APPARATUS AND METHODS FOR EXTRUSION PRODUCTION OF A POROUS SUPPORT CONTAINING A CENTRAL LINEAR CHANNEL AND NON-LINEAR CHANNELS

Abstract

The tangential filter membrane is described as consisting of a tubular porous support in the form of a sintered monolithic ceramic body, an apparatus and method for the extrusion of this support, and the support is produced by extrusion of a ceramic composition containing a powdered solid inorganic phase. It contains a linear channel centered on the symmetry axis of the support and at least one channel helically wound around the symmetry axis, which is extruded using punches to circulate the fluid medium to be processed. The wall roughness of the channels is limited and smaller than the particle size of the powdered solid inorganic phase of the ceramic composition.

Description

Technical Field

[0001] The present invention relates to the technical field of tangential separation using tubular filtration membranes adapted to ensure the separation of molecules or particles contained in a fluid medium to be treated, each tubular filtration membrane comprising a rigid tubular porous support in which one or more non-straight circulation channels for the fluid to be filtered are provided.

[0002] The object of the invention relates more specifically to the technical field of extrusion of rigid tubular porous supports for tubular filtration membranes.

[0003] The object of the invention finds a particularly advantageous application in the field of filtration in the broadest sense, and in particular nanofiltration, ultrafiltration, microfiltration, or reverse osmosis. Previous technique

[0004] In the prior art, extrusion is known to be used to shape a porous, tubular substrate containing a series of channels. Extrusion offers a significantly higher production rate than other manufacturing techniques, such as additive manufacturing methods like those described, for example, in US 2019 / 321890 and WO 2020 / 109715. The linear extrusion speed, measured in minutes, is generally equal to or greater than one meter per minute, while the vertical printing speed of additive methods is typically at best around ten meters per minute. It should be noted that the vertical printing speed of additive methods is highly dependent on the number of channels.It decreases as the number of channels increases, and a multi-channel substrate will thus be printed according to said number of channels, two to ten times slower than a single-channel substrate, while the linear extrusion speed remains independent of the number of channels.

[0005] Typically, the porous support, manufactured by extrusion and made of an inorganic material such as ceramic, can be combined with one or more separating layers, also made of an inorganic material, deposited on the surface of each flow channel and bonded to each other and to the support by sintering. These layers allow the filtration capacity of the filter element to be adjusted.

[0006] The porous support of these tubular filter elements is elongated and has a straight cross-section, most often polygonal or circular. Numerous extruded supports with a plurality of channels parallel to each other and to the longitudinal axis of the porous support have already been proposed. For example, filter elements with a series of non-circular channels are described in patent application WO 93 / 07959 in the name of CERASIV, patent application EP 0 780 148 in the name of CORNING, patent application WO 00 / 29098 in the name of ORELIS, patents EP 0 778 073 and EP 0 778 074 in the name of the applicant, and patent applications WO 01 / 62370 in the name of Société des Céramiques Techniques and FR 2 898 513 in the name of ORELIS.

[0007] In operation, the channels communicate, on one side, with an inlet chamber for the fluid to be treated and, on the other side, with an outlet chamber. The surface of the channels is most often covered with at least one separating layer that ensures the separation of molecules or particles contained in the fluid flowing inside the channels, in a given direction, from one end of the channels, called the inlet, to the other end, called the outlet. Such a filtration element achieves, by sieving, the separation of molecular or particulate species of the product to be treated, insofar as all particles or molecules larger than the diameter of the pores in the area of ​​the filtration element with which they are in contact are retained.During separation, the fluid transfer occurs through the support and, if present, through the separating layer(s). The fluid spreads through the porosity of the support towards its outer surface. The portion of the fluid to be treated that has passed through the separating layer and the porous support is called the permeate or filtrate and is collected by a collection chamber surrounding the filter element.

[0008] To increase the surface area of ​​the channels used for fluid filtration, it is often desirable to arrange a large number of channels within a single support. Due to the large number of channels, the number of possible arrangements relative to one another is significant. Among the claimed advantages of these different configurations is the increased filtering surface area without compromising the mechanical properties or intrinsic permeability of the porous support.

[0009] It should be noted that in the absence of a channel in the central zone of the support containing the axis of symmetry, the volume that would have been occupied by this channel is replaced by porosity. At the beginning of the operation of such a membrane lacking a central channel, the surface of the channels closest to and opposite this axis of symmetry releases a permeate that fills the porosity. The evacuation of this permeate from this central zone to the outer surface of the membrane must then occur along a path that is maximal for this membrane. This significant distance then generates a high pressure difference between the outer surface and the central zone around the axis of symmetry, the pressure value being maximal around this zone. During the operation of the membrane, this maximum value, which opposes the pressure in the retentate, will increase until it equals it.The flow rate in this zone is then zero, and under these conditions, an accumulation of liquid appears that is difficult, if not impossible, to replace, even by washing. This lack of circulation within the porosity of this central zone of the support, and its resulting inaccessibility to washing reagents, means that if this accumulated liquid contains bacteria, these bacteria can proliferate without being able to be eliminated, thus making the use of a membrane without a central channel unlikely in the food industry.

[0010] The shape and arrangement of the channels depend directly on the extrusion operation. As a reminder, extrusion is a (thermo)mechanical shaping process in which a ceramic composition is forced by compression through an orifice having the cross-section of the desired part. This orifice corresponds to the space left between one or more punches and the die that defines the outer edge of said cross-section.

[0011] In prior art, it has been proposed, in order to increase the filtrate flow rate and reduce clogging, to create a turbulent flow regime within the channel of a tubular filter element. It has thus been proposed to create indentations or reliefs on the inner wall of the channels to generate a disturbance in the fluid near the filter surface, thereby limiting the accumulation of matter and clogging.

[0012] Patent EP 0 813 445 describes a method for making impressions on the outside of a porous tube comprising a single channel, said impressions being made while the tube is still deformable, generating a homologous deformation of the inner wall of said channel.

[0013] French patent FR 2 736 843 teaches how to produce porous tubes with a single channel whose wall has indentations, while the peripheral wall of the support is smooth. To achieve this, the porous tube is shaped using a fixed extrusion die in which is mounted, as illustrated in the Fig. 1 A punch holder equipped with a punch P, driven in rotation by a motor around its axis, in any direction of rotation. The ceramic composition is forced, by an upstream feeding device, to pass under pressure through the punch holder and through the extrusion die at a linear extrusion speed. The punch P has one or more straight notches E allowing the extrusion of a porous support with a single channel in the inner wall of which one or more helical ribs are formed in relief.

