Magnetic nanoparticle-based flocculation polymer, preparation method and application thereof, and method for treating oily wastewater

Abstract

The present invention relates to the field of flocculants, and discloses a flocculating polymer based on magnetic nanoparticles, a preparation method and application thereof, and a method for treating oily wastewater. The flocculating polymer provided by the present invention has the characteristics of strong adsorption, and can efficiently remove oily substances and suspended matter in wastewater. Moreover, the flocculating polymer can achieve a good flocculation and oil removal effect when used in a small amount, and can also be combined with a magnetic separator for recycling and reuse. Applying it to the treatment of oily wastewater such as crude oil wastewater can achieve efficient, low-cost, and sustainable wastewater treatment.

Description

Technical Field

[0001] The invention relates to the field of flocculants, and in particular to a flocculating polymer based on magnetic nanoparticles, a preparation method and application thereof, and a method for treating oily wastewater. Background Art

[0002] With the development of the oil industry, the amount of oilfield wastewater to be treated has gradually increased, and the composition has become more and more complex, making the treatment more difficult. At present, the main problems in the treatment of oilfield wastewater are large dosage of reagents, high sludge production, slow floc sedimentation rate, and high treatment costs. The development of flocculants with fast sedimentation rate, small dosage, and high treatment efficiency can effectively solve the above problems.

[0003] Magnetic separation technology is one of the most promising sewage treatment technologies developed in recent years. Its main method is to add magnetic seeds that are magnetic and can adsorb pollutants in sewage into sewage, and then recover the adsorbed magnetic seeds through a magnetic separator. This not only achieves efficient sewage treatment, but also enables the recycling of magnetic seeds, which is more conducive to the realization of sustainable development.

[0004] Fe3O4 magnetic nanoparticles are an important type of flocculating magnetic species with unique magnetic properties, chemical stability, biological non-toxicity and compatibility. They are suitable for use in the magnetic separation treatment of oily wastewater, especially oilfield wastewater. Surface modification can further improve the adsorption performance of Fe3O4 magnetic nanoparticles, giving them new physical and chemical properties, making them more suitable for oilfield wastewater treatment. However, existing surface modification methods have many disadvantages, such as adverse effects on the magnetism of Fe3O4 magnetic nanoparticles, low modification efficiency, and unsatisfactory treatment effects. Summary of the invention

[0005] The purpose of the present invention is to overcome the above problems of the prior art and provide a flocculating polymer based on magnetic nanoparticles and its preparation method and application as well as a method for treating oily wastewater. The flocculating polymer has the characteristics of strong adsorption capacity, good colloid stability formed in water, and can efficiently remove oily substances and suspended matter in wastewater.

[0006] In order to achieve the above-mentioned object, the present invention provides a flocculating polymer based on magnetic nanoparticles on one hand, wherein the flocculating polymer based on magnetic nanoparticles comprises a structural unit provided by modified nano-Fe3O4;

[0007] The modified nano-Fe3O4 comprises nano-Fe3O4 particles coated with a polydopamine layer and a cationic polymer grafted onto the polydopamine layer.

[0008] A second aspect of the present invention provides a method for preparing a flocculating polymer based on magnetic nanoparticles, the method comprising the following steps:

[0009] Under the condition of free radical polymerization, the modified nano-Fe3O4 is mixed with an initiator;

[0010] The modified nano-Fe3O4 comprises nano-Fe3O4 particles coated with a polydopamine layer and a cationic monomer containing a double bond grafted onto the polydopamine layer.

[0011] The third aspect of the present invention provides a flocculating polymer based on magnetic nanoparticles prepared by the above method.

[0012] The fourth aspect of the present invention provides the use of the aforementioned magnetic nanoparticle-based flocculation polymer in the treatment of oily wastewater.

[0013] A fifth aspect of the present invention provides a method for treating oily wastewater, the method comprising contacting the oily wastewater with the magnetic nanoparticle-based flocculation polymer as described above.

