PARTIAL EXTRACTION OF BUTANOL FROM AN AQUEOUS SOLUTION CONTAINING ETHANOL AND BUTANOL

Description

TECHNICAL FIELD OF THE INVENTION

[0001] The invention relates to a process for treating a hydroalcoholic feedstock comprising ethanol and butanol, preferably in a small quantity relative to water and ethanol, allowing for the partial extraction of butanol and the production of an effluent rich in water, an effluent rich in ethanol, and an effluent rich in butanol. This process appears particularly advantageous for treating the hydroalcoholic effluent of the Lebedev process. STATE OF THE ART

[0002] The treatment of aqueous solutions containing ethanol is known to be difficult. The separation of water and ethanol by distillation is hampered by the formation of a water-ethanol azeotrope, which limits the recovery of pure ethanol at the top of the column. The presence of butanol in the water-ethanol mixture, even in small quantities, further complicates separation by distillation, as it leads to the formation of a second azeotrope: the water-butanol azeotrope. When the mixture also contains other impurities, such as the water-ethanol effluent from the Lebedev process, the separation problems are exacerbated.

[0003] It therefore appears interesting to extract butanol, at least partially, in order to produce from hydroalcoholic solutions comprising water, ethanol and butanol, particularly when the latter is in small quantities, an effluent rich in ethanol and an effluent rich in water.

[0004] Document FR 2 549 043 describes a process for fractionating an aqueous solution comprising butanol and acetone or an acetone-ethanol mixture, to produce an effluent consisting essentially of water, a practically pure butanol effluent, and an effluent rich in acetone or an acetone-ethanol mixture. The process includes a distillation section fed with the aqueous butanol and acetone solution mixed with a recycled water-butanol phase, and a second distillation section, fed with the overhead distillate from the first and comprising a separation system, notably by decantation, which allows the withdrawal and recycling of a water-butanol phase.

[0005] However, the aqueous solution treated by the process described in document FR 2 549 043 is relatively low in acetone, or in acetone-ethanol mixture, and gives no information on a possible transposition to the treatment of other ternary aqueous mixtures comprising butanol, in particular hydroalcoholic mixtures comprising water, ethanol and butanol containing small amounts of butanol.

[0006] The present invention proposes a process for treating water-ethanol-butanol mixtures, including small amounts of butanol, to produce a water-rich effluent, an ethanol-rich effluent and a practically pure butanol effluent.

[0007] This process appears particularly interesting for treating the hydroalcoholic effluent from the Lebedev process, since the separated ethanol will be more concentrated. It can then be recycled and used again as a reagent.

[0008] Indeed, in the Lebedev process, which produces butadiene by converting ethanol, as described, for example, in the book "Synthetic Rubber," Chapter 4, by WJ Toussaint and J. Lee Marah, or more recently in documents FR 3 026 100 and FR 3 026 101, the butadiene conversion rate per pass is limited. Recycling the unconverted reactants, particularly ethanol, is therefore necessary, especially for economic reasons. The ethanol must be separated as much as possible from the water produced (approximately 2 moles of water for one mole of butadiene) before being recycled back to the reactor. Water limits the reactivity and selectivity of the reaction catalyst. It also leads to larger equipment and increased utility consumption.

[0009] Furthermore, numerous impurities, including butanol, are generated during dehydration. Butanol is difficult to remove without significant energy consumption and risking pollution of the water drawn off during effluent treatment in the Lebedev process. It is therefore recycled with the ethanol and returned to the reactor. The butanol reacts only partially in the reactor and accumulates with each recycling cycle until the amount of transformed butanol equals the amount of butanol formed from ethanol. This transformation of butanol consequently reduces the selectivity of the Lebedev process's reaction catalyst, leading to a decrease in overall butadiene yield. Moreover, the recycled butanol carries with it a significant amount of water, resulting in larger equipment, increased utility consumption, and difficulties in separating the ethanol and acetaldehyde reactants.

[0010] The object of the present invention is to overcome these drawbacks by providing a process for treating hydroalcoholic water-ethanol solutions containing butanol, particularly in small quantities. Specifically, the present invention proposes a method for treating a hydroalcoholic feed comprising, in addition to water and ethanol, butanol, preferably in a small quantity relative to the water and ethanol, by partial extraction of the butanol, so as to produce an effluent rich in ethanol and an effluent rich in water, suitable for recycling, without significant loss of ethanol and without causing the problems mentioned above. SUMMARY OF THE INVENTION

[0011] The present invention relates to a process for treating a hydroalcoholic load comprising water, ethanol and butanol, to produce an effluent rich in ethanol, an effluent rich in water and an effluent rich in butanol, comprising: a) a water-ethanol separation step, comprising a water-ethanol separation section comprising a distillation column having at least 14 theoretical trays and a molar reflux ratio less than or equal to 1.2, said water-ethanol separation section comprising: ∘ a feed of said hydroalcoholic feed, located at or downstream of the third theoretical tray of the column, ∘ the lateral withdrawal of a hydroalcoholic solution comprising butanol, in the butanol accumulation zone of the distillation column, located downstream of the feed, ∘ an injection of the heavy phase from step b), located downstream and close to the withdrawal, ∘ an injection of the ethanol-water distillate from step c), located upstream of the feed and close to the top of said distillation column, said distillation section producing at the top of the column an ​​effluent rich in ethanol and at the bottom of the column an ​​effluent rich in water;b) a demixing step comprising: a mixing section of said hydroalcoholic solution withdrawn in step a) with the water / butanol / ethanol fraction withdrawn in step c); a settling section of the preceding mixture comprising a settling flask in which the pressure is less than or equal to 6 bar absolute, said settling section producing a heavy phase comprising mainly water and a light phase; c) a butanol separation step, comprising a butanol distillation section comprising at least one distillation column fed by the light phase from step b) and comprising a lateral withdrawal, located on said column in a zone between the feed and the bottom of the column, of a water / butanol / ethanol fraction, said butanol distillation section producing at the bottom of the column an ​​effluent rich in butanol and at the top of the column an ​​ethanol-water distillate.

