JP2000051668A - Liquid separation element and water making method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid separation element capable of ensuring a permeated liquid flow channel sufficient even under high pressure and excellent in properties such as a permeate flow rate, an obstruction ratio, an exclusion ratio or a concn. ratio and durability. SOLUTION: In a liquid separation element, a membrane unit including reverse osmosis membranes 1 and a permeated liquid flow channel material 10 having grooves of which the groove width is smaller than the thickness of the reverse osmosis membrane is formed to the periphery of a center pipe having water collecting holes and the exclusion ratio of salt after a supply soln. of 25 deg.C containing 5.0 wt.% of salt supplied for 2 hr while pressure is set to 13 MPa and a flow rate is set to 20 l/min is not less than the exclusion ratio of salt after 2 hr-supply under a condition wherein pressure is 5.5 MPa and a flow rate is 20 l/min.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a liquid separation element using a semi-permeable membrane used for separating and concentrating various liquids, and more particularly, to a pressure-resistant element which does not cause performance degradation even at a high pressure. The present invention relates to a liquid separation element having improved performance and durability.

[0002]

2. Description of the Related Art Conventionally, as a liquid separation element using a semipermeable membrane, a spiral type, a plate and frame type or a hollow fiber type liquid separation element using a reverse osmosis membrane has been used. In particular, a spiral liquid separation element using a reverse osmosis membrane can fill a large volume of a reverse osmosis membrane in a fixed volume and is most often used.
As shown in FIG. 1, a general spiral liquid separation element using a reverse osmosis membrane sandwiches a permeated liquid flow path material 2 between two reverse osmosis membranes 1 and supplies the permeated liquid flow path material 2 to the outside of the reverse osmosis membrane. The liquid flow path member 3 is arranged to form a set, and one set or a plurality of sets of the unit are wound around a hollow central pipe 5 in which the water collecting holes 4 are arranged.

Generally, in a liquid separation element using a reverse osmosis membrane, a differential pressure of about 0.5 to 7 MPa is applied to a supply liquid side and a permeate liquid side in order to efficiently separate and concentrate a liquid. It is necessary for the permeated liquid flow path material to maintain the reverse osmosis membrane without impairing the performance of the reverse osmosis membrane and secure a permeated liquid flow path for such an operating pressure. Therefore, as a permeate flow path material, for example, as proposed in JP-A-62-35802, a single tricot knitted material having a groove on one surface is impregnated with a resin or subjected to heat fusion to give rigidity. Is typical. FIG. 2 shows a cross-sectional shape of a single tricot knitted fabric as a typical permeate flow path material. Grooves 6 and projections 7 which are flow paths of the permeated liquid are formed on one surface at regular intervals.

[0004] In order to improve the performance of the liquid separation element such as the permeate flow rate, rejection rate, rejection rate and / or concentration rate using the permeate liquid flow path material as described above, the permeate flow through the flow path material is required. It is desired to minimize the flow resistance of the fluid.

In general, when the reverse osmosis membrane is not deformed by a pressure load, the flow resistance of the permeated liquid flow path material is determined by the groove width, the groove depth, and the groove density. It is known that at least one of the groove width, the depth, and the groove density should be increased.

[0006] For the reasons described above, in a liquid separation element usually used in a region where the operating pressure is relatively low, the groove width of the single tricot of the permeated liquid flow path material is set within a range in which the reverse osmosis membrane is not easily deformed by pressure. The flow resistance of the permeated liquid is reduced by setting the groove depth to 300 to 600 μm, the groove depth to 150 to 300 μm, and the groove density to about 30 to 40 grooves per inch.

On the other hand, in a liquid separation element used in a region where the operating pressure is high, for example, as shown in FIG. 3, a diameter of 5 μm is provided between a reverse osmosis membrane and a surface having a single tricot groove.
By interposing a porous sheet 9 made of polyester or the like having small holes 8 of 0 to 1000 μm at intervals of about 0.1 to 200 mm, deformation of the reverse osmosis membrane under high pressure is prevented and flow resistance of the permeate is reduced. It has been proposed in Japanese Patent Application Laid-Open No. 54-31087.

