Ethyl Acetate Production from Water-Containing Ethanol Catalyzed by

Selective oxidation of water-containing ethanol in the presence of excess ethanol provides a one- step preparation of ethyl acetate. Acetic acid is fo...
1 downloads 0 Views 167KB Size
Download PDF
Ind. Eng. Chem. Res. 1999, 38, 1271-1276

1271

Ethyl Acetate Production from Water-Containing Ethanol Catalyzed by Supported Pd Catalysts: Advantages and Disadvantages of Hydrophobic Supports Tzong-Bin Lin,‡ Dong-Lin Chung,† and Jen-Ray Chang*,† Department of Chemical Engineering, National Chung Cheng University, Chia-Yi, Taiwan, Republic of China, and Chinese Petroleum Corporation, R.M.R.C., Chia-Yi, Taiwan, Republic of China

Selective oxidation of water-containing ethanol in the presence of excess ethanol provides a onestep preparation of ethyl acetate. Acetic acid is formed from the oxidation of ethanol catalyzed by a supported Pd catalyst and is further catalytically esterified to ethyl acetate by the protons dissociated from acetic acid. The difference of the catalytic performance between hydrophilic and hydrophobic Pd catalysts was investigated by a continuous fixed-bed reactor run at 95 °C, 35.4 atm, and a air/ethanol molar ratio of 2.37. The experimental results indicated that, after the induction period, the conversion of ethanol catalyzed by a styrene-divinylbenzene copolymer (SDB)-supported Pd catalyst is more than 20 times that catalyzed by a γ-alumina-supported Pd catalyst at a weight hourly space velocity (WHSV) of 2.4 h-1. However, it may be caused by weak metal-support interactions and the formation of palladium(II) acetate during the reaction. For the Pd/SDB catalysts, the Pd clusters were leached out concomitantly with the growth of Pd particles. Inductively coupled plasma (ICP) optical emission spectroscopy characterizing the fresh and used catalysts shows that about 10% of Pd was leached after 60 h on stream. Extended X-ray absorption fine structure (EXAFS) spectroscopy results further indicate that the average particle size of the Pd clusters on SDB support increases from 6 to 20 Å. Introduction Ethyl acetate, a very useful chemical, is normally used as a solvent in the paint and coating industry. In addition, its physiologic harmlessness and oleophilic character has made it especially suitable for extraction in food industry and for the preparation of cosmetics. Its low boiling point properties has made it possible to be applied as a high-grade defatting agent.1,2 Recently, we patented a process for ethyl acetate production.3 The process provides one-step conversion of water-containing ethanol to ethyl acetate via a concomitant partial oxidation and esterification reaction. The partial oxidation reaction is catalyzed by a palladium-type catalyst, while the esterification reaction is catalyzed by a proton formed from the spontaneous dissociation of acetic acid or by a resin-type solid acid catalyst mixed with the Pd catalysts. When conventional hydrophilic catalysts are exposed to an aqueous solution, capillary condensation takes place until it reaches thermodynamic equilibrium dictated by the Kelvin equation,4 ln(P/P0) ) 2Vµ cos θ/(rRT), where r is the radius of the capillary, V is the molar volume of the liquid, and µ is the surface tension. For the contact angle θ less than 90°, liquid condenses in the capillary at a pressure P less than the saturated P0 at temperature T. For hydrophilic material-supported Pd catalysts, the contact angle with an aqueous solution would be close to zero. Thus, in the esterification reaction, the generated water not only impedes the forward chemical reaction but also forms a water film on the Pd clusters to retard the diffusion of reactants to active sites. * To whom correspondence should be addressed. † National Chung Cheng University. ‡ Chinese Petroleum Corporation.

