INDUSTRIAL AND ENGINEERING CHEMISTRY
2202
LITERATURE CITED (1) Aston, J. G., IND. ENG.CHEM.,3 4 , 6 1 4 (1942). (2) Atkina, D. C., Murphy, C . M., Saunders, C. E., Ibid., 39, 1395 (1947). (3) Baker, E. B., Barry, A. J., and Hunter. M. J., I W . , 38, 1117 (1946). (4) Barry, A. J., J . Applkd Phzls., 17, 1020 (1946). (6) Barry, A. J., and Gilkey, J. W., U. S. Patent 2,495,362 (Jan. 24, 1950). (6) Boyer, R. F., Spencer, R. S., and Dahl, R. B., The Dow Chem(7) (8) (9) (10) (11) (12) (13)
ical Co., Midland, Mich., unpublished data. Bridgnian, P. TV., Proc. Am. Acad. Arts Sci., 7 7 , 1 1 5 (1949).
Ibid., p. 129.
Burkhard, C. A., J. Am. Chem. Soc., 7 1 , 9 6 3 (1949). Ewell, R. H., and Eyring, H., J. Chem. Phys., 5 , 7 2 6 (1937). Flory, P. J., and Fox, T. G., Jr., J . Polymer Sci., 5, 745 (1950). Flory, P. J., and Rehner, J., J . Chem. Phys., 11, 521 (1943). Fox, H. W., Taylor, P. W., and Zisman, W. A., IND. ENG.CH%:M..
39, 1401 (1947). (14) Gee, G.. Tram. Faraday SOL, 3 8 , 4 1 8 (1942). (15) Goodwin. J. T., Jr., U. S.Patent 2,483,972 (Oct. 4, 1949). (16) Hannay, N. B., and Smyth, C. P., J. Am. Chem. Soc., 68, 171 (1946). (17) Hunter, M. J., Gordon, M. S., Barry, A. J., Hyde, J. F., and Heidenrich, R. D., IND.ENG.CHEM.,3 9 , 1 3 8 9 (1947). (18) Hunter, M. J., Hyde, J. F., Warrick, E. L., and Fletcher, H. J., J . Am. Chem. Soc., 68,667 (1946). (19) Hunter, M. J., Warrick, E. I,., Hyde, J. F., and Currie, C. C. Ibid., 68,2284 (1946). (20) Hurd, C. B., Ibid., 68, 364 (1946). (21) Murphy, C. M., Saunders, C. E., and Smith, D. C.. IND.ENO. CHEM.,42,2462 (1950).
Vol. 44, No. 9
Newing. M. J., Trans. Farudag Soc., 4 6 , 6 1 3 (1950). Ibid., p. 755. Patnode, W., and Wilcock, D. F., J . Am. C h m . SOC.,68, 358 (1946). Pauling, L., "Nature of the Chemical Bond," Ithaoa, N. Y . , Cornell University Press, 1948. Polmanteer, Keith, paper presented at the Gordon Research Conference on Elastomers, July 1951. Rochow, T. G., and Rochoa, E. G., Science, 111,271 (1950). Roth, W. L., J . Am. Chem. Soc., 6 9 , 4 7 4 (1947). Roth, W.L., and Harker, D., Acta Crista,1 , 3 4 (1948). Sauer, R. O., and Mead, D. J., J . Am. Chem. Soc.. 68, 1794 (1946).
Scott, D. W., Ibid., 68, 356 (1946). Ibid.. 8. 1877. Ibid.: 2294. Speier, J. L., Ibid., 71, 273 (1949). Warrick, E. L., U. S. Patent 2,560,498 (July 10, 1951). Weir, C. E., Lesser, W. H., and Wood, L. A., J . Research Natl Bur. Standards, 44,367 (1950). Wilcock, D. F., J . Am. Chm. Soc., 6 9 , 4 7 7 (1947). Ibid., p. 691. Wright, N., and Hunter, M. J., Ibid., 6 9 , 8 0 3 (1947). Young, C. W., Servaia, P. C., Currie, C. C., and Hunter, M. J., Ibid., 70,3758 (1948).
b.
