JP3467940B2 - Composite membrane, method of making and using the same - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a high performance composite membrane for separating a liquid mixture, a method for producing the same, and a method for using the same. The composite membrane of the present invention can be used for desalination of seawater, desalination of brackish water, treatment of wastewater, and concentration and recovery of valuable materials. In particular, the composite membrane of the present invention is effective in separating a high-concentration non-separated liquid 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 composite 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 the water permeability (low pressure and high water production), the separation function membrane is applied very thinly, which causes defects due to scratches on the microporous support membrane or foreign substances. 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 and a method of using the composite membrane, the performance of which is small with time when operating at a pressure of 0 atm or higher. Further, if the pressure resistance at 70 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]

To achieve the above object, the present invention basically has the following constitution.

That is, "a composite membrane comprising a separation functional membrane and a microporous support membrane, characterized by having a separation functional membrane having a fold with an equivalent circular diameter of 150 nm or less."

In the present invention, the microporous support membrane is a layer having substantially no separation performance, and in the composite membrane, the support membrane is used to give strength to the separation functional membrane having substantially separation performance. Is used as. Microporous membrane has uniform fine holes or dense and fine holes on one side,
It has an asymmetric structure with gradually increasing fine pores to the other side, and the size of the fine pores is 1 on the dense surface of one side.
A structure having a thickness of 00 nm or less is preferable.

In the present invention, a microporous support membrane is coated with a separation functional membrane to produce a composite semipermeable membrane. In the present invention,
Separation functional membrane is a very thin layer that has a substantial separation function in the composite membrane. Separation functional layer, active layer, ultra thin film,
It is also called an ultra-thin film layer. As a material for the separation functional membrane, a crosslinked or linear organic polymer can be used. In order for the composite membrane to exhibit high separation performance, the polymer is preferably polyamide, polyurethane, polyether, polyester, cellulose ester, polyimide, polyamic acid or vinyl polymer, more preferably polyamide, and particularly preferably aromatic polyamide. Further, in order to further increase the pressure resistance of the entire composite film and further maintain a high rejection rate even at a pressure of 70 atm or higher, these polymers are preferably crosslinked polymers.
In particular, in order to obtain a separation functional membrane having a pleated structure according to the present invention, a crosslinked aromatic polyamide and its copolymer are preferable.

The thickness of the separation functional membrane of the present invention is 1 to 1000.
nm, preferably 5-800 nm, more preferably 10-500 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 folds of the separation functional film have a height of 1 to 600 n.
m, a small protrusion having a diameter of 1 to 500 nm, which can be observed by a scanning electron microscope photograph or a transmission electron microscope photograph of the surface or cross section of the separation functional film shown below. Furthermore, the size and distribution of individual folds can be obtained by analyzing electron micrographs. For example, in the case of a surface photograph of a scanning electron microscope, platinum or ruthenium tetroxide, preferably ruthenium tetroxide is thinly coated on the surface of a film sample, and a high resolution field emission scanning electron microscope (UHR-) is used at an accelerating voltage of 3 to 6 kV. Observe by FE-SEM).
High resolution field emission scanning electron microscope is Hitachi S-90.
A 0 type electron microscope or the like can be used. Observation magnification is 5,000
0 to 100,000 times is preferable, and 10,000 to 50,000 times is preferable to obtain the distribution of fold size. From the obtained electron micrograph, the size of the folds can be directly measured by a scale or the like in consideration of the observation magnification.

