Process for the preparation of a molecular sieve adsorbent for selectively adsorbing oxygen from a gaseous mixture

The invention relates to the manufacture of novel molecular sieve adsorbents which are selective towards oxygen from its gaseous mixture with argon and/or nitrogen. More particularly, this invention relates to the manufacture of novel molecular sieve adsorbents useful for the separation of oxygen-argon-nitrogen gaseous mixture.

The invention relates to the manufacture of novel molecular sieve 
adsorbents which are selective towards oxygen from its gaseous mixture 
with argon and/or nitrogen. More particularly, this invention relates to 
the manufacture of novel molecular sieve adsorbents useful for the 
separation of oxygen-argon-nitrogen gaseous mixture. 
BACKGROUND OF THE INVENTION 
Adsorption processes for the separation of oxygen and nitrogen from air are 
being increasingly used for commercial purposes for the last two decades. 
Presently, 4-5% of the world's oxygen demand is met by adsorptive 
separation of air. However, the maximum attainable oxygen purity 
by-adsorption processes is around 95%. Separation of 0.934 mole percent 
argon present in the air from oxygen being a limiting factor to achieve 
100% oxygen purity by adsorption methods. However, there are many 
situations where high purity oxygen (&gt;99%) is desired. For example, the 
efficiency of welding and cutting processes using oxygen is greatly 
dependent upon the purity of oxygen available. For these applications, 
purity of at least 99.5% oxygen is customarily specified. Furthermore, 
oxygen-argon separation is also needed for purification of argon produced 
during cryogenic separation of oxygen and nitrogen from air. The crude 
argon (95-97%) produced in such processes will have nitrogen and oxygen 
and is required to be further purified. Presently high purity argon 
(99.999%) is produced by catalytic hydrogen combustion or low temperature 
oxygen adsorption in a synthetic zeolite. 
Oxygen and argon gaseous mixture is difficult to separate due to closeness 
in their physical properties. At present, commercially this is done by 
cryogenic fractionation techniques. The boiling points of oxygen 
(-182.97.degree.), argon (-185.9.degree. C.) and nitrogen (-195.8.degree. 
C.) being very low make these processes highly energy intensive. Thus, it 
is desired to develop a commercially attractive separation process for 
oxygen-argon separation. Adsorption based process can compete with highly 
energy intensive cryogenic fractionation of oxygen/argon mixture if a 
suitable adsorbent which is selective towards one of the components and 
which possesses requisite adsorption capacity is commercially available. 
In the prior art, adsorbents which are selective for argon from its mixture 
with oxygen has been reported (PCT Int. Appl. 94. 06. 541. Mar. 31, 1994) 
by impregnation of silver in commercial zeolites. However, the adsorption 
selectivity reported for argon is less than 2 in these adsorbents making 
it commercially unattractive. Oxygen with purity &gt;99% has been produced 
(U.S. Pat. No. 4,813,979, 1989) by using carbon molecular sieve adsorbent 
in which argon is selectively adsorbed due to its smaller kinetic diameter 
of 3.40A.degree. compared to 3.46A.degree. of oxygen. However, there are 
no reports on the development of adsorbent which is selective towards 
oxygen from its mixture with argon in the literature. The present 
invention deals with the development of synthetic zeolite based oxygen 
selective adsorbents which can for the first time separate oxygen from a 
gaseous mixture of oxygen and argon. 
Adsorption processes are also being used on a commercial scale for the 
production of nitrogen from air. These processes employ carbon molecular 
sieve type adsorbents in which oxygen diffuses faster than nitrogen 
resulting in the separation of the two components. Some efforts to develop 
zeolite type adsorbents for these applications have also been reported in 
the literature wherein the differences in the diffusion of oxygen and 
nitrogen have been used to achieve oxygen adsorption selectivity. It is 
desired to develop a zeolite based adsorbent which can result in the 
oxygen adsorption selectivity due to difference in equilibrium adsorption 
of oxygen and air. 
The characteristics which are highly desirable, if not absolutely 
essential, for an adsorbent to be suitable for selective adsorption 
process include adsorption capacity of the adsorbent and adsorption 
selectivity for a particular component. 
