Dynamic pH-responsive ultrafiltration membrane targeted acidic cleaning agent and intelligent cleaning method thereof

Abstract

The application relates to the technical field of membrane cleaning, and particularly discloses a dynamic pH response type ultrafiltration membrane targeted acidic cleaning agent and an intelligent cleaning method thereof. The dynamic pH response type ultrafiltration membrane targeted acidic cleaning agent comprises the following components in percentage by mass: 1-5% of a chelating agent, 0.5-5% of a metal oxide reducing agent, 0.3-3% of a Fenton catalyst, 0.1-1% of a corrosion inhibitor, 0.1-0.8% of a surfactant, 0.5-1.5% of a membrane repairing agent, and the balance of deionized water. The acidic cleaning agent is combined with a ternary chelation-grading reduction-targeted oxidation multi-mechanism synergistic cleaning system, can cope with various pollutants, has strong removal effects on organic pollutants and inorganic pollutants, has the advantages of high flux recovery rate, low membrane damage rate, environmental friendliness and the like, and is particularly suitable for treating an organic-inorganic composite contaminated ultrafiltration membrane system and has remarkable effects.

Description

Technical Field

[0001] This invention relates to the field of membrane cleaning technology, and in particular to a dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent and its intelligent cleaning method. Background Technology

[0002] Ultrafiltration membrane fouling is mainly caused by a combination of organic pollutants (humic acid or soluble organic colloids) and inorganic salts (calcium salts, aluminum salts, magnesium salts, silicates, etc.). Traditional acidic cleaning agents (such as citric acid, hydrochloric acid, oxalic acid, etc.) are used to remove inorganic scale (such as iron, calcium, magnesium salts) and metal oxide contaminants, but their removal rate for organic fouling is low (<30%), and the strong acid environment (pH < 2) easily leads to hydrolysis of the amide bonds in polyamide membranes, shortening membrane life. Therefore, traditional acidic cleaning agents still have many problems that need to be overcome: such as incomplete cleaning effect, poor effect on organic pollutants, damage to membrane materials, need for repeated cleaning, and lack of specificity.

[0003] Existing research, such as "Cleaning of Severely Fouled PVDF Ultrafiltration Membranes" (2023, Cleaning World), indicates that after cleaning with 2000 mg / L oxalic acid as originally designed, the membrane flux recovery rate was only 31%, and the parameters reverted to fouling after two days of operation. This demonstrates that traditional acid washing cannot effectively remove deep-seated contaminants (such as colloidal iron and sticky organic matter). Experiments revealed that yellow contaminants remained on the membrane fibers after a single acid wash, requiring four consecutive 1% citric acid washes to fully restore flux, increasing time and cost. "Analysis of Causes and Countermeasures for Ultrafiltration Membrane Fouling" (2020, Water Purification Technology) suggests that while ultrafiltration membrane flux recovers briefly after acid washing, the transmembrane pressure difference rises again to 70 kPa within two days, causing a sharp drop in permeate flow. Furthermore, studies have shown that acid washing primarily removes inorganic contaminants (Ca, Mg, Fe), but has no effect on organic polymers (such as polyacrylic acid) and microbial contamination. The total organic carbon (TOC) in alkaline washing solutions is as high as 351 mg / L, while the TOC in acid washing solutions is only 13.91 mg / L, confirming that acid washing cannot decompose organic matter. At the same time, direct acid washing without analyzing the type of contaminant has limited effectiveness. For example, humic acid-type organic contaminants require alkaline washing as the primary method, while traditional acid washing is ineffective against them. Strong acids such as hydrochloric acid may damage the structure of the PVDF membrane. Acid washing solutions with a pH < 2 may exceed the tolerance range of some ultrafiltration membranes (pH 2–12), and the membrane fibers may turn yellow after washing, indicating that strong acids accelerate membrane aging and lead to irreversible degradation of ultrafiltration membrane performance.

[0004] In summary, traditional cleaning methods, which use acidic cleaning agents to remove inorganic scale and alkaline cleaning agents to remove organic contaminants, are effective to some extent, but they have the following problems:

[0005] 1. Incomplete cleaning: Single acid and alkali cleaning is insufficient to remove organic-inorganic complex contaminants simultaneously, and the membrane flux recovery rate after cleaning is usually less than 70%;

[0006] 2. Risk of membrane damage: Strong acid (pH<2) or strong alkaline (pH>12) environments can easily lead to hydrolysis of the amide bonds in polyamide membranes, shortening the membrane's service life;

[0007] 3. Complex operation: It requires alternating acid and alkali cleaning, has a long process (usually 16-48 hours), and high energy consumption;

[0008] 4. Environmental issues: The cleaning waste liquid is difficult to treat, and phosphorus-containing formulas can easily cause eutrophication of water bodies.

