DD212493A1 - PROCESS FOR PREPARING A STORAGE STABLE CARBAMIDE PERHYDRATE - Google Patents

Abstract

The invention relates to a process for the preparation of storage-stable carbamide perhydrate, in particular for use as a bleaching and oxidizing agent in hair cosmetics. It is the object of the invention to achieve an almost isothermal conversion of urea with highly concentrated hydrogen peroxide and thereby to obtain a stable end product. According to the invention, preferably from 65 to 75% by mass of hydrogen peroxide is metered in at a rate of 0.02 to 1.0 mol / l.min at temperatures of 5 to 25 ° C. to a recycled mother liquor saturated with carbamide perhydrate, which contains urea and stabilizers and which is set to a ph value of 2 to 5. As stabilizers phosphonic acids, z. B. the N, N-dimethylaminometane diphosphonic added in amounts of 0.1 to 0.5% of the mother liquor. Compared with the cooling crystallization process, higher material and space-time yields are achieved with lower energy requirement.

Description

Title of the invention

Process for the preparation of a storage-stable carbamide perhydrate

Field of application of the invention

The invention relates to a process for the preparation of a storage-stable carbamide perhydrate, an additive compound of hydrogen peroxide and urea used predominantly as a bleaching and oxidizing agent in hair cosmetics.

Characteristic of the known technical solutions Since its introduction into the technology (s, eg W. Machu: the hydrogen peroxide, and the Perverbindungen, Springer publishing house Vienna 1951) becomes. Carbainide perhydrate ira essentially unchanged according to the same process, the cooling crystallization of a solution of urea in aqueous hydrogen percxidlöstangen produced (W, Weigert, Ed., Hydrogen peroxide and its derivatives, A, Hiithig Verlag Heidelberg 1978), this is, predominantly of 30 to 35 Ma .- per cent of hydrogen peroxide, assumed in which first with heating, the approximate, stoichiometric amount of urea is dissolved. By cooling by means of cooling brine to 0 to -5 C, then the Hauptinenge (ca, 70 ^) of the contained carbamide perhydrate brought to crystallization, further developments were mainly the optimization of the process conditions for the preparation of a stable end product with high material yield content. For this purpose, the resulting mother liquor is protected

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Nend. concentrated, z. In vacuum thin film evaporators, and. fed back to the crystallization process. Although it was possible to further increase the yield of the mother liquor, the mother liquor concentration is always associated with decomposition losses of hydrogen peroxide and hydrolysis of urea, whereby the product quality can be adversely affected (displacement of the pH due to ammonia cleavage). It was therefore always interested to further increase the proportion of car band, d-perhydrate, which is already present at the first crystallization, without mother liquor concentration and its recycling. This results in the effort, by using the highest possible starting concentrations of hydrogen peroxide, already to keep the amount of water supplied to the process as low as possible. A concentration of about ^ 5 Ma .- $ hydrogen peroxide, however, proved to be the upper limit for this process, since then for complete dissolution of the stoichiometric amounts of urea, a heating to about 50 C is required. It is with increasing hydrolysis rate of the urea and. As a result, a shift in the pH value into alkaline regions can be expected, as a result of which, in addition to the unfavorable influence on the product quality, a stormy decomposition reaction of the hydrogen peroxide can occur. Although by returning a portion of the mother liquor, this temperature increase can be kept within reasonable limits, but then there are disadvantages from an energy management point of view, since the first to be heated and. thereafter, the total mass to be cooled is further increased.

There has also been no lack of attempts to circumvent the heating of the reaction mixture until complete dissolution of the urea and. Add this before the start or during the cooling process with simultaneous precipitation of the carbamide perhydrate. It turned out, however,

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that the resulting ent finely crystalline product is difficult to dry and tabletted and. has a low storage stability. As a particularly cheap and. Also, commercially available, a crystal size in the range of 0.4 to 1 ram. It must be regarded as a further disadvantage of the coagulation-crystallization method that the cooling rate and thus the settling supersaturation can not be chosen arbitrarily, and that the ¥ armed acid reaction progresses as a result of deposition of crystal layers worsened on the cooling surfaces "Cooling times are very long, especially for large reactors, resulting in low space-time yields. The decisive economic disadvantage of the cooling crystallization process, however, is the unfavorable use of energy due to the initial heating and cooling. subsequent cooling of the reaction mixture to about -5 ° C. with simultaneous evaporation of the relatively large amount of water introduced by the hydrogen peroxide through the mother liquor to concentra tion.

