JP3134423B2 - Method for producing composite reverse osmosis membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a method for producing a composite semipermeable membrane for the selective separation of solutes in a solution. More specifically, the present invention relates to a method for producing a crosslinked polyamide-based composite reverse osmosis membrane suitable for desalting can water or seawater.

[0002]

2. Description of the Related Art There are various techniques for removing a substance (for example, a salt) dissolved in a solvent (for example, water). In recent years, a reverse osmosis separation technique has attracted attention as an energy saving and resource saving process. The application of this technology is in desalinating seawater or low-concentration saline water (canned water) to provide industrial, agricultural or domestic water. According to the present technology,
Desalted water can be produced by permeating water containing salt through a reverse osmosis membrane at a pressure higher than the osmotic pressure. For example, drinking water can be obtained from seawater, sewage, canned water, and the like by this technology, and this technology has also been used in the production of industrial ultrapure water, wastewater treatment, and concentration of valuable substances.

[0003] The membrane used in the reverse osmosis method was initially Rob (L
oeb) and cellulose acetate membranes developed by Sourirajan ("Sea Wat").
er Demineralization by means of an Osmotic Membran
e ", in Advances in Chemistry Series # 38, American
Chem. Soc., Washington DC (1963)). This membrane had the advantages of its excellent basic performance and easy manufacturing, but for the purpose of obtaining water of higher purity, salt rejection,
It is insufficient in terms of fresh water performance, and has a drawback in that, during long-term operation, the membrane surface is likely to be degraded by the generation of microorganisms or to be easily degraded by hydrolysis. This membrane is called an asymmetric membrane prepared by a method called a phase separation method, and a dense layer involved in separation and a porous layer involved in maintaining strength of the membrane are made of the same material. A new asymmetric membrane type reverse osmosis membrane made of a synthetic polymer, such as a reverse osmosis membrane made of an aromatic polyamide, has also been proposed to compensate for the drawbacks of the cellulose acetate membrane (USP 3567632).
However, although improvements in terms of biodegradability and the like were made, the reverse osmosis performance had the same problems as the cellulose acetate membrane, and a dramatic improvement in basic performance was expected.

[0004] In response to such demands of the industry, a porous layer is prepared in advance from a certain material, and a hydrophilic reactive polymer and / or monomer is reacted with a crosslinking agent on the membrane surface. A method of forming a thin dense layer has been proposed, and it has been suggested that in addition to the improvement of the basic performance, a significant improvement in hydrolyzability, microbial degradability, pressure tightness, dry storage property, and the like is observed. Such membranes are referred to as composite membranes, and due to their superior performance characteristics, this type of membrane is now widely used. The first example of this type of membrane was developed at the North Star Laboratory in the United States, which uses a polysulfone porous membrane as a porous support membrane, impregnated with polyethyleneimine,
This is obtained by crosslinking with toluene diisocyanate. (USP 4039440) It has been found that the membrane obtained in this way has a very weak crosslinked layer formed due to the amine content of polyethyleneimine being too large, and has major problems in handling such as modularization. In addition, Universal Oil Products has developed a new membrane by using amine-modified polyepichlorohydrin as a hydrophilic reactive polymer (USP 3951815) to remedy the above drawbacks. It has been found that it is difficult to obtain, and there is a problem in long-term durability.

[0005] Although the above-mentioned membranes use a polymer reactive to the formation of a crosslinked layer, Filmtech has developed a composite membrane using a reactive monomer (US Pat. No. 3,926,798).
This membrane uses a polysulfone-based porous membrane as a support membrane, impregnates with an aqueous solution of a polyfunctional amine such as metaphenylenediamine, paraphenylenediamine, and on the membrane surface, a polyfunctional acyl halide such as trimesic acid chloride. Is a so-called crosslinked polyamide-based composite film obtained by applying the above solution and crosslinking the above amine. Since this crosslinked polyamide-based composite membrane has the highest performance among the currently known reverse osmosis membranes and meets the high demands of users, several types of membranes have been announced. (USP 462
6468, USP 4830885, JP-A-60-185903, JP-A-2-187
135).

