Process for dehydration of ethanol into ethylene using pretreatment of the feedstock

Abstract

The invention relates to a process for dehydration of an ethanol feedstock into ethylene comprising at least the stages: a) A stage for pretreatment of the ethanol feedstock on an acidic solid, b) A stage for evaporation of said pretreated ethanol feedstock in a heat exchanger, c) A stage for superheating said evaporated feedstock in such a way as to bring it to an inlet temperature that is compatible with the temperature of a dehydration reaction, d) A stage for dehydration of said feedstock that is obtained from stage c) in at least one adiabatic reactor that contains at least one dehydration catalyst.

Claims

1. A process for dehydration of an ethanol feedstock into ethylene comprising at least the stages: a) pretreating the ethanol feedstock on an acidic solid operating at a temperature of between 100 and 130° C. in such a way as to produce a pretreated ethanol feedstock, wherein from 3% to 20% by weight of the ethanol that is present in said feedstock is converted into diethyl ether, b) evaporating an evaporation feedstock comprising said ethanol feedstock that is pretreated in a heat exchanger, with said evaporation feedstock being introduced into said evaporation stage at a pressure of between 0.1 and 2.5 MPa in such a way as to produce an evaporated feedstock, c) superheating said evaporated feedstock in such a way as to bring it to an inlet temperature that is compatible with the temperature of the dehydration reaction and, d) dehydrating said feedstock that is obtained from stage c) in at least one adiabatic reactor that contains at least one dehydration catalyst and in which the dehydration reaction takes place, operating at an inlet temperature of between 350 and 550° C. and at an inlet pressure of between 0.3 and 1.8 MPa.

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

3. The process according to claim 1, wherein said evaporation feedstock is introduced into said evaporation stage b) at a pressure of between 0.1 and 1.4 MPa and comprising a compression stage of said feedstock that is evaporated prior to said superheating stage c).

4. The process according to claim 3, wherein the pressure of the compressed feedstock is between 0.3 and 1.8 MPa.

5. The process according to claim 1, wherein said evaporated feedstock, optionally compressed, is heated in an exchanger of the gas single phase type, using a heat exchange with the effluent that is obtained from the last adiabatic reactor of stage d).

6. The process according to claim 1, wherein the effluent that is obtained from the last adiabatic reactor of stage d) has exiting the last adiabatic reactor of stage d) a temperature of between 270 and 450° C.

7. The process according to claim 1, wherein the effluent that is obtained from the last adiabatic reactor of stage d) has exiting from the last adiabatic reactor of stage d)—a pressure of between 0.2 and 1.6 MPa.

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

9. The process according to claim 1, wherein said dehydration catalyst that is used in stage d) is an amorphous acid catalyst or a zeolitic acid catalyst.

10. The process according to claim 1, wherein said ethanol feedstock is a concentrated ethanol feedstock, i.e., an ethanol feedstock that comprises a percent by mass of ethanol that is greater than or equal to 35% by weight.

11. The process according to claim 10, wherein said concentrated ethanol feedstock comprises a percent by mass of ethanol that is between 35 and 99.9% by weight.

12. The process according to claim 1, wherein the pretreatment stage a) is completed by a pretreatment using an anion exchange resin.

13. The process of claim 1, wherein the inlet temperature is between 350 and 550° C.

14. The process of claim 1, wherein from 8% to 12% by weight of the ethanol that is present in said feedstock is converted into diethyl ether from the stage for pretreatment.

Description

DESCRIPTION OF THE FIGURES

(1) FIG. 1 diagrammatically shows a particular arrangement of the process of dehydration of an ethanol feedstock that implements a pretreatment with a recycling of at least a portion of water treated during stage (e) of the process.

(2) The ethanol feedstock (1) is introduced into a pretreatment zone (a). The pretreated ethanol feedstock (2) is then mixed in the pipe (3) with a portion of the treated water stream that is obtained from the purification zone (f) that is recycled in such a way as to serve as reaction diluent via the pipe (14). This mixture, constituting the evaporation feedstock, is introduced via the pipe (3) into a gas/liquid exchanger E1 in which said mixture undergoes a heat exchange with the effluent that is obtained from the dehydration section (e) that penetrates the exchanger via the pipe (9) in such a way as to produce an evaporated feedstock. The latent heat, also called condensational enthalpy, of the effluent that is obtained from the dehydration zone (e) is used to evaporate the evaporation feedstock, without an external heat supply.

(3) The evaporated feedstock is then sent via the pipe (4) into a compressor C1.