RECPIVED for review December 7.1961. ACCEPTED April 24, 1962. Contribution from the Dow Corning Corp. and the Multiple Fellowship a t MPllon Institute, Pittsburgh, Pa., sustained by the Corning Glass Works and Daw Corning Corp. Presented as part of the Symposium on Silicone Polymers before the Division of Polymer Chemistry a t the Diamond Jubilee CHEMICAL SOCIETY, New York, Sept. 7,1951. Meeting of the AMERICAN
xygen 1 by Chemical Exchange
Concentration of d
U
WORTHY T. BOYD' AND ROBERT R. WHITE Department of Chemical a n d Metallurgical Engineering, University of Michigan, Ann Arbor, Mich.
HE heavy stable isotopes of hydrogen, carbon, nitrogen, and oxygen have been valuable as tracers in physiological research. Oxygen isotopes of masses 16, 17, and 18 occur naturally in the proportions 99.756, 0.04, and 0.204, respectively. For tracer studies, it is desirable t o have oxygen 18 in concentrations of to% or more, a fiftyfold increase in the naturally occurring concentration. Oxygen 18 has been concentrated by thermal diffusion and water distillation, but these processes are expensive, particularly on a production basis, and a more economical method ia desirable.
increase the solubility of the carbon dioxide in the water and results in higher rates of oxygen exchange. The purpose of this investigation was to provide the process data necessary t o construct and operate a unit for producing oxygen 18. The effect of ammonia concentration, temperature, and pressure on the concentration of oxygen 18 and its rate of production was determined by measuring the rate of increase of concentration as a function of time and by measuring the final steady state concentration. The results are given in terms of the separation factor or relative volatility and the height of column packing equivalent to an equilibrium stage.
THE CHEMICAL EXCHANGE PROCESS
When carbon dioxide is equilibrated with water, tho oxygen 18 tends t o concentrate in the gaseous carbon dioxide phase through the exchange reaction between dissolved carbon dioxide and water (10, 11). The concentration process based upon this phenomenon is illustrated in Figure 1.
+
CO2'@*'6(g) 2H2018(1) = C02'8'18(g)
+ 2Hz01'(1)
Carbon dioxide is fed to the bottom of a packed tower countercurrent to water reflux fed to the top of the column. The carbon dioxide withdrawn from the top of the column is enriched with respect t o oxygen 18, and is reduced mTith hydrogen over a catalyst t o form methane and water, the latter being condensed and returned to the column as the reflux. The water withdrawn from the bottom of the column is depleted with respect to oxygen 18 and is discarded. Ammonia is added t o the water reflux to 1
Preaent address, The Easo Co., Baton Rouge. La.
EQUIPMENT
The details of the equipment and its operation are evtensivr and are reported elsewhere ( 3 ) . The column was constructed of 1-inch schedule 160 steel pipe, 70 feet long, provided with external heating elements so that its temperature could be controlled from room temperature to 120" C. The packing consisted of oxidized 22 B. & S. gage a h minum wire helices, 1/8 inch in diameter, and of stainless steel 26 B. & S. gage Fenske helices, 6/82 inch in diameter. Packed heights of 70 and 22 feet were used. Suitable facilities for holding a water seat a t the bottom of the column, for sampling various streams, and for determining holdup were provided. The carbon dioxide was reduced with hydrogen in two successive reactors containing a large excess of nickel catalyst (Harshaw Chemical Co. NiBB) in the form of '/winch tablets.
