K2MgSiO4: A novel K+-trapped biodiesel heterogeneous catalyst produced from serpentinite Mg3Si2O5(OH)4

Abstract In this study, a new catalyst for biodiesel synthesis, based on K 2 MgSiO 4 , was produced from the mineral serpentinite. TG, SEM, XRD, AA, BET analyses showed that serpentinite Mg 3 Si 2 O 5 (OH) 4 impregnated with KOH (5,10 and 20 wt%), and thermally treated at 500 °C, 700 and 900 °C, can be converted to the main crystalline phase K 2 MgSiO 4 . Analyses by TPD-MS (CO 2 ) and titration suggested the presence of weak/medium basic sites in relatively high concentrations. Biodiesel production using soybean oil (methanol:soybean oil ratio of 1:12, 1:9; 1:6, 60 °C) showed yields higher than 95% with catalyst at 10 wt%, which can be reused for three consecutive times without significant decrease on the reaction yield. The obtained results are discussed in terms of a new catalytic phase based on K + ions trapped in the cavities of the MgSiO 4 2− structure containing negatively charged oxygen basic sites.