Novel strong-flocculation ultra-high molecular weight cationic polyacrylamide as well as preparation method and application thereof

Abstract

The invention relates to the technical field of high polymer materials, in particular to novel strong-flocculation ultra-high molecular weight cationic polyacrylamide as well as a preparation method and application thereof. The preparation method of the novel strong-flocculation ultra-high molecular weight cationic polyacrylamide comprises the following steps: mixing acrylamide, a cationic monomer and a steric hindrance isomerization functional monomer in water to obtain a mixed solution, and then adding an azo initiator, a complexing agent, a directional chain extender, an oxidizing agent and a reducing agent into the mixed solution to initiate a polymerization reaction to obtain the novel strong-flocculation ultra-high molecular weight cationic polyacrylamide. The ultra-high molecular weight cationic polyacrylamide is obtained; the method is simple in preparation process, short in reaction time, low in cost and high in production efficiency, the highest conversion rate reaches 99.3%, and the method is more suitable for industrial production; the cationic polyacrylamide monomer is low in content and ultrahigh in molecular weight, the molecular weight of the cationic polyacrylamide monomer exceeds the molecular weight of a conventional cationic polyacrylamide product in the market by 9000000-110000000, and the flocculation capacity is improved by 35%-59%.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a novel strong flocculating ultra-high molecular weight cationic polyacrylamide, its preparation method, and its application. Background Technology

[0002] Polyacrylamide (PAM) is a linear polymer formed by the free radical addition reaction of acrylamide (AM) monomer. PAM is a white granule or powder, easily soluble in water, non-toxic and non-corrosive. Solid PAM is hygroscopic. It is an important water-soluble polymer with special physicochemical properties. It can be easily modified into various branched or network structures through grafting or cross-linking. PAM molecules can be introduced with various ionic groups to obtain specific properties. It is widely used in various fields such as chemical industry, metallurgy, geology, coal, petroleum, papermaking and water treatment, and is known as the "auxiliary agent of all industries".

[0003] Cationic polyacrylamide is mainly used as a flocculant. Utilizing its various active groups, after hydrolysis, it exhibits excellent adsorption capacity for many micro-clusters and dissolved substances in wastewater, and is widely used in the treatment of various types of wastewater. The demand for cationic polyacrylamide from wastewater discharged by paper mills is increasing, and the requirements for its flocculation capacity are becoming increasingly stringent. Cationic polyacrylamide has a long molecular chain, and its amide groups can affinity and adsorb many substances, forming hydrogen bonds. This allows it to bridge between two adsorbed particles, forming flocs, which facilitates particle settling. Cationic polyacrylamide requires a high or even ultra-high relative molecular mass, so that in addition to chemical bonding and intermolecular forces, it mainly relies on bridging to cause impurities in wastewater to precipitate. The flocculation capacity of cationic polyacrylamide largely depends on its relative molecular mass.

[0004] The high molecular weight cationic polyacrylamide currently widely used in the market has the following characteristics: From a molecular structure perspective, the first type is linear cationic polyacrylamide copolymerized with acryloxyethyltrimethylammonium chloride (DAC) and acrylamide. Its advantages are: 1. High molecular weight, between 8 million and 14 million; 2. Fewer branches, good solubility, and strong flocculation ability. Its disadvantages are that it has high requirements for operating conditions when used on-site: 1. It needs to be dissolved into a 0.1% stock solution before use, and the storage time after preparing the stock solution is short (2 to 6 hours). The molecular weight loss rate reaches 73% after more than 5 hours; 2. It has strict requirements for the wastewater environment, and the effect is better when the wastewater pH value is between 6 and 8. The second type is a partially branched cationic polyacrylamide, which is produced by copolymerizing two or three of the cationic functional monomers methacryloyloxyethyltrimethylammonium chloride (DMC), acryloyloxyethyltrimethylammonium chloride (DAC), and dimethyl diallyl ammonium chloride (DMDAAC) with acrylamide. Its advantages are: 1. Longer storage time after dissolution (8-12 hours), with a molecular weight loss rate of 50% after 12 hours; 2. Strong adaptability to wastewater and a wide pH range. Its disadvantages are: 1. Lower molecular weight, between 5 and 8 million; 2. More branched chains, poorer solubility, and a utilization rate 15-30% lower than that of linear cationic polyacrylamide.

