EP1263680A1

EP1263680A1 - Method for directly obtaining hydrogen peroxide

Info

Publication number: EP1263680A1
Application number: EP01907809A
Authority: EP
Inventors: Michel Devic
Original assignee: Atofina SA
Current assignee: Arkema France SA
Priority date: 2000-03-17
Filing date: 2001-02-15
Publication date: 2002-12-11
Also published as: AU3568501A; CN1411422A; WO2001068519A1; JP4175534B2; CN1225403C; AU2001235685B2; FR2806399B1; FR2806399A1; KR20020092387A; KR100584636B1; CA2402803C; CA2402803A1; US20030086853A1; JP2003527283A; US7060244B2

Abstract

The invention concerns a method for making an aqueous solution of hydrogen peroxide. More particularly, it concerns a method for making hydrogen peroxide directly from hydrogen and oxygen, finely dispersed in an aqueous acid medium comprising a catalyst and at least a surfactant. The invention also concerns a device for implementing said method.

Description

PROCESS FOR THE DIRECT PRODUCTION OF HYDROGEN PEROXIDE

The present invention relates to a method of manufacturing an aqueous solution of hydrogen peroxide. More particularly, it relates to a process for the manufacture of hydrogen peroxide directly from hydrogen and oxygen, dispersed in an aqueous reaction medium in the presence of a catalyst. The present invention also relates to a device for implementing said method. A process for the production of hydrogen peroxide directly from hydrogen and oxygen, according to which hydrogen and oxygen are dispersed in an aqueous reaction medium at acid pH has been described in international applications WO 92/04277 , WO 96/05138 and patent application FR 2 774 674. The process described in these international applications is implemented in a tubular reactor, completely filled with a working solution in which the hydrogen and oxygen are dispersed , while that of the French patent application is implemented in a stirred reactor comprising a liquid phase containing the working solution and a continuous gas phase.

The working solution used both for the tubular reactor process and for that in the stirred reactor, comprises water, acid and optionally decomposition inhibitors or stabilizers of hydrogen peroxide. Hydrogen and oxygen are dispersed in the aqueous reaction medium, consisting of the working solution and the catalyst, in proportions above the lower flammability limit of the hydrogen-oxygen mixture. A very fine dispersion of hydrogen and oxygen is even required in the process described in documents WO 96/05138 and FR 2 774 674.

To avoid any risk of explosion, the document WO 96/05138 recommends injecting hydrogen and oxygen at very high speed into the tubular reactor, by imposing the injection of oxygen at a more advanced level in the direction displacement of the aqueous medium relative to that of hydrogen. The Applicant has now found that the presence of a surfactant in an aqueous reaction medium, as described above, surprisingly increases the productivity. The surfactant also makes it possible to work with a hydrogen / oxygen ratio in the aqueous reaction medium below the lower flammability limit of the hydrogen-oxygen mixture.

A first object of the present invention is a method of manufacturing an aqueous solution of hydrogen peroxide directly from hydrogen and oxygen. This process by which hydrogen and oxygen are injected, in the form of small bubbles, into an aqueous reaction medium made acid by the addition of an inorganic acid and comprising a catalyst in the dispersed state is characterized in that the aqueous reaction medium also comprises one or more surfactants.

The term “small bubbles” is intended to denote bubbles whose average diameter is less than 3 mm, preferably, of average diameter between 0, 1 and 2 mm.

Any surfactant stable in an acid medium, preferably at a pH of 1 to 3, and resistant to very oxidizing conditions (oxygen under high pressure and hydrogen peroxide) may be suitable. All molecules consisting of a hydrophilic part (polar head) and a hydrophobic part can be used as a surfactant. By way of example, mention may be made of dimethyl lauryl amine oxide (CH3) ₂ CnH ₂₃ NO; mono and di-phosphoric including C ₈ H ₁₇ - O - PO (OH) ₂ , (C ₈ H ₁₇ -O) ₂ -POOH, C ₉ H ₁₉ - C ₆ H ₄ - O - PO (OH) ₂ and C9H ₁ 9 - C ₆ H ₄ - O) ₂ - POOH; alkyl benzene sulfonic acid

