Process for producing alkenes from oxygenates by using supported partially neutralised heteropolyacid catalysts

Abstract

A process for the vapour phase chemical dehydration of ethanol in a reactor in the presence of a supported heteropolyacid catalyst, said process comprising a step of contacting the ethanol with the heteropolyacid catalyst, wherein the heteropolyacid catalyst comprises a partially neutralised silicotungstic acid salt, wherein the partially neutralised silicotungstic acid salt has from 30% to 70% of the hydrogen atoms replaced with cations selected from the group consisting of alkali metal cations, alkaline earth metal cations, transition metal cations, ammonium cations, and mixtures thereof; but with the proviso that the alkali metal cation is not lithium; and wherein, after attaining steady-state performance of the catalyst, said process is operated continuously with the same supported heteropolyacid catalyst for at least 150 hours, without any regeneration of the catalyst.

Claims

1. A process for vapour phase chemical dehydration of ethanol in a reactor in the presence of a supported heteropolyacid catalyst, said process comprising: a) contacting the ethanol with the supported heteropolyacid catalyst, wherein the supported heteropolyacid catalyst comprises: a partially neutralised silicotungstic acid salt, wherein the partially neutralised silicotungstic acid salt has from 30% to 70% of the hydrogen atoms replaced with cations selected from the group consisting of alkali metal cations, alkaline earth metal cations, transition metal cations, ammonium cations, and mixtures thereof; but with the proviso that the alkali metal cation is not lithium; b) attaining steady-state performance of the catalyst; c) operating continuously with the supported heteropolyacid catalyst for at least 150 hours, without any regeneration of the supported heteropolyacid catalyst.

2. A process according to claim 1, wherein the proportion of hydrogen atoms replaced with other cations in the partially neutralised silicotungstic acid salt is from 40% to 60%.

3. A process according to claim 1, wherein the catalyst retains at least 25% of its maximum activity observed for the operating temperature under steady-state conditions after at least 200 hours of operation of the process.

4. A process according to claim 1, wherein the partially neutralised silicotungstic acid salt has hydrogen atoms replaced by alkali metal cations, alkaline earth metal cations, or mixtures thereof.

5. A process according to claim 1, wherein the partially neutralised silicotungstic acid salt has hydrogen atoms replaced by cations selected from sodium, potassium, caesium, calcium or mixtures thereof.

6. A process according to claim 1, wherein the partially neutralised silicotungstic acid salt has hydrogen atoms replaced by ammonium cations.

7. A process according to claim 1, wherein the acid loading on the support is in the range of 10 wt % to 80 wt %, based on the total weight of the supported catalyst.

8. A process according to claim 1, wherein the catalyst support of the supported heteropolyacid catalyst is a silica support.

9. A process according to claim 1, wherein operating continuously in step c) is for at least 200 hours without any regeneration of the supported heteropolyacid catalyst.

10. A process according to claim 1, wherein the feed temperature of the feed-stream comprising ethanol is from 180 C. to 270 C.

11. A process according to claim 1, wherein the process is operated at an internal reactor pressure of from 0.1 MPa to 4.5 MPa.

12. A process according to claim 1, wherein the catalyst retains at least 85% of its maximum activity observed for the operating temperature under steady-state conditions after at least 200 hours of operation of the process.

13. A process according to claim 1, wherein the partially neutralised silicotungstic acid salt has hydrogen atoms replaced by caesium cations.

14. A process according to claim 1, wherein operating continuously in step c) is for at least 250 hours, without any regeneration of the supported heteropolyacid catalyst.

15. A method for increasing catalyst lifetime of a supported partially neutralised heteropolyacid catalyst in an alcohol dehydration process, said method comprising supplying to an alcohol dehydration process a supported partially neutralised heteropolyacid catalyst, wherein the partially neutralised heteropolyacid catalyst comprises a partially neutralised silicotungstic acid salt having from 30% to 70% of the hydrogen atoms replaced with cations selected from the group consisting of alkali metal cations, alkaline earth metal cations, transition metal cations, ammonium cations, and mixtures thereof, but with the proviso that the alkali metal cation is not lithium.

