Liquid Phase Esterification of Acrylic Acid with Isobutyl Alcohol

Article pubs.acs.org/IECR

Liquid Phase Esterification of Acrylic Acid with Isobutyl Alcohol Catalyzed by Different Cation Exchange Resins Simge Karakuş, Emine Sert,* Aslı Deniz Buluklu, and Ferhan Sami Atalay Ege University, Chemical Engineering Department, 35100, Bornova, Izmir, Turkey ABSTRACT: The esterification reaction of acrylic acid with isobutyl alcohol in the presence of ion exchange resins, Amberlyst 15, Amberlyst 131, and Dowex 50wX-400, has been studied. According to experimental results, Amberlyst 131 was a more effective catalyst compared with the other ion exchange resins. The effects of catalyst loading, stirrer speed, initial alcohol to acid molar ratio, and temperature on the conversion of acrylic acid were investigated. The experimental data were tested by using Pseudohomogeneous, Eley−Rideal and Langmuir−Hinshelwood−Haugen−Watson models. The nonideality of the reaction medium was taken into account by using activities instead of concentrations. The activity coefficients were calculated using the UNIQUAC group contribution method. The activation energy and kinetic and adsorption constants were determined according to the model representing the dual site adsorption, which comprises the data with minimum error. alcohols have been reported. Shiau et al.1 studied the esterification of acrylic acid with 1,4 butenediol by a homogeneous catalyst, sulfuric acid. Experiments were carried out with different acid/alcohol mole ratios and different amounts of sulfuric acid in the temperature range 70 to 90 °C and 1 atm. The reaction mechanism was found to be a twostep consecutive, reversible reaction. Each esterification step follows a first order rate expression, and activation energies were calculated as 49.1 and 51.3 kJ/mol for each step. Altıokka and Ö deş studied the kinetics of esterification of acrylic acid with propylene glycol in the presence of Amberlyst 15 as a heterogeneous catalyst. Taking into account the general esterification reaction as well as polymerization of acrylic acid and products, the reaction mechanism was obtained and the activation energy was found to be 80.37 kJ/mol.7 Chen et al. studied the esterification of acrylic acid with 1-butanol in the presence of tungstophosphoric acid (TPA) catalyst. The catalyst was prepared according to the proposed procedure and the activity of the catalyst was determined for this reaction.8 In our previous study, liquid phase esterification of acrylic acid with n-butanol, isobutyl alcohol and hexanol was investigated with zirconia supported TPA as heterogeneous catalyst. A catalyst was prepared with different TPA loadings and calcination temperatures. The most active catalyst, 25 wt % TPA, calcined at 650 °C, gave more than 33%, 31%, and 27% conversions of acrylic acid for n-butyl, iso-butyl, and hexyl acrylate synthesis, respectively.9 Essayem et al. investigated the esterification of acrylic acid with 1-butene over sulfated Fe and Mn promoted zirconia. The main result is that Mn and Fe did not improve the catalytic properties of sulfated zirconia as far as activity and selectivity to sec-butyl acrylate are concerned but strongly improved its resistance to deactivation.10

