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Kinetics of the Epoxidation of Castor Oil with Peracetic Acid Formed in Situ in the Presence of an Ion-Exchange Resin Milovan R. Janković, Snežana V. Sinadinović-Fišer,* and Olga M. Govedarica Faculty of Technology, University of Novi Sad, Bul. cara Lazara 1, 21000 Novi Sad, R. Serbia ABSTRACT: The kinetics of the epoxidation of castor oil in benzene with peracetic acid formed in situ from acetic acid and hydrogen peroxide in the presence of an ion-exchange resin as a catalyst was studied. Eighteen pseudo-two-phase models are established that, besides the main reactions of peracid and epoxy ring formation, also consider the side reaction of epoxy ring cleavage with acetic acid. Kinetic expressions for the heterogeneously catalyzed peracetic acid formation are developed on the basis of Eley−Rideal and Langmuir−Hinshelwood−Hougen−Watson postulates. An equation derived for the temperature dependency of the chemical equilibrium constant for peracetic acid formation is applied. Kinetic and adsorption parameters were estimated by fitting experimental data using the Marquardt method. The best-fit model correctly interprets data of double bond and epoxy group contents as a function of reactant ratios, catalyst concentrations, and temperatures applied during epoxidation. The proposed model better fits experimental data than the pseudohomogeneous model reported in the literature.

1. INTRODUCTION Castor oil is a natural polyol because ∼90% of the fatty acid chains in its triglycerides are monounsaturated hydroxy C18 acid chains, namely 12-hydroxy-9-octadecenoic acid, i.e., ricinoleic acid. This oil is used as a polyol component in polyurethane production.1 However, a more cross-linked polyurethane network may be formed by introducing additional hydroxy groups into fatty acid chains of castor oil prior to polycondensation. That can be achieved via epoxidation of castor oil triglyceride’s double bonds followed by the transformation of epoxy groups to hydroxy groups. The epoxidation of vegetable oils with percarboxylic acid generated in situ involves the acid-catalyzed percarboxylic acid formation in the water phase, the uncatalyzed epoxy group formation in the oil phase, and a few side reactions of acidcatalyzed epoxy ring cleavage. The percaboxylic acid is formed from hydrogen peroxide in an aqueous solution and a corresponding carboxylic acid, usually acetic acid. A mineral acid, mainly sulfuric acid, or an acidic ion-exchange resin can be used as a catalyst. This process is significantly influenced by reaction variables; thus, it is necessary to establish a kinetic model for its optimization. When an ion-exchange resin is used as the catalyst, the reaction system for epoxidation of vegetable oil is a three-phase, i.e., liquid−liquid−solid (oil−water−resin), system. Because of the complexity of developing a rigorous mathematical model describing such a system that must include kinetic and thermodynamic, as well as mass transfer, parameters, different simplifications can be found in the literature. The first kinetic model was based on an assumption of homogeneity of the epoxidation reaction system.2 Although their inadequacy was discussed,3 pseudohomogeneous models are still being used.4−6 The first pseudo-two-phase liquid−solid model for vegetable oil epoxidation in the presence of an ionexchange resin as a catalyst was developed in 2001.7 Besides the main reactions of peracetic acid and epoxy compound formation, the model takes into consideration two epoxy ring opening reactions, with water and acetic acid. The kinetics of this heterogeneous catalytic process is described on the basis of © 2014 American Chemical Society

Langmuir−Hinshelwood−Hougen−Watson postulates. The developed model was applied originally to experimental data for soybean oil epoxidation and later for mahua,8 karanja,9 jatropha,10 and cotton11 oil epoxidation. In these cases, all model parameters were determined simultaneously by fitting the experimental data for the variation of component concentrations with reaction time. However, the fact that such experimental data are inconvenient for the determination of the chemical equilibrium constant for peracetic acid formation was discussed, because the equilibrium of this reaction is shifted to the right due to the constant consumption of peracetic acid in the epoxidation reaction. Therefore, some model parameters should be determined either using expressions derived by correlating data of experiments designed for particular phenomena or using expressions derived semitheoretically or theoretically.12−15 Thus, a few authors who investigated peracetic acid formation separately from the epoxidation process reported the dependency of this reaction’s chemical equilibrium constant on temperature.12,16−20 In this work, in established pseudo-two-phase (liquid−solid) models for the epoxidation of castor oil in benzene with peracetic acid generated in situ from acetic acid and hydrogen peroxide in the presence of an acidic ion-exchange resin as a catalyst, an expression for the temperature dependency of the chemical equilibrium constant for peracetic acid formation in an aqueous solution, derived on the basis of the van’t Hoff and Kichoff equations, is used. Kinetic expressions for heterogeneously catalyzed peracetic acid formation were developed by applying Eley−Rideal and Langmuir−Hinshelwood−Hougen− Watson postulates. The models take into consideration the occurrence of the reactions during the incremental addition of reactants. Experimental data obtained for epoxidation of castor Received: Revised: Accepted: Published: 9357

February 28, 2014 May 7, 2014 May 9, 2014 May 9, 2014 dx.doi.org/10.1021/ie500876a | Ind. Eng. Chem. Res. 2014, 53, 9357−9364

Industrial & Engineering Chemistry Research

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evaporated at 333 K under 3.0−4.0 kPa to remove benzene, water, and ether. The sample was then analyzed for iodine number (IN) and epoxy oxygen content (EO). 2.3. Analytical Methods. The oil phase of each sample was analyzed in triplicate to determine the iodine number and epoxy oxygen content according to the Hanush and the standard HBr−acetic acid methods.21

oil were used to test the models that, besides the main reactions, involve the side reaction of epoxy ring cleavage with acetic acid. Among 18 proposed models, the best-fit model was chosen on the basis of the smallest deviation between the calculated and experimentally determined values of double bond and epoxy group concentrations. The accepted model was compared with one of the pseudohomogeneous models reported in the literature.

