Kinetics and mechanism of myristic acid and isopropyl alcohol esterification reaction with homogeneous and heterogeneous catalysts

Article abstract of DOI:10.1002/kin.20293

The reaction of myristic acid (MA) and isopropyl alcohol (IPA) was carried out by using both homogeneous and heterogeneous catalysts. For a homogeneously catalyzed system, the experimental data have been interpreted with a second order, using the power-law kinetic model, and a good agreement between the experimental data and the model has been obtained. In this approach, it was assumed that a protonated carboxylic acid is a possible reaction intermediate. After a mathematical model was proposed, reaction rate constants were computed by the Polymath program. For a heterogeneously catalyzed system, interestingly, no pore diffusion limitation was detected. The influences of initial molar ratios, catalyst loading and type, temperature, and water amount in the feed have been examined, as well as the effects of catalyst size for heterogeneous catalyst systems. Among used catalysts, p-toluene sulfonic acid (p-TSA) gave highest reaction rates. Kinetic parameters such as activation energy and frequency factor were determined from model fitting. Experimental K values were found to be 0.54 and 1.49 at 60°C and 80°C, respectively. Furthermore, activation energy and frequency factor at forward were calculated as 54.2 kJ mol^-1 and 1828 L mol^-1 s^-1, respectively.

Full text of DOI:10.1002/kin.20293

Kinetics and Mechanism of
Myristic Acid and Isopropyl
Alcohol Esterification
Reaction with
Homogeneous and
Heterogeneous Catalysts
.
1
1
2
2
¨
¨
¨
TUNCER YALC¸ INYUVA, HUSEYIN DELIGOZ, ISMAIL BOZ, MEHMET ALI GURKAYNAK
.
1Department of Chemical Engineering, Faculty of Engineering, Chemical Technologies Group, Istanbul University,
.
Avcılar 34320, Istanbul, Turkey
.
2Department of Chemical Engineering, Faculty of Engineering, Process and Reactor Design Group, Istanbul University,
.
Avcılar 34320, Istanbul, Turkey
Received 10 October 2006; revised 17 April 2007, 22 August 2007; accepted 1 September 2007
DOI 10.1002/kin.20293
Published online in Wiley InterScience (www.interscience.wiley.com).
ABSTRACT: The reaction of myristic acid (MA) and isopropyl alcohol (IPA) was carried out
by using both homogeneous and heterogeneous catalysts. For a homogeneously catalyzed
system, the experimental data have been interpreted with a second order, using the power-law
kinetic model, and a good agreement between the experimental data and the model has been
obtained. In this approach, it was assumed that a protonated carboxylic acid is a possible
reaction intermediate. After a mathematical model was proposed, reaction rate constants were
®
computed by the Polymath program. For a heterogeneously catalyzed system, interestingly,
no pore diffusion limitation was detected. The influences of initial molar ratios, catalyst loading
and type, temperature, and water amount in the feed have been examined, as well as the effects
of catalyst size for heterogeneous catalyst systems. Among used catalysts, p-toluene sulfonic
acid (p-TSA) gave highest reaction rates. Kinetic parameters such as activation energy and
frequency factor were determined from model fitting. Experimental K values were found to
be 0.54 and 1.49 at 60◦C and 80◦C, respectively. Furthermore, activation energy and frequency
factor at forward were calculated as 54.2 kJ mol−1 and 1828 L mol−1 s−1, respectively. ꢀ 2008
C
Wiley Periodicals, Inc. Int J Chem Kinet 40: 136–144, 2008
INTRODUCTION
Correspondence to: Tuncer Yalc¸ınyuva; e-mail: tuncery@
istanbul.edu.tr.
Esterification is an important reaction of alcohols and
carboxylic acids [1]. The esterification of carboxylic
acids and the acylation of alcohols are fundamental
Contract grant sponsor: Research Fund of Istanbul University.
Contract grant number: 945/090597.
