Synthesis of methyl butyrate using heterogeneous catalyst: Kinetic studies

Article abstract of DOI:10.1007/s10562-014-1313-6

This paper illustrates a kinetic investigation of esterification reaction involving butyric acid and methanol over amberlyst-15 catalyst. The catalytic reactions were performed in an isothermal well stirred batch reactor using excess of alcohol to prevent the reverse reaction. The experimental parameters studied were reaction temperature, molar ratios of reactants, catalyst loading, stirring speed, initial water present and quantity of molecular sieves added. The optimum reaction conditions for the ester synthesis were found at temperature 343 K, alcohol to acid ratio 3, stirrer speed 300 rpm, catalyst loading of 6.5 % (w/w basis) and molecular sieves 8.5 %. Addition of water to reactor contents has negative effect as expected. Conversion increased with temperature and catalyst loading whereas it decreased as the molar ratio of alcohol to acid increased beyond 3. Molecular sieves added adsorb water formed in the reaction hence favoring reaction in forward direction. Kinetic data was tested for pseudo-homogeneous model, Langmuir-Hinshelwood model and Eley-Rideal model. Studies show that dual site LHHW with reactants and products adsorbing on catalyst surface is most suited for the experimental data. Graphical Abstract: [Figure not available: see fulltext.]

Full text of DOI:10.1007/s10562-014-1313-6

Catal Lett (2014) 144:1537–1546
DOI 10.1007/s10562-014-1313-6
Synthesis of Methyl Butyrate Using Heterogeneous Catalyst:
Kinetic Studies
P. N. Dange
•
A. Sharma V. K. Rathod
•
Received: 5 May 2014 / Accepted: 1 July 2014 / Published online: 27 July 2014
Ó Springer Science+Business Media New York 2014
Abstract This paper illustrates a kinetic investigation of
esterification reaction involving butyric acid and methanol
over amberlyst-15 catalyst. The catalytic reactions were
performed in an isothermal well stirred batch reactor using
excess of alcohol to prevent the reverse reaction. The
experimental parameters studied were reaction tempera-
ture, molar ratios of reactants, catalyst loading, stirring
speed, initial water present and quantity of molecular
sieves added. The optimum reaction conditions for the ester
synthesis were found at temperature 343 K, alcohol to acid
ratio 3, stirrer speed 300 rpm, catalyst loading of 6.5 %
C
Methyl butyrate
CA0
Initial concentration of butyric acid
Concentration of butyric acid, methanol,
methyl butyrate and water respectively
at any time (t)
C , C , C
A C
B
and CD
D
Water
-
1
Activation energy (kJ mol )
Ea
k0
Pre-exponential factor in Arrhenius
Equation
-
Forward rate constant (lit mol min )
1
-1
kf
kr
ks
-
Reverse rate constant (lit mol min
1
-1
)
2
Surface reaction rate constant (lit /
(
w/w basis) and molecular sieves 8.5 %. Addition of water
-
1
Molgcat min )
to reactor contents has negative effect as expected. Con-
version increased with temperature and catalyst loading
whereas it decreased as the molar ratio of alcohol to acid
increased beyond 3. Molecular sieves added adsorb water
formed in the reaction hence favoring reaction in forward
direction. Kinetic data was tested for pseudo-homogeneous
model, Langmuir–Hinshelwood model and Eley–Rideal
model. Studies show that dual site LHHW with reactants
and products adsorbing on catalyst surface is most suited
for the experimental data.
K , K , K
C
Adsorption equilibrium constant for butyric
acid, methanol, methyl butyrate and water
respectively (lit/mol gcat s)
A
B
and KD
Ke
Equilibrium rate constant
M
Methanol to butyric acid ratio (CB0/CA0)
Reaction rate obtained based on butyric
(-rA)
-
1
-1
acid consumed (mol lit min
Universal gas constant
)
R
-
1
(8.314 kJ mol K)
Temperature (K)
T
Keywords Esterification ꢀButyric acid ꢀMethanol ꢀ
Amberlyst-15 ꢀKinetic model
xA
Conversion of butyric acid
[(CA0 - C )/C ]
A
A0
xAe
Equilibrium conversion of butyric acid at
equilibrium
Abbreviations
A
B
Butyric acid
Methanol
P. N. Dange ꢀA. Sharma ꢀV. K. Rathod (&)
Department of Chemical Engineering, Institute of Chemical
Technology, Matunga (E), Mumbai 400019, India
e-mail: vk.rathod@ictmumbai.edu.in;
1
Introduction
Methyl butyrate or methyl ester of butyric acid is an ester
with a fruity odor of apple, pineapple, and strawberry.
virendrakrathod@gmail.com
123

1
538
P. N. Dange et al.
Present in trace amounts in several plant products, espe-
cially pineapple flavor is produced by distillation from
essential oils of vegetable kind. This ester is also manu-
factured on a small scale for use in perfumeries or flavoring
food. Esters, in general, can be defined as the products of
reaction between carboxylic acids and organic alcohols.
