RU2800485C2 - Method for additive manufacturing of inorganic filtration substrate from heat-melting composition and obtained membrane - Google Patents

Abstract

FIELD: filtration of fluids.

SUBSTANCE: invention relates to a method for manufacturing a porous monolithic inorganic substrate, a method for producing a membrane for tangential filtration, a porous monolithic inorganic substrate, and a membrane for tangential filtration. A method for manufacturing at least one porous monolithic inorganic substrate having a porosity of 10% to 60% and an average pore diameter in the range from 0.5 mcm to 50 mcm includes preparing an inorganic composition containing a powdered solid inorganic phase, supplying the composition into the extrusion head of a 3D printing machine to build a raw 3D structure that can be manipulated. The resulting structure is then placed in a heat treatment oven for sintering at a temperature of 0.5 to 1 times the melting temperature of at least one material forming the inorganic phase.

EFFECT: mechanically strong porous substrate.

13 cl, 22 dwg

Description

The present invention relates to a process for the manufacture of a porous monolithic inorganic support which can be used in particular in a filtration membrane, in particular in a tangential filtration membrane. In particular, a porous substrate is obtained by a method carried out by adding a material.

The filtration membrane is a selective barrier and provides, under the action of the pumping force, the passage or retention of some components of the treated medium. The passage or retention of components may depend on their size relative to the pore size of the membrane that behaves like a filter. Depending on the pore size, these technologies are called microfiltration, ultrafiltration or nanofiltration.

The membrane is formed by a porous substrate on which one or more separating layers are applied. Classically, the substrate is first made by extrusion. The substrate is then sintered to obtain the required hardness while maintaining an open and interconnected porous texture. This method requires the production of straight channels, within which a separating layer or separating layers is then deposited and sintered. The membrane thus made goes through at least two sintering steps. Organic binders added during the preparation of the paste prior to its extrusion burn out completely during the sintering of the substrate.

In FR 3 006 606, the Applicant has described the manufacture of a filtration membrane whose porous support is obtained by additive technology with the gradual application of continuous layers of powder and subsequent local compaction in accordance with a predetermined pattern. This technology makes it possible to obtain filtration membranes of sufficient mechanical strength for use in tangential filtration. However, the disadvantage of this technology is the need to correct the fluidity of the powder to ensure its ideal flow during the application of the powder layer. In addition, this technology requires the removal of non-compacted powder, including for the purpose of its possible reuse, which can be a complex, time-consuming and expensive process, in particular, when this non-compacted powder is present in the non-straight channels of the porous substrate.

In the framework of the present invention, a new method for obtaining a porous substrate is proposed, which does not have the disadvantages of solutions from the prior art and which, in particular, is fast, easy to implement, makes it possible to obtain a mechanically strong porous substrate, the shape of which, and in particular the shape of non-rectilinear channels, can be easy to change. To do this, the method uses 3D printing technology to produce a manipulable raw three-dimensional structure, followed by a sintering step. The resulting porous substrate is homogeneous, mechanically strong and has a porosity corresponding to the filtration application, that is, a porosity of 10 to 60%, which is open and interconnected, with an average pore diameter of 0.5 µm to 50 µm.

The method according to the invention also makes it possible to obtain a monolithic porous substrate of a large size (i.e., a height of more than 1 m) and, in particular, a larger size than the substrate obtained by additive technology with the application of a continuous layer of powder and subsequent local compaction using the machines present in the present. time on the market, in particular the technology described in application FR 3 006 606.

In addition, the method according to the invention provides a substrate with an inclination without the need for support means.

In this context, the subject of the invention is a method for manufacturing at least one porous monolithic inorganic substrate having a porosity of 10% to 60% and an average pore diameter in the range of 0.5 µm to 50 µm using a 3D printing machine. , including at least one extrusion head mounted for movement in space relative to a fixed horizontal platform and above it, while the specified machine for 3D printing provides a strip of inorganic composition to build (based on a digital 3D model) a manipulable raw three-dimensional a structure intended to form a monolithic porous inorganic substrate or monolithic porous inorganic substrates, the method consisting of the following steps:

- preparing an inorganic composition containing a first powdered solid inorganic phase in the form of particles with an average diameter of 0.1 μm to 150 μm, and a second phase in the form of a matrix containing at least one thermofusible polymer,

- the inorganic composition is fed into the extrusion head of the 3D printing machine, while the specified extrusion head is at a temperature that ensures the extrusion of the inorganic composition, to form a strip,

- with the help of the specified strip on the specified horizontal platform, a rough three-dimensional structure that can be manipulated is built corresponding to the digital 3D model,

- this manipulable raw three-dimensional structure is placed in a heat treatment furnace for the purpose of performing a sintering operation at a temperature of from 0.5 to 1 times the melting temperature of at least one material forming this powdery solid inorganic phase.

Within the scope of the invention, the porous monolithic inorganic support can in particular be used as a support for a filtration membrane and in particular as a support for a tangential filtration membrane.

