Process for dehydrating methanol to dimethyl ether

Abstract

A process for dehydrating methanol to dimethyl ether product in the presence of an aluminosilicate zeolite catalyst and a promoter selected from (i) aldehyde of formula R.sup.1CHO (Formula I) in which R.sup.1 is hydrogen, a C.sub.1-C.sub.11 alkyl group or a C.sub.3-C.sub.11 alkyl group in which 3 or more carbon atoms are joined to form a ring; or (ii) acetal derivative of an aldehyde of Formula I; and the molar ratio of promoter to methanol is maintained at 0.1 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 aluminosilicate zeolite and the promoter is at least one (i) aldehyde of formula R.sup.1CHO (Formula I) wherein R.sup.1 is a C.sub.3-C.sub.11 alkyl group or a C.sub.3-C.sub.11 alkyl group in which 3 or more carbon atoms are joined to form a ring; or (ii) acetal derivative of an aldehyde of Formula I; and wherein the molar ratio of promoter to methanol is maintained at 0.1 or less.

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

3. A process according to claim 1 wherein R.sup.1 is a straight or branched alkyl chain group.

4. A process according to claim 3 wherein R.sup.1 is a straight alkyl chain group and the aldehyde of Formula I is selected from the group consisting of n-butanal, n-hexanal and n-octanal.

5. A process according to claim 3 wherein R.sup.1 is a branched alkyl chain group and the aldehyde of Formula I is selected from the group consisting of iso-butanal and 2-ethyl hexanal.

6. A process according to claim 1 wherein the acetal derivative of the aldehyde of Formula I is a dimethoxyacetal.

7. 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 10 mol %.

8. A process according to claim 1 wherein the molar ratio of promoter to methanol is maintained in the range 0.00001:1 to 0.1:1.

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

10. A process according to claim 1 wherein the zeolite is selected from the group consisting of zeolites of framework type FER, MWW, MTT, MFI, MOR, FAU, CHA, BEA and TON.

11. A process according to claim 1 wherein the zeolite is a large pore zeolite and R.sup.1 is a straight or branched chain C.sub.3-C.sub.7 alkyl group.

12. A process according to claim 1 wherein the zeolite is a medium pore zeolite and R.sup.1 is a straight chain C.sub.3-C.sub.7 alkyl group.

13. A process according to claim 1 wherein the zeolite is a 2-dimensional medium pore zeolite and R.sup.1 is a branched chain C.sub.3 alkyl group.

14. A process according to claim 1 wherein the acetal derivative of the aldehyde of Formula I is a dimethoxyacetal and the zeolite is a zeolite of framework type selected from the group consisting of TON, MOR and FER.

15. A process according to claim 1 wherein the zeolite is a hydrogen-form zeolite.

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

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. The process of claim 1, wherein the promoter improves the productivity to dimethyl ether product.

20. A process comprising dehydrating methanol to dimethyl ether in the presence of a catalyst and a promoter, and in the absence of methyl acetate, wherein the catalyst is at least one aluminosilicate zeolite and the promoter is at least one (i) aldehyde of formula R.sup.1CHO (Formula I) wherein R.sup.1 is hydrogen, a C.sub.1-C.sub.11 alkyl group or a C.sub.3-C.sub.11 alkyl group in which 3 or more carbon atoms are joined to form a ring; or (ii) acetal derivative of an aldehyde of Formula I; and wherein the molar ratio of promoter to methanol is maintained at 0.1 or less.

21. A process according to claim 20 wherein the molar ratio of promoter to methanol is maintained in the range 0.00001:1 to 0.1:1.

Description

EXAMPLES

(1) 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 provided. Smaller ring sizes have been omitted.

(2) TABLE-US-00001 TABLE 1 Framework Framework Catalyst Code Structure Ring Size SAR ZSM-22 TON 1-D 10 69 PSH-3 MWW 2-D 10 21 Ferrierite FER 2-D 10.8 20 ZSM-5 MFI 3-D 10 23 Mordenite MOR 1-D 12 20 SSZ-13 CHA 3-D 8 24 SAR is 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

(3) Catalysts Used in the Examples

(4) The zeolites were used in the methanol dehydration reactions of the Examples in their H-form.

(5) All zeolites (except ZSM-22) were obtained in ammonium-form from Zeolyst International and converted to H-form by calcination in air at 500° C. The zeolite, H-ZSM-22 was prepared in accordance with the method described below.

