Molecular sieve abstract
This invention relates to the manufacture of novel molecular sieve
adsorbents useful for the separation of a gaseous mixture of oxygen
and nitrogen. The adsorbent is useful for the separation of oxygen
and/or nitrogen from air. More particularly, the invention relates
to the manufacture of a molecular sieve adsorbent which is selective
towards nitrogen from its gaseous mixture with oxygen and/or an
inert gas such as argon or helium.
Molecular sieve claims
We claim:
1. A process for preparing a molecular sieve adsorbent for selectively
adsorbing nitrogen from a gaseous mixture comprising nitrogen and
oxygen; nitrogen and an inert gas or nitrogen, oxygen and an inert
gas said process comprising:
(a) preparing a mixture of zeolite powder, clay and an organic
binder, wherein the zeolite powder is prepared from a zeolite of
the formula,
where
a is from 0.0 to 0.70
b is from 0.1 to 0.33
c is from 2.0 to 5.5
M is alkali earth, alkaline earth or rare earth metal ion, Y represents
yttrium and w represents the moles of water;
(b) shaping said zeolite mixture to obtain adsorbent bodies;
(c) subjecting said 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 a rare earth salt
solution to affect surface modification of said adsorbent bodies
to obtain said molecular sieve adsorbent.
2. The process as claimed in claim 1 wherein said rare earth salt
solution is a salt solution of yttrium or a combination of yttrium
with lithium or calcium or a mixture thereof.
3. The process as claimed in claim 1 wherein M is lithium, sodium
or calcium.
4. The process as claimed in claim 1 wherein said clay comprises
bentonite clay.
5. The process as claimed in claim 1 wherein said clay is an inert
clay present in an amount of 2 to 40% by weight.
6. The process as claimed in claim 1 wherein said binder is selected
from the group consisting of sodium lignosulfate, starch and polyvinyl
alcohol.
7. The process as claimed in claim 1 wherein said zeolite mixture
is subjected to ball milling to produce powders of particle size
of less than 60 microns.
8. The process as claimed claim 1 wherein the adsorbent bodies
are dried at room temperature for about 6 to 12 hrs. followed by
oven drying at a temperature of 110.degree. C. for 6 to 18 hrs.
9. The process as claimed in claim 1 wherein said calcination
is carried out at a temperature of 450.degree. C. to 700.degree.
C.
10. The process as claimed in claim 9 wherein said calcination
is carried out for a period of from 2 to 18 hrs.
11. The process as claimed in claim 1 wherein said cation exchange
of the adsorbent bodies is carried out at a concentration of cations
of 1 to 10% by weight/volume of aqueous solution.
12. The process as claimed in claim 11 wherein said cation exchange
is carried out at a temperature of 30 to 100.degree. C. for 4 to
48 hrs.
13. A process as claimed in claim 12 wherein said cation exchanged
adsorbent bodies are washed with hot water.
Molecular sieve description
This invention relates to the manufacture of a molecular sieve
adsorbent which is selective towards nitrogen from its gaseous mixture
with oxygen and/or an inert gas such as argon or helium. More particularly,
this invention relates to the manufacture of novel molecular sieve
adsorbents useful for the separation of a gaseous mixture of oxygen
and nitrogen. The adsorbent is useful for the separation of oxygen
and/or nitrogen from air.
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. Oxygen requirements in sewage treatment, fermentation,
cutting and welding, fish breeding, electric furnaces, pulp bleaching,
glass blowing, medical purposes and in the steel industries particularly
when the required oxygen purity is 90 to 94% is being largely met
by adsorption based pressure swing or vacuum swing processes. It
is estimated that at present, 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% with separation
of 0.934 mole percent argon present in the air from oxygen being
a limiting factor to achieve 100% oxygen purity. Further-more, the
adsorption based production of oxygen from air is economically not
competitive to cryogenic fractionation of air for production levels
of more than 100 tonnes oxygen per day. Of the total cost of oxygen
production by adsorption processes, it is estimated that capital
cost of equipment and power consumption are the two major factors
influencing the overall cost with their share being 50% and 40%
respectively. Besides the other factors like process and system
designs, the adsorbent is the key component which can bring down
the cost of oxygen production by adsorption. The adsorbent selectivity
and capacity are important parameters for determining the size of
adsorption vessels, compressors or vacuum pumps. It is desirable
to have an adsorbent which shows a high adsorption capacity as well
as selectivity for nitrogen compared to oxygen. The improvement
in these properties of the adsorbent directly results in lowering
the adsorbent inventory of a system along with the size and power
consumption of the air compressor or vacuum pump. Furthermore, adsorbent
having a high nitrogen adsorption selectivity and capacity can also
be used to produce reasonably pure nitrogen along with oxygen by
evacuating nitrogen adsorbed on the adsorbent.
