M a r . , 1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
CONTRIBUTIONS FROM THE. CHEMICAL WARFARE SERVICE, U.S. A.
2 I3
I
THE REMOVAL OF CARBON MONOXIDE FROM AIR]
detonation of high explosives constitutes one of t h e most serious of t h e difficulties connected with this work, and has necessitated elaborate equipment and FIXEDNITROGEN RESEARCH LABORATORY, AMERICAN UNIVERSITY, extensive military training in mine rescue work.’ WASHINGTON. D c. C A R B O N M O N O X I D E I N PEACE-carbon monoxide is Received January 16, 1920 also a serious hazard in peace as well as in war. I n The following article is a summary of investigations the manufacture of power and illuminating gas, and o n t h e removal of carbon monoxide from air carried i n t h e metallurgical industries where this gas is largely on a t the American University Experiment Station2 and a t cooperating laboratories during 191 7 and 1918. employed, casualties, and indeed fatalities, are conThese investigations were supported mainly by funds stantly occurring. I n coal mining, in certain classes of allotted by t h e Navy Department, and led t o t h e de- copper mining, and wherever explosives are used i n velopment and manufacture of a carbon monoxide confined spaces, carbon monoxide is a serious menace responsible for t h e loss of many lives each year. Leaky mask for naval use. CARBON C TON OXIDE I N WAR-carbon monoxide, flues, exhaust gases from explosion engines, improper ventilation where coal fires are employed, and t h e air because of its cheapness, accessibility, and ease of manufacture, has been frequently considered as a t o which firemen are exposed in burning buildings, possible war gas. Actually, i t appears never t o have all constantly t a k e a not inconsiderable toll of lives. DIFFICUI TY O F REMOVING CARBON MONOXIDE F R O M been used intentionally for such purposes There are was and is, therefore, no question of the a number of reasons for this, b u t t h e decisive one cer- AIR-There tainly is its relatively slight toxicity. Several minutes’ importance of protection against this gas both in war inhalation of a mixture of one part in I O O parts of air and in peace. Yet a t t h e beginning of these investiis required t o produce unconsciousness, while with a gations t h e only effective means known for this purpose number of other toxic gases actually employed, such as was t h e completely enclosed oxygen helmet-so phosgene for instance, a similar length of exposure t o cumbersome and heavy (40-60 lbs.) t h a t it is burdenquite out of t h e one past i n I O O , O O O parts of air, t h a t is, t o a mixture some t o use even in rescue work-and a thousand times more dilute, will prove fatal. Since question for men i n action. Moreover, i t is far too i t is very difficult t o set up t h e required concentrations expensive for any wide application. The reasons why t h e removal of carbon monoxide of even t h e most toxic gases over significant areas in t h e open, it is evident t h a t no possible degree of cheap- from air has been found so difficult lie in t h e physical ness, accessibility, etc., could overcome so serious a and chemical properties of this gas. It has so low a boiling point and critical temperature t h a t one cannot handicap. Carbon monoxide is then quite out of t h e question expect adequate adsorption a t ordinary temperatures for a n y intentional use as a toxic war gas, yet i t is, even by an active adsorbent. Thus charcoal under nevertheless, a source of serious danger both in marine these conditions adsorbs very little of it, little more, and land warfare, and defense against i t has been found indeed, t h a n i t does of nitrogen.2 The known innecessary. Defective ventilation i n t h e boiler rooms solubility of carbon monoxide in all solvents similarly of ships, and fires below decks both in and out of ac- precludes its removal by physical absorption. Chemically, carbon monoxide is decidedly inert at tion, are specially dangerous because of t h e carbon monoxide which is produced. I n one of t h e naval room temperature. Caustic alkalies convert it into engagements between t h e Germans and t h e English, formate only when fused or when t h e solution is strongly defective high explosive shells after penetrating into heated. Heated sodium amide converts i t into enclosed portions of ships, evolved large quantities ~ y a n i d e . ~Solutions of ammoniacal cuprous salts of carbon monoxide, and this killed large numbers of t h e absorb a limited amount of this gas with formation crew. On shore, machine gun fire i n enclosed spaces of a n addition compound. I t is oxidized by many such as pill boxes and i n t a n k s liberates relatively large oxidizing agents; b u t , so far as was known i n 1917 quantities of carbon monoxide and has been responsible when this investigation was started, t h e reaction is for numerous casualties. Similarly i n mining and sap- rapid a t room temperature only with very powerful ping operations t h e carbon monoxide liberated from t h e and reactive oxidizing agent^,^ such as palladium chloride, gold chloride, platinum chloride, osmic acid 1 Published by permission of the Director of the Bureau of Mines, and the Director of the Chemical Warfare Service. and permanganic acid in solution. Certain solids, as 2 The Experiment Station was established by the Bureau of Mines in silver 0xide,4 yellow mercuric oxide,4 and cobaltic 1917, and on July 1, 1918, was constituted the Research Division of Chemical By Arthur B. Lamb, William C. Bray and J. C. W. Frazer
Warfare Service. The first investigations (1917) were initiated under the direction of J. F. Norris. As more emphasis was placed upon the problem because of the requirements of the N a v y a special Carbon Monoxide Unit was established in December 1917, in the Defense Chemical Research Section, A. B. Lamb, Chief. The work of the cooperating laboratories was also coordinated in this Section. In May 1918 W. C. Bray assumed charge of the Carbon Monoxide Unit in Washington, and was succeeded by R . G . VanName in September 1918.
