The Treatment Of Oil Shale Sludge Using Solvent Extraction And Thermo-chemistry

Oil shale sludge is a kind of semi-solid waste generated during the oil shaleretorting process and with a content of water, oil and sludge and is a by-productproduced in petroleum production. Oil shale sludge is hazardous to environments.The recovery of shale oil from oil shale sludge could both reduce environmentalpollution and reclaim secondary energy source. This paper introduces varioussludge treatments, draws a comparison among the pros and cons of these treatments,and finally chooses the combination of thermo-chemistry and solvent extraction forthe treatment of oil shale sludge, to recover shale oil. This is in accordance with themodern notion of comprehensive sludge treatment. The research highlights of thisproject include the determination of optimum washing condition, the comparisonbetween different solvent extractions, the interaction effect of two methods, and theanalysis of various extract components.This work sampled the oil shale sludge collected from shale oil refinery locatedin Huadian City. Three approaches, including solvent extraction, thermo-chemistryand the combination of the former two methods, were used for the treatment ofsludge, to reclaim shale oil. For solvent extraction alone, three organic solvents,including N-methyl pyrrolidone-CS2(NMP-CS2), Tetrahydrofuran (THF) andethanol (EA) were used to extract sludge. Results showed that EA achieved thehighest extraction yield,89.53%. SEM analysis showed that the remaining solidupon EA extraction was associated with completely dispersed particles structure,indicative of the good separation between oil, solid and water. GC-MS analysisshowed that THF was more suitable for extracting heavy hydrocarbons. Forthermo-chemistry alone, the determined optimum washing condition was the onewith the stirring rate of250rpm, the reaction temperature of80℃, the liquid-solidmass ratio of8:1, the duration of30min and the concentration of6g/L. Under thiscondition, SDS (surfactant sodium dodecyl sulfate, anionic surfactant) and OP-10 (non-ionic surfactant) could achieve residual oil rates of29.6%and29.83%,respectively. For combined treatment, first the sludge was washed with surfactantsof SDS and OP-10under the optimum washing condition, and then the residueswere extracted using four solvents, including methyl ethyl ketone (MEK),petroleum ether (PE), dichloromethane (DCM) and EA, respectively. Resultsshowed that EA is still the best-performing solvent and that solvent extractionperformed better than thermo-chemistry in oil removal. GC-MS analysis showedthat the extracts mainly contained aliphatic hydrocarbons continuously ranging fromC11to C35. SDS washing facilitated the following extraction process. SDS washingcombined with different solvent extractions could achieve better oil removal effectsthan individual methods. The process of surfactants SDS and OP-10washingenhanced the leaching behaviors of light hydrocarbons in the following MEK andDCM extraction processes. The extracts of individual and combined treatmentswere mainly straight chain hydrocarbons with a high heating value and lowerviscosity. Thus the extracts could be better applied to industrial purposes to turn outeconomic benefits if they underwent certain process to break the long-chainstructures.