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B. Erdem, A. Kara / Reactive & Functional Polymers 71 (2011) 219–224
Nomenclature
A, B, E, W propionic acid, n-amyl alcohol, amyl propionate and
T
R
t
XAe
CA
CB
CE
CW
temperature (K)
water, respectively
gas constant (kJ molꢀ1 Kꢀ1
time (min)
)
k1
CA,0
Ke
XA
A
forward reaction rate constant
initial concentration of propionic acid (mol Lꢀ1
equilibrium constant of the reaction
conversion of propionic acid
)
equilibrium conversion of propionic acid
concentration of propionic acid (mol Lꢀ1
concentration of methanol (mol Lꢀ1
concentration of methyl propionate (mol Lꢀ1
concentration of water (mol Lꢀ1
)
)
Arrhenius preexponential factor (L2 molꢀ1 minꢀ1
)
)
EA
apparent activation energy (kJ molꢀ1
)
)
our previous articles [16,17]. EGDMA and VTAZ were polymerized
in suspension with AIBN and PVAL as the initiator and the stabi-
lizer, respectively. Toluene was included in the polymerization rec-
ipe as the diluent (a pore former). A typical preparation procedure
with little differences is as follows. A continuous medium was pre-
pared by the dissolution of PVAL (200 mg) in purified water
(100 mL). For the preparation of dispersion phase, EGDMA (4 mL;
20 mmol) and toluene (10 mL) were stirred for 15 min at room
temperature. Then, VTAZ (3 mL; 35 mmol) and AIBN (100 mg)
were dissolved in the homogeneous organic phase. We dispersed
the organic phase in the aqueous medium by stirring the mixture
magnetically (700 rpm) in a sealed cylindrical Pyrex polymeriza-
tion reactor. The reactor content was heated to the polymerization
temperature (i.e. 323 K) within 2 h, and the polymerization was
conducted for 12 h with 800 rpm stirring rate at 343 K. The final
beads were washed extensively with ethanol and water to remove
any unreacted monomer or diluent and then stored in distilled
water at 277 K. The poly (EGDMA–VTAZ–SO3H) beads were pre-
pared by mixing of different percentages of H2SO4 solution (10%,
15%, 20% and 30%, respectively) with poly (EGDMA–VTAZ) polymer
at 298 K in a sealed cylindrical Pyrex reactor for 2 h. The solid was
filtered and vacuum dried at 343 K overnight and stored in the
glove box for characterizations.
titrated potentiometrically by drop-wise addition of 0.01 M NaOH
(aq) [18,19].
2.3. Catalytic tests
The esterification of propionic acid with methanol was carried
out in an isothermal glass reactor equipped with a heating jacket.
A reflux condenser was placed on top of the reactor in order to pre-
vent the escape of the volatile compounds. The stirring speed was
700 rpm and temperature was controlled within 0.1 °C by circu-
lating water from a thermostat into a cylindrical water-jacked of
the reactor. The reactions were realized in the solution of dioxane
of 99.8% purity (Merck). In a typical run, catalyst (about 1 g), meth-
anol and dioxane of known amount were charged into the reactor
and preheated to the reaction temperature and the esterification
was commenced by injecting preheated propionic acid into the
mixture. This was considered as the zero time for a run. The total
liquid volume was 100 cm3. Samples were withdrawn and the
amount of unreacted acid was analyzed by titration with 0.1 M
sodium hydroxide. Stoichiometric ratio of propionic acid to methanol
was changed from (2:1) to (1:2) in the experiments performed at
333 K. To calculate the apparent activation energy the reaction
temperature was changed from 318 K to 343 K.
3. Results and discussion
2.2. Catalyst characterization
3.1. FT-IR studies
FT-IR measurements were performed on a Thermo Nicolet 6700
series FT-IR spectrometer in normal transmission mode with a KBr
detector over the range 4000–400 cmꢀ1 at a resolution 8 cmꢀ1
averaged over 32 scans.
In order to test whether sulphur enters to the polymeric struc-
ture, poly (EGDMA-VTAZ) (Sample I), and poly (EGDMA–VTAZ–
SO3H) having different percentages of H2SO4 (Samples II–V) beads
were subjected to elemental analysis with LECO CHNS-932 model
elemental analyzer.
Thermal stabilities of the poly (EGDMA–VTAZ) (Sample I) and
its sulfonic acid functionalized forms (Samples II–V) were exam-
ined by TG analyses with SII-EXSTAR TG/DTA 6200. The samples
(ꢁ5–10 mg) were heated from room temperature to 800 °C under
dried-air atmosphere at a scanning rate of 10 °C/min.
The surface morphology of poly (EGDMA–VTAZ–SO3H) catalyst
was investigated by scanning electron microscopy (SEM, Carl Zeiss
Evo 40). All observations were made at Uludag University Science
and Art Faculty Microscopy Laboratory. Selected representative
materials were sputter-coated with gold–palladium for two min-
utes in a BAL-TEC SCD 005. The micrographs were obtained by
using a voltage of 20 kV.
The FT-IR spectra of poly (EGDMA–VTAZ) (Sample I) and poly
(EGDMA–VTAZ–%SO3H) with various degrees of sulfonation (10%,
15%, 20% and 30%) (Samples II–V) are shown in Fig. 1. Compared
to poly (EGDMA–VTAZ), the distinguished features of poly (EGD-
MA–VTAZ–SO3H) were the presence of new absorption bands at
1070 cmꢀ1 and 1009 cmꢀ1 which are attributed to SO3H groups
[20]. This indicates that the SO3H groups were successfully incor-
porated into the matrix by adding H2SO4 in the synthesis system.
The intensities of these peaks also increase in parallel with the in-
crease in the percentage of H2SO4 in the blends [21].
On the other hand, the bands due to C@O stretching at
1722 cmꢀ1, C–O vibrations at 1177 cmꢀ1 for EGDMA, C–N, C@N
vibrations in the 1448–1638 cmꢀ1 and N–N stretching at 1270
cmꢀ1 for triazole ring were observed for all samples independent
of sulfonation. Additionally, a broadening of the band between
3500 and 2000 cmꢀ1 can be related to hydrogen bonding network
formation [22].
3.2. Elemental analysis
The acid exchange capacities of the poly (EGDMA–VTAZ–SO3H)
(Samples II–V) were measured by means of titration, using sodium
chloride as exchange agent. In a typical experiment, 0.05 g of solid
was added to 10 g of aqueous solution of sodium chloride (2 M).
The resulting suspension was allowed to equilibrate and thereafter
Data from elemental analyses of pristine polymer and its
sulfonic acid modified forms (Samples I–V) are shown in Table 1.
This is clear evidence indicating that SO3H groups are located in
the polymer, thus being accessible and useful for adsorption and