JPS61129004A - Treatment of water containing silicic acid - Google Patents

Abstract

PURPOSE:To perform the reverse osmosis treatment of raw water containing silicic acid generating no contamination of a membrane due to silicic acid, by using a composite semi-permeable membrane having an ultra-thin membrane layer formed by crosslinking a polyfunctional amino compound having two or more of secondary amino groups in one molecule thereof by a crosslinking agent. CONSTITUTION:A polyfunctional amino compound having two or more of secondary amino groups in one molecule thereof or a solution prepared by mixing polyvinyl alcohol with said amino compound is applied to a porous base material having minute pores with a pore size of 10-100Angstrom formed to the surface thereof to impregnate said base material. the concn. of said amino compound is 0.05-10wt% and, when polyvinyl alcohol is used, said polyvinyl alcohol is used in an amount of 0.2-5 times of the amino compound. A polyfunctional crosslinking agent is contacted with the treated base material and the whole is heated at 80-180 deg.C to form an ultra-thin membrane layer with a thickness of 50-800Angstrom . The concn. of the crosslinking agent is pref. 0.05-10wt%.

Description

[Detailed Description of the Invention] Fields of Application of the Product'J/4> The present invention is applicable to water recovery from raw water containing silicic acid, such as groundwater, river water, seawater, tap water, various process waters, wastewater, etc. Alternatively, it relates to a method for recovering valuable materials, and is particularly applicable to ultrapure water production processes in the electronics industry and pure water production processes in the medical field.

<Prior art and its problems> In recent years, a method of separating raw water using a reverse osmosis membrane method has been used, as typified by the production of ultrapure water in the electronics industry and the production of pure water in the medical field.

For example, in the ultrapure water production process, raw water that has undergone pretreatment such as coagulation sedimentation treatment or activated carbon filtration treatment is first subjected to reverse osmosis treatment to obtain reduced-salt primary pure water, and then this secondary pure water is ionized. Methods of obtaining ultrapure water by treatment with exchange, boritzer, ultrafiltration, etc. have been put into practical use. In the above reverse osmosis treatment, the higher the concentration ratio of raw water, the more
A large amount of permeate water can be obtained from a given raw water supply, which is economically advantageous. Similarly, when collecting 7 agricultural shrinkage products, the higher the 15 shrinkage is, the more advantageous it is.

However, the raw water above contains silicic acid,
When such raw water is treated using a conventional reverse osmosis membrane made of cellulose acetate, which has a relatively high silicic acid removal rate, when the concentration ratio is increased, silicic acid with relatively low solubility is transferred to the concentrate side, especially near the membrane surface. There is a problem in that silica deposits (silica scale) and contaminates the membrane, reducing membrane performance and making it impossible to treat raw water with a high recovery rate. For example, silicic acid 4j)p
In the treatment of shrubs containing PM, the maximum concentration ratio is usually about 2.5 times (60% recovery rate).

Therefore, if raw water with a high silicic acid content is to be treated with a high recovery rate, it is necessary to perform a desilicating treatment on the raw water in the first stage in order to prevent the above-mentioned membrane contamination. Such desilicating methods include the coagulation-precipitation method and ion exchange method using magnesium hydroxide, iron salts, aluminum salts, etc. However, the coagulation-precipitation method has a low removal rate of silicic acid and generates a large amount of sludge. However, the ion exchange method is economically disadvantageous because other anions are also removed at the same time, which places a large load on the ion exchange resin. On the other hand, although there are ion exchange resins that can selectively remove only silicic acid, their use has the disadvantage of being expensive and uneconomical. In particular, in a normal ultrapure water production process, ion exchange treatment is required after reverse osmosis treatment, so it is economically very disadvantageous to perform ion exchange treatment before reverse osmosis treatment.

<Means for Solving the Problems> The present invention has been made to solve the drawbacks of the prior art, and involves reverse osmosis treatment of raw water containing silicic acid using a specific composite semipermeable membrane. The purpose of the present invention is to provide a method that can be processed at a high recovery rate without membrane contamination due to silicic acid.

That is, in the present invention, an ultra-thin film layer in which a polyfunctional amino compound having two or more secondary amino groups in one molecule is crosslinked with a polyfunctional crosslinking agent is integrally provided on a porous base material. The present invention relates to a method for treating silicic acid-containing water, characterized in that raw water containing silicic acid is subjected to reverse osmosis treatment using a composite semipermeable membrane containing silicic acid.

Furthermore, another aspect of the present invention is an ultra-thin 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.
Silicic acid is coated on the porous substrate via a porous layer made of water-insoluble polyvinyl alcohol as an inner layer that integrally supports the ultra-thin film layer. 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.

In the present invention, the raw water containing silicic acid is an aqueous solution containing silicic acid, and its content is usually expressed as a 5i02 equivalent value.

The first composite semipermeable membrane used in the present invention has an ultra-thin film layer in which a polyfunctional amino compound having two or more secondary amino groups in one molecule is crosslinked with a polyfunctional crosslinking agent. This is a composite semipermeable membrane (hereinafter referred to as composite semipermeable membrane A) that is integrally provided on the material.

