A New Process for Adsorption Separation of Gas Streams - ACS

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Adsorption and Ion Exchange with Synthetic Zeolites Downloaded from pubs.acs.org by UNIV OF MASSACHUSETTS AMHERST on 09/26/15. For personal use only.

A New Process for Adsorption Separation of Gas Streams GEORGE E. KELLER II and RUSSELL L. JONES Union Carbide Corporation, Box 8361, South Charleston, WV 25303

Separation of gas streams by adsorption is becoming increasingly popular as improved technology comes on the market. Some examples of commercially practiced adsorption processes are shown in Table 1. These processes take advantage of the selective adsorption properties of a number of microporous adsorbents, including activated carbon, silica, alumina, and various synthetic and natural zeolites. There are fundamentally two types of gas adsorption processes, which can be differentiated by the way in which adsorbed species are desorbed. In one type the adsorbed species are removed by raising the temperature of the adsorbent, thereby decreasing its capacity. In the second type the partial pressures of the adsorbed species are reduced to effect desorption. Of course a combination of the two desorption techniques can be and is sometimes used. In Figure 1 an isotherm diagram is shown which depicts these desorption techniques. If the adsorbing material constitutes only a small portion of the feed gas - usually a mole percent or two or less regeneration of the adsorbent by temperature increase is the preferred mode. However for higher concentrations of adsorbing materials - bulk separations - pressure reduction is the preferred mode of regeneration. The reasons f o r using a p r e s s u r e swing process f o r bulk s e p a r a t i o n s a r e ( i ) a d s o r p t i o n - p l u s regeneration times a r e much s h o r t e r (minutes vs. hours t o days f o r temperature-increase) and ( i i ) t h e l a r g e temperature i n c r e a s e s experienced during a d s o r p t i o n a r e l a r g e l y c a n c e l l e d out by t h e endothermic d e s o r p t i o n o f t h e adsorbed m a t e r i a l , thereby e l i m i n a t i n g l a r g e temperature excursions w i t h i n t h e bed. Processes i n v o l v i n g t o t a l - p r e s s u r e r e d u c t i o n t o remove t h e adsorbed s p e c i e s , c a l l e d pressure-swing a d s o r p t i o n (PSA) o r h e a t l e s s a d s o r p t i o n , a r e m e c h a n i c a l l y complex, s i n c e they must i n c l u d e separate a d s o r p t i o n , d e p r e s s u r i z a t i o n , d e s o r p t i o n , and r e p r e s s u r i z a t i o n s t e p s . To accommodate a steady flow o f feed and products, s e v e r a l beds - u s u a l l y three o r more i n p a r a l l e l are used. A t y p i c a l four-bed process flowsheet i s shown i n 0-8412-0582-5/80/47-135-275$05.00/0 © 1980 American Chemical Society

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TABLE 1


IMPORTANT COMMERCIAL ADSORPTIVE GAS SEPARATIONS M a t e r i a l Adsorbed Ammonia

Process Stream Cracked Ammonia, Reformer Hydrogen

Carbon Dioxide

E t h y l e n e , A i r , I n e r t Atmospheres, Flue Gas

Carbon Monoxide

Hydrogen

G a s o l i n e Components

Natural Gas

Hydrogen

Natural Gas, Reformer Hydrogen

Sulfide

Iso-olefins

Normal O l e f i n s

Krypton

Hydrogen

Mercaptans

Propane

Mercury

Hydrogen

Methane

Hydrogen

Nitrogen

Hydrogen, A i r

Nitrogen Oxides

Nitrogen, A i r

Normal P a r a f f i n s

Kerosine, G a s o l i n e

O i l Vapor

Compressed Gases

Oxygen

Argon

S u l f u r Dioxide

Vent Streams

Water

A c e t y l e n e , A i r , Argon, Carbon D i o x i d e , C h l o r i n e , Cracked Gas, Ethylene, Helium, Hydrogen, Hydrogen C h l o r i d e , Hydrogen S u l f i d e , Natural Gas, N i t r o g e n , Oxygen, Reformer Hydrogen, S u l f u r H e x a f l u o r i d e


