovorans ), Escherichia coli, yeasts, especially of the type Saccharomyces cerevisae. Naturally, these microorganisms can be native microorganisms, or derived from them by genetic modification using known techniques.

[0031] This must has the particularity of being highly diluted with water, which requires these various separations, and in particular a concentration stage such as stage (a) mentioned above.

[0032] The initial mixture treated according to the invention can thus have a concentration of organic compounds of 2 to 40 grams / liter, in particular 5 to 35 g / liter or 8 to 30 grams / liter, typical of the concentrations encountered in fermentation musts. Organic compounds are understood to mean the molecules of interest that the invention seeks to separate and recover, in particular from the family of alcohols and / or solvents.

[0033] According to one embodiment of the invention, the initial mixture (1) comes from only one source, from only one production process from a single charge; for example, it is a fermentation must obtained from a single fermentation with a single type of microorganism, the must comprising, by the chosen process, directly the mixture of organic compounds, of alcohols that the invention seeks to separate.

[0034] According to another embodiment, the initial mixture according to the invention may combine several mixtures of different compositions and each comprising one or more alcohols in the aqueous phase. This may involve mixing, in particular, several musts obtained by fermentation of sugary juices with different microorganisms, each must then having its own composition.The mixing of these different streams, of these different musts for example, can either be carried out prior to any separation treatment specific to the invention, or in a section dedicated to premixing, or be carried out during a separation step in the progress of the process according to the invention: the different streams / musts can for example be injected jointly into a separation device, for example into the first distillation column of the installation according to the invention (the beer column for example, as described below), the mixing then taking place directly in the device in question without premixing.

[0035] It is thus possible to provide: - on the one hand, to produce a first must in the form of a first mixture comprising isopropanol by fermentation, and - on the other hand, to produce a second must in the form of a second mixture comprising butanol by another fermentation, and to combine the two musts so that they are treated jointly according to the invention, (by being mixed upstream of the installation or in the installation implementing the invention, the mixing being de facto carried out during their treatment by the isopropanol-butanol column). Each of the two musts may include different impurities, or other molecules of interest (ethanol, etc.).

[0036] We thus combine the separation of several different musts using a single installation, a single process.

[0037] Thus, to produce a first must comprising mainly isopropanol, we can refer to the article “Employing Escherichia coli for C2-C6 Bioalcohol Production”, L.Liang et al., Front.Bioeng.Biotechnol., 03.07.2020).

[0038] And to produce a second must comprising mainly butanol, we can refer to the article “Genetic engineering of non-native hosts for 1-butanol production and its challenges: a review”, S. Nawab et al., Microb Cell Fact, 03 / 27 / 2020.

[0039] The invention also relates to any alcohol extraction installation implementing the method described above.

[0040] The invention also relates to an installation for extracting alcohols from an initial mixture comprising alcohols, including at least isopropanol and butanol, and optionally ethanol and / or acetone, in aqueous phase, said installation comprising a series of separation sections, including: a distillation separation section operated by at least one distillation column called isopropanol-butanol equipped with a condenser and aimed at separating at the top said initial mixture or a mixture derived from said initial mixture into a water-isopropanol or water-isopropanol-ethanol azeotrope flow and at the bottom into a water-butanol azeotrope flow, a distillation separation section aimed at separating the water-butanol azeotrope flow into water and butanol, operated by a hetero-azeotropic distillation system comprising at least one column called a water column recovering the water and at least one column called a butanol column equipped with a reboiler and recovering the butanol, such that it provides for heat transfer from the water-isopropanol or water-isopropanol-ethanol azeotrope stream from the overhead of the isopropanol-butanol distillation column entering the condenser to the stream entering the reboiler of the butanol column.

[0041] Preferably, the installation comprises a heat exchanger common to the isopropanol-butanol distillation column and to the butanol column and ensuring heat transfer from the water-isopropanol or water-isopropanol-ethanol azeotrope flow entering the condenser of the isopropanol-butanol distillation column to the flow entering the reboiler of the butanol column, this common exchanger integrating said condenser and said reboiler.

