Chemically and UV cross-linked high selectivity polyimide membranes for gas separations

A method of making a chemically and UV cross-linked polyimide membrane comprising:

• 1) preparing a casting solution of a polyimide polymer with a plurality of repeating units of a formula (I):
• wherein X1 is selected from the group consisting of
• and mixtures thereof, wherein X2 is selected from the group consisting of
• and mixtures thereof;
• Y1 is selected from the group consisting of
• and mixtures thereof;
• Y2 is selected from the group consisting of
• and mixtures thereof, and —R1 is selected from the group consisting of
• and mixtures thereof, and —R2 is selected from the group consisting of
• —CH3, —C2H5
• and —R3 is selected from the group consisting of
• and mixtures thereof;
• n and m are independent integers from 2 to 500;
• the molar ratio of n/m is in a range of 1:10 to 10:1 by:
• a) dissolving 3-isocyanatopropyltrialkyloxysilane and a polyimide polymer with a plurality of repeating units of formula (II)
• wherein X1 is selected from the group consisting of
• and mixtures thereof;
• wherein X2 is selected from the group consisting of
• and mixtures thereof;
• Y1 is selected from the group consisting of
• and mixtures thereof;
• Y3 is selected from the group consisting of
• and mixtures thereof, and —R4 is selected from the group consisting of —H, —COCH3, and mixtures thereof, and —R5 is selected from the group consisting of
• and mixtures thereof;
• n and m are independent integers from 2 to 500;
• the molar ratio of n/m is in a range of 1:10 to 10 in an organic solvent to form a homogeneous solution;
• b) heating said homogeneous solution for 4-8 hours at 40-70° C. to form said solution of the polyimide polymer via a reaction between 3-isocyanatopropyltrialkyloxysilane and said polyimide polymer with a plurality of repeating units of formula (II);
• 2) casting said casting solution of the polyimide polymer with a plurality of repeating units of formula (I) on a membrane substrate or on a polymeric cloth substrate or on a clean glass plate to form a thin layer of said casting solution of the polyimide polymer with a plurality of repeating units of formula (I);
• 3) removing the organic solvents from the thin layer of said casting solution of the polyimide polymer to form a flat sheet membrane;
• 4) drying the membrane to form chemically cross-linked polyimide membrane comprising the polyimide polymer with a plurality of repeating units of formula (I) wherein the trialkyloxysilane groups have reacted with each other and have formed covalent bonds among the polymer chains;
• 5) coating said dried membrane with a thin layer of high permeability material;
• and 6) UV cross-linking said coated and dried membrane via UV radiation to cross-link the membrane via covalent bonds between the UV cross-linkable sulfonyl or carbonyl group and methyl group on said new polyimide polymer chains with a plurality of repeating units of formula (I).

A process for separating at least one gas from a mixture of gases using a high selectivity, high plasticization-resistant and solvent-resistant, both chemically and UV cross-linked polyimide membrane the process comprising:

• (a) providing a both chemically and UV cross-linked polyimide membrane prepared from a polyimide polymer with a plurality of repeating units of a formula (I):
• wherein X1 is selected from the group consisting of
• and mixtures thereof;
• wherein X2 is selected from the group consisting of
• and mixtures thereof;
• Y1 is selected from the group consisting of
• and mixtures thereof;
• Y2 is selected from the group consisting of
• and mixtures thereof, and —R1 is selected from the group consisting of
• and mixtures thereof, and —R2 is selected from the group consisting of
• —CH3, —C2H5
• and —R3 is selected from the group consisting of
• and mixtures thereof;
• n and m are independent integers from 2 to 500;
• the molar ratio of n/m is in a range of 1:10 to 10:1 wherein said polyimide membrane is permeable to said at least one gas;
• (b) contacting the mixture on one side of the polyimide membrane to cause said at least one gas to permeate the membrane;
• and (c) removing from the opposite side of the membrane a permeate gas composition comprising a portion of said at least one gas which permeated said membrane.

A process for separating a liquid mixture comprising sending said liquid mixture to a high selectivity, high plasticization-resistant and solvent-resistant, both chemically and UV cross-linked polyimide membrane wherein the both chemically and UV cross-linked polyimide membrane is prepared from a polyimide polymer with a plurality of repeating units of a formula (I):

• wherein X1 is selected from the group consisting of
• and mixtures thereof;
• wherein X2 is selected from the group consisting of
• and mixtures thereof;
• Y1 is selected from the group consisting of
• and mixtures thereof;
• Y2 is selected from the group consisting of
• and mixtures thereof, and —R1 is selected from the group consisting of
• and mixtures thereof, and —R2 is selected from the group consisting of
• —CH3, —C2H5
• and —R3 is selected from the group consisting of
• and mixtures thereof;
• n and m are independent integers from 2 to 500;
• the molar ratio of n/m is in a range of 1:10 to 10:1 wherein said polyimide membrane is permeable to said at least one component of said liquid;
• (b) contacting the liquid mixture on one side of the polyimide membrane to cause said at least one liquid to permeate the membrane;
• and (c) removing from the opposite side of the membrane a permeate liquid composition comprising a portion of said at least one liquid which permeated said membrane.