1 See Mine Rescue Work, Capt. H. D. Trounce, Engineer Reserve Corps, U. S. A., Professional Memoirs, Corps of Engineers, U S A., 10 (1918), 549. 2 Freundlich, “Kapillrlrchemie,” 1909. 8 Beilstein and Geuther, Ainn , 108 (1858), 88, Gmelin-Kraut, 11, 1 , 299 (1906) 4 Abegg, “Handbuch,” 111, 2, 142-3 (1909); Fay, et el., Polytech. Eng , 10 (1910), 72
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oxide’ were also known t o react with t h e pure gas a t this temperature, b u t t h e reaction was presumably slow at low concentrations of t h e carbon monoxide. Catalysts for t h e reaction with gaseous oxygen were known, such as palladium or platinum, b u t nothing approaching a quantitative removal of carbon monoxide a t room temperature had been realized. R E Q U I R E M E K T S F O R A G O O D ABSORBENT-NOr is mere removal of carbon monoxide by any means t h e sole requirement of a satisfactory carbon monoxide absorbent. As was pointed out in a recent article entitled “Gas Mask there are a number of such requirements. I n t h e first place, t h e absorbent must have a high activity, t h a t is, because of t h e considerable velocity and volume of t h e inhaled air stream in any feasible, portable breathing apparatus, the absorbent must be able t o reduce concentrations of carbon monoxide in the inhaled air of, say, 0 . 2 per cent t o 4 per cent down t o 0.01 per cent in about one-tenth of a second, and, what proved t o be still more difficult, it must be able t o do this even at temperatures as low as 0’. Second, the absorbent must have a considerable absorptive c a p a c i t y . For, on t h e one hand, t h e mask must have a “life” of a t least an hour or two, t h a t is, i t should afford satisfactory protection under ordinary conditions for t h a t length of time. This can, of course, be secured b y using large amounts of absorbent. But on t h e other hand, t h e size of a portable equipment for men in action is decidedly limited. Again, t h e absorbent must offer a low breathing resistance, t h a t is, t h e wearers of t h e mask, particularly troops in action, must be able t o breathe freely and deeply. This means t h a t only a coarsely porous material or one made up of large granules can be employed, and t h e consequent limited area of t h e absorbent means a n additional tax upon the activity of t h e material. The use of a liquid absorbent can be considered only as last resort. Finally, the absorbent must have a considerable physical and chemical stability. T h a t is, t h e porous material, presumably granular in nature, must be hard and firm enough t o withstand t h e rough handling and jolts t o which i t will be subjected in actual field use; i t must not crush or be subject t o abrasion with the consequent formation of fines. Chemically, t h e absorbent must be sufficiently permanent t o withstand long storage a t varying temperatures u p t o s o o without deterioration. During use i t should be unaffected by the normal constituents of t h e air and should not disintegrate or become deliquescent. If t h e absorbent should be affected b y moisture, provision must be made for drying t h e entering gases and for keeping t h e canister tightly closed when not in use. The problem was, therefore, not merely t o find a carbon monoxide absorbent which would react a t oo, but one which would react very rapidly a t t h a t temperature, have a considerable capacity, be hard and firm enough t o retain a porous structure with rough handling and be chemically stable. Below are given brief 1
1
Wright and Luff, J . Chem S O C 83 , (1878), 1, 504. Lamb, Wilson and Chaney, THIS JOURNAL, 11 (19191, 420.
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accounts of the chief lines of attack, stated approximately in chronological order, which were followed. ABSORBENTS INVESTIGATED
OZONE-while almost out of t h e question for use in a portable mask, there was a possibility t h a t ozone electrically generated might be made t o react rapidly enough with carbon monoxide t o serve as a means of destroying this gas in confined spaces, such as in submarines or in boiler rooms where a permanent ozone generator could be installed. Better still, i t was hoped t h a t passage of t h e carbon monoxide-air mixture through t h e ozonizer might, by t h e alternate consumption and re-formation of ozone, result in t h e oxidation of more carbon monoxide t h a n would correspond t o t h e rates of ozone production of the ozonizer. This possibility was investigated in the fall of 1917 b y R . E. Wilson and A. B. R a y a t t h e American University Experiment Station, and later by F. 0 , Anderegg a t t h e University of Illinois and a t Purdue University. Wilson and R a y found t h a t in a 5 per cent carbon monoxide-air mixture, passed a t a rate of 500 cc. in 1 5 min. through an ozonizer capable of generating 3.5 per cent of ozone in air under the same conditions, a 50 per cent conversion t o carbon dioxide occurred a t room temperature, while at one-fifth t h e rate an 85 per cent conversion occurred. When oxygen was used in place of air no oxidation of t h e carbon monoxide could be detected.’ By passing t h e carbon monoxide-air-ozone mixture after leaving t h e ozonizer through various catalysts, of which silver, silver oxide, and lead were apparently t h e best, a more complete oxidation of t h e carbon monoxide was obtained, so t h a t a 4 per cent carbon monoxide mixture was 8 0 per cent oxidized in 2 0 min. a n d a 0.4 per cent mixture in I O min. F. 0.Anderegg confirmed t h e results of Wilson a n d Ray, b u t observed t h a t t h e silver after some t i m e appeared t o lose its effectiveness. He also tried introducing silvered asbestos directly into t h e discharge tube, in the hope of securing a more rapid decomposition and re-formation of ozone, with possibly a more complete oxidation of t h e carbon monoxide. The results were somewhat irregular but in general this procedure appeared t o be disadvantageous, a s t h e ozone concentration was reduced almost t o nothing without any apparent effect on t h e oxidation of t h e carbon monoxide. N o better results were obtained b y using a very large ( 2 0 liter) corona discharge t u b e in place of t h e usual ozonizer tube, and applying a n alternating potential of 60,000 volts. I n all of these experiments many inexplicable variations occurred, so t h a t a more careful investigation is desirable. The d a t a obtained b y these investigators all indicate t h a t t h e reaction occurs a t best only in stoichiometric proportions, t h a t is, a molecule of ozone is 1 This confirms the results of Remsen and his students, and of Jones and of Waters, Remsen and Southwerth, A m J. Sci., 2 (1876), 136; Ber., 8 (1875), 1414; Remsen, A m . Chem. J . , 4 (1882), 50; Remseo and Keiser, Ibid., 4 (1888), 454; Leeds, I b i d . , 5 (1883), 250; W. A. Jones, I b i d . , S@ (1903), 40; Waters, I b i d . , SO (1903), 50. I t is not clear, however, whether Jones and Waters used oxygen or air in their experiments.
