Process for recovering methane from a gas stream comprising methane and ethylene

1. A process for recovering methane from a gas stream comprising methane and ethylene, comprising:

a sorption step which comprises contacting the gas stream comprising methane and ethylene with a sorption agent which has a lower affinity for methane than for ethylene, wherein the gas stream comprising methane and ethylene also comprises a compound for which the sorption agent has a lower affinity than for methane and ethylene, resulting in sorption of ethylene and methane by the sorption agent and in a gas stream comprising the compound for which the sorption agent has a lower affinity than for methane and ethylene;

a first desorption step which comprises desorbing part of the sorbed methane resulting in a gas stream comprising methane in an amount of 1 to 99.9% based on the amount of methane in the gas stream that is subjected to the sorption step;

a second desorption step which comprises desorbing sorbed compounds resulting in a gas stream comprising the desorbed compounds; and

a rinse step between the first desorption step and the second desorption step, which rinse step comprises contacting a gas stream, comprising a compound for which the sorption agent has a higher affinity than for methane, with the sorption agent containing sorbed ethylene and methane, resulting in sorption of the compound for which the sorption agent has a higher affinity than for methane by the sorption agent, in desorption of methane from the sorption agent and in a gas stream comprising methane.

2. The process according to claim 1 , wherein the compound for which the sorption agent has a lower affinity than for methane and ethylene is nitrogen, carbon monoxide, hydrogen or a mixture of two or more of these.

3. The process according to claim 1 , wherein the gas stream that is subjected to the sorption step comprises 50 to 99 mol % of methane, 1 to 50 mol % of ethylene and 0.1 to 90 mol % of the compound for which the sorption agent has a lower affinity than for methane and ethylene.

4. The process according to claim 1 , wherein desorption in the first desorption step and the second desorption step is effected by reducing the pressure.

5. The process according to claim 4 , wherein the pressure in the sorption step is in the range of from 10 to 20 bar, the pressure in the first desorption step is in the range of from 5 to 15 bar, and the pressure in the second desorption step is in the range of from 0.1 to 3 bar.

6. The process according to claim 1 , wherein the second desorption step results in a gas stream comprising ethylene and methane, which process additionally comprises a distillation step which comprises distilling the gas stream comprising ethylene and methane resulting from the second desorption step, said distillation step resulting in a top stream comprising methane and a bottom stream comprising ethylene.

7. The process according to claim 1 , wherein the compound for which the sorption agent has a higher affinity than for methane comprises one or more compounds selected from the group consisting of ethylene, ethane and hydrocarbons having 3 or more carbon atoms.

8. The process according to claim 7 , wherein the gas stream comprising a compound for which the sorption agent has a higher affinity than for methane comprises ethylene, ethane or a mixture of ethylene and ethane.

9. The process according to claim 1 , wherein desorption in the first desorption step and the second desorption step is effected by reducing the pressure, and the pressure in the rinse step is in the range of from 5 to 15 bar.

10. The process according to claim 1 , wherein the gas stream that is subjected to the sorption step further comprises hydrogen, optionally nitrogen, carbon monoxide, carbon dioxide, ethane and hydrocarbons having 3 or more carbon atoms,

wherein the sorption step comprises contacting said gas stream with a sorption agent which has a lower affinity for hydrogen, nitrogen and carbon monoxide than for methane, ethylene, carbon dioxide, ethane and hydrocarbons having 3 or more carbon atoms, resulting in sorption of hydrocarbons having 3 or more carbon atoms, ethane, ethylene, carbon dioxide and methane by the sorption agent and in a gas stream comprising hydrogen, optionally nitrogen and carbon monoxide.

11. The process according to claim 10 , wherein the gas stream that is subjected to the sorption step comprises 40 to 90 mol % of methane, 0.5 to 45 mol % of ethylene, 0.01 to 3 mol % of hydrogen, 0 to 80 mol % of nitrogen, 0.1 to 5 mol % of carbon monoxide, 5 to 25 mol % of carbon dioxide, 0.1 to 25 mol % of ethane and 0.5 to 20 mol % of hydrocarbons having 3 or more carbon atoms.

12. The process according to claim 10 , additionally comprising a carbon dioxide removal step which comprises removing carbon dioxide from the gas stream resulting from the second desorption step, resulting in a gas stream comprising ethylene, ethane and hydrocarbons having 3 or more carbon atoms and optionally methane.

13. The process according to claim 12 , wherein the gas stream resulting from the carbon dioxide removal step comprises ethylene, ethane, hydrocarbons having 3 or more carbon atoms and methane, additionally comprising a distillation step which comprises distilling said gas stream, said distillation step resulting in a top stream comprising methane and a bottom stream comprising ethylene, ethane and hydrocarbons having 3 or more carbon atoms.

14. The process according to claim 12 , additionally comprising a distillation step which comprises distilling a gas stream comprising ethylene, ethane and hydrocarbons having 3 or more carbon atoms, which gas stream is a gas stream resulting from the carbon dioxide removal step of claim 12 or the bottom stream resulting from the distillation step of claim 13 , said distillation step resulting in a top stream comprising ethylene and a bottom stream comprising ethane and hydrocarbons having 3 or more carbon atoms.