JP2019214041A - Separation membrane element - Google Patents

Abstract

To provide a separation membrane element, which can exert stable separation/removal performance even during operation at high pressure.SOLUTION: The separation membrane element comprises a water collecting pipe, a separation membrane, a supply-side passage material, and a permeation-side passage material. The supply-side passage material has a plurality of regions X, arranged between two surfaces of the separation membrane, which contact the separation membrane in a thickness direction thereof, and a plurality of regions Y which do not contact the separation membrane in the thickness direction thereof. The regions X are firmly fixed to at least one surface of the separation membrane and the regions Y are held by the regions X.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a separation membrane element.

  In the technology for removing ionic substances contained in seawater, brackish water, and the like, in recent years, the use of separation methods using separation membrane elements has been expanding as a process for saving energy and resources. 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, for the production of drinking water from seawater, brackish water and water containing harmful substances, the production of industrial ultrapure water, and the treatment of wastewater and the collection of valuable resources. It is properly used depending on the separation component and the separation performance.

  There are various forms of separation membrane elements, but they are common in that supply water is supplied to one surface of the separation membrane and permeate is obtained from the other surface. The separation membrane element has a large number of bundled separation membranes, so that the membrane area per one separation membrane element is large, that is, the amount of permeated water obtained per one separation membrane element is large. It is formed so that it becomes. As the separation membrane element, various shapes such as a spiral type, a hollow fiber type, a plate-and-frame type, a rotating flat membrane type, and a flat membrane integrated type have been proposed in accordance with the use and purpose.

  For example, a spiral separation membrane element is widely used for reverse osmosis filtration. The spiral type separation membrane element includes a water collecting pipe and a separation membrane wound around the water collecting pipe. The separation membrane includes a supply-side channel material that supplies supply water (that is, water to be treated) to the surface of the separation membrane, a separation membrane that separates components contained in the supply water, and a permeation pipe that transmits permeated water separated through the separation membrane. It is formed by laminating a permeate-side flow path material for leading to the flow path. Spiral-type separation membrane elements are preferably used because a high pressure can be applied to feed water, and a large amount of permeated water can be taken out.

  In order to suppress the decrease in the performance of the separation membrane element due to concentration polarization, for example, the thickness of the supply-side flow path material is reduced, the linear velocity of the supply water on the membrane surface is increased, and a turbulent flow is generated near the separation membrane surface. The thickness of the supply-side flow path material may be reduced, but if the thickness of the supply-side flow path material is reduced, foulants due to impurities or microorganisms in the supply water block the flow path on the supply side, and the performance of the separation membrane element is reduced. Pressure loss increases and the required power of the pump that supplies the supply water increases, resulting in higher power costs and breakage of the separation membrane element. Has been proposed.

  Specifically, Patent Literatures 1 and 2 propose a net in which the flow resistance is reduced by controlling the arrangement of fibrous materials in a supply-side channel material. Further, Patent Document 3 discloses a woven channel material in which the warp and the weft have a non-circular cross section.

JP-T-2015-525282A JP 2000-000437 A JP-A-10-118468

  However, in the conventional supply-side flow path material, it cannot be said that the balance between the reduction of the flow resistance and the turbulence generation intensity is optimized, and furthermore, the stagnation of the supply water near the supply-side flow path material is regarded as a problem. It had been. Therefore, an object of the present invention is to provide a separation membrane element that can exhibit stable separation and removal performance even under high-pressure operation.

  In order to achieve the above object, according to the present invention, there is provided a water collection pipe, a separation membrane, a supply-side flow path material, and a permeation-side flow path material, and the supply-side flow path material is composed of the separation membrane. A plurality of regions X arranged between the two surfaces and in contact with the separation membrane in the thickness direction thereof, and a plurality of regions Y not in contact with the separation membrane in the thickness direction thereof. A separation membrane element is provided, which is fixed to one surface of the separation membrane, and the region Y is held by the region X.

  ADVANTAGE OF THE INVENTION According to this invention, the reduction of the flow resistance in the supply side flow path and the balance of the turbulence generation intensity are remarkably optimized, and furthermore, even under high pressure operation, the progress of fouling due to foulant adhesion is reduced. It is possible to obtain a separation membrane element having excellent operation stability.

