System and method for deep treatment of mdi production waste brine

Abstract

The application discloses a kind of MDI production waste brine deep processing system and method.The MDI production waste brine deep processing system includes neutralizing device, extraction column, brine stripping column and brine oxidation stripping column, neutralizing device is connected with extraction column, extraction column is connected with brine stripping column, brine stripping column is connected with brine oxidation stripping column, neutralizing device can be used to connect MDI production reaction device to collect waste brine from MDI production reaction device, neutralizing device is also used to neutralize reaction to obtain the mixture containing diphenylmethane polyamine and neutralized brine, extraction column is used to extract the mixture to obtain extracted brine, brine stripping column is used to strip the extracted brine to obtain stripped brine, and brine oxidation stripping column is used to oxidize and strip the stripped brine to obtain oxidized brine.The application can effectively improve the treatment effect and reduce the operating cost.

Description

Technical Field

[0001] This application relates to the field of chemical technology, and in particular to a system and method for the deep treatment of waste brine from MDI production. Background Technology

[0002] Polymethylene polyphenyl polyamine (MDA) is a key intermediate in the preparation of diaminodiphenylmethane isocyanates (MDI), and as a core raw material in the polyurethane industry, its production process has long been a focus of attention. Currently, the industrial process commonly involves condensation and transposition reactions of aniline and formaldehyde in the presence of an acidic catalyst, followed by neutralization with alkali and washing with water to obtain a crude product containing diamines and polyamines. This neutralization process generates a large amount of high-concentration waste brine (containing approximately 18wt%~20wt% salt), which not only contains a small amount of residual caustic soda but also various organic compounds such as carboxylic acids, phenylcyclic phenols, and amines. This results in the wastewater quality failing to meet the requirements for direct reuse in the ion-exchange membrane caustic soda production process.

[0003] Traditional technologies for treating wastewater in MDI processes typically employ pretreatment methods such as extraction and stripping to reduce organic matter content, followed by further treatment through oxidation or adsorption. For example, a process utilizing a high-gravity rotating bed to enhance extraction, combined with stripping and oxidation-adsorption, can reduce amine levels to below 3 ppm, but the process is complex and the total organic carbon (TOC) removal effect is limited. Another approach involves ultrasonic-assisted oxidation and activated carbon adsorption; however, ultrasonic technology lacks stability in large-scale continuous production, hindering industrial application. Furthermore, catalytic oxidation for deep treatment requires precise pH adjustment to prevent catalyst metal loss, and the oxidant is prone to self-decomposition, leading to increased consumption and difficulty in improving TOC treatment efficiency. Some traditional technologies reduce the organic content in waste brine by controlling the raw materials or production process. For example, controlling the ethanol content in methanol and the formaldehyde preparation parameters can reduce the generation of aniline impurities. Other methods include limiting the aminophenol content in the raw material aniline, strictly controlling the excess caustic soda rate during neutralization, and adjusting the organic amine content based on the turbidity of the reaction liquid. Although these methods alleviate the burden of subsequent treatment to some extent, they impose strict restrictions on raw material indicators or process parameters, which not only increases the upstream impurity removal cost but also reduces production flexibility. Furthermore, the overall TOC reduction effect is still not ideal.

[0004] It is evident that in traditional technologies, chloride ions quench hydroxyl radicals in high-salt environments, resulting in an oxidant utilization rate of less than 30%, necessitating a significant increase in dosage and leading to persistently high operating costs. Furthermore, the need for strict control of upstream impurities and the addition of multiple post-processing steps further exacerbates the overall cost and limits operational flexibility. Summary of the Invention

[0005] Therefore, it is necessary to provide a deep treatment system for MDI production waste brine that has low operating costs and good treatment effect.

[0006] One embodiment of this application provides an MDI production waste brine deep treatment system.

