Esterification reaction kinetics of acetic acid and n-pentanol catalyzed by sulfated zirconia

Article abstract of DOI:10.1002/kin.21365

This study reports experimental data and kinetic modeling of acetic acid esterification with n-pentanol using sulfated zirconia as a catalyst. Reactions were carried out in an isothermal well-mixed batch reactor at different temperatures (50-80°C), n-pentanol to acid molar ratios (1:1-3:1), and catalyst loadings (5-10?wt% in relation to the total amount of acetic acid). The reaction mechanism regarding the heterogeneous catalysis was evaluated considering pseudo-homogeneous, Eley–Rideal, and Langmuir–Hinshelwood model approaches. The reaction mixture was considered a nonideal solution and the UNIQUAC thermodynamic model was used to take into account the nonidealities in the liquid phase. The results obtained indicated that increases in the temperature and catalyst loading increased the product formation, while changes in the n-pentanol to acetic acid molar ratio showed no significant effect. The estimated enthalpy of the reaction was ?8.49?kJ?mol^?1, suggesting a slightly exothermic reaction. The Eley–Rideal model, with acetic acid adsorbed on the catalyst as the limiting step, was found to be the most significant reaction mechanism.

Full text of DOI:10.1002/kin.21365

Received: 28 June 2019
DOI: 10.1002/kin.21365
Revised: 2 April 2020
Accepted: 3 April 2020
A R T I C L E
Esterification reaction kinetics of acetic acid and n-pentanol
catalyzed by sulfated zirconia
Fabiane Hamerski
Giovana Gonçalves Dusi
Julia Trancoso Fernandes dos Santos
Vítor Renan da Silva
Fernando Augusto Pedersen Voll
Marcos Lúcio Corazza
Department of Chemical Engineering,
Federal University of Paraná (UFPR),
Curitiba, PR, Brazil
Abstract
This study reports experimental data and kinetic modeling of acetic acid esterification
with n-pentanol using sulfated zirconia as a catalyst. Reactions were carried out in an
Correspondence
◦
isothermal well-mixed batch reactor at different temperatures (50-80 C), n-pentanol
VítorRenan da Silva, DepartmentofChemical
Engineering, FederalUniversityofParaná,
Francisco H. SantosAv. 100, Curitiba, Paraná,
Brazil.
to acid molar ratios (1:1-3:1), and catalyst loadings (5-10 wt% in relation to the total
amount of acetic acid). The reaction mechanism regarding the heterogeneous catal-
ysis was evaluated considering pseudo-homogeneous, Eley–Rideal, and Langmuir–
Hinshelwood model approaches. The reaction mixture was considered a nonideal
solution and the UNIQUAC thermodynamic model was used to take into account the
nonidealities in the liquid phase. The results obtained indicated that increases in the
temperature and catalyst loading increased the product formation, while changes in
the n-pentanol to acetic acid molar ratio showed no significant effect. The estimated
enthalpy of the reaction was −8.49 kJ mol−1, suggesting a slightly exothermic reac-
tion. The Eley–Rideal model, with acetic acid adsorbed on the catalyst as the limiting
step, was found to be the most significant reaction mechanism.
Email:vrenan@ufpr.br
Fundinginformation
CNPq, Grant/AwardNumbers:1688/2018,
305393/2016-2, 435873/2018-0;CAPES;
ConselhoNacionaldeDesenvolvimentoCien-
tíficoeTecnológico, Grant/AwardNumbers:
1688/2018, 305393/2016-2, 435873/2018-0
K E Y W O R D S
Eley–Rideal, esterification, Langmuir–Hinshelwood, pentyl ethanoate, sulfated zirconia
direct esterification of carboxylic acids with alcohols in the
presence of acid catalysts.9
1
INTRODUCTION
Esterification is conventionally carried out using homo-
geneous catalysts with strong mineral acids, such as sulfu-
ric acid and p-toluenesulfonic acid. However, this chemi-
cal route is associated with several drawbacks in industrial
applications:9,10 (a) acid catalyst recovery is economically
expensive; (b) high operational and installations costs due to
the increases of corrosion rates; and (c) high costs of wastes
removal, treatment, and disposal of the homogeneous catalyst;
Thus, the use of a solid acid catalyst in heterogeneous catalysis
represents an alternative to the homogeneous reaction process
with advantages including: (a) the catalyst is solid, nontoxic,
and reusable; (b) corrosion in the reactor system is reduced;
and (c) the catalyst can be easily separated from the reaction
mixture by a physical process, such as filtration.11
Organic esters are important fine chemicals widely used in a
variety of areas including food, pharmaceuticals, cosmetics,
biofuels, and chemical industries. These compounds are used
as additives, plasticizers, solvents, or intermediates and can
be obtained through the transesterification or esterification of
either carboxylic acids or fatty acids with an alcohol.1–4 In the
food industry in particular, the organic esters derived from
fatty acids can be used as emulsifiers,5 and the acetate and
ethyl esters act as primary odorants in the perceptual response
of fruity aroma in food products, such as beverage, wine, and
juices.6 Similarly, amyl acetate (pentyl ethanoate) is an impor-
tant component of different fruit flavors (eg, pear, apple, and
banana).7,8 Chemical synthesis is an alternative way to pro-
duce these organic esters and the most common route is the
Int J Chem Kinet. 2020;1–14.
wileyonlinelibrary.com/journal/kin
© 2020 Wiley Periodicals, Inc.
1

