A tentacle-type double cationic modified tannin-based organic flocculant and its preparation method and application

Abstract

The present invention relates to the technical field of water treatment, and in particular to a tentacle-type dicationically modified tannin-based organic flocculant, and a preparation method and application thereof. The preparation method comprises: (1) adding tetrabutylphosphonium bromide to an alkaline solution of tannic acid, and reacting at 50-80°C for 2-4 hours; (2) dispersing the precipitate in water, continuously introducing nitrogen, adding a first free radical initiator at 50-80°C for reaction, and then adding dimethyldiallylammonium chloride and a second free radical initiator, and reacting for 2-4 hours; (3) extracting the precipitate product with a mixed solution of acetone and ethanol, filtering and washing, and obtaining the product. The present invention significantly improves the water solubility and flocculation effect of tannic acid by step-by-step grafting of a quaternary phosphonium salt and a quaternary ammonium salt with strong cationicity and good water solubility onto tannic acid, while maintaining its biodegradability and environmental friendliness, thereby achieving the technical effect of efficient algae removal and synergistic algal toxin removal.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a tentacle-type dicationically modified tannin-based organic flocculant, and a preparation method and application thereof. Background Art

[0002] In recent years, eutrophication of water bodies has become a frequent phenomenon. The "2022 China Environmental Bulletin" indicates that among the 204 key lakes (reservoirs) monitored for nutrient status, 29.9% and 60.3% were in eutrophic and mesotrophic states, respectively. In surface water-based water treatment, the excessive growth of algae caused by eutrophication in summer poses a serious threat to the water supply security of water plants. As algae grow, reproduce, and die, they release algal toxins that continuously enter the water body, further affecting water quality. Algal toxins are secondary metabolites of algae and have strong carcinogenic (liver cancer) effects. Once ingested by the human body, they can cause damage to the liver, kidneys, gastrointestinal tract, reproductive system, immune system, and nervous system. Efficiently removing algal toxins during the algae removal process is a challenging issue in water treatment.

[0003] Currently, commonly used algae removal processes include filtration, biological methods, and chemical methods. Chemical algae removal, which primarily includes algaecides, oxidants, and coagulants, requires no additional infrastructure and is easy to operate, thus attracting widespread attention. However, commonly used algaecides contain copper, which poses a health hazard to humans. Oxidants can cause algal cell lysis, leading to the release of intracellular algal toxins and increased production of disinfection byproducts. Coagulant algae removal offers advantages such as low cost, high algae removal efficiency, low algal cell damage, and the absence of toxic and hazardous intermediates. It is currently the most widely used process in water plants. Traditional coagulation processes can effectively remove algal cells, suspended particles, colloids, and large organic molecules, but are less effective at removing small, highly soluble algal toxins. Coagulation is the most common primary treatment unit in conventional water plants, and its efficiency directly impacts the operating load of all downstream treatment units. Therefore, overcoming the bottleneck of coagulation processes in removing algal toxins is the most economical and simple strategy for improving water quality.

[0004] Tannic acid, a polyphenolic compound with abundant phenolic hydroxyl groups and good biodegradability, can effectively remove algal cells through allelopathic action. It can bind to biomacromolecules such as proteins, enzymes, and nucleic acids on and within algal cells, interfering with cellular transport, metabolic regulation, gene expression, and protein synthesis, inhibiting algal growth and reproduction, and reducing the production of intracellular organic matter and algal toxins at the source. It can also cross-link with algal cell walls and membrane components, interfering with algal photosynthesis. By affecting related pigments, proteins, and the electron transport chain, it reduces the efficiency of light energy absorption and conversion, inhibiting algal energy and material acquisition, and thereby reducing the synthesis and release of algal toxins.

[0005] However, the uneven molecular weight distribution and inherent electrical defects of tannic acid severely limit its practical application in the field of flocculation and algae removal. The molecular weight of tannic acid is usually in the range of 500-3000 Da, and its flocculation performance is nonlinearly related to the molecular weight. Low-molecular-weight tannic acid cannot effectively bridge multiple algal cells to form large-sized flocs due to its short molecular chain, resulting in low flocculation efficiency; while high-molecular-weight components have longer molecular chains and more adsorption sites, their solubility in water is significantly reduced, making it difficult to diffuse quickly to the surface of algal cells. At the same time, excessively high molecular weight will trigger a "steric hindrance effect". After adsorption, the large size of tannic acid molecules hinders the proximity of adjacent algal cells, and instead inhibits floc aggregation.

