Preparation method and application of free nitrous acid composite citric acid reverse osmosis membrane cleaning agent

Abstract

The invention discloses a preparation method and application of a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent, and relates to a preparation method and application of a cleaning agent. The invention aims to solve the problems of poor cleaning effect, high cost and environmental pollution caused by two-step chemical cleaning of polluted membranes in a reverse osmosis system by adopting alkaline and acidic reagents in the prior art. The method comprises the following steps: 1, preparing free nitrous acid; and 2, dissolving free nitrous acid and citric acid in water, and adjusting the pH value of the system to 3-4 to obtain the free nitrous acid and citric acid composite reverse osmosis membrane cleaning agent. The free nitrous acid composite citric acid reverse osmosis membrane cleaning agent is used for cleaning a polluted membrane in a reverse osmosis system. The citric acid and the FNA are mixed and compounded, and the citric acid and the FNA show good synergy in the aspects of metal ion complexation and chemical stability in the oxidation-reduction reaction. The pollution condition of the reverse osmosis membrane can be improved to the greatest extent.

Description

Technical Field

[0001] The invention relates to a preparation method and application of a cleaning agent. Background Art

[0002] Circulating water wastewater has a variety of water quality characteristics, mainly including high temperature, large suspended solids and chemical oxygen demand (COD), low dissolved oxygen content, high salt content and possible heavy metal pollutants. In practical applications, the water quality of circulating water discharge is often accompanied by coupled pollution of organic and inorganic substances, and the pH value is easy to change. These characteristics make the discharged water have a certain impact on the ecological environment and the self-purification capacity of the water body. Since circulating water plays an important role in a variety of industrial and cooling processes, the complexity of its water quality requires effective treatment of wastewater to reduce the negative impact on the environment and ensure the sustainable use of water resources. Therefore, accurate assessment of the water quality of circulating water wastewater and optimization of treatment methods have become key tasks for protecting the water environment and improving water treatment efficiency.

[0003] As an efficient water treatment technology, the reverse osmosis (RO) process has many significant advantages. Reverse osmosis can effectively remove pollutants such as dissolved salts, heavy metals, organic matter, bacteria and viruses in water, especially in seawater desalination and wastewater reuse. With the large-scale application of reverse osmosis technology, membrane fouling is still the key to limiting the application of reverse osmosis technology. Before the reverse osmosis process, ultrafiltration or microfiltration is usually used as a pretreatment process for reverse osmosis, and chemical agents are added before the RO inlet water to reduce the content of pollutants or microorganisms in the RO inlet water. However, pollutants such as bacteria, organic matter, and inorganic matter can still accumulate and precipitate on the RO membrane surface, causing membrane fouling. In the membrane cleaning process, the cleaning effect of a single cleaning agent is limited. If the membrane assembly cannot be fully cleaned, it will cause corrosion to the membrane material, resulting in a decrease in membrane flux, a decrease in water quality, an increase in energy consumption, and a shortened service life. Among them, biological fouling is generally considered to be a major problem in reverse osmosis (RO) membrane filtration. A two-step chemical cleaning with alkaline and acidic reagents is usually used for a series of cleanings. Alkaline washing is used to remove organic matter and biofilm on the membrane, while acid washing is usually used to remove scaling. There are still some disadvantages in using current methods to remove biofilm pollution. In addition, the large amount of detergents used will greatly increase operating costs and cause certain environmental problems. Summary of the invention

[0004] The purpose of the present invention is to solve the problems of poor cleaning effect, high cost and environmental pollution of the contaminated membrane in the two-step chemical cleaning of the reverse osmosis system using alkaline and acidic reagents in the prior art, and to provide a preparation method and application of a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent.

