WO2003000597A1

WO2003000597A1 - Method for decomposing hydrazine contained in an aqueous liquid

Info

Publication number: WO2003000597A1
Application number: PCT/FR2002/002097
Authority: WO
Inventors: Arnaud Radigue; Hervé Suty
Original assignee: Atofina
Priority date: 2001-06-22
Filing date: 2002-06-18
Publication date: 2003-01-03
Also published as: FR2826354B1; FR2826354A1; EP1401772A1

Abstract

The invention relates to a method for decomposing hydrazine contained in an aqueous liquid such as water, arising from a nuclear or thermal boiler or other type of industrial unit producing aqueous effluents containing hydrazine. According to the inventive method, hydrazine contained in the aqueous liquid is reacted with at least one peroxide in the presence of a catalyst comprising at least one metal alloy. The invention also relates to a device for carrying out said method.

Description

HYDRAZINE DECOMPOSITION PROCESS

CONTAINED IN AQUEOUS LIQUID

The present invention relates to a process for decomposing hydrazine contained in an aqueous liquid such as water from a nuclear or thermal boiler, or any other industrial unit producing aqueous effluents containing hydrazine.

It is known to decompose, by catalytic oxidation, the hydrazine contained in waters.

The German patent application published under the number DE 36 44 080 proposes using hydrogen peroxide to purify industrial waste water containing in particular hydrazine, operating at a pH greater than 7 and in the presence of a salt d a heavy metal, such as copper sulphate, and / or a catalyst which may be potassium permanganate or a nickel, chromium or cobalt salt. The Japanese patent application published under the number JP 09234473 relates to a process for treating wastewater containing hydrazine, which essentially consists in adding hydrogen peroxide, as an oxidant, to the water to be treated. a copper-based compound as catalyst, and subjecting the hydrazine to oxidative decomposition by exposing it to air for 0.5 to 12 hours, the pH being maintained at a value of 10-11, 5.

More recently, the Japanese patent application published under the number JP 2000301171 and aiming to improve the method of the aforementioned Japanese patent application, has proposed a method consisting in subjecting the hydrazine contained in waste water to decomposition by oxidation to the double presence of a percarbonate of a metal such as sodium or potassium and of at least one catalyst chosen from compounds based on copper, manganese, cobalt or nickel. Examples of such compounds are cited sulfates and chlorides. All the processes which have just been mentioned have the major drawbacks of forming by-products (chlorides, sulphates, etc.) and of introducing metals into the treated water. The object of the invention is to propose a process for decomposing hydrazine contained in water which does not have these drawbacks.

According to this process, the hydrazine contained in an aqueous liquid is reacted with at least one peroxide, in the presence of a catalyst comprising at least one metal alloy. Such a method offers the following advantages: it can be implemented

• easily,

• at neutral pH or close to neutral,

• ambient temperature,

• without exposure to air or external oxygen supply; it does not give rise to an uncontrollable exotherm, it does not alter the catalyst, and it retains its effectiveness over long periods. The invention also relates to a device capable of implementing this method.

Other characteristics and advantages of the invention will appear on reading the description which follows and which is given with reference to the drawings in which:

- Figure 1 is a diagram showing a device according to the invention, capable of implementing the method according to the invention;

- Figure 2 is a graphical representation of the evolution curves of the hydrazine and hydrogen peroxide contents as a function of time, during the implementation of the method according to the invention and of a method of the prior art ; - Figure 3 is a graphical representation of the evolution curves, as a function of time, of the hydrazine contents of demineralized water, during three similar tests of implementation of the process according to the invention;

FIG. 4 is a graphic representation of the evolution curves, as a function of time, of the hydrazine contents of demineralized water and of water of the Seine type, during the implementation of the method according to the invention and a method of the prior art;

- Figure 5 is a graphical representation of the evolution of the hydrazine and hydrogen peroxide contents as a function of time, during the implementation of the process according to the invention according to two successive phases;

- Figure 6 is a graphical representation showing the evolution of the oxidant contents, namely hydrogen peroxide or sodium hypochlorite, during the implementation of the method according to the invention and three methods of prior art.

DETAILED DESCRIPTION OF THE INVENTION

According to the invention, hydrazine, generally in the form of hydrazine hydrate, contained in any aqueous liquid, for example, waste water, water coming from nuclear or thermal boilers at the outlet of the die, or water coming from waste or accidental spillage of hydrazine, can be destroyed quickly, using a peroxide as an oxidant, following a reaction catalyzed by a solid catalyst that includes a metal alloy.

As the metal alloy, an alloy of a transition metal is advantageously used.

