Kinetic and Reactive Distillation for Acrylic Acid Synthesis via

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Kinetic and reactive distillation for acrylic acid synthesis via transesterification Cuncun Zuo, Tingting Ge, Chunshan Li, Shasha Cao, and Suojiang Zhang Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01128 • Publication Date (Web): 15 Jun 2016 Downloaded from http://pubs.acs.org on June 17, 2016

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Industrial & Engineering Chemistry Research

Kinetic and reactive distillation for acrylic acid synthesis via transesterification Cuncun Zuoa, Tingting Geb, Chunshan Lia, *, Shasha Caoa, Suojiang Zhanga, * a

Beijing Key Laboratory of Ionic Liquids Clean Process, Key Laboratory of Green Process and Engineering, State Key Laboratory of Multiphase Complex Systems, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, PR China

b

School of Chemical and Environmental Engineering, China University of Mining & Technology-Beijing, Beijing 100083, PR China

Abstract Reaction distillation was firstly used for the process of acrylic acid synthesis through transesterification of methyl acrylate with acetic acid using a strongly acidic cationic exchange resin catalyst (NKC-9). Pseudo-Homogeneous (P-H) and Langmuir-Hinshelwood (L-H) heterogeneous kinetic models were presented and fitted with the experiment data obtained from batch reaction. The key factors of heterogeneous kinetic model were the four components adsorption equilibrium constants on the catalyst surface and they were determined by adsorption experiments. The activity coefficients were calculated using the NRTL method. The catalyst stability was evaluated in a fixed-bed reactor. Catalyst activity had no obviously decrease after 1000 hours running. A reactive distillation column for acrylic acid synthesis was proposed and designed with process simulation. Keywords: Reaction distillation; Acrylic acid; Methyl acrylate; Transesterification; Kinetic

*Corresponding author: Chunshan Li. TEL/FAX: +86-10-82544800; E-mail: [email protected] Suojiang Zhang.TEL/FAX:+86 10-82627080; E-mail: [email protected]

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1. Introduction Acrylic acid, an important organic raw material and synthetic resin monomer, is widely used in adhesives, paints, chemical fibers, leathers, textiles and photosensitive resin plates industries. The global market for acrylic acid has recently showed strong growth with the increasing demand of superabsorbent polymers, adhesives, and sealants.1,2 Emerging economies demand superabsorbent polymers, which has become the main driving force of the acrylic industry. In addition, the booming construction is another main thrust for the rapid growth in acrylic. Obtaining methyl acrylate using acrylic acid as the reacted material is a promising method.3-5 The primary drawbacks of methyl acrylate hydrolysis in synthesizing acrylic acid are the high activation energy and long time to reach equilibrium.6 Using acetic acid instead of water to synthesize acrylic acid can effectively alleviate the problems in these two areas. Transesterification, which is an important chemical reaction in industries, includes three reaction types-alcoholysis, acidolysis, and ester exchange reaction. These reactions can be performed using base catalysts7,8 such as metal hydroxides, metal alkoxides, alkaline-earth oxides, and hydrotalcites. Moreover, acid catalysts9-14 such as sulfuric, sulfonic, phosphoric, and hydrochloric acids can also be used to catalyze the transesterification reaction. Ion-exchange resin has recently received much attention because of its significant superiorities over the routine method of conducting the sequential reaction and separation15-17. The adsorption and kinetic parameters for the transesterification of methyl acetic with hexanol was determined under different experimental conditions using the ion-exchange resinAmberlyst-131 as the catalyst18. Y. Liu et al.19 investigated the kinetic of the transesterification of methyl acetic with n-octanol in a batch stirred reactor catalyzed by the cation exchange resin Amberlyst 15. Van de Steene et al.16 successfully obtained methyl acetic by the transesterification of ethyl acetic with methanol over the ion-exchange resin Lewatit K1221. J. He et al.15 established a non-equilibrium stage model to describe the reactive distillation and used the Newton-Homotopy method to simulate the transesterification of methyl


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acetic with n-butanol. Alonso et al.20 studied the polarity effect of the esters on the transesterification reaction rate with sulfuric acid (homogeneous) and Dowex DR2030 sulfonic resin (heterogeneous) as catalysts; the positive effect of the heterogeneous acid catalysis of H-bond in stabilizing the active intermediate involved in the rate determining step was identified. Sertet al.18 developed a heterogeneous Langmuir−Hinshelwood−Hougen−Watson (LHHW) type reaction rate model for the hexyl acetic synthesis , and the UNIQUAC model was used to account for the non-ideal thermodynamic behavior of reactants and products in the transesterification of methyl acetic with1-hexanol catalyzed by the cation exchange resin Amberlyst-131. A strongly acidic cation-exchange resin (NKC-9) was developed in this study for catalyzing transesterification to synthesize acrylic acid when azeotrope does not exist in the system and the equilibrium time is shorter compared with the hydrolysis reaction of methyl acrylate. The same experiment was repeated under different reaction conditions to obtain the optimised operating parameters, adsorption parameters, and kinetic parameters. Given the non-ideality of the liquid phase from the ideal solution in the reaction system, the NRTL model was selected to correct the molar fractions and the activity coefficients were calculated using the UNIFAC method; and the adsorption equilibrium constants for the four components with NKC-9 were determined by performing adsorption experiments between two non-reacting species. The kinetic data were correlated with the PH and LH models. Finally, the simulation and calculation of the catalytic transesterification for acrylic acid synthesis in the reactive distillation column were performed.

2. Experimental 2.1. Materials 2.1.1 Chemicals Acetic acid, acrylic acid, and methyl acetic, purchased from Sinopharm Chemical Reagent Co.,



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Ltd., are of analytical grade. Hydrochloric acid and sodium chloride were also purchased from the same chemical reagent factory. Methyl acrylate with a purity of more than 99.57 wt. %, was bought by Baishun Chemical Reagent (Beijing) Co., Ltd. Distilled water was homemade in our laboratory and used to wash the apparatus and catalysts. 2.1.2 Catalyst NKC-9, a highly cross-linked polystyrene-divinylbenzene resin functionalized with sulfonic groups, was used as the catalyst in our study. The relevant characteristics of the NKC-9 resin are summarized in Table 1. Before NKC-9 was used for the catalysts for the transesterification reaction, the purchased resins were soaked in 10 wt. % NaCl solution for more than 20 h. Then, the salt solution was removed and the resin was washed with clear water and dried at 353.15 K under vacuum for 14 h.

Table 1. Physicochemical characteristics of the resin (NKC-9).

