I h’ D U S T R I A 1, A N D E N G I N E E R I N G C H E M I S T R Y
274
centration of the titanium sulfate solutions in which maximum precipitation occurs is lower. 6. The maximum percentage precipitated in the time periods studied decreases with increased acidity. 7. The concentration of titanium oxide has more influence on the rate of precipitation than the acidit,y factor. Thus in those solutions a t the minimum of their respective precipitationconcentration curves the percentage precipitated increased in spite of increased acidity factor because these solutions occurring at the minima of the precipitation-concentration curves are more dilute as the acidity factor is raised. 8. In the most dilute and the most concentrated solutions the shape of the precipitation-time curves is the same for all acidities studied but the percentage precipitated in a given time decreases with increased acidity factor. 9. When the acidity factor is 2 or higher, titanyl sulfate is crystallized alone or with metatitanic acid from solutions containing more than 6 per cent by weight of titanium oxide. 10. When the acidity factor is 1 or less than 1, solutions of 6 t o 10 per cent by weight of titanium oxide may be 95 per cent precipitated by boiling for 8 hours.
T’ol. 25, No. 3
LITERATURECITED
A4CKSOWLEDGJlEST
Barton, L. E., U. S . Patent 1,155,462 (Oct. 15, 1915). Blumenfeld, J.,U. S. Patent 1,504,669 (Aug. 12, 1924). Dennison, Trans. Faradag Soc., 8, 20, 35 (1912). Fladmark, BZ.,U. S. Patent 1,288,863 (Dee. 24, 1918). Herz, IT., and Bulla, -L, 2. anorg. Chem., 61, 367 (1909). Hixson, A. IT.,and Plechner, IT. TI’., Chem. Le. M e t . Eng., 36, 76 (1929). Patent 503,124 (hug. 15, 1893). ( 8 ) Kolthoff, I. LI.,J . Phys. Chem., 36, 860 (1932). (9) Kullgren, C., 2. phusik. Chem., 85, 466 (1913). (10) Laugier, A , Ann. chim.p h y s . , 89, 306 (1614): Schzeigger’s J . , 19, 54 (1817). (11) Mecklenburg, IT., U. S.Patent 1,768,528 (May 13, 1930). (12) Morgan, J. L. R., J . An&.Che7rz. Soc., 38, 558 (1916). (13) Overton, J., British Patent 9825 (Dec. 23, 1893). (14) Rossi, A. J.,and Barton, I,. E., U. S. Patent 1,196,030 (Aug. 29, 1916). (15) Roth, IT. A . , and Recker, G., Z . ph~sik.Chem., BodensteinFestband, 55 (1931). (16) Ryan. L. IT-.,U. S.Patent 1,820,987 (Sept. 1, 1931). (17) Toungman, E. P., Bur. Mines, Circ. 6365 and 6386 (1930).
The authors are indebted to the Titanium Pigment Company for the phot,ographs used to illustrate this paper.
RECEIVED October 20, 1932. W. W.Plechner’e present address is Titanium Pigment Company, Inc., New Tork. N. Y .
(1) (2) (3) (4) (5) (6)
Amination by Ammonolysis IV. Design and Construction of Equipment’ P. H. GROGGIIVS, Bureau of Chemistry and Soils, U. S. Department of Agriculture, Washington, D. C.
T
HE preparation of amines
The reaction between organic compounds, containing replaceable substituents, and ammonia generally takes place at elerated temperatures. I t is therefore essential that ammonolysis be carried out either in high-pressure autoclaves or in tubular systems. Autoclaves are adapted .for discontinuous or batch operations, whereas pipe systems are particularly suitable ,for coniinuous high-pressure syntheses. Although direct-jired sysiems were at one time quife prevalent, these have been supplanted by jacketed vessels heated with steam or circulated fluid, or by tubular systems immersed in molten alloys. Such systems procide a safer, more HIGH-PRESSVRE EQUIPMEKT accurate, and practically automatic control of FOR A~LIMONOLYSIS the amination process.
through the reaction between a r o m a t i c c o m pounds and ammonia generally takes place a t e l e v a t e d temp e r a t u r e s . It is t h e r e f o r e essential that the ammonolysis be c a r r i e d out either in highpressure autoclaves or in tubular systems. A u t o c l a v e s are generally adapted for discont i n u o u s or batch operations, whereas pipe systems are particularly suitable for continuous high-pressure syntheses.
