Homogeneous and Heterogeneous Catalyzed Esterification of Acrylic Acid with Ethanol: Reaction Kinetics and Modeling

Article abstract of DOI:10.1002/kin.21167

Kinetics of esterification of acrylic acid with ethanol in the presence of homogeneous (H₂SO₄, HCl, p-TSA, HI) catalysts as well as heterogeneous catalysts (Dowex 50WX, Amberlyst 15) was studied. The effects and performance of these catalysts on the conversion of acrylic acid were evaluated. In the kinetics of homogeneous catalyzed reaction, both concentration and activity-based model were employed. Activity coefficients were predicted by the Universal Functional group Contribution (UNIFAC) method to consider nonideal behavior of the liquid phase. The heterogeneous catalyzed reaction mechanisms were developed using Eley–Rideal theory. The model results were compared with the experimental results and were in good agreement. The temperature dependency of the constants, reaction enthalpy, and entropy, and activation energy were determined. The conversion of acrylic acid was obtained as 63.2%, 61.02%, 53.3%, 21.4%, 34.96%, and 14.84% for H₂SO₄, p-TSA, HCl, HI, Dowex 50WX, and Amberlyst 15, respectively, under process temperature of 70°C, reactant molar ratio of 1:1, and catalyst concentration of 2% (v/v) for homogeneous and 2.17 g for heterogeneous catalyst. These outcomes provide an approach to understand the significant effect of each catalyst on the esterification kinetics of acrylic acid and ethanol.

Full text of DOI:10.1002/kin.21167

Homogeneous and
Heterogeneous Catalyzed
Esterification of Acrylic Acid
with Ethanol: Reaction
Kinetics and Modeling
1
1
1
2
GHOSHNA JYOTI, AMIT KESHAV, J. ANANDKUMAR, STUTEE BHOI
1Department of Chemical Engineering, National Institute of Technology Raipur, Raipur, India
2Department of Chemical Engineering, Indian Institute of Technology Kharagpur, Kharagpur, India
Received 23 August 2017; revised 22 February 2018; accepted 24 February 2018
DOI 10.1002/kin.21167
Published online 22 March 2018 in Wiley Online Library (wileyonlinelibrary.com).
ABSTRACT: Kinetics of esterification of acrylic acid with ethanol in the presence of homo-
geneous (H2SO4, HCl, p-TSA, HI) catalysts as well as heterogeneous catalysts (Dowex 50WX,
Amberlyst 15) was studied. The effects and performance of these catalysts on the conversion
of acrylic acid were evaluated. In the kinetics of homogeneous catalyzed reaction, both con-
centration and activity-based model were employed. Activity coefficients were predicted by
the Universal Functional group Contribution (UNIFAC) method to consider nonideal behavior
of the liquid phase. The heterogeneous catalyzed reaction mechanisms were developed using
Eley–Rideal theory. The model results were compared with the experimental results and were
in good agreement. The temperature dependency of the constants, reaction enthalpy, and
entropy, and activation energy were determined. The conversion of acrylic acid was obtained
as 63.2%, 61.02%, 53.3%, 21.4%, 34.96%, and 14.84% for H2SO4, p-TSA, HCl, HI, Dowex 50WX,
and Amberlyst 15, respectively, under process temperature of 70°C, reactant molar ratio of 1:1,
and catalyst concentration of 2% (v/v) for homogeneous and 2.17 g for heterogeneous catalyst.
These outcomes provide an approach to understand the significant effect of each catalyst on
the esterification kinetics of acrylic acid and ethanol. ꢀC 2018 Wiley Periodicals, Inc. Int J Chem
Kinet 50: 370–380, 2018
INTRODUCTION
widely employed in the application of solvents, plas-
ticizers, sealants, medicinal agents, flavors, and fra-
grances [1,2]. These reactions are reversible and hav-
ing low reaction rate, which shows limited conversion.
Owing to low and slow reaction rate, suitable catalyst
are employed in this reversible reaction. It takes a lot of
energy to remove the –OH from the carboxylic acid, so
appropriate catalyst and heat are needed to produce the
Esterification is an essential reaction-producing es-
ters in chemical industries. Desired product esters are
Correspondence to: Amit Keshav; e-mail: dr.amitkeshav@
gmail.com.
