Kinetic studies for the esterification of acetic acid with epichlorohydrin over an anion exchange resin catalyst

HAL Id: hal-00315665

https://hal.archives-ouvertes.fr/hal-00315665

Submitted on 31 May 2021

HAL is a multi-disciplinary open access archive for the deposit and dissemination of sci- entific research documents, whether they are pub- lished or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers.

L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Distributed under a Creative Commons Attribution - NonCommercial - NoDerivatives| 4.0

Emil Muresan, Spiridon Oprea, Vasile Hulea, Teodor Malutan, Mihai Vata

To cite this version:

Emil Muresan, Spiridon Oprea, Vasile Hulea, Teodor Malutan, Mihai Vata. Kinetic studies for the esterification of acetic acid with epichlorohydrin over an anion exchange resin catalyst. Central Eu- ropean Journal of Chemistry, Springer Verlag, 2008, 6 (3), pp.419-428. �10.2478/s11532-008-0046-z�.

�hal-00315665�

Central European Journal of Chemistry

Kinetic studies for the esterification of acetic acid with epichlorohydrin over an anion exchange resin catalyst

* E-mail: [email protected]

Received 26 February 2008; Accepted 2 July 2008 Abstract: ThekineticsoftheesterificationreactionbetweenaceticacidandepichlorohydrincatalysedbyPuroliteA-520Estrongbasicanion

exchangeresinwasstudied.Theeffectsofcertainparameterssuchasstirringspeed,particlediameter,temperature,catalystamount

andmolarratiobetweenreactantswereexperimentallydetermined.Itwasfoundthattheoverallreactionrateisintrinsicallykineti- callycontrolled.Thepartialordersofreactionwithrespecttocatalyst,aceticacidandepichlorohydrinweredetermined.Areaction

mechanismisproposed.Basedonchromatographicdataandtakingintoaccountthepartialordersofreaction,amoredetailedkinetic

modelissuggested.

© Versita Warsaw and Springer-Verlag Berlin Heidelberg.

Keywords:Chlorohydroxyalkyl esters • Heterogeneous catalysis • Kinetics

1 Departement of Organical and Biochemical Engineering,

The Faculty of Chemical Engineering, “Gh. Asachi” Technical University of Iassy, D. Mangeron Street, Iasi, 700050, Romania

2 Ecole Nationale Superieure de Chimie de Montpellier, 8, rue de l’Ecole Normale, Montpellier, Cedex 5, France

3 Departament of Natural and Synthetic Polymers,

The Faculty of Chemical Engineering, “Gh. Asachi” Technical University of Iassy, D. Mangeron street, 71A, Iasi, 700050, Romania

Emil Ioan Muresan^1*, Spiridon Oprea¹, Vasile Hulea², Theodor Malutan³, Mihai Vata³

Research Article

1. Introduction

Reactions between carboxylic acids and oxiranes are of great interest because of the practical significance of the products obtained. Thus, hydroxyalkyl esters of unsaturated carboxylic acids (acrylates and methacrylates) are used as components of dyeing coatings, printer inks, and medicinal preparations, whereas hydroxyalkyl esters of acetic acid are used as hardeners of sand blends in metallurgy, components of cooling agents for low temperature processes, solvents for dyeing compositions, components of anticorosive coatings and cement modifiers [1-3].

Because of the parallel-subsequent character of the reactions between carboxylic acids and oxiranes

and in the case of epichlorohydrin also due to chlorine atom presence, many side products are formed. As any non-symmetric compound epichlorohydrin leads to two isomeric esters (Scheme 1) [4,5]. Of the two possible isomeric products the normal ester is formed as the main product in neutral or basic medium, whereas an acidic medium favors the formation of the abnormal product.

A variety of homogeneous and heterogeneous catalysts were tested. Among homogeneous catalysts tertiary amines, quaternary ammonium salts, alkaline hydroxides, alkaline salts of carboxylic acids, and complexes of transition metals have been studied [6,7].

The highest yields and selectivities were obtained in the case of chromium compounds [8,9].

As heterogeneous catalysts, different linear polymers containing quaternary ammonium groups

Cent. Eur. J. Chem. • 6(3) • 2008 • 419–428 DOI: 10.2478/s11532-008-0046-z

419

were investigated [10]. Less studied in the esterification reaction of carboxylic acids with epichlorohydrin are anion exchange resin catalysts [11-15]. These catalysts have numerous advantages such as their easy separation from the reaction mixture through filtration or decantation, reduced corrosion, possible regeneration, and no need for additional work-up (neutralization, washing). In addition, they are cheap, easy to obtain and environmentally friendly.