Furthermore, the second composite semipermeable membrane used in the present invention has a second
An ultra-thin film layer formed by cross-linking a polyfunctional amino compound having two or more amino groups in one molecule and polyvinyl alcohol with a polyfunctional cross-linking agent serves as an inner layer that integrally supports the ultra-thin film layer. This is a composite semipermeable membrane (hereinafter referred to as composite semipermeable membrane B) that is integrally provided on a porous base material via a porous layer made of water-insoluble polyvinyl alcohol.

The above-mentioned composite semipermeable membrane A is produced by applying or impregnating a porous base material with a solution containing a polyfunctional amino compound (hereinafter referred to as a solution), bringing it into contact with a polyfunctional crosslinking agent, and then heating. can do.

Such polyfunctional amino compounds have two or more secondary amino groups in one molecule, and specific examples thereof include N, N'-;y methylethylenediamine, N, N'
-dimethylpropanediamine, N,N'-dimethyl-m-phenylenediamine, N,N'-dimethyl-
p-phenylenediamine, 2,6-dimethylaminopyridine, N,N'-dipiperazylmethane, 1.8-
(N, N'-dipiperazine) octane, N, N'
-dipiperidyl, N, N'-di(3,3'-dimethylpiperidyl), 4,4'-dibiperidylmethane, 1
．． 2(4,4'-dibiveridyl)ethane, 1,3-(4
, 4'-dipiperidyl)propane, piperazine, 2-methylbiperazine, 2,5-dimethylpiperazine, homopiperazi/(hequinahydrodiazebin), and the like.

Water is preferably used as the solvent for preparing the solution, and this solution contains 0.05 to 10% of the polyfunctional amino compound.
It is adjusted to % by weight, preferably 0.1 to 5% by weight.

In addition, this solution may contain a surfactant to reduce the surface tension when applying and impregnating the porous substrate, and if hydrochloric acid or the like is produced as a by-product during crosslinking with a crosslinking agent, basic substances, to capture its byproducts;
For example, it may contain sodium hydroxide, ammonia, sodium phosphate, etc.

In addition, the porous base material may be any porous material such as film, sheet, tube, or hollow fiber, as long as it is made of a hydrophobic polymer such as polysulfone, polyvinyl chloride, polycarbonate, cellulose acetate, or cellulose nitrate. It can be used in any form.

In particular, the surface has micropores with a diameter of about 10 to 100 A, and the micropores have an asymmetric structure in which the diameter gradually increases toward the inside, and the amount of pure water is at least 10-' 9 /
c+J・sec・atmospheric pressure, preferably 10−4 to 10”
An ultrafiltration membrane having a pressure of −'P/−·sec·atmospheric pressure is suitable.

The amount of the solution to be applied or impregnated into such a porous substrate is 0.05 to 59/n:, preferably 0.1 to 17/n in terms of solid content, and if necessary, the solution is applied to the porous base material. After being applied or impregnated onto a plastic substrate, the amount can be adjusted to fall within the above range by air drying, draining, etc.

The polyfunctional crosslinking agent used in the present invention is one type of functional group that can react with a secondary amino group, such as an acid halide group, a halogensulfonyl group, an N-haloformyl group, a heroformate group, or an acid anhydride group. or a compound having two or more of two or more types in one molecule, specific examples of which include inphthaloyl chloride, terephthaloyl chloride, trinonyl chloride, trimellitic acid chloride, hemimelitic acid chloride,
Examples include pyromellitic dianhydride, 2,6-dichloroformylpyridine, 3,5-dichloroformylbenzenesulfonyl chloride, and N,N'-dichloroformylpiperazine. Particularly, in the present invention, it is preferable to use benzenetricarboxylic acid chloride such as trimenoic acid chloride, trimellitic acid chloride, hemimelitic acid chloride as the crosslinking agent.

In order to bring the above-mentioned polyfunctional crosslinking agent into contact with a porous substrate coated with 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 added to the solution of the porous substrate. It may be applied onto the coating layer or the substrate may be immersed in a crosslinking agent solution. 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
The content is preferably 10 to 10% by weight, preferably 0.1 to 5% by weight.

After bringing the crosslinking agent solution into contact with the porous substrate coated or impregnated with the solution in this way, by heating at a temperature of 80 to 180 °C, preferably 100 to 150 °C,
A cross-linking reaction of the amino compound takes place in the surface layer of the solution-coated layer on the porous substrate, thus forming a semi-permeable, dense, ultra-thin film layer on the substrate, and forming the composite semi-conductor used in the present invention. A permeable membrane A is obtained. The thickness of this dense ultra-thin film layer varies depending on the concentration of the amino compound in the solution, the contact time with the crosslinking agent, the subsequent heating temperature and time, etc., but is usually 50 to 800 A, preferably 100 to 500 A.
It is.