[0006] The electrical properties of natural tannic acid are closely related to the dissociation state of its phenolic hydroxyl groups. In neutral water, the phenolic hydroxyl groups of tannic acid partially dissociate, resulting in a slightly negative surface charge. However, algal cells typically carry a strong negative charge due to the presence of carboxylic acid and sulfate groups. This repulsion of like charges results in a lack of electrostatic attraction between tannic acid and algal cells, resulting in adsorption relying solely on hydrogen bonding and hydrophobic interactions. The binding energy is far lower than that of electrostatic interactions, requiring a several-fold increase in flocculant dosage to achieve the same effect. Furthermore, tannic acid's electrical properties are highly sensitive to pH. Under acidic conditions, the protonation of the phenolic hydroxyl groups shifts the charge toward neutrality. While this improves flocculation efficiency, a strongly acidic environment can easily damage algal cell walls, triggering the release of intracellular toxins and posing a risk of secondary contamination. These factors combined result in unstable flocculation when used alone, making tannic acid ineffective in meeting the high-efficiency and stable flocculant requirements for practical applications such as industrial wastewater treatment. This, in turn, limits its widespread application as a flocculant. Summary of the Invention

[0007] In response to the technical problem that tannic acid alone has poor effect as a flocculant, the present invention provides a tentacle-type dicationic modified tannin-based organic flocculant, a preparation method and application thereof. By step-by-step grafting of quaternary phosphonium salts and quaternary ammonium salts with strong cationicity and good water solubility onto tannic acid, the flocculation effect of tannic acid is significantly improved while maintaining its biodegradability and environmental friendliness, thereby achieving the technical effect of efficient algae removal and synergistic removal of algal toxins.

[0008] In a first aspect, the present invention provides a method for preparing a tentacle-type dicationically modified tannin-based organic flocculant, comprising the following steps:

[0009] (1) Add tetrabutylphosphonium bromide to an alkaline solution of tannic acid, react at 50-80°C for 2-4 hours, precipitate in an acetone solution, and remove the lower precipitate for washing;

[0010] (2) Disperse the precipitate in water, continuously introduce nitrogen, add the first free radical initiator at 50-80°C, then add dimethyldiallylammonium chloride and the second free radical initiator, and react for 2-4 hours;

[0011] (3) Extract the precipitated product with a mixture of acetone and ethanol, filter and wash it.

[0012] Furthermore, in step (1), the alkaline solution of tannic acid is prepared by dissolving tannic acid in a NaOH solution with a concentration of 0.1-0.5 mol / L.

[0013] Furthermore, in step (1), the lower precipitate is washed with ethanol and then washed with deionized water.

[0014] Furthermore, in step (1), the amount of tetrabutylphosphonium bromide added is 0.5-2 mol / mol based on the amount of tannic acid.

[0015] Furthermore, in step (2), the amount of the first free radical initiator added is 0.01-0.1 g / 5 g, based on the mass of tannic acid;

[0016] Based on the mass of tannic acid, the added amount of the second free radical initiator is 0.01-0.1 g / 5 g.

[0017] Furthermore, in step (2), after the first free radical initiator is added, the reaction is continued for 20-40 minutes before adding dimethyldiallylammonium chloride and the second free radical initiator.

[0018] Furthermore, in step (2), the amount of dimethyldiallylammonium chloride added is 1-5 mol / mol based on the amount of tannic acid.

[0019] Furthermore, in step (2), the precipitate is dispersed in water and heated to 50-80° C. in a water bath.

[0020] Furthermore, the first free radical initiator is one of potassium persulfate, ammonium persulfate, and cerium ammonium nitrate;

[0021] The second free radical initiator is one of potassium persulfate, ammonium persulfate, and ceric ammonium nitrate.

[0022] Furthermore, the preparation method of the tentacle-type dicationically modified tannin-based organic flocculant is specifically as follows:

[0023] (1) Dissolve tannic acid in 170 mL of 0.3 mol / L sodium hydroxide solution, add tetrabutylphosphonium bromide to the alkaline solution of tannic acid, with the molar ratio of tetrabutylphosphonium bromide to tannic acid being 1:1, and react at 70°C for 3 hours. After the reaction, cool to room temperature and precipitate in acetone solution. Remove the lower precipitate, wash with ethanol, and then wash with deionized water three times;

[0024] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced and the first portion of potassium persulfate was added. The mass ratio of the first portion of potassium persulfate to tannic acid was 0.03:5. After reacting for 20 minutes, dimethyldiallyl ammonium chloride and the second portion of potassium persulfate were added. The molar ratio of dimethyldiallyl ammonium chloride to tannic acid was 3:1. The mass ratio of the second portion of potassium persulfate to tannic acid was 0.03:5. The reaction was continued for 4 hours.

[0025] (3) After the reaction is completed, cool to room temperature, extract the precipitated product with a mixture of acetone and ethanol, filter and wash to obtain the product.

[0026] In a second aspect, the present invention provides a tentacle-type dicationically modified tannin-based organic flocculant prepared by the preparation method.

[0027] In a third aspect, the present invention further provides a use of the above-mentioned tentacle-type dicationically modified tannin-based organic flocculant in treating algae liquid.

[0028] The synthesis mechanism of the tentacle-type dicationically modified tannin-based organic flocculant of the present invention is to completely or partially replace the H in each phenolic hydroxyl group of tannic acid with a quaternary phosphonium salt (tetrabutylphosphonium bromide) or a quaternary ammonium salt (dimethyldiallylammonium chloride). The specific synthesis route is as follows:

[0029] .

