Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
107343~
Background of the Invention
Field of the Invention
The present invention relates to the production of crystalline
alumino~silicates commonly referred to as molecular sieves. More
specifically, this invention relates-to the preparation of fauja-
site materials having a novel particle 8ize and shape.
- Description of the prior art
Crystalline aluminosilicate zeolitesj commonly referred to
as "molecular sieves," are well known in the art. These materials
are characterized by a very highly ordered crystalline structure
arranged such that uniformly dimensioned pores result. The cry-stal
structure of these zeolites involves a three-dimensional framework
of A104 and SiO4 tetrahe~ra which are cross-linked by the sharing
of oxygen a`toms, so that the ratio of oxygen atoms to the total of
aluminum and silicon atoms is equal to two. The electronegativity
of these tetrahedra is balanced by the presence within the crystal
of cations, usually alkali metal cations, such as sodium and po-
tassium ions.
Faujasite is a naturally occurring alumino-silicate. It has
a,characteristic x-ray structure. The synthetic materials designated
zeolite "X" and zeolite "Y" by the Linde Division of Union Carbide
Corporation are commonly referred to as synthetic fauiasites. Zeo-
lite Y is described in U.S. Patent 3,130,007 and is generally similar
to zeolit~ X described in U.S. Patent 2,882,244.- Thc chemical Lor-
mula for zeolite Y given in U.S. Patcnt 3,130,007 is as follows:
0,9 -i 0.2 N~20:~1203 WsiO2 Xll2o
wherein w has a value of greater than 2.5 and up to about 6 and x may
hav~ a'value ~g lligh as 9.
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The product recovered from the usual methods of preparing
synthetic fau~asite described in the patent and technical lit-
erature is a fine sized, uniformly~shaped crystalline zeolite.
Several of the uses for molecular sieves require a product in a
size range substantially larger than the size of the product re-
covered from the preparation processes of the prior art. To
meet this demand processes have been developed which add various
binders and use forming steps to prepare nodules and extrusions
containing molecular sieves as the principal ingredient. Thesc
products lose some of their effectiveness since the binder is gen-
erally inert and acts as a diluent of the molecular sieve activity.
Even in the case of the so called "binderless" molecular sieve bodies
the transformation of the binder is generally not 100% complete.
The activity of a zeolite composite has to do with the weight
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of zeolite per unit of volume. Hence, a composite with a higher
density of zeolite will be more active as well as being stronger.
Prior art synthetic faujasite crystallites had certain fixed
packing characteristics because of the shape and size of the
crystallites produced by prior art processes.
It would be hi~hly desirable to produce synthetic faujasite
in a platelet crystalllte form which would pack more densely and
could be used either alone to form highly active, strong
composites or in combination with normally shaped zeolite
crystallites as a strong active binder, or lubricant component.
SUMMARY
In accordance with the present invention a method for the
preparation of a novel crystalline form of synthetic faujasite
is provided. More spccifically, we have found that a platclet-
type form of synthetic faujaslte crystal can be prepared by adding
pota~ium ion~ in a concentration o~ from 0.~5 to ~.~ molcs pcr
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mole of alumina to a seeded synthetic faujasite reaction mixture,
heating, and recovering the product.
Thus, in accordance with the present teachings, a
process is provided for preparing a crystalline zeolite
aluminosilicate having a structure similar to faujasite, a
silica alumina molar ratio of from 2.2 to 6, and a novel
platelet-type crystallite shape which comprises:
(a) preparing a faujasite synthesis mixture,
-~b) adding potassium ions in a concentration of from
0.05 to 2.2 moles per mole of alumina of said mixture,
(c) seeding the synthesis mixture with amorphous
aluminosilicate zeolitic nucleation centers having a particle
size below about 0.1 micron,
(d) heating the resultant slurry to a temperature
of about 60 to 110C. until crystallization of the zeolite is
complete, and
(e) washing and recovering the zeolite product
wherein at least 25~ of the crystals comprising the product
are in the form of platelet flattened octahedron shapes.
