ELEMENT FOR SEPARATING A LIQUID MEDIUM WITH HIGH PARIETAL SHEAR STRESS

The subject of the invention relates to a separating element comprising:          an inorganic one-piece rigid porous support (2) having, on one side, a first outer planar surface (3) and, on an opposite side, a second outer planar surface (4);     at least two circulation ducts (6) for the liquid medium that are formed in the porous support so as to each have a rectangular cross section;     at least one internal connection system for the distribution (10) of the liquid medium in a series of circulation ducts, and at least one internal connection system for the collection (12) of the retentate coming from the series of circulation ducts, the internal connection system for the distribution (10), the circulation ducts (6) and the internal connection system for the collection (12) being provided with at least one separating layer continuously deposited between the inlet (11) and the outlet (13) of the porous support;     and a collection system (7) for the permeate that has passed through the separating layer or layers.

TECHNICAL FIELD

The present invention relates to the technical field of elements for separating, by tangential flow, a liquid medium to be treated into a filtrate or permeate and a retentate, commonly called filtration membranes.

More specifically, the invention relates to new geometries of these separating elements allowing to increase the flow of the filtrate and/or to reduce the energy consumption of the installations implementing these separating elements.

PRIOR ART

Separation methods using membranes are used in many sectors, in particular in the environment for the production of drinking water and the treatment of industrial effluents, in the chemical, petrochemical, pharmaceutical, food industry and in the field of biotechnology.

A membrane constitutes a selective barrier which allows, under the action of a transfer force, the passage or the stopping of certain components of the fluid medium to be treated. The passage or the stopping of the components results from their size compared to the size of the pores of the membrane which then behaves like a filter. Depending on the pore size, these techniques are called microfiltration, ultrafiltration or nanofiltration.

There are membranes of different structures and textures. The membranes are generally made up of a porous support which provides the mechanical strength of the membrane and which, defining the number and morphology of the circulation ducts for the liquid medium to be treated, determines the total filtering surface of the membrane. It is in fact on the inner walls of these circulation ducts that a layer called a separating layer, filtration layer, separation layer, active layer or skin ensures the separation. During the separation, the transfer of the filtered liquid medium takes place through the separating layer, then this liquid spreads in the porous texture of the support to move towards the outer perimeter surface of the porous support. This part of the liquid to be treated that has passed through the separation layer and the porous support is called permeate or filtrate and is recovered by a collection system. The other part is called retentate and is most often reinjected into the liquid to be treated upstream of the membrane, thanks to a circulation loop.

The main phenomenon antagonistic to the transfer of the filtrate through the separation layer is the appearance of clogging resulting from a concentration polarization, a deposition or a blockage of the pores. Regardless of the nature of the filtering layer used to carry out a filtration operation and regardless of the nature of the liquid medium to be treated, there always appears from the start of the filtration operation, a drop in the permeation flow which is the consequence of said clogging of the separation layer and which can sometimes be extremely strong and rapid.

The phenomenon of concentration polarization operates during a filtration operation when the macromolecules present in the liquid medium to be treated concentrate at the membrane/solution interface where they exert an osmotic counter-pressure opposite to the separation force or backdiffuse into the center of the liquid medium to be treated according to Fick's law. The phenomenon of concentration polarization results from the accumulation of the compounds retained in the vicinity of the membrane due to the permeation of the solvent.

It is when the concentration of particles at the surface of the membrane increases until it causes the appearance of a condensed phase in the form of a gel or a cohesive deposition that a hydraulic resistance additional to that of the diaphragm appears. Pore blocking occurs when there is intrusion of particles of size less than or equal to those of the pores, which leads to a reduction in the filtering surface.

Clogging, its reversibility or its irreversibility, are complex phenomena which depend on the filtration element and in particular on the separating layers, on the liquid to be treated and on the operating parameters.

Clogging is a major obstacle to the economic attractiveness of filtration because it leads, when sizing filtration installations, to increasing the installed surfaces in order to meet the volume requirements to be treated on the one hand and it necessitates the implementation of specific technical means to overcome this a posteriori, such as cleaning cycles using detergents or periodic retro-filtrations on the other hand.

To eliminate, limit or delay said accumulation of material, the positive effect of the continuous flow speed of a fluid to be treated tangentially to the surface of a filtering layer has been widely studied and described in the prior art.

It is thus in fact that the current interest of tangential filtration of liquids lies in a continuous and controlled circulation of the liquid medium to be treated (the retentate) inside circulation ducts under conditions of speed and pressure which act on the amplitude and the kinetics of the clogging of the filtering layer, the speed of movement of the retentate generating a parietal shear stress τpwhich slows down the clogging, hence an increase in the flow rate of the filtrate (of the permeate) in the porosities of the filtering layer and its support.

The higher the speed, the higher the value of the parietal stress τpand the more the clogging is reduced or delayed. But the disadvantage is that this “speed effect” on the one hand requires an increase in power which generally works against it and on the other hand does not allow to compare circulation ducts of different cross sections.

It is the access to the value of the parietal shear stress τp(wall shear stress) itself which allows to compare circulation ducts of different cross sections. First H. Barnier “Colmatage de membranes minérales d'ultrafiltration ou de microfiltration dans les bio-industries”, Membranes and Bio-industries Study Days, Paris (France), (1993) then G. Gésan-Guiziou, G. Daufin, E. Boyaval, O. Le Berre, “Wall shear stress: effective parameter for the characterisation of the cross-flow transport in turbulent regime during skimmed milk microfiltration”, Milk, 79, 347-354, (1999) consider that the parietal stress is the only parameter which allows, for the same fluid to be treated, to compare their performances.

The parietal shear stress represents the forces applied by the fluid flowing tangentially to the surface of the membrane on a membrane surface element.

It is a homogeneous quantity at a pressure and its unit is the pascal (Pa) or N·m−2. It can be experimentally determined with the following relationship:

where d is the hydraulic diameter and L the length of the circulation duct.

It is dependent on the nature of the liquid medium (its viscosity) via the pressure drop Δp, the Darcy friction factor fD(dimensionless number) and the Reynolds number Re in accordance with the following relationships:

where fD, in the case of a circulation duct with circular cross section and in laminar flow regime, is equal to: fD=64/Re, the coefficient 64 being characteristic of a circulation duct with a circular cross section.

The authors Yunus A. Cengel and John M. Cimbala, in their book “Mécanique des Fluides, Fondements et Applications” Copyright 2017 by De Boeck Superieur (Translation by A. Chagnes, S. Griveau, V. Lair and A. Ringuedé), specify that this coefficient varies according to the geometry of the cross section of the circulation duct of the fluid to be treated. It emerges from this work that at identical Reynolds, the friction factor becomes higher than that of a circulation duct with a circular cross section, for a circulation duct with a strongly flattened rectangular cross section.

