A process for the adsorption of p-aminophenol from waste water

Abstract

The application discloses a kind of adsorption processes to p-aminophenol in wastewater, belong to wastewater treatment technical field, including the following steps: adjusting wastewater pH value is 7-9, filtration removes suspended solids and mechanical impurities, obtains pretreated wastewater;Selective magnetic adsorbent is added to pretreated wastewater, after stirring 30min, magnet separation, obtain p-aminophenol extract and primary wastewater;Primary wastewater is subjected to chemical oxidation treatment, oxidation effluent is subjected to subsequent treatment again;P-aminophenol extract is placed in eluent, after ultrasonic elution 20-30min, magnet separation, obtain p-aminophenol mixed solution and regenerated selective magnetic adsorbent, p-aminophenol mixed solution is recycled p-aminophenol product, the adsorption process of p-aminophenol in wastewater provided by the application is not only simple, and the p-aminophenol recovery rate obtained is high, and the purity is high.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of wastewater treatment, and particularly relates to an adsorption process for p-aminophenol in wastewater. BACKGROUND

[0002] P-aminophenol is an important organic intermediate, which is widely used in the industrial fields of medicine, dye, rubber, photosensitive material and the like, and is a raw material for preparing the well-known antipyretic analgesic drug paracetamol. At present, the total production of p-aminophenol is increasing by 4% per year, and a large amount of high-concentration phenolic wastewater is generated in the production of p-aminophenol, which can be long-term retained in the environment and accumulated in the food chain, thereby causing waste of resources and endangering human health.

[0003] Due to the particularity of the structure and composition of p-aminophenol, the p-aminophenol is a typical aromatic amphoteric compound with an alkaline group (-NH2) and an acidic group (-OH), and the removal method for general phenolic wastewater has poor treatment effect and high operation cost. With the development of synthesis technology of hypercrosslinked adsorption resin, a new type of resin adsorption separation technology with multifunctional groups and excellent pore structure has been widely applied in the field of water pollution treatment. For example, the patent application No. 200610037919.3 discloses an integrated process for treating p-aminophenol production wastewater and a resource recovery method, in which p-aminophenol is selectively adsorbed by an amino-modified composite functional resin. Although the organic substance p-aminophenol is recovered, the obtained p-aminophenol has low purity and needs to be purified and the like, and the process is complex. SUMMARY

[0004] The application aims to provide an adsorption process for p-aminophenol in wastewater, and solve the problems of low recovery rate of p-aminophenol in wastewater and low purity of the recovered product.

[0005] The object of the application can be achieved by the following technical scheme.

[0006] An adsorption process for p-aminophenol in wastewater, comprising the following steps:

[0007] 1) adjusting the pH value of the wastewater to 7-9, removing suspended solids and mechanical impurities to obtain pretreated wastewater;

[0008] 2) adding a selective magnetic adsorbent to the pretreated wastewater, stirring for 30 min, and then separating by a magnet to obtain a p-aminophenol extract and first-stage wastewater;

[0009] 3) performing chemical oxidation treatment on the first-stage wastewater, and then performing subsequent treatment on the oxidation effluent;

[0010] 4) The p-aminophenol extract is placed in an eluent, and after ultrasonic elution for 20-30 min, the p-aminophenol mixture and the regenerated selective magnetic adsorbent are separated by a magnet. The regenerated selective magnetic adsorbent is dried for standby use. The p-aminophenol mixture is distilled under reduced pressure to recover methanol. Then, the pH is adjusted to 7 with sodium hydroxide, and the temperature is lowered to 10°C to precipitate p-aminophenol. The p-aminophenol product is obtained by filtration.

[0011] Further, the selective magnetic adsorbent is prepared by the following steps:

[0012] S1, trimethylolpropane triacrylate and 3-aminophenyl trimethoxysilane are added to tetrahydrofuran, and stirred at 50-70°C for 12 h under nitrogen protection. Tetrahydrofuran is removed by distillation under reduced pressure to obtain an end-vinyl hyperbranched polymer.

