DE2631917A1 - CONTINUOUS CRYSTALLIZATION PROCESS FOR THE PRODUCTION OF SODIUM CARBONATE PEROXIDE - Google Patents

Description

The invention relates to a continuous crystallization process for the production of stable sodium carbonate peroxide with high bulk density and uniform particle size distribution.

Sodium carbonate peroxide or sodium carbonate peroxohydrate is a crystalline compound of the formula 2Na ₂ CO, · 3HpOp, which can release hydrogen peroxide in aqueous solution. Because of this property, sodium carbonate peroxide is useful as a bleaching agent in detergent formulations. Much of the recent work on sodium carbonate peroxide has been aimed at improving manufacturing methods.

It is known that sodium carbonate peroxide by reacting Hydrogen peroxide with sodium carbonate alone or in the presence of a stabilizer either batchwise or in continuous Process can be produced. An example of a method for making sodium carbonate peroxide is in U.S. Patent 2,986,448. According to this process, an aqueous mixture of hydrogen peroxide and

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Sodium carbonate in a crystallization zone at a! Nioht temperature for about 5 ⁰ C implemented. After a decomposition time of at least 4 hours, a suspension of sodium carbonate peroxide crystals is formed, which is removed from the crystallization zone, filtered and then dried to give the sodium carbonate peroxide product. The filtered mother liquor containing dissolved sodium carbonate peroxide is carried out in the rapid flash evaporation under such conditions that excess water is removed from the system. The resulting mixture of the mother liquor and small crystals obtained by evaporation is returned to the crystallization zone.

While this U.S. patent process is generally satisfactory, it suffers from a number of disadvantages: 1. The crystallizer requires expensive external cooling equipment; 2. It must be out of the system in the flash evaporator large amounts of water reaching 34 or more moles of water per mole of product are removed using external heating means, which add significantly to the cost of the plant, as well as requiring overhead operation; and 3. the formation of large quantities of magnesium silicate during on-site crystallization leads to excess nucleation, resulting in a very large one Proportion of very fine crystals leads.

The present invention now provides a continuous crystallization process for the production of stable sodium carbonate peroxide created with high bulk density and a uniform particle size distribution, which consists of:

a) A fresh aqueous solution of hydrogen peroxide and a continuously introducing purified sodium carbonate solution into a crystallization zone;

b) The aqueous solution of hydrogen peroxide and the purified one To implement sodium carbonate solution in the crystallization zone in such a way that the sodium carbonate peroxide concentration above their Solubility saturation limit is, where at a temperature

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is carried out from about 15 "to about 3O ⁰ C, a pH of about 10.2" to about 11.5 and a Yerweilzeit from about 0.5 to about 15 hours;

c) water from the crystallization zone in a molar ratio from about 0.5 Ms to about 15.0 moles of water per mole of sodium carbonate peroxide produced to evaporate;

d) removing a slurry from the crystallization zone, which contains sodium carbonate peroxide crystals;

e) the crystals from the slurry from the crystallizer. separate the sodium carbonate peroxide and dry the sodium carbonate peroxide to be obtained with a bulk density between 0.90 and 1.00 g / ccm;

f) the mother liquor removed from the above filtration treat to decompose the hydrogen peroxide;

g) to add fresh sodium carbonate to the treated mother liquor in sufficient amounts to achieve a 25 to 33 percent by weight To prepare sodium carbonate solution; and

h) to purify the sodium carbonate solution and to use the purified sodium carbonate solution in step a).

In carrying out the process of the invention, hydrogen peroxide and sodium carbonate are used in a molar ratio of essentially 3: 2 implemented. The hydrogen peroxide is sent directly to the crystallization zone in the form of an aqueous solution brought in that $ 50 to $ 90 and preferably $ 70 based on the weight of hydrogen peroxide it contains.