It is therefore, highly desirable, if not absolutely essential,
for an adsorbent to have a good adsorption capacity and adsorption
selectivity for a particular component sought to be separated.
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 the desired components the better is the adsorbent
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
where .varies. is the adsorption selectivity, X is the adsorbed
concentration and Y is gas-phase concentration respectively. The
expression gas-phase concentraction means the amount of unadsorbed
component remaining in the gas-phase. The adsorption selectivity
of a component depends on
steric factors such as differences in the shape and size of the
adsorbate molecules;
equilibrium effect, i.e. when the adsorption isotherms of the component
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 the adsorption selectivity
is less than 2 it is difficult to design an efficient separation
process.
In the prior art, adsorbents which are selective for nitrogen from
its mixture with oxygen and argon have been reported wherein the
zeolites of type A, X and mordenite have been used after ion exchanging
with alkali and/or alkaline earth metal ions. However, the adsorption
selectivity reported for the commercially used adsorbents for this
purpose varies from around 3 to 5. The efforts to enhance the adsorption
capacity and selectivity has been reported by increasing the number
of exchangeable cations into the zeolite structure by modifying
the chemical composition of the zeolite (Reference Coe Si/Al ratio).
The adsorption selectivity for nitrogen has also been substantially
enhanced by exchanging the zeolite with cations like lithium and/or
calcium in some zeolite types. In the present invention, we report
a new chemical composition using faujasite type zeolite having alkali,
alkaline or rare earth metal ions which give substantially high
nitrogen adsorption capacity and selectivity compared to commercially
employed adsorbents for oxygen production from air.
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 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]
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 the zeolites 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. 2882244 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 the Formula 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.
Powdered 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 98 wt % depending on
the type of binder used. Clays such as bentonite, kaolin, and attapulgite
are normally used inorganic binders for agglomeration of zeolite
powders.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an adsorbent
composition which can be used for the separation of oxygen-nitrogen
and/or nitrogen-argon gaseous mixture.
Yet another object of this invention is to provide a nitrogen selective
adsorbent based on synthetic zeolites.
Yet another object of this invention is to provide a nitrogen selective
adsorbent by modification of surface characteristics of synthetic
zeolites.
Yet another object of the present invention is to provide an adsorbent
with increased adsorption selectivity and capacity for nitrogen
from its mixture with oxygen and/or argon.
Yet another object of the present invention is to provide nitrogen
selective adsorbents which can be used commercially.
BRIEF DESCRIPTION OF THE FIGURES
FIG. 1 is a chromatogram of mixture of nitrogen and oxygen on YXP-1.
FIG. 2 are chromatograms of mixtures of (a) nitrogen and helium
and (b) oxygen and helium on YXP-4.
FIG. 3 is a chromatogram of mixture of nitrogen and oxygen on LiYXE.
FIG. 4 is a chromatogram of mixture of nitrogen and oxygen on CaYXE.
DESCRIPTION OF THE INVENTION
According to the present invention, there is provided a molecular
sieve adsorbent having a composition
where the values of
a is from 0.0 to 0.70;
b is from 0.0 to 0.33;
c is from 2.0 to 5.5;
M is an alkali or alkaline earth metal ion such as lithium, sodium
or calcium and w is the number of moles of water.
The adsorbent of the present invention can be conveniently obtained
by: (i) preparing a mixture of zeolite powder type X as described
in U.S. Pat. No. 2882244 or zeolite Y as described in U.S. Pat.
