Carbonylation catalyst and process

Abstract

Carbonylation process for producing methyl acetate, by contacting dimethyl ether and carbon monoxide under carbonylation conditions in the presence of a catalyst having a zeolite of micropore volume of 0.01 ml/g. The zeolite is an as-synthesized organic structure directing agent-containing zeolite and contains at least one channel which is defined by an 8-member ring.

Claims

1. A carbonylation process for producing methyl acetate comprising contacting dimethyl ether and carbon monoxide under carbonylation conditions in the presence of a catalyst which catalyst comprises a zeolite of micropore volume of 0.01 ml/g and which zeolite is an as-synthesised organic structure directing agent-containing zeolite and contains at least one channel which is defined by an 8-member ring.

2. A process according to claim 1 wherein the carbonylation process is conducted in the presence of hydrogen.

3. A process according to claim 2 wherein the carbon monoxide to hydrogen molar ratio is in the range 1:3 to 15:1.

4. A process according to claim 2 wherein the source of carbon monoxide is a synthesis gas.

5. A process according to claim 1 wherein water is present at a concentration of less than 1 mol %, based on the total gaseous feed to the carbonylation process.

6. A process according to claim 1 which process is carried out at a temperature of from 240 C. to 320 C. and at a total pressure of from 20 to 80 barg.

7. A process according to claim 1 wherein the process is conducted as a vapour phase process.

8. A process according to claim 1 wherein methyl acetate is recovered from the carbonylation process and at least some of the recovered methyl acetate is converted to acetic acid.

Description

EXAMPLE 1

(1) Catalyst Preparation

(2) Catalyst A (not in Accordance with the Invention)

(3) GaAl H-mordenite was prepared in a 4 liter stainless steel autoclave under hydrothermal conditions from a synthesis mixture comprising sodium hydroxide, silica, sodium aluminate, gallium nitrate and tetraethyl ammonium bromide structure directing agent.

(4) 133.6 g SiO.sub.2 (fumed silica) was added to 40.5 g NaOH dissolved in 1080 g of water and stirred for 1 hour. An aqueous solution of tetraethyl ammonium bromide (56.8 g dissolved in 180 g water) was added to the stirred SiO.sub.2/NaOH/water mixture and stirred for 1 hour. An aqueous Ga(NO.sub.3).sub.3 solution (36.12 g of Ga(NO.sub.3).sub.3 hydrate, ex Aldrich dissolved in 210 g water) was added to the SiO.sub.2/NaOH/water/tetraethylammonium bromide mixture and stirred for 30 minutes. An aqueous sodium aluminate solution (3 g of NaAlO.sub.2 dissolved in 210 g water) was added to the SiO.sub.2/NaOH/water/tetraethylammonium bromide/Ga(NO.sub.3).sub.3 mixture and stirred for an hour. The resulting mixture was then transferred to a 4 liter stainless steel autoclave and hydrothermally treated for 14 days by maintaining it at a temperature of 150 C. under stirring at a speed of 200 rpm. The resulting precipitate was filtered, washed with deionised water and dried at 110 C. in an air oven. Elemental analysis of the dried zeolite showed it to contain about 5 weight % carbon. The dried zeolite was calcined at 550 C. for 12 hours under an atmosphere of static air to remove the organic structure directing agent. The calcined zeolite was converted to the ammonium form by three successive ion-exchanges in 1M NH.sub.4NO.sub.3 (aqueous) at 80 C. for 1 hour. The ammonium-exchanged zeolite was washed and filtered using deionised water, dried in an oven at 110 C. and then calcined in static air at 500 C. for 3 hours to obtain GaAl H-mordenite.

(5) The zeolite was compacted at 12 tonnes in a 32 mm die set using a pneumatic press, and crushed and sieved to a particle size fraction of 100 to 160 microns.

(6) Elemental analysis of Catalyst A showed it to contain less than 0.1 weight % carbon.

(7) Catalyst B

(8) Catalyst B was prepared by repeating the preparation of Catalyst A up to calcining of the zeolite at 550 C. This calcining step was omitted in the preparation of Catalyst B so as to retain the organic structure directing agent within the zeolite pores. The preparation was continued as follows. 4 g of dried as-synthesised zeolite was converted to the ammonium form by three successive ion-exchanges in 1M NH.sub.4NO.sub.3 (aqueous) at 80 C. for 1 hour. The ammonium-exchanged zeolite was washed and filtered using deionised water and then dried in an oven at 110 C. to obtain GaAl NH.sub.4-mordenite. This zeolite was compacted at 12 tonnes in a 32 min die set using a pneumatic press, and crushed and sieved to a particle size fraction of 100 to 160 microns.

