Hindawi Publishing Corporation
ISRN Chemical Engineering
Volume 2013, Article ID 520293, 6 pages
http://dx.doi.org/10.1155/2013/520293
Research Article
Kinetic Study of Catalytic Esterification of Butyric Acid
and Ethanol over Amberlyst 15
Nisha Singh,1 Raj kumar,2 and Pravin Kumar Sachan3
1
Department of Chemical Engineering, RNCET, Panipat, Haryana 132103, India
Department of Chemical Engineering, Bipin Tripathi Kumaon Institute of Technology, Dwarahat, Almora,
Uttarakhand 263653, India
3
Department of Biochemical Engineering, Bipin Tripathi Kumaon Institute of Technology, Dwarahat, Almora,
Uttarakhand 263653, India
2
Correspondence should be addressed to Raj kumar; [email protected]
Received 29 June 2013; Accepted 5 August 2013
Academic Editors: G. Bayramoglu and R. Mariscal
Copyright © 2013 Nisha Singh et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
The esterification reaction of butyric acid with ethanol has been studied in the presence of ion exchange resin (Amberlyst 15).
Ethyl butyrate was obtained as the only product which is used in flavours and fragrances. Industrially speaking, it is also one
of the cheapest chemicals, which only adds to its popularity. The influences of certain parameters such as temperature, catalyst
loading, initial concentration of acid and alcohols, initial concentration of water, and molar ratio were studied. Conversions were
found to increase with an increase in both molar ratio and temperature. The experiments were carried out in a batch reactor
in the temperature range of 328.15–348.15 K. Variation of parameters on rate of reaction demonstrated that the reaction was
intrinsically controlled. Experiment kinetic data were correlated by using pseudo-homogeneous model. The activation energy for
the esterification of butyric acid with ethanol is found to be 30 k J/mol.
1. Introduction
Organic esters are important fine chemicals used widely in
the manufacturing of flavors, pharmaceuticals, plasticizers,
and polymerization monomers. They are also used as emulsifiers in the food and cosmetic industries. Several synthetic
routes are available for obtaining organic esters, most of
which have been briefly reviewed by Yeramian et al. [1].
Several synthetic routes have been used to make organic ester,
but the most-used methodology for ester synthesis is direct
esterification of carboxylic acids with alcohols in the presence
of acid/base catalysts. Esterification is used. The most acceptable method is to react the acid with an alcohol catalyzed by
mineral acids, and the reaction is reversible [2]. Esterification
of carboxylic acid with alcohol in the presence of acid
catalyst has been the subject of investigation of many research
workers [3]. The traditional industrial process of synthesizing esters using homogeneous acid catalyst is conveniently
replaced by solid acid catalyst, ion exchange resins, clay, and
so forth [4]. The ion exchange resin is a promising material
for replacement of homogeneous acid catalysts. The use of ion
exchange resins as solid catalyst has many advantages over
homogeneous acid catalysts. They eliminate the corrosive
environment; they can separate from liquid reaction mixture
by filtration and have high selectivity [5]. They can also
be used repeatedly over a prolonged period without any
difficulty in handling and storing them. And the purity
of the products is higher since the side reactions can be
completely eliminated [6]. Fatty acid esters are used as raw
materials for emulsifiers, oiling agents for foods, spin finish
and textiles, lubricants for plastics, paint and ink additives
and for mechanical processing, personal care emollients, and
surfactants and base materials for perfumes. They are used
as solvents, cosolvents, and oil carriers in the agricultural
industries [7]. The esters of biobased organic acids fall into
the category of benign or green solvents and are promising
replacements for halogenated petroleum-based solvent in a
wide range of applications [8].
The ester of butyric acid and ethanol, namely, ethyl
butyrate, finds wide applications. It is commonly used as
2
0.007
0.006
−rA0 (mol/L·min)
artificial flavoring such as pineapple flavoring in alcoholic
beverage, as a solvent in perfumery products and as a
plasticizer for cellulose. Ethyl butyrate is one of the most
common chemicals used in flavors and fragrances. It can be
used in a variety of flavors: orange (most common), cherry,
pineapple, mango, guava, bubblegum, peach, apricot, fig, and
plum. Industrially speaking, it is also one of the cheapest
chemicals, which only adds to its popularity. Although, to the
best of our knowledge, no researcher has reported the kinetics
of esterification of butyric with ethanol in the presence of
Amberlyst 15, there are a number of studies related to the
other esterification reactions catalyzed by solid resins.
