Cationic polymer-based magnetic nano demulsifier as well as preparation method and application thereof

Abstract

The invention discloses a cationic polymer-based magnetic nano demulsifier as well as a preparation method and application thereof. The preparation method comprises the following steps: (1) preparing magnetic porous carbon by taking lignin as a raw material; (2) dropwise adding a pre-prepared sodium dodecyl benzene sulfonate aqueous solution into a pre-prepared magnetic porous carbon solution to obtain SDBSamp; an MPC; (3) dissolving chitosan in an acetic acid aqueous solution, initiating graft polymerization, and adding acryloyloxyethyl trimethyl ammonium chloride to obtain a product CTs-AETAC; (4) adding the CTs-AETAC solution into the SDBSamp (sodium dodecyl benzene sulfonate); in an MPC solution, CTs-AETAC (at) SDBSamp is obtained; the invention relates to MPC composite magnetic nanoparticles. The preparation method of the demulsifier provided by the invention is simple, green and environment-friendly, the demulsifier can quickly demulsify stable oil-containing wastewater at normal temperature, has a good demulsification effect, is clear in water phase, and can be recycled.

Description

Technical Field

[0001] This invention belongs to the field of oilfield chemical technology, specifically relating to a cationic polymer-based magnetic nano-demulsifier, its preparation method, and its application. Background Technology

[0002] Petrochemical production generates large amounts of oily wastewater. If this wastewater is discharged directly without treatment, it will have a significant impact on the natural environment and ultimately threaten human health. Therefore, the treatment of oily wastewater is essential. Demulsification treatment can be used to disrupt the stability of the oil-water emulsion system, separating the oil and water phases, thereby enabling effective subsequent treatment and resource recovery.

[0003] Currently, demulsification methods mainly include physical, biological, and chemical methods. Among them, chemical demulsification is one of the most widely used methods in oily wastewater treatment due to its simple process and low cost. Chemical demulsification breaks down the interfacial film by adding a demulsifier, offering advantages such as speed, low energy consumption, and small dosage. Its core mechanism is that demulsifier molecules migrate to the oil-water interface through diffusion, and their active components competitively adsorb and "replace" the original interfacial active substances (such as asphaltenes and gums), thereby reducing the strength of the interfacial film, promoting the coalescence of small droplets into larger droplets, and ultimately achieving effective stratification of the oil and water phases. However, its disadvantages include the fact that most demulsifiers currently used cannot be reused. This increases the cost of chemical demulsification, and the presence of demulsifiers in the oil or water phase may also adversely affect subsequent processes. Summary of the Invention

[0004] To address the problems existing in the prior art, the present invention aims to provide a cationic polymer-based magnetic nano-demulsifier, its preparation method, and its application. The cationic polymer-based magnetic nano-demulsifier of the present invention not only has a fast demulsification rate but is also reusable.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a cationic polymer-based magnetic nano-demulsifier includes the following steps: A suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate was added to an aqueous solution of CTs-AETAC graft copolymer and stirred during the addition process. After the reaction was completed, the particles were separated, washed, and dried to obtain the cationic polymer-based magnetic nano-demulsifier. The preparation process of the sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles includes: reacting an aqueous solution of sodium dodecylbenzenesulfonate with a magnetic porous carbon suspension, followed by magnetic separation, washing, and drying to obtain sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles. The preparation process of the CTs-AETAC graft copolymer includes: initiating graft polymerization by dissolving chitosan in an aqueous solution of acetic acid, then adding acryloyloxyethyltrimethylammonium chloride for free radical graft polymerization, followed by separation, washing, and drying to obtain the product CTs-AETAC graft copolymer.

[0006] Preferably, the magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate are prepared by the following steps: Sodium bicarbonate aqueous solution and lignin solution were mixed evenly to obtain mixture A; wherein, the solid-liquid ratio of lignin to deionized water in sodium bicarbonate aqueous solution was (2.0~3.0g):50mL; the solid-liquid ratio of sodium bicarbonate to water in sodium bicarbonate aqueous solution was (3.0~5.0g):(80~100mL); and the volume ratio of sodium bicarbonate aqueous solution to lignin solution was (80~100mL):50mL. Add the ferric nitrate nonahydrate aqueous solution to the mixture A and stir until homogeneous to obtain a uniformly dispersed system A; wherein the volume ratio of the ferric nitrate nonahydrate aqueous solution to the mixture A is 10 mL: (130-150 mL), and each 10 mL of the ferric nitrate nonahydrate aqueous solution contains 0.5~1.0 g of ferric nitrate nonahydrate; The uniformly dispersed system A was pyrolyzed at 500-700°C for 2-4 hours to obtain carbonized products; The carbonized product is ground into a fine powder, then washed with deionized water and ethanol alternately 3-5 times, and then dried to obtain the magnetic porous carbon.

[0007] Preferably, the carbonized product is ground into a fine powder with a particle size of <100μm.

[0008] Preferably, the step of reacting an aqueous solution of sodium dodecylbenzenesulfonate with a magnetic porous carbon suspension, followed by magnetic separation, washing, and drying to obtain sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles includes the following steps: An aqueous solution of sodium dodecylbenzenesulfonate was added to a magnetic porous carbon suspension at a rate of 1-2 mL / min, while the system was stirred at 25-35°C for 0.5-2 h. The sodium dodecylbenzenesulfonate content in the aqueous solution was 0.1 wt%-0.5 wt%, and the magnetic porous carbon content in the magnetic porous carbon suspension was 1 wt%-5 wt%. The volume ratio of the aqueous solution of sodium dodecylbenzenesulfonate to the magnetic porous carbon suspension was 1:1. After the reaction is complete, the particulate product is separated by magnetic adsorption, and then the particulate product is washed with distilled water 3-5 times to obtain the magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate; wherein the particulate product is separated by magnetic adsorption after each washing.

