Re-refining of waste engine oil using ultrafiltration membrane

Waste engine oils contain impurities which are known as hazardous compounds derived from combustion, abrasion, and chemical reactions. Removal of the impurities provides a possibility of reusing waste engine oils as well as decreasing waste disposal to the environment. In this study, the hydrophobic polypropylene membrane (PP) was used for ultrafiltration (UF) of waste engine oils. Membrane performance (in terms of oil flux and impurities rejection) as a function of operating pressure (0.4-1.2 bar) and temperature (30-60 oC) was investigated. Results show that the oil flux increases with applied pressure and temperature while rejections of impurities are relatively stable. Within the range of operating conditions, the oil flux is from 0.09 to 0.19 L.m−2. h−1. The membrane can remove ash content (90–99 %), water (78–82.5 %), carbon residue (52.6–65.9 %), acidity (44.9–73.3 %), calcium (50.1–58.9 %), and zinc (28.9–43.8 %) effectively. Removal of those impurities results in the improvement of treated oil quality evidenced by the change of kinematic viscosity, density, and color. It was also observed that the filtration of waste engine oil results in increasing PP membrane wettability towards oil-(water contact angle increased from 101.4° to 102.9° and oil contact angle decreased from 48.2° to 45.3°).