JPH09141067A - Liquid separation element, device and treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent liquid separation element without decreasing performance such as the flow rate of a permeated liquid or the inhibiting rate for a wide pressure range from low to high by disposing water-permeable cloth between a reverse osmosis membrane and a passage material for the liquid. SOLUTION: Multifilaments of a polyester fiber are knitted into a double denbidh structure and molten and welded, hardened and calendered to obtain a single tricot with specified width, depth and density of grooves. Further, a nonwoven fabric of a polyester short fiber is calendered to obtain a water- permeable nonwoven fabric having specified thickness, surface average roughness and permeability. The nonwoven fabric is laminated on the groove surface of the single tricot fabric to obtain a passage material for the permeated liquid in such a manner that the orientation direction of the fiber of the nonwoven fabric is perpendicular to the groove direction of the single tricot. The obtd. passage material 10 for the permeated liquid is disposed between two reverse osmosis membranes 1, and then a water-permeable nonwoven fabric 11 is disposed. Thereby, an enough passage can be maintained even under high pressure.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a liquid separating element using a semipermeable membrane used for separating and concentrating various liquids, and does not cause deterioration of performance in a wide pressure range from low pressure to high pressure. The present invention relates to a liquid separation element having improved pressure resistance and long-term durability.

[0002]

2. Description of the Related Art Conventionally, as a liquid separating element using a semipermeable membrane, a spiral type using a reverse osmosis membrane, a plate and frame type, or a hollow fiber type liquid separating element has been used. In particular, the spiral type liquid separation element using a reverse osmosis membrane is capable of filling a reverse osmosis membrane having a large membrane area in a fixed volume, and is most widely used.
A spiral type liquid separation element using a general reverse osmosis membrane, as shown in FIG. 1, sandwiches a permeated liquid flow channel material 2 between two reverse osmosis membranes 1 and supplies it to the outside of the reverse osmosis membrane. A liquid flow path member 3 is attached to form a set of units, and a set of the units is provided around a hollow central tube 5 in which water collecting holes 4 are arranged,
Alternatively, it is formed by winding a plurality of sets.

Usually, in a liquid separation element using a reverse osmosis membrane, a differential pressure of about 0.5 to 7 MPa is applied to the supply liquid side and the permeation liquid side in order to efficiently separate and concentrate the liquid. With respect to such operating pressure, the permeate flow channel material is required to hold the reverse osmosis membrane without impairing the performance of the reverse osmosis membrane and to secure the permeate flow channel. Therefore, as a permeate liquid flow path material of a liquid separation element used at a relatively low pressure, a single tricot knitted fabric having a groove on one surface is impregnated with a resin, as proposed in, for example, JP-A-62-35802. Alternatively, a material that is subjected to heat fusion processing to give rigidity is typical. FIG. 2 shows a typical permeated liquid channel material.
The cross-sectional shape of a single tricot knit is shown. The groove 6 and the convex portion 7 which are the channels of the permeated liquid are formed on one surface at regular intervals.

In order to enhance the performance of the liquid separation element such as the flow rate of the permeated liquid, the rejection rate, the rejection rate, or the concentration rate in the liquid separation element using the permeated liquid flow path material as described above, reverse pressure is used. It is desired to prevent the permeation membrane from being deformed and to reduce the flow resistance of the permeated liquid by the flow path member as much as possible.

Therefore, particularly in a liquid separation element used under high pressure, as shown in FIG. 3, for example, a diameter of 50 to 1 is provided between the reverse osmosis membrane and the surface having the groove of the single tricot.
A porous sheet 9 having a thickness of 70 to 400 μm, which has small holes 8 of 000 μm at intervals of about 0.1 to 200 mm, is interposed to prevent the reverse osmosis membrane from being deformed under high pressure, and to prevent permeation liquid. It has been proposed in JP-A-54-31087 to reduce the flow resistance of the above.