[0009] Preferably, the graft polymerization of chitosan dissolved in an aqueous acetic acid solution includes the following steps: Chitosan was dissolved in an aqueous solution of acetic acid with a content of 2wt%~3wt%, and stirred at 70~100°C under a protective atmosphere until the chitosan was completely dissolved to obtain a homogeneous and transparent solution. Add potassium persulfate and sodium bisulfite to the homogeneous and transparent solution, maintain a protective atmosphere, and continue stirring until the initiator is uniformly dispersed and activates the free radical active sites on the chitosan molecular chain, thus completing the process of initiating graft polymerization of chitosan dissolved in acetic acid aqueous solution. For every 2.0-3.0g of chitosan, 0.061-0.085g of potassium persulfate and 0.024-0.067g of sodium bisulfite are added. The mass ratio of chitosan to acetic acid aqueous solution is (2.0-3.0g): (85-90g).

[0010] Preferably, after initiating graft polymerization of chitosan dissolved in an aqueous acetic acid solution, acryloyloxyethyltrimethylammonium chloride is added to carry out a free radical graft polymerization reaction, followed by separation, washing, and drying to obtain the product CTs-AETAC graft copolymer, comprising the following steps: An aqueous solution of 15wt%~20wt% acryloyloxyethyltrimethylammonium chloride was added to the mixture after graft polymerization of chitosan-dissolved acetic acid was initiated at a rate of 1~2mL / min. The reaction temperature was maintained at 50~80°C, and the mixture was stirred continuously for 2~4h to complete the free radical graft polymerization reaction. The mass ratio of the aqueous solution of acryloyloxyethyltrimethylammonium chloride to the mixture after graft polymerization of chitosan-dissolved acetic acid was (23-25g):(87-90g). After the reaction is complete, the mixture is cooled and centrifuged. The separated product is then washed with deionized water 3-5 times and then vacuum dried to obtain the CTs-AETAC graft copolymer.

[0011] Preferably, the content of CTs-AETAC graft copolymer in the aqueous solution is 2wt%~5wt%; In the suspension of the sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles, the content of the sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles is 0.5wt%~2.5wt%. When a suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate is added to an aqueous solution of CTs-AETAC graft copolymer for reaction, the addition rate of the suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate is controlled at 1~2 mL / min. A suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate was added to an aqueous solution of CTs-AETAC graft copolymer and reacted. The reaction was carried out with stirring. After the reaction was completed, the particles were separated, washed, and dried. The specific steps included: After the reaction is complete, the composite particles are separated by magnetic adsorption and the supernatant is discarded. The composite particles are then washed alternately with deionized water and anhydrous ethanol 3-5 times. The washed composite particles are then vacuum dried to obtain the cationic polymer-based magnetic nano-demulsifier.

[0012] Preferably, during vacuum drying, the process involves vacuum drying at 50-80°C for 24-48 hours.

[0013] The present invention also provides a cationic polymer-based magnetic nano-demulsifier, which is prepared by the preparation method described above.

[0014] The present invention also provides the application of the cationic polymer-based magnetic nano-demulsifier as described above, wherein the cationic polymer-based magnetic nano-demulsifier is used for demulsification treatment of oily wastewater, and the addition amount of the cationic polymer-based magnetic nano-demulsifier is 150~200 mg / L.

[0015] The present invention has the following beneficial effects: This invention utilizes a reverse demulsifier grafted with core-shell structured magnetic microspheres, which not only possesses excellent demulsification performance but also achieves effective separation. The cationic polymer-based magnetic nano-demulsifier obtained in this invention has a positively charged MPC surface, which can combine with negatively charged emulsified oil droplets through electrostatic attraction, effectively neutralizing the charge at the oil-water interface, reducing the stability of the interface film, and accelerating the oil droplet coalescence and demulsification process. Therefore, this invention can achieve effective separation of oily wastewater, and due to its magnetic properties, the demulsifier can be recycled through magnetic recovery. The demulsifier preparation method provided by this invention is simple and environmentally friendly. This demulsifier can rapidly demulsify stable oily wastewater, especially oily wastewater with an oil content of 1%, exhibiting excellent demulsification effects, resulting in a clear aqueous phase, and can be recycled and reused. Attached Figure Description

[0016] Figure 1 This is a transmission electron microscope image of the reusable cationic polymer demulsifier obtained in Example 1 of the present invention; Figure 2 Fourier transform infrared (FTIR) spectra of carbon nanotubes and the reusable carbon-based nano-demulsifier obtained in Example 1 of this invention. Figure 3 Thermogravimetric analysis (TGA) of carbon nanotubes and the reusable carbon-based nano-demulsifier obtained in Example 1 of this invention.

[0017] Figure 4 This is the VSM diagram of CTs&AETAC@SDBS&MPC in Embodiment 1 of the present invention; Figure 5 This is a graph showing the effect of increasing the dosage of CTs&AETAC@SDBS&MPC on demulsification performance in Example 1 of the present invention. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0019] In a first aspect, the present invention provides a method for preparing a reusable cationic polymer demulsifier, the method comprising the following steps: Step (1) Calcine lignin at high temperature to obtain magnetic porous carbon (MPCs). Step (2) Add the pre-prepared sodium dodecylbenzenesulfonate (SDBS) aqueous solution dropwise to the pre-prepared MPCs solution to obtain SDBS & MPC; Step (3) Chitosan (CTs) is dissolved in an aqueous acetic acid solution to initiate graft polymerization. Acryloyloxy ethyl trimethylammonium chloride (AETAC) is added to obtain the product CTs-AETAC. Step (4) Add CTs-AETAC to SDBS&MPC to obtain CTs-AETAC@SDBS&MPC composite magnetic nanoparticles.

[0020] According to the present invention, the step (1) of calcining lignin at high temperature to obtain magnetic porous carbon includes the following steps: (a) Dissolve lignin in a homogeneous solution under magnetic stirring; (b) Mix sodium bicarbonate solution with lignin solution; slowly add aqueous solution of ferric nitrate nonahydrate to the above mixture and stir to form a uniform dispersion system; (c) Lignin is pyrolyzed at a constant temperature in a tube furnace to generate Fe3O4 magnetic nanoparticles, and sodium bicarbonate releases CO2 gas to form a porous structure. (d) The carbonization product was ground into a fine powder, washed three times alternately with deionized water and ethanol, and dried overnight to obtain pure magnetic porous carbon (MPCs).

