Preparation of Sodium Superoxide - Advances in Chemistry (ACS

Preparation of Sodium Superoxide WILLIAM H. SCHECHTER and RONALD H. SHAKELY Mine Safety Appliances Co., Callery, Pa.

Downloaded by UNIV OF GUELPH LIBRARY on August 26, 2014 | http://pubs.acs.org Publication Date: January 1, 1957 | doi: 10.1021/ba-1957-0019.ch013

The compound of sodium and oxygen known as sodium superoxide (NaO ) has been prepared by 2

two

different methods.

According

to the first

method a solution of sodium in liquid ammonia, when rapidly oxidized, yields a product corresponding to the empirical formula

Na O , 3

5

which

is thought to be a mixture of sodium superoxide and sodium peroxide in the ratio of 4 to 1. the

By

second method, which has been more fully

explored in this study, sodium superoxide is prepared by the treatment of sodium peroxide with oxygen and

under conditions

of

high temperature

pressure.

I n the present investigation, the m e t h o d of p r e p a r i n g s o d i u m superoxide b y treatment of s o d i u m p e r o x i d e w i t h o x y g e n has been m o r e f u l l y e x p l o r e d (2) ; a study has b e e n m a d e to define further the conditions of pressure, temperature, a n d l e n g t h of time necessary to prepare h i g h p u r i t y s o d i u m superoxide.

Experimental T w o apparatus w e r e e m p l o y e d i n this investigation to expose s o d i u m p e r o x i d e to o x y g e n at superatmospheric pressures; one w a s s i m i l a r to that used i n the o r i g i n a l investigation of this reaction (3-5) a n d needs n o f u r t h e r description. T h e second apparatus differed o n l y i n t h e size o f t h e stainless steel b o m b u s e d ; t h e b o m b m e a s u r e d 14 inches i n height a n d 5 1/16 inches i n inside diameter, a n d h a d a capacity of about 4.6 liters. I n this l a r g e r b o m b it w a s f o u n d inconvenient to measure the b o m b temperature b y means of a thermocouple inserted into a t h e r m o w e l l i n the w a l l of the b o m b (as was done i n the s m a l l b o m b ) . T h e t h e r m o w e l l used was a n i n t e g r a l p a r t of the b o m b enclosure a n d extended d o w n 4 inches f r o m the top of the b o m b . T h e b o m b was g e n e r a l l y loaded to a height so that the thermocouple was w i t h i n 1 o r 2 inches of the s o d i u m p e r o x i d e l e v e l . T h e starting m a t e r i a l u s e d i n the s m a l l b o m b w a s a p u r e grade of s o d i u m superoxide m a r k e t e d b y the P a r r Instrument C o . for calorific purposes. A n a l y s e s s h o w e d that i t l i b e r a t e d about 9 9 % of the theoretical o x y g e n f o r a p u r e p e r o x i d e w h e n c a t a l y t i c a l l y decomposed i n aqueous solution. S o d i u m p e r o x i d e f r o m t w o different sources was used i n the large b o m b . C o m m e r c i a l N a 0 (Solozone) w a s t r i e d , b u t was not f o u n d as satisfactory as a m a t e r i a l p r e p a r e d a c c o r d i n g to the patented process of J a c k s o n ( 1 ) . I n this process, m o l t e n s o d i u m m e t a l i s s p r a y e d into a n excess of d r y air a n d a white, fluffy, finely d i v i d e d f o r m of s o d i u m p e r o x i d e is p r o d u c e d . A n a l y s e s showed that it w o u l d liberate i n excess of 9 9 % of the theoretical o x y g e n f o r the p u r e c o m p o u n d . 2

2

124

In HANDLING AND USES OF THE ALKALI METALS; Advances in Chemistry; American Chemical Society: Washington, DC, 1957.

