Esterification of acrylic acid with 1,4-butanediol in a batch distillation column reactor over Amberlyst 15 catalyst.

Yang, Jung-Il ; Cho, Soon-Haeng ; Park, Jongki 等

INTRODUCTION

Currently, 2-hydroxyethyl acrylate (C[H.sub.2]=CH-COO-[(C[H.sub.2]).sup.2-] OH, 2-HEA) is used as a top coating material for automotives. 4-hydroxybutyl acrylate (C[H.sub.2]=CH-COO-[(C[H.sub.2]).sub.4-]OH, HBA) can be a good substitute for 2-HEA because it has better physical and chemical properties such as strong scratch resistance, good mechanical properties

and excellent acid rain resistance (Nippon Kasei Chemical Co., Ltd, 2006).

HBA has a hydroxyl functional group and a double bond group in the molecule which makes HBA easily copolymerized with various vinyl monomers (Klein and Elms, 1971). Especially, the HBA copolymer achieves a higher cross-linking ratio with curing agents compared to copolymers with other conventional hydroxyl functional monomers (HEA, HEMA, HPA and HPMA, etc.). This is because the OH group of HBA is farther away from the acrylic backbone chain than the OH group of other hydroxyl functional.

HBA is produced from esterification of acrylic acid (C[H.sub.2]=CH-COOH, AA) with 1,4-butanediol (HO-[(C[H.sub.2]).sub.4-]OH, BD). Two reactions take place when AA and BD contact with each other; esterification of AA with BD to form HBA and water, and esterification of AA with the produced HBA to form 1,4-butanediol diacrylate (C[H.sub.2]=CH-COO-[(C[H.sub.2]).sub.4-]OOC-HC=C[H.sub.2], BDA) and water, where HBA is the desired product.

AA + BD = HBA + [H.sub.2]O (1)

AA + HBA = BDA + [H.sub.2]O (2)

We carried out above reactions in a batch reactor over the Amberlyst 15 catalyst and obtained a kinetic expression for the HBA production. The kinetic equation was based on the quasi-homogeneous model (Yang et al., 2007).

Yokoyama et al. (2000) showed a similar process for producing hydroxyalkyl monoacrylate using stannoxane catalysts. In that process, hydroxyalkyl monoacrylate was produced from the reaction of acrylic acid or acrylic acid derivatives with alkane diol. The hydroxyalkyl monoacrylate was further purified by distillation and extraction processes. Sato and Kobayashi (1993) also reported another similar process for preparing 4-hydroxybutyl (meth)acrylate by reacting (meth)acrylic acid with 1,4-butanediol in the presence of an acidic catalyst. Especially, the by-product 1,4-butanediol di(meth)acrylate was returned to the reaction system to obtain the high yield of 4-hydroxybutyl (meth)acrylate.

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Furthermore, esterification is an equilibrium limited reaction and is therefore frequently carried out in a reactive distillation process to obtain higher yields of product and to increase reaction rates by removing one of the products from the reaction zone. Chopade et al. (1997a, b) reported not only the production of diethoxymethane by the reaction of ethanol and formaldehyde, but also 1,3-dioxolane production by cyclic acetalization of ethylene glycol with formaldehyde in the presence of the cation-exchange resin catalyst in a reactive distillation column. Saha and Sharma (1996) showed the esterification of formic acid with cyclohexane in a distillation column and they also used cation-exchange resins as catalysts.

In this work, we report the production of HBA in the esterification of AA with BD by the reactive distillation process. The reactive distillation process for HBA production is tried not to take a high yield of HBA in the reaction, but to get a high purity of HBA after the reaction in the separation process. Since the esterification is equilibrium limited reaction, there are unreacted AA and BD after the reaction. The unreacted AA is easily removed by distillation process because it takes very low boiling point compared to the produced HBA, but the unreacted BD is not simply removed because the BD takes very similar chemical and physical properties, viz. water solubility and boiling point, to the HBA (BASF Co., Ltd, 1997). After the reaction, it is very difficult to obtain a high purity of HBA by general separation techniques such as distillation and extraction. Therefore, to take a high purity of HBA, BD must be almost completely reacted in the reaction by the reactive distillation process. BDA is a final product in the esterification, and its yield can be increased highly in the reactive distillation process. However, BDA is easily separated with the HBA by extraction process because BDA takes a very low hydrophilicity compared to HBA (BASF Co., Ltd, 2004).

