1754
Ind. Eng. Chem. Res L988,27, 1754-1759
Table IV. Production of Gases (Weight Percent of C&) and Production of Aromatics ((Mass of Ci Aromatics in the Product - Mass of Ci Aromatics in the Charge) 100/Mass of Charge) by the Doped Cuts production of aromatics cuts doped with gases C, C, C9 16.1 11.5 12.5 4 none 12.3 20.2 13.0 11.1 5 n-C7 11.3 14.2 13.0 10.7 6 i-C, 13.0 25.3 15.8 10.0 8.3 7 n-C8 10.7 8.5 17.1 8 i-C8 13.5 10.5 23.9 9.3 9 n-C9 8.5 13.3 9.5 12.3 10 i-C9 14.6
by doping cut 4 with fractions rich in isomers is not equal to that of the corresponding n-paraffins when doping with pure paraffins. Then the results of Table IV are only qualitative. A decrease in the production of gases is clearly seen from the table when cuts doped with n-paraffins were fed. An inverse behavior is noticed for isomer doped cuts. In addition, for cuts doped with n-paraffins (n-C7-n-C9), the production of gases decreases when the length of the chain increases, as reported by Parera et al. (1987). Gases production increases as the number of carbon atoms in the isomers increases. This could be due to the fact that when the branched chain is long the possibility of obtaining a very stable carbenium ion is higher. Therefore, hydrocracking rate should be markedly favored. Table IV also shows the favorable effect on the production of aromatics due to the addition of the corresponding n-paraffins to the feed.
Literature Cited Barbier, J. Appl. Catal. 1986, 26, 1. Barbier, J.; Corro, G.; Zhang, Y.; Bournonville, J. P.; Franck, J. P. Appl. Catal. 1985, 13, 245. Beltramini, J. N.; Martinelli, E. E.; Chudn, E. J.; Figoli, N. S.; Parera, J. M. Appl. Catal. 1983, 7, 43. Castro, A. A.; Scelza, 0. A.; Benvenuto, E. R.; Baronetti, G. T.; Parera, J. M. J. Catal. 1981, 69, 222. Cooper, B. J.; Trimm, D. L. In Catalyst Deactivation; Delmon, B., Froment, G. F., Eds.; Elsevier: Amsterdam, 1980; p 63. Davis, S. M.; Somorjai, G. A. In The Chemical Physics of Solid Surfaces and Heterogeneous Catalysis; King, D. A., Woodnuff, D. P., Eds.; Elsevier: Amsterdam, 1982; Vol. IV, p 359. Figoli, N. S.; Sad, M. R.; Beltramini, J. N.; Jablonski, E. L.; Parera, J. M. Ind. Eng. Chem. Prod. Res. Deu. 1980, 19, 545. Figoli, N. S.; Beltramini, J. N.; Barra, A. F.; Martinelli, E. E.; Sad, M. R.; Parera, J. M. In Coke Formation on Metal Surfaces; ACS Symposium Series 202; American Chemical Society: Washington, DC, 1982; p 239. Figoli, N. S.; Beltramini, J. N.; Martinelli, E. E.; Alo6, P. E.; Parera, J. M. Appl. Catal. 1984, 11, 201. Figoli, N. S.; Beltramini, J. N.; Querini, C. A.; Parera, J. M. Appl. Catal. 1986,26, 39. Gault, F. G.; Amir-Ebrahimi, V.; Garin, F.; Parayre, P.; Weisang, F. Bull. Soc. Chim. Belg. 1979, 88, 475. Germain, J. E. Catalytic Conversion of Hydrocarbons; Academic: London, 1969; p 210. Guisnet, M.; Barbier, J.; Gnep, N. S.; Molina, N.; Elassal, L. Actas 8’ Simp. Iberoam. Catal.: Huelva 1982,8,189, Parera, J. M.; Figoli, N. S.; Beltramini, J. N.; Churin, E. J.; Cabrol, R. A. Proceedings of the 8th International Congress on Catalysis; Verlag Chemie: Berlin, 1984; Vol. 11, p 593. Parera, J. M.; Querini, C. A,; Beltramini, J. N.; Figoli, N. S. Appl. Catal. 1987, 32, 117. Sad, M. R.; Figoli, N. S.; Beltramini, J. N.; Jablonski, E. L.; Lazzaroni, R. A.; Parera, J. M. J . Chem. Technol. Biotechnol. 1980,30, 374.
