The aim of this work is to synthesise glycerol carbonate from carbon dioxide (CO2) and
glycerol. Two key challenges that were investigated in this work including:
(1) thermodynamic limitation of this work and (2) desirability of using crude glycerol as
a feedstock. In this work, carboxylation of glycerol is carried out over La2O3 (commercial)
and La2O2CO3 catalysts prepared via co-precipitation, sol-gel and hydrothermal methods.
These catalysts are characterised using BET, ATR-FTIR, SEM, XRD, TPD-CO2 and
TPD-NH3.
The carboxylation reaction is thermodynamically limited, therefore a range of dehydrating
agents were introduced to improve the glycerol conversion by shifting the reaction
equilibrium to the product side. The impact of dehydrating agents on glycerol conversion
and glycerol carbonate formation were therefore studied. Reaction conditions were as
follows: 6 wt.% La2O3, relative to glycerol, glycerol to dehydrating agent ratio of
22.5:50 mmol, 160 °C and reaction pressure, 45 bar CO2 and reaction time, 18 hours. High
selectivity to glycerol carbonate is observed upon the introduction of adiponitrile (17%),
followed by benzonitrile (5%), acetonitrile (4%), and no glycerol carbonate was detected
upon the introduction of acetic anhydride.
Additionally this work demonstrated for the first time the efficacy of lanthanum-based
catalysts to synthesise glycerol carbonate via the direct carboxylation of crude glycerol.
Crude glycerol employed herein comprises 74% glycerol, 20% of fatty acid methyl esters,
5 wt.% water, 1% methanol, and 7 g/L of sodium methoxide. It was analysed by GG-MS,
ICP-MS and Karl Fisher titration technique. The impact of single and multiple impurities
are the aspects investigated in this work. The addition of 10 wt.% water inhibited the
formation of glycerol carbonate while blending of glycerol and methanol (80:20 mol%)
increased the selectivity to glycerol carbonate to 22%. Only 4% selectivity to glycerol
carbonate over La2O3-C was observed in the presence of multiple impurities including
methanol, fatty acid methyl ester and sodium methoxide. As a result, modification of
La2O3-C catalyst is crucial. Introduction of ZrO2/La2O2CO3/Ga2O3 greatly improved the
selectivity to glycerol carbonate (21%); while a selectivity of 5% to glycerol carbonate
observed for the direct carboxylation of crude glycerol
