2848
INDUSTRIAL AND ENGINEERING CHEMISTRY STEAM-AIR AGING
The rubber compound used in curing bags for tire production must be capable of withstanding high temperature cyclic steam and air aging. Natural rubber compounds tend to harden in this +rvice with failure resulting from brittleness and eventual cracking, GR-I, on the other hand, has a tendency to become soft and the inside of tho curing bags deteriorates to the point of plugging -he valve stems. Figure 9 shows the effect of diolefin type on thr *team-air aging of Butyl polymers. Each cycle in this accelerated Tzst consists of 8 hours in 100 pounds per square inch gage stram rnd 8 hours in 80 pounds per square inch gage air a t 260 F. Thp .hange in Durometer hardness is an index of the resistance of Butjl compounds t o this type of aging. Considering first the GR-I type, improved results are obtained with inrreasrd unYaturation. The GR-1-25 compound is shown to have a Durom+ter hardness of 45 after twelve cycles compared to three cycles TI reach the same hardness in the GR-I compound. Piperylene is in the same class as isoprene. On the other hand, butadiene is much superior. Very little loss in Durometer hardness is noted inr the 2.2y0hutadirne Dolvmer and an increase in hardnev i s
Vol. 41, No. 12
observed with polymers above 3.0% butadiene. IIigher iwprrne polymers, on the other hand, continue to soften. ACKNOWLEDGMENT
The authors wish to acknowledge the assistance of their colleagues in the rubber laboratory of the Standard Oil Development Company in the evaluation of these polymers. I n particular, the work of L. T. Eb>--,D. J. Buckley, and F. P. Ford on developing methods for testing IOK temperature properties made that: portion of the paper possible, For other evaluations the authors are indrbted to S. B. Robison, A, W.Hubbard, and W. F Fischer. LITERATURE CITED
(1) Gallo, 8. G., Wiese, H. K., and Nelson, J Fa,IND.ENC.C : m x . " 40, 1277-80 (1948). (2) Haworth, J. P., and Baldwin, F. P., Ibl:d., 34,13014 (1942). (3) McKinley, R. B., Electric W ~ r l d 124, . N o . 25, 52 (Dec. 22, 1945).
!4) Thomas, R. M.,Lightbown, I. E., Sparks, W. J , , Frolich, P. K., and Murphree, E. V., IXD.ENG.CHEM.,32, 1253-92 (1940). (5) Turner, L. B . , Haworth, J. P., Smith, W. C., and %appg11,. L , Ibid., 35, 958-63 ( I 943). RECEIVED August 7. 1948. Presented before the meeting of the IXvision of Rubber Chemistry, A X E R I C A N CHEYICAJ.~ SOCIFTY,Lon Angeles, Calif., July 22: 1948.
Stabilization of Cyanogen Chloride 91. S. KHARASCH, AL4N R. STILES, ELWOOD V. AND
JEXSEN.
DANIEL W. LEWIS
University of Chicago, Chicago, I l l , Commercial cyanogen chloride, stored in steel containers, contains water and soluble iron compounds which catalyze its transformation into cyanuric chloride. Sodium pyrophosphate, 2 to 5 % by weight, inhibits the effect o f these impurities and is a very effective agent for stabilizing cyanogen chloride.
C
YAXOGEK chloride, when stored in steel containers, is gradually transformed into a nonvolatile solid consisting mainly of cyanuric chloride. This process is exothermic and is markedly accelerated with increasing temperature, When the material is stored in large containers so that the heat cannot be dissipated, the temperature and consequently the pressure may 4se rapidly; several explosions of containers filled with cyanogen ahloride have occurred during storage. i n an attempt to find a substanc? which would inhibit the oolymerization of cyanogen chloride, a study was made of the Factors which influence the rate of the polymerization. On the hasis of these findings, compounds were selected for testing as potential stabilizing agents for cyanogen chloride. One compound, sodium pyrophosphate, n a s found to be v x y effective in inhibiting the polymerization of cyanogen chloride a t temperalures between 25' and 125' C. FACTORS INFLUESCINC, THE POLYRIERIZATION O F CYANOGEN CHLORIDE
Commercial cyanogen chloride, prepared by the chlorination of hydrogen cyanide, is about 98% pure. The following impurities were found to be present, varying from batch to batch within the limits given: hydrogen cyanide, 0.37 to 2.350/00; hydrogen chloride, 0.06% ; arid water, 0.03 to 0.4%. After storage in steel containers t'lere is also present a small amount c.f a soluble iron compound, presumably formed by the action cf the container
either of cyanogen chloride or of the water and hydrogen chloride present as impurities. The presence of iron is probably the most important factor in promoting the polymerization of cyanogen chloride. The effect of iron is clearly shown by comparing the stability of cyanogen chloride in glass containers with that of material in similar containers to which have been added srnall amounts of steel turnings. The data recorded in Table I show the catalytic effect o f iron.
