Repair method of reverse osmosis element

Abstract

The invention discloses a reverse osmosis element repairing method. The method comprises the following steps: S1, carrying out acid-base cleaning and water washing on the reverse osmosis element which is damaged by oxidation; and S2, immersing the reverse osmosis element in a repair aqueous solution containing 4-(4, 6-dimethoxytriazine)-4-methylmorpholine hydrochloride, a polyamino compound, and rhodamine containing diamino or a derivative thereof, and washing with water to obtain the repaired reverse osmosis element. The desalination rate of the single reverse osmosis element repaired by the method can be recovered to 99% or above under standard test conditions, the repairing effect can be stably maintained for 3 months or above, and meanwhile, the high-pressure resistance and high-temperature resistance of the reverse osmosis element are further improved. The service life can be further prolonged and the operation and maintenance cost can be reduced when the method is applied to water treatment.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment, and in particular to a method for repairing a reverse osmosis element. Background Art

[0002] Reverse osmosis technology is widely used in household water purifiers, industrial pure water manufacturing, wastewater treatment and seawater desalination, and has made important contributions to the sustainable use of water resources. Commercial polyamide reverse osmosis elements mainly include reverse osmosis membranes, concentration and dilution nets, central tubes and outer glass fibers. Among them, the reverse osmosis membrane plays a decisive role in the desalination rate. However, in actual use, reverse osmosis elements still face a series of problems. Among them, oxidizing substances such as active chlorine destroy and degrade the polyamide separation layer of the reverse osmosis membrane, thereby causing the reverse osmosis element to reduce desalination rate, which is one of the huge challenges faced by the application of reverse osmosis technology.

[0003] Repairing reverse osmosis elements can not only save the purchase cost of new elements, but also reduce the pollution of discarded elements to the environment. Currently, the disclosed patents mainly restore the elements by strengthening the cleaning or cross-linking the coating method. Strengthened cleaning and slurry coating technology, such as CN106139906A, uses discarded reverse osmosis elements as raw materials, and improves the desalination performance of the elements by optimizing the selection of chemical cleaning processes and slurry coating repair processes. Cross-linking coating technology, such as CN111495193A, repairs the reverse osmosis elements by soaking in acrylic acid-2-acrylamide-2-methylpropane sulfonic acid copolymer, hydrolyzed polymaleic anhydride, sodium styrene sulfonate-maleic acid copolymer, sodium citrate, polycarboxylic acid terpolymer and deionized water components to improve the desalination rate; for example, CN112473391A uses dyes containing carboxyl or sulfonic acid groups in the molecular structure and a molecular weight greater than 400, including rhodamine, methyl blue, methyl orange, etc. in an aqueous solution as raw water, and uses dyes to preferentially dye the composite The characteristics of the bottom membrane material of the membrane seal the defective part of the polyamide to repair the desalination capacity of the element; for example, CN115105963B uses imine compounds and diamine compounds to repair the reverse osmosis element to improve the desalination rate; in addition, the patent CN114749029B uses a diazotization reaction to reconstruct the aniline structure contained in the separation layer of the degraded polyamide reverse osmosis membrane, and obtains more cis-azo structures by simply irradiating the membrane surface with ultraviolet light, thereby increasing the resistance of the separation layer to sodium ion penetration and achieving the effect of repairing the desalination performance of the membrane element. In terms of cross-linking coating technology in the preparation process of reverse osmosis membranes, for example, CN 118142359 A coats 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, bisaminoquinazoline aqueous solution A and maleic acid-acrylic acid copolymer aqueous solution B on the surface of the new polyamide separation layer to prepare a modified cross-linking coating to improve the anti-pollution and oxidation resistance of the membrane, but does not involve the improvement of the membrane / element desalination rate and the improvement of high temperature and high pressure resistance.

[0004] Although some technical solutions have been developed to improve the desalination rate of components after oxidation, these technical solutions still need to be further improved in terms of the stability of the repair effect and further improving the high temperature and high pressure resistance of the repaired components. Summary of the invention

[0005] The object of the present invention is to provide a method for repairing a reverse osmosis element, wherein the reverse osmosis element repaired by the method has excellent stability, high temperature resistance and high pressure resistance.