Besides the water formed from the esterification reaction, some water in the reaction system comes from the reaction feed. Since water-containing ethanol is much cheaper than that of pure ethanol (Chemical Marketing Reporter, Nov. 6, 1998), it was preferred for the process. For the water-containing reaction, hydrophilic catalysts are expected to have a relatively low reaction rate because of the strong mass-transfer limitation. Catalyst deactivation is one of the important performance factors for the application of a catalyst in the petrochemical industry. Although the general reasons for deactivation for supported metal catalysts such as chemical poisoning, sintering, fouling by solid contaminants, pore mouth plugging, phase change of supports, and volatility of metal in the catalysts have been thoroughly studied,5-7 the reasons for the deactivation for hydrophobic catalysts have been poorly understood. Therefore, besides the comparison of the catalytic performance between conventional hydrophilic catalysts (e.g., γ-alumina-supported Pd catalysts) and the hydrophobic catalysts (e.g., SDB(styrene-divinylbenzene copolymer)-supported Pd catalysts), the factors of the catalyst deactivation for the SDB-supported Pd catalysts are also of interest. Inductively coupled plasma (ICP) optical emission spectroscopy was used to investigate the metal loss during reaction. The reaction-induced morphology change of Pd clusters on the SDB support was characterized by EXAFS (extended X-ray absorption fine structure) spectroscopy, which has been shown to be useful for characterization of supported metal catalysts.8-10 Moreover, the bonding of Pd clusters to an SDB support and to an adsorbate during the reaction are important in rationalizing the catalyst deactivation and were determined by EXAFS as well.

10.1021/ie9805887 CCC: $18.00 © 1999 American Chemical Society Published on Web 03/17/1999

1272 Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999

Experimental Section Material and Catalyst Preparation. Preparation of the γ-Al2O3-supported Pd catalysts has been previously described.11,12 The support (A2U, Osaka Yogyo, γ-Al2O3 with a surface area of about 170 m2/g and particle size about 1 mm), impregnating Pd(CH3COO)2, was filtered to remove solvent and then was calcined at 350 °C for 6 h. The catalyst samples were then reduced with 6 L(NTP)/h of hydrogen at 150 °C and 1 atm for 8 h. The catalyst contained 1.0 wt % Pd, measured by inductively coupled plasma optical emission spectroscopy using a Jarnell-Ash 1100 instrument. The SDB-supported Pd catalysts were provided by Dr. Chuang and the details of the preparation method have been reported in the paper by Yaparpalvi and Chuang.13 The SDB support was obtained by polymerizing divinylbenzene in ethylvinylbenzene with 2,2-azobis(2methylpropionitrile) as the initiator. The resulting SDB had a BET surface area of 465 m2/g. The Pd/SDB catalysts were prepared by the impregnation of SDB with an ethanol solution containing a given amount of Pd(NH3)4Cl2‚H2O. The amounts were chosen so that adsorption of all the Pd precursors would have a solid containing 1.0 wt % Pd. After drying in a rotary evaporator at 95 °C, the catalysts were reduced in hydrogen at 200 °C until the pH of the furnace outlet became neutral. Since the catalyst samples may be oxidized during storage, prior to EXAFS measurement and catalytic performance test, the catalysts were reduced with 6 L(NTP)/h of hydrogen again at 100 °C and 1 atm for 1 h. Catalytic Performance. The catalytic performance tests were carried out in a continuous downflow fixedbed reactor with an inside diameter of 2.1 cm and an inside volume of 94.0 mL. The reactor was heated by a water-bath circulator and the reaction temperature was monitored with a sensor in the center of the catalyst bed. The reactor was packed with 2.0 g of catalysts mixed with a 1.6 mm glass ball in a ratio of 1:20 by volume. A gradient packing method was used to minimize bypassing effects.14 The reaction was carried out with a weight hourly space velocity (WHSV) of 2.4 h-1 (g of feed/h‚g of catalyst), at 95 °C, 35.4 atm, and a air/ ethanol molar ratio of 2.37. The reaction products were trapped by a condenser at -5 °C and analyzed by gas chromatography (Shimadzu Gas Chromatograph model GC-8A, TCD and FID detector, equipped with a Porapack R column and a SP4270 data processor). X-ray Absorption Spectroscopy. The X-ray absorption measurements were performed on an X-ray beamline X-11A of the National Synchrotron Light Source (NSLS) at Brookhaven National Laboratory with a storage ring energy of 2.5 GeV and a beam current between 150 and 250 mA. A Si(111) double-crystal monochromator was used for energy selection, and it was detuned 20% at Eo (energy of palladium K absorption edge) + 50 eV to suppress higher harmonic radiation; the resolution, ∆E/E, was estimated to be 2.0 × 10-4. The monochromator was scanned in energy from 200 eV below the palladium K absorption edge (24350 eV) to 1200 eV above the edge. The catalyst samples were pressed into a self-supporting wafer with the wafer thickness chosen to give an absorbance of 2.5 and measured in a transmission mode at the liquid nitrogen temperature. Electron Probe Microanalysis (EPMA). The palladium concentration profiles of the fresh and used