Chemically, an ester is formed as the condensation product
when a carboxylic acid is reacted with an alcohol [1].
Esterification of carboxylic acids with alcohols represents a
well-known class of liquid-phase reactions of considerable
industrial interest due to varied practical applications of
ester products. These esters are fine chemicals of immense
importance which are widely used in manufacturing of
flavors, pesticides, adhesives, pharmaceuticals, plasticizers,
solvents of paints, polymerization monomers. Esters are
also used in the preparation of biodiesel from lower quality
feedstock. Derivatives of few esters are useful as chemical
intermediates and monomers for resins and polymers with
high molecular weight. They are also used as emulsifiers in
the food and cosmetic industries [2, 3].
esterification kinetics of Dowex 50 W catalyzed esterifi-
cation of lactic acid with methanol was investigated by a
team of researchers. They correlated experimental reaction
rates by few models based on homogeneous as well as
heterogeneous catalytic mechanisms. Parameters of the
different models were obtained by the simplex search
method [18]. Xu and Chuang investigated the kinetic study
of Amberlyst-15 catalyzed esterification of dilute acetic
acid with methanol. A kinetic equation was developed and
proposed to be used in the design of a catalytic distillation
column for removing dilute acetic acid from wastewater
[19]. Robert et al. developed the kinetic model for the
esterification of methanol with acetic acid in the presence
of hydrogen iodide acid catalyst. Kinetics and equilibrium
parameters were estimated from experimental data with
regression analysis using rate equations. Although, con-
siderable literature is available on esterification of various
organic acids and range of alcohols using ion exchange
catalysts, there is no ample information available on syn-
thesis of methyl butyrate from butyric acid and methanol in
presence of Amberlyst-15 catalyst [20].
Many routes are available for the synthesis of organic
esters. The traditional route for preparing esters is by the
reaction of the carboxylic acid with an alcohol using
homogeneous catalysts such as sulfuric acid or para-tolu-
ene-sulfonic acid [4–7]. Esterification can take place
without adding catalysts due to inherent weak acidity of
carboxylic acids themselves. However, the reaction is
extremely slow and takes long time to reach equilibrium at
typical reaction conditions [8]. A common method of
operating equilibrium limited reactions is to use one
reactant in excess amounts in order to increase the con-
version of the limiting reactant. Some of the homogenous
acid catalysts such as H SO , HCl or HI are generally used
The objectives of the present work were to test the
suitability and efficacy of cation-exchange resin (Amber-
lyst-15) as a catalyst for the synthesis of methyl butyrate.
Effects of time, temperature, catalyst loading, speed of
agitation, alcohol to acid ratio, addition of molecular sieves
and initial water present on esterification reaction were also
undertaken.
2 Materials and Methods
2.1 Materials
2
4
but due to their miscibility with the reaction medium
separation becomes a problem. However, these acids are to
be neutralized after the reaction, due to the subsequent salt
formation. This problem can be solved by the use of het-
erogeneous, solid acids catalysts such as various sulfonic
ion-exchange resins [2, 9].
Butyric acid and methanol of 99.98 % purity (w/w) were
supplied by Merck. Both these chemicals were used as
supplied. The acidic ion exchange resin (Amberlyst-15 of
Rohm and Haas Co.) was supplied by Sigma Aldrich, USA.
A cation exchange resins are insoluble polymer matrix
which can exchange ions with the adjacent reacting mix-
ture. It is a macro-porous type styrene-DVB (20 %) resin.
The resin is formed by the copolymerization reaction
between styrene and divinyl-benzene which acts as cross-
linking agent. For cation exchange resins, acid sites are
deposited on the polymer matrix by the treatment of strong
acids such as sulphuric acid which gives sulphonated cat-
ion exchange resins.
Many ion-exchange resins, especially the cation-exchange
resins such as Dowex, and Amberlyst series are manufactured
mainly by sulfonation of ethylbenzene, followed by a cross-
linking with divinyl-benzene [8, 10, 11]. Owing to their
selective adsorption of reactants, features for surface acid
sites, and swelling nature, these resins not only catalyze the
esterification reaction but also influence the equilibrium
conversion. They also show many advantages such as
mechanical separation, reusability, and continuous operation
as a heterogeneous catalyst in esterification [12, 13].