2
HAMERSKI ET AL.
Sulfated metal oxides with both Brønsted and Lewis acid
Brazil) and it was monitored using a digital pH-meter. The
total volume of ammonia solution used during the precip-
itation process was approximately 12 mL. The suspension
obtained was maintained for 2 h under vigorous stirring, at
room temperature. The precipitate was filtered, washed with
distilled water until free of chlorine (verified by testing with
sites have been widely proposed and used as solid acid cat-
alysts and/or supports in organic synthesis, including esteri-
fication reactions.12 Sulfated zirconia (SO4–ZrO2) is a solid
catalyst of particular interest because it has high thermal sta-
bility, low cost, and presents a high amount of acid sites with
a Hammett acidity function of around −16.1.13 These prop-
erties have led to its application as a catalyst in isomeriza-
tion and alkylation processes14–16 and Fischer’s esterification
reactions.17–20
◦
an aqueous solution of AgNO3) and dried at 100 C for 16 h.
The solid phase comprised of zirconium hydroxides were
−1
crushed to a fine powder and impregnated with a 0.5 mol L
H2SO4 solution (5 mL of solution per 1 g of solids) for 2 h.
◦
In order to describe the kinetic behavior of heterogeneous
catalytic esterification reactions, several kinetic models have
been proposed in the literature. In some reaction systems,
such as a heterogeneous esterification of free fatty acids to
biodiesel and emulsifiers,17,21,22 the kinetic behavior of the
reactions can approach by the pseudo-homogeneous (PH)
model. On the other hand, several authors studying esterifi-
cation reactions with heterogeneous catalysts have proposed
mechanisms that involve surface phenomena for the interac-
tion between the reactant and active sites on the catalyst sur-
face, which have been successfully described by Langmuir–
Hinshelwood (LH) and Eley–Rideal (ER) models.2,23–26 The
LH model is applicable for correlating the kinetics data when-
ever the reaction occurs between the intermediate species,
formed by chemical adsorption of the reactants on the active
sites of the catalyst surface, while the ER model is nor-
mally applied when the reaction occurs between an adsorbed
species and a species in the bulk liquid phase (non-adsorbed
species).27
The solids were then filtered, dried at 100 C for 16 h, and
◦
calcined at 550 C for 3 h.
2.2 Characterization of sulfated zirconia
X-ray diffraction (XRD) data were collected on a Panalytical
X-ray powder diffractometer (Cambridge, United Kingdom)
˚
using Cu Kꢀ radiation (ꢁ = 1.5406 A, 40 kV, and 30 mA),
◦
at 2ꢂ, in the range of 20-80 with a step size of 0.02. Raman
mapping was carried out using a confocal Raman microscope
(Witec-alpha 300R, Ulm, Germany), with objective magnifi-
cation (10×), a power of 32.9 mW and a 532 nm frequency-
−1
doubled Nd:YAG laser with a resolution of 0.02 cm
.
Fourier transform infrared (FTIR) spectra of the sulfated
zirconia were obtained at room temperature in the wavenum-
ber range of 4 000-400 cm−1, with a resolution of 4 cm−1 and
32 scans, on a BIO-RAD, Excalibur Series (FTS 3500GX)
spectrophotometer (New York, USA). Pellets of the sample
were prepared for the analysis by mixing the fine catalyst pow-
der with KBr (Vetec; spectroscopic grade) in a weight ratio of
1:10.
Some studies have shown that both LH and ER models can
describe the mechanism involved in the kinetics of solid acid
zirconia-catalyzed esterification reactions.11,20,28,29 However,
to the best of our knowledge, there are no reports in the lit-
erature considering a detailed study and kinetic modeling of
pentyl ethanoate synthesis by the Fischer esterification reac-
tion with sulfated zirconia as the heterogeneous catalyst. Thus,
this work aims to bring a new set of experimental data and
the kinetic modeling investigation of acetic acid esterification
with n-pentanol using a sulfated zirconia-catalyst system.
Thermogravimetric (TG) and differential scanning calori-
metric (DSC) analyses were carried out with a Nestzsch ana-
lyzer (STA 449 F3 Jupiter, Selb, Germany), using approx-
imately 5 mg of sample, alumina crucibles, nitrogen atmo-
sphere, and a heating rate of 10 C min−1, in the temperature
◦
◦
range of 20-1 000 C.
The specific surface area and pore size distribution
were determined using the Brunauer–Emmett–Teller (BET)
method,31 with the N2 adsorption and desorption isotherms
◦
obtained at −163 C on a NOVA-1200 Quantachrome instru-
ment (Boynton Beach, Florida, USA).
2
EXPERIMENTAL
The particle size distribution and average diameter of sul-
fated zirconia particles were obtained using an automated par-
ticle size analyzer (CILAS; model 1064, Orleans, France).
Firstly, to have proper sample dispersion, the sulfated zirconia
(∼10 mg) was added to distilled water in the liquid dispersion
unit of the equipment. The dispersed sample was pumped into
a glass measurement cell, which is placed in front of the laser
and it was kept circulating until the end of the measurements.
The detected diffraction pattern was analyzed by software The
Particle Expert and the particle size distribution and average
diameter of the sulfated zirconia powder was obtained.
2.1 Synthesis of sulfated zirconia
The sulfated zirconia was prepared based on the procedure
described by Corma et al.30 Briefly, under magnetic stirring,
50 mL of an aqueous solution (0.4 mol L−1) of zirconium (IV)
oxychloride octahydrate (Vetec; 99.5%, Duque de Caxias, Rio
de Janeiro, Brazil) was added drop by drop to a beaker con-
taining distilled water (15 mL) at pH 10. The pH was main-
tained constant during the precipitation by adding an ammo-
nia solution (Vetec; 26%, Duque de Caxias, Rio de Janeiro,