3. KINETIC MODEL Epoxidation of vegetable oil with peracetic acid (P) generated in situ in the presence of an ion-exchange resin is a heterogeneous catalytic process in which the formation of peracid from acetic acid (A) and hydrogen peroxide (H) in an aqueous solution is acid-catalyzed (reaction I in Figure 1). Peracetic acid diffuses through the water (W) to the oil phase where it spontaneously reacts with the double bond (D) of the oil triglyceride forming an epoxy ring (E) (reaction II). Because of the continuous consumption, by epoxidation, the concentration of peracetic acid in the system is low; thus, its decomposition is negligible. Among the few side reactions, the selectivity of the epoxidation is mainly reduced by the acid-catalyzed reaction of the epoxy ring with acetic acid, which yields hydroxyl acetate (HA) (reaction III).22−24 In this work, the reaction system of epoxidation of castor oil is considered as a pseudo-two-phase liquid−solid system. The presence of a large amount of benzene in the reaction mixture reduces the viscosity of the oil phase. Therefore, under intense stirring, an effective mixing is achieved and a mass diffusion resistance can be neglected; consequently, the parameters related to the mass transfer phenomenon are omitted from the model. If only reactions I−III occur during the epoxidation, the whole process may be described with the following system of first-order differential equations:

2. EXPERIMENTAL SECTION 2.1. Chemicals. Castor oil was kindly provided by Hemiprodukt (Novi Sad, R. Serbia). Glacial acetic acid (>99.5%), benzene, diethyl ether, and a 30 wt % aqueous hydrogen peroxide solution were purchased from J. T. Baker. Anhydrous sodium sulfate was bought from Fluka, Chemie GmbH. An acid form of sulfonated polystyrene-type cationexchange resin Amberlite IR-120 from Rohm and Hass Co. (Philadelphia, PA) was used as a catalyst. 2.2. Epoxidation Procedure. Castor oil was epoxidized with peracetic acid formed in situ according to a method reported in detail in the literature.6 Equal masses of oil and benzene and appropriate masses of glacial acetic acid and an ion-exchange resin were loaded in the reactor, a 500 mL threeneck round-bottom flask. The reactor equipped with a magnetic stirrer, a thermometer, and a reflux condenser was placed in a water bath. To avoid an uncontrolled increase in temperature, a 30% aqueous hydrogen peroxide solution was gradually charged into the reaction mixture at a constant rate over the course of 1 h. The reaction conditions for all runs are listed in Table 1. Table 1. Reaction Conditions Related to the Epoxidation of Castor Oil in Benzene with Peracetic Acid Formed in Situ from Acetic Acid (A) and Hydrogen Peroxide (H) in the Presence of an Ion-Exchange Resin Used as a Catalyst temp (K) run

Da:A:H molar ratio

1 2 3 4 5 6

1:0.5:1.1 1:0.5:1.5 1:0.5:1.5 1:0.5:1.5 1:0.5:1.5 1:0.5:1.5

Amberlite (wt %)b 2.48 3.21 6.43 9.64 6.43 6.43

(5) (5) (10) (15) (10) (10)

H addition

reaction

323 323 323 323 323 303

323 323 323 323 348 303

a

The initial iodine number of the castor oil of 81.5 corresponds to 0.321 mol of double bonds (D) per 100 g of oil. bCatalyst concentration expressed as a percentage of oil weight and, in parentheses, as a percentage of acetic acid and hydrogen peroxide weight.

The beginning of the addition of the hydrogen peroxide solution was considered to be the “zero reaction time”. The temperature of hydrogen peroxide addition was 323 K, except as noted in Table 1. After addition, where applicable, the temperature of reaction mixture was increased to the reaction temperature at a uniform rate over the course of 1 h. The fluctuation of the reaction temperature, as well as of the hydrogen peroxide addition temperature, was less than ±1 K. The reaction mixture was continuously stirred at 1500 rpm. At defined time intervals, 10 mL samples of the reaction mixture were taken for determination of the extent of epoxidation. Each sample was filtered to remove the catalyst, quenched, and centrifuged. The oil phase of the sample was dissolved in diethyl ether, washed with distilled water (308 K) until the pH reached 7, and dried with anhydrous Na2SO4. Further, it was

⎛ d[H] ⎞ d[H] ⎟ = FH + ⎜ ⎝ dt ⎠1 dt

(1)

d[A] ⎛ d[H] ⎞ ⎟ + k 2[P][D] − k 3[E][A]n =⎜ ⎝ dt ⎠1 dt

(2)