Conclusions The results show that feedstocks with a higher proportion of n-paraffins than branched isomers with the same number of carbon atoms are able to produce a higher amount of the corresponding aromatics with a lower production of gases.
Thampi, K. R.; Rajagopal, S.; Murthy, K. R. “Advances in Catalysis Science and Technology”. Proceedings of the 7th National Symposium on Catalysis; Wiley: Baroda, 1985; p 751. Verderone, R. J.: Pieck. C. L.:. Sad.. M. R.: Parera, J. M. ADD/. _ - Catal.
Registry No. Pt, 7440-06-4; Re, 7440-15-5; Clz, 7782-50-5; S,
Received for review January 4, 1988 Accepted May 26, 1988
1986,
zi,239.’
Zhorov, Y. M.; Panchenkov, G. M.; Kartaschev, Y. N. Kinet. Catal. 1980, 21, 580.
1704-34-9.
An Ambient-Pressure Pulse Microreactor with Continuous Thermogravimetric and On-Line Chromatographic Analyses for Catalytic Cracking John W. Deant and Dady B. Dadyburjor* Department of Chemical Engineering, West Virginia University, Morgantown, West Virginia 26506-6101
An integrated system has been designed to permit thermogravimetric analysis of the weight change of a catalyst and chromatographic analyses of reactants and products using a pulsed reactant. A detailed analysis of the transient weight change is not necessary, a significant advantage to this technique. A sample collection system has been designed with semicontinuous, split-phase operation. This permits ambient pressure conditions in the reactor while higher pressures are used in the gas chromatograph, for quantitative sample analyses from the pulse. Weight changes of less than 1pg are detectable, and reactant volumes in the microliter range are used. The system has been used to study deactivation of cracking catalysts by coking. The design of improved catalysts for use in the cracking of hydrocarbons is of considerable interest for the pro-
* To whom inquiries should be addressed. t Present address: Union Carbide Corporation, Research and Development Laboratories, Bound Brook, NJ 08805.
duction of liquid fuels from petroleum and coal. Test reactors used to study effects of coke, i.e., high molecular weight unsaturated hydrocarbon deposits, on these catalysts include fluidized beds, packed beds, and gradientless reactors. Thermogravimetric analysis (TGA) techniques have been particularly useful for relating coking to specific
0888-5885/88/2621-1154$01.50/0 0 1988 American Chemical Society
Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 1755 reaction conditions and for developing a more comprehensive understanding of the process under observation. For a review, see Sears et al. (1982) and Massoth (1972). However, when applied to catalytic coking studies, the TGA approach suffers from a variety of shortcomings. Very small quantities of impurities can cause substantial variations in catalyst performance which require a secondary analytical technique to detect changes. On-line configuration of this secondary analytical technique eliminates the inaccuracy associated with sample handling but introduces a number of experimental difficulties. Packed bed testing has sometimes been accomplished with a micropulse reactor. Kokes et al. (1955) were the first to describe the microcatalytic pulse reactor analytical technique and develop calibration techniques. They used the method to study the cracking reaction. Stein et al. (1960) and Norton and Moss (1964) were among the first to use the technique to study amorphous silica-alumina and zeolite catalysts. The technique entails holding a small amount of catalyst in a fxed bed at a specific temperature. Inert gas is continually passed through the bed, and a small pulse of reactant is injected into the feed stream from time to time. Attributes of this technique are that it avoids the necessity for precise metering, eliminates the need for liquid feed pumps, and is simple to use. The micropulse reactor has been reviewed by Choudhary and Doraiswamy (1971). Gas chromatography (GC) has been the analytical technique of choice of monitoring cracking reactions in packed bed micropulse reactors. Choudhary and Srinivasan (1986) and Marin et al. (1986) are recent examples of studies which use the GC pulse method to measure sorption of hydrocarbons in zeolites. When TGA is coupled with GC, the difficulties lie in the selection of highly accurate metering devices and on-line sampling techniques. A moderately efficient GC column requires a carrier gas pressure of 4-5 atm in order to maintain an adequate flow of sample to the instrument detector. The straightforward approach would be to operate the TGA at 5 atm, using