Ind. Eng. Chem. Fundam. 1985, 2 4 , 257-260
257
Henderson, D.; Leonard, P. J. I n “Physical Chemistry-An Advanced Treatlse”, Eyrlng, H.; Henderson, D.; Jost, W. Ed. Academlc Press: New York, 1967; Vol. 8, Chapter 7. Kay, W. B.; Nevens, T. D. Chem. Eng. frog. Symp. Ser. 1957, 48, 108. Kirkwood, J. G. J . Chem. Phys. 1935, 3. 300. Mollerup, J. J. J. Chem. Soc., Faraday Trans. 1 1975, 71, 2351. Ohgakl, K.; Sano, F.; Katayama, T. J. Chem. Eng. Data 1976, 2 1 , 55. Peng, D.; Roblnson, D. B. Ind. Eng. Chem. Fundam. 1876, 15, 59. Prlgoglne, 1. “Molecular Theory of Solutions”, North-Holland: Amsterdam, 1957. Rowllnson, J. S. Mol. Phys. 1964, 8 , 107. Sebastiin, H. M.; Nageshwar, G. D.; Lln, H. M.; Chao, K. C. J. Chem. Eng. Data 1980, 2 5 , 145. Smith, W. R.; Henderson, D.; Barker, J. A. J. Chem. Phys. 1970, 53, 508. Vera, J. H.; Prausnitz, J. M. Chem. Eng. J. 1972, 3 , 1. Vrbancich, J.; Ritchie, G. L. D. J . Chem. SOC.,Faraday Trans. 2 1980, 76, 648. Zwanzig, R. W. J. Chem. Phys. 1954, 2 2 , 1420.
Literature Cited Alder, B. J.; Young, D. A,; Mark, M. A. J. Chem. Phys. 1972, 56, 3013. Bae, H. K.; Nagahama. K.; Hlrata, M. J. Chem. Eng. Data 1982, 2 7 , 25. Barker, J. A,; Henderson, D. J. Chem. Phys. 1967, 47, 4714. Barker, J. A.; Henderson, D. Rev. Mod. Phys. 1978, 48, 587. Beret, S . ; Prausnitz. J. M. AIChE J. 1975, 21, 1123. Calvert, R. L.; Rltchie, G. L. D. J . Chem. Soc., Faraday Trans. 2 1980, 76, 1249. Carnahan, N. F.; Starling, K. E. AIChE J. 1972, 78, 1184. Donohue, M. D. Ph.D. Dissertation, University of California, Berkeley, CA, 1977. Donohue, M. D.; Prausnitz, J. M. AIChE J. 1978, 24, 849. Donohue, M. D.; Shah, D. M.; Connaliy, K. G.; Venkatachalam, V. R . Ind. Eng. Chem. Fundam. 1985, In press. Flory. P. J. Discuss. Faraday Soc.1970, 49, 7. Fredenslund, Aa.; Mollerup, J. J. Chem. SOC.,Faraday Trans. 1 1974, 7 0 , 1653. Fredenslund, Aa.; Mollerup, J.; Hall, K. R. J. Chem. Eng. Data 1976, 21, 301. Gubblns, K. E.; Twu, C. H. Chem. Eng. Sci. 1978, 33, 863. Hanson, 0. H.; Hogan, R. J.; Ruehlen, F. N.; Cines, M. R. Chem. Eng. frog. Symp. Ser. 1953. 49, 37. Henderson, D. IBM Research Laboratory, Sen Jose, CA, personal communlcatlon, 1982.
Receiued for review December 1, 1982 Revised manuscript receiued June 24, 1984 Accepted July 26, 1984
EXPERIMENTAL TECHNIQUES
Laboratory Reactor System for the Evaluation of Catalysts in Gas-Phase Reactions under Realistic Process Conditions Ruud Snel Chemical Engineerlng Research Group, Council for Scientific and Industrial Engineering,
PO Box 395, Pretoria 0001, Republic of South Africa
A laboratory reactor system has been designed and developed for the safe testing of catalysts at elevated temperatures and pressures and suitable for unattended operation over prolonged periods of time under condltlons kg of powdered catalyst normally prevailing In Industry. The system is suitable for the testing of as ilttle as 5 X uslng a tubular microreactor, or up to 5 X lo-* kg of catalyst pellets In an internal gas recirculation reactor. In research on selective Fischer-Tropsch synthesis, the arrangement has proved to be reliable. It is suitable for appllcatlon In most catalyzed gas-phase reactions. The system is linked to a microcomputer for process data acqulsltion, control of reactor effluent sampling, chromatographic analysis, and the capture, integration, and evaluation of chromatographic data.
