Method for recovering ammonium chloride from o-nitroaniline waste liquid

Abstract

The application discloses a method for recovering ammonium chloride in o-nitroaniline waste liquid, and belongs to the technical field of wastewater treatment. The method comprises the following steps: S1, the o-nitroaniline waste liquid is sequentially passed through three-stage countercurrent washing devices, and the pH is adjusted step by step to obtain an ammonium chloride crude extract; S2, PS-DVB microspheres are prepared by using styrene and divinylbenzene as monomers, ammonium persulfate as an initiator and polyvinylpyrrolidone as a dispersant, a TiO2 shell layer is constructed on the outer layer of the PS-DVB microspheres, and graphene oxide is loaded on the TiO2 shell layer to obtain PS-DVB@TiO2 / GO resin; and S3, the PS-DVB@TiO2 / GO resin is loaded into a column, the ammonium chloride crude extract is passed into the adsorption column, effluent is collected, the effluent is subjected to multi-effect evaporation, ammonium chloride is obtained in solid phase, and the evaporation liquid and the resin are recycled and reused. Through the cooperation of multiple technologies, high recovery rate, low residue and circular economy of the ammonium chloride are realized, and the method has industrialization popularization value.

Description

Technical Field

[0001] This invention belongs to the field of wastewater treatment technology, specifically relating to a method for recovering ammonium chloride from wastewater used in the preparation of o-nitroaniline. Background Technology

[0002] o-Nitroaniline, as a basic chemical raw material, is an intermediate in many dyes, pesticides, and pharmaceuticals, and also has applications in auxiliaries. The current method for preparing o-nitroaniline involves mixing o-nitrochlorobenzene and ammonia in an ammoniation reactor under high temperature and pressure to obtain o-nitroaniline, ammonium chloride, and water. After separating the aqueous phase from the ammoniation products, the remaining product is washed several times with process hot water to remove ammonium chloride, followed by vacuum drying to obtain o-nitroaniline. Because o-nitroaniline is slightly soluble in water, some o-nitroaniline is dissolved and carried away with each wash. Even after several washes, it is impossible to completely remove chloride ions dispersed in o-nitroaniline, resulting in a low yield, poor product purity, and high chloride ion content.

[0003] Patent application CN102432033A discloses a post-treatment process for the mother liquor of high-purity o-nitro-p-chloroaniline. The mother liquor is obtained by reacting 2,5-dichloronitrobenzene with ammonia to produce high-purity o-nitro-p-chloroaniline, containing ammonium chloride and a small amount of o-nitro-p-chloroaniline. This process uses quicklime to separate ammonia and calcium chloride from the mother liquor, and then recycles the ammonia and calcium chloride, saving costs and achieving green production. However, the quicklime reaction preferentially produces calcium chloride, failing to efficiently separate ammonium chloride; the high-temperature reaction (150℃) and subsequent cooling and crystallization (5-10℃) consume double energy; and the lack of adsorption or extraction of residual nitroaniline organic matter in the wastewater may contaminate byproducts. Patent application CN107382746 A discloses a method for recovering ammonium chloride in the post-treatment of o-nitroaniline. The method involves an ammoniation reaction: nitrobenzene and concentrated ammonia react in a six-stage series autoclave to generate an o-nitroaniline mixture; water washing and desalination: the mixture is washed to separate ammonium chloride, and the washing liquid is adsorbed onto resin to recover residual o-nitroaniline; extraction and purification: the adsorbed liquid is extracted with o-nitrochlorobenzene to separate the aqueous phase; evaporation and crystallization: the extracted aqueous phase is evaporated using a triple-effect evaporator to obtain ammonium chloride, and the evaporator is recycled; this process recovers both ammonium chloride and o-nitroaniline. However, this method requires maintaining a triple-effect evaporation temperature of 70–100℃ and operating under reduced pressure, resulting in significant energy consumption; the resin adsorption and extraction steps increase equipment costs, and the organic solvent (o-nitrochlorobenzene) may cause secondary pollution, making the process complex. Therefore, developing a method for recovering ammonium chloride from o-nitroaniline waste liquid is essential. Summary of the Invention

[0004] The purpose of this invention is to provide a method for recovering ammonium chloride from o-nitroaniline waste liquid, so as to improve the recovery rate of ammonium chloride from o-nitroaniline waste liquid.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for recovering ammonium chloride from o-nitroaniline waste liquid includes the following steps:

[0007] S1. The o-nitroaniline waste liquid is passed through a three-stage countercurrent washing device in sequence. The volume ratio of washing water to waste liquid in each stage is 1:2-3. The pH is adjusted step by step to obtain a crude ammonium chloride extract.

