Manufacturing method of membrane envelope

Abstract

The invention relates to a method for manufacturing a filtration membrane envelope with a 3D spacer fabric sandwiched between two membrane layers, said two membrane layers being cast on said 3D spacer fabric, said method comprising a casting step, during which a polymer solution is applied to the outer surface of said 3D spacer fabric, said polymer being applied by an injection process by a casting module, excess coating material being removed by a casting head, before or during the casting process, the thickness and roughness variations of said fabric and / or the tapering of said fabric are measured, and the distance between said 3D spacer fabric and said casting head is adjusted based on said measurements.

Description

[Technical field]

[0001] The present invention relates to a method for producing filtration membrane envelopes for use in water treatment, and more particularly to water filtration and wastewater purification. [Background technology]

[0002] Polymer coatings on textile surfaces are used to produce filtration membranes. The coated membranes are formed by spreading a polymer solution (usually called "casting dope") into a thin film on a smooth substrate using a doctor knife, followed by deposition in an aqueous bath and drying at elevated temperature. If the dope casting is performed on a smooth surface, uniform spreading of the polymer solution is easily achieved. Uniform spreading of the coating is essential for uniform performance of the membrane along the entire surface of the membrane.

[0003] Methods for casting membranes or films are disclosed in Patent Documents 1-3.

[0004] Woven 3D textiles are used in industry as substrates for membrane casting. However, they lack surface uniformity and generally vary in thickness and roughness. The weaving process often results in a tapered textile.

[0005] Membranes with 3D spacer fabrics are known from US Pat. No. 5,399,433 and from US Pat. No. 5,423,663.

[0006] When such irregular surfaces are cast as 3D textiles, a thick coating layer is usually applied to compensate for the thickness and roughness variations and the tapering of the textile. Such an approach significantly increases the raw material usage. Furthermore, the coating deposits across the membrane are irregular because for thicker areas of the textile, the area embedded in the coating is small and the deposits at the top are small, while thinner areas of the textile may be fully embedded in the coating and the deposits at the top are thicker. Such irregularities may cause further problems for the membrane during use. Non-uniform surface porosity, backflow difficulties in some areas, and non-uniform filtration channel sizes are examples of such problems. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] US Patent Application Publication No. 2009 / 130517 [Patent Document 2] US Patent Application Publication No. 2020 / 360866 [Patent Document 3] European Patent Publication No. 1298740 [Patent Document 4] U.S. Patent No. 7,862,718 [Non-patent literature]

[0008] [Non-Patent Document 1] Doyen et al., 2009, Desalination, Volume 250, Issue 3 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to solve at least some of the problems and drawbacks mentioned above. It is an object of the present invention to provide a method for casting polymer coatings onto 3D textiles that takes into account variations in the textile surface and thickness so as to obtain a membrane with a uniform coating. [Means for solving the problem]

[0010] The present invention and its embodiments serve to provide a solution to one or more of the above mentioned disadvantages. To this end, the invention relates to a method for manufacturing a filtration membrane envelope according to claim 1. More particularly, the invention provides a method for casting a polymer solution on a 3D spacer fabric. During the casting stage, a polymer solution is applied to the outer surface of the 3D spacer fabric. The polymer is applied by an injection process by a casting module. Characterized in that the variations in thickness, roughness and / or taper of the textile are measured and the distance between the 3D textile and a casting head is adjusted based on the results of the measurements.

[0011] It was found that real-time measurement of the thickness variation of the 3D spacer fabric and adjusting the casting head accordingly resulted in a membrane with a uniform coating across the entire surface, providing a membrane with high uniformity in terms of pore size, surface porosity, filtration channel size, and backflow behavior.

[0012] Preferred embodiments of the method are set out in any of claims 2-13.

[0013] In a second aspect, the present invention relates to a filtration membrane envelope as claimed in claim 14. More particularly, the membrane envelope described herein has an overall flatness deviation of less than 10%.

[0014] A preferred embodiment of the filtration membrane envelope is given in claim 15.

[0015] In a third aspect, the present invention relates to a water filtration module as claimed in claim 16. More particularly, the water filtration module described herein comprises an array of planar membrane envelopes.

[0016] In a final aspect, the present invention relates to the use of a filtration module according to claim 17. More particularly, said filtration module is used for water filtration and / or wastewater purification. [Brief description of the drawings]

[0017] [Figure 1] 1 shows details of a membrane envelope according to an embodiment of the invention, consisting of a permeate channel interposed between two membrane layers. [Diagram 2] 1 shows a detailed representation of a coating apparatus according to one embodiment of the present invention. [Diagram 3] 1 shows a schematic diagram of a casting process for a 3D spacer fabric according to one embodiment of the present invention. [Figure 4] FIG. 2 is a scanning electron microscope (SEM) view of a cross section of a 3D spacer fabric used to manufacture a 3D membrane envelope according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] The present invention relates to a method for producing a filtration membrane envelope. Furthermore, the present invention relates to a filtration membrane envelope produced by said method, a filtration module comprising an array of planar membrane envelopes, and a method of using said filtration membrane envelope or filtration module.

