Device and method for extrusion manufacturing of porous supports having linear central channels and non-linear channels - Patents.com

Abstract

The present invention relates to a device for producing a porous tubular support from a ceramic composition by extrusion, comprising: a fixed extrusion die (6) fitted with a punch holder (7) provided with a centrally located straight punch (8a) and at least one helical punch (8) wound around an axis of symmetry (X) along a winding direction and winding pitch; a system (10) for rotationally driving the punch holder (7) about said axis of symmetry (X) along a direction of rotation opposite to the winding direction of the punch (8) and at a rotational speed coordinated with the linear extrusion speed of the ceramic composition.

Description

[Technical field]

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

[0002] The object of the present invention is more particularly directed to the technical field of extrusion of tubular rigid porous supports for tubular filtration membranes.

[0003] The object of the invention finds particularly advantageous applications in the broad sense in the field of filtration, in particular in the field of nanofiltration, ultrafiltration, microfiltration or reverse osmosis. [Background technology]

[0004] In the state of the art, it is known to use extrusion to form tubular porous supports in which a series of channels are arranged. Extrusion techniques have a much higher production rate than other manufacturing techniques, such as additive manufacturing techniques, such as those described in US Patent Application Publication No. 2019 / 321890 and WO 2020 / 109715. The extrusion linear speed, measured in minutes, is in practice generally more than one meter per minute, while the vertical printing speed of additive methods is generally up to about 10 hours per meter. It should be noted that the vertical printing speed of additive methods depends strongly on the number of channels. This speed decreases as the number of channels increases, so that a multi-channel support will be printed 2 to 10 times slower than a single-channel support according to the number of channels, but the extrusion linear speed remains independent of the number of channels.

[0005] Conventionally, the porous support, manufactured by extrusion of inorganic materials such as ceramics, can be associated with one or more separation layers of inorganic materials, which are deposited on the surface of each circulation channel and are connected to each other and to the support by sintering, and which allow the filtering power of the filtering element to be adjusted.

[0006] The porous supports of these tubular filtration elements have an elongated shape and a cross section that is mostly polygonal or circular. Numerous extruded supports have already been proposed that contain a plurality of channels that are parallel to each other and to the longitudinal axis of the porous support. For example, filtration elements that contain a series of non-circular channels are described in WO 93 / 07959 in the name of CERASIV, European Patent Application No. 0780148 in the name of CORNING, WO 00 / 29098 in the name of ORELIS, European Patent Nos. 0778073 and 0778074 in the name of the applicant, WO 01 / 62370 in the name of Technical Ceramic Company, and French Patent No. 2898513 in the name of ORELIS.

[0007] In operation, the channel communicates on one side with an inlet chamber for the fluid medium to be treated and on the other side with an outlet chamber. The surface of the channel is covered with at least one separation layer that allows to separate the molecules or particles contained in the fluid medium circulating inside the channel along a given direction, most often from one end of the channel called the inlet end to the other end called the outlet end. Such a filtration element achieves the separation of the molecular or particle species of the treated material by a sieving effect, so that all particles or molecules larger than the diameter of the pores in the area of ​​the filtration element in contact are stopped. During the separation, the movement of the fluid takes place through the support and possibly through the separation layer, if present, so that the fluid spreads in the porosity of the support and moves towards the outer surface of the porous support. The part of the treated fluid that has passed through the separation layer and the porous support is called the permeate or filtrate and is collected by a collection chamber surrounding the filtration element.

[0008] It is often desirable to have a large number of channels in the same support in order to increase the surface of the channels that allow for the filtration of fluids. The large number of channels increases the number of possible arrangements of the channels relative to each other. Among the purported advantages of these various configurations is the increase in the filter surface without compromising the mechanical properties or the inherent permeability of the porous support.

[0009] It should be noted that in the absence of channels in the central region of the support containing the axis of symmetry, the volume that would have been occupied by said channels is replaced by porosity. At the start of operation of such a membrane lacking a central channel, the surface of the channel closest to and facing this axis of symmetry produces a permeate that fills the porosity. The discharge of this permeate from the central region to the outer surface of the membrane must then be carried out along a path that is maximum for the membrane. This large distance therefore creates a high pressure difference between the outer surface and the central region around the axis of symmetry, the value of which is maximum around that region. During the operation of the membrane, this maximum value that opposes the pressure in the retentate increases until it is equal to it. The flow rate in this region is then zero, and under these conditions an accumulation of liquid occurs that is difficult or even impossible to replace by washing. This lack of circulation in the porosity of this central region of the support, and the resultant inaccessibility to washing reagents, means that if this accumulated liquid contains bacteria, they can multiply without being able to be eliminated, thus making membranes without a central channel difficult to use in the agri-food industry.

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

[0011] In the prior art, it has been proposed to create a turbulent flow regime inside the channels of tubular filter elements in order to increase the filtrate stream with the aim of reducing clogging phenomena, by creating imprints or reliefs on the inner walls of the channels to create turbulence in the fluid medium close to the filter surface, thereby inhibiting material accumulation and clogging.

[0012] EP 0813445 describes a method for creating an imprint on the outside of a porous tube containing a single channel, said imprint, created while the tube is still deformable, resulting in a corresponding deformation of the inner wall of the channel.

[0013] French Patent 2736843 teaches a method for making a porous tube containing a single channel, the peripheral wall of the support being smooth, but the wall containing an imprint. For this purpose, the porous tube is shaped by a fixed extrusion die, on which is mounted a punch holder provided with a punch P, as shown in FIG. 1, which is driven in rotation by a motor around its axis along any direction of rotation. The ceramic composition is forced under pressure across the punch holder by a feed device located upstream, so as to pass through the extrusion die at the linear extrusion speed. The punch P is provided with one or more linear cutouts E, which allow the extrusion to obtain a porous support with a single channel, the inner wall of which is formed in relief with one or more spiral ribs.

[0014] The methods described in these two documents (EP 0813445 and FR 2736843) only allow obtaining wall relief in tubes further comprising a single channel and cannot be transferred to the production of porous supports comprising several inner channels. However, multichannel filtration elements are increasingly in demand, as they allow to increase the filter surface and therefore the performance.

