Adsorption and Ion Exchange with Synthetic Zeolites - American

11 Liquid Phase Drying Applications of Zeolites GEORGE W. YOUNG, JOSEPH R. KIOVSKY, and PRAMOD B. KORADIA

Downloaded by TUFTS UNIV on November 27, 2015 | http://pubs.acs.org Publication Date: August 15, 1980 | doi: 10.1021/bk-1980-0135.ch011

Norton Company, P.O. Box 350, Akron, Ohio 44309

A major application of synthetic and natural zeol i t e s is i n dehydration processes. However, much of the published work has been concentrated on the drying of either gases or l i q u i d p a r a f f i n i c hydrocarbons, while r e l a t i v e l y little published information exists on commercial a p p l i c a t i o n of z e o l i t e s for dehydration of other l i q u i d feedstocks. Hales (1) mentions some of the non-paraffinic organic f l u i d s that may be dried with z e o l i t i c desiccants but he gives few q u a l i t a t i v e d e t a i l s . Dexant (2) provides some information on co-adsorbing species for dehydration of alcohols and aldehydes over small-port z e o l i t e s (3A, 4A, 5A). Although most l i q u i d drying studies have used the small-port z e o l i t e s to prevent co-adsorption, Koradia and Kiovsky (3) have reported on the drying of some chlorinated hydrocarbons using mordenite and have found commercially acceptable adsorption c a p a c i t i e s . In many processes (e.g. polymerizations, c a t a l y t i c reactions) even trace amounts (< 50 ppm) of water can cause problems and the only p r a c t i c a l solution for dehydration of these l i q u i d s is the use of an appropriate zeolite. For example, Stannet et a l . (4) report on the use of molecular sieves to dehydrate l i q u i d v i n y l monomers prior to radiation-induced ionic polymerization. Very o f t e n the l i q u i d s to be p r o c e s s e d may be contaminated w i t h substances d e t r i m e n t a l to some types of z e o l i t e s ; c o n s e q u e n t l y a complete knowledge of the p r o c e s s stream c o m p o s i t i o n and p h y s i c a l p r o p e r t i e s must be a v a i l a b l e b e f o r e p r e l i m i n a r y s i e v e s e l e c t i o n can be made. In the absence of p r i o r knowledge of separation f a c t o r s , competitive co-adsorption, environmental s t a b i l i t y , r e g e n e r a t i o n t e c h n i q u e s , or i r r e v e r s i b l e z e o l i t e c o n t a m i n a t i o n , zeoli'te c o n t a m i n a t i o n , z e o l i t e s p e c i f i c a t i o n must be proceded by time-con0-8412-0582-5/80/47-135-201$05.00/0 © 1980 American Chemical Society

In Adsorption and Ion Exchange with Synthetic Zeolites; Flank, W.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980.

