CN114906914A - Environment-friendly plant tannin-based flocculant and preparation method thereof - Google Patents

Abstract

The invention provides an environment-friendly plant tannin-based flocculant and a preparation method thereof. The method does not relate to the use of formaldehyde, has the advantages of environmental friendliness and low cost, and the obtained flocculating agent has a good flocculating effect, can remove a large amount of pollutants such as suspended matters and the like, quickly purifies the water body, and remarkably improves the water quality of the water body.

Description

Environmentally friendly plant tannin-based flocculant and preparation method thereof

technical field

The invention relates to the technical field of flocculants, in particular to an environment-friendly plant tannin-based flocculant and a preparation method thereof.

Background technique

The flocculation precipitation method, which is an important part of water treatment engineering, depends largely on the performance of the flocculant, but the traditional flocculants commonly used at present have different advantages and disadvantages.

Inorganic flocculants (such as ferric sulfate, aluminum sulfate, zinc sulfate, alum, etc.) have the characteristics of good flocculation effect and low price, but the residual inorganic metal ions in water will lead to secondary pollution. Among them, the iron salt flocculant should affect the color of the effluent, and the aluminum remaining in the aluminum salt flocculant will cause certain harm to the human body.

Compared with inorganic flocculants, organic polymer flocculants have excellent properties such as less dosage, wide application range, less influence by salts and environmental conditions, less sludge volume, and better treatment effect. Synthetic organic macromolecular flocculants have the advantages of small dosage, strong flocculation ability, fast flocculation speed, and small amount of sludge generated. However, the residual monomer content in the final product limits its development in food processing and water treatment.

Natural organic polymers are chemically modified flocculants. Compared with synthetic organic polymer flocculants, they have the advantages of wide source of raw materials, low cost, non-toxicity, easy biodegradation, and multifunctional flocculants. outstanding features. Plant tannins, also known as plant polyphenols, are secondary metabolites of complex phenols in plants. Plant tannins are abundant in nature and mainly exist in the bark, roots, leaves and pulp of plants, and are second only to fiber. It is the fourth largest forest by-product of lignin, lignin and hemicellulose. Naturally extracted plant tannins have a low isoelectric point (pHpzc = 2.0 to 3.0), while pollutants produced by natural water bodies and human activities are usually negatively charged, so plant tannins generally need to be cationized. Used as a flocculant.

At present, the mainstream modification method at home and abroad is to introduce amino groups into the plant tannin structure to increase its isoelectric point. The Mannich reaction can increase the isoelectric point of plant tannins to 7.0 to 8.0, but this reaction involves the addition of nitrogenous compounds and formaldehyde, and the use of formaldehyde will increase the cost of flocculants on the one hand, and on the other hand, residual in the final product. Formaldehyde can cause damage to the environment, as well as a risk to human health.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a preparation method of an environment-friendly plant tannin-based flocculant in view of the deficiencies of the prior art, which does not involve the use of formaldehyde, has the advantages of being environmentally friendly and low in cost, and the obtained flocculant flocculates Works well.

According to the first aspect of the object of the present invention, a preparation method of an environmentally friendly plant tannin-based flocculant is provided, wherein plant tannin and hexamethylene tetramine are placed under alkaline conditions to react, The tetramine is decomposed to generate an intermediate aminoimine group, and the tannin molecule with a nucleophilic reaction site is specifically combined with the aminoimine group, thereby increasing the isoelectric point of the flocculant, and obtaining the plant tannin-based flocculant.

Preferably, the following specific steps are included:

S1, the aqueous solution of plant tannin is heated in a water bath, and the aqueous solution of plant tannin is continuously stirred and nitrogen is passed through, after the temperature of the aqueous solution of plant tannin reaches the first temperature interval, the pH value of the aqueous solution of plant tannin is adjusted to alkali to obtain the first solution;

S2, keep the temperature of the first solution in the first temperature range, and keep stirring the first solution and pass nitrogen gas, under this condition, dropwise add hexamethylenetetramine solution to the first solution, add dropwise After completion, continue to stir and pass nitrogen until the reaction is completed to obtain the second solution;

S3, drying the pH value of the second solution to acidity to obtain the environment-friendly plant tannin-based flocculant.