[0030] The beneficial effects of the present invention are:

[0031] 1. This invention uses tannic acid as a raw material and grafts quaternary phosphonium and quaternary ammonium groups via a two-step process to produce an organic polymer flocculant that combines high flocculation performance, environmental friendliness, and structural stability. Compared to single-reaction systems, which suffer from low grafting efficiency and insufficient product stability, this invention covalently bonds a quaternary phosphonium salt (tetrabutylphosphonium bromide) to the phenolic hydroxyl groups of tannic acid to form rigid, short-chain quaternary phosphonium groups, enhancing charge neutralization. Quaternary ammonium salts (dimethyldiallylammonium chloride) are then grafted onto the tannic acid via free radical polymerization to form flexible, long-chain "tentacle" structures. These structures provide adsorption charge neutralization, bridging, and hydrophobic association, enhancing sludge floc density. Consequently, the tentacle-type, dicationically modified tannin-based organic flocculant provided by this invention features a "rigid core-flexible tentacle" network, significantly improving the removal efficiency of algal cells and algal toxins through a multi-mechanism of "charge neutralization, bridging, and netting."

[0032] 2. The quaternary phosphonium and ammonium cations in this organic flocculant rapidly adsorb to negatively charged algal cell surfaces through ionic and hydrogen bonds, destabilizing cell membranes. The long chains of polymerized dimethyldiallylammonium chloride bind to the hydrophobic structures of algal toxins, such as microcystins, detoxifying them through hydrophobic interactions. The tentacle-like structure forms a three-dimensional network, enhancing the ability to encapsulate algal cell clusters and toxins, providing stable treatment for highly turbid and high-organic-matter water. Furthermore, the quaternary phosphonium and ammonium groups maintain high charge density in both acidic and alkaline conditions, expanding the flocculant's pH range to 2-10.

[0033] 3. Tannic acid, the primary raw material used in this invention, is a renewable resource, and its degradation products are non-toxic, thus avoiding secondary pollution. The flocculant has high biocompatibility, and sludge can be easily dehydrated and recycled. Furthermore, tannic acid, quaternary phosphonium salt monomers, and quaternary ammonium salt monomers are all commercially available, making costs manageable. The preparation process is simple, requiring no complex equipment, and the reaction conditions are mild, making it suitable for large-scale production. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0035] Figure 1 In a specific embodiment, OD 680 Standard curve for measuring the density of Microcystis aeruginosa.

[0036] Figure 2 This is a transmission electron microscope photograph of the tentacle-type dicationically modified tannin-based organic flocculant of Example 8.

[0037] Figure 3 This is the removal rate curve of algae cells at different addition amounts of the tentacle-type dicationically modified tannin-based organic flocculant of Example 8.

[0038] Figure 4 This is the removal rate curve of algal toxins at different dosages of the tentacle-type dicationically modified tannin-based organic flocculant of Example 8.

[0039] Figure 5 This is a scanning electron microscope photograph of flocs after coagulation using the tentacle-type dicationically modified tannin-based organic flocculant of Example 8. DETAILED DESCRIPTION

[0040] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0041] A method for preparing a tentacle-type dicationically modified tannin-based organic flocculant comprises the following steps:

[0042] (1) Add tetrabutylphosphonium bromide to an alkaline solution of tannic acid, react at 50-80°C for 2-4 hours, precipitate in an acetone solution, and remove the lower precipitate for washing;

[0043] (2) Disperse the precipitate in water, continuously introduce nitrogen, add the first free radical initiator at 50-80°C, then add the quaternary ammonium salt and the second free radical initiator, and react for 2-4 hours;

[0044] (3) Extract the precipitated product with a mixture of acetone and ethanol, filter and wash it, and obtain the product;

[0045] Wherein, the quaternary phosphonium salt is tetrabutylphosphine bromide, and the quaternary ammonium salt is dimethyldiallylammonium chloride.

[0046] As a preferred embodiment of the present invention, in step (1), the alkaline solution of tannic acid is prepared by dissolving tannic acid in a NaOH solution with a concentration of 0.1-0.5 mol / L. Tannic acid molecules contain a large number of phenolic hydroxyl groups (-OH). Under alkaline conditions, the hydroxide ions (OH⁻) provided by NaOH can promote the dissociation of phenolic hydroxyl groups into phenolic oxide anions (-O⁻). This ionized form significantly enhances the nucleophilicity of the phenolic hydroxyl groups, making them more susceptible to nucleophilic substitution reactions with the quaternary phosphonium salt groups in tetrabutylphosphonium bromide, thereby improving the grafting efficiency of the quaternary phosphonium salt groups. Controlling the NaOH concentration to 0.1-0.5 mol / L can ensure sufficient phenolic oxide anions while avoiding excessive alkalinity that may cause damage to the tannic acid structure, thereby balancing the reaction activity and product stability.