[0042] The installation may comprise the following series of sections for separating the initial mixture comprising alcohols including at least isopropanol and butanol, and possibly ethanol, as well as acetone in the aqueous phase: (a) a section for separating said mixture, by distillation comprising at least one beer column intended to remove at least a portion of the water from the aqueous phase to obtain a concentrated mixture, (b) a section for separating the mixture concentrated in step a), by distillation comprising at least one so-called acetone column intended to separate the acetone from said concentrated mixture to obtain a concentrated mixture depleted in acetone, (c) a section for separating by distillation comprising at least one so-called isopropanol-butanol distillation column and intended to separate the concentrated mixture depleted in acetone obtained in step (b) at the top into a water-isopropanol or water-isopropanol-ethanol azeotrope stream and at the bottom into a water-butanol azeotrope stream, (d) a section for separating by distillation intended to separate the water-butanol azeotrope stream obtained in step (c) into water and butanol,comprising at least one heteroazeotropic distillation system comprising at least one column called a water column for recovering the water and at least one column called a butanol column for recovering the butanol.

[0043] The installation according to the invention may also comprise an additional condenser at the top of the isopropanol-butanol column to remove excess heat from the water-isopropanol or water-isopropanol-ethanol azeotrope stream at the top, in the case where the quantity of heat available in the azeotrope stream exceeds the quantity of heat required for the stream entering the reboiler of the butanol column.

[0044] The invention will be described below in more detail, using non-limiting examples and the following figures: List of figures

[0045] Figure 1 There figure 1 represents an example of a state-of-the-art installation for separating molecules of interest in aqueous solution. Figure 2 There figure 2 represents the installation of the figure 1 modified according to a non-limiting embodiment of the invention.

[0046] Identical references from one figure to another represent the same flows, devices and thermal exchanges.

[0047] These two figures are extremely schematic: they are basic diagrams, which are not to scale. The installations are represented in a simplified manner to facilitate reading, in particular to clearly understand the devices / flows used by the invention, without representing all the devices, such as furnaces, exchangers, coolers / compressors, column reboilers, column condensers, etc., actually provided in an industrial installation of this type and known to those skilled in the art.

[0048] In all figures: the numerical references designate fluid flows, the references in the form of Roman numerals designate the distillation columns, the references with letters the equipment, for the sake of clarity, the "separation sections" are represented with a single column of the distillation column type. But it is clear that the separation sections can contain / contain a plurality of columns, connected in series and / or in parallel, and that they can contain other separation devices to complete the role of at least one of the distillation columns, for example one or more liquid / gas separators of the balloon type etc.... Description of the embodiments

[0049] The objective of the invention is, in the following non-limiting example, to recover the majority products, namely isopropanol on the one hand and n-butanol on the other hand, from an aqueous solution, which also contains two other minority components, namely acetone, considered here as an impurity to be eliminated, and ethanol, which is chosen here to be kept with the isopropanol.

[0050] The composition of the initial wort (entering the beer column), as indicated above, is as follows: total concentration of isopropanol I and butanol B: 8 to 30 g / L mass ratio I / B (majority products isopropanol / butanol): between 0.25-0.5 / 0.75-0.5 total concentration of minor products acetone a and ethanol e: 0.1 to 2 g / l.

[0051] The fermentation must from which the invention is based, by way of non-limiting example, has the following composition and characteristics: concentration of isopropanol I, butanol B, ethanol e, and acetone a in water: 19.6 g / l weight ratio I / B / e+a = 40.8 / 56.1 / 3.1 concentration of acetone a approximately double that of ethanol e

[0052] This aqueous solution is a fermentation must from a juice composed of C5 and / or C6 sugars and fermented under the action of microorganisms derived from a strain of the genus Clostridium, in a known manner, for example according to the "batch" or continuous processes mentioned in the preamble. For more details on the fermentation process itself, please refer to the scientific publication cited for the "batch" process.

