FR3068259A1 - METHOD FOR SUPPRESSION, IN ALL OR PART, OF THE FOAM CONTAINED IN AN AQUEOUS MEDIUM COMPRISING ONE OR MORE SURFACTANT AGENTS OR FOR PREVENTING THE FORMATION OF SUCH A FOAM IN SUCH AQUEOUS ENVIRONMENT - Google Patents

Abstract

The invention relates to a method of suppressing, in part or in part, the foam contained in an aqueous medium comprising one or more surfactants or preventing the formation of such a foam in such a medium comprising a step of subjecting said aqueous medium with the combined action of ultraviolet irradiation, hydrogen peroxide and bubbling air.

Description

METHOD FOR THE SUPPRESSION, IN WHOLE OR IN PART, OF THE FOAM CONTAINED IN AN AQUEOUS MEDIUM COMPRISING ONE OR MORE SURFACTANTS OR OF PREVENTING THE FORMATION OF SUCH A FOAM IN SUCH AN AQUEOUS MEDIUM

DESCRIPTION

TECHNICAL AREA

The present invention relates to a process for removing, in whole or in part, the foam contained in an aqueous medium comprising one or more surfactants or for preventing the formation of such a foam in such an aqueous medium.

Thus, such a process finds its application in the treatment of aqueous effluents containing surfactants (for example, urban and / or industrial wastewater comprising surfactants) and in particular in industries which use industrial evaporators, in which a foaming phenomenon inherent in surfactants can harm all or part of the operation of the installation. Among the industries involving the treatment of aqueous effluents comprising surfactants, mention may be made of the paper industry, the food industry, the leather industry, the textile industry, the product industry. metals or chemical components (such as fertilizers), the water treatment industry, the nuclear industry.

PRIOR STATE OF THE ART

The treatment of aqueous effluents can involve an evaporation step with a view to concentrating these effluents. More specifically, evaporation consists of a unitary operation of separation of different constituents by passing one or more of them from the liquid state to the gaseous stage.

In the nuclear industry and more particularly in the treatment of radioactive effluents, concentration by evaporation is used to limit the volume of effluents by concentrating the radioactive elements (i.e., in other words, the heavy elements) in the concentrate following the evaporation of the light elements. The concentrate can then be packaged in a matrix, for example, by cementing.

Evaporation involves heating the effluent. If it contains impurities, which reduce the vapor pressure compared to that of the pure solvent entering into the constitution of the effluent, there is a phenomenon of foaming of the effluent in the evaporator, and in particular the formation of persistent foams, which can be generated by a decrease in interface tension induced by the presence of surfactants. The foams formed lead to a deposit on the heat exchange zones of the evaporator and to a phenomenon of pressure drop in the evaporation process, which limits the flow rate at the outlet of the evaporator. In parallel, there may be a phenomenon of entrainment of the foam with the distillate, which causes pollution of the latter.

Faced with the drawbacks induced by the presence of foams, several methods have been developed for eliminating them, once formed, using mechanical means (these methods being described hereinafter as "mechanical methods") or thermal means (these methods being qualified hereinafter as "thermal methods").

Concerning the mechanical methods, they consist in causing a shock on the bubbles to generate their rupture by various mechanical means such as:

-moss breezes made up of rotating bars, which cut down the foam if it is coarse;

-watering with a jet of gas or liquid directly on the foam layer;

-the spraying of liquid drops or solid particles on the foam;

-sending shock sonic waves to break down the moss.

Regarding thermal methods, they can consist of heating the foam present above the liquid phase by means of heating coils.

As indicated above, these two types of methods are intended to intervene on already formed foam. However, in certain contexts conducive to foaming, it may be advantageous to intervene upstream of this phenomenon to avoid or at least lessen the formation of foam. This is made possible in particular by means of chemical methods, which consist in adding to the liquid medium capable of foaming agents capable of inhibiting the formation of foams (also called anti-foaming agents). However, this type of method involves certain drawbacks, among which:

-the need to find an anti-foaming agent suitable for the liquid medium to be treated, for example, in terms of solubility, chemical stability;

-the pollution of the liquid medium caused by the addition of the anti-foaming agent;

-the effectiveness of anti-foam agents only under certain conditions of use (such as concentration, temperature).