[0006] To achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0007] A method for repairing a reverse osmosis element, the method comprising the following steps:

[0008] S1: Perform acid and alkali cleaning and water washing on the reverse osmosis elements that have been damaged by oxidation;

[0009] S2: Immerse the reverse osmosis element in a repair aqueous solution containing 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, polyamino compounds, rhodamine containing diamino groups or their derivatives, and wash with water to obtain a repaired reverse osmosis element.

[0010] In S1 of the present invention, acid and alkali cleaning is performed to remove pollutants on the membrane surface to obtain a clean reverse osmosis element.

[0011] As a preferred solution, the acid-base cleaning method described in S1 is a common method in the industry. Specifically, it includes the following steps: 0.1-1.0 bar cleaning pressure, pH between 2-4, acid cleaning time 20-30 minutes; then alkaline cleaning, pH between 11-13, alkaline cleaning time 20-30 minutes.

[0012] As a preferred solution, in S1, after the acid-base cleaning is completed, water washing is performed until the pH value of the effluent is between 6-9.

[0013] In one embodiment of the present invention, the polyamino compound described in S2 is a compound having at least 2 active amino groups. Preferably, it is one or more of an aromatic compound having at least 2 active amino groups, an aliphatic compound having at least 2 active amino groups, and an alicyclic compound having at least 2 active amino groups, more preferably one or more of m-phenylenediamine, isophenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4-diaminoanisyl, amphenol, xylene diamine, ethylenediamine, propylene diamine, ethylenediamine, hexamethylenediamine, tris(2-aminoethyl)amine, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine or 4-aminomethylpiperazine, and more preferably hexamethylenediamine.

[0014] In one embodiment of the present invention, the mass percentage of the polyamino compound in the repair aqueous solution is 0.3wt% to 10wt%, preferably 0.5 to 3wt%.

[0015] In one embodiment of the present invention, the diamino-containing rhodamine or its derivative in S2 includes one or more of rhodamine 110, rhodamine 123 or 2',7'-diiododihydrorhodamine 123, and rhodamine 110 is more preferred.

[0016] In one embodiment of the present invention, in the repair aqueous solution, the mass percentage of rhodamine or its derivatives containing diamino groups is 0.01 wt% to 10 wt%, preferably 0.05 to 0.5 wt%.

[0017] In one embodiment of the present invention, in the repair aqueous solution, the mass percentage of 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride is 0.01 wt% to 2 wt%, preferably 0.03 to 0.5 wt%.

[0018] In one embodiment of the present invention, the pumping pressure of the repair water solution in S2 is 0.1-1.0 bar, and the soaking time is 5-30 min.

[0019] The present invention also provides a regenerated reverse osmosis element obtained by the reverse osmosis element repair method, which has excellent separation performance and good high temperature and high pressure resistance. Under 1.55MPa and 2000ppm sodium chloride test, the single branch desalination rate of the repaired reverse osmosis element can be restored to more than 99%, and the repair effect can be stably maintained for more than 3 months. After the high temperature and high pressure tolerance test, the flux attenuation amplitude is ≤5%.

[0020] The present invention repairs the reverse osmosis element by immersing and introducing a repair aqueous solution containing 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, polyamino compounds and rhodamine or its derivatives containing diamino groups into the oxidized element. The reverse osmosis membrane separation layer of the oxidized element contains a large number of carboxyl groups, of which a part is generated by the hydrolysis of the acyl chloride groups that do not participate in the reaction when the polyamide separation layer is prepared by the interfacial polymerization reaction; the rest is generated by the amide bond breakage in the polyamide separation layer when it is in contact with oxidants such as residual chlorine during use. It is the large number of amide bond breakages in the polyamide separation layer that causes the desalination rate of the element to decrease. Catalyzed by 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, the amino groups in the polyamino compounds react with the carboxyl groups in the polyamide separation layer to "patch" the polyamide separation layer, thereby re-improving the crosslinking degree of the polyamide separation layer and improving the desalination rate. The introduction of rhodamine or its derivatives containing diamino groups can not only further repair the polyamide separation layer and improve the desalination rate, but also the rigid three-dimensional molecular skeleton of the hydrophilic polyphenyl ring anthracene derivatives also gives the element good water flux, high pressure resistance and high temperature resistance.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The present invention repairs the reverse osmosis element by immersing and repairing the oxidized element with a repair aqueous solution containing 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, polyamino compounds, rhodamine containing diamino groups or its derivatives. Under the catalysis of 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, the polyamino compounds react with the carboxyl groups in the polyamide separation layer to "patch" the polyamide separation layer, thereby re-increasing the crosslinking degree of the polyamide separation layer and improving the desalination rate. At the same time, the introduction of rhodamine containing diamino groups or its derivatives can not only give the reverse osmosis element good water production performance, but also achieve high temperature and high pressure resistance.

