0-3
General apparatus and manifold scheme for high pressure gas-handling equipment
T. P. S. 5. 2.
Oil storage tank Oil pump Gas pressure booster Gas buret Gage overrange cutout
R. L.
A. D.
Pressure regulator liquid addition buret Autoclave Blowout disk
ROBERT D. GOODWIN] Research and Engineering Department, Research Laboratories, Air Reduction Co., Inc., Murray Hill, N. J.
High Pressure Gas Handling Equipment for Autoclaves in Chemical Research Arrangements increase the versatility and productivity of autoclaves in industrial chemical research
WHEN
basic or exploratory chemical research leads to investigations under elevated pressure, there is no sure promise of success to justify the costly equipment indicated. A pitfall is the thought that an autoclave will suffice for high pressure investigations, employing compressed gases as purchased in cylinders. Serious loss of time can be incurred by chemists in recognizing and attempting to overcome the limitations inherent in handling gases and liquids under these conditions. Experience a t this Present address, Cryogenic Engineering Laboratory, National Bureau of Standards, Boulder, Colo.
laboratory has shown that satisfactory gas-handling equipment so greatly increases the versatility and research productivity of an autoclave as to be an essential part of any such installation. The purchase cost of all supplementary gas-handling equipment is approximately equal to that of a 1-liter autoclave rated at 5000 pounds per square inch (7E). A factor of three times the autoclave cost should be allowed for minimum costs of total apparatus. The equipment is designed for use with an autoclave rated at 5000 pounds per square inch. Some pressure vessels for handling gases, including the 10-liter, oildriven booster cylinder, also are limited
to this rating for reasons of cost. The gas valves and tubing, however, are suitable for pressures in excess of 15,000 pounds per square inch, and thus permit the application of heavier vessels without major plumbing changes. The equipment provides for the preparation of gas mixtures of known composition a t relatively low pressure; for subsequent mixing of these preparations; for compression of gases by a simple, booster method; and for quantitative measurement of rate and amount of consumption of a stoichiometric mixture while the autoclave is operated a t constant pressure, independent of any nonstoichiometVOL. 49, NO. 5
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ric initial pressure. For quantitative work, the compressibility of gases must be known. Techniques of high pressure research have been described (2, 3, 59 ) , and also safety precautions necessary with pressure equipment (7, 4 ) and in the handling of toxic materials ( 7 ) . General Apparatus
General apparatus and manifold schematic valves are indicated by numbered circles and check valves by triangles in the direction of flow. The apparatus includes an oil storage tank, T : oil pump, P, gas pressure booster, S. gas buret, B, gage overrange cutout, E, pressure regulator, R, liquid addition buret, L, and autoclave, A : with blowout disk, D. Nitrogen for flushing the system and other gases frequently employed are available at valves 1 to 4 from common supply cylinders for all autoclaves. Supply manifold pressure gages are employed. Mixtures are prepared in S at partial pressures indicated by lowpressure gage G-1. When the gases have been compressed by S, as indicated by G-2, they are mixed by rapid expansion into one end of buret B . The mixing procedure is continued by a further rapid expansion from the other end of B back to S after the piston therein has been lowered. Hydrogen, because it floats upon other gases, should be the first component of a mixture to he introduced into the top of S. Especially when hydrogen is a component, gas should be analyzed to indicate what manipulations are necessary to achieve proper mixing. From buret B the prepared gas mixture is fed through regulator R to the autoclave. The rate of buret pressure change provides a quantitative measure of reaction rate. The liquid addition buret, L , a suitable bomb elevated above the autoclave, is most useful for simple mixing of reagents under pressure. When applicable, it is less cumbersome and less costly than a pump (6E, 9 E ) .
ease of reassembly, even though this fitting may not be required for the relatively low pressures of industrially practical chemical reactions. For lines from gas supply cylinders, and for high pressure oil lines between pump P and shut-off valve 23, a 'j4-inch seamless 0.13 to tubing of larger bore-e.g., 0.1 6 inch--is used for compression collar fittings. As a guide for required tubing weights, the result, applicable to relatively thin-walled cylinders of stainless steel of tensile strength 75,000 pounds per square inch, obtained for a safety factor of 7.5, is
time will leak, a system of double block and bleed valves is preferable. The type of O-ring rubber in checks must be selected for the particular gases handled. High pressure checks (ZE) are employed in the manifold to protect the pressure regulator diaphragm and to prevent backflow from the autoclave. When large quantities of toxic or flammable gases are maintained under pressure outside of the laboratory building, the supply lines to the building are protected by surge checks (ZE) to prevent free discharge in the event of a break. A drain valve on the bottom of the autoclave eliminates the hazard o l ladling or siphoning highly toxic liquid products.
