(689a) Novel Reactor Design for the Production of Biodiesel from Free Fatty Acids

Authors: 
Cairncross, R. A., Drexel University
Melick, C., Drexel University
Mohammed, M., Drexel University


A semi-batch bubble column reactor has been developed for biodiesel production oils containing a high free fatty acid content. An acid catalyst was used to avoid soap formation because soap formation inhibits conversion and makes purification difficult. The reactor is operated at ambient pressure and temperatures above the boiling point of methanol. A major advantage of the bubble column design is continuous removal of byproduct water which enables overcoming equilibrium limitations of the reversible esterification reaction. A continuous reactor model is being developed to capture the kinetics of the esterification reaction and the effect mass transfer of the alcohol and water between the vapor and the oil phases. The reactor model will be validated based on a set of parametric studies consisting of alcohol flow rate; temperature and alcohol feed quality. Parametric studies were performed in a semi-batch lab scale to test the concept before the design and construction of a continuous reactor. The biodiesel conversion profile was obtained through titration of samples collected at regular intervals. The reactor is robust and efficient with conversion greater than 95% achieved within 60 minutes at 120ºC reactor temperature. The bubble column design is robust for a variety of feedstocks. It achieves greater than 95% conversion with pure triglycerides, pure free fatty acid, and blends. The conversion is also unaffected by the presence of water (up to 5% by volume) in the methanol feed or using pure ethanol instead. It was also found that agitation does not effect the overall conversion, but does affect the rate. The results from these studies are being used to design a continuous counter-current reactor.