[0023] (2) The repair effect of the method of the present invention is good, and the regenerated reverse osmosis element has stable performance and excellent oxidation resistance. Under the test of 1.55MPa and 2000ppm sodium chloride, the desalination rate of a single branch of the repaired reverse osmosis element can be restored to more than 99%, and the repair effect can be stably maintained for more than 3 months. After the high temperature and high pressure tolerance test, the flux attenuation amplitude is ≤5%

[0024] (3) The method of the present invention has low equipment requirements, simple operation method, fast repair speed and good repair effect, avoids the cumbersome operation of other repair processes, is convenient for large-scale operation, and the regenerated reverse osmosis membrane obtained by repair has broad application prospects in the field of water treatment. DETAILED DESCRIPTION

[0025] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0026] Unless otherwise specified, the raw materials used in the following examples or comparative examples are all commercially available industrial-grade conventional raw materials. The main raw material information is shown in Table 1 below.

[0027] Table 1 Raw materials

[0028]

[0029]

[0030] Performance testing method:

[0031] 1. Evaluation of desalination rate and water production

[0032] The separation performance of the reverse osmosis element was evaluated at a feed liquid of 2000 ppm sodium chloride aqueous solution, a solution pH of 7.5±0.5, an operating pressure of 1.55 MPa, a recovery rate of 15%, and an operating temperature of 25°C.

[0033] The desalination rate (R) is defined as: under certain operating conditions, the salt concentration of the feed solution (C f ) and the salt concentration in the permeate (C p ) and then divided by the feed solution salt concentration (C f ), as shown in formula (1).

[0034] R=(C f -C p ) / C f *100% Formula (1)

[0035] The water production is defined as: the volume of water passing through the element per unit time under certain operating conditions, and its unit is GPD, recorded as F.

[0036] 2. Evaluation of high temperature and high pressure resistance

[0037] The feed liquid is 10000ppm sodium chloride aqueous solution, the solution pH is 7.5±0.5, the operating pressure is 3.8MPa, the recovery rate is 15%, and the operating temperature is 40℃. After continuous operation for 0.5h, the first round of water production evaluation is carried out, which is recorded as F 高1 ; After continuous operation for 3 hours, the second round of water production evaluation is carried out, which is recorded as F 高2 .

[0038] The high temperature and high pressure resistance performance (N) is the attenuation amplitude of the two-round water production, as shown in formula (2):

[0039] N=(F 高1 -F高2 ) / F 高1 *100% of formula (2).

[0040] Example 1

[0041] Step 1: Acid and alkali cleaning of discarded reverse osmosis elements

[0042] The cleaning pressure is 0.45 bar, and the cleaning liquid is circulated and refluxed. Acid cleaning is performed first, with a pH of 3 and a time of 30 minutes. Alkaline cleaning is performed after the cleaning, with a pH of 12 and a time of 30 minutes. After the cleaning is completed, flush with tap water until the outlet water pH is 7.5.

[0043] Step 2: Repair of abandoned reverse osmosis elements

[0044] A repair aqueous solution of 0.05 wt% 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, 1 wt% hexamethylenediamine and 0.1 wt% rhodamine 110 was prepared, pumped at a pressure of 0.45 bar and completely immersed in an eight-inch low-pressure brackish water reverse osmosis element for 30 minutes, and rinsed with clean water to obtain a repaired reverse osmosis element.

[0045] Embodiment 2-3

[0046] The reverse osmosis elements in Examples 2 to 3 were prepared respectively in the same manner as in Example 1, with the only difference being that the amount of raw materials added to the repair aqueous solution in Table 2 and the conditions of each step were different.

[0047] Comparative Example 1

[0048] Compared with Example 1, the difference is that the repair aqueous solution does not contain 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, and the rest is the same.

