Effects of Temperature and Potassium Compounds on the Transformation Behavior of Sulfur during Pyrolysis of Oily Sludge

Sulfur compounds are one of the most concerning pollutants in the petroleum industry. As a potential energy resource with high sulfur content, oily sludge has received increasing attention, yet little effort has been made to characterize the behavior of sulfur compounds during utilization. In this paper, sulfur compounds in the raw oily sludge collected from a crude oil tank were identified, and influences of temperature and potassium compounds (KC1 and KOH) on the transformation behavior of sulfur were investigated during the pyrolysis. Sulfur species retained in the solid residues were analyzed by X-ray photoelectron spectroscopy. Possible sulfur-participating reactions during pyrolysis were discussed. Results showed that inorganic sulfur was mainly presented in the form of sulfate in solid particles, and organic sulfur was presented in the oil phase. During pyrolysis, H2S was released due to the decomposition of aliphatic and aromatic sulfurs. The emission of H2S can be promoted by 100% from 350 to 450 degrees C, and this value was further increased by 16.7% under 450 degrees C in the presence of KCl. On the contrary, the addition of KOH can inhibit the release of H2S by 75%, and metal sulfide was observed in the solid residues, implying the conversion of organic sulfur to inorganic sulfur during pyrolysis. The sulfur remaining in the solid residues after pyrolysis was mainly in the forms of thiophenes and sulfate. With the addition of KOH, the relative content of thiophenes declined from 97.1% to 4.3% under 550 degrees C; at the same time, the sulfur retention in the solid residues was increased by 39.5%, while the sulfur content of the oil product was reduced by 16.2%. The mass balance of sulfur can reach up to 98% except in the case of KOH, indicating other sulfur-containing gases, such as COS, may be generated during pyrolysis. Upper results can be used for guiding the desulfurization of oily sludge during treatment.