HAMERSKI ET AL.
3
The surface morphology and composition of the sul-
fated zirconia were determined, respectively, by scanning
electron microscopy (SEM) and energy dispersion spec-
troscopy (EDS) using a Tescan VEGA-3 LMU microscope
(Kohoutovice, Czech Republic). Results of elemental compo-
sition by EDS are average values of measurements obtained
on three different location of the catalyst sample.
Additional experiments of homogeneous reaction were per-
formed using 1.0 wt% of H2SO4 (Vetec; 98% of purity) in
relation to the total amount of acetic acid. The homogeneous
◦
reactions were carried out at temperatures of 50-80 C, with a
fixed n-pentanol to acetic acid molar ratio of 3:1 and stirring
speed of 500 rpm, using the same reactor setup used in the
heterogeneous reactions.
Equilibrium data were evaluated using the software Aspen
Plus v.8.4 (Aspen Technology, Inc, Bedford, Massachusetts,
USA). The activity coefficients and molar fractions of all
species at equilibrium were calculated by the Rigorous Reac-
tor Model based on Gibbs free energy minimization, where
the UNIQUAC thermodynamic model was used to calculate
the non-ideality corrections of all compounds in the phase liq-
uid. The reaction equilibrium constant (KEQ) was evaluated by
Equation 4:32
2.3 Reaction procedure
Esterification was used for the synthesis of pentyl ethanoate
(n-amyl-acetate) performed by reacting acetic acid and n-
pentanol, as shown in the following equation:
(
)
CH3 CH2 OH + CH3COOH ↔ C7H14O2 + H2O (1)
4
Kinetics study of the pentyl ethanoate esterification cat-
alyzed by sulfated zirconia was performed in a 40 mL jack-
eted glass reaction vessel (diameter of 3.5 cm and height of
6.0 cm), equipped with a magnetic stirrer (magnetic bar of
2 cm length), and coupled to a thermostatic bath with exter-
nal circulation (Vivo RT4). All reactions were performed in
(
)
ꢇAC,EQ × ꢇP,EQ
ꢇE,EQ × ꢇW,EQ
ꢈAC,EQ × ꢈP,EQ
ꢆEQ
=
=
ꢈE,EQ × ꢈW,EQ
(
)
ꢉAC,EQ × ꢉP,EQ
ꢉE,EQ × ꢉW,EQ
×
(4)
◦
a batch mode. The temperature ranged from 50 to 80 C. The
catalyst concentration in the reaction mixture was varied from
5.0 to 10 wt%, related to the total amount of acetic acid. The
initial n-pentanol to acetic acid molar ratio was varied from
1:1 to 3:1. The stirring speed was fixed at 500 rpm for all
experiments. A measured amount (weighted) of acetic acid
and catalyst were added to the reactor and the temperature of
the reactor was set to the reaction temperature setpoint. An
amount of n-pentanol (according to the pre-established initial
reactant molar ratio) was preheated and added to the reactor
and the reaction was started. Samples (around 300 ꢃL) were
collected during the reaction time and submitted to titration
with NaOH solution (0.1 mol L−1, standardized with potas-
sium hydrogen phthalate) for the calculation of acetic acid
consumption. The sum of the samples withdrawn from the
reactor for titration was less than 10% of the total volume of
the reaction to avoid significant variations in the reactant vol-
ume, which could interfere with the reaction.4 The amounts
of n-pentanol, pentyl ethanoate and water were obtained from
a stoichiometric balance for the esterification reaction.
where a
is the activity of species i (P, n-pentanol; AC,
i,EQ
acetic acid; E, pentyl ethanoate; W, water) at equilibrium,
x
is the molar fraction of species i at equilibrium, and
i,EQ
i
ꢉ is the activity coefficient of species i at equilibrium. The
enthalpy of the reaction (ΔHo) was estimated by the integrated
form of the Van’t Hoff equation, assuming it as constant in the
temperature range evaluated (Equation 5).
(
)
Δꢌo
dꢊ ꢆEQ
=
(5)
ꢍ × ꢋ 2
dꢋ
2.4 Kinetic modeling
In this study, the kinetic modeling of the esterification of
acetic acid with n-pentanol catalyzed by sulfated zirconia was
carried out using different approaches. The reaction mech-
anisms evaluated were PH, LH, and ER. Depending on the
assumptions regarding the reaction mechanism and the rate-
controlling step, different models can be development: (a) the
PH model assumes that the adsorption and desorption steps
can be neglected; (b) the LH model assumes that both reac-
tants are adsorbed onto the active sites of the catalyst; and
(c) the ER model assumes that one of the adsorbed reactants
reacts with another in the bulk phase. Table 1 summarizes all
reaction rate equations derived from the mechanisms evalu-
ated. In the first column, the nomenclature adopted to identify
each equation is indicated, while the reaction mechanism (PH,
LH, or ER) and the rate-controlling step (adsorption, surface
reaction, or desorption) are presented in the second and third
columns, respectively.
The software Statistica 7.0TM was used for the statistical
analysis (ANOVA effects) to evaluate the effects of tempera-
ture and the n-pentanol to acetic acid molar ratio. The effect
of the solid catalyst concentration on the esterification con-
◦
version was evaluated by kinetics studies carried out at 70 C
with a n-pentanol to acetic acid molar ratio of 3:1. The con-
version (XAC) and the observed reaction rate for acetic acid
(rAC) were calculated as follows:
moles of acetic acid consumed
initial moles of acetic acid
ꢄAC
=
(2)
In Table 1, M is the amount of catalyst in g, a is the
moles of AC consumed in reaction time (mol)
catalyst loading × reaction time (g) × (min)
cat
activity of species i (a = ꢉ x ), ꢉ is the activity coeifficient
ꢅAC
=
(3)
i
i
i
i

4
HAMERSKI ET AL.
TA B L E 1 Reaction rate equations for different reaction mechanisms
Model name
Mechanism
Rate controlling step Rate equation
[
]
ꢇꢐ × ꢇW
ꢆEQ
[
PH
Pseudo-homogeneous
Surface reaction
ꢅi = ꢎcat × ꢏf × ꢇAC × ꢇP
−
]
ꢇE × ꢇW
ꢎcat × ꢏADS,AC
ꢆAC ꢇE × ꢇW
×
ꢇAC
−
ꢇP × ꢆEQ
LH_AD_AC
LH_AD_P
Adsorption of the
acetic acid
ꢅi =
ꢅi =
1 +
×
+ ꢆP × ꢇP + ꢆE × ꢇE + ꢆW × ꢇW
ꢆEQ
ꢇP
[
]
ꢇE × ꢇW
ꢎcat × ꢏADS,P
×
ꢇP
−
ꢇAC × ꢆEQ
Langmuir–Hinshelwood
Adsorbed acetic acid reacts
with adsorbed n-pentanol
Adsorption of the
n-pentanol
ꢆP
ꢆEQ
ꢇE × ꢇW
1 + ꢆAC × ꢇAC
+
×
+ ꢆE × ꢇE + ꢆW × ꢇW
ꢇAC
[
]
ꢇꢐ × ꢇW
ꢆEQ
ꢎcat × ꢏf × ꢆAC × ꢆP
×
ꢇAC × ꢇP −
LH_SR
Surface reaction
ꢅi =
ꢅi =
2
[1 + ꢆAC × ꢇAC + ꢆP × ꢇP + ꢆE × ꢇE + ꢆW × ꢇW
]
[
]
ꢇAC × ꢇP
ꢇE
ꢆEQ
ꢎcat × ꢏDES,E × ꢆEQ
×
−
ꢇW
LH_DES_E
Desorption of pentyl
ethanoate
ꢇAC × ꢇP
ꢇW
1 + ꢆAC × ꢇAC + ꢆP × ꢇP + ꢆP × ꢆEQ
×
+ ꢆW × ꢇW
[
]
ꢇAC × ꢇP
ꢇW
ꢆEQ
ꢎcat × ꢏDES,W × ꢆEQ
×
−
ꢇE
LH_DES_W
ER_AC_ADS
Desorption of water
ꢅi =
ꢅi =
ꢇAC × ꢇP
1 + ꢆAC × ꢇAC + ꢆP × ꢇP + ꢆE × ꢇE + ꢆW × ꢆEQ
×
ꢇE
[
]
ꢇE × ꢇW
ꢇP × ꢆEQ
ꢎcat × ꢏADS,AC
×
ꢇAC
−
Eley–Rideal: Adsorbed acetic
acid reacts with n-pentanol in
the liquid phase
Adsorption of acetic
acid
ꢆAC ꢇE × ꢇW
1 +
×
+ ꢆW × ꢇW
ꢆEQ
ꢇP
[
]
ꢇE × ꢇW
ꢆEQ
ꢎcat × ꢏf × ꢆAC
×
ꢇAC × ꢇP
−
ER_AC_RS
Surface reaction
ꢅi =
ꢅi =
1 + ꢆAC × ꢇAC + ꢆW × ꢇW
[
]
ꢇAC × ꢇP
ꢇE
ꢆEQ
ꢎcat × ꢏDES,E × ꢆEQ
×
−
ꢇW
ER_AC_DES_E
Desorption of pentyl
ethanoate
ꢇꢑꢒ ⋅ ꢇꢔ
ꢇꢕ
1 + ꢆꢑꢒ ⋅ ꢇꢑꢒ + ꢆꢐ ⋅ ꢆꢐꢓ
⋅
[
]
ꢇAC × ꢇP
ꢇW
ꢆEQ
ꢎcat × ꢏDES,W × ꢆEQ
×
−
ꢇE
ER_AC_DES_W
ER_P_ADS
Desorption of water
ꢅi =
ꢅi =
ꢇAC × ꢇP
1 + ꢆAC × ꢇAC + ꢆW × ꢆEQ
×
ꢇE
[
]
ꢇE × ꢇW
ꢇAC × ꢆEQ
ꢎcat × ꢏADS,P
×
ꢇP
−
Eley–Rideal: Adsorbed
n-pentanol reacts with acetic
acid in the liquid phase
Adsorption of
n-pentanol
ꢆP
ꢇE × ꢇW
1 +
×
+ ꢆW × ꢇW
ꢆEQ
ꢇAC
[
]
ꢇE × ꢇW
ꢆEQ
ꢎcat × ꢏf × ꢆP
×
ꢇAC × ꢇP −
ER_P_RS
Surface reaction
ꢅi =
ꢅi =
1 + ꢆAC × ꢇAC + ꢆP × ꢇP
[
]
ꢇAC × ꢇP
ꢇE
ꢆEQ
ꢎcat × ꢏDES,E × ꢆEQ
×
−
ꢇW
ER_P_DES_E
Desorption of pentyl
ethanoate
ꢇAC × ꢇP
ꢇW
1 + ꢆP × ꢇP + ꢆE × ꢆEQ
×
[
]
ꢇAC × ꢇP
ꢇW
ꢆEQ
ꢎcat × ꢏDES,W × ꢆEQ
×
−
ꢇE
ER_P_DES_W
Desorption of water
ꢅi =
ꢇAC × ꢇP
1 + ꢆP × ꢇP + ꢆW × ꢆEQ
×
ꢇE
M
is the mass of the catalyst in g. a is the activity of species i (P, n-pentanol; AC, acetic acid; E, pentyl ethanoate; W, water). k is the forward reaction rate constant
i f
cat
−1
(mol g min−1). K is the surface reaction equilibrium constant. K is the adsorption equilibrium constant for species i.
EQ
i

