Method for cleaning silicon-polluted reverse osmosis membrane

Abstract

The invention relates to the technical field of water treatment cleaning agents, and discloses a silicon pollution type reverse osmosis membrane cleaning method, which comprises: 1) preparing an anionic surfactant and triethanolamine hydrochloride into a cleaning agent A with a pH value of 10-11; wherein the anionic surfactant is sodium dodecyl benzene sulfonate and / or lauryl sodium sulfate; 2) preparing a cleaning agent B with the pH value of 2-4 from ammonium bifluoride, citric acid, sulfosalicylic acid and an organic nitrogen-containing compound; (3) hydrochloric acid and / or citric acid are / is prepared into a cleaning agent C with the pH being 2-3; and 4) sequentially cleaning the reverse osmosis membrane by using the cleaning agent A, the cleaning agent B and the cleaning agent C. The medicament involved in the method is mild in performance and good in safety, the silicon scale can be thoroughly removed, the desalinization rate and the water flux of the cleaned reverse osmosis membrane element are well recovered, and the requirements of production and reuse are met.

Description

Technical Field

[0001] The invention relates to the technical field of water treatment cleaning agents, and in particular to a method for cleaning a silicon-contaminated reverse osmosis membrane. Background Art

[0002] Coal chemical production inevitably generates large quantities of wastewater with complex components, including high salt content, high hardness, silicon content, and organic matter. To improve water reuse and reduce the environmental impact of wastewater discharge, a process combining pretreatment with reverse osmosis desalination, nanofiltration salt separation, high-pressure reverse osmosis concentration, and evaporation and crystallization is currently commonly used to achieve "zero discharge" of chemical wastewater. The pretreatment unit first uses processes such as the double alkali method to remove most of the calcium and magnesium in the wastewater, while also removing some silicon. Advanced oxidation and other technologies then effectively remove organic matter. After qualifying pretreatment, the wastewater is processed through a reverse osmosis desalination unit for reuse, and the concentrate is further processed through a nanofiltration salt separation unit. Within the nanofiltration salt separation unit, the nanofiltration product water is primarily sodium chloride, while the concentrate is primarily sodium sulfate. The concentrate is further concentrated and reduced in the high-pressure reverse osmosis unit before entering the evaporation and crystallization unit, ultimately producing sodium chloride and sodium sulfate as industrial by-products.

[0003] In actual production, the high-pressure reverse osmosis membrane on the nanofiltration water production side of the nanofiltration salt separation unit was found to be frequently fouled and clogged, and conventional cleaning was ineffective, impacting the continuous and stable operation of the system. Testing revealed that the main contaminants were silica scale (68%), with small amounts of calcium scale (9%), magnesium scale (8%), aluminum salts (6%), and some organic matter (9%). Analysis revealed that the cause of the fouling was that while the pretreatment unit removed most of the calcium and magnesium in the wastewater, the remaining calcium, magnesium, and silicon ions reached the concentrate after reverse osmosis desalination, where the ion concentration was concentrated fourfold. Nanofiltration has a good retention rate of approximately 90% for calcium and magnesium ions and 95% for organic matter, but poor silicon retention, at only 15%-30%. As a result, a small amount of calcium, magnesium, and organic matter, along with the majority of silicon, entered the produce water side, where the silicon content was further concentrated by approximately twofold. Nanofiltration water is further concentrated 2-3 times through high-pressure reverse osmosis. At this point, the silicon content in the water exceeds the reverse osmosis membrane's feed water requirement. Silicon-based substances precipitate and deposit on the membrane surface, forming silica scale (such as polysilicic acid and colloidal silica). This scale not only clogs the membrane channels and affects membrane permeability, but also absorbs calcium and magnesium ions, metal compounds, and organic matter from the water, which deposit on the membrane surface as mixed scale, increasing membrane contamination and making descaling more difficult.

[0004] Silica scale is a common pollutant in the operation of reverse osmosis systems. The covalent bonds formed between it and the surface of the reverse osmosis membrane (for example, silicic acid reacts with the carboxyl or hydroxyl functional groups on the membrane surface to form acid anhydride) are difficult to remove through conventional liquid alkali combined with surfactants, chelating agents and other chemical cleaning methods. Mechanical flushing or hydrofluoric acid cleaning will cause irreversible damage to the membrane components. Therefore, silica scale is extremely difficult to remove once it is formed. Summary of the Invention

[0005] The present application aims to overcome the problems of incomplete cleaning of silicon scale in reverse osmosis membranes, poor safety of cleaning agents, and reduced desalination rate and unqualified water quality caused by membrane pore expansion after cleaning in the prior art, and provides a cleaning method for reverse osmosis membranes contaminated by silicon, which efficiently removes membrane surface pollutants while focusing on the health and stability of membrane elements after cleaning, and the cleaning agent is simple to prepare and does not damage the membrane material.

