Preparation method and application of cellulose nanofiber-based cationic polyacrylamide flocculant

Abstract

The invention discloses a preparation method and application of a cellulose nanofiber-based cationic polyacrylamide flocculant.The preparation method comprises the steps that during preparation, a mixed solution obtained through centrifugation is subjected to an esterification reaction under the ice bath condition, and a cellulose macroinitiator is obtained; under the absolute oxygen-free and ice bath conditions, grafting reaction is completed in an eggplant-shaped bottle through a Cu (0)-mediated reversible active free radical polymerization method, and a cellulose nanofiber-based cationic polyacrylamide flocculant solution is obtained. The prepared cellulose nanofiber-based cationic polyacrylamide flocculant is used as a water treatment flocculant to remove suspended particles in suspended matter wastewater. The cellulose dispersity and stability of the prepared cellulose nanofiber-based cationic polyacrylamide flocculant are remarkably improved, and compared with a traditional flocculation process, the flocculant has the flocculation and coagulation aiding effects at the same time and shows high settling speed.

Description

Technical Field

[0001] The invention belongs to the technical field of cellulose nanofiber preparation, and in particular relates to a preparation method and application of a cellulose nanofiber-based cationic polyacrylamide flocculant. Background Art

[0002] Flocculants play a vital role in the flocculation process, which has been widely used as one of the most widely used cost-effective technologies in water and wastewater treatment and sludge dewatering. Although inorganic and synthetic organic polymer flocculants have been favored for their high efficiency in the past few decades, some types of flocculants may cause secondary pollution and environmental exposure risks during use. The common usage is to use non-ionic polyacrylamide, anionic or cationic polyacrylamide together with metal ions (such as aluminum ions or iron ions). However, these methods also have some challenges, including the possible adverse effects of the use of metal ions and the high time cost due to slow sedimentation efficiency.

[0003] Polyacrylamide (PAM) is widely used in various environmental systems due to its high molecular weight and high viscosity characteristics, especially in the fields of viscosity increase, soil conditioning and water treatment. However, although polyacrylamide has a good flocculation effect, it still has some defects during use, such as a long dissolution time and low effective charge utilization rate, which limits its efficiency and economy in some application scenarios. More importantly, as a synthetic polymer material, the non-degradability and possible environmental risks of polyacrylamide are increasingly attracting attention. With the improvement of environmental protection awareness, how to reduce its environmental burden and improve its biodegradability and recyclability has become an important direction of current research.

[0004] Unlike unmodified natural polymers, chemically modified polymers not only maintain the unique properties of natural polymers, but also effectively improve other key properties such as solubility and electrostatic charge. In particular, grafted synthetic products, in addition to overcoming the shortcomings of raw materials such as insufficient charge and poor solubility, can also significantly enhance their flocculation properties by increasing molecular weight, thereby improving their application effects in water treatment and other fields.

[0005] Cellulose nanofibers (CNF) are non-toxic, biocompatible and biodegradable. Nanocellulose isolated from natural cellulose fibers is formed by chemically or mechanically destroying the intramolecular and intermolecular hydrogen bonds of cellulose units, and one-dimensional dimensions are all less than 100nm. Cellulose nanofibers (CNF) are highly efficient coagulants / flocculants, adsorbents, catalyst carriers and membrane materials that can remove a variety of organic, inorganic and biological water pollutants at multiple scales. Its pollutant removal ability is comparable to the best water remediation materials reported in the existing literature in some cases, and even shows better performance.

[0006] Reversible living radical polymerization (RDRP) is an advanced technology that can controllably synthesize graft copolymers, mainly including nitroxide radical polymerization (NMRP), reversible addition-fragmentation chain transfer polymerization (RAFT) and atom transfer radical polymerization (ATRP). RDRP can not only precisely control the molecular weight of the polymer and achieve chain extension, but also has the advantage of being able to polymerize under a wider range of reaction conditions, especially in aqueous media, showing good adaptability and flexibility. Summary of the invention

[0007] In order to prepare a cellulose nanofiber-based cationic polyacrylamide solution-type flocculant with good stability, the present invention provides a preparation method and application of a cellulose nanofiber-based cationic polyacrylamide flocculant.

[0008] The present invention provides a method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant, comprising the following steps:

[0009] Step 1: Preparation of cellulose macroinitiator:

[0010] The mixed solution obtained by centrifugation is subjected to esterification reaction under ice bath conditions to obtain a cellulose macromolecular initiator. The mixed solution raw materials include the following components 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] The grafting reaction was completed in an eggplant-shaped flask by a Cu(0)-mediated reversible living free radical polymerization method under absolutely oxygen-free and ice-bath conditions to obtain the grafted product.

