Sorption, acid, and catalytic properties of a sulfonic cation exchanger supported on the carbon fiber

Article abstract of DOI:10.1007/s11167-005-0155-9

Distribution in strength of the acid centers in sulfonic cation in the form of exchanger granules and fibers was studied by the novel modification of the thermal desorption method.

Full text of DOI:10.1007/s11167-005-0155-9

Russian Journal of Applied Chemistry, Vol. 77, No. 11, 2004, pp. 1761 1764. Translated from Zhurnal Prikladnoi Khimii, Vol. 77, No. 11,
2004, pp. 1779 1782.
Original Russian Text Copyright
2004 by Egiazarov, Shachenkova, Radkevich, Cherches, Gorbatsevich, Ermolenko.
SORPTION
AND ION-EXCHANGE PROCESSES
Sorption, Acid, and Catalytic Properties of a Sulfonic Cation
Exchanger Supported on the Carbon Fiber
Yu. G. Egiazarov, L. N. Shachenkova, V. Z. Radkevich, B. Kh. Cherches,
M. G. Gorbatsevich, and E. N. Ermolenko
Institute of Physical Organic Chemistry, Belarussian National Academy of Sciences, Minsk, Belarus
Received January 14, 2004; in final form, September 2004
Abstract Distribution in strength of the acid centers in sulfonic cation in the form of exchanger granules and
fibers was studied by the novel modification of the thermal desorption method.
Previously [1 3], we studied the activity of sul-
fonic cation exchanger granules and fibers in the
synthesis of methyl tert-alkyl ethers and found that
FIBAN K-1 surpasses in the activity KU2-8 (gel
structure) in the synthesis of methyl tert-butyl ether
(MTBE) and Dowex msm 31 (macroporous structure)
in the synthesis of methyl tert-amyl ether (MTAE).
K-1) and granular (Dowex msm 31) sulfonic cation
exchangers.
EXPERIMENTAL
The sorption of various liquids with the initial
Carbopon, synthesized samples of the supported sul-
fonic cation exchanger, FIBAN K-1 fibrous sulfonic
cation exchanger with gel structure, and Dowex msm
31 granular sulfonic cation exchanger with macropor-
ous structure was evaluated gravimetrically. A cation
exchanger sample ( 0.5 g) dried to the constant
weight at 90 C was introduced into a test tube, 10 ml
of a liquid was added, and the mixture was stored for
3 h. The sample was centrifuged (4000 rpm) for
15 min, weighed, and dried to the constant weight at
The main advantage of fibrous sulfonic cation
exchanger FIBAN K-1 is that the fiber diameter is
by approximately an order of magnitude smaller than
the diameter of KU-2-8 and Dowex msm 31 granules.
This decreases intradiffusion inhibition and intensifies
mass exchange.
The diameter of the Carbopon fiber can be es-
timated as 5 10 m, which is substantially smaller
than FIBAN K-1 fiber diameter. Hence, sulfonic
cation exchanger supported on Carbopon, when used
as a catalyst of acid base reactions, can provide more
intense mass exchange than FIBAN K-1.
1
90 C. The sorption value, G (g g ), was calculated
l
l
as the ratio of the liquid weight to the weight of dry
sample:
m1
m2
The performance of sulfonic cation exchanger sub-
stantially depends on its acidity, i.e., concentration
and strength of acid centers. The literature survey [4
6] shows that the most adequate method of its deter-
mination is ammonia thermal desorption. However,
for organic ion exchangers with a low thermal sta-
bility, ammonia is acceptable only for determination
of weak acid centers. To determine strong acid centers,
another thermal desorption method is required.
G =
,
m2
where m is the sample weight after centrifuging and
1
m , sample weight after drying at 90 C.
2
The average value of three parallel experiments
was used in calculations. Along with G , the volume
l
3
1
sorption V (cm g ) was also calculated.
l
l
As seen from Table 1, sorption of water with Car-
1
In this work, we studied sorption and acid proper-
ties and catalytic activity (by an example of MTAE
synthesis) of two samples of sulfonic cation exchanger
supported on Carbopon (sample I with gel structure
and sample II with macroporous structure) in com-
parison with their structural analogs, fibrous (FIBAN
bopon is 0.64 g g , which is substantially larger than
l
sorption of methanol and the other components of the
reaction mixture of the MTAE synthesis, and of
n-octane taken as a nonpolar liquid. The V values
l
show a clear correlation with the molecular size of
liquids [i.e., molecular-sieve effect characteristic for
1070-4272/04/7711-1761 2004 MAIK Nauka/Interperiodica

