PROCESS FOR THE DEHYDROGENATION OF ETHANOL IN A MULTITUBULAR REACTOR

Abstract

The invention relates to a process for the dehydrogenation of a feedstock comprising ethanol, using at least one multitubular reactor advantageously comprising a plurality of tubes comprising at least one dehydrogenation catalyst, and a calender, said feedstock being introduced into the tubes in gas form, at an inlet temperature of greater than or equal to 240° C., a pressure between 0.1 and 1.0 MPa, and a WWH between 2 and 15 h.sup.−1, wherein a heat-transfer fluid circulates in said calender at a flow rate such that the weight ratio of said heat-transfer fluid relative to said feedstock is greater than or equal to 1.0, and such that said heat-transfer fluid is introduced into said calender in gas form at an inlet temperature of greater than or equal to 260° C. and at an inlet pressure of greater than or equal to 0.10 MPa, and less than or equal to 1.10 MPa, and leaves the calender at least partly in liquid form.

Claims

1. A process for the dehydrogenation of ethanol to give acetaldehyde, comprising a stage of dehydrogenation of a feedstock comprising ethanol, said dehydrogenation stage employing a reaction section comprising at least one multitubular reactor which comprises one or a plurality of tubes and a shell, said tube(s) each comprising at least one fixed bed of at least one dehydrogenation catalyst, said feedstock feeding said tube(s) in gaseous form, at an inlet temperature of said feedstock of greater than or equal to 240° C., at an inlet pressure of said feedstock of between 0.1 and 1.0 MPa, and at a weight hourly space velocity (WWH) of the feedstock at the inlet of between 2 and 15 h.sup.−1, a heat-transfer fluid circulating in said shell so that said heat-transfer fluid is introduced into said shell in gaseous form and is, at the shell outlet, at least partly in liquid form, said heat-transfer fluid being introduced into the shell at a flow rate such that the ratio of the flow rate by weight of said heat-transfer fluid at the shell inlet, with respect to the flow rate by weight of said feedstock at the inlet of the tube(s), is greater than or equal to 1.0, said heat-transfer fluid being introduced into the shell at an inlet temperature of the heat-transfer fluid of greater than or equal to 260° C. and less than or equal to 400° C., and at an inlet pressure of the heat-transfer fluid of greater than or equal to 0.10 MPa and less than or equal to 1.10 MPa; said process producing a dehydrogenation effluent comprising at least acetaldehyde, hydrogen and unconverted ethanol.

2. The process as claimed in claim 1, in which the heat-transfer fluid is an oil comprising a eutectic mixture of organic compounds having saturated vapor pressures such that the difference between the saturated vapor pressures of the organic compounds of the oil, at a given temperature, is less than or equal to 50 Pa, preferably less than or equal to 20 Pa, in a preferred way less than or equal to 10 Pa.

3. The process as claimed in claim 1, in which the feedstock comprises at least 50% by weight of ethanol, preferentially at least 70% by weight of ethanol, in a preferred way at least 80% by weight of ethanol, and optionally water, preferably at a content of less than 50% by weight, preferentially of less than 30% by weight, in a preferred way of less than 20% by weight.

4. The process as claimed in claim 1, in which said at least one multitubular reactor a plurality of tubes, preferably at least 100 tubes, preferentially at least 1000 tubes and in a preferred way at least 2000 tubes, and preferably less than 20 000 tubes, in a preferred way less than 10 000 tubes, for example between 5000 and 6000 tubes.

5. The process as claimed in claim 1, in which the tube(s) of the multitubular reactor has (have) a length of between 1 and 6 m, in a preferred way between 2 and 3 m.

6. The process as claimed in claim 1, in which the tube(s) of the multitubular reactor exhibit(s) an internal diameter between 30.0 and 60.0 mm, preferentially between 40.0 and 50.0 mm, and a tube wall thickness preferably between 1.5 and 5.0 mm, preferentially between 2.0 and 4.0 mm and in a preferred way between 2.2 and 3.2 mm.

7. The process as claimed in claim 1, in which the dehydrogenation catalyst comprises at least the element copper on an inorganic support, preferably silica.

8. The process as claimed in claim 1, in which the dehydrogenation catalyst is in the form of particles with a mean equivalent diameter between 0.5 and 10.0 mm, preferably between 1.0 and 5.0 mm.

