Composite reverse osmosis membrane acid cleaning agent, preparation method and cleaning process thereof

Abstract

The present application relates to a kind of composite reverse osmosis membrane acidic cleaning agent, preparation method and cleaning process, belong to environmental protection water treatment technical field.The cleaning agent contains 4~8% inorganic acid, 20~40% organic acid, 1~3% surfactant, 0.5~1% chelating agent, 0.5~1% composite corrosion inhibitor by mass percentage, and the balance is deionized water.Composite corrosion inhibitor is compounded by 2-mercaptobenzothiazole etc.according to specific mass ratio, and the molecular weight of polyaspartic acid is 5000, and the molar ratio of Zn:Mo in zinc-molybdate complex is 2:1.The preparation method is divided into four steps, first, composite corrosion inhibitor premix is prepared, then acidic base fluid is prepared, then each component is added in turn, and finally cleaning solution is obtained.Cleaning process mixes cleaning agent with deionized water, and is cleaned through specific process, membrane flux recovery rate is ≥85%, can effectively clean reverse osmosis membrane, and restore its performance.

Description

Technical Field

[0001] This invention belongs to the field of environmental water treatment technology, and relates to a composite reverse osmosis membrane acid cleaning agent, its preparation method and cleaning process. Background Technology

[0002] Reverse osmosis membrane technology is widely used in seawater desalination, industrial wastewater treatment, and drinking water purification. However, its long-term operation is susceptible to fouling by inorganic scale (such as calcium carbonate and calcium sulfate), metal oxides, and organic matter, leading to a decrease in membrane flux and desalination rate. Regular chemical cleaning is required to restore performance. Traditional acidic cleaning agents such as hydrochloric acid and nitric acid can effectively dissolve inorganic scale, but the strongly acidic environment can easily corrode the polyamide layer on the membrane surface and metal pipes, shortening the membrane life. At the same time, a single corrosion inhibitor cannot provide comprehensive protection for both the membrane and the metal, resulting in a 5-10% decrease in membrane desalination rate after cleaning. Furthermore, frequent replacement of membrane modules is necessary, increasing operating costs.

[0003] In existing technologies, some cleaning agents reduce corrosivity by adding organic acids or chelating agents, but these methods suffer from problems such as poor dispersibility of the corrosion inhibitors and large pH fluctuations, affecting the uniformity of cleaning. In addition, research on composite corrosion inhibitors has mostly focused on binary systems, with insufficient utilization of multi-component synergistic mechanisms, resulting in a significant decrease in corrosion inhibition efficiency under low temperature (≤40℃) or low pressure conditions.

[0004] Therefore, developing a composite acidic cleaning agent that combines high efficiency in descaling, low corrosivity, and process adaptability, along with a standardized cleaning process, has become a key requirement for resolving the contradiction between reverse osmosis membrane fouling and lifespan. Summary of the Invention

[0005] The purpose of this invention is to provide a composite reverse osmosis membrane acid cleaning agent, its preparation method and cleaning process, which has the characteristics of high descaling efficiency and low corrosivity.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A composite reverse osmosis membrane acidic cleaning agent, comprising the following components by mass percentage: 4-8% inorganic acid, 20-40% organic acid, 1-3% surfactant, 0.5-1% chelating agent, 0.5-1% composite corrosion inhibitor, and the balance being deionized water;

[0008] The composite corrosion inhibitor is prepared by combining 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid, and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system in a mass ratio of (15~50):(8~10):(3~5):(1~2).

[0009] Furthermore, the inorganic acid is one or more of hydrochloric acid, nitric acid, and phosphoric acid.

[0010] Furthermore, the organic acid is one or more of anhydrous citric acid and ethylenediaminetetraacetic acid.

[0011] Furthermore, the surfactant is one or more of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

[0012] Furthermore, the chelating agent is one of aminotrimethylenephosphonic acid and sodium ethylenediaminetetramethylenephosphonate.

[0013] Furthermore, in the composite corrosion inhibitor, the molecular weight of polyaspartic acid is 5000.

[0014] Furthermore, in the zinc-molybdate complex, the molar ratio of Zn:Mo is 2:1.

