Effect of ZSM-5 Zeolite Modification with Nickel on Its Activity and Stability in the Isomerization of С5в€’С8 Alkanes of the Virgin Gasoline Fraction of Petroleum
L. M. VELICHKINA, D. A. KANASHAVICH, and A. V. VOSMERIKOV
Institute of Petroleum Chemistry, Siberian Branch of the Russian Academy of Sciences, Pr. Akademicheskiy 4, Tomsk 634055 (Russia)
Keywords: цеолит типа ZSM-5, модифицирование, нанопорошок никеля, алканы С5–С8, бензин, изомеризация, конверсия, селективность, активность, стабильность, кокс, ZSM-5 type zeolite, modification, nickel nanopowder, С5–С8 alkanes, gasoline, isomerization, conversion, selectivity, activity, stability, coke
Abstract
Russia is strongly behind the leading oil-processing countries in the production of high-octane nonaromatic components of motor petrol (in particular, isomerizate petrol) from light hydrocarbon raw material. One of the possible means to solve this problem is the use of ZSM-5 type zeolites as isomerization catalysts, which allows the process to be carried out under non-standard conditions: without the admission of hydrogen-containing gas into the reaction medium at atmospheric pressure, without the use of precious metals and superacid additives. In the present work, high-silica zeolite of the ZSM-5 structural type with the silica ratio equal to 40 was obtained by means of hydrothermal synthesis and then modified by nanometer-sized nickel powder. The catalytic activity of initial and Ni-containing zeolites and the dynamics of there deactivation were studied in the transformations of n-pentane, n-hexane, n-heptane, n -octane, a mixture of pentane and hexane and the virgin gasoline fraction of petroleum. It was shown that the major products of the transformation of light hydrocarbon raw material at the catalysts under study are n - and isoalkanes С4-С8, alkyl benzenes; naphthenes and olefins are formed in insignificant amounts. Zeolite modification with nanometer-sized nickel promotes an increase in the yield of liquid products with increased isoalkane content and makes the stability higher in comparison with the initial sample. This is due to the presence of active Ni-containing centres in the catalytic system; these centres participate in hydrogenation-dehydrogenation reactions. As a result, the rate of the formation of condensed molecules (which are coke precursors) decreases, and catalyst deactivation proceeds slower. The largest amount of carbon deposits having the dense structure is formed in the conversion of n-octane, while the smallest one is formed in the conversion of n-pentane.
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