ISRN Chemical Engineering
0.005
0.004
0.003
0.002
0.001
0
0
0.5
2. Experimental
2.1. Chemicals. Ethanol of >98.5% purity (Merck) and butyric
acid of 99.8% purity (Merck) are used as the reactants.
The reaction occurred in the solution of dioxane of 99.0%
purity (Merck). All the aqueous solutions used in the analysis
are prepared with distilled water, sodium hydroxide (SD
Fine Chemicals Ltd., Boisar, India), and phenolphthalein
indicator, (Qualigens Fine Chemicals, Mumbai, India).
2.2. Catalyst. Amberlyst 15 (Rohm and Hass) is used as
catalyst. It is synthesized from styrene-divinylbenzene by
suspension polymerization and finally sulfonated by sulfuric
acid. The esterification reaction of butyric acid with ethanol
was studied using different catalysts. The catalytic activity of
Amberlyst 15 is higher than the Amberlyst 35. It is due to
Amberlyst 15 has higher surface area and pore volume than
Amberlyst 35. So, Amberlyst 15 is found to be the best catalyst
to generate the data.
3. Apparatus and Procedure
Esterification reaction of butyric acid with ethanol with
the initial concentrations of 1.44 mol/L and 14.84 mol/L,
respectively, was carried out in three-necked flask of 500 mL
capacity fitted with a reflux condenser, a thermometer, and a
magnetic stirrer. The initial volume of reaction mixture was
approximately 150 mL. A reflux condenser is used to avoid the
loss of volatile compounds. The ion exchange resin suspends
in the reaction mixture with the help of stirrer. Temperature
inside the reactor is controlled within the accuracy of ±0.5 K.
In all the experiments, a known amount of butyric acid and
the catalyst charged into the reactor and heated to the desired
temperature. All of the reactants charged in the reactor are
volumetrically measured. This time is considered the starting
point of the reaction. Samples were withdrawn at a regular
time intervals for analysis. The progress of the reaction was
followed by withdrawing small enough samples to consider
them negligible compared to the volume of the reaction
mixture at regular intervals.
4. Analysis
All samples were measured in measuring cylinder of 1 mL,
taken periodically, and titrated against 1 N standard NaOH
solution using phenolphthalein as an indicator.
1
1.5
2
CA0 (mol/L)
Figure 1: Effect of acid concentration on initial reaction rate: (𝐶𝐵0 =
14.84 mol/L).
5. Kinetic Modeling
A pseudo-homogeneous model cab was effectively applied to
correlate the kinetic data of the liquid solid catalytic reaction.
The esterification reactions are known to be reversible reaction of second order. The general rate expression can be given
by
𝐴 + 𝐵 󳨀→ 𝐸 + 𝑊,
(1)
where 𝐴 = butyric acid, 𝐵 = ethanol, 𝐸 = ethyl butyrate, and
𝑊 = water, and
−𝑟𝐴 =
𝐾𝑓 (𝑚/𝑉) (𝐶𝐴 𝐶𝐵 − (𝐶𝐸 (𝐶𝑊/𝐾𝑒 )))
1 + 𝐾𝐵 𝐶𝐵 + 𝐾𝑊𝐶𝑊
,
(2)
where subscript 𝐶𝐴 and 𝐶𝐵 refer to acid and alcohol concentrations, respectively, 𝐾𝑓 is forward reaction rate constant,
𝐾𝑒 is the equilibrium constant of the reaction, 𝐾 is the
adsorption equilibrium constants, 𝑚 is the quality of dry
resin, and 𝑉 is the volume of the resin.
