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n-Butyl acrylate production by esterification of acrylic acid with n-butanol combined with pervaporation
Chemical Engineering and Processing 81 (2014) 41–47
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Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
n-Butyl acrylate production by esterification of acrylic acid with n-butanol combined with pervaporation Emine Sert ∗ , Ferhan S. Atalay Ege University, Chemical Engineering Department, Bornova, Izmir, Turkey
a r t i c l e
i n f o
Article history: Received 9 January 2014 Received in revised form 24 February 2014 Accepted 22 April 2014 Available online 30 April 2014 Keywords: Pervaporation Esterification Membrane n-Butyl acrylate
a b s t r a c t In this study, the esterification reaction of acrylic acid and n-butanol to produce n-butyl acrylate and water was studied using the pervaporation–esterification hybrid process to perform the separation and reaction simultaneously to increase the conversion of limiting reactant. A Pervap 2201 polymeric membrane was used to separate water and also to shift the equilibrium. The Pervap 2201 membrane showed high selectivity to water in the n-butanol, acrylic acid, n-butyl acrylate, and water reaction system. The effects of temperature, the initial molar ratio of n-butanol to acrylic acid, catalyst loading, and the ratio of membrane area to reaction volume (S/V) were studied. The maximum conversion of acrylic acid was calculated as 96.3% at a temperature of 358 K, a molar ratio of 8, with a catalyst loading of 10 g/L and an S/V ratio of 70 m−1 . © 2014 Elsevier B.V. All rights reserved.
1. Introduction The coupling of reaction and separation has become a current trend in the chemical industry in order to obtain more efficient processes and lower energy consumption. A classic example is the production of esters, which are traditionally obtained by reacting an organic acid and an alcohol in the presence of suitable catalysts. A major difficulty in such reactions is the limitation by the thermodynamic equilibrium, which requires a separation step with a subsequent reactant reflux allows to shift the chemical equilibrium toward the ester production [1]. According to the Le Chatelier principle, the yield and selectivity of the targeted compound are increased by the removal of the byproducts of the reaction. Esterification reactions produce water as byproduct that reduces both catalytic activity and forward reaction rate. Studies by Kusdiana and Saka [2] on the esterification and transesterification reactions reveal that the presence of water deactivates the catalyst activity, which decreases the reaction rate. Among the hybrid processes, reactive distillation which combines reaction and separation processes in a single unit was applied for n-butyl acrylate synthesis. Zeng et al. [3] studied the design and control of a reactive distillation column for the production of n-butyl acrylate. Also, Niesbach et al. [4] studied an experimental and theoretical investigation of butyl acrylate using reactive
∗ Corresponding author. Tel.: +90 232 3111493; fax: +90 232 388 7776. E-mail address: [email protected] (E. Sert). http://dx.doi.org/10.1016/j.cep.2014.04.010 0255-2701/© 2014 Elsevier B.V. All rights reserved.
distillation. They concluded that the process intensification can decrease the equipment needed, thereby reducing the investment and operating costs. Due to high risk of polymerization of acrylic acid and butyl acrylate, Niesbach et al. [5] present an experimental investigation of inhibition period of acrylic acid and n-butyl acrylate polymerization. In their study, hydroquinone and phenothiazine were used as inhibitors. The pilot plant reactive distillation experiments were conducted to show proper concept of polymerization inhibition successfully in the industrial application. The integration of a pervaporation process into a conventional esterification process is attractive because it provides the opportunity to continuously shift the conversion beyond the thermodynamic equilibrium by removing water from the chemical reactor [6,7]. Pervaporation has been proven to be a successful technique for selectively removing a certain component from a liquid mixture because of its low energy requirements and its ability to separate azeotropic mixtures [8]. Pervaporation solely relies on the solubility and transport rate of each component. Pervaporation also demonstrates incomparable advantages in separating heat sensitive, close-boiling, and azeotropic mixtures due to its mild operating conditions, no emission to the environment, and no involvement of additional species into the feed stream [9]. The application of pervaporation to reversible reactions such as esterification has been studied in recent studies. Figueiredo et al. [10] studied the pervaporation-assisted esterification of oleic acid with ethanol using hydrophilic Pervap 1000 membrane. The hydrophilic membrane was able to remove water from the reaction mixture, thus increasing the ester yield. In another study, Delgado et al. [11] studied the synthesis of ethyl lactate from ethanol and
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lactic acid in a batch reactor combined with a pervaporation unit. A hydrophilic membrane Pervap 2201 was used and almost total use of lactic acid was achieved. Korkmaz et al. [12] studied the esterification reaction between acetic acid and iso-butanol by using polydimethylsloxane (PDMS) membrane. The experiments indicate that the PDMS membrane can be used to remove iso-butyl acetate selectively by the pervaporation process. Polyvinyl alcohol (PVA) is a polyhydroxy polymer, which is very common in practical applications because of its easy preparation and biodegradability. It has been selected as polymer matrix in view of its film-forming capacities, hydrophilic properties and high density of reactive chemical functions favorable for cross-linking by irradiation, chemical or thermal treatments [13]. In general, polyvinyl alcohol (PVA) membranes when applied to the pervaporation aided esterification processes must be cross linked to avoid the esterification of the alcoholic groups of the membrane and its consequent loss of its separative properties. The polymeric material presents high hydrophilicity and stability under acidic conditions when undergoing the cross linking treatment. Butyl acrylate is a clear colorless liquid with a characteristic fruity odor. It is readily miscible with most organic solvents. It is readily polymerized and shows a wide range of properties dependent on the selection of the monomer and reaction conditions. n-Butyl acrylate is used in the production of homopolymers and co-polymers [3]. n-Butyl acrylate was synthesized from the catalytic esterification of acrylic acid with n-butanol catalyzed with acidic catalysts. In esterification reactions, homogeneous catalysts such as H2 SO4 , p-toluene sulphonic acid [14–16], and heterogeneous catalysts [17–19] can be used to accelerate the reaction. Catalysis with cation exchange resins offers several advantages over homogeneous acid catalysis. Resins are easily separated from the reaction medium and they can be reused without handling and storage concerns [20]. Moreover, ion exchange resins eliminate corrosion and environmental problems. However, they have low thermal, stability and possibility of diffusion and deactivation problems [21]. In the literature, several studies of pervaporation coupled esterification of some acids with alcohols have been stated, while esterification of acrylic acid with n-butanol was not investigated. In this study, pervaporation assisted esterification reaction of acrylic acid and n-butanol, yielding n-butyl acrylate and water was studied. Also, the effect of membrane process on the shift of the chemical equilibrium was considered. The influences of catalyst loading, temperature, the initial molar ratio of reactants, and ratio of membrane area to volume of the reaction mixture were investigated by using the polymeric membrane, Pervap 2201.
