CH638464A5 - METHOD FOR PRODUCING SODIUM PERCARBONATE FROM A SODAL SOLUTION OR -SUSPENSION. - Google Patents

Description

The invention is illustrated by the following example:

65 NaPc - sodium percarbonate

Hexa - sodium hexametaphosphate

Oa - active oxygen g-At / 1 - gram atom / 1

4th

Example!

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In a V4A container (0 = Î 530 mm, H = 1420 mm) v. I m '• NaP> lye of! 5 ° C, which contains 200 g NaCl, 72.2 g NaiCOs • î.5 H2O2, 4.5 g MgSGi- • 7 H2O and 0.15 g Hesa per liter, with stirring (stirring prop diameter = 500 mm, stirring speed = 220 Rpm) submitted.

In this template, i, 35 kg of hexa are dissolved.

Then with constant temperature (15 ° C) and with stirring within 25 minutes using an AEG

Metering trough 105 kg techn. calc. Soda (96%) dosed in the above template.

Immediately after the addition of soda has ended, 76 liters of HbCb solution (23.7 mol / l), which contain 52.6 g of MgSÛ4 • 7 H2O and 65.8 g of NaCl per liter, are metered in at 15 ° C. using rotameters.

After the addition of the H2O2 solution, 142 g of NaPc / 1 were in solution, which were broken down to io 71.4 g / 1 within 45 minutes.

Post-reaction time alkali analysis min Na Oa Oa / Na NaPc gAt / 1 gAt / 1 ratio dissolved g / 1

according to HiCh-Ziîg 0 1.81 1.43 0.79 142.0

45 0.91 0.79 0.87 71.4

The salt porridge was subjected to a continuous sieve analysis (by weight).

Centrifuge separated from the mother liquor, the salt in a 0.8 mm: 6%

F! I bed dryer dried. on 0.5 mm: 29%

150 kg of finished product with the following ana- to 0.4 mm were obtained: 15%

lysis data: on 0.2 mm: 38%

Active oxygen: 13.94% by weight 2s on 0.1 mm: 12%

Bulk weight: 941 g / 1 rest: 0%

Claims (3)

