Production of biodiesel from microalgae oil (Chlorella protothecoides) by non-catalytic transesterification: Evaluation of reaction kinetic models and phase behavior

• Non-catalytic transesterification of microalgae oil was conducted with methanol.
• The reaction system was transferring from a liquid state to a supercritical state.
• Ten kinetic models were evaluated, and they worked well in fitting the data.

The non-catalytic transesterification of microalgae oil with methanol was conducted at 300–400 °C, 150–300 bar, methanol-to-oil molar ratio (MOMR) of 6–12, and residence time of 0.5–10 min. A visualization system was built to study the phase transition, and it shows that at the conditions (T: 300–400 °C, P: 200 bar, τ: 0.5–10 min, MOMR of 9), the reactions were performed in homogeneous state. The dynamic phase behavior of the reacting systems was also investigated by RK-Aspen Equation of State. The results indicate that at 200 bar, MOMR of 9, and 300–385 °C, the reacting mixtures were in liquid state and moved toward supercritical region, while at 400 °C the reacting system was initially in liquid state and quickly approached supercritical state due to the fast reaction conversion. The critical points of the reaction mixtures were estimated. Ten commonly used kinetic models were evaluated, and it shows that three-step, reversible second-order model worked best in the data fitting. Reaction rate constants and activation energies for selected models were determined and compared with literature data.

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