Ind. Eng. Chem. Res. 2007, 46, 5271-5277
5271
Miniaturized Systems for Homogeneously and Heterogeneously Catalyzed Liquid-Phase Esterification Reaction Amol A. Kulkarni,*,†,‡ Klaus-Peter Zeyer,† Thomas Jacobs,† and Achim Kienle†,§ Max-Planck-Institut fu¨r Dynamik komplexer technischer Systeme, Sandtorstrasse 1, 39106 Magdeburg, Germany, and Lehrstuhl fu¨r Automatisierungstechnik/Modellbildung, Otto-Von-Guericke-UniVersita¨t Magdeburg, UniVersita¨tsplatz 2, 39106 Magdeburg, Germany
A miniaturized-plant concept is presented for the analysis of homogeneous and heterogeneous acid-catalyzed esterification of acetic acid with butanol. The plant configuration includes a micromixer followed by an isothermal microreactor. For the case of homogeneously catalyzed esterification, a long tube of 1.3 mm inner diameter acted as the reaction tube and also helped to achieve longer residence times. The results were found to be consistent with the data from literature obtained with conventional equipment on lab scale, while deviations were seen at long reaction times and high catalyst concentrations. A novel miniaturized fixed-bed reactor (mFBR) was designed for the heterogeneously catalyzed reaction, with Amberlyst-15 as a catalyst. The performance of the mFBR was satisfactory for a very long time, was reproducible, and could be used for continuous synthesis. A change in the residence time and the reactive length can be achieved by changing the total flow rate and the number of reaction plates in the stack, respectively. 1. Introduction Over the past decade or so, the research on microreaction systems has gained momentum, and in its early stage of development, much of the attention has been given to gas-phase reactions. A large body of literature1-6 covers the development of the concept of microreaction technology, various approaches toward the analysis of reactions, application in synthesis chemistry, and unit operations on microscale. Microreaction technology has been mainly used for carrying out highly exothermic and fast reactions and reactions posing selectivityrelated problems due to poor mixing or mass transfer.6 In the present paper, we study the feasibility of microreaction technology for homogeneously and heterogeneously acid-catalyzed equilibrium-limited liquid-phase reactions. Synthesis of butyl acetate is identified as the model system. It is an important solvent with many industrial applications, and it represents a large class of acid-catalyzed equilibrium-limited reactions, like esterifications, ester hydrolysis, transesterifications, etc., many of which are prospective candidates for integrated processes. Synthesis of alkyl acetates through the reaction of acetic acid with suitable alcohol takes place in the presence of strong acid catalysts. Typically these are homogeneous liquid-phase processes, and the chemical equilibrium determines the limiting conversion of the reactants. Thus, the resulting mixture contains products, ester and water, and also the unconverted reactants. The values of the equilibrium constants of esterification reactions are relatively high (depending upon temperature and initial mole ratio of reactants). In practice, the equilibrium limitation is overcome to some extent by continuous removal of one of the products (mostly water) with a suitable separation process. In these extremely slow reactions, the catalyst enhances the reaction rates by protonating the carboxylic acid. Mineral acids7-9 and strong organic acids are efficient homogeneous catalysts, and * Corresponding author. Tel.: +91-20-2590 2153. Fax: 91-20-2589 3260. E-mail:
[email protected]. † Max-Planck-Institut fu ¨ r Dynamik komplexer technischer Systeme. ‡ Present address: National Chemical Laboratory, Pune, India. § Otto-von-Guericke-Universita¨t Magdeburg.
ion-exchange resins containing sulfonic acid groups (-SO3H) are the typical heterogeneous acid catalysts.10-14 While the industrial processes for the synthesis of butyl acetate are based on homogeneous catalytic reactive distillation,15-17 use of heterogeneous catalysts18-22 eliminates the difficulties in catalyst separation. Although the subject of butyl acetate synthesis is quite old, the available literature brings out the scatter in the information about the kinetics of the homogeneous and heterogeneous catalytic processes and also the process conditions. Notably, a recent investigation23 brings out the kinetic information over a range of conditions for homogeneously catalytic synthesis and illustrates the importance of kinetic models that yield thermodynamically consistent results. However, in the limit of available information, a very careful selection of operating conditions and reliable kinetic data are required before they can be directly implemented for the design purpose. This gap in the information can be filled by doing some quick and elegant experiments, and here we illustrate such a possibility through the use of microreaction technology. Recent studies that deal with the esterification in microreactor systems include the following: (i) enzymatic esterification of diglycerol with lauric acid,24 (ii) esterification of 4-(1-pyrenyl)butyric acid,25 (iii) solid acid-catalyzed esterification in pressure-driven, heated plasma desorption mass spectrometry (PDMS)/glass microreactor,26 and (iv) solution-phase synthesis of organic esters using solvents having electroosmotic mobility.27,28 All of these studies24-28 focus on illustrating the performance of a microreaction system in terms of synthesis and final conversion, and in addition to these aspects, here we illustrate its utility for kinetic studies, process feasibility, and even for continuous production purpose. The present paper is organized as follows: In the next section, we give details of the miniaturized plant assembly for both homogeneous and heterogeneous catalytic processes, fabrication of the miniaturized fixed-bed reactor (mFBR), and the experimental work. This is followed by the results and discussions on the outlet product composition and its comparison with the literature. Before concluding the manuscript, we highlight some of the novelties the proposed system offers and a few applications.
