Applied Aspects of Zeolite Adsorbents

28 Applied Aspects of Zeolite Adsorbents HANJU LEE

Downloaded by PRINCETON UNIV on September 30, 2014 | http://pubs.acs.org Publication Date: June 1, 1973 | doi: 10.1021/ba-1973-0121.ch028

W. R. Grace & Co., Davison Chemical Division, Washington Research Center, Clarksville, Md. 21029

New applications of zeolite adsorption developed recently for sep aration and purification processes are reviewed. Major commercial processes are discussed in areas of hydrocarbon separation, drying gases and liquids, separation and purification of industrial streams, pollution control, and nonregenerative applications. Special emphasis is placed on important commercial processes and potentially important applications Important properties of zeolite adsorbents for these applicatio are adsorption capacity and selectivity, adsorption and desorption rate, physical strength and attrition resistance, low catalyti activity, thermal-hydrothermal and chemical stability, and particle size and shape. Apparent bulk density is important because it is related to adsorptive capacity per unit volume and to the rate of adsorption-desorption. However, more important factors controlling the raies are crystal size and macropore size distribution. / ~ V n e of t h e m a j o r i n d u s t r i a l a p p l i c a t i o n s of zeolites is i n t h e a r e a of a d s o r p t i o n processes.

Zeolite adsorbents are n o t o n l y t h e m o s t i m p o r t a n t

adsorbents t o d a y , b u t t h e i r i m p o r t a n c e is i n c r e a s i n g , m a i n l y because of t h e following unique adsorptive properties:

(a) selective a d s o r p t i o n of m o l e -

cules based o n m o l e c u l a r dimensions, (b) h i g h l y p r e f e r e n t i a l a d s o r p t i o n of p o l a r molecules, (c) h i g h l y h y d r o p h i l i c surface, a n d (d) v a r i a t i o n of p r o p erties b y i o n exchange. C o n t r a r y t o c a t a l y t i c a p p l i c a t i o n s , zeolite adsorbents are m o s t l y a p p l i e d i n a fixed-bed o p e r a t i o n . A n u m b e r of c o l u m n s p a c k e d w i t h zeolite adsorbent (s) are i n t e r c o n n e c t e d w i t h a n a u t o m a t i c v a l v e s y s t e m t o f a c i l i t a t e a c o n t i n u o u s flow of t h e i n d u s t r i a l s t r e a m b e i n g processed. E a c h b e d , however, goes t h r o u g h a stepwise c y c l i c o p e r a t i o n , a n d d u r i n g each c y c l e t h e adsorbed molecules i n t h e zeolite b e d are desorbed b y r a i s i n g t h e b e d t e m p e r a t u r e , l o w e r i n g t h e b e d pressure, d i s p l a c i n g t h e a d s o r b a t e w i t h a n o t h e r adsorbate, or c o m b i n a t i o n . 311 In Molecular Sieves; Meier, W., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.

