Isomerization reactions of n-butenes over isomorphously substituted B/A1-ZSM-11 zeolites

• Published in: Microporous materials Vol. 2; no. 5; pp. 477 - 486
• Main Authors: Simon, Mark W., Xu, Wen-Qing, Suib, Steven L., O'Young, Chi-Lin
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.06.1994
• Subjects: B/AP-25M-11; Butene isomerization; Kinetics; B/AP-25M-11; Butene isomerization; Kinetics
• ISSN: 0927-6513; 1873-3107
• DOI: 10.1016/0927-6513(94)00026-3

Low levels of boron have been isomorphously substituted into pentasil zeolites and are active in butene isomerization reactions. The acidity of B/A1-ZSM-11 zeolites, measured by NH 3 adsorption, is significantly lower than the acidity of B 3+-free Al/ZSM-11 zeolites. These materials exhibit both Brønsted and Lewis acidities as determined by pyridine adsorption studies. Adsorption/desorption experiments with 1-C 4H 8 and i-C 4H 8 were studied to determine reactant and product shape selectivities. Complete isomorphous substitution of framework Al 3+ by B 3+ in ZSM-11 zeolites results in inactivity. Our data show that the reaction is first order in 1-C 4H 8 with slow deactivation via coke formation. The effect of flow rates on conversion, yields, selectivities, and product distributions has been studied on B/A1-ZSM-11 materials. Isobutene yields of 22% and selectivities of 47% have been obtained under optimal operating conditions using B/Al-ZSM-11 catalysts. Lower yields of i-C 4H 8 were obtained using Pt/B/Al-ZSM-11 zeolites with n-C 4H 10 as a feed gas. A temperature of 523°C was used in isomerization reactions while a temperature of 580°C was required in dehydrogenation/isomerization reactions. Propene is the major byproduct of this reaction, believed to form as a result of cracking of dimerized (and polymerized) olefins. This side reaction is the primary cause for deactivation and coke formation on the catalyst.