FR3089131A1 - DYNAMIC FILTRATION DEVICE WITH CERAMIC POROUS PLATE OF SILICON CARBIDE - Google Patents

Abstract

Device for filtering a liquid loaded with mineral and / or organic pollutants comprising an enclosure delimited by walls, means for supplying the enclosure with said liquid, at least one porous filtering plate, said plate having two opposite main faces separated by an average thickness e, said plate comprising in its center a through opening of greater width l between the two main faces, means for evacuating the filtered liquid, in which said filter plate comprises a support made of a porous ceramic material solid and at least one porous separating layer covering at least partly, and preferably entirely, the surface portion of the support placed in contact with the liquid to be filtered, said material comprises silicon carbide, in which the porosity of said material, the porosity of the separating layer, the thickness e of the filter plate and the difference between the greatest length L of the wire plate trante and the largest width l of its central orifice are selected for the optimization of mechanical performance and filtration performance.

Description

Description

Title of the invention: DYNAMIC FILTRATION DEVICE WITH CERAMIC POROUS PLATE OF SILICON CARBIDE [0001] The invention relates to the field of filtration devices comprising an enclosure into which is injected a liquid to be filtered set in rotation, under vacuum or under pressure, said enclosure comprising at least one porous filtering plate made of a ceramic material in order to separate said liquid from its particles or from its molecules or even from its microorganisms. The present invention particularly finds its application in the treatment of liquids from processes in the chemical or pharmaceutical industry, the food or agrifood industry, or in the field of energy, in particular in the treatment of production water from the mining, oil and gas industry. The injection of gas, preferably air or even oxygen, is more particularly suited to the field of bioreactors in which the purification of the polluted liquid involves, in addition to filtration, a purification or a decomposition of the pollutants by microorganisms.

Filters have been known for a long time made from monolithic structures or supports of tubular geometry with or without membrane, formed of walls of a porous inorganic material delimiting one or more longitudinal channels parallel to the axis of said support.

In particular, front filters are known which typically comprise a portion of the blocked channels on their front face and a portion of the blocked channels on their rear face, in order to provide inlet channels and outlet channels separated by filter walls. through which the liquid to be filtered must pass. This is discharged by the passage of its molecules or particles or even of its microorganisms through the walls and the membrane, thus forming the retentate which then accumulates in the inlet channels while the purified liquid escapes through the output channels or even in part through the periphery of the filter if the latter is free. This technique is limited by the formation of a cake on the surface of the filter medium.

There are also techniques known as tangential filtration, which limit the accumulation of retentate, thanks to the longitudinal circulation of the fluid on the surface of the membrane. The particles to be treated remain in the circulation flow while the purified liquid can pass through the membrane under the effect of a pressure difference. This technique ensures stable performance and level of filtration. It is more particularly recommended for the filtration of fluids very charged with particles and / or molecules. This technique remains perfectible, however. In particular, the flow of liquid to be filtered is limited due to the deposition of a cake on the surface of the channels even if one takes place in the conditions of a turbulent regime. In addition, for liquids extremely charged with particles or very viscous, the productivity linked to this technique remains insufficient.

According to another technique, non-monolithic filtering devices are known which consist of a succession of porous plates within an enclosure, in which the liquid to be filtered is most often agitated so as to promote a turbulent regime. These devices promote the shearing forces within the liquid in contact with the porous plates and are more efficient for the depollution of highly charged or viscous liquids.

Publication DE3814373A1 discloses, for example, a device provided with mobile porous discs preferably made of corundum or silicon carbide, materials more mechanically resistant so as to allow regeneration unlike filters in the form of mat.

Publication DE19513759A1 also proposes a filtration module in which the parallel filtering discs are fixed in leaktight manner to a hollow movable axis which collects the filtrate having passed through the porous material of the discs.

Publication DE202004001955U1 also proposes a spring system placed on the axis to compensate for the expansion of the filter material which occurs during the high speed rotation of the filter elements in order to reduce the risk of breakage.

International application W02009 / 039861A1 proposes a device for treating wastewater comprising an enclosure and a set of parallel plates, including fixed filter plates permeable to liquid and permeable aeration plates in order to inject air in the reactor, said plates having a central cavity in which rotates an axis on which is fixed at least one rotating disk between the filtration plates and the aeration plates so as to agitate the liquid to be filtered.

Different forms of plates have been proposed, for example hollow ceramic plates comprising internal passages through which the filtrate can more easily be removed, as for example according to FIG. 7 of WO2009 / 039861A1 or even as proposed in publication EP2543420A1. Such plates can also have a membrane deposited on the largest faces of the filter plate as described for example DE202010015318U1.