[0019] Unless otherwise defined, all terms used in disclosing the present invention, including technical and scientific terms, have the meanings commonly understood by those of ordinary skill in the art to which the present invention belongs. By way of further guidance, definitions of terms are included to better understand the teachings of the present invention.

[0020] As used herein, the following terms have the following meanings:

[0021] The indefinite articles "a," "an," and "the," as used herein, refer to both singular and plural referents unless the context clearly dictates otherwise. By way of example, "a section" refers to one or more sections.

[0022] "About," as used herein, refers to a measurable value such as a parameter, amount, duration, etc., and is meant to encompass a variation of ±20% or less, preferably ±10% or less, more preferably ±5% or less, even more preferably ±% or less, even more preferably ±0.1% or less, so far as such variations are appropriate for implementation in the disclosed invention. However, it should be understood that the value to which the modifier "about" refers is itself specifically disclosed.

[0023] As used herein, "Comprise," "comprising," "comprises," "comprises" is synonymous with "include," "including," "includes," "contain," "containing," "contains," and is an inclusive or open-ended term that specifies the presence of what follows, for example, a component, but does not exclude or preclude the presence of additional, non-reproduced components, features, elements, materials, steps that are known in the art or disclosed therein.

[0024] Moreover, the terms first, second, third, etc. in this specification and claims are used to distinguish between similar elements and are not necessarily used to describe a sequential or chronological order unless specified. The terms so used are interchangeable under appropriate circumstances, and it is to be understood that the embodiments of the invention described herein are capable of operating in other arrangements than described or illustrated herein.

[0025] The recitation of numerical ranges by endpoints includes all numbers and fractions subsumed within that range, as well as the recited endpoints.

[0026] The descriptions "weight %, "weight percent", "% wt" or "wt%" herein and throughout the specification refer to the relative weight of each component based on the total weight of the formulation, unless otherwise defined.

[0027] The term "one or more" or "at least one", e.g., at least one member of a group of one or more members, will itself be apparent from further illustration, but the term specifically encompasses reference to any one of said members, or any two or more of said members, e.g., >=3, >=4, >=5, >=6 or >=7 of any of said members, etc., up to and including all of said members.

[0028] Unless otherwise defined, all terms used in disclosing the present invention, including technical and scientific terms, have the meaning commonly understood by those skilled in the art to which the present invention belongs. For further guidance, definitions of terms used in the description are included to better understand the teachings of the present invention. Terms or definitions used in this specification are provided solely to aid in the understanding of the present invention.

[0029] Throughout this specification, the phrase "one embodiment" or "an embodiment" means that at least one embodiment of the invention includes the particular feature, structure, or characteristic described in connection with that embodiment. Thus, the appearances of the phrase "in one embodiment" or "in an embodiment" in various places throughout this specification do not necessarily all refer to the same embodiment, but may refer to the same embodiment. Furthermore, particular features, structures, or characteristics can be combined in any suitable manner in one or more embodiments, as would be apparent to one of ordinary skill in the art from this disclosure. Furthermore, although some embodiments described herein include some embodiments that are included in other embodiments but do not include other features, combinations of features of different embodiments are meant to be within the scope of the invention and form different embodiments, as would be understood by one of ordinary skill in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

[0030] As used herein, "flatness" is defined as the minimum distance between two planes within which all points on a surface lie.

[0031] A surface whose all points lie along a single plane is called a perfectly flat surface.

[0032] As used herein, "roughness" refers to the irregularity of a surface texture as a result of any manufacturing process. The roughness of a woven fabric is imparted by the interweaving of warp and weft threads, said warp threads being of variable height and distributed over different distances. Roughness is quantified by the deviations in the direction of the normal vector of a real surface from its ideal form. If these deviations are large, the surface is rough; if they are small, the surface is smooth.

[0033] As used herein, an "anchorage section" is defined as a portion of a nonwoven fabric that is embedded in a polymer that has been cast onto said nonwoven fabric.

[0034] "Filtration layer" as used herein is defined as the portion of the membrane layer cast into the nonwoven that is not present in the nonwoven but is instead present on top of the anchoring portion. Usually, the filtration layer is defined by a certain porosity in the top layer formed by the precipitated polymer, typically with a pore size of 10 nm to 1 micron. As a result, the filtration layer can allow for the filtration of water.