[0021] In this invention, the temperature under magnetic stirring in step (a) is 70–100°C, such as 70°C, 80°C, 90°C, or 100°C, but not limited to the listed values; other unlisted values ​​within this range are also applicable. The stirring time is 30–90 min, such as 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, or 90 min, but not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 50–60 min. The stirring speed is 500–800 r / min, such as 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min, or 800 r / min, but not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 500–600 r / min.

[0022] In this invention, the amount of sodium bicarbonate in step (b) is 3.0–5.0 g, and the amount of ferric nitrate nonahydrate is 0.5–1.0 g. For example, the mass of sodium bicarbonate can be 3.0 g, 3.5 g, 4.0 g, 4.5 g, or 5.0 g, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. For example, the mass of ferric nitrate nonahydrate can be 0.5 g, 0.6 g, 0.7 g, 0.8 g, 0.9 g, or 1.0 g, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0023] In this invention, the high-temperature carbonization temperature in step (c) is 500–700°C, such as 500°C, 550°C, 600°C, 650°C, or 700°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 600°C–700°C; the carbonization time is 2–4 hours, such as 2 hours, 3 hours, or 4 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 2 hours; the carbonization is carried out under nitrogen protection. Preferably, when lignin is pyrolyzed at a constant temperature in a tube furnace, the heating rate is 10°C / min.

[0024] In this invention, the drying temperature in step (d) is 50-80°C, such as 50°C, 60°C, 70°C, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The drying time is 24-48h, such as 24h, 30h, 36h, 42h, or 48h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0025] According to the present invention, step (2), which involves adding a pre-prepared aqueous solution of sodium dodecylbenzenesulfonate dropwise to a pre-prepared MPCs solution to obtain SDBS & MPCs, includes the following steps: (e) Dissolve sodium dodecylbenzenesulfonate in deionized water, stir, and prepare a homogeneous solution with a content of 0.1wt%-0.5wt% to obtain mixture I; (f) Magnetic porous carbon is dispersed in deionized water and ultrasonically treated to obtain mixture II; (g) Add the above mixture I dropwise to the above mixture II at a rate of 1~2 mL / min, and stir to obtain mixture III; wherein the volume ratio of mixture I to mixture II is 1:1; (h) After the reaction is complete, the SDBS-modified MPCs particles are separated by adsorption using a permanent magnet or electromagnetic field. The product is washed 3-5 times with distilled water, and after each wash, it is separated by magnetic field to remove unadsorbed SDBS and impurities.

[0026] In this invention, the stirring speed in step (e) is 200 to 400 r / min, such as 200 r / min, 250 r / min, 300 r / min, 350 r / min or 400 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 200 to 300 r / min.

[0027] In this invention, the content of sodium dodecylbenzenesulfonate in step (e) is 0.1wt%-0.5wt%, such as 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt% or 0.5wt%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] In this invention, the ultrasonic dispersion time in step (f) is 5 to 30 minutes, such as 5 minutes, 10 minutes, 15 minutes, 20 minutes, 25 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The ultrasonic dispersion frequency is 60 Hz and the ultrasonic power is 200 W.

[0029] In this invention, the stirring time in step (g) is 0.5 to 2 hours, such as 0.5 hours, 1 hour, 1.5 hours, or 2 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. This invention does not impose any special restrictions on the stirring temperature; stirring at room temperature is sufficient.

[0030] In this invention, the stirring speed in step (g) is 200 to 500 r / min, such as 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 300 to 400 r / min.

[0031] In this invention, the stirring temperature in step (g) is 25 to 35°C, such as 25°C, 28°C, 30°C, 33°C or 35°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. According to the present invention, step (3) of dissolving chitosan in an aqueous acetic acid solution to initiate graft polymerization and adding acryloyloxyethyltrimethylammonium chloride to obtain the product CTs-AETAC includes the following steps: (i) Chitosan was dissolved in an aqueous acetic acid solution and placed in a three-necked flask equipped with a magnetic stirrer and a reflux condenser to form a homogeneous and transparent solution; (j) Add potassium persulfate and sodium bisulfite to the chitosan solution in sequence, and continue stirring for 30 min to make the initiator evenly dispersed and activate the free radical active sites on the chitosan molecular chain; (k) Slowly add an aqueous solution of acryloyloxyethyltrimethylammonium chloride to the above mixture to complete the free radical graft polymerization reaction; (l) After the reaction is complete, the mixture is cooled to room temperature and unreacted AETAC monomer and initiator residue are removed by centrifugation; after washing with deionized water three times and drying, CTs-AETAC graft copolymer is obtained.

[0032] In this invention, the temperature under magnetic stirring in step (i) is 70–100°C, such as 70°C, 80°C, 90°C, or 100°C, but not limited to the listed values; other unlisted values ​​within this range are also applicable. The stirring time is 30–90 min, such as 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, or 90 min, but not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 50–60 min. The stirring speed is 500–800 r / min, such as 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min, or 800 r / min, but not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 500–600 r / min.

[0033] In this invention, the chitosan in step (i) is 2.0–3.0 g, and the content of the acetic acid aqueous solution is 2 wt%–3 wt%. For example, the mass of chitosan can be 2.0 g, 2.5 g, or 3.0 g, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. For example, the content of the acetic acid aqueous solution can be 2 wt%, 2.2 wt%, 2.4 wt%, 2.6 wt%, 2.8 wt%, or 3.0 wt%, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0034] In this invention, the potassium persulfate in step (j) is 0.061–0.085 g, and the sodium bisulfite is 0.024–0.067 g. For example, the mass of potassium persulfate can be 0.061 g, 0.073 g, or 0.085 g, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable. Similarly, the mass of sodium bisulfite can be 0.024 g, 0.045 g, or 0.067 g, etc., but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0035] In this invention, the stirring speed in step (j) is 200 to 500 r / min, such as 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 300 to 400 r / min.

[0036] In this invention, the content of acryloyloxyethyltrimethylammonium chloride in step (k) is 15wt%-20wt%.

