JP2000061276A - Composite membrane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To impart high pressure resistance to a membrane and to suppress the change of the separation characteristics of the membrane even under a pressure of a prescribed pressure or higher and the change of the performance with time by forming a separation function layer on a two-layered support membrane consisting of a 1st layer and a 2nd layer having a larger pore diameter than that of the 1st layer and specifying the change rates of the permeation rate coefft. and solute permeation coefft. of the resultant membrane to be a prescribed value or below. SOLUTION: The composite membrane 4 comprises a porous support membrane 2 including a microporous layer 3 having ultrafiltration function or reverse osmotic separation function. The surface of the membrane 4 is coated with a separation function membrane 1 of a different material which exerts a substantial separation function. The change rates of the permeation rate coefft. and solute permeation coefft. of the composite membrane 4 are each <=30%. The membrane having a microporous layer has micropores densely in one face and has an asymmetric structure in which the pore diameter varies gradually and continuously toward the other face. When the composite membrane 4 is used, a high concn. coln. can be separated with high separation performance even in reverse osmotic separation under a pressure exceeding a prescribed value and the membrane 4 has high durability and can stably be used for a long time.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to desalination of seawater, desalination of brackish water, treatment of wastewater and concentration and recovery of valuables, and in particular,
The present invention relates to a composite membrane that can be preferably used when high-concentration non-separated liquid is separated at high pressure.

[0002]

2. Description of the Related Art Conventionally, an asymmetric membrane type cellulose acetate membrane has been used as a semipermeable membrane industrially used (for example, US Pat. Nos. 3,133,132 and 3,13).
3, 137). However, this membrane has problems such as hydrolysis resistance and microbial resistance, and the salt rejection and water permeability were not sufficient. For this reason, the cellulose acetate asymmetric membrane is used for some applications, but has not been put to practical use in a wide range of applications.

In order to make up for these drawbacks, a separation membrane is devised as a semipermeable membrane having a shape different from that of an asymmetric membrane, in which a microporous support membrane is covered with a separation functional membrane which substantially controls the membrane separation performance with different materials. Was done. In the composite membrane, it is possible to select the optimum material for each of the separation function membrane and the microporous support membrane, and various membrane forming techniques can be selected.

Most of the composite membranes currently on the market have a separation functional membrane formed by crosslinking a gel layer and a polymer on a microporous support membrane, and a separation membrane obtained by interfacial polycondensation of a monomer on the microporous support membrane. There are two types, one with a functional film. Specific examples of the former include Japanese Patent Laid-Open Nos. Sho 49-13282, Sho-55-38164, and PB Report 80-18.
2090, JP-B-59-27202, 61-2.
7102 and the like. Specific examples of the latter include US Pat. Nos. 3,744,942 and 3,926,926.
No. 798, No. 4,277,344, Japanese Patent Laid-Open No. 55-147106, No. 58-24303, No. 62-121603 and the like.

These composite membranes have higher desalination performance than the cellulose acetate asymmetric membrane. Further, these membranes are being improved in durability against chlorine and hydrogen peroxide used for sterilization, and are in the stage of expanding their applications. The problem with this type of membrane is that when it is attempted to increase water permeability (low pressure and high production of water), the separation function membrane is applied very thinly, so that defects such as scratches on the microporous support membrane or foreign substances may cause problems. When used as a spiral or plate-and-frame type element in the case of a flat membrane type composite membrane, the separation function membrane is damaged during the operation during element production, and the desalination performance inherent in the membrane On the other hand, the phenomenon that the desalination performance of the element deteriorated often occurred. These are obstacles to the high exclusion property, which has recently been particularly desired. These problems are being solved by improving manufacturing technology, and this high-performance composite membrane is in the stage of being commercially available.

In particular, in order to obtain a permeated liquid having a certain concentration or less, the higher the concentration of the liquid to be separated, the higher the exclusion rate is required. For example, when obtaining a 100 ppm permeate from a 1% solution, the rejection rate may be 99%, but in order to obtain a 100 ppm permeate from a 4% solution, an exclusion rate of 99.75% is required. The demand for high rejection membranes is becoming stronger and stronger.

Further, when performing separation by the reverse osmosis membrane, it is necessary to apply a pressure equal to or higher than the difference between the osmotic pressure of the feed liquid and the osmotic pressure of the permeate liquid to the feed liquid side, and particularly the concentration of the feed liquid is high. If the osmotic pressure is high, a high pressure is required as the operating pressure. Further, the higher the ratio of the amount of the permeated liquid to the supply liquid (this is called the yield), the higher the concentration of the concentrated liquid. For example, in the case of desalination of seawater, the osmotic pressure corresponding to a concentration of 3.5% of seawater is 25.4 atm, and when desalination is performed at a yield of 40%, the concentration of concentrated water is about 6% and the concentration of concentrated water is about 6%. An osmotic pressure corresponding to 6% and an operating pressure of about 45 atm or higher are required. In order to obtain sufficient quality and quantity of permeate, it is necessary to apply a pressure higher than the osmotic pressure corresponding to the concentration of concentrated water to the reverse osmosis membrane by about 20 atm (this pressure is called effective pressure). is necessary. Conventionally, seawater desalination is generally operated under a condition of a yield of about 40% under a pressure of about 60 to 65 atm.

