Blend polymer membranes comprising thermally rearranged polymers derived from aromatic polyimides containing ortho-positioned functional groups

Abstract

The present invention discloses blend polymer membranes comprising thermally rearranged polymers derived from aromatic polyimides containing ortho-positioned functional groups and methods for making and using these blend polymer membranes. The blend polymer membranes described in the current invention are prepared by heat treatment of blend polymer membranes comprising aromatic polyimides containing ortho-positioned functional groups such as —OH or —SH groups. In some instances, an additional crosslinking step is performed to improve the selectivity of the membrane. These blend polymer membranes have improved flexibility, reduced cost, improved processability, and enhanced selectivity and / or permeability compared to the comparable polymer membranes that comprise a single polymer.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application is a Division of copending application Ser. No. 12 / 412,639 filed Mar. 27, 2009, the contents of which are hereby incorporated by reference in its entirety.BACKGROUND OF THE INVENTION[0002]This invention pertains to a new type of blend polymer membranes comprising thermally rearranged polymers derived from aromatic polyimides containing ortho-positioned functional groups and methods for making and using these blend polymer membranes. In some embodiments of the invention, the blend polymer membranes may be subjected to an additional crosslinking step to increase the selectivity of the membrane.[0003]Membrane-based technologies have advantages of both low capital cost and high-energy efficiency compared to the much older and established techniques such as cryogenic distillation, absorption, and adsorption. Membranes, alone and in combinations with other methods, provide a comprehensive approach for solving energy, environment...

AI Technical Summary

Benefits of technology

[0013]In another embodiment of the invention, this invention pertains to blend polymer membranes that have undergone an additional crosslinking step, by chemical or UV crosslinking or other crosslinking process as known to one skilled in the art. The resulting cross-linked blend polymer membranes can be prepared by UV cross-linking of at least one polymer in a blend polymer membrane comprising at least one thermally rearranged polymer such as aromatic polybenzoxazole (PBO) or polybenzothiazole (PBT) polymer derived from an aromatic polyimide containing ortho-positioned functional groups. At least one polymer in this thermally rearranged polymer-comprising blend polymer membrane has UV cross-linkable functional groups such as benzophenone groups. The UV cross-linkable functional groups can be either in the thermally rearranged polymer such as aromatic PBO or PBT polymer or in the other different type of polymer in the thermally rearranged polymer-comprising blend polymer membrane. After UV cross-linking, the cross-linked blend polymer membrane comprises polymer chain segments where at least part of these polymer chain segments are cross-linked to each other through possible direct covalent bonds by exposure to UV radiation. The cross-linking of the blend polymer membranes comprising at least one thermally rearranged polymer such as aromatic PBO or PBT provides the membranes with superior selectivity and improved chemical and thermal stabilities compared to corresponding uncross-linked blend polymer membranes comprising at least one thermally rearranged polymer such as aromatic PBO or PBT.

[0014]The novel blend polymer membranes comprising thermally rearranged polymers derived from aromatic polyimides containing ortho-positioned functional groups have improved flexibility, reduced cost, improved processability, and enhanced selectivity and / or permeability compared to the pure thermally rearranged polymer membranes derived from aromatic polyimides containing ortho-positioned functional groups.

Problems solved by technology

However, polymers which are more permeable are generally less selective than less permeable polymers.

Various polymers and techniques have been used, but without much success.

In addition, traditional polymer membranes also have limitations in terms of thermal stability and contaminant resistance.

Although CA membranes have many advantages, they are limited in a number of properties including selectivity, permeability, and in chemical, thermal, and mechanical stability.

For example, UOP's early field practice found that polymer membrane performance can deteriorate quickly.

The primary cause of loss of membrane performance is liquid condensation on the membrane surface.

Although these pretreatment systems can effectively remove heavy hydrocarbons from natural gas streams to lower their dew point, the cost is quite significant.

For offshore projects, the footprint is a big constraint.

However, current polymeric membrane materials have reached a limit in their productivity-selectivity trade-off relationship.

In addition, gas separation processes based on the use of glassy solution-diffusion membranes frequently suffer from plasticization of the stiff polymer matrix by the sorbed penetrant molecules such as CO2 or C3H6.

These PBO, PBT, and PBI polymers with high thermal and chemical stability, however, have poor solubility in common organic solvents, preventing them from being used as common polymer materials for making polymer membranes by the most practical solvent casting method.

Images