In parallel, it has also been identified that certain agents present in aqueous effluents, such as surfactants, contributes to the formation and preservation of the foams formed, which opens a new way to prevent, in whole or in part, the phenomenon in foaming by playing on the elimination of these surfactants.

Thus, in view of what exists, the inventors have set themselves the objective of proposing a process for the removal, in whole or in part, of the foam formed in an aqueous medium comprising one or more surfactants or for preventing the formation of foam in such a medium, by elimination of these surfactants using a reasoned combination of physicochemical means.

STATEMENT OF THE INVENTION

Thus, the invention relates to a process for removing, in whole or in part, the foam contained in an aqueous medium comprising one or more surfactants or for preventing the formation of such foam in such a medium comprising a step consisting of subjecting said aqueous medium to the combined action of ultraviolet irradiation, hydrogen peroxide and air bubbling.

By carrying out this combined action, the authors of the present invention have been able to observe, surprisingly, an effective elimination of the surfactant (s) included in the aqueous medium thus treated.

Without being bound by theory, the effectiveness of the process can be explained by the following considerations.

Indeed, the presence of air bubbles linked to the implementation of bubbling generates a multiplicity of air / water interfaces, on which the surfactants are spontaneously adsorbed in a preferential orientation with the hydrophobic parts of the agents oriented towards the interior of the bubbles and the hydrophilic parts oriented towards the exterior of the bubbles, namely towards the aqueous medium. This phenomenon is illustrated in particular in FIG. 1 appended in the appendix schematically representing an air bubble 1 in the aqueous medium 3, around which molecules of surfactants 5 are arranged, each with a hydrophobic part 7 oriented towards the inside of the bubble and a hydrophilic part 9 oriented towards the outside of the bubble. Thus selectively concentrated, the surfactants effectively undergo the attack of the hydroxyl radicals generated by the degradation of hydrogen peroxide in the presence of ultraviolet irradiation, which radicals cause at the interface of the bubbles, the rupture of the connections between the hydrophilic parts. and the hydrophobic parts of the surfactant molecules. Once these parts are separated, the surfactants are completely inactive, thus increasing the surface tension and thus inhibiting their foaming power.

As mentioned above, in order to access the suppression of foam present in an aqueous medium comprising one or more surfactants or to prevent its formation, the method comprises the combined action of ultraviolet irradiation, of the hydrogen peroxide and air bubbling.

By ultraviolet irradiation, is conventionally understood to mean electromagnetic radiation having a wavelength shorter than that of visible light, but longer than that of X-rays, namely a wavelength which can range from 100 to 400 nm.

More specifically, the ultraviolet irradiation can be irradiation with UV-C rays, that is to say with rays having a wavelength ranging from 200 nm to 280 nm.

Ultraviolet irradiation can be carried out by means of a UV lamp emitting such irradiation. This UV lamp can be placed in a sheath, for example, made of quartz, which lets pass the majority of UV radiation.

When the aqueous medium to be treated is already topped with a layer of foam, the introduction of hydrogen peroxide can be carried out in several distinct ways:

or by injection of hydrogen peroxide directly into the aqueous medium (that is to say not into the foam overlying said aqueous medium); or

or by injection of hydrogen peroxide directly into the foam overlying said aqueous medium;

these two modes of addition having revealed a similar effectiveness in the context of the implementation of the method of the invention.

The hydrogen peroxide can be added in an amount chosen so that the ratio of molar concentrations (said concentrations being expressed in mol / L) between the hydrogen peroxide and the surfactant (s) in the aqueous medium is, preferably from 6 to 10.

Air bubbling can be carried out, in a conventional manner, by injecting air directly into the aqueous medium, the air thus coming into contact with this medium forming air bubbles within the aqueous medium.

According to the method of the invention, the combined action of ultraviolet irradiation, hydrogen peroxide and air bubbling can be carried out in different ways, provided that these means coexist together during the implementation of the method of the invention.

Thus, the aqueous medium comprising foam can be subjected to ultraviolet irradiation and air bubbling with the addition of hydrogen peroxide, the ultraviolet irradiation and air bubbling being maintained after this addition has been carried out for a period of time. sufficient to obtain the elimination of all or part of the surfactant (s).