On the other hand, in the case of separation / concentration of a high-concentration solution, there is an example in which the reverse osmosis membrane device is operated for a short period of time at a pressure of 70 atm or more.

[0009]

In the case of seawater desalination, the cost of the permeated water obtained depends on the yield, and it is preferable to increase the yield. However, in actual operation, increasing the yield corresponds to increasing the operating pressure. Conventional membranes are mainly used at medium pressure of 10-30 atm,
Most of the membranes used for desalination of seawater and separation / concentration of high-concentration solutions were used at 60 to 70 atm. These membranes have pressure resistance up to about 70 atm and exhibit sufficient membrane performance when used at pressures lower than this, but exhibit sufficient membrane performance when used at pressures higher than this. It was impossible.

Generally, when pressure is applied to the film, the film is consolidated, but when the pressure is removed, the film returns to its original form. However, when a pressure higher than the limit pressure is applied, the voids of the asymmetric membrane or the support membrane are crushed, or the separation functional membrane is further densified, and the membrane morphology and membrane performance are changed. Specifically, the membrane permeation coefficient becomes small and becomes smaller than the permeated water amount predicted from the original membrane permeation coefficient. On the other hand, since the unevenness of the membrane surface is emphasized, the separation functional film is stretched along with the unevenness and is likely to be damaged, so that the solute permeation coefficient becomes large and becomes lower than the expected rejection rate.

According to the present invention, the pressure resistance is high, and even if a pressure of 70 atm or more is applied, the change in the separation property of the membrane is small, and
It is an object of the present invention to provide a composite membrane having a small change in performance over time when operated at a pressure of 0 atm or higher. Furthermore, 70
If the pressure resistance at atm or higher is improved, the performance stability can be expected to be improved even at the conventional working pressure of 50 to 70 atm.

[0012]

In order to achieve the above object, the present invention basically has the following constitution. That is,
"A separation function layer is provided on a support membrane having a two-layer structure of a first layer having pores and the other layer having a pore diameter larger than the pore diameter of the first layer, The rate of change of the rate coefficient and the rate of change of the solute permeation coefficient are both 30% or less. "

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the determination of the pore size is based on an electron micrograph of a cross section. The electron microscope of the cross section can be measured by analyzing the observation photograph according to the following procedure. First, if there is a membrane backing material such as taffeta or non-woven fabric, these are peeled off, and if it is a hollow fiber membrane or the like, it is cut as it is by the freeze cleaving method to obtain a sample for cross-section observation. This sample was thinly coated with platinum or ruthenium tetroxide, preferably ruthenium tetroxide, and a high resolution field emission scanning electron microscope (UHR-FE-SE) was used at an accelerating voltage of 3 to 6 kV.
Observe in M). As the high resolution field emission scanning electron microscope, Hitachi S-900 type electron microscope or the like can be used.
The electron microscope has a magnification of 1,000 to 50,000.
About twice is preferable. In particular, when measuring the pore diameter and the layer thickness, it is preferably 5,000 to 20,000 times. The pore size can be directly measured from the obtained electron micrograph in consideration of the observation magnification. For example, in an electron micrograph of 5,000 times, a straight line parallel to the cross section having a length of 10 cm is drawn at an arbitrary position in the cross section, and the polymer portion and the polymer-free portion, that is, the pore portion are distinguished on the straight line. It is possible to measure the length of the pore portion of the. The length of each pore portion is the pore diameter.

Further, the main pore diameter of 200 nm or less means that
The number of pores having a pore diameter of 200 nm or less measured on a straight line parallel to the membrane surface is half or more of the number of all pores on a straight line of 10 cm, and the number average pore diameter is 200 nm or less. May be. Further, the thickness of the first layer having a main pore diameter of 200 nm or less (hereinafter, referred to as A layer) means the straight line or the number of boundaries at which the number of pores of 200 nm or less on the above straight line becomes half of all the pores. It is the distance between the straight line at the boundary where the average pore diameter is 200 nm or more and the membrane surface with the smaller pore diameter.
Similarly, the thickness of the second layer (hereinafter referred to as B layer) is the distance between the straight line of the boundary and the membrane surface having the larger pore diameter.

The thickness of the layer A is 2 μm or more, preferably 2 to 100 μm, more preferably 2 to 50 μm. If the thickness of the layer A is too small, the separation performance and pressure resistance are insufficient, and if it is too large, the permeability becomes too small. Also,
The thickness of layer B is 8 μm or more, preferably 8 to 400.
μm, and more preferably 8 to 200 μm. Layer A and B
The total layer thickness is 10 μm to several mm, preferably 10 μm or more from the viewpoint of film strength, and 400 μm or less from the viewpoint of easy handling and module processing. Further, in order for the separation membrane to have sufficient pressure resistance at a high pressure, the ratio X of the thickness of the A layer to the total thickness of the A layer and the B layer needs to be 20% or more. Preferably X is 30% or more,
More preferably, it is 50% or more.

