Acai seed ash as a novel basic heterogeneous catalyst for biodiesel synthesis: Optimization of the biodiesel production process

•Acai seed waste was used as precursor for synthesis of heterogeneous catalyst.•Potassium was the main active component responsible for high catalytic activity.•The transesterification process was optimized by response surface methodology.•98.5% ester content achieved at 12% catalyst, 18:1  M ratio at 100 °C in 1 h.•The regenerated catalyst promoted ester content >80% until the 6th cycle.