2.2 Batch Experiments
There are many solid catalysts reported in the literature
for esterification reactions [14, 15]. Ion exchange resins
have been used in esterification and hydrolysis of methyl
acetate in catalytic distillation column [16, 17]. The
Esterification reactions were performed in a batch reactor
with 250 mL capacity and made of borosilicate glass. The
three necked reactor was equipped with sample port, stirrer
1
23

Synthesis of Methyl Butyrate
1539
and condenser to reflux back liquid from condensed vapors
formed during reaction runs. Water bath with automatic
temperature control was used to keep reaction temperature
at constant value. Four blade turbine agitator was used to
ensure adequate mixing of reaction contents at different
speed (0–1,500 rpm) using speed controller. In a typical
experiment, a measured quantity of methanol and catalyst
successfully used in high polar reaction media [19]. A
generalized esterification reaction is written as:
kf
A + B
!C + D
ðaÞ
kr
where, A and B are the reactants (carboxylic acid and
alcohol), while C and D are the products (ester and water)
of the reaction. The notations, k and k are the rate con-
(
amberlyst-15) were charged into the reactor. The reactor
f
r
stants for forward and reverse reactions, respectively.
Based on the mechanism, numerous models have been
developed to represent the kinetic behaviors of esterifica-
tion reactions. The current study proposes to test the kinetic
data for synthesis of methyl butyrate using three models:
the PH reaction model [20], the Langmuir–Hinshelwood–
Hougen–Watson (LHHW) model and the ER model [22].
was sealed and heating was started with condenser water
on. Once the desired temperature was reached, the required
amount of butyric acid was injected into the reactor via
syringe and stirring was initiated—the instant was marked
as zero reaction time. Small amount of samples (0.2 mL)
were withdrawn at specified time intervals over the first 4 h
of reaction. Reaction mixture was filtered in the end to
separate the sample solution from the used solid catalyst.
3.1 Homogeneous Reaction Model
2
.3 Analysis
The PH model does not take into account the sorption
effect on the catalyst sites in a reacting medium [23, 24]. If
the reaction mixture is considered as a homogeneous liquid
phase, outcome by the PH model could be considered as a
satisfactory tool to correlate the esterification of butyric
acid with methanol in the presence of amberlyst-15 as a
catalyst. For the esterification reaction represented by
reaction (a), the rate of consumption of A is given by:
2
.3.1 Gas Chromatographic Analysis
The liquid samples were analyzed using a gas chromato-
graph (Chemito GC, Model 6890) for quantitative deter-
mination of methyl butyrate and water formed in the
esterification reaction. The GC consisted of two detectors,
a thermal conductivity detector and a flame ionization
detector, connected in series. A 30-m long HP-Innowax
column (Polyethylene glycol 320 micrometers in diameter
with 0.5 micrometer in thickness) was used with a tem-
perature programmed analysis. Nitrogen was used as the
carrier gas.
dxA
ðꢁrAÞ= CA0
= kfCACB ꢁkrCCCD
ð1Þ
dt
For one of the excess reactants the reverse reaction is
negligible
rA = kfCACB
ð2Þ
ð3Þ
2
.3.2 Titrimetric Analysis
dxA
dt
ðꢁr Þ= C
= k C C = k C ð1 ꢁx ÞðC
A
A0
f
A
B
f
A0
A
B0
Samples from the reaction mixtures were titrated for the
total acid content using 0.1 N NaOH with phenolphthalein
indicator and methanol as a quenching agent. The Methyl
butyrate obtained was also expressed in terms of percent
ꢁ
CA0xA
CB0
CA0
Taking, M ¼ , Eq. (3) becomes
dxA
(
%) conversion based on butyric acid consumption. The
2
A0
CA0
= kfCACB = kfC ð1 ꢁxAÞðM ꢁxAÞ
conversion obtained using both the analyses was similar
with only 2 % deviation.
dt
ð4Þ
Integration of (4) yields
3
Kinetic Modeling
ðMꢁxAÞ
ln
¼kfCA0ðMꢁ1Þt
ð5Þ
Mð1ꢁxAÞ
Kinetic analysis is needed to develop a model that
describes the rate of reaction as a function of reaction
variables. Different kinetic models are available to describe
the esterification reactions catalyzed by ion-exchange res-
ins based on homogeneous and heterogeneous approaches.
Although pseudo-homogeneous (PH) model does not take
into account the adsorption effects of the species in the
reactant medium on the surface of catalyst, it has been
dxA
At equilibrium, ðꢁr Þ¼C
¼0 and thus, the equi-
A
A0
dt
librium constant (K ) can be calculated from:
e
2
Ae
kf
X
Ke ¼
¼
ð6Þ
kr ð1 ꢁx ÞðM ꢁx Þ
Ae
Ae
xAe is the conversion of butyric acid at equilibrium.
123

1
540
P. N. Dange et al.
3
.2 Heterogeneous Models
1
.9
.8
.7
.6
0
0
0
0
In heterogeneous kinetic studies, the generally encoun-
tered problem is complicated rate expressions which may
obey LHHW or Eley–Rideal (ER) model [25, 26]. The
LHHW and the ER models both include the adsorption
effects of the species in the reactant medium. The basic
assumption of LHHW model is that all reactants are
adsorbed on the catalyst surface before chemical reac-
tions occur. The ER model assumes that the reaction
takes place between adsorbed and non-adsorbed
reactants.
