JP2001252538A - Reverse osmosis composite membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reverse osmosis composite membrane which is designed to prevent the decrease of the amount of filtrate even when the operation returns from a high pressure stable operation to a low pressure stable operation in the reverse osmosis separation of seawater. SOLUTION: A base material 2A, a support membrane 2B having communication holes 2b, and a separation function layer 2C are laminated in turn to form the reverse osmosis composite membrane. When, after a pressure of 5.5 MPa in the thickness direction is applied to the membrane for 3 h and the application is lifted, the average thickness of the support membrane is t0 (μm), and the permeation coefficient of pure water is P1 (g/cm2.s.MPa), and after a pressure of 10 MPa in the thickness direction is subsequently applied to the membrane for 3 h and the application is lifted, the average thickness of the support membrane is t1 (μm), and the permeation coefficient of pure water is p0 (g/ cm2.s.MPa), t0, p0, t1, and p1 simultaneously meet formulas: 0.7<=t1/p0<=1 (1) and 0.6<=p1/p0<=1 (2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reverse osmosis composite membrane incorporated in, for example, a seawater desalination apparatus. The present invention relates to a reverse osmosis composite membrane designed so as not to cause a decrease in the amount of fresh water even when the operation is restored to the above-mentioned steady operation after the operation is performed at a higher operation pressure for a predetermined time.

[0002]

2. Description of the Related Art In a reverse osmosis separation method, a solution containing a solute is permeated through a reverse osmosis membrane at a pressure higher than the osmotic pressure to partially remove the solute, thereby reducing the concentration of the solute. This method is used in, for example, fields such as desalination of seawater, desalination of irrigation, production of ultrapure water, concentration of waste liquid, and recovery of valuable resources therefrom.

[0003] In particular, in the case of seawater desalination, there is no phase change as compared with the evaporation method, energy is saved, and during operation, it is only necessary to apply a predetermined pressure to seawater and supply it to the reverse osmosis membrane. Reverse osmosis separation methods have begun to be widely adopted because operation management is easy. In carrying out this reverse osmosis separation method for seawater, for example, a spiral type reverse osmosis membrane element having a structure as shown in FIG. 7 which is a cross-sectional view along the line VII-VII of FIG. 6 is used.

This element has a plurality of through holes 1a on its surface.
Is formed at the center of the entire element, and its outer peripheral surface is composed of a reverse osmosis membrane 2, a permeated water flow path material 3, and a supplied seawater dew material 4 as shown in FIG. It has a structure in which a laminated sheet is spirally wound. Here, the above-mentioned laminated sheet will be described with reference to FIGS.

[0005] First, the reverse osmosis membrane 2 has a bag shape as a whole, in which a permeated water channel material 3 made of, for example, tricot is accommodated. A plurality of grooves 3a having a predetermined width and depth and extending from the bag binding end 2c of the reverse osmosis membrane 2 to the opening 2d are formed on one surface of the permeated water channel material 3.
Are formed. And since the opening 2d of the bag-shaped reverse osmosis membrane 2 is arranged on the outer peripheral surface of the water collecting pipe 1 so as to surround the through-hole 1a of the water collecting pipe,
The inside of the reverse osmosis membrane 2, that is, the permeated water flow path member 3 communicates with the through hole 1a of the water collecting pipe.

Further, between the respective reverse osmosis membranes 2, a supply seawater flow path material 4 having a mesh structure in which fibers 4a are woven, for example, a rhombus shape in plan view is interposed. Then, the whole of the laminated sheet is spirally wound as shown in FIG. 7, and the above-mentioned spiral structure is held by attaching the frame 5 having the liquid passing structure to both ends of the whole. I have.

The whole element is housed in a pressure vessel, and supplied seawater 6 is supplied at a predetermined pressure from one end (upstream side). The supply seawater 6 flows in the longitudinal direction of the element along the supply seawater flow path member 4 as shown by the arrow in FIG. 6, and in the process, reverse osmosis separation of permeated water and salt by the reverse osmosis membrane 2 Advances.

[0008] The permeated water 6a that has passed through the reverse osmosis membrane 2 passes through the groove 3a of the permeated water channel material 3, passes through the through hole 1a, is collected in the water collecting pipe 1, and is taken out from the downstream end of the element. On the other hand, the supplied seawater that does not permeate the reverse osmosis membrane 2 directly flows through the supplied seawater flow path material 4 and flows downstream, and in the process, takes in the salt separated and removed by the reverse osmosis membrane 2 to obtain a high salt concentration. Of concentrated water 6b.