The claimed method has one and/or other of the following additional characteristics:

compaction of the manipulated crude three-dimensional structure is accelerated as said strip is extruded by means of a compaction device;

the sealing device is a controlled cooling device for curing at least one thermofusible polymer contained in the matrix;

- a manipulable crude three-dimensional structure is performed with an inclination without the use of support means;

- the powdery solid inorganic phase contains one or more oxides and/or carbides and/or nitrides and/or metals, preferably selected from titanium oxide, alumina, zirconium oxide, magnesium oxide, silicon carbide, titanium and stainless steel, and in particular , titanium oxide;

- the rheology of the inorganic composition is controlled by at least one of the following characteristics: the grain size of the powdered inorganic solid phase, the nature and/or proportion of the thermofusible polymer or thermofusible polymers, the temperature of the inorganic composition;

- a manipulable raw three-dimensional structure is made in the form of several separable from each other three-dimensional substructures;

- a manipulable raw three-dimensional structure is made in the form of several three-dimensional substructures connected and fastened to each other by means of at least one destructible bridge made with a strip of inorganic composition;

- several extrusion heads connected to each other are moved to simultaneously perform several independent three-dimensional structures, each of which is created by one extrusion head;

- the inorganic composition is used in the form of a thread or in the form of granules.

The object of the invention is also a porous monolithic inorganic substrate, which can be obtained using the claimed method.

The subject of the invention is also a method for producing a membrane for tangential filtration, which includes obtaining, in accordance with the invention, a porous monolithic inorganic substrate in which at least one channel is made for circulation of the treated fluid, followed by the step of creating one or more separating layers. Finally, the subject of the invention is a tangential filtration membrane, which can be obtained using such a method.

Other various characteristics will be more apparent from the following description with reference to the accompanying drawings, which, as non-limiting examples, show embodiments of the invention.

Fig. 1 is a diagram illustrating a 3D printing machine used in the context of the invention.

Fig. 2 is a sectional view illustrating the application of a strip of inorganic composition to a horizontal platform.

Fig. 3 is a perspective view illustrating the application of the first strip on a horizontal platform.

Fig. 4 is a sectional view illustrating the application of a strip of inorganic composition to a first layer of inorganic composition.

Fig. 5 is a sectional view along axis AA of FIG. 4.

Fig. 6 is a schematic perspective view of two layers, each of which consists of adjacent strips, applied at an angle of 90° from one layer to another, with the strips of the first layer being continuous and the stripes of the second layer being discontinuous to obtain a rectangular cut.

Fig. 7 is a sectional view of a crude structure not according to the invention, in which the phenomenon of settling is observed.

Fig. 8 is a sectional view of a crude structure according to the invention in which no settling phenomenon is observed.

Fig. 9 is a sectional view illustrating the application of a strip of inorganic composition with an extrusion die including a convection sealing device.

Fig. 10A and 10B are sectional views along axis A of FIG. 8 extrusion die with a conical annular slot (FIG. 10A) or with oblique holes (FIG. 10B).

Fig. 11 is a sectional view illustrating the deposition of a strip of inorganic composition by means of an extrusion head associated with a radiant densifier.

Fig. 12A is a sectional view illustrating an embodiment in which the three-dimensional structure is tilted without support means.

Fig. 12B is a sectional view illustrating an embodiment in which the three-dimensional structure is sloped without support means, and in which each layer is formed by a plurality of adjacent strips.

Fig. 13 is a sectional view illustrating a non-inventive embodiment in which the three-dimensional structure is tilted with support.

Fig. 14 is a perspective view of a manipulable raw structure in the course of its creation in accordance with the invention.

Fig. 15 is a perspective view of a porous monolithic inorganic support in accordance with the invention.

(Fig. 16A-16B). Fig. 16A is a sectional view of a porous monolithic inorganic substrate containing a rectilinear central channel and seven helical channels formed around said central channel. Fig. 16B is a perspective view of the channels of the substrate shown in FIG. 16A, namely the central channel and the seven helical peripheral channels shown in FIG. 16A.

Fig. 17 is a perspective view of two separate, manipulable raw 3D structures formed in parallel.

Fig. 18 is a perspective view of a manipulable raw 3D structure consisting of two separable 3D substructures connected by destructible bridges.

Fig. 19 is a perspective view of a manipulable raw 3D structure in the form of three separable 3D substructures connected by breakable bridges.

The invention relates to the production of a porous monolithic inorganic substrate 1, as well as to a filtration membrane containing the claimed porous monolithic inorganic substrate 1 with channels, on the walls of which one or more separating layers are applied.

It is within the scope of the invention to provide porous monolithic inorganic membrane supports for fluid filtration, and in particular for tangential filtration membranes. Such porous substrates typically have a tubular geometry and contain at least one channel or path for circulation of the fluid to be filtered. These circulation channels have an inlet and an outlet. As a rule, the inlet of the circulation channels is located at one end of the porous substrate, and this end acts as an inlet zone for the treated fluid, and the outlet is located at the other end of the porous substrate, which acts as the retentate outlet zone. The inlet zone and the outlet zone are connected by a continuous peripheral zone in which the permeate is collected.

In the filtration membrane, the walls of the circulation channel(s) are continuously covered with at least one separating layer, which provides filtration of the treated fluid. The separating layer(s) is porous and has an average pore diameter smaller than the average pore diameter of the substrate. The separating layer can be applied directly to the porous substrate (single layer separating layer case) or to an intermediate layer with a smaller average pore diameter which is applied directly to the porous substrate (multilayer separating layer case). Thus, a portion of the fluid being filtered passes through the separating layer(s) and the porous substrate, and this treated portion of the fluid, called permeate, flows down the outer peripheral surface of the porous substrate. The separating layers define the surface of the filtration membrane which is intended to be in contact with the fluid to be treated and in contact with which the fluid to be treated is circulated.

The porosity of the monolithic inorganic substrate 1 is open-type porosity, that is, it forms a network of pores interconnected in all three dimensions, which allows the fluid filtered by the separating layer(s) to pass through the porous substrate and collect at the periphery. Thus, the permeate is collected on the peripheral surface of the porous support.