0.5
323 K
0
0
0
0
.4
.3
.2
.1
0
3
3
3
33 K
43 K
53 K
For the reversible reaction of butyric acid with metha-
nol, considering adsorption effects of the reactants and
products, we may have possible rate expressions as
follows:
0
50
100
150
200
250
Time (Minutes)
(
i) Single site LHHW model based on reactants only:
Reactants are adsorbed on the surface of catalyst
and reaction takes place with single-site mecha-
nism [27].
Fig. 1 Effect of temperature on conversion of butyric acid at alcohol
to acid ratio 3, catalyst loading 6.5 %, stirrer speed 300 rpm, initial
water present 0 mL, molecular sieves 8.5 %
ksCACB
ðꢁrAÞ¼
ð7Þ
ksCACB
ð1 þKACA þKBCBÞ
ðꢁrAÞ¼
ð11Þ
ð1 þKACAÞ
(
ii) Dual site LHHW based on reactants only: Reac-
tants are adsorbed on the catalyst surface. In this
case reaction takes place on the surface of catalyst
with dual-site mechanism [27].
(vi) Dual site ER model: Adsorbed A on catalyst
surface reacts with B in the bulk by a dual site
mechanism [27].
ksCACB
ksCACB
ðꢁrAÞ¼
ð8Þ
ðꢁrAÞ¼
ð12Þ
2
2
ð1 þKACA þKBCBÞ
ð1 þKACAÞ
(
iii) Single site LHHW model based on reactants and
products: All reactants and products are adsorbed
on the catalytic sites and reaction takes place by
single site mechanism [27].
4
Results and Discussion
ksCACB
4
.1 Effect of Temperature
ðꢁr Þ¼
A
ð1 þKACA þKBCB þKCCC þKDCDÞ
ð9Þ
The effect of temperature on the rate of reaction was
studied by conducting the reactions at 323, 333, 343 and
(
iv) Dual site LHHW based on reactants and products:
All reactants and products are adsorbed on catalyst
surface and reaction occurring by dual-site mech-
anism [27].
3
53 K. Molar ratio of methanol and butyric acid was kept
constant at 3 and catalyst loading was maintained at 6.5 %
w/w). The quantity of molecular sieves added to reaction
(
mixture to remove water produced during reaction was
8.5 % on weight basis. The reaction was continued for 4 h
with continuous agitation at 300 rpm. It was found that
with an increase in the reaction temperature increases the
rate of reaction and conversion up to 343 K. As tempera-
ture is raised to 353 K there is sharp increase in conversion
for first 30 min. However it further decreases with time and
gives lower value than 343 K. The effect of temperature on
conversion is shown in Fig. 1.
k C C
B
s
A
ðꢁrAÞ¼
2
ð1 þKACA þKBCB þKCCC þKDCDÞ
ð10Þ
(
v) Single site ER model: Reactant A is adsorbed on
catalytic sites reacts with B in the bulk. The
reaction between A and B takes place by single site
mechanism [27].
1
23

Synthesis of Methyl Butyrate
1541
1
1
.9
.8
.7
.6
0
0
0
0
0
0
0
0
0
.9
.8
.7
.6
.5
.4
.3
.2
.1
0
0
0
0
0
M=1
M=2
M=3
M=4
0.5
0
0
0
0
.4
.3
.2
.1
0
1 %
2 %
4
%
0
50
100
150
200
250
6 %
.5 %
8
Time (Minutes)
Fig. 2 Effect of alcohol to acid ratio (M) on conversion of butyric
acid at temperature 343 K, catalyst loading 6.5 %, stirrer speed
0
50
100
150
200
250
Time ( Minutes)
3
00 rpm, initial water content 0 mL, molecular sieves 8.5 %
Fig. 3 Effect of catalyst loading on the conversion of butyric acid at
temperature 343 K, alcohol to acid ratio 3, stirrer speed 300 rpm,
initial water content 0 mL, molecular sieves 8.5 %
Since the esterification reaction is exothermic; an increase
in the temperature increases the rate of reaction [21, 28]. The
effect of temperature is taken into account in the forward
reaction rate constant, meaning that high temperature gives
rise to more frequent and successful collisions for higher
conversion of reactants to ester products. Also, higher
temperature reduces the viscosity of the solution and thereby
increases the diffusion of material through the pores. How-
ever, if the reaction takes place at too high temperature, the
reactants especially methanol is vaporized with reduced
availability of it for the reaction. This is conflicting to
choose from high reaction rate due to increased temperature
and the decrease of reaction rate resulting from the vapori-
zation of reactants. Therefore, it is imperative to determine
the optimal reaction temperature considering the production
rate as well as the vaporizing rate of reactants. In the present
study, the optimum reaction temperature was found to be
equi-molar case, the conversion is about 82 %. When
the ratio is increased to 4.0, most available butyric acid
is consumed and thus, the product, methyl butyrate and
the excess reactant methanol remain in the reactor. The
maximum conversion is obtained at the optimum ratio
of alcohol to acid of 3. Reactants need to be in equi-
molar proportion as per the reaction stoichiometry, but
for reaction to move in forward direction one of the
reactants is taken in excess.