For example, salt water having a salt concentration of 3.5%
When the permeated water 6a is to be obtained at a fresh water rate of 0%, the seawater is supplied to the above-described element by increasing the pressure to about 6.5 MPa by a pressure increasing pump (not shown). Then, in that case, the concentrated water 6b having a salt concentration of about 5.8% is by-produced in an amount of 60% of the supplied seawater. As the reverse osmosis membrane 2 used in such an element, recently, a composite membrane having the following structure has become mainstream. This will be described with reference to FIG.

The composite membrane 2 is an integrated structure comprising a base material 2A, a support film 2B formed on one side thereof, and a separation functional layer 2C formed on the support film 2B. . The base material 2A is disposed on the permeated water flow path material 3 side, and the separation function layer 2C is disposed on the supplied seawater flow path material 4 side. In the composite membrane 2, the separation function layer 2C located at the uppermost layer
Separates the permeated water from the supplied seawater at a predetermined pressure supplied thereto. In this case, the permeation flux of the permeated water is inversely proportional to the thickness of the separation function layer. Therefore, in order to increase the permeation flux and increase the amount of permeation water, the thinner the separation function layer is, the more advantageous.

The support film 2B located below the separation function layer 2C is a film provided to support and reinforce the separation function layer 2C whose mechanical strength is reduced because it is extremely thin. is there. The support membrane 2B does not necessarily have to have a function of separating supplied seawater, and functions to transmit the permeated water that has passed through the separation function layer 2C to the base material 2A.

For this reason, as the support film 2B, there are usually formed communication holes 2b whose pore diameters gradually increase when viewed macroscopically in the film thickness direction from the separation function layer 2C to the substrate 2A. ing. The base material 2A located below the support membrane 2B is provided for maintaining the strength and shape of the entire composite membrane, and the permeated water that has passed through the support membrane 2B causes gaps between the fibers to pass through. The water then flows to the permeated water channel material.

[0013]

The actual plant changes its operating conditions, especially its operating pressure, in response to, for example, a change in seawater temperature, a change in water quality of the seawater, or a change in a target control value of fresh water production. May be caused. For example, when the actual plant is operated at a certain operating pressure, when high-temperature seawater is supplied, the amount of water permeated by the composite membrane increases. However, as the permeation rate increases,
Fouling components in seawater cause concentration polarization on the membrane surface of the composite membrane, causing a clogging phenomenon, which may make it impossible to secure a stable amount of fresh water for a long period of time.

[0014] Therefore, when the seawater temperature becomes high as in the summertime operation, usually, the operating pressure is reduced to reduce the amount of water permeation so as to suppress the occurrence of concentration polarization on the membrane surface. Is adopted. Also, when the seawater temperature is low, such as during winter operation,
Conversely, steady operation under a higher operating pressure than in summer operation is employed.

Therefore, in the case of this actual plant, in the summertime when the seawater temperature is high, the steady operation at a certain operating pressure (this is referred to as steady operation I) is continued. The operation is switched to the steady-state operation of the operating pressure (this is referred to as steady-state operation II), and the operation is switched to the steady-state operation I again in summer.

This mode of operation forces the composite membrane incorporated in the element to: That is, in both summer and winter, the composite film is forced to be compressed in the film thickness direction for a long period of time, and the film thickness is thinner than in the unused state. The degree of the compression is larger in the steady operation II (winter) than in the steady operation I (summer).

When the operating pressure is increased by switching from the steady operation I to the steady operation II, the base film 2A and the supporting film 2B are compressed in the composite membrane shown in FIG. It becomes thinner than when. In particular, the support film 2B
In the case of (1), the communication holes 2b having a predetermined pore size distribution in the matrix made of the polymer material are crushed, and the whole is brought into a compacted state. As a result, the flow path of the permeated water is closed, and although the separation capability of the separation function layer 2C is increased by the high-pressure operation, the water permeability of the support membrane 2b is reduced. The fresh water performance will be reduced.

