Agro-industrial residue of Pouteria sapota peels as a green heterogeneous catalyst to produce biodiesel from soybean and sunflower oils

We report the use of ash from the agro-industrial waste of Pouteria sapota peels as a reusable heterogeneous catalyst to produce biodiesel from soybean and sunflower oils. The heterogeneous catalyst was prepared by activating raw Pouteria sapota peel powder at 500 °C for 2 h. The physicochemical and structural properties of the ash were evaluated by SEM-EDS, XRD, FTIR, BET analyses, and its basicity was determined through acid-base titration. The good activity of the ash-based catalyst was attributed mainly to the presence of potassium chloride (KCl), a specific surface area of 1.432 m2 g−1, and its high basicity of 9.069 mmol g−1. A maximum conversion yield of 92% was achieved for both the oils under optimized reaction conditions. For the soybean and sunflower oils, the optimum parameters were 3 wt% and 5 wt% of catalyst charge, methanol to oil molar ratio of 6:1 and 9:1, and a reaction time of 240 min, respectively. The reactions were performed at 65 °C under stirring at 400 rpm. The physicochemical properties of soybean and sunflower biodiesel satisfactorily complied with the International Standard of the American Society for Testing and Materials (ASTM-D6751) and the European Standardization (EN-14214).