I n d . E n g . Chem. Res. 1996,34, 862-868
862
Membrane-AssistedDehydrogenation of Normal Butane Mary E. Rezact and William J. Koros* University of Texas, Department of Chemical Engineering, Austin, Texas 78712
Stephen J. Miller Chevron Research and Technology Company, 100 Chevron Way, Richmond, California 94802
Increases of up to 1.5 times the traditional equilibrium limit are reported for a membraneassisted reactor system with the dehydrogenation of butane as a model system. The use of thermally stable polymer-ceramic composite membranes to remove product hydrogen from the dehydrogenation reaction system has been evaluated as a function of the reaction temperature from 480 to 540 "C. At low temperatures, the system was stable for run times over 550 h with normal butane conversions increasing from 22 to 33%through the use of the membrane. Under these conditions, the selectivity of the catalyst for the production of butenes was greater than 90% and was not markedly affected by the presence of the membrane. At equivalent conversion levels, the catalytic selectivity was equivalent with or without the membrane in the system.
Introduction The concept of selectively removing products from an equilibrium-limited reaction mixture to affect the total conversion achieved is well-known. Originating in the 1960s, nonporous layers of palladium, or its alloys, were used to selectively remove hydrogen from dehydrogenation reactions and an increase in conversion above the traditional equilibrium limit was realized (Pfefferle, 1966; Wood, 1968). Large-scale use of this process has been hindered by the low gas-transport rates of the original palladium membranes (Armor, 1992), the propensity for crack formation due to hydrogen sorption (Shu et al., 1991), and the instability of palladium membranes in the presence of a number of probable stream contaminants (Shu et al., 1991). In an attempt to circumvent these problems, porous ceramic membranes were evaluated by a number of researchers (Raymont, 1975; Shinji et al., 1982; Kameyama et al., 1981; Itoh et al., 1984; Sun and Khang, 1988;Champagnie et al., 1992). The gas-transport rates through these materials are significantlyhigher, but the selectivities are generally limited to the Knudsen value, 5.8 for the separation of hydrogen from butane. To achieve significant hydrogen removal, a considerable level of hydrocarbon must also permeate through the membrane. At the same time, any sweep gas used would back-diffuse into the reaction zone. The results of this behavior are 2-fold. First, the addition of the sweep gas t o the reaction zone acts as a diluent and by itself shifts the equilibrium conversion to higher levels. Dixon has shown that in certain cases, overall membrane-reactor performance is very well predicted by calculating the conversion achieved by feeding a mixture comprised of the membrane reactor feed and the sweep gas directly to a conventional plug flow reactor (1992). On the basis of this finding, Dixon concluded that, in these cases, the membrane itself played no role in the shift in equilibrium. Rather, the addition of a diluent (i.e., sweep gas) controlled the overall conversion achievable. Second, to achieve any measure of hydrocarbon recovery, the membrane retentate and permeate must be mixed and this complex +
Current address: School of Chemical Engineering, Georgia
Institute of Technology, Atlanta, GA 30332-0100.FAX: 404894-2866.E-mail:
[email protected].
