A Novel Sulfonated Carbon Composite Solid Acid Catalyst for Biodiesel Synthesis
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A Novel Sulfonated Carbon Composite Solid Acid Catalyst for Biodiesel Synthesis Xunhua Mo Æ Edgar Lotero Æ Changqing Lu Æ Yijun Liu Æ James G. Goodwin
Received: 28 January 2008 / Accepted: 29 February 2008 / Published online: 14 March 2008 Ó Springer Science+Business Media, LLC 2008
Abstract A novel sulfonated carbon composite solid acid was successfully prepared by the pyrolysis of a polymer matrix impregnated with glucose followed by sulfonation. The title catalyst has higher acid site density, better esterification activity of both small and large free fatty acids (acetic acid and palmitic acid), and better reusability than the previously reported carbon-based catalyst prepared by sulfonating pyrolyzed sugar. This catalyst also exhibited higher esterification activity than tungstated zirconia (WZ) and Silica-Supported Nafion (NafionÒSAC-13). The higher activity of the sulfonated carbon composite solid acid catalyst was clearly due to the presence of a much higher acid site density than any of the other catalysts. Keywords Carbon Glucose Polymer matrix Pyrolysis Sulfonation Esterification Biodiesel Acid catalysis
1 Introduction The transesterification of triglycerides (TGs) and esterification of free fatty acids (FFAs) are the two main reactions for converting vegetable oils and animal fats into biodiesel. Currently, most commercial processes used for biodiesel synthesis employ homogeneous catalysts to carry out these two reactions. Homogeneous catalysts, however, are corrosive, X. Mo E. Lotero Y. Liu J. G. Goodwin (&) Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, SC 29634, USA e-mail: [email protected] C. Lu Department of Chemistry, Clemson University, Clemson, SC 29634, USA
can be used only once and require energy intensive separation operations that lead to waste formation and environmental pollution. The use of heterogeneous catalysts to replace homogeneous ones could eliminate the problems associated with homogeneous catalysts and should allow the application of more environmentally friendly biodiesel synthesis protocols. In addition, using heterogeneous catalysts should enable the design of efficient continuous processes, improving the economics of biodiesel production [1–3]. In addition to the use in the esterification of FFAs in vegetable oils and animal fats, heterogeneous acid catalysts for biodiesel synthesis could in principle be employed to catalyze the simultaneous reactions of TGs and FFAs with low molecular alcohols in transesterification and esterification, respectively [3]. Among the heterogeneous acid catalysts studied to date for trans/esterification are zeolites [4, 5], MCM-41 [6, 7], tungstated zirconia [8–10], sulfated zirconia [11–14], Amberlyst-15 [15–17] and Nafion [18–22]. Some common problems with solid acid catalysts have been: low acid site concentrations, microporosity, hydrophilic character of catalyst surfaces, and active site leaching. High cost is also an obstacle for commercialization using many of the current heteroge
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