Properties of Linde A in Aqueous, Nonaqueous, and Mixed Media

31 Properties of Linde A in Aqueous,

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Nonaqueous, and Mixed Media 1

R. B. BARRETT, J. A. MARINSKY, and P. PAVELICH The State University of New York, Buffalo, Ν. Y. 14214

+

+

The solvent and ion selectivity behavior of Na and K forms of Linde A have been measured in nonaqueous and mixed media. An osmotic pressure model accurately describes ion exchange in concentrated aqueous electrolyte solutions and is extended to solvent selectivity in mixed media. Water is preferentially adsorbed over alcohols, and ethylene glycol is preferred over ethanol in accord with the derived equation N

1nK = π/RT (V - V ) M

1

2

The strongly hydrophyllic nature of the exchanger and the resulting constancy of the internal environment permit as sessment of electrolyte activity coefficient ratios in the ex ternal mixed solvent through the equation N

1nK = π/RT (V - V ) + γM/γN - 21n γ±MX/γ±NX M

M

N

The first 2 terms on the right retain their known aqueous values until 70 wt% external alcohol, when serious alcohol invasionfirstoccurs.

T j l a t e k a n d M a r i n s k y (13)

first

suggested

that a zeolite m a y b e c o n -

* ·• s i d e r e d a h i g h l y c r o s s - l i n k e d i o n exchanger a n d t h a t a r e l a t i o n s h i p of t h e t y p e i n t r o d u c e d b y G r e g o r (7, 8) a n d G l u e c k a u f (6) f o r o r g a n i c resins also m a y a p p l y f o r t h e z e o l i t e ; n a m e l y In a = In a + j^pV y

1

5

3

Present address: Rosary Hill College, Buffalo, Ν. Y. 14226.

414 In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

(1)

31.

BARRETT E T AL.

Properties

of Linde

A

415

w h e r e a, a n d V, represent the a c t i v i t y a n d p a r t i a l m o l a r v o l u m e of c o m p o n e n t /, π is t h e difference i n o s m o t i c pressure b e t w e e n the i n t e r i o r of the z e o l i t e a n d the e x t e r n a l s o l u t i o n , a n d the b a r p l a c e d a b o v e the s y m b o l is u s e d to differentiate the r e s i n phase f r o m the a q u e o u s phase. E q u a t i o n 2 is t h e t h e r m o d y n a m i c r e p r e s e n t a t i o n of the u n i - u n i v a l e n t e x c h a n g e r e a c t i o n i n 1:1 electrolyte solutions w i t h the Α-zeolite i n the M the e x c h a n g e c a r r i e d out i n solutions of NX a n d MX


[ 2 Ξ ] - v . - ™

+

+

form and

(3)

> · > f

-

»

•

»

w h e r e Κ is the e x p e r i m e n t a l l y d e t e r m i n e d s e l e c t i v i t y coefficient, m is the m o l a l c o n c e n t r a t i o n of the species, γ is the a c t i v i t y coefficient of the i o n i n the z e o l i t e phase, a n d y±

is the m e a n m o l a l a c t i v i t y coefficient of the

electrolyte i n the e x t e r n a l phase. B u k a t a a n d M a r i n s k y ( 4 ) c o n s i d e r e d the zeolite's s t r u c t u r a l r i g i d i t y , h i g h resistance to electrolyte i n t r u s i o n ( a c o n s e q u e n c e of the h i g h n e g a tive c h a r g e p r o v i d e d b y the r i n g s of o x y g e n atoms i n its u n i t c u b i c c e l l ) , a n d the c o n s t a n c y of solvent u p t a k e u n t i l v e r y l o w e x t e r n a l solvent act i v i t y values sufficient to m a i n t a i n the In 4 - t e r m of E q u a t i o n 2 i n v a r i a n t at a n y e x t e r n a l electrolyte c o n c e n t r a t i o n so l o n g as the i n t e r n a l i o n c o m p o s i t i o n r e m a i n e d fixed. T h e y also suggested t h a t the o s m o t i c pressure, π, c o u l d b e e v a l u a t e d b y use of E q u a t i o n 1 i f a of this e q u a t i o n is c o n s

stant at e v e r y e x p e r i m e n t a l s i t u a t i o n . S i n c e the t h i r d t e r m of E q u a t i o n 2 is a v a i l a b l e as w e l l , b y u t i l i z a t i o n of t h e H a r n e d - C o o k e e q u a t i o n the v a l u e of K

