Improvement of the Waste-Oil Vacuum-Distillation Recycling by Continuous Extraction with Dense Propane

Dense propane has been used as a solvent for the continuous countercurrent extraction of base oil from waste lubricant oil. The aim of the work has been to identify the best processing conditions to separate base oil suitable for the formulation of new lubricants, avoiding the coextration of waste-oil impurities such us oxidation products and metallic compounds. Experiments have been performed during 6 h in a 1.7 m extraction column operated countercurrently at 30 kg/cm 2 and using an oil flow rate of 0.5 g/min. The effects of operation variables such us solvent/used oil ratio, column packing, and column temperature gradient have been investigated. From experimental results obtained, the best operating conditions have been determined: solvent/used oil ratio = 5 g/g, column packing = Raschig rings, and column temperature varying from 80 °C (at the column bottom) to 95 °C (at the column top). Finally, the propane-extracted oil at optimum conditions was vacuum-distilled and found to be comparable to a SN-150 virgin oil.