Synthesis of novel hypercrosslinked polymer-based solid acids with ionic liquid moiety and the catalytic activities for biodiesel synthesis

The novel hypercrosslinked polymer-based solid acid with ionic liquid moiety was synthesized via the phosphonium quaternization of triphenylphosphine and 4,4’-bis(chloromethyl)-1,1’-biphenyl (BCMBP), polycondensation, and sulfonation. The polymer owned a rigid aromatic framework, which provided sufficient sulfonation sites. The hypercrosslinked structure assured the high stability and surface area (574 m2/g) of the solid acid. The ionic liquid moiety in the polymer provided the special active sites, with free coordinating anions, which made the active sites quite accessible to reactants. A novel hypercrosslinked porous polymer-based solid acid with ionic liquid moiety showed high activity for the biodiesel synthesis from the esterification of oleic acid (98.8% conversion) and integrated esterification−transesterification of waste oil (99.2% total yield), respectively. The novel solid acid can be recycled 10 times with little decrease in activity (from 99.2% to 97.7%). The ionic liquid moiety, high surface area, high acidity (3.1 mmol/g), and the rigid aromatic framework were the key factors for the high activities, which made the novel solid acid a promising candidate in industrial applications.