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F o r a fixed-bed o p e r a t i o n , zeolite adsorbents s h o u l d h a v e a reasonable size t o a v o i d a n excessive pressure d r o p . S y n t h e t i c zeolites a n d some n a t u r a l zeolites p r o d u c e d i n a fine size powder h a v e t o be f o r m e d i n t o spheres, e x t r u d a t e s , o r pellets u s u a l l y w i t h a n i n e r t b i n d e r . S o m e c o m m e r c i a l m o l e c u l a r sieve adsorbents, however, are called " b i n d e r l e s s " because t h e y c o n t a i n a m u c h higher (up t o 9 5 % ) zeolite c o n t e n t t h a n most zeolite a d sorbents. I m p o r t a n t properties of zeolite adsorbents for a fixed-bed a p p l i c a t i o n are a d s o r p t i v e c a p a c i t y a n d s e l e c t i v i t y , a d s o r p t i o n - d e s o r p t i o n r a t e , p h y s i c a l s t r e n g t h a n d a t t r i t i o n resistance, l o w c a t a l y t i c a c t i v i t y , t h e r m a l h y d r o t h e r m a l s t a b i l i t y , c h e m i c a l s t a b i l i t y , a n d p a r t i c l e size a n d shape. A p p a r e n t b u l k d e n s i t y of zeolite adsorbents i s i m p o r t a n t because i t is r e l a t e d t o t h e a d s o r p t i v e c a p a c i t y per u n i t v o l u m e a n d also somewhat t o r a t e of a d s o r p t i o n a n d d e s o r p t i o n . H o w e v e r , m o r e i m p o r t a n t properties r e l a t e d t o t h e rates a n d therefore t o t h e a c t u a l useful c a p a c i t y w o u l d be t h e zeolite c r y s t a l size a n d t h e macropore size d i s t r i b u t i o n . A l t h o u g h t h e u l t i m a t e basis i n selecting a zeolite adsorbent f o r a specific a p p l i c a t i o n w o u l d be t h e performance, t h e p r i c e , a n d t h e p r o j e c t e d service life of a p r o d u c t , these factors depend l a r g e l y u p o n t h e a b o v e properties. M a j o r i n d u s t r i a l a d s o r p t i o n processes u s i n g zeolite adsorbents m a y be classified as f o l l o w s : (I) h y d r o c a r b o n s e p a r a t i o n processes, (II) d r y i n g gases a n d l i q u i d s , ( I I I ) s e p a r a t i o n a n d p u r i f i c a t i o n of i n d u s t r i a l streams, ( I V ) p o l l u t i o n c o n t r o l a p p l i c a t i o n s , a n d ( V ) nonregenerative a p p l i c a t i o n s . Some i m p o r t a n t c o m m e r c i a l processes i n each of these areas are d i s cussed b r i e f l y . Hydrocarbon Separation Processes π-Paraffin S e p a r a t i o n . η-Paraffins are separated f r o m a m i x t u r e of paraffins b y u s i n g a C a A m o l e c u l a r sieve w hich h a s a n effective p o r e d i a m e t e r of about 5 A . Because of i t s pore size, a C a A m o l e c u l a r sieve adsorbs o n l y η-paraffins, a n d t h e effluent f r o m a m o l e c u l a r sieve b e d c o n t a i n s m a i n l y isoparaffins a n d a s m a l l a m o u n t of a r o m a t i c s e x i s t i n g i n t h e feed s t r e a m . T h e adsorbed η-paraffins are l a t e r desorbed f r o m t h e b e d a n d recovered. T

T h e use of n-paraffins recovered i n c l u d e octane v a l u e enhancement of gasoline, solvents a n d r a w m a t e r i a l s for biodegradable detergents, fire r e t a r d a n t s , plasticizers, a l c o h o l , f a t t y acids, s y n t h e t i c p r o t e i n s , l u b e o i l a d d i t i v e s , a n d α-olefins. A d e t a i l e d discussion o n n-paraffin s e p a r a t i o n processes is a v a i l a b l e (1). M a j o r c o m m e r c i a l processes i n η-paraffin s e p a r a t i o n a r e U . O . P . ' s M o l e x process (2-5), B . P . ' s process (6-8), E x x o n ' s E n s o r b process (9, 10), U n i o n C a r b i d e ' s I s o S i v process (11-13), T e x a c o ' s T . S . F . process (14, 15), Shell's process (16), a n d V E B L e u n a W e r k e ' s P a r e x process (17). E x c e p t

In Molecular Sieves; Meier, W., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1973.


