Method for recovering o-nitroaniline and by-product ammonium chloride in wastewater

Abstract

The application discloses a method for recycling o-nitroaniline in wastewater and resource utilization of by-product ammonium chloride, and solves the problem that components of wastewater containing o-nitroaniline and ammonium chloride cannot be simultaneously resource utilized. The method comprises the following steps: 1) o-nitroaniline in wastewater is adsorbed by a selective adsorption resin, and o-nitroaniline is recovered after desorption and regeneration of the saturated selective adsorption resin; 2) after pH adjustment, the effluent is mixed with hydrogen peroxide, and catalytic wet oxidation degradation of COD is carried out by a fixed bed of a loaded metal catalyst; and 3) after oxidation, wastewater is evaporated and concentrated to crystallize, and ammonium chloride crystalline salt and condensate water are obtained, the condensate water is reused, and the mother liquor is returned to step 1. The orderly three-stage process realizes productized recovery of o-nitroaniline, reaches the industrial product standard of ammonium chloride, and realizes closed-loop treatment of wastewater.

Description

Technical Field

[0001] This application relates to the field of wastewater treatment technology, and in particular to a method for recovering o-nitroaniline from wastewater and for the resource utilization of by-product ammonium chloride. Background Technology

[0002] o-Nitroaniline (ONA) is an important raw material and intermediate in the synthesis of pesticides, dyes, and polymers. It is more toxic than aniline and can enter the human body through skin contact. It is a potent methemoglobin-forming agent and is classified as a priority environmental pollutant. Currently, the main production method for o-nitroaniline in China is ammonolysis, which involves placing o-nitrochlorobenzene and concentrated ammonia in a high-pressure reactor and carrying out ammonolysis at a temperature of 160–175°C and a pressure of 3.4–4.9 MPa. This production process generates a large amount of high-concentration organic wastewater containing o-nitroaniline and ammonium chloride.

[0003] Currently, the main methods for treating o-nitroaniline wastewater both domestically and internationally include catalytic degradation, advanced oxidation, and biodegradation. These methods suffer from high treatment costs, complex operations, and the inability to recycle treatment agents, making it difficult to achieve resource recovery and harmless treatment of the wastewater. Existing technologies have reported the use of macroporous adsorption resins for the adsorption treatment of o-nitroaniline wastewater. For example, Chinese patent CN117902667A discloses a process for treating o-nitroaniline production wastewater, which involves adsorbing o-nitroaniline from the wastewater using macroporous resin and then desorbing it with methanol. However, this process only involves the resin adsorption unit; the effluent still requires further treatment, and it does not address the resource recovery of ammonium chloride in the wastewater.

[0004] Chinese patent CN120794241A discloses a method for treating o-nitroaniline wastewater, employing a process route of "flocculation-oxidation-resin adsorption-elution-biochemical treatment". This process places the oxidation treatment before resin adsorption, and the wastewater after oxidation undergoes resin adsorption and biochemical treatment, ultimately requiring a final biochemical treatment step. The process is lengthy and fails to achieve full resource utilization of the wastewater.

[0005] Furthermore, existing technologies have reported methods for treating high-salt wastewater containing aniline compounds. This process combines resin adsorption with Fenton oxidation to treat aniline-containing high-salt wastewater. However, the advanced oxidation process in this report is a traditional Fenton process, a low-temperature reaction that cannot provide sufficient activation energy to fully destroy residual aniline in the wastewater. This leads to problems such as organic matter concentration and precipitation, heat exchanger blockage, and excessive levels of organic matter in byproduct salts during the subsequent evaporation and concentration process. On the other hand, the catalyst used in this report is ferrous sulfate, which catalyzes the decomposition of hydroxyl radicals in hydrogen peroxide to destroy the organic matter structure in the wastewater, thereby reducing COD. However, during the subsequent flocculation and sedimentation process, iron settles and enters the flocculant, making the flocculant difficult to treat.