[0009] Therefore, there is an urgent need to develop a targeted acidic cleaning agent for ultrafiltration membranes that combines high flux recovery rate, low membrane damage rate, and environmental friendliness, along with a standardized cleaning process, to achieve efficient cleaning results after ultrafiltration membrane fouling. Summary of the Invention

[0010] To address the aforementioned technical problems and enhance the cleaning effect while protecting the membrane material, a dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent and its intelligent cleaning method are provided; it is particularly suitable for ultrafiltration membrane systems that treat organic-inorganic complex fouling.

[0011] In a first aspect, this application provides a dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent, employing the following technical solution:

[0012] A dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent comprises, by weight percentage: 1-5% chelating agent, 0.5-5% metal oxide reducing agent, 0.3-3% Fenton catalyst, 0.1-1% corrosion inhibitor, 0.1-0.8% surfactant, 0.5-1.5% membrane repair agent, and the balance being deionized water;

[0013] The chelating agent is a composition of citric acid, EDTA and glycolic acid in a mass ratio of 3:(0.9-1):(0.9-1); the metal oxide reducing agent is a composition of oxalic acid and ascorbic acid in a mass ratio of 1:2.

[0014] Furthermore, the Fenton catalyst is either ferrous sulfate or ferrous chloride.

[0015] Furthermore, the corrosion inhibitor is Lan-826 corrosion inhibitor.

[0016] Furthermore, the surfactant is an isomeric alcohol polyoxyethylene ether.

[0017] Furthermore, the membrane repair agent is a combination of benzotriazole and sodium gluconate.

[0018] Secondly, this application provides an intelligent cleaning method for ultrafiltration membranes targeting acidic cleaning agents with a dynamic pH-responsive coating, employing the following technical solution:

[0019] A smart cleaning method for ultrafiltration membranes using a dynamic pH-responsive, acid-targeting cleaning agent includes the following steps:

[0020] S1: Pump the cleaning agent into the ultrafiltration membrane system. After circulation and soaking at 25-35℃, the pH will increase.

[0021] S2: When the pH of the cleaning solution rises to 3-3.5, open the hydrogen peroxide inlet valve, add 3-13% hydrogen peroxide by mass of the cleaning agent, and at the same time start the cleaning agent inlet valve. After circulation, the pH will decrease.

[0022] S3: As the pH drops to 2-2.5, the hydrogen peroxide inlet valve will automatically close, circulation will stop, and the air washing system will automatically start. Once the pH remains within 2-2.5 without change, the air washing will stop.

[0023] S4: Then soak in cleaning solution for several hours;

[0024] S5: Finally, rinse with ultrafiltration permeate until the effluent pH is 7-7.5, then restore the feed water to the ultrafiltration system;

[0025] In step S1, the prepared acidic cleaning solution is pumped into the ultrafiltration system and circulated for 1-4 hours, followed by soaking for 4-12 hours. This step can effectively remove inorganic scale layers such as carbonates, sulfates, and silicates adhering to the surface of the ultrafiltration membrane, forming soluble calcium salts, magnesium salts, aluminum salts, etc. During this process, the system automatically identifies the pH changes of the acidic solution, which usually show a slight upward trend.

[0026] In step S2, when the pH of the acidic solution suddenly rises to 3-3.5, the system automatically opens the hydrogen peroxide inlet valve, using 3-13% of the acidic solution's mass. Simultaneously, the cleaning agent inlet valve is activated. After circulation, the pH decreases as the hydrogen peroxide is consumed. This process automatically adjusts the pH from the initial 3-3.5 to 2-2.5 through the Fe²⁺ / H₂O₂ reaction, protecting the membrane material while enhancing the cleaning and removal of organic matter.

[0027] In step S3, as the pH drops to 2-2.5, the hydrogen peroxide inlet valve is automatically closed, circulation stops, and the air scrubbing system is automatically activated for 0.5-1.5 hours. Once the pH remains stable within the 2-2.5 range, the air scrubbing is stopped. If the pH is unstable, the stabilization time is appropriately increased. After the pH stabilizes, the system will automatically adjust the amount of hydrogen peroxide or hydrochloric acid added to lower the pH.

