Silicon scaling cleaning agent and cleaning method thereof

Abstract

The invention discloses a silicon scaling cleaning agent. The cleaning agent contains a polyphenol compound, a surfactant, a chelating agent, a pH regulator and water, the cleaning agent is prepared from the following components in percentage by mass: 1 to 5 percent of polyphenol compound, 0.1 to 1 percent of surfactant, 0.1 to 1 percent of chelating agent and the balance of pH regulator and water. A polyphenol compound is used as an effective component, and the solubility of silicon scale is improved through the interaction of a phenolic hydroxyl group and silicon dioxide, so that the purpose of elution is achieved. Compared with the prior art, the cleaning agent provided by the invention can be used under a mild alkalescent pH condition, corrosion to metal equipment is avoided, and safe operation of personnel is facilitated.

Description

Technical Field

[0001] The invention belongs to the field of cleaning agents, and in particular relates to a cleaning agent for silicon scaling and a cleaning method thereof. Background Art

[0002] Semi-permeable membranes represented by reverse osmosis and nanofiltration membranes are widely used in the fields of surface water desalination and wastewater treatment and regeneration and reuse. Reverse osmosis membranes intercept most of the small molecular organic matter and metal ions in the water body through size exclusion and electrostatic repulsion to obtain pure filtered water. The decrease in flux and the increase in pressure difference caused by the attachment of pollutants to the membrane surface are common problems in the use of reverse osmosis membranes. Industrial reverse osmosis membranes are mainly spiral membrane elements, which use cross-flow filtration for continuous filtration to eliminate the pressure increase caused by the accumulation of filter cakes and to alleviate the attachment of pollutants on the membrane surface to the greatest extent. However, due to the continuous concentration of raw water during the filtration process, the ion concentration in the raw water at the rear end of the filtration can reach several times that of the front end, resulting in the crystallization of inorganic salts and the formation of scaling.

[0003] The types of scaling in reverse osmosis membranes are commonly calcium sulfate, calcium carbonate, phosphate, calcium fluoride, silicon and other scaling, which are closely related to the types of ions in the raw water. Among them, silicon scaling is mainly derived from the abundant dissolved silicon in natural water bodies. Due to its particularity, silicon scaling has always been a difficult problem to overcome in the field of reverse osmosis. Different from the conventional ionic inorganic salt crystallization, silicon scaling is mainly dissolved silicon dioxide that forms hard silica gel on the membrane surface through polymerization. Its chemical properties are stable and it does not react with conventional acid and alkali chemical reagents.

[0004] Among the existing commonly used cleaning methods for silicon scaling, one is to use hydrofluoric acid or ammonium bifluoride. As in the CN106867691A patent, a cleaning agent with fluorine ammonium salt and fluorine-containing acid as the effective ingredients is used to clean the membrane system. Hydrofluoric acid has excellent reaction solubility to silicon scaling and is widely used in the fields of glass and wafer etching. However, hydrofluoric acid reacts with silicon to produce highly toxic silicon fluoride gas, and hydrofluoric acid itself also has strong toxicity and corrosiveness, which seriously damages the metal pipeline equipment of the membrane system, and is more unfavorable for personnel operation and cleaning fluid discharge, so that it is restricted in silicon scaling cleaning. Another method is to use a concentrated sodium hydroxide solution and soak it at the highest possible temperature. However, due to the limitation of the membrane material, it is very easy to cause irreversible damage to the membrane performance under the conditions of high temperature and strong alkali, and the cleaning effect is also very small. Summary of the invention

[0005] In order to overcome the above-mentioned defects, the present invention proposes a special cleaning agent for silicon scaling, which takes polyphenol compounds as the main active ingredients and adds a variety of additives to effectively remove silicon scaling under mild pH conditions, avoiding corrosion to metal equipment without damaging the performance of the membrane.

[0006] The specific technical solution of the present invention includes the following contents:

[0007] A silicon scale cleaning agent, the cleaning agent contains polyphenol compounds, surfactants, chelating agents, pH regulators and water; in the cleaning agent, the polyphenol compound content is 1-5%, the surfactant content is 0.1%-1%, the chelating agent content is 0.1-1%, and the balance is pH regulators and water.

[0008] In order to ensure that the cleaning liquid can be evenly mixed and dissolved, give full play to the synergistic effect of each component, and be widely applicable to different degrees of silicon scaling, it is further preferred that the polyphenol compound content is 5%, the surfactant content is 0.1%, the chelating agent content is 1%, and the balance is pH regulator and water.