[0008] S2. Using styrene and divinylbenzene as monomers, ammonium persulfate as initiator, and polyvinylpyrrolidone as dispersant, PS-DVB microspheres were prepared. A TiO2 shell was constructed on the outer layer of the PS-DVB microspheres, and then graphene oxide was loaded to obtain PS-DVB@TiO2 / GO resin.

[0009] S3. Pack the PS-DVB@TiO2 / GO resin column, pass the crude ammonium chloride extract into the adsorption column, collect the effluent, perform multi-effect evaporation on the effluent, and obtain ammonium chloride in the solid phase. The evaporator and resin are recycled.

[0010] Furthermore, the PS-DVB@TiO2 / GO resin is prepared by the following steps:

[0011] A1. Styrene, divinylbenzene, and polyvinylpyrrolidone were mixed evenly to obtain a monomer mixture; ammonium persulfate was dissolved in deionized water to obtain an initiator solution; the monomer mixture and 75% ethanol solution were heated to 70-80℃ under nitrogen protection, and the mixture was stirred continuously. The initiator solution was added dropwise, and the reaction was carried out at 70-80℃ for 6-8 hours. The mixture was then centrifuged, washed, and vacuum dried to obtain PS-DVB microspheres.

[0012] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid, ultrasonically treated at 50-60℃ for 3-4 hours, washed, and vacuum dried to obtain sulfonated PS-DVB microspheres.

[0013] A2. Dissolve tetrabutyl titanate in 75% ethanol, add template agent, adjust pH to 3-4 by adding acetic acid dropwise, stir to obtain sol; impregnate sulfonated PS-DVB microspheres in sol, centrifuge to coat, dry, calcine to obtain PS-DVB@TiO2.

[0014] A3. Mix the GO dispersion with PS-DVB@TiO2, sonicate, centrifuge and wash, vacuum dry, and heat treat to obtain PS-DVB@TiO2 / GO resin.

[0015] Furthermore, the weight ratio of styrene, divinylbenzene and polyvinylpyrrolidone is (15-25):(1-3):(1-2.5).

[0016] Furthermore, the weight ratio of ammonium persulfate to deionized water in the initiator solution is (0.2-0.4):(15-30).

[0017] Furthermore, the weight ratio of PS-DVB to concentrated sulfuric acid is 1:(8-12).

[0018] Furthermore, the weight ratio of the tetrabutyl titanate to the template agent is (8-12):(0.8-1).

[0019] Furthermore, the template agent is one or a combination of F127 and CTAB.

[0020] Furthermore, the centrifugal coating conditions are 3000-4000 rpm, 5-8 min, repeated 2-3 times.

[0021] Furthermore, the calcination is performed by heating at 2-5℃ / min to 430-450℃ for 2-3 hours.

[0022] Furthermore, the concentration of the GO dispersion is 0.5-1 mg / mL.

[0023] Furthermore, the heat treatment is performed at 180-200°C for 1-2 hours.

[0024] Furthermore, the stepwise pH adjustment is as follows: first stage pH = 6.0-6.5, second stage pH = 7.0-7.5, and third stage pH = 8.0-8.5.

[0025] Furthermore, the flow rate of the crude ammonium chloride extract into the adsorption column is 1-2 BV / h.

[0026] Furthermore, the evaporation temperature of the multi-effect evaporation is set to 70–100°C, and the evaporation method is reduced pressure evaporation.

[0027] Furthermore, the stirring rate of the multi-effect evaporation is set to 500-1000 r / min.

[0028] Furthermore, the resin recycling method is as follows: when the concentration of o-nitroaniline in the effluent reaches 0.4-0.55 ppm, adsorption is stopped, the resin is transferred to an autoclave, and a mixture of 150-200 mL CO2 and 50-65 mL ethanol is injected. The mixture is circulated at a flow rate of 1.5-2 BV / h for 1-1.5 hours while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed, and vacuum dried, and then the resin can be recycled.

[0029] The beneficial effects of this invention are:

[0030] (1) The three-stage countercurrent washing device used in this invention, combined with stepwise pH adjustment, significantly improves the separation efficiency of ammonium chloride. The first stage of weakly acidic conditions (pH 6.0-6.5) preferentially removes free acidic impurities, the second stage of neutral conditions (pH 7.0-7.5) promotes the precipitation of amphoteric metal hydroxides, and the third stage of weakly alkaline conditions (pH 8.0-8.5) reduces o-nitroaniline residue through electrostatic repulsion. This gradient washing strategy, combined with the countercurrent design, not only reduces the washing water volume but also improves the initial purity of the crude ammonium chloride extract by removing impurities in stages, which is beneficial for subsequent adsorption and evaporation processes.

