n -Heptane Hydroisomerization over Mesoporous Zeolites made by Utilizing Carbon Particles as the Template for Mesoporosi
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n-Heptane Hydroisomerization over Mesoporous Zeolites made by Utilizing Carbon Particles as the Template for Mesoporosity Douglas L. Moushey Æ Panagiotis G. Smirniotis
Received: 12 November 2008 / Accepted: 25 December 2008 / Published online: 30 January 2009 Ó Springer Science+Business Media, LLC 2009
Abstract Mesoporous zeolites were successfully synthesized by utilizing carbon black particles during the sol–gel synthesis as a template for the network of mesopores. Mesoporous samples of ZSM-12, and Zeolite Beta were synthesized with this method with an average pore size ˚ . The size and the percentage of mesopores about 400 A increases with the C/Si ratio. Our TEM investigations validate the formation of mesoporous networks and voids. This study proves that this method can be generalized for both high and low aluminum zeolites. Selected samples were tested for the hydroisomerization of n-heptane, a probe reaction of great importance for the upgrading of light naphthas. It was found that under identical operating conditions the mesoporous samples exhibited higher, almost fourfold, activity. The selectivity for C7 isomers was higher over the mesoporous samples in comparison with the regular ones. More specifically, the selectivities towards mono- and dibranched isomers increases monotonically with the degree of mesoporosity. The increase of branching over the mesoporous zeolite samples we observed is due to the combined effect of reduced residence times in the zeolite crystal for the reaction products, and the larger ‘‘average’’ pores of the mesoporous samples that allow the formation of bulkier reaction state intermediates. Moreover, the mesoporous samples resulted in generation of less light hydrocarbons (C3, C4). The above
D. L. Moushey P. G. Smirniotis (&) Chemical and Materials Engineering Department, University of Cincinnati, Cincinnati, OH 45221-0012, USA e-mail: [email protected] Present Address: D. L. Moushey Procter & Gamble, Cincinnati, OH, USA
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behavior is a testimony of the tremendous potential that mesoporous zeolite crystals offer and could be very beneficial for numerous refining processes. Keywords Mesoporous zeolites Carbon as template n-Heptane hydroisomerization
1 Introduction Modifying zeolites to achieve certain performance characteristics is a usual practice in catalysis involving zeolites. The advantageous characteristics of zeolites are described quite extensively in the open and patented literature [1–4]. However, the intracrystalline diffusion of species inside the pores of zeolites is severely limited, especially for cases of liquid phase reactions. This can have several negative implications for the success of the specific process, such as reduced selectivity and/or activity, need for higher or much higher operating pressure, or higher temperature. The increased diffusion limitations that zeolites impose are responsible for significant decreases of the product selectivities because of the increased residence time of the products in zeolite pores favoring undesire
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