[0015] It is noted that an extrusion method for the production of cooling channels using a helical punch is known from WO 93 / 20961 in the field of punching tools provided with cooling channels. Summary of the Invention [Problem to be solved by the invention]

[0016] The present invention therefore aims to overcome the drawbacks of the prior art by proposing to provide a new extruded filtration support with a multichannel structure of a geometry adapted to increase the filtrate stream, at a production rate much higher than the additive method. [Means for solving the problem]

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

[0018] One object of the present invention is to propose a porous tubular support for tangential filtration membranes in the form of a sintered monolithic ceramic porous body, manufactured by extrusion of a ceramic composition comprising a powdered solid inorganic phase, in which a straight channel centred on the axis of symmetry of the support and at least one circulation channel for the fluid medium to be treated, having a helical shape wound around the axis of symmetry, are arranged by extrusion using a punch, the channels having a limited wall roughness smaller than the grain size of the powdered solid inorganic phase of the ceramic composition.

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

[0020] Another object of the present invention is to provide a tangential filtration membrane, in which at least one separating layer covers the walls of the circulation channels for the fluid medium to be treated of the porous tubular support according to the invention.

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

[0022] The object of the invention is a device according to the invention for producing a porous tubular support from a ceramic composition by extrusion, comprising: a stationary extrusion die having a punch holder mounted thereon, the punch holder having at least one punch disposed therein; a system for rotary driving the punch holder; a feeding device for causing the ceramic composition to traverse the punch holder under pressure so as to pass through the extrusion die at the linear extrusion speed. a punch holder provided with a straight punch centered on an axis of symmetry and at least one helical punch wound around the axis of symmetry along a winding direction and a winding pitch; a drive system for rotationally driving the punch holder about said axis of symmetry along a rotational direction opposite to the winding direction of the punch at a rotational speed equal to a linear extrusion speed of the ceramic composition divided by the winding pitch of the helical shaped punch.

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

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

[0025] Advantageously, each helical shaped punch has a length along its axis of symmetry that is greater than or equal to one quarter of the winding pitch.

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

[0027] For example, the feed system may be a piston or worm type system.

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

[0029] According to one exemplary embodiment, a system for rotationally driving the punch holder is mounted downstream of the feed system.

[0030] According to another exemplary embodiment, the system for rotationally driving the punch holder is located to the side of the punch holder such that the axis of symmetry of the punch holder is parallel to the feed direction of the feed system.

[0031] According to another exemplary embodiment, the system for rotationally driving the punch holder is located behind the punch holder such that the axis of symmetry of the punch holder forms an angle of less than 90° with the feed direction of the feed system opening upstream or downstream of the punch holder.

[0032] Another object of the present invention is to provide a method for producing a porous tubular support from a ceramic composition, comprising the steps of: providing a fixed extrusion die fitted with a punch holder provided with a straight punch centred on an axis of symmetry and at least one helical punch wound around the axis of symmetry along a winding direction and a winding pitch; allowing the ceramic composition to traverse the punch holder through the extrusion die at an extrusion linear speed; making it possible to drive the punch holder in rotation along a direction of rotation opposite to the winding direction of the helical punch at a rotational speed equal to the linear extrusion speed of the ceramic composition divided by the winding pitch of the helical punch.

[0033] According to one advantageous feature of the method, the rotational speed of the punch holder alone, or the linear extrusion speed alone, or both the rotational speed of the punch holder and the linear extrusion speed are adjusted to equal the rotational speed of the punch holder divided by the winding pitch to the linear extrusion speed of the ceramic composition.

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

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

[0036] According to another feature of the method, at least one extrudate is collected at the outlet of the fixed extrusion die in a predetermined length to form a porous tubular support, and said extrudate is subjected to a post-sintering process. [Brief description of the drawings]

[0037] [Figure 1] FIG. 1 is a perspective view of a prior art punch and punch holder in the form of a pin having a linear notch around its periphery.

[0038] [Diagram 2] FIG. 2 is a perspective view of one exemplary embodiment of a punch holder according to the present invention, provided with a centrally located straight punch and a helical punch;

[0039] [Diagram 3] FIG. 2 shows a perspective view of another exemplary embodiment of a punch holder according to the invention, provided with a centrally placed straight punch and two punches having the same helical shape;

[0040] [Figure 4] FIG. 4 is a cross-sectional view of the three punches according to the present invention shown in FIG.

[0041] [Diagram 5] FIG. 13 is a perspective view of another exemplary embodiment of a punch holder according to the invention, provided with three punches having the same helical shape and a centrally located linear punch;

[0042] [Figure 6] 6 is a cross-sectional view of the four punches according to the present invention shown in FIG. 5.

[0043] [Figure 7] FIG. 1 is a perspective view of another exemplary embodiment of a punch holder according to the invention in which a centrally located straight punch is provided and three helical punches are distributed in a first ring concentric with a second ring containing eight helical punches, the three punches of the first ring having a shape different from the shape of the eight punches of the second ring, the eleven helical punches being wound around an axis of symmetry along the same winding direction with the same winding pitch.

[0044] [Figure 8] FIG. 8 is a cross-sectional view of the twelve punches according to the present invention shown in FIG.

[0045] [Figure 9] 1 is a schematic cross-sectional elevation view of a first exemplary embodiment of an extrusion manufacturing device according to the present invention;

[0046] [Figure 10] 2 is a schematic cross-sectional elevation view of a second exemplary embodiment of an extrusion manufacturing device according to the present invention; FIG.

[0047] [Figure 11A] 1 is a schematic cross-sectional elevation view of a third exemplary embodiment of an extrusion manufacturing device according to the present invention;

[0048] [Figure 11B] 11B is a schematic perspective view of a punch holder implemented in the exemplary embodiment of the manufacturing device shown in FIG. 11A.

[0049] [Figure 12] FIG. 6 is a perspective view of an example of a porous support obtained using an extrusion manufacturing device according to the invention implementing the punch holder shown in FIG. 5 . DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0050] The present invention relates to the production by extrusion of a porous support 1 according to the invention as well as a filtration membrane comprising the porous support 1, which comprises a linear channel 2a centered on the axis of symmetry of the porous support and at least one non-linear channel 2, on the walls of which one or more separation layers are deposited (Figure 12).

