GB704439A - Improvements relating to the extractive fractionation of hydrocarbon oils by formation of urea adducts - Google Patents

Abstract

Hydrocarbon oils of mineral origin are fractionated by treating them with a solution of urea in a ternary solvent, comprising (1) water, (2) a water-soluble monohydric alcohol and/or water-soluble ketone and (3) a polyhydric alcohol and/or amino-alcohol, to form an oil-in-water emulsion and separating the solid hydrocarbon-urea adduct which forms. Oils mentioned are petroleum naphtha, gasoline, kerosene, gas oil and thermally reformed distillates of mineral origin, and the fractionation may yield a raffinate practically free of normal aliphatic hydrocarbons and an extract essentially consisting of normal aliphatic hydrocarbons. Ingredient (2) of the ternary solvent may be methanol, ethanol, n-propanol, iso-propanol, 2-methyl propanol, acetone or methyl ethyl ketone while ingredient (3) may be ethylene glycol, glycerol, diethylene glycol, propylene glycols, butylene glycols, monoethanolamine, diethanolamine or triethanolamine. The solid adduct is formed as a suspension in the liquid phase, the raffinate remaining as an emulsion in the urea solution. Preferably the density of the urea solution is adjusted to be greater than that of the hydrocarbons and less than that of the adduct, and the emulsion is broken. Thereupon an upper raffinate layer separates out, leaving a suspension of the adduct in the urea solution as the lower layer. The layers are separated and the lower layer is heated, whereupon this lower layer in turn becomes a two phase system, one phase consisting essentially of the adduction extract released by decomposition of the adduct and the other phase consisting essentially of urea solution. The preferred method of breaking the emulsion is by the addition of an aqueous solution of a monohydric alcohol or ketone. Part of the recovered urea solution may be distilled to take overhead a fraction comprising an aqueous alcohol or ketone, which is employed again as emulsion breaking agent, while the part of the recovered urea solution which is not distilled may be recycled for further adduct formation. The distillation bottoms may either be added to this urea solution for recycling or returned to the system after separation of the adduction raffinate but prior to the adduct decomposition stage. The formation of the adduct preferably occurs when the urea solution is in the supersaturated state. Thus a saturated solution of urea in the ternary solvent may be cooled and then added to the hydrocarbon and the mixture passed through a colloid mill to emulsify the oil. Alternatively the oil itself may effect the cooling or the cooling may be effected after mixing. Petroleum naphtha may be thermally reformed and the gasoline thus obtained may be subjected to fractionation according to the invention, the adduction raffinate being a gasoline of increased octane number. If desired, the adduction extract may be recycled to the thermal reforming zone. Alternatively petroleum naphtha may be subjected to fractionation according to the invention and the adduction raffinate may be thermally reformed to give a gasoline of high octane number.