If the operation mode is returned to the normal operation I, the support film 2B made of the polymer material is restored to its original state by the elasticity, that is, the film thickness at the time of the normal operation I before switching to the normal operation II. Try to go back. In this case, when the support film 2B completely returns to the original film thickness, the communication holes 2b also return to the original hole diameter distribution. However, as a practical matter, the support film material forcibly keeps the above-mentioned state in the long-term steady operation II. Therefore, the restoring force is deteriorated due to material fatigue, and the state of the steady operation I is not completely restored.
In other words, the thickness of the support film does not completely return to the original state,
Further, the hole diameter distribution of the communication hole 2b does not return to the original state.

The substrate 2A was also operated in a steady operation I and a steady operation II.
A similar state is forced in the process, but the gap between the fibers 2a defining the water permeability of the base material 2A is
Since there is no crushing as in the case of b, the change in water permeability is not so large. As described above, when the steady operation I is switched to the steady operation II, and the steady operation II is switched again to the steady operation I, the water permeation amount at that time is larger than the water permeation amount at the time of the steady operation I before switching to the steady operation II. Also decreases. Therefore, in order to secure the set target management value of the fresh water amount, it is necessary to slightly increase the operating pressure in the steady operation I again to compensate for the reduced water permeation amount. This accelerates membrane deterioration, shortens the cycle of membrane replacement, and increases the operating cost of the actual plant and, consequently, the desalination cost.

According to the present invention, even in an operation mode in which the steady operation II and the steady operation I exemplified above are alternately repeated,
It is an object of the present invention to provide a reverse osmosis composite membrane provided with a support membrane that is designed so that deterioration of water permeability is unlikely to occur and that can solve the above-described problems.

[0021]

In order to achieve the above object, the present inventors have studied a reverse osmosis composite membrane having the structure shown in FIG. With respect to various reverse osmosis composite membranes having different pore distribution states, the pressure load-the change in the thickness of the support membrane when the pressure load was released under the conditions described below, and the pure water permeability coefficient of the support membrane, and the composite membrane were formed. The relationship with the water permeability was examined. As a result, the reverse osmosis composite membrane in which the support membrane behaves as described below, the fact that the water permeability of the reverse osmosis composite membrane is not likely to be reduced even when the switching operation between the steady operation I and the steady operation II is performed. As a result, the reverse osmosis composite membrane of the present invention was developed.

That is, the reverse osmosis composite membrane of the present invention
And a support membrane having a communication hole, and a separation functional layer in this order.
It is made by laminating, and the pressure of 5.5MPa
The average film thickness of the support film after adding and releasing₀(Μ
m), the pure water permeability coefficient is p₀(G / cm ^Two・ S ・ MPa)
Subsequently, a pressure of 10 MPa is applied in the film thickness direction for 3 hours to release
The average film thickness of the support film after the division is t₁(Μm), pure water permeation
Coefficient is p₁(G / cm^Two・ S ・ MPa) and t₀,
p₀, T₁And p₁Is the following equation (1) and (2): 0.7 ≦ t₁/ T₀≦ 1… (1) 0.6 ≦ p₁/ P₀.Ltoreq.1 (2).

Preferably, the following expressions (3) and (4) are satisfied simultaneously: 0.8 ≦ t ₁ / t ₀ ≦ 1 (3) 0.7 ≦ p ₁ / p ₀ ≦ 1 (4) Is a reverse osmosis composite membrane.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The reverse osmosis composite membrane of the present invention is shown in FIG. 1 in which a support membrane having communication holes is formed on a base material, and a separation function layer is further formed thereon. Although there is no difference from the conventional structure, the support film has the following characteristics. First, a pressure of 5.5 MPa was applied to the manufactured reverse osmosis composite membrane in the thickness direction for 3 hours, and the average thickness t ₀ (μm) of the support membrane after release and the pure water permeability coefficient were p ₀ (g).
/ Cm ² · s · MPa) by the method described later. Then, a pressure of 10 MPa is applied to the reverse osmosis composite membrane in the film thickness direction after receiving the above-mentioned pressure for 3 hours, and the average film thickness t ₁ (μm) of the support film after release and the pure water permeability coefficient Is measured as p ₁ (g / cm ² · s · MPa).