Preferably, in the aqueous solution of plant tannin, the mass ratio of plant tannin to deionized water is 1:(5-10).

Preferably, the first temperature range is 80°C to 90°C, and the nitrogen flow rate is 3 to 5 mL/min.

Preferably, sodium hydroxide solution is used to adjust the pH value of the aqueous solution of plant tannin to 10-11.

Preferably, the concentration of the hexamethylenetetramine solution is 0.1 mol/L, and the volume ratio of the aqueous solution of vegetable tannin to the hexamethylenetetramine solution is (2-10):1.

Preferably, the dropping rate of the hexamethylenetetramine solution is 2˜8 mL/min.

Preferably, the pH value of the second solution is adjusted to 2-3 by using a hydrochloric acid solution, and then vacuum dried at a drying temperature of 40°C to 60°C.

Preferably, the plant tannin is black wattle tannin.

According to the second aspect of the object of the present invention, an environment-friendly plant tannin-based flocculant is provided, which is prepared by the above-mentioned preparation method of the environment-friendly plant tannin-based flocculant.

Compared with the prior art, the beneficial effects of the present invention are:

1, the preparation method of the environment-friendly plant tannin-based flocculant of the present invention, the plant tannin and hexamethylene tetramine are placed under alkaline conditions, and the hexamethylene tetramine can be decomposed to produce amino groups in an alkaline solution It is an intermediate of imine group, which has high activity and is easy to react, and has a large number of nucleophilic sites on the tannin molecule, which can react with the aminoimine group to form a benzylamine bond on the tannin molecule.

When the pH of the reaction solution is greater than 10, not only the A ring of the tannin molecule can react, but the B ring will also participate in the reaction to form more benzylamine bonds, which can effectively increase the isoelectric point of the product, thereby improving the use of flocculants and negatively charged pollutants. The obtained flocculant has good flocculation effect, can remove a large amount of pollutants such as suspended solids, quickly purify the water body, significantly improve the water quality, and can be widely used in the flocculation and sedimentation of sewage treatment.

2. The preparation method of the environment-friendly plant tannin-based flocculant of the present invention has the advantages of simple preparation process, easy operation, no participation of formaldehyde in the whole preparation process, environmental friendliness, low cost, and is suitable for industrial production and application.

Description of drawings

Fig. 1 is the reaction schematic diagram of the preparation method of the environment-friendly plant tannin-based flocculant of the present invention.

2 is a ZETA potential diagram of the black wattle tannin and cationic black wattle tannin flocculants in Example 1.

3 is an FTIR chart of the black wattle tannin and cationic black wattle tannin flocculants in Example 1.

Detailed ways

In order to better understand the technical content of the present invention, specific embodiments are given and described below in conjunction with the accompanying drawings.

Aspects of the invention are described in this disclosure with reference to the accompanying drawings, in which a number of illustrative embodiments are shown. Embodiments of the present disclosure are not necessarily intended to include all aspects of the invention. It should be understood that the various concepts and embodiments presented above, as well as those concepts and implementations described in greater detail below, can be implemented in any of numerous ways.

Aiming at the situation that the Mannich reaction requires the participation of formaldehyde, the invention provides a preparation method of an environment-friendly plant tannin-based flocculant, which utilizes plant tannin and hexamethylenetetramine to prepare a cationic flocculant to replace the Mannich reaction method to produce tannin-based flocculants.

