WO1995035259A1

WO1995035259A1 - Low temperature synthesis process for crystalline disilicates-ii

Info

Publication number: WO1995035259A1
Application number: PCT/EP1995/002287
Authority: WO
Inventors: Helmut Blum; Wolfgang Breuer; Hans Dolhaine
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1994-06-22
Filing date: 1995-06-13
Publication date: 1995-12-28
Also published as: DE4421851A1

Abstract

A process for producing crystalline alkali metal disilicates 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 and 0.2 to 2 % by weight chelating complexing agents, in relation to the dry substance content of the alkali metal silicates, at a temperature range from 200 to 300 °C. These products are useful as builders for washing and cleaning agents.

Description

"Process for Low-Temperature Synthesis of Crystalline Disilicate-H"

The invention describes a process for the preparation of water-soluble crystalline alkali metal silicates by subjecting open alkali metal silicates to a temperature treatment between 200 and 300 ° C. in the presence of water and of chelating complexing agents. 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 gam a phases were obtained and characterized by their X-ray diffraction diagrams. When tempering previously melted amorphous sodium disilicate in the temperature range between 500 and 820 ° C. for 120 hours, products were obtained which had an oc phase content which increased with the tempering 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 oc- as ß-phase and above 650 ° C in the upper weft oc-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 θ2χ ₊ ι, where x is between 2 and 3, sand and soda are first melted in a molar ratio (“module”) of Siθ2 / a2θ from 2 to 3.5 at temperatures from 1,200 to 1,400 ° C. The lumpy water glass obtained after the melt has cooled is ground to particle sizes of less than 2 mm before being mechanically agitated in an elongated reaction zone 10 to Treated for 120 minutes at temperatures from 600 to 800 ° C. 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 “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 diagrams of the α, β and gamma modifications are also given. They are also included 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, according to the task, the production of the delta modification is aimed for, 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 anneals for a period of 1 to 60 minutes in the presence of at least 10% by weight of a return material. The two last-mentioned published publications have in common that for the production of the crystalline silicates with a layer structure, amorphous sodium silicate is first dissolved in water and then by evaporation of the water, for example by spray drying, this is converted into a water-containing, powdery form which is then above 450 ° C is annealed. Alternatively, 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 disate precipitates and is separated from the mother liquor. Here, the β modification is obtained.

German patent application P 44 01 527.5 discloses a process for the production of crystalline sodium disilicate, which has less than 40% of the α-modification, in which powdered, anhydrous, amorphous sodium water glass in a water-containing atmosphere with a water vapor partial pressure between 0.012 and 1 bar for a period of 5 minutes to 4 hours at a temperature between 500 and 740 ° C.

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

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 more favorable temperature range between about 200 and about 300 ° 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 SiO 2: 2 O, M = alkali metal) 1.8 to 2.5 in the presence of 5 up to 25% by weight of water and from 0.2 to 2% by weight of chelating complexing agent, in each case based on the dry matter content of the alkali metal silicates, in the temperature range between see 200 and 300 ° C annealed. This process gives crystalline alkali metal disilicates which are significantly more crystalline than those which are obtained in the absence of chelating complexing agents. The degree of crystallinity, as explained in the example section, can be determined by the ratio of the intensity of the strongest reflex to the height of the diffuse background.

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 liquid or vapor phase.

When 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 products 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 Na2Si2Ü5, 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 an analytically lower sodium content or an increased silicon content. Accordingly, the analytical ratio SiO 2: Na 2 O 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. When such amorphous starting products are tempered, crystalline substances with X-ray diffraction diagrams of disilicates, ie of products with the theoretical module of 2, are formed. It can be assumed that excess silicon is at least partially in the form of silica, excess alkali in the form of Metasilicates with a modulus of 1 are excreted. The crystallization times required for crystallization by thermal treatment in the temperature range between 200 and 300 ° C. are between approximately 20 and approximately 250 minutes, in particular between approximately 30 and approximately 180 minutes. With shorter crystallization times, there is a risk of the product not fully crystallizing out. Longer crystallization times are possible, but have no further advantage.