10.1021/ie060411+ CCC: $37.00 © 2007 American Chemical Society Published on Web 06/27/2007
5272
Ind. Eng. Chem. Res., Vol. 46, No. 16, 2007
Figure 1. Schematic of the experimental setup used for the homogeneous catalytic esterification reaction.
2. Experimental Section 2.1. Homogeneously Catalyzed Esterification. 2.1.1. Chemicals. The chemicals used for the experiments with homogeneous catalytic reaction were of synthesis grade (sulfuric acid, acetic acid, and n-butanol, 99.5%, all from Merck, Germany). Distilled water (specific conductivity < 10 µS/cm) was used for making aqueous solutions of the required analysis compounds for the titration (1.0 and 0.1 N sodium hydroxide). The purity of the chemicals was verified by gas chromatography. 2.1.2. Setup and Experiments. In the miniaturized plant, the reactants (n-butanol and mixture of acids) were pumped separately using high-performance liquid chromatography (HPLC) pumps (Knauer, Germany) and mixed using a micromixer (SIMM-V2: IMM, Germany) over a wide range of flow rates (0.019-1.36 mL/min). The desired quantity (0.005-4.5% w/w) of the homogeneous catalyst (H2SO4) was premixed in pure acetic acid. The reactants were charged in equal mole ratios. The mixed reactants were further passed through a reaction tube (Hastelloy, 1/16 in. o.d., Vindum Eng., U.S.A.) of 1.3 m length, by which the residence time in the range of 100-8300 s could be achieved for the above flow rates. The reactants were preheated to the desired temperature before mixing in the micromixer. The experiments were carried out under isothermal conditions using a thermostat (Lauda, Germany) at four temperatures (20, 60, 70, and 80 °C). On the basis of the analysis of outlet composition, the system was allowed to reach a steady state. At steady state, at minimum three samples were collected for every residence time for each catalyst concentration and temperature. The samples were collected at the outlet of the tube in an ice bath (60 °C) and at very low flow rates, excessive conversion led to side products formation. The investigations involving the heterogeneous catalytic system yielded good results. Performance of the system was consistently reproducible, and the reactor could be operated continuously for very long time. The amounts of catalyst and reactants used in this study were approximately 24% (homogeneous) and 17% (heterogeneous) in comparison to the conventional studies.8,35 These amounts can be further reduced to 0.22% and 0.8-1.0%, respectively, using built-in microsensors positioned along flow path for analysis. Similar to a micromixer and a micro-falling-film reactor,37 an mFBR also has a potential to become an integral component of a microplant. Acknowledgment A.A.K. gratefully acknowledges the financial support from the Alexander von Humboldt Foundation (Bonn) during this work. The authors also acknowledge the help of Mr. Frank Steyer during the GC analysis and also the mechanical workshop of the MPI for assistance in fabrication of the mFBR. Notations a ) activity of the ith component in the liquid phase a′i ) product of the adsorption constant and activity for component i dp ) particle size (µm) K ) equilibrium constant kf,Hom ) forward reaction rate constant for homogeneous catalytic reaction (1/s) kf,Het ) forward reaction rate constant for heterogeneous catalytic reaction (kmol/kg‚s) Ks,i ) adsorption constant of component i L ) total length of the fixed bed (m) mcat ) mass of the catalyst (kg) n ) molar hold-up (kmol) N ) number of plates Q ) volumetric flow rate (mL/min) ri ) rate of production of component i (kmol/s) T ) operating temperature (°C) t ) sample time (s), fluid residence time in mFBR (s), time in rate expressions 2 and 3 (s) u ) superficial liquid velocity (m/s) Greek Letters R ) constant in the modified LHHW models (ML: R ≈ 2, MLC: optimized R ≈ 1.48)
