CH650998A5 - PROCESS FOR STABILIZING AN AQUEOUS HYDROGEN PEROXIDE SOLUTION, SOLUTION THUS OBTAINED AND ITS USE FOR PERFORMING OXIDATION. - Google Patents

Description

The present invention relates to a process for stabilizing an aqueous solution of hydrogen peroxide, as well as to all the stable aqueous solutions obtained by the implementation of said process, mainly to concentrated solutions, for industrial use, the content by weight of hydrogen peroxide is between 27.5 and 70% corresponding, respectively, to solutions at 100 and 300 1 of gaseous oxygen releasable per liter of solution, and in the alternative to the extended commercial solutions, which release from 10 to 100 times their own volume of oxygen.

Additionally, the present invention relates to a process for using the oxidizing properties of an aqueous solution of hydrogen peroxide pre-stabilized according to the aforementioned technique.

Currently, it is known to make industrial solutions of hydrogen peroxide very stable under normal conditions of storage and handling.

Thus, the addition of small amounts of stabilizers, in particular tin salts, alone or in combination with other compounds derived from magnesium or phosphorus, allows hydrogen peroxide solutions to be stored at room temperature. with an active oxygen loss of less than 1% per year.

However, it is also known that certain bodies, compound or simple, catalyze the decomposition of hydrogen peroxide and cause an abundant release of active oxygen, detrimental to the yield of hydrogen peroxide solutions, which very often requires the use of these excess solutions.

Thus in the presence of alkaline and alkaline earth impurities, and even more in the presence of simple traces of metallic ions of silver, cobalt, chromium, copper, iron, manganese, nickel , thorium, zinc, the decomposition of hydrogen peroxide is catalyzed, hence also an obvious danger during storage and handling, when the oxygen loss becomes too great.

In the same spirit, it has been verified that any rise in pH, any rise in temperature, any exposure to ultraviolet rays, and any irregularity in the surface of the container (storage tank or reaction tank) promote the decomposition of peroxide. hydrogen as well as the presence of decomposition catalysts such as certain metals and metal salts from the above list.

Thus, for around fifteen years, these observations have led users of hydrogen peroxide to study its stability when said peroxide is more particularly stored in aluminum tanks.

We know that hydrogen peroxide has a corrosive action on aluminum, a corrosive action that conventional stabilizers, and in particular sodium stannate, do not succeed in destroying, because little by little they are coagulated by aluminum ions and thus lose their effectiveness as stabilizers.

To stop the coagulation of sodium stannate, it was then proposed to add to the hydrogen peroxide solution stabilized by stannate various products which sequester aluminum ions.

The patent of the United States of America No. 3429666 cites as suitable sequestrants some fluorides, the characteristic of all these fluorides being to form with aluminum ions a stable complex and solubilizes A1F6 ~ 3.

In the aqueous hydrogen peroxide solution thus protected, the sodium stannate which is and remains the only stabilizer retains all its effectiveness.

Furthermore, in the technique of bleaching skins, it is known to wash them in a solution of ferrous sulphate or ferri-que before immersing them in a solution of hydrogen peroxide until discoloration.

Ferrous ions decomposing hydrogen peroxide, it has been proposed to add to the ferrous or ferric sulfate bath fluorides intended to complex the iron before the addition of hydrogen peroxide in the bleaching bath.

U.S. Patent No. 2086123 suggests the addition of sodium, potassium or ammonium fluoride to complex the iron and put it in the form of ferrous fluorides which will not break down the hydrogen peroxide which will be added later.

From all the other observations, it follows that, in many cases of use of hydrogen peroxide, the excessive amounts of solution required, even the dangers of certain reactions, especially when the product is concentrated, in practice other products are used in place of hydrogen peroxide, although they are less effective than that of said peroxide.

In the foundry sector, a desired application of hydrogen peroxide is probably the best illustration

5

10

15

20

25

30

35

40

45

50

55

60

65

3

650 998

reservations that can be made about the use of said peroxide, taking into account the various incompatibilities presented by the reaction medium and the oxidation reaction for the implementation of this application with the usual techniques recommended for the best uses of hydrogen peroxide.