16. A method according to claim 15, wherein the alcohol dehydration process is an ethanol dehydration process.

Description

(1) The present invention will now be illustrated by way of the following examples and with reference to the following figures:

(2) FIG. 1: A comparison of results of the vapour phase dehydration of ethanol using catalysts A and C;

(3) FIG. 2: A comparison of results of the vapour phase dehydration of ethanol using catalysts A and I;

(4) FIG. 3: A comparison of results of the vapour phase dehydration of ethanol using catalysts A, C, G and H;

(5) FIG. 4: A comparison of results of the vapour phase dehydration of ethanol using catalysts A and F;

(6) FIG. 5: A comparison of results of the vapour phase dehydration of ethanol using catalysts A, B, C, D and E; and

(7) FIG. 6: A comparison of results of the vapour phase dehydration of ethanol using catalysts J, K, L and M.

EXAMPLES

(8) Catalyst Preparation (Silicotungstic Acid Catalysts)

(9) A silica support having a surface area of 156 m.sup.2/g, a pore volume of 0.93 cm.sup.3/g and a mean pore diameter of 239 was used for the silicotungstic acid catalyst preparations.

(10) Catalyst a (Comparative)H.sub.4SiW.sub.12O.sub.40.nH.sub.2O/Silica (24.5% w/w)

(11) Silica (512 g) was added to an aqueous solution of silicotungstic acid (H.sub.4SiW.sub.12O.sub.40.24H.sub.2O, 508 g in 1249 g water) and allowed to remain in contact with the solution for over 60 minutes with occasional shaking. The solution was then drained from the solid, leaving the support pores filled with acid solution, and the support was dried at 110 C. for 16 hrs. The weight of the dried catalyst was 678 g.

(12) The loading of the silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst.

(13) Catalyst B (Comparative)Cs.sub.1H.sub.3SiW.sub.12O.sub.40.nH.sub.2O/Silica (28.5% w/w)

(14) Silica (20.0194 g) was added to an aqueous solution of cesium carbonate (0.5958 g in 30.05 g water) and left to stand for 96 hrs before the solution was drained from the support and the solid material dried at 110 C. for 16 hrs. The weight gain of the support indicated 0.4563 g of cesium carbonate had been impregnated on to the support. The dried solid was heated under a nitrogen flow (40 ml/min) at 5 C./min from room temperature to 300 C. and held at this temperature for 5 hrs before being cooled to ambient temperature. The weight of the heat treated material was 20.3975 g.

(15) The Cs impregnated silica was added to an aqueous solution of silicotungstic acid (H.sub.4SiW.sub.12O.sub.40.24H.sub.2O, 11.54 g in 28.46 g water) and allowed to contact the solution for 5 minutes. The solution was then drained from the Cs impregnated support and the remaining solution retained in the pores of the support was allowed to contact with the solid material for a further 8 hrs before the material was dried at 110 C. for 16 hrs. The weight of the dried catalyst was 28.4720 g.

(16) The loading of the cesium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Cs/silicotungstic acid ratio in the final dried catalyst was estimated to be 1.16.

(17) Catalyst C (Example)Cs.sub.2H.sub.2SiW.sub.12O.sub.40.nH.sub.2O/Silica (29.9% w/w)

(18) Silica (20.0301 g) was added to an aqueous solution of cesium carbonate (1.1705 g in 30.14 g water) and left to stand for 96 hrs before the solution was drained from the support and the solid material dried at 110 C. for 16 hrs. The weight gain of the support indicated 0.9435 g of cesium carbonate had been impregnated on to the support. The dried solid was heated under a nitrogen flow (40 ml/min) at 5 C./min from room temperature to 300 C. and held at this temperature for 5 hrs before being cooled to ambient temperature. The weight of the heat treated material was 20.8244 g.

(19) The Cs impregnated silica was added to aqueous solution silicotungstic acid (H.sub.4SiW.sub.12O.sub.40.24H.sub.2O, 11.54 g in 28.46 g water) and allowed to contact the solution for 5 minutes. The solution was then drained from the Cs impregnated support and the remaining solution retained in the pores of the support was allowed to contact with the solid material for a further 8 hrs before the material was dried at 110 C. for 16 hrs. The weight of the dried catalyst was 29.4971 g.

(20) The loading of the cesium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Cs/silicotungstic acid ratio in the final dried catalyst was estimated to be 2.25.

