Note: Descriptions are shown in the official language in which they were submitted.
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~ he present invention relates in general to a
hydrothermal process for preparing zeolite Y and, more
particularly, to an improved process therefor having a con-
siderably reduced digestion-crystallization per~od and
consequen~ly a shorter cycle time.
Zeolite Y, the synthetic zeolite topologically
related to the rare mlneral aujasite, is described in
detail in U.S.P 3,130,007 issued April 21, 1964 to D. W.
Breck. In accordance with the disclosure of that paten~, -
zeolite Y is conventionally prepared from a gel comprising
an aqueous caustic solution, a solid reactive amorphous
silica and as the 30urce of aluminum, either gamma alumina,
alumina trihydrate or sodium aluminate. The reactant
mixture is first digested at am~ient room temperature for a
period of about 1~ hours up to 32 hours, dependent in part
,
on the precise gel composition and the desired Si/A12 ratio
of the product ~eolite, and thereafter heated to an elevated
temperature of from 80 to 125C for an additional 30 or -~
more hours to obtain good yields of high-purity product.
Numberous attempts have been made to shorten the
cycle period in the commercial processes for zeolite Y
synthesis, with varying degrees of success. The use of
much h~gher digestion temperatures, for example, has been
found to shorten the synthesis time as might be expected,
but the manufacturing and apparatus costs are greatly
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increased in those cases where the higher temperature
necessitates pressures well above atmospheric. Also, the
zeolite Y crystal structure is metastable; hence, other
zeolites such as Type S may be formed if digestion is
carried out too long at the higher temperatures.
It has now been discovered that by the selection
of particular sources of alumina and a particular type of
sillca coupled with a novel method of combining the in-
gredients to form a zeolite Y reactant mixture, the synthe-
sls aging and digestion period can be greatly reduced with-
out resort to increases in the reaction temperature.
We have found that a number of Important variables
are related to the rapid rate of nucleation or crystal
formation of Type Y in the method of the invention to be
described below. One is the dispersion of the solid silica
in water essentially free of any added alkali rather than
in the conventional alkali solution. Another is the con-
centration of aluminum and sodium in the solution or
slurry at the time of contact with the silica- water dis-
persion. Another variable is the temperature of such
solution or slurry at the time of contact with the silica-
water dispersion. The method of the invention also
includes provision for intimate mixing of (a) silica and
water and (b) the reactants in the formation of the re-
actant "gel", as accomplished by high- shear mixing rneans .
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The silica employed in the present process is a solid
reactive amorphous silica of the type represented by fume silica
and chemically-precipitated silicas preferably having a particle
size of less than one micron. These silicas are widely available
commercially. It has previously been proposed to employ solid
amorphous silicas in zeolite syntheses eitheras the sole source
of silica or in admixture with other sources such as silica
gels, silica sols or sodium silicate. In g~neral, the solid
silica has been introduced into the reactant mixture as a
slurry in an aqueous alkaline medium, typically a 5 wt-% solu-
tion of NaOH in water.
We have found, however, that in the process of the
present invention there is a marked improvement in the rate of
nucleation and crystallization of zeolite Y when the dispersion
medium for the solid amorphous silica is water rather than an
aqueous caustic solution. The preparation of such dispersions is
best accomplished by using high-speed, high-shear mixing means,
as described below.
In Table A are presented data demonstrating the effect
of the silica dispersion medium on the rate of crystallization of
Type Y. It is evident from these data, particularly from runs 82-1
through 82-6, that the use of aqueous alkali dispersion medium
did not lead to and
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crystallizatlon of Type Y. On the other hsnd, a rapid rate
. of Y crystal foxmation is evident from the X-ray data ~or :
the remaining experiments set forth in Table A wherein
water-dispersed silica was employed.
TABLE A
EFFECT OF SILICA DISPERSION MEDIUM ON :
R~TE OF CRYSTALLIZATION OF TYPE Y
Aging Time Dispersion % X-ray ¦ .