The reverse osmosis composite membrane of the present invention is characterized in that the above-mentioned t ₀ , p ₀ , t ₁ and p ₁ simultaneously satisfy the following expressions (1) and (2). 0.7 ≦ t ₁ / t ₀ ≦ 1 (1) 0.6 ≦ p ₁ / p ₀ ≦ 1 (2) At this time, the above-mentioned t ₀ , p ₀ , t ₁ and p ₁ are represented by the following formula ( It is even more preferable that the conditions (3) and (4) are simultaneously satisfied. 0.8 ≦ t ₁ / t ₀ ≦ 1 (3) 0.7 ≦ p ₁ / p ₀ ≦ 1 (4)

Here, the values of t ₁ / t ₀ and p ₁ / p ₀ are indices indicating the ability of the support film to resist consolidation, in other words, indices indicating the strength of the skeleton portion of the support film. It is. As the values of t ₁ / t ₀ and p ₁ / p ₀ are larger, even when a high pressure is applied to the reverse osmosis composite membrane, the voids and pore diameters of the support membrane are less changed, and the state where the communication holes are secured is reduced. Means to maintain. This means that the consolidation of the support film is suppressed and the passage of the processing liquid is maintained. In the case of a support membrane in which the above-mentioned consolidation does not occur at all, the values of t ₁ / t ₀ and p ₁ / p ₀ are 1
Becomes

In the present invention, the value of t ₁ / t ₀ is in the range of 0.7 to ₁ , and the value of p ₁ / p ₀ is 0.6.
By being within the range of ~ 1, consolidation is suppressed, and it is possible to obtain a reverse osmosis composite membrane capable of obtaining a stable amount of fresh water even under a high pressure of, for example, 10 MPa.
In the present invention, the average film thickness and the pure water permeability coefficient refer to values obtained by the method described below.

First, the base film is mechanically peeled from the reverse osmosis composite membrane using tweezers or the like, with an average film thickness. Next, the separation function layer formed on the surface of the remaining support film is removed. This may be removed by using a solvent that does not dissolve or decompose the support membrane but dissolves or decomposes the separation function layer. Specifically, when the constituent material of the separation function layer is polyamide, the separation function layer can be selectively decomposed and removed by immersion in an oxidizing agent such as an aqueous solution of sodium hypochlorite. Using the micrometer, n
= 5 and the average value is defined as the average film thickness.

Next, regarding the pure water permeability coefficient,
The support membrane obtained in this manner was incorporated into the cell shown in FIG.
Perform settings. That is, first, the cell union 1
1 is opened with the handle, and the cover 13 and the filter 16 are removed.
The area S (cm ^Two)) The above support membrane is
On the ring 14, set the filter 15, and hold down
Fit the lid 13 in the order, and finally tighten the union 11
And supply pure water at pressure P (MPa).
Measure the amount of pure water permeated per time T (s) W (g)
The pure water permeability coefficient (g / cm^Two・ S ・ MPa) is W /
It is a value calculated by (S · T · P).

In the present invention, the pressure values when applying pressure in the film thickness direction are set to 5.5 MPa and 10 MPa because the recovery rate of seawater having a salt concentration of about 3.5% using a reverse osmosis membrane ( The obtained percentage of permeate to feed seawater) is 4
This is because, when processing is performed within the range of 0 to 60%, the minimum value and the maximum value of the pressure applied at the time of the driving operation are about the same. Therefore, if the change in the average film thickness and the pure water permeability coefficient between the above pressure values is within a predetermined range, the amount of fresh water can be kept within a certain range even in actual seawater desalination. Specifically, for example, after treating seawater at a high pressure of about 8 MPa for 3 months using the above reverse osmosis composite membrane, and then treating seawater at a low pressure of about 5.5 MPa,
The reduction rate of the water permeability at the time of 5.5 MPa treatment with respect to the water permeability at the time of 8 MPa treatment is at most 1 excluding the effect of fouling.
It can be suppressed to about 5%.