The equivalent circular diameter in the present invention is the same as the area surrounded by the curved line when the folds of the separation functional film observed in the electron microscopic observation photograph of the composite film surface are surrounded by the closed curve. The diameter of the circle of area. The equivalent circle diameter can be obtained by the following method, for example. Obtained 20,000
A 0 × film surface scanning electron micrograph is divided into squares with a side of 10 cm. The actual area is 5 μm square and the area is 25 μm ² . Next, the folds in this square are traced from above, and each fold is represented by a closed curve, and the area is calculated. The area may be obtained by counting the squares of the graph paper, or by cutting the figure and calculating the weight. A circle having the same area as the area of this curve is an equivalent circle and its diameter is an equivalent circle diameter. The average equivalent circle diameter and the distribution of equivalent circle diameters can be obtained by obtaining the area of all the folds in the square and the equivalent circle diameter. Further, the diameter of the transmission circle and its distribution can be obtained by taking an electron micrograph or a morphological drawing of folds traced from the electron micrograph into a computer and performing image processing. For example, it can be calculated by the image processing software "P'-Analyzer" using the "PIAS-IV" device manufactured by Pierce Co., Ltd. Furthermore, after obtaining the equivalent circle diameters of all the folds shown in the electron micrographs by these methods, the size of the folds, that is, the distribution of the equivalent circle diameters can be calculated from these numerical values. In the present invention, the average value of the equivalent circle diameter is the average value of the equivalent circle diameters of the folds within an arbitrary 5 μm square obtained here, and in the present invention, the ratio of the number of folds of 150 nm or 120 nm or less is the equivalent. It is the ratio of folds of 150 nm or 120 nm or less in the distribution of circle diameters. It should be noted that there is no problem even if the folds below the observable limit of the electron microscope are cut off and calculated, and the lower limit value is not particularly limited, but preferably about 5
nm or more, more preferably 10 nm or more, still more preferably 20 nm or more.

Conventionally, it has been reported that such a fold structure is observed in the composite film formed by the interfacial polycondensation method, but the size thereof is larger than 150 nm on average,
Small pleats with an average of 150 nm or less found in the present invention have not been found. As a result of various studies, it has been found that, particularly in the case of a composite membrane used at high pressure, a smaller fold size is preferable because of higher separation performance and pressure resistance.
The size of the folds is preferably 150 nm or less in average value of equivalent circle diameters, and the distribution thereof is equivalent circle diameter 15
It is preferable that the ratio of the number of folds of 0 nm or less is 60% or more. More preferably, the equivalent circle diameter is 120 nm
The following is 60% or more. The distribution of these equivalent circular diameters is also preferably narrow, and those having a diameter of 150 nm or more are preferably 10% or less.

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

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. Further, among these materials, polysulfone, polyether sulfone, polyphenylene sulfide sulfone, and polyphenylene sulfone can be preferably used because they have high chemical, mechanical and thermal stability and are easy to mold. Further, these microporous support membranes may be backed with cloth, non-woven fabric, paper or the like.

The microporous support membrane of the present invention is prepared, for example, by casting a solution of polysulfone in dimethylformamide (DMF) on a densely woven polyester cloth or non-woven cloth to a certain thickness, and keeping the surface of the surface in air for a certain time. It can be obtained by removing the solvent 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.

The supporting film is not particularly limited, but a film having a structure size and pressure resistance equivalent to those of the separation functional film is preferable. If a specific example of a preferable support film is given, for example, it has two layers of an A layer having a pore diameter of mainly 200 nm or less and a B layer of 200 nm or more, and the A layer has a thickness of 2 μm or more and a B layer. Is 8 μm or more, and the ratio X of the thickness of the A layer to the total thickness of the A layer and the B layer is 20.
%, And a film having a microporous layer.

In such a supporting film, the pore diameter is determined by an electron micrograph of the 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 magnification of the electron microscope is preferably about 1,000 to 50,000 times. In particular, when measuring the pore diameter and the layer thickness, 5000 to 20000 times is preferable. The pore size can be directly measured from the obtained electron micrograph in consideration of the observation magnification. For example, in a 5000 times electron micrograph, a straight line parallel to the cross section having a length of 10 cm is drawn at an arbitrary position of the cross section, and the polymer portion and the polymer-free portion, that is, the pore portion are distinguished on the straight line, The length of the hole portion can be measured. The length of each pore portion is the pore diameter.

The main pore size 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. Furthermore, A with a main pore size of 200 nm or less
The layer thickness means the straight line of the boundary where the number of pores of 200 nm or less on the above straight line is half of all the pores or the straight line of the boundary where the number average pore diameter is 200 nm or more and the membrane having the smaller pore diameter. The distance from the surface. Similarly, the thickness of layer B is the distance between the straight line at 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 of the present invention to have sufficient pressure resistance at 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. X is preferably 30% or more, more preferably 50% or more.