The stabilities and processing characteristics of the products made by this process are known to be beyond the process conditions already described and. The purity of the chemicals used also depends to a considerable degree on the type, amount and. The distribution of the stabilizers used depends on the »stabilizing effect is predominantly acidic. © substances such as organic acids, eg. As citric acid (DRP 259 826), boric acid or sodium hydrogen sulfate (DRP 281 O83) or acid phosphates, eg. As monosodium phosphate (DRP 291 ^ 90) used. They work u. a) in the ¥ iron that the formation of alkaline, the decomposition of further catalyzing centers is prevented .. Primarily for the purpose of masking of catalytically active

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Heavy metal impurities serve organic complexing agents, such. B. 8-Hydro ~ tychinolin (GB-PS 1 267 618), ethylenediaminetetraacetic acid, EDTA (DE-OS 1 519 ^ 84) and organic phosphonic acids such as "B, aminotri- (lower allenyl) phosphonic acids (DE-OS

1 519 h8h) hydroxyethane diphosphonic acid (DE-OS

2 3hh 017) JT, JT-dialkylamino- ethane diphosphonic acids (DD-PS 157-58 ), alone or in combination with other stabilizers. ¥ hile. these compounds were originally added with the washing liquid, which z. B. led to concentrations of 0.1 to 0.3 i ini end product when using acidic phosphates, was later added to achieve a storage-stable even at higher temperatures to 50 C product admixture. first proposed to d.era dry final product. There were Zumischlingen of acid phosphates or zinc sulfate from 0.5 to 5 (DE-OS 1 768 583) od.er a mixture of Dinatriuinpyrophosphat and. EDTA in the preferred concentration range of $ 1 each, optionally with the addition of anhydrous SiO ₂ (DE-AS 2,043,571) recommended. In both cases, sufficient stabilization or buffering of the mother liquor is not ensured during the production process, in particular with regard to the required temperature increase in the dissolution of the urea and. the concentration of the relatively large accumulating Mutterlaugeniengen,

Aim of the invention

The aim of the invention is therefore a. Process which satisfies both the requirements of a high material and. Energy yield, as well as those of a storage-stable carbamide perhydrate with good processing properties is equally fair. and. overcomes the disadvantages of the known methods.

The essence of the invention The object of the invention is a process which, when used with higher concentrations of hydrogen peroxide, provides an approximate, isothermal route of the reaction and. Crystallization under consideration of the criteria for a stable end product allows.

Erf ind.ungsgemäß be equimolar amounts of hydrogen peroxide, and. Urea in a recycled, at 15 to 25 C of carbamide perhydrate saturated, stabilized and. to a pH of 2 to 5 adjusted mother liquor for the reaction and. Crystallization brought, whereby also recycled carbamide perhydrate Bristalle act as crystallization nuclei and the Übersät tigun.g by supplying the hydrogen peroxide in the form of 50 to 90 / iger solution, preferably 65 to 75 ^ ig> at a rate of 0.02 to 1, 0 mol / l.min, based on the reaction volume is adjusted. In this case, a residence time of at least 10 minutes to reduce the supersaturation after addition of hydrogen peroxide is observed. It has surprisingly been found that under these process conditions at approx. Isothermal process control well-formed crystals in the desired grain size range can be obtained, ie without prior increase in temperature and subsequent cooling to -5 C, uring. of the entire reaction and. Crystallization process is maintained, the temperature in the temperature range of 5 to 25 C, with no or only small ärmärmgen must be dissipated. As a result, the Produktd.urchsatζ largely independent of d.er cooling surface and. the heat transfer coefficient, the space-time yields can be increased several times. The rate of crystallization is determined primarily by the rate of delivery of hydrogen peroxide within the given range. Since the degradation of supersaturation and crystal growth but also by the hydrodynamics in the reactor or crystal!

Sat or strongly influenced, an adjustment of the rate of addition to the prevailing conditions within the erfind.ungsgemäß to be observed range is required. By using higher concentrated hydrogen peroxide. d ± e quantity of liquid fed to the process and. so that the resulting mother liquor quantity is greatly reduced, z. However, the proportion of the recirculated mother liquor in the process according to the invention can be reduced to less than one quarter instead of 35% by weight in the previous process, owing to the use of 70 parts by mass of hydrogen peroxide almost isothermal reaction without any adverse effect on the energy balance arbitrarily selected and. largely adapted to the requirements of the respective process. Higher temperatures are possible in principle, but the carbamide perhydrate content of the mother liquor then increases so much that leakage losses can lead to an unjustifiable increase in yield. According to a further feature of the present invention, the recycled mother liquor 0.01 to 2.0 $ of a suitable phosphonic acid, preferably 0.1 to 0.5 i »·» added as a stabilizer. Suitable phosphonic acids in the context of the present invention are to be considered those which, in addition to a good stabilizing effect, also have sufficient oxidation and oxidation properties. Have hydrolysis resistance, as the z. From the N, IT-dimethylaminomethane-diphosphonic acid or the hydroxyethane-diphosphonic acid. This not only results in a low decomposition rate of hydrogen peroxide for the time of the reaction and the concentration of the mother liquor, but it is also the prerequisite for good durability d. By complex binding of the present in the reaction mixture decomposition catalysts d. created carbamide perhydrate created. In addition, the phosphonic acid at higher addition levels ensures compliance with the intended pH value between 2 and 5 in that

