Continuous Production of Biodiesel from Soybean Oil in Supercritical Ethanol and Carbon Dioxide as Cosolvent

This work investigates the effect of carbon dioxide as cosolvent on the production of fatty acid ethyl esters from soybean oil transesterification in supercritical ethanol in a continuous catalyst-free process. The experiments were performed in a tubular reactor in the temperature range of 573-623 K, from 7.5 to 20 MPa, with an oil to ethanol molar ratio ranging from 1: 10 to 1:40 and cosolvent to substrates mass ratio from 0: 1 to 0.5: 1. Results showed that the yield of ethyl esters decreased with increasing addition of carbon dioxide to the system. The reaction conversion was noticed to decrease at lower substrates flow-rates due to products decomposition. Considerable reaction yields were achieved at 623 K, 10 MPa, oil to ethanol molar ratio of 1:40 and using a CO2 to substrate mass ratio of 0.05: 1. It is shown that the use of a tubular reactor with smaller inner diameter can provide high reaction conversions in short residence times, thus offering a promising route for the investigation of biodiesel production.