High Pressure-High Temperature Unit for Liquid-Solid Reactions WILLIAM H. DRESHER, THOMAS M. KANEKO, W. MARTIN FASSELL, JR., AND MILTON E. WADSWORTH University of Utah, Salt lake City, Utah
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ITH the current trend toward reaction studies a t elevated
pressures and temperatures it has become necessary to design equipment which is more specialized than that available commercially. Many studies have been made on the feasibility of various reactions under these conditions, but few studies have been made on the mechanism and kinetics of such reactions or on the fundamental effects of the numerous variables involved. Since rate studies require more exacting conditions than do feasibility studies, it has been necessary t o design a high pressure-high temperature reaction unit which will meet a number of special conditions. The pressure and the temperature of the reaction must be regulated accurately. I n fundamental studies it is frequently necessary to be able to follow the course of the reaction without disrupting the operation of the equipment. Therefore, some means must be provided for extracting a liquid sample from the reaction vessel for chemical analysis of the reaction products. I n addition to these considerations, mechanical difficulties must be virtually eliminated in order to obtain the maximum operating efficiency of the equipment and also to eliminate time-consuming adjustments and repairs. The high pressure-high temperature reaction unit described here is believed to meet these requirements with a minimum of expense. The basic design of this unit is adequate for most laboratory work with heterogeneous liquid-solid systems a t moderately high pressure and temperature.
4. Provisions have been made for lowering a sample into the reaction zone of the autoclave once thermal equilibrium has been obtained. 5 . .4 means has been provided for removing liquid samples from the reaction zone of the autoclave during the course of the reaction without disrupting the operation of the unit. 6. All parts in contact with the solution or its vapors are fabricated from 316 stainless steel.
The advantages of these features are self evident. The pressure and the temperature of the reaction can be maintained a t constant preset values. Experimental runs need not be interrupted to tighten packing glands, etc. Since the packing gland between the autoclave compartment and the motor compartment need withstand a pressure differential of not more than 2 pounds per square inch practically no adjustment is necessary. A complete set of data can be obtained from a single run by removing
liquid samples may be removed for analysis during course of reaction
The reaction unit hau been designed for medium pressures (atmospheric to 1000 pounds per square inch) hence extreme safety precautions necessary in super-pressure work do not hamper its compactness. The unit has been designed to be compact with control elements and indicating devices as close as possible to the individual unit. The essential components of the reaction unit, with the exception of the temperature recording instrument which is common bo a group of these units, are completely contained in a standard metal transmitter type cabinet with the dimensions: 43'/4 X 22 X 18 inches (Figure 1). Standard parts have been used in the design of the unit wherever possible in order to facilitate its construction. The general features of the reaction unit are as follows: 1. The temperature of the solution within the autoclave is constantly measured, recorded, and controlled. 2. The gas overpressure of the system is constantly regulated and indicated. 3. The agitator-drive motor, reduction gears, and tachometer are self-contained in a separate, pressurized chamber above the autoclave.
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Front view
Figure 1.
INDUSTRIAL AND ENGINEERING
Rear view
High pressure-high temperature reaction unit
CHEMISTRY
ENGINEERING, DESIGN, AND EQUIPMENT
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I.Autoclave Reaction Compartment 2. Autoclave Head 3.Closure Rings 4,lntermediate Compartment 5.Pressure Diaphragm 6.Motor Compartment ' 7.Agitator-Drive Motor 8 .Tachometer 9.Reduction Gear Train I0.Packing Gland IIConnecting Shaft l2.Drive Shaft 13.Bearing 14.Agitator 15.Sample Holder 16.Sample Holder Guide
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2o
17.Silver Chain 18.Thermocouple Well 19.Sampling Tube 20.Corrosion Resistant Liner 2 I .Sample Lowering Winch 22.Thermacouple Well Gland 23 Safety Blowout Assembly, 24.Sampling Valve 25.Gas Inlet Valve 26 .Electrical Lead Gland 27.Thermocouple Well Elbow 26.Pressure Discs 29.Silver Blowout Disc 30 Sample Disc 31 .Sampling Bomb