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
consumed for every molecule of carbon monoxide oxidized. So long as such is t h e case, this method of eliminating carbon monoxide appears hardly feasible on account of t h e large and expensive electrical installation required t o produce t h e ozone. Thus, on this basis, t o purify IOO,OOO cu. f t . per hr. of air containing one-tenth of one per cent carbon monoxide would require zoo kilowatts per hour of electric energy, with t h e most efficient ozonizer. P A L L A D I U M A S A CATALYST-one of the first methods t o give positive results a t room temperature was t h e use of palladium as a catalyst for the combustion of carbon monoxide with t h e oxygen of t h e air. This method was studied b y a group of men a t the University of Chicago, working under t h e direction of Professor J. Stieglitz. While it was recognized t h a t t h e limited supply and high cost of palladium were serious handicaps, it was hoped t h a t a method might be developed for using this substance in minute quantities. A large number of experiments were made with finely divided palladium, prepared by reduction under different conditions, and subjected subsequently t o different drying and heat treatments. Palladium oxide and mixtures of t h e oxide with t h e metal (palladium black) were also tested. Small glass tubes, usually about 3 mm. in diameter, were packed with alternate layers of glass wool and catalyst, 0.2 t o 0.7 g. palladium being used in each experiment. Air containing a known amount of carbon monoxide, 0.5 t o 3 per cent, dried over soda lime and calciun, chloride, was passed through t h e catalyst rapidly, usually 5 0 0 cc. in from I t o 5 min. Many samples were prepared which initially removed carbon monoxide completely, b u t the catalysts always “died” more or less rapidly with continued use; others showed a very slight activity. When t h e catalyst was active a marked heating effect was always observed and it is probable t h a t sintering of t h e catalytic material was one of t h e reasons for deterioration. The palladium was also found t o be sensitive t o impurities, and accordingly t h e results were not completely reproducible. I n August 1917 similar experiments with asbestos or clay impregnated with palladium were performed at t h e Bureau of Mines, Pittsburgh, by T. D. Stewart, who came from Chicago for this purpose. The results were not encouraging; t h e impregnated materials were less active t h a n the palladium alone, and always deteriorated with use. The activation of certain metal oxides with small amounts of palladium was also considered a t several laboratories. Some promising results were obtained with freshly prepared materials, b u t on account of t h e known sensitiveness of palladium t o impurities, a n d its cost, t h e work was not continued. As an example may be cited some experiments a t t h e University of California in January 1918, with a porous copper oxide (apparent density 1.38), which will be referred t o later. While alone the copper oxide removed initially only 50 t o 20 per cent carbon monoxide from a one per cent mixture with air, in two experiments with material containing 0.25 and 0.4 per cent palladium 95 t o I O O per cent were removed initially
2x5
a t room temperature and 80 t o 85 per cent after z or 3 hrs.’ use. A 5-cm. layer of absorbent wasemployed and t h e gas was passed through i t a t t h e rate of about 2 liters per min. per sq. cm. cross section. A simple calculation shows t h a t t h e action of the activated material was a i least partly catalytic. The copper oxide granules were impregnated with a dilute solution of palladium nitrate which had been prepared b y evaporating a solution in concentrated nitric acid t o a small volume a n d diluting with cold water. The impregnated granules were heated in air a t 450° t o 500’ in an electric oven for a short time before use. I n another experiment in which the palladium nitrate solution after dilution was boiled, a flocculent brown precipitate was formed, and t h e resulting granules showed no activity. It is not known whether this negative result was due t o a poisoning of t h e palladium or t o t h e observed change in t h e palladium nitrate solution on boiling. MERCURIC
O X I D E A N D C H R O M I C ACID ANHYDRIDE-
I n 1917, a t Johns Hopkins University, under t h e direction of J. C. W. Frazer, a large number of oxidizing agents were examined. Yellow mercuric oxide,’ prepared in t h e dark, and chromic acid anhydride were found t o react slowly a t room temperature with carbon monoxide. The discovery was made t h a t a mixture of these was more reactive t h a n either substance alone, and absorbents were prepared which oxidized 70 t o 80 per cent of a one per cent carbon monoxide-air mixture for a short time. Further experimentation failed t o improve t h e mixtures materially and work on this absorbent was discontinued. One of t h e best mixtures was prepared b y mixing I O O g. infusorial earth, impregnated with a solution of IOO g. chromic acid anhydride in 300 cc. water, with 5 g. of finely ground mercuric oxide; t h e mixture was evaporated t o a pasty mass on a water bath, mixed with pumice or porcelain granules, and finally dried on a water bath. SILVER OXIDE-The recognized activity of silver oxide toward carbon monoxide led t o its study by several investigators. Stieglitz, early in 1918, found t h a t carbon monoxide in air was rapidly oxidized at room temperature b y silver oxide and sodium peroxide arranged in alternate layers in a glass tube. The silver oxide was precipitated from a dilute solution of silver nitrate by t h e addition of a barium hydroxide solution i n about one per cent excess, with constant shaking during precipitation. The precipitate was washed two or three times b y decantation, filtered, pressed together on t h e filter, dried a t 85’ t o 120°, and finally heated t o 200’. It was shielded from carbon dioxide throughout this treatment. The final product was in t h e form of rather soft lumps, which were easily crushed t o t h e required size. The silver oxide and sodium peroxide in equal parts were placed in alternate layers, separated by glass wool, in glass tubes either I cm. or 3 . 2 cm. in diameter, t o depths not exceeding I O cm. At room temperature carbon monoxide at concentrations between 0.5 and 4.5 per cent was about 98 per cent absorbed when 500 cc. samples of gas were passed in 0.5 t o z min. Similar results were obtained
* Colson, Comfit. rend., 13% (1901),
467.
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with intermittent flow. At o o the reaction started fairly rapidly b u t not instantaneously. At room temperature neither of the two ingredients alone rapidly oxidizes carbon monoxide a t a low concentration in air. Silver oxide is much more reactive t h a n sodium peroxide; when it is heated t o 40’ or 50’ t h e reaction starts rapidly and continues without further application of heat on account of t h e heat generated in the reaction. The interesting question a s t o why the mixture operates so much better t h a n t h e silver oxide alone cannot be answered with certainty, b u t i t is probable t h a t t h e function of t h e sodium peroxide is t o remove t h e carbon dioxide formed, and t h u s prevent t h e formation of silver carbonate on t h e surface of t h e silver oxide. The net reaction is t h e formation of sodium carbonate and silver. Also when t h e gas is not completely dry t h e heat of t h e reaction between water and sodium peroxide serves t o raise t h e temperature of t h e absorbent, and thus increase its activity. It was in fact observed t h a t the presence of moisture in small amounts in t h e gas had a beneficial effect. Similarly, Frazer, late in 1917,studied a mixture of silver oxide and calcium hydroxide. Silver oxide precipitated and washed cold was mixed with calcium hydroxide as a thick paste, t h e mixture was dried on a steam bath and t h e n heated t o I I O O in a current of oxygen for about 2 hrs. For a mixture containing silver oxide and calcium hydroxide in t h e proportion of I t o 5 by weight, a laboratory test with one per cent carbon monoxide showed 90 per cent removal oi carbon monoxide a t t h e end of 5 min.; and a canister test showed 80 per cent efficiency a t t h e end of I O min., and 60 per cent efficiency a t t h e end of 2 2 min. This material is evidently much less satisfactory t h a n t h e silver oxide-sodium peroxide mixture, though it is not improbable t h a t t h e function of t h e calcium hydroxide (or oxide) is similar t o t h a t of t h e sodium. Meanwhile, as will be shown later, t h e possibility of using relatively small amounts of silver oxide t o activate certain metallic oxides or mixtures of oxides had been demonstrated. On account of t h e lower cost of these materials, absorbents rich in silver, such as t h e above, could not be considered. I t may also be added t h a t , since firm granules of silver oxide and sodium peroxide are not easily made, the resistance of t h e mixture in a canister t o t h e flow of gas would have been unduly high, IODINE PENTOXIDE-Iodine pentoxide is specifically active in oxidizing carbon ponoxide, and advantage has long been taken of this fact in the analysis of carbon monoxide-air mixtures. C. R. Hoover and A. B. Lamb, in September 1917, tested t h e efficacy of various metals, metallic oxides, and acidic oxides and acids as catalysts in this reaction. It was found t h a t strongly oxidizing or dehydrating acidic oxides, such as sulfur trioxide and phosphorus pentoxide, and concentrated nitric, sulfuric, and phosphoric acids and mixtures with their anhydrides, had marked accelerating effects independent of any moisture in the gas. so t h a t t h e oxidation would occur rapidly at room temperature, and in t h e most favorable instances even a t o o C.