[0008]

As described above, most spiral type liquid separation elements at present use a single tricot in which a groove serving as a flow path for a permeated liquid is formed on only one side. When the groove width is increased for the purpose of reducing the resistance, under high pressure, the reverse osmosis membrane is deformed by pressure as shown in FIG. 4 and the drop into the groove is increased, and the flow resistance is rather increased because the groove is closed. There is a problem. Conversely, when the groove width is reduced, the fall of the reverse osmosis membrane into the groove can be suppressed, but the flow path becomes narrow and the flow resistance increases.

In order to reduce the flow resistance of the permeated liquid by increasing the depth of the groove, it is necessary to increase the thickness of the permeated liquid channel material, and the area of the reverse osmosis membrane in the liquid separation element is reduced. As a result, there is a problem that a sufficient permeate flow rate cannot be obtained.

Further, the distance between adjacent grooves is reduced to reduce
When the groove density per inch is increased, the convex part supporting the reverse osmosis membrane also becomes narrow, it is impossible to support high pressure, the tricot itself is compressed and deformed, the groove is crushed and the flow resistance of the permeate is increased The problem arises.

For the above reasons, in order to use under a high pressure, a porous sheet as a permeate flow path material must be interposed between the tricot and the reverse osmosis membrane to secure a permeate flow path. There was no effective way. However, this method also has a disadvantage that the flow path material becomes thicker by the amount of the porous sheet, and if the diameter of the small holes of the porous sheet is large, the reverse osmosis membrane falls into the small holes due to pressure, and reverse osmosis occurs. There is a problem that the membrane is locally deformed and damaged, and the performance of the liquid separation element such as the rejection rate and the concentration rate is reduced.

The present invention solves the above problem, and can secure a sufficient permeate flow path even under high pressure.
It is another object of the present invention to provide a liquid separation element having excellent performance and durability such as a permeated liquid flow rate, a rejection rate, an exclusion rate, and a concentration rate.

[0013]

The object of the present invention can be basically achieved by the following constitution. That is, "a membrane unit including a reverse osmosis membrane and a permeated liquid channel material having a groove and having a groove width smaller than the thickness of the reverse osmosis membrane is formed around a central pipe having a water collection hole. And 5.0% by weight
After supplying a supply liquid at 25 ° C. containing sodium chloride at a pressure of 13 MPa and a flow rate of 20 liters / min for 2 hours, the rejection ratio of the salt is 5.5 MPa and a flow rate of 20 liters / min for 2 hours. A liquid separation element, wherein the liquid rejection rate does not fall below the salt removal rate after the separation. ".

In the present invention, the permeated liquid flow path material, which is a main component, has a structure having grooves parallel to each other on both surfaces as shown in FIG. At this time, the directions of the grooves on both sides of the structure need to be parallel to each other. if,
If the directions of the grooves on both sides are perpendicular to each other, the direction of the grooves on either side will be parallel to the longitudinal direction of the central pipe, so that the permeated liquid will not be smoothly guided to the water collecting holes of the central pipe, and the flow resistance will be reduced. Becomes extremely large and the performance decreases.

The grooves on both sides of the permeate flow path material are located at the same position on both sides, but the deformation of the flow path material itself under high pressure is reduced, and the increase in flow resistance is suppressed. Is preferred in that Although not particularly limited,
The deviation of the center position of the grooves on both sides is preferably 40 μm or less,
More preferably, it is 20 μm or less.

Regarding the groove width of the permeated liquid channel material, in order to prevent the reverse osmosis membrane from falling into the groove under high pressure, 100
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.

[0017] Regarding the depth of the groove of the permeate flow path material, if the depth of the groove is 50 µm or less, the flow path of the permeate liquid becomes small, and even if the reverse osmosis membrane is slightly deformed under high pressure, the flow resistance becomes large. May change. 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.

