Fabrication of H3PW12O40/agarose membrane for catalytic production of biodiesel through esterification and transesterification

Abstract

A membrane reactor containing heteropolyacids was designed by embedding tungstophosphoric acid (H₃PW₁₂O₄₀, abbreviated as HPW) onto the lattice of agarose. During the gelation of agarose, HPW molecules were embedded on the densely packed 3D network of agarose through strong interaction between the polyhydroxyl sites of agarose and oxygen from HPW. This avoided the aggregation of HPW molecules and resulted in the equal distribution of HPW in the membrane. Furthermore, a material with as high as 38% loading amount of HPW on agarose had been achieved. The acidic activity was evaluated in the esterification of free fatty acid and transesterification of Eruca Sativa Gars (ESGs) oil with methanol in batch reaction. Among all HPW/agarose, it was found that HPW/agarose membrane with 38 wt% HPW showed the highest efficiency in both reactions under the optimized reaction conditions with TOF values of 82 h⁻¹, and 27.6 h⁻¹ (based on the yield of MP), respectively, in the batch reactor. Then the reaction rates increased to 164 and 45.8 h⁻¹ in the membrane reactor. The solid and tough structure of HPW/agarose confirm its high stability and duration, it could be used at least ten times without significant loss of activity. Furthermore, the reaction rates could be increased at least two fold in membrane mode compared to those in batch mode, showing the separation ability of water or glycerol from the mixture by the HPW/agarose membrane. This is a potential strategy for the production of biodiesel based on heteropolyacid catalysts. The fuel properties of biodiesel from ESG oil showed that they were all satisfactory for the ASTM biodiesel standard.