1. INTRODUCTION The acrylic esters have been extensively used to produce various acrylate polymers utilized as coating, finishes binders for leather, textiles, and adhesives. Thus, the preparation of acrylic esters has long been an important research subject.1 To produce isobutyl acrylate, acrylic acid and isobutyl alcohol are esterified in an equilibrium limited reaction to isobutyl acrylate and water. Typical homogeneous catalysts like H2SO4, HCl, and ClSO3OH are used, but due to their miscibility with the reaction medium, separation becomes a problem; hence ion exchange resins are needed due to ease of product separation and catalyst recovery.2 Moreover there is an increasing tendency to develop processes that should meet the requirement of generation of nearly zero waste. So, several esterification reactions with different alcohols and acids have been reported in the literature using different types of solid acid catalysts such as zeolites and ion exchange resins.3,4 Ion exchange resin is a promising material for the replacement of the homogeneous acid catalysts. This solid type of material has good physical and chemical properties, and shows excellent performance as a heterogeneous catalyst in the esterification reaction. Mechanical separation with filtering is possible, and the ion-exchange resin is reusable.5 Ion exchange resins are also widely used in industrial water softening, food preparation, pharmaceuticals, and in medical applications.6 Ion exchange resins can be used in any type of reactor and in any solution. They offer a wide variety of support structures and functional groups. Acrylic acid and their esters are used in all types of paint formulations. Their excellent clarity, toughness, color retention, UV stability, and chemical inertness make acrylic ester emulsion polymers prime paint binders.7 Especially isobutyl acrylate is used in coatings, adhesives, and PE plastics. Because of its higher glass transition temperature and branching compared to n-butyl acrylate the resistance of the coating can be improved. Isobutyl acrylate can be produced directly from isobutyl alcohol and acrylic acid with the presence of suitable catalyst. Some studies on the esterification of acrylic acid with different © 2014 American Chemical Society

Received: Revised: Accepted: Published: 4192

November 6, 2013 February 23, 2014 February 23, 2014 February 24, 2014 dx.doi.org/10.1021/ie4037593 | Ind. Eng. Chem. Res. 2014, 53, 4192−4198

Industrial & Engineering Chemistry Research

Article

Komon et al.11 studied the kinetics of liquid phase synthesis of 2-ethylhexyl acrylate catalyzed by Amberlyst 46, Amberlyst 39, Amberlyst 70, and Amberlyst 131. The reaction mechanism was found to be second order. The activation energy was calculated as 52.3 kJ/mol. There are some studies about the esterification of acrylic acid, but no study has been stated in the literature for the catalytic esterification of acrylic acid with isobutyl alcohol. In the present work, Amberlyst 15, Amberlyst 131, and Dowex 50Wx-400, which contain sulfonic acid groups, were tested as the heterogeneous catalyst for the esterification of acrylic acid with isobutyl alcohol. The effects of different parameters such as temperature, catalyst loading, and isobutyl alcohol to acrylic acid mole ratio were studied. Also, the presence of external and internal diffusion limitations on the esterification system was studied. To provide a reaction mechanism, esterification kinetic data at varying temperatures were tested by using different kinetic models; adsorption and kinetic parameters were calculated for the esterification of acrylic acid with isobutyl alcohol.

Table 1. The Experimental Sets Studied run

catalyst

1 2 3 4 5 6 7 8 9

Amberlyst 15 Amberlyst 15 Amberlyst 15 Dowex 50Wx-400 Dowex 50Wx-400 Dowex 50Wx-400 Amberlyst 131 Amberlyst 131 Amberlyst 131

10 11 12 13 14 15 16

temp (K)

catalyst loading (g/L)

MR

stirrer speed (rpm)

Catalyst Selection 338 10 1 800 348 10 1 800 358 10 1 800 338 10 1 800 348 10 1 800 358 10 1 800 338 10 1 800 348 10 1 800 358 10 1 800 Effect of Stirrer Speed Amberlyst 131 358 10 1 600 Amberlyst 131 358 10 1 800 Amberlyst 131 358 10 1 1000 Amberlyst 131 358 10 1 1200 Effect of Temperature Amberlyst 131 338 10 1 800 Amberlyst 131 348 10 1 800 Amberlyst 131 358 10 1 800 Effect of Catalyst Loading Amberlyst 131 358 10 1 800 Amberlyst 131 358 15 1 800 Amberlyst 131 358 20 1 800 Effect of Molar Ratio of Isobutyl Alcohol to Acrylic Acid Amberlyst 131 358 10 1 800 Amberlyst 131 358 10 2 800 Amberlyst 131 358 10 3 800