[0037] For example, 15wt%, 16wt%, 17wt%, 18wt%, 19wt% or 20wt%, etc., but not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 15wt%-16wt% being preferred.

[0038] In this invention, the temperature in step (k) is 50 to 80°C, such as 50°C, 60°C, 70°C or 80°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, with 60°C being the preferred value.

[0039] In this invention, the stirring time in step (k) is 2-4 hours, such as 2 hours, 2.5 hours, 3 hours, 3.5 hours, or 4 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 2.5-3 hours. The stirring speed is 400-600 r / min, such as 400 r / min, 450 r / min, 500 r / min, 550 r / min, or 600 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable, preferably 450-500 r / min.

[0040] In this invention, the high-speed centrifugal separation in step (l) is achieved by a centrifuge, and the centrifuge speed is greater than 4000 rpm. For example, the centrifuge speed can be 4000 rpm, 5000 rpm, 6000 rpm, 7000 rpm or 8000 rpm, etc., but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0041] In this invention, the drying temperature in step (l) is 50 to 80°C, such as 50°C, 60°C, 70°C, or 80°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The drying time is 24 to 48 hours, such as 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0042] According to the present invention, step (4) of adding CTs-AETAC to SDBS&MPC to obtain CTs-AETAC@SDBS&MPC composite magnetic nanoparticles includes the following steps: (m) Disperse the dried SDBS & MPC powder in deionized water and sonicate to obtain a uniform suspension. The content of SDBS & MPC powder is 0.5wt%~2.5wt%. (n) Dissolve the dried CTs-AETAC graft copolymer in deionized water to prepare a homogeneous solution; (o) Under magnetic stirring, the CTs-AETAC solution is slowly added dropwise to the SDBS&MPC suspension, and the dropping rate is controlled at 1-2 mL / min; (p) After the reaction is complete, the composite particles are separated by adsorption using a permanent magnet or electromagnetic device, and the supernatant is discarded; the particles are washed three times alternately with deionized water and anhydrous ethanol to remove unbound CTs-AETAC and residual reagents; after drying, CTs-AETAC@SDBS&MPC powder is obtained.

[0043] In this invention, the ultrasonic dispersion time in step (m) is 15 to 30 minutes, such as 15 minutes, 20 minutes, 25 minutes or 30 minutes, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The ultrasonic dispersion frequency is 60 Hz and the ultrasonic power is 200 W.

[0044] In this invention, the content of CTs-AETAC in step (n) is 2wt%-5wt%, such as 2wt%, 3wt%, 4wt% or 5wt%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In this invention, the temperature under magnetic stirring in step (o) is 30–60°C, such as 30°C, 40°C, 50°C, or 60°C, but not limited to the listed values; other unlisted values ​​within this range are also applicable. The stirring time is 30–60 min, such as 30 min, 40 min, 50 min, or 60 min, but not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 50–60 min. The stirring speed is 500–800 r / min, such as 500 r / min, 550 r / min, 600 r / min, 650 r / min, 700 r / min, 750 r / min, or 800 r / min, but not limited to the listed values; other unlisted values ​​within this range are also applicable, preferably 500–600 r / min.

[0046] In this invention, the drying temperature in step (p) is 50–80°C, such as 50°C, 60°C, 70°C, or 80°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The drying time is 24–48 hours, such as 24 hours, 30 hours, 36 hours, 42 hours, or 48 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0047] As a preferred technical solution, the preparation method of the demulsifier of the present invention includes the following steps: (a) Add 2.0 g of lignin to 50 mL of deionized water and stir magnetically at 80 °C for 50 min to dissolve until a homogeneous solution is obtained; (b) Mix 3.0 g of sodium bicarbonate solution with lignin solution; slowly add 0.5 g of ferric nitrate nonahydrate aqueous solution to the above mixture and stir to form a uniform dispersion system; (c) Lignin was pyrolyzed at a constant temperature in a tube furnace at 700℃ for 2 hours to generate Fe3O4 magnetic nanoparticles. Sodium bicarbonate released CO2 gas to form a porous structure. (d) The carbonization product was ground into a fine powder, washed three times with deionized water and ethanol alternately, and dried in an oven at 60°C for 24 hours to obtain pure magnetic porous carbon (MPCs).

[0048] (e) Dissolve sodium dodecylbenzenesulfonate in deionized water, stir, and prepare a homogeneous solution with a concentration of 0.3 wt% to obtain mixture I; (f) Disperse magnetic porous carbon in deionized water and sonicate for 15 min to obtain mixture II; (g) Add the above mixture I dropwise to the above mixture II at a rate of 1-2 mL / min, while keeping the system magnetically stirred at 30°C. After stirring, mixture III is obtained. (h) After the reaction is complete, the SDBS-modified MPCs particles are separated by adsorption using a permanent magnet or electromagnetic field. The product is washed 3-5 times with distilled water, and after each wash, it is separated by magnetic field to remove unadsorbed SDBS and impurities.

[0049] (i) Dissolve 2.0 g of chitosan in 85 g of 2% acetic acid aqueous solution and place it in a three-necked flask equipped with a magnetic stirrer and a reflux condenser to form a homogeneous and transparent solution; (j) Add 0.061 g of potassium persulfate and 0.024 g of sodium bisulfite to the chitosan solution in sequence, and continue stirring for 30 min to make the initiator evenly dispersed and activate the free radical active sites on the chitosan molecular chain; (k) Slowly add 23 g of 15 wt% acryloyloxyethyltrimethylammonium chloride aqueous solution to the above mixture, controlling the dropping rate at 1-2 mL / min. Maintain the reaction temperature at 60 °C and stir continuously for 3 h to complete the free radical graft polymerization reaction; (l) After the reaction is complete, the mixture is cooled to room temperature and unreacted AETAC monomer and initiator residue are removed by centrifugation; it is washed three times with deionized water and dried in a vacuum oven at 60°C for 12 hours to obtain CTs-AETAC graft copolymer.

