A method of repairing a reverse osmosis element

Abstract

The application discloses a reverse osmosis element repairing method. The method comprises the following steps: S1, acid-base cleaning and water washing are performed on the reverse osmosis element which has been oxidatively damaged; and S2, a repairing aqueous solution containing 4-(4, 6-dimethoxytriazine)-4-methyl morpholinium chloride, a polyamino compound, rhodamine containing a double amino group or a derivative thereof is used to immerse the reverse osmosis element, and after water washing, the repaired reverse osmosis element is obtained. The desalination rate of the single reverse osmosis element repaired by the method can be restored to more than 99% under the standard test conditions, the repairing effect can be stably maintained for more than three months, and meanwhile, the high-pressure resistance and high-temperature resistance of the reverse osmosis element are further improved. When applied to water treatment, the service life can be further prolonged, and the operation and maintenance cost can be reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment, and particularly relates to a method for repairing a reverse osmosis element. BACKGROUND

[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, thick and thin nets, center pipes and outer glass fibers, among which, the reverse osmosis membrane plays a decisive role in the desalination rate. However, the reverse osmosis element still faces a series of problems in actual use. Among them, the degradation of the polyamide separation layer of the reverse osmosis membrane by oxidative substances such as active chlorine, and then the decrease of the desalination rate of the reverse osmosis element is one of the great challenges faced by the application of reverse osmosis technology.

[0003] Repairing the reverse osmosis element can not only save the procurement cost of new elements, but also reduce the pollution of waste elements to the environment. The currently disclosed patents mainly restore the element by strengthening cleaning or cross-linking coating. The strengthening cleaning and coating slurry technology, such as CN106139906A, uses waste reverse osmosis elements as raw materials, optimizes the selection of chemical cleaning process and coating repair process to improve the desalination performance of the element. The cross-linking coating technology, such as CN111495193A, repairs the reverse osmosis element by soaking acrylic-2-acrylamide-2-methylpropanesulfonic acid copolymer, hydrolyzed polymaleic anhydride, styrene sulfonic acid sodium-maleic acid copolymer, sodium citrate, polycarboxylic acid terpolymer and deionized water components to improve the desalination rate; such as CN112473391A uses an aqueous solution containing a dye with a molecular structure containing a carboxyl or sulfonic acid group and a molecular weight greater than 400, including rhodamine, methyl blue, methyl orange, etc., as raw water, uses the characteristics of the dye to preferentially dye the bottom membrane material of the composite membrane, and seals the polyamide defect part to obtain the repair of the desalination capacity of the element; such as CN115105963B uses imine compounds and diamine compounds to repair the reverse osmosis element to improve the desalination rate; in addition, the disclosed patent CN114749029B uses a diazotization reaction to reconfigure the aniline structure contained in the performance-degraded polyamide reverse osmosis membrane separation layer, and obtains more cis-azo structures on the membrane surface through simple ultraviolet light irradiation, improves the permeation resistance of the separation layer to sodium ions, and realizes the effect of repairing the desalination performance of the membrane element. The cross-linking coating technology in the preparation process of the reverse osmosis membrane, such as CN118142359A, coats 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride, bisamino quinazoline 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 improving the desalination rate of the membrane / element and improving the high-temperature resistance and high-pressure resistance.

[0004] Although the art has formed some technical solutions for improving the desalination rate of the oxidized element, the technical solutions still need to be further improved in the stability of the repair effect and the further improvement of the high-temperature resistance and high-pressure resistance of the repaired element. SUMMARY

[0005] The purpose of the present application is to provide a reverse osmosis element repair method, which has excellent stability, high-temperature resistance and high-pressure resistance.

[0006] To achieve the purpose of the present application, the following technical solutions are adopted:

[0007] A reverse osmosis element repair method, the method comprising the following steps:

[0008] S1: acid and alkali cleaning and water washing of the reverse osmosis element which has been oxidized and damaged;

[0009] S2: immersing the reverse osmosis element in a repair aqueous solution containing 4-(4, 6-dimethoxytriazine)-4-methyl morpholine hydrochloride, polyamino compound, rhodamine containing bisamino or its derivative, and then water washing to obtain the repaired reverse osmosis element.

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

[0011] As a preferred solution, the acid and alkali cleaning method of S1 is the industry general method. Specifically, it comprises the following steps: 0.1-1.0 bar cleaning pressure, pH between 2-4, acid washing time 20-30 min; then alkali washing, pH between 11-13, alkali washing time 20-30 min.

[0012] As a preferred solution, after the acid and alkali cleaning in S1, water washing is performed until the water pH is between 6-9.

[0013] In an embodiment of the present application, the polyamino compound 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 a cycloaliphatic compound having at least two active amino groups, more preferably one or more of m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4-diamino-benzoic acid, aminophenol, xylylenediamine, ethylenediamine, propylenediamine, hexamethylenediamine, tris(2-aminoethyl)amine, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, or 4-aminomethylpiperazine, and further preferably hexamethylenediamine.