[0006] In summary, the existing o-nitroaniline production wastewater treatment technologies have the following shortcomings: (1) Most processes only focus on pollutant removal and fail to achieve effective recovery of o-nitroaniline from the wastewater; (2) After treatment, the ammonium chloride in the wastewater containing high concentrations of ammonium chloride is still treated as hazardous waste and cannot be utilized as a resource; (3) A large amount of wastewater is discharged during the treatment process and the water resources are not recycled; (4) Some processes require biochemical treatment as a follow-up guarantee, which is complex, occupies a large area, and has high operating costs. Summary of the Invention

[0007] To address the shortcomings of the existing technologies, this invention provides a resource-based treatment process for o-nitroaniline production wastewater. Through a three-stage combined process of "resin adsorption and recovery - advanced oxidative degradation - evaporation and resource recovery", the process achieves a closed-loop resource-based treatment of o-nitroaniline product recovery, efficient COD removal, ammonium chloride resource utilization, and condensate reuse in the wastewater.

[0008] This invention provides a method for recovering o-nitroaniline from wastewater and producing ammonium chloride as a byproduct, comprising the following steps: (1) Wastewater containing o-nitroaniline and ammonium chloride is passed through an adsorption column packed with chelating resin to adsorb o-nitroaniline in the wastewater. (2) Adjust the pH of the adsorbed water obtained in step (1) to acidic, mix it with hydrogen peroxide, and send it into a fixed bed reactor filled with a supported metal catalyst for catalytic wet oxidation treatment. (3) The wastewater treated in step (2) is evaporated, concentrated and crystallized to obtain ammonium chloride crystal salt and evaporated condensate; part of the mother liquor is returned to step (1).

[0009] Furthermore, the backbone of the chelating resin is a polystyrene backbone or a polyacrylate backbone, and the chelating resin has aminophosphonic acid type functional groups or iminodiacetic acid type functional groups.

[0010] Furthermore, the chelating resin has a crosslinking degree of 6-12%, a specific surface area of ​​300-800 m² / g, and an average pore size of 2-20 nm.

[0011] Furthermore, in step (1), the adsorption temperature is 20-60℃, the pH of the wastewater is 7-10, and the adsorption flow rate is 1-5 BV / hour.

[0012] Further, in step (1), the concentration of o-nitroaniline in the wastewater is 5000~10000 mg / L, the mass concentration of ammonium chloride is 8~12%, the mass concentration of COD is 20000~40000 mg / L, the concentration of o-nitroaniline in the adsorbed water is 500~1000 mg / L, and the COD concentration is 10000~15000 mg / L.

[0013] Further, step (1) further includes desorbing and regenerating the chelating resin after adsorption saturation with a desorbent; preferably, the desorbent is methanol, ethanol, acetone or a mixture thereof, and the desorption temperature is 40-80°C.

[0014] Further, in step (2), the pH of the adsorbed water is adjusted to 3-5.

[0015] Further, in step (2), the support for the supported metal catalyst is selected from at least one of activated carbon, molecular sieve, titanium dioxide or zirconium dioxide; the supported metal is selected from at least one of iron, copper, manganese, cobalt and cerium; the metal loading is 1% to 10% based on the mass of the support.

[0016] Furthermore, in step (2), the reaction temperature of the catalytic wet oxidation treatment is 150-200℃, the operating pressure is 0.3-3.0 MPa, and the residence time of the wastewater in the fixed bed reactor is 0.5-3 hours.

[0017] Furthermore, in step (2), the amount of hydrogen peroxide added is 0.5 to 2.5 times the theoretical oxygen demand of the wastewater COD.

[0018] Furthermore, in step (3), the evaporation, concentration and crystallization are carried out by multi-effect evaporation or mechanical vapor recompression evaporation.

[0019] Furthermore, in step (3), the amount of mother liquor returned to step (1) is 10% to 30% of the total amount of mother liquor, and the COD of the mother liquor is controlled to be below 5000 mg / L.

