Skeletal isomerization of unsaturated fatty acids: the role of mesopores in HBeta zeolites
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Catalysis Letters, Vol. 115, Nos. 3–4, June 2007 ( 2007) DOI: 10.1007/s10562-007-9083-z
Skeletal isomerization of unsaturated fatty acids: the role of mesopores in HBeta zeolites Shuguang Zhanga,b and Z. Conrad Zhangc,* a
School of Environmental Engineering, Dalian University, Dalian Economic Technological Development Zone, Dalian 116622, China b School of Chemical Engineering, Dalian University, Dalian Economic Technological Development Zone, Dalian 116622, China c Pacific Northwest National Laboratory, MS K8-93, 902 Batelle Blvd, P.O. Box 999 Richland, WA 99352, USA
Received 11 March 2007; accepted 13 March 2007
Fatty acids are an important class of feedstock for the production of many chemicals, such as surfactants, lubricants, biodiesel, etc. Fatty acids derived from vegetable oils and animal fats typically have linear aliphatic chain, and are therefore called linear fatty acids. Products based on branched fatty acids offer many attractive properties over those based on linear ones, e.g. low melting points and low viscosity. Catalytic skeletal isomerization of linear fatty acids to branched ones is particularly important for industrial production of branched fatty acids. This paper for the first time reveals the key properties of the most active zeolite catalysts for this reaction. Among many solid acid catalysts studied, acidic Beta zeolites were found to stand out in their performance for the reaction. In this work, several acidic Beta zeolites (HBeta) from commercial sources were evaluated for their performance in fatty acid skeletal isomerization. The activities of these zeolites under identical test conditions were found to vary in a wide range, even with similar silica to alumina molar ratios (SAR). A combination of characterization techniques was used to systematically investigate the most critical property of the zeolites responsible for the observed superior activity. All the HBeta zeolites in this study have high crystallinity. Pore size distribution of the zeolites was identified to be the most important factor that unambiguously correlates the catalyst activity to the amount of mesopores in the HBeta zeolites.
KEY WORDS: isomerization; fatty acid; branched; zeolite; acidity; mesopore.
1. Introduction Fatty acids are aliphatic carboxylic acids of typically straight hydrocarbon chains having an even number of carbons, most commonly with 12–24 carbons. The *To whom correspondence should be addressed. E-mail: [email protected]
degree of unsaturation and the carbon chain length of a fatty acid are dependent on the triglyceride source from which it is derived. Linear fatty acids have been widely used as a raw material for surfactant and detergent applications. Mono-alkyl esters of fatty acids are particularly important derivatives of fatty acids. Fatty acid methyl ester (FAME), for example, is a well known 1011-372X/07/0600–0114/0 2007 Springer Science+Business Media, LLC
S. Zhang and Z. C. Zhang/Skeletal isomerization of unsaturated fatty acids
economically competitive biodiesel as an altern
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