LT3795B - Process for the production of sodium silicates - Google Patents

Abstract

For the production of crystal sodium silicates with a stratified structure, molar ratio SiO2/Na2O (1.9-2.1): 1 and less than 0.3 % of water, from a soluble glass solution, containing hard material 20 % of it's own weight, a soluble glass solution is obtained in a reaction of quartz sand with sodium alkali, molar ratio SiO2/Na2O (2-2.3): 1 at a temperature of 180-240 degrees Celsius and 10-30 bar pressure. This soluble glass solution is treated for 10-25 seconds in a spray dry zone of 200-300 degrees Celsius air temperature, when the temperature of the used gas exhausted from the spray dray zone is 90-130 degrees Celsius, forming at that moment a powder like shapeless sodium silicate, containing 15-23 percent of it's own weight of water (set as a heating loss at the temperature of 700 degrees Celsius) and having an alleged density less than 300 g/l. Powder like shapeless water containing sodium silicate is loaded into an inclined rotary tube oven with a device for hard material movement and treated by a fume with a counter-flow in a higher than 500-850 degrees Celsius, 1-60 minutes at the moment, forming crystal sodium silicate. The rotary tube stove is so insulated, that the outside wall temperature of the oven is less than 60 degrees Celsius. Finally the crystal sodium silicate that is let out from the rotary tube oven is made fine by a mechanical crusher up to 0.1-12 mm size grains.

Description

The present invention relates to a process for the preparation of a crystalline sodium silicate having a layered structure, S1O2 with a Na2 O molar ratio (1.9-2.1): 1 and less than 0.3% by weight, of water from a soluble glass solution having at least 20% by weight. % solids.

It is known from U.S. Pat. No. 3,471,253 that a soluble glass solution is prepared by placing 42% by weight of caustic soda and sand (silica) in a 2: 1 w / w autoclave with stirrer and left in it for 3 hours at 210 ° C and 16 bar. under pressure. After cooling the contents of the autoclave to 85 ° C, the hot sodium silicate solution was removed and, after filtering off excess sand and other impurities, had a 57.5% solids to S 2 O 2 ratio of 1.64: 1.

Crystalline anhydrous layered sodium silicate having a molar ratio S1O2 to Na2O (1.9-3.5): 1, obtained according to the process described in DE-OS 3 718 350 by treatment of a solution of soluble glass containing 20-65% by weight. In the case of solids, the spent gas discharged from the spray-drying zone in the spray-drying zone to produce water-amorphous sodium silicate has a temperature of at least 140 ° C. The water-containing, amorphous sodium silicate is heated in a heating zone at 500-800 ° C for 1 to 60 minutes, with at least 10% by weight of the recycled product obtained previously by mechanically crushing the crystalline sodium silicate discharged from the heating zone.

The disadvantage of the latter method is that the product obtained by spray drying, due to its low apparent density of 100-250 g / l, occupies a large volume and is highly volatile. In addition, charging the return product during annealing causes significant additional hardware costs and, due to the increased material throughput, requires a larger rotary tube. Finally, the reversible product, at a molar ratio of S1O2 to Na2O2: 1, produces a higher proportion of high temperature sodium silicate (α - Na2Si2C> 5) modifications, but not the high temperature modification, and the δ modification is desirable for better properties.

According to the present invention, the disadvantages of producing a crystalline layered sodium silicate from a soluble glass solution containing at least 20% by weight of a solid are overcome by the fact that the slab glass solution is obtained by reacting quartz sand with caustic soda at a molar ratio of SiO2 to Na2O. (2.0-2.3): 1 at 180-240 ° C and 10 at 30 bar;

(b) The slurry solution is treated in a spray drying zone with hot air at 200-300 ° C for a duration of 10-25 sec. and a spent gas emitted from the spray-drying zone at a temperature of 90-130 ° C to form a powdered amorphous sodium silicate having 15-23% by weight of water (defined as heating loss at 700 ° C) and an apparent density greater than 300 g / l;

c) Powdering the amorphous, water-containing sodium silicate into a tilted rotary tube furnace with a solid material movement and counter-flushing at temperatures above 500-850 ° C for 1 to 60 minutes to form crystalline sodium silicate, where the rotary tube is the furnace is insulated so that its outside wall temperature is less than 60 ° C;

(d) The crystalline sodium silicate from the rotary tube furnace is mechanically crushed to a grain size of 0.1 to 12 mm.