FIG. 4 is an exploded perspective view showing one mode of a separation membrane element. It is sectional drawing of an example of the supply side flow path material with which the separation membrane element of this invention is provided. It is sectional drawing of another example of the supply side flow path material with which the separation membrane element of this invention is provided. It is a top view of an example of the supply side channel material with which the separation membrane element of the present invention is provided.

  Hereinafter, embodiments of the present invention will be described in detail.

<Separation membrane element>
As shown in FIG. 1, the separation membrane element (100) includes a water collecting pipe (6) and a separation membrane (1) wound around the water collecting pipe (6). The direction of the x-axis shown in FIG. 1 is the longitudinal direction of the water collecting pipe. The directions such as the y-axis and the z-axis are perpendicular to the longitudinal direction of the water collecting pipe.

<Supply-side flow path material>
The supply-side channel material is disposed between the two surfaces of the separation membrane, and a supply-side channel is formed by the supply-side channel material and the separation membrane. Supply water is passed through the supply-side flow path, but it is important to reduce the flow resistance of the supply-side flow path and increase turbidity in order to suppress the adhesion of foulants contained in the supply water. It is.

  The supply-side flow path member provided in the separation membrane element of the present invention has a plurality of regions X that are in contact with the separation membrane in its thickness direction and a plurality of regions Y that are not in contact with the separation membrane in its thickness direction. The region X is fixed to at least one surface of the separation film, and the region Y needs to be held by the region X.

  By providing a plurality of voids between the region Y of the supply-side flow path material that does not contact the separation membrane and the separation membrane, the space of the supply-side flow path is further expanded, and the thickness of the supply-side flow path material is increased. The degree of freedom of movement of the supply water in the direction is increased, and the turbidity can be improved while reducing the flow resistance of the supply-side flow path. On the other hand, by the presence of the region Y held in the region X of the supply-side channel material, an appropriate turbulence is generated, thereby ensuring a suitable balance between the reduction of the flow resistance and the turbulence generation intensity. Is possible.

  In addition, the presence of the plurality of regions X, which are in contact with and adhere to the separation membrane, suppresses the displacement between the supply-side flow path material and the separation membrane while maintaining each area Y of the supply-side flow path material at a suitable position. And the separation and removal performance of the separation membrane element can be maintained. As for the region X of the supply-side flow path material, as shown in one embodiment in FIGS. 2A and 2B, a material that contacts only one surface of the separation membrane may be mixed, or FIG. As shown in one embodiment in a) or (b), all the regions X may be in contact with the two surfaces of the separation membrane. However, from the viewpoint of suppressing the above-described displacement, the supply-side flow path material is It is preferable to have a region X in contact with the two surfaces of the separation membrane in its thickness direction.

  The shape of the region Y is not particularly limited, but is preferably a cylindrical shape or a shape including a curved surface in order to make the effect of generating turbulence appropriate.

  As a method of fixing the supply-side flow path material region X to the surface of the separation membrane, for example, a method of heat-welding a supply-side flow path material made of resin molded in advance to the surface of the separation membrane, a method of interposing an adhesive, A method of bonding the formed supply-side flow path material to the surface of the separation membrane, or a method of directly forming the supply-side flow path material by performing 3D printing on the surface of the separation membrane with a 3D printer without using a support agent, Is mentioned.

(Confirmation of area X and area Y)
The separation membrane element is appropriately disassembled, and a portion where the cross-sectional area of the supply-side flow path material is as large as possible is selected, and the supply-side flow path material disposed between the two surfaces of the separation membrane is collected together with the separation membrane. The water pipe is cut in the longitudinal direction to expose a cross section (hereinafter, “cross section Z”) of the supply-side channel material and the separation membrane. Observe the cross-section Z with a microscope to confirm the presence and absence of contact and fixation between the supply-side channel material and the separation membrane in the thickness direction of the supply-side channel material, which corresponds to the direction perpendicular to the membrane surface of the separation membrane By doing so, the region X and the region Y in the supply-side channel material can be distinguished.

  Further, by observing the cross section Z with a microscope, the presence or absence of a region Y held by two adjacent regions X can be confirmed.

  Here, the region Y is “held by the region X” when the portion corresponding to the region Y in the supply-side channel material is fixed to the region X, or is molded or molded integrally with the region X. That is being done.

  Each of the cross sections in FIGS. 2 and 3 corresponds to the above cross section Z.

(Spacing of separation membrane)
In the above-mentioned cross section Z, the distance between the separation membranes is measured at ten locations selected at random, and the average value can be used as the separation between the separation membranes.

