57 Influence of Zeolite Cation Nature on Adsorption and Chromatographic Properties G. V. TSITSISHVILI and T. G. ANDRONIKASHVILI Institute of Physical and Organic Chemistry, Academy of Sciences of the Georgian SSR, Tbilisi, USSR
For zeolites
with 1-, 2-, and 3-charge
of adsorption cations
interaction
replacing
sodium
by population
of single-cation pronounced
positions, influence
sodium
ions on sorption
zeolites
of type A. Chromatographic
the number decreases,
the values
metal cations lattice
volumes
cations
essentially
volumes
type
fac
of
values
of the
for when zeolite
hydrocarbon
The nature of
and their positions
influence
of the compounds
the
replacing
data show that
decrease.
of type X zeolites
of
exchange,
has been established
of retention
monoxide
of
and by other
of
of cations in a unit cell of a faujasite
gases and carbon crystal
kinetics
specificity
by nature
ions, by the degree
tors.
A more
cations, the
is determined
alkali in the
retention
studied.
Ο tudies o f n e w p e r s p e c t i v e fine porous c r y s t a l zeolites h a v e s h o w n that ^
t h e i r properties d e p e n d s t r o n g l y o n cations c o m p e n s a t i n g t h e n e g a
tive charge of the aluminosilicate framework. W i t h i n one t y p e of zeolite, a d s o r p t i o n , c h r o m a t o g r a p h i c ,
catalytic,
a n d other properties are d e t e r m i n e d to a c e r t a i n extent b y t h e n a t u r e o f i o n exchange cations, b y t h e i r n u m b e r p e r u n i t c e l l , b y t h e degree of p o p u l a t i o n o f single centers ( p o s i t i o n s )
i n the crystal framework, a n d b y
other t h i n g s . T h e c r y s t a l structure of zeolites A , X , a n d Y is c o m p a r a t i v e l y w e l l s t u d i e d b y x-ray c r y s t a l analysis (5, 6, 7, 11, 24).
T h e existence of single
centers of c a t i o n l o c a l i z a t i o n is established f o r faujasite g r o u p zeolites, a n d their populations have been forms (7,9,
10,18,23,
d e t e r m i n e d f o r a n u m b e r of c a t i o n
26). 217
218
M O L E C U L A R SIEVE
ZEOLITES
II
T h i s is v e r y i m p o r t a n t i n analysis of the i n f l u e n c e of i o n exchange cations o n different p r o p e r t i e s of zeolites, a n d i t was t a k e n i n t o accounti n our work. T h i s p a p e r presents some results of the studies of the i n f l u e n c e of i o n exchange cations o n a d s o r p t i o n , k i n e t i c s , a n d c h r o m a t o g r a p h i c char acteristics of zeolites of types A , X , a n d Y . Κ. E . A v a l i a n i , D . N . B a r n a b i s h v i l i , M . S. S h u a k r i s h v i l i , E . P . G r i g o l i a , M . G . A d o l a s h v i l i , Sh. D . S a b e l a s h v i l i , Ζ. I. K o r i d z e , a n d S. S. C h k h e i d z e h a v e t a k e n p a r t i n this w o r k . D i f f e r e n t c a t i o n f o r m s of zeolites h a v e b e e n o b t a i n e d f r o m o r i g i n a l s o d i u m zeolites b y means of i o n e x c h a n g e a n d b y the t e c h n i q u e w o r k e d o u t earlier ( 2 8 ) .
T h e c o m p o s i t i o n w a s d e t e r m i n e d b y c h e m i c a l analysis,
a n d s t a b i l i t y of the z e o l i t e c r y s t a l lattice b y x-ray t e c h n i q u e . T h e studies of a d s o r p t i o n c a p a c i t y of vapors w e r e m a d e b y m i c r o b a l a n c e t e c h n i q u e , a n d k i n e t i c characteristics w e r e d e t e r m i n e d o n a d y n a m i c apparatus.
T h e statics of v a p o r a d s o r p t i o n w a s s t u d i e d at 20 ° C .
T h e specimens w e r e d e h y d r a t e d at 350 ° C a n d f o r a d s o r p t i o n studies the v a c u u m c o r r e s p o n d e d to 1 0 " m m of m e r c u r y .
