JPH0640946B2 - Method for treating silicic acid-containing water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Field of Industrial Application> The present invention is to recover water or valuables from raw water containing silicic acid, for example, groundwater, river water, seawater, tap water, various process waters, wastewater, etc. Is about how to
In particular, it can be used in the ultrapure water manufacturing process in the electronic industry and the pure water manufacturing process in the medical field and the like.

<Prior Art and Problems Thereof> In recent years, a method of separating raw water by a reverse osmosis membrane method has been used, as represented by ultrapure water production in the electronic industry and pure water production in the medical field and the like.

For example, in the ultrapure water production process, raw water that has been generally subjected to pretreatment such as coagulation-sedimentation treatment and activated carbon overtreatment is first subjected to reverse osmosis treatment to obtain reduced-purity primary pure water, and the primary pure water is ion-exchanged. , A method of obtaining ultrapure water by treating with a polisher or ultrafiltration has been put into practical use. In the reverse osmosis treatment, the greater the concentration ratio of raw water,
A large amount of permeate can be obtained from a constant supply raw water, which is economically advantageous. Similarly, in the case of recovering the concentrate, the higher concentration is more advantageous.

However, the raw water contains silicic acid,
When treating such raw water with a conventional reverse osmosis membrane made of, for example, cellulose acetate, which has a relatively high removal rate of silicic acid, when the concentration ratio is increased, silicic acid having a relatively low solubility is concentrated on the concentrate side, particularly near the membrane surface. However, there is a problem that the membrane is deposited (silica scale) to contaminate the membrane, the membrane performance is deteriorated, and the raw water cannot be treated with a high recovery rate. For example, in the treatment of brine containing 40 ppm silicic acid, the maximum concentration is usually about 2.5 times (recovery rate 60%).

Therefore, in order to treat raw water having a high silicic acid content with a high recovery rate, it is necessary to perform a desilicing treatment on the raw water in the preceding stage in order to prevent the above-mentioned membrane contamination. As such a silicic acid treatment method, there are a coagulation sedimentation method using magnesium hydroxide, iron salt, aluminum salt and the like, an ion exchange method, etc., but the coagulation sedimentation method has a low removal rate of silicic acid and a large amount of sludge is generated. However, the ion exchange method is also economically disadvantageous because it removes other anions at the same time and a large amount of load is applied to the ion exchange resin. On the other hand, there are ion exchange resins that can selectively remove only silicic acid, but using them has the drawbacks of high cost and lack of economy. Particularly, in the usual ultrapure water production process, since the ion exchange treatment is required after the reverse osmosis treatment, it is economically very disadvantageous to perform the ion exchange treatment before the reverse osmosis treatment.

<Means for Solving Problems> The present invention has been made to solve the above-mentioned drawbacks of the prior art, in which raw water containing silicic acid is subjected to reverse osmosis treatment using a specific composite semipermeable membrane, It is an object of the present invention to provide a method capable of treating with a high recovery rate without contamination of a film by silicic acid.

That is, according to the present invention, an ultrathin film layer obtained by crosslinking a polyfunctional amino compound having two or more secondary amino groups in one molecule with a polyfunctional crosslinking agent is integrally provided on a porous substrate. The present invention relates to a method for treating silicic acid-containing water, which comprises subjecting raw water containing silicic acid to reverse osmosis treatment using the composite semipermeable membrane described above.

Still another embodiment of the present invention is an ultrathin film layer obtained by crosslinking a polyfunctional amino compound having two or more secondary amino groups in one molecule and polyvinyl alcohol with a polyfunctional crosslinking agent.
By using a composite semipermeable membrane integrally provided on a porous substrate through a porous layer made of water-insoluble polyvinyl alcohol as an inner layer that integrally supports the ultrathin film layer, silicic acid is used. The present invention relates to a method for treating silicic acid-containing water, which comprises subjecting raw water containing water to reverse osmosis treatment.