[0014] The processes described in these two documents (EP 0 813 445 and FR 2 736 843) only allow for the creation of wall reliefs in a tube with a single channel, and they cannot be applied to the manufacture of porous media with multiple internal channels. However, multichannel filtration elements are increasingly sought after because they increase the filter surface area and thus improve their performance.

[0015] It should be noted that a method for manufacturing cooling channels using helical punches is known from document WO 93 / 20961 in the field of drilling tools equipped with cooling channels. This document discloses a method and apparatus for the continuous production of cylindrical bars having at least one internal helical channel, and the sintered metal or ceramic blank obtained by this method. Description of the invention

[0016] The present invention therefore aims to remedy the disadvantages of the prior art by proposing to provide new extruded filtration supports which have a multichannel structure with a geometry adapted to increase the flow of the filtrate, with a production rate much higher than that of additive methods.

[0017] One object of the invention is to provide a porous tubular support that can be used in all fields of application.

[0018] An object of the invention is to provide a porous tubular support for a tangential flow filtration membrane, in the form of a sintered monolithic ceramic porous body, manufactured by extrusion of a ceramic composition comprising a powdery solid inorganic phase and in which are formed by extrusion using punches, a straight channel centered on an axis of symmetry of the support and at least one circulation channel of a fluid medium to be treated with a helical shape wound around the axis of symmetry, the channels having a limited wall roughness lower than the granularity of the powdery solid inorganic phase of the ceramic composition.

[0019] Advantageously, the sintered monolithic ceramic porous body can withstand an internal pressure of at least 10 bars without bursting.

[0020] Another object of the invention is to provide a tangential filtration membrane according to which at least one separating layer coats the wall of the circulation channels of the fluid medium to be treated with the tubular porous support according to the invention.

[0021] Another object of the invention is therefore to propose a new device adapted to ensure the manufacture by extrusion of a porous tubular support having a multichannel structure with a geometry adapted to increase the flow of the filtrate.

[0022] The object of the invention is to provide a device according to the invention for the extrusion manufacturing of a porous tubular support from a ceramic composition, comprising: A fixed extrusion die in which a punch holder is mounted, equipped with at least one punch; a drive system for rotating the punch holder; and a feeding device for forcing the ceramic composition under pressure through the punch holder to pass through the extrusion die at a linear extrusion speed. According to the invention, the device comprises: a punch holder equipped with a straight punch centered on the axis of symmetry and at least one punch with a helical shape wound around an axis of symmetry in a winding direction and a winding pitch; a drive system rotating the punch holder around said axis of symmetry in a direction of rotation opposite to the winding direction of the punch(s) and at a rotational speed equal to the linear extrusion speed of the ceramic composition, divided by the winding pitch of the helical punch(s).

[0023] According to an advantageous embodiment, the punch holder is provided with several punches wound concentrically around a common axis of symmetry in the same direction of winding and the same winding pitch.

[0024] According to another advantageous embodiment, the punch holder is provided with several punches arranged in at least two concentric rings.

[0025] Advantageously, each punch having a helical shape has a length taken along the axis of symmetry, equal to or greater than a quarter of the winding pitch.

[0026] According to another feature of the invention, the drive system rotates the punch holder with a rotational speed equal to the linear extrusion speed of the ceramic composition, divided by the winding pitch of the punches, taking into account a tolerance margin of plus or minus 15%.

[0027] For example, the feeding system is a piston or worm gear type system.

[0028] Advantageously, the device includes a heating system for the extrusion die to maintain the punch holder, the punch(s) and the ceramic composition at a temperature between 50°C and 300°C.

[0029] According to one embodiment, the rotary drive system of the punch holder is mounted downstream of the feeding system.

[0030] According to another embodiment, the rotation drive system of the punch holder is located on the side of the punch holder so that the axis of symmetry of the punch holder is parallel to the feeding direction of the feeding system.

[0031] According to another embodiment, the rotation drive system of the punch holder is located at the rear of the punch holder so that the axis of symmetry of the punch holder makes an angle less than or equal to 90° with respect to the direction of supply of the supply system opening upstream or downstream of the punch holder.

[0032] Another object of the invention is to propose a method for manufacturing a porous tubular support from a ceramic composition, consisting of: to provide a fixed extrusion die in which is mounted a punch holder equipped with a straight punch centered on an axis of symmetry and at least one punch having a helical shape wound around an axis of symmetry according to a winding direction and a winding pitch; to ensure that the ceramic composition passes through the punch holder to cross the extrusion die at a linear extrusion speed; and to ensure the rotation of the punch holder in a direction of rotation opposite to the winding direction of the helical punch(s) and with a rotation speed equal to the linear extrusion speed of the ceramic composition, divided by the winding pitch of the helical punch(s).

[0033] According to an advantageous feature of this process, in order for the rotational speed of the punch holder to be equal to the linear extrusion speed of the ceramic composition, divided by the winding pitch, adjustment is made either solely on the rotational speed of the punch holder or solely on the linear extrusion speed or on the rotational speed of the punch holder and on the linear extrusion speed.

[0034] Advantageously, the fixed extrusion die is fed with a ceramic composition comprising a powdery solid inorganic phase in the form of particles with an average diameter between 0.1 and 150 micrometers and a matrix.

[0035] According to another advantageous feature, the fixed extrusion die is fed with a ceramic composition comprising a first inorganic solid powder phase in the form of particles with an average diameter between 0.1 and 150 micrometers and a second phase in the form of a matrix comprising at least one hot-melt polymer.

[0036] According to another characteristic of this process, at least one extrudate is recovered at the outlet of the fixed extrusion die with a determined length to form a porous tubular support and this extrudate is subjected to a post-treatment of sintering. Brief description of the drawings

