HK1081937B - Method for producing dust-free alkaline earth peroxides - Google Patents

Description

Process for preparing dust-free alkaline earth metal peroxides

The invention relates to a method for producing agglomerates composed of alkaline earth peroxide, as well as to the alkaline earth peroxide agglomerates obtained by this method and the alkaline earth peroxide granules obtained thereby, wherein the alkaline earth peroxide primary granules undergo compressive compaction agglomeration.

The understanding of alkaline earth metal peroxides essentially refers to the products magnesium, calcium and barium peroxide and to the zinc peroxide chemically close to said products. The preparation of these peroxides is known from the prior art. DE 2918137 and DE 19650686 describe the preparation of peroxides by rinse drying of respective concentrated suspensions obtained by reacting hydrogen peroxide with the corresponding oxides or hydroxides.

The alkaline earth metal peroxide is prepared by the technology, the particle size of the alkaline earth metal peroxide is 1-10 mu m, and therefore the alkaline earth metal peroxide has high granularity; on account of this high degree of fines, the alkaline earth metal peroxide approaches very closely to dust, which is very disadvantageous for further processing of the alkaline earth metal peroxide in different applications.

The object therefore exists of producing more or less dust-poor alkaline earth metal peroxides which, on the one hand, have the advantageous properties of fine-grained starting products in subsequent applications and, on the other hand, can also meet the relevant chemical properties.

To solve this problem, the invention proposes a process for producing alkaline earth metal peroxide agglomerates, characterized in that fine-grained alkaline earth metal peroxides produced by known processes are compressed by briquetting in the presence of a finely divided (desintegriferend) or hydrophobic compression aid, and the alkaline earth metal peroxide thus obtained is optionally comminuted to the form of particles having the desired particle size.

The process according to the invention is carried out by subjecting the alkaline earth metal peroxide to which the compression aid has been added to a pressing process and simultaneously carrying out vacuum compression in the compression zone under the pressure used for this purpose. This produces the desired agglomerates. Since the agglomeration is achieved by pressure, this process is called press granulation or pressure granulation. Suitable additives can be added to the alkaline earth metal peroxide to be compressed, depending on the subsequent application.

The compression aid is used in an amount of 0.1 to 10% by weight, preferably 1 to 5% by weight, based on the finished product.

Although it is known to agglomerate crystals such as sodium perborate monohydrate, the application to fine alkaline earth peroxides is new. Surprisingly, it has been found that, depending on the compression aid added, agglomerates can be produced by means of press granulation, which agglomerates are dust-poor relative to the starting product. In addition, there are obvious differences in application technology depending on the choice of compression aid. In the case of compressed alkaline earth metal peroxides which, in aqueous suspension, retain as far as possible the application-technical properties of the original peroxide, compression aids are considered which have a finely divided nature, such as sodium bicarbonate, crosslinked silicone compounds, cellulose compounds. In the case of the desired application-technical properties, such as a delayed release of oxygen, compression aids consisting of salts of long-chain fatty acids, preferably magnesium montanate, i.e. substances having hydrophobic properties, are provided. The compressed alkaline earth peroxides prepared by both routes can be used directly (with significantly less dust load relative to the starting product) or as a slurry (because of the presence of the fines, there is only little consumption of the energy necessary for resuspension).

The temperature range in which the press-agglomeration method of the present invention is carried out may preferably be in accordance with a temperature range in which the alkaline earth metal peroxide used has high thermal stability and the method can be carried out without problems in terms of safety. The pressing of the small alkaline earth peroxide particles to form agglomerates is carried out, for example, in an advantageous embodiment of the invention at a temperature of between approximately 0 and 60 c, preferably between 20 and 60 c. The process is carried out without problems in such a range in view of the active oxygen content of the alkaline earth metal peroxide particles to be pressed; no loss of active oxygen content affecting the product was observed.

The process is preferably carried out in vacuo. Advantageously, the pressure is at most 0.25 bar.

Although the magnitude of the pressure applied and the degree of vacuum applied in order to achieve the advantages of the invention can be freely chosen within wide limits and is thus adapted to the specific wishes or requirements of the product. However, the pressure is determined by two preset conditions together, according to the following data: the pressure applied should at least be sufficient to make the agglomerates of the alkaline earth primary particles sufficiently strong to avoid troublesome dust in the subsequent application. The minimum pressure applied to achieve the desired characteristics depends on the type of pressing machine used and can be easily determined by the skilled person through a few preliminary tests according to the desired product characteristics. The upper limit of the pressure applied is not critical and is limited only by the respective technically highest achievable or permissible pressure of the machines used in pressing the briquettes. In an exemplary roll press, for example, the alkaline earth primary particles are compacted by pressing at a pressure of at least 1.5t to 2.5t per cm of roll length (-95 to 165 bar). In a preferred variation, compaction is performed at a pressure of 2.35t per cm of roll length (-145 bar). Wherein at the same time the (air) pressure in the compression zone of the press machine is set to at most 0.25 bar, i.e. processing under vacuum.