[0035] In a first aspect, the present invention relates to a method for manufacturing a filtration membrane envelope comprising a 3D spacer fabric interposed between two membrane layers cast on said 3D spacer fabric, the method comprising a casting step, during which a polymer solution is applied to the upper and lower sides of said 3D spacer fabric to form the upper and lower surfaces of the membrane. More specifically, said polymer is applied by an injection process by a casting module comprising a casting head. Before or during the casting step, the changes in thickness, roughness and / or taper of the fabric are measured and the distance between the 3D fabric and the casting head is adjusted based on said measurements.

[0036] 3D woven fabrics used to manufacture filtration membranes lack surface uniformity and are generally variable in thickness and roughness. The result of the weaving process is often a tapered textile. It was found that by measuring the thickness variations of the 3D spacer fabric in real time and adjusting the casting head accordingly, a membrane with a uniform cast layer across the entire surface could be obtained.

[0037] Preferably, the thickness of the 3D spacer nonwoven fabric is measured over its entire length before it is lowered in the casting module. The measurements are used to adjust the distance between the 3D spacer fabric and the casting head. By adjusting the distance, a uniform cast layer is achieved over the entire membrane, taking into account the variations in thickness, roughness, and / or taper of the nonwoven fabric. The step of applying the membrane layer preferably includes a casting step with a casting material and a step of solidifying the casting material to form a membrane layer in which the fabric is embedded. This process is known as "immersion precipitation", in which a polymer solution is cast onto a support layer and then immersed in a coagulation bath containing a non-solvent. Precipitation occurs due to solvent and non-solvent exchange.

[0038] In one embodiment, the membrane envelopes disclosed herein are manufactured by a process that employs a particular casting step, which is believed to contribute to the advantageous properties of the membrane envelope, such as flux and permeability, and durability, as discussed above.

[0039] In one embodiment, the casting polymer solution is deposited successively on both sides of a 3D spacer fabric, which ultimately form the lower and upper sides of the membrane.

[0040] In one embodiment, the casting step is carried out on a fabric that is vertically positioned and lowers into a precipitation bath during casting. The precipitation bath preferably contains water.

[0041] The casting process may be a one-step process or a multi-step process where a polymer is cast or precipitated onto a material before or after a second round of casting or coating.

[0042] Alternatively, after deposition of the cast polymer solution onto the 3D spacer fabric, the polymer solution is immediately flattened into a homogenous wet film, followed by a solvent evaporation step before immersion in a precipitation bath.

[0043] In one embodiment, the casting material used in the method of the present invention comprises a hydrophilic filler material selected from the group consisting of HPC, CMC, PVP, PVP, PVA, PVAc, PEO, TiO2, HfO2, Al2O3, ZrO2, Zr3(PO4)4, Y2O3, SiO2, perovskite oxide materials, and SiC, an organic binder material selected from the group consisting of PVC, C-PVC, PSf, PESU, PPS, PU, ​​PVDF, PI, PAN, and grafted variations thereof, and a solvent selected from the group consisting of NMP, DMF, DMSO, or DMAC, or mixtures thereof. Solvent-free processing can be considered as well. It will be clear to those skilled in the art that other manufacturing methods are known in the art and can be applied.

[0044] The cast membrane layer obtained by the method of the present invention is subjected to densification during the solidification process. Densification is the action of reducing the porosity in the sample, thereby making it denser. Due to the casting process used, the porosity of the membrane layer gradually increases in the direction of the polymer penetration of the polymer in the 3D nonwoven. As a result, the cast membrane layer consists of two parts: a filtration layer with a relatively fine or small pore size, and a fixed part with a relatively large pore size. The filtration layer preferably has pores with a size of 10 nm to 1 micron, while the fine pore size of the fixed part has macrovoids.

[0045] In one embodiment, the thickness of the resulting fabric having a cast membrane layer is measured again after said fabric is removed from the plating bath.

[0046] In a preferred embodiment, the measurement of the thickness and / or roughness of said 3D fabric is performed by a laser, preferably a confocal laser, one or more sensors, or mechanically. Laser confocal measurement of the thickness and / or roughness of a surface is a non-contact measurement method that does not damage the measured surface. This is very important, especially when measuring the thickness and / or roughness of a membrane after casting has been performed. The light emitted by the laser is reflected by the nonwoven fabric, and most of the reflected light passes through a pinhole when the target point is on the focal plane. In the range of the depth of field (DOF) of the confocal system, the reflected light intensity detected by the photodiode forms a depth response curve (DRC). The peak point of the DRC detected by the photodiode indicates the focal plane of the target point on the measurement surface. With the high resolution encoder of the confocal system the height of the target point on the surface can be measured. Thus, by recording the height a profile of the fabric can be obtained and the roughness derived.

[0047] Alternatively, the thickness and / or roughness of the nonwoven fabric is measured by mechanical means, which may include using a measuring roll to detect thickness or a stylus to detect roughness, although any mechanical means known to those skilled in the art are possible.

