Process and Apparatus for Ethanol Dehydration

Abstract

The present invention provides a process for the preparation of ethene by vapour phase chemical dehydration of ethanol using an adiabatic reactor, wherein the interior of the adiabatic reactor is separated into at least three reaction zones, comprising a first reaction zone, at least one intermediate reaction zone and a final reaction zone, and wherein each zone contains an ethanol dehydration catalyst; said process comprising the steps of; a) feeding a pre-heated reactant feed-stream into an inlet of the first reaction zone; b) extracting an effluent-stream from an outlet of the first reaction zone; c) feeding said effluent-stream into an inlet of a subsequent intermediate reaction zone; d) extracting an effluent-stream from an outlet of the intermediate reaction zone; e) repeating steps (c) and (d) for any subsequent intermediate reaction zones, if present; f) feeding, into an inlet of the final reaction zone, the effluent-stream from the preceding intermediate reaction zone; g) extracting a product stream from an outlet of the final reaction zone; wherein the effluent-streams are re-heated prior to being fed into a subsequent reaction zone by means of one or more heat exchangers and; and wherein a single heat exchanger simultaneously re-heats at least two of the effluent-streams, such that no more than one heat exchanger is present for every two effluent-streams being re-heated in the process.

Claims

1. A process for the preparation of ethene by vapour phase chemical dehydration of ethanol using an adiabatic reactor, wherein the interior of the adiabatic reactor is separated into at least three reaction zones, comprising a first reaction zone, at least one intermediate reaction zone and a final reaction zone, and wherein each zone contains an ethanol dehydration catalyst; said process comprising the steps of; a) feeding a pre-heated reactant feed-stream into an inlet of the first reaction zone; b) extracting an effluent-stream from an outlet of the first reaction zone; c) feeding said effluent-stream into an inlet of a subsequent intermediate reaction zone; d) extracting an effluent-stream from an outlet of the intermediate reaction zone; e) repeating steps (c) and (d) for any subsequent intermediate reaction zones, if present; f) feeding, into an inlet of the final reaction zone, the effluent-stream from the preceding intermediate reaction zone; g) extracting a product stream from an outlet of the final reaction zone; wherein the effluent-streams are re-heated prior to being fed into a subsequent reaction zone by means of one or more heat exchangers; and wherein a single heat exchanger simultaneously re-heats at least two of the effluent-streams, such that no more than one heat exchanger is present for every two effluent-streams being re-heated in the process.

2. The process of claim 1, wherein a single heat exchanger re-heats between two and four effluent-streams simultaneously.

3. The process of claim 1 or claim 2, wherein a single heat exchanger re-heats two streams simultaneously.

4. The process of any one of the preceding claims, wherein there are more than two intermediate reaction zones; preferably where there are between three and five intermediate reaction zones; more preferably where there are three intermediate reaction zones.

5. The process of any one of the preceding claims, wherein the heat exchanger(s) is/are selected from shell and tube heat exchangers and/or plate/frame heat exchangers.

6. The process of any one of the preceding claims, wherein the difference in contact surface area between the two or more effluent-streams being re-heated in a single heat exchanger and respective heating elements of the heat exchanger is less than 10%, preferably less than 5%, more preferably less than 2%.

7. The process of any one of the preceding claims, wherein the contact surface area between the two or more effluent-streams being re-heated in a single heat exchanger and the respective heating element of the heat exchanger is identical.

8. The process of any one of the preceding claims, wherein the difference in pressure between individual reaction zones is less than 1 MPa; preferably wherein the difference in pressure between individual reaction zones is less than 0.5 MPa; and more preferably wherein the difference in pressure between individual reaction zones is less than 0.3 MPa.

9. The process of any one of the preceding claims, wherein the difference between the temperatures of the individual intermediate effluent-streams, after they are re-heated, is less than 20° C., more preferably less than 10° C. and most preferably less than 5° C.

10. The process of any one of the preceding claims, wherein the difference between the temperatures of the individual intermediate effluent-streams, before they are re-heated, is less than 20° C., more preferably less than 10° C. and most preferably less than 5° C.

11. An apparatus for preparing ethene by vapour phase chemical dehydration of ethanol, comprising; i. an adiabatic reactor, wherein the interior of the adiabatic reactor is separated into at least three reaction zones, comprising a first reaction zone, at least one intermediate reaction zone and a final reaction zone; ii. a means for feeding a pre-heated reactant stream into an inlet of the first reaction zone; iii. a means for extracting an effluent-stream from an outlet of the first reaction zone; iv. a means for feeding said effluent-stream into an inlet of a subsequent intermediate reaction zone; v. a means for extracting an effluent-stream from an outlet of the intermediate reaction zone; vi. one or more means for feeding to, and one or more means for extracting an effluent-stream from, any additional intermediate reaction zones if present; vii. a means for feeding, into an inlet of the final reaction zone, the effluent-stream from the preceding intermediate reaction zone; viii. a means for extracting a product stream from an outlet of the final reaction zone; ix. one or more heat exchangers for re-heating each effluent-stream, prior to being fed into a subsequent reaction zone, wherein a single heat exchanger is configured to simultaneously re-heat at least two of the effluent-streams, such that no more than one heat exchanger is present for every two effluent-streams being re-heated.