2. Experimental Procedures

2.1. Materials

Epichlorohydrin (1-chloro-2,3-epoxypropane) was dried over anhydrous sodium sulphate and vacuum distilled.

Acetic acid of 99.5% purity was purchased from Merck.

The anion exchange resin Purolite A-520E catalyst was supplied by Victoria S.A. Purolite (Romania). Before use, the catalyst was dried at 353 K for 12 hours.

2.2. Apparatus

Esterification reaction was carried out in a three-necked glass flask. The temperature was controlled within ± 0.5˚C by a thermostating bath. A magnetic stirrer was used to mix the reactants. The frequency was 600 rpm.

2.3. Procedure

Acetic acid and epichlorohydrin were loaded into the reactor and then heated to the desired temperature.

Finally a given amount of catalyst was added. This was taken as the zero time of reaction.

2.4. Sample analysis

The amount of unreacted acetic acid from the samples withdrawn at regular time periods was determined by titration against a standard solution of 0.1 M NaOH using a mixed indicator phenolphthalein - bromthymol blue, while the content of epichlorohydrin in the samples was determined using the method described by Jay [16].

The analysis of reaction mixture was carried out by gas chromatography using a Hewlet Packard 6890 chromatograph. A HP-1 column (30m length, 0.32 mm diameter, 0.17 μm film thickness) was used for separating the reactants and products. The conditions of GC analysis were: oven temperature program 50(3)- 10-250, amount of sample injected 0.5 μL, carrier gas Helium, detector temperature 250˚C. The identification of reaction products was carried out on a GS-MS QMD coupling.

2.5. Sorption equilibrium experiments

The solutions of acetic acid in hexane (45 mL) with concentrations in the range 7-15 g L^-1 were added to 0.9 g catalyst. The experiments were carried out at 40˚C, under stirring (150 rpm). Samples were withdrawn at regular time periods. The concentrations of acetic acid in solutions were measured using a Camspec M501 Single Beam Scanning UV-VIS Spectrophotometer at a wavelength of 230 nm. The amount of acetic acid adsorbed onto Purolite A-520E anion exchange resin, q_e (g g^-1) was calculated by a mass balance relationship as follows:

( )

M V C qe C ^e

⋅

= ⁰−

(1) where C₀ is the initial concentration of acid (g L^-1), C_e is the concentration of acid at equilibrium (g L^-1), V is the volume of solution (L) and M is the mass of anion exchange resin used in the adsorption experiments (g).

carboxylic

acid epichlorohydrin normal ester abnormal ester

Scheme 1. Esterification reaction between acetic acid and epichlorohydrin.

Product Mass spectrum (m/e) ¹HNMR (δ, ppm) IR (ν, cm^-1)

3-chloro-2-hydroxypropyl

acetate 43; 44; 49; 74; 79; 103 3.62 (d, 2H, ClCH₂); 3.81 (m, 1H, CH);

4.2 (d, 2H, CH2) 3437 (OH); 1739 (C=O); 1240, 1044 (C-O);

752 (C-Cl) 2-chloro-1-(hydroxymethyl)

ethyl acetate 43; 49; 86; 121 3.7 (m, 2H, ClCH2); 5.2 (m, 1H, CH), 4.08

(m, 2H, CH2) 3426 (OH); 1740 (C=O); 1237, 1047 (C-O);

707 (C-Cl)

Table 1. Spectral data of esters.

E.I. Muresan et al.

2.6. Analysis, isolation and characterization of products

The products were fractionated under reduced pressure and identified by ¹H-NMR, IR and MS. The spectral data of the two isomeric hydroxyalkyl esters are presented in Table 1.

3. Results and discussions

3.1. Proof of absence of external mass transfer resistance

For the heterogeneous reaction using ion exchange resin catalyst, it is essential to have the catalyst uniformly suspended in the reaction medium. According to Zweitering [17] the minimum speed of agitation (N_m) required to keep the solid particle in complete suspension can be predicted by the following relation:

( )

^0.45

0.2 0.1 0.45 0.13

0.55 0.85

p L L p

m

L I

B d g w

N d

× ×m × × r -r ×

= r × (2)

where 2 ^1.33

 



⋅

=

I

dT

B d

By solving the previous equation it was found that the minimum agitation speed required for the highest catalyst loading (112.5 kg m^-3) was 286 rpm.