[0037] [ Fig. 1 ] There Figure 1 is a perspective view illustrating a punch holder and punch of the earlier art, presented in the form of a pin with a straight notch around its periphery. Fig. 2 ] There Figure 2 is a perspective view of an example of an embodiment of a punch holder according to the invention, equipped with a centered straight punch and a punch with a helical shape. Fig. 3 ] There Figure 3 is a perspective view of another example of an embodiment of a punch holder according to the invention, equipped with a centered straight punch and two punches with the same helical shape. Fig. 4 ] There Figure 4 is a cross-sectional view of the three punches according to the invention, illustrated in the Fig. 3 . [ Fig. 5 ] There Figure 5 is a perspective view of another example of an embodiment of a punch holder according to the invention, equipped with three punches of the same helical shape and a centered straight punch. Fig. 6 ] There Figure 6 is a cross-sectional view of the four punches according to the invention illustrated in the Fig. 5 . [ Fig. 7 ] There Figure 7 is a perspective view of another embodiment of a punch holder according to the invention, provided with a centered straight punch, three helical punches distributed in a first concentric ring, and a second ring comprising eight helical punches, the three punches of the first ring having a different shape from the eight punches of the second ring, the eleven helical punches being wound around an axis of symmetry in the same direction and with the same pitch. Fig. 8 ] There Figure 8 is a cross-sectional view of the twelve punches according to the invention illustrated in the Fig. 7 . [ Fig. 9 ] There Figure 9 is a schematic cross-sectional elevation view of a first example of an embodiment of an extrusion manufacturing device according to the invention. Fig. 10 ] There Figure 10 is a schematic cross-sectional elevation view of a second example of an embodiment of an extrusion manufacturing device according to the invention. Fig. 11A ] There Figure 11A is a schematic cross-sectional elevation view of a third embodiment of an extrusion manufacturing device according to the invention. Fig. 11B ] There Figure 11B is a schematic perspective view of a punch holder implemented in the example of the manufacturing device illustrated in the figure 11A . [ Fig. 12 ] There Figure 12 is a perspective view of an example of a porous support obtained using an extrusion manufacturing device according to the invention, implementing a punch holder illustrated in the Fig. 5 . Description of the implementation methods

[0038] The invention relates to the manufacture by extrusion of a porous support 1, as well as a filtration membrane comprising the porous support 1 according to the invention including a straight channel 2a centered on an axis of symmetry of the porous support and at least one non-straight channel 2 on the walls of which one or more separating layers are deposited ( Fig. 12 ).

[0039] The invention relates to the manufacture of ceramic porous supports 1 for fluid filtration membranes, and more particularly for tangential flow filtration membranes. Such porous supports, as defined in the invention, have a tubular geometry and comprise a straight channel 2a and at least one channel 2, or flow path, for the fluid to be filtered. These flow channels 2, 2a have an inlet and an outlet. The inlet of the flow channels is positioned at one end of the porous support, this end acting as the inlet zone for the fluid to be treated, and their outlet is positioned at the other end of the porous support, acting as the outlet zone for the retentate. The inlet and outlet zones are connected by a continuous peripheral zone at which the permeate is collected.

[0040] When the porosity (average pore diameter) of the sintered support is adapted to the fluid medium to be treated (filtration threshold), the said sintered support is directly usable in filtration and is designated as a self-membrane or homogeneous membrane.

[0041] When the porosity of the sintered support is not suitable for the fluid being treated (pores too large relative to the required filtration threshold), the walls of the circulation channel(s) 2 are continuously covered by at least one separation layer that filters the fluid being treated. The separation layer(s) are porous and have an average pore diameter smaller than that of the support. The separation layer can be deposited either directly onto the porous support (in the case of a single-layer separation layer), or onto an intermediate layer with a smaller average pore diameter, itself deposited directly onto the porous support (in the case of a multi-layer separation layer). Thus, a portion of the fluid to be filtered passes through the separation layer(s) and the porous support, so that this treated portion of the fluid, called the permeate, flows out through the outer peripheral surface of the porous support.The separating layers delimit the surface of the filtration membrane intended to be in contact with the fluid to be treated and in contact with which the fluid to be treated flows.

[0042] The porosity of the ceramic porous support 1 is open, meaning it forms a network of interconnected pores in three dimensions, allowing the fluid filtered by the separating layer(s) to pass through the porous support and be collected at the periphery. The permeate is therefore collected on the peripheral surface of the porous support.

[0043] The porous support 1 has an average pore diameter in the range of 0.5 µm to 50 µm. The porosity of the porous support 1 is between 10 and 60%, preferably between 20 and 50%.

[0044] The mean pore diameter is defined as the d50 value of a volumetric distribution where 50% of the total pore volume corresponds to the volume of pores with a diameter smaller than d50. The volumetric distribution is the curve (analytical function) representing the frequencies of the pore volumes as a function of their diameter. d50 corresponds to the median dividing the area under the frequency curve obtained by mercury penetration into two equal parts. Specifically, the technique described in ISO 15901-1:2005 may be used for the mercury penetration measurement technique.

[0045] The porosity of a porous support, which corresponds to the total volume of interconnected voids (pores) present in the material, is a physical quantity that determines the flow and retention capacities of the porous body. For the material to be used in filtration, the total interconnected open porosity must be at least 10% for a satisfactory filtrate flow rate through the support, and at most 60% to ensure adequate mechanical resistance of the porous support.

[0046] The porosity of a porous material can be measured by determining the volume of liquid contained within it. This is achieved by weighing the material before and after prolonged immersion in the liquid (water or another solvent). Knowing the respective densities of the material and the liquid used, the difference in mass, converted into volume, directly represents the pore volume and thus the total open porosity of the porous material.

[0047] Other techniques allow for the precise measurement of the total open porosity of a porous substrate, including: Mercury intrusion porosimetry (ISO 15901-1 standard cited above): injected under pressure, mercury fills the pores accessible at the applied pressures, and the volume of injected mercury then corresponds to the volume of the pores; small-angle scattering: this technique, which uses either neutron radiation or X-rays, provides access to physical quantities averaged over the entire sample. The measurement consists of analyzing the angular distribution of the intensity scattered by the sample; analysis of 2D images obtained by microscopy; analysis of 3D images obtained by X-ray tomography.

[0048] The porous tubular support 1 according to the invention is prepared by sintering an extrudate corresponding to the extruded object using, for example, a device 5 according to the invention that manufactures a porous tubular support 1 from a ceramic composition. As will be more precisely shown in the Fig. 9, 10 , 11A et 11B The device 5 according to the invention comprises a fixed extrusion die 6 in which a punch holder 7 is mounted, the holder being equipped with at least two punches 8, 8a. The fixed extrusion die 6 defines the external shape of the extrudate exiting the die, which, within the scope of the invention, may be circular or non-circular (polygonal or other). The fixed extrusion die 6, together with the punches 8, 8a, delimits a free space or orifice through which the ceramic composition passes.

[0049] The device 5 according to the invention also includes a feeding device 9 for forcing the ceramic composition under pressure through the punch holder 7 to pass through the extrusion die 6 at a linear extrusion speed VI. For example, the feeding system 9 is a piston, pump, or screw type system of any known type, allowing the application of mechanical pressure to the ceramic composition. The linear extrusion speed VI is measured at the extrudate outlet of the fixed extrusion die 6, either discontinuously by simple timing or continuously by a remote linear speed sensor such as a laser Doppler velocimeter.

[0050] The porous tubular support 1 is manufactured by extrusion from a ceramic composition passing under pressure through the fixed extrusion die 6.