[0006]

As described above, most of the current spiral type liquid separation elements use the single tricot as the permeate flow path material, and the groove is used to reduce the flow resistance of the permeate. Width of 300-600 μm
The flow path area is expanded by making it relatively large. However, such a groove width is the thickness of a general reverse osmosis membrane2
Since it is large with respect to 00 to 300 μm, when the pressure is applied, the reverse osmosis membrane is deformed and falls into the groove of the tricot as shown in FIG. Also causes damage due to deformation, and there is a risk that the performance of the liquid separation element such as the permeated liquid flow rate, the blocking rate, the rejection rate, or the concentration rate may deteriorate. If the rigidity of the reverse osmosis membrane is not very high, the reverse osmosis membrane may be deformed at a relatively low pressure, and 1 MPa to
Performance deterioration may occur at a pressure of about 2 MPa.

When the porous sheet as described above is arranged on the surface having the tricot groove, the rigidity of the porous sheet prevents the reverse osmosis membrane from falling into the groove and suppresses the increase of the flow resistance. However, on the other hand, since the area of the permeated liquid when passing through the porous sheet is limited by the small holes, the permeation resistance is increased from several times to a dozen times more than when the porous sheet is not used, In some cases, sufficient performance may not be obtained at low operating pressure due to pressure loss.

In order to reduce the permeation resistance of the permeated liquid of the porous sheet, the diameter of the small holes provided in the porous sheet is increased, or the interval between the small holes is reduced to increase the number of small holes. Although it is necessary, if the diameter of the small pores is larger than the thickness of the reverse osmosis membrane, there is a problem that the reverse osmosis membrane falls into the small pores under high pressure and is damaged to deteriorate the performance. On the contrary, in order to prevent the reverse osmosis membrane from falling into the small holes,
If the diameter of the small pores is made smaller than the thickness of the reverse osmosis membrane, the permeation resistance of the permeated liquid passing through the small pores becomes approximately extremely inversely proportional to the fourth power of the diameter of the small pores. In order to suppress the increase in permeation resistance, an extremely large number of small holes are required, making it very difficult to process the porous sheet, and at the same time,
The rigidity of the porous sheet itself also decreases due to the increase in small holes,
There is a problem that it becomes difficult to obtain stable performance.

Further, if the cloth used for the base material of the reverse osmosis membrane is made thicker, the membrane is certainly less likely to be damaged. , It becomes more rigid and difficult to wind in a spiral.

As described above, in the conventional permeated liquid channel material,
It has been difficult to obtain a liquid separation element that exhibits sufficient performance over a wide operating pressure range from low pressure to high pressure.

The present invention solves the above-mentioned problems, and in a wide pressure range from low pressure to high pressure, the pressure resistance and the long-term pressure are maintained without deteriorating the performance such as the permeate flow rate, the rejection rate, the rejection rate, or the concentration rate. It is an object of the present invention to provide a liquid separation element having excellent durability.

[0012]

The object of the present invention can be basically achieved by the following constitution. That is,
“A liquid separation element characterized by comprising a water-permeable cloth between a reverse osmosis membrane and a permeate flow path material”.

In the present invention, the permeated liquid flow path material, which is a main constituent member, is not particularly limited, but preferably has a groove on at least one surface as shown in FIG. 5, and particularly has a groove. Woven and knitted fabrics are preferred.

The woven or knitted material of the permeate flow path material in the present invention is
It is preferable to have a groove that serves as a flow path for the permeated liquid on at least one surface thereof, but the groove width, groove depth, or groove density is not particularly specified, and the flow rate is sufficiently low for the permeated liquid. Any size may be used as long as it has resistance and can sufficiently support the water-permeable cloth disposed on the surface under high pressure.

As a concrete example, it is preferable that the permeated liquid channel material is composed of a structure having parallel grooves on both sides (hereinafter referred to as a double-groove type channel material). It is more preferable that the directions are parallel to each other. If the directions of the grooves on both surfaces are provided so as to be orthogonal to each other, the direction of the grooves on either side is parallel to the longitudinal direction of the central pipe, so that the permeate cannot be smoothly guided to the water collecting holes of the central pipe, The flow resistance becomes extremely large and the performance deteriorates. Regarding the positions of the grooves on both sides of the double-groove type channel material, the positions are the same on both sides, which means that the channel material itself is less deformed under high pressure and the increase in flow resistance is suppressed. Is more preferable. Although not particularly limited, the deviation of the center positions of the grooves on both sides is preferably 4
It is 0 μm or less, more preferably 20 μm or less.