[0047] As a preferred embodiment of the present invention, in step (1), the lower precipitate is washed with ethanol and then with deionized water. Ethanol can effectively remove residual reaction impurities and acetone in the precipitate, and deionized water further removes ethanol and other water-soluble impurities, thereby improving product purity, ensuring the smooth progress of subsequent reactions, and preventing impurities from adversely affecting product performance.

[0048] As a preferred embodiment of the present invention, in step (1), the amount of tetrabutylphosphonium bromide added is 0.5-2 mol / mol, based on the amount of tannic acid. Within this addition amount range, an appropriate amount of tetrabutylphosphonium bromide can be fully covalently bonded to the phenolic hydroxyl groups of tannic acid to form a sufficient number of rigid short-chain quaternary phosphine groups. If the addition amount is too small, the number of quaternary phosphine groups is insufficient, and the charge neutralization ability is limited; if the addition amount is too large, it may result in a waste of raw materials and affect the structure and performance of the product.

[0049] As a preferred embodiment of the present invention, in step (2), the amount of the first free radical initiator added is 0.01-0.1 g / 5 g, based on the mass of tannic acid. This amount range can effectively initiate a free radical polymerization reaction, promoting the successful grafting of dimethyldiallylammonium chloride onto the tannic acid derivative. The amount of the second free radical initiator added is 0.01-0.1 g / 5 g, which can effectively initiate the chain growth process and form a flexible long-chain "tentacle" structure. If the amount added is too small, the initiation efficiency is low and the grafting reaction is incomplete; if the amount added is too large, the reaction is too intense, which may lead to uneven product molecular weight distribution and homopolymerization of organic monomers, affecting the performance of the flocculant.

[0050] As a preferred embodiment of the present invention, in step (2), the first free radical initiator is added and reacted for 20-40 minutes before adding dimethyldiallyl ammonium chloride and the second free radical initiator. This reaction time interval allows the first free radical initiator to fully initiate the active sites on the tannic acid derivative. When dimethyldiallyl ammonium chloride and the second free radical initiator are subsequently added, chain polymerization and chain growth reactions can be carried out more efficiently, ensuring the orderly construction of the flexible long chain "tentacle" structure and improving product quality.

[0051] As a preferred embodiment of the present invention, in step (2), the amount of dimethyldiallylammonium chloride added is 1-5 mol / mol, based on the amount of tannic acid. This amount ensures the formation of flexible long-chain "tentacles" of sufficient length and quantity, providing sufficient adsorption sites and bridging functions for the flocculant. If the amount added is too small, the "tentacle" structure is insufficient, and the adsorption and bridging effects are weak; if the amount added is too large, it may lead to side effects such as overly complex product structure, high homopolymer content, and long-chain agglomeration, affecting solubility and flocculation effect.

[0052] As a preferred embodiment of the present invention, in step (2), the precipitate is dispersed in water and heated to 50-80°C using a water bath. Water bath heating can heat the reaction system evenly, facilitates precise control of the reaction temperature at 50-80°C, provides a stable and suitable reaction environment for the free radical polymerization reaction, helps ensure reaction consistency and product stability, and improves product quality.

[0053] In a preferred embodiment of the present invention, the first free radical initiator is one of potassium persulfate, ammonium persulfate, and ceric ammonium nitrate; the second free radical initiator is one of potassium persulfate, ammonium persulfate, and ceric ammonium nitrate. These free radical initiators effectively decompose in the reaction system to generate free radicals, initiating the polymerization reaction of the tannic acid derivative and the quaternary ammonium salt. They are stable, have high initiation efficiency, and are compatible with other system components under the reaction conditions, helping to ensure the reliability of the preparation process and the stability of the product performance.

[0054] A tentacle-type dicationically modified tannin-based organic flocculant prepared by the above preparation method can be used for treating algae liquid, and the treatment work specifically refers to removing algae cells and / or algae toxins in the algae liquid.

[0055] Example 1 Coagulation efficiency of tentacle-type organic flocculants under different pH conditions

[0056] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6 Tetrabutylphosphonium bromide solution was added at a rate of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 70°C and the reaction was carried out for a total of 3 hours. After the reaction was completed, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed and washed with ethanol and then three times with deionized water.

[0057] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced. 0.03 g of potassium persulfate was added and the reaction was continued for 20 min. 1×10 -6 mol / s, dimethyldiallyl ammonium chloride solution was added. The amount of dimethyldiallyl ammonium chloride added was 2 mol / mol based on the amount of tannic acid. 0.03 g of potassium persulfate was added again, and the reaction was continued for 4 hours.

[0058] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type dicationically modified tannin-based organic flocculant.