[0028] In step S4, the soaking time is generally controlled between 2 and 6 hours, and should not exceed 8 hours.

[0029] In step S5, first open the lower vent valve to discharge the cleaning solution into the wastewater collection tank, then close the lower vent valve, open the backwash inlet valve, and rinse with ultrafiltration permeate until the pH of the ultrafiltration effluent is about 7~7.5. The cleaning of the ultrafiltration system is basically completed, and normal inlet water is restored.

[0030] Furthermore, the concentration of hydrogen peroxide in step S2 is 27.5-31%.

[0031] Furthermore, the air washing adopts a microporous aeration method with a bubble diameter of 0.1-0.5 mm.

[0032] Furthermore, during the cleaning process, the cleaning fluid circulation, air washing, and water washing systems all utilize the operating equipment and systems integrated into the ultrafiltration membrane system. This fully leverages the existing ultrafiltration system's equipment and operating system, simplifying operation.

[0033] Furthermore, the cleaning process also includes the use of an online pH monitoring system and an automatic dosing system to achieve intelligent control of the cleaning process, reducing cleaning time by 40%.

[0034] This application pioneers a multi-mechanism synergistic cleaning system of "ternary chelation-stage reduction-targeted oxidation". Through ternary chelation of citric acid-EDTA-glycolic acid, staged reduction of oxalic acid-ascorbic acid, and surfactant-mediated Fenton oxidation, the system achieves the synergistic removal of organic and inorganic composite pollutants by citric acid chelating Ca²⁺, glycolic acid dissolving silicates, and oxalic acid reducing metal oxides.

[0035] Develop dynamic pH response technology. In the intelligent control cleaning process, the pH is first increased from the initial 2.5-3 to 3-3.5. The surfactant carries Fe²⁺ into the interior of the organic dirt. When it encounters the H2O2 microenvironment, it initiates the Fenton reaction and generates ·OH free radicals locally in the dirt layer. The pH is automatically adjusted to drop to 2-2.5, which protects the membrane material and enhances the cleaning effect, achieving the synergistic removal of organic and inorganic composite pollutants.

[0036] The zero-phosphorus, zero-halogen membrane repair formula, with the addition of sodium gluconate and benzotriazole, forms a protective film on the membrane surface, with a corrosion inhibition rate of ≥99%, and is environmentally friendly.

[0037] This application addresses most organic-inorganic fouling issues of ultrafiltration membranes using a specific acid cleaning agent, making it particularly suitable for ultrafiltration membranes with long operating times but uncontaminated internal fibers. The entire process is simple to operate, eliminating the damage to the ultrafiltration membrane caused by strong alkalis and sodium hypochlorite, and effectively preventing the membrane fibers from becoming brittle and soft after strong alkali cleaning.

[0038] The beneficial effects of this invention are as follows: the cleaning agent of this application has universality and multifunctionality, can deal with a variety of pollutants, has a strong removal effect on both organic and inorganic pollutants, greatly increases the water treatment capacity of ultrafiltration membrane, reduces the cleaning frequency, and reduces operating costs. Compared with traditional methods, it has advantages such as high flux recovery rate (≥90%), low membrane damage rate (<0.5%), and environmental friendliness (phosphorus-free and halogen-free). It has been successfully applied to the restorative cleaning of ultrafiltration membranes for large-scale reclaimed water reuse, with significant results. Detailed Implementation

[0039] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features, and effects of the present invention, in conjunction with embodiments, is provided below.

[0040] Example 1

[0041] A dynamic pH-responsive ultrafiltration membrane targeted acidic cleaning agent, its composition and preparation process are as follows: In a 12m³ water tank, add 7.5m³ of reverse osmosis permeate water at 25℃. First, add 200kg of citric acid, 62kg of EDTA, and 62kg of glycolic acid and stir to dissolve. Then add 50kg of oxalic acid and 100kg of ascorbic acid and continue stirring. Next, add 150kg of ferrous sulfate, 50kg of Lan-826, 10kg of isomeric alcohol polyoxyethylene ether, 80kg of benzotriazole, and 70kg of sodium gluconate, stirring until completely dissolved. The system pH value is 2.69, with an online pH monitoring instrument accuracy of ±0.1. The cleaning agent is applied to the cleaning process as follows:

[0042] S1: Pump the above acidic solution into the severely clogged ultrafiltration system I set (16 sets in total), turn on the circulation pump for 1 hour, and then soak for 10 hours. The ultrafiltration membrane used is type 8040, with a total of 84 membranes.