[0006] To achieve the above-mentioned purpose, the present application provides a cleaning method for reverse osmosis membranes contaminated by silicon, which comprises the following steps: 1) An anionic surfactant and triethanolamine hydrochloride are configured into a cleaning agent A with a pH of 10-11; wherein the anionic surfactant is sodium dodecyl benzene sulfonate and / or sodium dodecyl sulfate; 2) Ammonium bifluoride, citric acid, sulfosalicylic acid and an organic nitrogen-containing compound are configured into a cleaning agent B with a pH of 2-4; 3) Hydrochloric acid and / or citric acid are configured into a cleaning agent C with a pH of 2-3; 4) The reverse osmosis membrane is sequentially cleaned with the cleaning agent A, the cleaning agent B and the cleaning agent C.

[0007] Preferably, in the cleaning agent A, the content of the anionic surfactant is 0.02-0.1 wt.%, and further preferably 0.03-0.05 wt.%.

[0008] Preferably, in the cleaning agent A, the content of the triethanolamine hydrochloride is 0.1-0.5 wt.%, and further preferably 0.2-0.4 wt.%.

[0009] Preferably, in the cleaning agent B, the organic nitrogen-containing compound is at least one of urotropine, quinoline and Lan826.

[0010] Preferably, the content of the ammonium bifluoride is 0.5-2 wt.%, and further preferably 0.7-1 wt.%.

[0011] Preferably, the content of the citric acid is 0.5-1 wt.%, and further preferably 0.6-0.8 wt.%.

[0012] Preferably, the content of the sulfosalicylic acid is 0.05-0.1 wt.%, and further preferably 0.06-0.08 wt.%.

[0013] Preferably, the content of the organic nitrogen-containing compound is 0.2-0.4 wt.%, and further preferably 0.25-0.35 wt.%.

[0014] Preferably, in step 1), sodium hydroxide, an anionic surfactant and triethanolamine hydrochloride are mixed and configured into a cleaning agent A with a pH of 10-11.

[0015] Preferably, in step 4), after being cleaned with the cleaning agent A for 2-5 hours, the reverse osmosis membrane is cleaned with the cleaning agent B for 4-8 hours, and then cleaned with the cleaning agent C for 2-5 hours.

[0016] Preferably, in step 4), when the desalination rate of the reverse osmosis membrane reaches 70-75% of the initial desalination rate, the reverse osmosis membrane is sequentially cleaned with the cleaning agent A, the cleaning agent B and the cleaning agent C.

[0017] Compared with the prior art, the present application has the following advantages: 1) The present application selects triethanolamine hydrochloride to improve the soil removal capacity and foam stability of the surfactant, and also serves as a "corrosive agent" for silica scale, which changes the structure and microtopography of the silica scale so that the subsequent pollutants can contact and react with the active components.

[0018] 2) The present application selects ammonium bifluoride and citric acid for compounding, and adds sulfosalicylic acid and an organic nitrogen-containing compound as cleaning aids, which can further improve the cleaning efficiency compared with other dispersants, chelating agents and other aids in other formulations.

[0019] 3) The cleaning method for the reverse osmosis membrane with silica pollution in the present application includes pretreatment, removal of silica scale and shrinkage of membrane pores. The organic matter on the reverse osmosis membrane is removed through pretreatment, and the silica scale, calcium and magnesium scale and aluminum and iron oxides are removed, and finally the residual pollutants are removed while the membrane pores are shrunk. The cleaning method involves mild and safe reagents, and can achieve complete removal of silica scale. The desalination rate and water flux of the reverse osmosis membrane element after cleaning are restored well, meeting the requirements of production reuse.

[0020] 4) The present application starts cleaning when the desalination rate of the reverse osmosis membrane reaches 70-75% of the initial desalination rate. After one round of cleaning, the desalination rate of the reverse osmosis membrane can be restored to more than 97% of the initial desalination rate, which not only prolongs the service life of the reverse osmosis membrane element, but also greatly reduces the maintenance and use cost of the membrane without damaging the membrane material. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a SEM image of the fouled membrane surface before cleaning of the reverse osmosis membrane in one specific embodiment of the present application (200 times).

