Note: Descriptions are shown in the official language in which they were submitted.
~S7Z7~
The present invention relates to a process for produc-
ing A-type zeolitic molecular sieves based on crystalline alumino
silicates containing water of hydration and at least 99.5~ by
weight of particles having diameters smaller than 45 ~m by
.
hydrothermal crystallization o an aluminate/sodium tetrasilicate
synthesis mixtuxe. The present invention also relates to the
. .
molecular sieves obtainable by means of said process and to
their use.
:. . .
Zeolitic molecular sieves with their specific proper-
ties for ion exchange and adsorption have been known for a long
time. Their synthesis com~rising heating an aaueous synthesis
, ~ .
mixture with the components Na2O x b A12O3 x c SiO2 to tempera-
tures between 50 and 300C. Depending on the composit~on of the
. -. ~ .
.. . . . .
reactant mlxture, reactlon temperature and reactlon tlme, com-
,:f pounds having the general formula NaxAlxSiyO2(x+y). n H2O of
differing X-ray spectra are obtained. In these synthesis sodium
can be replaced by monoval2nt or divalent ions. Thus, for
., .
example, German Patent No. 1,038,017 issued October 22, 1969 to
Union Carbide Corporation describes a process ~or producing the
~J
~; 20 molecular sieve A having the summation formula 1.0 - 0.2 M2~nO o
A1~03 : 1.85 - 0.5 SiO2 : Y H2O, wherein M represents a metal
cation, n its valency and Y a value of up to 6. For the produc-
tion of the A type a synthesis mixture in which SiO2 and A12O3
~` (for example, in the form of sodium tetrasilicate or sodium
aluminate) are pxesent in ~he molar ratio of 2:1 and water and
~ alkali metal oxide (for example, Na2O) in the molar ratio of 17.5:
- 1 is usually used.
The fact that the synthesis yields crystals whose
average diameter is above approximately 2 and that a substantial
portion (usually hetween 3 and 12% by weight) has a limitiny
particle size above 45 ~m is common to the known processes. This
proportion is referred to as grit and according to DIN 53580 it
is determined by wet screeniny according to Mocker.
:. . . , , - ~ , . . , : '
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For use as adsorbents, catalyst supports or ion exch-
angers the molecula~ sieves are converted in~o molded articles
with a suitable hinder. The production of the molded article
involves great technical expendituxe while the effect of ~he ;
sieve is reduced due to the presence of the binder. Further,
because of the long diffusion paths the rate of reaction is
substantially reduced, so that the drying of organic liquids is
cumbersome. Further, for example, when removing me~al or radio-
active metals from added water and from waste water, ion exchange
and precipitation must be separated. Therefore, for the above ~-~
uses it is appropriate to use the molecular sieve in the form o~
a powder. In lacquers, too, it is used only in this form.
The present invention provides a process by means of
which powdery zeolitic A-type molecular sieves, particularly for `
use as ion exchangers, e.g. for water softening, are synthesized
with defined particle sizes without the formation of grit i.e.
particles of size > 45 ~m. For use of the molecular sieves of
the present invention, for example, as a phosphate substitute ~ ~
in detergents, the absence of grit is imperative. Washing and ~ ~ -
cleaning processes, particularl.y in machines, require that the
molecular sieve remains in suspension in the wash liquor (due to
a low tendency to deposit sediments) in order to assure rinsing
without leaving xesidues after the completed washing process.
According to the present invention therefore there is `
provided a process for producing A-type zeolitic molecular sieves -~
based on crystalline alumino silicates containin~ water of hydra- ;~
tion and containing at least 99.5, preferably 99.9 and particul- `~
arly 99.99~ by weight of particles having diameters less than ~5
~m by hydrothermal crystallization of an aluminate/sodium ~e~
silicate synthesis mixture, in which the components of the synth- ~ -
esis mixture which are present in molar ratio between SiO2 and
Al2O3 of less than l.9 : l and preferably in a molar ratio
... , ~. -. . .i , , .
between water and alkali metal oxide of at least 30 : 1, are
intimately mixed prior to the precipitation of the amorphous
; initial product and that upon cr~stallization the aluminium
silicate suspension is tempered under crystallizing conditions
and sheared during the crystallization and/or during the tem-
r~ pering.