However, it can be pointed out that this crosslinked polyamide-based composite membrane also has a serious drawback in its manufacturing process. That is, a solvent such as hexane or Freon 113 is generally used as a solvent for the polyfunctional acyl halide solution. Hexane has a low flash point and boiling point,
Sufficient safety measures such as explosion proof must be taken for the storage of the solution and the like, which is extremely disadvantageous from an economical viewpoint as an industrial scale manufacturing process. Freon 113
Such fluorocarbon solvents are considered to be the most frequently used because they are highly safe and easy to produce films with good performance, but their use has recently been regarded as a serious problem as a causative substance of global-scale environmental destruction. I have. Freon is a general term for chlorofluorocarbon solvents, and there are various types.
It has extremely characteristic properties such as non-flammability due to having a fluorine atom in the molecule, non-toxic, easy vaporization or liquefaction, and at the same time has moderate lipophilicity due to having a chlorine atom. It is a substance used in many applications including cleaning agents, refrigerants, and foaming agents. However, it has been pointed out that CFCs have the property of depleting the stratospheric ozone layer and may have a serious impact on the global environment. Among them, the use of fluorocarbons (specified fluorocarbons) listed in the "Law Concerning the Protection of the Ozone Layer by Restricting Specific Substances" is considered to cause particularly large environmental damage. At present, ultraviolet rays having a wavelength shorter than around 300 nm among rays emitted from the sun have not reached the ground because the ozone layer absorbs them. Since this ultraviolet light is a light beam with strong energy, it is extremely harmful to ecosystems, and it is clear that if the ozone layer is destroyed by chlorofluorocarbon, it will be a serious problem for all living things on the earth. The UNEP (United Nations Environment Program) called for the Vienna Convention on the Protection of the Ozone Layer (1985), the Montreal Protocol (1987), and the Helsinki Declaration (1989).
), Regulations on the use of CFCs are being enforced on a global scale. For example, the Helsinki Declaration states that the production and consumption of all specified CFCs will be abolished by about 2000.

[0007] In view of such a situation, it is urgently necessary to develop a process that does not use specific CFCs in the production of composite films. Looking at a specific example of the use of CFCs in the production of a composite membrane, for example, Japanese Patent Publication No. Sho 63-36803 discloses that polysulfone is used as a support membrane material, and m-phenylenediamine or p-phenylenediamine is trimesic acid chloride on the membrane surface. Alternatively, a method for producing a composite film which is crosslinked using isophthalic acid chloride is described, but Freon 113 is used as a solvent for the acid chloride. Also,
Japanese Patent Application Laid-Open No. 1-130707 discloses a production method in which a similar reaction is carried out using piperazine as an amine, but this is also a problem because Freon 113 is used as a reaction solvent.

[0008] When searching for an alternative solvent to CFCs, there is no or little ozone layer destruction, and at the same time flammability,
It is necessary to consider safety during handling such as toxicity. JP-A-62-49909 discloses a method in which polyvinyl alcohol and an amino compound such as piperazine are simultaneously crosslinked using trimesic acid chloride using a polysulfone porous membrane as a support membrane. Here, low-boiling hydrocarbon solvents such as n-hexane and cyclohexane are used as solvents for dissolving trimesic acid chloride.These solvents do not have ozone layer destruction ability and have low toxicity. Most have a flash point of 0 ° C. or lower, and can be said to be extremely flammable and extremely dangerous solvents for handling. This is particularly problematic for production on an industrial scale.

[0009]

SUMMARY OF THE INVENTION The present invention uses a non-flammable or high flash point fluorinated hydrocarbon solvent which is safe during handling without destroying the ozone layer, and provides high separation performance and high water production. It is an object of the present invention to provide a method for producing a composite semipermeable membrane having the following.