the TGA carrier gas to deliver the desired sample directly to the GC. Unfortunately, this effectively introduces a large dead space (Le., the TGA volume) which disrupts sample collection, separation, and analysis. In addition, highpressure TGA studies are accompanied by increasing convection which limits the accuracy of the gravimetric balance. High-pressure TGAs often require larger sample sizes, which complicate diffusion effects. A final concern in our work is that a TGA is not sufficiently sensitive at high pressures. This is not a trival problem since high sensitivity a t high pressure involves an economic investment which is an order of magnitude greater than that required for lower pressure work. Ozawa and Bischoff (1968) have also noted that conversion of the main reaction is not easily measured due to mixing of the reaction gas in the large dead space of the TGA reactor. In order to measure the conversion of the main reaction accurately, on-line chromatography was used with another reactor which had an "exactly similar geometry but no dead space". The conversion of the main reaction determined in this manner may be superimposed upon coking data determined by the TGA reactor. While this technique allows comparison of the same reaction in two similar reactors to study the effect of coke on the main reaction, it suffers from the shortcoming of using two reactors which, despite the researchers' best efforts, are clearly different. DePauw and Froment (1975), and later Dumez and Froment (1976), used a sequentially-designed experimental program for investigations of internal
1 ---I
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.
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Figure 1. Diagram of apparatus in the collection mode. CL, collector; CT, collector three-way valve; CV, control valve; EV, expansion valve; FB, Freon 12 bottle; FID, flame ionization detector; FR, furnace; HE, helium tank; IP, injection port; IV, injector three-way valve; RIV, rotary injection valve; RV, relief valve; SB, sample bomb; SP, sample pan; SV, sample bomb valve; TC, thermocouple; TW, tare weight.
transport limitations and could predict integral reactor performance. Despite the elegant treatment applied, their approach retains the shortcoming of the Ozawa-Bischoff method; that is, the reaction conversion and catalyst coking are not measured simultaneously in the same reactor. This paper presents an integrated TGA/GC system which can measure reaction conversion and catalyst coking simultaneously and in the same reactor. The system features the attributes of a highly-sensitive, low-pressure TGA. The reactant is introduced as a small pulse. Only initial and final values need be considered; transients are not of importance here. A central feature of the design is the sample collection system which has semicontinuous split-phase operation. Data are collected from the TGA and GC by computer, and the collector may be automated for operation by the same computer. (Computer data acquisition and control is convenient but is not an essential aspect of the apparatus.) Apparatus
A diagram of the apparatus (Figure 1)shows the main features-the TGA, the sample collection system, and the GC-and their relation to one another. A Cahn System 113, incorporating a Model 2000 microbalance, has been chosen for the TGA microreactor. When the microbalance is operated as a pulse-type microreactor, typical industrial riser-tube (hydrocarbon cracking) reaction conditions of 5-9 contact time and 500 "C reaction temperature may be simulated, virtually free from macroscopic gradients. A constant temperature is accurately maintained and controlled with an external furnace and a thermocouple just below the sample pan. The weight of a small amount of well-distributed solid catalyst on the platinum sample pan is continuously monitored to measure changes in weight, in this case by coke being deposited on the catalyst. The catalyst sample pan is suspended by a thin nichrome wire (inside the quartz reactor tube which is itself inside the TGA furnace) from the weight sensors. A taring system allows weight changes as little as 1.0 pg to be detected by the sensors even when the sample weight is as high as 50 mg. Weight changes cause a variable voltage output from the sensors, and this output is monitored continuously by an IBM PC. There is a constant flow of helium, as a carrier
1756 Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988
wvent Plote
Freon Expoision
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Figure 2. Exploded view of collector.