⎛ d[H] ⎞ d[P] ⎟ − k 2[P][D] = −⎜ ⎝ dt ⎠1 dt

(3)

⎛ d[H] ⎞ d[W] ⎟ = FW − ⎜ ⎝ dt ⎠1 dt

(4)

d[D] = −k 2[P][D] dt

(5)

d[E] = k 2[P][D] − k 3[E][A]n dt

(6)

d[HA] = k 3[E][A]n dt

(7)

where brackets denote the concentration of a compound or functional group in moles per 100 g of oil. The double bond concentration is determined with the equation [D] = IN/(2AI), where AI is the atomic mass of iodine, while the epoxy group concentration is calculated with the equation [E] = EO/ (100AO), where AO is the atomic mass of oxygen. t (minutes) is the reaction time. FH (moles per minute per 100 g of oil) and FW (moles per minute per 100 g of oil) are the molar flows of 9358

dx.doi.org/10.1021/ie500876a | Ind. Eng. Chem. Res. 2014, 53, 9357−9364


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Table 2. Assumptions Made in Modeling the Kinetics of Peracetic Acid Formation on the Basis of Eley−Rideal or Langmuir−Hinshelwood−Hougen−Watson Postulates chemisorptionb

Figure 1. Reaction system of vegetable oil epoxidation with peracetic acid generated in situ. Main reactions of peracetic acid (reaction I) and epoxy ring (reaction II) formation and the predominant side reaction of epoxy ring cleavage with acetic acid (reaction III).

hydrogen peroxide and water addition, respectively. (d[H]/dt)1 (moles per minute per 100 g of oil) is the rate of hydrogen peroxide consumption in reaction I. k2 (100 g of oil per mole per minute) and k3 [(100 g of oil)n/(mol·min)n] are the rate coefficients of reactions II and III, respectively. n is the order of reaction III with respect to acetic acid. Dropwise addition of the hydrogen peroxide solution to the reaction mixture is approximated with continuous flows of hydrogen peroxide (FH) and water (FW): mHSwH t ≤ t HS F = MHt HS t > t HS

FW =

A, A, A, A, A, A, A, A, A,

P H H, H, H, P H, P H,

rate-determining step

P W P, W P, W P, W

adsorption of A adsorption of A adsorption of A adsorption of A adsorption of A desorption of P desorption of P surface reaction surface reaction

[(kinetic factor)(driving force group)]/(adsorption group) (10)

and they comprise kinetic, thermodynamic, and chemisorption parameters. Depending on an assumed rate-determining step, the expression for the “kinetic factor” includes a rate coefficient either for the adsorption of the reactant or product or for the surface reaction. The temperature dependency of these rate coefficients, as well as of the rate coefficients for reactions II and III, is described by the Arrhenius equation. To avoid a strong correlation between its parameters, a reparameterized form of this equation is used:

(8)

t > t HS

aAP aAH aAHP aAHW aAHPW dAP dAHPW rAP rAHPW

For the notation of the models, the first letter indicates the ratedetermining step for peracetic acid formation, where “a” is the adsorption of acetic acid, “d” is the desorption of peracetic acid, and “r” is the surface chemical reaction, and uppercase letters are symbols for chemisorbed compounds. bSteps of chemisorption, i.e., adsorption, surface reaction, and desorption, are considered reversible. cAssociative adsorption is assumed.

mHS(1 − wH) t ≤ t HS MW t HS 0

adsorptionc

a

H

0

modela

(9)

where mHS (grams per 100 g of oil) is the mass of the hydrogen peroxide aqueous solution, wH is the mass fraction of hydrogen peroxide in its aqueous solution, MH and MW are molecular masses of hydrogen peroxide and water, respectively, and tHS (minutes) is the period of addition of the hydrogen peroxide solution.6 Of those occurring during the epoxidation process, reactions of epoxy ring (reaction II) and hydroxyl acetate (reaction III) formation are considered homogeneous and pseudohomogeneous, respectively, while peracetic acid formation (reaction I) is considered heterogeneous. To establish a mathematical model for the rate of hydrogen peroxide consumption in peracetic acid formation (d[H]/dt)1, Eley−Rideal (ER) or Lagmuir− Hinshelwood−Hougen−Watson (LHHW) approaches are applied to describe a chemisorption of this heterogeneous catalytic reaction. The reaction proceeds on active sites of the catalyst in three steps: (i) adsorption of at least one of the reactants onto the active site, (ii) surface chemical reaction between adsorbed molecules or between adsorbed and nonadsorbed reactant, and (iii) desorption of the products. Nine models were established assuming that different reactants and products are chemisorbed on the catalyst surface and that different steps control the overall reaction rate. In all models, the adsorption is considered associative, and adsorption, surface reaction, and desorption are thought to be reversible. The order of the surface reaction is considered as the first with respect to both reactants. In Table 2 are listed assumptions made in developing the models. Kinetic equations derived according to ER and LHHW postulates have the following general form:

⎡ ki , Ea ⎛ 1 1 ⎞⎤ ki = exp⎢ki ,0 − ⎜ − ⎟⎥ ⎢⎣ R ⎝T Ta ⎠⎥⎦

(11)

where ki is the rate coefficient for reaction i (ka,C, adsorption of component C; k1,sr, surface reaction related to reaction I; k2, reaction II; k3, reaction III). ki,0 and ki,Ea are constants related to the frequency coefficient and the activation energy, respectively. R is the universal gas constant (8.3143 J mol−1 K−1); T (kelvin) is the temperature, and Ta (kelvin) is the average temperature of the runs (accepted as 323 K). “Driving force group” in eq 10 indicates a displacement from the chemical equilibrium. The equation derived for the temperature dependency of the chemical equilibrium constant for peracetic acid formation, K1, in an aqueous solution is applied:12 K1 = exp(12.2324 ln T − 0.0229913T + 9.70452 × 10−6T 2 + 3045.76/T − 72.8758)

(12)

“Adsorption group” in eq 10 denotes a decrease in the overall reaction rate due to occupation of catalytic active sites by chemisorbed compounds. The adsorption equilibrium constant for component C, KC, defined as the ratio of adsorption and desorption rate coefficients, is also presented as a reparameterized Arrhenius type of temperature dependency (eq 11). By introducing the expression for (d[H]/dt)1, derived on the basis of ER or LHHW postulates, into the system of differential 9359



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Table 3. Comparison of the Numbers of Model Parameters, Discrimination Results, and Statistical Values of the Model Parameters Determined for Pseudo-Two-Phase and Pseudohomogeneous Models of the Reaction System for Castor Oil Epoxidation in Benzene with Peracetic Acid Formed in Situ in the Presence of Amberlite IR-120 as a Catalyst modela

no. of model parameters

aAP1 aAP2 aAH1 aAH2 aAHP1 aAHP2 aAHW1 aAHW2 aAHPW1 aAHPW2 dAP1 dAP2 dAHPW1 dAHPW2 rAP1 rAP2 rAHPW1 rAHPW2

10 10 10 10 12 12 12 12 14 14 10 10 14 14 10 10 14 14

ref 6

6

ki temperature profileb

F

Pseudo-Two-Phase Model correct 0.012516 correct 0.012181 k2 incorrect 0.012147 correct 0.012011 k2 incorrect 0.011547 correct 0.011839 correct 0.011425 correct 0.011719 correct 0.011358 correct 0.011610 k2 incorrect 0.021124 k2 incorrect 0.020140 k2 incorrect 0.015873 k2 incorrect 0.014774 correct 0.025211 correct 0.030974 correct 0.016803 k2 incorrect 0.016599 Pseudohomogeneous Model correct 0.031620

SDc

AAD[D]d

AAD[E]e

0.010571 0.010429 0.010414 0.010356 0.010154 0.010281 0.010100 0.010229 0.010070 0.010181 0.013733 0.013410 0.011905 0.011485 0.015003 0.016630 0.012249 0.012174

0.00886 0.00887 0.00874 0.00890 0.00862 0.00879 0.00849 0.00870 0.00849 0.00866 0.01275 0.01293 0.01019 0.01000 0.01343 0.01480 0.01164 0.01193

0.00653 0.00677 0.00649 0.00691 0.00623 0.00670 0.00612 0.00658 0.00606 0.00653 0.00820 0.00754 0.00672 0.00678 0.00847 0.00908 0.00797 0.00778

0.016802

0.01495

0.00916

a

The notation of models is done by adding a digit that indicates the order of hydroxyl acetate formation with respect to acetic acid at the end of the notation for the corresponding chemisorption model of the peracetic acid formation reaction. bModels in which any of the kinetic constants 1/2 d (ki) decreased with an increase in temperature were eliminated. cStandard deviation: SD = [F/(2∑NR k=1NSk)] . Average absolute deviation NR NR NSk calc exp e for double bond concentration: AAD[D] = 1/(∑k=1NSk)∑k=1∑l=1 |[D]k,l − [D]k,l |. Average absolute deviation for epoxy group concentration: NR NSk calc exp AAD[E] = 1/(∑NR k=1NSk)∑k=1∑l=1 |[E]k,l − [E]k,l |.

eqs 1−7 and by assuming the first or the second order of hydroxyl acetate formation with respect to acetic acid, we established 18 mathematical models for the reaction system of vegetable oil epoxidation (Table 3).

4. RESULTS AND DISCUSSION The time dependencies of experimentally determined values of iodine number and epoxy oxygen content for castor oil epoxidation in benzene with peracetic acid formed in situ from acetic acid and hydrogen peroxide, in the presence of Amberlite IR-120 as a catalyst, are shown as points in Figures 2−4. The initial iodine number of the castor oil was measured as 81.5, meaning 0.321 mol of double bond per 100 g of oil. Discussion related to the influence of reaction conditions on the conversion of double bonds, relative epoxy yield, and selectivity of epoxidation is detailed in previous work.6 The variations of double bond [D] and epoxy group [E] concentrations with reaction time, calculated on the basis of experimentally determined iodine number and epoxy oxygen content, were used to determine the model parameters. The following objective function F was minimized using the Marquardt algorithm:25 NR NSk