4.3 Effect of Catalyst Loading
The effect of catalyst loading on the conversion of the butyric
acid is shown in Fig. 3. Fresh resin was used for each new
run. As expected, the conversion increases with the amount
of catalyst due to more available active sites for the reaction
at higher catalyst loading, resulting in higher reaction rate. A
higher loading of catalyst also results in reduction of the time
required to reach the reaction equilibrium [28, 29].
3
43 K at which the conversion of butyric acid reached a
stable value of 0.945.
4
.2 Effect of Alcohol to Acid Ratio
Figure 3 depicts that no significant change in the equi-
librium conversion of butyric acid is observed when the
catalyst loading is changed from 6.5 to 8.5 % (w/w) for the
reaction volume. It is also observed that the conversion
curve is steep in the first 15 min indicating that conversion
is faster initially as the more catalyst sites are available for
the unconsumed reactants. There is no marked increase in
the conversion of butyric acid when the catalyst loading is
increased to 8.5 % w/w. Hence the optimum catalyst
loading was taken as 6.5 % and further esterification runs
were carried out using this value.
The mole ratio of methanol to butyric acid was varied from
to 4 and the results obtained are reported in Fig. 2. The
1
maximum conversion of 94.5 % was obtained for alcohol to
acid molar ratio of 3 with a catalyst loading of 6.5 %,
stirrer speed of 300 rpm, temperature of 343 K and added
molecular sieves in the proportion of 8.5 %.
As the ratio of methanol to butyric acid increased
from 1 to 3, the conversion of butyric acid is also
increased and thereafter decreased owing to the excess
amount of methanol available for reaction. For the
123

1
542
P. N. Dange et al.
1
.9
.8
.7
.6
.5
.4
.3
.2
.1
0
1
0
0
0
0
0
0
0
0
0
0.9
0
0
0
0
0
.8
.7
.6
.5
.4
0
mL
100 rpm
2
3
4
00 rpm
00 rpm
00 rpm
1 mL
2
3
4
mL
mL
mL
0.3
0
0
.2
.1
0
0
50
100
150
200
250
300
Time (Minutes)
0
50
100
150
200
250
Time (Minutes)
Fig. 4 Effect of initial water addition on the conversion of butyric
acid at temperature 343 K, alcohol to acid ratio 3, stirrer speed
Fig. 6 Effect of speed of agitation on the conversion of butyric acid
at temperature 343 K, alcohol to acid ratio 3, catalyst loading 6.5 %,
initial water present 0 mL, molecular sieves 8.5 %
3
00 rpm, catalyst loading 6.5 %, molecular sieves 8.5 %
1
0
0
0
0
0
0
0
0
0
.9
.8
.7
.6
.5
.4
.3
.2
.1
0
Table 1 Rate constants determined at various temperatures using PH
model
2
R
Sr.
No.
Temp.
(K)
%
k
Conv. (L mol
f
K
e
k
r
-1
-1
(L mol
min )
-
1
)
-1
(
x
A
)
min
1
2
3
4
323
333
343
353
70.74
77.38
94.50
86.83
0.001
0.002
0.004
0.002
0.7459 0.00134
1.1890 0.00168
7.9011 0.00050
1.1890 0.00168
0.984
0.960
0.923
0.747
0
2
4
6
%
%
%
.5 %
8.5 %
loading of 6.5 %. The catalytic activity was significantly
lowered with increase in amount of initial water content.
As is evident from the Fig. 4, the conversion was con-
siderably reduced to 61.0 % when water added was 4 mL
(8.5 % w/w) as compared to the conversion of 94.5 % when
the reaction was carried out without initial water present in
the reaction mixture. Liu and co-workers, attributed this
catalytic inhibition to the combined effect of water which is
initially added and that formed during the course of reaction.
The rate of reaction is directly proportional to the water
concentrations because of retardation effect of water
adsorbed onto the active surfaces and also due to the inev-
itable thermodynamic equilibrium [30]. In the next section it
has been confirmed that removal of water formed in the
course of reaction enhances the reaction conversion.