The duration of maintenance of ultraviolet irradiation, of air bubbling can be easily determined by a person skilled in the art:

or by taking samples from the aqueous medium at different treatment durations and by measuring the concentration of surfactant (s), the retention time selected corresponding to a concentration for which the retention of the foam is no longer possible. ;

-or simply visually, the holding time corresponding to that for which the foam is no longer visible to the naked eye (in other words, the method of the invention makes it possible to visually monitor the presence of agents foaming surfactants).

As surfactants capable of being present in the aqueous medium and capable of being treated by the process of the invention, there may be mentioned anionic surfactants, such as those comprising a fatty acid salt, an alkylsulfate salt (as sodium lauryl sulfate), an alkylbenzenesulfate salt (such as sodium dodecylbenzenesulfonate), an alkylphosphate salt or a sulfosuccinate diester salt, an ethylenediaminetetraacetate salt; nonionic surfactants, such as those comprising a polyoxyethylene alkyl ether, a polyoxyethylene fatty acid ester, alkyl polyglucosides; cationic surfactants, such as those comprising quaternary alkyl and / or aryl ammonium halides; zwitterionic or amphoteric surfactants, such as surfactants comprising a betaine group.

By way of specific examples, there may be mentioned, more specifically, nonionic surfactants of the family of alkyl polyglucosides and / or anionic surfactants comprising an ethylenediaminetetraacetate salt.

The process of the invention can be implemented in a single reactor provided with a source of UV radiation and connected to bubbling means.

Besides the destruction of the foam, if necessary, this process can also make it possible to overcome the foaming phenomenon (that is to say prevent this phenomenon), which can be particularly advantageous for effluents intended to be treated in evaporators. To do this, the method of the invention can be implemented upstream of the evaporator, which means that the effluents thus pretreated will be free of surfactants upon introduction into the evaporator, which will allow avoid the formation of foam in the evaporator and the associated disadvantages, namely:

the loss of evaporation charge due to the presence of foaming surfactants;

-the need to stop operating the equipment to ensure its cleaning.

Finally, the method of the invention is a green technology, since it implements non-polluting technical means. The only chemical used is hydrogen peroxide which generates hydroxide radicals, which oxidize organic compounds, such as surfactants, present in the aqueous medium to be treated. The hydroxide peroxide therefore generates products which are immediately consumed.

The invention will now be described with reference to the examples provided below given by way of illustration and not limitation.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a schematic representation of an air bubble in the aqueous medium, around which are arranged surfactant molecules.

FIG. 2 is a graph illustrating the change in the concentration of surfactants C (in mg.L ′ ¹ ) as a function of the treatment time t (in min) for two tests of Example 1.

FIG. 3 is a graph illustrating the evolution of the height of foam H (in cm) as a function of the test duration t (in minutes) for three tests of Example 2.

FIG. 4 is a graph illustrating the change in the concentration of surfactants C (in mg.L ¹ ) as a function of the treatment time t (in minutes) for four tests of Example 3.

FIG. 5 is a graph illustrating the change in the concentration of surfactants C (in mg.L ¹ ) as a function of the treatment time t (in minutes) for three tests of Example 5.

FIG. 6 is a graph illustrating the evolution of this treatment time t (in minutes) as a function of the initial concentration of surfactants C (in mg.L ¹ ) for three tests of Example 5.

FIG. 7 is a graph illustrating the evolution of the concentration of TFD4 C (in mg.L ¹ ) as a function of the duration of treatment t (in minutes) for a test of Example 6.

DETAILED PRESENTATION OF PARTICULAR EMBODIMENTS

Example 1

This example illustrates the implementation of the process of the invention and proves its effectiveness compared to a process not in accordance with the invention.

To do this, a tubular reactor is used, in which there is a UV-C lamp. This lamp is a low pressure tubular lamp (Model NNI 50/26 XL supplied by Heraeus Noblelight) with an emission peak in the UV-C range at 254 nm. The photonic power at 254 nm is 17 W (according to the supplier's specifications) and the electric power is 55 W. The lamp is allowed to heat for 5 minutes before the introduction of a solution into the reactor, so as to reach its full photonic power.