F=

∑ ∑ [([D]kcalc,l

Figure 2. Time dependency of the experimentally determined (points) and calculated (curves) iodine number (IN) and epoxy oxygen content (EO) for castor oil epoxidation in benzene with peracetic acid formed in situ, at 323 K in the presence of 10 wt % Amberlite IR-120, when the double bond (D) in oil:acetic acid (A):30 wt % hydrogen peroxide (H) molar ratio was 1:0.5:1.1 and 1:0.5:1.5.

exp 2 2 calc − [D]kexp , l ) + ([E]k , l − [E]k , l ) ]

end of the incremental addition of the oxidizing agent as the zero reaction time, the occurrence of the epoxidation reactions during that period is not neglected in established models. The addition of the hydrogen peroxide solution is described with molar flows of hydrogen peroxide and water. Additionally, the direct determination of constants in the Arrhenius type temperature dependency of kinetic and adsorption parameters (eq 11), when fitting the experimental data, allowed the

k=1 l=1

(13)

where NR is the number of runs and NSk is the number of samples in run k. Superscripts calc and exp indicate calculated and experimentally determined values, respectively. Unlike in pseudo-two-phase models reported in the literature,7−11 by considering the beginning instead of the 9360



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work, the increase in temperature from that at which the hydrogen peroxide solution is added to the reaction mixture to the reaction temperature was approximated with the following linear function of reaction time:

consideration of the difference in hydrogen peroxide addition and reaction temperature. However, as just mass balances are included, the developed mathematical models are applicable when the temperature is defined over the reaction time. In this THS T=

THS +

t ≤ t HS

Tr − THS (t HS + t TI − t ) t HS < t ≤ t HS + t TI t TI Tr

t HS + t TI < t ka,H

where THS (kelvin) is the temperature of hydrogen peroxide addition, Tr (kelvin) is the temperature of the reaction, and tTI (minutes) is the period of temperature increase. Also, the direct determination of constants related to frequency factor and activation energy makes possible the fitting of an experimental data set obtained for epoxidations conducted at different reaction temperatures. The chemical equilibrium constant for peracetic acid formation was the subject of a few studies. In some works, only experimental values were determined,16,17 while in others, the expression for the temperature dependency of the constant was developed.12,19,20 Except in one case,16 the values of the chemical equilibrium constant decrease with an increase in temperature. Also, the values are on the same order of magnitude in the investigated temperature ranges.12,17−20 Thus, in this work, eq 12 developed by Janković et al.12 was selected to calculate the chemical equilibrium constant. The system of differential eqs 1−7 was integrated by a fourth-order Runge−Kutta method. 4.1. Model Selection and Kinetic Parameter Determination. Once the experimental data had been fit, the pseudotwo-phase models were discriminated if estimated values of their parameters or calculated results were nonviable. The models in which any of the rate coefficients (ki) decreased with an increase in temperature were eliminated. For each of 11 noneliminated models, the calculated values of the concentration of all reactants and products were found to be positive. Among these models, aAHPW1 was chosen as the best because of the lowest least sum of squares, F, of 0.011358. In Table 3 are listed the numbers of model parameters and discrimination results, as well as the least sums of squares (objective function F) calculated by eq 13, the standard deviations (SD), and the average absolute deviations for double bond concentration (AAD[D]) and epoxy group concentration (AAD[E]) for established models. In accepted pseudo-two-phase kinetic model aAHPW1, adsorption of acetic acid, hydrogen peroxide, peracetic acid, and water is assumed. The order of hydroxyl acetate formation is considered as the first with respect to acetic acid. Besides the associative adsorption, the reversibility of the adsorption of reactants and desorption of products, as well as of the dual site surface chemical reaction between acetic acid and hydrogen peroxide, is accepted. The adsorption of acetic acid is thought to be the rate-determining step. Thus, the chemisorption mechanism of peracetic acid formation can be presented by the following equations:

H + s XoooY H·s kd,H

kd,A

(16)

k1,sr

A·s + H·s XooooY P ·s + W·s k −1,sr

(17)

kd,P

P ·s XoooY P + s ka,P

(18)

kd,W

W·s XoooY W + s ka,W

(19)

where s is an active site of the catalyst and k−1,sr indicates the rate coefficient for the reverse surface reaction related to reaction I. The corresponding (d[H]/dt)1 expression for model aAHPW1 is as follows: ⎡ ⎛ ⎛ d[H] ⎞ [P][W] ⎞⎤ ⎜ ⎟ = − ⎢mCska,A ⎜[A] − ⎟⎥ ⎝ dt ⎠1 K1[H] ⎠⎥⎦ ⎝ ⎣⎢ ⎛ ⎞ K [P][W] ⎜⎜1 + A + KH[H] + KP[P] + KW [W]⎟⎟ K1[H] ⎝ ⎠ (20)

where m (grams) is the mass of the catalyst and Cs (moles per gram of catalyst) indicates the concentration of catalytically active sites. According to eq 12, the values of the chemical equilibrium constant for peracetic acid formation were calculated as 2.701, 2.258, and 1.891 at 303, 323, and 348 K, respectively; i.e., values of K1 decrease with an increase in temperature. By fitting the experimental data with the accepted aAHPW1 model, we determined the temperature dependencies of the rate coefficient for acetic acid adsorption, rate coefficients for reactions II and III, and adsorption equilibrium constants for acetic acid, hydrogen peroxide, peracetic acid, and water as follows:

ka,A

A + s XoooY A·s

(14)

