Note: Descriptions are shown in the official language in which they were submitted.
1~8~31~
The subject of the invention is a process for the
preparation of an aqueous alkaline suspension of finely-
divided, low-grit, crystalline, zeolitic sodium alumino-
silicates by continuous mixing of an aqueous sodium
aluminate solution with an aqueous sodium silicate solu-
tion and subsequent intermittent crystallization of the
aqueous alkaline suspension of the X-ray-amorphous sodium
aluminosilicates formed.
X-ray amorphous sodium aluminosilicates are
prepared as a rule by intermittent or continuous mixing
of an aqueous sodium aluminate solution with an aqueous
sodium silicate solution in the presenc~ of excess soda
lye at elevated temperatures, that is, at temperatures in
the range of 55 to 70C. The mixing and concentration
ranges of the reaction partners used in the industry
correspond generally to a mathematical total composition
regarding the molar ratios of:
1.5 to 5 Na2O : 1 A12O3 : 1 to 4 SiO2 : 40 to 400 H2O-
With these mixing ratios, a suspension of an X-ray amor-
phous hydrous sodium aluminosilicate with a great excess
of soda lye is always formed. After separating the mother
liquor and washing out the excess alkali, corresponding
X-ray amorphous products can be isolated from such a
suspension, whose water content is determined to a great
extent by the degree of dryness and whose silicate content
is determined to a great extent by the SiO2/A12O3 molar
ratio in the reaction mixture. For most technical
purposes, however, such amorphous sod~um aluminosilicates
--1-- '
l~B~
are not used, but their crystalline, preferably zeolitic
secondary products are employed.
The so-called zeolites form a mineral class of
crystalline, water-containing alkali metal aluminosili-
cates with a defined pore and cavity structure of their
aluminosilicate lattice. Synthetic zeolites have gained
increasing technical importance and are used, for e~ample,
as cation exchangers primarily for softening water, as
catalyst substrates in chemical processes, as drying,
separating and sorption agents for solvents and gases
(molecular sieves), as well as heterogeneous inorganic
builder substances in washing and cleaning agents.
Depending on their use, structurally different zeolite
types are required, as well as different degrees of dry-
ness and purity. Normally these zeolites are produced
first in their sodium form and, if desired, converted
subsequently by cation-exchange into other forms.
In view of the above-mentioned applications,
the zeolitic sodium aluminosilicate of the NaA type has
gained particular technical importance. The chemical
composition of this zeolite corresponds substantially to
the summation formula:
0.8 to 1.3 Na2O : 1 A12O3 : 1.8 to 2.5 SiO2 : 0 to 6 H2O.
The characteristic X-ray diffraction diagram of zeolite
NaA is described, for example, in U. S. Patent No. 2,882,243.
The con~ersion of amorphous sodium aluminosili-
cates to the crystalline zeolitic forms is a crystalliza-
tion process which depends on various parameters and which
increases in speed with rising temperature. As a rule the
suspension of the amorphous product obtained in the first
:, . ~ ,. , : .
~ ~8~1~
stage, the mixing of the reaction partners, is kept at
elevated temperatures for a certain period. Depending
O]l the molar ratios of the reaction partners in the batch
and on the temperature control, the formation of crystal-
line products requires a period of several minutes to
several days. For the production of zeolite NaA, this
crystallization process is effected primarily under
normal pressure and at temperatures between 70 and 100C.
In this way, a highly crystalline zeolite NaA can
generally be obtained from a corresponding composition of
the aqueous alkaline suspension of X-ray amorphous sodium
aluminosilicates.
For most technical applications, a very finely-
divided zeolite with a possibly narrow-banded particle
size distribution and a mean grain size under lO~m is
preferred. Particularly when zeolite NaA is used in
washing and cleaning agents, its share of particles with
a particle size above 50,um, hereafter called "grit",
should not exceed 0.2% by weight and preferably be well
~elow this limit, and its cation exchanging capacity
should be as high as possible.
In the intermittent reaction of the components
and the subsequent intermittent crystallization, zeolites
of type NaA were heretofore obtained under conventional
reaction and crystallization conditions, which had grit
values in the range of 0.05% to 0.3~ by weight. In the
continuous mixing of the reaction partners and subsequent
intermittent crystallization, however, zeolites with grit
values between 0.1% and 0.2% by weight were obtained under
the usual working conditions.