2. EXPERIMENTAL SECTION 2.1. Chemicals. HPLC grade isobutyl alcohol and acrylic acid were used for all experiments, and phenothiazine was used as an inhibitor to prevent the polymerization reaction. Three strongly acidic (hydrogen form) cation exchange resins were used as catalyst; Amberlyst 15, Amberlyst 131, and Dowex 50Wx-400. Sulfuric acid with a purity of 99% was used as a catalyst for equilibrium experiments. The experiments were performed to find the optimum conditions for the production of isobutyl acrylate. The parameters studied were catalyst type, catalyst concentration, temperature, stirrer speed and molar ratio of isobutyl alcohol to acrylic acid. Table 1 represents the experiment sets carried out in this study. 2.2. Procedure. The kinetic and equilibrium experiments were carried out at different operating conditions. The experimental setup and procedure have been explained in the literature in detail.12 The samples taken during the experiments were analyzed by gas chromatography. The details and the temperature program were given in the previous study.12 The conversion of acrylic acid and reaction rates were determined, and also no side reaction was observed during the gas chromatographic analysis. The reproducibilty of the results was found to be ±2.41.

of acrylic acid with isobutyl alcohol. Experiments were performed at temperatures of 338, 348, and 358 K, an alcohol/acid ratio of 1, and catalyst loading of 10 g/L. At all temperatures, catalytic activity of catalysts can be ordered as follows; Amberlyst 131 > Dowex 50wX-400 > Amberlyst 15. Amberlyst 131 gave a conversion of 37.2%, whereas Amberlyst 15 and Dowex 50wX-400 gave conversion of 21.1% and 32.8%, respectively (Figure 1). So, all further experiments were performed using Amberlyst 131. Amberlyst 131 is a macroreticular type and Dowex 50wX-400 is a gel type catalyst. The difference between these two catalysts can be caused by the resin structure. Water produced during the reaction causes the the gel-type and macroreticular resin to catalyze systems to different amounts.14 Lee et al.15 studied the

3. RESULTS AND DISCUSSION 3.1. Selection of Catalyst. The accessibility of the acidic centers supported on the polymer backbone is very important in catalysis with sulfonated ion exchange resins. It essentially depends on the extent of swelling of the polymer matrix in the liquid reaction environment. For the gel-type ion exchangers the pores for the internal mass transport are exclusively generated by swelling, so that this kind of catalysts is completely inactive unless swollen to some extent. Macroreticular ion exchangers contain permanent pores independently of swelling, but only a small fraction of the catalytically active centers are available on their surface. Hence, also in this case the level of the catalytic activity can depend on swelling, even though not to the same extent as in gel-type catalysts.13 The cation exchange resins, Amberlyst 15, Amberlyst 131, and Dowex 50wX-400 were used to accelerate the esterification

Figure 1. Effect of catalyst type on the conversion at an alcohol to acid molar ratio of 1 and catalyst loading of 10 g/L.

17 18 19 20 21 22

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esterification of acetic acid and amyl alcohol, and they found that Dowex 50wX-10, a gel-type catalyst, to be more effective than Amberlyst 15, a macroreticular catalyst. Also, the difference between two macroreticular catalysts, Amberlyst 131 and Amberlyst 15, may be caused by the variation in the concentration of H+ ion on the surface of the catalyst, particle size of the catalyst, pore distribution, and also the initial water content in the resin bead.16 Although Amberlyst 131 gives the maximum conversion, all of the ion exchange resins studied in this work accelerate the reaction rate, whereas the esterification of acrylic acid with isobutyl alcohol does not take place autocatalytically. 3.2. Effect of Operating Parameters. The effects of temperature, catalyst loading, and isobutyl alcohol to acrylic acid mole ratio on the reaction rate for esterification of acrylic acid with isobutyl alcohol were investigated. Figures 2−4 show the effect of temperature, catalyst loading, and reactant mole ratio, respectively.

Figure 3. Effect of catalyst loading on conversion at 358 K and alcohol to acid ratio of 1.

catalyst loading was increased from 10 to 15 g/L than when it was increased from 15 to 20 g/L. A similar observation has been made by Ali and Merchant while studying the esterification of acetic acid with 2-propanol catalyzed by Amberlyst 15 and Dowex 50wX-400.22 Figure 4 illustrates the effect of alcohol to acid molar ratio on conversion of acrylic acid. Experiments were performed at a

Figure 2. Effect of temperature on conversion at an alcohol to acid ratio of 1 and catalyst loading of 10 g/L.