Catalysts comprising such an alloy have the particularity of self-regenerating during the process of decomposition of hydrazine.

In addition, they have the advantage of not forming a passivating protective layer on their surface, a layer which would prevent the passage of electrons and would decrease their activity. In addition, these catalysts, because they do not contain precious metals, have a relatively low Nernst potential, which amounts to saying that they easily transmit electrons to the environment. Finally, the surface of these catalysts corresponds to a metal-oxygen bronze. This type of structure is a very favorable condition for the reversibility of electron migration: the electrons are thus transmitted and recovered without generating metal cations in solution. As a result, the catalyst remains stable throughout the hydrazine decomposition process.

Preferably, as an alloy of at least one transition metal, a nickel-based alloy is used.

Among the nickel-based alloys, mention may be made of nickel and copper alloys, in particular those comprising from 25 to 35% of nickel and from 75 to 65% of copper, these percentages being expressed by weight relative to the total weight. of the alloy.

Mention may also be made of alloys of nickel, cobalt and chromium, in particular those comprising from 5 to 15% of nickel, from 80 to 60% of cobalt and from 15 to 25% of chromium, these percentages being expressed by weight by relative to the total weight of the alloy.

The catalyst may be in the form of a metal grid or a strip of wire mesh.

Catalysis is therefore of the heterogeneous type and, therefore, easy to implement.

On the surface of the catalyst, the peroxide is activated and generates OH- radicals, the oxidizing effect of which is very effective. Indeed, the electrochemical oxidation potential of an OH- radical is 2.8 V, against 1.78 V for hydrogen peroxide and 1.36 V for chlorine.

The peroxide used can be organic or mineral. Preferably, hydrogen peroxide is used. The decomposition of hydrazine by hydrogen peroxide can then be illustrated by the following simplified equation: N ₂ H ₄ + 2H ₂ 0 ₂ → N ₂ + 4H ₂ 0

Hydrogen peroxide is thus activated without any external energy supply (UV rays, etc.) or external oxygen and without forming by-products. Hydrogen peroxide is generally introduced in the form of an aqueous solution. The stability of the aqueous hydrogen peroxide solution is not affected by the catalyst as such.

In addition, the reaction does not release metals into the water during treatment. This has the great advantage of not causing induced pollution.

The hydrazine / hydrogen peroxide molar ratio is generally between 1 and 4, preferably between 1.6 and 2.2. The duration of the reaction between hydrazine and hydrogen peroxide can be between 1 minute and 8 hours. Preferably, it is between 30 minutes and 3 hours.

Another advantage of the process according to the invention is that it is not necessary to carry it out at a particular pH. It can therefore be implemented at a neutral pH or close to neutral, and there is also no need to maintain this pH at a particular value. However, it is desirable that the pH is not too low, as this could cause the metals in the catalyst to dissolve. In addition, the method according to the invention can be implemented in a very wide range of temperatures. Generally, it is carried out at a temperature between 15 and 60 ° C, and preferably between 20 and 25 ° C, so that it is not necessary to heat the reaction medium. The process according to the invention, due to the automatic regeneration of the catalyst, exhibits a high reproducibility of the hydrazine decomposition reaction without loss of efficiency over time.

It can therefore operate in a discontinuous or continuous mode.

It can be used to detoxify the water from nuclear or thermal boilers at the outlet of the pipeline, to decontaminate containers containing hydrazine or to safely decompose waste or accidental spillage of hydrazine.

Device according to the invention

The method according to the invention can be implemented by means of a device essentially comprising:

- a container containing the aqueous liquid to be treated;

- A catalyst comprising at least one metal alloy, this catalyst being in a container;

- means for introducing the peroxide into the aqueous liquid to be treated, -

- Means for passing the aqueous liquid containing the peroxide into the container, through the catalyst; and

- Optionally, means for bringing the aqueous liquid leaving the container into the container.

Such a device is shown schematically in Figure 1.

The liquid to be treated loaded with hydrazine is placed in a tank 1 to which is connected by a line 2 a pump 3 whose outlet is connected by a line 4 to the inlet of a column 5 containing the catalyst 6. The peroxide is introduced in the aqueous liquid to be treated by means of a metering pump (not shown) and a pipe 7 preferably connecting to the pipe 4 upstream of the column 5.

The operation of the pump 3 passes the aqueous liquid containing the hydrazine and the peroxide in the column 5, through the catalyst 6.

