JP2682071B2 - Cross-linked polyamide reverse osmosis membrane treatment method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a crosslinked polyamide-based reverse osmosis when a stock solution containing a very low concentration of an ionic substance is purified using a crosslinked polyamide reverse osmosis membrane. The present invention relates to a method for treating an osmotic membrane.

In particular, it is preferably used in a system for producing ultrapure water for electronic industry and pure water for boiler supply using the reverse osmosis membrane.

[Prior Art] Conventionally, various semipermeable membranes have been proposed and widely used as selective separation membranes by the reverse osmosis method, but these reverse osmosis membranes gradually deteriorate in separation performance during long-term operation. In such a case, an attempt has been made to maintain or improve the performance by treating the reverse osmosis membrane with an organic liquid in such a case.

As for a cellulose acetate membrane, for example, JP-B-52-32869 discloses a method of treating with polyvinyl alcohol, and JP-B-53-13431 discloses a vinyl acetate-unsaturated carboxylic acid copolymer. A treatment method has been proposed.

The present inventors have also shown a treatment method with a water-soluble amino compound for a semipermeable membrane made of a crosslinked polymer containing furfuryl alcohol as an essential component (Japanese Patent Publication No. 62-16122).
No.). Furthermore, in Japanese Patent Laid-Open No. 63-22163, a two-step treatment method is proposed, in which a similar semipermeable membrane is treated with a water-soluble polyfunctional amine aqueous solution and then treated with a water-soluble polyfunctional aldehyde aqueous solution.

On the other hand, the penetration of reverse osmosis method into the industrial world has been expanding remarkably in recent years, and its use in the most advanced technology fields such as ultrapure water for electronics industry, thermal power, and water supply for boilers such as nuclear power plants has been activated. I'm doing it. However, the water quality standard for the water used for the purpose is very strict, for example, even if very low concentration of sodium ion of about ppb (1/100 million) is present in the raw water for boiler supply, SG thin tube due to free alkali is generated. Is said to be the cause of stress corrosion cracking in the field {Haruhiko Oya "Pure water / Ultrapure water production method, Koushobo, p. 152 (1985)}" As a reverse osmosis membrane, since it has a high solute separation performance and a high water production rate, the fact that a crosslinked polyamide reverse osmosis membrane is trying to make a significant contribution is that metal ion separation performance in a very low concentration range is unsatisfactory. It had a problem of being sufficient.

[Problems to be Solved by the Invention] The present invention is intended to solve the drawbacks of the prior art, and an object thereof is to improve the metal ion selective separation performance at a concentration of 10 ppm or less by an easy means.

[Means for Solving the Problems] The present invention has the following configurations in order to achieve the above object.

"When separating a stock solution to be treated using a crosslinked polyamide reverse osmosis membrane, the stock solution to be treated has a metal ion concentration of 10 ppm or less, and the reverse osmosis membrane is contacted with an aqueous solution containing a water-soluble amino compound. A method for treating a crosslinked polyamide reverse osmosis membrane characterized by the above. ”The present invention is effective in improving the selective separation performance of a stock solution to be treated having a low concentration of metal ions of 10 ppm or less. That is, the crosslinked polyamide-based reverse osmosis membrane has an ion separation characteristic that ions of the same type as the fixed charges of the membrane are excluded and ions of different types are not excluded in the low salt concentration region due to the fixed charges that the crosslinked polyamide-based reverse osmosis membrane itself has. This tendency becomes more remarkable when the salt concentration is 10 ppm or less. On the contrary, when the salt concentration becomes high, the ion separation characteristic due to the fixed charge of the membrane becomes difficult to exist, the influence of the charged membrane disappears, and the separation performance is similar to that of an uncharged neutral membrane. Therefore, in the present invention,
It is effective in improving the selective separation performance of a stock solution to be treated having a low concentration of metal ions of 10 ppm or less.