[0015] In this mixture, molybdenum is either sodium molybdate or potassium molybdate, and zinc is either zinc sulfate, zinc chloride, or zinc nitrate. The zinc salt and molybdate are weighed and dissolved separately in deionized water. The molybdate solution is slowly poured into the zinc salt solution while stirring, and the temperature is controlled at 50℃ for 45 min. After the reaction is complete, the mixture is centrifuged at 3500 r / min for 15 min, filtered and washed, and then dried in a 70℃ drying oven for 4 h to obtain the zinc-molybdate complex.

[0016] A method for preparing a composite reverse osmosis membrane acidic cleaning agent, the specific process of which is as follows:

[0017] S1: Weigh 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system according to the mass ratio (15~50):(8~10):(3~5):(1~2), mix them and stir at 200~400 rpm for 10~20 min to prepare a uniform composite corrosion inhibitor premix;

[0018] S2: Add 40-60% of the total amount of deionized water, slowly add inorganic acid at 300-500 rpm, control the temperature ≤35℃, stir for 20 min, then add organic acid, continue stirring for 20-30 min to obtain acidic base solution;

[0019] S3: Add the following to the acidic base solution prepared in S2 at a speed of 300~500 rpm: surfactant, stir for 10~15 min; chelating agent, stir for 5~10 min; composite corrosion inhibitor premix, increase the speed to 400~600 rpm and stir for 20~30 min;

[0020] S4: Add the remaining deionized water, continue stirring for 15 minutes, check the pH value to be 1.5~3, filter, and obtain the cleaning agent.

[0021] A cleaning process for a composite reverse osmosis membrane acidic cleaning agent involves mixing the acidic cleaning agent with deionized water at a mass ratio of (1.5~2.5):100, stirring for 20~30 minutes, controlling the pH of the cleaning solution to 1.5~3.0, injecting the cleaning solution into the cleaning system, starting the circulation pump, controlling the flow rate to 3~6 m³ / h, pressure to 0.5~2 bar, and temperature to ≤40℃, circulating and cleaning for 30~60 minutes, stopping the circulation pump, soaking the membrane module for 1~2 hours, rinsing the system with deionized water until the effluent pH is ≥5.0, resuming operation, and testing the membrane flux recovery rate to complete the cleaning process.

[0022] Furthermore, the membrane flux recovery rate after the cleaning process is ≥85%.

[0023] The composite reverse osmosis membrane acidic cleaning agent of this invention has high descaling efficiency, a characteristic attributed to its scientifically formulated composition. The cleaning agent contains both inorganic and organic acids, which work synergistically to efficiently remove various types of fouling from the reverse osmosis membrane surface.

[0024] Inorganic acids such as hydrochloric acid, nitric acid, and phosphoric acid are strong acids that can quickly dissolve some metal oxide scale, such as iron scale and calcium scale. In an acidic environment, iron oxides will react chemically with the acid. The main component of rust is iron oxide, and the chemical equation for its reaction with hydrochloric acid is: Fe₂O₃ + 6HCl = 2FeCl₂ 3 + 3H₂O. Through the reaction, iron scale is converted into water-soluble iron salts, thereby being removed from the membrane surface. For calcium scale, such as calcium carbonate, the chemical equation for the reaction with hydrochloric acid is: CaCO₃ + 2HCl = CaCl₂ + H₂O + CO₂↑. Calcium carbonate is dissolved, and carbon dioxide gas is produced, further promoting the loosening and removal of the scale.

[0025] Organic acids, such as anhydrous citric acid and ethylenediaminetetraacetic acid (EDTA), also play an important role in the descaling process. The organic acids used in this invention all possess strong chelating abilities, capable of forming stable chelates with metal ions. During cleaning, they can bind to metal ions in the scale layer, pulling them out of their crystal structure, thus disrupting the scale layer's structure and making it easier to remove. For example, the chelate formed by citric acid and calcium ions has high stability and can effectively dissolve calcium scale. EDTA is an even stronger chelating agent, possessing multiple coordinating atoms and capable of forming stable cyclic chelates with various metal ions. When cleaning reverse osmosis membranes, EDTA can chelate various metal ions such as iron, copper, and calcium in the scale layer, causing the scale layer to gradually dissolve and disperse into the cleaning solution. In this invention, the synergistic effect of inorganic and organic acids enables the cleaning agent to achieve optimal descaling effects for different types of fouling. Inorganic acids rapidly dissolve metal oxide scale, while organic acids further disrupt the scale structure through chelation and penetration, removing metal ions and organic matter from the scale, thus greatly improving descaling efficiency.

