Cationic lignin-based flocculant and preparation method thereof

Abstract

The present invention relates to a cationic lignin-based flocculant and a preparation method thereof. The preparation method comprises two steps, the first step of which is to react lignin with formaldehyde, paraformaldehyde and concentrated hydrochloric acid in dioxane to obtain chloromethylated lignin; the second step of which is to react chloromethylated lignin with potassium iodide and hexamethylenetetramine in ethanol to prepare a cationic lignin-based flocculant. The present invention utilizes Blanc reaction to introduce chloromethyl groups on the benzene ring of lignin. The activity of benzyl chloride is very high. It can not only be converted into active groups such as cyano, carboxyl and amine groups to increase active adsorption points, but also can cross-link lignin molecules through Friedel-Crafts reaction to increase the molecular weight of lignin. The lignin used in the present invention is derived from papermaking black liquor, and the prepared cationic lignin-based flocculant has a good flocculation effect on a variety of pigment solutions, and has the dual significance of reducing papermaking black liquor pollution and effectively utilizing resources.

Description

Technical field:

[0001] The invention relates to a cationic lignin-based flocculant and a preparation method thereof, and belongs to the technical field of functional material science. Background technology:

[0002] In the plant kingdom, lignin is the second most abundant natural polymer after cellulose, but lignin has a complex molecular structure and is a polymer with a three-dimensional network structure. It is also one of the most difficult natural polymers to understand and utilize. Papermaking wastewater in my country accounts for 30% of the country's industrial wastewater, and lignin is the main pollutant in papermaking wastewater.

[0003] Lignin contains three basic structural units: guaiacylphenylpropane (G), syringylphenylpropane (S) and p-hydroxyphenylpropane (H). They form a three-dimensional network structure through various connection methods and irregular coupling. Generally, the lignin obtained from pulp and paper waste liquid contains several to dozens of phenylpropane structural units. This kind of lignin is generally chemically stable and has low activity. It is difficult to use if it is not treated. The usual treatment method is to modify the lignin to increase its reactivity.

[0004] Flocculation technology is one of the important methods for treating wastewater. As a natural polymer flocculant, lignin has the unique properties of high efficiency and non-toxicity. However, the average molecular weight of lignin is low and the number of active adsorption points is small, which directly affects its flocculation performance. Cross-linking reaction, condensation reaction, graft copolymerization and other methods are usually used to change the spatial configuration of lignin, increase its molecular weight, and introduce functional groups with flocculation properties to improve the flocculation performance of lignin. Summary of the invention:

[0005] The present invention provides a method for preparing a cationic lignin-based flocculant;

[0006] Another object of the present invention is to provide a product prepared by the above preparation method.

[0007] The lignin benzene ring structure contains alkyl, alkoxy, hydroxyl and other donor groups, which are very active. The present invention uses the Blanc reaction to introduce the active group chloromethyl on the lignin benzene ring, which further reacts with hexamethylenetetramine to obtain a lignin-based quaternary ammonium salt. The purpose of the present invention is to provide a method for preparing a cationic lignin-based flocculant, and the specific preparation steps are as follows:

[0008] (1) dissolving a certain amount of lignin in an appropriate amount of dioxane to prepare a solution, adding paraformaldehyde, formaldehyde and concentrated hydrochloric acid in sequence at room temperature, the mass ratio of lignin, formaldehyde and paraformaldehyde being (0.5-4):1:(1-8), stirring and refluxing for 4-8 hours, distilling under reduced pressure, washing the product with ethanol and water in sequence, and freeze-drying to obtain chloromethylated lignin;

[0009] (2) Dissolve a certain amount of chloromethyl lignin and potassium iodide in an appropriate amount of ethanol, heat to 30-60°C, stir for 30 min-2 h, and add dropwise an ethanol solution of hexamethylenetetramine under stirring. The mass ratio of chloromethyl lignin, potassium iodide and hexamethylenetetramine is (0.5-4):1:(1-8). Maintain the temperature at 30-60°C. After the addition is complete, continue the reaction at 30-60°C for 6-10 h, cool and filter, wash the precipitate with ethanol and water, and freeze-dry to obtain a cationic lignin-based flocculant.

