GB745632A - Improvements in or relating to process for refining hydrocarbon distillates - Google Patents

Abstract

Mercaptans are removed from sour hydrocarbon distillates with a minimum of colour degradation by contacting the distillate with about 5-200 per cent by volume of non-alkaline methanol which contains not more than about 10 volume per cent of water, separating the methanol and dissolved colour-forming bodies from the distillate, then treating the distillate with about 1-15 per cent by volume of an aqueous caustic alkali solution of 50-60 per cent concentration by weight, introducing an oxygen-containing gas into the caustic alkali-distillate mixture, maintaining the temperature at about 80-125 DEG F. and ensuring the presence in the mixture during treatment of 0.004-0.3 per cent of copper in the form of a copper compound which is active as an oxidation catalyst, and separating spent caustic alkali solution and associated reaction products from the treated distillate. Hydrocarbon distillates mentioned are heavy naphtha, kerosene, diesel oil, heater oil and furnace oil, which are derived from the distillation of crude oil or from cracking processes, either thermal or catalytic. The caustic alkali may be caustic soda or caustic potash, while the oxygen-containing gas may be air or oxygen. The copper can be added in the form of any compound which is somewhat soluble in the hot concentrated caustic alkali solution or which can be dispersed in the form of a water solution in the sour distillate before the caustic alkali solution is added. The preferred copper compounds to be added are cupric chloride and cupric sulphate, and it is believed that the copper salt reacts with the caustic alkali to form colloidal copper oxide which is the active catalyst. The sour distillate, before extraction with methanol, may be given a preliminary wash with a weak alkaline solution, for example a caustic soda solution, to remove hydrogen sulphide if this is present. The methanol extraction removes colour-forming bodies which are believed to be alkyl phenols, while the treatment with caustic alkali which follows yields a spent alkali which contains cresylates. Both the used methanol and the spent alkali may be regenerated for further use. The treated distillate may be passed through granular or fibrous material (e.g. glasswool, sand or gravel) and then washed with water to remove traces of alkali. Finally a small amount of a metal deactivator such as N, N1 disalicylidene -1, 2-diaminopropane may be added to the treated distillate. Specifications 728,057, 745,631 and 745,633 are referred to.