Table 1 The properties of Amberlyst 131 (as reported by the manufacturer). Amberlyst 131 Manufacturer Polymer type Matrix type Functional group Ionic form Exchange capacity, meq/mL Maximum operating temperature, ◦ C Particle size, mm
Rohm and Haas Macroreticular Styrene divinyl benzene Sulfonic acid H+ 1.35 120 0.7–0.8
Table 2 The properties of Pervap 2201 (as reported by the manufacturer). Pervap 2201 Manufacturer
Sulzer ChemTech. ◦
Maximum temperature ( C) Maximum water content in feed (%) Organic acids pH
105 <50 <50 2–7
2.2. Procedure To explore the pervaporation aided esterification process, experiments were done in a batch reactor given in Fig. 1. The membrane was placed in the stainless steel reactor with a volume of 2 L. The effective membrane area is about 179 cm2 . n-Butanol, catalyst, and inhibitor were put in the reactor together and heated up to the reaction temperature. The preheated acrylic acid was added to the reactor and the temperature was kept constant at the reaction temperature. The pressure at the permeate side was kept constant at 4 mbar using a Vacuubrand RZ 2.5 vacuum pump and permeates were collected using two cold traps. During the experiments, samples were taken from both the reaction mixture and permeate and analyzed by gas chromatograph (GC). The conditions of the GC analysis were reported in our previous study [22]. The amount of water in each sample was measured with a Mettler Toledo v20 Karl Fisher titrator during the experiment. The reproducibility of GC and Karl fisher analysis were found to be ±1.41 and ±3.12, respectively. The operational conditions are summarized in Table 3.
2. Materials and methods 2.1. Chemicals The membrane used in the esterification of acrylic acid with nbutanol was the commercial hydrophilic membrane Pervap 2201 (Sulzer ChemTech). Acrylic acid (Merck, purity >99) and n-butanol (Merck, purity >99) were used as reactants and phenothiazine was used as inhibitor to prevent any polymerization reaction. Amberlyst 131 is a macro porous resin made of styrene divinyl benzene copolymer functionalized with sulfonic groups that ensure strong acidity of the catalyst. Some characteristics and physical properties of Amberlyst 131 and Pervap 2201 are given in Tables 1 and 2, respectively. The catalyst reusability was discussed in previous study [22] and Amberlyst 131 was found to be reusable four times without deactivation and can be regenerated after deactivation.
Fig. 1. Diagram of the esterification coupling with pervaporation ((1) condenser, (2) heater, (3) mixer, (4) catalyst basket, (5) membrane, (6) stainless steel sheet, (7) traps, (8) valve, (9) pump).
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Table 3 The operational conditions for pervaporation-assisted esterification experiments.
Effect of temperature
Effect of catalyst loading
Effect of molar ratio of hexanol to acrylic acid
Effect of S/V
T (K)
Butanol/acrylic acid
CL (g/L)
S/V (m−1 )
338 348 358 358 358 358 358 358 358 348 348 348
4 4 4 4 4 4 4 6 8 4 4 4
10 10 10 10 15 20 10 10 10 10 10 10
70 70 70 70 70 70 70 70 70 35 52.5 70
The total flux was determined from the weight of the permeate and the area of the membrane;
3. Theory 3.1. Reaction kinetics
J= The esterification reaction between acrylic acid and n-butanol is given below: C3 H4 O2 + C4 H9 OH ↔ C7 H12 O2 +H2 O
(1)
The kinetic study was studied in our pervious study and the details of determination of reaction kinetics were given [22]. The Langmuir–Hinshelwood–Haugen–Watson (LHHW) model which takes into account the adsorption of reactants and desorption of products fits the experimental data;
ri =
Ccat kf Kacid Kalchohol aacid aalchohol −
1 a a K ester water
(1 + Kacid aacid + Kalchohol aalchohol + Kester aester + Kwater awater )2 (2)
where Ki is the adsorption constant of components, kf is the forward reaction rate constant, Ccat is the catalyst loading, ai are the activities of the species (ai = i xi ), i are the activity coefficients of the components which were determined by UNIQUAC method to consider the non-ideality of the reaction mixture. The temperature dependency of forward reaction rate constant, equilibrium constant and adsorption constants of compounds were determined in our specified work. These results illustrate that the reaction is exothermic, and because of exothermicity equilibrium constants decreased as the temperature was raised. The equilibrium constants were found to decrease in agreement with Ali et al. [23] who found the same trend while studying the esterification of 2-propanol with acetic acid.
W St
(5)
where W, S and t denote the permeate amount, effective membrane area, and reaction time, respectively. The partial fluxes of components (Ji ) are the function of total flux and weight fraction of the component in permeate. Ji = Jyi
(6)
As for the esterification–pervaporation coupling process, the ratio (F) of rates of water removal to water production rate is decided to be key factor defined as: F=
JD S/V dCD /dt
(7)
where F is a dimensionless parameter that refers for the relation between water removal rate and water production rate during the esterification–pervaporation hybrid process, and when • F < 1, the rate of water removal is less than the water production rate, showing that the conversion can be increased a little over the equilibrium conversion, and it is controlled by the water removal due to the pervaporation. • F > 1, the rate of water removal is larger than the water production rate, showing that the conversion of limiting reactant can reach 100%, and it is controlled by the water production rate by chemical reaction [24]. 3.3. Pervaporation in terms of the Hansen solubility parameters
3.2. Reaction and pervaporation The stoichiometry of the esterification of acrylic acid with nbutanol was defined in Eq. (1). This is reversible reaction which proceeds with the formation of the products, n-butyl acrylate and water. From the GC analysis, the conversion of limiting reactant was calculated as follows: Conversion of limiting reactant moles of limiting reactant consumed = initial moles of limiting reactant
ı2t = (ı2d + ı2p + ı2h ) (3)
By applying a material balance, the variation in the number of mole of species i can be expressed as dNi = ri VCcat − Ji S dt
In the separation of organic-liquid mixtures by pervaporation, selectivity is caused by the differences in solubility and/or diffusivity in a membrane among feed components. The increase of the solubility difference leads to further swelling of the membrane by its plasticization and results in reduction of the selectivity [25]. The Hansen solubility parameters (ıd , ıp , ıh ) have been defined as follows:
(4)
where Ji is the flux (mol/m2 h) of component i, and S is the membrane area (m2 ).