ꢀ
2018 Wiley Periodicals, Inc.
C

KINETICS AND MODELING OF ESTERIFICATION OF ACRYLIC ACID WITH ETHANOL
371
necessary energy. Once the –OH has been removed,
the hydrogen on the alcohol can be removed and that
oxygen can be connected to the carbon. Because the
oxygen was already connected to a carbon, it is now
connected to a carbon on both sides, and an ester is
formed.
Both homogeneous and heterogeneous catalysts are
used to increase the reaction rate. A homogeneous
catalyst such as sulfuric acid (H2SO4), hydrochloric
acid (HCl), and para-toluene sulfonic acid (p-TSA)
acts as a protonating catalyst during the esterifica-
tion reaction [3,4]. Drawbacks of homogeneous cat-
alyst such as corrosion of equipment, side reactions,
and difficult to separation from the product mixture
can be resolved by the employment of heterogeneous
catalysts. Many researchers have done comparative
study of homogeneous and heterogeneous catalysts
part in the reaction [14,17–19]. Finally, the E–R model
is applied when the reaction between one adsorbed
species and one nonadsorbed reactant from the bulk
liquid phase is assumed to occur [7,16,20].
The present work investigates the kinetics of esteri-
fication of acrylic acid and ethanol catalyzed by various
homogeneous and heterogeneous catalysts. The effect
of reaction temperature on kinetics of reaction was
described. For comparative study of catalysts, four ho-
mogeneous catalysts, namely H2SO4, HCl, p-TSA, HI,
and two heterogeneous catalysts, i.e., Dowex 50WX
and Amberlyst 15, are employed. The kinetic studies
of both homogeneous and heterogeneous catalyzed es-
terification reactions were performed. Nowadays, it is
essential to study the kinetics and reaction equilibrium
of reaction to understand and describe chemical reac-
tions in a better way. Both concentration and activity-
based model were considered for homogeneous as
well as heterogeneous catalysts. The E–R model was
employed to correlate the experimental data of ion-
exchange catalysts.
[4–7]. These literature reports suggest that the homo-
geneous catalyst favors more conversion of acid or
yield of product than a heterogeneous catalyst. But
heterogeneous catalysts lead easy recovery of cata-
lyst and more purity of product than the homogeneous
catalyst.
Compared to the homogeneous catalyst, the reac-
tion rate in the heterogeneous catalyst will proceed at
a slower rate. This is due to the fact that the homoge-
neous catalyst and reactants have a similar phase and
hence the reaction rate is faster [1]. This finding has
already been reported by several researchers. Aafaqi
et al. [8] reported that the homogeneous catalyst gives
better conversion than the heterogeneous catalyst for
esterification of palmitic acid with isopropanol. Yal-
cinyuva et al. [9] reported similar comparative results
for esterification of myristic acid with isopropyl alco-
hol. They concluded that heterogeneous catalysts gave
poor conversions due to the diffusion problem of fatty
acid into the pores of the catalyst. Henceforth, a lot
of reports [2,10,11] suggested that the homogeneous
catalyst induces more conversion compared to hetero-
geneous catalyst.
Generally, for performing the kinetics of the ho-
mogeneous catalytic esterification reaction, the power
law model is employed [1,12]. To describe the kinetic
behavior of heterogeneous catalytic esterification reac-
tions, several kinetic models have been reported. The
simplest one is the pseudo-homogeneous (P-H) model,
which is similar to the power law model for homo-
geneous reactions [13–16]. The other widely adopted
models are Langmuir–Hinshelwood (L–H) and Eley–
Rideal (E–R) models. The P-H model assumes that
the surface reaction is the controlling step, and adsorp-
tion is negligible for all components. The L–H model
is applicable for correlating the kinetic data whenever
their occurs the adsorption of the molecules is taking
EXPERIMENTAL
Material and Method
All reactants acrylic acid (99% pure; Loba Chemie,
Mumbai, India), ethanol (99% pure; Hayman, Pune,
India) and catalysts sulfuric acid (98% pure; Loba
Chemie, Mumbai, India), hydrochloric acid (98% pure;
Loba Chemie, Mumbai, India), and p-toluene sulfonic
acid (99% pure; Fisher Scientific) were of analytical
grade. Heterogeneous catalysts Amberlyst 15 hydro-
gen form and Dowex 50WX hydrogen form were ob-
tained from Sigma-Aldrich. No more purification was
performed for the experiments. Millipore ultrawater
was used for the preparation of aqueous solutions re-
quired for product analysis.