The porous monolithic inorganic substrate 1 has an average pore diameter in the range of 0.5 µm to 50 µm. The porosity of the monolithic inorganic substrate 1 is 10 to 60%, preferably 20 to 50%.

The mean pore diameter is to be understood as the d50 value of the volumetric distribution, in which 50% of the total pore volume corresponds to the volume of pores with a diameter smaller than this d50 value. Volumetric distribution is a curve (analytical function) that characterizes the frequency of pore volumes depending on their diameter. The d50 value corresponds to the median dividing into two equal parts the area under the frequency curve obtained by mercury porosimetry. In particular, the method described in ISO 15901-1:2005 regarding the measurement method by means of mercury porosimetry can be applied.

The porosity of the substrate, which corresponds to the total volume of interconnected voids (pores) in the material under consideration, is a physical quantity ranging from 0 to 1 or from 0% to 100%. It determines the transmission and retention capacity characteristic of said porous body. In order for the material to be used in filtration, the total interconnected open porosity must be at least 10% for sufficient filtrate flow through the substrate and not more than 60% to guarantee the mechanical strength of the respective porous substrate.

The porosity of a porous body can be measured by determining the volume of liquid contained in said porous body by weighing said material before and after prolonged exposure to said liquid (water or other solvent). Knowing the respective volumetric masses of the material under consideration and the liquid used, the mass difference, converted to volume, is determined, which directly characterizes the pore volume and hence the total open porosity of the porous body.

Other methods allow accurate measurement of the total open porosity of a porous body, and among them are:

- porosimetry by mercury intrusion (the aforementioned standard ISO 15901-1): the mercury injected under pressure fills the pores accessible at the applied pressures and the volume of the injected mercury corresponds to the pore volume,

- low-angle scattering of radiations: this method, in which either neutron radiation or X-rays are used, makes it possible to obtain averaged physical quantities over the entire sample. The measurement consists in analyzing the angular distribution of the radiation scattered by the sample,

- analysis of two-dimensional images obtained with a microscope,

- analysis of three-dimensional images obtained by X-ray tomography.

A porous monolithic inorganic substrate 1 according to the invention is obtained by sintering a manipulable raw three-dimensional structure 2, which is created in accordance with a 3D digital model M by superimposing layers 3 _i of an inorganic composition 4 using a three-dimensional printing machine I, comprising, in particular, a horizontal (optionally removable) platform 5, above which at least one extrusion head 6 is placed (Fig. 1).

Under the "raw three-dimensional structure" 2 should be understood as a three-dimensional structure obtained by superimposing layers 3 _i of the inorganic composition 4, but not yet subjected to sintering. The shape and dimensions of this crude structure are determined layer by layer according to the 3D digital model M. This raw 3D structure 2 is called "manipulable" because it does not deform under its own weight and can even be tilted due to accelerated compaction, which makes it resistant over time, mechanical stiffness, as will be explained below. This crude three-dimensional structure 2 can thus be separated from the horizontal platform 5 in order to move it without deformation or destruction, in particular in order to then subject it to the heat treatment necessary to obtain a monolithic porous substrate in accordance with the invention.

Within the scope of the invention, the "layer" 3 _i is formed by a set of strips 7 _{i, j} , which may be continuous or discontinuous, may or may not be located next to each other and which are extruded with the same height z in accordance with a digital 3D model M determined in advance for a specified height z (where i is an integer from 1 to n, with n being an integer representing the total number of layers forming the manipulated raw 3D structure 2 according to the 3D digital model M). For clarity, most of the figures show formations consisting of only one band. However, within the scope of the invention, the formation 3 _i often consists of several continuous or discontinuous strips 7 _ij located next to each other.

Within the scope of the invention, "strip" 7 _i,j corresponds to a ribbon of inorganic composition 4 that takes shape as it exits the extrusion head 6 (where i is an integer from 1 to n, n is an integer representing the total number of layers forming a manipulable green 3D structure 2, and j is an integer corresponding to a given band within the formation to which it belongs, where j is a number from 1 to m, where m is the total number of bands in the formation in question).

A 3D digital model M is defined by a computer-aided design program for constructing a crude 3D structure 2. This 3D digital model M corresponds to a virtual structure divided into successive layers 3i by a slicer program that allows, if necessary, when the 3D structure is tilted, determine the need for support means and their position to provide support for the crude three-dimensional structure during construction in order to avoid its settling.

The extrusion head 6 of the 3D printing machine I is mounted on a movement mechanism (not shown in the figures), such as a robot, which moves it in at least three axes (x, y and z). Thus, the die head 6 can be moved horizontally (x and y axes) and vertically (z axis) by means of a movement mechanism controlled by any known type of computer R. This computer R sets the movements of the movement system and hence the extrusion head 6 along a path predetermined depending on the 3D digital model M, from which a raw three-dimensional structure 2 is created, allowing the production of a porous monolithic inorganic substrate 1 after a heat treatment operation.

The extrusion head 6 contains an inlet (not shown in the figures) for an inorganic composition 4. As shown in these figures, the extrusion head 6 also contains a calibrated flow port 8, such as a nozzle, which can move in accordance with the specified digital 3D model M. According to According to the claimed method, the inorganic composition 4, preferably in the form of a thread or granules, is fed into the extrusion head 6 of the machine through the feed inlet of the flow hole 8. Mechanical action can be applied to introduce the inorganic composition 4 into the die 6 through this inlet.