[0013] S2, the end-vinyl hyperbranched polymer and the magnetic carrier are added to a solution composed of tetrahydrofuran and deionized water, and ultrasonically dispersed for 30-50 min. Then, the mixture is stirred at 50-60°C for 24 h. After the reaction, the mixture is washed with tetrahydrofuran by centrifugation for three times, and dried at 50°C under vacuum for 24 h to obtain a modified magnetic carrier.

[0014] S3, methanol, acetonitrile, ammonia water, and ammonium acetate solution are mixed uniformly, and p-aminophenol is added. After stirring, methacrylic acid is added. After ultrasonic treatment for 30 min, the mixture is reacted at 4°C for 12 h. Then, the modified magnetic carrier is added, and ultrasonic treatment is performed for 30 min. Ethylene glycol dimethacrylate and azobisisobutyronitrile are added, and ultrasonic treatment is performed for 30 min under nitrogen protection. The mixture is reacted at 60°C for 24 h. The product is separated by a magnet, washed with an eluent for 20-40 min, filtered, and dried at 60°C until the weight is constant to obtain the selective magnetic adsorbent.

[0015] First, trimethylolpropane triacrylate and 3-aminophenyl trimethoxysilane are used as raw materials to obtain an end-vinyl hyperbranched polymer containing siloxane structure by Michael addition reaction. Then, the end-vinyl hyperbranched polymer is introduced onto the surface of the magnetic carrier by coupling reaction to obtain a modified magnetic carrier. Finally, p-aminophenol is used as a template molecule, methacrylic acid is used as a functional monomer, ethylene glycol dimethacrylate is used as a crosslinking agent, and azobisisobutyronitrile is used as an initiator to perform copolymerization. Then, the template molecule is eluted with an eluent to obtain the selective magnetic adsorbent.

[0016] Further, the amount ratio of trimethylolpropane triacrylate, 3-aminophenyl trimethoxysilane, and tetrahydrofuran in step S1 is 30 mmol: 30 mmol: 100-200 mL.

[0017] Further, the amount ratio of end-vinyl hyperbranched polymer, magnetic carrier, tetrahydrofuran and deionized water in step S2 is 1-2g:0.5g:60-100mL:10-20mL.

[0018] Further, the amount ratio of methanol, acetonitrile, ammonia water, ammonium acetate solution, p-aminophenol, methacrylic acid, modified magnetic carrier, ethylene glycol dimethacrylate and azobisisobutyronitrile in step S3 is 10mL:2mL:5mL:3mL:0.05mmol:150-170μL:0.1-0.3g:1.5-1.9mL:0.04-0.06g, the concentration of ammonium acetate solution is 5mmol / L, and the mass fraction of ammonia water is 25-28%.

[0019] Further, the eluent in step S3 is composed of ammonium acetate solution with a concentration of 1mmol / L and methanol with a volume ratio of 15-25:75-85.

[0020] Further, the magnetic carrier is Fe304@SiO2, and the preparation steps are as follows:

[0021] The nano-Fe304, anhydrous ethanol and deionized water are ultrasonically mixed for 10-15min, ammonia water and tetraethyl orthosilicate are added, and the reaction is carried out at room temperature for 12h, then the product is separated by a magnet and washed, and dried at 60℃ until the weight is constant to obtain the magnetic carrier.

[0022] The amount ratio of nano-Fe304, anhydrous ethanol, deionized water, ammonia water and tetraethyl orthosilicate is 0.3-0.5g:50mL:4mL:5mL:2mL, and the mass fraction of ammonia water is 25-28%.

[0023] Further, the pH regulator in step 1) is sodium hydroxide.

[0024] Further, the amount ratio of pretreated wastewater and selective magnetic adsorbent in step 2) is 10mg:8-10mL.

[0025] Further, the amount ratio of p-aminophenol extract and eluent in step 4) is 1mg:1mL, and the eluent is composed of ammonium acetate solution with a concentration of 1mmol / L and methanol with a volume ratio of 20-30:70-80.

