A new method for utilization of hydrogel is proposed here for the preparation of solid base catalysts for the transesterification of vegetable oil. When a solution of KF is mixed with a solution of Ca(NO3)2, CaF2 is obtained and inactive as a catalyst in the transesterification of vegetable oils. The catalysts were synthesized by the sequential incorporation of KF and/or Ca(NO3)2 solutions into the hydrogel upon microwave irradiation and then the as-obtained hydrogel was calcined at 800°C for 5 hours to eliminate the template and yield catalysts for the biodiesel productions. The prepared catalysts obtained by the different ways in the incorporation of ions into the hydrogel showed different physical properties and catalytic activities in the transesterification of soybean oil. All catalysts, except the low concentration of Ca(NO3)2, exhibiting the high activity yielding more than 90% FAME after 1 hour at 65°C, using oil to methanol molar ratio of 1:15 and 10 wt% of catalyst amounts.
Keywords: biodiesel; hydrogel; solid base catalyst; transesterification.