HAMERSKI ET AL.
5
of species i in the liquid phase, k is the forward reaction rate
constant (mol g−1 min−1), KEQ isfthe surface reaction equilib-
As mentioned above, the UNIQUAC model was used to
calculate the activity coefficients for all components in the
liquid phase. The binary interaction parameters were used as
presented by Lee and Liang,34 and they are reported in the
Supplementary Material.
rium constant, and K is the adsorption equilibrium constant
i
for species i. In order to represent the temperature (T) sensitiv-
ity on the reaction system, the forward reaction rate constant
was expressed by an Arrhenius-like expression (Equation 6):
(
)
2.5 Mass transfer phenomena
ꢐA
ꢍ × ꢋ
ꢏf = ꢏ0 × exp
−
(6)
The effects of external and internal mass transfer limitations
were also evaluated. The external mass transfer is directly
related to the hydrodynamics of the reactant mixture during
the reaction in the batch reactor and it is determined by the stir-
ring speed. In order to assess this parameter, kinetic runs were
carried out varying the stirring speed (50, 250, 500, and 700
rpm), at a fixed n-pentanol to acetic acid molar ratio of 3:1,
where k is the effective kinetic constant, k is the pre-
f
exponential factor, E is the activation energy p0arameter, and
A
R is the gas constant. The model parameters (k , E , and
K ) were fitted to the experimental data obtained0within the
A
i
◦
temperature range of 50-80 C by minimizing the least square
objective function (RSS), as presented in Equation 7:
◦
70 C, and catalyst concentration of 10 wt%. Also, the Mears
ꢖ ꢘꢙ
ꢗ
(
)
∑
2
criterion (C ) was examined for the kinetic runs at different
temperatureMs, calculated according to Equation 12:[27]
RSS =
ꢄꢛexp − ꢄꢛcalc
(7)
ꢚ
ꢅAC,OBS × ꢝL × ꢍP × ꢊ
where N
is the number of experimental observations
obs
ꢒM
=
(12)
(experimental data points) and Xjexp and Xjcalc are the exper-
imental and calculated values of acid acetic conversion,
respectively. The fourth order Runge–Kutta method was used
to solve the differential equations and the “GRG non-linear”
optimization subroutine was used to minimize the objective
function.
ꢏC × ꢒAC
where r
is the experimental value of the reaction rate
AC,OBS
at a given time, n is the reaction order, ꢝ is the density of the
liquid reaction mixture, R is the catalysLt particle radius, C
is the acetic acid concentrPation in the liquid reaction mixtuAreC,
and k is the external mass transfer parameter. For a reaction
C
The mean relative error (%) (MRE) and root mean square
deviation (RMSD) were calculated for each model according
to Equations 8 and 9, respectively.
system with C lower than 0.15, the external mass diffusion
M
resistance can be neglected.27 The external mass transfer in a
well-mixed batch reactor was estimated based on the correla-
tion reported by Sert el al.,35 using Equation 13:
exp
calc
|
|
|
|
|
|
|
|
ꢄ
−ꢄ
∑
ꢖ ꢘꢙ
ꢗ
ꢚ
ꢛ
ꢛ
exp
ꢄ
2
3
ꢛ
[
]
−
MRE (%) =
× 100
(8)
ꢞAC,M
ꢍP
ꢃM
ꢝC × ꢞAC,M
ꢖꢗꢘꢙ
ꢏC =
+ 0.31 ×
√
√
√
√
√
(
)
2
∑
ꢖ ꢘꢙ
ꢗ
ꢚ
ꢄꢛexp − ꢄꢛcalc
1
3
[
]
(
)
ꢝC − ꢝL × ꢃM × ꢟ
RMSD (%) = 100 ×
(9)
×
(13)
ꢖꢗꢘꢙ
2
ꢝC
In order to evaluate which model of those tested best rep-
resents the reaction mechanism of the esterification reac-
tion under study, Fisher’s F-test (F) and the Akaike informa-
tion criterion (AIC) were applied, according to Equations 10
and 11, respectively.3)3
where DAC,M is the diffusivity of acetic acid in the liquid reac-
tion mixture, ꢃ is the viscosity of the reaction mixture, ꢝ
M
C
is the density of the solid catalyst, and ꢝ is the density of
liquid reaction mixture. The diffusivity wLas estimated using
the multi-component diffusivity correlation according to the
Perkin and Geankoplis method (Equation 14):36
(
2
∑
ꢖ
ꢛ
ꢘꢙ
ꢗ
calc
ꢄ
ꢛ
ꢊ
ꢆ
∑
ꢜ =
× 100
(10)
0.8
ꢞAC,M × ꢃM
=
ꢈj × ꢞAC,j × ꢃj0.8
(14)
SQR
ꢖ ꢘꢙ−ꢆ
(
)
ꢗ
ꢛ=1
[
]
[
]
SQR
ꢖobs
ꢆ + 1
ꢖobs + ꢆ − 1
where D
is the diluted binary diffusion coefficient of
AIC = ꢖ × ln
+ 2 × ꢆ × 1 +
acetic aciAdCi,nj the component j (n-pentanol, pentyl ethanoate,
and water, estimated using the Wilke–Chang correlation), x
(11)
j
is the molar fraction of species j, and ꢃ is the viscosity of
j
where K is the number of fitted parameters in the model eval-
species j. The values of ꢃ and ꢃ were obtained using the
j
uated.
Aspen Plus v8.4 software (MAspen Technology, Inc.).