[0048] In one embodiment, the measurements are made at discrete locations on the fabric or over the entire length of the fabric. Variations in fabric thickness, roughness, and / or taper are caused by the weave of the fabric and occur randomly, so it may be interesting to sample different locations on the fabric and identify them. Surface roughness measurement methods can be any means known to those skilled in the art, including linear roughness measurement (profile method), which measures the roughness on a single line of the sample surface, and areal roughness measurement (area method), which measures the roughness over a captured area of ​​the surface. Linear roughness measurement (profile method) measures the degree of roughness of a surface along an arbitrary straight line. Long, continuous dimensions are measured, and a contact stylus is commonly used to perform roughness measurements. Surface roughness measurement (surface method) measures the surface roughness over an arbitrary rectangular area. Area roughness measurement uses a larger sampling area of ​​the surface and provides a more accurate depiction of the surface condition. Laser scanners are commonly used to perform areal roughness measurements.

[0049] In a further embodiment, the fabric measurements are communicated to a data processor, said data processor communicatively coupled to a storage unit, said storage unit storing processor instructions that, when executed, cause said processor to determine and control the distance of said casting head. In one embodiment, the data processor is a personal computer, a smartphone, a cloud server, or any other data processor known in the art. The use of a data processor and a control system allows real-time adjustment of the distance between the casting head and the 3D spacer fabric. With each new measurement, a corresponding adjustment of said distance is applied, resulting in a highly controlled membrane casting layer with maximum coverage of the fabric. The advantage of such real-time adjustment of the membrane casting layer is that it minimizes the use of raw materials and provides a membrane with an equal layer of casting over the entire surface of the membrane. Furthermore, anchorages, defined as parts of the embedded fabric, are present throughout the membrane. Said anchorages ensure high resistance of the membrane to backflow procedures.

[0050] In one embodiment, the adjustment of the casting head further depends on input variables, including the final casting thickness, casting volume, and / or casting speed of the casting head. The resulting thickness of the membrane layer depends on the initial thickness, roughness, and / or taper of the 3D spacer fabric, as well as the volume of polymer applied and the speed at which it is applied. The desired thickness of the membrane layer must also be considered and accurately determined when the distance between the casting head and the nonwoven fabric is adjusted.

[0051] In a specific implementation, 350 cm 3 The polymer is preferably at a rate of 360 cm per minute. 3 / min, 370 cm 3 / min, 380 cm 3 / min, 390 cm 3 / min, 400cm / min, 450cm 3 / min, or 500 cm / min. Alternatively, 200 cm 3 The polymer is preferably pumped at a rate of 250 cm per minute. 3 / min, 260 cm 3 / min, 270 cm 3 / min, 280 cm 3 / min, 290 cm 3 / min, 300 cm 3 / min, 310 cm 3 / min, 320 cm 3 / min, 330 cm 3 / min, or 340 cm 3 / min.

[0052] In a further embodiment, the input variables are communicated to the data processor, which determines and controls the distance of the casting head based on the input variables. As a result of the input variable communication to the data processor, the distance between the casting head and the nonwoven may be increased, decreased, or maintained.

[0053] In one embodiment, the casting head distance is adjusted in real time in response to the measurements.

[0054] In one embodiment, the distance between the 3D nonwoven and the casting head is 0.3 mm. Preferably, said distance between the 3D nonwoven and the casting head is 0.2 mm, more preferably 0.1 mm, even more preferably 0.05 mm on each side of the 3D spacer nonwoven.

[0055] The 3D spacer fabric is provided as a web material that moves continuously during casting. By moving the material, its thickness can be continuously measured and subsequently cast continuously. Preferably, the 3D spacer fabric during coating moves at a speed of 0.5-5 m / min, more preferably 1-5 m / min, more preferably 1.5-5 m / min, even more preferably 2-5 m / min, even more preferably 2.5-5 m / min, even more preferably 3-5 m / min, even more preferably 3.5-5 m / min, even more preferably 4-5 m / min, even more preferably 4.5-5 m / min. Alternatively, the 3D spacer fabric can be cast at 0.5-1.5 m / min, 0.5-1 m / min, 0.5-1.5 m / min, 0.5-2 m / min, 0.5-2.5 m / min, 0.5-3 m / min, 0.5-3.5 m / min, 0.5-4 m / min, 0.5-4.5 m / min, 0.5-5.5 m / min, 0.5-6.5 m / min, 0.5-7.5 m / min, 0.5-8.5 m / min, 0.5-9.5 m / min, 0.5-10.5 m / min, 0.5-11.5 m / min, 0.5-12.5 m / min, 0.5-13.5 m / min, 0.5-14.5 m / min, 0.5-15.5 m / min, 0.5-16.5 m / min, 0.5-17.5 m / min, 0.5-18.5 m / min, 0.5-19.5 m / min, 0.5-20.5 m / min, 0.5-21.5 m / min, 0.5-22.5 m / min, 0.5-23.5 m / min, 0.5-24.5 m / min, 0.5-25.5 m / min, 0.5-26.5 m / min, 0.5-27.5 m / min, 0.5-28.5 m / min, 0.5-29.5 m / min, 0.5-30.5 m / min, 0.5-31.5 m / min, 0.5-32.5 m / min, 0.5-33.5 m / min, 0.5-35.5 m / min, 0.5-36.5 m / min,

[0056] In one embodiment, the total thickness of the coated fabric is measured after the casting process, this measurement serves as a control measure and is preferably performed by a non-contact measurement method that does not damage the measured surface.