The esterification reaction was carried out in a
1000-mL three-necked ball glass flask equipped with a
magnetic stirrer (Remi1 RML). The setup is shown in
Fig. 1. One of the measured reactant was fed to the
reactor and heated up to a desired temperature. An-
other reactant was heated in a separate flask and trans-
ferred to the reactor followed by addition of cata-
lyst. This time was taken as the initial (starting) time
of the reaction. In this study, the experiments were
performed at 50, 60, and 70°C reaction temperature
and the catalyst concentration of 2% (v/v) of reac-
tion mixture with a molar ratio of 1:1 (acrylic acid
to ethyl alcohol) of reactants. Samples were collected
at regular intervals for 6–7 h and analyzed by a gas
chromatograph (GC).
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JYOTI ET AL.
Figure 2 Effect of different catalysts on conversion of
acrylic acid at different temperatures (t = 420 min).
ditions were kept same for all experiment with same
temperature and the molar ratio acrylic acid/ethanol of
1:1. An amount of catalyst of 2% v/v of reaction mix-
ture was considered in case of homogeneous, and the
amount of catalyst corresponding to equivalent w/w%
of H2SO4 was considered in case of the heterogeneous
catalyst. Hence the resulted amount of heterogeneous
catalyst of 2.17 g was taken.
Figure 1 Experimental setup for the esterification process.
As evident from Fig. 2, the conversion of acrylic
acid increases with an increase in the temperature be-
cause of acceleration of the forward reaction. It is due
to the fact that high temperature gives rise to more
frequent and successful collision having sufficient en-
ergy (activation energy) to break the bonds, and hence
leads to higher conversion of reactants to ester prod-
ucts [1,21,22]. However, the reaction at too high tem-
perature leads to vaporization of reactants, which in
turn decreases the efficiency of the system. Hence,
there exists a trade-off between the high reaction rate
due to the increased temperature and the decrease of the
reaction rate, resulting from the vaporization of reac-
tants. It is therefore essential to determine the optimal
reaction temperature or temperature profile for efficient
operation of the system considering the production rate
as well as the vaporizing rate of reactants [23].
GC Analysis
The samples collected from the reactor and the per-
meate were analyzed by a NUCON series 5700 gas
chromatograph equipped with a thermal conductivity
detector, a cool glass lined injector, and a pressure pro-
grammable software. Separation was carried out on a
porapak column (id 2mm, od 1/8”, length 2 m). Hy-
drogen gas taken as a carrier gas with a flow rate of
60 mL/min. The GC was calibrated using a known sam-
ple of acrylic acid, ethanol, ethyl acrylate, and water.
One microliter of sample was injected into the chro-
matograph. From the obtained peak area and retention
time, the concentration of reactants, products, and per-
meates were found. The analysis was carried out with
the injection chamber temperature at 150°C; the oven
and detection chamber temperatures were set at 180°C.
Figures 3–5 show the effect of different homoge-
neous and heterogeneous catalysts on conversion of
acrylic acid at 50, 60, and 70°C, respectively. From the
figures, the obtained conversion of acrylic acid with
different catalysts is in the following order: H2SO4>
p-TSA > HCl > Dowex 50W > HI > Amberlyst
RESULTS AND DISCUSSION
Effect of Different Homogeneous and
Heterogeneous Catalyst
15. This trend is maintained at all temperature except
60°C where the conversion is nearly same for p-TSA
The effect of different types of catalysts on the perfor-
mance of the esterification reaction was studied by us-
ing four homogeneous catalysts, e.g., H2SO4, HCl, p-
TSA, and HI, and two heterogeneous catalysts Dowex,
e.g., 50WX and Amberlyst 15. The operational con-
and HCl. At 70°C, the final conversion is 63.2% for
H2SO4, 61.02% for p-TSA, 53.3% for HCl, 21.4%
for HI, 34.96% for Dowex 50WX, and 14.84 for Am-
berlyst 15. As expected, the conversion of acrylic acid
is higher for the homogeneous catalyst as compared to
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KINETICS AND MODELING OF ESTERIFICATION OF ACRYLIC ACID WITH ETHANOL
373
Figure 5 Effects of different catalysts on conversion of
acrylic acid for the esterification of acrylic acid and ethanol at
70°C, 1:1 acid/alcohol molar ratio, and catalyst concentration
of 2% (v/v) for homogeneous and 2. 17 gm for heterogeneous
catalysts.
