Note: Descriptions are shown in the official language in which they were submitted.
~31~95 12119
The present invention relates in general to modified
forms of zeolite Y, and more particularly to highly thermally
stable forms of zeolite Y which exhibit to an unique degree
an adsorptive preference for less polar organic molecules
relative to strongly polar molecules such as water. To
nominally disting~ish these novel compositions from those
heretofore known, they are hereinafter called ultrahydrophobic
type Y zeolites, or more briefly as UHP-Y.
In the main, the so-called hydrophobic zeolites are
those species which have quite high framework molar SiO2/A1203
ratios, either as a result of synthesis conditions or by virtue
of post-synthesis removal of aluminum atoms from the crystal
lattice by chelation, extraction with acids, or other well-
known techniques. No precise SiO2/A1203 molar ratio for
threshold hydrophobicity has been established or agreed upon
in the art, but significant development of the property is
generally evident when the ratio is 20 or higher. It has
been proposed that the hydrophobicity is attributable to the
relative absence of cation "sites" which are associated with
the framework A104 tetrahedra.
An apparent exception to the rule of correlation of
; hydrophobicity with high SiO2/A1203 ratios occurs in the case
of the modified zeolite Y compositions of C.V. McDaniel and
P. K. Maher denominated Z-14US and sometimes referred to as
ultra-stable forms of synthetic faujasite. These compositions
are described in detail and the method for their manufacture
disclosed in U.S.P. 3,449,070; U.S.P. 3,293,192; and
--2--
31~
12119
~5
"Molecular Sieves", p. 186, Society of Chemical Industry,
London (1968). It is theorized by Maher and McDaniel
that even though the SiO2/A1203 ratio of Z-14US does
not exceed 7, the hydrophobic character of the zeolite
is due to the thermal destruction of the cation sites
as a result of the rigorous high temperature calcination
in air which is an essential part of the formative
process. Whatever the reason, their experimental data
establish that the adsorption capacity of Z-14US for
water at 25C and a water relative humidity of 10
percent is within the range of 6 to 12 weight percent
based on the anhydrous weight of the zeolite. The
thermal stability of Z-14US is maintained only if the
Na20 content is maintained at or below 1.0 weight
percent.
In Canadian Patent No. 1,046,485 issued January
16, 1979 there is described another distinct modified
form of zeolite Y which is highly stable in the hydro-
thermal sense and which is not dependent upon a low
sodium content for its stability. Briefly, this
composition is prepared by calcining a hydrogen cation
form of zeolite Y containing from 10 to 25 equivalent
percent sodium cations in sufficient steam to prevent
dehydroxylation at a temperature of from 550C to 800C,
and quickly cooling the product to below 350C. The
relatively high sodium content of the starting
material prevents severe hydrolysis of the zeolite
during steaming and avoids the elimination of frame-
work A104-tetrahedra which occurs when low-sodium
forms of zeolite Y are steamed under these conditions.
Possible due to the relatively
B 3 -
1 1 3 1~95 12119
low ion-exchange capacity of the aforesaid steam stabilized
compositions, some hydrophobic character is evident, but is
less pronounced than in the Z-14US zeolites.
It has now been discovered that neither of the
aforesaid stabilized forms of zeolite Y need be considered
as ultimate products. On the contrary, it is found that
both can serve as~starting materials in the preparation of
an unique form of zeolite Y which not only retains the ex-
traordinary stability of such precursors, but also exhibits
a degree of hydrophobicity heretofore never observed in a
molecular sieve of the Y-type. Accordingly, the zeolites
of the present invention are called ultrahydrophobic type-Y
zeolites or simply UHP-Y.
UHP-Y zeolites can be characterized to distinguish
them from all other zeolite forms as being zeolitic alumino-
silicates having a sio2/A1203 molar ratio of from 4.5 to 35,
preferably 4.5 to 9, the essential X-ray powder diffraction
pattern of zeolite Y, an ion-exchange capacity of not greater
than 0.070, a unit cell dimension aO, of from 24.20 to 24.45
Angstroms, a surface area of at least 350 m2/g. (B-E-T), a
sorptive capacity for water vapor at 25C. and a p/pO value
of 0.10 of less than 5.00 weight percent, and a Residual
Butanol Test value of not more than 0.40 weight percent.