0
50
100
150
200
250
Time (Minutes)
Fig. 5 Effect of addition of molecular sieves on the conversion of
butyric acid at temperature 343 K, alcohol to acid ratio 3, stirrer speed
00 rpm, catalyst loading 6.5 %, initial water present 0 mL
3
4
.4 Effect of Water Addition
A cation exchange resins are known to have great affinity
to polar components. It has been observed that the presence
of water in the esterification reaction inhibits the rate of
reaction. The inhibiting effect of water has also been
observed earlier in the esterification of acetic acid and
methanol [30], synthesis of tetra-hydro-furan [31]. In order
to study effect of water on the rate of reaction between
butyric acid and methanol, the initial water concentrations
were varied from 0 to 4 mL (0–8.5 % w/w). Figure 4
shows butyric acid conversion on amberlyst-15 as a func-
tion of time at 343 K, stirrer speed of 300 rpm and catalyst
4.5 Effect of Addition of Molecular Sieves
Water is the second product during the esterification of
butyric acid with methanol. Thus, the water content is
another important parameter in esterification reactions.
Kumar and Kanwar [32] reported that addition of
1
23

Synthesis of Methyl Butyrate
1543
1
.2
of unstable substances. Therefore, the employment of
molecular sieves to remove the formed water is not always
suitable.
3
3
3
3
23 K
33 K
43 K
53 K
R² = 0.9171
R² = 0.7473
1
In order to study the influence of water produced in the
˚
reaction, molecular sieves (3 A type) were added in the
0
0
0
0
.8
.6
.4
.2
0
range of 0–8.5 % (w/w). The experiments were carried out
at agitation speed of 300 rpm, catalyst loading of 6.5 %
and a temperature of 343 K. Figure 5 shows that the con-
version of methyl butyrate increased with increasing
molecular sieves to reaction mixture. This could be
because of the adsorption of produced water in the pores of
molecular sieves and hence inhibiting the reverse reaction.
R² = 0.9608
R² = 0.9842
0
50
100
150
200
250
4.6 Effect of Speed of Agitation
Time (Minutes)
The experimental runs were performed at different stirring
speeds, varying from 100 to 400 rpm. It is vital to obtain the
intrinsic kinetics that the runs were carried out under suffi-
cient agitation speed to make external mass transfer by film
diffusion negligible. The experiments were conducted at
alcohol to acid ratio of 3, catalyst loading of 6.5 % (w/w),
reaction temperature of 343 K and added molecular sieves.
Figure 6 shows that the conversion of butyric acid is
greatly affected by the variation of stirrer speed. As the
speed is increased from 100 to 300 rpm, the conversion is
Fig. 7 Determination of rate constants at various temperatures using
PH model (alcohol to acid ratio 3, stirrer speed 300 rpm, catalyst
loading 6.5 %, initial water present 0 mL, molecular sieves added
8
.5 %)
molecular sieves or silica gel usually improves the equi-
librium conversion. However, Kuwabara et al. [33] also
reported that molecular sieves in some cases had negative
effects, such as the formation of di-esters and degradation
Table 2 Estimated kinetic parameters using heterogeneous models
Sr. No.
Temp
K)
Kinetic
parameters
Heterogeneous models (Eq. no.)
(
LHHW-dual
site (7)
LHHW-single
site (8)
LHHW-dual
site (9)
LHHW-single
site (10)
ER-dual
site (11)
ER-single
site (12)
2
(L /Molgcat min)
1
343
333
323
k
s
0.40
-8.13
1.36
–
4.09
3.15
1.85
1.12
8.20
8.20
0.99
2.10
4.60
1.37
10.4
10.48
0.96
2.53
7.21
1.53
19.15
19.17
0.92
1.47e ? 003
3.51e ? 005
-2.78e ? 03
1.40e ? 008
-1.39e ? 08
0.99
7.50e ? 013
4.80e ? 010
K
K
K
K
A
-3.7e ? 03
1.10e ? 016
5.00e ? 013
B
C
D
514.91
–
–
–
–
–
–
–
–
–
2
R
0.99
0.31
-10.30
1.85
–
0.99
0.219
0.111
2
(L /Molgcat min)
2
k
s
0.043
0.074
1.29e ? 010
3.12e ? 009
K
K
K
K
A
B
C
D
-82.99
-3.30
1.44e ? 011
5.76e ? 012
12.36
5.81
–
–
–
46.67
–
–
–
–
46.87
–
–
2
R
0.96
0.16
-12.86
2.01
0.96
0.96
0.86
0.1784
2
(L /Molgcat min)
3
k
s
2.04e ? 307
9.68e ? 39
-9.10e ? 43
1.10e ? 43
-1.73e ? 45
1.70e ? 045
0.82
1.81e ? 017
?
?
–
K
K
K
K
A
B
C
D
?
?
–
2.86e ? 018
–
–
–
–
–
–
2
R
0.82
0.96
0.86
–
123

1
544
P. N. Dange et al.
Experimental
Fig. 8 Comparison of predicted
vs experimental conversion at
different temperatures (alcohol
to acid ratio 3, stirrer speed
3
6
0
1
.9
.8
0
0
00 rpm, catalyst loading
.5 %, initial water present
mL, molecular sieves 8.5 %).
