The Sodium Peroxide Production Story


Figure 1, consisted of an iron pipe surrounded by a coal-fired furnace. The ends ... This process gives a uniform particle size which is dust-free. Th...
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The Sodium Peroxide Production Story H. R. T E N N A N T a n d R. B. S C H O W

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U . S. Industrial C h e m i c a l s C o . , 9 9 Park A v e . , N e w Y o r k 16, Ν. Y .

In 1951, USI started operating the first continuous process for the production of sodium peroxide. The process is unique in a second respect — it utilizes air rather than pure oxygen. For nearly 70 years, variations of a batch process have been used. The present batch procedure involves oxi­ dation of sodium to sodium monoxide with dry air, and subsequent oxidation of the monoxide to peroxide with 9 0 % oxygen. Details of process development and the improvements leading to a continuous process operated with air oxidation are r e v i e w e d . Sodium and sodium peroxide handling, peroxide uses, and estimated 1956 production are also given. Much of this infor­ mation w i l l s u g g e s t h o w others can handle sodium safely on a commercial scale. +

A T the present time, there are two plants i n the U n i t e d States p r o d u c i n g s o d i u m peroxide. B o t h units are operated b y s o d i u m producers adjacent to their m e t a l l i c s o d i u m plants. U S I ' s continuous process is located at A s h t a b u l a , O h i o ; D u Pont's unit at N i a g a r a F a l l s , N . Y . is a batch process. In 1951, U S I started operating the first continuous process for the p r o d u c t i o n of s o d i u m peroxide. T h e process is u n i q u e i n that it involves the reaction of s o d i u m w i t h peroxide a n d it utilizes a i r rather than pure o x y g e n f o r oxidation. T w o batch processes have been used c o m m e r c i a l l y . T h e one developed i n the '20's has since been modified b u t its basic principles are still b e i n g used effec­ t i v e l y today. T h e first c o m m e r c i a l process started p r o d u c i n g s o d i u m peroxide about 1890. A l t h o u g h it was a r a t h e r crude unit b y today's standards, it illustrates the relative ease w i t h w h i c h s o d i u m metal m a y be h a n d l e d , a n d it p r o d u c e d a peroxide of over 9 0 % p u r i t y . S o d i u m peroxide, l i k e m a n y other c h e m i c a l compounds, was k n o w n l o n g before it became a n i n d u s t r i a l c h e m i c a l . F o r decades it was little m o r e t h a n a laboratory curiosity used o n l y f o r fusion a n d the l i k e . A c t u a l l y , it was over a h u n d r e d years ago, i n 1811, that G a y - L u s s a c first described s o d i u m peroxide. H e p r e p a r e d it b y b u r n i n g s o d i u m i n a n atmosphere of o x y g e n . T h e r e w a s no need f o r c o m m e r c i a l quantities u n t i l near the t u r n of the century. A t that time, it was m a d e i n O l d b u r y , E n g l a n d , b y the A l u m i n u m C o . a n d i n G e r m a n y b y D e u t s c h G o l d - u n d Silber-Scheideanstatt, a n d a little later b y the o l d N i a g a r a F a l l s E l e c t r o c h e m i c a l C o .

First Commercial Process T h i s first process w a s developed b y Castner (3), one of the founders of the s o d i u m i n d u s t r y . H e developed his process as a n outlet for the metal, a n d a c c o r d 1

Present address, U n i o n Sales C o r p . , C o l u m b u s , I n d . 118

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

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i n g to one patent, used his p e r o x i d e i n the p r e p a r a t i o n of h y d r o g e n peroxide. O t h e r sources m e n t i o n the b l e a c h i n g of straw f o r hats as a m a j o r use 50 to 60 years ago. B l e a c h i n g remains the p r i n c i p a l use f o r s o d i u m peroxide. T o d a y its largest m a r k e t is i n the paper i n d u s t r y . I n this field, its o r i g i n a l use was i n the b l e a c h i n g of g r o u n d w o o d p u l p , a n d i n recent years it has become f i r m l y established for the b l e a c h i n g of c h e m i c a l pulps. S o m e textiles a n d certain flours such as tapioca also e m p l o y s o d i u m peroxide bleaches.