TABLE I.
EFFECT O F I R O N O S STABILITY OF PUR.E CYANOGEN
CHLORIDE .-.~~~ Days for Complete
Solidificationa Steel turnings added 65 66, 7 0 b (A-1). 22 (24-2) 100 40 7 128 20 1.5 a All tests v e r e carried o u t in duplicate; a different batch of cyanogen chloride was used a t each temperature. b Figures indicate that duplicate samples solidified a t different times. C .&-I and A-2 refer t o two different samples of steel used. 'Temp.,
c.
Glass alone 148
The tendency of cyanogen chIoride to polymerize in the presence of iron increases with increasing water content. When 0.2 and O.5y0of water, respectively, were added t o samples of cyanogen chloride, the stability of the cyanogen chloride was markedly decreased, both in the presence and absence of stecl. Itloreover, the performance of the stabilizing agent was adversely affected by the presence of excessive quantities of water. The data are summarized in Table 11. Higher concentrations of hydrogen chloride decrease the stability of cyanogen chloride somewhat, but the effect seems to be less marked than that of water and iron. The amount of hydrogen chloride in commercial cyanogen chloride F a s consistently
December 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY pyrophosphate.
2841
A t various time intervals tubes were opened
TABLE11. EFFECTOF WATER ON STABILITYOF CYANOGEN and their filtered contents were analyzed for water and soluble
iron content. Each filtered sample was tested for stability by incubating portions of i t a t 125' C. in glass alone, in glass with steel added, and finally with steel and sodium pyrophosphate added. Impurity Content When cyanogen chloride was aged without sodium pyrophosCommercial sample phate, the iron content became progremively higher and this HCN 1 1 4 7 ' material became less and less stable toward subsequent heating HCI, b,056'?$ Hz0 0.03% in glass alone. I n cyanogen chloride aged at 65" C. in the pres0 . 2 % HzO added 11, 1 2 c 7 89 ence of sodium pyrophosphate, the iron content remained very 0.574 Hz0 added 8, 120 3, 6 C 15 low, the water content decreased steadily, and the material rea For tubes containing 3 ml. of cyanogen chloride, 0.3 gram of steel turnmained resistant t o polymerization in glass. On subsequent ings and 0.18 gram ( 5 % ) of sodium pyro,phosphate were used. incubation at 125" C. sodium pyrophosphate proved a n effective b > signifies that sample was still liquid a t end of the given period. stabilizer for samples of cyanogen chloride treated in either of the c Duplicate samples solidified a t different times. ways described. The results of this experiment are summarized in Table IV. Twenty-five-milliliter tubes of cyanogen chloride were used for TABLE111. EFFECTOF STABILIZERSON POLYMERIZATION OF each aging experiment. To each tube there was added a 4 CYANOGEN CHLORIDE X 0.375 X 0.0625-inch strip of steel, and 1.54 grams (501,) of Days for Complete Solidification, in Presence of Steel sodium pyrophosphate were added t o each tube in the latter Temp Potassium Sodium series. For testing the stability of the aged samples the contents a C.d' Control Calcium oxide fluoride pyrophosphate of the 25-ml. tube were filtered with pressure through a porous 65 66, 700 >228b 173C >228b disk, and duplicate 3-ml. samples of the filtrate were incubated 75 35 159, 1810 69, 8 S C 247 100 7 20 13, 150 > 209 b at 125' C. I n these incubations a 2 X 0.375 X 0.0625-inch steeY 2.5 174, >209b,c 125 1, 1 . 5 C 3.5 strip and 185mg. ( 5 % ) of sodium pyrophosphate were used. CHLORIDE
Days for Complete Solidification a t 100' C. Steel turningsa, Glass alone . Steel turnings 5% Na4Pz0~ 40 7 >209b
a I n tests a t 6 5 O and 75O C. stabilizer in the amount of 2% of the weight of cyanogen chloride was used; in tests a t 100' and 125' C. 5% of stabilizer was used. b > indicates sample still liquid a t end of period. C Duplicate samples aolidified a t differenttimes.