[0012] It was thus surprisingly discovered that, under certain conditions, it is possible to create an accumulation of butanol in the water-ethanol distillation column. The inventors also demonstrated that drawing off this area, combined with a sophisticated system of separations and recycling, produces an ethanol-enriched effluent and a water-rich effluent, both of which can be recycled. For example, in the Lebedev process, the ethanol-rich effluent can be recycled as a reactant to the reaction section of the Lebedev process, and the water to a scrubbing section, thereby reducing utility consumption and the size of the equipment.

[0013] Advantageously, the process according to the invention makes it possible to produce an effluent that is as concentrated in ethanol as possible, without loss of ethanol, while limiting energy consumption.

[0014] The process according to the invention also makes it possible to recover a practically pure and therefore valuable butanol effluent and a butanol-free water effluent.

[0015] The invention is advantageously applicable to the treatment of the water-ethanol effluent from the Lebedev process. The water-ethanol effluent from the reaction unit of the Lebedev process comprises, in addition to water and ethanol, butanol, a by-product of the ethanol-to-butadiene conversion reaction, in small quantities. Water-ethanol distillation in a Lebedev process can thus be optimized by partial butanol extraction according to the process of the invention: the ethanol-rich effluent extracted at the top is therefore more concentrated in ethanol and can be recycled back to the reactor; the amount of butanol recycled is reduced compared to a so-called conventional Lebedev process in which butanol is not extracted. Thus, the accumulation of butanol in the butadiene production reactor no longer occurs, or does so less rapidly. The amount of water recycled with the ethanol-rich effluent is also reduced.The overall energy cost of the Lebedev process, incorporating the process according to the invention, is therefore limited. DESCRIPTION OF THE INVENTION

[0016] According to the invention, the numbering of the theoretical trays and the positioning of the different elements, particularly in the water-ethanol distillation section, with terms such as "upstream" / "downstream" are carried out in the direction of flow of the liquid in the distillation column, i.e. from the top to the bottom of the column.

[0017] The Lebedev process refers to a process for converting ethanol into butadiene, such as that described for example in document FR 3 026 100 or FR 3 026 101.

[0018] According to the present invention, the expression "between ... and ..." means that the limit values ​​of the interval are included within the described range of values. If this were not the case, and the limit values ​​were not included within the described range, this clarification would be provided by the present invention.

[0019] The present invention consists of a process for treating a hydroalcoholic load comprising water, ethanol and butanol, to produce an effluent rich in ethanol, an effluent rich in water and an effluent rich in butanol, comprising: a) a water-ethanol separation step, comprising a water-ethanol separation section comprising a distillation column having at least 14 theoretical trays and a molar reflux ratio less than or equal to 1.2, said water-ethanol separation section comprising: ∘ a feed of said hydroalcoholic feed, located at or downstream of the third theoretical tray of the column, ∘ the lateral withdrawal of a hydroalcoholic solution comprising butanol, in the butanol accumulation zone of the distillation column, located on the distillation column downstream of the feed, ∘ an injection of the heavy phase from step b), located downstream and close to the withdrawal, ∘ an injection of the ethanol-water distillate from step c), located upstream of the feed and close to the head of said distillation column,said distillation section producing at the top of the column an ​​effluent rich in ethanol and at the bottom of the column an ​​effluent rich in water; b) a demixing step comprising: a mixing section of said hydroalcoholic solution withdrawn in step a) with the water / butanol / ethanol fraction withdrawn in step c); a settling section of the preceding mixture comprising a settling flask in which the pressure is less than or equal to 6 bar absolute, said settling section producing a heavy phase comprising mainly water and a light phase; c) a butanol separation step, comprising a butanol distillation section comprising at least one distillation column fed by the light phase from step b) and comprising a lateral withdrawal located on the butanol column in a zone between the feed and the bottom of the column, of a water / butanol / ethanol fraction,said distillation section producing at the bottom of the column an ​​effluent rich in butanol and at the top of the column an ​​ethanol-water distillate.

[0020] Preferably, the process according to the invention consists of a) the water-ethanol separation step, b) the demixing step and c) the butanol distillation step, previously mentioned. The hydroalcoholic charge

[0021] The process according to the invention is applicable to the treatment of hydroalcoholic loads comprising water, ethanol, and butanol, preferably with butanol present in a small quantity relative to water and ethanol. Butanol represents, in particular, less than 5 mol / mol, more specifically less than 2 mol / mol, more specifically less than 1 mol / mol, or even less than 0.5 mol / mol of the hydroalcoholic load to be treated.