F o r chromatographic
6
studies, z e o l i t e granules w i t h a l k a l i m e t a l cations, b e f o r e t h e y w e r e p l a c e d i n t o a c h r o m a t o g r a p h i c c o l u m n , h a d b e e n h e a t e d at 4 5 0 ° C w i t h t h e r m a l treatment i n t h e flow of the c a r r i e r gas at 3 0 0 ° C . It is better to g i v e e x p e r i m e n t a l d a t a not o n l y i n the u s u a l f o r m of isotherms, w h e r e the a d s o r p t i o n v a l u e is expressed i n m i l l i m o l e s p e r mmo e g r a m of adsorbent as a f u n c t i o n of r e l a t i v e ( r e d u c e d ) pressure, a ^ / Ρ \ S = /( p- J, b u t also i n the f o r m of isotherms w h e n the v a l u e of a d s o r p t i o n r a m
is d e t e r m i n e d b y the n u m b e r of the a d s o r b e d m o l e c u l e s p e r u n i t c e l l d e p e n d i n g o n the r e l a t i v e pressure,
a ~ m
=
f(Jr^-
T h e n u m b e r of u n i t
cells c o r r e s p o n d i n g to a u n i t mass of z e o l i t e w a s d e t e r m i n e d b y M . M . D u b i n i n ( 12,13,15
). S u c h a n a p p r o a c h eliminates the influence of c a t i o n
masses, w h i c h is felt p a r t i c u l a r l y i n h e a v y cations.
D u r i n g the analysis
of a d s o r p t i o n d a t a , one s h o u l d p a y the m a i n a t t e n t i o n to the p o r t i o n of the i s o t h e r m c o r r e s p o n d i n g to l o w pressures.
T h e influence of cations
i n zeolites o n i n t e r a c t i o n w i t h m o l e c u l e s of the a d s o r b e d substances at l o w coverages is c l e a r l y seen w h i l e s t u d y i n g c h r o m a t o g r a p h i c processes (8,16,17,19,
20, 21,
37,39).
S t u d y of v a p o r a d s o r p t i o n o n p o t a s s i u m - s o d i u m zeolites of the f a u jasite t y p e ( t h e r a t i o of s i l i c a to a l u m i n a η =
2.49)
has s h o w n that a d
s o r p t i o n c a p a c i t y f o r w a t e r is decreased a n d for b e n z e n e i n c r e a s e d w i t h the degree of e x c h a n g e a =
0.44
=
t o
c o m p a r e i t w i t h the
s o d i u m f o r m . T h e o b s e r v e d character of the a d s o r p t i o n process m a y b e
57.
T s i T S i S H V i L i AND
Influence of Zeolite Cation
ANDRONiKASHViLi
c a u s e d b y w e a k e n i n g of electrostatic dispersion.
219
i n t e r a c t i o n a n d s t r e n g t h e n i n g of
A l m o s t l i n e a r decrease o f a d s o r p t i o n c a p a c i t y has b e e n w i t h t h a l l i u m - s o d i u m zeolites of t y p e A (n =
observed
1.98) f o r w a t e r v a p o r
w i t h a n increase o f t h e degree o f e x c h a n g e ( F i g u r e 1 ) . T h i s is a result of a decrease of t h e c a t i o n electric field w h i c h causes a decrease of t h e a d s o r p t i o n l a y e r density. U s i n g t h a l l i u m - s o d i u m zeolites o f t y p e X ( η =
2.30 ), w e o b s e r v e d
a n increase of a d s o r p t i o n c a p a c i t y f o r w a t e r v a p o r a n d b e n z e n e at 3 8 % r e p l a c e m e n t o f s o d i u m ions b y t h a l l i u m ions, a n d t h e n its decrease w i t h a n increase i n t h e degree of exchange. ions i n t h e p o s i t i o n S
m
A s t h a l l i u m ions r e p l a c e s o d i u m
(25) w e m a y assume r e d i s t r i b u t i o n of cations at
d e h y d r a t i o n u n d e r t h e c o n d i t i o n s of h i g h v a c u u m a n d t h e r m a l treatment at 3 5 0 ° C , a n d stronger c h e m i c a l b o n d s of t h a l l i u m atoms i n screened positions i n c o m p a r i s o n w i t h s o d i u m atoms. T h e r e p l a c e m e n t of s o d i u m ions b y ions of c a l c i u m a n d s t r o n t i u m leads to a decrease i n the a d s o r p t i o n v a l u e p e r u n i t c e l l . A s i m i l a r p i c ture is o b s e r v e d i n studies of a d s o r p t i o n of benzene v a p o r o n c a l c i u m forms. P r o p e r t i e s of c a l c i u m a n d s t r o n t i u m zeolites a p p a r e n t l y are c a u s e d b y t h e f a c t that ions of c a l c i u m ( s t r o n t i u m )
d u r i n g t h e process of ex
change o c c u p y t h e screened positions Si a n d S , a n d t h e n u m b e r n
(den