According to a preferred embodiment of the device according to the invention, the decontaminated aqueous liquid leaving the column 5 is brought back through a pipe 8 into the tank 1. Thus, the device according to the invention constitutes a system of "going around in circles" allowing to maintain a certain agitation of the liquid in contact with the catalyst. In order to avoid excessive temperature increases, it is preferable to work with relatively low reagent concentrations (for example hydrogen peroxide at 10% by weight of hydrogen peroxide). If necessary, an exchanger can be added to the recirculation loop to regulate the exotherm. If the proportions of the reactants and the catalyst are chosen appropriately, the decomposition of the hydrazine can be maintained at ambient temperature with satisfactory kinetics.

Examples

The following examples illustrate the present invention without, however, limiting its scope. The analytical means used in the examples are as follows:

- determination of hydrazine: by absorption in the visible at 455 nm on a HACH DR 2010 spectometer (method 8141); p-dimethylaminobenzaldehyde method, - - determination of hydrogen peroxide: with titanium chloride in sulfuric acid medium; absorption measurement in the visible at 410 nm on a HACH DR 2010 spectrometer;

- copper assay: by absorption in the visible at 560 nm on a HACH DR 2010 spectrometer (method 8506); bicinchoninate method;

- redox probe (ORION 9778BN combined electrode).

Example 1 Using the device in FIG. 1, the hydrazine contained in demineralized water solutions (pH approximately 7.2) is removed.

Each time, the container is filled with 1 liter of demineralized water containing 463 mg of hydrazine (molar mass: 32 g). Then 9.2484 g of hydrogen peroxide containing 10% hydrogen peroxide (molar mass: 34 g) are added. The hydrazine / hydrogen peroxide molar ratio is therefore 0.534.

The procedure is first according to the prior art, that is to say in the absence of catalyst.

Then, one proceeds according to the invention, that is to say that one introduces into the container 2.0058 g of a catalyst which is an alloy of 32% of nickel and 68% of copper (% by mass).

We follow the evolution of the hydrazine and hydrogen peroxide concentrations as a function of time.

The following table groups together the results obtained.

It is immediately noted that the use of the catalyst makes it possible to decompose more quickly the hydrazine contained in demineralized water.

The temperature remains substantially stable. The reaction is complete in about 2 hours. The pH progressively changes from 9 to 6. We make sure that it does not drop below 6, possibly adding sodium hydroxide.

No trace of metal is found in the solution at the end of the reaction. The yield of the elimination of hydrazine is therefore 99.9% and 87.2% of the hydrogen peroxide has been consumed.

The curves in Figure 2 represent the variations in the hydrazine and hydrogen peroxide contents as a function of time.

Example 2

In order to check the repeatability of the hydrazine elimination reaction, two successive new tests are carried out, as in Example 1, with the catalyst which has already been used in Example 1 and without changing or treating in no way whatsoever this catalyst during these two tests.

The results are represented by the curves in Figure 3.

It is observed that the repeatability of the reaction is perfect, the activity of the catalyst remaining identical in the three cases.

Example 3 In this example, synthetic water of the Seine type was used (pH approximately 8-8.5; TAC 20 ° F, - THCa 20 ° F) [Na ₂ S0 ₄ = 74 mg / 1; NaHC0 ₃ = 336 mg / 1; CaCl ₂ = 0.002 mol / 1; MgCl ₂ = 0.0005 mol / 1).

2 successive tests are carried out with the nickel / copper catalyst of Example 1, under conditions which are similar to those of Example 1.

The water initially contains 400 ppm of hydrazine. The amount of hydrogen peroxide (in 10% solution in water) added is 9 ml.

The amount of catalyst used is 2.0065 g / l. The catalyst is washed with demineralized water between the two tests.

The hydrazine / hydrogen peroxide molar ratio is 0.49.

The results are collated in the following table.

The curves in FIG. 4 represent the variations in the contents of hydrazine and of hydrogen peroxide as a function of time, for tests 1 and 2 of this example. Given that in the absence of a catalyst, no difference as regards the kinetics of decomposition of hydrazine by hydrogen peroxide was observed between demineralized water and synthetic water of the Seine type, the curve obtained in Example 1 (see Figure 2) was added to Figure 4.

In addition, for comparison purposes, the curve obtained in Example 1 was also added to Figure 4 using a catalyst and deionized water.

It can therefore be seen that, as previously, the use of the catalyst makes it possible to neutralize the hydrazine contained in the synthesis water more quickly.

It is also noted that the neutralization is slower than in the case of demineralized water, but nevertheless rapid enough to allow the disappearance of the hydrazine in approximately 2 hours.

The yield of hydrazine decomposition is 100% and the amount of hydrogen peroxide consumed is 95.9%.

