December, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
(6) Davis, T.L.,J. Am. Chem. Sac., 43,2234-8 (1921). (7) Davis, T. L., Org. Syntheses, 7,47 (1927). (8) Davis, T.L., U. S. Patent 1,417,369(May 23,1922). (9) Ibid., 1,440,063(Dec. 26, 1923). (10) Erlenmeyer, E.,Ann., 146,258 (1868). (11) Ewan, I.,and Young, J. H., J. SOC.Chem.Ind., 40,109-21 (1921). (12) Gockel, H.,Angew. Chem., 47,555-6 (1934). (13) Griessbach, R.. and Rossler, A., German Patent 490,876 (Dee. 15, 1925). (14) Hill, W. H a ,Swain, R, C., and Paden, J, H. (toAmerican Cyanamid Co.), U.S. Patent 2,252,400(Aug. 12,1941). (15) Jones, R. M., and Aldred, J. W. H . , IND.ENQ.CHEM.,28, 272-4 (1936). (16) Kat6, Y.,Sugino, K., Koidzumi, K., and Mitsushima, E., J. SOC.Chem. I n d . J a p a n , 36, Suppl. binding 133-4 (1933).
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(17) Pinck, L.A., IND. ENG.CHBM.,17,459-60(1925). (18) Sander, F.,Ger. Patent 527,237(Jan. 1, 1928). (19) Schmidt, E.,Arch. Pharm., 254,630 (1916). (20) Smith, G. B., Sabetta, V. J., and Steinbach, 0. F., IND. ENQ. C H ~ M23, . , 1124-9 (1931). (21) Spurlin, H. M. (to Hercules Powder Go.), U. S. Patent 2,109,934 (March 1, 1938). (22) Stickstoffwerke, s., G~~~~~ patent222,252(ace. 30, 1908). H'*Ibid** 600,869(Au& 27 1934). (23) Traube, and (24) Volhard, J., J. prakt. Chem., 9,15 (1874). (25)Vozarick~ *' Chem.f 670 (lgo2). (26) Werner, E.A,, Analyst, 65,268 (1940). (27) Werner, E*A.9 J. C h e m S0C.t 107,715 (1915). (28) Werner, E. A., and Bell, J., Ibid., 117, 1133 (1920).
Influence of Water Vapor on Ozonizer Egciency J
CLARK E. THORP AND WALTER J. ARMSTRONG Armour Research Foundation, Chicago, Ill. Graphs are presented to show the relation of ozonizer efficiency over a large range of absolute and relative humidities. Absolute humidity is shown to influence ozonizer efficiency greatly when it is above 0.001 gram of water per gram of air (dew point, -17' C.), but to have no influence below this optimum point. Relative humidity has no effect on ozonizer efficiency.
S
I N C E 1943 the Armour Research Foundation has been sponsoring a series of investigations (1) leading to the design and construction of industrial ozonizers of improved efficiency. I n this connection the influence of water vapor, temperature, pressure, and frequency on ozonizer efficiency had to be determined. A search of the literature provided a considerable amount of data of academic interest but of little actual engineering value. For example, it is well known that water vapor decreases the energy yield of the reaction 0 2 t o 03 (8) and increases the to O2 (417 but enough data are not energy yield Of the reaction given to allow calculation of the amount of drying required for most economical operation of industrial ozone equipment. An additional reason for further investigating the influence of water vapor on ozonizer equipment is brought about by the recent development of new types of generating elements which produce ozone without the production of large amounts of heat (2, 6). The elements, developed and manufactured by Ozo Ray Process Corporation, are flat, plastic plates with imbedded metallic electrodes. With a life of well over 10,000 hours and a total heat rise of 1' C. per square inch, they are well suited for industrial ozone equipment, although at the present time they are not being used for such equipment. This paper presents the results of an investigation of the effect of water vapor on the efficiency of ozonizers using the new type of generating elements. The general shape of the curves obtained for yield os. absolute humidity should apply t o any type of ozonizer using the silent discharge and adequate cooling.
lute humidity), such as the hair hygrometer, electrical conductivity, etc., were considered either too limited in range or too inaccurate. Theoretical determination of the absolute humidity under known conditions of temperature and pressure presented the most logical solution to the problem of controlling the amount of water vapor passing through the ozonizer. Accordingly air containing water vapor was cooled and brought t o dew point by passage through a series of cold traps a t known temperature. The amount of water vapor then present in the air can be calculated from the standard equation
where H = absolute humidity in grams of water per gram of dry air P = corrected barometric pressure p = vapor pressure of water at a cold trap temperature Below 0'0 c. the vapor pressure of supercooled water is used in preference to the vapor pressure of ice, because even if air is in contact with ice its humidity is more accurately calculated from the vapor pressure of supercooled water (3,5).