RC ₆ H - SO ₃ H, R can be for example an alkyl chain C n H ₂₃ or C9H- ₁ 9; naphthalene sulfonic acid R - Cι ₀ H ₆ - SO ₃ H; alkyl sulfonic acid R - O - SO H; polyoxyethyl sulfonic R- (OC ₂ H ₄ ) _n - OSO3H and R - C ₆ H ₄ - (OC ₂ H ₄ ) _n - OSO ₃ H. Fluorinated surfactants are particularly suitable because of the chemical stability and the hydrophobicity of the fluorocarbon chain. Indeed, fluorinated surfactants make it possible to lower the surface tension of water to 15-20 mN.rrf ¹ (Actualité Chimique, July 1999 page 3). The hydrophilic chain of these fluorinated surfactants can be chosen from acid or polar groups having good chemical stability, such as for example - SO ₃ H, - COOH, - PO (OH) ₂ . By way of example, mention may be made of fluorinated surfactants of general formula

C _n F _{2n + 1} - Q - G or C _n F _{2n + 1} - G in which: Q denotes a spacer arm, such as for example C ₂ H

G denotes a hydrophilic group, such as for example - SO ₃ H, - COOH, -O-PO (OH) ₂ , - PO (OH) ₂ .

The following surfactants: • C ₇ Fιs - COOH

• C ₆ F ₁₃ - (CH ₂ - CH ₂ - O) _n H

• C ₆ F ₁₃ - C ₂ H ₄ - SO ₂ - NH - C ₃ H ₆ - N ⁺ (CH ₃ ) ₂ CH ₂ - COOH and C ₆ Fi3 - HC (CH2CI) - O - PO (OH) ₂ are particularly preferred. The amount of surfactant used is not critical. It is sufficient that it is less than the minimum amount necessary to cause the appearance of the foams on the surface of the aqueous reaction medium.

The amount of surfactant used is preferably between 50 to 90% of this minimum amount. The optimal amount of surfactant involved depends on its nature and on the composition of the aqueous solution constituting the initial aqueous reaction medium.

The presence of a fluorinated surfactant in an amount of 1 to 50 ppm and preferably in an amount of 5 to 10 ppm in the aqueous reaction medium has given interesting results.

As inorganic acid, mention may in particular be made of sulfuric acid, orthophosphoric acid and nitric acid. The acid is used in an amount sufficient to preferably maintain the pH of the aqueous reaction medium between 1 and 3. The aqueous reaction medium can also contain stabilizers of hydrogen peroxide, such as, for example, phosphonates or tin, and decomposition inhibitors, such as, for example, halogen derivatives.

The stabilizing agents are generally present in the aqueous reaction medium at a rate of 100 to 5000 ppm. The stabilizing agents used can be chosen from commercial products or aminophosphonic acids of general formula RιR ₂ N - CH ₂ - PO (OH) ₂ . When the aqueous reaction medium is made acidic by orthophosphoric acid, the use of a stabilizing agent is not necessary.

The preferred halogen derivatives are chosen from alkali metal bromides and chlorides, hydrobromic acid, hydrochloric acid and bromine in the gaseous state or in solution in water (bromine water). Advantageously, bromide is used and, preferably, in combination with bromine in the free state (Br ₂ ).

The amount of bromide (in the form of NaBr or of HBr), when it is present in the aqueous reaction medium is generally between 10 and 200 ppm and preferably between 20 and 100 ppm. The amount of bromine (Br ₂ gas or in solution in water), when it is present in the aqueous reaction medium is generally between 1 and 50 ppm and preferably between 2 and 10 ppm.

The catalyst used is generally a supported catalyst based on at least one metal chosen from the group M formed of palladium, platinum, ruthenium, rhodium, iridium, osmium, holmium and gold and, in particular, a supported bimetallic catalyst. The supported bimetallic catalyst generally consists of a metal from the majority group M and another metal from the minority group M. The majority metal represents approximately 0.1 to 10% by weight of the catalyst and preferably between 0.5 to 1% by weight. The minority metal represents approximately 0.001 to 0.1% by weight of the catalyst and preferably between 0.01 and 0.05%.

As the majority metal, palladium and gold are advantageously chosen.

As a minority metal, platinum and holmium are advantageously chosen.

The particularly preferred supported bimetallic catalyst consists of palladium as the majority metal and platinum as the minority metal.

