SHAPE-SELECTIVE OLIGOMERIZATION OF ALKENES TO NEAR-LINEAR HYDROCARBONS BY ZEOLITE CATALYSIS

Oligomerization results of propene, 1-decene, and isobutene catalyzed by zeolite HZSM-5 and zeolite HZSM-5 surface deactivated with 2,6-di-t ert-butylpyridine show that faster oligomerization and a higher percen tage of C-20(+) products are obtained with the unmodified HZSM-5. Resu lts of C-13 NMR analysis show that when the oligomerization takes plac e inside ZSM-5 channels, the structures of the C-20(+) products are ne arly linear, with a small amount of methyl branching. A higher degree of methyl branching is obtained at higher reaction temperatures, The C -20(+) products obtained from different olefins with surface-deactivat ed HZSM-5 under the same experimental conditions have nearly identical structures. The near-linear structure of the product indicates that w hen the oligomerization reaction takes place inside HZSM-5 channels, m ost of the alkyl substituents at the double bond of the olefins become part of the polymer chain, due to the steric requirement. When the su rface acidity is unmodified, most oligomerization reaction takes place at the outer surface of the zeolite, and complex product structures r esult. (C) 1996 Academic Press, Inc.