(6) Preparation of H-ZSM-22

(7) For use in the preparation of the zeolite the following solutions were prepared:

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

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

(10) 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);

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

(12) 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.

(13) Aldehyde and Acetal Compounds Used in the Examples

(14) The aldehydes were obtained from Sigma-Aldrich. The acetal, 1,1-dimethoxyethane was obtained from Alfa Aesar.

(15) The methanol dehydration reactions of Examples 1 to 3 were carried out utilising the General Reaction Method and Apparatus I described below.

(16) General Dehydration Reaction Method and Apparatus I

(17) 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.

(18) Each reactor was maintained at a temperature of 150° C. and at a total pressure of 1100 kPa throughout the reaction. A gaseous feed comprising 10 mol % methanol and inert gas was introduced into a reactor and allowed to flow through the catalyst bed for a period of 48 hours at which point a promoter compound (relative to methanol) 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 flow rate of promoter of 0.27 mmol h.sup.−1.

(19) 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

(20) This Example demonstrates the effect of n-butanal on the dehydration of methanol employing a variety of aluminosilicate zeolite catalysts.

(21) With the exception of the zeolite ZSM-5, the methanol dehydration reactions were carried out using the General Reaction Method and Apparatus I described above and employing the promoter and catalysts specified in Table 2 below. In respect of ZSM-5 the reaction was carried out using the General Reaction Method and Apparatus described above but wherein methanol was fed for a period of 16 hours rather than 48 hours before the addition of 2 mol % butanal (relative to methanol) and analysed by gas chromatography at about 12 minute intervals.

(22) The observed space time yields to dimethyl ether product are provided in Table 2.

(23) TABLE-US-00002 TABLE 2 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 No Catalyst promoter n-butanal ferrierite 2618 7122 SSZ-13 1652 1969 mordenite 987 1054 PSH-3 915 1265 ZSM-5 857 1948 ZSM-22 352 656

(24) As the results in Table 2 show, the addition of t e aldehyde compound resulted in increased space time yield to dimethyl ether whereas no such increase was observed in those reactions carried out in the absence of the aldehyde.

Example 2

(25) This Example demonstrates the effect of various iso-butanal concentrations on methanol dehydration reactions carried out in the presence of the zeolite catalysts identified in Table 3 below. Zeolite ZSM-5 was utilised in the reaction at a silica to alumina molar ratio of 80 and also at a silica to alumina molar ratio of 280. These are designated in Table 3 as ZSM-5 (80) and ZSM-5 (280) respectively.

(26) The dehydration reactions were carried out using the General Reaction Method and Apparatus I described above utilising aldehyde concentrations relative to methanol of 2 mol % for 24 hours at an aldehyde flow rate of 0.27 mmol h.sup.−1 followed by 5 mol % aldehyde at a flow rate of 0.67 mmol h.sup.−1. The observed space time yields to dimethyl ether product are provided in Table 3.

(27) TABLE-US-00003 TABLE 3 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 No iso-butanal iso-butanal Catalyst promoter 2 mol % 5 mol % ferrierite 2600 2959 3354 PSH-3 863 3629 1716 ZSM-5 (80) 395 1662 870 ZSM-22 336 357 377 ZSM-5 (280) 94 489 394

(28) As the results in Table 3 show, the use of the different concentrations of aldehyde compound provides improved productivities to dimethyl ether compared to the productivities achieved in the absence of the aldehyde compound.

Example 3

(29) This Example demonstrates the effect of various dimethoxymethane concentrations on methanol dehydration reactions carried out in the presence of the zeolite catalysts identified in Table 4 below. Zeolite ZSM-5 was utilised in the reaction at a silica to alumina molar ratio of 23 and also at silica to alumina molar ratios of 80 and 280. These are designated in Table 4 as ZSM-5 (23), ZSM-5 (80) and ZSM-5 (280), respectively.

(30) The dehydration reactions were carried out using the General Reaction Method and Apparatus I described above utilising aldehyde concentrations relative to methanol of 2 mol % for 24 hours at a dimethoxymethane flow rate of 0.27 mmol h.sup.−1 followed by 10 mol % aldehyde at a flow rate of 1.3 mmol h.sup.−1. The observed space time yields to dimethyl ether product are provided in Table 4.

(31) TABLE-US-00004 TABLE 4 Dimethyl ether STY/g kg.sup.−1 h.sup.−1 No dimethoxymethane dimethoxymethane Catalyst promoter 2 mol % 10 mol % SSZ-13 1352 1454 1663 ZSM-5 (23) 846 867 903 ZSM-5 (80) 380 398 444 ZSM-22 341 364 430 ZSM-5 (280) 84 86 100

(32) As the results in Table 4 show, the use of the different concentrations of dimethoxymethane provides improved productivities to dimethyl ether compared to the productivities achieved in the absence of the dimethoxymethane.