In order to assess the external mass transfer resistance the stirring speed was varied between 400 and 800 rpm. It was observed that the conversion of acetic acid was practically the same in all the cases, which means that there was no external mass transfer limitation. A theoretical analysis of the external mass transfer resistance is given to support these observations. For this purpose the quantitative criterion α₂,which is defined as the ratio of the measured reaction rate to the maximum rate of mass transfer from the bulk liquid phase to the external surface of the solid, was evaluated [18].

2

, 0

A A

SL A p A

r k a c

a = × × (3a)

2 , 0

E E

SL E p E

r k a c

a = × × (3b) For a typical spherical particle, the particle’s external surface area a_p per unit liquid volume (m² m^-3) is given by: 6

p

P p

a w d

= ×

r × (4) where w is the catalyst loading (kg catalyst m^-3 reaction mixture), ρ_p the density of particle (kg m^-3), ρ_L the liquid density (kg m^-3) and d_p is the particle diameter (m).

For the maximum catalyst loading used (112.5 kg catalyst m^-3 reaction mixture) and for a mean particle size d_p of 0.0007 m, the value found for a_p was 1418

m² m^-3. The liquid-solid mass transfer coefficients were evaluated using the correlation proposed by Sano [19]

which takes into account the contributions of Reynolds and Schmidt numbers:

1/ 4 1/ 3

4 3

,

2 0.4 3

SL A p p L L

AE c L L AE

k d e d

D F D

é ù é ù

× = + ×êê × ×r úú ×êê m úú

× êë m úû_{1/ 4} ër × û_{1/ 3} (5a)

4 3

,

2 0.4 3

SL E p p L L

EA c L L EA

k d e d

D F D

é ù é ù

× = + ×êê × ×r úú ×êê m úú

× êë m úû ër × û (5b)

The energy supplied to the liquid is given by the following correlation described by Calderbank [20]:

3 5

2

8 _i

T L L

N d P

e d L V

× × × y

= =

× r × (6) The correction factor Ψ for the presence of gas bubbles is assumed to be unity when there is no gas phase in the reaction mixture.

Molecular diffusion coefficients of concentrated binary system (acetic acid and epichlorohydrin) were estimated from the equation of Leffler and Cullinan [21].

0 x^A 0 x^E 0 x^A 0 x^E

AE A AE E EA A EA E

AE EA

L L

D D D D

D =éëê ×m û ëú êù é ×m úùû D =êéë ×m ù éú êû ë ×m ùûú

m m (7)

in which the values of infinite dilution diffusion coefficients (D⁰_AE and DEA⁰ ) were calculated using the correlation proposed by Wilke-Chang [22]:

( )^{1/ 2} ( )^{1/ 2}

8 8

0 0

0,6 0,6

7.4 10 _A 7.4 10 _E

AE EA

A A E E

M T M T

D D

V V

- -

× × j× × × × j× ×

= =

m × m × (8)

The values found for infinite dilution diffusion coefficients of acetic acid and epichlorohydrin were 4.1891 × 10^-9 m² s^-1 and 2.8318 × 10^-9 m² s^-1 respectively, while the molecular diffusion coefficients for the equimolecular mixture acetic acid/epichlorohydrin used in the experiments were 4.19 × 10^-9 m² s^-1 and 2.83 × 10^-9 m² s^-1 respectively.

The solid-liquid mass transfer coefficients for both reactants were calculated from the limiting value of the Sherwood number (Sh_i = k_SL,i·d_p/D_ij = 2, where i = A, E and j = E, A). As can be seen from Equation 5, the real Sherwood numbers are typically higher by an order of magnitude in well agitated systems, but for safely estimations a value of 2 is taken. The calculated solid-liquid mass transfer coefficients were 1.1971 × 10^-5 m² s^-1 and 0.80928 × 10^-5 m² s^-1 for acetic acid and epichlorohydrin respectively. The initial rate of reaction calculated from the graphic dependence of conversion against time as 0.866 mol m^-3 s was inserted in Equations (3). The values obtained for liquid-solid mass transfer criterion α₂ 0.0061 and respectively 0.009 show that there is no influence of external mass transfer on overall reaction rate.