Figure 3 Effects of different catalysts on conversion of
acrylic acid for the esterification of acrylic acid and ethanol
at 50°C, 1:1 acid/alcohol molar ratio, and catalyst concen-
tration of 2% (v/v) for homogeneous and 2.17 g for the
heterogeneous catalysts.
reactions [12]. On the other hand, HCl is a gas and
needs to be dissolved in water to use in the liquid state.
The problem with this is that water is a product of
the esterification reaction, and more water increases
the rate of the reverse reaction thereby decreasing the
yield of the product ester. Besides, we have also used
p-TSA, which shows good catalytic activity due to
the presence of sulfonic acid groups, and subsequently
causes less acidity and less side reactions. Lastly, we
have considered the HI catalyst. HI shows very less
conversion as compared to other homogeneous cata-
lysts. It may be because of occurrence of side reaction,
which leads to formation of ethyl iodide. Ronnback
et al. [24] also revealed that in the esterification of
acetic acid with methanol in the presence of HI, a side
reaction appeared in which HI reacted with methanol
forms methyl iodide. The reaction was assumed to be
the nucleophilic, whereas the rate-determining step in
the hydrogen iodide esterification was supposed to be
the substitution of the iodide to protonated methanol.
Hydrogen iodide and acetic acid act as proton donors
in the mechanism.
There are some drawbacks of homogeneous cata-
lyst such as corrosive nature and existence of possible
side reactions. The use of heterogeneous catalyst such
as Dowex 50W and Amberlyst 15 may improve the
conversion, but due to the diffusion problem of acid
into the pores of the catalyst heterogeneous catalysts
provided poor conversions [25]. Besides, the poor con-
version may be due to unavailability of some acid sites
on the catalyst for reaction or reduced activity because
of resin swelling or hydrophilicity. Moreover, restricted
conformation of intermediate complexes adsorbed on
acid sites of the heterogeneous catalyst (as opposed
to unrestricted movement in solution in the presence
Figure 4 Effects of different catalysts on conversion of
acrylic acid for the esterification of acrylic acid and ethanol at
60°C, 1:1 acid/alcohol molar ratio, and catalyst concentration
of 2% (v/v) for homogeneous and 2. 17 gm for heterogeneous
catalysts.
the heterogeneous one. Overall, H2SO4 was found to
be the best among the all providing higher conversion
in the studied conditions. The conversion of acrylic
acid changes from 44.92% to 63.2% when tempera-
ture is increased from 50 to 70°C. The sulfuric acid is
the most efficient homogeneous catalyst for the ester-
ification reaction as it can lend two H+ ions for each
molecule of the acid present. Additionally, H2SO4 is
stable and liquid in (nearly) the pure form. Moreover,
concentrated sulfuric acid is a great dehydrating agent;
hence, it will even seize some of the water produced
in the reaction. Finally, sulfuric acid is neither a strong
oxidant (nitric acid) nor a strong reductant (hydroiodic
acid), thus reducing the possibilities for undesired side
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74
JYOTI ET AL.
of the homogeneous catalyst) can also be a factor
for reduced conversion [26]. It can be observed from
Figs. 3–5 that the performance of Dowex 50Wx8–100
is better than Amberlyst 15 for promoting the reac-
tion. Ali et al. [1] and Sert et al. [27] have also shown
higher conversions in the presence of Dowex compared
to Amberlyst for propionic acid with 1-propanol and
acrylic acid with n-butanol, respectively. In industries,
generally the concentrated H2SO4 catalyst is used for
the esterification reaction due to the reason that it is
more efficient and economical than other catalysts.