HIGH PR ESSUR E-H IGH T EMPER ATU RE AUTO C LAV E Figure 2
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samples for analysis during the course of the reaction. Corrosion problems are minimized by the materials of construction. T o protect the body of the autoclave from the corrosive action of various systems a series of protective liners has been made. Materials for the liners include silver, inconel, nickel, Monel, Nichrome, and 316 stainless steel. Contamination of the solution by corrosion products is minimized by the selection of a proper liner. Standard 2-liter autoclave provides basic reaction unit
The autoclave consists of three compartments (Figures 2 and 3). The reaction compartment is a standard 2-liter Parr autoclave (Parr Instrument Go., Moline, Ill.) made of 316 stainless steel. A flat head with a ring-type closure is employed between the reaction compartment and the intermediate compartment. The intermediate compartment provides space for the introduction of the various accessories to the autoclave. This compartment was fabricated from 3-inch Schedule 80, 316 stainless steel pipe. A a/,inch thick threaded internal flange was screwed and silver-soldered to the pipe to provide a means of fastening the upper compartments to the head of the autoclave. Six 1 X 6 / / 1 ~ inch NF-20, 316 stainless steel cap screws fasten this compartment to the head of the autoclave. -45 X 3/'* inch threaded external Range was screwed and silver-soldered to the upper portion of this compartment to provide an area for the mounting of the pressure diaphragm and the motor compartment. The motor compartment, the pressure diaphragm, and the intermediate compartment are held together with twelve 1 X 6/16 inch NF-20, 316 stainless steel cap screwa. The motor compartment contains the agitator-drive assembly consisting of motor, gearbox, and tachometer (Figures 4 and 5). Since corrosive materials are not present in this compartment mild steel pipe was sufficient for its construction. The motor compartment was fabricated by welding a 3 X 3 / s inch disk in the top end of a 7-inch section of 3 inch Schedule 80 mild steel pipe. A5 X inch threaded flange was silver-soldered to the opposite end of the pipe. A 5 X inch stainless steel diaphragm separates the motor compartment from the reaction compartment of the autoclave. The diaphragm contains a Teflon-packed pressure seal for the drive shaft of the agitator and provides a base plate for the motor and gearbox assembly. The seal between each of the sections of the autoclave was made by means of tongue-and-groove rings containing Teflon gaskets.
Figure 3. High pressure-high tern- Figure 4. perature autoclave September 1955
FOR STUDYING LIQUIDSOLID REACTIONS t h i s lab-scale pilot unit
.. . has automatic temperature and pressure regulation and indication . . . allows sampling without interfering with operation .. . virtually eliminates mechanical difficulties Unique feature i s an agitator drive assembly completely contained within a separately pressurized chamber in the autoclave
Intermediate compartment accommodates autoclave accessories
All accessories enter the autoclave through the walls of the intermediate compartment (Figures 2 and 4). The fittings, with the exception of the sample-lowering and raising winch, have '/r-inch pipe threads sealed with Teflon base-pipe cement. Gas is admitted to the reaction section of the autoclave through a l/4inch stainless steel needle valve. A thermocouple well was fabricated from '/r-inch 316 -stainless steel tubing. This tubing was sealed through the wall of the autoclave by means of a Teflon packing gland. To facilitate disassembly, a right angle tubing fitting was improvised in which the segment of tubing passing through the packing gland is permanently silver-soldered to the fitting, while the vertical portion of the tubing is attached to the fitting by means of a standard compression type tube fitting, The sample-lowering and -raising device was constructed from the valve stem and bonnet of a Hoke No. Y 348H inch) 316 stainless steel needle valve (Hoke Instrument Co., Englewood, K. J.). The valve bonnet was fastened to the shell of the intermediate compartment by the same type of standard machine
Intermediate compartment and a utocIave accessories
Figure 5. Motor compartment with cover removed
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N2 or
A
O2 01 H2
1 P r e r r u r s Gouges 2 6 d l a s t Valves
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3 Autoclove
Figure 6.