Introduction To evaluate the activity, selectivity, and stability of catalysts in a realistic manner, they must be tested under conditions normally employed in industrial practice. Under such conditions pressure increases attributable to laydown of carbonaceous deposits and heavy products or catalyst disintegration are not uncommon. These pressure increases may enhance the rate of reaction, causing further pressure increases and thermal runaway in the case of exothermic reactions. The phenomena normally preclude the use of prolonged operation. Such long-term runs, however, are vital in the search for catalysts that can exhibit suitable stability in operation. Therefore, a reactor system has been developed that includes the necessary safety aspects as well as a simple data acquisition system. The reactor system has 0196-4313/85/1024-0257801 .SO10
been developed for a vapor phase study of Fischel-Tropsch synthesis and is described in this context. However, it can be adapted easily to suit most catalytic studies of gas-phase reactions. Experimental Section Apparatus. A schematic representation of the reactor system is given in Figure 1. All components are made of stainless steel (304or 316), Teflon, or glass, unless stated otherwise. All valves are of the solenoid type unless indicated otherwise and, with the exclusion of the emergency valves, are operated electrically from a flow diagram type control panel. Each valve to vent is in series with a manually operated needle control valve which regulates the venting. Tubing with an outside diameter of 6.4 mm and a wall thickness of 0.89 mm has been used throughout the system. 0
1985 American Chemical Society
258
Ind. Eng. Chem. Fundam., Vol. 24, No. 2, 1985 VENT
t
Table I. Major Components and Suppliers manufaccomponent item no. turer mass flow controllers Emerson Electric co., Brooks Instr. Division
pressure gage
Bourdon
pressure transducer
Schaevitz Engineering Co. Bourdon
pressure gage
back-pressure regulator sample valve
temperature controller
Figure 1. Fixed bed reaction unit: (A) pressure regulator; (B) normally closed solenoid valve; (C) purifier and filter; (D) manually operated needle control valve; (E) mass flow controller; (F) normally open solenoid valve; (G) pressure gage with minimum and maximum capped spare inlet for liquid feed; (I) pressure pressure alarms; (H) transducer; (J)pressure relief valve, cracks at indicated pressure; (K) three-way solenoid valve; (L)20-pm filter; (M) quick connector; (N) pressure gage; (P) back-pressure regulator; (Q) gas samreactor; (0) pling valve; (R)condenser; (S)bubbler; (T) soap-film flowmeter; (T,) thermocouple.
Table I contains a list of the major components and their suppliers. The system may be safely used at pressures up to 2.5 MPa and at temperatures of up to 850 K. The maximum operating pressure may be raised to 6 MPa by removing the three-way solenoid valves in the reactor bypass. The total leak rate at 573 K and 2.0 MPa did not exceed 1.5 X lo-@m3 s-l (STP). Gas Distribution. The system has five gas inlet ports: one each for hydrogen and carbon monoxide, one for argon purge, one for air to regenerate catalysts, and one spare inlet port for use when mechanistic or kinetic studies are conducted. The gases are purified over zeolite 5A and filtered through a 6 X 10-5-mfrit filter, after which they pass through a vented inlet system. This consists of two valves in series, the interconnecting space being connected by a third solenoid valve and a manually operated regulating needle valve to vent. The vented inlet system allows for the change of gas introduced or renewal of the purifier without having to shut down the reactor system. Flow control is effected by mass flow controllers which are set and read in digital form from the control panel. The controllers are used in sets of two, placed in parallel. One controller covers a narrow range of flow rates and the
temperature indicator system controller
chromatography software
sDecifications sensor 5810
control valve 5835 blind control 5831 comm. potentiometer Model 150 Mix-B-'/,in. NPT-4000 kPa Model 2501-0001
Model 150 Mix/CESB-ll4-in. NPT-4000 kPa 2 contacts norm. open Tescom Co. Model 26-1726-24043 10-port high Valco Co. temp. 6-port high temp. Eurotherm Model Ltd 070-089-03024-02-0182-83-51-1 9-00 digital Model Omega 2170-K Engineering, Inc. (002 Systec (Pty) Syscom Ltd Model A3 Pretoria, RSA Interactive Chromatochart Microware, Inc.