Some plates have been described with an internal cavity comprising a drainage material (cf. EP2910299Al or even drainage channels as disclosed in W02009 / 039861A1). The different configurations comprising internal evacuation channels however lead to embrittlement of the porous plate.

There is today a need for a filtration device comprising a porous ceramic filter plate more mechanically robust while retaining an acceptable filtration efficiency, that is to say having an optimized and maximized flow of the filtrate, with equal dimensions.

Unlike previous solutions which offer different configurations taking into account only the geometric characteristics of the filter plates, the present invention is based on the principle of establishing a particular selection of ranges of said geometric characteristics and certain specific characteristics of the micro structure of the filter plate. Such a relationship, with the aim of solving the previously exposed problem, had never been described until now for such a device.

More particularly, the present application relates to a device for filtering a liquid loaded with mineral, inorganic and / or organic pollutants comprising:

- an enclosure delimited by walls,

- means for supplying the enclosure with said liquid,

at least one porous filtering plate, said plate having two opposite main faces separated by an average thickness e, said plate comprising in its center a through hole of greater width / between the two main faces,

- means of evacuation of the filtered liquid.

According to the invention, at least the two main faces of the filter plate (s) are in contact with the liquid to be filtered in the enclosure and the filter plate is in fluid communication with the means d evacuation, over a portion of its surface which is otherwise insulated in a sealed manner from the liquid to be filtered in the enclosure, so that the liquid passes through said plate, from the enclosure towards said evacuation means.

Still according to the invention, said filter plate comprises a support made of a solid porous ceramic material and at least one porous separating layer covering at least partly, and preferably entirely, the surface portion of the support placed in contact liquid to be filtered, said material comprises silicon carbide and its open porosity of said material is greater than 15% and less than 55% by volume and its volume distribution of pores has a median pore diameter greater than 10 micrometers and less than 100 micrometers.

The separating layer has an open porosity between 10% and 70%, preferably between 30% and 50% by volume and a median pore diameter in number between 5 nanometers and 5000 nanometers, preferably between 100 nanometers and 3000 nanometers, more preferably between 300 nanometers and 1000 nanometers.

According to the invention, the thickness e of the filter plate is between 3mm and 20 mm, preferably between 4mm and 15 mm, more preferably between 5mm and 10 mm and the difference between the largest length Z of the filter plate and the largest width / of its central orifice is between 50mm and 700mm, preferably between 50mm and 600mm, more preferably between 75mm and 500mm.

Preferably, the device has one or more of the following characteristics, which can of course be combined with each other if necessary:

- The plate has substantially the shape of a disc, its diameterD being equal liL.

- The orifice is substantially circular, its diameter d being equal to /.

- The filtration device comprises a plurality of filter plates, in particular between 2 and 200 filter plates.

- The filtration device further comprises at least one ventilation plate.

- The filter plate (s) are fixed, and comprising a system for agitating and / or rotating the liquid in the enclosure, in particular a propeller, a turbine or an axis provided with fins.

- The filter plate (s) are integral with a movable hollow axis constituting a means of evacuation of the filtered liquid, the filter plate (s) being in fluid communication with the cavity of the axis.

- The longest length of the filter plate is between 100mm and 800mm, preferably between 300mm and 600mm.

- The largest width / of the central opening is between 30mm and 200mm, preferably between 50mm and 150mm.

- The average thickness of the separating layer is between 1 micrometer and

100 micrometers, preferably between 20 micrometers and 80 micrometers.

- The separating layer is made of a material chosen from the group consisting of SiC, in particular recrystallized SiC, SiC linked by Si ₃ N ₄ , or by Si ₂ ON ₂ or by SiAlON, or again with BN or a mixture of at least two of these compounds.

- The supply pressure of the liquid to be filtered is between 0.1 and 0.5 MPa.

- The filtration device further comprises means for pressurizing the liquid upstream of said means for supplying the enclosure.

- The filtration device further comprises means for placing under vacuum, in particular means for sucking the liquid downstream of said means for evacuating the enclosure.

The invention also relates to a filter plate as previously described and having in particular the following characteristics:

- It comprises a support made of a solid porous ceramic material and at least one porous separating layer covering at least a portion of the surface of the support, [0035] - said material comprises silicon carbide, and [0036] - the open porosity of said material constituting the substrate is greater than 15 and less than 55% by volume and its pore volume distribution has a median pore diameter greater than 10 and less than 100 micrometers, the separating layer has a porosity open between 10 and 70%, preferably between 30 and 50% - the separating layer has a median pore diameter of between 5 and 5000 nanometers, preferably between 100mm and 3000 nanometers, [0039] - the thickness e of the plate is between 3mm and 20 mm, preferably between 4mm and 15 mm, more preferably between 5mm and 10 mm, - the difference between the longest length of the plate and the diameterof its central orifice is between 50mm and 700mm, preferably between 50mm and 600mm, more preferably between 75mm and 500mm.