A large number of chelating complexing agents suitable according to the invention are known. They can belong to different chemical groups. The following are suitable individually or in a mixture:

a) polycarboxylic acids such as, for example, polyacrylic acid or acrylic acid-maleic acid copolymers, b) hydroxyoligocarboxylic acids such as tartaric acid and citric acid, c) nitrogenous mono- or oligocarboxylic acids such as ethylenediaminetetraacetic acid (EDTA), N-hydroxyethylethylenediamine triacetic acid, diethylactonitrilesamine, acetic acid-3-propionic acid, isoserine diacetic acid, N, N-di- (ß-hydroxyethyl) -glycine, N- (1,2-dicarboxy-2-hydroxyethyl) -glycine, N- (1,2-dicarboxy -2-hydroxyethyl) -aspartic acid or nitrilotriacetic acid (NTA), d) ge inale diphosphonic acids such as l-hydroxyethane-l, l-diphosphonic acid (HEDP), their higher homologues with up to 8 carbon atoms and derivatives thereof containing hydroxyl or amino groups and 1-Aminoethane-1,1-diphosphonic acid, its higher homologues with up to 8 carbon atoms, and derivatives thereof containing hydroxyl or amino groups, where the amino nitrogen mono- or similar can be dialkylated (C1-C5), and nitrogen-containing heterocyclic diphosphonic acids, such as azacycloheptane-2,2-diphosphonic acid, e) aminophosphonic acids such as ethylenediaminetetrakis (methylenephosphonic acid), diethylenetriaminepentakis (methylenephosphonic acid) or nitrilotris (methylenephosphonic acid) as well as Phosphonooligocarboxylic acids such as 2-phosphonobutane-l, 2,4-tricarboxylic acid.

The complexing agents can be used as free acids or in the form of their alkali metal salts, in particular their sodium salts. Since the use of the free acids affects the module of the alkali metal silicates it is preferable to use the complexing agents as salts. The preferred amounts of the complexing agents, optionally in the form of their alkali metal salts, are between about 0.3 and about 1.5% by weight, based on the dry matter content of the alkali metal silicates. The dry matter content of the alkali metal silicates is defined as the residue after dewatering at 800 ° C.

The tempering is preferably carried out in such a way that a water glass solution, to which additional undissolved alkali metal silicate may be added and which has a solids content of between about 65 and about 93% by weight, is first brought to a mechanical movement under autogenous water vapor pressure Temperature between about 150 and about 200 ° C heats up. "Autogenous water vapor pressure" means the water vapor pressure which automatically sets itself at this temperature in a closed container. The pressure vessel, for example an autoclave equipped with a stirrer, is then depressurized to normal pressure. So much water escapes that a solid, possibly foamed body with a residual water content of between 5 and 25% by weight remains. This solid is then heated to a temperature between 200 and 300 ° C. and allowed to crystallize at this temperature for the times indicated above. The mixture is then allowed to cool to normal temperature, the product is removed and ground to a powder.

According to this process, crystalline alkali metal layer silicates are obtained which have a significantly higher degree of crystallization than in the absence of chelating complexing agents. Polyacrylic acid, citric acid, ethylenediaminetetraacetic acid and l-hydroxyethane-l, l-diphosphonic acid in the form of their sodium salts have proven to be particularly suitable as complexing agents which can be used. Since the complexing agent remains in the crystalline product which is subsequently to be used as a builder in detergents and cleaning agents, it is advisable to use those complexing agents whose use is permissible for the stated purpose and, if possible, offers product advantages. This applies in particular to polyacrylic acid and citric acid.

As alkali metal silicates, sodium or Potassium silicates or mixtures thereof can be used. Sodium silicates are preferred for economic reasons. However, potassium silicates have the advantage of increased solubility, so that preference is given to potassium silicates in those cases in which particularly good solubility is important. 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.

After grinding and classifying, the crystalline alkali metal layer silicates produced by the process according to the invention have a particle size of <0.2 mm bulk densities in the range from 730 to 830 g. If desired, these can be increased by suitable measures, for example compacting.

Examples

The crystallization according to the invention was carried out using two modified methods:

Procedure 1:

108 g of ground anhydrous sodium melting glass with a modulus of 2 and a grain size of less than 0.5 mm were added together with 242 g of water glass solution (modulus = 2, solids content 50% by weight) and with complexing agent according to Table 1 in an autoclave with stirring 200 ° C heated under autogenous water vapor pressure. At this temperature, stirring was first carried out for 30 minutes. The stirrer was then switched off and about 80 to 85 g of water were distilled off after expansion, so that the mixture still had a water content of about 15% by weight. The autoclave was then closed, heated to the temperature given in Table 1 and left at this temperature for the time indicated. The crystalline end products had a residual water content, determined by heating to 800 ° C., of about 5% by weight. Procedure 2:

282.4 g of ground anhydrous sodium melting glass with a modulus of 2 and a grain size between 0.1 and 0.2 mm were mixed with 121 g of water glass solution (module = 2, solids content 50% by weight) and with complexing agents according to Table 2, heated to 200 ° C. in an autoclave under autogenous steam pressure and stirred at this temperature for 30 minutes. At this temperature, the reaction mixture, which had a water content of about 15% by weight, was depressurized to normal pressure. The autoclave was then closed and kept at 200 ° C. for the time specified in table 2, or the temperature was set and maintained as indicated in table 2. After cooling, the products had water contents, determined by heating to 800 ° C., of about 1% by weight.