The raw water containing silicic acid in the present invention is an aqueous solution containing various silicic acids which are water-soluble or water-insoluble such as monomer, polymer, metal salt, and chelate coordination, and the content thereof is usually It is expressed as a SiO ₂ conversion value.

In the first composite semipermeable membrane used in the present invention, the ultrathin film layer obtained by crosslinking a polyfunctional amino compound having two or more secondary amino groups in one molecule with a polyfunctional crosslinking agent is a porous group. It is a composite semipermeable membrane (hereinafter referred to as composite semipermeable membrane A) provided integrally on a material.

Further, the second composite semipermeable membrane used in the present invention is the second
An ultrathin film layer obtained by cross-linking a polyfunctional amino compound having two or more primary amino groups in one molecule and polyvinyl alcohol with a polyfunctional cross-linking agent serves as an inner layer integrally supporting the ultra-thin film layer. The composite semipermeable membrane (hereinafter referred to as composite semipermeable membrane B) is integrally provided on a porous substrate via a porous layer made of water-insoluble polyvinyl alcohol.

The composite semipermeable membrane A is prepared by applying or impregnating a porous substrate with a solution containing a polyfunctional amino compound (hereinafter referred to as a solution), contacting the polyfunctional cross-linking agent, and then heating. It can be manufactured.

Such a polyfunctional amino compound has two or more secondary amino groups in one molecule, and specific examples thereof include N, N'-dimethylethylenediamine and N, N'-.
Dimethylpropanediamine, N, N'-dimethyl-m-
Phenylenediamine, N, N'-dimethyl-p-phenylenediamine, 2,6-dimethylaminopyridine, N,
N'-dipiperazyl methane, 1,8- (N, N'-dipiperazyl) octane, N, N'-dipiperidyl, N,
N'-di (3,3'-dimethylpiperidyl), 4,4 '
-Dipiperidyl methane, 1,2 (4,4'-dipiperidyl) ethane, 1,3- (4,4'-dipiperidyl) propane, piperazine, 2-methylpiperazine, 2,5-dimethylpiperazine, homopiperazine (hexa Hydrodiazepines) and the like.

Water is preferably used as the solvent for preparing the solution, and the solution is adjusted so as to contain the polyfunctional amino compound in an amount of 0.05 to 10% by weight, preferably 0.1 to 5% by weight.

Further, this solution may contain a surfactant in order to reduce the surface tension at the time of coating and impregnating the porous base material, and when hydrochloric acid or the like is by-produced when crosslinkable by the crosslinking agent. Is a basic substance to capture its by-products,
For example, it may contain sodium hydroxide, ammonia, sodium phosphate and the like.

Further, as the porous substrate, any porous film made of a hydrophobic polymer such as polysulfone, polyvinyl chloride, polycarbonate, cellulose acetate, cellulose nitrate, etc., such as a film, a sheet, a tube and a hollow fiber can be used. It can be used in any form. In particular, the surface has micropores with a diameter of about 10 to 100Å, and these micropores have an asymmetric structure in which the diameter gradually increases toward the inside, and at the same time the amount of pure water permeation is at least
10 ^-5 g / cm ² · second · atmospheric pressure, preferably 10 ^-4 to 10 ^-1
An ultra-supermembrane having g / cm ² · sec · atmosphere is suitable.

The coating amount or impregnation amount of the above solution on such a porous substrate is 0.05 to 5 g / m ^{2 in} terms of solid content, preferably 0.1 to 1
It is g / m ² , and it can be adjusted so as to fall within the above range by an operation such as air-drying or draining after coating or impregnating the porous substrate with the solution if necessary.