After these 5 minutes, an aqueous solution of 500 mL comprising 100 mg.L ¹ of surfactants, i.e. 156 mg.L ¹ of Glucopon, is introduced into the tubular reactor by nozzles above the level of the cover by means of a funnel.

Glucopon consists of 36% water and 64% of a mixture of nonionic surfactants, which are alkyl polyglucosides having linear carbon chains like hydrophobic tails and polar heads composed of one or more glucose units, the formula for alkyl polyglucosides being as follows:

in which l <x <5 and 6 <n <18.

Then, the solution is stirred by bubbling air at a flow rate of 6 Lh ¹ via a frit positioned in the lower part of the reactor. A first test is carried out without hydrogen peroxide and a second test is carried out with hydrogen peroxide (which is introduced simultaneously at the start of air bubbling, the start of air bubbling corresponding to time t = 0) according to a ratio of molar concentrations [H ₂ O ₂ ] / [Surfactants] of 10, ie a concentration of hydrogen peroxide of 2.57 * 10 ³ mol.L ¹ .

Samples are taken over time and are analyzed by surface tensiometry, which allows to return to the concentration of surfactants.

The results are shown in FIG. 2, which represents a graph illustrating the evolution of the concentration of surfactants C (in mg.L ′ ¹ ) as a function of the duration of treatment t (in min) (i.e. - say the time during which the solutions are subjected simultaneously to UV-C irradiation and air bubbling) with a curve a) for the first test and a curve

b) for the second test.

The degradation reaction of the surfactant by direct photolysis (that is to say without the action of hydrogen peroxide) is much slower than the reaction in the presence of hydrogen peroxide. By direct photolysis, the surfactants are degraded fairly quickly during the first ten minutes of the reaction, going from 100 to 70 mg.L ¹ . Then the kinetics decrease until reaching a plateau at 50 mg.L ¹ after 50 minutes.

Under the combined UV / H ₂ O ₂ / air bubbling action, the hydrogen peroxide, which is introduced into the reactor at t = 0, generates radical species which separate the hydrophobic and hydrophilic parts from the surfactants and stops the foaming power of surfactants. Glucopon degradation begins very quickly and the concentration of surfactant decreases sharply during the first two minutes of reaction to stabilize at 10 mg L ^-1. 73% of the surfactants are degraded in just 1 minute and the second minute makes it possible to degrade an additional 20%. This degradation time is extremely short.

Example 2

This example illustrates the implementation of the process of the invention in particular by playing on two modes of injection of hydrogen peroxide in an aqueous medium surmounted by a layer of preformed foam, the first mode being done directly in the foam overcoming the liquid phase and the second mode taking place in the underlying liquid phase. In addition, this example also demonstrates that the disappearance of the surfactants can be visually monitored by virtue of the height of the foam.

To do this, it is first carried out, the preparation of an aqueous medium surmounted by the foam layer.

This aqueous medium surmounted by a layer of foam is prepared by the introduction of 500 ml of 100 mg.L ^{1 solution} in Glucopon (of the same nature as that of Example 1 above) (i.e. 64 mg.L ¹ in surfactants) in a tubular reactor, the solution thus introduced then being subjected to air bubbling, the flow rate of which is fixed at 6 Lh ' ¹ . Foam gradually forms and fills the reactor in about two minutes. The air flow is lowered to 3.9 Lh ¹ , which allows the foam height to be stabilized to the maximum of its height, i.e. 13 cm in this case.

From this aqueous medium surmounted by a layer of foam subjected to bubbling fixed at a flow rate of 3.9 Lh ^1, 5 degradation tests are carried out:

a) a test in which the aqueous medium surmounted by a 13 cm layer of foam is subjected only to UV irradiation under the conditions defined in Example 1;

b) an assay in which the aqueous medium surmounted by a layer of foam of 13 cm is subjected, without UV irradiation, the addition of hydrogen peroxide at a concentration of 1,70.10 ³ mol L ^'1 to t = 0;

c) a test in which the aqueous medium surmounted by a 13 cm layer of foam is subjected to UV irradiation under the conditions defined in Example 1 and to the addition of hydrogen peroxide at a concentration of 1.70.10 ³ mol.L ¹ at t = 0 directly in the underlying aqueous medium;

d) a test in which the aqueous medium surmounted by a 13 cm layer of foam is subjected to UV irradiation under the conditions defined in Example 1 and to the addition of hydrogen peroxide at a concentration of 1.70.10 ³ mol.L ¹ at t = 0 directly in the foam layer;

e) a test in which the aqueous medium surmounted by a 13 cm layer of foam is neither subjected to UV irradiation nor to the addition of hydrogen peroxide, this test serving as a reference, the height of foam remaining constant .