0.7
LHHW Dual Site
(
Reactants only)
0
0
0
0
0
0
.6
.5
.4
.3
.2
.1
0
a Temperature 323 K.
b Temperature 333 K.
c Temperature 343 K
LHHW Dual Site
Reactants and
Products)
(
Eley Rideal Dual Site
PH Model
0
50
100
150
200
250
Time (Minutes)
a) Temperature 323 K
(
1
.9
.8
.7
.6
.5
.4
.3
.2
.1
0
Experimental
0
0
0
0
0
0
0
0
0
LHHW Dual Site
(Reactants only)
LHHW Dual Site
(
Reactants and
Products)
Eley Rideal Dual Site
PH Model
0
50
100
150
200
250
Time (Minutes)
b) Temperature 333 K
(
1
.9
.8
.7
.6
.5
.4
.3
.2
.1
0
Experimental
0
0
0
0
0
0
0
0
0
LHHW Dual
Site (Reactants
only)
LHHW Dual
Site (Reactants
and Products)
Eley Rideal
Dual Site
PH Model
0
50
100
150
200
250
Time (Minutes)
(c) Temperature 343 K
1
23

Synthesis of Methyl Butyrate
1545
increased from 0.82 to 0.945. As speed is increased further
from 300 to 400 rpm, conversion is marginally reduced. An
increase in conversion for increase in the speed of agitation
from 100 to 300 rpm can be attributed to the fact that mass
transfer resistance has decreased due to the increase in the
turbulence. However, the decrease in the conversion at
fit. All the kinetic constants estimated by this model are
real and positive with co-relation coefficients of more than
0.9. When the nonlinear rate model, Eq. (10) is solved with
the obtained kinetic constants for predicting concentration
profiles of A, B, C and D, the predicted conversion plots
show good agreement with the experimental values. All
other heterogeneous models predict vague kinetic param-
eters which give rise to estimated conversions inconsistent
with the experimental values. Conversions predicted by PH
model at different temperatures are widely differing with
experimental values as expected since PH model does not
take into account the sorption effects. Comparative plots
for conversion between experimental and predicted values
at various temperatures are given in Fig. 8a–c. Dual site
LHHW with reactants only adsorbed on catalytic sites
4
00 rpm can be reasoned by the shearing effect between
the catalyst particles at higher stirring speed. Hence the
mild stirring speed of 300 rpm was selected as optimum for
the esterification reaction.
4
.7 Estimation of Kinetic Parameters
The kinetic data of esterification reaction was correlated
with three kinetic models: the PH model, the ER model and
the LHHW model according to equations given in Sect. 3.
Firstly, the PH model was applied and plots were made
using Eq. (5) to determine the slope of the line from which
(
Eq. 8), Dual site LHHW with both reactants and products
adsorbed on catalytic sites (Eq. 10), Dual site Eley–Rideal
Eq. 12) and PH model (Eq. 4) have been compared with
(
the experimental values. Figure 8 shows that Dual site
LHHW model with reactants and products adsorbed on
catalytic sites predicts the conversions that are in good
conformity with the ones obtained experimentally.
the values of k were calculated (Table 1). These plots are
f
as shown in the Fig. 7.
The dependence of the forward rate constant on the
reaction temperature is described by the Arrhenius rate law,
as given in Eq. (13):
ꢁEa
RT
5 Conclusion
k ¼k e
ð13Þ
f
0
where, k is the pre-exponential factor, E is the activation
0
The esterification of butyric acid with methanol in presence
of acidic ion exchange resin as catalyst was successfully
carried out. The rate of butyric acid esterification with
methanol increases with an increase in temperature over
the range of study (323–343 K); passes through maximum
with increasing alcohol to acid ratio (1–4); increases with
an increase in catalyst loading (0–8.5 % w/w). Conversion
was optimum for the stirrer speed of 300 rpm indicating
the absence of film diffusion. The conversion of butyric
acid was dropped in the presence of added water due to
inhibiting effect of water. The maximum conversion of
94.5 % was observed at optimum reaction conditions.
Thus, the ion exchange catalyst was found to be very
effective for the methyl butyrate synthesis. The LHHW
Dual Site (considering reactants and products adsorbed on
catalyst surface) heterogeneous model could be success-
fully applied for representing esterification kinetics for the
reaction between butyric acid and methanol.
a
energy, R is the ideal gas constant and T is the reaction
temperature.
