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Baker, D. R., Industry and Power, 56, No. 3, 94-7; No. 4 , 86-8 (September and October 1950). (4) Baker, D. R., paper presented before 1951 Midwest Power Conference, April 1951. (5) Blohm, C. L., and Frazier, H. D., Oil Gas J . , 48, No. 45, 72-4 (3)
Vol. 45, No. 7
Technical Association of Pulp and Paper Industry, Xew York, "TAPPI Standards." (11) Wise, L. E., Murphy, M., and D'Addieco, A. A , , Paper Trade J . , (10)
122, NO. 2 , 35-43 (1946). (12)
Wise, L. E., and Ratliff, E. K., Anal. Chem., 19,469-62 (1947).
(1950).
(6) HBgglund, E., and Lange, P. W., Makromol. Chent., 6 , Staudinger
Festband, 280-91 (March 1951). (7) Heuser, E., Shema, B. F., Shockley, W., b p l i n g , J. W., and McCoy, J. F., Arch. Biochem., 21, NO. 2,343-50 (April 1949). (8) Luthardt, W., Holzforschung, 3, No. 4, 117-21 (1949). (9) Moberg, A. R., Calif. Oil World und Petroleum I n d . , second issue, 34, No. 14 (July 1941).
f o r review July 3, 1962. RECEIVED ACCEPTED March 9, 1953. Presented before the Division of Water, Sewage, and Sanitation Chemistry, SyrnDosium on K a t e r Conditioning for Use i n Cooling Towers, a t the 121st CHEMICAL SOCIETY,Milwaukee, Wis. This wurk Meeting of the AMERICAN represents in part the results of a cooperat.ive project of the California Redwood Association kt The Instirute of Paper Chemistrx, and is published with the approval of the association.
Self-Heating of Hydrogen Peroxide Storage Vessels E. S. SHANLEY Buffalo Electro-Chemical Co., Inc., Division of Food Machinery 6% Chemical Corp., Buffalo 7 , N. Y.
0
VER the course of many years, hydrogen peroxide has been
stored in hundreds of locations in quantities from a few to many thousands of gallons and at concentrations up to 90%. This experience has been almost free from untoward incident. However, hydrogen peroxide is an energy-rich material, and the constantly increasing interest in stronger solutions makes it advisable to gather all pertinent information about the behavior of this chemical in storage vessels. The first part of this paper is a theoretical study of the heat balance in hydrogen peroxide storage vessels; the latter part contains practical recommendations on the handling and storage of this material. The methods used for handling the heat balance calculations should be equally valid for predicting the storage behavior of other energy-rich materials. BEHAVIOR OF HYDROGEN PEROXIDE SOLUTIONS DURING STORAGE
All hydrogen peroxide solutions decompose a t a finite rate, and this decomposition releases a relatively large amount of heat (ca. 1200 B.t.u. for each pound of hydrogen peroxide consumed). Consequently, every hydrogen peroxide storage vessel must continually transfer heat to its surroundings, a corollary lbeing t h a t such storage vessels are always warmer than the surroundings. The magnitude of this temperature difference is ,established by the balance between heat released by decomposition and heat transferred t o the atmosphere. The actual mechanism, of course, involves a gradual temperature rise in the contents of the vessel until the rate of heat transfer t o the surroundings becomes equal t o the rate of heat liberation by decomposition. However, the rate of heat transfer t o the atmosphere increases only linearly with temperature, while the rate of decomposition increases exponentially. As a consequence, for any particular storage vessel there exists a critical decomposition rate beyond which the rate of heat liberation will always exceed the rate a t which heat can be transferred to the surroundings. Once a storage vessel passes the critical condition, a self-accelerating decomposition will set in which, unless checked, may reach a very high rate. As hydrogen peroxide solutions are nearly impossible to detonate (3) and vapor explosions are possible only over very strong solutions ( I ) , the primary hazard is due only to pressure rise in and possible rupture of the container. T h e actual outcome of sustained self-heating will depend in large measure upon the original concentration of the peroxide solution. Any solution stronger than about 12% hydrogen peroxide decomposing adiabatically in an open vessel can heat itself
t o about 100" C. Solutions weaker than 65% mossess insufficient energy t o evaporate all of the water present and formed by decomposition, so t h a t the temperature cannot esceed the boiling point. Adiabatic decomposition of stronger solutions leads to far higher temperatures-for example, 750" C. in the case of a 90% hydrogen peroxide solution. TlXiams, Satterfield, and Isbin ( 5 ) have recently published detailed calculations on these adiabatic decomposition temperatures. The possible behavior of hydrogen peroxide in a storage vessel can be visualized as follows. Entering storage a t or below ambient temperature, the solution will spontaneously heat itself until the rate of heat transfer to the surroundings equals the rate of heat liberation by decomposition. I n normal circumstances, this rise will be very small, of the order of l o C. or less. However, the tank contents may become contaminated so that the decomposition rate is increased. Depending upon the circumstances, a new equilibrium temperature may be reached, or the temperature and decomposition rate may increase a t an accelerating rate. At first, only oxygen is released, but approaching 100" C. the heat energy is available to vaporize w t e r , so that the reaction climaxeis with the production of large volumes of steam and oxygen. At t h e same time, any vents in the container are apt to become choked with liquid thrown up by the boiling action. At this point, the container is likely to fail, resulting in all of the effects to be expected upon rupture of a pressure vessel. FACTORS IZTVOLVED IN SELF-HEATING OF STOR4GE TANKS