[0014] In an embodiment of the present application, the mass percentage of the polyamino compound in the repair aqueous solution in S2 is 0.3wt% to 10wt%, preferably 0.5 to 3wt%.

[0015] In an embodiment of the present application, the double-amino-containing rhodamine or derivative thereof in S2 includes one or more of rhodamine 110, rhodamine 123, or 2',7'-diiododihydrorhodamine 123, more preferably rhodamine 110.

[0016] In an embodiment of the present application, the mass percentage of the double-amino-containing rhodamine or derivative thereof in the repair aqueous solution is 0.01wt% to 10wt%, preferably 0.05 to 0.5wt%.

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

[0018] In an embodiment of the present application, the pump pressure of the repair aqueous solution in S2 is 0.1 to 1.0 bar, and the soaking time is 5 to 30 min.

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

[0020] The application carries out reverse osmosis element repair by immersing and introducing a repair aqueous solution containing 4-(4,6-dimethoxytriazine)-4-methyl morpholine hydrochloride, a polyamino compound and a rhodamine or its derivative containing a double amino group into an oxidized element. The reverse osmosis membrane separation layer of the oxidized element contains a large number of carboxyl groups, part of which is generated by hydrolysis of acyl chloride groups that do not participate in the reaction when preparing a polyamide separation layer by interfacial polymerization, and the rest is generated by the breakage of amide bonds in the polyamide separation layer when contacting oxidizing agents such as residual chlorine. A large number of breakage of amide bonds in the polyamide separation layer leads to a decrease in the desalination rate of the element. Under the catalysis of 4-(4,6-dimethoxytriazine)-4-methyl morpholine hydrochloride, the amino groups in the polyamino compound cross-link with the carboxyl groups in the polyamide separation layer to repair the polyamide separation layer by "patching" and improve the cross-linking degree of the polyamide separation layer and the desalination rate. The introduction of the rhodamine or its derivative containing a double amino group not only further repairs the polyamide separation layer to improve the desalination rate, but also endows the element with good water flux, high-pressure resistance and high-temperature resistance due to the rigid three-dimensional molecular skeleton of the hydrophilic anthracene derivative with multiple benzene rings.

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

[0022] (1) The application carries out reverse osmosis element repair by immersing and repairing the oxidized element with a repair aqueous solution containing 4-(4,6-dimethoxytriazine)-4-methyl morpholine hydrochloride, a polyamino compound and a rhodamine or its derivative containing a double amino group. Under the catalysis of 4-(4,6-dimethoxytriazine)-4-methyl morpholine hydrochloride, the polyamino compound cross-links with the carboxyl groups in the polyamide separation layer to repair the polyamide separation layer by "patching", improve the cross-linking degree of the polyamide separation layer and the desalination rate. Meanwhile, the introduction of the rhodamine or its derivative containing a double amino group not only endows the reverse osmosis element with good water production performance, but also achieves high-temperature resistance and high-pressure resistance.

[0023] (2) The repair effect of the method of the application is good, and the regenerated reverse osmosis element obtained has stable performance and excellent oxidation resistance. Under the test of 1.55 MPa and 2000 ppm of 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 high-temperature and high-pressure resistance test, the flux attenuation amplitude is ≤5%

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

[0025] The technical solutions of the present application are further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are only for understanding the present application and should not be regarded as specific limitations of the present application.

[0026] The raw materials used in the following examples or comparative examples are all commercially available industrial-grade conventional raw materials if not specifically stated, and the main raw material information is shown in Table 1 below.

[0027] Table 1 Raw materials

[0028]

[0029]

[0030] Performance test method:

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

[0032] The feed liquid is a 2000 ppm sodium chloride aqueous solution, the solution pH is 7.5±0.5, the operating pressure is 1.55 MPa, the recovery rate is 15%, and the operating temperature is 25℃. The separation performance of the reverse osmosis element is evaluated under the above conditions.

[0033] The desalination rate (R) is defined as the difference between the salt concentration (C f ) of the feed liquid and the salt concentration (C p ) in the permeate under certain operating conditions, divided by the salt concentration (C f ) of the feed liquid, 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 permeating through the element per unit time under certain operating conditions, and its unit is GPD, denoted as F.

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

[0037] The feed liquid is a 10000 ppm sodium chloride aqueous solution, the solution pH is 7.5±0.5, the operating pressure is 3.8 MPa, 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, denoted as F 高1 ; after continuous operation for 3h, the second round of water production evaluation is carried out, denoted as F 高2 .

[0038] The high temperature and high pressure resistance (N) is the attenuation range of the two rounds of 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] First step: acid and base cleaning of the discarded reverse osmosis element

[0042] 0.45 bar cleaning pressure, cleaning liquid circulation backflow, first acid cleaning, pH 3, acid cleaning time 30 min; after the end of the acid cleaning, base cleaning, pH 12, base cleaning time 30 min, after the completion of the cleaning, tap water flushing, until the water pH 7.5.