[0014] Through the above technical solution, the present invention has the following beneficial effects:

[0015] (1) The flocculating polymer based on magnetic nanoparticles provided by the present invention has strong adsorption capacity and can efficiently remove oily substances and suspended matter in sewage;

[0016] (2) The flocculating polymer based on magnetic nanoparticles provided by the present invention can be used to treat oily wastewater in oil fields, and has the advantages of fast floc settling speed, high treatment efficiency, and low dosage;

[0017] (3) The preparation method of the flocculating polymer based on magnetic nanoparticles provided by the present invention is simple, mild in conditions, low in cost, and suitable for industrial large-scale production and promotion;

[0018] (4) The flocculating polymer based on magnetic nanoparticles provided by the present invention can also be recovered and reused by a magnetic separator during use (or after use), further reducing the cost of reagents in the oily wastewater treatment process;

[0019] (5) The magnetic nanoparticle-based flocculating polymer provided by the present invention can also be used in combination with other existing flocculants in the art according to the characteristics of pollutants in different sewage, so as to further improve the treatment efficiency and the broad spectrum of application. DETAILED DESCRIPTION

[0020] The specific implementation modes of the present invention will be explained and described in detail below. It should be understood that the following specific implementation modes are only used to explain and illustrate the contents of the present invention, but not to limit the present invention.

[0021] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0022] The inventors of the present invention discovered during the course of research that by combining the treatment methods of mussel bionics and redox free radical polymerization, a secondary reaction platform was built on the nano-Fe3O4 particles using a polydopamine layer to facilitate subsequent modification, and the above-mentioned treatment has a weak effect on the magnetism of nano-Fe3O4, which can make the modified Fe3O4 more in line with the needs of magnetic separation technology based on magnetic nanoparticles, especially for the needs of practical applications such as deoiling of oily wastewater.

[0023] The first aspect of the present invention provides a flocculating polymer based on magnetic nanoparticles, wherein the flocculating polymer comprises a structural unit provided by modified nano-Fe3O4;

[0024] The modified nano-Fe3O4 comprises nano-Fe3O4 particles coated with a polydopamine layer and a cationic polymer grafted onto the polydopamine layer.

[0025] Any nano-Fe3O4 that can be used for preparing flocculation polymer (flocculant) can be applied to the flocculation polymer provided by the present invention. According to a preferred embodiment of the present invention, the particle size of the modified nano-Fe3O4 is 10-20 nm.

[0026] In the flocculating polymer provided by the present invention, the cationic polymer can be a cationic polymer polymerized from any cationic monomer in the art that can react with the surface functional groups of polydopamine and can be further polymerized. According to a preferred embodiment of the present invention, the cationic polymer is selected from polymers composed of cationic monomers containing double bonds.

[0027] Preferably, the cationic monomer containing a double bond is selected from quaternary ammonium salts containing a double bond.

[0028] More preferably, the cationic monomer containing a double bond is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride and dimethyldiallylammonium chloride.

[0029] Any existing method in the art that can polymerize polydopamine-modified nano-silica loaded with cationic monomers containing double bonds can be applied to the nano-flocculated polymer provided by the present invention. According to a preferred embodiment of the present invention, the polymer is obtained by free radical polymerization catalyzed by a redox reaction initiated by an initiator.

[0030] Preferably, the initiator is selected from Ce(IV).

[0031] In the flocculating polymer provided by the present invention, the loading amount of polydopamine in the modified nano-Fe3O4 is not particularly limited and can be adjusted according to actual conditions and needs, as long as the polydopamine layer can be used to build a secondary reaction platform on the surface of the nano-silicon dioxide, thereby achieving the purpose of grafting the cationic monomer containing double bonds in the next step.

[0032] In the flocculating polymer based on magnetic nanoparticles provided by the present invention, the content of the cationic monomer containing double bonds can be adjusted according to actual conditions and needs, as long as it can easily make the modified nano-Fe3O4 undergo polymerization reaction in the presence of an initiator, thereby achieving the purpose of synthesizing the flocculating polymer provided by the present invention.

[0033] A second aspect of the present invention provides a method for preparing a flocculating polymer based on magnetic nanoparticles, the method comprising the following steps:

[0034] Under the condition of free radical polymerization, the modified nano-Fe3O4 is mixed with an initiator;

[0035] The modified nano-Fe3O4 comprises nano-Fe3O4 particles coated with a polydopamine layer and a cationic monomer containing a double bond grafted onto the polydopamine layer.

[0036] In the method provided by the present invention, the modified nano-Fe3O4 can be a commercially available related product, or can be prepared by itself according to the existing technology.

[0037] According to a preferred embodiment of the present invention, the modified nano-Fe3O4 is mixed with an initiator in the form of a modified nano-Fe3O4 suspension, and the preparation method of the modified nano-Fe3O4 suspension comprises:

[0038] (1) contacting nano-Fe3O4 with a dopamine hydrochloride solution, and then sequentially performing a first solid-liquid separation, a first washing, and a first drying to obtain nano-Fe3O4 coated with a polydopamine layer;

[0039] (2) The nano-Fe3O4 coated with the polydopamine layer obtained in step (1) is brought into second contact with a cationic monomer solution containing double bonds to obtain a modified Fe3O4 suspension.