In this particular foundry application, consisting in making molds and cores from a composition of molding materials comprising a granular filler (sand), an acid hardening resin serving as a binder between the grains of the filler and at least a hardening peroxide of said resin, the resin is cold-polymerized by gassing with sulfur dioxide which, by reaction on the peroxides - in particular hydrogen peroxide - produces instantaneously, within the same charge, and at each of its points, nascent sulfuric acid.

In the case of this search for agglomeration of the grains of the filler by the resin polymerized during the formation of sulfuric acid, the proportion of granular filler is so important with respect to the amount of hydrogen peroxide put in work (for example 100 parts of granular filler for 0.10 to 0.50 part of hydrogen peroxide) that the common stabilizers introduced into the peroxide, effective during transport and storage, are unfortunately ineffective as soon as there is contact with sand: in addition to the fact that it would be necessary to use excess hydrogen peroxide, therefore increasing the costs of operations, it has been possible to verify that these excess are such that hydrogen peroxide is no longer practically used due to the addition of water, directly proportional to the amount of reacted peroxide, which disturbs the polymerization reaction of the resin.

In addition, it is known that the various granular fillers used in foundries, silica, corundum, sillimanite, alumina, chromite, olivine, zircon, contain impurities and in particular metal salts which are sufficient to catalyze the decomposition of hydrogen peroxide.

The alkaline nature of some of these fillers and finally the unfavorable configuration of all the fillers due to the fact that they have a maximum of roughness (multiplicity of grains and, by definition, rough appearance of these) can only accelerate decomposition of hydrogen peroxide.

Also, in the application example summarized above, the hydrogen peroxide, because of its instability, is almost always neglected in favor of other peroxides or other oxidizing agents, however more dangerous and more expensive.

The present invention therefore aims to provide a stabilization process as well as a process for the use of an aqueous solution of hydrogen peroxide which in all circumstances, including in the particular application in which it is cured, by action of sulfuric acid, a composition of grains of sand intimately mixed with a resin and hydrogen peroxide, by blowing sulfur dioxide transformed by the peroxide into sulfuric acid, permanently guarantee the maintenance of the stability of the hydrogen peroxide used in such an oxidation reaction.

The present invention therefore has as its first object a method for stabilizing an aqueous solution of hydrogen peroxide, characterized in that fluorine ions F ~ are added directly to said solution of hydrogen peroxide, which is thus pre-stabilized for future use.

The invention also relates to an aqueous solution of hydrogen peroxide, obtained by this process and characterized in that it contains at least one fluorinated compound as stabilizer.

The fluorinated compound is chosen from acids, such as hydrofluoric acid, fluosilicic acid, fluoboric acid, boron trifluoride, or from salts, such as bifluorides and fluorides - of ammonium, potassium, d 'tin -, fluosilicates, fluoborates - in particular tin - and, more generally, among all fluorine derivatives which, in the presence of water, hydrolyze by generating hydrofluoric acid.

In a preferred embodiment, the fluorinated compound (s) are added to the aqueous hydrogen peroxide solution in a proportion of 0.10 to 10% by weight.

It is very clear that any aqueous solution marketing hydrogen peroxide, therefore in the range of hydrogen peroxide content of 3 to 98% by weight, can according to the invention be stabilized before any application by addition of ions fluorine.

In practice, however, and although this is in no way limiting, the oxygenated water contents which will be essentially taken into account will be between the values of 27.5 and 70% by weight, taking into account the too high water contents below 27.5% and handling hazards beyond 70%.

Finally, the subject of the present invention is the use of an aqueous solution of hydrogen peroxide pre-stabilized with at least one fluorinated compound, to carry out an oxidation reaction, for example in its application in foundry for the transformation of sulfur dioxide to sulfuric acid, characterized in that the pH is controlled and maintained at a value of the order of 0.1 to 5, either by increasing the amount of fluorinated compounds, or by adding to the compounds fluorinated with a mineral acid, a mineral salt, a persalt or mineral acid perhydrate, or urea.

It will then be taken into account that the joint action of several of these elements is sometimes more effective than that provided by the same elements taken separately: therefore the choice of these additions will ultimately depend on the intended final application for the peroxide thus stabilized.

