SE452975B - PROCEDURE FOR THE PREPARATION OF GRANULATED STABILIZED SODIUM PERCARBONATE - Google Patents

Description

The inorganic stabilizers for stabilizing sodium percarbonate usually consist of magnesium, silicon and phosphorus compounds, for example magnesium sulphate, sodium silicate and sodium polyphosphates, in particular sodium hexametaphosphate and so on. Different combinations of these compounds are generally used to stabilize sodium percarbonate.

Such a known process for the production of powdered sodium percarbonate Å (for example, GB patent specification 1 418 562, (1975)] is based on using a solution of calcined soda prepared in advance from heavy metal contaminants, prepared by technical soda ash and water with the addition of magnesium sulfate and sodium silicate, and then separates the precipitate of impurities. In this case, the magnesium sulphate forms insoluble carbonates, which precipitate and cause not only heavy metal-containing impurities but also the sodium silicate. This known process for the production of sodium percarbonate is carried out by mixing an aqueous solution of hydrogen peroxide with a pre-prepared aqueous solution of calcined soda, which has been previously purified from heavy metal compounds. The process is carried out in process devices or apparatus which ensure heat exchange while stirring the reaction mixture at a temperature of not more than 30oC. The final product is isolated by centrifugation or filtration, followed by subsequent drying of sodium percarbonate crystals, while the mother liquors are fed back to the process step or used. However, this known process has a limited area of use, since the mother liquor is present in the separation step for sodium percarbonate and is fed back to the process step, and in addition sodium percarbonate is obtained in the form of a powder which must be granulated.

Chemical stability and mechanical strength are, as pointed out above, a very important requirement but not the only requirement to be imposed on granular sodium percarbonate. In order for this to be used to advantage in synthetic detergents, it must have a combination of properties, the most important of which, in addition to the chemical stability and the mechanical strength, is the so-called compatibility in bulk density with main constituents of synthetic detergents, which contributes to the homogeneous composition of WW 452 975 and to the elimination of stratification and clumping during storage and transport of granular sodium percarbonate.

Granulated sodium percarbonate with a particle size of preferably 0.2 - 1.5 mm and a bulk density of preferably 0.5 - 0.6 g / cm 3 is best compatible with the main constituents of synthetic detergents.

In a number of known processes for the production of granulated sodium percarbonate, alkali metal phosphates are introduced into it during synthesis of the final product or during further granulation of the crystalline sodium percarbonate produced, which helps to reduce the bulk density of the final bread product. Such a known process. For example, DE patent specification 2,700,797 (1978L?) Is based on the newly prepared, moist, crystalline sodium percarbonate introducing alkali metal polyphosphates and / or alkali metal pyrophosphates and water in a mutual mixing weight ratio and final weight ratio. the phosphates vary between 1: 0, 2 and 1: 0.4 and in addition carry out fluidized bed granulation at a temperature of 30-70 ° C. The moist, crystalline sodium percarbonate is prepared in a manner known per se by adding aqueous solutions of hydrogen peroxide and calcined soda with stabilizer additives are mixed with each other and reaction mixtures of the solutions are cooled to a temperature of not more than 30 ° C to form crystals of sodium percarbonate, which are separated from the mother liquor by filtration or centrifugation.

Nor do these known processes enable the production of granular sodium percarbonate with a bulk density of less than 0.65 g / cm 3 and they have thus been given a limited range of use, due to the existence of mother solutions and the final product obtained in crystalline form. Also another known process for the production of granulated sodium percarbonate [compare, for example, French Pat. 2 359 789 (1978Lï is based on the solution of calcined soda being purified from heavy metal-containing impurities by adding sodium polyphosphate, for example sodium hexametaphosphate and sodium silicate to this solution. The aqueous solutions of hydrogen peroxide and 452,975 calcined soda with various supply pipes by means of an injection nozzle at a temperature of 35-95 ° C. The process is carried out under so-called fluidized bed process conditions, ie in a fluidized bed, where synthesis, granulation and drying of the formed sodium percarbonate are carried out simultaneously. .

