DEVICE FOR PURIFYING A FLUID, IN PARTICULAR WASTE WATER

Abstract

An electrochemical device for purifying a fluid, for example wastewater or sludge, includes an electrochemical filtering membrane, including a metallic support, for example chosen from a screen, a fabric or an open-pore foam, the support being permeable to the fluid, a coating layer of the support including a titanium oxide of general formula TiOx, with x between 1.5 and 1.9.

Claims

1. An electrochemical device for purifying a fluid by oxidation of organic compounds contained in said fluid comprising an electrochemical filtering membrane, said electrochemical filtering membrane comprising: a metallic support said metallic support being permeable to said fluid, a coating layer of said metallic support comprising or consisting of a titanium oxide of general formula TiO.sub.x, with x between 1.5 and 1.9.

2. The electrochemical device as claimed in claim 1, wherein the electrochemical filtering membrane is configured to act as electrode enabling the partial or complete degradation of said organic compounds.

3. The electrochemical device as claimed in claim 1, wherein the metallic support comprises or consists of a metal chosen from titanium, stainless steel.

4. The electrochemical device as claimed in claim 1, wherein the metallic support has a porosity of between 10% and 90%.

5. The electrochemical device as claimed in claim 1, wherein the metallic support has a median pore diameter, by volume, of between 10 micrometers and 10 millimeters.

6. The electrochemical device as claimed in claim 1, wherein the metallic support has a median pore diameter of less than 50 micrometers.

7. The electrochemical device as claimed in claim 1, wherein the metallic support has a median pore diameter of greater than 70 micrometers.

8. The electrochemical device as claimed in claim 25, wherein the metallic support is a screen.

9. The electrochemical device as claimed in claim 25, wherein the metallic support is a fabric of assembled metal wires.

10. The electrochemical device as claimed in claim 25, wherein the metallic support is a foam.

11. The electrochemical device as claimed in claim 10, wherein an overall open porosity of the foam is between 20% and 90%.

12. The electrochemical device as claimed in claim 10, wherein a median pore diameter of the foam, by volume, is between 2 micrometers and 10 millimeters.

13. The electrochemical device as claimed in claim 1, wherein the metallic support is in the form of a plate or a tube.

14. The electrochemical device as claimed in claim 1, wherein the material constituting the coating layer comprises more than 90% by weight, in total, of Magnéli phases selected from Ti.sub.4O.sub.7, Ti.sub.5O.sub.9, Ti.sub.6O.sub.11 or a mixture of at least two of these phases.

15. The electrochemical device as claimed in claim 1, further comprising means for introducing the fluid to be purified, means for circulating the fluid, for a possible pressurization thereof, means for powering the metallic support and means for recovering the purified fluid.

16. An electrochemical filtering membrane for the purification of a fluid, comprising: a metallic support, said metallic support being permeable to said fluid, a coating layer of said metallic support comprising or consisting of a titanium oxide of general formula TiO.sub.x, with x between 1.5 and 1.9.

17. A process for manufacturing an electrochemical filtering membrane as claimed in claim 16, wherein the metallic support comprises or consists of titanium, and wherein the method comprises manufacturing the coating layer by oxidation by anodization or chemical treatment of the metallic support in order to obtain a layer comprising TiO.sub.2 then reduction of said Ti O.sub.2 to give a titanium oxide of general formula TiOx, with x between 1.5 and 1.9.

18. A process for manufacturing an electrochemical filtering membrane as claimed in claim 16, comprising performing a first step according to which the metallic support is bought into contact with a solution of sol-gel type comprising titanium, said solution optionally including an additional source of carbon, then performing a second step of heat treatment of the sol-gel layer in order to obtain a coating layer of TiOx, at a temperature between 500° C. but not exceeding 1430° C. at atmospheric pressure, under an inert or reducing atmosphere.

19. A process for manufacturing an electrochemical filtering membrane as claimed in claim 16, comprising depositing the coating layer on the metallic support by impregnation starting from an aqueous suspension, or a suspension of another solvent, of a TiOx powder, followed by performing a heat treatment at a temperature between 500° C. but not exceeding 1430° C. at atmospheric pressure, under an inert or reducing atmosphere.