6
HAMERSKI ET AL.
The influence of the internal mass transfer was determined
Figure 1D presents the TGA and DSC curves for the sul-
fated zirconia, which show the high thermal stability of this
material. The first weight loss (<4%) is characterized by an
endothermic process on the DSC curve and is due to water
loss through physisorption and chemisorption. Physiosorbed
based on the Weisz–Prater criterion (CWP), defined by Equa-
tion 16,27 where DEF is effective diffusion of the acetic acid in
the liquid phase mixture (Equation 15, where ꢠ is the porous
tortuosity of the solid catalyst). For reaction systems with C
lower than 1.0, the internal mass transfer resistance canWbPe
neglected.
◦
water is released from room temperature to 120 C, while
◦
chemisorbed water is released between 300 and 500 C. The
◦
◦
second weight loss begins at close to 600 C up to 850 C.
This is an exothermic event and represents the decomposition
of the sulfated metal oxide to give zirconium oxide and the
volatile by-products sulfur dioxide and oxygen.47
ꢞEF = ꢠ2 × ꢞAC,M
(15)
(16)
2
ꢅAC,OBS × ꢝC × ꢍP
ꢞEF × ꢒAC
ꢒWP
=
Particle size distribution of the synthesized sulfated zirco-
nia (Figure 1E) indicates a material of small granulometry,
ranging from 0.4 to 145 ꢃm and the average particle diame-
ter of 22.56 ꢃm. The irregular size and shape of the catalyst
particles can be observed in the SEM images (Figure 1F).
The elemental composition of the catalyst, obtained by
3
RESULTS AND DISCUSSION
3.1 Catalyst characterization
EDS, was 52.86%
3.00 Zr, 45.04%
2.08 O, and
2.10% 0.76 S, resulting in a value of 0.61 0.05 in term
of SO4 to ZrO2 molar ratio. The chemical composition and
properties of the sulfated zirconia depend on the ZrO2 synthe-
sis conditions and method for sulfation and calcination. How-
ever, similar results for the elemental composition of sulfated
zirconia can be found in the work presented by Patel et al18
(58.96% Zr, 39.62% O, and 1.42% S). Moreover, Saravanan
et al48 obtained sulfated zirconia with 2.1 wt% of sulfur. The
Figure 1 summarizes the main characterization results for the
synthesized catalyst. Figure 1A depicts the diffraction pat-
terns for the sulfated zirconia, where the XRD spectrum shows
the crystalline nature of the zirconia and the tetragonal phase
(T) is predominant, as revealed by characteristic peaks high-
◦
◦
◦
lighted in Figure 1A, at 30 , 35 , 50 , and 60◦.37–39 Similarly,
the predominance of the tetragonal phase was confirmed by
the Raman shift (Figure 1B). According to Zyuzin et al40 and
Rabee et al,41 T-labeled peaks at 148, 267, 318, 462, 603, and
648 cm−1, are due to various Zr-O lattice vibrations of ZrO2
with the tetragonal phase. The predominance of this phase
may have been favored by the zirconia precipitation proce-
dure carried out with a high and constant pH (10). This result
is expected according to Corma et al.30 Moreover, the tetrag-
onal phase of sulfated zirconia is desirable, because it leads
to greater catalyst acidity and consequently a higher catalytic
activity in acid esterification reactions.30,42
values for the BET surface area, pore volume and average pore
diameter of the sulfated zirconia particles were 88.77 m2 g
,
−1
0.13 cm3 g−1, and 2.89 nm, respectively.
3.2 Mass transfer phenomena
As mentioned above, a set of experiments with different stir-
ring speed (50, 200, 500, and 700 rpm) were performed to
evaluate the effect of the external mass transfer, and the results
are presented in Figure 2. After 8 h, the acetic acid conversion
was around 66% for the reactions performed with a stirring
speed above 200 rpm. For the reaction carried out at 50 rpm,
the conversion reached 58%. Lower reaction rate observed for
the reaction at 50 rpm can be attributed to the low stirring
speed the solid catalyst that was probably not well distributed
inside the reactor.
FTIR spectrum for sulfated zirconia is shown in Figure 1C.
A broad band can be observed at 3 000-3 600 cm−1, assigned
to the sample hydration, corresponding to the OH stretching
−1
vibration. The band at 1 625 cm corresponds to ꢡ HOH
deformation, due to the presence of water coordinated to
the material.39,43 Furthermore, a low-wavelength band (500-
−1
750 cm ) is assigned to Zr O bonds.39 Bands at 998, 1 044,
–
−1
1 135, and 1 233 cm indicate the presence of SO4. These
Table 2 reports the Mears and Weisz–Prater criteria used to
assesses the external and internal diffusion steps in the acetic
acid esterification reaction catalyzed by sulfated zirconia, at
bands are assigned to chelating bidentate sulfate ions coordi-
nated to zirconium cations,42 which is probably responsible
for the high acidity of Zr4+, due to the sulfur–oxygen induc-
tive effect.44 The sulfate chelates a single Zr atom via a double
oxygen bond, attracting electrons away and making it a strong
Lewis acid.45 Moreover, Brønsted acid sites can be formed
and these contribute to the acid characteristic of this material.
This occurs via sulfur bridges across two zirconium atoms and
through water sorption the Lewis acid sites are converted to
Brønsted acid sites.46
◦
temperatures of 50-80 C, and a stirring speed of 500 rpm. The
−4
Mears criterion values obtained varied within 1.32 × 10
and 2.45 × 10−4. These values are significantly lower than
0.15 (C ≪ 0.15), indicating that external diffusion is not
the limiMting step for the acetic acid reaction with n-pentanol
over sulfated zirconia. Similarly, the Weisz–Prater values are
significantly lower than one (C ≪ 1), which suggests that
internal diffusion also does notWliPmit the reaction. Both mass

HAMERSKI ET AL.
7
F I G U R E 1 Catalyst characterization: (A) XRD patterns: T, tetragonal phase, (B) Raman spectra: T, tetragonal phase, (C) FTIR spectra, (D)
thermogravimetric analysis, (E) particle size distribution, (F) SEM image with magnification 500× [Color figure can be viewed at
wileyonlinelibrary.com]
transfer resistances can be neglected, mainly due to the small
particle size of the catalyst, with an average diameter of
22.56 ꢃm. Srilatha et al28 studied the esterification of palmitic
acid with methanol catalyzed by a 12-tungstophosphoric acid
support on ZrO2 oxide and observed that external mass
transfer resistance was not relevant at stirring speeds above
400 rpm for a catalyst with an average particle size of
90 ꢃm, while the internal mass transfer did not significantly
affect the reaction rate for the catalyst particle size ranged
of 0.4-145 ꢃm.

