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: Frdric Gouardres, European Commission,

Andrzej Grak, 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

Intelligent Column Internals for Reactive Separations Page 2 of 5 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 available1, 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:

(1)

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 used2,3. Cation exchange resins (typically containing sulfonic acid groups, e.g. Amberlyst 15, Purolite CT179) are also widely used, because of their high activity and selectiv-ity (possible side reactions are alcohol dehydration and etherification), and easy separation2. Cata-lyst deactivation appears to be negligible. In practice the equilibrium is often forced towards the

1 INTINT deliverable 21, February 2001 2 Ullmanns Encyclopedia of Industrial Chemistry, vol. A9 3 Chemical Economics Handbook CD-ROM

O

OH

OO

OHHOHO

O

O

O

O+

H+H++ H2O

Intelligent Column Internals for Reactive Separations Page 3 of 5 Deliverable 22 Issued: 24.08.01 ester by azeotropic water removal2. 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 be-low:

mAcOHEtOH xxkR 11 = (2)

OHEtOAc xxkR 222 = (3)

The equilibrium constant Keq is given by equation 4:

mAcOHEtOH

OHEtOAceq xx

xxkkK 2

1

2== (4)

All concentrations are given as mole fractions. Both k1 and k2 are functions of temperature, accord-ing to the Arrhenius equation:

RTEoii

Aekk /,

= (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 ob-jective 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 experi-mental 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-

Intelligent Column Internals for Reactive Separations Page 4 of 5 Deliverable 22 Issued: 24.08.01 sults was obtained for 1.5th 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/m3. The kinetic con-stants 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 reac-tor was modelled as an ideal plug flow reactor. The experimental and calculated ethyl acetate con-centrations in the reactor effluent are shown in figure 1.

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 4.24106 mol kgcat-1 s-1 for the ester formation and 4.55108 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 4.24106 k2,o mol kgcat-1 s-1 4.55108 EA,1 kJ mol-1 48.3 EA,2 kJ mol-1 66.2

Ethyl acetate parity plot (weight%)

0

20

40

60

0 20 40 60experimental

calc

ulat

ed

Intelligent Column Internals for Reactive Separations Page 5 of 5 Deliverable 22 Issued: 24.08.01 5 List of symbols 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 equilibrium constant - R 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/EtOAc4 EtOH 44.7 m%, bp 71.8 C Azeotrope water/EtOAc4 water 32.6 m%, bp 71.5 C Azeotrope water/EtOH4 water 10.4 m%, bp 78.2 C Azeotrope water/EtOH/EtOAc4 water 28.7 m%, EtOH 17.3 m%, bp 70.4 C Density AcOH4 1.047 kg/l (20 C), 0.995 kg/l (70 C) Density EtOAc4 0.900 kg/l (20 C), 0.838 kg/l (70 C) Density EtOH4 0.790 kg/l (20 C), 0.743 kg/l (70 C) Density water4 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 AcOH4 117.9 C Normal boiling point EtOAc4 77.1 C Normal boiling point EtOH4 78.3 C Normal boiling point water4 100 C Reaction enthalpy4 -27.5 kJ/mol (70 C) Solubility water in EtOAc4 14.1 m% (25 C), 22.6 m% (70 C) Solubility EtOAc in water4 1.6 m% (25 C), 1.1 m% (70 C)

4 Aspen properties