(8)
where ıd , ıp , and ıh are contributions from the non-polar interaction, dipole interaction and hydrogen bonding, respectively. Table 4 shows the solubility parameters of n-butanol, acrylic acid, n-butyl acrylate, water and polyvinyl alcohol (PVA). The difference in the solubility parameter was calculated from the differences between the compounds and PVA;
= ınBUOH − ıPVA , = ınBuAc − ıPVA
= ıAcAc − ıPVA ,
= ıwater − ıPVA , (9)
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Table 4 The solubility parameters of n-butanol, acrylic acid, n-butyl acrylate, water and PVA. ıp (cal1/2 cm−3/2 )
ıh (cal1/2 cm−3/2 )
8.7 9 8.6 7.6 7.8
3.0 3.2 3.9 7.8 6.9
7.7 7.5 2.45 20.7 11.7
As shown in Table 4, the differences in the solubility parameters were calculated from Eqs. (8) and (9). The water–PVA interaction gives the maximum solubility difference, , so the highest coupling is achieved between water and PVA. 4. Results and discussion In an esterification–pervaporation hybrid process there are mainly four operating variables: temperature, initial reactant molar ratio, ratio of membrane area to initial volume of reaction mixture, and catalyst loading. David et al. [26] divided these important variables into different groups: (1) factors which affect directly the esterification kinetics: catalyst loading and initial reactant molar ratio, (2) factors that affect directly pervaporation: ratio of effective membrane area to initial volume of reaction mixture, (3) factors that affect simultaneously the esterification and pervaporation: temperature. Internal mass transfer resistance was eliminated according to the Weisz Prater criterion for the esterification of acrylic acid with n-butanol in our previous study [22]. Also external mass transfer resistance can affect the heterogeneous catalytic esterification reaction negatively. It was proven in our previous study [22] that the external mass transfer resistance can be eliminated at 800 rpm. So, the experiments were performed at a stirring speed of 800 rpm. The polymerization tendency of acrylic acid and n-butyl acrylate is well-known. In this work, phenothiazine was used as inhibitor and polymerization was not observed during the experiments and analysis. Pervaporation assisted esterification experiments were performed at different operating parameters to study the effects of temperature, the initial reactant molar ratio, the ratio of membrane area to the initial volume of reaction mixture, and catalyst loading. 4.1. Effect of operating parameters 4.1.1. Temperature The esterification of acrylic acid with n-butanol was studied both with and without a membrane at a molar ratio of n-butanol to acrylic acid of 4 and a catalyst loading of 10 g/L. The experiments were performed at three different temperatures (338, 348, and 358 K) catalyzed by Amberlyst 131. Fig. 2 shows the conversion of acrylic acid versus time for all temperatures. As given in Fig. 2, the batch pervaporation process increases the conversion of acrylic acid significantly. Conversions of acrylic acid increased from 36% to 69%, from 53% to 84% and from 70% to 92% at temperatures of 338, 348, and 358 K, respectively. Due to the water removal from the reaction mixture, the conversion of acrylic acid obtained with the pervaporation–esterification hybrid process is significantly higher. The operating temperature has a dual effect on both the reaction kinetics and membrane structure [27]. The production rates of the products, water and n-butyl acrylate, are higher at a higher temperature. The diffusion of the permeats is facilitated, as the thermal motion of the polymer chains increases with an increase in the temperature [28]. The partial fluxes of components were calculated by using Eq (6) versus reaction time for Pervap 2201 and presented in
100 Conversion of acrylic acid (%)
n-Butanol Acrylic acid n-Butyl acrylate Water PVA
ıd (cal1/2 cm−3/2 )
without PV, 338 K
without PV , 348 K
without PV, 358 K
with PV, 338 K
with PV, 3 48 K
with PV, 358 K
80 60 40 20
Fig. 2. Effect of pervaporation on the conversion of acrylic acid.
Fig. 3. It can be seen that partial fluxes of components were found in the following order Jwater > JBuOH ∼ Jacid ∼ Jester ∼ 0. The Pervap 2201 membrane showed good selectivity for water when exposed to the reaction mixture. Water is clearly the dominant component in the total flux because of the high selectivity of the membrane for water [29]. The flux of water increases rapidly with time especially during the first five hours and then decreases because of a decreasing driving force. As the temperature increased, the flux of water increased. An increase in temperature enhances the esterification reaction because of the higher temperature and water removal by pervaporation. Fig. 4 shows the Arrhenius plot of water flux versus temperature. The activation energy of water permeation across the Pervap 2201 is 36.52 kJ/mol. These values show that high energy is needed for water permeation through the Pervap 2201; this is compatible with the strong temperature effect shown in Fig. 2. According to the Arrhenius relationship, an increase in temperature causes to an increase in the permeation flux of water. 4.1.2. Molar ratio of n-butanol to acrylic acid The effect of molar ratio on the conversion of acrylic acid was studied at a temperature of 358 K and a catalyst loading of 10 g/L. The initial molar ratio of n-butanol to acrylic acid varied between 4, 6 and 8 because of the pH limitation of the Pervap 2201 membrane. As shown in Fig. 5, the conversion of acrylic acid increased slightly due to an increased excess of n-butanol, as the mole ratio of n-butanol to acrylic acid was increased. It is well known that an excess amount of one reactant generally alcohol causes the increased conversions [30]. Fig. 6 shows the partial fluxes of each component through the membrane for different molar ratios of nbutanol to acrylic acid. As can be seen, the fluxes of water through membrane are much higher than those of n-butanol, acrylic acid, and n-butyl acrylate. This is not unexpected because the solubility parameter of Pervap 2201 is closer to water than other components. The difference in the solubility parameter between each pair is in the order of butyl acrylate-membrane > acrylic acid-membrane > nbutanol-membrane > water-membrane, indicating that water and the membrane pair has the strongest interaction since they have the closest solubility parameter compared to the other pairs. As shown in Fig. 6, there is a change in the total flux of water as the molar ratio is increased; this result is confirmed with the conversion of acrylic acid at different molar ratios of n-butanol to acrylic acid. At the end of 6 h, 91.95%, 94.52%, and 96.3% of acrylic acid conversion was achieved at a molar ratio of 4, 6, and 8, respectively. 4.1.3. Catalyst loading Experiments were carried out at a temperature of 358 K, with an initial molar ratio of 4. The effect of catalyst loading was
Acrylic acid
J (mol/hm2) J (mol/hm2)
60
Acrylic acid
Water
120
180 240 Time (min)
Butanol
300
Butyl acrylate
60
Acrylic acid
120
180 240 Time (min)
Butanol
300
Butyl acrylate
6
8
80 60 40 20 0
360
Water
45
4
100
Fig. 5. Effect of molar ratio of n-butanol to acrylic acid on the conversion of acrylic acid.
