K2MgSiO4 : a novel K+-trapped biodiesel heterogeneous catalystproduced from serpentinite Mg3Si2O5(OH)4.

Abstract

In this study, a new catalyst for biodiesel synthesis, based on K2MgSiO4, was produced from the mineralserpentinite. TG, SEM, XRD, AA, BET analyses showed that serpentinite Mg3Si2O5(OH)4impregnated withKOH (5,10 and 20 wt%), and thermally treated at 500◦C, 700 and 900◦C, can be converted to the main crys-talline phase K2MgSiO4. Analyses by TPD-MS (CO2) and titration suggested the presence of weak/mediumbasic sites in relatively high concentrations. Biodiesel production using soybean oil (methanol:soybean oilratio of 1:12, 1:9; 1:6, 60◦C) showed yields higher than 95% with catalyst at 10 wt%, which can be reusedfor three consecutive times without significant decrease on the reaction yield. The obtained results arediscussed in terms of a new catalytic phase based on K+ions trapped in the cavities of the MgSiO42−structure containing negatively charged oxygen basic sites.