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lecithin should not be used as an antioxidant until the oils have been cooled to at, least 50" C. ACKNOWLEDGMENT The author is indebted to R. Schonheimer for the plant sterols used, to Joseph Eichberg, of the American Lecithin Corporation, for the several samples of vegetable lecithin, and to R. W. Gerard for t,he determinations of oxygen uptake given in the table.
331
LITERATURE CITED Crawford and Mattill, IXD. ESQ.CHEX.,22, 341 (1930). Greenbank and Holm, Ibid., 25, 167 (1933). Ibid., 26, 243 (1934). Holm, Greenbank, and Deysher, Ibid., 19, 156 (1927). (5) Hyman and Wagner, J. Am. Chem. Sot., 53, 3019 (1933). (6) Markley and Mattack, Science, 80, 206 (1934). (7) Powick, W. C., J. Agr. Research, 26, 323 (1923).
(1) (2) (3) (4)
R ~ C E I V ESeptember D 8, 1934.
Oxygen Removal from Boiler Feed Water by Sodium Sulfite KENNETH A. KOBEAND WARDL. GOODING Department of Chemical Engineering, University of Washington, Seattle, Wash.
LTHOUGH scale formaMoberg (8) successfully used The factors governing the rate of oxygen referrous sulfate and sodium sulfite tion from boiler f e e d moval from water by sodium sulfite are shown to water has been scientifito prevent oxygen corrosion. be the p H of the water, temperature, catalysts, cally attacked from a chemical He found the ferrous sulfate sucand inhibitors present in the water. standpoint, the prevention of cessful in scaled boilers until all Sodium m b t e may be used to remove oxygen c o r r o s i o n resulting from disscale had dissolved; then violent solved oxygen has been chiefly foaming occurred. By changing f r o m boiler feed water with assurance that the treated mechanically (9). In to sodium sulfite, foaming ceased reaction is immediately completed at temperathe removal of oxygen and other and oxygen corrosion and pitting lures found in the boiler or hot process softener. dissolved gases from feed water were prevented. In one installaAt outdoor temperatures the reaction is less rapid by m e c h a n i c a l m e a n s , two tion corrosion above the water and time must be allowed for the reaction to be general methods are used: reducline was attributed to the addition of the air pressure above tional carbon dioxide liberated completed. The use of 0.1 p . p . m. copper sulthe water and preheating of the by the use of ferrous sulfate, fate (1 pound in 1,200,000 gallons) will catalyze water. Although differing in but by changing to sodium sulthe reaction to completeness in 2 minutes unless the details of operskion, both fite and feeding into the lower inhibitors are present. m e t h o d s are based upon the drum the corrosion was entirely same fundamental principle exprevented. pressed by Henry's law. This states that the solubility of a OXIDATION OF SODIUM SULFITE gas in a liquid is proportional to the pressure of the gas over the liquid; the pressure of the gas is the partial pressure calSodium sulfite appears to be an ideal chemical for oxygen culated by applying Dalton's law. In the first method the removal as it is cheap, oxidizes rapidly, and produces a comresult is accomplished by reducing the total pressure and thus pound beneficial in the boiler. It was the object of this work reducing the partial pressure of the oxygen over the water. to study the various factors affecting the rate and completeIn the second, the partial pressure of the oxygen is reduced by ness of the oxidation under conditions comparable to the addiraising the partial pressure of the water vapor by heating the tion of sodium sulfite to feed water. water. Various modifications of these two methods are emThe autoxidation of sulfite solutions has been studied from bodied in the equipment now in extensive use. Corrosion in the standpoint of chemical kinetics (4, 10, 14, 15). The rate this equipment itself represents a fault of the system. of solution of oxygen and oxidation of the sulfite solution was Chemical methods for the removal of oxygen have been determined by the decrease in pressure in the oxygen in the proposed and used to some extent. An apparatus, termed a reaction flask. The reaction has been shown to be a chain deactivator, contains iron turnings which are oxidized to rust reaction (6, 11), so that the rate will vary greatly with cataby the oxygen in the water (9, 13). The rate of removal is lysts or inhibitors present in the solution. influenced by the rate of flow of the water through the apparaEXPERIMENTAL METHOD tus and the amount of iron surface exposed. This method has proved to be too slow and cumbersome for commercial use. AnWater to be used was collected and allowed to stand in a other chemical method is the direct addition of chemical com- closed bottle for some time before use. The oxygen content was determined by the Winkler method (7). Two hundred millipounds to the feed water. Fager and Reynolds (6) state