[0007] A deep treatment system for MDI production waste brine includes a neutralization unit, an extraction tower, a brine stripping tower, and a brine oxidation stripping tower. The neutralization unit is connected to the extraction tower, the extraction tower is connected to the brine stripping tower, and the brine stripping tower is connected to the brine oxidation stripping tower. The neutralization unit is connected to the MDI production reactor to collect waste brine generated from the MDI production reactor. The neutralization unit is used to neutralize the waste brine to obtain a mixture containing diphenylmethane polyamine and neutralized brine. The extraction tower is used to extract the mixture to obtain extracted brine. The brine stripping tower is used to strip the extracted brine to obtain stripped brine. The brine oxidation stripping tower is used to oxidize the stripped brine to obtain oxidized brine.

[0008] In some embodiments, the MDI production waste brine deep treatment system further includes a first heat exchanger and a first circulation pipeline. The bottom of the brine stripping tower is circulated through the first circulation pipeline. The first heat exchanger is connected to the first circulation pipeline. The cold flow channel of the first heat exchanger is connected to the first circulation pipeline, and the hot flow channel of the first heat exchanger is used to introduce steam.

[0009] In some embodiments, the top of the brine oxidation stripping tower is also connected to the bottom of the brine stripping tower for reflux of the gas phase in the brine oxidation stripping tower back into the brine stripping tower.

[0010] In some embodiments, the MDI production waste brine deep treatment system further includes a second heat exchanger and a second circulation pipeline. The bottom of the brine oxidation stripping tower is circulated through the second circulation pipeline. The second heat exchanger is connected to the second circulation pipeline. The cold flow channel of the second heat exchanger is connected to the second circulation pipeline, and the hot flow channel of the second heat exchanger is used to introduce steam.

[0011] In some embodiments, the extraction tower is provided with an extractant interface for input of the extractant.

[0012] In some embodiments, the brine oxidation stripping tower is provided with an oxidant inlet for oxidant input, a reducing agent inlet for reducing agent input, and a stripping medium inlet for stripping medium input.

[0013] In some embodiments, the brine oxidation stripping tower is provided with multiple sections of packing material loaded with at least one metal nanoparticle selected from iron, cobalt, manganese, and nickel.

[0014] In some embodiments, the particle size of the metal nanoparticles is 10 nm to 50 nm.

[0015] In some embodiments, the loading of the metal nanoparticles in the filler is 0.5 wt% to 5 wt%.

[0016] This application also provides a method for deep treatment of MDI production waste brine according to embodiments.

[0017] A method for deep treatment of MDI production waste brine includes the following steps:

[0018] The waste brine generated during the MDI production process was neutralized to obtain a mixture containing diphenylmethane polyamine and neutralized brine;

[0019] The mixture is subjected to extraction treatment to obtain extractable brine;

[0020] The extracted brine is subjected to stripping treatment to remove diphenylmethane polyamine and extractant from the extracted brine, resulting in stripped brine.

[0021] Furthermore, the stripped brine is subjected to oxidative stripping treatment using a first oxidant to obtain oxidized brine.

[0022] In some embodiments, the oxidative stripping treatment includes the following steps:

[0023] The stripped brine is subjected to a first oxidation treatment using a first oxidant; the brine subjected to the first oxidation treatment is subjected to a second oxidation treatment using a second oxidant to obtain oxidized brine.

[0024] In addition, steam and stripping media are introduced to remove volatile organic intermediates and ammonia generated by the first oxidation treatment and the second oxidation treatment.

[0025] In some embodiments, the deep treatment method for MDI production waste brine further includes the following steps: after the second oxidation treatment, a reducing agent is added to reduce the nitrate nitrogen and nitrite nitrogen generated by oxidation to ammonium ions, and then convert them into ammonia gas under alkaline high-temperature conditions.

[0026] In some embodiments, the alkaline high-temperature conditions satisfy the following conditions: in a NaOH solution and / or KOH solution with a concentration of 0.1wt% to 10wt%, the temperature is 90℃ to 120℃.

[0027] In some embodiments, the reducing agent includes sodium sulfite.

[0028] In some embodiments, the mass ratio of the added reducing agent to the oxidized brine is (0.0001~0.001):1.

[0029] In some embodiments, the mass ratio of steam introduced after the second oxidation treatment to the stripped brine is (0.05~0.1):1.

