Kinetic Modeling of the Transesterification Reaction of Dimethyl

Nov 19, 2014 - Diphenyl carbonate (DPC) is an important industrial intermediate in the production of various organic and polymeric materials, particul...
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Kinetic Modeling of the Transesterification Reaction of Dimethyl Carbonate and Phenol in the Reactive Distillation Reactor Xia Yin,†,‡ Yi Zeng,‡ Jie Yao,‡ Hua Zhang,‡ Zhiyong Deng,‡ and Gongying Wang*,‡ †

University of Chinese Academy of Sciences, Beijing 100039, PR China Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, Chengdu 610041, PR China

‡

S Supporting Information *

ABSTRACT: The kinetic behavior of preparing diphenyl carbonate by the transesterification of dimethyl carbonate with phenol in a reactive distillation reactor has been explored experimentally and theoretically. The transesterification reaction was described to conform a pseudo-second-order kinetics, and a semi-empirical kinetic model has been derived to explain the kinetic behavior. The model parameters were fitted to experimental data by an improved genetic algorithm. The proposed model was determined to be useful in simulating the rate constant and the mole fraction of components, which agreed well with the experimental data for different operating temperatures and catalyst concentrations.

1. INTRODUCTION Diphenyl carbonate (DPC) is an important industrial intermediate in the production of various organic and polymeric materials, particularly for the synthesis of polycarbonate (PC).1 Several routes are available for preparing DPC, in which the transesterification route from DMC via methyl phenyl carbonate (MPC) to DPC appears to be more suitable to the commercial production. Currently, numerous catalysts are known to enhance the kinetic rate of transesterification reactions. Both acidic and basic catalysts, either homogeneous or heterogeneous, can be used for this purpose.2 Heterogeneous catalysts are usually preferred because of their reusability and facile separation from the reaction mixture. For the kinetics research, however, available heterogeneous catalysts suffer from problems such as the instability and mass transfer issue. Therefore, a homogeneous catalyst seems to be more suitable for our study. A tin-based homogeneous catalyst was finally selected because of high activity and its stability in both aqueous environments and air. These features ensure its predominance for industrial application. On the basis of the consideration above, a homogeneous catalyst dibutyltin oxide (n-Bu2SnO) was selected for our kinetics research. Generally, the transesterification reaction system consists of two equilibrium-limited steps, which involves a first transesterification reaction to MPC followed by a further transesterification and/or a disproportionation step to DPC. Haubrock and co-workers studied the kinetic behavior of this system in a closed batch reactor, and the equilibrium conversion to MPC is reported to be only about 3%.3 Thus, the reactive distillation technique is usually adopted to enhance the conversion and selectivity of desired products. In industry, a two-step process, 4 including the transesterification and disproportionation stage, is usually applied. In the first transesterification stage, a mixture with high MPC yield is obtained from reactive distillation5,6 through the instantaneous distilling of byproduct from the reaction zone, which is an important step for synthesizing DPC. Then, in the second © XXXX American Chemical Society

disproportionation stage, the purpose of high DPC yield is easily achieved. For the modeling and designing of the reactor, detailed knowledge about reaction kinetics behavior of this system is important, but only a few reports have been published about the kinetic data of this system up to now. Tao et al.7 gave an overview of the further disproportionation reaction kinetics using catalyst lead oxide (PbO). The result shows that the orders of the positive and reverse reaction were all one. Unfortunately, this article did not refer to the concrete experimental procedure on how to obtain kinetic data. Haubrock3,8 and co-workers studied the chemical equilibrium and kinetics of this system in a closed reactor using catalyst titanium-(n-butoxide), and an activity-based reaction rate model was used to fit kinetic parameters to the experimental data. This paper aims to investigate the kinetic data for the transesterification reaction in a reactive distillation reactor homogeneously catalyzed by n-Bu2SnO. Furthermore, a semiempirical kinetics model based on the reaction mechanism supposed by Wang et al.9 was established, which is an essential requirement for a reliable reactor design. The model parameters are finally fitted by an improved genetic algorithm (GA) in Matlab 7.1.

