Combined chlorine agent and production and use thereof

Abstract

A combined chlorine agent having a low concentration of free chlorine and a high concentration of combined chlorine whereby the combined chlorine concentration of water can be increased when added to water systems at a low concentration of free chlorine. The combined chlorine agent is an aqueous agent which contains an alkali metal hydroxide, sulfamic acid, and an oxidizing agent based on chlorine, wherein the compositional ratio of the oxidizing agent based on chlorine to the sulfamic acid is in the range from 0.45 to 0.6 by Cl/N (mole ratio), the compositional ratio of the oxidizing agent based on chlorine to alkali is in the range from 0.3 to 0.4 by Cl/alkali metal (mole ratio), and the free chlorine concentration in the aqueous agent is 2% by weight or lower of the total chlorine concentration.

Claims

1. A method of slime control for a reverse osmosis membrane, comprising the step of: adding a combined chlorine agent to a feed water system containing the reverse osmosis membrane, the combined chlorine agent comprising an aqueous agent containing an alkali comprising an alkali metal hydroxide, sulfamic acid or a salt thereof, and a chlorine-containing oxidizing agent, wherein the compositional ratio of the oxidizing agent to the sulfamic acid or salt thereof is in the range from 0.45 to 0.6 by Cl/N molar ratio, the compositional ratio of the oxidizing agent to alkali is in the range from 0.3 to 0.4 by Cl/alkali metal molar ratio, the compositional ratio of sulfamic acid or salt thereof to alkali in the aqueous solution agent is in the range from 0.5 to 0.7 by N/alkali metal molar ratio, the amount of alkali metal contained in the salt of sulfamic acid is calculated as alkali, the pH of the aqueous agent is 13 or more, and the free chlorine concentration in the aqueous agent is no more than 1000 mg/L and 2% by weight of the total chlorine concentration, and the chlorine agent is added to the feed water system containing the reverse osmosis membrane such that the free chlorine concentration in the feed water system is no more than 0.1 mg/L to prevent deterioration of the reverse osmosis membrane.

2. The method of slime control for a reverse osmosis membrane as claimed in claim 1, wherein the combined chlorine agent is added to the feed water system for the reverse osmosis membrane such that the free chlorine concentration is no more than 0.1 mg/L and total chlorine concentration is 1-50 mg/L.

3. The method of slime control for a reverse osmosis membrane as claimed in claim 1, wherein the reverse osmosis membrane is a polymer membrane having a nitrogen-containing group.

4. The method of slime control for a reverse osmosis membrane as claimed in claim 3, wherein the reverse osmosis membrane is a polyamide, polyurea or polypiperazine amide membrane.

5. The method of slime control for a reverse osmosis membrane as claimed in claim 1, wherein the combined chlorine agent consists of an alkali metal hydroxide, sulfamic acid or a salt thereof, a chlorine-containing oxidizing agent and water.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a graph showing the correlation between the Cl/N (mol ratio) and free chlorine concentration in Examples 1-3 and Comparative Examples 1-3.

(2) FIG. 2 is a graph showing the variations of permeate and pressure drop in Example 4.

(3) FIG. 3 is a graph showing the variation of salt rejection in Example 4.

(4) FIG. 4 is a graph showing the variation of permeate and pressure drop in Comparative Example 9.

(5) FIG. 5 is a graph showing the variation of salt rejection in Comparative Example 9.

(6) FIG. 6 is a graph showing the variation of permeate and pressure drop in Comparative Example 10.

(7) FIG. 7 is a graph showing the variation of salt rejection in Comparative Example 10.

EMBODIMENT OF THE INVENTION

(8) Below, the present invention is explained by way of Examples and Comparative Examples wherein % denotes % by weight and part denotes part by weight unless specific indication is given.

EXAMPLES

Examples 1-3

(9) To pure water in amount shown for each Example in Table 1, sodium hydroxide was added to dissolve therein, then sulfamic acid (powdery sulfamic acid wherein R.sup.1, R.sup.2 in the above formula 1 are each H) was added to dissolve therein, and then sodium hypochlorite in the amount shown for each Example in Table 1 was added to dissolve therein whereby the combined chlorine agent of the aqueous solution agent of each Example was produced. Characteristics, free chlorine concentration and total chlorine concentration of the obtained aqueous solution agents are shown in Table 1. In Tables 1-4, NaOH (Na mol/L), N (mol/L) and available chlorine (mol/L) are shown as values, each calculated with the specific gravity of the solution being 1.3.

