Biodiesel offers a sustainable alternative to petroleum based transport fuels, but in order for biodiesel to be viable, the production process must be improved to allow for a net positive energy balance and greater economic efficiency.  In this work, the use of carbon dioxide (CO2) as a green solvent is shown to improve heterogeneously catalyzed biodiesel production via advantages in terms of system phase behavior, mass transport, and selectivity.  A mixed CO2 and methanol system was used for transesterification of triglycerides into fatty acid methyl esters (FAME, biodiesel), and a fundamental approach was taken to understand the effect of system phase behavior of system yields.  The system was 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.  The effect of pressure, temperature, methanol loading, and subsequent influence on system phase behavior was shown to have significant impact on product yield and composition. Results indicate that high FAME 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) where it is assumed that the reaction mainly occurs in the now methanol rich phase now expanded with CO2.  The success of this CO2-expanded liquid is likely attributed to increased solubility of triolein in methanol as well as increased mass transfer.  Further work on system kinetics show that differences in substrate as well as catalyst active site availability can influence product fractionation.  Optimization of catalyst utilization as well as differential reaction kinetics between system species can enhance system selectivity potentially producing a more effective and efficient process.

Biodiesel production via transesterification in a mixed carbon dioxide-methanol system with a heterogeneous catalyst

248th National Meeting (2014)

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