GB556606A - Method of removing acidic organic compounds from hydrocarbon oil - Google Patents

Abstract

556,606. Purifying oils. ATLANTIC REFINING CO. Feb. 26, 1942, No. 2538. Convention date, Feb. 13, 1941. [Class 91] Acidic organic compounds, mercaptans and phenols, are removed from hydrocarbon oils by counter current extraction (1) with an aqueous solution of an alkaline reagent containing an organic solvent more soluble in said aqueous solution than in the hydrocarbon oil and (2) with an aqueous solution of the alkaline reagent alone. Sodium hydroxide is the preferred alkaline reagent and methanol the preferred organic solvent, but other reagents such as sodium or potassium carbonates, phenolates, or alcoholates, potassium isobutyrate, ammonia, amines, hydroxyamines, guanidine,- or quaternary ammonium bases may be used and other solvents such as ethanol, propanol, isopropanol, ethylene glycol, glycol ethers, ethylene chlorhydrin, glycerol, acetone, and ethyl methyl ketone, either anhydrous or mixed with water. In an example, hydrocarbon oil such as gasoline, preferably free from hydrogen sulphide, and having, for example, a sulphur content of 35 mg. of mercaptans per 100 cc., is introduced from a pipe 1 into the lower part of an extraction tower 2 containing packing 3 while methanol is introduced from the pipe 4 and from the recovery plant either with the gasoline or through pipes 7, 8, 9 at different levels. Caustic soda of 47 per cent. concentration is introduced through the pipe 11 at the top, the proportions of methanol and of caustic soda solution, based on the volume of oil to be treated, being 0.5 per cent. and 2 per cent. respectively. The treated gasoline substantially free from sulphur is withdrawn from the tower by the pipe 12. The spent treating solution is withdrawn through the pipe 13 to a heated stripping tower 16, into which steam may be injected by a pipe 19. The liberated mercaptans, methanol, gasoline, and a portion of the water pass off through the pipe 20 to a separator 23 to which a small amount of gasoline or other solvent may be added through pipe 25. Two layers are formed, the upper containing insoluble mercaptans which comprise about 95 per cent. of the mercaptans present and traces of gasoline, and the lower containing 15 to 30 per cent. methanol and soluble mercaptans. The upper layer is removed through the pipe 24, while the lower layer is passed to a fractionating tower 27 provided with bubble trays 28, heating coils 29 and dephlegmating coil 30. The fractionating tower may be used in two ways, viz. to distill off methanol containing small quantities of low molecular weight mercaptans through a condenser 32 to a storage tank 34, from which it is recycled through the extraction tower'2, or, when excessive amounts of low molecular weight mercaptans are present, the concentrated methanol vapour is drawn off through a pipe 38 while an azeotropic mixture of methanol and mercaptans is discharged through a condenser 40 back to the separator 23. Additional water may be supplied to the system through the pipe 48. The regenerated sodium hydroxide solution forming in the stripping tower 16 is run into a separator 50 where insoluble phenolates separate out as a top layer and are drawn off through pipe 51. The sodium hydroxide is recycled to the tower 2. When higher boiling hydrocarbons such as naphtha, kerosene, and furnace oil have to be treated, the quantity of aqueous alkaline solution may be increased to 100 per cent. by volume and its concentration may range from 10 to 50 per cent.