Process for dehydration of ethanol to ethylene at low energy consumption

Abstract

A process for dehydration of an ethanol feedstock to ethylene by: a) preheating ethanol feedstock by heat exchange with effluent from e), b) pretreating the ethanol feedstock to produce pretreated ethanol feedstock, c) vaporizing a vaporization feedstock containing pretreated ethanol feedstock and at least a portion of the flow of treated water recycled in an exchanger to produce a vaporized feedstock, d) compressing said vaporized feedstock to produce a compressed feedstock, e) dehydrating said compressed feedstock in at least one adiabatic reactor, f) separating the effluent from the last adiabatic reactor of e) into an effluent containing ethylene and an effluent containing water, g) purifying at least a portion of the effluent containing water from 0 and separating at least one flow of treated water and at least one flow of unconverted ethanol, h) recycling at least a portion of the flow of treated water from g) upstream of c).

Claims

1. A process for dehydrating an ethanol feedstock to ethylene comprising: a) a step of preheating said ethanol feedstock to a temperature between 100 and 130 C. by heat exchange with the effluent from step e), b) a step of pretreating the ethanol feedstock on an acidic solid operating at a temperature between 100 and 130 C. so as to produce a pretreated ethanol feedstock, c) a step of vaporizing a vaporization feedstock comprising said pretreated ethanol feedstock and at least a portion of the flow of treated water recycled according to step h) in an exchanger by heat exchange with the effluent from the last reactor of step e), said vaporization feedstock being introduced into said vaporization step at a pressure between 0.1 and 1.4 MPa so as to produce a vaporized feedstock, d) a step of compressing said vaporized feedstock in a compressor so as to produce a compressed feedstock, e) a step of dehydrating said compressed feedstock in at least one adiabatic reactor containing at least one dehydration catalyst and in which the dehydration reaction takes place, operating at an inlet temperature between 350 and 550 C. and at an inlet pressure between 0.3 and 1.8 MPa, f) a step of separating the effluent from the last adiabatic reactor of step e) into an effluent comprising ethylene at a pressure below 1.6 MPa and an effluent comprising water, g) a step of purifying at least a portion of the effluent comprising water from step f) and separating at least one flow of treated water and at least one flow of unconverted ethanol, and h) a step of recycling at least a portion of the flow of treated water from step g) upstream of step c).

2. The process according to claim 1, wherein said ethanol feedstock is an ethanol feedstock produced starting from a renewable source obtained from biomass.

3. The process according to claim 1, wherein the vaporization feedstock also comprises at least one flow of unconverted ethanol from step g) of purifying the effluent comprising water.

4. The process according to claim 1, wherein the pressure of the compressed feedstock is between 0.3 and 1.8 MPa.

5. The process according to claim 1, wherein said compressed feedstock is heated in an exchanger of the single-phase gas type, by heat exchange with the effluent from the last adiabatic reactor of step e).

6. The process according to claim 1, wherein the effluent from the last adiabatic reactor of step e) has a temperature between 270 and 450 C. at the outlet of the last adiabatic reactor of step e).

7. The process according to claim 1, wherein the effluent from the last adiabatic reactor of step e) has a pressure between 0.2 and 1.6 MPa at the outlet of the last adiabatic reactor of step e).

8. The process according to claim 1, wherein the dehydration step e) is carried out in one or two reactors.

9. The process according to claim 1, wherein said dehydration catalyst in step e) is an amorphous acid catalyst or a zeolitic acid catalyst.

10. The process according to claim 1, wherein said ethanol feedstock comprises a percentage by weight of ethanol greater than or equal to 35% by weight.

11. The process according to claim 10, wherein said ethanol feedstock comprises a percentage by weight of ethanol between 35 and 99.9% by weight.

12. The process according to claim 1, wherein the pretreatment step b) is supplemented with a pretreatment by an anion exchange resin.

13. The process according to claim 1, wherein the acidic solid is a silica-alumina, acid clay, zeolite, sulphated zirconia or acid resin.

14. The process according to claim 1, wherein the acidic solid has an exchange capacity for capturing basic and cationic species of at least 0.1 mmol H.sup.+ equivalent per gram.