Composite semipermeable membrane B used in another aspect of the present invention is prepared by adding a solution containing the above-mentioned polyfunctional amino compound and polyvinyl alcohol (hereinafter referred to as solution B) to a porous group using the same method as above. It can be produced by coating or impregnating a material, contacting it with a polyfunctional crosslinking agent, and then heating. The above solution B contains 10 to 5 ooii parts, preferably 20 to 300 parts by weight, of an amino compound per 100 parts by weight of polyvinyl alcohol, and the concentration of the total amount of polyvinyl alcohol and amino compound is 0.05 to 10 parts by weight.
The content is adjusted to 1% by weight, preferably 0.1 to 5% by weight.

By this method, a crosslinking reaction between the amino compound and polyvinyl alcohol is carried out in the surface layer of the solution coating layer on the porous substrate, and a semipermeable, dense, ultra-thin film layer is thus formed on the substrate as the surface layer. Ru. On the other hand, the unreacted polyvinyl alcohol that did not participate in the crosslinking reaction inside the solution-coated layer between the thin film layer and the porous base material becomes water-insoluble by heating, and the mono-amino compound evaporates, so that the inner layer becomes microscopic. A porous layer made of water-insoluble polyvinyl alcohol having a large number of pores is formed so as to integrally support the ultra-thin membrane layer, thereby obtaining the composite semipermeable membrane B used in the present invention.

The composite semipermeable membranes A and B formed in this manner have a large difference in 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 are capable of high selective separation. It is something that has a nature. In the present invention, the removal rate of silicic acid is 50% or less, preferably 30% or less, and the removal rate of the ions is 50% or more, preferably A material having a reverse osmosis performance of 80% or more, more preferably 90% or more is used.

Therefore, since the composite semipermeable membrane used in the present invention has excellent selective separation properties as described above, raw water containing silicic acid can be subjected to reverse osmosis treatment using such a composite semipermeable membrane (from
The cations and anions can be substantially removed and silicic acid can be permeated.

Therefore, it is possible to prevent membrane performance from deteriorating due to membrane contamination due to silicic acid precipitation, and raw water can be treated with a high recovery rate.

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

In particular, if the method of the present invention is applied to a primary pure water production line in the ultrapure water production process, it is extremely economically advantageous because the preceding desilication treatment process can be omitted.

<Example> The present invention will be specifically explained below using examples.

Production Example A Porous base material with an asymmetric structure made of polysulfone (
1% by weight of piperazine and 1% by weight of hydroxide)
After uniformly applying an aqueous solution containing +7 um, a solution of 25% by weight of trimenoic acid chloride in n-hexane
Soaked for 1 minute at a temperature of °C. Pull up this base material 3
After air drying for 0 seconds, the composite semipermeable membrane A was obtained by heating at a temperature of 110° C. for 10 minutes.

Production Example B Porous base material with an asymmetric structure made of polysulfone (
Pure water permeability 1.05 x 10-2F/- seconds, atmospheric pressure)
After uniformly applying an aqueous solution containing 0.25ffi-Jt% of polyvinyl alcohol, 0.25% by weight of piperazine and 0.5% by weight of sodium hydroxide, 0.5% by weight of trimesic acid σ-ride was applied on the top. 25° in hexane solution
It was immersed for 1 minute at a temperature of C. This base material was pulled up to volatilize hexano adhering to the membrane surface, and then heated at a temperature of 110° C. for 10 minutes to obtain composite semipermeable membrane B.

Evaluation Example An aqueous solution containing 2000 ppm of the following solutes and an aqueous solution containing 1100 ppm of sodium silicate were heated to 20 Ki9 using composite semipermeable membranes A and B obtained in the production example.
Table 1 shows the solute removal rate during reverse osmosis treatment under a pressure of /cIl.

Table 1 From this Table 1, it is understood that the composite semipermeable membrane described above has a large difference in removal rate between various solutes and silicic acid, and can be suitably used in the present invention. Degree 50 ppm %TDS concentration IQ' 1
Raw water containing 200 ppm was subjected to reverse osmosis treatment under a pressure of 20 to 9/- using the composite semipermeable membranes A and B obtained in the production example, and the results are shown in Table 2 below. As is clear from this result, since the degree of silicic acid in the concentrated liquid was below the saturated silicic acid concentration in this state, it was confirmed that silicic acid was not precipitated. Furthermore, the permeate could be recovered at a high recovery rate.

Comparative Example Raw water having the same properties as in the example was treated in the same manner as in the example using a reverse osmosis membrane made of cellulose acetate (silicic acid removal rate: 90%). The results are also shown in Table 2.

Claims (2)

[Claims] (1) An ultra-thin film layer made 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 base material. A method for treating silicic acid-containing water, which comprises subjecting silicic acid-containing raw water to reverse osmosis treatment using a composite semipermeable membrane. (2) An ultra-thin film layer formed by crosslinking a polyfunctional amino compound having two or more secondary amino groups in one molecule and polyvinyl alcohol with a polyfunctional cross-linking agent integrally supports the ultra-thin film layer. Raw water containing silicic acid is subjected to reverse osmosis treatment using a composite semipermeable membrane that is integrally provided on a porous substrate through a porous layer made of water-insoluble polyvinyl alcohol as an inner layer. A method for treating silicic acid-containing water.