For the sake of brevity, a filter plate according to the invention obviously also has all the preferred characteristics described above in relation to the filtration device.

In addition, the invention relates to the use of said device for the treatment of liquids from processes in the chemical or pharmaceutical industry, the food or agrifood industry, or in the field energy, in particular the treatment of production water from the mining, oil and gas industry.

The term “support” made from a solid porous ceramic material means that this support does not include any internal cavity (ies), apart of course from its intrinsic porosity.

The open porosity and the median diameter of the pores of the support filter plate according to the present invention are determined in known manner by mercury porosimetry. The porosity, corresponding to the overall volume of the pores, is measured by intrusion of Mercury at 2000 bars using a mercury porosimeter such as the Autopore IV porosimeter series 9500 Micromeritics, on a 1 cm ³ sample taken from a block. of the support, the sampling region excluding the skin typically extending up to 500 microns from the surface of the block. The applicable standard is ISO 15901-1.2005 part 1. The increase in pressure up to high pressure leads to "pushing" the mercury into increasingly smaller pores. The mercury intrusion is conventionally done in two stages. Initially, a mercury intrusion is carried out at low pressure up to 44 psia (approximately 3 bar), using air pressure to introduce the mercury into the larger pores (greater than 4 micrometers). In a second step, a high pressure intrusion is carried out with oil up to the maximum pressure of 30,000 psia (approximately 2,000 bar). In application of the Washbum law mentioned in the standard

ISO 15901-1.2005 part 1, a mercury porosimeter allows to establish a pore size distribution by volume. The median pore diameter of the support plate corresponds to the threshold of 50% of the population by volume.

The porosity of the separating layer, corresponding to the total volume of pores in said layer, and the median pore diameter of the layer are advantageously determined according to the invention using a scanning electron microscope. In the context of the present invention, it is considered that the porosity obtained by this method can be assimilated to open porosity. Typically, sections of a wall of the support are made in cross section, so as to display the entire thickness of the coating over a cumulative length of at least 1.5 cm. Image acquisition is performed on a sample of at least 50 grains, preferably at least 100 grains. The area and the equivalent diameter of each of the pores are obtained from snapshots by conventional image analysis techniques, possibly after a binarization of the image intended to increase the contrast. A distribution of equivalent diameters is thus deduced, from which the median pore diameter is extracted. The porosity of the layer is obtained by integrating the distribution curve of equivalent pore diameters. Likewise, a median size of the particles constituting the separating layer can be determined by this method. An example of determining the median diameter of pores constituting the separating layer, by way of illustration, comprises the succession of the following steps, conventional in the field:

A series of SEM photographs is taken from the support with its membrane separating layer observed in a cross section (that is to say throughout the thickness of a wall). For greater clarity, the photographs are taken on a polished section of the material. The acquisition of the image is carried out on a cumulative length of the membrane layer at least equal to 1.5 cm, in order to obtain values representative of the entire sample.

Snapshots are preferably subjected to binarization techniques, well known in image processing techniques, to increase the contrast of the outline of the particles or pores.

For each pore constituting said layer, a measurement of its area is carried out. An equivalent pore diameter is determined, corresponding to the diameter of a perfect disk with the same area as that measured for said pore (this operation can possibly be carried out using dedicated software, in particular Visilog® marketed by Noesis ). A pore diameter size distribution is thus obtained according to a conventional number distribution curve and a median diameter of pores constituting the membrane layer are thus determined, this median diameter corresponding respectively to the equivalent diameter dividing said number distribution into a first population. having only pores of equivalent diameter greater than or equal to this median diameter and a second population comprising only pores of equivalent diameter less than this median diameter.

The support is formed of a porous ceramic material of SiC, see SiC linked by Si ₃ N ₄ , Si ₂ ON ₂ , SiAlON or BN or a combination of these, preferably SiC recrystallized.

The separating layer is formed from a porous inorganic material, in particular a non-oxide ceramic material, such as SiC, in particular recrystallized SiC, Si ₃ N ₄ , Si ₂ ON ₂ , SiAlON, BN or a combination of these. this. Its porosity is typically from 10 to 70% and the median pore diameter from 10 nm to 5 μm. The permeability of the membrane K _m is preferably from 10 ¹⁹ to 10 ¹⁴ m ² , preferably between 1.0.10 ¹⁷ and 1.0.10 ¹⁶ m ² . It typically has an average thickness t _m of 0.1 to 300 µm, preferably 1 to 200 µm, more preferably 10 to 70 µm.