1762
EGIAZAROV et al.
Table 1. Sorption of liquids of various types with Carbopon and sulfonic cation exchangers
Initial Carbopon Sample I
Sample II
FIBAN K-1
Dowex msm 31
Liquid
Gl, gl g /Vl, cml3
g
1
1
Water
Methanol
Methylbutenes
Methanol : methylbutenes (1 : 1)
MTAE
0.64/0.64
0.34/0.44
0.19/0.29
0.23/0.33
0.19/0.24
0.19/0.27
0.95/0.95
0.47/0.60
0.22/0.34
0.33/0.48
0.27/0.34
0.16/0.23
0.44/0.44
0.20/0.25
0.14/0.21
0.16/0.22
0.14/0.18
0.15/0.21
1.04/1.04
0.67/0.85
0.26/0.40
0.70/0.97
0.42/0.53
0.14/0.20
0.96/0.96
0.59/0.75
0.23/0.35
0.62/0.86
0.41/0.52
0.08/0.11
n-Octane
finely porous sorbents (activated carbons, zeolites,
silica gels) appears].
attached to a carrier gas line in a chromatograph
thermostat. Then the thermostat heating is switched
on, and a sample is conditioned in a helium flow
The effect of molecular size of liquid is preserved
in samples of the sulfonic cation exchanger supported
on Carbopon, and, in addition, the effect of the struc-
ture of the grafted copolymer can be observed.
1
(30 ml min ) at 120 C for 2 h, cooled, and saturated
with ammonia for 30 min at room temperature. Phys-
ically adsorbed ammonia is eliminated from the cation
exchanger at room temperature in the helium flow.
The course of desorption and its completion were
monitored with a recorder. Then the stage of the ther-
mal desorption of the chemisorbed ammonia begins.
The temperature of the reactor is increased to 120 C,
and the sample is kept for 1 h in a helium flow. The
desorbed ammonia is trapped in a U-shaped glass
condenser cooled with liquid nitrogen and, after heat-
ing at 90 95 C with hot water, is transported with
helium flow to the katharometer, where it is moni-
tored as a chromatographic peak. Using a calibration
plot ammonia content peak area, we determined the
amount of ammonia desorbed and calculated from
the weight of the ion exchanger sample and its EC the
Sample 1 (2% DVB, gel structure) sorbs more
1
water (0.95 g g ) and the other polar components
l
than does Carbopon. However, as expected, sample I
sorbs nonpolar n-octane more weakly than does Car-
bopon. The fact that sample I is a weaker sorbent than
its structural analog, fibrous FIBAN K-1, can be
explained by lower exchange capacity (EC).
As compared to sample I and Carbopon, sample II
(25% DVB, macroporous structure) sorbs water
1
(0.44 g g ) and the other liquids substantially more
l
weakly, probably due to a rigid cellular structure of
the cation exchanger caused by the high degree of
cross-linking of the polymer chains. The difference
between the sorption properties of this sample and
Dowex msm 31 can also be explained by differences
1
concentration (mmol g ) and percentage of weak acid
centers in the sample.
1
To determine the concentration of strong acid cen-
ters, a cation exchanger sample is charged into a
reactor arranged in the thermostat of a chromatograph,
and the reactor is attached to an empty column func-
tioning as a preheater of the carrier gas. After sample
in their EC (1.3 and 4.4 mg-equiv g , respectively).
The novelty of the suggested method of the thermal
desorption of bases consists in using a weak base,
diethyl ether, as a desorbate to determine the concen-
tration of strong acid centers. It is desorbed from
the strongest acid centers of the dehydrated sulfonic
cation exchangers at 120 C, i.e., under conditions of
their thermal stability. In addition, diethyl ether is
characterized by low adsorption power, due to small
size of its molecule and low boiling point. Therefore,
the sorbed ether is readily eliminated from the cation
exchanger, which is important for obtaining correct
results.
1
training in a dried helium flow (30 ml mim ) at
120 C for 2 h, the reactor is cooled to room tempera-
ture and detached from the column, and diethyl ether
is added. After 1-h storage, excess ether is poured off,
the reactor is attached to the column and flame-ioniza-
tion detector, and the thermostat temperature is set at
75 C; the sample is kept in a helium flow until the
recorder pen returns to the zero level, which indicates
completion of ether desorption at this temperature.
Then the temperature is sharply elevated to 100 C, and
the peak of desorbed ether is recorded. After stabiliza-
tion of the baseline, the temperature of the thermostat
is elevated to 120 C, and the second desorption peak
The concentration of weak acid centers is deter-
mined performed as follows. A cation exchanger (ap-
proximately 0.2 g) is charged into a glass reactor
(70 mm long, 8 mm in diameter), and the reactor is
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 11 2004