sity ) o f c a t i o n centers p e r u n i t c e l l decreases ( 32, 34 ). I n p r i n c i p l e , h y d r o l i t i c e x c h a n g e ( 3 5 , 36) also m i g h t influence t h e a d s o r p t i o n c a p a c i t y ; h o w e v e r , s u c h a n a s s u m p t i o n is d i f f i c u l t to b r i n g into a g r e e m e n t w i t h t h e d a t a of x-ray c r y s t a l studies of c a l c i u m a n d
0
25
50
75
100%
Figure 1. Dependence of the num ber of adsorbed water molecules per unit cell on the degree of exchange of sodium ions by thallium ions at differ ent relative pressures from 0.05 to 0.50
220
M O L E C U L A R SIEVE
ZEOLITES
II
1.2
3 A
100
SO 0
0
0,2
0,04
Ο,Οδ
P/p
0,4
0,6
08
1,0 ρ
Figure 2. Isotherms of adsorption of water vapors on original sodium zeo lite X (4) and lanthanum forms (1,2,3, and 5). (1) a = 0.44; (2) a = 0.22; (3) a = 0.50; (5) a = 0.91. s t r o n t i u m zeolites ( 7 ) . B a r i u m zeolites are c h a r a c t e r i z e d b y properties close to those o f c a l c i u m a n d s t r o n t i u m forms. O u r studies h a v e s h o w n that r e p l a c e m e n t
of 2 9 % of s o d i u m ions
b y l a n t h a n u m ions i n a n A zeolite l i t t l e affects its a d s o r p t i o n c a p a c i t y f o r w a t e r v a p o r . O b v i o u s l y , l a n t h a n u m ions o c c u p y c o m p a r a t i v e l y screened positions i n a c r y s t a l . T h e presence of l a n t h a n u m ions u p to t h e degree o f e x c h a n g e a = 0.44 a n d a = a n d Υ (η =
0.64, r e s p e c t i v e l y , i n zeolites X ( n == 2.44)
4.16) promotes a n increase of w a t e r v a p o r a d s o r p t i o n ( F i g
u r e 2 ) . A t degrees of e x c h a n g e e x c e e d i n g 0.5-0.6, a d s o r p t i o n p r o b a b l y decreases o w i n g to w e a k e n i n g of the lattice. T h a t is s h o w n b y roentgeno g r a m s o f t h e c o r r e s p o n d i n g l a n t h a n u m zeolites. T h e d a t a s h o w that l a n t h a n u m ions i n zeolites X a n d Y , e v e n i n c o m p a r a t i v e l y screened
positions, interact w i t h p o l a r molecules
S u c h a p o i n t o f v i e w is c o n f i r m e d b y t h e results
of water.
of o u r studies of
water vapor adsorption o n sodium a n d lanthanum hydrosodalites. C o n s i d e r a t i o n of isotherms of b e n z e n e
v a p o r a d s o r p t i o n o n speci
mens of l a n t h a n u m zeolite X shows that u p to 5 0 % r e p l a c e m e n t s o d i u m ions leads to some
increase
of a d s o r p t i o n c a p a c i t y ,
d e e p e r e x c h a n g e promotes decrease of a d s o r p t i o n c a p a c i t y .
of
a n d that Adsorption
of b e n z e n e v a p o r is decreased o n l a n t h a n u m a n d y t t r i u m zeolites of t y p e Y i n c o m p a r i s o n w i t h s o d i u m zeolites ( F i g u r e 3 ) . S u c h a difference i n
57.
Influence of Zeolite Cation
TsiTsiSHviLi AND A N D R O N i K A S H V i L i
221
properties of zeolites X a n d Y a p p a r e n t l y is c a u s e d b y the f a c t
that
l a n t h a n u m ions o c c u p y s t r o n g l y screened positions i n zeolite Y . T h e kinetics o f w a t e r v a p o r a d s o r p t i o n has b e e n s t u d i e d at 25 ° C (j a n d the r e l a t i v e c o n c e n t r a t i o n of the w a t e r v a p o r = 0.10 ( C = 23.1 0
m g / 1 ) , u s i n g a s o d i u m zeolite of t y p e A ( n = l i t h i u m ( d e g r e e of exchange a = (a =
0 . 2 2 ) , a n d c e s i u m (a =
1.95), a n d o b t a i n e d f r o m i t
0 . 6 0 ) , p o t a s s i u m (a =
0.40), r u b i d i u m
0.27) f o r m s . T h e k i n e t i c c u r v e a =
f(t)
f o r t h e s o d i u m f o r m is the highest, w h i l e the l o w e s t is f o r c e s i u m zeolite. C a l c u l a t i o n s of the effective d i f f u s i o n coefficients a c c o r d i n g to D . P . T i m o fejev (27)
s h o w t h a t these values g r a d u a l l y decrease f r o m t h e s o d i u m
zeolite to the c e s i u m one.
D
E
· 10 c m / s e c 7
2
NaA
LiNaA
KNaA
RbNaA
CsNaA
9.0
7.0
6.5
6.3
5.8
T h e d a t a s h o w that a n a p p r e c i a b l e decrease of s o r p t i o n a n d its rate take p l a c e w i t h increase i n the c a t i o n r a d i u s .
W e obtained a smaller
v a l u e f o r the d i f f u s i o n coefficient of the l i t h i u m f o r m t h a n f o r s o d i u m zeolite.