Vol.
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Fuming sulfuric acid was found t o give t h e most active mixture with iodine pentoxide, and pumice was found t o be t h e most suitable base on which t o support it. Careful investigations were carried on b y C. R. Hoover a t Middletown, and under the direction of A. W. Kenney, R. G. VanName, and particularly W. C. Bray, a t t h e Washington laboratory, on t h e optimum proportions of sulfur trioxide, water, iodine pentoxide, and pumice, t o afford t h e maximum life, t h e most complete of oxidation, t h e quickest s t a r t (“pick up”) of t h e reaction, and t h e least concentration of sulfur trioxide in t h e effluent air Using a layer I O cm. deep of a favorable mixture and passing a one per cent carbon monoxide-air mixture a t t h e rate of 500 cc. per min. per sq. cm. cross-seetion (corresponding t o rapid breathing through a gas mask of t h e usual dimensions), a I O O per cent t o 90 per cent removal of carbon monoxide could be secured for 2 hrs. a t room temperature, and almost as long a t o o C. This corresponds t o a 75 t o 80 per cent utilization of t h e iodine pentoxide. The action is not instantaneous, and a brief induction period always occurs. At room temperature with one per cent carbon monoxide this is very brief, so t h a t t h e “pick up” requires b u t a fraction of a minute, but a t o o it may require several minutes, and a t lower concentrations still longer before absorption becomes substantially complete. This would allow an initial leakage of carbon monoxide which might well be dangerous. However, i t was shown t h a t t h e active agent in t h e oxidation of t h e carbon monoxide is an intermediate compound, and the time required for the formation of a n adequate amount of i t is responsible for the existence of t h e period of induction. It was further shown t h a t this same substance, or one similar t o i t , can be produced by t h e addition of a little iodine t o t h e original mixture. By a preliminary treatment of this kind t h e “pick up” is materially improved, so t h a t with a one per cent gas a t o o t h e induction period lasts less t h a n one minute. No serious initial leakage of carbon monoxide, therefore, can occur with this active material The sulfur trioxide given off is, of course, very irritating t o t h e lungs, b u t b y the use of a layer of active charcoal beyond t h e carbon monoxide absorbent this disadvantage was very completely eliminated. However, sulfur dioxide is slowly formed as a result of this adsorption, and after prolonged standing or long-continued use of the canister at a high rate gives serious trouble. This is partially remedied by t h e use of a soda lime-charcoal mixture, and could doubtless be more completely eradicated by t h e substitution of a chemically inert absorbent, such as silica-gel, for the charcoal. Considerable heat is given off in this reaction and a cooling attachment was required. The most satisfactory devices were a metal box filled with fused sodium thiosulfate pentahydrate which in melting 1 Later it was learned that the French had discovered and utilized the activating effect of sulfuric acid on the reaction between carbon monoxide and iodine pentoxide, though no mention of the use of fuming acid was made “Hoolamite,” U. S Patent 1,321,061.
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absorbed a very considerable amount of heat. or a long, flexible, metallic t u b e between t h e canister and t h e mouth, which cooled t h e effluent gases very effectively, or finally, a moistened sponge placed in t h e breathing t u b e between t h e absorbent and t h e mouth. This last not only cooled t h e air, b u t also humidified it and so obviated t h e somewhat irritating effect of t h e prolonged breathing of very dry air. This absorbent had t h e further disadvantage t h a t it became spent b y use, even in t h e absence of carbon monoxide, since i t absorbed enough moisture from air of average humidity i n several hours t o destroy its activity. These difficulties of sulfur trioxide formation, heat evolution, and moisture absorption were so troublesome t h a t this absorbent was finally supplanted by t h e more satisfactory metallic oxide absorbent t o be described later. Incidentally a simple and inexpensive method for t h e production of very pure iodic anhydride was perfected; also i t was shown t h a t t h e green color resulting from t h e action of carbon monoxide on t h e iodine pentoxide-fuming sulfuric acid-pumice mixture (Hoolamite) could be used as a very sensitive detector for t h e presence of carbon monoxide in airs1 S I L V E R PERMANGANATE-An investigation Of t h e oxidation of carbon monoxide by silver permanganate b y Ernest Bateman, of t h e Forest Products Laboratory, begun in November 1917,led t o some interesting results. While moist one per cent carbon monoxide was not oxidized rapidly by silver permanganate alone, t h e Teaction was very fast when solid calcium chloride was mixed with t h e permanganate, and t h e reaction usually culminated in a n explosion before t h e permanganate was completely reduced. By mixing i n a third ingredient, calcium oxide, and by avoiding t h e use of a large proportion of calcium chloride, a relatively safe absorbent was made, which had a long “life”-2 to 4 hrs. in t h e standard tests with one per cent carbon monoxide. T h e oxidation of t h e carbon monoxide was practically complete. T h e best proportions were, by weight, 85 parts AgMn04, 1 5 parts CaO, and 1 5 t o 2 0 parts C a C L T h e d r y materials were ground together i n a mortar and pressed together into a cake under high pressure; t h e cake was then broken up and meshed t o granules of t h e required size. The presence of moisture in t h e entering gas was essential for satisfactory operation. The first tests a t o o gave unsatisfactory results, and on this account t h e work was discontinued for some months. Later it m7as found t h a t the poor results a t o O were due t o t h e low moisture content of t h e cold gas. By providing for humidification of t h e entering gas, e. g., with a n agar jelly or suitable hydrated salt, t h e absorbent was made to operate efficiently at o O. At t h e time t h a t this very promising result was obtained in Madison, July 1918, intensive work had already been started i n Washington on t h e absorbent finally selected, Hopcalite, which functioned as a catalyst for t h e oxidation of carbon monoxide b y t h e oxygen of t h e air. On account of t h e pressure of this work it was not possible t o continue in Washington a
Forthcoming paper; also U. S. Patent 1,321,062.