mixture separated. Thus, the goal of reaction and separation in a single vessel is not achieved. In the present work, thermally stable polymerceramic composite membranes have been evaluated for use in a membrane-assisted dehydrogenation system. The goal of this work is to use a membrane-assisted reactor system to affect the separation. In contrast to previously reported membrane reactors, the present membrane-assisted system utilizes existing plug-flow reactors and heat-exchange equipment. By simply adding the correctly designed membrane systems between the existing reactors, the overall performance of the system can be improved. Schematics of typical membrane reactor systems previously evaluated and the current membrane-assisted reactor system are presented in Figure 1. Comparison of the properties of the three reactor configurations shown in Figure 1provides an indication of both the advantages and limitations of the membraneassisted reactor system studied here. A list of the major advantages offered by the membrane-assisted system follows: 1. The properties of the membrane and the catalyst can be individually optimized. 2. Due to the modular nature of the membrane system, changes in the flow rate of the system can easily be accommodated. 3. Existing multibed reactor systems can be easily retrofitted through the use of correctly sized interstage membrane modules. 4. Because the reactor and membrane are housed in separate units, it is not necessary for the membrane t o withstand the harsh conditions of catalyst regeneration or pretreatment. Catalyst deactivation caused by the deposition of elemental carbon on its surface is counteracted by a controlled burning to remove this carbon. This process is typically achieved by supplying an oxygen source to the reactor at temperatures of 400 "C or higher, Pretretment may include application of hydrogen-, halide-, sulfur-, or nitrogen-containing compounds over a wide range of temperatures. These processes generally require material stability not available in polymers. Palladium may not be stable in the presence of some of these gases (Shu, et al., 1991). Porous inorganics offer
Q888-5885/95/2634-Q862$09.QQIQ0 1995 American Chemical Society
Ind. Eng. Chem. Res., Vol. 34, No. 3, 1995 863 a
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the greatest material stability but are limited in the separation achieved, as previously detailed. 5. Membranes are simple, modular systems with no moving parts, no phase change of the feed, and no external energy input required. The use of more conventional methods for this interstage separation systems, such as pressure swing adsorption, requires much more complex separation equipment. These advantages provide significant flexibility that is generally not present in the catalytic membrane reactor or inert membrane reactor systems. The most significant of these advantages, in practical terms, may be the ability to make relatively minor additions to existing reactor systems and realize significant gains. In the conservative petrochemical environment, these types of small steps may provide a mechanism through which more complex membrane reactor systems with the potential for larger improvements in system performance are ultimately introduced (Van Swaaj et al., 1993). There are certain limitations in the use of membraneassisted reactor systems. The most significant is the inability to achieve complete hydrogen removal in the reactor system. In the proposed membrane-assisted system, hydrogen can be removed only at the interstage membrane modules, limiting the conversion achievable in each reactor by the amount of hydrogen produced therein. Theoretically, if complete hydrogen removal is achieved in the catalytic membrane reactor or the inert membrane reactor systems, conversions of 100% are possible. The level achievable in the membrane-assisted reactor systems is dependent upon the temperature and pressure of operation and the number of membrane modules and reactors employed. For the simple, two reactor system studied here at temperatures 480-540 "C, conversions 1.5 times the conventional levels should be possible. Increases of this magnitude were deemed sufficient to merit the following analysis. This report details the ability of a polymer-ceramic composite membrane to influence the product quality of a membrane-assisted butane dehydrogenation reactor system. Butane dehydrogenation has been selected as
a test reaction based on its industrial significance (Long, 1990; Zantti, 1990). Results are analyzed in terms of total butane conversion and yield of butenes. Frey and Huppke report on the equilibrium conversion of normal butane to produce a mixed butene yield for reaction near atmospheric pressure in a conventional plug flow reactor (1933). Numerous studies of this important reaction have been completed since that time; however, decades after the original publication, the work of Frey and Huppke was recognized for its outstanding quality (Kearby, 1954). A number of more recent studies are provided as reference for those interested in the kinetics of this reaction over a variety of catalysts (Kearby, 1950; Carra and Forni, 1971; Kramarz and Zajecki, 1980). The use of inert ceramic membrane reactors in butane dehydrogenation systems has been reported by several workers (Gokhale et al., 1993; Zaspalis et al., 1991a and 1991b). Each of these studies resulted in increased conversion;however, each suffered from poor membrane selectivity and required complicated product separation systems for both the permeate and retentate.
Methods The reactor system has been operated under pure normal butane feed at pressures slightly greater than atmospheric. These conditions offer the advantage of rather simple reactor design, as opposed to the use of subatmospheric feed pressures or the use of feed diluents (Calamur et al., 1992), but are limited in the total conversion achievable. This provides a clear opportunity for increasing conversion through the use of hydrogen-removal membrane systems.