SORPTION, ACID, AND CATALYTIC PROPERTIES
Table 2. Acid properties of sulfonic cation exchangers
Sulfonic cation exchanger
1763
Concentration and strength of acid centers
weak
medium
strong
very strong
DVB,
%
EC,
mg-equiv g
sample
1
1
1
1
1
mmol g
%
mmol g
%
mmol g
%
mmol g
%
I
II
2
25
2
1.7
1.3
3.1
4.4
0.27
0.17
0.40
0.86
16.3
13.3
12.9
19.5
1.16
0.97
2.35
3.32
69.2
74.8
75.6
75.4
0.16
0.10
0.27
0.18
9.4
7.9
8.8
4.1
0.09
0.05
0.08
0.04
5.1
4.0
2.7
1.0
FIBAN K-1
Dowex msm 31
25
is recorded. Then, using a calibration plot ether
content peak area, the amount of ether desorbed with-
in the 75 100 C range is determined and the concen-
tration and percentage of the strong acid centers in
the sample are calculated from the sample weight and
ion exchanger EC. Similarly, the amount of ether
desorbed within the 100 120 C range is determined
and the concentration of the very strong acid centers is
calculated.
device of the flow type. The reaction unit of the
device consisted of a catalytic reactor placed in a
thermostat, a vessel for the starting compounds, a
cooling system, and a product collector [2]. 1 g of
fibrous sulfonic cation exchanger was loaded into the
reactor, and the synthesis was performed under a pres-
sure of 0.8 MPa to ensure the liquid state of the reac-
tion system. In the case of granular sulfonic cation
exchanger, the resin sample was mixed with ground
glass of the same grain size to reach the volume of the
compacted fibrous sample (1.4 ml). In the experi-
ments, the process temperature was varied at a con-
In accordance with the conventional classification,
centers characterized by NH desorption at tempera-
3
1
1
tures of up to 120 C are weak acid centers, those
characterized by diethyl ether desorption within the
75 100 and 100 120 C ranges are strong and very
strong acid centers, respectively. The concentration of
medium-strength acid centers was determined as the
difference between the total amount the acid centers
in the sulfonic cation exchanger (numerically equal to
EC) and the sum of weak, strong, and very strong
centers. It follows from Table 2 that the sum of the
strong and very strong acid centers (strongly acidic
centers) in sample I amounts to 0.25 and in sample II,
stant rate of raw material feeding, 4 g g
h , and
ce
CH OH : i-C H molar ratio of 1 : 1.
3
5 10
Methylbutenes were prepared by dehydration of
isoamyl alcohol on -Al O at 330 C. The mixture
2
3
of isomers contained (%) 3-methyl-1-butene 45.8,
2-methyl-1-butene 19.4, and 2-methyl-2-butene 34.8.
The data on MTAE synthesis in the presence of
sulfonic cation exchangers studied are listed in
Table 3. The comparison of the sulfonic cation ex-
changers supported on Carbopon shows that sample I
is more active: the maximal content of MTAE in the
catalyzate reaches 42.4% at 80 C, while sample II
gives 35.4% MTAE at 100 C. These results coincide
with both the sorption properties of the samples and
the concentration of strongly acidic centers. The de-
crease in the MTAE content as a result of the higher
rate of the reverse reaction relative to the direct reac-
tion rate on sample I is observed at 90 C. For FIBAN
K-1 and Dowex msm 31, this decrease is observed
at 100 C, and for sample II still higher temperature is
required.
1
to 0.15 mmol g . In sulfonic cation exchangers
FIBAN K-1 (gel structure) and Dowex msm 31
(macroporous structure), which are structural analogs
of samples I and II, the concentration of strongly
acidic centers responsible for the catalytic activity of
the cation exchanger in the etherification reactions
1
amounts to 0.35 and 0.22 mmol g , respectively.
Thus, the concentration of strong acid centers in sam-
ples with gel structure is higher than in macroporous
samples. The content of strongly acidic centers in
the cation exchangers considered decreases in the
order FIBAN K-1 > sample I > Dowex msm 31 >
sample II.
When the MTAE content in the catalyzate at 80 C
is taken as a measure of the sulfonic cation exchanger
activity, the following activity order is observed:
sample I > FIBAN K-1 > Dowex msm 31 > sample II.
As seen, the position of Dowex msm 31 and sample II
in the catalytic activity series coincides with that in
It is interesting to compare the acid characteristics
of the sulfonic cation exchanger samples prepared
with their catalytic activity. The experiments on
MTAE synthesis were performed on a laboratory
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 11 2004