(21) Catalyst D (Comparative)Cs.sub.3H.sub.1SiW.sub.12O.sub.40.nH.sub.2O/Silica (29.8% w/w)

(22) Silica (20.0277 g) was added to an aqueous solution of cesium carbonate (1.7484 g in 29.97 g water) and left to stand for 96 hrs before the solution was drained from the support and the solid material dried at 110 C. for 16 hrs. The weight gain of the support indicated 1.3291 g of cesium carbonate had been impregnated on to the support. The dried solid was heated under a nitrogen flow (40 ml/min) at 5 C./min from room temperature to 300 C. and held at this temperature for 5 hrs before being cooled to ambient temperature. The weight of the heat treated material was 21.2103 g.

(23) The Cs impregnated silica was added to aqueous solution silicotungstic acid (H.sub.4SiW.sub.12O.sub.40.24H.sub.2O, 11.54 g in 28.46 g water) and allowed to contact the solution for 5 minutes. The solution was then drained from the Cs impregnated support and the remaining solution retained in the pores of the support was allowed to contact with the solid material for a further 8 hrs before the material was dried at 110 C. for 16 hrs. The weight of the dried catalyst was 29.8569 g.

(24) The loading of the cesium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Cs/silicotungstic acid ratio in the final dried catalyst was estimated to be 3.18.

(25) Catalyst E (Comparative)Cs.sub.4H.sub.0SiW.sub.12O.sub.40.nH.sub.2O/Silica (26.2% w/w)

(26) Silica (20.0471 g) was added to an aqueous solution of cesium carbonate (2.3554 g in 30.05 g water) and left to stand for 96 hrs before the solution was drained from the support and the solid material dried at 110 C. for 16 hrs. The weight gain of the support indicated 1.8366 g of cesium carbonate had been impregnated on to the support. The dried solid was heated under a nitrogen flow (40 ml/min) at 5 C./min from room temperature to 300 C. and held at this temperature for 5 hrs before being cooled to ambient temperature. The weight of the heat treated material was 21.6451 g.

(27) The Cs impregnated silica was added to an aqueous solution of silicotungstic acid (H.sub.4SiW.sub.12O.sub.40.24H.sub.2O, 11.54 g in 28.46 g water) and allowed to contact the solution for 5 minutes. The solution was then drained from the Cs impregnated support and the remaining solution retained in the pores of the support was allowed to contact with the solid material for a further 8 hrs before the material was dried at 110 C. for 16 hrs. The weight of the dried catalyst was 29.0184 g.

(28) The loading of the cesium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Cs/silicotungstic acid ratio in the final dried catalyst was estimated to be 5.23.

(29) Catalyst F (Comparative)Li.sub.2H.sub.2SiW.sub.12O.sub.40.nH.sub.2O/Silica (25.2% w/w)

(30) An aqueous solution of lithium carbonate (0.4487 g in 29.97 g of water) was added to an aqueous solution of silicotungstic acid (19.83 g in 18.89 g of water) with vigorous stirring. After 2 hrs silica (20.0951 g) was added to the lithium-silicotungstic acid solution and left in contact for 24 hrs before the solution was drained. The solid was then dried at 110 C. for 16 hrs. The weight of dried catalyst was 26.8892 g.

(31) The loading of the lithium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Li/silicotungstic acid ratio in the final dried catalyst was calculated to be 2.03.

(32) Catalyst G (Example)K.sub.2H.sub.2SiW.sub.12O.sub.40.nH.sub.2O/Silica (24.1% w/w)

(33) An aqueous solution of potassium carbonate (0.8292 g in 29.93 g of water) was added to an aqueous solution of silicotungstic acid (19.81 g in 0.8292 g of water) with vigorous stirring. After 2 hrs silica (19.9776 g) was added to the potassium-silicotungstic acid solution and left in contact for 24 hrs before the solution was drained. The solid was then dried at 110 C. for 16 hrs.

(34) The loading of the potassium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the K/silicotungstic acid ratio in the final dried catalyst was calculated to be 2.01.

(35) Catalyst H (Example)Ca.sub.1H.sub.2SiW.sub.12O.sub.40.nH.sub.2O/Silica (24.0% w/w)

(36) An aqueous solution of calcium nitrate (1.4270 g in 30.02 g of water) was added to an aqueous solution of silicotungstic acid (19.8 g in 18.82 g of water) vigorous stirring. After 2 hrs silica (19.9959 g) was added to the calcium-silicotungstic acid solution and left in contact for 24 hrs before the solution was drained. The solid was then dried at 110 C. for 16 hrs.

