Separation membrane elements and separation membrane systems

Abstract

This separation membrane element is provided with: a water collection tube; a separation membrane having a supply-side surface and a permeation-side surface; a supply-side flow path material disposed on the supply-side surface; and, a permeation-side flow path material disposed on the permeation-side surface. The separation membrane, the supply-side flow path material, and the permeation-side flow path material are wound around the water collection tube. When the side area of the separation membrane element is ST and the inlet cross-sectional area of a supply-side flow path of the separation membrane element is SP, SP / ST is 0.03 or more. The average thickness of the supply-side flow path material is 0.15-0.60 mm, inclusive. The rate of decrease in the amount of permeated water after filtration for one hour under prescribed conditions is 10% or less.

Description

[Technical Field]

[0001] The present invention relates to a separation membrane element and a separation membrane system that are suitably used for separating impurities from various liquids containing impurities, particularly for the purification of tap water. [Background technology]

[0002] In recent years, the use of separation methods using separation membrane elements has been expanding as a process for removing ionic substances contained in seawater and brine, as it is an energy-saving and resource-saving method. Separation membranes used in separation methods using separation membrane elements are classified into microfiltration membranes, ultrafiltration membranes, nanofiltration membranes, reverse osmosis membranes, and forward osmosis membranes in terms of their pore size and separation function. These membranes are used, for example, in the production of drinking water from seawater, brine, and water containing harmful substances, the production of industrial ultrapure water, and wastewater treatment and recovery of valuable materials, and are selected according to the target separation components and separation performance.

[0003] While separation membrane elements come in various forms, they all share the common feature of supplying feedwater to one side of the separation membrane and obtaining permeate fluid from the other side. Separation membrane elements are designed to have a large membrane area per element, and therefore a large amount of permeate fluid obtained per element, by comprising a bundle of multiple separation membranes. Various shapes of separation membrane elements have been proposed, such as spiral type, hollow fiber type, plate and frame type, rotating flat membrane type, and flat membrane stacking type, depending on the application and purpose.

[0004] For example, spiral-type separation membrane elements are widely used in reverse osmosis filtration. A spiral-type separation membrane element comprises a water collection pipe and a laminate wrapped around the water collection pipe. The laminate is formed by laminating a supply-side channel material that supplies the feedwater (i.e., the water to be treated) to the surface of the separation membrane, a separation membrane that separates the components contained in the feedwater, and a permeate-side channel material that guides the permeate-side fluid, which has permeated the separation membrane and been separated from the supply-side fluid, to the water collection pipe. Spiral-type separation membrane elements are preferred because they can apply pressure to the feedwater, thus allowing for the extraction of a large amount of permeate fluid.

[0005] To suppress the degradation of element performance due to fouling (accumulation of fouling in the supply water), one possible approach is to increase the porosity of the supply-side flow channel material to improve the discharge efficiency of foulant (fouling in the supply water). Specifically, for example, Patent Document 1 proposes a separation membrane element that can suppress fouling while reducing pressure loss by controlling the cross-sectional shape and thread diameter of the fibrous material in the supply-side flow channel material. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2007-117949 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] However, the separation membrane element disclosed in Patent Document 1 did not strike a sufficient balance between pressure loss reduction and fouling suppression, and its performance sometimes deteriorated during continuous operation.

[0008] The present invention provides a separation membrane element that reduces pressure loss in the separation membrane element by increasing the ratio of the inlet cross-sectional area of ​​the supply-side flow path to the side surface area of ​​the separation membrane element, and also suppresses fouling by preventing clogging of the supply-side end face of the separation membrane element and allowing for efficient discharge, thereby providing a separation membrane element with excellent permeate flow rate and operational stability. Means for Solving the Problems

[0009] The separation membrane element of the present invention that solves the above problems comprises a water collection pipe, a separation membrane having a feed-side surface and a permeate-side surface, a feed-side channel material disposed on the feed-side surface, and a permeate-side channel material disposed on the permeate-side surface, wherein the separation membrane, the feed-side channel material and the permeate-side channel material are wound around the water collection pipe, when ST is the side area of the separation membrane element and SP is the inlet cross-sectional area of the feed-side channel of the separation membrane element, SP / ST is 0.03 or more, the average thickness of the feed-side channel material is 0.15 mm or more and 0.60 mm or less, when a feed aqueous solution of pH 7.0 consisting of 1150 ppm of calcium chloride dihydrate, 660 ppm of sodium bicarbonate and water is filtered for 1 hour under conditions of an operating pressure of 0.41 MPa, a recovery rate of 50% and a temperature of 25° C., the rate of decrease in permeate water volume is 10% or less.

[0010] In the separation membrane element of the present invention, the length of the separation membrane in the longitudinal direction of the water collection pipe is preferably 300 mm or less.

