HK1102115B - A porous support, a membrane, and a process for the manufacture of a porous support - Google Patents

Description

Porous carrier, filter membrane and manufacturing method of porous carrier

Technical Field

The present invention relates to the field of tangential separation techniques using separation elements commonly referred to as filtration membranes. These membranes are generally made of inorganic material and comprise a porous support and at least one separation layer, the nature and morphology of which is designed to separate molecules or particles contained in the fluid medium to be treated. Membrane separation separates a liquid containing molecules and/or particles into two fractions: a filtrate fraction comprising molecules or particles that pass through the filter membrane and thereby through the support and the separation layer; and a retentate portion comprising molecules or particles retained by the filter membrane.

More precisely, the subject matter of the invention relates to the production of porous media and filter membranes incorporating such media. The filter membrane is a tangible structure that allows selective blocking or passage between the fluid volumes it separates, under the driving force of substance transport.

The separation achieved depends on the driving force employed for the transport. If the driving force for the transport is an electric field, the separation is called electrodialysis; if the driving force is pressure, the separation is referred to as microfiltration, ultrafiltration, nanofiltration or reverse osmosis; if the driving force is a chemical potential difference, the separation is called dialysis.

The subject matter of the invention can be applied particularly advantageously in the field of nanofiltration, ultrafiltration, microfiltration, filtration or reverse osmosis.

The separation filter membrane has two main uses:

-extraction, corresponding to the passage of the molecules or particles to be recovered through the filter membrane; and

concentration, corresponding to the situation in which the molecules or particles to be recovered are retained by the filter membrane.

Background

Conventionally, a filter membrane is defined as a combination of a porous support of inorganic material, such as ceramic, and one or more separate layers of inorganic material. The carrier has a surface facing the fluid to be treated and thus for filtrate entry and a surface for extraction. The one or more separation layers are placed on said surface facing the liquid to be treated and are bonded to the carrier by means of a sintering process. These types of filters are called composite filters. These membranes can take different geometries, in particular flat or tubular. The role of these layers is to perform the separation of molecular or particulate species, while the role of the support is to form very thin layers by virtue of its mechanical strength.

Considering that the filter membrane is characterized by holes that intersect the direction of the fluid and extend completely through its thickness, these holes generally have an asymmetrical morphology (of the "eiffel tower" type), the narrowest part of the holes being in contact with the fluid to be treated. This morphology allows for the smallest pore size in the active portion of each pore, thereby creating the greatest permeability. In the case of ceramic filter membranes, this morphology can be obtained by stacking porous media of decreasing grain size on the porous support.

When the force is pressure, the separation is merely a physical separation. These molecules or particles do not change and remain in their original state. Molecules or particles blocked by the filter membrane deposit on the surface of the filter membrane and cause blockages which can be very severe.

To reduce the latter, there are two techniques:

a tangential clearing of the blockage occurs, wherein the liquid to be treated flows tangentially to the surface of the filter membrane. This flow causes friction, which increases the transport coefficient,

-reverse filtration, comprising the return of a portion of the filtered liquid in reverse direction through a filter membrane.

Currently, industrial membrane type devices use only tangential plug removal or combine it with reverse filtration. However, whatever the technique adopted to remove the blockage, the graph of permeability as a function of time always has the shape of the graph shown in figure 1. It can be seen that the permeability decreases suddenly during the initial period of operation of the filter. This decrease tends to stabilize and eventually levels out substantially. The ratio between the permeability value after 720 minutes of operation and the permeability value after 4 minutes of operation was 20. Even though the permeability values obtained with this system are high enough to be economically acceptable, the magnitude of this reduction indicates that current blockage removal systems are not satisfactory.

The reason for this decrease in permeability over time is explained by the nature of the blockage. In fact, two types of blockage are present, namely surface blockage and deep blockage. Surface plugging is limited by the tangential flow of the fluid to be treated because deep plugging causes rubbing of the fluid to be treated on the flow surface, thereby eliminating any deposits on the surface. In principle, reverse filtration should be able to move particles that are physically fixed to the inside of the filter membrane, thus being able to limit clogging to any depth. However, the particular morphology of the elements making up the filter membrane can form an interconnected network of pores, which reduces the above-mentioned potential.