[0040] Any nano-Fe3O4 that can be used for preparing flocculation polymer (flocculant) in the art can be applied to the method provided by the present invention. According to a preferred embodiment of the present invention, in step (1), the particle size of the nano-Fe3O4 is 10-20 nm.

[0041] Any dopamine hydrochloride solution that can be used to modify nano-silica with polydopamine can be applied to the method provided by the present invention. According to a preferred embodiment of the present invention, in step (1), the dopamine hydrochloride solution is selected from a solution with dopamine hydrochloride as a solute and tris(hydroxymethyl)aminomethane buffer (Tris buffer) as a solvent.

[0042] Preferably, in step (1), the concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 0.1-4% by weight, preferably 1-2% by weight.

[0043] In order to enable dopamine to form a polydopamine layer on the surface of the nano-Fe3O4 more quickly, more preferably, in step (1), the pH of the dopamine hydrochloride solution is 8-9.

[0044] In the method provided by the present invention, the amount of the nano Fe3O4 can be adjusted according to the actual situation. In order to make the polydopamine modification reaction of the Fe3O4 more thorough, preferably, in step (1), the amount of the nano Fe3O4 is 0.1-1% by weight of the weight of the dopamine hydrochloride solution, and more preferably 0.3-0.8% by weight. On a dry weight basis, relative to 1g of nano Fe3O4, the amount of the dopamine hydrochloride is 1-5g, preferably 2-3.5g.

[0045] In order to make the polydopamine modification reaction of Fe3O4 easier to carry out, according to a preferred embodiment of the present invention, in step (1), the first contacting method includes: temperature 20-30°C, ultrasonic stirring for 10-30min, and then stirring at 100-1000rpm for 8-48h.

[0046] Any solid-liquid separation method currently available in the art can be applied to the method provided by the present invention. Considering the efficiency and effect of the solid-liquid separation process, preferably, in step (1), the first solid-liquid separation method is selected from centrifugal separation.

[0047] More preferably, in step (1), the first solid-liquid separation method is selected from centrifugal separation, and the conditions include: centrifugal speed 800-20000 rpm, centrifugal time 10-20 min.

[0048] In the method provided by the present invention, the first washing method can be used as long as it can achieve the purpose of removing unreacted dopamine hydrochloride. Preferably, in step (1), the first washing method includes: washing the solid phase obtained by the first solid-liquid separation with deionized water.

[0049] In order to achieve a better washing effect, the first washing can be repeated multiple times. More preferably, in step (1), the conditions of the first washing include: washing the solid phase with deionized water 3-5 times.

[0050] Any existing drying method in the art can be applied to the method provided by the present invention. Considering the drying efficiency and effect, combined with the characteristics of the material itself, preferably, in step (1), the first drying method is selected from vacuum drying.

[0051] More preferably, in step (1), the first drying method is selected from vacuum drying, and the conditions include: 50-80°C, time 24-72h.

[0052] In the present invention, any cationic monomer containing a double bond that can react with the surface functional groups of the nano-Fe3O4 coated with the polydopamine layer to be grafted on its surface can be applied to the method provided by the present invention. According to a preferred embodiment of the present invention, in step (2), the cationic monomer containing a double bond is selected from a quaternary ammonium salt containing a double bond.

[0053] Preferably, the cationic monomer containing a double bond is selected from at least one of methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride and dimethyldiallylammonium chloride.

[0054] In the method provided by the present invention, the type and concentration of the cationic solution containing double bonds can be adjusted according to actual needs. Preferably, in step (2), the cationic solution containing double bonds is selected from an aqueous solution of a quaternary ammonium salt containing double bonds, preferably at a concentration of 10-50% by weight, more preferably 20-40% by weight.

[0055] In the method provided by the present invention, the relative amount of the nano-Fe3O4 coated with the polydopamine layer and the cationic monomer containing double bonds can be adjusted according to actual conditions and needs. Preferably, in step (2), the amount of the cationic monomer containing double bonds is 10-20 g relative to 1 g of the nano-Fe3O4 coated with the polydopamine layer on a dry weight basis.

