A method for preparing natural flocculant using biogas residue

Abstract

This invention relates to a method for preparing natural flocculants from biogas residue. It involves constructing an ionic liquid-water supramolecular solvent by combining an ionic liquid with water as a green solvent. This improves both kinetic and thermodynamic properties, enhancing the extraction rate of active ingredients and enabling the simultaneous extraction of multipolar, multi-component groups from biogas residue. The supramolecular building blocks formed by the combination of the ionic liquid and active ingredients undergo macroscopic assembly under the induction of an electric field, ultimately yielding an extract with excellent flocculation performance. The advantages of this invention include: no need for high pressure or chemical modification; simplicity and environmental friendliness, reducing flocculant production costs; minimal environmental impact from chemical reagents; efficient dissolution of multiple active ingredients in biogas residue by the ionic liquid; and the ability to further assemble the dissolved active ingredients into larger molecules by applying an electric field to the ionic liquid, increasing the charge quantity of the product and thus avoiding the need for chemical modification.

Description

Technical Field

[0001] The invention relates to a method for preparing a natural flocculant by utilizing biogas residue, and belongs to the technical field of water treatment. Background Art

[0002] Organic polymer flocculants offer the advantages of high flocculation efficiency, rapid flocculation, low dosage, minimal impact on water salts and pH, and low sludge generation. However, existing technologies for synthesizing organic polymer flocculants generally require the use of large amounts of chemical reagents, which is not only costly but also potentially has significant environmental impacts. With the increasing emphasis on environmental protection in national policies, the production of chemical products is facing increasing restrictions. Therefore, the development of effective natural polymer flocculants is an inevitable trend.

[0003] Treating organic solid waste through anaerobic digestion can reduce carbon emissions by approximately 5.5 billion tons of CO2 per year, but this results in the production of large amounts of biogas residue, which is viscous and expensive to process, putting a certain amount of pressure on the environment. Biogas residue contains a large amount of undigested lignin, as well as a variety of macromolecular organic matter such as humus, tannins, polysaccharides, and proteins. These natural polymers can be used as natural polymer flocculants after chemical modification to increase their molecular weight, charge properties, and active groups. In the prior art, there is no method for preparing flocculants using organic matter in biogas residue without chemical modification.

[0004] Extraction technology directly impacts the type and quantity of active ingredients obtained. However, some substances with relatively large molecular weights and high cohesive energy have very limited solubility in water and alcohol, thus affecting subsequent flocculation. Ionic liquids have excellent solubility for components such as lignin, tannins, and polysaccharides, but they have high viscosity and are therefore expensive.

[0005] CN106241998A discloses a method for preparing a natural composite flocculant using traditional Chinese medicine residues, which requires high-pressure aeration treatment of the residues and consumes a lot of energy. Summary of the Invention

[0006] The present invention proposes a method for preparing a natural flocculant using biogas residue, which aims to overcome the above-mentioned shortcomings of the existing technology and achieve green and safe preparation of the natural flocculant without high pressure and chemical modification.

[0007] The technical solution of this invention involves combining ionic liquids with the green solvent water to form an ionic liquid-water supramolecular solvent. This improves both kinetic performance (reducing system viscosity) and thermodynamic properties (enhancing solubility and self-assembly), increasing the extraction rate of active ingredients and enabling the simultaneous extraction of multipolar, multi-component populations from biogas residue. Furthermore, the supramolecular building blocks formed by the combination of the ionic liquid and the active ingredients undergo macroscopic assembly under the induction of electric field forces, ultimately yielding an extract with excellent flocculation properties.

[0008] Specifically, a method for preparing a natural flocculant using biogas residue comprises:

[0009] 1) adding cysteine ​​to a 0.3 mol / L dilute nitric acid solution at a mass ratio of 1:1, and stirring for 48 hours to obtain an aqueous solution of ionic liquid cysteine ​​nitrate;

[0010] 2) Concentrating by rotary evaporation to concentrate the cysteine ​​nitrate aqueous solution to 2.4 mol / L;

[0011] 3) Grinding the dried biogas residue into powder and adding concentrated cysteine ​​nitrate aqueous solution;

[0012] 4) Place the mixture in a sealed container and heat to 105°C for 4 hours;

[0013] 5) After cooling, place the sample in a sealed container with two electrodes, one gold and one platinum. Use a function generator to generate an alternating electric field, which is then amplified by a DC power amplifier. The field strength is in the range of 40-50V and the square wave frequency is 500Hz. Apply power for 1 hour.

[0014] 6) Add 4 times the volume of anhydrous ethanol to the mixture in the sealed container and stir until precipitation is complete;

[0015] 7) Wash and dry the precipitate to obtain the finished natural flocculant.

[0016] The advantages of the present invention are: 1) the main raw material is solid waste biogas residue, no high pressure or chemical modification is required, the preparation method is simple and green, and the production cost of the flocculant is reduced;

[0017] 2) The chemical reagents for extracting the active ingredients only require amino acids and dilute nitric acid, which has little impact on the environment;

[0018] 3) The ionic liquid generated by amino acids and dilute nitric acid can efficiently dissolve various effective components in biogas residue, such as lignin, tannins, and polysaccharides;

[0019] 4) Ionic liquids have good electrical conductivity. Applying an electric field in their aqueous solution can further assemble the dissolved active ingredients to form larger molecules. Moreover, the residual ionic liquid in the product carries an electric charge, which increases the charge quantity of the product, thereby avoiding chemical modification and eliminating the need for a variety of environmentally harmful chemical reagents. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a schematic diagram of the structure of an embodiment of the device of the present invention that utilizes electric field force to induce macroscopic assembly of building blocks.

