GB876123A - Process for the preparation of a light hydrocarbon oil freed or substantially freed from mercaptans - Google Patents

Abstract

A colourless or substantially colourless light hydrocarbon oil, freed or substantially freed from mercaptans, is prepared by treating a light hydrocarbon oil (having a boiling point or end boiling point which is not higher than 350 DEG C., and containing mercaptans), in the presence of oxygen, with an aqueous alkali metal hydroxide solution which contains, as a solutizer, a mixture of one or more fatty acid salts with from 3 to 5 carbon atoms and one or more polyhydric alcohols or partial ethers thereof. The light hydrocarbon oil treated may be a gasoline, kerosine or jet fuel obtained by straight distillation of crude oils or from heavy base materials by thermal or catalytic cracking, or it may be a reformed gasoline. The oxygen required for the process may be supplied either as such or as a mixture of oxygen with another gas that is inert under the operating conditions; air is a suitable oxygen-containing mixture. The oxygen may be dissolved in the hydrocarbon oil in advance or may be injected into the oil while the latter is being brought into contact with the aqueous solution of an alkali metal hydroxide and the solutizer mixture. Where the mercaptan content of the gasoline or kerosine to be treated is small and the gasoline or kerosine is in equilibrium with the atmosphere, the quantity of oxygen present in the gasoline or kerosine may be sufficient to effect the desired oxidation. The solutizer may comprise salts of propionic or butyric acid, together with diethylene glycol, triethylene glycol, glycerol, methyl "Cellosolve" or ethyl "Cellosolve" (the word "Cellosolve" is a Registered Trade Mark). The action of the oxygen may be promoted by the simultaneous use of a peroxide while, when the process is applied to hydrocarbon oils obtained by cracking, an antioxidant may be added to the oil to prevent the formation of gum from the unsaturated components of the oil. Intimate contact between the oil and the aqueous phase may be effected during the process by energetic mixing or by the use of a packed column. Regeneration of the spent caustic alkali solution is described. The oil may be subjected to a pretreatment with dilute caustic alkali solution to remove any acids present, such as hydrogen sulphide, which are stronger than the mercaptans. The oil may also be subjected to a pretreatment to reduce its mercaptan content, when this is high; thus, the oil may be extracted (without oxidation) with an aqueous alkali metal hydroxide solution containing the solutizer mixture according to the invention. In an example, straight-run kerosine is pretreated with dilute aqueous sodium hydroxide in the absence of oxygen in order to remove the acid components. The pretreated kerosine is then aerated and passed into a Turbo mixer. Aqueous potassium hydroxide solution, to which has been added a mixture of isobutyric acid and triethylene glycol is also supplied to the mixer. The mixture of kerosine and aqueous solution discharged from the mixer is passed to a settling space in which the two phases separate. The purified kerosine is discharged and the aqueous solution is recycled to the mixer. The process removes not only mercaptans, but also alkyl phenols, from the kerosine. The effect of replacing the solutizer by isobutyric acid or by a mixture of isomeric cresols is described. Specifications 712,056, 759,560 and 775,015 are referred to.