Preparation method and application of cassava starch flocculant
By modifying, cross-linking, and grafting cassava starch, a highly efficient and non-toxic cassava starch flocculant was prepared, solving the problems of metal residue and stability of existing flocculants in wastewater treatment, and achieving efficient lead ion removal and flocculation effects.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- GUILIN UNIVERSITY OF TECHNOLOGY
- Filing Date
- 2026-03-30
- Publication Date
- 2026-05-12
AI Technical Summary
Existing flocculants have problems in wastewater treatment, such as high metal residue, limited applicability, non-biodegradable and toxic synthetic polymer flocculants, and insoluble and unstable natural polymer flocculants in cold water.
A cassava starch flocculant with high flocculation performance was prepared by using cassava starch as raw material, modifying it with NaCl and NaOH solutions, crosslinking it with epichlorohydrin, and then grafting it with acrylamide and sodium bisulfite.
The prepared cassava starch flocculant has a lead ion removal rate of over 90%, high flocculation rate, monomer conversion rate and grafting rate, and is non-toxic and environmentally friendly.
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Figure CN122011283A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of water treatment flocculant technology, specifically to a method for preparing and applying a cassava starch flocculant. Background Technology
[0002] Water treatment is a core component of environmental protection. Flocculation is a simple and cost-effective method, making it one of the most commonly used technologies in water treatment. Flocculants, as the core functional material of this technology, directly determine the water treatment effect. Flocculants are substances that adsorb dispersed particles in water and promote their coagulation and sedimentation for separation and removal. Based on their chemical composition, they can be divided into inorganic flocculants and organic flocculants.
[0003] Inorganic flocculants are readily available, simple to prepare, and inexpensive. They are highly adaptable to water treatment with various complex compositions and can effectively remove fine suspended particles. However, their large dosage in wastewater treatment may lead to excessively high residual metal concentrations in the water, thus limiting their applicability. Organic flocculants, on the other hand, have advantages such as high efficiency, low sludge production, fast flocculation speed, and minimal impact from environmental conditions, and are therefore widely used.
[0004] Organic flocculants can be divided into two main categories: synthetic polymeric flocculants and natural polymeric flocculants. Synthetic polymeric flocculants have disadvantages such as limited applicability, corrosiveness to instruments, non-biodegradability, and residual polyacrylamide (PAM) in the treated water, which can cause neurotoxicity and carcinogenicity, thus limiting their application. Natural polymeric flocculants, on the other hand, are receiving increasing attention due to their natural raw materials, easy biodegradability, and safety.
[0005] Starch molecules have a helical structure and contain abundant hydroxyl groups, giving them good hydrophilicity, biocompatibility, and biodegradability. Therefore, starch-based flocculants are commonly used in wastewater treatment. However, starch has a relatively small molecular weight, generally between 50,000 and 250,000, and is insoluble in cold water with low stability. Direct use as a flocculant is not very effective. To obtain specific flocculation properties, modification methods such as graft copolymerization, esterification, etherification, and cross-linking are usually required. Because polymer side chains with flocculation function are grafted onto starch, the side chain groups can form hydrogen bonds with many substances through affinity and adsorption, or physical cross-linking can occur between the side chain groups and the flocculated substances, causing the flocculated substances to precipitate. Summary of the Invention
[0006] To address the shortcomings of existing technologies, one objective of this invention is to provide a method for preparing a cassava starch flocculant, the method comprising the following steps: (1) Add cassava starch to a mixed solution I consisting of NaCl solution and NaOH solution, and stir until homogeneous to obtain starch slurry.
[0007] (2) Epichlorohydrin was added to the starch slurry obtained in step (1) to carry out the reaction. After the reaction was completed, the pH was adjusted to neutral. The precipitate was washed with anhydrous ethanol and dried to obtain cross-linked starch.
[0008] (3) The cross-linked starch prepared in step (2) is gelatinized to obtain gelatinized starch (the mass of water used during gelatinization is at least 10 times the mass of cross-linked starch). Under the condition of continuous nitrogen gas, monomeric acrylamide is added to the cooled gelatinized starch and stirred evenly (in order to make monomeric acrylamide mix with gelatinized starch more quickly and thoroughly, monomeric acrylamide can be prepared into a solution before being added). Then sodium bisulfite solution is added and stirred evenly. Finally, ammonium persulfate is added (in order to make ammonium persulfate mix with gelatinized starch more quickly and thoroughly, ammonium persulfate can be prepared into a solution before being added). The reaction is stirred to obtain precipitate. The precipitate is washed and dried to obtain coarse flocculant. (4) Wrap the coarse flocculant obtained in step (3) with filter paper and place it in a mixed solution II consisting of glacial acetic acid and ethylene glycol (the amount of mixed solution II is not particularly required, just enough to fully submerge the filter paper). After reflux extraction, wash with anhydrous ethanol until neutral and dry to obtain cassava starch flocculant.