[0056] Preferably, in step (2), the amount of the nano-Fe3O4 coated with the polydopamine layer is such that the content of the modified nano-Fe3O4 in the modified Fe3O4 suspension is 0.1-1% by weight, preferably 0.15-0.6% by weight;

[0057] In the method provided by the present invention, any method that can make the nano-Fe3O4 coated with the polydopamine layer and the cationic monomer solution containing double bonds uniformly mixed can be applied to the present invention. Preferably, in step (2), the second contacting method includes ultrasonic mixing and / or stirring mixing.

[0058] More preferably, in step (2), the second contacting method is selected from ultrasonic mixing, and the conditions include: ultrasonic mixing for 10-20 minutes.

[0059] In the method provided by the present invention, the initiator can be any initiator that can initiate polymerization of the modified Fe3O4. According to a preferred embodiment of the present invention, the initiator is selected from Ce(IV).

[0060] In the method provided by the present invention, the amount of the initiator can be adjusted according to the actual needs such as the type of initiator selected, the type of reaction, etc. Preferably, based on dry weight, the amount of the initiator is 0.1-0.6 g relative to 1 g (based on dry weight) of nano-Fe3O4 coated with a polydopamine layer.

[0061] According to a preferred embodiment of the present invention, the mixing method includes: bringing the modified Fe3O4 suspension into a third contact with an initiator solution, and then adjusting the pH to obtain a flocculated polymer suspension based on magnetic nanoparticles.

[0062] Preferably, the initiator solution is selected from a cerium ammonium nitrate solution using nitric acid as a solvent.

[0063] More preferably, the concentration of the (solvent) nitric acid is 0.5-2 mol / L, preferably 0.8-1.2 mol / L.

[0064] More preferably, the concentration of ammonium cerium nitrate in the initiator solution is 0.1-0.5 mol / L, preferably 0.2-0.3 mol / L.

[0065] Preferably, in the flocculated polymer suspension based on magnetic nanoparticles (hereinafter referred to as "flocculated polymer suspension"), the content of the modified nano-Fe3O4 is 1-10% by weight, preferably 1-5% by weight.

[0066] Preferably, the pH is adjusted using NaOH and / or KOH.

[0067] More preferably, the pH of the flocculated polymer suspension (after adjustment) is 6.8-7.2.

[0068] Any method that can make the modified Fe3O4 suspension and the initiator solution uniformly mixed so that the modified Fe3O4 and the initiator are fully in contact can be applied to the method provided by the present invention. According to a preferred embodiment of the present invention, the conditions of the third contact include: in an inert atmosphere, a temperature of 20-40°C, a stirring speed of 100-1200rpm, and a stirring time of 12-36h.

[0069] Preferably, the inert atmosphere is provided by nitrogen and / or an inert gas (such as argon, etc.).

[0070] According to a preferred embodiment of the present invention, the method further comprises the following steps:

[0071] The flocculated polymer suspension is subjected to a second solid-liquid separation, a second washing and a second drying to obtain a solid flocculated polymer based on magnetic nanoparticles (hereinafter referred to as "solid flocculated polymer").

[0072] Any solid-liquid separation method currently available in the art can be applied to the method provided by the present invention. Preferably, the second solid-liquid separation method is selected from centrifugal separation.

[0073] More preferably, the conditions for the second solid-liquid separation include: centrifugal speed of 1000-20000 rpm, and centrifugal time of 10-20 min.

[0074] In the method provided by the present invention, the purpose of the second washing is to remove the unreacted initiator. Any washing method that can achieve the above purpose can be applied to the method provided by the present invention. Preferably, the second washing method includes: washing the solid phase obtained by the second solid-liquid separation with deionized water.

[0075] More preferably, the second washing conditions include: washing the solid phase 3-5 times with deionized water having a volume 10-100 times that of the solid phase obtained by the second solid-liquid separation.

[0076] Any drying method available in the art can be applied to the method provided by the present invention. Preferably, the second drying method is selected from vacuum drying.

[0077] More preferably, the second drying conditions include: temperature 50-80°C, time 24-72h.

[0078] The third aspect of the present invention provides a flocculating polymer based on magnetic nanoparticles prepared according to the method as described above.

[0079] Preferably, the flocculating polymer comprises a flocculating polymer suspension and a solid flocculating polymer, the characteristics of which are as described above and will not be repeated here.

[0080] A fourth aspect of the present invention provides the use of the above-mentioned magnetic nanoparticle-based flocculation polymer in the treatment of oily wastewater.

