Process for preparing a substantially crystalline sodium aluminosilicate

A process for preparing a synthetic substantially crystalline sodium aluminosilicate of the zeolite A type is disclosed. The process comprises rapidly and simultaneously introducing a sodium silicate and a sodium aluminate solution under thorough agitation at a constant by volume ratio which provides for a reaction mixture the content of which is equivalent to a molar ratio of x' Na.sub.2 O/ 1 Al.sub.2 O.sub.3 / y SiO.sub.2 /z' H.sub.2 O wherein x' is from about 6.5 to about 9.0, y is from about 1.7 to about 2.2 and z' is from about 180 to about 250, maintaining the reaction mixture at a temperature of from about 70.degree. to about 100.degree. C. under stirring for a sufficient period of time, usually 1-3 hours, in order to allow the initially amorphous reaction product to crystallize and recovering the substantially crystalline product from the resulting suspension. The essential feature of the process is a continuously maintained constant molar ratio Na.sub.2 O/ Al.sub.2 O/ SiO.sub.2 /H.sub.2 O throughout the reaction mixture during the entire course of the process. The resulting product exhibits a small particle size, an excellent wettability and a high calcium binding power, and is especially suited as a detergent additive.

BACKGROUND OF THE INVENTION 
The present invention relates to the preparation of substantially 
crystalline sodium aluminosilicates. 
For a long period of time it has been common practice to use phosphates as 
builders in detergent compositions. Yet, lately it has been found that an 
excess of phosphates in waste waters can lead to an overfertilization of 
the natural waters. Even though detergent compositions are not the only 
source of this type of pollution, various efforts have been made to 
develop detergent compositions wherein the phosphate content is low, yet 
the overall activity is maintained. Yet, complexing agents, such as 
trisodium polyphosphates, have an essential importance for the course of 
the washing process and cannot easily be replaced. Yet, as far as their 
water softening function is considered, this can also be performed by 
other watersoftening materials. 
Therefore it has been proposed to utilize naturally occuring and/or 
synthetic sodium aluminosilicates which are insoluble in water for 
watersoftening purposes. The following properties are required for such 
sodium aluminosilicates: 
1. A small particle size, possibly a particle size of less than about 
10.mu., preferably of from about 3 to about 6.mu., in order to ensure an 
optimum distribution throughout the washing liquid. 
2. A very narrow particle size range, because too small particles are 
retained in a fabric during a laundering operation, whereas too large 
particles tend to sediment. 
3. Poor adhesive capacity towards textile fibers. This is achieved by using 
crystalline substances; the adhesive power of amorphous substances is too 
strong. 
4. A high calcium binding power. 
5. A good wettability, in order to be able to rapidly develop its full 
activity. 
Sodium aluminosilicates exhibit the advantage, that their calcium binding 
power which is dependent on the pH-value in the reaction medium, their 
concentration, and their particle size are not diminished under rising 
temperatures in the same manner as that of complexing agents. For certain 
ion exchangers, even an increase of the calcium binding power is observed 
under rising temperatures due to the increased diffusion rate and the 
reduction of the degree of hydration. 
Amongst the zeolites, those of type A exhibit the highest calcium binding 
power. Therefore detergent manufactures are especially interested in the 
latter type of sodium aluminosilicate ion exchangers. These sodium 
aluminosilicates are usually prepared by reacting a sodium silicate 
solution with a sodium aluminate solution at elevated temperatures. The 
crystallization takes place during several hours at temperatures of about 
100.degree. C. 
According to a process disclosed in the German Auslegeschrift No. 1,038,015 
synthetic molecular sieves are prepared by heating solutions containing 
sodium, silicate, and aluminate ions to a temperature of between 
80.degree. and 100.degree. C., rapidly and thoroughly mixing them, and 
maintaining the mixture at this temperature for at least 5 hours. Yet, the 
resulting products are not satisfactory for the use as detergent 
additives. For example, they remain unwetted for a large period after 
being rinsed or sprinkled into water, and lump or float on the water 
surface (like sawdust). In view thereof the German Offenlegungsschrift No. 