[0026] The beneficial effects of the present application are as follows:

[0027] The present application provides a kind of p-aminophenol adsorption process in wastewater, using self-made selective magnetic adsorbent to treat wastewater, since there are many cavities in selective magnetic adsorbent which match the shape and size of p-aminophenol, specific adsorption enrichment of p-aminophenol in wastewater can be realized, and interference of other organic pollutants is reduced.

[0028] The present application also introduces a hyperbranched polymer layer on the surface of the magnetic carrier, which has a unique spatial structure and abundant amino groups, can increase the specific surface area of the selective magnetic adsorbent, increase the adsorption capacity, increase the attachment sites and enhance the adsorption effect. In addition, the hyperbranched polymer also contains many benzene ring structures, which can combine with p-aminophenol through π-π interaction, further enhancing the adsorption effect.

[0029] The present application first controls the pH value of wastewater to be 7-9, and then uses self-made selective magnetic adsorbent to treat wastewater. At a lower pH value, p-aminophenol is protonated into a cation, and at a higher pH value, p-aminophenol is dissociated into an anion, neither of which exists in a molecular state, which is not conducive to the adsorption and separation of p-aminophenol by the selective magnetic adsorbent. Therefore, the present application strictly controls the pH value of wastewater to be 7-9 to ensure the adsorption effect of the selective magnetic adsorbent.

[0030] In addition, the selective magnetic adsorbent in the present application has magnetism, is easy to separate, and can be repeatedly used. The adsorbed and separated p-aminophenol is treated by elution and crystallization to obtain a p-aminophenol product with high purity. In summary, the p-aminophenol adsorption process in wastewater provided by the present application not only has simple steps, but also has high recovery rate and high purity of p-aminophenol. DETAILED DESCRIPTION

[0031] The technical solutions in the embodiments of the present application will be described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0032] Embodiment 1

[0033] The selective magnetic adsorbent is prepared by the following steps:

[0034] S1, 30mmol of trimethylolpropane triacrylate and 30mmol of 3-aminophenyl trimethoxysilane are added to 100mL of tetrahydrofuran, and stirred at 50℃ under nitrogen protection for 12h. The tetrahydrofuran is removed by distillation under reduced pressure to obtain an ethenyl-terminated hyperbranched polymer.

[0035] S2, 1 g of end-vinyl hyperbranched polymer and 0.5 g of magnetic carrier were added into a solution of 60 mL of tetrahydrofuran and 10 mL of deionized water, and after ultrasonic dispersion for 30 min, stirring reaction was carried out at 50°C for 24 h. After the reaction, the product was washed with tetrahydrofuran by centrifugation for three times, and vacuum drying was carried out at 50°C for 24 h to obtain the modified magnetic carrier;

[0036] S3, 10 mL of methanol, 2 mL of acetonitrile, 5 mL of 25 wt% ammonia water and 3 mL of 5 mmol / L ammonium acetate solution were uniformly mixed, 0.05 mmol of p-aminophenol was added, and after stirring, 150 μL of methacrylic acid was added. After ultrasonic treatment for 30 min, 4°C reaction was carried out for 12 h. 0.1 g of the modified magnetic carrier was added, and after ultrasonic treatment for 30 min, 1.5 mL of ethylene glycol dimethacrylate and 0.04 g of azobisisobutyronitrile were added. After ultrasonic treatment for 30 min under nitrogen protection, 60°C reaction was carried out for 24 h. The product was separated by magnet, washed with eluent for 20 min, filtered, and the filter cake was dried at 60°C to constant weight to obtain the selective magnetic adsorbent. The eluent was composed of 1 mol / L ammonium acetate solution and methanol at a volume ratio of 15:85.

[0037] The magnetic carrier was Fe304@SiO2, and the preparation steps were as follows:

[0038] 0.3 g of nano Fe304, 50 mL of anhydrous ethanol and 4 mL of deionized water were ultrasonically mixed for 10 min, 5 mL of 25 wt% ammonia water and 2 mL of tetraethyl orthosilicate were added, and reaction was carried out at room temperature for 12 h. The product was separated by magnet, and washed with anhydrous ethanol and deionized water until the washing liquid was neutral. Drying was carried out at 60°C to constant weight to obtain the magnetic carrier.

