Ionic Liquid Modified Macropore Resin AB-8 as an Efficient Catalyst for Biodiesel Production

In this paper, porous Brønsted acidic ionic liquid modified catalyst ILs-AB-8 was successfully synthesized by using 3 steps of Friedel–Crafts hyper-crosslinking synchronous chloromethylation, imidazlole grafting and sulfonic functionalization using macroporous polystyrene AB-8 resin as a raw material. The porous ionic liquid immobilized catalyst ILs-AB-8 exhibits a hierarchical pore structure by the coexistence of abundant macropore, mesopore, and micropore. The catalyst IL₂-AB-8 with dual Brønsted acid sites(-SO₃H acid site and p-methylbenzenesulfonic acid site), large surface area (327.19 m²/g), high ionic liquid loading amount (IEC 2.03 mmol/g) displayed excellent catalytic activity, with methyl oleate yield up to 95.65% at 338 K in 100 min. The enhanced catalytic performance of IL₂-AB-8 can be ascribed to the novel Friedel–Crafts hyper-crosslinking process in conjunction with chloromethylation, coupled with th in situ generated activating chloromethyl group incorporated onto the surface of the AB-8 carrier. The hyper-crosslinking approach also effectively transforms the macroporous AB-8 carrier into a multi-level pore structure. This work highlights that IL₂-AB-8 with high specific surface area, ionic liquid loading content, and strong covalent connection with carrier was coordinated to provide an efficient metal-free heterogeneous catalyst for biodiesel production.