  When the separation between the separation surfaces of the separation membrane is small, the linear velocity of the supply water on the separation surface of the separation membrane increases, and the flow on the separation membrane surface is disturbed. However, if the separation between the separation membranes is excessively reduced, the tendency of impurities in the supply water or foulants such as microorganisms to block the supply-side flow path may increase. Therefore, the separation distance of the separation membrane is preferably 0.20 to 1.5 mm, more preferably 0.32 to 0.85 mm, and still more preferably 0.50 to 0.80 mm. However, when using the supply-side flow path material provided in the separation membrane element of the present invention, it is possible to adopt a configuration in which the membrane area of the separation membrane is increased by thinning the supply-side flow path material as described later. In this case, it is preferable to appropriately change the membrane surface interval in the range of 0.20 mm to 0.50 mm according to the quality of the supply water.

<Higher film area>
As described above, when the supply-side flow path material is thinned, the flow path is narrowed and the flow resistance is high, so that the impurity in the supply water and foulants such as microorganisms may increase the tendency to block the supply-side flow path material. The supply-side channel material provided in the separation membrane element of the present invention has a structure with a larger gap than conventional products, and has excellent flow resistance and turbidity even when thinned so as to reduce the distance between the membrane surfaces.

  Therefore, even if the space between the membranes is reduced to create a space, and the space is filled with a separation membrane to increase the membrane area of the separation membrane element, the effect of the increase in flow resistance and deterioration of turbidity is negligible. In addition, the amount of fresh water can be improved by increasing the membrane area.

(material)
As a material for molding or molding the supply-side channel material, a thermoplastic resin is preferred from the viewpoint of moldability or moldability, and from the viewpoint of suppressing damage to the separation membrane, polyethylene, polypropylene, polylactic acid, ABS (acrylonitrile- Butadiene-styrene) resins or UV-curable resins are more preferred. In addition, as a method for molding or molding the supply-side channel material using the above-mentioned materials, for example, a method using a mold or a 3D printer can be mentioned.

(Interval between adjacent areas X)
In the above-mentioned cross section Z, the closest distance to the adjacent area X in a direction parallel to the surface of the separation membrane is measured with a microscope for 30 randomly selected areas X, and the average value is calculated as It can be calculated as the interval between the regions X to be performed.

  The distance between the adjacent regions X can be appropriately adjusted while taking into account the flow resistance of the supply-side flow path and the rigidity of the entire supply-side flow path material.

<Permeate-side channel material>
The separation membrane element of the present invention includes a permeate-side channel material. Examples of the permeation-side flow path material include a tricot, a nonwoven fabric, a porous sheet to which projections are fixed, or a film formed by forming irregularities and perforating. In addition, a projection functioning as a permeate-side channel material may be fixed to the surface of the separation membrane.

<Separation membrane>
The separation membrane element of the present invention includes a separation membrane. Examples of the separation membrane include a composite semipermeable membrane including a base material, a porous support, and a separation function layer.

  Examples of the above-mentioned base material include a cloth mainly composed of polyester or aromatic polyamide.

  Examples of the porous support include, for example, polysulfone, polyethersulfone, polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone or polyphenylene oxide formed on a base material. And a polymer layer.

  Examples of the separation functional layer include a separation functional layer containing polyamide as a main component, which is dense enough to sufficiently separate ions and the like and has high affinity for water. Polyamides can be formed, for example, by interfacial polycondensation of a polyfunctional amine and a polyfunctional acid halide.

<Arrangement of supply-side channel material>
The supply-side channel material may be disposed or arranged between the two surfaces of the separation membrane so that the supply-side surface is sandwiched between the separation membranes that are folded inward. It may be arranged between two surfaces of the separation membrane so as to be sandwiched between two facing separation membranes.

  The ends of the separation membrane sandwiching the supply-side flow path material are appropriately sealed, and the “sealing” method includes, for example, bonding with an adhesive or hot melt, heating or melting by laser or the like. Although a method of attaching or sandwiching a rubber sheet is mentioned, sealing by simple adhesion is preferable.

<Separation membrane module and water treatment device>
A separation membrane module can be configured by connecting a plurality of separation membrane elements including the separation membrane element of the present invention in series or in parallel and storing them in a pressure vessel.

