A silicon-removing composition and a method for preparing the same

Abstract

The application belongs to the technical field of water treatment, and specifically discloses a silicon-removing composition and a preparation method thereof. Silicon scale is dissolved by sodium hydroxide, aluminum hydroxide is activated to generate sodium metaaluminate, sodium metaaluminate reacts with silicate to generate aluminosilicate precipitate, and dissolved silicon is separated and fixed in a solid form, so that silicon removal is complete and re-deposition of silicon is avoided. On this basis, the fluorosilicone sulfonic acid surfactant molecule in the silicon-oxygen skeleton is similar in structure to the silicon scale, and can penetrate into the micropore inside the silicon scale. Meanwhile, the fluorocarbon chain provides ultra-low surface tension, so that the penetration depth of the alkali solution is improved. In addition, the sodium sulfonate group can also provide strong alkali stability and hard water resistance, and synergistically achieve efficient removal of dense silicon scale.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a silicon removal composition and its preparation method. Background Technology

[0002] Silica scale is a common, insoluble deposit found in industrial water treatment systems, boilers, heat exchangers, and reverse osmosis membranes. Current silica removal technologies are primarily based on the theory of gradually deprotonating silicic acid to form soluble silicates under alkaline conditions. CN111286421A discloses an environmentally friendly, high-efficiency alkaline cleaning agent for food processing, using sodium hydroxide and potassium hydroxide as the main alkaline agents, combined with tetrasodium diacetate, sodium silicate, and conventional surfactants. However, the introduction of sodium silicate into the formula can actually generate silicate scale during use, causing secondary pollution; furthermore, the surfactants used are conventional nonionic or anionic types, which are prone to hydrolysis or saponification in strongly alkaline environments, resulting in limited penetration and wetting ability against dense silica scale and making deep removal of silica scale difficult. CN119529945A discloses a cleaning agent and method for cleaning silica scale on reverse osmosis membranes. It uses polyphenolic compounds such as catechol as active ingredients, combined with surfactants (sodium dodecylbenzenesulfonate or sodium toluenesulfonate), chelating agents (EDTA), pH adjusters, and water. The solubility is improved through hydrogen bonding between phenolic hydroxyl groups and silica. While this method is relatively gentle on reverse osmosis membranes, it is susceptible to problems under weakly alkaline conditions. - Insufficient concentration results in a slow rate of silica scale dissolution, requiring subsequent acid washing steps to complete the cleaning process, making it complex and unsuitable for the rapid removal of high-concentration silica scale.

[0003] In summary, existing silicon removers suffer from problems such as insufficient alkalinity leading to low silicon removal efficiency and incompatibility between surfactants and strong alkaline systems. There is an urgent need to develop a silicon remover composition that combines strong alkaline dissolution driving force with efficient penetration and wetting ability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a strong alkaline desiliconization composition with a high concentration of alkali as the main component and fluorosiloxane sulfonic acid surfactant as a penetration enhancer, achieving highly efficient removal of dense silica scale. The composition has a simple preparation process, readily available raw materials, and controllable costs, and is suitable for online cleaning and maintenance of silica scale in industrial circulating water systems, boilers, heat exchangers, and other equipment.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: One aspect of the present invention provides a desiliconizing composition, which, by weight percentage (100%), comprises the following raw materials: 35-50% alkali agent, 1-3% fluorosiloxane sulfonic acid surfactant, and the balance being deionized water.

[0006] This formula uses a high concentration of alkali to provide a strongly alkaline environment to drive the dissolution reaction of silica scale. Combined with the ultra-low surface tension of the fluorosiloxane sulfonic acid surfactant and the specific affinity effect of the siloxane skeleton for silica scale, the alkaline solution can deeply penetrate the micropores of dense silica scale, so that the silica removal reaction can be promoted from the surface to the inside, thereby improving the silica removal efficiency.

[0007] In some embodiments, the alkaline agent is a mixture of sodium hydroxide and aluminum hydroxide.

[0008] In some embodiments, the mass ratio of sodium hydroxide to aluminum hydroxide is (10-15):(25-35).