Adsorption capacity of the adsorbent is defined as the amount in terms of 
volume or weight of the desired component adsorbed per unit volume or 
weight of the adsorbent. The higher the adsorbent's capacity for adsorbing 
the desired component the better the adsorbent is as the increased 
adsorption capacity of a particular adsorbent helps to reduce the amount 
of adsorbent required to separate a specific amount of a component from a 
mixture of particular concentration. Such a reduction in adsorbent 
quantity in a specific adsorption process brings down the cost of a 
separation process. 
Adsorption selectivity of component A over B is defined as 
EQU O.sub.AB =X.sub.A Y.sub.B /Y.sub.A X.sub.B 
where O is adsorption selectivity, X is the adsorbed concentration and Y is 
gas-phase concentration. The expression gas-phase concentration means the 
amount of unadsorbed component remaining in the gas-phase. The adsorption 
selectivity of a component depends on 
steric factors such as difference in the shape and see of the adsorbate 
molecules; 
equilibrium effect, i.e., when the adsorption isotherms of the components 
of the gas mixture differ appreciably; 
kinetic effect, when the components have substantially different adsorption 
rates. 
It is generally observed that for a process to be commercially economical, 
the minimum acceptable adsorption selectivity for the desired component is 
about 3 and when an adsorption selectivity is less than 2, it is difficult 
to design an efficient separation process. 
Zeolites which are microporous crystalline aluminosilicates are finding 
increased applications as adsorbents for separating mixtures of closely 
related compounds. Zeolites have a three dimensional network of basic 
structural units consisting of SiO.sub.4 and AlO.sub.4 tetrahedral linked 
to each other by sharing of apical oxygen atoms. Silicon and aluminum 
atoms lie at the center of the tetrahedral. The resulting aluminosilicate 
structure which is generally highly porous possesses three dimensional 
pores the access to which is through molecular sized windows. In a 
hydrated form, the preferred zeolites are generally represented by the 
following Formula [I] 
EQU M.sub.2/n O:Al.sub.2 O.sub.3 :xSiO.sub.2 :wH.sub.2 O [I] 
where "M" is a cation which balances the electrovalence of the tetrahedral 
and is generally referred to as extra framework exchangeable cation, n 
represents the valency of the cation, x and w represent the moles of 
SiO.sub.2 and water respectively. The cations may be any one of the number 
of cations which will hereinafter be described in detail. 
The attributes which make them attractive for separation include, an 
unusually high thermal and hydrothermal stability, uniform pore structure, 
easy pore aperture modification and substantial adsorption capacity even 
at low adsorbate pressures. Furthermore, zeolites can be produced 
synthetically under relatively moderate hydrothermal conditions. 
Zeolite of type X structure as described and defined in U.S. Pat. No. 
2,882,244 are the preferred adsorbents for adsorption separation of the 
gaseous mixture described in this invention. Zeolite of type X in hydrated 
or partially hydrated form can be described in terms of metal oxide of 
Formula II 
EQU (0.9+/-0.2)M.sub.2/n O:Al.sub.2 O.sub.3 :(2.5+/-0.5)SiO.sub.2 :wH.sub.2 
O[II] 
where "M" represents at least one cation having valence n, w represents the 
number of moles of water the value of which depends on the degree of 
hydration of the zeolite. Normally, the zeolite when synthesized has 
sodium as exchangeable cations. 
Zeolites as such have very little cohesion and it is, therefore, necessary 
to use appropriate binders to produce the adsorbent in the form of 
particles such as extrudates, aggregates, spheres or granules to suit 
commercial applications. Zeolitic content of the adsorbent particle vary 
from 60 wt % to 100 wt % depending on the type of binder used. Clays such 
as bentonite, kaolin and attapulgite are normally used as inorganic 
binders for agglomeration of zeolite powders. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide adsorbents which can be 
used for the separation of oxygen-argon, oxygen-nitrogen and 
oxygen-nitrogen-argon gaseous mixtures. 
Yet another object of the present invention is to provide an oxygen 
selective adsorbent based on synthetic zeolites. 
Yet another object of the present invention is to provide an oxygen 
selective adsorbent by modification of surface characteristics of 
synthetic zeolites. 
Yet another object of the present invention is to provide an adsorbent with 
high adsorption selectivity and capacity for oxygen from its mixture with 
argon and/or nitrogen. 
Yet another object of the present invention is to provide an oxygen 
selective adsorbent which can be used commercially.

