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.