168 Vol. 45, No. 1 (2023) 168-177, DOI: 10.24874/ti.1411.11.22.03 Tribology in Industry www.tribology.rs Refining Used Lubricant Oils with Different Concentration Levels of Sulfuric Acid and Nonylphenol José Abisenas Alvarez-Rivera a, *, Guillermo Castañón-Nájera a , Juan Manuel Urrieta-Saltijeral b , José Ramón Laínes-Canepa a , José Roberto Hernández-Barajas a , Liliana Pampillón-González a , Carlos Mario Morales-Bautista c a Academic Division of Biological Sciences. Universidad Juárez Autónoma de Tabasco (Juárez Autonomous University of Tabasco, México). Kilómetro 0.5 Carretera Villahermosa-Cárdenas, Entronque Bosques de Saloya, Villahermosa, Tabasco, México, b Instituto Tecnológico Nacional de México (National Technological Institute of Mexico) Tabasco, México . Carretera Villahermosa-Frontera, Kilómetro 3.5 Colonia Indeco, Villahermosa, Centro, Tabasco, México, c Academic Division of Biological Sciences. Universidad Juárez Autónoma de Tabasco (Juárez Autonomous University of Tabasco, México). Carretera Cunduacán-Jalpa de Méndez kilómetro 0.5, Colonia Esmeralda. Villahermosa, Tabasco, México. Keywords: Sulfuric acid Nonylphenol Engine oils A B S T R A C T The purpose of this research was to evaluate the refining of used lubricating oils (ULOs), and their possible use as drilling fluids. 17 treatments were evaluated and sulfuric acid and nonylphenol were used as reagents at concentrations of 0.12, 0.24 and 0.36 g/mL and temperatures of 40, 60, 80 and 100 o C. AT80 and AT100 ULOs treated at 80 and 100 o C without reagents, presented an average density of 0.84 g/cm -3 , a viscosity of 76.3 and 75.3 cP, an electrical stability of 1,731.3 and 1,394.6 V and a flash point of 183 and 190 o C as higher. The ST40C1 and ST40C2 treatments, added with reagents, showed similar results to AT80 and AT100 in the evaluated variables, but they are more expensive treatments. According to the results, it is concluded that the refined ULO can be a substitute for the oil used in the formulation of oil-based drilling fluids. © 2023 Published by Faculty of Engineering * Corresponding author: Jose Abisenas Alvarez Rivera E-mail: abisenas@gmail.com Received: 28 November 2022 Revised: 3 January 2023 Accepted: 10 March 2023 1. INTRODUCTION The amount of used lubricating oils (ULOs) has been growing exponentially worldwide, with the automotive sector as one of the leading ULO sources. ULOs are generated at gas stations, garages, mechanic workshops, car dealership showrooms, and other retail companies such as, truck fleets, transportation, and construction along with public transportation and airports [1]. Nowadays, researchers are focused on quantifying the adverse environmental effects of ULOs [2]. It is of particular concern that, the RESEARCH