[0009] Preferably, in step (1), the solid-liquid ratio of cassava starch to mixed solution I is (10:19) to (15:22), in g:mL, and the volume ratio of NaCl solution to NaOH solution in mixed solution I is (10:1) to (35:3), wherein the concentration of NaCl in the NaCl solution is 0.005 to 0.02 g / L, and the concentration of NaOH in the NaOH solution is 0.1 to 0.3 g / L.
[0010] Preferably, the stirring in step (1) is carried out at 30-45°C.
[0011] Preferably, in step (2), the volume ratio of epichlorohydrin to starch paste is (2-4):20.
[0012] Preferably, the reaction conditions in step (2) are: pH 10-11.5, reaction temperature 40-60℃ for 2-3 hours.
[0013] Preferably, in step (3), the mass ratio of cross-linked starch to monomeric acrylamide is 1:(5.1-7); the mass ratio of cross-linked starch to ammonium persulfate is 1000:(5.7-11.4); and the solid-liquid ratio of cross-linked starch to sodium bisulfite solution is 1:(1-1.5), in g:mL, wherein the concentration of sodium bisulfite solution is 0.05-0.1mol / mL.
[0014] Preferably, the conditions for gelatinizing the cross-linked starch in step (3) are: reacting at 70-90°C for 20-40 min under nitrogen gas.
[0015] Preferably, the stirring reaction conditions in step (3) are 30-40℃ for 6-8 hours.
[0016] Preferably, the method for washing the precipitate in step (3) is to wash and stir it sequentially with acetone and anhydrous ethanol.
[0017] Preferably, the volume ratio of glacial acetic acid to ethylene glycol in the mixed solution II in step (4) is 1:2 to 3:2.
[0018] The second objective of this invention is to provide an application of the prepared cassava starch flocculant in adsorbing Pb(II) in water.
[0019] Compared with the prior art, the present invention has the following beneficial effects: (1) Using cassava starch as raw material, the cassava starch was first modified by using a mixed solution composed of NaCl solution and NaOH solution to improve the solubility of the starch, and a modified starch slurry was obtained. Then, epichlorohydrin was used as a crosslinking agent to prepare crosslinked starch. Ammonium persulfate was used as an initiator to graft copolymerize the crosslinked starch with acrylamide to synthesize cassava starch flocculant. A cheap, practical, non-toxic and efficient flocculant was successfully developed. Compared with other flocculants, the cassava starch flocculant prepared by this invention has a lead ion removal rate of more than 90%, and has a high flocculation rate, monomer conversion rate, grafting rate and grafting efficiency. Attached Figure Description
[0020] Figure 1 This is a schematic diagram of the Pb(II) concentration standard curve.
[0021] Figure 2 Infrared spectra of cassava starch, cross-linked starch prepared in Example 1, and cassava starch flocculant prepared in Example 1.
[0022] Figure 3 This is a scanning electron microscope image of cassava starch.
[0023] Figure 4 The image shown is a scanning electron microscope image of the cross-linked starch prepared in Example 1.
[0024] Figure 5 The image shown is a scanning electron microscope image of the flocculant prepared in Example 1. Detailed Implementation
[0025] 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 embodiments of the present invention, and not all embodiments. 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.
[0026] Example 1 A method for preparing a cassava starch flocculant, the specific steps of which are as follows: (1) Add 20 mL of 0.01 g / L NaCl solution and 2 mL of 0.2 g / L NaOH solution to 15.00 g cassava starch, stir in a 40°C water bath for 20 min to obtain starch slurry.
[0027] (2) Slowly add 2.0 mL of epichlorohydrin to the starch paste (20 mL) from step (1), add 0.1 g / L NaOH solution until the pH of the starch paste is 10, react at 40 °C for 3 h, adjust the pH to neutral with 10% hydrochloric acid, wash the precipitate twice with anhydrous ethanol, and dry the precipitate in a constant temperature drying oven at 50 °C to obtain cross-linked starch.