SCHECHTER AND SHAKELY—SODIUM SUPEROXIDE

125


A s heated alkalies r e a d i l y attack stainless steel, it was f o u n d necessary to use liners or crucibles i n the above bombs. Borosilicate glass was f o u n d satisfactory u p to about 450 ° C . for short periods of time, b u t it c o u l d not be used above this temperature. V a r i o u s ceramic materials were t r i e d f o r possible use as c o n tainers for the s o d i u m p e r o x i d e - s u p e r o x i d e m i x t u r e s . S i n t e r e d a l u m i n u m oxide a n d m a g n e s i u m oxide w e r e satisfactory u p to 450 ° C , b u t above this temperature the s o d i u m oxides penetrated the sintered m a t e r i a l a n d corroded the stainless steel b o m b . C o m m e r c i a l ceramic coatings containing (as the p r i n c i p a l components) a l u m i n a , magnesia, a n d titania were also t r i e d without success at a temperature above 450 ° C . A f t e r extensive testing it was f o u n d that p u r e n i c k e l best withstood corrosive action encountered i n this p r e p a r a t i o n of s o d i u m superoxide. E v e n this m a t e r i a l shows definite signs of corrosion as a b l a c k n i c k e l oxide coating f o r m e d o n the liners d u r i n g a r u n . F o r t u n a t e l y , the rate of corrosion is r a t h e r slow b u t the effects of this corrosion are noticeable i n the tabulation of e x p e r i m e n t a l d a t a . A m a c h i n e d n i c k e l c r u c i b l e was used i n the s m a l l b o m b a n d a l i n e r fabricated f r o m a 12-inch length of 6 - i n c h n i c k e l t u b i n g a n d a n i c k e l plate was used i n the large b o m b .

Discussion of Experimental Results RESULTS USING SMALL BOMB. I n the e a r l y part of this investigation s o d i u m peroxide f r o m several different sources was used. A calorific grade of s o d i u m peroxide consistently u n d e r w e n t less conversion t h a n a less p u r e c o m m e r c i a l s o d i u m peroxide u n d e r i d e n t i c a l o x i d a t i o n conditions. T h i s suggested that i m purities i n the c o m m e r c i a l s o d i u m peroxide were acting catalytically. A group of m e t a l oxides were tested for catalytic activity, as they w e r e thought to be l i k e l y contaminants of s o d i u m peroxide. A b l e n d of 3 to 4 grams of s o d i u m peroxide containing 2.5% b y v o l u m e (1.5% b y weight) of the potential catalyst was c h a r g e d to the s m a l l b o m b i n a n i c k e l crucible. T h e m i x t u r e was subjected to treatment w i t h o x y g e n at 137 a t m . a n d 500 ° C . f o r 2 hours i n each case. T h e compositions of the resultant products are g i v e n as m i l l i l i t e r s of o x y g e n liberated for each g r a m of m a t e r i a l catalytically decomposed. [ B y a simple calculation (5) this v a l u e can be converted to p e r cent s o d i u m superoxide i n s o d i u m peroxide.] W h e n n o catalyst was used the product liberated 247 m l . of o x y g e n per g r a m . W h e n either zinc oxide or c o b a l t - p l a t i n u m p a l l a d i u m m i x e d oxides were used, the p r o d u c t liberated between 246 a n d 250 m l . of o x y g e n p e r g r a m ; w h e n g r o u n d borosilicate glass, m o l y b d e n u m trioxide, v a n a d i u m pentoxide, c h r o m i u m t r i o x i d e , n i c k e l sesquioxide, or f e r r i c oxide was used the product l i b e r a t e d 251 to 260 m l . of o x y g e n p e r g r a m ; w h e n m a g n e s i u m oxide or cobalt oxide was used the product l i b e r a t e d between 261 a n d 270 m l . of o x y g e n p e r g r a m . T h e product liberated over 270 m l . of o x y g e n p e r g r a m w h e n cupric oxide, t i t a n i u m oxide, or c a d m i u m oxide was used as a catalyst. O f a l l the materials tested, three compounds, c u p r i c oxide, t i t a n i u m oxide, a n d c a d m i u m oxide showed considerable promise as catalysts. S e v e r a l e x p e r i ments w e r e made u s i n g c u p r i c oxide, b u t the results were erratic a n d not r e p r o ducible a n d it was not f u r t h e r investigated. A series of runs was made i n w h i c h f r o m 0.3 to 1.5% b y weight each of c a d m i u m oxide a n d t i t a n i u m oxide was added as a catalyst. I n b o t h cases 0.6 to 0.7% b y weight of catalyst was sufficient to give m a x i m u m catalytic effect. T h e addition of catalysts i n greater amounts d i d not change the composition of the product. O n e object of this investigation was to determine the e q u i l i b r i u m composition of s o d i u m s u p e r o x i d e - s o d i u m p e r o x i d e m i x t u r e s w i t h o x y g e n at various pressures a n d temperatures. A group of experiments was p e r f o r m e d i n w h i c h the t e m p e r a ture was v a r i e d f r o m 450° to 550°C. a n d the o x y g e n pressure f r o m 102 to 137 a t m . B o t h c a d m i u m oxide a n d t i t a n i u m oxide catalysts were used. T h e product c o m position, expressed i n o x y g e n content, for various exposures at these conditions, is tabulated i n T a b l e I.