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F i g u r e 2. An a d d i t i o n a l problem i s t h e f a c t t h a t o n l y one h i g h l y p u r i f i e d (less-adsorbed) product can be produced, s i n c e part o f t h i s product i s used t o purge the more t i g h t l y adsorbed product and i s l o s t with t h a t product. Despite these problems, PSA i s o f t e n used f o r oxygen and hydrogen p u r i f i c a t i o n , and a recent runner-up K i r k p a t r i c k Award f o r Union Carbide's Polybed hydrogen process (1_) a t t e s t s t o t h e f a c t t h a t i t i s now both p r a c t i c a l and economical t o perform bulk s e p a r a t i o n s on feed streams i n excess o f one m i l l i o n c u b i c f e e t per hour. The o b j e c t i v e s o f t h e present study were t o decrease t h e b a s i c complexity o f PSA and t o i n c r e a s e i t s p r o d u c t i v i t y - the amount o f product produced p e r u n i t time per u n i t weight o f adsorbent. Success i n both o f these areas should f u r t h e r enhance process economics and i n c r e a s e the p o t e n t i a l a p p l i c a t i o n f o r pressure-swing-adsorption-based processes. The new process i s c a l l e d e i t h e r pressure-swing parametric pumping o r r a p i d pressure-swing a d s o r p t i o n ; the former name w i l l be used here. The name parametric pumping was coined by Wilhelm ( 2 ) , who d e s c r i b e d an adsorption-based s e p a r a t i o n process i n v o l v i n g r e v e r s i n g flows. When t h e flow i s i n one d i r e c t i o n a parameter, such as temperature, which i n f l u e n c e s a d s o r p t i v i t y , i s a t one v a l u e , w h i l e t h e parameter i s changed t o another value when t h e flow i s i n t h e o p p o s i t e d i r e c t i o n . Such a process w i l l c r e a t e a s e p a r a t i o n between components with d i f f e r e n t adsorpt i v i t i e s . Chen (_3) has c o r r e c t l y pointed out t h a t pressure-swing a d s o r p t i o n processes c o n s i t u t e a subset o f parametric pumping, i n which pressure i s t h e parameter used t o i n f l u e n c e a d s o r p t i v i t y . Process D e s c r i p t i o n T h i s s e c t i o n o u t l i n e s t h e b a s i c pressure-swing parametric pumping p r o c e s s , which w i l l be d e s c r i b e d below i n t h e context o f oxygen production from a i r . The p r e f e r r e d adsorbent f o r t h i s s e p a r a t i o n can be e i t h e r 5A o r 13X z e o l i t e . Flowsheet. A schematic diagram i s shown i n F i g u r e 3. The process c o n s i s t s o f a s i n g l e bed o f r e l a t i v e l y small adsorbent p a r t i c l e s (40 t o 80 mesh, o r 177 t o 420 microns, f o r example). The bed length can vary from about one t o f o u r o r more f e e t . Feed gas i s s u p p l i e d i n pulses o f up t o about a second i n l e n g t h from a compressor and a surge tank. The p u l s e i s c o n t r o l l e d by a s o l e n o i d v a l v e and a t i m e r . During t h i s feed p u l s e t h e exhaust s o l e n o i d v a l v e i s c l o s e d . Following t h e feed p u l s e both v a l v e s a t t h e feed end a r e c l o s e d f o r about 0.5 t o t h r e e seconds; t h i s p e r i o d i s c a l l e d t h e delay. F i n a l l y t h e s o l e n o i d v a l v e on t h e exhaust o r purge l i n e opens f o r a p e r i o d o f about f i v e t o 20 seconds. Since the pressure i n t h i s l i n e i s maintained below t h a t i n t h e feed l i n e , a r e v e r s e flow o f gas from the bed occurs. However, w h i l e pressures and flow d i r e c t i o n s a r e f l u c t u a t i n g s u b s t a n t i a l l y a t t h e feed end o f t h e bed, a continuous flow


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Figure 1.

