PROCESS

Abstract

A process for dehydrating methanol to dimethyl ether product in the presence of a solid Brønsted acid catalyst which is an aluminosilicate zeolite or a heteropolyacid and a promoter which is (i) a ketone of formula R.sup.1COR.sup.2 (Formula I) in which R.sup.1 and R.sup.2 are identical or different and are each a C.sub.1-C.sub.11 alkyl group and furthermore R.sup.1 and R.sup.2 together with the carbonyl carbon atom to which they are bonded may form a cyclic ketone; or (ii) a ketal derivative of a ketone of Formula I; and the molar ratio of promoter to methanol is maintained at 0.5 or less.

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 or heteropolyacids, and the promoter is at least one (i) ketone of formula R′COR.sup.2 (Formula I) wherein R.sup.1 and R.sup.2 are identical or different and are each a C.sub.1-C.sub.11 alkyl group and furthermore R.sup.1 and R.sup.2 together with the carbonyl carbon atom to which they are bonded may form a cyclic ketone; or (ii) ketal derivative of a ketone of Formula I; and wherein the molar ratio of promoter to methanol is maintained at 0.5 or less.

2. A process according to claim 1 wherein the ketone of Formula I is a straight alkyl chain ketone or branched alkyl chain ketone.

3. A process according to claim 1 wherein R.sup.1 and R.sup.2 are identical or different and each is a C.sub.1-C.sub.3 alkyl group

4. A process according to claim 1 wherein R.sup.1 and R.sup.2 are different and R.sup.1 is a C.sub.1-C.sub.3 alkyl group and R.sup.2 is a C.sub.1-C.sub.7 alkyl group.

5. A process according to claim 1 wherein the ketone of Formula I is a cyclic ketone comprising 4 to 12 carbon atoms.

6. A process according to claim 1 wherein the ketal derivative of the ketone of Formula I is of formula ##STR00002## wherein R.sup.1 and R.sup.2 are identical or different and each is a C.sub.1 to C.sub.7 alkyl group, and furthermore R.sup.1 and R.sup.2 together with the carbonyl carbon atom to which they are bonded may form a cyclic ketone and each of R.sup.3 and R.sup.4 is an alkyl group or hydrogen with the proviso that R.sup.3 and R.sup.4 are not both hydrogen.

7. A process according to claim 1 wherein the ketal derivative of the ketone of Formula I is a dimethoxy ketal.

8. A process according to claim 1 wherein the total amount of promoter relative to the total amount of methanol is maintained in an amount of 0.0001 to less than 50 mol %.

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

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

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

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

13. A process according to claim 1 wherein the Brønsted acid catalyst is a zeolite which zeolite is a medium pore zeolite and is suitably selected from framework types FER, MWW, MTT and TON.

14. A process according to claim 13 wherein in Formula I R.sup.1 and R.sup.2 are identical or different and each is a C.sub.1-C.sub.2 alkyl group.

15. A process according to claim 1 wherein the Brønsted acid catalyst is a zeolite which zeolite is a large pore zeolite and is suitably selected from framework types MFI, BEA and MOR.

16. A process according to claim 15 wherein in Formula I R.sup.1 and R.sup.2 are identical and each is a C.sub.3-C.sub.7 alkyl group.

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

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

19. 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 aluminosilicate zeolites or heteropolyacids, and the promoter is at least one (i) ketone of formula R.sup.1COR.sup.2 (Formula I) wherein R.sup.1 and R.sup.2 are identical or different and are each a C.sub.1-C.sub.11 alkyl group and furthermore R.sup.1 and R.sup.2 together with the carbonyl carbon atom to which they are bonded may form a cyclic ketone; or (ii) ketal derivative of a ketone of Formula I; and wherein the molar ratio of promoter to methanol is maintained at 0.5 or less.

20. (canceled)

21. The process of claim 1, wherein the yield to dimethyl ether product is improved.

Description

EXAMPLES

[0121] Details of the catalysts used in the Examples are provided in Table 1 below. In Table 1, only ring sizes of 8 T atoms or greater are given. Smaller ring sizes have been omitted.

TABLE-US-00001 TABLE 1 Framework Framework Ring Catalyst Code Structure 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 PSH-3 MWW 2-D 10 21 STA n/a n/a n/a n/a Gamma- n/a n/a n/a n/a alumina SAR indicates the silica: alumina molar ratio 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 and utilised in the dehydration reactions supported on silica. n/a means not applicable

Examples 1 to 6

[0122] Unless otherwise specified, all zeolites used in Examples 1 to 6 were utilised in the methanol dehydration reactions in their H-form.

[0123] Zeolite Y was obtained in H-form from Zeolyst International. All other zeolites (except ZSM-22 and MCM-41) were obtained in ammonium-form from Zeolyst International and converted to H-form by calcination in air at 500° C. The zeolite MCM-41(hexagonal) was obtained from Sigma-Aldrich and converted to H-form by calcination in air at 500° C.

[0124] The gamma-alumina used in Examples was SAS 200 gamma-alumina obtained from BASF AG.