[0011] The separation membrane system of the present invention comprises the separation membrane element of the present invention and is operated at an operating pressure of 1.0 MPa or less. Effect of the Invention

[0012] According to the present invention, fouling can be reduced while suppressing pressure loss, whereby a separation membrane element that can stably obtain a high permeate water volume can be obtained. Brief Description of the Drawings

[0013] [Figure 1] Fig. 1 is a perspective view showing an embodiment of the separation membrane element of the present invention, with a part of the separation membrane element developed. [Figure 2] Fig. 2 is a plan view illustrating an example of the feed-side channel material. [Figure 3] Fig. 3 is a cross-sectional view illustrating an example of a cross-section of a permeate-side channel material. [Figure 4] Fig. 4 is a perspective view illustrating an example of a permeate-side channel material. [Figure 5] Fig. 5 is a perspective view illustrating another example of a permeate-side channel material. DESCRIPTION OF EMBODIMENTS

[0014] Hereinafter, embodiments of the present invention will be described in detail. A separation membrane element according to an embodiment of the present invention includes a water collection pipe, a separation membrane having a feed side surface and a permeate side surface, a feed side channel material disposed on the feed side surface, and a permeate side channel material disposed on the permeate side surface, wherein the separation membrane, the feed side channel material and the permeate side channel material are wound around the water collection pipe. Letting ST be a side area of the separation membrane element, and SP be an inlet cross-sectional area of a feed side channel of the separation membrane element, SP / ST is 0.03 or more, an average thickness of the feed side channel material is 0.15 mm or more and 0.60 mm or less, and a permeate water amount reduction rate is 10% or less when feed water, which is an aqueous solution with pH 7.0 consisting of 1150 ppm calcium chloride dihydrate, 660 ppm sodium bicarbonate and water, is filtered for 1 hour under conditions of an operating pressure of 0.41 MPa, a recovery rate of 50% and a temperature of 25°C.

[0015] <Separation Membrane Element> Reference is made to Fig. 1. Fig. 1 shows one embodiment of the separation membrane element 1 of the present invention, and is a perspective view of a part of the separation membrane element 1 in an expanded state. The separation membrane element 1 includes a water collection pipe 10, a separation membrane 3 having a feed side surface and a permeate side surface, a feed side channel material 2 disposed on the feed side surface, and a permeate side channel material 4 disposed on the permeate side surface. The separation membrane 3, the feed side channel material 2 and the permeate side channel material 4 are integrally wound around the water collection pipe 10 to form a wound body, and end plates are attached to both ends of the wound body, which is a so-called spiral-type separation membrane element.

[0016] In the separation membrane element 1, a polymer net is preferably used as the supply-side channel material 2 that forms the supply-side channel. Furthermore, as the permeate-side channel material 4, tricot, a sheet with a textured surface (such as a film or nonwoven fabric), or a sheet with protrusions arranged on a porous surface (such as a nonwoven fabric) is preferably used to prevent the separation membrane 3 from falling and to form a permeate-side channel. In the embodiment illustrated in Figure 1, an envelope-shaped membrane 3a is formed by overlapping and bonding the separation membrane 3 to both sides of the permeate-side channel material 4 in an envelope shape. The inside of the envelope-shaped membrane 3a constitutes a permeate fluid channel, and the envelope-shaped membrane 3a, which is alternately laminated with the supply-side channel material 2, is bonded to the outer surface of the water collection pipe 10 at a predetermined portion on the opening side and spirally wrapped around it. The x-axis direction in Figure 1 is the longitudinal direction of the water collection pipe, and the y-axis direction is perpendicular to the longitudinal direction of the water collection pipe.

[0017] In a spiral-type separation membrane element, feedwater 7 is generally supplied from one side and flows parallel to the longitudinal direction of the collection pipe 10, gradually separating into permeate 8 and concentrated water 9. The permeate 8 passes through holes in the side of the collection pipe 10, through the inside of the collection pipe 10, and exits the separation membrane element from the end opposite to where the feedwater 7 is supplied. The concentrated water 9 also exits the separation membrane element from the side opposite to where the feedwater 7 is supplied. In this method, since the feedwater 7 flows from one side to the other of the separation membrane element 1, there is inevitably a sufficient distance in contact with the membrane, and as a result, the feedwater 7 is sufficiently separated into permeate 8 and concentrated water 9. There are various forms of separation membrane elements, but they all share the common feature of supplying feedwater to one side of the separation membrane and obtaining permeate from the other side.

[0018] In the separation membrane element according to the embodiment of the present invention, the lateral surface area of ​​the separation membrane element is ST, and the inlet cross-sectional area of ​​the supply side flow path of the separation membrane element is SP, such that SP / ST is 0.03 or more. Preferably, SP / ST is 0.04 or more. A large SP / ST means that SP is relatively large, i.e., the supply side flow path is wide, or that ST is relatively small, i.e., the longitudinal length L of the water collection pipe of the separation membrane element is short. Note that even if the outer diameter D of the separation membrane element is small, ST will also decrease, but as D decreases, SP also decreases, so a large SP / ST means that the longitudinal length L of the water collection pipe of the separation membrane element is relatively short. The outer diameter D of the separation membrane element is preferably 205 mm or less, considering the dimensions of a practical separation membrane element.

[0019] A relatively wide supply channel prevents blockage of the supply channel by foulant. A relatively short L prevents foulant from accumulating inside the separation membrane element, improving foulant discharge. At the same time, it is possible to reduce the pressure loss of the separation membrane element. While there is no particular upper limit to SP / ST, considering the dimensions of a practical separation membrane element, an upper limit of, for example, 0.5 is preferable. The inlet cross-sectional area SP of the supply channel and the lateral area ST of the separation membrane element are determined by the method described later in the example.

