Lubricating oil sludge and its demulsification

The oil sludge generated from the pretreatment of the used lubricating oil re-refinery is characterized as a complex and tight water/oil emulsion. The water content varies from 38 to 77 wt%. When the water content is low, the emulsion is of water in oil type. When the water content is high, small oil droplets exist in the dispersed water phase. The oil in the sludge is not different from the oil in the raw feed based on physical and thermal analyses. Centrifuging or gravitational settlement at elevated temperature does not show significant effects on water separation. The usage of inorganic chemicals and the typical demulsification agents from oil fields does not give satisfactory results either. The ultrasonic wave shows some dehydration on some samples. The freeze and thaw method proves to be the best method with over 90% of water removed from the on sludge at the energy cost of about 0.01 US$ liter.