[0020] Furthermore, in step (3), the wastewater comes from the production process of o-nitroaniline, and the evaporated condensate is used to prepare an ammonia solution and is recycled back to the production process of o-nitroaniline.

[0021] Compared with the prior art, the present invention has the following beneficial effects: (1) Achieve effective recovery of o-nitroaniline This invention utilizes chelating resin for the selective adsorption and recovery of o-nitroaniline from wastewater, unlike existing adsorption treatments that simply aim to remove pollutants. The chelating resin exhibits excellent selective adsorption capacity for o-nitroaniline, effectively adsorbing it even in the presence of high concentrations of ammonium chloride (8%–12%). After adsorption, the o-nitroaniline content in the wastewater decreases from 5000–10000 mg / L to 500–1000 mg / L. After adsorption saturation, the o-nitroaniline product can be recovered through desorption and regeneration, achieving the resource utilization of pollutants.

[0022] (2) Efficiently removes COD, ensuring the quality of ammonium chloride.

[0023] This invention employs a "pre-adsorption recovery followed by oxidative degradation" process sequence, significantly different from existing technologies that place oxidation before adsorption. First, most of the o-nitroaniline in the wastewater is recovered through resin adsorption, recovering valuable products and simultaneously reducing the COD concentration from 20,000-40,000 mg / L to 10,000-15,000 mg / L, greatly reducing the load on subsequent oxidation treatments. Then, catalytic wet hydrogen peroxide oxidation treatment at 150-200℃ deeply oxidizes and decomposes the remaining organic matter in the wastewater, reducing the COD from 10,000-15,000 mg / L to the standard required for evaporation (500-3000 mg / L). This process sequence ensures the purity and whiteness of the evaporated ammonium chloride, transforming it from "hazardous waste" into a marketable byproduct. On the other hand, compared with the traditional high-temperature wet oxidation process of 270-300℃, the highly active catalyst can meet the activation energy requirements for molecular chain breaking at a moderate temperature, avoiding the problem of frequent reactor blockage caused by the self-aggregation of organic matter at high temperatures.

[0024] (3) The process is simple and the operating cost is low.

[0025] This invention eliminates the need for a biochemical treatment process, avoiding the problems of large land area, complex operation and management, and significant susceptibility to water quality fluctuations inherent in traditional biochemical treatment methods. The entire process is simple and efficient, requires minimal equipment investment, and has low operating costs, making it suitable for large-scale industrial applications.

[0026] (4) Closed-loop resource utilization throughout the entire process

[0027] This invention forms a complete resource recovery closed loop of "product recycling → COD degradation → salt recovery → water reuse". Compared with existing technologies that only focus on pollutant removal or partial resource recovery, it realizes the full resource utilization of all valuable components (o-nitroaniline, ammonium chloride, and water) in wastewater, which has significant economic and environmental benefits. Detailed Implementation

[0028] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to specific examples. However, the embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] This invention provides a method for recovering o-nitroaniline from wastewater and producing ammonium chloride as a byproduct, comprising the following steps: (1) Wastewater containing o-nitroaniline and ammonium chloride is passed through an adsorption column packed with chelating resin to adsorb o-nitroaniline in the wastewater. (2) Adjust the pH of the adsorbed water obtained in step (1) to acidic, mix it with hydrogen peroxide, and send it into a fixed bed reactor filled with a supported metal catalyst for catalytic wet oxidation treatment. (3) The wastewater treated in step (2) is evaporated, concentrated and crystallized to obtain ammonium chloride crystal salt and evaporated condensate; part of the mother liquor is returned to step (1).

