INDUSTRIAL AND ENGINEERING CHEMISTRY
2842
reagent, grade calcium carbonate to 900 C. in a muffle furnace. Lat,er the commercial grade of unslaked lime obtained from t,he Marblehead Lime Company was found to be an equally efficient stabilizer. Anhydrous pot.assium fluoride was obtained by drying hydrated potassium fluoride in an oven a t 200 ' t,o 300,. C. Steel was introduced into the tubes of cyanogen chloride eit,her as a weighed amount of clean steel t'urnirigs or as a uniform bright strip of steel sheet. Met&od of Testing Stabilizers. Stability tests were carriel out in sealed 6-ml. Pyrex bomb t>ubes. To each tube there were added 3 ml. of cyanogen chloride from a jacketed buret cooled with circulating ice water. The filling of the tubes was carried out in a dry box to prevent condensation of moisture by the cold cyanogen chloride; the openings of the tubes were protected by calcium chloride tubes while the tubes were being sealed. When steel and stabilizer were added, these were placed in the tubes before filling with cyanogen chloride. The sealed tubes were incubated at, constant tcmperature unt,il the liquid had completely solidified. I n nearly every case complete solidification closely followed the initial appearance of a brown p r e c i p h t e and markpd volunie change. For tests at,
Vol. 41, No. 12
65' and 75" C:. the tubes were stored in constant temperature ovens; for tests a t 100" and 125" C. the t,ubes wore placed in metal jackets (as a precaution against explosion) and incubated in t~hermostaticallycontrolled oil baths. Analyses. T h e water content of the cyanogen chloride was determined by slowly evaporating a weighed sample of the material through a weighed U-tube containing phosphorus pentoxide. Soluble iron compounds were determined by evaporating a weighed amount of cyanogen chloride to dryness and digesting the residue in nitric acid. The excess nitric acid was removed by heating the material with concentrated sulfuric acid. The sample was then diluted with water and t,he iron was determined colorimetrically with thiocyanate. LITERATURE CITED
(1) Kharasch, Legault, Wilder, and Gerard, J . B i d . Chem., 113, 537 (1936).
RECEIVED hfarch 9 , 1949. Contribution from the George Herbert Jones Laboratory of t h e University of Chicago. T h i s paper is based in whole on work done for t h e Office of Scientific Research a n d Devrlopment under contract OEMsr-394 with t h e Vniversity of Chicago.
Oxygen Removal from Water by Ammine Exchange Resins J
J
U
G. F. RIILLS' AND B. N. DICKISSO3 Chemical Process Company, Redwood City, Calif. Dissolved oxygen i n water rnax be removed effectively to a level of less than 0.1 p.p.m. by treatment with an anion exchange resin on which reduced copper or silver has been deposited. The metal-resin complex mag be regenerated after use by treatment with suitable reducing agents. The method provides a means of deoxygenating water by chemical means without contamination of the resulting water by added chemicals. The economics of this method are discussed.
0
XPGEK which is dissolved in n~ater has always offered a major corrosion problem when such wat,er JYas heated in contact with iron or steel. Efforts to control this oxidative corrosion have taken two directions. Where contamination of the water with added salts was undesirable, recourse was had to mcchanical deaerators. These have tmhe furt,her advantage of also removing dissolved carbon dioxide which is another act'ive corrosion agent. Chemical methods for the most part have involved the additmionof an excess of sodium sulfite to the water. The oxygen is then removed by reaction with the sulfite. The disadvantage of this method is, of course, t.he contamination of the water by the added salts and t,he increase in the solids content of the water so treated. I n the present method ( 1 ) of removing dissolved oxygen from water, the adsorbent, employed is an anion exchange resin which contains copper in the monovalent or zerovalent form or silver in the metallic state. The resulting resin is then available to remove dissolved oxygen from aqueous media either in a columnar operation or in a batch process. All such anion exchange resins contain amine groups. Thew amine groups in the resin are capable of forming complexes with copper or silver salts which are very poorly dissociated. Such 1 Present addrees, Carbide Br Carbon Chemicals Corporation, Oak Ridge, Tenn.