  Further, a water treatment apparatus can be configured by combining a separation membrane element of the present invention or the above separation membrane module with a pump for supplying supply water, a pretreatment apparatus for supply water, and the like.

  The operating pressure of the water treatment device is preferably 0.2 to 10 MPa from the viewpoint of saving operating energy and preventing early deterioration of the supply-side channel material and the permeate-side channel material. The temperature of the supply water supplied to the water treatment device is preferably from 5 to 45 ° C. from the viewpoint of making the balance between the salt removal rate and the membrane permeation flux suitable. The pH of the supply water supplied to the water treatment apparatus is preferably in a neutral range from the viewpoint of suppressing generation of scale such as magnesium and deterioration of the separation membrane.

  Examples of the supply water supplied to the water treatment apparatus include seawater, brackish water, and drainage containing 500 mg / L to 100 g / L of TDS (Total Dissolved Solids: total dissolved solids).

  Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Production of supply-side channel material)
Using a 3D printer with polylactic acid as a model material, 3D printing was performed on the surface of the separation membrane with a 3D printer, and the supply-side flow path material was directly formed to fix the region X thereof. More specifically, the net shape shown in FIG. 4 is such that a part of the region X is in contact with the two surfaces of the separation membrane (the distance between adjacent regions X is 3.0 mm; the region Y is A supply-side flow path material A (cylindrical shape having a diameter of 0.2 mm) was formed. Also, on the surface of another separation membrane, a net-like (adjacent area) shown in FIG. 4 such that all the areas X are in contact with the two surfaces of the separation membrane (the thickness of the area that can be the area X is uniform) The supply-side flow path material B having an interval between X in all cases of 3.0 mm; and a region Y having a cylindrical shape with a diameter of 0.2 mm was formed. For each of the supply-side flow path material A and the supply-side flow path material B, two types were prepared, each having a different manner of holding the region Y by the region X.

(Turbulence intensity)
A separation membrane having a supply-side channel material formed on the surface thereof is cut into a sample side having a width of 40 mm and a length of 250 mm, and is sandwiched between acrylic cells of the same size. The acrylic cell was supplied from one end in the length direction so as to be 0.05 m / sec. Each of the net-shaped supply-side flow path members was disposed so as to be in the state shown in FIG. 4 with respect to the flow direction of distilled water, that is, the supply water. While flowing water, 10 mL of aqueous red ink was injected from the supply side end of the distilled water in the acrylic cell, and the spread of the ink in the acrylic cell was recorded by a digital video camera from vertically above the acrylic cell. Then, the image at the time when the spread of the ink reached a position 240 mm from the supply side end of the distilled water in the length direction of the acrylic cell was processed, and the value of the texture was set to zero to black and white the image. The obtained black and white image was analyzed with image analysis software (for example, ImageJ), and the ratio (%) of the area of the spread of the ink to the area of the acrylic cell (40 mm × 250 mm) was calculated as the turbulence intensity. The higher the value of the turbulence intensity, the greater the turbulence generation effect of the supply-side channel material.

(Example 1)
(Measurement of turbulence intensity)
The turbulence intensity of the separation membrane having the supply-side channel material A-1 formed on the surface thereof was measured.

(Preparation of separation membrane element)
A 15% by mass dimethylformamide (DMF) solution of polysulfone was cast at room temperature (25 ° C.) and a coating thickness of 180 μm on a nonwoven fabric (air permeability: 1.0 cc / cm ² / sec) made of polyester fiber produced by a papermaking method. Thereafter, the porous substrate was immediately immersed in pure water for 5 minutes to form a porous support on the nonwoven fabric as the substrate.

  Next, a base material on which a porous support is formed in an aqueous solution in which 2-ethylpiperazine is dissolved in an amount of 2.0% by mass, sodium dodecyldiphenyletherdisulfonate in an amount of 100 ppm, and trisodium phosphate in an amount of 1.0% by mass. Was immersed for 10 seconds, and nitrogen was blown from an air nozzle to remove excess aqueous solution. Subsequently, an n-decane solution containing 0.2% by mass of trimesic acid chloride heated to 70 ° C. was uniformly applied to the surface of the porous support, and was held at a film surface temperature of 60 ° C. for 3 seconds. The surface temperature was cooled to 10 ° C., and left at this temperature for 1 minute in an air atmosphere to form a separation functional layer. The obtained composite semipermeable membrane was held vertically and drained, and washed with pure water at 60 ° C. for 2 minutes to obtain a separation membrane.