2510675 discloses a method for improving the wettability by thoroughly 
mixing alkali aluminosilicates with ortho phosphoric acid or alkali ortho 
phosphates, drying the mixture and subsequently grinding the dried 
product. Similarly, the use of pentaerythrite as is disclosed in the 
German Offenlegungsschrift No. 2510676, pentasodium triphosphate as is 
disclosed in the German Offenlegungsschrift No. 2510741, and tartaric acid 
as is disclosed in the German Offenlegungsschrift No. 2510742 have been 
proposed for improving the wettability of alkali aluminosilicates. For the 
same purpose, the addition of polycarboxylic acids is disclosed in the 
German Offenlegungsschrift No. 2345432. 
The German Offenlegungsschriften Nos. 2333068, 2447021 and 2517218 disclose 
processes wherein synthesized mixtures are subjected to shearing forces in 
order to obtain a finely divided product. 
From the disclosure of the German Auslegeschrift No. 1667620, it is known, 
that at an increased alkali concentration in the reaction mixture, the 
rates of crystallization and particle growth are increased, and that the 
latter becomes difficult to control unless appropriate precautions are 
taken. According to the teaching of the German Auslegeschrift, an increase 
of the alkali content leads to the formation of coarser grains, and 
chemically uniform precipitates can only be obtained if the silicate 
solution is introduced into the aluminate solution. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a process for preparing 
a synthetic substantially crystalline sodium aluminosilicate, the 
overwhelming portion of which is of the zeolite A type structure. 
It is a further object of the present invention to provide such a process 
which yields a substantially crystalline product having a low average 
particle size and a narrow particle size distribution. 
It is a further object of the present invention to provide such a process 
which yields a substantially crystalline product having a high calcium 
binding power. 
It is a further object of the present invention to provide such a process 
which yields a substantially crystalline product having a good 
wettability. 
It is a further object of the present invention to provide such a process 
which yields a substantially crystalline product having only little 
adhesion towards textile fibers. 
It is a further object of the present invention to provide such a process 
which is not adversely affected by small variations of the process 
conditions which may readily occur during every day industrial production 
due to various causes. 
It is a further object of the present invention to provide such a process 
which involves only a small number of operations. 
It is a further object of the present invention to provide such a process 
which provides for a fast separation of the precipitated product from the 
remaining mother liquor. 
In order to accomplish the foregoing objects according to the present 
invention there is provided a process for preparing a synthetic 
substantially crystalline sodium aluminosilicate which comprises the steps 
of 
(a) thoroughly and rapidly mixing an aqueous sodium silicate solution with 
such an amount of an aqueous sodium aluminate solution that the content of 
the mixture is equivalent to a molar ratio x'Na.sub.2 O/1Al.sub.2 O.sub.3 
/ySiO.sub.2 /z'H .sub.2 O wherein x' is a value of from about 6.5 to about 
9.0, y is a value of from about 1.7 to about 2.2 and z' is a value of from 
about 180 to about 250 within the minimum period of time which is 
sufficient for obtaining a uniform mixture by simultaneously introducing 
said sodium silicate solution and said sodium aluminate solution at a 
constant ratio into a reaction zone under sufficiently intensive agitation 
to maintain a constant molar ratio of Na.sub.2 O/Al.sub.2 O.sub.3 
/SiO.sub.2 /H.sub.2 O throughout the reaction mixture whereby a reaction 
mixture containing an intermediate amorphous sodium alumino-silicate is 
formed; 
(b) maintaining the reaction mixture at a temperature of from about 
70.degree. to 100.degree. C. under sufficient agitation in order to 
continuously ensure the constant molar ratio of Na.sub.2 O/Al.sub.2 
O.sub.3 /SiO.sub.2 /H.sub.2 O throughout the reaction mixture during a 
period of time which is sufficient to transform the reaction mixture into 
a suspension of a substantially crystalline sodium aluminosilicate 
precipitate in a mother liquor, and 
(c) recovering said substantially crystalline sodium aluminosilicate from 
the suspension. 