[0013] The raw materials include the following components in parts by mass: 8 parts of cellulose macroinitiator, 8 parts of acrylamide (AM), 8 parts of acryloyloxyethyltrimethylammonium chloride (DAC), 8 parts of tris(2-dimethylaminoethyl)amine (ME6TREN), 8 parts of copper bromide (CuBr), and 8 parts of hydrochloric acid.

[0014] Furthermore, step 1 is specifically as follows:

[0015] The cellulose slurry and N,N-dimethylformamide (DMF) are centrifugally mixed, and then triethylamine, 4-dimethylaminopyridine (DMAP) and N,N-dimethylformamide (DMF) are added to a flask and mixed; 2-bromoisobutyryl bromide (BIBB) is added under ice bath conditions, and the reaction is allowed to proceed at room temperature for 24 hours. The final product is repeatedly washed with ethanol and deionized water to obtain a cellulose macromolecular initiator.

[0016] Furthermore, step 2 is specifically as follows:

[0017] Cellulose macroinitiator, acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DAC) were dispersed in pure water and stirred evenly. Subsequently, argon was continuously introduced into the bottle to completely remove oxygen. Under argon conditions, tris(2-dimethylaminoethyl)amine (ME6TREN) and copper bromide (CuBr) were added into the eggplant-shaped bottle to react for 15 minutes. Under anaerobic conditions, after reacting in an ice bath for 1 hour, hydrochloric acid was added and centrifuged repeatedly. The obtained product was dried in an oven at 80°C to constant weight.

[0018] The cellulose nanofiber-based cationic polyacrylamide flocculant prepared by the method for preparing the cellulose nanofiber-based cationic polyacrylamide flocculant of the present invention is used as a water treatment flocculant to remove suspended particles in suspended wastewater.

[0019] The beneficial technical effects of the present invention are:

[0020] The present invention adopts the living free radical polymerization method to graft AM and DAC onto the cellulose nanofiber (CNF) skeleton to obtain a cellulose nanofiber-based cationic polyacrylamide flocculant with good flocculation effect, which can effectively remove suspended particles in suspended wastewater as a water treatment flocculant. In addition, compared with the traditional flocculation process, the present flocculant has both flocculation and coagulant effects. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a bentonite solution without adding flocculant.

[0022] Figure 2 Schematic diagram of a bentonite solution to which a cellulose nanofiber-based cationic polyacrylamide flocculant prepared in an embodiment of the present invention is added.

[0023] Figure 3 Schematic diagram of adding bentonite solution of Comparative Example 1 of the present invention.

[0024] Figure 4 Schematic diagram of adding bentonite solution of comparative example 2 of the present invention

[0025] Figure 5 This is the SEM image of the bentonite solution without adding flocculant.

[0026] Figure 6 This is a SEM image of a bentonite solution treated with a cellulose nanofiber-based cationic polyacrylamide flocculant prepared in an embodiment of the present invention.

[0027] Figure 7 This is a SEM image of a bentonite solution treated with the solution of Comparative Example 1 of the present invention.

[0028] Figure 8 This is a SEM image of a bentonite solution treated with the solution of Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0030] Example 1

[0031] A method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant comprises the following steps:

[0032] (1) The aqueous solvent in 87 g of cellulose slurry (containing 1.125 g of cellulose) was replaced with DMF by repeated centrifugation. This was designated as E1.

[0033] (2) Add triethylamine (3 ml) and DMAP (30 mg) to E1, and add DMF until the total weight of the mixture in the flask is 50 g. The mixture is recorded as E2.

[0034] (3) BIBB (0.7, 2 ml) was added dropwise to the stirred E2 under ice bath conditions, and the mixture was designated as E3.

[0035] (4) E3 was reacted at room temperature for 24 h. The final product was repeatedly washed with ethanol and deionized water and stored in a refrigerator, which was recorded as E4.

[0036] (5) E4 (1.49 g, 2.21 g), AM and DAC (total molar weight of 0.02, molar ratio of 1:2, 1:1, 4:1) were dispersed in pure water and stirred evenly. Then, argon was continuously filled into the bottle to completely drive out oxygen. This was recorded as E5.

[0037] (6) Under argon conditions, 22 μL ME6TREN and 11.2 mg CuBr were added to the eggplant-shaped flask and reacted for 15 min. This reaction was recorded as E6.

[0038] (7) Quickly transfer E6 to E5 using an airtight syringe, and seal the eggplant-shaped bottle with a silicone rubber septum to maintain absolute anaerobic conditions. After reacting in an ice bath for 1 hour, centrifuge repeatedly. During the centrifugation process, add 0.5 ml of hydrochloric acid (1 wt%) to remove the remaining copper catalyst. Finally, the obtained product is dried in an oven at 80°C to constant weight and recorded as E7.