[0051] Within the framework of the present invention, the manufacture of a porous ceramic support 1 for fluid filtration membranes, more particularly for tangential filtration membranes, is of interest. Such a porous support is within the framework of the present invention of tubular geometry and comprises straight channels 2a and at least one circulation channel 2 or path for the fluid to be filtered. These circulation channels 2, 2a have an inlet and an outlet. The inlet of the circulation channel is arranged at one of the ends of the porous support, which end serves as an inlet area for the fluid medium to be treated, and the outlet of the circulation channel is arranged at the other end of the porous support, which serves as an outlet area for the retentate. The inlet and outlet areas are connected by a continuous peripheral area in which the permeate is collected.

[0052] If the porosity (average pore size) of the sintered support is adapted to the fluid medium to be treated (filtration threshold), said sintered support can be used directly for filtration and is called an autogenous or homogeneous membrane.

[0053] If the porosity of the sintered support is not adapted to the fluid medium to be treated (pores whose dimensions are too large compared to the required filtration threshold), the walls of the circulation channel 2 are covered successively with at least one separation layer that allows the fluid medium to be treated to be filtered. The separation layer is porous and has a smaller average pore size than the support. It can be deposited directly on the porous support (in the case of a single-layer separation layer) or on an intermediate layer of smaller average pore size that is deposited directly on the porous support (in the case of a multi-layer separation layer). A portion of the fluid medium to be filtered thus passes through the separation layer and the porous support, so that the treated portion of this fluid, called permeate, flows through the external peripheral surface of the porous support. The separation layer defines the surface of the filtration membrane that is intended to be in contact with the fluid to be treated and with which the fluid to be treated comes into contact as it circulates.

[0054] The porosity of the ceramic porous support 1 is open, i.e. it forms a network of interconnected pores in three dimensions, so that the fluid filtered by the separating layer passes through the porous support and is collected at the periphery, thus the permeate is collected on the peripheral surface of the porous support.

[0055] The porous support 1 has an average pore size in the range of 0.5 μm to 50 μm. The porosity of the porous support 1 is 10% to 60%, and preferably 20% to 50%.

[0056] "Average pore size" means the d50 value of the volume distribution, where 50% of the total pore volume corresponds to the volume of pores with a pore size less than this d50. The volume distribution is a curve (analytical function) that represents the frequency of the pore volume as a function of the pore size. The d50 corresponds to the median value that bisects the area under the frequency curve obtained by mercury porosimetry. In particular, the technique described in ISO standard 15901-1:2005 for the measurement technique by mercury porosimetry can be used.

[0057] 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 defines the flow rate and retention of said porous body. For a material to be used in filtration, the total interconnected open porosity must be at least 10% to ensure sufficient filtrate flow rate through the support and up to 60% to ensure suitable mechanical resistance of the porous support.

[0058] The porosity of a porous support can be measured by weighing the material before and after an extended residence time in liquid (water or other solvent) and determining the volume of said liquid contained in the porous body. If the densities of the material and the liquid used are known, the mass difference converted to volume directly represents the pore volume and thus the total open porosity of the porous support.

[0059] Other techniques can also be used to accurately measure the total open porosity of a porous support, including the following: Mercury intrusion porosimetry (ISO 15901-1 standard mentioned above): When mercury is injected under pressure, it fills the pores accessible at the pressure used, and the volume of injected mercury corresponds to the pore volume. Small angle scattering: this technique uses neutrons or X-rays, giving 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.

[0060] The porous tubular support 1 according to the invention is prepared by sintering an extrudate corresponding to an object extruded using, for example, a device 5 according to the invention allowing the production of the porous tubular support 1 from a ceramic composition. As can be seen in more detail in Figures 9, 10, 11A and 11B, the device 5 according to the invention comprises a fixed extrusion die 6 to which is attached a punch holder 7 provided with at least two punches 8, 8a. The fixed extrusion die 6 defines the external shape of the extrudate emerging from the extrusion die, which may be circular or non-circular (polygonal, etc.) within the framework of the invention. Together with the punches 8, 8a, the fixed extrusion die 6 defines the free space or orifice through which the ceramic composition passes.

[0061] The device 5 according to the invention also comprises a feed device 9 for driving the ceramic composition under pressure across the punch holder 7 through the extrusion die 6 at a linear extrusion velocity Vl. For example, the feed system 9 can be a piston, pump or worm type system, of any type known per se, capable of applying mechanical pressure to the ceramic composition. The linear extrusion velocity Vl is measured at the exit of the extrudate from the fixed extrusion die 6, discontinuously with simple timing or continuously, by a remote linear velocity sensor, for example a laser Doppler velocimeter.

[0062] The porous tubular support 1 is produced by extrusion of a ceramic composition passing under pressure through a fixed extrusion die 6 .

[0063] The ceramic composition consists of a powdered solid inorganic phase and a matrix.

[0064] The powdered solid inorganic phase of the ceramic composition comprises one or more solid inorganic materials, each in the form of particles having an average diameter of from 0.1 μm to 150 μm.

[0065] The concept of mean size is related to that of particle distribution. In fact, powder particles are rarely monosized or monodisperse, so powders are mostly characterized by their particle size distribution. The mean size therefore corresponds to the mean value of the particle size distribution. The distribution can be expressed in different ways, such as frequency or cumulative distribution. Some measurement techniques directly give the distribution based on numbers (microscopy) or mass (sieving). The mean size is a representative value (a measure of central tendency).

[0066] Thus, the most used measures of central tendency are the mode, the median and the mean. The mode is the most frequent diameter in a distribution and corresponds to the maximum of the frequency curve. The median represents the value above which the total frequency is the same as below it (in other words, the same total number or volume of particles are found around the median). The mean must be calculated on its own, to determine the point where the moments of the distribution are equal. In the case of a normal distribution, the mode, mean and median are coincident, in the case of a non-normal distribution they are different.

[0067] The average diameter of the particles constituting the inorganic powder can be measured particularly by the following method. For particles in the range of 3 mm to approximately 0.1 μm, laser light diffraction Sedimentation / Centrifugation For particles in the range of 0.5 μm to 2 nm, dynamic light scattering (DLS) Analysis of images obtained by microscopy Small angle X-ray diffraction

[0068] The particle size of the powdered solid inorganic phase means the size of the particles constituting the powdered solid inorganic phase. The particle size is characterized by the concept of average diameter explained above.