As the supported plurimetallic catalyst consisting of a metal of majority group M and of several other metals of minority group M, it is preferred to use that comprising palladium, as majority metal, platinum and at least one metal of group M other than palladium and platinum, as minority metals. The content of majority metal in the supported plimetallic catalyst is practically the same as that of the predominant metal in the bimetallic catalyst and, each minority metal can be present in the catalyst in an amount representing approximately 0.001 to 0.1% by weight of the catalyst and preferably between about 0.01 and 0.05%.

In the case of a supported monometallic catalyst, it is preferred to choose palladium or gold as metallic constituent of group M with a content generally between 0.1 and 10% by weight of the catalyst and preferably between 0.5 and 1% by weight. Although alumina, charcoal and silicoaluminates may be suitable as a support, it is however preferred to use silica and advantageously, silica particles of average size between 1 and 50 μm. It is also preferred to use silica with a BET specific surface greater than 200 m ² / g and most often between 300 and 600 m ² / g. The idrich microporous silica referenced 28.851 -9 has been found to be particularly advantageous.

The level of iron (Fe) in the support chosen is preferably less than 0.001% by weight.

The catalyst used in the process of the present invention can be prepared according to the method described in US 4,772,458, but it is preferred to prepare it according to the method consisting of: a) bringing a support, chosen from the group formed by silica, alumina, carbon and silicoaluminate, with a concentrated aqueous solution of salt (s) of at least one metal from group M so as to form a paste b) followed by filtration , wringing, then drying of the dough under conditions promoting slow crystallization c) then by reduction under hydrogen at about 200 to 400 ° C of the dried solid of step (b) d) then by treating the solid reduced from step (c) with an acidic aqueous solution (A), comprising bromine and bromide ions, at a temperature between 10 and 80 ° C. e) and finally, filtration of the solid treated in step ( d) and drying at a temperature between 100 and 140 ° C. The pH of the solution (A) is preferably between 1 and 3. The concentration of bromide ions in the solution (A) can be between 20 and 200 mg / l and preferably between 20 and 100 mg / l, and the bromine (Br ₂ ) concentration can be between 2 and 20 mg / l. According to the process of the present invention, it is possible to operate both continuously and semi-continuously.

The process can be carried out in a stirred reactor comprising a stirring system allowing the dispersion of the gases in a liquid phase, and provided with an internal or external cooling system capable of removing the heat of the reaction.

The agitated reactor can be, for example, a cylindrical autoclave provided with one or more stirring mobiles of the type of those used for gas-liquid reactions (self-aspirating turbine, flanged turbine, turbines with concave blades, etc.) and d '' an internal cooling system consisting of a coil, vertical tubular bundles or a flat or tubular spiral.

The usual reactors for carrying out hydrogenation reactions are very suitable. The process can also be implemented in a loop reactor, consisting of a reactor and a high-flow pump located outside the reactor sucking the aqueous reaction medium in the lower part of the reactor and returning it to the the top part. A heat exchanger can be placed in the circulation loop as well as a gas injection system (oxygen; hydrogen) such as for example a venturi.

The rapid circulation of the aqueous reaction medium ensures stirring in the reactor and the dispersion of the bubbles.

The process according to the invention can also be implemented in a tubular reactor made up of one or more tubes of great length.

Whatever the reactor, the temperature and the pressure inside are adjusted to optimize the selectivity of the reaction with respect to hydrogen and the productivity of hydrogen peroxide. This temperature is generally between 5 and 90 ° C and preferably between 30 and 60 ° C.

The pressure inside the reactor is generally above atmospheric pressure and preferably between 10 and 100 bars.

Although hydrogen and oxygen may be present in the aqueous medium, in proportions corresponding to the flammability range of the hydrogen-oxygen mixture, it is most often preferred to inject hydrogen and oxygen in the form of small bubbles. separately, with flow rates such that the ratio of hydrogen to oxygen molar flow rates is less than 0.0416.

When operating semi-continuously, the aqueous solution of hydrogen peroxide at the end of the reaction is separated from the catalyst then, optionally free of additives such as surfactants, inhibitors and stabilizers. The additives can thus be recovered and used in a new operation.

When operating continuously, the separation of the catalyst from the aqueous hydrogen peroxide solution and that of the additives can be carried out continuously.

The separation of the additives from the aqueous hydrogen peroxide solution is preferably carried out by reverse osmosis using membranes, identical to those used for the desalination of seawater. The transmembrane pressure is between 20 and 130 bars and preferably 30 to 80 bars depending on the type of membrane.