[0022] Figure 2 is a SEM image of the fouled membrane surface before cleaning of the reverse osmosis membrane in one specific embodiment of the present application (3000 times).

[0023] Figure 3is a SEM image of a fouled membrane surface after reverse osmosis membrane cleaning with cleaning agent A in one embodiment of the present application.

[0024] Figure 4 is a SEM image of a fouled membrane surface after reverse osmosis membrane cleaning with cleaning agent A in one embodiment of the present application.

[0025] Figure 5 is a SEM image of a reverse osmosis membrane after all cleaning is completed in one embodiment of the present application.

[0026] Figure 6 is a SEM image of a reverse osmosis membrane after all cleaning is completed in one embodiment of the present application. DETAILED DESCRIPTION

[0027] The specific embodiments of the present application are described below in detail. It should be understood that the specific embodiments described herein are merely illustrative and explanatory and are not intended to limit the present application.

[0028] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The endpoints of the ranges and any values are provided as approximate descriptions of the ranges and are understood to include values near the recited range or value. For numeric ranges, the endpoints of the various ranges, the endpoints of the various ranges and individual point values, and individual point values can be combined with each other to produce one or more new numeric ranges, which are to be considered as specifically disclosed herein.

[0029] In the description of the present application, the terms "first", "second", "third", etc., are used only to describe the purpose and are not to be understood as indicating relative importance or implying that the indicated technical features are limited to a certain number. Thus, unless otherwise stated, features defined with "first", "second", etc. can explicitly or implicitly include one or more of the features; the meaning of "a plurality" is two or more. The term "comprising" and any variation thereof means inclusive, and there can be one or more other features, integers, steps, operations, units, components and / or combinations thereof.

[0030] The cleaning method of the silicon pollution reverse osmosis membrane according to the present application comprises the following steps: 1) Anionic surfactant and triethanolamine hydrochloride are configured into cleaning agent A with pH of 10-11; wherein the anionic surfactant is sodium dodecyl benzene sulfonate and / or sodium dodecyl sulfate; 2) Ammonium bifluoride, citric acid, sulfosalicylic acid and organic nitrogen-containing compound are configured into cleaning agent B with pH of 2-4; 3) Hydrochloric acid and / or citric acid are configured into cleaning agent C with pH of 2-3; 4) sequentially washing the reverse osmosis membrane with the cleaning agent A, the cleaning agent B and the cleaning agent C.

[0031] In the cleaning agent A, the anionic surfactant is a kind of substance with both organic group and hydrophilic group. In the process of treating pollutants, the organic group first adsorbs organic pollutants to form colloidal particles, and then the hydrophilic group is brought into water to achieve the purpose of removing pollutants. In the present application, the selection of the anionic surfactant is not particularly limited, and at least one of sodium dodecyl benzene sulfonate, sodium dodecyl sulfate, sodium lauryl ether sulfate and potassium dodecyl phosphate can be selected, preferably sodium dodecyl benzene sulfonate and / or sodium dodecyl sulfate. In the cleaning agent A, the content of the anionic surfactant can be 0.02-0.1wt.%, preferably 0.03-0.05wt.%.

[0032] In the cleaning agent A, the content of the triethanolamine hydrochloride can be 0.1-0.5wt.%, preferably 0.2-0.4wt.%. The triethanolamine hydrochloride in the present application has good erosion effect on silica scale, which can dissolve and soften the flaky and blocky silica scale on the reverse osmosis membrane surface into spherical and irregular granular shape, and can also increase the pore between the silica scale, which is beneficial to the full contact of the subsequent cleaning agent with the silica scale, and significantly improves the subsequent cleaning efficiency.

[0033] In the preparation of the cleaning agent A, sodium hydroxide and / or potassium hydroxide can be used to adjust the pH value of the cleaning agent A, and sodium hydroxide is preferably selected. In some specific embodiments, deionized water, sodium hydroxide, anionic surfactant and triethanolamine hydrochloride can be mixed and configured into a cleaning agent A with a pH of 10-11.

[0034] In the cleaning agent A, under alkaline environment, the triethanolamine hydrochloride and the anionic surfactant are compounded and synergistically act, which can enhance the decontamination ability of the cleaning agent A, and soften the silica scale while cleaning the organic pollutants. The triethanolamine hydrochloride can further improve the foam stability after adding the anionic surfactant in the cleaning agent A, and prolong the residence time of the foam on the pollutants.