Autoclaves may Tary in size or shape according to the particular requirements of a plant or process. They may differ as to the materials of construction, depending on the nature of the reacting materials. Some are provided Kith stirrers, for agitation is essential when the contents of the vessel are not homogeneous; and finally, some are provided with jackets to permit temperature control by means of steam or a circulating liquid. I n general, industrial autoclaves are hollow cylindrical vessels ranging from 100 to 1000 gallons in capacity and are designed and constructed to operate up to 5000 pounds pressure per square inch. The steel shell may be forge- or hammer-welded, electric fusion-welded, or may be forged, rolled, and drawn so as to provide a seamless vessel. Hammer-welded apparatus having a wall thickness of 2 inches is 1 Parts I and I1 of this paper appeared in INDUSTRIAL AND CHDMIBTRP in January, and P a r t I11 i n February, 1933.
readily o b t a i n a b 1e ; seamless forgings or electric fusion vessels can be p r o d u c e d with walls of a n y desired d i m e n s i o n s . H a m m e r - w e l d e d vessels are being r e p l a c e d by the other t y p e s of apparatus, s i n c e the former are l i m i t e d to a comparatively light wall thickness and i n v o l v e t h e u s e of l o w c a r b o n a n d consequently low tensile strength plate. Table I gives the safe working p r e s s u r e that can be used on electric f u s i o n - w e l d e d autoclaves having a diameter ranging from 1 t o 5 feet, with shell thickness ranging from 1 to 3 inches.
DIRECT-FIRED AUTOCLAVES The use of direct-fired autoclaves for carrying out highpressure reactions was a t one time a general practice. Coke, fuel oil, and gas furnished the means of heating such vessels. Such systems possessed certain inherent defects, particularly in regard to the danger of igniting the inflammable contents of the autoclaves in case of a leaky connection, and in the difficulty encountered in accurately maintaining the optimum operating temperature. When gas or fuel oil is used as a source of heat, it is now possible to obtain accurate and automatic control. Gas is, however, distinctly more costly than fuel oil, and, when the duration of the operating cycle is long or the price of the intermediate is low, its employment on a large scale may be prohibitive. This problem is not so important in localities where natural gas can be obtained a t a ENGINEERIWQlow cost, nor is it of appreciable consequence where the gas for the combustion chamber is manufactured in the plant.
I N D U S T R I A L A N D E iu G I N E E 13 I N G C H E Wl I S T R Y
March, 1933
ALLOWABLE ARO OR KING PRESSURES" FUSION-WELDED AUTOCLAVES
TABLEI.
?vlAXIMCM
WALL THICKNESS Inches
(9t approximately 200' C.) WORKINQ PRESSURE --
,--12 in b
1543 2160 2700 3600
1.0 1.5 2.0 3.0
24 in. 36 in. Pounds p e r square inch
900 1200 1543 2 160
600 900
loso 1543
FOR
60 in.
-
360 540 720 1080
275
out of the operating room the products of combustion, which are exhausted through a central smoke stack. Electric heating is often used to obtain an accurate temperature control for small nonjacketed vessels. Heating by electricity may be accomplished by several types of installations, all of which may be automatically controlled. When
a Calculated in accordance with method prescribed by t h e American Society of Mechanicai Engineers ( I ) , using t h e formula: - = max. allowable working pressure, lb./sq. in.
R
max. allowable unit working stress in shell malerial, lb./sq. in. (60,000 Ib.) min. thickness of shell plate, in. (1 t o 3 in.) E efficiency of Iongitudinal joint To (90%) K inside radius of weakest course'of shell in. Since t h e maximum temperature which wiil obtain ddes not exceed 700' F , t h e factor of safety of 5 was used, in accordance with Table U-3 of t h e A. S. M: E. Code ( I ) . b Inside diameter of vessel.