[0043] S2: As step 1 proceeds, when the system pH gradually rises to 3.20 (system setting), the hydrogen peroxide inlet valve is automatically opened, and hydrogen peroxide (27%) is slowly added. At the same time, the cleaning agent circulation pump inlet valve is started. After 4 hours, the pH drops to 2.32 (system setting), and the system automatically closes the hydrogen peroxide inlet valve. At this time, a total of 500 kg of hydrogen peroxide has been added.

[0044] S3: After step 2 is completed, the system will automatically start the ultrafiltration gas washing system for 1 hour (system setting).

[0045] S4: Stop air washing after step 3 is completed, and soak in acidic cleaning agent for 2 hours (system setting).

[0046] S5: During step 4, the pH fluctuates between 2.1 and 2.5. Afterward, the system automatically opens the vent valve to release the acidic cleaning agent, turns on the backwash pump in the ultrafiltration permeate tank, and flushes the ultrafiltration system until the pH reaches 7.5 (system setting). Then, the backwash pump automatically shuts off, and the ultrafiltration system resumes water intake. The cleaning effect comparison is shown in Table 1.

[0047] Table 1

[0048]

[0049] Example 2

[0050] A dynamic pH-responsive ultrafiltration membrane targeted acidic cleaning agent, its composition and preparation process are as follows: In a 12m³ water tank, add 7.5m³ of reverse osmosis permeate water at 35℃. First, add 300kg of citric acid, 93kg of EDTA, and 93kg of glycolic acid and stir until dissolved. Then, add 65kg of oxalic acid and 130kg of ascorbic acid and continue stirring. Next, add 30kg of ferrous sulfate, 10kg of Lan-826, 50kg of isomeric alcohol polyoxyethylene ether, 50kg of benzotriazole, and 50kg of sodium gluconate, and stir until completely dissolved. The system pH value is 2.54, with an online pH monitor accuracy of ±0.1. The cleaning agent is applied to the cleaning process as follows:

[0051] S1: Pump this acidic solution into the severely clogged H set of the ultrafiltration system (a total of 16 sets). After turning on the circulation pump for 1 hour, soak for 10 hours. The ultrafiltration membrane used is the 8040 type, with a total of 84 membranes.

[0052] S2: As step 1 proceeds, when the system pH gradually rises to 3.20 (system setting), the hydrogen peroxide inlet valve is automatically opened, and hydrogen peroxide (27%) is slowly added. At the same time, the cleaning agent circulation pump inlet valve is started. After 4 hours, the pH drops to 2.32 (system setting), and the system automatically closes the hydrogen peroxide inlet valve. At this time, a total of 100 kg of hydrogen peroxide has been added.

[0053] S3: After step 2 is completed, the system will automatically start the ultrafiltration gas washing system for 1 hour (system setting).

[0054] S4: Stop air washing after step 3 is completed, and soak in acidic cleaning agent for 2 hours (system setting).

[0055] S5: During step 4, the pH fluctuates between 2.1 and 2.5. Afterward, the system automatically opens the vent valve to release the acidic cleaning agent, turns on the backwash pump in the ultrafiltration permeate tank, and flushes the ultrafiltration system until the pH reaches 7.5 (system setting). Then, the backwash pump automatically shuts off, and the ultrafiltration system resumes water intake. A comparison of cleaning results is shown in Table 2.

[0056] Table 2

[0057]

[0058] Example 3

[0059] A dynamic pH-responsive ultrafiltration membrane targeted acidic cleaning agent, its composition and preparation process are as follows: In a 12m³ water tank, add 7.5m³ of reverse osmosis permeate water at 30℃. First, add 60kg of citric acid, 18kg of EDTA, and 18kg of glycolic acid and stir to dissolve. Then, add 65kg of oxalic acid and 130kg of ascorbic acid and continue stirring. Next, add 100kg of ferrous sulfate, 100kg of Lan-826, 80kg of isomeric alcohol polyoxyethylene ether, 60kg of benzotriazole, and 52kg of sodium gluconate, stirring until completely dissolved. The system pH value is 2.93, with an online pH monitor accuracy of ±0.1. The cleaning agent is applied to the cleaning process as follows:

[0060] S1: Pump this acidic solution into the B set (a total of 16 sets) of the ultrafiltration system, which is more severely clogged. After turning on the circulation pump for 1 hour, soak for 10 hours. The ultrafiltration membrane used is the 8040 type, with a total of 84 membranes.