For the initial reaction rate, with no product present, (2)
can be reduced to
−𝑟𝐴0 = (
𝐾𝑓 𝑚𝐶𝐵0 /𝑉
1 + 𝐾𝐵 𝐶𝐵0
) 𝐶𝐴0 .
(3)
A plot of −𝑟𝐴0 versus 𝐶𝐴0 provides a straight line with slope
of (𝐾𝑓 𝑚𝐶𝐵0 /𝑉(1 + 𝐾𝐵 𝐶𝐵0 )). These lines were presented in
Figure 1 at temperature 348 K.
If (3) is rearranged for variables 𝐶𝐵0 values, the following
expression can be obtained:
𝐶𝐴0 𝐶𝐵0
𝑉𝐾𝐵
𝑉
=
+(
) 𝐶𝐵0 .
−𝑟𝐴0
𝐾𝑓 𝑚
𝐾𝑓 𝑚
(4)
A plot of 𝐶𝐴0 𝐶𝐵0 /(−𝑟𝐴0 ) versus 𝐶𝐵0 produces a straight line
with the slope of 𝑉𝐾𝐵 /𝐾𝑓 𝑚 and intersection of 𝑉/𝐾𝑓 𝑚.
These lines are presented in Figure 1 at 348 K. From the slope
and lines shown in Figure 2, the following equation can be
held.
3
3230
0.0047
3225
0.0046
3220
0.0045
−rA0 (mol/L·h)
CA0 ∗ CB0 /−rA0 (mol min/L)
ISRN Chemical Engineering
3215
3210
3205
3200
0.0044
0.0043
0.0042
0.0041
3195
13
13.5
14
CB0 (mol/L)
14.5
15
In order to evaluate the inhibiting effect of water concentration, (2), with no ester present initially, can be written as
−𝑟𝐴0 =
1 + 𝐾𝐵 𝐶𝐵0 + 𝐾𝑊𝐶𝑊0
,
(5)
from which the following equation can be obtained:
𝐶𝐴0 𝐶𝐵0 𝑉 (1 + 𝐾𝐵 𝐶𝐵0 )
𝑉𝐾
=
+ ( 𝑊 ) 𝐶𝑊0 .
−𝑟𝐴0
𝐾𝑓 𝑚
𝐾𝑓 𝑚
(6)
A plot of 𝐶𝐴0 𝐶𝐵0 /(−𝑟𝐴0 ) versus 𝐶𝑊0 at constant acid and
alcohol concentrations gives a straight line with slope of
𝑉𝐾𝑊/𝐾𝑓 𝑚 and intersection of 𝑉(1 + 𝐾𝐵 𝐶𝐵0 )/𝐾𝑓 𝑚. These
lines were presented in Figure 3.
At temperature 348 K,
𝐾𝑓 𝑚𝐶𝐵0
𝑉 (1 + 𝐾𝐵 𝐶𝐵0 )
𝑉𝐾𝐵
= 14.40,
𝐾𝑓 𝑚
= 0.0045,
𝑉
= 3012.06,
𝐾𝑓 𝑚
𝑉 (1 + 𝐾𝐵 𝐶𝐵0 )
= 3201.13,
𝐾𝑓 𝑚
(7)
Solving these equations by the “method of averages,” we
found the values of
𝐾𝑓 = 4.53 × 10−6 L2 /mol,
𝐾𝐵 = 4.78 × 10−6 L/mol,
𝐾𝑊 = 7.35 × 10−6 L/mol.
5.1. Integrated Rate Expression. If the reaction rate given in
(3) is expressed in terms of conversion of butyric acid, the
following equation can be obtained. Adsorption effect of
alcohol and water is neglected as discussed earlier and as
alcohol is taken in far excess, so 𝐶𝐵0 is taken as constant;
hence, (3) becomes a pseudo-first-order rate equation:
𝑤
𝐶 𝐶 .
𝑉 𝐵0 𝐴
0.5
1
1.5
Figure 3: Effect of water concentration on initial reaction rate:
catalyst loading = 73.2 kg/m3 ; temperature = 348 K.