1, in an exemplary embodiment of the present invention, a preparation method of an environmentally friendly plant tannin-based flocculant is provided, wherein plant tannin and hexamethylenetetramine are placed under alkaline conditions to react, and the When hexamethylenetetramine is decomposed to generate an intermediate aminoimine group (Fig. 1A), the tannin molecule with nucleophilic reaction site specifically binds to the aminoimine group (Fig. 1B), thereby improving the flocculant's performance isoelectric point to obtain the plant tannin-based flocculant

In a preferred embodiment, the following specific steps are included:

S1, the aqueous solution of plant tannin is heated in a water bath, and the aqueous solution of plant tannin is continuously stirred and nitrogen is passed through, after the temperature of the aqueous solution of plant tannin reaches the first temperature interval, the pH value of the aqueous solution of plant tannin is adjusted to alkali to obtain the first solution;

S2, keep the temperature of the first solution in the first temperature range, and keep stirring the first solution and pass nitrogen gas, under this condition, dropwise add hexamethylenetetramine solution to the first solution, add dropwise After completion, continue to stir and pass nitrogen until the reaction is completed to obtain the second solution;

S3, drying the pH value of the second solution to acidity to obtain the environment-friendly plant tannin-based flocculant.

In a more preferred embodiment, in the aqueous solution of plant tannin, the mass ratio of plant tannin to deionized water is 1:(5-10).

In a more preferred embodiment, the first temperature range is 80°C to 90°C, and the nitrogen flow rate is 3 to 5 mL/min.

In a more preferred embodiment, sodium hydroxide solution is used to adjust the pH value of the aqueous solution of plant tannin to 10-11.

In a more preferred embodiment, the concentration of the hexamethylenetetramine solution is 0.1 mol/L, and the volume ratio of the aqueous solution of vegetable tannin to the hexamethylenetetramine solution is (2-10):1 .

In a more preferred embodiment, the dropping rate of the hexamethylenetetramine solution is 2˜8 mL/min.

In a more preferred embodiment, a 1 mol/L hydrochloric acid solution is used to adjust the pH value of the second solution to 2-3, and then vacuum drying is performed at a drying temperature of 40°C to 60°C.

In a more preferred embodiment, the step S3 further includes:

First, ethanol or acetone is added to the second solution for dehydration and embrittlement to obtain a third solution, followed by drying to obtain a solid, and the solid is pulverized and ground to obtain the plant tannin-based flocculant.

It should be understood that adding ethanol and acetone for dehydration and embrittlement is a commonly used technical means in the field, the amount of ethanol and acetone can be added according to actual needs, and the amount will not affect the final effect; and after adding ethanol and acetone, it can be placed For a period of time, it can also be dried directly without placing it, which does not affect the final effect.

In a more preferred embodiment, the plant tannin is black wattle tannin.

In another preferred embodiment, in the step S2, the second solution is obtained by reacting for 1-4 hours.

In another exemplary embodiment of the present invention, an environment-friendly plant tannin-based flocculant is provided, which is prepared by the aforementioned method for preparing an environment-friendly plant tannin-based flocculant.

The isoelectric point of the obtained flocculant can be increased from about 2 of natural tannin to about 5, and the flocculation effect is good.

For better understanding, the present invention is further described below with reference to several specific examples, but the processing technology is not limited thereto, and the content of the present invention is not limited thereto.

[Example 1]

At room temperature, 10 g of black wattle tannin was dissolved in 50 mL of deionized water with magnetic stirring for 20 minutes to obtain an aqueous black wattle tannin solution.

The black wattle tannin aqueous solution was transferred to a three-necked flask, heated to 80° C. in a water bath, stirred and passed through nitrogen, and the pH was adjusted to 10 with sodium hydroxide solution.

5mL of hexamethylenetetramine solution (0.1M) was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 4mL/min. After the dropwise addition, the reaction was continued for 3h with stirring and nitrogen flow.

After the reaction, 1 mol/L hydrochloric acid solution was used to adjust the pH value of the above solution to 2, dried to constant weight in a 60°C vacuum drying oven, pulverized and milled to obtain a novel plant tannin-based flocculant.

Under the dosage of 120mg/L, the removal rate of the flocculant to 1g/L kaolin suspension liquid reached 97.18%, and the settling time was 1h.

[Example 2]

At room temperature, 10 g of black wattle tannin was dissolved in 100 mL of deionized water with magnetic stirring for 20 minutes to obtain an aqueous black wattle tannin solution.

The black wattle tannin aqueous solution was transferred to a three-necked flask, heated to 90° C. in a water bath, stirred and passed through nitrogen, and the pH was adjusted to 10.4 with sodium hydroxide solution.