As used herein in this Specification and the
appended claims, the following terms are intended to have
the meanings set forth immediately below:
--4-- -
2119
~13~195
Surface areas of all zeolitic compositions are
determined by the well-known Brunauer-Emmett-Teller
method (B-E-T) (S. Brunauer, P. Emmett and E. Teller,
J. Am. Chem. Soc. 60, 309 (1938)) using nitrogen as
the adsorbate.
The essential X-ray powder diffraction pattern of
zeolite Y is set forth in U.S.P. 3,130,007, issued
April 21, 1964. It will be understood by those
skilled in the art that the shrinkage of the unit cell
resulting from the present stabilization process will
cause some slight shift in the d-spacings. In all
events, the X-ray diffraction pattern of the UHP-Y
compositions will exhibit at least the d-spacings
corresponding to the Miller Indices of Table A below,
; and can contain all the other d-spacings permissible to the face-centered cubic system with a unit cell
edge of 24.20 to 24.45 Angstroms. The value of the
d-spacings in Angstroms can be readily calculated by
substitution in the formula:
dhkl aO
~ 2 2 2
The X-ray pattern of the UHP-Y zeolites is obtained
by standard X-ray powder techniques. The radiation
source is a high intensity, copper target, X-ray
tube operated at 50 Kv and 40 ma. The diffraction
pattern from the copper K radiation and graphite
monochromator is suitably recorded by an X-ray
spectrometer scintillation counter, pulse height
analyzer and strip chart recorder. Flat
;~
~ - 5 -
~ 9 S 12119
compressed powder samples are scanned at 1 per minute, using
a 2 second time constant, Interplanar spacings (d) are
obtained from Bragg Angle (2 theta) positions of peaks after
subtracting background, The crystal symmetry is cubic,
TABLE A
Miller Indices Intensity
hkl ~ I/Io
111 very strong
220 medium
311 medium
331 strong
333; 511 medium
440 medium
533 strong
642 strong
751; 555 strong
The anhydrous state of any zeolite composition
for purposes of determining constituent proportions in
terms of weight percent is the condition of the zeolite
after being fired in air at 1000C, for one hour.
The term ion exchange capacity or IEC is intended
to denote the number of active cation sites in the zeolite
which exhibit a strong affinity for water molecules and hence
appreciably affect the overall capacity of the zeolite to
adsorb water vapor, These include all sites which are either
occupied by metal or non-metal cations, or which are not
11 31 19 5 12119
occupied by any cation, but in any event are ca~able of be-
coming associated with sodium cations when the zeolite is con-
tacted at 25C. three times for a period of one hour each with
a fresh aqueous ion exchange solution containing as the solute
0.2 mole of NaCl per liter of solution, in proportions such
that 100 ml. of solution is used for each gram of zeolite.
After this contact of the zeolite with the ion-exchange solution,
routine chemical gravimetric analysis is performed to determine
the relative molar proportions of A1203, SiO2 and Na20. The
data are then substituted in the formula:
IEC = k~Na207SiO21
wherein "k" is the SiO2/A1203 molar ratio of the zeolite
immediately prior to contact with the NaCl ion-exchange
solution.
The Residual Butanol Test is a measure of the
adsorptive selectivity of zeolite adsorbents for relatively
non-polar organic molecules under conditions in which there
is active competition between water and less polar molecules
for adsorption on the zeolite. The test procedure consists
in activating the zeolite sample by heating in air at a
temperature of 300C. for 16 hours. Thereafter, the activated
zeo~ite crystals are slurried with a solution of l-butanol
- in water in proportions such that the slurry consists of
1.0 part by weight l-butanol, 100 parts by weight water and
10 parts by weight of the as-activated zeolite. The slurry
is mildly agitated for 16 hours while the temperature is
maintained at 25C. The supernatant liquid is then analyzed
for its residual l-butanol content in terms of weight percent.
For the determination of the sorptive capacity
....
~ 9S D-12119
of the UHP-Y composition for any particular adsorbate,
for example water, the test zeolite sample is activated
by preheating at 425C for 16 hours at a pressure of
5 micrometers of mercury in a conventional McBain
apparatus. Thereafter, the temperature of the sample
is adjusted to the desired value and contacted with
the vapor of the test adsorbate at the desired pressure.
In the preparation of UHP-Y a number of different
forms of zeolite Y can be used as starting materials.