[0020] In the separation membrane element according to the embodiment of the present invention, assuming a case where typical tap water with a TOC (Total Organic Carbon) of around 5 ppm is treated, the length L of the separation membrane element is preferably 300 mm or less. More preferably, L is 150 mm or less, and even more preferably 100 mm or less. By making the length L of the separation membrane element 300 mm or less, the accumulation of foulant inside the separation membrane element is more effectively suppressed, and the foulant discharge efficiency is improved. In this specification, the length L of the separation membrane element refers to the length from one edge-cut side to the opposite edge-cut side when the end plates are not attached.

[0021] The separation membrane element according to the embodiment of the present invention has excellent ability to suppress fouling, so even after filtering a feedwater solution consisting of calcium chloride dihydrate at a concentration of 1150 ppm, sodium bicarbonate at a concentration of 660 ppm, and water at a pH of 7.0 for 1 hour under operating pressure of 0.41 MPa, recovery rate of 50%, and temperature of 25°C, the decrease in permeate volume remains at 10% or less.

[0022] <Supply side flow path> (Supply side channel material) Refer to Figure 2. Figure 2 is a plan view illustrating an example of a supply-side flow channel material 2 used in this embodiment. This supply-side flow channel material 2 is composed of a fibrous row X made up of a plurality of first fibrous materials 21 arranged in one direction, and a fibrous row Y made up of a plurality of second fibrous materials 22 arranged in a direction different from the fibrous row X, with the first fibrous materials 21 intersecting the second fibrous materials 22 at multiple points.

[0023] (Thickness of the supply-side flow channel material) The average thickness of the supply-side flow channel material is 0.15 mm to 0.60 mm, preferably 0.25 mm to 0.35 mm. If the average thickness of the supply-side flow channel material is 0.15 mm to 0.60 mm, the membrane surface area of ​​the separation membrane is increased, and the linear velocity of the supply water on the membrane surface increases, causing turbulence in the flow on the membrane surface. This thins the concentration polarization layer and improves the separation performance of the element. Furthermore, it suppresses blockage of the supply-side flow channel by foulants such as impurities and microorganisms in the supply water, enabling stable operation of the separation membrane element over a long period without increasing the required power of the pump.

[0024] The average thickness of the supply-side flow channel material 2 is the average value of the thickness at the intersection of the first fibrous material and the second fibrous material at 10 or more randomly selected locations, i.e., the sum of the thicknesses of the first fibrous material 21 and the second fibrous material 22, measured using a microscope, X-ray CT measuring device, precision thickness gauge, etc., and can be calculated by dividing the sum of the measured values ​​by the number of measurement locations.

[0025] Furthermore, it is preferable that the variation in the thickness of the supply-side flow channel material 2 is between 0.9 and 1.1 times the average thickness of the supply-side flow channel material 2. If the variation in the thickness of the supply-side flow channel material 2 is within this range, the supply water can be uniformly supplied to the separation membrane element, thereby enabling the separation membrane to perform uniformly. Note that the variation in the thickness of the supply-side flow channel material 2 being between 0.9 and 1.1 times the average thickness means that all of the individual measurements used to calculate the average thickness of the supply-side flow channel material 2 are between 0.9 and 1.1 times the average thickness.

[0026] (intersection interval) The interval between intersections (intersection period) c in the direction perpendicular to the water flow direction of the supply-side flow channel material 2 is preferably in the range of 0.5 to 5.0 mm. Within this range, the phenomenon of the separation membrane body falling into the net void portion during the fabrication of the separation membrane element can be suppressed, and in particular, the flow channel at the supply water inlet end face can be stably formed.

[0027] Furthermore, the spacing d of the intersections parallel to the water flow direction of the supply-side flow channel material 2 is preferably in the range of 0.5 to 8.0 mm. Within this range, a balance can be achieved between the turbulence intensity and flow resistance of the supply water, thereby improving the desalination rate and water production capacity of the separation membrane element.

[0028] (material) The material of the supply-side flow channel material 2 is not particularly limited, but from the viewpoint of moldability, thermoplastic resins are preferred, and polyethylene and polypropylene are particularly suitable because they do not easily damage the surface of the separation membrane and are inexpensive.

[0029] <Permeate side flow path> (Permeate side channel material) In the spiral-type separation membrane element of this embodiment, the permeate-side channel material 4 is arranged on the permeate-side surface of the separation membrane. Tricot, which has been widely used as the permeate-side channel material 4 in the past, is a knitted fabric and is composed of three-dimensionally intersecting threads. In addition, as the permeate-side channel material 4, it is possible to use a sheet that has been processed to give a channel material function to a film or nonwoven fabric by creating a textured surface, or a sheet on which protrusions are arranged on a porous sheet such as a nonwoven fabric.

[0030] (cross-sectional area ratio) Refer to Figure 3. Figure 3 is a cross-sectional view illustrating an example of a cross-section of the permeable channel material 4 used in this embodiment. A cross-section is a cross-section obtained by cutting the permeable channel material 4 along a direction parallel to the longitudinal direction of the water collection pipe when the permeable channel material 4 is loaded into the spiral-type separation membrane element, passing through the convex portion of the permeable channel material 4. The cross-sectional area ratio is the ratio of the cross-sectional area S of the permeable channel material occupying the same range to the product of the distance P (hereinafter referred to as pitch) between the centers of convex portion 6 and convex portion 6' and the height H0 of the permeable channel material 4, within the range from the center of a certain convex portion 6 to the center of an adjacent convex portion 6'. As for specific measurement methods for pitch P, height H0, and cross-sectional area S, the permeable channel material 4 can be cut as described above and calculated using a microscope image analysis device.