[0061] S2: As step 1 proceeds, when the system pH gradually rises to 3.20 (system setting), the hydrogen peroxide inlet valve is automatically opened, and hydrogen peroxide (27%) is slowly added. At the same time, the cleaning agent circulation pump inlet valve is started. After 4 hours, the pH drops to 2.32 (system setting), and the system automatically closes the hydrogen peroxide inlet valve. At this time, a total of about 330 kg of hydrogen peroxide has been added.

[0062] S3: After step 2 is completed, the system will automatically start the ultrafiltration gas washing system for 1 hour (system setting).

[0063] S4: Stop air washing after step 3 is completed, and soak in acidic cleaning agent for 2 hours (system setting).

[0064] S5: During step 4, the pH fluctuates between 2.1 and 2.5. Afterward, the system automatically opens the vent valve to release the acidic cleaning agent, turns on the backwash pump in the ultrafiltration permeate tank, and flushes the ultrafiltration system until the pH reaches 7.5 (system setting). Then, the backwash pump automatically shuts off, and the ultrafiltration system resumes water intake. The cleaning effect comparison is shown in Table 3.

[0065] Table 3

[0066]

[0067] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent, characterized in that, By mass percentage, it consists of the following components: 1-5% chelating agent, 0.5-5% metal oxide reducing agent, 0.3-3% Fenton catalyst, 0.1-1% corrosion inhibitor, 0.1-0.8% surfactant, 0.5-1.5% membrane repair agent, and the balance being deionized water; The chelating agent is a composition of citric acid, EDTA and glycolic acid in a mass ratio of 3:(0.9-1):(0.9-1); the metal oxide reducing agent is a composition of oxalic acid and ascorbic acid in a mass ratio of 1:

2.

2. The dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent according to claim 1, characterized in that, The Fenton catalyst is either ferrous sulfate or ferrous chloride.

3. The dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent according to claim 1, characterized in that, The corrosion inhibitor is Lan-826 corrosion inhibitor.

4. The dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent according to claim 1, characterized in that, The surfactant is an isomeric alcohol polyoxyethylene ether.

5. The dynamic pH-responsive ultrafiltration membrane targeted acid cleaning agent according to claim 1, characterized in that, The membrane repair agent is a combination of benzotriazole and sodium gluconate.

6. A smart cleaning method using a dynamic pH-responsive ultrafiltration membrane targeted acidic cleaning agent as described in any one of claims 1-5, characterized in that, Includes the following steps: S1: Pump the cleaning agent into the ultrafiltration membrane system. After circulation and soaking at 25-35℃, the pH will increase. S2: When the pH of the cleaning solution rises to 3-3.5, open the hydrogen peroxide inlet valve, add 3-13% hydrogen peroxide by mass of the cleaning agent, and at the same time start the cleaning agent inlet valve. After circulation, the pH will decrease. S3: As the pH drops to 2-2.5, the hydrogen peroxide inlet valve will automatically close, circulation will stop, and the air washing system will automatically start. Once the pH remains within 2-2.5 without change, the air washing will stop. S4: Then soak in cleaning solution for several hours; S5: Finally, rinse with ultrafiltration permeate until the effluent pH is 7-7.5, then restore the influent to the ultrafiltration system.

7. The intelligent cleaning method according to claim 6, characterized in that, The concentration of hydrogen peroxide in step S2 is 27.5-31%.

8. The intelligent cleaning method according to claim 6, characterized in that, The air washing process uses microporous aeration with bubble diameters of 0.1-0.5 mm.

9. The intelligent cleaning method according to claim 6, characterized in that, During the cleaning process, the cleaning fluid circulation, air washing, and water washing systems all utilize the operating equipment system integrated with the ultrafiltration membrane system.

10. The intelligent cleaning method according to claim 6, characterized in that, The cleaning process also includes the use of an online pH monitoring system and an automatic dosing system to achieve intelligent control of the cleaning process.

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