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PREPARATION OF IODINE PENTOXtDE REAGENT
The iodine pentoxide reagent must completely oxidize low concentrations of carbon monoxide a t comparatively low temperatures in the presence of about 75% hydrogen and in addition must maintain its activity for a long period. The following procedure, using reagent-grade chemicals, gives a reagent that has an active life of 30 to 4 0 days. Seventy grams of calcined, crushed insulating brick (Armitrong A-25; -9 +14 mesh) are added to a solution containing 100 grams of iodine pentoxide and 4 grams of vanadium pentoxide. The mixture is evaporated to dryness over a steam bath, with frequent stirring during the latter part of the evaporation. This material is then oven-dried for several hours a t 125’ to 130” C. The oxidation tube, which holds about 50 prams, is filled with the oven-dried reagent and placed in the activation train. Activation is accomplished by passing purified air through the sample ns the temperature is gradually raised to 220’ C. Tlie air is purified by passage through three scrubbers containing concentiated sulfuric acid, solid potassium hydroxide pellets? and phosphorus pentoxide, respectively. The reagent is maintained a t 220’ C. for about 8 hours and is allowed to cool in a current of purified air, after which it is ready for use or for temporary *torage. The tube must be tightly sealed during storage. The activated reagent has a bright orange color and the spent reagent a brown color. The spent reagent is prepared for re-use by suspending it in water, evaporating to dryness, oven-drying, and iictivating as previously described. APPLICATION TO PLANT CONTROL
Two complete analyzers are required to serve the two production trains in the TVA ammonia plant. Figure 3 shows the control laboratory installation of analyzers (except for control desk and recorders) for the determination of low concentrations of carbon dioxide, carbon monoxide, or mixtures of the two in the purified hydrogen-nitrogen mixture from one production train. Z t the left is the constant-terriperature bath containing the absorption-conductivity cells. To the right, a t the end of the liath, are the preparation trains. The short (front) train is used in the determination of carbon dioxide in the pas from the caustic vxubber, sample point PS-17 (see flow sheet in 7 for specified sample points), and the second train is used to determine total c.urhon dioxide and carhot1 nionouide i n the makr-up gai to the
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synthesis system, sample point SS-19. The third and fourth trains are used in the determination of carbon monoxide in the gas leaving the copper scrubbers, sample point PS-15; while one train is in service, the other is kept in stand-by condition. This system of analytical control has been in operation for more than 2 years in the TVA ammonia plant and has proved very effective in preventing poisoning of the synthesis catalyst by oxides of carbon. ACKNOWLEDGMENT
The authors express their appreciation to the staR of the control laboratory, especially to R. Bowen Howard, Jr., for the cooperation received in the installation and initial operation of these analyzers. LITERATURE CITED
(1) Am. Gas. Assoc., “Gas Chemists’ Handbook”, pp. 289-95, New
York, Chemical Publishing Co., 1929. (2) Baldewyns, Joseph, Congr. pharm. Lidge, 1935, 183-5 (1934). (31 Bech. A.. Ann. huo. vubl. i n d . sociale. 1933. 376-80. (4) Berger, L. B., a-Gd‘Schrenk, H. H:, U. S. Bur. Mines, Tech. Paper 582 (1938). (5) Brown, E. H., I X D . ENG.CHEM., ANAL. ED., 14, 551 (1942). (6) Brown, E. H., Cline, J. E.. Felger, M. M.. and Howard, R. B., Jr., Ibid., 17, 280 (1945) (7) Brown, E. H., and Felger, M.M., Ibid., 17, 273 (1945). (8) Dely, J. G., private communication. (9) Edell, G. M., ISD.ENG.CHEM.,20,275 (19%). (lo) Graham, J. I., and Winmill, T. F., J. Chem. SOC.,105, 199h2003 (1914). (11) Haldane, J. S., and Graham, J. J., “Methods of Air Bnalysis”. pp. 116-29, London, J. B. Lippincott Co., 1935. (12) Katz, S. H., Reynolds, D. A., Frevert, H. W., and Bloornfield J. J., U. S. Bur. Mines, Tech. Paper 355 (1926). (13) Miller, A. M., and Junkins, J. N., Chem. & M e t . Eng.,50, No. 11. 119-25, 152-5 (1943). (14) ltotnashchenico, T. A., Zavodskayu Lob., 9, 912-13 (1940) Chem. Zentr., 1942, I, 2957. (15) Seidell, J. A., J. IXD. ENG.CHEM.,6, 321-3 (1914). (16) Stnith, A. S., IND. Exo. CHEM.,AXAL.ED.,6, 293-5 (1934). (17) Teague, M. C., J. IND.ENG.CHEM.,12, 964-8 (1920). (18) Tandaveer, F. E., and Gregg, R. C . , IND.ENG.CHEM..AXAL ED., 1, 129-33 (1929). (19) JVhite, E . C., J . Am. Chem. SOC.,50, 2148-54 (1928)
