Synthesis of Novel Hypercrosslinked Polymer-Based Solid Acids and the Catalytic Activities for Biodiesel Synthesis

A novel sulfonated hypercrosslinked aromatic polymer (HCP-SO 3 H) was synthesized through direct condensation of single 1,4-dichloroxylene followed by controlled sulfonation. The rigid aromatic architecture of the porous polymeric material provided abundant anchoring sites for sulfonic groups, endowing the acid catalyst with high acid density (2.6 mmol/g). Characterization revealed an exceptionally high specific surface area (555 m 2 /g) that significantly enhanced substrate accessibility and mass transfer kinetics during catalytic reactions. The water contact angle of 104° indicated the high hydrophobicity of the catalyst. When evaluated in biodiesel production via esterification and integrated esterification–transesterification, HCP-SO 3 H demonstrated remarkable catalytic performance: achieving >98% conversion efficiency for both pure oleic acid and waste frying oil feedstock. The catalyst maintained high activity (>97%) over nine reaction cycles without significant structural degradation. Mechanistic studies identified four critical performance factors: Hierarchical porosity facilitating molecular diffusion, hydrophobicity separated polar by-product from active sites, high-density acid sites ensuring rapid reaction kinetics, andrigid conjugated framework preventing active site leaching. These synergistic characteristics positioned HCP-SO 3 H as a potential heterogeneous catalyst for industrial-scale biofuel production, addressing key challenges in catalyst recyclability and feedstock versatility. Graphical The novel hydrophobic hypercrosslinked polymer based solid acid showed high activity for biodiesel synthesis from both pure oleic acid and waste frying oil feedstock.