[0005] The present invention provides a method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent. Free nitrous acid (FNA) is prepared by reacting hydrochloric acid and sodium nitrite. FNA itself has a weak acidity. In a chemical reaction, its acidity is enhanced and stabilized by HCl acidification. After acidification, the oxidation ability of FNA is significantly enhanced, and the acidified nitrous acid FNA can better participate in the coordination reaction. Citric acid has a good solubility for some metal salts and scale. Citric acid is a biodegradable organic acid that can be decomposed into harmless substances such as carbon dioxide and water by microorganisms in the natural environment. After industrial cleaning, the discharge of cleaning wastewater has little impact on the environment. The present invention mixes citric acid and FNA, and the two show good synergy in redox reactions, metal ion complexation, and chemical stability. It can improve the pollution of reverse osmosis membranes to the greatest extent.

[0006] A method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent is specifically completed according to the following steps:

[0007] 1. Preparation of free nitrous acid:

[0008] In a fume hood, add hydrochloric acid dropwise to sodium nitrite and react for a period of time in an ice-water bath to obtain free nitrous acid;

[0009] 2. Compound:

[0010] Dissolving free nitrous acid and citric acid in water, and adjusting the pH value of the system to 3-4, to obtain a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent;

[0011] In the free nitrous acid-combined citric acid reverse osmosis membrane cleaning agent described in step 2, the mass fraction of free nitrous acid is 2% to 5%, and the mass fraction of citric acid is 4%.

[0012] Free nitrous acid combined with citric acid reverse osmosis membrane cleaning agent is used to clean the contaminated membrane in the reverse osmosis system.

[0013] Principle of the present invention:

[0014] Reverse osmosis membrane pollution can be divided into four categories: colloidal pollution, inorganic pollution, organic pollution and biological pollution. In practical applications, these types of pollution often interact and occur simultaneously. The present invention uses free nitrous acid (FNA) + citric acid to remove pollutants to the greatest extent and improve cleaning efficiency. FNA is an unstable compound that is easily decomposed, especially at high temperatures and unsuitable pH. Citric acid can stabilize FNA to a certain extent. The acidity of citric acid is relatively mild. When it coexists with FNA, it can adjust the pH of the system to avoid the accelerated decomposition of nitrous acid due to excessive acidity. Citric acid and FNA can cooperate with each other in the redox reaction to enhance the oxidation effect. FNA itself is an oxidant that can oxidize some reducing substances. Citric acid can optimize the oxidation performance of FNA by adjusting the pH of the system. Both citric acid and FNA have the ability to complex metal ions. Citric acid can form stable complexes with metal ions through its carboxyl and hydroxyl groups, and FNA can also interact with metal ions. The present invention uses FNA + citric acid to perform one-step cleaning to remove biofouling and scaling, which is more cost-effective.

[0015] Advantages of the present invention:

[0016] 1. In view of the characteristics of high salt content and complex water quality of circulating water wastewater, the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent prepared by the present invention is used for cleaning, wherein free nitrous acid and citric acid can produce a synergistic effect and produce higher cleaning efficiency;

[0017] Second, the free nitrite composite citric acid reverse osmosis membrane cleaning agent of the present invention can effectively remove organic-inorganic coupling pollution, and the cleaning agent can simultaneously remove biological fouling and descaling;

[0018] 3. Conventional chemical cleaning methods are not very effective in removing organic matter. The free nitrous acid-compounded citric acid reverse osmosis membrane cleaning agent of the present invention can achieve efficient removal of polysaccharides and microbial metabolites.

[0019] Fourth, the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent of the present invention is used to treat the contaminated membrane in the reverse osmosis system, with high biomass removal rate, good synergy, and higher cleaning efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The figures are the surface morphologies of the reverse osmosis membrane after being cleaned with different chemical cleaning agents. (a) shows the cleaning effect of using 4% citric acid to clean the reverse osmosis membrane, (b) shows the cleaning effect of using 0.4% hydrochloric acid to clean the reverse osmosis membrane, and (c) shows the cleaning effect of using the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent prepared in Example 1 to clean the reverse osmosis membrane. DETAILED DESCRIPTION

[0021] Specific implementation method 1: This implementation method is a method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent, which is specifically completed according to the following steps:

[0022] 1. Preparation of free nitrous acid:

[0023] In a fume hood, add hydrochloric acid dropwise to sodium nitrite and react for a period of time in an ice-water bath to obtain free nitrous acid;

[0024] 2. Compound:

[0025] Dissolving free nitrous acid and citric acid in water, and adjusting the pH value of the system to 3-4, to obtain a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent;

[0026] In the free nitrous acid-combined citric acid reverse osmosis membrane cleaning agent described in step 2, the mass fraction of free nitrous acid is 2% to 5%, and the mass fraction of citric acid is 4%.