S u c h a result m a y b e c a u s e d b y a strong h y d r a t i o n of l i t h i u m
i o n that does n o t a l l o w , u n d e r t h e u s u a l c o n d i t i o n s of d e h y d r a t i o n , c o m p l e t e e l i m i n a t i o n of w a t e r m o l e c u l e s i n a l i t h i u m zeolite. M a y b e t h e d a t a (38)
i n d i c a t i n g that the effective d i a m e t e r of w i n d o w s i n l i t h i u m
Figure 3. Isotherms of adsorption of benzene vapors on the original sodium zeolite Y (1) and lanthanum forms (2,3, and 4). (2) a — 0.31; (3) a = 0.59;
(4)a
=
0.64.
222
M O L E C U L A R SIEVE
zeolites t y p e A is close to 3 A is c a u s e d b y this fact.
ZEOLITES
II
W e have not ob
s e r v e d s u c h a n a p p r e c i a b l e i n f l u e n c e o n s o r p t i o n rate f o r t y p e X zeolites w h e n s o d i u m i o n is r e p l a c e d b y cations of other a l k a l i metals.
Appar
e n t l y , this is d e t e r m i n e d b y a n essential difference i n the diameters e n t e r i n g " w i n d o w s " of zeolites of t y p e A ( 3 - 5 A ) a n d t y p e Χ
of
(8-9A).
C a t i o n s o c c u p y i n g positions i n the e n t e r i n g " w i n d o w s " of z e o l i t e A p r o b a b l y decrease t h e i r effective d i a m e t e r (14),
c a u s i n g a decrease of
the d i f f u s i o n coefficients. A m i x t u r e of h y d r o c a r b o n gases C i - C , c a r b o n m o n o x i d e , a n d h y 4
d r o g e n w a s u s e d as a m o d e l m i x t u r e f o r c h r o m a t o g r a p h i c studies. Zeolites of t y p e N a X a n d N a Y h a v e p r a c t i c a l l y i d e n t i c a l structure, b u t differ f r o m e a c h other b y the n u m b e r of cations p e r u n i t c e l l . A d e crease of c a t i o n d e n s i t y i n a zeolite takes p l a c e b e c a u s e of d e c a t i o n i z a t i o n of the positions S . m
A s o u r d a t a s h o w ( T a b l e I ), the values of the r e t e n t i o n v o l u m e s of a l l s t u d i e d c o m p o u n d s w e r e decreased w i t h a decrease of the t o t a l n u m b e r of cations p e r u n i t c e l l . T h e r e are 84 N a p e r u n i t c e l l for N a X a n d +
62 N a
+
f o r N a Y . T h e values of the r e t e n t i o n v o l u m e s for
o n h y d r o g e n a n d d e c a t i o n i z e d f o r m s also are d e c r e a s e d T h e m a x i m u m r e p l a c e m e n t of N a b y N H +
4
was 7 5 % .
+
components
(3). A t such an
exchange, r e p l a c e m e n t of cations a p p a r e n t l y takes p l a c e m a i n l y o n the sites S
n
and S
(25).
i n
T h e values of the r e t e n t i o n v o l u m e s o n the h y d r o g e n f o r m w i t h 3 5 % r e p l a c e m e n t of N a b y N H +
4
+
, w h e r e the S
m
sites are p r o b a b l y v a
cant, a p p r o a c h the values o b t a i n e d for z e o l i t e N a Y . T h e h i g h e r the re p l a c e m e n t of N a b y N H +
4
+
is, the greater decrease of the r e t e n t i o n v o l u m e s
f o r a l l s t u d i e d c o m p o n e n t s is o b s e r v e d . R e f . 22.
S i m i l a r results are o b t a i n e d i n
S u c h a decrease of r e t e n t i o n v o l u m e s o n these f o r m s m a y b e
c a u s e d b y a decrease of the c a t i o n c o n c e n t r a t i o n p e r u n i t c e l l ( the sites S and
S
in
become vacant)
zeolite structure. Table I. Specific Retention Volumes of Hydrocarbon Gases C i — C and C O , Expressed at Flowmeter Temperature, 2 0 ° C Components Methane Ethane Propane Butane Carbon monoxide Ethylene Propylene
Column Temp., °C
n
a n d p e r h a p s b y a p a r t i a l d e s t r u c t i o n of the
HX,
35%
DcX,
35%
HX,
4
DcX,
75%
75%
NaX
NaY
25 80 140 140
25.9 56.0 67.0 194.0
14.3 25.4 20.8 118.9
14.6 29.2 34.0 131.2
16.4 32.0 40.8 148.1
3.9 8.1 9.1 37.2
5.0 8.7 10.1 37.4
25 140 200
63.8 62.9 71.1
25.7 20.8 47.3
27.0 26.4 54.3
31.0 32.4 59.2
4.9 5.2
7.5 6.7
c
-
c
-
57.