M

N

as a f u n c t i o n of e x t e r n a l electrolyte c o n c e n t r a t i o n w a s

e x p e c t e d to b e c a l c u l a b l e after e v a l u a t i o n of t h e ^

ft!

y

(17),

(V

M

— V) N

+

In

M

—

t e r m f r o m a single m e a s u r e m e n t of K

M

N

at a n y e x t e r n a l electrolyte

concentration. T o demonstrate the v a l i d i t y of this m o d e l , a series of experiments was p e r f o r m e d ( 4 ). T h e e x c h a n g i n g i o n Ν was k e p t at r a d i o a c t i v e tracer level

concentrations i n solutions of MX

(0.05m a n d g r e a t e r ) .

S i n c e the

i o n - f r a c t i o n of M w a s essentially u n i t y i n b o t h the z e o l i t e a n d e x t e r n a l s o l u t i o n phases a n d since the i o n - c o n c e n t r a t i o n of the z e o l i t e w a s c o n stant i n a fixed g e o m e t r y b y this e x p e r i m e n t a l a r r a n g e m e n t , the v a l u e ΎΜ

of In

w a s p r e s u m e d to r e m a i n constant. T h e v a l u e of π w a s o b t a i n e d JN

as a f u n c t i o n of electrolyte c o m p o s i t i o n f r o m E q u a t i o n 1 b y c o n s i d e r i n g the c h a n g e i n the a c t i v i t y , a

jy

of the solvent c o m p o n e n t of the s o l u t i o n

phase w i t h e x p e r i m e n t a l c o n d i t i o n s . T h e v a l u e of âj w a s o b t a i n e d f r o m a d s o r p t i o n i s o t h e r m d a t a as d e s c r i b e d i n R e f . 4.

B r i e f l y , that solvent

In Molecular Sieve Zeolites-I; Flanigen, E., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1974.

416

MOLECULAR SIEVE ZEOLITES

1

a c t i v i t y v a l u e b e l o w w h i c h solvent a d s o r p t i o n s h o w e d a m a r k e d decrease w a s p r e s u m e d to i d e n t i f y âj. I t w a s a s s u m e d t h a t t h e p a r t i a l m o l a r v o l u m e of solvent ( 1 8 m l ) a n d ions (10)

w e r e constant.

T h e activity co-

efficient of M X , since N X w a s present i n trace q u a n t i t i e s , w a s i d e n t i c a l w i t h t h e p u r e MX solutions a n d w a s f r o m the l i t e r a t u r e (17).

T h e ac-

t i v i t y coefficient f o r trace N X i n t h e presence of M X w a s c a l c u l a t e d b y use of t h e H a r n e d - C o o k e e q u a t i o n (17)


log

ro(ivx)

=

log

Table I.

+

yNXiO)

am

(3)

NaA-NaCl-CsCl Kjv

a

C e

(ex ) P

Ki\ra (pred) CS

2.81 2.83 2.55 2.31

2.77 2.78 2.56 2.22 1.85 1.61 1.37 1.18

0.053 0.106 0.537 1.085 2.255 3.383 4.510 6.068 System:

a

1.52 1.32 1.09

KA-KCl-CsCL

External KCl Molality

K \pred) C

K

2.80 2.80 2.72 2.66 a 2.39 2.36

2.92 2.77 2.67 2.58 2.48 2.45 2.45

0.049 0.098 0.499 1.000 2.090 3.220 4.414 System: External KCl Molality 0.109 0.439 0.891 1.831 2.829 3.885

+

Selectivity D a t a

System: External NaCl Molality

i n the form

KA-KCl-NaCl Κκ (βχρ) Να

3.42 3.52 3.49 3.59 3.75 3.80

K

K

N a

i p r e d )

3.41 3.48 3.51 a 3.69 3.77

° Computation base.


31.

Properties

BARRETT ET A L .

where

of Linde

417

A

is the a c t i v i t y coefficient of a trace of N X i n the presence of

y (NX) 0

MX at m o l a l i t y m, y

M

(

0

)

is the a c t i v i t y coefficient of p u r e N X at m o l a l i t y

m, a n d a a n d β are e x p e r i m e n t a l l y d e t e r m i n e d parameters. R e p r e s e n t a t i v e results of these studies are p r e s e n t e d i n T a b l e I , where experimental K

N

M

values are c o m p a r e d w i t h the K

values p r e

N

M

d i c t e d f r o m E q u a t i o n 2 o n the basis of a single s e l e c t i v i t y measurement. The y

±

values a n d i n t e r a c t i o n parameters for use i n E q u a t i o n 3 w e r e

o b t a i n e d f r o m t h e d a t a of R o b i n s o n (14, 15, 16,

17).