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for t h e M o l e x process, a l l others operate u n d e r v a p o r phase a n d use t h e fixed-bed, c y c l i c a d s o r p t i o n technology. T h e processes are different, h o w ever, i n o p e r a t i n g pressure a n d t e m p e r a t u r e , m e t h o d of τι-paraffin desorp t i o n , a n d o t h e r o p e r a t i n g c o n d i t i o n s . M o s t processes operate u n d e r i s o t h e r m a l a n d isobaric c o n d i t i o n s w i t h desorption of η-paraffins b y displace m e n t . D i s p l a c e m e n t agents often m e n t i o n e d i n p a t e n t l i t e r a t u r e are l o w b o i l i n g η-paraffins s u c h as n - p e n t a n e a n d n-hexane, a n d a m m o n i a or a l k y l amines. I n e r t gases s u c h as n i t r o g e n or h y d r o g e n are m e n t i o n e d also, b u t t h e y m a y serve as c a r r i e r gases r a t h e r t h a n displacement agents. Some processes u t i l i z e a pressure s w i n g o p e r a t i o n , especially for s e p a r a t i n g l o w c a r b o n n u m b e r η-paraffins. I n pressure s w i n g o p e r a t i o n , t h e d e s o r p t i o n pressure is s u b s t a n t i a l l y lower t h a n t h e a d s o r p t i o n pressure t o f u r n i s h enough d r i v i n g force for a r e a s o n a b l y fast mass t r a n s f e r . I n cases where p r o d u c t p u r i t y is i m p o r t a n t , a n i n t e r m e d i a t e step (purge step) is used between a d s o r p t i o n a n d d e s o r p t i o n steps. P u r g i n g removes isoparaffins e x i s t i n g i n t h e v o i d space between m o l e c u l a r sieve adsorbents a n d macropores w i t h i n each adsorbent p a r t i c l e p r i o r t o desorp t i o n step. Because most i m p u r i t i e s c a n be r e m o v e d f r o m t h e adsorbent b e d i n t h e p u r g i n g step, t h e η-paraffins recovered i n t h e subsequent d e s o r p t i o n w o u l d be r e l a t i v e l y p u r e . T h e o p e r a t i n g t e m p e r a t u r e for v a p o r - p h a s e o p e r a t i o n m u s t be a b o v e t h e highest b o i l i n g p o i n t of t h e feed s t r e a m b u t generally lower t h a n 800° F t o a v o i d c r a c k i n g . T h e M o l e x process developed b y U . O . P . is u n i q u e n o t o n l y i n i t s l i q u i d - p h a s e o p e r a t i o n b u t also i n i t s a d s o r p t i o n s y s t e m (1-3). Its ad s o r p t i o n s y s t e m consists of a single a d s o r p t i o n t o w e r w i t h m u l t i p l e i n l e t o u t l e t p o i n t s a n d a special r o t a r y v a l v e . T h e a d s o r p t i o n t o w e r has m a n y smaller a d s o r p t i o n chambers i n t e r c o n n e c t e d i n series, a n d i t operates under t h e so-called " s i m u l a t e d m o v i n g b e d " o p e r a t i o n . I n s t e a d of m o v i n g t h e adsorbent bed, t h e s i m u l a t e d m o v i n g b e d operates b y s i m u l t a n e o u s l y a d v a n c i n g i n l e t - o u t l e t p o i n t s p e r i o d i c a l l y . A t a n y t i m e , t h e adsorber has four zones—viz., a d s o r p t i o n , p r i m a r y r e c t i f i c a t i o n , d e s o r p t i o n , a n d secondary r e c t i f i c a t i o n zones, a n d these zones a d v a n c e s i m u l t a n e o u s l y as t h e r o t a r y v a l v e t u r n s p e r i o d i c a l l y . D e s o r p t i o n of ra-paraffins is a c h i e v e d b y displacement. T h e r a t e of τι-paraffin d e s o r p t i o n generally controls t h e o v e r a l l p r o d u c t i o n r a t e (18, 19). T h e diffusion of τι-paraffins i n c o m m e r c i a l 5 A m o lecular sieves is r e p o r t e d t o be c o n t r o l l e d b y either m i c r o p o r e diffusion or macropore diffusion, or b o t h , depending o n t h e m o l e c u l a r sieve c r y t a l size a n d macropore size d i s t r i b u t i o n of t h e adsorbent (20). A 5 A molecular sieve adsorbent w i t h s m a l l e r c r y s t a l size a n d o p t i m u m m a c r o p o r e size d i s t r i b u t i o n w o u l d h a v e a faster a d s o r p t i o n - d e s o r p t i o n r a t e a n d , therefore, a higher effective c a p a c i t y . ^-Xylene Separation-U.O.P.'s P a r e x Process. T h e continued rapid increase i n t h e p - x y l e n e d e m a n d as a r a w m a t e r i a l for p o l y e s t e r p r o d u c t s i n


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recent y e a r s necessitated t h e d e v e l o p m e n t process.

U . O . P . developed

xylene from a C

8

of a n e w x y l e n e s e p a r a t i o n

a n e w a d s o r p t i o n process for s e p a r a t i n g p-

aromatics mixture containing xylenes and ethylbenzene

( U . O . P . ' s P a r e x process s h o u l d n o t be confused w i t h V E B L e u n a

(21, 22).

W e r k e ' s ( E . G e r m a n y ) P a r e x process w h i c h is a n n - p a r a f f i n s e p a r a t i o n process (see p r e c e d i n g section).)