8
HAMERSKI ET AL.
a
TA B L E 2 Significance of internal and external diffusion for different kinetics
Temperature
CAC at 60 min
rA,OBS at 60 min
(◦C)
(mmol cm−ꢀ
2.35
)
(mol g−1 s−1
)
DEF (cmꢁ s−1
)
kC (cm s−1
)
CM
CWP
−6
−5
−2
−4
−4
−4
−4
−4
50
60
70
80
4.12 × 10
3.35 × 10
2.97 × 10
3.57 × 10
4.43 × 10
5.54 × 10
2.45 × 10
2.04 × 10
1.64 × 10
1.32 × 10
1.23 × 10
−6
−5
−2
−4
2.28
3.99 × 10
4.02 × 10
1.02 × 10
−6
−5
−2
−2
−5
2.04
3.57 × 10
5.00 × 10
8.22 × 10
−6
−5
−5
1.72
3.02 × 10
6.24 × 10
6.58 × 10
aCatalyst loading of 10 wt%, n-pentanol to acetic acid molar ratio of 3:1, stirring speed of 500 rpm.
C
AC, acetic acid concentration at 60 min in the kinetics.
−1
r
A,OBS, experimental value of the reaction rate (mol g
s
−1) at 60 min of reaction.
D
EF, effective coefficient diffusion; kc, external mass transfer parameter; CM, Mears criterion; CWP, Weisz–Prater criterion.
of the effects indicated that the temperature is the most sig-
nificant factor in the acetic acid conversion through the ester-
ification reaction with n-pentanol, with a P value of .0267.
The molar ratio was not significant with a confidence level of
P = .05, within the range evaluated. Even though the ANOVA
suggested that the results obtained varying the molar ratio
were not statistically different, it can be observed in Figure 3A
that the maximum reaction conversion was obtained at a molar
◦
ratio of 3:1 and temperature of 80 C, suggesting that an excess
of the alcohol favors the pentyl ethanoate synthesis. However,
as confirmed by the statistical analysis, a high amount of alco-
hol excess is not necessary to promote a shift in the reac-
tion and increase the acetic acid conversion, while an increase
in the temperature favored the reaction rate allowing higher
conversions obtained for the same reaction time and catalyst
amount.
F I G U R E 2 Effect of stirring speed (rpm) on acetic acid
Figure 4A depicts the kinetics of the acetic acid esterifi-
◦
conversion at 70 C, catalyst loading of 10 wt%, n-pentanol to acetic
◦
cation with sulfated zirconia (10 wt%) at 70 C and different
acid molar ratio of 3:1. ●, 50 rpm; ■, 200 rpm; +, 500 rpm; ▲,
n-pentanol to acetic acid molar ratios. As discussed above,
an excess of alcohol did not improve the acetic acid conver-
sion for a long period of reaction. The acetic acid conversions
obtained after 8 h at n-pentanol to acetic acid molar ratios of
2:1 and 3:1 were 65.9% and 66.1%, respectively.
700 rpm
Therefore, as the external and internal mass transfer are
not limiting step for the reaction evaluated in this work, the
kinetic modeling can be performed considering the reaction
as the limiting step for this heterogeneous catalysis, including
the adsorption and desorption of the reactants in the catalyst
surface.
The effect of the catalyst concentration was also evaluated
◦
at 70 C, with a fixed n-pentanol to acetic acid molar ratio
of 3:1. In Figure 4B can be observed that a higher amount
of catalyst, in the range evaluated, led to higher acetic acid
conversions. It can be observed that the conversion of acetic
acid increased almost proportionally with the catalyst loading
after 2 h. As expected, a higher catalyst loading leads to an
increase in the amount of available active sites for the reac-
tion, affecting the adsorption and surface reaction step in the
catalyst mechanism.
3.3 Effect of the variables on acetic acid
conversion
Figure 3 shows the results obtained for the effects of the vari-
ables temperature and the n-pentanol to acetic acid molar
ratio (MR) on the acetic acid conversion catalyzed by sul-
fated zirconia. In general, it can be observed that the reac-
tion at a higher temperature and molar ratio favored the acetic
acid conversion (Figure 3A). The Pareto chart in Figure 3B
shows the estimated values for the effects based on the surface
response regression, expressed on the right side of the bars.
Factors that exceed the dashed line have a significant effect
in terms of acetic acid conversion (P < .05). The assessment
Figure 5 depicts a comparison for the kinetics of acetic acid
and n-pentanol esterification using homogeneous and hetero-
geneous catalyst. The effect of temperature on the acetic acid
esterification can be observed in Figure 5A for the homo-
geneous catalysis with H2SO4 (1 wt%), while the reaction
catalyzed by sulfated zirconia (10 wt%) is presented in Fig-
ure 5B. The homogeneous reaction resulted in a faster con-
version compared with the use of a heterogeneous catalyst

HAMERSKI ET AL.
9
F I G U R E 3 (A) Response surface plot showing the effect of temperature and molar ratio, on the acetic acid conversion. (B) Estimative of
variables in acetic acid conversion. The percentage of catalyst is constant (10 wt%). The reactions were conducted by 6 h
F I G U R E 4 (A) Kinetic of acetic acid esterification with n-pentanol by sulfated zirconia over different n-pentanol to acetic acid molar ratio: ▲,
◦
◦
1:1; +, 2:1; ○, 3:1 (T = 70 C, catalyst loading of 10 wt%), (B) different catalyst loading: +, 5 wt%; □, 7.5 wt%; ●, 10 wt% (T = 70 C, molar ratio
of n-pentanol/acetic acid 3:1)
◦
◦
◦
F I G U R E 5 Kinetic of acetic acid esterification with n-pentanol by sulfated zirconia over different temperatures: ○, 50 C; ■, 60 C; ◊, 70 C;
◦
▲, 80 C. (A) Homogeneous catalysis (H2SO4 at 1 wt%), (B) heterogeneous catalysis with sulfated zirconia (10 wt%)