[0049] Comparative Example 2

[0050] Compared with Example 1, the difference is that the repair aqueous solution does not contain hexamethylenediamine, and the other aspects are the same.

[0051] Comparative Example 3

[0052] Compared with Example 1, the difference is that the repair aqueous solution does not contain Rhodamine 110, and the other aspects are the same.

[0053] Comparative Example 4

[0054] Compared with Example 1, the difference is that no repair with repair aqueous solution is performed, and the other aspects are the same.

[0055] Comparative Example 5

[0056] Compared with Example 1, the difference is that the ethylenediamine and rhodamine 110 in the repair aqueous solution are replaced by 2,4-diaminoquinazoline, and the rest is the same.

[0057] Comparative Example 6

[0058] Compared with Example 1, the difference is that the rhodamine 110 with diamino group in the repair aqueous solution is replaced by rhodamine 610 without diamino group, and the rest is the same.

[0059] Table 2 Components and process conditions of the embodiments and comparative examples

[0060]

[0061] The reverse osmosis elements obtained in different embodiments and comparative examples were evaluated for desalination rate, water production, operation stability, and high temperature and high pressure resistance. The results are listed in Table 3.

[0062] Table 3 Evaluation results of embodiments and comparative examples

[0063]

[0064] It can be seen from the above test results that the regenerated reverse osmosis element obtained by the repair method of the present invention has excellent separation performance, high temperature resistance and high pressure resistance. The single branch desalination rate of the repaired reverse osmosis element can be restored to more than 99%, and the repair effect can be stably maintained for more than 3 months. The flux attenuation after high temperature and high pressure tolerance test is ≤5%.

[0065] The present invention illustrates the detailed method of the present invention through the above-mentioned embodiments, but the present invention is not limited to the above-mentioned detailed method, that is, it does not mean that the present invention must rely on the above-mentioned detailed method to be implemented. Those skilled in the art should understand that any improvement of the present invention, equivalent replacement of various raw materials of the product of the present invention, addition of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for repairing a reverse osmosis element, comprising the following steps: S1: Perform acid and alkali cleaning and water washing on the reverse osmosis elements that have been damaged by oxidation; S2: Immerse the reverse osmosis element in a repair aqueous solution containing 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, polyamino compounds, rhodamine containing diamino groups or their derivatives, and wash with water to obtain a repaired reverse osmosis element.

2. The method according to claim 1, characterized in that The acid-base cleaning in S1 comprises the following steps: 0.1-1.0 bar cleaning pressure, pH between 2-4, acid cleaning time 20-30 min; then alkaline cleaning, pH between 11-13, alkaline cleaning time 20-30 min.

3. The method according to claim 1 or 2, characterized in that: In S1, after the acid and alkali cleaning is completed, water washing is performed until the pH of the effluent is 6-9.

4. The method according to any one of claims 1 to 3, characterized in that: The polyamino compound described in S2 is a compound having at least two active amino groups, preferably one or more of an aromatic compound having at least two active amino groups, an aliphatic compound having at least two active amino groups, and an alicyclic compound having at least two active amino groups, and more preferably one or more of m-phenylenediamine, isophenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4-diaminoanisole, amphenol, xylene diamine, ethylenediamine, propylene diamine, ethylenediamine, hexamethylenediamine, tri(2-aminoethyl)amine, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine or 4-aminomethylpiperazine.

5. The method according to any one of claims 1 to 4, characterized in that: The mass percentage of the polyamino compound in the repair aqueous solution is 0.3wt% to 10wt%, preferably 0.5 to 3wt%.

6. The method according to any one of claims 1 to 5, characterized in that: The diamino-containing rhodamine or its derivatives described in S2 include one or more of rhodamine 110, rhodamine 123 or 2',7'-diiododihydrorhodamine 123.

7. The method according to any one of claims 1 to 6, characterized in that: In the repair aqueous solution, the mass percentage of rhodamine or its derivatives containing diamino groups is 0.01wt% to 10wt%, preferably 0.05 to 0.5wt%.

8. The method according to any one of claims 1 to 7, characterized in that: In the repair aqueous solution, the mass percentage of 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride is 0.01 wt % to 2 wt %, preferably 0.03 to 0.5 wt %.

Images