[0010]

The present invention has the following arrangement. That is, `` is nonflammable when producing a composite reverse osmosis membrane obtained by interfacial polycondensation of a polyfunctional amine and a polyfunctional acyl halide on a porous polymer support membrane, and a crosslinked polyamide layer as a barrier layer, Alternatively, a method for producing a composite reverse osmosis membrane, comprising using a fluorinated hydrocarbon solvent having a flash point of 20 ° C. or higher as a solvent for a polyfunctional acyl halide. ” Micropores having an average pore diameter (diameter) of 20 to 5000 angstroms, particularly those having an average pore diameter of 30 to 300 angstroms, are preferably used. A film having a thickness of 10 to 300 μm, particularly preferably 30 to 200 μm, is suitable. The material is, for example, polysulfone, polyethersulfone, polyacrylonitrile, cellulose ester, polyphenylene oxide, polypropylene, polyvinyl chloride, polyphenylene sulfide sulfone, polyphenylene sulfone, etc. are used, even if the shape is a hollow fiber even if the shape is a flat membrane, It may be tubular. These films may be reinforced with a woven or nonwoven fabric.

In one example of the method for producing the porous polymer support membrane, a dimethylformamide solution of polysulfone having a concentration of 12 to 25% by weight is cast on a support such as a nonwoven fabric, and immersed in a coagulation bath. I do. As the coagulation bath, water or a mixture of water and a solvent is preferable. After casting the polysulfone solution on a support, the solvent may be evaporated for a certain period of time and then immersed in a coagulation bath. In general, the time for evaporating the solvent is 0 to 60 minutes, particularly preferably 1 to 10 minutes, and the temperature is 0 ° C to the boiling point of the solvent, more preferably 5 ° C to {the boiling point of the solvent-50 ° C}.

The produced porous polymer support membrane can be stored in pure water. However, in order to prevent the generation of microorganisms on the membrane surface, an aqueous solution of sodium hypochlorite having a concentration of 1 to 10 ppm is used. It is desirable to carry out inside. The polyfunctional amine used in the present invention is an aliphatic, aromatic, hetero compound, alicyclic compound or polymer having two or more primary and secondary amino groups in the same molecule. Further, those having a solubility of 0.1% by weight or more in water at room temperature are preferable. Specific examples include m- or p-phenylenediamine, piperazine, 2-methylpiperazine, N, N-dimethylethylenediamine, 1,3,5-
Triaminobenzene and the like can be mentioned. Moreover, you may use these mixtures.

The water used for preparing the aqueous polyfunctional amine solution should preferably be pure water, and in particular, should not contain any substance that inhibits the reaction between the amine and the acyl halide. is there. Specifically, distilled water, reverse osmosis membrane permeated water and the like are preferably used.

The concentration of the polyfunctional amine aqueous solution is 0.5 to 1
The content is desirably 0% by weight. When hydrochloric acid or the like is generated during the reaction with the crosslinking agent, a scavenger such as sodium hydroxide, sodium carbonate, sodium phosphate, triethylamine and the like may be allowed to coexist.

The polyfunctional acyl halide used in the present invention is an aliphatic, aromatic, hetero compound or alicyclic compound containing two or more acyl halide groups in the same molecule. Examples thereof include isophthaloyl chloride, terephthaloyl chloride, trimesic acid trichloride, and 1,2,4-benzenetricarboxylic acid trichloride.

In the method of the present invention, the solvent for preparing such a polyfunctional acyl halide solution (crosslinking agent solution) is a non-flammable or fluorinated hydrocarbon solvent having a flash point of 20 ° C. or higher. Is used. The most important alternative to CFCs is that they have no or low ozone-depleting potential, but according to the current mechanism of ozone depletion, chlorine in ozone-depleting substances such as CFCs Atoms cause ozone depletion. Therefore, it is most desirable to select a substance that does not contain a chlorine atom as the chlorofluorocarbon alternative solvent, and from this point, these fluorinated hydrocarbons are suitable for use as a solvent. If the flash point is lower than 20 ° C., the fluorinated hydrocarbon solvent is dangerous in handling, and therefore is nonflammable or has a flash point of 2 ° C.
It must be at least 0 ° C. Further, it is necessary that the porous polymer support membrane is not affected. Preferably, a film having good film forming properties is selected.

