Biodiesel synthesis: A study of the triglyceride methanolysis reaction with alkaline catalysts

• The relative catalytic activities of NaOCH3, KOCH3, NaOH and KOH were compared.
• The kinetics of methanolysis were best described by a zero-order model.
• The potassium-based catalysts were more active than their sodium analogs.
• Methoxides are more active than hydroxides at nearly all of the temperatures used.
• The mechanism is thought to involve ionic pairs.

The rates of soybean oil methanolysis under NaOCH3, KOCH3, NaOH and KOH catalysis were determined at 30.0, 40.0, 50.0 and 60.0 °C using a refractometric method for online monitoring of this reaction. The influences of the metallic cations and anions on the catalysis were studied. Potassium promotes faster reactions than sodium. For the reactions catalyzed by hydroxides, the rate constants are less sensitive to temperature than those catalyzed by methoxides. The proposed reaction mechanism was based on the formation of ionic pairs at the interface of the methanol and oil phases and in the methanol phase.

Energy differences between the transition states along the triglyceride transesterification reaction in alkaline catalysis as a function of ion pair formation.Figure optionsDownload as PowerPoint slide