(15) 9361

⎡ 220417.3 ⎛ 1 1 ⎞⎤ ⎜ ⎟⎥ Cska,A = exp⎢2.007861 − − ⎝T ⎣ R 323 ⎠⎦

(21)

⎡ 3524.043 ⎛ 1 1 ⎞⎤ ⎜ ⎟⎥ k 2 = exp⎢ −1.403134 − − ⎝T ⎣ R 323 ⎠⎦

(22)

⎡ 10566.0 ⎛ 1 1 ⎞⎤ ⎜ ⎟⎥ k 3 = exp⎢ −5.389409 − − ⎝ ⎣ R T 323 ⎠⎦

(23)

⎡ 89489.52 ⎛ 1 1 ⎞⎤ ⎜ ⎟⎥ KA = exp⎢10.34923 − − ⎝ ⎣ R T 323 ⎠⎦

(24)



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basis of double bond and epoxy group concentrations, respectively, estimated with model aAHPW1, are presented as curves in Figures 2−4. As shown, the proposed pseudo-twophase model fits well the corresponding experimental values (points) measured during epoxidation of castor oil in benzene with peracetic acid generated in situ in the presence of Amberlite IR-120 at different reactant ratios, catalyst concentrations, and temperatures (Table 1). 4.2. Comparison of the Proposed Pseudo-Two-Phase Model with the Pseudohomogeneous Model Reported in the Literature. The experimental data obtained for epoxidations of castor oil in benzene with peracetic acid formed in situ from acetic acid and a 30% aqueous hydrogen peroxide solution in the presence of Amberlite IR-120, run under defined reaction conditions (Table 1), were fit by a pseudo-two-phase model proposed in this work and by a pseudohomogeneous model reported in the literature.6 Like in the accepted pseudo-two-phase aAHPW1 model, in the pseudohomogeneous model the kinetic parameters are temperature-dependent and the beginning of the addition of hydrogen peroxide to the reaction mixture is considered as the zero reaction time. The same expression that correlates the chemical equilibrium constant and temperature is used. In the latter model, the epoxy ring opening reaction with acetic acid is considered as the second-order reaction, while in the aAHPW1 model, it is considered as the first-order reaction, in both cases with respect to acetic acid. The least sum of squares of 0.011358 obtained for the model proposed in this work, which is >2.5 times lower than the value of 0.031620 obtained for the pseudohomogeneous model (Table 3), indicates that the pseudo-two-phase model better describes the reaction system for epoxidation of castor oil conducted under the investigated conditions. In Figure 5 are illustrated the variations of the

Figure 3. Time dependency of the experimentally determined (points) and calculated (curves) iodine number (IN) and epoxy oxygen content (EO) for castor oil epoxidation in benzene with peracetic acid formed in situ, when the double bond in oil:acetic acid:30 wt % hydrogen peroxide molar ratio was 1:0.5:1.5, at 323 K in the presence of 5, 10, and 15 wt % Amberlite IR-120.

Figure 4. Time dependency of the experimentally determined (points) and calculated (curves) iodine number (IN) and epoxy oxygen content (EO) for castor oil epoxidation with peracetic acid formed in situ, when the double bond in oil:acetic acid:30 wt % hydrogen peroxide molar ratio was 1:0.5:1.5, in the presence of 10 wt % Amberlite IR-120 at 303, 323, and 348 K.

⎡ 213104.1 ⎛ 1 1 ⎞⎤ ⎜ ⎟⎥ KH = exp⎢0.7595751 + − ⎝ ⎣ R T 323 ⎠⎦

(25)

⎡ 132215.0 ⎛ 1 1 ⎞⎤ ⎜ ⎟⎥ KP = exp⎢8.022979 − − ⎝T ⎣ R 323 ⎠⎦

(26)

⎡ 155250.8 ⎛ 1 1 ⎞⎤ ⎜ ⎟⎥ KW = exp⎢6.954228 − − ⎝T ⎣ R 323 ⎠⎦

(27)

Figure 5. Comparison between the experimentally determined (points) values of the iodine number (IN) and epoxy oxygen (EO) content and the corresponding values calculated with the pseudohomogeneous (···) model and the pseudo-two-phase () model proposed in this work, for the in situ epoxidation of castor oil with peracetic acid conducted in benzene at 323 K with a double bond in oil:acetic acid:hydrogen peroxide ratio of 1:0.5:1.5 in the presence of 15 wt % Amberlite IR-120.