[0010] The present invention also provides a cationic lignin-based flocculant, which is prepared according to the above method.

[0011] Beneficial effects of the present invention:

[0012] 1) The present invention utilizes the Blanc reaction to introduce chloromethyl groups on the benzene ring of lignin. Benzyl chloride is highly active and can not only be converted into active groups such as cyano, carboxyl, and amine through nucleophilic substitution reactions to achieve modification of lignin and increase active adsorption points, but can also cross-link lignin molecules through Friedel-Crafts reactions to increase the molecular weight of lignin;

[0013] 2) The cationic lignin-based flocculant prepared by the present invention has a good flocculation effect on pigment solutions such as methylene blue, ethyl violet, and fuchsin, and the removal rate can reach more than 85%, and has a good application prospect in dye wastewater treatment;

[0014] 3) The lignin used in the present invention is derived from papermaking black liquor, with low production cost, and the product can be completely biodegraded without causing environmental pollution. Therefore, the promotion and application of cationic lignin-based flocculants have the dual significance of reducing papermaking black liquor pollution and effectively utilizing resources. Specific implementation method:

[0015] In order to better understand the content of the present invention, the technical solution of the present invention is further illustrated by several specific embodiments below.

[0016] Example 1

[0017] Add 2g lignin and 30mL dioxane to a three-necked round-bottom flask equipped with a reflux condenser, stir thoroughly to dissolve, add 4.5g paraformaldehyde, 1.5mL formaldehyde, and 60mL concentrated hydrochloric acid to the solution at room temperature, heat and reflux for 5h, evaporate the solvent under reduced pressure, wash the solid with ethanol and water 2 to 3 times each, freeze-dry, and obtain brown powder chloromethylated lignin. The IR spectrum of lignin extracted from papermaking black liquor (see Appendix) Figure 1 ) and SEM images (attached Figure 2 ) compared with the IR spectrum at 835 cm -1 The stretching vibration absorption peak of C-Cl bond appears near Figure 3), SEM images show that its surface morphology has changed significantly (Appendix Figure 4 ).

[0018] Add 5g of chloromethylated lignin, 2.5g of potassium iodide and 100mL of ethanol to a three-necked round-bottom flask equipped with a reflux condenser, a constant pressure funnel and a thermometer, heat to 40°C and stir for 1h. Transfer 5g of the ethanol solution of hexamethylenetetramine to a constant pressure funnel and slowly drip it into the three-necked flask while stirring and maintaining the temperature at 40°C. After the addition is complete, continue the reaction at 40°C for 8h. Cool and filter, wash the precipitate with ethanol and water 2 to 3 times each, and freeze-dry to obtain a black powder cationic lignin-based flocculant, whose IR spectrum shows at 1450cm -1 The characteristic absorption peak of quaternary ammonium salt appears near Figure 5 ), SEM images show that its surface morphology has changed significantly (Appendix Figure 6 ).

[0019] Example 2

[0020] Dilute 20 mg / L methylene blue solution to 1 mg / L, 2 mg / L, 4 mg / L, 6 mg / L, and 8 mg / L, respectively, measure the absorbance at 667 nm with a UV-visible spectrophotometer, and draw a standard curve.

[0021] Take 50 mL of 20 mg / L methylene blue solution and place it in a beaker, add 200 mg of the cationic lignin-based flocculant prepared in Example 1 to the solution, stir at room temperature for 5 minutes, let it stand for 24 hours, and then measure the absorbance of the supernatant with a UV-visible spectrophotometer, and calculate the concentration of the methylene blue solution. The results show that the methylene blue removal rate is 96.75%.