where S t
=
= = =
To a large extent, however, the fire box has been replaced by the metal bath, or the jacket for steam or circulated fluid. Such installations provide a safer, more accurat'e, and automatic control of the reaction. In a limited number of operations, direct-fired operations are still used, principally on account of the fact that heating by such means sets up convection currents in the charge and thus obviates the necessity of using mechanical stirrers. Since the agitating mechanism is set on the vessel which operates at high temperatures and pressures and which contains ammonia and a n organic compound, mechanical agitation introduces increased operating problems in the form of motors, belts, and stuffing boxes. -!dlJIOSOLTSIS I X DIRECT-FIRED ,~UTOCI.ATES A hammer-welded autoclave for direct-firing that has found extensive use in the preparation of amines by the ammonolysis of aromatic halides is shown in Figure 1. It is provided with nozzles for charging and discharging coniiections and with a thermometer well. The head is a massive steel forging that seals the vehsel by means of a c a r e f u l l y m a c h i n e d t o n g u e and g r o o v e joint. The head is made fast with chrome steel bolts and is removed only when the autoclave is given a t h o r o u g h periodical i n s p e c t i o n . A h e a v y walled tube is frequently threaded and welded to the head. To this tube, connections are made for the safety valve and safety diaphragm, pressure gage, and vent lines. The autoclave is set inside a steel s h e l l w h i c h is lined with fire brick. A diamondshaped p i e r c o n s i s t i n g of high-grade refractory is built up directly under and almost t o u c h i n g the a u t o c l a v e . This construction prevents localization of the flame and FIGURE1. NONAGITATED minimizes the danger of local DIRECT-FIRED AUTOCLAVE overheating, TI h i c h is often responsible-for the deposition of a carbonaceous layer a t the base on the inside of the autoclave. The steel shell is provided with a combustion chamber in front, so that the atomized and ignited fuel oil, or gas flame, is directed a t the protective masonry pier from a distance, thus avoiding its rapid deterioration. A split steel ring on top of the shell serves to support the autoclave and to keep
FIGURE 2. TUBULAR PRESSURE SrsTEM FOR CONTINUOUS PREPARATION OF AMINES
the charge is a homogeneous mixture, it is possible to use the autoclave itself as the resistance unit. The container resistance method of heating utilizes a low-voltage heavy current, whereby rapid heat transfer combined with close temperature control is obtained. Inasmuch as the temperature of the heating elements is but a feiv degrees above that of the material being treated, there is no possibility of decomposing the charge. The equipment operates a t full heating capacity until it is worn out, thus eliminating repair and upkeep expenses. Such installations are known to contribute substantially to increasing the yields and purity of certain complex aromatic compounds. ~ ~ R I M O K O L Y S IISN JACKETED VESSELS When the operating temperature is sufficiently low-i. e., 190" C. (374' F.) or lower-steam is generally employed in jacketed vessels. Above 190" C. it is customary to employ a n oil-circulating system. The advantages of jacket equipment over nonregulated direct-fired apparatus are: (1) automatic control, (2) fuel economy, (3) saving of labor, ( 3 ) uniform temperature and product, ( 5 ) greater productivity per machine on account of the ease in cooling, and (6) better yields and purer product. Most of these advantages can be obtained in gas- or oil-fired systems which are equipped for automatic control. The inner vessel of the jacketed autoclave is identical with that described for direct fire. A steel shell designed to withstand the jacket pressures is welded to the outside, and the autoclave is then suspended on a suitable steel structure. When steam is used for heating, it is delivered to the upper portion of the jacket, and the condensate is drained by trap connections a t the base. Because heating with steam or oil creates a uniform temperature throughout the charge, it is necessary to provide mechanical agitation for charges which are not homogeneous. I n the ammonolysis of aromatic
27'6
INDUSTRIAL AND ENGINEERING CHEMISTRY
halides, such as p-nitrochlorobenzene, the denser molten aromatic compound would, in the absence of mechanical agitation, settle out a t the base with the lighter aqueous ammonia above it. Conversion to amine would then take place only a t the interface of the two layers. I n the ammonolysis of compounds which are difficult to wet out and which are converted only a t high temperatures, it is advisable to employ horizontal autoclaves. Such systems provide the necessary freeboard with a much smaller distance between the charge level and the top of the vessel. Such
Vol. 25, No. 3
removing the unconverted p-nitrochlorobenzene, (2) treating or removing secondary amines, or (3) removing traces of iron or other insoluble impurities which in discontinuous operations can readily be accomplished by filtration. Experience has demonstrated that, in cooling hot suspensions of p-nitroaniline, the coils become coated with the solid amine and their heat transfer efficiency becomes low. The product from such an operation has a brownish cast and in a highly competitive market would undoubtedly encounter serious sales resistance. I n Figure 3 is shown a pressure system designed by Aylsworth (8) for the synthesis of phenol from chlorobenzene which may be adapted to the preparation of aniline from chlorobenzene. According to Grebe (4) the continuous preparation of aniline may be carried out in copper-lined autoclaves (Figure 4) of relatively small diameter, which are connected in series. When liquid amines, such as aniline, are being prepared, the equipment of Aylsworth and Grebe can advantageously be employed. The products of reaction are led from the pressure system to a series of stills or other gas-tight vessels wherein the reaction mass is given a preliminary treatment to separate the amine from the aqueous portion of the charge. The crude aniline or other liquid amine is then purified by distillation to meet technical specifications. Grebe's a p p a r a t u s