[0031] (2) The PS-DVB@TiO2 / GO resin used in this invention not only has high adsorption capacity but also regenerative properties and can be recycled. Its core layer (PS-DVB microspheres) introduces sulfonic acid groups through sulfonation treatment, which enhances the electrostatic adsorption capacity for polar pollutants (o-nitroaniline); the mesoporous structure of TiO2 in the shell provides a high specific surface area, while graphene oxide enhances the capture of aromatic compounds through π-π interactions. The three work synergistically to significantly improve the adsorption capacity of o-nitroaniline; at the same time, the photocatalytic activity of TiO2 is activated in the subsequent regeneration process, and the supercritical CO2 / ethanol mixed fluid can efficiently degrade the adsorbed organic matter. The resin still maintains a high adsorption capacity after recycling. This adsorption-catalysis synergistic mechanism not only ensures a high recovery rate of high-purity ammonium chloride but also reduces costs. Detailed Implementation

[0032] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0033] Example 1

[0034] This embodiment provides a method for recovering ammonium chloride from o-nitroaniline waste liquid, including the following steps:

[0035] S1. The o-nitroaniline waste liquid is sequentially passed through a three-stage countercurrent washing device, with the volume ratio of washing water to waste liquid in each stage being 1:3. At the same time, the pH is adjusted step by step (first stage pH=6.5, second stage pH=7.5, third stage pH=8.5) to obtain crude ammonium chloride extract.

[0036] S2. Mix 18.5 parts of styrene (St), 1.5 parts of divinylbenzene (DVB), and 1.2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0037] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0038] Ten parts of tetrabutyl titanate (TBOT) were dissolved in 80 mL of 75% ethanol, and 1 part of F127 was added. Acetic acid was added dropwise to adjust the pH to 3-4, and the mixture was magnetically stirred for 2 hours to form a transparent sol. Sulfonated PS-DVB microspheres were immersed in the sol, centrifuged and coated (3000 rpm, 5 min), and the process was repeated 3 times. After drying at 60 °C for 12 hours, the mixture was placed in a muffle furnace and calcined at 450 °C at a rate of 2 °C / min for 2 hours to obtain PS-DVB@TiO2.

[0039] Mix 0.5 mg / mL GO dispersion with PS-DVB@TiO2, sonicate for 1 hour, centrifuge and wash (3000 rpm, 3 min), vacuum dry at 60℃, and heat treat at 200℃ for 1 hour to obtain PS-DVB@TiO2 / GO resin.

[0040] S3. The PS-DVB@TiO2 / GO resin was soaked in ultrapure water for 12 hours, rinsed with ethanol 3 times, vacuum dried at 60℃ and packed into a column. 5% HCl solution was passed through at a flow rate of 0.5 BV / h, and then rinsed with ultrapure water until neutral. The crude ammonium chloride extract was continuously passed through the adsorption column at a flow rate of 1.5 BV / h. The effluent was collected and transferred to a multi-effect evaporator. After setting the evaporation temperature and the stirring speed of the stirrer in the evaporator, multi-effect evaporation was performed to obtain ammonium chloride in the solid phase. The evaporation liquid was recovered and reused.

[0041] When the concentration of o-nitroaniline in the effluent reaches 0.5 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of CO2 and ethanol (150 mL CO2, 50 mL ethanol) is injected. The mixture is circulated at a flow rate of 2 BV / h for 60 minutes while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed three times with ultrapure water, and vacuum dried at 60°C for 12 hours. The resin can then be recycled.

[0042] Example 2

[0043] The difference between this embodiment and Embodiment 1 is that the pH concentration at each stage in S1 is adjusted. The specific implementation steps of S1 are as follows:

[0044] S1. The o-nitroaniline waste liquid is sequentially passed through a three-stage countercurrent washing device, with the volume ratio of washing water to waste liquid in each stage being 1:3. At the same time, the pH is adjusted step by step (first stage pH=6.0, second stage pH=7.0, third stage pH=8.0) to obtain crude ammonium chloride extract.

[0045] The remaining raw materials and preparation process are the same as in Example 1.

[0046] Example 3

[0047] The difference between this embodiment and Example 1 is that the flow rate of the crude ammonium chloride extract into the adsorption column is increased. The specific implementation steps of S3 are as follows:

[0048] S3. The PS-DVB@TiO2 / GO resin was soaked in ultrapure water for 12 hours, rinsed with ethanol 3 times, vacuum dried at 60℃ and packed into a column. 5% HCl solution was passed through at a flow rate of 0.5 BV / h, and then rinsed with ultrapure water until neutral. The crude ammonium chloride extract was continuously passed through the adsorption column at a flow rate of 2 BV / h. The effluent was collected and transferred to a multi-effect evaporator. After setting the evaporation temperature and the stirring speed of the stirrer in the evaporator, multi-effect evaporation was performed to obtain ammonium chloride in the solid phase. The evaporation liquid was recovered and reused.