(4) Said evaporated and compressed feedstock is then sent via the pipe (5) into an exchanger E2 of the gas single-phase type, in which said feedstock is heated using a heat exchange with the effluent that is obtained from the dehydration section (e) that is introduced into E2 via the pipe (8). In said exchanger of the gas single-phase type, said evaporated and compressed feedstock is superheated, and the effluent that is obtained, in the gaseous state, from the dehydration section (e) is “de-superheated,” without being condensed.

(5) Said evaporated, compressed and heated feedstock in the exchanger of gas single-phase type E2 is then introduced into a furnace H1 via the pipe (6) in such a way as to bring it to an inlet temperature in the dehydration section (e) that is compatible with the temperature of the dehydration reaction.

(6) The effluent that is obtained from the dehydration section (e) then undergoes the two successive exchanges described above in the exchangers E2 and E1 via the pipes (8) and (9).

(7) The effluent that is obtained from the exchanger E1 is sent via the pipe (10) into the purification section (f) where it is separated into at least one effluent that comprises ethylene (12), at least one purge that comprises water (13), at least one effluent that comprises water, and all (optionally a portion) of unreacted ethanol (14), and at least one effluent that comprises light gases (11).

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

EXAMPLES

Example 1: In Accordance with the Invention

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

(10) The ethanol feedstock under consideration is produced by fermentation of wheat, without extracting glutens, by a dry-milling-type process according to the English term.

(11) Stage a)

(12) The ethanol feedstock is introduced, at a flow rate of 45,664 kg/h, at a temperature of 120° C. and a pressure of 1.15 MPa into a pretreatment resin TA801 so as to eliminate traces of nitrogen-containing compounds. During this pretreatment, a portion of the ethanol is converted into DEE. The characteristics of the crude and pretreated ethanol feedstock are provided in Table 1.

(13) TABLE-US-00001 TABLE 1 Characteristics of the Ethanol Feedstock Before and After Pretreatment (Percent by Mass) ETHANOL ETHANOL AFTER FEEDSTOCK PRETREATMENT ETHANOL 91.2% 82.1% H20  8.7% 10.5% DEE   0%  7.3% NITROGEN-CONTAINING 0.005%  0.000%  COMPOUNDS
Stage b)

(14) The evaporation feedstock, constituted by the pretreated ethanol feedstock in a mixture with 141,252 kg/h of treated water and unconverted ethanol that are recycled according to stage (f), is depressurized and introduced into an exchanger E1 at a pressure that is equal to 0.27 MPa. The bubble temperature of this feedstock at this pressure is 127° C., taking into account the presence of DEE. The evaporation feedstock enters into the exchanger E1 at 113° C. and is therefore already evaporated at 8.6% by mass. The pressure entering the exchanger E1 was adjusted in such a way that the thermal approach with the stream that is obtained from the last adiabatic reactor of stage e) is at least 15° C.

(15) In stage b), the majority of the latent heat of the aqueous phase of the effluent that is obtained from the last adiabatic reactor of stage e) is recovered for evaporating the evaporation feedstock, without an external heat supply. Thus, 93.6 MW is exchanged between said evaporation feedstock and said effluent.

(16) Optional Compression Stage

(17) The evaporated feedstock is then compressed in the optional compression stage using a radial compressor with an integrated multiplier in such a way that the pressure of said evaporated feedstock is equal to 0.695 MPa at the end of the compression.

(18) Stage c)

(19) The compressed feedstock is then heated in an exchanger E2 of the gas single-phase type, using a heat exchange with the effluent that is obtained from the adiabatic reactor of stage d). In said exchanger of the gas single-phase type, said compressed feedstock is superheated to a temperature of 405° C., and the effluent that is obtained, in the gaseous state, from the last adiabatic reactor of stage d) is “de-superheated” without being condensed and has a temperature of 253° C.

(20) Said feedstock that is compressed and heated in said exchanger of the gas single-phase type is then introduced into a furnace in such a way as to bring it to an inlet temperature in the first adiabatic reactor of stage d) that is compatible with the temperature of the reaction for dehydration and conversion of DEE into highly endothermic ethylene, i.e., at a temperature of 440° C.

(21) Stage d)

(22) The trapping of nitrogen-containing compounds in the pretreatment stage a) makes it possible to reduce significantly the inlet temperature of the first adiabatic reactor of stage d).

(23) 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 exiting the last adiabatic reactor of stage e) is 0.500 MPa. The dehydration stage d) is performed at an hourly speed by weight of 7 h.sup.−1.