[0005] Furthermore, with increasingly stringent environmental protection requirements, the white water from the wet end system of paper machines in the papermaking industry needs to be recycled multiple times in a closed loop. This leads to the accumulation of fine fiber impurities, fillers, and inorganic salts within the wet end system, resulting in a significant increase in wastewater turbidity and mineralization. Conventional cationic polyacrylamide flocculants are ineffective in treating this high-turbidity, high-mineralization papermaking wastewater, failing to effectively remove pollutants. Therefore, there is an urgent need to develop new flocculants with more efficient adsorption and bridging capabilities. Summary of the Invention

[0006] The technical problem to be solved by this invention is that the existing cationic acrylamide has poor flocculation effect. In view of the defects in the prior art, this invention provides a novel strong flocculating ultra-high molecular weight cationic polyacrylamide with low cost, high molecular weight, high conversion rate, good solubility and high utilization rate, as well as its preparation method and application.

[0007] To address the aforementioned technical problems, in a first aspect, the present invention provides a method for preparing a novel strongly flocculating ultra-high molecular weight cationic polyacrylamide, the preparation method comprising the following steps: Acrylamide, cationic monomers, and sterically hindered isomer functional monomers are mixed in water to obtain a mixture. Then, an azo initiator, a complexing agent, a directional chain extender, an oxidant, and a reducing agent are added to the mixture to initiate a polymerization reaction, thereby obtaining the novel strong flocculating ultra-high molecular weight cationic polyacrylamide.

[0008] After the polymerization reaction is completed, the unformed ultra-high molecular weight cationic polyacrylamide obtained in this invention is further shaped by granulation, drying and pulverization.

[0009] In this invention, an azo initiator, a complexing agent, a directional chain extender, an oxidant, and a reducing agent are added sequentially at 0~2℃. At the same time, nitrogen is purged to remove oxygen before addition, and the nitrogen purging time is 40~80min (e.g., 40min, 50min, 60min, 70min, or 80min).

[0010] According to some preferred embodiments, the method further includes the steps of granulation, drying and pulverization of the ultra-high molecular weight cationic polyacrylamide obtained in step (2). In this invention, in order to make the ultra-high molecular weight cationic polyacrylamide obtained in step (2) into a dry powder product, it is preferable to subject the ultra-high molecular weight cationic polyacrylamide obtained in step (2) to a post-processing step of granulation, drying and pulverization in sequence.

[0011] According to some preferred embodiments, before the ultra-high molecular weight cationic polyacrylamide obtained in step (2) is successively subjected to granulation, drying and pulverization steps, the ultra-high molecular weight cationic polyacrylamide obtained in step (2) is cooled first.

[0012] In this invention, acrylamide, a cationic monomer, and a sterically hindered isomeric functional monomer are preferably used for ternary copolymerization to synthesize ultra-low branched, ultra-high molecular weight cationic polyacrylamide. In the early stage of the synthesis of ultra-high molecular weight cationic polyacrylamide, this invention utilizes a redox initiation system to initiate polymerization at low temperatures. In the later stage of the reaction, the azo initiator decomposes due to exothermic reaction. The azo initiator can accelerate the reaction rate in the later stage to ensure a stable reaction, thereby ensuring an increase in the relative molecular mass of the cationic polyacrylamide. The introduction of a directional chain extender can temporarily bind to the short molecular chains generated during the chain initiation and chain growth stages, giving the short molecular chains a targeted selection function, thus making them more inclined to polymerize with the high molecular weight main chain, further increasing the molecular weight of the main chain. The resulting polyacrylamide has extremely low branched content. The introduction of the sterically hindered isomeric functional monomer causes the polymer molecular chains to form irregular coils and folds and temporary stable intermolecular entanglement and bridging, forming a molecular sieve-like spatial structure, thereby increasing the adsorption space and significantly improving the flocculation effect on high-turbidity, high-mineralization papermaking wastewater.

[0013] Preferably, the total mass of the acrylamide, cationic monomer, and sterically hindered isomer functional monomer accounts for 23% to 33% of the mass percentage of the mixture (for example, it can be 23%, 25%, 30%, 30.5%, 31%, 31.5%, 32%, 32.5%, or 33%). In this invention, when the sum of the amounts of the acrylamide, cationic monomer, and sterically hindered isomer functional monomer is recorded as the total monomer amount, that is, the total weight percentage concentration of the monomer in the mixture (aqueous solution of the monomer) is 23% to 33%.

[0014] The mass ratio of acrylamide to the cationic monomer is (2~2.5):(1~1.5). Specifically, when the sum of the amounts of acrylamide, cationic monomer, and sterically hindered isomeric functional monomer accounts for 23%~33% of the mass percentage of the mixture, that is, when the weight percentage concentration of acrylamide monomer in the mixture is 20%~25%, the weight percentage concentration of cationic monomer in the mixture is 10%~15%, and the weight percentage concentration of sterically hindered isomeric functional monomer in the mixture is 0.5%~5%.

[0015] Preferably, the cationic monomer includes any one or a combination of at least two of methacryloyloxyethyltrimethylammonium chloride, methacryloylpropyltrimethylammonium chloride, dimethyldiallylammonium chloride, or diallyldiethylammonium chloride.

