PROCESS FOR PREPARING ETHENE

Abstract

The present invention provides a process for the preparation of ethene by vapour phase chemical dehydration of a feed-stream comprising ethanol and optionally water and/or ethoxy ethane, said process comprising contacting a dried supported heteropolyacid catalyst in a reactor with the feed-stream having a feed temperature of at least 200° C.; wherein before the supported heteropolyacid catalyst is contacted with the feed-stream having a feed temperature of at least 200° C., the process is initiated by: (i) drying a supported heteropolyacid catalyst in a reactor under a stream of inert gas having a feed temperature of from above 100° C. to 200° C.; and (ii) contacting the dried supported heteropolyacid catalyst with an ethanol-containing vapour stream having a feed temperature of from above 100° C. to 160° C.

Claims

1. A process for the preparation of ethene by vapour phase chemical dehydration of a feed-stream comprising ethanol and optionally water and/or ethoxyethane, said process comprising contacting a dried supported heteropolyacid catalyst in a reactor with the feed-stream having a feed temperature of at least 200° C.; wherein before the supported heteropolyacid catalyst is contacted with the feed-stream having a feed temperature of at least 200° C., the process is initiated by: (i) drying a supported heteropolyacid catalyst in a reactor under a stream of inert gas having a feed temperature of from above 100° C. to 200° C.; and (ii) contacting the dried supported heteropolyacid catalyst with an ethanol-containing vapour stream having a feed temperature of from above 100° C. to 160° C.

2. A process according to claim 1, wherein the supported heteropolyacid catalyst is dried in step (i) under a stream of inert gas having a feed temperature of from 100° C. to 180° C., preferably from 110° C. to 170° C., more preferably from 120° C. to 160° C., for example 150° C.

3. A process according to claim 1 or claim 2, wherein the dried supported heteropolyacid catalyst is contacted in step (ii) with an ethanol-containing vapour stream having a feed temperature of from 120° C. to 158° C., preferably from 130° C. to 156° C., more preferably from 140° C. to 154° C., most preferably from 148° C. to 152° C., for example 150° C.

4. A process according to any of claims 1 to 3, wherein the feed temperature of the feed-stream is at least 220° C., preferably where the feed-temperature is at least 240° C.

5. A process according to any of the preceding claims, wherein the upper limit of the feed temperature of the feed-stream is 350° C.; preferably wherein the upper limit of the feed temperature of the feed-stream is 325° C.

6. A process according to any of the preceding claims, wherein the pressure inside the reactor when the supported heteropolyacid catalyst is contacted with the feed-stream is from 0.1 MPa to 4.5 MPa; preferably wherein the pressure inside the reactor is from 0.5 MPa to 3.5 MPa; and most preferably wherein the pressure inside the reactor is from 1.0 MPa to 2.8 MPa.

7. A process according to any of the preceding claims, wherein the initiation of the ethanol dehydration process further comprises: (iii) ramping the feed temperature of the ethanol-containing vapour stream to at least 200° C., preferably over the course of 10 minutes to 8 hours, more preferably over the course of 20 minutes to 4 hours.

8. A process according to any of the preceding claims, wherein the feed-stream comprises water and/or ethoxyethane, preferably wherein the feed-stream comprises water and ethoxyethane.

9. A process according to any of the preceding claims, wherein the ethanol-containing vapour stream comprises or consists of ethanol, any balance being made up of inert gas diluents.

10. A process according to any of the preceding claims, wherein drying in step (i) is undertaken for a period of from 1 to 48 hours; preferably a period of from 2 to 16 hours; more preferably over a period of from 2 to 12 hours.

11. A process according to any of the preceding claims, wherein the catalyst is provided in the form of one or more catalyst beds in the reactor.

12. A process according to claim 11 wherein the catalyst is provided in the form of multiple catalyst beds; preferably arranged in series or in parallel.

13. A process according to claim 11 or claim 12, wherein the catalyst bed(s) is/are selected from adiabatic packed beds, tubular fixed beds or fluid beds, preferably adiabatic packed beds.

14. A process according to any of claims 11 to 13, wherein the temperature differential across the bed of supported hetereopolyacid catalyst in the reactor during drying of the supported hetereopolyacid catalyst in step (i) is no more than 20° C., preferably no more than 15° C., more preferably no more than 10° C., most preferably no more than 5° C.

15. A process according to any of the preceding claims, wherein the average diameter of the supported heteropolyacid catalyst particles is from 500 μm to 8,000 μm; preferably from 1,000 μm to 7,000 μm; more preferably from 2,000 μm to 6,000 μm, most preferably from 3,000 μm to 5,000 μm.

16. A process according to any of the preceding claims, wherein the amount of heteropolyacid in the supported heteropolyacid catalyst is in the range of from 10 wt. % to 50 wt. % based on the total weight of the supported heteropolyacid catalyst.

