Aluminum chloride-based composite flocculant and preparation method thereof

Abstract

The application discloses a composite flocculant based on aluminum chloride and a preparation method thereof, and belongs to the technical field of flocculant preparation, and is used for solving the technical problem that the stability and flocculation performance of the flocculant need to be further improved in the prior art; the branched polymer containing polycarboxyl groups is prepared by the reaction of tris(2-aminoethyl)amine and pyromellitic dianhydride, and the taurine groups are introduced to obtain the sulfobranched polycarboxyl polymer; the titanium phosphorus silicon aminopropyl composite is synthesized by using the sol-gel method, and the inorganic-organic network combination is realized; the polyimidazolium-hydroxy ether is obtained by the reaction of imidazole, epichlorohydrin and bisphenol A diglycidyl ether; the composite flocculant is formed by the reaction of the three under the acidic condition, the composite flocculant combines the polycarboxyl groups, the sulfonic acid groups, the imidazolium groups and the inorganic-organic skeleton, has high charge density, good adsorption and bridging performance, can rapidly form stable flocs, and can effectively remove the suspended particles and organic pollutants in water.

Description

Technical Field

[0001] This invention relates to the field of flocculant preparation technology, specifically to a composite flocculant based on aluminum chloride and its preparation method. Background Technology

[0002] As a commonly used material in water treatment, the technical performance of flocculants is reflected not only in their flocculation effect but also in their stability during storage. Although early inorganic salt flocculants were inexpensive, they were prone to moisture absorption and clumping during storage, affecting their effectiveness. The application of organic polymer flocculants has brought significant improvements in flocculation performance, but they may still experience performance degradation or decreased applicability during long-term storage. In recent years, with the deepening of materials research, while improving flocculation efficiency, flocculants have also paid increasing attention to storage stability, striving to maintain good performance during transportation, storage, and long-term use. The overall trend shows that flocculants are gradually developing towards a direction that "balances high efficiency and storage stability".

[0003] In existing technologies, flocculation technology is widely used due to its advantages such as simple operation, low cost and wide adaptability. However, conventional flocculants and their preparation processes still have some shortcomings, which limit their application under higher standard water treatment requirements.

[0004] First, the product stability is poor. Traditional flocculants are prone to hydrolysis, aggregation, or degradation during storage, leading to the gradual inactivation of active components and a typically short effective shelf life, making it difficult to meet the needs of long-term storage or cross-regional transportation.

[0005] Secondly, the treatment efficiency is not high. While traditional flocculants can achieve certain effects in removing suspended solids and reducing chemical oxygen demand (COD), the treated water often still has high levels of residual suspended solids and COD, making it difficult to meet stricter discharge standards.

[0006] Secondly, their ability to remove heavy metal ions is limited. The mechanism of action of many conventional flocculants mainly focuses on particle flocculation and adsorption of organic pollutants, which has poor removal effect on heavy metal pollutants such as chromium and lead, and the residual concentration is often higher than the relevant emission standards. In addition, single function is also a common problem. Most existing products are single-component or single-function materials, which often cannot achieve efficient removal of multiple pollutants when treating complex wastewater, thus limiting their application scope.

[0007] In summary, traditional flocculants still have shortcomings in terms of storage stability, pollutant removal efficiency, and functional diversity, and urgently need to be improved and optimized. Summary of the Invention

[0008] The purpose of this invention is to provide a composite flocculant based on aluminum chloride and its preparation method, in order to solve the technical problem that the stability and flocculation performance of flocculants in the prior art need to be further improved.

[0009] The objective of this invention can be achieved through the following technical solution: a method for preparing a composite flocculant based on aluminum chloride, comprising the following steps:

[0010] S1. Sulfonated polycarboxylic acid polymer, aluminum trichloride hexahydrate and deionized water are added to the reactor. The reaction system is stirred at room temperature for 1-2 hours under acetic acid conditions with pH=3-4. After stirring, titanium phosphosilane aminopropyl complex is added to the reactor and stirred at room temperature for another 1-2 hours. The flocculant precursor is obtained by post-treatment.

[0011] S2. Add the flocculant precursor and mixed solvent to the reactor and stir. Add polyimidazolium-hydroxy ether to the reactor and adjust the pH of the reaction system to 3-4 with acetic acid. Stir at room temperature for 1-2 hours. After stirring, raise the temperature of the reactor to 40-50℃ and keep it warm for 1 hour. The composite flocculant is then obtained through post-treatment.

[0012] The reaction principle for preparing composite flocculants is as follows:

[0013] Under acidic conditions, sulfonated polycarboxylic polymers react with aluminum trichloride hexahydrate to generate positively charged aluminum-based complexes, which in turn form precursors with high hydrophilicity and high surface activity. This process, through the introduction of titanium phosphide-silane aminopropyl complexes, further enhances the functionality of the complexes under acidic conditions and endows them with catalytic properties, giving the system strong adsorption and flocculation capabilities. At this point, the aluminum-based complexes interact with the polycarboxylic groups in the sulfonated polymers through multiple forces, which helps to form a powerful flocculant precursor.

[0014] The flocculant precursor and the polyimidazolium-hydroxy ether complex continue to react in the presence of a mixed solvent. By adjusting the pH of the reaction system and treating it under suitable temperature conditions, the cross-linking of the imidazolium and hydroxy ether groups further solidifies the functional groups of the precursor, forming a composite flocculant. In this process, the imidazolium salt and the polycarboxylic acid polymer are linked by hydroxy ether chemical bonds, which further enhances the stability of the complex and its adsorption performance on particulate matter in water. At the same time, its strong charge characteristics also improve the coagulation effect of the flocculant.

[0015] Further, in step S1, the ratio of sulfonated polycarboxylic acid polymer, aluminum trichloride hexahydrate, deionized water, and titanium phosphide-silane aminopropyl complex is 8-10g:1.5-2.0g:120-150mL:0.8-1.2g. The post-treatment includes: after the reaction is completed, the reaction solution is centrifuged at 8000-10000rpm for 10-15min, the precipitate is collected, and the precipitate is washed 2-3 times with anhydrous ethanol or deionized water. The precipitate is then transferred to a drying oven at 60-80℃ and dried under vacuum to constant weight to obtain the flocculant precursor.

[0016] Further, in step S2, the ratio of flocculant precursor, mixed solvent, and polyimidazolium-hydroxy ether is 8-10g:100-120mL:2.0-2.5g. The mixed solvent is obtained by mixing deionized water and anhydrous ethanol at a ratio of 8mL:2-4mL. The post-treatment includes: after the reaction is completed, the reaction liquid is centrifuged at 8000-10000rpm for 10-15min, the precipitate is collected, and the precipitate is washed 2-3 times with anhydrous ethanol or deionized water. The precipitate is then transferred to a drying oven at 60-80℃ and dried under vacuum until constant weight to obtain the composite flocculant.