(equimolar concentration), which is given as
2
k
1
C
EA
C
W
X
Ae
Keq =
=
=
(6)
2
k−1
CAACEOH
(1 − XAe)
Equation (6) can be rearranged in terms of conver-
sion of acrylic acid
ꢂ
ꢃ
2
dxA
dt
X
A
2
AA0
2
CAA0
= k1CCC
(1 − XA) −
(7)
(8)
Keq
ꢄ
xA
Kinetics of the Homogeneous Esterification
Reaction
dXA
=
k1CCCAA0t
2
2
XA
0
(1 − X ) −
A
Keq
The kinetic model of esterification of acrylic acid (AA)
with ethyl alcohol (EOH) to produce ethyl acrylate
where
(
EA) and water (W) can be presented as an elemen-
tary second-order reversible reaction, first-order with
respect to each reagent [28,29] and is represented as:
CAA
XA = 1 −
(9)
C
AA0
XA and CAA0 are the conversion and initial con-
centration of acrylic acid. Equation (9) was solved in
MATLAB by applying the experimental data in the
temperature range of 50–70°C. A plot of the left-hand
side of Eq. (9) against reaction time, t along with the
fitted linear curve is given in Fig. 6. The reaction tem-
perature was varied from 50 to 70°C. The forward
reaction rate constant, k1, was obtained from the slope
of straight lines shown in Fig. 6, and the values of the
backward reaction rate constant, k−1, was calculated
from the Keq relation.
AA + EOH ꢀ EA + W (without catalyst) (1)
AA + EOH + C ꢀ EA + W + C (with catalyst)
(2)
The rate expression for the second-order reversible
reaction is written as
−
ri = k1CAACEOH − k−1CEACW
(3)
The temperature dependency of the rate constants,
k1 and k−1, was determined from the Arrhenius expres-
sion and is given as
Equation (3) can be rewritten as considering a con-
centration term of catalyst, CC:
ꢀ
ꢁ
E1
−
dCi
k1 = k0 exp
(10)
−
ri =
= k1CAACEOHCC − k−1CEAcCWCC
RT
dt
(4)
ꢀ
ꢁ
E−1
RT
where CAA, CEOH, CEA, CW, and CC represent the con-
centration (mol/L) of acrylic acid, ethanol, ethyl acry-
late, water, and catalyst, respectively. k1 and k−1 are
the forward and backward reaction rate constants, and
t is the reaction time.
k−1 = k−0 exp
(11)
where R is a gas constant (8.31 J/mol·K). Table I
presents the activation energies of forward and back-
ward reactions for different catalysts used in the present
system. The obtained values of E1 from the litera-
ture are 52.3 ± 1.9 kJ/mol for acrylic acid with 2-
ethylhexan-1-ol, 40.7 kJ/mol for palmitic acid with
isopropanol, and 42.07 kJ/mol for propionic acid with
benzyl alcohol [8,30,31]. The difference in results
could be because of the different system and catalyst
employed in the present study.
Equation (4) can be written as
ꢀ
ꢁ
−
dCi
CEACW
Keq
−
ri =
= k1CC CAACEOH −
(5)
dt
The equilibrium constant, Keq, can be calculated
from the equilibrium conversion (XAe) of the mixture
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KINETICS AND MODELING OF ESTERIFICATION OF ACRYLIC ACID WITH ETHANOL
375
Figure 6 Plot of the left-hand side of Eq. (9) against reaction time t (catalyst used: H2SO4).
Table I Kinetic Parameters of Present System (Acrylic
Acid + Ethanol) for Different Catalysts
phase models such as Universal Functional group
Contribution (UNIFAC), Universal QUAsi Chemi-
cal (UNIQUAC), and non random two liquid model
ꢀH
ꢀS
(NRTL) models are used to describe a nonideal factor.
Catalyst E1(kJ/mol) E–1(kJ/mol) (kJ/mol) (kJ/mol·K)
The activity model accounts for the nonideal ther-
H2SO4
p-TSA
HCl
35.04
42.92
36.87
23.75
36.89
36.18
38.25
12.28
71.94
79.11
75.12
36.03
0.22
0.24
0.224
0.884
modynamic behavior of the reaction mixtures. It can
be developed from the concentration-based model by
defining the activity as
HI
ai = γixi = γiCi/Ct
(13)
The Van’t Hoff equation is employed for the predic-
tion of the nature of reaction endothermic or exother-
mic by using experimentally determined equilibrium
constant (Keq):
where, γ i, Ci, and xi represent the activity coefficient,
concentration, and mole fraction of each component.
The activity coefficients in the reaction mixture were
calculated by using the UNIFAC method.