[0057] In one embodiment, the present invention relates to a method for manufacturing a filtration membrane envelope, wherein the upper and lower nonwoven surfaces are at least partially embedded in the polymer casting layer, thereby forming upper and lower anchoring sections, and wherein the measuring step ensures that the anchoring sections have a minimum thickness of 100 microns, more preferably 150 microns, 200 microns, 250 microns or 300 microns. In a preferred embodiment, the anchoring sections have a thickness of 100-500 microns, preferably 100-450 microns, more preferably 100-400 microns, more preferably 100-350 microns, more preferably 100-300 microns, more preferably 100-250 microns, more preferably 100-200 microns, more preferably 100-150 microns.

[0058] In another embodiment, the thickness of the fixing portion is 100 to 600 microns, 150 to 600 microns, 200 to 600 microns, 250 to 600 microns, 300 to 600 microns, 350 to 600 microns, 400 to 600 microns, 450 to 600 microns, 500 to 600 microns, preferably 550 to 600 microns.

[0059] As will be appreciated by those skilled in the art, the thickness of the fastening portion can be measured by many methods known in the art, such as scanning electron microscopy. In one embodiment, the thickness is an average value determined by measuring the thickness of the fastening portion at multiple points on the envelope. The absolute thickness at such a discrete point is defined by the distance between the extreme filament, loop, or thread of the fabric and the end point of the polymer embedded in the fabric, after which the fabric is free of polymer.

[0060] In one embodiment, the 3D spacer fabric has warp threads and weft threads that extend through the warp threads and are inserted above and below the warp threads. The warp threads are preferably aligned in a plane to define a fixing section and a membrane layer. The filtration layer is preferably represented by the area extending from the plane of the warp threads to the outside of the filtration membrane envelope, while the area including from the plane of the warp threads to the permeate channel was the fixing section. In another preferred embodiment, the weft threads that cross the warp threads belong to the fixing section.

[0061] It has been observed that the membrane envelope with the anchoring portion should have a minimum thickness in order to produce a membrane envelope that is robust enough to withstand the high pressures generated during operating activities and backflow, where no peeling or delamination is observed. Furthermore, the inventors have observed that the membrane envelope of the present invention does not swell or expand its length or width when operated under immersion conditions.

[0062] Preferably, a filtration layer extends from each fastening portion in a direction facing the outside of the envelope, and the minimum thickness of the extended filtration layer facing the outside of the envelope is 50 to 300 microns, preferably 50 to 200 microns, more preferably 50 to 100 microns. In one embodiment, the thickness of the filtration layer is the same on both sides of the 3D spacer fabric. In a preferred embodiment, the thickness of the filtration layer may vary. For example, one side may have a thicker filtration layer than the other side of the 3D spacer fabric.

[0063] In one embodiment, each membrane layer has a minimum total thickness of 150 microns, more preferably 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900 microns. In another or further embodiment, each membrane layer has a total thickness of 150-900 microns, preferably 150-800 microns, more preferably 150-700 microns, more preferably 150-600 microns, more preferably 150-550 microns, more preferably 150-500 microns, more preferably 150-450 microns, more preferably 150-400 microns, more preferably 100-350 microns, more preferably 150-300 microns, more preferably 150-250 microns. In another embodiment, the membrane layer has a total thickness of 150-900 microns, 200-900 microns, 250-900 microns, 300-900 microns, 350-900 microns, 400-900 microns, 450-900 microns, 500-900 microns, 550-900 microns, 600-900 microns, 650-900 microns, 700-900 microns, 750-900 microns, 800-900 microns, or 850-900 microns.

[0064] The above-defined thickness of the fixing part, the thickness of the filtration layer and the embedment of the monofilaments in the spacer fabric ensure excellent properties of the membrane envelope. Said membrane envelope is robust, highly resistant to compression and flatness, and does not expand its length or width when operated under submerged conditions. Moreover, they show less than 10% peeling or delamination of the spacer fabric and membrane layer when subjected to a pressure of 2 bar, preferably they show less than 5% peeling or delamination, preferably less than 1% peeling or delamination. The percentage of peeling or delamination is understood as the amount of the coating layer surface that peels off from the 3D spacer fabric. In one embodiment, the compression of the membrane envelope is less than 5% when subjected to a static pressure of 0.5 bar, preferably 1 bar, up to 2 bar.