[0017] Furthermore, the preparation method of the sulfonated polycarboxylated polymer includes the following steps:

[0018] A1. Tris(2-aminoethyl)amine and N,N-dimethylformamide were added to a reaction vessel at a temperature of 3-5℃. The mixture was kept warm and stirred until all the reactants were dissolved. Then, the calculated amount of pyromellitic dianhydride was added to the reaction vessel in three portions. After the addition was completed, the temperature of the reaction vessel was raised to 30-50℃ and the reaction was kept warm for 2-4 hours. The branched polycarboxylic acid polymer was obtained after post-treatment.

[0019] A2. Add N,N-dimethylformamide to the reactor and stir. After lowering the reactor temperature to 3-5℃, add the branched polycarboxylic acid polymer to the reactor. After stirring for 5-10 min, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide dropwise to the reactor. After stirring for 20-30 min, raise the reactor temperature to room temperature and continue to add the calculated amount of taurine solution dropwise to the reactor. After stirring for 4-6 h, the sulfonated branched polycarboxylic acid polymer is obtained through post-treatment.

[0020] The reaction equation for preparing sulfonated polycarboxylated polymers is as follows:

[0021]

[0022] In the formula: .

[0023] The reaction principle for preparing sulfonated polycarboxylated polymers is as follows:

[0024] Tris(2-aminoethyl)amine undergoes a nucleophilic ring-opening reaction with pyromellitic dianhydride. The formation of amide bonds is accompanied by the exposure of carboxyl groups, causing the system to exhibit a branching growth trend under conditions where the functionality is greater than two. By controlling the amount of dianhydride to be lower than the molar amount of amino group, excessive cross-linking can be effectively avoided, resulting in a soluble polymer with a highly branched structure and a large number of terminal carboxyl groups.

[0025] Subsequently, under the action of condensing agents 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide, the carboxyl groups on the polymer molecules are activated into more stable NHS ester intermediates. These intermediates can undergo amidation reactions with the amino groups on the taurine molecules, thereby grafting sulfonic acid-containing side chains onto the polymer backbone. Since the substitution rate of taurine is limited to a portion of the carboxyl groups, the final product retains a high density of carboxyl groups while introducing hydrophilic and anionic side chains with sulfonic acid groups, forming a branched polymer structure that combines multi-carboxyl and sulfonation characteristics, thus preparing a sulfonated branched multi-carboxyl polymer.

[0026] Further, in step A1, the ratio of tris(2-aminoethyl)amine to N,N-dimethylformamide is 2-3 g:10 mL, wherein the total amount of pyromellitic dianhydride added is 0.55-0.60 times the molar amount of amino in the reaction system. The post-treatment includes: after the reaction is completed, adding an equal volume of deionized water to the reaction vessel, letting it stand for 10 min, and then transferring the reaction solution to a rotary evaporator at a temperature of 90 °C, and distilling under reduced pressure until no liquid is collected to obtain the branched polycarboxylated polymer;

[0027] Further, in step A2, the ratio of N,N-dimethylformamide, branched polycarboxylic acid polymer, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide is 100mL:8-10g:1.5-2.5g:0.8-1g. The taurine solution is obtained by mixing taurine and deionized water at a ratio of 2-3g:10mL. The molar amount of amino groups in the added taurine solution is 0.15-0.20 times the molar amount of carboxyl groups in the reaction system. The post-treatment includes: after the reaction is completed, after the temperature of the reaction vessel is reduced to room temperature, the reaction solution is transferred to a rotary evaporator at a temperature of 90°C and distilled under reduced pressure until no liquid is collected, thus obtaining the branched polycarboxylic acid polymer.

[0028] Furthermore, the preparation method of the titanium-phosphorus-silane-aminopropyl composite is as follows:

[0029] B1. Add anhydrous ethanol and tetrabutyl titanate to the reaction vessel and stir. After the temperature of the reaction vessel drops to 3-5℃, add the modified solution dropwise to the reaction vessel. After the addition is completed within 10-15 minutes, raise the temperature of the reaction vessel to 10-15℃ and keep it warm and stir for 2-3 hours to obtain the modified titanium phosphorus complex sol.

[0030] B2. Add the modified titanium-phosphorus complex sol to the reactor, stir at room temperature for 10-15 min, then add ethyl silicate and 3-aminopropyltriethoxysilane to the reactor, continue stirring for 4-6 h, and allow to stand for aging for 16-24 h. The post-treatment yields the titanium-phosphorus-silane-aminopropyl composite.

[0031] The reaction principle for preparing titanium phosphosilane aminopropyl complex is as follows:

[0032] The reaction principle for preparing titanium-phosphorus-silane-aminopropyl complex lies in the construction of a multi-component inorganic-organic hybrid network through a sol-gel process. First, tetrabutyl titanate undergoes alcoholysis and hydrolysis in anhydrous ethanol medium, generating a titanium-phosphorus complex sol containing Ti-OP bonds under the regulation of phosphoric acid. Phosphoric acid acts as both a rate regulator and stabilizes the hydrolysis intermediate of titanium through coordination, thus avoiding particle agglomeration caused by excessively rapid condensation.

[0033] Subsequently, tetraethyl orthosilicate and 3-aminopropyltriethoxysilane were introduced into the system. The two reacted through hydrolysis and condensation to form Si-O-Si and Si-O-Ti bonds, thereby covalently linking the silicon component with the titanium-phosphorus network and constructing a titanium-phosphorus-silicon ternary hybrid framework. At the same time, the organic aminopropyl side chain on the aminopropyltriethoxysilane was introduced into the inorganic network, achieving covalent bonding between the organic functional group and the inorganic framework. Through this multiple condensation and complexation, a composite structure that combines the stability of the Ti-OP-Si inorganic network with the functionality of the aminopropyl organic group was finally obtained, thus endowing the material with excellent stability, interfacial activity and functionalization potential. Finally, a titanium-phosphorus-silicon aminopropyl composite was prepared.

[0034] Furthermore, in step B1, the ratio of anhydrous ethanol, tetrabutyl titanate, and the modifying solution is 16mL:4-5g:6mL, wherein the modifying solution is obtained by mixing phosphoric acid, deionized water, and anhydrous ethanol in a ratio of 1.5-1.8g:3-5mL:25-27mL.

[0035] Further, in step B2, the ratio of modified titanium phosphide complex sol, ethyl silicate, and 3-aminopropyltriethoxysilane is 100mL:30-32g:3-4g. The post-treatment includes: after the reaction is completed, the reaction solution is centrifuged at 8000-10000rpm for 10-15min, the precipitate is collected, and the precipitate is washed 2-3 times with anhydrous ethanol or deionized water. The precipitate is then transferred to a drying oven at 60-80℃ and dried under vacuum to constant weight to obtain the titanium phosphide-silane-aminopropyl complex.

