Process for dehydrating methanol to dimethyl ether

Abstract

A process for dehydrating methanol to dimethyl ether using a Brønsted acid catalyst which is a 1-dimensional or a 3-dimensional aluminosilicate zeolite or a heteropolyacid, and a promoter of Formula I C.sub.nH.sub.(2n+1)CO.sub.2CH.sub.3 wherein n=1 to 11 or Formula II C.sub.mH.sub.2m(CO.sub.2CH.sub.3).sub.2 wherein m=2 to 7 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 (a) aluminosilicate zeolites which have a 1-dimensional or a 3-dimensional framework structure, and (b) heteropolyacids, and wherein the promoter is: (i) at least one an alkyl carboxylate ester, C.sub.nH.sub.(2n+1)CO.sub.2CH.sub.3 (Formula I); or (ii) at least one di-ester compound, C.sub.mH.sub.2m (CO.sub.2CH.sub.3).sub.2 (Formula II), wherein in Formula I, n is 2 to 11; and in Formula II, m is 2 to 7 and wherein the molar ratio of promoter to methanol is maintained at less than 1.

2. A process according to claim 1 wherein the alkyl carboxylate ester of Formula I is a straight chain alkyl carboxylate ester.

3. A process according to claim 1 wherein in Formula I, n is 2 to 9.

4. A process according to claim 1 wherein in Formula I, n is 3 to 7.

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

6. A process according to claim 1 wherein the molar ratio of promoter to methanol is maintained in the range 0.00001:1 to 0.2:1.

7. A process according claim 1 wherein the promoter is added to the dehydration process.

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

9. A process according to claim 1 in which process the feed components to the process are methanol, one or both of (i) at least one promoter compound of Formula I or Formula II and (ii) at least one precursor compound of a promoter compound of Formula I or Formula II; and one or both of dimethyl ether and water.

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

11. A process according to claim 1 wherein the Brønsted acid catalyst is a zeolite having a 1-dimensional framework structure selected from framework types MOR, MTT and TON.

12. A process according to claim 1 wherein the Brønsted acid catalyst is a zeolite having a 3-dimensional framework structure selected from framework types MFI, FAU, CHA and BEA.

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

14. A process according to claim 1 wherein the Brønsted acid catalyst is a zeolite which zeolite is composited with a binder material.

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

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

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

18. A method of improving the productivity to dimethyl ether product in a process for dehydrating methanol in the presence of a catalyst and a promoter, wherein the catalyst is at least one solid Brønsted acid catalyst selected from (a) aluminosilicate zeolites which have a 1-dimensional or a 3-dimensional framework structure, and (b) heteropolyacids, and wherein the promoter is: (i) at least one an alkyl carboxylate ester, C.sub.nH.sub.(2n+1)CO.sub.2CH.sub.3 (Formula I); or (ii) at least one di-ester compound, C.sub.mH.sub.2m (CO.sub.2CH.sub.3).sub.2 (Formula II), wherein in Formula I, n is 2 to 11; and in Formula II, m is 2 to 7 and wherein the molar ratio of promoter to methanol is maintained at less than 1.

Description

EXAMPLES

(1) Details of the catalysts 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-00001 TABLE 1 Framework Framework Catalyst Code Structure Ring Size SAR Zeolite beta BEA 3-D 12 25 Zeolite Y FAU 3-D 12 30 Mordenite MOR 1-D 12 20 ZSM-22 TON 1-D 10 69 ZSM-5 MFI 3-D 10 23 SSZ-13 CHA 3-D 8 24 Ferrierite FER 2-D 10.8 20 Clinoptilolite HEU 2-D 10.8 10 SAPO-34 CHA 3-D 8 n/a SAR indicates the silica:alumina molar ratio of a zeolite 1-D, 2-D and 3-D indicate a 1-dimensional, 2-dimensional and 3-dimensional framework structure respectively SAPO-34 is a silicoaluminophosphate n/a means not applicable

Examples 1 to 5

(3) The methyl ester compounds used in Examples 1 to 5 were essentially pure compounds (a total organic nitrogen content of about 0.1 ppm, expressed as nitrogen on a ppm by weight basis) and were obtained from Sigma-Aldrich or Brenntag UK Limited.