~ ~ .
;- Thus, the process of the present invention is based
.
on the following important interacting measures, which make the
practically quantitative synthesis of a product having the des-
ired limiting particle size and specific granular sizes possible.
In contrast to the conventional processes a substant- ;~
;~ ially higher proportion of aluminium oxide is present in the sy- ~ -
~ nthesis mixture. Care is taken that the precipitation is carried ~ ~
. . . .
out from an intimately mixed synthesis mixture in order to assure
~ uniform formation of nuclei. It is further essential that the
-; crystallization is followed by a tempering stage, in which the
conditions used for the crystallization are usually maintained.
Further, during the crystallization or during both process stages
~;, shearing forces must act on the aluminium silicate suspension.
! 20 A particularly low contant of particles having a limited size can
be obtained when the measures mentioned hereinbefore are combined
with the use of an alkali concentration in the synthesis mixture ~`
which is reduced as compared with that of conventional processes.
The decrease in the proportion of particles having a limited size
which is brought about in like manner by the tempering and by the
reduced alkali concentration is surprising insofar as is well -
known, in crystallizations both the tempering and the reduction in ;
concentration result in the formation of larger crystals and the ~ ~-
effects which can be obtained in the present system thus run coun-
3~ ter to the prevailing teaching.
The measures according to the invention for controlling ~
the limiting particle size and the proportion of particles having ~ `
- 3 -
,
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a limited size can be chosen that a desired average particle
diameter oE the crystals is obtained. The average particle
diameter can have values from below 1 ~m to lS ~m and is deter- -
~ mined primarily by the effect of the shearing intensity during
- the crystallization. For the intended purpose according to the
invention an average particle diameter of approximately 8 ~m in
` conjunction ~ith the limiting particle size below 45 ~m was found
`~ to be suitable. As the values for the limiting particle size de-
crease the distribution curve, which is flattened towards large
; 10 crystals, tends to an ideal Gaussian distribution. An optimum
and thus practice - favourable adjustment of the proportion of
the desired limiting particle size, which, according to the pre-
sent invention, can be decreased to 0.01% by weight and even to ~
a lower value, can be attained only by the interaction of the ~;
important measures of the process. From studies of the sedimen
s tation behaviour it can be estimated that according to the inven-tion the limiting particle size can be reduced to values of app-
roximately 20 ~m. The synthesis mixture can contain SiO2 and
A12O3 in molar ratios of 0.8 to 1.6 : 1, particularly about 1.3 :
1, and water and alkali metal o~ide in molar ratios of 35 to 50
-' A particularly favourable manner of carrying out the
process of the present invention is that in order to precipitate
the amorphous initial product, an amount of water or aluminate
solution which causes at least a stirring effect is used and sod-
.. . .
ium aluminate solution as well as sodium tetrasilicate solution ;
are added simultaneously while stirring thoroughly, particularly
in the zone of maximum turbulence.
By "shearing", as used herein is meant any comminuting ~ ~
mechanical stress on discrete particles in suspension, i.e., a ,
mechanical stress due substantially to a true shearing effect.
The shearing can be carried out either discontinously or contin-
uously. I~he recycling method f operation in which the material
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to be sheared is exposecl to the action of shear forces several
times in succession is preferred. A critarion thereof is the so- -
called throughput fre~uenc~, which indicates the numhPr of streams
passing throuyh per hour (dimension h 1) A turbine mixer, for
example, the EKATO (a trademark) turbine mixer, is the preferred
shear apparatus. However, a toothed-disc dissolver, dispersing
pumps, rotary pumps or the like can also be used for shearing.