[0009] Preferably, the polyphenol compound is a derivative containing a catechol structure, such as catechol and methyl catechol.

[0010] The dihydroxyl groups on the same side of the benzene ring of catechol can form a strong interaction with silica, improving the solubility of silica scale by coordination or bridging.

[0011] Preferably, the surfactant is sodium dodecylbenzene sulfonate or sodium toluene sulfonate. The surfactant enables the cleaning agent to more effectively penetrate into the deep scaling layer through emulsification and penetration, thereby achieving a better cleaning purpose.

[0012] Preferably, the chelating agent is EDTA. A portion of silicon scale is co-precipitated with aluminum and iron to form scale in the form of silicate. As an excellent metal chelating agent, EDTA can conjugate with most multivalent metal ions to improve the auxiliary cleaning effect on silicate.

[0013] Preferably, the pH of the cleaning agent after the addition of the pH adjuster is between 7 and 11. Alkaline conditions are conducive to the transformation of silicon scaling from silicic acid to silicate form, thereby increasing the solubility of silicon; but excessive alkalinity will cause the hydroxyl group of catechol to be deprotonated, forming hydroxyl anions, thereby weakening the interaction with silica. Therefore, adjusting the pH to a weak alkalinity of 7 to 11 helps to achieve a better cleaning effect. The pH adjuster can be a conventional inorganic base, such as sodium hydroxide, potassium hydroxide, or some buffer system solutions. In order to enhance the interaction between catechol and silica, it is further preferred that the pH of the cleaning agent is between 8 and 9.

[0014] The present invention also discloses a method for cleaning silicon scale, which comprises: a first step of using the silicon scale cleaning agent described in any one of claims 1 to 5 for soaking cleaning; a second step of using an acid solution for soaking cleaning when the pH of the cleaning agent is alkaline or weakly alkaline after the first step of cleaning.

[0015] Preferably, the silicon scale cleaning agent is mainly used for reverse osmosis membranes, and more preferably polyamide reverse osmosis membranes. Under mild pH conditions, the membrane performance and metal pipes of the membrane system are not damaged, solving the problem that the extreme pH conditions in the prior art are not suitable for reverse osmosis membrane cleaning.

[0016] First, a weak alkaline cleaning agent is used for soaking treatment to allow catechol to fully react and combine with the silica scale, and then an acid is used for soaking and cleaning to wash away the residual cleaning agent and residual metal silicate to achieve a better cleaning effect. Hydrochloric acid is preferably used for soaking and cleaning. On the other hand, using acid to contact the polyamide reverse osmosis membrane can protonate the carboxyl terminal of the polyamide, reduce electrostatic repulsion, achieve the effect of membrane pore tightening, and help restore a better desalination rate.

[0017] Preferably, the cleaning temperature is 30° C. to 50° C. Within the tolerance range of the reverse osmosis membrane, selecting a cleaning temperature as high as possible can accelerate the chemical reaction and achieve a better cleaning effect.

[0018] Compared with the prior art, the present invention provides a special cleaning agent for silicon scaling, which can be widely used in the cleaning and maintenance of water treatment membranes, especially the cleaning and maintenance of reverse osmosis membranes. It can be used at a relatively mild pH, has no corrosion to metal equipment, and is convenient for safe operation. At the same time, it has no damage to the performance of reverse osmosis membranes. DETAILED DESCRIPTION

[0019] The present invention is further described below in conjunction with the embodiments, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The invention can also be implemented or applied through other different specific examples, and the details in this specification can also be modified and changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0020] The present invention adopts polyphenol compounds as effective ingredients, and various additives are added and fully mixed to prepare a silicon scale cleaning solution. The cleaning solution of the present invention is used to soak the reverse osmosis membrane for a certain period of time, and then pure water is used to wash and replace the residual components of the cleaning agent. In the second step, the reverse osmosis membrane is soaked in a conventional acidic solution such as hydrochloric acid, and then pure water is used to wash and replace the residual acid solution to obtain a cleaned reverse osmosis membrane.