Crystallinity index

X-ray diffraction diagrams of the products obtained were recorded using the counting tube method using copper K _j χ radiation. This showed sharp reflections of crystalline disilicates, which could be assigned to the β phase, over a more or less pronounced diffuse background, depending on the test conditions. The ratio between the maximum intensity of the most intense reflex (at 2 theta = 37.1 °) and the diffuse background at a reflection-free point (at 2 theta = 31.8 °) is defined as the crystallinity index. To determine this, the height of the reflectance at 2 theta = 37.1 ° above the marked background was measured at this point on the graphically represented counter tube diagrams and divided by the height of the drawn diffuse background at 2 theta = 31.8 °. The greater the crystallinity index, the more pronounced the crystallinity of the sample.

Comparative examples

Comparative example 1: is contained in table 1. The following were carried out as further comparative examples:

Comparative Example 2: Anhydrous ground sodium melting glass with a Module of 2 and a grain size <0.5 mm was mixed with 12.5% by weight of water, heated to 210 ° C. in an autoclave under autogenous water vapor pressure and held at this temperature for 75 minutes. According to the X-ray diffraction diagram, a crystallinity index of 1.0 could be assigned to the product obtained.

Comparative Example 3: Melting glass powder as in Comparative Example 2 was mixed with 15% by weight of water, heated to 250 ° C. in an autoclave under autogenous water vapor pressure and kept at this temperature for 65 minutes. The end product had a crystallinity index of 9. 8 assign.

Table 1: Products according to method 1

No. complexing agent quantity ¹ ) temperature time crystallinity index ² )

Comp. L without - 270 ° C 3 h 8.9

Ex. 1 disodium-hy- 0.33 270 ° C 3 h 17.6 droxyethane-phosphonate

Ex. 2 disodium hy 1.2 270 ° C 3 h 14.2 droxyethanediphosphonate

Example 3 Na polyacrylate 1.52 270 ° C 3 h 22.0

1)% by weight with respect to anhydrous alkali metal silicate

2) cf. text Table 2: Products according to procedure 2

No. Complexing agent amount) temperature time crystallinity index ² )

Ex. 4 disodium hy 0.90 270 ° C 3 h 20.8 droxyethanediphosphonate

Ex. 5 disodium hy 0.90 200 ° C 3 h 22.0 droxyethanediphosphonate

Ex. 6 disodium-hy- 0.90 270 ° C 0.5 h 22.5 droxyethane-phosphonate

Ex. 7 trisodium 0.90 200 ° C 3 h 18.1 citrate

Ex. 8 disodium EDTA 1.04 270 ° C 3 h 17.3

!) Percent by weight with regard to anhydrous alkali metal silicate) cf. text

Claims

1. Process for the preparation of crystalline alkali metal disilicate, 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 and from 0.2 to 2 wt .-% chelating complexing agent, each based on the dry matter content of the alkali metal silicates, in the temperature range between 200 and 300 ° C.

2. The method according to claim 1, characterized in that one anneals for a period between 20 and 250 minutes, preferably between 30 and 180 minutes.

3. The method according to one or both of claims 1 and 2, characterized ge indicates that the chelating complexing agents are selected from at least one of the groups a) polycarboxylic acids, b) hydroxyoligocarboxylic acids, c) nitrogenous mono- or oligocarboxylic acids, d) geminale Diphosphonic acids, e) aminophosphonic acids, f) phosphonooligocarboxylic acids and the alkali metal salts of the acids of groups a) to f).

4. The method according to one or more of claims 1 to 3, characterized ge indicates that the chelating complexing agent is selected from polyacrylic acid, citric acid, ethylenediaminetetraacetic acid and l-hydroxyethane-l, l-diphosphonic acid or in each case their sodium salts.

5. The method according to one or more of claims 1 to 4, characterized ge indicates that in the presence of 0.3 to 1.5 wt .-%, based on the dry matter content of the alkali metal silicates, of chelating complexing agents, preferably in Form of their sodium salts, temper.

6. The method according to one or more of claims 1 to 5, characterized ge indicates that the reaction mixture under autogenous water vapor pressure to a temperature in the range between 150 and 200 ° C heats, at this temperature water vapor can escape until atmospheric pressure is reached and the residue is kept at 200 ° C. or heated to the higher crystallization temperature.

7. 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 2θ content of 5 wt .-% can be doped.