638464 PATENT CLAIMS 1. Process for the production of compact, coarse sodium percarbonate by reacting hydrogen peroxide with sodium carbonate at 10-20 ° C., starting from an aqueous solution containing sodium carbonate and saturated with sodium percarbonate in the presence of 100-200 g / 1 sodium chloride, active oxygen stabilizer and sodium hexametaphosphate, characterized in that in a solution containing 0.1-1.9 g / 1 sodium atrium hexametaphosphate, a weight ratio of soda to sodium hexametophosphate of 65: 1 up to 500: 1 and the soda feed solution or suspension thus obtained is mixed with an amount of hydrogen peroxide which is practically equivalent to the sodium carbonate dissolved and / or suspended in the starting solution while maintaining the temperature approximately constant throughout the precipitation process, and that during and until 60 minutes after the end of the hydrogen peroxide addition, the resulting supersaturation of dissolved sodium percarbonate is broken down by precipitation of the sodium percarbonate and the precipitated salt is separated off and dried. 2. The method according to claim 1, characterized in that the selected precipitation temperature varies during the entire precipitation process by at most ± 1 ° C. 3. The method according to claim 1 or 2, characterized in that the mother liquor obtained is returned to the working stage for the preparation of the starting solution. It is known to use sodium percarbonate by reacting a soda solution or suspension with aqueous hydrogen peroxide solutions according to the formula NazCOa + 1.5 H2O2 - NajCOs-1.5 H2O2 to produce, and thereby reduce the solubility of the percarbonate formed by adding inert salts such as table salt (CH-PS 90295). BR-PS 568 754 describes the continuous production of sodium percarbonate from hydrogen peroxide and sodium carbonate, in which the necessary amounts of hydrogen peroxide and sodium carbonate are added to the reaction solution only in small proportions. At the same time, the use of active oxygen stabilizers, such as. As magnesium compounds, and pointed to the beneficial influence of hexametaphosphate on the granular structure of the percarbonate. The disadvantage of the method is that - as mentioned - the soda and hydrogen peroxide are added only in small proportions, with reaction times being switched on between the additions. During the feeding the temperature rises from 15 to 22 ° C and is kept at this temperature until the end of the reaction. This procedure leads to a fine, bubbly percarbonate. Furthermore, according to DE-OS 2 328 803, an abrasion-resistant coarse percarbonate should be obtained by reacting a soda solution or suspension which contains 2-8 g of sodium hexametaphosphate per liter of solution with a hydrogen peroxide solution containing 3-10 g of magnesium ions per liter of solution. optionally in the presence of table salt. Great importance is attached to the exact observance of the quantities for sodium hexametaphosphate and magnesium ions. Otherwise fine or non-resistant particles would result. The disadvantage of the process, which only works batchwise, is that when the mother liquor is reused at the higher soda dissolving temperature of 24 ° C, the hydrogen peroxide yield is greatly reduced by decomposition of active oxygen, which is further increased when using technical soda due to the accumulating impurities in the mother liquor. Due to this active oxygen decomposition, which continues during the hydrogen peroxide feed, the sodium percarbonate crystallization conditions cannot be kept constant: The soda / sodium percarbonate ratio shifts in favor of the soda, which in turn exerts additional pressure on the sodium percarbonate still in solution as a more easily soluble component. The result is too rapid crystallization, a fine-grained product is obtained. Furthermore, as described in DE patent application P 26 44 147.4-41, certain amounts of sodium hexametaphosphate are required when using a solution saturated with sodium carbonate. If the amount of sodium hexametaphosphate is too large, an excessively stable supersaturation of the sodium percarbonate to be formed is built up, which does not or only partially decomposes. If the amount of sodium hexametaphosphate is too small, too little percarbonate oversaturation is built up, the percarbonate obtained is too fine. It is therefore important that a given ratio of soda conversion to the dissolved amount of sodium hexametaphosphate is selected for a given amount of soda to be converted with a constant concentration of the solution components still present and the reaction temperature. This was only possible up to soda solubility according to the procedure of the above-mentioned DE patent application. The aim of the invention is therefore a technically even simpler implementation of the method according to DE patent application P 26 44 147.4-41, which has already led to an absolutely reliable reproducibility of the coarse compact grain at 10-20 ° C., and also an increase in Soda sales. It has now been found that this goal can be achieved in the reaction of sodium carbonate with hydrogen peroxide, starting from an aqueous solution containing sodium carbonate and saturated with sodium percarbonate, in the presence of 100-200 g of sodium chloride per liter of solution, active oxygen stabilizer and sodium hexametaphosphate at 10-20 ° C can, if in such a solution, which contains 0.1-1.9 g of sodium hexametaphosphate per liter, a weight ratio of soda to sodium hexametaphosphate of 65: 1 to 500: 1 is set, whereupon the soda feed solution or suspension thus prepared with a Amount of hydrogen peroxide is added, which is practically equivalent to the sodium carbonate dissolved and / or suspended in the starting solution, while maintaining approximately one and the same temperature during the entire precipitation process, followed by the resulting supersaturation during and after completion of the hydrogen peroxide addition up to 60 minutes after this addition on dissolved sodium perca Rbonate is broken down by precipitation of the sodium percarbonate, the precipitated salt is separated off and dried and the mother liquor obtained is optionally returned to the working step for the preparation of the starting solution. In order to keep the active oxygen loss as low as possible, the process is not carried out at temperatures above 20 ° C. The temperature is preferably 14-16 ° C. 2nd s 10th 15 20th 25th 30th 35 40 45 50 55 fiO 65 In the process described, soda ash, soda p. a. or technical soda can also be used. It has now been found that with a constant concentration of the components present in addition to soda dissolved and at a constant reaction temperature, a certain ratio of the soda conversion to the dissolved amount of sodium hexameta-phosphate must be observed for a targeted build-up and breakdown of the sodium percarbonate supersaturation during and after the addition of hydrogen peroxide, and thus ultimately for a coarse, compact product. To determine the correct ratio of soda conversion to sodium hexametaphosphate, proceed as follows: After the reaction temperature has been set to a value between + 10 ° C and + 20 ° C, the sodium chloride content in solution is between 100 g / 1 and 200 g / 1, the approximately constant contents of approx. 