[0022] Example 3

[0023] Dilute 20 mg / L ethyl violet solution to 2 mg / L, 4 mg / L, 6 mg / L, 8 mg / L, and 10 mg / L, respectively, measure the absorbance at 596 nm with a UV-visible spectrophotometer, and draw a standard curve.

[0024] 20 mL of 20 mg / L ethyl violet solution was placed in a 100 mL beaker, and a certain amount of the cationic lignin-based flocculant prepared in Example 1 was added respectively, and the pH of the solution was adjusted to 9, and the mixture was stirred at 35°C for 40 min. After the reaction was completely cooled, the mixture was centrifuged for 5 min, and the absorbance of the supernatant was measured by a UV-visible spectrophotometer, and the concentration of the ethyl violet solution was calculated. The results are listed in the table below. When the amount of the cationic lignin-based flocculant used was 300 mg / L, the removal rate of ethyl violet could reach 92.98%.

[0025] Cationic lignin-based flocculant concentration (mg / L) 100 200 300 400 500 Ethyl violet removal rate (%) 57.96 78.09 92.98 90.65 85.47

[0026] Example 4

[0027] Dilute 20 mg / L fuchsin solution to 1 mg / L, 2 mg / L, 4 mg / L, 6 mg / L, and 8 mg / L, respectively, measure the absorbance at 542 nm with a UV-visible spectrophotometer, and draw a standard curve.

[0028] Take 20 mL of 20 mg / L fuchsin solution and place it in a 100 mL beaker, add 20 mg of the cationic lignin-based flocculant prepared in Example 1 to the solution, adjust the solution pH to 9, stir at 150 r / min for 1 h at 35°C, and then quickly take it out. After the reaction liquid is completely cooled, centrifuge it at 10000 r / min for 5 min, and then use a UV-visible spectrophotometer to measure the absorbance of the supernatant, calculate the concentration of the fuchsin solution, and the results show that the fuchsin removal rate is 86.03%. Description of the drawings:

[0029] Attached Figure 1 This is the IR spectrum of lignin extracted from papermaking black liquor;

[0030] Attached Figure 2 This is a SEM image of lignin extracted from papermaking black liquor;

[0031] Attached Figure 3 is the IR spectrum of chloromethylated lignin;

[0032] Attached Figure 4 is the SEM image of chloromethylated lignin;

[0033] Attached Figure 5 It is the IR spectrum of cationic lignin-based flocculant;

[0034] Attached Figure 6 is the SEM image of the cationic lignin-based flocculant.

Claims

1. A method for preparing a cationic lignin-based flocculant, the method comprising the following steps: (1) dissolving a certain amount of lignin in an appropriate amount of dioxane to prepare a solution, adding paraformaldehyde, formaldehyde and concentrated hydrochloric acid in sequence at room temperature, the mass ratio of lignin, formaldehyde and paraformaldehyde being (0.5-4):1:(1-8), stirring and refluxing for 4-8 hours, distilling under reduced pressure, washing the product with ethanol and water in sequence, and freeze-drying to obtain chloromethylated lignin; (2) Dissolve a certain amount of chloromethyl lignin and potassium iodide in an appropriate amount of ethanol, heat to 30-60°C, and stir for 30 min-2 h; add dropwise an ethanol solution of hexamethylenetetramine under stirring, wherein the mass ratio of chloromethyl lignin, potassium iodide and hexamethylenetetramine is (0.5-4):1:(1-8), and maintain the temperature at 30-60°C. After the addition is complete, continue the reaction at 30-60°C for 6-10 h, cool and filter, wash the precipitate with ethanol and water, and freeze-dry to obtain a cationic lignin-based flocculant.

2. A cationic lignin-based flocculant, characterized in that: Prepared according to the method of claim 1.

3. The use of the cationic lignin-based flocculant in the field of sewage treatment as claimed in claim 2, characterized in that: The sewage is sewage from the printing and dyeing industry.

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