Note: Descriptions are shown in the official language in which they were submitted.
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METHOD OF PREPARING CRYSTALLINE ALUMINOSILICATES
SPECIFICATION
The crystalline aluminosilicates are well known in the art, and
their description has been published in considerable detail. In general,
as found in nature or synthetically prepared, they comprise silica, alumina
and one or more exchangeable cations such as sodium. They are character-
ized by a three-dimensional network of fundamental structural units con-
sisting ofsilicon~entered SiO4 and aluminum-centered A104 tetrahedra
interconnected through a mutual sharing of the apical oxygen atoms. To
effect a chemical balance, each A104 tetrahedron has associated therewith
the aforementioned exchangeable cation. In most cases, at least a portion
of the exchangeable cations are subsequently ion exchanged with hydrogen
cations and/or other cations to yield a catalytically active form of the
crystalline aluminosilicate. The SiO4 and A104 tetrahedra are arranged
in a definite geometric pattern often visualized in terms of chains, layers
or polyhedra, all formed by the linking of the fundamental tetrahedra units.
In any case, the effect is a network of cages or cavities interconnected
by intracrystalline pores and channels whose narrowest cross-sections have
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essentially a uniform diameter. The various crystalline aluminosilicates
may be classified by the geometric pattern of their framework ~lith its
attendant pore size and by their silica-alumina mole ratios.
Methods of synthesizing the various crystalline aluminosilicates
are well known. Generally, a reaction mixture is prepared comprising
sodium aluminate or other suitable alumina precursor, and sodium silicate
or other suitable silica source, including colloidal silica, admixed with
an aqueous sodium hydroxide solution. The reaction conditions, as well
as the mole ratio of the reactants, are carefully controlled to precipitate
a particular crystalline aluminosilicate product. Typically, the reaction
mixture is allowed to digest at ambient temperature conditions for an
extended period up to a~out 40 hours or more, after which it is heated Wit~
stirring at a temperature of from about 85 to about 125C. The mother
liquor, comprising residual alkali metal silicate, is then filtered or
decanted from the crystalline aluminosilicate solid product which is
thereafter washed, dried and recovered as finely divided particles in the
0.05-0.5 micron range. `The present invention is particularly concerned
with the-preparation of crystalline aluminosilicates of the faujasite
family, especially type Xandtype Y. The preferred materials are charac-
terized by basically similar crystal lattice structures. Thus, the
aforementioned fundamental structural units, SiO~ and A104 tetrahedra,
are joined to form four-membered and six-membered rings and the rings are
so arranged that the resulting structure resembles a truncated octahedron
with the four-membered rings forming six sides or faces thereof and the
six-membered rings forming the remaining eight sides or faces. The result-
ing truncated octahedra are interconnected at the hexagonal faces through
a hexagonal prism formed by two of the six-membered rings of tetrahedra
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to form a crystal lattice comprising cavities or cages in open communi-
cation through channels permitting three-directional access thereto. In
general, the preferred crystalline aluminosilicates are characterized by
a SiO2/A1203 ratio of from about 2 to about 6 and by pore openings in the
range oF from about 6 to about 15 Angstroms, the synthetically prepared
X type having a SiO2/A1203 ratio of from about 2 to about 3, and the Y
type having a SiO2/A1203 ratio in excess of about 3. The preferred crystal-
line aluminosilicates have heretofore been prepared according to well-
known methods such as are described in U.S. Patent No. 2,~82,244 and U.S.
Patent No. 3,130,007.
It is an object of this invention to present an improved method
of preparing a crystalline aluminosilicate. It is a further object to
effect a substantial reduction in the reaction time required to produce
the crystalline aluminosilicate. It is~a still further object to present
an improved method of preparation to yield-a higher purity crystalline
aluminosilicate product.
In one of its broad aspects, the present invention embodies a
method of preparing a crystalline aluminosilicate which comprises forming
a reaction mixture comprising sodium, silica, alumina and water in a ratio
determined by the desired crystalline al~uminosilicate product; subjecting
said reaction mixture to high intensity shear-mixing conditions; maintain-
ing the resultant reaction mixture at a temperature of from about 25
to about 125C. until crystals are formed; and separating said crystals
from their mother liquor.
Another embodiment of this invention is in a method of prepara~
tion which comprises forming a reaction mixture comprising sodium, silica,
alumina and water ;n a ratio, expressed in terms of oxide mole ratios, in
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the following range: SiO2/Al203 from about 2 to about 20, Na20/SiO2
frorn about 0.3 to about lS, and H20/Na20 from about 25 to about 60; sub-
jecting said reaction mixture to high intensity shear-mixing conditions
which comprise processing said reaction mixture through a shear-mixer
adjusted to a clearance of less than about ~ and operated at an rpm
of at least about lO,OOO For a total contact time at said conditions of at
least about O.Ol minutes, maintaining the resultant reaction mixture at a
temperature of from about 85 to about l25C. until crystals are formed;
and separating said crystals from their mother liquor.