[0036] Furthermore, the preparation method of polyimidazolium-hydroxy ether includes the following steps:

[0037] C1. Add imidazole and deionized water to the reaction vessel and stir. After the temperature of the reaction vessel is reduced to 3-5℃, epichlorohydrin is added dropwise to the reaction vessel. After adjusting the pH of the reaction system to 7.5-8.0 with saturated sodium hydroxide aqueous solution, the temperature of the reaction vessel is raised to 30-35℃ and stirred for 2-4 hours. The post-treatment yields glycidyl imidazole onium salt.

[0038] C2. Add glycidyl imidazole onion salt and mixed solution to the reaction vessel and stir. Raise the temperature of the reaction vessel to 40-55℃ and adjust the pH of the reaction system to 8-10 using saturated sodium hydroxide aqueous solution. Then add bisphenol A diglycidyl ether to the reaction vessel, keep it warm and stir for 4-6 hours, and then proceed with post-treatment to obtain polyimidazolium-hydroxy ether.

[0039] The reaction principle for preparing polyimidazolium-hydroxy ether is as follows:

[0040] Imidazole undergoes a nucleophilic substitution reaction with epichlorohydrin. The nitrogen atom of imidazole acts as a nucleophile and reacts with the epoxy group in epichlorohydrin, opening the epoxy group and forming an imidazole onium group. This reaction not only chemically transforms the imidazole group, enhancing its hydrophilicity and charge density, but also introduces a chloropropyl segment with strong charge characteristics, providing an active site for subsequent grafting reactions.

[0041] Due to the presence of epoxy active sites and a cationic structure, glycidyl imidazolium salts can serve as intermediates for further ring-opening addition reactions. Bisphenol A diglycidyl ether molecules have two epoxy groups, which are easily activated and undergo ring-opening under alkaline conditions. These groups then undergo nucleophilic addition with the hydroxyl or nitrogen atom in the imidazolium salt, forming stable hydroxyether bonds and achieving covalent linkage of the structure. As the reaction proceeds, the imidazolium salt units gradually crosslink with bisphenol A diglycidyl ether, forming a polymer backbone containing imidazolium groups and hydroxyether structures, i.e., polyimidazolium-hydroxyether.

[0042] In the structure of polyimidazolium-hydroxy ether, the imidazolium group provides good ion exchange performance and water solubility, while the hydroxy ether group enhances the hydrophilicity and dispersibility of the polymer. The synergistic effect of this composite functional group makes the polymer exhibit good stability, high charge density and strong adsorption capacity in aqueous solution, especially with potential advantages in water treatment, dispersion and flocculation applications.

[0043] Furthermore, in step C1, the ratio of imidazole, deionized water and epichlorohydrin is 1g:3-4mL:1.5ml. The post-processing includes: after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at a temperature of 90℃, and distill under reduced pressure until no liquid is collected to obtain glycidyl imidazole onium salt.

[0044] Further, in step C2, the ratio of glycidyl imidazolium salt, mixed solution, and bisphenol A diglycidyl ether is 10g:27-30mL:10mL. The mixed solution is obtained by mixing dimethyl sulfoxide and deionized water at a ratio of 4mL:1mL. The post-treatment includes: after the reaction is completed, the reaction vessel temperature is lowered to room temperature, the reaction solution is transferred to a rotary evaporator at a temperature of 90℃, and the pressure is reduced and distilled until no liquid is collected to obtain polyimidazolium-hydroxy ether.

[0045] The present invention also discloses a composite flocculant based on aluminum chloride, which is prepared by the above-mentioned preparation method of a composite flocculant based on aluminum chloride.

[0046] The present invention has the following beneficial effects:

[0047] 1. The composite flocculant prepared by this invention is composed of inorganic and organic components. The inorganic part includes aluminum salt, titanium source, and silicon source. These three components form a stable polynuclear hydroxyl complex structure and a three-dimensional Si-O-Si framework network through hydrolysis and condensation reactions, effectively inhibiting secondary hydrolysis and sedimentation, and avoiding stratification and performance degradation during storage. The organic part consists of imidazolium salt and segments containing functional groups such as carboxyl and sulfonic acid groups, which can form stable complexes with metal ions. At the same time, it improves the dispersibility of the system through electrostatic interaction and steric hindrance effect, thereby preventing colloidal particle aggregation and crystallization. The inorganic framework structure provides strong resistance to hydrolysis and aging, while the organic segments give the system flexible protection and buffering effect against environmental fluctuations. The organic combination of the two ensures that the flocculant can maintain a uniform and stable state for a long time under normal temperature, normal pressure, and pH fluctuation conditions, thereby significantly improving the storage stability of the composite flocculant.

[0048] 2. The inorganic components of the composite flocculant prepared in this invention, including aluminum, titanium, and silicon, form polynuclear hydroxyl complexes and high-molecular-weight silicon-oxygen network structures after hydrolysis. These structures can rapidly form a large number of positively charged active centers in water, effectively neutralizing the negative charges on the surface of suspended particles and reducing the electrostatic repulsion between particles. Secondly, the imidazolium salt and hydrophilic segments containing carboxyl and sulfonic acid groups in the organic components not only form stable complexes with the inorganic components but also extend into the aqueous phase, acting as bridges and adsorbents to connect dispersed microparticles and promote the formation of larger and denser flocs. Furthermore, the inorganic framework in the composite system provides a basis for rapid charge neutralization and sedimentation, while the organic segments endow the flocs with stronger structural strength and shear resistance, preventing the flocs from breaking under hydraulic disturbance. Ultimately, through the synergistic effect of the inorganic and organic mechanisms, the flocculation capacity of the composite flocculant is significantly improved.

