Statistical optimization of biodiesel production from waste cooking oil using CaO as catalyst in a Robinson-Mahoney type reactor

This study presents a statistical optimization conducted with operating variables affecting the biodiesel production using calcium oxide (CaO, industrial grade) as heterogeneous catalyst, and waste cooking oil as triglyceride source. The experiments are carried out in a commercial Robinson-Mahoney reactor (600 cm³) using a fixed catalytic basket to analyze the advantages (e.g. optimal contact between phases, facile catalyst recovery, heat transfer) and challenges of this design upon the establishing of a bench-scale transesterification process. As a pretreatment, the catalyst was calcined at 700 °C for 2 h. A Box-Behnken design (BBD) is used to account for the catalyst dosage (3,6 and 9 wt%), particle size (1.18, 1.41 and 2 mm) and the methanol-oil molar ratio (6, 9 and 12), at fixed temperature of 60 °C, stirring of 700 rpm and reaction time of 2 h. Reaction conversions greater than 98.5% w/w of triglycerides into methyl esters were achieved for the optimized conditions estimated through the BBD at 8.75% w/w catalyst dosage, 2 mm of particle size and 8.72:1 of methanol-oil molar ratio.