[0016] Preferably, the sterically hindered isomeric functional monomer comprises any one or a combination of at least two of N-[(4-sulfonamide)phenyl]acrylamide, N-p-hydroxyphenylacrylamide, or N-isopropylacrylamide, preferably N-[(4-sulfonamide)phenyl]acrylamide; This invention introduces sterically hindered isomeric functional monomers to form sterically hindered groups during polymerization, causing the polyacrylamide molecular chains to be irregularly coiled and folded and temporarily stably entangled and bridged between molecules, forming a molecular sieve-type spatial structure. This significantly increases the adsorption space and improves the flocculation effect on papermaking wastewater with high turbidity and high mineralization.

[0017] The sterically hindered isomer functional monomer has a mass percentage of 0.5% to 5% in the mixture (for example, it can be 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%), preferably 1% to 3%.

[0018] Preferably, the azo initiator includes any one or a combination of at least two of 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide], azobisisoheptanenitrile, azobisisovaleratenitrile, or 4,4'-azobis(4-cyanovaleric acid), preferably 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide].

[0019] The mass percentage of the azo initiator in the mixture is 0.004% to 0.015% (e.g., 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.01%, or 0.015%), preferably 0.005% to 0.012%.

[0020] Preferably, the complexing agent comprises any one or a combination of at least two of disodium ethylenediaminetetraacetate, sodium ethylenediaminetetramethylenephosphonate, pentasodium diethylenetriaminepentamethylenephosphonate, or a substitute base, preferably disodium ethylenediaminetetraacetate and / or a substitute base; The complexing agent has a mass percentage of 0.004% to 0.008% in the mixture (e.g., it can be 0.004%, 0.005%, 0.006%, 0.007%, or 0.008%).

[0021] Preferably, the directional chain extender comprises any one or a combination of at least two of n-dodecyl mercaptan, 2-mercaptoethanol, or 3-mercaptoacetic acid, preferably 2-mercaptoethanol; the mass percentage of the directional chain extender in the mixture is 0.002% to 0.05% (e.g., 0.0002%, 0.0003%, 0.0004%, 0.0005%, 0.0006%, 0.0007%, 0.0008%, 0.0009%, 0.001%, 0.00%). 11%, 0.0012%, 0.0013%, 0.0014%, 0.0015%, 0.0016%, 0.0017%, 0.0018%, 0.0019%, 0.002%, 0.003%, 0.004%, 0.005%, 0.006%, 0.007%, 0.008%, 0.009%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%), preferably 0.003%~0.045%; This invention introduces a directional chain extender that briefly binds to the short molecular chains generated during the chain initiation and chain growth stages of polymerization. This gives the short molecular chains a targeted selection function, making them more inclined to polymerize with the high molecular weight main chain, thereby further increasing the molecular weight of the main chain. The polymerized polyacrylamide has extremely low branching content.

[0022] In this invention, the directional chain extender generates tertiary carbon free radicals in the later stage of the polymerization reaction. After coupling, it causes targeted carbon-carbon crosslinking between short-chain polyacrylamide polymer molecules and the main molecular chain. Adding a small amount of directional chain extender can improve the viscosity-average relative molecular mass of cationic polyacrylamide polymers, while greatly reducing the generation of branches, thereby reducing the content of insoluble matter.

[0023] In this invention, the preferred dosage of the directional chain extender is 0.002% to 0.05% of the mass of the mixture. This extremely small dosage significantly reduces production costs compared to conventional chain transfer agents (which typically account for 0.01 wt% to 2.5 wt% of the total monomer content). This invention unexpectedly reveals that a very small amount of the directional chain extender described herein can produce cationic polyacrylamide with extremely high molecular weight. The ultra-high molecular weight cationic polyacrylamide produced by this invention has a molecular weight exceeding that of conventional cationic polyacrylamide products on the market by 9 million to 11 million, and its flocculation capacity is increased by 35% to 59%. Furthermore, the ultra-high molecular weight cationic polyacrylamide produced by this invention dissolves in less than 20 minutes.

[0024] Preferably, the oxidant includes any one or a combination of at least two of benzoyl peroxide, potassium persulfate, or sodium persulfate, preferably benzoyl peroxide; the mass percentage of the oxidant in the mixture is 0.0006% to 0.0015% (for example, it can be 0.0006%, 0.0009%, 0.001%, 0.0011%, 0.0012%, 0.0013%, 0.0014%, or 0.0015%).

[0025] Preferably, the reducing agent comprises ferrous sulfite and / or sodium sulfite, preferably ferrous sulfite; the mass percentage of the reducing agent in the mixture is 0.0006% to 0.0013% (e.g., 0.0006%, 0.0011%, 0.0012% or 0.0013%).