[0022] The hydroalcoholic charge treated by the process according to the invention is a liquid charge, preferably a solution or suspension.

[0023] The hydroalcoholic solution, comprising water, ethanol, and butanol, may also contain other impurities, generally in proportions lower than that of butanol. These impurities may include, for example, saturated or unsaturated hydrocarbons, aromatics, or oxygenated products, saturated or unsaturated, aromatics, other than butanol.

[0024] Advantageously, when the process according to the invention is integrated into a Lebedev process, the hydroalcoholic feedstock is the water-ethanol effluent recovered from the outlet of the ethanol-to-butadiene conversion unit, after separation of the butadiene, washing of the liquid effluent and separation of acetaldehyde and other light impurities. Step a) of water-ethanol separation

[0025] The process according to the invention comprises a water-ethanol separation step (a), including a water-ethanol separation section. The water-ethanol separation section includes a distillation column comprising at least 14 theoretical plates. Advantageously, the distillation column of the water-ethanol separation section comprises between 14 and 40 theoretical plates, preferably between 20 and 35 theoretical plates, and more preferably between 24 and 33 theoretical plates.

[0026] Advantageously, the distillation column in the water-ethanol separation section includes a reflux (or condensation) device at the top and a reboiling device at the bottom. The distillation column operates at a molar reflux ratio less than or equal to 1.2, preferably between 0.25 and 1.2, preferably between 0.5 and 1.15, and even more preferably between 0.65 and 1.15.

[0027] The distillation column of the water-ethanol separation section is fed, preferably continuously, with the hydroalcoholic charge at an intermediate point in the distillation column located at or downstream of the third theoretical tray (or theoretical tray number 3). Preferably, the column is fed with the hydroalcoholic charge in a zone between one-quarter and three-quarters of the total height of said column, and more preferably in a zone between one-third and two-thirds of the total height of said column.

[0028] The area between the feed and the bottom of the column is called the bottom zone.

[0029] The inventors then discovered that, under these operating conditions of the distillation column, and with such architectural characteristics of the column, which advantageously remain economically reasonable, a zone of butanol accumulation formed, particularly in a zone located downstream of the feed.

[0030] According to the invention, the water-ethanol separation section includes a lateral withdrawal of a hydroalcoholic solution containing butanol. The butanol concentration of the withdrawn solution depends on several parameters related to both the composition of the feed and the characteristics of the distillation column. However, the withdrawn solution preferably comprises at least 2% mol / mol, at least 4% mol / mol, at least 7% mol / mol, or at least 10% mol / mol of butanol, and advantageously less than 60% mol / mol, in particular less than 50% mol / mol of butanol. This withdrawn hydroalcoholic solution also comprises at least water and optionally ethanol.

[0031] According to the invention, the lateral draw-off is located in the butanol accumulation zone of the distillation column in the water-ethanol separation section, downstream of the feed, i.e., in the bottom zone of the distillation column as defined above. Advantageously, the lateral draw-off is located in a zone downstream of the feed, between one-quarter and three-quarters of the height of the bottom zone, preferably between one-third and two-thirds of the height of the bottom zone. The position of the lateral draw-off on the column is defined, according to the invention, in the direction of the liquid flow in said water-ethanol distillation column, i.e., from the top to the bottom of the column.

[0032] In step a) of the water-ethanol separation of the process according to the invention, the water-ethanol separation section advantageously further comprises two injections for recycling the withdrawn water and optionally the ethanol. In particular, the water-ethanol separation section comprises: an injection of the heavy phase from step b) of demixing, located downstream and close to the lateral draw-off, preferably in an area between the lateral draw-off and the third theoretical plate downstream of said lateral draw-off, and an injection of the ethanol-water distillate from step c), located upstream of the feed and close to the head of the distillation column, preferably in the area of ​​the distillation column between the theoretical plate at the top of the column at which the reflux returns and the third theoretical plate.

[0033] The reflux (or condensation) devices at the top of the column and the reboiling device at the bottom of the column that can be used in step a) of water-ethanol separation of the process according to the invention are those well known to those skilled in the art. Advantageously, the reflux device at the top of the column comprises a heat exchanger using cooling water or air, a reflux flask, and a reflux pump for returning the reflux to the distillation column. Advantageously, the reboiling device uses low-pressure steam.

[0034] According to the invention, the distillation section of step a) produces at the top an effluent rich in ethanol and at the bottom an effluent rich in water.

[0035] Advantageously, the ethanol-rich effluent extracted from the top of the water-ethanol column in step a) of the process according to the invention comprises at least ethanol with a concentration greater than or equal to 60% mol / mol, preferably greater than or equal to 65% mol / mol, and more preferably greater than or equal to 70% mol / mol. The ethanol-rich effluent may also include water. If the process according to the invention is integrated into a Lebedev process, the ethanol-rich effluent can be recycled to the reaction section where the ethanol will be consumed as a reactant.