According to the present invention there are further provided a synthetic 
crystalline aluminosilicate, which is obtainable by means of the 
above-described process, as well as a detergent composition containing at 
least one surface active agent and said aluminosilicate. 
Further objects, features and advantages of the present invention will 
become apparent from the detailed description of the invention and its 
preferred embodiments which follow. 
DETAILED DESCRIPTION OF THE INVENTION 
The process according to the present invention yields a substantially 
crystalline sodium aluminosilicate having a small particle size and which 
exhibits a good wettability and a narrow range of particle size 
distribution. The composition of the resulting sodium aluminosilicate 
suitably corresponds to a molar ratio of oxides of the empirical formula 
xNa.sub.2 O/1Al.sub.2 O.sub.3 /ySiO.sub.2 /zH.sub.2 O wherein x is a value 
of from about 0.8 to about 1.2, y is a value of from about 1.7 to about 
2.2 and z is a value of from about 3.0 to about 10.0. Preferably the 
particle size distribution of at least 95% of the particles is in the 
range of from about 1 to about 10.mu.. 
According to the present invention, the substantially crystalline sodium 
aluminosilicate is prepared by rapidly and thoroughly mixing a sodium 
silicate solution with a sodium aluminate solution by simultaneously 
introducing both solutions into a reaction zone under thorough mixing 
whereby a uniform mixture is achieved within a very short period of time. 
The two solutions are unified under constantly maintaining a constant 
molar ratio between Na.sub.2 O, Al.sub.2 O, SiO.sub.2, and H.sub.2 O. The 
resulting reaction mixture contains an intermediary amorphous sodium 
aluminosilicate, which is then allowed to crystallize by maintaining the 
reaction mixture at a temperature of from about 70.degree. to about 
100.degree. C., preferably from about 80.degree. to about 85.degree. C. 
for a period of time which is sufficient to transform the reaction mixture 
into a suspension of a substantially crystalline sodium aluminosilicate in 
a mother liquor. This period of time suitably is from about 1 to about 3, 
preferably from about 1 to about 2 hours. 
In order to obtain the desired properties in the sodium aluminosilicate, it 
is essential that during the reaction of the components and the 
crystallization of the intermediary amorphous product, a constant molar 
ratio between Na.sub.2 O/Al.sub.2 O.sub.3 /SiO.sub.2 and H.sub.2 O is 
maintained. This is achieved by simultaneously introducing the two 
reacting solutions under intensive mixing into the reaction zone and by 
agitating the reaction mixture during the crystallization period. Hereby, 
shearing forces are not required; in some cases they even are undesirable. 
The two reacting solutions should be rapidly brought together. The period 
of time during which the solutions are introduced into the reaction zone 
suitably is from about 5 to about 20, preferably from about 5 to about 10% 
of the following period of crystallization. The fact that the reaction 
mixture has a relatively high content in Na.sub.2 O is a further essential 
feature of the process according to the present invention which, in 
addition to the continuously maintained constant molar ratio, is 
responsible for obtaining the desirable properties of the product. 