The self-heating rate of a peroxide solution under any given circumstances will be governed by the balance betyeen heat liberated by decomposition and heat lost to the surroundings. Quantitative estimates of the magnitude of these factors are presented below. The heat of deconiposition of h j drogen HEATLIBERATIOX. peroxide has been taken as 1230 B.t.u. per pound. The decomposition rate, hence the rate of heat liberation, for any given peroxide solution in a given state of purity or contamination is primarily a function of the temperature. The studies of Schumb ( 2 ) as well as studies in this laboratory indicate that over a range of temperatures, concentrations, and decomposition rates, the rate increases about 2.2- to 2.4-fold for each 10" C. rise in temperature. Accordingly, the average value of 2.3 has been used to calculate decomposition rates a t various temperatures for various assumed rates a t 25" C. The assumed 25" C. rates range from 1 yo loss per year, acceptable in commercial practice, to 50 and 100% loss per year which might be observed a t 25" C. in the case of
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1953
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40 50 TEMPERATURE, O C .
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Figure 1. Heat Balance i n Bare Aluminum Tank Filled with 90% Hydrogen Peroxide
---
Heat liberated i n tank Heat loss from tank Ambient temperature 25' C.
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102
90
Figure 2.
30
40 50 TEMPERATURE, 'C.
60
70
Heat Balance i n 25,000-Gallon Tank Filled with 90% Hydrogen Peroxide
-- - Heat liberated i n tank Heat loss from tank
HEAT Loss. Because all peroxide solutions decompose at a finite rate, it is essential to dissipate heat in order to avoid overheating. The ability of a container t o dissipate heat depends upon the exposed surface, while the amount of heat to be dissipated depends upon the tank volume. The ratio of exposed surface per unit volume is listed in Table I for certain types of hydrogen peroxide containers. Heat liberated to the atmosphere is readily estimated for various temperatures by means of published data ( 4 ) and the hr) A T. equation: B.t.u. per hour = (hc hr, the radiated heat coefficient, is very small for aluminum, so that the radiation loss has been assumed t o be nil for the purpose of these calculations. hc, the convection coefficient, is approximately the same for, vertical plates and tubes and for large horizontal cylinders. Values for hc and for heat loss are presented in Table I1 and are plotted in Figures 1 to 4 for comparison with ' the values for heat liberation. RATIOS OF COMMO'NLY USEDHYDROGEN PEROXIDE STORAGE VESSELS TABLE I. SURFACE-VOLUME I n using these diagrams it is Capacity, Total Surface Available for S / V Ratio, well t o remember that the conU.S. Dimensions, Length, Surface Heat Transfer, 9s. Feet/ Kind of Tank Gallons Diameter Feet Sq. Fee; Sq. Feet Cu. Foot vection coefficient, hc, is only an HlOz drum 30 1.42 2.25 13.2 10 (sides only) 2.5 average value for still air. T h e Tank car 4,000 5 26 450 450 0 84 Tank car 8,000 6.5 30 682 682 0.63 heat transfer coefficient in a Storage tank, horireal case may be severalfold zontal 5,000 6.5 19 455 455 0.68 Storage tank, ver800 (sides only) 0.24 larger if there is air movement. tical 25,000 17 15 1250 Storage tanka, verThe rate of heat transfer may tical 60,000 20 21.5 1960 1330 (sides only) 0.20 become much lower if t h e Storage tankn, vertical 500,000 44 42.5 9040 5900 (sides only) 0.09 tank is in a confined space 5 Hypothetical tank size. and the ambient temperature severely contaminated solutions. (However, gross contamination-for example, with permanganate, hypochlorite solutions, etc.-may cause almost immediate decomposition of hydrogen peroxide solutions. ) The above decomposition rates are expressed in terms of the fraction of the available oxygen which would be lost in one year a t the indicated rate. Figures 1 to 4 show the relation between calculated decomposition rate and temperature, each decomposition rate having been translated into corresponding values for rate of heat liberation, B.t.u. per hour. I n these calculations, no account has been taken of the peroxide used up during the heating process. This amounts to assuming a zero-order reaction, which is probably not the case. However, the error so introduced is not serious when the concentration change is small. This point is discussed in more detail below.
