WO1995019934A1

WO1995019934A1 - Production of crystalline sodium disilicates

Info

Publication number: WO1995019934A1
Application number: PCT/EP1995/000088
Authority: WO
Inventors: Gerald Schreiber; Wolfgang Breuer; Lothar Pioch; Beatrix Kottwitz
Original assignee: Henkel Kommanditgesellschaft Auf Aktien
Priority date: 1994-01-20
Filing date: 1995-01-11
Publication date: 1995-07-27
Also published as: AU1416295A; TR28305A; DE4401527A1

Abstract

A process for the production of crystalline sodium disilicates exhibiting the α modification to the extent of less than 40 %, in which molten amorphous sodium silicate reduced by milling or dividing the melt is malleableised in a water-containing atmosphere for a period of 5 minutes to 4 hours at a temperature of between 500 and 740 °C.

Description

PRODUCTION OF CRYSTALLINE SODIUM DISILICATES

The invention describes a process for the production of crystalline sodium disilicates, which consist of the β and / or delta modification and which have the crystallographic α modification only to a minor extent, from melted and crushed amorphous sodium water glass. 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 oc, ß and gamma phases were obtained and characterized by their X-ray diffraction diagrams. During the tempering 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 tempering temperature. Figure 2 of this work shows in the left half that after the annealing of previously melted water glass at 500 ° C there is little α phase along with a lot of gamma phase, while at 550 ° C approximately equal proportions of α and ß phase, at 600 ° C about 1/3 as much α- and ß-phase and above 650 ° C in the excess 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 Na ₂ Si _x O _{2x + 1} , where x is between 2 and 3, sand and soda are first melted in a molar ratio (“modulus”) of SiO ₂ / Na ₂ O 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 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 fineness of less than 1 mm. According to the exemplary embodiments in this case, in the case of the disilicate, a material is obtained which mainly consists 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 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-3417849 does not explicitly set itself the task of producing the delta modification of the layered disilicate, but is limited from the above-mentioned literature reference in glass technology. Report that the delta modification could not be obtained by the process there. A manufacturing 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 to be produced! dehydrated crystalline sodium silicate and the dehydrated reaction mixture 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 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 having a solids content of 20 to 65% by weight is 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 a period of 1 to 60 minutes in the presence of at least 10 wt .-% 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 converted into a water-containing, powdery form by evaporation of the water, for example by spray drying, which is then tempered. Alternatively, WO91 / 08171 describes a process for the hydrothermal production of crystalline sodium disilicate, in which an aqueous silicate solution is heated at a temperature of at least 235 ° C. under autogenous pressure in a pressure vessel, the crystalline layer-like sodium disilicate precipitating. Here, the β modification is obtained. Accordingly, a product is obtained by tempering a previously melted and ground sodium disilicate, that is to say not dissolved in water, which product consists primarily of the α-modification or at least contains high proportions of this modification. However, EP-B-164514 states that the β and delta modifications are particularly suitable for water softening. Accordingly, EP-A-548599 has the task of better controlling the temperature control during the tempering of previously spray-dried product, "so that the risk of producing undesired α-Na ₂ Si ₂ O _{5 is} minimized". In order to obtain the ß or delta modification, which are therefore preferred for use as builders in detergents and cleaning agents, it was previously necessary to go through an energy-intensive dissolving and drying process, or crystallization times of 120 hours to take.

In contrast, the object of the invention is to provide a process which can be carried out within a few minutes to hours for the production of crystalline sodium disilicate products which have less than 40% of the α-modification, and which avoids the energy-intensive dissolving and drying step directly Grinding or by crushing the melt crushed amorphous melting glass. The invention is based on the surprising finding that when such a starting product is tempered in a water-containing atmosphere, crystalline disilicates with a layer structure are obtained which have only minor amounts of α-modification.

The invention accordingly describes a process for the preparation of crystalline sodium disilicates which have less than 40% of the α-modification, characterized in that molten amorphous sodium water glass which has been comminuted by grinding or by splitting the melt in a water-containing atmosphere 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.

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 disilicates 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 Na ₂ Si ₂ O ₅ , but instead deviate 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 SiO ₂ : Na ₂ O of the crystalline sodium disilicates obtained by the process according to the invention can be approximately in the range between 1.9: 1 and 2.3: 1.