provides a practical FIGURE3. PRESSURE SYSTEM FOR CONTINUOUS PREPARATION l 3 method for k e e p i n g a OF LIQUID AMINES r e g u l a t e d quantity of horizontal vessels are provided with a number of rotating dissolved copper in- the splash arms which wash any suspended material from the aminating system. It is top of the autoclave. This type of vessel is particularly known that, in the amsuitable for the conversion of 2-chloroanthraquinone. I n monolysis of compounds vertical pressure vessels it is therefore necessary to use a containing a h a 1o g e n sleeve and turbine agitator which drags the 2-chloroanthra- substituent attached to an otherwise unsubstiquinone down into the aqueous ammonia. tuted phenyl nucleus, a TUBULAR PRESSURE SYSTEMS copper catalyst is necesFOR A tubular or pipe pressure system is often used to carry out sary. The action of am- FIGURE 5. PRESSURE SYSTEM OF ETHYLENE DIthe amination. The seamless steel tubing that is used for m o n i a and ammonium PREPARATION AMINE such construction is capable of withstanding pressures up to salts on this e x c e s s of 1000 atmospheres. Such a system is particularly useful c o p p e r furnishes what where exceptionally high pressures are encountered, or soluble copper is necessary in addition t o that originally inwhere continuous operations are practicable. A further corporated with the reactants. This expedient must be inadvantage rests in the fact that the pressure coils comprising terpreted as being essentially a practical measure which is enthe reaction system contain only a relatively small quantity of tirely suitable in plants or operations where the products of material in process. Such a system may be subdivided into a hydrolysis have a value comparable to the products of amnumber of units, each immersed in an oil or metal bath con- monolysis. By employing metallic copper instead of soluble trolled a t the desired temperature. Pressure gages and copper salts, a more economical method of preparing the safety diaphragms are placed on each unit of the system to amine is obviously available. Curme and Lommen (3) have developed an interesting insure safe operations. pressure system for the continuous conversion of ethylene dichloride to ethylene diamine. This compact assembly is shown diagrammatically in Figure 5. I n this system a n effort is made t o combine the reaction system and the ammonia recovery apparatus into a compact unit. It is questionable whether such an amalgamation of operations is FIGURE4. STEELAUTOCLAVE WITH IKSULATED COPPER practicable except in cases where amination takes place most LINER readily. I n the preparation of ethylene diamine or dinitroA tubular pressure system devised by Shannon (6) for the aniline, the operating temperature is only about 110' C. (230" F.), corresponding to an internal pressure of about manufacture of p-nitroaniline is shown in Figure 2. I n practice such an operating system suffers several handi- 140 pounds per square inch. I n the production of such caps. The manufacture of p-nitroaniline is beset with the compounds, even appreciable fluctuations in the strength of usual side reactions encountered in ammonolysis-viz., the the aqueous ammonia do not seriously affect the efficiency of formation of hydroxy compounds and secondary amines. I n amination, particularly when a large excess of ammonia is addition it has been found difficult to secure a complete provided. conversion of all of the halogeno compound. Shannon's AUXILIARYHIGH-PRESSURE EQUIPMENT apparatus, despite its apparent simplicity, would compare The design and selection of proper auxiliary equipment for unfavorably with discontinuous systems because no method is provided for (1) recovering the combined ammonia or high-pressure reactions is as essential as choosing the pressure I
March, 1933
INDUSTRIAL AND ENGINEERING CHEMISTRY
equipment itself. The successful operation of the whole system depends on the proper functioning of such accessories. I n well-organized plants, thermoelectric equipment is employed to regulate the temperature. Experience has shown that such devices can be relied upon to give satisfactory service. Asbestos and lead gaskets have been found most satisfactory for sealing flanged connections in the pressure system. The metal gasket is usually employed for joints which are opened only infrequently. Discharge lines from the autoclaves are equipped CUStomarily with two heavy-duty steel valves, one of which is a globe and the other a gate valve. The former is placed adjacent to the autoclave to hold the pressure and is supplied with cut asbestos gaskets which are renewed for each run. The gate valve has many important uses in technical operations, the most obvious being the feasibility of cutting out individual autoclaves from the rest of the system. I n plant operations it is not advisable to depend on safety or relief valves to release extraordinary pressures. It has been found best to employ a metal diaphragm supported between two steel flanges, these fittings being part of a pipe line leading directly from the autoclave. Such diaphragms
217
should be accurately tested under precise conditions to vouchsafe rupture a t definite pressures. Tin and nickel sheets have proved satisfactory for autoclaves containing ammonia. It is desirable to protect the face of the diaphragm next to the reaction vapors with a thin sheet of lead or asbestos. Some engineers approve of placing a pop valve after the diaphragm, which will reseat after the excessive pressure has been dissipated. The pop valve is always set to blow about 50 pounds below the bursting point of the diaphragm. Thus, a rupture in the diaphragm is sure to be followed by the opening of the relief valve, which has been completely protected from the corrosive vapors of the autoclave. With an arrangement of this character, it is usually feasible to complete the run, and then replace the diaphragm and overhaul the pop valve. The possibility of effecting material savings by such an arrangement is obvious. LITERATURE CITED (1) Am. SOC.Mech. Eng., Boiler Construction Code, Sect. VIII, Par. U-20 (1932). (2) Aylsworth, U. S. Patent 1,213,143 (1917). (3) Curnie and Lommen, U. S. Patent 1,832,534 (1931). (4) Grebe, U. S. Patent 1,814,796 (1931). (5) Shannon, British Patent 212,970 (1922).