catalyst samples were characterized by EPMA (JEOL 840A link AN10). Before EPMA measurement, the catalyst samples were embedded in a thermoplastic resin, polished by no. 1500 sandpaper and followed by no. 3000 sandpaper for fine polishing and then coated with a layer of carbon by vacuum deposition. The measurements were performed at an acceleration voltage of the electron beam of 20 kV, the sample current of 0.05 mA, and the scanning speed of 0.02 mm/min. Results and Discussion Mass-Transfer Limitation and Reaction Rate. The external mass-transfer limitation was examined by the ethanol conversion over the Pd/SDB catalysts, carried out at a constant WHSV (2.4 h-1) with a superficial mass velocity of ethanol ranging from 1 to 10 mg/cm2‚s. The experimental results indicated that the ethanol conversion increased with superficial velocity; after 50 h on stream, the conversions of ethanol were 0.32, 0.45, 0.67, and 0.74 for the superficial mass velocities of 1, 2, 5, and 10 mg/cm2‚s, respectively. The results suggested that the external mass-transfer limitation cannot be neglected in the given reaction system. The ethanol conversion for the Pd/SDB is much higher than that that for the Pd/γ-Al2O3 catalysts (Figure 1A), whereas the average pore diameter of Pd/γ-Al2O3 is about 2.3 times that of Pd/SDB catalysts (160 Å for the Pd/γ-Al2O3 catalysts). Since the metal dispersion of the two catalysts does not have a significant difference (CO/ Pd is 0.58 and 0.51 for the Pd/SDB and Pd/γ-Al2O3 catalysts, respectively), the much higher conversion for the Pd/SDB catalysts was thought to be caused by the less internal transfer resistance. Because of the change of catalyst activity and selectivity during the reaction, determining time-varying mass-transfer resistance is very difficult; thus, rigorous kinetic analysis was not attempted. Instead, an empirical power-law rate equation was used to fit the kinetic data. For the Pd/SDB catalysts, at about 50 h on stream, the ethanol conversions were 0.25, 0.34, 0.40, and 0.48 for the WHSV of 9.6, 7.2, 4.8, and 2.4 h-1, respectively. These data could roughly be fitted by a second-order kinetics with reaction rate constant of 0.11 L/h‚mol. Effects of Supports on the Catalytic Performance. Catalytic performance of the Pd catalysts prepared from SDB and γ-Al2O3 supports were investigated by comparing the total conversion and the selectivity to each one of the reaction products. As shown in Figure 1A, the ethanol conversion catalyzed by Pd/SDB catalysts is much higher than that catalyzed by the Pd/γ-Al2O3 catalysts; at about 50 h on stream, the conversion of the Pd/SDB catalysts was about 45%, about 25 times the conversion of the Pd/γ-Al2O3 catalysts. On the basis of second-order kinetics, the reaction catalyzed by a Pd/SDB catalyst has a rate constant about 40 times that of Pd/γ-Al2O3 catalysts. For both catalyst samples, the selectivity to acetaldehyde [(acetaldehyde yield/ethanol conversion) 100%; the value has about 2% deviation caused by the deviation of gas chromatography measurement] slightly increased with time on stream, then decreased, and finally became nearly time-invariant after 25 h on stream. The selectivity of the Pd/SDB catalysts is much lower than that of the other catalysts; at nearly steady state, the selectivity is 35% for Pd/γ-Al2O3 catalysts, while 4% for Pd/SDB catalysts (Figure 1B). The selectivity to ethyl acetate for both catalyst samples decreased with time on stream and became

Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999 1273

(a)

(b)

(c)

(d)

