Potassium supported on zeolite-geopolymer hybrid materials as a new solid base catalyst for transesterification of soybean oil

The heterogeneous base catalysts were developed from zeolite-geopolymer hybrid material (Zeo-Geo) as a new support for potassium in transesterification of soybean oil. Zeo-Geo was prepared by mixing Al metal, metakaolin, and fumed silica in NaOH solution and curing at 60 °C, 24 h and 110 °C, 12 h. The Zeo-Geo contained a mixed phase of geopolymer and X-type zeolite. The xK/Zeo-Geo with x = 5, 10 or 15 wt% potassium were prepared by impregnation of Zeo-Geo with potassium acetate followed by calcination at 400 °C for 3 h. The phases of potassium were mainly K2O and K2CO3 and the basicity increased with potassium loading. The 15K/Zeo-Geo was the most active catalyst in transesterification of soybean oil with methanol, at 70 °C providing 97.64% biodiesel yield under the optimum condition: reaction time = 3 h, methanol to oil molar ratio = 16:1 and catalyst amount = 2 wt%. The catalyst was reused in 5 cycles without a significant activity loss and leaching of active species. From this study, 15K/Zeo-Geo has a potential for further development in large-scale production.