Next, a method for producing the above reverse osmosis composite membrane will be described. First, a resin solution obtained by dissolving a polymer material to be a constituent material of a support film in an organic solvent solution is applied to one side of a base material cut into a predetermined size and shape at a predetermined thickness. Volatilize to form a support film. For example, when polysulfone is used as a polymer material, a predetermined amount thereof is dissolved in dimethylformamide (DMF) to prepare a polysulfone resin solution having a predetermined concentration. Then, after applying this resin liquid on the base material at a predetermined thickness,
Immediately immerse in coagulating liquid such as water. As a result, the surface portion that comes into contact with the coagulation liquid quickly evaporates the DMF of the solvent and coagulates the polysulfone rapidly,
Fine communication holes are formed with the DMF as a nucleus. Further, in the inside from the surface portion toward the base material side, the volatilization of DMF and the coagulation of polysulfone progress more slowly than on the surface, so that DMF easily aggregates to form a large nucleus, and thus is generated. The diameter of the communication hole increases. Of course, the above nucleation conditions gradually change depending on the distance from the membrane surface, so that a support membrane having a smooth pore size distribution without clear boundaries is formed. In the present invention, the above-described reverse osmosis composite membrane can be obtained by controlling the temperature of the resin solution used, the concentration of the polymer material, and the thickness of the coating in the step of forming the support membrane.

In the above, polysulfone has been exemplified as the polymer material. In addition, polyacrylonitrile, polyvinylidene fluoride, polyamide, polyester, polyphenylene sulfide sulfone, polyphenylene sulfone, cellulose acetate and the like can be used. Among them, polysulfone, polyacrylonitrile, and cellulose acetate are preferably used. In particular, polysulfone is preferable because a chemically, mechanically, and thermally stable supporting film can be obtained.

Further, the thickness of the support film to be formed is 1 to 100.
It is preferable to apply the above resin liquid so as to be within the range of μm. As the substrate to be used, for example, it is preferable to use a taffeta or a nonwoven fabric woven of polyester fibers and having a thickness in the range of 10 to 200 μm. By using a fabric made of such fibers as the base material, the resin liquid is filled into the space between the fibers of the base material and then solidified (a portion shown by 2D in FIG. 1). The film is firmly bonded to the substrate.

In the application of the resin liquid, the temperature of the resin liquid, the concentration of the polymer material, and the thickness of the applied liquid are important. First, regarding the temperature, in the present invention, when polysulfone is used as the resin, it is preferable to apply a resin liquid in the range of 20 to 30 ° C. If the temperature is lower than 20 ° C., solidification starts before the phase separation between the resin and the solvent has not sufficiently proceeded, so that the diameter of the formed communication hole tends to be small. On the other hand, when the temperature exceeds 30 ° C., the phase separation proceeds, and the solvent phase which becomes the communication hole grows large, and the communication hole tends to become large, and the change in the average film thickness or the pure water permeability coefficient falls within a predetermined range. It becomes difficult to obtain a certain supporting membrane.

As for the resin concentration, when polysulfone is used, it is preferable to use a resin liquid in the range of 12 to 20% by weight. If it is less than 12% by weight, the pore size of the communication hole tends to be large, and if it exceeds 20% by weight, the pore size of the communication hole tends to be small. It becomes difficult to obtain a support film whose change is within a predetermined range.

Further, the coating thickness is 40 to 70
It is good to be within the range of μm. When the thickness is less than 40 μm, the thickness of the obtained support membrane becomes thin, and the deformation amount of the support membrane under high pressure becomes small. However, it becomes difficult to apply uniformly, and a region where the amount of permeated water differs partially occurs. It will be easier. On the other hand, when it exceeds 70 μm, the water permeability of the support membrane is reduced, and the amount of water produced when the reverse osmosis composite membrane is formed tends to be reduced.

It is preferable to control the time from application of the resin solution to the base material to immersion in the coagulation solution to be 1 to 10 seconds. If the time is less than 1 second, solidification starts before the phase separation between the polymer material and the organic solvent has progressed sufficiently, so that the average pore size tends to be small.
If the time exceeds 0 second, phase separation proceeds, and the solvent phase which will later become a communication hole grows large, and the average pore diameter becomes too large. In any case, the rate of change of the average film thickness or the pure water permeability coefficient is a predetermined value. It becomes difficult to obtain a support film within the range.