In the context of the invention, "pellet" is understood to mean a small solid element, the largest size of which can vary from 1 mm to 1 cm, depending on the method of production and on the dimensional parameters of the extrusion head. The granule consists of various materials that are part of the specified hot melt composition, and in proportions corresponding to this composition. Granules can be obtained after an appropriate pre-mixing of the various components, either by hot extrusion or by pressing, or by dehydration or, in general, evaporation of the liquid phase that was used for said pre-mixing. The shape of the granules may vary depending on the method of their preparation:

- small cylinders in case of hot extrusion,

- small tablets of spherical or other shape in case of compression,

- small shapeless blocks in case of evaporation of the liquid phase (grinding dry "sludge").

For the purposes of the invention, "mechanical action" is to be understood as the application of pressure by any known means, such as, for example, a piston, a pump or an extruder. This step can be carried out in the usual manner known to a person skilled in the art, and its detailed description is omitted.

The flow hole 8 is positioned opposite and near the horizontal platform 5. The flow hole 8 can move vertically (i.e. along the z-axis) and horizontally (i.e. along the x and y axes) with respect to the horizontal platform 5, which is stationary. The vertical and/or horizontal movement of the flow hole 8 relative to the fixed horizontal platform 5 makes it possible to construct, in accordance with the 3D digital model M, a manipulable raw three-dimensional structure 2 supported on the horizontal platform 5 by extruding a strip 7i,j of the inorganic composition 4 through the flow hole 8.

According to the embodiment shown in the figures, the extrusion head 6 is provided with a flow hole 8 of circular cross section. When the flow hole 8 has a circular cross section, its diameter D is preferably 0.1 mm to 10 mm, preferably 0.1 mm to 1 mm, and even more preferably 0.1 mm to 0.7 mm. However, the flow hole 8 does not necessarily have a circular cross section, and another shape can be provided for it.

Preferably, the inorganic composition 4 is of a ceramic and/or metallic nature. The inorganic composition 4 consists of a powdery solid inorganic phase and a solid matrix at ambient temperature. Thus, the inorganic composition 4 is not a powder, but preferably has the form of a thread or granules.

The powdery solid inorganic phase of the inorganic composition 4 contains one or more solid inorganic materials, each in the form of particles with an average diameter ranging from 0.1 µm to 150 µm.

The concept of average diameter is related to the concept of particle distribution. Indeed, powder particles rarely have a uniform or monodisperse size, and hence the powder is characterized by a particle size distribution. The average diameter corresponds to the average value of the particle size distribution. The distribution can be displayed in different ways, such as frequency distribution or cumulative distribution. Some measurement methods show directly distribution based on quantity (microscopy) or mass (sieving). The mean diameter is a measure of the central tendency.

Among the most used central trends are the mode, median and mean. The mode is the diameter value that occurs most frequently in the distribution: it corresponds to the maximum of the frequency curve. The median is the value where the cumulative frequencies of the values above and below are equal (in other words, the number or total volume of particles below the median and above the median are the same). As for the average, it is calculated as (and it defines) the point at which the distribution moments equalize. In a normal distribution, the mode, mean, and median are the same, while in a non-normal distribution, they are different.

The average particle diameter of the inorganic powder can, in particular, be measured using:

- laser light diffraction for particles from 3 mm to about 0.1 µm,

- sedimentation/centrifugation,

- dynamic light scattering (DLS) for particles from 0.5 µm to 2 nm,

- analysis of images obtained with a microscope,

- small-angle X-ray scattering.

Most often, as powder(s) inorganic(s) material(s) inorganic composition 4 contains, individually or in mixtures, oxide and/or nitride and/or carbide and/or metal. Examples of oxides that can be used within the scope of the invention are metal oxides, and in particular titanium oxide, zirconium oxide, alumina and magnesium oxide, titanium oxide being the most preferred. As examples of carbides, mention may be made of metal carbides and in particular silicon carbide. Examples of nitrides that can be used are titanium nitride, aluminum nitride and boron nitride. As metals that can be used for the invention, titanium and stainless steel can be mentioned. According to a preferred embodiment, the inorganic composition 4 contains at least one metal oxide as a powdered inorganic material, preferably titanium oxide.

The inorganic composition matrix 4 consists of one or more thermofusible polymers. The matrix has an organic nature.

By "hot melt polymer" is meant a polymer that softens when subjected to heat.

As examples of a thermofusible polymer suitable for use within the scope of the invention, the following polymers or families of polymers, optionally functionalized, may be mentioned, alone or in admixture with a matrix: polylactic acid (PLA), polyvinyl alcohol (PVA), acrylonitrile butadiene styrene (ABS), polypropylene (PP), polyethylene, polyethylene terephthalate (PET), thermoplastic polyurethane (TPU), polyolefins, thermoplastic polymers (TPE), polyolefin-based polymers (TPE-O) and polycarbonate.

The mass content of the powdered inorganic material(s) in the inorganic composition 4 may be from 40 to 95 wt.%, preferably from 70 to 90 wt.%, relative to the total mass of the inorganic composition 4.

Within the scope of the invention, the inorganic composition 4 has a rheology adapted in terms of fluidity for its extrusion through a calibrated flow port 8.

Within the scope of the invention, the inorganic composition 4, preferably in the form of strands or pellets, is heated in the extrusion head 6 in such a way as to soften the thermofusible polymer or thermofusible polymers. Typically, only the flow port 8 of the extrusion head 6 is heated to soften the hot melt polymer or hot melt polymers at the level of the flow port 8, allowing the inorganic composition 4 to be extruded. 4.