2008 Wiley Periodicals, Inc.
c
ꢀ

KINETICS AND MECHANISM OF MYRISTIC ACID AND ISOPROPYL ALCOHOL ESTERIFICATION
137
reactions in organic chemistry. Esters, which include
a wide category of organic compounds ranging from
aliphatic to aromatic, are generally used as plasticizers,
solvents, perfume, flavor chemicals, and also precur-
sors for a gamut of pharmaceuticals, agrochemicals,
and other fine chemicals [2]. Conversions in esterifi-
cation reactions are limited by slow reaction rates and
low-equilibrium constants. A direct reaction of car-
boxylic acid with alcohol in equivalent ratios is gen-
erally avoided because of the equilibrium that is es-
tablished between the reactants and the products. This
requires the use of an excess amount of one of the re-
actants or the elimination of water from the reaction
mixture to help the completion of the process. Cat-
alysts are always used in liquid phase esterification
to accelerate the reaction rate. Despite a strong cat-
alytic effect, the use of homogeneous catalysts such as
H2SO4 and p-toluene sulfonic acid (p-PTSA) suffers
from the problems of side reactions, corrosions of the
equipment, and disposal of environmentally hazardous
acid. The use of a heterogeneous catalyst has the fol-
Kirumakki et al. have investigated the esterification of
benzyl alcohol with acetic acid over different types of
zeolite catalyst [12]. In addition, an enzymatic esteri-
fication reaction of fatty acids (oleic acid and ethanol)
has been recently presented [13]. The most recent work
has focused on the kinetics of oleic acid esterification
with methanol over a heterogeneous catalyst [14]. To
the best of our knowledge, no study has been reported
on the esterification reaction mechanism of myristic
acid as a fatty acid.
Isopropyl myristate (IPM) prepared by the reaction
of isopropul alcohol (IPA) and myristic acid (MA) is
one of the valuable esters. IPM can be used in the cos-
metic industry as an alternative to natural fats, bath
oils, cream, sun oil, and lubricants in the formula-
tion of lotions due to excellent distribution properties
and good absorbility [15]. The liquid phase esterifi-
cation of myristic acid in the presence of a suitable
acid catalyst yields IPM as the main reaction product.
The esterification reaction proceeds by the following
stoichiometric equation:
Here, we aimed to study the esterification kinetics
of myristic acid with isopropyl alcohol with both ho-
mogeneously and heterogeneously catalyzed systems.
For a homogeneously catalyzed system, catalytic rate
equations were derived from the well-known power-
law kinetic model and it was assumed that the reaction
mechanism follows (1) myristic acid protonated by
the catalyst to form a reaction intermediate that cannot
be isolated and (2) the esterification reaction proceeds
reversibly [3,4]. The influences of initial molar ratios,
catalyst loading and type, temperature and water
amount in the feed have been examined as have the
effects of catalyst size for heterogeneous catalyst
systems. In addition, we tried to determine the rate-
limiting step for the heterogeneously catalyzed system.
Kinetic parameters such as activation energy and fre-
quency factor were also determined from model fitting.
lowing inherent advantages over catalysis effected by
dissolved electrolytes: (a) they eliminate the corrosive
environment; (b) the catalyst can be easily recycled
from the reaction mixture by decantation or filtration;
(c) the purity of the products is higher since the side
reactions can be completely eliminated or are less sig-
nificant. There are very few reports on the esterifica-
tion kinetics of fatty acids for a homogeneous catalyst
system [3,4] and a heterogeneous catalyst system [5–
9]. Kinetic models and results were reported for the
reaction of fatty acids and various types of alcohols
with short chain such as methanol in the production of
biodiesel fuel [5,6]. When the reaction of oleic acid or
fatty acid mixtures with methanol was investigated in
the presence of H2SO4 and p-toluene sulfonic acid, it
was found that p-TSA is more effective [10].
Kocsisava et al. has reported the esterification of
fatty acids with methanol at elevated temperatures
above the boiling point of methanol [5]. Further-
more, the kinetics of free fatty acids esterification with
methanol was studied [6].
On the other hand, Altıokka and C¸ ıtak have re-
ported that the esterification kinetics of acetic acid with
isobutanol in the presence of amberlite catalyst [11].
EXPERIMENTAL
Materials
Isopropyl alcohol (purity >99.5), myristic acid (pu-
rity >98), and p-toluene sulfonic acid (purity >98)
International Journal of Chemical Kinetics DOI 10.1002/kin

138
YALC¸ INYUVA ET AL.
were purchased from the Merck Company (Darmstadt,
Germany) and used without further purification.