In the present invention, the crosslinked polyamide-based reverse osmosis membrane refers to a reverse osmosis membrane having an ultrathin film of a crosslinked polymer obtained from an in-situ interfacial polycondensation reaction of a polyfunctional amine and a polyfunctional acid halide, Both the functional amine and the polyfunctional acid halide may be aliphatic or aromatic, and are preferably bifunctional or more and tetrafunctional or less. As the polyfunctional acid halide, chloride, bromide,
Alternatively, iodide is preferably used. As such a reverse osmosis membrane, for example, there is a membrane described in Japanese Examined Patent Publication No. 62-36803, but membranes of the same kind are already known as UTC-70 and SU-40.
0, SU-700 (above, manufactured by Toray Industries, Inc.), FT-30 (produced by Film Tech Co., Ltd.), HR-95, HR-99 (above, DDS)
(Manufactured by Nitto Denko Corporation), NTR-729, NTR-739 (all manufactured by Nitto Denko Corporation). Of these, polyaramid-based ones such as SU-700, FT-30-, and HR-99 have a particularly high solute exclusion rate and are preferable.

As the water-soluble amino compound, 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. Specifically, examples of alkylamino compounds include ethylenediamine, monoethanolamine, diethanolamine, triethylenetetramine, and the like, and aromatic amino compounds include phenylenediamine, diaminodiphenylmethane, sulfenylic acid, diaminobenzoic acid, and the like. Is mentioned. Also,
Examples of the alicyclic amino compound include diaminocyclohexane and the like, and other examples include sulfamic acid, piperazine, aminomethylpiperidine and the like.

Further, it may be a monoamino compound or a polyamino compound, and may be a low molecular compound or a high molecular compound. Specific examples of the polymer compound include polyethyleneimine and phenylenediamine-modified polyepichlorohydrin.

In the present invention, the stock solution to be treated may be acidic, neutral or alkaline, but it is alkaline, that is, pH.
In the region where the value exceeds 7, the use of a quaternary ammonium salt as the water-soluble amino compound is particularly effective. The reason will be described below. Originally, a cross-linked polyamide reverse osmosis membrane is a difficult-to-charge reverse osmosis membrane in which anionic groups and cationic groups remain on the functional layer surface, but in the alkaline region, dissociation of amino groups is suppressed, so The film has a strong property. In such anion-charged reverse osmosis membrane, the exclusion rate of metal ions is lower than that in the cation-charged reverse osmosis membrane. Therefore, by using quaternary ammonium as the water-soluble amine, the property of anion chargeability can be weakened, and the metal ion can be more effectively eliminated. Specific examples of the quaternary ammonium salt include low molecular weight compounds such as ethyltrimethylammonium iodide, phenyltrimethylammonium chloride, benzyltrimethylammonium chloride, cetyltrimethylammonium bromide, cetyldimethylethylammonium bromide and polytrimethyl iodide. Examples thereof include high molecular weight compounds such as allylamine and trimethylamine iodide modified polyethyleneimine. Also,
As the anionic group, in addition to the above halogen ion,
Nitrate ion, sulfate ion and the like can also be used.

The membrane form of the present invention is not limited to a single film, but may be any form that is actually industrially used, such as a spiral type, a hollow fiber type, a tubular type, a pleated type or a plate and frame type. Good.

In the present invention, the concentration of the water-soluble amino compound is preferably in the range of about 1 ppb to about 1%, more preferably
Used at 10ppm or more and 1000ppm or less. If the concentration of the water-soluble amino compound is less than 100 ppm, the amino compound or the quaternary ammonium salt does not adhere sufficiently to the membrane,
The effect of improving the selective separation performance of low-concentration metal ions may not be perfect. On the other hand, when the concentration exceeds 1000 ppm, the selective separation rate of low-concentration metal ions has an initial effect, but the membrane permeation water flux is largely reduced, which may not be economical.

The operating pressure may be in the range of atmospheric pressure to 100 atm, but usually 1 to 70 atm is preferred.

The contact time between the amino compound-containing aqueous solution and the crosslinked polyaramid-based reverse osmosis membrane is such that the metal ion selective separation performance improves immediately after the contact, but it is preferably in the range of about 5 minutes to 1 hour. Such contact may be performed immediately after the production of the reverse osmosis membrane or during the operation of the reverse osmosis apparatus for a long time, and may be continuously or intermittently added.

