Lubricating oil dewaxing using membrane separation of cold solvent from dewaxed oil and recycle of cold solvent to filter feed

Claim 1

A process for solvent dewaxing a waxy oil feed comprising dilution of the waxy oil feed stream with solvent and cooling the waxy oil feed stream to a temperature of 40° to 140° F., and further cooling the waxy oil feed by indirect contact with the cold filtrate, then sequentially indirectly cooling the waxy oil feed in indirect heat exchangers to crystallize and precipitate wax crystals, sequentially directly injecting additional solvent into the waxy oil feed stream to further cool and dilute and to obtain a desired viscosity of the waxy oil feed stream to facilitate handling of the waxy oil feed stream through the process and to facilitate filtering crystallized wax from the waxy oil feed and to obtain the desired pour point of dewaxed oil product, and during the sequential cooling of the waxy oil feed crystallizing and precipitating wax from the waxy oil feed to obtain an oil/solvent/wax mixture at a temperature of -30° to +70° F., feeding the oil/solvent/wax mixture to a filter to remove the wax and obtain an oil/solvent filtrate stream, contacting the oil/solvent filtrate stream at a temperature of -30° to +70° F. with one side of a selective semipermeable membrane in a membrane module to selectively transfer solvent through the membrane to obtain a solvent permeate on the other side of the membrane, the oil/solvent filtrate stream side of the membrane is maintained at a positive pressure relative to a pressure on the solvent permeate side of the membrane, selectively transferring 20 to 75% by volume of the solvent from the filtrate side of the membrane to the solvent permeate side of the membrane, and recycling the solvent permeate at a temperature of -30° to +70° F. to the filter feed, withdrawing a filtrate stream containing the remaining solvent from the filtrate side of the membrane module, contacting the filtrate stream by indirect heat exchange with the warm waxy oil feed, and treating the withdrawn filtrate stream to separate the remaining solvent from the oil, and recovering a dewaxed oil product stream, and a slack wax product stream and recycling the separated solvent to the dewaxing process.