Ind. Eng. Chem. Res., Vol. 46, No. 16, 2007 5277
∆P ) pressure drop (MPa) ) voidage η ) liquid viscosity (mPa s) ν ) stoichiometric coefficient of ith component F ) liquid density (kg/m3) τ ) dimensionless operating time Literature Cited (1) Ehrfeld, W.; Hessel, V.; Lo¨we, H. Microreactors: New Technology for Modern Chemistry; Wiley-VCH: Weinheim, Germany, 2000. (2) Jensen, K. F. Microreaction EngineeringsIs Small Better? Chem. Eng. Sci. 2001, 56, 293. (3) Fletcher, P. D. I.; Haswell, S. J.; Pombo-Villar, E.; Warrington, B. H.; Watts, P.; Wong, S. Y. F.; Zhang, X. Microreactors, Principles and Applications in Organic Synthesis. Tetrahedron 2002, 58, 4735. (4) Hessel, V.; Hardt, S.; Lo¨we, H. Chemical Micro Process Engineering; Wiley-VCH: Weinheim, Germany, 2004. (5) Ja¨hnisch, K.; Hessel, V.; Lo¨we, H.; Baerns, M. Chemistry in Microstructured Reactors. Angew. Chem., Int. Ed. 2004, 43, 406. (6) Brivio, M.; Verboom, W.; Reinhoudt, D. N. Miniaturized Continuous Flow Reaction Vessels: Influence on Chemical Reactions. Lab Chip 2006, 6, 329. (7) Leyes, C. E.; Othmer, D. F. Continuous Esterification of Butanol and Acetic Acid, Kinetic and Distillation Considerations. Trans. Am. Inst. Chem. Eng. 1945, 41, 157. (8) Al-Saadi, A. N.; Jeffreys, G. V. Esterification of Butanol in a TwoPhase Liquid-Liquid System. Part 2: Reaction Rate Studies and The Analysis of Batch Esterification in Two-Phase Systems. AIChE J. 1981, 27, 761. (9) Hartig, H.; Regner, H. Verfahrenstechnische Auslegung einer Veresterungskolonne. Chem. Ing. Technol. 1971, 43 (18), 1001. (10) Chakrabarti, A.; Sharma, M. M. Cationic Ion Exchange Resins as Catalysts. React. Polym. 1993, 20, 1. (11) Sharma, M. M. Some Novel Aspects of Cationic Ion-Exchange Resins as Catalysts. React. Funct. Polym. 1995, 26, 3. (12) Harmer, M. A.; Sun, Q. Solid Acid Catalysis Using Ion-Exchange Resins. Appl. Catal., A 2001, 221, 45. (13) Lundquist, E. Publication from Rohm and Haas, US 5426199. (14) Yadav, G. D.; Krishnan, M. S. Synthesis of Perfumery Grade Methyl Anthranilate from Anthranilic Acid and Methanol. Org. Process. Res. DeV. 1998, 2, 86. (15) Minotti, M.; Doherty, M. F.; Malone, M. F. Design for Simultaneous Reaction and Liquid-Liquid Extraction. Ind. Eng. Chem. Res. 1998, 37, 4748. (16) Venimadhavan, G.; Malone, M. F.; Doherty, M. F. A Novel Distillate Policy for Batch Reactive Distillation with Application to Production of Butyl Acetate. Ind. Eng. Chem. Res. 1999, 38, 714. (17) Jimenez, L.; Costa-Lopez, J. The Production of Butyl Acetate and Methanol via Reactive and Extractive Distillation. II. Process Modeling, Dynamic Simulation, and Control Strategy. Ind. Eng. Chem. Res. 2002, 41 (26), 6735. (18) Liao, A.; Tong, Z. Synthesis of n-Butyl Acetate Catalyzed by Amberlyst. Huaxue Fanying Gongcheng Yu Gongy 1995, 11, 34-45; Chem. Abstr. 124, 179409. (19) Steinigeweg, S.; Gmehling, J. n-Butyl Acetate Synthesis via Reactive Distillation: Thermodynamic Aspects, Reaction Kinetics, PilotPlant Experiments, and Simulation Studies. Ind. Eng. Chem. Res. 2002, 41 (22), 5483.