Heterogeneous catalysts Amberlyst-15 and Degussa
(acidic cation exchange resin) were supported by
Merck and Degussa, respectively. Amberlyst-15 was
strongly acidic with sulfonic acid functionality (size:
500 µm, surface area: 55 m2 g−1, porosity %: 36, ion
exchange capacity: 4.5 meq g−1). The silica-based De-
gussa catalyst including sulfonic acid groups was man-
ufactured by Degussa Company. Karl-Fischer solution
was supplied from Riedel de Haen, England.
trogen was used as a carrying gas with the flowing rate
of 0.8 mL min−1. The amount of water in the organic
phase was determined by the Karl-Fischer method, and
analyses were carried out by the Metrohm 736 GP
titrino system. The reproducibility for this system is
0.5%, and methylene chloride was used as the solvent.
RESULTS AND DISCUSSION
Derivation of Catalytic Rate Equation
In this study, a previously reported reaction mecha-
nism for the reaction of alcohol with carboxylic acid
protonated by acidic catalysts was utilized [3,4,16].
p-TSA is the source of proton in our kinetic study. The
reaction mechanism can be written as follows:
k1
Reaction System and Procedure
Esterification reactions were carried out in a 250-mL
round-bottomed, five-necked reactor with a condenser,
nitrogen inlet–outlet, magnetic stirrer with 450 rpm
speed, and thermometer. First, 80.85 g of myristic acid
(0.354 mol) was placed in the reactor and then heated
up to reaction temperature. Meanwhile, 42.57 g of IPA
(0.708 mol) and 0.82 g of p-TSA were mixed in a
beaker and subsequently heated up to reaction temper-
ature too. This solution was then added into melted
myristic acid by means of a dropping funnel. This
time was taken as the beginning of the reaction. Sev-
eral samples of approximately 1 mL from the reaction
medium were collected during the experiment. A sam-
ple was drawn off every 5–15 min during the first hour
of the reaction. Subsequently, samples were collected
every 30 min during the next 2 h and thereafter every
hour. These reactions were carried out in the temper-
ature range of 60◦C–80◦C due to the melting point of
MA (58◦C) and the boiling point of the IPA (82.4◦C).
For equilibrium constant determination, reactions were
carried out in a glass tube with 5 mL of volume under
various reaction conditions for 48 h. In the equilib-
rium determination experiments, the total amount of
reactants charged was nearly 5 mL. The amounts of
IPA and MA were 1.79 mL (0.0234 mol) and 3.17 mL
(0.0117 mol), respectively.
RCOOH + H + ⇐⇒ RCOOH+2
(1)
k
−1
A + C ⇐⇒ AH
k2
RCOOH+2 + RꢁOH ⇐⇒
k
−2
RCOORꢁH + + H2O
(2)
AH + B ⇐⇒ EH + W
k3
RCOORꢁH + ⇐⇒ RCOORꢁ.. + ..H + (3)
k
−3
EH ⇐⇒ E + C
The rate equation given by Goto et al. [3] is as follows:
ꢀ
ꢁ
dCA
dt
CACB − CECW/K
CB + CWKW
−
= k
(4)
where K = k1k2k3/k−1k−2k−3, KW = k2k3/k−2k
and k = kCCC.
,
−3
The right-hand side of Eq. (4) was assumed to be
equal to zero at below 10% conversion of reactants
for determination of variables (CECW/K = 0). This
assumption cannot be considered as a coarse approach
due to the very small amount of water and nonpresence
of IPM at the beginning of the reaction. When the
inverse of this shortened Eq. (4a) is taken, then, the
reaction rate can be written in the linear form (4b),
Analysis
Acid value (AV) analyses were made for the sam-
ples collected at different times to follow the esteri-
fication reaction (ASTM 1639-70). Preheated pipettes
were used to collect samples from the reaction ves-
sel. Gas chromatography (GC) analyses were also
performed using the HP 6890 gas chromatography
system. The conversion was determined by capillary
GC, HP Innowax column, 30 m × 0.32 mm ID.
It was also equipped with thermal-conductivity and
flame-ionization detectors to determine the amount of
all species in the reaction mixtures. In GC analysis,
tetrahydrofuran (THF) was used as a solvent and ni-
ꢀ
1 1
k1 CA
ꢁ
dCA
dt
CACB
−
= k1
(4a)
(4b)
CB + CWKW
KW CW
1
=
+
rA−
k1 CACB
Using this linear equation, k1 and KW can be calculated
from experimental results by means of the multiple
linear regression method (see Fig. 1). The Polymath
program was used to calculate the rate constants.