[0069] The ceramic composition in most cases comprises oxides and / or nitrides and / or carbides, either alone or as a mixture, as powdered ceramic materials. Examples of oxides that may be suitable within the framework of the present invention include, in particular, metal oxides, in particular titanium oxide, zirconium oxide, aluminum oxide, and magnesium oxide, with titanium oxide being preferred. Examples of carbides include, in particular, metal carbides, in particular silicon carbide. Examples of nitrides that can be used include, in particular, titanium nitride, aluminum nitride, and boron nitride. According to one preferred embodiment, the ceramic composition comprises, as powdered inorganic material, at least one metal oxide, preferably titanium oxide.

[0070] Within the framework of the present invention, the ceramic composition has a suitable rheology with respect to plasticity when extruded through a fixed extrusion die 6 .

[0071] According to a first embodiment, the matrix of the ceramic composition comprises one or more solvents. The solvents may be aqueous or organic. Examples include water, ethanol or acetone.

[0072] In addition, the matrix of the ceramic composition contains one or more organic additives. Advantageously, these organic additives are soluble in the solvent of the matrix. Organic additives suitable within the framework of the present invention can be selected from the following, by way of non-limiting example: Binders, for example the polymer cellulose ethers such as hydroxyethyl cellulose, the polysaccharide gum arabic, or polyethylene glycol (PEG). Lubricants and plasticizers, such as glycerol or stearic acid. · Thickening and gelling agents, such as xanthan gum, or agar, which is a polymer of galactose.

[0073] The mass content of the powdered inorganic material in the ceramic composition can be in the range of 50% to 90% by weight, preferably 80% to 85% by weight, relative to the total weight of the ceramic composition.

[0074] The mass content of the matrix in the ceramic composition can be in the range of 10% by weight to 50% by weight, preferably 15% by weight to 20% by weight, based on the total weight of the ceramic composition.

[0075] The ceramic composition is a paste, not a powder. The rheology of the ceramic composition can be adjusted by the particle size of the powdered solid inorganic phase and / or by the nature of the organic additives, if present, and / or by their respective proportions. Indeed, the rheology of the ceramic composition can be modified, for example, by using a matrix that contains one or more organic additives that are soluble in one or more solvents contained in the matrix.

[0076] According to a second embodiment, the ceramic composition comprises a matrix of one or more heat-fusible polymers, the matrix being organic and solid at room temperature.

[0077] By heat-fusible polymer is meant a polymer which softens under the influence of heat.

[0078] Examples of heat-fusible polymers that may be suitable within the framework of the present invention include the following optionally functionalized polymers or polymer families, used alone or as a mixture in the matrix: polylactic acid (PLA), polyvinyl alcohol (PVA), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyethylene, polyethylene terephthalate (PET), thermoplastic polyurethanes (TPU), polyolefins, thermoplastic elastomers (TPE), polyolefin-based elastomers (TPE-O), and polycarbonates.

[0079] The mass content of the powdered inorganic material in the ceramic composition can be in the range of 40% to 95% by weight, preferably 70% to 90% by weight, relative to the total weight of the ceramic composition.

[0080] Within the framework of the invention, the ceramic composition, preferably in the form of granules, is preheated upstream in a feed device 9, so that the heat-fusible polymer softens so that the ceramic composition can be pressed upstream of the fixed extrusion head 6. Typically, the fixed extrusion head 6 is heated so that the heat-fusible polymer softens, thereby allowing the extrusion of the ceramic composition. The temperature of the fixed extrusion head 6 can be adjusted depending on the heat-fusible polymer present in the ceramic composition.

[0081] In addition, within the framework of the present invention, the rheology of the ceramic composition can be adjusted by its temperature in the fixed extrusion head, and / or by the particle size of the powdered solid inorganic phase, and / or by the nature of the heat-fusible polymer, and / or by their proportions.

[0082] According to the invention, the punch holder 7 is provided with a straight punch 8a, which is centered on the axis of symmetry X of the punch holder 7. The straight punch 8a is of circular cross section. The punch holder 7 is also provided with at least one helical punch 8, which is wound around the axis of symmetry X along the winding direction F1. In the example shown in FIG. 2, the punch holder 7 is provided with a straight punch 8a centered and a single helical punch 8 according to the invention. Naturally, the punch holder 7 can be provided with a different number of helical punches 8 according to the invention in addition to the straight punch 8a centered, for example two punches (FIGS. 3 and 4), three punches (FIGS. 5 and 6), eleven punches (FIGS. 7 and 8) or seven punches (FIG. 11B).

[0083] In general, the helical punch 8 is a punch having a shape that follows the shape of a circular helix without a central core. The helical punch 8 comprises a body having a cross section S that extends only along a circular helix H wound around an axis of symmetry X. Since the helical punch 8 does not comprise a central core, this helical punch 8 forms exclusively circular turns wound around the axis of symmetry X, outside and along the axis of symmetry X. This circular helix H corresponds to a curve inscribed in a column of revolution centered on an axis corresponding to the axis of symmetry X, the tangent of this curve making a certain angle with the axis of symmetry. Naturally, this column of revolution on which the circular helix H rests corresponds to an empty space of the helical punch 8, since the helical punch 8 does not comprise a material centered on the axis of symmetry X, but only has a helical body. All points belonging to this cross section S are located at a certain 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 passing through this axis of symmetry.

[0084] It should be noted that the cross section S of the helical punches 8 can have various shapes adapted to the desired shape of the channels 2 of the porous support 1. For example, each helical punch 8 comprises a round cross section in the examples of Figs. 2, 3-4 and 5-6. According to the exemplary embodiment shown in Figs. 7 and 8, all eight helical punches 8 belonging to the outer ring have the same pseudo-rectangular cross section, and all three helical punches 8 belonging to the inner ring have the same pseudo-oval cross section. According to the exemplary embodiment shown in Figs. 11A and 11B, all seven helical punches 8 belonging to the outer ring have the same pseudo-triangular cross section. It should be noted, however, that punches of the same ring do not necessarily have the same cross section. It should be noted that the shape of the cross section of the punches 8, 8a corresponds to the shape of the channels 2 in the extrudate obtained using the device 5 according to the invention.