very low; probably this impurity contributes less t o the instability of cyanogen chloride than the other substances mentioned. Hydrogen cyanide, within the limits found in commercial samples, appears to have no effect on the stability of cyanogen chloride. TESTING OF INHIBITORS
In accordance with the foregoing results, possible stabilizing agents were selected for testing on the basis of their ability t o overcome the effect of iron, water, or hydrogen chloride. The following substances were subjected to preliminary testing: barium oxide, boric anhydride, calcium oxide, tetraethyllead, magnesium oxide, potassium fluoride, sodium borate, sodium carbonate, sodium pyrophosphate, disodium hydrogen phosphate, trisodium phosphate, stannic oxide, titanium oxide, triphenylcarbinol, urea, and zinc oxide. Dimethylcyanamide and propylene oxide had been recommended by other investigators for stabilizing cyanogen chloride, and these compounds were also tested. Of all the substances mentioned only three showed promise as stabilizing agents for cyanogen chloride-calcium oxide, potassium fluoride, and sodium pyrophosphate-although many of the others showed some stabilizing effect (Table 111). While all three of these substances showed marked stabilizing effect at lower temperatures, only sodium pyrophosphate maintained its effectiveness at higher temperatures. From all considerations sodium pyrophosphate appeared to be the most effective stabilizing agent for cyanogen chloride.
The effectiveness of sodium pyrophosphate as a stabilizing agent is decreased when the water content of the cyanogen chloride is increased (Table 11). ' For adequate protection against polymerization the water content of the commercial cyanogen should be kept below 0.270. Since sodium pyrophosphate is virtually insoluble in cyanogen i t is necessary to use relatively large amounts of stabilizer. Although 2y0 by weight appeared t o be satisfactory at ordinarb temperatures, 5% was required at higher temperatures. The use of 5% of stabilizer under all conditions affords a margin of safety. Separation of cyanogen chloride from the stabilizer is easily accomplished by decantation, filtration, or distillation. EXPERIMENTAL
Materials Used. Commercial cyanogen chloride, analyzing about 98% pure, was obtained from t h e American Cyanamid Company. Material supplied in glass bottles contained little or no iron; material supplied i n steel containers already showed appreciable iron content. The sodium pyrophosphate first used was prepared by heating reagent grade disodium hydrogen phosphate dodecahydrate to 850" C. (red heat). Later the anhydrous product obtained from the Victor Chemical Company was found to be equally satisfactory. Calcium oxide was obtained by heating anhydrous
TABLEIV.
ACTIONOF SODIUMPYROPHOSPHATE ON IMPURITY CONTENT AND STABILITY OF CYANOGEN CHLORIDE
MECHANISM OF ACTION OF SODIUM PYROPHOSPHATE
Soluble iron compounds, formed by the attack of cyanogen chloride or its impurities on steel, markedly catalyze the polymerization of cyanogen chloride. Sodium pyrophosphate, which is known t o be a specific inhibitor for iron catalysis ( I ) , effectively overcomes this catalytic effect. However, sodium pyrophosphate not only inhibits the catalytic effect of iron already present in cyanogen chloride but also retards the attack on steel t o form soluble iron compounds. Moreover, sodium pyrophosphate decreases the water content of cyanogen chloride. These facts are demonstrated by the following experiment : Cyanogen chloride was allowed to age at 65' C. in contact with steel, in both the presence and absence of 5% of sodium
Material Aged a t 65" C. No aging (control) I n presence of steel, days 10 20 30 40 I n presence of steel and sodium pyrophosphate, days 10 20 30 40 a b
Analysis Soluble Hz0, iron,
%
%
. ..
0.080
0,008
0.012 01087 0.019
0.022
0.008
0.061 0.080
0,053 0.007 0.026 0.006 0 , 0 2 0 0.008 0,012
-
Stability of Previouely Aged Sample (Days for Complete Solidification a t 125' C.) Steel and Glass Steel NaaPzO, alone added added 20, 23O 1.5 64, 82Q
7
1.5
77
6 , 67O 4
1.5 1.5
68,50,>70u*b 64s 60, >60ai)
10, 160 >79b 52, >68a,b >59b
Duplicate samples solidified a t different times. > indicates sanple was still liquid a t end of period.
1.5
1.5 2 2 1.5
52 77, >79a~b >68b 43,>59aEb
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 t o 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 the University of Chicago. This paper is based in whole on work done for t h e Office of Scientific Research and Devrlopment under contract OEMsr-394 with the 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 in 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 t o 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 i n 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 t o reduce the cupric ion t o metallic copper according to the equation below: A'\
CuSO4
+ -IrTa2S2O4+ 2R2O-+-Cu + ZTazSOd + 2H2SO:(
(2)