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t h e study of this other absorbent. We have, therefore, no d a t a on t h e preparation of t h e material on a large scale, on canister tests, or on t h e durability or safety of t h e material when stored. The considerable expense of this absorbent and t h e fact t h a t i t is not catalytic and so is consumed i n use are serious drawbacks. METALLIC OXIDE MIXTURES
OXIDE-In t h e fall Of 191 7, G. N . Lewis, T. D. Stewart, C. C. Scalione, and D. R . Merrill, a t t h e University of California, found t h a t a specially prepared, precipitated copper oxide activated with one per cent silver oxide, was a n efficient catalyst for t h e oxidation of arsine by t h e oxygen of t h e air. Following this clue, t h e two last-named investigators, with W. C. Bray, found t h a t t h e mixtures which were most effective for arsine were also most reactive toward carbon monoxide-air mixtures. However, only jo per cent of t h e carbon monoxide was removed even a t t h e start, t h e “life” of t h e absorbent was short and t h e action appeared chemical rather t h a n catalytic. The activity of t h e material was riot increased by increasing t h e silver content above one per cent Though these results were, therefore, far from satisfactory, they showed t h a t t h e physical s t a t e of t h e absorbent was a controlling factor. I t was evident t h a t a highly porous and yet hard granule was t h e goal t o be striven f0r.l C O P P E R O X I D E A N D C O B A L T I C OXIDE-other more active oxidizing agents were now studied from this same point of view, and in particular, influenced by t h e work of Wright and Luff,2 cobaltic oxide and manganese dioxide were selected; and i t was decided t o s t u d y t h e influence of t h e physical nature of t h e granules by varying t h e method of preparation, and t o investigate t h e behavior of mixtures of oxides. The method of preparation was based on t h a t used by Huttner3 and consisted i n treating cobaltous sulfate solution a t room temperature with excess of a mixture of sodium hypochlorite and sodium hydroxide. The mixture was allowed t o s t a n d for one-half hour, in which time t h e excess hypochlorite was catalytically decomposed. The hydrated oxide was thoroughly washed by decantation and filtered, dried a t 120°, and meshed i n t h e usual way. T h e oxygen content of t h e oxide was uniformly somewhat greater t h a n would correspond with t h e formula CozOs, indicating t h e presence of some Cooz. The behavior of different samples of cobalt oxide granules toward one per cent carbon monoxide was COPPER OXIDE AND SILVER
1 The method of preparation is appended because i t illustrates the procedure used in the subsequent work. Copper sulfate solution was added to sodium hydroxide solution a t a temperature from 70’ to 100’. When excess sodium hydroxide was used this was neutralized by the addition of dilute sulfuric acid to the hot mixture; in later work the same results were accomplished by decreasing the amount of sodium hydroxide originally used. In all cases the precipitates were freed from salts by thorough wsshinm, usually by decantation. The hydrated oxide sludge was impregnated with silver oxide by stirring in the desired amount of silver nitrate solution and adding a sufficient quantity of sodium hydroxide solution. The mixture was washed twice by decantation and collected as a filter cake on a Biichner funnel or in a filter ’press. The cake was dried slowly in an air oven u p to 120°, crushed and meshed, the 10- t o 14-mesh material being used in the tests. 2 J . Chem. Soc., 88 (1881), 1, 504. 8 Z. anorg. Chem.. 27 (1901). 81.
2 I8
.
%
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
variable in t h e extreme. Changes in t h e method of preparation had a great effect on t h e physical nature of t h e granules; t h e apparent density, for example, varying from 0.7 t o 1.4. Better results were obtained in t h e test with dry one per cent carbon monoxide than with moist gas, b u t t h e life of t h e absorbent was usually short and in only a few instances was as long as one hour. With dry gas t h e initial efficiency varied from 1 5 per cent t o nearly I O O per cent, but t h e results were not reproducib1e.l To test whether mixtures were more active t h a n t h e single components, a mixture of 60 per cent active copper oxide and 40 per cent active cobaltic oxide was prepared from an intimate mixture of t h e moist hydrated oxides and was tested a t Berkeley in March 1918. It operated a t fairly high efficiency, had a long “life” (about z hrs.), and was apparently partially catalytic, since t h e decrease in available oxygen during t h e run was insufficient t o account for all t h e carbon monoxide oxidized. M A N G A N E S E DIOXIDE A N D SILVER OXIDE-A similar development of oxide absorbents had also been carried on a t Johns Hopkins University b y J. C. W Frazer a n d his assistants. They had proved t h a t , while neither manganese dioxide nor silver oxide reacted rapidly a t room temperature with one per cent carbon monoxide, mixtures of them from t h e beginning gave encouraging results. At first sodium hydroxide was included as a n ingredient in t h e mixtures and i t was found t h a t t h e reactivity increased with increasing amount of i t , a t least up t o 1 2 or 1 5 per cent. The presence of small amounts of fused granular calcium chloride in layers in the absorption tube increased t h e life of the absorbent. At room temperature with dry one per cent carbon monoxide, under standard conditions of testing, t h e removal of carbon monoxide was practically complete with t h e best mixtures for from 30 t o 40 min. and these absorbents, even in t h e absence of calcium chloride, continued t o operate for I O t o 1 5 min. longer before t h e efficiency fell t o go per cent, t h a t is, until t h e amount of unabsorbed carbon monoxide reached I O per cent. Tube tests indicated t h a t the presence of moisture in t h e gas increased t h e life of a n absorbent. At o o t h e materials operated a t high efficiency, b u t for a shorter time. The action in all cases was apparently t h e oxidation of carbon monoxide b y t h e silver oxide and manganese dioxide. All t h e active mixtures contained a greater weight of silver oxide t h a n of manganese dioxide and satisfactory results were obtained when t h e proportion of silver oxide t o manganese dioxide was 1.5-2.5 t o I . These investigators found t h a t t h e efficiencies varied greatly with t h e physical character of t h e manganese dioxide. The above reproducible results were obtained with material prepared by t h e action of methyl alcohol on a solution of potassium permanganate, heated t o 7 5 ° . 2 1 It was later, in August, found that these inconsistencies were chiefly due t o differences in the method of drying. 2 The suspended manganese dioxide was collected on a filter and washed 3 times with distilled water; the paste was dried until it contained about 5 0 per cent water, which was accurately determined and allowed for in making up the mixtures. The manganese dioxide paste was mixed with water and stirred until a uniform suspension was obtained. This was added with
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Slightly better results were obtained with a three component mixture containing cobaltic oxide, silver oxide, and manganese dioxide in the proportions of I : I : 0.5 t o I, respectively, t h e “life” being longer t h a n one hour against dry one per cent gas. Sodium hydroxide was found t o be undesirable in such mixtures and was omitted. When a smaller proportion of silver oxide was used t h e materials were much less active. HOPCALITE-BY May 1918,t h e group a t t h e University of California had all been transferred t o Washington, D. C., and from t h a t time on there was active collaboration between the Washington and t h e Baltimore laboratories, t h a t is, between t h e two groups engaged on the study of mixtures of metallic oxides. At t h e Johns Hopkins laboratory i t was soon found t h a t much more active varieties of manganese dioxide could be prepared and t h a t t h e omission of sodium hydroxide from t h e mixtures of silver oxide and manganese dioxide then increased t h e life. The first really active manganese dioxide was prepared by reducing with methyl alcohol a cold solution of ammonium permanganate instead of t h e potassium salt. Much more finely divided manganese dioxide was obtained, and the life of a mixture of equal parts of this material and silver oxide was over 3 hrs. Finally, with manganese dioxide prepared by the Fremy method,l where potassium