TsiTsiSHViLi AND A N D R O N i K A S H V i L i
«V
Influence of Zeolite Cation
223
U N Q X (9Ι·/Ο)
4
3
3 2 λ 0
2
4
G 16
2
18 20 min
4
G S
10 ro.ii
Figure 4. Order of elution of methane and carbon monoxide on type X zeolites containing either sodium or lithium; 1 = hydro gen, 2 = methane, 3 = carbon monoxide. The carrier gas is air; rate is 100 ml/min; column temperature is 25° C. CSNQX(5*%)
RINQK(5/%) 3
5
ζ
8 IQm.n
2
2
4
G S
i0 mm
Figure 5. Order of elution of methane and carbon monoxide on potassium, rubidium, and cesium type X zeolites; 1 = hydrogen, 2 — methane, 3 = car bon monoxide. The carrier gas is air; rate is 100 ml/min; column tempera ture is 25°C. A n increase i n the values of r e t e n t i o n v o l u m e s of c o m p o u n d s o n d e c a t i o n i z e d zeolites m a y b e e x p l a i n e d b o t h b y a stronger d e h y d r a t i o n o f t h e r e m a i n i n g s o d i u m cations a n d b y a p o s s i b l e f o r m a t i o n of a c t i v e three-coordinate a l u m i n u m groups. A n increase of t h e d i s p e r s i o n p a r t of interactions takes p l a c e w i t h enrichment of the cation electron shell, w h i l e the smaller the cation radius is—i.e., t h e h i g h e r t h e c o n c e n t r a t i o n of t h e p o s i t i v e c h a r g e — t h e
more
p r o n o u n c e d t h e electrostatic i n t e r a c t i o n is. T h i s m a y b e i l l u s t r a t e d t a k i n g the
e x a m p l e of s e p a r a t i o n of t h e m i x t u r e
hydrogen-methane-carbon
m o n o x i d e o n t y p e X zeolites w i t h a l k a l i m e t a l cations. A m e t h a n e m o l e c u l e , i n contrast to that o f c a r b o n m o n o x i d e , has n o dipole a n d quadrupole moment.
F o r l i t h i u m a n d s o d i u m f o r m s of a
z e o l i t e , t h e f o l l o w i n g o r d e r o f e l u t i o n is c h a r a c t e r i s t i c :
methane-carbon
m o n o x i d e ( F i g u r e 4 ). O n t h e specimens w i t h a h i g h degree of r e p l a c e m e n t of N a b y K , +
+
a p a r t i a l s e p a r a t i o n o f t h e c o m p o n e n t s takes p l a c e , b u t w i t h the i n v e r s e s e q u e n c e o f e l u t i o n . S e p a r a t i o n of m e t h a n e a n d c a r b o n m o n o x i d e p r o ceeds also w i t h i n v e r s e e l u t i o n o n zeolites c o n t a i n i n g e i t h e r
rubidium
or c e s i u m . M o r e c o m p l e t e s e p a r a t i o n of these c o m p o u n d s is character istic f o r c e s i u m f o r m ( F i g u r e 5 ).
224
M O L E C U L A R
SIEVE
ZEOLITES
Π
B o t h the extent o f c a t i o n exchange a n d the t e m p e r a t u r e of c h r o m a t o g r a p h i c c o l u m n h e a t i n g ( J , 2, 4, 29, 30, 31, 33) influence t h e o r d e r o f e l u t i o n o f different components. T e m p e r a t u r e rise leads to a n a p p r e c i a b l e decrease o f i o n - d i p o l e interactions.
Thus, on a specimen w i t h the re
p l a c e m e n t of N a b y K e q u a l to 2 6 % at 25 ° C , the v a l u e of the r e t e n t i o n +
+
v o l u m e f o r c a r b o n m o n o x i d e is greater t h a n f o r m e t h a n e , the same as o n N a X . H o w e v e r , s e p a r a t i o n of the components does not take p l a c e . T h e rise o f the c o l u m n t e m p e r a t u r e to 40 ° C leads to a l i g n m e n t of t h e values of t h e r e t e n t i o n v o l u m e s . F u r t h e r rise of the c o l u m n t e m p e r a t u r e
leads
to i n v e r s i o n o f e l u t i o n o r d e r f o r these c o m p o u n d s , w i t h their s e p a r a t i o n o n l y at 8 0 ° C .
O n the s p e c i m e n w i t h r e p l a c e m e n t of N a b y K +
+
( 4 8 % ),
t h e inverse e l u t i o n sets u p at r o o m t e m p e r a t u r e ; h o w e v e r , i t is f o l l o w e d b y s e p a r a t i o n o n l y at 6 0 ° C . A s to the f o r m w i t h a h i g h content of potas s i u m cations, at 16 ° C the r e t e n t i o n v o l u m e of m e t h a n e is c o n s i d e r a b l y h i g h e r t h a n the r e t e n t i o n v o l u m e of c a r b o n m o n o x i d e , a n d therefore s e p a r a t i o n m a y take p l a c e at the t e m p e r a t u r e m e n t i o n e d a b o v e
(Figure
6 ) and higher. T h e n a t u r e of a c a t i o n influences the sequence o f e l u t i o n of different p a i r s of h y d r o c a r b o n s ; f o r e x a m p l e , ethylene o n N a X is e l u t e d p r o p a n e at t h e c o l u m n t e m p e r a t u r e o f 8 0 ° - 1 0 0 ° C .