Figure 2 shows the conversion of acrylic acid with time at 338, 348, and 358 K. This plot illustrates that as temperature was increased, conversion of acrylic acid increased. High temperature gives rise to more frequent and successful collisions for higher conversion of reactants to ester products.17 It is evident that the increasing temperature increased acrylic acid, and these results are in line with the studies in literature.18−20 As known from the literature, the esterification rate decreased as degree of branching of alcohol increased, because of the steric hindrance. In our previous study, the esterification of acrylic acid with n-butanol catalyzed by Amberlyst 131 was carried out, and there is no remarkable difference between the conversion of acrylic acid for both esterified with n-butanol and isobutyl alcohol.21 Steric hindrance due to branching is not significant. This may be caused from the differences between adsorption characteristics of n-butanol and isobutyl alcohol. The n-butanol adsorption on the catalyst may cause a longer residence time for the acrylic acid on the Bronsted sites of Amberlyst 131. The effect of catalyst loading on the conversion of acrylic acid was studied at a temperature of 358 K and alcohol/acid mole ratio of 1. The catalyst loadings were varied as 10, 15, and 20 g/L for the esterification of acrylic acid with isobutyl alcohol. As seen in Figure 3, as catalyst loading was increased from 10 g/L to 15 g/L, the total number of exchangeable ions increased. The increase in conversion was more significant when the

Figure 4. Effect of alcohol to acid ratio on conversion at 358 K and catalyst loading of 10 g/L.

temperature of 358 K and catalyst loading of 10 g/L by changing the alcohol to acid molar ratio to 1, 2, and 3. The isobutyl alcohol to acrylic acid mole ratio was changed by varying the proportions of acrylic acid and isobutyl alcohol keeping the total volume of the mixture constant. As shown from the figure, with an increase in mole ratio of isobutyl alcohol to acrylic acid from 1 to 3, the conversion of acrylic acid increased. Since, at lower alcohol concentrations, the reaction equilibrium shifted toward the reactant side, by increasing the ratio more acid reacts because of the excess of alcohol.23 Also, with a rise in the mole ratio from 1 to 2, there was no change in the conversion of acrylic acid; a further increase in the molar ratio from 2 to 3 leads to more significant increase in conversion. Similarly, Kırbaşlar et al. found, while studying the esterification of acetic acid with ethanol catalyzed by Amberlyst 15,24 that the conversion decreases with an increase in the acid to alcohol ratio At the molar ratios of 1, 2, and 3, the conversion of acrylic acid are comparable during the early stage of the reaction (up to 60 min). After 1 h, raising the mole ratio from 1 to 2 does not cause a significant change. This suggests 4194



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that factors such as mass of catalyst (different in each set to obtain the same catalyst loading in g/L) and water during the reaction can mask the influence of excess isobutyl alcohol on the conversion of acrylic acid. 3.3. External and Internal Diffusion Significance. To explore the reaction mechanism, mass transfer resistance effects should be avoided. For heterogeneous catalytic systems, there are two types of limitations: internal and external mass transfer resistances.22 The effect of the external diffusion on the liquid phase esterification reaction is related to the stirrer speed.25 The experiments were conducted at 358 K, isobutyl alcohol to acrylic acid mole ratio of 1, catalyst loading of 10 g/L, and agitation speeds of 600, 800, 1000, and 1200 rpm to study the external mass transfer resistance on the reaction rate. Figure 5

Table 2. The Criteria for Internal Diffusion Resistance T (K)

catalyst loading (g/L)

