Biodiesel Production by Transesterification in Two Steps: Kinetic Effect or Shift in the Equilibrium Conversion?

MA. LAURA PISARELLO; MAIRA MAQUIRRIAIN; CARLOS ALBERTO QUERINI

CHEMICAL ENGINEERING RESEARCH & DESIGN

INST CHEMICAL ENGINEERS

Año: 2018

0263-8762

In continuous biodiesel production plants, practically all of technologies carry out the transesterification in two steps, feeding methanol and catalyst in each of them. The glycerin phase is separated after the first step. The explanation normally given to justify this procedure is that the glycerin separation after the first step shifts the equilibrium towards products, thus increasing the conversion. The reacting mixture is a system with partial miscibility, being the compositions of the biodiesel and glycerin phases different depending upon the global composition of the compounds present in the media (methanol, catalyst, soaps, water, etc). The results presented in this work make it possible to conclude that the most important cause of the conversion improvement when performing the reaction in two steps, is a change in the catalyst and methanol distribution between the biodiesel and glycerin phases. The separation of the glycerin phase leads to a positive impact in the kinetic of the second step, allowing that both the catalyst and the methanol concentrate in the biodiesel phase, due to the small quantity of glycerin phase present in the system.