ADVANCES IN CHEMISTRY SERIES

126

Table I. Product Composition from Small Bomb Runs (Milliliters of o x y g e n evolved per g r a m of product. Reaction pressure of 137 atm.) Catalyst Reaction T i m e , H o u r s 1 D 550 ° C . 500°C. 450 ° C . >2


550°C. 500°C. 450 ° C .

2

3

256 274

6

256 287 247

270 245

4

245

289

260

18

24

2èè

288 280

256

281

30

48

260

282

O n the basis of these data it is thought that the f o l l o w i n g e q u i l i b r i u m values have been d e t e r m i n e d : A t 5 5 0 ° C . a n d 137 a t m . of o x y g e n pressure the e q u i l i b r i u m composition is 69% b y weight s o d i u m superoxide i n s o d i u m p e r o x i d e ; at 5 0 0 ° C . a n d 137 a t m . of o x y g e n pressure the e q u i l i b r i u m composition is 89% b y weight s o d i u m superoxide i n s o d i u m peroxide. T h e v a l i d i t y of these e q u i l i b r i u m values is substantiated b y the fact that b o t h catalytic agents gave values that check w i t h i n the e x p e r i m e n t a l error. A s the exposure time at a n y one set of conditions was increased, the s o d i u m superoxide content of the product passed t h r o u g h a m a x i m u m . T h e decrease i n content of s o d i u m superoxide at longer exposure times is attributed to effects of corrosion of the n i c k e l l i n e r . A t 450 ° C . the reaction is so slow that these corrosion effects are apparent before e q u i l i b r i u m is r e a c h e d ; the e q u i l i b r i u m composition at this temperature should be above that of the 500 ° C . v a l u e . Because of these corrosion effects the e q u i l i b r i u m values at 500° a n d 550 ° C . m a y be s l i g h t l y l o w . A more satisfactory container m a t e r i a l must be f o u n d i n order to get m o r e accurate e q u i l i b r i u m points over a w i d e temperature range. RESULTS USING LARGE BOMB. In the experiments using the large b o m b the p r o cedure was to charge 3 to 3.5 pounds of s o d i u m peroxide i n the b o m b a n d heat the bomb to the desired temperature. O x y g e n was then t u r n e d into the b o m b to the desired pressure a n d the pressure was m a i n t a i n e d b y a d d i n g o x y g e n as it was consumed. A f t e r exposure, the m a t e r i a l was cooled to r o o m temperature w h i l e under o x y g e n pressure. T h e rate at w h i c h oxygen, at a n y one set of conditions, reacts w i t h s o d i u m peroxide is dependent o n the available surface area of the s o d i u m peroxide. W h e n a c o m m e r c i a l s o d i u m peroxide (Solozone) was exposed to o x y g e n at 137 a t m . at 3 0 0 ° C . f o r 4 hours a p r o d u c t e v o l v i n g 207 m l . of o x y g e n p e r g r a m was obtained. Solozone is a dense m a t e r i a l i n the f o r m of s m a l l h a r d granules about 40 mesh. Solozone was m i l l e d i n a b a l l m i l l u n t i l 100% w o u l d pass a 100-mesh screen a n d about 50% w o u l d pass 150-mesh screen. W h e n this b a l l - m i l l e d m a t e r i a l was e x posed to o x y g e n at the