[0039] Example 2

[0040] The selective magnetic adsorbent was prepared by the following steps:

[0041] S1, 30 mmol of trimethylolpropane triacrylate and 30 mmol of 3-aminophenyl trimethoxysilane were added into 200 mL of tetrahydrofuran, and stirring reaction was carried out at 70°C for 12 h under nitrogen protection. Tetrahydrofuran was removed by reduced pressure distillation to obtain end-vinyl hyperbranched polymer;

[0042] S2, 2 g of end-vinyl hyperbranched polymer and 0.5 g of magnetic carrier were added into a solution of 100 mL of tetrahydrofuran and 20 mL of deionized water, and after ultrasonic dispersion for 50 min, stirring reaction was carried out at 60°C for 24 h. After the reaction, the product was washed with tetrahydrofuran by centrifugation for three times, and vacuum drying was carried out at 50°C for 24 h to obtain the modified magnetic carrier;

[0043] S3, 10 mL of methanol, 2 mL of acetonitrile, 5 mL of 28 wt% ammonia water and 3 mL of 5 mmol / L ammonium acetate solution were mixed uniformly, 0.05 mmol of p-aminophenol was added, 170 μL of methacrylic acid was added after stirring uniformly, ultrasonic treatment was carried out for 30 min, reaction was carried out at 4°C for 12 h, 0.3 g of the modified magnetic carrier was added, 1.9 mL of ethylene glycol dimethacrylate and 0.06 g of azobisisobutyronitrile were added after ultrasonic treatment for 30 min, ultrasonic treatment was carried out for 30 min under nitrogen protection, reaction was carried out at 60°C for 24 h, the product was separated by a magnet, eluent was used for washing for 40 min, filtration was carried out, the filter cake was dried at 60°C until the weight was constant, and a selective magnetic adsorbent was obtained. The eluent was composed of 1 mol / L ammonium acetate solution and methanol in a volume ratio of 25:75.

[0044] The magnetic carrier was Fe304@SiO2, and the preparation steps were as follows:

[0045] 0.5 g of nano Fe304, 50 mL of anhydrous ethanol and 4 mL of deionized water were ultrasonically mixed for 15 min, 5 mL of 28 wt% ammonia water and 2 mL of tetraethyl orthosilicate were added, reaction was carried out at room temperature for 12 h, the product was separated by a magnet, and washing was carried out with anhydrous ethanol and deionized water until the washing liquid was neutral, and drying was carried out at 60°C until the weight was constant, thereby obtaining the magnetic carrier.

[0046] Comparative Example 1

[0047] The selective magnetic adsorbent was prepared by the following steps: compared with Example 1, 3-aminopropyltriethoxysilane was used to replace 3-aminophenyltrimethoxysilane in Example 1, and the remaining raw materials and preparation process were the same as those in Example 1.

[0048] Comparative Example 2

[0049] The selective magnetic adsorbent was prepared by the following steps:

[0050] 10 mL of methanol, 2 mL of acetonitrile, 5 mL of 28 wt% ammonia water and 3 mL of 5 mmol / L ammonium acetate solution were mixed uniformly, 0.05 mmol of p-aminophenol was added, 170 μL of methacrylic acid was added after stirring uniformly, ultrasonic treatment was carried out for 30 min, reaction was carried out at 4°C for 12 h, 0.3 g of the modified magnetic carrier was added, 1.9 mL of ethylene glycol dimethacrylate and 0.06 g of azobisisobutyronitrile were added after ultrasonic treatment for 30 min, ultrasonic treatment was carried out for 30 min under nitrogen protection, reaction was carried out at 60°C for 24 h, the product was separated by a magnet, eluent was used for washing for 40 min, filtration was carried out, the filter cake was dried at 60°C until the weight was constant, and a selective magnetic adsorbent was obtained. The eluent was composed of 1 mol / L ammonium acetate solution and methanol in a volume ratio of 25:75, and the preparation process of the magnetic carrier was the same as that in Example 1.