[0051] The ceramic composition consists of a powdery solid inorganic phase and a matrix.

[0052] The powdery solid inorganic phase of the ceramic composition comprises one or more solid inorganic materials, each in the form of particles with an average diameter between 0.1 µm and 150 µm.

[0053] The concept of mean diameter is associated with that of particle size distribution. Indeed, the particles in a powder are rarely of a single size or monodisperse, and a powder is therefore most often characterized by a size distribution of its particles. The mean diameter then corresponds to the average of a particle size distribution. The distribution can be represented in different ways, such as a frequency distribution or a cumulative distribution. Some measurement techniques directly provide a distribution based on number (microscopy) or mass (sieving). The mean diameter is a measure of central tendency.

[0054] Among the most commonly used measures of central tendency are the mode, the median, and the mean. The mode is the most frequent diameter in a distribution: it corresponds to the maximum of the frequency curve. The median represents the value where the total frequency of values ​​above and below it is identical (in other words, the same number or total volume of particles is found below the median as above it). The mean, on the other hand, must be calculated and determines the point where the moments of the distribution are equal. For a normal distribution, the mode, mean, and median coincide, whereas they differ in the case of a non-normal distribution.

[0055] The average diameter of the constituent particles of an inorganic powder can be measured, in particular, by: laser light diffraction for particles ranging from 3 mm to about 0.1 µm; sedimentation / centrifugation; dynamic light scattering (DLS) for particles ranging from 0.5 µm to 2 nm; analysis of images obtained by microscopy; small-angle X-ray diffraction.

[0056] The granularity of the powdered solid inorganic phase refers to the dimensions of the particles composing the powdered solid inorganic phase. Granularity is characterized by the concept of average diameter, which is described above.

[0057] Most often, the ceramic composition comprises, as powdered ceramic material(s), alone or in a mixture, an oxide and / or a nitride and / or a carbide. Examples of oxides suitable for the purposes of the invention include metal oxides, particularly titanium oxide, zirconium oxide, aluminum oxide, and magnesium oxide, with titanium oxide being preferred. Examples of carbides include metal carbides, particularly silicon carbide. Examples of nitrides that can be used include titanium nitride, aluminum nitride, and boron nitride. In a preferred embodiment, the ceramic composition comprises at least one metal oxide as a powdered inorganic material, preferably titanium oxide.

[0058] Within the framework of the invention, the ceramic composition has a suitable rheology in terms of plasticity for its extrusion through the fixed extrusion die 6.

[0059] According to a first embodiment, the matrix of the ceramic composition comprises one or more solvents. The solvent(s) may be aqueous or organic. Examples include water, ethanol, or acetone.

[0060] Furthermore, the matrix of the ceramic composition comprises one or more organic additives. Advantageously, these organic additives are soluble in the solvent(s) of the matrix. Suitable organic additive(s) for the purposes of this invention may be chosen, by way of non-limiting example, from: binders, and for example among cellulose ethers such as hydroxyethylcellulose which is a polymer, gum arabic which is a polysaccharide, or polyethylene glycol (PEG); lubricants and plasticizers, and for example among glycerol or stearic acid; thickeners and gelling agents, and for example among xanthan gum or agar-agar which is a polymer of galactose.

[0061] The mass content of powdered inorganic material(s) in the ceramic composition can range from 50 to 90%, preferably between 80 and 85% by weight, relative to the total weight of the ceramic composition.

[0062] The mass content of matrix in the ceramic composition can range from 10% to 50% by weight, preferably from 15% to 20% by weight, relative to the total weight of the ceramic composition.

[0063] Cette The ceramic composition is not a powder but a paste. It is possible to adjust the rheology of this ceramic composition through the particle size of the powdery solid inorganic phase, and / or through the nature of the organic additives when present, and / or through their respective proportions. Indeed, for example, using a matrix containing one or more organic additives soluble in one or more solvents within the matrix allows for modification of the rheology of the ceramic composition.

[0064] According to a second embodiment, the ceramic composition comprises a matrix made of one or more hot-melt polymers. The matrix is ​​organic in nature and solid at room temperature.

[0065] By "hot melt polymer" we mean a polymer that softens under the effect of heat.

[0066] Examples of suitable hot-melt polymers for use in the invention include the following polymers or families of polymers, possibly functionalized, used alone or in mixtures in the matrix: polylactic acid (PLA), polyvinyl alcohol (PVA), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyethylene, polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), polyolefins, thermoplastic elastomers (TPE), polyolefin-based elastomers (TPE-O), and polycarbonate.

[0067] The mass content of powdered inorganic material(s) in the ceramic composition can range from 40 to 95%, preferably between 70 and 90% by weight, relative to the total weight of the ceramic composition.

[0068] In the context of the invention, the ceramic composition, preferably in granular form, is preheated upstream in the feeding device 9 so that the hot-melt polymer(s) soften, allowing the ceramic composition to be pressurized upstream of the fixed extrusion head 6. Typically, the fixed extrusion head 6 is heated to soften the hot-melt polymer(s), thus enabling the extrusion of the ceramic composition. The temperature of the fixed extrusion head 6 can be adjusted according to the hot-melt polymer(s) present in the ceramic composition.

[0069] Furthermore, within the framework of the invention, it is possible to adjust the rheology of the ceramic composition through its temperature in the fixed extrusion head, and / or the granularity of the powdery solid inorganic phase, and / or through the nature of the hot-melt polymer(s) and / or through their proportions.

[0070] According to the invention, the punch holder 7 is equipped with a straight punch 8a centered on the axis of symmetry X of the punch holder 7. The straight punch 8a has a circular cross-section. The punch holder 7 is also provided with at least one punch 8 having a helical shape wound around an axis of symmetry X in a direction of winding F1. In the example illustrated in the Fig. 2 The punch holder 7 is equipped with the centered straight punch 8a and a single punch 8 having a helical shape, and conforming to the invention. Of course, the punch holder 7 can be provided, in addition to the centered straight punch 8a, with a different number of punches 8 having a helical shape conforming to the invention, such as, for example, two ( Fig. 3 et 4 ), three ( Fig. 5 et 6 ), 11 punches ( Fig. 7 et 8 ) or 7 punches ( figure 11B ).