Figure 1. (a) Total conversion of water-containing ethanol catalyzed by Pd/γ-Al2O3 catalysts and Pd/SDB, respectively at T ) 95 °C, P ) 35.4 atm, WHSV ) 2.4 h-1, and air/ethanol (mol) ) 2.262 (O, Pd/SDB; 4, Pd/γ-Al2O3). (b) Acetaldehyde selectivity of water-containing ethanol conversion catalyzed by Pd/γ-Al2O3 catalysts and Pd/SDB, respectively at T ) 95 °C, P ) 35.4 atm, WHSV ) 2.4 h-1, and air/ ethanol (mol) ) 2.262 (O, Pd/SDB; 4, Pd/γ-Al2O3). (c) Ethyl acetate selectivity of water-containing ethanol conversion catalyzed by Pd/ γ-Al2O3 catalysts and Pd/SDB, respectively at T ) 95 °C, P ) 35.4 atm, WHSV ) 2.4 h-1, and air/ethanol (mol) ) 2.262 (O, Pd/SDB; 4, Pd/γ-Al2O3). (d) Acetic acid selectivity of water-containing ethanol conversion catalyzed by Pd/γ-Al2O3 catalysts and Pd/SDB, respectively at T ) 95 °C, P ) 35.4 atm, WHSV ) 2.4 h-1, and air/ethanol (mol) ) 2.262 (O, Pd/SDB; 4, Pd/γ-Al2O3).

almost independent of time with values about 63% for the Pd/γ-Al2O3 catalysts and 57% for the others (Figure 1C). The selectivity to acetic acid for the Pd/SDB catalyst increased with time on stream and then became timeinvariant at about 25 h, with the value of 37%. In contrast, the selectivity for the Pd/γ-Al2O3 catalysts was observed to be close to zero (Figure 1D). In the case of a hydrophilic support, γ-Al2O3, the catalysts are rather inactive, compared to the hydrophobic support, SDB. On the basis of Kelvin equation, if a material with contact angle greater than 90° is selected as a catalyst support, its pore will remain dry and accessible to gaseous reactants. On the other hand, if a material has a contact angle close to zero, then because of capillary condensation, water accumulated in the catalyst pore, resulting in an increase of diffusion resistance. Experimental results showed that the contact angle between water and γ-Al2O3 is 4.6°, while it is 107.6° between water and SDB. Hence, the low activity of the Pd/γ-Al2O3 catalysts was thought to be caused by the diffusion hindrance. Similar results have been observed for the oxidation of water-containing organic compounds reported by Chuang et al.15,16 and Yaparpalvi and Chuang.13 For the reaction catalyzed by Pd/SDB catalysts, the ethanol conversion increased with time on stream to about 25 h on stream and then declined. In contrast, the conversion for the Pd/γ-Al2O3 catalysts decreased

with time on stream at the start of the run and became almost time-invariant after 7 h. The different reaction kinetics observed for those two catalyst samples may be caused by the difference in the affinity between reaction species and supports. For the reactor bed packed with catalysts of hydrophobic properties, the hydrocarbon is easier to diffuse into catalyst pores and is more readily to be adsorbed on the active sites, whereas the dispersion rate is relatively lower than that packed with hydrophilic catalysts. Hence, the hydrophobic catalysts should present a longer induction period. Within the induction period, the reaction rate increased with time on stream. Because the catalysts deactivated right at the start of the run, a maximum of conversion was observed before the induction period (Figure 1A). Selectivity to acetaldehyde, a reaction immediate, increased to a maximum and then slightly decreased, while selectivity to acetic acid, a reaction product formed from further oxidation of acetaldehyde, increased and then became time-invariant. The selectivity to ethyl acetate decreased with time on stream because of the increase of water formation promoting the reverse reaction of the irreversible esterification reaction. Since the Pd clusters on a hydrophilic may be more ready to be covered by a water film, less oxygen is expected to diffuse through the water film and be adsorbed on the Pd clusters. As a result, because of

1274 Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999

Figure 2. Palladium concentration of liquid product vs time on stream in the water-containing ethanol conversion catalyzed by Pd/SDB at T ) 95 °C, P ) 35.4 atm, WHSV ) 2.4 h-1, and air/ ethanol (mol) ) 2.262.

Figure 3. EPMA characterizing Pd concentration profile of (a) the fresh Pd/SDB catalyst and (b) the used Pd/SDB catalyst.