Under these conditions, and all other things being equal, the parietal shear stress τpin such a circulation duct is greater than that in a circulation duct with a circular or square cross section, thus allowing more effective unclogging and a gain on the permeation flux.

The prior art has proposed various embodiments of filtration membranes with circulation ducts of rectangular section. For example, patent FR 2 696 653 describes a filtration unit including a rigid porous structure interposed between a thrust plate and a counter-thrust plate. The rigid porous structure has main planar faces covered by a separating layer in contact with the liquid medium to be treated flowing between these main faces and the thrust and counter-thrust plates. This solution requires the implementation of thrust and counter-thrust plates.

The subject of the invention proposes to provide new rigid filtration elements with a geometry adapted to ensure effective unclogging with a view to increasing the flow of the filtrate while being easy to manufacture.

DISCLOSURE OF THE INVENTION

To achieve such a purpose, the subject of the invention relates to an element for separating a liquid medium to be separated into a permeate and a retentate including:an inorganic one-piece rigid porous support having, on one side, a first outer planar surface and, on an opposite side, a second outer planar surface connected to the first outer planar surface by at least one outer connecting surface;at least two circulation ducts for the liquid medium that are formed in the porous support so as to each have a rectangular cross section;at least one internal connection system for the distribution of the liquid medium, arranged in the porous support to distribute from an inlet formed in the porous support, the liquid medium, in a series of circulation ducts, and at least one internal connection system for the collection of the retentate, arranged in the porous support to collect up to an outlet formed in the porous support, the retentate coming from the series of circulation ducts, the internal connection system for the distribution, the circulation ducts and the internal connection system for the collection being provided with at least one separating layer continuously deposited between the inlet and the outlet of the porous support so that the liquid medium circulating in the porous support between the inlet and the outlet is only in contact with said separating layer, the porous support having a continuity of material and of porous texture and a mechanical strength allowing to prevent the breaking of the porous support for a pressure difference of the liquid medium of at least one bar between the separating layer and the outlet surface of the permeate;and a collection system for the permeate that has passed through the separating layer or layers.

Advantageously, the porous support is obtained by the implementation of an additive method adapted so that the porosity of the porous material ensures the routing of the permeate that has passed through the separating layer or layers.

Typically, the constituent material of the porous support has a maximum allowable bending stress of at least 10 MPa.

According to an advantageous embodiment characteristic, the rectangular cross section of the circulation ducts has two dimensions, one of the dimensions of which is at least four times smaller than the other dimension.

For example, several circulation ducts are formed in the porous support parallel to each other.

According to another example, at least one circulation duct has a flexible shape while following the main direction of circulation of the fluid to be treated.

For example, at least one circulation duct has a periodic flexible shape.

According to one embodiment, each circulation duct has a constant cross section over its entire extent between the internal connection system for the distribution and the internal connection system for the collection.

According to an exemplary embodiment, the circulation ducts are delimited by two parallel faces which are perpendicular or parallel to at least two outer planar surfaces of the porous support.

According to a variant embodiment, the internal connection system for the distribution and the internal connection system for the collection open onto the outside of the porous support via one or more orifices or nozzles arranged at an outer planar surface or at an outer connecting surface.

For example, the internal connection system for the distribution and the internal connection system for the collection are arranged asymmetrically on either side of the circulation ducts.

According to another example, the internal connection system for the distribution and the internal connection system for the collection are arranged symmetrically on either side of the circulation ducts.

According to one embodiment characteristic, the collection system for the permeate includes spaces arranged inside the porous support to collect the permeate that has passed through the separating layer or layers.

Typically, the collection system for the permeate opens onto the outside of the porous support via one or more orifices or nozzles for collecting said permeate.

The first outer planar surface, the second outer planar surface and the outer connecting surface are sealed.

According to one embodiment characteristic, the collection system for the permeate is recessed in at least one outer planar surface of the porous support to collect the permeate that has passed through the separating layer or layers, the rest of the outer planar surface not recessed being sealed.

For example, the porous support includes nozzles sealed on the outside, delimiting the inlet of the internal connection system for the distribution and the outlet of the internal connection system for the collection.

The nozzles extend along directions whose angles relative to the main direction of circulation of the liquid medium are comprised between 0° and 90°.

Another subject of the invention is to provide a separation unit including at least one separating element mounted in an apparatus provided with connections to ensure on the one hand the entry of the liquid medium to be treated and the exit of the retentate as well as on the other hand the collection of the permeate the nozzles of which delimit the inlet of the internal connection system for the distribution of the liquid medium to be treated and the outlet of the internal connection system for the collection of the retentate, the permeate collection nozzles being equipped with connections fixed in a sealed manner to said nozzles.

DESCRIPTION OF EMBODIMENTS

The subject of the invention relates to a separating element1, by tangential flow of a liquid medium M to be separated into a permeate or filtrate P and a retentate R. This liquid medium to be treated can be of any nature. In accordance withFIGS.1and2which generally illustrate the characteristics of the invention without representing all the details for reasons of clarity, the separating element1includes an inorganic one-piece rigid porous support2having, on one side, a first outer planar surface3and, on an opposite side, a second outer planar surface4connected to the first outer planar surface by at least one connecting surface5. At least two circulation ducts6for the liquid medium to be treated are formed in the porous support2being provided on their inner faces with at least one separating layer.

Given that the rigid porous support2has a first outer planar surface3and a second outer planar surface4located opposite or facing each other, the separating element1has an optimized geometry. It should be noted that in the example illustrated inFIGS.1and2, the first outer planar surface3and the second outer planar surface4are not parallel to each other. According to a preferred variant embodiment illustrated inFIG.3and subsequent figures, the first outer planar surface3and the second outer planar surface4are parallel to each other, offering the possibility of stacking the separating elements1on top of each other. The connecting surface5between these two outer planar surfaces3,4can be produced in any appropriate way, for example by a curved surface or a planar surface perpendicular to the outer planar surfaces3,4by defining one or more connecting faces. This connecting surface5can define, for example, two parallel to each other connecting faces as illustrated inFIGS.3to11or four connecting faces parallel to each other two by two as illustrated inFIG.14and subsequent figures so that the porous support2has the shape of a rectangular parallelepiped.