No. 3130007 with a clay such as herein described and an organic
binder such as herein described, (ii) forming adsorbent bodies of
desired shape or subjecting the adsorbent powder to cation exchange
with one or more cations and then forming adsorbent bodies, (iii)
subjecting the adsorbent bodies so formed to calcination (iv) subjecting
the calcined adsorbent bodies to cation exchange with one or more
cations if the cation exchange has not 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 a nitrogen selective adsorbent
from its gaseous mixture with oxygen and/or argon and/or helium.
The modification of the surface property hereinafter referred to
as surface modification is the most critical and important aspect
of the invention. It is a very specific surface modification which
renders the zeolite particularly selective towards nitrogen. It
has been surprisingly found that conventional zeolite particularly,
zeolite X is subjected to surface modification with treatment with
a rare earth salt solution, specifically of an alkali metal salt
solution specifically yttrium or combination of yttrium with lithium
and/or calcium, the zeolite becomes selective for nitrogen.
Accordingly, the present invention provides, a process for the
preparation of a molecular sieve adsorbent for selectively adsorbing
nitrogen from a gaseous mixture consisting of nitrogen, oxygen and/or
an inert gas 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 rare
earth salt solution such as hereinbefore described to effect surface
modification of said adsorbent bodies to obtain said molecular sieve
adsorbent which is nitrogen 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 aqueous 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 followed by oven drying at 110.degree. C.
The dried particles were subjected to air calcination at 450 to
700.degree. C. for 2 to 18 hours.
The adsorbent particles were then treated with an aqueous solution
of alkali, alkaline earth and/or rare earth metal cation or a combination
of these at a specified concentration (1 to 10% by weight) at 30-100.degree.
C. for 4 to 48 hours followed by a thorough wash with hot water.
The particles were then dried at 110.degree. C. in an air oven for
8 to 18 hours.
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 2.743 .ANG. 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/Nitrogen/Argon 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 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 a 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 nitrogen, oxygen and helium (or argon and helium)
in hydrogen was injected into 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 nitrogen, oxygen and argon.
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 of oxygen and argon employing standard formulae described
below:
where R is 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, 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.5
where F is carrier gas flow rate (ml/minute); t.sub.R is corrected
retention time (minute); T is the adsorbed column temperature in
Kelvin, p.sub.w is water vapor pressure (kPa) at room temperature
T.sub.R, p.sub.o is column out let pressure (kPa), W.sub.5 active
weight of the adsorbent present in the column and j is the compressibility
correction given by the equation shown below.
Compressibility correction, j+(3/2)[(p.sub.1 /p.sub.o).sup.2 -1)/p.sub.1
/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.0 =R dln(V.sub.N /T)/d(1/T)
In the formula -.DELTA.H.sub.0 =R dln(V.sub.N /T)/d(1/T) the letter
`d` represents the mathematical operation called `differentiation`
and 1n 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.0 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 the U.S. Pat. No. 2882244.
Water adsorption as given in Table 1 and X-ray diffraction data
showed that the starting zeolite powder is highly crystalline. Adsorbent
was evaluated for Nitrogen/Oxygen/Argon adsorption capacity and
selectivity by elution gas chromatography as per the procedure detailed
above. The adsorption data are given in Table 2. The data show that
the adsorbent is nitrogen selective .varies.N.sub.2 /Ar=3.2.
EXAMPLE 2
A mixture consisting of 200 g of zeolite powder having chemical
composition NaO:Al.sub.2 O.sub.3 :2.4SiO.sub.2 :w.H.sub.2 O, 50
g of bentonite clay powder and 1 gm 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 plugged
by adding water. The plugged mass was extruded though a 1.5 mm die
by a hand extruder. The extruded adsorbent was first dried at room
temperature followed by air oven drying at 110.degree. C. Dried
extrudates were calcined at 560.degree. C. in a muffle furnace for
6 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 nitrogen/oxygen/argon
adsorption capacity and selectivity by elution gas chromatography.
Adsorption data given in Table 2 show that the adsorbent is nitrogen
selective. Nitrogen adsorption selectivity of the adsorbent over
oxygen and argon are .varies.N.sub.2 /O.sub.2 =3.3 and .varies.N.sub.2
/Ar=3.5 respectively.