When the boundary between the A layer and the B layer is unclear, is complicatedly complicated, or 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 above description, the pore size is defined, but conversely, the present invention can be understood from the polymer substance. That is, in the membrane having such a microporous layer, the polymer substance has a fine structure in which polymer particles or cylinders are aggregated or fused. And the diameter is 1
It is preferable that the thickness of the fine structure formed by aggregating or fusing polymer particles or cylinders within the range of 100 nm is 20% or more of the total film thickness.

The average diameter of these particulate materials or cylindrical materials 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 columnar matter in the present invention is agglomerated or fused is 20% or more, preferably 30% of the total thickness of the membrane having the fine pore layer.
Or more, More preferably, it is 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 film having a micropore layer is a film having a micropore layer in at least a part of the film, and may further include a macrovoid layer, a uniform layer and the like.

The separation functional film is preferably formed on the surface of the dense A layer. The surface of the layer A is preferably a dense layer having an average pore diameter of 100 nm or less. 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 microporous support membrane of the composite membrane of the present invention preferably contains a particulate matter or a columnar article in a diameter range of 1 to 100 nm. Further, the thickness of the microporous layer formed by aggregating or fusing the particulate matter or the columnar matter is preferably 20% or more of the total thickness of the microporous support membrane.

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, the pore size is a gap between voids (voids) and polymer particles or columnar particles existing therein. The thickness of the layer having pores having a pore diameter of 200 nm or more is preferably 80% or less of the total film thickness. More preferably 70% or less, further preferably 50%
% Or less, and if the thickness ratio is larger than 80%, the porosity is too large and the pressure resistance of the separation membrane becomes low.

The porous support membrane of the present invention has a pore size of 1
It is preferable that the pore volume porosity of the pores of 00 nm or less is 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.

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

In the DSC measurement, the diameter of the pores and the weight of the water present in the pores can be measured 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 placed 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.

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

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,
The microporous support membrane can be obtained by removing the solvent on the surface in the air for a certain period of time and then coagulating it in a coagulating liquid such as water, but the microporous support membrane is not limited to these production methods.

The separation functional membrane of the present invention is coated with a polymer, a method of further crosslinking the coated polymer, a method of polymerizing a monomer on the 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 fold-separated separation functional membrane of the present invention can be easily obtained by a method of interfacial polycondensation on the membrane surface of the microporous support membrane. At this time, the size of the folds, that is, the equivalent circular diameter can be controlled by changing the concentration of each solution for interfacial polycondensation and the additives. In particular, after the aqueous solution of the polyfunctional water-soluble organic substance is applied to the supporting film during the interfacial reaction, the aqueous solution is concentrated on the supporting film,
The equivalent circle diameter can be reduced by reacting a polyfunctional organic substance that reacts with the polyfunctional water-soluble organic substance with a solution in which a solvent immiscible with water is dissolved. Further, using a hydrocarbon having 7 or more carbon atoms as a solvent that is not mixed with water is also effective for obtaining the separation functional membrane of the present invention.

The multifunctional water-soluble organic substances are aromatic that have a two or more reactive groups, which react with substantially be soluble in water polyfunctional reagent to form a crosslinked polymer of the water-insoluble Any reactive group may be used, and the reactive group may be an amino group, a hydroxyl group or the like, and two or more reactive groups may be the same or different. Generally, for example, m-phenylenediamine, p
- phenylenediamine, 1,3,5-triaminobenzene, aromatic amines such as p-xylylenediamine, di <br/> hydroxybenzene, aromatic alcohols such as trihydroxybenzene is used. Reactivity among these, surface or RaKaoru aromatic amines performance of the obtained membrane, particularly m
-Phenylenediamine, p-phenylenediamine, 1,
3,5-triaminobenzene is preferred. These water-soluble compounds having two or more reactive groups in one molecule can be used alone or in combination. These water-soluble compounds are used as a 0.1 to 20% by weight aqueous solution. If necessary, use DMAc, DMSO, D in the aqueous solution.
Other water-soluble compounds such as polar solvents such as MF and NMP may be mixed.