DESCRIPTION OF THE INVENTION 
According to the present invention, there is provided a molecular sieve 
adsorbent having a composition 
EQU x.M.sub.2/n O:y.Ce.sub.a O.sub.b :Al.sub.2 O.sub.3 :z. SiO.sub.2 :w.H.sub.2 
O 
where the value of 
x is from 0.0 to 0.8; 
y is from 0.06 to 0.50; 
a is from 1 to 2; 
b is from 2 to 3; 
z is from 2 to 5.5; 
M is alkali or alkaline earth metal ion such as lithium, sodium, potassium, 
calcium and w represents the number of moles of water. 
The initial zeolite, i.e. the starting material of the present invention 
may be prepared by any technique known in the art. Typically, (i) a 
mixture of Zeolite powder type X as described in U.S. Pat. No. 2,882,244 
or zeolite Y as described in U.S. Pat. No. 3,130,007 is prepared with a 
clay such as herein described and an organic binder such as herein 
described, (ii) adsorbent bodies of desired shape are formed or the 
adsorbent powder is subjected to cation exchange with one or more cations 
and then formed into adsorbent bodies, (iii) adsorbent bodies so formed 
are subjected to calcination (iv) the calcined adsorbent bodies are 
subjected to cation exchange with one or more cations if the cation 
exchange has been done in step (ii). 
The present invention employs the technique of modification of the surface 
properties of the adsorbent bodies by cation exchange with one or more 
cations to obtain oxygen selective adsorbent from gaseous mixture of 
oxygen and argon. 
The modification of the surface property, hereinafter referred to as 
surface modification is the most critical and important aspect of the 
invention. It is the very specific surface modification which renders the 
zeolite particularly selective towards oxygen. It has been surprisingly 
found that if zeolite at all x-type is treated with a cerium salt solution 
and/or a combination of cerium salt solution with lithium and/or calcium 
salt solution, it renders the zeolite particularly selective towards 
oxygen over argon. 
Accordingly, the present invention provides a process for the preparation 
of a molecular sieve adsorbent for selectively adsorbing oxygen from a 
gaseous mixture consisting of oxygen, nitrogen and/or an inert gas such as 
argon said process comprising: 
(a) preparing in any known manner a mixture of zeolite powder with 
conventional clay and organic binder; 
(b) shaping said zeolite mixture to obtain adsorbent bodies of desired 
shape; 
(c) subjecting adsorbent bodies to calcination; and 
(d) subjecting said adsorbent bodies either prior to or after calcination 
or both, to cationic exchange in the presence of at least a cerium salt 
solution to effect surface modification of said adsorbent bodies to obtain 
said molecular sieve adsorbent which is oxygen selective. 
While the aforesaid surface modification may be carried out at a wide range 
of temperature and concentration, excellent results are obtained if the 
surface modification supply is carried out with 1 to 10% by weight of the 
salt solution at a temperature of 30 to 100.degree. C. for 4 to 48 hrs. 
The adsorbent bodies are prepared from a mixture of zeolite of type X and 
clay powder with an addition of an organic binder like sodium 
lignosulfonate or starch or polyvinyl alcohol. Bentonite type clay 
preferably about 2 to 40% by weight is normally used for aggregation of 
zeolite powder. As the clay remains as an inert component in the adsorbent 
body and do not display any adsorption properties, the adsorption capacity 
and selectivity of the adsorbent body decreases in proportion to the 
amount of the clay added in the body. 
In a typical process for producing adsorbent pellets, zeolite powder of 
type X or type Y was mixed with desired quantity of clay. A known quantity 
of an organic binder like sodium lignosulfonate was added to this mixture 
which was then subjected to ball milling for some specified period to have 
powder particles less than 60 microns. The powder thus obtained was formed 
into bodies using a pan granulator or an extruder. The particles prepared 
by the above described method were first dried in air at room temperature 
(28 to 32.degree. C.) for about 6 to 18 hours followed by oven drying at 
110.degree. C. for 6 to 8 hours. The dried particles were subjected to air 
calcination at 450 to 700.degree. C. for 2-18 hours followed by aforesaid 
surface modification. 
The quantity of exchangeable cations in the adsorbent particles after the 
above treatment is determined by digesting the known amount of adsorbent 
particles in hot hydrochloric acid and then making the aqueous solution. 
The quantitative estimation of the cations in the aliquot solution is done 
by Atomic Absorption Spectroscopic measurement. 