[0026] Preferably, before the polymerization reaction, the pH of the mixture is adjusted to 3.5-5 using a pH adjuster (e.g., 3.8, 3.9, 4.1, 4.2, 4.8, or 5). In this invention, the pH adjuster is selected from the group consisting of glutaric acid, hydrochloric acid, and sulfuric acid, preferably glutaric acid, because compared to hydrochloric acid and sulfuric acid, glutaric acid gradually decomposes during dissolution and slowly participates in the reaction, ensuring stable system temperature during the adjustment process.

[0027] Preferably, the polymerization reaction takes 2 to 3 hours, for example, 2 hours, 2.5 hours, or 3 hours.

[0028] As a preferred technical solution: (1) Use deionized water to thoroughly mix acrylamide, methacrylpropyltrimethylammonium chloride (cationic monomer) and N-[(4-sulfonamide)phenyl]acrylamide (sterically hindered isomer functional monomer) to obtain a mixture (monomer aqueous solution) with a total monomer weight percentage concentration of 23%~33%. Adjust the pH of the mixture to 3.5-5.0 with glutaric acid, and then use a refrigeration device to lower the temperature of the mixture to 0~2℃. (2) When the temperature of the mixture obtained in step (1) drops to 0~2℃, transfer the mixture into an insulated reactor, insert a digital thermometer, and purge it with high-purity nitrogen gas for 40~80 min. Then, add to the mixture 0.005%~0.012% by mass of 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide] (azo initiator), 0.004%~0.008% by mass of disodium ethylenediaminetetraacetate (complexing agent), and 0.003%~0.045% by mass of [unspecified ingredient]. 2-Mercaptoethanol (directional chain extender), 0.0006%~0.0015% potassium persulfate (oxidant) by mass of the mixture, and 0.0006%~0.0013% ferrous sulfite (reducing agent) by mass of the mixture were used to initiate a polymerization reaction (aqueous solution polymerization under normal pressure). When the viscosity of the mixture increased and nitrogen gas bubbled, the nitrogen gas was stopped, the insulated reactor was sealed, and the temperature change was observed and recorded. The reaction was continued for 2~3 hours to obtain a colloidal novel strong flocculating ultra-high molecular weight cationic polyacrylamide. Then the colloidal ultra-high molecular weight cationic polyacrylamide was cooled. (3) The colloidal novel strong flocculating ultra-high molecular weight cationic polyacrylamide cooled in step (2) is successively subjected to granulation, drying and pulverization steps to obtain dry powder novel strong flocculating ultra-high molecular weight cationic polyacrylamide.

[0029] This invention involves adding an appropriate amount of complexing agent, particularly a highly efficient directional chain extender and a sterically hindered isomer functional monomer, during the synthesis of cationic polyacrylamide. A low-temperature composite initiation system is used, with a redox initiator (preferably benzoyl peroxide and low-valent metal sulfate) as the main initiator and an azo initiator as the auxiliary initiator. Through a batch-addition process of the initiator and preferably by controlling the pH of the mixed solution to 3.5-5.0, the initiation temperature to 0-2℃, and the total monomer concentration to 30-35%, the optimized process is employed to carry out aqueous solution polymerization under normal pressure. The entire polymerization reaction takes only 2-3 hours to obtain the ultra-high molecular weight cationic polyacrylamide (PAM) product.

[0030] The preparation method provided by this invention is a feasible method for producing a novel, highly flocculating, ultra-high molecular weight cationic polyacrylamide for water treatment, suitable for industrial production. The ultra-high molecular weight cationic polyacrylamide obtained by this invention has a high relative molecular mass, high conversion rate, low monomer content, excellent solubility, high production efficiency, and low cost. It is particularly suitable for treating high-turbidity, high-mineralization papermaking wastewater. Compared with other polyacrylamide products containing the same number of charged chain segments, it produces superior water quality indicators after wastewater treatment, requiring a smaller dosage. It is particularly noteworthy that this invention does not have special requirements for adding the initiator in batches. The polymerization reaction can be initiated simply by sequentially adding an azo initiator, a complexing agent, a directional chain extender, an oxidant, and a reducing agent to the mixture. That is, during the addition of these substances, the next substance can be added only after the previous substance has completely dissolved in the mixture. For example, when adding an azo initiator and a complexing agent, the complexing agent can be added only after the azo initiator has completely dissolved in the mixture.

[0031] Secondly, the present invention provides a novel strong flocculating ultra-high molecular weight cationic polyacrylamide prepared by the preparation method described in the first aspect, wherein the viscosity-average relative molecular mass of the novel strong flocculating ultra-high molecular weight cationic polyacrylamide is 20 million to 24 million.

