Methods for the separation of CO2 from a gas stream

A method for separating carbon dioxide from a feed gas stream, the method comprising:

• passing the feed gas stream comprising from 5% to 80%, by volume, carbon dioxide through a first selectively permeable membrane having a retentate side and an opposing permeate side to separate the feed gas stream into a first retentate stream and a first permeate stream;
• passing the first permeate stream through a second selectively permeable membrane having a retentate side and an opposing permeate side to separate the first permeate stream into a second retentate stream and a second permeate stream;
• passing a sweep gas comprising the first retentate stream, the second retentate stream, or a combination thereof across the permeate side of the first selectively permeable membrane;
• and
• withdrawing the second permeate stream,
• wherein the first selectively permeable membrane and the second selectively permeable membrane each comprise a gas permeable layer, and a selective polymer layer disposed on the gas permeable layer;
• wherein the first selectively permeable membrane and the second selectively permeable membrane each exhibit a carbon dioxide permeance of from 500 to 3000 GPU at 57° C. and 1 atm feed pressure and a carbon dioxide:nitrogen selectivity of from 10 to 1000 at 57° C. and 1 atm feed pressure,
• wherein the second permeate stream has a greater concentration of carbon dioxide than the feed gas stream, and
• wherein the second permeate stream comprises 90% or greater of carbon dioxide in the feed gas with a purity of 95% or greater.