The loss of crystallinity in the adsorbent particles, if any, was checked 
by comparing the X-ray diffraction data with literature X-ray data. The 
X-ray diffractions at `d` values 14.465, 8.845, 7.538, 5.731, 4.811, 
4.419, 3.946, 3.808, 3.765, 3.338, 3.051, 2.944, 2.885, 2.794 and 
2.743A.degree. were used for comparison. Water adsorption capacity data on 
the above treated adsorbent particles were also compared with a standard 
zeolite NaX. Water adsorption capacity was measured using a Mcbain-Bakr 
quartz spring balance. 
Oxygen/argon/nitrogen adsorption capacity and selectivity were measured by 
elution chromatography. In this technique, the adsorbent sample was ground 
and sieved to obtain 60-80 mesh particles and packed in a thoroughly 
cleaned 6.times.600 mm stainless steel column which was placed in an oven 
of a gas chromatography. In those cases where the starting material was 
zeolite powder, it was first pressed in to pellets in a hydraulic press to 
obtain compact particles and then ground and sieved to obtain 60-80 mesh 
particles. The adsorbent was activated by subjecting it to programmed 
heating from ambient to 400.degree. C. at the heating rate of 2.degree. 
C./minute and held at 400.degree. C. for 12 hours with the flow of 60 
ml/minute of ultra-high purity hydrogen. Alter the activation, the column 
temperature was brought down to ambient temperature and the hydrogen gas 
flow was reduced to 30 ml/minute. A 0.5 mL pulse of gas mixture consisting 
of oxygen, argon, nitrogen and helium in hydrogen was injected in to the 
adsorbent column using a sampling valve, and the retention times of gases 
measured. The procedure was repeated at 40, 50 and 60.degree. C. The 
column was equilibrated for at least 1 hour at each temperature before 
injecting the gas mixture. The corrected retention times were obtained by 
subtracting the helium retention time from those of oxygen, argon and 
nitrogen. In those cases where separation did not take place, retention 
times were measured by injecting individual gases. To check whether there 
was any contribution to measured retention time due to possible 
oxidation-reduction reactions, measurements without hydrogen were also 
done by using helium rather than hydrogen. The measured retention times 
were found within experimental errors indicating the absence of 
oxidation-reduction reactions. 
The corrected retention time was used to determine the Henry constant (i.e. 
a measure of equilibrium adsorption capacity of an adsorbent for a 
particular component), adsorption selectivity and heats of adsorption for 
oxygen and argon employing standard formulae described below: 
EQU Henry constant K/mmol. g.sup.-1.kPa.sup.-1 =V.sub.N /RT 
where R is a gas constant having value of 8.31451 JK.sup.-1 mol.sup.-1, T 
is the adsorbent column temperature in Kelvin and V.sub.N is the net 
retention volume per gram of adsorbent and is given by Net retention 
volume, 
EQU V.sub.N /cm.sup.3.g.sup.-1 =[Ft.sub.R j/(1-p.sub.w /P.sub.o)T/T.sub.R 
]/W.sub.s 
where F is carrier gas flow rate (ml/minute); t.sub.R is corrected 
retention time (minute); P.sub.w is water vapor pressure (kPa) at room 
temperature T.sub.R, T is the adsorbent column temperature in Kelvin, 
p.sub.o is column outlet pressure (KP.sub.a), W.sub.s, is active weight of 
the adsorbent present in the column and j is the compressibility 
correction given by the equation shown below 
EQU Compressibility correction, j=(3/2)[p.sub.i /p.sub.o).sup.2 -1)/(p.sub.i 
/p.sub.o)] 
where p.sub.i and p.sub.o are the column inlet and outlet pressures 
respectively. 
Adsorption selectivity .alpha.O.sub.2 /Ar=V.sub.n (O.sub.2)/V.sub.n (Ar) 
Heat of adsorption, -.DELTA.H.sub.o =R dln (V.sub.n /T)/d(1/T) 
In the formula -.DELTA.H.sub.o =R dln(V.sub.N /T)/d(1/T) the letter `d` 
represents the mathematical operation called `differentiation` and In 
presents `natual logarithm`. This can be alternatively written as follows: 
##EQU1## 
In fact, dln(V.sub.N /T)/d(1/T) represents the slope of the straight line 
plotted with 1/T as x-axis and V.sub.N /T as y-axis. T, V.sub.N and R are 
defined elsewhere in this specification. 
