Thermal Cracking of Used Lubricating Oil to Produce Fuel Fractions: A Laboratory Investigation in Kaduna State

Improper disposal of used lubricating oil by automotive workshops in Kaduna State, North West Nigeria, contributes to soil and groundwater contamination across urban and peri-urban areas. This study investigates the thermal cracking of used lubricating oil collected from automobile workshops in Kaduna Central as a waste valorisation and fuel recovery strategy. Oil samples were filtered, dehydrated, and subjected to thermal cracking in a laboratory-scale batch reactor at temperatures ranging from 350 to 500 degrees Celsius at atmospheric pressure, with residence times between 30 and 90 minutes. Product fractions, including light naphtha, kerosene, gas oil, and residue, were collected, weighed, and characterised for density, viscosity, flash point, distillation profile, sulphur content, and calorific value in accordance with ASTM standards. Cracking at 450 degrees Celsius for 60 minutes yielded the highest liquid product recovery of 71.4 weight percent, with the kerosene fraction constituting 28.3% and the gas oil fraction 31.7% of total liquid products. Flash point and calorific values of recovered fractions were within the reference ranges for commercial kerosene and automotive gas oil, though sulphur content marginally exceeded EN 590 limits. The study provides evidence that thermal cracking is a feasible route for re-refining used lubricating oil generated in Kaduna State, with potential for small-scale commercial implementation. Keywords: used lubricating oil, thermal cracking, fuel fractions, re-refining, Kaduna State