2.1.3 Analytics All samples were analyzed using gas chromatography (GC-2010, Shimadzu, Japan) with a BID detector and a chromatographic capillary column Rtx-Wax (30m×0.25mm×0.25µm). The column temperature increased to 433.15 K with a programmed temperature method. The vaporizing chamber and detector temperatures were set to 433.15 and 453.15 K, respectively. High purity helium gas (>99.9999%) was used as carrier. An external standard method was used to quantitatively analyze all samples. 2.2. Apparatus and procedure 2.2.1 Kinetic


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The kinetic experiments of the transesterification of methyl acrylate with acetic acid were performed in a 250 mL three-neck flask equipped with a reflux condensing tube, thermometer, and sampling device. A mechanical stirrer was used to mix the reactants. The reaction temperature was controlled to within ±0.1 K by Super thermostat water bath. First, methyl acrylate and the catalyst were heated to the desired reaction temperature in the reactor. Acetic acid was preheated to the desired reaction temperature and then quickly poured into the reactor. The transesterification reaction then started. The kinetic of the transesterification reaction was investigated by analyzing the composition of small samples which were withdrawn from the liquid mixture at regular intervals. After a steady state was achieved, the product was collected in a sampling flask. 2.2.2 Adsorption experiments The adsorption equilibrium constant of liquid on the surface of the catalyst was needed for the adsorption-based kinetic model. Four binary non-reactive mixtures considered the different reactants in the NKC-9 surface using the Popken et al. assumption26. The binary liquid mixture was formulated with a total weight of 20 g and a composition of 25 wt. % of the stronger adsorbing species at the beginning of the adsorption experiments. The liquid mixture and catalyst were heated at a constant temperature (298.15 K) for 24 h. The liquid samples were prepared and analyzed by GC after reaching adsorption equilibrium. 2.2.3 Swelling experiments Swelling experiments were conducted at 298.15 K in a sealed and graduated cylinder with a volume of 10±0.1 cm3 to investigate the swelling capacity of resin catalyst on single substrate. Approximately 5 cm3 of the vacuum-dried catalyst was placed in the cylinder, and then a single substrate was gradually added until the liquid level was about 1cm3 higher than the catalyst level. A



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sealed and graduated cylinder was placed in an ultrasonic bath, and the catalyst volume was measured after 24 h. The experiment was repeated at least thrice in order to increase experimental accuracy of the results. 2.2.4 Fixed-bed Experiments To obtain the optimised space-time, we investigated the transesterification in a fixed-bed reactor packed with the pretreated NKC-9 catalyst. The catalyst load (W) was 0.684 g catalyst/mL reactor volume for the basic case. The experiment was repeated to study the effect of space-time on the conversion rate of methyl acrylate with different space-time values.

3. Results and discussion 3.1. Calculation of activities and thermodynamic properties Considering that the reaction system of acrylic acid synthesis greatly deviated from ideal solution, the NRTL and UNIQUAC models were chosen to correct the non-ideality of the liquid phase. The multicomponent expressions for the activity coefficient for the NRTL and UNIQUAC equations are available in Supporting Information. Moreover, the experimental and calculated VLLE data for the acrylic acid/methyl acetate and acetic acid/methyl acrylate binary systems are also clearly listed in Supporting Information. The VLLE data for acetic acid/acrylic acid, acetic acid/methyl acetate, and methyl acrylate /acrylic acid binary systems are stored in the database of Aspen. With respect to the VLLE data of methyl acetic/methyl acrylate binary system, Tu et al. have conducted experiments and obtained detailed data.21 Furthermore, we investigated the deviations between the calculated and experimental values through the NRTL and UNIQUAC models for acrylic acid / methyl acetate and acetic acid / methyl acrylate, which were clearly shown in Table 2.


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According to the deviation above, the NRTL model demonstrated better results compared with the UNIQUAC model. Thus, we only calculate the binary interaction parameters of the NRTL model for acetic acid, methyl acrylate, acrylic acid, and methyl acetate (Table 3).

Table 2. Deviations between the calculated and experimental values on x1, y1, and T through the NRTL and UNIQUAC models for acrylic acid / methyl acetate and acetic acid / methyl acrylate.

Table 3. Binary interaction parameters of the NRTL model for acetic acid, methyl acrylate, acrylic acid, and methyl acetate.

3.2. Kinetic experiments and optimization of transestrification conditions 3.2.1. Elimination of Mass Transfer Resistance. To study the reaction kinetic, the effects of internal and external diffusion on transestrification must be excluded. To investigate the internal diffusion involved in the reaction system, NKC-9 resin catalyst was screened into several different particle sizes, including 28, 32, and 35 mesh. The same experiment was repeated with different particle sizes at the same stirring speed, reaction temperature, catalyst load, and reactants molar ratio. The conversion rate of methyl acrylate is defined as the ratio of the amount of methyl acrylate reacted and the initial amount of methyl acrylate. Figure 1 shows that when the catalyst particle size is ≥32 mesh, the conversion rate of methyl acrylate was almost unaffected by the particle size. However, when the catalyst particle size is 28 mesh, the conversion rate of methyl acrylates lightly decreased. External diffusion effects could be eliminated by increasing the stirring speed, and the experiment was repeated with the stirring speed range from 300



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to 500 rpm. As can be seen from Figure 2, when the stirring speed was increased to ≥300 rpm, the conversion rate of methyl acrylate was almost constant, which indicated the external mass transfer is not the rate limiting step at that time.22 Sanz et al.23 investigated the external diffusion and found that it does not usually control the overall reaction rate unless when the stirring speed was low or when the reactants were viscous. Thus, all further experiments were performed under stirring speed of 300 rpm. The catalyst particle size of ≥32 mesh and stirring speed ≥300 rpm were required to ensure the experimental accuracy.

Figure 1. Effect of the catalyst particle size on the conversion rate of methyl acrylate using NKC-9 as the catalyst (300 rpm; 80 °C; = 1:1; the catalyst load was 0.10 g catalyst / g liquid mixture).

Figure 2. Effect of the stirring speed on the conversion rate of methyl acrylate using NKC-9 as the catalyst (28 mesh; 80 °C; = 1:1; the catalyst load was 0.10 g catalyst / g liquid mixture).