~ .
~8~319
An object of the present invention is to develop
a process for the preparation of finely-divided zeolitic
sodium aluminosilicates which leads to a zeolite NaA with
a grit portion of less than 0.05% by weight, as well as
a high cation exchanging capacity.
Another object of the present invention is the
development of an improvement in the process for the
production of aqueous, alkaline suspensions of finely
divided low-grit, crystalline, zeolitic sodium alumino-
silicates of the formula
0.8 to 1.3 Na2O : 1 A12O3 : 1.8 to 2 SiO2
with a water content depending upon the degree of drying,and a high cation exchanging capacity comprising the
steps of
a) continuously mixing an aqueous sodium
aluminate solution with an aqueous sodium silicate solu-
tion in the presence of excess sodium hydroxide solution
at elevated temperatures, and
b~ subsequently batch crystallizing the
aqueous alkaline suspension of X-ray amorphous sodium
aluminosilicate, so produced, said suspension having a total
composition of the molar ratios of
3.6 to 5 Na2O : 1 A12O3 : 1.8 to 2 SiO2 : 70 to 105 H2O
at an elevated temperature the same or-higher than the
temperature in step a),
: the improvement consisting essentially of
c) conducting said mixing step a) at a tempera-
ture above room temperature but not exceeding 50CI
d) introducing finely dispersed steam into
--4--
. .,. , : ~ : ~
~8~9
said aqueous alkaline suspension of X-ray amorphous
sodium aluminosilicate for at least 15 minutes while
stirring,
e~ to heat said suspension to a crystallization
temperature of from 85C to 95C,
fl maintaining said crystallization temperature
for a period of 20 to 60 minutes, and
g) stirring said suspension during the course
of steps d) to f) with multistage agitators having a high
shearing effect at a circumferential agitator speed of
from 5 to 10 meters per second, whereby said
low-grit, crystalline, zeolitic sodium aluminosilicate is
obtained having a particle size of at least 99.95~ by
weight of less than 50~m and a high cation exchanging
capacity.
These and other objects of the invention will
become more apparent as the description thereof proceeds. -~
The above objects have been achieved by the
process of the present invention. The subject matter of
the invention is, therefore, a process for the preparation
of an aqueous, alkaline suspension of finely-divided,
low-grit, crystalline, zeolitic, sodium aluminosilicates
of the composition:
0.8 to 1.3 Na2O : 1 A12O3 : 1.8 to 2 SiO2
with a water content depending on the degree of drying
where at least 99.95% by weight have a particle size of
less than 50~m and having a high cation exchanging
capacity by the process of
~5~
8~
a) continuous mixing of an aqueous sodium ~
aluminate solutdon with an aqueous sodium silicate sQlu-
tion in the presence of excess sodium hydroxide solution
a1; elevated temperature and
b~ subsequent intermittent crystallizing of the
aqueous alkaline suspension of the X-ray amorphous,
sodium aluminosilicates formed, said suspension having a total
composition corresponding to molar ratios of
3 6 to 5 Na2O 1 A12O3 : 1.8 to 2 SiO2 : 70 to 105 H2O
likewise at elevated temperature, which is characterized
in that
c) the two reaction components in stage a) are
mixed with each other at a temperature not exceeding 50C,
d) finely dispersed steam is introduced into
the suspension in stage b) in the course of at least 15
minutes under stirring,
e) the suspension is heated this way until
crystallization temperature in the range of 85 to 95C
has been attained,
f) the suspension is left at this crystalliza-
tion temperature for a period of 20 to 60 minutes, and
g) the suspension is stirred at the same time
with multi-stage agitators having a high shearing effect
at a circumferential agitator speed of 5 to lO m/s.
More particularly, the present invention relates
to an improvement in the process for the production
;~ of aqueous, ~lkaline suspensions of finely divided
low-grit, crystalline, zeolitic sodium aluminosilicates
of the formula
.,, ~ ; . .