421

3.2. Proof of absence of intraparticle mass transfer resistance

Consequently, the rate may be either surface reaction controlled or intraparticle diffusion controlled. To evaluate the internal mass transfer resistance the commercial anion exchange resin, Purolite A-520E, was sieved obtaining four particle size ranges (400-500, 500-630, 630-800, 800-1000 μm). The change of acetic acid conversion with time was followed for each particle size range. The results obtained proved that there was no significant effect of particle size on conversion, which suggests the effectiveness factor for this reaction is almost unity and consequently the entire process is intrinsically kinetically controlled.

In order to establish if intraparticle diffusion is limiting the reaction rate, an additional theoretical approach involving Weisz-Prater (Φ_WP) criterion, defined as the ratio between the observed reaction rate (r_obs) and the maximum internal diffusion rate was also done

(Equation 9): ²

0

obs p

WP

i

r R De C w

× ×r

f = × × (9) (i) If Φ_WP << 1, there is no diffusion limitation.

(ii) If Φ_WP >> 1, then the reaction is limited by severe internal diffusion resistance.

The effective diffusivities (D_e,AE and D_e,EA ) of acetic acid and epichlorohydrin inside the pores of the catalyst were calculated to be 4.594 × 10^-10 m² s^-1 and 3.104 × 10^-10 m² s^-1 from D_e,AE = D_{AE ·}(ε/τ) and respectively D_e,EA= D_EA·(ε/τ), where the values of porosity (ε), and tortuosity (τ) were taken as 0.329 and 3 respectively. The values obtained for Φ_WP (0.0182 and 0.027 for acetic acid and epichlorohydrin respectively) are much less than unity and therefore, the reaction is intrinsically kinetically controlled.

3.3. Effect of catalyst loading

The catalyst loading was varied from 56.25 kg m^-3 to 168.75 kg m^-3 based on total volume of the reaction mixture (Fig. 1). One observes an increase in conversion with increasing catalyst loading because the increasing number of active sites.

The linear correlation between initial reaction rate and catalyst loading suggests that the reaction is first order with respect to the catalyst (Fig. 2). The fact that this straight line passes through the origin proves that the effect of uncatalysed reaction is not significant.

3.4. Effect of molar ratio

The initial molar ratio of acetic acid to epichlorohydrin was varied from 1 to 2, while keeping the rest of the experimental conditions unchanged. From Fig. 3 one observes a sharp increase in acetic acid conversion when an excess of epichlorohydrin is used.

By using acetic acid in excess, no significant change of epichlorohydrin conversion is noticed, which is in agreement with the zero order kinetics with respect to acid (Fig. 4).

3.5. Effect of temperature

Fig. 5 shows a sharp increase in conversion with increasing temperature, that is, the temperature has a very strong influence on the esterification process.

The flattening of curves increases with increasing temperature.

0 20 40 60 80 100

0 50 100 150 200 250 300

Time (min)

Conversion (%)

Figure 1. Effect of catalyst loading on acetic acid conversion; molar ratio acetic acid – epichlorohydrin 1:1; temperature 366 K;

stirring speed 600 r.p.m.; catalyst loading (kg cat m^-3): × 56.25; ▲84.375; ∆ 112.5; ■ 135; □ 168.75.

Figure 2. Initial reaction rate versus catalyst loading; molar ratio acetic acid – epichlorohydrin 1:1; temperature 366 K;

stirring speed: 600 r.p.m.

0 0.2 0.4 0.6 0.8 1 1.2

0 50 100 150 200

Catalyst loading (kg/m³) Initial reaction rate (mol/L. min)

E.I. Muresan et al.

4. Reaction kinetics

Several kinetic models based on homogeneous or heterogeneous catalysis are used to describe the esterification reactions catalyzed by ion exchange resins. When both external and internal mass transfer resistances are absent (kinetic regime) the intrinsic rate of reaction can be given by three models:

the power law model if there is very weak adsorption

-

of reactant species

Eley-Rideal model applied when an unabsorbed

-

molecule collides and reacts with adsorbed molecules of another reactant

Langmuir - Hinshelwood - Hougen - Watson model

-

applied when the rate determining step in a reaction involves only adsorbed reactants.