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terlauge. This ensures that the cleavage of ammonia, which is only insignificant owing to the low level of thermal stress, can not lead to a shift in the pH range into the alkaline range. However, especially at low phosphonic acid concentrations, it is advantageous to further increase the buffer capacity by adding 0.5 to 2 .mu.l of an acidic phosphate, preferably monosodium phosphate or disodium pyrophosphate, in a manner known per se. increase. The amounts of phosphonic acids and. optionally acidic phosphates are generally sufficient to ensure good storage stability. But it is also possible, in addition to add in known Tfeise the wet or dried end product further stabilizers such. As acid phosphates, zinc sulfate, EDTA, SiO "or phosphonates. This is particularly useful when larger Tiännebelastungen must be expected or if it also an improvement in the processing properties to be achieved (eg, when adding SiO ").

The manufacturing process characterized by the invention allows both a continuous and a discontinuous process control. Particularly favorable conditions are present when the urea is metered in at the same rate as the hydrogen peroxide, ie at from 0.02 to 1.0 mol / l.min of the recycled mother liquor. The desired isothermal process, which is proves to be particularly economically advantageous, can thereby be realized in a simple ¥ eise. Since d ± e solution heating of urea and. Carbamide perhydrate under the present conditions differ only slightly, the temperature change remains in relatively small limits and. it is only a certain temperature by cooling by means! Barrels required. The technological scheme of this continuous variant

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preferred embodiment the erfindungsgeraäßen method is shown in the figure 1.

The recirculated, on Carbamid.-perhydrate at d.er reaction temperatures of 5 to 25 C saturated mother liquor is in the mother liquor Vorrats- and. Dissolving vessel 7 the required amount of urea and. added to the stabilizers. By means of a metering pump 1 is. they are conveyed via a water-cooled heat exchanger 2 into the continuous crystallizer 3. From the storage vessel h ", more highly concentrated hydrogen peroxide is also supplied by the metering pump 5 to the crystallizer 3 at a feed rate of 0.02 to 1.0 mol / l, min, based on the volume of the crystallizer If "crystallizer 3 (stationary stirred reactor) is mixed in, no separate addition of crystal nuclei is required in this procedure. The crystallizer volume should be such that the average residence time is at least 10 minutes. The crystallizer leaving the crystallizer 3 is separated from the mother liquor in a drum cell filter and fed to the drier. The mother liquor passes into the reservoir or dissolving vessel 7. The temperature in the circuit is regulated by the heat exchanger 2 'to approximately constant values in the required temperature range. The excess mother liquor overflowing at the supply and dissolving vessel 7 becomes known ironed up.

In addition to this continuous procedure, it is also possible to combine a continuous reaction and crystallization procedure with a batchwise work-up. This will be. ¹ z . B. submitted the entire recycled mother liquor together with a likewise recirculated portion of the crystallized reaction mixture in the crystallizer, mixed with stabilizer and both Realctionskociponenten, urea and.

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At a rate of 0.02 to 1.0 mol / l.min, based on the volume of the mother liquor, the temperature constant in the range "from 10 to 30 ° C. is ensured by tempering the mother liquor or the reaction mixture Working up can then be carried out, for example, by centrifuging and subsequent batchwise drying.As a residence time for reducing the supersaturation of at least 10 minutes, the time between the metering closure for the reactants and the discharge of the crystal slurry into the centrifuges or filters must be considered Further process variant of the present invention consists in the semicontinuous reaction (semibateh) in which all the urea is dissolved in the recycled, stabilized mother liquor, which is treated with seed crystals and then by addition of the hydrogen peroxide at the rate of 0.02 to _v , 0 mol / l.min, again based on the entire vorgeleg te mother liquor, the carbamide perhydrate formed and. crystallized. As a result of the greater endothermic heat of reaction upon dissolution of the total quantity of urea, in this case it is necessary to add or remove ¥ arms during the process. It is preferable to start from a saturated at 5 b ± s 15 C mother liquor, which is heated at dissolution of the urea by about 5 to 10 C, to precipitate larger very fine Carbamid.-perhydrate crystals due to the case suddenly occurring supersaturation to avoid. Thereafter, the supply of hydrogen peroxide with uniform cooling by cold water or cooling brine to the starting temperature of about 5 to 15 C. Since in comparison with the previously applied Kühlungskri stalii sat onaverfähren much smaller ¥ argeneengen must be replaced, remains also In this variant of the process according to the invention, the controlled hydrogen peroxide feed is reduced.