4.5 g Mg SÛ4 • 7 H2O / I and approx. 0.1 g sodium hexametaphosphate / I, this solution is obtained by dissolving 51 g sodium carbonate and adding 30 ml hydrogen peroxide (70% by weight) about saturated, forming about 75 g of sodium percarbonate per liter. In this percarbonate mother liquor, the right ratio of soda conversion to sodium hexametaphosphate can be determined by a series of preliminary tests, in which a coarse, compact product is obtained by the targeted build-up and breakdown of the sodium percarbonate supersaturation. So z. B. at + 10 ° C in a saturated sodium percarbonate solution in the presence of 200 g sodium chloride / l, 4.5 g Mg SO4.7 H2O / I and 0.1 g sodium hexametaphosphate / 1 a ratio of Na2 CÛ3 :( NA PCh) 6 of 500: 1 to obtain a coarse, compact percarbonate. At + 20 ° C in a saturated sodium percarbonate solution in the presence of 100 g sodium chloride / l, 4.5 g Mg SO4 • 7 H2O / I and 1.9 g sodium hexametaphosphate / I the ratio of Na2 C03: (NA PÖ3) 6110: 1 to get a coarse, compact product. To avoid active oxygen losses, the entire precipitation process is carried out below 20 ° C. at about one and the same temperature, expediently at a maximum of ± 1 ° C. in relation to the selected temperature. As stated, the amount of hydrogen peroxide to be added should be approximately equivalent to the amount of sodium carbonate present, see formula above. For example, a ratio of active oxygen to sodium of 0.6 to 0.9: 1 is to be regarded as “approximately equivalent”. 70% by weight aqueous solutions are particularly suitable as hydrogen peroxide solutions; however, higher percentage commercial aqueous hydrogen peroxide solutions can also be used. Solutions less concentrated than 70% by weight can also be used; however, as the concentration of hydrogen peroxide decreases, more water is introduced into the system, which on the one hand reduces the crystallization pressure for percarbonate and on the other hand increases the excess of mother liquor. The usual active oxygen stabilizers can be used in the process, such as magnesium salts, alkali salts, preferably magnesium sulfate. The stabilizers are expediently added to the aqueous hydrogen peroxide solution. At the beginning of the process according to the invention, for example, a mother liquor consisting of - based on 1 liter of solution - 40 to 100 g sodium percarbonate, 0.1 to 1.9 g sodium hexametaphosphate, 100 to 200 g sodium chloride and saturated with basic magnesium carbonate and magnesium silicate, synthetically as aqueous solution. 3 638464 This synthetic mother liquor is used to produce the soda solution or suspension. This feed solution can also be prepared with the mother liquor obtained after the sodium percarbonate formed, which also contains 40 to 100 g of 5 sodium percarbonate per liter. However, this mother liquor must still be brought to the specified concentrations of sodium hexametaphosphate and table salt. When using water glass and reusing the mother liquor saturated with sodium percarbonate, which still contains some of the stabilizers from the previous batch, it is expedient to filter the mother liquor to remove the precipitated magnesium silicate before inserting the calcined soda. 15 At the same time, the magnesium concentration is reduced, which therefore fluctuates only slightly in this solution. The buildup and breakdown of supersaturation takes place, for example, with stirring. It is known that the nucleation rate is dependent on the stirring rate 20. With rapid stirring, the supersaturation breaks down too quickly and a product that is too fine precipitates. In contrast, if the stirring is too slow, the degradation is incomplete; If the mother liquor from such a batch is now used in the preparation of the soda feed solution, sodium percarbonate crystallizes out already during the preparation of this feed solution, since the more readily soluble soda pushes the less soluble sodium percarbonate out of the solution. 30 This sodium percarbonate then precipitates with the impurities and is therefore lost. In order to determine the optimum stirring speed, the supersaturation of sodium percarbonate which has occurred can be determined immediately after the addition of the hydrogen peroxide and its degradation determined. The stirring speed to be selected is ultimately determined by the salt quality obtained, i.e. H. the coarse compact grain. If the breakdown of supersaturation has been too rapid, the stirring speed must be reduced appropriately and vice versa until the desired breakdown rate has been reached. The same applies to the metering rate of the hydrogen peroxide solution in the soda solution. This dosing speed can be determined for operation in a laboratory experiment. Dosing speeds of 10-20 minutes are optimal for the quantities required for the reaction. The precipitated sodium percarbonate can be filtered off and dried in a known manner. The process can easily be carried out in conventional plants for the production of sodium perborate. The technical progress of the described process lies in the reuse of the mother liquor with the constancy of the crystallization parameters being largely constant, such as the composition of the soda feed solution, an approximately constant degree of contamination and approximately constant temperature as well as the very simple technical implementation. 60 As a result, a qualitatively uniform, i.e. H. rough, compact product.