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS AND MECHANISM OF MYRISTIC ACID AND ISOPROPYL ALCOHOL ESTERIFICATION
139
Figure 2 Comparison of experimental and theoretical re-
action rates.
Figure 1 Time dependency of myristic acid concentration
changes (M = 2/1, T = 80◦C).
Equilibrium constants (K = k1/k2) of esterification
reactions strongly depend on reactant composition and
reaction temperature [3,16,17]. In this study, exper-
imental equilibrium constants were calculated while
keeping molar ratios of reactants (M = 2) constant and
catalyst loading (0.0288 mol/L) at four different tem-
peratures (60◦C, 70◦C, 75◦C, 80◦C). As seen in Table I,
it was observed that equilibrium constants were in-
creased with increasing temperature. K values are in
the range of 0.54–1.49. k1 and k2 are the rate constants
for forward and backward reactions and were found to
CA (myristic acid concentration) was calculated by
means of acid value analysis for the samples that were
collected at intervals under different types of reaction
conditions. Subsequently, polynomial analysis was ap-
plied to a graph that was drawn between CA and time.
Taking derivatives of all corresponding reaction rates,
–dCA/dt values obtained from polinoms for all reac-
tions were determined. On the other hand, reaction
rates were calculated by using a derived model for the
same obtained data.
Regression results and goodness of fit are shown
in Fig. 2. In this case, rates calculated by experimen-
tal and derived models are compared. A solid line in
Fig. 2 indicates the result of curve fitting for Eq. (4b).
All experimental data are in excellent agreement with
the calculated results. Dashed lines show confidence
intervals and represent 95% confidence level, and they
were obtained from four repeat experiments by means
of two standard deviation.
be 2.083 × 10−5 and 1.401 × 10−5 L mol−1
s
−1, re-
spectively. Reaction rate constants were calculated by
using the above model for the reactions carried out at
various temperatures. Furthermore, activation energy
was calculated for k1 and k2 at different temperatures.
The frequency factor was also found by using the linear
Arrhenius equation.
ꢀ
ꢁ
Ea
R
1
Tave
1
ln k1,2 = ln A −
−
(6)
Calculation of Equilibrium Constants
T
Experimentallydetermined equilibriumconstants were
calculated using equilibrium conversions with the for-
mula given below:
where Ea = activation energy, Tave = average temper-
ature (K), and R = gas constant (8.31 J/(mol K)). With
linear regression between ln k and 1/T (K) data, ac-
tivation energy and frequency factor at forward were
calculated as 54.2 kJ/mol and 1828 L (mol · s)−1, re-
spectively.
CEeCWe
CAeCBe
XA2 e
Kexp
=
=
(5)
[(1 − XAe)(M − XAe)]
where M = CB0/CA0
.
Table I Temperature Dependency of k1, k2, and K
Temperature (◦C)
C (mol /L−1
)
M (CB0/C
)
XAe(%)
k (L /mol−1 s−1
)
k (L mol−1 s−1
)
K (k /k )
C
A0
1
2
1
2
60
70
75
80
0.0288
0.0288
0.0288
0.0288
2
2
2
2
57.5
67.4
69.6
72.4
0.647 × 10−5
0.841 × 10−5
1.206 × 10−5
2.083 × 10−5
1.190 × 10−5
0.799 × 10−5
0.984 × 10−5
1.401 × 10−5
0.54
1.05
1.22
1.49
International Journal of Chemical Kinetics DOI 10.1002/kin

140
YALC¸ INYUVA ET AL.
Figure 3 Effect of molar ratio of the reactants on the es-
terification conversion (M = CB0/CA0, isopropyl alcohol to
myristic acid).
Figure 5 Effect of catalyst (p-TSA) loading on the esteri-
fication conversion (T = 80◦C, M = 1).
Effect of Catalyst
Catalyst Loading. The effect of catalyst loading is
shown in Fig. 5. To investigate the influence of cat-
alyst concentration, four different p-TSA concentra-
tions were used while keeping the temperature at 80◦C
and the molar ratio at 1/1 (M = 1). The amount of cata-
lyst was varied from 0.2% to 2% mol up to acid concen-
tration. After a reaction for 6 h, 24.3% and 55.5% yields
were obtained for 0.2% and 2% wt catalyst-containing
systems, respectively. With increasing amount of cat-
alyst, it was observed that the reaction rate and yield
significantly increased. On the other hand, a catalyst-
free experiment was performed to follow and compare
the esterification reaction rates. In this experiment, it
was determined that the reaction was very low and
yield reached only 3.4% after 6 h. As proposed in the
literature [3,18], the establishment of equilibrium ac-
celerates with the increase of concentration of catalyst.