[0035] In the cleaning agent B, the organic nitrogen-containing compound can be at least one of urotropine, quinoline and Lan826; preferably Lan826. Lan826 is a product of Beijing Lansheng Cleaning Co., Ltd.

[0036] In the cleaning agent B described in the present application, the content of the ammonium bifluoride can be 0.5-2wt.%, preferably 0.7-1wt.%; the content of the citric acid can be 0.5-1wt.%, preferably 0.6-0.8wt.%; the content of the sulfosalicylic acid can be 0.05-0.1wt.%, preferably 0.06-0.08wt.%; and the content of the organic nitrogen-containing compound can be 0.2-0.4wt.%, preferably 0.25-0.35wt.%.

[0037] In the preparation of the cleaning agent B described in the present application, deionized water, ammonium bifluoride, citric acid, sulfosalicylic acid and an organic nitrogen-containing compound can be mixed and configured into a cleaning agent B with a pH of 2-4. In the above preparation process, there is no special restriction on the addition sequence of ammonium bifluoride, citric acid, sulfosalicylic acid and the organic nitrogen-containing compound, and they can be mixed to achieve sufficient dissolution.

[0038] In the cleaning agent B described in the present application, the ammonium bifluoride is compounded with the citric acid as the main cleaning agent, and the sulfosalicylic acid and the organic nitrogen-containing compound are used as cleaning aids to effectively remove silicon scale, calcium and magnesium scale, and metal oxides such as aluminum and iron on the reverse osmosis membrane. Among them, the ammonium bifluoride can dissociate into NH 4+ and HF 2- in water, and HF 2- is the main active ingredient that reacts with silicon. Compared with hydrofluoric acid, it has weaker acidity and slower reaction rate with silicon, so the operation risk is lower and it is safer and more controllable. The use of the ammonium bifluoride compounded with the citric acid not only takes advantage of the mild performance of citric acid, which can effectively remove calcium and magnesium scale and metal oxides, but also improves the synergistic removal effect of the ammonium bifluoride and the citric acid on silicon scale and other contaminants. As a cleaning aid, the sulfosalicylic acid can form stable complexes with calcium, magnesium, aluminum and other metal ions in water due to the sulfonic acid group and carboxylic acid group in its molecule, thereby reducing the secondary attachment of dirt on the membrane surface by chelating metal ions, helping to decompose inorganic salt dirt and improving cleaning efficiency. The organic nitrogen-containing compound as a corrosion inhibitor can prevent damage to the reverse osmosis membrane element and the cleaning device by the cleaning agent. Compared with the dispersants and chelating agents commonly used in the art, the sulfosalicylic acid and the organic nitrogen-containing compound as the aids in the cleaning agent B can further improve the cleaning efficiency in the acidic system.

[0039] In the cleaning agent C described in the present application, the type of acid is not limited, and can be a hydrochloric acid solution and / or a nitric acid solution with a pH of 2-3, or a mixed solution of the citric acid and / or oxalic acid and deionized water with a pH of 2-3, preferably a hydrochloric acid solution with a pH of 2-3 and / or a mixed solution of the citric acid and deionized water with a pH of 2-3. The cleaning agent C can remove residual dirt in the membrane surface and membrane holes of the reverse osmosis membrane, complete the shrinkage of the membrane holes after cleaning, improve the desalination rate, prolong the service life of the reverse osmosis membrane element, and reduce the water production electrical conductivity.

[0040] In the cleaning process of the reverse osmosis membrane, the cleaning agent A is used for cleaning for 2-5 h, the cleaning agent B is used for cleaning for 4-8 h, and then the cleaning agent C is used for cleaning for 2-5 h.

[0041] In the cleaning process of the reverse osmosis membrane, preferably when the desalination rate of the reverse osmosis membrane reaches 70-75% of the initial desalination rate, the cleaning agent A, the cleaning agent B and the cleaning agent C are used in sequence to clean the reverse osmosis membrane. When the desalination rate of the reverse osmosis membrane reaches 70-75% of the initial desalination rate, one cleaning can achieve efficient cleaning of the reverse osmosis membrane, so that the desalination rate of the cleaned reverse osmosis membrane is restored to more than 97% of the initial desalination rate. At the same time, the cleaning of the reverse osmosis membrane at this time can effectively save the amount of cleaning agent and the cleaning time.