[0085] More precisely, it is the shape of the cross section of the punch end that determines the shape of the cross section of the channel formed in the extrudate. The punch end corresponds to a cross section perpendicular to the axis of symmetry X parallel to the advance direction of the extrudate. A final or intermediate widening of the punch can be advantageous with regard to the compaction of the ceramic composition. In the example shown in FIG. 2, the centrally located straight punch 8a and the helical punch 8 have widenings at their ends. Naturally, the cross sections of the centrally located straight punch 8a and the helical punch 8 may vary at any other location. In any case, the cross section of the punch end is what gives its shape to the cross section of the channel in every case.

[0086] Each helical punch 8 is wound around the axis of symmetry X along a single predefined winding direction, i.e. right-handed (clockwise) or left-handed (counterclockwise). In the example shown in FIG. 2, the helical punch 8 is wound around the axis of symmetry X along a right-handed winding direction F1. According to one feature of the invention, if the punch holder 7 is provided with several helical punches, all the helical punches 8 provided in the punch holder 7 are wound around the axis of symmetry X along the same winding direction F1. All the helical punches 8 provided in the punch holder 7 thus have a winding direction which is, for example, right-handed in the examples shown in FIGS. 3, 5, 7 and 11B.

[0087] Additionally, according to another feature of the invention, all of the helical punches 8 provided in the punch holder 7 are concentrically wound around the same axis of symmetry X. Thus, the punch holder 7 includes an axis of symmetry X that is common to all of the helical punches 8.

[0088] According to one preferred feature of the embodiment, the helical punches 8 provided on the punch holder 7 are distributed symmetrically around the axis of symmetry X, as is clearly evident, for example, in Figures 4, 6, 8 and 11B. According to one variant of the embodiment, the helical punches 8 are attached to the punch holder 7 so that they are arranged in at least two concentric rings, as is evident in the exemplary embodiment shown in Figures 7 and 8. The punch holder 7 is thus provided with a first set of eight helical punches 8 arranged in an outer ring, which is concentric with the inner ring in which the three helical punches 8 are distributed. Advantageously, the eight helical punches 8 are distributed at equal angles in the outer ring, and the three helical punches 8 are also distributed at equal angles on the inner ring.

[0089] Each helical punch 8 is wound around the axis of symmetry X according to a given winding pitch P. The pitch P of the helical punch 8 corresponds to the distance between two successive points on the helix which intersect a straight line parallel to the axis of symmetry X. According to one feature of the invention, if the punch holder 7 is provided with several helical punches, all the helical punches 8 provided in the punch holder 7 have the same winding pitch P.

[0090] Advantageously, the winding pitch P, expressed in ° / mm, is between 1 ° / mm and 90 ° / mm. Preferably, the winding pitch is between 3.6 ° / mm and 36 ° / mm, considering that a winding pitch of 3.6 ° / mm is equivalent to a winding pitch of 100 mm and a winding pitch of 36 ° / mm is equivalent to a winding pitch of 10 mm. As will be better understood in the remainder of this description, the winding pitch P of the helical punch corresponds to the pitch of the channels 2 obtained in the extrudate.

[0091] It should be noted that each punch 8 has a helical portion between its distal end Ed and its proximal end Ep. According to one feature of the invention, each punch 8 has a helical portion having a length along its axis of symmetry X that is equal to or greater than one-quarter of the winding pitch P.

[0092] Each punch 8, 8a is fixed to the punch holder 7 in any suitable manner. Thus, the punches 8, 8a extend protruding or overhanging along one side of the punch holder 7. Typically, the helical portion of the punch 8 between the distal end Ed and the proximal end Ep is extended by a connecting or fixing portion Er to the punch holder. For example, in the example shown in FIG. 3, the helical punch 8 is extended beyond its proximal end Ep by a helical connecting portion Er fixed on the punch holder 7, and the centrally placed straight punch 8a is fixed on the end of the punch holder 7. In the example shown in FIG. 2, the helical punch 8 is extended beyond its proximal end Ep by a straight connecting portion Er, which forms part of the centrally placed straight punch 8a and is fixed to the punch holder 7. In the examples shown in FIGS. 5 and 7, the helical punch 8 is fitted into the punch holder 7 by the connecting portion Er, and the end of the centrally placed straight punch 8a is also fitted into the punch holder 7. In the example shown in Figures 11A, 11B, the connecting portions Er of the helical punches 8 converge towards the central portion of the punch holder 7, more specifically around the end of the centrally located straight punch 8a. As can be seen from the figures, the connecting portions Er of each helical punch 8 together form a cone converging towards the punch holder 7 and can define a collection volume 7c around it. The function of the collection volume 7c is shown in the remaining part of this specification.

[0093] It should be noted that the punch holder 7 and the punches 8, 8a can be made in any suitable manner. For example, the punch holder 7 and the punches 8, 8a can be in the form of a one-piece molding obtained by electrolytic erosion or the like. According to another mode of manufacture, the punches 8, 8a can be manufactured separately and then fixed, for example by crimping on the punch holder 7 or in a housing arranged in the punch holder 7. Conventionally, the punch holder 7 is designed or arranged to have one or more passages 7a that allow the ceramic composition to pass through the punch holder. It should be noted that the punch holder 7 shown in Figures 11A, 11B is not perforated but solid, since the connecting portion Er of the punch and the punch define between them a space for the passage of the ceramic composition that reaches laterally to the periphery.

[0094] According to the invention, the device 5 comprises a system 10 for rotary driving the punch holder 7. The rotary drive system 10 can be made in any suitable way for enabling the punch holder to rotate around the axis of symmetry X according to a predefined rotational speed and along a predefined direction of rotation. For example, this rotary drive system 10 can comprise a motor, for example an electric motor, which is connected to the punch holder 7 directly or by a transmission and whose operation is steered by a control device. Advantageously, the rotational speed of the motor is adjustable so that the rotational speed of the punch holder 7 can be adjusted.