[0030] In some preferred embodiments, the chelating resin has a polystyrene or polyacrylate backbone and possesses aminophosphonic acid or iminodiacetic acid functional groups. Through coordination and hydrogen bonding interactions between its functional groups and o-nitroaniline, the chelating resin can selectively adsorb o-nitroaniline even in high ammonium chloride concentrations, while ammonium chloride, as an ionic salt, is not retained by the chelating resin, thus achieving the adsorption and separation of organic matter in high-salt-concentration wastewater.

[0031] In some preferred embodiments, the chelating resin has a crosslinking degree of 6%–12%, a specific surface area of ​​300–800 m² / g, and an average pore size of 2–20 nm, preferably 2–10 nm. If the resin pore size is too small, organic molecules cannot enter the resin interior and cannot be adsorbed; if the pore size is too large, molecules will permeate. In wastewater with an ammonium chloride mass concentration of 8%–12%, the adsorption capacity of the chelating resin for o-nitroaniline is not less than 100 mg / g resin.

[0032] In some preferred embodiments, in step (1), the adsorption temperature is 20-60°C, the pH of the wastewater is 7-10, and the adsorption flow rate is 1-5 BV / hour.

[0033] In some preferred embodiments, in step (1), the concentration of o-nitroaniline in the wastewater is 5000~10000 mg / L, the mass concentration of ammonium chloride is 8~12%, the COD concentration is 20000~40000 mg / L, and the concentration of o-nitroaniline in the adsorbed water is 500~1000 mg / L, and the COD concentration is 10000~15000 mg / L.

[0034] In some preferred embodiments, step (1) further includes desorbing and regenerating the chelating resin after adsorption saturation using a desorbent.

[0035] In some preferred embodiments, the desorbent is methanol, ethanol, acetone, or a mixture thereof, and the desorption temperature is 40–80°C. Alcohols or ketones have good solubility for o-nitroaniline, which can efficiently elute o-nitroaniline adsorbed on the resin, thereby achieving resin regeneration and product recovery.

[0036] In some preferred embodiments, in step (2), the pH of the adsorbed water is adjusted to 3-5. Acidic conditions are conducive to the effective decomposition of hydrogen peroxide and the efficient generation of hydroxyl radicals, thereby improving the oxidative degradation efficiency of organic matter.

[0037] In some preferred embodiments, in step (2), the support for the metal catalyst is selected from at least one of activated carbon, molecular sieve, titanium dioxide, or zirconium dioxide; the supporting metal is selected from at least one or more combinations of iron, copper, manganese, magnesium, aluminum, cobalt, cerium, and their oxides, preferably Cu-Mn, Cu-Co, or Cu-Fe-Co composite oxide catalysts; the metal loading is 1% to 10% based on the mass of the support. The combination of the above support and active metal promotes the decomposition of hydrogen peroxide to generate hydroxyl radicals through a Fenton-like mechanism, which can meet the activation energy required for the chain scission mineralization of organic matter under medium temperature conditions, avoiding the problem of organic matter coking and clogging the reactor in high-temperature wet oxidation processes.

[0038] In some preferred embodiments, in step (2), the reaction temperature of the catalytic wet oxidation treatment is 150-200°C, the operating pressure is 0.3-3.0 MPa, and the residence time of the wastewater in the fixed bed reactor is 0.5-3 hours.

[0039] This invention optimizes parameters such as the activity of advanced oxidation catalysts, the amount of oxidant, and the reaction temperature, and selects the optimal reaction control point so that the reaction is carried out under the best temperature conditions, which can keep the oxidation in a more suitable activation energy range. This ensures the chain scission and decomposition of o-nitroaniline, while avoiding the coking and agglomeration of organic matter at high temperatures, which would generate tar and clog the reactor.

[0040] In some preferred embodiments, in step (2), the amount of hydrogen peroxide added is 0.5 to 2.5 times the theoretical oxygen demand of the wastewater COD.

[0041] In some preferred embodiments, in step (3), the evaporation, concentration and crystallization are carried out by multi-effect evaporation or mechanical vapor recompression evaporation.

