Preparation method and application of cellulose nanofiber-based cationic polyacrylamide flocculant
By grafting acrylamide and acryloyloxyethyltrimethylammonium chloride onto cellulose nanofibers, a cellulose nanofiber-based cationic polyacrylamide flocculant was prepared, which solved the environmental risks and low efficiency problems of traditional flocculants, achieved high-efficiency flocculation and coagulation aid effects, and improved the performance of water treatment.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SOUTHWEST JIAOTONG UNIV
- Filing Date
- 2024-12-13
- Publication Date
- 2026-06-23
AI Technical Summary
Existing flocculants in water treatment suffer from adverse effects from the use of metal ions, low sedimentation efficiency, high time costs, non-degradability, and environmental risks. Furthermore, traditional polyacrylamide has a long dissolution time and low charge utilization, which limits its efficiency and economy.
Acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DAC) were grafted onto cellulose nanofibers (CNF) using a reversible living radical polymerization method to prepare cellulose nanofiber-based cationic polyacrylamide flocculant. A stable flocculant solution was formed through Cu(O)-mediated flocculation reaction.
It achieves efficient flocculation and coagulation aid effects, significantly improves flocculation performance, enhances water solubility and cationic properties, reduces environmental burden, and exhibits stronger flocculation capacity and sedimentation efficiency.
Smart Images
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Abstract
Description
Technical Field
[0001] This invention belongs to the field of cellulose nanofiber preparation technology, and particularly relates to a method for preparing and applying a cellulose nanofiber-based cationic polyacrylamide flocculant. Background Technology
[0002] Flocculants play a crucial role in flocculation processes, which are widely used as one of the most widely applied and cost-effective technologies in water and wastewater treatment and sludge dewatering. While inorganic and synthetic organic polymeric flocculants have been favored for their high efficiency over the past few decades, certain types of flocculants can cause secondary pollution and environmental exposure risks during use. A common approach is to use nonionic, anionic, or cationic polyacrylamide in combination with metal ions (such as aluminum or iron ions). However, these methods also present challenges, including the potential adverse effects of using metal ions and slower settling efficiency leading to higher time costs.
[0003] Polyacrylamide (PAM), due to its high molecular weight and high viscosity, is widely used in various environmental systems, playing a crucial role particularly in thickening, soil conditioning, and water treatment. However, despite its excellent flocculation properties, PAM has some drawbacks in its application, such as long dissolution time and low charge utilization, which limit its efficiency and economic viability in some scenarios. More importantly, as a synthetic polymer, the non-degradability and potential environmental risks of PAM are increasingly concerning. With growing environmental awareness, reducing its environmental burden and improving its biodegradability and recyclability have become important research directions.
[0004] Unlike unmodified natural polymers, chemically modified polymers not only retain the unique properties of natural polymers but also effectively improve other key characteristics such as solubility and electrostatic charge. In particular, graft-synthesized products can overcome the shortcomings of insufficient charge and poor solubility in the raw materials, and can also significantly enhance their flocculation performance by increasing their molecular weight, thereby improving their application effects in water treatment and other fields.
[0005] Cellulose nanofibers (CNFs) are non-toxic, biocompatible, and biodegradable. Nanocellulose, isolated from natural cellulose fibers, is formed by chemically or mechanically disrupting the intramolecular and intermolecular hydrogen bonds of cellulose units, and all have a one-dimensional size of less than 100 nm. Cellulose nanofibers (CNFs) are highly efficient coagulants / flocculators, adsorbents, catalyst supports, and membrane materials, capable of removing a wide range of organic, inorganic, and biological water pollutants at multiple scales. Their pollutant removal capabilities are, in some cases, comparable to, or even superior to, the best-performing water remediation materials reported in the existing literature.
[0006] Reversible living radical polymerization (RDRP) is an advanced technology capable of controlling the synthesis of graft copolymers. It mainly includes nitrile radical polymerization (NMRP), reversible addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP). RDRP not only allows for precise control of polymer molecular weight and chain extension but also offers the advantage of polymerization under a wider range of reaction conditions, exhibiting excellent adaptability and flexibility, particularly in aqueous media. Summary of the Invention
[0007] In order to prepare a cellulose nanofiber-based cationic polyacrylamide solution-type flocculant with good stability, this invention provides a method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant and its application.
[0008] The present invention discloses a method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant, comprising the following steps:
[0009] Step 1: Preparation of cellulose macromolecular initiator:
[0010] The mixture obtained by centrifugation was subjected to esterification under ice bath conditions to obtain a cellulose macromolecular initiator. The raw materials of the mixture included the following components in parts by weight: 2 parts of 1.3% cellulose slurry, 2 parts of 2-bromoisobutyryl bromide (BIBB), 2 parts of triethylamine, 2 parts of 4-dimethylaminopyridine (DMAP), 1500 parts of N,N-dimethylformamide (DMF), and 5000 parts of deionized water.
