Rerefining of used oils — a review of commercial processes

The total demand for lubricants in India is in the region of 855,000 tonnes a year. This constitutes 1.5% of total petroleum products consumption. Presently, there are three lubricant refineries in the country with a total installed capacity of 535,000 tonnes. The shortfall, of about 370,000 tonnes (approximately 45% of demand), is met through imports. In addition, there are generated 60,000–65,000 tonnes a year of base oil through rerefining of used oils. The three refineries are being expanded in order to raise base oil production to 810,000 tonnes per annum. Some other refinery projects are also under consideration and approval by the government. The current expansion programmes, together with the projected new refineries, are expected to make India self-sufficient in terms of base stock production lubricant. Overall, lubricant production in India is entirely dependent on imported lubricant-bearing crudes, and not on the indigenous crudes, which are non-lube bearing. With recent advances in engine design, together with improved lubricant quality through high-performance lubricants, the consumption, or demand rate, has been in decline or unchanging in most countries. In India, a gap still exists between production and demand of lubricants, necessitating import. Since they are a high-value, non-energy product, lubricant conservation measures are therefore essential. Interest in rerefining of used oil is increasing, with more and more emphasis on making the processes environmentally friendly. The conventional acid-clay rerefining process is environmentally unfriendly, and hence needs modification. An attempt is made in this paper to highlight various rerefining processes available. The relative merits and demerits of each process are discussed, and among the various processes, that based on molecular/high vacuum distillation is covered in detail.