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Typical loading vs. partial pressure curves

P T , A L PRESSURE AR

REPRESSURE DÎPRESSURE-REPRESSURE DEPRESSURE-PHPRF

PURGE-EFFLUENT FEED

Figure 2.

%

DEPRESSURE

Pressure-swing adsorption system using four beds


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emerges from t h e product end and through a small surge tank. T h i s flow i s e n r i c h e d i n l e s s t i g h t l y adsorbed components; i n t h e case o f a i r s e p a r a t i o n , t h e product c o n s i s t s t y p i c a l l y o f 90 t o 95 percent oxygen, with the balance argon and a small amount o f n i t r o g e n . Conversely t h e exhaust stream i s somewhat d e p l e t e d i n oxygen and argon. The net e f f e c t o f t h i s process i s t o produce, using a s i n g l e adsorbing bed and two surge tanks, a constant flow o f l e s s t i g h t l y adsorbed product - p r i m a r i l y oxygen i n t h i s case - from a constant flow o f a i r from a compressor. Adsorbent. Standard 5A and 13X z e o l i t e can be used i n pressure-swing parametric pumping t o produce e n r i c h e d oxygen. However, i t i s e s s e n t i a l t h a t t h e adsorbent be f i n e l y d i v i d e d , and i n the case o f oxygen p r o d u c t i o n , about a 40 t o 80 mesh p a r t i c l e s i z e i s o p t i m a l . (The reasons f o r using small p a r t i c l e s w i l l be d i s c u s s e d l a t e r . ) Such a m a t e r i a l can be produced by c r u s h i n g and s c r e e n i n g the p e l l e t s , spheres, e t c . , normally used i n o t h e r a d s o r p t i o n processes. F o l l o w i n g t h i s procedure, t h e z e o l i t e p a r t i c l e s a r e a c t i v a t e d a t the same c o n d i t i o n s as would be used f o r r e g u l a r - s i z e p a r t i c l e a c t i v a t i o n and a r e then packed i n the adsorbent bed. A major p o t e n t i a l problem w i t h the use o f such small p a r t i c l e s i s f l u i d i z a t i o n o f t h e adsorbent f o l l o w i n g opening o f the exhaust v a l v e and r e v e r s a l o f the gas flow i n t h e bed. F l u i d i z a t i o n o f t h e bed under the p r e s s u r e g r a d i e n t s developed causes r a p i d p a r t i c l e a t t r i t i o n , attendant l o s s o f adsorbent through the r e s t r a i n i n g s c r e e n s , and c e s s a t i o n o f s e p a r a t i n g a b i l i t y . F l u i d i z a t i o n can be prevented by a p p l y i n g a s u f f i c i e n t f o r c e t o the upper hold-down p l a t e , e.g., by use o f a s p r i n g o r a h y d r a u l i c a l l y balanced f l o a t i n g head. E f f i c i e n t p r e - s e t t l i n g o f the adsorbent p a r t i c l e s w h i l e packing t h e bed w i l l a l s o tend to prevent f l u i d i z a t i o n l a t e r , as the bed i s s u b j e c t e d t o repeated pressure f l u c t u a t i o n s . An important f e a t u r e o f the adsorbent bed i n t h i s process i s i t s a b i l i t y t o accept a water-saturated feed without d i s p l a y i n g any tendency f o r t h e z e o l i t e t o become d e a c t i v a t e d by water a d s o r p t i o n . The r e v e r s e flow o f gas d u r i n g the exhaust p a r t o f the c y c l e s t a b i l i z e s the water p e n e t r a t i o n t o no more than about one-fourth t o o n e - h a l f i n c h from t h e top o f t h e bed. As a r e s u l t , no need e x i s t s f o r p r e - d r y i n g the feed a i r o r s u p p l y i n g a d e s i c c a n t a t the i n l e t t o t h e bed. Process Performance The key f e a t u r e o f pressure-swing parametric pumping i s the unusual pressure versus d i s t a n c e and time f e a t u r e o f t h e bed. In PSA, pressure drop i s purposely minimized, so t h a t , although the pressure w i t h i n a bed changes s u b s t a n t i a l l y d u r i n g a c y c l e , the pressures a t v a r i o u s p o i n t s i n a bed a t a given time are v i r t u a l l y the same. In pressure-swing parametric pumping, l a r g e


