A PROCESS FOR PREPARING ETHENE

Abstract

The present invention provides a process for the preparation of ethene by vapour phase chemical dehydration of a feed comprising ethanol and optionally water and/or ethoxyethane, said process comprising contacting a dried supported heteropoly acid catalyst in a reactor with the feed-stream having feed temperature of at least 200° C.; wherein the pressure inside the reactor is at least 0.80 MPa but less than 1.80 MPa; and 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 the pressure inside the reactor is at least 0.80 MPa but less than 1.80 MPa; and 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 wherein 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 proceeding claims, wherein the pressure inside the reactor when the supported heteropolyacid catalyst is contacted with the feed-stream is from 0.90 MPa to 1.60 MPa; preferably wherein the pressure inside the reactor is from 0.95 MPa to 1.30 MPa; and most preferably wherein the pressure inside the reactor is from 1.00 MPa to 1.20 MPa.

7. A process according to any of the preceding claims, wherein the feed-stream pressure is from 1.00 MPa to 1.80 MPa; preferably wherein the feed-stream pressure is from 1.20 MPa 1.60 MPa; and more preferably wherein the feed-stream pressure is from 1.30 MPa to 1.50 MPa, for example 1.40 MPa.

8. A process according to any of the preceding claims, wherein the effluent-stream pressure is from 0.80 MPa to 1.40 MPa; preferably wherein the effluent-stream pressure is from 0.85 MPa to 1.20 MPa; and more preferably wherein the effluent-stream pressure is from 0.90 MPa to 1.10 MPa, for example 1.00 MPa.

9. 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.

10. 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.

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

12. A process according to any of the preceding claims, wherein drying 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.

13. 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.

14. A process according to claim 13 wherein the catalyst is provided in the form of multiple catalyst beds; preferably arranged in series or in parallel.

15. A process according to claim 13 or claim 14, wherein the catalyst bed(s) is/are selected from adiabatic packed beds, tubular fixed beds or fluid beds, preferably adiabatic packed beds.

16. A process according to any of claims 13 to 15, 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.

17. 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.

18. 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.

19. 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.

20. 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).

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

Description

[0077] The present invention will now be illustrated by way of the following examples and with reference to the following figures:

[0078] FIG. 1: Graphical representation of ethene productivity against time of catalyst exposure to a feed-stream at 280° C. for Example 1 and Comparative Examples 1 to 3;

[0079] FIG. 2: Graphical representation of ethene productivity against time of catalyst exposure to a feed-stream at 280° C. for Example 1 and Comparative Examples 1 to 3 (including estimated deactivation time); and

[0080] FIG. 3: Graphical representation of effect of dehydration temperature on ethene productivity for Comparative Examples A to G.

CATALYST PREPARATION

[0081] A silicotungstic acid (STA) catalyst was used for conducting the dehydration reactions according to the following examples.

[0082] 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.

[0083] 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.

[0084] For Example 1 and Comparative Examples 1 to 3 below, the catalyst was crushed to a particle size of 850 to 1000 μm before being loaded into the reactor tube.

[0085] For Comparative Examples A to G below, the catalyst was crushed to a particle size of 100 to 200 μm before being loaded into the reactor tube.

Vapour Phase Dehydration Reactions for Example 1 and Comparative Examples 1 to 3

[0086] A mass of STA catalyst (as indicated in Table 1 below) prepared in accordance with the above method (850 to 1000 μm) was loaded into a reactor tube having an isothermal bed and pressurised to 0.501 MPa under inert gas (nitrogen) flow. The catalyst was heated at 2° C./min to either 150° C. or 240° C. (as indicated in Table 1 below) under nitrogen flow (0.4957 mol/hr) 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 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 1.428 MPa (Example C) or 2.857 MPa. The diethyl ether and water reagents were added to the ethanol and nitrogen flow. At this point the flows of the feed components were adjusted to give ethanol (0.5627 mol/hr), diethyl ether (0.1631 mol/hr), water (0.0625 mol/hr), and nitrogen (0.3347 mol/hr).

[0088] After 24 hrs the temperature of the feed to the catalyst bed was increased to 280° C. and the ethene productivity monitored, once steady state conditions were obtained, versus time by on-line GC analysis. The results of dehydration experiments are presented in Table 2 below.

