DE1057586B - Process for regulating the water of crystallization of alkali perborate - Google Patents

Description

GERMAN

The present invention relates to a method for regulating the water of crystallization content of alkali perborate, especially sodium perborate, by reacting alkali metaborate with hydrogen peroxide in a continuous process.

In the continuous preparation of alkali perborate, a metaborate solution already containing perborate is used continuously fed to a reaction vessel and by continuously feeding Alkali perborate is supersaturated with Met aborate. The resulting crystal slurry is removed from the reaction vessel withdrawn and the lye still containing perborate in the circuit after replenishing the consumed metaborate returned to the reaction vessel. The starting components alkali metaborate and hydrogen peroxide do not necessarily have to be used as such, rather Metaborat can also be used in an known way z. B. from alkali tetraborate and alkali hydroxide or from boric acid or even made from boric anhydride and alkalis and thus introduced into the process. Next to the Hydrogen peroxide can also be used containing mixtures or compounds that contain Supply hydrogen peroxide, e.g. B. sodium peroxide. If you try such a procedure alongside the sodium perborate tetrahydrate commonly used in industry, alternating with sodium perborate trihydrate To win, it is obvious to carry out the perborate crystallization in the realm of existence of the trihydrate, because it is known that sodium perborate trihydrate in comparison to the tetrahydrate above 15 ° C is the stable modification.

It has now been shown, however, that the temperatures are by no means the decisive factor for the result of the crystallization with regard to the state of hydration and that trihydrate and tetrahydrate cannot be obtained with certainty in pure form by carrying out the perborate crystallization above or below the transition point . Rather, it has been found that the composition of the crystallized liquor is far more decisive with regard to the ratio of the components forming the alkali perborate. It depends above all on how the free alkali, the active oxygen carrier and the boron carrier, i.e. the meta-Ιμιγ.ίΙ ιiiU'i "'IYt 1:11 χ) raI, in relation to the slöehiomet π shy composition (U's Nal' O ,, · IL ₁₎ (X _-, in li''gi'ii l'niiiiia I 'i ^ ilil uiili Tin ilir I cri'iilliiutMiiif;.! IRDP f>"crystal water content following the presentation of perborate new rule technical Action:

For the continuous crystallization of Alkalipe H> n rat Ie. trot yd rat must the crystallization liquor Procedure for regulation

the water of crystallization

of alkali perborate

Applicant:

German gold and silver refinery

formerly Roessler, Frankfurt / M., Weißfrauenstr. 9

Dr. Ernst Wagner, Dr. Helmut Brünner and Albert Langenfeld, Rheinfelden,

have been named as inventors

in addition to the ratio Na + BO ₂ ~, they also _{contain B 4} O ₇ ^-2 or BO, ~. In contrast, they must not contain any free alkali or free active oxygen.

For the continuous crystallization of alkali perborate tribydrate, the crystallization liquors must contain free alkali and free excess active oxygen in addition ^{to Na +} BO ₂ ^- -H ₂ O _2.

It follows that solely from the alkali composition according to the above-mentioned aspects the representation of perborate tetrahydrate or perborate trihydrate is controlled arbitrarily can be, largely independent of the temperature at which the crystallization takes place. Nevertheless, according to a preferred embodiment, when carrying out the invention, the Crystallization of tetrahydrate in the temperature range between 5 and 30 ° C, that of trihydrate in the Set a temperature range between 20 and 50 ° C.

The excess which comes into consideration for the individual components which are decisive for the type of hydrate formation can vary within certain limits. It is advantageous to add in an excess of 5 to 10% of the components used in a superstoichiometric manner _{via the NaBO 2} ^- H ₂ O _{2 ratio.}

As an example of the implementation of the procedure according to the Krlindunig is in the table below K i'itiliilli'iiil HHiiiVrHiiiii in the mouth of the hu-ii in certain Lye composition resulting from time intervals shown. The respective alkali analysis is included converted to the content of pcrborate-free alkali and free active ingredient in niMol / l compared to the

stoichiometric composition of NaBO ₂

the feed of the components was regulated in such a way that

H ₂ O ₂ . In addition, the last column of the table shows that the ratio NaBO ₂

the active oxygen content (Oa) in the crystallized salt listed.

hour NaBO ₂ Perborate Free
N / A*) Suitor
Oa Oa
in the salt mmol / 1 mmol / 1 mmol / 1 mmol / 1 ° / o 13th 42 118 n.d. *) 15th 22nd 118 30th - 10.48 17th 58 112 10 n.b. 19th 23 137 10 - 10.48 21. 25th 75 - n.b. 23 - 120 .— 36 10.54 25th - 130 20th 76 n.b. 27 - 140 --- 84 11.86 29 - ■ 120 30th 55 n.b. 31. - ■ 110 20th 108 11.84 33. - 100 30th 100 n.b. 35. - 70 30th 86 11.82 37. - 80 40 115 n.b. 39. - 80 20th 120 11.82

*) Not determined.

Although the entire crystallization took place in the temperature range between 40 and 45 ° C and thus in the area of existence of the sodium perborate trihydrate, one can see from the active oxygen content of the salt which crystallizes between the 13th and 23rd hour that pure tetraborate was deposited here, as long as there was an excess free active oxygen was not present in the liquor, but this contained free BO., ~. After free active oxygen was available after the 23rd hour of H ₂ O ₂ , but the free boron disappeared and free sodium + was also present, the crystallization changed significantly to the perborate trihydrate, as the sudden increase in the active oxygen content in the crystallized salt shows.

Claims (3)

Patent claims: 1. Process for regulating the water of crystallization of alkali perborate in its continuous Obtained by reacting alkali metaborate with hydrogen peroxide, characterized in that that for the formation of tetrahydrate per 1 mol of active oxygen and alkali more than 1 mole of boron in the form of boron compounds, especially sodium tetraborate, and for the formation of Trihydrate to 1 mole of boron or sodium metaborate or sodium tetraborate more than 1 mole of active oxygen and alkali in the form of alkali hydroxide or in solution such forming compounds in fed into the crystallization cycle. 2. The method according to claim 1, characterized in that the overstoichiometrically fed Components are used in an excess of 5 to 10%. 3. The method according to claim 1 or 2, characterized in that for the production of tetrahydrate the crystallization in the temperature range between 5 and 30 ° C and for the extraction of Trihydrate is carried out between 20 and 50 ° C. 909 527ß88 5.59