The reactive distillation process was tried to increase the reaction rate of BD disappearance for taking a high purity of HBA after the reaction and the process parameters were optimized to run the reactive distillation process without a serious problem, such as polymerization of reactants and products.

EXPERIMENTAL

Materials

Acrylic acid (C[H.sub.2]=CH-COOH, 99%), 1,4-butanediol (HO-[(C[H.sub.2]).sub.4-] OH, 99 + %), 4-hydroxybutyl acrylate (C[H.sub.2]=CH-COO-[(C[H.sub.2]).sub.4-]OH, 96%) and 1,4-butanediol diacrylate (C[H.sub.2]=CH-COO-[(C[H.sub.2]).sub.4-]OOC-HC = C[H.sub.2], 90%) were obtained from Aldrich Chemical Co. The commercial ion exchanged resin (Amberlyst 15, Rohm and Hass Co.) was used as the catalyst.

Apparatus and Procedure

Experiments were carried out in a batch reactor equipped with a distillation column as shown in Figure 1. The reactor volume was 1000 ml and an agitator was installed. The reaction temperature was maintained by circulating ethylene glycol of which the temperature was controlled in a hot bath. The distillation column (diameter 1 inch, length 150 cm) was installed on the top of the reactor and glass beads (diameter 2 mm) were packed inside the column. The batch distillation was run because the boiling point of water was much lower than those of reactants and other products (AA, BD, HBA and BDA). The water vapour was removed by a condenser. Since AA, HBA and BDA can be easily polymerized at high temperatures, vacuum distillation was operated from ambient pressure to 400 mm Hg to decrease the distillation temperature. The vacuum buffer tank of which the pressure was automatically controlled by a vacuum pump was used to control the reaction pressure. The temperature and the pressure were controlled by using LabVIEW program (LabVIEW 7.1, NI Co.).

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Analysis

The concentrations of reactants and products were analyzed by using a gas chromatograph (DsChrom6200, Donam Co., South Korea) with [N.sub.2] as a carrier gas. The GC was equipped with a flame ionization detector and a column (AT-capillary column, Alltech Co.). The oven temperature was set at 250[degrees]C which is higher than boiling points of both reactants and products. Again, the main product of the reaction was 4-hydroxybutyl acrylate (HBA), and the by-product was 1,4-butanediol diacrylate (BDA). The BD conversion, HBA yield, and HBA selectivity are defined as follows.

BD conversion (%) = (moles of BD reacted)/ (moles of initial BD) x 100 (3)

HBA yield (%) = (moles of HBA produced)/ (moles of initial BD) x 100 (4)

and

HBA selectivity (%) =(moles of HBA produced)/ (sum of mole of HBA and BDA) x 100 (5)

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RESULTS AND DISCUSSION

Reactive Distillation Activity

Firstly, the esterification of AA with BD for HBA production was carried out using a distillation column reactor at 100[degrees]C atmospheric pressure. The total amount of reactants was 700 ml and the mole ratio of AA and BD was 1.85:1. Since the reaction was carried out at the atmospheric pressure, the reaction must proceed as if there were no distillation unit. Figure 2 shows the change in concentrations of reactants and products as well as the calculated results from the kinetic expression obtained from our previous study (Yang et al., 2007). As can be seen, the esterification reaction behaviour of the reactor equipped with the reactive distillation unit was well described by the model. However, BD concentration was decreased more severely than the simulated result because the BD decomposition reaction by the acid catalyst seemed to occur more readily in the larger scale reactor (1000 ml) of this work than in the smaller flask reactor (150 ml) that was used to obtain the kinetic model. The reaction data obtained at 100[degrees]C and 760 mm Hg were used as the base data to compare those obtained with the reactive distillation. Figure 3 presents BD conversion, HBA yield and HBA selectivity by the reaction. As shown in Figure 3, HBA yield was reached to above 60 mol% during 7 h of the reaction, but BD conversion was still 93 mol%. Since the physical and chemical properties of BD are very similar to those of HBA, it is very difficult to separate the unreacted BD from the produced HBA after the reaction. Thus, the resultant HBA might be the low-purity product unless BD is consumed during the reaction as much as possible. Therefore, reactive distillation was considered to increase the reaction rate of BD.