relatively less oxygen available for the further oxidation of acetaldehyde to acetic acid, a higher selectivity to acetaldehyde was observed for the Pd/γ-Al2O3 catalysts. Loss of Metal during Reaction. In general, the reasons for the loss of metal sites in catalysts are (1) attrition of catalysts, (2) volatility of metal, and (3) leaching of metal clusters. In this study, leaching of Pd clusters from Pd/SDB catalysts evidenced by ICP and EPMA (electron probe microanalysis) measurements is the main reason for the metal loss. Figure 2 shows that the Pd concentration (measured by ICP optical emission spectroscopy) in the product stream decreased with time on stream and became time-invariant at about 30 h. Consistent with ICP measurements, palladium concentration profiles characterized by EPMA spectroscopy (Figure 3) indicate that palladium clusters deposited on the SDB support decreased after the reaction. Moreover, the comparison of the metal profiles for both fresh and used catalysts showed a core shrinking of the palladium clusters, suggesting that the palladium leaching is controlled by mass transfer.17 Morphology of Pd Clusters on the Fresh and the Used Pd/SDB Catalysts. The pre-edge and background was subtracted from X-ray absorption data of each sample. The resulting spectrum was divided by the edge height to obtain EXAFS functions.18 The comparison of EXAFS spectra for the fresh and used catalysts are shown in Figure 4. The raw EXAFS data for the samples have a signal-to-noise ratio > 40. (The noise amplitude was determined at k ) 14 Å-1 and the signal amplitude was determined at k ) 4 Å-1.) Prior to the detailed EXAFS data analysis, k3weighted Pd-Pd phase- and amplitude-corrected Fourier transforms were determined for the EXAFS func-

Figure 4. Raw EXAFS data for the fresh Pd/SDB catalyst (solid line) and the used Pd/SDB catalyst (dotted line).

Figure 5. Imaginary part and magnitude of Fourier transform (k3-weighted, ∆k ) 4.5-13.0 Å-1, Pd-Pd phase and amplitude corrected) of the raw EXAFS data for the fresh Pd/SDB catalyst (solid line) and the used Pd/SDB catalyst (dotted line).

tions (4.3 < k < 14.0 Å-1). The Fourier transforms provide the qualitative information about the structure change of the supported Pt clusters during the reaction. As shown in Figure 5, the Pd-Pd phase- and amplitude-corrected Fourier-transformed EXAFS functions of the fresh and used catalyst sample shows that the peaks corresponding to the first metal-metal shell (at about 2.8 Å) and higher shells are at the same positions, while the peaks for the used catalyst sample are much higher than that of the fresh catalyst. Since the intensity of the Fourier-transformed EXAFS functions is proportional to the coordination number of Pd,19 these results suggest that, besides the leaching of palladium, the reaction also induced the growth of palladium clusters. Detailed EXAFS Analysis. A k2-weighted Fourier transformation without correction was performed on the EXAFS function over the range 4.09 < k < 14.88 Å-1 for the fresh catalyst sample and 3.34 < k < 15.31 Å-1 for the used one. The major contributions were isolated by inverse Fourier transformation of the data in the range 1.11 < r < 3.14 Å for the fresh catalyst sample and 1.35 < r < 3.17 Å for the used catalyst sample. The Fourier-filtered EXAFS data were analyzed by a difference file technique with a nonlinear least-squares multiple-shell fitting routine.20 The reference files used for the data analysis were obtained from standard materials of known structure. The resulting coordination parameters and the corresponding standard deviations are summarized in Table 1a for the fresh catalyst sample and Table 1b for the used one.

Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999 1275 Table 1. EXAFS Results shell

N

R, Å

∆σ2

∆E0, eV

EXAFS reference

Pd-C(support) Pd-Pd

2.2 ( 0.2 3.0 ( 0.2

a. Fresh Pd/SDB Catalysta,b 2.02 ( 0.01 0.002 ( 0.001 2.741 ( 0.003 -0.0003 ( 0.0004

6(2 -2.5 ( 0.4

Ru-C Pd-Pd

Pd-O(Adsorbate) Pd-Pd

0.25 ( 0.05 7.9 ( 0.1

b. Used Pd/SDB Catalystc,d 2.16 ( 0.02 -0.009 ( 0.002 2.755 ( 0.001 -0.0016 ( 0.0001

13 ( 4 1.3 ( 0.1

Pd-O Pd-Pd

a Note: N the coordination number for the absorber-backscatterer pair; R the average absorber-backscatterer distance; ∆σ2 the DebyeWaller factor; ∆E0 the inner potential correction. b Note: The number of parameters used to fit the data in this first shell is 8; the statistically justified number is approximately 12 estimated from the Nyquist theorem, n ) (2∆k∆r/π) + 1, where ∆k and ∆r, respectively, are the k and r ranges used in the forward and inverse Fourier transform. c All footnotes are the same as in part a. d The number of parameters used to fit the data in this first shell is 8; the statistically justified number is approximately 11.