2. EXPERIMENTAL SECTION 2.1. Materials. Dimethyl carbonate (≥99.9 mass %) was purchased from Huasheng Co. Ltd., Shanghai, China. Phenol (≥99.5 mass %) was acquired form Guangdong Guanghua Scitech Co., Ltd., China. They were all used without further purification. Catalyst n-Bu2SnO was from Aldrich Ltd. and dried at 343.15 K for 5 h in a vacuum oven. 2.2. Experimental Procedure. The experiments were performed at atmospheric pressure in a 500 mL five-necked Received: July 27, 2014 Revised: November 18, 2014 Accepted: November 19, 2014

A

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round-bottomed glass flask connected with a distillation column and a reflux condenser. The flask also installed an electric mechanical agitator (Germany IKA RW20), which is presented in Figure 1. The distillation column was filled with a

each sampling. The analytic result described in the Supporting Information indicated that there was no phenol; only methanol and DMC existed. Systematic errors for each experiment were ruled out because identical results were obtained. A relative deviation of mass balance for each experiment was within 4%. The controlling of a stable temperature is a great difficulty in our experiments. Numerous attempts have been made to explore the influence degree of various operating conditions on temperature before kinetic experiments. Finally, we found two factors, namely, the DMC loading rate and reflux ratio, were critical to the temperature fluctuation of the reactive liquid. In a word, the larger the DMC loading rate is, the larger the reflux ratio is, and then the lower the temperature is. It is interesting to observe that if the temperature was maintained constant the concentration of DMC in the liquid would be constant. For each experiment, the concentration of DMC and temperature were constant with a variation of ±0.8 mol % and ±1 K, respectively. 2.3. Analytical Methods. A gas chromatograph (Agilent 7820) with a flame ionization detector (FID) was used to analyze all of samples offline. The analytic column was a 30 m long fused silica column (Agilent DB-35, 30 m × 0.32 mm × 0.25 mm), and nitrogen was used as carrier gas. The split ratio was 10:1, and the sample injection volume was 0.2 μL. The temperatures of injector and FID were operated at 553.15 and 573.15 K, respectively. The oven was programmed at 358.15 K, ramped at 40 K/min to 433.15 K, and then ramped at 50 K/ min to 553.15 K for 5 min. Calibration samples were prepared gravimetrically through a Sartorius CP224S scale with the precision of 0.01 mass %. The measurement reproducibility of GC was evaluated by repetitive measurements of sample. The relative standard deviations were determined to be 3% for MPC and phenol and 5% for DPC.

Figure 1. Setup for kinetic experiment.

3 mm Dixon packing. In a typical procedure, 236 g of phenol and a certain amount of catalyst were first put into the flask. Nitrogen was then purged from nitrogen inlet A into the whole setup for at least 60 min to remove air. Then, the flask was heated to 453.15 K through a thermostat-controlled oil bath and then was maintained stable at 453.15 K for 5 min. In the following, DMC (303.15 K) was injected into the liquid phenol at an appropriate speed through a peristaltic pump (YZ151, Tianjin Xieda Exectron Co., Ltd., China). After 40 min, temperature decreased to a desired temperature at which time was defined as the time zero. Then DMC (303.15 K) was injected at a smaller speed, and reflux distillate was taken out at a reflux ratio from the condenser in order to maintain a stable desired liquid temperature. The detailed operating conditions are listed in the Supporting Information. The total number of moles of DMC fed to the flask was equal to the number of moles of phenol initially placed in the flask for each experiment. During the experiment, 0.5 mL of sample was taken out at fixed time using a syringe and was transferred to precooled vials to stop the reaction. All samples were analyzed within 8 h using gas chromatography (GC). Reflux distillate was also collected at

3. KINETIC MODEL 3.1. Reaction Mechanism. Transesterification of DMC and phenol generally involves three reactions that were descried above. Besides, Ono et al.10 has also identified a side reaction, which would be ignored in the this article because the amount was very small under the studied range. Moreover, several investigators11,12 have studied extensively the tin-based catalyst due to its high activity, and some reaction mechanisms were proposed according to their experiment results. Particularly, Wang et al. demonstrated that an active intermediate I, which could be in situ synthesized from phenol/DPC and n-Bu2SnO, was the real active species when using n-Bu2SnO for the transesterification reaction. Considering the characteristic of reaction and structure of intermediate I, Wang et al. has assumed the intermediates III and IV were also formed in the reactive system. The structure of these intermediates is illustrated in Chart 1. On the basis of the analysis above, a simplified but more reasonable reaction mechanism shown in Scheme 1 is supposed for the kinetic model.