The generalized form of reaction rate is:

1

1

nA nE

A E

n i i i

k c c r

K c

× ×

=æç +ççè

å

× ÷ö÷÷÷ø (10)

where the exponent n is 2 for the Langmuir Hinshelwood model, 1 for the Eley-Rideal mechanism and 0 for the pseudo-homogeneous approach.

4.1. Pseudohomogeneous approach

The partial order of reaction with respect to acetic acid was determined by the isolation method, that is, by running a reaction with an excess of epichlorohydrin (molar ratio acetic acid/epichlorohydrin 1:10). Under such conditions the acid concentration could be considered constant and included into the apparent rate constant k₂. By this substitution the equation of the reaction rate becomes: r = k_2·c_A^nA where k₂ = k₁·c_E^nE.

The real concentration of acetic acid (C_A^/) was calculated by the equation C_A^/ = C_A + C_A^//, where C_A 0

20 40 60 80 100 120

0 50 100 150 200 250 300

Time (min)

Conversion (%)

Figure 3. Effect of molar ratio on acetic acid conversion; tempera- ture 366 K; stirring speed 600 r.p.m.; catalyst loading (112.5 kg m^-3); molar ratio acetic acid epichlorohydrin:

♦ 1:2; ■ 1:1.5; ▲ 1:1.1; × 1:1.

Figure 4. Effect of molar ratio on epichlorohydrin conversion; tem- perature 366 K; stirring speed 600 r.p.m.; catalyst loading (112.5 kg m^-3); molar ratio acetic acid/epichlorohydrin:

▲ 1.5:1; ♦ 2:1; ■ 1:1.

0 20 40 60 80 100

0 50 100 150 200 250 300

Time (min)

Conversion (%)

0 20 40 60 80 100

0 50 100 150 200 250 300

Time (min)

Conversion (%)

Figure 5. Effect of temperature on acetic acid conversion; molar ratio acetic acid – epichlorohydrin 1:1; stirring speed 600 r.p.m.; catalyst loading (112.5 kg m^-3): temperature:

× 343K; ■ 348K; ▲ 353K; ∆ 358K; ♦ 366K.

y = 6.0204x + 9.8752 R² = 0.9772

0 20 40 60 80

0 2.5 5 7.5 10 12.5

ce (g/L)

ce/qe (g/L)

Figure 6. Plotting of Langmuir isotherm.

423

represents the concentration of acid in the liquid phase and C_A^// is the amount of acid sorbed by anion exchange resin. C_A^// (mol L^-1), was experimentally determined from adsorption studies of binary mixture acetic acid/

heptane on Purolite A-520E anion exchange resin.

It was concluded that adsorption follows a Langmuir Hinshelwood model. The values of adsorption constants were calculated from plotting of c_e/q_e against c_e (Fig. 6).

It was found that the adsorption kinetics follows the first order kinetic model proposed by Lagergen, for which the equation is:

( )

ln q_e-q_t =lnq_e-k_ads×t (11) The values found for the constant of adsorption rate and Langmuir Hinshelwood constants were used to calculate C_A^// at different time intervals (Fig. 7).

By summing the values of C_A^// and C_A the real concentration of acetic acid C_A^/ was obtained. The plot of real concentration of acetic acid (C_A^/) against time is a straight line, typical behaviour for a zero order kinetics (Fig. 8).

The value of the overall reaction order determined by differential method is one (Fig. 9).

Consequently the expression of the reaction rate can be written as:

r = k₁·c_A⁰·c_E1 (12) The integrated form of Equation (12), where concentration was expressed as a function of conversion and taking into account the value of the molar ratio between reactants becomes:

( )

1

ln 1 XA k t k w tR

- - = × = × × (13) Plot of –ln(1-X_A) versus time is a straight line passing through the origin, which confirms the validity of the model (Fig. 10).

First, the value of k₁ from the slope of the straight line was determined, and then k_R as a ratio between k₁ and w was calculated.

From the Arrhenius plot ln k_R versus 1/T (Fig. 11), the 0

0.1 0.2 0.3 0.4 0.5

0 2 4 6 8 10

Time (min) CA// (mol/L)

Figure 7. Concentration of absorbed acetic acid versus time.