The pH corrector can be chosen from mineral acids, such as phosphoric acid, pyrophosphoric acid, meta-phosphoric acid, sulfuric acid, pyrosulfuric acid, per-oxysulfuric acid, peroxydisulfuric acid, nitric acid, boric acid, or among the salts of these acids such as phosphates, meta-phosphates, hexametaphosphates, sulfates, nitrates, borates, etc., or among persalts or perhydrates such as persulfates, perborates , per-carbonates, or among urea and percarbamide.

All these pH correctors can intervene either alone or in groups to reinforce the double action of fluorinated compounds: stabilization of hydrogen peroxide and better yield, as we will see a little later.

To better understand the advantages of the present invention, a description will now be given, by way of purely illustrative and nonlimiting example, of its application to the agglomeration of granular fillers which, without any doubt, currently constitutes one of the most common uses. more interesting for hydrogen peroxide, but also the most improper use since all the factors of decomposition of the peroxide - presence of metal ions, multiplicity of asperities and insufficient acidity - are combined.

In a standard series of experiments, mixtures were made with 1000 parts of a silica sand containing:

a) 0.09% Fe203,

b) 0.4% of A1203,

c) 0.4% MgO + CaO,

d) 0.03% K20 + Na20.

This sand was chosen voluntarily among those which contain a maximum of impurities, therefore among those which are the most difficult to agglomerate because of the loss of active oxygen which:

a) if it is not filled with an excess of hydrogen peroxide, causes a loss of sulfuric acid formed in situ, in which case the resin is under-catalyzed and the grains weakly agglomerated,

b) if it is filled with an excess of hydrogen peroxide, automatically generates a supply of water which disturbs the polymerization reaction of the resin just as much.

By mixing, the following were added to the silica sand:

- 13 parts of a cold hardenable furfuryl alcohol resin;

- 2 parts of hydrogen peroxide at 50% by weight.

From this composition of silica sand mixed with the resin and hydrogen peroxide, standard bending test pieces were produced which were tested with different qualities of fluorinated stabilizers proposed according to the invention, said test pieces, in the various qualities stabilizers, having been subjected to gassing by

5

10

15

20

25

30

35

40

45

50

55

60

65

650 998

4

sulfur dioxide, then broken after times of 15, 30, 60 and 120 s, 5, 20 and 60 min, then 24 h.

For all the test pieces, the same rest time of 1 hour was left between the end of the mixing and the start of gassing with sulfur dioxide.

The results obtained in these experiments are shown below in Table I.

In this table, the peroxide A is the control (commercial hydrogen peroxide at 50% by weight without additional stabilizer)

The comparison of the results obtained with the control peroxide A and the peroxides stabilized by an acid or a fluorinated salt provides the obvious demonstration of the improvement brought in surprising proportions by the incorporation of fluorine ions to the stability of the hydrogen peroxide. throughout its oxidation reaction transforming, within the composition of molding materials, gaseous sulfur dioxide into sulfuric acid which polymerizes the resin based on furfuryl alcohol.

From the same silica sand mixed in the same proportions as for the first series of tests with the same resin based

In this table where the peroxide A 'is the control hydrogen peroxide at 70% by weight without additional stabilizer, the peroxides G and H correspond to the same commercial hydrogen peroxide, of the same concentration, stabilized with:

- 3% fluoboric acid and 7% phosphoric acid 85% in peroxide G,

- 4% hydrofluoric acid, 3% 85% phosphoric acid and 7% sodium borate in H peroxide.

For short times and up to 120 s, the greater reactivity demonstrated by the last two peroxides G and H compared to the five peroxides B to F of the first tests is the normal consequence of the fact that the basic hydrogen peroxide used for the tests summarized in Table II has a lower water content than the base peroxide used for the tests summarized in Table I.

and the peroxides B, C, D, E and F correspond to the same commercial hydrogen peroxide, of the same concentration, stabilized by different fluorinated compounds incorporated in the hydrogen peroxide in an amount each of 3% by weight, namely:

- hydrofluoric acid HF in peroxide B,

- fluoboric acid HFB4 in peroxide C,

- fluosilicic acid H2SiF6 in peroxide D,

- sodium acid fluoride HNaF2 in peroxide E,

- tin fluoborate Sn (BF4) 2 in peroxide F.

cold curable furfuryl alcohol and a commercial hydrogen peroxide at 70% by weight this time, other standard bending swabs were produced, for the control on the one hand, and on the other hand for two mixtures stabilized in addition by a fluorinated compound, the said test pieces having been left to stand for 1 hour between the end of the kneading and the start of gassing with sulfur dioxide and having then been broken after times of 15, 30, 60 and 120 s, 5, 20 and 60 min, then 24 h.

