1070-4272/05/7811-1854+2005 Pleiades Publishing, Inc.
Russian Journal of Applied Chemistry, Vol. 78, No. 11, 2005, pp. 1854!1858. Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 11,
2005, pp. 1886 !1890.
Original Russian Text Copyright + 2005 by Agaeva, Dadashev, Tagiev, Abasov.
Increase in Selectivity of Toluene Disproportionation
and in p-Xylene Yield by Optimization
of Zeolite Microporous Structure
S. B. Agaeva, B. A. Dadashev, D. B. Tagiev, and S. I. Abasov
Mamedaliev Institute of Petrochemical Processes, National Academy of Sciences of Azerbaijan,
Received September 20, 2004
Abstract-The possibility of increasing the yield of target products and para-selectivity of toluene dispropor-
tionation on modified zeolites by optimization of their microporous structure was studied.
Benzene and xylenes (especially p-xylene) are
widely used in industry. The main method of the syn-
thesis of the above compounds is alkene dehydrocy-
clization. In the process, benzene (BZ) and xylenes
(XLs) are formed together with large amounts of
toluene (TL). Disproportionation of TL allows an in-
crease in the production of BZ and XLs.
The TL disproportionation (TD) is an acid-type
reaction and is catalyzed by H forms of zeolites [1, 2].
A study of TD on Y and M type zeolites and on pen-
tasils showed that TD proceeds with the highest effi-
ciency but with low selectivity on HY and on cata-
lysts based on Y, with rapid deactivation of the cata-
lysts. The catalysts based on mordenite are less active
but more selective and stable than Y-based catalysts.
The pentasil-based catalysts (ZSM-5) are less active
but very selective and stable. They are also character-
ized by high selectivity for p-xylene (p-XL).
Thus, development of new zeolite catalysts of TD
should involve either Y- and M-based zeolite catalysts
or enhancing the activity of ZSM-5. Taking into ac-
count that mordenite catalysts are highly active, selec-
tive , have commercial application , and are
more stable with respect to modification than Y, we
believe that the synthesis of more selective and active
M-based catalysts for TD is possible.
In this study, we examined the effects of modifying
synthetic mordenite on the selectivity of TD and p-XL
Na-exchanged zeolites Y (Y), synthetic mordenite
M (M), ZSM-5, and natural mordenite (NM) from
Chananab deposit (Azerbaijan) were initial materials
for the catalyst synthesis. The samples were syn-
thesized by decationization of the initial zeolites by
ion exchange with 2 M NH
Cl followed by calcina-
tions at 823 K and dealumination with 2.5 M HCl .
After these procedures, the SiO
ratio for M
was determined by the method suggested in . Then,
the zeolites obtained were modified with a rare-earth
element (REE) (Gd) by the ion-exchange procedure
(0.5 mol % Gd
) and with a transition metal (Co)
by ion-exchange impregnation (2.5 wt %). The modi-
fied zeolites were molded with a binding agent, alu-
mina gel, taken in the amount of 25 g of Al
100 g of dry catalyst.
The catalytic conversion of TL was studied at at-
mospheric pressure in a flow-type catalytic apparatus
equipped with an adiabatic reactor. Experiments were
performed within the 6733748 K range at the space
velocity of 1 h
/toluene ratio of 3.
The products of TL conversion were analyzed chro-
matographically on a capillary column (50 00.25 mm)
coated with liquid-crystalline phase, methoxyethoxy-
azobenzene (T = 360 K; carrier gas argon).
Adsorption properties of the catalysts were studied
gravimetrically on a vacuum device equipped with
a McBain quartz balance. Benzene was used as an
adsorbate. Experiments were performed at 293 K
within the range of relative pressures p/p
03 0.3. Iso-
therms of benzene adsorption on zeolites used as
catalysts are related to type I isotherms in accordance
with Brunauer classification and are well described by
the Dubinin3Radushkevich equation 
where a is the amount of the adsorbate sorbed