[0095] According to one feature of the invention, the drive system 10 rotationally drives the punch holder 7 around the axis of symmetry X along a rotation direction F2 opposite to the winding direction F1 of the punch 8. Thus, as appears in more detail in Figures 9, 10 and 11A, the helical-shaped punch 8 provided in the punch holder 7 has a right-handed winding direction F1, so that the punch holder 7 is rotationally driven in a left-handed direction F2. Of course, if the helical-shaped punch 8 provided in the punch holder 7 has a left-handed winding direction, it is envisaged that the drive system 10 rotationally drives the punch holder 7 along a right-handed rotation direction.

[0096] According to one feature of the invention, the drive system 10 rotationally drives the punch holder 7 at a rotational speed that is coordinated with the linear extrusion speed Vl of the ceramic composition. It should be understood that the rotational speed of the punch holder 7 is coordinated with the linear extrusion speed Vl of the ceramic composition such that the segment of the ceramic composition being extruded in the extrusion die 6 is not rotationally driven, i.e., this segment of the ceramic composition does not undergo twisting. This segment of the ceramic composition advances strictly linearly in the extrusion die 6 due to the fact that, as each helical punch 8 rotates, it gradually retreats ("twists out") from the ceramic material segment within which it is placed, while at the same time the segment advances linearly in the die.

[0097] According to one aspect of the invention, the drive system 10 rotationally drives the punch holder 7 at a rotational speed Vr equal to the linear extrusion speed Vl of the ceramic composition divided by the winding pitch P of the helical punch 8, where Vr is expressed, for example, in rpm, Vl is expressed, for example, in centimeters per minute, and P is expressed, for example, in centimeters, such that Vr=Vl / P. According to the invention, the winding pitch P of the helical punch is predefined, and it is believed that the equation Vr=Vl / P can be obtained by varying only the rotational speed of the punch holder 7, or only the linear extrusion speed, or both the rotational speed of the punch holder 7 and the linear extrusion speed.

[0098] It should be noted that the above equational relationship is considered to be satisfied taking into account a tolerance of plus or minus 15%. Thus, if the deviation between the quantity Vl / P (rpm) and the quantity Vr (rpm) varies by plus or minus 15%, the two quantities are equal. This tolerance allows a segment of the ceramic composition to be extruded by the helical punch 8 with an acceptable shape in the extrudate, even if this segment does not advance strictly linearly in the fixed extrusion die 6. Typically, with a pitch P equal to 10 cm and a linear extrusion speed Vl equal to 200 cm / min, the rotation speed Vr of the punch holder 7 must be 17-23 rpm.

[0099] FIG. 9 shows a first exemplary embodiment of the device 5 according to the invention, in which a system 10 for rotary driving the punch holder 7 is located at the rear of the punch holder 7. According to this illustrated exemplary embodiment, the rotary driving system 10 comprises, on the face opposite to the side on which the punch extends outward, a motor 10a which rotary drives a connecting shaft 10b fixed to the punch holder 7 while being centered on the axis of symmetry X. If the rotary driving system 10 is attached to the axis of the punch holder 7 at its rear, the axis of symmetry X of the punch holder 7 forms an angle of less than 90° with the feeding direction of the feeding system 9. The feeding system 9 is therefore located at the side of the punch holder 7, and the inlet 6a is arranged transversely to the fixed extrusion die 6 along a direction D which forms an angle of less than 90°, for example about 45°, with the axis of symmetry. By means of its inlet 6a, the feeding system 9 opens upstream of the punch holder 7 along the advancing direction of the ceramic composition. A passage 7a arranged in the punch holder 7 allows the ceramic composition to pass through the punch holder.

[0100] FIG. 10 shows a second exemplary embodiment of the device 5 according to the invention, in which the system 10 for rotary driving the punch holder 7 is located at the side of the punch holder 7. The system 10 for rotary driving the punch holder is therefore mounted downstream of the feed system 9 with respect to the movement direction of the ceramic composition. According to this example, the axis of symmetry X of the punch holder is parallel to the feed direction D of the feed system 9. The feed system 9 can therefore be located behind the punch holder 7, so that the ceramic composition can pass through it by means of a passage 7a provided in the punch holder 7. According to the illustrated exemplary embodiment, the rotary drive system 10 comprises a motor 10a which drives the punch holder 7 laterally in rotation by means of a transmission comprising a pinion 10b, which is rotationally fixed together with the motor output shaft and which meshes with a toothed ring 10c arranged on the periphery of the punch holder 7.

[0101] FIG. 11A shows a third exemplary embodiment of the device 5 according to the invention, in which the feed system 9 is located at the side of the punch holder 7 and the inlet 6a is arranged laterally in the fixed extrusion die 6 along a direction D that makes an angle of less than or equal to 90°, for example about 45°, with respect to the axis of symmetry. The inlet 6a of the feed system 9 is arranged to open laterally at the punches 8, 8a, more particularly at the level of the collection volume 7c surrounding the connecting part Er of the helical punch 8. It should be noted that the punches 8, 8a leave a space between them so that the ceramic composition can pass through to completely fill the extrusion die 6. The feed system 9 opens by its inlet 6a downstream of the punch holder 7 along the advancing direction of the ceramic composition. According to this illustrated exemplary embodiment, the rotary drive system 10 comprises a motor that rotary drives a connecting shaft 10b fixed to the punch holder 7, centered on the axis of symmetry X, on the face opposite to the side from which the punches project.

[0102] It is noted that the device 5 according to the invention can include a heating system 11 of the extrusion die 6 to maintain the punch holder 7, the punches 8, 8a and the ceramic composition at a predetermined temperature, which is between 50 ° C and 300 ° C. The heating system 11 can be made by any system adapted to maintain the extrusion die 6, the punch holder 7, the punches 8, 8a and the ceramic composition at a uniform temperature. This heating system 11 is implemented in particular when a ceramic composition is fed to the fixed extrusion die 6, comprising a first powdery solid inorganic phase in the form of particles having an average diameter between 0.1 and 150 micrometers and a second phase in the form of a matrix comprising at least one heat-fusible polymer.

[0103] The implementation of the device 5 according to the invention for producing a porous tubular support 2 by extrusion follows directly from the preceding description.