(37) The loading of the calcium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Ca/silicotungstic acid ratio in the final dried catalyst was estimated to be 1.01.

(38) Catalyst I (Example)Cs.sub.2H.sub.2SiW.sub.12O.sub.40.nH.sub.2O/Silica (45.5% w/w)

(39) Silica (20.03 g) was added to an aqueous solution of cesium carbonate (2.3442 g in 30.05 g water) and left to stand for 96 hrs before the solution was drained from the support and the solid material dried at 110 C. for 16 hrs. The weight gain of the support indicated 1.88 g of cesium carbonate had been impregnated on to the support. A portion of the dried solid (13.55 g) was heated under a nitrogen flow (40 ml/min) at 5 C./min from room temperature to 300 C. and held at this temperature for 5 hrs before being cooled to ambient temperature. The weight of the heat treated material was 13.40 g.

(40) A portion of the Cs impregnated silica (10.94 g) was added to an aqueous solution of silicotungstic acid (H.sub.4SiW.sub.12O.sub.40.24H.sub.2O, 21.50 g in 26.68 g water) and allowed to contact the solution for 5 minutes. The solution was then drained from the Cs impregnated support and the remaining solution retained in the pores of the support was allowed to contact with the solid material for a further 5 minutes before the material was dried at 110 C. for 16 hrs. The weight of the dried catalyst was 19.30 g.

(41) The loading of the cesium-silicotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Cs/silicotungstic acid ratio in the final dried catalyst was estimated to be 2.28.

(42) A silica support having a surface area of 182 m2/g, a pore volume of 1.00 cm3/g and a mean pore diameter of 219 was used for the phosphotungstic tungstic acid catalyst preparations.

(43) Catalyst Preparation (Phosphotungstic Acid Catalysts)

(44) Catalyst J (Comparative)H.sub.3PW.sub.12O.sub.40.nH.sub.2O/Silica (27.2% w/w)

(45) Silica (43.0 g) was added to an aqueous solution of phosphotungstic acid (H.sub.3PW.sub.12O.sub.40.24H.sub.2O, 43.0 g in 97.6 g water) and allowed to remain in contact with the solution for 1 hr. The solution was then drained from the solid, leaving the support pores filled with acid solution, and the support was dried at 130 C. for 16 hrs. The weight of the dried catalyst was 16.1 g.

(46) The loading of the phosphotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst.

(47) Catalyst K (Comparative)Li.sub.0.5H.sub.2.5PW.sub.12O.sub.40.nH.sub.2O/Silica (25.9% w/w)

(48) An aqueous solution of lithium carbonate (0.0417 g in 5.0242 g of water) was added to an aqueous solution of phosphotungstic acid (H.sub.3PW.sub.12O.sub.40.24H.sub.2O, 6.2538 g in 6.2538 g of water) with stirring. After 10 minutes, silica (6.4532 g) was added to the lithium-phosphotungstic acid solution and left in contact for 1 hr before the solution was drained. The solid was then dried at 130 C. for 16 hrs. The weight of dried catalyst was 8.7141 g.

(49) The loading of the lithium-phosphotungstic acid was calculated the by difference in weight of the silica and the final dried catalyst, and the Li/phosphotungstic acid ratio in the final dried catalyst was calculated to be 0.60.

(50) Catalyst L (Example)Na.sub.0.5H.sub.2.5PW.sub.12O.sub.40.nH.sub.2O/Silica (26.0% w/w)

(51) An aqueous solution of sodium carbonate (0.0560 g in 4.9135 g of water) was added to an aqueous solution of phosphotungstic acid (H.sub.3PW.sub.12O.sub.40.24H.sub.2O, 6.2727 g in 9.8199 g of water) with stirring. After 10 minutes, silica (6.4451 g) was added to the sodium-phosphotungstic acid solution and left in contact for 1 hr before the solution was drained. The solid was then dried at 130 C. for 16 hrs. The weight of dried catalyst was 8.7062.

(52) The loading of the sodium-phosphotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst, and the Na/phosphotungstic acid ratio in the final dried catalyst was calculated to be 0.56.