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

(25) The conversion of the ethanol feedstock in stage d) is 95%.

(26) The outlet temperature of the last adiabatic reactor of stage d) is 420° C.

(27) Stage e)

(28) The effluent that is obtained from the last adiabatic reactor of stage d) then undergoes two heat exchanges, described above, and is sent into the section for purification and recycling.

(29) An effluent that comprises ethylene meeting the final specifications is separated. An effluent that comprises water corresponding to the purge of the process is also separated.

(30) A stream that contains light gases and impurities is also separated by one or more optionally cryogenic distillation(s).

(31) A stream of water treated in a mixture with a portion of unconverted ethanol is recycled upstream from the evaporation stage b) in the proportions described in stage b).

(32) Information regarding the different streams, in kg/h, is given in Table 2 and Table 3.

(33) TABLE-US-00002 TABLE 2 Composition of the Primary Streams (1/2) Stream Stream Pretreated Entering Exiting Effluent Description of Ethanol into from Comprising the Stream Feedstock Stage (d) Stage (d) Ethylene Stream No. 2 7 8 12 Corresponding to the FIGURE Total Mass kg/h 45,664 186,916 186,916 25,692 Flow Rate Mass Flow kg/h Rate, by Components Ethylene 0 0 25,087 25,087 Ethane 0 0 8 8 C3 0 0 93 93 C4 0 0 87 87 DEE 3,352 3,352 14 14 Ethanol 37,504 39,310 2,187 151 H.sub.2O 4,808 143,730 158,602 198 Oxidized Compounds 0 325 586 42 (Other than Ethanol) Other Minority 0 199 252 12 Components

(34) TABLE-US-00003 TABLE 3 Composition of the Primary Streams (2/2) Effluent That Recycling Comprises of Ethanol Purged Light Description of the Stream Water and Water Water Gases Stream No. Corresponding 13 14 13 11 to the FIGURE Total Mass Flow kg/h 161,224 141,252 19,007 965 Rate 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 2,036 1,806 3 227 H.sub.2O 158,404 138,922 18,987 495 Oxidized Compounds 544 325 6 213 (Other than Ethanol) Other Minority Components 240 199 11 30

(35) The compounds C3 and C4 are C3 and C4 hydrocarbon-containing compounds.

(36) The selectivity of the process in terms of ethylene is 99%.

(37) It is calculated in the following way: (Ethylene that is contained in the effluent that comprises ethylene)/(0.61*amount of converted ethanol) where the amount of converted ethanol is the ethanol that is contained in the ethanol feedstock before pretreatment that is subtracted from the ethanol that is contained in the streams of purged water and in the effluent that comprises ethylene. 0.61 g is the maximum amount of ethylene that is obtained by dehydrating 1 g of pure ethanol.

(38) Information on the energy balance of the diagram according to Example 1 in accordance with the invention is given in Table 4:

(39) TABLE-US-00004 TABLE 4 Energy Balance Energy Exchanged Inside the System Energy Provided to the System by an External Supply Amount of Heat Amount of Heat Amount of Heat Exchanged in Exchanged in Amount of Heat Electricity Extracted in the First the Second Exchanged in Required for the Gas/Liquid Exchanger (E1) Exchanger (E2) the Furnace Compression Separation Column MW MW MW MW MW 93.6 18.32 10.4 10.9 22.53

(40) The estimation of the primary energy consumption was carried out by using the following bases:

(41) Effectiveness of 0.8 on the furnaces

(42) Effectiveness of 0.375 on the production of electricity

(43) The diagram according to Example 1 in accordance with the invention has an equivalent primary energy consumption or a specific consumption of 6.0 GJ equivalent per ton of ethylene that is produced.

Example 2: Comparison

(44) Example 2 illustrates a process in which the pretreatment stage has not taken place. The ethanol is not converted into DEE, and the process begins in stage b).

(45) Stage b)

(46) The evaporation feedstock, constituted by the non-pretreated ethanol feedstock in a mixture with 141,258 kg/h of treated water and unconverted ethanol that are recycled according to stage e), is introduced, at a flow rate of 186,922 kg/h, into the exchanger E1 at a pressure that is equal to 0.24 MPa and at a temperature of 120° C.

(47) Relative to Example 1, the pressure was lowered by 0.03 MPa. Without the presence of DEE, the bubble temperature of the evaporation feedstock at 0.27 MPa is 115° C. (127° C. in Example 1). The inlet pressure is modified by 0.03 MPa in such a way as to preserve a minimum thermal approach of 15° C. with the effluent that is obtained from the last adiabatic reactor of stage d).