An X-ray diffraction diagram of a crystal powder obtained by this method, taken with Cu-K _α radiation, is shown in the figure. The figure shows the assignment of the individual reflections to the different phases of Na ₂ Si ₂ O ₅ . The diagram can essentially be interpreted as a superimposition of the diagrams of the ß and delta modifications. It contains no reflexes from the gamma modification. A reflection at 2 θ = 27.1 ° (corresponding to a d-value of 3.29 Å) can be used as an indication of the α-modification content, since this represents a strong reflection of the α-modification and unlike others strong reflections of the α phase do not overlap with reflections of the β and / or delta modification. In the sense of this description, the ratio of the peak height is used as a measure of the content of α-modification Reflexes taken to the most intense reflex of the diagram. This most intense reflex occurs at a 2 Θ value of 22.4 ° and is created by superimposing a strong reflex of the ß and the delta modification with d values of 3.96 and 3.97 A. The diagram in the figure shows a height ratio of 0.06. Accordingly, the α-modification content of 6% is attributed to the crystal mixture.

During the tempering, the water content of the water-containing atmosphere is adjusted so that the water vapor partial pressure is between 0.012 and 1 bar, preferably between 0.02 and 0.70 bar. This can be done, for example, by keeping the tempered material in contact with a gas stream, for example an air stream, which has the corresponding water content during the tempering process. This water content can be adjusted, for example, by saturating the gas stream with water vapor by passing it through water of the appropriate temperature. The relationship between the saturation pressure of water and the water temperature is known, for example from Ullmanns Encyklopadie der Technische Chemie, 4th edition 1983, volume 24, page 170. The enrichment of the carrier gas with water vapor can be made more effective by increasing the exchange area. This can take place, for example, in trickle chambers which may be filled with packing material and into which water of the appropriate temperature is sprayed. Of course, the water-containing gas stream can also be prepared by mixing pure water vapor obtained with the boiling of water with the carrier gas, for example with air.

In the sense of the invention it is essential that the water content of the atmosphere is within the specified limits during the entire tempering process. As comparative experiments show, it is not sufficient to simply start with the starting product moisten with water. If the product dries during annealing and the water vapor evaporates, sufficient builder properties are not developed. However, it would be in the spirit of the present invention to anneal a moist product in a closed container so that the evaporating water cannot escape. However, this procedure is less preferred because of the more difficult pressure and temperature control for tempering under a steam atmosphere at approx. 600 ° C.

If a dry product is used and the mixture is tempered under a nitrogen atmosphere which has been saturated with water vapor at room temperature, a product mixture of mainly β and delta modification is obtained with crystallization times between 15 and 60 minutes at 600 ° C, which has an X-ray content α-modification between 30 and 35%. If, for example, the water vapor partial pressure is increased to 0.3 bar by saturating the gas stream passed through the furnace with water vapor at 70 ° C, the content of α modification in the product decreases to values between 15 and 25% under the same tempering conditions.

If the starting product is moistened with a water glass solution with a module SiO 2: Na 2 O between 1.8 and 2.4 such that the water content of the mixture thus obtained is between 3 and 30% by weight, preferably between 5 and 25% by weight , the tempering of this mixture in a water-containing atmosphere results in a lower content of α-modification (<10%) and improved builder properties. The solids content of the water glass solution used for moistening is preferably above 10% by weight, in particular between 20 and 55% by weight. In order to achieve a high yield of crystalline sodium disilicate, it is advantageous to use a melting glass as the amorphous starting product, the modulus of which is already close to the desired value of 2. For example, melting glasses with a module between 1.9 and 2.1 are suitable. However, silica-richer melting glasses can also be used in the process if, instead of using a water glass solution, the solution is preferably moistened with 50% by weight sodium hydroxide solution and the amount of sodium hydroxide solution is measured so that the moist tempering mixture has a SiO ₂ : Na ₂ O ratio between 1.1 9 and 2.1. If, for example, a melting glass with module 2.45 is assumed, this can be brought to a module of 2 before tempering if 100 g of melting glass are moistened with 17.2 g of 50% sodium hydroxide solution. Correspondingly, it is also possible to use a melting glass with module 3.3, which is brought to a module of 2 before tempering by moistening 100 g of the melting glass with 40 g of 50% sodium hydroxide solution. In this way, melting glass can be used up to a module of about 3.8.

An advantageous alternative to this is to use an amorphous sodium water glass with a module between 2.1 and 3.8, in particular one with a module of 2.45 or 3.3, and for setting an overall module in the range of 2 with a corresponding amount of one Mix amorphous or crystalline soda water glass with a modulus between 1 and 1.5. In particular, metasilicate hydrates of the composition Na ₂ SiO ₃ .nH ₂ O can be used for this, for example in the form of the pentahydrates or the nonahydrates.

