EP0000870A1 - Process for improving the properties of sodium aluminosilicate doughs and powders - Google Patents

Abstract

The process for improving the rheological properties and the redispersibility of sodium aluminosilicate doughs and powders consists in adding to the dough from 1 to 25% by weight of Na2SO4, based on the total solids content after sulphate addition.

Description

The production of aluminum silicates of the zeolite types, including type A, by reacting an aqueous alkali silicate solution with an alkali aluminate solution has been known for years.

In recent times, zeolite A has opened up further areas of application, such as as a builder in detergents. This new application places additional demands on the properties of the product. In addition to high alkaline earth binding capacity, high whiteness, e.g. Desired a small average particle diameter with a narrow grain spectrum. It is an important requirement that the product, regardless of the form in which it is present, shows the original distribution again when dispersed in water, that is to say that it has no irreversible agglomeration.

In addition, it is expected that the sodium aluminum silicate in the form of the filter dough, which can be used as such in the production of detergents, has certain properties which are explained in more detail below.

The filter dough produced in the manufacture of the sodium aluminum silicate after the mother liquor has been separated off and washed, which generally contains 40-50% solids, shows a high structural viscosity in addition to other rheological anomalies. In general, this enables the dough to be pumped through without further dilution. Furthermore, due to the rheological properties mentioned, the dough can generally be stored in suitable containers and from there can be brought to flow again after the application of relatively low energy by stirring, shaking or pump suction.

The expression "in general" is intended to mean that the flow properties described are found in the vast majority of cases. For the pumpability of the dough after storage, this applies in particular for a period of up to 48 hours of storage. With longer storage, however, a tough soil body gradually appears, which can neither be pumped nor stirred.

It has therefore been proposed in DOS 25 27 388 to add a dispersant to sodium aluminum silicate suspensions in order to improve the suspension stability and pumpability, i.e. primarily organic surface-active substances or swellable clays, such as bentonites and others As the experiments indicated in the DOS show, suspensions stabilized with organic surface-active substances are still pumpable and largely homogeneous after 24 hours. However, our own experiments have shown that a sediment forms after only two days and after three days the suspension can no longer be pumped. The DOS says nothing about the stability of suspensions containing bentonites. Processed clays also have the disadvantage that they have to be freed of iron very carefully and interfere with the washing process insofar as they are not completely removed during rinsing, so that deposits are formed on the fiber until crusting finally occurs.

It has now been found that, in the presence of sodium sulfate in the dough, the difficulties described in its further processing are eliminated. The addition of sodium sulfate not only has the advantage that it is an inexpensive component in the sodium aluminum silicate suspension is introduced, which is present in the detergent anyway, it also causes that when the dried product is dispersed in water, the sodium aluminum silicate is back in its original particle size distribution.

Spray drying is normally used as a convenient form of further processing of the sodium aluminum silicate dough. In addition to significant advantages over other types of drying, spray drying has one disadvantage: the product is obtained in the form of prills. However, this inherently desirable property means that the original grain distribution in the dough does not re-establish with sufficient certainty when dispersed in water. The prills (30 - 80ju average diameter) often do not completely disintegrate into the original primary particles with a fineness of approx. 98 - 99% <15 µ corresponding to 95% <10 µ. This phenomenon is remedied by the addition of sodium sulfate.

It was not to be expected that sodium sulfate would have such a favorable effect on the properties of sodium aluminum silicate suspensions. DOS 25 27 388 shows that sodium sulfate has no stabilizing effect on the suspension. Although it is pointed out that the sodium hydroxide still present in the washed filter dough is neutralized by sulfuric acid, the suspension must also be added to the suspension in order to achieve the desired degree of stability. It is recommended that the sodium hydroxide solution be at least partially neutralized with an acidic dispersant in order to replace non-stabilizing acids such as sulfuric acid.

With the addition of sodium sulfate, the filter dough maintained its advantageous consistency, possibly via the ge entire observation period of eight weeks. In particular, no tough, non-pumpable, non-stirrable soil body occurred. Even an addition of 1% Na ₂ so ₄ , based on the solid dough after the addition, already shows an effect. In practice, the addition of 2% sodium sulfate represents the lower limit. With increasing Na ₂ SO ₄ concentration, the effect of sodium sulfate initially increases, so that additions of 2 to 10% are expedient to improve the rheological properties. If the addition was increased by more than 10% up to 25%, based on the total solids, no rheological disadvantages were found.

To improve the dispersibility of the dried sodium aluminum silicate, additives of more than 10%, preferably of 15-20%, based on the total solids present, are required. If filter dough with _N a ₂ S0 ₄ contents of more than 10% up to approx. 25%, based on solids, is subjected to spray drying, the resulting dry products, after dispersion in water, show an extensive approximation to the original grain spectrum when determining the grain size.

The sodium sulfate can be added at any stage in the manufacturing process of sodium aluminum silicates as long as the type of addition does not structurally change the sodium aluminum silicate itself. Furthermore, care must of course be taken that it is not removed again in a subsequent washing process. So it is e.g. It does not matter whether the sodium sulfate is already present when the sodium aluminum silicate is precipitated, i.e. whether it is added to the alkali silicate and / or the alkali aluminate solution or whether it is added during the subsequent annealing phase. It can also be added to the washed filter dough.