The results obtained are reported in Figure 3 attached, which illustrates the evolution of the foam height H (in cm) as a function of the test duration t (in minutes) (curves a) for test a ), curve c) for test c), curve d) for test d) and curve e) for test e)).

For test a), the height of foam decreases over time and reaches 3 cm in height in 60 min then stabilizes, which is characterized by a plateau on curve a). The hypothesis which can be made is that the radicals formed preferentially degrade the majority organic reaction by-products (which no longer belong to the family of surfactants and which therefore have no foaming power) compared to the remaining surfactants minority (which always have a foaming power) which stabilize the foam. In this case, the height of the foam can no longer decrease.

Test b) carried out with an initial foam height of 13 cm without UV, in the presence of H ₂ O _{2 only} , resulted in a constant foam height over 120 min. The curve relating to this test b) is not shown since it merges with curve e), which also indicates a constant height of foam.

In the case of the process according to the invention involving the combined action UV-H ₂ O ₂ / bubbling (curves c) and d)), the drainage of the foam is total and rapid since it occurs after only six minutes of reaction, whether the addition of hydrogen peroxide is carried out in the foam or in the underlying liquid phase. In this case, the surface tension values at the end of the tests are the same as those for water, ie 71 mN / m, which means that all of the surfactants have been degraded.

When the addition of H ₂ O ₂ is carried out at t = 0, that is to say at the same time as bubbling, a film of foam of approximately one centimeter forms during the first minute of reaction and is immediately drained. The Glucopon solution therefore loses its foaming properties very quickly under these conditions.

Example 3

This example is intended to demonstrate the impact of air bubbling on the degradation of surfactants.

To do this, the following tests were carried out:

a test a), in which the solution described in Example 1 is subjected to the same treatment as that described in Example 1, except that the air bubbling is replaced by magnetic stirring in batch;

a test b), in which the solution described in example 1 is subjected to the same treatment as that described in example 1, except that the bubbling of air is replaced by a circulation of the solution in the reactor via a peristaltic pump at a flow rate of 0.44 L.min ' ¹ (to maintain a volume of 500 ml in the reactor, 750 ml of the solution of Example 1 are subjected to circulation);

-a test c) carried out under conditions similar to test b) except that air bubbling is reinstated under the conditions set out in the example

1.

The results are reported in Figure 4 attached, which illustrates the change in the concentration of surfactants C (in mg.L ' ¹ ) as a function of the treatment time t (in minutes) (curves a), b ) and c) for tests a), b) and c)). For comparison, the curve of the second test of Example 1 (called curve d) is added to this figure.

Under magnetic stirring, that is to say according to test a), the molecules degrade at a speed significantly slower than with bubbling, until reaching a value of 32 mg.L ¹ after 21 minutes, when this concentration is reached in less than a minute under bubbling. Beyond 21 minutes, the degradation is complete with the appearance of a plateau at 28 mg.L ¹ .

In circulation, according to test b), the degradation is even lower but the solution to be treated is greater since there is 750 mL. After one hour of reaction, the final concentration of surfactants is 45 mg.L ¹ .

Finally according to test c), the results are identical to those obtained with bubbling alone, which demonstrates the absence of contribution from circulation for the degradation of surfactants.

Example 4

In this example 4, a test reproduced under similar conditions of example 1 was carried out, except that the ratio [H ₂ O ₂ ] / [Surfactants] is no longer fixed at 10 but at a value of 6 (always keeping the initial concentration of surfactants at 2.57 * 10 ' ⁴ mol.L' ¹ ).

With a ratio of 6, about four centimeters of foam forms during the first two minutes, before disappearing. The reaction rate with a ratio of 6 is similar to that of the reference experiment (with a ratio of 10) and is completed in three minutes to reach the same final concentration of 5 mg.L ^_1 .