MR

338 348 358 358 358

10 10 10 15 20

1 1 1 1 1

CWP 1.66 2.02 2.74 1.57 1.32

× × × × ×

10−03 10−03 10−03 10−03 10−03

isobutyl alcohol, theoretical equilibrium constants at different temperatures were found in our study.9 To calculate the experimental equilibrium constant, the esterification runs at 338, 348, and 358 K, alcohol to acid molar ratio of 1 and 3% by volume of sulfuric acid produced the equilibrium mole fractions of acrylic acid, isobutyl alcohol, isobutyl acrylate, and water. Equilibrium was obtained after 24 h and the equilibrium conversions and mole fractions are given in Table 3. Equilibrium Conversions, Mole Fractions, and Equilibrium Constants for the Esterification of Acrylic Acid with Isobutyl Alcohol equilibrium mole fractions

shows that in the range of 600−1200 rpm, the conversion of acrylic acid is independent of the stirrer speed. So, all experiments were carried out at a speed of 800 rpm to ensure the absence of external mass transfer resistances. This result agrees with the previous studies26−28 wherein mass transfer processes do not control the reaction rate in ion-exchange resin catalyzed reactions. For determination of the internal mass transfer resistance on the reaction rate, the Weisz−Prater equation is used. The results obtained from some experiments were attempted to fit the Weisz−Prater equation for the esterification of acrylic acid with isobutyl alcohol catalyzed by Amberlyst 131:

iso-BuOH

AcAs

iso-BuAc

water

K

338 348 358

0.899 0.878 0.872

0.0555 0.061 0.064

0.0555 0.061 0.064

0.4445 0.439 0.436

0.4445 0.439 0.436

76.56 61.75 55.31

where xi is the mole fraction of component i at equilibrium. The equilibrium constant can be found experimentally from the concentrations of reactants and products determined at the equilibrium conditions. Correct determination of the thermodynamic equilibrium constant of real mixtures requires the activities of the compounds instead of their concentrations.11 The thermodynamic equilibrium constant is related to the heat of reaction by the Van’t Hoff equation, and the experimental equilibrium constants were calculated as 76.56, 61.75, and 55.31 at temperatures of 338, 348, and 358 K, respectively. The heat of reaction was calculated as −16.2 kJ/ mol from the linear plot of ln K and 1/T, which agrees with the prediction for an exothermic reaction. Activities of Components. In the calculations of equilibrium constants the UNIQUAC model was used to determine the activity coefficients in the liquid phase because of the strong nonideality of the reaction mixture. The activity coefficients of components were calculated by the UNIQUAC model. The volume and area parameters and equations for the UNIQUAC method are given in Table 4. Rate Equations. Esterification of acrylic acid with isobutyl alcohol can be represented by a single, reversible reaction as shown in eq 3:

−rA(obs)ρp R c2 DeC li

Xeq

Table 3. The equilibrium constants, K, at different temperatures for isobutyl acrylate synthesis were determined by the equation γ γ x x K = i ‐ BuAc water i ‐ BuAc water xi ‐ BuOH xAcAc γi ‐ BuOHγAcAc (2)

Figure 5. Effect of stirrer speed on conversion at 358 K, alcohol to acid ratio of 1, and catalyst loading of 10 g/L.

Cwp =

T (K)

(1)

The parameters involved in Weisz−Prater equation and the details of the procedure are given in the literature.29 The results are given in Table 2. As seen from Table 2, the values of the internal diffusion parameters were calculated as less than 1. 3.4. Kinetic Modeling. Thermodynamic Aspects for Isobutyl Alcohol−Acrylic Acid Esterification System. Determination of Equilibrium Constant. The equilibrium constant is a crucial parameter for equilibrium limited reactions such as esterification, transesterification, isomerization, etc. For isobutyl acrylate synthesis, theoretical equilibrium constants were determined at temperatures of 338, 348, and 358 K by using standard heat of formation and standard Gibbs energies of products and reactants. For the esterification of acrylic acid with

C3H4O2 + C4 H 9OH ⇄ C7H12O2 + H 2O

(3)

Heterogeneous kinetic models including Pseudohomogeneous model (PH), Eley−Rideal model (ER), and Langmuir− Hinshelwood−Haugen−Watson mechanism (LHHW) were applied to correlate the kinetic data available for different 4195



