Hydroisomerization of Cyclohexane and n-Pentane over Series of Mordenite Catalysts of Varying Silica-Alumina Ratio

Abstract

Four palladium-hydrogen mordenite catalysts of varying silica-alumina mole ratio were evaluated in the hydroisomerization reactions of cyclohexane and n-pentane. A kinetic model was developed for the cyclohexane reaction over these catalysts. One batch of sodium mordenite was used as the source from which each of the catalysts was prepared. The standard or parent mordenite preparation was caustic-leached to remove silica, producing a catalyst with a lower silica-alumina ratio than the standard mordenite, and two other catalysts with higher silica-alumina ratio than the standard mordenite were made by acid-extracting alumina from the standard mordenite preparation. Each of the catalysts contains about 1/2 wt % palladium. Isomerization rates were temperature sensitive for all of the catalysts, and energies of activation were presented for both the cyclohexane and n-pentane reactions. The effect of the partial pressure of the hydrocarbons and hydrogen was represented by a dual-site adsorption model. Isomerization activity was observed to initially increase with an increase in silica-alumina ratio and then decrease with additional increase in the ratio. It is felt that the reduction in surface area and active acid sites at the higher alumina extraction is primarily responsible for the loss in activity at the higher silica-alumina ratio. A general relationship for both reactions is not apparent.AAolecular sieve zeolites have in the past decade been demonstrated to be outstanding catalysts for isomerization reactions (Voorhies and Bryant, 1968; Beecher and Voorhies, 1969;Rabo et al., 1961). Mordenites particularly are active isomerization catalysts (Voorhies and Bryant, 1968; Beecher and Voorhies, 1969;Benesi, 1965). Thus, these catalytic qualities have prompted a number of kinetic studies by use of zeolites for isomerization reactions. Voorhies and Bryant (1968) have reported on the isomerization of -pentane, and Beecher and Voorhies (1969) on the isomerization of hexanes.Modifications of the SÍO2/AI2O3 ratio in the mordenite are also particularly interesting because of the changes in catalytic activity which have resulted. Beecher et al. (1968) have investigated activity changes for decalin and decane hydrocracking fora change in SÍO2/AI2O3 from 12 to 66. The cracking activity was greater at the higher ratio. Weller and Brauer (1969), however, observed that n-hexane cracking activity went through a maximum as the SÍO2/AI2O3 ratio was increased over a much narrower range. Eberly and Kimberlin (1970) reported that cumene cracking activity increased with SÍO2/AI2O3 ratio.However, Kranich et al. (1970) and Bierenbaum et al. (1971) observed from differential conversions a loss of cracking activity for cumene at high SÍO2/AI2O3 ratios. et al. (1971) reported on the effect of S1O2/AI2O3 ratio on acidic properties of mordenite and isomerization activity for -pentane; Kranich et al. (1970) investigated activity changes with SÍO2/AI2O3 ratios for butene isomerization; and Piguzova et al. (1969) on the change in isomeriza...

Solvate‐Supported Proton Transport in Zeolites

“…The broad academic and industrial interest in Brønsted‐acidic zeolites predominantly results from their technical importance in heterogeneous catalysis and gas sensing and separation. In heterogeneous catalysis zeolites have been used since the 1960s as shape‐selective acid catalysts in petrochemical processes, for example, conversion of methanol to gasoline1–6 and cracking and isomerization of hydrocarbons 7–10. More recently, increasing interest has arisen in the use of zeolites as gas‐sensitive materials.…”

Hydroisomerization and Hydrocracking of Cyclohexane in the Presence of a Paladium-Hydrogen-Faujasite Catalyst

“…However, the free energy change involved in the cyclohexane hydroisomerization is small, and erroneous results could be obtained when relying on a small difference between two large numbers. Consequently, the experimentally determined equilibrium constants obtained by Hopper and Voorhies (1972) in the range 400-600°F were used in the present study. The experimental equation relating K with temperature is…”

“…Research work on cyclohexane isomerization catalysis has been extensive. The catalyst types employed to isomerize cyclohexane can be grouped into four general categories: acidic halides (Condon, 1958; Stevenson and Morgan, 1948;Lien, et al, 1952;Pines, et al, 1950Pines, et al, , 1953, e.g., A1C13 and HC1; acidic chalcides (Condon, 1958), e.g., WS2; dual-function metal on amorphous supports (Ciapetta and Hunter, 1953), e.g., NÍ-SÍO2-AI2O3; and dual-function metals on zeolites (Hopper and Voorhies, 1972;Allan and Voorhies, 1972), e.g., crystalline aluminosilicates. In general, the same catalyst types employed for hydroisomerizing cyclohexane have been utilized to study the hydrocracking or ring-opening reactions (Cawley and Hall, 1944; Egan, et al, 1962;Hatcher and Voorhies, 1969).…”

Sorption and diffusivity characteristics of acid‐leached mordenites

“…Recent papers on H-mordenite-catalyzed reactions, which also give guidance to earlier literature, include studies of hydrocracking of n-hexane and cyclohexane (Voorhies and Hatcher, 1969), of hexane isomerization (Beecher and Voorhies, 1969), and of methanol dehydration (Swabb and Gates, 1972). Acid-leached mordenites of various silica-alumina ratios were studied by Eberly and Kimberlin (1970) far cracking of cumene, by Beecher et al (1968) for hydrocracking of n-decane and Decalin, by Hopper and Voorhies (1972) for hydroisomerization of cyclohexane and n-pentane, and by Thakur and Weller (1973) for cracking of hexane.…”