Kinetic study of transesterification of methyl acetate with n-butanol catalyzed by NKC-9

Article abstract of DOI:10.1002/kin.20378

The transesterification of methyl, acetate and n-butanol catalyzed by cation-exchange resin, NKC-9, was studied in this work to obtain the reaction kinetics. The experiments were carried out in a stirred batch reactor at different temperatures (328.15, 33

Full text of DOI:10.1002/kin.20378

Kinetic Study of
Transesterification of
Methyl Acetate with
n-Butanol Catalyzed
by NKC-9
BAOYUN XU, WEIJIANG ZHANG, XUEMEI ZHANG, CUIFANG ZHOU
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, People’s Republic of China
Received 18 December 2007; revised 10 June 2008, 15 July 2008, 20 July 2008; accepted 20 July 2008
DOI 10.1002/kin.20378
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The transesterification of methyl acetate and n-butanol catalyzed by cation-
exchange resin, NKC-9, was studied in this work to obtain the reaction kinetics. The exper-
iments were carried out in a stirred batch reactor at different temperatures (328.15, 333.15,
338.15, 343.15, 345.15 K) under atmospheric pressure. The effects of temperature, molar ratio
of reactants, and catalyst loading on the reaction rate were researched under the condition of
eliminating the effect of diffusion. The experimental data were correlated with a kinetic model
based on the pseudo-homogeneous catalysis. The kinetic equation describing the reaction cat-
alyzed by NKC-9 was developed. ꢀ 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 101–106,
C
2009
The esterification of acids and alcohols is one of
the most important applications of resin catalysis. Like
esterification, transesterification can be catalyzed by
ion-exchange resin. The advantage of a heterogeneous
catalyst is well known, and the use of solid ion-
exchange resin as the catalyst has the following inher-
ent advantages: (i) The catalyst can be easily separated
from the reaction products by decantation or filtra-
tion; (ii) continuous operation in column is possible;
(iii) the side reaction can be eliminated and the product
purity is high, etc. [1]. The strong acid cation-exchange
resin has been used commercially as solid acid cata-
lyst in many areas. Harmer and Sun [2] summarized
the recent development on the applications in alkyla-
tion, transalkylation, isomerization, esterification, etc.
Several papers show that the cation-exchange resin has
an excellent catalysis on the reaction.
INTRODUCTION
Methyl acetate is a by-product during the production of
PVA (poly(vinyl) alcohol). From 1 ton of PVA, about
1.68 ton of methyl acetate is produced. The industrial
application of methyl acetate is low. But as the prod-
ucts of transestrification of methyl acetate with n-butyl,
methanol is a raw material for PVA production; n-butyl
acetate is an important solvent in plastics, resins, gums,
and coatings, etc.; what is more, it can be used as an
extracting agent or intermediate in organic synthesis.
Thus the most attractive way will be to convert methyl
acetate into methanol and n-butyl acetate.
Correspondence to: Xuemei Zhang; e-mail: zhang-xby@163.
com.
c
ꢀ
2008 Wiley Periodicals, Inc.