Sample No. _ Hours Medium Crystallinity
82-1 0 5% ~aOH Amorphous ~ :
82-2 1 " "
82-3 5
82-4 24 " "
82-5 48 " "
82-6 72 " . "
80-1 0 Water 8.5
80-2 1 " 17
80-3 3 " 16 ~ -
80-4 5 " 43
80-5 10 " 13
80-7 24 " 16
80-9 72 " Trace
Note: The reactant gels in all the above runs was aged
at room temperature 24 hours and digested at 100C
for 9 hours.
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Mix Method: Aluminate solution (3.10 gram~ Al (OH)3 and 64.0
grams of NaOH in 100 ml H20) added to silica dispersion (133.3
g.solid amorphous silica in 440 ml of 5% NaOH or 440 ml of H20).
These runs were conducted only to ascertain rates of crystalli-
zation and hence were not continued to the point where greater
amounts of crystalline product would have resulted.
Table A also indicates that aging of the water-dispersed
silica for at least an hour and preferably f~r about five hours
prior to combination with the alumina solution has an advantageous
effect on crystallization rate.
In the method of the invention it is important to control
the concen~rations of alumina and alkali in the aqueous mixture
before combining into the overall reactant mix~ure. It has been
found that aqueous mixtures which are in the range of 4 to 5.5
molal with respect to alumina las Al (OH)3] and in the range of
16 to 22 molal with respect to alkali (as NaOH), result in the
most favorable rates of crystallization, with an Al (OH)3 molality
value of about 5 and an NaOH molality of about 21 being preferred. ~ -
Data are presented in Table B.
Surprisingly, it has also been found that the temperature
of the aqueous solution or slurry mixture of alimina and alkali
at the time it is combined with the silica-water di~persion also
has an important effect on rate of Type Y crystallization.
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TABLE B
Effect of Al(OH)3 and NaOH Concentration (Molality)
Prior to Mixing of the Reac~ant Gel
Concentration of % Na~Y in Product
Sample No. Al(OH)3 NaOH ~ Y X-ray~
l-A* 3.3 13.4 None
A-3 4.0 16.0 96.0
B-3 5.4 21.3 96.0
C-3 8.0 32.0 18.0
D-3 10.8 42.8 7.5
*Age time 24 hours
Note~ Solid amorphous silica dispersed in water and aged for 5
hours. Reactant ratios (moles of oxides) were
Na2O/Si02 = 0 4
SiO2/A1203 = 10 . O
H20/Na20 = 39.2 ,
Gel age time was 11 hours; digestion time was 10 hours at 100 C.
20 As the data of Table C demonstrate, solution temperatures of between
80 and 95 C gave the highest purity Type Y product. A temperature
range of between 85 and 90C is preferred.
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TABLE C
Effect of Alumina - NaOH Solution Mixture Temperature
at Time of Mixing with Silica-H~O D~spersion
Temperature oE Type Y
Sample Mixture C X-ray Crystallinity, %*
B 120 10 . :: :
A 104 5
67-1 95 98
67-2 84 93
67-3 79 92
67-4 64 69
67-5 55 43
67-6 45 45
67-7 25 38 `
*Average of duplicate runs
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Note: a)Reactant ratios (moles of oxidec):
Na20/SiO2 = 0.4
SiO2/A1203 = 10
H20/Na20 = 40
b) Gel age time = 20 hours at room temperature
a) Digestion time = 10 hoùrs at 100C
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In accDrdance with one aspect of the invention, therefore,
a typical procedure for preparing zeolite Y is as follows:
1) A solid reactive amorphous silica is dispersed as a dry
powder in water (25-28 weight percent) and mixed in a high-speed,
high-shear blender, such as for a period of 15 seconds at 21,500
rpm, followed by manual mixing to a homogeneous dispersion. Pref-
erably this dispersion, having a pH value in the range of 5.5 to
8, is then allowed to age for about 5 hours at room temperature.
If this dispersion is not used immediately, it is desirable to
redisperse it for the same period immediately prior to the addition
of the aluminate solution in step 3) below.
2) Alumina in the form of gibbsite, ~A1203.3H20, is combined
with NaOH solution and used as a clear solution or as a slurry
(see below) at concentrations of about 5.4 molal with respect to
Al(OH)3 and about 21 molal with respect to NaOH.