[0065] In one embodiment, the membrane envelope exhibits a compression of less than 5%, preferably less than 4%, more preferably less than 3%, more preferably less than 2%, more preferably less than 1% when subjected to a static pressure of 0.5 bar, preferably between 0.5 bar and 2 bar.

[0066] The ratio of the thickness of the filtration layer to the thickness of the fixing part is preferably 1:10 to 3:1, more preferably 1:9 to 3:1, 1:8 to 3:1, 1:7 to 3:1, 1:6 to 3:1, 1:5 to 3:1, 1:4 to 3:1, 1:3 to 3:1, 1:2 to 3:1, or 1:1 to 3:1.

[0067] In another embodiment, the ratio of the thickness of the filtration layer to the thickness of the fixing part is 1:10 to 3:1, 1:10 to 2:1, or 1:10 to 1:1.

[0068] Preferably, the total thickness of the filtration membrane envelope obtained by the method of the present invention is 1 to 6 mm, preferably 1 to 5.5 mm or 1 to 5 mm, preferably 1 to 4.5 mm, preferably 1 to 4 mm, preferably 1 to 3.5 mm, preferably 1 to 3 mm, preferably 1 to 2.5 mm, preferably 1 to 2 mm.

[0069] In another embodiment, the total thickness of the filtration membrane envelope is 1.5-6 mm, 2-6 mm, 2.5-6 mm, 3-6 mm, 3.5-6 mm, 4-6 mm, 4.5-6 mm, 5-6 mm, 5.5-6 mm.

[0070] The 3D spacer fabric present in the filtration membrane envelope is formed by interwoven warp and weft yarns. The warp yarns are arranged in the same plane. During the weaving process, the longitudinal or lengthwise longitudinal yarns are held stationary under tension on a frame or loom while the transverse weft yarns are drawn through the longitudinal yarns and inserted above and below the longitudinal yarns. The waving process, when the weft yarns create height variations, gives the surface of the 3D nonwoven fabric roughness. In one embodiment, the peaks and valleys formed between the weft and warp yarns are covered by a casting layer.

[0071] In one embodiment, the 3D spacer fabric present in the filtration membrane envelope forms a permeate channel, which is a free space for liquid extraction between two parallel cast layers of the filtration membrane envelope.

[0072] In one embodiment, the permeate channel of said membrane envelope has a channel height of 1-4 mm, more preferably 1.5-3 mm, more preferably 1.8-2.8 mm. When the above conditions exist, the pressure drop in the permeate channel is negligible during operation of the module.

[0073] It has been observed that the method described in the previous embodiment allows a controlled casting process, provides optimal coverage of the 3D spacer fabric by said casting, and at the same time reduces the amount of raw materials used. The filtration membrane envelope obtained by this method has 100% adhesion of the 3D fabric with the polymer coating. These advantages result in high resistance to backwashing operations, uniformity of pore size and permeability of the membrane, and an optimal proportion of the cast layer and the internal permeate channels.

[0074] The inventors have surprisingly observed that a membrane envelope in which deviations of the spacer fabric are taken into account during the casting process has a controlled and uniform thickness of the layer of said membrane envelope. The speed of the casting process, the volume of polymer applied, the positioning of the casting head, the composition of the dope, or the level in the water bath can affect the properties of the cast membrane. The controlled and uniform thickness of the layer, which is directly influenced by the method of casting, imprints specific properties on said membrane envelope, such as a specific permeability and achievable filtration flux. These specific properties of the membrane envelope allow an ideal mode of operation of a water filtration module as disclosed herein.

[0075] In a second aspect, the present invention relates to a filtration membrane envelope comprising a 3D spacer nonwoven interposed between two membrane layers, said 3D spacer nonwoven being a woven textile comprising upper and lower nonwoven formed by weft and warp yarns, and a polymeric material being present on said upper and lower nonwoven, whereby said polymeric material forms anchorages at least partially embedded in said nonwoven, such that the flatness deviation of the entire membrane envelope is less than 10%, preferably less than 8%, more preferably less than 7%, more preferably less than 6%, more preferably less than 5%, preferably less than 4%, more preferably less than 3%, more preferably less than 2%, more preferably less than 1%.

[0076] In one embodiment, the permeate channel of the filtration membrane envelope comprises open spaces formed by said 3D spacer fabric, and the number of open spaces in said permeate channel is 80-99%, preferably 85-95%, more preferably 90%-99%. The open spaces in the permeate channel ensure optimal flow distribution through the membrane envelope.

