Patent ID: 8318013

Claim:
A system for separation of mixtures of gases or liquids comprising a pre-membrane unit, a primary membrane unit and a secondary membrane unit wherein said pre-membrane comprises a UV cross-linked polybenzoxazole membrane prepared from a polyimide represented by formula (II) where X3 of formula (II) is selected from X4 of formula (II) is either the same as X3 or is selected from —Y— of formula (II) is selected from —R— is selected from and 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 and wherein a liquid or gas mixture is separated into a retentate stream and a permeate stream by each of said pre-membrane unit, said primary membrane unit and said secondary membrane unit in sequence.