Iranian Journal of Oil and Gas Science and Technology

Abstract In this study, acid oil, which is a by-product of oil refinery waste was used for acid-catalyzed esterification to produce biodiesel. The reaction variables were methanol: acid oil molar ratio (1:1, 5:1, and 10:1), catalyst concentration (1%, 2%, and 3%), and reaction time (5, 30, and 60 min). Conversion yield, mass yield, free fatty acid (FFA) content, and physical properties (viscosity, density, refractive index, color attributes) of all the biodiesel samples were investigated. With increasing the methanol: acid oil molar ratio, catalyst concentration, and time, conversion yield and density increased, while free fatty acid content, viscosity and refractive index decreased, displaying an asymptotic trend toward equilibrium. At methanol: acid oil molar ratio of 10:1, catalyst concentration of 3%, and reaction time of 60 min, a near-maximum conversion yield of 95.3% was achieved. These conditions were considered optimum practical conditions, balancing biodiesel yield with operational and economic feasibility. Final yield of produced biodiesel at the practical optimum condition was 84.25%, which confirms that acid oil is a suitable feedstock for biodiesel production.