Preparation method of cationic starch flocculant

Abstract

The invention discloses a preparation method of a cationic starch flocculant. The preparation method comprises the following steps: (1) carrying out oxidation pretreatment on starch; (2) activating the pretreated starch by using a strong alkali solution; and (3) cationizing the activated starch by using a cationic monomer to obtain the final product cationic starch flocculant. The preparation method disclosed by the invention is a low-temperature reaction process, the energy consumption is low, the obtained starch flocculant is well dispersed in high-turbidity wastewater, the flocculation efficiency can be effectively improved, and the starch flocculant is biodegradable and free of secondary pollution.

Description

Technical Field

[0001] The invention belongs to the technical field of sewage treatment, and in particular relates to a method for preparing a cationic starch flocculant. Background Art

[0002] In recent decades, with the progress of science and technology, natural polymers can be modified by different technologies to replace artificial synthetic polymers for wastewater treatment. Compared with synthetic polymers, natural polymers have the advantages of being cheap, environmentally friendly, renewable and degradable, and can be used to treat sludge and wastewater. In recent years, starch has been given functional groups through chemical modification, and various starch-based water purification materials have been widely used in wastewater treatment. Starches modified by different functional groups have different purification properties. Compared with other types of starch-based materials, cationic starch has better purification performance and is biodegradable in the natural environment. The most commonly used cationic monomers are reagents containing ammonium, amino or imine groups and quaternary amine groups, which are usually used to prepare cationic flocculants with high charge density. Chinese patent CN113121742A discloses a method for preparing a flocculant composed of corn starch or potato starch cross-linked with different amino groups in an aqueous phase and an oil phase. The flocculant has a high degree of substitution. Although it can be used as a flocculant for turbid wastewater treatment, the amount of reagent used is large and the cost is high. Therefore, it is necessary to seek a new flocculant preparation method which has a simple preparation method, low energy consumption in the preparation process and can obtain a high-purity naturally degradable flocculant. Summary of the invention

[0003] The purpose of the present invention is to provide a method for preparing a cationic starch flocculant to solve the problems existing in the prior art mentioned above.

[0004] In order to achieve the purpose of the invention, the present invention adopts the following technical solution: A method for preparing a cationic starch flocculant comprises the following steps: Step 100: Starch oxidation pretreatment: at a certain temperature, iodate solution is used as an oxidant and is mixed with the dried starch in a certain proportion, and the pH is adjusted, and the reaction is continuously stirred, and the precipitate obtained by precipitation is washed with anhydrous ethanol and then freeze-dried; Step 200 activates the pretreated starch: the dried precipitate obtained in step 100 is dissolved in ultrapure water, and then the pH is adjusted with a strong alkaline solution, and the reaction is carried out at a certain temperature for a period of time to activate the functional groups on the starch, thereby obtaining an activated mixed solution; Step 300 is to pre-treat the cationization of starch: a small amount of anhydrous ethanol and a cationic monomer solution are slowly added to the mixed solution activated in step 200 and mixed evenly, reacted at a certain temperature for a period of time, and the mixed solution after the reaction is dried to obtain a cationic starch flocculant.

[0005] Preferably, the starch described in step 100 is soluble starch.

[0006] Preferably, the oxidant in step 100 is one or more of sodium periodate and sodium iodate.

[0007] Preferably, the molar concentration of the iodate solution in step 100 is 0.05-0.2 M, and the weight ratio of the iodate solution to the dried starch is in the range of 5:1-30:1.

[0008] Preferably, the temperature in step 100 is 20-40° C. and the pH is 2-5.

[0009] Preferably, the reaction time in step 100 is 1-4 h.

[0010] Preferably, the strong alkaline solution in step 200 is one or more of sodium hydroxide or potassium hydroxide.

[0011] Preferably, the pH range of step 200 is 8-12.

[0012] Preferably, the reaction time in step 200 is 0.5-3 h and the temperature is 30-60°C.

[0013] Preferably, the cationic monomer in step 300 is a quaternary ammonium salt, specifically one or more of 2,3-epoxypropyltrimethylammonium chloride and 3-chloro-2-hydroxypropyltrimethylammonium chloride, and the molar concentration of the cationic monomer solution is 1-7 M.

[0014] Preferably, the volume ratio of the anhydrous ethanol in step 300 to the mixed solution in step (2) is 1:1-3:1, and the volume ratio of the cationic monomer solution to the mixed solution in step (2) is 1:1-2:1.