Even in a catalyst-free system, the reaction proceeded,
although the reaction rate was very low.
Effect of Reactant Composition
Esterification of myristic acid with isopropyl alcohol is
an equilibrium-limited chemical reaction, and the use
of excess isopropyl alcohol increases the utilization of
myristic acid. The initial ratio of isopropyl alcohol to
myristic acid was varied from 1:1 to 10:1 (2/1, 3/1, 5/1)
at a fixed temperature with a loading of 0.0288 mol/L
p-TSA to assess its effect on the rate of reaction.
Figures 3 and 4 present the effects of ratio of initial
concentration of isopropyl alcohol to myristic acid
(M = CB0/CA0). It was found that as the mole ratio
is increased from 1/1 to 3/1, the conversion of the alco-
hol increases. Beyond a mole ratio of 3/1, conversion
becomes independent of the mole ratio.
Comparison of Homogeneous and Heterogeneous
Catalysts. Both homogeneous (p-TSA and sulfuric
acid) and heterogeneous (Amberlist-15 and Degussa)
catalysts were used in the preparation of IPM. In a
set of experiments, the influences of catalyst type and
loadings were studied; they are plotted in Figs. 6a–6c.
Concentrated sulfuric acid, Amberlist-15, and silica-
based Degussa ion exchange resin were used in our
study. From Fig. 6a, one can see the effect of homo-
geneous and heterogeneous types of catalysts on the
reaction rate of the myristic acid esterification reac-
tion. In Fig. 6b, p-TSA, a monobasic organic acid,
was used equivalent (mole) to sulfuric acid, and the
same effectiveness was nearly observed. If we con-
sider that sulfuric acid releases two times higher H+
than p-TSA, it can be concluded that p-TSA is a more
Figure 4 Effect of molar ratio of reactants on the esteri-
fication conversion (T = 80◦C, C = 0.0288 mol/L, M =
C
CB0/CA0).
International Journal of Chemical Kinetics DOI 10.1002/kin

KINETICS AND MECHANISM OF MYRISTIC ACID AND ISOPROPYL ALCOHOL ESTERIFICATION
141
catalyzed reaction is affected by external/internal dif-
fusion, adsorption and desorption, the surface reaction,
and the nonideality of the reacting mixture [18].
For this purpose, in another set of experiment, the
size of the heterogeneous catalyst was investigated to
explain the mechanism properly. Esterification conver-
sion versus time plots for different particle sizes are
given in Fig 6c. It was aimed to determine whether
the pore diffusion problem is the rate-limiting step for
a heterogeneously catalyzed system in the fatty acid
esterification reactions. No data are available in the
literature for this phenomenon.
To evaluate the effect of internal diffusion on the
cation-exchange resins by using the Weisz-pourier cri-
teria, Eq. (7) was used [20]
(a)
r02k
φ =
(7)
9De
where r0 and De denote the radius of catalyst particle
and the effective diffusion coefficient, respectively. k is
the reaction rate constant, and φ is the Thiele modulus.
If the calculated value of φ was less than 1, the internal
diffusion could be neglected. The effective diffusion
coefficient was defined as follows:
(b)
DAε
De =
(8)
τ
where DA is the molecular diffusion coefficient, τ
is the particle tortuosity, and ε is the porosity. For
most resin catalysts, the values of ε/τ are between
0.25 and 0.50 [20]. In the calculation, the value of ε/τ
was taken as 0.5. The molecular diffusion coefficient
for liquid phase diffusion can be evaluated from the
Wilke–Chang equation.
(c)
According to our calculations made by using the
Weisz-pourier criteria, interestingly, no pore diffusion
limitation was detected. After this result, it can be
said that the reaction rate limiting step may be ad-
sorption/desorption of the species. Moreover, it was
observed that powdered Amberlist-15 (125–180 µm)
exhibited nearly the same effectiveness as the original
size.