gas introduced both just above the sample pan and also through a needle valve above the sensors to prevent diffusion of any corrosive gases to the sensors. Back-diffusion is further prevented by installing a small disk at the joint above the injection port. A small hole in the center allows the nichrome wire to pass through but decreases the cross-sectional area, thereby increasing the linear velocity of the helium stream passing downward. The sample collection system allows the TGA to operate at close to atmospheric pressure while the GC operates "on-line" at 4-5 atm. The collector gathers all of the unconverted reactant which leaves the TGA, without interrupting or altering the steady helium carrier gas flow through the TGA. Injection of the collected material to the GC must be complete, and the collector itself must have a minimum of dead space. While acquiring a sample from the TGA, the collector operates as a freon-cooled, low-pressure condensor. During the analysis mode, the collector operates as a medium-pressure,electrically-heated injector to the GC. The design allows for rapid alteration of condenser and injector cycles. Errors due to experimental sample handling are eliminated by maintaining a closed system for the reactant and product streams. As shown in Figure 2, the heart of the collector is a I/&. stainless steel tube, bent in the form of a U, with connections for inlet and outlet flows as shown in Figure 1. The contents of the U-tube can be flash-cooled by expanding Freon 12, which is introduced into the collector through the dip tube on top. The expansion valve for the Freon 12 is a II4-in. needle valve. The dip tube drops to the bottom of the collector and rests against the sample collecting tube. The inside of the collector is packed with glass wool, which concentrates the Freon 12 expansion (and cooling) to the desired location at the bottom of the Utube. The (liquid) contents of the U-tube can be vaporized by an electrical heating strip located directly below the U-tube on the outside of the lower plate of the collector. The U-tube is continuously soldered to the lower plate to provide optimum heat transfer from the lower heating strip through the plate and tube to the collected sample. During the heating cycle, the Freon 12 is allowed to escape through a ll4-in. bent tube soldered to the top plate of the collector. The collector is constructed of a 2-mm-thick copper plate, chosen for ease of forming and desirable heat-transfer characteristics. Two three-way inlet valves and a "zero-volume" rotary injection valve are connected to the collector as shown in Figure 1to allow split-phase operation. Each three-way valve is a high-temperature, trunnion ball valve with wetted parts of stainless steel and Teflon, chosen for
minimum dead space. The rotary injection valve is a high-pressure, stainless steel, four-port valve chosen for chromatograph injection performance. The outlet from the collector is analyzed by means of a Varian Model 3300 GC. The flame ionization detector (FID) on the GC is operated on-line in order to get a complete and rapid analysis. The other outlet from the collector passes through a glass sample bomb and to the vent. Aliquot samples of the vent gases are removed from the bomb with a hypodermic syringe. Special attention to safety features was a consideration in equipment design and construction. Judicious configuration allows pressure vessel considerations to be avoided with the collector; however, the possibility of overpressuring the TGA or the sample bomb requires installation of safety valves set at 5 psig and positioned on top of the TGA and before the sample bomb. A Plexiglas shield is placed around the TGA due to its large glass surface area. Vent headers are used to remove Freon 12 vapors and the TGA outlet from the work environment. All hot surfaces are well insulated. Operational Procedures The experimental procedure consists of spreading a thin layer of solid sample on the TGA balance pan. The solid sample is pretreated (apparatus not shown) in the presence of a constant heliumlsteam purge and at a constant temperature of 500 "C just prior to placing the sample in the TGA. The TGA maintains the sample at 500 "C under helium purge for approximately 'I2h to assure steady-state conditions. Injection of the reactant from a syringe into a separate, heated, helium carrier stream results in downflow of vapors directly onto the solid sample surface. As the reactant deposits coke on the sample, the weight gain is detected by the balance. Products and unconverted reactant leave the TGA in the helium stream from below the catalyst and proceed to the collector through the injector three-way valve and the collector