Process and system for producing dimethyl ether
The invention relates to an improved process and system for the synthesis of dimethyl ether (DME) from a feedstock comprising H 2 and CO x , wherein x=1-2. The process according to the invention comprises (a) subjecting the gaseous mixture comprising synthesis gas originating from step (c) to DME synthesis by contacting it with a catalyst capable of converting synthesis gas to DME to obtain a gaseous mixture comprising DME; (b) subjecting a gaseous mixture comprising the gaseous mixture originating from step (a) to a separation-enhanced reverse water gas shift reaction; and (c) subjecting the gaseous mixture originating from step (b) to DME/synthesis gas separation to obtain DME and a gaseous mixture comprising synthesis gas, which is recycled to step (a). Herein, the feedstock is introduced in step (a) or step (b) and the molar ratio of H 2 to CO x in the gaseous mixture which is subjected to step (b) is at least (x+0.8). Also a system for performing the reaction according to the invention is disclosed.
1. A process for the synthesis of dimethyl ether (DME) from a feedstock comprising H 2 and CO x , wherein x=1 or 2, comprising sequentially:
(a) subjecting the gaseous mixture comprising synthesis gas from step (c) to DME synthesis by contacting the gaseous mixture with a catalyst capable of converting synthesis gas to DME to obtain a gaseous mixture comprising DME;
(b) subjecting a gaseous mixture comprising the gaseous mixture from step (a) to a separation-enhanced reverse water gas shift reaction; and
(c) subjecting the gaseous mixture from step (b) to DME/synthesis gas separation to obtain DME and a gaseous mixture comprising synthesis gas, which is recycled to step (a),
wherein the feedstock is introduced in step (a) or step (b) and wherein the molar ratio of H 2 to CO x in the gaseous mixture which is subjected to step (b) is at least (x+0.8).
2. The process according to claim 1 , wherein the feedstock comprises CO x , wherein x is 1.5-2 and the feedstock is introduced in step (b).
3. The process according to claim 2 , wherein the feedstock comprises CO x , wherein x is 1.9-2 and the feedstock is introduced in step (b).
4. The process according to claim 1 , wherein the feedstock comprises CO x , wherein x is 1-1.5 and the feedstock is introduced in step (a).
5. The process according to claim 4 , wherein the feedstock comprises CO x , wherein x is 1-1.2 and the feedstock is introduced in step (a).
6. The process according to claim 1 , wherein the molar ratio of H 2 to CO x in the feedstock is in the range of (x+1) to (x+10).
7. The process according to claim 1 , wherein step (a) and/or step (b) is performed in a separation-enhanced DME synthesis (SEDMES) reaction zone.
8. The process according to claim 7 , wherein the SEDMES reaction zone is sorption-enhanced and comprises a catalyst system which contains a direct DME catalyst system and a water-selective adsorbent.
9. The process according to claim 8 , wherein the water-selective adsorbent is a zeolite.
10. The process according to claim 9 , wherein the zeolite has an average pore diameter of at most 4 Å.
11. The process according to claim 8 , wherein step (a) is performed in a SEDMES reaction zone comprising a catalyst system which contains a direct DME catalyst system and a water-selective adsorbent.
12. The process according to claim 1 , wherein step (a) is performed in a direct DME synthesis reaction zone, comprising a catalyst system which contains a direct DME catalyst system and no water-selective adsorbent.
13. The process according to claim 1 , wherein the gaseous mixture originating from step (b) is separated in step (c) in DME and a gaseous mixture comprising synthesis gas and wherein the synthesis gas consists of H 2 and CO x , wherein x=1-1.4.
14. The process according to claim 13 , wherein the gaseous mixture originating from step (b) is separated in step (c) in DME and a gaseous mixture comprising synthesis gas and wherein the synthesis gas consists of H 2 and CO x , wherein x=1-1.1.
15. The process according to claim 1 , wherein the direct DME catalyst system is a bifunctional DME synthesis catalyst or a combination of a methanol synthesis catalyst and a methanol dehydration catalyst.