Phosphorus-free biodegradable reverse osmosis scale inhibitor and preparation method thereof

Abstract

The application discloses a phosphorus-free biodegradable reverse osmosis scale inhibitor and a preparation method thereof, and belongs to the technical field of reverse osmosis water treatment. x The scale inhibitor is prepared by sequentially mixing components and adjusting pH, and the scale inhibitor is prepared. The scale inhibitor is phosphorus-free, biodegradable, environment-friendly, and can effectively prolong the reverse osmosis membrane cleaning period.

Description

Technical Field

[0001] This invention belongs to the field of reverse osmosis water treatment technology, specifically designing a phosphorus-free biodegradable reverse osmosis antiscalant and its preparation method. Background Technology

[0002] Reverse osmosis technology, with its highly efficient desalination and separation performance, has been widely used in industrial fields such as pharmaceutical purified water preparation, high-purity water for the electronics industry, beverage water, and chemical production. However, during long-term operation of reverse osmosis systems, scale-forming ions such as calcium and magnesium in the water concentrate and deposit on the membrane surface, easily forming inorganic salt scale layers such as calcium carbonate and calcium sulfate. This leads to decreased membrane flux, deterioration of product water quality, and increased operating energy consumption, and in severe cases, even irreversible damage to the membrane modules. Adding scale inhibitors is one of the simplest and most effective technical means to solve the scaling problem of reverse osmosis membranes.

[0003] Traditional reverse osmosis antiscalants primarily use phosphorus-containing compounds such as polyphosphates and organophosphates. While these antiscalants offer significant scale inhibition, they release phosphate ions during use. When these ions are discharged into natural water bodies with the concentrated reverse osmosis brine, phosphorus, a key limiting nutrient for algae growth, easily leads to eutrophication, causing abnormal algal proliferation, dissolved oxygen depletion, and disruption of the aquatic ecosystem. Simultaneously, with increasingly stringent national regulations on the use of phosphorus-containing, nitrogen-containing, and recalcitrant chemical agents, the application space for phosphorus-containing antiscalants is continuously shrinking. Therefore, developing phosphorus-free and easily biodegradable green antiscalants has become an inevitable trend in the industry. Currently, polyaspartic acid (PASP) and polyepoxysuccinic acid (PESA) are two widely studied types of biodegradable phosphorus-free antiscalants. Glutamic acid diacetic acid (GLDA), as a biodegradable green chelating agent, also shows application potential in scale inhibition and membrane cleaning. However, existing phosphorus-free antiscalants generally suffer from problems such as limited functional groups and insufficient synergistic scale inhibition capabilities against multiple scale-forming ions under complex water quality conditions. Although sodium carboxymethyl cellulose has been attempted to be used in the formulation of reverse osmosis antiscalants, there are no reports in the existing technology of ternary compounding of sulfonated modified tetrasodium glutamate diacetate with two-dimensional MXene nanosheets and sodium carboxymethyl cellulose to synergistically improve scale inhibition performance. Summary of the Invention

[0004] The present invention aims to solve the technical problem that existing phosphorus-free reverse osmosis antiscalants have insufficient synergistic inhibition ability against multiple scale-forming ions due to their single functional groups.

[0005] To achieve the above objectives, the present invention provides a phosphorus-free, biodegradable reverse osmosis antiscalant, comprising the following raw materials in parts by weight: 10-30 parts of composite active antiscalant; 60-85 parts of deionized water; 0.1-2 parts of pH adjuster; and 0.01-1 parts of preservative. The preparation method of the phosphorus-free biodegradable reverse osmosis antiscalant includes the following steps: S1: Add deionized water to the preparation vessel, and add the composite active scale inhibitor at 20-30℃ and a stirring rate of 200-400 rpm. After the addition is complete, continue stirring until the components are completely dispersed in the system. S2: Add preservative and continue stirring; S3: Adjust the pH of the system to 6.5-8.5 with a pH adjuster, and continue stirring until homogeneous to obtain the phosphorus-free biodegradable reverse osmosis antiscalant.

[0006] Preferably, the composite active scale inhibitor is composed of tetrasodium sulfonated glutamic acid diacetate, MXene nanosheets, and sodium carboxymethyl cellulose.

[0007] Preferably, the MXene nanosheets are Ti3C2T. x MXene nanosheets; the pH adjuster is sodium hydroxide; the preservative is isothiazolinone bactericide.

[0008] More preferably, the sodium hydroxide (pH adjuster) is selected from analytical grade sodium hydroxide from Nanjing Chemical Reagent Co., Ltd.; the preservative is isothiazolinone bactericide is selected from Y38 type from Xibao Biotechnology (Shanghai) Co., Ltd.

[0009] Preferably, the preparation method of the composite active scale inhibitor includes the following steps: (1) Preparation of sulfonated glutamic acid diacetic acid: Glutamic acid diacetic acid was dissolved in DMF, and EDC·HCl and NHS were added to activate the carboxyl group. The mixture was stirred at room temperature for 0.5-2 hours. Ethanolamine was added dropwise at a rate of 0.05-0.5 mL / min, and the reaction was carried out at room temperature for 4-6 hours. The monoamidation product of glutamic acid diacetic acid and ethanolamine was obtained by column chromatography. The obtained monoamidation product was dissolved in acetonitrile, and triethylamine was added as an acid-binding agent. 1,3-propanesulfonyl lactone was added dropwise at a rate of 0.05-0.5 mL / min, and the reaction was carried out at 40-60℃ for 4-12 hours. The mixture was concentrated under reduced pressure, precipitated with diethyl ether, filtered, recrystallized, and dried under vacuum to obtain sulfonated glutamic acid diacetic acid solid. The chemical reaction is illustrated below:

[0010] (2) Preparation of MXene nanosheet dispersion: Ti3AlC2 was pressed into sheets as the working electrode, with graphite or platinum sheets as the counter electrode, and 0.5-2 mol / L ammonium chloride aqueous solution as the electrolyte. Electrochemical etching was performed for 4-12 hours under a constant voltage of 5-15V, so that chloride ions in the electrolyte selectively etched the Al atomic layer in Ti3AlC2 to obtain multilayer Ti3C2T xStructure; repeatedly centrifuge and wash with deionized water until neutral; place in 0.5-2 mol / L electrolyte containing lithium salt, apply 3-10 V for electrochemical intercalation for 0.5-2 hours, so that lithium ions are intercalated into Ti3C2T. x Interlayer separation; transfer to deionized water for ultrasonic exfoliation for 10-60 minutes, centrifuge, collect the supernatant to obtain MXene nanosheet dispersion; wherein T x The functional groups (including -O and -OH) on the MXene surface are represented by x, which represents the number of functional groups and ranges from 0.5 to 2. (3) Preparation of composite active scale inhibitor: Sulfonated glutamic acid diacetic acid is added to deionized water, and sodium hydroxide aqueous solution with a mass fraction of 5-15% is added dropwise while stirring to adjust the pH of the system to 7.5-8.5 to obtain tetrasodium sulfonated glutamic acid diacetic acid aqueous solution. The solution is heated to 40-60℃ and stirred until completely dissolved. MXene nanosheet dispersion is added dropwise and stirred for 1-4 hours. Sodium carboxymethyl cellulose is added and stirred for 0.5-2 hours. The obtained composite dispersion system is vacuum dried at 60-80℃ for 12-24 hours, pulverized and sieved to obtain composite active scale inhibitor.

[0011] In this invention, the composite active scale inhibitor not only acts as a scale inhibitor in the reverse osmosis system, but also as a functional unit for self-sensing and adaptive regulation of scale-forming micro-regions. Its mechanism of action is as follows: when the concentration of scale-forming ions increases due to ion concentration polarization in a localized area of ​​the reverse osmosis membrane surface, and microcrystals begin to precipitate, the characteristic charges on the microcrystal surface will form a localized electrostatic field at the solid-liquid interface; the Ti3C2T... xMXene nanosheets, as two-dimensional transition metal carbides with metallic conductivity and abundant surface terminal groups, exhibit a high electronic state density near the Fermi level that is extremely sensitive to changes in the interfacial electrostatic field. The presence of a local electrostatic field alters the charge distribution on the surface of MXene nanosheets, inducing a shift in the protonation or deprotonation equilibrium of their surface terminal groups. This change in surface charge state is transmitted to the sulfonated tetrasodium diacetate sulfonate molecules through hydrogen bonding and electrostatic interactions, thereby regulating the ionization degree and spatial conformation of the sulfonic acid and carboxyl groups, significantly enhancing the coordination and capture ability of the chelating groups for calcium and magnesium ions. Simultaneously, the high specific surface area of ​​MXene nanosheets provides a large number of two-dimensional confined adsorption sites for nascent crystallites. Through the interfacial matching effect between the surface terminal groups and the crystallites, they preferentially adsorb at the active growth steps on the crystallite surface, inhibiting the ordered arrangement and three-dimensional expansion of the lattice, and forcing the crystallite growth towards a thermodynamically stable non-dense morphology. The enhanced chelation trapping and lattice distortion synergistic effect promotes the rapid chelation of scale-forming ions and the effective dispersion of microcrystals in the locally supersaturated region, preventing further scale deposition on the film surface. Once the ion concentration in the local scale-forming micro-region recovers to below the safe threshold, the interfacial electrostatic field disappears, and the surface charge state of the MXene nanosheets returns to its initial equilibrium. The regulatory effect on the conformation and coordination activity of tetrasodium sulfonated glutamate diacetate molecules ceases accordingly. The three-dimensional network structure of sodium carboxymethyl cellulose ensures that the MXene nanosheets maintain a uniform spatial distribution in the absence of external stimuli, avoiding loss of reversible responsiveness due to self-stacking. Therefore, this invention achieves a closed-loop self-feedback mechanism of sensing-response-regulation-recovery of scale-forming micro-regions by the scale inhibitor, endowing the scale inhibitor with intelligent adaptive scale inhibition capabilities of on-demand release, local response, and immediate cessation of scale formation, minimizing ineffective agent consumption while ensuring efficient scale inhibition.

[0012] Preferably, the molar ratio of glutamic acid diacetic acid to ethanolamine in (1) is 1:0.8-1.2.

[0013] Preferably, the molar ratio of the monoamidation product, triethylamine and 1,3-propanesulfonyl lactone in (1) is 1:1-2:1-1.5.

[0014] Preferably, in the column chromatography purification in (1), gradient elution is used, and the elution is carried out sequentially with a mixed solvent composed of dichloromethane and methanol in volume ratios of 8:2, 7:3, and 6:4.

[0015] Preferably, the solvent for recrystallization in (1) is a mixed solvent of ethanol and water, with a volume ratio of ethanol to water of 1:1-3:1.

[0016] Preferably, the electrolyte containing lithium salt in (2) is an aqueous solution of lithium chloride.

[0017] Preferably, the mass ratio of tetrasodium sulfonated glutamic acid diacetate to MXene nanosheets in (3) is 1:0.05-0.2.

[0018] Preferably, the mass ratio of sodium sulfonated glutamic acid diacetate to sodium carboxymethyl cellulose in (3) is 1:0.02-0.25.

[0019] Preferably, the particle size of the powder after pulverization and sieving in (3) is 10-100 μm.