(4) The zeolites used in Examples 1 to 5 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:

(7) i) aluminium chlorohydrol solution (25.3 g aluminium chlorohydrol in 253 g of deionised water);

(8) ii) potassium hydroxide solution (82 g 88.8% potassium hydroxide in 820 g of deionised water);

(9) 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);

(10) iv) ammonium chloride (200.6 g ammonium chloride in 3750 g deionised water)

(11) 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.

(12) Preparation of Silica-Supported Silicotungstic Acid Catalyst

(13) 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 was obtained which contained 19.5 wt % of tungsten.

(14) The methanol dehydration reactions of Examples 1 to 5 were carried out utilising the General Reaction Method and Apparatus described below.

(15) General Reaction Method and Apparatus

(16) 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.

(17) 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.

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

Example 1

(19) This Example demonstrates the effect of various alkyl carboxylate ester promoter compounds on the dehydration of methanol employing a variety of catalysts.

(20) Methanol dehydration reactions were carried out in accordance with the General Reaction Method and Apparatus described above using the alkyl carboxylate ester compounds and catalysts specified in Table 2 below. The observed space time yields to dimethyl ether product are also provided in Table 2.

(21) TABLE-US-00002 TABLE 2 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 for different promoters methyl methyl methyl methyl methyl methyl methyl Catalyst None acetate propionate n-butyrate n-pentanoate n-hexanoate n-heptanoate n-octanoate zeolite beta 209 568 — — 837 993 975 1045 ZSM-22 331 346 392 455 533 685 787 851 mordenite 885 1450 1615 1773 2221 2459 2399 2497 ZSM-5 862 1255 1391 1663 1999 2053 1863 1890 zeolite Y 36 59 67 84 119 135 150 153 SSZ-13 1402 — — 1766 1827 1809 1647 1662 ferrierite 2568 2460 2518 2534 2689 2613 2555 2571 clinoptilolite 1285 — — — — 1292 1267 1242 SAPO-34 1155 — — — 819 763 715 792 STA 1359 — — — 1611 1506 1481 1478

(22) As Table 2 shows, in the presence of the alkyl carboxylate ester compounds the productivities to dimethyl ether increased where a 1-dimensional or a 3-dimensional aluminosilicate zeolite or a heteropolyacid catalyst was used in the reactions. However, and taking into account experimental error, no increase in dimethyl ether productivity was observed where a 2-dimensional zeolite (ferrierite and clinoptilolite) or a silicoaluminophosphate (SAPO-34) was used as the catalyst.

Example 2

(23) This Example demonstrates the effect of straight chain and branched chain alkyl carboxylate ester compounds on the catalytic dehydration of methanol.

(24) Methanol dehydration reactions were carried out in accordance with the General Reaction Method and Apparatus described above in the presence of the catalysts and promoter compounds specified in Table 3 below. The observed space time yields to dimethyl ether product are provided in Table 3.

(25) TABLE-US-00003 TABLE 3 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 No Methyl n- Methyl iso- Catalyst promoter butyrate butyrate ZSM-5 841 1663 941 mordenite 835 1773 1182 ZSM-22 313 455 371 zeolite Y 35 84 58 ferrierite 2476 2534 2429

(26) As the results in Table 3 show, the addition of the straight chain and branched chain alkyl carboxylate ester compounds provided increased productivity to dimethyl ether in those reactions carried out using 1-dimensional or 3-dimensional zeolite catalysts. In contrast, no improvement in productivity was observed in the experiments which used a 2-dimensional zeolite catalyst (ferrierite).

Example 3

(27) This Example demonstrates the effect of different concentrations of methyl n-butyrate on the catalytic dehydration of methanol.

(28) Methanol dehydration reactions were carried out in accordance with the General Reaction Method and Apparatus 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.

(29) TABLE-US-00004 TABLE 4 Relative promoter concentration Dimethyl ether STY/g kg.sup.−1 h.sup.−1 (mol %) Ferrierite SSZ-13 ZSM-5 ZSM-22 0 2610 1404 831 338 2 2608 1653 1288 420 5 2646 1766 1567 449 10 2625 1803 1694 538 15 2624 1831 1738 587 20 2598 1821 1723 630

(30) As the results in Table 4 show, in those reactions which employed either a 1-dimensional or a 3-dimensional zeolite as the catalyst, the productivities to dimethyl ether increased at all promoter concentrations. However, and within experimental error, where the catalyst was a 2-dimensional zeolite (ferrierite), essentially no improvement in dimethyl ether productivity was observed at any level of promoter concentration.