As the polyfunctional reaction reagent capable of reacting with the water-soluble compound, a polyfunctional acid halide, a polyfunctional isocyanate compound or the like can be used. For example, examples of polyfunctional acid halides include trimesic acid halide, benzophenone tetracarboxylic acid halide, trimetic acid halide, pyrometic acid halide, isophthalic acid halide, terephthalic acid halide, naphthalenedicarboxylic acid halide, diphenyldicarboxylic acid halide, pyridinedicarboxylic acid halide. Aromatic polyfunctional acid halides such as benzenedisulfonic acid halide and chlorosulfonylisophthalic acid halide, and aromatic diisocyanate compounds such as toluene diisocyanate are used as the isocyanate compound. Among these compounds, aromatic acid chlorides, particularly isophthalic acid chloride, terephthalic acid chloride, trimesic acid chloride, and mixtures thereof are preferable from the viewpoints of easiness of reaction and separation performance of the obtained membrane. The solvent that dissolves the polyfunctional reactive reagent must be immiscible with water, and it must dissolve the polyfunctional reactive reagent and not destroy the microporous support membrane, forming a crosslinked polymer by interfacial polycondensation. Any one may be used as long as it can. Preferred examples include hydrocarbon compounds, cyclohexane, 1,1,2-trichloro-1,2,2 trifluoroethane and the like, but preferably heptane from the viewpoint of environmental protection, reaction rate and volatility of the solvent, Octane, nonane, decane, undecane, dodecane, etc. If necessary, the compound of the polyfunctional reaction reagent may be mixed with another compound miscible with the solution.

The obtained ultrathin film has a thickness of 5 nm to 10 μm.
m is 1 μm from the viewpoint of water permeability of the semipermeable composite membrane.
The following are preferred. If it is thicker than this, the water permeability may decrease, which is not preferable. If it is thinner than 5 nm, there are problems such as durability, scratches, and defects.

Next, the film forming method will be described.

First, 2 reactive groups were formed on the microporous support membrane.
An aqueous solution (hereinafter referred to as a composition) containing a water-soluble compound having one or more (hereinafter abbreviated as water-soluble compound) is coated. After removing the excess composition, the surface of the microporous support membrane and part of the water in the membrane are evaporated by heating or blowing hot air, and then an organic solvent solution of a polyfunctional reaction reagent is applied, i
An ultra thin film is coated by an n situ interfacial polycondensation reaction. After removing the excess organic solvent solution and volatilizing the organic solvent, the semipermeable composite membrane of the present invention is obtained. The obtained semipermeable composite film may be subjected to a post-treatment such as washing with pure water thereafter, if necessary.

As a method for coating the composition, there are a coating method and a method of immersing the microporous support membrane in the composition. After coating the composition on the microporous support membrane, a liquid draining step is generally provided in order to remove the excess composition, and the liquid draining method includes, for example, holding the membrane surface in the vertical direction. There is a method to let it flow naturally.

After draining, the surface of the microporous support membrane and part of the water in the membrane are evaporated.

As a method for evaporating water, the surface of the film and / or
Alternatively, a method of heating the film by contacting a back surface with a hot plate or a heating roll, a method of heating the film by placing the film in a heated container, a method of heating the film using infrared rays, a heater, or the like. There is a method of heating the film by blowing heated gas to the front surface and / or the back surface of the film.

The heating temperature is 30 to 150 ° C, preferably 60 to 100 ° C, more preferably 60 to 80 ° C. If the temperature is lower than 30 ° C., there is little evaporation of water and there is no effect. On the other hand, when the temperature exceeds 150 ° C, most of the water in the film is evaporated, and the film performance is deteriorated. 10 more
When heated at 0 ° C. or higher for a long time, the amount of evaporation is large and the film performance may be deteriorated.

Due to the relationship with the heating temperature, the heating time may be long if the temperature is low, but shorter if the temperature is high. Specifically, it is preferably 10 seconds to 2 minutes.
More preferably, it is 10 seconds to 1 minute. If it is less than 10 seconds, the amount of water vaporized is small and it is not effective. Also, 2 minutes or more,
Alternatively, if the temperature is higher than 1 minute, the performance may decrease due to excessive evaporation. Further, if the heating is performed for too long, the productivity will be poor.

When blowing hot air, the temperature of the hot air is 25
C. to 150.degree. C., preferably 60 to 100.degree. C., more preferably 60 to 80.degree. Similar to the heating temperature, it is ineffective at low temperatures, and performance is reduced if it is too high.