[0021] Figure 2 It is the infrared spectrum of the natural flocculant of the present invention.

[0022] Figure 3 Schematic diagram of the relationship between the addition amount and the removal rate of the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0023] The present invention will be further described in detail below with reference to examples and specific implementation methods.

[0024] Example 1

[0025] A method for preparing a natural flocculant using biogas residue comprises the following steps:

[0026] 1) adding cysteine ​​to a 0.3 mol / L dilute nitric acid solution at a mass ratio of 1:1, and stirring for 48 hours to obtain an aqueous solution of ionic liquid cysteine ​​nitrate;

[0027] 2) Concentrating by rotary evaporation to concentrate the cysteine ​​nitrate aqueous solution to 2.4 mol / L;

[0028] 3) Grinding the dried biogas residue into powder, and adding the concentrated cysteine ​​nitrate aqueous solution obtained in step 2);

[0029] 4) placing the mixture obtained in step 3) in a sealed container and heating to 105° C. for 4 h;

[0030] 5) After cooling, place the sample in a sealed container containing two electrodes, one gold and one platinum. Use a Wavetek 180 function generator to generate an alternating electric field, which is then amplified by a Hewlett-Packard 6824A DC power amplifier. The field strength is in the range of 40-50 V and the square wave frequency is 500 Hz. Apply power for 1 hour.

[0031] 6) Add 4 times the volume of anhydrous ethanol to the mixture in the sealed container and stir until precipitation is complete;

[0032] 7) Wash and dry the precipitate to obtain the finished natural flocculant.

[0033] like Figure 3 As shown, the prepared natural flocculant was used to treat 50 mg / L Congo red wastewater. When the flocculant was dissolved in a NaOH solution with a pH of 10 and the flocculant dosage was 1 g / L, the removal rate was the highest, which was 88%.

[0034] Comparative Example 2

[0035] A method for preparing a natural flocculant using biogas residue is the same as that of Example 1, except that in step 3), the concentrated cysteine ​​nitrate aqueous solution obtained in step 2) is first treated with a 2 mol / L NaOH solution before being added.

[0036] like Figure 3 As shown, the prepared natural flocculant was used to treat 50 mg / L Congo red wastewater. When the flocculant was dissolved in a NaOH solution with a pH of 10 and the flocculant dosage was 1 g / L, the removal rate was lower than that of Example 1, only 45%. To achieve a removal rate similar to that of Example 1, the dosage must reach 11 g / L.

[0037] Comparative Example 3

[0038] A method for preparing a natural flocculant using biogas residue is the same as that of Example 1, except that the cysteine ​​nitrate aqueous solution is replaced by a glycine chloride aqueous solution prepared using glycine and hydrochloric acid.

[0039] like Figure 3 As shown, the prepared natural flocculant was used to treat 50 mg / L Congo red wastewater. When the flocculant was dissolved in a NaOH solution with a pH of 10 and the flocculant dosage was 1 g / L, the removal rate was lower than that of Example 1, only 35%, and increasing the dosage could not achieve a removal rate similar to that of Example 1.

[0040] Comparative Example 4

[0041] A method for preparing a natural flocculant using biogas residue is the same as that in Example 1, except that step 5) is not performed.

[0042] like Figure 3 As shown, the prepared natural flocculant was used to treat 50 mg / L Congo red wastewater. When the flocculant was dissolved in a NaOH solution with a pH of 10 and the flocculant dosage was 1 g / L, the removal rate was lower than that of Example 1, only 25%, and increasing the dosage could not achieve a removal rate similar to that of Example 1.

[0043] The above description is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this field, several variations and improvements can be made without departing from the creative concept of the present invention, which all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a natural flocculant using biogas residue, characterized in that: The process steps include: 1) Add amino acids in a 0.3 mol / L dilute nitric acid solution at a mass ratio of 1:1, and stir for 48 hours to obtain an aqueous solution of ionic liquid nitrate amino acids; 2) Rotary evaporation concentration to concentrate the nitric acid and amino acid aqueous solution to 2.4 mol / L; 3) Grinding the dried biogas residue into powder, and adding the concentrated nitric acid and amino acid aqueous solution obtained in step 2); 4) placing the mixture obtained in step 3) in a sealed container, heating to 105°C, and maintaining for 4 hours; 5) After cooling, it is placed in a sealed container with two electrodes, one gold and the other platinum. An alternating electric field is generated by a wave function generator, and then amplified by a DC power amplifier. The field strength range is 40-50V / m, the square wave frequency is 500Hz, and the power is turned on for 1 hour; 6) Add 4 times the volume of anhydrous ethanol in the sealed container and stir until the precipitation is complete; 7) Wash and dry the precipitate to obtain the finished natural flocculant.

2. A method for preparing a natural flocculant using biogas residue according to claim 1, characterized in that: The amino acid is cysteine.

3. A flocculant, characterized in that , obtained by the method for preparing natural flocculant using biogas residue as described in claim 1 or 2.

4. The method for using a flocculant as claimed in claim 3, characterized in that: Dissolve the flocculant in NaOH solution with a pH of 10. When the Congo red wastewater is N mg / L, the dosage is 20N mg / L.

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