SYNTHETIC ZEOLITES

202


suming e x p e r i m e n t a l work. In o n l y a few cases i s i t p o s s i b l e to e x t r a p o l a t e from d i f f e r e n t l i q u i d types to make e n g i n e e r i n g e s t i m a t e s , but d e t a i l e d s p e c i f i c d e s i g n s must be based on e x p e r i m e n t a l v e r i f i c a t i o n . In t h i s paper we i n t e n d to demonstrate the p r o c e s s of z e o l i t e s e l e c t i o n f o r the d e h y d r a t i o n of two d i f f e r e n t l i q u i d s of s i g n i f i c a n t commercial importance, 80 ppm water i n benzene contaminated by HC1, and 1200 ppm of water i n 1,4 b u t a n e d i o l . We w i l l p r e s e n t the e x p e r i m e n t a l data o b t a i n e d from both s t a t i c f e a s i b i l i t y and dynamic d e s i g n t e s t i n g and make a comparison among these systems and e a r l i e r work on the l i q u i d phase d r y i n g of c h l o r i n a t e d hydrocarbons. Experimental The e x p e r i m e n t a l work can c o n v e n i e n t l y be c l a s s i f i e d i n t o f o u r major c a t e g o r i e s : (a) S t a t i c e q u i librium Testing; (b) Dynamic E q u i l i b r i u m T e s t i n g ; (c) R e g e n e r a t i o n Technique I n v e s t i g a t i o n ; (d) Operational Stability. The s t a t i c t e s t i n g served p r i m a r i l y as a f e a s i b i l i t y study to determine i f the proposed d e h y d r a t i o n c o u l d i n f a c t be c a r r i e d out as a p r a c t i c a l p r o c e s s . S t a t i c t e s t s were performed by p u t t i n g preweighed amounts (0.1-5 gm) of f r e s h l y a c t i v a t e d z e o l i t e i n t o s e a l e d v e s s e l s c o n t a i n i n g a p p r o x i m a t e l y 50 ml of the test l i q u i d . A v e s s e l c o n t a i n i n g o n l y the t e s t l i q u i d was a l s o prepared f o r use as an e x p e r i m e n t a l b l a n k . The s e a l e d v e s s e l s were a l l o w e d to s i t f o r a p p r o x i mately f i v e days to a t t a i n e q u i l i b r i u m and the r a t e of d e h y d r a t i o n observed by m o n i t o r i n g the l i q u i d phase water c o n c e n t r a t i o n as a f u n c t i o n of time. In t h i s manner, i t was p o s s i b l e to i n v e s t i g a t e the e f f i c i e n c y of v a r i o u s types of z e o l i t e w i t h a p a r t i c u l a r l i q u i d system and a l s o to i n v e s t i g a t e the e f f e c t of e q u i l i b r i u m water c o n c e n t r a t i o n on s t a t i c adsorption capacity. For the benzene t e s t program, t h r e e primary benzene s o l u t i o n s were p r e p a r e d : one was f u l l y s a t u r a t e d w i t h water, another was s a t u r a t e d w i t h water and hydroc h l o r i c a c i d , and the t h i r d s o l u t i o n was o n l y p a r t i a l l y saturated. These primary s o l u t i o n s were mixed i n various p r o p o r t i o n s t o p r o v i d e a wide range of concent r a t i o n s f o r the s t a t i c t e s t s . The b u t a n e d i o l - w a t e r s o l u t i o n s were much e a s i e r to prepare because of complete m i s c i b i l i t y ; due to the h y g r o s c o p i c n a t u r e of b u t a n e d i o l i t was n e c e s s a r y to keep a l l s o l u t i o n s under a dry n i t r o g e n b l a n k e t .



11.

YOUNG ET AL.