[0015] Preferably, the reaction temperature in step 300 is 30-50° C., and the reaction time is 2-6 h.

[0016] Preferably, the drying temperature in step 300 is 40-70°C.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The method for preparing the cationic starch flocculant of the present invention has low temperature, small amount of solvent used, and low amount of by-products generated during the flocculant preparation process; (2) The preparation method of the cationic starch flocculant of the present invention has a simple preparation process, low resource consumption and is environmentally friendly; (3) The cationic starch flocculant prepared by the present invention has good dispersion effect and high flocculation ability; (4) The cationic starch flocculant prepared by the present invention has a high charge density, a small amount of flocculant, a good flocculation effect, and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Electron microscope image of the flocculant prepared in Example 1 DETAILED DESCRIPTION

[0019] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the accompanying drawings. The following content is only an example and explanation of the concept of the present invention. The technicians in the field may make various modifications or supplements to the specific implementation cases described, or replace them with similar methods, as long as they do not deviate from the concept of the invention or exceed the scope defined by the claims, they should all fall within the scope of protection of the present invention. Example

[0020] A method for preparing a cationic starch flocculant comprises the following preparation steps: (1) Starch oxidation pretreatment: 5 g of soluble starch was added to 100 ml of 0.05 M sodium periodate solution at 25 °C, the pH was adjusted to 4, and the mixture was stirred for 2 hours. After precipitation, the precipitate was washed with anhydrous ethanol and freeze-dried in a vacuum dryer to obtain dialdehyde starch. (2) Activation of pretreated starch: The dried precipitate obtained in step (1) was dissolved in 10 mL of ultrapure water, the pH was adjusted to 11 using 5% sodium hydroxide solution, and stirred at 40° C. for 1 hour. (3) Cationization of pretreated starch: 2.3517 g of 2,3-epoxypropyltrimethylammonium chloride (EPTAC) was dissolved in 10 mL of pure water. 20 mL of anhydrous ethanol and 10 mL of this solution were slowly added to the mixed solution after activation in step (2). The mixture was stirred at 40°C for 3 hours and dried at 60°C for 6 hours to obtain a cationic starch flocculant with a degree of substitution of 0.102.

Claims

1. A method for preparing a cationic starch flocculant, characterized in that Follow these steps: (1) Starch oxidation pretreatment: at a certain temperature, iodate solution is used as an oxidant and mixed with the dried starch in a certain proportion, the pH is adjusted, and the reaction is stirred continuously, followed by precipitation. The obtained precipitate is washed with anhydrous ethanol and freeze-dried; (2) Activating the pretreated starch: dissolving the dried precipitate obtained in step (1) with ultrapure water, then adjusting the pH with a strong alkaline solution, and reacting at a certain temperature for a period of time to activate the functional groups on the starch, thereby obtaining an activated mixed solution; (3) Cationization of pretreated starch: slowly add a small amount of anhydrous ethanol and cationic monomer solution to the mixed solution after activation in step (2) and mix them evenly, react at a certain temperature for a period of time, and dry the mixed solution after the reaction to obtain a cationic starch flocculant.

2. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The starch described in step (1) is soluble starch.

3. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The oxidant in step (1) is one or more of sodium periodate and sodium iodate.

4. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The molar concentration of the iodate solution in step (1) is 0.05-0.2 M, and the weight ratio of the iodate solution to the dried starch is in the range of 5:1-30:

1.

5. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The temperature in step (1) is 20-40° C. and the pH is 2-5.

6. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The reaction time in step (1) is 1-4 h.

7. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The strong alkaline solution described in step (2) is one or more of sodium hydroxide or potassium hydroxide.

8. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The pH range described in step (2) is 8-12.

9. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The reaction time in step (2) is 0.5-3 h, and the temperature is 30-60°C.

10. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The cationic monomer described in step (3) is a quaternary ammonium salt, specifically one or more of 2,3-epoxypropyltrimethylammonium chloride and 3-chloro-2-hydroxypropyltrimethylammonium chloride, and the molar concentration of the cationic monomer solution is 1-7 M.

11. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The volume ratio of the anhydrous ethanol in step (3) to the mixed solution in step (2) is 1:1-3:1, and the volume ratio of the cationic monomer solution to the mixed solution in step (2) is 1:1-2:

1.

12. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The reaction temperature in step (3) is 30-50°C and the reaction time is 2-6 h.

13. The method for preparing a cationic starch flocculant according to claim 1, characterized in that: The drying temperature in step (3) is 40-70°C.

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