[0077] In one embodiment, the 3D spacer fabric of the filtration membrane envelope is of the knitted, woven or non-woven type. In a preferred embodiment, the 3D spacer fabric has a woven structure. In one embodiment, the 3D spacer fabric preferably comprises a material selected from the group consisting of polyester, nylon, polyamide, polyphenylene sulfide, polyethylene and polypropylene.

[0078] Preferably, the membrane envelope is planar. The membrane envelope may further comprise a seal around the periphery of the planar membrane envelope arranged to prevent direct fluid transfer from or to the permeate channel without passing through the membrane layer, and may comprise an inlet / outlet port connection in fluid communication with the permeate channel, the inlet / outlet port connection being provided with at least one edge around the periphery. Each membrane envelope may have an end covered by a U-shaped cap, the cap being a metal cap, preferably a stainless steel cap.

[0079] The filtration membrane envelope described in the previous embodiment is obtained according to the method described in the present invention.

[0080] In a third aspect, the present invention relates to a water filtration module comprising an array of planar filtration membrane envelopes according to any of the above-mentioned embodiments.

[0081] In a fourth aspect, the present invention relates to the use of a membrane envelope or a filtration module according to the above description for the purification and / or filtration of fluids such as water and / or wastewater. The membrane envelope or the filtration module can be used for the filtration and / or purification of surface water or wastewater. However, it is clear that the invention is not limited to this application. The membrane envelope or the filtration module according to the present invention can be applied to the treatment of any kind of liquid source.

[0082] Preferably, the membrane envelope or water filtration module is used in operation with a backwash transmembrane pressure of at least 300 mbar. Due to the nature of the membrane envelope, the membrane or module is particularly useful to be cleaned by backwashing, backpulsing or backflow. In one embodiment, said filtration module can be backwashed with a pressure of at least 20 mbar, more preferably at least 30 mbar, more preferably at least 40 mbar, more preferably at least 50 mbar, more preferably at least 60 mbar, more preferably at least 70 mbar, more preferably at least 80 mbar, more preferably at least 90 mbar, more preferably at least 100 mbar, more preferably at least 200 mbar, more preferably at least 300 mbar, more preferably at least 400 mbar, at least 500 mbar, at least 1 bar, at least 2 bar. This high pressure backpulsing is possible without compromising the mechanical cleaning efficiency of the backwash. During this operation, the membrane, and more particularly the pores present, are cleaned from any debris filtered from the water. This may also include chemically enhanced backwash cleaning, where the pores are chemically cleaned by a volumetric flow of chemicals across the membrane envelope. For either operation, this again requires optimal and even flow.

[0083] The membrane envelope or water filtration module described herein can be used for microfiltration, ultrafiltration, MBR, pervaporation, membrane distillation, supported liquid membrane, and / or pertraction.

[0084] Advantageously, it has been determined that the membrane envelope of the present invention does not expand in length or width when immersed. The structure of the membrane envelope has a 3D spacer fabric and monofilament yarns embedded in the casting layer, ensuring that when said membrane envelope is immersed in liquid, it maintains its shape and dimensions without any expansion. This allows the membrane envelope to stay in place during water filtration operations without the use of additional means for membrane stabilization, such as comb-like structures. The present invention will now be described in more detail with reference to non-limiting examples. Text description of the illustration image024.gif.

[0085] Figure 1 shows a schematic diagram of a part of a membrane envelope 1 according to an embodiment of the present invention. A 3D spacer fabric 2 is cast with a polymer casting layer 3 covering the 3D spacer fabric on both sides. The permeate channels formed by the 3D spacer fabric have 80-99% of the open space formed by the nature of the 3D spacer fabric. Advantageously, the thickness of the spacer fabric part of the membrane envelope is 1.5-3 mm.

[0086] Figure 2 shows a 3D view of a 3D spacer fabric according to an embodiment of the present invention, formed by interwoven warp 4 and weft 5 yarns. The warp yarns are of variable height and distributed at different distances that give a roughness to the surface of the 3D nonwoven fabric. A polymer solution is injected on both sides 6 of the 2D fabric during a casting process.

[0087] FIG. 3 shows a schematic diagram of the casting process of a 3D spacer fabric 7 according to an embodiment of the present invention. The thickness of the 3D spacer fabric 10 is measured in real time. The distance between the 3D nonwoven fabric and the casting head 9 is adjusted based on the desired final total membrane layer thickness 8, the volume of casting material used and / or the casting speed of the casting head, and the thickness of the 3D spacer nonwoven fabric. Feature 9 shows the distance between the 3D nonwoven fabric and the casting head, while feature 10 is the thickness of the 3D spacer nonwoven fabric. The polymer solution is applied using an injection process through the casting head 11 on both sides of the 3D spacer fabric. The deposition of the polymer material 12 is performed vertically while the 3D spacer fabric descends 13. The cast 3D spacer fabric with polymer is immediately thereafter immersed in a water precipitation bath for quick solvent / non-solvent exchange and solidifying the polymer (not shown). The casting process can be a one-step process or a multi-step process, where the polymer is cast and precipitated on the material, followed by a second round of casting.