[0059] According to the same preparation method, the concentration of the sodium hydroxide aqueous solution in step (1) was adjusted to 0.1 mol / L, 0.2 mol / L, 0.4 mol / L or 0.5 mol / L to obtain five groups of different tentacle-type dicationic modified tannin-based organic flocculants. Their treatment effects on algae liquid were compared to determine the optimal sodium hydroxide aqueous solution concentration in step (1). The specific method is as follows:

[0060] To 10 7 After adding 30 mg / L of tentacle-type organic flocculant to the 100 cell / mL Microcystis aeruginosa solution (pH = 8.5 ± 0.5), stir at 250 r / min for 1 min, then at 35 r / min for 15 min, and then settle for 30 min. After sedimentation, the supernatant was collected and the OD was measured using a UV spectrophotometer. 680 , through the standard curve (such as Figure 1 The algal cell concentration after treatment was calculated (as shown in Table 1), and the removal rate was then calculated. High-performance liquid chromatography-mass spectrometry was then used to determine the algal toxin content. The results are shown in Table 1.

[0061] Table 1 Coagulation effect of organic flocculants at different sodium hydroxide aqueous solution concentrations

[0062]

[0063] The results showed that when the concentration of the sodium hydroxide aqueous solution in step (1) was 0.3 mol / L, the coagulation effect of the finally prepared tentacle-type dicationically modified tannin-based organic flocculant was the best.

[0064] Example 2

[0065] On the basis of Example 1, the concentration of the sodium hydroxide aqueous solution in step (1) was selected to be 0.3 mol / L, and then the amount of tetrabutylphosphonium bromide added in step (1) was adjusted to prepare a tentacle-type dicationically modified tannin-based organic flocculant. The specific scheme is as follows:

[0066] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6 mol / s, adding a tetrabutylphosphonium bromide solution, wherein the amount of tetrabutylphosphonium bromide added is 0.5 mol / mol, 1 mol / mol, 1.5 mol / mol, or 2 mol / mol based on the amount of tannic acid, and controlling the reaction temperature at 70°C for a total of 3 hours. After the reaction is completed, the mixture is cooled to room temperature and precipitated in an acetone solution. The lower precipitate is removed and washed with ethanol and then washed three times with deionized water.

[0067] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced. 0.03 g of potassium persulfate was added and the reaction was continued for 20 min. 1×10 -6 mol / s, dimethyldiallyl ammonium chloride was added in an amount of 2 mol / mol based on the amount of tannic acid, and 0.03 g of potassium persulfate was added again, and the reaction was continued for 4 hours;

[0068] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type dicationically modified tannin-based organic flocculant.

[0069] The treatment effects of four different groups of tentacle-type dicationically modified tannin-based organic flocculants on algae liquid were compared to determine the optimal amount of tetrabutylphosphonium bromide added in step (1). The test method was the same as in Example 1. The results are shown in Table 2 below.

[0070] Table 2 Coagulation effect of organic flocculants at different addition amounts of tetrabutylphosphonium bromide

[0071]

[0072] The results show that when the amount of tetrabutylphosphonium bromide added in step (1) is 1 mol / mol based on the amount of tannic acid, the coagulation effect of the finally prepared tentacle-type dicationically modified tannin-based organic flocculant is the best.

[0073] Example 3

[0074] On the basis of Examples 1 and 2, the concentration of the sodium hydroxide aqueous solution in step (1) was selected to be 0.3 mol / L, the amount of tetrabutylphosphonium bromide added was selected to be 1 mol / mol tannic acid, and the reaction temperature in step (1) was adjusted to prepare a tentacle-type dicationically modified tannin-based organic flocculant. The specific scheme is as follows:

[0075] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6 mol / s, adding tetrabutylphosphonium bromide solution in an amount of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 50°C, 60°C, 70°C, or 80°C, and the reaction was carried out for a total of 3 hours. After the reaction, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed and washed with ethanol and then washed three times with deionized water.

[0076] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced. 0.03 g of potassium persulfate was added and the reaction was continued for 20 min. 1×10 -6 mol / s, dimethyldiallyl ammonium chloride was added in an amount of 2 mol / mol based on the amount of tannic acid, and 0.03 g of potassium persulfate was added again, and the reaction was continued for 4 hours;

[0077] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type quaternary phosphine-modified tannin-based organic flocculant.

[0078] The treatment effects of four different groups of tentacle-type dicationically modified tannin-based organic flocculants on algae liquid were compared to determine the optimal reaction temperature of step (1). The test method was the same as that of Example 1. The results are shown in Table 3 below.

[0079] Table 3 Coagulation effect of organic flocculants at different reaction temperatures

[0080]

[0081] The results show that when the reaction temperature of tannic acid and tetrabutylphosphonium bromide in step (1) is 70°C, the coagulation effect of the finally prepared tentacle-type dicationically modified tannin-based organic flocculant is the best.

[0082] Example 4

[0083] Based on Examples 1 to 3, the concentration of the sodium hydroxide aqueous solution in step (1) was selected to be 0.3 mol / L, the amount of tetrabutylphosphonium bromide added was selected to be 1 mol / mol tannic acid, and the reaction temperature was selected to be 70°C. Then, the types of the first free radical initiator and the second free radical initiator in step (2) were adjusted to prepare a tentacle-type dicationically modified tannin-based organic flocculant. The specific scheme is as follows:

[0084] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6 Tetrabutylphosphonium bromide solution was added at a rate of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 70°C and the reaction was carried out for a total of 3 hours. After the reaction was completed, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed and washed with ethanol and then three times with deionized water.

