Tubular membrane comprising longitudinal ribs and device with such

Abstract

Tubular membrane comprising: - a tubular base providing support and having an inner and outer surface, the tubular base defining a lumen for the supply stream; - a membrane layer mounted on the inside of the tubular base, the inner surface of the tubular membrane comprising a number of inwardly projecting ribs extending substantially in the longitudinal direction of the tubular membrane.

Description

[0001] The present invention relates to a tubular membrane. Such tubular membranes are used in the filtration of fluids, e.g., in wastewater treatment (in bioreactors), the recovery of valuable materials, the treatment of concentrates by reverse osmosis, and the concentration of feed streams.

[0002] Membranes, and in particular tubular polymer membranes, are known in practice and comprise a base made of a porous support material. Such a tubular base serves as a support tube and can be manufactured in various ways. For example, EP 0 684 068 A2, GB 1325673 A, and US 4 214 612 disclose manufacturing methods for such a tubular base, wherein an inner wall of the tubular base is provided with a membrane layer.

[0003] To minimize the buildup of a fouling layer, turbulence enhancers are sometimes provided to mix the boundary layer. For example, WO 2015 / 108415 discloses the provision of at least one inwardly projecting spiral rib on the membrane inner wall, wherein the spiral rib is covered by or forms part of the membrane layer. Although this reduces fouling buildup, the occurrence of fouling along the membrane layer remains a problem. Periodically, chemical cleaning of the membrane is required. However, if the membranes are heavily fouled or clogged, chemical cleaning may not be sufficient. Therefore, mechanical cleaning may occasionally be required to remove this heavy fouling from the lumen side of the tubes and restore membrane performance.This type of cleaning can damage the turbulence enhancers, thereby reducing their effectiveness. For example, mechanical cleaning can damage the turbulence enhancers, such as a spiral rib. This leads to a reduction in performance over the lifetime of the tubular membrane.

[0004] The invention aims to eliminate or at least reduce the above-mentioned problems and to provide an effective tubular membrane which allows an increase in the membrane surface area and improves the effectiveness of the membrane.

[0005] This object is achieved with the tubular membrane according to the invention, wherein the tubular membrane comprises: - a tubular base providing support and having an inner and outer surface, the tubular base defining a lumen for the supply flow; - a membrane layer applied to the inner surface of the tubular base, the inner surface of the tubular membrane comprising a number of inwardly projecting ribs extending substantially in the longitudinal direction of the tubular membrane.

[0006] The tubular polymer membrane according to the invention comprises a tubular base that serves as a support layer and is shaped like a support tube. This tubular base can be manufactured by bending or winding ribbons of porous material and sealing or welding these ribbons to obtain a tubular base that forms a lumen for the feed stream. This tubular base provides the (mechanical) stability of the tubular membrane. In ultrafiltration membranes, for example, the tubular base consists of a double-layer nonwoven support.

[0007] The tubular base has an inner and an outer surface. The inner surface is coated with a membrane material to form a membrane layer on the inner surface of the tubular base. This membrane layer can be applied to the inner surface in various ways. For example, a liquid polymer solution (dope) is poured onto the inner surface of the tube and then doctored. During the pouring and doctoring processes, the polymer solution can partially penetrate the tubular base layer.

[0008] The tubular membrane according to the invention comprises a number of inwardly projecting ribs provided on the inner surface of the tubular membrane, wherein the inwardly projecting ribs extend in a substantially longitudinal direction of the tubular membrane. In this context, it should be noted that an extension in a substantially longitudinal direction of the tubular membrane is understood by those skilled in the art to mean an extension in a substantially straight line parallel to a longitudinal axis of the membrane. The tubular membrane according to the invention is also referred to as a longitudinally ribbed membrane.

[0009] In a preferred embodiment of the invention, the ribs are formed essentially from membrane material. Furthermore, the shaping of the longitudinal ribs preferably takes place in the doctor blade section after the membrane material has been applied to the inner surface of the tube base. This shaping of the ribs is a manufacturing process that can be produced relatively easily and inexpensively on an industrial scale, thus providing a cost-effective tubular membrane with a larger membrane surface area.