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a reaction mechanism wherein the rate limiting step is the surface reaction between the adsorbed alcohol and adsorbed acid is found to correlate the experimental data by minimum error. For model 1, the errors in correlating experimental data including temperature effect were found to be 24.8, 14.7, and 22.5%, respectively. Model 2 which assumes that alcohol does not adsorb and remains in the bulk phase correlates the experimental data with errors of 9.8, 6.5, and 4.5%. Similarly, model 3 which assumes that the surface reaction is the limiting step and acid does not adsorb, was found to satisfy the experimental data with errors of 5.8, 5.4, and 7.8% at temperatures of 338, 348, and 358 K. In the dual site LHHW mechanism (model 4) the surface reaction between adsorbed acid and adsorbed alcohol was found to correlate with errors of 2.4, 2.5, and 3.7%. Among all of the models, the LHHW model is the best model that gives the least residual error. The forward reaction rate constant k listed in Table 6 is used to calculate the pre-exponential factor, A, and activation energy, E, using the Arrhenius relation. Figure 6 shows the Arrhenius plot between ln k and 1/T, which gives a straight line. The activation energy and pre-exponential factor were calculated as 53.8 kJ/mol and 4.92 × 1006, respectively. The higher value of activation energy shows that the surface reaction is the rate controlling step.23 We found the activation energy for the esterification of acrylic acid with n-butanol as 57.4 kJ/mol in the previous study.21 The steric hindrance may be overcome by the reaction mechanism and adsorption steps on the catalyst surface. Niesbach et al.31 studied the esterification of acrylic acid with n-butanol in a pilot plant reactive distillation column. The temperature was varied from 373 to 398 K, during the experimental investigation. Kinetic analysis was carried out for the results obtained by Amberlyst 46 and the LHHW approach was used. Activation energy was found as 81.26 kJ/mol. Maytan et al.32 investigated the esterification of acrylic acid with nbutanol in the liquid phase catalyzed by Al-MCM-41. The Eley−Rideal model describes their experimental data, and the activation energy was found at the temperature range of 333− 348 K. The maximum conversion was achieved as 20% at 348 K. The experimental and predicted reaction rates were compared in Figure 7. The order of the adsorption constants for the species determined as Kwater > KAcAc > Kiso‑BuOH > Kiso‑BuAc in the esterification of acrylic acid with isobutyl alcohol because of their solubility parameters. 3.5. Reusability of Catalyst. The reusability of ionexchange resin was also studied in order to check the

Table 4. Volume, Area Parameters, and Equations of UNIQUAC Activity Model volume and area parameters acrylic acid isobutyl alcohol isobutyl acrylate water

r

q

2.646 3.453 3.124 0.920

2.400 3.048 2.987 1.4

ln γ1 = ln γ1c + ln γ1R n

ln γ1c = ln φi + li +

z q ln vi − φ ∑ xjl j 2 i j=1 n

ln γ1R = qi(1 − ln(∑ θτ i ji)) −

∑ j=1

θτ i ji n

∑k = 1 θkτkj

temperatures. The PH model is similar to the power law model and assumes that surface reaction is the controlling step and adsorption is negligible for all components.30 The LHHW model represents the rate determining step as the reaction of both reactants adsorbed on the catalyst surface, whereas the ER model indicates that the rate determining step is the reaction between one reactant adsorbed on the catalyst surface and its counterpart reactant in the bulk region.17 These reaction mechanisms, which are classified according to the adsorption and desorption of reactants and products, were applied to the experimental results to achieve the kinetics of reaction. These reaction rate mechanisms are summarized in Table 5. In this table, k is the forward reaction rate constant in mol/min·gcat, Ki is the adsorption constant for species i, ai is the activity of species (ai = γi xi), xi is the mole fraction and γi is the activity coefficient of species i. Parameters for the models were estimated by minimizing the sum of the residual squares (SRS) between the experimental and calculated reaction rates: min SRS =

∑

(rexp − rcalc)2 (4)

all samples

Mean relative error (MRE) between the experimental and predicted mole fractions were calculated by the formula given below; mean relative error =