The sodium carbonate is added as a saturated aqueous solution that was previously used for removal; of iron and other transition metal impurities that catalyze the decomposition of hydrogen peroxide. The sodium carbonate solution is through Dissolve commercially available sodium carbonate, preferably

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anhydrous or monohydrated crystallines, produced in the recycled mother liquor in sufficient quantity to produce a 25 to 33 percent by weight sodium carbonate solution. It is not necessary to purify the mother liquor to remove iron or other transient metal impurities before dissolving the sodium carbonate therein Sodium carbonate solution must itself be purified to remove iron and other transition metal impurities before entering the crystallization zone. Purification of the sodium carbonate solution is expedient by adding 100 to 2000 parts per million (ppm) (based on the weight of the sodium carbonate solution) magnesium oxide or a soluble magnesium salt such as magnesium chloride and magnesium sulfate, materials that absorb the iron and other transition metals from solution, Other soluble salts can also be used, such as calcium and zinc salts Generating solids are removed by filtration and the purified sodium carbonate solution is then passed to the crystallization zone. The temperature of the sodium carbonate solution which is passed to the crystallization zone must at least be 27 ⁰ C and is preferably between 40 and 100 ⁰ C and more preferably between 50 and 60 ⁰ C, to the formation of solid sodium carbonate decahydrate to avoid in the feeding system . If sodium carbonate decahydrate is formed in the feed system, it precipitates out of the sodium carbonate solution and in this way changes the molar ratio of the reaction components of sodium carbonate and hydrogen peroxide in the crystallization zone in an unfavorable manner.

The reaction between sodium carbonate and hydrogen peroxide to produce the sodium carbonate peroxide is extremely difficult quickly and the sodium carbonate peroxide only needs a few Remain in a super-saturated state for a few seconds, after which crystallization occurs. Will be the super saturated or the supersaturated state is reached, the hydrogen peroxide solution and the purified sodium carbonate solutions are in the crystallization zone is introduced to a sufficient extent to keep the sodium carbonate peroxide concentration continuously

borrowed to keep above their solution saturation level in the reaction mixture. By using this procedure you will be maximum product formation and recovery without evaporation more than 1.5 Ms 15.0 moles of water per mole of sodium carbonate peroxide produced achieved.

The reaction temperature and the corresponding pressure in the crystallizer are kept "at about 15" to about 30 ^° C., at 10 "to 30 mm Hg, and preferably at about 21 to about 25 ^° C., at 15 to 19 mm Hg The specific temperature and the associated pressure during crystallization is essential to keep the sodium carbonate peroxide concentration above the solution saturation limit, while water from the crystallizer is in a molar ratio of about 1.5 to about 15 * 0 Mol and preferably about 2.5 to about 9.0 mol of water is removed per mole of sodium carbonate peroxide produced. By evaporating this amount of water, the reaction temperature is also controlled by removing the heat of crystallization resulting from the reaction of sodium carbonate and hydrogen peroxide. The concentration of the resulting sodium carbonate peroxide slurry in the crystallizer is about 10 to 40. Peststoffen-fo and preferably 20 to 28 parts by weight S ^ solids.

Lower temperatures and pressures, ie about 5 ° C at about 5 mm Hg, are not recommended as more expensive vacuum equipment and larger crystallizers are required. Higher temperatures and pressures, ie above 35 ^° C. at about 40 mm Hg, are not recommended, since this would lead to greater losses of hydrogen peroxide through decomposition.

The crystallizer is activated with a residence time of 0.5 to 15 Hours and preferably operated 1 to 8 hours. Dwell times of less than 0.5 hours lead to excessive Nuoleus formation, which leads to a substantial reduction in the mean crystal size. Residence times over 15 hours lead to a excessive decomposition of hydrogen peroxide which will reduce the product yield. The dwell time is than that Total weight of contaminants in the crystallizer divided by the production rate or production rate

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defined in pesticides per unit of time.

The crystallizer is at a pH of about 10.2 to about 11.5, and preferably 10.5 to 10.8. If the crystallizer is operated at a pH value above about 11.2, this is a 1 to 3 percent strength by weight sodium hydroxide solution used to adjust the pH. Although it was found that the operation of the crystallizer at a pH value of about 11.2 leads to a reduction in the decomposition of hydrogen peroxide, but the process according to the invention is more economical, when the mother liquor has a pH of 10.5 to 10.8.