Schematic wiring diagram
screw thread used in the body of the vaIve. A pressure-tight seal is maintained by the bearing of two flat machined surfaces. The valve stem was modified by the addition of a 1-inch diameter 316 stainless steel drum in place of the cone tip normally used in the valve. The sample holder is suspended on a silver or other suitable metal chain wound on the drum. A a/a,-inch channel was cut in a section of '/c-inch 316 stainless steel tubing to serve as a guide for the sample holder. The guide was fastened to the lid of the autoclave by lightly threading the tubing with '/(-inch NF-28 machine screw threads and screwing it into place. The sample holder is rudder shaped and contains a 6/,-inch diameter by '/lo-inch cut or pressed-powder sample. A 6/az-inch rod attached'to the sample holder guides the holder through the channeled tube. Samples are withdrawn from the autoclave while it is in operation, through a modified Hoke No. Y 342H inch) 316 stainless steel needle valve (Figure 2). Liquid is forced, by the internal pressure of the autoclave, through a 0.018-inch bore 316 stainless steel capillary tube. The Pample is collected in a 2-cc. capacity 316 stainless steel bomb which screws into the side of the modified valve. A nipple connecting the sampling valve to the wall of the autoclave was machined from 316 stainless steel. A hole the size of the external diameter of the capillary tube was bored through the nipple. A section of capillary tube was then peaned into the bored hole, thus making a capillary nipple. The sample valve was modified by plugging the outlet side and boring and tapping a '/(-inch hole into the valve chamber to fit the neck of the bomb. A blowout disk was included as a safety device. The disk holder was machined from 316 stainless steel hexagonal stock, and the disk is held in place by a a/8-inch machine screw which was bored for a '/(-inch outlet. The blowout disk was made from pure silver, cold rolled to 0.01 inch annealed a t 600' C. and stamped out. The actual diameter of the disk is 3/8 inch, but the effective diameter is ' / 4 inch. This disk has a bursting pressure of approximately 1500 pounds per square inch. Agitator drive assembly has separate pressurized unit mounted above reactor and accessories compartment
The solution within the autoclave is agitated by a lf/~-inch three-bladed impeller. The impeller is driven by a 7000 r.p.m., 27-volt1 direct current series wound motor which is geared to the stirrer through a 6:l gear reduction. A magnetic tachometer mounted directly on top of the motor is used to measure the rate of agitation. The motor, gearbox, and tachometer are mounted in a pressurized compartment directly above the reaction compartments of the autoclave (Figures 2 and 5 ) . The agitator drive shaft is */a inch in diameter where it extends 1684
Figure 7. Schematic tubing diagram
through the Teflon packing gland in the pressure diaphragm. The small diameter of the shaft a t this point is necessary to reduce Friction in the packing gland. Also, since this small diameter shaft is screwed into the larger '/(-inch shaft and into the gearbox, replacement is facilitated in the event of scoring of the shaft. The '/d-inch 316 stainless steel shaft serves as drive shaft to the impeller. A greaseless graphite-asbestos bearing guides the drive shaft through the head of the autoclave. The tachometer was adapted from the field coils of a small autosyn motor. An Alnico permanent magnet was substituted for the armature of the motor and the impulse is taken from two of the three field coils. One terminal of the motor is grounded to the autoclave and the second terminal of the motor and the two leads of the tachometer were sealed through the wall of the motor compartment by means of packing glands. The original design illustrated in the photographs has been modified as illustrated in Figure 2. The packing glands of the electrical terminals have been moved from the top of the motor compartment to the side of the compartment. This change facilitates assembly and disassembly of the unit. Temperature and pressure are automatically controlled and indicated
The temperature within the autoclave is maintained a t a constant preset value by means of a Leeds and Northrup Type C Micromax temperature controller (Figure 6). The sensing element of the controller is a pair of iron-constantan thermocouples wired in series and mounted adjacent to the heating element of the furnace. Thus, by short circuiting one of the thermocouples, it is possible to obtain two scale ranges on the controller. The controller activates a 115-volt, 30-ampere relay which makes or breaks the circuit to the heating element of the furnace. The voltage to the furnace is varied by means of a Powerstat (Superior Electric Company, Chicago, Ill.) variable transformer. Proper adjustment of the Powerstat setting minimizes the cycling of. the controller over the set point. An indicator light in parallel with the line side of the Powerstat indicates the period when the heating element is being energized. The gas pressure within the two respective compartments of the autoclave is regulated by means of two modified Hoke ballasttype regulating valves (Figure 7). These valves operate by balancing the delivery pressure against a preset pressure in a ballast chamber. Two such valves were adapted for use with this unit by connecting the ballast chamber of the two valves together with 1/8-inch copper tubing. Since the pressure in each of the ballast chambers is identical, the delivery pressure of each valve must be identical within the limits of accuracy of the valves. I n this manner the pressure of inert gas in the motor compartment