Both of these methods of clearing the blockage are therefore not entirely satisfactory. The reason for this limited effect is the initial period of filter operation. Indeed, in the above example, the permeability of the filter membrane decreases from a value of permeability to water to a value of permeability to the product. The ratio between these two values is about 20. The particles or molecules reach the filter membrane surface at a rate equal to the ratio of the flow rate to the filter surface. During the initial period of operation, the velocity is at a maximum and the degree of movement of the particles or molecules is at a maximum. When impact occurs with the wall, particles or molecules will penetrate the inside of the filter membrane to a depth proportional to its degree of movement. Now, particles or molecules penetrating the filter membrane are not accessible for tangential removal of the clogging. The deeper the particles or molecules penetrate, the more difficult it is to remove.

It is therefore desirable to avoid such penetration of particles or molecules into the filter membrane.

Disclosure of Invention

In the context of the present description, the present invention proposes a solution which makes it possible to avoid such infiltrations and to limit the permeability of the support and therefore of the filter membrane when it is combined with a separation layer to form a filter membrane. The invention therefore comprises as its subject a porous support for tangential filtration of a fluid to be treated, the porous support having at least one surface facing the fluid to be treated flowing in a given flow direction, and an output surface for a so-called filtrate fraction flowing through the porous support. The support is modified by the initial support, in particular by an increase in the average transverse porosity of the support from the surface facing the fluid to be treated to the extraction surface of the filtrate; and is obtained by partially plugging an initial support in such a way that the average longitudinal porosity of the support is uniform in the direction of flow of the fluid to be treated, parallel to the surface of the support facing the fluid to be treated, the permeability of the support being reduced compared to the initial support and the permeability of the support being uniform when moving parallel to said surface of the support facing the fluid to be treated in the direction of flow of the fluid to be treated. The permeability of the support is preferably reduced to 1 in 1 to 1 in 10 out of 1.5 compared to the initial support.

According to another aspect of the invention, the average transverse porosity of the support increases from said surface facing the fluid to be treated to said extraction surface of the filtrate, when moving across said surface facing the fluid to be treated towards the inside of the support, within a certain fixed depth measured from said surface facing the fluid to be treated; for this part, the average longitudinal porosity of the support is uniform when moving in the flow direction of the fluid to be treated, parallel to the surface of the support facing the fluid to be treated, towards the inside of the support.

The invention also comprises as its subject a filtration membrane for the tangential filtration of a fluid to be treated, combining a porous support such as described above with at least one separation layer for the fluid to be treated, covering the surface of the support facing the fluid to be treated with said separation layer having a porosity less than or equal to that of the support.

According to yet another aspect of the invention, the invention relates to a process for manufacturing a porous support for tangential filtration of a fluid to be treated, comprising: at least one surface facing a fluid to be treated flowing in a specific flow direction; and an output surface for a so-called filtrate portion flowing through the porous carrier. The manufacturing process comprises a step of modifying a porous initial support, i.e. infiltrating from said surface of the support facing the fluid to be treated, inorganic particles having an average diameter smaller than the average diameter dp of the pores of the initial support, over said surface of the support facing the fluid to be treated, from said surface of the support facing the fluid to be treated to said extraction surface for the filtrate, to a substantially fixed depth; for this part, the average longitudinal porosity of the support is uniform when moving in the direction of flow of the fluid to be treated, parallel to the surface of the support facing the fluid to be treated, towards the interior of the support.

Drawings

Various other features of the present invention can be understood from the following description with reference to the drawings.

Figure 1 shows the permeability of previously designed filters as a function of time.

Fig. 2 shows a longitudinal section through a carrier according to the invention.

FIG. 3 shows a cross section of a filter membrane according to the invention comprising a carrier according to FIG. 2.

Figure 4 compares the change in permeability of a filter membrane according to the invention over time with that of a previously designed filter membrane.