[0011] Step 2: Cationic polyacrylamide grafting:
[0012] Under absolute oxygen-free and ice bath conditions, the grafting reaction was completed in a flask by Cu(0)-mediated reversible living radical polymerization to obtain the grafted product.
[0013] The raw materials include the following components in parts by weight: 8 parts cellulose macromolecular initiator, 8 parts acrylamide (AM), 8 parts acryloyloxyethyltrimethylammonium chloride (DAC), 8 parts tris(2-dimethylaminoethyl)amine (ME6TREN), 8 parts cuprous bromide (CuBr), and 8 parts hydrochloric acid.
[0014] Furthermore, step 1 specifically involves:
[0015] Cellulose slurry and N,N-dimethylformamide (DMF) were centrifuged and mixed. Triethylamine, 4-dimethylaminopyridine (DMAP) and N,N-dimethylformamide (DMF) were then added to a flask and mixed. 2-bromoisobutyryl bromide (BIBB) was added under ice bath conditions, and the mixture was reacted at room temperature for 24 hours. The final product was washed repeatedly with ethanol and deionized water to obtain the cellulose macromolecular initiator.
[0016] Furthermore, step 2 specifically involves:
[0017] Cellulose macromolecular initiator, acrylamide (AM), and acryloyloxyethyltrimethylammonium chloride (DAC) were dispersed in pure water and stirred until homogeneous. Then, argon gas was continuously introduced into the flask to completely remove oxygen. Under argon conditions, tris(2-dimethylaminoethyl)amine (ME6TREN) and cuprous bromide (CuBr) were added to a flask and reacted for 15 minutes. After reacting in an ice bath for 1 hour under anaerobic conditions, hydrochloric acid was added and the mixture was repeatedly centrifuged. The resulting product was dried to constant weight in an oven at 80 °C.
[0018] The cellulose nanofiber-based cationic polyacrylamide flocculant prepared by the present invention can be used as a water treatment flocculant to remove suspended particles in wastewater.
[0019] The beneficial technical effects of this invention are as follows:
[0020] This invention employs a living radical polymerization method to graft AM and DAC onto a cellulose nanofiber (CNF) backbone, yielding a cellulose nanofiber-based cationic polyacrylamide flocculant with excellent flocculation performance. As a water treatment flocculant, it can effectively remove suspended particles from wastewater. Furthermore, compared to traditional flocculation processes, this flocculant simultaneously exhibits flocculation and coagulation-aiding effects. Attached Figure Description
[0021] Figure 1 This is a bentonite solution without added flocculant.
[0022] Figure 2 A schematic diagram of a bentonite solution containing the cellulose nanofiber-based cationic polyacrylamide flocculant prepared according to an embodiment of the present invention.
[0023] Figure 3 A schematic diagram showing the addition of the bentonite solution of Comparative Example 1 of this invention.
[0024] Figure 4 A schematic diagram showing the addition of the bentonite solution of Comparative Example 2 of this invention.
[0025] Figure 5 SEM image of bentonite solution without flocculant treatment.
[0026] Figure 6 SEM image of bentonite solution treated with cellulose nanofiber-based cationic polyacrylamide flocculant prepared according to the embodiments of the present invention.
[0027] Figure 7 SEM image of bentonite solution treated with the solution of Comparative Example 1 of this invention.
[0028] Figure 8 SEM image of bentonite solution treated with the solution of Comparative Example 2 of this invention. Detailed Implementation
[0029] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.
[0030] Example 1
[0031] A method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant includes the following steps:
[0032] (1) The aqueous solvent in 87g of cellulose slurry (containing 1.125g of cellulose) was replaced with DMF by repeated centrifugation. This is denoted as E1.
[0033] (2) Add triethylamine (3 ml) and DMAP (30 mg) to E1, and add DMF to the flask. The total weight of the mixture is 50 g. The mixture is labeled E2.
[0034] (3) Under ice bath conditions, add 0.7-2 ml of BIBB to the well-stirred E2, and record it as E3.
[0035] (4) E3 was reacted at room temperature for 24 hours. The final product was washed repeatedly with ethanol and deionized water and stored in a refrigerator, and was designated as E4.
[0036] (5) Disperse E4 (1.49g, 2.21g), AM and DAC (total molar amount 0.02, molar ratio 1:2, 1:1, 4:1) in pure water and stir until homogeneous. Then, continuously purge the bottle with argon gas to completely remove oxygen. This is denoted as E5.
[0037] (6) Under argon conditions, 22 μL of ME6TREN and 11.2 mg of CuBr were added to a flask and reacted for 15 minutes, which was recorded as E6.