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for aase crystallization, thereby achieving much higher space-time yields,

In all variants of the method according to the features of the present invention, the accumulated mother liquor quantity, which is greatly reduced as a result of the use of highly concentrated hydrogen peroxide, can be worked up in a known manner and. your process will be fed back. It is advantageous to bring first by freezing the circled portion to -5 to 10 C, the bulk of the carbamide perhydrate in solution to crystallize and. separate. In this case, a material yield of 95 i » is already achievable if it is assumed that a 65 to 75 Ma .-% hydrogen peroxide is preferably used. The resulting crystalline products can be recycled to the process as crystal nuclei in the sense of the invention become. By concentrating the resulting mother liquor, a further yield improvement can be achieved. However, it may also be necessary to remove a portion of the mother liquor in order to prevent an accumulation of impurities in the mother liquor cycle.

EXAMPLES Example 1

In an apparatus constructed according to FIG. 1, using a crystallizer of 10 l content, Carfoaidaid perhydrate was produced continuously. The recycled mother liquor was fed to the crystallizer at a rate of 60 l / h, which gave a mean residence time of about 10 min corresponds. The dosage of the urea and a 70 weight percent hydrogen peroxide solution was varied in the range of 0.04 to 0.12 mol / min. By addition of Ν, Ν-Dimethylaminomethandiphosphonsäure and. Monosodium phosphate was concentrated in the circulating mother liquor at a concentration of 1. $

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posed. The pH was 2.7 · The supplied urine * dissolved clearly in the circulating mother liquor. After an inflow time of about 1 h, a stationary state, in the crystallizer, with a temperature of 20 to 25 C turned on. The continuously overflowing mother liquor crystal mixture was separated off and washed with little stabilizer-containing barrels (1 $ phosphonic acid per monosodium phosphate). Thereafter, it was dried at 50 ° C. and the product was examined for particle size distribution and storage stability. The content of the final product of phosphonic acid and 2JaELPO.

was each 0.1 to 0.2 $, The results obtained are summarized in Table 1.

table 1 1 H 0 content 3 H Ό content 6 months naten 2 Peinkorn attempt 2 feeding 2 in i> 2 proportion of No. 3 speedy , 4 to 3 < 0.4 mm kei.t for 35 in % H ₂ O ₂ + urine 35 fabric in 35 Mo l / l »me. 35 6.8 o o4 35 10.6 0.06 35 20.6 0, 12

It becomes clear that with the new method a particle size distribution with good stability, which can be influenced by the feed rate, is achieved with good stability. At the selected temperature, only a minimal temperature rise of approximately 1 K / h was observed, so that the water cooling was hardly needed. Dia material yield was already at $ 85 without mother liquor preparation.

Example 2

For the semi-continuous preparation of carbamide perhydrate, hOO 1 at 10 C saturated mother liquor,

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which contained 0.5 in N, N-dimethylaminomethane-diphosphonic acid and 1-monosodium phosphate and their pH value was 2.5, placed in a teinperierbares mixing vessel and. mixed with 120 kg (2 kMol) of urea. The temperature dropped to SC with uniform precipitation of fine crystalline carbamide perhydrate. Heating to about 18 C produced a clear saturated solution. As crystallization nuclei about ko kg Carbamid.-Perhyd.rat were d.es preceding Ansätzes added and, while cooling 80 1 hydrogen peroxide. 70 Ma .- $ (ca, 2 kmol) is added within h h, which corresponds to a Dosiergeschwindigkeit of 0.02 mol / l.min, based on the volume of the mother liquor submitted. The cooling was adjusted so that during the addition of the hydrogen peroxides a g ± xig @ cooling to the starting temperature of 10 C was carried out. It was stirred for 10 min, then the product was removed by centrifugation and. covered with a solution of 0.5 kg of phosphonic acid in 15 l of mother liquor. In the dried final product were 0.31 $ phosphonic acid detectable. The Uiasetzungsausbeute was without Mutterlaugeaufkonzentration at 90 fa. The product obtained after omonate storage still had the starting content of hydrogen peroxide of 35> 3 $. The sieve analysis showed a share of about 15 $ <0, h nsn, during. the major part was 0.8 mm.