(9) Elemental analysis of Catalyst B showed it to contain 4.9 weight % carbon indicating that >99% of the organic structure directing agent was present within its structure.

(10) Catalyst Characterisation

(11) The physiochemical properties of Catalysts A and B were determined using N.sub.2 adsorption carried out at 77K in a Micromeritics Tristar 3000 apparatus equipped with Tristar 3000 v6.01 software for data analysis. Prior to analysis, samples of the Catalysts were degassed under vacuum at 60 C. for 30 minutes and then at 120 C. for 16 hours.

(12) BET surface area (S.sub.BET) was derived from data points in the relative pressure range of p/p.sub.0=0.01-0.05 based on a published model [S. Brunauer, P. H. Emmett, E. Teller, J. Am. Chem. Soc. 60 (1938) 309].

(13) The t-plot method was used to determine the micropore volume (V.sub.microp) and external surface area (S.sub.Ext) using a fitted thickness range of 0.35-0.5 nm [B. C. Lippens, J. H. de Boer, J. Catal. 4 (1965) 319-323].

(14) The mesopore volume (V.sub.mesop) was calculated by subtracting the micropore volume from the total pore volume (determined using the single point adsorption total pore volume; p/p.sub.0>0.98).

(15) Elemental analysis for carbon content of a zeolite as-synthesised was conducted by combustion using an Exeter Analytical CE440 CHN elemental analyser.

(16) The physiochemical properties of Catalysts A and B are given in Table 1 below.

(17) TABLE-US-00001 TABLE 1 S.sub.BET S.sub.Ext V.sub.microp V.sub.mesop Carbon (m.sup.2/g) (m.sup.2/g) (ml/g) (ml/g) (% wt) Catalyst A 420 39 0.14 0.06 <0.1 Catalyst B 29 20 0.00 0.07 4.9
Carbonylation Reaction

(18) Each of Catalysts A and B were used to catalyse the carbonylation of dimethyl ether with carbon monoxide as follows. The carbonylation reactions were carried out in a pressure flow reactor unit consisting of 16 identical parallel isothermal co-current tubular reactors of the type described in, for example WO2006107187. 100 micro liters (0.07 g) of the catalyst was loaded onto a metal sinter (20 micrometers pore size) within the reactor. 100 micro liters of gamma alumina was placed on top of the catalyst and the remainder of the reactor was filled with carborundum. The catalyst was activated by heating it at atmospheric pressure to a temperature of 300 C. under a gaseous feed of carbon monoxide, hydrogen and helium in a molar ratio of 1:2:0.1 at a gas flow rate of 6.1 ml/min. The reactor was then pressurised to 60 barg and left to equilibrate for two hours at which point catalyst activation was considered complete and the gaseous feed was replaced by a carbonylation gas feed comprising 29 mol % carbon monoxide, 58.2 mol % hydrogen, 2.8 mol % He, 5 mol % CO.sub.2 and 5 mol % dimethyl ether at a gas flow rate of 6.7 ml/min. The carbonylation reaction was allowed to continue under these conditions for 188 hours.

(19) The exit stream from the reactor was passed at periodic intervals to an Interscience Trace gas chromatograph equipped with one flame ionisation detector (FID) having a Rtx-1,1u (20 m*0.32 mm) column and a Rtx-wax, 0.25u (2 m*0.32 mm) column and two thermal conductivity detectors (TCD); a first TCD equipped with a Carboxen 1010 (2 m*0.32 mm) column and a Carboxen 1010 (28 m*0.32 mm) column and a second TCD equipped with a Poraplot U (2 m*0.32 mm) column and a Poraplot Q (12 m*0.32 mm) column.

(20) Table 2 below shows the impact of using a zeolite in accordance with the present invention on the space time yields (STY) to methyl acetate (MeOAc), acetic acid (AcOH) and C.sub.1-C.sub.3 hydrocarbons and selectivity to acetyls products.

(21) TABLE-US-00002 TABLE 2 Reaction STY STY STY C.sub.1-C.sub.3 time/ MeOAc AcOH hydrocarbons Selectivity Catalyst hours g kg.sup.1 h.sup.1 g kg.sup.1 h.sup.1 g kg.sup.1 h.sup.1 % A 2.6 6 239 85 32.3 B 3.0 496 23 2 96.4 A 9.3 264 277 34 67.3 B 9.8 922 72 6 94.2 A 175.6 783 47 5 95.4 B 176.1 797 41 3 96.8

(22) Catalyst B becomes highly selective for making acetyls products early in the reaction and the product is predominantly methyl acetate. In contrast, at a similar point in time, Catalyst A produces considerable amounts of hydrocarbon by-products and the product is predominantly acetic acid.