[0042] In some preferred embodiments, in step (3), the amount of mother liquor returned to step (1) is 10% to 30% of the total amount of mother liquor, and the COD of the mother liquor is controlled to be below 5000 mg / L.

[0043] In some preferred embodiments, in step (3), the wastewater comes from the production process of o-nitroaniline, and the evaporated condensate is used to prepare an ammonia solution and is reused in the production process of o-nitroaniline.

[0044] The present invention will be further described in detail below with reference to embodiments.

[0045] Unless otherwise specified, all raw materials used in the following examples are commercially available products.

[0046] Example 1

[0047] The chelating resin used in this embodiment is an aminophosphonic acid type polystyrene skeleton chelating resin (crosslinking degree 8%, specific surface area 500 m² / g, average pore size 4~8 nm).

[0048] Wastewater from the production of o-nitroaniline (o-nitroaniline concentration 7850 mg / L, ammonium chloride concentration 9.6%, COD 32600 mg / L, pH adjusted to 8-8.5) was passed through an adsorption column packed with chelating resin at an adsorption temperature of 30℃ and an adsorption flow rate of 3 BV / h. The effluent after adsorption treatment (adsorption section effluent) had an o-nitroaniline concentration of 680 mg / L and a COD of 6200 mg / L.

[0049] The pH of the adsorption effluent was adjusted to 4.0-4.5 with hydrochloric acid. Hydrogen peroxide was added at 1.5 times the theoretical oxygen demand of the wastewater's COD. After mixing, the mixture was fed into a fixed-bed reactor packed with a Cu-Fe-Co / activated carbon supported metal catalyst (metal loading 5%, based on carrier mass). Catalytic wet oxidation was carried out under the conditions of reaction temperature 160℃, operating pressure 0.65MPa, and residence time 1.5 hours. The concentration of o-nitroaniline in the oxidized effluent was 20 mg / L, and the COD was 780 mg / L.

[0050] The effluent from the oxidation section is sent to the MVR evaporation system for evaporation, concentration and crystallization to obtain ammonium chloride crystals (purity 99.0%, whiteness ≥90) and evaporation condensate (COD 175 mg / L).

[0051] Example 2

[0052] The difference between this embodiment and Embodiment 1 is that the amount of hydrogen peroxide added in the catalytic wet oxidation process is 0.8 times the theoretical oxygen demand for COD.

[0053] The effluent from Example 1 was taken, and the pH was adjusted to 4.0-4.5 with hydrochloric acid. Hydrogen peroxide was added at 0.8 times the theoretical oxygen demand of the wastewater COD. After mixing, the mixture was fed into a fixed-bed reactor packed with a Cu-Fe-Co / activated carbon supported metal catalyst (metal loading 5%, based on carrier mass). Catalytic wet oxidation was carried out under the conditions of reaction temperature 160℃, operating pressure 0.65MPa, and residence time 1.5 hours. The concentration of o-nitroaniline in the oxidized effluent was 62 mg / L, and the COD was 1200 mg / L.

[0054] The effluent from the oxidation section is sent to the MVR evaporation system for evaporation, concentration and crystallization to obtain ammonium chloride crystals (purity 99.0%, whiteness ≥90) and evaporation condensate (COD 575 mg / L).

[0055] Example 3

[0056] The chelating resin used in this embodiment is an aminophosphonic acid type polystyrene backbone chelating resin (crosslinking degree 10%, specific surface area 550 m² / g, average pore size 15 nm).

[0057] The above-mentioned o-nitroaniline production wastewater (o-nitroaniline concentration 7850 mg / L, ammonium chloride mass concentration 9.6%, COD 32600 mg / L, pH adjusted to 8-8.5) was passed through an adsorption column packed with chelating resin at an adsorption temperature of 30℃ and an adsorption flow rate of 3 BV / h. The o-nitroaniline concentration in the effluent after adsorption treatment (adsorption section effluent) was 1510 mg / L, and the COD was 10233 mg / L.