Therefore, it is advisable that the amounts of reactants are chosen such 
that the reaction mixture contains Na.sub.2 O, Al.sub.2 O.sub.3, SiO.sub.2 
and H.sub.2 O in a molar ratio of about 7.0 to about 10Na.sub.2 
O/1Al.sub.2 O.sub.3 /about 1.7 to about 2.2 SiO.sub.2 /about 180 to about 
250 H.sub.2 O. For the starting solutions, the following molar ratios are 
recommended: 
for the sodium aluminate solution: 
a molar ratio of Na.sub.2 O/Al.sub.2 O.sub.3 of from about 5.5 to about 
7.0/1 
and a molar ratio of H.sub.2 O/Na.sub.2 O of from about 23 to about 35/1 
for the sodium silicate solution: 
a molar ratio of Na.sub.2 O/SiO.sub.2 of from about 0.6 to about 0.9/1 
and a molar ratio of H.sub.2 O/SiO.sub.2 of from about 10 to about 16/1 
It is advisable, yet not absolutely necessary, to separately heat both 
solutions prior to the mixing to a temperature of at least about 
60.degree.; e.g., a temperature of between about 60.degree. and about 
100.degree. C., preferably of between about 80.degree. and about 
95.degree. C. This prior heating can be omitted, if the mixture can 
readily and quickly be heated to the reaction temperature. 
During the intensive mixing of the reacting solutions, an amorphous 
intermediary sodium aluminosilicate product is formed wherein the grain 
characteristics of the molecular sieve which later results from the 
crystallization are already preformed to a large extent. By agitating the 
reaction mixture in the reactor, the constant molar ratio of oxides is 
constantly maintained throughout the suspension. Thus it is a 
characteristic and essential feature of the process that a constancy of 
the molar ratio between the oxides is maintained from the start of the 
precipitation until the resulting substantially crystalline product is 
separated from the mother liquor at the end of the process. Special means 
for producing shearing forces are not required. The termination of the 
crystallization is predetermined by the reaction conditions in the process 
and can be clearly controlled by means of X-ray irridition determining the 
X-ray diffraction pattern. Usually the crystallization is completed within 
a period of from about 1 to about 3, preferably from about 1 to about 2 
hours. The temperature during the crystallization suitably is between 
about 70.degree. and about 100.degree. C., preferably between about 
80.degree. and about 95.degree. C. 
After the crystallization is terminated, the suspension preferably is 
cooled under continuing agitation so rapidly, that the period of time 
which is needed for cooling the suspension to about 50.degree. C. does not 
exceed 30% of the crystallization period. This is recommended merely as a 
precaution, yet is not necessarily required since a postgrowing of the 
crystals during the crystallization step occurs only to a minor degree. 
Subsequently the resulting substantially crystalline sodium 
aluminosilicate, which preferably is a sodium aluminosilicate the 
composition of which corresponds to the molar ratio of oxides of Na.sub.2 
O.Al.sub.2 O.sub.3.2SiO.sub.2.4.5H.sub.2 O, is separated from the mother 
liquor by filtration. The mother liquor can be used for preparing the 
starting solutions. The raw product is then washed until the washing water 
exhibits a pH value of from about 10 to about 11. Subsequently, the 
product is dried under mild drying conditions which are adjusted such, 
that the resulting product contains a residual water content of from about 
18 to about 22%. 
The sodium aluminosilicates which are obtained according to the present 
invention are especially useful as additives in detergent compositions. 
They may be incorporated into any type of detergent composition containing 
at least one conventional surface active agent and optionally additional 
conventional additives, e.g. builders, bleaching agents, foam inhibitors 
and the like.

The invention will now be further described by the following examples which 
are intended to be illustrative only. 
EXAMPLE 1 
4.46 m.sup.3 of a sodium aluminate solution the sodium aluminate content of 
which is equivalent to a molar ratio Na.sub.2 O/Al.sub.2 O.sub.3 of 6.2 
and a molar ratio H.sub.2 O/Na.sub.2 O of 28 and 0.54 m.sup.3 of a sodium 
silicate solution the sodium silicate content of which is equivalent to a 
ratio Na.sub.2 O/SiO.sub.2 of 0.83 and a ratio H.sub.2 O/NaO.sub.2 of 13.4 
are each heated seperately to a temperature of 90.degree. C. 