[0049] 3. The carboxyl and sulfonic acid groups introduced into the polymer skeleton, as typical hydrophilic anionic functional groups, can form stable complexes with positively charged metal ions in water, thereby effectively capturing and removing heavy metal pollutants such as Pb²⁺. Secondly, the imidazolium salt group not only provides additional cationic sites to enhance the electrostatic adsorption capacity for natural organic matter, but also has certain electron transfer characteristics, which can partially reduce hexavalent chromium Cr(VI) to trivalent chromium Cr(III), significantly reducing its toxicity and mobility. At the same time, this type of organic cationic chain segment exhibits strong adsorption affinity for recalcitrant hydrophobic organic matter in water, further improving COD removal efficiency. The inorganic component provides polynuclear hydroxyl complexes as a skeleton, promoting the rapid coagulation and sedimentation of pollutants. Finally, through the synergistic effect of organic and inorganic functional groups, the composite system achieves complementary enhancement in the removal of natural organic matter and heavy metals, ultimately achieving a synergistic removal effect of multiple pollutants such as COD and total chromium. Detailed Implementation

[0050] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0051] Example 1

[0052] This embodiment provides a method for preparing a sulfonated polycarboxylic acid polymer for the preparation of an aluminum chloride-based composite flocculant, comprising the following steps:

[0053] Step ①: Preparation of branched polycarboxylic polymers

[0054] Weigh 20.0 g of tris(2-aminoethyl)amine and 10 mL of N,N-dimethylformamide and add them to a reaction vessel at 3 °C. Keep the mixture warm and stir until all the reactants are dissolved. Then, add pyromellitic dianhydride to the reaction vessel in three portions, with a total addition amount equal to 0.55 times the molar amount of amino in the reaction system. After the addition is complete, raise the temperature of the reaction vessel to 30 °C and keep the reaction at this temperature for 2 h. After the reaction is complete, add an equal volume of deionized water to the reaction vessel. After standing for 10 min, transfer the reaction solution to a rotary evaporator at 90 °C and distill it under reduced pressure until no liquid is collected, thus obtaining the branched polycarboxylic acid polymer.

[0055] Step ②: Preparation of sulfonated polycarboxylic polymer

[0056] Weigh out 20.0g of taurine and mix it with 100.0mL of deionized water to obtain a taurine solution;

[0057] Weigh 100.0 mL of N,N-dimethylformamide and add it to the reaction vessel. After the temperature of the reaction vessel is lowered to 3°C, add 8.0 g of branched polycarboxylic acid polymer to the reaction vessel. After stirring for 5 min, add 1.5 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.8 g of N-hydroxysuccinimide dropwise to the reaction vessel. After stirring for 20 min, raise the temperature of the reaction vessel to room temperature and continue to add taurine solution dropwise in an amount equal to 0.15 times the molar amount of amino groups in the reaction system. Stir for 4 h. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 90°C, and distill under reduced pressure until no liquid is collected to obtain the branched polycarboxylic acid polymer.

[0058] Example 2

[0059] This embodiment provides a method for preparing a sulfonated polycarboxylic acid polymer for the preparation of an aluminum chloride-based composite flocculant, comprising the following steps:

[0060] Step ①: Preparation of branched polycarboxylic polymers

[0061] Weigh 30.0 g of tris(2-aminoethyl)amine and 100.0 mL of N,N-dimethylformamide and add them to a reaction vessel at 5 °C. After stirring and maintaining the temperature, the reactants are completely dissolved. Then, pyromellitic dianhydride is added to the reaction vessel in three portions, with a total addition amount equal to 0.60 times the molar amount of amino in the reaction system. After the addition is complete, the temperature of the reaction vessel is raised to 50 °C and the reaction is maintained for 4 h. After the reaction is completed, deionized water of the same volume as the reaction solution is added to the reaction vessel. After standing for 10 min, the reaction solution is transferred to a rotary evaporator at 90 °C and distilled under reduced pressure until no liquid is collected, thus obtaining the branched polycarboxylic acid polymer.

[0062] Step ②: Preparation of sulfonated polycarboxylic polymer

[0063] Weigh out 30.0g of taurine and mix it with 100.0mL of deionized water to obtain a taurine solution;

[0064] Weigh 100.0 mL of N,N-dimethylformamide and add it to the reaction vessel. After the temperature of the reaction vessel is lowered to 5°C, add 10.0 g of branched polycarboxylic acid polymer to the reaction vessel. After stirring for 10 min, add 2.5 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 1.0 g of N-hydroxysuccinimide dropwise to the reaction vessel. After stirring for 30 min, raise the temperature of the reaction vessel to room temperature and continue to add taurine solution dropwise in an amount equal to 0.20 times the molar amount of amino groups in the reaction system. Stir for 6 h. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 90°C, and distill under reduced pressure until no liquid is collected to obtain the branched polycarboxylic acid polymer.

[0065] Example 3

[0066] This embodiment provides a method for preparing a sulfonated polycarboxylic acid polymer for the preparation of an aluminum chloride-based composite flocculant, comprising the following steps:

[0067] Step ①: Preparation of branched polycarboxylic polymers

[0068] Weigh 24.0 g of tris(2-aminoethyl)amine and 10 mL of N,N-dimethylformamide and add them to a reaction vessel at 4 °C. After stirring and maintaining the temperature, the reactants are completely dissolved. Then, pyromellitic dianhydride is added to the reaction vessel in three portions, with a total addition amount equal to 0.58 times the molar amount of amino in the reaction system. After the addition is complete, the temperature of the reaction vessel is raised to 40 °C and the reaction is maintained for 3 h. After the reaction is complete, deionized water of the same volume as the reaction solution is added to the reaction vessel. After standing for 10 min, the reaction solution is transferred to a rotary evaporator at 90 °C and distilled under reduced pressure until no liquid is collected, thus obtaining the branched polycarboxylic acid polymer.

[0069] Step ②: Preparation of sulfonated polycarboxylic polymer

[0070] Weigh out 24.0g of taurine and mix it with 100.0mL of deionized water to obtain a taurine solution;

[0071] Weigh 100.0 mL of N,N-dimethylformamide and add it to the reaction vessel. After the temperature of the reaction vessel is lowered to 4°C, add 9.0 g of branched polycarboxylic acid polymer to the reaction vessel. After stirring for 8 min, add 2.0 g of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 0.9 g of N-hydroxysuccinimide dropwise to the reaction vessel. After stirring for 25 min, raise the temperature of the reaction vessel to room temperature and continue to add taurine solution dropwise in an amount equal to 0.18 times the molar amount of amino groups in the reaction system. Stir for 5 h. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 90°C, and distill under reduced pressure until no liquid is collected to obtain the branched polycarboxylic acid polymer.

[0072] Example 4

[0073] This embodiment provides a method for preparing modified titanium-phosphorus complex sol for the preparation of aluminum chloride-based composite flocculants, including the following steps:

[0074] Step I: Preparation of modified titanium phosphate complex sol

[0075] Weigh out 15.0g of phosphoric acid, 30.0mL of deionized water and 250.0mL of anhydrous ethanol and mix them to obtain the modified solution;

[0076] Weigh out 160.0 mL of anhydrous ethanol and 40.0 g of tetrabutyl titanate and add them to the reaction vessel and stir. After the temperature of the reaction vessel is lowered to 3°C, add 60.0 mL of the modified solution dropwise to the reaction vessel. After the addition is completed within 10 min, raise the temperature of the reaction vessel to 10°C and keep it at this temperature for 2 h to obtain the modified titanium phosphorus complex sol.