[0058] The pH of the adsorption effluent was adjusted to 4.0-4.5 with hydrochloric acid. Hydrogen peroxide was added at 1.0 times the theoretical oxygen demand of the wastewater's COD. After mixing, the mixture was fed into a fixed-bed reactor packed with a Cu-Fe-Co / activated carbon supported metal catalyst (metal loading 5%, based on carrier mass). Catalytic wet oxidation was carried out under the conditions of reaction temperature 160℃, operating pressure 0.65MPa, and residence time 1.5 hours. The concentration of o-nitroaniline in the oxidized effluent was 205 mg / L, and the COD was 2600 mg / L.

[0059] The effluent from the oxidation section is sent to the MVR evaporation system for evaporation, concentration and crystallization to obtain ammonium chloride crystals (purity 98.7%, whiteness ≥72) and evaporation condensate (COD 850 mg / L).

[0060] Example 4

[0061] The difference between this embodiment and Example 3 is that the catalytic wet oxidation reaction temperature is 180°C and the amount of hydrogen peroxide added is increased to 2.0 times the theoretical oxygen demand for COD.

[0062] The pH of the adsorption effluent from Example 3 was adjusted to 4.0-4.5 with hydrochloric acid. Hydrogen peroxide was added at 2.0 times the theoretical oxygen demand (COD) of the wastewater. After mixing, the mixture was fed into a fixed-bed reactor packed with a Cu-Fe-Co / activated carbon supported metal catalyst (metal loading 5%, based on carrier mass). Catalytic wet oxidation was performed at a reaction temperature of 180°C, an operating pressure of 1.05 MPa, and a residence time of 1.5 hours. The concentration of o-nitroaniline in the oxidized effluent was 42 mg / L, and the COD was 1100 mg / L.

[0063] The effluent from the oxidation stage is sent to an MVR evaporation system for evaporation, concentration, and crystallization to obtain ammonium chloride crystals (purity 99.0%, whiteness ≥85) and evaporation condensate (COD 450 mg / L). By increasing the hydrogen peroxide dosage in the catalytic oxidation stage, wastewater with higher concentrations of o-nitroaniline can be treated, ensuring control measures are in place for effluent exceeding the standards after resin adsorption. However, this method also increases treatment costs.

[0064] Example 5

[0065] The difference between this embodiment and Example 1 is that the catalyst used in the catalytic wet oxidation reaction is a Cu / activated carbon supported catalyst.

[0066] The pH of the adsorption effluent from Example 1 was adjusted to 4.0-4.5 with hydrochloric acid. Hydrogen peroxide was added at 1.5 times the theoretical oxygen demand of the wastewater's COD. After mixing, the mixture was fed into a fixed-bed reactor packed with a Cu / activated carbon supported metal catalyst (metal loading 5%, based on carrier mass). Catalytic wet oxidation was carried out under the conditions of reaction temperature 160℃, operating pressure 0.65MPa, and residence time 1.5 hours. The concentration of o-nitroaniline in the oxidized effluent was 85 mg / L, and the COD was 1350 mg / L.

[0067] The effluent from the oxidation section is sent to the MVR evaporation system for evaporation, concentration and crystallization to obtain ammonium chloride crystals (purity 99%, whiteness 88) and evaporation condensate (COD 355 mg / L).

[0068] Example 6

[0069] The difference between this embodiment and Example 1 is that the resin used for adsorption is an iminodiacetic acid modified resin (10% crosslinking degree, 750 m² / g specific surface area, and 6.5~8.5 nm average pore size).

[0070] Wastewater from o-nitroaniline production, identical to that in Example 1 (o-nitroaniline concentration 7850 mg / L, ammonium chloride concentration 9.6%, COD 32600 mg / L, pH adjusted to 8-8.5), was passed through an adsorption column packed with chelating resin at an adsorption temperature of 30°C and an adsorption flow rate of 3 BV / h. The effluent after adsorption treatment (adsorption section effluent) had an o-nitroaniline concentration of 540 mg / L and a COD of 5700 mg / L.