The filter plate according to the invention can be obtained by any technique well known to those skilled in the art. A conventional manufacturing process generally comprises the main stages of manufacturing the support and then depositing the filtration membrane comprising or consisting of the filtering separating layer.

The support for the plate is preferably obtained by casting a slip or pressing a semi-dry mixture, or even by extruding a paste through a die. This step is followed by drying and baking to sinter the material. A particular choice of powders of the mixture before shaping and the maximum baking temperature and the time to plateau at this maximum temperature making it possible to obtain the optimum porosity and mechanical strength characteristics.

For example, when it is a recrystallized SiC support, it can in particular be obtained according to the following manufacturing steps:

Kneading of a mixture comprising particles of silicon carbide with a purity greater than 98%, preferably in a mass proportion greater than 50%, or even greater than 70% or even even greater than 80% or even 90% by compared to dry mix. The mixture also includes additives such as a dispersant or even a PH regulator in the case of a slip; organic binders, for example of the cellulose derivative type, or even lubricants and plasticizers, in the case of a pressing or extrusion mixture. Water is added, typically between 5 and 40% of the mass of inorganic powders and kneaded until a homogeneous mixture is obtained. Preferably, in the case of a slip essentially comprising SiC, a dispersant such as sodium hydroxide can be added in order to correct the PH between 8.5 and 10, preferably between 9.0 and 9.5.

- shaping of the mixture, by extrusion, pressing, casting, preferably by casting. The drying step can be preceded by a hardening step, in particular before demolding in the case of shaping by casting.

- drying of the raw supports, for example in an oven and / or in a microwave, for a time sufficient to bring the water content not chemically bound to less than 1% by mass, [0057] - cooking until at a temperature of at least 1600 ° C and less than 2400 ° C typically maintained for at least 1 hour. The material obtained has an open porosity of 15 to 55%, preferably 20 to 45% by volume and a median pore diameter of the order of 10 micrometers to 100 micrometers, preferably from 15 micrometers to 40 micrometers, more preferably from 20 to 30 micrometers.

The support is then coated with a membrane. This membrane comprises or consists of the separating layer according to the invention. In a preferred embodiment, the membrane comprises, in addition to the separating layer, a bonding primer disposed between the surface of the support and the separating layer, most often whose porosity is intermediate between that of the support and that of said separating layer . The various layers of the membrane, in particular the separating layer, can be deposited according to various techniques known to those skilled in the art: deposition from suspensions or slips, chemical vapor deposition (CVD) or deposition by thermal spraying, for example plasma spraying. Preferably, the membrane layers are deposited by coating from slips or suspensions. As indicated above, the membrane can be obtained by depositing several successive layers. The membrane advantageously comprises a first layer, called the primer, deposited in direct contact with the substrate. The primary plays the role of bonding layer.

According to a particular embodiment, the slip used for the deposition of the primer preferably comprises between 30 and 70% by mass of SiC grains having a median diameter of 1 to 40 μm, the remainder being for example a metallic silicon powder , silica and / or carbon powder. According to another mode, 100% by mass of SiC grains are mixed, including 30 to 70% of a first fraction of one or more SiC powders which has a median diameter between 1 and 40 μm and 70 to 30% d '' a second fraction of one or more SiC powders which has a median diameter of between 0.2 and 5 µm, the first fraction having a diameter at least twice, even three times or even five times greater than the diameter of the second . The mass ratio of water added to the total SiC varies from 0.8 to 1.2. Obviously the slip may include adjuvants such as lubricants, temporary binders, plasticizers, defoamers.

To this mixture of powders, a mass of deionized water corresponding to 10 to 120% of the total mass of inorganic powders is added. The membrane also includes a separating layer deposited on the primer layer. It is in this separating layer that the porosity is controlled in order to give the filter its selectivity. The slip used for depositing the separating layer may comprise between 30 and 70% by mass of SiC grains having a median diameter of 0.5 to 20 μm or between 30 and 70% by mass, in total, of a mixture metallic silicon, silica and carbon, the balance being deionized water. According to a particular embodiment, the slip only has a mineral component in the form of an SiC powder having a median diameter between 0.1 and 11 micrometers. The mass ratio of water added to the total SiC varies from 0.8 to 1.2.