9. The process as claimed in claim 1, in which the inlet temperature of the feedstock in the tube(s) is between 240° C. and 350° C., preferentially between 250° C. and 300° C., in a preferred way between 260° C. and 290° C.

10. The process as claimed in claim 1, in which the inlet pressure of the feedstock in the tube(s) is between 0.2 and 0.5 MPa, preferentially between 0.3 and 0.4 MPa.

11. The process as claimed in claim 1, in which the weight hourly space velocity (WWH) of the feedstock at the inlet of the reactor is between 2 and 10 h.sup.−1.

12. The process as claimed in claim 1, in which the heat-transfer fluid is introduced into the shell of the multitubular reactor at a flow rate such that the ratio of the flow rate by weight of said heat-transfer fluid at the shell inlet, with respect to the flow rate by weight of said feedstock at the inlet of the tube(s), is greater than or equal to 1.5 and advantageously less than or equal to 10.0, preferably less than or equal to 5.0, in a preferred way less than or equal to 2.0.

13. The process as claimed in claim 1, in which the heat-transfer fluid is introduced into the shell of the multitubular reactor at an inlet temperature of greater than or equal to 260° C., preferably of greater than or equal to 270° C., in a preferred way of greater than or equal to 290° C., and of less than or equal to 400° C., preferably of less than or equal to 380° C., and at an inlet pressure of the heat-transfer fluid of greater than or equal to 0.10 MPa, preferably of greater than or equal to 0.13 MPa, in a preferred way of greater than or equal to 0.20 MPa, and of less than or equal to 1.10 MPa, in a preferred way of less than or equal to 0.85 MPa.

14. The process as claimed in claim 1, comprising a stage of conditioning of the heat-transfer fluid comprising a substage of recovery of the liquid heat-transfer fluid at the shell outlet of the multitubular reactor of the dehydrogenation stage and a stage of compression and/or heating of the heat-transfer fluid in order to obtain a heat-transfer fluid in gaseous form at the inlet temperature and pressure of the heat-transfer fluid in the shell of the dehydrogenation stage.

15. A process for the production of butadiene from an ethanol feedstock comprising at least 80% by weight of ethanol, comprising: A) a stage of conversion of ethanol into acetaldehyde employing the process for the dehydrogenation of ethanol as claimed in claim 1, in which said feedstock which feeds the tubes of the multitubular reactor is at least in part a fraction of an ethanol-rich effluent, advantageously resulting from stage E1), in order to produce a dehydrogenation effluent, and optionally a separation section in order to treat the dehydrogenation effluent and to separate at least a hydrogen effluent in gaseous form and an ethanol/acetaldehyde effluent in liquid form; B) a stage for conversion into butadiene comprising at least a reaction section B fed at least with a fraction or all of said dehydrogenation effluent resulting from stage A), or optional ethanol/acetaldehyde effluent resulting from the optional separation section of stage A), optionally with a liquid ethanol-rich effluent advantageously resulting from stage C1), with a fraction or all of an acetaldehyde-rich effluent advantageously resulting from stage E1), operated in the presence of a catalyst, preferably comprising the element tantalum and an inorganic support preferably comprising silica, at a temperature of between 300° C. and 400° C. and at a pressure of between 0.1 and 1.0 MPa, the feed flow rates being adjusted so that the molar ratio of the ethanol, with respect to the acetaldehyde, at the inlet of said reaction section is between 1 and 5, and a separation section in order to treat the effluent from said reaction section B and to separate at least a gaseous effluent and a liquid effluent; C1) optionally a stage of treatment of the hydrogen comprising at least a compression section compressing said hydrogen effluent resulting from stage A) to a pressure of between 0.1 and 1.0 MPa and a gas-liquid scrubbing section fed at a temperature of between 15° C. and −30° C. with a fraction of said ethanol-rich effluent advantageously resulting from stage E1) and with a fraction of said ethanol/acetaldehyde effluent resulting from stage A) and fed at a temperature of between 25° C. and 60° C. with said compressed hydrogen effluent, and producing at least a liquid ethanol-rich effluent and a purified hydrogen effluent; D1) a stage of extraction of the butadiene comprising at least: (i) a compression section compressing said gaseous effluent resulting from stage B) to a pressure of between 0.1 and 1.0 MPa, optionally said compressed gaseous effluent resulting from stage B) subsequently being cooled to a temperature between 25° C. and 60° C., (ii) a gas-liquid scrubbing section comprising a scrubbing column fed, at the top, at a temperature of between 20 and −20° C., with an ethanol flow consisting of the ethanol feedstock of the process and optionally of a fraction of the ethanol-rich effluent advantageously resulting from stage E1) and, at the bottom, with said gaseous effluent resulting from stage B) compressed and optionally cooled, producing at least a liquid scrubbing effluent and a gaseous by-products effluent, and (iii) a distillation section operated at a pressure of between 0.1 and 1 MPa, fed at least with the liquid effluent resulting from said stage B) and with the liquid effluent from said gas-liquid scrubbing section, producing at least a crude butadiene effluent and an ethanol/acetaldehyde/water effluent; D2) a stage of first purification of the butadiene comprising at least a gas-liquid scrubbing section fed at the bottom with the crude butadiene effluent resulting from D1) and at the top with a flow of water which is a flow of water of origin external to said process for the production of butadiene and/or a fraction of the aqueous effluent advantageously resulting from stage E1), said scrubbing section producing a pre-purified butadiene effluent at the top and a waste water effluent at the bottom; D3) a subsequent stage of purification of the butadiene, fed at least with said pre-purified butadiene effluent resulting from said stage D2) and producing at least a purified butadiene effluent; E2) a stage of removal of impurities and brown oils, fed at least with the ethanol/acetaldehyde/water effluent resulting from stage D1) and with at least a fraction of a water-rich effluent advantageously resulting from stage E1), and producing at least a water/ethanol/acetaldehyde raffinate, a light brown oils effluent and a heavy brown oils effluent; E1) a stage of treatment of the effluents which is fed at least with a water/ethanol/acetaldehyde raffinate advantageously resulting from stage E2), and producing at least an ethanol-rich effluent, an acetaldehyde-rich effluent and a water-rich effluent.