[0077] Step II: Preparation of titanium phosphosilanepropyl complex

[0078] Weigh 100.0 mL of modified titanium-phosphorus complex sol and add it to the reaction vessel. After stirring at room temperature for 10 min, add 30.0 g of ethyl silicate and 3.0 g of 3-aminopropyltriethoxysilane to the reaction vessel. Continue stirring for 4 h and then let it stand for 16 h. After the reaction is complete, centrifuge the reaction solution at 8000 rpm for 10 min. Collect the precipitate and wash it twice with anhydrous ethanol or deionized water. Then transfer the precipitate to a drying oven at 60℃ and dry it under vacuum to constant weight to obtain the titanium-phosphorus-silane-aminopropyl complex.

[0079] Example 5

[0080] This embodiment provides a method for preparing modified titanium-phosphorus complex sol for the preparation of aluminum chloride-based composite flocculants, including the following steps:

[0081] Step I: Preparation of modified titanium phosphate complex sol

[0082] Weigh out 18.0 g of phosphoric acid, 50.0 mL of deionized water and 270.0 mL of anhydrous ethanol and mix them to obtain the modified solution;

[0083] Weigh out 160.0 mL of anhydrous ethanol and 50.0 g of tetrabutyl titanate and add them to the reaction vessel. Stir the reaction vessel and lower the temperature to 5°C. Then add 60.0 mL of the modified solution dropwise to the reaction vessel. After the addition is completed within 15 min, raise the temperature of the reaction vessel to 15°C and keep it warm and stirred for 3 h to obtain the modified titanium phosphorus complex sol.

[0084] Step II: Preparation of titanium phosphosilanepropyl complex

[0085] Weigh 100.0 mL of modified titanium-phosphorus complex sol and add it to the reaction vessel. After stirring at room temperature for 12 min, add 32.0 g of ethyl silicate and 4.0 g of 3-aminopropyltriethoxysilane to the reaction vessel. Continue stirring for 5 h and then let it stand for 20 h. After the reaction is complete, centrifuge the reaction solution at 9000 rpm for 12 min. Collect the precipitate and wash it three times with anhydrous ethanol or deionized water. Then transfer the precipitate to a drying oven at 70 °C and dry it under vacuum to constant weight to obtain the titanium-phosphorus-silane-aminopropyl complex.

[0086] Example 6

[0087] This embodiment provides a method for preparing modified titanium-phosphorus complex sol for the preparation of aluminum chloride-based composite flocculants, including the following steps:

[0088] Step I: Preparation of modified titanium phosphate complex sol

[0089] Weigh out 16.0 g of phosphoric acid, 40.0 mL of deionized water and 260.0 mL of anhydrous ethanol and mix them to obtain the modified solution;

[0090] Weigh out 160.0 mL of anhydrous ethanol and 50.0 g of tetrabutyl titanate and add them to the reaction vessel and stir. After the temperature of the reaction vessel is lowered to 4°C, add 60.0 mL of the modified solution dropwise to the reaction vessel. After the addition is completed within 12 min, raise the temperature of the reaction vessel to 12°C and keep it at this temperature for 3 h to obtain the modified titanium phosphorus complex sol.

[0091] Step II: Preparation of titanium phosphosilanepropyl complex

[0092] Weigh 100.0 mL of modified titanium-phosphorus complex sol and add it to the reaction vessel. After stirring at room temperature for 12 min, add 32.0 g of ethyl silicate and 4.0 g of 3-aminopropyltriethoxysilane to the reaction vessel. Continue stirring for 5 h and then let it stand for 20 h. After the reaction is complete, centrifuge the reaction solution at 9000 rpm for 12 min. Collect the precipitate and wash it three times with anhydrous ethanol or deionized water. Then transfer the precipitate to a drying oven at 70 °C and dry it under vacuum to constant weight to obtain the titanium-phosphorus-silane-aminopropyl complex.

[0093] Example 7

[0094] This embodiment provides a method for preparing polyimidazolium-hydroxy ether for the preparation of aluminum chloride-based composite flocculants, including the following steps:

[0095] Step (1): Preparation of glycidyl imidazolium salt

[0096] Weigh out 10.0 g imidazole and 30.0 mL deionized water and add them to the reaction vessel. Stir the mixture. After the temperature of the reaction vessel is reduced to 3°C, add 15.0 mL epichlorohydrin dropwise to the reaction vessel. Adjust the pH of the reaction system to 7.5 using a saturated sodium hydroxide aqueous solution. Then, raise the temperature of the reaction vessel to 30°C and keep it at that temperature for 2 hours with stirring. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 90°C and distill it under reduced pressure until no liquid is collected, to obtain glycidyl imidazole onium salt.

[0097] Step 2: Preparation of polyimidazolium-hydroxy ether

[0098] Weigh out 40.0 mL of dimethyl sulfoxide and 10.0 mL of deionized water and mix them to obtain a mixed solution;

[0099] Weigh out 10.0 g of glycidyl imidazole onion salt and 27.0 mL of mixed solution and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 40 °C. Adjust the pH of the reaction system to 8 using a saturated sodium hydroxide aqueous solution. Then add 10.0 mL of bisphenol A diglycidyl ether to the reaction vessel and keep it warm and stirred for 4 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature and transfer the reaction solution to a rotary evaporator at 90 °C. Distill the solution under reduced pressure until no liquid is collected to obtain polyimidazolium-hydroxy ether.

[0100] Example 8

[0101] This embodiment provides a method for preparing polyimidazolium-hydroxy ether for the preparation of aluminum chloride-based composite flocculants, including the following steps:

[0102] Step (1): Preparation of glycidyl imidazolium salt

[0103] Weigh out 10.0 g imidazole and 40.0 mL deionized water and add them to the reaction vessel. Stir the mixture. After the temperature of the reaction vessel is reduced to 5°C, add 15.0 mL epichlorohydrin dropwise to the reaction vessel. Adjust the pH of the reaction system to 8.0 using a saturated sodium hydroxide aqueous solution. Then, raise the temperature of the reaction vessel to 35°C and keep it at this temperature for 4 hours with stirring. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 90°C and distill it under reduced pressure until no liquid is collected, to obtain glycidyl imidazole onium salt.

[0104] Step 2: Preparation of polyimidazolium-hydroxy ether

[0105] Weigh out 40.0 mL of dimethyl sulfoxide and 10.0 mL of deionized water and mix them to obtain a mixed solution;

[0106] Weigh out 10.0 g of glycidyl imidazole onion salt and 30.0 mL of mixed solution and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 55°C. Adjust the pH of the reaction system to 10 using a saturated sodium hydroxide aqueous solution. Then add 10.0 mL of bisphenol A diglycidyl ether to the reaction vessel and keep it warm and stirred for 5 hours. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature and transfer the reaction solution to a rotary evaporator at 90°C. Distill the solution under reduced pressure until no liquid is collected to obtain polyimidazolium-hydroxy ether.