The solidification of the solidified melt of the amorphous water glass is preferably carried out by grinding. The common grinding units are suitable for this. For example, grinding the lumpy water glass with a robust, slow-running Beater mill, for example a hammer mill. The further fine grinding can be carried out with the aid of a vibratory mill, a ball mill or an air jet mill. If the method is to be used in the embodiment in which the ground amorphous water glass is moistened with a water glass solution or with sodium hydroxide solution, this moistening can already take place during the grinding process. In order to avoid contamination of the product with metal abrasion, it is advisable to use mills and grinding media that have a ceramic, in particular a silicate-ceramic lining. Before the tempering process is carried out, the regrind should preferably have a maximum particle size of less than 1.0 mm, which can be ensured by a suitable classification, for example screening. Of course, oversize will be returned to the grinding process.

Alternatively, a water glass powder or granulate can be used, which was obtained directly by dividing and cooling the melt. For example, the liquid melt can be pressed through nozzles with, preferably, a maximum diameter of 1 mm and the solidified water glass threads can preferably be broken to a length of <1 mm, for example by means of a suitable grinding unit, a pan mill or a roller mill. The nozzle diameter is limited at the bottom by the viscosity of the water glass melt used. A cooling medium, for example an air or water vapor stream, is advantageously used to cool the molten threads.

For later use in detergents and cleaning agents, the product is preferably ground and classified so that the maximum particle size is between 0.01 and 0.5 mm. The actual annealing process can be carried out with a stationary or a moving product. Accordingly, the tempering can take place, for example, in a fixed bed, but also in a rotating rotary kiln or in a fluidized bed.

The annealing process described provides crystalline sodium disilicate with a layer structure, which is suitable as a builder for detergents and cleaning agents. The process already shows the desired success without the addition of seed crystals. However, the required annealing time can optionally be reduced by adding seed crystals of crystalline sodium disilicate, which have less than 10% of the α-modification, to the amorphous water glass before or during the annealing in quantities of 0.01 to 30% by weight of the amorphous water glass admits.

Execution examples

To carry out the tests, amorphous sodium water glass with a module SiO ₂ : Na ₂ O = 2.05, which was obtained by melting quartz sand with soda, was ground in a cross-beat mill and the sieved fraction with a particle size <0.2 mm was used. The powder obtained was examined for comparative experiment 1 without tempering. For comparative experiments 2 to 4, the powder was moistened with 15% by weight of water and annealed at 600 ° C. for 15, 30 or 60 minutes. As a comparative product 5, the commercially available product Na-SKS-6 from Hoechst, which mainly consists of the delta phase, was investigated without further processing. In the exemplary embodiments and the comparative examples, the annealing was carried out in such a way that the powders with a filling height of about 3 cm were placed in porcelain crucibles and heated to 600 ° C. for the times indicated in the table Simon Müller ovens were provided. The water vapor atmosphere in the ovens was adjusted by a stream of nitrogen at a rate of 60 l / h. was blown into the oven, which was previously bubbled with water of different temperatures. The corresponding water vapor partial pressure of this nitrogen flow is entered in the tables. In Examples 1 to 3, the ground amorphous water glass was filled dry into the crucible. In Examples 4 to 8, the powder was moistened with a water glass solution WG I before tempering under a water vapor atmosphere, in Examples 9 to 13 with a water glass solution WG II. The total water content of the mixture was between 5 and 20% by weight. The water glass solution WG I was a commercial water glass solution with a total solids content of 28.1% by weight and a module SiO ₂ : Na ₂ O = 3.97, which by mixing with 50% by weight sodium hydroxide solution Module of 2 was set. The water glass solution WG II had a total solids content of 47.0% by weight and a modulus of 2.48, which was also adjusted to 2 by adding sodium hydroxide solution.

In the picture is a typical X-ray diffraction pattern

(Cu-Ktf radiation) of a product obtained by the process according to the invention (Example 6). The most prominent reflexes are assigned to the phases α, β and delta.

Table 2 contains further examples for the practice of the method according to the invention, it now being assumed that a ground amorphous melting glass with a higher modulus and the total modulus was adjusted to 2.0 by moistening with the calculated amount of 50% strength by weight sodium hydroxide solution.

Table 3 contains examples in which powdered amorphous soda water glass with a modulus of 2.45 or 3.3 before tempering was mixed with a quantity of sodium metasilicate of the hydrate stage indicated in Table 3 such that the modulus of the total mixture was 2.0 under a steam atmosphere. To adjust the module, for example, 100 g of ground sodium water glass with module 2.45 were mixed with 45.7 g of sodium metasilicate pentahydrate or with 61.1 g of sodium metasilicate nonahydrate. The heat treatment was then carried out under the conditions given in Table 3. The annealing products consisted of over 80% crystalline sodium disilicate in the delta form.