102
XU ET AL.
Several papers have reported on this transesterifi-
cation, catalyzed by a heterogeneous catalyst. Bott re-
ported the method that is used to produce acetic acid
esters by alkali-transesterification of acetic acid es-
ter with an alcohol. The reaction was carried out in
the middle section of a distillation column. The alco-
hol or the mixture of alcohol and ester is drawn from
the top of the column. The higher boiling ester was
taken from the lower zone of the column [3]. Jime´nez
et al. reported the production of n-butyl acetate and
methanol via reactive and extractive distillation. In this
study, Amberlyst 15 was used as a catalyst. The kinet-
ics, mass-transfer, and process modeling were studied
[4]. Steinigeweg and Gmehling reported the transes-
terification process of methyl acetate and n-butanol
by combination of reactive distillation and pervapora-
tion. The result shows that it is favorable since conver-
sions close to 100% can be obtained with a reasonable
size of the reactive section [5]. Bozek-Winkler and
Gmehling studied the kinetic behavior of the reaction
of methyl acetate and butanol, leading to butyl acetate
and methanol catalyzed by Amberlyst 15. Two dif-
ferent kinetic models have been built to describe the
reaction kinetics that can be applied to the designing
of the reactive distillation process or the membrane
reactor [6].
Apparatus
The experiments were performed in a 500-mL
round-bottom glass reactor dipped in the constant-
temperature water bath. The reactor was equipped
with the temperature indicator (Pt-100) and a speed-
monitoring facility. The reflux condenser was used to
avoid any possible loss of volatile components.
Procedure
The methyl acetate, n-butanol, and catalyst were
charged into the separate vessels dipped in the wa-
ter bath. Once the desired temperature was attained,
methyl acetate and catalyst were charged into the
n-butanol, it was considered as the zero reaction time.
One-milliliter samples, which were considered negli-
gible to the total volume of reactants, were withdrawn
at specified time intervals.
Samples were analyzed by SP-2100 gas chromatog-
raphy with a thermal conductivity detector (H2 as a
carrier gas, a stainless-steel column packed with PEG
20 M 3 m × 2 mm, column temperature 140◦C, detector
temperature 160◦C, injector temperature 200◦C; reten-
tion time: methanol 0.98 min, methyl acetate 1.4 min,
n-butanol 3.6 min, and n-butyl acetate 5.4 min).
Chromatography data were collected at a workstation
N2000 (Zhejiang University Zhida Information En-
gineering Co. Ltd.) and processed with the modified
area normalization method to determine the product
composition.
In this paper, the chemical equilibrium and the re-
action kinetics of transestrification of methyl acetate
with n-butanol producing n-butyl acetate and methanol
were studied. The reaction can be presented as
CH3COOCH3 + CH3(CH2)3OH
RESULTS AND DISCUSSION
Calculation of Activities
ꢀ
CH3COO(CH2)3CH3 + CH3OH
(1)
ꢁ
A strong acid cationic exchange resin, NKC-9, was
used as a heterogeneous catalyst. The forward and
reverse reactions were investigated, and the pseudo-
homogeneous model was studied in this work.
Nonideality of the liquid phase was corrected by re-
placing components’ concentration with activities. The
components’ activity coefficients were calculated by
the UNIFAC group contribution methods. The split-
ting of the groups is shown in Table I. The volume
and area parameters of the groups and their interaction
parameters are quoted from Peisheng Ma [7].
EXPERIMENTAL
Materials
Mass-Transfer Resistance
n-Butanol (99.9% w/w) and methyl acetate (99.9%
w/w) were obtained from Ke Wei Co. Ltd., Tianjin,
China. The catalyst, i.e., the cationic exchange resin,
NKC-9 in the form of H+, was purchased from Chem-
ical Plant of Nankai University, Tianjin, China. Its ap-
pearance is like a camel bead, the particle size was
0.4–0.7 mm, and the volume exchange capacity was
4.7 mmol/g. The catalyst was washed with methanol
to remove impurities and dried at 343.15 K.
To evaluate the effect of external mass-transfer resis-
tance on the conversion of methyl acetate, the reaction
was carried out at three different stirring speeds, mean-
while the rest of the reaction conditions were similar.
As we can see from Fig. 1, the speed of agitation had
no effect on the reaction rate at third and fourth gears,
which ensured the absence of external mass-transfer
resistance. All further experiments were performed at
International Journal of Chemical Kinetics DOI 10.1002/kin

TRANSESTERIFICATION OF METHYL ACETATE WITH n-BUTANOL CATALYZED BY NKC-9
103
Table I UNIFAC Group Identification of the Components
Group Identification
Volume Parameter,
Rj
Area Parameter,
Qj
Molecular
Group Name
Main
Secondary
vj(i)
Methyl acetate
CH3COO
CH3
CH3
CH2
OH
CH3COO
CH2
CH3
11
1
1
1
5
11
1
1
22
1
1
1
1
1
3
1
1
3
1
1
1.9031
0.9011
0.9011
0.6744
1.000
1.9031
0.6744
0.9011
1.4311
1.728
0.848
0.848
0.54
1.200
1.728
0.54
n-Butanol
2
15
22
2
1
16
n-Butyl acetate
0.848
1.432
Methanol
CH3OH
6
the third gear to ensure that the reaction rate was not
restricted by external diffusion.
To evaluate the effect of internal diffusion on the
conversion of methyl acetate, the commercial NKC-9
resin was screened into four different sizes. Identical
operations were carried out with each of the fractions
obtained. The experimental results in Fig. 2 show that
Figure 3 Effect of temperature on the conversion of
MeOAc (BuOH/MeOAc = 1, catalyst mass concentra-
tion = 87.06 g/L).
the internal mass transfer was to be considered negligi-
ble in the particle diameter range used in this work. Be-
cause the resin was composed of small microspheres
with large internal macropores, mass transfer can be
excluded for this reaction. Unsifted resin was used for
all further experiments.
Figure 1 Effect of the stirring rate on the conversion
of MeOAc (BuOH/MeOAc = 1, reaction time = 200 min,
343.15 K, catalyst mass concentration = 87.06 g/L).
Effect of the Reaction Temperature
To investigate the effect of the reaction temperature,
operations were carried out at 328.15, 333.15, 338.15,
343.15, and 345.15 K. The initial molar ratio of
n-butanol to methyl acetate was 1, and the catalyst
mass fraction was 20% (by mass of methyl acetate).
The experimental results in Fig. 3 show that the
conversion of methyl acetate increased rapidly with
the increase of the temperature.
Effect of Catalyst Loading
The effect of catalyst loading on the conversion of
MeOAc is depicted in Fig. 4. With the catalyst loading
increasing, the reaction rate increased and thus the time
Figure 2 Effect of the internal diffusion on the conversion
of MeOAc (BuOH/MeOAc = 1, reaction time = 200 min,
343.15 K, catalyst mass concentration = 87.06 g/L).
International Journal of Chemical Kinetics DOI 10.1002/kin