[0081] According to a preferred embodiment of the present invention, the application may include deoiling of oily wastewater.

[0082] A fifth aspect of the present invention provides a method for treating oily wastewater, the method comprising contacting the oily wastewater with the magnetic nanoparticle-based flocculation polymer as described above.

[0083] Any existing oily wastewater in the art (such as oilfield wastewater, chemical wastewater, domestic wastewater, etc.) can be treated by the method provided by the present invention. According to a preferred embodiment of the present invention, the oil content in the oily wastewater is 100-500 mg / L, preferably 200-300 mg / L.

[0084] Preferably, relative to 1L of the oily wastewater, the amount of the flocculating polymer used is 10-200 mg, preferably 20-100 mg, calculated as the solid matter therein.

[0085] Preferably, the contacting conditions include: temperature 40-70° C., time 0.5-6 h.

[0086] More preferably, the contacting conditions include: temperature 45-55°C, time 1-3h.

[0087] The present invention will be described in detail below by way of examples. It should be understood that the following examples are only used to further explain and illustrate the content of the present invention by way of example, and are not intended to limit the present invention.

[0088] The raw materials used in the following examples, such as dopamine hydrochloride, tris(hydroxymethylaminomethane) buffer, nano-Fe3O4 (average particle size is about 12±2 nm), methacryloyloxyethyltrimethylammonium chloride, acryloyloxyethyltrimethylammonium chloride, and dimethyldiallylammonium chloride, were all purchased from regular chemical suppliers.

[0089] In the following examples, the "room temperature" refers to 25±3°C. Unless otherwise specified, the operating temperature is room temperature.

[0090] Example 1

[0091] Preparation of nano-Fe3O4-A1 coated with polydopamine layer:

[0092] 2 g of dopamine hydrochloride was weighed and dissolved in 200 ml of tris(hydroxymethyl)aminomethane buffer, the pH was adjusted to about 8.5, and ultrasonication was performed until the solid was completely dissolved to obtain dopamine hydrochloride solution S1.

[0093] 1 g of nano-Fe3O4 was added to the dopamine hydrochloride solution S1, ultrasonicated for 15 min, and then stirred at room temperature at 300 rpm for 24 h.

[0094] After the reaction was completed, the obtained mixture was centrifuged at 2000 rpm for 20 min, washed with deionized water for 3 times, and the obtained solid was vacuum dried at 60° C. for 36 h to obtain nano-Fe3O4-A1 coated with a polydopamine layer.

[0095] Preparation of modified Fe3O4 suspension-1:

[0096] Weigh 10 g of methacryloyloxyethyltrimethylammonium chloride and dissolve it in 20 ml of deionized water, then add 0.6 g of nano-Fe3O4-A1 coated with a polydopamine layer, and ultrasonically treat for 15 minutes to form a uniform and stable suspension, which is the modified Fe3O4 suspension-1.

[0097] Preparation of flocculated polymer suspension-1:

[0098] The modified Fe3O4 suspension-1 was stirred continuously at 30°C and 500 rpm for 30 min under nitrogen atmosphere. Then 3 mL of ammonium cerium nitrate solution (1 mol / L nitric acid as solvent, ammonium cerium nitrate concentration of 0.2 mol / L) was quickly injected. Under nitrogen protection, stirring was continued at 30°C and 500 rpm for 24 h. After the reaction was completed, the pH was adjusted to 7±0.2 with 1 mol / L NaOH solution to obtain flocculated polymer suspension-1.

[0099] Preparation of solid flocculated polymer-1:

[0100] The flocculated polymer suspension-1 was centrifuged at 8000 rpm for 10 min, and washed with deionized water for 3 times. The obtained solid was vacuum dried at 60° C. for 24 h to obtain solid flocculated polymer-1, which appeared as gray-black solid powder.

[0101] Example 2

[0102] Preparation of nano-Fe3O4-A2 coated with polydopamine layer:

[0103] 5 g of dopamine hydrochloride was weighed and dissolved in 400 ml of tris(hydroxymethyl)aminomethane buffer, the pH was adjusted to about 8.5, and ultrasonication was performed until the solid was completely dissolved to obtain dopamine hydrochloride solution S2.

[0104] 1.6 g of nano-Fe3O4 was added to the dopamine hydrochloride solution S2, ultrasonicated for 30 min, and then stirred at room temperature at 100 rpm for 40 h.