0 0.2 0.4 0.6 0.8 1 1.2 1.4

0 2 4 6 8

Time (min)

Concentration (mol/L)

Figure 8. Change of the real concentration for acetic acid in time;

speed of agitation: 600 rpm; catalyst loading (112.5 kg m^-3); temperature 366 K, molar ratio acetic acid : ep- ichlorohydrin 1:10.

y = 1.067x - 2.1215 R² = 0.9915

-3.5 -3 -2.5 -2 -1.5 -1 -0.5 0

-0.8 -0.6 -0.4 -0.2 0

log (1-XA)

log dXA/dt

Figure 9. Determination of the overall reaction order by differential method.

0 0.5 1 1.5 2

0 50 100 150 200 250 300

Time (min)

- ln (1-XA)

Figure 10. Integrated form for the equation of reaction rate; molar ratio acetic acid: epichlorohydrin 1:1; speed of agita- tion 600 rpm; catalyst loading (112.5 kg m^-3); tempera- ture: ◊ 343K; ■ 348K; ▲ 353K; × 358K; ∆ 366K.

E.I. Muresan et al.

energy of activation and the preexponential factor were calculated. The value found for the energy of activation was 65.24 kJ mol^-1.

This high value confirms again that this process is intrinsically kinetically controlled.

4.2. Selectivity

The GC-MS analysis of the final reaction mixture confirmed that it contains unreacted acetic acid (t_r = 2.65-2.68), unreacted epichlorohydrin (t_r = 3.54-3.55), 3-chloro-2-hydroxypropyl acetate (t_r = 8.45-8.52), 2-chloro-1-(hydroxymethyl)ethyl acetate (t_r = 8.66-8.71), dichlorohydrin glycerine (t_r = 5.99-6.03), glycidyl acetate (t_r = 6.58-6.59) and a very small amount (less than 1%) of 1-chloro-3-[2- chloro-1-(chloromethyl)ethoxy]propan-2-ol (t_r = 9.7- 9.72), 3-chloro-2-(3-chloro-2-hydroxypropoxy) propyl acetate (t_r = 12.93-12.95), and 2-chloro-1-[(3-chloro-2-

hydroxypropoxy)methyl]ethyl acetate (t_r = 10.004-10.34) [t_r represents the retention time of reaction products (min)].

The ratio between the two isomers was found to be 84/16. Different results for this reaction were previously obtained by Belov using AV17 anion exchange resin as catalyst. He reported for the ratio between the two isomeric esters a value of 98/2 for chloride form of resin and 95/5 for acetate and hydroxide forms [14].

The variation in time for concentrations of reactants and products are shown in Fig. 12.

The results of the chromatographic analysis lead to the following conclusions regarding the reaction mechanism (Scheme 2):

(a)

(b)

(c)

(d)

(e)

Scheme 2. Possible reaction mechanisms.

y = -7.8471x + 7.622 R² = 0.9883 -15.6

-15.2 -14.8 -14.4 -14 -13.6

2.7 2.75 2.8 2.85 2.9 2.95

1/Tx10³ (K^-1)

ln kR

Figure 11. Arrhenius plot of lnk_R vs 1/T × 10³, K^-1.

0 1 2 3 4 5 6 7 8

0 50 100 150 200 250 300

Time (min)

Concentration (mol/L)

Figure 12. Concentration time profiles for reactants and products, molar ratio acetic acid: epichlorohydrin 1:1; speed of agitation 600 rpm; catalyst loading (112.5 kg m^-3);

temperature 366 K; ♦ acetic acid; □ epichlorohydrin;

■ 3-chloro-2-hydroxypropyl acetate; ∆ 2-chloro-1- (hydroxymethyl)ethyl acetate; ◊ dichlorohydrin glycer- ine; x glycidyl acetate; ● 3-chloro-2-(3-chloro-2-hydrox- ypropoxy)propyl acetate

425

Reaction (d) is a complex reaction which is assumed to proceed in two steps. In the first step, the dehydrochlorination of the normal ester under the action of acetate ion leads to formation of acetic acid and chloride ion. The second step proceeds with the addition of chloride ion to epichlorohydrin followed by rapid exchange of protons between acetic acid and alcoholate ion, with acetate ion being regenerated.