3.2.2 Effect of Catalyst Load. The same experiment was repeated at 353.15 K with initial molar ratio of acetic acid and methyl acrylate being 1 ( = 1: 1), catalyst particle size of 28 mesh, and stirring speed of 300 rpm. The effect of catalyst load on the conversion rate of methyl acrylate can be determined by changing the amount of catalyst load. To detection the autocatalytic effect of the acetic acid, a blank assay experiment was performed in the absence of catalyst. Figure 3 indicated without catalyst the autocatalytic behavior of acetic acid can be negligible because the conversion rate of methyl acrylate below to 4% after 30 h. In addition, the reaction equilibrium time of transesterification was


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decreased with the increase in catalyst load. As shown in Figure 4, it is obvious that the reaction rate constant increases linearly with the addition of catalyst load. The reaction rate constant, k0 and the concentration of catalyst load, Ccat can be expressed as: k+ / k+ (0.08 g catalyst / g liquid mixture)=114.7Ccat.(g/ g liquid mixture)-8.26. Such behavior is attributed to the increased amount of acidic sites for reaction with the addition of catalyst load.23

Figure 3. Effect of catalyst load (NKC-9) on the conversion rate of methyl acrylate (353.15 K, = 1: 1, 28 mesh, and 300 rpm).

Figure 4. Effect of catalyst load on the forward reaction rate constant at 353.15 K with initial molar ratio of acetic acid and methyl acrylate being 1.

3.2.3. Effect of molar ratio of acetic acid and methyl acrylate. The experiments were conducted at the initial molar ratio of acetic acid and methyl acrylate varying from 1:1 to 3:1 at 353.15 K with catalyst load being 0.1 g/g, catalyst particle size of 28 mesh, and stirring speed of 300 rpm. According to the theories of reversible equilibrium reaction, increased the amount of one reactant can enhance the equilibrium conversion rate of the other reactants. Figure 5 shows the effect of molar ratio of reactants on the conversion rate of methyl acrylate. It was obvious that the conversion rate of methyl acrylate was gradually increased with the increase in the initial molar ratio of reactants. When the initial molar ratio increased from 1:1 to 2:1, the increment of equilibrium conversion rate of methyl acrylate was about 8%, and the increment was almost the same when the initial molar ratio increased from 2:1 to 3:1. However, the residual amounts of acetic acid were about 51%, 71.5%, and 78.4%, respectively. The separation between acetic acid and acrylic acid liquid mixture was hard, which can be attributed to the H-bonds interactions of acid



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molecules. Hence, in despite of high conversion rate of methyl acrylate, the high molar ratio of reactants will increase the difficulty in the separation of acrylic acid at the same time. Combining two considerations, the initial ratio of reactants of 1:1 was the best choice.

Figure 5. Effect of molar ratio of reactants on the conversion rate of methyl acrylate using NKC-9 as catalyst (353.15 K, 28 mesh, 300 rpm, and the catalyst load was 0.10 g catalyst/g liquid mixture).

3.2.4. Effect of reaction temperature. The experiments were conducted at the reaction temperature varying from 343.15 to 363.15 K with catalyst load being 0.1 g/g, initial molar ratio of 1:1, catalyst particle size of 28 mesh, and stirring speed of 300 rpm. As shown in Figure 6, the conversion rate of methyl acrylate remarkably increase with the elevated temperature, but the increment of equilibrium conversion rate for methyl acrylate from 343.15 to 353.15 K was higher compared with the change in the conversion rate of methyl acrylate when the reaction temperature increase from 353.15 to 363.15K. According to the Arrhenius law, high temperature make molecules move faster, collide more vigorously, and therefore greatly increased the likelihood of bond cleavages and rearrangements, but the excessive high reaction temperature was inadvisable due to the presence of double bond in methyl acrylate and acrylic acid. Thus, the optimized reaction temperature for the transeatrification was 353.15 K through synthetically consideration.8, 24

Figure 6. Effect of reaction temperature on the conversion rate of methyl acrylate using NKC-9 as the catalyst ( = 1: 1, 28 mesh, 300rpm, and the catalyst load was 0.1 g catalyst/g liquid mixture).


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3.3. Kinetic Model and Equilibrium Constant The rate expression −rA is determined by the hypothesis ofthe reaction mechanism. A pseudo-homegeneous (PH) and an adsorption Langmuir-Hinshelwood (LH)16, 18, 25, 26 models were adopted to investigate the kinetic of the catalytic transesterification of methyl acrylate with acetic acid over NKC-9 catalyst. The reaction rate r expression in a constant volume reactor can be listed as follows: =

1 1 (1)

where, is the quality of the catalyst; is the stoichiometric coefficients of substance in reaction; is the molarity of substance; t is the recation time.

What is the main difference between the PH (ideal) and PH modelsis that the latter one takes molecular properties into consideration such as the size, inter-atomic forces, spatial structures. Moreover, the PH model was modified by using the activity instead of concentration. In the PH (ideal) model, rPH was listed as below: = −

(2)

where , , and were the molar fraction of acetic acid, methyl acrylate, acrylic acid

and methyl acetate, respectively. and were the forward reaction rate constant and the

equilibrium constant. In order to simplify the reaction kinetic equation, pseudo homogeneous dynamic model was applied to the catalysis reaction. With the reference to other ester hydrolysis reaction26, the reaction was assumed to be the second order reaction. The reaction rate r of reversible reaction can be expressed as follows:



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− =

" = # (" " − " " ⁄ ) (3)

After organized and integral, equation was shown as follows: &=

1 2,C.. ⁄(/ − g(.* ) + 1 + = # (4) g (.* 2,C.. ⁄(/ + g(.* ) + 1

Where " , " represent the concentration of acrylic acid and methyl acetate. " was selected as the variable, and other variables were calculated on basis of stoichiometric numbers and the following several formulas: g = β4 − 45γ, α = "( ∗ "( , β = −(C( + "( ), γ = 1 − 1/ , where CMA0 and CHAc0 represent the initial concentration of methyl acrylate and acetic acid. "( , "( , and the equilibrium constant Keq as well as the concentration value of every point in Figure 6 were brought into the Eq 4, and the relationship of Z and t was plotted in Figure 7. The straight line was obtained from fitting the data using the least squares method, and the slope represents the forward reaction rate constant, as shown in Table 4. The correlation coefficient R2 are all above 0.98, indicating a better linear fitting and reliable experimental data.

Figure 7. The curve of Z and t

Table 4. The reaction rate constants at different temperatures The experimental results demonstrate the temperature had a great effect on the reaction rate, and the relationship between them can be described using Arrhenius equation (5): : = ( ;? ) (5) The above formula was taken the logarithm, getting the equation (6): +: = +( − = ⁄>? (6)


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ln k1 and 1 / T were plotted in one figure, the forward and adverse reaction rate constant were illustrated in Figure8, respectively. The slope of the straight line fitted was -E / R.

