GB763625A - Improvements in or relating to the purification of hydrocarbons - Google Patents

Abstract

The mercaptan content of a hydrocarbon distillate, for example a gasoline, is reduced by leading the distillate through at least one column containing a layer of active carbon impregnated with an aqueous alkaline liquor and the used impregnated active carbon is subsequently regenerated by means of an oxygen-containing gas in the absence of steam. According to a modification of the process, the regeneration of the active carbon, instead of being effected subsequently, is effected continuously during the passage of the distillate through the column by adding air to the hydrocarbon distillate, either in the column or before the column. The alkaline liquor may be an aqueous solution of an alkali metal hydroxide, particularly sodium hydroxide, or of ammonium hydroxide, and the oxygen-containing gas may be air of oxygen. The alkaline liquor may contain organic or inorganic activators and a list of substances suitable for this purpose is given. Mercaptans in the hydrocarbon distillate are converted, by contact with the active carbon, to disulphides which remain dissolved in the distillate. The active carbon becomes contaminated with mercaptides and the regeneration with oxygen-containing gas effects removal of the mercaptides. The active carbon in time may become contaminated with phenolates and regeneration by steaming is then necessary. The hydrocarbon distillate, before contact with the active carbon, may be freed of hydrogen sulphide, for example by washing with aqueous sodium hydroxide solution, followed by water-washing and drying in a coalescer containing iron filings. In the examples, gasoline is sweetened by contact with active carbon impregnated with aqueous sodium or potassium hydroxide, air being introduced with the gasoline or used subsequently to regenerate the active carbon. Activators mentioned in the examples are methanol, glycol, dimethylamine, hydrochloride, diethanolamine, butyric acid, naphthenic acids, tartaric acid, acetaldehyde, acetone, grape sugar, phenol, m-cresol, petroleum phenols, alpha-naphthol, pyrocatechol, resorcinol, hydroquinone, pyrogallol, salicylic acid, resorcylic acid, gallic acid, tannin, p - aminophenol, N - benzyl - p - aminophenol, p - aminosalicylic acid, anthraquinone, alizarin, quinizarin, sodium salt of m - nitrobenzene sulphonic acid, picric acid, pyridine, hydrazine hydrate, hydroxides or sulphides of copper, ferric iron, chromium, manganese, lead, cobalt or nickel (formed in situ by the addition of a water-soluble salt of the metal and reaction between the salt and the alkaline liquor or sodium sulphide contained therein) and a mixture of ferric chloride and sodium potassium tartrate. Apparatus is described wherein the process employing air introduced with the hydrocarbon distillate is carried out in four towers, three being used in series and the fourth being out of action for steaming.