The reaction scheme seems to be well described by the following set of differential equations where the partial orders of reaction previously determined were taken into account:

The rate constants were determined by the least squared method, minimizing the sum of squares of differences between experimental points and the concentrations of reactants obtained by solving the set of differential equations. The values obtained for the constants of reaction rates are: k₁ = 0.0191 L mol^-1 min;

k₂ = 0.0190 L mol^-1 min; k₃ = 0.0051 L mol^-1 min;

k₄ = 0.0077 L² mol^-2 min; k_-4 = 0.1121 L² mol^-2 min;

k₅ = 0.0003 L² mol^-2 min. The relative average deviation of experimental reaction rates reported to the values of reaction rates calculated with Equations 14-20 is smaller than 5%, which confirms the validity of the proposed model.

5. Conclusions

The kinetics of the esterification reaction of acetic acid with epichlorohydrin catalysed by Purolite A-520E resin was studied. The effects of certain parameters, such as stirring speed, particle diameter, temperature, catalyst amount and molar ratio, were studied. Whereas mass transfer limitations are not observed, the temperature and the amount of catalyst exert a marked influence on reaction rate. The high value of activation energy confirms again that the rate controlling step is the surface reaction. The reaction follows first order kinetics with respect to both catalyst and epichlorohydrin, while the partial order of reaction with respect to acetic acid is zero. Based on determined reaction orders and taking into account the chromatographic results, a more detailed kinetic model was proposed.

Acknowledgements

The financial contribution to this work from Romanian Minister of Education and Research, program PNII, TD122/337-2007, is gratefully acknowledged.

3 1 2 3 3 3

CH COOH

ECH Cl ECH CH COO ECH CH COO

dc k c c k c c k c c

dt ^{- - -}

- = × × + × × + × × ⁽¹⁴⁾

1 2 3 3 3

4 3 4 3 5 3

ECH ECH Cl ECH CH COO ECH CH COO

CHPA ECH CH COO GA ECH CH COO CHPA ECH CH COO

dc k c c k c c k c c

dt

k c c c k c c c k c c c

- - -

- - - -

- = × × + × × + × ×

+ × × × - × × × + × × ×

(15)

2 3 4 3 4 3

5 3

CHPA ECH CH COO CHPA ECH CH COO GA GD CH COO

CHPA ECH CH COO

dc k c c k c c c k c c c

dt k c c c

- - -

-

= × × - × × × + - × × × -

- × × ×

(16)

3 3

CHEA ECH CH COO

dc k c c

dt = × × ^{- (17)}

1 4 3 4 3

GD ECH Cl CHPA ECH CH COO GA GD CH COO

dc k c c k c c c k c c c

dt = × × ^-+ × × × ^-- ^- × × × ^- (18)

- -

4 3 k-4 3

GA CHPA ECH CH COO GA GD CH COO

dc k c c c c c c

dt = × × × - × × × ⁽¹⁹⁾

5 3

PAE CHPA ECH CH COO

dc k c c c

dt = × × × ^{- (20)}

3 DG GA

CH COO

c -=c -c ⁽²¹⁾

Since both the acetate and chloride forms of the catalyst are active, the scheme has to be supplemented by the catalyst balance equation:

0catalyst CH COO3 Cl

c =c -+c - ⁽²²⁾

E.I. Muresan et al.

Nomenclature

a_p = liquid-solid external surface area per unit volume of liquid phase, m² m^-3

AE0

D , ^D0EA= infinite dilution diffusion coefficients, m² s^-1

C_A0 = initial concentration of acetic acid in bulk liquid phase, mol L^-1 C_E0 = initial concentration of epichlorohydrin in bulk liquid phase, mol L^-1 C_i = molar concentration of component i, mol L^-1

C_i0 = initial molar concentration of component i, mol L^-1

D_e,AE; D_e,EA = effective diffusivities inside the pores of the catalyst, m² s^-1 d_I = impeller diameter, m

D_AE, D_EA = molecular diffusion coefficients of concentrated system, m² s^-1 d_p = catalyst particle diameter, m

d_T = diameter of flask, m

e = energy supplied per unit mass of slurry by agitation, m² s^-3 Fc = shape factor, assumed to be unity for spherical particles g = acceleration due to gravity, m² s^-3

k₁ = pseudo-first order rate constant, min^-1 kads = constant of adsorption rate, g g^-1 min

K_i = adsorption equilibrium constant for species i, m³ mol^-1 k_R = second order rate constant, m³ kg^-1∙s

k_SL,A = liquid-solid mass transfer coefficient for acetic acid, m s^-1 k_SL,E = liquid-solid mass transfer coefficient for epichlorohydrin, m s^-1 L = total height of the slurry, m