[0030] In some embodiments, the volume ratio of the stripping medium introduced after the second oxidation treatment to the stripped brine is (0.5~2):1.

[0031] In some embodiments, the gas phase following the second oxidation treatment is controlled to be returned to the stripping process as a heat source.

[0032] In some embodiments, the effluent from the oxidized brine has a TOC ≤ 10 ppm and a TN ≤ 1 ppm, and the oxidized brine is controlled to be reused in the ion-exchange membrane caustic soda production process.

[0033] In some embodiments, the alkaline solution used in the neutralization reaction includes one or both of NaOH and KOH.

[0034] In some embodiments, the extractant used in the extraction process includes one or more of aniline, toluene, benzene, and chlorobenzene.

[0035] In some embodiments, the first oxidant comprises persulfate.

[0036] In some embodiments, the second oxidant includes one or more of persulfate, sodium hypochlorite, hydrogen peroxide, and ozone.

[0037] In some embodiments, the molar ratio of the first oxidant to the TOC in the stripped brine is (0.5~4):1.

[0038] In some embodiments, the molar ratio of the first oxidant to the TOC in the stripped brine is (1~3):1.

[0039] In some embodiments, the molar ratio of the second oxidant to the TOC in the stripped brine is (1~5):1.

[0040] In some embodiments, the molar ratio of the first oxidant to the second oxidant is 1:(1~3).

[0041] In some embodiments, the TOC content of the stripped brine obtained after the stripping treatment is controlled to be 20ppm to 200ppm.

[0042] In some embodiments, the deep treatment method for MDI production waste brine adopts the deep treatment system for MDI production waste brine described in any of the above embodiments.

[0043] The aforementioned MDI production waste brine deep treatment system overcomes the technical bias of low oxidation efficiency in high-salt environments, achieving synergistic effects of oxidation decomposition and stripping removal. It has advantages such as high treatment efficiency, low operating cost, simple process flow, and safety and reliability. It solves the safety hazards of TOC accumulation and nitrogen trichloride explosion in the reuse of MDI waste brine in traditional technologies, and significantly reduces the system operating cost.

[0044] The method for deep treatment of MDI production wastewater in this application utilizes the high temperature and high alkalinity of the stripped brine itself to induce free radicals generated by the first and / or second oxidants to selectively ring-open the aromatic phenols and aromatic amines in the wastewater, generating quinone or semiquinone intermediates with stripping volatility. These intermediates are then stripped away using steam and a stripping medium, thereby achieving deep removal of total organic carbon (TOC). In this method, the saline wastewater generated during MDI production undergoes sequential extraction, stripping, and oxidative stripping coupled treatment. During the oxidative stripping coupled treatment, oxidants are added stepwise to the stripped brine to form a dual oxidation system. Steam heating and the introduction of a stripping medium are used for immediate stripping to remove volatile intermediates and ammonia. After treatment, the total organic carbon (TOC) in the saline wastewater is ≤10ppm and the total nitrogen (TN) is ≤1ppm, which can be directly reused in the ion-exchange membrane caustic soda production process. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] To gain a more complete understanding of this application and its beneficial effects, the following description will be provided in conjunction with the accompanying drawings. In the following description, the same reference numerals denote the same parts.

[0047] Figure 1 This is a schematic diagram of an MDI production waste brine deep treatment system according to an embodiment of this application;

[0048] Figure 2 This is a schematic diagram of an embodiment of the deep treatment method for MDI production waste brine described in this application.

[0049] Explanation of reference numerals in the attached figures

[0050] 10. MDI production waste brine deep treatment system; 100. Neutralization device; 200. Extraction tower; 300. Brine stripping tower; 400. Brine oxidation stripping tower; 500. First heat exchanger; 600. First circulation pipeline; 700. Second heat exchanger; 800. Second circulation pipeline. Detailed Implementation

[0051] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0052] In this application, unless otherwise expressly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two elements or the interaction between two elements, unless otherwise expressly limited. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. In this application, unless otherwise expressly specified and limited, "on" or "below" a second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium.