INDUSTRIAL AND ENGINEERING CHEMISTRY
September 1952
2203
The enrichment for the column is the quotient of the isotope ratio at the top and that of the carbon dioxide feed according to Equation 2. Enrichment =
(Ratio)T (Rati0)F
The reproducibility of analysee was f 0.275 of the isotope ratio. RAW MATERIALS
Commercial cylinder hydrogen was used for this research. The purity of the gas is critical as any oxygenated material is reduced in the catalytic reactors t o water diluting the oxygen Isenriched reflux. The hydrogen contained about 0.10% carbon monoxide, Figure 1. Flow Sheet of Oxygen 18 Development Unit carbon dioxide, water, and oxygen expressed a s equivalent of water. The carbon dioxide was purchased from the Pure Carbonic The flow of carbon dioxide and hydrogen feed gases and the Corp, in standard 50-pound cylinders and contained negligible pressure on the system were automatically controlled by conimpurities which contained oxygen. trolling and recording rotameters and Grove gas-loaded pressure The anhydrous ammonia was purchased from the Armour Co. regulators. The water discharge rate was adjusted manually. in 50-pound cylinders. No analysis was made since the quantiDuring a portion of the investigation, the ammonia was added ties used were small. to the system through a heated line and a size 08 Fischer and Porter rotameter. After much difficulty with this system from dirt and ammonium carbamate formation at the junction of the EXPERIMENTAL DATA ammonia feed line and the water return line, the ammonia was added by bubbling a metered flow of hydrogen through liquid The experimental data are presented in Table I. The condiammonia and introducing the saturated gas to the water reflux line. A wet-test meter installed behind the back pressure regutions reported are the averages of the hourly readings throughM o r metered the tail gas. out the run. Typical approach t o equilibrium curves is presented in Figures 2 through 5. In some of the figures the data During runs samples of the carbon dioxide leaving the top of have been transposed t o give continuous curves. The transthe column were analyzed for isotope ration, samples of the water posed data are represented by solid points. discharge from the bottom of the column were analyzed for The pressures of operation recorded in Table I varied about ammonia, and samples of the tail gas were analyzed for water, 5 pounds per square inch from the average during the runs. The carbon dioxide, and carbon monoxide to determine oxygen losses. temperatures of operation varied about 4" C. in the first 15 runs. DETERMINATION O F HOLDUP
The holdup in the column was determined after steady conditions had been reached by draining the column into the bottom receiver. The water remaining in the packing and in the pores was determined by raising the column temperature to 100" C. and drying the packing by passing hydrogen through the column. The water in the hydrogen gas was determined gravimetrically by absorbing it in silica gel and Drierite. ANALYSIS
The ratio of the concentration of oxygen isotope of mass 18 to the concentration of oxygen of mass 16 in the gas at the top of the column was measured by a Nier isotope ratio mass spectrometer, manufactured by the Consolidated Engineering Corp. Each sample was analyzed twice by each of two operators. The mass spectrometer records the ratio Ratio =
46 + 44
45
(1)
where the numbers are the ionic abundances of thecarbondioxide. This is equal to the ratio C1* Ole O16/Cla 0 1 6 0 1 6 if the contributions of 0 9 and 0 1 7 are neglected, as is justified in this cme.
Figure 2.
Enrichment for Runs 6,11, and 12 0 Originaldata 0 Transposeddata
INDUSTRIAL AND ENGINEERING CHEMISTRY
2204
Vol. 44, No. 9
TABLEI. EXPERIXEKTAL DAT.4
Run No. la
25
3Q 40
55Q 6 7 8 9
Column Ht. and Type of Packing 70, Al. 70, Al. 70, Al. 70, Al. 70, Al. 70, Al. 70, AI. 70, Al. 70, 41.
Press., Lb./ Sq. In. 93 88 215 207 199 170 148 155 148
24 22 21 22 20 15 28 30 25
Wat e? Flow in Column, G. Moles/ Hr. 10.03 9.21 11.50 11.38 11.35 12.20 (15 . 9 5 ) b 15.93 15.70
17
15.20
Av. Column Temp.,
c.
Tail Gas Rate, Cu. Ft./Hr.
Loss of Oxygen in Tail Gas, G. Moles Water / Cubic Ft.
Ammonia Concn., G./100 G. of Soln.
.. ...
0 0 0 0
Holdup in Column and Reactors, G. Moles of Water
..
..
Est. Equilib. riiim Enrichment 1,059 1.041 1.116 1.092 1.136 1.077 1 102
7.a 7.5 18.0 20.5 7.7 11.6 10.6 10.7
0.00010
0.6ba65
0 1 09 3 06 4 42 1 21
77:7
1: is3
8.2
n . 00336
0
..
1.050
9.95
...
,..
, .
.. , .
..
10
70, Al.
155
11
70. Al.
159
17
19.18
(0.00314)b
1 70
..
1.056
12 13
70, AI. 70, AI.
156 153
50 51
18.66 16.40
10.6 11.5
0.00314 0,00349
0 1 63
83:G
1 :285
14
70,Al.
153
100
15.30
10.0
0.00284
4 06
68.9
15
70, Al.
