Batch and Continuous Ultrasonic Reactors for the Production of Methyl Esters from Vegetable Oils

Abstract

Mass transfer is a rate limiting step in biodiesel production. Ultrasound can accelerate tremendously the mass transfer in both triglycerides transesterificationTransesterification and free fatty acid esterification by finely emulsifyingEmulsifying reagents that are poorly miscible. We describe reactor configurations for both transesterification and esterification, with emphasis on the work published by the authors. Ultrasound in the esterification increases the mass transfer in raw oils at temperatures below 40 °C. The Eley–Rideal kinetic modelKinetic eley Rideal of the esterification including the mass transfer resistance between the phases is in excellent agreement with the experimental data. The Rosett cellRosett cell reactor combines acoustic cavitation and turbulence and transesterifies 90 % of the feedstock in 5 min, whereas it takes 90 min in a conventional batch reactor. Continuous and semi-continuous tubular reactors irradiated at a power density of 40 kW/cm3 converts 90 % of the oil in 10 min. A Sonitube® (Synetude) converts 90 % of the oil after a single passage in a continuous reactor. This corresponds to 18 s and a rate 300 times faster than the conventional process. SonitubeSonitube ® improves mass transfer substantially and is worthy of scaling up.