[0107] Example 9

[0108] This embodiment provides a method for preparing polyimidazolium-hydroxy ether for the preparation of aluminum chloride-based composite flocculants, including the following steps:

[0109] Step (1): Preparation of glycidyl imidazolium salt

[0110] Weigh out 10.0 g imidazole and 36.0 mL deionized water and add them to the reaction vessel. Stir the mixture. After the temperature of the reaction vessel is reduced to 4 °C, add 15.0 mL epichlorohydrin dropwise to the reaction vessel. Adjust the pH of the reaction system to 8.0 using a saturated sodium hydroxide aqueous solution. Then, raise the temperature of the reaction vessel to 32 °C and keep it at this temperature for 3 hours with stirring. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature. Transfer the reaction solution to a rotary evaporator at 90 °C and distill it under reduced pressure until no liquid is collected, to obtain glycidyl imidazole onium salt.

[0111] Step 2: Preparation of polyimidazolium-hydroxy ether

[0112] Weigh out 40.0 mL of dimethyl sulfoxide and 10.0 mL of deionized water and mix them to obtain a mixed solution;

[0113] Weigh out 10.0 g of glycidyl imidazole onion salt and 30.0 mL of mixed solution and add them to the reaction vessel. Stir the mixture and raise the temperature of the reaction vessel to 50 °C. Adjust the pH of the reaction system to 9 using a saturated sodium hydroxide aqueous solution. Then add 100 mL of bisphenol A diglycidyl ether to the reaction vessel and keep it warm and stirred for 5 h. After the reaction is complete, wait for the temperature of the reaction vessel to drop to room temperature and transfer the reaction solution to a rotary evaporator at 90 °C. Distill the solution under reduced pressure until no liquid is collected to obtain polyimidazolium-hydroxy ether.

[0114] Example 10

[0115] This embodiment provides a method for preparing a composite flocculant based on aluminum chloride, including the following steps:

[0116] Step 1: Preparation of flocculant precursor

[0117] Weigh 8.0g of the sulfonated polycarboxylic polymer prepared in Example 1, 1.5g of aluminum trichloride hexahydrate, and 120.0mL of deionized water and add them to the reaction vessel. After the reaction system is at pH=3 under acetic acid conditions, stir at room temperature for 1h. After stirring, add 0.8g of the titanium phosphosilane aminopropyl complex prepared in Example 4 to the reaction vessel and continue stirring at room temperature for 1h. After the reaction is completed, centrifuge the reaction solution at 8000rpm for 10min, collect the precipitate, wash the precipitate twice with anhydrous ethanol or deionized water, and then transfer the precipitate to a drying oven at 60℃ and dry it under vacuum to constant weight to obtain the flocculant precursor.

[0118] Step 2: Preparation of composite flocculant

[0119] Weigh out 80.0 mL of deionized water and 20.0 mL of anhydrous ethanol and mix them to obtain a mixed solvent;

[0120] Weigh 8.0g of flocculant precursor and 100.0mL of mixed solvent and add them to the reaction vessel and stir. Add 2.0g of polyimidazolium-hydroxy ether prepared in Example 7 to the reaction vessel and adjust the pH of the reaction system to 3 with acetic acid. Stir at room temperature for 1h. After stirring, raise the temperature of the reaction vessel to 40℃ and keep it warm for 1h. After the reaction is complete, centrifuge the reaction liquid at 8000rpm for 10min. Collect the precipitate and wash it twice with anhydrous ethanol or deionized water. Then transfer the precipitate to a drying oven at 60℃ and dry it under vacuum until constant weight to obtain the composite flocculant.

[0121] Example 11

[0122] This embodiment provides a method for preparing a composite flocculant based on aluminum chloride, including the following steps:

[0123] Step 1: Preparation of flocculant precursor

[0124] Weigh 10.0g of the sulfonated polycarboxylic polymer prepared in Example 2, 2.0g of aluminum trichloride hexahydrate, and 150.0mL of deionized water and add them to the reaction vessel. After the reaction system is at pH=4 under acetic acid conditions, stir at room temperature for 2h. After stirring, add 1.2g of the titanium phosphide-silane aminopropyl complex prepared in Example 5 to the reaction vessel and continue stirring at room temperature for 2h. After the reaction is completed, centrifuge the reaction solution at 10000rpm for 15min, collect the precipitate, wash the precipitate 3 times with anhydrous ethanol or deionized water, and then transfer the precipitate to a drying oven at 80℃ and dry it under vacuum to constant weight to obtain the flocculant precursor.

[0125] Step 2: Preparation of composite flocculant

[0126] Weigh out 80.0 mL of deionized water and 40.0 mL of anhydrous ethanol and mix them to obtain a mixed solvent;

[0127] Weigh 10.0g of flocculant precursor and 120.0mL of mixed solvent and add them to the reaction vessel and stir. Add 2.5g of polyimidazolium-hydroxy ether prepared in Example 8 to the reaction vessel and adjust the pH of the reaction system to 4 with acetic acid. Stir at room temperature for 2h. After stirring, raise the temperature of the reaction vessel to 50℃ and keep it warm for 1h. After the reaction is complete, centrifuge the reaction liquid at 10000rpm for 12min. Collect the precipitate and wash it 3 times with anhydrous ethanol or deionized water. Then transfer the precipitate to a drying oven at 80℃ and dry it under vacuum to constant weight to obtain the composite flocculant.

[0128] Example 12

[0129] This embodiment provides a method for preparing a composite flocculant based on aluminum chloride, including the following steps:

[0130] Step 1: Preparation of flocculant precursor

[0131] Weigh 9.0g of the sulfonated polycarboxylic polymer prepared in Example 3, 1.8g of aluminum trichloride hexahydrate, and 150.0mL of deionized water and add them to the reaction vessel. After the reaction system is at pH=4 under acetic acid conditions, stir at room temperature for 2h. After stirring, add 1.0g of the titanium phosphosilane aminopropyl complex prepared in Example 6 to the reaction vessel and continue stirring at room temperature for 2h. After the reaction is completed, centrifuge the reaction solution at 9000rpm for 12min, collect the precipitate, wash the precipitate 3 times with anhydrous ethanol or deionized water, and then transfer the precipitate to a drying oven at 70℃ and dry it under vacuum to constant weight to obtain the flocculant precursor.

[0132] Step 2: Preparation of composite flocculant

[0133] Weigh out 80.0 mL of deionized water and 20.0 mL of anhydrous ethanol and mix them to obtain a mixed solvent;

[0134] Weigh 9.0g of flocculant precursor and 100.0mL of mixed solvent and add them to the reaction vessel and stir. Add 2.4g of polyimidazolium-hydroxy ether prepared in Example 9 to the reaction vessel and adjust the pH of the reaction system to 3 with acetic acid. Stir at room temperature for 2h. After stirring, raise the temperature of the reaction vessel to 45℃ and keep it warm for 1h. After the reaction is complete, centrifuge the reaction liquid at 9000rpm for 12min. Collect the precipitate and wash it 3 times with anhydrous ethanol or deionized water. Then transfer the precipitate to a drying oven at 70℃ and dry it under vacuum to constant weight to obtain the composite flocculant.