Preferably 1 to 3 separation stages are used. Preferably, the permeate flow rate is between 0.7 and 0.95 times the supply flow rate of the stage. Preferably, the membranes used are of the bilayer type (2 layers of superimposed polymers including at least one layer of polyamide), or else of the tri-layer type (3 layers of superimposed polymers of which at least one layer of polyamide).

As the two-layer membrane we used the "DOW Filmtec - SW30" membrane and as the three-layer membrane we used the "OSMONICS-DESAL 3" membrane.

A second object of the invention is a device allowing the implementation of the method as described above. This device shown diagrammatically in FIG. 1 comprises a reactor 1, provided with one or more inlets (2) of gaseous hydrogen and one or more inlets (3) of gaseous oxygen, with a liquid inlet (5 ), a liquid outlet (4) and a gas outlet (6), which can possibly be connected to the inlet (3). According to a variant, the outlet (4) is connected to a filter (7), which is itself connected to membranes (8).

A device and an operating diagram, illustrating a particular embodiment of the method of the present invention, represented in FIG. 2, are described below. The device comprises a stirred reactor 1, provided with several centrifugal turbines arranged along a single vertical stirring shaft. At start-up, the reactor contains the catalyst in suspension in the aqueous solution containing the surfactant, the inhibitor and the stabilizer, the whole being brought to reaction temperature

Is injected separately, using two contiguous nozzles placed under the suction port of the turbine located at the bottom of the reactor, the new hydrogen in 2 and oxygen in 3, in the form of small bubbles, into the lower part of the reactor The flow rates of hydrogen in 2 and of oxygen in 3 are chosen so as to obtain a gaseous composition in the aqueous reaction medium, preferably non-flammable, that is to say with a concentration of hydrogen not exceeding the lower flammability limit of the hydrogen-oxygen mixture at the pressure prevailing inside the reactor In general, this limit is 4% by volume of hydrogen at 1 bar (absolute) and 6% at 50 bars

New oxygen is injected in 4, in the upper part of the reactor, occupied by the continuous gas phase, to replace the oxygen consumed and also to keep the composition in this phase below the lower flammability limit of the mixture. hydrogen- oxygen

The oxygen injected at 3 comes partly or entirely from the gas flow taken at 5 and circulated by the pump 6 II can contain a small amount of unreacted hydrogen The oxygen used can contain a small proportion of inert gases such as than those present in the air, for example nitrogen or argon

When the oxygen is accompanied by inert gases, it is then necessary to carry out purges, using the control valve 7, so that the concentration of inert gases in the continuous gas phase is less than 50% by volume. and preferably less than 30%

The temperature of the reaction medium is kept constant by circulation of cooling water in the coils 8

The aqueous solution containing the hydrogen peroxide formed leaves the reactor via outlet 9, then is cooled in exchanger 10 and then filtered into 1 1 The catalyst suspension which has not passed through the filtering surface 1 1 returns to the reactor at 13. The filter at 1 1 is alternately unclogged by injection against the flow of demineralized water optionally containing acid and additives ( surfactant, inhibitor, stabilizer) at 14 across the filtering surface. The resuspended catalyst returns to the reactor at 13.

The clear aqueous solution of hydrogen peroxide from 1 1 is then introduced into the battery of reverse osmosis membranes 12. The permeate of the n ^th cell is introduced into the cell (n + 1) and the retentate (or concentrate) returns to the reactor at 13 and so on for each stage of the reverse osmosis unit.

The permeate in the last cell is an almost pure aqueous solution of H ₂ O ₂ 15. Most of the additives are recycled to the reactor at 13.

Demineralized water is introduced at 14 to keep the level of the liquid phase constant in the reactor. The additives (surfactant, inhibitor, stabilizer) are added to this water to maintain their constant contents in the aqueous reaction medium. A device and an operating diagram shown in the figure

3 illustrate another particular embodiment of the method of the present invention.

The device of Figure 3 comprises a reservoir 21 containing at startup the aqueous solution containing the additives and the suspended catalyst.

A pump 17 circulates at high speed this aqueous suspension of catalyst in a tubular reactor 1, consisting of one or more tubes of great length immersed in a thermostatted bath 20. The oxygen is withdrawn at 5 from the continuous gas phase of the reservoir 21 by means of the compressor 6, then injected at 3 into the tubular reactor, in the form of small bubbles by means of the venturi 18 and thanks to the high speed of circulation of the aqueous suspension of catalyst.