1764
EGIAZAROV et al.
Table 3. Synthesis of MTAE on sulfonic cation ex-
CONCLUSIONS
changers. Rate of raw material feeding 4 g gce1 h , molar
1
ratio CH3OH : i-C5H10 = 1 : 1
(1) Sorption properties of sulfonic cation ex-
changers supported on carbon fiber depend on the
degree of cross-linking of the styrene divinylbenzene
matrix: sample I (gel structure) substantially better
sorbs polar liquids than does sample II (macroporous
structure), whereas sorption of a nonpolar liquid
(n-octane) with these sorbents is virtually the same.
Content in catalyzate, wt %,
at indicated T,
C
Component
70
80
90
100
Sample I
(2) The study of the acid properties of samples I
and II by the modified method of the thermal desorp-
tion of bases showed that the concentration of strong-
ly acidic centers in sample I is substantially higher
than in sample II.
Methylbutenes
Methanol
MTAE
43.5
19.9
36.6
39.6
18.0
42.4
42.3
19.3
38.4
42.7
19.6
37.7
FIBAN K-1
Methylbutenes
Methanol
MTAE
48.6
22.2
29.4
41.5
19.0
39.5
39.2
17.9
42.9
46.0
21.0
33.0
(3) By an example of the synthesis of methyl
tert-amyl ether, it was shown that the catalytic activity
of sulfonic cation exchangers in acid base reactions
depends on both the resin acid properties and the dif-
fusion factors affecting the intensity of the mass
exchange.
Sample II
Methylbutenes
Methanol
MTAE
57.1
26.0
16.9
50.2
22.9
26.9
45.1
20.7
34.2
44.3
20.3
35.4
REFERENCES
Dowex msm 31
Methylbutenes
Methanol
MTAE
45.1
20.0
34.9
42.2
18.8
39.0
41.5
18.7
39.8
44.9
19.9
35.2
1. Cherches, B.Kh., Shunkevich, A.A., Belotserkov-
skaya, T.N., and Egiazarov, Yu.G., Zh. Prikl. Khim.,
1999, vol. 72, no. 4, pp. 623 627.
2. Cherches, B.Kh., Kovalenko, M.A., Shunkevich, A.A.,
et al., Neftekhimiya, 2002, vol. 42, no. 1, pp. 28 31.
the series of acid properties. FIBAN K-1 suprasses all
the other cation exchangers studied in the content of
strongly acidic centers; however, it is inferior in the
activity to sample I. Probably, in this case a size
factor (the diameter of the Carbonpon fibers is by an
order of magnitude smaller than that of FIBAN K-1
fibers), and the nature of sulfonic cation exchanger
support (carbon or polypropylene fiber), which can
affect the structure of the matrix formed, can contri-
bute to the catalyst activity.
3. Egiazarov, Yu.G. and Soldatov, V.S., Sorbts. Khroma-
togr. Prots., 2001, vol. 1, no. 4, pp. 591 599.
4. Tanabe, K., Solid Acids and Bases. Their Catalytic
Properties, Tokyo: Kodansha, 1970.
5. Topchieva, K.V. and Thoang Kho Shi, Aktivnost’ i fizi-
ko-khimicheskie svoistva vysokokremnistykh tseolitov
(Activity and Physicochemical Properties of High-
Silica Zeolites), Moscow: Mosk. Gos. Univ., 1976.
6. Egiazarov, Yu.G., Savchits, M.F., and Ustilov-
skaya, E.Ya., Geterogenno-kataliticheskaya izomeriza-
tsiya uglevodorodov (Heterogeneous Catalytic Isomeri-
zation of Hydrocarbons), Minsk: Nauka i Tekhnika,
1987.
Thus, sulfonic cation exchangers supported on
Carbopon show much promise, opening prospects for
development of the theory and practice of the catalysis
with cation exchangers.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 77 No. 11 2004