Abstract: A method for the molecular filtration of predominantly aliphatic hydrocarbon liquids (e.g. spent diesel lubrication oil, crude oil or pipeline blend crude oils and heavy oils, and bitumen), wherein, at a viscosity less than 600 centipoise, the predominantly aliphatic hydrocarbon liquid is passed through a membrane, having at least a swelled outer layer on the high pressure side comprising a microporous, membrane of an aliphatic hydrocarbon liquid swellable, polysulfone compound, at a pressure differential in the range 1 to 100 atmospheres oil. The microporous membrane having been swelled in the aliphatic hydrocarbon liquid from having a molecular weight cut off less of than 20,000 when measured in an aqueous medium to, after adsorption of hydrocarbon liquid and having been swelled thereby, a molecular weight cut off less than 4,000 when measured in hydrocarbon liquid, so that oil depleted in the substance to be filtered therefrom permeates the membrane.

Abstract: Polysulfone cast films, including polyethersulfone cast films, are partially gelled with mineral acid prior to or during the conventional water gelation to control the porosity of and improve the productivity of reverse osmosis and ultrafiltration membranes thus produced. The partial gelation may be carried out prior to the water gelation by contacting the cast film with the mineral acid in a gaseous or aqueous form and the gaseous form may be diluted with air. The partial gelation may, in different embodiments, be carried out simultaneously with the conventional gelation by dissolving the mineral acid in the gelation liquid.