Large crystals of sodium carbonate peroxide are continuously withdrawn from the crystallizer as a slurry in the crystallizer mother liquor containing about 10 to 40 weight percent, and preferably 20 to 28 weight percent, sodium carbonate peroxide solids. The mother liquor also contains 10 to 30 wt -fo and preferably 15 to 19 wt .- ^ sodium carbonate. and 1 to 6% by weight, and preferably 1.5 to 2.5% by weight, hydrogen peroxide. If the concentration of sodium carbonate in the mother liquor more than 30 wt .- # when the Kriställisator is operated at about 30 ⁰ C, then a solid phase is formed of sodium carbonate decahydrate. Likewise, if the sodium carbonate concentration in the mother liquor is greater than about 20% by weight, when the crystallizer is operated at the preferred temperature of 21 to 25 ^° C., a solid phase of sodium carbonate decahydrate is formed. The formation of the solid phase is undesirable because it dilutes the active oxygen content in the final product and because it causes excessive nucleation in the crystallizer, thereby yielding crystals of smaller size.

The sodium carbonate peroxide crystals are made from the mother liquor removed by customary separation operations or facilities and then dried quickly to remove excess moisture, using conventional means such as Trough, rotation, belt or fluidized bed or fluidized bed

dryer "operated.

The resulting sodium carbonate peroxide crystals, according to the invention are obtained, surprisingly have a high bulk density, a high stability and a uniform Particle size distribution. These properties are highly desirable as the crystals are easily separated from the solution, can be dried easily and are less crumbly or crumbly, making them easy to use without breaking and unwanted dusting can be handled. These crystal properties also reduce the tendency for the crystals to secrete their use in commercial formulations with similar bulk densities, which is of commercial importance. Furthermore allows a sodium carbonate peroxide product to be formed consistently with a uniform particle size distribution an economical operation for continuous production of a consistently good product with no fluctuation in properties. In addition, the crystals produced have a high active oxygen content, i.e. at least 15.0 mole active Oxygen, with the maximum theoretical active oxygen content being $ 15.28.

The term "high bulk density" as used herein refers to sodium carbonate peroxide crystals having bulk densities of 0.9 to 1.0 g / cc and preferably from 0.91 to 0.98 g / cc. The term "uniform particle size distribution" refers to refer to the uniformity or continuity of the sodium carbonate crystal particle size distribution, which is achieved during crystallization in relation to the time, i.e. crystals with more uniform Particle size distribution during the entire crystallization process, with at least 50 $ of the crystals having a grain size of ^ 0.297 mm (+ 50 mesh; U.S. Standard Sieve Series A.S.S.M. - E-11-61).

The resulting mother liquor contains the dissolved sodium carbonate and hydrogen peroxide. This mother liquor cannot go directly into to be returned to the crystallizer, as they contain impurities from reaction components and impurities from transitional

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Contains metals. In the same way, the mother liquor cannot be used directly as a water source for the preparation of the sodium carbonate solution, since when sodium carbonate is added to this liquor, a reaction with the remaining hydrogen peroxide results in excessive foaming and heat generation. Accordingly, the hydrogen peroxide remaining in the mother liquor is decomposed and the mother liquor is then treated with additional sodium carbonate and purified as described above. The decomposition of the hydrogen peroxide can be achieved in a conventional manner, such as by adding conventional agents for decomposing hydrogen peroxide. Preferably, the mother liquor to a heat treatment is subjected to, for example, by passing steam through the mother liquor and thereby increasing the temperature of the mother liquor up to a point at which the hydrogen peroxide is rapidly decomposed, such as 40 to 7O ⁰ C for a few minutes.

The accompanying drawing shows a flow diagram according to an embodiment of the process according to the invention, which is carried out in a continuous manner. According to this scheme, a aqueous hydrogen peroxide solution at a concentration of 70 wt .- $ through the line 4 from the storage container 2 in a conventional suction tube crystallizer ("draft tube" crystallizer) 6, equipped with a stirrer that is rotated at a speed that controls the level of pesticides in the Keeps crystallizer 6 evenly dispersed. (Other types of crystallizers can also be used, such as Oslo-type crystallizers.) A purified sodium carbonate solution is through the line 8 from a supply container into the crystallizer 6 or optionally through the line fed into the fine particle cycle. The sodium carbonate solution and the hydrogen peroxide solution are simultaneously fed in at a rate sufficient that the Sodium carbonate peroxide concentration above its solution saturation level lies. The hydrogen peroxide and sodium carbonate are generally used in molar ratios of about 3: 2.