[0009] Sodium hydroxide serves as the primary alkali agent, providing OH- - The process drives the dissolution of silica scale. Alumina hydroxide in a strong alkali produces sodium aluminate, which further reacts with dissolved silicates to form insoluble aluminosilicate precipitates. This fixes and separates the dissolved silicon in solid form, preventing the redeposition of silicon.

[0010] In some embodiments, the alkali agent further comprises potassium hydroxide.

[0011] In some embodiments, the potassium hydroxide is 0.5% to 0.9% by mass.

[0012] The introduction of potassium hydroxide can form a mixed alkali system with sodium hydroxide, K + Ionic radius greater than Na + It can affect the dissolution behavior of silicates and improve the wetting and penetration of silica scale; at the same time, K + The presence of [agent name] can regulate the crystal transformation of aluminosilicate precipitates and optimize their filtration and separation performance. This invention, by controlling the dosage range, allows K [agent name] to [be used in conjunction with other agents]. + It leverages the synergistic effect of ions without significantly interfering with the total alkalinity of the system, ensuring that the main reaction of sodium hydroxide and aluminum hydroxide is not inhibited.

[0013] In some embodiments, the aluminum hydroxide has a particle size of 500 nm to 2 μm.

[0014] Aluminum hydroxide in this particle size range has a large specific surface area and a moderate dissolution rate in strong alkalis, enabling the slow-release supply of sodium aluminate.

[0015] In some embodiments, the preparation steps of the fluorosiloxane sulfonic acid surfactant are as follows: S1. Under an inert atmosphere, hydrogen-containing methylsiloxane and allyl chloride were stirred and mixed, and a chloroplatinic acid catalyst-isopropanol solution was added dropwise. After the reaction was heated and completed, the mixture was distilled under reduced pressure to obtain intermediate A. S2. Under an inert atmosphere, perfluorohexylethanol was added to dry THF, and NaH was added. The mixture was stirred at room temperature until no gas was released, yielding a sodium perfluorohexylethanol solution. Intermediate A was dissolved in dry THF and then added dropwise to the sodium perfluorohexylethanol solution. The mixture was heated to react. After the reaction was complete, the mixture was filtered, and the filtrate was distilled under reduced pressure. The residue was extracted, washed, dried, filtered, and then distilled under reduced pressure to obtain intermediate B. S3. Refluxing intermediate B, diethanolamine, and anhydrous toluene, removing toluene by vacuum distillation, dissolving in acetonitrile, and then adding 1,3-propanesulfonic acid lactone dropwise to react. After the reaction is complete, cooling, filtering, washing, and vacuum drying are performed to obtain the fluorosiloxane sulfonic acid surfactant.

[0016] This surfactant uses hydrogen-containing methylsiloxane as its backbone, introduces fluorocarbon and chloropropyl chains through hydrosilylation, and then obtains it through etherification and quaternization-sulfonation reactions. Its molecular structure simultaneously contains fluorocarbon low surface tension end groups, siloxane flexible backbone, and sodium sulfonate hydrophilic groups. It has ultra-low surface tension, specific affinity for silica scale, and strong alkali stability. A small amount (1-3%) can achieve the wetting and penetration effect of 5-10% of conventional surfactants.

[0017] In some embodiments, the alkane Mn of the hydrogen-containing methylsiloxane is 300 to 600.

[0018] This molecular weight range ensures that the siloxane chains have moderate flexibility and length, providing sufficient affinity and penetration into silica deposits without causing increased viscosity or dispersion difficulties due to excessive chain length.

[0019] In some embodiments, the molar ratio of the hydrogen-containing methylsiloxane to allyl chloride is 1:(1.0 to 1.2).

[0020] Another aspect of the present invention provides a method for preparing the above-mentioned desiliconizing composition, comprising the following steps: preparing an aqueous solution of an alkaline agent, then adding an aqueous solution of a fluorosiloxane sulfonic acid surfactant, stirring and dispersing, followed by high-pressure homogenization and circulation treatment, allowing it to stand and mature at room temperature, after maturation, replenishing the remaining deionized water, filtering, taking samples for testing and filling after passing the test, thus obtaining the desiliconizing composition.