three-way valve as shown in Figure 1. During this condenser mode, the TGA and the collector are essentially at atmospheric pressure. All flow points are heated above 250 "C except for the U-tube itself, which is chilled to below 0 "C by the liquid Freon 12. Unconverted reactant and higher boiling products are condensed in the U-tube and removed from the gas stream. The outlet stream from the collector passes through the rotary injection valve and the glass bomb. The bomb is used occasionally, to collect the gas stream and to analyze an aliquot, in order to confirm quantitative removal of material of interest in the collector. During this mode, the helium purge, maintained at approximately 4 atm, passes through the GC by way of the rotary injection valve. At the end of the collection process, the rotary injection valve outlet currently connected to the sample bomb is capped, the injector three-way valve setting is changed, and the sample bomb valve is opened; thus, the outlet from the TGA is vented and the condensed sample is isolated in the collector. The collector now functions as an injector. The Freon 12 needle valve is closed, and the electric heat tape is turned on. When the injector temperature reaches 240 "C, the contents are back in the vapor phase. The collector three-way valve setting and the rotary injection valve setting are then changed. The 4-atm helium stream now passes through the injector, forcing the contents directly into the GC. The slug of material is separated and analyzed by a FID in the GC. Trial and error establishes values of the collection time for quantitative detection of the sample. A more detailed discussion of the technique
Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 1757
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5ul n-hexadecane on 50ng CLbSS BEbDS at. furnace temp 600 C .
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Figure 3. Raw data from TGA to data acquisition system when 5 p L of n-hexadecane is injected onto 50 mg of inert glass beads at 600 "C.(a, top) Data are collected once per second (l/s) for 1500 s. (b, bottom) Data are collected at the rate of 5/s for the first 30 s and then at the rate of l / s for the last 50 a, up to 1500 9. (Note the break and change of scale after t = 30 8 . )
is presented by De'an (1987).
Results and Discussion Weight Calibration and Coking. The experimental apparatus has been calibrated by choosing unreactive materials as standards. The result of this calibration establishes the control for the equipment. On the sample pan of the TGA, glass beads are used as a solid sample which is inert to reaction and has low surface adsorption. After heating the TGA above the normal, catalytic cracking reaction temperature (600 "C compared to 500 "C) and maintaining the temperature at that value in a steady stream of helium, a hydrocarbon reactant, n-hexadecane, is introduced as a micropulse to the TGA. Figure 3 shows raw data processed by the IBM PC from the TGA for an injection of 5 p L of n-hexadecane on a 50-mg sample of glass beads. Part a of Figure 3 is obtained by recording one datum per second for 1500 s after injection, while part b of Figure 3 consists of five data points per second for the first 30 s after injection and one datum per second for the last 50 s of the run. Part a provides an overall look, while part b concentrates on the critical beginning and end periods. In both parts, raw data are observed to lie on a single line with only about 1 pg of noise. The noise is perhaps due to hydrodynamic or electronic noise inherent to the TGA. While the computer can average the signals, we have not done so for these figures. Data obtained 500 s prior to injection (not shown) indicate that the base line varies by less than 0.3 pg during this time period. The data obtained after injection can be manipulated by computer software to account for the base-line drift; however, this has not been done for Figure 3. Both parts of Figure 3 show a disturbance at the beginning of the plot. The deflection is perhaps due to volume expansion of the pulse when the liquid is vaporized in the flowing stream and due to the change in density of
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Figure 4. TGA response when 5 pL of n-hexadecaneis injected over 11.4 mg of zeolite. (a, top) One datum per second (I/$. (b, bottom) Data are taken at 5/s for the first 30 s and I/s for the last 50 s. (Note the break and change of scale after t = 30 8.) The primary peak seen earlier on inert glass beads, Figure 3b, is clearly visible. The beginning of the second peak can also be seen in the first 30 s. Data from the last 50 s show the increase in weight due to coking of the sample.