Liquid Phase Drying

203

The water a n a l y s e s were c a r r i e d out u s i n g an automatic K a r l F i s c h e r t i t r a t o r (Aquatest I I ) and n o r m a l l y no problems were encountered. However, f o r the b e n z e n e - w a t e r - h y d r o c h l o r i c a c i d system, the a c i d s t r o n g l y i n t e r f e r e d w i t h the water a n a l y s e s . With a s l i g h t m o d i f i c a t i o n of o p e r a t i n g p r o c e d u r e , r e a s o n a b l y s a t i s f a c t o r y , but low p r e c i s i o n , r e s u l t s were o b t a i n e d . For these a n a l y s e s , the sample was i n t r o d u c e d i n t o the a n a l y z e r by i n j e c t i o n w i t h the s y r i n g e needle below the s u r f a c e of the v e s s e l s o l u t i o n and every benzene i n j e c t i o n was preceded by a 100 μΐ methanol sample. In a d d i t i o n to t h i s p r o c e d u r e , the reagent s o l u t i o n s were r e p l a c e d every ten to twelve hours. Dynamic t e s t i n g was c a r r i e d out u s i n g the e q u i p ment shown s c h e m a t i c a l l y i n F i g u r e 1. The t e s t l i q u i d was pumped from the r e s e r v o i r R l u s i n g a p e r i s t a l t i c pump and passed through the a d s o r p t i o n bed c o n t a i n ed i n a s t a i n l e s s s t e e l tube. For each of the i n i t i a l dynamic r u n s , the bed was loaded w i t h f r e s h l y a c t i v a t ed z e o l i t e CO.16 cm p e l l e t s ) and when o p e r a t i o n a l s t a b i l i t y was b e i n g i n v e s t i g a t e d , r e g e n e r a t i o n c o u l d be accomplished i n s i t u . The a d s o r p t i o n bed c o u l d be operated v e r t i c a l l y or h o r i z o n t a l l y and was surrounded by a m u f f l e f u r n a c e f o r the r e g e n e r a t i o n s t u d i e s . V a r i o u s l e n g t h s of bed were employed and the adsorbent i n the bed was s u p p o r t ed at both ends w i t h p o r c e l a i n s a d d l e s . When operated i n a h o r i z o n t a l mode, i n l e t and out l e t r i s e r s were l o c a t e d a t SI and S2 to i n s u r e com p l e t e f l o o d i n g of the a d s o r p t i o n bed. Septa a t SI and S2 a l s o p r o v i d e d a c c e s s f o r i n l e t or o u t l e t l i q u i d samples t h a t c o u l d be a n a l y z e d . When r e g e n e r a t i o n s t u d i e s were b e i n g performed, an i n t e r n a l thermocouple was used to monitor the a d s o r p t i o n bed temperature and the dry n i t r o g e n r e g e n e r a t i o n gas was passed through the bed by s w i t c h i n g v a l v e VI. For p r e l i m i n a r y r e g e n e r a t i o n s t u d i e s , d i f f e r e n t i a l thermal a n a l y s e s (DTA) were c a r r i e d out u s i n g a duPont 990 i n s t r u m e n t . The temperature r i s e r a t e was u s u a l l y 10°C/minute and the sample was purged with dry n i t r o g e n a t 10 seem. Gas chromatographic s t u d i e s performed on the benzene system employed a Hewlett Packard 5840A i n s t r u m e n t equipped w i t h a 1/8" χ 6 column packed w i t h Chromosorb 101 at 180°C and w i t h 25 seem h e l i u m f l o w ; d e t e c t i o n was by thermal c o n d u c t i v i t y and the gas sample (from n i t r o g e n r e g e n e r a t i o n ) was i n t r o d u c e d by a heated automatic gas sample v a l v e . For these s t u d i e s , some z e o l i t e t h a t been s a t u r a t e d w i t h the benzene-water m i x t u r e , was loaded i n t o a m i c r o - d e s o r p t i o n bed (0.6 cm diameter) c o n t a i n e d w i t h i n a heated v a l v e compartment of the 1


204

SYNTHETIC ZEOLITES

Rl-

BENZENE ^Sl


Vl«

FURNACE

S2

R2

THERMOCOUPLE ZEOLON BED VZZZZZZZZZZZZZTu

No

CERAMIC SADDLES Figure 1.

Schematic of dynamic adsorption test equipment

1

1

100

1

200 HOURS

1

300

1

400

Figure 2. Static adsorption test for preliminary Zeolon screening for butanediolwater system: (A) blanks, (Θ) 5 g Z200H, (Β) 5 g Z500, (Ύ) 5 g Ζ900Να, (·) 5 g Ζ500 powder with agitation, (+) 5 g Z500 pellets with agitation (X) 1 g Z500 with agitation y


11.

YOUNG E T AL.

chromatograph and a n i t r o g e n used f o r d e s o r p t i o n .


Static

205

Liquid Phase Drying

purge

(< 100 seem) was

Testing.