[0021] Compared with the prior art, the present invention has the following beneficial effects: 1. The process involves dissolving silica scale with sodium hydroxide, activating it with aluminum hydroxide to generate sodium aluminate, and then reacting sodium aluminate with silicates to form aluminosilicate precipitate. This process fixes and separates the dissolved silicon in solid form, ensuring thorough silicon removal and preventing silicon redeposition.

[0022] 2. By utilizing the structural similarity between the siloxane skeleton in the fluorosiloxane sulfonic acid surfactant molecule and the silica scale, it can penetrate deep into the micropores of the silica scale; at the same time, the fluorocarbon chain provides ultra-low surface tension, which increases the penetration depth of the alkaline solution; in addition, the sulfonic acid group can also provide strong alkali stability and hard water resistance.

[0023] 3. Using ultrafine aluminum hydroxide of 500 nm to 2 μm, sodium aluminate is supplied in a slow-release manner, avoiding local oversaturation and precipitation agglomeration caused by a large release at one time; the generated aluminosilicate precipitate has a uniform particle size and is easy to filter and separate.

[0024] 4. Potassium hydroxide and sodium hydroxide form a mixed alkali system, which can differentially regulate the dissolution balance of silicates and the crystal form of aluminosilicates, thereby optimizing the filtration performance and silicon removal efficiency of the precipitate. Detailed Implementation

[0025] The present invention will be described below with reference to specific implementation schemes. It should be noted that the following embodiments and comparative examples are examples of the present invention and are used only to illustrate the invention, not to limit it. Other combinations and various modifications within the scope of the present invention can be made without departing from its spirit or scope. It is worth noting that, unless otherwise specified, the raw materials used in the following preparation examples and embodiments are all from any commercially available manufacturer.

[0026] Preparation Example 1 The preparation steps of fluorosiloxane sulfonic acid surfactant A are as follows; S1. Under nitrogen protection, hydrogen-containing methylsiloxane (SiSiB® HF2030-M400) with Mn≈400 and allyl chloride were mixed by stirring at a molar ratio of 1:1.1. A 0.5wt% chloroplatinic acid catalyst-isopropanol solution (Pt content of 5ppm of total reactant mass) was added dropwise. The temperature was increased to 76℃ at 1℃ / min and the reaction was carried out for 3h. After the reaction was completed, the mixture was distilled under reduced pressure (60℃ / 10mmHg). The endpoint was determined by GC monitoring that the allyl chloride content was <0.5%, yielding intermediate A. S2. Under dry nitrogen protection, 1200g of perfluorohexylethanol was added to 5L of dry THF, and 29g of NaH was added in three batches. The mixture was stirred at room temperature until no gas was released, resulting in a sodium perfluorohexylethanol solution. 1500g of intermediate A was dissolved in 2L of dry THF and then added dropwise to the sodium perfluorohexylethanol solution. The mixture was heated to 65℃ and reacted for 8 hours. After the reaction was completed, the generated NaCl was removed by filtration. The filtrate was distilled under reduced pressure to recover THF. The residue was extracted with toluene, washed with water until neutral, dried over anhydrous sodium sulfate, filtered, and then distilled under reduced pressure (80℃ / 5mmHg) to remove toluene, resulting in intermediate B. S3. 2000g of intermediate B, 500g of diethanolamine and 4L of anhydrous toluene were refluxed at 110℃ for 6h. After removing the toluene by vacuum distillation, 3L of acetonitrile was added to dissolve the toluene. 380g of 1,3-propanesulfonic acid lactone was added dropwise and the mixture was reacted at 60℃ for 4h. After the reaction was completed, the mixture was cooled to room temperature, filtered to collect the precipitate, washed with acetonitrile, and dried under vacuum to obtain fluorosiloxane sulfonic acid surfactant A.