This known process is more complete than the previous known process, since synthesis, granulation and drying are carried out simultaneously. However, the end product produced by this known process does not exhibit the desired stability, strength and bulk density. Because the final product contains heavy metal-containing impurities which are bound to each other by means of sodium polyphosphate, the stability of the granulated sodium percarbonate to be produced is reduced, at the same time as the losses of active oxygen are increased. By adding the solutions of hydrogen peroxide and calcined soda separately to the starting particles of sodium percarbonate, the stability and strength of the granules formed by the final product is reduced due to the synthesis time of the granules being reduced by the granulation and drying being carried out simultaneously. The bulk density of the product produced is 0.8 - 0.9 g / cm 3, while the relative losses of active oxygen (stability) amount to 20% and the average granule size in strength testing was 300 μm.

The known process technology thus does not make it possible to produce reasonably stable and durable granules of sodium percarbonate, the bulk density of which is close to the bulk density of the constituents of synthetic detergents with rather good physical and mechanical properties.

The main object of the present invention is to provide such a process for the production of granulated sodium percarbonate, which makes it possible to produce stable and solid granules of sodium percarbonate, the bulk density of which is close to the bulk density of the constituents of synthetic detergents.

The present invention thus relates to a process for the preparation of granulated, stabilized sodium percarbonate, which is useful as a component in synthetic detergents, which process comprises reacting aqueous solutions of hydrogen peroxide and calcined soda in the presence of stabilizers and additives. of the reactant solutions to sodium percarbonate seedlings with subsequent drying of sodium percarbonate in a fluidized bed at a temperature of 35-95 ° C, which process is characterized in that a mixture of the aqueous solutions of hydrogen peroxide and calcined soda is added while adding a stabilizer-containing aqueous suspension of sodium percarbonate at a weight ratio of the suspension to the aqueous reaction solution of 0.25: 1 to 4: 1.

The stabilizers consist of sodium polyphosphates and sodium silicates, sodium hexametaphosphate being used as the sodium polyphosphate, for example.

In order to control the bulk density of the final product, the mixture of the above-mentioned aqueous solutions of hydrogen peroxide and calcined soda is suitably added, while feeding a stabilizer-containing suspension of sodium percarbonate, which is a product obtained in the reaction between calcined soda and the aqueous solution of hydrogen peroxide.

In the synthesis of the final product, two flows are thus added to the starting particles at the same time, namely the mixture of the aqueous solutions of calcined soda and hydrogen peroxide and the suspension of sodium percarbonate.

Due to the fact that the aqueous suspension of sodium percarbonate is added to the starting particles during the synthesis of granulated sodium percarbonate, a porous structure of agglomerated particles of sodium percarbonate is formed at the particle surface of the final product, which helps to reduce the bulk density of the product. If the content of the suspension to be introduced is less than 0.25: 1, a dense layer of sodium percarbonate is formed on the particles formed, which increases the bulk density of the finished product to 0.8-0.9 g / cm 3 and reduces process capacity due to the higher amount of water to be evaporated. If the content of the suspension to be introduced is higher than 4: 1, the granule formation deteriorates considerably, which in turn is accompanied by dust formation and other negative processes. The process proposed according to the present invention for the preparation of granulated sodium percarbonate thus makes it possible to produce stable and strong granules with a bulk density of less than 0.6 g / cm 3.

The procedure is carried out as follows. In a container equipped with a stirrer and heating mantle, distilled water is introduced from a supply container provided with a measuring scale and a calculated amount of calcined soda to prepare an 18-20% solution, after which sodium hexametaphosphate in an amount of 1% of the calcined the weight of the soda is added and dissolved at a temperature of 50-60 ° C with simultaneous stirring. The reconstituted solution is then filtered. The filtered solution of calcined soda is fed with simultaneous stirring into a heated container, in which sodium silicate (water glass) is also introduced in an amount of 5-10% of the weight of the soda.

