Highly durable superhydrophobic activated biochar catalyst for biodiesel synthesis: process optimization and economic feasibility analysis

Abstract

The rational design of superhydrophobic solid acid catalysts with enhanced chemical stability is critical for overcoming water-induced deactivation in biodiesel synthesis. Herein, we developed a novel etherified sulfonic acid-functionalized activated biochar catalyst (ESAB@PhSO₃H) for efficient conversion of non-edible feedstock, Jatropha curcas oil to biodiesel. The strategy overcomes hydrolytic instability by incorporating chemically resilient ether bonds that prevent alkyl chain detachment in an acidic environment while maintaining remarkable surface hydrophobicity with a water contact angle of 167.6°. The catalyst demonstrated a high surface area (1256 m² g⁻¹) and strong acid density (6.1 mmol g⁻¹), achieving a maximal biodiesel yield of 99.2% under optimal conditions (methanol-to-oil molar ratio of 14.07 : 1, catalyst loading of 6.14 wt% with respect to mass of oil, reaction temperature of 78.02 °C and time of 41.8 min) employing Response Surface Methodology based on a Central Composite Design (RSM-CCD) approach. In addition, the ESAB@PhSO₃H catalyst exhibited exceptional durability, with excellent catalytic activity (89.6 ± 0.3% biodiesel yield) even after ten cycles of reuse with negligible loss of hydrophobicity. Life Cycle Cost Analysis (LCCA) estimated the biodiesel production cost to be $0.374 per litre. This approach highlights the potential of such superhydrophobic acid catalysts for efficient and economically viable biodiesel production at a commercial scale.