the gas stream containing hexadecane as the stream passes over the sample pan. The shape of the disturbance is not always the same and is perhaps merely a function of the flow dynamics and the dynamics of the balance. (Similar behavior is noted when water is injected over glass; hence, the peak is certainly not due to a chemical reaction.) Further, no steady-state change in weight of the sample is seen; i.e., there is no coke formation over the glass beads. Since the temperature of the glass beads has been maintained above the normal catalytic cracking temperature, coke formation on the hot glass wall of the apparatus is expected to be negligible. Results from a reacting system are shown in Figure 4. In this case, a 5-pL pulse of n-hexadecane was injected on an 11.4-mg sample of zeolite catalyst. The overall balance trend is seen in part a, but part b is more useful in determining the weight gain due to coking. In this case, the coke laydown is 35 pg, after accounting for base-line drift. Note that only the beginning and end points of the weight change during each run need to be considered, due to the introduction of the reactant as a micropulse. Hence, it becomes unnecessary to account for the details in the transient response. This is advantageous since, as noted in the introduction, transient response is closely coupled with the kinetics of the reaction, the flow pattern in the reactor, and the dynamics of the balance. GC Calibration and Reaction. Figure 5a shows a typical chromatogram for an injection of 5.0 p L of n-hexadecane on inert glass beads in the TGA, as condensed in the collector and then injected into the GC. Figure 5b corresponds to an injection of 4.0 p L of hexadecane doped with small amounts of n-tetradecane, n-pentadecane, and other lower molecular weight hydrocarbons. This was done to verify that the n-hexadecane peak from the GC is dis-
1758 Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988
Figure 6. Typical calibration curve for n-hexadecane injection over glass beads. Points represent experimental data. The line is the least-squares fit. The correlation coefficient is 0.9964. Ln rl
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Figure 5. (a, top) FID output when 5 pL of n-hexadecane is introduced as a pulse over 50 mg of glass beads, condensed in the collector, and injected into the GC. (b, bottom) Trace amounts of expected products from cracking have been added aa dopants to the pulse. The chromatographs indicate that the collector and chromatograph are efficient for separating and identifying n-hexadecane reactant.
Crete. Comparing parts a and b shows that the hexadecane peak is uncontaminated by the hydrocarbons of lower molecular weight. When a series of different-sized injections of pure nhexadecane are run on glass beads under the same con-
ditions of sample collection, a good calibration curve is developed. A typical calibration is shown in Figure 6. The curve has two highly desirable qualities: it is linear, and it passes through the origin. The calibration is repeated from time to time, due to changes in the GC column and detector performance. However, after numerous calibrations in which the slope has been observed to vary, the curve has remained a straight line through the origin. As a measure of reproducibility, it might be of interest to note that Figure 6 has points taken before and after an 8-day equipment shutdown, during which the TGA was dismantled and reassembled. Approximately half of the points were taken with an empty sample pan, while the rest were taken with glass beads on the TGA pan. No significant differences can be distinguished in points collected before or after the shutdown and in points with a loaded or empty pan. This calibration technique is an elaboration of the original technique of Kokes et al. (1955), the main difference in the two methods being due to the added complexity of the sample collector in the present study. In the case of a reacting system, some of the pure nhexadecane injected will be reacted to lower molecular weight hydrocarbons such as those added to the injectant of Figure 5b. These products of the cracking reaction are not collected to any significant extent. This can be seen in the chromatograph of Figure 7, which represents an injection of 5 p L of n-hexadecane onto a typical zeolitecontaining cracking catalyst. The absence of products in the collector condensate is due to the low partial pressure of the products, in addition to their lower boiling points. This fact was verified by taking aliquot samples (not shown) from the collector vent at the gas sample bomb. In studies of catalyst activity, it is not necessary to analyze the products of reaction. By using the calibration curve in Figure 6 and the area of the peak in Figure 7, the extent of reaction may be calculated. For studies in which it is desired to collect lower boiling products or reactants, the result may be achieved by lowering the collector con-
Ind. Eng. Chem. Res., Vol. 27, No. 10, 1988 1759 * 0
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back-pressure events and provides for effective on-line introduction of the collected sample to the GC. The calibration techniques used for the GC analysis provide for a standard which allows for periodic changes in equipment sensitivity and efficiency. This design and technique should find use in applications where a very small weight change causes a significant change in performance. Such occasions commonly occur in coking and poisoning of catalysts. Acknowledgment Acknowledgment is made to NSF EPSCoR, Institutional Matching Project RII-8011453,and the Exxon Foundation for support of this work. Registry No. C, 7440-44-0; H3C(CH2),CH3, 544-76-3. Literature Cited
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Figure 7. Typical GC collector chromatogram during cracking. Same as Figure 5a except that the n-hexadecane pulse has passed over a catalyst on the TGA pan. This case is for the first 5-pL pulse of reactant on 11.4 mg of zeolite-containing cracking catalyst.