One of the more specific embodiments of the present invention
resides in a method of preparation which comprises forming a reaction mix-
ture comprising sodium, silica, alumina and water in a ratio, expressed
in terms of oxide mole ratios, in the following range: SiO2/Al203 fro~
about 2.5 to about 5, ~la20/SiO2 from about 0.5 to about l.O, and H20/Na20
from about 25 to about ~5; subjecting said reaction mixture to high inten-
sity shear-mixing conditions which comprise processing said reaction mix-
ture throu~h-a shear-mixer adjusted to a clearance of from about 0.25 to
1.27 mm and operated àt an rpm of from about lO,OOO to about l5,QOO
for a total contact time at said conditions at from about O.Ol to about
3 minutes; maintaining the resulting reaction mixture at a temperature of
from about 85 to about l25C. for a period of from about l8 to about 36
hours.
Other objects and embodiments of this invention will become
apparent in the following detailed specification.
Pursuant to the method of this invention, a reaction mixture
comprising sodium, silica, alumina and water is first prepared substantially
in accordance with prior art practice. The reaction mixture will generally
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comprise sodium aluminate or other suitable alumina precursor, and sodium
silicate, or other suitable silica source including colloidal silica, ad-
mixed with an aqueous sodium hydroxide solution, the mole ratio pF the
reactants being carefully controlled to precipitate a particular crystal-
line aluminosilicate product. Contrary to prior art practice whereby the
reaction mixture is allowed to react or digest at ambient temperature con-
ditions for extended periods of time measured in hours, the method of the
present invention, whereby the reaction mixture is subjected to high inten-
sity shear-mixing conditions, permits said reaction or digestion to be
effected in a substantially lesser period measured in minutes.
In accordance with the present invention, the reaction mixture,
comprising sodium, silica, alumîna and water, is subjected to high inten-
sity shear-mixin~ conditions. High intensity shear-mixing is commonly
practiced to achieve a uniform dispersion of a paste or dough. Generally,
the-shear-mixing means will compri~e a multitude of blades or pacldles
rotating in adjacent planes and at high velocity about a com~on shaft.
In some cases, the blades will rotate in adjacent planes in the same
di~ection while`in other cases they will rotate in opposite directions.
The high intensity shear-mixing results in part from the high speed ro-
tation, and in part from a minimal clearance between the blades of adjacent
planes, blades and sidewalls and/or blades and one or more stationary
shear bars. Shear-mixers are typically designed to maintain ~he total
mixture in close proximity to the spinning blades to take full advantage
of the high intensity shear-mixing affect. High intensity shear-mixing
is suitably effected at from about 3000 to about 18,000 rpm utilizing
shear-mixing means having a minimal clearance of from about .025 to i.27
mm . Preferred shear-mixing conditions include an rpm of from about 10,000
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to about 14,000, and a minimal clearance of from about 0.25 to 1.27
Inm . The reaction mixture is effectively exposed to the high intensity
shear-mixing conditions ~or a relatively brief period of at least about .01
minute and not necessarily in excess of about 5 minutes. ~hile high
intensity shear-mixin~ has been described with reference to one type of
shear-mixing means, it is understood that other shear-mixing means, for
example the various dispersion of colloidal mills, may be employed to
impart the desired high intensity to the shear-mixing operation.
In any case, the resulting reaction mixture is allowed to age
and further react unt;l crystals are formed as is the common pract;ce.
The reaction mixture is suitably maintained at a temperature of from about
25 to about 125C. at quiescent aging conditions, and preferably at a
temperature of from about 85 to about 125~C. for a period of from about
12 to about 36 hours.
The crystalline aluminosilicate product is readily separated
from the mother liquor by conventional means such as filtration, decanta-
tion, or by the use of a centrifuge. The separated crystalline alumino-
silicate product is then thoroughly water-washed and dried, typically at
an elevated temperature up to about 350C.
~0 The following examples are comparative examples presented in
illustration of the improved method of this invention and are not intended
as an undue limitation of the generally broad scope of the invention as
set out in the appended claims.