[0042] In some specific embodiments, the cleaning method of the reverse osmosis membrane contaminated by silicon includes: 1) preparing a cleaning agent A with a pH of 10-11 from deionized water, sodium hydroxide, an anionic surfactant and triethanolamine hydrochloride, wherein the anionic surfactant is sodium dodecyl benzene sulfonate and / or sodium dodecyl sulfate; 2) preparing a cleaning agent B with a pH of 2-4 from deionized water, ammonium hydrogen fluoride, citric acid, sulfosalicylic acid and an organic nitrogen-containing compound; 3) preparing a cleaning agent C with a pH of 2-3 from hydrochloric acid and / or citric acid; 4) when the desalination rate of the reverse osmosis membrane reaches 70-75% of the initial desalination rate, using the cleaning agent A prepared in step 1) to clean the reverse osmosis membrane for 2-5 h, and then using deionized water to clean the reverse osmosis membrane until the water cleaned out is neutral; 5) using the cleaning agent B prepared in step 2) to clean the reverse osmosis membrane for 4-8 h, and then using deionized water to clean the reverse osmosis membrane until the water cleaned out is neutral; 6) using the prepared cleaning C to clean the reverse osmosis membrane 2-5h, and then using deionized water to clean the reverse osmosis membrane until the water cleaned out is neutral, that is, the cleaning of the reverse osmosis membrane is completed.

[0043] In the present application, after each cleaning of the cleaning agent, the reverse osmosis membrane is preferably flushed with deionized water, so that the pollutants cleaned out can be flushed away in time, and the contact between the cleaning agent and the pollutants in the next cleaning is more sufficient.

[0044] For the heavily polluted reverse osmosis membrane, the above steps 4)-6) can be repeated to further improve the desalination rate of the reverse osmosis membrane after cleaning.

[0045] In the present application, the reverse osmosis membrane is sequentially cleaned with cleaning agent A, cleaning agent B and cleaning agent C to sequentially achieve the pretreatment of pollutants, the removal of silica scale and the aftercare repair of the reverse osmosis membrane, so that the pollutants of the reverse osmosis membrane are efficiently removed while the material quality of the reverse osmosis membrane is ensured to be undamaged.

[0046] The cleaning method of the silicon pollution type reverse osmosis membrane according to the present application will be further illustrated by examples. The examples are implemented on the premise of the technical scheme of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following examples.

[0047] In the following examples, the experimental methods are the conventional methods in the art unless otherwise specified. The experimental materials used in the following examples are commercially available unless otherwise specified.

[0048] Example 1 The high-pressure reverse osmosis membrane of Ningmeng Water Company Branch was used as the experimental object. When the desalination rate of the reverse osmosis membrane was 73.6% of the initial desalination rate, the SEM image of the fouled membrane surface of the reverse osmosis membrane was as shown in Figure 1 、 Figure 2 The following cleaning method was used to clean the reverse osmosis membrane: 1) sodium hydroxide, sodium dodecyl benzene sulfonate, triethanolamine hydrochloride and deionized water were configured into cleaning agent A with pH of 10.5, the reverse osmosis membrane was cleaned with the cleaning agent A for 4h, and then flushed with deionized water until the water cleaned out was neutral, wherein the content of sodium dodecyl benzene sulfonate in the cleaning agent A was 0.05wt.%, and the content of triethanolamine hydrochloride was 0.2wt.%; after the cleaning of the cleaning agent A was completed, the SEM image of the fouled membrane surface of the reverse osmosis membrane was as shown in Figure 3 、 Figure 4 .

[0049] 2) Deionized water, ammonium hydrogen fluoride, citric acid, sulfosalicylic acid and Lan826 are configured into cleaning agent B with pH of 2.2, the reverse osmosis membrane is cleaned by cleaning agent B for 6 hours, then washed by deionized water until the water washed out is neutral, wherein the content of ammonium hydrogen fluoride in cleaning agent B is 1wt.%, the content of citric acid is 0.8wt.%, the content of sulfosalicylic acid is 0.06wt.% and the content of Lan826 is 0.3wt.%.