The d e h y d r a t i o n o f the w a t e r - b u t a n e d i o l system was i n v e s t i g a t e d u s i n g t h r e e d i f f e r e n t z e o l i t e s : Zeolon 200H (Z200H), Zeolon 900 Na (Z900Na) (both s y n t h e t i c l a r g e p o r t m o r d e n i t e s ) , and Zeolon 500 (Z500) (a n a t u r a l c h a b a z i t e - e r i o n i t e ) . The approach to s t a t i c e q u i l i b r i u m f o r these z e o l i t e s i s shown i n F i g u r e 2. A s u r p r i s i n g r e s u l t from t h i s t e s t was the behavi o r of Z200H, which showed e s s e n t i a l l y no d e h y d r a t i o n effect. T h i s was s u r p r i s i n g s i n c e Z900Na, which i s a l s o a l a r g e p o r t m o r d e n i t e , demonstrated good s e l e c t i v i t y f o r water a d s o r p t i o n . Gehrhardt and K y l e (_5) c l a i m that the e f f e c t i v e n e s s of n a t u r a l z e o l i t e s as d r y i n g agents i s due to a s i e v i n g e f f e c t as w e l l as a s t r o n g a f f i n i t y f o r water. While t h i s may be t r u e f o r s m a l l - p o r t z e o l i t e s (3A or 4A) i n a system where the o r g a n i c component has a l a r g e e f f e c t i v e m o l e c u l a r diameter compared to the s i e v e p o r t s i z e , we cannot c l a i m such a s i e v i n g e f f e c t w i t h the b u t a n e d i o l - w a t e r system over any of the t e s t e d z e o l i t e s . R a t h e r , we are most l i k e l y d e a l i n g w i t h r e l a t i v e a d s o r p t i o n a f f i n i t i e s of the o r g a n i c s and water f o r the p a r t i c u l a r z e o l i t e s t r u c t u r e as commented on by S a t t e r f i e l d and Cheng ( 6 ) . In l i g h t of t h i s argument, the c o m p l e t e l y d i f f e r e n t b e h a v i o r of Z200H and Z900Na w i t h b u t a n e d i o l water can r e a d i l y be e x p l a i n e d by the p r e s e n c e of s t r o n g hydrogen bonding f o r c e s between the d i o l oxygen atoms and the z e o l i t i c hydrogen of Z200H; c o n s e q u e n t l y t h e r e i s no p r e f e r e n t i a l a d s o r p t i o n of water. On the other hand t h e r e would be no hydrogen bonding w i t h Z900Na and the n a t u r a l p r e f e r e n c e of z e o l i t e s f o r water r e s u l t s i n the d e s i r e d dehydration. As might be expected, s t a t i c t e s t s a r e s e v e r e l y h i n d e r e d by d i f f u s i o n a l r e s i s t a n c e s ; thus, when the t e s t i s c a r r i e d out w i t h a g i t a t i o n , the approach to e q u i l i b r i u m i s much more r a p i d . No attempt was made to o b t a i n s t a t i c e q u i l i b r i u m c a p a c i t y d a t a . However, i t was apparent from the data i n F i g u r e 2 t h a t e i t h e r Z900Na or Z500 c o u l d be used to c o m m e r c i a l l y dehydrate butanediol. From the p r a c t i c a l v i e w p o i n t , Z500, bei n g much l e s s expensive than Z900Na, was s e l e c t e d f o r r e g e n e r a t i o n and dynamic e q u i l i b r i u m t e s t i n g . For the b e n z e n e - h y d r o c h l o r i c a c i d - w a t e r system there was no p o i n t i n s c r e e n i n g s e v e r a l z e o l i t e s f o r


In Adsorption and Ion Exchange with Synthetic Zeolites; Flank, W.; ACS Symposium Series; American Chemical Society: Washington, DC, 1980. 160 (S ENDO) 80 (S ENDO) 160-180 (L ENDO)230 (S ENDO) 120 (S ENDO) 150 (S ENDO)

BDO-H 0 Regenerated H 0 wash followed by 400°C f o r 2 hrs

BDO-H 0 Regenerated at 200°C f o r 2 hrs

BDO-H 0


BDO-H 0 Regenerated at 200OC f o r 2 hrs

Z500

Z500

Z200H

Z200H

Z200H

L * Large Peak M » Medium Peak S « Small Peak

2

2

2

2

2

2

2

ENDO = Endothermic EXO = Exothermic

180 (S ENDO)

160 (M ENDO)

BDO-H 0 Regenerated by H 0 Wash followed by 200°C f o r 2 hrs

Z500

2

-

170 (S ENDO)

BDO-H2O Regeneration 316°C f o r 2 hrs

Z500

2

-

160 (S ENDO)


Z500

-

300 (L EXO)

-

240 (S ENDO)

520 (Μ EXO) 550 (Μ EXO) 520 (Μ EXO)

280 (S EXO) 300 (L EXO)

—

-

Peak 4 Temp, OC

310 (L EXO)

350 (L EXO)

350 (L EXO)

470 (M EXO)

—

330-400 (L EXO)

240 (S ENDO)

175 (L ENDO)

2

BDO-H 0

Z500

Peak 3 Temp, °C

Peak 2 Temp, °C

160 (L ENDO)

Peak 1 Temp, °C

Water

Adsorbates

Z500

Zeolon

2

DIFFERENTIAL THERMAL ANALYSES RESULTS

BUTANEDIOL (BDO) WATER (H 0)

TABLE I



11.