348 K
0
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
Butyl acrylate
338 K
0
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
Butanol
Conversion of acrylic acid (%)
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
360
Water
358 K
Fig. 6. Effect of molar ratio on the partial fluxes of components.
10 g/L
15 g/L
20 g/L
100
Fig. 3. Effect of temperature on the partial fluxes of components.
Conversion of acrylic acid (%)
J (mol/hm2)
E. Sert, F.S. Atalay / Chemical Engineering and Processing 81 (2014) 41–47
80 60 40 20 0
2.5
ln (water lux)
2 Fig. 7. The effect of catalyst loading on the conversion of acrylic acid.
1.5 1 0.5
ln(water lux) =14.223 -4393.6 (1/T) R² = 0.9329
0
Fig. 4. Arrhenius plot of water flux vs. temperature.
investigated by changing the catalyst loading to 10, 15, and 20 g/L. In this study, the catalyst loading is defined as the ratio of mass of catalyst to the initial volume of the reaction mixture. The conversion of acrylic acid (Fig. 7) and also the water production rate was proportional to the catalyst loading. As expected increasing the catalyst loading favors the formation and removal of water. But, above 15 g/L of catalyst loading, there was no change in the flux of water (Fig. 8) because of the maximum permeability of water. As the catalyst loading was increased, the conversion of acrylic acid increased slightly due to the increase in active sites and about 94% of the acrylic acid conversion was obtained at a catalyst loading of 15 g/L.
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E. Sert, F.S. Atalay / Chemical Engineering and Processing 81 (2014) 41–47
12
338 K
348 K
358 K
4
6
8
10 g/L
15 g/L
20 g/L
10
F
8 6 4 2 0
Fig. 8. Effect of catalyst loading on the partial fluxes of components.
Conversion of acrylic acid (%)
100
35 m⁻¹
52.5 m⁻¹
70 m⁻¹
Fig. 11. The variation of F with time.
permeability can be compensated by using a larger membrane area [31].
80
4.2. Pervaporation performance 60 40 20 0
Fig. 9. Effect of S/V on the conversion of acrylic acid.
To evaluate the performance of pervaporation, the F factor should be calculated. The variations of F versus time at different temperatures (338, 348, and 358 K), catalyst loadings (10, 15, and 20 g/L) and molar ratios of n-butanol to acrylic acid (4, 6, and 8) are given in Fig. 11. The F factor increased with increasing temperature due to the acceleration of the water removal rate. As expected, the water production and permeability are higher at a higher temperature. As stated earlier, the Pervap 2201 membrane showed high water selectivity. The water selection of the membrane increased as the reaction time increased. So, as time increased, the permeation of the flux of water exceeds the water production rate so F becomes greater than 1 after 4 h. As shown in Fig. 11, the highest value of F is obtained from experiments which are performed at a molar ratio of 8. This result is consistent with the conversion of acrylic acid. Maximum conversion of acrylic acid was found to be 96.3% at a temperature of 358 K, a molar ratio of 8, a catalyst loading of 10 g/L and a S/V ratio of 70 m−1 . F was obtained as 10.43 at these conditions. The equilibrium constants were calculated as 88.8%, 87.4% and 87.1% at temperatures of 338, 348 and 358 K in our previous work [22]. By pervaporation-assisted esterification, equilibrium conversions were achieved in a 6 h of operation time. 5. Conclusion
Fig. 10. Effect of S/V on the partial fluxes of components.
4.1.4. S/V ratio The ratio of membrane area to reactor volume (S/V) is one of the most important parameters for the pervaporation process. The effect of the ratio of membrane area to reactor volume on the conversion of acrylic acid is given in Fig. 9. Experiments were performed at a temperature of 348 K, a catalyst loading of 10 g/L, and the S/V ratio varied as 35, 52.5, and 70 m−1 . As shown in Fig. 9, the conversion of acrylic acid decreased with the decrease of the S/V. The conversion of acrylic acid was obtained as 72.58%, 79.30%, and 83.67% at S/V ratios of 35, 52.5, and 70 m−1 , respectively. Also, the rate of water removal increased with the increase of S/V (Fig. 10). In the esterification–pervaporation process, low membrane
In reversible reactions such as esterification, chemical equilibrium limits the conversion and so, additional process is required to shift the chemical equilibrium toward the side of products. Removing of the one of the products usually water increases the forward reaction rate. The different technologies are developed to remove water from a reaction mixture such as reactive distillation, adsorption, pervaporation, or vapor permeation. Among of them, pervaporation–esterification is one of the promising processes, as it combines reaction and product separation to reduce cost and enhance performance. In this study, a pervaporation–esterification hybrid process for n-butyl acrylate production by the esterification of n-butanol and acrylic acid was performed by using the Pervap 2201 polymeric membrane. The Pervap 2201 membrane showed high selectivity to water in the n-butanol/acrylic acid/n-butyl acrylate/water system. The coupling of pervaporation with the esterification reaction was an
E. Sert, F.S. Atalay / Chemical Engineering and Processing 81 (2014) 41–47
efficient method for shifting the equilibrium toward n-butyl acrylate production. The effects of some operating conditions on the esterification– pervaporation performance have been studied. The most important parameter found was temperature due to the dual effect. Both the pervaporation and reaction rate increased with the operating temperature. There are no significant effects of catalyst loading and molar ratio of n-butanol to acrylic acid for the water removal. Nomenclature
Ccat J Ji Ni ri S t V W
concentration of catalyst (gcat /m3 ) total flux (mol/m2 h) flux of component i (mol/m2 h) number of moles of component i (mol) reaction rate (mol/gcat h) membrane area (m2 ) time (h) volume of reaction mixture (m3 ) permeate amount (mol)
Greek letter ı Hansen solubility parameters
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
Subscripts d non-polar interaction p dipole interaction h hydrogen bonding Acknowledgements The authors acknowledge the financial supports from TUBITAK (The Scientific and Technological Research Council of Turkey) under grant no. 110M 462, from EBILTEM (Research and Application Center of Science and Technology) under grant no. 2012 BIL 022.