10 mL of hexamethylenetetramine solution (0.1 M) was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 8 mL/min. After the dropwise addition, the reaction was continued for 1 h with stirring and nitrogen flow.

After the reaction, the product is dehydrated and embrittled by adding ethanol or acetone, dried in a vacuum drying oven at 60°C to constant weight, pulverized and ground to obtain a new type of plant tannin-based flocculant.

Under the dosage of 125mg/L, the removal rate of the flocculant to 1g/L kaolin suspension liquid reached 99.22%, and the settling time was 1.5h.

[Example 3]

At room temperature, 10 g of black wattle tannin was dissolved in 50 mL of deionized water with magnetic stirring for 20 minutes to obtain an aqueous black wattle tannin solution.

The black wattle tannin aqueous solution was transferred to a three-necked flask, heated to 80° C. in a water bath, stirred and passed through nitrogen, and the pH was adjusted to 10.8 with sodium hydroxide solution.

15mL of hexamethylenetetramine solution (0.1M) was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 6mL/min. After the dropwise addition, the reaction was continued for 4h with stirring and nitrogen flow.

After the reaction, 1 mol/L hydrochloric acid solution was used to adjust the pH value of the above solution to 2, dried to constant weight in a 40° C. vacuum drying oven, pulverized and milled to obtain a novel plant tannin-based flocculant.

Under the dosage of 25mg/L, the removal rate of the flocculant to 1g/L kaolin suspension liquid reached 97.04%, and the settling time was 1h.

[Example 4]

At room temperature, 10 g of black wattle tannin was dissolved in 100 mL of deionized water with magnetic stirring for 20 minutes to obtain an aqueous black wattle tannin solution.

The black wattle tannin aqueous solution was transferred to a three-necked flask, heated to 90° C. in a water bath, stirred and passed through nitrogen, and the pH was adjusted to 11 with sodium hydroxide solution.

20 mL of hexamethylenetetramine solution (0.1 M) was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 2 mL/min. After the dropwise addition, the reaction was continued for 4 h with stirring and nitrogen flow.

After the reaction, 1 mol/L hydrochloric acid solution was used to adjust the pH value of the above solution to 2, dried to constant weight in a 50°C vacuum drying oven, pulverized and milled to obtain a novel plant tannin-based flocculant.

Under the dosage of 130mg/L, the removal rate of the flocculant to 1g/L kaolin suspension liquid reaches 98%, and the settling time is 1.5h.

[Example 5]

At room temperature, 10 g of black wattle tannin was dissolved in 50 mL of deionized water with magnetic stirring for 20 minutes to obtain an aqueous black wattle tannin solution.

The black wattle tannin aqueous solution was transferred to a three-necked flask, heated to 90° C. in a water bath, stirred and passed through nitrogen, and the pH was adjusted to 11 with sodium hydroxide solution.

25mL of hexamethylenetetramine solution (0.1M) was slowly added dropwise through a constant pressure dropping funnel at a dropping rate of 4mL/min. After the dropwise addition, the reaction was continued for 3h with stirring and nitrogen flow.

After the reaction, the product is dehydrated and embrittled by adding ethanol or acetone, dried in a vacuum drying oven at 60°C to constant weight, pulverized and ground to obtain a new type of plant tannin-based flocculant.

Under the dosage of 135mg/L, the removal rate of the flocculant to 1g/L kaolin suspension liquid reached 79.35%, and the settling time was 1.5h.

Potential test

Potential test was performed on the flocculant obtained in Example 1, and the results are shown in Figure 2.

It can be seen from Figure 2 that the isoelectric point of the unmodified black wattle tannin is 2, and the isoelectric point of the modified black wattle tannin is increased to about 5, which significantly improves the isoelectric point of the flocculant. Therefore, , the flocculant can efficiently combine with negatively charged pollutants through electrostatic attraction.

Infrared test

An infrared test was performed on the flocculant obtained in Example 1, and the results are shown in Figure 3.