153
96
(15.30)b
10.9
(0.00284)b
0
71.2
1.815
16 2 2 , 6.S.C 159 17 22, 6.S.C 156 18 22, 6.S.C 152 a Water adsorbers used. b.Estimated value, 0 Stainless steel.
86 86 122
15.69 15.22 15.30
11.1 10.6 9.8
2 13 3 97 2 98
(41.6)b 41.6 50.2
1,250 1.364 2,575
00258 0.00258 0.00238 h).
The last runs were controlled to about 1' C. The water production rate seldom varied more than 2% The tail gas rate changed about 15% on a regular daily cycle. The determinations of the loss of oxygen in the tail gas were the average of two values taken near the end of the runs. These always agreed to better than 5%. The ammonia analyses were taken near the end of the run. The ammonia concentration varied about 10% during most of the runs. The holdup values reported in Table 1 may be in error as much aa 10%. Table I1 presents the calculated quantities required t o determine the separation factors and the number OC equilibrium stages for those runs which had high equilibrium enrichments. The losses of oxygen, reported as moles of water, were calculated by multiplying the determined loss per cubic foot by the average tail gas rate. The impurities added to the top of the column were all considered to come from the hydrogen. A hydrogen balance 1% as made from the water formed and the tail gas rate. The impurities \\ere' theu figurrd as 0.001 mole of matc,i per mole of hydrogen.
..
Run Shutdown Equilibrium Equilibrium Checking leaks in system Checking losses in tail gas Water adsorber plugged Equilibrium Column plugged with solids Column plugged with solids Equilibrium and ammonia feed fluctuating Equilibrium and ammonia feed failure Heatina of column started. column plugLed Column heaters shorted out Equilibrium and ammonia fluctuating Bad !eaks in ammonia system a t enrichment of 3.42 Equilibrium during ammonia failure in run 14 Equilibrium Equilibrium Equilibrium
The water flon- rates consist'ed of the measured water rate plus the calculated quantity of dissolved carbon dioxide. This carbon dioxide was considered as equivalent moles of water. The data for the solubility of carbon dioxide in ammonia water had to be extrapolated. As such, the final results of water flow may be in error by 3 or 4%. The value of holdup above the packing consisted of the water in the liquid seal and overflow box, water in the first reactor, and carbon dioxide in the lines above the packing. Of the overhead holdup, 12.2 moles were in t'he overflow lines and overflow box. Only t'he first reactor was considered to contain oxygen. With a catalyst porosity of 0.4 and complete conversion, about 0.4 mole of water as contained in the reactor and lines to the condenser. In the 70-foot column there was about 10 feet of 1-inch pipe filled with carbon dioxide above the packing. I n the 22-foot column there was about 35 feet of 1-inch pipe. This carbon dioxide as water was about 0.86 mole and 3 moles, respectively. CORKEIATIOX OF DATA. The factors which describe the operation of an isotope column are: the separation factor, 01; the number of transfer units or its equivalent, the number of equilibrium stages, and the holdup in addition t o the various flow rat,es. Tn order to determine values of 01 and N from the experimental data it is necessary to solve simultaneously the relation between o( and A' at steady state conditions with that for transient conditions under substantially total reflux operation. The separation factor is essentially the relative volatility
.L +which for low aoncentrations and values of 1 - y 1-s close t,o unity may he wit,ten
a!= 01
01
= v/.c
(3)
where y, x = the mole fraction of oxygen 18 in all of the oxygen present in the gas phase and liquid phase, respectively. Under steady conditions at tot'al reflux
Figure 3.
Enrichment Curve for R u n 13
where 1' and R refer to the top and hottom of the column, respectively. The differential equations describing the approarh to equilibrium of the column were solved rigorously for the case where the overheltd holdup was assumed to be completely mixed a t all times and for the case where the overhead holdup (material in
September 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
TIME
Figure 4.