17. A process according to any of the preceding claims, wherein at least a portion of the supported heteropolyacid catalyst has previously been employed in a process for the preparation of an ethene from a feed-stream comprising ethanol, water and ethoxyethane

18. A process according to any of the preceding claims, wherein the supported heteropolyacid catalyst is a supported heteropolytungstic acid catalyst, preferably a supported silicotungstic acid catalyst, for example 12-tungstosilicic acid (H.sub.4[SiW.sub.12O.sub.40].XH.sub.2O).

19. A composition comprising a product obtained by a process according to any preceding claim, and/or derivatives thereof.

Description

[0074] The present invention will now be illustrated by way of the following examples and with reference to the following figures:

[0075] FIG. 1: Graphical representation of ethene productivity against time of catalyst exposure to a feed stream at 260° C. for Example 1 and Comparative Examples 1 to 3; and

[0076] FIG. 2: Graphical representation of ethene productivity against time of catalyst exposure to a feed stream at 260° C. for Example 2 and Comparative Example 4.

CATALYST PREPARATION

[0077] A silicotungstic acid (STA) catalyst was used for conducting the dehydration reactions according to the following examples.

[0078] A high purity silica support with a surface area of 147 m.sup.2/g, pore volume of 0.84 ml/g and a mean pore diameter of 230 Å was used for preparation of the STA catalyst. The catalyst was prepared by adding silica (512 g) to a solution of silicotungstic acid (508 g) in water (1249 g). Once the silicotungstic acid solution had fully impregnated the pores of the support the excess solution was drained, under gravity, from the support and this was then dried.

[0079] The STA loading on the catalyst support as STA.6H.sub.2O, on a dry weight basis, was estimated to be 24.5% w/w, based on the weight gained by the silica during the catalyst preparation.

[0080] For Example 1 and Comparative Examples 1 to 3 below, the catalyst was crushed to a particle size of 100 to 200 μm before being loaded into the reactor tube.

[0081] For Example 2 and Comparative Example 4 below, the catalyst was crushed to a particle size of 850 to 1000 μm before being loaded into the reactor tube.

VAPOUR PHASE DEHYDRATION REACTIONS FOR EXAMPLE 1 AND COMPARATIVE EXAMPLES 1 TO 3

[0082] A mass of STA catalyst (as indicated in Table 1 below) prepared in accordance with the above method was loaded into a reactor tube having an isothermal bed and pressurised to 0.501 MPa under inert gas (nitrogen and helium) flow. The catalyst was heated at 2° C./min to either 150° C. (Example 1) or 240° C. (Comparative Examples 1 to 3) under a combined nitrogen (0.01500 mol/hr) and helium flow (0.00107 mol/hr) and held at this temperature for 8 hours before being cooled to 150° C., if not already at this temperature.

[0083] Ethanol (0.04084 mol/hr) was then added to the nitrogen/helium flow and the temperature was increased at 2° C./min to 225° C. Once at 225° C. the feed pressure was increased at a rate of 0.1 MPa/min such that the pressure inside the reactor was increased to the value of 2.858 MPa. The diethyl ether and water reagents were added to the ethanol, helium and nitrogen flow. At this point the flows of the feed components were adjusted to give ethanol (0.02677 mol/hr), diethyl ether (0.00776 mol/hr), water (0.00297 mol/hr), helium (0.00106 mol/hr) and nitrogen (0.01479 mol/hr).

[0084] Once the catalyst performance had stabilised at 225° C., typically after around 100 hrs, the catalyst temperature, which is the same as the feed temperature in this particular reactor, was increased to 260° C. and the ethene productivity monitored versus time by on-line GC analysis. The results of dehydration experiments at varying pressure are presented in Table 1 below.

TABLE-US-00001 TABLE 1 Max. Temp. Time on Ethylene under Mass of Stream Process Total Productivity N.sub.2 flow catalyst at 260° C. Temp. Pressure (mole/kg Example (° C.) (mg) (hrs) (° C.) (MPa) catalyst/hr) Example 1 150 27.2 4.11 260 2.858 478 Example 1 150 27.2 37.8 260 2.858 397 Example 1 150 27.2 72.47 260 2.858 379 Example 1 150 27.2 139.84 260 2.858 281 Example 1 150 27.2 186.99 260 2.858 268 Example 1 150 27.2 207.19 260 2.858 263 Example 1 150 27.2 254.33 260 2.858 215 Comparative Example 1 240 27.16 0.84 260 2.858 411 Comparative Example 1 240 27.16 27.97 260 2.858 314 Comparative Example 1 240 27.16 48.14 260 2.858 271 Comparative Example 1 240 27.16 81.94 260 2.858 239 Comparative Example 1 240 27.16 115.66 260 2.858 164 Comparative Example 1 240 27.16 183.1 260 2.858 9 Comparative Example 1 240 27.16 230.26 260 2.858 5 Comparative Example 1 240 27.16 250.43 260 2.858 5 Comparative Example 2 240 27.3 5.36 260 2.858 397 Comparative Example 2 240 27.3 38.97 260 2.858 344 Comparative Example 2 240 27.3 72.67 260 2.858 257 Comparative Example 2 240 27.3 139.89 260 2.858 210 Comparative Example 2 240 27.3 186.95 260 2.858 101 Comparative Example 3 240 27.1 5.77 260 2.858 342 Comparative Example 3 240 27.1 32.67 260 2.858 287 Comparative Example 3 240 27.1 66.29 260 2.858 232 Comparative Example 3 240 27.1 140.99 260 2.858 154 Comparative Example 3 240 27.1 200.38 260 2.858 30 Comparative Example 3 240 27.1 257.72 260 2.858 4