To characterize the products obtained, the solution behavior in water and the calcium binding capacity (CaBV) were measured in mg CaO / g active substance. The relative solubility was determined by measuring the electrical conductivity of the solution relative to the commercial product Na-SKS-6 from Hoechst. For this purpose, 0.5 g of substance was stirred into 1,000 ml of water at room temperature and the electrical conductivity measured as a function of time. The value obtained for Na-SKS-6 after 10 minutes was set as 100% relative solubility and the other conductivity values related to it. The table shows the relative solubilities after one and after 3 minutes.

To determine the calcium binding capacity, a Ca ²⁺ solution of 30 ° dH was adjusted to pH 10 with sodium hydroxide solution, a defined amount of sample material was added, the mixture was stirred for 10 minutes at room temperature and then filtered through a membrane filter with a pore size of 0.45 μm. The residual Ca ²⁺ content in the filtrate was determined by complexometry. The calcium binding capacity in mg CaO / g active substance entered in the table was calculated from this. The products according to the invention had bulk densities of 870 +/- 50 g / l, which, if desired, can be increased further by suitable measures, for example compacting.

Claims

claims

1. A process for the preparation of crystalline sodium disilicates which have less than 40% of the α-modification, characterized in that molten and crushed by grinding or by breaking the melt amorphous sodium water glass in a water-containing atmosphere with a water vapor partial pressure between 0.012 and 1 bar is annealed for a period of 5 minutes to 4 hours at a temperature between 500 and 740 ° C.

2. The method according to claim 1, characterized in that the water content of the atmosphere is adjusted so that the water vapor partial pressure is between 0.02 and 0.70 bar.

3. A process for the preparation of crystalline disilicates which have less than 10% of the α-modification, according to one or both of claims 1 and 2, characterized in that the amorphous sodium water glass before tempering with a water glass solution with a module SiO ₂ : Na ₂ O between 1.8 and 2.4 and a solids content> 10% by weight, preferably between 20 and 55% by weight, provided that the mixture is moistened so that the water content of the mixture is between 3 and 30% by weight, preferably between 5 and 25 wt .-% is.

4. The method according to one or both of claims 1 and 2, characterized in that the amorphous sodium water glass has a module SiO ₂ : Na ₂ O between 2.1 and 3.8 and before annealing with such an amount of sodium hydroxide solution, preferably with 50 % by weight sodium hydroxide solution is moistened so that the moist tempering mixture has a modulus between 1.9 and 2.1.

5. The method according to one or both of claims 1 and 2, characterized in that the amorphous sodium water glass has a module SiO ₂ : Na ₂ O between 2.1 and 3.8 and before annealing with such an amount of an amorphous or crystalline sodium silicate is mixed with a modulus between 1 and 1.5 so that the total modulus of the mixture is between 1.9 and 2.1.

6. The method according to claim 5, characterized in that used as an amorphous or crystalline sodium silicate with a modulus between 1 and 1.5 crystalline water-containing metasilicate, preferably Na ₂ SiO ₃ • 5H ₂ O and / or Na ₂ SiO ₃ • 9H ₂ O. becomes.

7. The method according to one or more of claims 1 to 6, characterized in that the crushing of the amorphous sodium water glass is carried out by grinding a solidified melt and the grinding product preferably to a maximum particle size below 1.0 mm, in particular to a maximum particle size between 0, 01 and 0.5 mm is classified.

8. The method according to one or more of claims 1 to 6, characterized in that the crushed amorphous sodium water glass was obtained by cutting and cooling a melt, preferably in that the melt is pressed through nozzles with a maximum diameter of 1 mm and the solidified Water glass threads break to a length of <1 mm.

9. The method according to claim 8, characterized in that a cooling medium, preferably an air or water vapor stream is used to cool the molten water glass filaments.

10. The method according to one or both of claims 8 and 9, characterized in that the solidified water glass melt is adjusted to a maximum particle size between 0.01 and 0.5 mm.

11. The method according to one or more of claims 1 to 10, characterized in that the annealing takes place in a fixed bed.

12. The method according to one or more of claims 1 to 10, characterized in that the annealing is carried out with thorough mixing of the powder, preferably in a rotating rotary kiln or in a fluidized bed.

13. The method according to one or more of claims 1 to 12, characterized in that the pulverized amorphous water glass before or during the tempering seed crystals of crystalline sodium disilicate, which have less than 10% of the α-modification, in amounts of 0.01 Adds up to 30 wt .-% based on the amorphous water glass.