High-Performance Catalysis of Cold-Rolling Sludge for the Recovery of Combustible Gas and Tar from Waste Demulsification Oil Scum

Abstract

Oil scum is a blackish gel collected from the air flotation of the oil-bearing wastewater from oil refinery plants. It commonly contains 37.5% water, 52.3% tar, and 10.2% inorganic substance. It is categorized as a regulated hazardous waste and often disposed of as an additive in cement rotary kiln. In this study, the tar in the oil scum was converted to valuable volatiles using Fe-rich cold-rolling sludge as the catalyst in the pyrolysis process. Results showed that the conversion efficiency of tar to gas reached 52.2% with the addition of cold-rolling sludge, a 73% increase from direct pyrolysis. This conversion efficiency was also higher than using other additives, for example, alumina, KOH, and dolomite. The oil scum contained 34.5% aromatics and 33.2% saturated hydrocarbons, both of which were completely converted to base oil and gas product during the pyrolysis process. The base oil contained 79.5% chain hydrocarbons, and the combustible gas had 20.6% H2, 12.8% CH4, and 48.4% C2/C4 hydrocarbons. The abundant hematite in the added cold-rolling sludge was converted to magnetite, FeO, and Fe during the pyrolysis process, and the redox cycling of Fe-oxides/element-Fe enabled the dehydrogenation of aromatics and the deoxygenation of the oxygen-containing chain hydrocarbons. As a result, the polycondensation of polycyclic aromatic hydrocarbons was effectively inhibited, and a magnetic char was generated. This work provided a promising strategy of “treating wastes with wastes” for converting oil scum to valuable gas, base oil, and magnetic char.