[0010] The longitudinal ribs increase the effective total surface area of ​​the membrane. This increases the total capacity of the tubular membrane and thus the total capacity of a tubular membrane module, resulting in higher module fluxes.

[0011] Another advantage and effect achieved by providing the tubular membrane with longitudinal ribs is that surface turbulence is increased. This increased surface turbulence can be caused by increased circulation due to the ribs and / or by velocity differences between the center of the tube and the area between adjacent ribs near the inner surface of the tube base. The increased turbulence results in higher flow because fouling is reduced.

[0012] Furthermore, cleaning, e.g. mechanical cleaning, can be carried out relatively easily with the tubular membrane with longitudinal ribs according to the invention. The risk of damage to the longitudinal ribs is reduced to a minimum, so that the performance of the membrane modules can be restored and further used after cleaning, which ensures a longer service life of the tubular membrane module. In other words, in the case of heavy fouling, membranes with longitudinal ribs are more resistant to mechanical cleaning and can be (mechanically) cleaned, so that the performance of the membranes can be restored. The improved resistance to mechanical cleaning (i.e. less damage during mechanical cleaning) is mainly due to the fact that the ribs extend in a substantially straight line along the length of the membrane. Due to the longitudinal (i.e.By means of straight ribs running parallel to the membrane's longitudinal axis, the mechanical cleaning agents exert a continuous force on the membrane surface, resulting in less stress on the membrane wall and thus less damage to the membrane wall.

[0013] In addition, the tubular membrane with longitudinal ribs has a lower pressure drop across the module, resulting in lower operating costs for a membrane module.

[0014] In a preferred embodiment of the invention, the inner surface of the tubular membrane comprises more than one inwardly projecting, longitudinally extending web.

[0015] By providing more than one inwardly projecting, longitudinally extending ridge, the membrane surface area is further increased and local turbulence is improved to reduce fouling, further enhancing the performance of the tubular membrane.

[0016] Preferably, the inner surface of the tubular membrane comprises more than 4 ribs, preferably more than 6 ribs, and most preferably a number of ribs in the range of 7-12. Experiments have shown that a number of ribs in the range of 4-12 further improves overall performance while maintaining a (substantially) constant pressure drop across the tubular membrane.

[0017] In a further preferred embodiment of the invention, the ribs comprise a cross-section perpendicular to the average flow direction of the feed through the lumen, wherein the cross-section of the ribs has a non-circular shape.

[0018] A non-circular shape of the ribs further increases the effective membrane area. Furthermore, the non-circular shape allows for additional support, ensuring the ribs are robust and firmly connected to the tubular base. This is especially true when the shape resembles an ellipse, or more precisely, a half-ellipse.

[0019] In a preferred embodiment of the invention, the rib or ribs have or have an average height in the range of 50 - 2000 µm, preferably in the range of 100 - 500 µm, particularly preferably in the range of 150 - 400 µm and most preferably in the range of 200 - 350 µm.

[0020] Preferably, the rib(s) has a width in the range of 0.1 to 10 mm, preferably in the range of 0.5 to 5 mm, more preferably in the range of 1 to 4 mm, and most preferably in the range of 1.5 to 3 mm. It is understood that the stated width is the average width and that variations may occur between ribs, with occasional widths outside the desired range.

[0021] These ranges for the average height and width of the rib(s) are preferably used here for tubular membranes with an (inner) diameter of approximately 8 mm. It is understood that other tubular membranes according to the present invention may also have other (inner) diameters, for example in the range of 5 - 14 mm with a circumference in the range of approximately 15.7 - 44.0 mm. Alternatively, the rib height is related to the membrane inner diameter, such that the rib height is in the range of 0.4 - 40% of the membrane inner diameter, preferably 1 - 10% of the membrane inner diameter, more preferably in the range of 1.5 - 8% of the membrane inner diameter, and most preferably in the range of 2 - 7% of the membrane inner diameter.Similarly, the rib width is related to the inner membrane circumference, so that the width is in the range of 0.2 - 63.7% of the inner membrane circumference, preferably in the range of 1.6 - 31.8% of the inner membrane circumference, more preferably in the range of 3.2 - 25.5% of the inner membrane circumference and most preferably in the range of 4.8 - 19.1% of the inner membrane circumference.