[0104] It is first necessary to provide an extrusion device 5 comprising a fixed extrusion die 6 on which is mounted a punch holder 7 provided with a straight punch 8a centred on the axis of symmetry X and at least one helical shaped punch 8 wound around the axis of symmetry X along a winding direction and winding pitch P. To produce a porous tubular support from a ceramic composition, the method comprises: allowing the ceramic composition to traverse the punch holder 7 through the extrusion die 6 at an extrusion linear speed; The punch holder 7 can be driven in a rotational manner along a direction of rotation opposite to the winding direction of the helical punch 8 at a rotational speed that is matched to the linear extrusion speed of the ceramic composition.

[0105] Advantageously, the punch holder 7 is rotationally driven at a rotational speed equal to the linear extrusion speed of the ceramic composition divided by the winding pitch P of the helical shaped punch 8 .

[0106] In order to make the rotational speed of the punch holder 7 equal to the linear extrusion speed of the ceramic composition divided by the winding pitch P, the method consists of adjusting only the rotational speed of the punch holder 7, or only the linear extrusion speed adjusted by the flow rate of the feeding device 9, or both the rotational speed of the punch holder 7 and the linear extrusion speed adjusted by the flow rate of the feeding device 9.

[0107] It should be remembered that the fixed extrusion die 6 can be fed with any type of ceramic composition using the feeding device 9. Preferably, the ceramic composition comprises a powdered solid inorganic phase in the form of particles having an average diameter between 0.1 and 150 micrometers and a matrix. According to another example, the fixed extrusion die 6 can be fed with a ceramic composition using the feeding device 9, comprising a first powdered solid inorganic phase in the form of particles having an average diameter between 0.1 and 150 micrometers and a second phase in the form of a matrix comprising at least one heat-fusible polymer. Naturally, the feeding device 9 is adapted so that the ceramic composition fed to the fixed extrusion die 6 can have all the properties, in particular pressure and malleability, for obtaining an effective extrusion.

[0108] At the outlet of the fixed extrusion die 6, the extrudates are collected and conventionally cut stepwise in predetermined lengths to form the porous tubular support 1. Each extrudate, corresponding to a length of the porous tubular support, is conventionally subjected to any type of post-sintering treatment known per se. After this post-sintering treatment of the extrudates, a porous tubular support 1 is obtained, comprising a straight channel 2a centered on the axis of symmetry of the support and at least one circulation channel 2 for the fluid medium to be treated, having a helical shape resulting from the imprint of the helical-shaped punch 8. It is conventionally known that the post-sintering treatment leads in particular to a dimensional shrinkage of the porous tubular support with respect to the corresponding extrudate. This sintering shrinkage can be between 5% and 25%, more particularly between 12% and 15%. Since the helical shape of the channels 2 obtained in the extrudate corresponds to the negative of the helical punch 8, this sintering shrinkage is taken into account when defining the characteristics of the helical punch in order to obtain channels 2 in the porous tubular support after sintering with the desired final dimensional characteristics. After sintering, the hydraulic diameter and pitch of the channels 2 are reduced. Therefore, in particular the winding pitch P of the helical punch 8, as well as the shape and dimensions of the cross section, take this sintering shrinkage into account. The same is true for the straight channels 2a centred on the axis of symmetry of the support.

[0109] Such a manufacturing method allows to obtain by extrusion a porous tubular support in the form of a monolithic ceramic porous body in which a centrally placed straight channel 2a corresponding to the imprint of the straight punch 8a and at least one circulation channel 2 for the fluid medium to be treated, the circulation channel having a helical shape corresponding to the imprint of the helical-shaped punch 8, are arranged. Pressing of the material to be extruded upstream of the die causes the powder grains of the powdered solid inorganic phase to be compressed in the die against the surface of the punches 8, 8a. Pressing of the material to be extruded not only serves to generate a linear velocity VL, but also, within the framework of the invention, to compress the material against the surface of the punches 8, 8a. As a result, a wall smoothing effect of the material is obtained at the level of the channel walls, which persists even after sintering. The channels 2, 2a therefore have a limited wall roughness that is smaller than the grain size of the powdered solid inorganic phase used in the extruded ceramic composition. The walls of the channels 2, 2a have a rough-feeling wall roughness that is smaller than the grain size of the powdered solid inorganic phase used in the extruded ceramic composition.

[0110] The measurement of the wall roughness of the walls of the channels 2, 2a can be carried out in any known suitable manner. For example, a profilometer can be used, with a probe that is moved on one or more generatrices of the channel. The arithmetic mean deviation, denoted Ra, which indicates the average roughness of the observed surface, directly characterizes the overall condition of the surface. The measurement results obtained according to the ISO 21920 standard are expressed in microns and compared with the grain size of the powdered solid inorganic phase of the ceramic composition, which is characterized by the average diameter of the particles of the powdered solid inorganic phase used in the extruded ceramic composition.

[0111] The walls of the circulation channels 2, 2a for the treated fluid medium of the porous tubular support can be coated with at least one separating layer so as to constitute a tangential filtration membrane. Typically, such a tubular support 1 after a conventional sintering operation has been carried out constitutes a rigid element capable of withstanding an internal pressure of at least 10 bar without bursting, preferably at least 30 bar without bursting, advantageously at least 50 bar without bursting. The burst pressure corresponds according to the invention to the pressure at which a support with pores previously blocked (for example with a heat-fusible material such as paraffin) bursts under the effect of an internal overpressure relative to the external pressure of the support. This overpressure is applied to the channels with water, the external pressure of the support being atmospheric pressure.

[0112] It can be seen from the above that the device 5 according to the invention allows easy production by extrusion of porous tubular supports 1 with helical shaped channels 2 capable of generating turbulence to increase the filtrate stream by reducing clogging phenomena. The production of tubular supports by extrusion allows much higher production rates to be obtained than additive methods. The linear extrusion speed, measured in minutes, is in fact generally more than one meter per minute, while the vertical printing speed of additive methods is generally up to about 10 hours per meter. It should be noted that the vertical printing speed of additive methods strongly depends on the number of channels. This speed decreases as the number of channels increases, so that multi-channel supports will be printed 2 to 10 times slower than single-channel supports according to said number of channels, while the linear extrusion speed remains independent of the number of channels.

