One-pot conversion Allium sativum peels into a cost-effective carbon-based heterogeneous acid catalyst for renewable biodiesel production using palm oil refining by-products

Abstract

In accordance with the demand for eco-friendly synthesis, this research aims to develop a renewable and economical heterogeneous acid catalyst sourced from garlic peels (Allium sativum bulb) through direct sulfonation, in ordre to improve biodiesel production via the esterification process, utilizing refinery by-products from palm oil as the primary raw material. A detailed characterization of the catalyst’s physicochemical and structural attributes was carried out through a variety of analytical techniques, such as SEM-EDX, XRD, BET, Boehm titration, DLS, and FT-IR. The findings showed that the catalyst featured a significant total acid density of 6.5 mmol/g with an amorphous carbon structure, which was obtained through sulfonation using sulfuric acid concentrate (18.66 mol/l) over a period of 10 h at 343 K. Moreover, the catalyst (GPASB-(OPT)-SO₃H) demonstrated a notable conversion of FFA rate of 94.4 % after 3 h of reaction, using a catalyst amount of 6 wt%, carried out at 353 K and a molar ratio of PFAD/methanol of 1:15. The esterification reaction is thermodynamically non-spontaneous and endothermic with activation energy found to be 39.02 kJ/mol. The catalyst exhibited remarkable stability, retaining its catalytic efficiency over four consecutive regeneration cycles. The biodiesel produced adhered to ASTM D-6751 specifications, confirming its high-quality output. In conclusion, the garlic peel-derived acid catalyst demonstrated exceptional performance in terms of activity, stability, and recyclability, making it a viable option for cost-effective and environmentally sustainable biodiesel production.