GB827384A - 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 exceeding 370 DEG C. and containing mercaptans are purified by the oxidation process described in the parent Specification but employing as the aqueous phase, an 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 solution being initially capable of co-existing in heterogeneous equilibrium with an alkali metal hydroxide solution containing less phenolate, both solutions containing the same three components in aqueous homogenous solution. The hydrocarbon oils, phenols and oxidation procedure are as described in the parent Specification. However, the oxygen may be used in conjunction with other oxygen-yielding compounds such as ozone or a peroxide, for example, as described in Specification 769,208. The compositions of the aqueous solutions used only vary slightly from those described in the parent Specification, being representable for the system in graph 1 therein by the boundary line AE but they allow of the use of less of the alkaline solution and facilitate regeneration. Thus, the alkaline solution, which becomes diluted with water in use, may be regenerated by contact with sufficient of an alkali metal hydroxide solution containing phenolate in amount less than that in the solution being regenerated and which is capable of co-existing in heterogeneous equilibrium with the original alkaline solution whereby all or substantially all the diluting water is removed. An example described a continuous process for the oxidation treatment of a mercaptan-containing gasoline using an aqueous KOH/potassium cresolate solution and regeneration of the latter; suitable apparatus is illustrated and that described in Specification 659,241 may also be used.ALSO:Oil-soluble mercaptons or alkali-metal mercaptans 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 boiling at not above 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, and being initially capable of co-existing in heterogeneous equilibrium with an alkali metal hydroxide solution containing less phenolate, both solutions containing the same three components in aqueous homogeneous solution. The term "phenol" denotes phenol as a monohydric alkyl phenol containing a total of not more than 3 carbon atoms in the alkyl group or groups present and no other substituents. The compositions of the aqueous solutions differ little from those of the solutions used in the parent Specification, being representable for the system in graph 1 therein by the boundary line AE but they allow the use of smaller quantities of the solution and facilitate regeneration. The oxidation procedure is generally as described in the parent Specification. However, the oxygen may be used in conjunction with oxygen-yielding compounds such as ozone or a peroxide, for example as described in Specification 769,208. Regeneration of the aqueous alkaline solution, which in use becomes diluted with water, may be effected by contacting the used solution with a sufficient amount of an alkali metal hydroxide solution containing alkali metal phenolate in an amount less than that in the solution being regenerated and which is capable of co-existing in heterogeneous equilibrium with the original alkali metal hydroxide/phenolate solution, whereby all or substantially all the diluting water is removed. The process is described with particular reference to mercaptan-containing gasolines and kerosines, the disulphides remaining 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 described. The contact apparatus described in Specification 659,241, [Group III], may also be used.