permanganate was treated with a cooled mixture of concentrated sulfuric acid with 0.3 of its weight of water,2 t h e discovery was made t h a t with dry gas t h e action of a mixture of equal parts of manganese dioxide and silver oxide became catalytic, t h a t is, t h e carbon monoxide w a s oxidized continuously b y the oxygelz of the air. Simultaneously, in the Washington laboratory, Bray, Scalione, and Merrill discovered a n equally active catalyst consisting of a three component mixture of cobaltic oxide, manganese dioxide, and silver oxide, in t h e proportion of 2 0 : 34 : 46, which was prepared b y t h e interaction of silver permanganate with moist hydrated cobaltic oxide. The catalytic behavior of these mixtures against dry one per cent carbon monoxide was a t once verified in both laboratories. The behavior of fresh samples of t h e manganese dioxide-silver oxide mixture was found t o be identical with t h a t of t h e first sample. While this catalyst had a n apparently indefinite life with dry gas, moist gas “killed” i t fairly rapidly and t h e amount of available oxygen in t h e material was found t o decrease a t t h e same time. However, i t restirring t o a silver nitrate solution containing sufficient silver nitrate to give the desired amount of silver oxide. The sodium hydroxide solution was added with vigorous stirring until a distinct alkaline reaction was observed. The brownish yellow mixture was stirred until it became dark brown, or almost black in color. The material was washed three times b y decantation and collected as a filter cake on a Bdchner funnel To this cake the required amount of sodium hydroxide in solution was added and mixed in b y stirring. The material was dried on a water bath, broken up, and finally dried for about 3 hrs. at 140” in a current of dry oxygen. It was groundand meshed, 10- t o 20-mesh granules being used in the tests. 1 Compt y e n d , 82 (1876), 1231. 2 The mixture was allowed to stand for several days during which time the permanganic acid slowly decomposed with evolution of oxygen. The mixture was then poured into a large volume of water and the resulting finely divided manganese dioxide washed, first by decantation and then on a filter, until the filtrate showed no test for sulfate.
Mar., rgzo
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
vived very quickly when again treated with dry gas. This behavior towards moisture was found t o be char,acteristic of all catalysts subsequently prepared, and was used as a criterion for catalytic behavior. A large variety of mixtures of t h e above-mentioned oxides were then investigated. I n their preparation, the hydrated oxides were usually prepared separately, washed thoroughly, and intimately mixed. When impregnation with small amounts of silver oxide was desired, t h e necessary amount of silver nitrate solution was stirred i n , and enough sodium hydroxide added to precipitate t h e silver oxide. The final material was always thoroughly washed, collected in a funnel or in a filter press, dried slowly up t o 120~-130', meshed, and finally dried a t 200'. I n all subsequent treatment exposure t o moist air was, of course, avoided. The method of drying was important and i t was found t h a t t h e amount of water of hydration left in the granules was a determining factor in the preparation of active catalysts. I n general much better results were obtained when t h e granules were heated for a short time at 200°, after t h e preliminary slow drying u p t o I Z O O or 130'. This was especially important for mixtures containing t h e highly hydrated cobaltic oxide, and a number of such mixtures behaved as catalysts only after this heat treatment. I n fact cobaltic oxide itself when treated in this way acted catalytically, and furnished t h e only example t o date of a catalyst at room temperature which consists of a single oxide. Prolonged heat treatment a t a high temperature, on the other hand, spoils these catalysts, presumably on account of t h e destruction of t h e porous nature of t h e granules. Materials containing a, large amount of silver oxide are apparently more easily injured by heating. As has already been indicated, i t was necessary t o determine carefully t h e exact conditions for the preparation of each oxide in t h e most suitable form. It may be said, in general, t h a t t h e physical state of t h e final granules, and t h e behavior of t h e catalyst, depend upon t h e size and composition of t h e particles of which t h e original precipitates are composed. If t h e particles are extremely fine, and are not made t o clump together or combine before filtration, hard and relatively non-porous granules result, which are less active as catalysts than are more porous granules. On t h e other hand, if t h e particles are too coarse, soft though usually active granules are obtained, which are not robust enough for use in canisters. The latter condition can be remedied t o a considerable extent b y subjecting t h e filter cake t o high pressure before drying it. The granules are very porous, and t h e action of t h e catalysts a t low temperatures is believed t o be dependent on t h e large surface exposed t o t h e carbon monoxide and oxygen. I O O cc. of 14-16 mesh granules of one sample of this material were found b y Dr. G. A. Hulett, of Princeton, t o contain only 8.8 cc. of solid material, while t h e volume of t h e large spaces between t h e granules was about 4 7 cc. This left a capillary volume of about 44 cc. T h e high porosity, also, must be responsible for t h e poisoning effect of water
219
vapor, which was observed with all catalytic mixtures a t room temperatures. The decreasing effect of t h e water vapor a t high temperature is in agreement with this view. The best catalysts contained active manganese dioxide as the chief constituent. While this substance prepared by t h e Fremy method seemed better t h a n t h a t from t h e ammonium permanganate-methyl alcohol method, t h e latter material was found t o be satisfactory. A third method of preparation was developed in the Washington laboratory, which was similar t o t h a t covered by a German patent' and depended on t h e reaction between potassium permanganate and anhydrous manganese sulfate in t h e presence of fairly concentrated sulfuric acid. This method is t h e one t h a t was used in t h e preparation of active manganese dioxide on a large scale. I t may be mentioned t h a t manganese dioxide did not prove satisfactory when prepared b y t h e oxidation of the manganous salt in neutral or alkaline solution; t h a t is, mixtures made from i t usually were not catalytic. Active copper oxide and cobaltic oxides were prepared on a large scale by t h e methods previously mentioned. Many mixtures of widely different composition show catalytic behavior and t h e possible range of compositions seems t o increase with t h e number of components. Thus, for a comparable series of mixtures in each of which manganese dioxide is t h e chief constituent, the minimum silver oxide content necessary t o ensure catalytic action decreases progressively as t h e number of components increases from z t o 3 t o 4. The limit is about 38 per cent AgnO in the two component mixtures, about 1 5 per cent in t h e three component mixtures containing copper oxide, and 5 per cent or less when cobalt oxide also is present. A four component mixture containing 5 0 per cent MnOz, 30 per cent CuO, 1 5 per cent C0203 and 5 per cent AgzO was chosen in August as a standard catalyst t o be tested on a larger scale. This particular mixture was named Hopcalite I, Hopcalite being used t o designate any catalyst of this type. A small scale manufacturing plant was built and operated a t t h e American University Experiment Station; t u b e tests and canister tests proved t h a t t h e resulting material behaved as well as t h a t which had been prepared on a small scale in t h e laboratory. This material acted as a catalyst a t o o with as low a concentration of carbon monoxide as 0 . 2 per cent when t h e tests were made with dry gas. While this work of development was in progress, t h e search for a cheaper catalyst was continued in both laboratories. The most promising material discovered was a two component mixture of MnOz ( 6 0 per cent) and CuO (40 per cent), developed in t h e Baltimore laboratory, which was prepared from active manganese dioxide and copper carbonate. The latter was transformed almost completely into the oxide in t h e drying process. However, this material was still in t h e laboratory stage of developBad. An. Sod. Fab. D. R. P , 163.813 (1905); Z Elektrockem., 11 (1905),
853.