As the coagulating liquid, alcohol or water can be used, but pure water is preferably used. After forming the support film as described above, a separation functional layer is formed thereon. This is, for example, by forming a mixed solution containing a monomer and a catalyst on a support film and then proceeding with a polymerization reaction by heating or the like, or by applying an aqueous solution of a polymer on the support film, and then forming a crosslinking agent on the support solution. Or a method of applying an organic solvent solution containing a catalyst and a catalyst, and promoting the cross-linking reaction by heating or the like at the interface between the two to form a solution. Specifically, when forming a separation function layer of polyamide, an aqueous solution containing an amine monomer such as metaphenylenediamine or triaminobenzene is thinly applied on a support film, and then, as a crosslinking agent, an acid chloride such as trimesic acid chloride is used. A method in which an organic solvent solution containing the components is applied and heated to cause a polycondensation reaction at the interface between the two and cross-linking can be employed.

The thickness of the separation function layer is preferably as small as possible because the amount of permeated water increases. However, if the thickness is too small, the strength of the membrane is reduced and defects are likely to occur due to entry of foreign matter. It is preferable to apply the above solution so as to be in the range of 0.1 to 1 μm. The reverse osmosis composite membrane of the present invention described above can be suitably used for a spiral type reverse osmosis membrane element as shown in FIGS.
In addition, as shown in FIG. 5, a reverse osmosis membrane module in which a plurality of elements are housed in series in a pressure vessel can be used.

In FIG. 3, the element 31 includes a supply liquid flow path material 32, a reverse osmosis composite membrane 33, and a permeate liquid flow path material 34.
Is wound around the water collecting pipe 35, and a brine seal 36 is arranged at an end. As shown in FIG. 4, the arrangement of the membrane unit is such that the bag-like body of the reverse osmosis composite membrane of the present invention is interposed between the supply liquid flow path material 32 and the permeate flow path material 34, Is wound in a spiral shape around the entirety, and the whole is housed in a cylindrical case. One end of the bag-shaped body is adhered so as to open and communicate with the through-hole 35a of the water collecting pipe, and the supply liquid flows outside the bag-shaped body, passes through the bag-shaped body, and passes through the inside. And flows into the water collecting pipe through the opening.

In the above-mentioned membrane unit, when a rhombic net is used as the supply liquid flow path material, the flow of the stock solution (supply liquid) is disturbed, and the thickness of the concentration polarization layer can be reduced. This is preferable because the quality of water can be improved. Further, as the permeated liquid flow path material, it is preferable that the permeated liquid flow path material is less deformed by pressure and hardly damages the reverse osmosis composite membrane. For example, a polyester tricot having a groove serving as a permeated water flow path may be used. it can. Further, for the purpose of further suppressing deformation under high pressure, a water-permeable sheet such as a nonwoven fabric may be arranged on the tricot grooved surface.

As shown in FIG. 5, the above-mentioned elements are connected in series via a joint 37 in order.
It can be configured as a membrane module 50 by being housed inside. Note that one end of the water collecting pipe is sealed with a product end cap 42. A supply liquid introduced from a supply liquid port 39 provided on one end side of the pressure-resistant container 38 is guided into the element 31 and supplied to the supply liquid flow path member 32 and the reverse osmosis composite membrane 3.
3. After passing through the permeated liquid flow path material 34 in this order, the water collecting pipe 35
And taken out from the permeated liquid port 40. The concentrated water that has not passed through the reverse osmosis composite membrane 33 is sequentially guided to the downstream element, separated into the permeated water and the concentrated water in the same manner as described above, and finally discharged from the outlet 41. .

The above-mentioned reverse osmosis composite membrane, spiral reverse osmosis membrane, and membrane module use seawater or brackish water as a supply liquid, take out fresh water therefrom, and produce fresh water for use in drinking water or industrial water. Can be used for
In particular, since seawater has a high salt concentration and a high operating pressure, the use of the reverse osmosis composite membrane of the present invention can provide a freshening method in which the quality of permeated water does not deteriorate even at a high pressure.

As the membrane separation apparatus using the above-mentioned membrane module, for example, an apparatus of a single-stage arrangement in which a booster pump and a membrane module or a unit in which a plurality of the membrane modules are connected may be used. Alternatively, a membrane module or unit may be connected in two stages, and a concentrated solution obtained from the first stage may be used as a feed solution in the subsequent stage to form a concentrated solution two-stage apparatus. In this case, it is preferable to provide a first booster pump that supplies the supply liquid by increasing the pressure in the first stage and a second booster pump that further increases and supplies the supply liquid to the subsequent stage. In particular, it is preferable to use energy recovery means such as a turbocharger as the second booster pump, because it is possible to reduce energy consumption and reduce fresh water production costs.