[0050] (m) Disperse the dried SDBS & MPC powder in 50 mL of deionized water and sonicate to obtain a uniform suspension; (n) Dissolve the dried CTs-AETAC graft copolymer in 50 mL of deionized water to prepare a 3 wt% homogeneous solution; (o) Under magnetic stirring, the CTs-AETAC solution is slowly added dropwise to the SDBS&MPC suspension, and the dropping rate is controlled at 1-2 mL / min; (p) After the reaction is complete, the composite particles are separated by adsorption using a permanent magnet or electromagnetic device, and the supernatant is discarded. The particles are washed three times alternately with deionized water and anhydrous ethanol to remove unbound CTs-AETAC and residual reagents. The washed composite particles are dried in a vacuum oven at 60°C for 12 hours to obtain CTs-AETAC@SDBS&MPC powder.

[0051] In this invention, the method is simple, green and environmentally friendly. The demulsifier can quickly demulsify stable oily wastewater, especially for oily wastewater with an oil content of 1%, and has a good demulsification effect, resulting in clear aqueous phase and the ability to be recycled and reused.

[0052] Example 1 This embodiment provides a reusable cationic polymer-based magnetic nano-demulsifier, which is obtained through the following steps: Step 1: Add 2.0g of lignin to 50mL of deionized water and stir magnetically at 70℃ for 30min to dissolve until a homogeneous solution is obtained; Step 2: Mix 3.0g of sodium bicarbonate solution with the lignin solution obtained in Step 1 and stir for 10 minutes to obtain a mixture; Step 3: Add 0.5g of ferric nitrate nonahydrate aqueous solution dropwise to the mixture obtained in Step 2 above at a rate of 1mL / min, and stir to form a uniformly dispersed system; Step 4: The uniformly dispersed system obtained in Step 3 is pyrolyzed in a tube furnace at 500℃ for 2 hours to generate Fe3O4 magnetic nanoparticles. Sodium bicarbonate releases CO2 gas to form a porous structure. Step 5: Grind the carbonized product (i.e. the product obtained in step 4) into a fine powder with a particle size of <100μm, wash it three times alternately with deionized water and ethanol, and dry it in an oven at 50°C for 24h to obtain pure magnetic porous carbon (MPCs).

[0053] Step 6: Dissolve sodium dodecylbenzenesulfonate in deionized water, stir, and prepare a homogeneous solution with a content of 0.1 wt% to obtain mixture I; Step 7: Disperse 1g of the magnetic porous carbon obtained in step 5 in 100mL of deionized water and sonicate for 5min to obtain mixture II; Step 8: Add 10 mL of mixture I obtained in Step 6 to 10 mL of mixture II obtained in Step 7 at a dropping rate of 1 mL / min, while maintaining magnetic stirring at 25°C. After stirring, mixture III is obtained. After the reaction is complete, the SDBS-modified MPCs particles (i.e., magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate) are separated by adsorption using a permanent magnet. The product (i.e., magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate) is then washed three times with distilled water. After each wash, it is separated by magnetic field to remove unadsorbed SDBS and impurities, obtaining pure magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate.

[0054] Step 9: Dissolve 2.0g of chitosan in 85g of 2wt% acetic acid aqueous solution, place it in a three-necked flask equipped with a magnetic stirrer and a reflux condenser, and stir continuously for 30 minutes at 70°C under nitrogen protection until the chitosan is completely dissolved and a homogeneous and transparent solution (i.e., chitosan solution) is formed. Step 10: Add 0.061g of potassium persulfate and 0.024g of sodium bisulfite to the chitosan solution obtained in step 9, and continue stirring for 30 minutes to ensure that the initiator is evenly dispersed and activates the free radical active sites on the chitosan molecular chain. Step 11: Slowly add 23g of a 15wt% acryloyloxyethyltrimethylammonium chloride aqueous solution to the mixture obtained in Step 10, controlling the dropping rate at 1mL / min. Maintain the reaction temperature at 50℃ and continue stirring for 2h to complete the free radical graft polymerization reaction; Step 12: After the reaction in step 11 is completed, cool the mixture to room temperature, remove unreacted AETAC monomers and initiator residues by centrifugation; wash three times with deionized water, and dry in a vacuum oven at 50°C for 24 hours to obtain CTs-AETAC graft copolymer.

[0055] Step 13: Disperse 7.5 mg of dried SDBS & MPC powder (i.e., magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate, also known as SDBS modified MPCs particles) in 50 mL of deionized water and sonicate to obtain a uniform suspension. Step 14: Dissolve 2g of dried CTs-AETAC graft copolymer in 50mL of deionized water to prepare a 2wt% homogeneous solution (i.e., CTs-AETAC solution). Step 15: Under magnetic stirring, the CTs-AETAC solution obtained in step 14 is slowly added dropwise to the SDBS & MPC suspension obtained in step 13, and the dropping rate is controlled at 1 mL / min. Step 16: After the reaction in step 15 is completed, the composite particles are separated by adsorption using a permanent magnet and the supernatant is discarded; then the composite particles are washed three times alternately with deionized water and anhydrous ethanol to remove unbound CTs-AETAC and residual reagents. Step 17: Place the composite particles obtained in Step 16 in a vacuum oven at 50°C and dry for 24 hours to obtain CTs-AETAC@SDBS&MPC powder (i.e., cationic polymer-based magnetic nano-demulsifier).

[0056] Step 18: The cationic polymer-based magnetic nano-demulsifier is used for demulsification treatment of oily wastewater, with an addition amount of 150 mg / L and a demulsification rate of 97.6%.

[0057] See Figure 1 It can be seen that the particle size of the cationic polymer-based magnetic nano-demulsifier is between 10 and 50 nm.