[0071] In general, a helical punch 8 is a punch whose shape, without a central core, follows that of a circular helix. A helical punch 8 has a body with a cross-section S extending only along a circular helix H wound around the axis of symmetry X. Since the helical punch 8 has no central core, this helical punch 8 exclusively forms circular turns wound around, along, and outside the axis of symmetry X. This circular helix H corresponds to a curve inscribed on a cylinder of revolution about an axis corresponding to the axis of symmetry X, the tangent to this curve making a constant angle with the axis of symmetry.Naturally, this cylinder of revolution on which the circular helix H rests corresponds to an empty space in the helical punch 8, since the latter does not contain any material centered on the axis of symmetry X but consists exclusively of a helical body. All points belonging to this cross-section S are located at a constant, non-zero distance R from the axis of symmetry X. In other words, the helical body of the punch 8 is wound around the axis of symmetry X without being crossed by this axis of symmetry X.

[0072] It should be noted that the cross-section S of the helical punches 8 can have different shapes adapted to the desired shapes for the channels 2 of the porous support 1. For example, each helical punch 8 has a round cross-section in the examples of Fig. 2 , 3-4 And 5-6 According to the example of implementation illustrated in Fig. 7 et 8 The eight punches 8, having a helical shape and belonging to the outer ring, all have the same pseudo-rectangular cross-section, while the three punches 8, having a helical shape and belonging to the inner ring, all have the same pseudo-ovoid cross-section. According to the embodiment illustrated in Fig. 11A et 11B The seven punches 8, which have a helical shape and belong to the outer ring, all have the same pseudo-triangular cross-section. It should be noted, however, that the punches of the same ring do not have to have identical cross-sections. It is also worth noting that the cross-sectional shape of punches 8 and 8a corresponds to the shape of the channels 2 in the extrudate obtained using the device 5 according to the invention.

[0073] More precisely, it is the shape of the cross-section at the end of a punch that determines the shape of the cross-section of the channel formed in the extrudate. The end of a punch corresponds to the cross-section perpendicular to the axis of symmetry X, which is parallel to the direction of extrudate flow. A final or intermediate enlargement of the punch can be advantageous with regard to the compression of the ceramic composition. In the example illustrated in the figure 2 The centered straight punch 8a and the helical punch 8 have a widening at their ends. Of course, the cross-sections of the centered straight punch 8a and the helical punch(s) 8 may vary in other areas. In any case, the terminal straight cross-section of a punch is the one that always determines the shape of the canal cross-section.

[0074] Each helical punch 8 is wound around the axis of symmetry X in a single, predetermined direction of winding, namely a dextrorotatory (clockwise) or levorotatory (counterclockwise) direction. In the example illustrated on the Fig. 2 The helical punch 8 is wound around the axis of symmetry X in a dextrorotatory direction F1. According to a feature of the invention, when the punch holder 7 is provided with several helical punches, all the helical punches 8 equipping a punch holder 7 are wound around the axis of symmetry X in the same direction F1. Thus, all the helical punches 8 equipping a punch holder 7 have a direction of winding, for example, dextrorotatory in the examples illustrated in Fig. 3 , 5 , 7 And 11B .

[0075] Furthermore, according to another feature of the invention, all the helical-shaped punches 8 equipping a punch holder 7 are wound concentrically around the same axis of symmetry X. Thus, the punch holder 7 has an axis of symmetry X which is common to all the helical-shaped punches 8.

[0076] According to a preferred embodiment, the helical punches 8 equipping a punch holder 7 are distributed symmetrically around the axis of symmetry X, as is clearly shown in the Fig. 4 , 6 , 8 And 11B For example, according to one embodiment, the helical punches 8 are mounted on the punch holder 7 so as to be arranged in at least two concentric rings, as shown in the embodiment illustrated in Fig. 7 et 8 Thus, the punch holder 7 is provided with a first series of eight helical punches 8 arranged in an outer ring concentric with an inner ring along which three helical punches 8 are distributed. Advantageously, the eight helical punches 8 are regularly distributed at regular angles along the outer ring, while the three helical punches 8 are also regularly distributed at regular angles along the inner ring.

[0077] Each helical punch 8 is wound around the axis of symmetry X with a predetermined winding pitch P. The pitch P of a helical punch 8 corresponds to the distance along the helix between two consecutive points of intersection with a line parallel to the axis of symmetry X. According to one feature of the invention, when the punch holder 7 is equipped with several helical punches, all the helical punches 8 fitting a punch holder 7 have the same winding pitch P.

[0078] Advantageously, the winding pitch P, expressed in ° / mm, is between 1° and 90° / mm. Preferably, the winding pitch is between 3.6° and 36° / mm, considering that a winding pitch of 3.6° / mm is equivalent to a winding pitch of 100 mm and that a winding pitch of 36° / mm is equivalent to a winding pitch of 10 mm. As will be better understood later in the description, the winding pitch P of the helical punch corresponds to the pitch of the channels 2 obtained in the extrudate.

[0079] It should be noted that each punch 8 has a helical portion between a distal end Ed and a proximal end Ep. According to one feature of the invention, each punch 8 has a helical portion whose length along the axis of symmetry X is equal to or greater than one-quarter of the winding pitch P.

[0080] Each punch 8, 8a is fixed in any suitable manner to the punch holder 7. The punches 8, 8a thus extend in projection or cantilever along one side of the punch holder 7. Typically, the helical portion of the punch 8, taken between a distal end Ed and a proximal end Ep, is extended by a connecting or fixing portion Er to the punch holder. For example, in the example illustrated in the Fig. 3 The helical punch 8 extends beyond its proximal end Ep by means of a helical connecting portion Er fixed to the punch holder 7, while the centered straight punch 8a is fixed to the end of the punch holder 7. In the example illustrated in the figure 2 The helical punch 8 extends beyond its proximal end Ep by a straight connecting portion Er, which forms part of the centered straight punch 8a and is fixed to the punch holder 7. In the examples illustrated in figures 5 And 7 The helical punches 8 are fitted into the punch holder 7 by the connecting part Er, while the end of the centered straight punch 8a is also fitted into the punch holder 7. In the example illustrated in figures 11A, 11B The connecting parts Er of the helical-shaped punches 8 converge towards the central part of the punch holder 7 and more precisely around the end of the centered straight punch 8a. As can be seen from the drawings, the connecting parts Er of the helical-shaped punches 8 together form a cone converging towards the punch holder 7, making it possible to delimit around it a collection volume 7c whose function will become apparent in the rest of the description.

[0081] It should be noted that the punch holder 7 and the punches 8, 8a can be manufactured in any suitable manner. For example, the punch holder 7 and the punches 8, 8a can be a single piece obtained by electro-erosion, for instance. Alternatively, the punches 8, 8a can be manufactured separately and then fixed, for example, by crimping onto the punch holder 7 or in recesses provided within the punch holder 7. Typically, the punch holder 7 is designed or configured to have one or more openings 7a allowing the ceramic composition to pass through the punch holder. It should be noted that the punch holder 7 illustrated in figures 11A, 11B is not openwork but solid insofar as the connecting parts Er of the punches and the punches between each other delimit spaces for the passage of the ceramic composition arriving laterally at the periphery.