The process of the invention may further be optionally expanded so that (aa) the ground sodium silicate is milled to a grain size of 2 to 400 microns; (bb) operates a mechanical mill with a speed of between 0,5 and 60 m / s; (cc) operates an air-flow mill;

(dd) uses a ceramic-lined ball mill; (ee) uses a ceramic-lined vibration mill;

(ff) extracting the spent gas from the central part of the rotary kiln and the part for charging amorphous sodium silicate in powder form and purifying it by dry filtration to remove dust, whereby the dry soda ash from the dust extraction filter is mixed almost continuously with the in the form of an amorphous, water-containing sodium silicate;

gg) depositing the ground crystalline sodium silicate in a roller press which, at a roller press pressure of 20 - 40 kN / cm, rolls into compact particles;

(hh) converting compact particles after sieving to a granular product with a specific gravity of 700 to 1000 g / l.

Crystalline sodium silicates are suitable for use as fillers, giving strength to natural and synthetic rubbers. In addition, they have ionic properties and can therefore be used as passivators.

Using the low temperature and short processing time of the present invention, spraying a solution of soluble glass produces sodium silicate with a high apparent density.

In addition, lower thermal conductivity due to good insulation through the walls of the rotating tubular furnace reduces the viscosity (propensity) of sodium silicate.

According to the method of the present invention, it is necessary to use a slow rotating mechanical mill (for example, a disk mill, impact mill, hammer mill or roll mill) to prevent iron dust due to abrasion of the milling equipment.

If, according to the invention, a ceramic-lined ball mill or vibratory mill or an air-jet mill for fine-grained products having a diameter of from 6 to 10 µm are used, it also avoids contamination of sodium silicate metal dust due to abrasion.

According to the method of the invention, the dustiness of the spent gas is significantly reduced by suctioning the spent gas from the middle rotary tube area and its material loading area, since the dust is primarily formed by charging the sodium silicate into the rotary tube furnace and containing water, sodium silicate in the charge area.

The process of the present invention provides a compression-resistant, abrasion-resistant granular product which dissolves very rapidly in water.

If a soluble glass solution having a molar ratio of SiO2 / Na2O (2.0 to 2.1): 1 is placed in accordance with the process of the present invention, treatment with a rotary tube furnace at a temperature of 600 to 800 [deg.] C. δ - Modifications, layered sodium disilicate, free of S1O2 and having a calcium binding capacity of at least 80 mg Ca / g at 20 ° C.

example (according to prior art)

An amorphous sodium disilicate containing 45% water (determined as heating loss at 700 ° C) and apparent density was prepared from a soluble glass solution containing 45% solids in a hot air spray drying tower (spent gas temperature 145 ° C). - 220 g / l.

60 kg / h of amorphous sodium disilicate and 15 kg / h of reflux product, which was obtained by crushing the product of the previous batch to a particle size of less than 250 µm, were charged through a worm feeder to a directly heated rotary tube furnace (length 5, diameter- 78 cm, inclination 1, 2 °) to the opposite end of the flame while the crystalline product was being discharged on the flame side. The temperature of the hottest rotary tube furnace was 740 ° C.

No glue was formed on the walls of the rotating tubular furnace; the unloaded crystalline sodium disilicate was mainly powdered and had a calcium binding capacity of 74 mg Ca / g.

example (according to the invention)

The nickel-plated, cylindrical autoclave was mixed with sand (99 wt% S1O2, grain size 90% <0.5 mm) and 50 wt% sodium hydroxide in a SiC> 2 molar ratio with Na2O 2.15: 1. heated in an autoclave with stirring at a vapor pressure of 16 bar at 200 ° C for 60 minutes, then the contents of the autoclave are transferred to a reservoir through an evaporator and added with 0.3% by weight of perlite acting as a filter for insoluble particles For separation, filter at 90 ° C through a disk filter operating in the pressure zone. The resulting filtrate is a clear soluble glass solution having a SiO2 / Na2O molar ratio of 2.04: 1. When diluted with water, the solids content reaches 50%.