other a wide range. This is to ensure high accuracy and flexibility of operation. The gases are led through non-return valves into an inlet manifold which has a spare inlet for liquid feed. This inlet is capped, but if liquid feed is required, it can be connected to a dosing pump. For small feed rates a liquid chromatography dosing pump is ideal as it is able to pump with a very accurate rate against very high pressures. For safety reasons this inlet should then be connected to a drain through a bursting disk. In addition, the manifold is connected to an emergency argon supply and a venting system. The manifold can be connected to either a fixed-bed microreactor or to an internal gas recirculation reactor; for this purpose quick connectors are provided in the feed and product lines. After the gas has been depressurized over a back-pressure regulator, it is led through two gas sampling valves, a condenser, a bubbler, and a soap-film flowmeter. The bubbler prevents any back-diffusion of air and serves as a flow indicator. Reactors. The microreactor is a double concentric tube type (Snel, 1982) made of 321 type stainless steel. This
Ind. Eng. Chem. Fundam., Vol. 24, No. 2, 1985 250
reactor permits rapid evaluation of catalysts with little interference from transport restrictions. The reactor is heated by a tubular swing-out furnace. The heating element consists of four concentric coils which are connected in parallel. The temperature is regulated by a proportional controller which holds the catalyst within h0.5 K in the range of 500 to 600 K. It is measured by a traveling thermocouple located in the thermowell. The temperature is controlled in the heating element to minimize thermal lag caused by the large heat sink and reactor walls. To overcome this temperature difference a calibration curve is used for determining the set temperature for the controller, corresponding to the desired reaction temperature. The internal gas recirculation reactor (Caldwell, 1982, 1983) exhibits considerable improvements over previously used Berty and Carberry-type reactors. The reactor is particularly suitable for the simulation of conditions in many industrial reactors. The versatility of the two reactors makes the system suitable for testing as little as 5 X kg up to 5 X kg of catalyst in gas flow rates in the range 1 X lo-’ m3 s-l to 8 X m3 s-l (STP). Product Sampling. All lines, with the exception of a frit-type in-line filter, downstream of the reactor, are kept at a temperature of 450 K to facilitate on-line sampling in the vapor phase. This temperature is chosen as it is more than adequate to maintain the products of the processes under investigation in the vapor phase and low enough to prevent the laydown of carbonaceous material on the interior walls. At higher temperatures, notably above 570 K, the Boudouard reaction becomes significant when synthesis gas is in contact with an iron catalyst (Dry, 1980). Under such conditions rapid carbon formation may occur in the pipe lines. The frit is situated immediately downstream of the reactor and functions as a trap for solids as well as a wax. To ensure that no products condense in the product line, the frit is kept at the lower temperature of 400 K. The entire product is passed through the sample valves in the vapor phase. As the water concentration is an important parameter in analysis of the reaction kinetics, it is not removed from the product stream, despite its harmful action on certain chromatographic columns used in the analysis. Periodic replacement of the columns is carried out.
Analysis Product Analysis. The product stream from the reactor is analyzed by gas chromatography with helium as a carrier gas. Because of the complexity of the mixture, which contains water vapor, gaseous and condensable hydrocarbons, oxygenated hydrocarbons, and carbon dioxide together with unconverted carbon monoxide and hydrogen, a direct single-column chromatographic analysis is not possible. Therefore, two samples are taken from the product stream. One sample is analyzed for organic products having a carbon number of 3 and higher using a flame ionization detector and a 140 m long glass capillary column (0.d. 0.5 mm) coated with OV-101. The other sample is separated through a 3 m long column packed with Porapak-Q and the amounts of carbon monoxide, carbon dioxide, water, and light hydrocarbons are measured by means of a thermal conductivity detector. Hydrogen was not analyzed because of its concentration-dependent thermal conductivity in helium mixtures. The combined areas of propene and propane, measured on each column, are used to link the data from the two detectors. A Carlo-Erba Model 4200 gas chromatograph is used to house both columns.
Data Acquisition. The signals from the two detectors are analyzed by a microcomputer using Chromatochart software developed for the Apple computer. This allows simultaneous and independent data capture from four channels. The data system incorporates a system controller which reads relevant experimental data, such as temperature, pressure, and the flow rates of both hydrogen and carbon monoxide. The system controller is an intelligent interface containing an eight-channel, twelve-bit analogue-to-digital converter, eight digital inputs, eight digital outputs, communications capability and relays for actuation of valves, and electrical switches at preprogrammed times. Any other interface with such capabilities is, of course, equally suitable. The system can deal with as many as four reactor and analytical systems, simultaneously and independently. It is dedicated to the reactor systems and is not used for any other purpose. Data Processing System. The raw chromatographic and other reactor data are processed on a separate microcomputer using the adapted Chromatochart software and software specifically developed for our FischerTropsch research. Both data systems are interfaced with a CDC mainframe computer for added versatility. The transfer of data between the two systems may be effected via a networking link, computer disks, or the mainframe computer. Safety All relevant gas lines are protected by spring-loaded pressure relief valves and velocity check valves. The reactor system is located under a ventilation hood containing flash arrestors. In the event of the reactor pressure or temperature deviating substantially from their set points or in the event of electrical power failure, the reactor furnace is shut down and the solenoid valve located on the hydrogen cylinder and all the other valves and flow controllers are closed automatically. In such events the solenoid valve of the emergency argon line is deenergized and opens. The system is then automatically purged to prevent wax formation until the reactor temperature has reached a safe limit, e.g., 400 K, when the emergency line is closed again. An alarm light on the control panel indicates the nature of the event leading to system shutdown, i.e., high pressure, low pressure, or high temperature. Reactor Operation Gases. Hydrogen, argon, and air of ultrahigh purity and carbon monoxide of technical grade are purchased from Afrox Ltd. Catalysts. All catalysts at present being tested are complex derived iron catalysts specifically designed for the production of lower olefins from synthesis gas. They are crushed and screened to particle sizes in the range of 2 to 6X m and reduced at a pressure of 300 kPa in hydrogen at a flow rate of 1.6 X lo4 m3 s-l (STP) for 3-5 h at 433 K, 16-20 h at 523 K, and finally 20-24 h at 573 K. Typically, a quantity of 4 X kg of unreduced catalyst is employed in the microreactor and 3 X kg in the internal recirculation reactor. Operating Procedures. For the production of lower olefins, the typical conditions needed are a pressure of 2.0 MPa, a temperature of 543 K, and a flow of 0.4 X 10* m3 s-l (STP) of synthesis gas with a mole ratio H2/C0 = 0.5. After reduction the catalyst is allowed to cool down in a hydrogen stream to a temperature of 473 K. Then the pressure is slowly raised with hydrogen and carbon monoxide to a pressure of 2.0 MPa so that the correct synthesis gas ratio is reached at the operating pressure.
