Optimization of Tunisian Olive Pomace Oil Esterification Using Response Surface Methodology

Abstract

Several countries around the world are interested in the valorization of agricultural waste. Olive pomace oil is claimed to be a promising feedstock for biodiesel production. Alkaline transesterification is the most used method for biodiesel production, but the high amount of free fatty acids in feedstock prevents its occurrence. A pretreatment step, which is an acid esterification reaction, is necessary for the reduction of free fatty acids. The main purpose of this work is to optimize experimentally the olive pomace oil esterification using Response Surface Methodology (RSM) combined with the Central Composite Design (CCD). RSM was employed to study the relationships of reaction time, reaction temperature, methanol to oil molar ratio and catalyst concentration on olive pomace oil acidity. RSM predicted optimal conditions for esterification reaction. The oil acidity was reduced from 15 to 0.8 mg KOH g−1 with methanol to oil molar ratio 10.5:1, sulfuric acid 2.5%, reaction temperature 70 °C and reaction time 90 min. The quadratic term of temperature and catalyst concentration were the most significant effects while reaction time was not significant.