YOUNG E T AL.

Liquid Phase Drying

207

p r o c e s s s u i t a b i l i t y , s i n c e the p r e s e n c e of the a c i d environment demanded the use of h i g h l y a c i d - r e s i s t a n t z e o l i t e Z200H. Since benzene i s not l i k e l y t o undergo hydrogen bonding, i t was expected t h a t Z200H would be s u i t a b l e . There was, however, some u n c e r t a i n t y about the s e l e c t i v e a d s o r p t i o n of the water over the a c i d , so some v e r y p r e l i m i n a r y s t a t i c e q u i l i b r i u m c a p a c i t y data were g e n e r a t e d . F i g u r e 3 shows the r e s u l t s o b t a i n e d f o r the benzene-water system and compares these w i t h the r e s u l t s from the b e n z e n e - w a t e r - h y d r o c h l o r i c a c i d system. The a c i d - f r e e system e x h i b i t e d the almost l i n e a r a d s o r p t i o n i s o t h e r m expected a t low water c o n c e n t r a t i o n s , w h i l e the data from the a c i d system, a l t h o u g h somewhat s c a t t e r e d , suggest t h a t the a d s o r p t i o n c a p a c i t y was i n c r e a s e d when some HC1 was p r e s e n t . In any case, the f e a s i b i l i t y of u s i n g Z200H to dehydrate the benz e n e - h y d r o c h l o r i c a c i d system was demonstrated, and j u s t i f i e d embarking on r e g e n e r a t i o n and dynamic equilibrium test studies. Regeneration T e s t i n g . To i n v e s t i g a t e the d e s o r p t i o n c h a r a c t e r i s t i c s of water and b u t a n e d i o l s e v e r a l d i f f e r e n t i a l thermal a n a l y s e s (DTA) were performed on samples of Z500 and Z200H t h a t had been p r e v i o u s l y s a t u r a t e d w i t h water, b u t a n e d i o l , or both. Other samples t h a t had been r e generated by a v a r i e t y of t e c h n i q u e s were a l s o s t u d i e d . T a b l e I summarizes the r e s u l t s o b t a i n e d from t h i s work. Z200H was examined, i n p a r t , to determine i f , i n f a c t , t h e r e was s i g n i f i c a n t a d s o r p t i o n of both components. The water d e s o r p t i o n from Z500 was c h a r a c t e r i z e d by a l a r g e endotherm a p p e a r i n g a t a p p r o x i m a t e l y 160°C. With b u t a n e d i o l and water p r e s e n t ( F i g u r e 4 ) , t h i s endotherm was s h i f t e d s l i g h t l y to 175°C and a second s m a l l endotherm was observed a t 240°C. A l s o , a l a r g e exotherm appeared a t about 330-400°C. S i n c e the des o r p t i o n of a p h y s i c a l l y adsorbed s p e c i e s should produce an endotherm, i t i s apparent t h a t the exotherm must be a s s o c i a t e d w i t h some m o l e c u l a r rearrangement. The most l i k e l y e x p l a n a t i o n i s t h e c y c l i z a t i o n r e a c t i o n of b u t a n e d i o l to produce t e t r a h y d r o f u r a n . F i g u r e 4 a l s o shows the DTA curve from water and b u t a n e d i o l adsorbed on Z200H. In a d d i t i o n t o the water endotherm a t a p p r o x i m a t e l y 160-170°C, the s m a l l endotherm a t 230°C and the exotherm a t 310OC, t h e r e i s a l s o a second endotherm a t 520°C and a s m a l l endo-


208

SYNTHETIC ZEOLITES

•70

•5.0


•30

100

Figure 3. Static adsorption equilibrium tests on Z200H: (Θ) benzene-water sys tem, ([·]) benzene-water-HCl system

200

300

EQUILIBRIUM WATER CONCENTRATION (MEG/G)

Figure 4. Differential thermal analysis results: (1) benzene-water-HCl on Z200H, (2) butanediol-water on Z500, (3) butanediol-water on Z200H

TEMPERATURE c 0

ÏÂ

CO

.