[0105] After the reaction was completed, the obtained mixture was centrifuged at 12000 rpm for 15 min, washed with deionized water for 4 times, and the obtained solid was vacuum dried at 60° C. for 48 h to obtain nano-Fe3O4-A2 coated with a polydopamine layer.

[0106] Preparation of modified Fe3O4 suspension-2:

[0107] Weigh 10g of acryloyloxyethyltrimethylammonium chloride and dissolve it in 30ml of deionized water, then add 1g of nano-Fe3O4-A2 coated with a polydopamine layer, and ultrasonically treat for 20min to form a uniform and stable suspension, which is the modified Fe3O4 suspension-2.

[0108] Preparation of flocculated polymer suspension-2:

[0109] The modified Fe3O4 suspension-2 was stirred continuously at 30°C and 800 rpm for 30 min under nitrogen atmosphere. Then 2 mL of ammonium cerium nitrate solution (1 mol / L nitric acid as solvent, ammonium cerium nitrate concentration of 0.2 mol / L) was quickly injected. Under nitrogen protection, stirring was continued at 30°C and 300 rpm for 24 h. After the reaction was completed, the pH was adjusted to 7±0.2 with 1 mol / L NaOH solution to obtain flocculated polymer suspension-2.

[0110] Preparation of solid flocculated polymer-2:

[0111] The flocculated polymer suspension 2 was centrifuged at 15000 rpm for 12 min, washed with deionized water for 5 times, and the obtained solid was vacuum dried at 60° C. for 36 h to obtain solid flocculated polymer 2. The appearance of the solid flocculated polymer 2 was gray-black solid powder.

[0112] Example 3

[0113] Preparation of nano-Fe3O4-A3 coated with polydopamine layer:

[0114] 8 g of dopamine hydrochloride was weighed and dissolved in 400 ml of tris(hydroxymethyl)aminomethane buffer, the pH was adjusted to about 8.5, and ultrasonication was performed until the solid was completely dissolved to obtain dopamine hydrochloride solution S3.

[0115] 2.4 g of nano-Fe3O4 was added to the dopamine hydrochloride solution S3, ultrasonicated for 30 min, and then stirred at room temperature and 500 rpm for 48 h.

[0116] After the reaction was completed, the obtained mixture was centrifuged at 1000 rpm for 20 min, washed with deionized water for 3 times, and the obtained solid was vacuum dried at 60° C. for 40 h to obtain nano-Fe3O4-A3 coated with a polydopamine layer.

[0117] Preparation of modified Fe3O4 suspension-3:

[0118] Weigh 20g of dimethyldiallylammonium chloride and dissolve it in 30ml of deionized water, then add 2g of nano-Fe3O4-A3 coated with a polydopamine layer, and ultrasonically treat for 30min to form a uniform and stable suspension, which is the modified Fe3O4 suspension-3.

[0119] Preparation of flocculated polymer suspension-3:

[0120] The modified Fe3O4 suspension-3 was stirred continuously at 30°C and 700 rpm for 30 min under nitrogen atmosphere. Then 5 mL of ammonium cerium nitrate solution (1 mol / L nitric acid as solvent, ammonium cerium nitrate concentration of 0.2 mol / L) was quickly injected under nitrogen protection, and stirred continuously at 30°C and 300 rpm for 36 h. After the reaction was completed, the pH was adjusted to 7±0.2 with 1 mol / L NaOH solution to obtain flocculated polymer suspension-3.

[0121] Preparation of solid flocculated polymer-3:

[0122] The flocculated polymer suspension-3 was centrifuged at 15000 rpm for 10 min, washed with deionized water for 5 times, and the obtained solid was vacuum dried at 60° C. for 72 h to obtain solid flocculated polymer-3, which appeared as gray-black solid powder.

[0123] Test Example 1

[0124] According to the dosage in Table 1, the solid flocculating polymer obtained in the above example, commercially available polyaluminium ferric chloride (purchased from Gongyi Haizhou Water Treatment Materials Co., Ltd., brand PAC) and cationic polyacrylamide (purchased from Wenxian Sifang Water Treatment Materials Co., Ltd., brand SF-Y001) were prepared into suspensions with water at a ratio of 1.5 wt % for standby use.

[0125] The above suspension was reacted with crude oil wastewater (oil content of 289 mg / L) from a joint station of Shengli Oilfield at 55°C for 0.5 hours. The oil-water interface after contact was observed according to the method of SY / T 5797-93, and then the oil-water separation was performed. The oil content in the obtained water phase was tested according to the method of SY / T 5797-93, and the appearance of the water phase was observed. The results are shown in Table 1 below. The concentration of the reagent added in Table 1 is the ratio of the amount of solid flocculant (flocculation polymer) (mg) to the amount of oily wastewater (L).