[0082] According to the invention, the device 5 includes a rotational drive system 10 for the punch holder 7. The rotational drive system 10 can be implemented in any suitable manner to ensure the rotation of the punch holder about the axis of symmetry X at a predetermined speed and in a predetermined direction. For example, this rotational drive system 10 may include a motor, for example an electric motor, connected directly or via a transmission to the punch holder 7, and whose operation is controlled by a control device. Advantageously, the rotational speed of the motor is adjustable so as to allow the rotational speed of the punch holder 7 to be regulated.

[0083] Selon A feature of the invention is that the drive system 10 rotates the punch holder 7 around the axis of symmetry X, in a direction of rotation F2 opposite to the winding direction F1 of the punch(s) 8. Thus, as is more precisely shown in Fig. 9, 10 And 11A The punch holder 7 is driven in rotation in the left-hand direction F2 since the helical punches 8 equipping the punch holder 7 have a right-hand winding direction F1. Of course, it can be provided that the drive system 10 drives the punch holder 7 in rotation in a right-hand direction if the helical punches 8 equipping the punch holder 7 have a left-hand winding direction.

[0084] According to one feature of the invention, the drive system 10 rotates the punch holder 7 at a speed synchronized with the linear extrusion speed VI of the ceramic composition. It should be understood that the rotational speed of the punch holder 7 is synchronized with the linear extrusion speed VI of the ceramic composition in such a way that the section of ceramic composition being extruded in the extrusion die 6 is not rotated, meaning that this section of ceramic composition is not subjected to torsion. This section of ceramic composition advances strictly linearly in the extrusion die 6 because each helical punch 8, as it rotates, gradually withdraws (unscrews) from the section of ceramic material in which it is located, which advances simultaneously linearly in the die.

[0085] According to one feature of the invention, the drive system 10 rotates the punch holder 7 at a rotational speed Vr equal to the linear extrusion speed VI of the ceramic composition, divided by the winding pitch P of the helical punches 8. This is the relationship Vr = VI / P, where Vr is expressed, for example, in revolutions per minute, VI in centimeters per minute, and P in centimeters. According to the invention, the winding pitch P of the helical punches is predefined, and the equality Vr = VI / P can be obtained by adjusting either only the rotational speed of the punch holder 7, only the linear extrusion speed, or both the rotational speed of the punch holder 7 and the linear extrusion speed.

[0086] It should be noted that the above equality relationship is considered to be satisfied within a tolerance margin of plus or minus 15%. Thus, the quantity VI / P (in revolutions per minute) is equal to the quantity Vr (in revolutions per minute) if the difference between these two quantities varies by plus or minus 15%. Within this tolerance range, even if the ceramic composition section does not advance strictly linearly in the fixed extrusion die 6, the helical punches 8 ensure the extrusion of this ceramic composition section with an acceptable shape into the extrudate. Typically, for a pitch P equal to 10 cm and for a linear extrusion speed VI equal to 200 cm / min, then the rotational speed Vr of the punch holder 7 must be between 17 and 23 revolutions per minute.

[0087] There Fig. 9 This illustrates a first embodiment of the device 5 according to the invention, in which the rotary drive system 10 of the punch holder 7 is located at the rear of the punch holder 7. According to this illustrated embodiment, the rotary drive system 10 comprises a motor 10a that drives a connecting shaft 10b fixed to the punch holder 7 and centered on the axis of symmetry X, on the opposite face from which the punches protrude. Given the rearward and axial mounting of the rotary drive system 10 of the punch holder 7, the axis of symmetry X of the punch holder 7 forms an angle of less than or equal to 90° with respect to the feed direction of the feed system 9.The feed system 9 is thus located on the side of the punch holder 7, with an inlet 6a arranged laterally in the fixed extrusion die 6 along a direction D making an angle of less than or equal to 90° with respect to the axis of symmetry, for example, around 45°. The feed system 9 opens, via its inlet 6a, upstream of the punch holder 7, in the direction of progression of the ceramic composition. The passages 7a provided in the punch holder 7 allow the ceramic composition to pass through the punch holder.

[0088] There Fig. 10 This illustrates a second embodiment of the device 5 according to the invention, in which the rotational drive system 10 of the punch holder 7 is located on the side of the punch holder 7. The rotational drive system 10 of the punch holder is thus mounted downstream of the feeding system 9 with respect to the direction of movement of the ceramic composition. In this example, the axis of symmetry X of the punch holder is parallel to the feeding direction D of the feeding system 9. The feeding system 9 can therefore be located at the rear of the punch holder 7 so that the passages 7a provided in the punch holder 7 allow the ceramic composition to pass through the punch holder.According to the illustrated embodiment, the rotation drive system 10 comprises a motor 10a laterally driving the punch holder 7 in rotation, using a transmission comprising a pinion 10b locked in rotation with the motor output shaft and engaging with a toothed ring 10c arranged on the periphery of the punch holder 7.

[0089] There figure 11AThis illustrates a third embodiment of the device 5 according to the invention, in which the feeding system 9 is located on the side of the punch holder 7 with an inlet 6a arranged laterally in the fixed extrusion die 6 along a direction D making an angle of less than or equal to 90° with respect to the axis of symmetry, for example, around 45°. The inlet 6a of the feeding system 9 is arranged to open laterally to the punches 8, 8a, and more precisely at the level of the collection volume 7c surrounding the connecting portions Er of the helical punches 8. It should be noted that the punches 8, 8a leave spaces between them allowing the passage of the ceramic composition so that it completely fills the extrusion die 6. The feeding system 9 opens, via its inlet 6a, downstream of the punch holder 7, in the direction of progression of the ceramic composition.According to this illustrated embodiment, the rotation drive system 10 comprises a motor driving in rotation a connecting shaft 10b fixed to the punch holder 7, centered on the axis of symmetry X, on the opposite face from which the punches extend in projection.

[0090] It should be noted that the device 5 according to the invention may include a heating system 11 for the extrusion die 6 to maintain the punch holder 7, the punch(s) 8, 8a, and the ceramic composition at a predetermined temperature, between 50°C and 300°C. The heating system 11 may be implemented by any suitable system for maintaining the extrusion die 6, the punch holder 7, the punch(s) 8, 8a, and the ceramic composition at a homogeneous temperature. This heating system 11 is implemented in particular when the fixed extrusion die 6 is fed with a ceramic composition comprising a first inorganic solid powder phase in the form of particles with an average diameter between 0.1 and 150 micrometers and a second phase in the form of a matrix comprising at least one thermofusible polymer.