When the boundary between the A layer and the B layer is unclear, complicated or complicated, or when the layer is not clearly formed, the pore diameter is counted to be 200 nm.
With the border as the boundary, the following are group A and the above are group B
Classified into groups, A and B groups are A and B respectively
The determination may be made by virtually reconfiguring the layers and calculating the provisional layer thickness and the ratio X.

In the present invention, the pore size is defined as described above, but conversely the present invention can be understood from the polymer substance. That is, the membrane having the microporous layer has a microstructure in which the polymer substance is agglomerated or fused with polymer particles or cylinders. The thickness of the fine structure formed by aggregating or fusing polymer particles or cylinders having a diameter in the range of 1 to 100 nm is preferably 20% or more of the total film thickness.

The average diameter of these particles or columnar particles is 5 to 80 nm, preferably 10 to 70 nm, more preferably 15 to 50 nm. If the average diameter is too small, the permeability of the separation membrane decreases, which is not preferable. On the other hand, if the average diameter is too large, the surface of the film tends to have irregularities, which is not preferable.

The thickness of the fine pore layer in which the particulate matter or the columnar matter is aggregated or fused in the present invention is 20% or more of the total thickness of the membrane having the fine pore layer, and preferably 30.
% Or more, more preferably 50% or more. When the thickness ratio is small, the relative thickness of the layer having pores with a pore diameter of 200 nm or more is large, and when the pressure is applied, the entire membrane is largely consolidated, which causes a large change in the membrane performance of the separation membrane, which is not preferable. . The absolute value of the thickness of the layer formed by aggregating or fusing the particulate matter or the columnar article varies depending on the total thickness of the film having the microporous layer, but is 1 to 50 μm, preferably 5 to 40 μm, and more preferably It is 10 to 40 μm. If the absolute value of the thickness is too small, the pressure resistance of the separation membrane will be insufficient, and if the absolute value of the thickness is too large, the permeation rate of the membrane will be too low, which is not preferable.

The membrane having a fine pore layer is a membrane having a fine pore layer on at least a part of the membrane, and has a macrovoid layer, a uniform layer, or an ultrafiltration function or a reverse osmosis separation function. A separation functional layer and the like may also be included. The membrane having a microporous layer can, of course, be used as an asymmetric membrane which itself has a separating function such as ultrafiltration or reverse osmosis and in which each part of the membrane is made of the same material. However, especially for use in the reverse osmosis method for desalination of seawater, it is preferable to use a composite membrane in which the membrane surface is coated with a separation functional membrane that substantially controls the separation performance with different materials. That is,
It is a composite membrane in which the membrane having the microporous layer of the present invention is used as a porous support membrane. At this time, the separation functional film is preferably formed on the surface of the dense A layer. The surface of layer A has an average pore diameter of 100.
A dense layer having a thickness of nm or less is preferable. In particular, in the case of an asymmetric membrane in which each part of the membrane is made of the same material, the average pore diameter of the dense layer is preferably 50 nm or less, more preferably 10 nm or less.

The present invention is described in detail below based on a composite membrane using a membrane having a microporous layer as a microporous support membrane, although not particularly limited thereto. Therefore, hereinafter, when simply referred to as "microporous support membrane", it mainly refers to a membrane having a microporous layer, and when simply referred to as "separation membrane", a membrane having a microporous layer or It refers to a composite membrane used as a microporous support membrane.

In the present invention, the term "microporous support membrane" refers to a layer having substantially no reverse osmosis separation performance, and in a composite membrane, it gives strength to a separation function membrane having substantially separation performance. Is used as a support film.

The microporous support membrane of the composite membrane of the present invention is characterized in that the diameter of the particulate matter or the cylindrical article is within the range of 1 to 100 nm. Further, the feature of the present invention is that the thickness of the fine pore layer in which the particulate matter or the columnar matter of the present invention is aggregated or fused is 20% or more of the total thickness of the microporous support membrane.

The present invention will be described with reference to the drawings. Figure 1
FIG. 4 is a schematic view of a cross section of a composite membrane prepared by using a membrane having a microporous layer as a support membrane. A separation membrane, that is, a membrane having a microporous layer or a composite membrane prepared by using it as a supporting membrane is characterized in that the A layer (4) is thicker than the conventional membrane shown in FIG. It should be noted that, since these figures are schematically drawn to facilitate understanding, they are not limited to these, and in an actual separation membrane, for example, the separation functional layer (1) or the microporous layer is used. When the supporting membrane (2) or the boundary between them is not clear, it is possible that the material components of the separation functional layer intrude into the microporous supporting membrane more complicatedly, or the A layer (4) or 200 nm. In some cases, it is difficult to distinguish the void (5) from the layer (B layer) and the boundary.

The total thickness of the microporous support membrane of the present invention is 1 μm
It is preferably from several mm to 10 mm or more from the viewpoint of film strength, and 100 μm or less from the viewpoint of ease of handling and module processing.

Further, in the present invention, the pore size means the voids existing therein and the gaps between polymer particles or columnar particles. In the present invention, the thickness of the layer in which the pores having a pore diameter of 200 nm or more is 8 is the total thickness.
It is preferably 0% or less. More preferably 70%
Hereafter, it is more preferably 50% or less, and if the thickness ratio is larger than 80%, the porosity becomes too large and the pressure resistance of the separation membrane becomes low.

