Separation of Ozone from Oxygen by a Sorption Process G. A. COOK, A. D. KIFFER, C. V. KLUMPP, A. H. MALIK, and L. A. SPENCE
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Research and Development Laboratory, Liηde Co., A Division of Union Carbide Tonawanda, Ν. Y.
Corp.,
O z o n e is separated from oxygen by adsorption on refrigerated silica gel, followed by desorption, either in pure form at reduced pressure, or diluted by air, nitrogen, argon, or other gas not strongly adsorbed on silica gel. This is a practical method, free from hazard when correctly performed.
T h e r e a r e s e v e r a l reasons w h y i t m i g h t be d e s i r a b l e t o s e p a r a t e ozone f r o m o x y g e n . B e c a u s e ozone is u s u a l l y p r o d u c e d i n c o n c e n t r a t i o n s of o n l y 1 t o 4 m o l e % i n a s t r e a m of a i r o r o x y g e n , a n y o n e w i s h i n g t o use m o r e c o n c e n t r a t e d ozone, o r ozone i n t h e absence of o x y g e n , m u s t s e p a r a t e t h e t w o gases. I n a l a r g e p l a n t i t is m o r e e c o n o m i c a l t o p r o d u c e ozone f r o m o x y g e n t h a n f r o m a i r , i f t h e u n c o n v e r t e d o x y g e n c a n b e s e p a r a t e d c h e a p l y e n o u g h f r o m t h e ozone a n d r e c y c l e d t o t h e ozone g e n e r a t o r . T h e s e p a r a t i o n m a y be a c c o m p l i s h e d i n s e v e r a l w a y s . O n e w a y is c o n d e n s i n g t h e ozone o u t as a l i q u i d a t a l o w t e m p e r a t u r e a n d t h e n p u m p i n g off a n y o x y g e n t h a t c o n densed a l o n g w i t h t h e o z o n e ; t h i s presents t h e h a z a r d s of h a n d l i n g c o n c e n t r a t e d l i q u i d ozone, a t o u c h y a n d b r i s a n t e x p l o s i v e . A n o t h e r p o s s i b i l i t y is t o pass t h e gas s t r e a m t h r o u g h a s o l v e n t w h i c h w i l l d i s s o l v e t h e ozone w h i l e l e t t i n g m o s t of t h e o x y g e n pass t h r o u g h . E a r l y i n 1948 t h e a u t h o r s discovered that cold, liquid dichlorodifluoromethane ( C F C 1 ) , chlorotrifluoromethane ( C F C 1 ) , o r m i x t u r e s of t h e t w o , c o u l d be u s e d f o r t h i s p u r p o s e . E v a p o r a t i n g ozone gas f r o m one of these s o l v e n t s e n t a i l s a loss of s o l v e n t a n d is s o m e w h a t h a z a r d o u s ; i t s h o u l d b e d o n e o n l y w i t h s u i t a b l e p r e c a u t i o n s , p r e f e r a b l y a t l o w p a r t i a l p r e s s u r e of ozone. A safer w a y of r e c o v e r i n g t h e ozone is t o b l o w i t o u t w i t h a s t r e a m of some gas, s u c h as n i t r o g e n o r a i r , t h a t is n o t a p p r e c i a b l y soluble i n t h e h a l o g e n a t e d m e t h a n e solvent. 2
2
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A n o t h e r w a y of s e p a r a t i n g o x y g e n f r o m ozone is t o pass t h e m i x t u r e t h r o u g h a vessel c o n t a i n i n g m a t e r i a l t h a t w i l l r e a c t w i t h t h e ozone. T h e o x y g e n t h a t passes t h r o u g h t h e vessel is p u r i f i e d , i f necessary, a n d r e c y c l e d t o t h e ozone g e n e r a t o r . This m e t h o d is s a t i s f a c t o r y i f t h e presence of o x y g e n i n t h e ozone r e a c t i o n vessel is n o t harmful. A m e t h o d w h i c h is free of h a z a r d i f p e r f o r m e d c o r r e c t l y , a n d represents a p r a c t i c a l w a y of s e p a r a t i n g ozone f r o m o x y g e n , consists o f a d s o r b i n g ozone o n r e f r i g e r a t e d s i l i c a gel a n d t h e n d e s o r b i n g i t , e i t h e r i n p u r e f o r m a t r e d u c e d p r e s s u r e , o r d i l u t e d b y a i r , n i t r o g e n , a r g o n , o r o t h e r gas n o t s t r o n g l y a d s o r b e d o n s i l i c a g e l . 44
OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
COOK, KIFFER, KLUMPP, MALIK, A N D SPENCE—SEPARATION FROM
Adsorption
of O z o n e o n Silica
45
OXYGEN
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I n 1950 extensive m e a s u r e m e n t s w e r e m a d e of t h e a d s o r p t i o n of ozone i n t h e presence of o x y g e n o n c o m m e r c i a l G r a d e 4 0 a n d P A 100 s i l i c a g e l p u r c h a s e d f r o m D a v i s o n C h e m i c a l C o r p . T h e technique used i n measuring the adsorption was simple. A s t r e a m of d r y o x y g e n a t a t m o s p h e r i c pressure a n d c o n t a i n i n g a k n o w n c o n c e n t r a t i o n of ozone w a s passed t h r o u g h a vessel i m m e r s e d i n a b a t h k e p t a t a c o n s t a n t , k n o w n temperature. T h e vessel c o n t a i n e d a k n o w n w e i g h t of s i l i c a g e l f r e s h f r o m D a v i s o n , a n d n o t t r e a t e d i n a n y w a y before b e i n g u s e d . T h e d i l u t e s t r e a m of ozone i n o x y g e n was passed t h r o u g h t h e b e d of s i l i c a gel u n t i l t h e c o n c e n t r a t i o n of ozone i n t h e off-gas was e q u a l t o t h a t i n t h e e n t e r i n g gas. T h e o z o n e - o x y g e n flow w a s t h e n s t o p p e d a n d
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Figure 1. Adsorption isotherms at 0 ° a n d 2 5 ° C. for ozone in oxygen on Davison silica gel Total pressure 1 atm.
