REACTION KINETICS OF THE ESTERIFICATION OF ETHANOL ...

REACTION KINETICS OF THE ESTERIFICATION OF ETHANOL AND
ACETIC ACID TOWARDS ETHYL ACETATE
Deliverable 22
Workpackage 6
Technical Report
Name of Partner:
DSM
Authors:
Geert Hangx, Gerard Kwant, Harrie Maessen, Peter Markusse, Ioana Urseanu
Date:
24 August 2001
Distribution:
Frédéric Gouardères, European Commission,
Andrzej Górak, University of Dortmund
Eugeny Kenig, University of Dortmund
Peter Moritz, SULZER
Klaus Althaus, BASF
Gerard Kwant, DSM
Jacob Moulijn, University of Delft
Hans Hasse, University of Stuttgart
Wieslaw Salacki, PLOCK
Jiri Klemes, UMIST
Andrzej Kraslawski, Lappeenranta University of Technology
Bjoern Kaibel, MONTZ
Florian Menter, AEA
Maria Majchrzak, ICSO
Andrzej Kolodziej, IIC
Ion Ivanescu, PETROM
Valentin Plesu, University „Politehnica” of Bucharest
PROGRAMME GROWTH
Intelligent Column Internals for Reactive Separations (INTINT)
Project No. GRD1 CT1999 10596
Contract No. G1RD CT1999 00048

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Deliverable 22 Issued: 24.08.01
1 SUMMARY AND CONCLUSIONS 2
2 INTRODUCTION 2
3 EXPERIMENTAL 3
4 RESULTS AND DISCUSSION 3
5 LIST OF SYMBOLS 5
6 SELECTION OF PHYSICAL PROPERTIES 5
1 Summary and conclusions
The kinetic parameters have been determined for INTINT reaction system 3: ethanol/acetic
acid/ethyl acetate. The reactions considered are the esterification of ethanol (CH3CH2OH, EtOH)
and acetic acid (CH3COOH, AcOH) towards ethyl acetate (CH3COOCH2CH3, EtOAc) and water,
and the reverse reaction, ester hydrolysis. The catalyst used is the cation exchange resin Purolite
CT179.
2 Introduction
The work described in this report is a part of the European project “Intelligent Column Internals for
Reactive Separations” (INTINT). The report contains the kinetics of reaction system 3. Originally,
reaction system 3 was the aldol condensation of acetone towards diacetone alcohol. However, since
no stable catalyst for this reaction was available 1 , this process was abandoned. The reaction studied
instead is the esterification of ethanol (CH3CH2OH, EtOH) and acetic acid (CH3COOH, AcOH),
resulting in the products ethyl acetate (CH3COOCH2CH3, EtOAc) and water, see equation 1:
O
OH
+
HO
H + H +
AcOH EtOH EtOAc
This reaction is reversible, and the equilibrium composition is a weak function of temperature. The
reaction is acid catalysed, and as for most esterifications usually strong mineral acids (hydrochloric
acid, sulfuric acid) are used 2,3 . Cation exchange resins (typically containing sulfonic acid groups,
e.g. Amberlyst 15, Purolite CT179) are also widely used, because of their high activity and selectivity
(possible side reactions are alcohol dehydration and etherification), and easy separation 2 . Catalyst
deactivation appears to be negligible. In practice the equilibrium is often forced towards the
1 INTINT deliverable 21, February 2001
2 Ullmann’s Encyclopedia of Industrial Chemistry, vol. A9
3 Chemical Economics Handbook CD-ROM
O
O
+ H 2 O
(1)

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Deliverable 22 Issued: 24.08.01
ester by azeotropic water removal 2 . In the present investigation the cation exchange resin Purolite
CT179 will be used.
The intrinsic kinetics of the reaction system are more or less known from literature: the forward
reaction rate (ester formation, R1) is a function of EtOH and AcOH concentrations, and the reverse
reaction rate (ester hydrolysis, R2) is a function of EtOAc and water. See the kinetic equations below:
m
EtOH AcOH x x k R1 1
R2 = k2
xEtOAc
xH
2O
(3)
= (2)
The equilibrium constant Keq is given by equation 4:
K
eq
k x x
2
= =
(4)
k x
1
EtOAc H 2O
m
EtOH x AcOH
All concentrations are given as mole fractions. Both k1 and k2 are functions of temperature, according
to the Arrhenius equation:
k
−E
A / RT
i = ki,
oe
(5)
For porous particles with typical particle diameter 1 mm, intra-particle diffusion and mass transfer
from the liquid bulk to the particles are expected to be very important. The kinetics determined in
this study therefore only apply to Purolite CT179 with the same particle size distribution. The objective
of this study is to find kinetic parameters for the reactions described above (formation and
hydrolysis of ethyl acetate).
3 Experimental
The catalyst used is the ion exchange resin Purolite CT179, purchased from Purolite. Purolite
CT179 is a porous cation exchange resin, containing sulfonic acid groups. The particle diameter
was 0.6-1.4 mm. The reagents ethanol (>99.9%), acetic acid (>99%) and ethyl acetate (>99%) were
purchased from J.T. Baker, and used as received. Demineralised water was used. Apart from the
reactants and products (AcOH, EtOH, EtOAc and water) no other solvents were used. The experimental
set-up consisted of a thermostated jacketed glass tube, inner diameter 20 mm. Typically 12 g
of catalyst was used, and a constant flow rate of 0.1-25 ml/min was applied. The reactor was kept at
55-65 °C. The effluent was analysed off-line by GC over a CP-wax 58CB column, using a flame
ionisation detector. The samples were diluted with acetone prior to injection, and methyl iso-butyl
ketone was used as internal standard.
4 Results and discussion
The equilibrium constant Keq was determined by leading 0.1 ml/min of a feed solution containing
ethanol and acetic acid (in several ratios) through the reactor, containing 12.3 g of Purolite CT179.
It was verified that equilibrium was reached by comparison with effluent concentrations reached at
higher flow rates: no difference was observed between 0.1 and 0.5 ml/min. The best fit of the re-