The chemical activities instead of concentrations
can be used in the reaction rate equation:
ꢀ
H
ꢀS
+ R
ln keq = −
(12)
RT
Reaction enthalpys for ꢀH and entropy ꢀS were
obtained for various catalyzed reactions and are shown
in Table I. The positive value of reaction enthalpy
shows that the reaction is endothermic. These values
are in a good agreement with the literature findings of
− r = k a
i
1
AA EOH
a
− k−1
EA W
a a
(14)
Keq is an equilibrium constant, which can be cal-
culated from the equilibrium molar concentration of
components (Ci)eq as given in the equation below
70.1–74.6 kJ/mol for acrylic acid with 2-ethylhexan-
1-ol, 69.03 kJ/mol for acrylic acid with n-butanol, and
69–75 kJ/mol for acrylic acid with 2-ethylhexyl alco-
k1
(aEA)eq (aW)eq
=
(aAA) (aEOH)
hol [30,32,33].
Keq =
To study the nonideality associated with the reaction
mixture, we need to consider the activity coefficients
along with the molar concentration or mole fractions
to show the departure from the ideal case [34]. Real
mixtures involve the activity term of the component in-
stead of their concentration term for the calculation of
thermodynamic equilibrium constant [30]. Commonly
k−1
eq
eq
EA eq W eq EA W
C γ
( ) (C ) γ
= (C
= K K (15)
) γ
γ
EOH eq AA EOH
c
γ
) (C
AA eq
Based on the equilibrium conversion or concentra-
tion, the activities are computed and using Eq. (16) into
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JYOTI ET AL.
Table II Activity Coefficients of Components
in the Equilibrium State of the Reaction
at Different Temperatures
Component
50°C
60°C
70°C
Ethanol
1.275
0.794
1.480
2.247
1.269
0.802
1.476
2.229
1.264
0.810
1.471
2.212
Acrylic acid
Ethyl acrylate
Water
Eq. (15), the kinetic rate equation becomes
γAAγEOH
Figure 7 Comparison of acrylic acid conversion be-
tween experimental data and simulation results using the
concentration-based model with estimated parameters at 2%
H2SO4 catalyst and 1:1 acrylic acid to the ethanol molar
ratio (symbols represent experimental data, and solid lines
represent concentration-based model results).
−
ri = k1
CAACEOH
2
Ct
γEAγW
−
k−1
CEACW
(16)
2
Ct
In this work, it is assumed that the reaction volume
is constant and also observed that the product between
the activity coefficients of both reactants and both prod-
ucts do not vary significantly, so the rate constants of
forward and backward of Eq. (17) can be grouped as
−
ri = k1,act CAACEOH − k−1,act CEACW
(17)
where
k1,act
Keq =
k−1,act
The forward rate parameter k1,act is related to the
temperature through an Arrhenius relation
Figure 8 Comparison of acrylic acid conversion between
experimental data and simulation results using the activity-
based UNIFAC model with estimated parameters at 2%
H2SO4 catalyst and 1:1 acrylic acid to the ethanol molar
ratio (symbols represent experimental data, and dotted lines
represent the activity-based model results).
ꢀ
ꢁ
E
K1,act = k0,act exp −
(18)
RT
In present work, the UNIFAC model was consid-
ered to determine the activity coefficients. The coeffi-
cients are directly determined from Aspen Plus soft-
ware. Truong et al. [35] also used same interface (As-
pen Plus) for the determination of activity coefficient
by the NRTL model for the same reaction system.
The obtained activity coefficients and experimental
equilibrium mole fractions of components in the se-
lected temperature range of 50–70°C are presented in
Table II.
ODE solver, ode15s implemented in the MATLAB.
The simulated values of conversion of acrylic acid
mentioned in the kinetic modeling section were com-
pared to that obtained experimentally. Figure 7 shows
a plot between simulated and experimental values of
conversion. It can be seen from the figure that the model
(Eq. (9) predicted and experimental values are in good
agreement.
The experimental results and the activity-based
model predicted values were plotted for acrylic acid
conversion at different reaction temperatures as shown
in Fig. 8. The model values match reasonably well with
experimental values. It can be observed that beyond
200 min, the activity-based model prediction matches
well with the experimental data. The sum of squared
error is 0.033 for the concentration-based model
Comparison of Experimental and Model
Predicted Results
The numerical integration of Eq. (9) for each compo-
nent namely acrylic acid, ethanol, ethyl acetate, and
water, which was required during each iterative step
in the nonlinear regression, was accomplished by the
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KINETICS AND MODELING OF ESTERIFICATION OF ACRYLIC ACID WITH ETHANOL
377
and 0.030 for the activity-based model. Hence, the
UNIFAC model predicts the experimental data slightly
better than the concentration-based model. In the
present system, the obtained value of error is less,
which proves the accuracy of the UNIFAC model for
estimating the activity coefficients of the components.