[0125] Preparation of H-ZSM-22 and silica-supported silicotungstic acid were carried out in accordance with the methods described below.

[0126] The ketones and ketal derivatives used in Examples 1 to 6 were obtained from Sigma-Aldrich or Fisher Scientific.

Preparation of H-ZSM-22

[0127] 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)

[0128] 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 it to be 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.

Preparation of Silica-Supported Silicotungstic Acid Catalyst

[0129] 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.

General Reaction Method and Apparatus

[0130] The methanol dehydration reactions were carried out using a 16-channel parallel fixed-bed stainless steel reactor system. Each reactor (2 mm internal diameter) 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.

[0131] 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 2 mol % promoter compound (relative to methanol). The gaseous feed comprising the promoter 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 0.27 mmol h.sup.−1.

[0132] 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

[0133] This Example demonstrates the effect of various promoter compounds on methanol dehydration reactions employing various catalysts.

[0134] The methanol dehydration reactions were carried out using the General Reaction Method and Apparatus described above utilising the promoter compounds and catalysts specified in Table 2 below. The observed space time yields to dimethyl ether product are provided in Table 2. In Table 2, DME=dimethyl ether; MEK=butanone; DEK=3-pentanone; DnPK=4-heptanone; and DiPK=2,4-dimethyl-3-pentanone

TABLE-US-00002 TABLE 2 DME STY/g kg.sup.−1 h.sup.−1 for different promoters No Catalyst promoter Acetone MEK DEK DnPK DiPK ferrierite 2588 4154 3307 — — — ZSM-5 905 2228 2936 3789 5223 1177 mordenite 886 1132 1570 1283 3729 2155 PSH-3 864 4837 3844 1545 1610 1467 ZSM-22 320 924 750 465 648 356 zeolite beta 240 416 1373 1975 3006 852 zeolite Y 45 77 123 96 107 175 SSZ-13 1448 — — — — 1624 STA 615 — — 920 1011 —

[0135] As Table 2 shows, in the presence of the ketone compounds, the space time yields to dimethyl ether were seen to increase where an aluminosilicate zeolite or a heteropolyacid catalyst was used in the reactions. However, no increase in dimethyl ether productivity was observed in those reactions which were carried out in the absence of a ketone compound.

Example 2

[0136] This Example demonstrates the effect of various promoter concentrations on zeolite-catalysed methanol dehydration reactions.

[0137] The methanol dehydration reactions were carried out using the General Reaction

[0138] Method and Apparatus described above in the presence of the catalysts and at the acetone concentrations specified in Table 3 below. The various promoter concentrations (relative to methanol) were achieved by adjusting the flow rate of acetone to be in the range 0.03 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 3.

TABLE-US-00003 TABLE 3 Relative promoter concentration Dimethyl ether STY/g kg.sup.−1 h.sup.−1 (mol %) ferrierite PSH-3 ZSM-22 0 2555 815 327 0.25 2793 2370 475 0.50 3060 3095 563 1 3475 3950 701 2 4131 4892 923 5 5180 5939 1121 10 5947 6449 1295 15 6199 6397 1356 20 6481 6455 1452

[0139] As can be seen from an inspection of Table 3, the ketone compounds of the present invention can be used at a wide range of concentrations to provide an increase in space time yield to dimethyl ether in methanol dehydration reactions.

Example 3

[0140] This Example demonstrates the effect of ketal compounds on the catalytic dehydration of methanol.

[0141] Methanol dehydration reactions were carried out using the General Reaction Method and Apparatus described above in the presence of the ketal, 2,2-dimethoxybutane and the catalysts identified in Table 4 below. The observed space time yields to dimethyl ether product are provided in Table 4.

TABLE-US-00004 TABLE 4 Dimethyl ether STY g kg.sup.−1 h.sup.−1 Catalyst No promoter 2,2-DMB ferrierite 2622 3511 mordenite 926 1432 ZSM-5 898 2667 PSH-3 870 4383 ZSM-22 333 1025 zeolite beta 246 1529 zeolite Y 44 81 gamma- 2 2 alumina 2,2-DMB = 2,2-dimethoxybutane

[0142] As can be seen from Table 4, the addition of the ketal compound provided increased productivity to dimethyl ether in those reactions carried out using a zeolite catalyst. However, no increase in dimethyl ether productivity was observed in those reactions in which the reaction was carried out in the absence of the ketal or which were carried out in the presence of the ketal compound and gamma-alumina catalyst.

Example 4

[0143] This Example demonstrates the effect of various ketone compounds on the catalytic dehydration of methanol in the presence of ZSM-5 of various silica:alumina molar ratios (SAR).

[0144] The methanol dehydration reactions were carried out using the General Reaction Method and Apparatus described above and utilising the ketone compounds identified in Table 5 below. The observed space time yields to dimethyl ether product are provided in Table 5.