Example 4 The purpose of this example is to show the maintenance of the efficiency of the process according to the invention in continuous mode operation. In a first phase, demineralized water containing 400 ppm of hydrazine is treated with a 10% aqueous solution of hydrogen peroxide, in the presence of the catalyst of Example 1. At the end of the reaction , 400 ppm of hydrazine and 920 ppm of hydrogen peroxide are reinjected to carry out a second phase of decomposition of the hydrazine, in the same medium and without washing the catalyst.

The amount of catalyst used is 2.0065 g / l. During the first phase, the hydrazine / hydrogen peroxide molar ratio is 0.47. The yield of hydrazine decomposition is 100%. The amount of hydrogen peroxide consumed is 93%. The reaction time is 2 hours. During the second phase, the hydrazine / hydrogen peroxide molar ratio is 0.444. The yield of hydrazine decomposition is 100%. The amount of hydrogen peroxide consumed is 85.2%. The reaction time is 30 minutes. The results are collated in the following table.

It is observed that there is no loss of efficiency of the system after continuous reinjection of the reagents. In addition, the second phase seems to take place more quickly.

The curves representing the variations in the hydrazine and hydrogen peroxide contents as a function of time, for the first and second phases are visible in Figure 5.

Example 5 In this example, the method according to the invention is compared with the following methods of the prior art:

- a process A where the catalyst is nonexistent;

- a process B implementing a homogeneous catalysis by means of an aqueous solution of copper sulphate; and - a process C where the catalyst is nonexistent and where the oxidant is no longer hydrogen peroxide but sodium hypochlorite. The starting aqueous solution is demineralized water containing 400 ppm of hydrazine. Hydrogen peroxide is used in a 10% aqueous solution. In process B, the copper sulphate is used in the form of an aqueous solution at 5 ppm of Cu.

In method C, the sodium hypochlorite is in the form of an aqueous solution at 13.5% (weight / weight percentage) or 42 ° C1. In process D according to the invention, the catalyst of Example 1 is used, at a rate of 2 g / 1.

The results are recorded in the following table.

It is observed that the presence of a catalyst makes it possible to significantly accelerate the decomposition of hydrazine by hydrogen peroxide. The homogeneous catalysis by addition of copper sulphate in aqueous solution is faster than the process according to the invention. However, it has the disadvantage of introducing copper into the solution.

The use of sodium hypochlorite leads to instant elimination of the hydrazine, but it has the disadvantage of requiring a high mass of oxidant, i.e. 149 g of sodium hypochlorite per 32 g of hydrazine and of introducing chloride sodium in the solution because hydrazine reacts with sodium hypochlorite to give sodium chloride, nitrogen and water.

The curves representing the variations of the hydrazine, hydrogen peroxide and sodium hypochlorite contents as a function of time are visible in Figure 6.

Claims

1. Process for the decomposition of hydrazine contained in an aqueous liquid, in which the hydrazine is reacted with at least one peroxide, in the presence of a catalyst, characterized in that the catalyst comprises at least one metal alloy.

2. Method according to claim 1, characterized in that the metal alloy is an alloy based on at least one transition metal.

3. Method according to claim 2, characterized in that the alloy based on at least one transition metal is a nickel-based alloy.

4. Method according to claim 3, characterized in that the nickel-based alloy is an alloy of nickel and copper.

5. Method according to claim 4, characterized in that the alloy comprises, by weight, from 25 to 35% of nickel and from 75 to 65% of copper.

6. Method according to claim 3, characterized in that the nickel-based alloy is an alloy of nickel, cobalt and chromium.

7. Method according to claim 6, characterized in that the alloy comprises, by weight, from 5 to 15% of nickel, from 80 to 60% of cobalt and from 15 to 25% of chromium.

8. Method according to one of claims 1 to 7, characterized in that the peroxide is hydrogen peroxide.

9. Method according to claim 8, characterized in that the hydrazine / hydrogen peroxide molar ratio is between 1 and 4, preferably between 1.6 and 2.2.

10. Method according to claim 8 or claim 9, characterized in that the hydrazine and the hydrogen peroxide are reacted together for a period of between 1 minute and 8 hours, preferably between 30 minutes and 3 hours.

11. Device suitable for implementing the method according to one of claims 1 to 10, comprising:

- a container (1) containing the aqueous liquid loaded with hydrazine to be treated; - a catalyst (6) comprising at least one metal alloy, this catalyst being in a container (5), -

- means (7) for introducing the peroxide into the aqueous liquid to be treated; - Means (2,3,4) for passing the aqueous liquid containing the peroxide into the container (5), through the catalyst (6); and

- Optionally, means (8) for bringing the aqueous liquid leaving the container (5) into the container (1).

12. Use of a metal alloy as defined in claims 1 to 7, for the catalytic oxidation of hydrazine contained in an aqueous liquid.