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[22] [23] [24] [25] [26] [27] [28] [29] [30] [31]
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Contents lists available at ScienceDirect
Chemical Engineering and Processing: Process Intensification journal homepage: www.elsevier.com/locate/cep
n-Butyl acrylate production by esterification of acrylic acid with n-butanol combined with pervaporation Emine Sert ∗ , Ferhan S. Atalay Ege University, Chemical Engineering Department, Bornova, Izmir, Turkey
a r t i c l e
i n f o
Article history: Received 9 January 2014 Received in revised form 24 February 2014 Accepted 22 April 2014 Available online 30 April 2014 Keywords: Pervaporation Esterification Membrane n-Butyl acrylate
a b s t r a c t In this study, the esterification reaction of acrylic acid and n-butanol to produce n-butyl acrylate and water was studied using the pervaporation–esterification hybrid process to perform the separation and reaction simultaneously to increase the conversion of limiting reactant. A Pervap 2201 polymeric membrane was used to separate water and also to shift the equilibrium. The Pervap 2201 membrane showed high selectivity to water in the n-butanol, acrylic acid, n-butyl acrylate, and water reaction system. The effects of temperature, the initial molar ratio of n-butanol to acrylic acid, catalyst loading, and the ratio of membrane area to reaction volume (S/V) were studied. The maximum conversion of acrylic acid was calculated as 96.3% at a temperature of 358 K, a molar ratio of 8, with a catalyst loading of 10 g/L and an S/V ratio of 70 m−1 . © 2014 Elsevier B.V. All rights reserved.
1. Introduction The coupling of reaction and separation has become a current trend in the chemical industry in order to obtain more efficient processes and lower energy consumption. A classic example is the production of esters, which are traditionally obtained by reacting an organic acid and an alcohol in the presence of suitable catalysts. A major difficulty in such reactions is the limitation by the thermodynamic equilibrium, which requires a separation step with a subsequent reactant reflux allows to shift the chemical equilibrium toward the ester production [1]. According to the Le Chatelier principle, the yield and selectivity of the targeted compound are increased by the removal of the byproducts of the reaction. Esterification reactions produce water as byproduct that reduces both catalytic activity and forward reaction rate. Studies by Kusdiana and Saka [2] on the esterification and transesterification reactions reveal that the presence of water deactivates the catalyst activity, which decreases the reaction rate. Among the hybrid processes, reactive distillation which combines reaction and separation processes in a single unit was applied for n-butyl acrylate synthesis. Zeng et al. [3] studied the design and control of a reactive distillation column for the production of n-butyl acrylate. Also, Niesbach et al. [4] studied an experimental and theoretical investigation of butyl acrylate using reactive
∗ Corresponding author. Tel.: +90 232 3111493; fax: +90 232 388 7776. E-mail address: [email protected] (E. Sert). http://dx.doi.org/10.1016/j.cep.2014.04.010 0255-2701/© 2014 Elsevier B.V. All rights reserved.
distillation. They concluded that the process intensification can decrease the equipment needed, thereby reducing the investment and operating costs. Due to high risk of polymerization of acrylic acid and butyl acrylate, Niesbach et al. [5] present an experimental investigation of inhibition period of acrylic acid and n-butyl acrylate polymerization. In their study, hydroquinone and phenothiazine were used as inhibitors. The pilot plant reactive distillation experiments were conducted to show proper concept of polymerization inhibition successfully in the industrial application. The integration of a pervaporation process into a conventional esterification process is attractive because it provides the opportunity to continuously shift the conversion beyond the thermodynamic equilibrium by removing water from the chemical reactor [6,7]. Pervaporation has been proven to be a successful technique for selectively removing a certain component from a liquid mixture because of its low energy requirements and its ability to separate azeotropic mixtures [8]. Pervaporation solely relies on the solubility and transport rate of each component. Pervaporation also demonstrates incomparable advantages in separating heat sensitive, close-boiling, and azeotropic mixtures due to its mild operating conditions, no emission to the environment, and no involvement of additional species into the feed stream [9]. The application of pervaporation to reversible reactions such as esterification has been studied in recent studies. Figueiredo et al. [10] studied the pervaporation-assisted esterification of oleic acid with ethanol using hydrophilic Pervap 1000 membrane. The hydrophilic membrane was able to remove water from the reaction mixture, thus increasing the ester yield. In another study, Delgado et al. [11] studied the synthesis of ethyl lactate from ethanol and
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lactic acid in a batch reactor combined with a pervaporation unit. A hydrophilic membrane Pervap 2201 was used and almost total use of lactic acid was achieved. Korkmaz et al. [12] studied the esterification reaction between acetic acid and iso-butanol by using polydimethylsloxane (PDMS) membrane. The experiments indicate that the PDMS membrane can be used to remove iso-butyl acetate selectively by the pervaporation process. Polyvinyl alcohol (PVA) is a polyhydroxy polymer, which is very common in practical applications because of its easy preparation and biodegradability. It has been selected as polymer matrix in view of its film-forming capacities, hydrophilic properties and high density of reactive chemical functions favorable for cross-linking by irradiation, chemical or thermal treatments [13]. In general, polyvinyl alcohol (PVA) membranes when applied to the pervaporation aided esterification processes must be cross linked to avoid the esterification of the alcoholic groups of the membrane and its consequent loss of its separative properties. The polymeric material presents high hydrophilicity and stability under acidic conditions when undergoing the cross linking treatment. Butyl acrylate is a clear colorless liquid with a characteristic fruity odor. It is readily miscible with most organic solvents. It is readily polymerized and shows a wide range of properties dependent on the selection of the monomer and reaction conditions. n-Butyl acrylate is used in the production of homopolymers and co-polymers [3]. n-Butyl acrylate was synthesized from the catalytic esterification of acrylic acid with n-butanol catalyzed with acidic catalysts. In esterification reactions, homogeneous catalysts such as H2 SO4 , p-toluene sulphonic acid [14–16], and heterogeneous catalysts [17–19] can be used to accelerate the reaction. Catalysis with cation exchange resins offers several advantages over homogeneous acid catalysis. Resins are easily separated from the reaction medium and they can be reused without handling and storage concerns [20]. Moreover, ion exchange resins eliminate corrosion and environmental problems. However, they have low thermal, stability and possibility of diffusion and deactivation problems [21]. In the literature, several studies of pervaporation coupled esterification of some acids with alcohols have been stated, while esterification of acrylic acid with n-butanol was not investigated. In this study, pervaporation assisted esterification reaction of acrylic acid and n-butanol, yielding n-butyl acrylate and water was studied. Also, the effect of membrane process on the shift of the chemical equilibrium was considered. The influences of catalyst loading, temperature, the initial molar ratio of reactants, and ratio of membrane area to volume of the reaction mixture were investigated by using the polymeric membrane, Pervap 2201.
