Сoagulation purification of used motor oils

Abstract

Waste petroleum oils are toxic compounds with low biodegradability and pose a significant environmental hazard. Their release into soils and water bodies causes particularly severe ecological damage. To restore the properties of used mineral motor oils, various technological operations based on physical, chemical, and physicochemical processes are applied to remove degradation products and contaminants. However, the most challenging for regeneration are water-contaminated used oils (oil emulsions), which contain substantial amounts of water or aqueous solutions of cooling mixtures that enter the oils during emergency situations. The difficulty in regenerating such oils arises from the fact that the water present inhibits physical purification methods – such as filtration, settling, sedimentation, and dehydration by atmospheric-vacuum distillation – due to the high stability of water – oil emulsions. The study examined the coagulation behavior of used mineral motor oil in the presence of several inexpensive and commercially available coagulants, including starch, carboxymethylcellulose, sodium laureth sulfate, and cocamidopropyl betaine. The effect of the type and dosage of these coagulants on the operational properties of the purified oil was determined. The application of 10 wt.% starch at 80 °C for 30 min. resulted in complete removal of emulsified water from the waste oil, decreased the concentration of solid impurities, and slightly improved its viscosity-temperature characteristics. The incorporation of carboxymethylcellulose in the coagulation process also enabled complete removal of emulsified water, improved viscosity-temperature properties, reduced the amount of solid impurities, and lowered the acid number of the oil. In contrast, achieving the desired level of coagulation using sodium laureth sulfate required the addition of more than 20 wt.%. It was further demonstrated that cocamidopropyl betaine, used at a dosage of 10 wt.%, provided nearly complete removal of emulsified water, slightly reduced solid impurities, and improved viscosity - temperature properties. However, at a fixed dosage of cocamidopropyl betaine, the acid number of the refined motor oil increased. The effective performance of the selected coagulants in purifying used mineral motor oil was confirmed by both experimental results and IR spectroscopic analysis. The dehydrated and partially purified oil should subsequently undergo combined regeneration methods to achieve complete restoration of its operational properties.