[0026] In terms of the cleaning process, acidic cleaning agent and deionized water are mixed in a certain proportion and injected into the cleaning system, and the circulation pump is started for circulating cleaning. During the circulating cleaning process, the cleaning solution flows continuously, allowing it to fully contact the dirt on the membrane surface and enhancing the descaling effect. The circulation flow rate is controlled at 3~6m³ / min. 3 A flow rate of [flow rate] / h ensures a moderate flow velocity of the cleaning solution on the membrane surface, allowing the cleaning agent to fully react with the scale, while avoiding excessive flow that could cause mechanical damage to the membrane. After circulating and cleaning for 30-60 minutes, stop the circulation pump and soak the membrane module for 1-2 hours. The soaking process is a crucial step in descaling. In a static state, the cleaning agent can penetrate deeper into the scale layer, fully reacting with its components to further dissolve and remove the fouling. Through these two stages of circulation cleaning and soaking, the fouling on the membrane surface can be efficiently removed, thus improving descaling efficiency.

[0027] This invention reduces the corrosiveness of cleaning agents by adding a composite corrosion inhibitor. The composite corrosion inhibitor is prepared by combining 2-mercaptobenzothiazole, a zinc-molybdate complex, polyaspartic acid, and a sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system. 2-Mercaptobenzothiazole is a commonly used corrosion inhibitor that can form an adsorption film on metal surfaces. Its thiol group (-SH) has a strong adsorption capacity, allowing it to adsorb onto metal surfaces and form a dense protective film, preventing acidic components in the cleaning agent from directly contacting the film surface.

[0028] Zinc-molybdate complexes also exhibit good corrosion inhibition properties. In solution, zinc-molybdate complexes can form a special precipitate film. When zinc salts and molybdates react in solution to form zinc-molybdate complexes, these complexes deposit on the metal surface, forming a dense precipitate film. This precipitate film can isolate the cleaning agent from contact with the film surface, thus inhibiting corrosion. Simultaneously, the zinc and molybdenum elements in the zinc-molybdate complex also have a certain synergistic corrosion inhibition effect. Zinc ions can form a zinc oxide protective film on the metal surface, while molybdate ions can further stabilize this protective film and enhance its corrosion resistance. In acidic environments, zinc ions are preferentially oxidized to form zinc oxide, which adheres to the film surface. Molybdate ions then interact with zinc oxide to form a more stable protective structure, thereby effectively reducing the corrosion rate.

[0029] Polyaspartic acid is an environmentally friendly corrosion inhibitor with excellent chelating and dispersing abilities. The carboxyl and amide groups in the polyaspartic acid molecule can chelate with metal ions, forming a chelated film on the membrane surface. Simultaneously, it can disperse metal ions and microparticles in the solution, preventing their deposition and aggregation on the metal surface, thereby reducing under-deposit corrosion. For example, during cleaning, polyaspartic acid can chelate iron ions, calcium ions, etc., in the solution, keeping them in the solution and preventing the formation of localized corrosion cells on the membrane surface.

[0030] The sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system can regulate the pH of the cleaning solution, maintaining it within a relatively stable range. During the cleaning process, the pH of the cleaning solution may change due to the reaction and consumption of acidic components. Excessive pH fluctuations can corrode the membrane surface. The sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system can stabilize the pH of the cleaning solution through acid-base neutralization, avoiding corrosion problems caused by pH changes. For example, when excessive acidic components in the cleaning solution cause a drop in pH, disodium hydrogen phosphate reacts with hydrogen ions to generate sodium dihydrogen phosphate, thereby neutralizing some of the acidity and raising the pH. Conversely, when the pH rises, sodium dihydrogen phosphate releases hydrogen ions, lowering the pH and maintaining the stability of the cleaning solution's pH.