[0053] The composition of the flow entering the isopropanol-butanol column is in particular as follows: water: 35 to 45% by weight, the remainder being made up of IBea the mass ratio r I / B (majority products isopropanol / butanol): 0.25-0.5 / 0.75-0.5 acetone concentration a: 0.1 to 1 g / l ethanol concentration e: 2 to 10 g / l

[0054] The isopropanol obtained can have two uses: it can be converted into propylene. Indeed, the hydrated isopropanol product obtained (with ethanol as a minor product) with the process and installation according to the invention is a raw material suitable for conversion into propylene, since it leads to the production of a hydrated isopropanol cut (and a little ethanol), because isopropanol has an azeotrope with water that is impossible to separate completely by distillation alone. it can also be used as a solvent, after the removal of water. An additional dehydration process must then be considered to remove the water from the isopropanol / water azeotrope. Examples include distillation with a third body (benzene, cyclohexane, etc.)), "pressure swing distillation" (acronym PSD), which is an Anglo-Saxon term designating distillation at two different pressures, "Temperature Swing Adsorption" (acronym TSA) which is an Anglo-Saxon term to designate temperature-modulated adsorption or "Pressure Swing Adsorption" (acronym PSA) which is an Anglo-Saxon term designating pressure-modulated adsorption, or pervaporation.

[0055] The butanol obtained (n-butanol here), for its part, is produced almost pure in the process and installation according to the invention. “Almost pure” means a butanol content of at least 98% by weight, in particular at least 98.5 or 99% in the liquid phase considered (or an impurity content of at most 2%, in particular at most 1.5 or 2% by weight).

[0056] In this text, the mixture of isopropanol, butanol, ethanol, and acetone in water may be referred to as the mixture "IBea" or simply as "IBea" for the sake of brevity. Examples Example 1 (comparative)

[0057] This example corresponds to the implementation of the installation according to the figure 1 .

[0058] The separation installation shown in the figure 1 will be described from “upstream” to “downstream”, understanding these terms according to the overall flow direction of the fermentation must and extracted products through the installation.

[0059] Wort 1 arrives from the fermentation section (not shown) with an IBea mix concentration of approximately 8 to 30 g / L and a temperature between 34 and 37°C.

[0060] The first column I, usually called the beer column, pre-concentrates the wort 1 to approximately 60% by weight of IBea, leaving at the top of the column in the form of a stream 2 of concentrated IBea mixture, and eliminates at the bottom of the column approximately 97 to 99% of the incoming water. This water 3 from the bottom of column I contains from 50 to 1000 ppm by weight of IBea and is called "Vinasses". This column I operates, conventionally, substantially at atmospheric pressure, it can also be operated at a maximum of 3 bars absolute. It has between 10 and 20 theoretical plates. It represents approximately 70 to 90% of the steam consumption of the complete separation process (this term is understood to mean the process implemented in an installation such as shown in figure 1 ). Column I operates, depending on its pressure, in a temperature range of approximately 100 to 140 °C (excluding the condenser). A charge / effluent exchanger can be placed on this column I in order to preheat the charge (wort 1).

[0061] This, initially at 34-37°C, enters column I, after passing through the load / effluent exchanger e1, at a temperature between 70 and 85°C.

[0062] The second column II, called the Acetone column, is intended to remove acetone, which is considered an impurity here. It operates conventionally, at approximately atmospheric pressure, and can also be operated at a maximum of 3 bars absolute. It comprises between 30 and 50 theoretical plates. It represents approximately 2 to 6% of the steam consumption of the overall separation process. Stream 2 enters column II. The acetone stream 4 leaves at the top, and the acetone-depleted stream 5 at the bottom.

[0063] The third column III, called the isopropanol-butanol column, allows the isopropanol / water azeotrope to be obtained at the top; this is stream 6, which also includes the little ethanol entering with the must as a minor compound. The composition of this azeotrope is between 11 and 15% by weight in water. At the bottom of the column, a stream with a composition close to that of the water / n-butanol azeotrope is obtained, i.e. a composition of approximately 50% / 50% (weight); this is stream 7. This column III operates here at atmospheric pressure, and the column has a top pressure of 1.5 bars absolute. It has between 30 and 70 theoretical plates, in this example it has 50. Under these pressure conditions, we observe a three-phase vapor / liquid / liquid zone between plates 27 and 50, starting the numbering of the plates at the level of condenser c3, with plates specific to the three-phase operating mode of the column.This column III represents approximately 7 to 15% of the steam consumption of the complete separation process.