In such separating elements1, the body constituting the porous support2has a porous texture. This porous texture is characterized by the average pore diameter. It is recalled that the average pore diameter means the value d50 of a volume distribution for which 50% of the total pore volume corresponds to the volume of pores with a diameter less than this d50. The volume distribution is the curve (analytical function) representing the frequencies of the pore volumes as a function of their diameter. The d50 corresponds to the median dividing into two equal parts the area located under the frequency curve obtained by mercury penetration. In particular, the technique described in standard ISO 15901-1:2005 can be used as regards the measurement technique by penetration of mercury.

The porosity of the porous support, which corresponds to the total volume of the interconnected voids (pores) present in the material considered, is a physical quantity which conditions the flow and retention capacities of said porous body. In order for the material to be used in filtration, the total interconnected open porosity must be at least 10% for a satisfactory flow of filtrate through the support, and at most 60% in order to guarantee an appropriate mechanical strength of the porous support.

The porosity of a porous support can be measured by determining the volume of a liquid contained in said porous body by weighing said material before and after a prolonged stay in said liquid (water or other solvent). Knowing the respective densities of the material considered and of the liquid used, the mass difference, converted into volume, is directly representative of the volume of the pores and therefore of the total open porosity of the porous support.

Other techniques allow to precisely measure the total open porosity of a porous support, including:mercury intrusion porosimetry (ISO 15901-1 standard mentioned above): injected under pressure, the mercury fills the pores accessible to the pressures applied, and the volume of mercury injected then corresponds to the volume of the pores;small-angle scattering: this technique, which uses either neutron radiation or X-rays, gives access to physical quantities averaged over the entire sample. The measurement consists of analyzing the angular distribution of the intensity scattered by the sample;the analysis of 2D images obtained by microscopy;the analysis of 3D images obtained by X-ray tomography.

The porous support2has an average pore diameter in the range from 0.5 μm to 50 μm. The porosity of the porous support2is comprised between 10 and 60%, preferably between 20 and 50%.

The porosity of the porous support2is open, that is to say it forms an array of interconnected pores in three dimensions, which allows the fluid filtered by the separating layer or layers to pass through all or part of the porous support2to a collection system7for the permeate P that has passed through the separating layer or layers. As described in detail in the remainder of the description, the collection system7for the permeate P is arranged in the porous support2or as illustrated inFIGS.1to5, outside the porous support2. In the case where the collection system7for the permeate P is arranged in the porous support2, the collection system7opens onto the outside of the porous support2through one or more orifices8or nozzles9for collecting the permeate communicating with an external permeate recovery circuit. Such an external permeate recovery circuit can be made in any appropriate way and includes in particular, for example, either an apparatus provided with connections as described inFIGS.30and31when the collection system7opens onto the outside of the porous support2through orifices8or pipes provided with connections intended to be fixed in a sealed manner on the nozzles9when the collection system7opens onto the outside of the porous support2through such nozzles.

It is customary to measure the water permeability of the porous support2to qualify the hydraulic resistance of the porous support. Indeed, in a porous medium, the stationary flow of an incompressible viscous fluid is governed by Darcy's law. The speed of the fluid in the porosity (the permeate) is proportional to the pressure gradient and inversely proportional to the dynamic viscosity of the fluid, via a characteristic parameter called permeability which can be measured, for example, according to the French standard NF X 45-101 in December 1996.

Conventionally, the separating layer or layers used in the context of the invention ensure the filtration of the liquid medium to be treated. The filtration separating layers, by definition, must have an average pore diameter smaller than that of the porous support. The separating layers delimit the surface of the tangential flow separating element intended to be in contact with the liquid medium to be treated and along which the liquid medium to be treated will circulate.

The thicknesses of the filtration separating layers typically vary between 1 μm and 100 μm in thickness. Of course, to ensure its separation function and serve as an active layer, the separating layers have an average pore diameter less than the average pore diameter of the porous support. Most often, the average pore diameter of the filtration separating layers is at least less by a factor of 3, and preferably, by at least a factor of 5 relative to that of the porous support.

The notions of microfiltration, ultrafiltration and nanofiltration separating layer are well known to the person skilled in the art. It is generally accepted that:microfiltration separating layers have an average pore diameter comprised between 0.1 μm and 10 μm;the ultrafiltration separating layers have an average pore diameter comprised between 10 nm and 0.1 μm;the nanofiltration separating layers have an average pore diameter comprised between 0.5 nm and 10 nm.

It is possible for this micro or ultrafiltration layer, called active layer, to be deposited directly on the porous support, or else on an intermediate layer of smaller average pore diameter, itself deposited directly on the porous support.

The separation layer may, for example, consist of a ceramic, selected from oxides, nitrides, carbides or other ceramic materials and mixtures thereof, and, in particular, titanium oxide, alumina, zirconia or a mixture thereof, titanium nitride, aluminum nitride, boron nitride, silicon carbide optionally mixed with another ceramic material.

The separation layer can also, for example, consist of one or more polymers such as PAN, PS, PSS, PES, PVDF, cellulose acetate or other polymers.

According to one characteristic of the invention, the separating element1includes at least one internal connection system for the distribution10of the liquid medium to be treated, arranged in the porous support2to distribute from at least one inlet11formed in the porous support2, the liquid medium to be treated, in a series of circulation ducts6. The separating element1also includes at least one internal connection system for the collection12of the treated liquid medium, arranged in the porous support2to collect up to at least one outlet13formed in the porous support2, the treated liquid medium coming from the series of circulation ducts2. It should be understood that the internal connection system for the distribution10, the series of circulation ducts6and the internal connection system for the collection12are formed by empty spaces for the circulation of the liquid medium, that is to say by areas of the porous support2not including any porous material.

The internal connection system for the distribution10is arranged so as to distribute the liquid medium in a series of circulation ducts6from an inlet11for the liquid medium M formed in the porous support2. Typically, this internal connection system for the distribution10includes from an inlet11, a common inlet segment10eopening into a bifurcation or crossing10bmade by the porous support to include as many distribution channels as circulation ducts6. As will be explained in detail in the following description, the internal connection system for the distribution10opens via its inlet11, onto the outside of the porous support10via one or more nozzles15or orifices16formed at an outer planar surface3,4or at an outer connecting surface5. The inlet11for the liquid medium to be treated communicates with an external circulation circuit that can be produced in any appropriate manner. This external circulation circuit includes in particular, for example, either an apparatus provided with connections as described for example inFIGS.30and31when the internal connection system for the distribution10opens onto the outside of the porous support2through orifices16or pipes provided with connections intended to be fixed in a sealed manner on the nozzles15when the internal connection system for the distribution10leads to the outside of the porous support2through such nozzles15.