Materials Catalyst. The catalyst used in this evaluation was selected because it provided rather time-independent conversions and selectivities. This allowed the determination of the impact of the hydrogen removal with an interstage membrane without the added complication of catalyst deactivation overlaid on the results. The catalyst was a noble metal supported on a porous inorganic substrate. This proprietary material was developed and prepared at Chevron Research Company, Richmond, CA. The range of liquid hourly space velocities studied varied from 2 to 10 for each reactor. Butane. Instrument-grade normal butane (minimum purity of 99.5 mol %) purchased from Matheson Gas Products was used as received without further purification or dilution. Polymer-Ceramic Composite Membrane. Polymer-ceramic composite membranes were prepared by a solution deposition method using the thermally stable GFDA-IPDA polyimide as the polymer layer and porous ceramic filters as the substrates (Rezac and Koros, 1992). The polyimide material, shown in Figure 2, was chosen based on its promising room-temperature h e l i d nitrogen selectivity, high helium transport rates, and the prospect of high thermal stability as indicated by a
864 Ind. Eng. Chem. Res., Vol. 34, No. 3, 1995
Optional Membrane
Key: P T
= Pressure Measurement = TemperatureMeasurement MFC = Mass Flow Control
= Sample Port MFM = Mass Flow Measurement
GC
Figure 3. Schematic of membrane-reactor system.
glass transition temperature of 310 "C (Kim, 1987). Porous ceramic filters with a surface pore size of approximately 200 A, commercially marketed by Anotech Separations under the trade name Anopore, were used as the substrate layer. Each membrane was evaluated at room temperature for the separation of helium from nitrogen, using a constant pressurevariable volume test system (Barigou and Davidson, 1993) to determine both the perfection and thickness of the polymer layer. Only membranes that possessed defect-free polymeric layers, as determined from pure gas selectivities, were used for further evaluation. Equipment. The system consists of two plug flow reactors in series with the possibility of interstage hydrogen removal through a polymer-ceramic composite membrane as detailed in Figure 3. The commercially supplied membrane cell (Millipore Corporation, Bedford, MA) was operated in a pseudocross-flow configuration. The product of the first reactor acted as feed for the membrane unit. A fraction of this feed permeated through the membrane and was removed via a vacuum pump. The retentate from this system was fed to the second reactor where further conversion was possible. Analysis was completed using a gas chromatograph equipped with a flame ionization detector and a megabore capillary column (J&W Scientific part 1153552). The polymeric membranes used in this evaluation were stable only t o temperatures of 300 "C (Rezac et al., 1995). As the reactors and membrane unit were operated at different temperatures, the feed stream was cooled prior to membrane separation and reheated following this unit. The temperature of each unit was individually controlled. Cooling between the units was accomplished by convective heat losses from the uninsulated tubing. The feasibility of operating these units a t different temperatures has been previously demonstrated (Rezac et al., 1994). Membrane-AssistedEvaluation Procedure. The conversion of normal butane in the conventional plugflow reactor system was monitored as a function of time at the desired reaction temperature. During this period, a membrane was heated from room temperature to the desired test temperature under
a nitrogen atmosphere. Test temperatures of 250-300 "C were employed. In this temperature range, the mixed gas selectivity of the membrane for the separation of hydrogen from the hydrogenhydrocarbon mixture was over 150 (Rezac et al., 1994). The nitrogentransport rate at the test temperature was measured and confirmed to agree with that predicted from the room-temperature flux,the measured pure-gas activation energy (Rezac, 1993), and the final temperature of operation. Following the establishment of a base catalytic activity, the operation of the system was changed to switch the membrane "in-line" between the catalytic reactors. Under this operation, the conversion and selectivity were monitored through gas analysis. The flow rate and composition of the permeate stream were also monitored. Predicted Reactor Performance. The overall conversion achievable in a membrane-assisted reactor system is controlled by the level of hydrogen that remains in the system following the last membrane separation step. To interpret the results presented, it is necessary to appreciate these limiting values. For the simple test system studied here, with two plug-flow reactors in series with a single hydrogen-selective membrane interstage, the achievable conversion of the system has been calculated based on the system temperature, pressure, percentage of hydrogen removed at the interstage membrane, and reported thermodynamic values (Reid et al., 1977). Calculated results are presented in Figure 4. Increases in the absolute value of conversion of between 11 and 22% should be possible for reactor systems operating at between 482 and 538 "C, respectively.