The Arrhenius plot of the rate constant for forward
reaction in the temperature range of 323–353 K gives the
regression coefficient of 0.990. The slope could be applied
to calculate the activation energy. Calculated activation
energy for the synthesis of methyl butyrate is
-
1
2
7.719 kJ mol . The higher value obtained for the ester-
ification reaction indicates that the resistance to mass
transport is negligible. Also strong dependence of reaction
rate on the temperature proves that the conversion rate is
controlled by the reaction steps, rather than the mass
transport phenomena.
The heterogeneous kinetic data of the methyl butyrate
synthesis reaction was correlated with the PH, ER and the
LHHW models according to Eqs. (7)–(12). Rate data was
subjected to find most suited rate expression and various kinetic
parameters involved therein. Nonlinear regression was carried
out using MATLAB software. Surface reaction rate constant
and adsorption equilibrium constants must be positive in the
determined values of parameters with correlation coefficient of
more than 0.9 to judge the validity of the model. Table 2 gives
the summary of predicted values of kinetic parameters using
heterogeneous models given by Eqs. (7)–(12).
References
1
. Toor AP, Sharma M, Thakur S, Wanchoo RK (2011) Bull Chem
React Eng Catal 6:39
2
3
. Liu YJ, Lotero E, Goodwin JG Jr (2006) J Mol Catal A 245:132
. Kirk RE, Othmer DF (1980) Encyclopedia of chemical technol-
ogy. Wiley, New York
Regression studies show that, dual site LHHW model
given by Eq. (11) is giving the correct perspective of data
123

1
546
P. N. Dange et al.
4
5
6
. Yadav GD, Mehta PH (1994) Ind Eng Chem Res 33:2198
. Grob S, Hasse H (2006) Ind Eng Chem Res 45:1869
. De Jong MC, Feijt R, Zondervan E, Nijhuis TA, de Haan AB
20. Xu ZP, Chuang KT (1996) Can J Chem Eng 74:493
21. R o¨ nnback R, Salmi T, Vuori A, Haario H, Lehtonen J, Sundqvist
A, Tirronen E (1997) Chem Engg Sci 52(19):3369
22. Song W, Venimadhavan G, Manning JM, Malone MF, Doherty
MF (1998) Ind Eng Chem Res 37:1917
23. Lilja J, Murzin DY, Salmi T, Aumo J, M a¨ ki-Arvela P, Sundell M
(2002) J Mol Catal A182–183:555
24. Adnadjevic BK, Jovanovic JD (2012) ChemEnggTech 35:761
25. Satterfield CN (1990) Industrial heterogeneous catalytic pro-
cesses. McGraw-Hill, New-York
26. Foggler HS (2006) Elements of chemical reaction engineering.
Prentice-Hall, New York
(
2009) Appl Catal A 365:141–147
. Wang J, Gu S, Pang N, Wang F, Wu F (2013) J Serb Chem Soc
8(7):1023
7
7
8
9
. Liu WT, Tan CS (2001) Ind Eng Chem Res 40:3281
. Clark JH (2002) Acc Chem Res 35:791
1
1
0. Alexandratos SD (2009) Ind Eng Chem Res 48:386
1. Tesser R, Casale L, Verde D, Di Serio M, Santacesaria E (2010)
Chem Eng J 157:539
2. Yang JI, Cho SH, Kim HJ, Joo H, Jung H, Lee KY (2007) J Chem
Eng 85:83
1
1
27. Ozdemir B, Gultekin S (2009) Open Cataly J 2:1
28. Kirbaslar I, Baykal B, Dramur U (2001) Turk J Engg Env Sci
25:569
3. Ju IB, Lim HW, Jeon W, Suh DJ, Park MJ, Suh YW (2011) Chem
Eng J 168:293
1
1
4. Chakrabarti A, Sharma MM (1993) React Polym 20:1
5. Vievelle C, Moulooungui Z, Gaset A (1993) Ind Eng Chem Res
29. Yixin Q, Shaojun P, Shui W, Zhiqiang Z, Jidong W (2009) Chin J
Chem Eng 17(5):773
3
6. Fuchigami Y (1990) J Chem Eng Jpn 23:354
7. Savkovic-Stevanovic J, Misic-Vukovik M, Boncic-Caricic G,
Trisovic B, Jezdic S (1992) Sep Sci Tech 27:613
8. Sanz MT, Murga R, Beltran S, Cabezas JL (2002) Ind Eng Chem
2:2065
30. Liu Y, Lotero E, Goodwin JG Jr (2006) J Catal 243:221
31. Limbeck U, Altwicker C, Kunz U, Hoffman U (2001) Chem
Engg Sci 56:2171
32. Kumar A, Kanwar SS (2011) Bioresour Technol 102(3):2162
33. Kuwabara K, Watanabe Y, Adachi S, Nakanishi K, Matsuno R
(2003) Biochem Eng J 16:17
1
1
1
1
4
1:512
9. Sanz MT, Murga R, Beltran S, Cabezas JL, Coca J (2004) Ind
Eng Chem Res 43:2049
1
23