Biodiesel production from supernatant waste cooking oil by a simple one-step technique: calorific value optimization using response surface methodology (RSM) based on D-optimal design

Present work studied the use of waste cooking oil (WCO) from catering facilities in Iran, to produce biodiesel under optimal conditions, using a novel modeling approach. Response surface methodology based on D-optimal design, was used to maximize biodiesel calorific value. Collected WCO samples were centrifuged leading to a supernatant phase (S-WCO), used to produce biodiesel, and a bottom phase (B-WCO). According to the modeling results, optimal conditions for maximum calorific value (9500.74 kcal/kg) were determined as 50 °C, 45 min, methanol to S-WCO ratio 10:1, and 0.56 wt% catalyst. Regression analysis of experimental data founded a significant relationship between methanol to oil ratio, catalyst and temperature, with the calorific value in a 95% confidence level. Based on the results of ANOVA´s analysis, it can be assured that the proposed quadratic model is suitable for the optimization of biodiesel calorific values. Physicochemical properties of the obtained biodiesel were consistent with fuel specifications of German, American or European standards. Moreover, considering that B-WCO shows an excellent potential for production of solid alcohol, it can be concluded that WCOs are a valuable, sustainable, accessible and safe alternative for the development of large-scale biorefinery facilities that may help reducing environmental and energy supply concerns.