[0021] A faulty reverse osmosis membrane was obtained after replacement at a coal chemical wastewater treatment site in Ningxia. After disassembly EDX elemental analysis, it was confirmed that the membrane surface was severely covered with silica scaling. Under an operating pressure of 5.2MPa, the water production performance of the cut membrane sample was tested. The water production was reduced from the nominal 1.2m / d to 0.44m / d, confirming that the membrane had a water production attenuation due to silicon scaling. The membrane sample was chemically cleaned according to the method described in the following embodiment, and the recovery effect was compared. The cleaning recovery rate was calculated by the following formula: (water production after cleaning - water production before cleaning) / (nominal water production - water production before cleaning)×100%.

[0022] The raw materials used in the embodiments and comparative examples are as follows:

[0023] Catechol: Vokai, AR, 99.5%

[0024] Sodium dodecyl sulfate: Shanghai test, CP, 97.0%

[0025] EDTA (ethylenediaminetetraacetic acid): Alfa-A10713, 99%

[0026] Sodium hydroxide: Shanghai test, AR, >96.0%

[0027] Hydrochloric acid: Shanghai test, AR, (36.0~38.0%)

[0028] Methylcatechol: 4-Methylcatechol, Vokai, 98%

[0029] Methylresorcinol: 4-Methylresorcinol, Vokai, 98%

[0030] The water production and recovery rate are tested using the following test methods.

[0031] 1. Water production: Using 32000mg / L sodium chloride solution, the water permeability per unit area of ​​the membrane sample is tested at an inlet pressure of 5.52MPa, measured in meters per day (m / d).

[0032] 2. Recovery rate: (water production after cleaning - water production before cleaning) / (nominal water production - water production before cleaning) × 100%.

[0033] Example 1

[0034] 1% catechol, 0.1% sodium dodecyl sulfate, 0.1% EDTA were added in sequence, and the balance was water and sodium hydroxide regulator. The sodium hydroxide regulator was added after sufficient mixing, and the pH was adjusted to 7 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 25°C for 24 hours, and the residual cleaning solution was cleaned with pure water. The test membrane was soaked in hydrochloric acid with pH 2 for 24 hours, and the residual acid solution was cleaned with clean water.

[0035] Example 2

[0036] 3% catechol, 0.5% sodium dodecyl sulfate, 0.5% EDTA were added in sequence, and the balance was water and sodium hydroxide regulator. The sodium hydroxide regulator was added after sufficient mixing, and the pH was adjusted to 11 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 45°C for 24 hours, and the residual cleaning solution was cleaned with pure water. The test membrane was soaked in hydrochloric acid with pH 2 for 24 hours, and the residual acid solution was cleaned with clean water.

[0037] Example 3

[0038] 5% catechol, 1% sodium dodecyl sulfate, 1% EDTA were added in sequence, and the balance was water and sodium hydroxide regulator. The sodium hydroxide regulator was added after sufficient mixing, and the pH was adjusted to 9 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 30°C for 24 hours, and the residual cleaning solution was cleaned with pure water. The test membrane was soaked in hydrochloric acid with pH 2 for 24 hours, and the residual acid solution was cleaned with clean water.

[0039] Example 4

[0040] 3% catechol, 0.1% sodium dodecyl sulfate, 1% EDTA were added in sequence, and the balance was water and hydrochloric acid regulator, and the hydrochloric acid regulator was added after being fully mixed to adjust the pH to 3 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 50°C for 24 hours, and the residual cleaning solution was cleaned with pure water.

[0041] Example 5

[0042] 3% catechol, 0.1% sodium dodecyl sulfate, 1% EDTA were added in sequence, and the balance was water and sodium hydroxide regulator. The sodium hydroxide regulator was added after sufficient mixing, and the pH was adjusted to 9 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 30°C for 24 hours, and the residual cleaning solution was cleaned with pure water. The test membrane was soaked in hydrochloric acid with pH 2 for 24 hours, and the residual acid solution was cleaned with clean water.

[0043] Example 6

[0044] 5% methylresorcinol, 0.1% sodium dodecylsulfonate, 1% EDTA were added in sequence, and the balance was water and sodium hydroxide regulator. The sodium hydroxide regulator was added after sufficient mixing, and the pH was adjusted to 12 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 30°C for 24 hours, and the residual cleaning solution was cleaned with pure water. The test membrane was soaked in hydrochloric acid with pH 2 for 24 hours, and the residual acid solution was cleaned with clean water.

