Stable poly (ionic liquid) with unique crosslinked microsphere structure as efficient catalyst for transesterification of soapberry oil to biodiesel

Usually, traditional poly (ionic liquid)s are prepared to nanoparticles with high surface areas for achieving a quasi-homogeneous reaction system. In this work, a novel poly (ionic liquid) P(VB-VS)HSO4, synthesized by simply using ionic liquids immobilized on the 1-vinylimidazole-based crosslinked copolymer microsphere, was used as heterogeneous catalyst for transesterification of a novel non-edible feedstock soapberry oil to biodiesel. The structure, thermal stability and wetting property characteristics of the crosslinked copolymer microsphere particles and poly (ionic liquid) microspheres were investigated. The results indicated that ionic liquids were successfully functionalized on crosslinked copolymer microsphere, and P(VB-VS)HSO4 possessed high surface areas (100.1 m(2)/g), abundant meso-macropores (with diameter of similar to 18.9 nm), good mechanical strength (81 N) and superior thermal stability. Benefiting from the unique structure features, these poly (ionic liquid) micro spheres manifested excellent catalytic performance for transesterification of soapberry oil with methanol. A maximum fatty acid methyl esters (FAMEs) yield of 95.2% could be obtained under the response surface methodology (RSM) optimized conditions of 8.0 h reaction time, 29.1 methanol to oil molar ratio, and 8.7 wt% catalyst amount. Impressively, it was also efficient for the esterification of oleic acid, giving methyl oleate yield of 97.5%. Catalytic tests exhibited that P(VB-VS)HSO4 presented high catalytic activity and good reusability in comparison with traditional acid catalysts. The main physicochemical of the obtained soapberry biodiesel met the biodiesel standard ASTM D6751. Therefore, this work provides a cheap and facile route to the synthesis of size-controlled poly (ionic liquid) microspheres (the diameter of the catalyst was about 500 pm) for catalyzing the production of clean biofuels.