In a hot air spray drying tower (cola) with a mounted disc nozzle, a gas fired combustion chamber and a pneumatic purifying filter for product separation, a glass solution is sprayed and the combustion chamber is arranged so that the temperature of the inlet hot gas reaches 260 ° C. . The application rate of the spray liquid solution is adjusted so that the temperature of the silicate-gas mixture discharged from the spray drying tower was 105 ° C. Based on the volume of the spray drying tower and the gas throughput of the spray drying tower, the processing time is 16 seconds. The amorphous sodium disilicate released by the sleeve filter has an apparent density of 2.04: 1 and 19.4% water (determined as heating loss at 700 ° C) with a low particle diameter of 52 µm.

The rotary tubular furnace described in Example 1 was insulated with multilayer mineral wool and lead sheath so that when inside the rotary tubular furnace at a temperature of 730 ° C, it had a maximum temperature of 54 ° C. 60 kg of amorphous sodium disilicate are charged every hour into this rotary tubular furnace, where no glue has formed. Sodium disilicate (Na2Si2Ū5, with a layered structure), which contained 0.1% by weight of water (determined as heating loss), is discharged from the rotary tube furnace

At 700 ° C), crushed to a particle size of less than 6 mm by a mechanical crusher and, after intermediate cooling, milled in a disk mill (diameter 30 cm.) At 400 rpm to 110 μτη for medium size particles; without lo, the iron content of the ground product and the amorphous sodium disilicate remained identical.

The spent gas from the rotary tube furnace was pumped out only in the charge area of amorphous sodium disilicate and fed to the wash tower. With the spent gas, 5 kg of sodium disilicate was removed every hour.

example (according to the invention)

The product obtained in Example 2 was further pulverized in a counter-flow mill, based on a fluidized bed, with a built-in mechanical sieve, which sieves up to 110 µm of medium-sized particles. Depending on the rotation speed of the installed screen, a dust-free sodium disilicate having an average particle diameter of 2 to 15 µm and 0.18% by weight of water is obtained, while the layered structure remains unchanged.

example (according to the invention)

The product obtained in Example 2 was further crushed in a porcelain-lined and corundum-filled ball mill. A dust-free sodium disilicate having an average particle size of 5 to 14 µm, depending on the milling time, was obtained without any change in the layered structure.

example (according to the invention)

Ί

The product obtained in Example 2 was subjected to a rolling press under a roller press at a roller width of 30 kN / cm and further crushing in a sieve granulator to a dust-free granular product having an average particle diameter of 750 µm, an apparent density of 820 g / l and high abrasion resistance.

To determine the resistance to abrasion, 50g of granulated product is treated in a roll-ball mill (length 10 cm; diameter 11.5 cm, 8 steel balls 2 cm diameter) for 5 minutes at 100 rpm.

In the abrasion test, the mean particle diameter was 585 µm, which corresponds to a 22% reduction.

Example (according to the invention) the example was repeated with modifications such that the spent gas from the rotating tubular furnace was sucked out at two locations, namely, adjacent to the amorphous sodium disilicate charging zone and additionally to a rotating tubular furnace within 2 m of the so-called charging zone. in the direction of the tube axis. The two streams of spent gas were combined and the solids contained therein were separated using a heat-resistant sleeve filter. The separated solid was again loaded into a rotary tube furnace along with amorphous sodium disilicate, so that no sodium disilicate was lost. This increased the capacity of the rotary tube furnace to 70 kg / h, but there was no adhesive inside the rotary tube furnace.

Example (Example for Comparison) The sample was repeated with modifications so that the gas used at the top of the hot air jet drying tower had a temperature of 330 ° C. The temperature of the spray-drying silicate-gas mixture was 140 ° C. The sodium disilicate separated in the sleeve filter had an apparent density s

250 g / l, heating loss at 700 ° C - 17, 9% by weight and average particle diameter of 60 µm. This sodium disilicate was heavily dusted.

Example (Example for Comparison) Example was repeated with modifications to give a soluble glass solution in a molar SiO ₂ : Na ₂ O ratio of 2.15: 1 and sprayed in a hot air jet drying tower with amorphous sodium silicate containing SiO ₂ : Na ₂ The ratio was 2.15: 1. From this a crystalline disilicate of sodium was obtained in a rotary tube furnace at 730 ° C, which showed on the radiograph an undesirable by-product, cristobalite (SiO ₂ ), which reduced the calcium binding capacity and worsened its properties.