10
HAMERSKI ET AL.
a
TA B L E 3 Equilibrium conversion and enthalpy of reaction
values for enthalpy of the reaction, which is suggesting a
weakly temperature-dependent reaction in liquid phase.11
Temperature Equilibrium
Equilibrium
ꢂH◦
b
(◦C)
50
conversion (XEQ
0.902
)
constant (KEQ
)
(kJ mol−1
)
28.63
26.48
24.46
21.65
3.4 Kinetics modeling of sulfated
zirconia-catalyzed esterification
60
0.897
−8.49
70
0.891
The heterogeneous, PH, LH, and ER kinetic models with dif-
80
0.885
ferent controlling steps (Table 1) were applied to correlate the
aH2SO4 catalyst loading of 1 wt%, n-pentanol to acetic acid molar ratio of 3:1,
◦
kinetics data obtained for the temperature range of 50-80 C.
stirring speed of 500 rpm.
bEquilibrium conversion data obtained by simulation with software Aspen Plus
v8.4.
The values of mean relative errors (MRE) and root mean
square deviation (RMSD) obtained for the different kinetic
models used are reported in Table 4. The PH model did not
show satisfactory agreement with the experimental data, sug-
gesting that the reaction mechanism is dependent on the inter-
action between the reactants and the active acid sites of the
sulfated zirconia. The surface reaction models based on the
LH (LH_RS) and ER (ER_AC_RS and ER_P_RS) theories
showed good fits to the kinetics data, with the lowest values
for the mean relative errors (1.1% and 3.1%, respectively) and
the root mean square deviation (0.4% and 1.9%, respectively).
These results suggest that the step of the surface reaction at
the active acid sites is the limiting step of the reaction mech-
anism.
for the operational conditions evaluated. This is expected, as
the nucleophilic attack of the alcohol on the protonated car-
bonyl group of the carboxylic acid occurs in the whole reac-
tion mixture, due to the homogeneous phase between the reac-
tant and strong mineral acid (H2SO4). In the heterogeneous
catalyst, this step occurs only at the active Lewis and Brøn-
sted acid sites of the solid catalyst, and is thus dependent on
the amount of solid catalyst added to the system along with
its morphology (structural, textural and acidic properties).9 In
this study, the maximum acetic acid conversion obtained at 50
◦
and 80 C was 86.7% and 88.3%, respectively, while the equi-
In order to evaluate the most adequate reaction mechanism
to describe the acetic acid esterification with n-pentanol over
sulfated zirconium oxide, the Fisher’s F-test (F) and AIC were
adopted. Table 5 reports the F and AIC values for the surface
reaction models based on LH (LH_RS) and ER (ER_AC_RS
and ER_P_RS) theories.
librium conversion estimated by software Aspen Plus v8.4 was
90.2% and 88.5% (Table 3), at the same temperatures. These
results suggest that an increase in the temperature increases
the rate of collisions between the reactants (in the homoge-
neous reaction) or between the reactants and the active sites
of the catalyst (in the heterogeneous reaction), promoting a
faster reaction, that is, reducing the residence time required to
approximate equilibrium conversions, even that the equilib-
rium conversion showed a slight decrease with temperature
As reported in Tables 4 and 5, the models of LH and ER
with acetic acid adsorbed showed a good fit in correlating
the experimental kinetic data of acetic acid and n-pentanol
esterification over sulfated zirconia. Osatiashtiani et al51 sug-
gest the mechanism of esterification reaction between car-
boxyl acids and light aliphatic alcohols catalyzed by sulfated
zirconia occurs between 02 vicinal Brønsted sites, among
the nucleophilics species generated from the coordinations
of alcohol and acid onto the Brønsted active sites of ZrO2.
Other studies, however, suggest the presence of Lewis acid
sites induces the interaction of one of the reactants with
the active site and the nucleophilic attack by the other free
reactant.11,19,48 Sert and Ataly11 identify the Eley-Rideal
(with acetic acid adsorbed onto the active acid sites) theory as
the model more suitable to describe the esterification of acetic
acid with n-butanol catalyzed by sulfated zirconia. Sankar
et al19 suggested ER (with levunilic acid adsorbed) as plau-
sible reaction mechanism for esterification of levulinic acid
over ZrO2/SBA-15. Saravanan et al48 suggested the ER the-
ory to describe the mechanism of the kinetic of esterification
of stearic acid with methanol over sulfated zirconia, where the
Lewis acid route consists of the direct coordination of the car-
◦
◦
(from 90.2% at 50 C to 88.5% at 80 C).
Table 3 reports the values for the equilibrium conversion
of acetic acid and the equilibrium constant for the esteri-
fication reaction. Both showed a small decrease within the
temperature range evaluated, suggesting an exothermic reac-
tion and that the equilibrium reaction is not strongly depen-
dent on temperature. The estimated enthalpy of reaction was
−8.49 kJ mol−1, also suggesting a slightly exothermic reac-
tion in the temperature range evaluated. Similar result was
report by Sert and Ataly11 for acetic acid esterification with
n-butanol (−18.7 kJ mol−1) and Ali et al2 for the esterifi-
cation of propionic acid with n-propanol (−6.4 kJ mol−1),
although other studies have reported endothermic behavior, as
presented Liu and Tan49 for propionic acid esterification with
n-butanol (+1.92 kJ mol−1), and Jyoti et al50 for acrylic acid
esterification with ethanol (+2.35 kJ mol−1). Such differences
reported in the literature can be attributed at the approaches
used to estimate the equilibrium conversions concerning the
pure component parameters and thermodynamic models used
in these calculations. However, all cited studies reported low
+
boxyl group of a carboxyl acid to the Zr acid site, followed by
a nucleophilic attacked by the oxygen of the alcohol and the