∑All data samples

|x exp − x pred|

nsample

x exp

100 (5)

Adsorption and kinetic parameters were calculated for each mechanism and tabulated in Table 6. Model 4 corresponding to Table 5. Rate Expressions for Different Reaction Mechanisms limiting step

adsorption status of reactants

mechanism

⎛ ⎞ 1 ri = Ccatk f ⎜aacidaalcohol − aestera water ⎟ ⎝ ⎠ K

I

surface reaction

II

surface reaction

adsorbed acid and nonadsorbed alcohol

ri =

III

surface reaction

adsorbed alcohol and nonadsorbed acid

ri =

IV

surface reaction

adsorbed alcohol and adsorbed acid

ri =

4196

1

(

Ccatk f K acid aacidaalcohol − K aestera water

)

(1 + K acidaacid + K watera water) 1

(

Ccatk f K alcohol aacidaalcohol − K aestera water

)

(1 + K alcoholaalcohol + K watera water)

(

1

Ccatk f K acidK alcohol aacidaalcohol − K aestera water

)

(1 + K acidaacid + K alcoholaalcohol + KesteraesterK watera water)2 dx.doi.org/10.1021/ie4037593 | Ind. Eng. Chem. Res. 2014, 53, 4192−4198


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Table 6. Kinetic and Adsorption Constants for Different Reaction Mechanisms model I

II

III

IV

T (K)

k (mol/min·gcat)

338 348 358 338 348 358 338 348 358 338 348 358

0.00345 0.00425 0.00685 0.04469 0.06403 0.07746 0.05478 0.06856 0.07987 0.01987 0.04558 0.176

KAcAc

Kiso‑BuOH

Kiso‑BuAc

0.252 0.194 0.158 0.259 0.189 0.112 1.012 0.989 0.895

1.589 1.258 1.008

Figure 6. ln k vs 1/T.

0.212 0176 0.143

Kwater

MRE (%)

8.456 7.324 3.258 8.356 7.112 6.789 5.489 5.002 4.589

22.1 18.4 21.7 5.7 8.2 6.2 6.5 7.8 8.7 1.8 2.5 3.5

Figure 8. Catalyst reusability at 358 K and catalyst loading of 10 g/L.

for the esterification of acrylic acid with isobutyl alcohol. Therefore, the kinetic behavior of the esterification of acrylic acid with isobutyl alcohol catalyzed by Amberlyst 131 was studied. The experiments were carried out to observe the effects of temperature, catalyst loading, and alcohol to acid molar ratio. Among four different kinetic models employed in this study, the esterification of acrylic acid with isobutyl alcohol catalyzed by Amberlyst 131 was presented by the LHHW model. The activation energy for the forward reaction was calculated as 53.8 kJ/mol.

■

Figure 7. Parity between predicted and experimental reaction rates.

AUTHOR INFORMATION

Corresponding Author

deactivation of the catalyst during the reaction. The reusability of Amberlyst 131 was checked by performing some experiments at 358 K. Amberlyst 131 was rinsed with distilled water and dried at 363 K to reuse. The same catalyst was used three times, and the results were given in Figure 8. Amberlyst 131 was found to be reusable four times giving conversions comparable to the fresh catalyst.

*E-mail: [email protected]. Tel.: 90 232 311 1493, 90 232 388 7776. Notes

The authors declare no competing financial interest.

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■

ACKNOWLEDGMENTS

̇ AK The authors acknowledge the financial support from TÜ BIT (The Scientific and Technological Research Council of Turkey) under Project No. 110M462, from EBILTEM (Research and Application Center of Science and Technology) under Project No. 2012BIL022, and from Ege University Scientific Research Fund under Project No. 12MÜ H039.

CONCLUSION The esterification reaction of acrylic acid with isobutyl alcohol was carried out over three types of ion exchange resins, Amberlyst 15, Amberlyst 131, and Dowex 50xW-400. The experimental results indicated that Amberlyst 131 was a more effective catalyst compared with the other ion exchange resins 4197



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