[0050] 3) The reverse osmosis membrane is cleaned by cleaning agent C, hydrochloric acid solution with pH of 2.5, for 4 hours, then washed by deionized water until the water washed out is neutral, and the cleaning of the reverse osmosis membrane is completed. The SEM diagram of the reverse osmosis membrane after cleaning is shown in FIG. 2. Figure 5 、 Figure 6

[0051] Example 2 The clogged high-pressure reverse osmosis membrane of Ningmei Water Company Branch is used as the experimental object, when the desalination rate of the reverse osmosis membrane is 70.2% of the initial desalination rate, the reverse osmosis membrane is cleaned by the following cleaning method: 1) Sodium hydroxide, sodium dodecyl benzene sulfonate, triethanolamine hydrochloride and deionized water are configured into cleaning agent A with pH of 10.0, the reverse osmosis membrane is cleaned by cleaning agent A for 2 hours, then washed by deionized water until the water washed out is neutral, wherein the content of sodium dodecyl benzene sulfonate in cleaning agent A is 0.03wt.% and the content of triethanolamine hydrochloride is 0.4wt.%.

[0052] 2) Deionized water, ammonium hydrogen fluoride, citric acid, sulfosalicylic acid and Lan826 are configured into cleaning agent B with pH of 2.7, the reverse osmosis membrane is cleaned by cleaning agent B for 4 hours, then washed by deionized water until the water washed out is neutral, wherein the content of ammonium hydrogen fluoride in cleaning agent B is 0.7wt.%, the content of citric acid is 0.6wt.%, the content of sulfosalicylic acid is 0.06wt.% and the content of Lan826 is 0.25wt.%.

[0053] 3) The reverse osmosis membrane is cleaned by cleaning agent C, hydrochloric acid solution with pH of 2.0, for 2 hours, then washed by deionized water until the water washed out is neutral, and the cleaning of the reverse osmosis membrane is completed.

[0054] Example 3 The clogged high-pressure reverse osmosis membrane of Ningmei Water Company Branch is used as the experimental object, when the desalination rate of the reverse osmosis membrane is 74.8% of the initial desalination rate, the reverse osmosis membrane is cleaned by the following cleaning method: ​1) Sodium hydroxide, sodium dodecylbenzenesulfonate, triethanolamine hydrochloride, and deionized water were used to prepare a cleaning agent A with a pH of 11.0. The reverse osmosis membrane was cleaned with cleaning agent A for 5 hours, and then rinsed with deionized water until the cleaned water was neutral. The content of sodium dodecylbenzenesulfonate in cleaning agent A was 0.05 wt.%, and the content of triethanolamine hydrochloride was 0.4 wt.%.

[0055] 2) Deionized water, ammonium bifluoride, citric acid, sulfosalicylic acid, and Lan826 were prepared into a cleaning agent B with a pH of 2.4. The reverse osmosis membrane was cleaned with cleaning agent B for 8 hours, and then rinsed with deionized water until the cleaned water was neutral. The cleaning agent B contained 0.9 wt.% of ammonium bifluoride, 0.8 wt.% of citric acid, 0.08 wt.% of sulfosalicylic acid, and 0.35 wt.% of Lan826.

[0056] 3) Use cleaning agent C, hydrochloric acid solution with a pH of 3.0, to clean the reverse osmosis membrane for 5 hours, then rinse with deionized water until the water is neutral, completing the cleaning of the reverse osmosis membrane.

[0057] Example 4 The reverse osmosis membrane was cleaned according to the cleaning method of Example 1, except that the content of sodium dodecylbenzenesulfonate in the cleaning agent A was 0.08 wt.%.

[0058] Example 5 The reverse osmosis membrane was cleaned according to the cleaning method of Example 1, except that the content of triethanolamine hydrochloride in the cleaning agent A was 0.1 wt.%.

[0059] Example 6 The reverse osmosis membrane was cleaned according to the cleaning method of Example 1, except that the content of ammonium bifluoride in the cleaning agent B was 1.5 wt.%.

[0060] Example 7 The reverse osmosis membrane was cleaned according to the cleaning method of Example 1, except that the content of ammonium bifluoride in the cleaning agent B was 0.5 wt.%.

[0061] Example 8 The reverse osmosis membrane was cleaned according to the cleaning method of Example 1, except that the content of citric acid in the cleaning agent B was 0.9 wt.%.

[0062] Example 9 The reverse osmosis membrane was cleaned according to the cleaning method of Example 1, except that the content of sulfosalicylic acid in the cleaning agent B was 0.09 wt.%.

[0063] Example 10 The reverse osmosis membrane was cleaned according to the cleaning method of Example 1, except that the content of sulfosalicylic acid in the cleaning agent B was 0.2 wt.%.