The uncertainties in the values of V.sub.n, .alpha.O.sub.2 /Ar and 
-.DELTA.H.sub.o as calculated using the method of propagation of errors 
from the known errors in the experimental parameters were +0.8, +1.6 and 
+1.8% respectively. 
The invention will now be illustrated with the help of typical Examples. It 
may be understood that the following Examples do not limit the scope of 
the invention. It is possible to work the invention outside the parameters 
specified in the following Examples. 
EXAMPLE-1 
Zeolite NaX powder (Na.sub.2 O:Al.sub.2 O.sub.3 :2.4SiO.sub.2 :w.H.sub.2 O) 
was prepared by the method described in U.S. Pat. No. 2,882,244. Water 
adsorption as given in Table 1 and X-ray diffraction data showed that the 
starting zeolite powder was highly crystalline. Adsorbent was evaluated 
for Oxygen/Argon adsorption capacity and selectivity by elution gas 
chromatography as per procedure detailed above. Oxygen and argon did not 
give separate chromatographic peaks showing thereby that these are not 
getting separated by the adsorbent in the column. Hence the retention time 
of oxygen and argon were measured separately. The adsorption data are 
given in Table 2. The data show that the adsorbent posses little oxygen 
selectivity (.varies.O.sub.2 /Ar=1.1) over argon. 
EXAMPLE-2 
Zeolite NaY powder (Na.sub.2 O:Al.sub.2 O.sub.3 :5.4.SiO.sub.2 :w.H.sub.2 
O) was prepared by the method described in the U.S. Pat. No. 3,130,007. 
Water adsorption as given in Table 1 as well as X-ray diffraction data 
showed that the starting zeolite powder is highly crystalline. Adsorbent 
was evaluated for Oxygen/Argon adsorption capacity and selectivity by 
elution gas chromatography as per procedure detailed above. Oxygen and 
argon did not show separate chromatographic peaks showing thereby that 
these are not getting separated by the adsorbent in the column. The 
retention times of oxygen and argon were measured separately. The 
adsorption data given in Table 2 show that the adsorbent does not possess 
oxygen selectivity (.varies.O.sub.2 /Ar=1.0) over argon. 
EXAMPLE-3 
Zeolite NaY powder prepared by the method described earlier was further 
treated with 1.5 wt % aqueous cerium (III) chloride at 95.degree. C. for 
48 hours. The solution was thereafter filtered and the solid was washed 
with hot distilled water until solution showed the absence of chloride in 
it. Equilibrium water adsorption capacity is given in Table 1 and X-ray 
diffraction data show that the zeolite structure is retained after cerium 
(III) chloride solution treatment. The elution gas chromatography data of 
thus prepared adsorbent, CeVP having chemical composition of 0.07.Na.sub.2 
O:0.31.Ce.sub.2 O.sub.3 :Al.sub.2 O.sub.3 :5.4.SiO.sub.2 :w.H.sub.2 O is 
as given in Table 2 (and show that the adsorbent is oxygen selective 
(.varies.O.sub.2 /Ar=1.5). 
EXAMPLE-4 
A mixture consisting of 800 g of zeolite NaX powder with chemical 
composition, Na.sub.2 O:Al.sub.2 O.sub.3 :2.4SiO.sub.2 :w.H.sub.2 O, 200 g 
of bentonite clay powder and 4 g of sodium lignosulfonate was ball milled 
for 1 hour and particles larger than 60 microns were removed by sieving. 
The ball milled mixture was then hand pugged by adding water and pugged 
mass was extruded though a die by a hand extruder. The extruded adsorbent 
was dried at room temperature for 10 hours and then at 110.degree. C. for 
6 hours. This was followed by calcination at 560.degree. C. for 4 hours. 
Water adsorption given in Table 1 on thus obtained adsorbent particles, 
NaXE show that the decrease in adsorption capacity compared to zeolite NaX 
powder is in proportion to bentonite amount in the adsorbent. X-ray 
diffraction data also supports the retention of zeolite structure. 
Adsorbent was evaluated for oxygen/argon/nitrogen adsorption capacity and 
selectivity by elution gas chromatography. Oxygen and argon did not show 
separation by the adsorbent. Hence, the retention times of oxygen and 
argon were measured independently. The adsorption data as given in Table 2 
show little selectivity towards oxygen over argon (.varies.O.sub.2 
/Ar=1.1). 