A particularly preferred starting composition is the
low-sodium form of the steam stabilized zeolite Y
described and claimed in the aforementioned Canadian
Patent No. 1,046,485. That form of zeolite Y is
prepared by the process which comprises providing an
ion-exchanged zeolite Y having the following composi-
tion in terms of mole ratios of oxides:
0.75-0.9 (A)20 : 0.1-0.25 Na20 : A1203 : 4.6-5.4 SiO2 : yH20
wherein "A"represents H or NH4 or a mixture thereof,
and wherein "y" has a value of from 0-9, heating the
zeolite at a temperature between 550C and 800C
for a period of at least 0.25 hour in an inert atmos-
phere comprising sufficient steam, preferably an
atmosphere of pure steam at greater than 10 psia, to
prevent dehydroxylation of the zeolite, removing at
least a major proportion of any ammonia generated by .-
the heated zeolite from contact with the zeolite, and
cooling the steamed zeolite to a temperature below
350C at a rate sufficiently rapid that the cooled
zeolite exhibits
.1~ .
12119
gci
of the UHP-Y compositions for any particular adsorbate,
for example water, the test zeolite sample is activated
by preheating at 425C for 16 hours at a pressure of 5
micrometers of mercury in a conventional McBain
apparatus. Thereafter, the temperature of the sample
is adjusted to the desired value and contacted with
the vapor of the test adsorbate at the desired pressure.
In the preparation of UHP-Y a number of different
forms of zeolite Y can be used as starting materials.
A particularly preferred starting composition is the
low-sodium forms of the steam stabilized zeolite Y
described and claimed in the aforementioned Canadian
Patent No. 1,046,485. That form of zeolite Y is
prepared by the process which comprises providing an
ion-exchanged zeolite Y having the following composi-
tion in terms of mole ratios of oxides:
0.75-0.9 (A)20 : 0.1-0.25 Na20 : A1203 : 4.6-5.4 SiO2 : yH20
wherein "A" represents H+ or NH4+ or a mixture thereof,
and wherein "y" has a vlaue of from 0-9, heating
the zeolite at a temperature between 550C and 800C
for a period of at least 0.25 hour in an inert atmosphere
comprising sufficient steam, preferably an atmosphere
of pure steam at greater than 10 psia, to prevent
dehydroxylation of the zeolite, removing at least a
major proportion of any ammonia generated by the
heated zeolite from contact with the zeolite, and
cooling the steamed zeolite to a temperature below
350C at a rate sufficiently rapid that the cooled
zeolite exhibits
~- . _ g _
12119
31 lg 5
thereafter cooling and ion-exchanging the steamed
zeolite to replace sufficient of the residual sodium
cations with hydrogen or ammonium cations to reduce
the Na20 content to below 0.5 weight percent on an
anhydrous basis. This procedure is illustrated in
Example 1 hereinafter.
It is feasible to reduce the sodium content of
zeolite Y to below 0.5 weight percent without a
calcination step, providing the ion-exchange procedure
is carried out consecutively using a number of fresh
ion-exchange media. This procedure is illustrated
in Example 2 below.
Generally, it is found that the Z14-US composi-
tions prepared by the so-called double calcination
procedure of U.S.P. 3,293.192 and U.S.P. 3,449,070,
are suitable starting materials for the process of
the present invention provided the calcination
temperatures employed are not rigorous enough to reduce
the surface area of the Z14-US products to below
400 m2/g. In the double calcination procedure, the
first step is the reduction of the sodium content
of a sodium zeolite Y having a SiO2/A1203 molar ratio
of 1.5 to 4.0 by ion exchange with an aqueous solution
of an ammonium salt, amine salt, or other salt which
on calcination decomposes and leaves the hydrogen
cation. This exchange is carried out rapidly at a
temperature between 25C and 150C using an exchange
medium containing a stoichiometric excess of about
5 to 600 percent to attain a residual sodium level in
- 10 -
~3
~13119S 12119
the zeolite of from 1.5 to 4 weight percent, preferably
less than 2.9 weight percent. The wa6hed and dried product
is then calcined in air mildly, preferably at a temperature
in the range of 700F. to 1000F. for purposes of the
present invention, to substantially deaminate the zeolite
while avoiding the substantial dehydroxylation thereof.