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S o d i u m perborate is no doubt the largest v o l u m e c h e m i c a l d e r i v e d f r o m s o d i u m peroxide, a n d it is used i n m a k i n g organic peroxide catalysts a n d other specialty chemicals. S o d i u m peroxide is p r o d u c e d a n d shipped as a y e l l o w - w h i t e g r a n u l a r m a t e r i a l w i t h a p u r i t y of at least 9 5 % . M o r e important, s o d i u m peroxide contains about 20% a v a i l a b l e o x y g e n a n d is cheaper than h y d r o g e n p e r o x i d e o n this basis. S o d i u m peroxide w i l l n o r m a l l y be dissolved i n water, where it p a r t i a l l y h y d r o lyzes, a n d , therefore, reacts as h y d r o g e n p e r o x i d e i n a n a l k a l i n e solution. A l l of the a l k a l i metals f o r m a monoxide, M 0 , a n d a peroxide, M 0 . S i n c e the peroxides of a l l these metals are similar, only s o d i u m peroxide is used o n a large c o m m e r c i a l scale. T h i s is because of the l o w cost a n d a v a i l a b i l i t y of s o d i u m as w e l l as the relative ease of p r e p a r i n g the peroxide. 2

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In p r i n c i p l e , Castner's o r i g i n a l process was a g r a d u a l oxidization of m o l t e n s o d i u m i n a countercurrent stream of purified a n d d r i e d a i r . T h e equipment, F i g u r e 1, consisted of a n i r o n pipe s u r r o u n d e d b y a c o a l - f i r e d furnace. T h e ends of the pipe h a d tight-fitting e n d plates outside of the furnace. S h a l l o w layers of s o d i u m about 0.5 i n c h deep were placed i n a l u m i n u m pans, loaded o n t a n d e m carts. T h e carts w e r e then sealed i n the heated i r o n tube for reaction at about 200° C . A i r free of moisture a n d carbon dioxide was f e d to the tube at a c o n -

Figure 1. Drawing of Castner's equipment

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

A D V A N C E S IN CHEMISTRY SERIES

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t r o l l e d rate. A t the a i r inlet e n d of the tube, the s o d i u m was b r o u g h t i n contact w i t h a r i c h m i x t u r e of o x y g e n a n d nitrogen. A t the other e n d , fresh s o d i u m was s l o w l y o x i d i z e d b y a i r poor i n o x y g e n . A s w o u l d be expected, a n oxide crust was f o r m e d . M o l t e n m e t a l was d r a w n to the surface of the crust b y c a p i l l a r y action. H o w e v e r , c a p i l l a r y action was incomplete, a n d e v e n t u a l l y became ineffective before a l l the s o d i u m was o x i d i z e d . T h e product consisted of three i n t e r m i x e d layers w i t h s o d i u m below, s o d i u m p e r o x i d e above, a n d m o n o x i d e i n between.

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A s the f o r w a r d pans reached this condition, they were cooled a n d w i t h d r a w n . T h e mass was b r o k e n u p a n d passed t h r o u g h a second o r finishing tube. A g a i n a countercurrent stream of purified d r y a i r was used, b u t the temperature is r e p o r t e d to have been higher t h a n i n the first tube.