T h e h a r d w a r e for t h e P a r e x process seems

t o be s i m i l a r t o t h a t for t h e U . O . P . M o l e x process for n - p a r a f f i n s e p a r a t i o n , a n d i t uses t h e c o n t i n u o u s l i q u i d phase, s i m u l a t e d m o v i n g b e d o p e r a t i o n . T h i s process, i n a p i l o t - p l a n t o p e r a t i o n , d e m o n s t r a t e d t h a t i t c a n separate p - x y l e n e f r o m v a r i o u s t y p e s of feedstocks w i t h 9 9 . 5 % p u r i t y a n d r e c o v e r y


as h i g h as 9 8 . 4 % (21).

T h e h i g h p - x y l e n e r e c o v e r y i n p a r t i c u l a r is be-

l i e v e d t o be a significant i m p r o v e m e n t over c o n v e n t i o n a l c r y s t a l l i z a t i o n processes.

P a t e n t s issued t o U . O . P . i n r e g a r d t o a r o m a t i c s e p a r a t i o n

suggest t h a t t h e adsorbent u s e d is a s y n t h e t i c f a u j a s i t e c o n t a i n i n g c a t i o n s of g r o u p I A , g r o u p I I A , or b o t h (23-25).

R e c e n t p a t e n t l i t e r a t u r e (27, 28)

also c l a i m s t h a t s o d i u m m o r d e n i t e a n d m o d i f i e d t y p e - Y zeolite c o n t a i n i n g p r e d o m i n a n t l y p o t a s s i u m ions c a n separate p - x y l e n e f r o m a x y l e n e m i x t u r e a n d a C aromatic mixture, respectively. 8

H o w e v e r , n e i t h e r is k n o w n t o

be c o m m e r c i a l i z e d y e t . Olefin Separation.

U.O.P.'s

OLEX

PROCESS.

U.O.P.'S

other h y d r o -

c a r b o n s e p a r a t i o n process d e v e l o p e d r e c e n t l y — i . e . , t h e O l e x

process—is

u s e d to separate olefins f r o m a feedstock c o n t a i n i n g olefins a n d paraffins. T h e zeolite adsorbent used, a c c o r d i n g t o p a t e n t l i t e r a t u r e (29, 30), i s a synthetic faujasite w i t h 1-40 w t % groups I A , I I A , I B , a n d I I B .

of at least one c a t i o n selected f r o m

T h e O l e x process i s also b e l i e v e d t o use t h e

same s i m u l a t e d m o v i n g - b e d o p e r a t i o n i n l i q u i d phase as U . O . P . ' s o t h e r h y d r o c a r b o n s e p a r a t i o n processes—i.e., t h e M o l e x a n d P a r e x processes. UNION

CARBIDE'S

OLEFINSIV

PROCESS.

U n i o n Carbide's OlefinSiv

process is used m a i n l y t o separate n - b u t y l e n e s f r o m i s o b u t y l e n e (31).

The

basic h a r d w a r e is t h e same as for t h e I s o S i v process for n - p a r a f f i n s e p a r a t i o n , a n d t h e process uses a r a p i d cycle,

fixed-bed

adsorption.

Since t h i s

process separates s t r a i g h t - c h a i n olefins f r o m b r a n c h e d - c h a i n olefins, i t is reasonable t o assume t h a t a 5 A m o l e c u l a r sieve is used as t h e adsorbent. P r o d u c t p u r i t i e s are c l a i m e d t o be a b o v e 9 9 % for b o t h n - b u t y l e n e a n d i s o b u t y l e n e streams.

Drying Gases and Liquids A l l zeolites h a v e a h i g h l y h y d r o p h i l i c surface a n d are v e r y efficient desiccants.

C o n t r a r y t o o t h e r n o n z e o l i t i c desiccants such as s i l i c a gel a n d

a c t i v a t e d a l u m i n a , zeolite adsorbents h a v e t y p e I a d s o r p t i o n i s o t h e r m s for w a t e r — i . e . , a h i g h w a t e r a d s o r p t i o n c a p a c i t y at a l o w c o n c e n t r a t i o n of water.

T o o b t a i n e x t r e m e l y d r y gases a n d l i q u i d s , therefore, zeolite a d -

sorbents are s t r o n g l y preferred over a m o r p h o u s desiccants.

The 3A mo-


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l e c u l a r sieve adsorbent i n p a r t i c u l a r has t h e a d d i t i o n a l a d v a n t a g e of select i v e a d s o r p t i o n of w a t e r because of i t s s m a l l pore size, a n d i t is v e r y useful i n d r y i n g p o l a r l i q u i d s a n d gases.


