Choline ionic liquid modified soybean protein flocculant, and preparation method and application thereof

Abstract

The present application relates to the technical field of water treatment, and discloses a choline ionic liquid modified soybean protein flocculant, a preparation method and application thereof.The flocculant is prepared by grafting methacryloxyethyl choline chloride monomers onto a soybean protein skeleton under the initiation of an oxidation-reduction system.The flocculant has high charge neutralization capacity, excellent biodegradability and antibacterial activity, and is suitable for the purification treatment of domestic sewage, algae-containing wastewater and drinking water, and is eco-friendly.

Description

Technical Field

[0001] This invention belongs to the field of water treatment technology, specifically relating to a choline ion liquid modified soybean protein flocculant, its preparation method, and its application. Background Technology

[0002] With increasing global emphasis on green chemistry and ecological safety, the "detoxification" of water treatment agents has become a crucial issue in the environmental protection field. While current flocculation technologies can effectively remove suspended solids from water, commonly used polyacrylamide (PAM) flocculants are extremely difficult to degrade in nature, and the monomers produced during degradation have significant biotoxicity. Furthermore, although traditional quaternary ammonium salt-modified biomass flocculants improve charge neutralization capacity, the modifying agents used often pose certain environmental risks, and the treated water often fails to meet high standards for ecological reuse.

[0003] Soy protein isolate (SPI), a natural protein composed of 7S and 11S globulin subunits with complex conformations, exhibits excellent biodegradability. However, natural soy protein has a low charge density, resulting in insufficient flocculation efficiency in high-salinity or complex microbial environments. Ionic liquids, as a novel "designable" functional material, offer new insights into the modification of biomolecules due to their unique charge distribution and physicochemical properties. Choline-based ionic liquids, in particular, as functional monomers derived from natural nutrients, not only possess extremely high positive charge density but also exhibit excellent biocompatibility and antibacterial activity.

[0004] Current protein modification technologies largely rely on traditional chemical reagents, making it difficult to achieve a perfect balance between efficient flocculation and ecological safety. Therefore, exploring a preparation process that utilizes choline-based ionic liquids to modify soybean protein can not only significantly enhance the charge neutralization and bridging capabilities of soybean protein flocculants but also endow them with unique antibacterial properties and extremely low ecotoxicity. This has profound technological value for developing next-generation "zero-footprint" environmentally friendly water treatment agents and ensuring the recycling of high-quality water resources. Summary of the Invention

[0005] The purpose of this invention is to address the imbalance between flocculation efficiency and toxic residues in existing turbidity-reducing flocculants by providing a highly efficient, green, and multifunctional choline ionic liquid-modified soybean protein flocculant, along with its preparation method and application.

[0006] This invention provides a method for preparing a choline ionic liquid-modified soybean protein flocculant, comprising the following steps:

[0007] S1. Adjust the pH of the soy protein isolate aqueous solution to 8.5-10.5, stir at 40℃-50℃ and purge with nitrogen for at least 20 minutes to induce protein subunit unfolding.

[0008] S2. Under nitrogen protection, a redox initiator is added, followed by a solution of methacryloyloxyethylcholine chloride monomer to carry out a graft copolymerization reaction.

[0009] S3. Add buffer solution to adjust pH to 6.5-7.5, terminate the reaction, and let it stand at room temperature for 2-4 hours to age.

[0010] S4. The product is precipitated and washed with anhydrous ethanol and then freeze-dried to obtain the flocculant.

[0011] The present invention also provides a choline ionic liquid modified soybean protein flocculant, which comprises a soybean protein backbone and methacryloyloxyethylcholine groups grafted thereon, and has a cationic charge center, biodegradability and antibacterial activity.

[0012] When the above-mentioned flocculant can be used for decolorization of domestic sewage, treatment of algae-containing wastewater, restoration of landscape water or pretreatment of drinking water, the dosage of the flocculant is 5 mg / L-25 mg / L.

[0013] The beneficial effects of this invention are as follows:

[0014] (1) Ecological safety and environmental protection are achieved. The choline-based ionic liquid selected in this invention is derived from natural nutrient groups. The modified flocculant is not only completely degradable, but its degradation products are also harmless to the environment. Its ecotoxicity is far lower than that of traditional polyacrylamide and quaternary ammonium salt flocculants, making it suitable for scenarios with stringent safety requirements, such as drinking water pretreatment and landscape water restoration.

[0015] (2) It endows the flocculant with unique antibacterial function. Choline-based ionic liquids have a certain penetrating and destructive effect on the cell membranes of bacteria and algae. While removing suspended solids in water, it can effectively avoid the problem of microbial growth in the treated water during storage or reuse, and significantly reduce the subsequent disinfection cost of the system.