IN
2205
HOURS
Enrichment Curves for Runs 14 and 15
0 Originaldata
0 Transposed data
the reactors and reflux handling system) was assumed t o be completely unmixed. I n addition, other methods used were the simplification of the first two methods where the overhead holdup is added to the column holdup; the method of Huffman and Urey (6);and a method of integration. The mathematical development of the equations and their applications are so extensive that only a summary of the results are presented here. The complete detailed information may be obtained elsewhere (3). The summary of the resulting factors, a , and the - separation number of equilibrium stages or transfer units, N , are presented in Table I11 for five of the runs which were analyzed in detail. The results are compared with the theonetical separation factors calculated by Urey and Grieff (9) and the number of equilibrium stages by Equation 4.
more than 15%, there is no reasonable explanation of the discrep ancy except in the assumptions made in deriving the equations. I n order t o secure consistent values of the number of stapes and heights equivalent t o a reactor unit, it is desirable to use the statistical values of a, reported by Urey and Grieff (9) t o be 1.047 a t 0" C., 1.039 at 25' C., and 1.014 a t 600' C. The value8 of
TABLE11. CALCUL4TED DATA Impuri-
ties
Run
DISCUSSION
NO.
4
13
Added G. Mol& Water/
Hr.
0.0354 0.0376
Loss of Ox gen
Total Moles Oxygen Flowing
Down
Column G. hol&G. Mole; Water/ Water/ Hr. Hr. 0 0479 16 76 0.0402 17 71 17 54 0.0284 0 0310 15 36 0.0286 16 73 0 0273 17 01 0 0233 16 74
Total Moles Oxygen, Flowing Up Column G . Mole; Water/ Hr. 16 7743 17 7126 17 5343 15 3559 16 7227 17 0173 16 7295
Holdup Overhead,
Ho!dup In Column,
Moles of Water 13 64 13.73 13.84 13 72 15 78 15 72 15 68
Moles of Water 84 9 92 0 80.5 73 0 45 7 47 1 55 4
G.
G.
0.0341 The calculated values of a are considerably lower than those 14 15 0.0351 obtained by the statistical calculations of Urey and Grieff (9). 16 0.0359 17 0.0346 In the other methods, the (a-1) 18 0.0338 values are about 50% of the statistical values. Weber, 'Wahl, and Urey TABLE 111. SUMMARY OF SEPARATION FACTOR CALCULATIONS (11) have reported close agreeRun 9, 25" C. Run 13,51° C. Run 14,96' C. Run 16,86O C. Run 18, 122O C. Method Of analysis U N a N L Y N a N a N ment with the statistical value at 0 0 C. Urey has also exOverhead completely mixed .. .. 1.028 .. .. 1.028 79.1 1.015 72.6 pressed the opinion (8) that n;;E;eio .. .. . . 9... 0 .. .. 8..2 1.014 .. 1.015 68.4 the value of (a-1)by theory oolumn .. .. .. .. .. cannot be more than 10% io Huffman and lJrey 1 006 23 8 1.010 25 3 1 0075 . . 1.012 18 7 1,0085 111.6 M z h o d of Integraerror for this system. .. .. l1 0177 14 3 l 0174 54 6 1 0121 11.8 1.0164 13 7 tion Since the inaccuracies in the Theoretical a ' s 1 039 3 72 1.0331 7 7 1.0264 0276 8 2 1 0236 40 5 data could hardly amount to
:;:;:E;!