[0058] See Figure 2 It can be seen that at 3421.2 cm -1 At a broad absorption band, hydroxyl groups (-OH) are present in MPCs, SDBS&MPC, CTs&AETAC, and CTs&AETAC@SDBS&MPC, and this peak has a very high intensity in the MPC spectrum. The absorption band is between 2920-2850 cm⁻¹. -1 At this location, the CH stretching vibration peak is commonly found in all three substances. At 1600 cm⁻¹... -1 The peak at 1565.9 cm⁻¹ mainly originates from the C=C stretching vibration of the aromatic ring in lignin; -1 The CN at this location is likely a quaternary ammonium salt group of AETAC; at 1159.0 cm⁻¹ -1 The characteristic absorption peak at 706.8 cm⁻¹ mainly originates from the sulfonate structure of sodium dodecylbenzenesulfonate. -1 The absorption peak at the specified location is attributed to the stretching vibration peak of Fe-O. The above results indicate that SDBS&MPC and CTs&AETAC@SDBS&MPC have been successfully synthesized.

[0059] See Figure 3 It can be seen that CTs & AETAC@SDBS & MPC experience a weight loss of 10-15% at 100-300℃, mainly due to the decomposition of the grafted acryloyloxyethyltrimethylammonium chloride (AETAC) side chain. The weight loss at 300-700℃ is primarily due to CTs. SThe cleavage of the main chain glycosidic bonds, along with the oxidative decomposition of the alkyl chain and benzene ring of SDBS, constitutes the main decomposition stage of the composite material. High-temperature testing (above 700°C) confirmed the structural stability of the carbon skeleton under nitrogen protection, with no significant phase transition or oxidation of the magnetic component (Fe3O4). The carbon skeleton and Fe3O4 nanoparticles of the magnetic porous carbon (MPC) remained stable, with a slowing weight loss (<5%). This analysis provides evidence of the thermal stability of the composite material for applications in high-temperature environments. TGA corroborated FT-IR, indirectly proving the successful grafting of CTs&AETAC with SDBS&MPC.

[0060] See Figure 4 As can be seen, the saturation magnetization of the cationic polymer-based magnetic nano-demulsifier reaches 14.3 emu / g, and the material can generate sufficient magnetic response under the action of an external magnetic field to achieve rapid separation.

[0061] See Figure 5 It can be seen that the residual oil concentration in the aqueous phase gradually decreases with the increase of demulsifier dosage. The decreasing trend is very obvious when the demulsifier dosage increases from 50 mg to 150 mg. The dehydration rate is highest when the demulsifier dosage is 150 mg. When the dosage increases, the demulsification ability weakens and may even lead to an increase in the residual oil content in the aqueous phase.

[0062] Example 2 This embodiment provides a reusable cationic polymer-based magnetic nano-demulsifier, which is obtained through the following steps: Step 1: Add 2.5g of lignin to 50mL of deionized water and stir magnetically at 85℃ for 60min to dissolve until a homogeneous solution is obtained; Step 2: Mix 4.0g of sodium bicarbonate solution with the lignin solution obtained in Step 1 and stir for 13 minutes to obtain a mixture; Step 3: Add 0.75g of ferric nitrate nonahydrate aqueous solution dropwise to the mixture obtained in Step 2 above at a rate of 1.5mL / min, and stir to form a uniformly dispersed system; Step 4: The uniformly dispersed system obtained in Step 3 is pyrolyzed in a tube furnace at 600℃ for 3 hours to generate Fe3O4 magnetic nanoparticles. Sodium bicarbonate releases CO2 gas to form a porous structure. Step 5: Grind the carbonized product (i.e. the product obtained in step 4) into a fine powder with a particle size of <100μm, wash it three times alternately with deionized water and ethanol, and dry it in an oven at 65°C for 36h to obtain pure magnetic porous carbon (MPCs).

[0063] Step 6: Dissolve sodium dodecylbenzenesulfonate in deionized water, stir, and prepare a homogeneous solution with a content of 0.3 wt% to obtain mixture I; Step 7: Disperse 1.5g of the magnetic porous carbon obtained in Step 5 in 100mL of deionized water and sonicate for 15min to obtain Mixture II; Step 8: Add 15 mL of mixture I obtained in Step 6 dropwise to 20 mL of mixture II obtained in Step 7 at a dropping rate of 2 mL / min, while simultaneously stirring the system under magnetic force at 30°C for 1 h. After stirring, mixture III is obtained. After the reaction is complete, the SDBS-modified MPCs particles are separated by electromagnetic field adsorption. The product is then washed four times with distilled water, and after each wash, it is separated by magnetic field to remove unadsorbed SDBS and impurities, yielding pure sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles.

[0064] Step 9: Dissolve 2.5g of chitosan in 88g of 2.5wt% acetic acid aqueous solution, place it in a three-necked flask equipped with a magnetic stirrer and a reflux condenser, and stir continuously for 60 minutes at 85°C under nitrogen protection until the chitosan is completely dissolved and a homogeneous and transparent solution (i.e., chitosan solution) is formed. Step 10: Add 0.073 g potassium persulfate and 0.045 g sodium bisulfite to the chitosan solution obtained in step 9, and continue stirring for 30 min to ensure that the initiator is evenly dispersed and activates the free radical active sites on the chitosan molecular chain. Step 11: Slowly add 25g of an 18wt% acryloyloxyethyltrimethylammonium chloride aqueous solution to the mixture obtained in Step 10 above, controlling the dropping rate at 2mL / min. Maintain the reaction temperature at 65℃ and continue stirring for 3h to complete the free radical graft polymerization reaction; Step 12: After the reaction in step 11 is completed, cool the mixture to room temperature, remove unreacted AETAC monomers and initiator residues by centrifugation; wash three times with deionized water, and dry in a vacuum oven at 65°C for 36 hours to obtain CTs-AETAC graft copolymer.

[0065] Step 13: Disperse 10 mg of dried SDBS & MPC powder in 50 mL of deionized water and sonicate to obtain a uniform suspension. Step 14: Dissolve 1.75g ​​of dried CTs-AETAC graft copolymer in 50mL of deionized water to prepare a 3.5wt% homogeneous solution (i.e., CTs-AETAC solution). Step 15: Under magnetic stirring, the CTs-AETAC solution obtained in step 14 is slowly added dropwise to the SDBS&MPC suspension obtained in step 13, and the dropping rate is controlled at 2 mL / min. Step 16: After the reaction in step 15 is completed, the composite particles are separated by adsorption using an electromagnetic device, and the supernatant is discarded; then the composite particles are washed 4 times alternately with deionized water and anhydrous ethanol to remove unbound CTs-AETAC and residual reagents. Step 17: Place the composite particles obtained in step 16 into a vacuum oven at 65°C and dry for 36 hours to obtain CTs-AETAC@SDBS&MPC powder.