T h e excellent agreement over the large c o n c e n t r a t i o n r a n g e e x a m i n e d of K

N


M

(exp)

and K

N

M

( p r e d ) i n these a n d the other u n i - u n i v a l e n t sys

tems s t u d i e d s t r o n g l y s u p p o r t the v a l i d i t y of the osmotic m o d e l that was employed. Solvent-Selectivity

of the Synthetic

Α-Zeolite

in Mixed

Media

T h e o s m o t i c m o d e l has b e e n s h o w n b y B a r r e t t , M a r i n s k y , a n d P a v e lich (2)

to be a p p l i c a b l e as w e l l f o r the i n t e r p r e t a t i o n of the solvent-

s e l e c t i v i t y p r o p e r t i e s of the s y n t h e t i c Α-zeolite i n m i x e d m e d i a .

They

s t u d i e d the c o m p e t i t i v e s o r p t i o n of s e v e r a l alcohols a n d w a t e r b y the Α-zeolite f r o m t w o - c o m p o n e n t m i x t u r e s . T h e results of these solvent d i s t r i b u t i o n studies are r e p o r t e d i n T a b l e I I as s t o i c h i o m e t r i c d i s t r i b u t i o n coefficients, K , 8

1

2

defined b y E q u a t i o n 4 K

8

l

t

= ^

· -

X

2

(4)

Xi

w h e r e χ is the m o l e f r a c t i o n of solvent, a n d subscripts 1 a n d 2 i d e n t i f y the c o m p e t i n g solvent components.

A s before, the b a r over the s y m b o l

designates the i n t e r n a l phase. It was not possible to o b t a i n a d i r e c t m e a s u r e m e n t of the solvent c o m p o s i t i o n of the i n t e r n a l phase at e q u i l i b r i u m i n these studies. A m a t e r i a l b a l a n c e n e e d e d to be effected b y accurate analysis of the i n i t i a l phases a n d the final e q u i l i b r i u m s o l u t i o n to y i e l d this i n f o r m a t i o n . T h i s e x p e r i m e n t a l r e s t r i c t i o n b l u n t e d the a c c u r a c y a n d range of the e x p e r i m e n t a l p r o g r a m as d e s c r i b e d b e l o w . E x p e r i m e n t s w e r e confined to a l c o h o l - r i c h solutions because of the h i g h affinity of the w a t e r c o m p o n e n t for the zeolite phase.

B y limiting

experiments to this c o m p o s i t i o n range, the i n t e r n a l solvent r a t i o w a s m a i n t a i n e d n e a r u n i t y to assure r e a s o n a b l y r e l i a b l e results. W i t h

one

i n t e r n a l c o m p o n e n t s i g n i f i c a n t l y i n excess of the other, this r a t i o is sus c e p t i b l e to sizeable d i s t o r t i o n b y s m a l l errors i n analysis of the e x t e r n a l phase. I n spite of these p r e c a u t i o n s , the d e t e r m i n a t i o n of K 8

1

2

remained

subject to large u n c e r t a i n t y . I n a g i v e n e x p e r i m e n t , the i n i t i a l c o m p o s i -


418


1

Table II. x

No.

x

w


System: A-l 2 3 4 5 6 7 8 9 10 11 12 13 14

K

m

w

ΝaA-Water-Methanol

0.0203 0.0270 0.0242 0.0253 0.0262 0.0262 0.0262 0.0301 0.0520 0.0700 0.0700 0.0900 0.0900 0.1340

0.34 0.55 0.56 0.49 0.53 0.52 0.54 0.675 0.635 0.57 0.78 0.675 0.834 0.877

System: B-l 2 3 4 5 6 7 8 9 10

s

w

4 < 2 5 . 0 < 67 24 < 4 4 . 0 < 76 51.3 37.0 41.9 40.3 43.6 35 < 6 8 . 5 < 1 3 7 32.0 18.0 30 < 4 7 . 0 < 1 0 0 21.5 33.0 46.0