[0038] (7) Quickly transfer E6 to E5 using an airtight syringe, and seal the flask with a silicone rubber diaphragm to maintain absolutely oxygen-free conditions. After reacting in an ice bath for 1 hour, perform repeated centrifugation. During centrifugation, add 0.5 ml of hydrochloric acid (1 wt%) to remove the remaining copper catalyst. Finally, dry the obtained product in an oven at 80 °C to constant weight, and record it as E7.
[0039] Comparative Example 1
[0040] Commercially available ferric chloride and commercially available polyacrylamide are combined.
[0041] Comparative Example 2
[0042] Commercially available polyaluminum chloride is compounded with commercially available polyacrylamide.
[0043] Experimental steps:
[0044] Four groups of suspended solids wastewater (50 mL) were simulated using a 300 mg / L bentonite solution. The first group consisted of a bentonite solution without added flocculant, such as... Figure 1 As shown. The second group is a bentonite solution with the cellulose nanofiber-based cationic polyacrylamide flocculant prepared in Example 1 of this invention added, such as... Figure 2 As shown. The third group contains a bentonite solution added to Comparative Example 1, such as... Figure 3 As shown. The fourth group contains a bentonite solution added to Comparative Example 2, such as... Figure 4 As shown.
[0045] For each group of experiments, the mixture was stirred for 3 minutes at room temperature and 250 rpm, and then allowed to settle for 30 minutes. The flocculation behavior of the suspended solids was obtained by measuring the concentration of the suspended solids in the supernatant and calculating the results, as shown in Table 1.
[0046] Table 1 Experimental flocculation behavior
[0047]
[0048] SEM image of the bentonite solution without flocculant treatment according to this invention is shown below. Figure 5 As shown, the SEM images of the three groups of treated bentonite solutions are as follows: Figure 6 , Figure 7 , Figure 8 As shown.
[0049] This invention utilizes acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DAC) grafted onto cellulose nanofibers (CNF) for the efficient adsorption of anionic dyes. Similarly, for negatively charged suspended particles in wastewater, the cationic polyacrylamide-modified CNF exhibits potential as a sustainable, efficient, and environmentally friendly flocculant. Furthermore, the quaternization modification of CNF not only significantly improves its water solubility but also enhances its cationic properties. Experimental results show that, compared to traditional flocculation processes, this flocculant exhibits stronger flocculation capacity and coagulation aid effect.
Claims
1. A method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant, characterized by comprising the following steps: Step 1: Preparation of cellulose macromolecular initiator: The mixture obtained by centrifugation was subjected to esterification under ice bath conditions to obtain a cellulose macromolecular initiator; the raw material of the mixture included the following components in parts by weight: 1.3% cellulose slurry 2 parts, 2-bromoisobutyryl bromide 2 parts, triethylamine 2 parts, 4-dimethylaminopyridine 2 parts, N,N-dimethylformamide 1500 parts, deionized water 5000 parts; Step 2: Cationic polyacrylamide grafting: Under absolute oxygen-free and ice bath conditions, the grafting reaction was completed in a flask by Cu(0)-mediated reversible living radical polymerization to obtain the grafted product; The raw materials include the following components by weight: 8 parts cellulose macromolecular initiator, 8 parts acrylamide, 8 parts acryloyloxyethyltrimethylammonium chloride, 8 parts tris(2-dimethylaminoethyl)amine, 8 parts cuprous bromide, and 8 parts hydrochloric acid.
2. The method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant according to claim 1, characterized in that, Step 1 specifically involves: Cellulose slurry and N,N-dimethylformamide were centrifuged and mixed, and then triethylamine, 4-dimethylaminopyridine and N,N-dimethylformamide were added to a flask and mixed. Under ice bath conditions, 2-bromoisobutyryl bromide was added and the mixture was reacted at room temperature for 24 h. The final product was washed repeatedly with ethanol and deionized water to obtain the cellulose macromolecular initiator.
3. The method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant according to claim 2, characterized in that, Step 2 specifically involves: Cellulose macromolecular initiator, acrylamide, and acryloyloxyethyltrimethylammonium chloride were dispersed in pure water and stirred until homogeneous. Then, argon gas was continuously introduced into the flask to completely remove oxygen. Under argon conditions, tris(2-dimethylaminoethyl)amine and cuprous bromide were added to a flask and reacted for 15 minutes. Under anaerobic conditions, the reaction was carried out in an ice bath for 1 hour, followed by repeated centrifugation with hydrochloric acid. The resulting product was dried to constant weight in an oven at 80 °C.
4. The method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant according to claim 1, characterized in that, The prepared cellulose nanofiber-based cationic polyacrylamide flocculant was used as a water treatment flocculant to remove suspended particles from wastewater.