Furthermore, as described above, the flow resistance of the permeate flow path material changes depending on the groove density, that is, the number of grooves per unit length. Is preferably in the range of 45 to 70 grooves per inch. More preferably, the number is 50 to 60 per inch. Groove density 45 per inch
Below this, the number of flow paths is small, so that the overall flow path area is reduced and the flow resistance is increased. 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. for that reason,
There is a risk that the depth of the groove becomes smaller and the flow resistance increases.

The structure of the permeated liquid channel material in the present invention may be any structure having the above-mentioned structural characteristics, and the type of the structure is not particularly limited. It is preferable to use a double tricot in that the structural characteristics of the above can be realized at high quality and at low cost. In addition, for the double tricot, for example, double half, double denbi, Queen's cord, three-piece, etc., depending on the difference in knitting organization, there are various types, but secure the flow path of the permeate, and even under high pressure Any material that is not easily deformed may be used, and is not particularly limited.

The fiber material of the woven or knitted fabric may be any material as long as it retains the shape of the channel material and has a small amount of components eluted into the permeate. 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 perform a hardening treatment for increasing the rigidity of the woven or knitted fabric in order to suppress deformation of the flow path material itself under 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, when the convex portion of the woven or knitted fabric of the permeate flow path material is not flat, in order to prevent local or non-uniform deformation of the reverse osmosis membrane under high pressure, Preferably, the woven or knitted material of the permeate flow path material is calendered. 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 width is 1
The load per m is 20 to 80 t, more preferably the heating temperature is 60 to 100 ° C., and the load per 1 m width is 40.
６０60t. Needless to say, with respect to fibers of a material other than the polyester fiber, the conditions of the calendering treatment may be appropriately changed according to the difference in physical properties such as the melting point and elasticity. The surface of the woven / knitted fabric by calendering
Fine undulations due to the shape of the fibers are crushed, and the projections become very smooth and flat. For this reason, when calendering is performed with respect to the case where calendering is not performed, the contact area between the reverse osmosis membrane and the convex portion of the flow path material increases, and the entire surface comes into uniform contact, Damage to the reverse osmosis membrane under high pressure is reduced, and as a result, performance degradation such as rejection and concentration is reduced, and durability is improved.

A feature of the present invention resides in an improved permeate flow path material, and is a member of a liquid separation element other than the permeate flow path material, that is, a hollow center tube having a hole on its surface, a semi-finished center tube, or the like. The permeable membrane and the supply liquid channel material 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. However, as described above, the effects of the present invention can be excellently exerted 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 preferable that the reverse osmosis membrane used also has pressure resistance. For example, as a support membrane or an asymmetric membrane of a composite membrane, an A membrane having a pore diameter of 200 nm or less is mainly used.
A layer having a thickness of at least 2 μm, a layer B having a thickness of at least 8 μm, and an A layer having a thickness of at least 8 μm.
The ratio X of the thickness of the layer A to the total thickness of the layer and the layer B is 2
A film having a microporous layer characterized by being at least 0%.

[0026]

EXAMPLES Example 1 and Comparative Example 1 As Example 1 of the present invention, a multifilament of polyester fibers was knitted into a double half structure (yarn diameter 50 denier, knitting condition well 35 / inch, course 50 / inch). Then, this is subjected to heat fusion processing (temperature 250 ° C., processing time 1
Minutes) and cured, calendering (temperature 60 ° C,
By applying a load of 40 t / m), a double tricot having a groove width of 150 μm, a groove depth of 120 μm, a groove density on one side of 50 per inch, and a thickness of 320 μm as shown in FIG. This was used as a permeate flow path material, which was incorporated between two reverse osmosis membranes to obtain a sample for flow resistance measurement.

On the other hand, as Comparative Example 1, a multifilament of polyester fibers was knitted into a double denbi structure (yarn diameter: 60 denier, knitting condition: 25 wells / inch, course: 4).
0 / inch), and heat-sealing (temperature: 245 ° C.,
After processing for 1 minute) and curing, calendering (temperature 60 ° C., load 40 t / m), groove width 300 μm,
A 230 μm thick single tricot with a groove depth of 150 μm, a single-sided groove density of 35 per inch, and a smooth convex portion was prepared and used as a permeate flow path material. Was incorporated between the reverse osmosis membranes to prepare a sample for flow resistance measurement.