TABLE-US-00001 TABLE 1 Catalyst Pre-treatment Operating Pressure Example Mass (g) Temperature (° C.) (MPa) Example 1 0.3375 150 1.428 Comparative Ex. 1 0.3399 240 1.428 Comparative Ex. 2 0.3399 150 2.857 Comparative Ex. 3 0.3993 240 2.857

TABLE-US-00002 TABLE 2 Total Time Initial Ethylene Estimated on Productivity time to Stream at 280° C. Deactivation complete at 280° (g/kg Rate (g/kg deactivation Example C. (hrs) catalyst/hr) catalyst/hr/hr) (hrs) Example 1 152 23120 −30.968 747 Comparative Ex. 1 127 23218 −35.721 650 Comparative Ex. 2 140 17831 −31.738 562 Comparative Ex. 3 134 14647 −45.677 321

[0089] The results in Table 2, which are represented graphically in FIGS. 1 and 2, illustrate the benefits of the process of the invention with regard to catalyst lifetime. It is clear from FIGS. 1 and 2 that ethene productivity remains high and is retained for a significantly longer period of time compared with Comparative Examples 1 to 3. Example 1 benefits from having had a catalyst drying step at a temperature of 150° C. followed by low pressure dehydration in accordance with the invention. The catalysts according to Comparative Examples 1 to 3 have either had a high temperature drying stage (Comparative Examples 1 and 3) or a high pressure dehydration (Comparative Example 2), which is not in accordance with the present invention. FIGS. 1 and 2 also illustrate that the maximum ethene productivity in the ethanol dehydration reaction may also be increased by virtue of a low temperature drying step and a low pressure dehydration in accordance with the present invention, in comparison with a high temperature drying step and/or high pressure dehydration not in accordance with the invention, as in the case of Comparative Examples 2 and 3. In particular, the maximum ethene productivity observed for Example 1 was 23120 mole/kg catalyst/hr, whilst the maximum ethene productivity observed for Comparative Examples 2 and 3 was only 17831 mole/kg catalyst/hr and 14647 mole/kg catalyst/hr, respectively.

Vapour Phase Dehydration Reactions for Comparative Examples A to G

[0090] A mass of STA catalyst (as indicated in Table 3 below) prepared in accordance with the above method (100 to 200 μm) was loaded into a reactor tube and pressurised to 0.501 MPa under inert gas (nitrogen and helium) flow. The catalyst was heated at 2° C./min to 240° C. 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.

[0091] 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 to the value of 1.430 MPa (Examples C and F), 2.144 MPa (Example E), or 2.858 MPa (Examples A, B, D and G). The diethyl ether and water reagents were then 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).

[0092] Once the catalyst performance had stabilised at 225° C., typically after around 100 hrs, the temperature of the feed to the catalyst bed was modified to 220° C., 240° C., 260° C., 280° C., or 295° C. (as indicated in Table 3) and the ethylene productivity monitored versus time by on-line GC analysis in each case. The results of these dehydration experiments at varying pressure are presented in Table 3 below.

TABLE-US-00003 TABLE 3 Time on Ethylene Mass of Stream at Temperature Total Productivity catalyst temperature on Stream Pressure (g/kg) Example (mg) (hrs) (° C.) (MPa ) catalyst/hr) Example A 13.7 2 225 2.858 1176 Example A 13.6 3.94 240 2.858 3052 Example A 13.7 1.99 260 2.858 13916 Example A 13.7 5.09 280 2.858 29624 Example A 13.6 7.41 295 2.858 37128 Example B 13.69 1.69 225 2.858 1092 Example B 13.69 1.57 260 2.858 14028 Example C 13.6 1.36 220 1.430 2800 Example C 13.6 1.37 225 1.430 4256 Example C 13.6 1.68 225 1.430 3920 Example C 13.6 4.73 225 1.430 3500 Example C 13.6 6.2 225 1.430 3332 Example C 13.6 4.72 240 1.430 8764 Example C 13.6 1.68 260 1.430 24276 Example C 13.6 6.19 280 1.430 40964 Example D 13.5 6.62 225 2.858 784 Example D 13.5 6.62 260 2.858 13832 Example E 13.6 1.36 220 2.144 1288 Example E 13.6 1.37 225 2.144 2380 Example E 13.7 2.56 225 2.144 1876 Example E 13.6 4.66 225 2.144 1792 Example E 13.6 6.65 225 2.144 1820 Example E 13.6 4.2 240 2.144 5824 Example E 13.7 2.1 260 2.144 19460 Example E 13.6 6.2 280 2.144 40880 Example F 13.6 6 220 1.430 2632 Example F 13.6 2.63 225 1.430 4116 Example F 13.6 3.47 260 1.430 19152 Example G 13.6 2.82 260 2.858 10864

[0093] The results in Table 3, which are represented graphically in FIG. 3, illustrate that ethylene productivity is generally increased by increasing the temperature at which the dehydration process is conducted, for all pressures tested.

[0094] 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.”

[0095] 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.

[0096] 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.