Similarly, the internal connection system for the collection12is arranged in the porous support2to recover the liquid medium from the liquid ducts and convey it to the outlet13arranged in the porous support2and ensuring the evacuation of the retentate R. Typically, the internal connection system for the collection12includes, from an outlet13, a common outlet segment12sopening into a branch or crossing12emade by the porous support to include as many collection paths as circulation ducts6. As will be explained in detail in the following description, the internal connection system for the collection12opens via the outlet13, onto the outside of the porous support2by one or more nozzles15or orifices16arranged at an outer planar surface3,4or at an outer connecting surface5. The outlet13for the retentate communicates with an external circulation circuit that can be produced in any appropriate manner. This external circulation circuit includes in particular, for example, either an apparatus provided with connections as described for example inFIGS.30and31when the internal connection system for the collection12opens onto the outside of the porous support2through orifices16or pipes provided with connections intended to be fixed in a sealed manner on the nozzles15when the internal connection system for the collection12opens onto the outside of the porous support2via such nozzles15.

In the example illustrated inFIGS.1and2, the internal connection system for the distribution10and the internal connection system for the collection12are arranged asymmetrically on either side of the circulation ducts6. It should be noted that the internal connection system for the distribution10and the internal connection system for the collection12can be arranged symmetrically on either side of the circulation ducts6, as in the examples illustrated inFIG.3and subsequent figures.

In the example illustrated inFIGS.1and2, the separating element1includes two circulation ducts6communicating on one side with an inlet11, via the internal connection system for the distribution10and on the opposite side with an outlet13via the internal connection system for the collection12. Of course, as will be described in detail in the various variant embodiments, the separating element1may include between an inlet11and an outlet13, a series of circulation ducts6greater than two. Similarly, the separating element1can include several inlets11and several outlets13, as well as several series of circulation ducts6, each of which communicates with an inlet11and an outlet13.

According to an advantageous characteristic of the invention, the internal connection system10for the distribution of the liquid medium to be treated, the circulation ducts6and the internal connection system for the collection12of the treated liquid medium are provided with at least one separating layer continuously deposited between the inlet11and the outlet13of the porous support2so that the liquid medium circulating in the porous support2between the inlet11and the outlet13is only in contact with said separating layer. In other words, the internal faces of the internal connection system for the distribution10, of the circulation ducts6and of the internal connection system for the collection12are provided with at least one separating layer. It follows that the liquid medium circulates in the porous support2while only being in contact with a separating layer.

According to a characteristic of the subject of the invention, the circulation ducts6for the liquid medium to be treated are formed in the porous support2so as to each have a rectangular cross section defined by two long sides parallel to each other of length a and two short sides parallel to each other of width b. The rectangular cross section of the circulation ducts6is taken perpendicular to the flow lines of the liquid to be treated. As it appears fromFIG.1, it should be noted that the sides of the rectangular cross section of the circulation ducts6are not necessarily rectilinear. However, according to a preferred variant embodiment, all the sides of the rectangular cross section of the circulation ducts6are rectilinear. Advantageously, the rectangular cross section of the circulation ducts6is constant along their entire length or extended, namely over the distance taken between the internal connection system for the distribution10and the internal connection system for the collection12.

According to an advantageous embodiment characteristic, one of the dimensions, namely the width b of the short sides of the rectangular cross section, is at least four times less than the other dimension, namely the length a of the long sides of the rectangular cross section of the circulation ducts6. For example, the width b of the short sides of the rectangular cross section is between 4 and 80 times less than the length a of the long sides of the rectangular cross section of the circulation ducts6.

The description which follows gives, by way of non-limiting illustration, various variant embodiments of the separating element1in accordance with the invention, the general principle of which is described in relation toFIGS.1and2. All the characteristics of the invention described in relation toFIGS.1and2are implemented by these different embodiments even if these characteristics are not described in detail for each of them.

According to the example illustrated inFIGS.1and2, the circulation ducts6are formed in the porous support2while not being parallel to each other. According to the embodiments illustrated inFIG.3and subsequent figures, the circulation ducts6are formed in the porous support2parallel to each other. It should be noted that in the examples illustrated inFIGS.3to13and25to29, the circulation ducts6are delimited by two parallel planar faces which are parallel to the two outer planar surfaces3,4of the porous support2whereas in the examples ofFIGS.14to24, the two parallel planar faces of the circulation ducts6are perpendicular to the two outer planar surfaces3,4of the porous support2.

It should be noted that according to an exemplary embodiment not illustrated, the porous support2may include at least one circulation duct6with a flexible volume while following the main direction of circulation of the fluid to be treated; a flexuous volume being defined by the displacement around a reference axis along a curvilinear trajectory, of a planar generating section, this reference axis not passing through said generating section and being contained in the volume of the porous support. At least one circulation duct has a periodic flexuous shape.

FIGS.3to5illustrate an exemplary embodiment of a separating element1made in the form of a flattened block of generally rectangular shape provided with nozzles15intended to be connected to an external circulation circuit for the liquid medium. This separating element1includes a porous support2including a first outer planar surface3and a second outer planar surface4parallel to each other located facing each other and interconnected by a connecting surface5arranged to form two connecting faces parallel to each other and two nozzles15at each of the two opposite ends of the porous support2. The nozzles15extend in a direction whose angle relative to the main direction of flow of the fluid to be treated is equal to 0°. Of course, the nozzles15can extend in different directions, such as in directions whose angles relative to the main direction of circulation of the liquid medium are comprised between 0° and 90°.

Two circulation ducts6are formed in the porous support2parallel to each other and opposite each other and each have a rectangular cross section with a width at least four times less than the length. These two circulation ducts10are parallel to the outer planar surfaces3,4. These circulation ducts6are connected on one side with the internal connection system for the distribution10arranged in the porous support2and on the other side, with internal connection system for the collection12arranged in the porous support2. The internal connection system for the distribution10opens onto the outside of the porous support2via a nozzle15in which the inlet11is formed, while the internal connection system for the collection12opens onto the outside of the porous support2through the other nozzle15in which the outlet13is formed. According to this example, the collection system7for the permeate P is not arranged in the porous support2so that the permeate is collected at the outer planar surfaces3,4and at the connecting surface5. Also, the collection system7which is located outside the porous support2, is made by any appropriate systems to recover the permeate leaving the outer surface of the porous support2, as a receptacle.

