Process for dehydrating methanol to dimethyl ether product

Abstract

A process the dehydration of methanol to dimethyl ether in the presence of a solid Brønsted acid catalyst selected from aluminosilicate zeolites which have a maximum free sphere diameter of greater than 3.67 Angstroms and heteropolyacids and a promoter selected from methyl formate, dimethyl oxalate and dimethyl malonate and the molar ratio of promoter to methanol is maintained at less than 1.

Claims

1. A process comprising dehydrating methanol to dimethyl ether product in the presence of a catalyst and a promoter, wherein the catalyst is at least one solid Brønsted acid catalyst selected from aluminosilicate zeolites that have a maximum free sphere diameter of greater than 3.67 Angstroms and heteropolyacids, and the promoter is selected from methyl formate, dimethyl oxalate and dimethyl malonate, wherein the molar ratio of promoter to methanol is maintained in the range 0.005:1 to 0.5:1, and wherein the total amount of promoter relative to methanol is maintained in an amount of at least 2 mol %.

2. A process according to claim 1 wherein the total amount of promoter relative to methanol is maintained in an amount of at least 5 mol %.

3. A process according to claim 1 wherein the molar ratio of promoter to methanol is maintained in the range 0.01:1 to 0.2:1.

4. A process according to claim 1 wherein a promoter is added to the methanol.

5. A process according to claim 1 wherein a promoter is generated in-situ in the dehydration process.

6. A process according to claim 1 wherein methyl acetate is not a component of the feed to the process.

7. A process according to claim 1 wherein the Brønsted acid catalyst is a H-form zeolite.

8. A process according to claim 1 wherein the Brønsted acid catalyst is a medium pore zeolite or large pore zeolite.

9. A process according to claim 8 wherein the Brønsted acid catalyst is a medium pore zeolite selected from framework types FER, MFI, MWW, MTT and TON.

10. A process according to claim 1 wherein the zeolite is selected from framework types CHA, MOR, FAU and BEA.

11. A process according to claim 1 wherein the zeolite is composited with a binder material.

12. A process according to claim 1 wherein the Brønsted acid catalyst is a heteropolyacid which is a silicotungstic acid.

13. A process according to claim 1 wherein the process is carried out at a temperature of from 100° C. to 300° C.

14. A process according to claim 1 wherein the process is carried out as a heterogeneous vapour phase process.

15. A method of improving the productivity to dimethyl ether product, comprising dehydrating methanol in the presence of a catalyst and a promoter, wherein the catalyst is at least one solid Brønsted acid catalyst selected from aluminosilicate zeolites which have a maximum free sphere diameter of greater than 3.67 Angstroms and heteropolyacids and the promoter is selected from methyl formate, dimethyl oxalate, and dimethyl malonate, wherein the molar ratio of promoter to methanol is maintained in the range 0.005:1 to 0.5:1, and wherein the total amount of promoter relative to methanol is maintained in an amount of at least 2 mol %.

16. A process according to claim 1 wherein the molar ratio of promoter to methanol is maintained in the range 0.02:1 to 0.5:1, and wherein the Brønsted acid catalyst is a medium pore zeolite or large pore zeolite.

17. A process according to claim 16 wherein methyl acetate is not a component of the feed to the process.

18. A process according to claim 1 wherein the molar ratio of promoter to methanol is maintained in the range 0.01:1 to 0.5:1.

19. A process according to claim 1, wherein the catalyst is an aluminosilicate zeolite having a maximum free sphere diameter of greater than 3.67 Angstroms.

20. A process according to claim 1 wherein the total amount of promoter relative to methanol is maintained in an amount of at most 50 mol %.

Description

EXAMPLES

(1) Details of the zeolites used in the Examples are provided in Table 1 below. In Table 1 only rings having 8 T atoms or greater are given. Smaller ring sizes have been omitted.