The spraying time is 10 seconds to 2 minutes, preferably 10 seconds to 1 minute. This is the same as when heating
There is no effect in a short time, and if it is carried out for a long time, the film performance may deteriorate.

The hot air is blown onto the film surface from a blow-out port or a nozzle using a fan or the like, and the wind speed is 0.
It is 5 to 20 m / sec, preferably 5 to 15 m / sec. If the wind speed is low, the evaporation effect is low, and if it is too high, it may evaporate too much to cause deterioration of the membrane performance.

The gas used for the hot air may be air or an inert gas such as nitrogen or argon. Further, it is preferable to use a dry gas for the purpose of evaporating water.

Next, ins of the composition and the polyfunctional reaction reagent
The ultra-thin film is coated by the in situ interfacial polycondensation reaction. The polyfunctional reactive reagent is preferably a polyfunctional acid halide as indicated above. Further, the organic solvent is immiscible with water as described above, and it is necessary that it does not destroy the microporous support membrane by dissolving the reagent, and can form a crosslinked polymer by interfacial polycondensation. Either may be used. The concentration of the reagent is not particularly limited, but if it is too low, the formation of the ultrathin film that is the active layer may be insufficient, which may be a drawback, and if it is high, it is disadvantageous in terms of cost, and therefore, it is preferably 0. 05-1.0 wt%, more preferably 0.1-
It is about 0.5% by weight.

The excess organic solvent solution of the polyfunctional reaction reagent is removed by the subsequent draining step, and the organic solvent is generally evaporated during this period. In some cases, the semipermeable composite membrane of the present invention is obtained by further volatilizing the organic solvent by applying wind or the like.

The composite semipermeable membrane obtained as described above can be used as it is, but it is preferable to remove unreacted residue by washing with water or the like before use. Moreover, you may contact with a chemical | medical solution and may heat-process as needed.

The form of the composite membrane of the present invention may be a flat membrane or a hollow fiber. The obtained composite 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. It does not depend on the usage of these membranes.

The composite membrane of the present invention can be used at an operating pressure of about 10 atm, but when it is used at a pressure of 50 atm or more, preferably 70 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 if the yield is 0% or less, the membrane and separation method of the present invention have the effect of stable operation and durability, but the effect is large when operating at a yield of 10% or more, more preferably 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.

[0066]

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 rejection rate (R) of the composite membrane is calculated by the following equation 1, and the permeation rate (F) of the composite membrane is calculated by the following equation 2.

R (%) = {(concentration of feed liquid−concentration of permeate) / concentration of feed liquid} × 100 (1) F (m ³ / m ² · day) = (amount of permeate per day) / (Membrane area) (2) On the other hand, the solution permeation coefficient (represented by A) is the weight of the solution that permeates the membrane at a unit membrane area and 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 (3) where F is 1 day per 1 m ² of the film. 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 a
It is the operating pressure expressed in tm. Further, π ₁ is the osmotic pressure of the feed liquid, and π ₂ is the osmotic pressure of the permeate.

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 (4) 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.

Example 1 Taffeta made of polyester fiber having a length of 30 cm and a width of 20 cm (a multifilament yarn of 150 denier for both vertical and horizontal threads, weave density vertical 90 threads / inch, horizontal 67 threads / inch, 160 μm thick is fixed on a glass plate, and polysulfone (Udel P manufactured by Amoco Co., Ltd.
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.

The obtained microporous support membrane was immersed in a 2% by weight aqueous solution of m-phenylenediamine for 1 minute. After removing the excess aqueous solution from the surface of the microporous support membrane, the aqueous solution was concentrated with a hot air dryer at 80 ° C. for 1 minute, and then,
A 0.1% by weight solution of trimesic acid chloride in n-decane was coated so that the surface was completely wet, and the solution was 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. When the surface of the obtained composite film was observed with an electron microscope (UHR-FE-SEM), the separation functional layer had fine folds. After tracing the photo, it was imported into a computer with the "PIAS-IV" device manufactured by Pierce Co., Ltd., and the image processing software "P'-Analyze" was used.
Image analysis was performed using r ". The mean value of the equivalent circular diameter of the folds was 13
At 2.9 nm, the distribution is 65% of the total number of folds of 150 nm or less, and 55% of the total number of folds of 120 nm or less.
Met.