At the same time as all the work steps for the preparation of the aqueous solution of calcined soda are carried out, a 25-40% aqueous solution of hydrogen peroxide is poured into a second container, which is added with orthophosphoric acid so that the pH value of the solution is brought to 1 - 2.5, after which the solution mixed. The prepared solutions of calcined soda and hydrogen peroxide are mixed in dosed amounts in a mutual molar ratio of 1: 1.5.

The synthesis of sodium percarbonate begins, while the solutions of calcined soda and hydrogen peroxide are mixed in a mixing chamber.

The sodium percarbonate is dried and granulated simultaneously in a fluidized bed device and the final fraction is removed from the fluidized bed of the device.

The suspension of sodium percarbonate is prepared by mixing dry soda with a 25-40% aqueous solution of hydrogen peroxide in a molar ratio equal to the stoichiometric molar ratio in the preparation of sodium percarbonate. The suspension is prepared at a temperature of between 1 ° C and -SOC with simultaneous stirring for a period of 0.5 - 1 hour. Thereafter, the prepared aqueous suspension of sodium percarbonate is added to the starting particles, at the same time as the mixture of the aqueous solutions of hydrogen peroxide and calcined soda is added thereto, the weight mixing ratio between the suspension to be added. and the mixture of the solutions is between 0.25: 1 to 4: 1.

The sodium percarbonate formed is dried and granulated simultaneously in a fluidized bed type drying and granulating device, i.e. with a fluidized bed. At the same time as the process is carried out, the temperature of the layer above the grid and the temperature and amount of the air to be used for drying are measured. The temperature below the grid is between 125 and 250 ° C, provided that the fluidized bed temperature is 65-95 ° C.

Particles of sodium percarbonate with a size of between 200 and 500 μm are introduced into the process device in advance, which are prepared in any way. The mixture of the solutions and the suspension of sodium percarbonate are simultaneously fed separately to these particles by means of respective dosing devices. In this way, end product granules with a desired size from 0.2 mm to 2.5 mm are obtained.

The bulk density of the product produced is determined as the ratio between the weight of the product, which is freely fed into a cylinder, and the volume taken up by the product.

The test of the manufactured product with regard to its storage stability is carried out as follows.

In a chamber in a so-called ultratermostat control device is generated at a temperature of SOOC process conditions, which are typical of 100% relative humidity. In the chamber, 0.15 g of granulated sodium percarbonate and 0.85 g of synthetic detergent, which is free from bleach additive, are placed in open boxes. The weighings are kept in the chamber for a period of 15 hours, after which the losses of active oxygen (Oa) are determined by a so-called permanganatometric method.

The stability of the product is estimated depending on the relative losses of active oxygen over a period of 15 hours.

The strength of the granules of the final product is determined by means of a ball mill using metal balls, the size distribution of which is determined by means of a sieve fi and an image analyzer. The test 452 975 is carried out for a period of 5 minutes at a so-called rotational amplitude equal to 5. The granules of sodium percarbonate have an average size of 830-835 Pm.

The invention is further elucidated below by means of the following examples of carrying out the process.

Example 1 To prepare a sodium percarbonate solution, 1207 ml of water, 265 9 (2.5 mol) of calcined soda and 2.65 g (10% by weight of the soda) of sodium hexametaphosphate were introduced into a flask equipped with a stirrer. The dissolution was carried out at a temperature of 50-60 ° C. The prepared solution was then filtered. The filtered solution was added with simultaneous stirring to 13.25 g (5% by weight) of sodium silicate (water glass). In a second, stirring flask, 425 g (3.75 mol) of perhydrol (30% aqueous solution of hydrogen peroxide) was poured in, adding 1 g of orthophosphoric acid having a density of 1.7 g / cm 3 to bring the pH of the solution to 1.0. In a fluidized bed type reaction vessel, the lower part of which was provided with a distribution grating for hot air supply, sodium percarbonate particles of any size 200-500 [mu] m in an amount of 300 g were charged as starting material in any known manner.

The prepared solutions of hydrogen peroxide and calcined soda were mixed for a period of 50 seconds, after which the mixture of the solutions was added to the fluidized bed of starting particles.