(2) TABLE-US-00002 TABLE 1 Maximum free sphere Framework Framework Ring diameter/ Catalyst Code Structure Size Angtroms SAR Ferrierite FER 2-D 10, 8 4.69 20 PSH-3 MWW 2-D 10 4.92 21 ZSM-22 TON 1-D 10 5.11 69 Mordenite MOR 1-D 12 6.45 20 SSZ-13 CHA 3-D  8 3.72 24 ZSM-5 MFI 3-D 10 4.46 23 Zeolite beta BEA 3-D 12 5.95 25 Zeolite Y FAU 3-D 12 7.35 30 Clinoptilolite HEU 2-D 10 3.67 10 SAR indicates the silica:alumina molar ratio of a zeolite 1-D, 2-D and 3-D indicate a 1-dimensional, a 2-dimensional and a 3-dimensional zeolite framework structure respectively.

Examples 1 and 4

(3) The methyl formate used in Examples 1 to 4 was essentially pure (a total organic nitrogen content of less than 0.5 ppm, expressed as nitrogen on a ppm by weight basis) and was obtained from Sigma-Aldrich

(4) The zeolites used in Examples 1 to 4 were utilised in their H-form. The zeolites Y and SAPO-34 were obtained in H-form from Zeolyst International. All other zeolites (except ZSM-22) were obtained in ammonium-form from Zeolyst International and converted to H-form by calcination in air at 500° C. H-ZSM-22 and silica-supported silicotungstic acid were prepared in accordance with the methods described below.

(5) Preparation of H-ZSM-22

(6) For use in the preparation of the zeolite the following solutions were prepared: i) aluminium chlorohydrol solution (25.3 g aluminium chlorohydrol in 253 g of deionised water); ii) potassium hydroxide solution (82 g 88.8% potassium hydroxide in 820 g of deionised water); iii) Ludox solution (900 g Ludox AS40 (silica sol with 40 wt % SiO.sub.2 stabilised with ammonium hydroxide ex Aldrich) diluted in 2694 g of deionised water); iv) ammonium chloride (200.6 g ammonium chloride in 3750 g deionised water)

(7) The aluminium chlorohydrol solution was added slowly with vigorous stirring to the potassium hydroxide solution of to form an aluminate solution. 226 g diaminohexane (DAH) was added to the aluminate solution. The DAH/aluminate solution was added to the Ludox solution under vigorous stirring and stirred for at least 30 minutes until a gel formed. The gel was transferred to an autoclave and agitated (500 rpm) at a temperature of 160° C. for 48 hours to form a slurry. The autoclave was allowed to cool, under agitation, to a temperature below 60° C. and the slurry centrifuged to separate the solids from the mother liquor. The solids were washed with sufficient deionised water such that the pH of was less than 8 and then dried overnight at a temperature of 110° C. to generate a dried zeolitic material. The X-ray diffraction pattern of the zeolitic material showed that the zeolite was ZSM-22. The dried zeolitic material was calcined at 600° C. for 12 hours to effect removal of the diaminohexane from the pores of the pores of the zeolite. The calcined zeolite was converted into the ammonium-form of the zeolite by ion-exchange with the ammonium chloride solution at a temperature of 80° C. for 4 hours and then repeated. The ion-exchanged zeolite was separated from the liquid by filtration, washed with deionised water and dried overnight at 110° C. The ammonium-exchanged zeolite was converted to the H-form by calcination in air at 500° C. for 8 hours.

(8) Preparation of Silica-Supported Silicotungstic Acid Catalyst

(9) 30.1 g silica (ex Grace Chemicals) was added to a solution of 14.30 g silicotungstic acid (ex Nippon Organic Chemicals) in 39.9 g water. The silica/silicotungstic acid solution was left to stand for 30 minutes before being oven dried at a temperature of 120° C. for a period of 16 hours. The dried catalyst material was then cooled to 50° C. 40.93 g catalyst were obtained which comprised 19.5 wt % of tungsten.

(10) The methanol dehydration reactions of Examples 1 and 2 were carried out utilising the General Reaction Method and Apparatus I described below.

(11) General Reaction Method and Apparatus I

(12) The methanol dehydration reactions were carried out using a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (2 mm internal diameter) was heated to maintain a temperature of 150° C. Each reactor housed a 25 mg bed of catalyst (having particle size fraction of 100 to 200 microns diameter) loaded on top of a 6 cm deep bed of an inert material (carborundum). The reactor volume above the catalyst was also packed with carborundum.