[0032] Thirdly, the present invention provides an application of the novel strong flocculating ultra-high molecular weight cationic polyacrylamide described in the first aspect in the preparation of flocculants.

[0033] The novel strong flocculating ultra-high molecular weight cationic polyacrylamide of this invention is particularly suitable for use in treating high-turbidity, high-mineralization papermaking wastewater.

[0034] The preparation method of the present invention has the following beneficial effects: (1) The preparation process of the present invention is simple, the reaction time is short, the cost is low, the production efficiency is high, and the highest conversion rate reaches 99.3%, which is more suitable for industrial production. The ultra-high molecular weight cationic polyacrylamide obtained by the present invention has low monomer content and ultra-high molecular weight. Its molecular weight exceeds the molecular weight of conventional cationic polyacrylamide products on the market by 9 million to 11 million, and the flocculation ability is improved by 35% to 59%.

[0035] (2) In some preferred embodiments of the present invention, the cationic polyacrylamide molecules with fewer branches are reduced by 85% compared to the multi-component copolymer cationic polyacrylamide, resulting in significantly improved solubility and utilization. In wastewater flocculation tests, the dosage is reduced by 38% to 57% compared to conventional cationic polyacrylamide, and the sludge flocs are compacted, improving the sludge removal efficiency of the desludge removal equipment by approximately 33% and reducing energy consumption by approximately 23%. Compared to other polyacrylamide products containing the same number of charged chain segments used as flocculants for wastewater treatment, the water quality indicators treated with the ultra-high molecular weight cationic polyacrylamide of the present invention are superior, requiring less dosage.

[0036] (3) By introducing a directional chain extender, which briefly binds to the short molecular chains generated during the chain initiation and chain growth stages, the short molecular chains acquire a targeted selection function, making them more inclined to polymerize with the high molecular weight main chain, thereby further increasing the molecular weight of the main chain. The polymerized polyacrylamide has very few branched chains, increasing the number of charged groups on the main chain; by introducing sterically hindered isomeric functional monomers, the polyacrylamide molecular chains form irregular coils and folds and temporary stable entanglement and bridging between molecules, constructing a molecular sieve-type spatial structure, significantly increasing the adsorption space, and is particularly suitable for the treatment of high turbidity and high mineralization papermaking wastewater, with a significant improvement in flocculation effect. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. 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.

[0038] The following embodiments of the present invention describe the experimental raw materials, experimental instruments and equipment used for preparing cationic polyacrylamide and for testing its performance, as well as the methods for performance testing: Experimental materials: Acrylamide (AM), cationic monomer (methacryloylpropyltrimethylammonium chloride), sterically hindered isomer functional monomer (N-[(4-sulfonamide)phenyl]acrylamide), deionized water, and 2.5 mol / L NaCl solution.

[0039] Experimental instruments and equipment: Analytical balance, electronic balance, precision pH meter, 2000mL insulated reaction vessel, digital thermometer, high-pressure nitrogen cylinder, rotary viscometer, Ubbelohde viscometer, constant temperature water bath, mechanical stirrer, 250mL volumetric flask, 80-mesh standard sieve, stopwatch, scientific calculator, pipette bulb, 100mL pipette, refrigeration unit, constant temperature drying oven, weighing bottle, 753 spectrophotometer, and desliming equipment.

[0040] Test method: (a) Determination of viscosity-average relative molecular mass: The outflow times of NaCl solution and 0.1% sample solution (0.1% cationic polyacrylamide aqueous solution) were measured by Ubbelohde viscometer and recorded as t0 and t1, respectively. The viscosity-average relative molecular mass was then converted according to the following formula: Where A represents the solid content of the sample, and m represents the mass of the sample. Average molecular weight, ηsp = ηr-1, ηr = t1 / t0, [η] - intrinsic viscosity.

[0041] (b) Determination of insoluble content: Weigh approximately 0.4 g of cationic polyacrylamide sample, completely dissolve it in 1000 mL of deionized water, filter the solution through an 80-mesh standard sieve and dry to constant weight, and calculate the insoluble content according to the following formula: Where w1 is the insoluble content, m1 is the total mass of the standard sieve and insoluble matter, m2 is the mass of the standard sieve, and m is the mass of the sample.

