| A considerable amount of oily sludge has been generated annually in petroleum industrial,the compositions of oil sludge are very complex,the environment can be damaged and the human health can be endangered by the toxic and noxious material in oily sludge.Therefore,the oily sludge has been list as hazardous waste by every country in the world.Oily sludge contains petroleum pollutants,high petroleum hydrocarbon particularly,which can be reused as resource.Scholars at home and abroad have researched on the traditional treatment of oily sludge,such as reduction,reuse and harmless.However,there is less study supercritical extraction on oily sludge.At present,supercritical fluid extraction technology has been used for research and application on plant extracts,thus a new method of treatment of petroleum solid waste has been proposed in this paper,which is the resource and harmlessness of oily sludge has been achieved by the technology of supercritical fluid extraction.Supercritical fluid has good application and development prospects because of its unique advantage,which not only are.the value of viscosity and diffusion coefficient close to that of gas,but also the density and dissolving capacity close to the liquid.Supercritical carbon dioxide is one kind of clean,environmentally and efficient extraction solvent,therefore,supercritical carbon dioxide has been employed as solvent in this work.The supercritical extraction of oily sludge has been researched with the central composite design,four parameters,which are extraction temperature,pressure,CO2 flow rate and extraction time respectively,have been studied.Three models have been fitted and discussed which takes the residual oil yield as response value,they are linear model,two factors interaction model and quadratic polynomial model.The quadratic polynomial model has been fitted experiment data well and optimized to improve correlation coefficient,thus the residual oil yield was predicted better than the original one.The effects of independent variables have been analyzed on residual oil yield with individual factor method and the effects of two interaction factors on residual oil yield have been analyzed by the response surface.The operation parameters have been optimized and the minimum value of residual oil yield is 0.398%.The oily sludge has been analyzed by thermo gravimetric balance,the microstructure of oily sludge before and after supercritical extraction have been observed by scanning electron microscope.Meanwhile,the component of extracts which were extracted by supercritical carbon dioxide and n-hexane have been analyzed by gas chromatography mass spectrometry(GC-MS).Not only have been compared the extracts which extracted by two methods,but the petroleum hydrocarbon pollutants also have been quantitative and qualitative analyzed in oily sludge.The mathematical model of supercritical carbon dioxide extraction of oil from solid phase has been established to simulate the behavior of mass transfer in this paper.Three kinds of dynamic model of supercritical carbon dioxide extraction have been compared and the most suitable one to this research has been selected.According to the experimental condition,a series of hypothetical condition has been proposed and the equation of mathematical model has been improved.The solution of model equations have been solved by mathematical computing platform,and the physical properties parameters are needed in mathematic model have been determined experimentally and correction calculated.The rest of the parameters have been fitted by nonlinear least square method to get the overall volumetric external mass transfer coefficient and overall and the overall volumetric internal diffusion coefficient.Finally,the mathematic model has been tested statistically,which the correlation coefficient is high relatively and the result are computed by mathematic model are consistent with experimental data.The F-value of fitted curve is greater than the critical value.Therefore,the mathematical model has a good reliable. |
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