[0027] Preparation Example 2 The preparation steps of fluorosiloxane sulfonic acid surfactant B differ from those in Preparation Example 1 in that the Mn of the hydrogen-containing methylsiloxane is approximately 134 (SiSiB® HF2030-M134).

[0028] Preparation Example 3 The preparation steps of the fluorosiloxane sulfonic acid surfactant C differ from those in Preparation Example 1 in that the Mn of the hydrogen-containing methylsiloxane is approximately 1250 (SiSiB® HF2030-M1250).

[0029] Preparation Example 4 The preparation steps of the fluorosiloxane sulfonic acid surfactant D differ from those in Preparation Example 1 in that 1200g of perfluorohexylethanol is replaced with 850g of perfluorobutylethanol.

[0030] Example 1 A desilicon removal composition, by weight percentage (100%), comprises the following components: 12% sodium hydroxide, 30% aluminum hydroxide (particle size 1 μm), 2% fluorosiloxane sulfonic acid surfactant A, 0.65% potassium hydroxide, and the balance being deionized water.

[0031] The preparation steps of the silicon-removing composition in this embodiment are as follows: Prepare a 40wt% sodium hydroxide aqueous solution. First, add potassium hydroxide and stir until completely dissolved. Then, add aluminum hydroxide, stir until evenly dispersed, and heat to 65℃. Keep warm and stir for 2 hours. Under conditions of 35℃ and 400 rpm, add a 50wt% aqueous solution of fluorosiloxane sulfonic acid surfactant A. After stirring and dispersing, process the mixture three times using a high-pressure homogenizer (pressure 40 MPa). Let it stand at room temperature for 12 hours to mature. After maturation, add the remaining deionized water, filter through a 200-mesh filter, and after sampling and testing, fill the package to obtain the desiliconized composition.

[0032] Example 2 A desilicon removal composition, by weight percentage (100%), comprises the following components: 10% sodium hydroxide, 25% aluminum hydroxide (particle size 500 nm), 1% fluorosiloxane sulfonic acid surfactant A, 0.5% potassium hydroxide, and the balance being deionized water.

[0033] The preparation steps of the silicon-removing composition in this embodiment are the same as in Example 1.

[0034] Example 3 A desiliconizing composition, by weight percentage (100%), comprises the following components: 15% sodium hydroxide, 35% aluminum hydroxide (particle size 2 μm), 3% fluorosiloxane sulfonic acid surfactant A, 0.9% potassium hydroxide, and the balance being deionized water.

[0035] The preparation steps of the silicon-removing composition in this embodiment are the same as in Example 1.

[0036] Example 4 This embodiment provides a silicon removal composition and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that potassium hydroxide is replaced by an equal mass of deionized water.

[0037] Example 5 This embodiment provides a silicon removal composition and its preparation method. The specific implementation method is the same as that in Example 1, except that the particle size of aluminum hydroxide is 8 μm.

[0038] Example 6 This embodiment provides a silicon-removing composition and its preparation method. The specific implementation method is the same as that in Embodiment 1, except that the fluorosiloxane sulfonic acid surfactant A is replaced by an equal mass of fluorosiloxane sulfonic acid surfactant B.

[0039] Example 7 This embodiment provides a silicon-removing composition and its preparation method. The specific implementation method is the same as that in Example 1, except that the fluorosiloxane sulfonic acid surfactant A is replaced by an equal mass of fluorosiloxane sulfonic acid surfactant C.

[0040] Example 8 This embodiment provides a silicon-removing composition and its preparation method. The specific implementation method is the same as that in Example 1, except that the fluorosiloxane sulfonic acid surfactant A is replaced by an equal mass of fluorosiloxane sulfonic acid surfactant D.

[0041] Comparative Example 1 This embodiment provides a silicon-removing composition and its preparation method. The specific implementation method is the same as that in Example 1, except that the fluorosiloxane sulfonic acid surfactant A is replaced by sodium dodecylbenzene sulfonate of equal mass.