[0022] It is understood that the height and width refer to the average height and width when more than one rib is present in the tubular membrane. Tests have demonstrated effective ribs with these dimensions in a commercially available tubular membrane geometry.

[0023] The invention further relates to a membrane module and a (filter) device for filtering a fluid, wherein the membrane module and the device in one embodiment according to the present invention comprise a number of tubular membranes.

[0024] The membrane module and / or device offer the same or similar effects and benefits as those described with respect to the tubular membrane. These modules and / or devices can be used in various processes, such as wastewater treatment (in bioreactors), the recovery of valuable materials, the treatment of concentrates by reverse osmosis, and the concentration of feed streams.

[0025] The use of the tubular membranes in the filter device according to the invention, e.g., a water treatment device, improves the overall capacity and reduces fouling, so that the performance of the tubular membranes is improved compared to conventional membranes and / or remains substantially constant over their lifetime.

[0026] The provision of a tubular base can, for example, be produced by helically winding one or more ribbons of porous material, the overlapping edges being sealed together to create the tubular base structure. A membrane structuring tool is provided to enable the application of membrane layers to the inner surface of the tubular base. According to the invention, the membrane structuring tool is designed to provide a number of inwardly projecting ribs on the inner surface of the tubular component, extending substantially in the longitudinal direction of the tubular membrane. This preferably occurs in the casting section, where the polymer dope leaves the mandrel and enters above the doctor blade section. The membrane structuring tool preferably forms a defined layer of polymer dope on the inner lumen of the tubular base.This structuring tool can be provided in various embodiments and / or types. For example, the structuring tool can comprise a number of longitudinal grooves such that the membrane material is formed by these grooves and is provided on the inner surface as a longitudinal rib thereon. Alternatively, the structuring tool can comprise a series of longitudinal or helical grooves, and the structuring tool rotates such that the membrane material forms ribs on the inner surface of the tubular base that extend substantially longitudinally. To this end, for example, the structuring tool is rotated at the same rotational speed as the tubular base layer. This requires effective control of the tool rotation and preferably the winding speed during the formation of the tubular base.This can be achieved by a special speed control and / or by a connection between the structuring tool and the winding of the tubular base so that the ribs are arranged longitudinally to form the tubular membrane. This can be achieved, for example, by friction or clamping the structuring tool against the tubular base. Furthermore, a sufficiently thick polymer membrane layer should be applied between the ribs to maintain consistent membrane performance and to prevent pinholes or other defects in the thin part of the membrane layer.

[0027] Further advantages, features and details of the invention are explained using preferred embodiments, with reference to the accompanying drawings, in which: - Fig. 1A schematically shows a tubular membrane of the embodiment according to the invention; - Fig. Figure 1B shows a cross section through the tubular membrane of Fig. 1A; - Fig. Figure 1C shows schematically a device with a number of tubular membranes made of Fig. 1A; - Fig. Figure 2A shows a detailed cross-section of the rib of the tubular membrane made of Fig. 1A; - Fig. Figure 2B shows a detailed cross-section of the surface area between two ribs in the tubular element of Fig. 1A; and - Fig. 3A-B show test results with a tubular membrane according to the invention.

[0028] The tubular membrane 2 ( Fig. 1A) has a length L, an inner diameter D in and an outer diameter D outFurthermore, the tubular membrane 2 has an outer wall 4 and an inner wall 6. The outer wall 4 is delimited by an outer layer 8, which in the illustrated embodiment comprises a nonwoven material. The nonwoven material optionally comprises PET, PBT, PP, PE, PA, PAN, or combinations thereof. The cross-section of the tubular element is substantially circular, although other shapes such as oval or elliptical shapes are also conceivable. It is understood that other dimensions for the tubular membrane 2 and / or its parts can also be considered according to the present invention.