Chart 1. Structure of Intermediates I, III, and IV

B

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Thus, there is [cat]0 ≪ [Phenol]0, [H2O] ≪ K[Phenol]0, eq 8 can be rewritten as eq 9.

Scheme 1. Reaction Scheme of Proposed Transesterification Reaction Mechanism

[I] =

K[cat]0 [Phenol]0 K[Phenol]0 + [H 2O]

(9)

Then [I] = [cat]0 can be obtained. Namely, the mole fraction of I equals to that of n-Bu2SnO. From the steady state assumption, the formation rate of the intermediates III and IV can be expressed as follows

As shown in Scheme 1, n-Bu2SnO reacts with phenol to intermediate I at first. Intermediate I reacts with DMC/MPC to form MPC/DPC with the I itself changing into III, followed by a further transformation of DMC/MPC to MPC/DPC through intermediate III turning into IV. Phenol, as an aryloxy group donator, substitutes the methoxyl group of intermediates III or IV for the formation of I or III, thereby completing the whole catalysis cycle. 3.2. Mathematical Model and Treatment. In order to obtain the kinetic model, we make following assumptions: (1) Reaction occurs only in the liquid phase because the catalyst dissolves only in the liquid, and the generated MPC and DPC also exist only in the liquid. (2) For each experiment, there is a bit fluctuation of the catalyst concentration owing to the distillation procedure, but the variation was less than 0.02 mol %. Thus, it is reasonable to assume the catalyst concentration was constant. (3) Both the forward and reverse reactions follow pseudo-second-order kinetics. (4) Intermediates III and IV were assumed to conform to the steady-state assumption.13 From the above assumptions, the rate of reactions (Scheme 1) can be expressed in the following forms r1 = k1[cat][Phenol] − k −1[I][H 2O]

(1)

r2 = k 2[I][DMC] − k −2[III][MPC]

(2)

r3 = k 3[III][DMC] − k −3[IV][MPC]

(3)

r4 = k4[I][MPC] − k −4[III][DPC]

(4)

r5 = k5[III ][MPC ] − k −5[IV ][DPC ]

(5)

r6 = k6[III][Phenol] − k −6[I][Methanol]

(6)

r7 = k 7[IV][Phenol] − k −7[III][Methanol]

(7)

k1 [I][H 2O] = k −1 ([cat]0 − [I])([Phenol]0 − [I])

(10)

d[IV] = r3 + r5 − r7 = 0 dt

(11)

Hence, we can get the mole fraction of intermediates III and IV. [III] =

[IV] =

k 2[DMC] + k4[MPC] + k −6[Methanol] [I] k −2[MPC] + k −4[DPC] + k6[Phenol]

(12)

k 3[DMC] + k5[MPC] + k −7[Methanol] [III] k −3[MPC] + k −5[DPC] + k 7[Phenol] (13)

Meanwhile, the reaction rates governing each component from the mass balance are expressed as d[MPC] = r2 + r3 − r4 − r5 dt

(14)

d[DPC] = r4 + r5 dt

(15)

−

d[Phenol] = r6 + r7 dt

(16)

As described above, the concentration of DMC at a fixed temperature would be constant. Therefore, it was lumped into the reaction rate constants k2 and k3 in the course of the model treatment. Then, the kinetic parameters are optimized by an improved GA program14,15 in which the parameters were iteratively adjusted until a predefined criterion was satisfied. The criterion is the minimization of the objective function. 3

F=

In eqs 1−7, [DMC], [DPC], and [MPC] denote the mole fraction of DMC, DPC, and MPC in the liquid mixture, respectively, mol mol−1, in which “cat” denotes n-Bu2SnO; k1, k2, k3, k4, k5, k6, and k7 are the forward rate constants, k−1, k−2, k−3, k−4, k−5, k−6, and k−7 are the reverse rate constants. From the reaction 1, [I] can be deduced as follows. K=

d[III] = r2 − r3 + r4 − r5 − r6 + r7 = 0 dt

t

∑ ∑ [wi([i]t ,exp i=1 t=0

− [i]t ,calc )]2

(17)

where [i]t,exp and [i]t,calc is the experimental and calculated mole fraction of component i at time t, respectively, and wi is the weight of component i. Here MPC, DPC, and phenol are 0.35, 0.35, 0.3, respectively. An iteration of the optimization search is performed as follows. A series of initial genes are first generated at random in the GA, and then, their fitness function is calculated through solving a set of differential equations. A minimal fitness value will be selected out according to a certain regulation. To acquire a globally optimal solution, the corresponding gene is optimized again and again through crossover and mutation until a predefined criterion is satisfied. Finally, the globally optimal solution is improved by an fmincon function to search a locally more optimal solution.