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Figure 3. Heat Balance in Bare Aluminum Tank Filled with 50% Hydrogen Peroxide
- - - Heat liberated i n tank Heat from tank C. Ambient temperature loss
TABLE11. HEATLoss
FROXI
AT
hc
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72 50
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22 11 0
B.t.u./Horir/ Sq. Foot I43 81
0.75 0.71
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0.50
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40 50 TEMPERATURE, OC.
60
70
Heat Balance i n 3000-Gallon Tank Filled w i t h 50% Hydrogen Peroxide
- - - Heat liberated i n tank from tank Heat loss
A L U A ~ N USURFACES M
ToC.
28
Figure 4.
25'
(Ambient temperature 25' C.)
75 53 47 36 25
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RITE OF SELF-HE~TING. Taking the case of 90% hydrogen peroxide, for example, Figure 1 shows the rate of heat, release a t every temperature for a variety of 25" C. decomposition rates. For any one of these, the average rate of heat release for the 5' C. interval between 25" and 30" C. and the average rate of heat dissipation for this temperature interval are readily estimatcd from the curve. The difference betveen these two quantities is the heat available t o warm the solu'tion. If the specific heat of the solution is known, the average rate of temperature rise and total time for 5" C. rise can be calculated. The process can then be repeated for the next 5" C. interval. The time-temperature curves (Figures 5 and 6 ) have been constructed in this way. For these calculations the specific heat of 90% hydrogen peroxide has been taken as 0.68 and that of the 50% solution as 0.81. The calculations indicated above make no allowance for the amount of peroxide used up in the heating process. This is equivalent t o assuming that the reaction is zero order, while the actual reaction is probably nearer first order. I n the case of fastheating tanks the concentration changes are s7malland no appreciable error is introduced. The assumption is least valid for very
slow-heating solutions, which finally undergo Iargcr changes in concentrations. Consequently, Figures 5 and 6 are to be regarded as liniit,ing cases, reasonably valid for fast-heating tanks, but indicating faster than actual rates for slow-heating tanks. From the same data used in setting up the curves in Figures 5 and 6 one can estimate the total amount of peroxide used up in the self-heating process. Table I11 contains examples.
nIscussioN
OF RESULTS
The interactions among decomposition rate, ratio of surface to volume (tank size), and temperature can be readily visualized by the use of Figures 1t o 4. For example, Figure 2 shows that 90y0 hydrogen peroxide in a 25,000-gallon tank, largest of present-day containers, undergoes only very slight heating a t the "normal" decomposition rate of about 1% per year. If the decomposition rate reaches 5% per year a t 25" C., the "heat liberation" line intersects the "heat loss" curve for 25' C. ambient a t about 30" C., indicating that the solution will come to
TABLE111. EXAMPLES O F COSCESTR4TIOII' CHANGE D U R I K G SELF-HEATIXG OF HYDROGEN PEROXIPE Tank Size, U. S. Gallons
Orig. RzOz Concn., %
Decomposition Hours t o Rate, %/Year 80" C.
Calculated for adiabatic decomposition.
Approx. € 1 0 Concn. at 800 C.
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Decompn. Rate a t 25O C., %/Year 500 50 50 25
SAFETYPRECAUTIONS FOR HYP E R O X I D E STORlGE VESSELS. Commercial hydrogen peroxide solutions are tested be0.6 fore shipment to ensure that t h e decomposition rate is extremely low. I n order to maintain this condition, it is necessary to use proper storage vessels and to avoid all contamination. Peroxide tanks should be located so as to permit free movement of the surrounding air. Heat dissipation is necessary for the safety of any peroxide tank. Insulation of peroxide storage vessels is highly undesirable. There is a maximum safe tank size for any given peroxide solution a t a given ambient temperature. Present practice with 5000gallon and even with 25,000-gallon tanks allows a reasonable margin of safety for tanks in temperate climates where there is free circulation of the surrounding air. Care should be taken regarding the design of storage areas for strong peroxide in the tropics or in confined places.