The shearing energy to be applied in order to obtain the limiting
particle size under the operating conditions according to the
invention is practically negligible as compared with the shearing
energy required for drastically reducing the average particle
diameter (see German Auslegeschrift 2,333,068 published September
1, 1977). Une~pectedly it was found that if the limiting particle
size and the proportion of particles having a limited size are
correctly adjusted, then the average particle diameter can also ~;~
be above 2 ~m without impairing an important property of the
application techni~ue, namelv the capabilit~ of washing out the
zeolite softening agents according to t:he present invention used
in detergents. Thus, if a turbine impeller is used, then it can
be operated with a rate of power input of 0.4 to 2, preferably
0.6 to 1, particularly 0.8 KW per cu m.
While the crystallization can be carried out, for
example, at 94C, it was found to be advantageous to carry out
the tempering at a temperature between 85 and 105C in the
cxystallizing mother li~uor. Tempering times between 0.2 and 6,
preferably from 0.8 to 1.8, hours, particularly one haur are
favourable. The tempering time starts at the point at which the
crys~allization is completed. This point i5 evident from the
development of maximum X-ray line intensity and attainment of a ~
steam adsorption of approximately 22O5%. In practice an empirical ;
value determined ~y means of an optimized formula is used.
In order to optimi2e the process products for a specific
-5-
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purpose, tempering and shearing conditions in particular must be
adjusted to one another, whereas with respect to the A1203/SiO2
molar ratio or also with respect to the alkali content in the
synthesis mixture it is sufficient to maintain the specified
limits.
Shearing which is effective towards the end of the
crystallization phase can be so intensified that the average
particle diameter can be decreased to very small values and the
values for particles having a limited size and their percentage -
in the product can thus also be reduced. However, the effect of
shearing on the average particle diameter and limiting particle
size or on the proportion of particles having a limited size is
not parallel under all the conditions of the process. Thus, for
example, with the preferred use of lower alkali concentrations in
the synthesis mixture the average particle diameter increases -
while the limiting particle sizes and the proportion of particles
having a limited size decrease. However, when shearing was
carried out during the tempering stage it affected exclusively
~ the particles having a limited size and their proportion.
; The present invention also provides an A-type zeolitic ~ -
molecular sieve with at least 99.5%~ preferably 99.9% and part-
icularly 99.99% of particles having diameters below 45 ~m and a
- particle spectrum containing ~ ~`
fraction proportion
(~m) (% by weight)
: - :
<3 <15
<5 <35 -~
<10 <82
<15 <96
<2Q <100
: , ~ , . , , : . . . ..
: . , . . :
:, . .. , , . . ::
:, ,. : : , : ,
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preferably Eraction proportion
(~m) (~ by weight3
<3 4-15
~5 11-35
<10 50-82
<15 79-96
<20 93-100
The A-type zeolitic molecular sieve can be obtained by means of
the process measures described hereinbefore.
Finally, the invention relates to the use of the mole-
cular sieve as an ion exchanger, for example, to soften water,
particularly as a phosphate substitute in detergents. The products
according to the invention have the advantage that they are free
i from grit even during their production. Therefore, when they are
used as softeners in detergents they can be readily kept in sus-
pension in the wash liquors concerned and they can be rinsed out
of washing machines and their loads with particular ease and with-
out leaving residues.
The present invention will be further illustrated by way
of the following examples.
Example 1
7 kg of commercial moist hydrate, i.e. an aluminium
oxide hydrate having a water content of 42.5%, which can be det-
ermined by means of the loss on ignition, is dissolved in 50
litres of a 12% by weight solution of caustic soda at 100C. The
clear solution thus obtained is cooled to 80C. The further ; -
treatment is carried out in a 60-litre glass vessel, which is
fitted with a mixer. The power consumption can be measured wikh
a superposed ammeter. The velocity of stirring is infiniteIy
variable. The mixer is an Eka~o ( a trademark) turbine mixer
according to DIN 28131 and has a diameter of 15 cm. The agitating
tank has a diameter of 40 cm and 4 baffles, each baffle being
- 7 -
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arranged at an angle of 90.
The precipitation is initiated by dosing in 8.8 litres
of sodium tetrasilicate, which contains 26.5% by weight of SiO2
and 8% by weight of Na2O, with a tube ending approximately 0.5
cm above -the disc of the turbine mixer.
