The alkylation of toluene with 1-heptene and 1-dodecene were used as model
reactions for the synthesis of long-chain linear alkylbenzenes, the precurs
ors of biodegradable surfactants. The effect of the pore structure of large
pore zeolites: HFAU (framework Si/Al = 15) and HBEA (framework Si/Al = 12.
5) on their catalytic properties was determined in liquid phase at 90 degre
esC with a toluene/alkene molar ratio of 3. With these large pore zeolites,
the main reactions are alkene double bond shift and toluene alkylation. Mo
noalkyltoluenes are the main reaction products, whereas bimonoalkyltoluenes
and alkene dimers appear in low amount from, respectively, HFAU and HBEA.
HBEA, despite the small size of its crystallite is practically inactive for
the toluene alkylation by 1-dodecene. This low activity can be attributed
to the slow desorption of the reaction product from the narrow pore of this
zeolite and more particularly the non-desorption of the 3- to 6-monododecy
ltoluenes. These steric constraints lead to the formation of bulky aromatic
compounds in the HBEA micropores. These components formed in larger amount
than over HFAU, are responsible to the blockage of the alkenes (dodecene m
ixture and dimers) in the zeolite pores. However, the limitation effect of
diffusion steps observed in the pore of HBEA leads to increase the selectiv
ity to 2-phenylalkanes which are the most biodegradable isomers. (C) 2001 E
lsevier Science B.V. All rights reserved.