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INDUSTRIAL A N D ENGINEERING CHEMISTRY
The process described above uses ammonium sulfate. Instead of this salt, ammonium nitrata can be employed. The ooncentration of the liquor in this case will be 1.3-1.45 at 180" F.
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LITERATURE CITED (1) Fox, E.
J., and Turrentine, I. W., IND. EKG.CHEM.,26, 493
(1934).
Hoohberger, Ernst, Chem.-Ztg., 52, 22-3 (1928). (3) Jukes, T. H., private communication, 1942.
(2)
POSTWAR OUTLOOK
The availability of large domestic and foreign supplies of potash salts after the war would not warrant the recovery of the potash and char by concentrating and carbonizing the molasses stillage a t a low temperature unless some local or operating condition, especially in the West Indian or other sugar producing countries, offered favorable circumstances. Since the organic nonsugars are of vegetable origin, they yield products similar to those obtained by the low-temperature carbonization of wood. Therefore, the char has possibilities Of being used in feed Or for other purposes similar to those for which wood charcoal is utilized.
H. I., IKD.ENG* C H E M . i l 9 222 ~ (lga7). (5) Perry, J. H., Chemical Engineer's Handbook, p , 1079, New York, McGraw-Hill Pub. Co.. 1934. (6) Reich, G. T., u. s. Patents, 1,552,732 (1925); 1,559,185 (1926) ; 1,698,171 (1929); 1,823,408 (1931); 1,886,045 (1932); 2,002,797 (1935); 2,043,009 (1936). (7) Seidell, Atherton, "Solubilities of Inorganic and Metal Organic Compounds", 3rd ed., Vol. 1, New York, D. Van Nostrand Co., 1940. (8) U. S. Bur. of Standards, Circ.145, 53-6, 60-1 (1924). (4)
P R ~ ~ E N Tbefore E D the Division of Sugar Chemistry and Technology at the 108th Meeting ,f the A~~~~~~~ cHsMilcaL s~~~~~~in N~~ Yo&, N. y.
HIGH SPEED AGITATOR FOR PRESSURE VESSELS M. W. KIEBLER Coal Research Lubora tory Carnegie Znstitute of Technology, Pittsburgh, Po.
T
HE use of pressure equipment in research laboratories has increased steadily over the last several decades to the point of being commonplace. Many investigators have found it possible, through temperature or mass action effects, to increase greatly a reaction velocity or to shift an equilibrium in a desirable direction by conducting the reaction under pressure. I n those cases where the reactants occur in a single phase, such as gaseous or liquid solutions, stationary apparatus is often satisfactory. However, if two or even three phases are involved, the rate of reaction can be further increased by providing some means of agitation. At the same time heat transfer between the stirred mass and the vessel wall is materially increased. Numerous devices to mix or stir the contents of a pressure vessel have been reported in the literature. Phillips ( I d ) and Groggins and Hellback (7) described an arrangement whereby cylindrical bombs are rotated in a constant temperature bath. Other designs which depend on either rotation of the reactor itself or of internal blades for agitation are described by Tongue (13), Laupichler (Q),and Fischer (6). Several authors (1,4, 11) 4sve described a shaking or rocking autoclave of a type which has been commercially available for a number of years. Mechanical difficulties-such as bleeding gases in and/or out of a vessel, attaching gages, condensers, heat exchangers, or safety disks, maintaining constant pressure, etc.-which are encountered with rotating, shaking, or rocking autoclaves can be greatly reduced by an externally powered and internally stirred autoclave (9, IS). However, this type of equipment is not entirely without fault. If the vessel is to be used a t pressures in e x c w of several thousand pounds, it is di5cult to obtain a stuffing box which will remain gastight for any considerable length of time; and while gas leakage can be reduced by a lantern-lubricated gland, contamination of the reaction mixture with the lubricant then becomes a problem. Power losses, through a packing gland, result in a high initial and operating cost and tend to reduce the rotation speed of the stirrer so that, from the standpoint of agitation and cost, the value of this type of autoclave is often questionable, A 750-00. autoclave built in
the Coal Research Laboratory for service at a pressure of 3000 to 6000 pounds per square inch required l/, horsepower to turn a stirrer at 120 revolutions per minute. Tongue (13) described several small laboratory autoclaves of the same type which had similar power requirements. These faults exceed reasonable limits as the size of the autoclave is reduced, since amount of leakage, size of power installation, and amount of agitation will remain fairly constant with wide variation in the volume of the pressure vessel. A more nearly ideal reactor would be one in which the stiriing mechanism and reactants are contained within the same wall. Calvert (3) in 1914 obtained a patent on this basic ides which covered not only motor-driven stirrers, but also circulating pumps. MacMillan and Krase (IO) and Holloway (8) published a detailed description of an autoclave in which the stirrer and motor operate under the same gas pressure. Recently (6) a method of obtaining agitation by means of a magnetically operated