Detailed Description

The porous support according to the invention is composed of an inorganic material whose transport resistance is suitable for the separation to be achieved. The porous support 1 is formed of an inorganic material such as metal oxide, carbon, or metal. In the embodiment shown in fig. 2, the porous support 1 is tubular extending along the longitudinal central axis a, but may also take a flat shape extending along the central plane. The porous carrier 1 has a polygonal straight-sided cross section or, as in the example shown in fig. 2, a circular cross section.

The porous support 1 has at least one surface 3 facing the fluid to be treated, which surface 3 corresponds to the surface through which the fluid to be treated flows when using the support alone. The support 1 is usually combined with a separation layer 5 to form a filter membrane 4, in which case the fluid to be treated does not flow directly over the support surface 3 facing the fluid to be treated, but over the separation layer 5. For such a filter membrane operating in tangential mode, said carrier surface 3 facing the fluid to be treated is subsequently covered by the separation layer 5, which separation layer 5 is intended to be in contact with the fluid medium to be treated flowing in a specific direction and in a flow direction between the upstream and downstream ends of the carrier. The properties of the one or more separation layers 5 are selected in dependence on the separation to be obtainedOr the power of the filtration, and is brought into intimate contact with the porous carrier 1. For example, the layer(s) may be placed in a suspension comprising at least one metal oxide and may be conventionally used for the production of mineral filter elements. After drying, the layer(s) is/are subjected to a sintering treatment which serves to strengthen the layers and to bond them together and then to the porous support 1. A part of the fluid medium passes through the separation layer 5 and the porous carrier 1, the carrier 1 having an output surface 1 for extracting a fluid part of the treated so-called filtrate₁。

In the example shown in fig. 2, a porous support 1 may be provided having at least one channel 2 formed parallel to the axis a of the support. In the example shown, the channel has a straight cross-section along the axis a of the cylindrical carrier. The channel 2 has an inner surface 3, which inner surface 3 corresponds to said carrier surface 3 facing the fluid to be treated. The support 1 is combined with the separation layer 5 to form a filter 4. FIG. 3 shows an example of a filter membrane formed into a tubular shape. According to this example, the channel 2 is covered by a separation layer 5, which separation layer 5 is intended to be in contact with a fluid medium flowing in the channel 2 in a certain flow direction between two open ends of the channel 2. One end is referred to as the upstream end 6 and the other end is referred to as the downstream end. The fluid to be treated enters the channel via the upstream end 6 and the retentate exits the channel via the downstream end 7. Surface 1 for extracting filtrate in case of a filter membrane with one or more channels₁Corresponding to the peripheral surface 1 of the carrier₁Which in the example shown in fig. 2 and 3 has a cylindrical cross section and a circular cross section.

Before describing the present invention in more detail, some definitions need to be established. The porosity of the support refers to the ratio of the volume of the pores of the support to the total apparent volume of the support. Porosity is measured, for example, by mercury porosimetry. This involves an instrument that feeds mercury into the porous sample while applying pressure. Such an instrument can give not only the distribution of pore diameters but also the porosity of the porous body.

Average porosity is measured on a volume slice of a certain fixed thickness extending in the central direction, along which the change in porosity, if any, needs to be measured. The average porosity is uniform or approximately constant meaning that: when a slice of fixed thickness is divided into a series of equal volume elements corresponding to a cross-section that is shifted laterally with respect to the central axis of the slice corresponding to the measurement direction, the average porosity of the volume elements does not vary along the central axis of the slice. An increase in average porosity refers to an increase in average porosity of these volume units.

We will define:

the average longitudinal porosity of the support is the porosity measured when moving within the support in the direction of flow of the fluid to be treated parallel to said surface facing the fluid to be treated (corresponding to the inner zone of one or more channels in a single-channel or multi-channel support).

The transverse porosity is the porosity measured when moving transversely (i.e. perpendicular to said surface facing the fluid to be treated) within the support.

