Skeletal isomerization of n-butenes

Journal Article · Thu Feb 01 04:00:00 EST 1996 · Journal of Catalysis

DOI:https://doi.org/10.1006/jcat.1996.0053· OSTI ID:263707

Guisnet, M; Andy, P; Gnep, N S ^[1]

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1. Laboratoire de Catalyse en Chimie Organique, Poitiers (France); and others

The transformation of n-butenes and of isobutene was carried out at 350{degrees}C on a fresh H-FER zeolite (Si/Al = 13.8) with various contact times so as to obtain a large range of conversion (from 5 to 65%). With both reactants the skeletal isomerization was accompanied by the formation of various products. The skeletal isomer, propene, pentenes, octenes (traces), and n-butane (from n-butenes) or isobutane (traces from isobutene) appeared as primary products. The simultaneous formation of the skeletal isomer and of propene and pentenes proved the presence of a dimerization-cracking process. Moreover, the low amount of octenes in the products showed that dimerization was the limiting step of the process. The dimerization step involved two secondary carbenium ions, which explained its slow rate. The dimer was rapidly isomerized through Type A (alkyl shift) or Type B (via protonated cyclopropanes) isomerization into the other octenes. Lastly octenes with a trimethylpentane or a dimethylhexane skeleton were rapidly cracked into isobutene, propene, and pentenes through Type A (involving two tertiary and one secondary carbenium ions) mechanisms. The transformation of n-pentenes and of n-octenes confirmed the high rate of the Type A and B isomerization and cracking steps. The slow rate of octene formation from butenes was also due to an inhibition of the diffusion of branched octenes in the narrow pores of H-FER. The shape selectivity of H-FER was also responsible for the very slow formation of isobutane by hydrogen transfer from coke precursors to isobutene and for the unexpected slow formation of propene and of pentenes from isobutene. 43 refs., 5 figs., 2 tabs.

• OSTI ID: 263707
• Journal Information: Journal of Catalysis, Journal Name: Journal of Catalysis Journal Issue: 2 Vol. 158; ISSN 0021-9517; ISSN JCTLA5
• Country of Publication: United States
• Language: English

Related Subjects

02 PETROLEUM
40 CHEMISTRY
BUTENES
CATALYTIC CRACKING
CATALYTIC EFFECTS
HETEROGENEOUS CATALYSIS
ISOMERIZATION
ZEOLITES