a resin-metallic complex for copper may be formally represented as shown below:
4RXHz
+ CUSO~+
[Cu(RNHz)r]S04
(1)
where R = anion exchange resin. In this equation the complex with divalent copper is shown. Such a complex is, of course, not effective in oxygen removal. However, reduction of the copper would yield a complex capable of reacting similarly to the familiar cuprous copper-ammonia solutions which have long been used for oxygen removal in gas analysis. This reduction may be accomplished by the use of suitable reducing agents. The most convenient manner of preparing the oxygen-removing resin is first to impregnate the anion exchange resin with ti soluble cupric or silver salt solution. The resulting complex is then preferably reduced with an alkaline solution of sodium hydrosulfite, yielding metallic copper or silver extremely stisceptible to oxidation. The procedure employed and the rcactions involved will be given in the following description of laboratory tests of the method. EXPERIMEKTA L
A sa,mple of Duolite A-3 (Chemical Process Company) after preliminary cycling with first 2 N sulfuric acid and t,heii 1.5 sodium hydroxide was washed free of alkali and treated by passing 0.1 dd cupric sulfate through the bed until saturated. Excess salt was washed from the bed leaving 0.90 mole per lit,cr of wet, tamped resin. This provided two 86-ml. (tamped) beds for parallel runs in 1-inch tubes. The samples were each treated rvith sodium hydrosulfite, using about a 29% excess of reducing agent over that theoretically necessary to reduce the cupric ion to metallic copper according to the equation below: A'\
CuSO4
+ -IrTa2S2O4+ 2R2O-+-Cu + ZTazSOd + 2H2SO:(
(2)
December 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
126 volumes per hour against tap water containing 6.1 p.p.m. of dissolved nitrogen. A removal of 1.15 To Break-through grams of oxygen was obtained per liter Reducing Bath Bed Vol. t o per Liter Bed Moles OP of bed (tamped), corresponding to 0.16 Liters of s o h - Bed Vol. Wash Free of G. Oa Moles On Removed per reMole Copper reof Oa-Free Excess tion per Compomole of oxygen per mole of silver. Sample sition liter bedb Effluentb Regenerant moved moved in Resin Heavier concentrations of silver in the 0.2125 0.24 41 6.81 2,628 2.33 1 0.5 N Duolite A-2 were tried, but the perNazSzOI 0.295 0.33 6 9.42 4,302 2.33 2 0.5 N formance in oxygen removal was far NaaSnOi in 1.25 N from being in direct proportion to conNaOH c e n t r a t i o n . I m p r o v e m e n t in the Flow rate: 30 bed volumes per hour for the first 581 volumes and 50 bed volumes per hour thereaverage performance of this bed could gfter This corresponds t o 3.74 and 6.23 gallons per cubic foot per minute, respectively. b in order to obtain these results in gallons per cubic foot, merely multiply the value given by undoubtedly have been achieved by 7.48. the inclusion of sodium hydroxide in the regenerating bath and by using slower kow rates. A sample of Duolite A-2 treated with ferrous sulfate and reFor one sample, sodium hydroxide (1.25 N ) was incorporated duced with sodium hydrosulfite performed well in the removal of in the reducing bath to neutralize the sulfurous acid formed. dissolved oxygen from water, although tending to lose considerBefore adding the reducing agent, the cupric ion-resin complex able iron upon regeneration. For this reason, these experimente was blue-green in color. As the reducing agent passed down were not continued. through the column (at a 5 volume per hour rate) the blue color was replaced by a deep purple color with overtones of a metallic copper sheen. Some colloidal copper and/or cuprous oxide also STABILITY appeared in the effluent. The resin was again washed with water Small amounts of metal are leached from the resin during until free of excess regenerant. Copper lost in this step is known regeneration, especially when the bed is first put into operation. to be small and was neglected. Such losses seem negligible after the first few cycles. In the The resin prepared as described was then tested for its oxygensilver complex described above, no loss during the regenerative removing capacity, with the results summarized in Table I. phase was detectable although measurable leaching occurred with heavier silver concentrations. The following items are noteworthy in Table I: (1) the drastic The metallic-resin complex has a very small but definite reduction in rinse water requirements resulting from the sodium dissociation