where P is design pressure, pounds per square inch; t is wall thickness; r is radius of the bore; S is tensile strength, pounds per square inch; and F is the safety factor. Gas manifold valves with threaded and coned fittings provide simplicity of assembly. Such valves, rated by the fabricators no lower than 30,000 pounds per square inch. afford leakproof, trouble-free service at 5000 pounds per square inch. For oil lines. a similar type of valve with lower rating, larger orifice size, and compression collar fittings, is satisfactory (2E). Adapters for the plumbing problems encountered are available from gas cylinder vendors and pressure equipment fabricators. Machine shop services nevertheless are desirable. Tight-sealing check valves (5E) on all inlet gas lines-i.e., valves 1 to 4-are a minimum safety requirement to prevent accidental contamination of supply cylinders -4s check valves in
Pressure gages
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A standard type of solid-front safety gage is superior for simplicity of servicing (7E). The recommended practice of mounting gages well above eyelevel is followed. The low pressure gage, G-1, is .protected by an overrange cutout ( 8 E ) . All gages are protected against surges by micrometallic snubbers (3E). Every gage must be provided with a shutoff valve: as leaks and failures are unpredictable. For safety indication in the event of a plug in the lines between autoclave and valve manifold panel gages, a small gage, G-4, is mounted directly on the autoclave, together with vent valve 21. For testing gages and setting cutouts and reliefs, a manual, high-pressure oil pump (5E):is required on the work bench. Pressure Booster
The gas pressure booster, 5' ( 8 E ) , contains a free-floating piston. A s comI
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Fittings, Tubing, a n d Valves
High pressure gas manifolds and lines are constructed throughout of '/4 (outside diameter) X 3/32 inch (inside diameter) stainless steel tubing. The bore is a compromise between the requirement for minimum gas dead space and the probability of plug formations in small tubes. This material is immune to the external corrosion of steel tubing under some laboratory exposure conditions in climates of extreme humidity. Use of the standard type of threadedand-coned high pressure fitting (5) is preferred to the simpler compression collar fitting ( 7 7E)throughout the high pressure manifolds for leaktightness and
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4 Floor This is a scale layout for a simple valve manifold arrangement corresponding to general schematic for high pressure gas-handling equipment..
INDUSTRIAL A N D ENGINEERING CHEMISTRY
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GAS H A N D L I N G EQUIPMENT pared with a simple cylinder in which oil is in contact with the gas, the piston cylinder eliminates the complications and cost of equipment required to provide safety in case high pressure oil and toxic, combustible, or spontaneously explosive gases are blown back to the oil storage tank. I t further prevents pumping oil into the reaction system. with attendant wasted time and confusion in identification of chemical reaction products. The oil pump, P ( E )is, of the differential area piston type, driven by compressed air. Its advantages are simplicity, low cost, and ease of setting to stall at a given maximum safe pressure. One such pump may serve several autoclave gas boosters If, however, one pump is employed per booster, the oil level in tank T will indicate the position of the piston in S. The rubber O-ring seals in the end plugs of S cannot be resistant to all possible gases. Losses of shutdown time may be prevented by replacing the O-rings initially by universally resistant, even though more costly materials-e.g., Teflon. An air trap and bleed valve are employed in the high pressure oil line to the bottom of S, and a small oil trap and bleed in the gas line from the top of S. Pressure Regulators
Pneumatically balanced regulators are available for service to 2000 (4E) and 10,000 pounds per square inch (9E, 70E). More convenient and compact spring-loaded regulators are preferable at pressures to 1000 pounds per square
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inch (4E). Similar instruments, employed as “back-pressure regulators,” maintain accurate relief pressure in liquid or gas flowing systems (4E, 9E). The regulator, R, may be removed by high pressure fittings which serve as unions. The manifold connection then is plugged to restore utility of gas buret B via manual valve 13. Valve Manifolds
In the absence of careful planning based upon experience and the specific needs of a particular research, valves and tubing multiply to an intolerably confusing and hazardous maze. The assembly of inflexible, heavy-walled tubing into neat valve manifolds requires precision work, especially in confined spaces. For safety, any individual should be able to follow the plumbing scheme without reference to paper diagrams which may be obsolete. Therefore, the valves are mounted on the outside, vertical face of the steeland-sand bunker surrounding the autoclaves. This is not permissible for ultra-high pressure work, for which valves must be behind the barricade. Leak testing is simplified. Each doublestem valve is supported upon a welded bracket, 2.5 inches from the bunker surface. The two figures indicate the scale of a simple valve manifold arrangement corresponding to the general schematic on page 861 and a corresponding arrangement for a restricted horizontal space. Check valves are indicated by rectangles containing arI