.AIR
LINE
K
Figure 1. THEORETICAL CONSIDERATIONS
The determination of the influence of water vapor on ozonizer efficiency requires passage of air containing known amounts of water vapor through the ozonizer, with subsequent analysis of the air stream t o determine the quantity of ozone produced. Simple methods of determining the amount of water vapor in air (abso-
L
J
Flow Sheet for Determining Effect of Water Vapor on Ozonizer Efficiency
A . Air cleaner B. Dew point trap in Dewar C. Humidity-regulating traps in Dewar D. Thermometer, $30' to 1000 c. E. Heat exchanger coil F. Manometer
-
G . Thermometer, +30° to
-1000 e.
FI. Ozonizer
Insulated tank J. Gam absorption bottler, K. Wet test .as meter L. Vacuum pump I.
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Vol. 38, No. 12
All four humidity-regulating traps were placed in one largc Dewar flask t o ensure equality of temperature between a11 four trap,. The traps n-ere of the spiral glass type to ensure adeqiintc surfarc contact between glass and air. The ozonizer (Figure 2) in a steel liquid-tight housing was immersed in a large, insulated cold bath containing liquid chloroform. Approximately 12 feet of copper tubing were coiled around the ozonizer; since it XTas in the same bath, it served as a heat exchanger ( E , Figure 1) t o bring the air to ozonizer temperaturc. before entering the ozonizer. The ozonizer and heat eschangertemperatures were controlled by adding dry ice to the bath. Analysis of ozone was made by reaction in three standard Allihn bottles, J , a-ith buffered potassium iodide solution ( 7 ) . In order to keep pressure conditions in the ozonizer and humidity regulating traps as near atmospheric as possible. a vacuum pump, L , was used to draw the ozone-containing air through the absor1)tion bottles. The electrical characteristics of the ozonizer were meawrcd by milliameters and voltmeters on both the input and otitput of tht. ozonizer transformer.
Figure 2.
External View of Ozonizer i n Cold Bath
After regulation and drtermination of absolute humidity, the air \\-as passed through a heat exchanger operating a t the same temperature as the ozonizer. This brought the air temperature into equilibrium with thP ozonizer temperature and allowed determination of the relatlw humidity by means of the following standard equation:
where p i = vapor pressure of water a t the cold trap temperature p o = vapor pressure of water a i the ozonizer temperature
The following procedure was used in making the tests: Air was passed through the system until all temperature and humidity conditions were a t the desired equilibrium. The ozonizer was then operated for 5 minutes. After the ozonization period the air n-as allowed to continue through the system for an additional period of 30 minutes to ensure removal of all ozone. I n all cases the amount of air passing through the ozonizer during ozonization was held constant a t 1.5 cubic feet, or a rate of 0.3 cfm. EFFECT OF ABSOLUTE HUMIDITY ON OZONIZER YIELDS
The influence of absolute humidity on ozonizer yield 15 B C determined for three different ozonizer conditions. The conditions under which each series of tests were made axe given i r t Table I. The results of the tests are compositely illustrated in Figure 3. Under varying conditions of ozonizer-generating arba and pon-el the general shape of the curves representing yield vs. absolutc humidity shows an optimum point for highest ozonizer efficiency. The optimum point appears to be approximately 0.001 gram of
Wheii using the above methods of determining absolute and relative humidities, care must be taken to establish equilibrium in the entire system. Changes in humidities must be made in small increments to ensure more rapid establishment of equilibrium between runs. In any series of runs it was found necessary always to change from lo^ to high humiditiesthat is, to change from a high to a low humidity often requires many hours for establishment of equilibrium. EXPERIMENTAL PROCEDURE
Figure 1 illustrates the apparatus used in determining the effect of water vapor on ozonizer efficiency. Air from a low pressure air line n-as passed through paper air cleaner A into primary d e x point trap B maintained a t a temperature sufficient to bring the air to dew point. The air was then passed through a series of four more traps, C, to reduce further its temperature t o a predetermined degree. Dry ice and petroleum ether were used to attain temperatures down to - 6 5 " C., and liquid nitrogen and ethyl ether were used for temperatures down to -100" C.
ABSOLUTE
Figure 3.
HUMIDITY - q H20 / q AIR
Influence of Absolute Humidity on Ozonizer Yields 0 Data from runs 24-13 Data from runs 75-83 A Data from runs 85-101
December, 1946
INDUSTRIAL AND ENGINEERING CHEMISTRY
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per gram of air, ozonizer efficiency is no longer dependent on absolute humidity. Table I (runs 103-113) shows the conditions under which such tests were made, and Figure 4 illustrates the results obtained. It is evident that relative humidity does not effect ozonizer efficiency; in future tests involving temperature variations, only absolute humidity must be controlled.