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Figure 4. Pressure profiles in an adsorbent bed producing 90 mol % oxygen: 1, middle of feed; 2, middle of delay; 3, early in exhaust; 4, late in exhaust


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pressure d i f f e r e n c e s are developed i n the bed d u r i n g the c y c l e ; t h i s can be seen by r e f e r e n c e t o Figure 4. The curves i n t h i s Figure were obtained from a bed equipped with a number o f f a s t response pressure transducers along i t s l e n g t h . The feed pressure was 10 p s i g and the exhaust pressure 0 p s i g . During t h e feed p e r i o d (which l a s t s about one second o r l e s s ) , a l a r g e pressure g r a d i e n t develops (see curve 1) as feed gas rushes i n t o t h e bed. I f the feed p e r i o d were extended much l o n g e r , i t would not be p o s s i b l e t o produce t h e d e s i r e d 90+ percent oxygen product. Following the feed p e r i o d , the delay p e r i o d (curve 2) permits the pressure wave t o penetrate f u r t h e r i n t o the bed without o v e r l o a d i n g the bed with e x t r a feed. The s l o p e o f the pressure curve i s e s s e n t i a l l y zero a t t h e feed end o f the bed, a t t e s t i n g t o the f a c t t h a t no gas e n t e r i n g o r l e a v i n g t h i s end. Part o f t h e time during t h e exhaust p e r i o d , gas a c t u a l l y flows simultaneously toward both ends o f the bed (curve 3) from a pressure maximum. As the exhaust p e r i o d c o n t i n u e s , the pressure maximum both d e c l i n e s and moves toward t h e product end, so t h a t near t h e end o f t h e exhaust p e r i o d t h e maximum i s e s s e n t i a l l y a t the product end. Thus, a l l p a r t s o f the bed u l t i m a t e l y a r e subjected t o t h e reverse flow necessary t o purge adsorbed n i t r o g e n . The f a c t t h a t the purge gas f o r r e g e n e r a t i n g the adsorbent comes from the bed i t s e l f c o n s t i t u t e s a major d i f f e r e n c e between t h i s process and PSA, i n which purge gas comes p r i m a r i l y from another bed. The pressure a t t h e product end f l u c t u a t e s about two p s i ; the amount o f t h i s f l u c t u a t i o n can be c o n t r o l l e d t o some extent by the s i z e o f the product surge tank and the length o f the exhaust p a r t o f the c y c l e . T h i s surge tank permits a constant product flow t o be maintained i n s p i t e o f these small f l u c t u a t i o n s . The small adsorbent p a r t i c l e s a r e o b v i o u s l y r e s p o n s i b l e f o r the s u b s t a n t i a l pressure g r a d i e n t s i n t h e bed. The use o f l a r g e r p a r t i c l e s i n t h e same bed r e s u l t s i n decreased s e p a r a t i n g a b i l i t y , i . e . , t h e high degree o f s e p a r a t i o n cannot be maintained a t t h e same p r o d u c t i v i t y . Extending t h e length o f the bed i n combinat i o n with the use o f l a r g e r p a r t i c l e s ( t o maintain t h e same o v e r a l l flow restance) a l s o r e s u l t s i n a d e t e r i o r a t i n g product i v i t y and e v e n t u a l l y i n t h e i n a b i l i t y t o make h i g h - p u r i t y product. The l a r g e r p a r t i c l e s have l a r g e r i n t r a - p a r t i c l e r e s i s tances, and these l a r g e r r e s i s t a n c e s may become an important f a c t o r i n bed performance with the f a s t c y c l e times used i n pressure-swing parametric pumping. Using p a r t i c l e s s u b s t a n t i a l l y s m a l l e r than about 40 t o 80 mesh leads t o t o o l a r g e a flow r e s i s t a n c e , and p r o d u c t i v i t y drops. Thus, an optimal p a r t i c l e s i z e e x i s t s , and i n general t h i s w i l l l i e i n t h e range o f 20 t o 120 mesh. In Figure 5 are shown t h e c o n c e n t r a t i o n p r o f i l e s o f oxygen i n t h e gas phase during v a r i o u s times i n the c y c l e . These curves were obtained from the same bed as the one used f o r t h e pressure data. As would be expected, the S-shaped curve moves toward t h e