[0031] The cross-sectional area ratio of the permeate-side channel material 4 is preferably 0.4 or more and 0.75 or less. By arranging the permeate-side channel material 4 with a cross-sectional area ratio of 0.75 or less in the spiral-type separation membrane element, the flow resistance of the permeate-side channel can be reduced, and as a result, the water permeability per unit area can be improved. An improvement in water permeability per unit area means that the water-producing capacity of the entire spiral-type separation membrane element is improved, and consequently, the flow resistance of the channel and the risk of membrane surface fouling increase. However, in the separation membrane element according to the embodiment of the present invention, even when equipped with a permeate-side channel material 4 with low flow resistance, it is possible to stably achieve higher performance than conventional separation membrane elements. Furthermore, if the cross-sectional area ratio is 0.4 or more, the channel can be stably formed even under pressure filtration.

[0032] (Height of the permeable channel material) The height H0 of the permeable channel material 4 is preferably 0.1 mm or more and 1 mm or less. When the height H0 is 0.1 mm or more, the permeable channel material 4 has sufficient strength and tends to be handled without crushing or tearing even when stress is applied. Furthermore, when the height H0 is 1 mm or less, the number of separation membranes and channel materials that can be inserted into the element can be increased without impairing the ability to wrap around the water collection pipe.

[0033] (Material of the permeable channel material) Examples of sheet-like materials used in the permeable channel material 4 include porous films and nonwoven fabrics. Nonwoven fabrics are particularly preferable because the spaces that form channels between the fibers constituting the nonwoven fabric are wider, allowing water to flow easily, and as a result, the water production capacity of the spiral-type separation membrane element is improved. When the sheet-like material is composed of multiple fibers, the fibers may, for example, have a polypropylene / polyethylene core-sheath structure.

[0034] (Flow channel due to permeable channel material) When separation membranes 3 are arranged on both sides of the permeate channel material 4, the space between the protrusion 6 and the adjacent protrusion 6' becomes the channel 5 for the permeate water. The channel may be formed by the permeate channel material 4 itself being shaped into a corrugated, rectangular, or triangular wave shape, or by one surface of the permeate channel material 4 being flat and the other surface being processed to be uneven, or by other members being laminated on the surface of the permeate channel material 4 in an uneven shape.

[0035] (Shape of the permeable channel material) Refer to Figures 4 and 5. Figure 4 is a perspective view illustrating an example of a permeable channel material 4 used in this embodiment, and Figure 5 is a perspective view illustrating another example. The permeable channel material 4 may have protrusions 6a forming the channel 5a arranged in a dot pattern as shown in Figure 4. When the dots are arranged in a staggered pattern, the stress when the supplied water is pressurized is distributed, which is advantageous in suppressing collapse. Although Figure 4 shows cylindrical protrusions with a circular cross-section, i.e., the shape of the plane parallel to the sheet plane, the cross-sectional shape of the protrusions may be polygonal, elliptical, etc., and is not particularly limited. In addition, multiple types of protrusions with different cross-sectional shapes may be mixed. Furthermore, as shown in Figure 5, the permeable channel material 4 may have an uneven shape with continuous groove-shaped recesses 5b, formed by arranging elongated protrusions 6b in one direction. The grooves are preferably continuous in a direction perpendicular to the longitudinal direction of the water collection pipe in order to introduce the permeable water into the water collection pipe over the shortest distance.

[0036] The cross-sectional shape of the protrusion 6b in the direction perpendicular to the winding direction may be a trapezoidal wall-like structure with varying widths, an ellipse, a square, or a semicircle.

[0037] <Separation membrane> As the separation membrane 3 exemplified in Figure 1, etc., a membrane having separation performance according to the method of use, purpose, etc., is used. The separation membrane 3 may be a single layer, or it may be a composite membrane comprising a separation functional layer and a substrate. Furthermore, in the case of a composite membrane, there may be an additional porous support layer between the separation functional layer and the substrate. An example of a preferred embodiment of the separation membrane is shown below.

[0038] (separation functional layer) The separation function layer may be a layer that has both separation and support functions, or it may have only separation functions. Note that "separation function layer" refers to a layer that has at least separation functions. When the separation function layer has both separation and support functions, the separation function layer is preferably a layer mainly containing a polymer selected from the group consisting of cellulose, polyvinylidene fluoride, polyethersulfone, and polysulfone. On the other hand, as a separation functional layer, a crosslinked polymer layer is preferred from the viewpoint of ease of pore size control and excellent durability. Among these, polyamide separation functional layers obtained by polycondensation of a polyfunctional amine and a polyfunctional acid halide, and organic-inorganic hybrid functional layers are preferred from the viewpoint of excellent separation performance of components in the feedwater. These separation functional layers can be formed by polycondensation of monomers on a porous support layer. A separation functional layer containing polyamide as the main component can be formed by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide using a known method. For example, by coating a porous support layer with an aqueous solution of a polyfunctional amine, removing the excess aqueous solution with an air knife or the like, and then coating it with an organic solvent solution containing a polyfunctional acid halide, polycondensation occurs and a polyamide separation functional layer is formed.