[0064] The last two columns IV and V are coupled: this is a heteroazeotropic distillation system, known in principle, applied to the binary water / n-butanol. At the bottom of the water column IV, the water (stream 8) contained in the heteroazeotrope is obtained and at the bottom of the butanol column V, the n-butanol (stream 9) is obtained with a purity ranging from 98% to 99.5% by weight. Both columns operate at substantially atmospheric pressure, up to 2 bar absolute. Both columns IV and V have between 7 and 15 theoretical plates. The water column IV represents 1 to 3% of the steam consumption of the complete separation process, and the butanol column V represents 4 to 8% of the complete separation process.

[0065] All columns I to V are equipped, in a manner known for distillation columns, of a condenser c1, c2, c3, c4 at the top of the column, the last condenser c4 being common to columns IV and V, and of a reboiler r1, r2, r3, r4, r5 at the bottom of the column to heat the column bottom flow. In a known manner, these reboilers can be chosen from the following reboilers: vertical thermosiphon reboilers, so-called "kettle" type reboilers, furnace reboilers or even so-called "once-through" reboilers or "traversant" reboilers in French and possibly of a reflux drum b1, b2, b3, b4 downstream of the condensers c1 to c4.

[0066] The steam consumption of the complete separation process as described varies between 12 and 50 MJ steam / kg of IBea. It depends on the IBea concentration of the initial charge 1 (i.e. the must recovered after fermentation), as well as on the various design choices of the installation (operating conditions of the columns, design of the columns such as the number of trays, position of the feeds, etc.).

[0067] In terms of energy consumption of isopropanol III and butanol V columns: the condenser c3 of column III with isopropanol must evacuate 1.43 MJ / kg IBea of ​​available heat at a temperature of the order of 80°C, the reboiler r3 of this same column III consumes 1.48 MJ / kg IBea of ​​heat in the form of reboiling steam, the column V with butanol consumes 0.9 MJ / kg IBea of ​​heat in the form of reboiling steam (reboiler r5). This heat is required at a thermal level of approximately 120°C at the operating pressure considered. Example 2 (according to the invention)

[0068] This example corresponds to the implementation of the installation according to the figure 2 , which modifies and improves the installation of the figure 1 . Only the differences with the installation diagram of the figure 1 , all other things being equal.

[0069] According to this example 2, a heat transfer is added from the isopropanol-butanol column III to the butanol column V. To do this, the pressure of column III is increased: instead of operating it at atmospheric pressure, it is chosen to operate it at pressure, between 4 and 7 bars absolute, and more precisely here towards 5.5 bars absolute (measured at the column head). This increase in pressure leads to an increase in the operating temperatures of column III. Thus, the column head temperature increases to at least 120°C, in particular up to 125°C to 130°C, whereas with the standard operation close to atmospheric pressure according to example 1, it is only around 80°C.However, at the top of the column, calories must be evacuated, and with this increase in temperature, it turns out that the quantity of calories to be evacuated from the top effluent in the condenser c3 of column III is close to, or even a little higher than, the quantity of calories to be supplied at the level of the reboiler r5 of the butanol column V, which operates at around 120°C at atmospheric pressure.

[0070] By increasing the top temperature of column III, the heat removed at the level of the condenser c3 of this column III can be transferred to the reboiler r5 of the butanol column, which operates at around 120°C at near atmospheric pressure, via a new thermal connection T. We then only need one exchanger common to the two columns constituting both the condenser c3 of column III and the reboiler r5 of column V, which can be grouped into the same equipment c3+r5. We thus replace two pieces of equipment (condenser of column III with isopropanol-butanol and the reboiler of column V with butanol) with a single heat exchanger. And we can eliminate the steam production means associated with the reboiler r5 of column 5.

