JPS6216122B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a treatment method for improving the selective separation ability of a semipermeable membrane made of a crosslinked polymer containing furfuryl alcohol as an essential component. In the past, various semipermeable membranes have been proposed as selective separation membranes using reverse osmosis, and attempts have been made to use these semipermeable membranes widely in fields such as desalination of seawater and can water and recovery of valuables. There is. These semipermeable membranes include asymmetric membranes typified by cellulose acetate membranes, that is, so-called Loeb membranes, as well as semipermeable barrier layers on the surface of various porous supports. There are a wide variety of composite membranes with ultra-thin membranes made of polyamides different from the polymer constituting the support, crosslinked polymers of furfuryl alcohol, etc., but the latter, like cellulose acetate membranes, are constantly There is no need to store it in water or in a wet state, and it is not susceptible to hydrolysis by acids, alkalis, or biological organisms. By selecting the support and barrier layer independently, it is possible to create the optimal solution according to the application and purpose. It has the advantage of being able to manufacture semipermeable membranes. For example, composite membranes in which a thin film made of a crosslinked polymer of furfuryl alcohol is provided as a barrier layer on a porous support made of polysulfone, chlorinated polyvinyl chloride, cellulose acetate, etc. (US Pat. No. 3926798), polyethyleneimine crosslinked There are composite membranes with a barrier layer made of a polymer (Japanese Patent Application Laid-open No. 127481/1983). The present inventors developed a cross-linked polymer obtained by polycondensing furfuryl alcohol, a polyhydric alcohol such as inositol or sorbitol, and trishydroxyethyl isocyanurate in the presence of an acid such as sulfuric acid as such a semipermeable composite membrane. The semi-permeable composite membrane which has a barrier layer of We have already proposed a method that has been found to have excellent selective separation ability. These semipermeable membranes have a structure in which a thin dense layer or barrier layer, which substantially determines the reverse osmosis performance, is supported by a layer called a porous layer or a support layer, respectively. This dense layer or barrier layer is said to have a thickness of about 0.1 micron, and it is said that the thinner the thickness, the better the water permeability, but in that case the quality tends to be unstable. It is. For example, in order to actually use the reverse osmosis method industrially, it is necessary to modularize it, and furthermore,
In practice, it is operated under high pressure conditions of several tens of kg/ ^cm2 , so physical factors such as defects on the surface of the semipermeable membrane, slight mechanical defects, expansion and contraction of the semipermeable membrane, and cellulose acetate, etc. The selective separation performance of semipermeable membranes generally decreases due to deterioration caused by chemical factors such as hydrolysis. Other attempts have been made to treat such semipermeable membranes to maintain or improve their desalination performance.
There are a lot of reports on those mainly targeting cellulose acetate membranes.
No. 28650 describes a method of adding surfactants to raw water;
Japanese Patent Publication No. 52-32869 describes a method for improving the selective separation performance of membranes degraded by polyvinyl alcohol;
Furthermore, Japanese Patent Publication No. 13431/1983 proposes a method for improving selective separation performance using a copolymer of vinyl acetate and unsaturated carboxylic acid. The present inventors have also previously proposed a membrane treatment agent containing a vinyl polymer having a carboxylic acid-modified saponified acetate group as a main component. However, the membrane treating agents for cellulose acetate as described above are not sufficient to restore the reduced selective separation ability of the semipermeable membrane made of furfuryl alcohol polymer. Moreover, in liquid separation methods that use seawater or industrial water as the raw liquid to be treated, chlorine is generally mixed in to prevent microorganisms, algae, or shellfish from adhering to and accumulating in the piping of reverse osmosis equipment. is normal. However, in general, semipermeable membranes, especially synthetic semipermeable membranes other than cellulose acetate membranes, are subject to chemical factors such as chlorine in addition to physical factors such as membrane compaction and cuts. Usually, the selective resolution is reduced and the lifetime is shortened. The above-mentioned semipermeable membrane made of furfuryl alcohol-based polymer shows a similar tendency, but this can be fatal, especially in applications such as one-stage desalination of seawater, which requires extremely high selective separation performance. It will become. The present inventors have conducted intensive studies on a method for restoring the selective separation ability of a semipermeable membrane made of a crosslinked polymer containing furfuryl alcohol as an essential component, whose performance has deteriorated due to long-term use, and discovered the present invention. It has been reached. That is, the present invention has the following configuration. A method for treating a semipermeable membrane, which comprises bringing a semipermeable membrane made of a crosslinked polymer containing furfuryl alcohol as an essential component into contact with an aqueous solution containing a water-soluble amino compound. A feature of the present invention is that a semipermeable membrane made of a furfuryl alcohol polymer with a reduced selective separation ability is brought into contact with an aqueous solution containing a trace amount of a compound having an amino group for a short period of time. The point is that improvement effects can be obtained. In the present invention, a semipermeable membrane made of a furfuryl alcohol-based polymer refers to a reaction component system made of furfuryl alcohol or it, trishydroxyethyl isocyanurate, inositol, sorbitol, methylolated polyvinylphenol, etc., and sulfuric acid or phosphorus as an acid catalyst. A semipermeable membrane consisting of a thin film coated with an aqueous solution containing an acid, toluenesulfonic acid, preferably sulfuric acid, and polymerized by heating.