plunger was reported. This paper describes a totally enclosed motor and agitator, built to operate under more severe conditions with respect to pressure, temperature, and chemical attack than those mentioned above. The stirrer assembly (Figure 1) is constructed as an integral unit which is attached to the bomb head by means of the threaded lower end. The autoclave, shown dismantled as well as assembled to run in Figure 2, was built in these laboratories several years ago to study the hydrogenation of coal in aqueous alkali a t temperatures and pressures up to 400' C. 750' F.) and 6000 pounds per square inch. Violent agitation is required in this reaction to produce not only the maximum possible gas-liquid interface, but to prevent the coal particlea from fusing together. Sufficient turbulence was obtained in this autoclave by rotating a 2-inch nickel propeller at 1500 r.p.m. in a 750-cc. nickel-lined cylindrical bomb of 3-inch internal diameter. The body and top closure for the assembly were machined from chrome-vanadium steel (SAE-6145) forgings which were heat-treated and drawn at 900' F. in a salt bath after all machine work had been finished. Data available for this alloy indicate
June, 194s
b
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INDUSTRIAL AND ENGINEERING CHEMISTRY
that the resulting product should have a tensile strength of 210,000 pounds per square inch and a Brinell hardness of 470 (48 Rockwell C). The studs were made of a chrome-nickel steel (SAE-3140) drawn at slightly lower temperatures to give a tensile strength of about 200,000 pounds per square inch. The nuts, made of the same alloy except for a lower carbon content (SAE-3120), were carburized for surface hardness. To reduce contamination of the bomb contentq the interior of the assembly was given a thick coat of silver and burnished. The top closure was made up against an unconfined copper gasket which had an internal diameter of 4 inches. Silver gaskets were used between the assembly and head and between the head and the reactor body. A tight-fitting copper condenser on the neck of the amembly served to remove the heat which flowed up from the heated reactor. Six nickel disks were attached to the nickel stirrer shaft to create turbulence and expedite heat removal. All parts of the electrical system had to be resistant to attack from hydrogen, water, and any organic vapors which might be formed during the course of a reaction. A shaded-pole 1/30. horsepower motor was obtained (model 123, A. G. Redmond Company), and the outer cover removed. Two bearing supports (Figure 1) were made for the top and bottom of the motor. An Oilite bearing was pressed into each support to take the rotor shaft. It was planned to replace these bearings with graphite bushings if hydrogen or organic vapors should remove the lubricant, but this has never been necessary. The supports were held tightly against the stator ends by two bent bolts which passed through slots at opposite sides of the stator. These bolts were salvaged from the motor parts. Two stators have given satisfactory service in this apparatus. The first was taken as it came from the manufacturer and was given about six coats of a Bakelite varnish. The second was made by winding Formex wire onto a Redmond stator frame and alternately coating the coils with Heresite varnish (No. L-100) and General Electric varnish No. 1676. Each stator was impregnated by suspending it in a container of varnish which could be placed in a vacuum desiccator. The pressure in the desiccator was then alternately decreased and allowed to return to atmospheric to remove entrapped air. The stator was then drained, allowed to air-dry, and finally baked. After each of several impregnations, the stator was supported in a different position for drying and baking. Any varnish which adhered to the outside diameter of the stator was removed with sandpaper. The assembled motor was tested by allowing it to run under water. Because this motor has no starter brushes or windings, only one lead has to be taken out through the reactor wall with, the other lead internally grounded. However, in this design both leads were brought out so that the motor insulation could be more accurately checked. The leads were made by brazing a copper disk on a short piece of heavy Nichrome wire and slipping a Bakelite disk over the wire on each side, The three disks were then crushed together under a gland nut in the top closure. Both the diameter and thickness of the Bakelite must not be less than that of the copper disk. Nichrome wire was used in preference to copper because of greater strength and stiffness. The resistance to ground through this type of seal (8) haa always been more than 600,000 ohms. A coil which serves to remove heat from the motor stator waa made by bending a piece of X inch mild steel tubing to form a long narrow U,which was then wound into a helix. The two ends were separated 180" apart, bent at right angles to the helix, and dropped through holes at the bottom of the motor compartment where they were made up against the wall with compression cones. The only change contemplated for this autoclave is to increase the internal diameter of BEARING SUPPORT tubing used in the coil.