The obtained separation membrane was cut to a width of 920 mm, folded so that the effective area of the separation membrane element was 1.8 m ^2, and supplied to the surfaces of the three separation membranes so as to be sandwiched between the folded separation membranes. The road material A-1 was formed. Further, a tricot sheet is disposed as a permeate-side flow path material on the surface of the separation membrane opposite to the side on which the supply-side flow path material A-1 is formed, and these laminates are collected into an ABS resin water collecting pipe. (Width: 1000 mm, diameter: 18 mm, number of holes: 40 × two straight lines) and spirally wound. Finally, both edges were cut to produce a separation membrane element having a diameter of 2 inches. Each of the net-shaped supply-side flow path members A-1 was formed so as to be in the state shown in FIG. 4 with respect to the flow direction of the supply water.

(TDS removal rate)
The separation membrane element is placed in a pressure vessel, and after operating for 30 minutes while circulating the supply water under the conditions of an operating pressure of 0.48 MPa, a temperature of 25 ° C., and a recovery rate of 20%, using the water of Lake Biwa as the supply water, for 1 minute Permeated water was sampled.

  The TDS concentration of the sampled permeated water and the supply water of Lake Biwa was measured using a commercially available electric conductivity meter, and the TDS removal rate was calculated from the following equation.

TDS removal rate (%) = 100 × {1- (TDS concentration in permeated water / TDS concentration in feed water)}
Table 1 shows a series of evaluation results.

(Examples 2 to 4)
Table 1 shows the results of the same evaluation as in Example 1 except that the supply-side channel material was changed as shown in Table 1.

(Examples 5 and 6)
A separation membrane element was produced in the same manner as in Example 1 except that the supply-side channel material was thinned as shown in Table 1 and the effective membrane area was increased.

  Each performance was evaluated under the same conditions as in Example 1 by placing the separation membrane element in a pressure vessel, and the results were as shown in Table 1.

(Comparative Example 1)
Instead of molding the supply-side channel material with a 3D printer, a general polypropylene net (distance between intersections 2.5 mm x 2.5 mm, angle formed by the fiber 45 °, thickness 0.75 mm, unidirectional The turbulence intensity was measured for a separation membrane in which fibers arranged in the other direction were laminated on the arranged fibers). The results are shown in Table 1.

  In addition, three polypropylene nets were arranged so as to be sandwiched between the folded separation membranes, used as a supply-side flow path material, and a separation membrane element was produced. 1 is shown.

(Comparative Examples 2 and 3)
A separation membrane element was produced in the same manner as in Comparative Example 1 except that the supply-side flow path material was as shown in Table 1 and the effective membrane area was increased.

  In Comparative Examples 1 to 3, since the entire region of the net was in contact with any of the separation membranes in the thickness direction and the region Y was not present, not only the flow resistance was increased but also the turbulence intensity was significantly reduced, and the removal rate was accordingly reduced. Also fell.

  As is clear from the results shown in Table 1, in the separation membrane elements of Examples 1 to 6, the flow resistance of the supply water was sufficiently reduced, and a favorable turbulence generation effect in the supply-side flow path was obtained. Therefore, it can be said that excellent separation and removal performance is stably exhibited.

  The separation membrane element of the present invention can be suitably used for desalination of brackish water or seawater.

DESCRIPTION OF SYMBOLS 1 Separation membrane 2 Supply side flow path material 6 Water collecting pipe 100 Separation membrane element 201 Flow direction H of supply water Separation membrane surface X area X
Y area Y

Claims (4)

A collecting pipe, a separation membrane, a supply-side flow path material, and a permeation-side flow path material,
The supply-side channel material is disposed between two surfaces of the separation membrane,
A plurality of regions X in contact with the separation membrane in the thickness direction thereof;
It has a plurality of regions Y that do not contact the separation membrane in its thickness direction,
The region X is fixed to at least one surface of the separation membrane,
The region Y is a separation membrane element held by the region X.   The separation membrane element according to claim 1, wherein the region (Y) is held by two adjacent regions (X).   3. The separation membrane element according to claim 1, wherein the supply-side flow path member has the region X in contact with two surfaces of the separation membrane in a thickness direction. 4. The separation membrane element according to any one of claims 1 to 3, wherein an interval in a thickness direction of the separation membrane is 0.20 to 0.50 mm.

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