15. The process according to claim 1, wherein the acidic solid has acidic sulphonic groups and has been prepared by polymerization or co-polymerization of aromatic vinyl groups followed by sulphonation, said aromatic vinyl groups being selected from the group consisting of styrene, vinyl toluene, vinyl naphthalene, vinyl ethyl benzene, methyl styrene, vinyl chlorobenzene and vinyl xylene, said resin having a level of cross-linking between 20 and 35%.

16. The process according to claim 1, wherein the acidic solid is a copolymer of divinyl benzene and polystyrene having a level of cross-linking between 20 and 45%.

17. The process according to claim 1, wherein the acidic solid is a TA801 resin.

18. The process according to claim 1, wherein step b) is performed at a temperature between 110 and 130 C.

19. The process according to claim 1, wherein step b) is performed at a temperature between 110 and 120 C.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) FIG. 1 is a diagrammatic representation of the process for dehydration of ethanol in the case of dehydration of a concentrated ethanol feedstock with recycling of at least a portion of the water treated during step h) of the process.

(2) The ethanol feedstock (1) is preheated in an exchanger E1 with the effluent of the last adiabatic reactor R2, which enters via pipeline (14). The preheated ethanol feedstock is then introduced into a pretreatment zone (3) via pipeline (2). The pretreated ethanol feedstock (4) is then mixed in pipeline (5) with a portion of the flow of treated water from the purification zone (20), which is recycled so as to serve as reaction diluent via pipelines (25) and (26). The ethanol feedstock is also mixed with a portion of the flow of unconverted ethanol from the purification zone (20), via pipeline (23), then (26). This mixture, constituting the vaporization feedstock, is introduced via pipeline (5) into a gas/liquid exchanger E2, in which said mixture undergoes heat exchange with the effluent from the last adiabatic reactor R2, which enters the exchanger via pipeline (13) so as to produce a vaporized feedstock. The latent heat, also called enthalpy of condensation, of the effluent from the last adiabatic reactor R2 is used to vaporize the vaporization feedstock, without external heat supply.

(3) The vaporized feedstock is then sent via pipeline (6) to a compressor C1.

(4) Said vaporized and compressed feedstock is then sent via pipeline (7) to an exchanger E3 of the single-phase gas type, in which said feedstock is heated by means of heat exchange with the effluent from the last adiabatic reactor R2, which is introduced into E3 via pipeline (12). In said exchanger of the single-phase gas type, said vaporized and compressed feedstock is superheated and the effluent leaving, in the gaseous state, the last adiabatic reactor R2 is desuperheated, without being condensed.

(5) Said vaporized and compressed feedstock, heated in the exchanger of the single-phase gas type E3, is then introduced into a furnace H1 via pipeline (8) so as to bring it to an inlet temperature in the first adiabatic reactor R1 compatible with the temperature of the dehydration reaction. The effluent from the first reactor R1 is sent to a second furnace H2 via pipeline (10) before being introduced into the second reactor R2 via pipeline (11).

(6) The effluent from the second reactor R2 then undergoes the three successive exchanges described above in exchangers E3, E2 and E1 via pipelines (12), (13) and (14).

(7) The effluent from exchanger E1 is sent via pipeline (15) to a gas/liquid separating column (16), where it is separated into an effluent comprising ethylene (17) and an effluent comprising water (18). A portion of the effluent comprising water is recycled after cooling to column (16) via pipeline (19).

(8) The portion of the effluent comprising water not recycled to column (16) is sent via pipeline (18) to a step (20) of purification and separation. At least one flow of treated water (24) and (25) and at least one flow of unconverted ethanol (22) and (23) are then separated. A flow containing the light gases (21) is also separated.

(9) All (optionally a portion) of said flow of unconverted ethanol from the purification step (20) is recycled via pipeline (23) and is mixed with the flow of treated water recycled via pipeline (25) in pipeline (26). The mixture of these two streams is incorporated upstream of exchanger E2 with the pretreated ethanol feedstock (4).

(10) The following examples illustrate the invention without limiting its scope.

EXAMPLES

Example 1

According to the Invention

(11) Example 1 illustrates a process according to the invention.

(12) The ethanol feedstock under consideration is produced by fermentation of wheat, without extraction of glutens, by a process of the dry milling type.

(13) Step a)

(14) Said ethanol feedstock is introduced, at a flow rate of 45,664 kg/h, into an exchanger E1 at a pressure equal to 1.15 MPa and is heated, remaining in the liquid phase, to a temperature of 120 C. against the effluent from the last adiabatic reactor of step e).