[0135] Comparative Example 1

[0136] The difference between this comparative example and Example 12 is that step ② is omitted in the preparation process of the sulfonated polycarboxylic polymer used in step one.

[0137] Comparative Example 2

[0138] The difference between this comparative example and Example 12 is that polyimidazolium-hydroxy ether was omitted in step two.

[0139] Comparative Example 3

[0140] The difference between this comparative example and Example 12 is that the titanium phosphide-silane aminopropyl compound was omitted in step one.

[0141] Performance testing:

[0142] The stability of the composite flocculants prepared in Examples 10-12 and Comparative Examples 1-3 was evaluated in accordance with the standard YS / T 802-2012 "Flocculants for Alumina Production".

[0143] The suspended solids content, COD content, total chromium content and total lead content of the composite flocculants prepared in Examples 10-12 and Comparative Examples 1-3 after flocculation were compared with the standard GB 18918-2002 "Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants". The specific data are shown in Table 1.

[0144] Table 1 - Performance Test Data for Each Sample

[0145] Project Group Example 7 Example 8 Example 9 Comparative Example 1 Comparative Example 2 Comparative Example 3 Stability / month 13 13 13 11 5 8 <![CDATA[Suspended solid content / mg·L -1 > 6 5 5 18 36 22 <![CDATA[COD content / mg·L -1 > 32 30 29 102 126 109 <![CDATA[Total chromium content / mg·L -1 > 0.07 0.06 0.06 0.52 0.78 1.01 <![CDATA[Total lead content / mg·L -1 > 0.06 0.06 0.06 0.23 0.32 0.29

[0146] Data Analysis:

[0147] Comparative analysis of the data in Table 1 reveals that the composite flocculant prepared in this invention can be stably stored for 13 months, and after flocculation of wastewater, the suspended solids content of the wastewater is 5 mg·L⁻¹. -1COD content is 29 mg·L -1 At the same time, the total chromium content and total lead content were both 0.06 mg·L. -1 All data points are better than the comparative data, indicating that:

[0148] The sample in Comparative Example 1 failed to form hydrophilic side chains with sulfonic acid groups during preparation, resulting in uneven surface charge distribution of the molecular chains and significantly weakened hydrophilicity. After losing the balanced hydration layer, the polymer's extensibility in water was limited, and the molecular chains were more prone to entanglement or aggregation, making it impossible to fully expose the effective adsorption sites during use. At the same time, the surface charge was insufficient to form stable electrostatic repulsion between colloidal particles, and the particles were prone to re-aggregation, causing some of the adsorbed pollutants to be released back into the water during the coagulation and sedimentation stage. As the adsorption kinetics decreased, the removal efficiency of recalcitrant organic matter and heavy metals decreased simultaneously, ultimately resulting in increased COD and high metal residues in the effluent. Furthermore, during long-term storage, due to the lack of a hydrophilic protective layer, the interaction between molecular chains within the system was enhanced, and the colloidal structure stability was slightly weakened, thus shortening the stabilization time.

[0149] The sample in Comparative Example 2 lacked the introduction of an inorganic hybrid framework during preparation, resulting in a lack of a stable three-dimensional support network in the overall polymer structure. Without this rigid framework, the spatial architecture upon which the molecular chains depend could not form uniform channels and trapping units, weakening the bridging effect between particles. Initially adsorbed pollutants were difficult to quickly fix within the stable flocs. Furthermore, during flocculation, floc formation depended on the physical entanglement and chemical bridging of molecular chains. However, due to the insufficient framework, the resulting flocs had low density and mechanical strength, significantly reducing the settling velocity. Some suspended particles were disturbed and redispersed into the water during the settling stage. Simultaneously, the lack of a framework led to a decrease in specific surface area, making the adsorption sites more concentrated and easily blocked by pollutants, thus affecting the continuous adsorption capacity. During the storage stage, due to the lack of steric hindrance protection within the system, the molecular chains were more prone to shrinkage or aggregation under external environmental stress, causing rapid deterioration of colloidal properties and a significantly shortened stable storage period.

[0150] Comparative Example 3 failed to introduce polymer units with strong cationic properties during the preparation process, resulting in a lack of balanced charge distribution and multi-point coordination ability in the polymer molecular structure. After losing these high charge density groups, the electrostatic adsorption between the polymer and negatively or weakly negatively charged pollutants in the water weakened, making it difficult to effectively capture some pollutants that rely on ion exchange or complexation fixation. During the floc formation stage, due to the reduced charge neutralization rate, the efficiency of particle binding after collision decreased, resulting in flocs with small particle size distribution and loose structure, which are prone to disintegration during subsequent hydraulic impact or stirring. Insufficient adsorption kinetics also led to a decrease in the binding stability of polyvalent metal ions, and metals may be re-released during sedimentation or filtration. Furthermore, during storage, the inter-chain interactions of polymers lacking balanced charge distribution are unstable, and structural loosening is more likely to occur when temperature or pH changes, the colloidal morphology gradually deteriorates, and the stable storage period is significantly shortened.

[0151] In conclusion, this scheme prepares a branched polymer containing multiple carboxyl groups by reacting tris(2-aminoethyl)amine with pyromellitic dianhydride, and introduces taurine groups to obtain a sulfonated branched polycarboxyl polymer. A titanium-phosphorus-silane-aminopropyl complex is synthesized using the sol-gel method to achieve an inorganic-organic network combination. Imidazole reacts with epichlorohydrin and bisphenol A diglycidyl ether to obtain polyimidazolium-hydroxy ether. The rational combination of multiple components enables the material to exhibit stable and efficient performance in water treatment. The hydrophilic side chains provide a balanced hydration layer, preventing floc re-aggregation. The inorganic framework provides stable three-dimensional support, enhancing settling velocity and mechanical strength. The charged units strengthen the adsorption and fixation of pollutants. This composite flocculant combines multiple carboxyl groups, sulfonic acid groups, imidazolium groups, and an inorganic-organic framework, exhibiting high charge density, good adsorption and bridging properties, and can rapidly form stable flocs, effectively removing suspended particles and organic pollutants from water.