[0042] (c) Determination of flocculation rate: Domestic sewage from a wastewater treatment plant or high-turbidity, high-mineralization papermaking wastewater was collected, and the absorbance value (Dγ value) of the upper phase liquid of the original wastewater was measured at a wavelength of 550 nm using a 753 spectrophotometer and recorded as A1; 100 mL of this wastewater was added to a 250 mL Erlenmeyer flask, and 0.1 g of cationic polyacrylamide was added, mixed evenly, and allowed to stand for 1 h. Then, the absorbance value (Dγ value) of the upper phase liquid of the treated wastewater was measured at a wavelength of 550 nm using a 753 spectrophotometer and recorded as B1. The flocculation rate of the cationic polyacrylamide was thus obtained as follows: Flocculation rate (%) = (A1-B1) / A1×100%.

[0043] (d) Using cationic polyacrylamide as a flocculant, 10 tons of domestic sewage or high-turbidity, high-mineralization papermaking wastewater were treated on-site using a desludge dewatering equipment. The dosage of cationic polyacrylamide and the desludge dewatering efficiency of the equipment were calculated.

[0044] Example 1 (1) Acrylamide, methacrylpropyltrimethylammonium chloride (cationic monomer) and N-[(4-sulfonamide)phenyl]acrylamide (sterically hindered isomeric functional monomer) are thoroughly mixed with deionized water to obtain a mixture with a total monomer weight percentage concentration of 35%. The pH of the mixture is adjusted to 4.0 with glutaric acid, and then the temperature of the mixture is lowered to 1°C using a refrigeration device. The acrylamide monomer weight percentage concentration in the mixture is 23%, the cationic monomer weight percentage concentration is 10%, and the sterically hindered isomeric functional monomer weight percentage concentration is 2%.

[0045] (2) When the temperature of the mixture obtained in (1) drops to 1°C, the mixture is transferred into an insulated reactor, a digital thermometer is inserted, and high-purity nitrogen is introduced into it for 40 min. Then, 0.006% of the mass of 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide], 0.006% of the mass of ethylenediaminetetraacetic acid disodium salt, 0.0005% of the mass of 2-mercaptoethanol, 0.0012% of the mass of potassium persulfate and 0.0005% of the mass of ferrous sulfate are added to the mixture in sequence. When the viscosity of the mixture increases and nitrogen bubbles, the nitrogen is stopped, the insulated reactor is sealed, the temperature change is observed and recorded, and the reaction is continued for 3 h to obtain colloidal ultra-high molecular weight cationic polyacrylamide. The colloidal ultra-high molecular weight cationic polyacrylamide is then cooled.

[0046] (3) The colloidal novel strong flocculating ultra-high molecular weight cationic polyacrylamide obtained in (1) is successively subjected to granulation, drying and pulverization steps to obtain dry powder ultra-high molecular weight cationic polyacrylamide.

[0047] The performance of the dry powdered ultra-high molecular weight cationic polyacrylamide prepared in this embodiment was tested, and the results are shown in Table 1. The dry powdered ultra-high molecular weight cationic polyacrylamide prepared in this embodiment was used as a flocculant for the treatment of high turbidity and high mineralization papermaking wastewater, and the wastewater treatment effect (flocculation rate, desludge efficiency and cationic polyacrylamide dosage) is shown in Table 1.

[0048] Example 2 Experiment on the effect of the amount of azo initiator on the relative molecular mass of ultra-high molecular weight cationic polyacrylamide.

[0049] Example 2 is basically the same as Example 1, except that: The effect of varying the amount of 2,2'-azo [2-methyl-N-(2-hydroxyethyl)propionamide] (an azo initiator) on the relative molecular mass of ultra-high molecular weight cationic polyacrylamide was investigated. The relationship between the amount of azo initiator and the viscosity-average relative molecular mass of ultra-high molecular weight cationic polyacrylamide is shown in Table 2.

[0050] As shown in Table 2, adding an appropriate amount of 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide] (AIBA) can further increase the relative molecular mass of the cationic polyacrylamide in this invention. When the amount of azo initiator is 0.006% of the mass of the mixture, the viscosity-average relative molecular mass of the cationic polyacrylamide reaches its maximum value.

[0051] In this embodiment, when the amount of 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide] is 0.001%, the viscosity-average relative molecular mass obtained is 24.09 × 10⁻⁶. 6 The performance of the dry powdered ultra-high molecular weight cationic polyacrylamide was tested, and the results are shown in Table 1. The dry powdered ultra-high molecular weight cationic polyacrylamide was used as a flocculant for the treatment of high turbidity and high mineralization papermaking wastewater, and the wastewater treatment effect is shown in Table 1.

[0052] Example 3 Experiment on the effect of type and dosage of directional chain extender on the relative molecular mass of ultra-high molecular weight cationic polyacrylamide.

[0053] Example 3 is basically the same as Example 1, except that: Dodecyl mercaptan, 2-mercaptoethanol, and 3-mercaptoacetic acid were used as directional chain extenders, respectively. The effects of the type and amount of directional chain extenders on the viscosity-average molecular weight of ultra-high molecular weight cationic polyacrylamide were studied by changing the amounts of dodecyl mercaptan, 2-mercaptoethanol, and 3-mercaptoacetic acid. The results are shown in Table 3.