C r a c k e d G a s D r y i n g . E t h y l e n e a n d p r o p y l e n e are t w o of the m o s t i m p o r t a n t p e t r o c h e m i c a l r a w m a t e r i a l s t o d a y . T h e y are m a n u f a c t u r e d b y a t h e r m a l c r a c k i n g of ethane, p r o p a n e , or n a p h t h a . O n e of t h e i m p o r t a n t s e p a r a t i o n - p u r i f i c a t i o n steps i n t h e p r o d u c t i o n of e t h y l e n e a n d p r o p y l e n e is r e m o v a l of w a t e r before l o w t e m p e r a t u r e s e p a r a t i o n . A l t h o u g h a l u m i n a has been t h e m o s t c o m m o n l y u s e d desiccant i n d r y i n g c r a c k e d gas i n t h e past, 3 A m o l e c u l a r sieve adsorbents h a v e a n o v e r a l l economic a d v a n t a g e (32), a n d m a n y c r a c k e d gas p l a n t s are u s i n g t h e 3 A m o l e c u l a r sieves t o d a y . T h e m a i n advantages of 3 A m o l e c u l a r sieve o v e r a l u m i n a a n d s i l i c a gel are i t s higher c a p a c i t y a n d , therefore, s m a l l e r a d s o r p t i o n t o w e r size a n d i t s longer service life. T h e d e g r a d a t i o n of 3 A m o l e c u l a r sieve i n c r a c k e d gas d r y i n g is n o t f r o m a c h e m i c a l d e s t r u c t i o n of zeolite c r y s t a l s b u t r a t h e r f r o m a n a c c u m u l a t e d deposit of c a r b o n m a t e r i a l o n t h e zeolite. Since a regular 3 A — i . e . , p o t a s s i u m - e x c h a n g e d t y p e A , is n o t t h e r m a l l y stable enough t o w i t h s t a n d a n in situ c a r b o n burnoff o p e r a t i o n , i t is r e p l a c e d w i t h a fresh charge of 3 A m o l e c u l a r sieve w h e n i t has a c c u m u l a t e d excessive c a r b o n a n d other h y d r o c a r b o n d e r i v a t i v e s . A recent p a t e n t (33), h o w e v e r , described a r a r e e a r t h c o n t a i n i n g 3 A m o l e c u l a r sieve h a v i n g sufficient t h e r m a l s t a b i l i t y t o w i t h s t a n d n o r m a l c a r b o n burnoff c o n d i t i o n s . T h i s s h o u l d p r o l o n g t h e service life of t h e zeolite adsorbent a n d , therefore, enhance t h e a d v a n t a g e of zeolite adsorbent i n c r a c k e d gas d r y i n g o v e r n o n zeolitic desiccants. O t h e r L i q u i d a n d G a s D r y i n g . A p p l i c a t i o n s of zeolite adsorbents i n d r y i n g other i n d u s t r i a l gases a n d l i q u i d s are w e l l k n o w n a n d h a v e been discussed i n R e f s . 34~36. T h e r e f o r e , a l t h o u g h i t is a n i m p o r t a n t a p p l i c a t i o n , i t is n o t discussed here. Separation and Purification of Industrial Streams P u r i f i c a t i o n of A i r P r i o r to L i q u e f a c t i o n . S e p a r a t i o n of a i r b y c r y o genic f r a c t i o n a t i o n processes requires r e m o v a l of w a t e r v a p o r a n d c a r b o n d i o x i d e t o a v o i d heat exchanger freeze-up. M a n y p l a n t s t o d a y are u s i n g a 1 3 X ( N a - X ) m o l e c u l a r sieve adsorbent t o r e m o v e b o t h w a t e r v a p o r a n d c a r b o n d i o x i d e f r o m a i r i n one a d s o r p t i o n step. S i n c e t h e r e is no necessity for size selective a d s o r p t i o n , 1 3 X m o l e c u l a r sieves are generally p r e f e r r e d over t y p e A m o l e c u l a r sieves. T h e 1 3 X m o l e c u l a r sieves h a v e n o t o n l y higher a d s o r p t i v e capacities b u t also faster rates of C 0 a d s o r p t i o n t h a n t y p e A m o l e c u l a r sieves. T h e r a t e of C 0 a d s o r p t i o n i n a c o m m e r c i a l 1 3 X molecular sieve seems t o be c o n t r o l l e d b y m a c r o p o r e diffusion (37). The o p t i m u m o p e r a t i n g t e m p e r a t u r e for C 0 r e m o v a l b y 1 3 X m o l e c u l a r sieve is r e p o r t e d as 1 6 0 - 1 9 0 ° K (38). 2

2

2


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Natural Gas Purification.

