re-refining of used lubricating oil by silica sulfuric acid (ssa)

used or waste oil, as its name implies is any petroleum-based or synthetic oil that has been used for different applications1,2. during normal use, impurities such as dirt, metal scrapings, water or chemicals can get mixed in with the oil or be generated in it due to thermal degradation or oxidation. the oil quality gradually decreases to a level that the used oil should be replaced by a new one3. also the polyaromatic hydrocarbons (pahs) will be formed during combustions in petrol engines and accumulate in lubricates over time. pahs are well known as carcinogens. disposing the used oil off in nature creates an intense dangerous pollution. therefore, recycling and refining waste to virgin lubricating oil, may be a suitable solution for protecting the environment from hazardous waste. but by proper recovery and refinement of it, a lot of valuable product can be obtained. this article studies one of the best methods of used oil re-refining and comparing its product specifications with those of virgin base oil. some of re-refining methods produce pollutants which are not less environmentally harmful than the used oil itself such as sulfuric acid method of re-refining which produce acid sludge. here we wish to report a convenient method for re-refining processes in order to re-refining the used or waste lubricating oils using silica sulfuric acid under heterogeneous condition. the silica sulfuric acid would be a superior proton source comparing to the all of the reported acidic solid supports such as polystyrene sulfonic acid. the physico-chemical properties of the product were determined by the instrumental analytical techniques such as atomic absorbsion and ft-ir spectroscopy, refractometer, viscometer and other techniques. the proposed method of re-refining produces high quality re-refined oil rapidly and economically.