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The trial reactive distillation was carried out at 100[degrees]C and 600 mm Hg. In this run, the partial vacuum was maintained to remove the water, thereby increasing the reaction rates. However, polymerization of both reactants and products took place at that reaction condition. When polymerization occurred in the reactor, there was a sudden increase in both the reactor temperature and the distillation column temperature. The temperature increase was due to the exothermic heat of the polymerization reaction. Since it was condensation-type polymerization, polymerization was accelerated by the removal of water. The product sample had the visible solid resulting from the polymerization.

Effect of Air-Bubbling

The air-bubbling operation was used in the reactive distillation procedure to solve the polymerization problem caused by water removal at vacuum condition. Oxygen in air was reported to be an inhibitor of polymerization (Yokoyama et al., 2000). While maintaining the reaction temperature at 100[degrees]C and the reaction pressure at 600 mm Hg, 70 ml/min of air was introduced to the bottom of the reactor. As expected, there was no polymerization and the reaction proceeded well for at least 8 h at 600 mm Hg. Figure 4 shows the change of component concentrations during the reactive distillation and the line represents simulation results of the atmospheric operation at 100[degrees]C without distillation. Reaction rates of AA, BD, HBA, and BDA definitely increased when the reactive distillation was applied with air-bubbling. The water content of the product after the reaction was 3.17 wt%, which was much lower than the water content of 8.17 wt% without the reactive distillation. The air-bubbling operation was proved to be very effective to prevent polymerization during the reactive distillation. BD conversion, HBA yield, and HBA selectivity by the reactive distillation were also displayed in Figure 5. Although HBA yield was slightly decreased to 56.5 mol%, BD conversion was increased to above 95 mol%. Therefore, it was confirmed that the reactive distillation was a suitable process to increase BD conversion by the enhanced reaction rate of BD.

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Effect of Pressure

To investigate the effect of pressure in the reactive distillation, the reaction pressure in the reactive distillation was changed from 760 to 400 mm Hg and the results are shown in Figures 6, 7, 8 and 9. The reactive distillation was progressed with air-bubbling. Carbon molar balance of the reactions was also calculated and expressed in Table 1.

As shown in Figure 7, the reaction rates of BD disappearance at 400, 500 and 600 mm Hg were much higher than that at 760 mm Hg. After 10 h of the reaction, the concentration of BD was 3.8 vol% at the ambient pressure. However, the BD concentration was lower than 1.5 vol% at the sub-ambient pressure after the same time of the reaction. The reactive distillation process by vacuum operation not only reduced the reaction time by increase of reaction rates, but also provided the high-purity of HBA production by the low concentration of the unreacted BD.

The HBA production profiles at different reaction pressures are shown in Figure 8. Since HBA is the mid-product for the series reaction, the concentration and the yield of HBA did not change significantly with the reaction pressure. The reason for a slight increase in the HBA concentration and the yield was that both the reaction rate of AA and BD for HBA production and the reaction rate of AA and HBA for BDA production increased simultaneously by the reactive distillation. Thus, most of the increase in the HBA production rate was compensated by the increase in the HBA disappearance rate during the vacuum operation.

The BDA production profiles are also displayed in Figure 9. It was clear that the production rate of BDA increased significantly with the reduction in the reaction pressure since BDA was the final product.

Although the HBA production was not enhanced significantly by the reactive distillation process under vacuum, it can be a critical process for taking a highly pure HBA production and also a useful process in term of energy saving because the separation process for removing BD can be obviated. Furthermore, the water content in the reactor after the reaction was 2.22 wt% in the case of 400 mm Hg runs, while the content at ambient-pressure operation was 8.17 wt%. Thus, we conclude that the by-product water was properly removed by the reactive distillation operation and it enhanced reaction rates, especially for the reaction rate of BD.