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Figure 5. Concentration profiles in an adsorbent bed producing 90 mol % oxygen: 1, middle of feed; 2, middle of delay; 3, early in exhaust; 4, late in exhaust

Figure 6. Effect of feed pressure on productivity and recovery for producing a 98 mol % hydrogen stream from a 33/67 mol ratio methane/hydrogen feed: bed length, 4 ft; exhaust pressure, 0 psig; temperature, ambient; adsorbent, 30/60 to 40/80 mesh activated carbon; cycle, 0.5 sec feed—1.0 sec delay—5.0 sec exhaust

FEED PRESSURE, PSIG


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product end during the feed and d e l a y p e r i o d s , and then toward the feed end d u r i n g the exhaust p e r i o d . The net e f f e c t o f the pressure and c o n c e n t r a t i o n p r o f i l e s i s to produce a h i g h - p r o d u c t i v i t y , simple process. In Table 2 i s shown a comparison o f performance between PSA and p r e s s u r e swing parametric pumping. Most n o t a b l e i s the f o u r - t o - f i v e - f o l d i n c r e a s e i n p r o d u c t i v i t y f o r the l a t t e r over the former. T h i s i n c r e a s e i s achieved with a fundamentally s i m p l e r process and o n l y a s l i g h t l y higher power input per c u b i c f o o t o f product. (Higher power input i s r e l a t e d to h i g h e r a i r supply pressure and lower oxygen recovery.) A second example of s e p a r a t i o n performance i s shown i n F i g u r e 6. The feed mixture was a one-to-two mol r a t i o o f methane t o hydrogen, which i s t y p i c a l o f the composition o f the l i g h t f r a c t i o n from steam-cracking o f a mixture o f ethane and propane. The product was 98 mol percent hydrogen, and the F i g u r e shows the e f f e c t o f v a r y i n g the f e e d p r e s s u r e to the column. P r o d u c t i v i t y was found t o i n c r e a s e almost l i n e a r l y with feed p r e s s u r e , and values reached at the upper range were very high. Thus, at a feed pressure o f 350 p s i g , a column with a c r o s s - s e c t i o n a l area o f one s q u a r e - f o o t c o u l d produce about 25,000 standard c u b i c f e e t per hour o f 98 percent hydrogen. Hydrogen r e c o v e r y , on the o t h e r hand, reached a value o f s l i g h t l y l e s s than 60 percent a t a feed pressure o f 50 p s i g and remained v i r t u a l l y constant a t higher p r e s s u r e s . Prior Literature Although pressure-swing parametric pumping i s q u i t e d i f f e r e n t from the more t r a d i t i o n a l temperature-swing parametric pumping f i r s t promulgated by Wilhelm (2J, t h e r e i s some precedent i n the l i t e r a t u r e f o r t h i s type o f o p e r a t i o n . Turnock (4), Turnock and Kadlec (J5), Kowler (6) and Kowler and Kadlec (7^,8j s t u d i e d a s i m i l a r pressure-swing d e v i c e f o r s e p a r a t i n g n i t r o g e n and methane. However, they were unable t o s o l v e the problem o f long-term mechanical s t a b i l i t y o f the adsorbent, and the time c y c l e s used were s u b s t a n t i a l l y d i f f e r e n t than those suggested here. T h e i r c y c l e s l i m i t e d both adsorbent p r o d u c t i v i t y and product recovery. The p r e f e r r e d c y c l e s f o r pressure-swing parametric pumping are the s u b j e c t o f a recent patent a p p l i c a t i o n (i).