Within the scope of the invention it is possible to correct the rheology of the inorganic composition 4 using its die temperature and/or grain size of the powdered inorganic solid phase and/or the nature of the thermofusible polymer or thermofusible polymers and/or their respective proportions.

By "grain size of the powdered inorganic solid phase" is meant the dimensions of the particles forming the powdered inorganic solid phase. Graininess is characterized by the concept of average diameter, which was described above.

As shown in FIG. 2, a strip 7 _1.1 of the inorganic composition 4 is formed by passing the inorganic composition 4 through a calibrated flow hole 8, applying mechanical action to the inorganic composition 4 to provide the pressure required to extrude the inorganic composition 4.

At the outlet of the calibrated flow port 8, the temperature of the strip 7 _1.1 of the inorganic composition 4 is lowered (possibly to ambient temperature) and hence its stiffness is increased, which ensures the stability of the crude three-dimensional structure. However, given the geometry of said three-dimensional structure, subsidence phenomena may occur during its construction. In this case, the invention provides for accelerated curing of the strip and three-dimensional structure using a controlled cooling device, which will be discussed below.

As shown in FIG. 3, when the strip 7 _{i, j} of the inorganic composition 4 is extruded through the flow hole 8, it lies on the horizontal platform 5, forming the first layer 3 ₁ in accordance with the digital 3D model M, determined in advance by the computer design program, due to the horizontal movement of the flow hole 8 above a horizontal platform 5.

The flow hole 8 moves horizontally and therefore parallel to the horizontal platform 5 along a path predetermined depending on the 3D digital model M to form the first formation 3 ₁ . At this stage, only one layer was obtained on the horizontal platform 5. In the exemplary embodiment shown in FIG. 3, the first layer 3 ₁ has a circular shape containing four triangular holes 9 with rounded corners. This form is shown by way of example and does not limit the invention.

After the application of the first layer 3 _1, the flow hole 8 is moved so that the applied strip 7 _2.1 forms the second layer 3 ₂ in accordance with the 3D digital model M, as shown in FIG. 4 and 5. To do this, the flow hole 8 is moved vertically (ie along the z-axis) and horizontally (ie along the x and y axes) to the required position. The extrusion of the inorganic composition 4 through the flow port 8 may be continuous or intermittent. Thus, the second layer 3 ₂ is placed on the first layer 3 ₁ by overlaying the strip 7 _2,j on the previously applied layer 3 ₁ in accordance with the digital 3D model M.

In the example shown in FIG. 4 and 5, each seam 3 _i contains only one strip 7 _i,j of the inorganic composition 4, with the strips superimposed on each other from seam 3 _i to adjacent seam 3 _i+1 . However, preferably each layer 3 _i may consist of several bands 7 _i,j . In the exemplary embodiment shown in FIG. 6, layers 3 ₁ and 3 ₂ are formed, each, by five adjacent strips, respectively, 7 _1.1 , 7 _1.2 , 7 _1.3 , 7 _1.4 , 7 _1.5 , on the one hand, and 7 _2.1 , _72.2 , _72.3 , _72.4 , _72.5 on the other hand. Strips 7 _1.1 -7 _1.5 and 7 _2.1 -7 _2.5 are laid at an angle of 90° to each other from one layer to another. Stripes 7 _1.1 -7 _1.5 are located next to each other and are continuous. Stripes 7 _2.1 -7 _2.5 are discontinuous to create a rectangular recess in the example shown.

After applying the strip or strips 7 _2,j thus forming the second layer 3 ₂ , the described step of moving the extrusion die 6 vertically and horizontally is repeated as many times as necessary to form a manipulable raw three-dimensional structure 2 in accordance with the 3D digital model M determined by a computer-aided design program and a slicer program. The build-up of the manipulated raw three-dimensional structure 2 is carried out along the z-axis. In particular, a manipulable raw three-dimensional structure 2 is created on a horizontal platform 5 by superimposing layers 3 ₁ -3 _n formed by strips 7 _1.1 -7 _n,m in accordance with the digital 3D model M.

As shown in the figures, each layer 3 _i is characterized by a thickness e, and strips 7 _i,j - thickness e and width L. The thickness e of the strip 7 _i,j is the size of the specified strip 7 _i,j measured between the flow hole 8 of the extrusion head 6 and the surface of the previous layer 3 _i-1 or the surface of the horizontal platform 5 on which it is laid. Thus, the thickness of the reservoir 3 _i is identical to the thickness of the strip 7 _{i, j} , and each strip 7 _{i, j} has the same thickness e. The width L of the strip depends on the volumetric flow rate of the inorganic composition 4 extruded through the calibrated hole 8, on the speed of movement of the calibrated hole 8 and from the ratio e/D, where D is the diameter of the flow hole 8. In the exemplary embodiments shown in FIGS. 5 and 8, stripes 7 _i,j and 7 _i+1,j+1 have the same width L.

The Applicant has observed that the mechanical strength of the raw three-dimensional structure may in some cases be insufficient, leading to deformation of the raw three-dimensional structure as a result of its settling. This deformation may be associated with the subsidence of insufficiently compacted layers, deformed under the action of the weight of the layers deposited on top. This settling phenomenon is shown in Fig. 7. The Applicant has observed that this deformation can also be the result of strip sagging immediately after extrusion: strip sagging can occur immediately after it exits the extrusion die, which leads to a deformation of the strip section and, in particular, to a final strip height that is less than the height of the strip. provided by the 3D digital model M. In the case where the 3D structure is tilted, the deformation may also be the result of settling of the overhanging portions of the strip if the crude 3D structure is constructed without support means.