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The first step in the process of the present invention is
the preparation of a faujasite precursor mixture. We will con-
sider the preparation of both Type "X" and type "Y" fau~asites
having the novel crystallite shape and size of the present in-
vention.
It has been reported in U.S. Patent 2,882,244 that the so- -~
dium form of zeolite "X" can be prepared essentially free of con-
taminating materials from a reactant-mixture which composition falls
within the following range: .
Na20/SiO2 0.8 to 1.5
SiO2/A1203 3 to 5
H20/Na20 30 to 50
~ When aqueous colloidal silica sol or reactive amorphous silica
: sol is used as the silica source, it has been reported that zeolite
: "Y" c-an be obtained if the reactant mixture has a composition in the
following range:
Na20/SiO2 0.4.to 6
. SiO2/A1203 15 to 25
H20/Na20 20 to 50
When sodium silicate, silica gels or silicic acid are used,
. the preferred reaction mixture for.preparing zeolite Y falls with-
,
n the following range:
Na20/SiO2 . Ø3 to 9 -'
SiO2/A1203 8 to 25
H2/Na20 12 to 90
A typ~cal, simple and inexpensive preparation of a zeolite
X precursor mixture involves combining the desired amount of meta-
kaolin, (A12O3:2SiO2), and sufficient sodium hydroxide.
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"Y" type zeolite precursor mixtures can be formed by the
proper quantities of metakaolin and sodium silicate, or by dis-
solving alumina trihydrate in sodium hydroxide and adding suffi-
cient sodium silicate. Although any alkali metal silicate would
give satisfactory results, the zeolites are normally prepared in
the sodium form. Since this is the case, the silicate used is a
commercially available sodium silicate having a SiO2 to Na2O ratio
of 3.3:1 to 3.4:1. This silicate is diluted with water when
necessary to provide a silicate solution having the desired con-
centration. Additional Na2O may be added as NaOH.
The clay used can be a kaolin clay that has been cal- --
cined to convert it to metakaolin. This conversion is effected by
calcination of raw kaolin clay to a temperature of 1200 to 1500 F.
The sources of the reactants, silica, alumina, sodium
. . . are rather immaterial. It is the ratios of these reactants
in the precursor mixture which is crucial to the type of zeolite -
produced.
The next step in the process of the present invention is
the addition of potassium ions to the zeolite precursor mixture.
It has been found that this addition of potassium ions brings
about an alteration in the shape and size of the end product
zeolite crystallites. Whereas, normal sodium X and Y-type crystals
made by the seeding process of (U. S. Patent 3,574,538) have uni-
form dimensions on the order of 0.4-0.8 microns, the crystals
produced by the process of the invention are flattened and plate-
let shaped.
Any water soluble compound of potassium is suitable for
this addition step. However, it is generally desirable to keep
the amounts of contaminating ions to a minimum as these must be
subsequently washed or exchanged form the product zeolite in order
to produce the most active and stable form. For this reason the
potassium ions are usually added as the hydroxide and calculated
as moles of K2O. For our purposes from 0.05 to 1.0 moles or more
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preferably 0.05 to 0.7 K20 are a~ded as KOI~ to either a sodium X
X or sodium Y-type precursor mixture, per mole A1203 in the
slurry.
In the synthesis of modified sodium X zeolite 0.35 moles
K20 yielded approximately 25% flattened crys-tals mixed with
75~ normal ones, while the higher amount gave approximately
50% of each type. The flattened crystals were about 0.5 by
0.25 microns and the normal crystals 0.4 by 0.5 microns.
In the case of modified sodium Y, all of the product
crystals were flattened upon the addition of 0.35 to 0.7 moles
K20 in the slurries of examples 2 and 3. The slurry of
-example 3 yields platelet Y crystals approximately 0.2 to 0.3
microns-wide and 0.1 to 0.15 thick while the Y slurries of
examples 2 and 5 produce ~ 0.25 x ~ 0.5 x ~0.5 platelet crystals.
The larger amount of K20 produced the most flattening.