[0016] (3) Conformational stability and wide pH applicability. Due to the special solvation effect of ionic liquids, the grafted protein molecular chains can remain in an extended state under different salt concentrations and pH (5.0-10.0) environments, avoiding the decrease in flocculation effect caused by the coiling and inactivation of natural proteins under specific environments. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort, wherein:

[0018] Figure 1This is a schematic flowchart illustrating the preparation method of the choline ionic liquid modified soybean protein flocculant provided by the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0020] The terms "first," "second," etc., used in the specification and claims of this invention are used to distinguish similar objects and not to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that embodiments of the invention can be implemented in orders other than those illustrated or described herein, and the objects distinguished by "first," "second," etc., are generally of the same class and the number of objects is not limited; for example, a first object can be one or more. Furthermore, in the specification and claims, "and / or" indicates at least one of the connected objects, and the character " / " generally indicates that the preceding and following objects are in an "or" relationship.

[0021] Please see Figure 1 As shown in the figure, this invention provides a method for preparing a choline ionic liquid modified soybean protein flocculant, comprising the following steps:

[0022] S1. Adjust the pH of the soy protein isolate aqueous solution to 8.5-10.5, stir at 40℃-50℃ and purge with nitrogen for at least 20 minutes to induce protein subunit unfolding.

[0023] S2. Under nitrogen protection, a redox initiator is added to the system obtained in step S1, followed by the addition of a solution of methacryloyloxyethylcholine chloride monomer to carry out a graft copolymerization reaction.

[0024] S3. Add buffer solution to the reaction system obtained in step S2 to adjust the pH to 6.5-7.5. After terminating the reaction, let it stand at room temperature for 2-4 hours to age.

[0025] S4. The product aged in step S3 is precipitated and washed with anhydrous ethanol, and then freeze-dried to obtain the choline ion liquid modified soybean protein flocculant.

[0026] In step S1, the mass concentration of the soy protein isolate aqueous solution is 30 g / L-45 g / L.

[0027] Adjust the pH using one or more of sodium hydroxide, potassium hydroxide, or sodium carbonate.

[0028] In step S2, the mass ratio of the soy protein isolate to the methacryloyloxyethylcholine chloride monomer is 1:(0.5-1.5).

[0029] The redox initiator is composed of potassium persulfate and sodium bisulfite, and its total addition amount is 1%-3% of the soybean protein isolate. The graft copolymerization reaction is carried out at 45℃-55℃ for 4-5 hours.

[0030] In step S3, the buffer solution is a sodium bicarbonate solution.

[0031] In step S4, the freeze drying is carried out at a temperature of -50°C or below, and the drying time is not less than 24 hours.

[0032] This invention also provides a choline ionic liquid modified soybean protein flocculant, prepared by the aforementioned method, which is obtained by graft copolymerization of soybean protein isolate and methacryloyloxyethylcholine chloride monomer; the flocculant has cationic charge centers, biodegradability and antibacterial activity.

[0033] This invention also provides an application of choline ion liquid modified soybean protein flocculant in water treatment, wherein the water treatment includes decolorization of domestic sewage, treatment of algae-containing wastewater, restoration of landscape water or removal of microorganisms in drinking water pretreatment.

[0034] It should be further noted that when used for decolorizing domestic sewage or treating algae-containing wastewater, the dosage of the flocculant is 5 mg / L-25 mg / L.

[0035] The present invention will be further described below with reference to embodiments, but these are not intended to limit the scope of the invention.

[0036] Example 1: Preparation of choline ionic liquid modified soybean protein flocculant

[0037] S1 (Protein Activation and Unfolding): Weigh 30g of soy protein isolate (SPI) and dissolve it in 1L of deionized water to prepare a suspension with a mass concentration of 30 g / L. Adjust the pH to 9.8 with 1.0 mol / L NaOH solution. Place the system in a 45℃ water bath, stir at 250 rpm, and purge with nitrogen for 25 minutes to remove oxygen. This step, under alkaline conditions (pH 8.5-10.5) and gentle heating (40℃-50℃), effectively induces the unfolding of globulin subunits, exposing more active sites and creating conditions for subsequent grafting reactions.

[0038] S2 (Graft Copolymerization): Under nitrogen protection, first add 0.3 g of potassium persulfate and 0.15 g of sodium bisulfite as redox initiators (total addition is 1.5% of the SPI mass). Then, add 20 g of a 50% (w / w) solution of methacryloyloxyethylcholine chloride ([ChMA]Cl) dropwise over 20 minutes (SPI to monomer mass ratio is 1:1). Raise the reaction temperature to 55°C and stir continuously for 5 hours. Using the potassium persulfate / sodium bisulfite redox initiation system can efficiently initiate free radical polymerization at 45°C-55°C, ensuring effective grafting of the monomer onto the protein backbone. Controlling the monomer drop rate and reaction time helps to obtain products with uniform grafting ratio and stable structure.

[0039] S3 (Termination of Reaction and Aging): After the reaction is complete, add sodium bicarbonate buffer solution to adjust the pH to 7.0. Stop heating and allow to age at room temperature for 3 hours. Neutralizing with a weakly alkaline buffer solution can smoothly terminate the reaction and prevent localized over-acidity from damaging the product structure. Aging at room temperature for 2-4 hours helps the modified protein molecular chains re-establish a stable conformational equilibrium, improving their adaptability in different water qualities.

