This study aimed to evaluate and optimize a pilot-scale microreactor to convert waste cooking oil (WCO) into biodiesel using kettle limescale. Box-Behnken design was used to determine the optimum conditions for producing biodiesel. Effects of main variables including reaction temperature, catalyst concentration, and alcohol/oil volume ratio were evaluated at a constant residence time of 10 min. Based on the results of analysis of variance, the quadratic regression model had the best coefficient of determination (R2=0.9930) and adjusted coefficient of determination (R2adj.= 0.9804). After the optimization of temperature, catalyst concentration, and methanol/oil volume ratio, the residence time was optimized to achieve the maximum purity of the produced biodiesel. At a reaction temperature of 61.7 °C, catalysts concentration (oil based) of 8.87 wt %, methanol to oil volume ratio of 1.7:3, and a residence time of 15 min, we observed the optimal conditions for obtaining a maximum biodiesel purity of 93.41%.