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Deliverable 22 Issued: 24.08.01
sults was obtained for 1.5 th order in AcOH (m in equations 2 and 4 is 1.5). The resulting equilibrium
constants at 55 °C and 65 °C are 6.68 and 5.51, respectively.
For determination of the kinetic constants k1 and k2 the same reactor was used, but at higher liquid
flow rates: 2-25 ml/min. The corresponding W/F ratios are 0.03-0.37 s kgcat/m 3 . The kinetic constants
were calculated from the product concentrations (EtOAc when AcOH and EtOH were fed,
AcOH and EtOH when EtOAc and water were fed) using a Mathcad worksheet, in which the reactor
was modelled as an ideal plug flow reactor. The experimental and calculated ethyl acetate concentrations
in the reactor effluent are shown in figure 1.
calculated
60
40
20
0
Figure 1. Experimental (x-axis) and simulated (y-axis) ethyl acetate concentrations in the reactor effluent.
The kinetic equations 2 and 3, and the parameters given in table 1 were used for the simulations.
At 65 °C the value for k1 is 0.147 mol kgcat -1 s -1 , and k2 is 0.0268 mol kgcat -1 s -1 . At 55 °C the value
for k1 is 0.0874 mol kgcat -1 s -1 , and k2 is 0.0131 mol kgcat -1 s -1 . The activation energy for the ester
formation reaction is 48.3 kJ mol -1 . The activation energy for the ester hydrolysis reaction is 66.2 kJ
mol -1 . The pre-exponential factors (see equation 5) are 4.24⋅10 6 mol kgcat -1 s -1 for the ester formation
and 4.55⋅10 8 mol kgcat -1 s -1 for the ester hydrolysis. The most important parameters are summarised
in the table below.
Table 1. Kinetic parameters for ethyl acetate formation and hydrolysis on Purolite CT179.
Parameter Units Value
Keq 55 °C - 6.68
Keq 65 °C - 5.51
k1 55 °C mol kgcat -1 s -1 0.0874
k1 65 °C mol kgcat -1 s -1 0.147
k2 55 °C mol kgcat -1 s -1 0.0131
k2 65 °C mol kgcat -1 s -1 0.0268
k1,o mol kgcat -1 s -1 4.24⋅10 6
k2,o mol kgcat -1 s -1 4.55⋅10 8
EA,1 kJ mol -1 48.3
EA,2 kJ mol -1 66.2
Ethyl acetate parity plot (weight%)
0 20 40 60
experimental

5 List of symbols
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Deliverable 22 Issued: 24.08.01
EA activation energy J mol -1
k1 esterification reaction rate constant mol kgcat -1 s -1
k2 ester hydrolysis reaction rate constant mol kgcat -1 s -1
Keq
R
equilibrium constant
gas constant
-
J mol -1 K -1
R1 esterification reaction rate mol kgcat -1 s -1
R2 ester hydrolysis reaction rate mol kgcat -1 s -1
T temperature K
xAcOH mole fraction acetic acid -
xEtOAc mole fraction ethyl acetate -
xEtOH mole fraction ethanol -
xH2O mole fraction water -
6 Selection of physical properties
Azeotrope EtOH/EtOAc 4 EtOH 44.7 m%, bp 71.8 °C
Azeotrope water/EtOAc 4 water 32.6 m%, bp 71.5 °C
Azeotrope water/EtOH 4 water 10.4 m%, bp 78.2 °C
Azeotrope water/EtOH/EtOAc 4 water 28.7 m%, EtOH 17.3 m%, bp 70.4 °C
Density AcOH 4 1.047 kg/l (20 °C), 0.995 kg/l (70 °C)
Density EtOAc 4 0.900 kg/l (20 °C), 0.838 kg/l (70 °C)
Density EtOH 4 0.790 kg/l (20 °C), 0.743 kg/l (70 °C)
Density water 4 0.997 kg/l (20 °C), 0.971 kg/l (70 °C)
Molecular weight AcOH 60.05 g/mol
Molecular weight EtOAc 88.11 g/mol
Molecular weight EtOH 46.07 g/mol
Molecular weight water 18.02 g/mol
Normal boiling point AcOH 4 117.9 °C
Normal boiling point EtOAc 4 77.1 °C
Normal boiling point EtOH 4 78.3 °C
Normal boiling point water 4 100 °C
Reaction enthalpy 4 -27.5 kJ/mol (70 °C)
Solubility water in EtOAc 4 14.1 m% (25 °C), 22.6 m% (70 °C)
Solubility EtOAc in water 4 1.6 m% (25 °C), 1.1 m% (70 °C)
4 Aspen properties