According to an embodiment, in order to avoid any settling, a densification acceleration is carried out before the sintering step in order to quickly increase the mechanical strength of the three-dimensional structure according to the 3D digital model M, as shown in FIG. 8. In this case, each layer 3 _i retains its original shape and its original dimensions over time, and in particular its original thickness e and width L.

This compaction acceleration can be performed as the manipulable crude three-dimensional structure 2 is constructed by the compaction device 10, which moves in the same manner as the flow port 8. As shown schematically in FIG. 1, the sealing device 10 is located in the vicinity of the die 6, whether it is mounted on the die 6 or not. In particular, sealing device 10 may or may not be connected to die head 6, or it may be part of die head 6. If sealing device 10 is not mounted on die head 6, it follows its movements. Thus, the densification acceleration is carried out as the inorganic composition 4 is extruded. Preferably, the densification acceleration is carried out immediately after the extrusion of the strip 7 _i,j at the exit of the flow hole 8.

This densifier 10 makes it possible to accelerate the solidification of at least one thermofusible polymer contained in the inorganic composition 4. In other words, the solidification of the thermofusible polymer or thermofusible polymers by the densification device 10 is fast enough to impart mechanical strength to the manipulated raw three-dimensional structure 2, and sufficient to avoid any settling of it, even if it has slopes.

Controlled cooling is carried out using a sealing device 10, which may be convection or radiative.

In the case of a convection sealing device 10, one or more air jets are directed onto the strip 7 _i,j : in this case, cooling occurs only due to the renewal of the atmosphere around said strip 7 _i,j . As shown in FIG. 9, 10A and 10B, the sealing device 10 can be built into the extrusion head 6 around the flow hole 8. The convection sealing device 10 can be in the form of a conical annular slot 10 ₁ located around the flow hole 8 (FIG. 10A), or in the form several holes 10 ₂ located around the flow hole 8 (Fig. 10B).

In the case of a studying sealing device 10, the device may be located around the flow hole 8, connected or not connected to the extrusion head 6, as shown in FIG. eleven.

The compaction acceleration can be adjusted depending on the inorganic composition 4 used. Indeed, depending on the nature of the inorganic composition 4 and in particular its rheology, the compaction acceleration must be more or less significant in order to avoid any settling phenomena of the manipulated crude three-dimensional structure 2 The compaction acceleration can be adjusted by adapting the airflow, temperature and/or radiant energy generated by the compactor 10 .

According to the embodiment shown in FIG. 5 and 8, the layers 3 _i have the same shape and the same size and are aligned with each other (ie superimposed on each other along the z-axis). Thus, it is possible to produce a porous monolithic inorganic substrate 1 containing one or more straight channels 11. This embodiment does not limit the invention. For example, according to the embodiments shown in FIG. 12A and 12B, different layers 3 _i are stacked on top of each other along the z-axis so that the manipulated raw three-dimensional structure 2 has a slope or overhang or cantilever shape de due to the misalignment of the strip 7 _i,j with respect to the layer 3 _i-1. on which it is applied. The overhang angle α (corresponding to Arctg (e/de)) characterizes the slope amplitude: the smaller the angle α, the greater the slope amplitude.

The inventive method and possibly the acceleration of compaction of the strip 7 _i,j at the time of its application and optionally the rheology of the inorganic composition 4 imparts sufficient mechanical strength so that the manipulated raw three-dimensional structure 2 does not deform and is mechanically stable over time, even if it has slope, which eliminates the use of support 12, which is usually necessary to prevent the subsidence of the raw three-dimensional structure having a slope (see Fig. 13, where the temporary support 12 is printed at the same time, the shape of which corresponds to the shape of the created three-dimensional structure). For a given inorganic composition 4 and given printing parameters (flow hole diameter 8, strip extrusion speed 7 _i,j , extrusion head 6 travel speed), this compaction acceleration allows adaptation to the slope amplitude. Thus, raw three-dimensional structures 2 can be created without settling even if the structure is tilted and has no support means.

The presence of at least one tilt region in the manipulable raw three-dimensional structure 2 allows the manufacture of a porous monolithic inorganic substrate 1 containing at least one helical channel, as described in the application FR 3 060 410 filed in the name of the applicant. Such a porous support provides a tangential filtration membrane having a suitable geometry to reduce the risk of blockage of the separating layer and hence to increase the filtrate flow.

As shown in FIG. 14, the inventive method makes it possible to create a manipulable raw three-dimensional structure 2 by stacking layers 3 ₁ -3 _n in accordance with the digital 3D model M.

Finally, after obtaining a manipulable raw three-dimensional structure 2, it is subjected to heat treatment in order to carry out the sintering operation. To do this, the manipulated raw three-dimensional structure 2 is placed in an oven at a temperature of 0.5 to 1 times the melting point of at least one of the powdery solid inorganic materials present in the inorganic composition 4, and for a sufficiently long time to ensure that all of this manipulable raw 3D structure is sintered 2.

During the sintering step, the dimensions of the porous substrate 1 may change compared to the dimensions of the manipulated raw three-dimensional structure 2. Such a change depends on the nature of the inorganic composition 4 and on the sintering conditions. The computer-aided design program used within the scope of the invention allows for this change, and the 3D digital model M is determined taking this phenomenon into account.