CONCLUSIONS

Esterification of acrylic acid with 1,4-butanediol to produce 4-hydroxybutyl acrylate was studied in a batch reactive distillation mode to increase reaction rates, especially for the reaction rate of BD by removing water. Amberlyst 15 was used as a solid acid catalyst. Air-bubbling was highly effective to prevent the polymerization of both the product and the reactant during the reactive distillation operation. Although the HBA yield was not enhanced significantly by the reactive distillation operation, the reaction rate of BD disappearance became higher by the reactive distillation operation in vacuum condition, resulting in a product easily separable to obtain a high purity of HBA.

ACKNOWLEDGMENT

The financial support from Korea Ministry of Commerce, Industry and Energy (A2C-07-02) is gratefully acknowledged.

Manuscript received September 28, 2006; revised manuscript received April 11, 2007; accepted for publication April 22, 2007.

REFERENCE

BASF Company, "Technical Data Sheet--1,4-Butanediol," (http://www.basf.com/diols/bcdiolsbdo.html), New Jersey, NJ (1997).

BASF Company, "Technical Information--Laromer BDDA," www.performancechemicals.basf.com/ev-wcms-in/internet/ en_GB/function/evproducts:/document/30041345/TI, Ludwigshafen, Germany (2004).

Chopade, S. P. and M. M. Sharma, "Reaction of Ethanol and Formaldehyde: use of Versatile Cation-Exchange Resins as Catalyst in Batch Reactors and Reactive Distillation Columns," React. Funct. Polym. 32, 53-64 (1997).

Chopade, S. P. and M. M. Sharma, "Acetalization of Ethylene Glycol with Formaldehyde using Cation-Exchange Resins as Catalysts: Batch Versus Reactive Distillation," React. Funct. Polym. 34, 37-45 (1997).

Klein, D. H. and W. J. E. Elms, "4-Hydroxybutyl Arylate," Paint Tech. 43, 68 (1971).

Nippon Kasei Chemical Company, "Product- 4-Hydroxybutyl Arylate," http://www.nkchemical.co.jp/ver_03/japanese/ product_j/prod_4hba01_j.html), Tokyo (2006).

Saha, B. and M. M. Sharma, "Esterification of Formic Acid, Acrylic Acid and Methacrylic Acid with Cyclohexane in Batch and Distillation Column Reactors: Ion-Exchange Resins as Catalysts," React. Funct. Polym. 28, 263-278 (1996).

Sato, T. and M. Kobayashi, "Method for Producing 4-Hydroxybutyl (Meth)acrylate," U.S. Patent No. 5,206,421 (1993).

Yang, J. I., S. H. Cho, H. J. Kim, H. K. Joo, H. Jung and K. Y. Lee, "Production of 4-Hydroxybutyl Acrylate and Its Reaction Kinetics over Amberlyst 15 Catalyst," Can. J. Chem. Eng. 85(1), 83-91 (2007).

Yokoyama, T., Y. Kawaragi and K. Murai, "Process for Producing Hydroxyalkyl Monoacrylate using Stannoxane Catalysts," U.S. Patent No. 6,087,538 (2000).

Jung-Il Yang (1), Soon-Haeng Cho (1), Jongki Park1 and Kwan-Young Lee (2) *

(1.) Korea Institute of Energy Research, Daejeon 305-343, South Korea

(2.) Department of Chemical and Biological Engineering, Korea University, Seoul 136-701, South Korea

* Author to whom correspondence may be addressed. E-mail address: [email protected]

Table 1. Experimental conditions and carbon molar balances of the
reactive distillation processes at 760, 600, 500, and 400 mm Hg

 Reactants mole ratio
 Temp
Run number AA BD [[degrees]C ]

1 1.85 1 100
2 1.85 1 100
3 1.85 1 100
4 1.85 1 100

 Pressure Air-Bubbling Carbon Balance
Run number [mm hg] [ml/min] [mol%]

1 760 0 97.3
2 600 70 95.5
3 500 70 98.3
4 400 70 96.9