Transesterification of waste cooking oil to biodiesel by walnut shell/sawdust as a novel, low-cost and green heterogeneous catalyst: Optimization via RSM and ANN

Walnut shell/sawdust catalyst was synthesized through a pyrolysis process using agricultural wastes and then utilized as a novel and cheap catalyst to generate biodiesel from waste cooking oils (WCO). XRD, FT-IR, TGA, SEM, and BET analyses were conducted to appraise the catalyst properties. Also, GC analysis was employed to find the fatty acid compounds in WCO. Besides, artificial neural network (ANN) and response surface methodology (RSM) were utilized to determine the optimal conditions. According to the outcomes, there is little difference between the laboratory data, RSM approach, and ANN approach. In optimized conditions, the utmost biodiesel yield was 92.25 ± 0.1%, which was attained at WCO to methanol molar ratio of 1:10.31, catalyst concentration of 9.76 ± 0.02 wt%, ultrasonic time of 30.14 ± 0.01 min, and temperature of 56.58 ± 1 °C. Also, the recyclability of the catalyst indicated that it can be used in 5 reuse steps without a significant decline in its yield. Moreover, the kinetics and thermodynamics of the transesterification process demonstrated that the reaction is endothermic and non-spontaneous. The produced biodiesel is characterized through HNMR and FTIR analyses. Furthermore, investigating the physical features of WCO-derived biodiesel indicated that they are in the ASTM D6751 standard range. The outcomes illustrated that utilizing WCO as feedstock and walnut shell/sawdust as a heterogeneous catalyst for biodiesel generation is a cost-effective and promising oil-recycling approach.