Interaction of Alkali Metals and Liquid Arnrnoni CATALY SI§ BY METALS AND ALLOYS GEORGE W. WATT, GORDON D. BARNETT', AND LAURP VASKA The University of Texas, Austin, Ten.
T
EXPERIMEYTA E ?4ETHOD S
HE unusual chemical and phyaical properties of solutions of
alkali and alkaline earth metals in liquid amonia ( 7 , 8, 10) have in several instances led to the consideratioii of such solutions for use in potentiallp practical processes of a strictly chemical or electrochemical nature. This invariably leads t o questions relative to suitable materials of construction for process equipment. Although there are undoubtedly many applications in R hirh the use of glass-lined or other ceramic containers would be entirely satisfactory, this might be impractical \There large quantitiw of such solutions are involved or where the solutions must be transferred through equipment including moving parts. I t has long been known that the reaction
(where M is an alkali met,al) is catalyzed by metals in general and most, effectively by those of the transitional series (4, 10). The frequently encountered statement that this reaction is also catalyzed by oxides and salts is misleading, as in most cases these compounds are reduced to the elemental metals which arc responsible for the observed catalytic effects ( I O ) . It is an unfortunate fact that some of the most effective catalysts for this reaction are the metals most commonly employed as materials of construction. The only worth-while quantitative data relative to catalysis of the foregoing reaction by metals are those provided by the very thorough studies of Burgess and Kahler (2). Their work, which Bras primarily a st'udy of the kinetics of the interaction of liquid ammonia at its boiling point with sodium, potassium, and calcium, included only the metals silver, zinc, niobium, tant,a!um, iron, and platinum as catalysts. The problem, of course, is that of finding a metal or alloy suhstant,ially devoid of catalytic act,ivity toward the metal-ammonia reaction and otherwise suitable for the fabrication of equipment in n-hich solutions of metals may be stored, transferred, or oiherwise processed. With t'he exceptions noted above, information relative to the catalytic activity of metals is largely qualitative and there are available no data concerning alloys. Accordinglj-, the experiments described in this paper were undertaken to provide quant'itative data covering a reasonably Tvide select'ion of metals and alloys.
With only minor modifications, the equipment and procedures used were essentially the same as those described by Burgejs and Kahler (2). Provision x a s t'hereby made for the addit,ion of a known weight of alkali metal to a knovn volume of liquid ammoiiia in an anhydrous oxygen-free system. Rate measurements were made by collecting the hydrogen evolved from the catalyzed reactions a t suitable time intervals; p r o d o n was also made for analysis of the hydrogen by combustion in a Haldane-type combustion pipet. The equipment described by Burgess and Kahlcr v a s modified so that the evolved hydrogen was led into a manifold and diverted to any one of four gas burets, each of which \vas independently connected to bhe gas analysis equipment. The reaction mixtures were stirred at 250 r.p.m. by means of a motor-driven st,irrer; the agitator blade consisted of a coupon comprising the metal or alloy catalyst under inveet,igation, anti having a total exposed surface of ea. 600 sq. mm. Where ncccssary, the coupons n'ere polished with Carborundum (grain FFF), attached to the glass stirrer shaft, immersed for a few minutes in 8 S hydrochloric acid, rinsed thoroughly with distilled watw, and dried under a heat lamp. The total exposed surface of the catalyst was computed Eroni the dimensions of the coupon and !vas known to the nearest square millimeter. Preliminary expcrimente showed thal data satisfactorily reproducible for present purposes could be obtained 75-ithout correcting for differences in roughness factors. Unless otherLT-ise indicated, all rates of alkali amide formation r e r e made using potassium in order t o have a common basis for comparison and at the same time provide reaction rates satiefai:tory for measurement evrn in the presenre of the least effective . K h e n the more active catalysts n-ere involved, the reactions bemeen pot,asaium and ammonia were carried to com-
d
//
/
MATERI9LS
Commercial liquid ammonia was dried over sodium amide The allcali metals were reagent grade and were a t all times protected from exposure t o the atmosphere. The source and composition of the metals and alloys used are included in Table I. With but few exceptions, the data relative to composition are those provided by the indicated sources. (6) in order t o ensure complete removal of water.
I 0
2
4
I
I
I
6
8
10
12
TIME,HR.
Figure 1. Reproducibility of Rate Data Obtained Using Nickel Catalysts
1 Present address, Department of Ohernistry, University of Riaalliniton, Seattle, Wash
1022
INDUSTRIAL AND ENGINEERING CHEMISTRY
M a y 1954 T.4BLE
I.