[0066] Step 18: The cationic polymer-based magnetic nano-demulsifier is used for demulsification treatment of oily wastewater, with an addition amount of 200 mg / L and a demulsification rate of 96.3%.

[0067] Example 3 This embodiment provides a reusable cationic polymer-based magnetic nano-demulsifier, which is obtained through the following steps: Step 1: Add 3.0g of lignin to 50mL of deionized water and stir magnetically at 100℃ for 90min to dissolve until a homogeneous solution is obtained; Step 2: Mix 5.0g of sodium bicarbonate solution with the lignin solution obtained in Step 1 and stir for 15 minutes to obtain a mixture; Step 3: Add 1.0 g of ferric nitrate nonahydrate aqueous solution dropwise to the mixture obtained in Step 2 above at a rate of 2 mL / min, and stir to form a uniformly dispersed system; Step 4: The uniformly dispersed system obtained in step 3 is pyrolyzed at a constant temperature of 700℃ in a tube furnace for 4 hours to generate Fe3O4 magnetic nanoparticles. Sodium bicarbonate releases CO2 gas to form a porous structure. Step 5: Grind the carbonized product (i.e. the product obtained in step 4) into a fine powder with a particle size of <100μm, wash it three times alternately with deionized water and ethanol, and dry it in an oven at 80°C for 48h to obtain pure magnetic porous carbon (MPCs).

[0068] Step 6: Dissolve sodium dodecylbenzenesulfonate in deionized water, stir, and prepare a homogeneous solution with a content of 0.5 wt% to obtain mixture I; Step 7: Disperse 2g of the magnetic porous carbon obtained in step 5 in 100mL of deionized water and sonicate for 30min to obtain mixture II; Step 8: Add 20 mL of mixture I obtained in Step 6 dropwise to 25 mL of mixture II obtained in Step 7 at a dropping rate of 1.5 mL / min, while simultaneously stirring the system under magnetic force at 35°C for 2 hours. After stirring, mixture III is obtained. After the reaction is complete, the SDBS-modified MPCs particles are separated by electromagnetic field adsorption. The product is washed five times with distilled water, and after each wash, it is separated by magnetic field to remove unadsorbed SDBS and impurities, yielding pure sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles.

[0069] Step 9: Dissolve 3.0g of chitosan in 90g of 3wt% acetic acid aqueous solution and place it in a three-necked flask equipped with a magnetic stirrer and a reflux condenser. Under nitrogen protection, the magnetic stirring temperature is 100°C and the stirring is continued for 90 minutes until the chitosan is completely dissolved and a homogeneous transparent solution (i.e., chitosan solution) is formed. Step 10: Add 0.085g potassium persulfate and 0.067g sodium bisulfite to the chitosan solution obtained in step 9, and continue stirring for 30 minutes to ensure that the initiator is evenly dispersed and activates the free radical active sites on the chitosan molecular chain. Step 11: Slowly add 24g of a 20wt% acryloyloxyethyltrimethylammonium chloride aqueous solution to the mixture obtained in Step 10 above, controlling the dropping rate at 1.5mL / min. Maintain the reaction temperature at 80℃ and continue stirring for 4h to complete the free radical graft polymerization reaction; Step 12: After the reaction in step 11 is completed, cool the mixture to room temperature, remove unreacted AETAC monomers and initiator residues by centrifugation; wash three times with deionized water, and dry in a vacuum oven at 80°C for 48 hours to obtain CTs-AETAC graft copolymer.

[0070] Step 13: Disperse 12.5g of dried SDBS & MPC powder in 50mL of deionized water and sonicate to obtain a uniform suspension. Step 14: Dissolve 10g of dried CTs-AETAC graft copolymer in 50mL of deionized water to prepare a 5wt% homogeneous solution (i.e., CTs-AETAC solution). Step 15: Under magnetic stirring, the CTs-AETAC solution obtained in step 14 is slowly added dropwise to the SDBS&MPC suspension obtained in step 13, and the dropping rate is controlled at 1.5 mL / min. Step 16: After the reaction in step 15 is completed, the composite particles are separated by adsorption using an electromagnetic device, and the supernatant is discarded; then the composite particles are washed 5 times alternately with deionized water and anhydrous ethanol to remove unbound CTs-AETAC and residual reagents. Step 17: Place the composite particles obtained in Step 16 into an 80℃ vacuum oven and dry for 48 hours to obtain CTs-AETAC@SDBS&MPC powder.

[0071] Step 18: The cationic polymer-based magnetic nano-demulsifier is used for demulsification treatment of oily wastewater, with an addition amount of 230 mg / L and a demulsification rate of 95.5%.

[0072] Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0073] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing a cationic polymer-based magnetic nano-demulsifier, characterized in that, The process includes the following: A suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate was added to an aqueous solution of CTs-AETAC graft copolymer and stirred during the addition process. After the reaction was completed, the particles were separated, washed, and dried to obtain the cationic polymer-based magnetic nano-demulsifier. The preparation process of the sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles includes: reacting an aqueous solution of sodium dodecylbenzenesulfonate with a magnetic porous carbon suspension, followed by magnetic separation, washing, and drying to obtain sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles. The preparation process of the CTs-AETAC graft copolymer includes: initiating graft polymerization by dissolving chitosan in an aqueous solution of acetic acid, then adding acryloyloxyethyltrimethylammonium chloride for free radical graft polymerization, followed by separation, washing, and drying to obtain the product CTs-AETAC graft copolymer.

