Solvent resistant asymmetric integrally skinned membranes

Abstract

There is provided an asymmetric integrally skinned membrane comprising a polyimide and another polymer selected from the group consisting of polyvinylpyrrolidone, sulfonated polyetheretherketones and mixtures thereof. The membrane which is substantially insoluble in an organic solvent and substantially defect-free can be useful as a separation membrane. Methods for preparing asymmetric integrally skinned polyimide membranes are also disclosed

Description

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] The present application is a continuation-in-part of International Patent Application No. PCT / CA2004 / 001047 filed on Jul. 16, 2004, which claims priority on Canadian Patent Application No. 2,435,538 filed on Jul. 18, 2003. The above-mentioned applications are incorporated herein by reference in their entirety.TECHNICAL FIELD [0002] The present invention relates to improvements in the field of separation membranes. In particular, this invention relates to solvent resistant asymmetric integrally skinned membranes. BACKGROUND OF THE INVENTION [0003] The preparation of asymmetric integrally skinned membranes having a defect-free skin is a complicated and tedious task. The presence in the skin layer of pores or defects having a diameter of about 1.0 nm reduces drastically the membrane selectivity. Asymmetric membranes are usually prepared by a phase inversion process as described in U.S. Pat. No. 3,133,132. The permeance or capacity of integ...

AI Technical Summary

Benefits of technology

The resulting membranes exhibit excellent separation selectivities, mechanical stability, and thermal resistance, enabling their use in industrial applications without the need for solvent exchange processes, thus overcoming the limitations of existing methods.

Problems solved by technology

The preparation of asymmetric integrally skinned membranes having a defect-free skin is a complicated and tedious task.

The presence in the skin layer of pores or defects having a diameter of about 1.0 nm reduces drastically the membrane selectivity.

However, if the skin thickness is reduced, it is more difficult to eliminate the defect pores.

This step increases the polymer concentration at the membrane surface and leads to the formation of a defect-free skin.

Another drawback of this method is that it uses volatile organic compounds which have workers health and environmental concerns.

Also, since chlorinated hydrocarbons are commonly used as the volatile solvent, water can not be used as the coagulating medium due to mutual immiscibility.

For the immiscible layers, there are limitations due to penetration of one liquid layer into the other.

For the two bath method, there are limitations due to the fact that the membrane is not coagulated prior to leaving the first bath.

It is also difficult to transport the membrane to the second bath without damaging it.

This method is also limited in view of the insufficient residence time for the dense skin region to form for continuous casting.

However, it is known that such a method is very sensitive to the coagulation rate as indicated in U.S. Pat. No. 4,460,526.

Another drawback inherent to this method is that it requires a solvent exchange drying method to prevent collapse of the transition layer below the skin layer.

The latter steps increase the costs and complexity of membrane preparation.

However, the H2 permeance is low, which indicates that a relatively thick skin is obtained by using such a method.

Such a drawback considerably limits the usefulness of these membranes.

Continuous preparation of large membrane quantities using this method is limited by the costs and complexity of regeneration of the non-solvent reaction bath and the usual problems associated with the delayed demixing method.

However, the membranes described in this document are not solvent resistant.

However, these membranes provided a low selectivity for acetic acid / water.

Moreover, the mechanical properties of these membranes were not adequate since the membranes were too brittle and fragile for practical use.

Unfortunately, such a coating layer increases the cost and renders the production of these membranes more tedious.

Also, operational failure may occur due to delamination of the coating layer from the asymmetric support membrane for various reasons such as differences in absorption properties and thermal expansion of the two layers.

In many cases, the coating layer limits the range of the operating conditions of the membrane.

However, the latter patent does not teach or suggest how to prepare asymmetric integrally skinned membranes.

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