A p p l i c a t i o n s o f Pressure-Swing Parametric Pumping Pressure-swing parametric pumping would seem to have many a p p l i c a t i o n s f o r s e p a r a t i o n o f from very small to q u i t e l a r g e gas streams. One area o f promise i s the p r o d u c t i o n o f oxygen from a i r . Union Carbide i s c u r r e n t l y marketing a small d e v i c e f o r producing up to about s i x l i t e r s per minute o f 90+ percent oxygen f o r medical use i n homes. T h i s d e v i c e a c t u a l l y c o n t a i n s

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TABLE 2


COMPARISON OF PRESSURE-SWING ADSORPTION AND PRESSURE-SWING PARAMETRIC PUMPING FOR PRODUCTION OF OXYGEN FROM AIR

Pressure-Swi ng Adsorption Number o f Adsorbent Beds Supply Pressure ( p s i g ) Adsorbent Bed Length ( f t ) Adsorbent P a r t i c l e S i z e

Pressure C y c l e Length

Pressure-Swi ng Parametric Pumping

3

1

45

50

6-10

3-4

1/16 i n c h

40-80 mesh

pellets

granules

3-4 minutes

18.5 seconds

Exhaust Pressure ( p s i g )

0

0

Product Pressure ( p s i g ) Product P u r i t y (Mol % Oxygen)

2-5

2-5

90

90

40

38

0.5

2.3

Oxygen Recovery, % Adsorbent P r o d u c t i v i t y (Ton 100% Oxygen/Ton Adsorbent)