(13) Each reactor was maintained at a temperature of 150° C. and at a total pressure of 1100 kPa throughout the reactions. A gaseous feed comprising 10 mol % methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol % methanol and 5 mol % promoter compound (relative to methanol). This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 13 mmol h.sup.−1 and a constant promoter flow rate of 0.7 mmol h.sup.−1.

(14) The effluent stream from each reactor was diluted with inert gas (nitrogen) and was periodically analysed by online gas chromatography, at 3 hour intervals, to determine the yield of dimethyl ether product.

Example 1

(15) This Example demonstrates the effect of methyl formate on methanol dehydration reactions employing various catalysts.

(16) The methanol dehydration reactions were carried out using the General Reaction Method and Apparatus I described above and employing the catalysts specified in Table 2 below. The observed space time yields to dimethyl ether product are also provided in Table 2.

(17) TABLE-US-00003 TABLE 2 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 Catalyst Structure No Promoter Methyl formate ferrierite 2-D 2589 3107 PSH-3 2-D 897 1380 ZSM-22 1-D 328 440 SSZ-13 3-D 1478 1623 ZSM-5 3-D 867 1181 zeolite Y 3-D 35 39 zeolite beta 3-D 207 352 mordenite 1-D 876 1031 clinoptilolite 2-D 1253 1254 STA n/a 1398 1522 1-D, 2-D and 3-D indicate a 1-dimensional, a 2-dimensional and a 3-dimensional zeolite framework structure respectively. STA is silicotungstic acid as prepared above. n/a means not applicable

(18) The results in Table 2 show that the use of methyl formate enhances the space time yields to dimethyl ether in reactions utilising aluminosilicate zeolites which have a maximum free sphere diameter of greater than 3.67 Angstroms. In the case of the zeolite clinoptilolite which has a maximum free sphere diameter of 3.67 Angstroms no promotion was observed.

Example 2

(19) This Example demonstrates the effect of methyl formate on the catalytic dehydration of methanol in the presence of the zeolite ZSM-5 at various silica:alumina molar ratios (SAR). The dehydration reactions were carried out using the General Reaction Method and Apparatus I described. The observed space time yields to dimethyl ether product are provided in Table 3 below.

(20) TABLE-US-00004 TABLE 3 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 ZSM-5 ZSM-5 ZSM-5 Promoter SAR 23 SAR 80 SAR 280 no promoter 867 390 85 methyl formate 1181 792 232

(21) As can be seen from an inspection of Table 3, the use of methyl formate provided increased dimethyl ether productivities in reactions utilising zeolite catalysts of different silica:alumina molar ratios.

Example 3

(22) This Example demonstrates the effect of different concentrations of methyl formate on the catalytic dehydration of methanol.

(23) Methanol dehydration reactions were carried out in accordance with the General Reaction Method and Apparatus I described above utilising the catalysts and promoter concentrations as specified in Table 4 below. The various promoter concentrations (relative to methanol) were achieved by adjusting the the flow rate of promoter to be in the range 0.27 mmol h.sup.−1 to 2.7 mmol h.sup.−1 depending on the desired promoter concentration to be achieved. The observed space time yields to dimethyl ether product are provided in Table 4.

(24) TABLE-US-00005 TABLE 4 Relative promoter Dimethyl ether STY/g kg.sup.−1 h.sup.−1 concentration (mol %) ferrierite STA PSH-3 zeolite beta 0 2486 1227 866 213 2 2678 1275 1088 272 5 2919 1372 1307 336 10 3324 1505 1570 410 20 3808 1687 1890 533 STA is silicotungstic acid as prepared above.

(25) As the results in Table 4 show, the productivities to dimethyl ether increased at all promoter concentrations tested.

Example 4

(26) This Example demonstrates the effect of different concentrations of dimethyl malonate on the catalytic dehydration of methanol.

(27) Methanol dehydration reactions were carried out in accordance with the General Reaction Method and Apparatus I described above utilising the catalysts and promoter concentrations as specified in Table 5 below. The various promoter concentrations (relative to methanol) were achieved by adjusting the the flow rate of promoter to be in the range 0.0013 mmol h.sup.−1 to 0.013 mmol h.sup.−1 depending on the desired promoter concentration to be achieved. The observed space time yields to dimethyl ether product are provided in Table 5.