Certain additives such as thickening agents, binding agents and / or dispersing agents can be added to the slip to control in particular their rheology. The viscosity of the slip is typically from 0.01 to 0.8 Pa.s, preferably from 0.05 to 0.7 Pa.s, measured at 22 ° C under a shear gradient of 1 s ¹ according to the DIN standard. -53019-1: 2008. Slips can typically comprise from 0.1 to 1% of the water mass of thickening agents preferably chosen from cellulose derivatives. They can typically comprise from 0.1 to 5% of the mass of SiC powder of binding agents preferably chosen from poly (vinyl alcohol) (PVA) or and acrylic derivatives. The slip can also comprise from 0.01 to 1% of the mass of SiC powder of dispersing agents preferably chosen from ammonium polymethacrylate. One or more layers of slip can be deposited to form the membrane. The deposition of a slip layer typically makes it possible to obtain a membrane with a thickness of 2 to 80 μm, but thicker membranes typically of 100 to 300 μm can be obtained by the deposition of several successive layers of slip.

The coated product is then dried at room temperature typically for at least 30 minutes and then at 60 ° C for at least 6 hours. The supports thus dried are sintered at a baking temperature typically between 1200 ° C and 2200 ° C, preferably between 1500 ° C and 2000 ° C, under a non-oxidizing atmosphere, preferably under argon so as to obtain a measured membrane porosity. by image analysis from 10 to 70% by volume and an equivalent median pore diameter measured by image analysis from 5 nm to 5 μm, preferably between 100 nanometers and 3000 nanometers.

The filter plate according to the invention can be used for various applications of purifying liquids and / or separating particles or molecules or microorganisms from a liquid.

The filter plate according to the invention can be used in particular for various liquid purification applications and makes it possible to maximize the flow of filtrate regardless of the viscosity of the liquid to be filtered. It can be used to filter liquids having for example a dynamic viscosity of 100 to 5000 mPa.s, or even up to 10000 mPa.s. The dynamic viscosity of the fluid to be filtered can be measured at 20 ° C, under a shear gradient of 1 s ¹ according to DIN 53019-1: 2008. The present invention relates in particular to the use of a filtering plate as described above for the purification of production water from petroleum extraction or shale gas. It also finds its application in various industrial processes for the purification and / or separation of liquids in the chemical, pharmaceutical, food, agrifood or bioreactor fields, as well as in swimming pool water.

The invention also relates to a device which may further comprise one or more ventilation plates. The aeration plate or plates are in fluid communication with means for supplying the aeration gas over a portion of its surface which is otherwise sealed in a sealed manner from the liquid to be filtered in the enclosure, so that the liquid to be filtered cannot pass between said aeration plate and said means for supplying aeration gas. The aeration gas can be air, or even oxygen, in particular to act on the biological activity in the case of a membrane bioreactor. It can also be a gas in order to chemically treat the liquid to be filtered, for example by reduction or by oxidation. The said ventilation plate (s) can be fixed or mobile, just like the filtration plate. Each ventilation plate can advantageously be interposed between two filter plates. It can include silicon carbide. It can have substantially the same material characteristics as the filter plate.

According to a possible embodiment, a filtering plate can also constitute an aeration plate, the means for supplying the aeration gas then being able to be or not connected to the means of evacuating the filtrate or the permeate, the plate operating alternately in filtration mode or in ventilation mode.

The attached attached figures illustrate in more detail certain aspects of the present invention. The information given below should not however be considered as limiting the scope of the invention, under any aspect of the invention described in the figures.

Figure 1 illustrates a sectional view of a filter device 1 according to the invention comprising an enclosure 2 surrounded by walls (not shown in the figure) supplied by a pipe 3 with liquid to be filtered, a typical path in the 'enclosure is symbolized by the arrows 5. The liquid to be filtered is set into turbulence by means 4 which can be a propeller, a turbine or an axis provided with fins. The means 4 passes through the filter plate 6, the support 7a of which is coated with a membrane comprising a separating layer 7b of the type previously described. After passing through the membrane and in particular its separating layer which has the role of retaining the polluting particles, the filtrate 8 obtained crosses the thickness of the porous filter plate and joins the discharge means 9, which is otherwise isolated so watertight of the liquid contained in the enclosure thanks to the seals 10. The filtration plate according to the invention as shown in FIG. 1 is a disc of diameter D and of thickness e, pierced in its center with an orifice of diameter d. The plate 6 is substantially identical to that described in relation to Example 1.

2 shows a sectional view of another filter device 11 according to the invention incorporating a filtration plate 16 and comprising an enclosure 12 supplied by a tube 13 with liquid to be filtered including a typical path in the enclosure is illustrated by the arrows 15. The plate 16 comprises a porous support 17a coated with a filtration membrane 17b comprising a separating layer The filtration plate is integral with a hollow axis 14, the two elements being movable in rotation in the enclosure . The liquid to be filtered is put into turbulence this time by means of the movable hollow axis 14 and the plate, itself driven in rotation with the axis. The liquid to be filtered crosses the filter plate and the filtrate 18 obtained progresses in the thickness of the filter plate and joins the evacuation means in the hollow axis 14. The sealed contact between the axis 14 and the filter plate 16 being secured by a gasket 19.