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.And here i s a corresponding manifold arrangement for a restricted horizontal space
rows in the direction of permitted flow. Tubing leading to the autoclave, booster, burets, and vents is conducted over the top or under the bottom of the bunker, which is supported on I - b e a m to provide for ventilation, drainage, and plumbing For each group of valves leading from a common portion of the manifold, at least one spare connection is employed as a “cross” union (otherwise only a “tee” would be required) to facilitate the attachment of additional valves for gas analysis sampling or introduction of novel gases. Operating Procedures
The following detailed descriptions illustrate necessary conventional procedures for readers unfamiliar with autoclaves, and indicate in some measure the flexibility of the apparatus. 1. To Charge Chemicals and Remore Air. A liquid reagent is placed in buret L, and solids or liquids in autoclave A , both of which then are sealed. Nitrogen gas is introduced to the entire system at 10 to 20 atm. and then is vented. This procedure is twice repeated. All valves should be open, except gas inlets and vents. To conserve nitrogen, the booster piston is at the top of S. T o assure flushing of the pressure regulator, valves 8 and 13 are closed. Testing for gross leaks is by 5-minute observation of the low pressure gage. If desired, the remaining 1 atm. of nitrogen may be displaced by a reagent gas in a similar manner. 2. To Charge Autoclave with Gas Mixtures. No mixing is required of gases placed directly in the autoclave. The increase of pressure, occurring when the autoclave subsequently is heated, may be estimated initially by ideal gas law, solvent vapor pressure, and gas solubilities. The initial required partial pressure of a component is placed directly in the flushed autoclave via valves 2 and 8. If higher pressures are required, the gas is admitted to the booster via valve 6, displacing oil through valve 24. I t is compressed and transferred to the autoclave via valve 8, after valves 2, 5, and 24 are closed by applying the compressed air power to pump P and valve 23 is opened. Gage G-2 indicates when the pressure produced in S equals or exceeds that of the autoclave, shown by G-3, whereupon valve 8 is opened. The check valve between manifold and autoclave is not assumed to be leak-tight. The process is repeated, as required, by alternate-use of valves 2 and 8, 23 and 24, for each component. O n occasion the high solubility of a gas in the reaction solvent precludes using the autoclave directly as a measure of the volume of gas VOL. 49, NO. 5
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introduced. I t may then be desirable to employ booster cylinder S as a buret for all gas transferred from supply to autoclave. Finally, with the autoclave at maximum pressure in the cold, the system is tested for leaks by a pressure gage observation for a t least 15 minutes. 3. To Charge Buret with Gas Feed Mixture. These gases will be fed to the autoclave to maintain pressure as reaction proceeds. They must be adequately mixed and have a pressure greater than that of the autoclave. Only valves 6, 9, 10, and 11 are opened. A supply component is compressed in S, transferred to buret B, and isolated by closing valve 10. When a second charge is compressed in S, gage G-2 indicates the rise of pressure approaching the pressure existing in B. Before a second component is taken into S, the residual first component pressure may be discharged via valve 7 . The composition of a mixture is determined from the pressure increments in the buret when the gas has cooled. The gas preparations contained in B are mixed by expansion into S. removing gas from the end of B opposite to that of its introduction; closing valves 9 and 11 ; opening 6 , 10, and 12; lowering the piston in S; and opening valve 9. Then the gas is recompressed, entering B through valve 11 as originally charged. The process is repeated. 4. To Start Chemical Reaction. If reagents contained in buret L are to be mixed under pressure with those in A , valves 16; 18, and 19 are opened for the calibrated drainage time. Alternatively excess pressure is applied in L to blow the contents into A . Then L is isolated or vented as desired. Thermoregulator is set for autoclave heating. Autoclave pressure is observed at equilibrium temperature. Then, with valves 8, 9, 13 closed. and 10 and 11 open, pressure regulator R is set at this or higher reaction pressure desired. If necessary, the output pressure of R may be checked by gage G-3, G-1, or G-2, provided valves 15, 16, 17, and 18 are closed-e.g., G-3 is vented slightly via valve 17, then 14 is opened and R is set at a value on G-3 at least equal to autoclave pressure. 5. To Maintain Chemical Reaction. Assuming a stoichiometric gas mixture in buret B, the rate of reaction is a function of the rate of pressure drop therein. A fixed concentration of gaseous reactants in the autoclave is a desirable kinetics condition. This may be achieved by manual operation of valve 13 or automatically bv regulator R. Several procedures may be followed for recharging buret B during the course of reaction. One method is first to conduct gases from the supply lines into booster S at required relative pressures; then to isolate B from A , close valves 13 and 14, to achieve mixing by expanding
