Application of calcined waste cupuaçu (Theobroma grandiflorum) seeds as a low-cost solid catalyst in soybean oil ethanolysis: Statistical optimization

Abstract In this work, waste cupuacu seeds were calcined for 4 h at 800 °C and evaluated as a heterogeneous catalyst for the biodiesel synthesis. The catalyst (CCS) was characterized by X-ray powder diffraction (XRD), wavelength dispersive x-ray fluorescence (WDXRF), Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric and differential thermal analysis (TG-DTA) and soluble alkalinity. The catalytic activity was evaluated by CCS-catalyzed ethanolysis of soybean oil and the process was optimized using response surface methodology (RSM) and analysis of variance (ANOVA). The significance of the different process parameters and their combined effects were established through a central composite design (CCD) and the optimum process (catalyst loading of 10% (w/w) relative to oil mass, reaction time 8 h, ethanol:oil molar ratio 10:1 and temperature 80 °C) resulted in a conversion of 98.36% with good agreement with predicted conversion, 97%. The catalyst was recycled, maintaining its great catalytic activity and resulting in conversions close to 98% in the first two cycles. The high potential of CCS as a catalyst for biodiesel production was demonstrated.