The polyfunctional crosslinking agent used in the present invention is a functional group capable of reacting with a secondary amino group, for example, an acid halide group, a halogensulfonyl group, an N-haloformyl group, a haloformate group, an acid anhydride group, or the like, or A compound having two or more kinds in one molecule, such as isophthaloyl chloride, terephthaloyl chloride, trimesic acid chloride, trimellitic acid chloride, hemimellitic acid chloride, pyromellitic dianhydride, 2,6-dichloroformyl. Pyridine, 3,5-dichloroformylbenzenesulfonyl chloride, N, N'-dichloroformylpiperazine and the like can be mentioned. Particularly, in the present invention, it is preferable to use benzene tricarboxylic acid chloride such as trimesic acid chloride, trimellitic acid chloride and hemimellitic acid chloride as the cross-linking agent.

To bring the above-mentioned polyfunctional crosslinking agent into contact with a porous substrate coated or impregnated with a solution, a crosslinking agent solution prepared by dissolving the crosslinking agent in an organic solvent that is not miscible with the solution is usually a solution of the porous substrate. It may be applied on the coating layer, or the above substrate may be dipped in a solution of a crosslinking agent. As the organic solvent, hydrocarbon solvents such as pentane, hexane, heptane, cyclohexane and petroleum ether, and halogenated hydrocarbon solvents such as trichlorotrifluoroethane are preferably used. The concentration of the crosslinking agent in the crosslinking agent solution is usually 0.05 to 10% by weight, preferably 0.1 to 5% by weight.

After contacting the cross-linking agent solution to the porous substrate coated or impregnated with the solution in this manner, 80 ~ 180 ° C., preferably 1
By heating at a temperature of 00 to 150 ° C., a cross-linking reaction of the amino compound is carried out in the surface layer of the solution coating layer on the porous substrate, and thus a semipermeable dense ultra-thin film layer is formed on the substrate. A composite semipermeable membrane A formed as a surface layer and used in the present invention is obtained. The thickness of the dense ultra-thin film layer is usually 50 to 800 Å, preferably 100 to 500 Å, though it varies depending on the concentration of the amino compound in the solution, the contact time with the cross-linking agent, the heating temperature and time thereafter.

In addition, the composite semipermeable membrane B used in another embodiment of the present invention is a solution containing the above-mentioned polyfunctional amino compound and polyvinyl alcohol (hereinafter referred to as solution B), which is used as a porous substrate in the same manner as described above. After coating or impregnation, it can be produced by contacting with a polyfunctional crosslinking agent and then heating. The above solution B is 10 to 500 parts by weight, preferably 20 to 300 parts by weight of an amino compound per 100 parts by weight of polyvinyl alcohol.
It is contained by weight, and the concentration of the total amount of polyvinyl alcohol and amino compound is 0.05 to 10% by weight, preferably 0.
It is prepared to be 1 to 5% by weight.

By such a method, the cross-linking reaction of the amino compound and polyvinyl alcohol is carried out in the surface layer of the solution coating layer on the porous substrate, thus forming a semipermeable dense ultrathin film layer on the substrate as a surface layer. It On the other hand, unreacted polyvinyl alcohol that was not involved in the cross-linking reaction inside the solution coating layer between the ultra-thin film layer and the porous substrate becomes water-insoluble by heating and the amino compound volatilizes, so the inner layer is A porous layer made of water-insoluble polyvinyl alcohol having a large number of pores is formed so as to integrally support the ultrathin film layer, and the composite semipermeable membrane B used in the present invention is obtained.

The composite semipermeable membranes A and B thus formed have a large difference between the removal rate for silicic acid and the removal rate for cations such as sodium, calcium and magnesium ions and anions such as chlorine and sulfate ions, and high separation separation. It has a sex. In the present invention, when the reverse osmosis treatment is performed under a pressure of, for example, 20 kg / cm ² , the removal rate of silicic acid is 50% or less, preferably 30% or less, and the ion removal rate is 50% or less.
% Or more, preferably 80% or more, more preferably 90% or more having reverse osmosis performance is used.