9
ACCURACY OF TEST DATA 7
Several experimental procedures were tried and discarded before the procedure described wa8 chosen. I n spite of the obvious failure t o account for noncorrection of the gas laws in Equation 1 and the possibility of supersaturation in the humidity controlling traps, the method gave reproducible results throughout a series of ninety runs. The procedure was checked by actually freezing out the water in a liquid nitrogen trap and weighing the amount of water found in a measured quantity of air. The results showed that less than 5% error was experienced by relying on the equation and method, if not less than four cold traps in series were used. If' care waa taken to keep the traps from filling with water or ice, the error remained fairly constant and, because the determination was concerned with only comparative results and not absolute yield values, the method was considered sufficiently accurate for the determination of the effect of water vapor on ozonizer efficiency.
'> -E
0
3
% 4
w
a w 3
2
CONCLUSION
The general effect of water vapor on ozonizer efficiency has been known by practically all designers of ozone equipment, and large installations usually include air drying provisions. This paper provides curves illustrating the effect of absolute humidity over a large range of humidities, t o enable the engineer to predict in advance how much drying will be required for ozone equipment. It has been shown t h a t variance in generating capacity and current density does not materially affect the shape of the curves. Relative humidity does not influence ozonizer efficiency and may be disregarded if absolute humidity is controlled.
I
Mq Os/ Hr.
1
100
Figure 4. Influence of Relative Humidity on Ozonizer Yields Data from run8 103-113
water per gram of air and corresponds to a dew point of approximately -17" C. From a practical standpoint, therefore, the air used in industrial ozonizers shduld be dried to a dew point of -17" C. for highest efficiency. Greater absolute humidities result in greatly decreased efficiencies, as shown by the sharp slope of the curves above 0.001gram of water per gram of air. EFFECT OF RELATIVE HUMIDITY ON YIELD AT LOW ABSOLUTE HUMIDITIES
I
It was of interest to determine whether relative humidity would effect ozonizer efficiency, because, in later tests to be made on temperature influence,, if the relative humidity effect were unknown it would make interpretation of results difficult by introducing two variables. I n order t o study the effect of relative humidity, the tests must be made with ozonizer temperature constant and with absolute humidity either constant or noneffective. Figure 3 shows that, below an absolute humidity of 0.001 gram of water
TABLEI. CONDITIONE FOR TESTRUNS Runs Primary volts Primary amperes Secondary volts Secondary amperes Generating area,.sq. in. 0 aoniser constant temp.,,
24-78 118.0 0.810
c.
6000.0 0.006 260.0 20.5
76-83 118.0 0.310 8000.0
86-101 118.0 0.800
210.0 10.0
210.0
0.005
6000.0 0.005
5.1
103-113 118.0 0.310 6000.0 0.008
210.0
-56.0
LITERATURE CITED
(1) Armour Research Foundation, Chern.Eng. News,22, 2101 (1944). (2) Dawson, W.J., Ry. EEec.Engr., 31, 251-9 (1940). Ref&. Eng., 27, 131 (1934). (3) Ewell, A. W., (4) Forbes, G. S., and Heidt, L. J., J. Ana. Chem. SOC., 56, 1671-6 (1934). (5) Keyes, F. G.,and Smith, L. B., Refrig. Eng., 27, 127-30 (1934). (6) Thorp, C.E., C h m . Eng. News, 19, 686 (1941). (7) Ibid., IND.ENQ.CHEY.,ANAL.ED., 12, 209 (1940). (8) Warburg, E., and Leithauser, Ann. Physik, 20, 743 (1906); 23, 209 (1907).
Viscosity of Pine Gum-Correction With reference to our article which appeared in the May, 1946, issue (page 555), our attention has been called t o an article entitled "Production of Clean Gum Rosin" by W. C. Smith in INDUSTRIAL AND ENGINEERING CHEMISTRY, Volume 26, pagee 408-13 (1936). On page 411 of this article there are graphs showing the Engler visccsity of water-free long-leaf and slash pine gums of original turpentine content and these gums diluted t o 30 and 40y0turpentine and covering temperature ranges up t o 100' C. We regret t h a t through an unfortunate oversight we made no reference t o Smith's article. W. J. RUNCKEL AND I. E. KNAPP NAVALSTORES RESEARCH DIVISION
U. 8. DEPARTMENT OF AQRICVLTURE NEWORLlhNS, IJA.