densing temperature. Conclusions TGA analysis is often encumbered by difficulties in metering reactants accurately, in sampling gaseous products leaving the TGA, and in combining reactivity and deactivation measurements. The present apparatus uses a micropulse technique to overcome these difficulties. The micropulse technique coupled with the sample collection system employs the TGA and GC for analysis of extremely small weight changes on solid samples of 10 mg or less. The micropulse technique allows us to bypass consideration of the transient details of the run. The TGA apparatus described here is capable of yielding weight changes accurate to less than 1 pg. The sample collection system is capable of collecting unconverted reactant in a reproducible manner, allowing for accurate calculation of the amount of reactant leaving the TGA after each injection. The collection system allows the TGA to operate at essentially atmospheric pressure without disruption from
Choudhary, V. R.; Doraiswamy, L. K. "Applications of Gas Chromatography in Catalysis". 2nd. Eng. Chem. Prod. Res. Dev. 1971, 10, 218. Choudhary, V. R.; Srinivasan, K. R. "Desorptive Diffusion of Benzene in H-ZSM-5 Under Catalytic Conditions Using Dynamic Sorption/Desorption Technique". J. Catal. 1986, 102, 316-37. DePauw, R. P.; Froment, G. F. "Deactivation of a Platinum Reforming Catalyst in a Tubular Reactor". Chem. Eng. Sci. 1975, 30, 789-801. Dean, J. W. "Composite Catalyst Activity From Component Coking". Ph.D. Dissertation, West Virginia University, Morgant", 1987. Dumez, F. J.; Froment, G. F. "Dehydrogenation of 1-Butene into Butadiene. Kinetics, Catalyst Coking, and Reactor Design". Znd. Eng. Chem. Process Des. Dev. 1976, 15, 291-301. Kokes, R. J.; Tobin, H.; Emmett, P. H. "New Microcatalytic-ChromatographicTechnique for Studying Catalytic Reactions". J. Am. Chem. SOC.1955, 77, 5860-2. Marin, G. B.; Beekman, J. W.; Froment, G. F. "Rigorous Kinetic Models for Catalyst Deactivation by Coke Deposition: Application to Butene Dehydrogenation". J. Catal. 1986, 97, 416-26. Massoth, F. E. "Catalyst Studies with the Flow Microbalance". Chem. Tech. 1972, May, 285. Norton, C. J.; Moss, T. E. "Oxidative Dealkylation of Alkylaromatic Hydrocarbons". 2nd. Eng. Chem. Process Des. Dev. 1964, 3, 23-32. Ozawa, Y.; Bischoff, K. B. "Coke Formation Kinetics on Silica-Alumina Catalyst". 2nd. Eng. Chem. Process Des. Dev. 1968,7,67-71. Sears, J. T.; Maxfield, E. A.; Tamhankar, S. S. "Pressurized Thermobalance Apparatus for Use in Oxidizing Atmospheres at High Temperatures". 2nd. Eng. Chem. Fundam. 1982, 21, 474-478. Stein, K. C.; Feeman, J. J.; Thompson, G. P.; Schultz, J. F.; Hofer, C. J. E.; Anderson, R. B. "Catalytic Oxidation of Hydrocarbons". Ind. Eng. Chem. 1960,52,671-4.
Received f o r review December 9, 1987 Revised manuscript received May 27, 1988 Accepted June 6, 1988