The separation membrane of the present invention has a pore size of 100 n.
The pore volume porosity of the pores of m or less is preferably 25% or more. It is more preferably 35% or more, still more preferably 50% or more. When the pore volume porosity of the pores having a pore diameter of 100 nm or less is less than 25%, the entire separation membrane is largely consolidated when pressure is applied, and the change in the membrane performance is large.

Here, the pore volume porosity can be obtained from the results of DSC (differential scanning calorimetry) measurement or gas adsorption measurement and water content measurement of the separation membrane.

In the DSC measurement, it is possible to measure the diameter of the pores and the weight of the water present in the pores from the DSC curve by utilizing the fact that the freezing point of water in the pores changes depending on the size of the pores. . Considering the specific gravity of water in the pores, the pore distribution curve can be obtained from this. The pore distribution curve shows the pore volume and the total volume of the pores corresponding to it. The total volume of pores with a pore diameter of 100 nm or less is calculated by integrating the portion of the curve with a pore diameter of 100 nm or less. can do. The DSC method can be measured as follows. First, a membrane sample stored in water is taken out, lightly attached water is removed, and then a small amount of sample is packed in a closed pan and weighed. This is loaded on a differential scanning calorimeter (DSC-2 manufactured by Perkin-Elmer). The sample is cooled once and then reheated to -0.3 ° C.
Then, the cooling process is measured at a temperature lowering rate of 0.5 ° C./min or less. When the DSC measurement is performed in this manner, a freezing curve having a peak at a temperature corresponding to the pore radius is obtained. The melting point depression degree or freezing point depression degree ΔT of the pore water has the following relationship with the pore radius r.

R = α / ΔT + t where α is a proportional constant relating to the interfacial tension of water / ice, and t is the thickness of antifreezing water. Antifreeze water is water that is adsorbed on the polymer surface of the membrane and does not freeze. Assuming that t is 1 nm, the horizontal axis of the DSC curve is the pore radius, and the vertical axis heat flux dq / dt is the pore volume change rate dV / dr considering the specific gravity.
By converting to, the pore size distribution curve can be calculated from the DSC curve. The total pore volume of pores having a pore diameter of 100 nm or less can be obtained by integrating the portion of the curve having a pore diameter of 100 nm or less.

On the other hand, in the gas adsorption method, a fixed amount of the freeze-dried sample was put in a measuring cell, and nitrogen gas was used to generate D
The pore distribution curve can be obtained by the H method (Dollimore and Heal method). However, depending on the sample, the morphology changes during freeze-drying and the pore size changes, so care must be taken in the sample used and the treatment method.

The pore volume porosity can be calculated by dividing the pore volume per unit weight of the absolutely dry sample thus obtained by the pore volume per unit weight of the absolutely dry sample.

Further, the water content of the separation membrane is determined by carefully wiping off the water adhering to the sample immersed in water,
The amount of water is weighed and the difference from the absolute dry weight of the sample is taken as the water content, and the amount of water per unit dry weight is calculated. Furthermore, the pore volume per unit weight of the sample can be determined in consideration of the specific gravity of water.

The membrane having a microporous layer of the present invention is preferably an asymmetric membrane. In addition, the layer A or B in the present invention
The layers may have a structure having fine pores each having a uniform pore size, but preferably have an asymmetric structure. The asymmetric structure is a structure that has dense and minute holes on one side and gradually increases to the other side. Further, the pore diameters of the A layer and the B layer are continuously changed, and a film having an asymmetric structure in which the A layer and the B are integrated is preferable.

On the other hand, in the present invention, the permeation rate coefficient (represented by a) represents the weight of the solution that permeates the membrane at a unit time, a unit membrane area and a unit effective pressure, and can be calculated by the following formula.

A (g · cm ⁻² · sec ⁻¹ · atm ⁻¹ ) = F / (P−π ₁ + π ₂ ) × 115.7 × 10 ⁻⁵ (1) where F is 1 day per 1 m ² of the membrane The amount of water permeated into the water is shown in m ³ and is called the permeation flux or the amount of water produced. P is the operating pressure expressed in atm. Further, π ₁ is the osmotic pressure of the feed liquid, and π ₂ is the osmotic pressure of the permeate. The larger a is, the easier the film is to permeate.

Further, the solute permeation coefficient (represented by b) of the membrane represents the amount of solute permeated by the unit membrane area and the unit concentration difference on both sides of the membrane per unit time, and can be calculated by the following equation.

B (cm · sec ⁻¹ ) = (1−R) × a × (P−π ₁ + π ₂ ) / R (2) Here, R is the solute exclusion rate of the membrane, and is the concentration of the supply liquid. It is a value (%) obtained by dividing the difference in the concentration of the permeated liquid by the concentration of the supplied liquid. The smaller this b is, the higher the rejection rate is.