EXAMPLE-5 
40 g of zeolite NaX powder prepared by the method described earlier was 
treated with 1.4 wt % aqueous solution of cerium (III) chloride at 
95.degree. C. The solution was thereafter filtered and the solid was 
washed with hot distilled water until the solution showed the absence of 
chloride in it. The adsorbent was then dried in an air oven. Equilibrium 
water adsorption capacity is given in Table 1 and X-ray diffraction data 
shows that the zeolite structure is retained after cerium (III) chloride 
solution treatment. The chromatogram for the mixture of oxygen and argon 
eluted from this adsorbent at 30.degree. C. is shown in FIG. 1. The 
elution gas chromatography data of thus prepared adsorbent CeXP-1 having 
chemical composition as 0.09.Na.sub.2 O:0.30.Ce.sub.2 O.sub.3 :Al.sub.2 
O.sub.3 :2.4.SiO.sub.2 :w.H.sub.2 O given in Table 2 show that the 
adsorbent is oxygen selective with .varies.O.sub.2 /Ar and .varies.O.sub.2 
/N.sub.2 of 4.1 and 1.5 respectively. 
EXAMPLE-6 
The adsorbent obtained by the method as described in Example-4 was further 
treated with 1 wt % aqueous solution of cerium (III) chloride twice using 
the procedure described in Example-5. The adsorbent was, then dried at 
110.degree. C. Equilibrium water adsorption capacity as given in Table 1 
and X-ray diffraction data show that the zeolite structure is retained 
after cerium chloride treatment. The chromatogram for the mixture of 
oxygen and argon eluted from this adsorbent at 30.degree. C. is shown in 
FIG. 2. The elution gas chromatography data of thus prepared adsorbent, 
CeXP-3 having chemical composition, 0.04. Na.sub.2 O:0.32.Ce.sub.2 O.sub.3 
:Al.sub.2 O.sub.3 :2.4. SiO.sub.2 :w.H.sub.2 O given in Table 2 show that 
adsorbent is oxygen selective with .varies.O.sub.2 /Ar of 2.1. 
EXAMPLE 7 
The adsorbent obtained by the method as described in Example-5 was further 
treated with aqueous solution of 1 wt % cerium (III) chloride in a 5 liter 
flask in three stages employing the same procedure as given in Example-5. 
Thereafter the adsorbent was washed with hot distilled water until the 
solution showed the absence of chloride. The adsorbent was then dried at 
110.degree. C. for 6 hours. Equilibrium water adsorption capacity as given 
in Table 1 and X-ray diffraction data show that the zeolite structure is 
intact after cerium (III) chloride treatment. The chromatogram for the 
mixture of oxygen and argon eluted from this adsorbent at 30.degree. C. is 
shown in FIG. 3. The elution gas chromatography data of thus prepared 
adsorbent, CeXP-4, having chemical composition 0.02.Na.sub.2 
O:0.33.Ce.sub.2 O.sub.3 :Al.sub.2 O.sub.3 :2.4.SiO.sub.2 :w.H.sub.2 O 
given in Table 2 show that adsorbent is oxygen selective over argon with 
.varies.O.sub.2 /Ar of 3.8. 
EXAMPLE-8 
Zeolite NaX extrudates made using the method described in Example 4 were 
further treated with aqueous solution of 2 wt % cerium (III) chloride. The 
adsorbent was then washed with hot distilled water until the solution 
contained no traces of chloride in it. Thereafter the adsorbent was dried 
in an air oven. Equilibrium water adsorption capacity as given in Table 1 
and X-ray diffraction data show that the zeolite structure is retained 
after cerium chloride treatment. The chromatogram for the mixture of 
oxygen, nitrogen and argon eluted from this adsorbent at 30.degree. C. is 
shown in FIG. 4. The elution gas chromatography data of thus prepared 
adsorbent, CeXE, having chemical composition 0.07. Na.sub.2 
O:0.31.Ce.sub.2 O.sub.3 :Al.sub.2 O.sub.3 :2.4. SiO.sub.2 :w.H.sub.2 O 
given in Table 2 show that adsorbent is oxygen selective with 
.varies.O.sub.2 /Ar and (.varies.O.sub.2 /N.sub.2 of 5.9 and 2.0 
respectively. 