[0039] (porous support layer) The porous support layer is a layer that supports the separation function layer, and when resin is the material, it can also be called a porous resin layer. The material used for the porous support layer and its shape are not particularly limited, but for example, it may be formed on a substrate using a porous resin. Examples of porous support layers include layers of polysulfone, cellulose acetate, polyvinyl chloride, epoxy resin, or mixtures thereof, or laminates thereof. However, a layer containing polysulfone is preferred because it has high chemical, mechanical, and thermal stability and its pore size is easy to control. A porous support layer containing polysulfone can be manufactured, for example, by pouring a solution of polysulfone in N,N-dimethylformamide onto a substrate (e.g., a densely woven polyester nonwoven fabric) to a certain thickness and then wet-coagulating it in water. Furthermore, the porous support layer can be formed according to the method described, for example, in “Office of Saleen Water Research and Development Progress Report” No. 359 (1968). The polymer concentration, solvent temperature, poor solvent, etc., can be adjusted as appropriate to obtain the desired form.

[0040] (base material) From the viewpoint of strength, dimensional stability, etc., the separation membrane 3 may be provided with a substrate. As the substrate, it is preferable to use a fibrous substrate from the viewpoint of strength or fluid permeability. Examples of base materials include long-fiber nonwoven fabrics or short-fiber nonwoven fabrics.

[0041] Separation membrane flux (m 3 / m 2 The number of days is not particularly limited, but for example, 0.3m 3 / m 2 Preferably 0.6m / day or more. 3 / m 2 / day or more is more preferable. This increases the feed water flow rate of the separation membrane element, increases the cross-flow velocity on the membrane surface, thins the concentration polarization layer, and improves the separation performance of the element. Further, the separation membrane flux is, for example, 1.5 m 3 / m 2 / day or less is preferable, and 1.0 m 3 / m 2 / day or less is more preferable. This can reduce the fouling risk of the separation membrane. In this specification, the separation membrane flux (m 3 / m 2 / day) refers to the amount of permeated water per day obtained under the following conditions: cutting out the separation membrane to 47 cm 2 , placing it in a membrane evaluation cell, using a sodium chloride aqueous solution with a concentration of 200 ppm and a pH of 6.5 as feed water, operating for 15 minutes under the conditions of an operating pressure of 0.20 MPa, a temperature of 25°C, and a recovery rate of 1% or less, and then performing sampling for 1 minute.

[0042] <Formation of Envelope-shaped Membrane> The envelope-shaped membrane 3a may be formed by folding the separation membrane 3 such that the feed-side surface faces inward, or may be formed by sealing two separate separation membranes 3 such that their feed-side surfaces face each other.

[0043] Examples of the "sealing" method include adhesion using an adhesive or hot melt, fusion using heating or laser, and a method of sandwiching a rubber sheet. Sealing by adhesion is particularly preferable because it is the simplest and highly effective.

[0044] <Water Treatment System> The separation membrane element according to the embodiment of the present invention is preferably driven at an operating pressure of 1.0 MPa or less. The operating pressure is more preferably 0.4 MPa or less. Driving at an operating pressure of 1.0 MPa or less tends to prominently exhibit the effect of increasing the amount of produced water by reducing the pressure loss of the separation membrane element. The separation membrane element according to the embodiment of the present invention is suitably used for water treatment systems such as RO (reverse osmosis membrane) water purifiers and pump-less water purifiers directly connected to water supply, for example. In other words, the separation membrane system according to the embodiment of the present invention is equipped with a separation membrane element according to the embodiment of the present invention and is driven at an operating pressure of 1.0 MPa or less. Such a separation membrane system is suitable for water treatment systems such as RO (reverse osmosis) water purifiers and pumpless water purifiers directly connected to the water supply.

[0045] The temperature of the feedwater supplied to the separation membrane element tends to decrease the salt removal rate as it rises, but the membrane permeation flux also tends to decrease as it falls, so a temperature of 5°C to 45°C is preferable. In addition, if the pH of the feedwater is in the neutral range, even if the feedwater is a liquid with a high salt concentration, the formation of scale such as magnesium is suppressed, and membrane degradation is also suppressed.

[0046] The feedwater treated by the separation membrane element is not particularly limited, but when used for water treatment, it can be a liquid mixture containing 10 g / L or less of TDS (Total Dissolved Solids). Generally, TDS refers to the amount of total dissolved solids and is expressed as "mass ÷ volume," but it is sometimes expressed as a "weight ratio" with 1 L considered to be 1 kg. According to the definition, it can be calculated from the weight of the residue after evaporating a solution filtered through a 0.45 μm filter at a temperature of 39.5 to 40.5°C, but a simpler method is to convert it from the practical salinity. [Examples]

[0047] The present invention will be described in more detail below with reference to examples, but the present invention is not limited in any way by these examples.

[0048] (Fabrication of permeable channel material tricot using weft knitted fabric) For the weft knitted fabric, a multifilament yarn (48 filaments, 110 decitex) was made by blending polyethylene terephthalate filament (melting point: 255°C) with polyethylene terephthalate-based low-melting-point polyester filament (melting point: 235°C). A jersey knit weft structure (gauge (number of needles per unit length of the knitting machine)) was knitted, and after heat setting treatment at 245°C, it was calendered to produce the permeable channel material tricot. In Table 2, the form of this permeable channel material is indicated as "A".