[0039] Comparative Example 1

[0040] Commercially available ferric chloride is compounded with commercially available polyacrylamide.

[0041] Comparative Example 2

[0042] Commercially available polyaluminium chloride is compounded with commercially available polyacrylamide.

[0043] Experimental steps:

[0044] Four groups of suspended solid wastewater (50 mL) were simulated with 300 mg / L bentonite solution. The first group was bentonite solution without flocculant added, e.g. Figure 1 The second group is a bentonite solution to which the cellulose nanofiber-based cationic polyacrylamide flocculant prepared in Example 1 of the present invention is added, such as Figure 2 The third group is the bentonite solution of Comparative Example 1, as shown. Figure 3 The fourth group is the bentonite solution of Comparative Example 2, as shown. Figure 4 shown.

[0045] For each group of experiments, the mixture was stirred at room temperature and 250 rpm for 3 min, and then allowed to settle for 30 min. The flocculation behavior of the suspended matter was obtained by measuring the concentration of the suspended matter in the supernatant and calculating it as shown in Table 1.

[0046] Table 1 Experimental flocculation behavior

[0047] project Drug dosage (mg / L) Average removal rate (%) Settling time (min) Comparative Example 1 60+1 87％ 30 Comparative Example 2 60+1 99％ 30 Example 1 60 98％ 2

[0048] The SEM image of the bentonite solution without adding flocculant is as follows: Figure 5 As shown, the SEM images of the three groups of bentonite solutions after treatment are as follows: Figure 6 , Figure 7 , Figure 8 shown.

[0049] The present invention uses acrylamide (AM) and acryloyloxyethyltrimethylammonium chloride (DAC) to graft onto cellulose nanofibers (CNF) for efficient adsorption of anionic dyes. Similarly, for negatively charged suspended particles in wastewater, cationic polyacrylamide-modified CNF shows potential as a sustainable, efficient and environmentally friendly flocculant. In addition, the quaternary ammonium modification of CNF not only significantly improves its water solubility, but also enhances its cationic properties. Experimental results show that compared with traditional flocculation processes, the flocculant exhibits stronger flocculation ability and coagulant effect.

Claims

1. A method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant, characterized in that: The following steps are involved: Step 1: Preparation of cellulose macroinitiator: The mixed solution obtained by centrifugation is subjected to esterification reaction under ice bath conditions to obtain a cellulose macromolecular initiator; the raw materials of the mixed solution include the following components by weight: 2 parts of 1.3% cellulose slurry, 2 parts of 2-bromoisobutyryl bromide, 2 parts of triethylamine, 2 parts of 4-dimethylaminopyridine, 1500 parts of N,N-dimethylformamide, and 5000 parts of deionized water; Step 2: Cationic polyacrylamide grafting: The grafting reaction was completed in an eggplant-shaped flask by a Cu(0)-mediated reversible living free radical polymerization method under absolutely oxygen-free and ice-bath conditions to obtain the grafted product. The raw materials include the following components in parts by weight: 8 parts of cellulose macromolecular initiator, 8 parts of acrylamide, 8 parts of acryloyloxyethyltrimethylammonium chloride, 8 parts of tris(2-dimethylaminoethyl)amine, 8 parts of copper bromide, and 8 parts of hydrochloric acid.

2. The method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant according to claim 1, characterized in that: The step 1 is specifically as follows: The cellulose slurry and N,N-dimethylformamide are centrifugally mixed, and then triethylamine, 4-dimethylaminopyridine and N,N-dimethylformamide are added to a flask and mixed; 2-bromoisobutyryl bromide is added under ice bath conditions, and the mixture is reacted at room temperature for 24 hours. The final product is repeatedly washed with ethanol and deionized water to obtain a cellulose macromolecular initiator.

3. The method for preparing a cellulose nanofiber-based cationic polyacrylamide flocculant according to claim 2, characterized in that: The step 2 is specifically as follows: Cellulose macroinitiator, acrylamide and acryloyloxyethyltrimethylammonium chloride were dispersed in pure water and stirred evenly. Subsequently, argon was continuously introduced into the bottle to completely remove oxygen. Under argon conditions, tris(2-dimethylaminoethyl)amine and copper bromide were added to the eggplant-shaped bottle for reaction for 15 minutes. Under anaerobic conditions, after ice bath reaction for 1 hour, hydrochloric acid was added for repeated centrifugation. The obtained product was dried in an oven at 80°C to constant weight.

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 is used as a water treatment flocculant to remove suspended particles in suspended wastewater.

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