EXAMPLE-9 
The adsorbent bodies obtained by the method as described in Example-4 were 
further treated several times with lithium chloride solution (1% wt) to 
arrive at chemical composition of 0.02.Na.sub.2 O:0.98.Li.sub.2 O:Al.sub.2 
O.sub.3 :2.4.SiO.sub.2 :w.H.sub.2 O. The adsorbent LiXE, thus obtained was 
dried at 110.degree. C. for 6 hours in an air oven. The zeolite structure 
is retained after lithium chloride treatment as all the prominent 
diffractions present in pure zeolite X powder were present. The water 
equilibrium adsorption capacity is given in Table 1. The adsorption data 
given in Table 2 shows that adsorbent has very small selectivity 
(.varies.O.sub.2 /Ar of 1.3) for oxygen from its mixture with argon. 
EXAMPLE 10 
The adsorbent bodies having a chemical composition of 0.02.Na.sub.2 
O:0.98.Li.sub.2 O:Al.sub.2 O.sub.3 :2.4.SiO.sub.2 :w.H.sub.2 O prepared 
using the method Example-9 were further treated with 1 wt % aqueous cerium 
(III) chloride solution at 95.degree. C. The adsorbent was then washed 
with hot distilled water until all the chloride is removed and dried in am 
air oven. The zeolite structure, LiCeXE, thus obtained having a chemical 
composition of 0.18Li.sub.2 O.0.27Ce.sub.2 O.sub.3.Al.sub.2 
O.sub.3.2.4SiO.sub.2.wH.sub.2 O was retained after the above treatment as 
all the prominent diffractions present in pure zeolite X powder were 
present. The water equilibrium adsorption capacity is given in Table 1. 
The adsorption data given in Table 2 shows that adsorbent is oxygen 
selective over argon with .varies.O.sub.2 /Ar of 4.1. 
EXAMPLE-11 
100 g of the adsorbent extrudates prepared by the method as described in 
Example-4 were treated with 10 wt % aqueous solution of potassium chloride 
in a one liter round bottomed flask at 95.degree. C. The solution was 
thereafter decanted and the adsorbent was washed with hot distilled water 
until the decanted solution showed the absence of chloride. The adsorbent 
was then dried in an air oven. The zeolite structure is retained after 
potassium chloride treatment as all the prominent diffractions typical of 
pure zeolite X powder are present. The water equilibrium adsorption 
capacity is given in Table 1. The elution gas chromatography data of thus 
prepared adsorbent, KXE, having chemical composition of 0.39.Na.sub.2 
O:0.61.K.sub.2 O: 0.61.K.sub.2 O:Al.sub.2 O.sub.3 :2.4. SiO.sub.2 
:w.H.sub.2 O given in Table 2 does not show selectivity for oxygen over 
argon with .varies.O.sub.2 /Ar of 1.1. 
EXAMPLE-12 
The adsorbent extrudates obtained by the method as described in Example-4 
were further refluxed with 10 wt % aqueous calcium chloride solution in 
three stages. The solution was thereafter decanted and the adsorbent was 
washed with hot distilled water until all the chloride is removed. The 
adsorbent thus obtained CaXE, had a chemical composition of 0.07.Na.sub.2 
O:0.93CaO:Al.sub.2 O.sub.3 :2.4. SiO.sub.2 :w.H.sub.2 O. The zeolite 
structure was intact after calcium chloride treatment as all the prominent 
diffractions present in pure zeolite K powder are present. The water 
equilibrium adsorption capacity is given in Table 1. The adsorption data 
given in Table 2 shows that adsorbent has very small oxygen selectivity 
with .varies.O.sub.2 /Ar of 1.3. 
EXAMPLE-13 
The adsorbent bodies having a chemical composition of 0.07.Na.sub.2 
O:0.93.CaO:Al.sub.2 O.sub.3 :2.4. SiO.sub.2 :w.H2O prepared using the 
method described in Example-12 were further treated with lwt% aqueous 
cerium chloride solution at 95.degree. C. The adsorbent was then washed 
with hot distilled water until all the chloride is removed and dried in 
air oven. The zeolite structure, CaCeXE, thus obtained had a chemical 
composition of 0.15CaO:0.28Ce.sub.2 O.sub.3 :Al.sub.2 O.sub.3 
:2.4.SiO.sub.2 :w.H.sub.2 O and showed that the structure is intact after 
the above treatment as all the prominent diffractions present in pure 
zeolite powder were present. The water equilibrium adsorption capacity is 
given in Table 1. The adsorption data given in Table 2 shows that the 
adsorbent is oxygen selective over argon (.varies.O.sub.2 /Ar of 3.7). The 
chromatogram for the mixture of oxygen and argon eluted from this 
adsorbent is shown in FIG. 5. 