same conditions, a p r o d u c t e v o l v i n g 259 m l . of o x y g e n per g r a m was obtained. A t this time some s o d i u m peroxide p r e p a r e d b y the m e t h o d of J a c k s o n (1) was m a d e available. W h e n this l i g h t fluffy m a t e r i a l reacted at the same conditions, a p r o d u c t e v o l v i n g 280 m l . of o x y g e n p e r g r a m was obtained. B y c h a n g i n g the temperature or the o x y g e n pressure, b o t h the c h e m i c a l c o m position a n d the p h y s i c a l properties of the p r o d u c t c o u l d be v a r i e d . A t 450 ° C . or above, the m a t e r i a l appeared to have passed t h r o u g h a l i q u i d phase d u r i n g the reaction as the product was r e c o v e r e d as a h a r d fused mass. B e l o w about 400 ° C . the p r o d u c t was r e c o v e r e d f r o m the b o m b i n one piece w h i c h was o n l y p a r t i a l l y sintered. T h i s p r o d u c t could be easily b r o k e n into c h u n k s or g r o u n d into a p o w d e r . B y using the specially p r e p a r e d h i g h surface s o d i u m p e r o x i d e a product containing considerable s o d i u m superoxide c a n be p r e p a r e d u n d e r m u c h m o r e moderate conditions t h a n was o r i g i n a l l y b e l i e v e d possible. A product containing 75% s o d i u m superoxide i n s o d i u m peroxide c a n be p r e p a r e d at conditions as m i l d at 300 ° C . a n d 86 atm., a n d a p r o d u c t containing over 9 9 % s o d i u m superoxide was obtained f r o m a reaction at 400 ° C . a n d 122 a t m . THERMO-STABILITY OF SODIUM PEROXIDE. Because of the difficulty encountered i n t r y i n g to obtain e q u i l i b r i u m values at l o w e r temperatures it seemed advisable to


127

SCHECHTER A N D SHAKELY—SODIUM SUPEROXIDE

a p p r o a c h e q u i l i b r i u m f r o m the other d i r e c t i o n — that is, take h i g h p u r i t y m a t e r i a l and heat it at various temperatures for l o n g periods of time. It is k n o w n f r o m experience w i t h potassium superoxide that s u c h results are affected b y the amount of water present ( p r o b a b l y as a h y d r o x i d e h y d r a t e ) i n the m a t e r i a l ; the superoxides are e x t r e m e l y hygroscopic. A s a measure of this water of h y d r a t i o n , the oxide samples are heated at 130°C. for 15 m i n u t e s ; this allows the water present to react w i t h excess oxide a n d gives a n essentially a n h y d r o u s product. T h i s heat treatment gives rise to a loss of o x y g e n a n d is r e f e r r e d to i n T a b l e s II a n d III as the heat loss.


Table II. Stability of Superoxides at 6 5 C . Initial A n a l y s i s T o t a l O2 H e a t loss 302 8.1 209 4.2 260 6.2 230 — 236 13.0

Sample

Na0 Na0 Na0 KO2

2 2 2

Sample Weight, Grams 89 76 79 80

O x y g e n L o s s at 650°C. T i m e , days M l . / g r a m loss 0.54 31 0.58 31 0.70 13 0.33 23

Table III. Stability of Sodium Superoxide at 100C. Sample I, H e a t Loss = 9.3 M l . p e r G r a m 0 7 281 277 NaU2 analysis, m l . 02/g.