If the mechanical stresses are obviously different according to the modes of Figures 1 and 2, the filter plate in both cases must be able to withstand varying degrees of high mechanical stresses due to the highly turbulent regime of the liquid to be filtered which can be particularly viscous or even abrasive.

The present invention and its advantages are illustrated with the aid of the following examples. The examples according to the invention should not, of course, be considered to be limiting of its implementation.

EXAMPLES:

Substrates or supports were obtained by casting a slip in a plaster mold. The different basic compositions of the mixture of grains making up the pouring slip and the dimensions of the plates obtained for each example are described in Table 1. After hardening in air and demolding, the supports were then dried at 110 ° C./ 12h then cooked under Argon at 2200 ° C in a 6h stage. The porosity and the median pore diameter of the substrates are obtained by adapting the particle size composition of the mixture of grains of the slip. A series of five supports has been produced, for example. The substrates all have the shape of a disc of diameter D pierced in its center with an orifice of diameter d.

A filtration membrane was then deposited on the surface of the supports except the peripheral thickness which was masked (evacuation face). The membrane is deposited by coating with slip. For this, a primary bonding of the membrane is formed first, from a slip whose formulation is specified in Table 1 below.

A separating layer is then deposited on the primer layer from a slip whose formulation is specified in Table 1 below. The viscosity of the slip, measured at 22 ° C. under a shear gradient of 1 s ¹ according to standard DINC33-53019-1: 2008, is adjusted to 0.1 Pa.s using well-known additives of l skilled in the art.

The primer and the separating layer are deposited according to the same process. The slip is introduced into a tank with stirring at 20 revolutions / min. After a deaeration phase under light vacuum, typically 25 mbar, while retaining agitation. The tank is put under overpressure of about 300 mbar in order to supply a protective gun with a suitable nozzle, with a diameter of 1 mm to 2 mm. The projection is obtained via a carrier gas (air) adjusted to a pressure of 1 to 3 bars. The slip coats the unmasked surfaces of the support. The coated support is then dried at room temperature for 30 minutes and then at 60 ° C for 30 h. The coated support thus dried is then sintered at a temperature of 1650 ° C. under an argon atmosphere for 2 hours to obtain a porosity of the membrane of 40% with a median pore diameter of 600 nm. In Table 1 below, the main characteristics of the process for obtaining the filter plates according to the invention are reported:

[Tables 1]

example 1 according to Γ inventi we example 2 according to the invention example 3 according to the invention example 4 according to the invention example if 1 example if 2 example if 3 Formulation of the initial mixture and manufacture of the support Alpha SiC powder d ₅ o = 2pm FCP07 / AW1 39% 34% 52% 34% 26% 34% Alpha SiC powder d ₅ o = 55pm F240 58% 63% 63% 25% 14% 63% Alpha SiC powder d ₅₀ = 155pm 90F 48% 65% 59% Silica powder d50 = 2pm SF800 3% 3% 3% 10% 1% 3% dispersant Amount of NaOH to reach a pH between 9 and 9.5 Water added (% by weight of the mixture of inorganic powders) + 15% Heat treatment 2200 ° C / Ar / 6h 2200 ° C / Ar / 6h 2200 ° C / Ar / 6h 2200 ° C / Ar / 6h 2200 ° C / Ar / 6h 2200 ° C / Ar / 6h Primary formulation: Powder alpha SiC d ₅ o = lOpm DPF-C 30% Alpha SiC powder d ₅ o = 36pm F280 30% Alpha SiC powder d ₅ o = 2pm 40%

FCP07 Other additives: (dispersant, binder) MEG, PVA, Tylose Water added (% by weight of the mixture of inorganic powders) + 30% Formulation of the separating layer: Alpha SiC powder d ₅₀ = 0.5pm SINTEX 15 100% Other additives: (dispersant, binder) MEG, PVA, Tylose Water added (% by weight of the mixture of inorganic powders) 36% Cooking the filter plate Cooking temperature ° C 1650 ° C Level of cooking 2h Oven atmosphere Argon

In Table 2 below, the main characteristics of the filter plates thus synthesized are reported:

[Tables!]