[0027] Specific implementation method 2: This implementation method is different from specific implementation method 1 in that the mass fraction of hydrochloric acid in step 1 is 30%; the mass ratio of sodium nitrite to hydrochloric acid in step 1 is 15g:30mL. The other steps are the same as those in specific implementation method 1.

[0028] Specific implementation method 3: This implementation method is different from specific implementation method 1 or 2 in that the temperature of the ice water bath in step 1 is 0° C. to 5° C. The other steps are the same as those in specific implementation method 1 or 2.

[0029] Specific embodiment 4: This embodiment differs from specific embodiments 1 to 3 in that the reaction time in step 1 is 0.5 h to 1 h. The other steps are the same as those in specific embodiments 1 to 3.

[0030] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that: in step 2, 1% to 5% by mass of citric acid and 0.5% to 2% by mass of ammonia water are used to adjust the pH value of the system to 3 to 4. The other steps are the same as those of specific embodiments 1 to 4.

[0031] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that the mass fraction of free nitrous acid and the mass fraction of citric acid in the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent described in step 2 is 2%, and the mass fraction of citric acid is 4%. The other steps are the same as specific embodiments 1 to 5.

[0032] Specific embodiment 7: This embodiment differs from specific embodiments 1 to 6 in that the free nitrous acid and citric acid reverse osmosis membrane cleaning agent described in step 2 contains 3% free nitrous acid and 4% citric acid. The other steps are the same as those of specific embodiments 1 to 6.

[0033] Specific embodiment 8: This embodiment differs from specific embodiments 1 to 7 in that the free nitrous acid and citric acid reverse osmosis membrane cleaning agent described in step 2 has a mass fraction of 4% free nitrous acid and a mass fraction of 4% citric acid. The other steps are the same as those of specific embodiments 1 to 7.

[0034] Specific embodiment 9: This embodiment differs from specific embodiments 1 to 8 in that the mass fraction of free nitrous acid in the free nitrous acid-combined citric acid reverse osmosis membrane cleaning agent described in step 2 is 5%, and the mass fraction of citric acid is 4%. The other steps are the same as specific embodiments 1 to 8.

[0035] Specific implementation method ten: This implementation method is that free nitrous acid combined with citric acid reverse osmosis membrane cleaning agent is used to clean the contaminated membrane in the reverse osmosis system.

[0036] The following examples are used to verify the beneficial effects of the present invention:

[0037] Example 1: A method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent, which is specifically completed according to the following steps:

[0038] 1. Preparation of free nitrous acid:

[0039] In a fume hood, add hydrochloric acid dropwise to sodium nitrite and react for a period of time in an ice-water bath to obtain free nitrous acid;

[0040] The mass fraction of the hydrochloric acid described in step 1 is 30%;

[0041] The mass ratio of sodium nitrite to hydrochloric acid described in step 1 is 15g:30mL;

[0042] The temperature of the ice water bath in step 1 is 0°C

[0043] The reaction time in step 1 is 0.5 h;

[0044] 2. Compound:

[0045] Dissolving free nitrous acid and citric acid in water, and adjusting the pH value of the system to 3, to obtain a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent;

[0046] The free nitrous acid-compounded citric acid reverse osmosis membrane cleaning agent described in step 2 has a mass fraction of free nitrous acid of 2% and a mass fraction of citric acid of 4%;

[0047] In step 2, the pH value of the system is adjusted to 3 using 4% by mass citric acid and 2% by mass ammonia water.