104
XU ET AL.
Figure 4 Effect of catalyst loading on the conversion of
MeOAc (BuOH/MeOAc = 1,343.15 K).
Figure 6 Effect of the molar ratio of reactants on the
conversion of MeOAc (343.15 K, catalyst mass concentra-
tion = 87.06 g/L).
to reach the reaction equilibrium reduced. The increase
of the reaction rate was due to the increase in the total
number of acid sites available for the reaction with the
increase of catalyst loading. Furthermore, the catalyst
loading had no effect on the equilibrium constant.
The effect of catalyst loading on the reaction rate
constant is shown in Fig. 5. The forward reaction rate
constant increased with the increase of the catalyst
loading. The relationship between catalyst loading and
rate constant could be expressed as
experiments. Figure 6 shows that the equilibrium
conversion of methyl acetate increased with the in-
crease in the molar ratio of n-butanol to methyl
acetate.
Kinetic Model
Kinetic Equation. Most resin-catalyzed reactions
could be expressed as either quasi-homogeneous
or two adsorption-based models, i.e., Langmuir–
Hinshelwood (L–H) and Elay–Rideal (E–R) model
[6,8–10]. The idealized homogeneous state required
complete swelling of the resin and total dissociation
of the polymer-bound-SO3H group. However, the het-
erogeneous state was characterized by a direct inter-
action of the substance with the polymer-bound-SO3H
group. A pseudo-homogeneous model could be ap-
plied for the system where the mass-transfer resistance
was absent. One of the reactants or solvents was high
polar; the rate of the reaction could be expressed as
a simple pseudo-homogeneous model. The pseudo-
homogeneous model was based on the Helfferich ap-
proach, which treated catalysis confined within the in-
ternal catalyst mass, wherein the reactants, products,
and solvents were in distribution equilibrium with the
bulk solution. The swelling of the resin particle in the
presence of polar solvents led to an easy accessibility
of the acid groups for the reaction and free mobility of
all components [11].
k0 = k1 × mcat
(2)
= 1.95 × 10−4 × mcat
Effect of the Molar Ratio of n-Butanol to
Methyl Acetate
The initial molar ratio of n-butanol to methyl ac-
etate was varied between 1:1 and 1.5:1 during the
The transesterification reaction was known to be a
reversible second-order reactions. Therefore, the reac-
tion rate could be expressed as a pseudo-homogeneous
model:
Figure 5 Effect of catalyst loading on the forward reaction
rate constant (BuOH/MeOAc = 1,343.15 K).
International Journal of Chemical Kinetics DOI 10.1002/kin