[0152] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a composite flocculant based on aluminum chloride, characterized in that, Includes the following steps: S1. Sulfonated polycarboxylic acid polymer, aluminum trichloride hexahydrate and deionized water are added to the reactor. The pH of the reaction system is adjusted to 3-4 with acetic acid and stirred at room temperature for 1-2 hours. After stirring, titanium phosphosilane aminopropyl complex is added to the reactor and stirred at room temperature for another 1-2 hours. The flocculant precursor is obtained by post-treatment. S2. Add the flocculant precursor and mixed solvent to the reactor and stir. Add polyimidazolium-hydroxy ether to the reactor and adjust the pH of the reaction system to 3-4 with acetic acid. Stir at room temperature for 1-2 hours. After stirring, raise the temperature of the reactor to 40-50℃ and keep it warm for 1 hour. The composite flocculant is obtained after post-treatment. In step S1, the ratio of sulfonated polycarboxylic acid polymer, aluminum trichloride hexahydrate, deionized water, and titanium phosphide-silane aminopropyl complex is 8-10g:1.5-2.0g:120-150mL:0.8-1.2g; in step S2, the ratio of flocculant precursor, mixed solvent, and polyimidazolium-hydroxy ether is 8-10g:100-120mL:2.0-2.5g, wherein the mixed solvent is obtained by mixing deionized water and anhydrous ethanol in a ratio of 8mL:2-4mL. The post-processing of steps S1 and S2 is as follows: After the reaction is completed, the reaction solution is centrifuged at 8000-10000 rpm for 10-15 min. After collecting the precipitate, the precipitate is washed 2-3 times with anhydrous ethanol or deionized water. Then the precipitate is transferred to a drying oven at 60-80℃ and dried under vacuum until constant weight. The preparation method of the sulfonated polycarboxylic polymer includes the following steps: A1. Tris(2-aminoethyl)amine and N,N-dimethylformamide were added to a reaction vessel at a temperature of 3-5℃. After stirring at this temperature, the reactants were kept completely dissolved. Then, the calculated amount of pyromellitic dianhydride was added to the reaction vessel in three portions. After the addition was completed, the temperature of the reaction vessel was raised to 30-50℃ and the reaction was kept at this temperature for 2-4 hours. After the reaction was completed, an equal volume of deionized water was added to the reaction vessel. After standing for 10 minutes, the reaction solution was transferred to a rotary evaporator at a temperature of 90℃ and distilled under reduced pressure until no liquid was collected, thus obtaining a branched polycarboxylic acid polymer. A2. Add N,N-dimethylformamide to the reaction vessel and stir. After the temperature of the reaction vessel is lowered to 3-5℃, add the branched polycarboxylic acid polymer to the reaction vessel. After stirring for 5-10 min, add 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide dropwise to the reaction vessel. After stirring for 20-30 min, raise the temperature of the reaction vessel to room temperature and continue to add the calculated amount of taurine solution dropwise to the reaction vessel. After stirring for 4-6 h, after the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 90℃, and distill under reduced pressure until no liquid is collected to obtain the sulfonated polycarboxylic acid polymer. In step A1, the ratio of tris(2-aminoethyl)amine to N,N-dimethylformamide is 2-3 g:10 mL, and the total amount of pyromellitic dianhydride added is 0.55-0.60 times the molar amount of amino groups in the reaction system. In step A2, the ratio of N,N-dimethylformamide, branched polycarboxylic acid polymer, 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide is 100 mL:8-10 g:1.5-2.5 g:0.8-1 g, and the taurine solution is obtained by mixing taurine and deionized water at a ratio of 2-3 g:10 mL, and the molar amount of amino groups in the added taurine solution is 0.15-0.20 times the molar amount of carboxyl groups in the reaction system. The preparation method of the titanium-phosphorus-silane-aminopropyl composite is as follows: B1. Add anhydrous ethanol and tetrabutyl titanate to the reaction vessel and stir. After the temperature of the reaction vessel drops to 3-5℃, add the modified solution dropwise to the reaction vessel. After the addition is completed within 10-15 minutes, raise the temperature of the reaction vessel to 10-15℃ and keep it warm and stir for 2-3 hours to obtain the modified titanium phosphorus complex sol. B2. Add the modified titanium-phosphorus complex sol to the reaction vessel, stir at room temperature for 10-15 min, then add ethyl silicate and 3-aminopropyltriethoxysilane to the reaction vessel, continue stirring for 4-6 h, and then let it stand for aging for 16-24 h. After the reaction is complete, centrifuge the reaction solution at 8000-10000 rpm for 10-15 min, collect the precipitate, wash the precipitate 2-3 times with anhydrous ethanol or deionized water, and then transfer the precipitate to a drying oven at 60-80℃ and dry it under vacuum to constant weight to obtain the titanium-phosphorus-silane-aminopropyl complex. In step B1, the ratio of anhydrous ethanol, tetrabutyl titanate, and the modifying solution is 16 mL: 4-5 g: 6 mL, wherein the modifying solution is obtained by mixing phosphoric acid, deionized water, and anhydrous ethanol in a ratio of 1.5-1.8 g: 3-5 mL: 25-27 mL; in step B2, the ratio of modified titanium-phosphorus complex sol, ethyl silicate, and 3-aminopropyltriethoxysilane is 100 mL: 30-32 g: 3-4 g. The preparation method of the polyimidazolium-hydroxy ether includes the following steps: C1. Add imidazole and deionized water to the reaction vessel and stir. After the temperature of the reaction vessel is reduced to 3-5℃, epichlorohydrin is added dropwise to the reaction vessel. After adjusting the pH of the reaction system to 7.5-8.0 with saturated sodium hydroxide aqueous solution, the temperature of the reaction vessel is raised to 30-35℃ and stirred for 2-4 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 90℃, and distill under reduced pressure until no liquid is collected to obtain glycidyl imidazole onium salt. C2. Add glycidyl imidazole onion salt and mixed solution to the reaction vessel and stir. After raising the temperature of the reaction vessel to 40-55℃ and adjusting the pH of the reaction system to 8-10 using saturated sodium hydroxide aqueous solution, add bisphenol A diglycidyl ether to the reaction vessel and keep it warm and stirred for 4-6 hours. After the reaction is completed, wait for the temperature of the reaction vessel to drop to room temperature, transfer the reaction solution to a rotary evaporator at 90℃, and distill under reduced pressure until no liquid is collected to obtain polyimidazolium-hydroxy ether. In step C1, the ratio of imidazole, deionized water, and epichlorohydrin is 1g:3-4mL:1.5ml; in step C2, the ratio of glycidyl imidazole onium salt, mixed solution, and bisphenol A diglycidyl ether is 10g:27-30mL:10mL, wherein the mixed solution is obtained by mixing dimethyl sulfoxide and deionized water in a ratio of 4mL:1mL.

2. A composite flocculant based on aluminum chloride, characterized in that, The aluminum chloride-based composite flocculant is prepared using the method described in claim 1 for preparing an aluminum chloride-based composite flocculant.

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