[0085] The results in Table 1, which are represented graphically in FIG. 1, illustrate the benefits of the process of the invention with regard to catalyst lifetime. It is clear from FIG. 1 that ethene productivity remains high with Example 1, which benefits from having had a catalyst drying step at a temperature of 150° C. in accordance with the invention, for a significantly longer period of time compared with Comparative Examples 1 to 3, which have had a catalyst drying step at high temperature (240° C.) not in accordance with the present invention. FIG. 1 also illustrates that the maximum ethene productivity in the ethanol dehydration reaction may also be increased by virtue of a drying step according to the present invention, in comparison with a high temperature drying step not in accordance with the invention as in the case of Comparative Examples 1 to 3. The maximum ethene productivity observed for Example 1 was 478 mole/kg catalyst/hr, whilst the maximum ethene productivity observed for Comparative Examples 1 to 3 was only 411 mole/kg catalyst/hr (Comparative Example 1).

VAPOUR PHASE DEHYDRATION REACTIONS FOR EXAMPLE 2 AND COMPARATIVE EXAMPLE 4

[0086] A mass of STA catalyst (as indicated in Table 2 below) prepared in accordance with the above method described above was loaded into a reactor tube and pressurised to 0.5 MPa under nitrogen flow. The catalyst was heated to either 150° C. or 240° C. under nitrogen (0.4957 mol/hr) flow and held at this temperature for 2 hours before being cooled to 150° C., if not already at this temperature.

[0087] Ethanol (1.3228 mol/hr) was then added to the nitrogen flow and the temperature of the feed to the catalyst bed was increased to 225° C. Once at 225° C. the feed pressure was increased to the value of 2.857 MPa. The diethyl ether and water reagents were then added to the ethanol and nitrogen flow. At this point the flows of the feed components were adjusted to give ethanol (0.8544 mol/hr), diethyl ether (0.2476 mol/hr), water (0.0949 mol/hr) and nitrogen (0.4957 mol/hr).

[0088] After 24 hrs the temperature of the feed to the catalyst bed was increased to 260° C. and the ethylene productivity monitored versus time by on-line GC analysis. The results of dehydration experiments at varying pressure are presented in Table 2 below.

TABLE-US-00002 TABLE 2 Max. Temp. Time on Ethylene under Mass of Stream Process Total Productivity N.sub.2 flow catalyst at 260° C. Temp. Pressure (mole/kg Example (° C.) (g) (hrs) (° C.) (MPa) catalyst/hr) Example 2 150 0.507 0 260 2.857 444 Example 2 150 0.507 15 260 2.857 427 Example 2 150 0.507 29 260 2.857 424 Example 2 150 0.507 45 260 2.857 413 Example 2 150 0.507 59 260 2.857 415 Example 2 150 0.507 89 260 2.857 402 Example 2 150 0.507 115 260 2.857 411 Example 2 150 0.507 130 260 2.857 415 Example 2 150 0.507 145 260 2.857 410 Example 2 150 0.507 160 260 2.857 395 Example 2 150 0.507 175 260 2.857 410 Example 2 150 0.507 190 260 2.857 404 Example 2 150 0.507 206 260 2.857 401 Comparative Example 4 240 0.508 0 260 2.857 436 Comparative Example 4 240 0.508 16 260 2.857 402 Comparative Example 4 240 0.508 30 260 2.857 398 Comparative Example 4 240 0.508 45 260 2.857 383 Comparative Example 4 240 0.508 60 260 2.857 376 Comparative Example 4 240 0.508 115 260 2.857 335 Comparative Example 4 240 0.508 130 260 2.857 334 Comparative Example 4 240 0.508 145 260 2.857 330 Comparative Example 4 240 0.508 160 260 2.857 319 Comparative Example 4 240 0.508 176 260 2.857 316 Comparative Example 4 240 0.508 191 260 2.857 300 Comparative Example 4 240 0.508 206 260 2.857 287

[0089] The results in Table 2, which are represented graphically in FIG. 2, illustrate the benefits of the process of the invention with regard to catalyst lifetime. It is clear from FIG. 2 that ethene productivity remains high with Example 2, which benefits from having had a catalyst drying step at a temperature of 150° C. in accordance with the invention, for a significantly longer period of time compared with Comparative Example 4, which has had a catalyst drying step at high temperature (240° C.) not in accordance with the present invention. It will also be appreciated that ethene productivity is generally higher for Example 2 than for Example 1. For instance, even after 206 hours on stream, the ethene productivity for Example 2 is above 401 mole/kg catalyst/hr, whereas after 207 hours on stream the ethene productivity for Example 2 is above 263 mole/kg catalyst/hr.

[0090] The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.”

[0091] Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

[0092] While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope and spirit of this invention.