Results and Discussion Conventional Reactor Performance. Normal butane conversions increase with increasing temperature. However, the selectivity of the catalyst for the production of butenes decreases concurrently. As an illustration of this behavior, the properties of the conventional system operated a t a constant space velocity of 5 h-' and 15.8 psia for each bed were measured and presented
Ind. Eng. Chem. Res., Vol. 34, No. 3, 1995 70
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Figure 4. Effect of degree of hydrogen removal on the achievable conversion possible in a two-reactors in series system with interstage hydrogen removal. All calculations completed with a feed pressure of 15.8 psia and less than 2% hydrocarbon losses in the hydrogen removal step. 100
480
490
500
510
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530
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Temperature ("C)
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Temperature ("C) Figure 5. Tradeoff between increasing catalytic conversion and decreasing selectivity to total butene production with increasing reactor temperature in a system with no interstage membrane. Results for feed pressure of 15.8 psia, lhsv = 5 for each bed.
in Figure 5. At low temperatures, selectivities were very high and conversion was a t the equilibrium limit. At 482 "C, over 97% of the butane converted went to form the desired butene product. Yet, as the temperature increased, the selectivity decreased to only 81% at 538 "C. High conversion in this process allows for efficient utilization of the feedstock and minimizes the need for product separation and recycling. High levels of selectivity are equally important. High selectivity is a direct indication of the production of the desired reaction product. Just as important, it indicates a low level of production of the undesired byproduct, elemental car-
Figure 6. Effect of interstage hydrogen removal on the conversion achieved in a two-reactor in series system at 482-538 "C. Points represent experimental data, lines represent the equilibrium conversion with 0% and 100% hydrogen removal.
bon. As will be discussed in the Stability section, elemental carbon production leads to catalytic deactivation and degenerated performance. The run time between catalytic regenerations is directly related to this carbon production rate with higher production rates leading to very short run times. Membrane-AssistedReactor Performance. Over the range of temperatures studied, the membraneassisted reactor system was able to generate an increase in the dehydrogenation conversion above the conventional equilibrium limits. For each case studied, the conversion of the membrane-assisted system was nearly equivalent to the newly imposed limit detailed above. The selectivity of the catalyst was not markedly affected by the presence of the membrane but appears to be more influenced at the higher reaction temperatures. Detailed results are presented in Table l and illustrated in Figure 6 . At 482 "C, nearly 100% of the hydrogen produced in the first reactor was removed at the interstage membrane. The overall system conversion increased to 33% with a selectivity t o total butenes of nearly 96% under these conditions. As the temperature of the reactor system was increased, the equilibrium degree of dehydrogenation increased. This increase in dehydrogenation has an associated increase in the amount of hydrogen produced in the first reactor. Due to limitations in our ability t o produce membranes with film thicknesses of less than about 1000 A, complete hydrogen removal was not achieved a t the higher reactor temperatures. Rather, only 75% of the hydrogen produced in the first reactor was removed at this membrane unit. This limited the
Table 1. Effect of Interstage Hydrogen Removal on the Conversion Achieved in a Two-Reactor in Series System at 482-538 "C reactor temp membrane-assisted n-butane conversion (%) selectivity to total butenes (%) selectivity to butadiene (%) selectivity to C1-C3's (%) LHSV per bed (h-l) reactor pressure (psia) hydrogen removal by membrane (%) maximum conversion possible a t this level of hydrogen removal (%)b hydrocarbon losses to permeate (% of feed)
482 "C no 21.6 95.4 1.2 4.1
538 "C
510 "C
Yes 33.0 95.8 1.4 3.0 5.0 15.8 '95 33 x1.5
no 30.1 96.7
Yes 45.2 91.9
no 43.4 91.0
1.9
2.2
3.0
3.7
2.1
6.4 3.5 15.8 75 45
6.2
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11.0
Yes 54.1 87.1
c2.0
Membrane-assisted "no" refers t o performance of conventional reactor system. Membrane-assisted "yes" refers to performance of membrane-assisted reactor system. Calculated as shown in Figure 4.