[0028] (3) Add 2g of the cross-linked starch prepared in step (2) to 20mL of distilled water, stir and gelatinize in a constant temperature water bath at 80℃ for 30min with nitrogen gas, cool to room temperature, take 10.2g of monomer acrylamide (dissolved in 5mL of deionized water before addition) under continuous nitrogen gas purging, add it to the cooled gelatinized starch solution and stir for 20min, then slowly add 2mL of 0.05mol / L sodium bisulfite solution, stir for 5min and then add 11.4mg of ammonium persulfate (dissolved in 2mL of deionized water before addition), stir and react at 30℃ for 6h to obtain precipitate, take out the product, cool to room temperature, wash and stir with acetone and anhydrous ethanol in sequence, filter the precipitate and dry at 50℃ to obtain coarse flocculant.
[0029] (4) Wrap the coarse flocculant in filter paper and place it in a mixed solution of glacial acetic acid and ethylene glycol (the volume ratio of glacial acetic acid to ethylene glycol is 3:2) and reflux for 10 h to remove the homopolymer; then wash with anhydrous ethanol until neutral, and vacuum dry at 50°C for 24 h to obtain the refined flocculant, which is the cassava starch flocculant.
[0030] The cassava starch used in this embodiment, the cross-linked starch prepared in step (2), and the finally prepared cassava starch flocculant were subjected to infrared spectroscopy detection. The results are as follows: Figure 2As can be seen from the figure, cross-linked starch has a characteristic absorption peak of C3H5ClO, while cassava starch flocculant, based on cross-linked starch, also has an absorption peak of monomeric acrylamide, and retains the absorption peaks that starch should have. This indicates that the cassava starch flocculant still uses natural starch as its backbone and retains the good biodegradability of starch.
[0031] The cassava starch used in this embodiment, the cross-linked starch prepared in step (2), and the finally prepared cassava starch flocculant were observed using electron microscopy. The results are as follows: Figures 3-5 As shown in the figure, it can be seen that cross-linked starch ( Figure 4 ) and flocculants ( Figure 5 The surface morphology also changed, proving that the shape of the starch had changed. Cassava starch is in powder form, but after cross-linking, it becomes blocky. Then, grafting is carried out on the basis of cross-linked starch, and the flocculant is in powder form, but it is finer and smaller in diameter than the original starch. From this, it can be inferred that the cassava starch flocculant increases the specific surface area of the starch, improves the adsorption performance of the starch and the efficiency of adsorbing pollutants.
[0032] Example 2 A method for preparing a cassava starch flocculant, the specific steps of which are as follows: (1) Add 35 mL of 0.005 g / L NaCl solution and 3 mL of 0.3 g / L NaOH solution to 20.00 g cassava starch, and stir in a 40°C water bath for 20 min to obtain starch slurry.
[0033] (2) Add 3.0 mL of epichlorohydrin slowly to the starch paste (20 mL) from step (1), add 0.1 g / L NaOH solution until the pH of the starch paste is 11, react at 40 °C for 3 h, adjust the pH to neutral with 10% hydrochloric acid, wash the precipitate twice with anhydrous ethanol, and dry the precipitate in a constant temperature drying oven at 50 °C to obtain cross-linked starch.
[0034] (3) Add 2g of the cross-linked starch prepared in step (2) to 20mL of distilled water, stir and gelatinize in a 90℃ constant temperature water bath with nitrogen gas for 20min, cool to room temperature, take 12.0g of monomer acrylamide (dissolved in 6mL of deionized water before addition) under continuous nitrogen gas purging, add to the cooled gelatinized starch solution and stir for 20min, slowly add 3mL of 0.06mol / L sodium bisulfite solution, stir for 5min, and then add 16mg of ammonium persulfate (dissolved in 2mL of deionized water before addition), stir and react at 35℃ for 7h to obtain precipitate, take out the product, cool to room temperature, wash and stir with acetone and anhydrous ethanol in sequence, filter the precipitate and dry at 50℃ to obtain coarse flocculant.
[0035] (4) Wrap the coarse flocculant in filter paper and place it in a mixed solution of glacial acetic acid and ethylene glycol (the volume ratio of glacial acetic acid to ethylene glycol is 1:2) and reflux for 10 h to remove the homopolymer; then wash with anhydrous ethanol until neutral, and vacuum dry at 50°C for 24 h to obtain the refined flocculant, which is the cassava starch flocculant.