The groove width of the permeate flow channel material is 100 in order to prevent the reverse osmosis membrane from falling into the groove under high pressure.
The thickness is preferably in the range of 200 to 200 μm. More preferably, it is in the range of 100 to 150 μm. This is because a reverse osmosis membrane used for a liquid separation element usually has a thickness of about 200 to 300 μm.
m, but the width of the groove is substantially equal to or smaller than the thickness of the reverse osmosis membrane, thereby substantially preventing the reverse osmosis membrane from falling into the groove of the permeated liquid flow path material. Because you can do it. Considering the lower limit of the groove width from the viewpoint of suppressing the fall of the reverse osmosis membrane into the groove, 1
A thickness of at least 00 μm is sufficient, while a thickness of at most 100 μm is not preferred because it only increases the flow resistance of the permeate. Regarding the groove depth of the permeate flow channel material, when the groove depth is 50 μm or less, the permeate flow channel becomes small, and even a slight deformation of the reverse osmosis membrane under high pressure greatly changes the flow resistance. There is a risk that On the other hand, when the thickness is 200 μm or more, the thickness of the permeate flow path material becomes large, and the area of the packed membrane of the reverse osmosis membrane when incorporated in the liquid separation element becomes small. In addition, the thickness is preferably in the range of 50 to 200 μm so that the flow resistance of the permeate is small. More preferably, it is in the range of 80 to 150 mm. Further, the flow resistance of the permeate flow channel material varies depending on the groove density, that is, the number of grooves per unit length as described above, but in the liquid separation element of the present invention, The groove density is preferably in the range of 45 to 70 per inch. More preferably 50 to 60 per inch
It is a book. If the groove density is 45 or less per inch, the total number of flow passages is small and the flow passage area becomes small, resulting in a large flow resistance. Further, the upper limit of the groove density is desirable to reduce the flow resistance, but when the groove density is substantially 70 or more per inch, the flow path material for supporting the reverse osmosis membrane under high pressure is preferably used. Since the width of the convex portion is reduced and the area of the portion receiving the pressure is reduced, the flow path material itself is deformed. Therefore, there is a risk that the depth of the groove becomes small and the flow resistance increases.

The woven or knitted material of the permeated liquid flow path material is not particularly limited as long as it has the above-mentioned structural characteristics, but it can be manufactured with high quality and at low cost. In this respect, tricot is preferably used as a woven or knitted fabric. Regarding the tricot, for example, there are various types such as double denbi, quinz code, three-piece os, etc., depending on the organization structure.
Any material may be used as long as it can secure the flow path of the permeated liquid and is hardly deformed even under high pressure, and there is no particular limitation.

The material of the fibers of the woven or knitted material may be any as long as it retains the shape of the channel material and little elution of the components into the permeate, for example, a polyamide-based material such as nylon. Fiber, polyester fiber, polyacrylonitrile fiber, polyolefin fiber such as polyethylene and polypropylene, polyvinyl chloride fiber,
Polyvinylidene chloride-based fibers, polyfluoroethylene-based fibers, carbon fibers, and the like can be mentioned.In particular, in consideration of the strength that can withstand high pressure and the ease of processing of a woven or knitted fabric described later, polyester fibers are used. Is preferred.

Also in the present invention, it is preferable to carry out a hardening treatment for increasing the rigidity of the woven or knitted fabric in order to suppress the deformation of the flow path material itself under a high pressure. Examples of the curing method include a method of impregnating a woven or knitted product with a resin such as melamine or epoxy, or a method of applying a heat fusion process of fusing and solidifying fibers to each other by heating the woven or knitted material. ,
In the present invention, any method can be used as long as it is a processing method capable of obtaining a hardness such that the channel material itself is not deformed under high pressure.

Further, in the present invention, in order to prevent local or non-uniform deformation of the water-permeable cloth or reverse osmosis membrane under high pressure, the woven or knitted material of the permeate flow channel material may be calendered. good. The calendering makes the woven / knitted fabric very smooth and flat by crushing the fine undulations caused by the shape of the fibers. Therefore, the water-permeable nonwoven fabric and the reverse osmosis membrane do not undergo uneven deformation under high pressure, and the performance and durability can be further improved.

The present invention is characterized in that a cloth having water permeability is further arranged on the surface of the woven or knitted material as described above.