These values a and b are values specific to the membrane and do not depend on the operating pressure or the concentration of the feed liquid. However, in the conventional membrane, if the membrane is used at a pressure exceeding 60 atm, the membrane will be deformed by the pressure and the pressure will be 60 atm.
The values of a and b obtained by measuring below m are different. Expressing the change as a ratio, for example, the value of a becomes smaller by about 40% in the measurement of 90 atm than in the measurement of 56 atm. Further, the value of b becomes larger than 30%. However, the rate of change of these is preferably close to 0, and the rate of change of the value of A is 3 in the composite membrane of the present invention.
It is 0% or less, and is 20% or less in a film having higher withstand voltage. Furthermore, the composite film of the present invention also has a rate of change in the value of b of 3
The rate of change is 0% or less, and the rate of change is 20% or less for a film having higher withstand voltage.

The material of the microporous support membrane is polysulfone,
Homopolymers or copolymers of polyamide, polyester, cellulosic polymer, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, polyphenylene sulfone, polyphenylene oxide and the like can be used alone or as a blend. Here, cellulose acetate, cellulose nitrate and the like can be used as the cellulosic polymer, and polyethylene, polypropylene, polyvinyl chloride, polyacrylonitrile and the like can be used as the vinyl polymer. Among them, polysulfone, polyamide, polyester, cellulose acetate, cellulose nitrate, polyvinyl chloride, polyacrylonitrile,
Homopolymers or copolymers such as polyphenylene sulfide, polyphenylene sulfide sulfone are preferred. More preferably, cellulose acetate, polysulfone, polyphenylene sulfide sulfone, or polyphenylene sulfone is mentioned.Furthermore, among these materials, polysulfone is high in chemical, mechanical and thermal stability and easy to mold. Generally available. Also,
The microporous support membrane may be lined with a cloth, non-woven fabric, paper or the like. When used as a membrane having both a support function and a separation function such as reverse osmosis separation, polyamide, cellulose acetate and the like are particularly suitable as the membrane material.

In the present invention, the term "microporous support membrane" refers to a layer having substantially no reverse osmosis separation performance, and in a composite membrane, it gives strength to a separation function membrane having substantially separation performance. Is used as a support film.

Asymmetric membranes or microporous support membranes are described, for example, in "Office of Saline Water Research and Development Progress Report" No. 359 (1968). Specifically, a solution of polysulfone in dimethylformamide (DMF) is cast on a densely woven polyester cloth or nonwoven cloth to a certain thickness,
It can be obtained by removing the solvent on the surface in air for a certain period of time and then coagulating it in a coagulating liquid such as water, but the microporous support membrane of the present invention is not limited by these production methods.

This microporous support membrane is coated with a separation functional membrane to produce a composite membrane. In the present invention, the separation functional film is a very thin layer having a substantial separation function in the separation film, and may be called a separation functional layer, an active layer, an ultrathin film, or an ultrathin film layer. As a material for the separation functional membrane, a crosslinked or linear organic polymer can be used. In order for the separation membrane to exhibit high separation performance, the polymer should be polyamide, polyurethane, polyether, polyester,
Cellulose ester, polyimide, polyamic acid and vinyl polymer are preferable, and polyamide is more preferable, and aromatic polyamide is particularly preferable. Further, in order to further increase the pressure resistance of the entire separation membrane and further maintain a high rejection rate even at a pressure of 70 atm or higher, these polymers are preferably crosslinked polymers. Crosslinked aromatic polyamides and copolymers thereof are particularly preferable.

The separation functional membrane in the composite membrane of the present invention has a thickness of 1 to 1,000 nm, preferably 5 to 800 n.
m, and more preferably 10 to 500 nm. If the thickness of the separation function membrane is too small, defects will often occur during film formation, or the film will be easily scratched during handling, and defects will also occur when pressure is applied, leading to a reduction in the rejection rate.
On the other hand, if the thickness of the separation functional film is too large, the permeation rate coefficient is extremely reduced, and a sufficient permeation amount cannot be obtained.

The coating of the separation functional membrane in the present invention is a method of coating a polymer, a method of further crosslinking the coated polymer, a method of polymerizing a monomer on the membrane surface of the microporous support membrane, or a membrane of the microporous support membrane. It can be performed by a method of interfacial polycondensation on the surface. In particular, the interfacial reaction method is preferable because a thin and uniform separation functional film can be obtained.

The form of the separation membrane may be a flat membrane or a hollow fiber. In the case of a flat membrane, the separation membrane may be lined with cloth, non-woven fabric, paper or the like. The obtained separation membrane can be used by incorporating a flat membrane into a spiral, tubular, or plate-and-frame module, or by bundling hollow fibers and incorporating them into the module.
The present invention does not depend on the usage of these membranes.

The separation membrane can be used at an operating pressure of about 10 atm, but 50 atm or more, preferably 70 atm.
When used at a pressure of atm or more, more preferably 90 atm or more, the pressure resistance effect can be exhibited and a high permeation rate can be obtained. Considering the capacity of the high-pressure pump, the piping material, the pressure resistance of the membrane element or the member of the module, the working pressure is 60 to 200 atm, preferably 70 to 150 atm.