EXAMPLE 3
NaX powder obtained by the method described in Example-1 was refluxed
with 1 wt % aqueous yttrium (III) acetate solution for 48 hours.
The zeolite powder was then filtered from the solution and washed
with hot distilled water until the wash water was free from chloride.
The zeolite powder thus obtained, YXP-1 with a chemical composition
of 0.22Na.sub.2 O:0.26Y.sub.2 O.sub.3 :Al.sub.2 O.sub.3 :2.4SiO.sub.2
:w.H.sub.2 O, was dried at 110.degree. C. in an air oven. The zeolite
structure was retained after yttrium acetate treatment as all the
prominent X-ray diffractions typical of pure zeolite X powder were
present. The water equilibrium adsorbent capacity is given in Table
1. Nitrogen/oxygen/argon adsorption capacity and selectivity data
measured by elution gas chromatography are given in Table 2. Chromatogram
of nitrogen and oxygen mixture eluted from this adsorbent at 30.degree.
C. is shown in FIG. 1. The adsorbent possesses very good nitrogen
selectivity (.varies.N.sub.2 /O.sub.2 =5.8; .varies.N.sub.2 /Ar=6.7)
over oxygen or argon.
EXAMPLE 4
NaX powder (about 35 g) obtained by the method described in Example-1
was treated at 95.degree. C. in four stages with 1 wt % aqueous
solution of yttrium (III) acetate for 48 hours at each stage. The
adsorbent was thereafter washed with hot distilled water until the
wash water showed the absence of chloride. The adsorbent YXP-4
thus obtained had a chemical composition 0.1Na.sub.2 O:0.30Y.sub.2
O.sub.3 :Al.sub.2 O.sub.3 :2.4SiO.sub.2 :w.H.sub.2 O. The zeolite
structure is intact after yttrium acetate treatment as all the prominent
x-ray diffractions present in pure zeolite X powder are present.
The water equilibrium adsorption capacity is given in Table 1. The
adsorption data given in Table 2 shows that adsorbent possesses
very good nitrogen selectivity (.varies.N.sub.2 /O.sub.2 =8.6; .varies.N.sub.2
/Ar=10.2) over oxygen and argon. Chromatograms of the mixtures of
helium and nitrogen and helium and oxygen eluted from this adsorbent
at 30.degree. C. are shown in FIG. 2.
EXAMPLE 5
35 g of zeolite NaX adsorbent pellets produced as described by
the method in Example-2 were refluxed with 1 wt % aqueous yttrium
(III) acetate solution in two stages each for 48 hours. The adsorbent
pellets were then filtered from the solution and washed with hot
distilled water until the wash water was free from chloride. The
adsorbent thus obtained, YXE-1 had a composition 0.16Na.sub.2 O:0.28Y.sub.2
O.sub.3 :Al.sub.2 O.sub.3 ;2.4Si0.sub.2 :w.H.sub.2 O. The adsorbent
was dried at 110.degree. C. for 6 hours. The zeolite structure was
retained after yttrium acetate treatment as all the prominent x-ray
diffractions typical of pure zeolite X powder were present. The
water equilibrium adsorption capacity is given in Table 1. Nitrogen/oxygen/argon
adsorption capacity and selectivity data measured by elution gas
chromatography are given in Table 2. The results shown that adsorbent
exhibited very good nitrogen selectivity (.varies.N.sub.2 /O.sub.2
=8.8; .varies.N.sub.2 /Ar=9.9) from its mixture with oxygen or argon.
EXAMPLE 6
Zeolite NaX bodies as obtained by the method described in Example-2
were treated with 2.5 wt % of aqueous lithium chloride solution
at 90.degree. C. in five stages for 48 hours at each stage. The
solution was then decanted and the adsorbent was washed with hot
distilled water until the wash water contained no chloride. The
adsorbent thus obtained was further treated with 1 wt % yttrium
acetate solution using the following procedure. 40 g of the above
obtained adsorbent was treated with 1 wt % aqueous solution of yttrium
(III) acetate at 95.degree. C. for 48 hours. Then the solution was
decanted and the adsorbent washed with hot distilled water three
times. The adsorbent was again treated with 1 wt % yttrium acetate
solution in a manner similar to that described above. Thereafter
the adsorbent was washed with hot distilled water until the wash
water showed no traces of chloride. The resultant adsorbent, LiYXE-1
had a composition 0.06Li.sub.2 O:0.32Y.sub.2 O.sub.3 :Al.sub.2 O.sub.3
:2.4SiO.sub.2 :w.H.sub.2 O. The adsorbent was dried at 110.degree.