[0029] The inner wall 6 comprises a polymer membrane material 10. The polymer membrane material preferably comprises one or more of the following materials: polyethersulfone (PES), polysulfone (PSf), polyphenylsulfone (PPSU), polyvinylidene fluoride (PVDF), polyamide (PA), polyacrylonitrile (PAN), polyethylene (PE), polypropylene (PP), and combinations thereof. A portion of the tubular base is interspersed with a polymer membrane material that defines a transition region 12.

[0030] The inner wall 6 of the tubular membrane 2 comprises a series of longitudinal ribs 14. In the illustrated embodiment, the tubular membrane 2 comprises eight ribs 14 which extend substantially parallel to two central axes 16 of the tubular membrane 2.

[0031] Rib 14 ( Fig. 1B) has a height H and a width W. In the illustrated embodiment, the height H is in the range of 200-350 µm and the width W is in the range of 1.5-4 mm. Preferably, all ribs have a height H and a width W within this range.

[0032] The device 18 ( Fig. 1C) comprises a bundle 20 of tubular membranes 2 in a holder or housing 22. This allows the feed stream to enter the lumen side of the bundle 20. On the shell side, the permeate is collected and removed from the system through permeate ports. It is understood that those skilled in the art may consider various embodiments of the device 18 comprising a series of tubular membranes 2.

[0033] Rib 14 ( Fig. 2A) has an asymmetric pore structure 24 with small surface pores on the lumen side 26, which, viewed in cross-section, is arranged towards the center of the tubular membrane 2, and a large pore area 28 located near and / or connected to the tubular base 8. In the illustrated embodiment, the (average) total height H of the rib 14 is in the range of 250-350 µm. The membrane area between adjacent ribs 14 has a much lower height ( Fig. 2B). The thickness of this membrane material layer is approximately 40-60 µm.

[0034] The tubular membrane 2 is formed by a tubular base 8. In the illustrated embodiment, the tubular base 8 is formed by helically winding porous material, preferably a nonwoven fabric, and sealing or welding the overlap between adjacent strips. In a next step, the membrane material is cast and doctored onto the inner surface with a structuring tool provided with grooves, forming ribs 14.

[0035] Tests were conducted with tubular membrane 2. Unfiltered apple juice was used in the tests to determine the effects of fouling. Tubular membrane 2 is compared to conventional membranes without fins. The tests were conducted at a TMP of 1 bar, with tubular membrane 2 having eight fins. Flux is defined as the permeate volume collected through a specific membrane area at a specific time interval. Flux / TMP is expressed in L / m 2 / h / bar at a cross flow velocity of 1-4 m / s. Results with a first membrane are shown in Fig. 3A and results with a second membrane are shown in Fig.3B. The tubular membrane with longitudinal ribs shows results (▪) that are significantly higher than the reference membrane (▲). This results in a significant flux increase (◯, in %). This flux increase is achieved by increasing the effective membrane surface area and by the increased turbulence caused by the ribs acting as turbulence enhancers. These combined effects act synergistically and are surprisingly higher than one would expect from an increase in the membrane surface area. Therefore, the performance of the tubular membrane 2 according to the invention is even better than expected, thereby improving the possibilities for its industrial application. These possibilities are further enhanced by the improved cleaning possibilities. Example 1 - Experimental Results

[0036] The tubular membranes according to the invention were tested in an MBR plant for leachate treatment at a landfill. The purpose of the test was to compare the tubular membranes according to the invention with reference membranes, which are tubular membranes without ribs (i.e., with a flat membrane wall). For the purposes of the test, the membranes according to the invention were referred to as longitudinally ribbed membranes, while the reference membranes with a flat membrane wall were referred to as reference membranes.

[0037] The design inflow to the test facility is 1.8 MLD (minimal liquid outflow), but actual peak loads of 2.2 MLD (minimal liquid outflow) were treated. The process is a classic BIOMEMBRAT® with a pressurized bioreactor tank operating at a hydraulic retention time (HRT) of 15 hours, a fixed retention time (SRT) of 53 days, and an aeration rate of 4000 Nm 3 / h. After flow equalization, the leachate is treated in two parallel lines, each consisting of one denitrification and two nitrification tanks. The sludge from each line is pumped into two ultrafiltration (UF) units, comprising three streams of six modules arranged in series, with the permeate being discharged directly.

