Response surface optimization of biodiesel synthesis over a novel biochar-based heterogeneous catalyst from cultivated (Musa sapientum) banana peels

In this work, response surface methodology (RSM) was utilized to optimize the biodiesel yield of the transesterification reaction. A novel solid carbon-supported potassium hydroxide catalyst derived from the pyrolysis of cultivated banana (Musa sapientum) peels and potassium carbonate (K₂CO₃) was used as the catalyst for biodiesel production. A five-level (− 2, − 1, 0, + 1, and + 2) RSM with a four-factor central composite design of independent variable factors (methanol to palm oil molar ratio (6:1–18:1), catalyst loading (3–7 wt.%), reaction time (30–150 min), and reaction temperature (50–70 °C)) were randomly setup using the Design of Experiment program. The 30 wt.% K₂CO₃ catalyst calcined at 600 °C under atmosphere pressure exhibited the highest catalytic activity, since the pyrolysis ash was rich in K that formed a basic heterogeneous catalyst. Within the range of selected operating conditions, the optimized methanol:oil molar ratio, catalyst loading, reaction time, and reaction temperature were found to be 15:1, 4 wt.%, 120 min, and 65 °C, respectively, to give a biodiesel yield of 99.16%. The actual biodiesel yield of 98.91% was obtained under the predicted optimal conditions. The high R² (96.76%) and R²_adj (92.97%) values indicated that the fitted model showed a good agreement with the predicted and actual biodiesel yield.