Patent ID: 8231785
Filing Date: 2012-07-31
Classification: B01D,Y02C

Abstract:
1. A process for separating a mixture of gases or liquids comprising sending said mixture of gases or liquids to a pre-membrane to separate them into a first permeate stream which passes through the pre-membrane and a first retentate stream that does not pass through the pre-membrane; sending said first retentate stream to a primary membrane to separate said first retentate stream into a second permeate stream and a second retentate stream; and then sending said second permeate stream to a secondary membrane to separate it into a third permeate stream and a third retentate stream and wherein said pre-membrane comprises a UV cross-linked polybenzoxazole membrane prepared from a polyimide represented by formula (I): where X1 of formula (I) is or mixtures thereof, X2 of formula (I) is either the same as X1or is selected from or mixtures thereof, —Y— of formula (I) is or mixtures thereof, —R— is or mixtures thereof, and wherein said primary membrane comprises a membrane selected from the group consisting of cellulose acetate membrane, polyimide membrane, UV cross-linkable polybenzoxazole membrane, UV cross-linked polybenzoxazole membrane, and mixtures thereof and said secondary membrane comprises a UV cross-linkable polybenzoxazole membrane or a UV cross-linked polybenzoxazole membrane.