(15) Step b)

(16) The heated ethanol feedstock is pretreated on TA801 resin to remove the traces of nitrogen-containing compounds. During this pretreatment, a portion of the ethanol is converted to DEE. The characteristics of the raw ethanol feedstock and of the pretreated feedstock are given in Table 1.

(17) TABLE-US-00001 TABLE 1 Characteristics of the ethanol feedstock before and after pretreatment (percentages by weight) ETHANOL ETHANOL AFTER FEEDSTOCK PRETREATMENT ETHANOL 91.2% 82.1% H.sub.2O 8.7% 10.5% DEE 0% 7.3% NITROGEN- 0.005% 0.000% CONTAINING COMPOUNDS
Step c)

(18) The vaporization feedstock, constituted by the pretreated ethanol feedstock mixed with 141,252 kg/h of treated water and of unconverted ethanol recycled according to step h), is depressurized and introduced into an exchanger E2 at a pressure equal to 0.27 MPa. The bubble point of this feedstock at this pressure is 127 C. taking into account the presence of DEE. The vaporization feedstock enters exchanger E2 at 113 C. and is therefore already vaporized at 8.6% by weight. The pressure at the inlet of exchanger E2 was adjusted in such a way that the temperature approach with the flow from the last adiabatic reactor of step e) is at a minimum of 15 C.

(19) In step c), most of the latent heat of the aqueous phase of the effluent from the last adiabatic reactor of step e) is recovered for vaporizing the vaporization feedstock, without external heat supply. Thus, 93.6 MW is exchanged between said vaporization feedstock and said effluent.

(20) Step d)

(21) The vaporized feedstock is then compressed in a radial compressor with an integrated multiplier so that the pressure of said vaporized feedstock is equal to 0.695 MPa at the end of the compression.

(22) The compressed feedstock is then heated in an exchanger E3 of the single-phase gas type, by means of heat exchange with the effluent from the adiabatic reactor of step e). In said exchanger of the single-phase gas type, said compressed feedstock is superheated to a temperature of 405 C. and the effluent leaving, in the gaseous state, the last adiabatic reactor of step e) is desuperheated without being condensed, and has a temperature of 253 C.

(23) Step e)

(24) Said compressed feedstock, heated in said exchanger of the single-phase gas type, is then introduced into a furnace so as to bring it to an inlet temperature in the first adiabatic reactor of step e) compatible with the temperature of the highly endothermic reaction of dehydration and of conversion of DEE to ethylene, i.e. to a temperature of 440 C. The outlet temperature of the last adiabatic reactor of step e) is 420 C.

(25) The trapping of the nitrogen-containing compounds in the pretreatment step b) makes it possible to reduce the inlet temperature of the first adiabatic reactor of step e) significantly.

(26) Said compressed and heated feedstock is introduced into the first adiabatic reactor at an inlet pressure of 0.595 MPa. The pressure of the effluent at the outlet of the last adiabatic reactor of step e) is 0.500 MPa. The dehydration step e) is carried out at a weight hourly space velocity of 7 h.sup.1.

(27) The adiabatic reactor contains a fixed bed of dehydration catalyst, said catalyst comprising 80% by weight of zeolite ZSM-5 treated with H.sub.3PO.sub.4 so that the content of phosphorus P is 3% by weight.

(28) The conversion of the ethanol feedstock in step e) is 95%.

(29) Step f)

(30) The effluent from the last adiabatic reactor of step e) then undergoes the three heat exchanges described above and is sent to a gas/liquid separating column. An effluent comprising ethylene at a pressure equal to 0.36 MPa is separated, as well as an effluent comprising water. This separation is carried out using a gas/liquid separating column, with recycling of the water produced at bottom of the column to the top of the column and after cooling and injection of neutralizing agent.

(31) The effluent comprising ethylene then undergoes a compression to bring its pressure back up to 2.78 MPa prior to its final purification.

(32) Step g)

(33) A flow of treated water and a flow of unconverted ethanol as well as a flow containing the light gases are then separated by conventional low-pressure distillation of the raw water.

(34) Step h)

(35) A portion of the flow of treated water and a portion of the flow of unconverted ethanol are recycled upstream of the vaporization step c) in the proportions described in step c). The different streams, in kg/h, are presented in Table 2 and in Table 3.