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ENGINEERING, DESIGN, AND EQUIPMENT is always very close to the pressure of gas in the reaction compartments of the autoclave. The temperature within the autoclave is indicated and recorded by a Leeds & Northrup Speedomax multipoint recorder. The measuring element, an iron-constantan thermocouple with a 316 stainless steel protection sheath, is suspended in the reaction compartment of the autoclave. For accurate point measurements a Leeds & Northrup portable precision potentiometer is used. Switching from the recorder to the potentiometer is accomplished by the use of a double-throw, double-pole telephone type switch. The pressure in the reaction compartment of the autoclave is indicated by a Marsh (J. P. Marsh Corp. Skokie, Ill.) Type 100 gage mounted in the unit. A similar gage indicates the pressure in the motor compartment. However, this latter gage serves for a bank of similar units and hence is not an integral part of any single unit. The rate of stirring is indicated by a Simpson alternate current voltmeter with a 0-15 volt range (Simpson Electric Co., Chicago, Ill.). The scale of the voltmeter is calibrated in revolutions per minute of the agitator. Preparation of solids gives homogeneous sample with known surface area
Solid samples for study in the reaction unit are prepared by grinding the solid t o -100 mesh and pressing the powder into a disk by means of a die under pressures of 25 to 100 tons per square inch (depending on the solid under consideration). The disk is then pressed by hand into the sample holder. Samples which cannot be pressed are cut from massive crystals, in the case of minerals or from thin sheet, in the case of metals. The weight of the sample in the disk is adjusted to provide a disk with the same thickness as the sample holder. This method of sample preparation provides a homogeneous sample with a known physical surface area. I n initiating the operation of the reaction unit the autoclave is filled with the appropriate volume of reactant and the sample holder with the sample in place is placed a t the top of the guide. The cutout valve between the motor compartment and the reac-
tant compartment is opened, and the entire apparatus is evacuated, flushed with nitrogen, and re-evacuated. The cutout valve is then closed, and the solution within the autoclave is brought to the temperature required for the reaction. The overpressure of gas is applied simultaneously t o both the motor compartment and the reaction compartment. The agitator is set a t the required speed and the system allowed to come to thermal equilibrium. When equilibrium has been reached the sample is lowered into the solution, and the reaction is started. At definite intervals, depending on the rate of the reaction, liquid samples are withdrawn from the autoclave and analyzed. I n removing a sample from the autoclave the capillary tube is first flushed by slightly opening the valve and allowing the solution to flash into a beaker. The bomb is chilled in cold water and screwed into place on the sampling valve. The sampling valve is then opened for a brief period of time, then closed. Care must be used in removing the bomb from the valve since it is still under pressure. A slight turn of the bomb releases the pressure, and the bomb can then be unscrewed from the valve body without flashing the contents. By prechilling the bomb the solution is cooled enough to prevent flashing when the pressure is qemoved. The contents of the bomb are then removed with a hypodermic syringe and prepared for analysis. Acknowledgment
The authors wish to express their appreciation to the Atomic Energy Commission and to the University of Utah Research Fund for the financial support which made the construction of this unit possible. They are also deeply greatful t o the University of Utah Experiment Station and to Roscoe H. Woolley for their assistance in the mechanical aspects and the machine work on the autoclave part of the unit. This project was sponsored by t h e Atomic Energy Commission, Contract No. AT(ll-1)-82. Funds f o r the construction of equipment were provided by the University of Utah Research Fund. This paper comprises part of a thesis to be presented by W. H. Dreaher and T. M. Kaneko in partial f u l fillment of the requirements for the degree of doctor of philosophy, Depaitment of Metallurgy. University of Utah.
Improved Integral for Petroleum Distillation Calculations WAYNE C. EDMISTER California Research Corp., Richmond, Calif.
R
ECEXTLY (1-6)an integral method was proposed for making petroleum distillation calculations. Although the principle of the method is simple, previous applications were made by equations which were either awkward or approximate. Because chemical engineers are more accustomed to numerical and graphical solutions of distillation problems, this type of application of the integral technique has been developed and is presented. The principles of this procedure are illustrated for three calculations on petroleum fractions by examples on: 1. equilibrium flash vaporization; 2. bubble and dew points; and 3. fractional distillation. Integral principle i s defined
ZKz: = 1.0 for finite mixture
Petroleum fractions may be regarded as continua (mixtures) of an indefinite numbers of hydrocarbon components, each appearing in an infinitesimal amount. On the true boiling point September 1955
( T B P ) distillation curve for the mixture, each of these components will be a point, as contrasted to the plateaus that represent the finite amounts of components on the true boiling point curves of light hydrocarbon mixtures. I n distillation calculations for finite mixtures, the vapor-liquid distribution and properties of the equilibrium phases are found by the summations of component distributions and properties. For continua (mixtures) of an indefinite number of components, the distillation calculations follow the same basic principles, but the summation becomes an integration. This distinction is illustrated by the following bubble point relationships:
sd
KdmF = 1.0 for continuum
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