When
after
temperature
rises to 1 2 0 ° - 1 4 0 ° C , there is n o a p p r e c i a b l e s e p a r a t i o n of these c o m ponents.
A t 160 ° C
a n d h i g h e r , separation of the m i x t u r e p r o p a n e -
Figure 6. Separation of the mix ture of hydrogen-methane-carbon monoxide on type X potassium zeo lites. The carrier gas rate is 100 m l / min; column temperature is 80°C. 1 = NaX, 2 = KNaX (degree of exchange of Na by K is 26% ), 3 = KNaX (degree of exchange of Na by K is 48% ), and 4 = KNaX (degree of exchange of Na by K is 84% ). +
+
+
+
+
+
57.
TsiTSisHviLi AND ANDRONiKASHviLi
Influence of Zeolite Cation
225
e t h y l e n e p r o c e e d s w i t h the i n v e r s e sequence o f e l u t i o n . O n a z e o l i t e w i t h 9 1 % r e p l a c e m e n t of N a b y L i at a n y t e m p e r a t u r e of t h e c o l u m n +
+
h e a t i n g , p r o p a n e is e l u t e d first a n d t h e n e t h y l e n e . O n p o t a s s i u m , r u b i d i u m , a n d c e s i u m f o r m s , after e a c h
saturated
c o m p o u n d a n u n s a t u r a t e d o n e is e l u t e d w i t h the same n u m b e r of c a r b o n atoms i n a m o l e c u l e .
T h e f o l l o w i n g sequence
o f e l u t i o n is o b s e r v e d :
methane-ethane—ethylene—propane-propylene-butane—butylène. S u c h cations as s o d i u m a n d l i t h i u m s h o w a greater a b i l i t y to r e t a i n a c o m p o u n d c h a r a c t e r i z e d b y 7r-bonds t h a n l a r g e r cations
(potassium,
rubidium, cesium). T h e c a t i o n a c t i o n is n o t a l w a y s v e r y s t r o n g . It d e p e n d s o n t h e ar r a n g e m e n t of cations i n the c r y s t a l l a t t i c e of a zeolite a n d h e n c e b o t h o n the degree of c a t i o n s c r e e n i n g b y o x y g e n atoms of t h e lattice a n d o n t h e degree of its h y d r a t i o n . T h u s , f o r e x a m p l e , o n a z e o l i t e c o n t a i n i n g l i t h i u m cations at 4 7 % r e p l a c e m e n t o f N a b y L i , a decrease o f t h e r e t e n t i o n +
+
v o l u m e s a n d heats o f a d s o r p t i o n takes p l a c e f o r u n s a t u r a t e d h y d r o c a r bons a n d c a r b o n m o n o x i d e i n s t e a d o f t h e e x p e c t e d increase.
Only an
increase o f t h e degree of exchange to 8 7 % a n d h i g h e r leads to a g r a d u a l increase of the a b o v e q u a n t i t i e s , w h i c h at t h e m a x i m u m L i
+
content
exceeds the values c o r r e s p o n d i n g to these q u a n t i t i e s o n N a X . Table II.
Ratio of Heats of Adsorption
D e g r e e of R e p l a c e m e n t of N a + b y Li+ % QC H /QC H 2
4
2
6
QC H4/QC H6 2
2
5
QC H /QC3H8
0
5
22
43
87
91
1.45
1.38
1.37
1.36
1.75
1.88
3
6
NaX LiX 1.44 1.24
QC H /QC3H 3
6
In
1.38
8
Table
I I , t h e ratios
(?propyiene/Qpro ane P
a
r
e
1.26
1.29
1.29
1.49
o f a d s o r p t i o n heats
(20)
(20)
1.83
Qethyiene/Qethane
and
g i v e n o n N a X a n d zeolites w i t h d i f f e r e n t content
of L i , as w e l l as t h e d a t a o b t a i n e d i n (20). +
T h e r a t i o o f heats is h i g h e r
f o r the s p e c i m e n s w i t h h i g h L i content i n c o m p a r i s o n w i t h N a X . +
A t h i g h degree o f exchange, L i cations are l o c a t e d i n t h e least h y +
d r a t e d sites (25).
S u c h sites m a y b e Si, S/, S u ' (26).