FIGS.6to10illustrate another exemplary embodiment of a separating element1made in the form of a flattened block of generally rectangular shape provided with nozzles15intended to be connected to an external circulation circuit for the liquid medium and nozzles9intended to be connected to an external permeate collection circuit, the collection system for the permeate7arranged in the porous support2. This separating element1includes a porous support2including a first outer planar surface3and a second outer planar surface4parallel to each other and opposite each other by being interconnected by a connecting surface5arranged to form two connecting faces51parallel to each other. These two connecting faces51are interconnected at each of their ends, by the connecting surface5arranged to form, at one end, a nozzle15delimiting the inlet11for the liquid medium and a permeate collection nozzle9and at the other end, a nozzle15for the outlet13of the retentate R and another permeate collection nozzle9. As shown in the drawings, the two nozzles15for the fluid medium and the retentate are aligned along the longitudinal axis of the separating element1while the permeate collection nozzles9are arranged symmetrically on either side of the nozzles15for the fluid medium and the retentate. Moreover, the nozzles9,15extend in a direction whose angle relative to the main direction of circulation of the fluid to be treated is equal to 0° but it is clear that the nozzles9,15can extend along different directions such as in directions whose angles relative to the main direction of circulation of the liquid medium are comprised between 0° and 90°.

Two circulation ducts6are formed in the porous support2parallel to each other and each have a rectangular cross section with a width substantially thirty times less than the length. These two circulation ducts6are parallel to the outer planar surfaces3,4. These circulation ducts6are connected on one side with the internal connection system for the distribution10and on the other side, with the internal connection system for the collection12.

The internal connection system for the distribution10includes a common inlet segment10eformed by a tubular conduit arranged in the nozzle15and opening onto the outside of the porous support2at the end of the nozzle15, via the inlet11(FIG.10). The common inlet segment10ecommunicates opposite the inlet11via a bifurcation10bformed in the porous support, with the two circulation ducts6. Similarly, the internal connection system for the collection12includes a common outlet segment12sformed by a tubular conduit arranged in the nozzle15and opening onto the outside of the porous support2, at the end of the nozzle, via the outlet13. The common outlet segment12scommunicates opposite the outlet13, via a branch12earranged in the porous support2, with the two circulation ducts6.

According to this exemplary embodiment, the internal connection system for the distribution10and the internal connection system for the collection12are arranged symmetrically on either side of the circulation ducts6, so that the nozzles15are centered on the longitudinal axis passing through the middle of the porous support2. Of course, as indicated above, the internal faces of the internal connection system for the distribution10, the internal faces of the circulation ducts6and the internal faces of the internal connection system for the collection12are provided with at least one separating layer.

According to this exemplary embodiment, the collection system7for the permeate P is arranged in the porous support2so that the outer planar surfaces3,4and the connecting surface5are sealed. Of course, the nozzles15delimiting the inlet11and the outlet13and the two permeate collection nozzles9which are formed by the connecting surface5, are also sealed externally. As shown more precisely inFIGS.8and9, the collection system7includes an array of eight channels7aarranged in the support2parallel to each other according to the same plane and between the two circulation ducts6to recover the permeate P that has passed through the separating layer or layers and the support2. The channels7aare separated from each other by longitudinal partitions2aand are separated from the circulation ducts6by partition walls2b. These channels7acommunicate with each other at each end, by a collecting channel7cextending by a conduit7darranged in a nozzle9to open onto the outside of the porous support2, at the end of the nozzle9. As is apparent from the drawings, a first outlet nozzle9for the permeate P is arranged parallel to the nozzle15defining the inlet11for the liquid medium, while a second outlet nozzle9for the permeate P is arranged parallel to the nozzle15defining the outlet13for the liquid medium.

According to this example ofFIGS.6to10, the nozzles9,15for connection respectively to an external permeate recovery circuit and to the liquid medium supply and retentate outlet circuits are of the fluted tubular type. Of course, the connection nozzles9,15can be arranged to have a connection system of a different type.FIG.11illustrates an exemplary embodiment of a separating element1identical to the example illustrated inFIGS.6to10with the difference that the nozzles9,15are smooth. According to another embodiment not shown, the nozzles9,15can be threaded.

FIGS.12and13,13A-13Dillustrate another exemplary embodiment of a separating element1having a design identical to the example illustrated inFIGS.6to10, with the difference that the internal connection system10for the distribution of the liquid medium to be treated and the internal connection system12for the collection of the treated liquid medium are arranged asymmetrically on either side of the circulation ducts6. Thus, the common elements between the separating element1described inFIGS.6to10and this other exemplary embodiment will not be repeated. The nozzle15defining the inlet11for the liquid medium is offset on one side with respect to the longitudinal axis passing through the middle of the porous support2while the nozzle15defining the outlet13for the permeate P is offset on the other side relative to the longitudinal axis passing through the middle of the porous support2. Thus, the separating element1includes at each of its ends, an outlet nozzle9for the permeate P extending symmetrically with respect to the longitudinal axis passing through the middle of the porous support2A, with a nozzle15defining the inlet11or the outlet13.

As shown in the figures, this separating element1of generally flattened rectangular shape thus includes, at a first end, a nozzle15defining the inlet11and aligned with an outlet nozzle9for the permeate located at the second end, while this second end is provided with a nozzle15defining the outlet13and aligned with an outlet nozzle9for the permeate.

Six circulation ducts6are formed in the porous support2parallel to each other and each have a rectangular cross section with a width of the short sides substantially 50 times less than the length of the long sides. These six circulation ducts6are parallel to the outer planar surfaces3,4. These circulation ducts6are connected on one side with the internal connection system for the distribution10and on the other side, with the internal connection system for the collection12.

The internal connection system for the distribution10includes a common inlet segment10eformed by a tubular conduit arranged in the nozzle15and opening onto the outside of the porous support2at the end of the nozzle15, via the inlet11(FIG.13B). The common inlet segment10ecommunicates opposite the inlet11via a bifurcation10bformed in the porous support2, with the six circulation ducts6. Similarly, the internal connection system for the collection12includes a common outlet segment12sformed by a tubular conduit arranged in the nozzle15and opening onto the outside of the porous support2, at the end of the nozzle, via the outlet13(FIG.13A). The common outlet segment12scommunicates opposite the outlet13, via a branch12earranged in the porous support2, with the six circulation ducts6.

According to this exemplary embodiment, the internal connection system for the distribution10and the internal connection system for the collection12are arranged asymmetrically on either side of the circulation ducts6. Of course, as indicated above, the internal faces of the internal connection system for the distribution10, the internal faces of the circulation ducts6and the internal faces of the internal connection system for the collection12are provided with at least one separating layer.