Figure 8.Relationship between the forward reaction or the adverse reaction rate constant and the temperature. The linear equation of the forward reaction rate constant and the temperature was described with Y=7.722-7.175X, E+ and k+.0 were calculated: =# = 59.65C · E+ F: and #.( = 2.26 × 10I . Overall, the relationship formula 9 of forward reaction rate constant and temperature in methyl acrylate hydrolysis reaction was obtained： # = 2.257 × 10I exp(−7174.8⁄?) (7) The linear equation of the adverse reaction rate constant and the temperature was described with Y=-11.368-0.362X, E- and k-.0 were calculated: =F = 3.010C · E+ F: and F.( = 1.156 × 10F* . Overall, the relationshipformula10 of adverse reaction rate constant and temperature in methyl acrylate hydrolysis reaction was obtained： F = 1.156 × 10F* exp(−361.8⁄? ) (8) Experimental conversion curve of methyl acrylate and the dynamics simulation curve were compared under the condition that temperature of 353.15 K, catalyst load of 0.75 g/g, and θ B of 1. 0

The results were shown in Figure 9.

Figure 9. Comparison between the experimental data and simulation data.

As shown in Figure 9, the experimental values and dynamics simulation results had a good inosculation, indicating the validity of the kinetic equation.



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Related parameter identification based on the above model, kinetic equation of transesterification were shown the general expression, as follows: r=

(5 5 − 5 5 / ) (9) (1 + 5 + 5 + 5 + 5 )P

where 5 refer to the activity of substances, refer to the adsorption equilibrium constant of substances; when n=2 or 0, equation will be turned into LH model (assuming the reaction on the catalyst was the rate determining step) and PH model, respectively. Among of the equations , the rate constant of reaction, k can be calculated by Arrhenius equation, as shown equation (10). −=, R (10) = ( exp Q >? Where ke0 and EA,e refer to pre-exponential Arrhenius factor and activation energy. To sum up, the kinetic models for transesterification were obtained, as shown in Table 5.

Table 5. Different kinetic models and their identification parameters.

3.3.1. Determination of reaction equilibrium constant. By definition,Chemical reaction equilibrium constant Keq can be solving by Eq 11, where , , refer to the mole fraction and activity coefficient of component respectively. The chemical equilibrium constant for the reaction was shown in Table 6,based on the experimental data. 5 5 , , = ( ) = Q R Q R = S × T (11) 5 5 , ,

Table 6. Reaction equilibrium constants at different temperatures.


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According to the equation of Van’t Hoff, there was a certain relationship between the chemical equilibrium constant and temperature. From the equation, the enthalpies of reactions in non-ideal and ideal liquid were about 57.45 and 56.64 kJ/mol, respectively. To the activity meter: ln = −6.910 × 10I /? + 19.12 (12) To the concentration meter: ln = −6.813 × 10I /? + 19.09 (13) 3.3.2. Determination of adsorption equilibrium constant. The results of our measurements of the swelling ratio which is the volume of solvent-equilibrated resin divided by the dry volume of the resin in a sealed graduated cylinder are reported in Table 7. The values given are mean values of at least three experiments conducted at 298.15 K. Assuming that the resin bed’s volume changes in the same way as the volumes of the individual resin microspheres, adsorbed volumes can be calculated from the swelling ratio. Also assuming ideal mixing, that is, no excess volume, the adsorbed mass and amount per gram of catalyst can be calculated.

Table 7. Specific volumetric dilatation of NKC-9 resin catalyst for single substrate.

According to Popken et al.,26 the relationship between the liquid and resin polymer can be described by Eq. 14:

( (W( − WX ) Y WZX − ZY WX = (14)

where ( refers to the initial total solvent weight (g); refers to the catalyst mass (g); W(



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refers to the overall weight fraction of component i; WX and WZX refer to the equilibrium

liquid-phase weight fraction of solvent i and j, respectively; Y and ZY refer to the adsorbed mass of solvent i and j. Assuming Langmuir-type adsorption based on mass, the following relationship for the mass coverage mis/ms can be obtained, with ms being the total adsorbed mass and αj the liquid phase activities. K refers to the adsorption equilibrium constant for the solvents.

Y 5 = (15)

Y 1 + ∑Z Z 5Z Combining Eqs.14 and 15 for the binary case, the following relation is obtained :

( (W:( − W:X )

Y : 5: W4X − 4 54 W:X = (16)

1 + : 5: + 4 54 Four nonreactive binary pairs including acetic acid/acrylic acid (1), methyl acrylate/acrylic acid

(2), acrylic acid/methyl acetate (3), and methyl acrylate/methyl acetate (4) were investigated to maximize the adsorption strength differences in order to ensure the experimental accuracy. The results of a fit of all four adsorption equilibrium constants fited to all the data are illustrated in Figures 10 and 11 and reported in Table 8.

Figure 10. Relative adsorption of acrylic acid from acrylic acid (AA)/acetic acid (HAc) and acrylic acid (AA)-methyl acrylate (MA) mixtures over NKC-9 catalyst and calculated dependence assuming constant adsorbed mass.

Figure 11. Relative adsorption of methyl acrylate from a mixture of methyl acrylate (MA)/methyl acetic (MeAc) and relative adsorption of acetic acid from a mixture of acetic acid (HAc)/methyl


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acetic (MeAc) over NKC-9 catalyst and calculated dependence assuming constant adsorbed mass.

Table 8. Results of the regression for the nonreactive binary adsorption data at 298.15 K.

3.3.3. Determination ofreaction rate constant, activation energy and pre-exponential. According to the dynamic model, the relevant parameter was identified by using nonlinear least square method on the basis of the experimental data. Taking SRS in the Eq 17 as the objective function of recognition, the identification parameters were obtained when the objective function acquire the minimum. P

SRS = ^( _ − S` )4 (17)

where _ , S` refer to the value of calculated and experimental reaction rate, respectively. As shown in Figure 12 and Table 9, different model identification have different refers to the former factor, this is because of a description of the different model in a different way.27-29 However, the value of activation energy was almost the same, and equal to 99.75 kJ/mol.

Table 9. Identification of activation energy =, and pre-exponential for ( for different models. Figure 12. ln ~ 1000/? relationship.

3.3.4. Verification the results of different models. Based on the kinetic modelsobtained from the experiments, the experimental values (the initial



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conditions) involved in reaction process were recalculted to get a series of caluculated values. By comparing the experimental and calculation values using mean relative deviation (MRD) as the standard, the accuracy of the LH and PH models turned out to be higher than that of the LH model (ideal). Taking the non-ideal of liquid mixture into consideration, the reaction process can be better described, as shown in Table 10. MRD/% =

1

Pghijkl

Y e`_

( ^ f

_ − S` f) × 100 (18) S`

Table 10. Comparison between experimental and calculated values using different models.

