GB754875A - Improvements in or relating to process for sweetening thermally cracked naphthas - Google Patents

Abstract

A process for sweetening a thermally cracked naphtha feed having a mercaptan number greater than 1.2, comprises contacting the feed, in the presence of freeoxygen, with an aqueous alkaline treating agent containing alkyl-phenols, wherein the agent is present in an amount to exceed the solubility of the agent in the feed, and with free sulphur, at a temperature above 80 DEG F., for a time sufficient to produce sweet naphtha, which is separated from an aqueous phase. The alkaline treating agent may contain sodium hydroxide or potassium hydroxide or mixtures thereof, in an amount of free caustic alkali between 5 and 50 weight per cent, and alkylphenols, which may be cresols or xylenols, preferably those obtained from petroleum hydrocarbons, in an amount of 2 to 30 volume per cent. The alkaline treating agent may be used in an amount of 10 to 200 volume per cent., based on the feed naphtha. Oxygen or air may be used in amounts of 0.2 to 2 cubic feet of oxygen, or 1 to 10 cubic feet of air, per barrel of feed naphtha. Free sulphur may be used in amounts between 0.5 and 1.8 lbs. per 1,000 barrels of naphtha feed per mercaptan number. The feed may be a naphtha with an A.S.T.M. end point of not more than 425 DEG F., and may be prewashed with weak caustic alkali solution, or extracted with a caustic alkali - cresylate solution to reduce the mercaptan number to below 20 before sweetening by the present process. The temperature of the process may be between 80 DEG F. and 210 DEG F., and the contact time may be between 1 and 60 minutes. In an embodiment of the process feed naphtha, free sulphur, air, and aqueous caustic alkali-cresylate solution are introduced into a contactor, from which an aqueous phase is withdrawn, naphtha passing to a second contactor in which further aqueous phase settles out, the treated naphtha passing to one or more settlers, where a sweetened naphtha, i.e. with a mercaptan number below 1, is obtained The aqueous phase from the contactors and setllers is recycled for further use.