An increase in all reaction rate coefficients with an increase in temperature proved the correctness of the determined dependences. Obtained positive values of all calculated reactant and product concentrations additionally confirmed the viability of the accepted kinetic model. The variations in iodine number and epoxy oxygen content with reaction time, calculated on the

experimentally determined values (points) as well as the values calculated with pseudohomogeneous (dotted curve) and pseudotwo-phase (solid curve) models of the iodine number and epoxy oxygen content over time during the epoxidation of castor oil 9362



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FW = molar flow of addition of water [mol min−1 (100 g of oil)−1] H = hydrogen peroxide [H] = hydrogen peroxide concentration (mol/100 g of oil) HA = hydroxy acetate [HA] = hydroxy acetate concentration (mol/100 g of oil) IN = iodine number (g of iodine/100 g of oil) K1 = chemical equilibrium constant for reaction I KC = adsorption equilibrium constant for component C ki = rate coefficient for reaction i ka,C = rate coefficient for adsorption of component C kd,C = rate coefficient for desorption of component C k1,sr = rate coefficient for surface reaction related to reaction I ki,0 = constant of the reparameterized Arrhenius equation related to the frequency coefficient ki,Ea = constant of the reparameterized Arrhenius equation related to activation energy LHHW = Langmuir−Hinshelwood−Hougen−Watson MC = molecular mass of component C m = mass of the catalyst (g) mHS = mass of the hydrogen peroxide aqueous solution (g) NR = number of runs NSk = number of samples in run k P = peracetic acid [P] = peracetic acid concentration (mol/100 g of oil) R = universal gas constant (J mol−1 K−1) SD = standard deviation s = active site of the catalyst T = temperature (K) Ta = average temperature of runs (K) THS = temperature of hydrogen peroxide addition (K) Tr = temperature of the reaction (K) t = reaction time (min) tHS = period of addition of the hydrogen peroxide aqueous solution (min) tTI = period of temperature increase (min) W = water [W] = water concentration (mol/100 g of oil) wH = mass fraction of hydrogen peroxide in its aqueous solution

(performed at 323 K with 0.5 mol of acetic acid and 1.5 mol of a 30% aqueous hydrogen peroxide solution per mole of double bond in oil in the presence of 15 wt % Amberlite IR-120 as a catalyst) when the relative epoxy yield of 78.32%, the highest compared to yields obtained under other examined conditions,6 was achieved.

5. CONCLUSIONS A pseudo-two-phase kinetic model for the epoxidation of vegetable oil in an organic solvent with a perorganic acid generated in situ from an organic acid and hydrogen peroxide in the presence of an acidic ion-exchange resin, used as a catalyst, was established assuming that only perorganic acid formation is heterogeneously catalyzed. To describe the kinetics of the latter reaction, Langmuir−Hinshelwood−Hougen−Watson postulates were applied. The model took into consideration the occurrence of the reactions during incremental addition of the oxidizing agent solution, as well as defined temperature changes over time during the epoxidation process. The variation in temperature of the chemical equilibrium constant for peracetic acid formation is defined by applying the derived expression. The temperature dependencies of the kinetic and adsorption parameters were obtained simultaneously by fitting the experimentally determined values of double bond and epoxy group contents. An increase in all reaction rate coefficients with an increase in temperature and low square deviation of the calculated and experimental values of double bond and epoxy group concentrations indicated the correctness of the developed kinetic model. A comparison was made between the model proposed in this work and a pseudohomogeneous model reported in the literature. The application of a more rigorous pseudo-two-phase model was recommended.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: ssfi[email protected]. Telephone: +381 (021) 485 3748. Fax: +381 (021) 450 413. Notes

The authors declare no competing financial interest.

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Subscript

ACKNOWLEDGMENTS This work is part of Project III45022 financially supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia.

A = acetic acid a = adsorption C = component d = desorption H = hydrogen peroxide P = peracetic acid sr = surface reaction W = water

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NOMENCLATURE A = acetic acid [A] = acetic acid concentration (mol/100 g of oil) AI = atomic mass of iodine AO = atomic mass of oxygen AAD = average absolute deviation Cs = concentration of catalytically active sites (mol/g of catalyst) D = double bond [D] = double bond concentration (mol/100 g of oil) E = epoxy group, i.e., ring [E] = epoxy group concentration (mol/100 g of oil) EO = epoxy oxygen content (wt %) ER = Eley−Rideal F = objective function FH = molar flow of addition of hydrogen peroxide [mol min−1 (100 g of oil)−1]

Superscript

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calc = calculated value exp = experimentally determined value n = order of reaction

REFERENCES

(1) Petrović, Z. S. Polyurethanes from Vegetable Oils. Polym. Rev. 2008, 48, 109. (2) Wisniak, J.; Navarrete, E. Epoxidation of Fish Oil: Kinetic and Optimization Model. Ind. Eng. Chem. Prod. Res. Dev. 1970, 9, 33. (3) Janković, M.; Sinadinović-Fišer, S. Kinetic Models of Reaction Systems for the in situ Epoxidation of Unsaturated Fatty Acid Esters and Triglycerides. Hem. Ind. 2004, 58, 569.

