USE OF UREA FOR CLEANING USED SEMI-SYNTHETIC MOTOR OILS

During the operation of motor vehicles with gasoline or diesel internal combustion engines, motor oil is exposed to high temperatures, is constantly in contact with metals, its hydrocarbon part undergoes chemical transformations, is contaminated by wear products of metal surfaces, decomposition of additives, and residues of incomplete combustion of fuel. As a result, motor oil undergoes irreversible changes in its high-quality chemical composition and loss of operational properties. The paper describes the results of the study of the process of cleaning exhausted semi-synthetic motor oils in the presence of crystalline urea. Castrol 10W-40 oil, widely used in truck diesel engines, and ELF Evolution 700 STI oil, used in passenger car gasoline engines, were chosen as used semi-synthetic motor oils. The influence of the main factors of process control (the amount of urea, duration, and temperature) on the change in the functional properties of refined motor oils was studied. It was established that the lowest values of defective indicators (acid number, water content, ash content, content of mechanical impurities) were obtained at 140 ºС, duration of 80 min., and 5 mass. % of crystalline urea. In addition, there is a slight increase in the values of kinematic viscosity and viscosity index. The method of X-ray fluorescence analysis confirmed that the content of metals decreased in urea-treated oils compared to used ones. IR spectroscopic research demonstrated that under the established optimal conditions of the purification process with crystalline urea, the content of oxygen-containing "aging" products (aldehydes, ketones, alcohols, ethers, esters, organic acids) in purified semi-synthetic motor oils significantly decreased. It is proposed to use the process of cleaning used semi-synthetic motor oils in the presence of crystalline urea as an intermediate stage of the combined technological cycle of regeneration of used motor oils.