Furthermore, in order to enhance the durability of the selective separation performance improving effect, after the treatment with the aqueous solution amino compound, a post treatment with a water-soluble polyfunctional aldehyde or the like may be performed.

The present invention, using a crosslinked polyamide-based membrane as a reverse osmosis membrane, by contacting with an aqueous solution containing a water-soluble amino compound, the effect of improving the selective separation performance of the stock solution to be treated having a low concentration of 10 ppm or less metal ions Demonstrate. In particular, when the liquid to be treated is alkaline, it is effective to use a quaternary ammonium salt among water-soluble amino compounds.

[Examples] The present invention will be specifically described with reference to the following examples, but the present invention is not limited to these examples.

Examples 1 to 3 An element using a reverse osmosis membrane mainly composed of a trifunctional aromatic amine and a trifunctional acid chloride as a spiral element having a diameter of 4 inches using a crosslinked polyaramid-based reverse osmosis membrane, Toray ( Co., Ltd. product name "SU-710", film
Using three types of membrane elements, product name "BW-30" manufactured by Tech Co., Ltd. and product name "NTR-739" manufactured by Nitto Denko Corporation, pressure 1
The primary pure water with a sodium concentration of 0.30 ppb was used as the raw water under the operating conditions of 5 kg / cm ² , the amount of water supplied was 10 / min, and the water temperature was 25 ° C.
A reverse osmosis test was performed. 80 hours after the start of operation, polyethyleneimine (manufactured by Nippon Shokubai Kagaku Kogyo Co., Ltd., molecular weight 60 to 80,000)
After adding the raw material water at a concentration of 0 ppm for 1 hour to perform the operation, the operation was resumed.

Table 1 shows the results of measuring the sodium concentration in the permeated water and the concentrated water obtained from the raw water and each membrane element at 5 hours and 72 hours after restarting the operation. The sodium concentration was measured with a flameless atomic absorption spectrometer.

Comparative Examples 1 to 3 Spiral type elements using the crosslinked polyaramid-based reverse osmosis membrane used in Examples 1 to 3 were treated with raw material water and each membrane element at 65 hours after the start of operation before treatment with polyethyleneimine. The sodium concentration in water and concentrated water was confirmed. The results are shown in Table 2, and in SU-710 and NTR-739, the sodium concentration in the permeate was higher than that in the raw water.

Example 4 The SU-710 element of Example 1 is continued 1
A reverse osmosis test was carried out under the same operating conditions as in Examples 1 to 3 using the following pure water as the raw water for supply.
Even after 880 hours, the sodium concentration in the permeate was 0.05 ppb, and the improvement of the sodium ion selective separation rate was maintained.

Example 5 Using a membrane similar to that used for SU-710 in Example 1,
Water supplied with Toray's ultrapure water production equipment (“Trepur LV10T”), which is 500 ppb of ultra-pure pure LiBr, was used as the feed water at a pressure of 15 Kg / cm ² , a feed rate of 3.5 / min, and a water temperature of 25 ° C. Reverse osmosis test was carried out. 50 hours after the start of operation, the concentration of lithium ion in the permeated water was stable and showed a value of 4 ppb. When 10 ppm of benzalkonium chloride, which is a quaternary amino compound, was added to the operating system, the lithium ion concentration in the permeated water was 0.05 ppb. After that, when the addition of the same drug was stopped and the reverse osmosis operation was continued, the concentration of lithium ions in the permeated water returned to 4 ppb after 30 hours. The analysis was performed with an ion chromatography analyzer using a concentration column.