Example 4

(31) This Example demonstrates the effect of various alkyl carboxylate ester compounds on the catalytic dehydration of methanol in the presence of the zeolite ZSM-5 at various silica:alumina molar ratios (SAR). The methanol dehydration reactions were carried out in accordance with the General Reaction Method and Apparatus described above using the promoter compounds identified in Table 5 below. The observed space time yields to dimethyl ether product are provided in Table 5.

(32) TABLE-US-00005 TABLE 5 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 862 377 92 methyl 1255 949 264 acetate methyl 1391 1166 320 propionate methyl n- 1663 1564 399 butyrate methyl iso- 941 701 177 butyrate methyl n- 1999 2332 646 pentanoate methyl n- 2053 2648 998 hexanaoate methyl n- 1863 2470 897 heptanoate methyl n- 1890 2274 889 octanoate

(33) As can be seen from an inspection of Table 5, the use of the straight and branched chain alkyl carboxylate ester compounds enabled an increase in dimethyl ether productivity to be achieved in reactions utilising zeolite catalysts of different silica:alumina molar ratios.

Example 5

(34) This Example demonstrates the effect of different concentrations of various alkyl carboxylate ester and di-ester compounds on the catalytic dehydration of methanol in the presence of the zeolite mordenite and the zeolite ZSM-5 with a silica:alumina molar ratio (SAR) of 20 and 80, respectively.

(35) Methanol dehydration reactions were carried out in accordance with the General Reaction Method and Apparatus described above using the alkyl carboxylate ester and diester compounds and concentration as specified in Tables 6 and 7 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 Tables 6 and 7 for the zeolite mordenite and zeolite ZSM-5 catalysts, respectively.

(36) TABLE-US-00006 TABLE 6 ZSM-5 SAR 80 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 for different co-feed concentrations Co-feed 0 mol % 0.01 mol % 0.1 mol % methyl n- 387 516 1123 hexanoate methyl n- 418 979 1396 nonanoate dimethyl 382 774 1487 succinate dimethyl 371 1345 2177 glutarate

(37) TABLE-US-00007 TABLE 7 Mordenite SAR 20 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 for different co-feed concentrations Co-feed 0 mol % 0.01 mol % 0.1 mol % methyl n- 835 880 1053 hexanoate methyl n- 926 1159 1663 nonanoate dimethyl 912 1134 1797 succinate dimethyl 936 1485 2349 glutarate

(38) As the results in Tables 6 and 7 show, in the presence of the alkyl carboxylate ester compounds the productivities to dimethyl ether increased at all promoter concentrations tested.

Example 6

(39) This Example demonstrates the effect of different concentrations of di-ester on the catalytic dehydration of methanol in the presence of the zeolite mordenite and the zeolite ZSM-5 with a silica:alumina molar ratio (SAR) of 20 and 80, respectively. Methanol dehydration reactions were carried out in accordance with the General

(40) Reaction Method and Apparatus described above using dimethyl adipate and concentration as specified in Tables 8 and 9 below. The various promoter concentrations (relative to methanol) were achieved by adjusting the the flow rate of promoter to be in the range 0.00013 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 Tables 8 and 9 for the zeolite mordenite and zeolite ZSM-5 catalysts, respectively.

(41) TABLE-US-00008 TABLE 8 ZSM-5 SAR 80 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 for different co-feed concentrations 0 mol % 0.001 mol % 0.01 mol % 0.1 mol % dimethyl 390 652 1430 2265 adipate

(42) TABLE-US-00009 TABLE 9 Mordenite SAR 20 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 for different co-feed concentrations 0 mol % 0.001 mol % 0.01 mol % 0.1 mol % dimethyl 817 965 1327 2030 adipate

(43) As the results in Tables 8 and 9 show, the productivities to dimethyl ether increased at all promoter concentrations tested.

Example 7

(44) This Example demonstrates the effect of dimethyl adipate on the catalytic dehydration of methanol in the presence of various zeolite and heteropolyacid catalysts.