Present Batch Process I n 1928 a n d 1931, C a r v e t h assigned patents (1, 2) on a two-stage process for p r o d u c i n g s o d i u m m o n o x i d e a n d s o d i u m peroxide. T h e first step of the process is the p r o d u c t i o n of s o d i u m m o n o x i d e i n a r o t a r y i r o n b u r n e r , F i g u r e 2. E i t h e r l i q u i d o r solid s o d i u m is f e d i n t e r m i t t e n t l y t h r o u g h the top inlets of the r o t a r y b u r n e r a n d its m e t a l housing. A b o u t 10% s o d i u m is m i x e d w i t h p u l v e r i z e d s o d i u m m o n o x i d e to fill the retort about one t h i r d to one h a l f f u l l . D r y a i r is introduced t h r o u g h one e n d of the retort a n d exhaust gas, substantially nitrogen, passes out of the other e n d to a dust collector. A temperature of about 200° C . is m a i n t a i n e d b y heating the shell. C o o l i n g before d i s c h a r g i n g c a n be accomplished b y b l o w i n g cool a i r t h r o u g h the s h e l l o r s p r a y i n g water o n the outside of the s h e l l . P a r t of the m o n o x i d e is e m p t i e d t h r o u g h the bottom port f o r c h a r g i n g to the p e r o x i d e b u r n e r s , l e a v i n g a heel for the next s o d i u m charge.

Figure 2.

Drawing of Carveth's equipment

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M o n o x i d e is converted to peroxide b y p u r e o x y g e n or o x y g e n - e n r i c h e d a i r i n the second r o t a r y b u r n e r . T e m p e r a t u r e s are said to v a r y f r o m 240° to 390° C . A l t h o u g h this reaction is also exothermic, some heating is needed to m a i n t a i n the oxidization. T h e p r i n c i p l e s of this process are still e m p l o y e d at D u Pont's p e r o x i d e plant at N i a g a r a F a l l s , N . Y . It has obvious advantages over the o r i g i n a l c o m m e r c i a l m e t h o d — e.g., a h i g h e r p u r i t y a p p r o x i m a t i n g about 96%, shorter reaction time, l o w e r investment, a n d less l a b o r .

USI Continuous Process It was f o u n d that a i r r a t h e r t h a n p u r e o x y g e n c a n be used i n m a k i n g a h i g h p u r i t y product, a n d U S I has been able to control the reaction of s o d i u m w i t h s o d i u m peroxide. T h i s process gives a u n i f o r m particle size w h i c h is dust-free. T h e process operates as three stages integrated into a continuous system. I n the first stage, a s m a l l amount of s o d i u m is continuously m i x e d w i t h a n

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

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TENNANT A N D S C H O W — S O D I U M PEROXIDE PRODUCTION

Figure 3.

USI continuous

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excess of s o d i u m peroxide. T h e m i x t u r e flows b y g r a v i t y to the second or r e d u c i n g stage. I n the second reactor, the temperature is increased so that s o d i u m reduces a n equivalent amount of p e r o x i d e to m o n o x i d e . G r a v i t y feed is used again f o r c h a r g i n g the l o w test o r p a r t i a l l y r e d u c e d p e r o x i d e into the o x i d i z e r w h e r e the t h i r d stage takes place. T h e h i g h test product discharging f r o m the o x i d i z e r b r e e c h i n g is p i c k e d u p b y a screw c o n v e y o r w h i c h empties into a n a i r conveyor. T h e a i r conveyor empties into a cyclone, w h i c h feeds to the s c r e e n ing section. P e r o x i d e is either r e c y c l e d i n the process or f e d to the p a c k a g i n g section. M e t a l l i c s o d i u m is p u l l e d b y v a c u u m f r o m the company's a d j o i n i n g s o d i u m p r o d u c t i o n plant t h r o u g h a 2 - i n c h insulated pipeline to the top floor of the peroxide b u i l d i n g . T h i s pipeline is suspended f r o m telegraph poles a n d is heated b y resistant heaters w h i c h h o l d the temperature above the m e l t i n g point of s o d i u m . T h e p o w e r i n p u t for these heaters is about 30 to 40 watts p e r foot. T h e tanks f o r r e c e i v i n g the s o d i u m are protected f r o m overflowing b y electrodes situated i n the top of the tanks. W h e n the l i q u i d l e v e l touches the electrodes, the v a c u u m line is automatically closed a n d the receiver is flooded w i t h nitrogen. T h e s o d i u m p i p e l i n e is a p p r o x i m a t e l y 75 y a r d s long, a n d is t y p i c a l of p i p e lines i n plants c o n s u m i n g s o d i u m i n large quantities. I n a d d i t i o n to b e i n g the simplest m e t h o d f o r t r a n s f e r r i n g sodium, the use of v a c u u m offers another d i s tinct advantage. I n the event of a leak i n the line, the a i r d r a w n into the l i n e w o u l d freeze the s o d i u m and stop the flow. A reciprocating p u m p d r i v e n b y a v a r i a b l e speed d r i v e is used i n the short line between the storage tanks a n d the m i x e r . B y adjusting the speed, the desired ratio of s o d i u m to peroxide c a n be m a i n t a i n e d i n the m i x e r . N o r m a l l y , s o d i u m w i l l not exceed about 1 0 % of the charge to the m i x e r . S o d i u m peroxide enters the m i x e r b y g r a v i t y f r o m the surge b i n t h r o u g h a r o t a r y lock.

