Separation membrane and method of preparing and using same
First Claim
1. A process of preparing an asymmetric separation membrane suitable for use as a gas-permeation or reverse-osmosis separation membrane, which process comprises:
- (a) treating a preformed dried leached high-flux, asymmetric, polymeric membrane, having a top skin surface with large pores of about 50 angstroms or more and an underlying bulk porous layer, with a posttreatment solution which comprises a volatile nonsolvent for the polymer of the membrane in the presence of a swelling agent for the polymer or a solvent for the polymer; and
(b) drying the solution-treated, asymmetric membrane, while the membrane is under one-sided constraint, to provide for the evaoporating of the nonsolvent substantially through the top skin layer and for the differential collapsing of the pores of the top skin surface of the asymmetric membrane to a selected, smaller pore size of about 10 angstroms or less.
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Accused Products
Abstract
A differential pore-collapsed separation membrane particularly useful as a gas-separation membrane and a method of preparing such differential pore-collapsed membrane, which method comprises treating an asymmetric membrane, while under one-sided constraint, with a treating solution comprising a volatile nonsolvent and a swelling agent and/or a solvent, and drying the treated membrane, to provide for the controlled, differential pore collapse of the small pores of the top skin of the membrane to a smaller pore-size distribution in the membrane generally less than about 10 Angstroms.
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Citations
40 Claims
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1. A process of preparing an asymmetric separation membrane suitable for use as a gas-permeation or reverse-osmosis separation membrane, which process comprises:
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(a) treating a preformed dried leached high-flux, asymmetric, polymeric membrane, having a top skin surface with large pores of about 50 angstroms or more and an underlying bulk porous layer, with a posttreatment solution which comprises a volatile nonsolvent for the polymer of the membrane in the presence of a swelling agent for the polymer or a solvent for the polymer; and (b) drying the solution-treated, asymmetric membrane, while the membrane is under one-sided constraint, to provide for the evaoporating of the nonsolvent substantially through the top skin layer and for the differential collapsing of the pores of the top skin surface of the asymmetric membrane to a selected, smaller pore size of about 10 angstroms or less. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. In a process for preparing a cellulose-ester separation membrane, which process comprises:
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(a) preparing a casting solution which comprises a solvent and a cellulose-ester polymer; (b) coating the casting solution to form a wet film of the casting solution; (c) removing at least part of the solvent of the casting solution, to form a gelled membrane film; (d) washing the gelled membrane film with water; (e) removing the water by solvent exchange; and (f) recovering a dry, high-flux, asymmetric, cellulose-ester, separation membrane having a top-skin surface membrane layer, having pores therein of about 50 Angstroms or more, and an integral, underlying, porous bulk layer, the improvement which comprises (i) immersing the dry-film, washed high-flux, asymmetric membrane in a treating solution comprising a volatile hydrocarbon nonsolvent for the cellulose ester of the membrane and less than about 1% by volume of a solvent for the cellulose ester in the nonsolvent or present as residual solvent in the high-flux membrane, and (ii) drying by evaporation the solution-treated, asymmetric membrane, while constraining evaporation of the treating solution from the porous bulk layer, to remove preferentially initially the volatile nonsolvent and to concentrate temporarily the solvent in the top skin surface, so as to cause differential pore collapse of the small pores of the top skin surface of the membrane to a controlled and selected smaller pore size of less than about 10 Angstroms. - View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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Specification