The flux density per unit pressure and the permeability of the porous support reflect the ease with which the fluid medium can pass through the support. In the context of the present invention, the flow density is the flow through a unit area (m) in a unit time(s)²) Amount of filtrate (m) of carrier³). Thus, the measured flow density per unit pressure is m³/m²/s/Pa×10^-12。

In the context of the present invention, permeability corresponds to the flow density per unit pressure normalized by thickness, expressed in m³/m²/m/s/Pa×10^-12. Permeability is the inverse of resistance. The resistance of the filter is equal to the sum of the resistance of the support and the resistance of the separation layer. Of course, in the filter membrane, since the average pore diameter of the support is larger, the resistance of the support is smaller than that of the separation layer. The transport resistance of a fluid through a porous body depends on the pore diameter, porosity and thickness of the porous body. When standing alongWhen the flow direction of the treatment fluid moves parallel to said surface facing the fluid to be treated (corresponding to the inner zone of one or more channels in the case of a single-channel or multi-channel support), the support or filter membrane has a uniform permeability, which is said to mean: if the filter membrane or the support is cut into slices of equal thickness perpendicular to the longitudinal axis of the support (taken from a thickness parallel to the longitudinal axis) in the case of a tubular support or perpendicular to the central plane of the support (taken from a thickness parallel to the central plane) in the case of a planar support, the permeability measured for each of these slices is approximately constant.

According to the invention, the support near a certain depth of the support surface 3 has a modified porosity with respect to the rest of the support. The support 1 has a lower porosity in the region adjacent to said surface 3 facing the fluid to be treated and, therefore, when passing over said surface 3 facing the fluid to be treated, from the surface 3 towards the surface 1 for extracting the filtrate₁When moving, the porosity of the support increases. In the example shown in figures 2 and 3, which show a single channeled tubular support and associated filter membrane, when passing over the surface 3 of the channel 2, from the channel 2 towards the outer surface 1₁When moving, the porosity of the support increases. This variation in the transverse porosity is due, for example, to a partial blockage along the support 1 from said surface 3 facing the fluid to be treated. However, when moving parallel to the surface facing the fluid to be treated in the direction of flow of the fluid to be treated (i.e. from one end to the other along the channel in the example shown in fig. 2), the longitudinal porosity remains substantially constant for this part of the support. Such clogging is described as "partial" because the carrier is not completely clogged, yet allows fluid to pass through. The average lateral porosity of the carrier 1 increases when moving across said carrier surface 3 facing the fluid to be treated, towards the inside of the carrier and away from said surface 3 facing the fluid to be treated, within a certain fixed depth measured from said carrier surface 3 facing the fluid to be treated. Preferably, when moving perpendicular to said surface 3 facing the fluid to be treatedThe partial plugs c vary and form a gradient of average porosity in the range of a fixed depth p, which gradient increases with distance from the surface 3. The part of the support 1 with the lowest average porosity, which is most clogged, is close to the surface 3 facing the fluid to be treated and therefore the channel 2 of the example shown, while the part with the highest porosity, which is least clogged, is facing the surface 1 for filtrate extraction₁(in the example shown in FIG. 2, the outer peripheral surface 1 of the carrier 1₁)。

According to a preferred variant of the invention, the surface 1 for filtrate extraction is started from the surface 3 facing the fluid to be treated when passing over the surface 3 facing the fluid to be treated₁The average diameter of the support pores within the support 1 increases as one moves.

The gradient of average porosity is formed by the infiltration of particles having an average diameter smaller than the average diameter of the pores of the initial support in the initial support from said support surface 3 facing the fluid to be treated, which is being used to obtain the partial plugging c of the support 1. According to the example shown in fig. 2, the partial plug is formed in the range of a certain fixed depth p (less than or equal to depth e) measured from the carrier surface 3 towards the fluid to be treated. The depth p is determined from said carrier surface 3 facing the fluid to be treated. The blockage c corresponding to the infiltration of the particles occurs in the range of a depth p which depends on the size (i.e. diameter) of the particles and on the infiltration conditions of the experiment. In general, the penetration depth p is large, corresponding to the expected decrease in permeability. For example, during the plugging process, the support 1 has a plugging depth p, which is greater than the average radius of the agglomerated particles constituting the initial support, and preferably greater than the average diameter of these agglomerated particles, and the maximum depth of plugging is determined by the finest particles. In a preferred manner, the partial plugs are formed in a depth p range equal to or greater than 2.5 μm, preferably equal to or greater than 5 μm. The permeability of the support of the present invention may be artificially reduced with respect to the initial support, but is uniform when moving parallel to the surface facing the fluid to be treated in the flow direction of the fluid to be treated.