The reaction mixture is in the crystallizer 6 with stirring

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for at least 0.5 hours "held at a temperature of about 21 Ms about 25 ⁰ C in order to achieve a 20 to 28 weight percent slurry of sodium carbonate peroxide crystals. The crystallizer 6 is preferably operated at a reduced pressure of 15 to 19 mm Hg using conventional vacuum systems whereby water is removed by evaporation through line 14 in a molar ratio of 2.5 to about 9.0 moles of water per mole of sodium carbonate peroxide produced, the oxygen formed by the decomposition of hydrogen peroxide in the crystallizer is also removed through line 14. Suspended Sodium carbonate peroxide fines are removed from the reaction chamber of crystallizer 6 via line 16 and passed through a heat exchanger 18 which helps dissolve the fine particles and provides heat to evaporate the water; this heated solution is returned to the bottom of the crystallizer 6.

Large crystals of sodium carbonate peroxide are continuously withdrawn from crystallizer 6 through line 20 as a crystallizer mother liquor slurry, which preferably contains 20 to 28 weight percent solids in a mother liquor containing 15 to 19 weight percent sodium carbonate and 1.5 to 2.5 wt .- ^ hydrogen peroxide contains. The slurry is fed to centrifuge 22, which removes crystallizer mother liquor from the crystals and reduces the moisture content of the crystals to about 2 to 10 $. The centrifuge 22 can be replaced by conventional rotary filters or filter presses. The centrifuged crystals are passed through the conduit into the dryer 26, whereby the crystals are suitably dried at a temperature of about 40 to 60 ⁰ C, which is achieved a trokenes ITatriumcarbonat peroxide product containing less than 0.2 wt ^ Contains moisture.

The crystallizer mother liquor removed in centrifuge 22 is passed through line 28 into the mother liquor container 30 led. The dissolved sodium carbonate and hydrogen peroxide as well as smaller amounts of remaining IT sodium carbonate peroxide crystals containing mother liquor is through the line 32

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into a Plussig solid separator 34 or, alternatively, directly to the hydrogen peroxide decomposition tank 38, the line 36 passed. The liquid-solid separation device 34 is a common device for separating liquids and solids, such as a hydroclone. A high weight percent solids stream, the second slurry containing 50 to 50,000 sodium carbonate peroxide crystals, is withdrawn through line 40 and returned to crystallizer 6. The resulting mother liquor stream is withdrawn through line 36 and fed into hydrogen peroxide decomposition vessel 38. The mother liquor is kept in the container 38 at about 40 to 50 ^° C. for a time sufficient to decompose the remaining hydrogen peroxide in water and oxygen.

The decomposed liquid from the hydrogen peroxide decomposition tank 38 is through line 42 into the sodium carbonate make-up tank 44 headed. The sodium carbonate is preferably in the anhydrous form or in the crystalline form of Monohydrates and is fed through line 46 into the top-up tank 44 in. Brought in an amount so that a 25 to 33 percent by weight Sodium carbonate solution is obtained. If necessary, water can also be added through line 48. In addition, 100 to 2000 ppm of magnesium oxide or a water-soluble magnesium salt are added through line 50 to the Solution filled in the refill tank 44.

After treatment with the magnesium compound, the solution is transferred from the refill tank 44 through line 52 to filter 54, wherein solids containing magnesium, iron and other transition metals are removed through line 56 and discarded. The filtered solution is withdrawn through line 58 and fed into the storage tank 10, where the purified sodium carbonate solution is temporarily stored prior to charging into the crystallizer 6.

The following example serves to further explain the invention,

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All proportions or parts mentioned in this example and in the description are based on weight, unless stated otherwise.

Example:

A 70 weight percent solution of hydrogen peroxide was reacted with a 28 weight percent purified sodium carbonate solution in a crystallizer in proportions such that the resulting mixture continuously contained about 175 g / l sodium carbonate and about 25 g / l hydrogen peroxide. The sodium carbonate solution was prepared by dissolving anhydrous sodium carbonate in a recycled mother liquor, which was heated to about 50 ⁰ C to the decomposition of its total hydrogen peroxide content, was mixed with 1000 ppm of magnesium oxide and filtered. The resulting purified sodium carbonate solution contained less than 1 ppm iron and traces of other transition metals. The crystallizer was operated at a pH of 10.8, at a temperature of 22.5 ^° C., a pressure of 15 mm Hg, a residence time of 7 hours with a destruction circuit for fine particles and a solids concentration of 28%. About 12 moles of water per mole of sodium carbonate peroxide produced were continuously removed from the crystallizer. The slurry was removed from the crystallizer and centrifuged. The resulting sodium carbonate peroxide crystals containing about 5% by weight of water were dried in a fluidized bed dryer to produce a sodium carbonate peroxide product.