(20) Gangadwala, J.; Kienle, A.; Stein, E.; Mahajani, S. Production of Butyl Acetate by Catalytic Distillation: Process Design Studies. Ind. Eng. Chem. Res. 2004, 43 (1), 136. (21) Janowsky, R.; Groeble, M.; Knippenberg, U. Bundesministerium fur Bildung und Forschung (BMBF) Project, 1997 (funded by BMBF FKZ 03 D 0014 B0). (22) Hanika, J.; Kucharova, M.; Kolena, J.; Smejkal, Q. Multifunctional Trickle Bed Reactor for Butylacetate Synthesis. Catal. Today 2003, 7980, 83. (23) Grob, S.; Hasse, H. Reaction Kinetics of the Homogeneously Catalyzed Esterification of 1-Butanol with Acetic Acid in a Wide Range of Initial Compositions. Ind. Eng. Chem. Res. 2006, 45, 1869. (24) Garcia, E.; Ferrari, F.; Carcia, T.; Martinez, M.; Aracil, J. Use of Microreactors in Biotransformation Processes: Study on the Synthesis of Diglycerol Monolaurate Ester. In 4th IMRET; 2000; p 201. (25) Brivio, M.; Oosterbroek, E. R.; Verboom, W.; Goedbloed, M. H.; van den Berg, A.; Reinhoudt, D. N. Surface Effects in the Esterification of 9-Pyrenebutyric Acid within a Glass Micro Reactor. Chem. Commun. 2003, 15, 1924. (26) McCreedy, T.; Wilson, N. G. Microfabricated Reactors for OnChip Heterogeneous Catalysis. Analyst 2001, 126 (1), 21. (27) Wiles, C.; Watts, P.; Haswell, S. J.; Pombo-Villar, E. Solution Phase Synthesis of Esters within a Micro Reactor. Tetrahedron 2003, 59 (51), 10173. (28) Watts, P. QSAR Combinat. Sci. 2005, 24 (6), 701. (29) Singh, A.; Hiwale, R.; Mahajani, S. M.; Gudi, R. D.; Gangadwala, J.; Kienle, A. Production of Butyl Acetate by Catalytic Distillation. Theoretical and Experimental Studies. Ind. Eng. Chem. Res. 2005, 44 (9), 3042. (30) Luyben, W. L.; Pszalgowski, K. M.; Schaefer, M. R.; Siddons, C. Design and Control of Conventional and Reactive Distillation Processes for the Production of Butyl Acetate. Ind. Eng. Chem. Res. 2004, 43 (25), 8014. (31) Mazzotti, M.; Neri, B.; Gelosa, D.; Kruglov, A.; Morbidelli, M. Kinetics of Liquid Phase Esterification Catalyzed by Acidic Resins. Ind. Eng. Chem. Res. 1997, 36 (1), 3. (32) Silva, V. M. T. M.; Rodrigues, A. E. Dynamics of a Fixed Bed Adsorptive Reactor for Synthesis of Diethylacetal. AIChE J. 2002, 48 (3), 625. (33) Gelosa, D.; Ramaioli, M.; Valente, G.; Morbidelli, M. Chromatographic Reactors: Esterification of Glycerol with Acetic Acid using Acidic Polymeric Resins. Ind. Eng. Chem. Res. 2003, 42 (25), 6536. (34) Yu, W.; Hidajat, K.; Ray, A. K. Determination of Adsorption and Kinetic Parameters for Methyl Acetate Synthesis Reaction in Amberlyst 15 Ion Exchange Resin. Appl. Catal., A 2004, 260, 191. (35) Gangadwala, J.; Mankar, S.; Mahajani, S.; Kienle, A.; Stein, E. Esterification of Acetic Acid with Butanol in the Presence of Ion-Exchange Resins as Catalysts. Ind. Eng. Chem. Res. 2003, 42 (10), 2146. (36) Kulkarni, A. A.; Zeyer, K.-P.; Jacobs, T.; Kaspereit, M.; Kienle, A. Feasibility Studies and Dynamics of Catalytic Liquid Phase Esterification Reactions in a Micro Plant. Presented at the 9th IMRET, Potsdam, Germany, 2006; J. Chem. Eng. 2007, in press. (37) Yeong, K. K.; Gavriilidis, A.; Zapf, R.; Hessel, V. Catalyst Preparation and Deactivation Issues for Nitrobenzene Hydrogenation in a Microstructured Falling Film Reactor. Catal. Today 2003, 81, 641.
ReceiVed for reView April 1, 2006 ReVised manuscript receiVed December 1, 2006 Accepted May 14, 2007 IE060411+