[0053] In the description of this application, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the number itself, while "above," "below," and "within" are understood to include the number itself. The terms "first" and "second" are used only to distinguish technical features and should not be construed as indicating or implying relative importance, or implicitly specifying the number of technical features indicated, or implicitly specifying the sequential relationship of the technical features indicated.

[0054] In this document, "optionally," "optionally," and "optional" mean that something is optional, meaning that one can choose between two parallel options: "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. In this application, descriptions such as "optionally contains" and "optionally includes" indicate "contains or does not contain."

[0055] In this application, unless otherwise stated, the sum of the parts of each component in the composition may be 100 parts by weight. Unless otherwise specified, the percentages (including weight percentages) in this application are based on the total weight of the composition, and "wt%" in this document means mass percentage.

[0056] In this document, unless otherwise stated, the reaction steps may be performed in the order described herein or not. For example, other steps may be included between reaction steps, and the order of reaction steps may be appropriately interchanged. This is something that those skilled in the art can determine based on conventional knowledge and experience. Preferably, the reaction methods described herein are performed sequentially.

[0057] In this application, the term "numerical interval" (i.e., numerical range) refers to a range of values. Unless otherwise specified, the distribution of selectable values ​​within this numerical interval is considered continuous, and includes the two endpoints (i.e., the minimum and maximum values) of the interval, as well as every value between these endpoints. Unless otherwise specified, when a numerical interval refers only to integers within that interval, it includes the two endpoints of the range and every integer between them, effectively listing every integer. When multiple numerical ranges are provided to describe features or characteristics, these ranges can be merged. In other words, unless otherwise specified, the numerical ranges disclosed in this application should be understood to include any and all subranges included therein. The "numerical value" in this numerical interval can be any quantitative value, such as a number, percentage, or proportion. The term "numerical interval" can broadly include percentage intervals, proportion intervals, ratio intervals, and other quantitative intervals.

[0058] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0059] This application provides an MDI production waste brine deep treatment system to solve at least one of the following technical problems in the traditional MDI production waste brine treatment method: (1) The oxidation efficiency is extremely low in high-salt environments. The high concentration of chloride ions in the brine will quench the hydroxyl radicals generated by the conventional oxidation process, resulting in an effective utilization rate of less than 30% for the oxidant, which forces a significant increase in the dosage of the reagent and keeps the operating cost high. (2) The existing treatment system is constrained by both the process and the raw materials. In order to meet the reuse standard, it is necessary to strictly control upstream impurities (such as aminophenol in aniline ≤10ppm and carboxylic acid in formaldehyde ≤100ppm) and add multiple post-treatment steps such as activated carbon adsorption and ion exchange, which leads to an increase in the overall process cost and limited operational flexibility. (3) The removal of nitrogen-containing organic matter poses a major safety hazard. Aniline and amide nitrogen-containing compounds in the waste brine are difficult to completely degrade. The existing technology can only reduce the total nitrogen to 5ppm~10ppm. After the residual nitrogen-containing matter enters the ion membrane electrolyzer with the brine, it will generate explosive nitrogen trichloride (NCl). 3） When its concentration in liquid chlorine exceeds 5%, it poses an explosion risk and has become a significant safety hazard in the chlor-alkali industry. The following description, in conjunction with the accompanying diagram, illustrates the advanced treatment system for MDI production wastewater.

[0060] Through long-term research, the inventors of this application discovered that traditional technologies have fallen into the technical misconception of "solely oxidizing and degrading organic matter," failing to realize that coupling oxidative decomposition with stripping to remove intermediates can simultaneously solve the aforementioned three major problems. Based on this, this application proposes a novel oxidative stripping coupled treatment process, breaking through the technical bias of low oxidation efficiency in high-salt environments, achieving efficient and deep removal of TOC and TN, and significantly reducing raw material requirements and costs.

[0061] This application provides an embodiment of an MDI production waste brine deep treatment system 10, which is exemplary. Please refer to [link to embodiment 1]. Figure 1 As shown, Figure 1 This is a schematic diagram of the structure of an MDI production waste brine deep treatment system 10 provided in one embodiment of this application. The MDI production waste brine deep treatment system 10 of this application can be used for efficient and low-cost treatment of waste brine in the MDI production process, and the treatment effect is good.