The product consisted of single crystals in the shape of hexagonal prisms with a particle size distribution of about $ 27 > 0.42 mm (+40 mesh); $ 36 <0.42mm> 0.297mm (-40 + 50 mesh); $ 29 <0.297 mm ^ 0.210 mm (-50 + 70 mesh) and $ 8 <0.210 mm (-70 mesh U.S. Standard Sieve). The product had a bulk density of 0.95 g / cc, an active oxygen content of 15.18% by weight and a Moisture content less than $ 0.2 wt.

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Claims (9)

Claims (V) Continuous crystallization process for production of stable sodium carbonate peroxide with high bulk density and uniform particle size distribution, characterized in that: a) continuously a fresh aqueous solution which contains 50 "to 90 wt. Fo hydrogen peroxide and a purified sodium carbonate solution is fed into a crystallization zone; b) the aqueous solution of hydrogen peroxide and the purified sodium carbonate solution are fed into the crystallization zone in such a way that the formation of a solid phase of sodium carbonate decahydrate is prevented and the concentration of sodium carbonate peroxide is above its solution saturation limit, at temperatures from ~ 15 to 3O ⁰ C, at a pressure of 10 to 30 mm Hg, a pH value of 10.2 to 11.5, while a residence time of 0.5 to 15 hours reacted; c) the water from the crystallization zone in a molar ratio of 1.5 to 15.0 ha of water per mol of sodium carbonate peroxide produced evaporates; d) removing a slurry containing sodium carbonate peroxide crystals from the crystallization zone; e) separating the crystals from the crystallizer slurry, the sodium carbonate peroxide dries and one: sodium carbonate peroxide wins with a bulk density of 0.90 to 1.00 g / ccm; f) the mother liquor separated off in the above filtration treated to decompose the hydrogen peroxide; g) fresh sodium carbonate to the treated mother liquor in sufficient quantities to form a 25 to 33 percent by weight Sodium carbonate solution at a temperature of 809885/0846 - 13 adds at least 27 ⁰ C; and h) the sodium carbonate solution for removing iron and other transition metal contaminants and cleaned them up Sodium carbonate solution is used again in stage a). 2. The method according to claim 1, characterized in that the reaction is carried out at a temperature of 21 to 25 ⁰ C, at a pH of 10.5 to 10.8 for a residence time of 1 to 8 hours . 3. The method according to claim 1, characterized in that 2.5 to 9.0 moles of water per mole of sodium carbonate peroxide from the Crystallization zone evaporates. 4. The method according to claim 1, characterized in that the crystals from the crystallizer slurry according to step e) removed; a second slurry containing 50 to 90 wt .- ^ sodium carbonate peroxide crystals from the mother liquor separated off from step e) removed; treating the resulting mother liquor to decompose hydrogen peroxide; and the second slurry returns to the crystallization zone. 5. The method according to claim 1, characterized in that the sodium carbonate solution of step h) with 100 to 2000 ppm Contacting magnesium oxide or a soluble magnesium salt based on the weight of the sodium carbonate solution; the Sodium carbonate solution filtered; and directing the resulting purified sodium carbonate solution to the crystallization zone. 6. The method according to claim 1, characterized in that a sodium carbonate peroxide product is obtained with a bulk density from 0.91 to 0.98 g / cc, an active oxygen content of at least $ 15.00 and a particle size distribution of at least $ 50> 0.297 mm (+ 50 mesh U.S. Standard Sieve Series ASTM - E-.11-61). 7. The method according to claim 1, characterized in that one S098eS / 0S46 a sodium carbonate solution with a temperature of at least 27 ^° C. is used in stage a). 8. The method according to claim 1, characterized in that a sodium carbonate solution with a temperature of 40 to 10O ⁰ C is used in step a). 9. The method according to claim 1, characterized in that a sodium carbonate solution with a temperature of 50 to 60 ⁰ C is used in step a). 609885/0846