In the present invention, the degree of water permeability of the fabric,
That is, the water permeability is not specified, but the permeability coefficient of pure water at 25 ° C. is 0.5 m ³ / (m ² · MPa · mi
n or more is preferable in order to reduce the permeation resistance of the nonwoven fabric. More preferably 0.8 m ³ / (m ² ·
MPa · min) or higher.

Further, the present invention does not limit the thickness of the fibers used for the cloth at all, and any thickness can be used as long as the cloth has the above-mentioned water permeability and sufficient rigidity can be obtained. Saori fibers may be used.

Also, the material of the fibers constituting the cloth is not particularly specified, and any material may be used as long as it does not deform under pressure and the components are little eluted into the permeate. . For example, polyamide fibers such as nylon, polyester fibers, polyacrylonitrile fibers, polyolefin fibers such as polyethylene and polypropylene, polyvinyl chloride fibers, polyvinylidene chloride fibers, polyfluoroethylene fibers, etc. can be used. .

The surface of the water-permeable fabric of the present invention preferably has an average roughness Rz of 20 μm or less.
It is more preferably 5 μm or less. Here, the average surface roughness R
z is the average of the heights of the peaks from the highest to the fifth measured in the vertical direction from a straight line parallel to the average line of the cross-section and not crossing the cross-sectional curve, and It is obtained by calculating the difference between the value and the average value of the fifth valley bottom. Although there is no particular lower limit for the surface roughness, it is preferably 2 μm or more in consideration of resistance and manufacturing cost.

In the present invention, in order to obtain the above-mentioned surface roughness, the cloth may be calendered to make the surface smooth. By performing such a treatment to make the surface smooth, unevenness on the cloth surface is obtained. The damage of the reverse osmosis membrane resulting from this can be reduced and durability can be improved. Although not particularly limited, as the conditions of the calendering treatment, for example, in the case of polyester fiber, preferably, the heating temperature is 50 to 150 ° C., and the weight per 1 m width is 20 to 8;
0t, and more preferably the heating temperature is 60 to 100.
The load per ° C and 1 m width is 40-60t. Of course, for fibers of materials other than polyester fiber,
The conditions of the calendering process may be appropriately changed according to the difference in physical properties such as the melting point and the elasticity.

Regarding the thickness of the water-permeable cloth, if it is too thin, the rigidity becomes low and it deforms under high pressure, and if it is too thick, it is good in terms of rigidity, but conversely, the flow path material itself becomes too thick and the liquid Since there is a problem that the film area is reduced when incorporated in the separation element, the thickness is preferably in the range of 50 to 200 μm, more preferably 70 to 150 μm.

In the present invention, the kind of cloth is not particularly specified, but any kind of cloth having the above-mentioned water permeability, surface smoothness and rigidity may be used. Further, it is preferable to use a water-permeable nonwoven fabric from the viewpoint that the above-mentioned characteristics can be easily obtained.

For non-woven fabrics, generally several mm to several c
It is a structure in which short fibers with a length of about m are intricately entangled with each other. Depending on the density of the fibers and the degree of post-processing, there are no gaps between the fibers at all, and there is no liquid permeation. There are various types such as those having a large gap and allowing liquid to easily permeate, but in the present invention, in order to smoothly guide the liquid permeated through the reverse osmosis membrane to the groove of the woven or knitted fabric which is the flow path, the permeated liquid flow path is used. The non-woven fabric used for the material must have a liquid-permeable property, that is, it must have water permeability.

Depending on the manufacturing method, the non-woven fabric may be a so-called non-oriented one in which the fibers have no directionality, a non-oriented one in which the fibers are oriented in a fixed direction, or an intermediate between the two. In the present invention, It is preferable to use fibers in which the fibers are oriented in a fixed direction.

Further, it is preferable that the non-woven fabric in which the fibers are oriented in a certain direction is such that the orientation direction of the fibers is orthogonal to the groove direction of the woven or knitted fabric when placed on the surface of the woven or knitted fabric.