The high-concentration solution in the present invention is a solution having a solute concentration of 0.1% by weight or more. As described above, the reverse osmosis method requires separation at a pressure higher than the osmotic pressure. Is effective for separating a solution having a high concentration of 0.5% by weight or more, preferably 3% or more, more preferably 5% or more. The yield of fresh water is 1
Even with a yield of 0% or less, the membrane of the present invention can stably operate and has an effect of improving durability, but preferably 10% or more,
More preferably, the effect is large when operating at a yield of 20% or more. An aqueous solution is preferable as the type of solution to be separated, and it is particularly effective for desalination of highly concentrated brine, seawater, and concentrated seawater.

[0049]

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

In the following examples, the separation rate (R) of the separation membrane is calculated by the following equation 3, and the permeation rate (F) of the separation membrane is calculated by the following equation 4.

R (%) = {(concentration of feed liquid−concentration of permeate) / concentration of feed liquid} × 100 (3) F (m ³ / m ² · day) = (amount of permeate per day) / (Membrane area) (4) Example 1 Taffeta made of polyester fiber having a length of 30 cm and a width of 20 cm (multi-filament yarn of 150 denier for both warp yarn and weft yarn, weave density length 90 yarns / inch, weft) 67 pieces / inch, thickness 160μ) is fixed on a glass plate, and polysulfone (Udel P manufactured by Amoco Co., Ltd.) is fixed on the glass plate.
3500) 15 wt% dimethylformamide (DM
F) The solution was cast to a thickness of 200 μm at room temperature (20 ° C.), left in the air for a while, and then immersed in pure water for 5 minutes.
A polysulfone microporous support membrane was prepared by standing for a minute.

As a result of electron microscopic observation, the obtained microporous support film was found to have a layer having a thickness of 17 μm in which the particles having a particle size of 5 to 50 nm were aggregated on the film surface side in the A layer. Total film thickness (A
The ratio X of the layer A to the layer + layer B) 55 μm was estimated to be 37%. In addition, the thickness of the layer in which the pores having pore diameters larger than 200 nm exist was 28 μm, which was 51% of the total film thickness in each portion. Furthermore, the pore volume porosity determined by the DSC method was 37%.

The resulting microporous support membrane was immersed in a 3% by weight aqueous solution of 1,3,5-triaminobenzene for 1 minute.
After removing the excess aqueous solution from the surface of the microporous support membrane, a 0.1 wt% solution of isophthalic acid chloride in n-decane was coated so that the surface was completely wet, and allowed to stand for 1 minute. Next, the membrane was made vertical and the excess solution was drained and removed, and then washed with water. The separation membrane thus obtained was adjusted to pH with 3.5% aqueous sodium chloride solution.
Reverse osmosis evaluation was conducted under the conditions of 6.5 at 25 ° C and 56 atm. As a result, the rejection rate was 99.5% and the amount of water produced was 0.6 m ³ / m.
² days performance was obtained. At this time, the permeation rate coefficient a was 2.2 × 10 ⁻⁵ , and the solute permeation coefficient b was 4.9 × 10 −6. Using the same composite membrane, a reverse osmosis evaluation was carried out at a pH of 6.5 at 3.5%, 25 ° C. and 90 atm. As a result, the rejection rate was 99.6% and the permeated water amount was 1.19 m ³ /
It was m ² · day. The transmission speed coefficient a at this time is 2.1 ×
10 ^-5 , solute permeation coefficient b is 5.0 × 10 ^-6 , 90
The ratios of the values of a and b with respect to 56 atm in terms of atm were 0.95 and 1.02, respectively. That is, the rate of change of the permeation rate coefficient was 5%, and the rate of change of the solute permeation coefficient was 2%.

Further, the polysulfone membrane was
The thickness was 55 μm, but after the reverse osmosis evaluation, the thickness was 34 μm.
μm, which is a 38% decrease.

Comparative Example 1 Taffeta made of polyester fibers having a length of 30 cm and a width of 20 cm (vertical yarn, weft multi-filament yarn of 150 denier, weft density 90 warps / inch, weft 6)
7 pieces / inch, thickness 160μ) is fixed on the glass plate,
Polysulfone (Udel P-3 manufactured by Amoco Co., Ltd.
500) 15% by weight of dimethylformamide (DMF)
The solution was cast at a thickness of 200 μm at room temperature (20 ° C.), immediately immersed in pure water and left for 5 minutes to prepare a polysulfone microporous support membrane. As a result of electron microscopic observation, the microporous support film thus obtained had a layer A having a thickness of 10 μm in which particles having a particle diameter of 5 to 20 nm were aggregated on the film surface side, and the entire film was obtained. The thickness of the A layer was estimated to be 15% for the thickness of 65 μm. Also, the pore size is 20
The thickness of the layer with pores larger than 0 nm is 55 μm
Was estimated to be 84 to 90% with respect to the total film thickness in each part. Furthermore, the pore volume porosity determined by the DSC method is 17
%Met.