More specifically, it is disclosed in U.S. Pat. Reactive component systems are preferred. Such semipermeable membranes are typically made of polysulfone, polyvinyl chloride,
It is used as a composite membrane integrated with a porous support made of polyvinylidene chloride, cellulose nitrate, or a copolymer thereof, especially polysulfone. In the present invention, as the water-soluble compound having an amino group, any of ordinary alkylamino compounds, aromatic amino compounds, alicyclic amino compounds, and other amino compounds can be used as long as they are water-soluble. Further, it may be a monoamino compound or a polyamino compound, or a low molecular compound or a high molecular compound. Examples of alkylamino compounds include ethylenediamine, monoethanolamine, diethanolamine, triethylenetetramine, and the like. Examples of aromatic amino compounds include phenylene diamine, diaminodiphenylmethane, sulfanilic acid, diaminobenzoic acid, and the like.
An example of an alicyclic amino compound is diaminocyclohexane. Other examples include:
Examples include sulfamic acid, piperazine, aminomethylpiperidine, and the like. In addition, examples of polymer compounds include polyethyleneimine, phenylenediamine-modified polyepichlorohydrin, and polyethyleneimine-modified polyiodohydrin. Among these amino compounds, polyethyleneimine is preferred in terms of initial effect and durability of effect. and polyethyleneimine-modified polyepihalohydrin are most preferred. The selective separation ability improvement effect of these semipermeable membranes made of furfuryl alcohol-based polymers of water-soluble amino compounds is not necessarily limited to so-called deteriorated membranes whose selective separation ability has decreased after long-term operation, but also to membranes immediately after membrane formation. The effect can also be seen on unused membranes. In addition, although the above-mentioned water-soluble amino compounds are effective in restoring the selective separation ability even without pretreatment, pretreatment such as washing can be effective in recovering the selective separation ability, especially after long-term operation. For membranes that have deteriorated over time, the recovery rate of selective separation ability is improved and the durability is increased. Such pretreatment (membrane cleaning) may be performed by a generally known method. For example, when contamination such as microorganisms or organic matter is considered, methods using surfactants, enzyme detergents, etc. are used. In addition, when stains such as poorly soluble metal salts or inorganic colloids are considered, ammonium citrate, ethylenediaminetetraacetic acid disodium salt, etc. are effective. The selective separation ability recovery effect according to the present invention does not necessarily take effect only once, but can take effect again at the point when its effect has weakened or disappeared. Furthermore, it goes without saying that the effects of the present invention are exerted not only on single films but also on modules which are actually used in industrial applications. Further, the shape of the module may be a tubular type, a spiral type, or a hollow fiber type, and the shape is not particularly limited. In the method of the present invention, the concentration of the amino compound in the aqueous solution may range from 1 ppm to about 1%;
Preferably, about 10 ppm to 1000 ppm is used. Further, the solvent for the amino compound is preferably demineralized water, but it may be used by directly adding it to the stock solution to be treated. In addition, the operating pressure can be used in the range of 1Kg/cm ² to 100Kg/cm ² , but the range of 3 to 70Kg/cm ² is usually preferred.

[Table] Example 2 Taffeta made of rectangular polyester fibers with a size of 20 cm x 30 cm (multifilament of 150 denier in both warp and weft, weaving density: 90 pieces/inch vertically, 67 pieces/inch horizontally, thickness 160μ) ) was fixed on a glass plate, and a 15% by weight solution of polysulfone (Udel p-3500, manufactured by Union Carbide) in dimethylformamide (DMF) was cast onto it to a thickness of 200μ at room temperature (15~~30℃). and immediately add sodium dodecylbenzenesulfonate to room temperature.
A fiber-reinforced polysulfone support (hereinafter abbreviated as FR-PS support) was obtained by immersing it in an aqueous solution containing 0.5% by weight, leaving it for 5 minutes, and then washing it with pure water for 1 hour.
