Isomerization of n -heptane on platinum-zeolite catalysts promoted by chlorine and fluorine
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Isomerization of n-heptane on platinum-zeolite catalysts promoted by chlorine and fluorine* I. M. Kalashnikov, E. A. Belopukhov, M. D. Smolikov, D. I. Kir´yanov, T. I. Gulyaeva, and A. S. Belyi Center of New Chemical Technologies BIC**, Boreskov Institute of Catalysis, 54 ul. Neftezavodskaya, 644040 Omsk, Russian Federation. E-mail: [email protected] The isomerization of n-heptane on BEA supported platinum catalysts with the addition of chlorine and fluorine as promoters was studied. The use of the halides decreased the operating temperature of the n-heptane conversion. The samples prepared at the stage of peptization showed an increase in the total conversion accompanied by a decrease in the yield of heptane isomers of 6 for chlorine and 27 wt.% for fluorine. Promotion by the halides at the stage of platinum application led to an increase in the catalyst activity without decrease in the selectivity values. Key words: isomerization, n-heptane, zeolite, alumina, zeolite BEA, chlorine, fluorine.
Isomerization of paraffins is widely used in the production of high-octane non-aromatic gasoline components.1,2 In particular, high-octane non-aromatic products are obtained by isomerization of the heptane fraction. At the same time, the processes of catalytic isomerization of paraffin have been developed primarily for the conversion of the С5—C6 fraction. There are two types of isomerization catalysts. Medium-temperature zeolite catalysts are used at temperatures of 250—300 °С. Lowtemperature catalysts are synthesized on the basis of chlorinated alumina (120—180 °С) and sulfated zirconium dioxide (130—200 °С). Industrial catalysts for the isomerization of С5—С6 paraffins possess3 a strong acidic function and their use in isomerization of C7 paraffins can lead to an increase in the contribution of side hydrocracking reactions. Therefore, the isomerization of the heptane fraction requires development of new catalysts, which can demonstrate high selectivity for the target products and reasonable activity at low temperatures favorable from the point of view of the thermodynamics of the process. It has been established4 that catalysts based on BEA zeolite exhibit high selectivity in heptane isomerization. This zeolite has a high specific surface area (about 700 m2 g–1) and a three-dimensional system of internal pores. The channels of two types are characterized by apertures with diameters of 0.66—0.67 nm,5,6 which makes * Based on the materials of the XXI Mendeleev Congress on General and Applied Chemistry (September 9—13, 2019, St. Petersburg, Russia). ** Boreskov Institute of Catalysis, Siberian Branch, Russian Academy of Sciences.
possible the diffusion of heptane isomers with kinetic diameters of molecules of 0.43—0.62 nm.7 Narrower channels of the third type with a kinetic diameter of 0.56 nm allow only the diffusion of normal and monomethylsubstituted isomers of heptane. The main advantages of zeolite systems are their simple preparation, developed pore structure, good performance characteristics, and the possibility to co
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