According to a first variant of the invention, the average transverse porosity increases substantially continuously when moving away from said support surface 3 facing the fluid to be treated. According to another variant, the average transverse porosity can be increased in steps Pi. The steps preferably all take substantially the same length across the surface 3 facing the fluid to be treated.

It should be noted that the examples depicted in fig. 2 and 3 relate to a single channel carrier comprising a cylindrical channel with a substantially oval vertical cross-section. Of course, the subject matter of the present invention can be implemented quite equally well on one or more carriers having channels of various shapes. Likewise, the subject of the invention can obviously be applied to supports comprising at least one channel 2 of polygonal section, wherein these channels are arranged in porous blocks. In the case of a flat or planar type of support 1, it is possible to circulate the fluid to be treated directly on one face 3 of the support, while the filtrate is on the other face 1₁And (3) flowing out, wherein no channel is arranged in the pellet block. In such a porous support 1 of the planar type, a series of channels 2 each having a rectangular straight-sided cross section may also be superimposed. In the case of a support comprising a plurality of channels, the support has a porosity as defined hereinabove, within a certain depth extending from the respective inner region 3 defining the channels 2. Thus, the volume adjacent to the inner region 3 is located between the channel 2 and the outer surface 1 of the carrier₁And between the two channels 2, the support has a modified porosity.

Therefore, the porous carrier of the present invention has a porosity such that when moving in the same direction as the filtrate flow direction within the carrier block, the average transverse porosity is increased and the average longitudinal porosity is fixed, which is being used to obtain a permeability of the carrier lower than that of the conventional carrier of the previous design.

The subject of the invention is also a process for forming the aforementioned filter support 1. The process comprises the step of forming a modified initial supportThe step of infiltrating the inorganic particles having an average diameter smaller than the initial support pore average diameter dp from the support surface 3 towards the fluid to be treated before modification. This infiltration is carried out such that: from the surface 3 towards the surface 1 of the carrier 1 for filtrate extraction when moving towards the interior of the carrier across said surface 3 towards the fluid to be treated₁The average transverse porosity increases; for this part, the average longitudinal porosity of the carrier 1 is uniform when moving towards the interior of the carrier 1 along the flow direction of the fluid to be treated parallel to said carrier surface facing the fluid to be treated.

Said average diameter being smaller than the average diameter dp of the initial support pores preferably means that the average diameter of the inorganic particles is between dp/100 and dp/2.

The penetration of the particles into the interior of the initial support is achieved by a non-agglomerating suspension of these particles. The non-agglomeration of the suspension is necessary to prevent the formation of agglomerates of particles and thus to keep these particles in an individual form so as to be able to penetrate inside the pores of the support. Preferably, the suspension has a low viscosity.

Such particles are composed of an inorganic material, such as a metal oxide, which inorganic material forms inorganic particles that can be equivalent to the inorganic particles constituting the support and/or any separation layer 5.