[0020] Compared with the prior art, the present invention has the following beneficial effects: 1. The scale inhibitor of this invention is phosphorus-free, using tetrasodium sulfonated glutamic acid diacetate as the main organic chelating agent, exhibiting excellent biodegradability. Traditional phosphorus-containing scale inhibitors release phosphate ions during use, which enter natural water bodies after being discharged with reverse osmosis brine. Phosphorus, as a key limiting nutrient element for algal growth, easily leads to eutrophication, causing abnormal algal proliferation, rapid depletion of dissolved oxygen, and irreversible damage to aquatic ecosystems. Given the increasingly stringent national regulations on the use of phosphorus-containing, nitrogen-containing, and recalcitrant chemical agents, this invention avoids the introduction of phosphorus at the source, completely eliminating the environmental risks of phosphorus emissions. Furthermore, tetrasodium sulfonated glutamic acid diacetate itself possesses excellent biodegradability, with degradation products being non-toxic small-molecule organic acids and inorganic salts, which will not cause secondary pollution to the receiving water body, fully complying with the development direction of green and environmentally friendly water treatment agents and the stringent requirements of environmental regulations.

[0021] 2. This invention modifies glutamic acid diacetic acid by sulfonation, introducing sulfonic acid groups into the molecular structure. Sulfonic acid groups possess strong anionicity and good hydrophilicity, forming stable coordination chelate structures with polyvalent metal ions such as calcium, magnesium, barium, and strontium. The chelation stability constant is significantly higher than that of unmodified glutamic acid diacetic acid. Simultaneously, the introduction of sulfonic acid groups increases the steric hindrance and charge density of the molecule, making it difficult for the chelated scale-forming ions to further aggregate and form an ordered lattice. This achieves stable capture and dispersion of scale-forming ions in a homogeneous system. Furthermore, the water solubility of the sulfonated molecule is significantly improved, maintaining good solubility in the high-concentration brine phase of a reverse osmosis system. It is less prone to failure due to salting-out effects, effectively broadening the adaptability of the scale inhibitor to complex water qualities such as high hardness and high alkalinity.

[0022] 3. This invention utilizes Ti3C2T xThe high specific surface area and two-dimensional layered structure of MXene nanosheets construct a triple synergistic scale inhibition system that is distinctly different from the single chelation mechanism of traditional scale inhibitors. The abundant terminal groups on the surface of MXene nanosheets endow them with a specific affinity for inorganic crystal surfaces, allowing them to preferentially adsorb onto the active growth steps of nascent microcrystals through interfacial matching effects. This occupies active sites for lattice growth, effectively inhibiting the ordered arrangement of the lattice and the three-dimensional expansion of crystals, forcing microcrystal growth towards a thermodynamically stable, non-dense morphology. Simultaneously, the two-dimensional layered structure of MXene nanosheets has a strong physical encapsulation and dispersion effect on precipitated microcrystal particles, effectively preventing the aggregation and fusion of microcrystals and preventing their deposition on the film surface to form a dense scale layer. The above-mentioned three-fold action of chemical chelation capture—lattice distortion inhibition—physical encapsulation and dispersion works in tandem to achieve full-process intervention in scale-forming ions from homogeneous capture to microcrystal inhibition and then to dispersion stabilization, resulting in a scale inhibition efficiency significantly superior to the sum of the effects of each component used individually.

[0023] 4. This invention constructs an organic-inorganic hybrid structure through the synergistic effect of electrostatic adsorption and hydrogen bonding between tetrasodium sulfonated glutamate diacetate and MXene nanosheets, giving the entire composite system reversible stimulus-response characteristics. When the concentration of scale-forming ions increases and microcrystals begin to precipitate in a localized area on the reverse osmosis membrane surface due to ion concentration polarization, the characteristic charges on the microcrystal surface will form a localized electrostatic field at the solid-liquid interface. As a two-dimensional material with metallic conductivity, MXene nanosheets are extremely sensitive to changes in the interfacial electrostatic field due to their high electronic state density near the Fermi level. They can quickly sense this signal and transfer it to the tetrasodium sulfonated glutamate diacetate molecules through hydrogen bonding and electrostatic interactions, thereby regulating the ionization degree and spatial conformation of the chelating groups and achieving responsive chelation. When the ion concentration in the localized scale-forming micro-region returns to below the safe threshold, the interfacial electrostatic field disappears, and the system automatically returns to its initial equilibrium state. This adaptive closed-loop mechanism of sensing-response-recovery enables scale inhibitors to release their activity on demand, respond locally to scaling risks, and stop scaling once the scale has formed. This avoids the ineffective consumption of traditional scale inhibitors due to continuous addition, and significantly reduces operating costs.

[0024] 5. The preparation method of this invention operates under mild conditions, with each step within the normal temperature range. It eliminates the need for harsh reaction conditions such as high temperature and high pressure, requiring minimal production equipment, consuming little energy, and avoiding hazardous chemical reactions, thus ensuring high operational safety. The entire preparation process of the composite active scale inhibitor uses water as the dispersion medium, avoiding the large-scale use of organic solvents and reducing volatile organic compound emissions, aligning with the clean production concept of green chemistry. Furthermore, the composite active scale inhibitor obtained by this invention exists in solid powder form, offering advantages over traditional liquid scale inhibitors, such as lighter weight, smaller volume, and no need for large amounts of water diluents. This significantly reduces packaging, transportation, and storage costs. Simultaneously, the powdered product exhibits stable chemical properties and a long shelf life. On-site application allows for flexible formulation of scale inhibitor solutions to the required concentration based on actual water quality, offering high convenience and making it suitable for large-scale industrial promotion and application in the reverse osmosis water treatment field. Detailed Implementation

[0025] The present invention will be further illustrated below with specific embodiments. These embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Those skilled in the art can make various modifications and alterations to the present invention without departing from its spirit and scope.

