Abstract:

The alkali residue wastewater has obvious irritating malodorous odour with high concentration of sulphide and organic matter，which is a kind of difficult to degrade，toxic and strongly alkaline sulphur⁃containing hazardous wastewater produced by the petroleum refining industry in the process of oil product refining.The wastewater liquid must be treated with sulphur stabilization before it can be utilized for resource use or discharged to the standard.A petrochemical plant's diesel fuel alkali residue wastewater was studied，which was strongly alkaline，with S^2- concentration as high as 24.22 g/L，and contains a small amount of SO₄^2-.The complexity of organic sulfur components was also a feature of the waste liquid，including methyl mercaptan，dimethyl disulfide，methyl ethyl disulfide and other organic sulfur compounds.In this paper，the oxidation effect of medium⁃temperature and low⁃pressure wet oxidation technology on S^2- was systematically investigated，and the complete oxidation of S^2- could be achieved，with the final oxidation product being SO₄^2-.When the temperature of wet oxidation was 60 ℃，methyl mercaptan was oxidized to dimethyl disulfide，and the heat release was intense.With the increase of temperature，organic sulfur dominated by dimethyl disulfide was deeply oxidized to sulfoxide and sulfone compounds，and finally organic sulfur existed in the waste liquid as soluble SO₄^2-.Wet oxidation of alkali residue wastewater at medium temperature and low pressure not only achieved complete oxidation of S^2- and organic sulfur，but also sulfur could be stabilized in the wastewater，and at the same time to remove irritating odour effectually and reduce toxicity，providing conditions for the recycling of alkali residue wastewater and contributing to environmental protection.

Key words: alkali residue wastewater liquid, wet oxidation, sulphur oxidation