[0049] When the concentration of o-nitroaniline in the effluent reaches 0.5 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of CO2 and ethanol (150 mL CO2, 50 mL ethanol) is injected. The mixture is circulated at a flow rate of 2 BV / h for 60 minutes while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed three times with ultrapure water, and vacuum dried at 60°C for 12 hours. The resin can then be recycled.

[0050] The remaining raw materials and preparation process are the same as in Example 1.

[0051] Example 4

[0052] Compared with Example 1, the difference in this embodiment is that the flow rate of the crude ammonium chloride extract into the adsorption column is reduced. The specific implementation steps of S3 are as follows:

[0053] S3. The PS-DVB@TiO2 / GO resin was soaked in ultrapure water for 12 hours, rinsed with ethanol 3 times, vacuum dried at 60℃ and packed into a column. 5% HCl solution was passed through at a flow rate of 0.5 BV / h, and then rinsed with ultrapure water until neutral. The crude ammonium chloride extract was continuously passed through the adsorption column at a flow rate of 1 BV / h. The effluent was collected and transferred to a multi-effect evaporator. After setting the evaporation temperature and the stirring speed of the stirrer in the evaporator, multi-effect evaporation was performed to obtain ammonium chloride in the solid phase. The evaporation liquid was recovered and reused.

[0054] When the concentration of o-nitroaniline in the effluent reaches 0.5 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of CO2 and ethanol (150 mL CO2, 50 mL ethanol) is injected. The mixture is circulated at a flow rate of 2 BV / h for 60 minutes while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed three times with ultrapure water, and vacuum dried at 60°C for 12 hours. The resin can then be recycled.

[0055] The remaining raw materials and preparation process are the same as in Example 1.

[0056] Example 5

[0057] Compared with Example 1, the difference in this embodiment is that the amount of styrene and divinylbenzene is increased. The specific implementation steps of S2 are as follows:

[0058] S2. Mix 24 parts of styrene (St), 2.5 parts of divinylbenzene (DVB), and 2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0059] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0060] Ten parts of tetrabutyl titanate (TBOT) were dissolved in 80 mL of 75% ethanol, and 1 part of F127 was added. Acetic acid was added dropwise to adjust the pH to 3-4, and the mixture was magnetically stirred for 2 hours to form a transparent sol. Sulfonated PS-DVB microspheres were immersed in the sol, centrifuged and coated (3000 rpm, 5 min), and the process was repeated 3 times. After drying at 60 °C for 12 hours, the mixture was placed in a muffle furnace and calcined at 450 °C at a rate of 2 °C / min for 2 hours to obtain PS-DVB@TiO2.

[0061] Mix 0.5 mg / mL GO dispersion with PS-DVB@TiO2, sonicate for 1 hour, centrifuge and wash (3000 rpm, 3 min), vacuum dry at 60℃, and heat treat at 200℃ for 1 hour to obtain PS-DVB@TiO2 / GO resin.

[0062] The remaining raw materials and preparation process are the same as in Example 1.

[0063] Example 6

[0064] Compared with Example 1, the difference in this embodiment is that the amount of styrene and divinylbenzene is reduced. The specific implementation steps of S2 are as follows:

[0065] S2. Mix 15 parts of styrene (St), 1.2 parts of divinylbenzene (DVB), and 1 part of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0066] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0067] Ten parts of tetrabutyl titanate (TBOT) were dissolved in 80 mL of 75% ethanol, and 1 part of F127 was added. Acetic acid was added dropwise to adjust the pH to 3-4, and the mixture was magnetically stirred for 2 hours to form a transparent sol. Sulfonated PS-DVB microspheres were immersed in the sol, centrifuged and coated (3000 rpm, 5 min), and the process was repeated 3 times. After drying at 60 °C for 12 hours, the mixture was placed in a muffle furnace and calcined at 450 °C at a rate of 2 °C / min for 2 hours to obtain PS-DVB@TiO2.

[0068] Mix 0.5 mg / mL GO dispersion with PS-DVB@TiO2, sonicate for 1 hour, centrifuge and wash (3000 rpm, 3 min), vacuum dry at 60℃, and heat treat at 200℃ for 1 hour to obtain PS-DVB@TiO2 / GO resin.

[0069] The remaining raw materials and preparation process are the same as in Example 1.

