Potato peel waste-derived carbon-based solid acid for the esterification of oleic acid to biodiesel

Bio-waste valorization to generate carbon-based solid acid catalysts for biodiesel production from the low-grade, highly acidic feedstocks has been a research hot spot over the last decade. In this study, an abundant bio-waste from the household kitchens, restaurants, and food processing industries, potato peel (PP), was adopted as a raw material for the production of a solid acid catalyst (SO3H-PPAC). Firstly, PP was mixed with ZnCl2 and activated at 450 °C for 1 h to obtain a porous carbon material (PPAC), which was subsequently sulfonated via concentrated sulfuric acid treatment. Various physicochemical techniques, such as XRD,
physisorption measurements, FTIR spectroscopy, and high-resolution transmission electron microscopy (HR-TEM), were used to study the structural properties of the prepared materials. The catalytic behavior of the catalyst was tested in the acid-catalyzed esterification of oleic acid with methanol for biodiesel production. The combination of the high surface area of 827.7 m2/g and high concentration of acidic active sites of 1.6 mmol/g led to a high oleic acid conversion efficiency of 97.2% at 5 wt.% SO3H-PPAC, methanol/oleic acid molar ratio of 12:1 at 80 °C after 2.5 h. Moreover, the kinetic results unveiled that the esterification reaction obeyed the pseudo-first-order kinetic model, with an activation energy of 32.9 kJ/mol. Importantly, SO3H-PPAC has satisfying recyclable features and could maintain 70 % of its initial catalytic performance in the 5th catalytic run.