(178e) Production of Biodiesel Fuel Via Sub/Supercritical Transesterification Reactions with Trace Amount of Homogeneous Catalysts

Liu, J., Syracuse University
Nan, Y., Syracuse University
Tavlarides, L. L., Syracuse University
2016 AIChE Annual Meeting

November 13th to 18th, San Francisco, CA



Jiuxu Liu, Yue Nan and Lawrence L. Tavlarides*

Department of Biomedical and Chemical Engineering, Syracuse University,

329 Link Hall, Syracuse, NY 13244, USA

* Corresponding author. Tel.: 315-443-1883; Fax: 315-443-9175

Email: lltavlar@syr.edu (Tavlarides); jliu23@syr.edu(Liu)


Refined oils and anhydrous alcohols are required in conventional biodiesel industry since impurities as free fatty acids (FFA) and water poison the catalysts. One of the most promising advantages of the non-catalytic sub/supercritical technology (SCTE) over the conventional method is that it does not require high quality feedstocks, so low-cost waste oils which contains FFA and water, and hydrous alcohols which contains water can be used. However, it is difficult to reach a high biodiesel yield since extending reaction time at those required temperatures will thermally decompose biodiesel product, which has been proved to lower the fuel qualities such as viscosity and cold flow properties. We have known that employing catalysts in the SCTE reactions with high quality feedstocks (refined oils and anhydrous alcohol) will complete the reactions in shorter residence times to avoid decomposition, but we have not determined if those catalysts can still function under the presence of impurities such as FFA and water. Another issue related to biodiesel studies is that much fewer investigations have been done on kinetics of synthesizing FAEEs, which is a potential replacement of FAMEs, than FAMEs. Presently, the kinetic analyses of SCTE ethanolysis reactions have been based on the overall reaction and the model of first-order reaction with respect to triglycerides, and the temperature range is very limited.

In this study, we are investigating FAEEs and FAMEs biodiesel synthesis under sub and supercritical alcohol conditions catalyzed by trace amounts of homogeneous catalysts including sulfuric acid, potassium hydroxide, and potassium m/ethoxide. The objectives include: a) a kinetic study of FAEEs biodiesel synthesis at SCTE conditions with 0.1 wt% sulfuric acid, b) comparison of catalytic ability to improve yields of FAEEs and FAMEs biodiesel between sulfuric acid and other catalysts including potassium hydroxide and potassium m/ethoxide under sub and supercritical conditions, c) effect of impurities such as FFA (up to 30 wt%) and water (up to 10 v%) on these catalysts, and d) effect of reaction pressure on product yield.

At this writing we have completed the first aim which is the kinetic study of synthesizing FAEEs biodiesel under sub and supercritical conditions. The reactions were conducted at temperatures from 175 to 350 oC, residence times from 1 to 120 min, pressure of 200 bar, and 0.1 wt% sulfuric acid based on oil mass. A three-step partially reversible second-order reaction model was employed to best fit the data, and the activation energy for each reaction step was calculated. It was found that the catalytic activity of sulfuric acid decreased when switching from subcritical to supercritical conditions. Comparison of the kinetic parameters for sub and supercritical reactions will be shown, and the mechanism will be discussed. High biodiesel yields (> 90%) were reached at 175, 200, 225, 300, and 325 oC with 0.1 wt% sulfuric acid concentration.

Experiments to complete the remaining objectives are in progress and will also be reported.