C. in an air oven. The zeolite structure was intact after yttrium
acetate treatment as all the prominent diffractions present in pure
zeolite X powder were present. The water equilibrium adsorption
capacity is given in Table 1. Nitrogen and oxygen adsorption data
given in Table 2 shows that adsorbent possesses nitrogen selectivity
(.varies.N.sub.2 /O.sub.2 =9.1) from its mixture with oxygen. Chromatogram
of mixture of nitrogen and oxygen eluted from this adsorbent at
30.degree. C. is shown in FIG. 3.
EXAMPLE 7
40 g of zeolite X bodies as obtained by the method described in
Example-2 were treated with 2.5 wt % calcium chloride solution at
90.degree. C. for 48 hours. The solution was then decanted and the
adsorbent washed with hot distilled water three times. The adsorbent
thus obtained was further treated with 2.5 wt % calcium chloride
solution four times in a manner similar to that described above.
Thereafter the adsorbent was washed with hot distilled water until
the wash water contained no chloride. The resultant adsorbent was
further treated with 1 wt % aqueous solution of yttrium acetate
solution at 95.degree. C. for 48 hours. Then the solution was decanted
and the adsorbent washed with hot distilled water three times. The
adsorbent was again treated with 1 wt % yttrium acetate solution
in a manner similar to that described above. Thereafter, the adsorbent
was washed with hot distilled water until the wash water showed
no traces of chloride. The adsorbent thus obtained, CaYXE had a
composition 0.24CaO:O0.25Y.sub.2 O.sub.3 :Al.sub.2 O.sub.3 :2.4SiO.sub.2
:w.H.sub.2 O. The adsorbent was dried at 110.degree. C. in an air
oven. The zeolite structure is intact after yttrium acetate treatment
as all the prominent x-ray diffractions present in pure zeolite
X powder are present. The water equilibrium adsorption capacity
is given in Table 1. Nitrogen, oxygen and argon adsorption data
given in Table 2 shows that adsorbent possesses nitrogen selectivity
(.varies.N.sub.2 /O.sub.2 =9.5; .varies.N.sub.2 /Ar=12.1) from its
mixture with oxygen or argon. Chromatogram of mixture of nitrogen
and oxygen eluted from this adsorbent at 30.degree. C. is given
in FIG. 4.
EXAMPLE 8
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 U.S. Pat. No.
3130007. Water adsorption as given in Table 1 and X-ray diffraction
data showed that the starting zeolite powder is highly crystalline.
Adsorbent was evaluated for nitrogen, oxygen and argon adsorption
capacity and selectivity by elution gas chromatography as per the
procedure detailed above. Chromatography of oxygen and nitrogen
mixture showed overlap of nitrogen and oxygen peaks indicating incomplete
separation of these two gases in the column. Hence, the retention
times of nitrogen, oxygen and argon were measured by injecting these
gases separately. The adsorption data given in Table 2 show that
the adsorbent is nitrogen selective over oxygen (.varies.N.sub.2
/O.sub.2 =2.3) and argon .varies.N.sub.2 /Ar=2.4).
EXAMPLE 9
Zeolite NaY powder prepared by the method described earlier was
refluxed at 95.degree. C. with 1 wt % aqueous solution of yttrium
chloride in two stages for 48 hours at each stage. The solution
was thereafter filtered and the solid was washed with hot distilled
water until the 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 yttrium chloride
solution treatment. The elution gas chromatography data of the thus
prepared adsorbent, YYP having chemical composition of 0.16.Na.sub.2
O:0.28.Y.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 show that the adsorbent is nitrogen selective
with .varies.N.sub.2 /O.sub.2 and .varies.N.sub.2 /Ar of 3.0 and
3.1 respectively. |