Putting 𝐶𝐴 = 𝐶𝐴0 (1 − 𝑋𝐴),
𝑑𝑥𝐴
𝑤
= 𝐾𝑓 𝐶𝐵0 𝐶𝐴0 (1 − 𝑋𝐴) ,
𝑑𝑡
𝑉
𝑑𝑥
𝑤
− 𝐴 = 𝐾𝑓 𝐶𝐵0 (1 − 𝑋𝐴 ) ,
𝑑𝑡
𝑉
(9)
𝑥𝐴
𝑑𝑋𝐴
𝑤
= ∫ 𝐾𝑓 𝐶𝐵0 𝑑𝑡,
∫ −
𝑉
(1 − 𝑋𝐴 )
0
𝑤
− ln (1 − 𝑋𝐴) = 𝐾𝑓 𝐶𝐵0 𝑡,
𝑉
where 𝑋𝐴 is the fractional conversion of 𝐴. Thus, a plot
of − ln(1 − 𝑋𝐴) against time 𝑡 gives a slope which represents
𝐾.
−𝐶𝐴0
6. Results and Discussion
𝑉𝐾𝑊
= 22.18.
𝑘𝑓 𝑚
−𝑟𝐴0 = 𝐾𝑓
0
CW0 (mol/L)
Figure 2: 𝐶𝐴0 𝐶𝐵0 /−𝑟𝐴0 versus 𝐶𝐵0 : temperature = 348 K; catalyst
loading = 73.2 kg/m3 .
𝐾𝑓 (𝑚/𝑉) 𝐶𝐴0 𝐶𝐵0
0.004
(8)
The esterification reaction of butyric acid with ethanol was
studied in a batch reactor in the presence of acidic ion
exchange resin catalyst, Amberlyst 15. The kinetics of esterification of butyric acid is studied at different temperatures from
328.15 to 348.15 K with different molar ratios and varying
catalyst loading (Figure 11). A pseudo-homogeneous model
has been used to describe the esterification reaction catalyzed
by Amberlyst 15. The effects of temperature, catalyst loading,
and molar ratio are studied.
6.1. Catalyst Performance. In Figure 5, a comparison of the
behavior of the Amberlyst 15 and Amberlyst 35 catalysts
is shown. Catalysts are used to access their efficacy in the
esterification of butyric acid with ethanol. Amberlyst 15 is
shown to be an effective catalyst as compared to Amberlyst
35. The catalytic activity of Amberlyst 15 has higher activity
than Amberlyst 35. It is due to Amberlyst 15 has higher
total exchange capacity, surface area, and pore volume than
Amberlyst 35. So, Amberlyst 15 is found to be the best catalyst
to generate the data (Table 1).
6.2. Effect of Catalyst Loading. In Figure 6 experiments work
conducted by varying the catalyst loading from 24.4 kg/m3
4
ISRN Chemical Engineering
Table 1: Characteristics of the catalysts.
Amberlyst 35
5.32
34
5.20
0.28
329
1.542
Amberlyst 15
4.75
42
4.70
0.36
343
1.416
70
60
Fractional conversion
Property
Acidity (eq. H+ kg−1 )
Surface area (m2 g−1 )
Total exchange capacity (eq/kg)
Pore volume (cm3 g−1 )
Mean pore diameter (Å)
Skeletal density (g cm−3 )
80
50
40
30
CA0 ∗ CB0 /−rA0 (mol·min/L)
20
3230
3225
10
3220
0
0
3215
200
400
Time (min)
3210
Figure 5: Variation with type of catalyst. Amberlyst 15 (⧫) and
Amberlyst 35 (◼), catalyst loading = 48.8 kg/m3 , temperature = 75∘ C,
and molar ratio = 1 : 10 (butyric acid : ethanol).
3205
3200
3195
0
0.5
1
1.5
CW0 (mol/L)
3
to 81.4 kg/m . Keeping butyric acid and ethanol molar ratio
1 : 10 and and the reaction temperature 75∘ C. It is found that
with increase in catalyst loading, the conversion of butyric
acid increased with the proportional increase in the active
sites. At higher catalyst loading, the rate of mass transfer is
high, and therefore, there is no significant increase in the rate
[9].
