Influence of pyrolysis mode of waste compressor oil on the properties of the obtained products

Abstract

This work investigates the potential for recycling waste lubricants and their conversion into alternative energy resources. The study established the feasibility of recycling used compressor oil MHD-20S by low-temperature pyrolysis under two temperature regimes: a mild regime, involving slow heating of the reactor loaded with the feedstock, and a severe regime, characterized by rapid heating to the final process temperature. The main product of the process was a pyrocondensate. The obtained pyrocondensates were dark brown, low-viscosity liquid products with a characteristic odor. Under the investigated conditions, their yield did not exceed 89.9 wt.% relative to the initial feedstock. It was found that pyrocondensates produced under both temperature regimes contained a significant proportion of unsaturated hydrocarbons, as evidenced by increased iodine values. Gasoline and diesel fractions, as well as a hydrocarbon residue, were isolated from the pyrocondensates by fractional distillation. It was demonstrated that the gasoline fraction samples contained a considerable amount of paraffinic hydrocarbons and sulfur-containing compounds, which negatively affected their octane number. The diesel fractions were characterized by elevated iodine values and sulfur contents exceeding standard limits, resulting in an increased tendency toward resin formation and carbon deposition in the engine combustion chamber, as well as a significant reduction in storage stability. It was also established that unsaturated and sulfur-containing hydrocarbons were present in the fractional distillation residues of the pyrocondensates obtained from the pyrolysis of used compressor oil MHD-20S. Based on the measured kinematic viscosity values, the residue samples can be classified as Group I and Group II base petroleum oils and, after further purification, may be used as components for the formulation of plastic lubricants. The practical significance of this work lies in the development of a comprehensive approach to MHD-20S waste processing, where heavy residues, following additional purification, can serve as components for lubricating greases, while light fractions can be utilized as feedstocks for petrochemical synthesis or as alternative boiler fuels.