[0126] Table 1

[0127]

[0128] It can be seen from the test results that the flocculating polymer provided by the present invention has very excellent demulsification and oil removal performance for crude oil wastewater, and the water quality after treatment is high. In addition, after the treatment, the flocculating polymer provided by the present invention can be easily recovered under the action of an external magnetic field, and its comprehensive performance is significantly better than commercially available cationic polyacrylamide and polyaluminium ferric chloride.

[0129] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A method for treating oily wastewater, characterized in that: The method comprises contacting the oily wastewater with a flocculating polymer based on magnetic nanoparticles, wherein the oil content in the oily wastewater is 200-300 mg / L; The flocculating polymer includes structural units provided by modified nano-Fe3O4; The modified nano-Fe3O4 comprises nano-Fe3O4 particles coated with a polydopamine layer and a cationic polymer grafted onto the polydopamine layer. The particle size of the modified nano-Fe3O4 is 10-20 nm. The flocculating polymer is obtained by free radical polymerization catalyzed by a redox reaction initiated by an initiator, and the initiator is selected from Ce (IV).

2. The method according to claim 1, wherein: Relative to 1L of the oily wastewater, the amount of the flocculating polymer used is 10-200 mg in terms of solid matter therein.

3. The method according to claim 2, wherein: Relative to 1L of the oily wastewater, the amount of the flocculating polymer used is 20-100 mg in terms of solid matter therein.

4. The method according to claim 1, wherein: The contact conditions include: temperature 40-70° C., time 0.5-6 h.

5. The method according to claim 4, wherein: The contact conditions include: temperature 45-55° C., time 1-3 h.

6. The method according to claim 1, wherein: The cationic polymer is selected from polymers composed of cationic monomers containing double bonds.

7. The method according to claim 6, wherein: The cationic monomer containing a double bond is selected from quaternary ammonium salts containing a double bond.

8. A flocculating polymer for use in the method of any one of claims 1 to 7.

9. The method for preparing a flocculating polymer used in any one of claims 1 to 7, characterized in that: The method comprises the following steps: Under the condition of free radical polymerization, the modified nano-Fe3O4 is mixed with an initiator, wherein the initiator is selected from Ce (IV); Wherein, the modified nano-Fe3O4 comprises nano-Fe3O4 particles coated with a polydopamine layer and a cationic monomer containing a double bond grafted onto the polydopamine layer; The modified nano-Fe3O4 is mixed with an initiator in the form of a modified nano-Fe3O4 suspension. The preparation method of the modified nano-Fe3O4 suspension includes: (1) contacting nano-Fe3O4 with a dopamine hydrochloride solution, and then sequentially performing a first solid-liquid separation, a first washing, and a first drying to obtain nano-Fe3O4 coated with a polydopamine layer, wherein the particle size of the nano-Fe3O4 is 10-20 nm; (2) The nano-Fe3O4 coated with the polydopamine layer obtained in step (1) is brought into a second contact with a cationic monomer solution containing double bonds to obtain a modified Fe3O4 suspension.

10. The method according to claim 9, wherein: In step (1), in step (1), the dopamine hydrochloride solution is selected from a solution with dopamine hydrochloride as solute and tris(hydroxymethyl)aminomethane buffer as solvent.

11. The method according to claim 10, wherein: In step (1), the concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 0.1-4% by weight; And / or, in step (1), the pH of the dopamine hydrochloride solution is 8-9; And / or, in step (1), the amount of the nano-Fe3O4 is 0.1-1% by weight of the dopamine hydrochloride solution.

12. The method according to claim 10, wherein: In step (1), the concentration of dopamine hydrochloride in the dopamine hydrochloride solution is 1-2% by weight; And / or, in step (1), the amount of the nano-Fe3O4 used is 0.3-0.8% by weight of the dopamine hydrochloride solution.

13. The method according to claim 9, wherein: In step (1), the first solid-liquid separation method is selected from centrifugal separation; And / or, in step (1), the first washing method comprises: washing the solid phase obtained by the first solid-liquid separation with deionized water; And / or, in step (1), the first drying method is selected from vacuum drying.