This is because when the fibers of the non-woven fabric are oriented in a certain direction, anisotropy occurs in the strength and rigidity of the non-woven fabric, and in the case of deformation such as bending and bending, the direction parallel to the orientation direction of the fibers. Since it becomes stronger in the vertical direction than that, by making the groove direction of the woven and knitted fabric and the orientation direction of the fibers of the nonwoven fabric orthogonal,
This is because deformation of the nonwoven fabric under high pressure and falling into the groove of the woven or knitted fabric can be suppressed. Therefore, it is preferable to dispose the water-permeable cloth on the surface of the flow path member on the side having the groove.

If the cloth used as the base material of the reverse osmosis membrane is made thicker, the step of forming the porous layer becomes difficult. Therefore, both the base material of the reverse osmosis membrane and the water permeable cloth are made into one cloth. It is not preferable to combine the two with each other or to combine them at the time of forming the composite film. Further, when the thickness of the unit layer is large, the rigidity becomes high and it becomes difficult to wind it in a spiral. Therefore, at the time of winding the spiral, both the base material of the reverse osmosis membrane and the water-permeable fabric are integrated by adhesion or the like. That is also not preferable.

Further, a feature of the present invention is that a water-permeable cloth is arranged on the surface of the permeate flow channel material, and the member of the liquid separation element other than the permeate flow channel material, that is, the surface is provided. The hollow central tube having holes, the semipermeable membrane, and the supply liquid flow path member are not specified at all. Therefore, for these members, for example, conventional members can be used as they are.

The use conditions are not particularly limited, but as described above, the effects of the present invention are excellently exhibited particularly under high pressure conditions. The pressure applied is preferably 5 to
15 MPa, more preferably 7 to 12 MPa. Suitable application fields include desalination by reverse osmosis of 0.5% or more of salt water, particularly seawater.
This is suitable when the high-pressure concentrated water is further subjected to reverse osmosis membrane treatment.

It is also preferable that the reverse osmosis membrane used has pressure resistance. For example, as a support membrane or asymmetric membrane of a composite membrane, A having a pore diameter of 200 nm or less is mainly used.
And a B layer having a thickness of 200 nm or more, the A layer having a thickness of 2 μm or more, the B layer having a thickness of 8 μm or more, and
The ratio X of the thickness of the layer A to the total thickness of the layers B and 2 is 2
A film having a microporous layer characterized by being 0% or more can be mentioned. Further, as the base material layer provided with the porous layer,
A woven or non-woven fabric having a thickness of 50 to 150 μm is preferable.

[0037]

【Example】

Example 1 and Comparative Example 1 As Example 1 of the present invention, a multifilament of polyester fiber was knitted into a double Denbi structure (thread diameter 60 denier, knitting condition well 30 / inch, course 50 / inch) and heated. Fusing processing (temperature 250 ℃, processing time 1
After curing), calendering (temperature 60 ℃,
50 t / m) (temperature: 60 ° C, load: 40 t / m), groove width is 200 μm, groove depth is 150 μm, and groove density on one side is 40 per 1 inch and the convex part is smooth and thick. A single tricot having a length of 200 μm is produced, and a nonwoven fabric made of polyester short fibers is calendered to have a thickness of 100 μm and an average surface roughness R
A water-permeable nonwoven fabric having z of 5 μm and a pure water permeability coefficient at 25 ° C. of 0.9 m ³ / (m ² · MPa · min) was prepared, and the orientation direction of the fibers of the nonwoven fabric was a single tricot groove. A sample for flow resistance measurement, which was placed on a surface having a single tricot groove so as to be orthogonal to the direction to obtain a permeate flow path member having a structure shown in FIG. 5 and was incorporated between two reverse osmosis membranes. And

On the other hand, as Comparative Example 1, the same single tricot as in Example 1 was used, and a water-permeable non-woven fabric was not placed on the surface, and as it was as in Example 1, it was incorporated between two reverse osmosis membranes and flowed. A resistance measurement sample was prepared.

Using these samples, a hydrostatic pressure of 0.5 to 10 MPa was applied to the reverse osmosis membrane under the condition of the liquid temperature of 25 ° C., and the flow resistance of pure water passing through the permeate flow path material after 1 hour. Table 1 shows the result of measurement.

[0040]

[Table 1] Whereas the conventional permeate flow path material of Comparative Example 1 has a flow resistance that rapidly increases due to pressure load, the flow path material of the present invention is
Sufficient permeate flow path is secured even under high pressure.
Even at a pressure of MPa, the increase in flow resistance could be suppressed to about 2.5 times that at low pressure.