[0113] Furthermore, during extrusion through the die, the ceramic composition is not rotationally driven, i.e., is not subjected to twisting, which would otherwise alter the mechanical properties of the extrudate.

[0114] The helical shape of the channels 2 obtained in the extrudate corresponds to the negative of the helical punch 8. The number, winding pitch P, arrangement, as well as the cross-sectional shape and dimensions of the helical punches 8 offer flexibility in the definition of the channels 2 arranged in the porous tubular support.

[0115] It should be noted that the winding pitch obtained in the extrudate is predefined by the helical punch 8, and that it is the rotational speed Vr of the punch holder 7 and the linear speed Vl of the ceramic composition in the die that must be jointly adapted to this predefined winding pitch. The helical punch 8 defines in the extrudate not only the cross section of the channels 2, which are negative, but also the pitch of the channels. The winding pitch P of the helical punch 8 therefore determines the effectiveness of the declogging.

[0116] Each channel 2 thus has a tortuous circulation volume between the ends of the porous tubular support, which of course corresponds to the area of ​​the porous support 1 that is bounded by the channel walls and does not contain porous material. It should be noted that the porous tubular support 1 has a variable thickness between its outer surface and the walls of the channel 2 along a cross section perpendicular to its longitudinal axis.

Claims

1. 1. A porous tubular support (1) for tangential filtration membranes in the form of a sintered monolithic ceramic porous body, manufactured by extrusion of a ceramic composition comprising a powdered solid inorganic phase, wherein a straight channel (2a) centered on the axis of symmetry of the support and at least one circulation channel (2) for the fluid medium to be treated, having a spiral shape wound around the axis of symmetry, are arranged by extrusion using a punch, said channel having a limited wall roughness smaller than the particle size of the powdered solid inorganic phase of the ceramic composition.

2. 10. The porous tubular support of claim 1, wherein the sintered monolithic ceramic porous body withstands an internal pressure of at least 10 bar without bursting.

3. A tangential filtration membrane, in which at least one separating layer covers the walls 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 producing a porous tubular support (1) from a ceramic composition by extrusion, comprising: a fixed extrusion die (6) fitted with a punch holder (7) provided with at least one punch (8); a system (10) for rotary driving said punch holder (7); a feeding device (9) for forcing the ceramic composition across the punch holder (7) under pressure so as to pass through the extrusion die (6) at an extrusion linear velocity (Vl); The punch holder (7) is provided with a linear punch (8a) centered on an axis of symmetry (X) and at least one helical punch (8) wound around the axis of symmetry (X) along a winding direction and a winding pitch (P), The drive system (10) drives the punch holder (7) in a rotational direction opposite to the winding direction of the helical punch (8) around the axis of symmetry (X) at a rotational speed (Vr) equal to the linear extrusion velocity (Vl) of the ceramic composition divided by the winding pitch (P) of the helical punch (8).

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

6. 6. A device according to claim 4 or 5, wherein the punch holder (7) is provided with a plurality of spiral-shaped punches (8) arranged in at least two concentric rings.

7. 6. A device according to claim 4 or 5, wherein each spiral-shaped punch (8) has a length along said axis of symmetry (X) that is equal to or greater than one-fourth of said winding pitch (P).

8. 6. The device according to claim 4 or 5, wherein the drive system (10) rotationally drives the punch holder (7) at a rotational speed (Vr) equal to the extrusion linear speed (Vl) of the ceramic composition divided by the winding pitch (P) of the punch (8), taking into account a tolerance of plus or minus 15%.

9. A device according to claim 4 or 5, wherein said supply system (9) is a piston or worm type system.

10. 6. The device of claim 4 or 5, including a system (11) for heating the punch holder, the punch, and the extrusion die to maintain the ceramic composition at a temperature of between 50°C and 300°C.

11. 6. A device according to claim 4 or 5, wherein the system (10) for rotary driving the punch holder (7) is mounted downstream of the feeding system (9).

12. 6. A device according to claim 4 or 5, wherein the system (10) for rotary driving the punch holder (7) is located to the side of the punch holder (7) so that the axis of symmetry (X) of the punch holder is parallel to the feed direction (D) of the feed system (9).

13. 6. A device according to claim 4 or 5, wherein the system (10) for rotary driving the punch holder (7) is located behind the punch holder (7) so that the axis of symmetry (X) of the punch holder forms an angle of less than or equal to 90° with the feeding direction (D) of the feeding system (9) opening upstream or downstream of the punch holder (7).

14. A method for producing a porous tubular support (1) from a ceramic composition, comprising the following steps: providing a fixed extrusion die (6) fitted with a punch holder (7) provided with a linear punch (8a) centred on an axis of symmetry (X) and at least one spiral-shaped punch (8) wound around said axis of symmetry (X) along a winding direction and winding pitch (P); allowing the ceramic composition to traverse the punch holder (7) so as to pass through the extrusion die (6) at an extrusion linear velocity (Vl); and rotating the punch holder (7) along a rotational direction opposite to the winding direction of the helical punch (8) at a rotational speed (Vr) equal to the linear extrusion velocity (Vl) of the ceramic composition divided by the winding pitch (P) of the helical punch (8).

15. 15. The method according to claim 14, wherein the rotational speed (Vr) of the punch holder (7) alone, or the extrusion linear speed (Vl) alone, or both the rotational speed of the punch holder and the extrusion linear speed are adjusted so that the rotational speed (Vr) of the punch holder (7) is equal to the extrusion linear speed (Vl) of the ceramic composition divided by the winding pitch P.

16. 16. The method according to claim 14 or 15, wherein the fixed extrusion die (6) is supplied with a ceramic composition comprising a powdered solid inorganic phase in the form of particles having an average diameter of 0.1 to 150 micrometers and a matrix.

17. 16. The method according to claim 14 or 15, wherein the fixed extrusion die (6) is supplied with a ceramic composition comprising a first powdery solid inorganic phase in the form of particles having an average diameter of 0.1 to 150 micrometers and a second phase in the form of a matrix comprising at least one heat-fusible polymer.

18. 16. The method according to claim 14 or 15, wherein at least one extrudate is collected at the outlet of said fixed extrusion die (6) in a predetermined length to form a porous monolithic tubular support, and said extrudate is subjected to a post-sintering treatment.

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