Reverse osmosis process employing polybenzimidazole membranes

Claim 1

A process for the desalination of water comprising: a. providing a solution of a polybenzimidazole polymer consisting essentially of recurring units of the formula: whereiN R is a tetravalent aromatic nucleus, with the nitrogen atoms forming the benzimidazole rings paired upon adjacent carbon atoms of said aromatic nucleus, and R'' is selected from the group consisting of (1)an aromatic ring, (2) an alkylene group having from four to eight carbon atoms, and (3)a heterocyclic ring selected from the group consisting of (a) pyridine, (b) pyrazine, (c) furan, (d) quinoline, (e) thiophene, and (f) pyran in a solvent capable of dissolving said polymer, b. depositing a film of said solution upon a support, c. evaporating an amount of solvent from said film sufficient to allow the formation of a thin solid layer on the exposed surface of said film having a density which is substantially greater than that of the remaining portion of said film on which said solid layer of increased density is formed, d. washing the resulting film with a non-solvent for said polymer to remove residual solvent thereby producing a reverse osmosis semipermeable membrane, of unusually high physical durability and chemical stability, e. positioning said semipermeable membrane while adjacent a porous support within an aqueous sodium chloride solution wherein the concentration of dissolved sodium chloride in said solution is greater on one side of said membrane than upon the other side of said membrane, f. applying a pressure of about 600 to 3000 pounds per square inch to that portion of said sodium chloride solution having a greater concentration of sodium chloride dissolved therein thereby causing water to pass through said semipermeable membrane via reverse osmosis to the substantial exclusion of dissolved sodium chloride, and g. recovering said solution from said side of said membrane having a lesser concentration of sodium chloride dissolved therein.