The new oxygen is injected in 4 into the continuous gas phase of the tank 21. The new hydrogen 2 is injected in the form of small bubbles into the tubular reactor 1 also by means of the venturi 18. At the outlet of the tubular reactor, the aqueous suspension of catalyst and the unreacted H ₂ and O ₂ bubbles are returned at 16 to the tank 21.

The aqueous solution of hydrogen peroxide containing the suspended catalyst is taken at 9 from the tank 21 by the pump 19 and then feeds the filter 11. The excess catalyst suspension is returned to 13 in the reactor.

The filtered H ₂ O _{2 solution} leaves at 15 from filter 1 1. The filter 1 1 is periodically unclogged by injection of the acidic aqueous solution at 14, (the outlet 15 is then closed).

A pressure regulator 7 removes excess O ₂ and H ₂ and inert gas from the reactor. A reverse osmosis unit can also be connected to outlet 15 to recycle the additives.

EXPERIMENTAL PART

Device for the direct synthesis of an aqueous solution of hydrogen peroxide

The device is similar to that shown in Figure 2.

The reactor with a capacity of 1,500 cm ³ consists of a cylindrical tank 200 mm high and 98 mm in diameter.

The bottom and the cover are flat.

A removable 1.5 mm thick PTFE sleeve is placed in the reactor bowl.

Agitation is ensured by a vertical stainless steel axis 180 mm long and 8 mm in diameter driven by a magnetic coupling placed on the cover of the reactor.

Two or three flanged turbines with an outside diameter of 45 mm, a thickness of 9 mm (between the two flanges) fitted with a suction port of 12.7 mm in diameter, oriented downwards, and 8 radial blades plates 9 mm wide, 15 mm long and 1.5 mm thick, can be fixed to the stirring shaft at different heights chosen so as to divide the liquid phase into substantially equal volumes.

The lower turbine is placed 32 mm from the bottom, the second turbine 78 mm from the bottom and the third turbine 125 mm from the bottom. Four counter blades 190 mm high, 10 mm wide and 1 mm thick are placed vertically in the tank perpendicular to the inner wall of the reactor and held 1 mm from this wall by two centering rings. Cooling or heating is provided by eight vertical tubes of 6.35 mm in diameter and 150 mm in length arranged in a crown 35 mm from the axis of the tank.

This stream is traversed by a stream of water at constant temperature.

The injection of hydrogen and oxygen into the liquid phase is done by means of two separate stainless steel pipes, 1.58 mm in diameter for H ₂ and 3.17 mm for O _2, leading the gases to the center of the lower turbine. The injection of gaseous reactants into the aqueous medium as well as that of oxygen into the continuous gas phase are regulated using mass flowmeters. Some tests have been carried out by replacing the oxygen with an oxygen-nitrogen mixture in different proportions.

The pressure inside the reactor is kept constant thanks to an overflow valve. The hydrogen, oxygen and optionally nitrogen constituting the gas flow leaving the reactor are dosed online by gas phase chromatography.

Preparation of the catalyst The catalyst used contains 0.7% by weight of metallic palladium and 0.03% by weight of platinum supported on a microporous silica.

It is prepared by impregnating silica (Aldrich ref. 28,851 -9) with the following characteristics:

- Average particle size = 5 to 15 μm - BET surface = 500 m ² / g

- Pore volume = 0.75 cm ³ / g

- Average pore diameter = 60 A, with an aqueous solution containing PdCI ₂ and H ₂ PtCI ₆ , followed by slow drying and finally a heat treatment under hydrogen sweep at 300 ° C for 3 hours.

The catalyst is then suspended (10 g / l) in a solution, containing 60 mg of NaBr, 5 mg of Br ₂ and 12 g of H ₃ PO * heated at 40 ° C for 5 hours, then is filtered, washed with demineralized water and dried. Initial aqueous solution (examples 1 -19)

An aqueous solution is prepared by adding 12 g of H ₃ PO ₄ '58 mg of NaBr and 5 mg of Br ₂ in 988 g of demineralized water.

Initial aqueous solution (examples 20-24)

The aqueous solution used contains 3.4% H ₃ PO ₄ , 90 ppm of bromide (NaBr) and 5 ppm of Br ₂ .