Continuous Determination of Ammonia Activity in Ammoniacal Solutions EARL
H. BROWN, JAMES E. CLINE, MAURICE M. FELGER, AND R. BOWEN HOWARD, JR.
S T H E T V A syiith(8tic :uiniionia platit, an animoniacal “copper solution” (3) is employed for the removal of harmful inipurit,ies, such as carbon inonoxide, carbon dioxidc, and oxygen,
I
from the synthesis gas. The dolutiori contains cupric ammino, cuprous ammino, ammonium, formate, and carbonate ions, as \r.c\ll tis uncombined ammonia. There is a r:tnge of concentratioils of unrunibined nmmouia below which thcb removal of carboil dioxide froin the hynthc gas is inconiplete and above which the loss of aniirionia is excessi\,e during regeneration of the copper solution. The uncombined ammonia is an important factor also iii niaintnining the coppcr complexes necessary for tlic complete rriiioval of carbon monoxide. The concentration of uncombiiird antmonia cannot be calculated accurat,ely from chemical tleterminations of the componeiits in the copper solution, how~ Y ( ’ I ’ . for there are several cquilihrimns involved n-1iic.h have not, yt’t I)(YII rlvtermined prrcisely.
.in empirical formula t)risc’d on five analytical determirintionstotal animonia, formic acid, carbon dioxide, and monovalent and bivalent copper-was employed, prior to the development of the present niethod, t o give a value related to uncombined ammonia for plant control. The utilization of thr. empirical formula had several disadvantages. Values n Ith 110 strong theoretical foundation were obtained, many analytiral determinations were necessaiy, aiid considerable time was required before the results could be reported to the plant operators. This paper describes the drvelopment and application of an instrument that gives rapid and continuous information regarding the unconibined ammonia 111 the coppcr wlution. THEORETICAL CONSIDERATIONS
The thermodynamic activity of ammonia was selected as the function of the uncombined ammonia to hc> tlctcrniined, ticc:iu-e
ANALYTICAL EDITION
May, 1945
28 1
sure is 0.99 ( h ) ] . Using partial pressures and the chosen $randaid state, the following equation resulta:
A method for the automatic, continuous determination of the thermodynamic activity of ammonia in ammoniacal solutions i s based on the linear relationship between ammonia activity and vapor pressure of ammonia over the solution. A constant flow of inert gas is brought to equilibrium with the flowing solution at a given temperature and the concentration of ammonia i n the saturated gas is determined. The ammonia activity is an important factor in maintaining the efficiency of the ammoniacal copper solution used in the TVA ammonia plant for absorbing the oxides of carbon and other harmful impurities from the synthesis gas.
