WATER TREATMENT CHEMICAL FOR MEMBRANE, AND MEMBRANE TREATMENT METHOD

Abstract

A water treatment chemical for a membrane, being is a water treatment chemical for preventing membrane contamination caused by an organic compound having a phenolic hydroxy group and including an organic amine having two or more nitrogen atoms and having five or more carboxyl groups or four or more phosphate groups. A membrane treatment method including adding the water treatment chemical for a membrane to water to be treated which contains an organic compound having a phenolic hydroxy group and then subjecting the water to be treated to membrane separation treatment.

Claims

1. A water treatment chemical for a membrane, being a water treatment chemical for preventing membrane contamination caused by an organic compound having a phenolic hydroxy group, and comprising an organic amine having two or more nitrogen atoms and having five or more carboxyl groups or four or more phosphate groups.

2. The water treatment chemical for a membrane according to claim 1, wherein the organic amine is an organic amine represented by any one of the following (1) to (3): ##STR00007## wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each represent a phosphate group, and n is an integer of 1 or more, ##STR00008## wherein R.sup.11, R.sup.12, R.sup.13, R.sup.14 and R.sup.15 each represent a carboxyl group or a phosphate group, and p and q are each independently an integer of 1 or more, ##STR00009## wherein R.sup.21, R.sup.22, R.sup.23, R.sup.24, R.sup.25 and R.sup.26 each represent a carboxyl group, and m is an integer of 1 or more.

3. The water treatment chemical for a membrane according to claim 2, wherein n in the general formula (1), p and q in the general formula (2), and m in the general formula (3) are each an integer of 1 to 5.

4. The water treatment chemical for a membrane according to claim 1, wherein a molecular weight of the organic amine is 100 to 1000.

5. The water treatment chemical for a membrane according to claim 1, being a water treatment chemical for a reverse osmosis membrane for carrying out reverse osmosis membrane treatment of water to be treated, the water containing an organic compound having a phenolic hydroxy group, wherein a concentration of non-purgeable organic carbon in concentrated water obtained by the reverse osmosis membrane treatment is 0.01 to 100 mg/L.

6. The water treatment chemical for a membrane according to claim 5, wherein a concentration ratio of the reverse osmosis membrane is 3 times or more.

7. A membrane treatment method comprising adding the water treatment chemical for a membrane according to claim 1 to water to be treated, the water containing an organic compound having a phenolic hydroxy group, and then subjecting the water to be treated to membrane separation treatment.

8. The membrane treatment method according to claim 7, wherein the water treatment chemical for a membrane is added to the water to be treated in such a manner that the concentration of the organic amine becomes 0.01 to 20 mg/L.

Description

BRIEF DESCRIPTION OF DRAWING

[0027] FIG. 1 is a graph showing results of Examples 1 to 4, Comparative Examples 1 to 6, and Reference Example 1.

DESCRIPTION OF EMBODIMENT

[0028] An embodiment of the present invention is described in detail hereinafter.

[0029] The present invention is described below giving, as an example, a case where the water treatment chemical for a membrane of the present invention is applied to membrane separation treatment mainly using an RD membrane, but the water treatment chemical for a membrane of the present invention is also effectively applied to water to be treated (feed-water) in treatment using separation membranes other than the RO membrane, such as MF membrane, UF membrane and NF membrane.

[0030] The water treatment chemical for a membrane of the present invention is a water treatment chemical for preventing membrane contamination caused by an organic compound having a phenolic hydroxy group, and contains, as an active substance, an organic amine having two or more nitrogen atoms and having five or more carboxyl groups (COOH) or four or more phosphate groups (P(O)(OH).sub.2).

[0031] Details of mechanism that membrane contamination caused by an organic compound having a phenolic hydroxy group can be prevented by the organic amine having two or more nitrogen atoms and having five or more carboxyl groups or four or more phosphate groups, which is used in the present invention, are not clear, but are thought to be as follows.

[0032] The carboxyl group or the phosphate group of the organic amine and the phenolic hydroxy group of the organic compound having a phenolic hydroxy group in the water to be treated interact with each other through a hydrogen bond to disperse the organic compound having a phenolic hydroxy group, thereby preventing adhesion of the organic compound to the membrane surface. In that case, if the organic amine is an organic amine having five or more carboxyl groups or four or more phosphate groups, the interaction between this organic amine and the organic compound having a phenolic hydroxy group is large, and a good dispersion effect can be obtained. The upper limit of the number of the carboxyl groups or the phosphate groups in the organic amine is not particularly limited, but in usual, the number of the carboxyl groups is 15 or less, and the number of the phosphate groups is 10 or less.