On the other hand, if the boiling point is higher than 300 ° C., the time required for evaporating the solvent becomes extremely long, so that a film having high performance cannot be obtained, and it is difficult to handle a solvent having a boiling point of 20 ° C. or lower at room temperature. It is preferably a fluorinated hydrocarbon solvent having a boiling point of about 20 ° C. or more and about 300 ° C. or less.

The fluorinated hydrocarbon used in the present invention is a hydrocarbon in which a hydrogen atom in a molecule is partially or entirely replaced with a fluorine atom. Among them, a saturated aliphatic, alicyclic aliphatic hydrocarbon or aromatic hydrocarbon in which a hydrogen atom in a molecule is partially substituted with a fluorine atom is preferably used.
In this case, the aliphatic hydrocarbon preferably has about 6 or more carbon atoms. Further, the higher the substitution ratio of fluorine atoms, the lower the boiling point and the higher the flash point. Therefore, the substitution ratio at which the boiling point is not lower than about 20 ° C. and the flash point is 20 ° C. or higher is desirable. . On the other hand, if the substitution ratio of fluorine is too high, the solubility of the acyl halide decreases, which is not preferable. The optimum substitution rate depends on the substance, but is about 4
It is in the range of 0 to 100%. Specific examples of solvents suitable for the method of the present invention include perfluoromethylcyclohexane, perfluorodimethylcyclohexane, perfluorohexane, 1-hydryl-perfluoro-n-heptane, 1,1-dihydryl-perfluoro-n-heptane, pentafluoro Toluene, α, α, α, α ', α
', Α'-hexafluoro-m-xylene, α, α,
α, 2,3,5,6-heptafluoro-p-xylene,
Bis (trifluoromethyl) benzene and the like can be mentioned. Further, a mixture thereof may be used.

The concentration of the crosslinking agent solution is preferably from 0.01 to 1% by weight. If the concentration is lower than this, a crosslinked layer is not easily formed, and a film having a low salt rejection rate is obtained. Conversely, if the concentration is high, a thick crosslinked layer is formed and a film having a low water production amount is obtained.

The time for applying the crosslinking agent solution to the film surface is preferably from 10 seconds to 5 minutes. If the coating is applied for a longer time than this, a film having a low amount of fresh water tends to be formed.

After the application of the crosslinking agent solution to form a dense layer, it is necessary to evaporate the solvent. This means that the concentration of the crosslinking agent liquid is increased by evaporating the solvent to promote the crosslinking reaction, and the reaction is completed when the solvent is completely evaporated. In evaporating the solvent, it is necessary to efficiently evaporate the solvent at a constant speed. If the time required for the evaporation is too long, the reaction proceeds for a long time, and a thick crosslinked layer tends to be formed, which tends to form a film with a low water production amount. When a solvent having a relatively low boiling point is used in the solvent specified in the present invention, the solvent is drained and the solution is allowed to stand at room temperature for 20 seconds to 1
The solvent can be properly evaporated by leaving it alone for about a minute, but if the boiling point is higher than about 100 ° C., it is necessary to devise heating and blowing. Among these, the evaporation method by heating may not be able to obtain a film with a high water production amount depending on the type of the solvent to be used. In this method, the wind speed on the film surface during solvent evaporation is 2 to 20 m / s.
ec, particularly preferably 3 to 10 m / sec, and a temperature of 10
It is important to blow air at 80 ° C., particularly preferably 20-40 ° C., onto the membrane. The wind speed and temperature are 1
Measure at 0 mm point. The use of air at a lower temperature and a lower wind speed than the above range lowers the efficiency of evaporation and degrades the performance of the film, while the use of a high-temperature air causes oxidation of the amine and does not provide good results. Further, it is desirable that the atmospheric humidity at the time of solvent evaporation is in the range of 0 to ³⁰ g / m ³ in absolute humidity and 0 to 70% in relative humidity. When the humidity is higher than this, the performance of the obtained film tends to decrease.