This data is once again used to plot − ln(1 − 𝑋𝐴 ) versus 𝑡
in Figure 7 and get a straight line passing through origin, the
slope of which gives the value of 𝐾.
The values of 𝐾 are plotted against catalyst loading, 𝑤
(kg/m3 ) in Figure 8, and it is observed that with the increase
in 𝑤, there is a linear increase in 𝐾; thus, it validates the
model.
6.3. Effect of Molar Ratio. The concentration of ethanol had
an influence on the reaction rate and on the conversion. The
results are given in Figure 9. It can be seen that the conversion
of acid increases with increasing the initial molar ratio of
ethanol to butyric acid. For the esterification with ethanol,
the equilibrium conversion of butyric acid increases from
31% to 81% on varying ethanol to butyric acid ratio from 1 : 1
to 1 : 15 for catalyst loading 73.2 kg/m3 at temperature 348 K
(Figure 4). The result observed for the effect of initial molar
ratio of ethanol to butyric acid indicated that the equilibrium
conversion of butyric acid can be effectively enhanced by
using a large excess of ethanol.
For calculating 𝐾, these data are once again used to plot
− ln(1 − 𝑋𝐴 ) versus 𝑡 to get a straight line passing through
origin shown in Figure 10 the slope of which gives the value
of 𝐾.
Fractional conversion (XA )
Figure 4: (𝐶𝐴0 𝐶𝐵0 /−𝑟𝐴0 ) versus 𝐶𝑊0 : temperature = 348 K; catalyst
loading = 73.2 kg/m3 .
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
100
200
300
Time (min)
400
500
Figure 6: Comparison of the effect of catalyst loading (⧫)
24.4 kg/m3 , (◼) 32.5 kg/m3 , (󳵳) 48.8 kg/m3 , (×) 56.9 kg/m3 , (∙)
65.06 kg/m3 , (+) 73.2 kg/m3 , and (−) 81.4 kg/m3 on the conversion of
butyric acid with ethanol; molar ratio = 1 : 10 (butyric acid : ethanol),
and temperature = 75∘ C.
The values of 𝐾 are plotted against catalyst loading, 𝑤
(kg/m3 ), and it was observed that with the increase in 𝑤, there
was a linear increase in 𝐾; thus, it validates the model.
6.4. Effect of Temperature. The study of the effect of temperature is very important because this information is useful in
calculating the activation energy. In order to investigate the
effect of temperature, esterification reactions are carried out
in the temperature region from 328 to 348 K while keeping
the acid : alcohol ratio at 1 : 10 and the catalyst loading of
73.2 kg/m3 dry resin (Figure 13). With an increase in reaction
temperature, the initial reaction rate or the conversion of
the butyric acid is found to increase substantially as shown
in Figure 12. It shows that the higher temperature yields
the greater conversion of the acid at fixed contact time.
ISRN Chemical Engineering
5
1.8
2
1.6
1.8
1.6
1.2
1.4
1
−(ln (1 − XA ))
− ln (1 − XA )
1.4
0.8
0.6
0.4
1.2
1
0.8
0.2
0.6
0
0
100
200
Time (min)
300
0.4
400
0.2
0
Figure 7: Typical kinetic plot of comparison of different catalyst loadings: (⧫) 24.4 kg/m3 , (◼) 32.5 kg/m3 , (󳵳) 48.8 kg/m3 , (×)
56.9 kg/m3 , (∗) 65.06 kg/m3 , (∙) 73.2 kg/m3 , and (−) 81.4 kg/m3 .
0
200
Time (min)
300
400
Figure 10: Typical kinetic plot of comparison of different molar
ratios: (⧫) 1 : 5, (◼), 1 : 10, and (󳵳) 1 : 15, temperature: 348.15 K, and
catalyst loading: 73.2 (kg/m3 ).
