Ultrafiltration polyamide membrane and its use for recovery of dewaxing aid (OP-3454)

A method for recovering dewaxing aids used in the solvent dewaxing of waxy hydrocarbon oils wherein the dewaxing aid is present in a dewaxed oil stream, a precipitated wax stream or both and wherein the dewaxing aid present in said dewaxed oil stream, precipitated wax stream or both is recovered by heating said stream so that the wax is in the liquid state and contacting said heated stream with an ultrafiltration polymeric membrane to selectively permeate through said membrane the oil or wax component of said heated stream while producing retentate containing the dewaxing aid which retentate can be recycled to the solvent dewaxing process wherein the ultrafiltering polymeric membrane comprises a polyimide membrane made by dissolving a fully imidized polyimide polymer in a pro solvent or mixture of pro solvents and a pore forming agent characterized by having at least about 50% more molar volume than the solvent or solvent mixture used, a solubility parameter equal to a greater than that of the solvent and a polar end and substantial hydrocarbon character, to produce a casting solution, using said casting solution to produce a thin layer of said polyimide polymer/solvent/pore former, and quenching the layers in a quenching solvent.