(45) The methanol dehydration reactions were carried out using the H-form of the zeolites and the heteropolyacids specified in Table 10 below.

(46) Zeolite Y was obtained in H-form from Zeolyst International. Ferrierite, ZSM-22, ZSM-5, zeolite beta and mordenite were obtained in ammonium form from Zeolyst International and converted to H-form by calcination in air at 500° C. The silicoaluminophosphate SAPO-34 can be prepared using known literature methods or can be purchased commercially.

(47) Dimethyl adipate was obtained from ACROS ORGANICS.

(48) The silicotungstic acid used in the dehydration reactions was supported on silica and prepared in accordance with the method described below.

(49) 512 g silica (ex Evonik) was added to a solution of 508 g silicotungstic acid (ex Nippon Organic Chemicals) in 1249 g water to form a silica/silicotungstic acid solution which was left to stand for 30 minutes. Excess silicotungstic acid solution was removed by filtration and the resultant solid catalyst material was oven dried at a temperature of 110° C.

(50) The dried catalyst was cooled to a temperature of 50° C. 685 g of catalyst was obtained which contained 18.9 wt % of tungsten.

(51) The dehydration reactions for this Example 6 were carried out as follows, using a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (10 mm internal diameter) housed a catalyst bed of 0.168 g catalyst diluted with 0.337 g silica. The particle sizes of the catalyst and silica were in the range 450 to 900 microns in diameter. The catalyst 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.

(52) Each reactor was maintained at a temperature of 150° C. and at a total pressure of 1100 kPa throughout the dehydration 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 h.sup.−1 and a constant promoter flow rate of 2.3 mmol h.sup.−1.

(53) 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. The observed space time yields to dimethyl ether product are given in Table 8 below.

(54) TABLE-US-00010 TABLE 10 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 Dimethyl Catalyst Structure No Promoter adipate ZSM-22 1-D 375 593 ZSM-5 SAR23 3-D 586 1636 ZSM-5 SAR50 3-D 312 1432 ZSM-5 SAR280 3-D 93 593 zeolite Y 3-D 55 205 zeolite beta 3-D 156 866 mordenite 1-D 620 1912 STA/silica n/a 402 1477 ferrierite 2-D 1558 1227 SAPO-34 3-D 637 167 SAR indicates the silica:alumina molar ratio of the ZSM-5 zeolite 1-D, 2-D and 3-D indicate a 1-dimensional, a 2-dimensional and a 3-dimensional framework structure respectively. n/a means not applicable.

(55) As can be seen from an inspection of Table 10, in the presence of the di-ester compound, the space time yields to dimethyl ether were seen to increase in the case of the 1-dimensional and 3-dimensional aluminosilicate zeolites and heteropolyacid catalysts. However, in the case of the 2-dimensional and non-aluminosilicate zeolite catalyst (SAPO-34), the addition of the di-ester compound was found to inhibit the space time yields to dimethyl ether.

Example 8

(56) Preparation of H-ZSM-5

(57) Zeolite ZSM-5 in the ammonium form (ex. Zeolyst International) was converted to H-form by calcination in air at 500° C.

(58) Preparation of Dimethyl Adipate Impregnated H-ZSM-5

(59) A 1.5196 g sample of the H-form zeolite prepared as described above was added to a solution of 0.0891 g of dimethyl adipate in 10 ml deionised water. The mixture stirred at room temperature for 10 minutes and then concentrated in vacuo before being dried in an oven at 110° C. for 24 h.

(60) Reaction Testing

(61) Samples of the H-ZSM-5 and the dimethyl adipate impregnated H-ZSM-5 were pressed and sieved to a particle size fraction of 100 to 200 microns diameter and The methanol dehydration reactions of Example 8 were carried out utilising the General Reaction Method and Apparatus described above without the addition of a promoter compound to the gaseous feed. The observed space time yields to dimethyl ether product are provided in Table 11 below.

(62) TABLE-US-00011 TABLE 11 DME STY/g kg.sup.−1 h.sup.−1 ~3 hours after ~12 hours after introduction introduction Catalyst of MeOH feed of MeOH feed H-ZSM-5 SAR 80 409 385 H-ZSM-5 SAR 80 1009 543 impregnated with dimethyl adipate