General procedure The selected quantity of initial aqueous solution is introduced into the autoclave and then the determined quantity of surfactant and catalyst is added. The autoclave is pressurized by injecting a selected flow of oxygen into the continuous gas phase. The pressure remains constant thanks to the pressure regulator. The liquid medium is brought to the chosen temperature by circulation of water thermostatically controlled in the bundle of cooling tubes.

Stirring is set at 1,900 rpm and the selected flow rates of oxygen and hydrogen are injected into the center of the lower turbine.

The flow rate and the hydrogen content of the gas mixture leaving the pressure regulator are measured.

After 1; 1.5; 2 or 3 hours of reaction, the arrival of hydrogen and oxygen in the aqueous reaction medium is cut off and the injection of oxygen into the gaseous phase is continued until the complete disappearance of hydrogen therein . The oxygen supply is then cut off, then the reactor is decompressed and finally the aqueous hydrogen peroxide solution is recovered.

The aqueous solution of hydrogen peroxide recovered is subsequently weighed and then separated from the catalyst by filtration through a Millipore ^® filter.

The resulting solution is then dosed by iodometry thus making it possible to determine the concentration of hydrogen peroxide. The selectivity of the synthesis is defined as being the percentage of the number of moles of hydrogen peroxide formed on the number of moles of hydrogen consumed.

The conversion rate is defined as the percentage of the volume of hydrogen consumed over the volume of hydrogen introduced. Tables 1, 2 and 3 show the results obtained under different reaction conditions. Example 25

Separation of additives by reverse osmosis

A solution containing 200 g / l of hydrogen peroxide, 6 g / l of orthophosphoric acid and 50 mg / l NaBr is pumped into a reverse osmosis unit consisting of 3 cells connected in series with an operating pressure of 80 bar and a volume concentration factor of 10 per cell. Each cell is provided with a three-layer OSMONICS-DESAL 3 reference membrane supplied by the company DESAL. The following results are obtained:

Q being the feed rate of the first cell. It can be seen that 89% of the bromides and 99% of the phosphates are recycled.

όWOO / IOMJ / lDd n 61S89 / 10O / W HOO / lOMd / _LDd SI 61S89 / 10OΛV ro ro t ro ro ro o Example

OOO n O τι Tl ι ^* τ -π oooo O Φ Z

X X X X X - • c

- ^ O -i α> ω> ω ω 00 o

O O C) O O

X X X X X

en en en en 3 Amount of surfactant

en en en o o o o o Amount of o o o o o initial acid solution

Quantity of ro ro ro ro ro catalyst ro ro ro ro ro Number of tnrhinpς oo ro - - ^" in Reaction time

H ₂ flow injected

Z

00 00 o o o o in the lower turbine>

CD v ro *. *. *. Flow 0 ₂ injected

Z m

00 00 00 00 ro ro ro ro ro in the turbine> o o o o o o lower ω

_ N ₂ flow injected

Z o o o o o o in the lower turbine o

Flow 0 ₂ injected

Z

§ o ° o o o _ in the gas phase en en en σ> σ Pressure in the reactor ro ro en en in Temperature in oo o o o o O the reactor

--s Concentration in oo -jo _ ". o H 0 ₂ of the solution

-J: ro o a aqueous after reaction

Selectivity of the reaction by in ro with respect to hydrogen

->. ro oo ro ro -t --- o eo o Rate of oo -j ro in hydrogen conversion

δWOO / IOHJ / lDd 91 61S89 / 10 OW

Claims

1 - Process for the manufacture of an aqueous solution of hydrogen peroxide directly from hydrogen and oxygen, according to which hydrogen and oxygen are injected, in the form of small bubbles, into an aqueous reaction medium rendered acid by the addition of an inorganic acid and comprising a catalyst in the dispersed state characterized in that the aqueous reaction medium further comprises one or more surfactants. 2 - Process according to claim 1 characterized in that the surfactant is stable in an acid medium and withstands very oxidizing conditions.

3 - Method according to claim 1 or 2 characterized in that the surfactant is a fluorinated surfactant.

4 - Process according to claim 3 characterized in that the fluorosurfactant is of general formula C _n F _{2n + 1} -QG or C _n F _{2n +} ι-G in which Q denotes a spacer arm and G denotes a hydrophilic group.

5 - Process according to any one of claims 1 to 4 characterized in that the amount of surfactant used is less than the minimum amount necessary to cause the appearance of foams on the surface of the aqueous reaction medium.