The next step in the instant process involves adding nucieation
centers to the precursor mixture containing potassium. U.S. Patent
3,574,5~8 issued April 13, 1971 describes a process for preparing
crystalline aluminosilicates using the "seeding" technique. The
zeolite seèds are nucleation centers having an average size below
about a tenth of a micron. As pointed out in this patent, the
seeding technique is advantageous in that it decreases the aging
time necessary fo-r the formation of the zeolite. In the conven-
tional processes, the reaction product is aged at varying temperatures
for periods of 1 to 4 days.
Using the seeding technique, this aging time can be reduced to
lower values, sometimes as low as 10 to 30 ~inutes.
The-nucleation centers are small particles that may be either
amorphous or crystalline. They are prcpared by a spccial techniquc.
'l'he method of preparing these seeds is not a part of this invention.
Broadly, the method of preparing the crystalline seeds comprises
mixing solutions of sodium aluminate, sodium silicate, and sodium
hydroxide in the desired proportions. These solutions are then
cooled and aged.
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.
Seeds are normally added as from 0.1 to 10 weight percent
(based on the weight of the final theoretical yield of the zeolite
product). ~owever, amounts of seeds in excess of about 10% may
be used, but do not increase the rate of zeolite production in
proportion to the economic value of the additional seed material
except that high seedirg levels produce s~all particles.
Likewise less than 0.1 weight percent of the seeds may be used.
However, the reaction is very slow under these conditions. The
mixing procedure used in combining the seeds with the precursor
mixture should be one which results in a rapid and-thorough
dispersion of the seeds throughout the mixture.
At this point, it should be noted that in another embodiment
of the present inventive process potasslum ions may be added as KOH
subsequent-to the addition of the nucleation centers to the precursor
mixture without adversely affecting the end product and crystals.
The slurry of potassium containing precursor mlxture and
seeds is heated at temperatures of about 60 to 110C. until
crystallizatlon occurs, generally for a period ranging from 10
minutes to 30 hours. It has been found that during this reaction
period the desired crystalline zeolite`forms, and the yields
which approach the theoretical yield expected from the starting
materials present in the reaction mixture can be recovered.
The reaction may be conducted at relatlvely uniform temperatures
or lf desired may be conducted at a series of different temperatures;
that is, the slurry may be first aged at temperatures of from
about 25-to 40C. for a period of 2 minutcs to 24 hours and
subsequently heated to a higher temperature of from about 40
to 110C. for a l~criod o ~bout 10 minutcs to 30 l~ours. -rt
lS al50 to be under,tood that the reactlon ma~ be conductod where the
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temperature is continuously varied. Subsequent to the reaction,
the resultant crystalline product is recovered by any convenient
technique which may involve filtration or cetrifugation. The
recovered product is preferably washed to remove excess reactants
and subsequently may be dried or used in the form or an aqueous
slurry.
Our invention is further illustrated by the following
specific but non-limiting examples.
EXAMPLE 1
This example illustrates the process of preparing amor-
phous nucleation centers. A 290 gram quantity of sodium aluminate
was dissolved in 2 liters of water. A sodium silicate solution
was made up by dissolving 1120 grams of sodium hydroxide and 2680
grams of water and 4200 grams of sodium silicate solution contain-
ing 28% SiO2 was added. The sodium aluminate solution was mixed
with sodium hydroxide-sodium silicate solution. The resulting
solution was cooled to 15 and aged without stirring for 16 hours.
At the end of this time, the slurry of amorphous nucleation
centers was ready for use.
EXAMPLE 2
This example details the preparation of the modified
sodium Y-type zeolite of the present invention.
An aluminate solution was made by dissolving 35.5 grams
alumina trihydrate in a solution of 32 grams sodium hydroxide in
50 grams of water. Next a solution of 22 grams potassium hydrox-
ide in L25 grams of water was added. The aluminate solution was
bl~nded into a mixture of 412 grams water and 823 grams sodium
silicate ~olution (27% SiO2 and 8.2% Na2O). Then 70 milliliters
of a seeding mixture (slurry ratio 16 Na2O : 1 A12O3 : 15 SiO2 :
320 H2O) was stirred into the above mixture and the entire slurry
was heated to 95-105C for 3-7 hours. The product was a mixed
(Na,K)Y type faujasite whose analysis was:
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1.4% K2O
11.4% Na2O
65,2% sio2
22.1% A12O3
` The individual crystaLs have a flattened platelet-like shape
of ~ 0.25 X ~ 0.5 micron. Thc surfacc area was 830 m /~J a~ter
calcination at 1000F. for 1 hour.