Figure 6 (a) Effect of various types of catalyst on the es-
terification conversion (T = 80◦C, M = 2). (b) Effect of
H2SO4 and p-toluenesulfonic acid as a catalyst on the es-
terification conversion comparatively (T = 80◦C, M = 2),
(c) Effect of heterogeneous catalyst (Amberlyst-15) size
on the esterification conversion. Average sizes are 230 and
80 µm for original and powdered catalyst, respectively.
effective catalyst than sulfuric acid for the esterification
reactions. A similar result was reported earlier [3].
On the other hand, surprisingly, heterogeneous cat-
alysts (neither Amberlist 15 nor Degussa) caused poor
conversions (5%–10% after 5 h) in the esterification re-
action of fatty acid (myristic acid), although some suc-
cessful results were reported for carboxylic acids with
short alkyl chains [11,19]. This phenomenon might be
explained by the diffusion problem of myristic acid,
which is a long alkyl chain fatty acid, into the pores
of catalyst. In general, the rate of a heterogeneously
Effect of Temperature. To investigate the temperature
effect on the esterification reaction, the reactions were
carried out in the temperature region of 60◦C–80◦C
while keeping the molar ratio of acid to alcohol at 2:1.
The conversion versus time graph belongs to experi-
ments that were carried out at 60◦C, 70◦C, 75◦C, and
80◦C to determine reaction rates and reaction rate con-
stants and is depicted in Fig. 7. In general, the ester con-
version was found to increase with increasing reaction
temperature. Increasing the temperature is apparently
International Journal of Chemical Kinetics DOI 10.1002/kin

142
YALC¸ INYUVA ET AL.
Figure 7 Effect of temperature on the esterification
conversion.
Figure 9 Changes in weight percentage of reactants and
products determined by gas chromatography (GC) during
reaction time and comparison of myristic acid weight per-
centages obtained by GC and acid value (AV) methods
favorable for the acceleration of the forward reaction.
The conversion value is nearly two times higher for ex-
periment at 80◦C than the one for experiment at 60◦C.
(M = 2, T = 80◦C, C = 0.0288 mol/L).
C
Effect of Water Content at the Beginning
of the Reaction
selected experiment for comparison and is depicted in
Fig. 9. In this reaction, the molar ratio of the reactants
was taken as M = CIPA/CMA = 2, and p-TSA was used
as a catalyst with a concentration of 0.0288 mol L−1 at
80◦C.
One can see from Fig. 9 that 65 wt% myristic acid
and 33 wt% isopropyl alcohol (in weight) are available
at the beginning of the reaction. After 6 h, there are 50%
IPM, 16% IPA, 30% MA, and 3.7% water contents in
the reaction medium. On the other hand, the myristic
acid concentration of some samples was determined
by acid value analysis too. It was found that the results
of acid concentrations determined by GC and titration
were in good agreement.
The effect of water available at the beginning of the
reaction is shown in Fig. 8. Two different experiments
were carried out by adding 20% and 40% of excess
water compared to the initial molar amount of myristic
acid to investigate the effect of water presence on the
reaction rate and conversion. In these reactions, p-TSA
was used as a catalyst (CC = 0.0288 mol L−1, T =
80◦C, and M = 2).
It was observed that the reaction rate consider-
ably decreased with increasing the amount of water
available at the beginning. While water-free system
reached 62% conversion after 6 h, 20% and 40% water-
containing systems reached 55.7% and 40%, respec-
tively, at the end of the same period of time.
Water Determination in Organic Phase
GC Analysis
Apart from previously published articles, preliminary
studies on both water amount in organic phase and
alcohol amount in water phase were performed. As
is well known, water evolved during the esterification
reaction causes a multiphase reaction medium. During
the reaction, myristic acid, isopropyl alcohol, and IPM
exist in organic phase, whereas formed water and a
small amount of isopropyl alcohol are dissolved in the
water-rich phase.
The time dependency of concentration of products
(IPM and water) and reactants (MA and IPA) was in-
vestigated by both GC and acid value analysis for a
In our experiments, evolved water was dispersed
in the reaction medium and there was no observa-
tion of a separate water phase in the first few hours
of reaction. However, small droplets dispersed in the
reaction medium were associated and formed as a dif-
ferent phase with time. This can be explained by the
fact that a part of available water dissolves in organic
phase whereas the other part forms a water phase in
the reaction.
Figure 8 Effect of initial water content on the esterification
conversion (C = 0.0288 mol/L, T = 80◦C, and M = 2).