(53) Catalyst M (Example)Cs.sub.1H.sub.2PW.sub.12O.sub.40.nH.sub.2O/Silica (27.4% w/w)

(54) Silica (6.5286 g) was added to an aqueous solution of cesium carbonate (0.3130 g in 7.2836 g water) and left to stand for 1 hr before the solution was drained from the support and the solid material dried at 130 C. for 16 hrs.

(55) The Cs impregnated silica was added to an aqueous solution of phosphotungstic acid (H.sub.3PW.sub.12O.sub.40.24H.sub.2O, 2.8272 g in 12.8920 g water) and allowed to contact the solution for 1 hr. The solution was then drained from the Cs impregnated support and was dried at 130 C. for 16 hrs.

(56) The loading of the cesium-phosphotungstic acid was calculated by the difference in weight of the silica and the final dried catalyst and the Cs/phosphotungstic acid ratio in the final dried catalyst was estimated to be 1.56.

(57) TABLE-US-00001 TABLE 1 Summary of Catalyst Compositions for Catalysts A to M Mass of Cata- catalyst Tests Data lyst Catalyst Composition (mg) used in A H.sub.4SiW.sub.12O.sub.40xH.sub.2O/Silica (24.5 wt %) 108.54 Example 1, 2, 3, 5 A H.sub.4SiW.sub.12O.sub.40xH.sub.2O/Silica (24.5 wt %) 27.3 Example 4 B Cs.sub.1H.sub.3SiW.sub.12O.sub.40xH.sub.2O/Silica (28.5 wt %) 64.2 Example 5 C Cs.sub.2H.sub.2SiW.sub.12O.sub.40xH.sub.2O/Silica (29.9 wt %) 92.14 Example 1, 3 D Cs.sub.3H.sub.1SiW.sub.12O.sub.40xH.sub.2O/Silica (29.8 wt %) 91.2 Example 5 E Cs.sub.4H.sub.0SiW.sub.12O.sub.40xH.sub.2O/Silica (26.2 wt %) 90.24 Example 5 F Li.sub.2H.sub.2SiW.sub.12O.sub.40xH.sub.2O/Silica (25.2 wt %) 53.4 Example 4 G K.sub.2H.sub.2SiW.sub.12O.sub.40xH.sub.2O/Silica (24.1 wt %) 113.97 Example 3 H Ca.sub.1H.sub.2SiW.sub.12O.sub.40xH.sub.2O/Silica (24.0 wt %) 114.72 Example 3 I Cs.sub.2H.sub.2SiW.sub.12O.sub.40xH.sub.2O/Silica (45.5 wt %) 60.4 Example 2 J H.sub.3PW.sub.12O.sub.40nH.sub.2O/Silica (27.2 wt %) 2701 Example 6 K Li.sub.0.5H.sub.2.5PW.sub.12O.sub.40nH.sub.2O/Silica 25.9 wt %) 4424 Example 6 L Na.sub.0.5H.sub.2.5PW.sub.12O.sub.40nH.sub.2O/Silica (26.0 t %) 4420 Example 6 M Cs.sub.1.0H.sub.2.0PW.sub.12O.sub.40nH.sub.2O/Silica (27.4 wt %) 4614 Example 6
General Procedure for Vapour Phase Dehydration of Ethanol with Silicotungstic Acid Catalysts A to I:

(58) A mass of silicotungstic acid catalyst shown in Table 1 above (A to I), having 100-200 m particle diameter and prepared in accordance with the above methods, was loaded into a reactor tube having an isothermal bed and pressurised to 0.501 MPa under an 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.

(59) 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 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).

(60) Once the catalyst performance had stabilised to a steady-state 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 ethylene productivity monitored versus time by on-line GC analysis for up to 260 hours.

Example 1

(61) Vapour phase dehydration of ethanol was conducted independently with catalysts A and C according to the above procedure. The results of the reactions are illustrated graphically in FIG. 1. These results show the benefit of 50% neutralization by cesium per unit mass of silicotungstic acid salt compared to the free acid for similar loading of silicotungstic acid on the support. These results illustrate that, in contrast to the free acid, a partially neutralized silicotungstic acid catalyst according to the invention retains at least 25% of its maximum activity, observed for the same operating conditions, even after 200 hours of operation of the process with the same catalyst under the same conditions and without regeneration.