[0042] Performance testing The compositions provided in Examples 1-8 and Comparative Example 1 were tested as follows, and the results are shown in Table 1: 1. Silicon scale removal rate test: The removal capacity of the silicon removal composition on standard silicon scale was determined by gravimetric method; Silicon scale removal rate = (initial silicon scale mass - residual silicon scale mass) / initial silicon scale mass × 100%.

[0043] 2. Silicon element residual content test: The dissolved silicon content in the solution after cleaning reflects the degree of thoroughness of the silicon removal reaction; the silicon molybdenum blue spectrophotometric method of GB / T12149-2017 "Determination of silicon in industrial circulating cooling water and boiler water" is adopted.

[0044] 3. Aluminosilicate Precipitation Filtration Performance Test: The aluminosilicate precipitate generated by the silicon removal reaction should be easy to filter and separate, otherwise it will cause secondary pollution. The precipitation performance is evaluated by measuring the filtration rate and turbidity of the filtrate. The specific steps are as follows: Take 200 mL of the cleaning solution after test 1, filter it under vacuum of 0.05 MPa using a Buchner funnel, record the time (s) required to filter out 100 mL of filtrate, and measure the turbidity of the filtrate (NTU, turbidity meter method).

[0045] 4. Surface tension test: Dilute the silicon removal composition to be tested to 1% (mass fraction), and use a surface tension meter with a hanging plate method to measure the surface tension at a constant temperature of 25℃.

[0046] 5. Carbon steel corrosion rate test: Take a Q235 carbon steel test piece (50mm×25mm×2mm), grind, degrease, dry, and weigh it for later use; immerse the test piece in the silicon removal composition to be tested, and soak it at a constant temperature of 70℃ for 72h; take out the test piece, remove the corrosion products, dry and weigh it; calculate the corrosion rate (mm / a).

[0047] Table 1 Performance Test Results

[0048] As shown in Table 1, the silica scale removal rate in Examples 1-3 all exceeded 94%, with residual silica concentrations as low as 35-58 mg / L, indicating that the dissolution-conversion-precipitation mechanism was successfully implemented. Combined with filtration times of 75-90 s / 100 mL and filtrate turbidity of 9-14 NTU, this indicates that the generated aluminosilicate precipitate has good crystallinity and is easy to separate from the solid. Simultaneously, the surface tension (21.6-22.8 mN / m) is much lower than that of conventional surfactant systems (>30 mN / m), and the corrosion rate is within the industrially acceptable range (<0.1 mm / a).

[0049] Compared to Example 1, Example 4 lacks potassium hydroxide, resulting in a decrease in silica scale removal rate, an increase in residual silica concentration, and increases in filtration time, filtrate turbidity, and corrosion rate. This may be due to the absence of potassium ions, which regulates silicate dissolution equilibrium and aluminosilicate crystal structure. In Example 5, the aluminum hydroxide particle size increased from 1 μm to 8 μm. The reduced contact area between 8 μm aluminum hydroxide and NaOH led to a slower and less uniform formation rate of sodium aluminate. Simultaneously, the aluminosilicate precipitates formed from larger aluminum hydroxide particles had a wide particle size distribution, poor crystallinity, and contained a large amount of unreacted aluminum hydroxide encapsulation, making filtration difficult and prone to filter penetration. Furthermore, it's possible that a large amount of silica scale was only dissolved by NaOH without being converted into aluminosilicate precipitates, leading to a high residual silica concentration as the dissolved silica stopped reacting after reaching saturation in the cleaning solution. The increased corrosion rate may be due to the poor slow-release effect of large aluminum hydroxide particles, resulting in pitting corrosion caused by excessively high local alkalinity.

[0050] Based on Examples 1 and 6-7, it is evident that excessively short siloxane chain lengths may prevent effective embedding within the micropores of silica scale. Simultaneously, increased surface tension indicates a relatively increased density of fluorocarbon chains, leading to a decrease in overall wetting and penetration performance. The increased residual silica concentration and deteriorated filtration performance may be due to uneven alkaline solution penetration, resulting in non-uniform particle size of the generated aluminosilicate precipitates. Conversely, longer siloxane chains enhance molecular flexibility and theoretically improve affinity with silica scale. However, increased molecular weight may cause some surfactant molecules to form micelles rather than adsorbing as single molecules onto the silica scale surface, reducing the concentration of free molecules for effective penetration.