The analysis results showed that, after the reaction, the Pd-Pd first shell coordination number increased from 3.0 to 7.9, indicating the increasing size of Pd clusters. A Pd-Pd first-shell coordination number of 3.0 for the fresh catalysts represents an average particle size of about 6.0 Å and the coordination number of 7.9 for the used catalysts represents an average particle size of about 20.0 Å.21 Irreversible Activity Loss Induced from the Reaction. The deactivation of the Pd/SDB catalysts after 30 h on stream is clearly shown in Figure 1. Inferred from the ICP and EXAFS results, we conclude that the leaching of palladium and the aggregation of Pd clusters during the reaction lead to a decrease of the active sites, thereby decreasing the catalytic activity. The oxylchlorination method is normally used to reactivate a catalyst by redispersing the aggregated Pd clusters. However, the method is quite complicated.22 Moreover, the catalyst deactivation caused by the metal leaching is unable to be recovered. From an industrial perspective, a catalyst, which is unable to be regenerated, is economically unfavorable. Thus, the decrease of metal leaching is very crucial in improving the Pd/ SDB catalysts for industrial application. The distance of the Pd-O contribution of the used Pd/ SDB catalysts characterized by EXAFS spectroscopy is about 0.13 Å longer than the bond distance of palladium oxide. Thus, the possibility of palladium-oxide formation has been ruled out. Inferred from the structure of palladium(II) acetate23 together with the light reddishbrown color of the liquid product, the Pd-O contribution is suggested to be caused by the interactions between palladium and acetate ligands; although the secondary EXAFS results, such as the Pd-O contribution, are not as reliable as the primary results such as Pd-Pd. The assignment of the Pd-O contribution based on the bond distance is not conclusive, but it is consistent with the leaching of palladium clusters via the formation of palladium(II) acetate. Inhibiting the formation of acetic acid, thereby decreasing the leaching rate of palladium clusters, is one of the possible ways to improve the catalytic performance of Pd/SDB. Some results related to this topic will be reported in our next paper.24 Conclusions Because of capillary condensation, Pd/γ-Al2O3 catalysts presented a much lower ethanol conversion than Pd/SDB catalysts did. However, the activity of the Pd/ SDB catalysts decreases with time on stream. The deterioration of the catalytic performance during reaction is mainly caused by the leaching of the Pd metal and the aggregating of Pd clusters evidenced by ICP

determining the Pd concentration of the liquid product and EXAFS characterizing the morphology of Pd clusters on the Pd/SDB catalysts. X-ray absorption experiments further indicate the existence of EXAFS spectroscopy contributed from the interactions between Pd clusters and the acetate ligands. The leaching of the Pd metal is thus regarded to be a consequence of the formation of palladium acetate. The Pd-C contribution of the EXAFS spectroscopy characterizing the fresh Pd/ SDB catalysts suggests the interaction between palladium clusters and SDB support. Since the interactions between the Pd clusters and the SDB support may be too weak to anchor the palladium clusters from migration, the growth of palladium clusters was observed after the reaction. Acknowledgment The EXAFS data were analyzed using the XDAP Data Analysis Program, developed by M. Vaarkamp, J. C. Linders, and D. C. Koningsberger, and the reference files were provided by Dr. B. C. Gates. This research was supported by the National Science Council of the Republic of China (Contract No. NSC 87-2214-E-194004) and by the Refining & Manufacturing Research Center of the Chinese Petroleum Corp. (RMRC). We are grateful to the staff of beamline X-11A at the National Synchrotron Light Source, U.S.A., for their assistance. Literature Cited (1) Gurule, R. A. Ethyl AcetatesUnited States. Chemical Economics Handbook; SRI International: Menlo Park, CA, 1988. (2) Stark, D. Ethyl Acetate. Encyclopedia of Chemical Processing and Design, McKetta, J. J., Ed.; Marcel Dekker Inc.: New York, 1984; Vol 20, p 62. (3) Lin, T. B.; Chuang, K. T.; Tsai, K.-Y.; Chang, J.-R. Process for Ethyl Acetate Production. U.S. Patent 5,770,761, 1998. (4) Thomas, J. M.; Thomas, W. T. Principle and Practice of Heterogeneous Catalysis; VCH Publishers Inc.: New York, 1997; p 268. (5) Butt, J. B. Catalyst Deactivation. Adv. Chem. Ser. 1972, 109, 259. (6) Buyanov, R. A. Mechanism of Deactivation of Heterogeneous Catalysts. Kinet. Catal. 1987, 28 (1), 138. (7) Ruckenstein, E. The Role of Interaction and Surface Phenomena in Catalysts, Sintering, and Redispersion; Stevenson, S. A., Dumesic, J. A., Baker, R. T. K., Ruckenstein, E. Eds.; Van Nostrand Reinhold Co.: New York, 1987; Section II, p 139. (8) Vaarkamp, M.; Miller, J. T.; Modica, F. S.; Lane, G. S.; Koningsberger, D. C. Sulfur Poisoning of a Pt/BaK-LTL Catalyst: A Catalytic and Structural Study Using Hydrogen Chemisorption and X-ray Absorption Spectroscopy. J. Catal. 1992, 138, 675. (9) Chang, J. R.; Chang, S. L.; Lin, T. B. Alumina-Supported Pt Catalysts for Aromtics Reduction: A Structural Investigation of Sulfur-Poisoning Catalyst Deactivation. J. Catal. 1997, 169, 338.