[0049] (Preparation of a permeable channel material having protrusions on a nonwoven fabric) Using an applicator loaded with comb-shaped shims with a slit width of 0.5 mm and a pitch of 0.9 mm, composition pellets consisting of 60% by mass of highly crystalline PP (MFR 1000 g / 10 min, melting point 161°C) and 40% by mass of low-crystalline α-olefin polymer (manufactured by Idemitsu Kosan Co., Ltd.; low stereoregular polypropylene "L-MODU·S400" (product name)) were discontinuously applied onto a nonwoven fabric at a resin temperature of 205°C and a running speed of 10 m / min, while the backup roll temperature was controlled to 20°C. The protrusions applied to the nonwoven fabric were applied so that, when used as a spiral-type separation membrane element, they were perpendicular to the longitudinal direction of the water collection pipe, and when used as an envelope-type membrane, they extended from the inner end to the outer end in the winding direction. The nonwoven fabric had a thickness of 0.07 mm and a basis weight of 35 g / m². 2 The pattern was embossed (circular with a diameter of φ1 mm, and a grid pattern with a pitch of 5 mm). In Table 2, the form of this permeable channel material is indicated as "B".

[0050] (Void ratio of the supply-side flow channel material) Area S(m 2 The mass M (kg) of the supply channel material cut out at ), the thickness d (m) of the supply channel material, and the density ρ (kg / m³) of the material of the supply channel material. 3 The void ratio ε of the supply-side channel material was calculated from ε = 1 - (M / ρ) / (S × d). The thickness d of the supply-side channel material was the average thickness of the supply-side channel material as described above. In addition, "thickness (mm)" in Table 2 refers to the average thickness of the supply-side channel material.

[0051] (Inlet cross-sectional area of ​​the supply channel) SP was calculated using the formula SP = εdl, where ε is the porosity of the supply channel material, d is the thickness of the supply channel material (m), and l is the total length (m) of the supply channel material constituting the separation membrane element in the direction perpendicular to the longitudinal direction of the water collection pipe. In Table 2, "Total length (m)" refers to this total length l, and "Length (m)" refers to the length of a single supply channel material in the direction perpendicular to the longitudinal direction of the water collection pipe.

[0052] (Side surface area of ​​the separation membrane element) The outer diameter of the wound portion of the separation membrane element, excluding the end plates at both ends, was defined as D (m), and the length of the water collection pipe in the longitudinal direction was defined as L (m). ST was calculated using the formula ST = π × D × L. D was the average of 20 diameters measured at arbitrary points. The 20 diameters were selected so that adjacent diameters intersected at approximately the same angle.

[0053] (Recovery rate) In measuring the amount of permeate, the supply water flow rate V supplied over a predetermined time. F (m 3 (per day) and the amount of water permeated during the same time period V P (m 3 The ratio of / day is defined as the recovery rate, V P / V F It was calculated from ×100(%).

[0054] (Flux of the separation membrane) Separation membrane 47 cm 2 The membrane was cut out and, in a membrane evaluation cell, using 200 ppm saline solution and pH 6.5 NaCl aqueous solution as feedwater, the cell was operated for 15 minutes under conditions of operating pressure 0.20 MPa, temperature 25°C, and recovery rate of 1% or less, followed by a 1-minute sampling, and the daily permeate volume was determined by the separation membrane flux (m³). 3 / m 2 ( / day)

[0055] (Fabrication of separation membranes and separation membrane elements, and permeate volume) Nonwoven fabric made of polyethylene terephthalate fibers (fineness: 1 decitex, thickness: approximately 90 μm, air permeability: 1 cc / cm²)2 / sec, density 0.80g / cm 3 A porous support layer (130 μm thick) roll made of a fiber-reinforced polysulfone support film was fabricated by casting a 16.0% by mass DMF solution of polysulfone to a thickness of 180 μm at room temperature (25°C) onto the material, immediately immersing it in pure water for 5 minutes, and then immersing it in 80°C hot water for 1 minute.

[0056] Subsequently, the surface of the polysulfone layer of the porous support film was immersed for 2 minutes in an aqueous solution containing 1.5% by mass of m-PDA (m-Phenylene Diamine) and 1.0% by mass of ε-caprolactam, and then slowly withdrawn vertically. Furthermore, excess aqueous solution was removed from the support film surface by blowing nitrogen from an air nozzle.

[0057] Subsequently, an n-decane solution containing 0.08% by mass of trimesinate chloride was applied to the surface of the membrane until it was completely wet, and then allowed to stand for 1 minute. After that, excess solution was removed from the membrane by air blowing, and the membrane was washed with 80°C hot water for 1 minute to obtain a composite separation membrane roll, which was used as the separation membrane for each example. However, in Example 4, a separation membrane prepared under the same conditions was used, except that the m-PDA concentration and trimesinate chloride concentration were changed.

[0058] The resulting separation membrane was folded and cut to the dimensions of the separation membrane element shown in Table 1, and a polypropylene net shown in Table 2 was sandwiched in between as a supply-side flow channel material to create a leaf.

[0059] The permeable channel material shown in Table 2 was laminated onto the permeable side of the obtained leaf, leaf adhesive was applied, and it was spirally wrapped around a PVC (polyvinyl chloride) water collection pipe. After fixing the outer surface of the wrapped body with tape, the edges at both ends were cut and end plates were attached, and a separation membrane element as shown in Table 1 was fabricated, in which supply water is supplied from one side and concentrated water is discharged. The number of leaves shown in Table 1 refers to the number of envelope-shaped membranes that make up one separation membrane element, and the effective membrane area represents the area of ​​the separation membrane that can be used for filtration. In addition, the number of holes and hole shape per unit length of each water collection pipe were kept constant even if the length L was different.

