Kinetic Modeling of Pervaporation Aided Esterification of Propionic

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Kinetic Modeling of Pervaporation Aided Esterification of Propionic Acid and Ethanol Using T-Type Zeolite Membrane Wenying Zhang, Shasha Na, Weixing Li, and Weihong Xing Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b00505 • Publication Date (Web): 24 Apr 2015 Downloaded from http://pubs.acs.org on April 27, 2015

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Industrial & Engineering Chemistry Research

Kinetic Modeling of Pervaporation Aided Esterification of Propionic Acid and Ethanol Using T-Type Zeolite Membrane Wenying Zhang, Shasha Na, Weixing Li*, Weihong Xing State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing Tech University, Nanjing 210009, China

ABSTRACT: As a reversible reaction, the esterification conversion is limited by thermodynamic equilibrium. Pervaporation has been a very useful tool to enhance the esterification reaction by removing its products. In this paper, a T-Type zeolite membrane was used to intensify the esterification of propionic acid and ethanol. Based on the Maxwell-Stefan equation, a kinetic model for pervaporation aided esterification of propionic acid and ethanol was developed. The experimental data were in good agreement with the simulation results. The effects of temperature, molar ratio of ethanol to acid and ratio of membrane area to amount of initial reaction liquid (S/m) on PV-aided esterification were investigated. It was shown that the equilibrium conversion of the esterification without PV was 82.6% but increased to 90.8% with PV aided in 5 h. The conversion of esterification enhanced by pervaporation reached 99.8% in 10 h at 363 K when the molar ratio of ethanol to acid was 2:1 and ratio of membrane area to amount of initial reaction liquid (S/m) was 0.1059 m2·kg-1.

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1. INTRODUCTION During the past few decades, pervaporation (PV) has drawn a lot of attention for its high separation efficiency, simple equipment, low energy consumption and other advantages.1-3 PV has superiority especially in separating azeotropes, close-boiling mixtures, and thermally sensitive compounds. Ethyl propionate is a kind of important organic ester which can be used as flavors, perfumes, pharmaceuticals, plasticizers, solvents, intermediates and so on.4-5 Esterification is a normal method to synthetize the esters production. However, the esterification reaction is limited by equilibrium. PV is a very useful intensification method to enhance the esterification by removing one of the products.6-8 Sert et al.9 produced n-butyl acrylate by using pervaporation esterification hybrid process and the conversion of acrylic acid reached 96.3% at optimal conditions. Ethyl lactate was synthesized from lactic acid and ethanol in a batch reactor coupled with a pervaporation unit by Delgado et al.10 and the result showed that yield of ethyl lactate broke the corresponding thermodynamic equilibrium via water removing through the membrane. Hasanoglu et al.11 prepared ethyl acetate by combing pervaporation and esterification. The conversion was increased by continuous removal of ethyl acetate using PDMS membrane. In our previous work, a NaA zeolite membrane was used to promote the esterification of acetic acid and n-propanol12 and the conversion was tremendously increased. The driving force of pervaporation is the difference of the chemical potential across the membrane. The flux depends on the permeance and the driving force. The permeance value is function of the temperature and it is usually explained following Arrhenius correlation.13-16 The method based on data regression is experiential and semi-empirical. In order to investigate the mass transfer mechanism in pervaporation membranes, Maxwell-Stefan theory was used to


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describe the multi-component mass transfer for inorganic pervaporation membranes.17-20 Mengers et al.21 calculated the flux through the boundary layer using Maxwell–Stefan equations. At the same time, the flux of component i through the membrane is assumed to be proportional to its molar fraction in the feed. Rewagad et al.22 combined Maxwell-Stefan equation with the solution-diffusion model to describe multicomponent mass transfer behavior in the organic membrane. The free volume theory was used to describe the diffusivities between the quaternary mixtures of ethanol-oleic acid-water-ethyl oleate among them. In this work, a T-Type zeolite membrane was used to enhance the esterification of propionic acid and ethanol. A kinetic model based on Maxwell Stefan equation was to be developed for the coupling process of esterification with PV. The diffusion coefficient was obtained from experimental data and we found that it conformed to the Arrhenius relationship with temperature. The effects of reaction temperature, ratio of membrane area to initial reaction liquid (S/m) and initial molar ratio of reactants on the PV-aided reaction were investigated in detail. 2. EXPERIMENTAL SECTION 2.1. Reagents. The T-Type zeolite membrane was prepared by our research team.23 The inner and external diameter of the tube membrane is 8 mm and 12 mm respectively. The thickness of the dense layer coated in the out wall of the membrane is about 6 µm. Propionic acid (purity≥99.5 wt%) and ethanol (purity ≥99.7 wt%) were bought from Sigma-Adrich Co.. Ethyl propionate (purity ≥99.0 wt%) was supplied by Aladin Industrial Corporation. Deionized water was used in all preparation steps. In the experiments, the catalyst 002CR purchased from Jiangsu Suqing Co. was a strong-acid ion-exchange resin. The exchange capacity of the resin was over 5.0 mequiv of H+/g.