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In accordance with the procedure set forth in example II, a
series of X and Y type modified zeolites were prepared, the data
covering which are set forth in Table I.
, ' , ' , " ' ' .
.
.
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., ~ , .
., ' ' ' ' .
-- g _
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R o. c n ~ ~ w ~ q w
3 ~ ~ (D ~ ~ 3~ ~- ~ ~ ~ ~
~' ~ ~ I_ ~ P~ ~ o ~ ~
W P~ N ~ (D O
X It 3~P ~1 tn.
~ ' O p~ ~ O W O ~o ~o
O ~ ~, ~ ~ ~ ~ , X l_
~D _ 3 _ _ 3 H
~ ~ ~D ~ o w o (D
14' Pl .~. ~I ~Jl . ~) p) X ~ ',~
5 . I'' W
(D o ;~ ~ o ~ ~ ~ ~) o ~0 No :-
C ~ o ~ ~ o
.~. . .
~_ 3 __ 3 ~
o ~D ~ ~ ~ o o (D "
, W O~ ~n ~n W ~
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EXAMPLE 4
887.5 grams of alumina trihydrate were dissolved in a
solution of 800 grams sodium hydroxide in 1250 grams water. After
,the alumina trihydrate dissolved, a solution of 550 grams
potassium hydroxide in 3125 grams water was added. The alum-
inate solution was blended into a mixture of 20,570 grams
sodium silicate solution (27% SiO2 and 8.2% Na20) and 10, 228
grams water. ,Then 1750-milliliters of a seeding mixture - '-
(slurry ratio 16 Na20: l~A1203: 15 SiO2: 320 ~l20) were added,
and the entire slurry was~ heated to 100C for 7 hours. The
product is a mixed (Na,K)Y type faujasite having a platclet
particle shape'of ~,25 x ~ 0.5 mic,ron. The calcined product had
a surface area of 710 M2/g. It contained 11.3~ Na?O and 1.2%
K2O, by weight.
A portion of this batch was made into a cracking cataly.st
promoter. A Promoter sample had the following analysis:
6urface Area 700 M2/g RE203 19.2%
Na20 0.46%
This promoter was made into catalyst containing 2.42 wt. per-
cent RE203 and pilot'tested after S-20 steam deactivation at
920F, a catalyst to oil ratio oE 4, and weight hourly space
velocity of 40. It converted 69.5 volume % of feed and made
4.5% coke (wt.% feed). The detailed results are given in the
appended ~l~able'II. ~his t-est shows that cracking catalyst
ade frolll p'la~elc~ Y has cssentially ~he sallle activi~y as ~he ,
standard catalyst made Erom regular Y.
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TABLE II
~ .
Example 4 standard
Pilot Unit Data: 920-F, 4 c/o, 40 WHSV, WTGO Feed~Catalytst deactivated by
Cooversion ' WV% 0.04 S-20 r2e m)
Total C3 : V% - 7 5 7.8
C3~ ~: V% 6.o 5i7
Totnl C4 . V/ 9 9 1~ 1
C5+ Gasoline V% 4 7 6ilo
RON + O . 0 87 o 85
MON ~ O 76.o 76.5
- MON + 3 . ~5;4 84.o
~Aniline Pt.: F 96 93
Br. Number : 46 ., . 36
Coke : W% FF 4.5 5.7
* 2~ steam atmosphere for 12 hours at 1520F.
-This example shows that platelet-type Y zeolites can be
. substituted for normal Y in catalyst compositions without adverse
afect on catalyst performance.
