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

Abstract

In the present study, the catalytic activity of acai seed ash (ASA) was investigated for the synthesis of biodiesel from the methyl transesterification of soybean oil. Acai seeds were calcined at different temperatures (500–900 °C) and times (2–5 h) to determine the best catalyst synthesis conditions. The catalyst obtained by calcination at 800 °C for 4 h was characterized by thermogravimetric analysis (TG-DTG), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS), and alkalinity. Subsequently, response surface methodology based on a face-centered composite design (FCCD 24) was applied to examine the best conditions to conduct the transesterification reaction. The optimal conditions were: temperature of 100 °C, molar ratio alcohol:oil of 18:1, catalyst concentration of 12.0% (w/w), and reaction time of 1 h, yielding biodiesel with an ester content of 98.5 ± 0.21%. The catalyst characterization showed that its catalytic activity is due to the high metal oxide content and carbonates with basic surface sites, making them highly efficient towards biodiesel production. The reuse of the catalyst showed that its catalytic activity resulted in an ester content above 92.5% in the first two reaction cycles. After the regeneration process, the catalyst yielded biodiesel with an ester content above 80.0% during four more reaction cycles. The production of a catalyst from acai seeds has several advantages, namely being obtained from widely available biomass waste, being low cost, and being easily synthesized, making it a sustainable and efficient catalyst for biodiesel production.