Example 3

A mother liquor saturated at 20 ° C. from the carbamide perhydrate crystallization (without stabilizers) is used to adjust the pH value to be maintained according to the invention between 2 and 3. 5 each with 1 ^ o monosodium phosphate (a) and / or ^, JT-dimethylaminomethane-diphosphonic acid (b). The solutions prepared in this way were heated to 50 ° C. for 5 μl and the pH was determined every hour. Before and. after storage, the water peroxide content was also determined (Table 2).

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Table 2

Experiment No. 0 H to 1 1 2 3 A H + B stabilizer 1 H - A B 2.3 pH value after 2 H 1 7.0 4.6 2.1 2.6 3 H i 7.8 5.0 2.3 2.7 4 H 3 8.1 5.4 2.4 2.7 5 H 8.4 5.6 2.4 2.8 in front On- 8.6 5.7 2.4 2.8 f ° 8.7 5.8. 2.5 H 0 content 1 7.9 storage 7.3 17.7 17.7 H 0 content 1 7.7 warehousing 1.9 17.2 17.5 H 0 loss 1.1 relative 1.2 2.3 1.1

The comparative solution without stabilizer additive is, after only one-hour warming to 50 C alkaline and. the decomposition loss of hydrogen peroxide reaches 31.2 ^ after 5 h. On the other hand, with the addition of phosphonic acid alone or in admixture with monosodium phosphate, the pH range according to the present invention of 2 to 5 is surely maintained even with prolonged tempering. The hydrogen peroxide loss is very low at $ 1.1. Ausreicnende.e values were achieved even when using Monosatriumphospfaat, however, the desired range is already exceeded during prolonged thermal stress this without ever reaching the alkaline range.

example H

By adding 11Ö g of Carbamid.-perhydrate, 5 S phosphonic acid and 120 g of urea (2 mol) to 300 ml of water and tempering to 10 C, a saturated under these conditions solution was prepared. 79 ml 70 Ma .-% hydrogen peroxide (about 2 mol) were added with stirring and.

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Tempering to 10 C at different speeds added. 20 min after dosing, the carbaraid perhydrate crystals formed were separated, dried and. the content of fines 40.4 determined. The results are summarized in Table 3 V

Table 3

H _? Ο - Dosing speed Mol / l.min Fe inlc ο man t e i 1 ml / min 0.05 <0.4 mm 0.79 0.1 14.8 1.6 0.2 12.3 3.2 0.5 17.5  7.9 1.0 24.9 15.8 27.8

It becomes clear that with increasing dosing speed the proportion of fine particles increases.

Claims (8)

έ * ϊ * τ-. * s <* «4 Γ" / / η Q 1 K 1. A process for the preparation of a storage-stable carbamide perhydrate by reacting equimolar amounts of urea and hydrogen peroxide, characterized in that 50 to 90 Ma .- $, preferably .65 to 75 / iger er pererstoffperoxid at 5 to 25 C at a rate of 0.02 to 1.0 mol / l.min is metered to a recycled mother liquor containing urea, and one or more stabilizers, and. is adjusted to a pH of 2 to 5. 2. The method according to item 1, characterized in that the crystallization takes place in the presence of recirculated crystal nuclei with a residence time of at least 10 minutes, 3. Method according to point 1. and 2., characterized in that the recycled mother liquor as a stabilizer 0.01 to 2.0 $, preferably 0.1 to 0.5 $ of a suitable phosphonic acid _; preferably N / 2-J-dimethylaminoinethane diphosphonic acid or hydroxyäthandiphosphonsäure is added., k. Procedure according to point 1. and. 2., characterized in that d.er mother liquor additionally 0.5 to 2 % of an acidic phosphate, preferably monosodium phosphate od.er disodium pyrophosphate are added * £. * 4 ν / -j W W Claim for invention 5. The method according to the points 1 to k _t , characterized in that an additional stabilization of the % * Ml j / 3 aoa jo o - 16 - moist or dried final product by spraying stabilizer solution or mixing of
Stabilizers in solid form takes place. 6 » Process according to the points 1 to 5 ·» characterized in that the urea is also supplied to the recycled mother liquor at a rate of 0.02 to 0.2 mol / l.min. 7. The method according asu points 1 to 6, characterized in that the return of crystal nuclei by using a stationary, continuous stirred reactor takes place with Rückvennischung. 8. The method according to the points 1 to 5 ·> characterized in that the total quantity of urea is added to the recirculated mother liquor prior to the delivery of ass erstoffstoffperoxids. For this purpose 1 ropes drawings