Catalytic synthesis of biodiesel fuel under sub/supercritical conditions: kinetics and phase behavior
Date of Award
Doctor of Philosophy (PhD)
Biomedical and Chemical Engineering
Lawrence L. Tavlarides
biodiesel, catalysis, kinetics, supercritical
In this thesis, transesterification of triglycerides and esterification of free fatty acids were executed under subcritical and supercritical alcohol conditions, and discussed in Chapter 2-5. The project was initiated by studying the phase behavior and kinetics of transesterification reactions under severe reaction conditions (T: 300-400 oC, P=200 bar), since those conditions were suggested and commonly used in the literature. At these conditions, triglycerides reacted with alcohol within minutes, and the oil-alcohol mixture formed a homogeneous phase which minimized the boundary mass transfer resistance. The composition change of the reaction mixture made the critical point of the system approach supercritical region quickly, as calculated by RK Aspen EOS. The kinetic data were well fitted by a three-step second order model. However, thermal degradation of biodiesel fuel was found especially at temperatures higher than 325 oC. A thorough study on biodiesel thermal degradation clearly proves that the degradation at temperatures above 325 oC decreased the biodiesel quality, which suggests future experiments be performed at lower temperatures. The degradation reactions were found to be isomerization, polymerization, and pyrolysis reactions. Accordingly, catalysts were employed in order to reach a high product yield in short residence times at milder conditions. A trace amount of sulfuric acid and potassium ethoxide was separately used under subcritical conditions to catalyze the transesterification reactions (T: 175-225 oC, P: 200 bar). All the reactions were conducted in homogeneous phase. Lastly, esterification reaction of oleic acid was carried out in a packed-bed reactor containing unmodified gamma-alumina. A kinetic study suggests that the mass transfer resistance of the esterification reaction was not significant. Both reaction systems were capable of converting the oil feedstocks to biodiesel product in a few minutes with high conversions.
Liu, Jiuxu, "Catalytic synthesis of biodiesel fuel under sub/supercritical conditions: kinetics and phase behavior" (2017). Dissertations - ALL. 833.