[0060] The separation membrane element was placed in a pressure vessel, and measurements were performed under the following evaluation conditions. (Evaluation Criteria A) As the feedwater, an aqueous solution with a pH of 7.0 consisting of calcium chloride dihydrate at a concentration of 1150 ppm, sodium bicarbonate at a concentration of 660 ppm, and water was used. The separation membrane was washed by operating under conditions of an operating pressure of 0.41 MPa, a recovery rate of 50%, and a temperature of 25°C for 30 minutes, after which a 1-minute sample was taken, and the amount of permeate per day was determined. Initial permeate volume (m³) 3 The amount of permeate after 1 hour of filtration (m³) was calculated as follows. After that, the filtration was run for another hour (total of 1 hour and 30 minutes), and then the amount of permeate after 1 hour of filtration was calculated in the same manner as above. 3 The calculation was performed using the formula shown below. The percentage decrease in permeate was calculated using the formula below. Permeate reduction rate (%) = 100 × {1 - (Permeate after 1 hour of filtration / Initial permeate)}

[0061] (Evaluation Criteria B) As the supply water, a cylindrical pressure vessel loaded with a separation membrane element was directly connected to a tap water faucet with a total carbon (TC) of 35 ppm, total organic carbon (TOC) of 3.8 ppm, a TDS concentration of 350 ppm, a pH of 7.3, and a static pressure of 0.2 MPa. The opening of the concentrated water valve was adjusted to achieve a dynamic water pressure of 0.15 MPa, and a 1-minute sample was taken. The amount of permeate per day was then measured as the initial permeate (m³). 3The amount was calculated as ( / day). Furthermore, after the total permeate volume of the separation membrane element reached 3000L, the amount of permeate after producing 3000L of water was calculated in the same manner as above. The percentage decrease in permeate volume was calculated from the following formula. Permeate reduction rate (%) = 100 × {1 - (Permeate after 3000L of water production / Initial permeate)}

[0062] (Removal rate (TDS removal rate)) For the supply water and sampled permeate used in the 1-minute operation during the measurement of permeate volume, the TDS concentration (ppm) was determined by conductivity measurement, and the TDS removal rate was calculated using the following formula. TDS removal rate (%) = 100 × {1 - (TDS concentration in permeate water / TDS concentration in supply water)}

[0063] (Element pressure loss) The upstream (supply water side) and downstream (concentrated water side) of a cylindrical pressure vessel containing a separation membrane element were connected by piping via a differential pressure gauge (model DG16) manufactured by Nagano Keiki Co., Ltd., and the initial pressure loss (kPa) of the element was measured when the concentrated water flow rate was 4.0 L / min. Furthermore, after the total permeate volume of the separation membrane element reached 3000 L, the pressure loss (kPa) after 3000 L of water production was measured in the same manner as above. The differential pressure rise (kPa) was calculated using the following formula. A good result is considered to be when the initial pressure loss is 5.0 kPa or less and the differential pressure rise is 15 kPa or less. Pressure difference increase (kPa) = Pressure loss after 3000L of water production - Initial pressure loss

[0064] (Ratio of cross-sectional area of ​​permeable flow channel material) When the permeable channel material was loaded into the spiral-type separation membrane element, the permeable channel material was cut along a direction parallel to the longitudinal direction of the water collection pipe, passing through the protrusions. The cross-section was observed using a microscope image analysis device, and the distance between the centers of two protrusions and the height of the permeable channel material were measured within the range from the center of one protrusion to the center of an adjacent protrusion. The ratio of the cross-sectional area of ​​the permeable channel material to the product of these values ​​within the same range was calculated. Similar measurements were performed at 30 locations, and the average value was taken as the cross-sectional area ratio of the permeable channel material.

[0065] (Example 1) The conditions for the separation membrane element prepared in Example 1 are shown in Tables 1 and 2. The prepared separation membrane element was placed in a pressure vessel and evaluated under the above conditions, and the results are shown in Table 3.

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] (Examples 2-10, Comparative Examples 1-4) The separation membrane elements described in Tables 1 and 2 were fabricated, and their performance was evaluated. The results are shown in Table 3.

[0070] (Comparison of each example and comparative example) In Example 1, the SP / ST was 0.03 or higher, the average thickness of the supply-side flow channel material was 0.15 mm to 0.60 mm, and the permeate rate reduction rate under evaluation condition A was 10% or less. As a result, the initial pressure loss under evaluation condition B was 5.0 kPa or less and the differential pressure rise was 15 kPa or less.

[0071] In Examples 2 and 8, L was kept constant and D was increased compared to Example 1, resulting in an increase in the initial permeate amount under evaluation condition A.

[0072] In Example 3, L was made smaller and SP / ST was made larger than in Example 1, resulting in a decrease in the initial pressure loss and differential pressure rise under evaluation condition B. Also, since SP / ST became 0.04 or higher, the initial pressure loss under evaluation condition B became less than 5.0 kPa.