0.4
0.35
0.006
0.3
Rate constant K (hr−1 )
Rate constant K (min−1 )
100
0.25
0.2
0.15
0.1
0.005
0.004
0.003
0.002
0.001
0.05
0
0
0
0
20
40
60
Catalyst loading (kg/m3 )
80
10
Molar ratio
15
20
Figure 11: Effect of different molar ratios: rate constant (𝐾)
versus molar ratio, temperature: 348.15 K, and catalyst loading: 73.2
(kg/m3 ).
Figure 8: Effect on 𝐾 with catalyst loading.
0.9
0.9
0.8
0.8
Fractional conversion (XA )
Fractional conversion (XA )
5
100
0.7
0.6
0.5
0.4
0.3
0.2
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0.1
0
0
0
0
100
200
300
Time (min)
400
500
Figure 9: Comparison of the effect of molar ratio 1 : 1 (⧫), 1 : 5 (◼),
1 : 10 (󳵳), and 1 : 15 (×) on the conversion of butyric acid with ethanol,
with catalyst loading of 73.2 kg/m3 and temperature of 75∘ C.
100
200
300
Time (min)
400
500
Figure 12: Comparison of the effect of temperature: 328 K (⧫), 333 K
(◼), 338 K (󳵳), 343 K (×), and 348 K (∗), on the conversion of butyric
acid with ethanol, with catalyst loading of 73.2 kg/m3 and molar ratio
of 1 : 10 (butyric acid : ethanol).
6
ISRN Chemical Engineering
1.8
7. Conclusion
1.6
The kinetics of esterification of butyric acid with ethanol in
the temperature ranging between 328.15 K and 348.15 K and
at molar ratio 1 : 5 to 1 : 15 is investigated experimentally in
a stirred batch reactor using Amberlyst 15. The optimum
conditions for synthesizing ethyl butyrate have been delineated. It has also been observed that the initial reaction rate
increases linearly with acid and alcohol concentrations. And
rate of reaction is found to increase with the increase in
catalyst loading, temperature, and molar ratio. Eley-Rideal
model is applied to study the kinetics of the reaction. As
a result, it is concluded that the acidic resin, Amberlyst 15,
is a suitable catalyst for this reaction, since in the presence
of it, the reaction has been found to take place between an
adsorbed alcohol molecule and a molecule of acid in the
bulk phase (Eley-Rideal model). It is also observed that water
has inhibiting effect of reaction. Temperature dependency
of the kinetic constants has been found to apply Arrhenius
equation. The activation energy is found to be 30 KJ/mol.
− ln (1 − XA )
1.4
1.2
1
0.8
0.6
0.4
0.2
0
0
100
200
Time (min)
300
400
Figure 13: Typical kinetic plot of comparison of different temperatures: 328 K (⧫), 333 K (◼), 338 K (󳵳), 343 K (×), and 348 K (∗).
6.2
6.1
References
6
− ln (K)
5.9
5.8
5.7
5.6
5.5
5.4
5.3
2.85
2.9
2.95
3
3.05
3.1
1000 (T)
Figure 14: Arrhenius plot of − ln 𝐾 versus 1/𝑇 (molar ratio = 1 : 10;
catalyst loading = 73.2 kg/m3 ).
Thus, 75∘ C is chosen as the maximum working temperature
for the butyric acid esterification.
Arrhenius law expresses the temperature dependency of
the rate constant:
𝐾 = 𝑘0 exp (−
𝐸0
),
𝑅𝑇
(10)
where 𝑘0 = frequency factor, 𝐸0 = activation energy, and 𝑅 =
gas constant.
This data is once again used to plot − ln(1−𝑋𝐴) versus 𝑡 to
get a straight line passing through origin, the slope of which
gives the value of 𝐾.
Equation (1), a plot of − ln 𝐾 versus 1/𝑇, at constant acid
and alcohol concentrations, gives a straight line with a slope
of (𝐸𝑎 /𝑅) as shown in Figure 14.
The study on the effect of temperature is very important
for heterogeneously catalyzed reaction as this information is
useful in calculating the activation energy for this reaction.
An Arrhenius plot for the initial rate of reaction is given in
Figure 14. The activation energy for the esterification reaction
based on the initial rate is found to be 30 KJ/mol.
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