The infiltration step is followed by a sintering step for grouping together the particles present in the pores of the solid (solid) support 1, thus causing the expansion and coalescence of said particles and determining the clogging of the porous support 1. The following description relates to a process for forming the carrier shown in fig. 2, wherein the carrier has at least one internal channel 2. In this case, particles of the same grain size or a mixture of particles of different grain sizes penetrate into the pores of the support within a depth p measured from said inner region 3 facing the fluid to be treated, the penetration being fixed when moving along a plane parallel to said surface 3 of the support 1 facing the fluid to be treated. Such penetration, which is fixed in the length direction of the support and variable in the depth direction (meaning that the deeper the relative movement to the inner region 3 of the channel 2, the less the penetrating particles will be), can be achieved by means of coating. The method comprises the following steps: vertically placing the porous carrier 1; and filling the channel 2 with a non-agglomerated suspension of inorganic particles having an average diameter smaller than the average diameter dp of the pores of the support (before plugging), by means of a pump of the peristaltic type and with variable rotation speed. The channel fill time is referred to as Tr. The time during which the support is kept filled with the suspension by the action of the rotational speed of the pump is called Ta. The carrier is then emptied by rotating the pump in the reverse direction, the time of emptying being referred to as Tv. These three times Tr, Ta and Tv determine the contact time Tc between the respective point (point) of the inner region 3 of the carrier 1 and the suspension.

At a point x of the internal region 3 of the support 1, located at a height h, the contact time Tc with the suspension is equal to:

Tc＝(Tr+Ta+Tv)-Ss/Qpr*h-Ss/Qpv*h......(I)

wherein:

tr is the filling time;

ta is the waiting time for filling the pipe;

tv is the emptying time;

tc is the contact time;

qpr is the pump flow during filling;

qpv is pump flow during evacuation;

ss is the sectional area of the channel;

h is the fill height.

The depth p of penetration of the particles into the interior of the support depends on the contact time Tc between the porous support 1 and the suspension. Also, by adjusting the parameters Tr, Ta and Tv, a substantially fixed penetration depth p from the top to the bottom of the support can be obtained. By using different values of the contact time Tc and adjusting Tr, Ta and Tv according to the relation (I), the amount of inorganic particles infiltrating into the interior of the carrier 1 can be selected. The penetration depth of these particles is naturally changed by reducing the capillary suction of the support 1 in parallel with the measurement of the internal agglomeration of the support 1.

Another technique that can be used to achieve uniform blockage c along the channel is to achieve vertical infiltration in two steps, i.e., by turning the support over and thus reversing its top and bottom ends in the middle of the infiltration process.

Indeed, the present invention allows the manufacture of customized supports, thereby producing filtration membranes according to any desired porosity and corresponding permeability. In particular, the present invention can be used to reduce the permeability of a filter membrane obtained from such a support by reducing the permeability of the support. This process also has the advantage of controlling the final permeability of the support and even the filter membrane. In fact, the permeability level can be modulated by adjusting the following different parameters:

the size of the particles is selected, which influences, inter alia, the penetration depth and the plug density,

-the concentration of the non-agglomerating suspension,

-the time of impregnation,

-the number of impregnation operations. In fact, by using particles of the same or different diameter, it is possible to carry out a plurality of infiltrations in succession, and in particular for the case of a step gradient Pi.

Of course, the manufacture of the porous support comprising a porosity determined by an increasing average transverse porosity and a fixed average longitudinal porosity as described above may also be achieved by other processes than those described above. In particular, in the case of a channel-free planar support, infiltration from the surface 3, which surface 3 is intended to face the fluid to be treated, will be achieved, wherein the surface 3 is placed horizontally.

According to another aspect of the invention, it is possible to arrange continuously or even simultaneously in a continuous process to achieve the clogging of the support and the deposition of the separation layer on said surface 3 of the support 1 facing the fluid to be treated. Thus, for clogging of the support, inorganic particles of the same size and composition as those used for depositing the separation layer 5 can be used during the filter membrane manufacturing process.

The support according to the invention can be used alone, in particular for filtration of corrosive media, in view of the low porosity of the support in the region directly adjacent to the surface 3 of the support 1 facing the fluid to be treated, which allows an already satisfactory filtration. The surface 3 of the carrier 1 facing the fluid to be treated thus delineates the flow surface of this fluid.

Depending on one of the main applications of the support, the support is used for the design of a filter membrane and is combined with a separation layer 5, wherein the porosity of the separation layer 5 is smaller than or possibly equal to the lowest porosity in the vicinity of the surface 3 of the support 1 facing the fluid to be treated. According to a preferred variant, the separating layer 5 can have a thickness which decreases in the flow direction f of the fluid to be treated, as described in EP 1074291.