3) The resultant solution or slurry of alumina i9 added to
the dispersion of "Silica" in water from 1) at temperatures prefe-
rably between 85 and 90C. If this solution or slurry is to be
used immediately, the heat of the reaction of NaOH in H20 is
sufficiently high (110-115C) to permit the addition of the
aluminate solution or slurry at the above-mentioned temperature
(85-90C) without the application of additional heat.
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4) Homogeneous gelation of the mixture from 3) is
accomplished by manual-mixing at first and finally by
blender-mixing for one minute at 21, 500 rpm. Temper-
ature of the gel at this point is around 50 C.
5) The mixed gel having an overall composition, -
expressed in terms of oxide-mole-ratios, of:
N a 2 O / S i O 2 = o . 4
S i O 2 / A 1 2 3
H2O/Na2O = 40
is aged at ambient tempera~ure for 10-12 hours and subse-
quently digested at 100C for 8-12 hours, resulting in a I ~-
total cycle time between 18 and 24 hours. , -
6) The product of this process is high-purity NaY
~eolite as determined by X-ray powder diffraction and 2
adsorpt}on capacity measurements. The Si/A12 ratio as
determined by unit cell constant (aO) measurements aver-
ages 4. 4.
In another aspect of the invention certain types
of alumina, namely, alumina trihydrate, alumina monohydrate -
and transition alumina may be effecti vely used in the
particular rnanner described below, provided they exhibit
the following characteristics:
1) A water content within the range of 21-40 wt. %,
and the A12O3 content within the range of 60-77 wt. %;
2) Preferably, an average particle size range between
0. 04 and 2 microns.
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3) Impurity content not more than 2 wt.%, and
organic or inorganic surface coatings or additive~. -
Of the above-named three types of alumina, the
trihydrates and monohydrates are preferred because of their
relative ease of manufacture, general avàilability and good
stability characteristics. Gibbsite, bayerite and nord-
strandite are classified as alumina trihydrates; bohmite
snd diaspore are alumina monohydrates. Bohmite may be pre-
pared by heating gibbsite at a temperature of about 200C
for at least two hours. Representative aluminas and their
performance are included in the data of Table D. Calcined
alpha alumina (corundum) however, was found to be insuffi-
ciently reactive (samples J-M).
Surprisingly, it has been found that to be
suitably incorporated into the reactant mixture, those
aluminas having the above-described characteristics need
not be solubilized in caustic solution as has been the
almost universal practice, but can in fact be added to the
reactant mixture merely as a slurry of 801id alumina
particles in aqueous alkali. In the same manner, slurries
of ~olid sodium aluminate have also been found qu~te satis-
factory.
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TABLE D
Performance of Various Aluminas in Synthesis of TYpe Y
Chem. Comp. ~verage
Common(moles/100~.) Particle
Name Sample Phase A1203 H20 Size ~ Product
Gibbsite A A1203~ 0.63 1.94 --- Type Y
B 3H20 0.64 1.92 1 - 6 Type Y
C 0.63 1.91 1 - 6 Type Y .
D 0.62 1.92 1 - 6 Type Y
E 0.63 1.95 0.5 - 2 Type Y
Bohmite F A123 0.90 0.63 ___ Bohmite . .
G H20 0.66 1.67 --- Type Y
H 0.64 1.92 1 - 8 Type Y
Transition I A123 0.75 1 19 04 Type Y
}
Calcined J Al 03 0.97 1.00 --- Corundum
Alpha 2
K 0.5 " -
L 0.2 " -
M 2.0 " -
*X i8 between 0 and 1
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In preparing the reactant mixtur~ or gel from
which the zeolite Y is ultimately obtained, the overall
composition, expressed in terms of mole-ratios of oxides,
should be within the range
Na20/SiO2 = 0.36 - 0.46
Si~2/A1203 ~ 8 - 10
H20/Na20 ~ 35 ~ 45
The order of mixing ic not narrowly critical, but advanta-
geous results are obtained by following the typical pro-
cedure of pages 8 and 9.