(8)

where K is the equilibrium constant of the reaction 1, [cat]0 and [Phenol]0 are the initial mole fractions of n-Bu2SnO and phenol, mol mol−1. In the experimental procedure, n-Bu2SnO reacted completely with the excessive phenol in the temperature-raised period before DMC loading into the flask. In this case, the conversion of reaction 1 can be understood to be 1. C

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4. RESULT AND DISCUSSION 4.1. Effect of Mass Transfer. The reaction product methanol is continuously and instantaneously removed from the liquid phase in the reaction process. To suppress the mass transfer effect, some basic measurements were performed to compare the reaction rates at different stirrer speeds (J) at a high catalyst concentration and temperature in the studied range. Figure 2 showed an increase in reaction rate as the stirrer

kinetics, which can be enhanced by increasing catalyst concentration or temperature. The initial rate of reaction r0 (mol mol−1 h−1), which is defined as the initial consumption rate of phenol, can be obtained by differentiation of the phenol mole fraction in the liquid system. Figure 4 showed a linear

Figure 4. Effect of the catalyst concentration on the consumption rate of phenol. Reaction conditions: DMC/Phenol mole ratio = 1.0, T = 433.15 K, and J = 600 rpm. Figure 2. Effect of the stirring speed (J) on the conversion of phenol. Reaction conditions: DMC/Phenol mole ratio = 1.0, T = 443.15 K, and [cat]0 = 2.3%; ■ 200 rpm,● 400 rpm, and, ▲ 600 rpm.

relationship between the initial reaction rate and the catalyst concentration. The fitted equation is 1/(−d[Phenol]/dt|t=0) = 0.0802/[cat]0, and the correlation coefficient is 0.9976. This offers additional support to the kinetic model with a linear dependence of the reaction rate on the catalyst mole fraction. 4.3. Effect of Temperature. Information about the temperature dependence of the reaction rate constants is important to develop a kinetic model. To obtain that information, a series of experiments were carried out at different temperatures (423.15−443.15 K) with other experimental conditions same. The result was illustrated in Figure 5.

speed increased, and the rate finally converged to a fixed value as the stirrer speed increased from 200 to 400 and 600 rpm. Therefore, the stirrer speed in the further kinetic experiments is typically adjusted to 600 rpm. 4.2. Effect of Catalyst Concentration. To investigate the effect of catalyst concentration on the reaction rate, a series of experiments are carried out on the condition of different catalyst concentrations ([cat]0 = 0.01−2.29 mol %), which is illustrated in Figure 3. From Figure 3, we can observe that

Figure 5. Effect of reaction temperature on the conversion of phenol. Reaction conditions: DMC/Phenol mole ratio = 1.0, [cat]0 = 1.1%, and J = 600 rpm; ▲ 423.15 K, ● 433.15 K, and ■ 443.15 K.

Figure 3. Effect of the catalyst concentration on the conversion of phenol. Reaction conditions: DMC/Phenol mole ratio = 1.0, T = 433.15 K, and J = 600 rpm; ▼ [cat]0 = 2.29%,▲ [cat]0 = 1.15%, ◀ [cat]0 = 1.14%,● [cat]0 = 0.59%, and ■ [cat]0 = 0.01%.

