Device and method for separating a gas mixture

1. A device for separating a gas mixture into product gas and offgas by way of gas permeation, the device comprising

a first membrane unit comprising a gas inlet, a retentate outlet, and a permeate outlet,

a second membrane unit comprising a gas inlet, a retentate outlet, and a permeate outlet,

a first compressor placed upstream from the first membrane unit and comprising an intake side,

an upstream membrane unit comprising a gas inlet, a retentate outlet, and a permeate outlet, and

at least one other membrane unit comprising a gas inlet, a retentate outlet and a permeate outlet and disposed upstream from the upstream membrane unit,

a first line connecting the retentate outlet of the first membrane unit to the gas inlet of the second membrane unit,

a second line connecting the permeate outlet of the second membrane unit on the intake side with the first compressor or with a gas supply leading into the first compressor,

a third line connecting the first compressor with the gas inlet of the first membrane unit,

a fourth line connecting the permeate outlet of the upstream membrane unit with the gas supply of the first compressor, and

a fifth line connecting the retentate outlet of the at least one other membrane unit with the gas inlet of the upstream membrane unit,

wherein the product gas is obtained via the retentate outlet of the second membrane unit,

wherein the offgas is obtained via the permeate outlet of the first membrane unit,

wherein additional product gas is obtained via the retentate outlet of the upstream membrane unit, and

wherein additional offgas is obtained via the permeate outlet of the at least one other membrane unit.

2. The device according to claim 1 , further comprising a sixth line connecting the retentate outlet of the upstream membrane unit with the retentate outlet of the second membrane unit so that the product gas is jointly removed from the second membrane unit and from the upstream membrane unit.

3. The device according to claim 1 , further comprising a sixth line connecting the permeate outlet of the at least one other membrane unit with the permeate outlet of the first membrane unit so that the offgas is jointly removed from the first membrane unit and from the at least one other membrane unit.

4. The device according to claim 1 , wherein, and

wherein the device further comprises a second compressor placed upstream from the gas inlet of the at least one other membrane unit.

5. A method for separating a gas mixture into product gas and offgas by way of gas permeation, the method comprising steps of

using retentate of a first membrane unit as feed gas of a second membrane unit,

mixing permeate of the second membrane unit with pressurized feed gas of the first membrane unit,

removing retentate of the second membrane unit as the product gas,

removing permeate of the first membrane unit as the offgas,

using permeate of an upstream membrane unit as feed gas of the first membrane unit,

using retentate of an additional upstream membrane unit as feed gas of the upstream membrane unit,

obtaining retentate of the upstream membrane unit as additional product gas, and

obtaining permeate of the additional upstream membrane unit as additional offgas.

6. The method according to claim 5 , wherein the gas mixture comprises CH 4 /CO 2 ,

wherein CH 4 is the product gas, and

wherein CO 2 is the offgas.

7. The method according to claim 5 , wherein the retentate of the second membrane unit and the retentate of the upstream membrane unit are jointly removed as the product gas.

8. The method according to claim 5 , wherein the permeate of the first membrane unit and the permeate of the additional upstream membrane unit are jointly removed as the offgas.

9. The method according to claim 5 , wherein feed gas of the additional upstream membrane unit is pressurized.