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2.2. Apparatus. The apparatus for esterification coupled with PV was shown in Figure 1. The volume of the reactor is 150 mL and the effective length of the membrane is about 80 mm. The temperature was controlled by a constant temperature tank. The permeated solution was collected with two liquid nitrogen traps and the pressure difference between feed side and permeate side was controlled by a vacuum pump. The pressure of the permeate side can be controlled bellow 200 Pa. Firstly, catalyst was placed into the reactor. Then the reaction liquid propionic acid and ethanol were put into the membrane reactor after the reaction temperature was reached. This time was taken as the starting time for the experiment. The magnetic stirrer was used to mix the reactants. 2.3. Analysis Method. The permeate composition was analyzed by the gas chromatograph (GC-2014, Shimadu, Japan) equipped with a thermal conductivity detector (TCD). The column packed with PORAPAK Q (mesh 50-80) was 2 m in length. Helium (99.9999%) was used as the carrier gas. The column and injector temperatures were both 473 K, and the detector temperatures was 453 K. The bridge current was 110 mA, and the sample size for GC was 1µL. The concentration of ethyl propionate was determined by gas chromatograph (GC-2014, Shimadu, Japan) equipped with aflame ionization detector (FID). The capillary column (30 m ×Φ0.32 mm×0.5µm, SE-30) used was held at 373 K. The injector and detector temperatures were 473 K. The carrier gas was nitrogen (99.99%). The injection sample size for GC was 0.2 µL. 3. THEORETICAL CALCULATIONS The reaction between propionic acid and ethanol was represented as (1)


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where A is ethanol, B is propionic acid, E is ethyl propionate, W is water. A pseudohomogeneous kinetic model can be used to describe the behavior of the reaction which is reversible and exothermic24. So the reaction rate equation can be written as: r = k + C A C B − k − C E CW

(2)

where r is the reaction rate (mol·kg-1·h-1), C is the concentration based on mass of solid catalyst (mol·kg-1), and k+ and k- are the forward and backward rate constants (kg·mol-1·h-1), respectively. In normal conditions, the rate constants are function of activation energy and reaction rate constant. r = k0 exp(−

Ea 1 )(C ACB − CE CW ) RT K eq

(3)

where k0 is reaction rate constant (kg·mol-1·h-1) and Ea is activation energy (J·mol-1). Keq is equilibrium constant which is the quotient of forward and backward rate constants. In this work, it was calculated from the equation ‫ܭ‬௘௤ =

஼ಶ ஼ೈ ஼ಲ ஼ಳ

when the reaction reached equilibrium.

By combining pervaporation with the esterification, the change of concentration can be written as d (Ci ) S = ri Ji dt m

(4)

where S is effective membrane area (m2) and m is catalyst amount (kg), Ji is permeate flux of component i (kg·m-2·h-1). In this work, a theoretical formula based on Maxwell-Stefan equation was combined with esterification to simulate this process. The adsorption-diffusion theory was very appropriate to describe the mass transport through inorganic membranes.25 The reaction solution was very complicated which includes four kinds of liquid. The Maxwell Stefan (MS) equation was often used to describe the transport of multicomponent through membranes. The MS equation can be written as:



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−

n x x (u − u ) xi i j i j ∇T , p µi = ∑ RT D j =1 ij

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(5)

where xi is the mole fraction of component i in the adsorbed phase, T is temperature (K), µi is chemical potential of component i (J·mol-1), ui is diffusive velocity of component i (m/s), Dij is the Maxwell–Stefan diffusivity between component i and j (m2·s-1). Four components A, B, E, W were existed in pervaporation-esterification coupled system. But only water passed through pervaporation membranes in most conditions, as a result, binary mixture calculation was often used to simplify the calculation.8, 26 Hence, the MS equation can be presented as −

x 1 d µi x j = (ui − u j ) + M' (ui − uM ) RT dz Dij DiM

(6)

where M represents membrane and DiM’ is Maxwell–Stefan diffusivity of component i in the membrane (m2·s-1). z represents direction perpendicular to the membrane surface (m). Since the xM could not be calculated, so xM/DiM’ was replaced by DiM. What’s more, the relation between flux and velocity is J i = ui ctot xi = ui ci . Therefore, equation (5) changed to −