0.8 to 1.3 Na2O : 1 A12O3 : 1.8 to 2 SiO2
with a water content depending upon the degree of drying,
and a high cation exchanging capacity comprising the
steps of
a) continuously mixing an aqueous sodium
aluminate solution with an aqueous sodium silicate
solution in the presence of excess sodium hydroxide
solution at elevated temperatures, and
. b) subsequently batch crystallizing the
aqueous alkaline suspension of X-ray amorphous sodium
aluminosilicate, so produced, said suspension having a
total composition of the molar ratios of
3.6 to 5 Na2O : 1 A12O3 : 1.8 to 2 SiO2 : 70 to 105 H2O
at an elevated temperature the same or higher than the
temperature in step a),
the improvement consisting essentially of
c) conducting said mixing step a) at a
temperatur~ above room temperature but not exceeding
50C,
d) introducing finely dispersed steam into
said aqueous alkaline suspension of X-ray amorphous
sodium aluminosilicate for at least 15 minutes while : .
stirring,
e) to heat said suspension to a crystallization
temperature of from 85C to 95C,
f) maintaining said crystallization temperature
for a period of 20 to 60 minutes, and
g) stirring said suspension during the course
o~ steps d) to f) with multistage agitators having a high
shearing effect at a circumferential agitator speed of
~`, msA~ .
~8~1~
from 5 to 10 meters per second, whereby said
low-grit, crystalline, zeolitic sodium aluminosilicate is
obtained having a particle size of at least 99.95% by
weight of less than 50~m and a high cation exchanging
capacity.
It was found,surprisingly,that maintaining the
above-mentioned measures, in the continuous reaction
stage, on the one hand, and in the intermittent or batch
crystallization stage, on the other hand, leads to the
formation of zeolitic sodium aluminosilicates type NaA
with the desired extremely low-grit content of less than
0.05% by weight. This objective is aahieved according to
the invention by the cooperation of the parameters sub-
stantially influencing the formation of finely-divided
zeolite particles, as characterized above in the process
features c) to g). In addition, the sodium alumino-
silicates thus obtained have a high cation exchanging
capacity.
For the first stage of the process according to
the invention, hereafter called the precipitation stage,
which leads to the formation of an aqueous alkaline suspen-
sion of X-ray amorphous, sodium aluminosilicates, those
methods generally are used which permit continuous mixing
of the reaction partners, sodium aluminate solution and
sodium silicate solution, in suitable reactors. Examples
of such methods are, for example:
Mixing the components by means of suitable
spray nozzles, whereby the reaction partners
meet only in the spray jet, with formation of
an X-ray amorphous product.
--8--
. ~ ~
~1~8~'319
Mixing the components in a mixing zone acting
in stages, where one of the two reaction compo-
nents is divid~d into sevexal partial currents,
one of which is added directly and continuously
to the total current of the other reaction com-
ponent, and the othe partial currents are
added, likewise, continuously downstream to the
current of the reaction mixture formed. As a
.
mixing zone acting in stages in the foregoing
sense, particularly stirring ~essel cascades,
stirrer columns with chambers separated by
partitions, stepped differential worm mixers
and tu~ular reactors, can be used.
The foregoing methods mentioned by way of example
are described in detail in the;copending Canadian patent
.. . . . . . . . .
applications,Serial No. 342,139 filed Dec mber 18, 1979,
now Patent No. 1,109,638; Serial No. 347,661, filed
March 14, 1980; and Serial No. 347,662, filed Maxch 14,
1980.
Beyond that all corresponding continuous méthods
for the production of X-ray amorphous sodium alumino-
silicates can be used according to the invention, provided
a precipitation or mixing temperature of not more than
50C is maintained in the precipitation stage. Particu-
larly pxeferred in the sense of the invention is miY~ing
the reaction components at a temperature in the range of
40 to 50~C.
In order to obtain a zeolitic sodium alumino-
silicate type NaA, th?t i5, a zeolite ~ith a composition
having the molar ratios of
~ . .