EXAMPLE I
In this example, representative of a prior art method of manu-
facture, 1827 grams of colloidal silica powder ~86% SiO2) was admixed
with an aqueous solution oF 1458 grams of sodium aluminate (31% Na20,
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46% A1203 and 23% H20) and 909 grams of sodium hydroxide (99% NaOH) in
7 liters of water. The mixture was subsequently diluted to a smooth
slurry with an additional 1.2~t liters of water. The resulting slurry
was stirred for about 19 hours in a closed vessel utili~ing a conventional
propeller type mixer air-driven at an rpm ranging from 2200 to 2400. In
this time, an initial reaction mixture temperature of 35C. increased to
60C. and the reaction mixture became slightly more viscous. The result-
ant reaction mixture was aged under quiescent conditions for 24 hours at
a temperature of 96~C. -- said aging being hereinafter referred to as the
1~ hot aging period. The crystallization product was recovered from themother liquor by filtration and dried at 204C. The dried product was then
reslurried in water, filtered, water-washed and further dried at 204C.
The final product was shown by X-ray defraction to be 86% type X faujasite
and had a surface area of 513 square meters per gram.
EXAMPLE II
The preparation of Example I was repeated substantially as
described except that the hot aging period was extended to 27 hours.
After filtering, washing and drying as in Example I, the product was shown
by X-ray defraction to be 74% type X fauiasite, the balance being phillip-
2~ site -- an undesirable low surface area crystalline form. The product had
a surface area of 451 square meters per gram.
EXAMPLE III
The preparation of Example I was again repeated substantially
as described except that the hot aging period was further extended to
36 hours. After filtering, washing and drying as per the previous exam-
ples, the product proved to have a surface area of only 16 square meters
per gram and was shown by X-ray defraction to contain 2.6% type X fauja-
site, the remainder beiny phillipsite.
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EXA~PLE IV
In this example, 1827 grams of colloidal silica powder (86%
SiO2) was admixed with an aqueous solution of 1458 grams of sodium alumi-
nate (31% Na20, 46~ A1203 and 23% H20) and 909 grams of sodium hydroxide
(99% NaOH) in 8.284 liters of water. Pursuant to the method of this inven-
tion, the mixture was then subjected to hiyh intensity shear-rnixing for
about 3 minutes -- the shear mixer being operated at 14,000 rpm. The
reaction mixture achieved the consistency of a thick paste. The result-
ant reaction mixture was then aged under quiescent conditions for 24
hours at a temperature of 96C. The crystalline product was separated
from the mother liquor by filtration and dried at 204C. The dried
product was reslurried in water, filtered, water-washed, and Further dried
at 204C. The over-all reaction time was about 24 hours as opposed to
Example I over-all reaction time of abou~ 43 hours. The final product
- 15 had a surface area oF 556 square meters per gram, and was shown by X-ray
defraction to be 106% type X faujasite -- that is, it was more pure than
the material utilized as an X-ray standard for pure faujasite.
EXAMPLE V
The preparation of Example IV was repeated substantially as
~described except that the hot aging period was extended to 27 hours as
was the case in the previous Example II. After filtering, washing and
drying as in the foregoing examples, the X-ray defraction revealed the
product to be 97% type X faujasite with no other crystalline material
being discernable by X-ray defraction. The product had a surface area
f 537 square meters per gram. This is in contrast to the 74% type X
faujasite product of Example II recovered after a total reaction time of
about 46 hours and having a surface area of 451 square meters per gram.
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EXA~PLE VI
The preparation of Example IV was again repeated substantially
as described except that the hot aging period was further extended to
36 hours as was the case in Example III. After filtering, washing and
drying as in the previous examples, the product proved to have a 461
square meter per gram surface area and was shown by X-ray defraction
to be 87% type X faujasite with no other crystalline material being iden-
tifiable by X-ray defraction. The total reaction time of about 36 hours
is in contrast to the 55 hours of Example III where a 2.6% faujasite
product was obtained with a surface area of only 16 square meters per gram.
EXAMPLE VII
In this example, 1827 grams of colloidal silica powder (86%
SiO2) was admixed with an aqueous solution of 1~58 grams of sodium alumi-
nate (31% Na20, 46% A1203 and 23% H20) and 909 grams of sodium hydroxide
(99% NaOH) in 7 liters of water. The mixture was subsequently diluted
to a smooth slurry with an additional 1.284 liters of water. The mixture
was then subjected to high intensity shear-mixing utilizing a colloid
mill with a minimal clearance of 0.51 mm and operated at 10,000 rpm.
The reaction mixture was recycled through the mill about 25 times for a
total contact time within the mill of about 1 second. The reaction mix-
ture was recovered as a thick paste. The resultant reaction mixture was then
aged for 24 hours at quiescent conditions and at a temperature of 96C.
The crystalline product was separated, washed and dried as in the previous
examples. The product in this case proved to be 95% type X ~aujasite by
X-ray defraction and contained no other crystalline form. The surface
area was 546 square meters per gram.
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