Description

EXAMPLES

Example 1: In Accordance with the Invention

[0095] Example 1 illustrates a dehydrogenation process according to the invention.

[0096] The feedstock to be treated comprises 82% by weight of ethanol and 18% by weight of water. The dehydrogenation reaction is carried out in a multitubular reactor made of alloy steel, the tubes of which comprise a fixed bed of Octolyst® 2001 catalyst sold by Evonik. The feedstock is introduced into the tubes in gaseous form, simultaneously. The heat-transfer fluid used is Dowtherm™ A oil from Dow, and is introduced into the shell in gaseous form, in particular in saturated vapor form.

[0097] All of the parameters of the reactor and of the operating conditions used are summarized in Table 1.

TABLE-US-00001 TABLE 1 Parameters (unit) Value Number of tubes (—) 5312 Height of the tubes (m) 2.5 Internal diameter of the tubes (mm) 45.2 Thickness of the wall of the tubes (mm) 2.77 Weight of catalyst (kg) 15 670 Mean equivalent diameter of the catalyst particles (mm) 4 Inlet temperature of the feedstock (° C.) 270 Inlet pressure of the feedstock (MPa) 0.35 Flow rate of the feedstock (kg/h) 78 346 WWH (h.sup.−1) feedstock, total 5 Temperature of the oil at the inlet of the shell (° C.) 290 Pressure of the oil at the inlet of the shell (MPa) 0.198 Flow rate of the oil at the shell inlet (kg/h) 120 000  Ratio of the flow rates by weight of the oil to the Approxi- feedstock mately 1.53

[0098] The dehydrogenation effluent is recovered at the reactor outlet at a flow rate of 78 346 kg/h, a temperature of approximately 277° C. and a pressure of approximately 0.29 MPa (i.e. a drop in pressure of approximately 0.6 bar, that is to say approximately 0.06 MPa). At the shell outlet, a gas-Dowtherm™ A oil liquid mixture, at 290° C., is recovered.

[0099] The dehydrogenation effluent obtained is analyzed by gas chromatography. It exhibits the following composition: [0100] 57% by weight of ethanol, [0101] 22% by weight of acetaldehyde, [0102] 18% by weight of water, [0103] 2% by weight of other compounds, and in particular: ethyl acetate, acetic acid and butanol, [0104] approximately 1% by weight of hydrogen.