[0033] The organic amine as an active substance of the water treatment chemical for a membrane of the present invention is, for example, an organic amine represented by any one of the following general formulae (1) to (3).

##STR00004##

wherein R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each represent a phosphate group, and n is an integer of 1 or more.

##STR00005##

wherein R.sup.11, R.sup.12, R.sup.13, R.sup.14 and R.sup.15 each represent a carboxyl group or a phosphate group, and p and q are each independently an integer of 1 or more.

##STR00006##

wherein R.sup.21, R.sup.22, R.sup.23, R.sup.24, R.sup.25 and R.sup.26 each represent a carboxyl group, and m is an integer of 1 or more.

[0034] n in the general formula (1), p and q in the general formula (2), and m in the general formula (3) are each preferably an integer of 1 to 5, and more preferably 1 to 3.

[0035] The molecular weight of the organic amine for use in the present invention is preferably 100 to 1000, and particularly 100 to 800. In the present invention, the molecular weight of the organic amine is a total of atomic weights in its molecular formula.

[0036] When the numbers n, p, q and m of the repeating units of the methylene groups in the general formulae (1) to (3) are each in the above range and the molecular weight is in the above range, the organic amine is easily bonded to the organic compound having a phenolic hydroxy group, and the effect of dispersing the organic compound having a phenolic hydroxy group becomes excellent.

[0037] Specific examples of the organic amines for use in the present invention include organic amines used in Examples described later, but the organic amines are in no way limited to those described later. The organic amines may be used singly, or may be used in combination of two or more. The organic amine may be used in the form of a salt, such as a sodium salt.

[0038] The water treatment chemical for a membrane of the present invention only needs to be one containing the above-described organic amine, and may be one containing other scale preventive agents or slime control agents in addition to the organic amine.

[0039] Examples of the organic compounds having a phenolic hydroxy group that are contained in membrane feed-water to which the water treatment chemical of the present invention is applied include the following ones.

[0040] The phenolic hydroxy group refers to a hydroxy group bonded to an aromatic ring, and examples of the organic compounds having this group include humic acid, fulvic acid, ellagic acid, phenolic acid, tannin, catechin, rutin, anthocyanin, and a synthesized phenolic resin.

[0041] The molecular weight (in the case of low-molecular compound) or the weight-average molecular weight (in the case of high-molecular compound) of the organic compound having a phenolic hydroxy group is usually 500 to 1000000, preferably 1000 to 500000, and more preferably 1000 to 100000. When the molecular weight or the weight-average molecular weight of the organic compound having a phenolic hydroxy group is about 500 to 1000000 (preferably 1000 to 100000), it becomes possible to effectively disperse the organic compound by the water treatment chemical for a membrane of the present invention.

[0042] When the organic compound having a phenolic hydroxy group is a high-molecular compound such as polyphenol, its weight-average molecular weight is a value in terms of pullulan that is measured by GPC method and calculated using a calibration curve for pullulan standard.

[0043] Examples of the water to be treated that contains the organic compound having a phenolic hydroxy group include surface water and groundwater that contain humic substances including polyphenol, and wastewater that is from food/beverage manufacturing factories and contains polyphenol derived from raw materials.

[0044] The coagulation treated water described in the aforesaid Patent Literature 1, which is obtained after coagulation treatment using an alkali solution of a phenolic resin as a coagulant and contains a residual phenolic resin, is also preferred water to be treated.

[0045] The concentration of the organic compound having a phenolic hydroxy group contained in such water to be treated as above varies depending on the type of the water to be treated, but is usually about 0.01 to 10 mg/L.

[0046] pH of the water to be treated that is subjected to membrane treatment is not particularly limited, but is preferably 3.5 to 8.5, more preferably 4.0 to 7.5, and still more preferably 5.0 to 7.0. Therefore, it is preferable to add an acid agent and/or an alkali agent to the water to be treated to thereby adjust its pH to this range, when needed.

[0047] The water treatment chemical for a membrane of the present invention can be preferably used as, for example, a water treatment chemical for RO membranes, and by adding this chemical to RO membrane feed-water containing an organic compound having a phenolic hydroxy group especially in such RO membrane separation treatment that the concentration of non-purgeable organic carbon (NPOC) in the resulting concentrated water becomes 0.01 to 100 mg/L, particularly 0.1 to 50 mg/L, or in such RO membrane separation treatment that the concentration ratio is 3 times or more, for example, 3 to 5 times, a good effect can be obtained.