that of water were placed in a 250-ml. bottle and allowed t o alkaline tannates have been used with success. Ferrous liters come to e uilibrium in a thermostat. From an oxygen deterhydroxide, sodium sulfide, sodium thiosulfate, and sodium mination t%e amount of sodium sulfite necessary to remove all sulfite (12) have been considered. The objections to the use ox gen from the water Sam le could be calculated. A sodium of such chemicals have been stated by Solberg (12) to be the suhte solution was then mage up t o such a stren h that 10 ml. solution contained this calculated amount ot@sulfite. This increase in the soluble salt content of the boiler water, or for- of could not be done exactly because of air oxidation of the sulfite mation of a precipitate from ferrous hydroxide, failure to solution, but the solutions were very nearly equivalent. In remove carbon dioxide or other gases, and lack of assurance making a determination, 10 ml. of the sulfite solution were added that the required reaction will be completed between the time to the 200 ml. of water in the bottle, and at the end of a specified time 25 ml. of standard iodine solution were added to stop the the chemical is introduced and the water evaporated from the reaction and the excess iodine was titrated with standard sodium boiler. thiosulfate solution. Blanks were run t o determine the relative
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332
strength of the sodium sulfite solution used in each run. The air in the bottle would cause some error, but this would be small and the results would all be relative. Some difficulty was encountered in obtaining check results, but, after a standard practice was established in which each bottle was inverted twice after the sulfite solution was added, the results checked very well.
It was proved that the reaction studied was the thermal reaction and not photochemical. Determinations in black bottles checked those made in clear glass bottles.
Thus, maintaining an excess of sulfite in the boiler or preheater causes such an increase in the rate of oxidation that oxygen removal must certainly take place. EFFECTOF CATALYSTS. Various catalysts have been studied by other workers (IO,14, 15) using various conditions. This work was confined to the study of copper sulfate as the cheapest effective catalyst a t a pH of 9.8 representing boiler conditions. The percentage of oxygen removed in 2 minutes at 20' C. from distilled water with the pH adjusted to 9.8, using one equivalent of sodium sulfite (8.1 mg. oxygen per liter of water), is as follows:
cuso4
%
0.01
24.6 100 100
PH
EFFECT OF PH. A study was made of the effect of pH on the reaction, covering a range from 4.0 to 12.0 a t 20" C. The pH of distilled water was adjusted by using acetic acid on the acid side and sodium carbonate and hydroxide on the alkaline side. The pH values were determined with a LaMotte or Hellige-Klett indicator set. The percentage oxygen removed in 2 minutes was determined a t various pH values. The results a t 20" C. showed such a low removal of oxygen a t the higher pH values that the range 9.5 to 11.5 was repeated a t 50' C. This range more nearly represents pH values found in the boiler water. The results of these tests are shown in Figure 1. The pH for maximum rate found in this work does not correspond with that reported by Reinders and Vles (IO) whose value of pH 10 was the p H of the sulfite solution absorbing oxygen. In this work pH 6 is the value for the water before the sulfite solution equivalent to the oxygen was added. This latter method corresponds to the necessary control method in feed water treatment, for the p H of the untreated water is the essential factor. EFFECTOF TEMPERATURE. The rate of oxidation was studied in distilled water and in Seattle city water. The results are shown in Figure 2. The difference between the rates of oxidation in distilled and in Seattle city water can be explained by the theory of inhibition (3). The presence of traces of certain organic compounds in the city water would decrease the rate of oxygen removal, since certain classes of compounds are known to inhibit this reaction greatly, The difference in pH between the distilled and city water was not enough to cause this pronounced effect. The pH of the distilled water mas 5.8 to 6.1 while that of the city water was 7.0 t o 7.2. Figure 1 shows that this difference in p H would cause about 10 per cent less oxidation in the city water, while the difference is seen in Figure 2 to be much greater than this. EFFECT OF CONCENTRATION. An excess of sulfite over that necessary for the oxidation causes a great increase in the rate of oxygen removal, The percentage of oxygen removed in 2 minutes a t 20" C. from distilled water with the pH adjusted to 9.6 (8.0 mg. oxygen per liter of water) is as follows' 1.0
On REMOVED
CuSO4
P. p .
%
m.