(28) TABLE-US-00006 TABLE 5 Relative promoter Dimethyl ether STY/g kg.sup.−1 h.sup.−1 concentration (mol %) ZSM-5 PSH-3 mordenite ZSM-22 0 895 886 877 335 0.01 956 910 922 352 0.1 1146 931 1093 376

(29) As the results in Table 5 show, the productivities to dimethyl ether increased at all promoter concentrations tested.

Examples 5 to 6

(30) The diester compounds used in Examples 5 to 6 were obtained from Alfa Aesar or Acros Organics.

(31) The zeolites used in Examples 5 to 6 were utilised in their H-form. Zeolite Y was obtained in H-form from Zeolyst International. All other zeolites (except ZSM-22) were obtained in ammonium-form from Zeolyst International and converted to H-form by calcination in air at 500° C. H-ZSM-22 was prepared in accordance with the preparation method described above.

(32) The methanol dehydration reactions of Examples 5 to 6 were carried out utilising the General Reaction Method and Apparatus II described below.

General Reaction Method and Apparatus II

(33) The methanol dehydration reactions were carried out using a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (10 mm internal diameter) housed a bed of catalyst mixed with silica dioxide diluent (0.168 g catalyst diluted with 0.337 g silica dioxide). The catalyst and silica dioxide each had a particle size of 450 to 900 microns diameter. The mixture was loaded on top of a 6.5 cm deep bed of an inert material (quartz sand). The reactor volume above the catalyst bed was also packed with quartz sand.

(34) Each reactor was maintained at a temperature of 150° C. and at a total pressure of 1100 kPa throughout the reactions. A gaseous feed comprising 10 mol % methanol and inert gas was introduced into the reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol % methanol and 5 mol % promoter compound (relative to methanol). This gaseous feed comprising the promoter compound was introduced into the reactor for a period of 24 hours at a constant flow rate of methanol of 45 mmol.sup.−1 and a constant promoter flow rate of 2.3 mmol.sup.−1.

(35) The effluent stream from each reactor was cooled to 5° C. in a condenser and the gas phase from the condenser was periodically analysed by online gas chromatography to determine the yield of dimethyl ether product.

Example 5

(36) This Example demonstrates the effect of dimethyl oxalate on dehydration reactions of methanol employing various catalysts.

(37) The dehydration reactions were carried out using the General Reaction Method and Apparatus II described above and employing the catalysts identified in Table 6 below.

(38) TABLE-US-00007 TABLE 6 Max free sphere diameter/ Dimethyl ether STY/g kg.sup.−1 h.sup.−1 Catalyst Angstroms No Promoter Dimethyl oxalate ferrierite 4.69 1517 2006 ZSM-22 5.11 346 415 ZSM-5 4.46 567 926 zeolite Y 7.35 63 102 zeolite beta 5.95 178 394 mordenite 6.45 577 676 1-D, 2-D and 3-D indicate a 1-dimensional, a 2-dimensional and a 3-dimensional framework structure respectively.

(39) The results in Table 6 show that the use of dimethyl oxalate enhances the space time yield to dimethyl ether in reactions utilising aluminosilicate zeolites which have a maximum free sphere diameter of greater than 3.67 Angstroms.

Example 6

(40) This Example demonstrates the effect of dimethyl malonate on dehydration reactions of methanol employing various catalysts.

(41) The dehydration reactions were carried out using the General Reaction Method and Apparatus II described above and employing the catalysts identified in Table 7 below.

(42) TABLE-US-00008 TABLE 7 Max free sphere diameter/ Dimethyl ether STY/g kg.sup.−1 h.sup.−1 Catalyst Angstroms No Promoter Dimethyl malonate ferrierite 4.69 1635 2329 ZSM-22 5.11 382 546 ZSM-5 4.46 598 1429 zeolite Y 7.35 59 139 zeolite beta 5.95 178 557 mordenite 6.45 630 1092 1-D, 2-D and 3-D indicate a 1-dimensional, a 2-dimensional and a 3-dimensional framework structure respectively.

(43) The results in Table 7 show that the use of dimethyl malonate enhances the space time yield to dimethyl ether in reactions utilising aluminosilicate zeolites which have a maximum free sphere diameter of greater than 3.67 Angstroms.