GB847289A - Recovery of hydrocarbons from spent caustic - Google Patents

Abstract

Hydrocarbons are obtained from acidic organic material dissolved as salts in spent aqueous caustic solution from the treatment of petroleum naphtha by recovering the acidic material as a water-insoluble oil and subjecting this to catalytic hydrogenation to obtain hydrocarbons. The acidic materials are naphthenic acid, phenols, thiophenols and mercaptans. The mercaptides in the caustic solution can be removed by boiling, steaming or oxidation to convert the mercaptides to insoluble disulphides. Preferably, however, all materials are liberated together by acidification with SO2, CO2, flue gas or a mineral acid preferably sulphuric. The gases can be used at 100-200 DEG F. and atmospheric pressure; if steam is also used the liberated materials are stripped overhead. Temperatures of 70-130 DEG F. and pressures of 200-500 p.s.i.g. are more effective for the naphthenic acids. Mineral acids above 0,1 N can be used at 70-150 DEG F. The hydrogenation is performed with catalysts normally used in hydrofining, e.g. 5-15% molybdena on alumina, mixtures of 2-6% cobalt oxide and 6-15% molybdena or an equivalent amount of cobalt molybdate on alumina, nickel tungsten sulphide or molybdenum sulphide. Preferred conditions are similar to those used in hydrofining operations, viz., 500-750 DEG F. p 100-1000 p.s.i.g., 0,1-16 vol./vol./hr., with 200-3500 SCF of hydrogen per barrel, the hydrogen consumption being 10-1000 SCF per barrel. In an example spent caustic from the caustic treatment of a heavy catalytic naphtha and containing 23 volume per cent of acid oil was neutralised and the acid oil separated. Mercaptans were not present but were added to demonstrate that they are also effectively handled. The oil (25 parts by volume) was diluted with a hydrofined naphtha (octane No. 46,1) (75 parts) and the mixture hydrofined over a cobalt molybdate-alumina catalyst at 650 DEG F., 400 p.s.i.g., 1 vol./vol./hr. with 1500 SCF of hydrogen per barrel to give a product containing 0,02 wt. per cent sulphur and 0,05 wt. per cent phenols with an octane number of 57,5. This represents a conversion of 99% of sulphur compounds and 99,9% of phenols to hydrocarbons.