Example 1 was carried out using the obtained microporous support membrane.
A separation membrane was prepared in the same manner as in. The separation membrane thus obtained was subjected to reverse osmosis evaluation using a 3.5% aqueous sodium chloride solution under the conditions of pH 6.5, 25 ° C. and 56 atm, and as a result, the rejection rate was 99.3% and the amount of water produced. 0.65
Performance of m ³ / m ² · day was obtained. At this time, the permeation rate coefficient a was 2.4 × 10 ⁻⁵ , and the solute permeation coefficient b was 5.3 × 10 5.
It was ^-6 . Using the same separation membrane, reverse osmosis evaluation was carried out at 3.5% sodium chloride aqueous solution pH 6.5, 25 ° C., 90 atm. As a result, the rejection rate was 99.3% and the permeated water amount was 0.88.
It was m ³ / m ² · day. At this time, the permeation rate coefficient a was 1.56 × 10 ⁻⁵ , and the solute permeation coefficient b was 7.69 × 10 ^−6.
And the ratio of the values of a and b to 56 atm at 90 atm was 0.65 and 1.45, respectively. That is, the rate of change of the transmission rate coefficient is 35%,
The change rate of the solute permeability coefficient was 45%.

In addition, the polysulfone membrane was
Although the thickness was 65 μm, it was 36 after the reverse osmosis evaluation.
μm, which is a decrease of 45%.

Example 2 A microporous support film was obtained in the same manner as in Example 1. The resulting microporous support membrane was treated with m-phenylenediamine and 1,3,5
Immersed in a 2% by weight aqueous solution of triaminobenzene for 1 minute. After removing the excess aqueous solution from the surface of the microporous support membrane, a 0.1 wt% n-decane solution of trimesic acid chloride and isophthalic acid chloride was coated so that the surface was completely wet, and the mixture was allowed to stand for 1 minute. did. Next, the membrane was made vertical and the excess solution was drained and removed, and then washed with water. The separation membrane thus obtained was treated with 3.5% aqueous sodium chloride solution at pH 6.5, 25 ° C. and 56 at.
As a result of performing reverse osmosis evaluation under the condition of m.
Performance of 6% and water production of 0.65 m ³ / m ² · day was obtained. At this time, the permeation rate coefficient a was 2.39 × 10 ⁻⁵ , and the solute permeation coefficient b was 3.02 × 10 ⁻⁶ . Using the same separation membrane, a 3.5% sodium chloride aqueous solution pH 6.5, 25
As a result of performing reverse osmosis evaluation at 90 ° C and 90 atm, the rejection rate was 9
The water content was 9.7% and the amount of permeated water was 1.12 m ³ / m ² · day.
At this time, the permeation rate coefficient a was 1.98 × 10 ⁻⁵ , the solute permeation coefficient b was 3.41 × 10 ⁻⁶ , and the ratio of the values of a and b to 56 atm at 90 atm was 0.83. , 1.19. That is, the rate of change of the permeation rate coefficient is 17%, and the rate of change of the solute permeation coefficient is 19%.
%Met.

Further, the polysulfone membrane was
The thickness was 55 μm, but after the reverse osmosis evaluation, the thickness was 29 μm.
μm, which is a 38% decrease.

Comparative Example 2 A microporous support film was obtained in the same manner as in Comparative Example 1. A separation membrane was produced in the same manner as in Example 2 using the obtained microporous support membrane. When the produced separation membrane was subjected to reverse osmosis evaluation in the same manner as in Example 2, the performance at 56 atm was an exclusion rate of 99.4% and a permeated water amount of 0.63 m ³ / m ² · day. At this time, the permeation rate coefficient a was 2.3 × 10 ⁻⁵ , and the solute permeation coefficient b was 4.4 × 10 ⁻⁶ . Using the same separation membrane, 3.5% sodium chloride aqueous solution, pH 6.5, 2
As a result of performing reverse osmosis evaluation at 5 ° C. and 90 atm, the exclusion rate was 99.3% and the amount of permeated water was 0.79 m ³ / m ² · day. The permeation rate coefficient a at this time was 1.4 × 10 ⁻⁵ , the solute permeation coefficient b was 6.25 × 10 ⁻⁶ , and the ratio of the values of a and b to 56 atm at 90 atm was 0.62 each. , 1.42. That is, the rate of change of the permeation rate coefficient is 38%, and the rate of change of the solute permeation coefficient is 4%.
It was 2%.

Further, the polysulfone membrane was
Although the thickness was 65 μm, it was 36 after the reverse osmosis evaluation.
μm, which is a decrease of 45%.

Example 3 Microporous support was carried out in the same manner as in Example 1, except that the 15% DMF solution of polysulfone used in Example 1 was replaced with an 18% dimethylimidazolidinone (DMI) solution of polyphenylene sulfide sulfone. A film was obtained. As a result of electron microscopic observation, the obtained microporous support membrane had a layer A having a layer of 20 μm in thickness, in which particles having a particle diameter of 5 to 60 nm were aggregated, and the total thickness was 50 μm. A layer is 40%
Was estimated. Further, the thickness of the layer in which the pores having pore diameters larger than 200 nm were 30 μm, which was 60% of the total film thickness in each portion. Furthermore, the pore volume porosity determined by the DSC method was 52%.

