Manganese glycerolate catalyzed simultaneous esterification and transesterification: the kinetic and mechanistic study, and application in biodiesel and bio-lubricants synthesis

Abstract

Several characterizations (BET, BJH, XPS, and elemental analysis) were employed further to examine the manganese glycerolate. The elemental analysis proved that the ratio of manganese-to-glycerol is 3:4. The MnGly catalyst is formed as a mixed-valence compound in an Mn2+ to Mn3+ ratio of 1:2 that aligned the results of the surface ratio of Mn2+ to Mn3+ from XPS analysis. This compound provides a total of eight positive charges to compensate for the eight negative charges generated from the hydroxyl group (-OH) in four glycerol ligands. The activation energy (112.7 kJ mol−1) suggests that the reaction undergoes surface-mediated catalysis. The XPS analysis and kinetic study prove the co-existence of divalent and trivalent manganese in MnGly catalyst, demonstrating a flexible coordination geometry between tetrahedral and octahedral. It facilitates the coordination of two methanol to Mn2+ center with an octahedral geometry as the first step of the mechanism for biodiesel synthesis. The yield could achieve more than 99% in 1.5 h under the optimized reaction conditions. The ANOVA revealed that reaction temperature is the most significant factor affecting the production of FAME, with a contribution of 82.84%. This catalytic system also demonstrated high compatibility with higher alcohols for exploring bio-lubricants.