GB787914A - Improvements in or relating to oxidation of mercaptans - Google Patents

Abstract

Mercaptans are oxidized to the corresponding disulphides by a process comprising forming a solution of a mercaptan in an aqueous solvent medium containing a catalytic amount of at least one alkali metal salt of selenous or selenic acid, intimately contacting the solution with free-oxygen and separating the disulphide formed from the aqueous phase of the reaction mixture. Specified catalysts, which may be formed in situ, are sodium biselenite, silenite, biselenate and selenate, suitably used in amounts of from 0.01 to 2 per cent by weight or the aqueous medium. The aqueous medium may be an aqueous solution of an alcohol or a caustic alkali; solutizers may be present, e.g., cresols, xylenols, water-soluble fatty acid salts and naphthenic acid salts. The mercaptans treated may be aliphatic, cycloaliphatic or aromatic, for example, those present in sour hydrocarbon oils and the process may be applied to the sweetening of such sour oils (see Group III). Temperatures of between about 60 DEG and 200 DEG F. are used. The free oxygen, which may be in the form of air, is preferably used under elevated pressure. In examples: (1) hexyl mercaptan dissolved in aqueous ethanol is oxidized in the presence of sodium biselenite with oxygen under 80 p.s.i.g. pressure at 75 DEG F. and the resulting disulphide separated from the aqueous phase; (2) hexyl mercaptan is oxidized in aqueous ethanolic caustic soda solution in the presence of sodium biselenite using oxygen at 85 DEG C. and 1 atmos. pressure. Reference is made to the oxidation of methyl sulphide in aqueous sodium hydroxide solution containing sodium selenite yielding methyl disulphide and of the mercaptans extracted from a sour diesel oil by means of an aqueous methanolic caustic soda solution containing xylenols, regeneration of the aqueous medium being effected in the presence of sodium selenate.ALSO:Sour hydrocarbon oils are sweetened, according to one method, by intimately contacting the oil with an aqueous medium in which mercaptans are soluble and containing a catalytic amount of an alkali metal salt of selenous or selenic acid, and with at least sufficient of a free-oxygen containing gas to oxidize substantially all of the mercaptans to disulphides and thereafter separating the resulting sweetened oil from the aqueous phase. Alternatively, the sour oil may be extracted with an aqueous medium in which the mercaptans are soluble, the resulting sweetened oil is separated from the aqueous phase and the latter intimately contacted with sufficient of a free-oxygen containing gas in the presence of a catalytic amount of an alkalimetal salt of selenous or selenic acid whereby the extracted mercaptans are oxidized to disulphides; the disulphides are separated from the aqueous phase which may be used for the sweetening of further quantities of sour hydrocarbon oil. The oxidation is generally effected at between 60 DEG and 200 DEG F. The aqueous medium may be an aqueous solution of an alcohol, e.g. a solution of methanol or ethanol, water and a mercaptan-solutizer, e.g. a cresol, xylenol, water-soluble fatty acid salt or a naphthenic acid salt or an aqueous alkaline or aqueous alcoholic alkaline solution, which generally also contains a solutizer for mercaptans. Sour hydrocarbon oils which may be treated include naphthas, kerosene, diesel oil, heater oil and other petroleum distillates obtained by cracking, coking or acid treatments. The free-oxygen, which may be in the form of air, is preferably used under elevated pressure.