[0071] The pH of the adsorption effluent was adjusted to 4.0-4.5 with hydrochloric acid. Hydrogen peroxide was added at 1.5 times the theoretical oxygen demand of the wastewater's COD. After mixing, the mixture was fed into a fixed-bed reactor packed with a Cu-Fe-Co / activated carbon supported metal catalyst (metal loading 5%, based on carrier mass). Catalytic wet oxidation was carried out under the conditions of reaction temperature 160℃, operating pressure 0.65MPa, and residence time 1.5 hours. The concentration of o-nitroaniline in the oxidized effluent was 12 mg / L, and the COD was 740 mg / L.

[0072] The effluent from the oxidation section is sent to the MVR evaporation system for evaporation, concentration and crystallization to obtain ammonium chloride crystals (purity 99.0%, whiteness ≥90) and evaporation condensate (COD 180 mg / L).

[0073] Comparative Example 1

[0074] The chelating resin in Example 1 was replaced with XDA-1 type macroporous adsorption resin (specific surface area 650~750㎡, average pore size 6.5~9.5nm), and the other operating conditions were exactly the same as in Example 1.

[0075] Wastewater from o-nitroaniline production, identical to that in Example 1 (o-nitroaniline concentration 7850 mg / L, ammonium chloride concentration 9.6%, COD 32600 mg / L, pH adjusted to 8-8.5), was passed through an adsorption column packed with macroporous adsorption resin at an adsorption temperature of 30°C and an adsorption flow rate of 3 BV / h. The concentration of o-nitroaniline in the effluent was 1850 mg / L, and the COD was 15200 mg / L. Compared to Example 1 (effluent from the adsorption section with o-nitroaniline concentration of 680 mg / L and COD of 6200 mg / L), the macroporous adsorption resin showed significantly lower selective adsorption capacity for o-nitroaniline in the presence of high concentrations of ammonium chloride compared to the chelating resin.

[0076] The pH of the adsorption effluent was adjusted to 4.0-4.5 with hydrochloric acid, and hydrogen peroxide was added at 1.5 times the theoretical oxygen demand of the wastewater's COD. Catalytic wet oxidation was carried out under conditions of a reaction temperature of 160℃, an operating pressure of 0.65 MPa, and a residence time of 1.5 hours. The concentration of o-nitroaniline in the oxidized effluent was 670 mg / L, and the COD was 3500 mg / L. Because the organic load in the adsorption section effluent was much higher than in Example 1, the COD in the oxidation section effluent remained high.

[0077] The effluent from the oxidation section was sent to the MVR evaporation system for evaporation, concentration and crystallization. The resulting ammonium chloride crystal salt had a purity of 95.2%, a whiteness of only 62, and a pale yellow appearance, which failed to meet the industrial ammonium chloride product standard.

[0078] Comparative Example 2

[0079] Using the same chelating resin and adsorption conditions as in Example 1, the catalytic wet oxidation in step (2) was replaced with high-temperature wet oxidation.

[0080] The adsorption effluent from Example 1 (o-nitroaniline concentration 680 mg / L, COD 6200 mg / L) was adjusted to pH 5.5 with hydrochloric acid, and cuprous chloride was added as a catalyst (dosage 100 mg / L). The reaction was carried out at 250-280°C for 2 hours using pure oxygen as the oxidant. The o-nitroaniline concentration in the oxidized effluent was 15 mg / L, and the COD was 2700 mg / L. A large amount of black tar residue remained in the reactor. Compared to Example 1 (o-nitroaniline concentration in the oxidized section effluent 12 mg / L, COD 320 mg / L), due to the higher reaction temperature and relatively slower oxidation rate, o-nitroaniline and its derivatives in the wastewater mainly underwent polymerization and coking, adhering to the reactor wall cavity as solid tar, easily leading to reactor blockage. Because the high-temperature, humid oxygen oxidation effluent is clogged with tar, it is unsuitable for subsequent evaporation, concentration, and crystallization to produce ammonium chloride.