Both solutions are introduced into a siphon pipe reactor at the above 
indicated by volume ratio and are mixed under high agitation as intensely 
as possible within 7 minutes. From the beginning, the suspension of the 
precipitate which is formed in the reaction is maintained in an agitated 
state by means of a propeller agitator (diameter 550 mm, inner diameter of 
the reactor 1700 mm) which is placed close to the bottom of the reactor 
and is turning at a speed of 240 revolutions per minute. After a 
crystallization period of 75 minutes at a temperature of 90.degree. C. the 
mixture is cooled to a temperature of 50.degree. C. within a period of 
about 20 minutes and is filtered. The filtered precipitate product is 
washed until the filtrating wash water exhibits a pH value of 10.7. The 
product is then dried at a temperature of 80.degree. C. in a dryer heated 
by means of circulating hot air. The properties of the resulting product 
are as follows: 
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composition: zeolite A, crystal content 86.4% 
calcium binding power 
(determined according to 
the method described in 
the German Offenlegungs- 
schrift No. 2412837, page 
27): 186 mg Ca O/g waterfree 
substance 
grainsize distribution 
&lt;15 .mu. 99% 
&lt;10 .mu. 98% 
&lt; 3 .mu. 50% 
&lt; 1 .mu. 3% 
wettability* less than 18 seconds 
______________________________________ 
*Determination of the wettability :1 g of the dried sodium aluminosilicat 
is triturated in a mortar and is passed through a sieve having a mesh siz 
of 100 .mu. onto the surface of 600 ml of water which are contained in a 
glass beaker. The period of time during which the sodium aluminosilicate 
is completely wetted with water is determined and is used as a measure of 
the degree of wettability of the product. 
For comparative purposes the wettability of the following prior art 
molecular sieves are given below: 
______________________________________ 
product wetting time 
______________________________________ 
Untreated molecular sieve according to 
&gt;10 minutes 
DOS 2510675 
zeolite A + Na.sub.2 HPO.sub.4 according to DOS 2510675 
120 seconds 
zeolite A + trisodium polyphosphate according to 
DOS 2510741 110 seconds 
zeolite A + tartaric acid according to 
20 seconds 
DOS 2510742 
zeolite A + pentaerythrite according to 
50 seconds 
DOS 2516676 
______________________________________ 
EXAMPLE 2 
The same amount of the same starting solutions as described in Example 1 
are each heated to 90.degree. C. and are mixed at a constant by volume 
ratio within 6 minutes prior to entering the reactor. The turbulance is 
reduced as compared to that in example 1 by using a siphon pipe reactor 
having a diameter which is enlarged one third. After introducing the 
solutions, the mixture is maintained at a temperature of 90.degree. C. for 
90 minutes under agitation with a stirrer turning at 240 revolutions per 
minute. The mixture is then further treated as is described in Example 1. 
The resulting product has the following properties: 
______________________________________ 
composition: zeolite A, crystal content 90.3% 
calcium binding 
power: 180 mg Ca O/g waterfree substance 
grainsize distribution: 
&lt;15 .mu. 99% 
&lt;10 .mu. 99% 
&lt; 4 .mu. 50% 
&lt; 1 .mu. 2% 
wettability less than 18 seconds 
______________________________________ 
From the above data it is apparent, that by reducing the mixing intensity 
the particle size distribution is shifted towards larger particle 
diameters. 
EXAMPLE 3 
In this test the amounts and the compositions of the starting solutions as 
defined in Example 1 are used and the mixing intensity and the 
precipitation period are corresponding to those in Example 2. In the 
reactor the mixture is stirred at a speed of 240 revolutions per minute. 
The crystallization takes place at a temperature of 90.degree. C. within a 
period of 105 minutes. The mixture is then further treated as is described 
in Example 1. 
______________________________________ 
Resulting product: 
composition: zeolite A crystal content 96.4% 
calcium binding power: 
172 mg Ca O/g waterfree 
substance 
grainsize distribution: 
&lt;15 .mu. 99% 
&lt;10 .mu. 97% 
&lt;3.2 .mu. 50% 
&lt; 1 .mu. 1% 
wettability less than 18 seconds 
______________________________________