Prior to the start of the precipitation, 15 litres of
aluminate solution are put into the agitating tank. The remainder
is added to the reaction mixture simultaneously with the sodium
tetrasilicate. The precipitation is completed after 30 minutes.
The precipitated product i5 amorphous to X-rays. In the reaction
mixture the components are in the molar ratio of
H2O : Na2O = 33
and Si2 A123 = 1-3
At the end of the precipitation the mixer has an energy :~
consumption of 0.8 XW per cu m. The temperature of the reaction
mixture is increased to 90C with the aid of steam. The course
of the starting crystallization is ohserved by means of the Ca-
bonding power.
By Ca-bonding power is meant the ion exchangeability of -~
1 g of the product dried for 2 hours at 200C. For its determin~
ation this amount is added to 1 litre of water, which contains ;~
CaC12 corresponding to 300 mg of CaO. This is followed by filter-
ing and the amount of CaO remaining in the water is titrated com~
plexometrically. The difference with respect to the initial 300
mg constitutes the bonding power of the zeolite. The crystalliz-
ation is completed when the Ca-bonding power ceases to change. ;~
After a reaction time of 80 minutes the Ca-bonding power reaches `
the value of 16.4 and then remains constant.
Upon completed crystalli2ation the temperature is raised
30 to 95C, followed by tempering for 30 minutes while shearing. The ,~ -
crystalline product thus obtained is then washed to pH 10.0, -
~whereupon it is dried in a drying cabinet at 200C. It has the ; ;
~ 8 -
i7~
.
;~ X-ray diffraction pattern of the zeolite A, as indicated in the
German Patent No. 1 038 017.
In order to determine the limiting particle size, wet
- screening is carried out in accordance with DIN 53580. For this
purpose, the sample, suspended in water, is put into a Mocker
tester and is kept in a turbulent motion by water sprayed from
rotating nozzles. The fine particles are flushed through the
fabric of the test sieve while the coarse particles remain on the
test sieve. The residue is tested on the sieve and weighed. A ~
sieve according to DIN 4188, i.e., a sieve having a width of mesh ~ ~-
of 45 ~m is used as the test sieve fabric.
The product thus obtained has a proportion of 0.010~ of
particles having a limited size > 45 ~m and this proportion was
determined in the manner described above.
An analysis of granular sizes on a sedimentation balance
is used for the further characterization of the product.
The sample to be measured is dispersed in water with the `
aid of an Ultra-Turrax and the sedim~ntation is then observed. ~
The particle distribution is as follows: `
fraction ~ proportion
(~m~ (% by weight)
` <3 7 9 `~
; <5 14.9
<10 60.4
<15 85.9
<20 95
:
;~ <25 99 3
` <30 100.0
-~ Example 2
5.5 kg of moist hydrate having a water content of 42.5
are dissolved in 50 litres of a 10~ by weight solution of caustic
soda. The reactor described in Example 1 is fitted with a
~5~ 2r~
propeller mixer having a diameter of 15 cm according to DIN 28131.
During the precipitation and crystallization the energy consump-
tion of the mixer is 0.3 KW per cu m. As in example 1, 15 litres
of the aluminate solution were put into the reactor first, in
order to assure sufficient efficiency of the mixer at the begin-
ning of the addition of sodium tetrasilicate. The rest of the
aluminate liquor is added within 30 minutes. At the same time
6.8 litres of sodium tetrasilicate containing 26.5% of SiO2 and
8~ of Na2O are added directly on the propellerO The synthesis
mixture thus obtained which has a molar ratio of
S 2 2 3 ~ ?
and H2O : Na2O = 39 : 1
is then crystallized at 93C. After 90 minutes a Ca-bonding power
of 168 mg of CaO per gram is obtained and the reaction is completed.
