Method for partially extracting butanol from an aqueous solution comprising ethanol and butanol

Abstract

The invention relates to a process for treating an hydroalcoholic feedstock comprising ethanol and butanol in order to produce an ethanol-rich effluent, a water-rich effluent and a butanol-rich effluent, comprising a) a water-ethanol separation step comprising a distillation column fed with said hydroalcoholic feedstock and comprising at least 14 theoretical plates, a molar reflux ratio of less than or equal to 1.2, a side withdrawal in the butanol accumulation zone and two injections of recycled streams resulting from steps b) and c); b) a demixing step comprising a section for mixing the stream withdrawn in step a) and the fraction withdrawn in step c), and a decanting section, the heavy phase being recycled to the distillation column of step a); c) a butanol separation step comprising a distillation column fed with the light phase resulting from step b), comprising a side withdrawal of a water/butanol/ethanol fraction recycled to the mixing section of step b) and producing a butanol-rich effluent and an ethanol-water distillate which is recycled to the distillation column of step a). This process appears to be particularly advantageous for the treatment of the hydroalcoholic effluent from the Lebedev process.

Claims

1. A process for treating a hydroalcoholic feedstock comprising water, ethanol and butanol in order to produce an ethanol-rich effluent, a water-rich effluent and a butanol-rich effluent, the process comprising: step a) separating water and ethanol in an area comprising a water-ethanol separation section comprising a distillation column comprising at least 14 theoretical plates and having a reflux ratio of less than or equal to 1.2, said water-ethanol separation section additionally comprising: a feed of said hydroalcoholic feedstock, located at the level of or downstream of a theoretical plate number 3 and forming a bottom zone located between the feed and the bottom of the column and a top zone between the feed and the top of the column, a side withdrawal of a hydroalcoholic solution comprising butanol in the butanol accumulation zone of the distillation column located downstream of the feed, an injection of a heavy phase resulting from step b), into the distillation column in a zone between the side withdrawal and a third theoretical plate downstream of the side withdrawal which is positioned in the bottom zone, an injection of an ethanol-water distillate resulting from step c), into the distillation column upstream of the feed and in a zone bounded upstream by the top zone of the column where the reflux returns and the theoretical plate number 3, said distillation section producing, an ethanol-rich effluent at the top zone of the column and, a water-rich effluent at the bottom zone of the column; step b) demixing wherein said demixing is provided in an area comprising: a section for mixing said hydroalcoholic solution withdrawn in step a) with a water/butanol/ethanol fraction withdrawn in step c) to form a mixture; a section for decanting the mixture, comprising a decantation tank in which the pressure is less than or equal to 6 bar absolute, said decanting section producing the heavy phase mainly containing water and a light phase; step c) separating butanol in an area comprising a butanol distillation section comprising at least one distillation column fed with the light phase resulting from step b) and comprising a side withdrawal of the water/butanol/ethanol fraction, located on said column in the bottom zone, said butanol distillation section producing, a butanol-rich effluent at the bottom of the column and, the ethanol-water distillate at the top of the column.

2. The process as claimed in claim 1, in which the butanol is present in the hydroalcoholic feedstock but represents less than 5% mol/mol of the hydroalcoholic feedstock.

3. The process as claimed in claim 1, in which the distillation column of the separation section of step a) comprises between 20 and 35 theoretical plates.

4. The process as claimed in claim 1, in which the distillation column of the separation section of step a) has a molar reflux ratio of between 0.5 and 1.15.

5. The process as claimed in claim 1, in which the distillation column of the separation section of step a) is fed with said hydroalcoholic feedstock in a zone between one-third and two-thirds of the total height of said column.

6. The process as claimed in claim 1, in which 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. The process as claimed in claim 1, in which the hydroalcoholic solution withdrawn in step a) represents between 15 and 40% mol/mol of the mixture of the mixing section of step b).

8. The process as claimed in claim 1, in which the pressure in the decantation tank is between 1 and 2 bar absolute.

9. The process as claimed in claim 1, in which the mixture obtained from the mixing section of step b) is cooled to a temperature between 80 and 95° C., before being sent to the decantation tank.

10. A Lebedev process comprising: treating a hydroalcoholic feedstock utilizing the process of claim 1, wherein the hydroalcoholic feedstock is a water-ethanol and butanol 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.

11. The process of claim 2, wherein the butanol is present in the hydroalcoholic feedstock but represents less than 2% mol/mol.

12. The process of claim 2, wherein the butanol is present in the hydroalcoholic feedstock but represents less than 1% mol/mol.

