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ABSTRACT Used lubricating oil is generated by various machinery after extended operation. It is also referred to as spent mobile oil. Extremely hazardous waste lubricating oil is detrimental to the environment because it produces oxidative products when additives break down. Used lubricating oil is classified as a hazardous waste substance and has a negative impact on the environment. Polychlorinated biphenyls (PCBs), carcinogenic substances and other impurities make lubricating oil poisonous and pose a serious threat to human health and the environment. Re‐refining is considered the preferred technology for resource conservation, waste minimisation and reduced environmental hazards. The present study focuses on optimising the method of re‐refining waste lubricating oil. The effects of various operating parameters such as refining time, refining temperature, solvent‐to‐used oil ratio and flocculant dosage have been extensively studied to maximise the percentage recovery of lubricating oil. Optimum process parameters are (i) a refining time of 80 min, (ii) a refining temperature of 48°C, (iii) solvent‐to‐waste oil ratio of 5:1 (w/w) and (iv) a flocculant dosage of 2 g/kg of solvent; the optimum yield was found to be 75% with the solvent extraction method and 78% with the extraction–flocculation method, respectively. The purity and physico‐chemical properties of the recovered oil were thoroughly analysed using Fourier transform infrared spectroscopy and ASTM standard methods. It was concluded that refined oil can effectively reduce the ongoing oil crisis and create a clean, healthy environment.
Sarkar et al. (Mon,) studied this question.