[0064] Comparative Example 1 The same high-pressure reverse osmosis membrane blocked by pollution as in Example 1 was used as the experimental object. When the desalination rate of the reverse osmosis membrane was 73.6% of the initial desalination rate, the reverse osmosis membrane was cleaned using the following cleaning method: 1) Sodium hydroxide, sodium dodecylbenzene sulfonate, and deionized water were prepared into a cleaning agent with a pH of 11.5. The reverse osmosis membrane was cleaned with the cleaning agent for 4 hours, and then rinsed with deionized water until the water was neutral. The content of sodium dodecylbenzene sulfonate in the cleaning agent was 0.05 wt.%.

[0065] 2) After cleaning the reverse osmosis membrane with a hydrochloric acid solution with a pH of 2.5 for 4 hours, rinse with deionized water until the washed water is neutral, completing the cleaning of the reverse osmosis membrane.

[0066] Comparative Example 2 The difference from Example 1 is that only cleaning agent A and cleaning agent C are used to clean the reverse osmosis membrane in sequence.

[0067] Comparative Example 3 The difference from Example 1 is that only cleaning agent A and cleaning agent B are used to clean the reverse osmosis membrane in sequence.

[0068] Comparative Example 4 The difference from Example 1 is that only cleaning agent B is used to clean the permeable membrane.

[0069] Comparative Example 5 The difference from Example 1 is that only cleaning agent B and cleaning agent C are used to clean the reverse osmosis membrane in sequence.

[0070] Comparative Example 6 The difference from Example 1 is that when the desalination rate of the reverse osmosis membrane is 60.3% of the initial desalination rate, the reverse osmosis membrane is cleaned with cleaning agent A, cleaning agent B and cleaning agent C in sequence.

[0071] Comparative Example 7 The difference from Example 1 is that the sulfosalicylic acid in the cleaning agent B is replaced by polyacrylic acid, and Lan826 is replaced by thiourea.

[0072] Comparative Example 8 The same Ningmei Water Service Branch clogged high-pressure reverse osmosis membrane as in Example 1 was used as the experimental object, when the desalination rate of the reverse osmosis membrane was 73.6% of the initial desalination rate, the following cleaning method was used to clean the reverse osmosis membrane: Sodium dodecyl benzene sulfonate, triethanolamine hydrochloride, ammonium hydrogen fluoride, citric acid, sulfosalicylic acid, Lan826 and deionized water were configured into a cleaning solution, the reverse osmosis membrane was cleaned with the above cleaning agent for 8h, and then rinsed with deionized water until the water cleaned out was neutral.

[0073] In the cleaning solution, the content of sodium dodecyl benzene sulfonate was 0.05wt.%, the content of triethanolamine hydrochloride was 0.2wt.%, the content of ammonium hydrogen fluoride was 1wt.%, the content of citric acid was 0.8wt.%, the content of sulfosalicylic acid was 0.06wt.%, and the content of Lan826 was 0.3wt.%.

[0074] The water flow and desalination rate of the reverse osmosis membrane before and after cleaning of Examples 1-10 and Comparative Examples 1-8 were detected and recorded in Table 1.

[0075] The test conditions were: the water inlet conductivity was controlled to be 2200 μs / cm, the pH value was about 8, and the operating pressure was 1.55 Mpa.

[0076] Table 1

[0077] As can be seen from the results in Table 1, the cleaning method of Examples 1-10 using cleaning agent A to remove organic matter and soften silica scale, then using cleaning agent B to remove silica scale, calcium and magnesium scale and aluminum-iron and other metal oxides, and finally using cleaning agent C to remove residual pollutants and shrink the membrane pores can completely remove mixed pollutants mainly composed of silica scale, the involved reagents have mild performance and good safety, and the desalination rate and water flux of the membrane element after cleaning are well recovered, meeting the production recycling requirements.

[0078] As can be seen from the comparison of Example 1 and Comparative Example 1, the desalination rate of the reverse osmosis membrane after cleaning using the conventional alkaline cleaning agent was only improved by 2.6% compared with the desalination rate before cleaning.

[0079] As can be seen from the comparison of Example 1 and Comparative Example 2, only using cleaning agent A and cleaning agent C to clean the reverse osmosis membrane in turn, due to the lack of effective silicon removal components, the desalination rate after cleaning was only improved by 4.9% compared with the desalination rate before cleaning.

