Ultrasound assisted transesterification of soybean oil using supported zirconate based solids as catalysts

Application of heterogeneous catalysts for biodiesel production represents an important advance to improve the productive process. However, the solid-catalyzed transesterification process is a three-phase system with mass transfer limitations. Biodiesel production using ultrasound mixing is a promising alternative since ultrasound helps in the formation of fine emulsion of two immiscible liquids, generating large interfacial area. Here we propose the application of sodium zirconate (Na₂ZrO₃) and calcium zirconate (CaZrO₃) supported in a polyvinyl alcohol (PVA) as catalysts for biodiesel production in an ultrasonic mixing reactor. Experiments were performed by transesterification of soybean oil with methanol at a molar ratio of 6: 1 (oil:methanol), temperature of 55°C, and with 6 wt% of catalyst (related to the oil mass). Samples (1 ml aliquot) were removed from the reaction mixture at specified times during the progress of the reaction. The ester content in each sample was measured by gas chromatography according to the standard procedure. Results showed that ester phase purity was greater than 90% when using supported or unsupported catalysts, as well as when using magnetic or ultrasonic mixings. Both catalysts presented equilibrium reaction time at 10 h for the ultrasonic mixing, while this time increase to more than 15 h when using magnetic stirring. Both innovative propositions (supported catalyst and ultrasonic mixing reactor) should represent advantages for catalyst reuse. Moreover, the proposed catalyst was efficient for biodiesel production at the studied conditions.