As shown in Figure 5, the reaction rate increases with a temperature increase from 423.15 to 433.15 K. Nevertheless, the reaction rate decreased when temperature was further raised to 443.15 K. The phenomenon above is different from the conventional discipline that temperature has a simple positive or negative effect on the reaction rate. This is mainly attributed to the influence of mass transfer. Namely, the DMC concentration in the liquid is severely affected by temperature

reaction did not happen in the absence of catalyst. Meanwhile, the reaction rate increased with the catalyst concentration increasing and got to a fixed value when the catalyst concentration began up to 1.15 mol %. This phenomenon is in agreement with many literatures16,17 and could be attributed to the reason that the reaction began to be controlled mainly by the mass transfer limitations and no longer the reaction D

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owing to the vapor−liquid equilibrium (VLE) phenomenon. In the experiments, the higher the temperature is, the smaller the concentration of DMC is. The temperature has a positive influence on the reaction rate; however, the concentration of DMC has a negative effect. Thus, the phenomenon above about the influence of temperature on the reaction rate can be understood as a compromise between temperature and DMC concentration. 4.4. Calculation of Kinetics Parameters and Verification. The reaction rate constants were fitted to experimental kinetic data at different temperatures. This process used the experimentally determined temporal courses of molar fractions for all reactants. To obtain the reaction rate constants, a computerized kinetics program was performed in Matlab 7.1. In the genetic algorithm, the function of fitness scaling, selection, mutation, and crossover were the rank, stochastic uniform, adaptive feasible, and scattered, respectively. The acquired optimal model parameters are summarized in Table 1. In

Figure 6. Modeling curves and measured points for the mole fraction of phenol at different temperatures. Reaction conditions: DMC/ Phenol mole ratio = 1.0, J = 600 rpm, and [cat]0 = 1.1%. Point symbols denotes the experimental points. Line of corresponding color denotes the simulated curves.

Table 1. Regressed Reaction Rate Constant for Kinetic Model temperature (K) rate constant (mol h−1) a

k2 k−2 a k3 k−3 k4 k−4 k5 k−5 k6 k−6 k7 k−7 F

423.15

433.15

443.15

6.492 20.183 9.615 6.839 6.111 123.667 6.874 38.581 0.913 47.714 7.844 128.429 0.296

8.773 1.235 6.387 40.205 0.000 4.214 2.290 4.814 0.669 49.001 6.175 141.516 0.847

21.511 48.520 33.439 294.786 11.803 182.942 13.416 33.946 2.743 30.768 81.609 210.007 0.100

a k2 and k3 are the data that have been divided by the mole fraction of DMC, which is 21.37% at 423.15 K, 16.06% at 433.15 K, and 10.09% at 443.15 K.

Figure 7. Modeling curves and measured points for the mole fraction of MPC and DPC at different temperatures. Reaction conditions: DMC/Phenol mole ratio = 1.0, J = 600 rpm, and [cat]0 = 1.1%. Point symbols denotes the experimental points. Line of corresponding color denotes the simulated curves.

addition to the experimental data, the time course of the molar fractions calculated using the optimal reaction rate constants is also shown at different temperatures, which is presented in Figures 6 and 7. In Figure 6, we know that the agreement between the experimental and correlated result of phenol is excellent with an average deviations of being less than 10% in the 95% confidence interval. As shown in Figure 7, the mole fraction of MPC is obviously larger than that of DPC. This could be attributed to the disproportionation reaction that contributes mainly to the formation of DPC. However, it was inhibited to a degree when the DMC concentration in the liquid is much larger than the MPC concentration, especially at the beginning stage of reaction. The correlated result of MPC and DPC was in close proximity to the experimental data with the average deviation of being less than 5% and 12% in the 95% confidence interval, respectively. However, it is worth noting that the experimental data of methanol in the liquid has also been correlated by GA. It is a pity that a bad result was obtained, which was mainly attributed to the influence of the mass transfer of the vapor and liquid phase. Namely, plentiful generated methanol evaporated into

the vapor from the liquid in the process of reaction. Thus, the model equation failed to correlate the concentration of methanol in the liquid, which is just one part of the total generated methanol. From the perspective of mass balance, we know that the total amount of generated methanol separated in three parts: partly dwelling in the reactive liquid, partly going out from the distillate receiver, and partly existing in the liquid of packing column and the vapor in the setup. Moreover, the generation rate of total methanol equals the minus consumption rate of phenol. Therefore, the generation rate of methanol in the liquid can be obtained theoretically through subtracting the changing rate of methanol in the column and reflux distillate from the generation rate of total methanol. However, it seems difficult to get a real-time amount of methanol in the column and vapor in the setup. Even though the vapor amount of methanol in the setup was neglected, and the total amount of liquid in the packing column can be E