[0038] Modules containing the longitudinally ribbed membranes and the reference membranes were fabricated. To create similar test conditions, the longitudinally ribbed membranes and the reference membranes were placed in two different parallel circuits fed from the same bioreactor.

[0039] Each module was a type 83G module with a diameter of 20.32 cm (8") and a module length of 3 meters. Each membrane in the module had a diameter of 8 mm, resulting in a total membrane area of ​​27.2 m 2 in each module.

[0040] The following test parameters were used in the test: - Filtration type: continuous, supply and discharge, from bottom to top; - Cross flow velocity (CFV): 4 m / s; - Transmembrane pressure (TMP): 2.0 - 2.2 bar; - Temperature 25 - 30 °C; - Mixed liquor suspended solids (MLSS): 21 - 23 g / L; - Chemical oxygen demand (COD) in the inlet: 1500 - 2300 mg / L.

[0041] The test results show that the COD removal of the inventive tubular membranes reached 85%-87%, while the total suspended solids (TSS) were below 75 mg / L. Furthermore, due to the straight, longitudinally extending ribs, the inventive tubular membranes achieved a significantly higher flux rate than the reference membranes without ribs. This is also evident in Diagram 1 below.

[0042] The present invention is in no way limited to the preferred embodiments described above. The rights sought are described in the following claims, the scope of which many modifications may be considered. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] EP 0 684 068 A2

[0002] GB 1325673 A

[0002] US 4,214,612

[0002] WO 2015 / 108415

[0003]

Claims

[1] Tubular membrane comprising: - a tubular base providing support and having an inner and outer surface, the tubular base defining a lumen for the supply stream; - a membrane layer mounted on the inside of the tubular base, the inner surface of the tubular membrane comprising a number of inwardly projecting ribs extending substantially in the longitudinal direction of the tubular membrane. [2] A tubular membrane according to claim 1, wherein the rib comprises membrane material. [3] A tubular membrane according to claim 1 or 2, wherein the inner surface of the tubular membrane comprises more than one inwardly projecting, longitudinally extending rib. [4] A tubular membrane according to claim 3, wherein the inner surface of the tubular membrane comprises more than 4 ribs, preferably more than 6 ribs, and most preferably a number of ribs in the range of 7-12. [5] A tubular membrane according to any one of the preceding claims, wherein the ribs comprise a cross-section perpendicular to the average flow direction of the feed through the lumen, the cross-section having a non-circular shape, such as an ellipse. [6] A tubular membrane according to any one of the preceding claims, wherein the rib or ribs have an average height in the range of 50 - 2000 µm, preferably in the range of 100 - 500 µm, more preferably in the range of 150 - 400 µm and most preferably in the range of 200 - 350 µm. [7] Tubular membrane according to one of the preceding claims, wherein the rib or ribs have a width in the range of 0.1 - 10 mm, preferably 0.5 - 5 mm, more preferably in the range of 1 - 4 mm and most preferably in the range of 1.5 - 4 mm. [8] Tubular membrane according to one of the preceding claims, wherein a rib height of the rib or ribs is in such a ratio to the membrane inner diameter that the rib height is in the range of 0.4 - 40% of the membrane inner diameter, preferably 1 - 10% of the membrane inner diameter, more preferably in the range of 1.5 - 8% of the membrane inner diameter and most preferably in the range of 2 - 7% of the membrane inner diameter. [9] Tubular membrane according to one of the preceding claims, wherein a rib width of the rib or ribs is in such a ratio to the membrane inner circumference that the rib width is in the range of 0.2 - 63.7% of the membrane inner circumference, preferably in the range of 1.6 - 31.8% of the membrane inner circumference, more preferably in the range of 3.2 - 25.5% of the membrane inner circumference and most preferably in the range of 4.8 - 19.1% of the membrane inner circumference. [10] Membrane module comprising a number of tubular membranes according to any one of the preceding claims. [11] Device for filtering a fluid, the device comprising a number of membrane modules and / or tubular membranes according to any one of the preceding claims.

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