[0070] Example 7

[0071] The difference between this embodiment and embodiment 1 is that F127 is replaced with CTAB, and the specific implementation steps of S2 are as follows:

[0072] S2. Mix 18.5 parts of styrene (St), 1.5 parts of divinylbenzene (DVB), and 1.2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0073] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0074] Ten parts of tetrabutyl titanate (TBOT) were dissolved in 80 mL of 75% ethanol, 0.8 parts of CTAB were added, and acetic acid was added dropwise to adjust the pH to 3-4. The mixture was magnetically stirred for 2 hours to form a transparent sol. Sulfonated PS-DVB microspheres were immersed in the sol, centrifuged and coated (3000 rpm, 5 min), and the process was repeated 3 times. After drying at 60 °C for 12 hours, the mixture was placed in a muffle furnace and calcined at 450 °C for 2 hours at a rate of 2 °C / min to obtain PS-DVB@TiO2.

[0075] Mix 0.5 mg / mL GO dispersion with PS-DVB@TiO2, sonicate for 1 hour, centrifuge and wash (3000 rpm, 3 min), vacuum dry at 60℃, and heat treat at 200℃ for 1 hour to obtain PS-DVB@TiO2 / GO resin.

[0076] The remaining raw materials and preparation process are the same as in Example 1.

[0077] Example 8

[0078] The difference between this embodiment and Example 1 is that the concentration of the GO dispersion is increased. The specific implementation steps of S2 are as follows:

[0079] S2. Mix 18.5 parts of styrene (St), 1.5 parts of divinylbenzene (DVB), and 1.2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0080] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0081] Ten parts of tetrabutyl titanate (TBOT) were dissolved in 80 mL of 75% ethanol, and 1 part of F127 was added. Acetic acid was added dropwise to adjust the pH to 3-4, and the mixture was magnetically stirred for 2 hours to form a transparent sol. Sulfonated PS-DVB microspheres were immersed in the sol, centrifuged and coated (3000 rpm, 5 min), and the process was repeated 3 times. After drying at 60 °C for 12 hours, the mixture was placed in a muffle furnace and calcined at 450 °C at a rate of 2 °C / min for 2 hours to obtain PS-DVB@TiO2.

[0082] Mix 1 mg / mL GO dispersion with PS-DVB@TiO2, sonicate for 1 hour, centrifuge and wash (3000 rpm, 3 min), vacuum dry at 60℃, and heat treat at 200℃ for 1 hour to obtain PS-DVB@TiO2 / GO resin.

[0083] The remaining raw materials and preparation process are the same as in Example 1.

[0084] Comparative Example 1

[0085] The difference between this comparative example and Example 1 is that no GO modification is performed. The specific implementation steps are as follows:

[0086] S1. The o-nitroaniline waste liquid is sequentially passed through a three-stage countercurrent washing device, with the volume ratio of washing water to waste liquid in each stage being 1:3. At the same time, the pH is adjusted step by step (first stage pH=6.5, second stage pH=7.5, third stage pH=8.5) to obtain crude ammonium chloride extract.

[0087] S2. Mix 18.5 parts of styrene (St), 1.5 parts of divinylbenzene (DVB), and 1.2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0088] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0089] Ten parts of tetrabutyl titanate (TBOT) were dissolved in 80 mL of 75% ethanol, and 1 part of F127 was added. Acetic acid was added dropwise to adjust the pH to 3-4. The mixture was magnetically stirred for 2 hours to form a transparent sol. Sulfonated PS-DVB microspheres were immersed in the sol, centrifuged and coated (3000 rpm, 5 min), and repeated 3 times. After drying at 60 °C for 12 hours, the mixture was placed in a muffle furnace and calcined at 450 °C at a rate of 2 °C / min for 2 hours to obtain PS-DVB@TiO2 resin.

[0090] S3. The PS-DVB@TiO2 resin was soaked in ultrapure water for 12 hours, rinsed with ethanol 3 times, vacuum dried at 60℃ and packed into a column. 5% HCl solution was passed through at a flow rate of 0.5 BV / h, and then rinsed with ultrapure water until neutral. The crude ammonium chloride extract was continuously passed through the adsorption column at a flow rate of 1.5 BV / h. The effluent was collected and transferred to a multi-effect evaporator. After setting the evaporation temperature and the stirring speed of the stirrer in the evaporator, multi-effect evaporation was performed to obtain ammonium chloride in the solid phase. The evaporation liquid was recovered and reused.

[0091] When the concentration of o-nitroaniline in the effluent reaches 0.5 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of CO2 and ethanol (150 mL CO2, 50 mL ethanol) is injected. The mixture is circulated at a flow rate of 2 BV / h for 60 minutes while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed three times with ultrapure water, and vacuum dried at 60°C for 12 hours. The resin can then be recycled.

[0092] The remaining raw materials and preparation process are the same as in Example 1.