Create. This FR-PS support (thickness 200μ)
The pure water permeability coefficient of is 0.01 to 0.020 g/cm ² ·sec·atm when measured at a pressure of 1 Kg/cm ² and a temperature of 25°C. Trishydroxyethyl isocyanurate (hereinafter
THEIC) 1% by weight, furfuryl alcohol (hereinafter abbreviated as FA) 2% by weight (THEIC/FA molar ratio = 16/84), sulfuric acid 2% by weight, sodium dodecyl sulfate 1% by weight, and isopropyl alcohol 20% by weight.
% by weight is prepared, and the FR-PS support wetted with water is immersed in this aqueous solution at 15° C. for 5 minutes. Next, the FR-PS support was taken out, both long sides were sandwiched between 2 cm wide iron plates (150 g/sheet), hung for 1 minute at 20°C, held vertically, and then placed in a hot air dryer for 130°C. It is dried at 150°C for 3 minutes and then heat treated at 150°C for 5 minutes. Next, this membrane was fixed on a glass plate, and a 1% by weight aqueous solution of polyvinyl alcohol (NM-14, manufactured by Nippon Gosei Kagaku Co., Ltd.) with a degree of saponification of 100 mol% and a degree of polymerization of 1500 was poured onto the surface of the membrane at room temperature ( Coat with a thickness of 50μ using a doctor knife at 20°C), place in a hot air dryer, and heat treat for 2 minutes. Interference fringes due to the polyvinyl alcohol thin film were observed on the surface of the resulting composite film. Further, when the thickness of each layer of the composite film was measured by electron microscopy, the thickness of the barrier layer was 30 μm, and the thickness of the protective film layer was 0.4 to 0.5 μm. When the reverse osmosis performance of this membrane was measured under saline conditions, the salt rejection rate was 99.8%, and the amount of permeated water was 0.35 m ³ /
It was warm for m ² days. This membrane was used to remove chlorine added in the pretreatment process using 3.5% by weight seawater.
A seawater desalination test was conducted under the same conditions as in Example 1 (hereinafter referred to as seawater conditions) except for adding 10 ppm of sodium bisulfite, and the initial value was 99.8% salt rejection rate and 0.34 m ³ / m ² ·day, but after 5000 hours of operation, the salt rejection rate decreased to 98.9% and the amount of permeated water changed to 0.38m ³ /m ² ·day.
The reverse osmosis performance under saline conditions at that time was a salt rejection rate of 98.8% and a permeate amount of 0.39 m ³ /m ² ·day. Using this membrane, each of various amino compounds
Table 2 shows the results of measuring the reverse osmosis performance of salt under saline conditions after operating for 1 hour using a 100 ppm aqueous solution at 4 Kg/cm ² , 25°C, and a membrane surface flow rate of 50 cm/sec for the raw solution supplied. .

[Table] Example 3 1, 10, and 100 ppm each of 4,4'-diaminodiphenylmethane (hereinafter abbreviated as DDM) was added to the supplied brine stock solution using the membrane of Example 2 with reduced selective separation ability.
Table 3 shows the results of measuring the reverse osmosis performance under saline conditions after 2 hours of operation in the system to which . however,
In the system where 100 ppm of DDM was added, a part of the DDM was not completely dissolved and remained suspended as a solid.

[Table] Even in the system in which 10 ppm of DDM was added, the salt rejection rate increased to 99.5% after 10 hours. Example 4 1% by weight of inositol, 2% by weight of furfuryl alcohol, 1% by weight of sulfuric acid, 1% by weight of sodium dodecyl sulfate
After preparing an aqueous solution containing 20% by weight and 20% by weight of isopropyl alcohol and aging at room temperature for 15 minutes,
A film was formed in the same manner as in Example 2 using the FR-PS support of Example 2. The reverse osmosis performance of this membrane under salt conditions has a salt rejection rate of 99.6% and a permeated water volume of 0.30 m ³ /
It was warm for m ² days. Using this membrane, 5% by weight of ε-
When reverse osmosis performance was measured again under saline conditions after 8000 hours of operation with caprolactam aqueous solution, the salt rejection rate decreased to 98.5%, and the amount of permeated water was 0.33%.