The characteristic peaks of black wattle tannins can be seen from Fig. 3: the broad peak at 3415 cm ^-1 is attributed to the stretching vibration of -OH; the peaks appearing at 1620 and 1507 cm ^-1 are aromatic C=C bond elongation Characteristics. These characteristic peaks also appear in the spectrum of cationic black wattle tannins with slight wavenumber changes. The spectrum of cationic black wattle tannins showed two new peaks at 3222 and 1402 cm ^-1 , corresponding to the stretching of -NH-, which indicated that the aminoimine group was successfully combined with black wattle tannins.

Combined with the above test, it can be seen that the flocculant obtained by the preparation method of the plant tannin-based flocculant of the present invention effectively increases the isoelectric point of the flocculant through the reaction, thereby improving the electrostatic binding capacity of the flocculant and the negatively charged pollutants, and can To achieve the purpose of removing a large amount of pollutants such as suspended solids, quickly purifying the water body, and significantly improving the water quality. Under the condition of low dosage and short settling time, the removal rate of kaolin is very high, up to 99.22%.

In addition, the flocculant has a simple preparation process, is easy to operate, no formaldehyde is involved in the whole preparation process, is environmentally friendly, has low cost, and is suitable for industrial production and application.

Although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Those skilled in the art to which the present invention pertains can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention should be determined according to the claims.

Claims (10)

1. The preparation method of the environment-friendly plant tannin-based flocculant is characterized in that plant tannin and hexamethylenetetramine are placed under alkaline conditions to react, at the moment, hexamethylenetetramine is decomposed to generate an intermediate aminoimine group, and tannin molecules with nucleophilic reaction sites are specifically combined with the aminoimine group, so that the isoelectric point of the flocculant is improved, and the plant tannin-based flocculant is obtained.

2. The method for preparing the environment-friendly plant tannin-based flocculant according to claim 1, characterized by comprising the following specific steps:

s1, heating the aqueous solution of the plant tannin in a water bath, continuously stirring the aqueous solution of the plant tannin, introducing nitrogen, and adjusting the pH value of the aqueous solution of the plant tannin to be alkaline after the temperature of the aqueous solution of the plant tannin reaches a first temperature interval to obtain a first solution;

s2, keeping the temperature of the first solution in a first temperature interval, keeping stirring and nitrogen introduction of the first solution continuously, dropwise adding a hexamethylenetetramine solution into the first solution under the condition, and after dropwise adding, continuously stirring and introducing nitrogen until the reaction is finished to obtain a second solution;

and S3, drying the second solution after the pH value of the second solution is acidic to obtain the environment-friendly plant tannin-based flocculant.

3. The preparation method of the environment-friendly plant tannin-based flocculant according to claim 2, wherein the mass ratio of the plant tannin to the deionized water in the aqueous solution of the plant tannin is 1 (5-10).

4. The preparation method of the environment-friendly plant tannin based flocculant according to claim 2, wherein the first temperature interval is 80-90 ℃ and the nitrogen flow is 3-5 mL/min.

5. The method for preparing the environment-friendly plant tannin-based flocculant according to claim 2, wherein a sodium hydroxide solution is adopted to adjust the pH value of an aqueous solution of the plant tannin to 10-11.

6. The preparation method of the environment-friendly plant tannin-based flocculant according to claim 2, wherein the concentration of the hexamethylenetetramine solution is 0.1mol/L, and the volume ratio of the plant tannin aqueous solution to the hexamethylenetetramine solution is (2-10): 1.

7. The preparation method of the environment-friendly plant tannin-based flocculant according to claim 2, wherein the dropping rate of the hexamethylenetetramine solution is 2-8 mL/min.

8. The method for preparing the environment-friendly plant tannin based flocculant according to claim 2, wherein the pH value of the second solution is adjusted to 2-3 by hydrochloric acid solution, and then vacuum drying is carried out at 40-60 ℃.

9. The method for preparing environment-friendly plant tannin-based flocculant according to any one of claims 1 to 8, wherein the plant tannin is black wattle tannin.

10. An environment-friendly plant tannin-based flocculant, which is characterized by being prepared by the preparation method of the environment-friendly plant tannin-based flocculant according to any one of claims 1 to 10.

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