N a t u r a l gas c o n t a i n i n g w a t e r v a p o r , s u l f u r

c o m p o u n d s ( m o s t l y h y d r o g e n sulfide), a n d c a r b o n d i o x i d e i s p u r i f i e d b y m o l e c u l a r sieve adsorbents.

S i n c e , w i t h t h e e x c e p t i o n of feed p r e p a r a t i o n

for L N G , t h e complete r e m o v a l of c a r b o n dioxide i s u s u a l l y n o t necessary, t h e m o l e c u l a r sieve b e d i s used m a i n l y t o r e m o v e w a t e r v a p o r a n d s u l f u r compounds.

T h e a d s o r p t i o n step is c o n t i n u e d e v e n after t h e c a r b o n d i -

oxide b r e a k t h r o u g h b u t i s s t o p p e d through.

before t h e h y d r o g e n sulfide b r e a k -

4 A a n d 5 A m o l e c u l a r sieves are generally used t o r e m o v e w a t e r

a n d h y d r o g e n sulfide f r o m n a t u r a l gas a l t h o u g h 1 3 X c a n be used w h e n t h e n a t u r a l gas c o n t a i n s a significant a m o u n t

of large s u l f u r

compounds.


T h e r e is, h o w e v e r , some evidence t h a t N a - X c a n p r o d u c e C O S c a t a l y t i c a l l y from H S and C 0 . 2

2

O t h e r i m p o r t a n t a p p l i c a t i o n s of m o l e c u l a r sieves i n

n a t u r a l gas p u r i f i c a t i o n i n c l u d e p u r i f i c a t i o n of p i p e l i n e n a t u r a l gas f o r l i q u e f a c t i o n , d r y i n g n a t u r a l gas p r i o r t o cryogenic h y d r o c a r g o n

recovery

u s i n g a t u r b o e x p a n d e r , a n d sweetening n a t u r a l gas feed t o a m m o n i a p l a n t s (89-42). Oxygen Enrichment of Air.

R e c e n t d e v e l o p m e n t s i n a p p l i c a t i o n of

oxygen or oxygen-rich air i n biological wastewater treatment plants gene r a t e d a necessity for a l o w cost, on-site o x y g e n generator.

M a n y waste-

w a t e r t r e a t m e n t s i n t h e U . S . r e q u i r e less t h a n 100 t o n s p e r d a y of c o n tained oxygen.

F o r t h e l o w - t o - i n t e r m e d i a t e range, t h e pressure s w i n g

a d s o r p t i o n process u s i n g zeolite adsorbents i s c o m p e t i t i v e w i t h , o r a d v a n t a g e o u s over, t h e c o n v e n t i o n a l c r y o g e n i c a i r s e p a r a t i o n process (48, 44)· C o m m e r c i a l processes k n o w n t o d a y a r e : E s s o R e s e a r c h a n d E n g i n e e r i n g processes (45-48), t h e W . R . G r a c e process (43), t h e U n i o n C a r b i d e process (49), t h e L ' A i r L i q u i d e process (50), t h e B a y e r - M a h l e r process (51), a n d t h e N i p p o n S t e e l process (52, 53).

Differences b e t w e e n

these

processes a r e t y p e of zeolites used, n u m b e r of adsorbent beds, o p e r a t i n g pressures, a n d c y c l i c o p e r a t i n g steps.

T h e pressure s w i n g a d s o r p t i o n p r o -

cess c a n produce u p t o 9 5 % oxygen, t h e r e m a i n d e r m a i n l y a r g o n , a n d i s d e f i n i t e l y advantageous over t h e cryogenic a i r s e p a r a t i o n process a t b e l o w 25 t o n s - p e r - d a y c a p a c i t y .