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(4) Goud, V. V.; Patwardhan, A. V.; Pradhan, N. C. Strongly Acidic Cation Exchange Resin of Sulphonated Polystyrene Type used as Catalyst for Epoxidation of Castor Oil with Peracetic Acid and Performic Acid. Solid State Sci. Technol. 2006, 14, 62. (5) Cai, C.; Dai, H.; Chen, R.; Su, C.; Xu, X.; Zhang, S.; Yang, L. Studies on the Kinetics of in situ Epoxidation of Vegetable Oils. Eur. J. Lipid Sci. Technol. 2008, 110, 341. (6) Sinadinović-Fišer, S.; Janković, M.; Borota, O. Epoxidation of Castor Oil with Peracetic Acid Formed in situ in the Presence of an Ion Exchange Resin. Chem. Eng. Process. 2012, 62, 106. (7) Sinadinović-Fišer, S.; Janković, M.; Petrović, Z. Kinetics of in situ Epoxidation of Soybean Oil in Bulk Catalyzed by Ion Exchange Resin. J. Am. Oil Chem. Soc. 2001, 78, 725. (8) Goud, V. V.; Patwardhan, A. V.; Pradhan, N. C. Kinetics of in situ Epoxidation of Natural Unsaturated Triglycerides Catalyzed by Acid Ion Exchange Resin. Ind. Eng. Chem. Res. 2007, 46, 3078. (9) Goud, V. V.; Patwardhan, A. V.; Dinda, S.; Pradhan, N. C. Epoxidation of Karanja (Pongramia glabra) Catalyzed by Ion Exchange Resin. Eur. J. Lipid Sci. Technol. 2007, 109, 575. (10) Goud, V. V.; Patwardhan, A. V.; Dinda, S.; Pradhan, N. Kinetics of Epoxidation of Jatropa Oil with Peroxyacetic and Peroxyformic Acid Catalyzed by Acidic Ion Exchange Resin. Chem. Eng. Sci. 2007, 62, 4065. (11) Dinda, S.; Goud, V. V.; Patwardhan, A. V.; Pradhan, N. C. Selective Epoxidation of Natural Triglycerides using Acidic Ion Exchange Resin as Catalyst. Asia-Pac. J. Chem. Eng. 2011, 6, 870. (12) Janković, M.; Sinadinović-Fišer, S. Prediction of the Chemical Equilibrium Constant for Peracetic Acid Formation by Hydrogen Peroxide. J. Am. Oil Chem. Soc. 2005, 82, 301. (13) Sinadinović-Fišer, S.; Janković, M. Prediction of the Partition Coefficient for Acetic Acid in a Two-phase System Soybean Oil-Water. J. Am. Oil Chem. Soc. 2007, 84, 669. (14) Campanella, A.; Mandagarán, B.; Campanella, E. Partitioning of Carboxylic Acid between Oil and Water Phases. Experimental, Correlation and Prediction. J. Am. Oil Chem. Soc. 2009, 86, 513. (15) Janković, M.; Sinadinović-Fišer, S.; Lamshoeft, M. Liquid-liquid Equilibrium Constant for Acetic Acid in an Epoxidized Soybean OilAcetic Acid-Water System. J. Am. Oil Chem. Soc. 2010, 87, 591. (16) Musante, R. L.; Grau, R. J.; Baltanás, M. A. Kinetics of Liquidphase Reactions Catalyzed by Acidic Resins: The Formation of Peracetic Acid for Vegetable Oil Epoxidation. Appl. Catal., A 2000, 197, 165. (17) Dul’neva, L. V.; Moskvin, A. V. Kinetics of Formation of Peroxyacetic Acid. Russ. J. Gen. Chem. 2005, 75, 1125. (18) Zhao, X.; Zhang, T.; Zhou, Y.; Liu, D. Preparation of Peracetic Acid from Hydrogen Peroxide. Part I: Kinetics for Peracetic Acid Synthesis and Hydrolysis. J. Mol. Catal. A: Chem. 2007, 271, 246. (19) Zhao, X.; Zhang, T.; Zhou, Y.; Liu, D. Preparation of Peracetic Acid from Hydrogen Peroxide: Experimental and Modeling. Guocheng Gongcheng Xuebao 2008, 8, 35. (20) Leveneur, S.; Wärna, J.; Salmi, T.; Murzin, D. Yu.; Estel, L. Interaction of Intrinsic Kinetics and Internal Mass Transfer in Porous Ion-exchange Catalysts: Green Synthesis of Peroxycarboxylic Acids. Chem. Eng. Sci. 2009, 64, 4101. (21) Standard Methods for the Analysis of Oils, Fats and Derivatives; Blackwell Scientific Publications: London, 1987. (22) Campanella, A.; Baltanás, M. A. Degradation of the Oxirane Ring of Epoxidized Vegetable Oils with Solvated Acetic Acid using Cation-exchange Resin. Eur. J. Lipid Sci. Technol. 2004, 106, 524. (23) Campanella, A.; Baltanás, M. A. Degradation of the Oxirane Ring of Epoxidized Vegetable Oils in Liquid-liquid Heterogeneous Reaction Systems. Chem. Eng. J. 2006, 118, 141. (24) Campanella, A.; Baltanás, M. A. Degradation of the Oxirane Ring of Epoxidized Vegetable Oils in a Liquid-liquid-solid Heterogeneous Reaction Systems. Chem. Eng. Process. 2007, 46, 210. (25) Marquardt, D. W. An Algorithm for Least-squares Estimation of Nonlinear Parameters. J. Soc. Ind. Appl. Math. 1963, 11, 431.

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