Magnetic Material Grafted Poly(phosphotungstate-based acidic ionic liquid) As Efficient and Recyclable Catalyst for Esterification of Oleic Acid

A magnetically recyclable catalyst was prepared by embedding magnetic nanoparticle in poly(phosphotungstate-based ionic liquid) matrix. The obtained hybrid material was characterized by XRD, FT-IR, SEM, TEM, TGA, and VSM. The results indicated that Fe₃O₄ was successfully implanted in multilayer poly(ionic liquid), and the catalyst possessed open active sites (see SEM) to reactants and a high magnetization value. The combination of poly(ionic liquid) matrix with magnetic nanoparticle enhanced the structure stability and favored the separation performance. Esterification of oleic acid with ethanol was conducted in the presence of prepared catalyst, and the Box-Behnken response surface methodology was applied for maximizing the oleic acid conversion by optimizing process variables at 90 °C. Under the optimum conditions (reaction time, 5 h; catalyst amount, 13 wt %; alcohol/acid molar ratio, 12:1), the conversion of oleic acid reached 93.4%. Besides, the catalyst presented fine reusability after six runs and could be facilely recovered in magnetic field based on its superparamagnetism property.