[0088] FIG. 4 is a scanning electron microscope (SEM) image of a cross section of a 3D spacer fabric used to manufacture a 3D membrane envelope according to the present invention.

[0089] [Example] The invention will now be further illustrated with reference to the following examples. The invention is in no way limited to the examples given or to the embodiments shown in the figures.

[0090] Example 1: Determination of layer thickness of filtration membrane envelope Scanning electron microscopy (SEM) was used to determine the thickness of the filtration membrane envelope layer. The membrane samples were cut into 6 x 20 mm pieces and coated with a conductive platinum (Pt) layer to prevent static buildup on the top and sides of the samples.

[0091] Electron micrographs were recorded on an FEI Quanta FEG microscope using secondary electrons (SE) and / or backscattered electrons (BSE). By using SE electrons, mainly the surface structure is displayed, whereas by using BSE electrons the recording mainly shows the difference in (electron) density of the different materials. This means that areas with higher density and / or higher concentration of heavier elements appear the brightest, and areas with lower density material appear darker.

[0092] The samples were placed with the side view facing upwards. Four pictures were taken at 13x magnification from four different samples.

[0093] In SEM micrographs, the warp thread cut-throughs could be seen in cross section as round objects protruding from the membrane structure and arranged in one plane by design (Figure 4). The diameter of the warp threads was 150 μm. The plane of the warp threads defined the anchoring section and the filtration layer. The filtration layer was the area extending from the plane of the warp threads to the outside of the filtration membrane envelope, while the area including from the plane of the warp threads to the permeate channel was the anchoring section.

[0094] The thickness of each layer was measured once for each micrograph based on the magnification used (Figure 4) and the average of four samples was determined. [Explanation of symbols]

[0095] 1. Membrane envelope 2 3D Spacer Fabric 3 Polymer Casting Layer 3D Non-Woven Fabric and Casting Head 4. Warp 5. Weft 6. Polymer solution injection direction 7 3D Spacer Fabric 8 Total membrane thickness 3D nonwoven fabric and casting head distance 9 3D Spacer Fabric Thickness 10 Casting Head 11 Deposition of polymeric materials 12 Downward direction of 3D spacer fabric during casting

Claims

1. 1. A method for manufacturing a filtration membrane envelope having a woven or knitted 3D spacer fabric sandwiched between two membrane layers, the two membrane layers being cast on the 3D spacer fabric, the method comprising a casting step, during which a polymer solution is applied to an outer surface of the 3D spacer fabric, the polymer being applied by an injection process by a casting module having a casting head, the 3D spacer fabric serving as a continuously moving woven material during the casting; a method characterized in that, before or during the casting process, the variations in thickness and roughness of the fabric and / or the tapering of the fabric are measured by a laser, by one or more sensors or mechanically, and the distance between the 3D spacer fabric and the casting head is adjusted in real time as a function of the results of the measurements. the results of the measurements are sent to a data processing device, the data processing device being communicatively coupled to a memory, the memory storing processor instructions that, when executed, cause the processor to determine the distance of the casting head and to control the distance of the casting head.

2. The method of claim 1 , wherein the laser is a confocal laser.

3. 3. The method of claim 2, wherein measurements are taken at a plurality of different locations on the 3D spacer fabric or along the entire length of the 3D spacer fabric.

4. 10. The method of claim 1, wherein the adjustment of the casting head is further dependent on input variables, the variables including a final casting thickness of the casting head, a casting volume, and / or a casting speed.

5. 5. The method of claim 4, wherein the input variables are sent to the data processing device, and the data processing device determines and controls the distance of the casting head based on the input variables.

6. 6. The method of claim 5, wherein the 3D spacer fabric moves at a speed of 0.5 to 5 m / min during casting.

7. 7. The method of claim 6, wherein after said casting, the total thickness of said coated 3D spacer fabric is measured.

8. 8. The method of claim 7, wherein each of the membrane layers has a minimum total thickness of 150 μm.

9. The method according to any one of claims 1 to 8, wherein the casting material is selected from the group consisting of HPC, CMC, PVP, PVPP, PVA, PVAc, PEO, and TiO ２ , HfO ２ , Al ２ O ３ , ZrO ２ , Zr ３ (P.O. ４ ) ４ , Y ２ O ３ , SiO2, perovskite oxide materials, and SiC; an organic binder material selected from the group consisting of PVC, C-PVC, PSf, PESU, PPS, PU, ​​PVDF, PI, PAN, and grafted variations thereof; and a solvent selected from the group consisting of NMP, DMF, DMSO, or DMAC, or mixtures thereof.

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