[0040] S4 (Purification and Drying): The reaction solution was poured into 4 times its volume of anhydrous ethanol, resulting in a white flocculent precipitate. After multiple ethanol washes, the precipitate was placed in a freeze dryer and freeze-dried at -50°C for 36 hours. The resulting powdered product, designated SPI-IL-1, was then ground. Ethanol precipitation effectively removes unreacted monomers and initiator residues. Freeze-drying at -50°C or below for at least 24 hours maximizes the preservation of the product's porous structure and surface activity, yielding a powdered flocculant that is easy to store and use.

[0041] Example 2: Product Performance Verification

[0042] The SPI-IL-1 obtained in Example 1 was prepared into a 1% aqueous solution.

[0043] Antibacterial performance test: Following GB / T 20944, tests were conducted against *Escherichia coli* and *Staphylococcus aureus*. Results showed that the inhibition rate against both pathogens was ≥98.5%. This indicates that the grafted methacryloyloxyethylcholine group endows the flocculant with significant antibacterial activity, simultaneously inhibiting microbial growth during wastewater treatment and reducing subsequent disinfection costs.

[0044] Biodegradability evaluation: The OECD 301B closed-circuit breather method was used for testing. SPI-IL-1 achieved a biodegradability rate of 82.5% within 28 days, meeting the "easily biodegradable" standard. This demonstrates that the flocculant of this invention is derived from natural sources, is environmentally degradable, and has a far higher ecological safety than traditional synthetic flocculants that are difficult to degrade.

[0045] Application Example: Effluent from the primary sedimentation tank of a domestic wastewater treatment plant was treated with 15 mg / L SPI-IL-1 for flocculation. Results showed a turbidity removal rate of 98.4%, a COD removal rate of 76.2%, and rapid floc formation (<30s). This demonstrates that the flocculant possesses extremely high charge neutralization and bridging capabilities, enabling rapid and effective removal of colloids and suspended solids from water, making it suitable for the efficient purification of domestic wastewater.

[0046] Comparative Example: SPI was modified using a conventional quaternary ammonium salt monomer (2,3-epoxypropyltrimethylammonium chloride, GTA) under the same conditions. The resulting product exhibited a turbidity removal rate of 92.5%, an antibacterial rate of only 45.0%, a 28-day biodegradation rate of only 58%, and some aquatic toxicity. This comparison highlights the advantages of this invention, which utilizes a specific choline-based ionic liquid monomer, achieving a significant improvement in antibacterial properties and ecological safety while maintaining efficient flocculation.

[0047] The above description is merely a preferred embodiment of the present invention, and the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a choline ionic liquid-modified soybean protein flocculant, characterized in that, Includes the following steps: S1. Adjust the pH of the soy protein isolate aqueous solution to 8.5-10.5, stir at 40℃-50℃ and purge with nitrogen for at least 20 minutes to induce protein subunit unfolding. S2. Under nitrogen protection, a redox initiator is added to the system obtained in step S1, followed by the addition of a solution of methacryloyloxyethylcholine chloride monomer to carry out a graft copolymerization reaction. S3. Add buffer solution to the reaction system obtained in step S2 to adjust the pH to 6.5-7.

5. After terminating the reaction, let it stand at room temperature for 2-4 hours to age. S4. The product aged in step S3 is precipitated and washed with anhydrous ethanol, and then freeze-dried to obtain the choline ion liquid modified soybean protein flocculant.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass concentration of the soy protein isolate aqueous solution is 30 g / L-45 g / L.

3. The preparation method according to claim 1, characterized in that, In step S1, the pH is adjusted using one or more of sodium hydroxide, potassium hydroxide, or sodium carbonate.

4. The preparation method according to claim 1, characterized in that, In step S2, the mass ratio of the soy protein isolate to the methacryloyloxyethylcholine chloride monomer is 1:(0.5-1.5).

5. The preparation method according to claim 1 or 4, characterized in that, In step S2, the redox initiator is composed of potassium persulfate and sodium bisulfite, and its total addition amount is 1%-3% of the soybean protein isolate. The graft copolymerization reaction is carried out at 45℃-55℃ for 4-5 hours.

6. The preparation method according to claim 1, characterized in that, In step S3, the buffer solution is a sodium bicarbonate solution.

7. The preparation method according to claim 1, characterized in that, In step S4, the freeze drying is carried out at a temperature of -50°C or below, and the drying time is not less than 24 hours.

8. A choline ionic liquid modified soybean protein flocculant, characterized in that, The flocculant prepared by any one of claims 1 to 7 has cationic charge centers, biodegradability, and antibacterial activity.

9. The application of the choline ionic liquid modified soybean protein flocculant as described in claim 8 in water treatment, characterized in that, The water treatment includes decolorization of domestic sewage, treatment of algae-containing wastewater, restoration of landscape water, or removal of microorganisms in drinking water pretreatment.

10. The application according to claim 9, characterized in that, When used for decolorizing domestic sewage, treating algae-containing wastewater, restoring landscape water, or pretreating drinking water, the dosage of the flocculant is 5 mg / L-25 mg / L.

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