[0045]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Production of Reverse Osmosis Composite Membrane A taffeta woven fabric composed of polyester fibers and having an average thickness of 100 μm and a porosity of 25% was prepared. Also, a nonwoven fabric having the same specifications as above was prepared. On the other hand, polysulfone (Udel P-3500 manufactured by Teijin Acomo Co., Ltd.) was dissolved in dimethylformamide and applied to one surface of the substrate under the conditions shown in Table 1. After the time shown in Table 1, the same temperature as the resin solution was applied. Was immersed in pure water adjusted as described above and left for 5 minutes to take out to form a support film.

Next, each support membrane was immersed in an aqueous solution containing 0.864% by weight of metaphenylenediamine for 2 minutes. Next, after removing excess aqueous solution from the surface of the support membrane, trimesic acid chloride was added at 0.05% by weight.
Was coated so that the membrane surface was completely wetted, and allowed to stand for 1 minute. Then, after removing the excess solution by draining the membrane vertically, thoroughly washed with warm water,
A separation functional layer made of a crosslinked aromatic polyamide and having a thickness of about 0.2 μm was formed.

[0047]

[Table 1]

2. Performance Evaluation of Reverse Osmosis Composite Membrane Three sheets of each of composite membranes 1 to 9 shown in Table 1 were prepared, and FIG.
Each of the cells was set in the cell indicated by, and seawater was supplied at a pressure of 5.5 MPa using a high-pressure pump. After elapse of 3 hours, the desalination rate and the amount of permeated water were measured. The seawater used at this time had a salt concentration of 3.5% by weight, a pH of 6.5, and a temperature of 25 ° C. Then
The pressure is released, and one of the composite membranes is taken out of the cell, and only the support membrane is separated to obtain an average thickness t.
₀ was measured. The support membrane was set in another cell, pure water was supplied under the conditions of a pressure of 0.01 MPa and a temperature of 25 ° C., and the pure water permeability coefficient p ₀ was measured.

Subsequently, the above seawater was supplied to the remaining composite membranes set in the cell at a pressure of 10 MPa for 3 hours, the pressure was released, and one of the composite membranes was taken out. Alone and the average film thickness t ₁ was measured. In addition, this support membrane is set in another cell,
Pure water was supplied under the conditions of a pressure of 0.01 MPa and a temperature of 25 ° C., and a pure water permeability coefficient p ₁ was measured.

Subsequently, the above seawater was again supplied to each of the remaining composite membranes set in the cell at a pressure of 5.5 MPa for 3 hours, and the desalting rate and the amount of permeated water were measured. Table 2 shows the properties and measurement results of the composite membrane.

[0051]

[Table 2]

The following is clear from Tables 1 and 2. (1) A composite membrane having a small change in the thickness of the support membrane due to the application of pressure and a small pure water permeability coefficient shows little change in membrane performance even after application of a high pressure. (2) The change in the thickness of the support film and the change in the pure water permeability coefficient due to the application of pressure differ depending on the film forming conditions such as the concentration of polysulfone, temperature, and coating thickness. (3) The change in the thickness of the support membrane, the pure water permeability coefficient, and the change in the performance of the composite membrane also differ depending on the type of the base material.

From the above, according to the reverse osmosis composite membrane according to the present invention, for example, after operation at 5.5 MPa, 10 MPa
Even if it is operated at a high pressure of 5.5 MPa and then again at a pressure of 5.5 MPa, the support membrane is hardly densified by the application of high pressure, so the performance change of the composite membrane is small and the amount of fresh water is stable within a certain range. Can be realized.

[0054]

As is apparent from the above description, the reverse osmosis composite membrane of the present invention can be used in an actual plant for desalination of seawater into which it is incorporated, from a low-pressure steady operation state to a high-pressure steady operation state. Even if the operation mode is shifted to the normal operation state again at a low pressure, the decrease in water permeability due to the consolidation of the support membrane can be suppressed, so that a stable amount of fresh water can be secured. .

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing an example of a sectional structure of a reverse osmosis composite membrane.

FIG. 2 is a cross-sectional view showing a cell for performance test of a composite membrane.

FIG. 3 is a partially cutaway perspective view showing one example of a reverse osmosis membrane element including the reverse osmosis composite membrane of the present invention.