[0036] The water-rich effluent produced at the bottom of the column consists essentially of water, i.e., at least 95 mol% water, preferably at least 98 mol% water, preferably at least 99 mol% water. Advantageously, the water-rich effluent contains less than 10 mol ppm, preferably less than 5 mol ppm, more preferably less than 1 mol ppm, and even more preferably less than 0.1 mol ppm of ethanol, and less than 10 mol ppm, preferably less than 5 mol ppm, preferably less than 1 mol ppm of butanol, and preferably is free of butanol. Step b) of separation

[0037] The process according to the invention includes a step b) of demixing comprising a mixing section of the hydroalcoholic solution withdrawn in step a) with a water / butanol / ethanol fraction withdrawn in step c), and a decantation section of the mixture comprising a decanting flask having a pressure less than or equal to 6 bar absolute. The demixing step b) produces a heavy phase comprising mainly water and a light phase.

[0038] In the mixing section, the hydroalcoholic solution withdrawn in step a) from the butanol accumulation zone of the distillation column is mixed with a water / butanol / ethanol cut withdrawn in step c). Advantageously, the water / butanol / ethanol cut withdrawn in step c) contains little ethanol and is concentrated in butanol. Preferably, the water / butanol / ethanol cut withdrawn in step c) comprises between 15 and 45 mol / mol, preferably between 20 and 40 mol / mol, butanol, for example between 25 and 35 mol / mol butanol, less than 3 mol / mol ethanol, preferably less than 1 mol / mol ethanol, and water. Advantageously, the hydroalcoholic solution withdrawn in step a) represents between 15 and 40 mol / mol % of the mixture in the mixing section of step b) of the process according to the invention and the water / butanol / ethanol cut withdrawn in step c) between 60 and 85 mol / mol % of the mixture in the mixing section of step b) of the process according to the invention.

[0039] The mixing section allows obtaining a mixture of composition such as that found in the phase separation zone, also called "demixing lens", of the ternary water / ethanol / butanol diagram.

[0040] Advantageously, the pressure inside the settling tank is less than or equal to 6 bar absolute. More particularly, the pressure inside the settling tank is between 1 and 6 bar absolute, preferably between 1 and 4 bar absolute, more preferably between 1 and 2 bar absolute, and in particular equal to 1.5 bar absolute.

[0041] In the settling section, under the operating conditions of the invention, the mixture obtained at the end of the mixing section of step b) of the process according to the invention will separate into two phases: an aqueous phase, the heavy phase, comprising mainly water, that is to say preferably at least 85 mol% water, more particularly between 85-99 mol% water, especially between 90-98 mol% water, and a light phase advantageously concentrated in butanol, comprising in particular less than 15 mol / mol ethanol, between 60 and 85 mol / mol water and at least 5 mol / mol butanol, preferably between 5% and 40 mol / mol butanol, preferably between 10% and 40% mol / mol butanol and especially between 15% and 38 mol / mol butanol.

[0042] The heavy phase is advantageously recycled and returned to the water-ethanol distillation column of step a) into which it is reinjected. The light phase, on the other hand, is recovered and treated in the following step, step c), of the process according to the invention.

[0043] In a preferred embodiment of the invention, the mixture prepared in the mixing section is cooled, for example in a heat exchanger using cooling water or air, preferably below its bubble point, for example below 95°C, in particular between 80 and 95°C, preferably between 85 and 95°C, before being sent into the settling flask. Step c) of distillation and separation of butanol

[0044] The process according to the invention includes a step (c) for separating butanol, comprising a distillation section and producing an ethanol-water distillate at the top of the column and a butanol-rich effluent at the bottom. The distillation column of the butanol distillation section, referred to as the butanol column according to the invention, is fed with the light phase from step (b) at an intermediate point between the top and the bottom. This column also includes a lateral withdrawal point located in a zone between the feed and the bottom of the column for a water / butanol / ethanol fraction.

[0045] A person skilled in the art will easily be able to size the distillation column used in this butanol separation step. Typically, the butanol separation column comprises between 10 and 30 theoretical plates, has a molar reflux between 0.5 and 15, and is fed into the zone located in its upper half.

[0046] Advantageously, the withdrawn water / butanol / ethanol fraction comprises between 15 and 45 mol / mol of butanol, preferably between 20 and 40 mol / mol of butanol, for example between 25 and 35 mol / mol of butanol, less than 5 mol / mol of ethanol, preferably less than 3 mol / mol of ethanol, more preferably less than 1 mol / mol of ethanol, and water. According to the invention, the withdrawn liquid is recycled to the mixing section of step b) of the process according to the invention.

[0047] The ethanol-water distillate extracted at the top of the column in step c) of the process according to the invention essentially comprises a mixture of ethanol and water, the ethanol-water mixture representing at least 80 mol%, preferably at least 90 mol%, and even more preferably at least 95 mol% of the extracted distillate. Advantageously, the ethanol represents at least 50 mol / mol of said ethanol-water distillate, preferably at least 60 mol / mol, and even more preferably at least 70 mol / mol of said ethanol-water distillate. Said ethanol-water distillate, extracted at the top of the butanol distillation column, is advantageously returned to the water-ethanol distillation column of step a) of the process according to the invention, thereby limiting ethanol losses.

[0048] The effluent extracted from the bottom of the column in the butanol distillation section of step c) of the process according to the invention is rich in butanol. It comprises, in particular, at least 90 mol%, preferably at least 95 mol%, and even more preferably at least 97 mol% butanol. This effluent, being practically pure butanol, can be utilized.