~1~8~9
0.8 to 1.3 Na2O : 1 A12O3 : 1.8 to 2 SiO2
and a water content depending on the degree of drying,
the dosage of the reaction components must be so selected
in this precipitation stage that the aqueous alkaline
suspension of the X-ray amorphous sodium aluminosilicates
formed has a total composition corresponding to molar
ratios of
3.6 to 5 Na2O : 1 A12O3 : 1.8 to 2 SiO2 : 70 to 105 H2O-
In the intermittent or batch crystallization
stage following the continuous precipitation stage, the
maintenance of additional parameters is of essential
importance according to the invention.
The aqueous alkaline suspension of X-ray amorphous
sodium aluminosilicates formed in the continuous precipi-
tation stage i~ as a rule first transferred to one of
several parallel connected crystallization vessels whose
number and dimensions should preferably be so selected
that they ensure the reception of the continuous suspension
current flowing from the continuous precipitation stage.
The intermittent crystallization of the amorphous product
then takes place in these crystallization vessels, which
should be equipped according to the invention with multi-
stage agitators having a high shearing action.
The crystallization process proper is started by
heating the suspension, under constant stirring, to the
required crystallization temperature. It is of essential
importance that the suspension is not heated too fast.
According to the invention, the suspension is heated in
the course of at least 15 minutes, preferably in the
course of 20 to 30 minutes, until the crystallization
--10--
~ c~19
temperature is attained. Furthermore, the manner of
heating is also important according to the invention.
It was found that best results are obtained by introducing
finely-dispersed steam directly into the suspension in
view of obtaining a low-grit content of the resulting
crystalline product. The introduction of the finely-
dispersed steam into the suspension can be effected,for
example, by ring conduits arranged on the bottoms of the
respective crystallization vessels and provided with many
small orifices. However, other arrangements which ensure
direct introduction of finely-dispersed steam into the
suspension can also be used,
According to the invention, the suspension is
heated this way until a temperature of 85 to 95C,
preferably 90 to 93C, is attained over the period of at
least 15 minutes, preferably over 20 to 30 minutes. The
heated suspension is left subsequently at this temperature
for 20 to 60 minutes, preferably 30 to 40 minutes, during
which time the amorphous product crystallizes to a zeo-
litic sodium aluminosilicate, type NaA.
During the entire crystallization process, that
is, from the start of heating, the suspension of the
amorphous product or the forming crystalline product
should be stirred vigorously by means of a multi-stage
agitator with a high shearing power. According to the
invention, the strength and the intensity of this agitator,
that is, the circumferential agitator speed, is 5 to 10
meters per second, preferably to 6 to 8 meters per second.
Agitators that are suita~le for this purpose are, for
example, turbines or turbine-like stirring apparatus with
multi-stage propellers, which are characterized by a
--11--
,: :
strong shearing action. The number of stages of the
agitator depends primarily on the geometric form of the
selected crystallization vessel. Since the shearing
action of these agitators is greatly influenced by the
shape of the agitator, it was found particularly advanta-
geous in the sense of the invention to stir the suspension
with axially moving agitators with a high shearing action,
particularly trapezoidal agitators with curved stirring
blades.
If the essential features of the process accord-
ing to the invention are maintained, particularly in the
procedures characterized as preferred, a finely-divided,
crystalline zeolitic sodium aluminosilicate, type NaA,
is obtained after the crystallization, which is charac-
terized by a grit portion of less than 0.05% by weight and
high cation exchanging capacity.
For the identification of the crystallization
product obtained, samples are filtered off, washed alkali-
free, dried overnight in a vacuum drying cabinet at 100C
and identified on the basis of their X-ray diffraction
diagram. The particle size distribution is measured as
the % by volume distribution of the crystallized particles
by means of a Coulter-Counte ~ , for example, model TA.
The grit portion in the crystallized product,
that is, the portion of particles with a particle size
above 50~um, is determined by a modified wet-screening
method according to Mocker, where a weighed sample of the
crystalline material suspended with water is placed in a
testing apparatus by Mocker (DIN 53 580) on a test screen
with a mesh aperture of 50,um (DIN 4188~ and whirled by
means of water sprayed from rotating nozzles. The fine
-12-
3S~3~9
portions of the crystalline material are flushed this way
without pressure through the screen, while the coarse
portions (grit) remain on the screen. After 2 minutes,
with a spray of 80 liters of water per hour, the test
screen is dried in the drying cabinet at 110C and subse-
quently, the screenings are determined by a differential
weighing. The screenings result from the formula
% by weight screenings = (a-b) .100
with a = weight of screen with screenings
b = weight of screen without screenings
E = weight of sample in gm based on the dry material.