20. A process for manufacturing an electrochemical filtering membrane as claimed in claim 16, comprising depositing the coating layer on the metallic support by impregnation starting from an aqueous suspension, or a suspension of another solvent, of a mixture of titanium oxide TiO.sub.2 powder, supplemented by an additional source of carbon, the coating layer of TiOx being obtained by reduction of said TiO.sub.2 layer by a subsequent heat treatment at a temperature between 800° C. but not exceeding 1430° C. at atmospheric pressure, under an inert or reducing atmosphere.

21. A process for manufacturing an electrochemical filtering membrane as claimed in claim 16, comprising depositing the coating layer on the metallic support by thermal spraying of TiOx particles on said metallic support.

22. A method comprising oxidizing a fluid comprising organic compounds with the electrochemical device as claimed in claim 1.

23. The method as claimed in claim 22, wherein the metallic support is a metallic foam, comprising or consisting of a metal chosen from titanium, stainless steel.

24. A process for purifying a fluid, said fluid comprising organic compounds, said process comprising introducing said fluid into the electrochemical device as claimed in claim 1, bringing said fluid into contact with said electrochemical filtering membrane acting as electrode, under conditions for oxidation of said organic compounds, and drawing off the fluid thus decontaminated.

25. The electrochemical device as claimed in claim 1, wherein the metallic support is a screen, a fabric, an open-pore foam or a honeycomb.

26. The electrochemical device as claimed in claim 2, wherein the electrochemical filtering membrane is configured to act as an anode, enabling the partial or complete degradation of said organic compounds.

Description

EXAMPLES

[0102] in these examples, the performance for degradation of paracetamol by two embodiments according to the invention was measured.

Example 1 (Comparative)

[0103] A first membrane is obtained by a process comprising the plasma deposition of a TiO.sub.x powder on a water-impermeable titanium metal plate.

[0104] The powder used for the plasma spraying is an electrically melted powder (i.e. a TiOx powder melted, then cooled and ground), having a mean particle size of the order of 30 micrometers, essentially containing the Ti.sub.4O.sub.7, Ti.sub.5O.sub.9, Ti.sub.3O.sub.5 and Ti.sub.6O.sub.11 phases. This powder is injected, by means of an argon carrier gas with a flow rate of 4 l/min, into a plasma generated by a Saint-Gobain Pro-Plasma torch fed with plasma gases (mixture of Ar with a flow rate of 45 l/min and of H2 with a flow rate of 11 l/min) under a voltage of 63-66 V (current 600 A); an argon shield makes it possible to prevent the reoxidation of the TiO.sub.x particles during the spraying. The substrate is sandblasted beforehand with alumina-zirconia grains under a pressure of 5 bar. The spraying distance is 110 mm.

[0105] The characteristics of the membrane are the following: the substrate is a TA6V plate with a thickness of 2 mm. The TiO.sub.x layer is deposited on the 2 faces until a coating thickness of around 300 micrometers is obtained.

At the same time as the deposition on the plate according to the invention, another deposition was carried out under the same conditions, this time on a substrate consisting of a non-sandblasted pellet of a titanium alloy TA6V with a diameter of 15 mm. After the plasma deposition, the coating is recovered and analyzed by XRD so as to determine the phases constituting the TiO.sub.x coating. The XRD analysis gave the following results: predominant main phase: Ti.sub.4O.sub.7; minority secondary phases: rutile; Ti.sub.3O.sub.5; Ti.sub.5O.sub.9; Ti.sub.8O.sub.15.

Example 2 (According to the Invention)

[0106] A second membrane is obtained by a process comprising the plasma deposition of a TiO.sub.x powder this time on a titanium metal screen.