[0048] When the water treatment chemical for a membrane of the present invention is added to RO membrane or another membrane feed-water in order to prevent membrane contamination caused by an organic compound having a phenolic hydroxy group, the addition amount of the chemical is preferably such an amount that the concentration of the aforesaid organic amine having two or more nitrogen atoms and having five or more carboxyl groups or four or more phosphate groups becomes 0.01 to 20 mg/L, particularly 0.01 to 10 mg/L. If the addition amount of the organic amine is too small, the effect of dispersing an organic compound having a phenolic hydroxy group due to the organic amine cannot be sufficiently obtained, and if the amount thereof is too large, there is a possibility that the organic amine itself causes membrane contamination.

EXAMPLES

[0049] The effect of the present invention is described in more detail with reference to specific examples. The present invention is in no way limited to the following examples.

[0050] Evaluation chemicals which were used in the following Examples and Comparative Examples are set forth in Table 1 described below.

TABLE-US-00001 TABLE 1 Molecular Compound name weight Ex. 1 ethylenediaminetetramethylenephosphonic 380 acid Ex. 2 diethylenetriaminepentamethylenephosphonic 573 acid Ex. 3 diethylenetriaminepentaacetic acid 436 Ex. 4 triethylenetetraminehexaacetic acid 626 Comp. addition of no chemical Ex. 1 Comp. ethylenediaminetetraacetic acid 292 Ex. 2 Comp. hydroxyiminodiacetic acid 221 Ex. 3 Comp. amino trimethylene phosphonic acid 611 Ex. 4 Comp. hydroxyethanephosphonic acid 206 Ex. 5 Comp. hexamethylenediamine 492 Ex. 6 tetra(methylenephosphonic acid)

[0051] Test methods in Examples and Comparative Examples are as follows.

<Preparation of Test Solution>

[0052] An aqueous solution containing a Canadian Fulvic Acid solution (adjusted so that the UV260 value became 0.5) as an organic compound having a phenolic hydroxy group, calcium chloride (100 mg/L), 30 mg/L of Ca and 2 mg/L of the evaluation chemical was prepared, and further, pH of the aqueous solution was adjusted to 6.5 to 7.0 by using a small amount of a sodium hydroxide aqueous solution or a sulfuric acid aqueous solution, thereby preparing a test solution I.

[0053] The Canadian Fulvic Acid was an organic compound having a phenolic hydroxy group and having a molecular weight of 10000, and the concentration of the organic compound having a phenolic hydroxy group in the test solution I was 7.4 to 7.6 mg/L.

[0054] Separately, a test solution II was prepared in the same manner as for the test solution I, except that the Canadian Fulvic Acid and the evaluation chemical were not added (Reference Example 1).

[0055] Moreover, a test solution III was prepared in the same manner as for the test solution I, except that the evaluation chemical was not added (Comparative Example 1).

<RO Membrane Pass Test>

[0056] Using the above test solutions I to III, RO membrane pass tests were carried out under the following conditions.

[0057] RO membrane: polyamide-based RO membrane (ES20 manufactured by Nitto Denko Corporation)

[0058] Temperature: 24 to 25 C.

[0059] Membrane recovery ratio: 75% (four times concentration)

[0060] NPOC concentration in concentrated water of test solutions I to III: 29.6 to 30.4 mg/L

[0061] The NPOC concentration is a concentration given when the evaluation chemical is not added.

[0062] In the above test, changes of a flux ratio (ratio of flux after the elapse of a certain period of time to initial flux) with time were examined, and the results are shown in FIG. 1.

[0063] From FIG. 1, the following has become apparent.

[0064] In Comparative Example 1 in which the chemical was not added, the flux ratio markedly decreased with time.

[0065] Also in Comparative Examples 2 to 6, this decrease was not able to be sufficiently prevented.

[0066] In Examples 1 to 4, 50% or more of the initial flux was able to be maintained even in the continuous pass for 50 hours or more.

[0067] The chemicals used in Examples 1 to 4 include chemicals publicly known as usual scale dispersants, but the effect of dispersing an organic compound having a phenolic hydroxy group has not been conventionally known.

[0068] On the other hand, in the test solution II containing Ca but not containing Canadian Fulvic Acid, a decrease in flux was not observed, and therefore, it can be understood that the effect of the present invention (flux-enhancing effect in comparison with Comparative Example 1 containing no chemical) is an effect of dispersing the organic compound having a phenolic hydroxy group, and is an effect of a different nature from the effect due to the Ca scale preventive agent.

[0069] The present invention has been described in detail using a specific embodiment, but it is obvious to a person skilled in the art that various modifications can be made without departing from the spirit and scope of the present invention.

[0070] The present application is based on Japanese Patent Application No. 2017-050167 filed on Mar. 15, 2017, and the whole thereof is incorporated herein by reference.