12. An apparatus according to claim 11, wherein each of the heat exchangers is selected from shell and tube heat exchangers or plate/frame heat exchangers.

13. An apparatus according to claim 12, wherein at least one of the one or more heat exchangers is a shell and tube heat exchanger and is configured to re-heat between two and four effluent-streams simultaneously, preferably two effluent-streams simultaneously

14. An apparatus according to claim 12, wherein at least one of the one or more heat exchangers is a plate/frame type heat exchanger and is configured to re heat at least two, and preferably at least four, effluent-streams simultaneously.

15. An apparatus according to any one of claims 11 to 14, wherein there are more than two intermediate reaction zones; preferably where there are between three and five intermediate reaction zones; more preferably where there are three intermediate reaction zones.

Description

[0062] The invention will now be described in greater detail with reference to the embodiments of the invention illustrated in the accompanying figures, in which;

[0063] FIG. 1 shows a conventional system comprising multiple reactors in series (01, 03, 05) with multiple re-heating means (02, 04), such as heat exchangers, wherein the effluent-stream from each reactor is individually heated prior to being fed into a subsequent reactor;

[0064] FIG. 2 shows a simplified reactor system comprising three reaction zones in series, sharing a single heat exchanger for re-heating two streams, in accordance with the present invention; and

[0065] FIG. 3 shows a different embodiment of a simplified reactor system comprising five reaction zones in series, with two heat exchangers re-heating two streams each, in accordance with the present invention.

[0066] The embodiment of the present invention shown in FIG. 2 demonstrates a simplified reactor system compared to the equivalent conventional multiple reactor and heat exchanger system shown in FIG. 1. Specifically, in the embodiment of the invention according to FIG. 2, an adiabatic reactor (10) is internally separated into a first reaction zone (11), an intermediate reaction zone (12), and a final reaction zone (13), each containing a fixed bed dehydration catalyst (11a, 12a, and 13a respectively).

[0067] A pre-heated reactant stream (1) is fed into an inlet of the first reaction zone (11) and comes into contact with the first dehydration catalyst (11a). An effluent-stream (2a) is extracted from an outlet of the first reaction zone (11) and fed into a heat exchanger (5), wherein the effluent-stream (2a) is re-heated by heat exchange with a heat carrying stream (5a). The re-heated stream (2b) is fed into an inlet of the intermediate reaction zone (12), wherein it comes into contact with the intermediate dehydration catalyst (12a). An effluent-stream (3a) is extracted from an outlet of the intermediate reaction zone (12) and fed into the same aforementioned heat exchanger (5), wherein the effluent-stream (3a) is re-heated by heat exchange with heat carrying stream (5a). The reheated stream (3b) is fed into an inlet of the final reaction zone (13), wherein it comes into contact with the final dehydration catalyst (13a). An effluent product stream (4) is then extracted from an outlet of the final reaction zone (13).

[0068] The invention is also particularly effective for simplifying the arrangement of larger reactor systems. This is demonstrated in the embodiment of the invention shown in FIG. 3, wherein an adiabatic reactor (20) is internally separated into a first reaction zone (21), three intermediate reaction zones (22, 23, and 24), and a final reaction zone (25), each containing a fixed bed dehydration catalyst (21a, 22a, 23a, 24a, and 25a respectively).

[0069] A pre-heated reactant stream (31) is fed into an inlet of the first reaction zone (21) and comes into contact with a dehydration catalyst (21a). An effluent-stream (32a) is extracted from an outlet of the first reaction zone (21) and fed into a first heat exchanger (210), wherein the effluent-stream (32a) is re-heated by heat exchange with a heat carrying stream (210a). The re-heated stream (32b) is fed into an inlet of the first intermediate reaction zone (22), wherein it comes into contact with a dehydration catalyst (22a). An effluent-stream (33a) is extracted from an outlet of the first intermediate reaction zone (22) and fed into the same aforementioned first heat exchanger (210), wherein the effluent-stream (33a) is re-heated by heat exchange with heat carrying stream (210a).

[0070] The reheated stream (33b) is fed into an inlet of the second intermediate reaction zone (23), wherein it comes into contact with a dehydration catalyst (23a). An effluent-stream (34a) is extracted from an outlet of the second intermediate reaction zone (23) and fed into a second heat exchanger (211), wherein the effluent-stream (34a) is re-heated by heat exchange with heat carrying stream (211a). The reheated stream (34b) is fed into an inlet of the third intermediate reaction zone (24), wherein it comes into contact with a dehydration catalyst (24a). An effluent-stream (35a) is extracted from an outlet of the third intermediate reaction zone (24) and fed into the same aforementioned second heat exchanger (211), wherein the effluent-stream (35a) is re-heated by heat exchange with heat carrying stream (211a). The reheated stream (35b) is fed into an inlet of the final reaction zone (25), wherein it comes into contact with the final dehydration catalyst (25a). An effluent product stream (36) is then extracted from an outlet of the final reaction zone (25).

[0071] A conventional system comprising five reactors would require four heat exchangers between the reactors in order to re-heat intermediate streams. The layout and piping arrangement of such a large system would be geometrically awkward and costly to set up and maintain, potentially rendering the use of a system of this size and complexity not economically viable. The present invention provides a means for reducing the number of pressure vessels required for a reactor system, which simplifies the layout of the system and reduces the difficulty and cost of construction and maintenance operations.