After the reaction is completed and the solvent is evaporated, the film needs to be sufficiently washed with water to remove unreacted acyl halide.

[0023]

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

The reverse osmosis performance of the membrane obtained in the example was determined by using a 1500 ppm saline solution at a temperature of 25.degree.
It was supplied under the condition of kg / cm ² , and evaluated by measuring the salt exclusion rate and the amount of fresh water. The salt exclusion rate was determined by the following equation.

Salt rejection (%) = (1- (NaCl concentration in permeate) / (NaCl concentration in feed solution)) × 100 Example 1 A dimethylformamide solution comprising 15% by weight of polysulfone on a nonwoven fabric made of polyester Was cast to a thickness of about 100 microns and immediately immersed in a water bath at room temperature to cause gelation, thereby obtaining a non-woven fabric reinforced polysulfone porous support membrane. The polysulfone porous support membrane thus obtained was sufficiently washed with water to replace the solvent in the membrane.

The polysulfone porous support membrane was immersed in an aqueous solution of m-phenylenediamine (concentration: 2.0%) for 1 minute and then pulled up. After removing the droplets remaining on the film surface, a solution of trimesic acid chloride (concentration: 0.1% by weight, solvent: 1,1-dihydryl-perfluoro-n-heptane) was applied to the film surface for 1 minute. After completion of the reaction, the solution on the membrane surface was drained, and then left at room temperature for 30 seconds to evaporate the solvent. The manufactured composite membrane was washed with running water for 20 minutes to remove unreacted acid chloride.

[0027] The reverse osmosis performance of the obtained membrane is as follows:
The water production amount was 99.5%, which was high performance of 0.98 m ³ / m ² · day. Example 2 The polysulfone porous support membrane obtained in Example 1 was immersed in an aqueous solution of triaminobenzene (concentration: 3%) for 1 minute, and then pulled up. After removing the droplets remaining on the film surface, a solution of trimesic acid chloride (concentration: 0.1% by weight, solvent: perfluorodimethylcyclohexane) was applied to the film surface.
Minutes. After completion of the reaction, the solution on the membrane surface was drained, and then left at room temperature for 60 seconds to evaporate the solvent. The manufactured composite membrane was washed with running water for 20 minutes to remove unreacted acid chloride.

The reverse osmosis performance of the obtained membrane was evaluated. As a result, the salt rejection rate and the amount of fresh water were 99.1% and 1.23 m ^3.
/ M ² · day.

Example 3 The polysulfone porous support membrane obtained in Example 1 was immersed in an aqueous piperazine solution (concentration: 6%) for 1 minute and then pulled up. After removing the droplets remaining on the film surface, a solution of trimesic acid chloride (concentration: 0.5% by weight, solvent: 1,1-
Dihydryl-perfluoro-n-heptane)
Minutes. After completion of the reaction, the solution on the membrane surface was drained, and then left at room temperature for 30 seconds to evaporate the solvent. The manufactured composite membrane was washed with running water for 20 minutes to remove unreacted acid chloride.

The reverse osmosis performance of the obtained membrane was evaluated. As a result, the salt rejection rate and the amount of fresh water were 82.0% and 0.85 m ^3.
/ M ² · day.

Example 4 The polysulfone porous support membrane obtained in Example 1 was immersed in a mixed aqueous solution of m-phenylenediamine and triaminobenzene (molar ratio 50/50, total amine concentration 2%) for 1 minute. , Raised. After removing the droplets remaining on the film surface, a mixed solution of trimesic acid chloride and terephthalic acid chloride (molar ratio 50/50, concentration: 0.1% by weight, solvent:
α, α, α, α ', α', α'-hexafluoro-m-
(Xylene) was applied to the film surface for 1 minute. In order to evaporate the solvent remaining on the film surface, air at a wind speed of 6 m / sec and a temperature of 40 ° C. was blown on the film surface for 1 minute. The manufactured composite membrane was washed with running water for 20 minutes to remove unreacted acid chloride.