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Industrial & Engineering Chemistry Research calculated through the column volume, void ratio of packing, and density of species, it still seems difficult to determine the composition of liquid in the packing column at each liquid sampling. In a word, the rate of methanol in the liquid is complex and difficult to be correlated through the perspective of mass balance. Actually, many literatures3,6,18 have used the concept of activity, which can describe the vapor−liquid equilibrium (VLE) behavior in the development of kinetic model to modify the effect of the mass transfer. Unfortunately, only the VLE data of binary systems (methanol + DMC, DMC + phenol, methanol + phenol, MPC + methanol, and MPC + DMC) have been determined at atmospheric pressure in the past decades.19−21 There has been no data reported about DPC up to now. That is to say, to calculate the accurate activity coefficients of all transesterification species, the reported VLE data are not enough. Thus, the determination of VLE data containing DPC is valuable work that deserves to be done to develop a kinetic model based on activity in the future. In a word, the agreement between the experimental data of phenol, MPC, DPC, and correlated values was excellent, which demonstrated a good accuracy of the optimal rate constants.

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REFERENCES

(1) Kim, W. B.; Joshi, U. A.; Lee, J. S. Making polycarbonates without employing phosgene: An overview on reactive chemistry of intermediate and precursor syntheses for polycarbonate. Ind. Eng. Chem. Res. 2004, 43, 1897. (2) Gong, J.; Ma, X.; Wang, S. Phosgene-free approaches to reactive synthesis of diphenyl carbonate and its intermediates. Appl. Catal., A 2007, 316, 1. (3) Haubrock, J.; Wermink, W.; Versteeg, G. F.; Kooijman, H. A.; Taylor, R.; Annaland, M. V.; Hogendoorn, J. A. Reaction from dimethyl carbonate (DMC) to diphenyl carbonate (DPC). 2. kinetics of the reactions from DMC via methyl phenyl carbonate to DPC. Ind. Eng. Chem. Res. 2008, 47, 9862. (4) Fu, Z.; Ono, Y. Two-step synthesis of diphenyl carbonate from dimethyl carbonate and phenol using MoO3SiO2 catalysts. J. Mol. Catal. A: Chem. 1997, 118, 293. (5) Wang, F.; Zhao, N.; Li, J. P.; Zhao, W. B.; Xiao, F. K.; Wei, W.; Sun, Y. H. Modeling of the reactive distillation process for the synthesis of dimethyl carbonate by urea methanolysis method. Ind. Eng. Chem. Res. 2007, 46, 8972. (6) Keller, T.; Holtbruegge, J.; Niesbach, A.; Gorak, A. Transesterification of dimethyl carbonate with ethanol to form ethyl methyl carbonate and diethyl carbonate: a comprehensive study on chemical equilibrium and reaction kinetics. Ind. Eng. Chem. Res. 2011, 50, 11073. (7) Tao, S. C.; Tian, H. S.; Zhu, Y. F.; Liu, J. C. Study on the disproportionation reaction kinetics of methyl phenyl carbonate. J. Anhui Univ. Sci. Technol. 2003, 23, 3 (in Chinese). (8) Haubrock, J.; Raspe, M.; Versteeg, G. F.; Kooijman, H. A.; Taylor, R.; Hogendoorn, J. A. Reaction from dimethyl carbonate to diphenyl carbonate. 1. Experimental determination of the chemical equilibria. Ind. Eng. Chem. Res. 2008, 47, 9854. (9) Wang, Y.; Yao, J.; Zeng, Y.; G.Y, W. Mechanism study of di-nbutyltin oxide catalyzed transesterification of dimethyl carbonate with phenol. Acta. Chim. Sin. 2005, 63, 603. (10) Ono, Y. Catalysis in the production and reactions of dimethyl carbonate, an environmentally benign building block. Appl. Catal., A 1997, 155, 133. (11) Shivarkar, A. B.; Gupte, S. P.; Chaudhari, R. V. Carbamate synthesis via transfunctionalization of substituted ureas and carbonates. J. Mol. Catal. A: Chem. 2004, 223, 85. (12) Du, Z.; Xiao, Y.; Chen, T.; Wang, G. Reactive study on the transesterification of dimethyl carbonate and phenol to diphenyl carbonate. Catal. Commun. 2008, 9, 239. (13) Fu, X.; Shen, W.; Yao, T.; Hou, W. Physical Chemistry; Higher Education Press: Beijing, 2005; Vol. 5. (14) Chipperfield, A. J.; Fleming, P. J.; Fonseca, C. M. Genetic Algorithm Tools for Control Systems Engineering, In Proceedings of Adaptive Computing in Engineering Design and Control, Plymouth, U.K., September, 1994; pp 21. (15) Long, Q.; Wu, C. A hybrid method combining genetic algorithm and Hooke-Jeeves method for constrained global optimization. J. Ind. Manage. Optim. 2014, 10, 1279. (16) Du, Z. P.; Kang, W. K.; Chen, T.; Yao, J.; Wang, G. Y. Novel reactive systems containing n-BuSn(O)OH for the transesterification of dimethyl carbonate and phenol. J. Mol. Catal. A: Chem. 2006, 246, 200. (17) Niu, H. Y.; Guo, H. M.; Yao, J.; Wang, Y.; Wang, G. Y. Transesterification of dimethyl carbonate and phenol to diphenyl carbonate catalyzed by samarium diiodide. J. Mol. Catal. A: Chem. 2006, 259, 292.