866 Ind. Eng. Chem. Res., Vol. 34, No. 3, 1995 Table 2. Effect of Membrane-Assisted Reactor Conditions on Catalyst Yield to Butenes (Reactor Pressure = 16.8 psia) reactor temp membrane-assisted conversion yield
482 "C no yes 21.6 33.0 20.6 31.6
510 "C no yes 30.1 45.2 29.1 41.6
538 "C no yes 43.4 54.1 39.5 47.1
conversion achievable in the overall system to 45%, which was closely approximated by the measured value for the membrane-assisted system at this temperature. The level of hydrogen removed at the interstage membrane unit was dependent upon the hydrogen transport rate of the membrane used and the feed conditions. In this evaluation, the membrane area is fixed at 13.85 cm2 by the housing used. Further, the feed flow rates were limited by the reactor size and the requirement to achieve equilibrium conversion in the first reactor. Under these restraints, the amount of hydrogen removed in the interstage unit was varied by varying the membrane's polymer layer thickness. As the temperature was increased to 538 "C,the hydrogen removal achieved by the interstage membrane was only 55% of that produced in the first reactor. With this level of hydrogen removal, the conversion of the second reactor was increased to 54%, which closely approximates the maximum conversion achievable at this temperature and level of hydrogen removal. In the evaluation of reactor performance, both the catalytic activity, measured in terms of conversion, and selectivity are important. A tradeoff exists between these two values, as conversion increases, selectivity decreases. One measure of the combined performance of these variables is termed the catalytic yield. For normal butane dehydrogenation, yield is defined as the product of the selectivity to butenes, SButenes, and the total butane conversion, XnButane:
The yields for all measured conditions are reported in Table 2. The yield of the membrane-assisted systems is generally higher than that of the conventional system at equivalent conversions as can be seen in Figure 7. Conversely, the temperatures at which equivalent yields occur are lower in the membrane-assisted case. The results presented represent hydrogen removal rates of 55-95% at the interstage membrane unit. In each case, the overall catalytic conversion is well predicted by Figure 4. The amount of hydrocarbon lost through the membrane is controlled by the membrane properties and operating conditions. For membranes operated at 250-300 "C,hydrocarbon losses of less than 1.5% were achieved. This very limited level of hydrocarbon loss allows for the permeate of the membrane to be treated as hydrocarbon-free and eliminates the need for further separation equipment. Catalyst Selectivity as a Function of System Operation. One important driving force for the use of elaborate reactor systems for dehydrogenation reactions is that the conversions achievable at relatively low temperatures increases with their use. While energy savings are realized by lower operating temperatures, the true motivation for this shift in temperatures is to maintain the selectivity of the catalyst and limit the production of deactivating carbon, as was shown in Figure 5. This allows more efficient utilization of feedstock for conversion t o useful products and much
3
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490
500
510
520
530
540
Temperature (W
Figure 7. Butene yield for conventional and membrane-assisted systems as a function of reactor temperature.
longer run times between catalyst regenerations. This result has been realized through the use of membraneassisted reaction systems. Since the membrane-assisted systems studied here is capable of producing high levels of conversion with concurrently high selectivities for the production of butene, the added cost associated with these systems may be justified. Stability. One of the main causes of deactivation for dehydrogenation catalysts is believed to be the formation and deposition of elemental carbon on the catalyst surface (Swift et al., 1976; Shum, 1990;Jothimurugesan et al., 1985). Hydrogen present in the reactor, either as a product gas or as an added diluent, is believed to decrease the rate of carbon formation and aid in maintaining catalyst stability (Jothimurugesan et al., 1985). If this hydrogen is effectively removed in an interstage membrane system, will the selectivity of the second reactor be adversely affected? To monitor the impact of hydrogen removal on catalyst selectivity, the performance of the reactor system was measured as a function of time and membrane properties. In these tests, the reactor system was started up in the conventional configuration. Then, a membrane was placed in line between the two reactors. The composition of the product stream was measured as a function of time in this configuration. After tests were complete at these conditions, generally less than 60 h, the membrane was switched off line and the properties of the conventional reactor system were once again monitored. This pattern of testing the effect of various membrane properties and then reestablishing conventional results was repeated over a 600 h period. For simplicity, only the results relating to the conventional system are plotted in Figure 8 in terms of the catalytic conversion and selectivity at the system outlet. Neither the long-term catalytic conversion nor selectivity was adversely affected by removal of hydrogen from the system. The catalyst is remarkably stable over the 550 h test period with no increase in the rate of carbon formation detected. As the reactor temperature is increased, the selectivity of the catalyst decreases and the maintenance of a hydrogen atmosphere may be important. Direct comparison of the levels of selectivity at various temperatures with and without the membrane in the system may not be appropriate because the level of conversion is also changing in this comparison. Rather, we have chosen to evaluate the level of selectivity achieved as a function of conversion for the systems with and without membrane assistance. This allows for the composition
Ind. Eng. Chem. Res., Vol. 34, No. 3,1995 867 35
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Figure 8. Stability of butane dehydrogenation catalyst in a membrane-assisted reactor system. Data taken under conventional reactor conditions. Reactor temperature = 482 "C, pressure = 15.8 psia, lhsv = 5hed. Normal butane conversion (above) and selectivity to butenes (below). 100
butene yield increased from 20.6 to 31.6%. Corresponding increases were observed a t higher reaction temperatures. At equivalent conversion levels, the catalytic selectivity was equivalent with or without the membrane in the system. Further, at 482 "C, the catalyst was stable for over 550 h. The use of a membrane-assisted reaction system will allow for equivalent or higher product yields a t lower reaction temperatures. This decrease in temperature will realize a small decrease in operating costs related to heating but a much larger savings relating to the enhanced covnersion at a given temperature. This translates directly into longer catalyst lifetimes and less frequent regeneration cycles. The results achieved here are well predicted by thermodynamic calculations. Therefore, it is possible to predict the performance of more complicated systems, operating with more reactors and/or membrane units, within the range of temperatures reported here. Prediction of adiabatic reactor performance should also be possible in this manner.