The composite film thus obtained was 3.5%
Of sodium chloride aqueous solution of pH 6.5, 25 ℃,
As a result of performing reverse osmosis evaluation under the conditions of 56 atm, a rejection rate of 99.6% and a water production amount of 0.6 m ³ / m ² · day were obtained. The transmission rate coefficient A at this time is 2.48 × 10 ⁻⁵ ,
The solute permeability coefficient B was 2.79 × 10 ⁻⁶ . Using the same composite membrane, 3.5% sodium chloride aqueous solution pH 6.5,
As a result of performing reverse osmosis evaluation at 25 ° C. and 90 atm, the rejection rate was 99.73% and the permeated water amount was 1.06 m ³ / m ² · day. At this time, the permeation rate coefficient A was 1.98 × 10 ⁻⁵ , the solute permeation coefficient B was 3.32 × 10 ⁻⁶ , and the ratio of the values of A and B to 56 atm at 90 atm was 0.8. , 1.19.

Further, a reverse osmosis evaluation was conducted using a 6% sodium chloride aqueous solution under the conditions of pH 6.5, 25 ° C. and 90 atm. As a result, the rejection rate was 99.6% and the amount of water produced was 0.7 m.
Performance of ³ / m ² · day was obtained.

Example 2 The microporous support membrane obtained in Example 1 was immersed in a 3% by weight aqueous solution of m-phenylenediamine and 1,3,5-triaminobenzene for 1 minute. After removing the excess aqueous solution from the surface of the microporous support membrane, the aqueous solution was concentrated with a hot air dryer for 1 minute at 80 ° C., and then a 0.2 wt% n-decane solution of isophthalic acid chloride and trimesic acid chloride. 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. When the surface of the obtained composite film was observed with an electron microscope (UHR-FE-SEM), the separation functional layer had fine folds. When the photograph was image-analyzed in the same manner as in Example 1 to find the equivalent circle diameter of the folds, the average value of the equivalent circle diameters was 92.8 nm, and the number of folds of 150 nm or less was 95% of the whole, and the folds of 120 nm or less. The number was 90% of the whole. The composite membrane thus obtained was adjusted to pH 6.5 with a 3.5% sodium chloride aqueous solution.
As a result of performing reverse osmosis evaluation under the conditions of 25 ° C. and 56 atm, a rejection rate of 99.7% and a water production amount of 0.65 m ³ / m ² · day were obtained. The transmission speed coefficient A at this time is 2.69 ×
The solute permeation coefficient B was ^{10.sup.- 5} and 2.27.times.10.sup.- ⁶ .
3.5% sodium chloride aqueous solution pH using the same composite membrane
As a result of performing reverse osmosis evaluation at 6.5 at 25 ° C. and 90 atm, the exclusion rate was 99.8%, and the amount of permeated water was 1.23 m ³ / m ² · day. The transmission speed coefficient A at this time is 2.29 × 1.
0 ^-5 , solute permeability coefficient B is 2.84 x 10 -6, 90
The ratios of the values of A and B to 56 atm in terms of atm were 0.85 and 1.24, respectively.

Further, a reverse osmosis evaluation was conducted using a 6% sodium chloride aqueous solution under the conditions of pH 6.5, 25 ° C. and 90 atm. As a result, the rejection rate was 99.7% and the amount of water produced was 0.83.
Performance of m ³ / m ² · day was obtained. Comparative Example 1 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 surface of the obtained composite film was observed with an electron microscope (UHR-FE-
When observed by SEM), the separation functional layer had relatively large folds. When the photograph was subjected to image analysis in the same manner as in Example 1 to find the equivalent circle diameter of the folds, the average equivalent circle diameter was 170.2 nm, and the number of folds of 150 nm or less was 3 in total.
7%, and the number of folds of 120 nm or less was 17% of the whole.