[0107] The characteristics of the membrane are the following: The substrate is a titanium screen from the company ITALFIM, the dimensional characteristics of which are the following:

[0108] The titanium screen has holes in the shape of diamonds with a period along the long diagonal of 4 mm; and along the short diagonal of 2.2 mm, the width of the strand being 0.6 mm and its thickness 0.5 mm. Its overall porosity is measured as being of the order of 33% and the median diameter of its pores (its holes) is measured as substantially equal to 1.1 mm in the following way:

[0109] On an image obtained by a binocular microscope, image analysis processing is carried out using the ImageJ image processing software in order to estimate the surface area of the openings. From this data, the diameter of a disk of the same surface area and ultimately a median diameter of the openings are calculated. The result obtained was verified by measuring, on the same image, the length of each of the diagonals of the diamonds of the screen. The surface area of said diamonds and then the diameter of the disk of the same surface area are deduced therefrom.

[0110] The overall porosity of the screen was deduced from its length, width and thickness in order to determine a “geometric density” by dividing the calculated volume (length×width×thickness) by the mass of the screen. By dividing by the theoretical density of Ti, the porosity of the screen is obtained (in %). The calculation was verified by the Archimedes method.

[0111] The conditions of the plasma deposition are identical to those of example 1.

[0112] After plasma spraying on the 2 faces of the screen, the strand thickness is measured as substantially equal to 900 μm (micrometers) by observation with a binocular magnifier; the strand thickness being initially 600 μm, it is possible to estimate a deposition thickness substantially equal to 150 μm.

Example 3 (According to the Invention)

[0113] A third membrane is obtained by a process comprising the plasma deposition of a TiO.sub.x powder according to the same conditions as described above, this time on a titanium metal foam. The foam originates from the company American Elements.

[0114] Its porosity is characterized by mercury porosimetry; the pore volume is 35% and the median pore size by volume is 88 micrometers. Its thickness is 2.5 mm.

A plasma deposition of TiO.sub.x is carried out on the 2 faces of the foam under the same conditions as described above.
The deposit thus obtained was observed on a previously polished surface. A thickness of the TiO.sub.x layer on the walls of the foam of around 30 micrometers is measured.
The performance for degradation of paracetamol is measured by providing the membranes described in examples 1 to 3 in a purification device comprising:

[0115] In a 500 ml glass beaker containing demineralized water, 3.55 mg of Na.sub.2SO.sub.4 from the company VWR, and 30 mg of paracetamol (98%) from the company Acros Organics are dissolved; a magnetic stirrer rotating at 400 rpm; a water bath making it possible to regulate the temperature of the beaker at 30° C.

[0116] Immersed in this beaker are the following: [0117] an anode (consisting of the Ti plate coated with TiO.sub.x for example 1; the Ti screen coated with TiO.sub.x for example 2, the foam coated with TiO.sub.x for example 3). 33 cm.sup.2 of the membrane are immersed in each case. [0118] a platinum cathode from the company HANNA Instruments. [0119] a KCl-saturated Ag/AgCl reference electrode from the company BioLogic.

[0120] A current of 165 mA is imposed by a Princeton Applied Research Model 273 potentiostat.

[0121] In order to measure the performance for degradation of the organic species, the reduction in chemical oxygen demand (COD), expressed in mg of oxygen per liter, is measured. It represents the total content of oxidizable substances in the water. This parameter corresponds to the amount of oxygen that it is necessary to provide in order to chemically oxidize these substances.

[0122] The COD is measured as follows: at regular intervals, 2 ml of the sample to be characterized are poured into a COD reagent tube from the company Hanna Instruments; the tube is brought to 150° C. and maintained for 2 h at 150° C., then stirred and cooled; the COD value is given by colorimetric assay by means of a photometer from the company Hanna Instruments; before each measurement, a “blank” standard, consisting of the solution salted by Na.sub.2SO.sub.4, but with no paracetamol, is characterized in the same way.

[0123] The percentage reduction in COD as a function of time is given in the following table for the plate (comparative example), for the screen (example 2) and for the foam (example 3):

TABLE-US-00001 TABLE 1 t = 0 t = 4 h Plate 0% 15% (example 1) Screen 0% 22% (example 2) Foam 0% 70% (example 3)