1 dpi x j Ji J j 1 Ji = ( − )+ ( ) pi dz Dij ci c j DiM ci

(7)

where pi is the partial pressure of component i in the gas phase (Pa), which is driving force in the pervaporation process. For a dehydration membrane, the water flux was much larger than ethanol flux, even the ethanol flux can be neglected. We assume the loading of component i is proportional with the partial vapor pressure of this component in the membrane25, Ai = ci / pi . The water flux is: JW =

1 xA 1 + DWA DWM

AW * ( pW − pWP ) L


(8)

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where AW is adsorption coefficient of membrane (mol·m-3·Pa-1). L is membrane thickness (m). pw* and pwP are partial vapor pressure of water at the retentate side and permeate side, respectively. pW* = γ W xW pWsat

(9)

pWP = xW p P

(10)

where γW is activity coefficient of water which was calculated by Aspen Plus 8.0 with NRTL equation. pWsat is saturated vapor pressure of water (Pa) and pP is permeate pressure (Pa). In brief, the concentration of the water changes with the time can be expressed in the following formula: d (CW ) AW * S 1 = rW ( ( pW - pWP )) dt m xA + 1 L DWA DWM

(11)

4. RESULTS AND DISCUSSION. 4.1 Characterization of membrane and estimation of Maxwell–Stefan diffusivity of water in membrane. The SEM images of the T-Type zeolite membrane used in this work were shown in Figure 2. As can be seen from Figure 2(a), the zeolite particles are compacted densely. From Figure 2(b), the dense layer thickness is about 6 µm. Flux is one of the most important indexes for the characterization of pervaporation performance of the membrane. The effect of water content on water flux and water content in permeate at 353 K was shown in Figure 3. Water flux and its content in permeate both increased with water content. The water content in permeate increased from 93.5% to 98.8% when the water content in feed increased from 3% to 10% and then it increased slowly. Figure 4 showed the effect of temperature on water flux and water content in permeate with water content at 10 wt%. The water content in the permeate and water flux increased with



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temperature from 313 to 343 K. However the water content in the permeate suddenly decreased at higher temperatures. This fact could be related to the ethanol flux through the membrane that was considered negligible. Maxwell–Stefan diffusivity is a very important factor for the prediction of the membrane flux. The Maxwell–Stefan diffusivity of water in the membrane can be calculated by equation (8). Figure 5 showed the effect of temperature on pure water flux. As can be seen, the water flux increased with temperature and it was about 2400 g·m-2·h-1 at 353 K. Wolf et al.25 studied adsorption behaviors of pure water and isopropanol on silica gel and silica coated ceramics, and in this work their adsorption equilibrium data was used to calculate the adsorption coefficient AW which was conformed to an Arrhenius equation. And the Arrhenius type law can also be assumed for the temperature dependency of the diffusion coefficient DWM.27 As can be seen from Figure 6, the diffusion coefficient of water in membrane showed a exponential relationship with temperature. The relationship between adsorption coefficient, diffusion coefficient and temperature was as equation (12) and (13). AW = AW ,0 exp(

− EA,W RT

DWM = DWM ,0 exp(

(12)

)

−ED,W RT

)

(13)

where AW,0 and DWM,0 are pre-exponential factor (mol·m-3·Pa-1), EA,W and ED,W are apparent activation energy of adsorption and diffusion (J). The parameters are listed in Table 1. The Maxwell–Stefan diffusivity between component water and ethanol (DWA) in equation (8) can be obtained from Figure 7 and its scape is about 0.6-2.2×10-11 mol·m-3·Pa-1. The relationship between DWA and temperature can be assumed as linearity: DWA = (0.031× T-9.05) ×10−11 .