[0026] Preparation Example 1: A method for preparing a composite active scale inhibitor, comprising the following steps: (1) Preparation of sulfonated glutamic acid diacetic acid: Dissolve 50.0 g of glutamic acid diacetic acid in 250 mL of DMF, add 38.3 g of EDC·HCl and 23.0 g of NHS to activate the carboxyl group, and stir at 300 r / min for 1 hour at room temperature. Add 12.2 g of ethanolamine dropwise at a rate of 0.2 mL / min, and react at room temperature for 5 hours after the addition is complete. After the reaction is complete, concentrate the reaction solution to 50 mL under reduced pressure and purify it by column chromatography. Elute sequentially with a gradient of dichloromethane and methanol in volume ratios of 8:2, 7:3, and 6:4. Collect the target fractions, combine them, and concentrate under reduced pressure to obtain the monoamidation product of glutamic acid diacetic acid and ethanolamine. The monoamidated product was dissolved in 200 mL of acetonitrile, and 30.3 g of triethylamine was added. After stirring until homogeneous, 20.1 g of 1,3-propanesulfonyl lactone was added dropwise at a rate of 0.2 mL / min. After the addition was complete, the mixture was stirred at 50 °C for 8 hours. After the reaction was completed, the acetonitrile was removed by concentration under reduced pressure. The residue was slowly poured into 300 mL of anhydrous diethyl ether, and a white precipitate was formed. The precipitate was filtered, and the filter cake was washed three times with anhydrous diethyl ether. The crude product was recrystallized with a mixed solvent of ethanol and water in a volume ratio of 2:1 and dried under vacuum at 50 °C for 12 hours to obtain a white solid of sulfonated glutamic acid diacetic acid. (2) Preparation of MXene nanosheet dispersion: 10.0 g of Ti3AlC2 powder was pressed into a sheet-shaped working electrode. A graphite sheet was used as the counter electrode, and a 1.0 mol / L ammonium chloride aqueous solution was used as the electrolyte. Electrochemical etching was performed at a constant voltage of 10 V for 8 hours. The electrode was then repeatedly washed with deionized water by centrifugation until neutral. The washed Ti3C2T... x Placed in a 1.0 mol / L lithium chloride aqueous solution, electrochemical intercalation was performed by applying a 5V voltage for 1 hour. The product was then transferred to 300 mL of deionized water and ultrasonically exfoliated at 200W power for 30 minutes under ice-water bath protection. The resulting suspension was centrifuged at 3500 r / min for 30 minutes, and the upper black supernatant was collected to obtain the MXene nanosheet dispersion. (3) Preparation of composite active scale inhibitor: Add 45.0 g of sulfonated glutamic acid diacetate obtained in (1) to 500 mL of deionized water, stir at 300 r / min, add 10% sodium hydroxide aqueous solution at 3 mL / min, adjust the pH of the system to 8.0, and obtain tetrasodium sulfonated glutamic acid diacetate aqueous solution. Heat to 50 °C and stir until completely dissolved; take 180 mL of MXene nanosheet dispersion obtained in (2), add it dropwise to tetrasodium sulfonated glutamic acid diacetate aqueous solution at 0.5 mL / min at 50 °C, and continue stirring at 50 °C for 2 hours after the addition is complete; add 4.5 g of sodium carboxymethyl cellulose and continue stirring for 1 hour; dry the obtained composite dispersion system under vacuum at 70 °C for 18 hours, place the dried solid in a pulverizer to pulverize, and pass through a 200 mesh sieve to obtain the composite active scale inhibitor.

[0027] Preparation Example 2: A method for preparing a composite active scale inhibitor, comprising the following steps: (1) Preparation of sulfonated glutamic acid diacetic acid: Dissolve 50.0 g of glutamic acid diacetic acid in 300 mL of DMF, add 30.7 g of EDC·HCl and 18.4 g of NHS to activate the carboxyl group, and stir at 250 r / min for 2 hours at room temperature. Add 9.8 g of ethanolamine dropwise at a rate of 0.1 mL / min, and react at room temperature for 6 hours after the addition is complete. After the reaction is complete, concentrate the reaction solution under reduced pressure to 60 mL, and purify it by column chromatography. Elute the solution sequentially with a gradient of dichloromethane and methanol in volume ratios of 8:2, 7:3, and 6:4. Collect the target fractions, combine them, and concentrate under reduced pressure to obtain the monoamidation product of glutamic acid diacetic acid and ethanolamine. The monoamidated product was dissolved in 150 mL of acetonitrile, and 12.1 g of triethylamine was added. After stirring until homogeneous, 14.6 g of 1,3-propanesulfonyl lactone was added dropwise at a rate of 0.1 mL / min. After the addition was complete, the mixture was stirred at 40 °C for 12 hours. After the reaction was completed, the acetonitrile was removed by concentration under reduced pressure. The residue was poured into 250 mL of anhydrous diethyl ether, and a white precipitate was formed. The precipitate was filtered, and the filter cake was washed three times with anhydrous diethyl ether. The crude product was recrystallized with a mixed solvent of ethanol and water in a volume ratio of 1:1 and dried under vacuum at 50 °C for 12 hours to obtain a white solid of sulfonated glutamic acid diacetic acid. (2) Preparation of MXene nanosheet dispersion: 10.0 g of Ti3AlC2 powder was pressed into a sheet-shaped working electrode. A platinum sheet was used as the counter electrode, and a 0.5 mol / L ammonium chloride aqueous solution was used as the electrolyte. Electrochemical etching was performed at a constant voltage of 15 V for 4 hours. The electrode was repeatedly washed with deionized water by centrifugation until neutral. The washed Ti3C2T... x Placed in a 0.5 mol / L lithium chloride aqueous solution, electrochemical intercalation was performed by applying a voltage of 10 V for 0.5 hours; transferred to 300 mL of deionized water, and ultrasonically exfoliated at 200 W power for 60 minutes under ice-water bath protection; the resulting suspension was centrifuged at 3500 r / min for 30 minutes, and the supernatant was collected to obtain the MXene nanosheet dispersion. (3) Preparation of composite active scale inhibitor: Add 40.0 g of sulfonated glutamic acid diacetate obtained in (1) to 500 mL of deionized water, stir at 300 r / min, and add 5% sodium hydroxide aqueous solution at a rate of 1 mL / min to adjust the pH of the system to 7.5, to obtain tetrasodium sulfonated glutamic acid diacetate aqueous solution. Heat to 40 °C and stir until completely dissolved. Take 120 mL of MXene nanosheet dispersion obtained in (2), and add it dropwise to tetrasodium sulfonated glutamic acid diacetate aqueous solution at a rate of 1 mL / min at 40 °C. After the addition is complete, continue stirring at 40 °C for 4 hours. Add 2.0 g of sodium carboxymethyl cellulose and continue stirring for 2 hours. Dry the obtained composite dispersion system under vacuum at 60 °C for 24 hours. Place the dried solid in a pulverizer and pulverize it. Pass it through a 100-mesh sieve to obtain composite active scale inhibitor powder.

