408
KOZLOVA et al.
atmospheric pressure, and phenol : acetone molar ratio
in the starting mixture equal to 8 : 1 for 4 h.
are micropores. In the course of swelling, the solvent
penetrates into them, considerably expanding the
molecular network. As for the porosity of a macroporous
copolymer, it is similar to that of a sponge. The solvent
occupies the free space in the copolymer with only
insignificant expansion of the molecular network.
As catalyst base we used commercial cation-
exchange resins produced in Russia and other countries,
including the resins produced by Rohm & Hass/Dow
Chemical Company: Dowex HCR-S/S, Amberlite IR-
120H, Amberlite SR1L, Amberlyst 35WET, Amberlyst
15H; by LANXESS Deutschland GmbH: Lewatit C 267,
Lewatit S1567; by Purolite International Ltd: Purolite C
100EC, Purolite C 150; and by TOKEM Research and
Production Association (Kemerovo, Russia): KU-2-8
and KU-23 15/100. Both gel and macroporous resins
were used.
In the course of swelling, the volume of porous ion-
exchange resins changes to a considerably lesser extent
than the volume of nonporous ion exchangers does. For
example, the volume of granules of KU-2-8 nonporous
sulfonic cation exchanger increases upon hydration
by more than 100%, whereas for a macroporous ion-
exchange resin the volume change does not exceed 50%.
The properties of the commercial cation-exchange
resins used are given in Table 1.
The common property of the tested cation-exchange
resins is high acidity. It is known to play a crucial role in
the synthesis of bisphenols. The activity of the resin is
determined by the number of acid sites on the surface.As
we found, all the tested cation-exchange resins exhibit
high acidity (from −9 to −11 units in the Hammett acidity
function scale). KU-23 cation exchanger produced in
Russia and Amberlyst 35WET imported ion exchanger
exhibit the strongest acid properties. These cation
exchangers also demonstrated higher activity (Table 1).
As can be seen, the properties of porous ion-exchange
resins differ significantly from those of gel nonporous
ion exchangers. The porous resins have lower bulk
density (0.2–0.6 g cm–3) compared to the nonporous
resins (0.7–0.8 g cm–3). Porous and macroporous ion
exchangers contain numerous microscopic channels
(pores) already in the dry state. Therefore, the area of
contact of the resin with the reagents increases by a
factor of tens and hundreds (to 20–60 m2 g–1) relative
to gel ion-exchange resins for which the specific surface
area is extremely low and is determined, as a rule, by
the external geometric surface and ranges from tenth
fractions to several square meters per gram depending
on the grain size. The porous resins have large total pore
volume (up to 1.4 cm3 g–1) with the mean pore diameter
of approximately 300 Å. Resins with the gel structure
are virtually nonporous in both dry and swollen states.
The catalysts prepared from the gel resins are usually
less active than the macroporous cation exchanges in
the bisphenol synthesis by condensation of phenol with
acetone. The catalyst based onAmberlyst 35WET cation
exchanger exhibits the highest activity.
To optimize the process parameters of swelling
of Amberlyst 35WET resin, we studied the influence
exerted on the physicochemical properties of the catalyst
by the nature of the solvent causing swelling, its amount,
and temperature and time of the resin swelling. Swelling
was performed in water, ethanol, isopropyl alcohol,
acetone, phenol, and dichloroethane. The amount of the
agent causing swelling was varied from 40 to 60%. As
shown by the experiments, the nature and amount of the
solvent causing swelling do not influence the swelling
coefficient of the cation exchanger, the total exchange
capacity, and the pore structure of the resin.
Theporousresinsconsiderablysurpassthenonporous
resins in the mechanical strength, which is an extremely
important operation characteristic of the catalyst. For
example, the wear resistance of the macroporous cation
exchangers exceeds 99.9%, whereas for a gel cation
exchanger it is lower: 98.6–99.2%. The disintegration
pattern is different for these two types of the ion
exchangers: granules of a nonporous ion exchanger
crack into fine particles, whereas granules with the
macroporous structure crack into halves, or external
layers separate off.
As shown by our studies, the catalyst samples
prepared by swelling of Amberlyst 35WET cation
exchanger in distilled water at room temperature for
24 h, followed by drying at 70°С, modification with a
5% aqueous solution of 2-mercaptoethylamine (pH 3) at
room temperature for 20 h, and final drying in a vacuum
at 72°С for 12 h (modifier content 10 wt %), exhibit the
highest levels of activity and mechanical strength.
The favorable effect of the macroporosity on
the mechanical strength of the framework is due to
different, compared to the gel cation exchanger, swelling
mechanism. In a gel cation exchanger, the voids in the
molecular network formed in the course of cross-linking
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 89 No. 3 2016