[0081] Table 1 Summary of Results from Examples and Comparative Examples

[0082] Note: ONA is an abbreviation for o-Nitroaniline.

[0083] As can be seen from the comparison between Example 1 and Comparative Examples 1-2, the adsorption, low-temperature wet oxidation and evaporation salt recovery process of the present invention can effectively remove pollutants from raw water, while realizing the resource utilization of o-nitroaniline and ammonium chloride.

Claims

1. A method for recovering o-nitroaniline from wastewater and producing ammonium chloride as a byproduct, characterized in that, Includes the following steps: (1) Wastewater containing o-nitroaniline and ammonium chloride is passed through an adsorption column packed with chelating resin to adsorb o-nitroaniline in the wastewater. (2) Adjust the pH of the adsorbed water obtained in step (1) to acidic, mix it with hydrogen peroxide, and send it into a fixed bed reactor filled with a supported metal catalyst for catalytic wet oxidation treatment. (3) The wastewater treated in step (2) is evaporated, concentrated and crystallized to obtain ammonium chloride crystal salt and evaporated condensate; part of the mother liquor is returned to step (1).

2. The method according to claim 1, characterized in that, The chelating resin has a polystyrene backbone or a polyacrylate backbone, and the chelating resin has aminophosphonic acid type functional groups or iminodiacetic acid type functional groups.

3. The method according to claim 2, characterized in that, The chelating resin has a crosslinking degree of 6-12%, a specific surface area of ​​300-800 m² / g, and an average pore size of 2-20 nm.

4. The method according to claim 1, characterized in that, In step (1), the adsorption temperature is 20–60℃, the pH of the wastewater is 7–10, and the adsorption flow rate is 1–5 BV / hour; and / or, The wastewater contains 5000-10000 mg / L of o-nitroaniline, 8-12% of ammonium chloride, and 20000-40000 mg / L of COD. The adsorbed water contains 500-1000 mg / L of o-nitroaniline and 10000-15000 mg / L of COD.

5. The method according to claim 1, characterized in that, Step (1) further includes desorbing and regenerating the chelating resin after adsorption saturation using a desorbent; preferably, the desorbent is methanol, ethanol, acetone or a mixture thereof, and the desorption temperature is 40-80°C.

6. The method according to claim 1, characterized in that, In step (2), the pH of the adsorbed water is adjusted to 3-5.

7. The method according to claim 1, characterized in that, In step (2), the support for the metal catalyst is selected from at least one of activated carbon, molecular sieve, titanium dioxide or zirconium dioxide; the supporting metal is selected from at least one of iron, copper, manganese, cobalt and cerium; the metal loading is 1 to 10% based on the mass of the support.

8. The method according to claim 1, characterized in that, In step (2), the reaction temperature of the catalytic wet oxidation treatment is 150-200℃, the operating pressure is 0.3-3.0 MPa, and the residence time of the wastewater in the fixed bed reactor is 0.5-3 hours.

9. The method according to claim 1, characterized in that, In step (2), the amount of hydrogen peroxide added is 0.5 to 2.5 times the theoretical oxygen demand of the wastewater COD.

10. The method according to claim 1, characterized in that, In step (3): The evaporation, concentration, and crystallization are performed using multi-effect evaporation or mechanical vapor recompression evaporation; and / or, The amount of mother liquor returned to the evaporator in step (1) is 10-30% of the total amount of mother liquor, and the COD of the mother liquor is controlled to be below 5000 mg / L; and / or, The wastewater comes from the production process of o-nitroaniline, and the evaporated condensate is used to prepare an ammonia solution and is reused in the production process of o-nitroaniline.

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