[0028] Preparation Example 3: A method for preparing a composite active scale inhibitor, comprising the following steps: (1) Preparation of sulfonated glutamic acid diacetic acid: 50.0 g of glutamic acid diacetic acid was dissolved in 300 mL of DMF. 46.0 g of EDC·HCl and 27.6 g of NHS were added to activate the carboxyl group. The mixture was stirred at 350 rpm for 0.5 hours at room temperature. 14.6 g of ethanolamine was added dropwise at a rate of 0.5 mL / min. After the addition was complete, the mixture was reacted at room temperature for 4 hours. After the reaction was complete, the reaction solution was concentrated to 50 mL under reduced pressure and purified by column chromatography. A gradient elution was performed sequentially using a mixed solvent of dichloromethane and methanol in volume ratios of 8:2, 7:3, and 6:4. The target fractions were collected, combined, and concentrated under reduced pressure to obtain the monoamidation product of glutamic acid diacetic acid and ethanolamine. The monoamidation product was dissolved in 20 mL of DMF. 30.3 g of triethylamine was added to 0 mL of acetonitrile and stirred until homogeneous. Then, 27.4 g of 1,3-propanesulfonyl lactone was added dropwise at a rate of 0.5 mL / min. After the addition was complete, the mixture was stirred at 60 °C for 4 hours. After the reaction was completed, the acetonitrile was removed by concentration under reduced pressure. The residue was slowly poured into 350 mL of anhydrous diethyl ether, and a white precipitate was formed. The precipitate was filtered, and the filter cake was washed three times with anhydrous diethyl ether. The crude product was recrystallized with a mixed solvent of ethanol and water in a volume ratio of 3:1 and dried under vacuum at 50 °C for 12 hours to obtain a white solid of sulfonated glutamic acid diacetic acid. (2) Preparation of MXene nanosheet dispersion: 10.0 g of Ti3AlC2 powder was pressed into a sheet-shaped working electrode. A graphite sheet was used as the counter electrode, and a 2.0 mol / L ammonium chloride aqueous solution was used as the electrolyte. Electrochemical etching was performed at a constant voltage of 5 V for 12 hours. The electrode was repeatedly washed with deionized water by centrifugation until neutral. The washed Ti3C2T... x Placed in a 2.0 mol / L lithium chloride aqueous solution, electrochemical intercalation was performed with a voltage of 3V for 2 hours; then transferred to 300 mL of deionized water and ultrasonically exfoliated at 200 W for 10 minutes under ice-water bath protection. The resulting suspension was centrifuged at 3500 r / min for 30 minutes, and the supernatant was collected to obtain the MXene nanosheet dispersion. (3) Preparation of composite active scale inhibitor: Add 50.0 g of sulfonated glutamic acid diacetate obtained in (1) to 600 mL of deionized water, stir at 350 r / min, and add 15% sodium hydroxide aqueous solution at a rate of 5 mL / min to adjust the pH of the system to 8.5, to obtain tetrasodium sulfonated glutamic acid diacetate aqueous solution. Heat to 60 °C and stir until completely dissolved. Take 290 mL of MXene nanosheet dispersion obtained in (2), and add it dropwise to tetrasodium sulfonated glutamic acid diacetate aqueous solution at a rate of 1.5 mL / min at 60 °C. After the addition is complete, continue stirring at 60 °C for 1 hour; add 10 g of sodium carboxymethyl cellulose and continue stirring for 0.5 hours. Vacuum dry the obtained composite dispersion system at 80 °C for 12 hours, place the dried solid in a pulverizer to pulverize, and pass through a 150 mesh sieve to obtain composite active scale inhibitor powder.

[0029] Comparative preparation example 1: The difference between comparative preparation example 1 and preparation example 1 is that MXene nanosheet dispersion is not added in (3).

[0030] Comparative preparation example 2: The difference between comparative preparation example 2 and preparation example 1 is that sodium carboxymethyl cellulose is not added in (3).

[0031] Comparative Preparation Example 3: The difference between Comparative Preparation Example 3 and Preparation Example 1 is that in (3), unsulfonated tetrasodium glutamate diacetate is used instead of sulfonated tetrasodium glutamate diacetate.

[0032] Comparative Preparation Example 4: The difference between Comparative Preparation Example 4 and Preparation Example 1 is that: in (3), the dropwise addition and composite process of MXene nanosheet dispersion is not carried out. Instead, the three components, sodium diacetate sulfonated glutamic acid, MXene nanosheets and sodium carboxymethyl cellulose, are directly physically mixed and then dried.