[0080] By comparing Example 1 with Comparative Examples 3-4, it can be seen that in Comparative Example 3, the reverse osmosis membrane is cleaned using cleaning agent A and cleaning agent B. After cleaning, the desalination rate of the reverse osmosis membrane is significantly improved compared to the desalination rate before cleaning. The desalination rate of the reverse osmosis membrane is significantly restored, but there is still a gap compared to the recovery to more than 97% of the initial desalination rate that can be achieved by the present invention. The comparison between Example 1 and Comparative Example 3 shows that by cleaning with cleaning agent C, the residual scale on the surface of the reverse osmosis membrane and in the membrane pores can be further cleared, the shrinkage of the membrane pores after cleaning is completed, and the desalination rate is improved. In Comparative Example 4, only cleaning agent B and cleaning agent C are used to clean the reverse osmosis membrane. After cleaning, the desalination rate of the reverse osmosis membrane is reduced by 6.9% compared to Comparative Example 3. The comparison between Example 1 and Comparative Example 4 shows that by cleaning with cleaning agent A, the structure and morphology of the silica scale can be changed, which promotes the cleaning process. At the same time, the water flux in Comparative Examples 3-4 increased significantly. This is because due to incomplete cleaning, pollutants such as silica scale blocked the membrane pores, causing the toughness of the membrane to change. The expansion of the membrane pores is reflected in a significant increase in flux.

[0081] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A method for cleaning a silicon-contaminated reverse osmosis membrane, characterized in that: The cleaning method comprises the following steps: 1) Anionic surfactant and triethanolamine hydrochloride are prepared into a cleaning agent A with a pH of 10-11; wherein the anionic surfactant is sodium dodecylbenzenesulfonate and / or sodium dodecyl sulfate; 2) Prepare a cleaning agent B with a pH of 2 to 4 by mixing ammonium bifluoride, citric acid, sulfosalicylic acid and an organic nitrogen-containing compound; 3) Prepare cleaning agent C with hydrochloric acid and / or citric acid to a pH of 2-3; 4) Cleaning the reverse osmosis membrane with the cleaning agent A, the cleaning agent B, and the cleaning agent C in sequence.

2. The cleaning method according to claim 1, wherein In the cleaning agent A, the content of the anionic surfactant is 0.02-0.1 wt.%.

3. The cleaning method according to claim 2, wherein In the cleaning agent A, the content of the anionic surfactant is 0.03-0.05 wt.%.

4. The cleaning method according to any one of claims 1 to 3, characterized in that In the cleaning agent A, the content of triethanolamine hydrochloride is 0.1-0.5 wt.%.

5. The cleaning method according to claim 4, wherein: In the cleaning agent A, the content of triethanolamine hydrochloride is 0.2-0.4 wt.%.

6. The method according to any one of claims 1 to 5, characterized in that In the cleaning agent B, the organic nitrogen-containing compound is at least one of hexamethylenetetramine, quinoline and Lan826; and / or The content of the ammonium bifluoride is 0.5-2 wt.%; and / or The content of the citric acid is 0.5-1 wt.%; and / or The content of the sulfosalicylic acid is 0.05-0.1 wt.%; and / or The content of the organic nitrogen-containing compound is 0.2-0.4 wt.%.

7. The method according to claim 6, characterized in that In the cleaning agent B, The content of the ammonium bifluoride is 0.7-1 wt.%; and / or The content of the citric acid is 0.6-0.8 wt.%; and / or The content of the sulfosalicylic acid is 0.06-0.08 wt.%; and / or The content of the organic nitrogen-containing compound is 0.25-0.35 wt.%.

8. The method according to any one of claims 1 to 7, characterized in that In step 1), sodium hydroxide, anionic surfactant and triethanolamine hydrochloride are mixed and prepared into a cleaning agent A with a pH of 10-11.

9. The method according to any one of claims 1 to 8, characterized in that In step 4), after cleaning with the cleaning agent A for 2 to 5 hours, cleaning with the cleaning agent B for 4 to 8 hours, and then cleaning with the cleaning agent C for 2 to 5 hours.

10. The method according to any one of claims 1 to 9, characterized in that In step 4), when the desalination rate of the reverse osmosis membrane reaches 70-75% of the initial desalination rate, the reverse osmosis membrane is cleaned with the cleaning agent A, the cleaning agent B and the cleaning agent C in sequence.

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