constant so that infinitesimal leakage occurred during hydroxide in the regenerant; (2) the evidence of better regenerathe service run a t neutral or higher pH’s. This leakage could be tion arising from the inclusion of alkali in the reducing bath; and (3) the extremely high flow rates possible. (The top rate detected for the copper complex by passing the effluent through a in most water-treating installations is about 16 bed volumes per trap bed of regenerated Duolite A-2 where a green zone slowly hour. I n small beds, a rate of 5.to 6 volumes per hour is usually built up in the top of the bed. With acid solutions, the leakage necessary to minimize channelmg.) It should also be noted that the achieved oxygen to copper ratio to the break-through becomes quite perceptible. point of sample 2 is well above 0.25; obvlously the total potential I n cases where traces of the impregnating metal in the water capacity is much greater. Dissolved oxygen continues to be would be objectionable, a trap bed of resinous cation exchanger removed long after break-through with the ratio in question approaching 0.5, the theoretical maximum. This is conclusive in the sodium state could be employed t o treat the deoxygenated evldence of the zero valence of the reduced copper and the effluent. I n general, even calcium or magnesium ions should not validity of Equation 2. interfere too seriously with trapping the heavy metal cations The mechanism by which the amine resin could retain zerovalent copper is not apparent, unless it is simply deposited on the which are preferentially adsorbed. A trap bed of anion exexternal and internal surfaces of the resin granules and held there changer in the free amine state would also function to keep this mechanically or by physical adsorption of colloidal copper. metallic cation level in the effluent to practically nil. Despite the leaching of metals by acid, it is still possible to use the resin-metallic complex for oxygen removal in moderately acid During the service run the influent of deionized water containing from 1.6 to 3.7 p.p.m. of dissolved oxygen was passed solutions. The authors have actually tested a resin-copper downflow through the resin bed and delivered into the bottom of a complex in the removal of oxygen from solutions having a pH Bask which overflowed continuously, sweeping out any water as low as 1.5. In this case oxygen is completely removed but the contaminated with oxygen from the air. The dissolved oxygen adsorption capacity is only about 3oy0 of that obtained on a content of the effluent was determined by the Winkler (3)method, neutral water. Furthermore, the copper is removed from the Break-through was taken a t the first appearance of dissolved resin fairly rapidly and the material must be reimpregnated with oxygen in the effluent (0.1 p.p.m. or less). In the course of the copper after only a few cycles of use and regeneration. test the resin regained the blue-green color which it showed iniCapacity losses resulting from leaching of metal can be retially. The state of exhaustion of the resin could thus be approxistored by periodic treatments of the bed with a solution of the mately followed by observing the advance of this blue-green color appropriate copper or silver salt, but over a long period of time down the column. there could be an accumulation of inert copper or silver in the A sample of Duolite A-2 containing 0.23 mole of silver per liter bed which would represent a permanent capacity loss. of wet, tamped bed was reduced with 84 grams of sodium hydroHowever, no evidence of such a capacity loss could be demonsulfite per liter with no loss of silver and run at 59 volumes per strated in a program of continuous cycling covering 100 cycles. hour with tap water containing 6.1 p.p.m. of dissolved oxygen Moderately high flow rates (about 50 volumes per hour), water taking up 1.61 grams of oxygen per liter t o break-through. The containing about 7 p.p.m. of oxygen, and a small bed (38 ml.) ratio of oxygen to silver was just under 0.22. A ratio of 0.25 were employed. The bed became permanently darkened and a would correspond to complete exhaustion of the metallic silver 10% volume increase was observed. As yet a rigorous testing by oxidation to the monovalent form. This run is somewhat program more nearly simulating actual field condition has not atypical in having such a delayed break-through in a small tube. The bed was regenerated with sodium hydrosulfite and rerun a t been undertaken.
