Patent ID: 11857916
Assignee: EVONIK OPERATIONS GMBH
Field: Chemical engineering (Chemistry)
Classification: CPC B  C | IPC B

Claim 0:
1. A device for separating methane from a gas mixture containing methane, carbon dioxide and hydrogen sulfide, comprising:
a) a gas compressor;
b) a feed line for feeding said gas mixture to said gas compressor;
c) a first membrane separation stage downstream from said gas compressor, comprising a gas separation membrane having higher permeability for carbon dioxide than for methane, providing a first retentate and a first permeate;
d) a second membrane separation stage, connected to said first membrane separation stage to receive the first retentate as feed, said second membrane separation stage comprising a gas separation membrane having higher permeability for carbon dioxide than for methane, providing a second retentate as a product gas enriched in methane and a second permeate;
e) optionally a third membrane separation stage, connected to said first membrane separation stage to receive the first permeate as feed, said third membrane separation stage comprising a gas separation membrane having higher permeability for carbon dioxide than for methane, providing a third retentate and a third permeate;
f) a recycle conduit connected to a recycle feed point on said feed line upstream from said gas compressor, wherein:
i) said recycle conduit is connected to said second membrane separation stage to receive said second permeate; or,
ii) if the optional third membrane separation stage is present, either:
said recycle conduit is connected to said third membrane separation stage to receive said third retentate; or alternatively,
said recycle conduit is connected to both said second membrane separation stage and said third membrane separation stage to receive said second permeate and said third retentate; and

g) at least one hydrogen sulfide adsorber comprising a bed of activated carbon having catalytic activity for oxidizing hydrogen sulfide with oxygen, said hydrogen sulfide adsorber being arranged between said recycle feed point and said first membrane separation stage.