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~xample 5
This, example demonstrates the use of a low level of
K2O to produce a ~-type faujasite which has a mixture of
platelet and regular octahedral crystals in approximately
50-50 ratio.
~ solution of sodium aluminate was prepared by dissolving -*
28 g. alumina trihydrate in a solution of 20 g.~ sodium hydroxidc
in 40 ml. water. ~ter the alumina trihydrate dissolved,
40 ml. more water was added and the solution coolcd to room
temperature; then the aluminate solution was added to a
mixture of 598 g. sodium silicate (25.5% SiO2; 7.8% Na2O)
and 119 g. seeds ln a reaction vessel with rapid stirring.
- Next a solution of 3 g. potassium hydroxide in 42 ml. water
was added with stirring. Finally 134 g. aluminum sulfate
solution (8.33~ A12O3) was added with rapid stirring. This
yielded a synthesis slurry having the following ratios of
reactants: 3Na2O:0.08K20:1 A12O3:9SiO2:130 H2O.
-,' The reaction vessel was fitted with a reflux condenser
and the slurry was heated to 100 + 2. for 18 hours. The
product was collected on a filter, washcd frec of soluble
salts and dried at 110C. The zeolite thus synthesized was
a Y-type ~aujasite which had a surface area of 733 m2/g and
a unit cell size of 24.64~. Chemical analysis showed the K2O
content to bc 0.6% on a dry basis. Scanning electron
micrographs showed t~e particles to bc 0.25 x 0.5 x 0.5
m,icron platclets and 0.4-0.6 microll octalledra in a~out a
1:1 mixt-lre. ~ -
~xalllple 6
-This exalllple demonstrates th~t 3/32 inch pills (3/32
incll dialn~ter and 1/16 inch long) nlade rrolll elat~let Y-type
fauja~ite are ~tronger tllan tlle ~ nade ~roln conventional
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Y-type faujasite which has an octahedral crystal shape.
A sample of mixed platelet and octahedral Y-type
faujasite, prep~red in ~xample 5, was dried at 110C. to
about 20% moisture content. A sample of conventional Y-type
fau]asite made ~rom essentially the same slurry oxide ratio
as used in Example 5, but lacking any K2O in the slurry,
had 0.4-0.8 micron particles having an octahedral shape;
this was also dried at 110C. to about 20% moisture content.
49 gram portion of each zeolite was thoroughly ~ixed with
1 gram of Sterotex (a lubricant for pilling and extruding
dies, supplied by Capital City Product Co., Columbus, Ohio).
The mixtures were pressed into 1/2 inch dia. x 1/2
inch long pellets using a cornmercially available pellet press.
Then the pellets were pulverized to granules and the granules
sieyed. The 40-80 mesh fraction of granules was made into
pills on a Stokes Tablet Machine Model 511-5 (F. J. Stokes
Corporation, Philadelphia, Pennsylvania) using 3/16 inch
diameter dies.
~ Ten pills from each lot were selected at random for
crushing on a Chatillon crush strength meter for pills,
tablets and extrudates. Each pill was crushed perpendicular
to its diameter. The average crush strength of the pills
prepared from the mixed platelet/octahedral shaped Y-type
faujasit~ from Rx~mple 5 was 1.1 poun~s/~ill while ~hc
average crush strength of the pills prcpared from conventional
Y-type faujasite w*s only 0.5 pound/pill.
Thus it is apparent, the addition of platelct sllal~d
Y cry~taLs to collv~ntiorlal octahed~ally shaped crystals,
yields a product of significantly greater crushing strength.
l~olin, platelet ~haped, inert nlirleral is oftell added to
zeolite pills-, extrusions and spheres to enhance binding,
irllprovc strellyth and help in the forming step. Unlortunately,
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kaolin in lnert and therefore reduces the sorptive capacity
of the zeolite sor~ent, or the catalytic activity of the
catalyst. By replacing the kaolin with the above disclosed
platelet form of faujasite, the advantages of ~sing kaolin
are retained, and the disadvantages eliminated, as the platelet
faujasite has similar sorptive and catalytic properties to
the convcntional~octahcdral faujasitc.
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