[0093] Comparative Example 2

[0094] The difference between this comparative example and Example 1 is that TiO2 coating is not performed. The specific implementation steps are as follows:

[0095] S1. The o-nitroaniline waste liquid is sequentially passed through a three-stage countercurrent washing device, with the volume ratio of washing water to waste liquid in each stage being 1:3. At the same time, the pH is adjusted step by step (first stage pH=6.5, second stage pH=7.5, third stage pH=8.5) to obtain crude ammonium chloride extract.

[0096] S2. Mix 18.5 parts of styrene (St), 1.5 parts of divinylbenzene (DVB), and 1.2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0097] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0098] Mix 0.5 mg / mL GO dispersion with sulfonated PS-DVB microspheres, sonicate for 1 hour, centrifuge and wash (3000 rpm, 3 min), vacuum dry at 60 °C, and heat treat at 200 °C for 1 hour to obtain PS-DVB@GO resin;

[0099] S3. The PS-DVB@GO resin was soaked in ultrapure water for 12 hours, rinsed with ethanol 3 times, vacuum dried at 60℃ and packed into a column. 5% HCl solution was passed through at a flow rate of 0.5 BV / h, and then rinsed with ultrapure water until neutral. The crude ammonium chloride extract was continuously passed through the adsorption column at a flow rate of 1.5 BV / h. The effluent was collected and transferred to a multi-effect evaporator. After setting the evaporation temperature and the stirring speed of the stirrer in the evaporator, multi-effect evaporation was performed to obtain ammonium chloride in the solid phase. The evaporation liquid was recovered and reused.

[0100] When the concentration of o-nitroaniline in the effluent reaches 0.5 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of CO2 and ethanol (150 mL CO2, 50 mL ethanol) is injected. The mixture is circulated at a flow rate of 2 BV / h for 60 minutes while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed three times with ultrapure water, and vacuum dried at 60°C for 12 hours. The resin can then be recycled.

[0101] The remaining raw materials and preparation process are the same as in Example 1.

[0102] Comparative Example 3

[0103] The difference between this comparative example and Example 1 is that neither GO modification nor TiO2 coating is performed. The specific implementation steps are as follows:

[0104] S1. The o-nitroaniline waste liquid is sequentially passed through a three-stage countercurrent washing device, with the volume ratio of washing water to waste liquid in each stage being 1:3. At the same time, the pH is adjusted step by step (first stage pH=6.5, second stage pH=7.5, third stage pH=8.5) to obtain crude ammonium chloride extract.

[0105] S2. Mix 18.5 parts of styrene (St), 1.5 parts of divinylbenzene (DVB), and 1.2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB resin;

[0106] S3. The PS-DVB resin was soaked in ultrapure water for 12 hours, rinsed with ethanol 3 times, vacuum dried at 60℃ and packed into a column. 5% HCl solution was passed through at a flow rate of 0.5 BV / h, and then rinsed with ultrapure water until neutral. The crude ammonium chloride extract was continuously passed through the adsorption column at a flow rate of 1.5 BV / h. The effluent was collected and transferred to a multi-effect evaporator. After setting the evaporation temperature and the stirring speed of the stirrer in the evaporator, multi-effect evaporation was performed to obtain ammonium chloride in the solid phase. The evaporation liquid was recovered and reused.

[0107] When the concentration of o-nitroaniline in the effluent reaches 0.5 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of CO2 and ethanol (150 mL CO2, 50 mL ethanol) is injected. The mixture is circulated at a flow rate of 2 BV / h for 60 minutes while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed three times with ultrapure water, and vacuum dried at 60°C for 12 hours. The resin can then be recycled.

[0108] The remaining raw materials and preparation process are the same as in Example 1.

[0109] Comparative Example 4

[0110] The difference between this comparative example and Example 1 is that the S1 coarse extraction is not performed. The specific implementation steps are as follows:

[0111] S1. Mix 18.5 parts of styrene (St), 1.5 parts of divinylbenzene (DVB), and 1.2 parts of polyvinylpyrrolidone (PVP) evenly to obtain a monomer mixture; dissolve 0.3 parts of ammonium persulfate (APS) in 20 parts of deionized water to obtain an initiator solution; heat the monomer mixture with 80 parts of 75% ethanol solution to 70°C under nitrogen protection, stir continuously (500 rpm), add the initiator solution dropwise, and react at 80°C for 6 hours to generate a white emulsion. Collect the microspheres by centrifugation (6000 rpm, 10 min), wash three times with ethanol, and vacuum dry at 60°C for 12 hours to obtain PS-DVB microspheres;

[0112] The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid (solid-liquid ratio 1:10), ultrasonically treated at 60℃ for 3 hours, washed with deionized water until neutral, and vacuum dried at 60℃ to obtain sulfonated PS-DVB microspheres.