B e c a u s e of t h e i r
l o c a t i o n i n the s c r e e n e d p o s i t i o n s , t h e y i n t e r a c t w e a k l y w i t h m o l e c u l e s of a d s o r b e d substances b u t , as u n d e r t h e a c c e p t e d c o n d i t i o n s of t h e r m a l a c t i v a t i o n other cations are s u r r o u n d e d b y w a t e r m o l e c u l e s , one m a y assume that just these cations f o r m the m a i n centers r e s p o n s i b l e f o r t h e increase o f b o t h r e t e n t i o n v o l u m e s a n d h e a t a d s o r p t i o n of u n s a t u r a t e d compounds a n d carbon monoxide. F r o m the a b o v e a n d other d a t a o n p h y s i c o - c h e m i c a l p r o p e r t i e s o f zeolites, i t f o l l o w s that f o r m o l e c u l a r sieves w i t h one-charge cations, o n e
226
M O L E C U L A R SIEVE
ZEOLITES
Π
observes b o t h some s i m i l a r i t y a n d some d i s c r e p a n c y . T h e same c o n c l u s i o n m a y b e m a d e f o r zeolites w i t h t w o - a n d three-charge
cations.
E a c h c a t i o n f o r m o f a z e o l i t e , i n t h e r e g i o n o f s t a b i l i t y o f t h e i r struc t u r e a n d c o m p o s i t i o n , is a n i n d i v i d u a l fine p o r o u s b o d y r e p r e s e n t i n g c o n s i d e r a b l e interest f o r d e t a i l e d studies.
Literature Cited (1) Andronikashvili, T. G., Sabelashvili, Sh. D., Mater. All-Onion Conf. Zeo lites, 1st, Akad. Nauk SSSR, Moscow, 1962, 65. (2) Andronikashvili, T. G., Sabelashvili, Sh. D., Tsitsishvili, G. V., Neftekhimiya 1962, 248. (3) Andronikashvili, T. G., Tsitsishvili, G. V., Sabelashvili, Sh. D., Bull. Acad. Sci. Georg. SSR 1969, 56, 113. (4) Andronikashvili, T. G., Tsitsishvili, G. V., Sabelashvili, Sh. D., Chumburidze, Τ. Α., Mater. All-Union Conf. Zeolites, 2nd, Nauka, MoscowLeningrad, 1965, 179. (5) Barrer, R. M., Meier, W. M., Trans. Faraday Soc. 1958, 54, 1074. (6) Baur, W. H., Am. Mineralogist 1964, 49, 697. (7) Bennet, I. M., Smith, I. V., Mater. Res. Bull. 1968, 3, 633. (8) Bosacek, V., Symp. Mol. Sieves, London, April 1967. (9) Breck, D. W.,J.Chem. Educ. 1964, 41, 678. (10) Breck, D. W., Flanigen, Ε. M., Symp. Mol. Sieves, London, April 1967. (11) Broussard, L., Shoemaker, D. P.,J.Am. Chem. Soc. 1960, 82, 1041. (12) Dubinin, M. M., Dokl. Akad. Nauk SSSR 1961, 138, 866. (13) Ibid., 1964, 159, 166. (14) Ibid., 1966, 168, 860. (15) Dubinin, M.M.,Izv. Akad. Nauk SSSR, Ser. Khim. 1961, 1192. (16) Eberly, P. E., Jr., J. Phys. Chem. 1961, 65, 69. (17) Ibid., 1962, 66, 812. (18) Eulenberger, G. R., Shoemaker, D. P., Keil, I. G., J. Phys. Chem. 1967, 71, 1812. (19) Habgood, H. W., Can. J. Chem. 1964, 42, 2340. (20) Habgood, H. W., Chem. Eng. Progr. Symp. Ser. 1967, 63, 45. (21) Kiselev, Α. V., Cheren'kova, Yu. L., Yashin, Ya. I., Neftekhimia 1965, 1, 141. (22) Neddenriep, R. S.,J.Colloid Interface Sci. 1968, 28, 293. (23) Olson, D. H., Kokotailo, G. T., Charnell, J. F., Natl. Colloid Symp., 41st, Buffalo, Ν. Y., 1967. (24) Reed, T. B., Breck, D. W., J. Am. Chem. Soc. 1956, 78, 5972. (25) Sherry, H. S.,J.Phys. Chem. 1966, 70, 1158. (26) Smith, J. V., Bennett, I. M., Flanigen, Ε. M., Nature 1967, 215, 5098, 241. (27) Timofejev, D. P., Erashko, I. T., Izv. Akad. Nauk SSSR, Ser. Khim. 1961, 1192. (28) Tsitsishvili, G. V., Andronikashvili, T. G., Mater. All-Union Conf. Zeo lites, 1st, Akad. Nauk SSSR, Moscow, 1962, 117. (29) Tsitsishvili, G. V., Andronikashvili, T. G., Sabelashvili, Sh. D., Chkheidze, S. S., Neftekhimiya 1967, 305. (30) Tsitsishvili, G. B., Andronikashvili, T. G., Sabelashvili, Sh. D., Koridze, Ζ. I., Bull. Akad. Sci. Georg. SSR 1967, 46, 611. (31) Tsitsishvili, G. V., Andronikashvili, T. G., Sabelashvili, Sh. D., Urotadze, S. L., Neftekhimiya 1969, 790.
