Heterogeneous catalyzed FFA esterification of soybean oil in a pressurized PFR reactor

Biodiesel is an alternative diesel fuel, produced from vegetable oils through a transesterification reaction with methanol and an alkaline catalyst. In order to reduce biodiesel production costs crude oils should be used, which are characterized by an high content of Free Fatty Acids (FFA). FFA should be eliminated to avoid soap formation during the transesterification step. In this work, the direct esterification reaction of FFA in crude rapeseed oil (CRO) is studied in the presence of Amberlyst 46 acid catalysts in a pressurized PFR reactor. The FFA esterification has been widely studied since it allows to obtain biodiesel from FFA, thus improving the final biodiesel yield. Large part of the literature reports studies conducted in non-pressurized batch reactors [1,2], which represents a limit because the maximum temperature allowed corresponds to the normal boiling point of methanol, i.e. 64.7 °C. The scope of this work is to study the FFAs esterification with methanol using a PFR reactor suitable for working at high pressure (from 2 to 10 bar), that allows higher operative temperatures. In Fig.1 the scheme of the PFR experimental set-up is reported: CRO is mixed with methanol using an FFA:methanol molar ratio of 1:5 in a feeding chamber (FC), where via compressed air are fluxed into the reactor, heated by an external hot circuit. The whole system is thus under pressure. The reactor is an iron cylinder 20.3 cm long and with an internal diameter of 4.7 cm with 3 intermediate samplings The catalytic bed is placed at 7.4 cm from the bottom of the reactor to a volume of 86 cm3. The CRO studied was characterized by an initial FFAs content of 2.23%w. The esterification reaction was conducted at 2 bar and at two different operative temperatures, i.e. 65 and 75°C and regulating the flow of reagents in order to obtain residence time from 3 to 325 minutes. The experimental results, reported in Fig. 2, demonstrate the expected trend following residence time and T variation. On the basis of the collected data the main kinetic parameters will be calculated and discussed. References. [1] Boffito D.C. et al, (2013): J Cat, 297, 17-26; [2] Boffito D. C. et al, (2013): Fuel, 108, 612-619.