(10) TABLE-US-00001 TABLE 1 Example 1 Example 2 Example 3 Main component Comb. Cl Comb. Cl Comb. Cl agent agent agent Pure water (part) 15.5 13.2 8.6 48% NaOH (part) 19.5 20.8 23.4 Sulfamic acid (part) 15.0 16.0 18.0 12% (Cl.sub.2) NaClO (part) 50.0 50.0 50.0 Total (part) 100 100 100 NaOH (Na mol/L) 3.043 3.246 3.651 N (mol/L) 2.009 2.143 2.411 Available Cl (mol/L) 1.099 1.099 1.099 N/Na (mol ratio) 0.66 0.66 0.66 Cl/N (mol ratio) 0.55 0.51 0.46 Cl/Na (mol ratio) 0.36 0.34 0.30 pH (when prepared) pH > 13 pH > 13 pH > 13 Free Cl (when prepared) (mg/L) <1000 <1000 <1000 Total Cl (when prepared) (%) 6.9 6.9 6.9 Appearance (when prepared) Good Good Good pH (after 7 days storage at 40 C.) pH > 13 pH > 13 pH > 13 Free Cl (after 7 days storage 930 920 940 at 40 C.) (mg/L) Total Cl (after 7 days storage 6.9 6.9 6.9 at 40 C.) (%) Appearance Good Good Good (after 7 days storage at 40 C.) Appearance Good Good Good (after 7 days storage at 5 C.)

Comparative Examples 1-3

(11) Examples 1-3 were pursued except that the composition of each component was changed as described in Table 2. The results of Comparative Examples 1-3 are shown in Table 2. In Comparative Example 1, two parts of benzotriazole was added as another component to a sum total amount of 100 parts which was shown with *1 in Table 2.

(12) TABLE-US-00002 TABLE 2 Comp. Comp. Comp. Example 1 Example 2 Example 3 Main component Comb. Cl Comb. Cl Comb. Cl agent agent agent Pure water (part) 6.7 12.4 6.6 48% NaOH (part) 19.3 15.6 18.9 Sulfamic acid (part) 12.0 12.0 14.5 12% (Cl.sub.2) NaClO (part) 60.0 60.0 60.0 Total (part) 100 *1 100 100 NaOH (Na mol/L) 3.012 2.434 2.949 N (mol/L) 1.607 1.607 1.942 Available Cl(mol/L) 1.319 1.319 1.319 N/Na (mol ratio) 0.53 0.66 0.66 Cl/N (mol ratio) 0.82 0.82 0.68 Cl/Na (mol ratio) 0.44 0.54 0.45 pH (when prepared) pH > 13 pH > 13 pH > 13 Free Cl (when prepared) (mg/L) 6000 6000 2000 Total Cl (when prepared) (%) 7.7 7.7 7.7 Appearance (when prepared) Good Good Good pH (after 7 days storage at 40 C.) pH > 13 pH > 13 pH > 13 Free Cl (after 7 days storage 8000 at 40 C.) (mg/L) Total Cl (after 7 days storage 7.1 at 40 C.) (%) Appearance Good Good Good (after 7 days storage at 40 C.) Appearance Good Good Good (after 7 days storage at 5 C.)

Comparative Examples 4-6

(13) Examples 1-3 were pursued except that the composition of each component was changed as described in Table 3, wherein the sulfamic acid was not able to dissolve into the aqueous solution of pure water added with sodium hydroxide (shown as Deposit). The results of Comparative Examples 4-6 are shown in Table 3.

(14) TABLE-US-00003 TABLE 3 Comp. Comp. Comp. Example 4 Example 5 Example 6 Main component Comb. Cl Comb. Cl Comb. Cl agent agent agent Pure water (part) 6.6 4.0 6.7 48% NaOH (part) 24.4 26.0 27.3 Sulfamic acid (part) 19.0 20.0 21.0 12% (Cl.sub.2) NaClO (part) 50.0 50.0 45.0 Total (part) 100 100 100 NaOH (Na mol/L) 3.808 4.057 4.260 N (mol/L) 2.545 2.678 2.812 Available Cl (mol/L) 1.099 1.099 0.989 N/Na (mol ratio) 0.67 0.66 0.66 Cl/N (mol ratio) 0.43 0.41 0.35 Cl/Na (mol ratio) 0.29 0.27 0.23 pH (when prepared) Free Cl (when prepared) (mg/L) Total Cl (when prepared) (%) Appearance (when prepared) Deposit Deposit Deposit pH (after 7 days storage at 40 C.) Free Cl(after 7 days storage at 40 C.) (mg/L) Total Cl (after 7 days storage at 40 C.) (%) Appearance (after 7 days storage at 40 C.) Appearance (after 7 days storage at 5 C.)

Comparative Examples 7-8

(15) Examples 1-3 were pursued except that the composition of each component was changed as described in Table 4, wherein the sulfamic acid was not able to dissolve into the aqueous solution of pure water added with sodium hydroxide. Results of Comparative Examples 7-8 ware shown in Table 4.