[0105] The performance qualities of the process which are obtained are satisfactory since the process makes it possible to achieve a conversion of 35% by weight of the ethanol with a selectivity for acetaldehyde of 92%.

Example 2: Not in Accordance with the Invention

[0106] Example 2 illustrates a process implementing the dehydrogenation reaction in adiabatic reactors.

[0107] The same feedstock as that of example 1 is treated by the process of example 2: it comprises 18% by weight of water and 82% by weight of ethanol.

[0108] The same Octolyst® 2001 catalyst from Evonik is used as dehydrogenation catalyst.

[0109] The dehydrogenation reaction is carried out in a sequence of 11 axial adiabatic reactors in series, each comprising a fixed bed of dehydrogenation catalyst (Octolyst® 2001) and between which heat exchangers are inserted in order to heat the liquid flow between each bed. The reaction unit thus comprises 11 adiabatic reactors in series and 10 heat exchangers.

[0110] The feedstock, which comprises 82% by weight of ethanol and 18% by weight of water, is introduced into the first reactor at an inlet temperature of 275° C., at an inlet pressure of 0.57 MPa and at a flow rate of 78 346 kg/h, corresponding to a WWH of 2 h.sup.−1 with respect to the ethanol.

[0111] The parameters of the adiabatic reactors having axial fixed beds, the operating conditions and the degrees of conversion of the ethanol which are obtained are presented in table 2. The outlet pressure of the eleventh reactor is 0.25 MPa.

TABLE-US-00002 TABLE 2 Reactor No. 1 2 3 4 5 6 7 8 9 10 11 Volume of the 1.7 3.3 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2 catalytic bed (m.sup.3) Cumulative volume 1.7 5.0 9.2 13.4 17.6 21.8 26.0 30.2 34.4 38.6 42.8 (m.sup.3) T.sub.inlet (° C.) 275 275 275 275 275 275 275 275 275 275 275 T.sub.outlet (° C.) 233 244 253 259 262 265 267 267 267 267 267 Conversion (%) 8 14 18 21 24 26 28 29 31 33 34

[0112] At the outlet of the reaction unit, a conversion of ethanol of 34% is achieved and the selectivity for acetaldehyde is 92%.

Example 3: Not in Accordance with the Invention

[0113] Example 3 illustrates a process implementing the dehydrogenation reaction in adiabatic reactors in the presence of a thermal diluent.

[0114] The same Octolyst® 2001 catalyst from Evonik as that used in the processes described in example 1 and example 2 is used as dehydrogenation catalyst.

[0115] The feedstock which is treated by the process of example 3 is for its part diluted with steam to a dilution of 60% by weight of water per 40% by weight of ethanol. This feedstock is introduced into a series of radial adiabatic reactors each comprising a fixed bed of dehydrogenation catalyst and between which heat exchangers are inserted in order to heat the liquid flow between each bed. The feedstock, which comprises 40% by weight of ethanol and 60% by weight of water, is introduced into the first reactor at an inlet temperature of 275° C., at an inlet pressure of 0.37 MPa and at a flow rate of 78 346 kg/h.

[0116] The parameters of the adiabatic reactors having radial fixed beds, the operating conditions and the degrees of conversion of the ethanol which are obtained are presented in table 3. The outlet pressure of the reactor No. 4 is 0.20 MPa.

TABLE-US-00003 TABLE 3 Reactor No. 1 2 3 4 Volume of the catalytic bed (m.sup.3) 1.7 3.3 4.2 4.2 Cumulative volume (m.sup.3) 1.7 5.0 9.2 13.4 T.sub.inlet (° C.) 275 275 275 275 T.sub.outlet (° C.) 225 254 255 260 Conversion (%) 16 23 30 35

[0117] A dilution of the ethanol of 60% by weight with steam makes it possible to achieve a conversion of the ethanol of 35% after only 4 adiabatic reactors.

[0118] However, under the conditions of the process of example 3 and in particular with an ethanol feedstock diluted to 60% by weight of water, a deactivation of the dehydrogenation catalyst which is faster than in the process of example 2 is observed.