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 dm(3) 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 degrees C), pressure (1-15 bars) and reaction time (1.5-5.5 h). The temperature of 100 degrees 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 degrees C. The catalyst activation in air leading to the formation of strong basic sites was found to occur at 900 degrees 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 degrees 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. (C) 2009 Elsevier Ltd. All rights reserved.