a s t r e a m of p u r e , d r y o x y g e n w a s passed t h r o u g h t h e s i l i c a g e l a n d i n t o a s o l u t i o n of p o t a s s i u m i o d i d e i n w a t e r . W h e n a l l t h e ozone h a d b e e n d e s o r b e d , t h e l i b e r a t e d i o d i n e was t i t r a t e d w i t h s t a n d a r d s o d i u m t h i o s u l f a t e s o l u t i o n (1). T h e i s o t h e r m s o b t a i n e d f o r 0 ° a n d 2 5 ° C . a r e s h o w n i n F i g u r e 1, a n d f o r l o w e r t e m p e r a t u r e s i n F i g u r e 2. T h e a d s o r p t i o n a t 0 ° C . w a s v e r y m u c h less t h a n t h a t at —78° C . a n d below. ( T h e u n i t s f o r t h e o r d i n a t e i n F i g u r e 1 a r e i n p o u n d s of ozone p e r 1000 p o u n d s of g e l ; i n F i g u r e 2, i n p o u n d s of ozone p e r 100 p o u n d s of gel.) I n f o r m a t i o n f r o m D a v i s o n i n d i c a t e d t h a t t h e t w o grades of s i l i c a g e l differed o n l y i n p a r t i c l e size, G r a d e 4 0 b e i n g 6 t o 12 m e s h , a n d P A 100 b e i n g 14 t o 20 m e s h . Dif ferences i n ozone a d s o r p t i o n b e t w e e n t h e t w o grades were w i t h i n e x p e r i m e n t a l e r r o r .
OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.
Downloaded by RUTGERS UNIV on March 15, 2016 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch007
46
ADVANCES
10
20
30
IN CHEMISTRY SERIES
40
50
OZONE PARTIAL PRESSURE, MM. OF HG.
Figure 2. Smoothed adsorption isotherms for ozone in oxygen on Davison silica gel at temperatures ranging from - 7 8 . 5 ° t o - 1 4 0 ° C. Total pressure 1 atm.
A d s o r p t i o n of o x y g e n , a r g o n , a n d n i t r o g e n o n s i l i c a g e l w a s m e a s u r e d a n d f o u n d to b e v e r y s m a l l c o m p a r e d t o t h e a d s o r p t i o n of ozone. T h e h e a t of a d s o r p t i o n of ozone o n s i l i c a g e l w a s c a l c u l a t e d f o r v a r i o u s c o n d i t i o n s w i t h t h e h e l p of t h e C l a u s i u s - C l a p e y r o n e q u a t i o n ( F i g u r e 3 ) . I n t h e r e g i o n of t e m p e r a t u r e a n d ozone c o n c e n t r a t i o n of m o s t i n t e r e s t , t h e h e a t of a d s o r p t i o n i s a b o u t 5400 c a l . p e r g r a m - m o l e of ozone. O n l y t w o p a p e r s g i v e d a t a f o r ozone a d s o r p t i o n o n s i l i c a g e l . T h e r e s u l t s r e p o r t e d b y M a g n u s a n d G r a n t i n g (3) a p p e a r t o b e i n g o o d a g r e e m e n t w i t h t h e p r e s e n t w o r k , a l t h o u g h t h e i r m e t h o d of r e p o r t i n g is s o m e w h a t a m b i g u o u s . B r i n e r a n d L a c h m a n n (2) m a d e o n l y s i x i s o l a t e d e x p e r i m e n t a l m e a s u r e m e n t s . T h e r e s u l t s of t h r e e of these a r e
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