The following description is intended to provide an example of implementation of the filter membrane according to the invention.

A multi-channel carrier with an outer diameter of 25mm and a length of 1200mm was used. The average equivalent pore diameter of the porous support was 5 μm.

A suspension of zirconia particles having a grain size of 0.6 μm was prepared. The aqueous suspension is kept from coagulation by adjusting the pH with acetic acid, followed by milling or dispersion of the agglomerates in a vessel containing vitreous (vitrefined) zirconium spheres. The suspension does not contain an organic binder and the concentration of particles is less than 100 g/l. These two values of the parameter will be obtained at very low viscosities.

With this suspension, the modification of the support is carried out by a coating process. Two depositions were performed followed by drying. Followed by the formation of one or more filter layers. The final filter obtained had a cut-off threshold of 0.14 μm.

The permeability to water measured was 500l/h/m²A/bar. As a comparison, the permeability of the filter membrane obtained in the same manner but without the modification of the support was measured at 1500l/h/m²/bar。

Fig. 4 shows the permeability of these two filters when filtering milk and perfectly illustrates the value of the invention. It can be clearly seen that the loss of permeability of the filter membrane using the support of the present invention will be limited by the working time.

Claims (24)

1. A porous support (1) for tangential filtration of a fluid to be treated, having: at least one surface (3) facing the fluid to be treated, the fluid to be treated flowing in a given flow direction; and an extraction surface (1) for the filtrate fraction flowing through the porous carrier₁) Characterized in that the support has an increasing average transverse porosity through the support from the surface facing the fluid to be treated to the extraction surface of the filtrate; and in the direction of flow of the fluid to be treated, parallel to the surface of the support facing the fluid to be treated, the average longitudinal direction of the supportThe porosity is uniform in such a way that partial plugging of the initial support is obtained, the support having a reduced permeability compared to the initial support and the permeability of the support is uniform when moving parallel to the support surface (3) facing the fluid to be treated in the flow direction of the fluid to be treated.

2. The porous carrier (1) according to claim 1, characterized in that the permeability of the carrier is reduced to 1 of 1.5 to 10 minutes compared to the initial carrier.

3. A porous support (1) for tangential filtration of a fluid to be treated, having: at least one surface (3) facing the fluid to be treated, the fluid to be treated flowing in a given flow direction; and an extraction surface (1) for the filtrate fraction flowing through the porous carrier₁) Characterized in that, in the range of a certain fixed depth (p) measured from said carrier surface (3) facing the fluid to be treated, when moving towards the inside of the carrier across said carrier surface (3) facing the fluid to be treated, from said carrier surface (3) facing the fluid to be treated towards said extraction surface (1) of the filtrate₁) The average transverse porosity of the support increases; and for the part of the carrier, the average longitudinal porosity of the carrier is uniform when moving towards the inside of the carrier (1) in the flow direction of the fluid to be treated, parallel to said carrier surface (3) facing the fluid to be treated.

4. Carrier (1) according to claim 3, characterized in that the extraction surface (1) from the carrier surface (3) facing the fluid to be treated towards the filtrate when moving towards the inside of the carrier (1) over the carrier surface (3) facing the fluid to be treated₁) The average diameter of the pores of the support increases with the depth (e) of the support (1).

5. The vector according to any one of claims 1 to 4, characterized in that the vector (1) is obtained by: -partially plugging (c) the initial carrier (1) formed by said carrier surface (3) facing the fluid to be treated within a certain fixed depth (p) measured from said carrier surface (3) facing the fluid to be treated.

6. The carrier of claim 5, wherein the partial blockage (c) is achieved such that: from the carrier surface (3) facing the fluid to be treated towards the extraction surface (1) of filtrate while moving towards the interior of the carrier over the carrier surface (3) facing the fluid to be treated₁) An increasing average lateral porosity is achieved over the fixed depth (p).