To prepare the aqueous suspension of sodium percarbonate, 701 g of dry, calcined soda and 1125 g of perhydrol (30% solution of hydrogen peroxide) were introduced into a stirred vessel, after which 36 g of sodium silicate and 7 g of sodium hexametaphosphate were introduced.

The weight ratio between the solid phase and the liquid phase in the suspension prepared using the 30% solution of hydrogen peroxide was 1: 0.75. The prepared suspension was stirred at a temperature of from 1 ° C to -5 ° C for a period of 0.5 hours. The prepared suspension was fed to the fluidized bed of starting particles, at the same time as the mixture of the aqueous solutions was added thereto, the weight ratio of the suspension to the mixture of the solutions being 1: 1. n, 452 975 The growth of the particles, the granulation and the drying were carried out at a temperature of 95 ° C for a period of 20 minutes.

The granules of sodium percarbonate removed from the process device in an amount of 1432 g (11.03 mol) had a size of 0.7-1.0 mm, contained 14.37% of active oxygen, the bulk density of the sodium percarbonate produced being 0.51 g / cm 3. The relative losses of active oxygen amounted to 11%. The average size of the granules in the strength test was 467 μm.

Example 2 Granulated sodium percarbonate was prepared under the conditions described in Example 1 starting from feeding 482 ml of water, 106 g (1 mol) of calcined soda and 1.06 g of sodium hexametaphosphate into the flask. After filtration was complete, the resulting solution was added with 5.3 g of sodium silicate. Into the second flask was introduced 170 g (1.5 moles) of 30% aqueous solution of hydrogen peroxide, which was added with orthophosphoric acid in an amount required to bring the pH of the solution to 1.0. To prepare the aqueous suspension of sodium percarbonate, 1190 g of dry, calcined soda and 1914 g of hydrogen peroxide were fed into a container, after which 59.5 g of sodium silicate and 11.9 g of sodium hexametaphosphate were introduced. The suspension thus prepared was added to the starting particles, at the same time as the mixture of the aqueous solutions of calcined soda and hydrogen peroxide was added thereto, the weight ratio of the suspension to the mixture of the solutions being 4: 1. The granulation and drying were carried out at a temperature of 65 ° C for a period of 40 minutes. The granules of sodium percarbonate discharged from the process device showed a bulk density of 0.5 g / cm 3, the relative losses of active oxygen being 10.5%, while the average size of the granules in the strength test was 451 μm.

Example 3 Granulated sodium percarbonate was prepared under the conditions described in Example 1 starting from the introduction into the flask in 1889. ml of water, 414.8 g (3.9 mol) of calcined soda and 4.15 g of sodium hexametaphosphate. After filtration was complete, the resulting filtered solution was added with 20.75 g of sodium silicate. In the second flask, 664.7 g (5.8 moles) of hydrogen peroxide were introduced, with the addition of orthophosphoric acid in an amount required to bring the pH of the brine solution to 1.5. To prepare the aqueous suspension of sodium percarbonate, 279 g of dry, calcined soda and 448 g of hydrogen peroxide were fed into the container, after which 14 g of sodium silicate and 2.79 g of sodium hexametaphosphate were introduced. The weight ratio of the suspension to the mixture of calcined soda and hydrogen peroxide aqueous solutions to be added to the starting particles was 0.25: 1. The granules of sodium percarbonate produced had a bulk density of 0.53 g / cm 3, the relative losses of active oxygen being 11%, while the average size of the granules in the strength test was 485 μm. 57)

Claims (1)

A process for the preparation of granular stabilized sodium percarbonate, which is useful as a component in synthetic detergents, which process comprises reacting aqueous solutions of hydrogen peroxide and calcined soda in the presence of stabilizers and supplying the reaction solutions. to seed seedlings of sodium percarbonate with subsequent drying of sodium percarbonate a fluidized bed at a temperature of 35-95 ° C, characterized in that a mixture of the aqueous solutions of hydrogen peroxide and calcined soda is added while adding a stabilizer content. aqueous suspension of sodium percarbonate at a weight ratio of the suspension to the aqueous reaction solution of 0.25: 1 to 4: 1.