[0045] Example 7

[0046] 5% methyl catechol, 0.1% sodium dodecyl sulfate, 1% EDTA were added in sequence, and the balance was water and hydrochloric acid regulator, and the hydrochloric acid regulator was added after being fully mixed to adjust the pH to 2 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 30°C for 24 hours, and the residual cleaning solution was cleaned with pure water.

[0047] Example 8

[0048] 5% methyl catechol, 0.1% sodium dodecyl sulfate, 1% EDTA were added in sequence, and the balance was water and hydrochloric acid regulator. The hydrochloric acid regulator was added after sufficient mixing, and the pH was adjusted to 9 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 30°C for 24 hours, and the residual cleaning solution was cleaned with pure water. The test membrane was soaked in hydrochloric acid with pH 2 for 24 hours, and the residual acid solution was cleaned with clean water.

[0049] Comparative Example 1

[0050] Add 6% catechol to water, the balance is water, mix thoroughly, add sodium hydroxide to adjust the pH to 7, and obtain a silicon scale cleaning agent. Soak the test membrane in the silicon scale cleaning agent at 25°C for 24 hours, and use pure water to clean the residual cleaning solution. Soak the test membrane in hydrochloric acid with pH 2 for 24 hours, and use clean water to clean the residual acid solution.

[0051] Comparative Example 2

[0052] 0.1% sodium dodecyl sulfate, 1% EDTA, and the rest water and sodium hydroxide regulator were added in sequence. The sodium hydroxide regulator was added after being fully mixed and the pH was adjusted to 13 to obtain a silicon scale cleaning agent. The test membrane was soaked in the silicon scale cleaning agent at 30°C for 24 hours, and the residual cleaning solution was cleaned with pure water.

[0053] According to the above implementation, the silicon scaled reverse osmosis membrane was cleaned and treated, and the water production under a water supply pressure of 5.52 MPa was tested to obtain the membrane performance and calculate the recovery rate effect, as shown in Table 1.

[0054] Table 1. Reverse osmosis membrane flux test results after cleaning

[0055]

[0056] As shown in Table 1, by comparing Examples 3, 6, and 7, it can be seen that the weakly alkaline pH condition exerts the best cleaning effect. By comparing Examples 3, 4, and 7, it can be seen that the use of a weakly alkaline cleaning agent followed by additional acid washing has a better cleaning effect. By comparing Examples 3, 6, and 8, it can be seen that catechol has a relatively better cleaning effect than monomethyl substituted derivatives. By comparing Examples 1-3, it can be seen that while ensuring that all components are soluble, a relatively high component content has a better cleaning effect.

[0057] In Comparative Example 1, an excessive amount of polyphenol compounds was added, and no other additives were added, so the water production and recovery rate were slightly lower than those of the embodiment.

[0058] Comparative Example 2 shows that compared with the high-concentration alkaline washing of the prior art without adding polyphenol compounds, the cleaning agent of the present invention has the same or better cleaning effect at a mild pH.

[0059] In summary, the synergistic effect of catechol, surfactants and chelating agents can achieve a good removal effect on silicon scale, especially when the pH is still alkaline or weakly alkaline after soaking in the cleaning agent, conventional acid washing can achieve the best cleaning effect.

Claims

1. A silicon scale cleaning agent, characterized in that: The cleaning agent contains polyphenol compounds, surfactants, chelating agents, pH regulators and water; in the cleaning agent, the polyphenol compound content is 1-5%, the surfactant content is 0.1%-1%, the chelating agent content is 0.1-1%, and the balance is pH regulators and water.

2. The silicon scale cleaning agent according to claim 1, characterized in that: The polyphenol compounds include catechol, methyl catechol and other derivatives containing catechol structure.

3. The silicon scale cleaning agent according to claim 1, characterized in that: The surfactant is sodium dodecylbenzenesulfonate or sodium toluenesulfonate.

4. The silicon scale cleaning agent according to claim 1, characterized in that: The chelating agent is EDTA.

5. The silicon scale cleaning agent according to claim 1, characterized in that: The pH of the cleaning agent after the pH adjuster is added is between 7 and 11.

6. A method for cleaning silicon scale, characterized in that: The cleaning method comprises: a first step of using the silicon scale cleaning agent described in any one of claims 1-5 for soaking cleaning; a second step of using an acid solution for soaking cleaning when the pH of the cleaning agent is alkaline or weakly alkaline after the first step of cleaning.

7. The cleaning method according to claim 6, characterized in that The cleaning temperature is 30℃~50℃.

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