TRANSESTERIFICATION OF METHYL ACETATE WITH n-BUTANOL CATALYZED BY NKC-9
105
1 1 1 dni
mcat νi V dt
1 dCBuOAc
r =
=
mcat
dt
= k1CBuOHCMeOAc − k2CMeOHCBuOAc
= k1(aMeOAcaBuOH − aMeOHaBuOAc/K)
(3)
To obtain a general model to produce the reaction ki-
netics with a set of parameters, the data obtained from
the experiment in this work were correlated. Parame-
ters for the models were estimated by minimizing the
sum of the residual squares (SRS) between the exper-
imental and calculated mole concentration of n-butyl
acetate through the simplex Nelder method.
Figure 8 Arrhenius plot for reactions (BuOH/MeOAc = 1,
catalyst mass concentration = 87.06 g/L).
ꢀ
2
SRS =
(rexp − rcalc
)
(4)
all..samples
Equilibrium Constant. The equilibrium constant of
the reaction in this work could be obtained from the
equilibrium composition of the mixture
indicated by Eq. (6)
276
ln K = 0.365 −
(6)
T
aBuOAc,eaMeOH,e
K =
(5)
aMeOAc,eaBuOH,e
The reaction enthalpy could be calculated from the plot
of lnK vs. 1/T as indicated by the Van’t Hoff equation.
The standard enthalpy of this reaction obtained from
the experiment was ꢀ Hro = 2.29 kJ/mol, which agrees
with the anticipation for an endothermic reaction.
Most of the kinetic experiments lasted long enough
until the chemical equilibrium was reached. The
equilibrium constant K could be calculated from the
equilibrium concentration, which was measured in
each operation. The reaction equilibrium was reached
in 7–23 h based on the reaction temperature and
catalyst loading. Figure 7 shows that the equilibrium
constant slightly increased with an increase in the
reaction temperature.
Activation Energy. The Runge–Kutta method was
used to integrate the rate equation with the kinetic pa-
rameter determined by experiments. As could be seen
from Figs. 3–6, a good agreement between calculated
curve and the experimental points was observed.
The value of k1 and k2 is a function of the tempera-
ture and could be expressed as the Arrhenius equation:
The dependence of the equilibrium constant on the
temperature was obtained by the traditional method as
a,1/RT )
k1 = A1e(−E
(7)
(8)
k2 = A2e(−E
a,2/RT )
The kinetic parameters could be obtained from the lin-
ear regression of the Arrhenius plot (Fig. 8). The values
of A1, Ea,1, A2, Ea,2 are given in Table II.
Table II Kinetic Parameter for the Pseudo-
homogeneous Model
Ai (L · mol−1
·
Ea,i
(J · mol−1
54,315
52,021
Reaction
i
min−1 · g-cat−1
)
)
Figure 7 Effect of the reaction temperature on the equilib-
rium constant (BuOH/MeOAc = 1, catalyst mass concentra-
tion 87.06 g/L).
Forward reaction
Reverse reaction
1
−1
3.45 × 104
2.39 × 104
International Journal of Chemical Kinetics DOI 10.1002/kin

106
XU ET AL.
CONCLUSION
R
general gas constant, 8.314 J · mol−1 · K−1
reaction rate, mol · L−1 · min−1 · g-cat−1
calculated value
experimental value
residual squares
absolute temperature, K
time, min
volume of reaction mixture, L
stoichiometric coefficient of component i
r
The kinetic behavior for the synthesis of n-butyl acetate
catalyzed by the cationic-exchange resin, NKC-9, from
methyl acetate and n-butanol was carried out in the
experiments described in this paper. The reaction was
performed in the stirred batch reactor. The effects of
temperature, reactants’ molar ratio and catalyst load-
ing were studied. The kinetic data were correlated with
the pseudo-homogeneous kinetic model, and as a re-
sult the experiment agreed with the model very well.
Then the kinetic parameters were obtained from the
linear regression of the Arrhenius plot and the kinetic
equation describing the reaction catalyzed by cationic
exchange resin was developed.
rcalc
rexp
SRS
T
t
V
νi
Subscripts
BuOAc n-butyl acetate
BuOH
MeOAc methyl acetate
MeOH methanol
n-butanol
NOMENCLATURE
BIBLIOGRAPHY
A1
A2
frequency factor for forward reaction,
L · mol−1 · min−1 · g-cat−1
1. Roy, R.; Bhatia, S. J. Chem Technol Biotechnol 1987,
37, 1–10.
2. Harmer, M. A.; Sun, Q. Appl Catal A 2000, 221, 45–62.
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E. US Patent 4370491, 1983.
4. Jime´nez, L.; Garvin, A.; Costa-Lo´pez, J. Ind Eng Chem
Res 2002, 41, 6663–6669.
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43, 447–456.
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Eng Chem Res 2004, 43, 2049–2053.
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2006, 61, 316–331.
frequency factor for reverse reaction,
L · mol−1 · min−1 · g-cat−1
ai
activities of component i, mol · L−1
equilibrium activities of component i,
mol · L−1
ai,e
Ci
concentration of component i, mol · L−1
activation energy for forward reaction,
J · mol−1
Ea,1
Ea,2
activation energy for reverse reaction,
J · mol−1
K
k0
k1
equilibrium constant
used in Eq. (2); L · mol−1 · min−1
reaction rate constant of forward reaction,
L · mol−1 · min−1 · g-cat−1
k2
reaction rate constant of reverse reaction,
L · mol−1 · min−1 · g-cat−1
mcat
ni
catalyst mass in reaction mixture, g-cat
moles of component i in reaction mixture,
mol
11. Helfferich, F. Ion Exchange; McGraw-Hill: New York,
1962; pp 519–550.
International Journal of Chemical Kinetics DOI 10.1002/kin