SOURCE AND
COMPOSITION
OF hfETAL AIiD
1023
ALLOY
CATALYSTS IO
Composition, % A1 normal trace impurities Cu 99.90 Au' >99.9 Ni,' >Y9.4
Zirconium
Source Metal Goods Corp Metal Goods Corp. From stock International Nickel co. Am. Platinum Works From stock Fansteel Rletallurgical Corp. Remington Arms co. National Lead Co.
Alloy Alclad aluminum
Metal Goods Corp.
Aluminuni. 3SH14
Metal Goods C o r n
Berylco 25
Beryllium Corp.
Brass, half hard, yellow Cobalt steel FC
Metal Goods Corp.
Al, 93.4. Cu, 4.5; M g , 1.5; Mn, 6.65 hln, 1.2: remainder A1 normal trace impurities Cu, 97.36; Be, 1.85-2.00; Co, 0.18-0.30. Fe 0.15 (max.). AI, 0 . ~ 6 Si, 0.15 '(maxi). (max.): minbr impurities Cu, 65; Zn, 35
Bethlehem Steel Co.
Co 1.5. C 0.11. Mn 0.38; Si,
Hastelloy B-1G
Haynes Stellite Co.
Hastelloy F-3 Monel Phosphor bronze Stainless steel 430
Haynes Stellite Co. International Nickel Co. Metal Goods Corp. Carpenter Steel Co.
Stainless steel 302
Meta Goods Corp.
Stainless steel 347
Metal Goods Corp.
Stainless steel 309 SCB
Republic Steel Co.
Stainless-steel, Carpenter 20
Carpenter Steel Co.
Tungsten steel GK
Bethlehem Steel Co.
Vanadium steel GN
Bethlehem Steel Co.
Metal A uniinum Copper cold rolle Gold Nickel Platinum Silver Tantalum Titanium
+
8
Pt, >99.99
v
A g , >99.9 Ta, >99.9
$6
C, 0.73; Fe, 0.25; remainder, Ti H f , 1.9; remainder Zr t norma trace impurities
0
I >4
b,
pletion ; with the less active catalysts, measurements were discontinued after the reactions had proceeded sufficiently far to establish the relative rate. All rate measurements were made a t -33.5O i0.5O c. EXPERIMENTAL DATA
Kunierous preliminary experiments were carried out for the purpose of establishing that the equipment and procedures adopted would provide adequately reproducible data. A limiting factor in these runs was the unavoidable small differences in the weights of potassium introduced into a predetermined volume of ammonia (50 ml,). Data for four runs employing nickel as the catalyst are given in Figure 1 as a typical example. Similar experiments were carried out using the metals and alloys listed in Table I as catalysts. Typical of these runs are the data for five stainless steels given in Figure 2. From these and similar curves, the reavtion rate data which provide a direct comparison of activity of the corresponding catalysts were calculated; these data are assembled in Table 11. I n order to provide a direct comparison of rates of reaction of sodium and potasw m , runs under strictly comparable conditions of initial concentration of the alkali metal were made using sodium in the presence of catalysts selected to represent three different ranges of cata-
0 430
0
302
a347 b 309SCB ICARPENTER 2 0
2
0
+
0.13.' rekainder FL Ni, 63.38; >Io, 26130; Fe, 4-7; Cr 1 (max.)' Mn 1 (max.). Si ' I (max.).' c 6.12 (max,j Data. not rtvailhbleb Xi, 57; Cu, 30; Fe, 1.4. Mn, 1; C, 0.15. Si, 0.1; S, b.01 Cu, 95; s'n: 5 Fe, 81.4; Cr, 17.2; Si, 0.46; Mn, 0.44; Ni, 0.18; Cu, 0.16; t minor impurities Fe, 69.6; Cr, 17-19; S i , 8-10; Mg, 2 (max.). Si, 1 (rnax.); t trace impuiities Fe, 67.5; Cr, 17-19; Xi, 9-12; M n 2 (max.). Si 1 (rnax.) C 6.01 (max.)! N6 8 X min Cl P, 0.04 (kax.i; S, 0.Oi (max.) Fe 60.2. C r 22-24. Ni, 12-15; l i n i (mltx.). di, 1 (max.). c '0.20 (mix.). P, 0.04 &ax.); 9, 0.03 (max.) Fe, 44.2; Xi, 2 9 . 0 ; Cr, 20.0; Cu, 3.0 (min.). Mo 2.0 Imin.); ,Si, 1.0; Mn, '0.75; ti, 0.07 (rnax.) W, 0.4. M n 0 . 5 , Si 0.17; C, 0.11! remainddr Fk V, 0.4b. hln 0 . h . Si 0.18; C, 0.i3; remainddr, Fe
STAINLESS STEELS
a
+
Gross composition Cut surfaces were exposed during course of reaction rate measurements. b Nominal composition of Hastelloy F is: Cr 21-23. Xi 44-47. &Io, 5.5-7 5 , N b T a 1.75-2.5. T a 0.5 (min.). C '0.06 (m'ax.).' M n 112. P 0.04 (max.): Si, 1 '(rnax.); 1 '(rnax.): C& 2.k (rnax.): C;, 0.15 (mix.): 5, 0 03 (rnax.); remainder, Fe
+
0
2
4
IO
6
.
