Volumetric, chromatographic, refractometric studies on the esterification of methanol with acetic acid in the presence of cation-exchange resins

Article abstract of DOI:10.1524/zpch.2006.220.6.735

Esterification of methyl alcohol with acetic acid catalysed by commercially available polymeric ion-exchange resins Amberlyst-15, Dowex 50W and Amberlite IR-120 was carried out in the temperature ranging between 323-338 K. Mesh sizes and divinylbenzene contents had virtually no effect on the rate the data of which were correlated with a second-order homogeneous reaction. The samples were analysed with gas chromatography, refractometry and volumetry. The reproducibilities were the order of ±2.89%, ±5.07% and the order of ±6.58% respectively for the volumetric, chromatographic and refractometric methods. by Oldenbourg Wissenschaftsverlag.

Full text of DOI:10.1524/zpch.2006.220.6.735

Z. Phys. Chem. 220 (2006) 735–738 / DOI 10.1524/zpch.2006.220.6.735
 by Oldenbourg Wissenschaftsverlag, München
Volumetric, Chromatographic, Refractometric
Studies on the Esterification of Methanol
with Acetic Acid in the Presence
of Cation-Exchange Resins
∗
By Beyhan Erdem and Mustafa Cebe
Department of Chemistry, Faculty of Science and Arts, Uludag University,
ˇ
Bursa 16059, Turkey
(Received March 2, 2006; accepted March 17, 2006)
Esterification / Ion-Exchange Resin / Experimental Methods / Kinetics /
Acetic Acid
Esterification of methyl alcohol with acetic acid catalysed by commercially available
polymeric ion-exchange resins Amberlyst-15, Dowex 50 W and Amberlite IR-120 was
carried out in the temperature ranging between 323–338 K. Mesh sizes and divinylben-
zene contents had virtually no effect on the rate the data of which were correlated with
a second-order homogeneous reaction. The samples were analysed with gas chromatog-
raphy, refractometry and volumetry. The reproducibilities were the order of 2.89%,
5.07% and the order of 6.58% respectively for the volumetric, chromatographic and
refractometric methods.
Conversions for the esterification reactions have long been known to be limited
by a slow reaction rate and the existence of reversible reactions. To accelerate
the reaction rate, the use of solid acid catalysts has received great attention [1].
Homogeneous catalysis can be carried out using an ion-exchange resin con-
taining the catalyst ion as its counter ion. The reaction mechanism and kinetic
orders remain those of homogeneous catalysis [2]. The preliminary mathemati-
cal modelling of the observed esterification kinetics was based on second order
kinetics which principally could be applied to both homogeneous and hetero-
geneous catalysts [3].
In the present study we chose a known reaction as a model and this reaction
between methanol and acetic acid over a catalytically active synthetic resin is
*
Corresponding author. E-mail: gbeyhan@uludag.edu.tr

736
B. Erdem and M. Cebe
as follows:
k
1
CH3COOH+CH3OH ꢀ CH3COOCH3 +H2O
(1)
k
2
HAc
MeOH
MeAc
Water
The aim of this communication is to find that which method (volumetry,
chromatography and refractometry) is more useful and sensitive for the model
reaction. Furthermore, the important variables such as mesh size, divinylben-
zene content, temperature, different catalysts affecting the rate of the reaction
were studied.
Ion-exchange resins and other chemicals used of analytical grade purity
were supplied by Sigma-Aldrich, Merck A.G.
The experimental assembly consisted of a 0.25 dm3 reactor fitted with a re-
flux condenser to prevent any loss of products. The reaction vessel was kept in
a stirred constant temperature bath where the temperature could be controlled
within an accuracy of 0.1 K by a controller. Amberlyst-15(macroporous),
Dowex 50 W (microporous) and Amberlite IR-120 (microporous) were used
to assess their efficacy in this reaction. In a typical experiment 10% (by mass)
catalyst concentration of all resins was used at a molar ratio of acetic acid
to methanol of 1 : 1 at 333 K (700 rpm). The liquid samples were analysed
by using a gas chromatography (UNICAM model 610 series) equipped with
flame ionisation detector (FID) and the Supel-Q-Plot, porous divinylbenzene
polymer; 30.0 m×320.0 µm ID×0.5 µm F column. Nitrogen was used as the
carrier gas. In the second method, liquid samples were titrated with the stan-
dard NaOH solution together with the phenolphthalein indicator. In the last
method, the refractive indexes of the liquid samples were measured by Abbe
digital refractometer (ATAGO DR-A1 Model).
The external and the internal diffusion don’t generally control the overall
rate in the ion-exchange resin catalysed process unless the viscosity of the re-
actant mixture is very high or the speed of agitation is very low [4, 6] and the
ion-exchange resins having small particles (500–570 µm) aren’t been chosen
as catalysts. The effect of divinylbenzene content on the rate of reaction was
studied by conducting the reactions with Dowex 50 W having 2%, 4% and 8%
DVB under otherwise the similar conditions. As the %DVB contents increase,
the acetic acid conversion was found to decrease slightly. Table 1 shows the
values of k1 for different cases.
The activity order of the catalysts was determined as follows: Amberlyst-
15 > Dowex 50 W > Amberlite IR-120. In a macroporous resin the pores are
so large that the reactants are able to diffuse into the pores and the products
to diffuse out without any resistance. Therefore the concentrations of the re-
actants in the bulk and inside the pores are almost the same and thus led to
a homogeneous reaction in the liquid phase [5, 7]. When the catalyst used was
a macroporous ion-exchange resin, a homogeneous reaction could be assumed.
Amberlite IR-120 has a tighter pore structure as compared to the others and

