Alkaline treatment of garlic peel as a key strategy for synthesis a high performance catalyst for the efficient biodiesel production

The effective conversion of low-cost lignocellulosic residues using active acid catalysts requires a pretreatment strategy that can disrupt their dense structural matrix while enhancing the accessibility of reactive sites. In this context, this study evaluated alkaline treatment as a strategy for improving the catalytic properties derived from garlic peel for biodiesel synthesis. The findings indicate that the optimized alkaline conditions (6 h, 70 °C, 1 mol/l) promoted the dissolution of hemicellulose and partial degradation of lignin, thereby increasing porosity and facilitating the formation of more accessible acidic sites during the subsequent acid functionalization step. Under the optimized reaction parameters (5 wt% catalyst dosage, 80 °C, 3 h, and PFAD-to-methanol ratio of 1:15), the catalyst exhibited a maximum PFAD conversion of 98.5 %. The process followed pseudo-first-order kinetics, whereas the thermodynamic parameters indicated the non-spontaneous nature of the reaction. Also, the catalyst was extremely stable as it retained its activity over five cycles, and the biodiesel produced complied with all the requirements according to the ASTM D-6751 standards. Consequently, the results of this study demonstrate that alkaline treatment improves the activity of the catalyst derived from garlic peel for renewable biodiesel production. • The alkaline treatment of garlic peel-derived catalysts enhances catalytic activity. • The maximum conversion of 98.5 % was obtained under optimized conditions. • The esterification reaction is endothermic, endergonic, and non-spontaneous. • The biodiesel produced from palm fatty acid distillate satisfied ASTM D6751 . • The catalyst was successfully recycled for five successive cycles.