The claimed method makes it possible to obtain a monolithic inorganic substrate 1 with an interconnected porous texture adapted for use in filtration and, in particular, in tangential filtration. In addition, the thus obtained porous monolithic inorganic substrate 1 has a mechanical strength suitable for use in filtration and in particular in tangential filtration. In particular, the porous monolithic inorganic substrate 1 withstands an internal pressure of at least 30 bar without rupture, and preferably at least 50 bar without rupture. The burst pressure corresponds to the pressure at which the substrate collapses under the action of internal pressure created in the channels with water.

The generated three-dimensional structure may be of any shape, and in particular an elongated shape with a circular cross section and a cylindrical outer surface as shown in FIG. 15. However, this form is not mandatory and any other form may be provided depending on the desired application. Indeed, the claimed method makes it possible to produce porous monolithic inorganic substrates 1 of various shapes. In particular, when the porous monolithic inorganic substrate 1 is intended for use in a tangential filtration membrane, this substrate contains at least one channel 11 for circulation of the treated fluid, and preferably several channels 11. These channels 11 may be straight or non-straight, interconnected or not related. In the example shown in FIG. 15, the porous inorganic substrate 1 contains four channels 11 formed as a result of the superposition of holes 9 of layers 3 ₁ -3 _n superimposed on each other, while these channels 11 are straight and not connected to each other and have a triangular cross section with rounded corners. The geometry and number of channels 11 are determined by the selected 3D digital model M and are therefore not limited to the embodiment shown in FIG. For example, as shown in FIG. 16A and 16B, the substrate may comprise a rectilinear central channel 11 ₁ and helical channels 11 _a , 11 _b , 11 _c , 11 _d , 11 _e , 11 _f , 11 _g forming a spiral around the rectilinear central channel 11 ₁ .

In a first embodiment, the inventive method produces one manipulated raw three-dimensional structure 2 at a time, resulting in one porous monolithic substrate 1 after sintering.

According to the second embodiment shown in FIG. 17, the above-described claimed method allows the simultaneous production of two independent manipulated raw three-dimensional structures 2 ₁ and 2 ₂ , that is, structures that are not interconnected, intended for the sintering step to obtain two porous monolithic substrates 1 ₁ and 1 ₂ . To do this, the machine comprises two flow holes 8 ₁ and 8 ₂ : each independent manipulated raw three-dimensional structure 2 ₁ and 2 ₂ is obtained by superimposing layers formed, each, respectively, by a strip emerging from a separate flow hole 8 ₁ and 8 ₂ , respectively. In the example shown in FIG. 17, both manipulated raw three-dimensional structures 2 ₁ and 2 ₂ have identical shapes and sizes and are created by identical movements of the flow holes 8 ₁ and 8 ₂ , which are preferably rigidly connected to each other. However, the example shown is not limiting: it is possible to produce more than two manipulable raw three-dimensional structures at the same time, and in particular three or four, and these manipulable raw three-dimensional structures can have identical or different shapes and/or sizes.

According to a third embodiment, the method described above makes it possible to obtain a manipulable raw three-dimensional structure 2 in the form of several identical or different separable three-dimensional substructures. According to this embodiment, the three-dimensional substructures are connected to each other by at least one destructible bridge 13, made using a strip 7 _i,j of the inorganic composition 4, preferably by several bridges 13 with the same or different shapes and/or sizes, spaced from each other and preferably located in a row.

According to this embodiment, shown in FIG. 18, the inventive method produces a manipulable raw 3D structure 2 in the form of two 3D substructures ₂₃ and ₂₄ connected by several identical destructible bridges 13 over the entire height of the raw 3D substructures ₂₃ and ₂₄ . Both three-dimensional substructures 2 ₃ and 2 ₄ have identical shapes and sizes and contain four rectilinear channels 11 of triangular cross section with rounded corners.

As shown in FIG. 19, this third embodiment also allows the fabrication of a manipulable raw 3D structure in the form of three raw substructures ₂₅ , ₂₆ , ₂₇ connected in series by several destructible bridges distributed along the height of the 3D structure. The three raw substructures 2 ₅ , 2 ₆ , 2 ₇ shown are identical and contain, each, a central rectilinear channel 11 ₁ of circular cross section and seven helical channels 11 _a , 11 _b , 11 _c , 11 _d , 11 _e , 11 _f , 11 _g triangular section with rounded corners, forming a spiral around the central rectilinear channel 11 ₁ .

In an alternative not shown, the 3D substructures may be connected by a single destructible bridge 13, present or absent over the entire height of the manipulated raw 3D structure 2, and may contain channels of varying numbers and shapes. Similarly, in a variant not shown, the claimed method makes it possible to obtain more than three separable three-dimensional substructures. The three-dimensional substructures obtained according to this last embodiment may have different shapes and/or sizes.

Before the sintering step, the bridge or bridges 13 linking the three-dimensional substructures can be destroyed, allowing the creation of monolithic porous substrates after the sintering step.

The advantage of the claimed method is the obtaining of constant and uniform characteristics of the porous monolithic inorganic substrates 1 during a single production step and the availability of a wide variety of forms. The claimed method also makes it possible to obtain porous monolithic inorganic substrates 1 with slopes without the need for support means during their manufacture.

The object of the invention is also a porous monolithic inorganic substrate 1 obtained by the claimed method. Such a substrate has a uniform structure and can be used as a filtration membrane substrate.

Finally, objects of the invention are a method for producing a tangential filtration membrane, as well as a tangential filtration membrane obtained using such a method.