14. The method according to claim 13, wherein: In step (1), the conditions for the first solid-liquid separation include: centrifugal speed of 800-20000 rpm, centrifugal time of 10-20 min; And / or, in step (1), the first washing conditions include: washing the solid phase 3-5 times with deionized water; And / or, in step (1), the first drying conditions include: 50-80°C, time 24-72h.

15. The method according to claim 9, wherein: In step (1), the first contacting method includes: temperature 20-30°C, ultrasonic stirring for 10-30 minutes, and then stirring at 100-1000 rpm for 8-48 hours.

16. The method according to claim 9, wherein: In step (2), the cationic monomer containing a double bond is selected from a quaternary ammonium salt containing a double bond.

17. The method according to claim 16, wherein: In step (2), based on dry weight, the amount of the cationic monomer containing a double bond is 10-20 g relative to 1 g of nano-Fe3O4 coated with a polydopamine layer.

18. The method according to claim 9 or 16, wherein: In step (2), the cationic solution containing double bonds is selected from an aqueous solution of a quaternary ammonium salt containing double bonds.

19. The method according to claim 18, wherein: The concentration of the aqueous solution of the double bond-containing quaternary ammonium salt is 10-50% by weight.

20. The method according to claim 19, wherein: The concentration of the aqueous solution of the double bond-containing quaternary ammonium salt is 20-40% by weight.

21. The method according to claim 9, wherein: In step (2), the amount of the nano-Fe3O4 coated with the polydopamine layer is such that the content of the modified nano-Fe3O4 in the modified Fe3O4 suspension is 0.1-1% by weight.

22. The method according to claim 21, wherein: In step (2), the amount of the nano-Fe3O4 coated with the polydopamine layer is such that the content of the modified nano-Fe3O4 in the modified Fe3O4 suspension is 0.15-0.6% by weight.

23. The method according to claim 9, wherein: In step (2), the second contacting method includes ultrasonic mixing and / or stirring mixing.

24. The method according to claim 23, wherein: In step (2), the second contacting method is selected from ultrasonic mixing, and the conditions include: ultrasonic mixing for 10-30 minutes.

25. The method according to claim 9, wherein: Based on dry weight, the amount of the initiator used is 0.1-0.6 g relative to 1 g of nano-Fe3O4 coated with a polydopamine layer.

26. The method according to claim 9, wherein: The mixing method includes: bringing the modified Fe3O4 suspension into a third contact with an initiator solution, and then adjusting the pH to obtain a flocculated polymer suspension based on magnetic nanoparticles.

27. The method according to claim 26, wherein: The initiator solution is selected from a cerium ammonium nitrate solution using nitric acid as a solvent; And / or, adjusting pH is performed using NaOH and / or KOH; And / or, in the flocculation polymer suspension based on magnetic nanoparticles, the content of the modified nano-Fe3O4 is 1-10% by weight.

28. The method according to claim 27, wherein: In the flocculation polymer suspension based on magnetic nanoparticles, the content of the modified nano-Fe3O4 is 1-5% by weight.

29. The method according to claim 27, wherein: The concentration of the nitric acid is 0.5-2 mol / L; and / or, the concentration of ammonium cerium nitrate in the initiator solution is 0.1-0.5 mol / L; And / or, the pH of the magnetic nanoparticle-based flocculated polymer suspension is 6.8-7.

2.

30. The method of claim 26, wherein: The conditions for the third contact include: under an inert atmosphere, a temperature of 20-40° C., a stirring speed of 100-1200 rpm, and a stirring time of 12-36 h.

31. The method according to claim 30, wherein: The inert atmosphere is provided by nitrogen and / or an inert gas.

32. The method of claim 26, wherein: The method further comprises the following steps: The flocculated polymer suspension based on the magnetic nanoparticles obtained after mixing is subjected to a second solid-liquid separation, a second washing and a second drying to obtain a solid flocculated polymer based on the magnetic nanoparticles.

33. The method of claim 32, wherein: The second solid-liquid separation method is selected from centrifugal separation; And / or, the second washing method comprises: washing the solid phase obtained by the second solid-liquid separation with deionized water; And / or, the second drying method is selected from vacuum drying.

34. The method of claim 33, wherein: The conditions for the second solid-liquid separation include: centrifugal speed of 1000-20000 rpm, centrifugal time of 10-20 min; And / or, the second washing conditions include: washing the solid phase 3-5 times with deionized water; And / or, the second drying conditions include: temperature 50-80° C., time 24-72 h.

35. A flocculating polymer based on magnetic nanoparticles prepared according to the method of any one of claims 9 to 34.

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