In preparing the individual slurries or disper- -
sions of alumina or solid amorphous silica, respectively,
as well as in the formation of the overall reactant mixture,
vigorous and intensive mixing methods are found to be the
most salutary. Commercially available impeller-type
devices such as axial-flow turbine mixers, high-speed
blenders, high-shear impellers, turbo-dispersers and the
like, which are able to create high-shear conditions in the
mixtures being combined, are preferably employed here. The
operation of high-shear impeller-type mixing equipment is
characterized by mixing under substantially-turbulent to
fully-turbulent conditions, that is, at Reynolds numbers
in the range of about 2100 to 104, and above. For the high-
speed mixing steps of the present invention, Reynolds
numbers of approximately 2000 (substantially turbulent)
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and upwards were calculated. The above-named devices are
well suited for conducting intimate m~xing and dispersing
on a production scale according to the method of the inven-
tion.
The significance of intensive, high-shear mixing
in carrying out this process was emphasized by the results
of a series of teQts with a high-speed blender operated at
three dif~erent speeds, name, 750, 15,000 and 21,500 rpm.
It was found that the crystallization of Type Y after nine
hours digestion at 100C was 40% (by X-ray analysis) for a
gel mixed at 750 rpm, but 98% for a gel mixed at 21,500 rpm.
After the constituents of the gel compo~ition are
combined according to the method of the invention the gel
is permitted to age at about ambient temperature (within
the range of 20 to 26C) for a period of about 1 ~o 12 hours
and is thereafter raised in temperature to the range of 95
to 110C and maintained thereat until zeolite Y crystals are
produced. In general, the post-aging crystallization
period is at least 7 hours and up to about 15 hours. Without
a previous aging period, crystallization periods of from 15
to 24 hours are used, preferably 20-24 hours to obtain the
higher SilA12 ratios in the product.
Particularly preferred conditions are about 12
hours aging at room temperature and about 8 hours digestion -
at 100C, resulting in an overall synthesis time of about
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20 hours. If it i8 desired to conduct the digestion-crystall-
ization at 110C, a one-hour aging period at room temperature snd
about seven hours of digestion at 110~ a~e preferred.
When slurries of solid alumina or of solid sodium alu-
minate are employed as the alumina source, typical reaction
conditions for producing Type Y are 24 hours at 100C for crystall-
ization without a prior aging period.
In its generic aspects, therefore, the process of the present
invention comprises forming an aqueous aluminosilicRte reaction
mixture having a uniform composition, expressed in terms of oxide-
mole ratios, within the range
Na20/SiO2 ~ 0.36-0.46
SiO2/A1203 - 8-10
H20/Na20 ' 35~45,
said composition being formed by intensively admixing under high-
shear conditions (a) a substantially homogeneous and essentially
alkali-free water-medium dispersion of a reactive solid amorphous
silica having a particle size of less than one micron formed under
high-shear conditions, and (b) a mixture of alumina, water and
sodium hydroxide wherein the molal concentration of alumina as
Al(OH)3 is between about 4 m and 5.5 m and the concentration of
NaOH is between about 16 m and 22 m
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wherein the temperature of said mixture (b) i8 between 80 and
95 C at the time of said admixing, maintaining the composition
thus formed for a period of from about 1 to 24 hours at tempera-
ture within the range of 20 to 110C, and recovering the zeolite
Y crystals produced thereby.
The invention is illustrated by the following examples:
Example 1
Thirty-one (31.0) grams of Al (OH)3 (reagent grade gibbsite)
were dissolved in a concentrated sodium hydroxide solution (64.0
grams of NaOH containing 77.5 wt.-% Na20, and 80 ml. H20) by
stirring and heating to form a clear solution. The molal concen-
trations of NaOH and Al (OH)3 were 20.0 m and 4.97 m, respec~ively.
Next, 133.3 grams of solid reactive amorphous silica containing
85.6 wt.-% SiO2 were placed in a quart blender ~ar; 480 ml. of
water were sdded slowly to the Silica as blending proceeded at
a speed of 15,000 rpm. The sodium aluminate solution prepare~ as
above was slowly added at a temperature of 85C to the Silica-water
dispersion in the blender over a period of about 3 minutes. After
the intensive mixing was completed, the resulting homogeneous gel,
20 which had a molar composition of 4.0 Na20:A1203:10.0 SiO2:160 H20,
was digested at 100C for 15 hours without a previous
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aging step. The crystalline solids were thereafter separated from
the mother liquor by suction filtration, washed and dried at 100C.