100 100 23.6
2 10
80
These data show that copper sulfate acts not only as a catslyst in low concentrations but also apparently a$ an inhibitor in higher concentrations. As best economy is secured by using the least amount which gives complete oxidation, 0.1 p. p. m. or 1 pound of copper sulfate in 1,200,000gallons of water is the optimum concentration.
IN 2 MINUTESAT FIGURE1. OXYGENREMOVED VARIOUSPH VALUES
1.5 2.0
02 REMOVED
P. p . m. 0.1 1
EQUXVALENTE OB SIJLFIT~
Vol. 27, No. 3
01REMOVED % 2.5 18.3 58.0
METHOD OF UTILIZATION In chemical plants where the steam is directly used for process heating, no condensate is returned and large amounts of fresh feed water must be used. In those portions of the country where the water naturally has low hardness content, the water goes to the preheater in which most of the dissolved gases are removed. All carbon dioxide is removed and dissolved oxygen is reduced to 0.1 or 0.2 p. p. m. Further re-
T I M E IN MINUTES
FIGURE2. RATEOF OXYGENREMOVAL A . Distilled .water B. Seattle city water
1. 2. 3.
15" C. 25'
C.
50" C.
duction by mechanical methods requires expensive vacuum deaerating equipment. Sodium sulfite can be used to reduce the preheated water to zero oxygen content by introducing the sulfite through a chemical proportioner in the feed line t o the boiler. By maintaining an excess of sulfite in the boiler, protection is assured against air leakage or entrainment of bubbles from the preheater. Moberg (8) cites three examples of laundry operation where hot water for laundry purposes was taken from the boiler preheater. Here the water could not be preheated above 80" C., leaving 1.5 p. p. m. of oxygen in the boiler feed water to be removed with sodium sulfite. This degree of preheating may decrease to no oxygen removal in the cold process softener, with a corresponding increase in the amount of sodium sulfite used. The economics of the latter case are not so favorable, and sufficient time must be allowed for the reaction to go to completion in the cold. The experimental work reported here removes all doubt that the reaction will not be immediately completed at boiler temperatures. If the hot-process softener is used, the softener acts as a deaerator and removes a large part of the dissolved gases due to the temperature rise of the water. However, to produce a
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zero-oxygen water, it, is necessary to treat the softened water with an oxygen-absorbing chemical. Because of the deaeration of the water by the temperature rise, much smaller amounts of chemical are needed to remove the remaining oxygen. Applebaum (a) has described a hot-process plant of 2,500,000 gallons per day capacity in which ferrous sulfate is used to remove the remainder of the dissolved oxygen. The equations show that this chemical is less efficient than sodium sulfite for the purpose: 2Na2SOs O2+2NazS04 (1) 4FeSOa O2 8NaOH 2Hz0 + 4Fe(OH)3 4Na~S04 (2)
++ +
+
++ + +
water is valid only under certain conditions. In order to prevent caustic embrittlement, the A. s. M. E. Boiler Code Committee (1)recommends that there be maintained in the boiler a certain ratio of sodium sulfate to total alkalinity. This ratio increases with the boiler pressure as follows: BOILER PRESSURES Lb./aq. in.
++ + +
It must be stressed that very close chemical control is necessary when the bisulfite is used, for an excess of the bisulfite will rapidly change the water to an acid condition as shown by Equation 3. The use of bisulfite would also be limited to a preheater, as the release of carbon dioxide (Equal ions 4 8 and 4B) in the boiler would be undesirable. Sodium sulfite does not possess these disadvantages, since the simple reaction (Equation 1) with oxygen occurs without changing the alkalinity of the water. The objection to the increase of soluble salts in the feed
PARTSNazSO4 PER PARTTOTAL ALKALINITY EXPRESSED ~8 NalCOs 1
Up t o 150 150-250
2 3
Greater than 250
+
Thus, the use of ferrous sulfate removes alkali from the m-ater, necessitating the addition of caustic soda or more lime in the water treatment. Careful control is necessary to prevent the water from becoming acid. However, if the water is too alkaline, or too high in bicarbonate, as in the plant Applebaum describes, then the use of ferrous sulfate will be equivalent to the addition of acid t o remove the excess alkali or bicarbonate. The presence of the precipitate of the ferric hydroxide may or may not be desirable, depending upon other factors. In cases where very alkaline water or water high in bicarbonates must be treated with acid, or an acid salt, crystalline sodium metabisulfite (Xa2SzO5) may be used. This would undergo the following series of reactions when added to the feed water: NazS206 HzO+2NaHS03 (3) 2NaHSOa 2NaHCOa --it 2NazSOs 2H20 2cOz ( 4 4 2NaHS03 Na2C03-+ 2?u’azSO8 HzO cO2 (4B) 2Na2S03 Oz +2NazS04 (1)
333
A certain amount of alkalinity is carried in the boiler to prevent calcium sulfate scale and retard corrosion. Thus there is always a certain soluble salt content in the feed water, and the addition of sodium sulfate is usually beneficial. ACKNOWLEDGMENT The miters wish to thank W. L. Beuschlein for his practical suggestions during the course of this work.
