WO1995035258A1

WO1995035258A1 - Low temperature synthesis process for crystalline disilicates-i

Info

Publication number: WO1995035258A1
Application number: PCT/EP1995/002286
Authority: WO
Inventors: Hans Dolhaine; Helmut Blum; Wolfgang Breuer
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1994-06-22
Filing date: 1995-06-13
Publication date: 1995-12-28
Also published as: DE4421850A1

Abstract

A process for producing crystalline alkali metal disilicates useful as builders for washing and cleaning products is characterised in that amorphous alkali metal silicates in a modular range (i.e. molar ratio SiO2 : M2O, in which M stands for alkali metal) from 1.8 to 2.5 are after-baked in the presence of 5 to 25 % by weight water, in relation to the dry substance content of the alkali metal silicates, at a temperature ranging from 200 to 400 °C and under an autogenous steam pressure.

Description

"Method for Low-Temperature Synthesis of Crystalline Disilicate-I '

The invention describes a process for producing water-soluble crystalline alkali metal silicates by subjecting amorphous alkali metal silicates to a temperature treatment between 200 and 400 ° C. in the presence of water under autogenous water vapor pressure; The. Products can be used as builder substances and as anti-corrosion agents in washing and cleaning agents.

By Willgallis and Range, glass techn. Ber. 37 (4), pp. 194-200 (1964), the crystallization behavior of previously melted or unmelted amorphous sodium disilicate was investigated under heat treatment. The α, β and gamma phases were obtained and characterized by their X-ray diffraction diagrams. During the annealing of previously melted amorphous sodium disilicate in the temperature range between 500 and 820 ° C. for 120 hours, products were obtained which had an α-phase content which increased with the annealing temperature. Figure 2 of this work shows in the left half that after the tempering of previously melted water glass at 500 ° C there is little α phase in addition to a lot of gamma phase, while at 550 ° C about the same proportions of α and β phases 600 ° C about 1/3 as much α- as ß-phase and above 650 ° C in the upper part of the α-phase.

This finding coincides with the results of the process according to DE-A-4000705. The document states: For the production of crystalline sodium silicates with a layer structure of the formula Na2Si _x 02χ + i, where x is between 2 and 3, sand and soda are first melted in a molar ratio (“module”) of SiO 2 / Na 2 O of 2 to 3.5 at temperatures from 1,200 to 1,400 ° C. The lumpy water glass obtained after cooling of the melt is ground to particle sizes of less than 2 mm before being treated in an elongated reaction zone with mechanical circulation at temperatures of 600 to 800 ° C. for 10 to 120 minutes. Finally the material leaving the reaction zone is ground to a particle size of less than 1 mm. According to the exemplary embodiments, a material is obtained in the case of the disilicate which consists predominantly of the α modification and contains small amounts of a delta modification. The delta modification is characterized by its X-ray diffraction diagram in DE-A-34 17649. The X-ray diffraction patterns e of the α, β and garnma modifications are also given. They are also contained in the JCPDS file familiar to the crystallographer. The X-ray characterization can also be found in EP-B-164514, which also gives the numbers of the corresponding entries in the JCPDS file.

DE-A-3417649 does not explicitly set itself the task of producing the delta modification of the layered disilicate, but is limited from the above-mentioned reference in glass technology. Report that the delta modification could not be obtained by the process there. A production process is claimed in which an aqueous solution of an amorphous sodium silicate with a modulus between 1.9 and 3.5 with the addition of 0.01 to 30 parts by weight of the crystalline sodium silicate to be produced is dewatered and the dehydrated reaction mixture as long at a temperature between 450 ° C and the melting point until the sodium silicate has crystallized.

In EP-A-293640 the production of the delta modification is aimed at, but in the main claim a process for the production of crystalline sodium silicates with a layer structure and a module of 1.9 to 3.5 is more generally claimed. The process is characterized in that

a) a water glass solution with a solids content of 20 to 65 wt .-- spray dried such that the exhaust gas from the spray drying has a temperature of at least 140 ° C, b) the spray-dried product in a moving solid layer at temperatures of 500 to 800 ° C for one Duration of 1 to 60 minutes in the presence of at least 10% by weight of a return material.

The latter two publications have in common that for Production of the crystalline silicates with a layer structure, first of all amorphous sodium silicate dissolved in water and then converted into a water-containing, powdery form by evaporation of the water, for example by spray drying, which is then tempered at a temperature above 450 ° C. As an alternative to this, WO91 / 08171 describes a process for the hydrothermal production of crystalline sodium disilicate, in which an aqueous silicate solution with a solids content of between 50 and 75% by weight is heated in a pressure vessel at a temperature of at least 235 ° C. under autogenous pressure, the crystalline layered sodium disilicate precipitates and is separated from the mother liquor. Here, the β modification is obtained.

