Supported anisotropic reverse osmosis membranes based on synthetic polyamides and processes for their preparation

A process for preparing a supported anisotropic reverse osmosis membrane based on synthetic polyamides, said process comprising the following steps in the order given:

• (a) preparing a support by treating a material suited for serving as a support for a polyamide membrane, with a water soluble polymeric material selected from the group consisting of polyacrylic acid having a molecular weight of about 50,000, methyl cellulose having a viscosity of 4000 cp au at 25.degree. C., a copolymer of acrylamide and acrylic acid, polyvinylpyrrolidone, polyvinyl alcohol having a molecular weight of 14,000 and a copolymer of vinylpyrrolidone and vinyl acetate, said water soluble polymeric material being resistant to high temperatures and insoluble in the polar solvents to be used for preparing the polyamide solution described below in step (b);
• (b) preparing a solution of the polyamide in an organic polar solvent, in the presence of a water soluble salt which is also soluble in the organic polar solvent, wherein the polyamide concentration is between 5% and 60% by weight and the weight ratio of polyamide/salt is between 1 and 10;
• (c) spreading the thus prepared polyamide solution onto the support prepared according to step (a);
• (d) partially evaporating the solvent by heating same at a temperature between 40.degree. C. and 180.degree. C. and for a time between 1 minute and 3 hours;
• (e) coagulating the membrane in an aqueous medium to dissolve the water soluble polymeric material and remove it from said support;
• and
• (f) thermally treating the thus obtained membrane.