m ³ /m ² · day. Using this membrane, polyethyleneimine (“P-” manufactured by Nippon Shokubai Chemical Co., Ltd.,
After 2 hours of treatment with 100 ppm of ``1000''), the reverse osmosis performance was measured again under saline conditions, and the salt rejection rate improved to 99.3%. On the other hand, the amount of permeated water was 0.29m ³ /m ² ·day. Example 5 The membrane of Example 4 with reduced selective separation ability was first
After treating with a 0.1% by weight aqueous sulfanilic acid solution for 1 hour under the same conditions as those used to measure reverse osmosis performance, reverse osmosis performance was measured under saline conditions, and the salt rejection rate improved to 99.0%. On the other hand, the amount of permeated water is 0.33
It remained at m ³ /m ² ·day. Next, this membrane was further treated for 2 hours under the same conditions as the reverse osmosis performance measurement except that a 50 ppm polyethyleneimine aqueous solution was used as the stock solution, and then the reverse osmosis performance was measured again under saline conditions. Salt elimination rate is even higher
This has improved to 99.3%. On the other hand, the amount of permeated water is 0.29
It decreased slightly to m ³ /m ² ·day. Example 6 A 4-inch spiral-wound module (membrane area:
7.0m ² ). 3.5% by weight saline solution of this module, 56Kg/cm ² , 25℃, PH6.5, supply stock solution amount 10
/min, under operating conditions with a water recovery rate of 15%, the reverse osmosis performance has a salt rejection rate of 99.7% and a permeated water volume of ^0.28m3 /min.
It was warm for m ² days. Using this module, a seawater desalination test was conducted under the same operating conditions as above, except that the supplied stock solution was a solution containing 20ppm of sodium bisulfite to remove chlorine added in the pretreatment process to 3.5% seawater. When carried out, the initial value was that the salt rejection rate was 99.8.
%, the amount of permeated water was 0.25m ³ /m ² ·day, but 5000
After hours of operation, the salt rejection rate drops to 98.7%,
Furthermore, the amount of permeated water decreased by 0.20 m ³ /m ² ·day. Under the same conditions at that time, the reverse osmosis performance with 3.5 wt% saline was as follows: salt rejection rate was 98.6%, permeated water amount was 0.26 m ³ /
It was warm for m ² days. This module was operated for 1 hour under the same conditions as the reverse osmosis performance measurement except that it was operated with a 0.1% by weight aqueous sulfanilic acid solution at a pressure of 4 kg/cm ² , and then:
After operating for 2 hours under the same conditions as above using a 100 ppm polyethyleneimine aqueous solution, reverse osmosis performance was measured again using 3.5% by weight saline, and the salt rejection rate improved to 99.6%. On the other hand, the amount of permeated water was 0.27 m ³ /m ² ·day. Example 7 The module with reduced selective resolution of Example 6 was
After treatment for one day under the same operating conditions as in Example 6, except for using a 0.1% by weight sodium dodecyl sulfate aqueous solution and operating at a pressure of 3 kg/cm ² ,
After operating for 2 hours under the same operating conditions as above except for using a 100 ppm polyethyleneimine aqueous solution,
When the reverse osmosis performance was measured by returning it to 3.5% seawater, the salt rejection rate improved to 99.7%. On the other hand, the amount of permeated water was 0.22 m ³ /m ² ·day. When this module was continued to operate under the same operating conditions as before using the membrane treatment agent, the salt rejection rate decreased after 1000 hours.
It dropped to 99.2%. On the other hand, the amount of permeated water is 0.24
The temperature was m ³ /m ² ·day. Therefore, this time, we used a 0.5% by weight oxalic acid aqueous solution to
After 1 ^{hour of treatment under the same reverse osmosis operating conditions except for operation at a pressure of Kg/cm 2 ,} a 100 ppm polyethylene The mixture was treated with an imine aqueous solution at a pressure of 56° C./cm ² for 1 hour. Thereafter, when the reverse osmosis performance was evaluated again using 3.5% by weight seawater, the salt rejection rate improved to 99.8% and the amount of permeated water was 0.24m ³ /m ² ·day. When this module was continued to be operated as it was, 700
Even after hours, the salt rejection rate remained 99.6%. Note that the amount of permeated water also hardly changed. Example 8 Using the as-prepared membrane of Example 4, a 30 ppm aqueous solution of polyethyleneimine was used under the same operating conditions as the saline solution except that an operating pressure of 3 Kg/cm ² was used.
After operating for several hours, reverse osmosis performance was measured under saline conditions, and the salt rejection rate improved to 99.8%.
The amount of permeated water was 0.27m ³ /m ² ·day.

Claims (1)

[Scope of Claims] 1. A method for treating a semipermeable membrane, which comprises bringing a semipermeable membrane made of a crosslinked polymer containing furfuryl alcohol as an essential component into contact with an aqueous solution containing a water-soluble amino compound. 2. The semipermeable membrane made of a crosslinked polymer is a thin film made of a furfuryl alcohol homopolymer or a copolymer of furfuryl alcohol and a polyhydroxy compound. Treatment method for semipermeable membranes. 3. The method for treating a semipermeable membrane according to claim 1, wherein the semipermeable membrane is integrated with a porous support to form a semipermeable composite membrane.