The solid product was identified as 100% zeolite Y by its charac-
teristic X-ray powder diffraction pattern. The oxygen adsorption
capacity of an activated sample was found to be 33.2 wt.-% at 100
mm Hg and -183C.
Examl~le 2
The sodium aluminate solution and the s~lica water
dispersion were prepared as in Example l using the same procedures
and quantities of reactants, except that She silica-water dispe-
rsion was aged for 20 hours at room temperature prior to combina-
tion with the aluminate solution. The resulting homogeneous gel
was aged at room temperature for 8 hours and thereafter digested
st 100C for 15 hours. The solid product was recovered by filtra-
tion, washing and drying. A sample thereof was identified by its
X-ray powder diffraction pattern as Type Y zeolite of at least 96%
purity.
Example 3
An alumina slurry was prepared by mixing 31.0 grams of
reagent grade gibbsite alumina (containing 64.4 w~.-% A1203;
average particle size 1 - 6~) into a concentrated sodium hydroxide
solution (64.0 grams NaOH containing 77.5 wt.-% Na20, and 100 ml
H20) for several
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seconds. The resultant slurry was added at a temperature of about
85 C to a homogeneous dispersion of silica and water (prepared by
intensively blending 133.3 grams of solid amorphous silica into
440 ml. of water~. After several minutes of manual mixing the
resultant mixture was intensively blended for one minute.
The resultant homogeneous gel had a molar composition, in terms
of component oxides, of 4.0 Na20:A1203:10.0 SiO2:160 H20.
This gel was digested at 100C for 24 hours without a
previous aging step. The crystalline solids were then separated
from the mother liquor by suction filtration, washed and dried.
X-ray diffraceion analysis of a sample of the product showet about
87% Type Y along with a small amount of unreacted gibbsite.
Example 4
An 11.85-gram quantity of reagent grade gibbside alumina
(containing 64.4 wt.-% A1203) was dissolved in a concentrated
caustic solution (24.0 grams of NaOH containing 77.5 wt.~% Na20,
and 37.0 ml. of water) by stirring and heating to form a clear
solution. The molal concentrations of Al(OH)3 and NaOH were
4.3 M and 16.2 M, respectively. This solution, at a temperature
of 85C, was added to a silica-water dispersion that had been ;-
prepared by high-shear blending of 50.0 grams of silica with 165
ml. of water. After several -
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minutes of manual mixing, the resultant mixture was intensively
blended for one minute. This homogeneous gel, having a molar
oxide composition of
Na20/SiO2 ~ 0.40
Si2/A123 ~ 9-7
H20tNa20 ~ 40.
was aged or 40 minutes at ambient temperature. This gel was next
digested at 110C for 7.0 hours. The crystalline solids were
recovered by filtration, washing and drying (at 100C). A sample
10 Of the solid product was identified by X-ray powder diffraction
analysis as Type Y zeolite.
Example 5
Solid sodium aluminate (43.9 ~rams), containing 44.1
wt.-X A1203 and 30.2 wt.-~ Na20, was slurried into a caustic
solution (46.4 grams of NaOH, containing 77.5 wt.-% Na20, and
100 ml. of H20). A dispersion of solid silica and water was
prepared by intensive blending of 133.3 grams of solid amorphous
silica with 440 ml. of H20. The aluminate slurry at a temperature
of 85C and the silica dispersion were mixed manually for ~everal
20 minutes, then intensively blended for one minute. The resulting
homogeneous gel had an overall composition in terms of oxide mole-
ratios of
Na20/SiO2 = 0.4 t
2/ 2 3 10
H20/Na20 - 40.
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This gel was digested at 100C for 2~ hours without a
prior aging step at room temperature. At the conclusion
of the cry~tallization period the solid product was
separated from the mother liquor by suction filtration,
followed by washing and drying. The product was identi-
fied as Type Y zeolite of at least 80% purity by X-ray
powder diffraction analysis.
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