260
Ind. Eng. Chem. Fundam.
The reactor is allowed to operate continuously without interruption. With the exception of the first day on stream, when samples are taken frequently to monitor possible unsteady states, the product stream is sampled automatically every six hours. Experimental Results Continuous runs lasting more than 1month have been performed. One such run showed a reaction rate of 5 X mol of carbon monoxide converted to hydrocarbons per second per kg of catalyst. Calculations indicate that the heat of reaction generated 1 J s-l in the reactor volume
1985, 2 4 , 260-262
of 3 x lo4 m3. Despite this high activity, the reaction could be maintained uninterrupted for more than 1 month. During this particular run no significant changes in activity or selectivity were observed.
Literature Cited CaMwell. L. Appl. Catal. 1982, 4, 13. Caldwell,L. Appl. Catal. 1983, In press. Dry, M. E. Hydrocarbon Process. Fob 1980, 92. Snel, R. Chern. Scr. 1982, 20(3),99.
Receiued for review November 21, 1983 Accepted October 11, 1984
New Vapor-Liquid Equilibrium Apparatus for Elevated Temperatures and Pressures Ho-Mu Lln, Hwayong Kim, Willlam A. Leet, and Kwang-Chu Chao' School of Chemlcal Engineering, Purdue University, West Lafayette, Indiana 4 7907
An apparatus of the flow type is developed for the determination of vapor-liquid equilibrium at elevated temperatures
and pressures for mixtures of diverse types including those containing water, coal liquids, etc. The heart of the apparatus is an equilibrium cell equipped with transparent sapphire windows sealed with gold O-rings for the visual observation of the liquid level. The apparatus has been tested with mixtures of known equilibrium behavior.
Introduction Efforts have recently been directed toward study of vapor-liquid equilibrium (VLE) at temperatures and pressures substantially higher than the ambient in response to intensified development of coal conversion and other synthetic fuel processes. In spite of the considerable progress that has been made, there remains much need for fundamental vapor-liquid equilibrium data. Connolly (1962)used a static apparatus for measurement of VLE for H2 benzene over the temperatures 430-530 K and pressures 2-18 MPa. Grayson and Streed (1963) employed a flow type of apparatus to measure VLE data of H2+ gas oils at temperatures to 750 K and pressures to 20 MPa. Laugier and co-workers (1980) demonstrated an apparatus for VLE measurements to moderate temperatures. Other apparatus which are capable of determining VLE at elevated temperatures and pressures have been reported by Simnick et al. (19771, Wilson et al. (1981), Nasir et al. (1989), and by Sung (1981). In this work we develop a versatile flow apparatus for pressures to 25 MPa and temperatures to 710 K for mixtures containing water, coal liquids, and/or other complex substances. The Apparatus The apparatus is intended for the measurement of vapor-liquid equilibrium at elevated temperatures and pressures for diverse mixtures including those containing water, coal liquids, and other complex substances. We adopt a flow design to reduce residence time of the sample in the high-temperature zone, and thereby to minimize thermal decomposition. We decided to use a transparent window for visual observation of the liquid level in the cell after we had examined all alternatives. For
Blower
1
Temperature Measurement Pressure Gauges
m Metering Valve
+
Heater8
7
Thermostofed
N p Bath
LI
Damping Coil
Purging Liquid
Regulator
Damping Pot
Figure 1. Vapor-liquid equilibrium apparatus.
instance, the eledric capacitor level indicator that had been satisfactory in our previous studies (Simnick et al., 1977) 0 1985 American Chemical Society
