Separating wax from hydrocarbon mixture boiling in the lubricating oil

Abstract

In order to separate wax from lubricating oil, it is necessary both to introduce free excess charge which is net positive or net negative into the wax-laden oil, preferably by charge injection, and to reduce the solubility for the wax (for example by cooling the lubricating oil) sufficiently so that dissolved wax forms a dispersion of wax particles and crystals in the oil. The resulting electrophoretic effect results in wax particle agglomeration and particle size growth in the oil itself and/or on collector surfaces in contact with the charged oil. The charge injection and the wax solubility reduction such as by cooling can occur simultaneously, or one before the other in either order. Cooling can conveniently be effected wholly or in part by mixing with the oil an auto-refrigerant liquid which vaporizes to reduce the oil temperature. Ideally the auto-refrigerant liquid additionally has oil solvent properties, propane being an example of a suitable such liquid additive. The cooling can also be at least partially effected by heat exchange with a cooling fluid, for example, using a cooling jacket surrounding a separation vessel in which the wax agglomeration and growth occurs or a heat exchanger in the wax-laden oil feed to the separation vessel.