14 277

21 260

9.9 M l . per G r a m 14 286

21 276

28 266

Time,

days

T i m e , days

Na02 analysis, m l . 02/g.

Sample II, H e a t Loss : 0 7 301 295

T h e data s h o w n i n T a b l e II were collected b y heating samples of the s u p e r oxide i n a n atmosphere of d r y air i n a 65 ° C . thermostatic b a t h a n d m e a s u r i n g the e v o l v e d o x y g e n b y means of a buret. A sample of potassium superoxide was r u n for comparison. F r o m these data it is seen that the superoxides are stable at 65 ° C . a n d that it w o u l d be most difficult to study the e q u i l i b r i u m i n this m a n n e r . T h e o x y g e n lost over a p e r i o d as l o n g as 31 days is m u c h less t h a n the amount of o x y g e n lost i n the heat loss analysis. C o m p a r a b l e data were desired at 100 ° C , so containers of s o d i u m superoxide were p l a c e d i n a n o v e n at this temperature. T h e containers were a l l o w e d to breathe t h r o u g h a d r y i n g tube, so that the water w o u l d not contaminate the sample. T h e results of two such experiments are tabulated i n T a b l e III. F r o m these data it c a n be seen that s o d i u m superoxide is not t h e r m a l l y stable at 100 ° C . b u t that a p e r i o d of s e v e r a l months w o u l d be r e q u i r e d to ensure that e q u i l i b r i u m conditions were reached.

Summary T h e conditions for the p r e p a r a t i o n of s o d i u m superoxide f r o m s o d i u m p e r o x ide a n d o x y g e n at elevated temperatures a n d pressures have been f u r t h e r defined. T h e rate at w h i c h the reaction proceeds is dependent u p o n the surface area of the reactant s o d i u m p e r o x i d e . A p r o d u c t c o n t a i n i n g i n excess of 9 9 % s o d i u m superoxide has been obtained f r o m a reaction at 400 ° C . a n d a n o x y g e n pressure of 122 a t m . T h e data presented indicate that the e q u i l i b r i u m composition contains 6 9 % b y weight of s o d i u m superoxide i n s o d i u m peroxide at 550 ° C . a n d 8 9 % b y weight of s o d i u m superoxide i n s o d i u m peroxide at 500 ° C . u n d e r a n o x y g e n pressure of 137 a t m . E v i d e n c e indicates that s o d i u m superoxide is stable i n d r y air at 65 ° C . b u t at 100°C. decomposes a p p r e c i a b l y . N o satisfactory containing m a t e r i a l has been f o u n d i n w h i c h to c a r r y out this reaction. N i c k e l is at present the best k n o w n containing m a t e r i a l , b u t it


ADVANCES

128

IN CHEMISTRY SERIES

corrodes a p p r e c i a b l y a n d contaminates the reaction m i x t u r e d u r i n g longer runs. Because of this, insufficient data h a v e been collected to define extensively the e q u i l i b r i u m compositions existing i n the system u n d e r consideration.

Literature Cited J a c k s o n , C . B., U. S. Patent 2,405,580 ( A u g . 13, 1946); B r i t . Patent 626,644 ( J u l y 19, 1949). Schechter, W . H., U. S. Patent 2,648,596 ( A u g . 11, 1953). Schechter, W . H., Sisler H. H., K l e i n b e r g , J., J. Am. Chem. Soc. 70, 267 (1948). Schechter, W . H., T h o m p s o n , J. K., K l e i n b e r g , J., Ibid., 71, 1816 (1949). Stephenou, S. E., Schechter, W . H., A r g e r s i n g e r , W . J., K l e i n b e r g , J., ibid., 71, 1819 (1949).


(1) (2) (3) (4) (5)


Preparation of Sodium Superoxide - Advances in Chemistry (ACS

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