6 - Process according to claim 3 or 4 characterized in that the surfactant is present in an amount of 1 to 50 ppm and preferably in an amount of 5 to 10 ppm in the aqueous reaction medium. 7 - Process according to any one of claims 1 to 6 characterized in that the reaction medium can contain stabilizers of hydrogen peroxide.

8 - Process according to any one of claims 1 to 7 characterized in that the reaction medium can contain decomposition inhibitors.

9 - Process according to claim 8 characterized in that the inhibitor is the bromide of an alkali metal or hydrobromic acid optionally in combination with bromine in the free state.

10 - Process according to claim 9 characterized in that the amount of bromide is between 10 and 200 ppm; preferably between 20 and 100 ppm. 1 1 - Process according to claim 9 or 10 characterized in that the amount of bromine in the aqueous reaction medium is between 1 and 50 ppm, preferably between 2 and 10 ppm.

12 - Process according to any one of claims 1 to 1 1 characterized in that the catalyst is a supported catalyst based on at least one metal chosen from the group M formed of palladium, platinum, ruthenium, rhodium, iridium , osmium, holmium and gold.

13 - Process according to claim 12 characterized in that the supported catalyst is a bimetallic catalyst consisting of palladium as the majority metal and platinum as the minority metal.

14 - Process according to claim 13 characterized in that the bimetallic catalyst is supported on silica.

15 - Process according to any one of claims 12 to 14 characterized in that the catalyst is prepared according to the method consisting of: a) bringing a support, chosen from the group formed by silica, alumina , carbon and silicoaluminate, with a concentrated aqueous solution of salt (s) of at least one metal from group M so as to form a paste b) followed by filtration, spinning, then drying of the paste under conditions favoring slow crystallization c) then by the reduction under hydrogen at about 200 to 400 ° C of the dried solid of step (b) d) then by the treatment of the reduced solid of step (c) with an acidic aqueous solution (A), comprising bromine and bromide ions, at a temperature between 10 and 80 ° C e) and finally, filtration of the solid treated in step (d) and drying at a temperature between 100 and 140 ° C.

16 - Process according to claim 15 characterized in that the pH of the solution (A) is between 1 and 3.

17 - Process according to claim 15 or 16 characterized in that the concentration of bromide ions in the solution (A) is between 20 and 200 mg / l, preferably between 20 and 100 mg / l.

18 - Process according to claim 17 characterized in that the bromine concentration is between 2 and 20 mg / l. 19 - Process according to any one of claims 1 to 18 characterized in that it is implemented in a stirred reactor or tubular reactor.

20 - Process according to any one of claims 1 to 19 characterized in that the temperature of the reaction medium is between

5 and 90 ° C, preferably between 30 and 60 ° C.

21 - Process according to any one of claims 1 to 20 characterized in that the reaction medium is under pressure from 10 to 100 bars. 22 - Method according to any one of claims 1 to 21 characterized in that the hydrogen and the oxygen are injected separately into the aqueous reaction medium with flow rates such that the ratio of the molar flow rates hydrogen to oxygen is less than 0, 0416.

23 - Process according to any one of claims 1 to 22 characterized in that the aqueous solution of hydrogen peroxide formed is separated from the catalyst, then freed from the additives by reverse osmosis using the membranes.

24 - Process according to claim 23 characterized in that the membranes are of the bilayer or trilayer type of polymer including at least one layer based on polyamide.

25 - Device for implementing the method according to any one of claims 1 to 24 comprising a stirred reactor 1, provided with several centrifugal turbines arranged along a single vertical stirring shaft, of one or more arrivals of gaseous hydrogen 2 and of gaseous oxygen 3 located at the bottom of the reactor, of a gas inlet 4 and of a gas outlet 5 in the upper part of the reactor, of a liquid outlet 9 connected to an exchanger 10, itself connected to a filter 11, the outlet of which being connected to a battery of reverse osmosis membrane 12.

26 - Device for implementing the method according to any one of claims 1 to 24 comprising a tubular reactor 1 equipped with means 6 and 18 for injecting oxygen 3 and hydrogen 2 in the form of small bubbles, an outlet 16 connected to a reservoir 21 provided with a gas outlet 5 connected to the inlet 3 via the pump 6, an oxygen inlet 4, two liquid outlets 9 and 15, the outlet 9 being connected to a filter 14, which can optionally be connected to a reverse osmosis battery.