The sodium sulfate can also be introduced during the washing process, which is carried out for the purpose of lowering the pH, by completely or partially neutralizing the sodium hydroxide which is in the wash water, which is expediently conducted in countercurrent, with sulfuric acid. However, the amount of sodium sulfate introduced in this way is generally not sufficient to improve the properties of sodium aluminum silicate doughs and powders, and further addition of sodium sulfate is required. Because of the exact dosage of sodium sulfate, an additional addition is usually necessary.

example 1

4.46 m 3 sodium aluminate solution of the molar composition Na ₂ O / Al ₂ O ₃ ⁼ 6.2 and H ₂ 0 / Na ₂ 0 = 28 were rapidly stirred with 0.54 m sodium silicate solution of the molar composition Na ₂ 0 / Si0 ₂ = 0.83 and H ₂ O / Na ₂ O = 13.4 mixed. The mixture was stirred at 90 ° C. for 100 minutes, cooled rapidly, filtered and washed until pH 10.5. The filter dough contained 40.2% solids.

Part of the filter dough remained in a 200 liter container (filling height 60 cm) without any additives. After 24 hours, the dough was still flowable, such as was seen during the slow tilt of the vessel 45 to ^{the 0th} With a slowly inserted rod (diameter: 25 mm, flat end), no inhomogeneity in the texture of the dough could be determined.

After 48 hours, a 1 cm high clear layer was visible over the dough. However, the dough was still fluid. With the stick inserted vertically, an approx. 2 cm high base was attached, which was tougher than the rest of the dough. After 72 hours there was an 8 cm high, clear overhanging layer above the dough and an approximately 8 cm thick bottom layer that was tougher than the dough. The dough was no longer flowable.

After a week, the clear, protruding layer had grown to 28 cm. When the vessel was tilted by 135 °, the top half of the dough immediately ran off into a template, the mass of the bottom layer followed within 2 hours to an approx. 1 cm thick residue adhering to the bottom.

A sample of the dough, which had been homogenized and made flowable again by shaking for two hours and had a residual water content of 19.6%, was dried in a laboratory spray dryer (outlet temperature 110 ° _C. ).

The particle size distribution was carried out after dispersing in water (10 g of product; 700 ml of H ₂ O; 60 min. Stirring at 1000 rpm) according to the Andreasen method.

Der Vergleich der dispergierten Probe aus der Sprühtrocknung mit einer nicht getrockneten Probe zeigt die unbefriedigende Dispergierbarkeit des getrockneten Produkts. Die Vergleichsprobe aus dem Teig entspricht den Anforderungen der Waschmittelindustrie.The results are summarized in Table 1 below.

The comparison of the dispersed sample from the spray drying with an undried sample shows the unsatisfactory dispersibility of the dried product. The comparative sample made from the dough meets the requirements of the detergent industry.

Example 2

In another part of the dough produced according to Example 1, after washing, 10 g of solid Na ₂ SO ₄ , corresponding to 2.4% of the amount of solids present in the dough, were mixed in per 1 kg of dough. The dough was also placed in a 200 liter jar to a filling height of 60 cm and observed as in Example 1. The simple tests, slowly tilting the container 45 °, inserting the stick, showed that after 7 days the dough was still homogeneous. After that, the phenomena that began to appear in a dough without Na ₂ S0 ₄ addition began to appear.

Example 3

In a further part of the dough produced according to Example 1, 45 g of solid sodium sulfate were mixed in per 1 kg of dough, which corresponded to approximately 10% of the amount of solids now present. The dough was observed, as described in the previous examples, when stored in a 200 l container (60 cm filling height).

The tests described above showed that settling only began after about 4 weeks, in the sense of the formation of a clear overhanging layer and a denser body. However, even after 8 weeks of storage when the vessel was inclined by 135 °, this soil body flowed virtually quantitatively and immediately into the template with the main mass, without having to stir it up.

Example 4

In a further part of the dough produced according to Example 1, 100 g of solid Na ₂ SO _{4 were} mixed in per 1 kg of dough, which corresponded to approximately 20% of the total amount of solids. The dough was observed when stored in the 200 liter jar with a filling height of 60 cm. In terms of flowability, the dough showed the same behavior as that in Example 3.

After 4 weeks of standing, a sample of the homogenized dough was dried in a laboratory spray dryer. The grain size distributions of the dried product and directly from the dough without addition of Na ₂ SO ₄ were determined after dispersion in water according to Andreasen. The influence of sodium sulfate on the density and viscosity of the aqueous medium was taken into account. The results are shown in Table 2.

From the table it can be seen that the dried product practically breaks down again into the original primary particles when dispersed in water.

Claims (5)

1. A method for improving the properties of sodium aluminum silicate doughs and powders, characterized in that 1-25% Na ₂ so ₄ , based on the total solids present after the addition of Na ₂ so ₄ , are added to the dough. 2. A method for improving the rheological properties of a sodium aluminum silicate dough according to claim 1, characterized in that 2-10% sodium sulfate, based on the total solid present, is added to the dough. 3. A process for improving the dispersibility of sodium aluminum silicate powder, characterized in that 15-20% sodium sulfate is added to the sodium aluminum silicate before it is dried. 4. Process according to claims 1 and 2, characterized in that the sodium sulfate is added to either one or both reaction solutions before the precipitation of the sodium aluminum silicate or the washed filter dough. 5. The method according to claims 1-3, characterized in that the sodium sulfate is introduced at least partially by using wash water neutralized with sulfuric acid during the washing process of the precipitated sodium aluminum silicate.