[0049] The butanol distillation section may further include an upstream reflux device, comprising, for example, a heat exchanger using cooling water or air, a reflux flask, and a reflux pump for returning the reflux to the butanol distillation column and the liquid distillate to the water / ethanol separation column of step a) of the process according to the invention. The butanol distillation section may also include a bottom reboiling device, using, for example, low-pressure steam.

[0050] The method according to the invention will be better understood in view of the following examples 1 to 4 and the figures, which are given by way of illustration and not limitation. FIGURES

[0051] Figure 1 Diagram of an embodiment of the process according to the invention. Description of Figure 1:

[0052] The hydroalcoholic feedstock is supplied via conduit (1) to the water-ethanol separation column (2). The column (2) includes a reflux (or condensation) device at the top, comprising, for example, a heat exchanger (3) using cooling water or air, a reflux flask (4), a reflux pump (5) returning the reflux to the column (2) via conduit (6), and a reboiling device (8) at the bottom. The ethanol-rich effluent is extracted from the top of the column (2) via conduit (7). The water-rich effluent is extracted from the bottom of the column (2) via conduit (9). The column (2) also includes a side draw-off (10) installed in the butanol accumulation zone and two return injections, one (25) near the top and the other (17) downstream and near the draw-off.

[0053] The hydroalcoholic solution withdrawn from the separation column (2) via line (10) is mixed with a water / butanol / ethanol fraction coming from the butanol distillation column (20) via line (11). The mixture is sent via line (12), possibly through, for example, a heat exchanger (13) using water or air as the cooling fluid, to a settling flask (14). The heavier phase exits the settling flask (14) via line (15) and is carried, by pump (16) through line (17) to the water-ethanol separation column (2), to a theoretical plateau close to and downstream of the withdrawal point (10). The lighter phase is carried by pump (18) through line (19) to the column (20).

[0054] The distillation column (20) includes a reflux (or condensation) device at the top, with, for example, a heat exchanger (21), a reflux flask (22), a reflux pump (23) returning the reflux to the column (20) via the line (24), and the ethanol-liquid water distillate to the separation column (2) via the line (25). The column (20) also includes a reboiling device (26) at the bottom. The column (20) includes a side draw-off located in the area between the feed (19) and the bottom of the column. The drawn-off fraction is sent via the line (11) to the mixer, along with the hydroalcoholic solution from the column draw-off (2). At the bottom of the column (20), a butanol-rich effluent is extracted via the line (27).

[0055] Figure 2: ternary water / ethanol / butanol diagram obtained at a pressure of 1.5 bar, with the phase separation zone (D), called the "demixing zone". At this pressure of 1.5 bar, the demixing zone (D) of the water / ethanol / butanol ternary is located at molar contents between 60% and 98% water, between 2% and 40% butanol and less than 14% molar ethanol. EXAMPLES

[0056] The following examples are based on process simulations incorporating thermodynamic data calibrated on experimental points (in particular binary liquid-vapor equilibrium data, liquid-liquid partition coefficient).

[0057] Example 2 illustrates the process according to the invention, compared to Example 1 which shows a simple distillation.

[0058] Example 4 illustrates the application of the process according to the invention in a Lebedev process, compared to Example 3 which shows the Lebedev process with a simple water-ethanol separation column.

[0059] In accordance with the invention, and in particular in the examples below, "traces" of a compound in a stream (such as an effluent) means a content of said compound less than 10 ppm mol, this content being considered negligible in said stream, for example effluent. Example 1 (comparative):

[0060] A hydroalcoholic load comprising water, ethanol and a low content of butanol, is treated by distillation.

[0061] The characteristics of the hydroalcoholic load to be treated are as follows: 100 tonnes / h (3773 Kmole / h), at a temperature of 90°C and a pressure of 1.8 bar abs; Molar composition of the charge: 70% water, 29.75% ethanol and 0.25% butanol (corresponding to 699 kg / h of butanol).

[0062] The hydroalcoholic feedstock is supplied to a distillation column comprising 22 theoretical trays, with the feed located at tray 15 (counting from the top). The column includes a reflux system. It has an absolute pressure of 1.1 bar after the top condenser and 1.6 bar at the bottom, and a molar reflux ratio of 0.65 relative to the distillate.

[0063] For this simulation, the ethanol specification at the bottom of the column is set at 0.1 ppm molar.

[0064] An effluent (60.87 tonnes / h) containing 70.11 mol% ethanol, 29.30 mol% water, and 0.59 mol% butanol is extracted from the top of the column, while nearly pure water (39.13 tonnes / h) containing 0.1 mol ppm ethanol is extracted from the bottom. All the butanol (699 kg / h) is recovered in the effluent extracted from the top due to the formation of the butanol-water azeotrope, which is lighter than water (boiling point of the butanol-water azeotrope = 92.4°C). Example 2 (according to the invention):

[0065] The same hydroalcoholic load as that treated according to Example 1 is treated by the process according to the invention (cf. Figure 1 ).

[0066] The characteristics of the hydroalcoholic load to be treated are as follows: 100 tonnes / h (3773 Kmole / h), at a temperature of 90°C and a pressure of 1.8 bar abs; Molar composition of the charge: 70% water, 29.75% ethanol and 0.25% butanol (corresponding to 699 kg / h of butanol).