[0036] Example 3 A method for preparing a cassava starch flocculant, the specific steps of which are as follows: (1) Add 40 mL of 0.02 g / L NaCl solution and 4 mL of 0.1 g / L NaOH solution to 25.00 g cassava starch, stir in a 40 °C water bath for 20 min to obtain starch slurry.
[0037] (2) Slowly add 4.0 mL of epichlorohydrin to the starch paste (20 mL) from step (1), add 0.1 g / L NaOH solution until the pH of the starch paste is 11.5, react at 60 °C for 2 h, adjust the pH to neutral with 10% hydrochloric acid, wash twice with anhydrous ethanol, and dry the precipitate in a constant temperature drying oven at 50 °C to obtain cross-linked starch.
[0038] (3) Add 2g of the cross-linked starch prepared in step (2) to 20mL of distilled water, stir and gelatinize in a constant temperature water bath at 70℃ with nitrogen gas for 40min, cool to room temperature, take 14.0g of monomer acrylamide (dissolved in 7mL of deionized water before addition) under continuous nitrogen gas purging, add it to the cooled gelatinized starch solution and stir for 20min, then slowly add 3mL of 0.1mol / L sodium bisulfite solution, stir for 5min and then add 22.8mg of ammonium persulfate (dissolved in 2mL of deionized water before addition), stir and react at 40℃ for 8h to obtain precipitate, take out the product, cool to room temperature, wash and stir with acetone and anhydrous ethanol in sequence, filter the precipitate and dry at 50℃ to obtain coarse flocculant.
[0039] (4) Wrap the coarse flocculant in filter paper and place it in a mixed solution of glacial acetic acid and ethylene glycol (the volume ratio of glacial acetic acid to ethylene glycol is 3:2) and reflux for 10 h to remove the homopolymer; then wash with anhydrous ethanol until neutral, and vacuum dry at 50°C for 24 h to obtain the refined flocculant, which is the cassava starch flocculant.
[0040] Comparative Example 1 In contrast, this comparative example differs from Example 1 in that the starch is not modified, that is, steps (1) and (2) in Example 1 are not performed. The specific steps are as follows: (1) Add 2g of cassava starch to 20mL of distilled water, stir and gelatinize in a constant temperature water bath at 80℃ for 30min under nitrogen gas, cool to room temperature, take 10.2g of monomeric acrylamide (dissolved in 5mL of deionized water before addition) under continuous nitrogen gas purging, add to the cooled gelatinized starch solution and stir for 20min, then slowly add 2mL of 0.05mol / L sodium bisulfite solution, stir for 5min, and then add 11.4mg of ammonium persulfate (dissolved in 2mL of deionized water before addition), stir and react at 30℃ for 6h to obtain precipitate, take out the product, cool to room temperature, wash and stir with acetone and anhydrous ethanol in sequence, filter the precipitate and dry at 50℃ to obtain coarse flocculant.
[0041] (2) Wrap the coarse flocculant in filter paper and reflux it in a mixed solvent of glacial acetic acid and ethylene glycol (the volume ratio of glacial acetic acid to ethylene glycol is 3:2) for 10 hours to remove the homopolymer; then wash it with anhydrous ethanol until neutral, and vacuum dry it at 50°C for 24 hours to obtain the refined flocculant, which is the cassava starch flocculant.
[0042] The effectiveness of the flocculant prepared according to this invention was determined: 1. The specific steps for determining lead ion removal rate using atomic absorption spectrometry are as follows: To construct a standard curve: Weigh solid lead nitrate and prepare a 1.0 g / L lead nitrate standard solution. Then dilute this solution to prepare lead nitrate solutions of 1.0 mg / L, 2.0 mg / L, 3.0 mg / L, 4.0 mg / L, and 5.0 mg / L. Measure the absorbance of the lead nitrate solutions of different concentrations at 283 nm. Plot a standard curve with the lead nitrate solution concentration on the x-axis and absorbance on the y-axis. The results are shown below. Figure 1 As shown, the linear fitting equation is: y = 0.1982x - 0.2199; R² = 0.9971.
[0043] Prepare 50 mL of 50 mg / L Pb(II) solution to simulate the wastewater to be treated. Add 0.5 g of flocculant prepared in Examples 1-3 and Comparative Example 1 respectively. Stir evenly and react at 30 °C for 60 min. Take the supernatant and measure its absorbance. Calculate the Pb(II) concentration according to the linear equation and the removal rate according to the formula. Use the sample without flocculant as the control sample.