SI



216

SYNTHETIC ZEOLITES

was l o n g e r than the l e n g t h of the a d s o r p t i o n bed. K o r a d i a and K i o v s k y a t t r i b u t e d t h e i r non-symmet r i c a l b r e a k t h r o u g h curve to the presence of n o n - d i s s o l v e d water, f i n e l y d i s p e r s e d water d r o p l e t s which were p r e s e n t as a r e s u l t of the way i n which they p r e pared t h e i r t e s t s o l u t i o n s . While they may have had a heterogeneous l i q u i d m i x t u r e , t h e i r e x p l a n a t i o n can not be a p p l i e d to the p r e s e n t cases of b u t a n e d i o l or benzene. For these c a s e s , i t i s more l i k e l y t h a t the d i s placement of adsorbed o r g a n i c by water i s the c o n t r o l l i n g r a t e p r o c e s s O , .10) . T h i s would a l s o appear to be the case i n some of the s t u d i e s r e p o r t e d by Goto (_7) where c o m p e t i t i v e c o - a d s o r p t i o n was o b v i o u s l y o c c u r r i n g ( e t h a n o l over 4A). In the absence of the c o - a d s o r p t i o n phenomenon, as f o r the case of benzene d r y i n g over 4A (7) , symmetric breakthrough i s observed a l o n g w i t h s m a l l MTZ and h i g h c a p a c i t i e s . Practical Drier

Design

S e v e r a l important a s p e c t s of p r a c t i c a l d r i e r d e s i g n have been covered i n t h i s a r t i c l e , and i t i s w o r t h w h i l e summarizing them and t h e i r i m p l i c a t i o n s . F i r s t , the z e o l i t e s e l e c t i o n p r o c e s s has demonstrated the need f o r a case-by-case examination based on f l u i d c h a r a c t e r i s t i c s and economic c o n s i d e r a t i o n s . Con s e q u e n t l y , the c h o i c e of Z200H f o r the benzene-hydro c h l o r i c a c i d a p p l i c a t i o n and the c h l o r i n a t e d hydro carbon d r y i n g (3) was made because of the a c i d n a t u r e of these f l u i d s . On the o t h e r hand, the c h o i c e of Z500 f o r b u t a n e d i o l d r y i n g was made because of s t r o n g c o m p e t i t i v e c o - a d s o r p t i o n (Η-bonding) on Z200H and the lower c o s t of Z500 compared to Z900Na. Second, the l e n g t h of the mass t r a n s f e r zone and the dynamic e q u i l i b r i u m c a p a c i t y are g r e a t l y i n f l u e n c ed by the p r e s e n c e of c o m p e t i t i v e c o - a d s o r p t i o n which appears to produce a v e r y long zone (up to 180 cm) w i t h a non-symmetrical b r e a k t h r o u g h p r o f i l e and a c a p a c i t y of 5-10%. T h i s type of b e h a v i o r was observed i n the s t u d i e s of benzene and b u t a n e d i o l d r y i n g r e p o r t e d here and i n the S e r i e s I I s t u d i e s of 1,2 d i c h l o ropropane r e p o r t e d by K o r a d i a and K i o v s k y where they observed an MTZ l e n g t h of 80-90 cm w i t h a c a p a c i t y of 5-7%. C o - a d s o r p t i o n of e t h a n o l on 4A produced an MTZ l e n g t h of 180 cm and reduced the e q u i l i b r i u m c a p a c i t y to 5-6% (_7 ) . However, c o - a d s o r p t i o n i s not the o n l y cause of long mass t r a n s f e r zones. Koradia and K i o v s k y r e p o r t t h a t f o r the case where d i s p e r s e d water i s p r e s e n t i n 0 - d i c h l o r o b e n z e n e , they o b t a i n e d



11.