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4.2 Esterification coupled with pervaporation. The esterification of propionic acid and ethanol and the PV-aided esterification were compared and the propionic acid conversion results were shown in Figure 8. As can be seen, the conversion with PV-aided esterification was higher than normal reaction obviously. It was shown that the equilibrium conversion of the esterification without PV was 82.6% but increased to 90.8% with PV aided in 5 h. The conversion of esterification enhanced by pervaporation reached 99.8% in 10 h. As time going, the difference between the esterification with PV and without PV became more and more clear. This is because at the start period little water produced and the effect of PV process was slightly. As the reaction proceeded, the water accumulated in the reactor which limited the reaction rate. By PV water was removed from the membrane reactor and the reaction was promoted. As can be seen from Figure 9, mass of water in reactor arrived at the maximum at 1 h and then it decreased because water removal rate was larger than the producing rate. In addition, water molecular has a stronger binding force with cation exchange resin catalysts than acid, alcohol and ester5. The contact between reaction liquid and catalysts would be promoted with water removing and as a result esterification reaction rate with PV was higher than that without PV. What’s more, we have compared the conversion of ethyl propionate with pervaporation (PV) and vapor permeation (VP). As can be seen from figure 8, the conversion of the esterification with VP was higher than without VP but lower than that with PV, that’s because the permeate flux of VP was lower than PV under the same condition. However, the water content in permeate with VP was higher than PV. The variations of permeate flux, water in permeate for the esterification of propionic acid and ethanol with PV/VP were shown in figure 9. 4.3 Effect of reaction temperature. The temperature has a very important influence on the reaction rate. As can be seen from Figure 10, the conversion obviously increased from 90.0% to



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99.8% as the temperature rose from 343 K to 363 K at 10 h. The acceleration of temperature on the reaction can be explained in two aspects. On the one hand, the reaction rate improved when temperature increased and the time approached to equilibrium would be shortened. On the other hand, according to the principle of "adsorption - diffusion - desorption", the molecular diffusion rate was enhanced at high temperature. Thus, the permeation flux was increased which was agreed to Figure 11. From equation (8), the driving force of total pressure difference increased with temperature so the flux increased. What’s more, the diffusion coefficient increased from 3.56×10-11 to 6.83×10-11 and the adsorption coefficient decreased from 0.167 to 0.067 when temperature increased from 343 K to 363 K. However, as the controlling factor, the diffusion coefficient was much lower than diffusion coefficient, thus permeate flux increased with increasing temperature. 4.4 Effect of molar ratio of ethanol to acid. One excess reactant could enhance the reversible esterification. Different alcohol to propionic acid initial molar ratio range from 1:1 to 3:1 was shown in Figure 12. The conversion had a remarkable increase from 87.7% to 98.0% at 8 h when the initial molar ratio of ethanol to acid increased from 1:1 to 2:1, and then the conversion had no obvious increase. That is because the redundant ethanol reduced the chance of water contacted with membrane and it resulted in inadequate water removal during the pervaporation process. Hence, the increase of conversion was limited. The effect of the initial alcohol/acid molar ratio on the ethanol content in permeate was shown in Figure 13. 4.5 Effect of S/m. The effect of membrane area to initial reaction liquid (S/m) on esterification with pervaporation through decreasing the quality of initial reaction liquid under the same membrane area was investigated and the results were presented in Figure 14. As shown, the conversion has a remarkable increase from 90.0% to 99.8% at 10 h with S/m range from 0.01589


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to 0.1059 m2·kg-1. Larger membrane area could remove the byproduct water sufficiently and thus the esterification was enhanced. Obviously, larger membrane area means more equipment cost but a smaller membrane area would lead to longer time reaching to the same conversion. 5. CONCLUSIONS. The esterification conversion of propionic acid and ethanol was significantly enhanced by pervaporation from 82.6% but increased to 90.8% with PV aided with alcohol/acid molar ratio 2:1 in 5 h. The Maxwell Stefan equation was used to predict water flux in combined process. The experimental data was in good agreement with the simulation results. The temperature has a great influence on conversion and flux. A high temperature could improve both conversion and flux. The conversion increased from 90.0% to 99.8% when the temperature increased from 343 K to 363 K at 10 h. The molar ratio of ethanol to acid is important for the process. The conversion increased apparently from 87.7% to 98.0 % with molar ratio increasing from 1:1 to 2:1 in 8 h. The S/m also has a great influence on the conversion and the suitable ratio was 0.1059 m2·kg-1. AUTHOR INFORMATION Corresponding Author *E-mail: [email protected]. Tel.: (+86)-25-83172286. Fax.: (+86)-25-83172292. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT



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This work was financially supported by National Key Science and Technology Program of China (No.2013BAE11B01) and Jiangsu Province 333 Foundation of China (No. 2013-XCL027). NOMENCLATURE r = reaction rate (mol·kg-1·h-1) C = concentration based on mass of solid catalyst (mol·kg-1) k+ = forward rate constants (kg·mol-1·h-1) k- = backward rate constants (kg·mol-1·h-1) k0 = reaction rate constant (kg·mol-1·h-1) Ea = activation energy (J·mol-1) Keq = equilibrium constant S = effective membrane area (m2) m = catalyst amount (kg) Ji = permeate flux of component i (kg·m-2·h-1) xi = mole fraction of component i in the adsorbed phase T = temperature (K) µi = chemical potential of component i (J·mol-1) ui = diffusive velocity of component i (m/s)


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Dij = Maxwell–Stefan diffusivity between component i and j (m2·s-1) DiM = Maxwell–Stefan diffusivity of component i in the membrane (m2·s-1) z = direction perpendicular to the membrane surface (m) pi = partial pressure of component i in the gas phase (Pa) AW = adsorption coefficient (mol·m-3·Pa-1) L = membrane thickness (m) pw* = partial vapor pressure of water at retentate side (Pa) pwP = partial vapor pressure of water at permeate side (Pa) γW = activity coefficient of water pWsat

= saturated vapor pressure of water (Pa)

pP = permeate pressure (Pa) AW0 = pre-exponential factor (mol·m-3·Pa-1) DWM,0 = pre-exponential factor (mol·m-3·Pa-1) EA,W = apparent activation energy of adsorption (J) ED,W = apparent activation energy of diffusion (J) Subscript and Superscript A = ethanol



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B = propionic acid E = ethyl propionate W = water i = component * = retentate side P = permeate side sat = saturate REFERENCES (1) Bowen, T. C.; Noble, R. D.; Falconer, J. L. Fundamentals and Applications of Pervaporation Through Zeolite Membranes. J. Membr. Sci. 2004, 245, 1-33. (2) Wee, S. L.; Tye, C. T.; Bhatia, S. Membrane Separation Process-Pervaporation Through Zeolite Membrane. Sep. Purif. Technol. 2008, 63, 500-516. (3) Viana, W. O.; Taquez, H. N. I.; Gomez, I. D.; Garcia, M. A. G. Hybrid Membrane and Conventional Processes Comparison for Isoamyl Acetate Production. Chem. Eng. Process. 2014, 76, 70-82. (4) Metwally M.S. Kinetic study of resin catalyzed hydrolysis of ethyl propionate in aqueousorganic systems. React. Kinet. Catal. Lett. 1992, 47, 319-326.


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(19) Kubaczka, A.; Burgrardt, A.; Mokrosz, T. Generalized Maxwell-Stefan Equations for Multicomponent Mass Transport in Porous and Dense Membranes. Inz. Chem. Procesowa 2001, 22, 825-830. (20) Bettens, B.; Verhoef, A.; van Veen, H. M.; Vandecasteele, C.; Degreve, J.; der Bruggen, B. V. Pervaporation of Binary Water-Alcohol and Methanol-Alcohol Mixtures through Microporous Methylated Silica Membranes: Maxwell-Stefan Modeling. Comput. Chem. Eng. 2010, 34, 1775-1788. (21) Mengers, H.; Benes, N. E.; Nijmeijer, K. Multi-Component Mass Transfer Behavior in Catalytic Membrane Reactors. Chem. Eng. Sci. 2014, 117, 45-54. (22) Rewagad, R. R.; Kiss, A. A. Modeling and Simulation of A Pervaporation Process for Fatty Ester Synthesis. Chem. Eng. Commun. 2012, 199, 1357-1374. (23) Wang, X.; Yang, Z.; Yu, C.; Yin, L.; Zhang C.; Gu X. Preparation of T-Type Zeolite Membranes Using A Dip-Coating Seeding Suspension Containing Colloidal SiO2. Microporous Mesoporous Mater.2014, 197, 17-25. (24) Delgado, P.; Sanz, M. T.; Beltran, S. Kinetic Study for Esterification of Lactic Acid with Ethanol and Hydrolysis of Ethyl Lactate Using An Ion-Exchange Resin Catalyst. Chem. Eng. J. 2007, 126, 111-118. (25) Wolf, H. E.; Schlunder, E. U. Adsorption Equilibrium of Solvent Mixtures on Silica Gel and Silica Gel Coated Ceramics. Chem. Eng. Process.1999, 38, 211–218. (26) Khajavi, S.; Jansen, J. C.; Kapteijn, F. Application of A Sodalite Membrane Reactor in Esterification-Coupling Reaction and Separation. Catal. Today 2010, 156, 132-139.