EXAMPLE-14 
The adsorbent extrudates obtained by the method as described in Example-4 
were further treated several times with 10 wt % aqueous solution of 
strontium nitrate solution to arrive at a chemical composition of 
0.04.Na.sub.2 O:O.96.SrO:Al.sub.2 O.sub.3 :2.4.SiO.sub.2 :w.H.sub.2 O. The 
adsorbent, SrXE, thus obtained was dried at 110.degree. C. for 6 hours in 
an air oven. The zeolite structure was intact after strontium nitrate 
treatment as all the prominent diffractions typical of pure zeolite X 
powder were present. 
Wherever the treatment temperature and time are not mentioned in the 
examples these should be read as 95.degree. C. and 24 hours respectively. 
The water equilibrium adsorption capacity is given in Table 1. The 
adsorption data given in Table 2 shows that adsorbent has very small 
oxygen selectivity over argon with .varies.O.sub.2 /Ar of 1.3. 
TABLE 1 
______________________________________ 
Oxide formula and equilibrium water adsorption capacity at 
30.degree. C. of various adsorbents 
Equilibrium Water 
Adsorption 
Example Adsorbent 
mmol/g of adsorbent 
______________________________________ 
Example-1 NaXP 18.3 
Example-2 NaYP 15.8 
Example-3 CeYP 12.2 
Example-4 NaXE 14.4 
Example-5 CeXP-1 14.8 
Example-6 CeXP-3 14.5 
Example-7 CeXP-4 13.9 
Example-8 CeXE 12.8 
Example-9 LiXE 16.6 
Example-10 LiCeXE 12.7 
Example-11 KXE 12.3 
Example-12 CaXE 15.2 
Example-13 CaCeXE 11.8 
Example-14 SrXE 13.3 
______________________________________ 
TABLE 2 
__________________________________________________________________________ 
Adsorption data for oxygen/argon/nitrogen gaseous mixture on different 
adsorbents at 30.degree. C. 
Henry constant Adsorption Selectivity, 
K/mmol.g.sup.-1 kPa.sup.-1 
kJmol.sup.-1 Heat of adsorption, 
Adsorbent 
O.sub.2 
N.sub.2 
Ar .varies.O.sub.2 /Ar 
.varies.O.sub.2 //N.sub.2 
.varies.N.sub.2 /Ar 
O.sub.2 
N.sub.2 
Ar 
__________________________________________________________________________ 
NaXP 1.60 
4.78 
1.49 
1.1 0.3 3.2 11.9 
16.5 
11.5 
NaXE 0.97 
3.17 
0.91 
1.1 0.3 3.5 12.0 
18.5 
11.2 
NaYP 0.97 
2.19 
0.93 
1.0 0.4 2.4 11.4 
15.5 
10.9 
CeYP 1.25 
1.20 
0.76 
1.6 1.0 1.6 13.4 
13.5 
10.9 
CeXP-1 
3.17 
2.15 
0.77 
4.1 1.5 2.8 30.6 
19.4 
10.8 
CeXP-3 
1.50 
2.63 
0.72 
2.1 0.6 3.6 23.1 
22.5 
11.3 
CeXP-4 
2.65 
2.60 
0.71 
3.8 1.0 3.7 28.9 
23.6 
12.9 
CeXE 4.25 
2.16 
0.72 
5.9 2.0 3.0 33.1 
20.7 
13.1 
CaXE 1.49 
12.63 
1.14 
1.3 0.1 11.1 
15.3 
28.8 
13.6 
SrXE 1.44 
8.62 
1.12 
1.3 0.2 7.7 13.9 
25.2 
13.4 
KXE 0.95 
1.72 
0.87 
1.1 0.6 2.0 11.6 
16.2 
11.2 
LiXE 1.28 
11.93 
1.01 
1.3 0.1 11.8 
13.4 
27.0 
12.3 
LiCeX 
2.75 
2.24 
0.67 
4.1 1.2 3.3 25.7 
22.5 
11.3 
CaCeX 
2.50 
2.76 
0.68 
3.7 0.9 4.1 27.3 
23.4 
11.8 
__________________________________________________________________________