[0085] (2) The precipitate was dispersed in water and placed in a water bath at 70 °C. Nitrogen was continuously introduced. 0.03 g of the first free radical initiator was added and the reaction was continued for 20 min. 1×10 -6 mol / s, dimethyldiallyl ammonium chloride was added in an amount of 2 mol / mol based on the amount of tannic acid, and 0.03 g of the second free radical initiator was added again, and the reaction was continued for 4 hours;

[0086] The first free radical initiator and the second free radical initiator are both potassium persulfate, ammonium persulfate or ceric ammonium nitrate;

[0087] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type quaternary phosphine-modified tannin-based organic flocculant.

[0088] The treatment effects of three different groups of tentacle-type dicationically modified tannin-based organic flocculants on algae liquid were compared to determine the optimal reaction temperature of step (1). The test method was the same as that of Example 1. The results are shown in Table 4 below.

[0089] Table 4 Coagulation effect of organic flocculants under different free radical initiators

[0090]

[0091] The results show that when potassium persulfate is selected as the first free radical initiator and the second free radical initiator in step (2), the coagulation effect of the finally prepared tentacle-type dicationically modified tannin-based organic flocculant is the best.

[0092] Example 5

[0093] On the basis of Examples 1 to 4, the concentration of the sodium hydroxide aqueous solution in step (1) was selected to be 0.3 mol / L, the amount of tetrabutylphosphonium bromide added was 1 mol / mol tannic acid, the reaction temperature was 70°C, the first free radical initiator and the second free radical initiator in step (2) were potassium persulfate, and then the amount of dimethyldiallylammonium chloride added in step (2) was adjusted to prepare a tentacle-type dicationically modified tannin-based organic flocculant. The specific scheme is as follows:

[0094] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6 Tetrabutylphosphonium bromide solution was added at a rate of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 70°C and the reaction was carried out for a total of 3 hours. After the reaction was completed, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed and washed with ethanol and then three times with deionized water.

[0095] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced. 0.03 g of potassium persulfate was added and the reaction was continued for 20 min. 1×10 -6mol / s, adding dimethyldiallyl ammonium chloride solution, based on the amount of tannic acid, the amount of dimethyldiallyl ammonium chloride added is 1 mol / mol, 2 mol / mol, 3 mol / mol, 4 mol / mol or 5 mol / mol, and adding 0.03 g of potassium persulfate again, and continuing the reaction for 4 hours;

[0096] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type dicationically modified tannin-based organic flocculant.

[0097] The treatment effects of five different groups of tentacle-type dicationically modified tannin-based organic flocculants on algae liquid were compared to determine the optimal amount of dimethyldiallylammonium chloride added in step (2). The test method was the same as in Example 1. The results are shown in Table 5 below.

[0098] Table 5 Coagulation effect of organic flocculants at different addition amounts of dimethyldiallylammonium chloride

[0099]

[0100] The results show that when the amount of dimethyldiallylammonium chloride added in step (2) is 3 mol / mol based on the amount of tannic acid, the coagulation effect of the finally prepared tentacle-type dicationically modified tannin-based organic flocculant is the best.

[0101] Example 6

[0102] On the basis of Examples 1 to 5, the concentration of the sodium hydroxide aqueous solution in step (1) was selected to be 0.3 mol / L, the amount of tetrabutylphosphonium bromide added was 1 mol / mol tannic acid, the reaction temperature was 70°C, the first free radical initiator and the second free radical initiator in step (2) were potassium persulfate, and the amount of dimethyldiallylammonium chloride added was 3 mol / mol tannic acid. Then, the amount of the first free radical initiator added in step (2) was adjusted to prepare a tentacle-type dicationically modified tannin-based organic flocculant. The specific scheme is as follows:

[0103] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6 Tetrabutylphosphonium bromide solution was added at a rate of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 70°C and the reaction was carried out for a total of 3 hours. After the reaction was completed, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed and washed with ethanol and then three times with deionized water.

[0104] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced. 0.01 g, 0.03 g, 0.05 g, 0.07 g, and 0.1 g of potassium persulfate were added and the reaction was continued for 20 min. 1×10 -6 mol / s, dimethyldiallyl ammonium chloride solution was added. The amount of dimethyldiallyl ammonium chloride added was 3 mol / mol based on the amount of tannic acid. 0.03 g of potassium persulfate was added again, and the reaction was continued for 4 hours.

[0105] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type dicationically modified tannin-based organic flocculant.

[0106] The treatment effects of five different groups of tentacle-type dicationically modified tannin-based organic flocculants on algae liquid were compared to determine the optimal addition amount of the first free radical initiator in step (2). The test method was the same as in Example 1. The results are shown in Table 6 below.

[0107] Table 6 Coagulation effect of organic flocculants at different first radical initiator addition amounts

[0108]

[0109] The results showed that when the amount of the first free radical initiator added in step (2) was 0.03 g, the coagulation effect of the finally prepared tentacle-type dicationically modified tannin-based organic flocculant was the best.