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 905 409 102 acetone 2228 3368 1132 2-butanone 2936 2882 918 3-pentanone 3789 3753 1426 4-heptanone 5223 5872 2436 2,4-dimethyl- 1177 978 317 3-pentanone

[0145] As can be seen from an inspection of Table 5, the use of the straight and branched chain ketone compounds enabled an increase in dimethyl ether productivity to be achieved in reactions utilising zeolite catalysts of different silica:alumina molar ratios.

Example 5

[0146] In this Example, the effect of the straight chain di-n-propyl ketone and the branched chain di-iso-propyl ketone was investigated in methanol dehydration reactions employing the zeolite ZSM-5.

[0147] The methanol dehydration reactions were carried out using the General Reaction Method and Apparatus described above and employing the ketone promoters at a concentration of 2 mol % relative to methanol.

[0148] The results of this Example are shown in FIG. 1, wherein the circles represent periods in which methanol was used as the feed to the process i.e. no ketone addition. The black squares represent periods in which 5 mol % of di-n-propyl ketone (relative to methanol) was present in the methanol feed and the white squares represent periods in which 5 mol % of di-iso-propyl ketone (relative to methanol) was present in the methanol feed. As is illustrated in FIG. 1, during the periods in which a ketone compound was used, the space time yield (STY) to dimethyl ether was observed to increase compared to the periods carried out in the absence of the ketone compound. It was also observed that the use of the branched chain ketone, di-iso-propyl ketone, resulted in little or no catalyst deactivation at the concentration of promoter tested.

Example 6

[0149] This Example demonstrates the effect of various promoter concentrations on zeolite-catalysed methanol dehydration reactions and the effect on the catalytic dehydration of methanol in the presence of zeolite catalysts of various silica:alumina molar ratios (SAR).

[0150] The methanol dehydration reactions were carried out using the General Reaction Method and Apparatus described above in the presence of the catalysts and at the 5-nonanone concentrations specified in Table 1 below. The various promoter concentrations (relative to methanol) were achieved by adjusting the flow rate of 5-nonanone 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 Table 6.

TABLE-US-00006 TABLE 6 Relative 5-nonanone Dimethyl ether STY/g kg.sup.−1 h.sup.−1 concentration ZSM-5 ZSM-5 zeolite beta zeolite beta (mol %) SAR 23 SAR 80 SAR 25 SAR 150 0 852 429 218 113 0.001 1125 1019 981 1008 0.01 2287 3207 1929 1896 0.1 3433 4496 2336 2227

[0151] As can be seen from an inspection of Table 6, 5-nonanone can be used at a wide range of concentrations to provide an increase in space time yield to dimethyl ether in methanol dehydration reactions utilising zeolite catalysts of different silica:alumina molar ratios.

Examples 7 and 8

[0152] The diester compounds used in Examples 7 and 8 were obtained from Alfa Aesar or Acros Organics.

[0153] The zeolite used in Examples 7 and 8 was utilised in its H-form. The zeolite was obtained in ammonium-form from Zeolyst International and converted to H-form by calcination in air at 500° C.

[0154] The methanol dehydration reactions of Examples 7 and 8 were carried out utilising the General Reaction Method and Apparatus II described below.

General Reaction Method and Apparatus II

[0155] 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.

[0156] 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 0.01 or 0.1 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 0.0045 or 0.045 mmol h.sup.−1.

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 7

[0157] This Example demonstrates the effect of various concentrations of cyclohexanone on dehydration reactions of methanol employing various catalysts.

[0158] The dehydration reactions were carried out using the General Reaction Method and Apparatus II described above and in the presence of the zeolite ZSM-5 with a silica:alumina molar ratio (SAR) of 20. The various promoter concentrations (relative to methanol) were achieved by adjusting the flow rate of cyclohexanone to be in the range 0.0045 mmol h.sup.−1 to 0.045 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 7.

TABLE-US-00007 TABLE 7 Relative cyclohexanone Dimethyl ether STY/g concentration (mol %) kg.sup.−1 h.sup.−1 0 519 0.01 943 0.1 2192

[0159] As can be seen from an inspection of Table 6, cyclohexanone can be used at a range of concentrations to provide an increase in space time yield to dimethyl ether in methanol dehydration reactions.

Example 8

[0160] This Example demonstrates the effect of various concentrations of cyclopentanone on dehydration reactions of methanol employing various catalysts.

[0161] The dehydration reactions were carried out using the General Reaction Method and Apparatus II described above and in the presence of the zeolite ZSM-5 with a silica:alumina molar ratio (SAR) of 20. The various promoter concentrations (relative to methanol) were achieved by adjusting the flow rate of cyclopentanone to be in the range 0.0045 mmol h.sup.−1 to 0.045 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 8.

TABLE-US-00008 TABLE 8 Relative cyclopentanone Dimethyl ether STY/g concentration (mol %) kg.sup.−1 h.sup.−1 0 485 0.01 737 0.1 1462

[0162] As can be seen from an inspection of Table 8, cyclopentanaone can be used at a range of concentrations to provide an increase in space time yield to dimethyl ether in methanol dehydration reactions.