example 1 (according to the invention) example 2 (according to the invention) example 3 (according to the invention) example 4 (according to the invention) example comparison 1 comparative example 2 example if 3 Seal Nature of the seal between the plate and the filtrate outlet O-ring elastomer 13mm thick Filter plate support Material of the support R-SiC R-SiC R-SiC R-SiC R-SiC R-SiC R-SiC D ₅₀ of pores (micrometers) 19 22 25 25 95 20 21 porosity (% volume) 27.5 30 17.0 35.0 55.0 13.0 30.0 SiC content (% by weight) > 98 > 98 > 98 > 98 > 98 > 98 > 98 Average support thickness (mm) 8 8 8 8 30 3 10 Internal hole diameter d (mm) 100 100 100 100 100 100 50 Plate diameter D (mm) 400 400 400 400 400 400 800 D-d difference (mm) 300 300 300 300 300 300 750 Separating layer of the filter plate

Material of the layer SiC grains SiC grains SiC grains SiC grains SiC grains SiC grains SiC grains D ₅₀ of pores (micrometers) 0.6 0.6 0.6 0.6 0.6 0.6 0.6 porosity (% volume) 40% 40% 40% 40% 40% 40% 40% SiC content (% by weight) > 98% > 98% > 98% > 98% > 98% > 98% > 98% Average thickness of the separating layer (micrometers) 100 100 100 100 100 100 100

For each example, a flexural rupture modulus at 20 ° C. was determined according to a test no. 1. (MOR 20 ° C), measured in air on a test piece with dimensions (in mm ³ ) of 80x20xthickness of the plate. The 3-point bending assembly is carried out with a distance of 60 mm between the two lower supports and the speed of descent of the punch is equal to 0.5 mm / min. The value is an average resulting from three successive measurements. The results are reported in Table 3 below.

A test No. 2 of bending on the plate was also carried out in order to measure the load leading to rupture, thus determining the force at rupture. A punch with a diameter greater than the internal diameter of the disc with lower supports is applied to the plate maintained at its periphery on a circular support with upper supports as shown diagrammatically in FIG. 3. A force is applied to the upper face of the punch with the using a press at a substantially constant speed (100 Kg / min) until breaking. The failure load expressed as a percentage relative to Example 2 according to the invention, for which the value of 100% has been assigned, is reported in Table 3.

According to a test No. 3, the filtration capacity was evaluated by flow measurement by placing a filter plate in an enclosure as described in Figure 1. The fluid consists of demineralized and deionized water at a temperature 25 ° C. It is injected into the enclosure at a pressure of 2 bars and at a rotation speed of 350 rpm in order to ensure a transmembrane pressure of 1.5 bars. The seal between the recovery means at the periphery and the peripheral evacuation face of each plate is ensured by an O-ring with a thickness of 13mm. The characteristic flux of the plate of the example in percentage as compared to Example 1 according to the invention is reported in Table 3 for which an efficiency of 100% has been assigned.

[Tables3]

example 1 according to the invention example 2 according to the invention example 3 according to the invention example 4 according to the invention example compare! fl example compare! f2 example compare! f3 Test n ° l MOR (Mpa) 73 61 65 45 5 100 60 Test # 2 Maximum charge 120% 100% 107% 74% 38% 23% Not measured Filtered liquid flow 100% 151% 43% 365% 278% 17% 30%

It appears that if the best flows are obtained with filter plates whose substrate is the most porous. A rapid fall in the modulus of rupture in bending is however observed and the force at rupture remains insufficient for sufficient mechanical strength despite a significant increase in the thickness of the filter plate (see Comparative Example 1). Comparative examples 1 to 3 show that a porosity of 15% or 55% or a difference between the maximum length and the diameter of the upper central orifice lead to a bad compromise between filtration capacity and mechanical properties (mechanical resistance MOR and / or flexural strength). Conversely, the filter plates of Examples 1 to 2 according to the invention present the best compromise in terms of filtration capacities and mechanical properties with regard to the comparative examples. The filter of Example 3 according to the invention is characterized by good mechanical properties but however with lower filtration capacities than Examples 1 and 2, although these remain acceptable. According to the invention, such an embodiment will be preferred in a purification device in which the filter plates are subjected to high mechanical stresses. The filter according to example 4 is characterized by very high filtration capacities but lower mechanical properties, although these remain entirely acceptable for use in a purification device, requiring a very high flow and constraints. weaker mechanical.