[0067] The separation column (2) comprises 33 theoretical trays and has a reflux ratio of 0.65. It is fed with the hydroalcoholic load at theoretical tray 15. At the bottom of the column, 39.85 tonnes / h of water containing 0.1 ppm ethanol are extracted. At the top of the column, 59.75 tonnes / h of an ethanol-rich effluent containing 72.14% ethanol, 27.6% water, and 0.26% butanol is extracted. 100 kmol / h (2.6 tonnes / h) are withdrawn at tray 26. The withdrawn liquid contains 79% water, 7.67% butanol, and 13.33% ethanol.

[0068] The liquid withdrawn from column (2) is mixed with a portion withdrawn (11) from column (20) (withdrawn from between the feed and the bottom) and having a flow rate of 186 kmmol / h (6.8 tonne / h) and a molar composition of 67.06% water, 32.82% butanol and 0.13% ethanol. The mixture is then cooled from 102°C to 92°C in a heat exchanger (13).

[0069] The mixture settles in the flask (14) at a pressure of 1.05 bar absolute. The flow (15) of the heavy phase returning to column (2), at the theoretical plateau 27, has a flow rate of 78 kmmol / h (1.6 tonne / h) and a molar composition of 95.41% water, 1.83% ethanol, and 2.76% butanol. The light phase, comprising 62.12 mol / mol water, 32.03 mol / mol butanol, and 5.85 mol / mol ethanol, is sent, at a flow rate of 208.7 kmmol / h (7.85 tonne / h), to column (20).

[0070] The molar reflux ratio of column (20) relative to its charge is 1.2.

[0071] At the top of column (20), 16.39 Kmole / h (0.64 tonne / h) are returned by conduit (25) to the theoretical tray 3 of column (2): the molar composition of the distillate extracted at the top of column (20) is 72.92% ethanol, 25.55% water and 0.53% butanol.

[0072] At the bottom of column (20) is extracted butanol of 99.99% mol / mol purity.

[0073] Thus, the process according to the invention makes it possible to recover 400 kg / h (5.4 Kmole / h) of butanol at the bottom of the column (20) compared to the 699 kg / h of butanol contained in the feed supplying the column (2).

[0074] Overall, compared to simple distillation as illustrated in Example 1, the process recovers a more concentrated ethanol effluent (72.14% molar instead of 70.11% in Example 1), with half the butanol content (0.26% molar butanol instead of 0.59% molar butanol in the ethanol effluent illustrated in Example 1). The process according to the invention also allows for the recovery of more than half of the butanol entering the process in the form of nearly pure, and therefore usable, butanol. Example 3 (comparative):

[0075] This example shows the simulation of the Lebedev process described in document FR 3 026 100 in which the water-ethanol effluent is treated by simple distillation in a separation column.

[0076] The production unit is fed by 48670 kg / h of feed comprising 93.3% by weight of ethanol and 6.7% by weight of water.

[0077] According to this Lebedev process, 18850 kg / h of product comprising 99.84% butadiene are produced, consuming a total of: 201.3 t / h of steam (117.4 MW) 86.81 MW of furnace heating 8377 kW of electricity 21 t / h of process water 25120 m3 / h of cooling water.

[0078] More specifically, the water-ethanol separation column of the simulated Lebedev process comprises 30 theoretical trays and has a molar reflux ratio of 1. It is fed at theoretical tray 15 by the water-ethanol effluent from the butadiene production / separation unit of the overall process, at a flow rate of 167.6 tonnes / h. This water-ethanol effluent entering the separation column has the following molar composition: 25.39% mol of ethanol; 73.74% mol of water; 0.23% mol of butanol (corresponding to 1.1 tonnes / h of butanol); 0.51% mol of acetic acid; 0.13% mol of other impurities.

[0079] At the bottom of this separation column, the extracted effluent has the following molar composition: 99.09% water, 0.86% acetic acid and 0.05% other impurities (traces of ethanol and butanol).

[0080] At the top of this separation column, 96.38 tonnes / h are extracted, with the following molar composition: 62% mol of ethanol; 37.2% mol of water; 0.55% mol of butanol (corresponding to 1.1 tonnes / h of butanol); 0% mol of acetic acid; 0.25% mol of other impurities.

[0081] The reboiler of the water-ethanol separation column consumes 58.4 MWh / h, i.e. 100 tonnes / h of low pressure steam, and the cooling of the column requires 59.6 MWh / h, i.e. 6921 tonnes / h of cooling water.

[0082] Thus, all the butanol entering the separation column is extracted at the top of the column with the ethanol effluent intended to be recycled to the butadiene production unit, leading to butanol accumulation problems at the reactors and a loss of activity and selectivity of the butadiene conversion catalysts.

[0083] It also appears that the steam consumption of this separation column represents about half of the total consumption of the overall process (100 tonnes / h of steam compared to 201 in total), without the butanol being separated. Example 4 (according to the invention):

[0084] This example simulates the Lebedev process as in the previous example, but in which the treatment process has been inserted (cf. Figure 1 ) according to the invention instead of the simple separation column.

[0085] The same feed as in Example 3, comprising 93.3% by weight of ethanol and 6.7% by weight of water, feeds the production unit at a flow rate of 48670 kg / h. The water-ethanol effluent treatment unit from the conversion unit includes the separation section (step a) of the process according to the invention), the mixing and settling sections (step b) of the process according to the invention) and the butanol separation section (step c).