where k1 is the forward reaction rate constant, m is the
quantity of dry resin, V the volume of the reaction mix-
ture, Ke the equilibrium constant of the reaction, KEOH
and KW the adsorption equilibrium constants. Consid-
ering chemical activities instead of concentrations, the
reaction rate equation for a nonideal mixture can be
written as
dai
k1 (m/V ) (aAAaEOH − (aEAaW/K e))
1 + KEOHaEOH + KWaW
Kinetics of the Heterogeneous
Esterification Reaction
−
ri = −
=
dt
(21)
The heterogeneous reaction mechanism experimen-
tally performed can be modeled by the E–R model,
which is the reaction on the basis of the assumption
that one of the adsorbed reactants is reacting with an-
other in the bulk fluid [1]. In this work, it was assumed
the reaction between adsorbed ethyl alcohol on acid
sites of the catalyst and acrylic acid in the bulk so-
lution, as proposed by Santos et al. [36]. However,
ethyl acrylate molecules adsorbed were neglected and
adsorption of water by resin has an inhibiting effect
on the reaction mechanism [28]. Thus in the present
work the adsorption/desorption of water on this ion-
exchange resin (solid) was considered.
The model equations described for all the compo-
nents consists of nonlinear differential equations and
are solved by an ODE solver, ode45 in MATLAB, to
obtain the concentration profile of reactants and prod-
uct. The set of kinetic parameters were estimated by a
nonlinear optimization subroutine fmincon from MAT-
LAB. The objective function of the optimization prob-
lem is
NC
ꢅ ꢆ
ꢇ
2
cal
i
exp
φ =
C
− Ci
(22)
i=1
The esterification reaction of acrylic acid (AA) with
ethyl alcohol (EOH) for producing ethyl acrylate (EA)
and water (W) in the presence of ion-exchange resin
For a nonideal mixture
Na
ꢅ ꢆ
ꢇ
2
cal
i
exp
(Dowex 50WX and Amberlyst 15) catalyst is given as
φ =
a
− ai
(23)
follows:
i=1
exp
where C ic al and Ci are calculated and experimental
values of acrylic acid concentration of each experimen-
tal point “i,” respectively. NC is the number of experi-
mental data points for the concentration of acrylic acid.
AA + EOH ꢀ EA + W
(19)
The reaction mechanism can be given as following
steps [36]:
exp
cal
Similarly, ai and ai are calculated and experimental
values of acrylic acid activities of each experimental
point “i,” respectively. Na is the number of experi-
mental data points for activity of acrylic acid. The ki-
netic parameters are obtained by solving the model
equation based on the successive guess values of the
kinetic parameters. The resulting values are given in
Table III.
EOH + S ↔ EOH · S adsorption of ethanol
EOH · S + AA ↔ EA · S + W surface reaction
EA · S ↔ EA + S desorption of ester
As mentioned previously for the homogeneous sys-
tem, reaction enthalpy for Dowex and Amberlyst 15 is
evaluated as 38.85 and 45.70 kJ/mol, respectively. The
positive value of reaction enthalpy shows that the reac-
tion is endothermic. Activation energy of the forward
reaction for Dowex and Amberlyst 15 was calculated
as 31.04 and 35.52 kJ/mol, respectively.
W + S ↔ W · S adsorption/desorption of water
where S represents solid site of catalyst. Depending
on this mechanism, the reaction rate expression can be
given by
Comparison of Experimental and
Model-Predicted Results
dCi
k1 (m/V ) (CAACEOH − (CEACW/Ke))
1 + KEOHCEOH + KWCW
−
ri = −
=
dt
A comparative plot between experimental and
model values of conversion of acrylic acid using
(20)
International Journal of Chemical Kinetics DOI 10.1002/kin.21167

3
78
JYOTI ET AL.