[0048] The free nitrite composite citric acid reverse osmosis membrane cleaning agent prepared in Example 1 was circulated in the reverse osmosis system, with a soaking time of 2 h, a cleaning temperature of 25 ° C, a circulation time of 2 h, a flushing time of 1.5 h, and a cleaning flow rate of 8 m 3 / h, the flux recovery rate of the reverse osmosis membrane after cleaning reached 46.84%.

[0049] Example 2: The difference between this example and Example 1 is that the mass fraction of free nitrous acid in the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent described in step 2 is 3%, and the mass fraction of citric acid is 4%. Other steps and parameters are the same as those in Example 1.

[0050] The free nitrite composite citric acid reverse osmosis membrane cleaning agent prepared in Example 2 was circulated in the reverse osmosis system, with a soaking time of 2 h, a cleaning temperature of 25 ° C, a circulation time of 2 h, a flushing time of 1.5 h, and a cleaning flow rate of 8 m 3 / h, the flux recovery rate of the reverse osmosis membrane after cleaning reached 44.63%.

[0051] Example 3: The difference between this example and Example 1 is that the mass fraction of free nitrous acid in the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent described in step 2 is 4%, and the mass fraction of citric acid is 4%. Other steps and parameters are the same as those in Example 1.

[0052] The free nitrite composite citric acid reverse osmosis membrane cleaning agent prepared in Example 3 was circulated in the reverse osmosis system, with a soaking time of 2 h, a cleaning temperature of 25 ° C, a circulation time of 2 h, a flushing time of 1.5 h, and a cleaning flow rate of 8 m 3 / h, the flux recovery rate of the reverse osmosis membrane after cleaning reached 40.32%.

[0053] Example 4: The difference between this example and Example 1 is that the mass fraction of free nitrous acid in the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent described in step 2 is 5%, and the mass fraction of citric acid is 4%. The other steps and parameters are the same as those in Example 1.

[0054] The free nitrite composite citric acid reverse osmosis membrane cleaning agent prepared in Example 4 was circulated in the reverse osmosis system, with a soaking time of 2 h, a cleaning temperature of 25 ° C, a circulation time of 2 h, a flushing time of 1.5 h, and a cleaning flow rate of 8 m 3 / h, the flux recovery rate of the reverse osmosis membrane after cleaning reached 37.76%.

[0055] Example 5: The difference between this example and Example 1 is that in step 2, free nitrous acid and citric acid are dissolved in water, and the pH value of the system is adjusted to 3 to obtain a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent; the cleaning temperature of the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent is increased to 40° C. The other steps and parameters are the same as those in Example 1.

[0056] The free nitrite composite citric acid reverse osmosis membrane cleaning agent prepared in Example 5 was circulated in the reverse osmosis system, with a soaking time of 2 h, a cleaning temperature of 40°C, a circulation time of 2 h, a flushing time of 1.5 h, and a cleaning flow rate of 8 m 3 / h, the flux recovery rate of the reverse osmosis membrane after cleaning reached 32.08%.

[0057] Example 6: The difference between this example and Example 1 is that in step 2, free nitrous acid and citric acid are dissolved in water, and then the pH value of the system is adjusted to 2. The other steps and parameters are the same as those in Example 1.

[0058] The free nitrite composite citric acid reverse osmosis membrane cleaning agent prepared in Example 6 was circulated in the reverse osmosis system, with a soaking time of 2 h, a cleaning temperature of 25 ° C, a circulation time of 2 h, a flushing time of 1.5 h, and a cleaning flow rate of 8 m 3 / h, the flux recovery rate of the reverse osmosis membrane after cleaning reached 35.42%.

[0059] Example 7: The difference between this example and Example 1 is that in step 2, free nitrous acid and citric acid are dissolved in water, and then the pH value of the system is adjusted to 5. The other steps and parameters are the same as those in Example 1.

[0060] The free nitrite composite citric acid reverse osmosis membrane cleaning agent prepared in Example 7 was circulated in the reverse osmosis system, with a soaking time of 2 h, a cleaning temperature of 25 ° C, a circulation time of 2 h, a flushing time of 1.5 h, and a cleaning flow rate of 8 m 3 / h, the flux recovery rate of the reverse osmosis membrane after cleaning reached 38.89%.