ΚA~Water-Methanol

0.0130 0.0130 0.0143 0.0154 0.0177 0.0552 0.0770 0.0820 0.121 0.124

0.62 0.68 0.62 0.66 0.63 0.845 0.83 0.86 0.964 0.92

123 163 114 125 96 96 58 67 152 93

t i o n of b o t h phases was p r e c i s e l y k n o w n b y t h e i r c o n t r o l l e d p r e p a r a t i o n . A s s a y of the s o l u t i o n phase at e q u i l i b r i u m was b a s e d o n d e n s i t y a n d K a r l F i s c h e r d e t e r m i n a t i o n at t h e l o w e s t w a t e r concentrations, w i t h

good

agreement. A t the h i g h e r w a t e r concentrations, the d e t e r m i n a t i o n of K S

w a s b a s e d solely o n d e n s i t y measurements.

2

1

A n error l i m i t of ± 0 . 1 % i n

the d e n s i t y measurements, w h i c h is b e l i e v e d to b e r e a l i s t i c , leads to the representative e r r o r l i m i t s i n K 8

2

±

t h a t are listed. S i n c e the K a r l - F i s c h e r

m e t h o d at l o w w a t e r concentrations is m o r e accuate t h a n the

±0.1%

u n c e r t a i n t y a s c r i b e d to the d e n s i t y measurements, the solvent s e l e c t i v i t y coefficients p r e s e n t e d are b e l i e v e d to f a l l w i t h i n the error h m i t s because of the g o o d agreement b e t w e e n the 2 m e t h o d s of m e a s u r e m e n t w h e n both were

employed.

A p p l i c a b i l i t y of the o s m o t i c m o d e l for i n t e r p r e t a t i o n of these solvent selectivity data was demonstrated (2)

as f o l l o w s : T h e t h e r m o d y n a m i c

expression for the exchange r e a c t i o n of 2 solvent components

between

zeolite a n d s o l u t i o n phases ( E q u a t i o n 1 ) is a c c o r d i n g to t h e osmotic m o d e l


31.

Properties

BARRETT ET A L .

of Linde

419

A

Solvent Selectivity No.

Xw System: NaA,


No.

0.667 0.604 0.667

Xeg

Xeg

-

44.9 32.3 27.2

Ethylene Glycol-Ethanol-NaA

0.045 0.048 0.017 0.018 0.019 0.019 0.043 0.036 0.032 0.032

In

w

Glycol

0.0425 0.0451 0.0601

System: D-l 2 3 4 5 6 7 8 9 10

e

156 155 806 631

0.74 0.76 0.89 0.87

System: NaA-Water-Ethylene C-l 2 3

K

Ka-Water-Ethanol

0.0184 0.0209 0.0130 0.0104

ïaA 1 2 Ka 1 2

s

1

36.5 28.5 50.6 38.8 34.9 29.4 23.7 33.3 51.2 40.8

0.637 0.594 0.451 0.427 0.405 0.360 0.520 0.554 0.634 0.578

= In r * Kl

= J L (Fx -

(5)

V) t

I n o r d e r to use E q u a t i o n 5 successfully, the α p a r a m e t e r m u s t b e k n o w n for each component.

I n t h e case of w a t e r , i t w a s possible

to

assign a v a l u e of 0.0127 for the N a - f o r m zeolite f r o m recent a d s o r p t i o n i s o t h e r m d a t a ( 1 ) b y a s s u m i n g the v a l i d i t y of the B u k a t a a n d M a r i n s k y ( 4 ) analysis of s u c h data. T h e v a l u e for â

m

( m e t h a n o l ) was less c e r t a i n

( 5 ) , a n d s i m i l a r d a t a w e r e u n a v a i l a b l e f o r e t h a n o l a n d ethylene g l y c o l . B e c a u s e of the u n a v a i l a b i l i t y of p e r t i n e n t a d s o r p t i o n i s o t h e r m d a t a for the v a r i o u s solvents s t u d i e d , the i n t e r p r e t a t i o n of solvent selectivity b y the m o d e l p r o p o s e d c o u l d n o t b e e x p l i c i t . Resort to the m o d e l itself was c o n s e q u e n t l y m a d e to estimate the c h e m i c a l c o m p o s i t i o n t e r m In a) c o n t r i b u t i n g to the c h e m i c a l p o t e n t i a l (μ)

(RT

of e a c h solvent c o m p o

nent for w h i c h a d s o r p t i o n i s o t h e r m d a t a w e r e l a c k i n g i n the zeolite phase of e q u i l i b r i u m m i x t u r e s . T h i s a p p r o a c h to the e v a l u a t i o n of a, because i t w a s not e x p l i c i t , h a d to b e justified i n a n u n a m b i g u o u s m a n n e r . was a t t e m p t e d i n t h e f o l l o w i n g f a s h i o n .