Table 1 The properties of Amberlyst 131 (as reported by the manufacturer). Amberlyst 131 Manufacturer Polymer type Matrix type Functional group Ionic form Exchange capacity, meq/mL Maximum operating temperature, ◦ C Particle size, mm
Rohm and Haas Macroreticular Styrene divinyl benzene Sulfonic acid H+ 1.35 120 0.7–0.8
Table 2 The properties of Pervap 2201 (as reported by the manufacturer). Pervap 2201 Manufacturer
Sulzer ChemTech. ◦
Maximum temperature ( C) Maximum water content in feed (%) Organic acids pH
105 <50 <50 2–7
2.2. Procedure To explore the pervaporation aided esterification process, experiments were done in a batch reactor given in Fig. 1. The membrane was placed in the stainless steel reactor with a volume of 2 L. The effective membrane area is about 179 cm2 . n-Butanol, catalyst, and inhibitor were put in the reactor together and heated up to the reaction temperature. The preheated acrylic acid was added to the reactor and the temperature was kept constant at the reaction temperature. The pressure at the permeate side was kept constant at 4 mbar using a Vacuubrand RZ 2.5 vacuum pump and permeates were collected using two cold traps. During the experiments, samples were taken from both the reaction mixture and permeate and analyzed by gas chromatograph (GC). The conditions of the GC analysis were reported in our previous study [22]. The amount of water in each sample was measured with a Mettler Toledo v20 Karl Fisher titrator during the experiment. The reproducibility of GC and Karl fisher analysis were found to be ±1.41 and ±3.12, respectively. The operational conditions are summarized in Table 3.
2. Materials and methods 2.1. Chemicals The membrane used in the esterification of acrylic acid with nbutanol was the commercial hydrophilic membrane Pervap 2201 (Sulzer ChemTech). Acrylic acid (Merck, purity >99) and n-butanol (Merck, purity >99) were used as reactants and phenothiazine was used as inhibitor to prevent any polymerization reaction. Amberlyst 131 is a macro porous resin made of styrene divinyl benzene copolymer functionalized with sulfonic groups that ensure strong acidity of the catalyst. Some characteristics and physical properties of Amberlyst 131 and Pervap 2201 are given in Tables 1 and 2, respectively. The catalyst reusability was discussed in previous study [22] and Amberlyst 131 was found to be reusable four times without deactivation and can be regenerated after deactivation.
Fig. 1. Diagram of the esterification coupling with pervaporation ((1) condenser, (2) heater, (3) mixer, (4) catalyst basket, (5) membrane, (6) stainless steel sheet, (7) traps, (8) valve, (9) pump).
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Table 3 The operational conditions for pervaporation-assisted esterification experiments.
Effect of temperature
Effect of catalyst loading
Effect of molar ratio of hexanol to acrylic acid
Effect of S/V
T (K)
Butanol/acrylic acid
CL (g/L)
S/V (m−1 )
338 348 358 358 358 358 358 358 358 348 348 348
4 4 4 4 4 4 4 6 8 4 4 4
10 10 10 10 15 20 10 10 10 10 10 10
70 70 70 70 70 70 70 70 70 35 52.5 70
The total flux was determined from the weight of the permeate and the area of the membrane;
3. Theory 3.1. Reaction kinetics
J= The esterification reaction between acrylic acid and n-butanol is given below: C3 H4 O2 + C4 H9 OH ↔ C7 H12 O2 +H2 O
(1)
The kinetic study was studied in our pervious study and the details of determination of reaction kinetics were given [22]. The Langmuir–Hinshelwood–Haugen–Watson (LHHW) model which takes into account the adsorption of reactants and desorption of products fits the experimental data;
ri =
Ccat kf Kacid Kalchohol aacid aalchohol −
1 a a K ester water
(1 + Kacid aacid + Kalchohol aalchohol + Kester aester + Kwater awater )2 (2)
where Ki is the adsorption constant of components, kf is the forward reaction rate constant, Ccat is the catalyst loading, ai are the activities of the species (ai = i xi ), i are the activity coefficients of the components which were determined by UNIQUAC method to consider the non-ideality of the reaction mixture. The temperature dependency of forward reaction rate constant, equilibrium constant and adsorption constants of compounds were determined in our specified work. These results illustrate that the reaction is exothermic, and because of exothermicity equilibrium constants decreased as the temperature was raised. The equilibrium constants were found to decrease in agreement with Ali et al. [23] who found the same trend while studying the esterification of 2-propanol with acetic acid.
W St
(5)
where W, S and t denote the permeate amount, effective membrane area, and reaction time, respectively. The partial fluxes of components (Ji ) are the function of total flux and weight fraction of the component in permeate. Ji = Jyi
(6)
As for the esterification–pervaporation coupling process, the ratio (F) of rates of water removal to water production rate is decided to be key factor defined as: F=
JD S/V dCD /dt
(7)
where F is a dimensionless parameter that refers for the relation between water removal rate and water production rate during the esterification–pervaporation hybrid process, and when • F < 1, the rate of water removal is less than the water production rate, showing that the conversion can be increased a little over the equilibrium conversion, and it is controlled by the water removal due to the pervaporation. • F > 1, the rate of water removal is larger than the water production rate, showing that the conversion of limiting reactant can reach 100%, and it is controlled by the water production rate by chemical reaction [24]. 3.3. Pervaporation in terms of the Hansen solubility parameters
3.2. Reaction and pervaporation The stoichiometry of the esterification of acrylic acid with nbutanol was defined in Eq. (1). This is reversible reaction which proceeds with the formation of the products, n-butyl acrylate and water. From the GC analysis, the conversion of limiting reactant was calculated as follows: Conversion of limiting reactant moles of limiting reactant consumed = initial moles of limiting reactant
ı2t = (ı2d + ı2p + ı2h ) (3)
By applying a material balance, the variation in the number of mole of species i can be expressed as dNi = ri VCcat − Ji S dt
In the separation of organic-liquid mixtures by pervaporation, selectivity is caused by the differences in solubility and/or diffusivity in a membrane among feed components. The increase of the solubility difference leads to further swelling of the membrane by its plasticization and results in reduction of the selectivity [25]. The Hansen solubility parameters (ıd , ıp , ıh ) have been defined as follows:
(4)
where Ji is the flux (mol/m2 h) of component i, and S is the membrane area (m2 ).
