J. Houzvicka et al., THE ROLE OF BIMOLECULAR MECHANISM IN THE SKELETAL ISOMERIZATION OF N-BUTENE TO ISOBUTENE, Journal of catalysis, 164(2), 1996, pp. 288-300
Several methods were used to evaluate the potential role of bimolecula
r mechanism in skeletal isomerisation of n-butene to isobutene, Dimers
of n-butene were prepared and their reaction monitored. Product distr
ibutions of these reactions were compared with those obtained with n-b
utene. Comparison was performed with different catalysts at 1 bar tota
l pressure in an apparatus which makes both continuous dow and pulse e
xperiments possible. Com positions of products of the reactions of n-b
utene and of dimers were found to be very different an catalysts selec
tive to isobutene, On highly acidic catalysts, which form isobutene no
nselectively and show a high formation of by-products (C-3(=) and C-5(
=)), distributions were similac. Skeletal isomerisation is suppressed
by a higher pressure of butene while the rate of formation of by-produ
cts increases with increasing pressure. Optimum temperatures of dimeri
sation and of skeletal isomerisation differ considerably. All these re
sults indicate that bimolecular mechanism is responsible mainly for th
e byproducts. It is concluded that the skeletal isomerisation of n-but
ene to isobutene runs via a monomolecular mechanism whereas the by-pro
ducts are formed by cracking of dimers of n-butene. Another source of
the by-products seems to be dimers arising from isobutene, the latter
being first formed by a monomolecular skeletal isomerisation of n-bute
ne. The formation of by-products is suppressed when 10-membered ring z
eolite is used as a catalyst. (C) 1996 Academic Press, Inc.