[0054] As shown in Table 3, when different types of directional chain extenders are added, the ultra-high molecular weight cationic polyacrylamide prepared by adding 2-mercaptoethanol as a directional chain extender has the highest viscosity-average relative molecular mass and requires the least amount of directional chain extender.

[0055] The viscosity-average relative molecular mass obtained in this embodiment using 3-mercaptoacetic acid as a directional chain extender (at 0.04% of the mass of the mixture) is 23.33 × 10⁻⁶. 6The performance of the dry powdered ultra-high molecular weight cationic polyacrylamide was tested, and the results are shown in Table 1. The dry powdered ultra-high molecular weight cationic polyacrylamide was used as a flocculant for the treatment of high turbidity and high mineralization papermaking wastewater, and the wastewater treatment effect is shown in Table 1.

[0056] Example 4 Experiment on the effect of 2-mercaptoethanol dosage on the relative molecular mass and insoluble content of ultra-high molecular weight cationic polyacrylamide.

[0057] Example 4 is basically the same as Example 1, except that: Based on Example 3, the effect of the amount of 2-mercaptoethanol on the relative molecular mass and insoluble content of ultra-high molecular weight cationic polyacrylamide was further studied by changing the amount of 2-mercaptoethanol. The relationship between the amount of 2-mercaptoethanol and the viscosity-average relative molecular mass and insoluble content is shown in Table 4.

[0058] The results in Table 4 show that when the amount of 2-mercaptoethanol as the directional chain extender is 0.0005%, the viscosity-average molecular weight of the prepared ultra-high molecular weight cationic polyacrylamide is the highest, and the insoluble content is 0. When the amount of 2-mercaptoethanol is greater than 0.008%, the viscosity-average molecular weight of the prepared ultra-high molecular weight cationic polyacrylamide is significantly reduced.

[0059] In this embodiment, when the amount of 2-mercaptoethanol used was 0.0015%, the viscosity-average relative molecular mass obtained was 23.65 × 10⁻⁶. 6 The performance of the dry powder ultra-high molecular weight cationic polyacrylamide was tested, and the results are shown in Table 1. The dry powder of ultra-high molecular weight cationic polyacrylamide was used as a flocculant for the treatment of high turbidity and high mineralization papermaking wastewater, and the wastewater treatment effect is shown in Table 1.

[0060] Example 5 Experiment on the effect of the amount of sterically hindered isomer functional monomers on the flocculation effect of ultra-high molecular weight cationic polyacrylamide.

[0061] Example 5 is basically the same as Example 1, except that: The effect of varying the dosage of N-[(4-sulfonamide)phenyl]acrylamide on the flocculation effect of ultra-high molecular weight cationic polyacrylamide in treating high-turbidity, high-mineralization papermaking wastewater was investigated. The results are shown in Table 5. Other properties are shown in Table 1.

[0062] As shown in Table 5, when the dosage of sterically hindered isomer functional monomer is 2%, the flocculation rate is the highest, reaching 96.8%, and the sludge removal efficiency is increased to 88.5%, while the dosage of cationic polyacrylamide is reduced to 9.5 kg / 10 tons of wastewater.

[0063] Comparative Example 1 Comparative Example 1 is basically the same as Example 1, except that: N-hydroxymethylacrylamide was used instead of 2-mercaptoethanol as the directional chain extender, and the amount used was the same as that of 2-mercaptoethanol in Example 1. Other differences are shown in Table 1.

[0064] Comparative Example 2 Comparative Example 2 is basically the same as Comparative Example 1, except that: The amount of N-hydroxymethylacrylamide used is 0.1 wt% of the total amount of acrylamide and methacryloylpropyltrimethylammonium chloride. Other differences are shown in Table 1.

[0065] Comparative Example 3 Comparative Example 3 is basically the same as Example 1, except that: Boric acid was used instead of 2-mercaptoethanol as the directional chain extender, and the amount used was the same as that of 2-mercaptoethanol in Example 1. Other differences are shown in Table 1.

[0066] Comparative Example 4 Comparative Example 4 is basically the same as Comparative Example 3, except that: The amount of boric acid used is 0.1 wt% of the total amount of acrylamide and methacrylpropyltrimethylammonium chloride. Other differences are shown in Table 1.

