FI76055B - FOERFARANDE FOER FRAMSTAELLNING AV GRANULERAT SODRIUMPERKARBONAT. - Google Patents

Description

This invention relates to a process for the preparation of granular sodium percarbonate.

5 Sodium percarbonate is used in synthetic detergents as a bleaching agent alone or as a single component.

The particle size of the sodium percarbonate used for said purpose should be 0.2 to 1.0 mm, preferably 0.5 to 10 0.7 mm.

In a previous process in which finely divided sodium percarbonate is prepared by reacting aqueous solutions of hydrogen peroxide and soda ash to form an aqueous solution of sodium percarbonate, the process comprises dewatering the final product and separating the crystals (cf. DE Patent No. 2,644,147). C01B 15/10).

However, the known method is not efficient enough, the particle size distribution of the final product is wide and a lot of dust fractionation is generated. In addition, in the practical applications of said method, a lot of mother liquors are generated.

In another process for preparing granular sodium percarbonate (cf. GB Patent No. 1,403,449), aqueous solutions of hydrogen peroxide and soda ash are fed to a blender with granular elements of sodium percarbonate.

In general, the above aqueous solutions contain sodium polyphosphate and sodium silicate as stabilizers. When the hydrogen peroxide solution and the calcined soda solution react with each other in the presence of sodium percarbonate granules, moist sodium percarbonate granules with a moisture content of 5-10% by weight are formed and passed to a dryer where they dry at a granular bed temperature of 35-95 ° C. The dry granules are removed from the dryer and divided into two fractions according to size, i.e. end product-35 granules that are the required size and granules that are 2 76055 too large. The final product granules, which are of the required size, are removed from the process and the larger particles are passed to a secondary crusher to obtain granular elements that are smaller than the granules of the final product, after which the granular elements are returned to the mixer.

The ratio of the particle size of the final product to the granules is 0.5: 1 and their weight ratio is 1: 1. Particles that travel with the air flowing out of the dryer are also returned to the mixer.

In the process described above, the particle size of the final product increases as the solid phase of the sodium percarbonate solution accumulates layer by layer on top of the individual granules or the larger granules absorb the smaller ones or the smaller granules agglomerate with the larger ones in some other way. The latter phenomenon is undesirable, as it leads to the formation of unacceptably large particles during the wetting phase. To reduce this phenomenon, the moisture content of the granular embryos must not exceed 10% by weight, which in turn limits the efficiency of the process and results in a high concentration of particles of polydis-20 circulating in the process. Another factor that limits the efficiency of the process is the use of sodium percarbonate granules that are smaller than the final product granules. This can be explained by the fact that on the one hand the supply of heat transfer medium during drying is low (in the order of 0.5 to 0.65 m / s) and on the other hand that the temperature of the heat transfer medium cannot be raised above 200 ° C to make the process more efficient. the product is not thermally stable. Therefore, the efficiency of the method is too low, only 15 kg / h per m of dryer. The main object of the present invention is to provide a process for the preparation of granular sodium percarbonate which makes it possible to increase the efficiency.

The object of the invention is achieved by a process in which granular sodium percarbonate is prepared by reacting aqueous solutions of hydrogen peroxide and soda ash in the presence of sodium percarbonate granules, drying the resulting sodium percarbonate granules and separating the final product. the weight ratio and the weight ratio of the amounts of granules of said size to the granules of the final product is 1.1 to 8: 1.

By using sodium percarbonate granules having an average size of 1.1 to 5 times the particle size of the final product 10 and using them to a weight ratio of sodium percarbonate to the final product of 1.1 to 8: 1, an increase in the heat transfer medium feed rate and moisture removal intensity is increased.

When the granules of sodium percarbonate are more than 5 to 15 times as large as the granules of the final product, the amount of sodium percarbonate granules larger than the desired size in the process increases greatly, so that the number of final product granules obtained by the process becomes so small that small.

If the average grain size of the sodium percarbonate granules is equal to or smaller than the granules of the final product, too many fine particles are formed in the process, leading to a reduction in the heat transfer medium feed rate and thus a reduction in heat to the wet granules.

If the weight ratio of sodium percarbonate granules to the final product is less than 1.1: 1, for example 0.8: 1, many granules are formed with an average size smaller than the size of the final product granules, leading to a reduced heat transfer medium feed rate and thus lower product production.

If the weight ratio between the sodium percarbonate granules and the final product is greater than 8: 1, for example 4 76055 9: 1, the amount of fine fractions obtained by the process is reduced and then the production is also reduced.

The process for the preparation of sodium percarbonate presented here makes it possible to increase the efficiency 2.5 to 5 times higher than the efficiency of the already known methods used for the production of a high-quality product. The amount of active oxygen in the final product is at least 14.2% and the variation in the amount of active oxygen tested for stability at 50 ° C and 100% relative humidity over 10 hours is as low as 11.3%.

The process for preparing granular sodium percarbonate described in the present invention is technically simple and can be carried out as follows.

Dry sodium percarbonate granules are fed to a mixer. At the same time, some aqueous solution of soda ash containing sodium polyphosphate and sodium silicate and aqueous hydrogen peroxide is fed to the mixer, the reaction of which produces sodium percarbonate solution. In the mixer, the dry grain embryos are wetted and the resulting sodium percarbonate granulates on top of the grain embryos. As the mixer, any continuous mixing device can be used, such as a tank equipped with a mixer, a rotating drum, a screw mixer, etc. Moist sodium percarbonate granules having a moisture content of 25 to 15% by weight are dried. A variety of drying equipment can be used in industrial production, for example a rotary tumble dryer or a vibratory dryer, although it would be best to use a fluid bed dryer where the temperature of the heat transfer medium can be as high as 200 ° C and the grain bed temperature 35-95 ° C. In practice, the drying and wetting zones can be combined, i.e. the stock solutions of calcined soda and hydrogen peroxide are fed directly to the imaging device. The spent heat transfer medium is passed to a dust collection cyclone, from where the dust is returned to the mixer.