(8)
where ıd , ıp , and ıh are contributions from the non-polar interaction, dipole interaction and hydrogen bonding, respectively. Table 4 shows the solubility parameters of n-butanol, acrylic acid, n-butyl acrylate, water and polyvinyl alcohol (PVA). The difference in the solubility parameter was calculated from the differences between the compounds and PVA;
= ınBUOH − ıPVA , = ınBuAc − ıPVA
= ıAcAc − ıPVA ,
= ıwater − ıPVA , (9)
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Table 4 The solubility parameters of n-butanol, acrylic acid, n-butyl acrylate, water and PVA. ıp (cal1/2 cm−3/2 )
ıh (cal1/2 cm−3/2 )
8.7 9 8.6 7.6 7.8
3.0 3.2 3.9 7.8 6.9
7.7 7.5 2.45 20.7 11.7
As shown in Table 4, the differences in the solubility parameters were calculated from Eqs. (8) and (9). The water–PVA interaction gives the maximum solubility difference, , so the highest coupling is achieved between water and PVA. 4. Results and discussion In an esterification–pervaporation hybrid process there are mainly four operating variables: temperature, initial reactant molar ratio, ratio of membrane area to initial volume of reaction mixture, and catalyst loading. David et al. [26] divided these important variables into different groups: (1) factors which affect directly the esterification kinetics: catalyst loading and initial reactant molar ratio, (2) factors that affect directly pervaporation: ratio of effective membrane area to initial volume of reaction mixture, (3) factors that affect simultaneously the esterification and pervaporation: temperature. Internal mass transfer resistance was eliminated according to the Weisz Prater criterion for the esterification of acrylic acid with n-butanol in our previous study [22]. Also external mass transfer resistance can affect the heterogeneous catalytic esterification reaction negatively. It was proven in our previous study [22] that the external mass transfer resistance can be eliminated at 800 rpm. So, the experiments were performed at a stirring speed of 800 rpm. The polymerization tendency of acrylic acid and n-butyl acrylate is well-known. In this work, phenothiazine was used as inhibitor and polymerization was not observed during the experiments and analysis. Pervaporation assisted esterification experiments were performed at different operating parameters to study the effects of temperature, the initial reactant molar ratio, the ratio of membrane area to the initial volume of reaction mixture, and catalyst loading. 4.1. Effect of operating parameters 4.1.1. Temperature The esterification of acrylic acid with n-butanol was studied both with and without a membrane at a molar ratio of n-butanol to acrylic acid of 4 and a catalyst loading of 10 g/L. The experiments were performed at three different temperatures (338, 348, and 358 K) catalyzed by Amberlyst 131. Fig. 2 shows the conversion of acrylic acid versus time for all temperatures. As given in Fig. 2, the batch pervaporation process increases the conversion of acrylic acid significantly. Conversions of acrylic acid increased from 36% to 69%, from 53% to 84% and from 70% to 92% at temperatures of 338, 348, and 358 K, respectively. Due to the water removal from the reaction mixture, the conversion of acrylic acid obtained with the pervaporation–esterification hybrid process is significantly higher. The operating temperature has a dual effect on both the reaction kinetics and membrane structure [27]. The production rates of the products, water and n-butyl acrylate, are higher at a higher temperature. The diffusion of the permeats is facilitated, as the thermal motion of the polymer chains increases with an increase in the temperature [28]. The partial fluxes of components were calculated by using Eq (6) versus reaction time for Pervap 2201 and presented in
100 Conversion of acrylic acid (%)
n-Butanol Acrylic acid n-Butyl acrylate Water PVA
ıd (cal1/2 cm−3/2 )
without PV, 338 K
without PV , 348 K
without PV, 358 K
with PV, 338 K
with PV, 3 48 K
with PV, 358 K
80 60 40 20
Fig. 2. Effect of pervaporation on the conversion of acrylic acid.
Fig. 3. It can be seen that partial fluxes of components were found in the following order Jwater > JBuOH ∼ Jacid ∼ Jester ∼ 0. The Pervap 2201 membrane showed good selectivity for water when exposed to the reaction mixture. Water is clearly the dominant component in the total flux because of the high selectivity of the membrane for water [29]. The flux of water increases rapidly with time especially during the first five hours and then decreases because of a decreasing driving force. As the temperature increased, the flux of water increased. An increase in temperature enhances the esterification reaction because of the higher temperature and water removal by pervaporation. Fig. 4 shows the Arrhenius plot of water flux versus temperature. The activation energy of water permeation across the Pervap 2201 is 36.52 kJ/mol. These values show that high energy is needed for water permeation through the Pervap 2201; this is compatible with the strong temperature effect shown in Fig. 2. According to the Arrhenius relationship, an increase in temperature causes to an increase in the permeation flux of water. 4.1.2. Molar ratio of n-butanol to acrylic acid The effect of molar ratio on the conversion of acrylic acid was studied at a temperature of 358 K and a catalyst loading of 10 g/L. The initial molar ratio of n-butanol to acrylic acid varied between 4, 6 and 8 because of the pH limitation of the Pervap 2201 membrane. As shown in Fig. 5, the conversion of acrylic acid increased slightly due to an increased excess of n-butanol, as the mole ratio of n-butanol to acrylic acid was increased. It is well known that an excess amount of one reactant generally alcohol causes the increased conversions [30]. Fig. 6 shows the partial fluxes of each component through the membrane for different molar ratios of nbutanol to acrylic acid. As can be seen, the fluxes of water through membrane are much higher than those of n-butanol, acrylic acid, and n-butyl acrylate. This is not unexpected because the solubility parameter of Pervap 2201 is closer to water than other components. The difference in the solubility parameter between each pair is in the order of butyl acrylate-membrane > acrylic acid-membrane > nbutanol-membrane > water-membrane, indicating that water and the membrane pair has the strongest interaction since they have the closest solubility parameter compared to the other pairs. As shown in Fig. 6, there is a change in the total flux of water as the molar ratio is increased; this result is confirmed with the conversion of acrylic acid at different molar ratios of n-butanol to acrylic acid. At the end of 6 h, 91.95%, 94.52%, and 96.3% of acrylic acid conversion was achieved at a molar ratio of 4, 6, and 8, respectively. 4.1.3. Catalyst loading Experiments were carried out at a temperature of 358 K, with an initial molar ratio of 4. The effect of catalyst loading was
Acrylic acid
J (mol/hm2) J (mol/hm2)
60
Acrylic acid
Water
120
180 240 Time (min)
Butanol
300
Butyl acrylate
60
Acrylic acid
120
180 240 Time (min)
Butanol
300
Butyl acrylate
6
8
80 60 40 20 0
360
Water
45
4
100
Fig. 5. Effect of molar ratio of n-butanol to acrylic acid on the conversion of acrylic acid.