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t h r e e small beds i n p a r a l l e l , e l i m i n a t i n g surge tanks by proper sequencing o f the bed time c y c l e s . Pressure-swing parametric pumping can a l s o be used to produce oxygen i n up t o tonnage q u a n t i t i e s f o r h o s p i t a l s , welding u n i t s , waste-water treatment, etc. Many other a p p l i c a t i o n s e x i s t f o r s e p a r a t i o n o f v a r i o u s chemical and r e f i n e r y streams. For i n s t a n c e , Union Carbide has demonstrated on a p i l o t s c a l e the f e a s i b i l i t y o f producing hydrogen, as shown i n F i g u r e 6, from both high- and low-pressure hydrogen-methane and hydrogen-carbon monoxide streams. Another major area o f a p p l i c a t i o n i s the removal o f o r g a n i c s from vent and o t h e r waste gas streams. A commercial u n i t has been i n o p e r a t i o n f o r over a y e a r a t Union Carbide's Texas C i t y , TX, p l a n t , p r o c e s s i n g a stream c o n t a i n i n g p r i m a r i l y n i t r o g e n and e t h y l e n e . An e n r i c h e d n i t r o g e n "product" i s vented from the p r o c e s s , while an e n r i c h e d e t h y l e n e stream - the exhaust - i s r e c y c l e d t o the process. Two o t h e r p i l o t p l a n t s are i n o p e r a t i o n making o t h e r s e p a r a t i o n s o f importance. A major concern r e g a r d i n g the use o f t h i s technology under such r a p i d l y f l u c t u a t i n g pressures i s the s t a b i l i t y o f the adsorbent. Long-term t e s t i n g o f s e v e r a l types o f s y n t h e t i c z e o l i t e s and a c t i v a t e d carbon i n bench-scale, l a r g e - p i l o t - s c a l e , and commercial u n i t s has demonstrated t h a t adsorbent l i f e t i m e s o f w e l l over one y e a r are t o be expected i n most a p p l i c a t i o n s . Summary Pressure-swing parametric pumping i s a r e c e n t l y commerciali z e d , simple, pressure-swing a d s o r p t i o n process. Compared to standard PSA, pressure-swing parametric pumping accomplishes a l l o f the f o u r b a s i c o p e r a t i o n s - p r e s s u r i z a t i o n , a d s o r p t i o n , d e p r e s s u r i z a t i o n and d e s o r p t i o n - i n a s i n g l e bed i n such a way t h a t a continuous flow o f l e s s t i g h t l y adsorbed product i s produced. With the a i d o f a surge tank on the feed l i n e , the process a l s o accepts a constant feed flow. The o v e r a l l c y c l e time i s i n the order o f about 20 seconds o r l e s s , compared t o s e v e r a l minutes f o r PSA. The adsorbent p a r t i c l e s i n pressure-swing parametric pumping are s u b s t a n t i a l l y s m a l l e r than those i n PSA and produce r a p i d l y f l u c t u a t i n g pressure p r o f i l e s i n the bed d u r i n g a c y c l e . These p r o f i l e s and the c y c l e times which i n f l u e n c e them are r e s p o n s i b l e f o r the continuous product f l o w , the high p r o d u c t i v i t i e s and the high product p u r i t i e s which can be a t t a i n e d i n the p r o c e s s . The process i s capable o f performing a number o f commerc i a l l y important s e p a r a t i o n s , u s i n g a wide range o f adsorbents. For oxygen p r o d u c t i o n from a i r , e i t h e r 5A or 13X z e o l i t e can be used as the adsorbent. P a r t i c l e s i z e s are i n the range o f 40 to 80 mesh, and oxygen p r o d u c t i v i t y i s about f i v e times t h a t o f PSA f o r s i m i l a r feed p r e s s u r e s .

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SYNTHETIC ZEOLITES

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2. 3. 4. 5. 6. 7. 8. 9.

Corr, F.; Dropp, F.; Rutelstorfer, E., Hydrocarbon Processing, 1979, 58, 119. Wilhelm, R. Η., Ind. Eng. Chem. Fund., 1966, 5, 141. Chen, H. T., "Parametric Pumping"; in Schweitzer, P. Α., Ed., "Handbook of Separation Techniques for Chemical Engineers"; McGraw-Hill: New York, Ν. Y., 1979; p. 1-467. Turnock, P. H., "The Separation of Nitrogen and Methane by Pulsating Flow Through a Fixed, Molecular Sieve Bed"; Ph.D. Thesis, Univ. of Michigan, Dept. of Chemical and Metallur gical Engineering: Ann Arbor, MI, 1968. Turnock, P. H., Kadlec, R. H., A.I.Ch.E.J., 1971, 17, 335. Kowler, D. Ε., "Optimization of the Cyclic Operation of a Molecular Sieve Adsorber"; Ph.D. Thesis, Univ. of Michigan, Dept. of Chemical and Metallurgical Engineering: Ann Arbor, MI, 1969. Kowler, D. Ε., Kadlec, R. H., A.I.Ch.E.J., 1972, 18, 1207. Kowler, D. Ε., Kadlec, R. H., A.I.Ch.E.J., 1972, 18, 1212. Jones, R. L.; Keller, G. E.; Wells, R. C., U. S. and foreign patents applied for.

RECEIVED

April 24, 1980.

A New Process for Adsorption Separation of Gas Streams - ACS

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