The measure of the cation exchanging capacity of
the crystalline zeolitic material i8 the calcium-binding
power of 1 gm of sodium aluminosilicate (active sub-
stances = AS] per liter in a liter of water with an
initial hardness of 30dH (German hardness). For the
determination of the calcium-binding power, 1 liter of
an aqueous solution containing 0.594 gm of CaC12 (corres-
ponding to 300 mg CaO/1=30dH) is adjusted with diluted
sodium hydroxide solution to a pH value of 10 and mixed
with 1 gm of aluminosilicate ~AS). The suspension formed
is subsequently stirred vigorously for 15 minutes at
a temperature of 22 + 2C. After the sodium alumino-
silicate is filtered off, the residual hardness X in the
filtrate is determined by complexometric titration by
means of ethylenediamine tetraacetic acid. The calcium-
binding power in mg CaO/gm~AS is calculated according to
the formula: (30 - X) . 10.
-13-
~8~
The suspension of finely-divided, low-grit,
crystalline zeolitic sodium aluminosilicates, type NaA,
iis~ as a rule, further processed after the crystallization
i'3 completed. To this end the crystalline solid substance
is filtered off, washed and dried or prepared in any other
way, depending on the desired application. Thus, an a~ue-
ous suspension of the crystalline, sodium aluminosilicate
can also be used, if necessary, for the production of wash-
ing and cleaning agents. Mother liquor and wash liquor are
preferably returned into the production process.
Due to the great cation-exchanging capacity of
the zeolitic sodium aluminosilicate obtained, which mani-
fests itself in a calcium-binding power of 150 to 200 mg
CaO/gm AS, it is preferably used as a heterogeneous inor-
ganic builder (phosphate su~stitute) in detergents, rinses
and cleansers~
The f~llowing examples describe the procedure
used in the process accoxding tQ the invention but are not
limitative thereto.
EXAMPLE 1
For the continuous precipitation stage, a
vértical agitator column with an effective volume of 188
liters was used, which was divided by partitions into a
total of 28 chambers and which was equipped with the same
number of MIG agitators. The shaft common to all agi-i
tators was driven by means of a corresponding motor at a
speed of 390 min 1. The~entire column cylinder was pro-
vided with a heating jacket. The reaction components,
which had been preheated to a precipitation temperature of
50C, were fed through suitable dosing devices, such as
-14-
.. . . .
.
~8~3~9
pumps and rotameters, into the bottom chambers of the agi-
t:ator column. The movement of the reaction mixture from
chamber to chamber was effected through staggered ring
slots provided in the partitions, so that a continuously
rising product flow was obtained in the column. The dos-
ing of the reaction components was: 549 kg/h of sodium
silicate solution, 1315 kg/h of sodium aluminate solution,
as well as 1136 kg/h of alkaline mother liquor from one
of the preceding crystallization stages, the composition
of the reaction product formed corresponded to molar
ratios of
4.2 Na2O : 1 A12O3 : 1.8 SiO2 : 95 H2O.
The suspension of the amorphous reaction product
issuing continuously from the top of the agitator column
was gradually transferred into three crystallization
vessels with a volume of 6 cu. meters each, which were
equipped with two-stage propeller agitators with a high
shearing power. As soon as the bottom blade dipped com-
pletely into the suspension, the respective agitator was
start~ed with a circumferential agitator speed of 6.9
m.s 1. After a crystallization vessel was filled, finely-
dispersed steam was injected directly into the suspension
under a pressure of 4 bar through a ring conduit arranged
on the bottom of each vessel, and the temperature of the
suspension was thus increased within 20 minutes to 93C.
The suspension remained at this crystallization tempera-
ture for a period of 40 minutes under constant stirring,
at a circumferential agitator speed of 6.9 m.s 1.
Su~sequently, the contents of each crystallization vessel
was transferred to a filter unit, where the crystalline
products obtained were washed and dried, and the resulting
-15-
.