[0091] The implementation of the device 5 according to the invention of manufacturing by extrusion, of a porous tubular support 2 follows directly from the preceding description.

[0092] First, an extrusion device 5 must be made available, comprising a fixed extrusion die 6 in which is mounted a punch holder 7 equipped with a straight punch 8a centered on the axis of symmetry X and at least one punch 8 having a helical shape wound around an axis of symmetry X with a winding direction and a winding pitch P. For the manufacture of a porous tubular support from a ceramic composition, the process consists of: to ensure that the ceramic composition passes through the punch holder 7 to go through the extrusion die 6 at a linear extrusion speed; and to ensure the rotation of the punch holder 7 in a direction of rotation opposite to the winding direction of the helical punch 8 and with a rotation speed synchronized with the linear extrusion speed of the ceramic composition.

[0093] Advantageously, the punch holder 7 is rotated with a rotational speed equal to the linear extrusion speed of the ceramic composition, divided by the winding pitch P of the helical punch(s) 8.

[0094] In order that the rotational speed of the punch holder 7 is equal to the linear extrusion speed of the ceramic composition, divided by the winding pitch P, the process consists of acting on the setting either only of the rotational speed of the punch holder 7 or only on the linear extrusion speed set by the flow rate of the feeding device 9 or on the rotational speed of the punch holder 7 and on the linear extrusion speed set by the flow rate of the feeding device 9.

[0095] It is recalled that the fixed extrusion die 6 is fed, using the feeding device 9, with a ceramic composition of any type. Preferably, the ceramic composition comprises a powdery solid inorganic phase in the form of particles with an average diameter between 0.1 and 150 micrometers and a matrix. As another example, the fixed extrusion die 6 is fed, using the feeding device 9, with a ceramic composition comprising a first powdery solid inorganic phase in the form of particles with an average diameter between 0.1 and 150 micrometers and a second phase in the form of a matrix comprising at least one thermoplastic polymer. Naturally, the feeding device 9 is adapted to ensure that the ceramic composition delivered to the fixed extrusion die 6 has all the necessary characteristics, particularly in terms of pressure and malleability, to achieve efficient extrusion.

[0096] Upon exiting the fixed extrusion die 6, the extrudate is collected and conventionally cut to a predetermined length to form porous tubular supports 1. Each extrudate, corresponding to a length of porous tubular support, is subjected to a post-treatment of sintering of various known types. After this post-treatment, a porous tubular support 1 is obtained, comprising a straight channel 2a centered on the support's axis of symmetry and at least one flow channel 2 for a fluid medium to be treated, with a helical shape resulting from the impression of a helical punch 8. It is known that the post-treatment sintering process leads to a dimensional shrinkage of the porous tubular support relative to the corresponding extrudate. This sintering shrinkage can range from 5% to 25%, and more specifically from 12% to 15%.Since the helical shape of the channels 2 obtained in the extrudate corresponds to the negative shape of the helical punches 8, the definition of the helical punch characteristics takes this sintering shrinkage into account in order to obtain, after sintering in the tubular porous support, channels 2 with the desired final dimensional characteristics. After sintering, the hydraulic diameter and pitch of the channels 2 are reduced. Thus, in particular the winding pitch P, the shapes and dimensions of the cross-sections of the helical punches 8 take this sintering shrinkage into account. The same applies to the straight channel 2a centered on the axis of symmetry of the support.

[0097] Such a manufacturing process makes it possible to obtain, by extrusion, a porous tubular support in the form of a monolithic ceramic porous body in which are formed a centered straight channel 2a corresponding to the imprint of the straight punch 8a and at least one helical channel 2 for the circulation of a fluid medium to be treated, corresponding to the imprint of a helical punch 8. Pressurizing the material to be extruded upstream of the die compresses the powder grains of the inorganic solid phase against the surfaces of the punches 8 and 8a. Pressurizing the material to be extruded not only serves to generate the linear velocity VL but also, within the scope of the invention, to compress the material against the surfaces of the punches 8 and 8a. This results in a wall smoothing effect on the material, which persists after sintering at the level of the channel walls.Consequently, channels 2 and 2a exhibit limited wall roughness, less than the granularity of the powdery solid inorganic phase used in the extruded ceramic composition. The walls of channels 2 and 2a have a wall roughness with asperities to the touch that are less than the granularity of the powdery solid inorganic phase used in the extruded ceramic composition.

[0098] The measurement of the wall roughness of the channels 2 and 2a can be carried out using any known suitable method. For example, a roughness tester can be used, with its probe moved along one or more generatrices of the channel. The arithmetic mean deviation, denoted Ra, which indicates the average roughness of the surface being measured, directly characterizes the overall surface condition. The measurement result, obtained according to ISO 21920, is expressed in microns. It is compared to the particle size distribution of the powdered solid inorganic phase of the ceramic composition, characterized by the average particle diameter of the powdered solid inorganic phase used in the extruded ceramic composition.

[0099] The wall of the channel(s) 2, 2a carrying the fluid medium to be treated in the tubular porous support can be coated with at least one separating layer to form a tangential flow filtration membrane. Typically, such a tubular support 1, after undergoing a conventional sintering operation, constitutes a rigid element capable of withstanding an internal pressure of at least 10 bar without bursting, and preferably at least 30 bar without bursting, and advantageously at least 50 bar without bursting. According to the invention, bursting pressure corresponds to the pressure at which a support whose porosity has been previously sealed (with a hot-melt material such as paraffin) bursts under the effect of an internal overpressure relative to the external pressure on the support; this overpressure being applied in the channels with water, the external pressure on the support being atmospheric pressure.

[0100] It is clear from the preceding description that the device 5 according to the invention makes it easy to manufacture, by extrusion, a porous tubular support 1 with helical channels 2 capable of generating turbulence to increase the filtrate flow while reducing clogging. The extrusion manufacturing of tubular supports allows for a production rate far exceeding that of additive manufacturing methods. The linear extrusion speed, measured in minutes, is generally equal to or greater than one meter per minute, whereas the vertical printing speed of additive manufacturing methods is generally at best around ten meters per minute. It should be noted that the vertical printing speed of additive manufacturing methods is highly dependent on the number of channels.It decreases as the number of channels increases, and a multi-channel substrate will thus be printed two to ten times slower than a single-channel substrate, while the linear extrusion speed remains independent of the number of channels.

[0101] Furthermore, during extrusion through the die, the ceramic composition is not driven into rotation or subjected to torsion which would otherwise alter the mechanical properties of the extrudate.