[0073] In Example 4, a separation membrane with a larger membrane flux than in Example 3 was used, resulting in increased initial permeate volume under evaluation condition A and increased differential pressure rise under evaluation condition B. Furthermore, since SP / ST was 0.04 or higher, the initial pressure loss under evaluation condition B became less than 5.0 kPa.

[0074] In Example 5, the average thickness of the supply-side flow channel material was increased compared to Example 3, resulting in a decrease in the effective membrane area, which reduced the initial permeate volume and removal rate under evaluation condition A, and the initial pressure loss under evaluation condition B. Furthermore, since SP / ST became 0.04 or higher, the initial pressure loss under evaluation condition B became less than 5.0 kPa.

[0075] In Example 6, the cross-sectional area ratio of the permeate-side flow channel material was reduced compared to Example 3, resulting in a cross-sectional area ratio of 0.75 or less, which increased the initial permeate volume under evaluation condition A. Furthermore, since SP / ST was 0.04 or higher, the initial pressure loss under evaluation condition B was less than 5.0 kPa.

[0076] In Example 7, L was increased compared to Example 2, resulting in increased initial permeate volume under evaluation condition A, and increased initial pressure loss and differential pressure rise under evaluation condition B.

[0077] In Example 9, the average thickness of the supply-side flow channel material was reduced compared to Example 3, resulting in an increased effective membrane area, an increase in the initial permeate volume under evaluation condition A, a decrease in the removal rate, and an increase in the initial pressure loss under evaluation condition B. Furthermore, since SP / ST became 0.04 or higher, the initial pressure loss under evaluation condition B became less than 5.0 kPa.

[0078] In Example 10, L was made smaller and SP / ST was made larger than in Example 1, resulting in a decrease in the initial pressure loss and differential pressure rise under evaluation condition B. Also, since SP / ST became 0.04 or higher, the initial pressure loss under evaluation condition B became less than 5.0 kPa.

[0079] In Comparative Examples 1 and 2, the SP / ST was less than 0.03, resulting in a differential pressure increase of more than 15 kPa under evaluation condition B.

[0080] In Comparative Example 3, the average thickness of the supply-side flow channel material was less than 0.15 mm, resulting in a differential pressure increase exceeding 15 kPa under evaluation condition B. Furthermore, because the permeate volume reduction rate under evaluation condition A was greater than 10%, the permeate volume reduction rate under evaluation condition B exceeded 30%.

[0081] In Comparative Example 4, the average thickness of the supply-side flow channel material was greater than 0.60 mm, resulting in a differential pressure increase exceeding 15 kPa under evaluation condition B. Furthermore, because the permeate volume reduction rate under evaluation condition A was greater than 10%, the permeate volume reduction rate under evaluation condition B exceeded 30%.

[0082] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2021-121228 filed on July 26, 2021, the contents of which are incorporated herein by reference. [Industrial applicability]

[0083] The separation membrane element of the present invention can be suitably used in RO (reverse osmosis) water purifiers. [Explanation of Symbols]

[0084] 1. Spiral-type separation membrane element 2 Supply side channel material 21. First fibrous material 22. Second fibrous material 3 Separation membrane 3a Envelope-shaped membrane 4 Permeate side channel material 5, 5a, 5b Recesses (flow channels) 6, 6a, 6b convex parts 7 Supply water 8 Permeate water 9 Concentrated water 10 Water collection pipe D Outer diameter of the separation membrane element L Length of the water collection tube of the separation membrane element c. Intersection of the supply-side flow channel material perpendicular to the water flow direction. d. Intersection of the supply-side flow channel material in a direction parallel to the water supply flow direction. Pitch of the permeable channel material S Cross-sectional area of ​​the permeable channel material H0 Height of the permeable channel material X fibrous row Y-shaped fibrous rows

Claims

1. The system comprises a water collection pipe, a separation membrane having a supply side surface and a permeable side surface, a supply side flow channel material disposed on the supply side surface, and a permeable side flow channel material disposed on the permeable side surface. The separation membrane element is wound around the water collection pipe and comprises the separation membrane, the supply-side channel material, and the permeate-side channel material. Let D be the outer diameter of the wound portion of the separation membrane element excluding the end plates at both ends, and L be the length of the separation membrane element in the longitudinal direction of the water collection pipe. Then, let ST be the lateral surface area of ​​the separation membrane element, where π × D × L. Let ε be the porosity of the supply-side channel material, d be the thickness of the supply-side channel material, and l be the total length of the supply-side channel material constituting the separation membrane element in the direction perpendicular to the longitudinal direction of the water collection pipe. Then, let εdl be the inlet cross-sectional area SP of the supply-side channel of the separation membrane element. SP / ST is 0.03 or higher, The thickness d of the supply-side flow channel material is 0.15 mm or more and 0.60 mm or less. A separation membrane element in which, when a feedwater solution consisting of a pH 7.0 aqueous solution of calcium chloride dihydrate at a concentration of 1150 ppm, sodium bicarbonate at a concentration of 660 ppm, and water is filtered for 1 hour under operating pressure of 0.41 MPa, recovery rate of 50%, and temperature of 25°C, the rate of decrease in permeate volume is 10% or less.

2. The separation membrane element according to claim 1, wherein the length L of the separation membrane element in the longitudinal direction of the water collection pipe is 300 mm or less.

3. A separation membrane system comprising a separation membrane element according to claim 1 or 2, and driven at an operating pressure of 1.0 MPa or less.

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