[0110] Example 7

[0111] On the basis of Examples 1 to 6, the concentration of the sodium hydroxide aqueous solution in step (1) was selected to be 0.3 mol / L, the amount of tetrabutylphosphonium bromide added was 1 mol / mol tannic acid, the reaction temperature was 70°C, the first free radical initiator and the second free radical initiator in step (2) were potassium persulfate, the amount of dimethyldiallylammonium chloride added was 3 mol / mol tannic acid, and the mass ratio of the first free radical initiator to tannic acid was 0.03 g:5 g. Then, the amount of the second free radical initiator added in step (2) was adjusted to prepare a tentacle-type dicationically modified tannin-based organic flocculant. The specific scheme is as follows:

[0112] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6Tetrabutylphosphonium bromide solution was added at a rate of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 70°C and the reaction was carried out for a total of 3 hours. After the reaction was completed, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed and washed with ethanol and then three times with deionized water.

[0113] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced. 0.03 g of potassium persulfate was added and the reaction was continued for 20 min. 1×10 -6 mol / s, dimethyldiallyl ammonium chloride solution was added. The amount of dimethyldiallyl ammonium chloride added was 3 mol / mol based on the amount of tannic acid. Potassium persulfate was then added in 0.01 g, 0.03 g, 0.05 g, 0.07 g, and 0.1 g steps, and the reaction was continued for 4 hours.

[0114] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type quaternary phosphine-modified tannin-based organic flocculant.

[0115] The treatment effects of five different groups of tentacle-type dicationically modified tannin-based organic flocculants on algae liquid were compared to determine the optimal addition amount of the second free radical initiator in step (2). The test method was the same as in Example 1. The results are shown in Table 7 below.

[0116] Table 7 Coagulation effect of organic flocculants at different addition amounts of second free radical initiator

[0117]

[0118] The results showed that when the amount of the second free radical initiator added in step (2) was 0.03 g, the coagulation effect of the finally prepared tentacle-type dicationically modified tannin-based organic flocculant was the best.

[0119] Example 8

[0120] Based on Examples 1 to 7, the best method for preparing the tentacle-type dicationically modified tannin-based organic flocculant is as follows:

[0121] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6Tetrabutylphosphonium bromide solution was added at a rate of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 70°C and the reaction was carried out for a total of 3 hours. After the reaction was completed, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed and washed with ethanol and then three times with deionized water.

[0122] (2) The precipitate was dispersed in water and placed in a water bath at 70°C. Nitrogen was continuously introduced. 0.03 g of potassium persulfate was added and the reaction was continued for 20 min. 1×10 -6 mol / s, a predetermined mass of dimethyldiallyl ammonium chloride solution was added. The amount of dimethyldiallyl ammonium chloride added was 3 mol / mol based on the amount of tannic acid. 0.03 g of potassium persulfate was added again, and the reaction was continued for 4 hours.

[0123] (3) After the reaction is completed, the mixture is cooled to room temperature, and the precipitated product is extracted with a mixture of acetone and ethanol, filtered and washed to obtain a tentacle-type dicationically modified tannin-based organic flocculant.

[0124] Since the flocculant has good water solubility, it can rely on its high molecular structure to interact with pollutants and then destabilize and precipitate them. Therefore, the morphology of the tentacle-type quaternary phosphine-modified tannin-based organic flocculant in water was observed under a transmission electron microscope. Figure 2 As shown in the figure, the flocculant molecules have a long chain structure, and its chain structure is highly branched, presenting a tentacle-like structure. This molecular configuration can provide more adsorption sites, which is more conducive to contact and flocculation with pollutants.

[0125] The treatment effect of the algae solution by the dosage of the tentacle-type dicationically modified tannin-based organic flocculant was studied. The specific method is as follows:

[0126] To 10 7 After adding 5-30 mg / L of tentacle-type organic flocculant to the 100 cell / mL Microcystis aeruginosa solution, stir at 250 r / min for 1 min, then at 35 r / min for 15 min, and then settle for 30 min. After settling, take the supernatant and measure the OD value using a UV spectrophotometer. 680 The concentration of algal cells after treatment was calculated using the standard curve, and then the removal rate was calculated; and the content of algal toxins was detected using high performance liquid chromatography-mass spectrometry.

[0127] Figure 3 The removal rate of algae cells under different dosages is shown. The results show that when 20-30 mg / L flocculant is added, the removal rate of algae cells can reach more than 90%, especially when the dosage is above 25 mg / L, the removal rate can reach more than 95%, and the removal effect tends to be stable.

[0128] Figure 4 The removal rate of algal toxins at different dosages is shown. The results show that when 25-30 mg / L flocculant is added, the removal rate of algal toxins can basically reach more than 35%.

[0129] Figure 5 The flocs after coagulation were observed under a scanning electron microscope. It can be seen that the algae cells are basically intact, thus avoiding the release of a large amount of intracellular algal toxins.