3.4. Determination of Space-Time of the Fixed-Bed Reactor. To investigate the effect of space-time (τ) on the conversion rate of methyl acrylate under the optimised reaction conditions achieved by the batch reactor, a series of experiments were performed with different space-time in a fixed-bed reactor packed with NKC-9 resin catalyst. The space-time for the fixed-bed reactor was defined as the function of the effective volume of reactor (m ) and

volumetric flow rates of reactants (F), and the equation was described asτ = m /n. As shown in

Figure 13, it is obvious that the conversion rate of methyl acrylate gradually increase before the space-time achieves to 4h, but the conversion rate value keeps almost as a constant after 4 h. These results demonstrate that 4h was the optimised space-time for the fixed-bed reactor.

Figure 13. Effect of space-time on the conversion rate of methyl acrylate in the fixed-bed reactor (353.15 K； = 1: 1；the catalyst load (W) was 0.684 g catalyst/mL reactor volume).


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3.5. Reaction Distillation. A simulation model of a reactive distillation process is indispensable to design columns and optimise processes incorporating the reactive distillation technology. The EQ–EQ approach, the simplest modeling approach, was used in our study. Assuming phase and chemical equilibrium in each stage, a reactive distillation column was modeled. The column was axially discretized into equilibrium stages and the height of each stage was equivalent to the height of a theoretical plate (HETP) of the used packing. The kinetic model obtained from the stationary solution in a batch reactor (Section 3.3) was used to describe the chemical equilibrium of the reactive distillation column. It was assumed that the chemical equilibrium was reached in each stage in the column. The RADFRAC block of Aspen Plus30-35 and the Newton homotopy arc length differential method with a good convergence were used to determine the optimised reactive distillation column set-up, and maximising yield was the optimisation target. The reactive distillation column is separated into four sections by two feed inlets, and the four sections are rectifying section, the extractive distillation section, reaction section, and stripping section (Figure 14). The main function of the rectifying section is to separate the low-boiling product and acetic acid, and the important function of the extractive distillation section is to separate some minimum-boiling point azeotrope by acetic acid to ensure the purity of low-boiling product, although there is no azeotropic phenomenon in this reaction system. The reaction section is the main place where the transesterification takes place, and the function of the stripping section is to separate the high-boiling product (acrylic acid) from the reaction mixtures. Acetic acid is fed at the top inlet, and methyl acrylate is fed at the bottom inlet. In the paper, the kinetic results obtained from the experiments in a batch reactor were used for the simulation of the reactive distillation (RD) process, and the amount of catalyst that is immobilised in the reactive section was set to 0.10 g catalyst / g liquid mixture. Figure 15 shows the temperature/pressure vs. column height in the reactive



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

distillation column. The temperature within the reactive distillation column was in the vicinity of 353.15 K used to study the reaction kinetic. And he operating pressure of the column was 0.065 MPa. The optimisation of theoretical plates number, reflux ratio, HAc feeding position, and MA feeding position were clearly shown in the Supporting Information, and the optimization results were given in Table 11. Figure 16 illustrates the vapor-liquid composition distribution in the reactive distillation column.

Figure 14. Schematic diagram of reactive distillation column.

Table 11. Parameters and results of simulation and optimization.

Figure 15. Distribution of temperature and pressure in reactive distillation column.

Figure 16. Vapor−Liquid composition distribution in reactive distillation column.

3.6. Long-life evaluation. The mixture solution of acetic acid and methyl acrylate with a molar ratio of 1:1 is formulated. The reaction temperature and space-time were set to 353.15K and 4h to investigate the life of the catalyst- NKC-9.

Figure 17. Lifetime evaluation of NKC-9.


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As can be seen from Figure 17, the conversion rate and selectivity of methyl acrylate did not change visibly after a long period of running such as 1200 h in a fixed-bed reactor, which convincingly verified the long life of the catalyst. Compared with the catalyst after a short time running, there was a slight decrease in the conversion rate of methyl acrylate, which may be attributed to the adsorption of macromolecular polymerization inhibitor on NKC-9 resin catalyst. The macromolecular polymerization inhibitor can occupy the acid site of the catalyst and block its pore structure, resulting in the weakening of the catalytic activity to some extent. Figure 18 shows the PM photomicrographs of the fresh and used NKC-9 catalyst in the fixed-bed reactor, the changes in the catalyst morphology are clearly shown. No. 1 is the photomicrograph of fresh catalyst, which is an inerratic ball with the smooth and uniform surface. No. 2, 3, and 4 present the morphology structure of the used catalyst, and there are different damages containing pits, cracks, and fragmentation caused by collision and squeeze in the fix-bed reactor after over 1000 h long time running. However, the catalyst breakage was found less than 5 wt. % after sieving the catalyst.

Figure 18. PM photomicrographs (of the fresh and used NKC-9catalyst (1. Fresh catalyst; 2, 3, and 4. Used catalyst; magnification: eyepiece 20×objective lens 30×).

4. Conclusions The NKC-9 resin catalyst has shown a good catalytic activity for the transesterification of methyl acrylate with acrylic acid. By batch reaction experiments, the optimised operating parameters were obtained including a catalyst load of 0.1 g catalyst/g liquid mixture, reaction temperature of 353.15 K, molar ratio of reactants of 1:1, stirring speed of 300rpm, and catalyst particle size of >32 mesh. According to the swelling and adsorption equilibrium experiments, the adsorption of methyl acetic and acetic acid was found to stronger than that of acrylic acid and methyl acrylate. Using



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several models to fit the kinetic experimental data, the LH model turned out to be the most suitable for the transesterification involved, having taken the activity and adsorption equilibrium constants into consideration. In addition, 4.0 h was the most appropriate space-time in the fixed-bed reactor for the acrylic acid synthesis. At last, a reaction distillation process was proposed and simulated, and the methyl acrylate conversion rate of 94.5 % and the acrylic acid concentration of ≥98.0% in the tower bottom were achieved under the optimised parameters.

Acknowledgments The authors gratefully acknowledge the National Program on Key Basic Research Project (No. 2015CB251401), National Science Fund for Excellent Young Scholars (No. 21422607), Key Program of National Natural Science Foundation of China (NO. 91434203), and Research Supported by the CAS/SAFEA International Partnership Program for Creative Research Teams.