7. Support according to claim 5, characterized in that the specific fixed depth (p) is a plugging depth (p) which is greater than the average radius of the agglomerated particles constituting the initial support.

8. The carrier according to claim 7, characterized in that the plugging depth (p) is greater than the average diameter of the agglomerate grains.

9. Carrier according to claim 8, characterized in that the plug depth (p) is equal to or greater than 2.5 μm.

10. The carrier according to claim 9, characterized in that the plug depth (p) is equal to or greater than 5 μm.

11. Support according to claim 5, characterized in that the partial plugging (c) of the support is achieved by infiltration of inorganic particles from said support surface (3) facing the fluid to be treated, wherein the average diameter of said inorganic particles prior to plugging is smaller than the average diameter (dp) of the pores of the support.

12. The carrier according to claim 11, wherein the average diameter of the inorganic particles prior to plugging is between dp/100 and dp/2.

13. The carrier of claim 11, wherein the inorganic particles are sintered after infiltration.

14. Carrier as in claim 6, characterized in that the extraction surface (1) from the carrier surface (3) towards the fluid to be treated towards the filtrate when moving towards the inside of the carrier (1) over the carrier surface (3) towards the fluid to be treated₁) The average lateral porosity increases regularly and continuously over the depth (p).

15. Carrier as in claim 6, characterized in that the extraction surface (1) from the carrier surface (3) towards the fluid to be treated towards the filtrate when moving towards the inside of the carrier (1) over the carrier surface (3) towards the fluid to be treated₁) The average lateral porosity increases stepwise.

16. The porous carrier (1) according to any of claims 1 to 4, characterized in that it comprises at least one internal channel open at both ends, said channel being defined by said carrier surface (3) facing the fluid to be treated.

17. A filter membrane (4) for tangential filtration of a fluid to be treated, combining a porous support (1) according to any of claims 1 to 16 with at least one separation layer (5) for the fluid to be treated, said support surface (3) facing the fluid to be treated being covered with a separation layer (5) having a porosity lower than the porosity of the support (1).

18. The filtration membrane according to claim 17, characterized in that the thickness of the separation layer (5) decreases in the direction of flow (f) of the fluid to be treated.

19. A method for manufacturing a porous carrier (1) for forming a filter membrane (4) for tangential filtration of a fluid to be treated, the porous carrier comprising at least one surface (3) facing the fluid to be treated flowing in a specific flow direction, and an extraction surface (1) for a filtrate fraction flowing through the porous carrier₁) Characterized in that the manufacturing process comprises a step of modifying a porous initial support, i.e. the inorganic particles having an average diameter smaller than the average diameter (dp) of the pores of the initial support, penetrate a fixed depth (p) from the surface (3) of the support facing the fluid to be treated, so that: from the surface (3) facing the fluid to be treated to the extraction surface (1) of the filtrate when moving towards the interior of the carrier over the surface (3) facing the fluid to be treated₁) The average transverse porosity of the support (1) increases; for the part of the carrier, the average longitudinal porosity of the carrier (1) is uniform when moving towards the inside of the carrier (1) parallel to the carrier surface (3) facing the fluid to be treated in the flow direction of the fluid to be treated.

20. The method of claim 19, wherein the step comprising modifying the porous support by infiltration is followed by a sintering step.

21. The method of claim 19, wherein the inorganic particles have an average diameter between dp/100 and dp/2.

22. The method according to any one of claims 19 to 21, characterized in that the infiltration of the inorganic particles is achieved within the range of the depth (p) which is greater than the average radius of the agglomerated particles constituting the initial support.

23. A method according to claim 22, wherein the depth (p) is greater than the average diameter of the agglomerate particles.

24. A method according to any one of claims 19-21, c h a r a c t e r i z e d in that the extraction surface (1) from the carrier surface (3) facing the fluid to be treated towards the filtrate is moved from the carrier surface (3) facing the fluid to be treated towards the interior of the carrier when passing over the carrier surface (3) facing the fluid to be treated towards the interior of the carrier₁) The clogging of the carrier decreases progressively.