[0044] Calculation formula: Removal rate = (A1 - A2) / A1 × 100% A1: Pb(II) concentration of the control sample; A2: Pb(II) concentration of the supernatant after flocculant adsorption. 2. Flocculation rate determination, the specific steps are as follows: The starch flocculant solutions prepared in Examples 1-3 and Comparative Example 1 were added to a kaolin-simulated water sample, stirred, and allowed to stand. The supernatant was collected, and distilled water was used as a control sample. The absorbance of the supernatant was measured using a UV spectrophotometer (λ = 550 nm). The flocculation rate was calculated based on the measured absorbance.
[0045] Calculation formula: Flocculation rate = (A3 - A4) / A3 × 100% A3: Absorbance value of kaolin water sample; A4: Absorbance value of supernatant after flocculation.
[0046] Table 1. Test results of flocculants prepared in Examples 1-3 and Comparative Example 1 As can be seen from the table, the flocculants prepared in Examples 1-3 have high lead ion removal rate and flocculation rate, and the monomer conversion rate and grafting rate of the cross-linked starch flocculant obtained by the method of the present invention are also significantly higher than those of the flocculant prepared by unmodified starch. In the examples, step (1) modifies starch to increase starch solubility, constructs a mildly activated starch reaction precursor system, opens the starch particle structure in advance, forms a uniform and stable starch paste, increases the efficiency of cross-linking reaction in subsequent step (2), prepares cross-linked starch through step (2), and grafts acrylamide monomers onto the cross-linked starch skeleton through free radical initiation to form a starch-polyacrylamide graft copolymer with high molecular weight and strong flocculation performance. The flocculant obtained in this way has a high grafting rate and a high flocculation rate.
Claims
1. A method for preparing a cassava starch flocculant, characterized in that: The preparation method includes the following steps: (1) Add cassava starch to a mixed solution I consisting of NaCl solution and NaOH solution, and stir until homogeneous to obtain starch slurry; (2) Epichlorohydrin was added to the starch paste obtained in step (1) to carry out the reaction. After the reaction was completed, the pH was adjusted to neutral. The precipitate was washed with anhydrous ethanol and dried to obtain cross-linked starch. (3) The cross-linked starch prepared in step (2) is gelatinized to obtain gelatinized starch. Under the condition of continuous nitrogen gas, the monomer acryloyl is added to the cooled gelatinized starch and stirred evenly. Then, sodium bisulfite solution is added and stirred evenly. Finally, ammonium persulfate is added and stirred to react to obtain precipitate. The precipitate is washed and dried to obtain coarse flocculant. (4) The coarse flocculant obtained in step (3) is wrapped in filter paper and placed in a mixed solution II consisting of glacial acetic acid and ethylene glycol for reflux extraction. After washing with anhydrous ethanol until neutral, it is dried to obtain cassava starch flocculant.
2. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: In step (1), the solid-liquid ratio of cassava starch to mixed solution I is (10:19) to (15:22), with units of g:mL. The volume ratio of NaCl solution to NaOH solution in mixed solution I is (10:1) to (35:3), where the concentration of NaCl in the NaCl solution is 0.005 to 0.02 g / L, and the concentration of NaOH in the NaOH solution is 0.1 to 0.3 g / L.
3. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: Step (1) Stirring is carried out at a temperature of 30-45℃.
4. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: In step (2), the volume ratio of epichlorohydrin to starch paste is (2-4):
20.
5. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: The reaction conditions in step (2) are a pH of 10 to 11.5 and a temperature of 40 to 60°C for 2 to 3 hours.
6. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: In step (3), the mass ratio of cross-linked starch to monomeric acrylamide is 1:(5.1-7); the mass ratio of cross-linked starch to ammonium persulfate is 1000:(5.7-11.4); the solid-liquid ratio of cross-linked starch to sodium bisulfite solution is 1:(1-1.5), with units of g:mL, and the concentration of sodium bisulfite solution is 0.05-0.1mol / mL.
7. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: In step (3), the conditions for gelatinizing the cross-linked starch are to react at 70-90°C for 20-40 minutes under nitrogen gas.
8. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: The reaction conditions in step (3) are 30-40℃ for 6-8 hours.
9. The method for preparing a cassava starch flocculant according to claim 1, characterized in that: In step (4), the volume ratio of glacial acetic acid to ethylene glycol in mixed solution II is 1:2 to 3:
2.
10. The application of the cassava starch flocculant prepared by the method according to any one of claims 1 to 9 in the adsorption of Pb(II) in water.