Nomenclature of the signs, marks, and simplified characters used. Signs/marks /simplified characters

Physical meaning/meaning

P-H

Pseudo-Homogeneous

L-H

Langmuir-Hinshelwood

LHHW

Langmuir−Hinshelwood−Hougen−Watson

θp

initial molar ratio of acetic acid to methyl acrylate

r

reaction rate

ccat

catalyst load (g catalyst / g liquid)

quality of the catalyst molarity of substance

ν

stoichiometric coefficient

t

the recation time

x

molar fraction

k

reaction rate constant (L mol-1 s-1)

Keq

thermodynamic equilibrium constant

c

molar concentration

α

activity


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γ

activity coefficient

EA/E

apparent activation energy (kJ mol−1)

ko

pre-exponential Arrhenius factor (mol s−1 g−1)

W

weight fraction

MRD

mean relative deviation

eq

equilibrium

i, j

components

cal

calculated value

exp

experimental value

τ

space-time



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References (1) Zuo, C., Pan, L., Cao, S., Li, C., Zhang, S. Catalysts, kinetics, and reactive distillation for methyl acetate synthesis. Ind. Eng. Chem. Res. 2014, 53, 10540-10548. (2) Ma, J.; Zhang, M.; Lu, L.; Yin, X.; Chen, J.; Jiang, Z. Intensifying esterification reaction between lactic acid and ethanol by pervaporation dehydration using chitosan-TEOS hybrid membranes. Chem. Eng. J. 2009, 155, 800-809. (3) Yang, X. G., Zhang, J. Q., Liu, Z. T. The nickel-catalyzed hydroesterification of acetylene with methyl formate to methyl acrylate. Appl. Catal. A. Gen. 1998, 173, 11-17. (4) Tang, C. M., Li, X. L., Wang, G. Y. A highly efficient catalyst for direct synthesis of methyl acrylate via methoxycarbonylation of acetylene. Korean. J. Chem. Eng. 2012, 29, 1700-1707. (5) Jiao, T., Li, C., Zhuang, X., Cao, S., Chen, H., Zhang, S. The new liquid–liquid extraction method for separation of phenolic compounds from coal tar. Chem. Eng. J. 2015, 266, 148-155. (6) Li, Y. P., Huo, Q., Zuo, C. C., Cao, S. S., Wang, E. Q. Resin Material Used in Methyl Acrylate Hydrolysis Reaction. Adv. Mater. Res. 2014, 1035, 307-312. (7) Zhang, B., Ding, G., Zheng, H., Zhu, Y. Transesterification of dimethyl carbonate with tetrahydrofurfuryl alcohol on the K2CO3/ZrO2 catalyst—Function of the surface carboxylate species. Appl. Catal. B: Environ. 2014, 152, 226-232. (8) Thimmaraju, N., Shamshuddin, S. Z. M., Pratap, S. R., Venkatesh.Transesterification of diethyl malonate with benzyl alcohol catalyzed by modified zirconia: Kinetic study. J. Mol. Catal. A-Chem. 2014, 391, 55-65. (9) Wang, J. Q., Sun, J., Cheng, W. G., Shi, C. Y., Dong, K., Zhang, X. P., et al. Synthesis of dimethyl carbonate catalyzed by carboxylic functionalized imidazolium salt via transesterification reaction.


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Catal. Sci. Technol. 2012, 2, 600-605. (10) Kuschnerow, J. C., Titze-Frech, K., Schulz, P. S., Wasserscheid, P., Scholl, S. Continuous Transesterification with Acidic Ionic Liquids as Homogeneous Catalysts. Chem. Eng. Technol. 2013, 36, 1643-1650. (11) Schenzel, A. Catalytic transesterification of cellulose in ionic liquids: sustainable access to cellulose esters. Green. Chem. 2014, 16, 3266-3271. (12) Peng, Y., Cui, X., Zhang, Y., Feng, T., Tian, Z., Xue, L. Kinetics of Transesterification of Methyl Acetate and Ethanol Catalyzed by Ionic Liquid. Int. J. Chem. Kinet. 2014, 46, 116-125. (13) Haken, J. K., Ho, D. K. M. Studies in transesterification VI. Ion-exchange catalysis. J. Appl. Chem. 2007, 20, 101-104. (14) Kotadia D A, Soni S S. Sulfonic acid functionalized solid acid: an alternative eco-friendly approach for transesterification of non-edible oils with high free fatty acids. Monatshefte Fuer Chemie/chemical Monthly. 2013, 144, 1735-1741. (15) He, J., Xu, B., Zhang, W., Zhou, C., Chen, X. Experimental study and process simulation of n-butyl acetate produced by transesterification in a catalytic distillation column. Chem. Eng. Process. 2010, 49, 132-137. (16) Steene, E. V. D., Clercq, J. D., Thybaut, J. W.Adsorption and reaction in the transesterification of ethyl acetate with methanol on Lewatit K1221. J. Mol. Catal. A-Chem. 2012, 359, 57-68. (17) Shen, L., Wang, L., Wan, H., Guan, G. Transesterification of Methyl Acetate with n-Propanol: Reaction Kinetics and Simulation in Reactive Distillation Process. Ind. Eng. Chem. Res. 2014, 53, 3827-3833. (18) Sert E, Atalay F S. Determination of Adsorption and Kinetic Parameters for Transesterification



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of Methyl Acetate with Hexanol Catalyzed by Ion Exchange Resin. Ind. Eng. Chem. Res. 2012, 51, 6350-6355. (19) Liu, Y., Wei, M., Gao, L., Li, X., Mao, L. Kinetics of transesterification of methyl acetate and n-octanol catalyzed by cation exchange resins. Korean. J. Chem. Eng. 2013, 30, 1039-1042. (20) Alonso, D. M., Granados, M. L., Mariscal, R., Douhal, A. Polarity of the acid chain of esters and transesterification activity of acid catalysts. J. Catal. 2009, 262, 18-26. (21) Tu, C. H., Wu, Y. S., Liu, T. L. Isobaric vapor-liquid equilibria of the methanol, methyl acetate and methyl acrylate system at atmospheric pressure. Fluid. Phase. Equilibr. 1997, 135, 97-108. (22) Tesser, R., Casale, L., Verde, D. Kinetics and modeling of fatty acids esterification on acid exchange resins. Chem. Eng. J. 2010, 157, 539-550. (23) Sanz, M. T., Murga, R., S. Beltrán, A., Cabezas, J. L., Coca, J. Autocatalyzed and Ion-Exchange-Resin-Catalyzed Esterification Kinetics of Lactic Acid with Methanol. Ind. En. Chem. Res. 2002, 41, 512-517. (24) Ali, S. H., Merchant, S. Q. Kinetics of the esterification of acetic acid with 2-propanol: Impact of different acidic cation exchange resins on reaction mechanism. Inter. J. Chem.Kinet. 2006, 38, 593-612. (25) Ewa BożekWinkler, Jurgen Gmehling. Transesterification of Methyl Acetate and n-Butanol Catalyzed by Amberlyst 15. Ind. En. Chem. Res. 2006, 45, 6648-6654. (26) Popken, T., Gotze, L., Gmehling, J. Reaction Kinetics and Chemical Equilibrium of Homogeneously and Heterogeneously Catalyzed Acetic Acid Esterification with Methanol and Methyl Acetate Hydrolysis. Ind. En. Chem. Res. 2000, 39, 2601-2611. (27) Zuo, C., Li, Y., Li, C., Cao, S., Yao, H., Zhang, S. Thermodynamics and Separation Process for