EP-B-425427 shows that amorphous products with a water content of 0.3 to 6% by weight are obtained in the (pressure-free) tempering of spray-dried water glasses in the temperature range between 250 and 500 ° C.

In contrast, the object of the invention is to provide a process for the production of crystalline alkali metal disilicates from amorphous precursors which can be carried out in the more energetically favorable temperature range between about 200 and about 400 ° C. and in which the product is not separated off a liquid phase is required.

The invention accordingly relates to a process for the preparation of crystalline alkali metal disilicates, characterized in that amorphous alkali metal silicates in the module range (= molar ratio S1O2: 2O, M = alkali metal) 1.8 to 2.5 in the presence of 5 up to 25% by weight of water, based on the dry matter content of the alkali metal silicates, is tempered in the temperature range between 200 and 400 ° C. under autogenous water vapor pressure.

The water can be bound to the alkali metal silicates, for example as water of hydration or as hydroxyl groups. In this case, the water content is defined as the weight loss which occurs when the water-containing alkali metal silicates are heated to 800 ° C. The residue represents the dry matter content. According to the invention, however, the water can also be present as physically adhering moisture or as a separate liquid or vapor phase. This means that during the A two-phase system solid / water vapor or a three-phase system solid / liquid water / water vapor can crystallize.

"Autogenous water vapor pressure" means the water vapor pressure which, when the alkali metal silicates are heated in the presence of the specified amount of water in a closed container, adjusts itself to the temperatures indicated. For reasons of economy, the container volume is dimensioned such that it does not exceed 5 times the volume of the substances introduced. On the other hand, the container volume must of course be at least as large as the volume of the substances introduced. Under these conditions, the autogenous water vapor pressure lies between atmospheric pressure and the equilibrium vapor pressure of pure water at the set temperature.

If the term "crystalline sodium disilicate" is used in the context of this invention, it means products which have the X-ray diagrams typical of crystalline sodium disilicate with a layer structure, as are given, for example, in the literature cited at the beginning. In practice it is possible that these products do not have the exact composition a2Sι ^* 2θ5, but differ from this strictly stoichiometric composition. In particular, it is possible for some of the sodium ions to be replaced by hydrogen ions, so that the products have a lower analytical sodium content or an increased silicon content. Accordingly, the analytical ratio SiÜ Na2θ of the crystalline sodium disilicate obtained by the process according to the invention can be approximately in the range between 1.9: 1 and 2.3: 1. It has been shown that the modulus of the amorphous alkali metal silicates used can deviate further from this range and can be in the range from 1.8 to 2.5. The tempering of such amorphous starting products gives rise to crystalline substances with X-ray diffraction diagrams of disilicates, that is to say of products with the theoretical module of 2. It can be assumed that excess silicon is at least partially in the form of silica, excess alkali in the form of metasilicates be eliminated with a module of 1.

Crystallization by thermal treatment under autogenous water Steam pressure in the temperature range between 200 and 400 ° C required crystallization times are between about 10 and about 180 minutes, in particular between about 30 and about 120 minutes. With shorter crystallization times, there is a risk of the product not completely crystallizing out. Longer crystallization times are possible, but have no further advantage. Preferred temperatures are between 210 and 300 ° C.

The desired conversion of the amorphous alkali metal silicates into crystalline alkali metal disilicates occurs at water contents between about 5 and about 25% by weight, based on the dry matter content of the alkali metal silicates. It is surprisingly irrelevant whether the water is in the form of physically or chemically bound water or in free form. Lower water contents reduce the yield of crystalline product, higher water contents lead to moist products and require post-drying. It is preferred, when using largely anhydrous, i.e. a ground melting glass having a water content of <1%, the water content before the tempering to 7 to 20% by weight. If water-containing water glass powder, flakes or granules obtained by drying a water glass solution are used, these should preferably have a water content of between 15 and 25% by weight.

Starting products which have a corresponding water content, for example as water of hydration or as water chemically bound in the form of hydroxyl groups, are therefore suitable for the heat treatment. Amorphous alkali metal silicates with such water contents are usually obtained if water glass solutions are dried according to methods known in the art. Suitable are, for example, water glass powders which can be obtained by spray drying water glass solutions, water glass scales which are formed when water glass solution is dried on a roller mill, or water glass granules such as are obtained, for example, by turbo drying according to EP-A-526978 and EP A-542131. However, largely anhydrous, ground, melted melting glass can also be used as the amorphous starting product. Such products usually have water contents, which can be determined by heating to 800 ° C., of less than 1% by weight. In the crystallization of such a starting product according to the invention, it is necessary to separate the necessary amount of water into the Introduce pressure vessel. This can be done, for example, by moistening the largely water-free, ground melting glass with a corresponding amount of water. However, the water can also be added directly to the pressure vessel in liquid form.