[0031] The composite corrosion inhibitor, prepared by combining the components in a mass ratio of (15-50):(8-10):(3-5):(1-2), can fully utilize the advantages of each component to form a multi-layered corrosion-inhibiting protective film. On the membrane surface, an adsorption film is first formed by 2-mercaptobenzothiazole, followed by a precipitation film formed by the zinc-molybdate complex, and a chelating film formed by polyaspartic acid. In addition, a sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system stabilizes the pH value. The combined action of these multiple protective films effectively prevents the acidic components in the cleaning agent from contacting the membrane surface, greatly reducing the corrosiveness of the cleaning agent to the reverse osmosis membrane.

[0032] In terms of the cleaning process, controlling the temperature of the cleaning solution to ≤40℃ is also an important measure to reduce corrosion. In the cleaning process of this invention, controlling the temperature of the cleaning solution at a low level can slow down the corrosion rate of the metal. At the same time, controlling the cleaning pressure at 0.5-2 bar avoids excessive pressure from causing mechanical damage to the membrane, further protecting the reverse osmosis membrane.

[0033] The components in the cleaning agent remove dirt without damaging the reverse osmosis membrane material. Although inorganic and organic acids have some acidity, they do not chemically react with the membrane material under the protection of the composite corrosion inhibitor. Reverse osmosis membranes are usually made of polymers such as polyamides, which are prone to hydrolysis and other reactions in acidic environments, leading to a decline in membrane performance. The composite corrosion inhibitor in this invention can form a protective film on the membrane surface, preventing acidic components from contacting the membrane material, thereby protecting the membrane's chemical stability. The addition of surfactants also helps reduce the impact on membrane performance. Surfactants such as fatty alcohol polyoxyethylene ethers and alkylphenol polyoxyethylene ethers have good wetting, dispersing, and emulsifying effects. During the cleaning process, surfactants can reduce the surface tension of the cleaning solution, allowing the cleaning solution to better wet the membrane surface and promote dirt removal. At the same time, it can also disperse the removed dirt in the cleaning solution, preventing dirt from redepositing on the membrane surface and avoiding secondary pollution. Chelating agents, such as aminotrimethylenephosphonic acid and sodium ethylenediaminetetramethylenephosphonate, can chelate metal ions in solution, preventing them from depositing on the membrane surface and forming fouling. The deposition of metal ions on the membrane surface affects membrane flux and separation performance; chelating agents, by forming stable chelates with metal ions, keep the metal ions in solution, preventing membrane fouling.

[0034] In terms of cleaning process, the combination of circulating cleaning and soaking can thoroughly remove fouling from the membrane surface and restore membrane flux. During circulating cleaning, the cleaning solution continuously flows over the membrane surface, quickly carrying away the removed fouling and providing uniform cleaning. The soaking process allows the cleaning agent to penetrate deeper into the membrane's microporous structure, removing fouling hidden within the micropores and further restoring membrane flux. After cleaning, the system is rinsed with deionized water until the effluent pH is ≥5.0, thoroughly removing any residual cleaning solution from the membrane surface and preventing long-term effects of residual acidic components on the membrane. After resuming operation, the membrane flux recovery rate is tested. The cleaning process of this invention achieves a membrane flux recovery rate of ≥85%, indicating that the cleaning agent and process effectively restore membrane performance, allowing the reverse osmosis membrane to return to optimal working condition. Detailed Implementation

[0035] 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.

[0036] Example 1

[0037] A composite reverse osmosis membrane acidic cleaning agent, comprising the following components by mass percentage: 6% hydrochloric acid, 30% ethylenediaminetetraacetic acid, 2% fatty alcohol polyoxyethylene ether, 0.5% aminotrimethylenephosphonic acid, 1% composite corrosion inhibitor, and the balance being deionized water.

[0038] The composite corrosion inhibitor is prepared by combining 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid, and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system in a mass ratio of 30:7:4:1.

[0039] In the zinc-molybdate complex, the molar ratio of Zn:Mo is 2:1.

[0040] Weigh out the corresponding amounts of sodium molybdate and zinc sulfate, and dissolve them separately in deionized water. Slowly pour the molybdate solution into the zinc salt solution while stirring, and control the temperature at 50℃ for 45 min. After the reaction is complete, centrifuge the mixture at 3500 r / min for 15 min, filter and wash, and then dry it in a 70℃ drying oven for 4 h to obtain the zinc-molybdate complex.