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Quaternary Acrylic Systems. Aiche. J. 2015, 62, 228-240. (28) Li, C., Zhang, X., He, X., Zhang, S. Design of separation process of azeotropic mixtures based on the green chemical principles. J. Clean. Prod. 2007, 15, 690-698. (29) Ray, N. M., Ray, A. K. Determination of adsorption and kinetic parameters for methyl oleate (biodiesel) esterification reaction catalyzed by amberlyst 15 resin. Can. J. Chem. Eng. 2016. (30) Li, C., Zhang, X., Zhang, S., Suzuki, K. Environmentally conscious design of chemical processes and products: Multi-optimization method. Chem. Eng. Res. Des. 2009, 87, 233-243. (31) Gangadwala, J., Surendra Mankar, A., Mahajani, S., And, A. K., Stein, E. Esterification of Acetic Acid with Butanol in the Presence of Ion-Exchange Resins as Catalysts. Ind. Eng. Chem. Res .2003, 42, 2146-2155. (32) Ewa BożekWinkler, Jürgen Gmehling. Transesterification of Methyl Acetate and n-Butanol Catalyzed by Amberlyst 15. Ind. En. Chem. Res. 2006, 45, 6648-6654. (33) Lee, M. J., Hsientsung Wu, A., Lin, H. Kinetics of Catalytic Esterification of Acetic Acid and Amyl Alcohol over Dowex. Ind. En. Chem. Res. 2000, 39, 4094-4099. (34) Li, C., Wozny, G., Suzuki, K. Design and synthesis of separation process based on a hybrid method. Asia-Pac. J. Chem. Eng. 2009, 4, 905-915. (35) Li, C., Zhang, X., Zhang, S. Environmental Benign Design of DMC Production Process. Chem. Eng. Res. Des. 2006, 84, 1-8.



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Figure and Table Captions Figure 1. Effect of the catalyst particle size on the conversion rate of methyl acrylate using NKC-9 as the catalyst (300 rpm; 80 °C; = 1:1; the catalyst load was 0.10 g catalyst / g liquid mixture). Figure 2. Effect of the stirring speed on the conversion rate of methyl acrylate using NKC-9 as the catalyst (28 mesh; 80 °C; = 1:1; the catalyst load was 0.10 g catalyst / g liquid mixture). Figure 3. Effect of catalyst load (NKC-9) on the conversion rate of methyl acrylate (353.15K, =

1: 1, 28 mesh, and 300 rpm).

Figure 4. Effect of catalyst load on the forward reaction rate constant at 353.15 K with initial molar ratio of acetic acid to methyl acrylate being 1. Figure 5. Effect of molar ratio of reactants on the conversion rate of methyl acrylate using NKC-9 as catalyst (353.15K, 28 mesh, 300rpm, and the catalyst load was 0.10 g catalyst/g liquid mixture). Figure 6. Effect of reaction temperature on the conversion rate of methyl acrylate using NKC-9 as the catalyst ( = 1: 1, 28 mesh, 300rpm, and the catalyst load was 0.10 g catalyst/g liquid mixture). Figure 7. The curve of Z and t Figure 8. Relationship between the forward reaction or the adverse reaction rate constant and the temperature. Figure 9. Comparison between the experimental data and simulation data. Figure 10. Relative adsorption of acrylic acid from acrylic acid (AA)/acetic acid (HAc) and acrylic acid(AA)-methyl acrylate(MA) mixtures over NKC-9 catalyst and calculated dependence assuming constant adsorbed mass. Figure 11. Relative adsorption of methyl acrylate from a mixture of methyl acrylate(MA)/methyl acetic(MeAc) and relative adsorption of aceticacid from a mixture of acetic acid(HAc)/methyl


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acetic(MeAc)over NKC-9catalyst and calculated dependence assuming constant adsorbed mass. Figure 12. ln ~ 1000/? relationship. Figure 13. Effect of space-time on the conversion rate of methyl acrylate in the fixed-bed reactor (353.15K； = 1: 1；the catalyst load (W) was 0.684g catalyst/mL reactor volume). Figure 14. Schematic diagram of reactive distillation column. Figure 15. Distribution of temperature and pressure in reactive distillation column. Figure 16. Vapor−Liquid composition distribution in reactive distillation column. Figure 17. Lifetime evaluation of NKC-9. Figure 18. PM photomicrographs of the fresh and used NKC-9catalyst (1. Fresh catalyst; 2.3.4. Used catalyst; magnification: eyepiece 20×objective lens 30×). Table 1. Physicochemical characteristics of the resin (NKC-9). Table 2. Deviations between the calculated and experimental values on x1, y1, and T through the NRTL and UNIQUAC models for acrylic acid / methyl acetate and acetic acid / methyl acrylate. Table 3. Binary interaction parameters of the NRTL model for acetic acid, methyl acrylate, acrylic acid, and methyl acetate. Table 4. The reaction rate constants at different temperatures. Table 5. Different kinetic models and their identification parameters. Table 6. Reaction equilibrium constants at different temperatures. Table 7. Specific volumetric dilatation of NKC-9 resin catalyst for single substrate. Table 8. Results of the regression for the nonreactive binary adsorption data at 298.15 K. Table 9. Identification of activation energy =, and pre-exponential for ( for different models. Table 10. Comparison between experimental and calculated values using different models.



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Table 11. Parameters and results of simulation and optimization.


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Figure 1.

50

Conversion rate of methyl acrylate / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40

30

20

35 mesh 32 mesh 28 mesh

10

0 0

3

6

9

12

15

18

Reaction time / h


21


Figure 2.

55 50


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

45 40 35 30 25 20

500rpm 400rpm 300rpm 0 rpm

15 10 5 0 0

5

10

15

20

Reaction time / h


25

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Figure 3.

50


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40

30

20

0.12g Catalyst/g Liquid mixture 0.10g Catalyst/g Liquid mixture 0.08g Catalyst/g Liquid mixture None

10

0 0

5

10

15

20

25

Reaction time / h


30


Figure 4.

6

k+/k+(0.08 g catalyst / g liquid mixture)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

5

4

3

2

1

0.08

0.09

0.10

0.11

Catalyst Concentration (g/g)


0.12

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Figure 5.