Example 1 was carried out using the obtained microporous support membrane.
A separation membrane was prepared in the same manner as in. The separation membrane thus obtained was subjected to reverse osmosis evaluation using a 3.5% aqueous sodium chloride solution under the conditions of pH 6.5, 25 ° C. and 56 atm, and as a result, the rejection rate was 99.3% and the amount of water produced. 0.56m
Performance of ³ / m ² · day was obtained. At this time, the permeation rate coefficient a was 2.06 × 10 ⁻⁵ , and the solute permeation coefficient b was 4.57 × 1.
It was 0 ^-6. Using the same separation membrane, reverse osmosis evaluation was carried out at 3.5% sodium chloride aqueous solution pH 6.5, 25 ° C. and 90 atm. As a result, the rejection rate was 99.6% and the amount of permeated water was 1.1.
It was 3 m ³ / m ² · day. The permeation rate coefficient a at this time was 2.0 × 10 −5, the solute permeation coefficient b was 5.2 × 10 ⁻⁶ , and the ratio of the values of a and b to 56 atm at 90 atm was 0.97. , 1.14.
That is, the rate of change of the permeation rate coefficient was 3%, and the rate of change of the solute permeation coefficient was 14%.

In addition, the polysulfone membrane was
Although the thickness was 50 μm, it was 33 after the reverse osmosis evaluation.
μm, which is a decrease of 34%.

Comparative Example 3 A microporous support membrane was prepared in the same manner as in Example 3, except that the polymer solution was cast and then immediately solidified. As a result of electron microscopic observation, the obtained microporous support film had a layer 5 A having a thickness of 5 μm, in which particles having a particle size of 5 to 25 nm were aggregated, on the film surface side, with respect to the total film thickness 45 μm. Layer A was estimated to be 11%. Further, the thickness of the layer having pores having pore diameters larger than 200 nm was 40 μm, and was estimated to be 89% of the total film thickness in each portion. Further DSC
The pore volume porosity determined by the method was 18%.

Example 2 was performed using the obtained microporous support membrane.
A separation membrane was prepared in the same manner as in. The separation membrane thus obtained was subjected to reverse osmosis evaluation in the same manner as in Example 2. As a result, the performance at 56 atm was an exclusion rate of 99.4% and a water production of 0.63 m ³ / m ² · day. Was given. At this time, the permeation rate coefficient a was 2.3 × 10 ⁻⁵ , and the solute permeation coefficient b was 4.4 × 10 ⁻⁶ . 3.5% using the same separation membrane
Aqueous sodium chloride solution pH 6.5, 25 ° C, 90 atm
As a result of reverse osmosis evaluation, the exclusion rate was 99.3%, and the permeated water amount was 0.79 m ³ / m ² · day. At this time, the permeation rate coefficient a was 1.4 × 10 ⁻⁵ , and the solute permeation coefficient b was 6.25.
X10 ^-6 , and the ratio of the values of a and b to 56 atm at 90 atm is 0.62 and 1.4, respectively.
It was 2. That is, the rate of change of the transmission rate coefficient is 38%
The rate of change in the solute permeability coefficient was 42%.

Further, the polysulfone membrane was
Although the thickness was 45 μm, it was 24 after the reverse osmosis evaluation.
μm, which is a decrease of 47%.

Since the A layer is hard to be crushed and the B layer is easily crushed, the conventional film and the film of the present invention have the same crushing method of voids of 200 nm or more, but the ratio of the A layer and the B layer is different, so that the total film thickness changes and The change in porosity was different.

By verifying the separation performance, it was revealed that the composite membrane of the present invention has a sufficient exclusion rate and a sufficient water permeation rate, has high durability, and can be stably used for a long time. Further, it was revealed that the film having a microporous layer has a strong pressure resistance due to the reduction rate of the thickness.

[0070]

According to the composite membrane of the present invention, especially 60 at
When performing reverse osmosis separation at a pressure exceeding m, a high-concentration solution can be separated with high separation performance. Further, in the desalination of seawater, seawater and high-concentration seawater can be desalinated with high yield, low energy, and low cost, and the obtained water has good water quality and a large amount. The composite membrane of the present invention has high durability and can be used stably for a long time.

[Brief description of drawings]

FIG. 1 is a schematic view of a cross-sectional shape of a conventional separation membrane parallel to the machine direction.

FIG. 2 is a schematic view of a cross-sectional form parallel to the machine direction of the separation membrane of the present invention.

[Explanation of symbols]

1: Separation functional membrane 2: Microporous support membrane 3: Micropore 4: Layer A 5: 200nm or more void

Claims (6)

[Claims] 1. A separation functional layer is provided on a support membrane having a two-layer structure of a first layer having pores and a second layer having a pore diameter larger than the pore diameter of the first layer. And
A composite membrane, characterized in that the rate of change of permeation rate coefficient and the rate of change of solute permeation coefficient are both 30% or less. 2. The composite membrane according to claim 1, wherein the main pore diameter of the first layer is 200 nm or less. 3. The composite membrane according to claim 1, wherein the separation functional layer is provided on the first layer. 4. The composite membrane according to claim 1, wherein the ratio of the thickness of the first layer to the thickness of the support membrane is 20% or more. 5. The composite membrane according to claim 1, wherein the separation functional layer contains a crosslinked aromatic polyamide. 6. A method for producing water, which comprises using the composite membrane according to any one of claims 1 to 5 to treat seawater at an operating pressure of 50 atm or more.