Insight into water-enhanced CO₂ extraction in the treatment of oily sludge

Oily sludge produced in the petroleum industry is a hazardous waste without treatment. Oil recovery from the oily sludge can reduce environmental pollution and make recycling resources. Water-enhanced CO2 extraction (WECE) is a novel method which could recycle oil from oily sludge efficiently, which has been proposed by our group. Although the operating conditions of WECE method had been determined by a single factor test with small experimental range in our previous work, which ignored the interaction between the other factors. This is an ideal condition which is uncertain for its actual application. In this work, correlational research for WECE method was further performed by the orthogonal test to obtain comprehensive analysis of various factors. All the experiments are tested in the visible autoclave, from which the macro morphology of treating oily sludge can be observed directly. WECE method is proved to have a better oil recovery than supercritical CO2 and liquid CO2 extraction at low temperature and middle pressure. In the experimental range which is larger than previous study, CO2 pressure and system temperature are confirmed the main controlling factors of WECE which is 3 MPa and 60 degrees C. From the variance results of orthogonal test, stirring time has little effect on oil recovery which could have discretionary consideration of reducing time to increase efficiency. Additionally, WECE method can dispose the oily sludge with high watercut directly. It could avoid drying process which is more economic and efficient than the traditional methods. WECE method has a potential application in the petroleum company.