A continuous high-efficient demetallization strategy for used lubricating oils resource utilization

Resource utilization of used lubricating oils (ULO) has attracted a great deal of attention over the last few decades, but remains a huge challenge. Hydrogenation has been used as an environmentally friendly ULO regeneration process. In this research, a novel high-efficient continuous process based on thermal demetallization has been proposed to solve the critical problem that high metal content limits the regeneration hydrogenation process of ULO. Metal removal rate can reach 99.2%. At the same time, a reaction kinetic model of demetallization has been established. The demetallization products which have been rarely identified using experimental methods, have been studied using FT-IR and XPS. Results estimated that the pyrolysis demetallization process is accomplished by the transformation of the additives in ULO into sludge and carbonaceous deposits. To understand the demetallization pathway, a simulation of the carbon deposition process has been carried out using tubing bomb experiment. SEM of the carbon deposit products was consistent with the results obtained for the demetallization residues. Finally, distillation process analysis of the ULO thermal demetallization samples obtained at the highest temperature verified that heating has little effect on the basic properties of lubricant base oil, which further verifies the feasibility of the method.