According to this exemplary embodiment, the collection system7for the permeate P is arranged in the porous support2so that the outer planar surfaces3,4and the connecting surface5are sealed. Of course, the nozzles15delimiting the inlet11and the outlet13and the two permeate collection nozzles9which are formed by the connecting surface5, are also sealed externally. As shown more precisely inFIGS.13C and13D, the collection system7includes an array of seven channels7aarranged parallel to each other and to the outer planar surfaces3,4, each in the form of a sheet. The channels7aare inserted between the circulation ducts6and the outer planar surfaces3,4, being separated from the circulation ducts6by partitions2bso as to recover the permeate P that has passed through the separating layer or layers and the partitions2bof the support2. These channels7acommunicate with each other via a collection chamber7cextending by a conduit7darranged in each nozzle9to open onto the outside of the porous support2, at the end of the nozzle9, as illustrated inFIG.13Dfor example. It should be noted thatFIG.13Dshows the shape of the partitions2barranged in the porous support2to delimit the channels7abut also the bifurcation10band the branch12e.

It should be noted thatFIG.12illustrates an exemplary embodiment of a separating element1for which the nozzles9,15are smooth whereas in the exemplary embodiment illustrated inFIG.13, the nozzles9,15are threaded.

FIGS.14to18illustrate another exemplary embodiment of a separating element1belonging to the mode with connection orifices and produced in the shape of a rectangular parallelepiped block intended to be mounted in an apparatus20illustrated inFIGS.30and31and provided with connections to ensure on the one hand the entry of the liquid medium to be treated and the exit of the retentate as well as on the other hand the collection of the permeate. This separating element1includes a porous support2including a first outer planar surface3and a second outer planar surface4parallel to each other and opposite to each other, being interconnected by a connecting surface5arranged to form two large connecting faces5gparallel to each other and interconnected at their ends by two small connecting faces5pparallel to each other.

In the example illustrated, the separating element1includes five inlets11for the liquid medium M and five outlets13for the retentate R opening onto the outside of the porous support10through orifices16formed at the outer planar surface3, or even also as illustrated inFIG.17, at the second outer surface4to allow superimposed mounting of the separating elements1and communication for the fluid medium between the separating elements. The separating element1also includes two superimposed rows of five series of circulation ducts6, each of which communicates with an inlet11via the internal connection system for the distribution10and an outlet13via the internal connection system for the collection12.

In each superimposed row, three series have three circulation ducts6while two series include two circulation ducts6. These circulation ducts6are formed in the porous support2parallel to each other, being separated by partition walls2b. These circulation ducts6each have a rectangular cross section with a width substantially ten times less than the length. These circulation ducts6are perpendicular to the outer planar surfaces3,4. These circulation ducts6are connected on one side with the internal connection system for the distribution10including for each series of circulation ducts, a common inlet segment10eformed by a tubular conduit communicating via a bifurcation10bformed in the porous support2, with all the ducts of a series and opening onto at least one, and in the example illustrated, onto the two outer planar surfaces3,4through the orifices16. These circulation ducts6are connected on the other side, with the internal connection system for the collection12including for each series of circulation ducts, a common outlet segment12sformed by a tubular conduit communicating via a branch12earranged in the porous support2, with all the ducts of a series and opening onto at least one, and in the example illustrated, onto the two outer planar surfaces3,4, through the orifices16.

For the circulation ducts6of each series, the internal connection system for the distribution10and the internal connection system for the collection12are arranged in the porous support2symmetrically on either side of the circulation ducts6, with the orifices16arranged along two lines symmetrical with respect to the longitudinal axis parallel to the large connecting faces5gand passing through the middle of the porous support2. The common inlet segments10eand the common outlet segments12sextend parallel to a direction which is perpendicular to the outer planar surfaces3,4but also perpendicular to the main direction of circulation of the liquid medium. The common inlet segments10eare arranged parallel to each other and close to a large connecting face5gwhile the common outlet segments12sare arranged parallel to each other and close to the other large connecting face5g.

Of course, the number of circulation ducts6per series, the number of series of circulation ducts6and the number of rows of circulation ducts6are given only by way of illustration. Similarly, as indicated above, the internal faces of the internal connection system for the distribution10, the internal faces of the circulation ducts6and the internal faces of the internal connection system for the collection12are provided with at least one separating layer.

According to this example, the collection system7for the permeate P is arranged in the porous support2but also recessed in at least one, and in the example illustrated, the two outer planar surfaces3,4of the porous support2to collect the permeate that has passed through the separating layer or layers. The collection system7thus includes, as illustrated inFIGS.16and18, on the one hand, four series of three superposed channels7earranged in the porous support2between the two outer planar surfaces3,4and between two adjacent series of circulation ducts6and on the other hand, a gutter7farranged in each outer planar surface3,4, in alignment with each series of channels. The three channels7eand the two gutters7fof each of these series communicate at each end with tubular cavities7gopening out through orifices8formed on at least one, and in the example illustrated, on the two outer planar surfaces3,4. The tubular cavities7gare arranged parallel to each other but also parallel to the common inlet segments10eand to the common outlet segments12s. Advantageously, part of the tubular cavities7gand the common inlet segments10eare arranged in the same plane while another part of the tubular cavities7gand the common outlet segments12sare arranged in the same plane.

It should be noted that the rest of the outer planar surfaces3,4not arranged in recesses or in gutters7fis sealed. In other words, all the outer planar surfaces3,4are sealed with the exception of the gutters7f. Similarly, the connecting surface5is sealed. The connection of the orifices8,16respectively to an external permeate recovery circuit and to a circulation circuit for the liquid medium will be described in more detail in the following description in relation toFIGS.30and31.

FIGS.19to24illustrate another exemplary embodiment of a separating element1relating to the mode with connection orifices and produced in the form of a rectangular parallelepiped. This exemplary embodiment is identical in design to the example illustrated inFIGS.14to18, with the difference that the permeate recovery system7is produced only on the surface of the porous support2. This separating element1includes a porous support2including a first outer planar surface3and a second outer planar surface4parallel to each other and opposite to each other while being interconnected by a connecting surface5arranged to form two large connecting faces5gparallel to each other and interconnected at their ends by two small connecting faces5pparallel to each other.

The separating element1includes five inlets11for the liquid medium M and five outlets13for the retentate R opening out onto the outside of the porous support10through orifices16formed at the outer planar surface3, or also as illustrated inFIG.21, at the second outer surface4to allow superimposed mounting of the separating elements1. In the example illustrated inFIGS.19to22, the separating element1includes a row of five series of circulation ducts6, each of which communicates with an inlet11via the internal connection system for the distribution10and an outlet13via the internal connection system for the collection12. Of course, the number of circulation ducts6per series, the number of series of circulation ducts6and the number of rows of circulation ducts6are given only by way of illustration. By way of example,FIGS.23and24illustrate a variant embodiment identical to the variant embodiment illustrated inFIGS.19to22with the difference that the circulation ducts6are distributed in two superimposed rows.