[0051] The selective magnetic adsorbent obtained in Example 1-2 and Comparative Example 1-2 is tested, and the specific process is as follows:

[0052] In a conical flask, 30 mg of the test substance is added, 60 mL of a 1 mg / mL p-aminophenol methanol solution is added to the conical flask, and oscillation is performed for 12 h. Centrifugal separation is performed at 10000 r / min for 15 min, 0.2 mL of supernatant is taken, diluted to 10 mL with methanol, and the concentration of p-aminophenol in the supernatant is determined by ultraviolet spectrophotometry. The adsorption capacity Q is calculated according to the formula Q = (C0-C)·Vm (1) wherein Q is the adsorption capacity of the test substance (mg / g), C0is the concentration of p-aminophenol before adsorption (mg / mL), C is the concentration of p-aminophenol after adsorption (mg / mL), V is the volume of the p-aminophenol solution taken (L), and m is the mass of the molecularly imprinted polymer taken (g);

[0053] The same test substance is used, and the above adsorption step is repeated 6 times. The adsorption capacity of the test substance for p-aminophenol in the seventh time is tested;

[0054] The test results are shown in Table 1:

[0055] Table 1

[0056] Item Example 1 Example 2 Comparative Example 1 Comparative Example 2 Adsorption amount (mg / g) 121.54 122.34 114.35 89.24 Adsorption amount (mg / g) after 6 cycles 119.25 119.87 109.24 75.16

[0057] As can be seen from the test results in Table 1, compared with Comparative Example 1 and Comparative Example 2, the selective magnetic adsorbent obtained in Example 1 and Example 2 has a larger adsorption capacity for p-aminophenol and better recycling performance.

[0058] Example 3

[0059] An adsorption process for p-aminophenol in wastewater includes the following steps:

[0060] 1) The pH value of the wastewater is adjusted to 7 with sodium hydroxide, and suspended solids and mechanical impurities are removed by filtration to obtain pretreated wastewater;

[0061] 2) The selective magnetic adsorbent of Example 1 is added to the pretreated wastewater, and the dosage ratio of the pretreated wastewater to the selective magnetic adsorbent is 10 mg:8 mL. After stirring for 30 min, the first-stage wastewater and the p-aminophenol extract are obtained by magnetic separation;

[0062] 3) The first-stage wastewater is subjected to chemical oxidation treatment, and the oxidized water is subjected to subsequent treatment;

[0063] 4) The p-aminophenol extract is placed in an eluent, the use amount ratio of the p-aminophenol extract and the eluent is 1 mg: 1 mL, the eluent is composed of 1 mmol / L ammonium acetate solution and methanol according to a volume ratio of 20:80, after ultrasonic elution for 20 min, the p-aminophenol extract and the eluent are separated by a magnet, a p-aminophenol mixture and a regenerated selective magnetic adsorbent are obtained, the regenerated selective magnetic adsorbent is dried for standby, the methanol in the p-aminophenol mixture is recovered by reduced pressure distillation, then the pH is adjusted to 7 by sodium hydroxide, the temperature is reduced to 10℃, the p-aminophenol is precipitated, and the p-aminophenol product is obtained by filtration.

[0064] Example 4

[0065] An adsorption process for p-aminophenol in wastewater, comprising the following steps:

[0066] 1) The pH of the wastewater is adjusted to 8 by sodium hydroxide, and the suspended solids and mechanical impurities are removed by filtration to obtain pretreated wastewater;

[0067] 2) The selective magnetic adsorbent of Example 2 is added to the pretreated wastewater, the use amount ratio of the pretreated wastewater and the selective magnetic adsorbent is 10 mg: 9 mL, after stirring for 30 min, the pretreated wastewater and the selective magnetic adsorbent are separated by a magnet, a p-aminophenol extract and primary wastewater are obtained;

[0068] 3) The primary wastewater is subjected to chemical oxidation treatment, and the oxidized water is subjected to subsequent treatment;

[0069] The p-aminophenol extract is placed in an eluent, the use amount ratio of the p-aminophenol extract and the eluent is 1 mg: 1 mL, the eluent is composed of 1 mmol / L ammonium acetate solution and methanol according to a volume ratio of 20:80, after ultrasonic elution for 20 min, the p-aminophenol extract and the eluent are separated by a magnet, a p-aminophenol mixture and a regenerated selective magnetic adsorbent are obtained, the regenerated selective magnetic adsorbent is dried for standby, the methanol in the p-aminophenol mixture is recovered by reduced pressure distillation, then the pH is adjusted to 7 by sodium hydroxide, the temperature is reduced to 10℃, the p-aminophenol is precipitated, and the p-aminophenol product is obtained by filtration.