t
Figure 1. Bomb Stirrer Assembly
By)
INDUSTRIAL AND ENGINEERING CHEMISTRY
The find assembly was made by attaching the stirrer ehaft to the motor by means of a bushing, and then pushing the shaft and motor through the coil so that the motor rested against a shoulder near the lower part of the compartment. A ring which served to
Vol. 37, No. 6
held a graphite bushing to take the stirrer shaft. At various times this fitting has been replaced with a simple packing gland, in which case the pressure in the assembly and bomb were equalized by a connecting tube. The assembly and head, which
Figure 2. Open Autoclave at Left, Showing Head Construction, Thermocouple Tube, Stirrer, and Bearing; Assembled Autoclave at Right
center the motor and hold it firmly against the shoulder was then premed against the top bearing support, and a low-melting alloy (!M% lead-400Jo tin400Jo bismuth, melting at 202’ F.) was poured through a hole in the ring. This ring, which has two set screws to hold it in place, was removed after the alloy had solidified to facilitate making up the electric connections. The alloy providea good heat transfer between the coil and stator. The motor can be removed by turning the assembly upside down and passing superheated steam through the coil to melt the alloy. The gasket was put in place, several studs were removed, and the top closure was held a short distance above the assembly so that the motor leads could be soldered to the Nichrome wires. After all exposed wires were carefully insulated and coated with thickened varnish, the final closure was made. The solid nickel head to which the assembly was attached was fitted with a thermocouple well, a safety disk, a gas inlet, and an outlet which could be used in conjunction with a siphon tube to charge and empty the bomb without removing the head. The nickel fitting on the lower side of the head, shown in Figure 2,
weighed about 80 pounds, could be conveniently raised above the stationary nickel-lined bomb by a cable and by one fixed and qne movable pulley. LITERATURE CITED
(1) Adkins, H., IND. ENO.CHIW..ANAL.ED.,4,3424,379(1932). (2) Asbury, R.S.,Ibid., 8,152 (1936). (3) Calvert, G.,U.8.Patent 1,123,092 (1914). (4) Dykstra, F. J., and Calingaart, G., IND. ENQ.CHIM.,ANAL. ED.,6,383-4 (1934). ( 5 ) Fisoher, F., ass. Abhandl. Ksnntnis Kohls,4, 13-25 (1919). (6) Gileon, A. R., and Baskerville, T.W., Chemistry & Industry, 63, 450 (1943). (7) Groggins, P. € and I.Hellback, , R., Chem. &. Mct. Enu., 37,6934 (1930). (8) HoLloway, J, H., and Krese, N. W., IND.ENQ.C ~ Y .25, , 497502 (1933). (9) Laupichler, F.,C h m . Fabrik, 5, 305-11 (1932). (10) MacMillan, A. H., and Kraae, N. W., Im. ENO.CHSH.. 24, 1001-2 (1932). (11) Peters, F.N.,Jr., and Stanger, 0. C., Ibid..20, 7 4 5 (1928). (12) Phillips, M., Ibid., 17,7216 (1925). (13) Tongue. H., “Deaign and Construction of Hiah Pressure Chemical Plants",-London, Chapman & Hall, 1934,