Example 6, Comparative Example 4 The same BW-30 membrane element as that used in Example 2 was disassembled to obtain a flat membrane. This flat membrane was subjected to reverse osmosis operation at a pressure of 15 Kg / cm ² , a water temperature of 25 ° C. and a pH of 6.5 using NaCl aqueous solutions having a concentration of 1 ppm (Example 6) and 1500 ppm (0.15%) (Comparative Example 4) as feed water. Next, for both systems, amine-based cationic flocculant "HISET C500 (Daiichi Kogyo Seiyaku Co., Ltd., molecular weight 50
Table 3 shows the results of observing the selective separation performance of sodium ions with the addition of 1 ppm. In the 1 ppm NaCl system, the selective separation performance of sodium ions was improved by the addition of “HISET C500”, while in the 1500 ppm NaCl system, it was not particularly improved.

Examples 7 to 12 JP-A-62-121603 DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Using a crosslinked polyaramid-based composite membrane comprising an interfacial polycondensation reaction of a polyfunctional aromatic amine and a polyfunctional aromatic acid chloride described in Example 1, a pressure of 15 Kg / c is used.
A reverse osmosis experiment was conducted by adjusting the pH of the raw water to about 8 with potassium hydroxide, using pure water containing sodium ion concentration of 1 ppm as the feed raw water under the operating conditions of m ² , supply water amount of 3.5 / min and water temperature of 25 ° C. It was

Then, as quaternary ammonium salts, ethyltrimethylammonium iodide, phenyltrimethylammonium chloride, benzyltrimethylammonium chloride, cetyltrimethylammonium bromide, cetyldimethylethylammonium bromide, and trimethylamine iodide-modified polyethyleneimine at a concentration of 100 ppm each were added. After continuous addition for a time and reverse osmosis operation, the same reverse osmosis operation as in the initial stage was performed.

Table 4 shows changes in the sodium ion exclusion rate and changes in the permeated water flux before and after the treatment with the quaternary ammonium salt.

Here, the experimental data was measured 6 hours after adjusting the pH to about 8.

Example 13 Using a crosslinked polyaramid-based composite membrane obtained by the interfacial polycondensation reaction of m-phenylenediamine and trimesoyl chloride described in Example 1, a reverse osmosis experiment similar to that of Example 7 was performed at pH 9. went.

Poly iodyl trimethylallylamine was used as the quaternary ammonium salt.

 The results of the reverse osmosis experiment are shown in Table 5.

Example 14 At pH 9 using a crosslinked polyamide-based composite membrane by an interfacial polycondensation reaction of 4- (aminomethyl) piperidine-modified polyepiiodohydrin and isophthalic acid chloride described in Example 1 of JP-B-62-59604. The same reverse osmosis experiment as in Example 7 was performed.

Tetraethylammonium iodide was used as the quaternary ammonium salt.

 The results of the reverse osmosis experiment are shown in Table 5.

Example 15 Using the crosslinked polyamide-based composite membrane described in Example 14 of JP-A-62-201606, the pressure is 7.5 Kg / cm ² , and the amount of supplied water is 3.5.
The change in the sodium ion exclusion rate before and after the addition of the quaternary ammonium salt was examined under the operating conditions of a water temperature of 25 ° C./min.

 Table 5 shows the results.

As the quaternary ammonium salt treatment condition, phenyltrimethylammonium iodide was continuously added at 10 ppb.

[Effect of the Invention] According to the present invention, in a reverse osmosis water production system using a crosslinked polyamide reverse osmosis membrane, the reverse osmosis membrane is contacted with a trace amount of a water-soluble amino compound to give 10 pp
The selective separation performance of metal ions below b can be remarkably improved, which greatly contributes to a pure water production system such as ultrapure water for electronic industry and pure water for boiler supply.

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Miho Hirai 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Industries, Inc. Shiga Business Office Examiner Koichi Nakano (56) References JP 62-16122 (JP, B2) )

Claims (2)

(57) [Claims] 1. An aqueous solution having a metal ion concentration of 10 ppm or less when separating a stock solution to be treated using a crosslinked polyamide reverse osmosis membrane and containing the water-soluble amino compound in the reverse osmosis membrane. A method for treating a crosslinked polyamide-based reverse osmosis membrane, which comprises contacting with a membrane. 2. The method for treating a crosslinked polyamide reverse osmosis membrane according to claim 1, wherein the stock solution to be treated is alkaline and the water-soluble amino compound is a quaternary ammonium salt.