[0067] Table 1 sample Dissolution rate (min) Insoluble matter content (%) Viscosity-average molecular weight (×10⁶) Flocculation rate (%) Desliming efficiency (%) Dosage of cationic polyacrylamide (kg / 10 tons of wastewater) Example 1 20 0 22.83 96.3 89.6 8.1 Example 2 19 0 20.19 93.1 83.9 9.9 Example 3 18 0 17.15 89.6 78.1 13.3 Example 4 13 0 14.69 80.0 77.8 13.1 Example 5 19 0 21.81 93.9 86.5 10.6 Comparative Example 1 20 1.5 10.9 65.9 61.7 21.9 Comparative Example 2 21 1.3 13.1 68.3 63.3 19.8 Comparative Example 3 24 1.5 11.1 63.9 63.5 15.3 Comparative Example 4 23 1.5 15.0 66.9 63.9 14.5 Table 2 Azo initiator dosage (%) 0.004 0.005 0.006 0.008 0.010 <![CDATA[Viscosity-average relative molecular weight (×10 6 )]]> 19.58 22.31 23.03 20.01 20.16 Table 3 Table 4 Table 5 Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a novel strong flocculating ultra-high molecular weight cationic polyacrylamide, characterized in that: The preparation method includes the following steps: Acrylamide, cationic monomers, and sterically hindered isomer functional monomers are mixed in water to obtain a mixture. Then, an azo initiator, a complexing agent, a directional chain extender, an oxidant, and a reducing agent are added to the mixture to initiate a polymerization reaction, thereby obtaining the novel strong flocculating ultra-high molecular weight cationic polyacrylamide.

2. The preparation method according to claim 1, characterized in that: The total mass of the acrylamide, cationic monomer, and sterically hindered isomer functional monomer accounts for 23% to 33% of the mass of the mixture. The mass ratio of the acrylamide to the cationic monomer is (2~2.5):(1~1.5).

3. The preparation method according to claim 1, characterized in that: The cationic monomer includes any one or a combination of at least two of methacryloyloxyethyltrimethylammonium chloride, methacryloylpropyltrimethylammonium chloride, dimethyldiallylammonium chloride, or diallyldiethylammonium chloride.

4. The preparation method according to claim 1, characterized in that: The sterically hindered isomeric functional monomer includes any one or a combination of at least two of N-[(4-sulfonamide)phenyl]acrylamide, N-p-hydroxyphenylacrylamide or N-isopropylacrylamide, preferably N-[(4-sulfonamide)phenyl]acrylamide; The sterically hindered isomer functional monomer has a mass percentage of 0.5% to 5% in the mixture, preferably 1% to 3%.

5. The preparation method according to claim 1, characterized in that: The azo initiator includes any one or a combination of at least two of 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide], azobisisoheptanenitrile, azobisisovaleratenitrile, or 4,4'-azobis(4-cyanopentanoic acid), preferably 2,2'-azo[2-methyl-N-(2-hydroxyethyl)propionamide]. The azo initiator has a mass percentage of 0.004% to 0.015% in the mixture, preferably 0.005% to 0.012%.

6. The preparation method according to claim 1, characterized in that: The complexing agent includes any one or a combination of at least two of the following: disodium ethylenediaminetetraacetate, sodium ethylenediaminetetramethylenephosphonate, pentasodium diethylenetriaminepentamethylenephosphonate, or a substitute base; preferably, disodium ethylenediaminetetraacetate and / or a substitute base. The complexing agent has a mass percentage of 0.004% to 0.008% in the mixture.

7. The preparation method according to claim 1, characterized in that: The directional chain extender comprises any one or a combination of at least two of n-dodecyl mercaptan, 2-mercaptoethanol, or 3-mercaptoacetic acid, preferably 2-mercaptoethanol; the mass percentage of the directional chain extender in the mixture is 0.002% to 0.05%, preferably 0.003% to 0.045%; Preferably, the oxidant comprises any one or a combination of at least two of benzoyl peroxide, potassium persulfate, or sodium persulfate, with benzoyl peroxide being the most preferred; the mass percentage of the oxidant in the mixture is 0.0006% to 0.0015%. Preferably, the reducing agent comprises ferrous sulfite and / or sodium sulfite, more preferably ferrous sulfite; the mass percentage of the reducing agent in the mixture is 0.0006%~0.0013%.

8. The preparation method according to claim 1, characterized in that: Before the polymerization reaction, the pH of the mixture is adjusted to 3.5-5 using a pH adjuster. Preferably, the polymerization reaction takes 2 to 3 hours.

9. The novel strongly flocculating ultra-high molecular weight cationic polyacrylamide prepared by the preparation method according to any one of claims 1 to 8, wherein the viscosity-average relative molecular mass of the novel strongly flocculating ultra-high molecular weight cationic polyacrylamide is 20 million to 24 million.

10. The application of the novel strong flocculating ultra-high molecular weight cationic polyacrylamide according to claim 9 in the preparation of flocculants.

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