[0086] The water-ethanol separation column (2) comprises 30 theoretical trays and has a molar reflux ratio of 0.779. It is fed by the water-ethanol effluent from the conversion unit at theoretical tray 15. In this case, the water-ethanol effluent at the inlet of the separation column (2) has a flow rate of 158.5 tonnes / h and the following molar composition: Ethanol: 26.94% mol; Water: 72.27% mol; Butanol: 0.17% mol (corresponding to 787 kg / h of butanol); Acetic acid: 0.53% mol; Other impurities: 0.09% mol.

[0087] A water-rich effluent is extracted from the bottom of column (2). It has the following molar composition: Ethanol: traces; Water: 99.15% mol; Butanol: traces; Acetic acid: 0.85% mol; Other impurities: traces.

[0088] The product extracted at the top of column (2) is recycled to the ethanol-to-butadiene conversion reactor at a rate of 88.69 tonnes / h. It has the following molar composition: Ethanol: 71.02% mol; Water: 28.40% mol; Butanol: 0.33% mol (corresponding to 574 kg / h of butanol); Acetic acid: 0.0% mol; Other impurities: 0.25% mol.

[0089] The separation column also includes a lateral withdrawal at the theoretical tray 23, of a liquid at a flow rate of 3772 kg / h (i.e. 161.5 kmol / h) and comprising 4.6% mol of butanol (i.e. a butanol flow rate of 550 kg / h), 8.99% mol of ethanol, 85.84% mol of water, 0.57% mol of acetic acid and traces of impurities.

[0090] The liquid withdrawn from the separation column (2) is mixed with the cut withdrawn from the column (20). The mixture is then cooled to 92.5°C in a heat exchanger (13) and then sent to the settling flask (14) which has a pressure of 1.05 bar.

[0091] The heavy phase drawn from the settling tank has a flow rate of 2776 kg / h and a molar composition of 95.35% water, 1.16% ethanol, 2.88% butanol, and 0.6% acetic acid (trace impurities). This flow is sent to tray 24 of column 2.

[0092] The light phase drawn from the settling tank has a flow rate of 20040 kg / h and a molar composition of 62.17% water, 3.71% ethanol, 33.39% butanol, and 0.74% acetic acid (trace impurities). This flow rate is the column feed (20).

[0093] Column (20) has 22 theoretical trays and is fed at tray 9. The molar reflux ratio of this column (20) is 11.76.

[0094] Lateral sampling is performed on column (20) at theoretical plate 17. The sample taken from column (20) is sent to the mixing section at a flow rate of 19.05 tonne / h (i.e., 502 kmol / h). Its molar composition is: 63.63% water, 1.31% ethanol, 34.31% butanol, and 0.76% acetic acid (trace impurities).

[0095] The distillate extracted at the top of column (20) is returned to the water-ethanol separation column (2) at a flow rate of 780 kg / h. Its molar composition is: 60.84% ​​ethanol, 36.34% water, 2.82% butanol and traces of acetic acid (traces of other impurities).

[0096] The effluent at the bottom of column (20) is extracted at a flow rate of 218 kg / h and has the following molar composition: Ethanol: traces Water: traces Butanol: 97.15% mol Acetic acid: 2.85% mol Other impurities: traces.

[0097] Utility consumption is 43.88 MW for reboiling column (2) and 3.28 MW for reboiling butanol separation column (20), for a total of 47.16 MW.

[0098] Table 1 below summarizes the results of the water-ethanol effluent treatment unit of the Lebedev process using the treatment process according to the invention and compares them to those of the treatment unit comprising a simple distillation column (Comparative Example 3). Table 1: Results of water-ethanol effluent treatment units using the process according to the invention or using a simple distillation column (Comparative Example 3) With the method according to the invention With a simple distillation Unit charge Total flow rate (tonnes / h) 158,5 167,6 BuOH flow rate (tonne / h) 0,787 1,1 Effluent extracted at the top of the water-ethanol column and recycled Flow rate (tonnes / h) 88,69 96,38 EtOH content (%mol) 71,02 62 Water content (%mol) 28,40 37,2 Butanol content (%mol) 0,33 0,55 Recycled butanol flow rate (tonne / h) 0,574 1,1 Butanol-rich effluent extracted 218 kg / h at 97.15% mol of BuOH N / A Energy consumption for reboiling (MW) 47,16 58,4

[0099] When the process according to the invention is used in the water-ethanol effluent treatment unit of the Lebedev process, it appears that: The quantity of hydroalcoholic feed (158.5 tonne / h) feeding the water-ethanol separation column (2) is reduced compared to the quantity of feed (167.6 tonne / h) of a simple separation column like that of Example 3. This is explained by a reduced quantity of water recycled with the ethanol in the butadiene conversion reaction unit (28.40 mol% water compared to 37.2 mol%); the ethanol-rich effluent, recovered at the top of the water-ethanol separation column (2), has a lower flow rate (88.69 tonne / h compared to 96.38 tonne / h); the ethanol-rich effluent, recovered at the top of column (2), contains more ethanol (71.02 mol%) with a gain of more than 10 points compared to the composition of the ethanol effluent in the case of a simple distillation (62 mol%); a portion of the butanol entering the processing unit is extracted in the case of the process according to the invention whereas all the butanol is recycled back to the reactor in the case of simple distillation.The purity of the butanol, recovered at the bottom of the column (20), is very satisfactory and allows for the possibility of valorizing the butanol (for example, marketing the butanol, possibly as bio-based butanol); the consumption of utilities for reboiling is reduced by 20% in the case of the process according to the invention (47.16 MW) compared to the case of simple distillation (58.4 MW).