[0043] Second step: repair of the discarded reverse osmosis element

[0044] A repair aqueous solution of 0.05 wt% 4-(4,6-dimethoxytriazine)-4-methyl morpholine hydrochloride, 1 wt% hexanediamine and 0.1 wt% rhodamine 110 was prepared, pumped at 0.45 bar pressure and completely immersed for 30 min in the eight-inch low-pressure brackish water reverse osmosis element, after the water flushing, the repaired reverse osmosis element was obtained.

[0045] Examples 2-3

[0046] The reverse osmosis elements in examples 2-3 were prepared according to the same method as example 1, the only difference was the raw material addition amount in the repair aqueous solution and the conditions of each step in table 2.

[0047] Comparative example 1

[0048] Example 1 comparison, the only difference was that the repair aqueous solution did not contain 4-(4,6-dimethoxytriazine)-4-methyl morpholine hydrochloride, and the others were the same.

[0049] Comparative example 2

[0050] Example 1 comparison, the only difference was that the repair aqueous solution did not contain hexanediamine, and the others were the same.

[0051] Comparative example 3

[0052] Example 1 comparison, the only difference was that the repair aqueous solution did not contain rhodamine 110, and the others were the same.

[0053] Comparative example 4

[0054] Example 1 comparison, the only difference was that the repair aqueous solution was not repaired, and the others were the same.

[0055] Comparative example 5

[0056] Example 1 comparison, the only difference was that the repair aqueous solution of ethylenediamine and rhodamine 110 was replaced by 2,4-diamino quinazoline, and the others were the same.

[0057] Comparative Example 6

[0058] Example 1 Comparison, the difference is that the rhodamine 110 with double amino in the repair aqueous solution is replaced by rhodamine 610 without double amino, and the others are the same.

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

[0060]

[0061] The reverse osmosis elements obtained in different examples and comparative examples are evaluated in terms of desalination rate, water production, operation stability, and high temperature resistance and high pressure resistance, and the results are shown in Table 3.

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

[0063]

[0064] From the above test results, it can be seen that the regenerated reverse osmosis element obtained by the repair method of the present application has excellent separation performance, excellent high temperature resistance and excellent high pressure resistance. The 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 amplitude is ≤5% after high temperature and high pressure resistance test.

[0065] The detailed method of the present application is illustrated by the above examples, but the present application is not limited to the above detailed method, that is, it does not mean that the present application must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for repairing reverse osmosis elements, comprising the following steps: S1: Perform acid and alkali cleaning and water washing on the reverse osmosis element that has been oxidized and damaged; the reverse osmosis membrane of the oxidized and damaged reverse osmosis element contains a polyamide separation layer; 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 its derivatives, and wash with water to obtain the repaired reverse osmosis element. The polyamino compound is one or more of the following: an aliphatic compound having at least two active amino groups, an alicyclic compound having at least two active amino groups, m-phenylenediamine, pyromellitic diamine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, 3,5-diaminobenzoic acid, 2,4-diaminotoluene, 2,6-diaminotoluene, 2,4-diaminoanisole, and amiphenol.

2. The method according to claim 1, characterized in that, The acid and alkali cleaning described in S1 includes the following steps: cleaning pressure of 0.1 to 1.0 bar, pH between 2 and 4, acid washing time of 20 to 30 minutes; followed by alkali washing, pH between 11 and 13, alkali washing time of 20 to 30 minutes.

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

4. The method according to claim 1, characterized in that, The polyamino compound mentioned in S2 is one or more of the following: ethylenediamine, propylenediamine, ethylenediamine, hexamethylenediamine, tris(2-aminoethyl)amine, 1,3-diaminocyclohexane, 1,2-diaminocyclohexane, 1,4-diaminocyclohexane, piperazine, 2,5-dimethylpiperazine, or 4-aminomethylpiperazine.

5. The method according to claim 1, characterized in that, The mass percentage of polyamino compounds in the remediation aqueous solution is 0.3 wt% to 10 wt%.

6. The method according to claim 1, characterized in that, The mass percentage of polyamino compounds in the remediation aqueous solution is 0.5–3 wt%.

7. The method according to claim 1, 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.

8. The method according to claim 1, characterized in that, The mass percentage of diamino rhodamine or its derivatives in the remediation aqueous solution is 0.01 wt% to 10 wt%.

9. The method according to claim 1, characterized in that, The mass percentage of diamino rhodamine or its derivatives in the remediation aqueous solution is 0.05–0.5 wt%.

10. The method according to claim 1, characterized in that, In the remediation aqueous solution, the mass percentage of 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride is 0.01wt% to 2wt%.

11. The method according to claim 1, characterized in that, In the remediation aqueous solution, the mass percentage of 4-(4,6-dimethoxytriazine)-4-methylmorpholine hydrochloride is 0.03–0.5 wt%.

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