Each row includes five series of circulation ducts6of which the three central series each include six circulation ducts6while the two end series located close to the small connecting faces5peach include four circulation ducts6. These circulation ducts6are formed in the porous support2parallel to each other and each have a rectangular cross section with a width substantially ten times less than the length. These circulation ducts6are perpendicular to the outer planar surfaces3,4. These circulation ducts6are connected on one side with the internal connection system for the distribution10arranged in the porous support2and including for each series of circulation ducts, a common inlet segment10eformed by a tubular conduit communicating, via a bifurcation10bformed in the porous support2, with all the ducts of a series and opening onto at least one, and in the example illustrated, onto the two outer planar surfaces3,4through the orifices16. These circulation ducts6are connected on the other side, with the internal connection system for the collection12arranged in the porous support2and also including for each series of circulation ducts, a common outlet segment12sformed by a tubular conduit communicating via a branch12earranged in the porous support, with all the ducts of a series and opening onto at least one, and in the example illustrated, onto the two outer planar surfaces3,4through the orifices16. For the circulation ducts6of each series, the internal connection system for the distribution10and the internal connection system for the collection12are arranged symmetrically on either side of the circulation ducts6, with the orifices16arranged along two lines symmetrical with respect to the longitudinal axis parallel to the large connecting faces5gand passing through the middle of the porous support2. As indicated above, the internal faces of the internal connection system for the distribution10, the internal faces of the circulation ducts6and the internal faces of the internal connection system for the collection12are provided with at least one separating layer.

According to the exemplary embodiments illustrated inFIGS.19to24, the collection system7for the permeate P is not arranged inside the porous support2but only recessed in at least one and, in the example illustrated, the two outer planar surfaces3,4of the porous support2to collect the permeate that has passed through the separating layer or layers. The collection system7thus includes, as illustrated inFIGS.19to24, four series of two superimposed gutters7farranged in the outer planar surfaces3,4, as already described in the example illustrated inFIGS.14to18. The two gutters7fof each of these series communicate at each end with tubular cavities7gformed in the porous support, opening out through orifices8formed on at least one and, in the example illustrated, on both outer planar surfaces3,4. It should be noted that the rest of the outer planar surfaces3,4not arranged in recesses or gutters7fis sealed. Similarly, the connecting surface5is sealed. The connection of the orifices8,16respectively to an external permeate recovery circuit and to a circulation circuit for the liquid medium will be described in more detail in the following description in relation toFIGS.30and31.

FIGS.25to29illustrate another exemplary embodiment of a separating element1relating to the mode with connection orifices and produced in the shape of a rectangular parallelepiped block intended to be mounted in an apparatus20illustrated inFIGS.30and31and provided with connections to ensure on the one hand the entry of the liquid medium to be treated and the exit of the retentate as well as on the other hand the collection of the permeate. This exemplary embodiment differs from the exemplary embodiment illustrated inFIGS.14to18insofar as the circulation ducts6are arranged parallel to the outer planar surfaces3,4unlike the example ofFIGS.14to18for which the circulation ducts6are arranged perpendicular to the outer planar surfaces3,4.

This separating element1includes a porous support2including a first outer planar surface3and a second outer planar surface4parallel to each other and opposite to each other, being interconnected by a connecting surface5arranged to form two large connecting faces5gparallel to each other and interconnected at their ends by two small connecting faces5pparallel to each other.

The separating element1includes five inlets11for the liquid medium M and five outlets13for the retentate R opening out onto the outside of the porous support10through orifices16formed at the outer planar surface3, or also as illustrated inFIG.26, at the second outer surface4to allow a superposed assembly of the separating elements1. The separating element1also includes circulation ducts6arranged in the porous support to communicate with the inlets11via the internal connection system for the distribution10and the outlets13via the internal connection system for the collection12. The circulation ducts6are arranged on four superimposed stages by forming two series of four superimposed circulation ducts and three series of four pairs of superimposed circulation ducts. As shown more specifically inFIG.29, in each stage, the circulation ducts6are separated by partition walls2cmade by the porous support2extending parallel to each other and to the main direction of circulation of the liquid medium between the inlets11and the outlets13of the liquid medium. Note that these partition walls2care not continuous from one end to the other of the porous support, thus allowing communication between the circulation ducts6of each stage, at the inlets11and the outlets13of the liquid medium.

These circulation ducts6are formed in the porous support2parallel to each other and parallel to the outer planar surfaces3,4. These circulation ducts6each have a rectangular cross section with a width at least four times less than the length. These circulation ducts6are connected on one side with the internal connection system for the distribution10including, for each series of circulation ducts, a common inlet segment10eformed by a tubular conduit communicating via a bifurcation10b, with all the ducts of a series and opening onto at least one, and in the example illustrated, onto the two outer planar surfaces3,4through the orifices16and on the other side, with the internal connection system for the collection12including for each series of circulation ducts, a common outlet segment12sformed by a tubular conduit communicating via a branch12ewith all the ducts of a series and opening onto at least one, and in the example illustrated, onto the two outer planar surfaces3,4through the orifices16.

For the circulation ducts6of each series, the internal connection system for the distribution10and the internal connection system for the collection12are arranged in the porous support2symmetrically on either side of the circulation ducts6, with the orifices16arranged along two lines symmetrical with respect to the longitudinal axis parallel to the large connecting faces5gand passing through the middle of the porous support2. The common inlet segments10eand the common outlet segments12sextend parallel to a direction which is perpendicular to the outer planar surfaces3,4but also perpendicular to the main direction of circulation of the liquid medium. The common inlet segments10eare arranged parallel to each other and close to a large connecting face5gwhile the common outlet segments12sare arranged parallel to each other and close to the other large connecting face5g.

Of course, the number of circulation ducts6per series, the number of series of circulation ducts6and the number of rows of circulation ducts6are given only by way of illustration. Similarly, as indicated above, the internal faces of the internal connection system for the distribution10, the internal faces of the circulation ducts6and the internal faces of the internal connection system for the collection12are provided with at least one separating layer.

According to this example, the collection system7for the permeate P is arranged in the porous support2but also recessed in at least one, and in the example illustrated, the two outer planar surfaces3,4of the porous support2to collect the permeate that has passed through the separating layer or layers. The collection system7thus includes, as illustrated inFIGS.25,27and28, three superimposed collection layers7jarranged in the porous support2between the two outer planar surfaces3,4and between two neighboring stages of circulation ducts6as well as a recessed area7kformed in each outer planar surface3,4. The collection sheets7jare interposed between two adjacent circulation ducts6, being separated from the circulation ducts6by partition walls2b.