LITERATURE CITED
.
(1) Am. SOC.hlech. Engr. Boiler Code Comm., Boiler Construction Codes, Combined Ed., pp. 402-3 (1931). (2) Applebaum, S. B., Mech. Eng., 56, 273, 341 (1934). (3) Backstrom, H. L. J., Trans. Faraday Soc., 24, 601 (1938). (4) Backstrom, H. L. J., 2.phys. Chem., B25, 122 (1934). (5) Crist, R H., J . Chem. Education, 8, 504 (1931). (6) Fager, E. P., and Reynolds, A. H., IND.ENG.CHEM.,21, 357 (1929). (7) Griffin, R. C., “Methods of Technical Analysis,” p. 703, New York, McGraw-Hill Book Co., 1927. (8) Moberg, A. R., Combustion, 3 (a), 36 (1931). (9) Powell, S. T., “Boiler Feed Water Purification,” Chap. VIII, N e w York, McGraw-Hill Book Co., 1927. (10) Reinders, TV., and Vles, S. I., Rec. trav. chim., 44, 249 (1925). (11) Semenoff, N., Chem. Rev., 6, 347 (1929). i (12) Solberg, T. W., Holmes, J. A., Summers, R. E., and Baker, L. R., i Power, 75, 70 (1932). (13) Speller, F. N.,J . Franklin Inst., 193, 515 (1922). (14) Titoff, .4.,2. phys. Chem., 45, 641 (1903). (15) Volkovich, S. I., and Belopolskii, A. P., J. Applied Chem. (E. S. S. R.), 5, 509 (1932). RECEIVED October 16, 1934. Presented before the Division of Water, Sewage, and Sanitation Chemistry a t the 88th Meeting of the American Chemical Society, Cleveland, Ohio, September 10 to 14, 1934.
Hygroscopicity of Sugars and Sugar Mixtures JOHNH. DITTMAR, Arbuckle Brothers, Brooklyn, N.Y A definite relatiomhip between the sucrose, to increase the t e n d e n c y to OR many purposes it is invertsugar, and water content of various sugars absorb moisture, and probably desirable to know a t just to be due to the fructose in the what r e l a t i v e humidity and the relative humidity of the surrounding atinvert sugar. H o w e v e r , no a sugar or sugar mixture must mowhere has been found, and the equilibrium definite relationship was estabb e m a i n t a i n e d so t h a t i t s water content will remain conpoints have been graphed. The equilibrium lished between the amount of relative hum,idity or vapor pressure of pure SUinvert s u g a r i n t h e s u c r o s e stant, or below what point the erose, dextrose, fructose, invertSugar, or sucroseproduct, the amount of water alrelative humidity must be held ready present, and the relative in order to overcome the hygroinvert sugar mixtures with rarying percentages of humidity. Browne in 1922 scopic tendencies of the sugar. This is especially truefor invert water can be determined directly f r o m the graph. measured the moisture absorption of various sugars a t 60 and sugar and f r u c t o s e (levulose) which begin to absorb water a t comparatively low relative 100 per cent relative humidity during various periods of time. humidities. The importance of maintaining a controlled No relationship was established for any other relative humidity, amount of moisture in sugars is especially to be stressed in nor were mixtures considered. In 1930 Whittier and Gould relation to bacterial growth, inversion, fermentation, and (8) measured the vapor pressure of sucrose, glucose, and gahardening or softening of sugars and sugar mixtures in stor- lactose a t 25” C. in saturated solution and used these figures age, and in the general troubles experienced with hygroscopic as a measure of their tendencies to absorb moisture; they argued that the hygroscopic tendencies of solids are, for pracsugars. The presence of invert sugar in a sucrose product was known tical purposes, those of their saturated solutions. These
F
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