[0041] A method for preparing a composite reverse osmosis membrane acidic cleaning agent, the specific process of which is as follows:

[0042] S1: Weigh 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system according to the mass ratio of 30:7:4:1, mix them and stir at 300 rpm for 10 min to prepare a uniform composite corrosion inhibitor premix.

[0043] S2: Add 50% of the total amount of deionized water, slowly add inorganic acid at 300 rpm, control the temperature ≤35℃, stir for 20 min, then add organic acid, continue stirring for 20 min to obtain acidic base solution;

[0044] S3: Add the following to the acidic base solution prepared in S2 at a speed of 300 rpm: surfactant, stir for 10 min; chelating agent, stir for 5 min; composite corrosion inhibitor premix, increase the speed to 500 rpm and stir for 20 min.

[0045] S4: Add the remaining deionized water, continue stirring for 15 minutes, check the pH value to be 1.5~3, filter, and obtain the cleaning agent.

[0046] A cleaning process for a composite reverse osmosis membrane acidic cleaning agent involves mixing the acidic cleaning agent with deionized water at a mass ratio of 2:100, stirring for 20 minutes, controlling the pH of the cleaning solution to 1.5~3.0, injecting the cleaning solution into the cleaning system, starting the circulation pump, and controlling the flow rate to 4m³ / min. 3 At a pressure of 1 bar and a temperature of ≤40℃, the system is circulated for 45 minutes. The circulation pump is then stopped, and the membrane module is soaked for 2 hours. The system is then rinsed with deionized water until the drainage pH is ≥5.0. Operation is resumed, and the membrane flux recovery rate is tested. If the membrane flux recovery rate is ≥85%, the cleaning process is complete.

[0047] Example 2

[0048] A composite reverse osmosis membrane acidic cleaning agent, comprising the following components by mass percentage: 4% nitric acid, 20% anhydrous citric acid, 1% alkylphenol polyoxyethylene ether, 0.5% sodium ethylenediaminetetramethylenephosphonate, 0.5% composite corrosion inhibitor, with the balance being deionized water;

[0049] The composite corrosion inhibitor is prepared by combining 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid, and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system in a mass ratio of 15:8:3:1.

[0050] In the zinc-molybdate complex, the molar ratio of Zn:Mo is 2:1.

[0051] Weigh out the corresponding amounts of potassium molybdate and zinc chloride, and dissolve them separately in deionized water. Slowly pour the molybdate solution into the zinc salt solution while stirring, and control the temperature at 50℃ for 45 min. After the reaction is complete, centrifuge the mixture at 3500 r / min for 15 min, filter and wash, and then dry it in a 70℃ drying oven for 4 h to obtain the zinc-molybdate complex.

[0052] A method for preparing a composite reverse osmosis membrane acidic cleaning agent, the specific process of which is as follows:

[0053] S1: Weigh 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system according to the mass ratio of 15:8:3:1, mix them and stir at 400 rpm for 20 min to prepare a uniform composite corrosion inhibitor premix.

[0054] S2: Add 40% of the total amount of deionized water, slowly add inorganic acid at 400 rpm, control the temperature ≤35℃, stir for 20 min, then add organic acid, continue stirring for 20 min to obtain acidic base solution;

[0055] S3: Add the following to the acidic base solution prepared in S2 at a speed of 400 rpm: surfactant, stir for 10 min; chelating agent, stir for 5 min; composite corrosion inhibitor premix, increase the speed to 600 rpm and stir for 20 min.

[0056] S4: Add the remaining deionized water, continue stirring for 15 minutes, check the pH value to be 1.5~3, filter, and obtain the cleaning agent.

[0057] A cleaning process for a composite reverse osmosis membrane acidic cleaning agent involves mixing the acidic cleaning agent with deionized water at a mass ratio of 1.5:100, stirring for 20 minutes, controlling the pH of the cleaning solution to be 1.5~3.0, injecting the cleaning solution into the cleaning system, starting the circulation pump, and controlling the flow rate to 3m³ / min. 3 At a pressure of 0.5 bar and a temperature of ≤40℃, the system is circulated for 30 minutes. The circulation pump is then stopped, and the membrane module is soaked for 1 hour. The system is then rinsed with deionized water until the drainage pH is ≥5.0. Operation is resumed, and the membrane flux recovery rate is tested. If the membrane flux recovery rate is ≥85%, the cleaning process is complete.