[0130] Comparative Example 1

[0131] Comparative Example 1 provides a method for treating algae liquid using tannic acid alone, specifically, adding tannic acid in equal moles to 10 7 The cells / mL of Microcystis aeruginosa were stirred at 250 rpm for 1 minute, then at 35 rpm for 15 minutes, and then allowed to settle for 30 minutes. The supernatant was collected after sedimentation, and the algal cell removal efficiency was calculated to be 56.2% and the algal toxin removal efficiency was 0.9%.

[0132] Comparative Example 2

[0133] Comparative Example 2 provides a method for treating algae liquid using a modified tannin-based organic flocculant, wherein the preparation method of the modified tannin-based organic flocculant is as follows:

[0134] (1) Disperse 5 g of tannic acid in 170 mL of 0.3 mol / L sodium hydroxide aqueous solution and stir rapidly (200 rpm) at a temperature of 1 × 10 -6 mol / s, tetrabutylphosphonium bromide solution was added in an amount of 1 mol / mol based on the amount of tannic acid. The reaction temperature was controlled at 70°C and the reaction was carried out for a total of 3 hours. After the reaction was completed, the mixture was cooled to room temperature and precipitated in acetone solution. The lower precipitate was removed, washed with ethanol, and then washed three times with deionized water to obtain the product.

[0135] The modified tannin-based organic flocculant was added to the 10 7 The cells / mL of Microcystis aeruginosa were stirred at 250 rpm for 1 minute, then at 35 rpm for 15 minutes, and then allowed to settle for 30 minutes. The supernatant was collected after sedimentation, and the algal cell removal efficiency was calculated to be 49% and the algal toxin removal efficiency was 1.6%.

[0136] Comparative Example 3

[0137] (1) Disperse 5 g of tannic acid in water, place in a water bath, maintain the temperature at 70 °C, and continuously introduce nitrogen. Stir rapidly (200 rpm) at a rate of 1 × 10 -6 mol / s, dimethyldiallyl ammonium chloride solution was added in an amount of 2 mol / mol based on the amount of tannic acid, and then 0.03 g of potassium persulfate was added and the reaction was continued for 4 hours;

[0138] (2) After the reaction is completed, cool to room temperature, extract the precipitated product with a mixture of acetone and ethanol, filter and wash to obtain the product.

[0139] The modified tannin-based organic flocculant was added to the 10 7 The cells / mL of Microcystis aeruginosa solution was stirred at 250 rpm for 1 minute, then at 35 rpm for 15 minutes, and then allowed to settle for 30 minutes. The supernatant was collected after sedimentation, and the algal cell removal efficiency was calculated to be 62% and the algal toxin removal efficiency was 15.1%.

[0140] Although the present invention has been described in detail with reference to the accompanying drawings and in conjunction with preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, persons of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any changes or substitutions that can be easily conceived by persons skilled in the art within the technical scope disclosed in the present invention shall be within the scope of protection of the present invention.

Claims

1. A method for preparing a tentacle-type dicationically modified tannin-based organic flocculant, characterized in that: The steps include: (1) Add tetrabutylphosphonium bromide to an alkaline solution of tannic acid, react at 50-80°C for 2-4 hours, precipitate in an acetone solution, and remove the lower precipitate for washing; (2) Disperse the precipitate in water, continuously introduce nitrogen, add the first free radical initiator at 50-80°C, then add dimethyldiallylammonium chloride and the second free radical initiator, and react for 2-4 hours; (3) Extract the precipitated product with a mixture of acetone and ethanol, filter and wash.

2. The preparation method according to claim 1, wherein In step (1), the lower precipitate is washed with ethanol and then with deionized water.

3. The preparation method according to claim 1, wherein In step (1), the amount of tetrabutylphosphonium bromide added is 0.5-2 mol / mol based on the amount of tannic acid.

4. The preparation method according to claim 1, wherein In step (2), the amount of the first free radical initiator added is 0.01-0.1 g / 5 g based on the mass of tannic acid; Based on the mass of tannic acid, the added amount of the second free radical initiator is 0.01-0.1 g / 5 g.

5. The preparation method according to claim 1, wherein In step (2), after the first free radical initiator is added, the reaction is continued for 20-40 minutes before adding dimethyldiallylammonium chloride and the second free radical initiator.

6. The preparation method according to claim 1, wherein In step (2), the amount of dimethyldiallylammonium chloride added is 1-5 mol / mol based on the amount of tannic acid.

7. The preparation method according to claim 1, wherein In step (2), the precipitate is dispersed in water and heated to 50-80° C. in a water bath.

8. The preparation method according to claim 1, wherein The first free radical initiator is one of potassium persulfate, ammonium persulfate, and ceric ammonium nitrate; The second free radical initiator is one of potassium persulfate, ammonium persulfate, and ceric ammonium nitrate.

9. A tentacle-type dicationically modified tannin-based organic flocculant prepared by the preparation method according to any one of claims 1 to 8.

10. Use of the tentacle-type dicationically modified tannin-based organic flocculant according to claim 9 in treating algae liquid.

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