The results obtained in these new experiments are reproduced in Table II.

By now comparing the fluorinated stabilizers used in the first experiments and summarized in Table I, it is observed that, in equal proportions, hydrofluoric acid, fluosilicic acid and tin fluoborate ensure the stability of the hydrogen peroxide slightly higher than that guaranteed by fluoboric acid and sodium fluoride.

60 Naturally, this proportion by weight of fluorinated compounds in hydrogen peroxide can vary, and in this regard it is necessary to take into account the extreme values of 0.10 and 10% of the weight of hydrogen peroxide, depending on the quality of the granular filler used according to the desired storage time for the premixing of 65 filler, resin and peroxide before blowing in. sulfur dioxide for the final hardening of the composition.

It is also obvious that with a charge other than that experienced, either with a higher content of metal ions, or more

Table I

Peroxides

Flexural strength (kg / cm2) after

15 s

30 s

60s

120s

5 min

20 mins

60 mins

24h

A (witness)

8.5

12

14.5

19.5

20.5

20

20

20

B

15.5

19

21.5

31.5

36.5

38

40

40

VS

15

18.5

23

29.5

32.5

34

33

35

D

15

18

20.5

30

34.5

36

38

39

E

13

16.5

19.5

28.5

31

33

32

32

F

15

18.5

22

30.5

35.5

38

40

39.5

30

35

Table II

Peroxides

Flexural strength (kg / cm2) after

15 s

30 s

60s

120s

5 min

20 mins

60 mins

24h

A '(witness)

11

14

16.5

20

20

20

20

20

G

18

22

24

31

35

37

39

38

H

20

25

28

32

37

39

40

40

strong alkalinity, the quantity of fluorinated stabilizing compounds will be advantageously increased, or in certain cases supplemented by at least one chemical compound correcting the pH, chosen from the following bodies:

a) a mineral acid such as phosphoric acid, pyro-phosphoric acid, metaphosphoric acid, sulfuric acid, pyrosulfuric acid, peroxysulfuric acid, peroxydisulfuric acid, nitric acid, l 'boric acid,

b) a salt of these mineral acids, such as phosphates, metaphos-phates, hexametaphosphates, sulfates, nitrates, borates, especially sodium, or among persalts or perhydrates, such as persulfates, perborates and percarbonates, especially sodium, being observed here that sodium perborate can prove to be particularly interesting since it has the advantage of releasing appreciable quantities of hydrogen peroxide which is added to the pure mixed peroxide, to the sand and to the resin,

c) urea and percarbamide.

The pH will for example be permanently adjusted to a value of the order of 0.1 to 5, this very acidic medium being justified by the simple fact that one is in the presence of hydrogen peroxide and of an acid. fluorinated and / or a fluorinated salt.

To illustrate the above, a mixture of silica sand was made, to which 2 and 4% of ferric oxide Fe304 were added. This prepared sand - instead of being used within 60 min following the addition of the resin and the peroxide, as was the case for the tests summarized above - was checked over time until that a loss of the initial characteristics of 10% is noted.

As a result, the characteristics of the table remained constant (to within 10%) during periods which were essentially variable depending on the degree of stabilization.

Thus, with 2% Fe304 in the sand, the degradation of the results appeared:

- after 90 min with peroxide A (control),

- after 4 h with peroxides B, C, D and E,

- after 5 'A h with peroxide F,

- after 6 Vi h with peroxide G,

- after 8 p.m. with peroxide H.

And when the addition of Fe304 was brought to 4% in the sand, the degradation of the results appeared:

- immediately with peroxides A and A '(controls),

- after 70 min with peroxides B, C, D and E,

- after 90 min with peroxide F,

- after 2 h with peroxide G,

- after 4 Vz h with peroxide H.

650 998

It can thus be seen that a correct choice of stabilizers makes it possible not only to significantly increase the mechanical characteristics obtained, thanks to a better yield, but also to remarkably prolong the preservation of the premix silica sand (more or less pure) with resin and peroxide, before use.