[0100] In the case of integrating the treatment process according to the invention into the Lebedev process, the total utility consumptions for the entire Lebedev process, compared to those obtained for the process described in Example 3, are: 181.4 t / h of steam (i.e. 105.8 MW), i.e. a decrease of 10%; 81 MW of furnace heating, i.e. a decrease of 6.7%; 8168 kW of electricity, i.e. a decrease of 2.5%; 21 t / h of process water (unchanged); 22125 m3 / h of cooling water, i.e. a decrease of 12%.

[0101] It is clear that savings on utilities can be made in the case of the Lebedev process including the treatment process according to the invention.

[0102] Furthermore, by including such a treatment step in the Lebedev process, since the butanol is partially extracted, catalytic performance can be improved. A reduction in the amount of heavy impurities resulting from butanol degradation, as well as a limitation of effluents that could demix in the process, can also be observed.

[0103] In the case of the Lebedev process incorporating the treatment process according to the invention, the ethanol-rich effluent recycled to the reaction unit of the Lebedev process being more concentrated in ethanol (less water and less butanol) allows a gain in utilities in the reaction sections (gain at the level of the vaporization of the feed) and during the treatments downstream of the reaction sections (gain at the level of distillations and washings), compared to the Lebedev process without the treatment process according to the invention.

Claims

1. Process for treating an aqueous-alcoholic feedstock (1) comprising water, ethanol and butanol in order to produce an ethanol-rich effluent (7), a water-rich effluent (9) and a butanol-rich effluent (27), comprising: a) a water-ethanol separation step, comprising a water-ethanol separation section comprising a distillation column (2) comprising at least 14 theoretical plates and having a reflux ratio of less than or equal to 1.2, said water-ethanol separation section comprising: o a feed of said aqueous-alcoholic feedstock (1), located at the level of or downstream of the third theoretical plate, o the side withdrawal of an aqueous-alcoholic solution (10) comprising butanol in the butanol accumulation zone of the distillation column located downstream of the feed, o an injection of the heavy phase (17) resulting from step b), located downstream and in a zone between the side withdrawal and the third theoretical plate downstream of the side withdrawal, o an injection of the ethanol-water distillate (25) resulting from step c), located upstream of the feed and in a zone of the distillation column between the theoretical plate at the top of the column at which the reflux (6) returns and the third theoretical plate, said water-ethanol separation section producing, at the top of the column, an ethanol-rich effluent (7) and, at the bottom of the column, a water-rich effluent (9); b) a demixing step comprising o a section for mixing said aqueous-alcoholic solution (10) withdrawn in step a) with the water / butanol / ethanol fraction (11) withdrawn in step c); o a section for decanting the previous mixture (12), comprising a decantation tank (14) in which the pressure is less than or equal to 6 bar absolute, said decanting section producing a heavy phase (15, 17) mainly containing water and a light phase (19); c) a butanol separation step, comprising a butanol distillation section comprising at least one distillation column (20) fed with the light phase (19) resulting from step b) and comprising a side withdrawal, located on said column (20) in a zone between the feed and the bottom of the column, of a water / butanol / ethanol fraction (11), said butanol distillation section producing, at the bottom of the column, a butanol-rich effluent (27) and, at the top of the column, an ethanol-water distillate (25).

2. Process according to Claim 1, wherein the butanol of the aqueous-alcoholic feedstock (1) represents less than 5% mol / mol, in particular less than 2% mol / mol, more particularly less than 1% mol / mol or even less than 0.5% mol / mol, of the aqueous-alcoholic feedstock.

3. Process according to Claim 1 or 2, wherein the distillation column (2) of the separation section of step a) comprises between 20 and 35 theoretical plates.

4. Process according to one of the preceding claims, wherein the distillation column (2) of the separation section of step a) has a molar reflux ratio of between 0.5 and 1.15, preferably between 0.65 and 1.15.

5. Process according to one of the preceding claims, wherein the distillation column (2) of the separation section of step a) is fed with said aqueous-alcoholic feedstock (1) in a zone between one-third and two-thirds of the total height of said column.

6. Process according to one of the preceding claims, wherein the side withdrawal of step a) is located in a zone between one-third and two-thirds of the height of the bottom zone of the column, said bottom zone being the zone located between the feed and the bottom of the column.

7. Process according to one of the preceding claims, wherein the aqueous-alcoholic solution (10) withdrawn in step a) represents between 15 and 40% mol / mol of the mixture (12) of the mixing section of step b).

8. Process according to one of the preceding claims, wherein the pressure in the decantation tank (14) is between 1 and 2 bar absolute.

9. Process according to one of the preceding claims, wherein the mixture (12) obtained from the mixing section of step b) is cooled (13) to a temperature between 80 and 95°C, before being sent to the decantation tank (14).

10. Lebedev process comprising a treatment step utilizing the process according to any one of the preceding claims, wherein the aqueous-alcoholic feedstock is the water-ethanol effluent obtained from the reaction unit of said Lebedev process and the ethanol-rich effluent produced in step a) is recycled to the reaction unit.