Continuous catalyst-free production of fatty acid ethyl esters from soybean oil in microtube reactor using supercritical carbon dioxide as co-solvent

This work reports the transesterification of soybean oil in supercritical ethanol in a continuous catalyst-free process in microtube reactor using carbon dioxide as co-solvent. For this purpose it was employed two microtube reactors with different internal diameter, 0.775 and 0.571 mm. The experiments were performed in the temperature range of 523–598 K, pressure of 10 MPa and 20 MPa, oil to ethanol molar ratio of 1:20 and 1:40, and co-solvent to substrates mass ratio from 0.05:1 to 0.2:1. Results demonstrated that temperature, pressure and co-solvent to substrate mass ratio had a positive effect on fatty acid ethyl esters (FAEE) production, with appreciable yields achieved at 598 K, 20 MPa, oil to ethanol molar ratio of 1:20, using a CO2 to substrate mass ratio of 0.2:1. The micro-reactor with the smallest inner diameter led to slightly higher FAEE yields at the specified reactions conditions compared to the micro-reactor with greater internal diameter. A semi-empirical kinetic model was proposed in attempt to represent the experimental data with satisfactory fitting results found.