Volumetric, Chromatographic, Refractometric Studies on the Esterification . . .
737
Table 1. According to Eq. (3), the calculated rate constants of the model reaction carried
out with different types of catalysts, different mesh sizes of catalysts and different DVB
contents of catalysts by the volumetric method and the suitability of the kinetic equation
to the experimental data.
Catalyst type
k1 (×103 dm3 mol−1 min−1 %2.89)
R2
Amberlyst-15
4.60
3.56
2.11
0.9996
0.9984
0.9956
Dowex 50 W × 4
Amberlite IR-120
Dowex 50 W × 2
Dowex 50 W × 4
Dowex 50 W × 8
Dowex 50 W × 4 (50–100 mesh)
Dowex 50 W × 4 (100–200 mesh)
Dowex 50 W × 4 (200–400 mesh)
3.64
3.56
3.49
0.9944
0.9984
0.9956
3.56
3.62
3.50
0.9984
0.9960
0.9959
Table 2. According to Eq. (3), the calculated rate constants of the model reaction carried
out with different methods, standard deviations and the relative errors for these methods.
Experimental method
k1 (×103 dm3 mol−1 min−1 std. error)
% error
volumetric
chromatographic
refractometric
5.19 0.15
3.75 0.19
3.19 0.21
2.89
5.07
6.58
there is likely to be substantial intraparticle diffusional resistance [8, 9]. The
rate of model reaction (1) can be written by using the homogeneous model in
terms of the fractional conversion of the acetic acid.
dXHAc
2
= k1(1− XHAc)2 −k2(XHAc
)
(2)
dt
ꢀ
ꢁ
XHAc,e −(2XHAc,e −1)XHAc
XHAc,e − XHAc
1
ln
= 2k1
−1 CHAc,0
t
(3)
XHAc,e
ꢀ
ꢁ
EA
R
1
ln k1 = ln A −
.
(4)
T
According to Eq. (4), the activation energy was found to be 48.16 kJ mol−1.
Rate constants of the model reaction followed by different methods are given
in Table 2. The sensitivity order of these experimental methods was determined
as follows: volumetric > chromatographic > refractometric.

738
B. Erdem and M. Cebe
Acknowledgement
This work was supported by the Research Fund of The University of Uludagˇ
Project number 2003/66 and this support is gratefully acknowledged.
References
1. W. T. Liu and C. S. Tan, Ind. Eng. Chem. Res. 40 (2001) 3281.
2. Y. Gerasimov, V. Dreving, and E. Eremin, Physical Chemistry. Vol. 1. MIR Publish-
ers, Moscow (1974) p. 505–510.
3. J. Lilja, D. Yu. Murzin, T. Salmi, J. Aumo, P. Maki-Arvela, and M. Sundell, J. Mol.
Catal. A 182–183 (2002) 555.
4. S. I. Kırbas¸lar, H. Terziogˇluve, and U. Dramur, Chinese J. Chem. Eng. 9 (2001) 90.
5. A. Chakrabarti and M. M. Sharma, Reactive Polym. 20 (1993) 1.
6. Z. P. Xu and K. T. Chuang, The Canadian J. Chem. Eng. 74 (1996) 493.
7. R. Roy, and S. Bhatia, J. Chem. Technol. Biotechnol. 37 (1987) 1.
8. G. D.Yadav and H. B. Kulkarni, Reactive & Functional Polym. 44 (2000) 153.
9. G. D.Yadav and P. H. Mehta, Industrial Eng. Chem. Res. 33 (1994) 2198.