C
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KINETICS AND MECHANISM OF MYRISTIC ACID AND ISOPROPYL ALCOHOL ESTERIFICATION
143
Figure 10 Comparison of dissolved water in organic phase and evolved total water during the reaction. (Isopropyl alcohol,
dichloromethane, and THF contain 0.05, 0.02, and 0.17 wt% water, respectively. Required corrections for the calculation were
made.)
In general, kinetic studies can be carried out for
such a multiphase reaction by assuming all reaction
media as a homogeneous phase. In this approach, some
correction factors are used. An experiment was carried
out, and the water dissolved in the organic phase was
determined by the Karl-Fischer method. In Fig. 10,
the amount of water determined by the Karl-Fischer
method and the amount of theoretical water calculated
by the acid value method are given for comparison.
As one can see from the results, the amount of wa-
ter (wt%) was calculated by using the stochiometric
amount as 3.13%, and it was also determined for 1.53
(wt%) of the evolved water dissolved in the organic
phase. In other words, after 5 h reaction, roughly 48.9%
of the total evolved water dissolved in the organic
phase. On the other hand, GC analysis was carried
out for the sample collected from bottom of the re-
actor and it was found that the water phase contains
43.3 (wt%) of IPA. This result confirms that some of
the reactant IPA goes through the water phase. In our
further studies, it will be tried to create and improve a
model for only a homogeneous phase by determination
of water in the homogeneous phase.
the homogeneous catalyst system, catalytic rate equa-
tions were derived by the reaction mechanism in which
first myristic acid is protonated by the catalyst to form
a reaction intermediate and then the esterification re-
action proceeds reversibly. It can be concluded that a
protonated carboxyl acid is a possible reaction inter-
mediate. The experimental data have been interpreted
with a second-order kinetics, and a good agreement
between the experimental data and the model has been
obtained. For heterogeneously catalyzed reactions, in-
terestingly, no pore diffusion limitation was detected.
On the other hand, both powdered and sifted catalysts
showed the lowest efficiency, among all the heteroge-
neous catalysts used.
The influences of initial molar ratios of isopropyl
alcohol to myristic acid (1:1 to 10:1), catalyst loading
and type, temperature (60◦C–80◦C), and water amount
in the feed have been examined, as well as the ef-
fects of catalyst size for heterogeneous catalyst sys-
tems. Among used catalysts, p-TSA gave the high-
est reaction rates for the fatty acid esterification re-
action. The equilibrium conversion of myristic acid
was found to increase slightly with an increase in
temperature and also it increased appreciably with an
excess of isopropyl alcohol in the reaction system.
In addition, it was found that the changes in the re-
action rate also depend on the catalyst loading and
type.
CONCLUSIONS
The reaction of MA and IPA was carried out by using
both homogeneous and heterogeneous catalysts. For
International Journal of Chemical Kinetics DOI 10.1002/kin

144
YALC¸ INYUVA ET AL.
Experimental K values were found to be 0.54 and
1.49 at 60◦C and 80◦C, respectively. Kinetic param-
eters such as activation energy and frequency fac-
tor were also determined from model fitting. Acti-
vation energy and frequency factor at forward were
Da molecular diffusion coefficient
τ
particle tortuosity
porosity
ε
BIBLIOGRAPHY
calculated as 54.2 kJ mol−1 and 1828 L mol−1 s−1
respectively.
,
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rate constant for backward reaction,
L mol−1 s−1
K
equilibrium constant
Kw
CA
equilibrium constant for water
outlet concentration of myristic acid,
mol L−1
CB
CE
CW
CC
outlet concentration of isopropyl alcohol,
mol L−1
outlet concentration of isopropyl myristate,
mol L−1
outlet concentration of evolved water,
mol L−1
catalyst concentration,
mol L−1
ratio of concentration of alcohol to acid
temperature, K
M
T
−rA reaction rate of myristic acid
XA conversion of myristic acid
XAe conversion of myristic acid at equilibrium
CAe concentration of myristic acid at equilibrium,
mol L−1
CBe concentration of isopropyl alcohol
at equilibrium, mol L−1
CEe concentration of isopropyl myristate
at equilibrium, mol L−1
Cwe concentration of water at equilibrium,
mol L−1
R
gas constant, kJ (mol K)−1
activation energy
Ea
r0
radius of catalyst particle effective diffusion
coefficient
effective diffusion coefficient
Thiele modulus
De
φ
International Journal of Chemical Kinetics DOI 10.1002/kin