Subsequent ion-exchange with a salt solution as in the
first ion-exchange procedure results in the reduction of
the Na20 content to below 0.5 weight percent as required
for the starting material of the present invention. For
purposes of this invention, it is preferred that the second
calcination be limited to a temperature of from 300C. to
600C. or eliminated altogether. A preparation of this type
is illustrated in Example 2 below.
In steaming the above-defined starting forms of
zeolite Y to form the UHP-Y compositions of the present
invention, the important process conditions are the tem-
perature and pressure of the steam and the length of the
steaming period. The steaming environment should contain
at least 0.2 atmospheres steam and can be as high as about
10 atmospheres, or even higher. Preferably, a pure steam
environment of from 0.25 to 1.0 atmospheres is employed.
- The steam can be used in admixture with gases inert toward
the zeolite such as air, nitrogen, helium, hydrogen and the
like, particularly when the steam pressure is less than one
atmosphere.
In general, the higher the steam temperature and
-11-
1131195 12119
pressure, the shorter the time period required to transform
the low-sodium starting materials to the ultrahydrophobic
zeolite compositions of the present invention. Minimum
steaming time is also dependent to some degree upon the
particular starting zeolite employed and cannot, therefore,
be set forth herein in terms of a mathematical relation-
ship which is univ'ersally applicable. For example, using
a steam pressure of about 1 atmosphere, it has been found
that at 725C. at least about 4 hours steaming time is
required, but 16 hours is preferable. At 750C. this
minimum steaming time can be halved, and at 800C. only
about 0.5 hours is required. At 870C. about 5 to 10
minutes steaming time can suffice, but these times are
preferably longer by a factor of three or four to ensure
optimum results. In any event, the efficacy of a given
time, temperature, steam pressure and starting material
can readily be validated by routine analysis of the product
obtained to determine if the water adsorption capacity at
25C. and 10 percent relative humidity is less than 5.00
weight percent and the Residual Butanol Test value is not
greater than 0.40 weight percent. Unduly protracted steam-
ing periods, i.e., greater than about 16 hours at 750C.
and 4 hours at 850C., should be avoided since under the
relatively rigorous steaming conditions imposed, the zeolite
tends to lose structure and surface area due to hydrolytic
~ide reactions.
The present compositions and the method for
-12-
11 31 ~9S 12119
their preparation are illustrated in the following Examples:
EXAMPLE 1
(a) Preparation of a Low-sodium Zeolite Y
Starting Material.
A sample of air-dried ammonium exchanged type
Y zeolite having a composition exclusive of water of
hydration: ~ -
56 Na2 : 849 (NH4)20 : A1203 : 5.13 SiO2was tableted into 1/2 inch diameter slugs and charged to
a Vycor tube 24 inches in length and 2.5 inches in diameter
and provided with an external heating means. Over a period
of 0.25 hours, the temperature of the charge was raised to
600C. and thereafter maintained at this temperature for
one hour. During this 1.25 hour period, a pure steam
atmosphere at 14.7 psia generated from demineralized water
was passed upward through the charge in the tube at a rate
of 0.1 to 0.5 pounds per hour. Ammonia gas generated during
the heating by deamination of the zeolite was passed from
the system continually. At the termination of the heating
period the steam flow through the tube was stopped and the
temperature of the charge in the tube was lowered to
ambient room temperature over a period of 5 minutes.
Analysis of this composition indicated the characteristic
X-ray powder diffraction pattern of zeolite Y, a surface
area of 760 m2/g- and an aO value of 24.52 Angstroms.
Thereafter the sodium cation content of the first steamed
material was reduced to 2.0 equivalent percent (0.27
weight percent as Na20) by ion exchange using an aqueous
-13-
1131~95 12119
solution of NH4Cl (30 wt.-%) at reflux.
(b) Preparation of UHP-Y.
The low-sodium starting material prepared in
part (a) supra was converted to the UHP-Y composition of
the present invention using the same apparatus and condi-
tions as in part (a) except that the pure steam calcination
environment was passed over the sample in the reactor at
14.7 psia at a temperature of 800C. for 4 hours. The
product was cooled to ambient room temperature in a
desiccator and portions thereof analyzed for ion-exchange
capacity, B-E-T nitrogen surface area, adsorption capacity
for water, nitrogen and n-hexane and Residual Butanol Test
value. The data from the analyses are set forth below:
Adsorptive Capacity:
Pressure TOemp., Loading,
Adsorbate mm. Hg. C. wt.-%
Nitrogen 35 -196 15.8
" 66 " 16.5
" 137 " 17.3
" 528 " 19.2
Water 2.0 25 3.1
" 4.6 " 4.6
" 20.0 " 15.0
n-Hexane 5.0 25 10.8
" 20.0 " 14.2
" 50.0 " 16.0
" 75.0 " 19.8
Ion-Exchange Capacity: = 0.04
Surface Area = 530 m2/g.