[0070] Example 5

[0071] An adsorption process for p-aminophenol in wastewater, comprising the following steps:

[0072] 1) The pH of the wastewater is adjusted to 9 by sodium hydroxide, and the suspended solids and mechanical impurities are removed by filtration to obtain pretreated wastewater;

[0073] 2) The selective magnetic adsorbent of Example 2 is added to the pretreated wastewater, the use amount ratio of the pretreated wastewater and the selective magnetic adsorbent is 10 mg: 10 mL, after stirring for 30 min, the pretreated wastewater and the selective magnetic adsorbent are separated by a magnet, a p-aminophenol extract and primary wastewater are obtained;

[0074] 3) The primary wastewater is subjected to chemical oxidation treatment, and the oxidized water is subjected to subsequent treatment;

[0075] The p-aminophenol extract is placed in an eluent, and the ratio of the amount of the p-aminophenol extract to the eluent is 1 mg: 1 mL. The eluent is composed of 1 mmol / L ammonium acetate solution and methanol in a volume ratio of 20:80. After ultrasonic elution for 30 min, the mixture is separated by a magnet to obtain a p-aminophenol mixture and a regenerated selective magnetic adsorbent. The regenerated selective magnetic adsorbent is dried for standby use. The p-aminophenol mixture is subjected to vacuum distillation to recover methanol. Then, the pH of the mixture is adjusted to 7 by sodium hydroxide, and the mixture is cooled to 10°C to precipitate p-aminophenol. The p-aminophenol is filtered to obtain a p-aminophenol product.

[0076] Comparative Example 3

[0077] An adsorption process for p-aminophenol in wastewater is provided. Compared with Example 3, the pH of the wastewater is adjusted to 6 by sodium hydroxide or 35 wt% hydrochloric acid solution in the adsorption process. The other raw materials and preparation processes are the same as those in Example 3.

[0078] Comparative Example 4

[0079] An adsorption process for p-aminophenol in wastewater is provided. Compared with Example 3, the pH of the wastewater is adjusted to 10 in the adsorption process. The other raw materials and preparation processes are the same as those in Example 3.

[0080] Comparative Example 5

[0081] An adsorption process for p-aminophenol in wastewater is provided. Compared with Example 3, the selective magnetic adsorbent in Example 3 is replaced by the material in Comparative Example 1. The other raw materials and preparation processes are the same as those in Example 3.

[0082] Comparative Example 6

[0083] An adsorption process for p-aminophenol in wastewater is provided. Compared with Example 3, the selective magnetic adsorbent in Example 3 is replaced by the material in Comparative Example 2. The other raw materials and preparation processes are the same as those in Example 3.

[0084] A wastewater produced by a p-aminophenol production plant in Anhui is taken as an example. The p-aminophenol is obtained by hydrogenation of p-nitrophenol. The content of p-aminophenol in the wastewater is 3782 mg / L, the TOC is 1154 mg / L, and the wastewater contains 20% sodium chloride. The adsorption processes in Example 3-Example 5 and Comparative Example 3-Comparative Example 6 are used to treat the wastewater, respectively. The yield and purity of the p-aminophenol product are measured and calculated. The test results are shown in Table 2.

[0085] Table 2

[0086]

[0087] As can be seen from Table 2, the adsorption process described in Examples 3-5 resulted in higher yield and purity of p-aminophenol than the adsorption processes described in Comparative Examples 3-6.

[0088] It is to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting; it is also possible in the present application that steps can be executed in different sequence, where this is implicitly or explicitly suggested within this document. It is also possible that some steps can be left out, others can be added, or some steps can be performed in an order other than that described herein. Furthermore, any desired features of the different aspects and embodiments described can be implemented in any combination.