Example 2 and Comparative Example 2 The same permeate flow channel material as in Example 1 and the surface having the groove of the single tricot of Comparative Example 1 were formed with small holes of 400 μm in diameter at intervals of 10 mm and a thickness of 100 μm. The permeated liquid flow path member having the shape shown in FIG.
It was installed between two reverse osmosis membranes, and a polypropylene net was installed on the outside of the reverse osmosis membrane as a feed liquid flow path material. These were wound around a FRP central pipe and the outer diameter was 4 inches. A kind of liquid separation element was obtained. These were separately loaded into the pressure vessels of the liquid separation device shown in FIG. 6, and a separation experiment was conducted using saline as the supply liquid. As the experimental conditions, the salt concentration of the feed liquid was 5.0%, the operating pressure was 8 to 13 MPa, the feed liquid flow rate was 20 liters / min, and the liquid temperature was 25 ° C., and the salt rejection rate after 120 h at each pressure was calculated. The measured results are shown in Table 2.

[0042]

[Table 2] In the conventional liquid separation element, the rejection rate of salt sharply decreases when the operating pressure is 10 MPa or more, and the rejection rate of salt decreases when evaluated at a low pressure for a long time. The rejection of salt did not decrease until 13 MPa. In addition, even when evaluated for a long period of time, the rejection rate of salt was not decreased, and the durability was superior to that of the conventional liquid separation element.

[0043]

According to the present invention, sufficient permeate flow passages are secured even under high pressure to suppress an increase in permeate flow resistance, and performances such as permeate flow rate, rejection rate, rejection rate and concentration rate are obtained. It is possible to provide a liquid separation element having excellent durability.

[Brief description of the drawings]

FIG. 1 is a sectional view of a conventional spiral type liquid separation element using a reverse osmosis membrane.

FIG. 2 is an explanatory diagram of a single tricot, which is a conventional typical permeate flow path material.

FIG. 3 is an explanatory view of a conventional permeate flow path member used in a liquid separation element used under high pressure.

FIG. 4 is an explanatory diagram showing deformation of a reverse osmosis membrane under high pressure that occurs in a conventional liquid separation element.

FIG. 5 is an explanatory view of a permeated liquid flow path material of a liquid separation element based on the present invention.

FIG. 6 is a schematic view of a liquid separation device used in an example of the present invention.

[Explanation of symbols]

 1: Reverse osmosis membrane 2: Permeate liquid flow path material 3: Supply liquid flow path material 4: Water collection hole 5: Central tube 6: Groove 7: Convex part 8: Small hole 9: Porous sheet 10: Woven / knitted fabric 11: Water-permeable fabric 12: Raw water (saline solution) 13: Supply pump 14: Filter 15: High-pressure pump 16: Supply water line 17: Liquid separation element (pressure vessel) 18: Concentrated water line 19: Permeate water line

Claims (8)

[Claims] 1. A liquid separation element comprising a water permeable cloth disposed between a reverse osmosis membrane and a permeate liquid flow path member. 2. The average roughness Rz of the surface of the water-permeable fabric is 20.
The liquid separation element according to claim 1, wherein the liquid separation element is in a range of μm or less. 3. The liquid separation element according to claim 1, wherein the water-permeable cloth is a non-woven fabric. 4. The liquid separation element according to claim 3, wherein the fibers constituting the water-permeable nonwoven fabric are oriented in a fixed direction. 5. A groove is formed in the permeate flow path member,
The liquid separating element according to claim 1, wherein the orientation direction of the fibers of the water-permeable nonwoven fabric is orthogonal to the direction of the groove. 6. A reverse osmosis device comprising the liquid separation element according to claim 1. 7. A method for treating a reverse osmosis membrane, wherein the liquid separation element according to claim 1 is used. 8. A unit consisting of two semipermeable membranes, a permeate flow channel material interposed between the two semipermeable membranes, and a supply liquid flow channel material is wound around a hollow central tube having holes on the surface. In the liquid separating element which is rotated, the permeated liquid flow path material is a woven or knitted fabric having grooves on the surface, and a water-permeable cloth is arranged on the surface of the permeated liquid flow path material. Separation element.