Example 5

In this example, tests reproduced under conditions similar to example 1 were carried out, except with different surfactant concentrations (100 mg / L respectively for test 1, 250 mg / L for test 2 and 500 mg / L for test 3).

The results of the tests are reported in Figure 5 attached, which illustrates the change in the concentration of surfactants C (in mg / L) as a function of the treatment time t (in minutes) (curves a) to c ) respectively for tests 1 to 3).

The results presented in this figure demonstrate rapid kinetics for test b) (that is to say with the solution at an initial concentration of 250 mg.L ¹ ) at the start of the reaction. The curve joins the values obtained for test a) (that is to say with the solution at an initial concentration of 100 mg.L ¹ ) from three minutes indicating an almost total degradation of the surfactants. It therefore takes just 33% additional treatment time to degrade 150% more surfactants.

For test c) (that is to say with the solution at an initial concentration of 500 mg.L ¹ ), the height of foam formed reaches a maximum of about four centimeters after two minutes. It is considered that this small amount of foam does not modify the concentration of surfactants in the solution. The concentration decreases rapidly to 50 mg.L ¹ after four minutes, then it decreases more slowly until it reaches a level below 10 mg.L ¹ after 16 minutes.

The treatment time required to reach 90% (+/- 5%) reduction in surfactants was also determined according to the initial concentrations.

The results are reported in Figure 6 attached, which illustrates the evolution of this treatment time t (in minutes) as a function of the initial concentration of surfactants C (ie in our case, respectively for 100 mg.L ¹ , 250 mg.L ¹ and 500 mg.L ¹ ).

The degradation times are extremely rapid even with the solution at an initial concentration of 500 mg.L ¹ , since 90% of the amount of surfactants are degraded in four minutes.

Example 6

This example illustrates the implementation of the process of the invention in accordance with the invention under the conditions of Example 1, except that the composition used is no longer Glucopon but a solution of TFD4 (which is a mixture of tetrapotassium ethylenediaminetetraacetate, potassium hydroxide and tetrasodium pyrophosphate).

This example was carried out under conditions similar to Example 1, except that the concentration of 0.1 gL ¹ relates to the concentration of the solution of TFD4 and no longer of the surfactants as such. This test shows very rapid kinetics (from one minute of reaction) degrading all of the surfactants present in this solution.

A second test is carried out with a higher concentration of 2g.L ^_1 of TFD4 and a concentration of hydrogen peroxide of 3.89.10 ³ mol.L ¹ . At this concentration, TFD4 does not foam under bubbling at room temperature but can foam at operating temperatures above room temperature.

The results of this second test are shown in FIG. 7, which illustrates the change in the concentration of TFD4 C (in mg.L ′ ¹ ) as a function of the duration of treatment t (in minutes).

The concentration of surfactants contained in TFD4 10 drops rapidly to reach a value close to zero after two minutes of reaction. Degradation of these surfactants has been shown to be very effective, as has been shown for Glucopon. A magnetic stirring test would confirm that the combined UV / H ₂ O ₂ / air bubbling action is indeed at the origin of this rapid kinetics.

Claims (4)

1. A method for removing, in whole or in part, the foam contained in an aqueous medium comprising one or more surfactants or for preventing the formation of such foam in such a medium comprising a step consisting in subjecting said aqueous medium to the 'combined action of ultraviolet irradiation, hydrogen peroxide and air bubbling. 2. Method according to claim 1, in which the ultraviolet irradiation is an irradiation with UV-C rays. 3. Method according to any one of the preceding claims, in which the surfactant (s) are anionic surfactants, such as those comprising a fatty acid salt, an alkylsulfate salt, an alkylbenzenesulfate salt, an alkylphosphate salt or a salt sulfosuccinate diester, an ethylenediaminetetraacetate salt; nonionic surfactants, such as those comprising a polyoxyethylene alkyl ether, a polyoxyethylene fatty acid ester, alkyl polyglucosides; cationic surfactants, such as those comprising quaternary alkyl and / or aryl ammonium halides; zwitterionic or amphoteric surfactants, such as surfactants comprising a betaine group. 4. Method according to any one of the preceding claims, in which the surfactant (s) are nonionic surfactants from the family of alkyl polyglucosides and / or anionic surfactants comprising an ethylenediaminetetraacetate salt.