57. TSITSISHVILI AND
ANDRONIKASHVILI
Influence of Zeolite Cation
227
(32) Tsitsishvili, G. V., Bagratishvili, G. D., Avaliani, Κ. E., Andronikashvili, T. G., Barnabishvili, D. N., Intern. Congr. Pure Appl. Chem., 20th, A23, USSR, Moscow, 1965. (33) Tsitsishvili, G. V., Krupennikova, A. Yu., Andronikashvili, T. G., Urotadze, S. L., Bull. Akad. Nauk Georg. SSR 1969, 54, 581. (34) Tsitsishvili, G. V., "Surface Phenomena of Aluminosilicates," p. 5-15, Mecniereba Publ., Tbilisi, 1965. (35) Ward, J. W.,J.Catalysis 1967, 9, 225, 396. (36) Ibid., 1968, 10, 34. (37) Wolf, F., Furtig, H., Symp. Mol. Sieves, London, April 1967. (38) Wolf, F., Furtig, H., Tonind. Ztg. Keram. Rundschau 1966, 90, 297. (39) Wolf, F., Hadicke, U., Tonind. Ztg. Keram. Rundschau 1967, 91, 45. RECEIVED January 23, 1970.
Discussion G . C . Blytas ( S h e l l D e v e l o p m e n t C o . , O a k l a n d , C a l i f . 94623): Y o u r d a t a o f r e t e n t i o n v o l u m e s refer t o l o w degree o f coverage of sorbent. W o u l d y o u care to c o m m e n t o n t h e s e p a r a t i o n factors, f o r e x a m p l e b e t w e e n ethylene a n d ethane, at h i g h e r G . Tsitsishvili:
coverages?
O u r studies o f zeolite c h r o m a t o g r a p h i c
properties
i n d i c a t e d that t h e r e t e n t i o n v o l u m e s , s e p a r a t i o n factors, a n d other c h a r acteristics are strongly d e p e n d e n t o n c a t i o n n a t u r e , degree of exchange, a n d temperature.
W e h a v e o b s e r v e d t h e i n v e r s i o n o f t h e sequence o f
e l u t i o n b y t e m p e r a t u r e alteration. J . D . Eagan ( M c M a s t e r U n i v e r s i t y , H a m i l t o n , O n t a r i o , C a n a d a ) : Is there a n e x p l a n a t i o n f o r t h e decrease i n ^ °
2 H 4
, f o r l o w degrees of L i
VC2H6
exchange, w i t h i n c r e a s i n g L i exchange? +
G . Tsitsishvili: I n t e r a c t i o n o f L i w i t h m o l e c u l e s o f u n s a t u r a t e d h y +
d r o c a r b o n s a n d C O is v e r y sensitive to t h e presence of w a t e r m o l e c u l e s i n a z e o l i t e a n d t o c o l u m n t e m p e r a t u r e increase.
O n a zeolite containing
h y d r o p h i l i c l i t h i u m cations, w i t h most o f t h e substitutions c o r r e s p o n d i n g to L i i n o p e n positions S +
n
and S
m
, t h e a d s o r p t i o n heat o f t h e s t u d i e d
c o m p o u n d s is l o w e r t h a n w i t h t h e s o d i u m f o r m . I n l i t h i u m forms w i t h a h i g h percentage o f l i t h i u m ions, t h e L i i n n o n h y d r a t e d positions i n f l u +
ence adsorbate
m o l e c u l e s , c a u s i n g a n increase
c o m p a r i s o n w i t h N a X zeolite.
o f a d s o r p t i o n heat i n
M i g r a t i o n of L i ions f r o m Si to other +
positions is also possible. J. R. Katzer ( U n i v e r s i t y o f D e l a w a r e , N e w a r k , D e l . 19711): I w a s interested i n t h e c o m m e n t i n y o u r p a p e r that y o u o b s e r v e d a v a r i a t i o n i n t h e rate o f s o r p t i o n w i t h a c h a n g e i n t h e c a t i o n present i n t h e t y p e X zeolite. H o w m u c h v a r i a t i o n d i d y o u find, a n d h o w w e r e y o u r rates o f adsorption determined?
+
228
MOLECULAR
G . T s i t s i s h v i l i : T h e v a r i a t i o n was a b o u t 2 0 - 3 0 %
SIEVE
ZEOLITES
II
at the t r a n s i t i o n
f r o m the s o d i u m to other f o r m s . Rates of a d s o r p t i o n w e r e m e a s u r e d b y f o l l o w i n g the w e i g h t of pellets d u r i n g u p t a k e . F. W o l f ( M a r t i n Luther University, Halle/Salle, Germany, D D R ) : T s i t s i s h v i l i ' s results that there are m a x i m a a n d m i n i m a i n the curves f o r the a d s o r p t i o n amounts as f u n c t i o n s of the degree of i o n exchange w e r e r e p o r t e d at the M o l e c u l a r Sieves
Conference
i n L o n d o n , 1967.
This
seems to b e the general b e h a v i o r of m o l e c u l a r sieves w h e n a d s o r b i n g molecules.
