Polyimide blend membranes for gas separations

A process for separating at least one gas from a mixture of gases, the process comprising

• (a) providing a polyimide blend membrane comprising a miscible blend of a first aromatic polyimide that comprises a plurality of repeating units of formula (I) and a second aromatic polyimide that comprises a plurality of repeating units of formula (II), wherein formula (I) is represented by:
• wherein n, m, o, and p are independent integers from 20 to 500;
• and wherein formula (II) is represented by:
• wherein q and r are independent integers from 20 to 500;
• and wherein the weight ratio of said first aromatic polyimide to said second aromatic polyimide is in a range from about 10:1 to 1:10 wherein said polyimide blend membrane is permeable to said at least one gas;
• (b) contacting a mixture of gases to one side of the polyimide blend membrane to cause said at least one gas to permeate the polyimide blend membrane;
• and
• (c) removing from an opposite side of the polyimide blend membrane a permeate gas composition comprising a portion of said at least one gas which permeated said membrane.