Kinetic studies on biodiesel production using a trace acid catalyst

• A kinetic model is formulated for trace acid catalyzed ethanolysis of corn oil.
• Monoglyceride yields are significant at 100% oil conversion.
• Corn oil exhibited higher conversion than Pennycress oil.
• Methanolysis is faster than ethanolysis.
• Trace acid catalyzed transesterification is tolerant to water and FFA.

Biodiesel was produced by transesterification in the presence of trace sulfuric acid (0.02–0.1 wt% of oil mass). The kinetics for the transesterification of corn oil with ethanol was investigated between 155–195 °C. The transesterification in the pseudo-homogeneous system consisted of three consecutive steps. All steps were found to be second order reactions, with the first and the second steps being irreversible, while the third step was reversible. It was observed that the apparent rate constants of the forward reactions increased linearly with increasing acid concentration. Compared to the initial two steps of the ethanolysis reaction, the effect of the reversible transformation in the third step is significant, as the conversion of monoglyceride to glycerol is difficult. In addition, the presence of free fatty acids (<30 wt%), water (<3 wt%), and the use of stirring had little effect on the final content of biodiesel. Finally, it was observed that methanol exhibited a higher reactivity than ethanol in transesterification, while corn oil exhibited higher reactivity than Pennycress oil.

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