In the claimed tangential filtration membrane, the wall of the circulation channel or circulation channels 11, made in a porous monolithic inorganic substrate 1, is covered with at least one separating filtration layer, which is designed to contact with the treated fluid and to provide filtration of the treated fluid. The separating layer(s) are obtained after the formation of a porous monolithic inorganic substrate 1. The method for producing a membrane for tangential filtration in accordance with the invention includes the steps of obtaining a porous monolithic inorganic substrate 1 in accordance with the method described above, after which (that is, after the final sintering step for obtaining a porous monolithic inorganic substrate 1) follows the stage of creating one or more separating filtration layers. This method is described in the patent FR 2 723 541 in the name of the applicant.

The separating filter layer can be obtained using any technology known to the person skilled in the art. In particular, the separating layer can be applied to the walls of the channels 11 of the substrate 1 by applying a slurry containing at least one sinterable composition, which is intended to obtain a separating filtration layer after heat treatment. This composition has a composition traditionally used in the manufacture of inorganic filtration membranes. This composition contains at least one oxide, nitride, carbide or other ceramic material or one of mixtures thereof, with metal oxides, nitrides and carbides being preferred. The composition to be sintered is diluted as a suspension, for example in water. To eliminate the risk of the presence of aggregates and to optimize the dispersion of grains in the liquid, the resulting suspension is agitated to break up the aggregates and obtain a composition mainly consisting of elementary particles. The slurry rheology is then corrected with organic additives to meet the hydrodynamic requirements for penetration characteristics into the channels of the substrates. After application, the separating layer is dried, then sintered at a temperature which depends on its nature, on its average grain size and on the intended fracture threshold.

In the case of a multi-layer separating layer, this step of applying the separating filter layer is repeated.

The claimed membrane has good mechanical strength. In particular, the claimed membrane withstands an internal pressure of at least 30 bar without rupture, and preferably at least 50 bar. Typically, an internal pressure of 50 bar is used because it is necessary and sufficient to ensure the mechanical strength of the membranes during operation.

The invention is not limited to the examples described and shown, and without departing from its scope, various changes can be made to it.

Claims (17)

1. A method for manufacturing at least one porous monolithic inorganic substrate (1) having a porosity of 10% to 60% and an average pore diameter in the range of 0.5 µm to 50 µm using a 3D machine (I) - printing, containing at least one extrusion head (6), installed with the possibility of movement in space relative to a fixed horizontal platform (5) and above it, while the specified machine for 3D printing ensures the application of a strip (7 _{i, j} ) of an inorganic composition (4) to build, based on a digital 3D model (M), a manipulable raw three-dimensional structure (2) intended to form a monolithic porous inorganic substrate or monolithic porous inorganic substrates (1), while the method consists of the following steps: - an inorganic composition (4) is prepared, wherein said inorganic composition (4) contains a first powdery solid inorganic phase in the form of particles with an average diameter of 0.1 μm to 150 μm, and a second phase in the form of a matrix containing at least one thermofusible polymer, - the inorganic composition (4) is fed into the extrusion head (6) of the machine (I) for 3D printing, while the specified extrusion head (6) is at a temperature that ensures the extrusion of the inorganic composition (4), to form a strip (7 _i,j ), - using the specified strip (7 _{i, j} ) on the specified horizontal platform (5) build a manipulable raw three-dimensional structure (2), corresponding to a digital 3D model (M), - this manipulable raw three-dimensional structure (2) is placed in a heat treatment furnace in order to carry out the sintering operation at a temperature of 0.5 to 1 times the melting temperature of at least one material forming a powdery solid inorganic phase. 2. Method according to claim 1, in which compaction of the manipulated raw three-dimensional structure (2) is accelerated as said strip (7 _{i, j} ) is extruded by means of a compaction device (10). 3. The method of claim 2, wherein the sealing device (10) is a controlled cooling device for curing at least one thermofusible polymer contained in the matrix. 4. The method according to claim 2 or 3, wherein the manipulated raw three-dimensional structure (2) is tilted without the use of support means. 5. Process according to any one of the preceding claims, wherein the powdered solid inorganic phase contains one or more oxides and/or carbides and/or nitrides and/or metals, preferably selected from titanium oxide, alumina, zirconium oxide, magnesium oxide , silicon carbide, titanium and stainless steel, and in particular contains titanium oxide. 6. The method according to any one of the preceding claims, wherein the rheology of the inorganic composition (4) is controlled by at least one of the following characteristics: grain size of the powdered inorganic solid phase, nature and/or proportion of the thermofusible polymer or thermofusible polymers, temperature of the inorganic composition (4) . 7. The method according to any one of the preceding claims, wherein the manipulated raw 3D structure (2) is made up of several separable 3D substructures (2 ₃ , 2 ₄ ). 8. The method according to the previous paragraph, in which a manipulable raw three-dimensional structure (2) is made in the form of several three-dimensional substructures (2 ₃ , 2 ₄ ) connected and fastened to each other by means of at least one destructible bridge (13) made using the strip (7 _i,j ). 9. A method according to any one of the preceding claims, wherein the inorganic composition (4) is used in the form of a thread. 10. The method according to any one of paragraphs. 1-8, in which the inorganic composition (4) is used in the form of granules. 11. A method for producing a membrane for tangential filtration, including manufacturing, in accordance with any of the previous paragraphs, a porous monolithic inorganic substrate (1), in which at least one channel (11) is made for circulation of the treated fluid, followed by the step of performing at least at least one separating layer on the walls of the channel or channels (11). 12. Porous monolithic inorganic substrate (1), obtained according to any one of paragraphs. 1-10, which can withstand an internal pressure of at least 30 bar without rupture. 13. A tangential filtration membrane obtained according to claim 11, which can withstand an internal pressure of at least 30 bar without rupture.

Images