US 5,494,566 AGranted

Lubricating oil dewaxing with membrane separation of cold solvent

AssigneeMobil Oil Corporation

InventorsRonald M. Gould, Albert R. Nitsch

Life of this patent

Estimating the term…

Loading patent…

Abstract

A process for solvent dewaxing petroleum feedstock to separate crystallized wax from lubricant oil by filtration of a wax/oil/solvent mixture. The feedstock is sequentially cooled and mixed with cold polar solvent to form a wax crystal phase and oil-solvent phase, and-the oil-solvent filtrate stream is contacted with solvent permeable selective membrane at low temperature to recover an internal circulating permeate solvent stream and an oil-rich retentate stream containing dewaxed oil product and residual solvent. Improved operation is achieved by splitting the internal circulating solvent stream into a multiple cold solvent recycle streams and injecting a plurality of the cold solvent recycle streams into the waxy petroleum feedstock during sequential cooling and mixing. By initially injecting a cold recycle solvent stream in to the waxy petroleum feedstock at a small temperature differential near the wax crystallization temperature, shock cooling and excess small wax crystal formation is avoided.

A process for solvent dewaxing a waxy petroleum oil feed stream comprising the steps of:

diluting of the waxy oil feed stream with solvent;
cooling the waxy oil feed stream in successive heat exchange stages to a temperature of 40.degree. to 140.degree. F., and further cooling the waxy oil feed by indirect contact with cold filtrate by sequentially indirectly cooling the waxy oil feed in indirect heat exchangers to crystallize and precipitate wax crystals and
sequentially directly injecting additional solvent in incrementally colder solvent injection stages 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.degree. to +70.degree. 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.degree. to +70.degree. 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 stream 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;
and wherein the volume ratio of solvent in the permeate stream to retentate stream is 1:1 to 3:1;
selectively transferring a major amount of 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.degree. to +70.degree. 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.

5 more elements

Abstract

Claims11