[0061] In summary, the free nitrite combined with citric acid reverse osmosis membrane cleaning agent has a free nitrite mass fraction of 2% and a citric acid mass fraction of 4%. The best cleaning effect can be achieved by stirring the cleaning solution at 10-20°C and adjusting the pH value between 3-4 under normal pressure.

[0062] The reverse osmosis membrane was cleaned with different chemical cleaning agents. The surface morphology of the reverse osmosis membrane was shown in Figure 2. Figure 1 As shown;

[0063] Figure 1 The surface morphology of the reverse osmosis membrane after the reverse osmosis membrane is cleaned with different chemical cleaning agents, wherein (a) shows the cleaning effect of using 4% citric acid to clean the reverse osmosis membrane, (b) shows the cleaning effect of using 0.4% hydrochloric acid to clean the reverse osmosis membrane, and (c) shows the cleaning effect of using the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent prepared in Example 1 to clean the reverse osmosis membrane;

[0064] from Figure 1 From (a) in the figure, it can be seen that: after the reverse osmosis membrane is cleaned with 4% citric acid, there is still scale on the surface of the reverse osmosis membrane after cleaning;

[0065] from Figure 1 From (b) in the figure, it can be seen that when the reverse osmosis membrane is cleaned with 0.4% hydrochloric acid, there is fine scale on the surface of the reverse osmosis membrane after cleaning, and the cleaning effect is improved.

[0066] from Figure 1 From (c) in the figure, it can be seen that the reverse osmosis membrane is cleaned by using the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent prepared in Example 1. After cleaning, the surface scale of the reverse osmosis membrane is obviously removed, and the pollutants remaining on the surface are minimal.

[0067] The specific implementation modes of the present invention are described in detail above, but the present invention is not limited to the above implementation modes, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent, characterized in that The preparation method is specifically completed according to the following steps:

1. Preparation of free nitrous acid: In a fume hood, add hydrochloric acid dropwise to sodium nitrite and react for a period of time in an ice-water bath to obtain free nitrous acid; 2. Compound: Dissolving free nitrous acid and citric acid in water, and adjusting the pH value of the system to 3-4, to obtain a free nitrous acid-compounded citric acid reverse osmosis membrane cleaning agent; In the free nitrous acid-combined citric acid reverse osmosis membrane cleaning agent described in step 2, the mass fraction of free nitrous acid is 2% to 5%, and the mass fraction of citric acid is 4%.

2. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that The mass fraction of the hydrochloric acid described in step one is 30%; the volume ratio of the mass of the sodium nitrite described in step one to the hydrochloric acid is 15g:30mL.

3. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that The temperature of the ice water bath described in step 1 is 0°C to 5°C.

4. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that The reaction time in step 1 is 0.5 h to 1 h.

5. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that In step 2, 1% to 5% by mass of citric acid and 0.5% to 2% by mass of ammonia water are used to adjust the pH value of the system to 3 to 4.

6. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that The free nitrous acid combined with citric acid reverse osmosis membrane cleaning agent described in step 2 contains 2% free nitrous acid by mass and 4% citric acid by mass.

7. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that The free nitrous acid combined with citric acid reverse osmosis membrane cleaning agent described in step 2 contains 3% free nitrous acid by mass and 4% citric acid by mass.

8. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that The free nitrous acid combined with citric acid reverse osmosis membrane cleaning agent described in step 2 contains 4% free nitrous acid by mass and 4% citric acid by mass.

9. The method for preparing a free nitrous acid composite citric acid reverse osmosis membrane cleaning agent according to claim 1, characterized in that The free nitrous acid combined with citric acid reverse osmosis membrane cleaning agent described in step 2 contains 5% free nitrous acid by mass and 4% citric acid by mass.

10. Application of the free nitrous acid composite citric acid reverse osmosis membrane cleaning agent prepared by the preparation method according to claim 1, characterized in that Free nitrite combined with citric acid reverse osmosis membrane cleaning agent is used to clean the contaminated membrane in the reverse osmosis system.

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