- . .
mother liquor returned into the precipitation stage of
the process.
The crystalline reaction products formed were
according to the X-ray diffraction diagram type NaA zeo-
lites. The particle size determined with the Coulter-
Counter showed a maximum of the particle size distribution
of 3 to 5~m. The calcium binding power was 175 mg CaO/gm
AS. The grit portion was 0.02~ by weight.
EXAMPLE 2
The example was carried ~t in analogy to
Example 1 with the following modification:
The molar composition of the reaction mixture was
4 Na2O : 1 A12O3 : 1.8 SiO2 : 105 H2O
A crystalline of type NaA zeolite with a calcium-binding
power of 181 mg CaO/gm AS and a grit portion of 0.03% by
we~ght, was obtained.
EXAMPLE 3
This example was carried out in analogy to
Example 1 with the following modification:
The molar composition of the reaction mixture was
4.5 Na2O : 1 A12O3 : 1.8 SiO2 : 95 H2O.
A crystalline of type NaA zeolite with a calcium-binding
power of 172 mg CaO/gm AS and a grit portion of 0.03~ by
weight, was obtained.
EXAMPLE 4
The precipitation stage was carried out in
analogy to Example 1. The crystallization stage was
carried out in three crystallization vessels which
were equipped with different agitators of different
-16-
, ~ ' '' "-
shearing action. In vessels A and B, the stirring was
effected with straight-arm paddle agitators at a circum-
i-erential speed of less than 5 m.s l. In vessel A, the
stirring speed waS3.6 m.slandin vessel B, it was4.5 m.s l.
:[n vessel C, the stirring was effected with an axially
moving trapezoidal agitator with curved blades at a
circumferential speed of 7.1 m.s 1. The heating rate to
the crystallization temperature of 90C was in all three
vessels 25 minutes, the following stay period 30 minutes.
Otherwise, we proceeded as described in Example l. The
NaA zeolites formed in all cases differed substantially
in the following features:
Vessel A B
calciu~bi~ p~wer in mg CaO/gm AS177 171 172
grit portion in % by weight 0.720.08 0.01
EXAMPLE 5
The example was carried out as in Example 1
but under the following modified reaction conditions:
precipitation temperature: 44C; heating time: 26 minutes;
subsequent stay period: 30 minutes.
The type NaA zeolites formed had a calcium-
binding power oi 169 mg CaO/gm ~S and a grit portion of
0.02% b~ weight.
The following comparison tests, where the criti-
cal process features essential for the invention were not
maintained, will likewise illustrate the impo~rtance of
these features in the grit portion of the zeolites formed.
-17-
:
19
COMP~RISON EXAMPLE 1
This example was carried out as in Example 1
but the reaction components were mixed in the precipita-
t:ion stage at a temperature of 65C. Type NaA zeolites
were obtained which had a calcium-binding power of 178 mg
CaO/gm AS and a grit portion of 0.2% by weight.
CO~PARISON EXAMPLE 2
This example was carried out likewise as in
Example 1. The heating in the crystallization vessel of
the suspension formed in the precipitation stage was
effected, however, within 7 minutes by direct injection of
steam by means of a steam lance. The resulting type NaA
zeolites had a calcium~binding power of 174 mg CaO/gm AS
and a grit portion of 0.34% by weight.
COMPARISON EXAMPLE 3
Comparison Example 2 was repeated, with the
suspension in the crystallization vessel heated slower,
within 28 minutes, but likewise ~y direct injection of
steam by means of a steam lance. The resulting type NaA
zeolites had a calcium-binding power of 168 mg CaO/gm AS
and a grit portion of 0.2% by weight.
The first comparison tests show the importance
of the relatively low precipitation temperature according
to the invention. The other two comparison tests show
clearly the determinant influence of the heating time, on
the one hand, and the manner of heating, without finely-
dispersed steam, on the other hand, on the grit content
of the crystalline product.
. ~
-18-
:
~8~19
The preceding specific embodiments illustrate
the practice of the invention. It is to be understood,
however, that other expedients known to those skilled in
the art or disclosed herein, may be employed without
departing from the spirit of the invention or the scope
of the appended claims.
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