[0058] Example 3

[0059] A composite reverse osmosis membrane acidic cleaning agent, by mass percentage, comprises the following components: 8% phosphoric acid, 40% ethylenediaminetetraacetic acid, 3% fatty alcohol polyoxyethylene ether, 1% aminotrimethylene phosphonic acid, 1% composite corrosion inhibitor, and the balance being deionized water.

[0060] The composite corrosion inhibitor is prepared by combining 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid, and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system in a mass ratio of 50:10:5:2.

[0061] In the zinc-molybdate complex, the molar ratio of Zn:Mo is 2:1.

[0062] Weigh out the corresponding amounts of potassium molybdate and zinc nitrate, and dissolve them separately in deionized water. Slowly pour the molybdate solution into the zinc salt solution while stirring, and control the temperature at 50℃ for 45 min. After the reaction is complete, centrifuge the mixture at 3500 r / min for 15 min, filter and wash, and then dry it in a 70℃ drying oven for 4 h to obtain the zinc-molybdate complex.

[0063] A method for preparing a composite reverse osmosis membrane acidic cleaning agent, the specific process of which is as follows:

[0064] S1: Weigh 2-mercaptobenzothiazole, zinc-molybdate complex, polyaspartic acid and sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system according to the mass ratio of 50:10:5:2, mix them and stir at 400 rpm for 20 min to prepare a uniform composite corrosion inhibitor premix.

[0065] S2: Add 60% of the total amount of deionized water, slowly add inorganic acid at 500 rpm, control the temperature ≤35℃, stir for 20 min, then add organic acid, continue stirring for 30 min to obtain acidic base solution;

[0066] S3: Add the following to the acidic base solution prepared in S2 at 500 rpm: surfactant, stir for 15 min; chelating agent, stir for 10 min; composite corrosion inhibitor premix, increase the speed to 600 rpm and stir for 30 min.

[0067] S4: Add the remaining deionized water, continue stirring for 15 minutes, check the pH value to be 1.5~3, filter, and obtain the cleaning agent.

[0068] A cleaning process for a composite reverse osmosis membrane acidic cleaning agent involves mixing the acidic cleaning agent with deionized water at a mass ratio of 2.5:100, stirring for 30 minutes, controlling the pH of the cleaning solution to 1.5~3.0, injecting the cleaning solution into the cleaning system, starting the circulation pump, and controlling the flow rate to 6m³ / min. 3 At a pressure of 2 bar and a temperature of ≤40℃, the system is circulated for 60 minutes. The circulation pump is then stopped, and the membrane module is soaked for 2 hours. The system is then rinsed with deionized water until the drainage pH is ≥5.0. Operation is resumed, and the membrane flux recovery rate is tested. If the membrane flux recovery rate is ≥85%, the cleaning process is complete.

[0069] Comparative Example 1

[0070] This comparative composite corrosion inhibitor does not contain zinc-molybdate complex, and the remaining steps are the same as in Example 1.

[0071] Comparative Example 2

[0072] This comparative composite corrosion inhibitor does not contain polyaspartic acid, and the remaining steps are the same as in Example 1.

[0073] Comparative Example 3

[0074] This comparative composite corrosion inhibitor does not include a sodium dihydrogen phosphate-disodium hydrogen phosphate buffer system; the remaining steps are the same as in Example 1.

[0075] Membrane flux recovery rates were tested for the examples and comparative examples, and the experimental data are summarized in Table 1 below.

[0076] Membrane flux recovery rate is an important indicator for evaluating the cleaning effect of cleaning agents. The calculation formula is as follows:

[0077] Membrane flux recovery rate = (membrane flux after cleaning - membrane flux before cleaning) / (initial membrane flux - membrane flux before cleaning) × 100%.

[0078] Table 1:

[0079]

[0080] Corrosion tests were conducted on the examples and comparative examples. The corrosion rate was calculated by measuring the change in the mass of the reverse osmosis membrane before and after cleaning. The lower the corrosion rate, the less corrosive the cleaning agent is to the membrane. The experimental data are summarized in Table 2 below.