The agglomerates produced according to the invention can be shaped products (e.g. tablets) or agglomerated fillers (e.g. granules) which are relatively less prone to sintering or dusting in use and are therefore easier to meter. Not only the physical properties but also the agglomerate form or the particle form and the size are accordingly in accordance with the requirements of the application technology as described above. The desired product properties each determine an advantageous manufacturing method.

Essentially all conventional equipment for pressing the agglomerates can be used for the process according to the invention. Suitable briquetting apparatuses are, for example, presses, punches or roller presses. Depending on the compaction equipment used, the primary particles are either formed under pressure while under vacuum in the compression zone into a defined form (e.g. tablets) or compacted into a dense scabbed. The scab is crushed into particles in a desired size.

In a particularly advantageous embodiment of the process according to the invention, roller pressing is used. As long as the product obtained by pressing the agglomerates does not yet take the form of the final product, the resulting scabs can be comminuted by means of a granulator (granulation screen).

The alkaline earth metal peroxide particles according to the invention exhibit excellent meterable properties and dust-free properties with respect to very fine-grained starting materials and, depending on the compression aid, can be easily resuspended or are difficult to resuspend in particulate form due to their hydrophobic character and thus have a delayed oxygen evolution.

By the present invention a simple process for the preparation of dust-free alkaline earth peroxide granules is provided.

The following examples are intended to further illustrate the process without limiting it.

Examples

Example 1:

alkaline earth metal peroxides prepared according to the teaching of DE 2918137 and DE 19650686 are mixed with additives, such as magnesium montanate (manufacturer: Clariant, D-86368Gersthofen), Arbocell (type TF 0406, a fibrous cellulose, manufacturer: J.Rettenmaier und S ö hne, D-73494 Rosenberg) or sodium bicarbonate, and are placed in a roller press of simple construction for pressing the granules, the primary granules are pressed to a scab having a thickness of 1mm at a pressure of 2t/cm roller length (-130 bar) to 2.35t/cm roller length (-145 bar) and a vacuum of 0.75 bar (i.e. a pressure of 0.25 bar) and are subsequently adjusted to the target particle size by means of a crusher via a granulation screen.

The results of the experiments shown are given in table 1; % represents% by weight.

Example 2:

to investigate the fineness (Designationation), 50g of alkaline earth peroxide particles were stirred at 350rpm for 10 minutes in 250ml of water in a 500ml standard beaker with the aid of a stirrer (stainless steel stirrer with two vertical blades, 42mm long, 11mm wide, placed 1cm above the bottom of the beaker). The fines are the residual material on a 400 μm sieve in%.

Evaluation: analytical values > 55% indicate high fineness.

The results are shown in table 1.

Example 3:

to determine the attrition number, a 70g sample was screened to manually separate the fine fraction. Subsequently, the entire 50g are shaken on a corresponding sieve (1.0mm) for 3 minutes with a laboratory sieve JEL. The resulting fine fraction < 0.425mm gives the attrition number in [% ].

Evaluation: an analytical value of < 20% is an acceptable abrasion resistance of the compressed product.

Table 1:

product(s)	Compression aid	Fraction of compression aid (%)	Degree of attrition (%)	Fineness of division (%)
					IXPER®75C	Magnesium montanate NaHCO3Arbocell	251354	19.812.023.17.77.28.4	25.623.554.059.062.059.6
IXPER®35M	Magnesium montanate NaHCO3Arbocell	251245	17.916.422.918.014.216.7	24.618.952.255.760.258.6

IXPER^®75C is a Solvay Interox GmbH product having at least 75% by weight calcium peroxide.

IXPER^®35M is a Solvay Interox GmbH product having at least 35% by weight magnesium peroxide.

Claims (7)

1. Process for the manufacture of dust-free alkaline earth peroxide by compression, characterized in that a compression aid is incorporated into the dried alkaline earth peroxide and compressed under pressure while under vacuum in a compression zone, said compression aid having a finely divided or hydrophobic character.

2. The process for producing a dust-free alkaline earth metal peroxide according to claim 1, wherein the compression is carried out at a pressure of 95 to 165 bar and a vacuum of up to 0.25 bar in the compression zone.

3. Process for manufacturing non-dusting alkaline earth metal peroxide according to claim 1 or 2, characterized in that the compression is carried out at a temperature of 0 ℃ to 60 ℃.

4. The method for producing a dust-free alkaline earth metal peroxide according to claim 1 or 2, wherein sodium bicarbonate, a crosslinked silicone compound, a cellulose compound, or a magnesium salt of a long-chain fatty acid is used as the compression aid.

5. The method of making a non-dusting alkaline earth metal peroxide according to claim 4, wherein the compression aid comprises magnesium montanate.

6. The method for producing a dust-free alkaline earth metal peroxide according to claim 1 or 2, wherein 0.1 to 10 wt% of the compression aid is used based on the final product.

7. The method for producing a dust-free alkaline earth metal peroxide according to claim 6, wherein 1 to 5 wt% of the compression aid is used based on the final product.