[0113] Ten parts of tetrabutyl titanate (TBOT) were dissolved in 80 mL of 75% ethanol, and 1 part of F127 was added. Acetic acid was added dropwise to adjust the pH to 3-4, and the mixture was magnetically stirred for 2 hours to form a transparent sol. Sulfonated PS-DVB microspheres were immersed in the sol, centrifuged and coated (3000 rpm, 5 min), and the process was repeated 3 times. After drying at 60 °C for 12 hours, the mixture was placed in a muffle furnace and calcined at 450 °C at a rate of 2 °C / min for 2 hours to obtain PS-DVB@TiO2.

[0114] Mix 0.5 mg / mL GO dispersion with PS-DVB@TiO2, sonicate for 1 hour, centrifuge and wash (3000 rpm, 3 min), vacuum dry at 60℃, and heat treat at 200℃ for 1 hour to obtain PS-DVB@TiO2 / GO resin.

[0115] S3. The PS-DVB@TiO2 / GO resin was soaked in ultrapure water for 12 hours, rinsed with ethanol 3 times, vacuum dried at 60℃ and packed into a column. 5% HCl solution was passed through at a flow rate of 0.5 BV / h, and then rinsed with ultrapure water until neutral. The o-nitroaniline waste liquid was continuously passed through the adsorption column at a flow rate of 1.5 BV / h. The effluent was collected and transferred to a multi-effect evaporator. After setting the evaporation temperature and the stirring speed of the stirrer in the evaporator, multi-effect evaporation was carried out. Ammonium chloride was obtained in the solid phase, and the evaporation liquid was recovered and reused.

[0116] When the concentration of o-nitroaniline in the effluent reaches 0.5 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of CO2 and ethanol (150 mL CO2, 50 mL ethanol) is injected. The mixture is circulated at a flow rate of 2 BV / h for 60 minutes while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed three times with ultrapure water, and vacuum dried at 60°C for 12 hours. The resin can then be recycled.

[0117] The remaining raw materials and preparation process are the same as in Example 1.

[0118] Comparative Example 5

[0119] The difference between this comparative example and Example 1 is that S2 resin adsorption is not performed. The specific implementation steps are as follows:

[0120] S1. The o-nitroaniline waste liquid is sequentially passed through a three-stage countercurrent washing device, with the volume ratio of washing water to waste liquid in each stage being 1:3. At the same time, the pH is adjusted step by step (first stage pH=6.5, second stage pH=7.5, third stage pH=8.5) to obtain crude ammonium chloride extract.

[0121] S2. Transfer the crude ammonium chloride extract into a multi-effect evaporator, set the evaporation temperature and the stirring speed of the stirrer in the evaporator, and perform multi-effect evaporation to obtain ammonium chloride in the solid phase.

[0122] The remaining raw materials and preparation process are the same as in Example 1.

[0123] Performance testing

[0124] The ammonium chloride recovery rate (%), ammonium chloride purity (%), o-nitroaniline residue (%), and regeneration efficiency (%) after 50 cycles were tested for Examples 1-8 and Comparative Examples 1-5.

[0125] The results are shown in Table 1:

[0126] Table 1

[0127]

[0128]

[0129] As can be seen from Table 1, by comparing the data of Examples 1-4 and Comparative Example 4, the significant advantages of three-stage countercurrent washing combined with pH gradient control can be observed:

[0130] The ammonium chloride recovery rate (98.5%) and purity (99.2%) of Example 1 (pH 6.5→7.5→8.5) were significantly higher than those of Comparative Example 4 (unwashed, recovery rate 88.4%, purity 96.5%), indicating that gradient pH washing effectively removed impurities and improved the initial purity of the crude extract. Data from Examples 2 (adjusted pH range) and Examples 3-4 (flow rate changes) show that precise control of the pH gradient design plays a crucial role in impurity removal. Weakly alkaline conditions (pH 8.5) reduced o-nitroaniline residue through electrostatic repulsion (0.003% residue in Example 1 vs. 0.061% in Comparative Example 4).

[0131] Example 1 (0.003% residual o-nitroaniline) was significantly superior to Comparative Example 1 (no GO modification, 0.031% residual) and Comparative Example 2 (no TiO2 coating, 0.054% residual). This is due to the synergistic effect of the shells: the mesoporous structure of TiO2 provides a high specific surface area, and GO enhances adsorption through π-π interactions, resulting in a synergistic adsorption capacity of 450 mg / g (compared to only 120 mg / g for conventional resins). After 50 cycles, the regeneration efficiency of Example 1 was 92.7%, far higher than that of Comparative Example 3 (62.5%). The supercritical CO2-ethanol mixed fluid efficiently desorbed organic matter through synergistic dissolution and photocatalytic degradation by TiO2. The performance of Example 7 (CTAB template) was slightly lower than that of Example 1 (F127 template) because the pore size formed by CTAB was smaller, limiting the uniformity of GO loading and resulting in a slightly higher residual amount.