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(27) Garcia, M.; Sanz, M. T.; Beltran, S. Separation by Pervaporation of Ethanol from Aqueous Solutions and Effect of other Components Present in Fermentation Broths. J. Chem. Technol. Biotechnol. 2009, 84, 1873-1882.


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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 1. Schematic diagram of the apparatus for the pervaporation experiments. 1-constant temperature tank; 2-reactor; 3-stirrer; 4-membrane module; 5-digital vacuum gauge; 6,7-cold traps; 8-buffer bottle; 9-vacuum pump. Figure 2. SEM images of T-Type zeolite membrane: (a) surface of membrane, (b) cross section of membrane. Figure 3. Water flux and water content in permeate varied with water content in feed (temperature 343 K). Figure 4. Water flux and water content in permeate varied with temperature (water content in feed 10 wt%). Figure 5. Pure water flux varied with temperature (pure water in feed). Figure 6. Diffusion coefficient (DWM) of water in membrane varied with temperature. Figure 7. Diffusion coefficient (DWA) between water and ethanol varied with temperature. Figure 8. Dependence of conversion on time with PV/VP and without PV (reaction temperature 363 K, initial molar ratio 2:1, S/m 0.3178 m2•kg-1). The solid lines indicate the values predicted by the kinetic model. Figure 9. Variations of permeate flux, mass of water remained in reactor, water in permeate for the esterification of propionic acid and ethanol with PV/VP (reaction temperature 363 K, initial molar ratio 2:1, S/m 0.1059 m2·kg-1). The solid lines indicate the values predicted by the kinetic model.



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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Figure 10. Effect of the reaction temperature on the conversion of the PV-aided esterification of propionic acid and ethanol (initial molar ratio 2:1, S/m 0.1059 m2·kg-1). The solid and hollow tags represented reaction with PV and without PV respectively. The solid lines indicate the values predicted by the kinetic model. Figure 11. Variation of permeate flux with time for the PV-aided esterification of propionic acid and ethanol at various reaction temperatures (initial molar ratio 2:1, S/m 0.1059 m2·kg-1). The solid lines indicate the values predicted by the kinetic model. Figure 12. Effect of the initial alcohol/acid molar ratio on the conversion of the PV-aided esterification (reaction temperature 363 K, S/m 0.1059 m2·kg-1). The solid lines indicate the values predicted by the kinetic model. Figure 13. Effect of the initial alcohol/acid molar ratio on the ethanol content in permeate (reaction temperature 363 K, S/m 0.1059 m2·kg-1). Figure 14. Effect of the membrane area to initial quality of reaction liquid on the conversion of the PV-aided esterification (reaction temperature 363 K, initial molar ratio 2:1). The solid lines indicate the values predicted by the kinetic model.

Table 1. Kinetic parameters for PV coupled esterification of propionic acid with ethanol.


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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 1. Schematic diagram of the apparatus for the pervaporation experiments. 1-constant temperature tank; 2-reactor; 3-stirrer; 4-membrane module; 5-digital vacuum gauge; 6,7-cold traps; 8-buffer bottle; 9-vacuum pump.



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

a

b

Figure 2. SEM images of T-Type zeolite membrane: (a) surface of membrane, (b) cross section of membrane.


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98

1000 -1 -2

800

96 Water flux

600

Water content

94

400 92

200 0

0

5

10

15

20

25

Water content in permeate (wt%)

100 1200

Water flux(g·m ·h )

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


90 30

Water content in feed (wt%)

Figure 3. Water flux and water content in permeate varied with water content in feed (temperature 343 K).



Water flux Water content

500 -1

99

-2

98 400 97 300 96 200 310

320

330

340

350

Water content in permeate (wt%)

100

600

Water flux(g·m ·h )

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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95 360

Temperature(K)

Figure 4. Water flux and water content in permeate varied with temperature (water content in feed 10 wt%).


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2400 2000

-2

-1

Flux(g·m ·h )

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


1600 1200 800 400 290

300

310

320

330

340

350

Temperature(K)

Figure 5. Pure water flux varied with temperature (pure water in feed).


