GB778700A - Improvements in or relating to the separation of hydrocarbons - Google Patents

Abstract

A process for the extractive crystallization of a hydrocarbon mixture comprises fractionally distilling a hydrocarbon oil in a fractionation column to obtain a lower boiling fraction and a higher boiling fraction, treating the higher boiling fraction with a urea solution to form a complex slurry comprising a liquid phase of urea adduction raffinate and urea solution, the slurry comprising, in suspension, a solid urea adduct with or without solid urea, separating part of the raffinate from the slurry, mixing the remaining slurry with a washing solvent comprising at least part of the lower boiling fraction, separating, preferably by decanting, the major part of the solvent from the slurry and recovering the extract from the remaining mixture, and recycling the solvent to the fractionating column at a level below that at which the lower boiling fraction is withdrawn. Mineral oils such as petroleum distillates or crude oil may be treated; the lower boiling fraction may have a boiling range of 40-150 DEG C. and the higher boiling fraction, e.g. gas oil or kerosene, may have a boiling range of 240-310 DEG C. The n-paraffins form complexes with the urea. The urea solvent may comprise water and/or methanol, and may be a solvent described in Specification 704,439, [Group III], e.g. a mixture of 75 parts of 80 per cent aqueous methanol and 25 parts of ethylene glycol. The urea may contain 0.2-5 per cent of biuret, as described in Specification 716,068. The separation of raffinate from complex slurry and/or of the solvent from the slurry may be effected by decantation; the separation may be assisted by the methods described in Specifications 745,546 and 778,699. The urea solution with the adduct in suspension may be heated to recover the extract hydrocarbons and regenerate urea. A method and apparatus for the continuous operation of the process is described.ALSO:A process for the extractive crystallization of a hydrocarbon mixture comprises fractionally distilling a hydrocarbon oil in a fractionation column to obtain a lower boiling fraction and a higher boiling fraction, treating the higher boiling fraction with a urea solution to form a complex slurry comprising a liquid phase of urea adduction raffinate and urea solution, the slurry comprising, in suspension, a solid urea adduct with or without solid urea, separating part of the raffinate from the slurry, mixing the remaining slurry with a washing solvent comprising at least part of the lower boiling fraction, separating, preferably by decanting, the major part of the solvent from the slurry and recovering the extract from the remaining mixture, and recycling the solvent to the fractionating column at a level below that at which the lower boiling fraction is withdrawn. Mineral oils such as petroleum distillates or crude oil may be treated; the lower boiling fraction may have a boiling range of 40-150 DEG C. and the higher boiling fraction, e.g. gas oil or kerosene, may have a boiling range of 240-310 DEG C. The n-paraffins form complexes with the urea. The urea solvent may comprise water and/or methanol, and may be a solvent described in Specification 704,439, e.g. a mixture of 75 parts of 80 per cent aqueous methanol and 25 parts of ethylene glycol. The urea may contain 0.2-5 per cent of biuret, as described in Specification 716,068. The separation of raffinate from complex slurry and/or of the solvent from the slurry may be effected by decantation; the separation may be assisted by the methods described in Specifications 745,546 and 778,699. The urea solution with the adduct in suspension may be heated to recover the extract hydrocarbons and regenerate urea. A method and apparatus for the continuous operation of the process is described.