mwo= p / p "
123
where U S H ~is the amriionia activity of the solutioii; p , thc p:wtial pressure of ammonia over the solution; and p o , the partial pressure of animonia over normal ammonium hydroxide at tlit: sanie t,emperature. By means of Equation 2 the activity of aninionia in the copper solution can be determined directly by measurement of the partial pressnrr of ammonia i r i eqllilihriiim ivith the sohition. DESCRIPTION OF APPARATUS
'h basic . design of the apparatns for continuous rcc:ording of the activity is easily riicasurad and is dirt;ct,ly related t o tlir efi'ect of t,he ammonia on any equilibrium of components in the copper solution, The concept of activity was introduced by Le Kandall (8). I n an ideal solution the activity is equal to the concentration, and either can be used for calculating cquilibriuiii constants, partial molal free energiw, or other thermodynamic. functions. I n any solution, ideal or nonideal, at a given t,cniperatnrc the activity of :I c~omponentis clrfinetf by thv rquation: fl
=
f/f"
ill
where u is the activity of the coniporient in d u t i o n ; f , t'he fugacity of t'he component in the vapor phase in equilibrium with the solution; a n d j " , the fugacity of the component in the vapor phase in equilibrium with the standard st,ate. The standard state often is taken to be the pure liquid component. T o simplify the calibration procedure, homever, the ammonia activity in a normal ammonium hydroxide solution was set as unity in this xork. Activity referred to any other standard state can hc rald a t e d from fugacity data. With partial pressures of annnonia less than atniospli(~ric, pressure can be substituted for fugacity in Equation 1 [for ammonia at 1 atmosphere and 25' C., the rat,io of fugarity t o pres-
INERT
GAS
PRESSURE STABILIZER
FLOWMETER
c( sol
ER 'ION
r DILUTE
I- I
TO COPPER
SOLUTION SYSTEM
THERMOSTAT
1
Figure 1. Schematic Didgrdm of Ammonia Activity Analyzer
the ammonia activity i y s1ion.n in Figure I . .i gas, chemically inert to the copper s o l u t i o n , ~ U W Ythrough a pressure stabilizer itnil a floTvmcter at a constant, rate. and hecomes saturated with animonia and other vapor: it, bubbles through the copper solution in a gas saturator imin ,(I in a thermostat. The copper solution flows through the s haturator a t a rate great enough to prevent significant alteration of the composition of the solution by loss of vapors t o the gap strcwn. The saturated gas passes into a,n electrocondiic,tivit!. w11 ( 1 ) where the ammonia is absorbed by dilute acid flowing a t a constant rate. The ammonia content of the g a s affect- the conductivity of the acid, a.hich is niearurcd by a rcwrdinp alt,ernaliiig ciirrrnt Wheatstone l,ritlge (1 ) .
r t gas uwd to carry tlie ainrnonia vapor is purifieti "11consisting of hydrogen, nitrogen, argon, and niet,hane. is used because of its ready availabilit,y in the control laboratory and because, by pressure scrubbing with the copprr solution, it has been frpetl o f impurities n-hich react with thtx sollition. The piston-type pressure stsbilizer used in this byork t,o iiiailitain a co~istantflow of inert gas operates niore moothly and reliably than the usual type, which allo~vs#a* to escape through a constant head of liquid. The piston of the stabilizer (Figure 2 ) fits into the cylinder with a clearaim of about 0.075 nim. (0.003 inch) and is supported by the pressure of the gas n.ithin the chamber; excess gas leaks out betxet~n Except for slight frictional losses, the pr the chamber, under equilibrium conditio of the piston dividcd by the horizontal c chamber. When the flow of incoming gas varies, the vertical movement of the pist,oii alters the resistance to pay leakiLge between the piston and cylinder and automatically stabilizes the pressure within the chamber. Because of piston inertia.. a ra.pid change in gas flon. will cause a momentary fluctuation in prezsure until the pist.on reaches its new equilibrium position. The shoulder on t,hr piston wrvei; to prevent its tlropping Iolv enough in the cylinder to interfert: with thc gab flow. Grooves may be placed in the piston to increaae the rate of gas leakage or to enabltl the leaking gas to r o t a t e t h e piston. L u b r i c a t i o n of t h e piston with graphite improves the operation of the Ytahilizer. The piston itnd cylinder should be made of the 5ame metal, such as brass, to avoid variations in the fit due to differer!ce of thermal expansion. The glass funnel connected to a vent collects the excess gas leaking past the piston. The pressure CYLINDER 4 stabilizer, used in comGAS CHAMBER bination with a capillary flowmeter, proved satisfactory in maintaining a constant flow of inert gas through the apparatus. Figure 2. Pressure Stabilizer
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The function of the gas saturator is to bring the gas stream and the flowing copper solution into contact long enough to establish a reproducible approach to equilibrium. The saturator must offer a constant resistance to the gas flow, in order that a constant rate of gas flow can be maintained. The type of gas saturator used is shown in Figure 3. The copper solution flows into the apparatus a t the inlet, A Some of the copper solution constantly flows from B to an overflow tube that is set a t a predetermined height to maintain a constant head. The copper solution flows through stopcock SI a t about 20 ml. per minute and is brought to the thermostat temperature in coil C. The solution enters the main body, D, of the saturator near the middle and flows out from the bottom through outlet E . The copper solution from B and E is returned to the plant regeneration system. The inert gas enters a t F a t about 100 ml. per minute and passes through stopcock Sz, through temperature stabilization coil G, and into the bottom of D. The gas becomes saturated with ammonia as i t bubbles through the solution, and then passes through stopcock Saand tube H to the apparatus for determination of ammonia vapor. In an emergency the operator may close both Szand Sato avoid contamination of the electroconductivity cell connected to outlet H . The stopcocks are all above the level of the thermostat liquid to simplify the operation of the apparatus and to avoid danger of flooding the electroronductivitv cell n ith copper solution.
