Process for the co-production of acetic acid and dimethyl ether

1. A process for the co-production of acetic acid and dimethyl ether by dehydration-hydrolysis of a feed mixture of methanol and methyl acetate in the presence of at least one catalyst, which catalyst is a solid acid catalyst, to generate a crude reaction product comprising acetic acid and dimethyl ether , said process comprising feeding to said co-production process a feed comprising methanol, methyl acetate and dimethyl ether, wherein the dimethyl ether is present in the feed in a total amount of 25 mol % or less based on the total feed.

2. A process according to claim 1 wherein the feed to the co-production process comprises methyl acetate in an amount of from 10 to 95 mol %, dimethyl ether in an amount of from 0.1 to 25 mol %, methanol in an amount of 5 to 20 mol % and contaminants in a total amount of 0 to less than 1 mol %.

3. A process according to claim 2 wherein the contaminants are selected from one or more of acetaldehyde, acetone and methyl formate.

4. A process according to claim 2 wherein the feed comprises dimethyl ether in an amount of 0.1 to 5 mol %.

5. A process according to claim 2 wherein the feed further comprises water.

6. A process according to claim 1 wherein the methyl acetate feed comprises dimethyl ether and is derived from a crude methyl acetate stream produced in processes for carbonylation of dimethyl ether with carbon monoxide in the presence of a carbonylation catalyst to produce a crude methyl acetate stream comprising dimethyl ether which crude methyl acetate stream is treated to reduce its dimethyl ether content to provide a methyl acetate feed to the co-production process which comprises dimethyl ether in an amount of >0 to 25 mol %.

7. A process according to claim 6 wherein the treated crude methyl acetate comprises dimethyl ether in an amount of >0 to 5 mol %.

8. A process according to claim 6 wherein the crude methyl acetate comprises dimethyl ether in an amount of 5 to 50 mol %.

9. A process according to claim 8 wherein the crude methyl acetate further comprises contaminants in a total amount of up to 1 mol %.

10. A process according to claim 6 wherein the crude methyl acetate is treated to reduce its dimethyl ether content by distillation.

11. A process according to claim 10 wherein the distillation is carried out at a pressure of from 10 to 30 barg (1000 to 3000 kPa) and a heads temperature of 40 to 90 ° C.

12. A process according to claim 1 wherein the solid acid catalyst is a zeolite catalyst.

13. A process according to claim 1 wherein the co-production process is carried out at a temperature in the range 100 to 350 ° C. and at a pressure selected from atmospheric and pressures greater than atmospheric.

14. A process according to claim 1 which further comprises recovering dimethyl ether from the crude reaction product comprising acetic acid and dimethyl ether.

15. A process according to claim 14 wherein recovered dimethyl ether, or a part thereof, is utilised as a feed to a carbonylation process in which dimethyl ether is carbonylated with carbon monoxide in the presence of a carbonylation catalyst to produce a crude methyl acetate.

16. A process according to claim 1 wherein acetic acid is recovered from the crude reaction product comprising acetic acid and dimethyl ether.

17. A process according to claim 1 wherein the co-production process forms part of an integrated process which integrated process comprises carbonylating dimethyl ether with a carbon monoxide-containing gas in the presence of a zeolite carbonylation catalyst wherein conversion of dimethyl ether is 5 to 90 mol % per pass based on total feed to carbonylation to produce a crude carbonylation product comprising methyl acetate and dimethyl ether, recovering from the crude carbonylation product a crude methyl acetate stream comprising methyl acetate and dimethyl ether, treating the crude methyl acetate stream, or part thereof, to recover a stream comprising mainly dimethyl ether and a stream comprising methyl acetate and a reduced amount of dimethyl ether and wherein the stream, or a part thereof, comprising methyl acetate and a reduced amount of dimethyl ether which is an amount of >0 to 25 mol % based on total feed to the process, is utilised as a feed to the co-production process.

18. A process according to claim 1 wherein the co-production process is operated as a continuous process.