In the example illustrated, it should be noted that in each collection layer7j, stiffening ribs7nare arranged in the porous support parallel to each other to delimit parallel channels joining at each of their ends to lead on each side, to a series of four tubular cavities7gopening out via orifices8formed on at least one, and in the example illustrated, on the two outer planar surfaces3,4. The tubular cavities7gare arranged parallel to each other but also parallel to the common inlet segments10eand to the common outlet segments12s. Advantageously, a first series of tubular cavities7gand the common inlet segments10eare arranged in the same plane while a second series of the tubular cavities7gand the common outlet segments12sare arranged in the same plane.

Similarly, stiffening ribs7nproduced by the porous support are arranged projecting in the outer planar surfaces3,4parallel to each other so that each recessed area7khas parallel channels joining at each of their ends to lead on each side, to a series of four tubular cavities7g. The three layers of channels7jand the two recessed areas7kof each of these series communicate at each end with tubular cavities7gopening out through orifices8formed on at least one, and in the example illustrated, on both outer planar surfaces3,4.

It should be noted that the rest of the outer planar surfaces3,4which are not recessed are sealed. Thus, the stiffening ribs7nmade by the porous support projecting into the outer planar surfaces3,4are sealed. Similarly, the connecting surface5is sealed. The connection of the orifices8,16respectively to an external permeate recovery circuit and to a circulation circuit for the liquid medium will be described in more detail in the following description in relation toFIGS.30and31.

FIGS.30and31illustrate an exemplary embodiment of a commercial apparatus20provided with connections for the connection of at least one separating element1relating to the mode with connection orifices8,16and in accordance with one of the variants illustrated inFIGS.14to29. This apparatus provided with one or more separating elements1thus form a separation unit for a fluid medium of all types. According to this example, the apparatus20includes a connection plate21on which at least one separating element1, mounted in a sealed manner by seals24, is intended to be fixed by threaded rods22and nuts23between this connection plate21and a tie plate26. The connection plate21includes orifices21M positioned to communicate on the one hand with the orifices16of the inlets11of the separating element1and on the other hand, with a circuit for supplying the liquid medium 27 of which only part is shown in the drawings. The connection plate21also includes orifices21R positioned to communicate on the one hand with the orifices16of the outlets13of the separating element1and on the other hand, with a retentate recovery circuit28only a part of which is shown in the drawings. The connection plate21also includes orifices21P positioned to communicate on the one hand with the orifices8of the collection system for the permeate and on the other hand, with an external permeate recovery circuit29.

In the context of the invention, the manufacture of the porous support2, or even of the separating element as a whole, can be carried out using an additive technique, the method consisting in obtaining one-piece parts by adding or agglomeration of material, the subject taking shape as successive layers are stacked. Of course, this additive method is configured or adapted so that the porosity of the porous material of the porous support ensures the routing of the permeate that has passed through the separating layer or layers. The method has the advantage, compared to other techniques such as the assembly by gluing of different parts manufactured separately, of producing the support in a single production step and of allowing access to a wide range of shapes and sizes and of forming the circulation ducts for the liquid medium to be treated and for the collection of the permeate. Among the additive techniques, SLS (Selective Laser Sintering), FDM (Fused Deposition Modeling) from a filament or granules, PEM (Paste Extrusion Modeling) and BJ (Binder Jetting) are particularly well adapted.

In the case of the use of a solid material such as a powder, the thickness of the powder bed and therefore of each successively consolidated stratum is relatively low to allow its connection to the lower stratum, by application of a contribution of energy (SLS) or the projection of a binder liquid (BJ). In particular, a thickness of 20 μm to 200 μm of powder will be deposited, this thickness depending on the additive technique selected. It is the repetition of the binary sequence depositing a bed of powder followed by consolidation which allows, stratum after stratum, to build the desired three-dimensional shape. The consolidation pattern may vary from one stratum to another. The growth of the desired three-dimensional shape is carried out according to a chosen direction of growth. In the case of the use of a ceramic composition in the form of a ceramic paste (PEM) or a filament or hot-melt granules (FDM), the thickness of a stratum is defined by a set of cords, whether continuous or discontinuous, juxtaposed or not juxtaposed, which are extruded at the same altitude taken along the chosen direction of growth.

According to an advantageous embodiment characteristic, the material constituting the porous support has a maximum admissible bending stress of at least 10 MPa, this characteristic resulting from the three-dimensional continuity and the three-dimensional homogeneity that allow additive techniques on the one hand and necessary post sintering heat treatment on the other hand.

This maximum bending characteristic associated with the geometry of the porous support (dimensioning, thickness of the external or internal walls, . . . ) as well as the continuity of the material and the porous texture allow to define a porous support capable of offering sufficient mechanical strength to prevent this porous support2from breaking under the effect of a stress generated by the pressure difference of the liquid medium between the separating layer and the permeate outlet surface, said permeate outlet surface corresponding either to the inner surface delimiting the collection system for the permeate7when the latter is arranged in the porous support2, or to the outer surface of the separating element1when the collection system7is not arranged in the porous support2.

The difference in pressure of the liquid medium between the separating layer and the outlet surface of the permeate commonly corresponds to what the person skilled in the art calls the transmembrane pressure (TMP). This pressure difference is defined in the context of the invention by the average of the supply PA (this is the absolute pressure measured at the inlet of the liquid medium to be treated) and retentate PR pressures (this is the absolute pressure measured at the outlet of the treated liquid medium) from which one subtracts either the absolute pressure Pp measured in the collection system for the permeate7when the latter is arranged in the porous support2, or the atmospheric pressure Pa when the collection system7is arranged outside the porous support2. The transmembrane pressure (TMP) is such that:

On the basis of this definition, the characteristics of the material and the dimensioning of the porous support, these last two points being developed above, the porous support2is defined so that no degradation by breaking the porous material appears for a pressure difference of the liquid medium greater than or equal to 1 bar.

There is breakage as soon as the inorganic one-piece rigid porous support2has at least one crack or a fracture with or without localized displacement of the porous material at the location of said crack(s) or fracture(s) and when said breakage, interrupting the porous continuity, opens a direct passage for the liquid between, on the one hand, the assembly formed by the internal connection system10for the distribution of the liquid medium to be treated, by the circulation ducts6and by the internal connection system12for the collection of the retentate and on the other hand the collection system7for the permeate without said liquid having to pass through the filtration layer.

Such a breakage is immediately observable by a drop in the transmembrane pressure defined as the pressure difference of the liquid medium between the separating layer and the outlet surface of the permeate on the one hand as well as by an increase in the flow present in the collection system for the permeate on the other hand. The flow rate of treated liquid being abnormally increased by that of the untreated liquid, this mixture of permeate and retentate causes the breakage to make the use of the separating element unsuitable. The latter is then considered destroyed and must be replaced.