348 K
0
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
Butyl acrylate
338 K
0
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
Butanol
Conversion of acrylic acid (%)
0.18 0.16 0.14 0.12 0.10 0.08 0.06 0.04 0.02 0.00
360
Water
358 K
Fig. 6. Effect of molar ratio on the partial fluxes of components.
10 g/L
15 g/L
20 g/L
100
Fig. 3. Effect of temperature on the partial fluxes of components.
Conversion of acrylic acid (%)
J (mol/hm2)
E. Sert, F.S. Atalay / Chemical Engineering and Processing 81 (2014) 41–47
80 60 40 20 0
2.5
ln (water lux)
2 Fig. 7. The effect of catalyst loading on the conversion of acrylic acid.
1.5 1 0.5
ln(water lux) =14.223 -4393.6 (1/T) R² = 0.9329
0
Fig. 4. Arrhenius plot of water flux vs. temperature.
investigated by changing the catalyst loading to 10, 15, and 20 g/L. In this study, the catalyst loading is defined as the ratio of mass of catalyst to the initial volume of the reaction mixture. The conversion of acrylic acid (Fig. 7) and also the water production rate was proportional to the catalyst loading. As expected increasing the catalyst loading favors the formation and removal of water. But, above 15 g/L of catalyst loading, there was no change in the flux of water (Fig. 8) because of the maximum permeability of water. As the catalyst loading was increased, the conversion of acrylic acid increased slightly due to the increase in active sites and about 94% of the acrylic acid conversion was obtained at a catalyst loading of 15 g/L.
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12
338 K
348 K
358 K
4
6
8
10 g/L
15 g/L
20 g/L
10
F
8 6 4 2 0
Fig. 8. Effect of catalyst loading on the partial fluxes of components.
Conversion of acrylic acid (%)
100
35 m⁻¹
52.5 m⁻¹
70 m⁻¹
Fig. 11. The variation of F with time.
permeability can be compensated by using a larger membrane area [31].
80
4.2. Pervaporation performance 60 40 20 0
Fig. 9. Effect of S/V on the conversion of acrylic acid.
To evaluate the performance of pervaporation, the F factor should be calculated. The variations of F versus time at different temperatures (338, 348, and 358 K), catalyst loadings (10, 15, and 20 g/L) and molar ratios of n-butanol to acrylic acid (4, 6, and 8) are given in Fig. 11. The F factor increased with increasing temperature due to the acceleration of the water removal rate. As expected, the water production and permeability are higher at a higher temperature. As stated earlier, the Pervap 2201 membrane showed high water selectivity. The water selection of the membrane increased as the reaction time increased. So, as time increased, the permeation of the flux of water exceeds the water production rate so F becomes greater than 1 after 4 h. As shown in Fig. 11, the highest value of F is obtained from experiments which are performed at a molar ratio of 8. This result is consistent with the conversion of acrylic acid. Maximum conversion of acrylic acid was found to be 96.3% at a temperature of 358 K, a molar ratio of 8, a catalyst loading of 10 g/L and a S/V ratio of 70 m−1 . F was obtained as 10.43 at these conditions. The equilibrium constants were calculated as 88.8%, 87.4% and 87.1% at temperatures of 338, 348 and 358 K in our previous work [22]. By pervaporation-assisted esterification, equilibrium conversions were achieved in a 6 h of operation time. 5. Conclusion
Fig. 10. Effect of S/V on the partial fluxes of components.
4.1.4. S/V ratio The ratio of membrane area to reactor volume (S/V) is one of the most important parameters for the pervaporation process. The effect of the ratio of membrane area to reactor volume on the conversion of acrylic acid is given in Fig. 9. Experiments were performed at a temperature of 348 K, a catalyst loading of 10 g/L, and the S/V ratio varied as 35, 52.5, and 70 m−1 . As shown in Fig. 9, the conversion of acrylic acid decreased with the decrease of the S/V. The conversion of acrylic acid was obtained as 72.58%, 79.30%, and 83.67% at S/V ratios of 35, 52.5, and 70 m−1 , respectively. Also, the rate of water removal increased with the increase of S/V (Fig. 10). In the esterification–pervaporation process, low membrane
In reversible reactions such as esterification, chemical equilibrium limits the conversion and so, additional process is required to shift the chemical equilibrium toward the side of products. Removing of the one of the products usually water increases the forward reaction rate. The different technologies are developed to remove water from a reaction mixture such as reactive distillation, adsorption, pervaporation, or vapor permeation. Among of them, pervaporation–esterification is one of the promising processes, as it combines reaction and product separation to reduce cost and enhance performance. In this study, a pervaporation–esterification hybrid process for n-butyl acrylate production by the esterification of n-butanol and acrylic acid was performed by using the Pervap 2201 polymeric membrane. The Pervap 2201 membrane showed high selectivity to water in the n-butanol/acrylic acid/n-butyl acrylate/water system. The coupling of pervaporation with the esterification reaction was an
E. Sert, F.S. Atalay / Chemical Engineering and Processing 81 (2014) 41–47
efficient method for shifting the equilibrium toward n-butyl acrylate production. The effects of some operating conditions on the esterification– pervaporation performance have been studied. The most important parameter found was temperature due to the dual effect. Both the pervaporation and reaction rate increased with the operating temperature. There are no significant effects of catalyst loading and molar ratio of n-butanol to acrylic acid for the water removal. Nomenclature
Ccat J Ji Ni ri S t V W
concentration of catalyst (gcat /m3 ) total flux (mol/m2 h) flux of component i (mol/m2 h) number of moles of component i (mol) reaction rate (mol/gcat h) membrane area (m2 ) time (h) volume of reaction mixture (m3 ) permeate amount (mol)
Greek letter ı Hansen solubility parameters
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
Subscripts d non-polar interaction p dipole interaction h hydrogen bonding Acknowledgements The authors acknowledge the financial supports from TUBITAK (The Scientific and Technological Research Council of Turkey) under grant no. 110M 462, from EBILTEM (Research and Application Center of Science and Technology) under grant no. 2012 BIL 022.
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[22] [23] [24] [25] [26] [27] [28] [29] [30] [31]
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