Table III Values of Kinetic Parameters at Different Temperatures
KEOH
−1
KW
−1
3
−1
−1
3 2
−1
3 2
−1
)
k1 (m mol min
)
Ke
((m ) mol min
)
((m ) mol min
Concentration Activity Concentration Activity Concentration Activity Concentration Activity
Catalyst
T (°C)
Model
Model
Model
Model
Model
Model
Model
Model
Amberlyst 15
50
0.0040
0.0079
0.0086
0.0330
0.0285
0.0589
0.0700
0.1110
0.1890
0.0007
0.0011
0.0019
0.0060
0.0010
0.0020
0.0053
0.0009
0.0009
0.0258
0.0301
0.0502
0.0258
0.0301
0.0499
60
0
7
Dowrex 50WX 50
0.0264
0.0374
0.0518
0.0502
0.0800
0.1870
0.0900
0.1155
0.2100
0.0090
0.0116
0.0210
0.0007
0.0009
0.0036
0.0007
0.0009
0.0013
0.0266
0.0557
0.0564
0.0266
0.0557
0.5640
60
0
7
Rate constants of channels 29, 30, 36, 37, and 43 were calculated with VTST, otherwise with CTST.
Figure 10 Comparison of acrylic acid conversion between
experimental data and simulation results using the activity-
based UNIFAC model with estimated parameters at 2.17 g
of catalyst and 1:1 acrylic acid to the ethanol molar ratio
Figure 9 Comparison of acrylic acid conversion be-
tween experimental data and simulation results using the
concentration-based model with estimated parameters at 2.17
g of catalyst and 1:1 acrylic acid to the ethanol molar ratio
(
symbols represent experimental data, and solid lines repre-
sent model results; the filled symbol represents Amberlyst
5, and the hollow symbol represents Dowex 50WX).
(
symbols represent experimental data, and solid lines repre-
sent model results; the filled symbol represents Amberlyst
5, and the hollow symbol represents Dowex 50WX).
1
1
values of the kinetic parameters (k1, Ke, KEOH, KW) was
also performed. To perform the sensitivity analysis, we
considered the kinetic parameters obtained for Dowex
heterogeneous catalysts is presented in Figs. 9 and 10.
Figures explain the precision of the model for predict-
ing conversion of acrylic acid and well agreed with the
conversion obtained experimentally for both catalysts
Dowex 50WX and Amberlyst 15. The sum of squared
error for Dowex 50WX and Amberlyst 15 is 0.017 and
50WX case (reaction temperature = 60°C) using the
UNIFAC model. The values of the parameters were
varied in the range of ± 50% of the estimated value. One
parameter was varied at a time to realize its effect on
system performance. The most sensitive parameter was
found to be k1, and comparatively the most insensitive
parameters were KEOH and KW. The final conversion
of the acrylic acid was changed by nearly 8.5% when
the value of k1 was changed by 10% of its base value,
whereas even a 50% change of the Ke value changes
the conversion by only 0.15%.
0
0
.00314, respectively, for the activity-based model and
.021 and 0.005, respectively, for the concentration-
based model, respectively. In the present system, the
obtained value of error is less, which proves the accu-
racy of the UNIFAC model for estimating the activity
coefficients of the components.
The sensitivity of the model prediction (or more
precisely final conversion of acrylic acid) to changes in
International Journal of Chemical Kinetics DOI 10.1002/kin.21167

KINETICS AND MODELING OF ESTERIFICATION OF ACRYLIC ACID WITH ETHANOL
379
CONCLUSIONS
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Esterification of acrylic acid with ethanol was studied
using different homogeneous (H2SO4, HCl, p-TSA,
HI) and heterogeneous (Dowex 50WX, Amberlyst 15)
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has the higher activity and gives higher conversion than
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2
a
CAA
Activity of components
Concentration of acrylic acid, mol/m
2
3
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CAA0 Initial concentration of acrylic acid, mol/m
CC
CEA
Concentration of catalyst, mol/m3
3
Concentration of ethyl acrylate, mol/m
3
CEOH Concentration of ethyl alcohol, mol/m
Concentration of water, mol/m3
Activation energy, J/mol
CW
Ea
k1
1
2
2
Forward
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rate
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2
(
m ) /kmol ·min
Backward reaction
m ) /kmol ·min
Equilibrium constant
k−1
3
2
2
(
1976, 27–35.
Keq
R
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Rate constant, 8.314 J/mol K
Reaction time, min
2
t
T
XAA
XAe
ꢀ
ꢀ
γ
Reaction temperature, °C
Conversion of acrylic acid
Equilibrium conversion of acrylic acid
Reaction enthalpy, J/mol
Reaction entropy, J/mol K
Activity coefficient of components
2
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S
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International Journal of Chemical Kinetics DOI 10.1002/kin.21167