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gases from B into S through valve 9 ; recompress from S into B; then feed the autoclave from B while preparing another mixture in S. 6. To Remove Products. To avoid loss of volatile components, the autoclave is cooled to room temperature, generally overnight, while isolated from fresh gas supply. Water- or air-cooled coils inside the autoclave, as required for the control of exothermic reactions, are desirable, standard equipment. The cold autoclave must be vented slowly to avoid loss of liquid froth and mist from the boiling liquid. For this problem, buret L may be employed as a dephlegmator. Every means should be essayed to avoid bailing out toxic liquid products. Suspensions of solids in some cases may be held back by a filter in the autoclave to prevent plugging of the autoclave drain valve. Applications
An example of the need for a comparable gas-handling system is the problem with acetylene. Because low partial pressure of acetylene is necessary for safe operation, insufficient amounts can be placed in an autoclave initially. With diluent gases present also, the total autoclave pressure generally exceeds the available acetylene cylinder supply pressure, and additional acetylene cannot be introduced directly from the cylinder. With the equipment described, either pure acetylene or mixtures may be prepared and forced into the autoclave during the course of a chemical reaction. A further example is derived from oxo-type reactions, in which a constant partial pressure of carbon monoxide might be required over the cobalt carbonyl catalyst. With this equipment it is possible to feed the chemical reaction with stoichiometric gas mixtures, independent of the initial pressure of carbon monoxide, which is held constant at any desired value. Acknowledgment
The author is indebted to Julius
G. Shukps for comments on his use of some of this equipment, and to Joseph Improta for his observations on assembly problems. Literafure Cited
(1) Brodkey, R. S., Newberg, R. G., Stewart, Joseph, IND. ENG. CHEM. 48,223 (1956). 12) Clark. E. L.. Golden. P. L.. Whitehouse, A. kf., Storch, H. H . , Zbid., 39. 1555 (1947). Comings, E. W.,’Zbid., 39, 948 (1947). Crowe, J. J., Zbid., 48, 230 (1956). Dodge, B. F., “High Pressure Techniiue,” in “Ch:mical Engineer’s Handbook” (J. H. Perry, ed.), 3rd ed., Section 18, McGraw-Hill, New York. 1950. ( 6 ) Dodge, B. F., Trans. A m . Soc. Mech. Engrs. 75, 331 (1953).
INDUSTRIAL AND ENGINEERING CHEMISTRY
(7) Dresher, W. H., Kaneko, T. M., Fassell, W. M. Jr., Wadsworth, M. E., IND.ENG.CHEM.47, 1681 (1955). (8) Glasebrook, A. L., Montgomery, J. B., Ibid., 41, 2368 (1949). (9) Savage, R. L., “High Pressure Laboratories,” in “Laboratory Design” (H. S. Coleman, ed.), p. 241, Reinhold, New York, 1951.
Equipment References
(IE) Acragage Corp., Milford Conn., solid-front safety gages, Model 713-B. (2E) Autoclave Engineers, Inc., Erie, Pa.: 30,000 Ib./sq. inch coned fittings-e.g., tees, No. 2 4 3 ; 30,000 lb./sq. inch valves with coned fittings, No. 1CC5; 6,000 lb./sq. inch valves with compression collar fittings, No. 1A-A2; high pressure surge check, No. 4E-C; high pressure check No. 4C-C. (3E) Chemiquip Co., New York 12, N. Y., Micro-Metallic, stainless steel gage snubbing protectors. (4E) Grove Regulator Co., Oakland 8, Calif., pressure regulators, pneumatically balanced, also springloaded as 1000 lb./sq. inch, Model 16-SX. (5E) Mansfield & Green, Cleveland 14, Ohio, Type 1F2SS Twinseal, stainless check valves with O-ring seals for 10,000 lb./sq. inch; Type !O, 10,000 lb./sq. inch Twinseal pressure test unit. (6E) Milton Roy Co., Philadeluhia 18, Pa., controlled Golume pumps-e.g., Duplex Minipump, plunger Type VMM2-B-96. (7E) Pressure Products Industries, Hatboro, Pa., autoclaves-e.g., 1-liter, 5000 lb./sq. inch with gas dispersating agitator, internal cooling coils, dip-tube, bottom drain, and simplified head closure. (8E) Sprague Engineering Co., Gardena, Calif., booster cylinder, Model S-375-A, 580 cubic inch; air-motor pump, Model 440-60, and pump assembly 216C-60 for 50001b./sq. inch; gage protector S-214A-1500. (9E) U. S. Bur. Mines, Bruceton, Pa., pneumatically balanced regulators for 10,000 Ib./sq. inch; pressure regulator, drawing C5759; relief regulator, drawing D-5212. (IOE) Victor Equipment Co., San Francisco, Calif., pneumatically balanced 10,000 lb./sq. inch regulator. ( I I E ) Weatherhead Co.. Cleveland 8, Ohio, Ermeto compression collar fittings and adaptors.
RECEIVED for review June 16, 1956 A4CCEPTEDNovember 17, 1956