2206
INDUSTRIAL AND ENGINEERING CHEMISTRY
a semilog reciprocal temperature plot. The results of the calculation of the number of transfer units and heights equivalent to a transfer unit are presented in Table DV. All of the runs are reported here. The effect of pressure may be noted in the first five rum and the effect of temperature and ammonia concentration in the rest of the runs which were made at about 150 pounds per square inch. A plot of the H.T.U. values is given in Figure 6. The pressure and the ammonia concentration are shown with each of the points. Since the effect of pressure is small compared t o ammonia concencentration, lines of constant ammonia concentration are shown for pressures of 100 to 200 pounds per square inch. The addition of ammonia nearly doubles the number of stages in a given column length. The effect of pressure is also considerable. Doubling the pressure approximately doubles the number of stages. It would appear from Figure 6 that still higher temperatures would be favorable in securing high enrichments. At some point, the mass transfer resistance rather than the reaction rate will be the controlling factor. From distillation experience on this type of packing, the H.T.U. limit will he about 0.1 foot. The curves are extrapolated t o this value. Since the ma= transfer resistance is negligible in the range of operation, the activation energy of the reaction may he calculated. The Arrhenius equation may be written (a-1) form B straight line on
The value of the activation energy is 7740 calories per gram mole for runs containing no ammonia. When the H.T.U.'s are rorrected to equal solubility of carbon dioxide, the activation energy bzcomes 12,000 calories per gram mole. Most reactions are in the range 10,000 to 20,000 calories per gram mole. Mills and Urey (6) reported a value of 16,800. From Figure 6, the three runs 16, 17, and 18 on the 22-foot column using stainless steel packing agree with the rest of the runs using aluminum packing. The limits of allowable ammonia concentrations before ammonium carbamatp and ammonium bicarbonate formed were also determined (4). The concentrations are only approximate. At 25" C. there were instances of the column packing plugging with solids a t ammonia concentrations of 2.5 grams per 100 grams
Vol. 44, No. 9
of solution. However, it was found possible to run a t higher concentrations occasionally for long periods before the column plugged. At 122' C., carbamate formed in the vapor phase whenever the ammonia concentration went above 3.5 grams per 100 grams of solution. At intermediate temperatures, it appeared possible to run as high as 4.5 to 5.0 grams of ammonia per 100 grams of solution. The point of difficulty shift,ed from within the liquid in the packing to the vapor phase above the packing. Some solid bicarhoriate probably existed in the column packing a t all concentrations above 2.0 grams of ammonia per 100 grams of solution. The ammonia concentration could be raised for the high temperature runs if the entire unit above the packing were heated. This would appear worth while in a larger production unit. Higher pressures also help in keeping the ammonia in the liquid phase. The conversion of the carbon dioxide to water would be increased and loxer H.T.U. values would be obtained. The conversion of the carbon dioxide to the water for reflux offered no difficulties in any of the experiments. The catalyst maintained activity well during 6 months of operation. The reactors were cooled to room temperature about 10 t,imes and pure carbon dioxide %-as txice put through the reactors a t the operating temperature with no subsequent loss of activity. The hot zone in the reactor appeared to shift from the top layer of catalyst to about 4 inches from t,he t,op in the 6 months of operation. The only part of the operation causing difficulty was the ammonia feed fiystem and the plugging due t o the carbamate,
0
Figure 6 . H.E.T.P. or H.T.U. Values mmonia concentration given in grams per 100 grams of solution
September 1952
INDUSTRIAL AND ENGINEERING CHEMISTRY
2207
KT TABLE IV. 1 Equilibrium Temp., Temp. (" IC.) Run Enrichment O C. 10' 24 3.37 1.059 22 3.39 1.041 21 3.40 1.116 22 3.39 1.092 20 3.41 1.136 15 3.47 1.077 28 3.32 1.102 30 3.30 (1.164)a 25 3.36 1.153 17 3.45 1.050 17 3.45 1.056 50 3.10 (1.193)' 51 3.09 1.285, 100 2.68 (4.70) 96 2.72 1.815 86 2.79 1.250 86 2.79 1.364 122 2.53 2.575 5 Calculated results.
H.T.U. EVALUATION a
1.0392 1.0398 1.0400 1.0398 1.0402 1.0417 1.0381 1.0376 1.0390 1.0412 1.0412 1.0332 1.0331 1 .0258 1.0264 1.0276 1.0276 1.0236
N 1.49 1.03 2.79 2.25 3.22 1.82 2.60 (4.11Ia 3.72 1.21 1.35 (5.39)a 7.70, (60.8) 22.9 8.20 11.4 40.5
H.T.U., Ft. 47.0 68.0 25.1 31.1 21.7 38.4 26.9 (17.0)" 18.8 57.8 51.9 (13.O)a 9.08 (1.15)* 3.06 2.68 1.93 0.543
Press., Lb./Sq. In. 93 88 215 207 199 170 148 155 148 155 159 156 153 153 153 159 156 152
NHa G./ldO G. 0 0 0 0
0 1.09 3.06 4.42 1.21 0
T
perature, T total number of transfer units = gas constant, caloriee per mole per ' K. = temperature, C. and
2
= mole fraction of oxygen
N
R
g CY
1.70 0 1.63 4.06 0
2.13 3.97 2.98
= reaction rate at tem-
' K.