(48) In stage c), the majority of the latent heat of the aqueous phase of the effluent that is obtained from the adiabatic reactor of stage d) is recovered for evaporating the evaporation feedstock, without a supply of external heat. Thus, 98 MW is exchanged between the evaporation feedstock and the effluent from the reactor.

(49) Optional Compression Stage

(50) The evaporated feedstock is then compressed in the optional compression stage using a radial compressor with an integrated multiplier in such a way that the pressure of said evaporated feedstock at the end of the compression is equal to 0.695 MPa.

(51) Stage c)

(52) The compressed feedstock is then heated in an exchanger E2 of the gas single-phase type, using a heat exchange with the effluent that is obtained from the last adiabatic reactor of stage d). In said gas single-phase-type exchanger, said compressed feedstock is superheated to a temperature of 405° C., and the effluent that is obtained, in the gaseous state, from the last adiabatic reactor of stage d) is “de-superheated” without being condensed and has a temperature of 269° C.

(53) Stage d)

(54) Said compressed and heated feedstock in said gas single-phase-type exchanger is then introduced into a furnace in such a way as to bring it to an inlet temperature in the first adiabatic reactor of stage d) that is 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 stage d) 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 exiting the last adiabatic reactor of stage d) is 0.500 MPa. The dehydration stage d) is performed at an hourly speed by weight of 7 h.sup.−1.

(56) The conversion of the ethanol feedstock in stage d) is 95%.

(57) Stage e)

(58) The effluent that is obtained from the last adiabatic reactor of stage d) then undergoes the two heat exchanges described above and is sent into the section for purification and recycling.

(59) An effluent that comprises ethylene meeting the final specifications is separated. An effluent that comprises water corresponding to the purge of the process is also separated.

(60) A stream that contains light gases and impurities is also separated by one or more optionally cryogenic distillation(s).

(61) A stream of treated water in a mixture with a portion of unconverted ethanol is recycled upstream from the evaporation stage b) in the proportions described in stage b).

(62) Information regarding the different streams, in kg/h, is given in Table 5 and Table 6.

(63) TABLE-US-00005 TABLE 5 Composition of the Primary Streams (1/2) Stream Stream Effluent Description of Ethanol Entering Exiting Comprising the Stream Feedstock into R1 from R2 Ethylene Stream No. 2 7 8 12 Corresponding to the FIGURE Total Mass kg/h 45,664 186,922 186,922 25,964 Flow Rate Mass Flow kg/h Rate by Components Ethylene 0 0 25,087 25,087 Ethane 0 0 8 8 C3 0 0 93 93 C4 0 0 87 87 DEE 0 0 14 14 Ethanol 41,671 43,496 2,187 151 H.sub.2O 3,993 142,947 158,602 311 Oxidized Compounds 0 413 586 62 (Other than Ethanol) Other Minority 0 66 258 151 Components

(64) TABLE-US-00006 TABLE 6 Composition of the Primary Streams (1/2 [sic]) Effluent That Recycling Comprises of Ethanol Purged Light Description of the Stream Water and Water Water Gases Stream No. Corresponding 13 14 13 11 to the FIGURE Total Mass Flow kg/h 160,958 141,258 19,007 693 Rate 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 2,036 1,825 3 208 H.sub.2O 158,291 138,954 18,987 350 Oxidized Compounds 524 413 6 105 (Other than Ethanol) Other Minority Components 107 66 11 30

(65) The compounds C3 and C4 are C3 and C4 hydrocarbon-containing compounds.

(66) The selectivity of the process in terms of ethylene is 99%.

(67) Information regarding the energy balance of the diagram according to Example 2 is given in Table 7.

(68) TABLE-US-00007 TABLE 7 Energy Balance Energy Exchanged Inside the System Energy Provided to the System by an External Supply Amount of Heat Amount of Heat Amount of Heat Amount of Heat Exchanged in Exchanged in Exchanged in Electricity Extracted on the First the Second the First Required for the Gas/Liquid Exchanger (E1) Exchanger (E2) Furnace Compression Separation Column MW MW MW MW MW 93.8 17.1 13.9 12.4 26.7

(69) The diagram according to Example 2 for comparison with the invention has an equivalent primary energy consumption or specific consumption of 7.23 GJ equivalent per ton of ethylene produced.

(70) Without pretreatment, the primary energy consumption therefore increases by 1.2 GJ equivalent per ton of ethylene that is produced.