Sq. Foot Tank Surface/ Cu. Foot Capacity 0 2 0 2 10
equilibrium after self-heating itself about 5" C. If this same vessel and solution were heated by external means t o any temperature below about 65" C., it would spontaneously cool back to 30" C., since the rate of heat loss from the tank is higher than the predicted rate of heat liberation throughout this range. At 65" C. there is a metastable equilibrium point, and above this temperature self-accelerating decomposition will occur. Figure 2 also shows that if the solution in this tank were t o decompose a t a rate exceeding 10% per year at 25' C., the heat loss from the tank would never equal the heat liberated by decomposition, and a selfaccelerating decomposition would set in a t once. The allowable 25" C. decomposition rate is very much dependent upon the ambient temperature. Again taking the case of 90% hydrogen peroxide in a 25,000-gallon tank (Figure 2 ) , a solution decomposing a t t h e rate of 2.5% per year is safe a t 25" C. ambient, but will probably overheat and erupt if kept a t 40" C. ambient. This should be kept in mind if large peroxide tanks are to be used in the tropics or in a confined space like a ship's hold. -4s might be expected, there is considerably larger margin of safety in the case of 50% hydrogen peroxide solutions. In a 25,000-gallon tank, the rate of decomposition must exceed 25% per year before susI tained self-heating can occur. I n a typical consumer's tank of 5000Figure 6. gallon capacity, 50% hydrogen peroxide will overheat dangerously Curve only if the decomposition rate a t 1 2 25' C. approaches 100% per year. I n c o n t r a s t , c o m m e r c i a l 50% hydrogen peroxide ordinarily decomposes at the rate of less than 1% per year. Hydrogen peroxide solutions may warm themselves as much as 15" C. and still level off in temperature. If the spontaneous rise exceeds 15" C.. i t will probably continue indefinitely unless checked by external means. A rapid rise in temperature, say 1 " or 2" C. per hour, while the solution is relatively cool (30" to 35' C.) indicates that eruption
is sure t o occur unless checked by external means. Drastic action is called for in such a case. If a time-temperature record is available for a self-heating tank, the curve can be extrapolated into the future by the use of the temperature coefficient 2.3-that is, the time for the next 10" C. rise will be 1/2.3 times as long as required for the preceding 10" C. interval. This estimate ignores the heat loss completely, but is reasonably accurate for fast-heating tanks. It will overestimate the heating rate for slow-
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TIME, HOURS
Self-Heating Rate for 50% Hydrogen Peroxide Decompn. Rate a t 25O C., %/Year 1000 100
Sq. Foot Tank Surface/ Cu. Foot Capacity 07 0.7
It may be advisable to keep time-temperature records for large hydrogen peroxide tanks, especially those containing solutions stronger than 50% hydrogen peroxide. In this way any increase in the decomposition rate can be detected far in advance of any hazard, so that appropriate action can be taken. It is not possible t o set a hard and fast rule about permissible temperature rise or rate of rise, especially in view of the complications caused by daily fluctuations in ambient temperature. However, a tem-
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perature more than 2' or 3' above the recent maximum amtemperature curve into the future by the methods eeiggested in bient, or a rapid rise in temperature (0.5" C. or more per hour), this report, it is well to bear in mind the several approximations should serve as a warning. made in these calculations. Most of these approximations overPROCEDURES FOR DEALIKG WITH SELF-HEATING HYDROGEX estimate the hazard and underestimate the time before eruption. PEROXIDE TANKS.As shown in Figures 5 and 6, long delays will However, a t least two factors may operate in the opposite direcusually occur between the inception of rapid decomposition and tion-possible breakdown of stabilizers a8 the reaction proceeds the attainment of excessive temperatures. This delay allows time and the formation of a blanket of gas bubbles on the interior surfor extended efforts to control the reaction. faces, which might reduce heat transfer. In the early stages of elf-heating, the decomposition can be curbed by the addition of stabilizers or by cooling with water. It LITERATURE CITED is advisable t o stock packages of e6ergency stabilizers a t large (1) Satterfield, C . N.,K a m n a g h , G. AI., and Resuick, H., ISD. ESQ. storage locations. External cooling with water sprays may dissiCHEX.,43,2507 (1951). pate heat a t least ten times as fast as air convection, with obvious (2) Schumb, W C., Ibid., 41,992 (1949). advantages in bringing a self-heating tank under control. In(3) Shanley, E. S., and Greenspan, F. P., Ibid.. 39, 1536 (1947). ternal cooling n-ith clean water, thus diluting the peroxide, is also (4) Stoever, H. J., "Xpplied Heat Transmission," K e x York, &ICGraw-Hill Book Co.. 1941. a very effective means of control. ( 5 ) Williams, G. C., Satterfieid, C . N., and Isbin, E. S., J . Am. Rocket While attempting to control a self-heating tank, a careful timeSoc., 22, No. 2, 7 0 (1952). temperature record should be kept to provide a running record of RECEIVED f o r review December 20, 1952. the effectiveness of the control means. I n projecting the timeA C C E P T E D April 15, 1953.