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

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T h e m i x e r is a continuous K n e a d - m a s t e r type of unit made of m i l d steel, as corrosion is no p r o b l e m at this point i n the process. T h e temperature of the m i x e r is m a i n t a i n e d slightly above the m e l t i n g point of s o d i u m b y a i r cooling a n d b y strip heaters. A g i t a t i o n is p r o v i d e d w i t h steel single span o v e r l a p p i n g type dispersion blades (modified sigma arrangement) a r r a n g e d for c o u n t e r r o t a tion, a n d the speed m a y be v a r i e d . S e a l i n g the unit f r o m contamination w i t h outside atmosphere has always been of m a j o r concern as this operation must proceed u n d e r a n inert atmosphere. T h i s is done b y b l a n k e t i n g the m i x e r w i t h nitrogen under a slight pressure. I n addition, the agitator shaft's p a c k i n g glands are p r o v i d e d w i t h nitrogen connections at the l a n t e r n rings to give positive pressure at these points a n d prevent the s u c k i n g of a i r a n d moisture into the process. T h e peroxide a n d s o d i u m m i x t u r e , h a v i n g the appearance of wet sand, drops b y g r a v i t y into the reducer, w h i l e the temperature is elevated to 200° to 440° C . A c h e m i c a l reaction takes place as the s o d i u m reduces a n equivalent amount of surface s o d i u m peroxide to s o d i u m m o n o x i d e . Heat is p r o v i d e d b y gas b u r n e r s controlled b y thermocouples i n the reaction b e d a n d at the reducer shaft shell. T h i s unit is s i m i l a r to the m i x e r , except that it is n i c k e l - l i n e d , as corrosion is a p r o b l e m at this stage, because of the r a p i d attack of most metals b y s o d i u m m o n o x i d e at h i g h temperatures. A g i t a t i o n for the reducer is p r o v i d e d b y c o u n t e r rotating p a d d l e - t y p e blades w h i c h give the vigorous m o v e m e n t necessary at this point. P r e v i o u s to the development of the continuous process, it was b e l i e v e d that the reaction of s o d i u m a n d p e r o x i d e c o u l d not be controlled. E a r l y patents state that a fused mass w a s obtained w h i c h c o u l d not be oxidized. T h e p a r t i a l l y r e d u c e d s o d i u m p e r o x i d e drops b y g r a v i t y f r o m t h e reducer directly into the oxidizer w h e r e the t h i r d stage takes place. T h e s o d i u m p e r o x i d e is o x i d i z e d at h i g h temperatures (200° to 440° C.) b y a continuous flow of c o u n t e r c u r r e n t a i r , y i e l d i n g high-test s o d i u m p e r o x i d e again. T h e oxidizer is a s l o w l y r e v o l v i n g " k i l n " of steel construction w h i c h is p r o v i d e d w i t h i n t e r n a l n i c k e l flights. T h e s o d i u m p e r o x i d e is p i c k e d u p b y the flights a n d c o n t i n u a l l y showered as it makes i t w a y towards the oxidizer discharge. S h o w e r i n g gives excellent contact w i t h the a i r w h i c h speeds u p the o x i d a t i o n process. T h e temperature i n the o x i d i z e r is m a i n t a i n e d b y gas heaters at the m i d - s e c t i o n of the unit. T