(16) TABLE-US-00004 TABLE 4 Comp. Comp. Example 7 Example 8 Main component Comb. Comb. Cl agent Cl agent Pure water (part) 13.6 9.0 48% NaOH (part) 23.4 26.0 Sulfamic acid (part) 18.0 20.0 12% (Cl.sub.2) NaClO (part) 45.0 45.0 Total (part) 100 100 NaOH (Na mol/L) 3.651 4.057 N (mol/L) 2.411 2.678 Available Cl (mol/L) 0.989 0.989 N/Na (mol ratio) 0.66 0.66 Cl/N (mol ratio) 0.41 0.37 Cl/Na (mol ratio) 0.27 0.24 pH (when prepared) Free Cl (when prepared) (mg/L) Total Cl (when prepared) (%) Appearance (when prepared) Deposit Deposit pH(after 7 days storage at 40 C.) Free Cl(after 7 days storage at 40 C.) (mg/L) Total Cl (after 7 days storage at 40 C.) (%) Appearance (after 7 days storage at 40 C.) Appearance (after 7 days storage at 5 C.)

(17) In Examples 1-3 and Comparative Examples 1-3, the correlation between the Free chlorine concentration/Sulfamic acid (mol ratio), namely Cl/N (mol ratio) and Free chlorine concentration is shown in FIG. 1, wherein the free chlorine concentrations in Comparative Examples 1-3 were calculated so that the total chlorine concentration was 6.9%, the same as Examples 1-3.

(18) The above results show that, in Examples 1-3, the free chlorine concentration in the aqueous agent is 1000 mg/L or lower, which falls in 2% by weight or lower of the total chlorine concentration, and that in Comparative Examples 1-3, the free chlorine concentration in the aqueous agent is higher than 1000 mg/L, which is higher than 2% by weight of the total chlorine concentration. Although the total chlorine concentration in Examples 1-3 is lower than in Comparative Examples 1-3, the difference in the total chlorine concentration is smaller than the difference in the free chlorine concentration. It is also shown that, in Comparative Examples 4-8, an aqueous agent cannot be produced because a deposit occurs.

Example 4

(19) Cooling water discharged from a cooling tower was mixed with a combined chlorine agent and subjected to coagulation treatment, filtration and active carbon treatment to obtain a pretreated water having a total chlorine concentration of 5 mg/L and free chlorine concentration of 0.5 mg/L. The pretreated water was mixed with 10% by weight of an aqueous solution of sodium bisulfite, added at sodium bisulfite concentration of 15 mg/L, to reduce the total chlorine and free chlorine contained in the pretreated water to zero whereby the water to be treated was prepared. To this water to be treated, the combined chlorine agent obtained in Example 2 was added so that the total chlorine concentration was 1.2 mg/L and free chlorine concentration was 0.05 mg/L. The water to be treated was pressurized to 1.5 MPa by a pump and supplied to a concentrate room of a RO membrane treatment apparatus to carry out RO treatment. The RO membrane treatment apparatus was installed with a 4 inch spiral type RO membrane element of aromatic polyamide (ES 20-D4 of Nitto Electric Industrial Co., Ltd) in a vessel.

(20) During 3 months of continuous operation under the above condition, no deterioration of the RO membrane, no increase in pressure drop and no slime trouble occurred. During the period, variations of permeate and pressure drop are shown in FIG. 2 and variation of salt rejection is shown in FIG. 3 wherein it is affirmed that there occurs no clogging by slime because there is no increase in pressure drop and no decrease of flux since the start of the operation. Further, it is also affirmed that there occurs no deterioration in the water quality of the produced water by the adhesion of contaminants to the RO membrane or deterioration of the RO membrane because there occurs no decrease of salt rejection from the start of the operation.

Comparative Example 9

(21) Example 4 was pursued except that the pretreated water to be supplied to the RO membrane was further mixed with a chlorine agent so that the total chlorine concentration was 13 mg/L and free chlorine concentration 0.2 mg/L. In the period, the variation of permeate and pressure drop is shown in FIG. 4 and variation of salt rejection is shown in FIG. 5, wherein it is recognized that there occurs a deterioration in the RO membrane.

Comparative Example 10

(22) Example 4 was pursued except that the water to be treated in the pretreatment was not mixed with a chlorine agent and that the pretreated water of a free chlorine concentration of 0.0 mg/L was supplied to the RO membrane. During the period, the variations in permeate and pressure drop are shown in FIG. 6 and variation of salt rejection is shown in FIG. 7, wherein it is recognized that there occurs a decrease in flux by slime formation.

INDUSTRIAL APPLICATION OF THE INVENTION

(23) The present invention can be applied as a combined chlorine agent used for a slime control agent for a reverse osmosis membrane and used for other chlorine treatment agents, method of production thereof and method of chlorine treatment as the use thereof, especially a method of chlorine treatment for the slime control of a reverse osmosis membrane.