GB827385A - Improved process for oxidising mercaptans or mercaptides to disulphides in a two-phase system consisting of a light hydrocarbon oil phase and an aqueous alkali metal hydroxide phase - Google Patents

Abstract

Light hydrocarbon oils having a boiling-point not above 370 DEG C and containing mercaptans, are purified by the oxidation process described in the parent Specification but employing, as the aqueous phase, a homogeneous aqueous solution of an alkali metal hydroxide and an alkali metal salt of a phenol containing at least 2 mols. per litre of free alkali metal hydroxide and not more than 54% by volume of water based on the total volumes of the components of the solution before they are mixed together, the aqueous solution being initially capable of co-existing in heterogeneous equilibrium with, and being initially saturated but not supersaturated with respect to, one or more solid compounds of the alkali metal hydroxide with either the phenol or the phenol and water. The hydrocarbon oils, phenols and general oxidation procedure are as described in the parent Specification. However, oxygen-yielding compounds such as ozone or a peroxide may be used in conjunction with the oxygen, for example as described in Specification 769,208. The compositions of the aqueous alkaline phenolate solutions only vary slightly from those described in the parent Specification and may be represented for the system in the graph 1 therein by the boundary lines DE and CD, but they allow use of smaller quantities of the solutions and regeneration of the latter is facilitated. Thus, the used alkaline solutions, which become diluted with water in use, may be regenerated by contact with a sufficient amount of a solid compound of the alkali metal hydroxide with the phenol or phenol and water, capable of coexisting in heterogeneous equilibrium with the original solution, whereby all or substantially all of the diluting water is drawn off. An example describes a continuous process for the sweetening of a gasoline using an aqueous KOH-potassium cresolate solution and the regeneration of the latter by means of anhydrous potassium cresolate; suitable apparatus is described.ALSO:Oil-soluble mercaptans or alkali-metal mercaptides derived therefrom are oxidized to disulphides by means of oxygen in the absence of an oxidation catalyst, the mercaptans or mercaptides being initially in a two-phase system, one phase of which is formed by a light hydrocarbon oil having a boiling-point or end boiling-point not exceeding 370 DEG C., and the other phase of which is formed by an aqueous solution of an alkali metal hydroxide and an alkali metal salt of a phenol as hereinafter defined, the two phases being brought into intimate contact with each other during the oxidation, the aqueous solution being a homogeneous solution containing at least 2 mols. per litre of free alkali metal hydroxide and not more than 54% by volume of water based on the total volumes of the components of the solution before they are mixed together, the aqueous solution also being initially capable of co-existing in heterogeneous equilibrium with, and initially being saturated but not supersaturated with respect to, one or more solid compounds of the alkali metal hydroxide with the phenol or of the alkali metal hydroxide with the phenol and water. The term "phenol" denotes phenol or a monohydric alkyl phenol containing a total of not more than 3 carbon atoms in the alkyl group or groups present and having no other substituents. The compositions of the aqueous solutions differ only slightly from those of the solutions used in the parent Specification, being representable for the system in graph 1 thereof by the boundary lines DE and CD, but they allow the use of smaller quantities of the alkaline solution and regeneration of the latter is facilitated. The oxidation is generally effected as described in the parent Specification. However, other oxygen-yielding compounds such as ozone or a peroxide may be used in conjunction with the oxygen; thus, a peroxide may be added as described in Specification 769,208. Regeneration of the aqueous alkaline solution, which becomes diluted with water in use, may be effected by contacting the used solution with a sufficient amount of a solid compound of the alkali metal hydroxide with the phenol or phenol and water, capable of co-existing in heterogeneous equilibrium with the original solution, whereby all or substantially all the diluting water is drawn off. The process is described with particular reference to mercaptan-containing gasolines and kerosenes, the sulphur remaining as disulphide in the treated oil. An example describes a continuous process for the oxidation of a mercaptan-containing gasoline using an aqueous KOH-potassium cresolate solution and the regeneration of the latter and suitable apparatus is illustrated.