TIME. HR.
Figure 2.
T.4BLE
11.
Rates of Reactions Catalyzed by Stainless Steels
C.4TALYSIS OF POT.4SSIUM
.hfIDE
FORMATION BY
METALSAND ALLOYS
Metal or Alloy Tantalum
Reaction Metal or Reaction Rate" Alloy Rate" 0.27 lllonel 2.5 (0.24)b (1.0jb Silver 2.7 Brass 0.28 Titanium 0.28 3.3 Stainless steel 430 0.30 Stainless steel 309 3.3 Alclad aluminum 0.32 Hastelloy F-3 4.0 Platinum 0.46 4.6 Nickel Zirconium 0.57 5.1 Stainless steel, Carpenter 20 Aluminum 1.1 Gold ( I .3) b 1.2 Cobalt steel F C 6.1 Aluminum 3SH14 Copper 1.8 6.3 Hastellog B-16 7.0 Berylco 25 Stainless steel 302 2.0 Tungsten steel G K 8.0 Stainless steel 347 2.3 8.3 Phosphor bronze Vanadium steel G N 2.5 Expressed as (cc. of Hz/hour,'gram K!sq mm. of catalyst area) X 10'. b Reaction between sodium and ammonia. Q
lytic activity. The data from these runs are included in parentheses in Table XI. The dependence of reaction rate upon potassium concentration was studied using Berylco 25, Carpenter 20, and stainless steel 309 a8 catalysts. The results in the three cases were similar; typical data for runs employing Carpenter 20 are given in Figure 3.
I.1
K,M 0 00115 0.0115 0 0.0171 0 0171 P 0.0310 00310
m 0,0522 a 0.0878
0
1
2
3
I
I
1
I
I
1
4
5
6
7
8
9
TIME. H R
Figure 3. Dependence of Rate upon Potassium Concentration for Reactions Catalyzed by Stainless Steel (Carpenter 20)
INDUSTRIAL AND ENGINEERING CHEMISTRY
1024
After each use as a catalyst, the coupons were examined visually: there waa no evidence of alteration in the surface except in the cases of Berylco 25 and gold. Repetition of use of a given catalyst both with and without the pretreatment specified ahove showed that the activity of those catalysts that were visuallv tinaltered remained substantially const,ant. Berylco 25 exhibited a brighter luster after use, but lvas otherwise apparently unchanged. The surface of the gold coupons became mott'led with dark areas upon contact with ammonia solutions of potassium, and exposure of the liquid ammonia solution to the atmosphere upon coinpic tion of a run resulted in the separation of a sniall amount of a flocculent black precipitate.