The reverse osmosis performance of the obtained membrane was evaluated. As a result, the salt rejection rate and the amount of fresh water were 99.3% and 1.15 m ^3.
/ M ² · day.

Example 5 The polysulfone porous support membrane obtained in Example 1 was replaced with N, N-
1 in an aqueous solution of dimethylethylenediamine (concentration 5%)
After soaking for a minute, it was pulled up. After removing the droplets remaining on the film surface, a solution of terephthalic acid chloride (concentration: 0.2
% By weight, solvent: pentafluorotoluene) was applied to the film surface for 1 minute. In order to evaporate the solvent remaining on the film surface, a wind having a wind speed of 6 m / sec and a temperature of 30 ° C. was blown on the film surface for 2 minutes. The manufactured composite membrane was washed with running water for 20 minutes to remove unreacted acid chloride.

The reverse osmosis performance of the obtained membrane was evaluated. As a result, the salt rejection rate and the amount of fresh water were 72.5% and 1.10 m ^3.
/ M ² · day.

Example 6 A solution of 18% by weight of polyethersulfone and the remainder of dimethylformamide was coated on a polyester taffeta to a thickness of about 100%.
It was cast to a micron and immediately immersed in a water bath at room temperature for gelation to obtain a polyethersulfone porous support membrane. The polyethersulfone porous support membrane thus obtained was sufficiently washed with water to replace the solvent in the membrane, and was used in later studies.

The polyethersulfone porous support membrane was immersed in an aqueous solution of m-phenylenediamine (concentration: 4%) for 1 minute and then pulled up. After removing the droplets remaining on the membrane surface, a solution of trimesic acid chloride (concentration: 0.1%) was added.
2% by weight, solvent: 1,1-dihydryl-perfluoro-
n-heptane) was applied to the film surface for 1 minute. After the reaction,
After the solution on the membrane surface was drained, the solvent was evaporated by leaving the solution at room temperature for 30 seconds. The manufactured composite membrane was washed with running water for 20 minutes to remove unreacted acid chloride.

The reverse osmosis performance of the obtained membrane was evaluated. As a result, the salt rejection rate and the amount of fresh water were 98.0% and 1.01 m ^3.
/ M ² · day.

Example 7 The polysulfone porous support membrane obtained in Example 1 was immersed for 1 minute in a mixed aqueous solution of m-phenylenediamine and triaminobenzene (molar ratio 50/50, total amine concentration 2%). , Raised. After removing the droplets remaining on the film surface, a mixed solution of trimesic acid chloride and terephthalic acid chloride (molar ratio 50/50, concentration: 0.1% by weight, solvent:
α, α, α, α ', α', α'-hexafluoro-m-
(Xylene) was applied to the film surface for 1 minute. In order to evaporate the solvent remaining on the film surface, the film was left for 5 minutes in a drier at a temperature of 60 ° C. and no air flow. The obtained composite membrane was washed with running water for 20 minutes to remove unreacted acid chloride.

The reverse osmosis performance of the obtained membrane was evaluated. As a result, the salt rejection rate and the amount of fresh water were 87.6% and 0.69 m ^3.
/ M ² · day, compared to Example 4 (all conditions were the same except for the solvent evaporation method), and only a membrane with a lower salt rejection rate and lower water production amount could be obtained.

[0040]

According to the present invention, it is possible to produce a high-performance composite reverse osmosis membrane using a nonflammable or high flash point fluorinated hydrocarbon solvent which does not destroy the ozone layer and is safe to handle. it can.

Claims (1)

(57) [Claims] 1. A non-flammable composite reverse osmosis membrane comprising a crosslinked polyamide layer obtained by interfacial polycondensation of a polyfunctional amine and a polyfunctional acyl halide on a porous polymer support membrane as a barrier layer. Or the flash point is 20 ° C
A method for producing a composite reverse osmosis membrane, comprising using the above fluorinated hydrocarbon solvent as a solvent for a polyfunctional acyl halide.