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Next, the dry granules are passed from the dryer to a classifier, where they are divided into two fractions, the finer of which is removed as the final product and the coarser one, which contains granules of the required size, is returned to the mixed granules.

To facilitate the understanding of this method, the following practical examples illustrate the matter.

Example 1

The mixer is charged with 50 kg of granular sodium percarbon-10 carbonate with an average particle size of 1.85 mm (ranging from 1.0 to 2.5 mm). 181.4 kg of an 18% aqueous solution of soda ash (34.2 kg of dry soda ash) containing 0.85 kg of sodium silicate and 0.34 kg of sodium polyphosphate and 54.88 kg of a 30% aqueous solution of hydrogen peroxide are then fed from the storage tanks to the mixer. (16.48 kg of 100% hydrogen peroxide) which react to form a sodium percarbonate solution with a molar ratio of hydrogen peroxide to soda ash of 1.5: 1. Next, the moist (moisture content is 9% by weight) 20 sodium percarbonate granules are passed to the dryer.

The hot air stream (initial temperature 180 ° C) is passed through the Lei bed in a dryer at a flow rate of 2.23 m / s, the temperature of the sodium percarbonate granules in the dryer being 60 ° C. The dry sodium percarbon-25 carbonate granules are then fed to a classifier at a flow rate of 201.3 kg / h to separate the final product with a particle size of 0.2 to 1.0 mm (average 0.52 mm) at a rate of 50.3 kg / h and granular embryos with a particle size of is 1.0 to 2.5 mm (average 1.85 mm) at a rate of 151 kg / h, after which the granules are returned to the mixer. The amount of active oxygen in the final product is 14.26% and the bulk density is 0.96 g / cm.

The relative loss of active oxygen in the final product with respect to stability is 11%.

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Example 2

The mixer is charged with 50 kg of sodium percarbonate granules with a size of 0.8 to 1.4 mm. 113.43 kg of a 30% aqueous solution of soda ash (33.7 kg of dry soda ash) containing 0.35 kg of sodium polyphosphate and 0.88 kg of sodium silicate and 52.6 kg of a 30% aqueous solution of hydrogen peroxide are then fed from the storage tanks to the mixer. the reaction yields 164.8 kg of a 30% sodium percarbonate solution with a molar ratio of hydrogen peroxide of 10 to soda ash of 1.5: 1. The moisture content of the sodium percarbonate granules leaving the mixer is 8.2%. A hot air stream with an initial temperature of 200 ° C is passed through the fluidized bed in a dryer at a flow rate of 1.75 m / s, the temperature of the granules in the fluidized bed being 65 ° C. The dry granules are fed at a flow rate of 105 kg / h to a classification which separates the final product with a particle size of 0.2 to 0.8 mm (average 0.54 mm), at a rate of 49.5 kg / h and granules with a particle size of 0, 8 to 1.4 mm (average 1.1 mm), at a rate of 55.5 kg / h, and the granules 20 are returned to the mixer.

The amount of active oxygen in the final product is 14.3% and the bulk density is 0.97 g / cm 3. The relative loss of active oxygen in the final product when tested for stability is 11.2%.

Example 3 The mixer is charged with 50 kg of sodium percarbonate granules with a size of 1.2 to 5.0 mm. 15.3 kg of a 25% aqueous solution of soda ash (37.6 kg of dry soda ash) containing 0.35 kg of sodium polyphosphate and 0.88 kg of sodium silicate and 54.6 kg of a 30% solution of hydrogen peroxide are then fed to the mixer from storage tanks, with a molar ratio of hydrogen peroxide to soda ash of 1.5: 5. The moisture content of the sodium carbonate granules leaving the mixer is 9.5%. A hot air stream with an initial temperature of 165 ° C is passed through the fluidized bed in a dehumidifier at a flow rate of 3.5 m / s,

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7 76055 at a temperature of 67 ° C. The dry granules are then passed to a classification at a flow rate of 487 kg / h, whereby the final product with a particle size of 0.2 to 1.2 mm (average 3.15 mm) separates at a rate of 422 kg / h, after which the granules are returned to the mixer. The amount of active oxygen in the final product is 14.25% and the bulk density is 0.37 g / cm 2. The loss of active oxygen in the final product when tested for stability is 11.3%.

Example 4 A mixer is charged with 50 kg of sodium percarbonate granules with a size of 0.2 to 1.4 mm. 169.5 kg of an 18% aqueous solution of soda ash (30.5 kg of dry soda ash) containing 0.3 kg of sodium polyphosphate and 0.6 kg of sodium silicate and 45.9 kg of 35% by weight of the soda ash are then fed to the mixer from the storage tanks. hydrogen peroxide solution which reacts to form a sodium percarbonate solution with a molar ratio of hydrogen peroxide to soda ash of 1.5: 1. The moisture content of the sodium percarbonate granules leaving the mixer is 9.5%. A hot air stream with an initial temperature of 210 ° C is passed through the fluidized bed in a dryer at a flow rate of 1.89 m / s, the temperature of the sodium percarbonate granules in the dryer being 61 ° C.

The dry granules are subjected to a classification at a flow rate of 405 kg / h, which separates the final product with a particle size of 0.2 to 1.0 mm (average 0.6 mm), at a rate of 45 kg / h and the granules with a particle size of 0.2 - 1.4 mm (average 0.66 mm) and the granules are returned to the mixer.

The amount of active oxygen in the final product is 14.35% 30 and the bulk density is 1.0 g / cm. The relative loss of active oxygen in the final product when tested for stability is 11%.