(36) TABLE-US-00002 TABLE 2 Composition of the main streams (1/2) Pretreated Flow Flow Effluent ethanol entering leaving comprising Description of the flow feedstock R1 R2 ethylene Corresponding flow No. in 4 9 12 17 the figure Total mass flow rate kg/h 45664 186916 186916 25692 Mass flow rate by kg/h components ethylene 0 0 25087 25087 ethane 0 0 8 8 C3 0 0 93 93 C4 0 0 87 87 DEE 3352 3352 14 14 ethanol 37504 39310 2187 151 H.sub.2O 4808 143730 158602 198 oxygenated compounds 0 325 586 42 (other than ethanol) Other minor components 0 199 252 12

(37) TABLE-US-00003 TABLE 3 Composition of the main streams (2/2) Ethanol Effluent and comprising water Purged Light Description of the flow water recycle water gases Corresponding flow No. in the 18 26 24 21 figure Total mass flow rate kg/h 161224 141252 19007 965 Mass flow rate by kg/h components ethylene 0 0 0 0 ethane 0 0 0 0 C3 0 0 0 0 C4 0 0 0 0 DEE 0 0 0 0 ethanol 2036 1806 3 227 H.sub.2O 158404 138922 18987 495 oxygenated compounds (other 544 325 6 213 than ethanol) Other minor components 240 199 11 30

(38) Compounds C3 and C4 are C3 and C4 hydrocarbon-containing compounds.

(39) The selectivity of the process for ethylene is 99%.

(40) It is calculated as follows: (Ethylene contained in the effluent comprising ethylene)/(0.61*quantity of ethanol converted) where the quantity of ethanol converted is the ethanol contained in the ethanol feedstock before pretreatment subtracted from the ethanol contained in the streams of purged water and in the effluent comprising ethylene. 0.61 g is the maximum quantity of ethylene obtained on dehydrating 1 g of pure ethanol.

(41) The energy balance of the scheme according to Example 1 according to the invention is presented in Table 4:

(42) TABLE-US-00004 TABLE 4 Energy balance Energy exchanged within Energy supplied to the system by the system external supply Quantity Quantity Quantity Quantity of heat of heat of heat of heat exchanged exchanged Quantity extracted exchanged in the in the of heat Power on the in the first second third exchanged required gas/liquid exchanger exchanger exchanger in the for separating (E1) (E2) (E3) furnace compression column MW MW MW MW MW MW 4.21 93.6 18.32 10.4 10.9 22.53

(43) The primary energy consumption was estimated on the following basis: efficiency of 0.8 for the furnaces efficiency of 0.375 for electricity generation

(44) The scheme according to Example 1 according to the invention has an equivalent primary energy consumption or specific consumption of 6.0 GJ equivalent per tonne of ethylene produced.

Example 2

Comparison

(45) Example 2 illustrates a process in which the steps a) and b) of preheating and pretreatment do not take place. The ethanol is not converted to DEE and the process starts at step c); exchanger E1 is no longer present.

(46) Step c)

(47) The vaporization feedstock, constituted by the unpretreated ethanol feedstock mixed with 141,258 kg/h of treated water and of unconverted ethanol recycled according to step h), is introduced at a flow rate of 186,922 kg/h into exchanger E2 at a pressure equal to 0.24 MPa.

(48) The pressure was lowered by 0.03 MPa compared with Example 1. Without the presence of DEE, the bubble point of the vaporization feedstock at 0.27 MPa is 115 C. (127 C. in Example 1). The inlet pressure is altered by 0.03 MPa so as to maintain a minimum temperature approach of 15 C. with the effluent from the last adiabatic reactor of step e).

(49) In step c), most of the latent heat of the aqueous phase of the effluent from the adiabatic reactor of step e) is recovered for vaporizing the vaporization feedstock, without external heat supply. Thus, 98 MW is exchanged between the vaporization feedstock and the effluent from the reactor.

(50) Step d)

(51) The vaporized feedstock is then compressed in a radial compressor with an integrated multiplier so that the pressure of said vaporized feedstock at the end of the compression is equal to 0.695 MPa.