2. The method for preparing a cationic polymer-based magnetic nano-demulsifier according to claim 1, characterized in that, The preparation process of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate includes the following steps: Sodium bicarbonate aqueous solution and lignin solution were mixed evenly to obtain mixture A; wherein, the solid-liquid ratio of lignin to deionized water in sodium bicarbonate aqueous solution was (2.0~3.0g):50mL; the solid-liquid ratio of sodium bicarbonate to water in sodium bicarbonate aqueous solution was (3.0~5.0g):(80~100mL); and the volume ratio of sodium bicarbonate aqueous solution to lignin solution was (80~100mL):50mL. Add the ferric nitrate nonahydrate aqueous solution to the mixture A and stir until homogeneous to obtain a uniformly dispersed system A; wherein the volume ratio of the ferric nitrate nonahydrate aqueous solution to the mixture A is 10 mL: (130-150 mL), and each 10 mL of the ferric nitrate nonahydrate aqueous solution contains 0.5~1.0 g of ferric nitrate nonahydrate; The uniformly dispersed system A was pyrolyzed at 500-700°C for 2-4 hours to obtain carbonized products; The carbonized product is ground into a fine powder, then washed with deionized water and ethanol alternately 3-5 times, and then dried to obtain the magnetic porous carbon.

3. The method for preparing a cationic polymer-based magnetic nano-demulsifier according to claim 2, characterized in that, The carbonized product is ground into a fine powder with a particle size of <100μm.

4. The method for preparing a cationic polymer-based magnetic nano-demulsifier according to claim 1, characterized in that, The method of reacting sodium dodecylbenzenesulfonate aqueous solution with a magnetic porous carbon suspension, followed by magnetic separation, washing, and drying to obtain sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles includes the following steps: An aqueous solution of sodium dodecylbenzenesulfonate was added to a magnetic porous carbon suspension at a rate of 1-2 mL / min, while the system was stirred at 25-35°C for 0.5-2 h. The sodium dodecylbenzenesulfonate content in the aqueous solution was 0.1 wt%-0.5 wt%, and the magnetic porous carbon content in the magnetic porous carbon suspension was 1 wt%-5 wt%. The volume ratio of the aqueous solution of sodium dodecylbenzenesulfonate to the magnetic porous carbon suspension was 1:

1. After the reaction is complete, the particulate product is separated by magnetic adsorption, and then the particulate product is washed with distilled water 3-5 times to obtain the magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate; wherein the particulate product is separated by magnetic adsorption after each washing.

5. The method for preparing a cationic polymer-based magnetic nano-demulsifier according to claim 1, characterized in that, The graft polymerization of chitosan in an aqueous solution of acetic acid includes the following steps: Chitosan was dissolved in an aqueous solution of acetic acid with a content of 2wt%~3wt%, and stirred at 70~100°C under a protective atmosphere until the chitosan was completely dissolved to obtain a homogeneous and transparent solution. Add potassium persulfate and sodium bisulfite to the homogeneous and transparent solution, maintain a protective atmosphere, and continue stirring until the initiator is uniformly dispersed and activates the free radical active sites on the chitosan molecular chain, thus completing the process of initiating graft polymerization of chitosan dissolved in acetic acid aqueous solution. For every 2.0-3.0g of chitosan, 0.061-0.085g of potassium persulfate and 0.024-0.067g of sodium bisulfite are added. The mass ratio of chitosan to acetic acid aqueous solution is (2.0-3.0g): (85-90g).

6. A method for preparing a cationic polymer-based magnetic nano-demulsifier according to claim 1 or 5, characterized in that, After initiating graft polymerization of chitosan dissolved in an aqueous acetic acid solution, acryloyloxyethyltrimethylammonium chloride was added to carry out a free radical graft polymerization reaction. Following separation, washing, and drying, the product CTs-AETAC graft copolymer was obtained, comprising the following steps: An aqueous solution of 15wt%~20wt% acryloyloxyethyltrimethylammonium chloride was added to the mixture after graft polymerization of chitosan-dissolved acetic acid was initiated at a rate of 1~2mL / min. The reaction temperature was maintained at 50~80°C, and the mixture was stirred continuously for 2~4h to complete the free radical graft polymerization reaction. The mass ratio of the aqueous solution of acryloyloxyethyltrimethylammonium chloride to the mixture after graft polymerization of chitosan-dissolved acetic acid was (23-25g):(87-90g). After the reaction is complete, the mixture is cooled and centrifuged. The separated product is then washed with deionized water 3-5 times and then vacuum dried to obtain the CTs-AETAC graft copolymer.

7. The method for preparing a cationic polymer-based magnetic nano-demulsifier according to claim 1, characterized in that, The CTs-AETAC graft copolymer aqueous solution contains 2wt% to 5wt% of the CTs-AETAC graft copolymer. In the suspension of the sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles, the content of the sodium dodecylbenzenesulfonate-modified magnetic porous carbon particles is 0.5wt%~2.5wt%. When a suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate is added to an aqueous solution of CTs-AETAC graft copolymer for reaction, the addition rate of the suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate is controlled at 1~2 mL / min. A suspension of magnetic porous carbon particles modified with sodium dodecylbenzenesulfonate was added to an aqueous solution of CTs-AETAC graft copolymer and reacted. The reaction was carried out with stirring. After the reaction was completed, the particles were separated, washed, and dried. The specific steps included: After the reaction is complete, the composite particles are separated by magnetic adsorption and the supernatant is discarded. The composite particles are then washed alternately with deionized water and anhydrous ethanol 3-5 times. The washed composite particles are then vacuum dried to obtain the cationic polymer-based magnetic nano-demulsifier.

8. A method for preparing a cationic polymer-based magnetic nano-demulsifier according to claim 6 or 7, characterized in that, For vacuum drying, vacuum dry at 50~80°C for 24~48 hours.

9. A cationic polymer-based magnetic nano-demulsifier, characterized in that, The cationic polymer-based magnetic nano-demulsifier is prepared by any one of the preparation methods of claims 1-8.

10. The application of the cationic polymer-based magnetic nano-demulsifier according to claim 9, characterized in that, The cationic polymer-based magnetic nano-demulsifier is used for demulsification treatment of oily wastewater, and the addition amount of the cationic polymer-based magnetic nano-demulsifier is 150~230 mg / L.

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