Patent ID: 7201860
Filing Date: 2007-04-10
Classification: B01D

Abstract:
1. A method for production of a hydrolytically stable polyamide membrane, the method comprising: a) preparing a homogeneous solution containing 10–90% by weight of an aliphatic polyamide in 90–10% by weight of a solvent system, wherein the solution of polyamide and solvent system has a critical demixing temperature and a solidification temperature, and shows a miscibility gap below the demixing temperature in the liquid state, and wherein the solution contains an antioxidant agent as a stabilizer for the polyamide, the antioxidant agent being essentially insoluble in the solvent system at or below the demixing temperature; b) shaping the solution into a shaped object in a die at a die temperature, the die temperature being above the critical demixing temperature; c) cooling the shaped object with a cooling medium conditioned to a cooling temperature below the solidification temperature, at such a cooling rate that a thermodynamic non-equilibrium liquid-liquid phase separation into a polymer-rich phase and a polymer-poor phase occurs, followed by solidification of the polymer-rich phase to a membrane structure when the temperature falls below the solidification temperature; and d) removing the solvent system from the shaped object, wherein the antioxidant is a sterically hindered phenol selected from the group consisting of pentaerythritol tetrakis(3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate) (CAS no. 6683-19-8), 3,3′,3′,5,5′,5′-hexa-tert-butyl-α,α′,α′-(mesitylene-2,4,6-triyl)tri-p-cresol (CAS no. 1709-70-2) and N,N′-hexane-1,6-diylbis(3-(3,5-di-tert-butyl-4-hydroxyphenylpropionamide)) (CAS no. 23128-74-7).