Figure 4.
Activity of Ammonia in Ammonium Hydroxide Solutions
ing stopcock SI to the proper position. Using Equation 2 and ammonia vapor pressure data of Wilson (6) the activities of animonium hydroxide solutions of normalities 0 to 7 were calculated a t 26.7” and 32.2” C. and are plotted in Figure 4. Up to an ammonia activity of 3, the maximum found in the copper solution, there is no significant temperature effect on the ratio of activity to concentration. With this method of calibration the actual temperature of the thermostat (about 30” C.) is not a critical factor, provided the temperature is the same for both calibration and operation. Activity measurements in the range 0 t o 3 are reproducible to within 10.05 with the apparatus. APPLICATION
The apparatus for continuous determination of ammonia activity has been in operation for over 15 months in the ammonia plant control laboratory. The device is automatic and requires very little maintenance. The plant operators use the results to control closely the addition of ammonia to the copper solution. The ammonia activity is an important factor in maintaining the copper solution at peak efficiency for scrubbing carbon monoxide and carbon dioxide from the synthesis gas. By keeping the ammonia activity close to the optimum value (2.5 in the TVA ammonia plant) excessive ammonia addition with resultant high loss of ammonia in the regeneration step is avoided. ACKNOWLEDGMENT Figure 3.
Gas Saturator
The electroconductivity cell is the same as that described for the determination of carbon monoxide and carbon dioxide (1). The gas from the saturator contains 4 to 5% ammonia, which is absorbed by 0.1 iV sul.furic aFid flowing a t the rate of 15 ml. per minute. The ammonia activity is indicated on a Leeds & Northrup recording alternating current JJ7heatstone bridge. The zero point of the apparatus can be set by turning stopcocks 8 2 and Sa(Figure 3) to allow the inert gas t? flow through byrpass J to the electroconductlvity cell without picking up ammonia from the copper solution. The recorder is calibrated directly in terms of ammonia activity. For calibration, solutions of ammonium hydroxide are allowed to flow through the calibration solution inlet, I , by turn-
The authors are grateful to J. G. Dely, consultant to the TYA, E. J. O’Brien, superintendent of the TVA ammonia plant, and J. R. Hall, supervisor of the control laboratory, for their cooperation and encouragement in this work. LITERATURE CITED
(1) Brown, E. H., and Felger, M. M., I N D .ENG.CHEM.,ANALE D . , 17, 277 (1945). (2) Lewis, G. N., and Randall, M., “Thermodynamics”, pp. 254-77, New York, McGraw-Hill Book Co., 1923. (3) Miller, A. M., and Junkins, J. N., Chem. & Met. Eng., 50, No. 11, 119-25,152-5 (1943). (4) Newton, R., IND.ENG.CHEM.,27, 302-6 (1935). (5) Perry, J. H., “Chemical Engineers’ Handbook”, p. 352, New York, McGraw-Hill Book Co., 1934.