[0102] The helical shape of the channels 2 obtained in the extrudate corresponds to the negative shape of the helical punches 8. The number, the winding pitch P, the arrangement, and the shapes and dimensions of the cross-sections of the helical punches 8 offer flexibility in defining the channels 2 formed in the porous tubular support.

[0103] It should be noted that the winding pitch obtained in the extrudate is predefined by the helical punch 8, and that the rotational speed Vr of the punch holder 7 and the linear speed VI of the ceramic composition in the die must be jointly adapted to this predefined winding pitch. The helical punch 8 defines in the extrudate not only the cross-section of the channel 2, of which it is the negative, but also the channel pitch. Thus, the winding pitch P of the helical punch 8 determines the effectiveness of the unclogging.

[0104] Each channel 2 thus presents a flexible circulation volume between the ends of the porous tubular support. This flexible circulation volume corresponds, of course, to a zone of the porous support 1 that does not contain porous material and is bounded by the walls of the channel. It should be noted that the porous tubular support 1 has a variable thickness in a cross-section perpendicular to its longitudinal axis, between its outer surface and the wall of the channel 2.

Claims

1. A porous tubular support (1) for a tangential filtration membrane, in the form of a sintered monolithic ceramic porous body, manufactured by extrusion of a ceramic composition including a powdery solid inorganic phase and in which are arranged by extrusion using punches, a rectilinear channel (2a) centered on an axis of symmetry of the support and at least one circulation channel (2) for a fluid medium to be treated with a helical shape wound around the axis of symmetry, the channels having a limited wall roughness and lower than the granularity of the powdery solid inorganic phase of the ceramic composition.

2. The porous tubular support according to claim 1 according to which the sintered monolithic ceramic porous body supports an inner pressure of at least 10 bars without bursting.

3. A tangential filtration membrane according to which at least one separating layer coats the wall of the circulation channels (2, 2a) for the fluid medium to be treated of the porous tubular support (1) according to claim 1 or 2.

4. A device for the manufacture by extrusion of a porous tubular support (1) from a ceramic composition, the device including: - a fixed extrusion die (6) in which a punch holder (7) provided with at least one punch (8) is mounted; - a system (10) for driving in rotation the punch holder (7); - and a supply device (9) to force the ceramic composition to cross under pressure the punch holder (7) in order to pass through the extrusion die (6) at a linear speed of extrusion (VI), the device being characterized in that: - the punch holder (7) is provided with a rectilinear punch (8a) centered on an axis of symmetry (X) and with at least one helically-shaped punch (8) wound around an axis of symmetry (X) along a winding direction and a winding pitch (P); - the drive system (10) drives in rotation the punch holder (7) around said axis of symmetry (X) along a direction of rotation opposite to the direction of winding of the helically-shaped punch(es) (8) and at a speed of rotation (Vr) equal to the linear speed of extrusion (VI) of the ceramic composition, divided by the winding pitch (P) of the helically-shaped punches (8).

5. The device according to claim 4, according to which the punch holder (7) is provided with several helically-shaped punches (8) concentrically wound around a common axis of symmetry (X) along the same winding direction and the same winding pitch (P).

6. The device according to the preceding claim, according to which the punch holder (7) is provided with several helically-shaped punches (8) disposed in at least two concentric rings.

7. The device according to any of claims 4 to 6, according to which each helically-shaped punch (8) has a length taken along the axis of symmetry (X), equal to or greater than a quarter of the winding pitch (P).

8. The device according to any of claims 4 to 7, according to which the drive system (10) drives in rotation the punch holder (7) with a speed of rotation (Vr) equal to the linear speed of extrusion (VI) of the ceramic composition, divided by the winding pitch (P) of the punches (8), by taking into account a tolerance margin of plus or minus 15%.

9. The device according to any of claims 4 to 8, according to which the supply system (9) is a piston or worm-type system.

10. The device according to any of claims 4 to 9, according to which it includes a system (11) for heating the extrusion die to maintain the punch holder, the punch(es) and the ceramic composition at a temperature comprised between 50°C and 300°C.

11. The device according to any of claims 4 to 10, according to which the system (10) for driving in rotation the punch holder (7) is mounted downstream of the supply system (9).

12. The device according to any of claims 4 to 11, according to which the system (10) for driving in rotation the punch holder (7) is located on the side of the punch holder (7) so that the axis of symmetry (X) of the punch holder is parallel to the supply direction (D) of the supply system (9).

13. The device according to any of claims 4 to 11, according to which the system (10) for driving in rotation the punch holder (7) is located at the rear of the punch holder so that the axis of symmetry (X) of the punch holder makes an angle less than or equal to 90° relative to the supply direction (D) of the supply system (9) opening out upstream or downstream of the punch holder (7).

14. A method for manufacturing a porous tubular support (1) from a ceramic composition, including the following operations: - providing a fixed extrusion die (6) in which is mounted a punch holder (7) provided with a rectilinear punch (8a) centered on an axis of symmetry (X) and with at least one helically-shaped punch (8) wound around the axis of symmetry (X) along a winding direction and a winding pitch (P); - ensuring that the ceramic composition crosses the punch holder (7) in order to pass through the extrusion die (6) at a linear speed of extrusion (VI); - and ensuring that the punch holder (7) is driven in rotation along a direction of rotation opposite to the direction of winding of the helically-shaped punch (8) and with a speed of rotation (Vr) equal to the linear speed of extrusion (VI) of the ceramic composition, divided by the winding pitch (P) of the helically-shaped punches (8).

15. The method according to claim 14, according to which, for the speed of rotation (Vr) of the punch holder (7) to be equal to the linear speed of extrusion (VI) of the ceramic composition, divided by the winding pitch P, we act on the adjustment either of only the speed of rotation of the punch holder (7) or only the linear speed of extrusion (VI) or the speed of rotation of the punch holder and the linear speed of extrusion.

16. The method according to any of claims 14 or 15, according to which the fixed extrusion die (6) is supplied with a ceramic composition including a powdery solid inorganic phase in the form of particles with an average diameter comprised between 0.1 and 150 micrometers and a matrix.

17. The method according to any of claims 14 to 16, according to which the fixed extrusion die (6) is supplied with a ceramic composition including a first powdery solid inorganic phase in the form of particles with an average diameter comprised between 0.1 and 150 micrometers and a second phase in the form of a matrix comprising at least one hot-melt polymer.

18. The method according to any of claims 14 to 17, according to which at least one extrudate is recovered at the outlet of the fixed extrusion die (6) with a determined length to form a porous monolithic tubular support and in that this extrudate is subjected to a sintering post-treatment.