[0051] In Example 8, the perfluorobutyl fluorocarbon chain is shorter than that of the perfluorohexyl fluorocarbon chain, which weakens the hydrophobic and oleophobic effects of the fluorocarbon chain and its ability to reduce surface tension. Increased surface tension directly reduces the penetration of alkaline solution into the micropores of silica scale, leading to a lower silica scale removal rate. The high residual silica concentration may be due to the silicate layer formed on the surface hindering further reactions. Comparative Example 1 uses the conventional hydrocarbon chain anionic surfactant LAS, whose penetration into silica scale relies solely on physical wetting. More importantly, LAS exhibits extremely poor stability in strongly alkaline environments (pH>13) and may even form aluminum soap flocs that encapsulate aluminum hydroxide particles, hindering their activation reaction.

[0052] The embodiments and comparative examples described above do not 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 silicon removal composition, characterized in that, Based on a 100% weight percentage, it contains the following raw materials: 35-50% alkali agent, 1-3% fluorosiloxane sulfonic acid surfactant, and the balance is deionized water.

2. The silicon removal composition according to claim 1, characterized in that, The alkaline agent is a mixture of sodium hydroxide and aluminum hydroxide.

3. The silicon removal composition according to claim 2, characterized in that, The mass ratio of sodium hydroxide to aluminum hydroxide is (10-15):(25-35).

4. The silicon removal composition according to claim 2, characterized in that, The alkaline agent also includes potassium hydroxide.

5. The silicon removal composition according to claim 4, characterized in that, The mass percentage of potassium hydroxide is 0.5% to 0.9%.

6. The silicon removal composition according to claim 4, characterized in that, The aluminum hydroxide has a particle size of 500 nm to 2 μm.

7. The silicon removal composition according to claim 1, characterized in that, The preparation steps of the fluorosiloxane sulfonic acid surfactant are as follows: S1. Under an inert atmosphere, hydrogen-containing methylsiloxane and allyl chloride were stirred and mixed, and a chloroplatinic acid catalyst-isopropanol solution was added dropwise. After the reaction was heated and completed, the mixture was distilled under reduced pressure to obtain intermediate A. S2. Under an inert atmosphere, perfluorohexylethanol was added to dry THF, and NaH was added. The mixture was stirred at room temperature until no gas was released, yielding a sodium perfluorohexylethanol solution. Intermediate A was dissolved in dry THF and then added dropwise to the sodium perfluorohexylethanol solution. The mixture was heated to react. After the reaction was complete, the mixture was filtered, and the filtrate was distilled under reduced pressure. The residue was extracted, washed, dried, filtered, and then distilled under reduced pressure to obtain intermediate B. S3. Refluxing intermediate B, diethanolamine, and anhydrous toluene, removing toluene by vacuum distillation, dissolving in acetonitrile, and then adding 1,3-propanesulfonic acid lactone dropwise to react. After the reaction is complete, cooling, filtering, washing, and vacuum drying are performed to obtain the fluorosiloxane sulfonic acid surfactant.

8. The silicon removal composition according to claim 7, characterized in that, The Mn of the hydrogen-containing methylsiloxane is 300 to 600.

9. The silicon removal composition according to claim 8, characterized in that, The molar ratio of the hydrogen-containing methylsiloxane and allyl chloride is 1:(1.0-1.2).

10. A method for preparing the silicon-removing composition according to any one of claims 1-9, characterized in that, The process includes the following steps: preparing an alkaline aqueous solution, adding an aqueous solution of fluorosiloxane sulfonic acid surfactant, stirring and dispersing, then high-pressure homogenization and circulation treatment, allowing it to stand and mature at room temperature, replenishing the remaining deionized water after maturation, filtering, taking samples for testing, and filling to obtain the desiliconized composition.

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