O t h e r p o t e n t i a l a p p l i c a t i o n s of o x y g e n r i c h a i r

p r o d u c e d b y pressure s w i n g a d s o r p t i o n processes a r e p o l l u t i o n c o n t r o l i n t h e p u l p a n d p a p e r i n d u s t r y , secondary s m e l t i n g p l a n t s , r i v e r a n d p o n d a e r a t i o n , feed gas t o ozone generators, m e d i c a l a p p l i c a t i o n s a n d c h e m i c a l o x i d a t i o n processes. Pollution Control.

Z e o l i t e adsorbents

c a n effectively

remove

pol-

l u t a n t s s u c h as S 0 , H S , a n d N O * f r o m i n d u s t r i a l off-gas s t r e a m s a t near 2

2

a m b i e n t t e m p e r a t u r e (54-57).

Since w a t e r v a p o r u s u a l l y exists a l o n g w i t h

these a c i d i c c o m p o u n d s , a n a c i d - s t a b l e o r a c i d - r e s i s t a n t z e o l i t e a d s o r b e n t is necessary for a l o n g service life.

U n i o n C a r b i d e announced three new pro-

cesses f o r p o l l u t i o n c o n t r o l r e c e n t l y .

T h e y a r e t h e P u r a S i v - H g process

for m e r c u r y v a p o r r e m o v a l , t h e P u r a S i v - N process for N O ^ r e m o v a l f r o m n i t r i c a c i d p l a n t off-gas, a n d t h e P u r a S i v - S process for S 0 r e m o v a l f r o m 2


28. LEE

Applied Zeolite Absorbents

317

sulfuric acid plant off-gas (58). A recent British patent (57) described a process using a molecular sieve bed preadsorbed with 0.1-10 wt % of am monia before the gas stream containing acidic gases is introduced.


Nonregenerative Applications Applications of zeolite adsorbents are not limited to the fixed-bed, cyclic operation discussed above. Some applications involve no regenera tion and therefore no cyclic operation. Important nonregenerative ap plications are drying Freon-type refrigerants and manufacture of dualpane windows. Every refrigerator and air conditioner using halogenated hydrocarbon refrigerants require a desiccant cartridge to keep the refriger ants super dry. The 3A molecular sieve can effectively dry refrigerants, but its catalytic activity to decompose refrigerant should be suppressed. In the dual-pane window application, zeolite adsorbents are often used to gether with other adsorbents such as silica gel to keep the vapor pressure of gases inside the dual pane window sufficiently low. It is important to re move water vapor and organic solvent vapors from the sealing compound to avoid fogging in winter months. Literature Cited 1. Ries, H. C., "n-Paraffins," Process Economics Program, Report No. 55, 1969, Stanford Research Institute, Menlo Park, Calif. 2. Broughton, D. B., et al., Proc. Amer. Petrol. Inst., Sect. IV (1961) 41, 237. 3. Broughton, D. B., Lickus, A. G., Petrol. Refiner (1961) 40, 173. 4. Broughton, D. B., Chem. Eng. Progr. (1968) 64, 60. 5. Sterba, M. J., Proc. Amer. Petrol. Inst., Sect. IV (1965) 45, 209. 6. Yeo, Α. Α., et al., World Petrol. Congr., 6th, Sect. IV (1963) 161. 7. Yeo, Α. Α., Hicks, C. L., British Patents 898,058 and 898,059 (June 6, 1962). 8. Lacey, R. N., et al., U. S. Patent 3,201,490 (Aug. 17, 1965). 9. Asher, W. J., et al. U. S. Patent 3,070,542, (Dec. 25, 1962). 10. Richards, H. Α., et al. U. S. Patent 2,988,502 (June 13, 1961). 11. Avery, W. F., Lee, M. N. Y., Oil Gas J. (1962) 60, 121. 12. Griesmer, G. J., et al., Hydrocarbon Proc. (1965) 44, 147. 13. Guiccione, E., Chem. Eng. (April 26, 1965), 72, 104. 14. Franz, W. R., et al., Petrol. Refiner (1959) 38, 125. 15. Cooper, D. E., et al., Chem. Eng. Progr. (1966) 62, 69. 16. Shell Internationale, British Patent 1,059,879 (Feb. 22, 1967). 17. Wehner, K., et al., British Patents 1,135,801 and 1,135,802 (Dec. 4, 1968). 18. Chi, C. W., Lee, H., Chem. Eng. Progr. Symp. Ser. (1969) 65, 65. 19. Besik, F., Sitnai, O., Collect. Czech. Chem. Commun. (1968) 33, 706. 20. Ruthven, D. M., Loughlin, K. F., Can. J. Chem. Eng. (1972) 50, 550. 21. Broughton, D. B., et al., Chem. Eng. Progr. (1970) 66, 70. 22. Atkins, R. S., Hydrocarbon Proc. (1970) 49, 132. 23. Neuzil, R. W. U. S. Patent 3,558,732 (Jan. 26, 1971). 24. Neuzil, R. W. U. S. Patent 3,626,020 (Dec. 9, 1971). 25. Neuzil, R. W. U. S. Patent 3,663,638 (May 16, 1972). 26. Stine, L. O., Broughton, D. B. U. S. Patent 3,636,121 (Jan. 18, 1972).