[0132] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for recovering ammonium chloride from waste liquid used in the preparation of o-nitroaniline, characterized in that, Includes the following steps: S1. The o-nitroaniline waste liquid is passed through a three-stage countercurrent washing device in sequence. The volume ratio of washing water to waste liquid in each stage is 1:2-3. The pH is adjusted step by step to obtain a crude ammonium chloride extract. S2. Using styrene and divinylbenzene as monomers, ammonium persulfate as initiator, and polyvinylpyrrolidone as dispersant, PS-DVB microspheres were prepared. A TiO2 shell was constructed on the outer layer of the PS-DVB microspheres, and then graphene oxide was loaded to obtain PS-DVB@TiO2 / GO resin. S3. Pack the PS-DVB@TiO2 / GO resin column, pass the crude ammonium chloride extract into the adsorption column, collect the effluent, perform multi-effect evaporation on the effluent, and obtain ammonium chloride in the solid phase. The evaporator and resin are recycled.

2. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 1, characterized in that, The PS-DVB@TiO2 / GO resin is prepared by the following steps: A1. Styrene, divinylbenzene, and polyvinylpyrrolidone were mixed evenly to obtain a monomer mixture; ammonium persulfate was dissolved in deionized water to obtain an initiator solution; the monomer mixture and 75% ethanol solution were heated to 70-80℃ under nitrogen protection, and the mixture was stirred continuously. The initiator solution was added dropwise, and the reaction was carried out at 70-80℃ for 6-8 hours. The mixture was then centrifuged, washed, and vacuum dried to obtain PS-DVB microspheres. The dried PS-DVB microspheres were immersed in 98% concentrated sulfuric acid, ultrasonically treated at 50-60℃ for 3-4 hours, washed, and vacuum dried to obtain sulfonated PS-DVB microspheres. A2. Dissolve tetrabutyl titanate in 75% ethanol, add template agent, adjust pH to 3-4 by adding acetic acid dropwise, stir to obtain sol; impregnate sulfonated PS-DVB microspheres in sol, centrifuge to coat, dry, calcine to obtain PS-DVB@TiO2. A3. Mix the GO dispersion with PS-DVB@TiO2, sonicate, centrifuge and wash, vacuum dry, and heat treat to obtain PS-DVB@TiO2 / GO resin.

3. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 2, characterized in that, The weight ratio of styrene, divinylbenzene and polyvinylpyrrolidone is (15-25):(1-3):(1-2.5); the weight ratio of ammonium persulfate and deionized water in the initiator solution is (0.2-0.4):(15-30).

4. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 2, characterized in that, The weight ratio of PS-DVB to concentrated sulfuric acid is 1:(8-12).

5. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 2, characterized in that, The weight ratio of the tetrabutyl titanate to the template agent is (8-12):(0.8-1); the template agent is one or a combination of F127 and CTAB.

6. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 2, characterized in that, The centrifugal coating conditions are 3000-4000 rpm for 5-8 min, repeated 2-3 times; the calcination is carried out by heating at 2-5℃ / min to 430-450℃ for 2-3 hours.

7. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 2, characterized in that, The concentration of the GO dispersion is 0.5-1 mg / mL; the heat treatment is performed at 180-200℃ for 1-2 hours.

8. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 1, characterized in that, The stepwise pH adjustment is as follows: first stage pH = 6.0-6.5, second stage pH = 7.0-7.5, and third stage pH = 8.0-8.

5.

9. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 1, characterized in that, The flow rate of the crude ammonium chloride extract into the adsorption column is 1-2 BV / h; the evaporation temperature of the multi-effect evaporation is set to 70-100℃, and the evaporation method is vacuum evaporation; the stirring rate of the multi-effect evaporation is set to 500-1000 r / min.

10. The method for recovering ammonium chloride from o-nitroaniline waste liquid according to claim 1, characterized in that, The method for recycling the resin is as follows: when the concentration of o-nitroaniline in the effluent reaches 0.4-0.55 ppm, adsorption is stopped. The resin is then transferred to an autoclave, and a mixture of 150-200 mL CO2 and 50-65 mL ethanol is injected. The mixture is circulated at a flow rate of 1.5-2 BV / h for 1-1.5 hours while maintaining constant temperature and pressure. After depressurization, the resin is removed, rinsed, and vacuum dried. The resin can then be recycled.

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