Abstract: A membrane cast in the form of either a hollow filament or a flat film formed of a polybenzimidazole polymer is subjected to an annealing process by contacting the membrane with a non-aqueous annealing medium comprised of a solvent for the polymer and a non-solvent for the polymer. Such an annealing step can advantageously occur at an annealing temperature below about 125.degree. C. (e.g., below 100.degree. C.) These polybenzimidazole membranes find particular utility in reverse osmosis desalination processes. The annealing step of the present invention improves the mechanical and separative properties of the membrane.

Abstract: A membrane cast in the form of either a hollow filament or a flat film formed of a polybenzimidazole polymer is subjected to an annealing process by contacting the membrane with an annealing medium comprised of a solvent for the polymer and water. Such an annealing step can advantageously occur at an annealing temperature below the boiling point of water, thus avoiding the necessity for removing water present in the membrane in a conventional pre-annealing treatment step. These polybenzimidazole membranes find particular utility in reverse osmosis desalination processes. The annealing step of the present invention improves the mechanical and separative properties of the membrane and is simple in comparison to conventional annealing procedures.

Abstract: A microporous membrane having a thin surface skin and a cellular body is described. The membrane is effective for separating soluble oils, proteins and other substances having large molecular weights from water or other carriers by means of the ultrafiltration process or for removing salts from liquids by means of the electrodialysis process.

Abstract: An ultra-filter comprising a stack of alternating feed fluid conducting cells and permeate fluid conducting cells separated by semipermeable membranes. The feed cells comprise two facing gaskets which are separable to permit cleaning their interface area. The membranes are on the non-interfacing surfaces of the feed cell gaskets. Isolated passages extend through the stack for introducing feed solution to the cells and for discharging permeate solution and a residual portion of the feed solution. Planar flow passages connect the isolated passages by means of cutout portions in the feed and permeate cells. The permeate cells include a solid back-up sheet and a porous element is interposed between the back-up sheet and the adjacent membrane to support the membrane against excessive distention by pressurized feed solution. The filter stack is sealed by compression between end plates. Alignment pins extend through the stack to maintain the relative position of the components during disassembly and reassembly.