As a pressure vessel, for example, autoclaves are suitable in which the product remains motionless during crystallization. The temperature treatment can also be carried out by mixing the material to be tempered, for example in a heated rotating drum which is preferably provided with mixing internals.

For the purposes of this invention, sodium or potassium silicates or mixtures thereof can be used as alkali metal silicates. Sodium silicates are preferred for economic reasons. However, potassium silicates have the advantage of increased solubility, so that in those cases where particularly good solubility is important, potassium silicates will be preferred. A compromise in terms of cost and solubility is represented by potassium-doped sodium silicates, in which, for example, the sodium is replaced by potassium to such an extent that the product has a K2O content of up to 5% by weight.

The crystalline alkali metal layered silicates produced by the process according to the invention have bulk densities in the range from 320 to 450 g / l. If desired, these can be increased by suitable measures, for example compacting.

Examples

Amorphous sodium water glass with a module of 2 was used for the examples. For examples 1 to 6, anhydrous melting glass was used, which was ground and sieved to a particle size below 0.5 mm. For Example 7, was used as starting product a spray dried water glass with hollow spherical structure and a water content (determined as Ge weight loss at 800 ° C) of 19 wt .-% is used (Porti1 ^R A, Henkel KGaA, Dusseldorf). In Examples 1 to 5, the specified water quantity introduced as a separate phase next to the water-free water glass powder in the autoclave. In Example 6, the water glass powder was moistened with the specified amount of water. In Example 7, apart from the water bound in the spray product, no further water was added. The amounts of water used in each case (in% by weight based on the anhydrous amorphous sodium silicate) are given in Table 1.

In each case, about 1 1 of the starting substances were heated in closed 2 1 autoclaves to the final temperatures given in Table 1, the autogenous water vapor pressure being set. Table 1 also contains the times for which the samples were at a temperature of 210 ° C or above. These times are made up of the heating-up time between 210 ° C and the final temperature and the holding time at the final temperature. The heating time between 210 and 240 ° C was about 10 minutes. After these times, the autoclave was let down and cooled.

The products obtained were characterized by their X-ray diffraction diagram (Table 1).

The tests prove that crystalline line silicates can be obtained under the conditions according to the invention, the suitability of which is known in the prior art as a builder for detergents and cleaning agents. As a control, the solution behavior of the product obtained according to Example 7 was compared with the commercial detergent builder Na-SKS-6 (crystalline Na disilicate, mainly delta phase, Hoechst AG). No significant differences were found.

Table 1: Crystallization conditions and results

Test H 01) temperature pressure time 2) result according to No. wt.% ° C bar min X-ray diffraction

Ex. L 20 240 8 100 crystalline product, mixture of α, β and delta phase

Ex. 2 10 240 8 100 crystalline product, mixture of α, β and delta phase

Example 3 7.5 240 3 100 semi-crystalline product with a residual amorphous phase

Ex. 4 15 250 10 65 crystalline β-disilicate, very small proportions of the α and delta phase

Example 5 12.4 210 5 75 largely amorphous, but significant proportions of crystalline phase

Ex. 6 10 240 10 100 crystalline ß-disilicate, very small proportions of α and delta phase

Ex. 7 19 240 8 10 crystalline ß-disilicate without recognizable secondary components 1) Type of addition: see text

2) total time above 210 ° C (= holding time at final temperature + heating-up time)

Claims

1. Process for the preparation of crystalline alkali metal disilicates, characterized in that amorphous alkali metal silicates in the modulus range (= molar ratio SiO 2: M2O, M = alkali metal) 1.8 to 2.5 in the presence of 5 to 25% by weight % Water, based on the dry substance content of the alkali metal silicates, is tempered in the temperature range between 200 and 400 ° C. under autogenous water vapor pressure.

2. The method according to claim 1, characterized in that tempering in the temperature range between 210 and 300 ° C.

3. The method according to one or both of claims 1 and 2, characterized ge indicates that annealing for a period between 10 and 180 minutes, preferably between 30 and 120 minutes.

4. The method according to one or more of claims 1 to 3, characterized ge indicates that largely anhydrous, ground melting glass in the presence of 5 to 25 wt .-%, preferably 7 to 20 wt .-% annealed water.

5. The method according to one or more of claims 1 to 3, characterized ge indicates that by drying a water glass solution obtained water-containing water glass powder, flakes or granules with a water content between 15 and 25 wt .-%.

6. The method according to one or more of claims 1 to 5, characterized ge indicates that the alkali metal silicates are sodium or potassium silicates, preferably sodium silicates, which if desired with potassium up to a K2θ content of 5 wt .-% can be doped.