HAMERSKI ET AL.
11
TA B L E 4 Mean relative errors (MRE) and root mean square deviation (RMSD) for different reaction mechanisms at different reaction
a
temperatures
50◦C
MRE (%)
12.4
8.0
60◦C
MRE (%)
12.1
4.9
70◦C
MRE (%)
15.1
3.5
80◦C
MRE (%)
8.4
RMSD (%)
7.2
MRE (%)
5.6
RMSD (%)
6.6
RMSD (%)
Model
PH
5.6
2.5
7.2
2.2
3.2
8.7
1.8
1.7
3.0
2.1
6.3
2.1
1.8
1.8
LH_AD_AC
LH_AD_P
2.3
5.3
1.6
4.0
12.5
2.0
2.3
1.7
1.0
6.0
4.8
9.4
LH_SR
0.5
1.4
0.8
1.1
0.5
3.1
LH_DES_E
LH_DES_W
ER_AC_ADS
ER_AC_RS
ER_AC_DES_E
ER_AC_DES_W
ER_P_ADS
ER_P_RS
15.7
21.8
4.5
4.0
2.9
1.2
6.0
3.3
5.1
8.5
15.4
1.8
10.9
0.9
13.8
3.0
9.3
12.4
2.8
1.4
1.4
2.6
0.8
1.1
0.7
1.8
0.8
2.4
8.1
4.3
9.1
5.5
9.9
5.9
4.5
14.7
5.7
5.2
11.1
2.8
5.8
6.8
4.3
3.3
1.6
2.4
6.0
5.8
8.6
3.2
0.9
1.1
0.7
2.6
1.0
3.3
ER_P_DES_E
ER_P_DES_W
13.9
15.3
5.4
8.8
5.6
6.8
3.8
2.8
5.5
5.0
3.0
10.7
5.1
2.7
an-pentanol to acetic acid molar ratio of 3:1 and catalyst loading of 10 wt%.
TA B L E 5 Fischer F-test (F) and Akaike criteria (AIC) for chosen the model between surface reaction models based on
a
Langmuir–Hinshelwood and Eley–Rideal theories
50◦C
F
60◦C
F
70◦C
F
80◦C
F
AIC
AIC
AIC
AIC
−98
Model
LH_SR
3 262
1 627
1 502
−118
−116
−114
1 985
3 785
3 164
−106
−121
−120
21 152
17 064
12 460
−138
−125
−121
1 964
6 202
4 189
ER_AC_RS
ER_P_RS
−113
−107
aKinetic data obtained at different temperatures, n-pentanol to acetic acid molar ratio of 3:1 and catalyst loading of 10 wt%.
TA B L E 6 Kinetic constant and adsorption parameters for
deprotonation and water loss releasing the ester formed; while
the Brønsted acid catalyzed mechanism consists of the trans-
ER_AC_RS mechanism
+
kf × 102
fer of H from the ZrO2 acid site to the carbonyl group of the
Temperature
(◦C)
(mol g−1 min−1
)
KAC
KW
carboxyl acid, followed by a nucleophilic attack of the oxy-
gen from the alcohol, deprotonation and water loss followed
by the formation of the ester product.
50
60
70
80
0.856
1.4330
2.668
4.813
0.379
0.370
0.356
0.321
14.690
13.239
12.890
12.530
Both models consider the hypotheses that all active acid
sites are uniform and with equal energy, and the one of the
adsorbed acid site does not influence the activity of the vic-
inal acid site,27 but both models did not evaluate the pres-
ence and activity of different kind of actives acid sites or the
heterogeneous morphology reported at Figure 1. Due to the
non-ideality of the catalyst and reaction system, hypotheses
assumed by the models employed in this study, and the results
observed from the fitted models on the experimental data, it is
reasonable consider that esterification under sulfated zirconia
could occur by both LH and by ER concept.
◦
values for set of experimental data obtained at 60 and 80 C.
Moreover, for set of experimental data obtained at 50 and
◦
70 C, the ER_AC_RS showed as good as the LH model.
Figure 6 presents a comparison between the experimen-
tal data and predicted values obtained from the ER_AC_RS
model with the surface reaction as the limiting step, for the
◦
temperatures from 50 to 80 C. The predicted values for the
According with the Akayke’s criteria, the ER_AC_RS
showed more significant mathematical model to represent the
esterification reaction herein studied, once it requires less
parameters, provided the lowest AIC values and the highest F
acetic acid conversion are in good agreement with the exper-
imental data in the temperature range evaluated in this study.
The kinetics parameters and adsorption equilibrium constants
are reported in Table 6.

12
HAMERSKI ET AL.
◦
◦
◦
F I G U R E 6 Kinetics of acetic acid esterification with n-pentanol by sulfated zirconia over different temperature: (A) 50 C, (B) 60 C, (C) 70 C,
◦
and (D) 80 C. Line is the kinetic model and ● is the experimental data
Based on the fitting of the Arrhenius-like expression
ence is that esterification occurs by the nucleophilic attack
of the n-pentanol on acetic acid adsorbed onto the Lewis acid
−1
(Eq. 6), the activation energy was found to be 55.6 kJ mol
,
+
+
which is of the same order of magnitude of activation energy
observed in other reaction systems catalyzed by sulfated zir-
sites (Zr ) and Brønsted acid sites (H ), and that the presence
of water decreases the reaction rates by competitive adsorp-
tion on the acid sites. A high reaction temperature reduces the
adsorption interaction between water and the active acid sites
and increases the surface reaction rates, promoting higher
conversions.
conia: Yadav and Kundu14 (85.7 kJ mol−1) for alkylation of
−1
diphenyl oxide with 1-decene, Omota et al17 (66.5 kJ mol
)
for esterification of dodecanoic acid with 2-ethylhexanol, Sert
and Ataly11 (49 kJ mol−1) for the esterification of acetic acid
with n-butanol, both catalyzed by sulfated zirconia. As com-
parison, the results obtained in our study are in the same order
of other catalyst usually employed in esterification reactions:
Ali et al2 (67.3 kJ mol−1) for esterification of propionic acid
with n-propanol catalyzed with ion-exchange resin Dowex
4
CONCLUSIONS
50Wx8-400, Santos et al25 (123.1 kJ mol ) for esterification
−l
The kinetics data obtained regarding the esterification of
acetic acid with n-pentanol, using sulfated zirconia as a cat-
alyst, to obtain pentyl ethanoate indicated that an increase
in temperature and catalyst loading were favorable to the
ester formation. Moreover, higher temperature led to a slight
decrease in the acetic acid equilibrium conversion and in the
reaction equilibrium constant. The estimated enthalpy of the
of lauric acid ethanol catalyzed by acid activated montmoril-
lonite (STx1-b).
Kinetic parameters and adsorption equilibrium constant
reported in Table 6 indicate that the affinity of water for the
active acid sites is higher than for the acetic acid, and this
decreases as the reaction temperature increases. The infer-

HAMERSKI ET AL.
13
reaction was −8.49 kJ mol−1, suggesting a slightly exothermic
reaction. The models of LH and ER with acetic acid adsorbed
onto the active sites, considering the reaction surface as the
limiting step, showed good fit of the experimental data, but by
the Akayke’s criteria, the ER model showed to be most capa-
ble model to describe the kinetics of the reaction mechanism
involved in the esterification of acetic acid with n-pentanol
over sulfated zirconia.
12. Wang X, Wang H, Liu Y, Liu F, Yu Y, He H. A direct sulfation
method for introducing the transition metal cation Co2+ into ZrO2
with little change in the Brønsted acid sites. J Catal. 2011;279:301-
309.
13. Arata K. Organic syntheses catalyzed by superacidic metal
oxides: sulfated zirconia and related compounds. Green Chem.
2009;11:1719-1728.
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ORCID
Vítor Renan da Silva
https://orcid.org/0000-0002-0109-4155
Marcos Lúcio Corazza
https://orcid.org/0000-0003-2305-1989
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SUPPORTING INFORMATION
Additional supporting information may be found online in the
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How to cite this article: Hamerski F, Dusi GG, Fer-
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ML. Esterification reaction kinetics of acetic acid and
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