[0071] In the case where the quantity of heat to be evacuated at the level of column III is not strictly equal to the quantity of heat to be supplied to column V, there are several options: If it is higher, an additional condenser c3' is added (for example a cooler of the type known as a "trim cooler") at the head of column III, which will be smaller than the initial column head condenser c3, because it must evacuate less heat than the condenser c3 of example 1. Example 2 and figure 2represents this scenario. The entire overhead stream 6 of III enters the common exchanger c3+r5, integrating the condenser c3 of column III and the reboiler r5 of column V. The hot effluent leaving this common exchanger enters the additional condenser c3'. At the outlet of this condenser c3', the stream is divided into 2: a portion returns to reflux in column III, the remaining portion, the distillate, leaves the process, it is a product. If it is lower, a steam make-up must be provided at the reboiler r5 of column V, therefore using a heating means (not shown in the figure) to produce steam, but this make-up remains significantly lower than the quantity of steam required without this heat transfer between the two columns, so a much smaller heating means (oven type) can be used, with a much lower heating capacity than in the case of example 1.

[0072] Surprisingly, it turned out that increasing the pressure of column III brought another advantage: at atmospheric pressure, there is a liquid / liquid demixing zone in this column, due to the presence of the ternary Isopropanol / n-Butanol / Water. However, this type of three-phase liquid / liquid / vapor zone generally requires the installation of specific column internals, which are more expensive and more complex to implement than conventional distillation trays. With the increased pressure according to the invention, the three-phase demixing zone disappears in the column, and therefore the column can be operated with conventional internals such as valve or perforated trays, loose or structured packing, which further reduces installation investments.

[0073] In terms of energy consumption of columns III with isopropanol-butanol and V with butanol: the condenser c3 of this third column III must evacuate 1.44 MJ / kg IBea of ​​heat, available at a temperature of 129.5°C, this increase in temperature compared to example 1 resulting from the increase in the operating pressure of the column.

[0074] However, the fifth butanol column V requires a reboiling heat of 0.9 MJ / kg IBea in the form of steam, at a thermal level of 119.5°C. Heat transfer between the condenser of column III and the boiler of column V therefore becomes possible. Here, 1.44 - 0.9 = 0.54 MJ / kg IBea will have to be evacuated at the level of condenser c3 of column III with isopropanol-butanol (instead of 1.43 MJ / kg IBea according to example 1): the heat to be evacuated is less than in the case of example 1 and the equipment will be smaller. Finally, the heat to be supplied to the reboiler r3 of column III isopropanol is 1.71 MJ / kg instead of 1.48 MJ / kg, i.e. an increase of 0.23 MJ / kg (due to the increase in pressure).

[0075] Table 1 below summarizes the energy data from columns III and V according to example 1 and example 2, and details the calculation of the resulting energy gains: Table 1 Example 1 (comparative) Example 2 (Invention) Gain G1,G2 Column III at Isopropanol / Butanol Head pressure (abs. bars) 1,5 5,5 Condenser c3 (MJ / kg IBea) 1,43 1,44 Reboiler r3 (MJ / kg IBea) 1,48 1,71 Column V in Butanol Head pressure (abs bars) 1,15 1,15 Reboiler r5 (MJ / kg IBea) 0,9 0,9 Heat to be removed (MJ / kg IBea) 1,43 1,44 - 0,9 = 0,54 G2 = 1,43 - 0,54 = 0,89 Heat to be supplied (MJ / kg IBea) 1,48 + 0,9 = 2,38 1,71 + 0,9 - 0,9 = 1,71 G1 = 2,38 -1,71 = 0,67

[0076] By comparing these data on the energy operation of columns III and V, we verify that with the invention, we gain both: in terms of energy to evacuate the heat from column III, with a gain G2 on the heat to be evacuated of 0.89 MJ / kg IBea, which corresponds to a reduction in cooling energy consumption of (0.89 / 1.43 x 100 =) 62%; and in terms of energy to be supplied to column V, with a gain G1 on the heat to be supplied of 0.67 MJ / kg IBea, which corresponds to a reduction in heating energy consumption of (0.67 / 2.38 x 100 =) 28%.

[0077] We therefore see that overall the heat transfer between the two distillation columns according to the invention results in considerable energy gains compared to conventional use of these two columns, both in cooling (spectacular reduction of more than half of consumption), and in heating (significant reduction of at least 20%), without causing any significant additional cost in terms of equipment. The condenser c3 and the reboiler r5 having been integrated into a single piece of equipment and the heat to be evacuated at the level of the additional condenser c3' (the "trim-cooler") being 62% lower, this additional condenser c3' of example 2 according to the invention is / can be significantly smaller than the condenser c3 of example 1. Note that the addition of this additional condenser remains optional, depending on the cases encountered, as indicated above.

