Kinetics of biodiesel synthesis from sunflower oil over CaO heterogeneous catalyst

Calcium oxide as a heterogeneous catalyst was investigated for its effect on the biodiesel synthesis from refined sunflower oil. Experiments were carried out using a commercial bench stirred tank reactor of 2 dm3 volume, at 200 rpm, with a methanol to oil ratio 6 to 1 and 1 mas.% catalyst loading as constant parameters. Ester yields were followed as a function of temperature (60–120 °C), pressure (1–15 bars) and reaction time (1.5–5.5 h). The temperature of 100 °C was found to be optimal for the maximum (91%) conversion to methyl esters, while pressure had a positive impact up to 10 bars at 80 °C. The catalyst activation in air leading to the formation of strong basic sites was found to occur at 900 °C. Catalyst particle coalescence took place during the reaction, giving a gum-like structure, and resulted in a significant catalyst deactivation. The pseudo-first order reaction was established, with a “knee” at 80 °C in the Arrhenius plot separating the kinetic and diffusion regimes. During the reaction progress, an activation energy decrease from 161 to 101 kJ/mol, and from 32 to (−3) kJ/mol, was found for the kinetic and diffusion regimes, respectively.