GB769208A - Process for oxidising to disulphides oil soluble mercaptans or alkali metal mercaptides derived from oil soluble mercaptans - Google Patents

Abstract

Disulphides are prepared by oxidation of oilsoluble mercaptans or alkali-metal mercaptides derived from oil-soluble mercaptans initially present in a two-phase system, one phase of which is formed by a hydrocarbon oil and the other by an aqueous alkali-metal hydroxide solution, the two phases being intimately contacted in the presence of oxygen and a peroxide, the peroxide being present in an amount of from 10 to 40 per cent of the stoichiometric amount required to oxidize to disulphides, the total mercaptan-mercaptide content of the reaction mixture. The presence of the peroxide allows the oxidation to be effected with an amount of total oxygen which is stoichiometric for complete conversion of the mercapto-compounds and under atmospheric as well as higher pressure. Specified peroxides are ozone, hydropropane peroxide, cumene hydroperoxide, t.-butyl hydroperoxide, benzoyl peroxide and tetrahydro-naphthalene peroxide; also the peroxides may be formed in situ by passing oxygen into the hydrocarbon at 75-125 DEG C. The oxygen required may be dissolved in the hydrocarbon before or during its contact with the aqueous alkali. Ozonized oxygen may be passed into the hydrocarbon to provide both the oxygen and the peroxide. The aqueous alkali-metal hydroxide solution may contain solutizers, many of which are mentioned. The preferred solutions are 2-N or higher caustic soda or potash solutions and, in particular, contain at most 54 per cent by volume of water, at least two mols. of free alkali metal hydroxide per litre and a phenolate which may be unsubstituted or contain alkyl substituents having not more than a total of 3 carbon atoms. The intimate contacting of the phases may be effected by means of a centrifugal mixer or a contact tower or by spraying one phase into the other. The oxidation is generally effected at 0 DEG to 80 DEG C. and may be operated batchwise or continuously. The process may be applied to the sweetening of sour hydrocarbons by direct treatment with the aqueous alkali metal solution, oxygen and peroxide or by extracting the hydrocarbon with aqueous alkali-metal hydroxide solution and then regenerating the spent alkaline solution admixed with another hydrocarbon in the above-described two-phase system. Sour hydrocarbon oils specified are kerosines and gasolines. Oils such as cracked or reformed gasolines containing unsaturated compounds are preferably treated in the additional presence of an anti-oxidant. When the oils have a high sulphur content or contain H2S or aromatic mercaptans, they are preferably pretreated, e.g. with dilute aqueous alkali, to reduce the sulphur content to below 0.05 per cent. Examples describe the sweetening of straight distillation and cracked gasolines, into which various of the above-mentioned peroxides are injected, by means of oxygen and aqueous caustic potash solutions containing cresol and the results obtained using the stipulated amount of peroxide are compared with those obtained when less than 10 per cent or no peroxide is present.ALSO:Sour hydrocarbon oils are sweetened, according to one method, by oxidizing the mercaptans therein to disulphides by intimately contacting the sour oil with an aqueous alkali-metal hydroxide solution in the presence of oxygen and an amount of peroxide which is 10-40 per cent of the stoichiometric amount required to oxidize the mercaptans to disulphides; the disulphides formed dissolve in the hydrocarbon oil. Alternatively, the sour hydrocarbon oil is extracted with an aqueous alkalimetal hydroxide solution which is then separated from the resulting purified oil and is regenerated by being intimately contacted with another hydrocarbon oil, preferably a light oil, in the presence of oxygen and an amount of a peroxide which is 10-40 per cent of the stoichimetric amount required to oxidize the mercaptides in the aqueous solution being regenerated. Specified peroxides are ozone, hydrogen peroxide and various organic peroxides and hydro peroxides; the peroxides may be formed in situ in the oil before the oxidation is effected. The oxygen required may be dissolved in the hydrocarbon oil before or during its contact with the aqueous alkali. The oxygen and peroxide required may be provided by passing ozonized oxygen into the oil. The aqueous alkali solutions may contain solutizers, many of which are mentioned. The preferred solutions are 2-N or higher aqueous caustic potash or soda solution, in particular, those containing at least 2 moles of free alkali per litre, at most 54 per cent by volume of water and a phenolate which is unsubstituted or contains alkyl groups having a total of not more than 3 carbon atoms. The oil and aqueous alkali may be intimately contacted with each other by means of a centrifugal mixer or contact tower or by spraying one liquid into the other. Temperatures of 0 DEG to 80 DEG C. and atmospheric or higher pressure may be used. Sour hydrocarbon oils specified are kerosines and gasolines. Oils containing unsaturated compounds, e.g. cracked or reformed gasolines are preferably treated in the additional presence of an anti-oxidant. Oils containing H2S or aromatic mercaptans or having a high sulphur content are preferably pretreated with, e.g. dilute aqueous alkali, to reduce the sulphur content to below 0.05 per cent. Examples describe the sweetening of straight distillation or cracked gasolines by treatment with aqueous caustic potash containing cresol in presence of oxygen and various of the above-mentioned peroxides. The results obtained using the stipulated amounts of peroxides are compared with those obtained when less than 10 per cent or no peroxide is present.