Solvent extraction and supercritical water oxidation; A hybrid method for oil sludge remediation

In this research, a dual approach involving solvent extraction and supercritical water oxidation was employed to recover and enhance oil sludge. Initially, for the solvent extraction phase, experiments were performed utilizing Design Expert software to analyze the impact of temperature settings ranging from 25 to 50 °C, duration between 10 and 30 min, and a solvent-to-sludge ratio varying from 2 to 8. Additionally, the influence of using different solvents, specifically ethanol and hexane, for hydrocarbon extraction from the sludge was examined. The experimental findings indicated that the ideal conditions for solvent extraction were a temperature of 35 °C, a duration of 20 min, and a solvent-to-sludge ratio of 5.5, under which the solvents successfully separated 68 % of the petroleum hydrocarbons present in the oil sludge sample. In the subsequent phase, the supercritical water oxidation process was implemented to recover and enhance the quality of the resultant products. The experimental design was executed using response surface methodology, under the following parameters: temperature between 390 and 450 °C, duration of 30 to 90 min, a water-to-feed ratio of 1 to 5, and a hydrogen-to-feed ratio of 2 to 1. Among these variables, the water-to-feed ratio was found to have the most significant impact on the efficiency of the supercritical oxidation process. The optimal conditions were identified as a temperature of 420 °C, a duration of 60 min, and a water-to-feed ratio of 3, under which 64 % of hydrocarbon compounds were recovered. The presence of water enhances the concentration of OH radicals, thereby increasing the reaction rate, which ultimately boosts the yield of recovered products. In the final stage, the influence of various weight ratios of zeolite catalyst (5, 50, 20, 10, and 100 %) was assessed to improve product quality. The test results revealed that at a catalyst ratio of 10 %, 84 % of the products were successfully recovered. The findings of this research demonstrate that the integration of solvent extraction and supercritical catalytic oxidation with water is both effective and efficient in recovering hydrocarbons from oil sludge.