Granular Adsorbents for Sugar
Refining SOME PHYSICAL PROPERTIES OF BONE CHAR AND SYNTHAD ELLIOTT P. BA4RRETT Baugh and Sons Co., Philadelphia, Pa., and Mellon I n s t i t u t e , Pittsburgh, P a .
AIRIISON JONNARD1 AND J. H. RIESSMER Mellon Institute, Pittsburgh, P a .
T
HE increasingly general use of Synthad (a synthetic adsorbent manufactured by Baugh and Sons Co.. Philadelphia, Pa.) as a granular adsorbent in sugar refining, makes it desirable to report results of comparisons between three of its important physical properties and those of bone char, to which no reference has been made in earlier publications ( 1 , 2). The heat of wetting is important because it causes a rise in temperature when the sugar liquors come in contact with freshly regenerated adsorbents. Thermal conductivity and specific heat arc of obvious importance in connection with the thermal regeneration of the products. Because Synthad is used in the same way as bone char and in the same equipment, obtaining strictly comparable results for the two adsorbents, rather than absolute accuracy, was stressed in making the measurements. HEAT OF WETTING
The calorimeter was a cylindrical Dewar flask of 66O-ml capacity, A Beckman thermometer, which could be read to f0.002' C., was so placed, in the center of the flask, that its bulb was near the bottom. A small Nichrome wire coil, of measured resistance, was located a t one side of the thermometer, This was utilized to measure the heat capacity of the svstem bv applying a measured voltage for a measured time. Diametrically opposite the resistance coil was a wire-mesh basket suspended from a thread attached t o a motor-driven reciprocating mechanism. This served both as a stirrer to accelerate the attainment of thermal equilibrium within the system, and as a receptacle for the adsorbent, when introduced into the calorimeter. I n each measurement, 350 ml. of water were introduced into the flask, stirring was begun, and temperature readings were made a t predetermined time intervals until the time-temperature curve
could be accurately extrapolated to the time a t which a wcighed amount of the adsorbent, 60 to 80 grams. was dumped into the basket. After addition of the adsorbent to the calorimeter, temperature readings weie continued until a steadr state was reached, following which a known amount of heat was liberated electrically within the system, and the resultant rise in temperature, corrected for heat losses, waq used as the measure of the heat capacity of the system. The magnitude of the heat of wetting is dependent on the dryness of the surface of the adsorbent as determined by the pretreatment of the material. Table I compares the results obtained when new adsorbents a e r e maintained a t 72" F. and 61% relative humidity for several days n i t h results for the same adsorbents maintained a t 220' F. for 5 days, and with those obtained when the adeoi bents aere heated to 1100' F. for 156 t o 157 minutes, in the absence of air, prior to wetting. Evidently, once the superficial moisture has been removed, the heat of wetting of Synthad C-38 is only about 58 to 60% that of bone char.
TABLE I. HEATSOF WETTING OF BOXE CHARAND SYNTHAD C-38 Sdsorbent Bone char EH-1
Synthad C-38 Bone char EH-1 Synthad (2-38 Bone char EH-1 Synthad C-38 0
1
Present addreaa, Shell Chemical Corp., New York, N. Y.
Pretreatment 72' F 61% R.H 72' F:: 61% R.H: 220' F., 5 days 220' F., 5 days l l O O o F., 157 min. 11OO0 F., 166 min.
Heat of Wetting, Ratio, Cal./G. Synthad/ a t i 2 O F. Bone Char 1 . 8 0 rt. 0,07= 1.066 1 . 9 0 -+: 0.07 9.45 i .0 . 0 6 0.600 5 . 6 6 -+: 0 . 0 i 1 5 . 9 rt. 0 . 9 0.584 9 . 3 =t0 . 4
Limits average deviations from mean of 5 observations.
