Optimization of Biodiesel Yield and Cost Analysis from Waste Cooking Oil Using Box–Behnken Design with TiO2–ZnO-Based Nano-catalyst

The present work deals with the optimization of waste cooking oil biodiesel yield (WCOBD) and its preparation cost with the help of Box–Behnken design (BBD) using response surface methodology (RSM) in design expert software. Initially, TiO₂–ZnO (nanocatalyst) was prepared with the help of the sol–gel method and ratio of TiO₂–ZnO was optimized by single parameter study. The doping of ZnO over TiO₂ surface was studied by FTIR, XRD, SEM, and EDAX analysis. ANOVA suggests the quadratic model is closely fitted for both biodiesel yield and biodiesel cost. The value of adjusted and predicted R² was found to be 0.9309 and 0.8465 for biodiesel yield. While the value of adjusted and predicted R² was found to be 0.9313 and 0.8472 for biodiesel cost. The maximum actual and predicted yield of 88% was obtained at catalyst dose: 2.5 g/l; methanol: 50 ml; waste cooking oil (WCO): 50 ml; time: 120 min, and temperature: 65 °C. The % error between actual and predicted biodiesel varies in the range of −7.90–7.19%. The minimum actual and predicted WCOBD cost was found to be INR 47.29/l and INR 44.68/l with % error in the range of −19.56–13.87% at catalyst dose: 2.5 g/l; methanol: 25 ml; waste cooking oil (WCO): 75 ml; time: 120 min, and temperature: 65 °C, respectively. Overall, the model used to predict the waste cooking oil biodiesel yield, and its cost is closely fitted with the actual result.