M_A = molecular weight of acetic acid, kg mol^-1 M_E = molecular weight of epichlorohydrin, kg mol^-1 n = overall reaction order

N = stirring speed, Hz

n_A, n_E = partial order of reaction with respect to acetic acid and epichlorohydrin q_t = sorption capacity at time t, g g^-1

R = mean particle radius, m t = time, min

T = temperature, K

V = volume of acetic acid solution used in adsorption experiments, mL V_A = molar volume of acetic acid, m³ mol^-1

V_E = molar volume of epichlorohydrin, m³ mol^-1 V_L = liquid volume, m³

w = catalyst loading, kg m^-3 X_A = fractional conversion of A x_A= molar fraction of acetic acid x_{E =} molar fraction of epichlorohydrin ε = fractional porosity, dimensionless μ_A = acetic acid viscosity, kg m^-1 s μ_{E =} viscosity of epichlorohydrin_, kg m^-1 s μ_L= liquid viscosity, kg m^-1 s

ρ_L = liquid density, kg m^-3 ρp = density of particle, kg m^-3 τ = tortuosity factor, dimensionless

Ψ = correction factor for the presence of gas bubbles, dimensionless

427

References

[1] R.A. Kozlovskii, M.G. Makarov, V.F.Shvets and N.A.

Maksimova, Kinet. Catal., 41, 737 (2000)

[2] L.G. Shode, M.F. Sorokin and A.I. Kuzmin, Lakokras.

Mater I ikh prim., 4, 20 (1982)

[3] W. Bukowski, Org. Process Res. Dev., 6, 10 (2002) [4] A. Bukowska, A.K. Guskov, M.G. Makarov, E.

Rokaszewski and V.F. Svets, J. Chem. Technol.

Biot., 63, 379 (1995)

[5] A. Bukowska, A.K. Guskov, M.G. Makarov, E.

Rokaszewski and V.F. Svets, J. Chem. Technol.

Biot., 63, 374 (1995)

[6] M.F. Sorokin, L.G. Shode, A.I. Kuzmin, A. Novikova, V.A. Pekarski, L.A. Dobrovinski, M. Brusilovski, R.K.

Sidorova, and S.V. Vladimirov, Khim I khim Teknol., 27, 658 (1984)

[7] A. Bukowska, W. Bukowski and J. Noworol, J. Mol.

Catal. A: Chemical, 203, 95 (2003)

[8] A. Bukowska and W. Bukowski, J. Chem. Technol.

Biot., 74, 675 (1999)

[9] A. Bukowska and W. Bukowski, J. Chem. Technol.

Biot., 73, 341 (1998)

[10] S. Oprea, E. Dumitriu, L. Stefanel, Rev. Roum.

Chim., 25, 1039 (1980)

[11] P.S. Belov, N.S. Baraj and C.D. Korenev, Izvestia VUZ-ov, Khimia i Khim. Technol., 26, 668 (1983) [12] V.A. Podgornova, N.F. Orehova, B.F. Ustavshchik-

ov, V.D. Koryolova, V.B. Kargman and N.B. Galits- kaya, Osnovy Org.Sintez Neftekhim., 2, 89 (1975) [13] E. Dumitriu, S. Oprea, M. Dima and S. Avramescu,

Rev. Chim. (Bucharest), 32, 225 (1981)

[14] P.C. Belov, K.D. Korenev, I.S. Baraj, Izvestia VUZ- ov.Khimia i Khim. Ttechnol., 25, 31 (1982)

[15] E.I. Muresan, S. Oprea, T. Malutan, M. Vata, CEJC, 5, 715 (2007)

[16] R.Jay, Anal. Chem., 36, 667 (1964)

[17] T.N. Zewtering , Chem. Eng. Sci., 8, 244 (1958), [18] H.S. Fogler, Elements of Chemical Reaction Engi-

neering (Prentice-Hall India, New Delhi, 1995) [19] Y. Sano, N. Yamaguchi and T .Adachi, J. Chem.

Eng. Japan, 7, 255 (1974)

[20] P. H Calderbank, Trans. Inst. Chem. Eng, 36, 443 (1958).

[21] J. Leffler, H.T. Cullinan, Ind. Eng. Chem. Fund., 9, 84 (1970)

[22] C.R. Wilke, P. Chang, A.I.Ch.E.J., 1, 264 (1955)