13. The process of claim 2, wherein the butanol is present in the hydroalcoholic feedstock but represents less than 0.5% mol/mol.

14. The process of claim 4, wherein the distillation column of the separation section of step a) has a molar reflux ratio of between 0.65 and 1.15.

Description

FIGURES

(1) FIG. 1: Diagram of an embodiment of the process according to the invention.

DESCRIPTION OF FIG. 1

(2) The hydroalcoholic feedstock feeds the water-ethanol separation column (2) via the pipe (1). The column (2) comprises a reflux (or condensation) device at the top, comprising for example a heat exchanger (3) using cooling water or air, a reflux tank (4), a reflux pump (5) returning the reflux to the column (2) via the pipe (6), and a reboiling device (8) at the bottom. The ethanol-rich effluent is extracted at the top of the column (2) via the pipe (7). The water-rich effluent is extracted via the pipe (9) at the bottom of the column (2). The column (2) also comprises a side withdrawal (10) installed in the butanol accumulation zone and two return injections, one (25) close to the top and the other (17) downstream of and close to the withdrawal.

(3) The hydroalcoholic solution withdrawn and leaving the separation column (2) via the pipe (10) is mixed with a water/butanol/ethanol fraction coming via the pipe (11) from the butanol distillation column (20). The mixture is sent via the pipe (12), optionally via, for example, a heat exchanger (13) using water or air as the cooling fluid, into a decantation tank (14). The heavy phase leaves the decantation tank (14) via the pipe (15) and is taken, by virtue of the pump (16), via the pipe (17) to the water-ethanol separation column (2), to a theoretical plate close to and downstream of the withdrawal (10). The light phase is taken by the pump (18) through the pipe (19) to the column (20).

(4) The distillation column (20) comprises a reflux (or condensation) device at the top, with for example a heat exchanger (21), a reflux tank (22), a reflux pump (23) returning the reflux to the column (20) via the pipe (24) and the liquid water-ethanol distillate to the separation column (2) via the pipe (25). The column (20) also comprises a reboiling device (26) at the bottom. The column (20) comprises a side withdrawal located in the zone between the feed (19) and the bottom of the column. The fraction withdrawn is sent via the pipe (11) to the mixer, with the hydroalcoholic solution from the withdrawal from the column (2). At the bottom of column (20), a butanol-rich effluent is extracted via the pipe (27).

(5) FIG. 2: water/ethanol/butanol ternary diagram obtained at a pressure of 1.5 bar, with the phase separation zone (D), called “demixing loop”. At this pressure of 1.5 bar, the demixing loop (D) of the water/ethanol/butanol ternary is located at molar contents of between 60% and 98% water, between 2% and 40% butanol and less than 14 mol % ethanol.

EXAMPLES

(6) The examples that follow are based on process simulations integrating thermodynamic data matched to experimental points (in particular binary liquid-vapor equilibrium data, liquid-liquid partition coefficient).

(7) Example 2 illustrates the process according to the invention, in comparison to example 1 which shows a simple distillation.

(8) Example 4 illustrates the application of the process according to the invention in a Lebedev process, in comparison to example 3 which shows the Lebedev process with a simple water-ethanol separation column.

(9) In accordance with the invention, and in particular in the examples hereinbelow, “traces” of a compound in a stream (such as an effluent) is understood to mean a content of said compound of less than 10 ppm mol, this content being considered to be negligible in said stream, for example effluent.

Example 1 (Comparative)

(10) An hydroalcoholic feedstock comprising water, ethanol and a low content of butanol is treated by distillation.

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

(12) The hydroalcoholic feedstock feeds a distillation column comprising 22 theoretical plates, the feed being placed at theoretical plate 15 (starting from the top). The column comprises a reflux system. The column has a pressure of 1.1 bar abs. after the top condenser and 1.6 bar at the bottom and has a molar reflux ratio of 0.65 with respect to the distillate.

(13) For this simulation, the specification for ethanol at the bottom of the column is set at 0.1 ppm molar.

(14) An effluent (60.87 tonnes/h) comprising 70.11 mol % of ethanol, 29.30 mol % of water and 0.59 mol % of butanol is extracted at the top of the column and virtually pure water (39.13 tonnes/h), comprising 0.1 ppm molar of ethanol, is extracted at the bottom of the column. All of the butanol (699 kg/h) is found in the effluent extracted at the top, due to the formation of the butanol-water azeotrope which is lighter than water (boiling temperature of the butanol-water azeotrope=92.4° C.).