[0033] Example 1: A phosphorus-free, biodegradable reverse osmosis antiscalant, comprising the following raw materials in parts by weight: 200g of a composite active antiscalant prepared by the method of Example 1, 780g of deionized water, 15g of sodium hydroxide, and 5g of isothiazolinone bactericide; the preparation method is as follows: S1: Add 780g of deionized water to the preparation vessel, turn on the stirrer, stir at a rate of 300r / min, and control the temperature inside the vessel at 25℃; add 200g of composite active scale inhibitor under stirring conditions, and control the feeding rate at about 10g / min during the feeding process. After the addition is completed, continue stirring at 25℃ and 300r / min for 30min. Take a sample for testing. The system is a uniform milky white dispersion with no visible particulate matter. S2: Add 5g of isothiazolinone bactericide to the above dispersion system and continue stirring for 15min at 25℃ and 300r / min. S3: Add 15g of sodium hydroxide to the above system, and continue stirring for 10min at 25℃ and 300r / min. The pH value of the system is measured to be 7.5 using a pH meter. Stop stirring to obtain the phosphorus-free biodegradable reverse osmosis antiscalant.

[0034] Example 2: A phosphorus-free, biodegradable reverse osmosis antiscalant, comprising the following raw materials in parts by weight: 100g of a composite active antiscalant prepared by the method of Example 2, 850g of deionized water, 10g of sodium hydroxide, and 0.1g of isothiazolinone bactericide; the preparation method is as follows: S1: Add 850g of deionized water to the preparation vessel, turn on the stirrer, stir at a rate of 200r / min, and control the temperature inside the vessel at 20℃; add 100g of composite active scale inhibitor under stirring conditions, and control the feeding rate to about 5g / min during the feeding process. After the addition is completed, continue stirring at 20℃ and 200r / min for 40min. Take a sample for testing. The system is a uniform milky white dispersion with no visible particulate matter. S2: Add 0.1g of isothiazolinone bactericide to the above dispersion system and continue stirring for 20min at 20℃ and 200r / min. S3: Add 10g of sodium hydroxide to the above system, and continue stirring for 15min at 20℃ and 200r / min. The pH value of the system is measured to be 6.5 using a pH meter. Stop stirring to obtain the phosphorus-free biodegradable reverse osmosis antiscalant.

[0035] Example 3: A phosphorus-free, biodegradable reverse osmosis antiscalant, comprising the following raw materials in parts by weight: 300g of a composite active antiscalant prepared by the method in Example 3, 600g of deionized water, 20g of sodium hydroxide, and 10g of isothiazolinone bactericide; the preparation method is as follows: S1: Add 600g of deionized water to the preparation vessel, turn on the stirrer, stir at a rate of 400r / min, and control the temperature inside the vessel at 30℃; under stirring conditions, add 300g of composite active scale inhibitor, and control the feeding rate to about 15g / min during the feeding process. After the addition is completed, continue stirring for 20min at 30℃ and 400r / min. Take a sample for testing. The system is a uniform milky white dispersion with no visible particulate matter. S2: Add 10g of isothiazolinone bactericide to the above dispersion system and continue stirring for 10min at 30℃ and 400r / min. S3: Add 20g of sodium hydroxide to the above system, and continue stirring for 10min at 30℃ and 400r / min. The pH value of the system is measured to be 8.5 using a pH meter. Stop stirring to obtain the phosphorus-free biodegradable reverse osmosis antiscalant.

[0036] Comparative Example 1: The difference between Comparative Example 1 and Example 3 is that the composite active scale inhibitor used is replaced with the composite active scale inhibitor prepared by the method of Comparative Preparation Example 1.

[0037] Comparative Example 2: The difference between Comparative Example 2 and Example 3 is that the composite active scale inhibitor used is replaced with the composite active scale inhibitor prepared by the method of Comparative Example 2 without the addition of sodium carboxymethyl cellulose.

[0038] Comparative Example 3: The difference between Comparative Example 3 and Example 3 is that the composite active scale inhibitor used is replaced by the composite active scale inhibitor prepared by the method of Comparative Example 3, which is a non-sulfonated tetrasodium glutamate diacetate instead of sulfonated tetrasodium glutamate diacetate.

[0039] Comparative Example 4: The difference between Comparative Example 3 and Example 3 is that the composite active scale inhibitor used is replaced by the composite active scale inhibitor prepared by the method of Comparative Preparation Example 4, which is obtained by directly physically mixing and drying the three components: tetrasodium sulfonated glutamic acid diacetate, MXene nanosheets and sodium carboxymethyl cellulose, without in-situ composite process.

[0040] Performance testing: The testing standards are shown in Table 1: Table 1 Performance Test Items and Standards

[0041] The performance test results of Examples 1-3 and Comparative Examples 1-4 are shown in Table 2: Table 2 Performance test results of each embodiment and comparative example

[0042] Data Analysis: The test results in Table 2 show that: The scale inhibition rates of calcium carbonate in Examples 1-3 were 92.7%, 88.6%, and 94.5%, respectively, while those of calcium sulfate were 91.4%, 86.9%, and 93.2%, respectively. The membrane flux decline rates were 12.3%, 17.1%, and 9.7%, respectively, all of which were at excellent levels. Example 3 exhibited the best scale inhibition performance, with the highest scale inhibition rates for both calcium carbonate and calcium sulfate, and the lowest membrane flux decline rate. This indicates that when the amount of composite active scale inhibitor added was 30 parts, the mass ratio of tetrasodium sulfonated glutamate diacetate to MXene nanosheets was 1:0.2, and the mass ratio of tetrasodium sulfonated glutamate diacetate to sodium carboxymethyl cellulose was 1:0.25, the ternary synergistic effect was most fully released. Example 1 showed the second-best scale inhibition performance, with calcium carbonate at 92.7%, calcium sulfate at 91.4%, and membrane flux decline of 12.3%. Example 2 also achieved excellent performance, with calcium carbonate at 88.6%, calcium sulfate at 86.9%, and membrane flux decline of 17.1%. The calcium carbonate scale inhibition rate of all three examples met the industrial application requirement of ≥85% for reverse osmosis system scale inhibitors, indicating that the technical solution of the present invention can maintain excellent scale inhibition effect within a wide range of proportions.