Example 2

(62) Vapour phase dehydration of ethanol was conducted independently with catalysts A and I according to the above procedure. The results of the reactions are illustrated graphically in FIG. 2. These results show the benefit to catalyst lifetime of 50% neutralization by cesium at increased loading, which affords the same initial activity per unit mass catalyst as the free acid analogue. These results illustrate that, in contrast to the free acid, a partially neutralized silicotungstic acid catalyst according to the invention retains at least 25% of its maximum activity, observed for the same operating conditions, even after 200 hours of operation of the process with the same catalyst under the same conditions and without regeneration.

Example 3

(63) Vapour phase dehydration of ethanol was conducted independently with catalysts A, C, G and H according to the above procedure. The results of the reactions are illustrated graphically in FIG. 3. These results show the benefit to catalyst lifetime of 50% neutralization by cesium, potassium and calcium per unit mass of silicotungstic acid salt compared to the free acid, for similar loading of silicotungstic acid. These results illustrate that, in contrast to the free acid, a partially neutralized silicotungstic acid catalyst according to the invention retains at least 25% of its maximum activity, observed for the same operating conditions, even after 200 hours of operation of the process with the same catalyst under the same conditions and without regeneration.

Example 4

(64) Vapour phase dehydration of ethanol was conducted independently with catalysts A and F according to the above procedure. The results of the reactions are illustrated graphically in FIG. 4. These results show that no benefit is observed with 50% neutralization by lithium compared to the free acid for similar loading.

Example 5

(65) Vapour phase dehydration of ethanol was conducted independently with catalysts A, B, C, D and E according to the above procedure. The results of the reactions are illustrated graphically in FIG. 5. These results show the optimum benefit to catalyst lifetime is with 50% neutralization for a series of cesium containing catalysts. These results illustrate that, in contrast to the free acid, a partially neutralized silicotungstic acid catalyst according to the invention retains at least 25% of its maximum activity, observed for the same operating conditions, even after 200 hours of operation of the process with the same catalyst under the same conditions and without regeneration.

(66) General Procedure for Vapour Phase Dehydration of Ethanol with Phosphotungstic Acid Catalysts J to M:

(67) A mass of phosphotungstic acid catalyst, shown in Table 1 above (J to M), prepared in accordance with the above method was loaded into a reactor tube and pressurized to 0.5 MPa under nitrogen gas flow.

(68) The catalyst was heated at to 240 C. under a nitrogen flow (0.0375 mol/ml catalyst/hr) and held at this temperature for between 22 and 24 hrs. The catalyst was subsequently steamed under a water (0.0178 mol/ml catalyst/hr) and nitrogen flow (0.0375 mol/ml catalyst/hr) for between 17 and 19 hrs before this was replaced by a feed comprising ethanol (0.0141 mol/ml catalyst/hr), water (0.0180 mol/ml catalyst/hr) and nitrogen (0.0352 mol/ml catalyst hr). After approximately 3 hrs the this feed was replaced by one comprising ethanol (0.0310 mol/ml catalyst/hr), water (0.0087 mol/ml catalyst/hr) and nitrogen (0.0307 mol/ml catalyst hr) and the pressure increased to 0.7 MPa. After 90 minutes under these conditions the pressure was increased to 3.1 MPa and the feed was replaced by one containing ethanol (0.0512 mol/ml catalyst/hr), diethyl ether (0.0322 mol/ml catalyst/hr), water (0.0117 mol/ml catalyst/hr) and nitrogen (0.0429 mol/ml catalyst/hr). After a further 15 minutes the temperature was increased to 250 C. The catalyst was operated at steady state under these conditions for up to 290 hrs. The ethylene productivity was monitored versus time by on-line GC analysis.

Example 6

(69) Vapour phase dehydration of ethanol was conducted independently with catalysts J, K, L and M according to the above procedure. The results of the reactions are illustrated graphically in FIG. 6. These results show the benefit to catalyst lifetime of neutralization by alkali metals other than lithium of phosphotungstic acid, compared to the free acid per unit mass of PTA salt for similar levels of loading. These results also illustrate that, in contrast to the free acid, a partially neutralized phosphotungstic acid catalyst (M) according to the invention retains at least 25% of its maximum activity, observed for the same operating conditions, after 150 hours of operation of the process with the same catalyst under the same conditions and without regeneration.

(70) 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.

(71) 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.

(72) 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.