Selective conversion of n-butene to isobutylene at extremely high space velocities on ZSM-23 zeolites

Journal Article · Tue Nov 01 04:00:00 EST 1994 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1994.1320· OSTI ID:28668

Xu, Wen-Qing; Yin, Yuan-Gen; Suib, S L ^[1]; O`Young, C L ^[2]

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1. Univ. of Connecticut, Storrs, CT (United States)
2. Texaco, Inc., Beacon, NY (United States)

n-Butene has been isomerized to isobutylene on zeolite ZSM-23 catalysts at extremely high space velocities from 171 to 342 WHSV. The zeolite catalysts were prepared with hydrothermal methods by using pyrrolidine as a structure-directing template. The prepared materials have been characterized by SEM-EDX, XRD, FTIR, AA-ICP, TPD, BET surface area/pore size distributions, and pyridine chemisorption. Selectivities to isobutylene ranged from 85 to 95% and yields of isobutylene from 30 to 20%, depending on the space velocity of but-1-ene. Good stability in the catalytic activity for n-butene skeletal isomerization is an important characteristic of such ZMS-23 zeolites. Isobutylene is believed to be formed from n-butene via a methyl cyclopropane carbenium intermediate and this is a reversible process. Dimerization of butene molecules is a primary side reaction for n-butene skeletal isomerization. The dimerized products (octenes) are further cracked into propylene and pentenes via {beta}-scission of carbenium intermediates. Propylene, a product of the secondary reaction, is then dimerized to form hexenes or codimerized with butene to form heptenes. Conversion of but-1-ene to cis/trans-but-2-enes is greater than one predicts from thermodynamic equilibrium data. cis-But-2-ene is observed to be the preferential product for but-1-ene double bond migration. The preferential formation of cis-but-2-ene is due to a steric interaction of the methyl group in the secondary butyl carbenium intermediate with the pore wall of the small pore zeolite, ZSM-23. Zeolite ZSM-23 also shows shape selectivity for adsorption of ammonia, but-1-ene, and isobutylene. The shape selectivities of these materials are further improved after aging of catalysts used in but-1-ene skeletal isomerization. 26 refs., 14 figs., 2 tabs.

• OSTI ID: 28668
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 1 Vol. 150; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
2-METHYLPROPENE
40 CHEMISTRY
BUTENES
CATALYTIC EFFECTS
ISOMERIZATION
REACTION INTERMEDIATES
ZEOLITES