TABLEI. CAPACITY AND WASHING CHARACTERISTICS O F DUOLITEA-2-cOPPER COMPLEXa
e
*
a:
-
2843
INDUSTRIAL A N D E N G I N E E R I N G CHEMISTRY
2844
OTHERREGENERANTS
Because sodium hydrosulfite is a relatively expensive chemical, considerable effort was expended in a search for cheaper regenerants. However, potential agents which are relatively cheap, such as alkaline sodium sulfite and alkaline formaldehyde, are either very inefficient in the reduction of the copper-amine resin complex or do not work a t all. The only additional reducing agents found so far which work efficiently are sodium hydrosulfite and sodium formaldehyde sulfoxalate. The latter, prepared by the method of Wood ( S ) , is of interest in that the cupric ion-resin complex is reduced only to the cuprous state.
Vol. 41, No. 12
flow rates and larger beds would increase efficiency and reduce the 4.8-cent charge appreciably. The 4.8-cent figure is also somewhat inflated because excessive regenerant unquestionably was used. However, it is seen that the method is not competitive on a cost basis with sodium sulfite dosing nor is it competitive with mechanical deaeration of boiler feed water at high dissolved-oxygen concentrations. I t is anticipated, nevertheless, that there will be numerous commercial applications for this novel method of removing dissolved oxygen from aqueous solutions.
ECONOMICS OF THE OXYGEN-REMOVAL PROCESS
The cost of oxygen removal by this new method is a matter of prime interest. The largest item of cost in this method is the cost of regenerating the oxygen-removing resin. Other costs, such as the regeneration of the cupric ion trap and the occasional reimpregnation of the anion exchange resin with cupric salts, are not considered here but would be relatively small. Overhead and amortization items, although appreciable, cannot be calculated with any exactness here. The calculated cost of this treatment on the basis of a 25cent per pound price for sodium hydrosulfite and 4 cents per pound for sodium hydroxide is 4.8 cents per 1,000 gallons of water containing 1 p.p.m. dissolved oxygen. Data listed for sample 2, Table I, are employed in arriving a t this figure. Slower
ACKNOWLEDGMENT
hluch of the work here reported was carried out under contract with the Bureau of Ships, Navy Department, Washington, D. C. Permission to publish this information has been granted. LITERATURE CITED
(1) Milla, G. F., patent applied for. (2) Scott, W. W., “Standard Methods of Chemical Analysis,” 5tb ed., Vol. 11,p. 2079, New York, D. Van Nostrand Co., Inc.. 1939. (3) Wood, H., Chem. Age (London),38,85(1938).
RECEIVEDM a y 10, 1949. Presented before the Division of Industrial and Engineering Chemistry a t t h e 115th Meeting of the ~ M E R I C A NCHEXICAI, SOCIETY, San Francisco, Calif.
ractional Distillation of Multicomponent Mixtures NUMBER OF TRANSFER UNITS A. J. V. UNDERWOOD 38 Victoria S t . , London, S . W . I , England Equations are presented for calculating the number of transfer units required for the fractionation of multicomponent mixtures. Constant relative volatility and constant molaI reflux are assumed.
Considering, for example, a ternary mixture and applying Equation 2 to each of the three components, then
THE
number of transfer units required to effect a given separation in a packed column is defined by Chilton and Colburn (1)as d&I dl\7 = 7:)
The same integral occurs in the expression given by Thormann (6) for the height equivalent to a theoretical plate in a packed column and in the expression given by Hausen ( 4 ) as a proposed conception of a theoretical plate. For binary mixtures matbematical solutions of this integral have been given by Chilton and Colburn ( 1 ) for the case of total reflux and by Hausen ( d ) , Dodge and Huffman (S),Colburn ( 2 ) and by the author (8,9) for the case of partial reflux. In all these cases constant relative volatility and constant molal reflux were assumed. For multicomponent mixtures, when constant relative volatility and constant molal reflux are assumed, the equations corresponding to Equation 1 can be integrated readily by making use of a mathematical transformation that has been employed by the author (‘7, 10-18) for calculating the number of theoretical plates. Differentiating Equation 1 gives
-
(3c3
Yl
where the subscripts 1, 2, and 3 denote the components.
Xow
ya = 7?1X3 i- a3
and
* Ys -
ff3x3 a323
f apx2
+
01151
mith similar expressions for the other two components and Equations 3a, b, and c become