ASSOCIATED CONTENT

S Supporting Information *

Detailed operating parameters of the kinetic experiments of transesterification reaction at different temperatures, linear relationship between the speed of peristaltic pump and loaded DMC mass, experimentally determined temporal courses of molar fractions for all of the reactants at different temperatures, and catalyst concentrations. This material is available free of charge via the Internet at http://pubs.acs.org.

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ACKNOWLEDGMENTS

We are grateful to the National Science and Technology Ministry of China (2013BAC11B05) and Sichuan Youth Science and Technology Innovation Team Special Plan (2013−2015) for financial support.

5. CONCLUSION The purpose of this study is to provide basic kinetic data for the transesterification reaction of dimethyl carbonate with phenol in a reactive distillation reactor. The continuous loading of DMC and extracting of the methanol−DMC mixture are combined to implement a constant temperature for kinetic experiments. The result shows the the stirring speed of 600 rpm is efficient enough to eliminate the influence of mass transfer. Meanwhile, a high yield of MPC compared to DPC was found to be acquired with a constant reaction temperature in a reactive distillation reactor. A simplified but more reasonable reaction mechanism was attempted to develop a kinetic model. The model parameters were then optimized by an improved genetic algorithm. The agreement between the experimental and calculated values was excellent, which illustrated a good accuracy of the optimal rate constants and indirectly demonstrates the rationality of the supposed reaction mechanism. Nevertheless, it is worth noting that the final kinetic equation is too complex to be applied in the engineering calculation. In the future, we will continuously investigate the simplification of this kinetic model at different experimental conditions and determine the VLE data containing DPC.

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AUTHOR INFORMATION

Corresponding Author

*Tel: +86 28 85250005. Fax: +86 28 85220713. E-mail: [email protected]. Notes

The authors declare no competing financial interest. F

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(18) Frank, S.; Kai, S. Cyclohexanol production via esterification of cyclohexene with formic acid and subsequent hydration of the esters reaction kinetics. Ind. Eng. Chem. Res. 2007, 46, 1099. (19) Rodŕıguez, A.; Canosa, J.; Doḿ ınguez, A.; Tojo, J. Isobaric vapour−liquid equilibria of dimethyl carbonate with alkanes and cyclohexane at 101.3 kPa. Fluid Phase Equilib. 2002, 198, 95. (20) Hu, W. M.; Shen, L. M.; Zhao, L. J. Measurement of vapor− liquid equilibrium for binary mixtures of phenol−dimethyl carbonate and phenol−methanol at 101.3 kPa. Fluid Phase Equilib. 2004, 219, 265. (21) Hwang, I. C.; Shin, S. H.; Jeong, I. Y.; Jeon, Y. H.; Park, S. J. Isobaric vapor−liquid equilibrium at 101.3 kPa and excess properties at 298.15 K for binary mixtures of methyl phenyl carbonate with methanol or dimethyl carbonate. Fluid Phase Equilib. 2013, 360, 260.

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