1276 Ind. Eng. Chem. Res., Vol. 38, No. 4, 1999 (10) Chang, J. R.; Cheng, C. H. Catalytic Properties of Eggshell Pd/-Al2O3 Catalysts for Isoprene Selective Hydrogenation: Regeneration of Water-Poisoned Catalysts. Ind. Eng. Chem. Res. 1997, 36, 5096. (11) Lin, T. B.; Chou, T. C. Pd Migration. 1. A Possible Reason for the Deactivation of Pyrolysis Gasoline Partial Hydrogenation Catalysts. Ind. Eng. Chem. Res. 1995, 34, 128. (12) Lin, T. B.; Chou, T. C. Selective Hydrogenation of Isoprene on Eggshell and Uniform Palladium Profile Catalysts. Appl. Catal. 1994, 108, 7. (13) Yaparpalvi, R.; Chuang, K. T. Room-Temperature Purification of Humid Air Containing Low Levels of Carbon Monoxide. Ind. Eng. Chem. Res. 1991, 30, 2219. (14) Satterfield, C. N. Trickle Bed Reactors (Review). AIChE J. 1975, 21, 209. (15) Chuang, K. T.; Zhou, B.; Tong, S. Kinetics and Mechanism of Catalytic Oxidation of Formaldehyde over Hydrophobic Catalyst. Ind. Eng. Chem. Res. 1994, 33, 1680. (16) Chuang, K. T.; Cheng, S.; Tong, S. Removal and Destruction of Benzene, Toluene, and Xylene from Wastewater by Air Stripping and Catalytic Oxidation. Ind. Eng. Chem. Res. 1992, 31, 2466. (17) Froment, G. F.; Bischoff, K. B. Chemical Reactor Analysis and Design; John Wiley & Sons: New York, 1988; pp 198-218. (18) van Zon, J. B. A. D. Extended X-ray Absorption Fine Structure Spectroscopy Design of a Spectrometer and Application

to Rhodium Supported on Alumina Catalysts. Ph.D. Dissertation, Eindhoven University of Technology, The Netherlands, 1988; p 18. (19) Kampers, F. W. H. EXAFS in Catalysis: Instrumentation and Application; Ph.D. Dissertation, Eindhoven University of Technology, The Netherlands, 1988; pp 32-39. (20) Varrkamp, M. XDAP User’s Guide. XAFS Services International: The Netherlands, 1996. (21) Gates, B. C.; Katzer, J. R.; Schuit, G. C. Chemistry of Catalytic Process; McGraw-Hill: New York, 1979; p 246. (22) Fung, S. C. Regenerating a Reforming Catalyst. CHEMTECH 1994, (Jan), 40. (23) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry; John Wiley & Sons: New York, 1988; p 925. (24) Lin, T. B.; Su, S. F.; Chang, J. R. Improvement in the Catalytic Performance of Supported Pd Catalysts for Ethyl Acetate Production from Water-Containing Ethanol. 1999, in preparation.

Received for review September 15, 1998 Revised manuscript received January 11, 1999 Accepted January 15, 1999 IE9805887