Claims (1)

[Claim 1] Claims Filtration device (1) of a liquid (5) loaded with mineral, inorganic and / or organic pollutants comprising: - an enclosure (2) delimited by walls, - means (3) for supplying the enclosure with said liquid, at least one porous filtering plate (6), said plate having two opposite main faces separated by an average thickness e, said plate (6) comprising in its center a through opening of greater width / between the two main faces, means for evacuating the filtered liquid, at least the two main faces of the filter plate (s) being in contact with the liquid to be filtered in the enclosure, the filter plate being in fluid communication with the evacuation means, on a portion of its surface which is otherwise sealingly insulated from the liquid to be filtered in the enclosure, so that the liquid passes through said plate, from the enclosure towards said evacuation means, said device being characterized in that: - said filter plate comprises a support (7a) made of a solid porous ceramic material and at least one porous separating layer (7b) covering at least partly, and preferably entirely, the surface portion of the support placed in contact with the liquid to filter, and said material comprises silicon carbide, and the open porosity of said material is greater than 15% and less than 55% by volume and its pore volume distribution has a median pore diameter greater than 10 micrometers and less than 100 micrometers, the separating layer has an open porosity of between 10% and 70%, preferably between 30% and 50%, by volume, and the separating layer has a number median pore diameter between 5 nanometers and 5000 nanometers, preferably between 100 nanometers and 3000 nanometers, more preferably between 300 nanometers and 1000 nanometers, and - the thickness e of the filter plate is between 3mm and 20mm, preferably between 4mm and 15mm, more preferably between 5mm and 10mm, and - The difference between the greatest length Z of the filter plate and the greatest width / of its central orifice is between 50mm and 700mm, preferably between 50mm and 600mm, more preferably between 75mm and 500mm. [Claim 2] Filtration device according to claim 1 wherein the plate has substantially the shape of a disc, its diameter /? being equal to L. [Claim 3] Filtration device according to one of the preceding claims, in which the orifice is substantially circular, its diameter d being equal to /. [Claim 4] Filter device according to one of the preceding claims comprising a plurality of filter plates, in particular between 2 and 200 filter plates. [Claim 5] Filtration device according to one of the preceding claims, further comprising at least one ventilation plate. [Claim 6] Filter device according to one of the preceding claims, in which the filter plate or plates are fixed, and comprising a system for agitating and / or rotating the liquid in the enclosure, in particular a propeller, a turbine or an axis provided with fins. [Claim 7] Filtration device according to one of claims 1 to 5, in which the filter plate (s) are integral with a movable hollow axis constituting a means for discharging the filtered liquid, the filter plate (s) being in fluid communication with the axis cavity. [Claim 8] Filter device according to one of the preceding claims, in which the longest length of the filter plate is between 100mm and 800mm, preferably between 300mm and 600mm. [Claim 9] Filtration device according to one of the preceding claims, in which the largest width / of the central opening is between 30mm and 200mm, preferably between 50mm and 150mm. [Claim 10] A filtration device according to one of the preceding claims, in which the average thickness of the separating layer is between 1 micrometer and 100 micrometers, preferably between 20 micrometers and 80 micrometers. [Claim 11] Filtration device according to one of the preceding claims, in which the separating layer is made of a material chosen from the group consisting of SiC, in particular recrystallized SiC, SiC bound by Si ₃ N ₄ , or by Si ₂ ON ₂ or by SiAlON, or by BN or a mixture of at least two of these compounds. [Claim 12] Filter device according to one of the preceding claims, in which the supply pressure of the liquid to be filtered is between 0.1 and 0.5 MPa. [Claim 13] Filter device according to one of the preceding claims, further comprising means for pressurizing the liquid upstream of said means for supplying the enclosure. [Claim 14] Filtration device according to one of the preceding claims, further comprising means for placing under vacuum, in particular means for sucking the liquid downstream of said means for evacuating the enclosure. [Claim 15] Filter plate as described in one of the preceding claims, characterized in that: it comprises a support made of a solid porous ceramic material and at least one porous separating layer covering at least a portion of the surface of the support, said material comprises silicon carbide, and the open porosity of said material constituting the substrate is greater than 15 and less than 55% by volume and its volume distribution of pores has a median pore diameter greater than 10 and less than 100 micrometers, the separating layer has an open porosity of between 10 and 70%, preferably between 30 and 50% the separating layer has a median pore diameter, in number, of between 5 and 5000 nanometers, preferably between 100mm and 3000 nanometers, the thickness e of the plate is between 3 mm and 20 mm, preferably between 4 mm and 15 mm, more preferably between 5 mm and 10 mm, - The difference between the longest length of the plate and the diameter of its central opening is between 50mm and 700mm, preferably between 50mm and 600mm, more preferably between 75mm and 500mm. [Claim 16] Use of the filter device according to one of claims 1 to 14 or the filter plate according to claim 15 for the treatment of liquids from processes in the chemical or pharmaceutical industry, the food industry or the food industry , or in the energy sector, in particular the treatment of production water from from the mining, oil and gas industry.