2 20
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
ment in September, when i t was necessary t o decide what mixture would be used in large scale production; and t h e four component mixture was chosen for this purpose. THE M A N U F A C T U R E O F H O P C A L I T E I
The particular mixture of oxide selected for large scale1 manufacture, on t h e basis of t h e extensive laboratory and small scale manufacturing tests, had t h e components MnO? 50 per cent, CuO 30 per cent, C O Z O1~5 per cent, and A g 2 0 j per cent, as mentioned above. The process of manufacture was merely an extension of what had proved t h e best laboratory technique, namely, t h e separate precipitation a n d washing of t h e manganese dioxide, copper oxide,. and cobaltic oxide, and t h e subsequent precipitation of t h e silver oxide in t h e mixed sludge. After further washing t h e sludge was r u n through a filter press, kneaded in a machine, and t h e cake dried and ground t o size. The fines were ball-milled wet and re-pressed. While it was not difficult t o obtain a product which was catalytically active, i t required a rigorous control of all t h e conditions and operations t o assure a product a t once active, hard, dense, and as resistant as possible t o t h e deleterious action of water vapor. The temperatures, concentrations, rates of additions, stirring, etc., during t h e precipitations particularly t h a t of t h e manganese dioxide, h a d t o be carefully studied a n d controlled. The precipitates had t o be washed very carefully b y decantation down t o t h e point at which they began t o be colloidal; t h e kneading of t h e pulp had t o be sufficient b u t not prolonged; t h e drying had t o be carried out according t o a carefully regulated schedule; and, finally, since t h e material a t best is comparatively soft, much study and attention had t o be given t o the grinding and sieving t o prevent t h e formation of an excessive amount of fines. These difficulties were all eventually overcome, a n d a plant was constructed and operated in cooperation with t h e Rare Metal Products Company a t their works a t Belleville, N . J., under t h e immediate supervision of D. R . Merrill a n d A. T. Larson. This plant had a daily capacity of joo lbs. of finished product. The product was required t o meet t h e following rigorous tests: A screen analysis must show not more t h a n ~j per cent above 8 mesh; ,at least 5 2 per cent 8-12 mesh; not more t h a n 6 per cent 14-16 mesh and not more t h a n 2 per cent less t h a n 16 mesh. T h e apparent density of a n 8-14 mesh sample must be a t least 0.55. The hardness had t o meet a definite test on the Rotap machine, corresponding t o rough handling in t h e field. Rapidity of starting, t h a t is, a quick “pick up,’’ was assured by requiring t h a t a layer j cm. deep should initially remove a t 2 0 ’ not less t h a n g o per cent of t h e carbon monoxide from a dry 0.25 per cent carbon monoxide-air mixture flowing a t a rate of j o o cc. per sq. cm. cross-section per min. True catalytic behavior was assured b y requiring t h a t this sample should continue a t least g o per cent efficient for a further period of 3 hrs. against a dry one per cent gas. Finally, t h e best possible behavior against moist 1 Fifteen tons of the material were required for the N a v y carbon monoxide canister.
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gas was assured b y requiring t h a t i t should not drop below 85 per cent efficiency when tested, a t t h e same temperatures and rates of flow as with t h e dry gas, against a one per cent gas containing water vapor at a pressure of 14 mm. mercury. These tests against carbon monoxide-air mixtures required rapid and frequent analyses of t h e affluent a n d effluent air mixtures. By t h e very slow iodine pentoxide method, which was t h e only known method sufficiently accurate for t h e requirements, these analyses would have been very difficult t o execute. Fortunately, a rapid calorimetric method had already been developed at t h e Washington laboratory by Larson and Lamb’ which permitted a continuous a n d nearly instantaneous analysis of t h e affluent and effluent gas streams. This greatly facilitated and accelerated t h e development of t h e large scale manufacture. U S E O F H O P C A L I T E I N CANISTERS-HOpCalite has several characteristics which necessitate certain a n d permit other modifications in t h e usual gas mask canister. I n t h e first place, since its action is normally a catalytic one, there is b u t slight advantage in any considerable depth of absorbent. A depth sufficient t o insure close contact of all t h e air with t h e catalyst, t h a t is, t o avoid any so-called channeling is all t h a t is required. One and a half inches were found ample for t h e purpose and as a result only about 300 g. of absorbent were required per canister. I n t h e second place, t h e normal catalytic activity of Hopcalite requires a d r y gas mixture. A drier had therefore t o be provided a t t h e inlet side of each canister, and since t h e life of t h e Hopcalite and, therefore, of t h e canister, depends upon t h a t of t h e drier, as much as possible of i t was used, enough indeed t o give a layer 3 in. deep. After extensive experiments with a variety of drying materials, a specially prepared, dry, granular calcium chloride was chosen. With a drier of this material and with t h e affluent air flowing a t the rate of 32 liters per min. and containing water. vapor a t a pressure of 14 mm. mercury, t h e vapor pressure of water in t h e effluent air did not rise t o 4 mm. mercury until after a lapse of 3 hrs. Finally, there is a n evolution of sufficient heat in t h e catalytic oxidation of a one per cent carbon monoxide-air mixture t o raise its temperature adiabatically about 100’. There is also a considerable heating effect when moisture is absorbed b y t h e drier. However, because of t h e considerable heat capacity of t h e canister and its contents, and because of t h e rapid dissipation of heat b y radiation and conduction, t h e temperature of t h e effluent air does not rise higher t h a n 50’ during t h e first 1 5 min. r u n against a one per cent mixture, and never exceeds goo even after several hours. An exposure of more t h a n I j min. t o so concentrated a gas as this is unlikely. so t h a t for most purposes t h e temperature rise would be of no consequence; b u t t o insure a still greater margin of safety additional cooling was provided. This consisted of a small hermetically sealed metal box containing 1 3 0 g. of sodium thiosulfate pentahydrate placed between t h e calcium chloride a n d t h e Hopcalite layers. 1
J . Am. Chem. Soc., 61 (1919), 1968.