There is therefore a double improvement: one which relates to yield and efficiency, the other which relates to ease of use over time, and therefore ultimately to the flexibility of the process.

Likewise, it is obvious that the present invention is not limited to the stabilization of hydrogen peroxide for the foundry application described above. Indeed, the fluorinated compounds which stabilize the hydrogen peroxide can be used each time the said peroxide risks losing its active oxygen, for example in the presence of metal ions or alkaline and alkaline earth impurities, but also whenever any peroxide, peracid or persalt, is in the presence of a decomposition catalyst.

Another application of the invention can for example be given in the field of the production of insulating panels,

in which beads of ceramic, glass or expanded or unexpanded polystyrene are agglomerated to each other by a binder polymerized by the action of hydrogen peroxide.

It is quite obvious that, if one of the applications of the hydrogen peroxide solution stabilized according to the invention with at least one fluorinated compound requires a correction of the pH, either before or during the reaction, or an adjustment of the pH to a constant value throughout the duration of the reaction, depending on the application considered:

- either a solution of peroxide normally stabilized by the fluorinated compound, and completed before or during the reaction of this same fluorinated compound or of a correcting acid, salt or urea,

- Or a peroxide solution normally stabilized by the fluorinated compound, and permanently adjusted to the desired pH by controlled addition of one of the correctors given above; a relatively slow speed of the oxidation reaction will easily allow such constant control and adjustment of the pH of the composition to be treated.

The examples of applications and the test results which have just been given fully illustrate the original role of the fluorine ions F-, highlighted by the holder, this role being to stabilize all the hydrogen peroxide solutions, also both during storage and during their various uses, whereas, until today, it was only known to use the properties of certain fluorides to sequester aluminum ions or to complex iron.

5

5

10

15

20

25

30

35

40

45

R

Claims (10)

650 998 1. A method for stabilizing an aqueous solution of hydrogen peroxide, characterized in that fluorine ions F are added directly to said peroxide solution. 2. Method according to claim 1, characterized in that the fluorinated compound added directly to the hydrogen peroxide solutin is chosen from fluorinated acids, such as hydrofluoric acid, fluosilicic acid, fluoboric acid, boron trifluoride, or among fluorinated salts, such as bifluorides and fluorides, fluosilicates, fluoborates, and more generally among all fluorine derivatives which, in the presence of water, hydrolyze generating hydrofluoric acid. 2 3. Method according to one of claims 1 or 2, characterized in that from 0.10 to 10% by weight of fluorinated compound is added to the hydrogen peroxide solution. 4. Aqueous solution of hydrogen peroxide obtained by the process according to claim 1, characterized in that it contains at least one fluorinated compound as stabilizer. 5. Solution according to claim 4, characterized in that it contains from 0.10 to 10% by weight of fluorinated compound. 6. Solution according to one of claims 4 or 5, characterized in that the fluorinated compound is chosen from acids, such as hydrofluoric acid, fluosilicic acid, fluoboric acid, boron trifluoride, or among the salts, such as ammonium, potassium, or tin bifluorides and fluorides, fluosilicates and fluoborates, in particular tin, and more generally among all fluorine derivatives which, in the presence of water, hydrolyze generating hydrofluoric acid. 7. Use of the aqueous hydrogen peroxide solution obtained by the process according to claim 1 for carrying out an oxidation reaction, characterized in that the pH is controlled and maintained at a value of the order of 0.1 to 5. 8. Use according to claim 7, characterized in that the pH is maintained at the desired value by increasing the amount of fluorinated compound. 9. Use according to claim 7, characterized in that the pH is maintained at the desired value by adding to the fluorinated compounds a pH correcting agent chosen from the following compounds: mineral acid, mineral salt, persalt d 'mineral acid, mineral acid perhydrate, urea and percarbamide. 10. Use according to claim 9, characterized in that the pH correcting agent is chosen from the following mineral acids: phosphoric acid, pyrophosphoric acid, meta-phosphoric acid, sulfuric acid, pyrosulfuric acid, per-oxysulfuric acid, peroxydisulfuric acid, nitric acid and boric acid, or among the salts of these acids, such as phosphates, metaphosphates, hexametaphosphates, sulfates, nitrates, borates, or also among their persalts and their perhydrates, such as persulfates, perborates and percarbonates.