This material is based in part upon work supported by the Governor's Energy Management Center-State of Texas Energy Research in Applications Program under Contract No. 003658-101. Financial support from Chevron Research and Technology Co. is also gratefully acknowledged.
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Literature Cited
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35
40
45
50
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60
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Figure 9. Correlation between normal butane conversion and catalytic selectivity to total butenes. Conventional system (O), membrane-assisted system (0).
of the systems compared t o be essentially equivalent while allowing the temperature to vary. Graphical results are presented in Figure 9. Evaluation of this figure indicates that while there is some scatter in data, at equivalent conversions, the selectivity achieved with or without membrane assistance was comparable. The catalytic selectivity achieved decreases as the normal butane conversion increases for both systems with and without membrane assistance.
Conclusions The butene yield of a normal butane dehydrogenation system was markedly increased through the use of a single membrane unit housed between two fmed-bed reactors. The exact increase was dependent upon the reaction temperature and the amount of hydrogen removed at the membrane unit. At 482 "C, nearly complete hydrogen removal was achieved and the
Armor, J. Challenges in Membrane Catalysis. Chemtech, 1992, September, 560. Barigou, M.; Davidson, J. F. The Fluid Mechanics of the Soap Film Meter. Chem. Eng. Sci. 1993,48,2587. Calamur, N.; Carrera, M. E.; Wilsak, R. A. In Encyclopedia of Chemical Technology;Kroschwitz, J. I., Howe-Grant, M., Eds.; John Wiley and Sons: New York, 1992; p 701. Carra, S.;Forni, L. Catalytic Dehydrogenation of Cq Hydrocarbons over Chromia-Alumina. Catal. Rev. 1971,5,159. Champagnie, A.; Tsotsis, T.; Minet, R.; Wagner, I. The Study of Ethane Dehydrogenation in a Catalytic Membrane Reactor. J. Catal. 1992,134, 713. Dixon, A. G.; Becker, Y. L.; Ma, Y. H.; Moser, W. R. Topical Conference on Separation Technologies,AICHE Preprints Paper Number 23d, Miami, FL, 1992. Frey, F. E.; Huppke, W. F. Equilibrium Dehydrogenation of Ethane, Propane, and the Butanes. Znd. Eng. Chem. 1933,25, 54. Gokhale, Y. V.; Noble, R. D.; Falconer, J. L. Analysis of a membrane enclosed catalytic reactor for butane dehydrogenation. J. Membr. Sci. 1993,77, 197. Itoh, N.; Shindo, Y.; Hakuta, T.; Yoshitome, H. Enhanced Catalytic Decomposition of HI by Using a Microporous Membrane. Znt. J. Hydrogen Energy 1984,9,835. Jothimurugesan, K.;Bhatia, S.; Srivastava, R. D. Kinetics of dehydrogenation of methylcyclohexane over a platinum-rhenium-alumina catalyst in the presence of added hydrogen. Znd. Eng. Chem., Fundam. 1986,24,433. Kameyama, T.;Dokiya, M.; Fujishige, M.; Yokokawa, H.; Fukuda, K. Possibility for Effective Production of Hydrogen from Hydrogen Sulfide by means of a Porous Vycor Glass Membrane. Znd. Eng. Chem., Fundam. 1981,20,97. Kearby, K. K. Catalytic Dehydrogenation of Butenes. Znd. Eng. Chem. 1960,42, 295. Kearby, K. K. Catalytic Dehydrogenation. In Catalysis; Emmett, P. H., Ed.; Reinhold Press: New York, 1954. Kim, T. H. Gas Sorption and Permeation in a Series of Aromatic Polyimides. Ph.D. Dissertation, The University of Texas, Austin, TX, 1987.