Claims

1. Process for extracting alcohols from an initial mixture (1) comprising alcohols, including at least isopropanol and butanol, and optionally ethanol and / or acetone, in aqueous phase, said process comprising a series of separating operations, including: - a distillative separation performed by at least one distillation column referred to as isopropanol-butanol column (III) and equipped at the top with a condenser (c3), and intended for separating said initial mixture or a mixture deriving from said initial mixture into a water-isopropanol azeotrope stream (6) at the top and into a water-butanol azeotrope stream (7) at the bottom, - a distillative separation intended for separating the water-butanol azeotrope stream into water and butanol, performed by a hetero-azeotropic distillation system comprising at least one water-recovery column referred to as water column (IV), and at least one butanol (9)-recovery column referred to as butanol column (V) and equipped with a reboiler (r5), characterized in that a heat transfer is performed from the top water-isopropanol azeotrope stream (6) entering the condenser of the isopropanol-butanol distillation column (III), to the stream entering the reboiler of the butanol column (V).

2. Process according to the preceding claim, characterized in that the heat transfer is performed by a heat exchanger (c3+r5) which is common to the two columns (III, V), incorporating said condenser (c3) and said reboiler (r5).

3. The process according to one of the preceding claims, characterized in that the operation of the isopropanol-butanol distillation column (III) is regulated for maintaining a two-phase liquid / gas mixture in the column, especially by imposing a temperature of at least 120°C and / or a pressure of at least 3 bar absolute.

4. Process according to one of the preceding claims, characterized in that the pressure of the isopropanol-butanol distillation column (III) is regulated to a value of at least 3 bar absolute, especially at least 4 bar absolute, preferably of at most 10 bar absolute, especially of at most 7 bar absolute, especially between 4.5 and 6.5 bar absolute.

5. Process according to one of the preceding claims, characterized in that the isopropanol-butanol distillation column (III) and the butanol column (IV) are operated at temperatures selected in such a way that the top water-isopropanol azeotrope stream (6) from the isopropanol-butanol distillation column (III) is at a temperature T1 at least 8°C, especially at least 10°C, greater than the temperature T2 of the stream exiting the bottom of the butanol column (V).

6. Process according to one of the preceding claims, characterized in that the isopropanol-butanol distillation column (III) and the butanol column (V) are operated at temperatures selected in such a way that the top water-isopropanol azeotrope stream (6) from the isopropanol-butanol distillation column (III) is at a temperature T1 of at least 120°C, especially of at most 140°C.

7. Process according to one of the preceding claims, characterized in that the initial mixture (1) also comprises ethanol, and in that the distillative separation which is performed by at least the isopropanol-butanol distillation column (III) is intended for separating said mixture or a mixture deriving from said initial mixture into a water-isopropanol-ethanol azeotrope stream (6) at the top and into a water-butanol azeotrope stream (7) at the bottom.

8. Process according to one of the preceding claims, characterized in that the thermal transfer to the stream entering the butanol column (V) provides the entirety of the heat required to the stream entering the reboiler (r5) of the butanol column (V) for the operation of said column.

9. Process according to one of Claims 1 to 7, characterized in that the thermal transfer to the stream entering the butanol column (V) provides a portion of the heat required to the stream entering the butanol column (V) for the operation of said column, the heat complement being supplied by another heat source, especially by an external steam source.

10. Process according to one of Claims 1 to 7, characterized in that the thermal transfer to the stream entering the butanol column (V) provides more heat than that required to the stream entering the reboiler (r5) of the butanol column (V) for the operation of said column, and in that a cooler (c3') is added for evacuating the excess heat.