YOUNG E T AL.

Liquid Phase Drying

217

a v e r y long MTZ (up to 140 cm) w i t h a non-symmetrical breakthrough p r o f i l e . However, they a l s o observed v e r y h i g h c a p a c i t i e s ( a p p r o x i m a t e l y 40%). Consequentl y , i f e i t h e r c o m p e t i t i v e c o - a d s o r p t i o n o c c u r s or d i s p e r s e d water d r y i n g i s attempted, s u b s t a n t i a l pena l t i e s a r e i n c u r r e d . However, f o r many a p p l i c a t i o n s , l i k e some of the ones d i s c u s s e d here, t h e r e may be no better alternatives. A t h i r d aspect of d r i e r d e s i g n of s i g n i f i c a n t importance i s the r e g e n e r a t i o n t e c h n i q u e . T h i s i s of p a r t i c u l a r importance to l i q u i d d r y i n g a p p l i c a t i o n s because of the p o s s i b i l i t y of decomposing o r g a n i c s to produce f o u l i n g or i r r e v e r s i b l e p o i s o n i n g of the zeolite. I t i s , t h e r e f o r e , important to d e v i s e a r e g e n e r a t i o n procedure t h a t w i l l a v o i d s h o r t e n i n g the z e o l i t e l i f e and a d e q u a t e l y remove the adsorbed water. S e v e r a l t e c h n i q u e s have been employed i n these s t u d i e s , but a l l u s u a l l y i n v o l v e d r a i n i n g the l i q u i d p r i o r to a thermal r e g e n e r a t i o n . The use of DTA can h e l p d e c i d e the approximate temperature and can a l s o f o r e warn of u n d e s i r a b l e r e a c t i o n s . In t h i s work we used a low-temperature n i t r o g e n r e g e n e r a t i o n f o r benzene, but the vacuum t e c h n i q u e employed f o r the c h l o r i n a t e d hydrocarbons (3) might have helped minimize the d e c o m p o s i t i o n observed. A h i g h - t e m p e r a t u r e r e g e n e r a t i o n u s i n g i n e r t gas s t r i p p i n g was found to be adequate f o r the b u t a n e d i o l case. Other r e g e n e r a t i o n t e c h n i q u e s t h a t have been used i n c l u d e steam s t r i p p i n g , s o l v e n t washing p r i o r to thermal r e g e n e r a t i o n and temperature-programmed desorption. The bulk of t h i s paper has d e s c r i b e d the r e s u l t s of some of t h e e x t e n s i v e t e s t i n g needed to o b t a i n d e s i g n i n f o r m a t i o n f o r p a r t i c u l a r l i q u i d phase a p p l i cations. While we s t r o n g l y recommend o b t a i n i n g data l i k e these f o r s p e c i f y i n g a d e t a i l e d d e s i g n , we a l s o recommend making an i n i t i a l h e u r i s t i c f e a s i b i l i t y estimate. T h i s p r o c e s s w i l l permit n o t o n l y a p r e l i m i n a r y c o s t e v a l u a t i o n of the proposed system b u t , more i m p o r t a n t l y , w i l l h e l p prevent embarking on a l e n g t h y and expensive t e s t program with an inadequate z e o l i t e or f o r an e c o n o m i c a l l y u n r e a l i s t i c a p p l i c a t i o n . To h e l p c a r r y out such an e v a l u a t i o n we have prepared a f l o w c h a r t , shown i n T a b l e V, which p r e s e n t s the important c o n s i d e r a t i o n s i n a s y s t e m a t i c manner. These a r e two main branches, z e o l i t e s e l e c t i o n and p r o c e s s f e a s i b i l i t y . The p r o c e s s f e a s i b i l i t y i n i t i a l l y assumes the worst case f o r the d e s i g n parameter e s t i m a t e s , but these can be r e v i s e d i f the z e o l i t e s e l e c t i o n process i n d i c a t e s that higher c a p a c i t y or s h o r t e r MTZ might be e n c o u n t e r e d . Having