EXAMPLE 2

(23) Preparation of Catalyst C

(24) 133.35 g SiO.sub.2 (Cab-osil M5, fumed silica) was dispersed in 900 g water. An aqueous solution of tetraethyl ammonium bromide (56.82 g dissolved in 180 g water) was added to the silica dispersion and thoroughly mixed for 1 hour. After 1 hour an aqueous NaOH solution (40.71 g dissolved in 180 g water) was added to the mixture and thoroughly stirred for 90 minutes. After 90 minutes an aqueous NaAlO.sub.2 solution (17.51 g of NaAlO.sub.2 (Fischer Scientific GP grade) dissolved in 210 g H.sub.2O) was added to the stirred mixture which was then stirred for a further 1 hour before being transferred to a 4 liter stainless steel autoclave where it was hydrothermally treated for a period of 3.5 days under conditions of 170 C. and a stirring speed of 550 rpm. After 3.5 days zeolite crystals had formed which were separated from the mother liquor by filtration and then washed with deionised water and dried at 90 C. in an air oven. 10 g of the dried zeolite was subjected to an ammonium exchange procedure by treating it with an aqueous solution of NH.sub.4NO.sub.3 (100 mL, 1 M), warmed to 80 C. and the mixture stirred at this temperature for 1 hour. The resultant suspension was filtered and the solid was washed with NH.sub.4NO.sub.3. This ammonium exchange procedure was repeated twice more. In the final filtration step the solid was washed with deionised water instead of NH.sub.4NO.sub.3 before the washed solid was dried in an oven at 90 C. for 24 hours. The dried solid was ammonium form mordenite.

(25) Elemental analysis of Catalyst C showed it to contain 4.7 weight % carbon indicating that >99% of the organic structure directing agent was present in its structure. The micropore volume (V.sub.mesopore) of Catalyst C was determined to be 0.01 ml/g.

(26) Carbonylation Reaction

(27) Catalyst C was used to catalyse the carbonylation of dimethyl ether with carbon monoxide as follows. The carbonylation reactions were carried out in a pressure flow reactor unit consisting of 64 identical parallel isothermal co-current tubular reactors of the type described in, for example WO2006107187. The reactors were arranged in 4 blocks of 16 reactors, each block having an independent temperature control. 100 micro liters of Catalyst C (pressed and sieved to 100-160 m fraction) was loaded onto a metal sinter having a pore size of 20 micrometers within each reactor to provide a GHSV of 4000 h.sup.1. The catalyst was activated by heating it at atmospheric pressure to a temperature of 100 C. under an inert gas stream at a flow rate of 6.7 mL/min. per reactor and held at this temperature for 1 hour. The reactors were then pressurised to 70 barg and allowed to equilibrate for one hour at which point catalyst activation was considered complete. The reactors were heated to a temperature of 260 C. and the inert gas stream was replaced by a carbonylation reaction gas feed comprising 43.5 mol % carbon monoxide, 43.5 mol % hydrogen, 6 mol % dimethyl ether, 5 mol % N.sub.2 and 2 mol % He for a period of 2 hours. After 2 hours the composition of the gas feed was changed to 43.5 mol % carbon monoxide, 43.5 mol % hydrogen, 10 mol % dimethyl ether, 1 mol % N.sub.2 and 2 mol % He for a period of 22 hours. After 22 hours, the composition of the gas feed was changed to 29 mol % carbon monoxide, 58 mol % hydrogen, 10 mol % dimethyl ether, 1 mol % N.sub.2 and 2 mol % He for a period of 24 hours after which time the temperature was increased from 260 C. to 280 C. The carbonylation reaction was allowed to continue under these conditions for about 10 days.

(28) The exit stream from a reactor was analysed by passing it to two Interscience Trace gas chromatographs. One gas chromatograph was equipped with one thermal conductivity detector (TCD) having a Molsieve 5A (25 m*0.32 mm) column and one flame ionisation detector (FID) having a DB 624 (28*0.25 mm) column. The second gas chromatograph was equipped with one TCD detector having a Carboxen 1010 (28 m*0.32 mm) column and two FID detectors; a first FID was equipped with a Wax FFAP (18 m*0.25 mm) column and a second FID was equipped with a Gaspro (20 m*25 mm) column.

(29) At 280 C., the average space time yields were: methyl acetate 465 g/l/h; acetic acid 9.9 g/l/h; C.sub.1-C.sub.3 hydrocarbons 1.15 g/l/h and the average selectivity to methyl acetate was 96.9%.