h e high-test s o d i u m p e r o x i d e discharges into the oxidizer breeching, w h e r e it is p i c k e d u p b y a screw conveyor. T h e screw discharges the m a t e r i a l into a n air c o n v e y o r w h i c h transports it to the screens. T h e a i r c o n v e y o r is a pressure type made of steel pipe, w h i c h serves two purposes. I n a d d i t i o n to transporting m a t e r i a l it acts as a cooler, cooling the peroxide f r o m 200° to 370° C . as it enters the c o n v e y o r a n d to u n d e r 150° C . as the m a t e r i a l enters the screen. C o o l i n g is p r o v i d e d b y water sprays along the l e n g t h of the conveyor. S o d i u m p e r o x i d e is screened into three parts i n a h u m m e r - t y p e v i b r a t i n g screen. T h e top cut is over 20 mesh. T h i s m a t e r i a l goes t h r o u g h a g r i n d e r a n d is r e c y c l e d t h r o u g h the process again. T h e next cut is a l l m a t e r i a l between 20 a n d 80 mesh. T h i s is p r o d u c t a n d drops b y g r a v i t y to the p r o d u c t hopper. H o w e v e r , a certain amount of 20- to 80-mesh m a t e r i a l is also r e c y c l e d . T h e m a t e r i a l u n d e r 80 mesh is r e c y c l e d i n its entirety. T h e s o d i u m peroxide i n the product hopper is b a r r e l e d for shipment i n 400-pound d r u m s . P e r o x i d e is shipped i n t r u c k lots or freight car lots. T h e equipment, instrumentation, a n d h a n d l i n g procedures used i n this process a n d i n the s o d i u m plant offer a n o p p o r t u n i t y to show prospects h o w they can use metallic s o d i u m o n a plant scale. T h e c o m p a n y is p r o u d of a 4 - y e a r r e c o r d of no lost-time accidents, w h i c h is the result of a vigorous safety p r o g r a m c o m b i n e d w i t h w e l l - p l a n n e d engineering design a n d operating procedures. S o d i u m p e r o x i d e m a n u f a c t u r e is one of m a n y applications w h e r e m e t a l l i c s o d i u m is b e i n g used safely i n tonnage lots b y f o l l o w i n g p r o p e r h a n d l i n g procedures. P a p e r p u l p b l e a c h i n g is the p r i n c i p a l application, a l t h o u g h some v a l u a b l e chemicals are d e r i v e d f r o m the product. A paper t o w e l o r f a c i a l tissue whose appearance is p a r t i c u l a r l y attractive m a y owe its whiteness to this product. M o r e specifically, Time, Life, Fortune, Chemical Week, a n d Chemical Engineering

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

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use paper bleached w i t h s o d i u m peroxide. O n the c h e m i c a l side, a large percentage of the catalyst used for p o l y m e r i z i n g v i n y l chloride or v i n y l i d e n e chloride is m a d e w i t h s o d i u m peroxide, a n d p o w d e r e d l a u n d r y bleaches are often d e r i v e d f r o m s o d i u m peroxide.

Literature Cited (1)

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C a r v e t h , H. R. (to Roessler & Hasslacher C h e m i c a l C o . ) , U. S. Patent 1,685,520 1928). Ibid., 1,796,241 ( M a r c h 10, 1931). Castner, Ibid., 494,757 ( A p r i l 4, 1893).

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

(Sept. 25,