Examples 4 and 5

(33) The methanol dehydration reactions of Examples 4 and 5 were carried out utilising the General Reaction Method and Apparatus II described below.

(34) General Reaction Method and Apparatus II

(35) 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 (0.337 g catalyst diluted with 1.348 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 was also packed with quartz sand.

(36) Each reactor was maintained at a temperature of 160° 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 100 hours at which point a promoter compound was added to the feed to achieve a gaseous feed comprising 10 mol % methanol and 0.23 mol % promoter compound (relative to methanol). This gaseous feed comprising the promoter compound was fed to the reactor for a period of 120 hours at a constant methanol flow rate of 90 mmol h.sup.−1 and a constant promoter flow rate of 0.2 mmol h.sup.−1.

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

Example 4

(38) In this Example, the effect of the acetal 1,1-dimethoxyethane was investigated in methanol dehydration reactions employing the zeolites, mordenite and ferrierite.

(39) The methanol dehydration reactions were carried out using the General Reaction Method and Apparatus II described above and wherein the concentration of aldehyde relative to methanol was 0.23 mol %.

(40) The observed space time yields to dimethyl ether product are also provided in Table 5 below.

(41) TABLE-US-00005 TABLE 5 DME STY/g kg.sup.−1 h.sup.−1 No Catalyst promoter 1,1-dimethoxyethane ferrierite 1014 1305 mordenite 915 1019

(42) As can be seen from Table 5, the space time yields to dimethyl ether were higher in the reactions carried out with the addition of the acetal compound compared to the reactions carried out in the absence of the acetal.

Example 5

(43) This Example demonstrates the effect of various n-octanal concentrations on methanol dehydration reactions.

(44) The dehydration reactions were carried out using the General Reaction Method and Apparatus II described above using the zeolite ZSM-22 as catalyst except the gaseous feed comprising 10 mol % methanol and inert gas initially introduced into the reactors was supplied for a period of 170 hours, instead of 100 hours, and wherein at 170 hours, n-octanal was added to the feed to achieve a gaseous feed comprising 10 mol % methanol and 0.5 mol % n-octanal relative to methanol. This feed was supplied to the reactors for a period of 169 hours whereupon the addition of n-octanal was ceased and a gaseous feed comprising 10 mol % methanol continued to be introduced into the reactors for a period of 43 hours. At 382 hours on stream n-octanal was added to the gaseous feed such that the feed comprised 10 mol % methanol and an n-octanal concentration of 2 mol % relative to methanol. This gaseous feed was supplied to the reactors for a period of 47 hours whereupon the addition of n-octanal was ceased and the reactions were allowed to continue for a further period of 61 hours with a gaseous feed comprising 10 mol % methanol and inert gas. The results of this Example are shown in FIG. 1. As is illustrated in FIG. 1, during the periods in which the aldehyde promoter was a component of the feed, the space time yields (STY) to dimethyl ether was observed to increase. In the periods where the aldehyde was not employed in the feed, the STY to dimethyl ether was seen to decrease. It was also observed that the STY's to dimethyl ether achieved in the periods which followed the addition of aldehyde compound (i.e. 339 to 382 hours on stream and 439 to 500 hours on stream), were higher than the dimethyl ether STY seen in initial methanol only period (0 to 179 hours on stream).

Example 6

(45) In this Example, the effect of the straight chain n-butanal and the branched chain iso-butanal was investigated in methanol dehydration reactions employing the zeolite ferrierite.

(46) The methanol dehydration reactions were carried out using the General Reaction Method and Apparatus I described above and employing the aldehyde promoters at a concentration of 2 mol % relative to methanol.

(47) The results of this Example are shown in FIG. 2. In FIG. 2, the circles represent periods in which methanol was used as the feed to the process i.e. no aldehyde addition; the black squares represent periods in which 2 mol % of n-butanal (relative to methanol) was present in the methanol feed and the white squares represent periods in which 2 mol % of iso-butanal (relative to methanol) was present in the methanol feed. As is illustrated in FIG. 2, during the periods in which an aldehyde promoter 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 aldehyde promoter. It was also observed that the use of the branched chain aldehyde, iso-butanal, resulted in little or no catalyst deactivation.