[0043] In contrast, Comparative Example 1 (without MXene nanosheets) showed a scale inhibition rate of only 68.3% for calcium carbonate and only 65.1% for calcium sulfate, with a membrane flux decay rate as high as 38.5%, a solid content of 19.8%, a viscosity of 5.2 mPa·s, and a scale retention rate of only 72.5% after aging. Compared with Example 1, its scale inhibition rate decreased by 24 percentage points, its membrane flux decay rate increased by 26 percentage points, and its viscosity decreased by 72%. This is because the absence of MXene nanosheets completely eliminates the latter two links in the triple synergistic mechanism of chemical chelation + lattice distortion + physical dispersion. The single chelating effect of tetrasodium diacetate sulfonated glutamic acid cannot perform lattice distortion and physical encapsulation dispersion of scale-forming microcrystals, resulting in continuous deposition of scale-forming ions on the membrane surface and a sharp decline in membrane flux. At the same time, the absence of MXene nanosheets also significantly reduced the viscosity of the system, further confirming the contribution of the two-dimensional layered structure of MXene nanosheets to the rheological properties of the system.

[0044] Comparative Example 2 (without sodium carboxymethyl cellulose) showed a scale inhibition rate of 71.6% for calcium carbonate and 68.9% for calcium sulfate, a membrane flux decay rate of 35.2%, a solid content of 20.1%, a viscosity of 6.8 mPa·s, and a scale retention rate of 74.0% after aging, with a small amount of white precipitate appearing after 6 months of storage. Compared with Example 1, its scale inhibition rate decreased by 21 percentage points, the membrane flux decay rate increased by 23 percentage points, and the aging retention rate decreased by 23 percentage points. These results indicate that the three-dimensional network structure of sodium carboxymethyl cellulose is indispensable for the binding effect of MXene nanosheets in the water system—without this component, irreversible stacking and aggregation of MXene nanosheets occurs during preparation and storage, leading to a reduction in the effective active component and a significant decrease in scale inhibition performance during use; the substantial decrease in viscosity further proves that the thickening and three-dimensional network anchoring effects of sodium carboxymethyl cellulose are key to maintaining system stability.

[0045] Comparative Example 3, using unsulfonated tetrasodium glutamate diacetate instead of sulfonated tetrasodium glutamate diacetate, showed the lowest scale inhibition rate of only 65.2% among all samples. Calcium sulfate exhibited a scale inhibition rate of 62.0%, a membrane flux decay rate of 42.1%, a solid content of 19.5%, a viscosity of 4.9 mPa·s, and a scale retention rate of 68.5% after aging. Compared to Example 1, its scale inhibition rate decreased by 27 percentage points, its membrane flux decay rate increased by 30 percentage points, and its aging retention rate decreased by 28 percentage points. This indicates that the introduction of sulfonic acid groups plays a decisive role in enhancing chelating ability. Unsulfonated tetrasodium glutamate diacetate lacks the strong anionic sulfonic acid groups, resulting in significantly insufficient coordination and capture ability for polyvalent metal ions such as calcium and magnesium. Its molecular steric hindrance and charge density are much lower than those of the sulfonated products, making it unable to effectively inhibit scale deposition. At the same time, the lowest viscosity also indicates that the organic-inorganic hybrid structure formed by electrostatic adsorption between the sulfonated products and MXene nanosheets also contributes to the thickening of the system. The unsulfonated system exhibits the lowest viscosity due to the lack of this interaction.

[0046] Comparative Example 4 (physical mixing, non-in-situ composite) showed a scale inhibition rate of 74.0% for calcium carbonate, 71.3% for calcium sulfate, a membrane flux decay rate of 32.6%, a solid content of 20.5%, a viscosity of 9.2 mPa·s, and a scale retention rate of 76.3% after aging. Significant stratification was observed after 6 months of storage. Compared to Example 1, its scale inhibition rate decreased by 19 percentage points, its membrane flux decay rate increased by 20 percentage points, and its aging retention rate decreased by 20 percentage points. These results indicate that the organic-inorganic hybrid structure formed between tetrasodium sulfonated glutamic acid diacetate and MXene nanosheets through electrostatic adsorption and hydrogen bonding during the in-situ composite process is crucial for ensuring synergistic effects. Physical mixing cannot achieve uniform composite and interfacial bonding at the molecular level; the free MXene nanosheets in the system gradually aggregate and settle during storage, resulting in significant stratification.

[0047] Solid content test results showed that the solid content of each sample was basically consistent with the formulation design: Example 2 had the lowest solid content, Example 3 had the highest, and Examples 1 and Comparative Examples 1-4 all had a solid content of 20%, with deviations within a reasonable range, indicating that the preparation process had good controllability and reproducibility. Viscosity data showed obvious regularity: Example 3 had the highest viscosity at 45.3 mPa·s, consistent with its highest sodium carboxymethyl cellulose ratio; Example 2 had the lowest viscosity at 8.7 mPa·s, consistent with its lowest sodium carboxymethyl cellulose ratio; Comparative Example 2 (without sodium carboxymethyl cellulose) had a viscosity of 6.8 mPa·s, and Comparative Example 3 (without sulfonation) had a viscosity of 4.9 mPa·s, both significantly lower than Example 1's 18.5 mPa·s, demonstrating the dominant contribution of sodium carboxymethyl cellulose to the system viscosity and the auxiliary contribution of electrostatic adsorption between sulfonation products and MXene nanosheets to thickening. The scale retention rate test results after high-temperature accelerated aging showed that the retention rates of Examples 1-3 were 96.8%, 95.2%, and 97.5%, respectively, all maintaining an extremely high level above 95%, indicating that the scale inhibitor of the present invention can still maintain the structural integrity of the active component and the scale inhibition function under high-temperature accelerated aging conditions. The retention rates of Comparative Examples 1-4 were only 68.5%-76.3%, a decrease of 20.5-28.3 percentage points compared to Example 1, further demonstrating the key contribution of the complete ternary synergistic structure to the thermal stability of the scale inhibitor.