Therefore, since the composite semipermeable membrane used in the present invention has excellent selective separation properties as described above, by performing reverse osmosis treatment of raw water containing silicic acid using such a composite semipermeable membrane, the cations and anions are removed. It can be substantially removed and permeable to silicic acid. Therefore, it is possible to prevent deterioration of the membrane performance due to membrane contamination due to silicic acid precipitation, and it is possible to treat raw water with a high recovery rate.

<Effects of the Invention> As described above, according to the method of the present invention, when the raw water containing silicic acid is subjected to reverse osmosis treatment, since a specific composite semipermeable membrane is used, film contamination occurs due to silicic acid precipitation. It is possible to prevent deterioration of the membrane performance.

In particular, if the method of the present invention is applied to the primary pure water production line during the ultrapure water production process, the desilicic acid treatment step in the previous stage can be omitted, which is extremely economically advantageous.

<Examples> The present invention will be specifically described below with reference to Examples.

Production Example A Containing 1% by weight of piperazine and 1% by weight of sodium hydroxide on a porous substrate having an asymmetric structure made of polysulfone (pure water permeation rate 1.02 × 10 ^-2 g / cm ² · second · atmosphere) The solution was uniformly applied and then immersed in a 1% by weight solution of trimesic acid chloride in n-hexane at a temperature of 25 ° C. for 1 minute. Pull this substrate up and air dry for 30 seconds, then
The composite semipermeable membrane A was obtained by heating at a temperature of 0 ° C. for 10 minutes.

Production Example B Polyvinylsulfone 0.25% by weight, piperazine 0.25% by weight, and sodium hydroxide 0.5 on a porous substrate having an asymmetric structure (pure water permeation rate 1.05 × 10 ^-2 g / cm ² · second · atmosphere) made of polysulfone. After uniformly applying an aqueous solution containing 10% by weight, 0.5% by weight of trimesic acid chloride n
Immersed in hexane solution for 1 minute at a temperature of 25 ° C. The substrate was pulled up to volatilize hexane attached to the membrane surface, and then heated at 110 ° C. for 10 minutes to obtain a composite semipermeable membrane B.

Evaluation Example An aqueous solution containing 2000 ppm of the following solute and an aqueous solution containing 100 ppm of sodium silicate were subjected to reverse osmosis treatment under pressure of 20 kg / cm ² using the composite semipermeable membranes A and B obtained in the Production Example. Table 1 shows the removal rate of the solute in this case.

It is understood from Table 1 that the above composite semipermeable membrane has a large difference in removal rate between various solutes and silicic acid and can be suitably used in the present invention.

Example A raw water containing a silicic acid concentration of 50 ppm and a TDS concentration of 1200 ppm,
Using the composite semipermeable membranes A and B obtained in the production example, 20 kg / c
The results of reverse osmosis treatment under a pressure of m ² are shown in Table 2 below. As is clear from this result, the concentration of silicic acid in the concentrated liquid was not more than the saturated silicic acid concentration in this state, so that it was confirmed that silicic acid did not precipitate. Further, the permeated liquid could be collected at a high recovery rate.

Comparative Example Raw water having the same properties as in Example was treated in the same manner as in Example using a reverse osmosis membrane made of cellulose acetate (silica removal rate: 90%).

Claims (2)

[Claims] 1. An ultrathin film layer obtained by crosslinking a polyfunctional amino compound having two or more secondary amino groups in one molecule with a polyfunctional crosslinking agent is integrally provided on a porous substrate. A method for treating silicic acid-containing water, which comprises subjecting raw water containing silicic acid to reverse osmosis using the composite semipermeable membrane described above. 2. An ultrathin film layer in which a polyfunctional amino compound having two or more secondary amino groups in one molecule and polyvinyl alcohol are crosslinked with a polyfunctional crosslinking agent, the ultrathin film layer is integrated. Reverse osmosis of raw water containing silicic acid using a composite semipermeable membrane integrally provided on a porous substrate through a porous layer composed of water-insoluble polyvinyl alcohol as an inner layer supporting A method for treating silicic acid-containing water, which comprises treating.