FIG. 4 is a sectional view taken along line IV-IV in FIG. 3;

FIG. 5 is a schematic view showing a membrane module including the reverse osmosis composite membrane of the present invention.

FIG. 6 is a partially cutaway perspective view showing a spiral reverse osmosis membrane element.

FIG. 7 is a sectional view taken along line VII-VII in FIG.

FIG. 8 is a cross-sectional view showing a sheet-like material arranged on the outer periphery of a water collecting pipe.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 water collection pipe 1a through hole 2 reverse osmosis membrane 2A base material 2a fiber constituting base material 2A 2B support film 2b communication hole of support film 2B 2C separation function layer 2D bonding interface between base material 2A and support film 2B Material 4 Supply seawater flow path material 4a Fiber 5 Frame 6 Supply seawater 6a Permeate 6b Condensed water 11 Tightening union 12 Cell housing 13 Holding lid 14 O-ring 15 Reverse osmosis composite membrane 16 Filter 31 Spiral reverse osmosis membrane element 32 Feed liquid Flow path material 33 Reverse osmosis composite membrane 34 Permeate liquid flow path material 35 Water collecting pipe 35a Through hole 36 Brine seal 37 Joint 38 Pressure-resistant container 39 Supply liquid port 40 Permeate liquid port 41 Outlet 42 Product end cap 50 Membrane module

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) C08J 7/04 CFD C08J 7/04 CFDZ // C08L 67:00 C08L 67:00 (72) Inventor Masahiro Kihara 1-1-1, Sonoyama, Otsu-shi, Shiga Prefecture Toray Industries, Inc. Shiga Plant F-term (reference) 4D006 GA03 HA61 HA65 JA02A JA05A JA06A JA06C KA14 KA52 KA54 KA56 KE03P KE07P KE12P KE15P KE16P KE30P MA03 MA31 MA02 MA02 MC39 MC48X MC54 MC56X MC61 MC62X NA05 NA16 NA17 NA44 NA46 PA02 PB03 PB04 PB05 4F006 AA35 AB00 BA00 CA00 DA04

Claims (7)

[Claims] 1. A support having a structure in which a base material, a support film having communication holes, and a separation function layer are laminated in this order, and a pressure of 5.5 MPa is applied in a film thickness direction for 3 hours to release the support. The average thickness of the membrane is t ₀ (μm) and the permeability coefficient of pure water is p ₀ (g / cm ² ·
s · MPa), a pressure of 10 MPa is applied in the thickness direction for 3 hours, and the average film thickness of the support film after release is t ₁ (μm).
m), and assuming that the pure water permeability coefficient is p ₁ (g / cm ² · s · MPa), t ₀ , p ₀ , t ₁ and p ₁ satisfy the following expressions (1) and (2) simultaneously. Reverse osmosis composite membrane characterized by the following. 0.7 ≦ t ₁ / t ₀ ≦ 1 (1) 0.6 ≦ p ₁ / p ₀ ≦ 1 (2) 2. The reverse osmosis composite membrane according to claim 1, wherein t ₀ , p ₀ , t ₁ and p ₁ simultaneously satisfy the following expressions (3) and (4). 0.8 ≦ t ₁ / t ₀ ≦ 1 (3) 0.7 ≦ p ₁ / p ₀ ≦ 1 (4) 3. The reverse osmosis composite membrane according to claim 1, wherein the support membrane contains polysulfone, and the separation functional layer contains a crosslinked aromatic polyamide. 4. A membrane unit comprising a supply liquid flow path material, the reverse osmosis composite membrane according to any one of claims 1 to 3, and a permeate liquid flow path material wound around a water collection pipe. Spiral reverse osmosis membrane element characterized by the following. 5. A membrane module comprising a plurality of spiral reverse osmosis membrane elements according to claim 4 connected in series and housed in a pressure vessel. 6. A fresh water producing method comprising supplying seawater to the membrane module according to claim 5 to obtain permeated water. 7. An organic solvent solution containing polysulfone in a range of 12 to 20% by weight and having a temperature in a range of 20 to 30 ° C. on a substrate has a film thickness in a range of 40 to 70 μm. A method for producing a reverse osmosis composite membrane, comprising forming a support membrane by immersing the support membrane in a coagulation liquid after coating as described above, and then forming a separation functional layer on the support membrane.