Example 2 (in Accordance with the Invention)

(15) The same hydroalcoholic feedstock as that treated according to example 1 is treated by the process according to the invention (cf. FIG. 1).

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

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

(18) The liquid withdrawn from column (2) is mixed with a fraction (11) withdrawn on column (20) (withdrawn between the feed and the bottom) and having a flow rate of 186 kmol/h (6.8 tonnes/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).

(19) The mixture is decanted in the tank (14) at a pressure of 1.05 bar absolute. The stream (15) of the heavy phase returning to the column (2), at theoretical plate 27, has a flow rate of 78 kmol/h (1.6 tonnes/h) and a molar composition of 95.41% water, 1.83% ethanol and 2.76% butanol. The light phase comprising 62.12% mol/mol of water, 32.03% mol/mol of butanol and 5.85% mol/mol of ethanol is sent, at a flow rate of 208.7 kmol/h (7.85 tonnes/h), to column (20).

(20) The molar reflux ratio of column (20) relatively to its feedstock is 1.2.

(21) At the top of column (20), 16.39 kmol/h (0.64 tonne/h) are returned via pipe (25) onto theoretical plate 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.

(22) Butanol having a purity of 99.99% mol/mol is extracted at the bottom of column (20).

(23) Thus, the process according to the invention makes it possible to recover 400 kg/h (5.4 kmol/h) of butanol at the bottom of column (20), relatively to the 699 kg/h of butanol present in the feedstock feeding column (2).

(24) Overall, compared to a simple distillation as illustrated in example 1, the process makes it possible to recover an ethanol effluent which is more concentrated in ethanol (72.14 mol % instead of 70.11% in example 1), with two times less butanol (0.26 mol % of butanol instead of 0.59 mol % of butanol in the ethanol effluent illustrated in example 1). The process according to the invention also makes it possible to recover, in this case, more than half of the butanol entering the process in the form of virtually pure, and therefore profitably exploitable, butanol.

Example 3 (Comparative)

(25) 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.

(26) The production unit is fed with 48 670 kg/h of feedstock comprising 93.3% by weight of ethanol and 6.7% by weight of water.

(27) In this Lebedev process, 18 850 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 25 120 m.sup.3/h of cooling water.

(28) More particularly, the water-ethanol separation column of the simulated Lebedev process comprises 30 theoretical plates and has a molar reflux ratio of 1. It is fed at theoretical plate 15 with the water-ethanol effluent obtained from the butadiene production/separation unit of the overall process at a flow rate of 167.6 tonnes/h. This water-ethanol effluent has the following molar composition on entry into the separation column: 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.

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

(30) At the top of the 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.

(31) The reboiler of the water-ethanol separation column consumes 58.4 MWh/h, that is to say for example 100 tonnes/h of low-pressure steam, and the cooling of the column requires 59.6 MWh/h, that is to say for example the circulation of 6921 tonnes/h of cooling water.

(32) Thus, all of 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 problems with the accumulation of butanol in the reactors and a loss of activity and selectivity of the butadiene conversion catalysts.

(33) It is also apparent that the steam consumption of this separation column represents approximately half of the total consumption of the overall process (100 tonnes/h of steam compared to a total of 201), without the butanol being separated.

Example 4 (According to the Invention)

(34) This example simulates the Lebedev process as in the previous example, but into which the treatment process (cf. FIG. 1) according to the invention has been inserted in place of the simple separation column.

(35) The same feedstock as that 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 48 670 kg/h. The unit for treating the water-ethanol effluent obtained from the conversion unit comprises the separation section (step a) of the process according to the invention), the mixing and decanting sections (step b) of the process according to the invention) and the butanol separation section (step c).

(36) The water-ethanol separation column (2) comprises 30 theoretical plates and has a molar reflux ratio of 0.779. It is fed with the water-ethanol effluent obtained from the conversion unit at theoretical plate 15. In this case, the water-ethanol effluent at the inlet to the separation column (2) has a flow rate of 158.5 tonnes/h and the following molar composition: Ethanol: 29.94 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 %.

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

(38) The product extracted at the top of column (2) is recycled to the reactor for converting ethanol into butadiene at a flow 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 %.

(39) The separation column also comprises a side withdrawal at theoretical plate 23 of a liquid at a flow rate of 3772 kg/h (that is to say 161.5 kmol/h) and comprising 4.6 mol % of butanol (that is to say a flow rate of butanol of 550 kg/h), 8.99 mol % of ethanol, 85.84 mol % of water, 0.57 mol % of acetic acid and traces of impurities.