Example (Example for Comparison) The sample was repeated with modifications such that the rotary tube furnace was insulated such that, at a temperature of 710 ° C inside the rotary tube furnace, its outer shell temperature reached a maximum of 205 ° C. As a result, large surface areas are formed on the inner walls of the rotating tubular furnace, which usually had to be mechanically broken. From the rotating tubular furnace, a very solid, poorly crystallized football ball sized product was unloaded, which could only be hardly crushed by a mechanical crusher.

Example (Example for Comparison) The sample was repeated with modifications so that the sodium disilicate, which was crushed by a mechanical crusher, was milled with a disk impact reflector

10,000 rpm to an average particle diameter of 98 µm. The powdered product was gray in color and contained 0.25% by weight of iron.

Example (Example for Comparison) The sample was repeated with modifications so that the pressure of the vale press was only 15 kN / cm for the roller width. The resulting granular product had an average particle diameter of 680 μιη and an apparent density of 265 µm, which corresponds to a 61% reduction. The granulate was soft and decomposed, already packing, into a smaller agglomerate.

The following table shows the calcium binding capacity of the sodium disilicates obtained in the samples having a layered structure according to the following procedure:

One liter of distilled water was mixed with CaCly solution (corresponding to 300 mg CaO) to give a water of 30 ° hardness.

To 1 liter of this water, which was stored at 20 or 60 ° C, was added 1 g of the crystalline sodium disilicate obtained in the samples, as well as 0 to 6 ml of 1M glycocoll solution (obtained from 75.1 g of glycol and 58.4 NaCl). dissolve in water to 1 liter) at pH 10, 4. The suspension was stirred for 30 min. at the selected temperature (20 or 60 ° C), at which time the pH value remained constant. It was finally filtered off and the calcium in the filtrate solution was determined by complexometry. From the difference with the former amount, calcium binding was obtained.

TABLE

Calcium binding capacity of sodium silicates (pH 10.4) (mgCa / g Na ₂ Si ₂ O5)

An example 20 ° C 60 ° C 1 74 123 2, 3, 4,5,10,11 82 132 6th 84 136 8th 75 125 9th 77 126

n

Claims (9)

DEFINITION OF INVENTION A method for obtaining crystalline sodium silicates having a layered structure, SiO2 / Na2O (1.9-2.1) molar ratio: 1 and less than 0.3% by weight of water, from a soluble glass solution containing at least 20% by weight of a solid. , characterized in that (a) the solution obtained by reacting the solution in quartz sand with a caustic soda ratio of SiO2 / Na2O (2,0-2,3): 1 at 180 to 240 ° C and a pressure of 10 to 30 bar; b) treating the soluble glass solution in a spray drying zone with hot air at 200 and 300 ° C for 10 to 25 s and at a temperature of 90 to 130 ° C for spent gas discharged from the spray drying zone to form a powdered amorphous sodium silicate containing 15 to 25 % by weight of water (determined as heating loss at 700 ° C) and an apparent density of more than 300 g / i; c) Powdered, amorphous, water-sodium silicate is charged into a tilted rotary tube furnace with a device for moving solids and flushed at 500-800 ° C for 1 to 60 minutes to form crystalline sodium silicate, wherein the rotary tube furnace is isolated that its outside wall temperature is less than 60 ° C; d) The crystalline sodium silicate discharged from the rotary tube furnace is crushed to a particle size of 0.1 to 12 mm by a mechanical crusher. 2. The method of claim 1, wherein the milled sodium silicate is milled to a particle size of 2 to 400 microns. 3. A method according to claim 2, characterized in that it uses a mechanical mill operating at a speed between 0.5 and 60 m / s. 4. A method according to claim 2, characterized in that an air flow mill is used. 5. A method according to claim 2, characterized in that it uses a ceramic-lined ball mill. 6. A method according to claim 2, characterized in that it uses a ceramic-lined vibrating mill. 7. A method according to any one of claims 1 to 6, wherein the spent gas from the middle portion of the rotary tubular furnace and the portion serving to charge the amorphous sodium silicate in powder form is aspirated and purified by a dry dust removal filter, wherein the dry dust removal filter the resulting sodium silicate is mixed almost continuously with a powdered, amorphous, aqueous sodium silicate for charging into the furnace. 8. A process according to any one of claims 1 to 7, characterized in that the milled anhydrous sodium silicate is introduced into a rolling press, which is compressed into compact particles at a roller press pressure of 20 to 40 kN / cm. 9. A process according to claim 8, characterized in that the compacted particles are processed after sieving into a granular product having a specific gravity of 700 to 1000 g / l.