70

Conversion rate of methyl acrylate/%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


60

50

40

θB0=3:1 θB0=2:1

30

θB0=1:1 Pred. θB0=3:1

20

Pred. θB0=2:1 Pred. θB0=1:1

10

0 0

5

10

15

20

25

Reaction time/h


30


Figure 6.

60

Conversion rate of methyl acrylate /%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

50

40

30

363.15K 353.15K 343.15K Pred.363.15K Pred.353.15K Pred.343.15K

20

10

0 0

5

10

15

20

25

Reaction time / h


30

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Figure 7.

343.15K 353.15K 363.15K

0.4

0.3

Z

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2

0.1

0.0 0

2

4

6

8

10

12

14

Reaction time / h


16


Figure 8.

-11.7

The forward reaction The adverse reaction Y=7.722-7.175X Y=-11.368-0.362X

-12.0

-12.3

lnk

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

-12.6

-12.9

-13.2

2.70

2.75

2.80

2.85 -1

1000/T(K )


2.90

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Figure 9.

55 50 45

Conversion ratio of MA / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


40 35 30 25 20 15

Experimental data Model simulation data

10 5 0 0

5

10

15

20

Reaction time / h


25


Figure 10.

0.2

AA+MA AA+HAc

0.1

0.0

m0 (w10-w1L)/mcat

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

-0.1

-0.2

-0.3

-0.4

-0.5 0.0

0.2

0.4

0.6

0.8

wL AA


1.0

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Figure 11.

0.4

MeAc+MA MeAc+HAc 0.3

m0 (w10-w1L)/mcat

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


0.2

0.1

0.0

-0.1

-0.2 0.0

0.2

0.4

0.6

0.8

wL MeAc


1.0


Figure 12.

PH(ideal) PH LH

-4

lnke

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

-5

-6 2.76

2.80

2.84 3

-1

2.88 -1

10 T /K


2.92

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Figure 13.

60

Conversion rate of methyl acrylate /%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50

40

30

20

10

0 0

1

2

3

4

5

6

7

8

Space-time / h


9

10


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Figure 14.


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Figure 15. Pressure in the column 0.07

0.08

0.09

0.10

50 MA feeding position

40

Number of theoretical plates

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


30

20

HAc feeding position

10

0 420

400

380

360

340

Temperature in vapor phase / K


320


Figure 16.

1.0 0.9 0.8

Liquid phase composition HAc MeAc MA AA

0.7

Mass Fraction

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

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0.6 0.5

Vapor phase composition HAc MeAc MA AA

0.4 0.3 0.2 0.1 0.0 0

5

10

15

20

25

30

35

Stage Number


40

45

50

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Figure 17.

100

80

Ratio / %

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Selectivity Yield

60

40

20

0 0

100

200

300

400

500

600

700

800

900

Run time / h


1000 1100 1200


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Figure 18.


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Table 1. Properties

Parameters

Skeleton

Styrene-divinybenzene

Type

Strong acid

Structure

Macroreticular

Functional group

Sulfonic(SO3H)

Ionic form

H+

Moisture (by weight)

Less than 10%

Surface area (m2/g)

50

Particle size

28-35(mesh)

Internal porosity(ml pore/ml bead)

0.36

Concentration of acid sites (meq./g dry)

4.7

Bulk density(Kg/m3)

608

Average pore diameter (nm)

48.2



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Table 2. Model

AAD(x1)b

AAD(T)b

AAD(y1)b

VLE for Acrylic acid (1)+ Methyl acetic (2) NRTL

0.0012

UNIQUAC

0.0029

0.0314

0.0003

0.0336

0.0005

VLE for Acetic acid (1)+ MA (2) NRTL

0.0025

0.045

0.0002

UNIQUAC

0.0028

0.054

0.0002

S` S` S` AAD(y)b=(1/N)∑s − r _ q;AAD(T)b=(1/N)∑s − ? _ q;AAD(x)b=(1/N)∑s − t:qr t:q? t:q

_ q


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Table 3. (i)/(j)

uZ

uZ

vZ (K)

vZ (K)

α

Acetic acid(1)/Methyl acrylate (2)

13.4560

-28.4105

-5151.3602

11039.0889

0.3

Acetic acid (1)/Acrylic acid (3)

0

0

283.0157

42.5680

0.3

Acetic acid (1) / Methyl acetic (4)

0

0

-239.2462

415.2702

0.3

Methyl acrylate (2)/Acrylic acid (3)

0

0

620.1444

-295.8599

0.3

Methyl acetic (4)/ Methyl acrylate (2)

0.5018

-0.6913

463.8299

-361.4648

0.3

Acrylic acid (3)/ Methyl acetic (4)

4.9081

23.5597

-2250.4919

-6440.8516

0.3



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Table 4. Forward reaction rate

Adverse reaction rate

Reaction temperature constants

constants

K k+×106(L·mol-1·s-1)

k-×106(L·mol-1·s-1)

343.15

1.8106

4.1953

353.15

3.2869

6.2853

363.15

6.5658

11.061


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Table 5.

Model

Chemical Equilibrium constant

Pre-exponential factor

Activation energy

PH(ideal)

(

=,

PH LH

( (

=, =,


Adsorption equilibrium constant -

-

-

-

-

-

-

-


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Table 6. Chemical equilibrium constant

Chemical equilibrium constant

(Activity)

(concentration)

343.15

0.3452

0.4321

353.15

0.6906

0.9224

363.15

1.3727

1.6984

Temperature/K


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Table 7. Substrate

Swelling ratio of volume

Methyl acrylate

1.267

Acetic acid

1.283

Acrylic acid

1.251

Methyl acetic

1.242



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Table 8. Equilibrium Adsorbed Mass mS/mcat= 0.95 Adsorption Equilibrium Constants KHAc=3.15 KMA=3.07 KAA=2.89 KMeAc=4.15


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Table 9. Model PH(ideal) PH LH

k (x （mol ∙ g F: ∙ s F: ） 9.42 × 10:: 1.30 × 10* 2.17 × 10*


=, (kJ ∙ E+ F: ) 107.84 99.75 99.75


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Table 10. Model

SRS

MRD/%

PH(ideal)

1.962×10-8

4.727

PH

0.1951×10-8

1.717

LH

0.1534×10-8

1.302


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Table 11. parameters

results

Operating pressure

0.065MPa

Theoretical plates number

50

HAc feeding position

11

MA feeding position

45

Reflux ratio

2.5:1

Feed

1.0

Methyl acrylate conversion rate

≥94.5%

Acrylic acid concentrations in the tower bottom

≥98.0%


Kinetic and Reactive Distillation for Acrylic Acid Synthesis via

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