(52) The compressed feedstock is then heated in an exchanger E3 of the single-phase gas type, by means of heat exchange with the effluent from the last adiabatic reactor of step e). In said exchanger of the single-phase gas type, said compressed feedstock is superheated to a temperature of 405 C. and the effluent leaving, in the gaseous state, the last adiabatic reactor of step e) is desuperheated without being condensed and has a temperature of 269 C.

(53) Step e)

(54) Said compressed feedstock, heated in said exchanger of the single-phase gas type, is then introduced into a furnace in order to bring it to an inlet temperature in the first adiabatic reactor of step e) compatible with the temperature of the dehydration reaction, i.e. to a temperature of 470 C. The outlet temperature of the last adiabatic reactor of step e) is 420 C.

(55) Said compressed and heated feedstock is introduced into the adiabatic reactor at an inlet pressure of 0.595 MPa. The pressure of the effluent at the outlet of the last adiabatic reactor of step e) is 0.500 MPa. The dehydration step e) is carried out at a weight hourly space velocity of 7 h.sup.1.

(56) The conversion of the ethanol feedstock in step e) is 95%.

(57) Step f)

(58) The effluent from the last adiabatic reactor of step e) then undergoes the two heat exchanges described above and is sent to a gas/liquid separating column. An effluent comprising ethylene at a pressure equal to 0.39 MPa is separated, as well as an effluent comprising water. This separation is performed using a gas/liquid separating column, with recycling of the water produced at the bottom of the column to the top of the column and after cooling and injection of neutralizing agent.

(59) The effluent comprising ethylene then undergoes a compression to bring its pressure back up to 2.78 MPa prior to its final purification.

(60) Step g)

(61) The raw water from step f) is then neutralized with soda, then undergoes conventional low-pressure distillation to be separated into three streams: a flow of treated water, a flow of unconverted ethanol and a flow containing the light gases.

(62) Step h)

(63) A portion of the flow of treated water and a portion of the flow of unconverted ethanol are recycled upstream of the vaporization step c).

(64) The different streams, in kg/h, are presented in Table 5 and Table 6.

(65) TABLE-US-00005 TABLE 5 Composition of the main streams (1/2) Flow Flow Effluent Ethanol entering leaving comprising Description of the flow feedstock R1 R2 ethylene Corresponding flow No. in 4 9 12 17 the figure Total mass flow rate kg/h 45664 186922 186922 25964 Mass flow rate by kg/h components ethylene 0 0 25087 25087 ethane 0 0 8 8 C3 0 0 93 93 C4 0 0 87 87 DEE 0 0 14 14 ethanol 41671 43496 2187 151 H.sub.2O 3993 142947 158602 311 oxygenated compounds 0 413 586 62 (other than ethanol) Other minor components 0 66 258 151

(66) TABLE-US-00006 TABLE 6 Composition of the main streams (1/2) Effluent Ethanol comprising and water Purged Light Description of the flow water recycle water gases Corresponding flow No. in the 18 26 24 21 figure Total mass flow rate kg/h 160958 141258 19007 693 Mass flow rate by kg/h components ethylene 0 0 0 0 ethane 0 0 0 0 C3 0 0 0 0 C4 0 0 0 0 DEE 0 0 0 0 ethanol 2036 1825 3 208 H.sub.2O 158291 138954 18987 350 oxygenated compounds (other 524 413 6 105 than ethanol) Other minor components 107 66 11 30

(67) Compounds C3 and C4 are C3 and C4 hydrocarbon-containing compounds.

(68) The selectivity of the process for ethylene is 99%.

(69) The energy balance of the scheme according to Example 2 is presented in Table 7.

(70) TABLE-US-00007 TABLE 7 Energy balance Energy supplied to the system by an external supply Quantity Energy exchanged Quantity of heat within the system of Electricity extracted Quantity of heat Quantity of heat heat required on the exchanged in the exchanged in the exchanged for gas/liquid first exchanger second in the com- separating (E2) exchanger (E3) furnace pression column MW MW MW MW MW 98.0 17.1 13.9 12.4 22.53

(71) The scheme according to Example 2, as a comparison with the invention, has an equivalent primary energy consumption or specific consumption of 7.23 GJ equivalent per tonne of ethylene produced.

(72) Without pretreatment, the primary energy consumption therefore increases by 1.2 GJ equivalent per tonne of ethylene produced.