11. Process according to one of the preceding claims, characterized in that it comprises the following series of operations for separating the initial mixture (1) comprising alcohols, including at least isopropanol and butanol, and optionally ethanol, and also acetone, in aqueous phase: - (a) a separation of said mixture, by distillation performed in a beer column (I) and intended for removing at least a portion of the water from the aqueous phase, to give a concentrated mixture (2), - (b) a separation of the concentrated mixture obtained from step (a), by distillation performed in a column referred to as acetone column (II), and intended for at least partly separating the acetone from said concentrated mixture (2), to give an acetone-depleted concentrated mixture (5), - (c) the distillative separation performed by at least one distillation column referred to as isopropanol-butanol column (III) and intended for separating the acetone-depleted concentrated mixture obtained in step (b) into a water-isopropanol or water-isopropanol-ethanol azeotrope stream (6) at the top and into a water-butanol azeotrope stream (7) at the bottom, - (d) the distillative separation intended for separating the water-butanol azeotrope stream obtained in step (c) into water and butanol, performed by a hetero-azeotropic distillation system comprising at least one water-recovery column referred to as water column (IV), and at least one butanol-recovery column referred to as butanol column (V).

12. Process according to one of the preceding claims, characterized in that the initial mixture (1) comprising alcohols, including at least isopropanol and butanol, and optionally ethanol and / or acetone, in aqueous phase is a must obtained by fermentation of sugary liquors, especially derived from lignocellulosic biomass, under the action of microorganisms, especially obtained from a solvent-producing strain, preferably selected from at least one of the following microorganisms: bacteria, especially of the genus Clostridium, Escherichia coli, yeasts, especially of Saccharomyces cerevisiae type.

13. Process according to one of the preceding claims, characterized in that the initial mixture (1) combines two or more mixtures of different compositions, each comprising one or more alcohols in aqueous phase, especially two or more different musts obtained by fermentation of sugary liquors.

14. Facility for extracting alcohols from an initial mixture (1) comprising alcohols, including at least isopropanol and butanol, and optionally ethanol and / or acetone, in aqueous phase, said facility comprising a series of separating sections, including: - a section for distillative separation performed by at least one distillation column (III) referred to as isopropanol-butanol column and equipped at the top with a condenser (c3), and intended for separating said initial mixture or a mixture deriving from said initial mixture into a water-isopropanol or water-isopropanol-ethanol azeotrope stream (6) at the top and into a water-butanol azeotrope stream (7) at the bottom, - a section for distillative separation intended for separating the water-butanol azeotrope stream (7) into water and butanol, performed by a hetero-azeotropic distillation system comprising at least one water (8)-recovery column referred to as water column, and at least one butanol (9)-recovery column referred to as butanol column and equipped with a reboiler (r5), characterized in that the facility comprises a heat exchanger which is common to the isopropanol-butanol distillation column (III) and to the butanol column (V) and ensures a thermal transfer from the top water-isopropanol or water-isopropanol-ethanol azeotrope stream (6) from the isopropanol-butanol distillation column (III), entering the condenser (c3), to the stream entering the reboiler (r5) of the butanol column (V), said heat exchanger common to the two isopropanol-butanol distillation (III) and butanol (V) columns incorporating said condenser (c3) and said reboiler (r5), and optionally an additional condenser (c3') at the top of the isopropanol-butanol column (III) for evacuating the excess heat of the top water-isopropanol or water-isopropanol-ethanol azeotrope stream (6).

15. Facility according to Claim 14, characterized in that it comprises the following series of sections for separating the initial mixture comprising alcohols, including at least isopropanol and butanol, and optionally ethanol, and also acetone, in aqueous phase: - (a) a section for separating said mixture, by distillation comprising at least one beer column (I) and intended for removing at least a portion of the water from the aqueous phase, to give a concentrated mixture, - (b) a section for separating the concentrated mixture of step (a), by distillation comprising at least one column referred to as acetone column (II), and intended for separating the acetone from said concentrated mixture, to give an acetone-depleted concentrated mixture, - (c) said section for distillative separation comprising at least one distillation column referred to as isopropanol-butanol column (III) and intended for separating the acetone-depleted concentrated mixture obtained in step (b) into a water-isopropanol or water-isopropanol-ethanol azeotrope stream at the top and into a water-butanol azeotrope stream at the bottom, - (d) said section for distillative separation intended for separating the water-butanol azeotrope stream obtained in step (c) into water and butanol, comprising at least one hetero-azeotropic distillation system comprising at least one water-recovery column referred to as water column (IV), and at least one butanol-recovery column referred to as butanol column (V) .