Using these samples, a hydrostatic pressure of 0.5 to 10 MPa was applied to the reverse osmosis membrane at a liquid temperature of 25 ° C., and the flow resistance of pure water passing through the permeate flow path material after one hour was measured. Are shown in Table 1.

[0029]

[Table 1] In contrast to the conventional permeated liquid flow path material of Comparative Example 1, the flow resistance rapidly increases due to the pressure load, whereas the flow path material of the present invention is:
A sufficient permeate flow path is ensured even under high pressure,
Even at a pressure of MPa, an increase in the flow resistance could be suppressed up to about twice that under low pressure.

Example 2, Comparative Example 2 Small triangular holes having a diameter of 400 μm were formed at intervals of 10 mm on the same surface as the double tricot permeate flow path material of Example 1 and the single tricot groove of Comparative Example 1. Thickness 1
A permeate flow path material having a shape shown in FIG. 3 on which a 00 μm polyester sheet is laid is incorporated between two reverse osmosis membranes, and a polypropylene net is incorporated outside the reverse osmosis membrane as a supply liquid flow path material. These were wound around a center pipe made of FRP to obtain two types of liquid separation elements having an outer diameter of 4 inches. These were separately loaded into the pressure vessels of the liquid separation apparatus shown in FIG. 6, and a separation experiment was performed using a saline solution as a supply liquid. As the experimental conditions, the salt concentration of the feed solution was 5.0%, the operating pressure was 8 to 13 MPa, the flow rate of the feed solution was 20 liters / min, and the temperature of the solution was 25 ° C. Table 2 shows the measured results.

[0031]

[Table 2] In the conventional liquid separation element, the rejection rate of salt rapidly decreases when the operating pressure is 10 MPa or more, and the rejection rate of salt decreases when evaluated for a long time even at low pressure. The salt exclusion rate did not decrease until 13 MPa. Further, even in the long-term evaluation, no decrease in the salt rejection rate was observed, and the durability was superior to the conventional liquid separation element.

[0032]

According to the present invention, a sufficient permeate flow path is ensured even under high pressure to suppress an increase in permeate flow resistance, and the permeate flow rate, rejection rate, rejection rate, concentration rate, etc. And a liquid separation element having excellent durability.

[Brief description of the drawings]

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

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

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

FIG. 4 is an explanatory view showing deformation of a reverse osmosis membrane under high pressure, which 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 according to the present invention.

FIG. 6 is a schematic diagram 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 collecting hole 5: Central pipe 6: Groove 7: Convex part 8: Small hole 9: Porous sheet 10: Permeation of the present invention Liquid flow path material 11: Raw water (saline) 12: Supply pump 13: Filter 14: High pressure pump 15: Supply water line 16: Liquid separation element (pressure vessel) 17: Concentrated water line 18: Permeate water line

Claims (4)

[Claims] 1. A membrane unit comprising a reverse osmosis membrane and a permeated liquid channel material having a groove and having a groove width smaller than the thickness of the reverse osmosis membrane is provided around a central pipe having a water collecting hole. After supplying a supply liquid at 25 ° C. containing 5.0% by weight of sodium chloride at a pressure of 13 MPa and a flow rate of 20 liter / min for 2 hours, the rejection ratio of the sodium chloride was 5.5 MPa. ,
A liquid separation element, wherein the rejection rate of sodium chloride after supply for 2 hours at a flow rate of 20 liter / min does not fall below. 2. The liquid separating element according to claim 1, wherein the groove width is in a range of 100 to 200 μm. 3. The liquid separating element according to claim 1, wherein the density of the grooves is in a range of 45 to 70 grooves per inch. 4. A fresh water producing method using the liquid separating element according to claim 1 to treat seawater with an operating pressure in a range of 5 to 15 MPa.