Synthesis of Biodiesel from Soybean Oil using Heterogeneous KF/ZnO Catalyst
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Catalysis Letters Vol. 107, Nos. 1–2, February 2006 (Ó 2006) DOI: 10.1007/s10562-005-9731-0
Synthesis of biodiesel from soybean oil using heterogeneous KF/ZnO catalyst Wenlei Xie* and Xiaoming Huang School of Chemistry and Chemical Engineering, Henan University of Technology, Zhengzhou, 450052, P.R. China
Received 1 October 2005; accepted 24 November 2005
Biodiesel was produced by transesterification of soybean oil with methanol using ZnO loaded with KF as a solid base catalyst. It was found that the catalyst with 15 wt.% KF loading and calcined at 873 K showed the optimum activity. XRD, IR and Hammett indicator method were employed for the catalyst characterization. The results showed the activity of the catalysts was correlated with their basicity. The influence of various reaction variables on the conversion was also discussed. KEY WORDS: methyl esters of fatty acids; heterogeneous catalyst; transesterification; biodiesel.
1. Introduction Over the past couple of decades alternative fuels for diesel engines are becoming increasingly important due to the limited resources of fossil fuel, increasing prices of crude oil and environmental concerns [1]. Methyl esters of fatty acids, better known as biodiesel, are nontoxic, biodegradable and an excellent substitute for conventional diesel fuels. The energy content, cetane number and viscosity of biodiesel are similar to those of petroleum-based diesel fuel. Moreover, biodiesel is essentially sulfur-free and the engines fueled by biodiesel emit significantly fewer particulates, unburnt hydrocarbons and less carbon monoxide than operating on conventional diesel fuels [1–3]. Methyl esters of fatty acids are usually produced by transesterification of triglyceride to methyl esters using sodium or potassium hydroxide dissolved in methanol as homogeneous catalysts; however, in this conventional method removal of these catalysts is technically difficult and a large amount of waste water was produced to separate and clean the catalyst and the products [4–6]. Therefore, for the development of an environmentally benign process and the reduction of the production cost, a new process using heterogeneous catalyst should be introduced. Heterogeneous catalysts could improve the synthesis methods by eliminating the additional processing costs associated with homogeneous catalysts and minimizing the production of pollutants. Many different heterogeneous catalysts have been developed to catalyze the transesterification of vegetable oils to prepare fatty acid methyl esters. For example, modified zeolites, anionic clays (hydrotalcites-like), calcium carbonate rock, EST-4, Li/CaO andNa/NaOH=c-Al2O3 have been * To whom correspondence should be addressed. E-mail: [email protected]
found to be efficient heterogeneous catalyst for transesterification of vegetable oils with methanol [7–12]. However, they are quite expensive or complicated to prepare or sensitive to water and acid, which limited their industrial application. Thus, it is desirable to find more efficient and cheap catalysts for transesterificati
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