[0081] Table 2:

[0082]

[0083] The experimental data above show that the composite reverse osmosis membrane acid cleaning agent prepared by this invention has a good cleaning effect, can significantly improve the membrane flux recovery rate, and reduce the corrosion rate of the membrane.

[0084] 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 composite reverse osmosis membrane acid cleaning agent, characterized by, The acidic cleaning agent component is as follows in percentage by mass: 4-8% inorganic acid, 20-40% organic acid, 1-3% surfactant, 0.5-1% chelating agent, 0.5-1% composite corrosion inhibitor, and the balance being deionized water; The composite corrosion inhibitor is prepared by compounding 2-mercaptobenzothiazole, zinc-molybdate composite, polyaspartic acid, and sodium dihydrogen phosphate-sodium hydrogen phosphate buffer system, and the mass ratio is (15-50):(8-10):(3-5):(1-2). In the composite corrosion inhibitor, the molar ratio of Zn:Mo in the zinc-molybdate composite is 2:

1. The cleaning agent preparation method has the following specific process, S1: 2-mercaptobenzothiazole, zinc-molybdate composite, polyaspartic acid, and sodium dihydrogen phosphate-sodium hydrogen phosphate buffer system are weighed according to the mass ratio (15-50):(8-10):(3-5):(1-2), mixed, and stirred at a speed of 200-400 rpm for 10-20 min to prepare a uniform composite corrosion inhibitor premix; S2: 40-60% of the total amount of deionized water is added, and inorganic acid is slowly added at a stirring speed of 300-500 rpm, with the temperature controlled to be ≤35℃, and after stirring for 20 min, organic acid is added, and stirring is continued for 20-30 min to obtain an acidic base solution; S3: the surface active agent is added to the acidic base solution prepared in S2 at a stirring speed of 300-500 rpm, and stirring is continued for 10-15 min; the chelating agent is added and stirred for 5-10 min; the composite corrosion inhibitor premix is added, and the stirring speed is increased to 400-600 rpm and stirring is continued for 20-30 min; S4: the remaining deionized water is added, and stirring is continued for 15 min, and the pH value is detected to be 1.5-3, and the cleaning agent is obtained by filtration.

2. The composite reverse osmosis membrane acid cleaning agent according to claim 1, characterized in that, The inorganic acid is one or more of hydrochloric acid, nitric acid, and phosphoric acid.

3. The composite reverse osmosis membrane acid cleaning agent according to claim 1, characterized in that, The organic acid is one or more of anhydrous citric acid and ethylenediaminetetraacetic acid.

4. The acidic cleaning agent for composite reverse osmosis membranes according to claim 1, characterized by The surfactant is one or more of fatty alcohol polyoxyethylene ether and alkylphenol polyoxyethylene ether.

5. The composite reverse osmosis membrane acid cleaning agent according to claim 1, characterized in that, The chelating agent is one of aminotri(methylene) phosphonic acid and sodium ethylenediaminetetramethylene phosphonate.

6. The acidic cleaning agent for composite reverse osmosis membranes according to claim 1, characterized by In the composite corrosion inhibitor, the molecular weight of polyaspartic acid is 5000.

7. A cleaning process of a composite reverse osmosis membrane acid cleaning agent according to any one of claims 1 to 6, characterized by, The acid cleaning agent is mixed with deionized water at a mass ratio of (1.5-2.5):100, stirred for 20-30 min, the pH value of the cleaning solution is controlled at 1.5-3.0, the cleaning solution is injected into the cleaning system, the circulating pump is started, and the flow rate is controlled at 3-6 m 3 / h, pressure 0.5-2 bar, temperature ≤40℃, the circulating cleaning is performed for 30-60 min, the circulating pump is stopped, the membrane module is soaked for 1-2 h, the system is washed with deionized water until the drainage pH value is ≥5.0, the operation is resumed, and the recovery rate of the membrane flux is detected, and the cleaning process is completed.

8. The cleaning process of a composite reverse osmosis membrane acid cleaning agent according to claim 7, characterized in that, The membrane flux recovery rate after the completion of the cleaning process is ≥85%.

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