Effect of System Conditions for Biodiesel Production via Transesterification Using Carbon Dioxide–Methanol Mixtures in the Presence of a Heterogeneous Catalyst

A mixed carbon dioxide (CO2) and methanol (MeOH) system is shown to successfully transesterify triolein into methyl oleate at moderate pressures and temperatures below 100 °C in the presence of Nafion NR50, a heterogeneous catalyst. An experimental design was developed to explore the effects of mono-, bi-, and tri-phasic CO2–MeOH–triolein systems through pressure, temperature, and methanol loading, all of which influence the system phase behavior. It was found that one particular set of conditions (>80 °C, 9.5 MPa, 3.6% v/v reactor, ambient MeOH) demonstrated nearly complete yields due to the preferable phase behavior at these conditions. Cloud point curves of the ternary system (MeOH, CO2, and substrate, including triolein, diolein, monoolein, glycerol, and methyl oleate) are reported to describe this complex system phase behavior. Results indicate that optimized yields (>98% methyl oleate at 95 °C) are achieved when the reaction is carried out in a three-phase system (not including the solid catalyst as a separate phase), which can partially be attributed to increased solubility of triolein in methanol as well as increased mass transfer due to the presence of dissolved CO2.