(40) The liquid withdrawn on the separation column (2) is mixed with the fraction withdrawn from column (20). The mixture is then cooled to 92.5° C. in a heat exchanger (13) and then sent to a decantation tank (14) having a pressure of 1.05 bar.

(41) The heavy phase withdrawn from the decanting 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 (traces of impurities). This stream is sent to plate 24 of column 2.

(42) The light phase withdrawn from the decanting tank has a flow rate of 20 040 kg/h and a molar composition of 62.17% water, 3.71% ethanol, 33.39% butanol and 0.74% acetic acid (traces of impurities). This stream is the feedstock for column (20).

(43) Column (20) includes 22 theoretical plates and is fed at plate 9. The molar reflux ratio for this column (20) is 11.76.

(44) A side withdrawal is carried out on column (20) at theoretical plate 17. The fraction withdrawn from column (20) is sent to the mixing section at a flow rate of 19.05 tonnes/h (that is to say 502 kmol/h). Its molar composition is: 63.63% water, 1.31% ethanol, 34.31% butanol and 0.76% acetic acid (traces of impurities).

(45) 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).

(46) 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.

(47) The consumption of utilities is 43.88 MW for the reboiling in column (2) and 3.28 MW for the reboiling in the butanol separation column (20), i.e. a total of 47.16 MW.

(48) Table 1 below summarizes the results of the unit for treating the water-ethanol effluent from the Lebedev process using the treatment process according to the invention and compares these results to those of the treatment unit comprising a simple distillation column (comparative example 3).

(49) TABLE-US-00001 TABLE 1 Results of the units for treating the water-ethanol effluent using the process according to the invention or using a simple distillation column (comparative example 3). With the process With a according to the simple invention distillation Unit Total flow rate 158.5 167.6 feedstock (tonnes/h) BuOH flow rate 0.787 1.1 (tonnes/h) Effluent Flow rate (tonnes/h) 88.69 96.38 extracted at EtOH content (mol %) 71.02 62 the top of Water content (mol %) 28.40 37.2 the water- Butanol content 0.33 0.55 ethanol (mol %) column and Flow rate of recycled 0.574 1.1 recycled butanol (tonnes/h) Butanol-rich effluent extracted 218 kg/h at NA 97.15 mol % BuOH Energy consumption for the reboiling 47.16 58.4 (MW)

(50) When the process according to the invention is used in the unit for treating the water-ethanol effluent from the Lebedev process, it is apparent that: the amount of hydroalcoholic feedstock (158.5 tonnes/h) feeding the water-ethanol separation column (2) is reduced compared to the amount of feedstock (167.6 tonnes/h) for a simple separation column such as that of example 3. This is explained by a reduced amount of water recycled with the ethanol into the unit for the conversion reaction to butadiene (28.40 mol % of 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 tonnes/h compared to 96.38 tonnes/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 treatment unit is extracted in the case of the process according to the invention, whereas all of the butanol is recycled to the reactor in the case of a simple distillation. The purity of the butanol, recovered at the bottom of column (20), is very satisfactory and makes it possible to envisage profitable exploitation of the butanol (for example marketing of the butanol, possibly as bio-based butanol); the consumption of utilities for the 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).

(51) In the case of the integration of the treatment process according to the invention into the Lebedev process, the overall consumption of utilities for the entire Lebedev process are, in comparison with those obtained for the process described in example 3: 181.4 t/h of steam (i.e. 105.8 MW), that is to say a reduction of 10%; 81 MW of furnace heating, that is to say a reduction of 6.7%; 8168 kW of electricity, that is to say a reduction of 2.5%; 21 t/h of process water (unchanged); 22 125 m.sup.3/h of cooling water, that is to say a reduction of 12%.

(52) It is clearly apparent that savings on utilities can be made in the case of the Lebedev process including the treatment process according to the invention.

(53) Moreover, by including such a treatment process in the Lebedev process, insofar as the butanol is partially extracted, the catalytic performance will be able to be improved. A reduction in the amount of heavy impurities resulting from the degradation of the butanol and also a limitation of the effluents which could demix in the process will also be able to be observed.

(54) In the case of the Lebedev process integrating the treatment process according to the invention, the fact that the ethanol-rich effluent recycled to the reaction unit of the Lebedev process is more concentrated in ethanol (less water and less butanol) makes it possible to save on utilities in the reaction sections (saving in the vaporization of the feedstock) and during the treatments downstream of the reaction sections (saving in the distillations and washing operations) compared to the Lebedev process without the treatment process according to the invention.