360


40 35

-12

2

-1

m ·s )

30

DWM (×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

25 20 15 10 5 290

300

310

320

330

340

350

360

Temperature (K)

Figure 6. Diffusion coefficient (DWM) of water in membrane varied with temperature.


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2.4 2.2 2.0

2

1.8 1.6

-11

-1

DWA(×10 m ·s )

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


1.4 1.2 1.0 0.8 0.6 310

320

330

340

350

360

Temperature(K)

Figure 7. Diffusion coefficient (DWA) between water and ethanol varied with temperature.



100 90 80 With PV With VP Without PV/VP

70 Conversion (%)

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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60 50 40 30 20 10 0

0

1

2

3

4

5

6

7

8

9

10

Time (h)

Figure 8. Dependence of conversion on time with PV/VP and without PV (reaction temperature 363 K, membrane temperature 363 K, initial molar ratio 2:1, S/m 0.3178 m2·kg-1). The solid lines indicate the values predicted by the kinetic model.


450

2.0

VP water in permeate PV water in permeate

-2

300

1.5

250 Water in reactor PV flux VP flux

200 150 100

1.0 0.5

Mass of water in reactor(g)

350 -1

100

2.5

400 Water flux (g·m ·h )

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


95 90 85 80

Water in permeate (%)

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75

50 0

0

1

2

3

4

5

6

7

8

0.0

70

Time (h)

Figure 9. Variations of permeate flux, mass of water remained in reactor, water in permeate for the esterification of propionic acid and ethanol with PV/VP (reaction temperature 363 K, initial molar ratio 2:1, S/m 0.1059 m2·kg-1). The solid lines indicate the values predicted by the kinetic model.



100 80 Conversion (%)

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

With PV

60

Without PV 363 K 353 K 343 K

40 20 0

0

1

2

3

4

5

6

7

8

9 10 11 12 13

Time (h)

Figure 10. Effect of the reaction temperature on the conversion of the PV-aided esterification of propionic acid and ethanol (initial molar ratio 2:1, S/m 0.1059 m2·kg-1). The solid and hollow tags represented reaction with PV and without PV respectively. The solid lines indicate the values predicted by the kinetic model.


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300 343 K 353 K 363 K 200

-2

-1

Flux (g·m ·h )

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


100

0

0

1

2

3

4

5

6

7

8

9

10

Time (h)

Figure 11. Variation of permeate flux with time for the PV-aided esterification of propionic acid and ethanol at various reaction temperatures (initial molar ratio 2:1, S/m 0.1059 m2·kg-1). The solid lines indicate the values predicted by the kinetic model.



100 90 80 70 Conversion (%)

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

3:1 2:1 1.5:1 1:1

60 50 40 30 20 10 0

0

1

2

3

4

5

6

7

8

Time (h)

Figure 12. Effect of the initial alcohol/acid molar ratio on the conversion of the PV-aided esterification (reaction temperature 363 K, S/m 0.1059 m2·kg-1). The solid lines indicate the values predicted by the kinetic model.


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30 Ethanol content in permeate(%)

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


1:1 1.5:1 2:1 3:1

20

10

0

0

1

2

3

4

5

6

7

8

Time(h)

Figure 13. Effect of the initial alcohol/acid molar ratio on the ethanol content in permeate (reaction temperature 363 K, S/m 0.1059 m2·kg-1).



100 80 2

Conversion(%)

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

-1

0.1059 m ·kg 2 -1 0.03178 m ·kg 2 -1 0.01589 m ·kg

60 40 20 0

0

1

2

3

4

5

6

7

8

9

10

Time(h)

Figure 14. Effect of the membrane area to initial quality of reaction liquid on the conversion of the PV-aided esterification (reaction temperature 363 K, initial molar ratio 2:1). The solid lines indicate the values predicted by the kinetic model.


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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


Table 1. Kinetic parameters for PV coupled esterification of propionic acid with ethanol.

k0

Ea

AW,0

DWM,0

EA,W

ED,W

(kg·mol-1·h-1)

(J·mol-1)

(mol·m-3·Pa-1)

(mol·m-3·Pa-1)

(J·mol-1)

(J·mol-1)

5144.59

3.379×105

1.172×10-8

4.88×10-6

-4.697×104

3.373×104


Kinetic Modeling of Pervaporation Aided Esterification of Propionic

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