SYNTHETIC

218

ZEOLITES

TABLE V PROCESS


ftgoutg

EVALUATION

FLOW

:ONVENTIÔNÀL .ABSORBENTI ALUMlNIAiSIUEA SSL ETÇi I :OSf ESTIMATION^. AND SIZING / PURITY, CHEMICAL fcoMPOsrriONJ REACTIVITY, EEC,

JgLgcTiorfl-

VISCOSITY, DENSITY, IMOLECULARI SIZE, BOILING PI,

1

^FLUID CHARACTERS ACID gM^lR6NMENl>NO

-YES-

®

n

FLUID l o LECULES &L SMALL? > ° 1 < SIEVE ACTION NEEDED PREVENT REACTIONS ? i-C^TOPf ?^-NOPOLYMERIZATIONS

•ACID RESISTANTL ZEOLITE eg MORDENITE EMALL PORT! ZEOLITES 3Α.4Α.5Α

CHART

r

Y E S

YES

STftÔNô COMPETITION?' •NOeg. H-BONDING

LIST PftoBApLE ÎEoLtTESI

IH-CATIQNI

®

ESTIMIATES ! CAPACITY 3-10% MTZ 20-l50cm. FLUID VELOCITY 0.5-50cm./min. flCYCLE TIME 8-24 hrs. MVLTIBSPS

[ESTIMATED DESI6N| PARAMETER ESTIMATE DRIER LOAD KgHjO/CYCLEl

Ι ί*ο«έέ IIREQUIREMENTSI-

r

IESTIMATE Si2E| AND COST

-YESN0-

IEXPERIMENTAL TESTI PROGRAM DYNAMIC TESTS REGENERATION MFE STUDY

CHECK ASSUMPTIONS! PARAMETERS. STATIC TESTS* I— NO < CHANGE ? >YES -

m

m


11.

YOUNG E T A L .

219

Liquid Phase Drying

f o l l o w e d the flow c h a r t , the outcome w i l l be a l i s t of p o t e n t i a l l y s u i t a b l e z e o l i t e s , an e c o n o m i c a l l y f e a s i b l e p r o c e s s , a p o s s i b l e r e g e n e r a t i o n scheme, and a much b e t t e r a p p r e c i a t i o n of p o t e n t i a l d i f f i c u l t i e s . With t h i s knowledge, the d e t a i l e d e x p e r i m e n t a l program can be commenced and the s p e c i f i c d e s i g n data o b t a i n e d to permit the d e t a i l e d e n g i n e e r i n g d e s i g n of the d r y i n g system.


Acknowledgment The a u t h o r s wish to thank the Norton Company f o r support of t h i s work and f o r p e r m i s s i o n to p u b l i s h these f i n d i n g s .

Literature Cited 1.

Hales, G.E., CEP, 1971, 67, (11), 45-48.

2.

Dexant, Α., LaTechnique Moderne, 1972, (Nov.), 47-50.

3.

Koradia, P.B., Kiovsky, J.R., CEP, 1977, 73, (4), 105-106.

4.

Stannet, V.T., DuPlessis, T.A., Goineau, A.M., J. Appl. Polymer Sci., 1972, 16, 2847-2852.

5.

Gehrhardt, H.M., Kyle, B.G., IEC (Process Design Development, 1967, 6, (3), 265-267.

6.

Satterfield, C.N., Cheng, C.S., AIChE Journal, 1972, 18, (4), 720-723.

7.

Goto, C., Joko, I., Tokunaga, Κ., Nippon Kagaku Kaishi, 1972, 2070-2075.

8.

Michaels, A.S., IEC, 1952, 44, (8), 1922-1930.

9.

Eagle, S., Scott, J.W., IEC, 1950, 42, (7), 1294.

10.

1287-

Kostecki, J . A . , Manning, F.S., Cansar, L . N . , AIChE Symposium Series, 1967, 63, (74), 90-95.

RECEIVED April 24,

1980.


Adsorption and Ion Exchange with Synthetic Zeolites - American

Recommend Documents