318

MOLECULAR SIEVES

27. Chen, N. Y., Lucki, S. J., U. S. Patent 3,668,266 (June 6, 1972). 28. Bearden, R., Jr., DeFeo, R. J., Jr., U. S. Patent 3,686,343 (Aug. 22, 1972). 29. Neuzil, R. W., deRosset, A. J. South African Patent 692,327 (April 5, 1968). 30. Neuzil, R. W., deRosset, A. J., British Patent 1,236,691 (June 23, 1971). 31. Barber, J. B., et al., 68th National Meeting of the American Institute of Chemi cal Engineers, Houston, Tex., 1971. 32. Pierce, J. E., Stieghan, D. L., Hydrocarbon Proc. (1966) 45, 170. 33. Lee, H., Chi, D., U. S. Patent 3,679,604 (July 25, 1972). 34. Milton, R. M., "Molecular Sieves," pp. 201-202, Society of Chemical Industry, London, 1968. 35. Collins, J. J., Oil Gas J. (1962) 60, 97. 36. Collins, J. J., Chem. Eng. Progr. (1968) 64, 66. 37. Lee, H., Chi, C. W., 68th National Meeting of the American Institute of Chemical Engineers, Houston, Tex., 1971 38. Webber, D. Α., Chem. Eng. (Jan., 1972) 18. 39. Schoofs, R. J., Gas (1966) 42, 85. 40. Harris, T. B., Pipeline Gas J. (June, 1972) 76. 41. Hales, G. E., Can. Petrol. (Jan., 1972) 42. 42. Lee, Μ. Ν. Y., Collins, J. J., Safety Air Ammonia Plants (1969) 11, 59. 43. Lee, H., "Application of Commercial Oxygen to Water and Wastewater Systems" Symposium, University of Texas, Austin, Tex., Nov. 1972 44. Lee, H., Stahl, D. E . , 65th Annual Meeting of the American Institute of Chemical Engineers, New York, Ν. Y., Nov. 1972. 45. Skarstrom, C. W., U. S. Patent 2,944,627 (July 12, 1960). 46. Berlin, N. H., U. S. Patent 3,280,536 (Oct. 25, 1966). 47. Skarstrom, C. W., U. S. Patent 3,237,377 (March 1, 1966). 48. Feldbauer, G. F., Jr., U. S. Paten 3,338,030 (Aug. 29, 1967). 49. Davis, J. C., Chem. Eng. (Oct. 16, 1972) 79, 88. 50. Domine, D., Hay, L., "Molecular Sieves," pp. 204-216, Society of Chemical Industry, London, 1968. 51. Bayer, F., Mahler, J. F., Chem. Eng. (Oct. 5, 1970) 77, 54. 52. Tamura, T., British Patent 1,258,418 (Dec. 30, 1971). 53. Takahashi, H., et al., Ed., "Zeolites and Their Applications," p. 96, Gihodo, Tokyo, 1967. 54. Martin, D. Α., Brantley, F. E., U. S. Bur. Mines Rept., (1963) 6321, 15. 55. Joubert, J. J., Zwiebel, I., ADVAN. CHEM. SER. (1971) 102, 209-16. 56. Gupta, J. C., et al., 68th National Meeting of the American Institute of Chemical Engineers, Houston, Texas, 1971. 57. Lee, Μ. Ν. Y., Schoofs, R. J., German Patent 1,911,670 (Oct. 9, 1969). 58. Fornoff, F., 64th National Meeting of the American Institute of Chemical Engineers, San Francisco, Calif., 1971. RECEIVED December 4, 1972.


Applied Aspects of Zeolite Adsorbents

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