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T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
T h e thiosulfate melting a t 48 ’ absorbed about I I O , O O O cal. of heat, and so reduced considerably t h e rate of temperature increase in t h e effluent air. At first, one i n every I O O and later one in every 2 0 0 of t h e manufactured canisters was run against 0.5 or one per cent carbon monoxide-air mixtures containing water vapor a t a pressure of 14 mm. mercury and a t t h e rate of 32 liters per min. K O canister or t h e lot i t represented was accepted which showed a leakage of 0.1 per cent carbon monoxide within 2 hrs.; actually t h e average life was over 3 hrs. I t was found t h a t t h e higher t h e temperature t h e longer t h e life, which agrees with the fact previously mentioned t h a t Hopcalite is less sensitive t o water vapor a t higher temperatures. I t was further found t h a t the net life of t h e canister was t h e same irrespective of whether its use was continuous or intermittent, t h a t is, no deterioration occurred when a partially spent canister was allowed t o stand. SERVICE TIMEI N I-IOWRSFOR HC CANISTER Temp. ---Relative FOR MEN = F. 25% At Rest . . . . . . . . . . . . . 32 60 50 40 75 24 100 12 I n Action.. . . . . . . . . . 32 15
ESTIMATED
50 75
10 6
100 3 1 Ordinary winter conditions on deck. 2 Summer conditions on deck. 3 Engine (boiler) room conditions.
CARBON MONOXIDE NAVY 50% 40 24
12 6 10 6
3 1.5
Humidity75%
100%
241
18
16
12
8 4 6 4
22
13
6 3 4.5 3 1.5 0.75
I n agreement with t h e fact t h a t t h e Hopcalite absorbent functions indefinitely against any concentration of carbon monoxide, provided the effluent air is adequately dried, and hence t h a t t h e life of t h e canister is limited solely by t h e life of t h e drier, i t was found t h a t the net gain in weight of t h e canister was a sure criterion of its condition. At t h e time of a breakdown, t h a t is, when t h e leakage reached 0.1 per cent, as tested by t h e above-mentioned routine method, the average gain i n weight of all canisters was j 4 g.; none gained more t h a n 71 g. and none less t h a n 42 g. It was recommended, therefore, t h a t any canister which had gained more t h a n 3 5 g. above its original weight stamped on t h e canister should be withdrawn. Since it is t h e absorption of water which limits t h e activity of these canisters, t h e lower t h e actual humidity of t h e air in which t h e canister is used t h e longer its life. T h e accompanying table was, therefore, prepared of t h e estimated service times of these canisters in use on shipboard under conditions which men both a t rest and in action might reasonably encounter. THE PREPARATION OF ARSENIC TRICHLORIDE FROM WHITE ARSENIC AND PHOSGENE’ By L. H. Milligan, W. A. Baude and H. G. Boyd CHEXICALLABORATORY, EDGEWOOD ARSENAL,EDGEWOOD, MARYLAND Received November 3, 1919 I S T R 0 D U C T I 0N
At Edgewood Arsenal phosgene was manufactured for use as a war gas b y t h e direct union of carbon monoxide and chlorine in t h e presence of carbon. J t was 1 This article has been approved for publication by Major-General Wiiliam L. Sibert, Director of the Chemical Warfare Service, U. S. A.
221
condensed a t about - 2 0 ’ C. under atmospheric pressure, b u t considerable phosgene was lost in t h e “tail gas” from t h e condensers. Means were sought t o recover t h e phosgene in this tail gas and convert i t into a commercially valuable product. It was suggested t h a t this phosgene might be satisfactorily converted into arsenic trichloride by reaction with arsenic trioxide (“white arsenic”). Tests showed t h a t this reaction proceeded very slowly up t o t h e subliming temperatures of arsenic trioxide, and the results were not satisfactory. Experiments made with catalyzers, however, showed t h a t very satisfactory conversion was obtained in t h e presence of carbon. This paper gives a n account of t h e work done in this connection. HISTORICAL
The reaction between phosgene and inorganic oxides and sulfides has been studied in detail by Chauvenet.1 A great number of oxides and sulfides were used, b u t arsenic was not among them. The reaction was carried out simply by heating t h e inorganic compound in a t u b e t o a temperature which varied from 300’ to 1400’ C. according t o t h e material, and passing t h e phosgene gas over it. Chlorides, and sometimes oxychlorides, were produced, t h e general reactions being: MO COC12+MCl2 coz MS COClz+MCI: COS N o catalyzer was used. Ribanj2 many years before, found t h a t when chlorine is passed over a mixture of tricalcium phosphate and carbon. or when chlorine and carbon monoxide are passed over tricalcium phosphate alone, heated t o incipient redness, a small quantity of calcium chloride and m-phosphate is formed, b u t no further change takes place. When, however, carbon monoxide and chlorine together are passed over a heated mixture of calcium phosphate and carbon (boneblack) a t 3 3 0 ’ t o 340’ C., P0Cl3, CaClz and COZ are produced in quantity. He thought t h a t t h e carbon acted as a catalyzer by condensing t h e gases in its pores, and suggested t h a t this reaction might be applied t o phosphates in general and t o irreducible oxides, like AlzOa, from which A1C13 could be produced. However, he made no experiments using phosgene instead of t h e did he mixture of carbon monoxide and chlorine-nor attempt t o decompose arsenic compounds.
+ +
+ +
EXPERIMENTAL
EXPERIMENTS-EXperimentS were made in t h e laboratory as follows: Phosgene (analyzing 99.7 per cent COClz). from a small t a n k , was dried with sulfuric acid, measured in a flow meter (calibrated for phosgene), and then mixed with air which had been dried and metered in a similar manner. The resulting mixture was run through a Pyrex glass tube containing t h e charge, generally a mixture of white arsenic and carbon. The t u b e was heated in a n electric oven, and t h e temperature measured by a long thermometer which LABORATORY
1 Comfit. rend., 152 (1911), 87, 1250; Barlot and Chauvenet, Ibid., 157 (1913), 11.53. 2 Ibid., 95 (1882), 1160; 157 (1913), 1432.