The propeller is then replaced by a turbine mixer as described in
Example 1, whereupon tempering is carried out at the same temper- ~ `
ature (i.e., 93~C) under the action of shearing energy, the energy ;~
consumption being 0.8 KW per cu m. After 1 hour the reaction is
terminated, the product is washed to pH 10.0 and then spraydried. ; '
The A-type zeolite obtained is~radiographically pure and, in the
grit determination according to Mocker (DIN 53580), it no longer ~;
has any measurable proportion of particles > 45 ~m. The accuracy
of measurement of this method is 0.001%. An analysis of granular
sizes on the sedimentation balance shows the following particle ~
distribution: f ; `-
fraction proportion
(~m) (% by weight)
<3 15-3
<5 35.2
<10 82.6 ;
<15 96.3
<20 100.0 ~ ~
~ , . - ,.:
`:
., - 10 ;
,, , : . .: : . . ~ .. : . .
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Example 3
A synthesis mixture is produced analogously to that
of example 2. It contains the components SiO2 and A12O3 in the
ratio of 1.3 : 1 as well as water and sodium oxide in the ratio
of 39 : 1. After the preclpitation stage a turbine mixer having
a diameter of 10 cm is used for shearing during the crystalliza-
tion. The energy consumption is 0.6 KW per cu m and the crystall-
ization temperature 90C. After 110 minutes the Ca-bonding power
of the crystallized zeolite reaches a Einal value of 161 mg of
CaO per gram. The turbine mixer is then replaced by a 3-stage
MIG ( a trademark) mixer of the firm of Ekato, whereupon the syn-
thesis mixture is tempered at an energy-consumption of 0.1 KW per
cu m for 4 hours at 92C while stirring (no shearing). The pro-
duct obtained :is a radiographically pure zeolite and has a pro-
portion of 0.13~ of particles having a limited size (which can be
determined with the Mocker tester) and the following particle
spectrum (as determined on a sedimentation balance):
fraction proportion
m) (% by weight) -~
<3 4 2
<5 10.8 ;
<10 50.3
<15 78.6
93 3
<25 98.1
` <30 99.5
; Example 4
5.5 kg of commercial moist hydrate are dissolved in 53
litres of an 11% by weight solution of caustic soda. The aluminate
solution ohtained is pumped into a 60-litre reactor by means of a
Static ( a trademark) Mixer. Ahead of the mixing unit 8.2 litres -'
of sodium tetrasilicate are added. After the mixing process a
'~
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mixture clear as water flows into the reactor. At the bottom of
the reactor the solution is drawn off by suction and, while re-
cycling at 40 h 1, it is pumped by a rotary pump in a shearing
manner. The pump has an energy consumption of 1.8 KW per cu m.
The synthesis mixture, which has a ratio of SiO2 : A12O3 = 1.6 : 1
and H2O : Na2O = 37 : 1, is heated to 95C. The crystallization
is completed after 50 minutes. The temperature is then increased
to 105C and tempering is carried out for 30 minutes while shear-
ing continuously. The product obtained has a grit proportion of
0.03~ above 45 ~m as determined according to Mocker and the foll-
owing particle spectrum (as determined on a sedimentation balance):
fraction proportion
(~m)(% by weight)
<3 8-5
<5 16.2
<1063.5 `~ ~-
<1586.4 ~;
<2097.8 ;
<25 99.6
~30 100.0 ` ~-
Example 5 `~-
4.5 kg of commercial moist hydrate are dissolved in 50
litres of an 8% by weight solution of caustic soda. The solution
obtained is then thoroughly mixed with 4.3 litres of sadium tetra~
silicate according to the method described in Example 1. The ~-
crystallization is then carried out at 92C under the action of
shear forces in the manner described in example 1, the energy
consumption being 1 KW per cu m. ;
Upon completed crystallization, tempering is carried out
with the same shearing energy and at a temperature of 94 C . The
; zeolite A obtained, which is radiographically pure, contains no
limiting particle size of 45 ~m and has the following particle
spectrum: -
- 12 -
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~ , . . - ~ . . ~ .
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fract.ion proportion ~.
(~Im) (% by weight)
~3 5.3
<5 13.1
<10 50 3
<20 96.8
<25 100.0
All the zeolite .ion exchangers produced according to
the examples 1 to 5 can at least partially replace the phosphates
used heretofore in the conventional detergents. The detergents
produced with said ion exchangers leave no deposits which can be ~ ;
seen with the na:ked eye on the la~ndry.
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