[0048] Environmental and safety test results showed that the 28-day biodegradation rates of Examples 1-3 were 78.4%, 82.5%, and 75.2%, respectively, all significantly higher than the standard qualification line of 60%, indicating that the scale inhibitor of the present invention can be rapidly decomposed by microorganisms in natural water bodies. The degradation rates of Comparative Examples 1-4 were 72.0%-79.1%, at the same level as the Examples, indicating that the above comparative factors mainly affected the scale inhibition performance and system stability, while having no significant impact on the biodegradability properties of the product itself.

[0049] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, various modifications, equivalent substitutions, and improvements can be made to the technical solutions of the present invention without departing from the spirit and principles thereof, and all such modifications, equivalent substitutions, and improvements should be included within the protection scope of the present invention.

Claims

1. A phosphorus-free, biodegradable reverse osmosis antiscalant, characterized in that, It consists of the following components in parts by weight: 10-30 parts of compound active scale inhibitor; 60-85 parts of deionized water; 0.1-2 parts of pH adjuster; and 0.01-1 parts of preservative. The composite active scale inhibitor is composed of tetrasodium sulfonated glutamic acid diacetate, MXene nanosheets, and sodium carboxymethyl cellulose; the MXene nanosheets are Ti3C2T. x MXene nanosheets; the pH adjuster is sodium hydroxide; the preservative is isothiazolinone bactericide.

2. The phosphorus-free biodegradable reverse osmosis antiscalant according to claim 1, characterized in that, The preparation process of the composite active scale inhibitor includes the following steps: (1) Preparation of sulfonated glutamic acid diacetic acid: Glutamic acid diacetic acid was dissolved in DMF, and EDC·HCl and NHS were added to activate the carboxyl group. The mixture was stirred at room temperature for 0.5-2 hours. Ethanolamine was added dropwise at a rate of 0.05-0.5 mL / min, and the reaction was carried out at room temperature for 4-6 hours. The monoamidation product of glutamic acid diacetic acid and ethanolamine was obtained by column chromatography. The obtained monoamidation product was dissolved in acetonitrile, and triethylamine was added as an acid-binding agent. 1,3-propanesulfonyl lactone was added dropwise at a rate of 0.05-0.5 mL / min, and the reaction was carried out at 40-60℃ for 4-12 hours. The mixture was concentrated under reduced pressure, precipitated with diethyl ether, filtered, recrystallized, and dried under vacuum to obtain sulfonated glutamic acid diacetic acid solid. (2) Preparation of MXene nanosheet dispersion: Ti3AlC2 was pressed into sheets as the working electrode, with graphite or platinum sheets as the counter electrode, and 0.5-2 mol / L ammonium chloride aqueous solution as the electrolyte. Electrochemical etching was performed for 4-12 hours under a constant voltage of 5-15V, so that chloride ions in the electrolyte selectively etched the Al atomic layer in Ti3AlC2 to obtain multilayer Ti3C2T x Structure; repeatedly centrifuge and wash with deionized water until neutral; place in 0.5-2 mol / L electrolyte containing lithium salt, apply 3-10 V for electrochemical intercalation for 0.5-2 hours, so that lithium ions are intercalated into Ti3C2T. x Interlayer separation; transfer to deionized water for ultrasonic exfoliation for 10-60 minutes, centrifuge, collect the supernatant to obtain MXene nanosheet dispersion; (3) Preparation of composite active scale inhibitor: Sulfonated glutamic acid diacetic acid is added to deionized water, and sodium hydroxide aqueous solution with a mass fraction of 5-15% is added dropwise while stirring to adjust the pH of the system to 7.5-8.5 to obtain tetrasodium sulfonated glutamic acid diacetic acid aqueous solution. The solution is heated to 40-60℃ and stirred until completely dissolved. MXene nanosheet dispersion is added dropwise and stirred for 1-4 hours. Sodium carboxymethyl cellulose is added and stirred for 0.5-2 hours. The obtained composite dispersion system is vacuum dried at 60-80℃ for 12-24 hours, pulverized and sieved to obtain composite active scale inhibitor.

3. The phosphorus-free biodegradable reverse osmosis antiscalant according to claim 2, characterized in that, In step (1), the molar ratio of glutamic acid diacetic acid to ethanolamine is 1:0.8-1.2; the molar ratio of the monoamidated product, triethylamine, and 1,3-propanesulfonyl lactone is 1:1-2:1-1.5; the column chromatography purification uses gradient elution, sequentially eluting with a mixed solvent of dichloromethane and methanol in volume ratios of 8:2, 7:3, and 6:4; the recrystallization solvent is a mixed solvent of ethanol and water, with a volume ratio of ethanol to water of 1:1-3:

1.

4. The phosphorus-free biodegradable reverse osmosis antiscalant according to claim 2, characterized in that, The electrolyte containing lithium salt in (2) is an aqueous solution of lithium chloride.

5. The phosphorus-free biodegradable reverse osmosis antiscalant according to claim 2, characterized in that, In step (3), the mass ratio of tetrasodium sulfonated glutamic acid diacetate to MXene nanosheets is 1:0.05-0.2; the mass ratio of tetrasodium sulfonated glutamic acid diacetate to sodium carboxymethyl cellulose is 1:0.02-0.25; and the particle size of the powder after pulverization and sieving is 10-100 μm.

6. The method for preparing the phosphorus-free biodegradable reverse osmosis antiscalant according to any one of claims 1-5, characterized in that, Includes the following steps: S1: Add deionized water to the preparation vessel, and add the composite active scale inhibitor at 20-30℃ and a stirring rate of 200-400 rpm. After the addition is complete, continue stirring until the components are completely dispersed in the system. S2: Add preservative and continue stirring; S3: Adjust the pH of the system to 6.5-8.5 with a pH adjuster, and continue stirring until homogeneous to obtain the phosphorus-free biodegradable reverse osmosis antiscalant.

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