18 in t h e liquid mole fraction of oxygen 18 in the vapor = separation factor or relative volatility =:
BIBLIOGRAPHY (1) Akers, W. W., and White,
R. R., Chem. Eng. Progress. 44. 553 (1948). R. R., Zbid.,
46, 563
(1950).
About 99% of the upsets were a result of the ammonia. With no ammonia it was not necessary t o watch the operation. For larger units it will be desirable t o devise a more satisfactory ammonia system. ACKNOWLED~MENT
This work was sponsored by the American Cancer Society upon recommendation of the Committee on Growth of the National Research Council. NOMENCLATURE
A* H.T.U.
= activation energy, calories per mole height of column equivalent to one transfer unit, feet
--
(3) Boyd, W. T.. Ph.D. dissertation in chemical engineering, University of Michigan, Ann Arbor, Mich., 1951. (4) Gmelin, "Handbuch der anorganischen Chemie," System Num-
ber 23-2, Berlin, Verlag Chemie, 1936. (5) Huffman, J. R., and Urey, H. C., IND.ENG. CHEM.,29, 531 (1937). (6) Mills, G. A,, and Urey, H. C., J . Am. Chew. SOC.,62, 1010 (1 940). (7)Nier, A. O., priv&e communication (1949). (8) Urey, H. C., private communication (1947). (9) Urey, H. C., and Grieff, L. J., J. Am. C h m . SOP..57, 321 (1935). (IO) Reid, A., and Urey, H. C., J. Chem. Phys., 11, 403 (1943). (11) Weber, L. A., Wahl, M. H., and Urey, H. C., ZW., 3, 129 (1935).
RECEIVED for review November 30, 1951.
ACCEPTEDApril 3, 1952.
Ozone by Electrolysis of Sulfuric +
Acid
JUNIOR D . SEADER' AND CHARLES W. TOBIAS University of California, Berkeley, Calif.
I
N 1840 Schonbein (14) discovered t h a t with oxygen, ozone
is also liberated when electrolyzing aqueous acid and salt solutions. Investigations by Soret (16), McLeod ( I 1 ), Targetti (16), Grafenberg (6), and Kremann (7), led t o the conclusion that sulfuric acid of 1.075 t o 1.100 specific gravity gives the highest yields (up t o 18% by weight), using platinum anodes and keeping the temperature of the cell close to 0" C. Fischer and co-workers (3, 4)recognized the importance of low anode surface temperature. The platinum anode surface was believed t o catalyze the decomposition of primarily formed ozone. The highest ozone yields were obtained by using a n inside cooled platinum tube anode of triangular cross section, coating i t with Jena glass and grinding away the glass over one of the edges so as t o expose a horizontal platinum strip, 0.1 mm. wide and 11.5 mm. long. This anode gave a very short contact time for gas bubbles and hence was believed to have reduced the decomposition rate of ozone. The best yield (28%) resulted when the anode was cooled inside by a circulating salt solution t o -14' C.; the current density was 87 A. per square cm., and the electrolyte was sulfuric acid, specific gravity, 1.075. Fischer also studied the ozone process using various other electrolytes. None of the salts, acids, and 1
Present address, University of Wiseonsin, Madison,Wis.
bases, other than sulfuric acid, gave high ozone yields, On the basis of t h e available free energy data, Fischer calculated the potential of the OH-/Os couple t o be -1.69 volts. Wartenberg and Archibald (18) investigated the effect of superimposed alternating current on ozone yield. They claimed to have attained very high (up t o 35% by weight) concentrations of ozone in oxygen, but the energy yield in these experiments was exceptionally poor. Their results were not substantiated by other workers (1, l a ) . Briner and coworkers ( I , 2) were the first to investigate the anodic liberation of ozone a t temperatures around -50" C. These low temperatures required the use of eutectic sulfuric acid-water compositions. The highest ozone yields reported by Briner were below 8.5% by weight. However, by using a 4070 solytion of perchloric acid instead of sulfuric acid as electrolyte, yields up t o 16% were observed. Briner cooled the electrolyte instead of the anode. The experimental procedures, electrode potential data, and theoretical treatment extended by this group invite severe criticism and are partly unacceptable. Putnam and coworkers (IS)undertook a systematic study of the effects of temperature, current density, acid concentration, and pressure on the ozone yield, using perchloric acid as electrolyte. The yield waa found to increase with current density and