[0089] While embodiments of the application have been shown and described, it is to be understood that the application is not limited to these embodiments. Rather, it is the intention that all variations and modifications which fall within the spirit and scope of the application shall be considered. The scope of the application is to be determined by the following claims and their equivalents.

Claims

1. An adsorption process for p-aminophenol in wastewater, characterized in that, Includes the following steps: The pH of the wastewater is adjusted to 7-9, and suspended solids and mechanical impurities are removed by filtration to obtain pretreated wastewater. A selective magnetic adsorbent was added to the pretreated wastewater, and after stirring for 30 minutes, the water was separated by magnets to obtain p-aminophenol extract and primary wastewater. The primary wastewater is chemically oxidized, and the effluent from the oxidation process is then further treated. The p-aminophenol extract was placed in the eluent and ultrasonically eluted for 20-30 minutes. Then, it was separated by magnetism to obtain a p-aminophenol mixture and a regenerated selective magnetic adsorbent. The p-aminophenol mixture was then distilled under reduced pressure to recover methanol. The pH was then adjusted to 7 with sodium hydroxide and cooled to 10°C to precipitate p-aminophenol. The mixture was then filtered to obtain the p-aminophenol product. Selective magnetic adsorbents are prepared by the following steps: S1. Trimethylolpropane triacrylate and 3-aminophenyltrimethoxysilane were added to tetrahydrofuran and stirred at 50-70°C for 12 h under nitrogen protection to obtain a vinyl-terminated hyperbranched polymer. S2. Add the vinyl-terminated hyperbranched polymer and the magnetic support to a solution composed of tetrahydrofuran and deionized water, disperse ultrasonically for 30-50 min, and then stir at 50-60℃ for 24 h to obtain the modified magnetic support. S3. Mix methanol, acetonitrile, ammonia and ammonium acetate solution evenly, add p-aminophenol, stir evenly, add methacrylic acid, sonicate, react at 4℃ for 12h, add modified magnetic carrier, sonicate for 30min, add ethylene glycol dimethacrylate and azobisisobutyronitrile, sonicate for 30min under nitrogen protection, react at 60℃ for 24h, separate the product with a magnet to obtain selective magnetic adsorbent. The magnetic carrier is Fe3O4@SiO2; Step 4) The ratio of p-aminophenol extract to eluent is 1 mg: 1 mL. The eluent is composed of 1 mmol / L ammonium acetate solution and methanol in a volume ratio of 20-30: 70-80.

2. The adsorption process for p-aminophenol in wastewater according to claim 1, characterized in that, In step S1, the ratio of trimethylolpropane triacrylate, 3-aminophenyltrimethoxysilane and tetrahydrofuran is 30 mmol: 30 mmol: 100-200 mL.

3. The adsorption process for p-aminophenol in wastewater according to claim 1, characterized in that, In step S2, the ratio of the terminal vinyl hyperbranched polymer, the magnetic carrier, tetrahydrofuran, and deionized water is 1-2 g: 0.5 g: 60-100 mL: 10-20 mL.

4. The adsorption process for p-aminophenol in wastewater according to claim 1, characterized in that, In step S3, the ratio of methanol, acetonitrile, ammonia, ammonium acetate solution, p-aminophenol, methacrylic acid, modified magnetic carrier, ethylene glycol dimethacrylate, and azobisisobutyronitrile is 10 mL: 2 mL: 5 mL: 3 mL: 0.05 mmol: 150-170 μL: 0.1-0.3 g: 1.5-1.9 mL: 0.04-0.06 g, the concentration of ammonium acetate solution is 5 mmol / L, and the mass fraction of ammonia is 25-28%.

5. The adsorption process for p-aminophenol in wastewater according to claim 1, characterized in that, In step S3, the eluent is composed of a 1 mol / L ammonium acetate solution and methanol in a volume ratio of 15-25:75-85.

6. The adsorption process for p-aminophenol in wastewater according to claim 1, characterized in that, In step 2), the ratio of pretreated wastewater to selective magnetic adsorbent is 10 mg: 8-10 mL.

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