Residual Butanol Test
Value = 0.23 weight percent
-14-
` ~ 1 3 1 ~9S 12119
EXAMPLE 2
(a) Preparation of Low-sodium
Zeolite Y Starting Material
A 150 gram sample of an ammonium-exchanged zeolite
Y containing 2.8 weight percent Na20 and having a SiO2/A12O3
molar ratio of 4.9 was treated with a solution of 150 grams
NH4Cl in 1500 ml water. The exchange solution-zeolite
slurry was refluxed for one hour with moderate stirring,
and the procedure repeated for a total of eight times.
The zeolite was then washed chloride-free with distilled
water and dried in air at room temperature. The Na20
content of the product was 0.23 weight percent and the
surface area (B-E-T) was greater than 900 m2/g.
(b) Preparation of UHP-Y
The low-sodium zeolite Y prepared in part (a)
of this Example was converted to UHP-Y by treatment in
pure steam at 14.7 psia at 800C. for 4 hours using the
apparatus described in Example 1. The product was analyzed
to determine its hydrophobicity in terms of the Residual
l-Butanol Test, its ion exchange capacity, its surface
area and its adsorption capacity for water at 25C. The
pertinent data are set forth below:
; Residual Butanol Test Value = 0.27 wt.-%
Ion Exchange Capacity = 0.028
Surface Area (B-E-T) = 450 m2/g.
Water Adsorption Capacity
(25C.) = p/pO = 0.084; 3.02 wt.-~
-15- .
3 1 1~ S 12119
p/pO ~ 0.19; 4.03 wt.-V/o
p/pO = 0.84; 22.8 wt.-%
EXAMPLE 3
A low-sodium zeolite Y having a Sio2lAl2o3 molar
ratio of 6.4 and a Na20/A12O3 molar ratio of 0.2 was pre-
pared (Example VIII of U.S.P. 3,449,070) by treating a
40 lb. charge of a zeolite Y (having an initial Sio2/Al2o3
ratio of 5.42) with a solution of 80 lbs. of ammonium
sulfate in 400 lbs. of water. The exchange solution was
heated to a temperature of 100C. for one hour with
stirring. After this exchange the zeolite was filtered
and washed in 50 lbs~ of water containing 6 lbs. of
ammonium sulfate. The zeolite was then returned to another
solution containing 80 lbs. of ammonium sulfate in 400
lbs. of water for a second exchange. A third exchange
using the same quantities of ammonium sulfate and water
was effected. The zeolite was then rewashed by slurrying
three times in water, filtered, dried and calcined for
2 hours at 1500F. At this point, the zeolite contained
2.08 wt.-% Na2O. The final exchange of this zeolite
product was effected by mixing ten pounds of the zeolite
with a solution containing 30 lbs. of ammonium sulfate
and 600 lbs. of water, at a temperature of 100C. for one
hour with stirring. The product was then filtered and
washed free of sulfate, dried and analyzed, The chemical
analysis was (wt.-%, dry basis):
-16-
11 31 ~95 12119
Na2O - - - 0.2
SiO2 - - - 77.1
A12O3 - - - 21.2
The unit cell was found to be 24.44 Angstrom units and
the surface area was greater than 600 m2/g. This com-
position is converted to the UHP-Y of the present invention
by calcining it ~in steam at a partial pressure of 10 psia
for sixteen hours at a temperature of 750C.
The UHP-Y compositions are especially suitable
for use as adsorbents in applications where it is desired
to preferentially adsorb organic constituents from solu-
tions or mixtures thereof with water. For example, in
the formation of synthesis gas by the distillation of coal9
there is produced a condensate fraction which is principally
water containing a relatively small proportion of phenol.
For environmental and economic reasons the phenol is
advantageously recovered from the condensate. This is
readily accomplished by contacting the condensate at ambient
room temperature with UHP-Y which selectively adsorbs the
phenol. Desorption and recovery of the adsorbed phenol is
accomplished by the well-known methods.
-17-