This

420


Table III.

No.

Mole

2.03 2.70 3.0 7.0

34 55 67.5 78

System: Sodium

K »

s

2

A-l 2 8 11


Mole %H 0

1

Tm

m

1.47 1.28 1.13 1.10

25 44 68.5 47

1.00 1.03 1.16 1.30

2.80 2.70 2.60 2.41

B y using an experimental selectivity point obtained w i t h m e t h a n o l w a t e r - N a A a n d the adsorption isotherm deduced a

w

value, the internal

pressure o f t h e e x p e r i m e n t a l m i x t u r e w a s e v a l u a t e d first w i t h E q u a t i o n 6a. In

^

w

^^«j RT

w

(6a)

S i n c e t h e i n t e r n a l m e t h a n o l c o m p o n e n t m u s t b e subject also to t h e same pressure, E q u a t i o n 6 b c o u l d b e e m p l o y e d to evaluate â ° m

In

*^

T

for methanol. (6b)

TC^WI

O

RT

v

7

E q u a t i o n s 6 a a n d 6 b are b a s e d o n E q u a t i o n 1. I n t h e m i x e d solvent syst e m , t h e dj p a r a m e t e r o f E q u a t i o n 1 has to b e m o d i f i e d to a c c o u n t f o r the fact t h a t there are 2 solvent components o c c u p y i n g t h e zeolite m a t r i x . It has b e e n c o n s i d e r e d , a priori,

that â

=

J ( E q l )

âj°Ê/yy . (Eq

6aib)

where

â°,

t h e a c t i v i t y p a r a m e t e r o b t a i n e d i n t h e p u r e solvent m e d i u m , m u s t b e m o d i f i e d to a c c o u n t f o r its f r a c t i o n a l c o n s t i t u t i o n of t h e zeolite (XJ) Xj =

phase

a n d f o r s o l v e n t - s o l v e n t i n t e r a c t i o n ( γ ) . I n t h e l i m i t i n g case of ;

1, γ =

1, a n d E q u a t i o n s 6 a a n d 6 b r e d u c e to E q u a t i o n 1.

;

T o f a c i l i t a t e t h e c o m p u t a t i o n of a °, m

t h e a s s u m p t i o n w a s m a d e that

the a c t i v i t y coefficients o f t h e 2 components as a f u n c t i o n of c o m p o s i t i o n w e r e t h e same i n b o t h phases.

D a t a from experiment A - 2 i n T a b l e I I

were used for the computation.

S o l u t i o n of E q u a t i o n 6 a y i e l d e d a v a l u e

of 2850 a t m f o r π. T h e v a l u e of a ° that r e s u l t e d f r o m E q u a t i o n 6 b w a s m

0.020, i n reasonable a g r e e m e n t w i t h t h e â ° m

v a l u e of 0.03 d e d u c e d

from

the o n l y a d s o r p t i o n i s o t h e r m d a t a ( 5 ) a v a i l a b l e f o r m e t h a n o l . A s a c o n s e q u e n c e of this agreement, i t w a s t h o u g h t justifiable to suggest t h a t t h e a d s o r p t i o n i s o t h e r m d a t a w e r e r e l i a b l e a n d s u p p o r t e d the use of this a p p r o a c h to t h e e v a l u a t i o n of a. B y a p p l y i n g these parameters to t h e data listed i n T a b l e I I , the selectivity that was predicted b y m u l t i p l y i n g K

8

w

m

b y the ratio _ ™ ° M

t h e v a l u e of K , T

w

m

m

to o b t a i n K T

w

m

is c o m p a r e d i n T a b l e I I I w i t h

t h e t h e r m o d y n a m i c s e l e c t i v i t y constant p r e d i c t e d b y


31.

Properties

BARRETT ET A L .

of Linde

421

A

A-H 0-MeOH 2

antilog ( V - Vw) 2.3 R T

(&w TfwYra\

m

\3;m Ύ m Y w /


1.4 7 8.3 6.9

< 8.4

Properties of Linde A in Aqueous, Nonaqueous, and Mixed Media

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