The composite membrane thus obtained is
Of sodium chloride aqueous solution of pH 6.5, 25 ℃,
As a result of performing reverse osmosis evaluation under the conditions of 56 atm, a rejection rate of 99.0% and a water production amount of 0.96 m ³ / m ² · day were obtained. The transmission speed coefficient A at this time is 3.97 × 1.
0 ^-5 , the solute permeation coefficient B was 1.12 x 10 ^-5 . 3.5% sodium chloride aqueous solution pH using the same composite membrane
As a result of reverse osmosis evaluation at 6.5 at 25 ° C. and 90 atm, the rejection rate was 99.1% and the permeated water amount was 1.53 m ³ / m ^2.
It was a day. The transmission rate coefficient A at this time is 2.86 × 10.
^-5 , solute permeability coefficient B is 1.59 × 10 ^-5 , 90a
The ratios of the values of A and B with respect to 56 atm at tm were 0.72 and 1.42, respectively, which were large changes.

Further, a reverse osmosis evaluation was carried out using a 6% sodium chloride aqueous solution under the conditions of pH 6.5, 25 ° C. and 90 atm. As a result, the rejection rate was 98.7% and the amount of water produced was 1.03.
Performance of m ³ / m ² · day was obtained, and the desalination rate was low.

[0080]

According to the composite membrane of the present invention and the method of using the same, a high concentration solution can be separated with high separation performance when performing reverse osmosis separation at a pressure of more than 60 atm. Particularly in the desalination of seawater, it is possible to desalinate seawater and high-concentration seawater with high yield, low energy, and low cost, and the obtained water has good water quality and a large amount of water. Further, 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 particle structure electron micrograph (20,000 times) of the composite film of Example 1.

2 is a particle structure electron micrograph (50,000 times) of the composite film of Example 1. FIG.

FIG. 3 A particle structure electron micrograph (20,000 times) of a composite film of Comparative Example 1.

4 is a particle structure electron micrograph (50,000 times) of the composite film of Comparative Example 1. FIG.

FIG. 5: Distribution of fold-equivalent circular diameters by image analysis of particle structure electron micrographs of the composite membranes of Examples 1, 2 and Comparative Example 1.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01D 67/00-71/82 510

Claims (12)

(57) [Claims] 1. A composite membrane comprising a separation functional membrane and a microporous support membrane, which comprises a separation functional membrane having a fold with an average equivalent circular diameter of 150 nm or less. 2. The composite membrane according to claim 1, wherein the number of pleats having an equivalent circular diameter of 150 nm or less of the separation functional membrane is 60% or more of the total number of pleats. 3. A composite film according to claim 1 or 2 wherein the number of equivalent circular diameter 120nm or less folds of the separation function layer is characterized in that at least 50% of the total number of folds. 4. The composite membrane according to claim 1, wherein the polymer forming the separation functional membrane is a crosslinked polymer obtained by an interfacial reaction. 5. The composite membrane according to claim 1, wherein the polymer forming the separation functional membrane is a crosslinked aromatic polyamide. 6. The composite membrane according to claim 1, wherein the microporous support membrane has an asymmetric structure. 7. The microporous support membrane has a pore size of about 200.
nm has a two-layer below the A layer and primarily 200nm or more B layer, the thickness is 2μm or more A layers, a thickness of B layer is 8μm or more and the sum of the thicknesses of the A layer and the B layer the composite membrane of 請 Motomeko 1 wherein you wherein a ratio X of the thickness of the a layer is 20% or more relative to. 8. The composite membrane according to claim 1, wherein the microporous support membrane comprises at least one selected from polysulfone, polyamide, polyester, vinyl polymer, polyphenylene sulfide, polyphenylene sulfide sulfone, and polyphenylene oxide. 9. A polyfunctional compound which reacts with a polyfunctional water-soluble organic compound by applying an aqueous solution of an aromatic polyfunctional water-soluble organic compound to a microporous support film in an interfacial reaction and then concentrating the aqueous solution on the support film. claims organics were reacted with a solution in a solvent of water and non-mixed, characterized by being manufactured by Rukoto
The composite membrane according to any one of 1 to 8 . 10. The composite membrane according to claim 9, which is produced by using a hydrocarbon having a carbon number of 7 or more as a solvent immiscible with water . 11. A high- concentration solution , according to claim 1.
Composite membrane used, the use of multiple Gomaku you characterized by membrane <br/> separated by more than the operating pressure 50atm described. 12. The method of using a composite membrane according to claim 11, wherein the high-concentration solution is a solution having a solute concentration of 0.5% or more.