..*.*
V.
Control of Ammonia Recovery System
PROPERTIES OF AQUEOUS HE successful industrial The successful industrial preparation of AMMONIA preparation of amines by amines by ammonolysis of organic halides, the ammonolysis of aroBefore d e s c r i b i n g some of phenols, and sulfonic acids depends largely on matic halides, phenols, and sulthe types of ammonia recovery the proper functioning of the ammonia system. fonic acids depends largely upon e q u i p m e n t , it is desirable to It is essential that the excess of aqueous ammonia the proper f u n c t i o n i n g of the review some of the properties of ammonia system. This matter which is used be recovered and returned to the aqueous ammonia. G a s e o u s derives its i m p o r t a n c e f r o m ammonia is absorbed by water reaction system at a constant and optimum t h e f a c t t h a t 5 to 1.5 m o l e s with great avidity and, as can strength. I n properly conducted operations, the of ammonia are employed per be seen from the data in Table recovery is efficiently and almost automatically m o l e of aromatic c o m p o u n d I, considerable heat is developed carried out by the choice of suitable equipment undergoing treatment. A large d u r i n g t h e process. T h e c a p i t a l i n v e s t m e n t is thereand the installation of mechanically controlled quantity of ammonia gas that fore involved. It is essential, can be d i s s o l v e d in water is den ices. f u r t h e r m o r e , that the excess affected by the temperature and Problems involved in the recocery of ammonia ammonia be recovered and depressure of the aqueous solution. are ( I ) removal of the heat of solution, and (2) livered to the reaction system a t The equilibrium: controlling the solubility by regulating the tema constant and optimum XHa (gaseous) e strength. This is a b s o l u t e l y perature, pressure, and concentration of the NHa (dissolved) necessary to insure a maximum aqueous ammonia in the absorption system. shifts to the left with increasconversion to amine of uniform q u a l i t y . I n p r o p e r l y coning t e m p e r a t u r e , and to the ducted operations, the recovery is efficiently and almost auto- right with increasing pressure. These relationships are matically carried out. This is accomplished by the choice of brought out in Tables I1 and 111. suitable equipment and the installation of mechanically controlled devices. TABLEI. ABSORPTIOXOF GASEOUS AMMONIABY WATER(4) The type of apparatus that may be used for the recovery --HE.~T O F SOLUTION OF 1 K Q “3Gaseous (15’ c. and of the excess of ammonia may be varied within wide limits. 1 atin.) calcd. with x ”3 IN SOLN Calcd. Liquid dissolving heat of I N WHICHNHs The physical properties of the amine and the compound from from P, t , x , Is DISSOLVED (13’ C ) liquid NH3 relationshi pa which it is derived, along with the means utilized to effect the Calories per kilogram % .. separation of the amine, are the principal guides in the selec0 193 493 480 5 483 183 464 tion of the proper apparatus. 10 471 171 450 15 458 158 I n the ammonolysis of chlorobenzene there is no danger of 436 144 422 any of the reaction products solidifying in the vapor lines 119 410 113 397 leading from the autoclaves to the recovery system. This is 97 385 ._ 374 true also in the preparation of 2-aminoanthraquinone. I n the 59 364 preparation of p-nitroaniline, however, there is danger of 39 354 19 .. unconverted p-nitrochlorobenzene solidifying in and stopping up the gas lines if the vapors containing the halogeno compound are excessively precooled in a tubular system before From these data it is obvious that the absorption system for entering the absorbers. the recovery of ammonia should be able t o withstand moder-
T