solutions of alkali metals in ammonia (6,9: I I ) , silver is eliminated, because silver(1) oxide is instantaneously reduced to elemental silver (fl), and the oxides of platinum would undoubtedl:), exhibit similar behavior. Of the remaining possibilities, and despite the fact that aluminum is slight,ly soluble in liquid ammonia (1, 3). it appears that the optimum combination would consist of the use of liquid ammonia solutions of sodium in contact with a preoxidized surface of Alclad aluminum. I n the absence of additional experimental evidence, however, this suggestion does not preclude the possibility t h a t an equally or more favorable situation might result from the similar use of tantalum, titanium, or zirconium. ACKNOW LEDGMEST
DlsC~sslOs
While i t n a s not the prim purpose of the present inv tion t o make either precise rate measurements or detailed I studies, sufficient data were obtained to substantiate and cstcnd the earlier work of Burgess and Kahler ( 2 ) . From the data oi Figure 3, it is evident that the reaction between potassium and ammonia is zero order with respect to potavsium a t thc higher concentrations but approaches first order as the concentrntioii of potassium is decreased. The various metals and alloys involved in the present studies are listed in Table I1 in increasing cider of catalytic activity. From these dat'a i t is apparent that none of the alloys except Alclad aluminum and none of the metals in the list beyond aluminum offers promise as a material for construction of containers for solutions of metals in liquid ammonia a t or near its boiling point. Use of any of the materials from tantalum to aluminum inclusive would result in liberation of sufficient hydrogen to constitute a hazard, and even if the vessels were adequately vented; the rates of reaction viould still be sufficient to result in significant changes in the concentration of the metal solution over estcnded periods of time. An obvious alternative would involve the use of tantalum, silver, titanium, hlclad aluminum: platinum, zirconiuni. or aluminum carrying a thin oxide film. From the limited stvsilable information relative to the reactions between metal ouitlcv a n d
Vol. 46,No. 5
The authors wish to express their appreciation for partial support of t,liis work by the Office of Kava1 Research, Contract, NBonr-26610. The assistance of Peggy I. Mayfield, and of those who supplied samples of metals and alloys, is also gratefully aclmowledged. The ammonia \vas generously supplied by the Polychemicala Department, E. 1. du Pont de Nemours & Co. LITERhTURE CITED
(1) Bergstrom, F. W., J . Am. Chrm. Soc., 45, 2789 (1923); 46, 1549 (1924). (2) Burgess, W.A I . , a n d Kahler, H. L., Ibid., 60, 189 (1938). (3) Davidson, A. W., Kleinberg, J., Bennett, W.E., a n d McEhoy, A. D., Ibid., 71, 377 (1949). (4) Franklin. E. C., "The Nitrogen System of Compounds," p. 53, Kew T o r k , Reinhold Publishing Carp., 1935. ( 5 ) Holt, 13. B., and 'Il'att, G. W.,J . Am. Chem. Soc., 6 5 , 9% (1943). (61 Johnson, IT. C., and Fernelius. W. C., J . Chem. E d i ~ 6, , 445 (1929). j o h n s o n , W.C., a n d Meyei, A. W., Chem. Revs., 8, 273 (1931). Jolly, W. L., IOid., 50, 361 (1952). Moore. T. E . , and Watt, G . W., J . Am. Chem. S O C . , 64, 2772 (1942). (IO) Watt, G. W., C'hem. Revs., 46, 289, 317 (1950). (11) Watt, 0 . W., and Fernelius, W. C., J . Am. Chem. Soc.. 61, 2503
(1939). R E C E I V E for D review J ~ l y20, 1953.
ACCEPTEDJanuary 2 0 , 19.54.
Preflarne Oxidation A. J . PAMNKE, P. )I. COHEN, AXD B.
M. S'P'URGHS
Petroleum Laboratory, Organic Chemicals Department, E . I . d u Pont de .\rerr~orars & Co., Znc., Wilmington, Del.
K
NOCK in spark-ignition engines is believed to result from
extremely rapid chemical reactions taking place in the unburned charge ahead of the flame front. Considerable progress could be made in understanding the knocking process if the exact nature of these reactions were knoKn. Physical manifestations of these reactions have been extensively investigated (.$, It?), b u t the data obtained do not explain the chemistry of the reactions involved. I n order to obtain such information, the nature of the high-temperature, vapor-phase oxidation reactions of hydrocarbons in engines has been studied. A motored engine (in which a fuel-air mixture is compressed without passage of a spark) was operated with a sampling probe placed in the exhaust manifold. Samples of exhaust gas were analyzed quantitatively for peroxides, carbonyl compounds, unsaturatee, and other stable intermediates. The COUI'SE :wd
rate of t,he hydrocarbon oxidat,ion reactions were followed by determining the concentration and type of stable intermediates formed as the degree of t'hermal stressing of the cylinder charge was increased. Operating conditions were varied from those producing no observable reactions to t,hose producing aut oignition. Information from these experiments has provided valuable knowledge of the roactions preceding h o c k and of the role of organic peroxides and tetraethyllead in such reactions. EKPERIMENT4L
The ASTM supercharge method engine used in these investigations was operated a t the motoring conditions shown in Table I. The engine cylinder head m s equipped with a quartz window and phototube asseiiihly for detecting the presence of cool flames.
