Process of separating gases using polyimide membranes
The present invention discloses a new type of polyimide membrane with high permeances and high selectivities for gas separations and particularly for CO 2 /CH 4 and H 2 /CH 4 separations. The polyimide membranes have CO 2 permeability of 50 Barrers or higher and single-gas selectivity for CO 2 /CH 4 of 15 or higher at 50° C. under 791 kPa for CO 2 /CH 4 separation. The polyimide membranes have UV cross-linkable functional groups and can be used for the preparation of UV cross-linked polyimide membranes having CO 2 permeability of 20 Barrers or higher and single-gas selectivity for CO 2 /CH 4 of 35 or higher at 50° C. under 791 kPa for CO 2 /CH 4 separation.
1. A process for separating at least one gas from a mixture of gases, the process comprising:
a) providing a polyimide gas separation membrane comprising an aromatic polyimide polymer that comprises a plurality of first repeating units of formula (I)
wherein X1 is
X2 is selected from the group consisting of
and mixtures thereof, wherein Y is selected from the group consisting of
and mixtures thereof and wherein n and m are independent integers from 2 to 500;
b) contacting the mixture to one side of said polyimide gas separation membrane to cause said at least one gas to permeate the said polyimide gas separation membrane; and
c) removing from an opposite side of the said polyimide gas separation membrane a permeate gas composition comprising a portion of said at least one gas which permeated said membrane.
2. The process of claim 1 wherein X2 is
wherein Y is
and wherein n and m are independent integers from 2 to 500.
3. The process of claim 1 wherein X2 is
wherein Y is
and wherein n and m are independent integers from 2 to 500.
4. The process of claim 1 wherein X2 is a mixture of
wherein Y is
and wherein n and m are independent integers from 2 to 500.
5. The process of claim 1 wherein X2 is a mixture of
wherein Y is
and wherein n and m are independent integers from 2 to 500.
6. The process of claim 1 wherein said mixture of gases comprises a mixture of at least one gas selected from carbon dioxide and hydrogen sulfide that is mixed with methane.