868 Ind. Eng. Chem. Res., Vol. 34, No. 3, 1995 Kramarz, W.; Zajecki, J. Wplyw stracania wodorotlenkow glinu i chromu na aktywnosc katalizatora chromoglinowegow procesie odwodorniania butanu. Nafta 1980,11,374. Long, J. Federal Alert-New Regulations. Chem. Eng. News 1990, 68 (29),22. Pfefferle, W. Process for Dehydrogenation. US Patent 3,290,406, 1966. Raymont, M. Make Hydrogen for Hydrogen Sulfide. Hydrocarbon Processing 1975,54, 139. Reid, R.; Prausnitz, J.; Shenvood, T. The Properties of Gases and Liquids, 3rd ed.; McGraw-Hill: New York, 1977. Rezac, M. E. Polymer-Ceramic Composite Membranes for Reactor Applications. Ph.D. Dissertation, The University of Texas, Austin, Tx, 1993. Rezac, M. E.; Koros, W. J. Preparation of Polymer-Ceramic Composite Membranes with Thin Defect-Free Polymer Layers. J. Appl. Polym. Sci. 1992,37, 1927. Rezac, M. E.; Koros, W. J.; Miller, S. J. Membrane-Assisted Dehydrogenation of Normal Butane: Influence of Membrane Properties on System Performance. J. Membr. Sci. 1994, 93, 193. Rezac, M. E.; Koros, W. J.; Miller, S. J. Thermo-mechanical Stability of Polymer-Ceramic Composite Membranes. Sep. Sci. Technol., 1995,in press. Shinji, 0.; Misono, M.; Yoneda, Y. The Dehydrogenation of Cyclohexane by the use of a Porous-glass Reactor. Bull. Chem. SOC.Jpn. 1982,55,2760. Shu, J.;Grandjean, B.; Van Neste, A.; Kaliaguine, S. Catalytic Palladium-based Membrane Reactors: A Review. Can. J . Chem. Eng. 1991,69,1036. Shum, V. K. Process to convert linear alkanes. U.S.Patent 4,962,266, 1990.
Sun,Y.; Khang, S. Catalytic Membrane for Simultaneous Chemical Reaction and Separation Applied to a Dehydrogenation Reaction. Znd. Eng. Chem. Res. 1988,27,2064. Swift, H.; Beuther, H.; Rennard, R. Elimination of Excess Carbon Formation during Catalytic Butene Dehydrogenation. Znd. Eng. Chem., Prod. Res. Dev. 1976,15 (21, 131. Van Swaaj, W. P. M.; Versteeg, G. F.; Saracco, G. Current Hurdles to the Success of High-Temperature Membrane Reactors. International Congress on Membranes, Heidelberg, Germany, 1993. Wood, B. Dehydrogenation of Cyclohexane on a Hydrogen-Porous Membrane. J . Catal. 1968,11,30. Zantti, R. Cleaner Fuels Will Cost Refiners Billions. Chem. Eng. 1990,97(71, 5 . Zaspalis, V. T.; Keizer, K.; Ross, J. R. H.; Burggraaf, A. J. Porous ceramic membranes in high temperature applications. Key Eng. Mater. 1991,61-62,359. Zaspalis, V. T.; van Praag, W.; Keizer, K.; van Ommen, J. G.; Ross, J. R. H.; Burggraaf, A. J. Reactor studies using alumina separation membranes for the dehydrogenation of methanol and n-butane. Appl. Catal. 1991, 74, 223. Received for review June 13, 1994 Accepted November 3, 1994 @
IE940374Z
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Abstract published in Advance ACS Abstracts, February
1, 1995.