[0062] To more clearly illustrate the structure of the MDI production waste brine deep treatment system 10, the following will describe the MDI production waste brine deep treatment system 10 in conjunction with the accompanying drawings.

[0063] For example, please refer to Figure 1As shown, an MDI production waste brine deep treatment system 10 includes a neutralization unit 100, an extraction tower 200, a brine stripping tower 300, and a brine oxidative stripping tower 400. The neutralization unit 100 is connected to the extraction tower 200, the extraction tower 200 is connected to the brine stripping tower 300, and the brine stripping tower 300 is connected to the brine oxidative stripping tower 400. For example, the neutralization unit 100, extraction tower 200, brine stripping tower 300, and brine oxidative stripping tower 400 are connected sequentially. The neutralization unit 100 can be connected to an MDI production reactor to collect waste brine generated from the MDI production reactor. The neutralization unit 100 is used to neutralize the waste brine to obtain a mixture containing diphenylmethane polyamine and neutralized brine. The extraction tower 200 is used to extract the mixture to obtain extracted brine. The brine stripping tower 300 is used to strip the extracted brine to obtain stripped brine, and the brine oxidation stripping tower 400 is used to oxidize the stripped brine to obtain oxidized brine.

[0064] The aforementioned MDI production waste brine deep treatment system 10 overcomes the technical bias of low oxidation efficiency in high-salt environments, achieves synergistic effect of oxidation decomposition and stripping removal, and has the advantages of high treatment efficiency, low operating cost, simple process flow, safety and reliability. It also solves the safety hazards of TOC accumulation and nitrogen trichloride explosion in the reuse of MDI waste brine in traditional technologies.

[0065] It should be noted that the core function of the brine stripping tower 300 is physical separation. It separates or concentrates volatile components by introducing steam, air, or other carrier gases (such as nitrogen, carbon dioxide, or other industrial gases) into the brine, utilizing the heat and mass transfer driving force provided by the rising gas in the liquid phase. In brine treatment, the brine stripping tower 300 is used to remove organic impurities. In MDI (diphenylmethane diisocyanate) production, the brine stripping tower 300 is used to reduce the content of organic matter (such as aniline) in waste brine to below specified standards. After stripping from the brine stripper 300, the high-temperature brine is first treated with a chemical oxidant, usually persulfate. Under specific temperature and pressure, the organic matter dissolved in the brine is oxidized and decomposed, causing its structure to be destroyed or transformed into substances that are easier to remove. The oxidized brine then enters the brine oxidation stripper 400, where a stripping medium (such as steam or nitrogen) and a chemical oxidant (such as hydrogen peroxide, sodium hypochlorite, or ozone) are introduced. At this point, the task of the brine oxidation stripper 400 is to remove the remaining volatile products after the oxidation reaction and to further oxidize and decompose the residual organic matter, or to continue to remove moisture, ammonia, etc.

[0066] In some embodiments, the MDI production waste brine deep treatment system 10 further includes a first heat exchanger 500 and a first circulation pipe 600. The bottom of the brine stripping tower 300 is circulated through the first circulation pipe 600, the first heat exchanger 500 is connected to the first circulation pipe 600, the cold flow channel of the first heat exchanger 500 is connected to the first circulation pipe 600, and the hot flow channel of the first heat exchanger 500 is used to introduce steam.

[0067] In some embodiments, the top of the brine oxidation stripping tower 400 is also connected to the brine stripping tower 300 for recirculating the gas phase in the brine oxidation stripping tower 400 back into the brine stripping tower 300.

[0068] In some embodiments, the MDI production waste brine deep treatment system 10 further includes a second heat exchanger 700 and a second circulation pipe 800. The bottom of the brine oxidation stripping tower 400 is circulated through the second circulation pipe 800; that is, the bottom of the bottom of the brine oxidation stripping tower 400 is connected to the bottom of the brine oxidation stripping tower 400 through the second circulation pipe 800, realizing the circulation of the bottom liquid in the bottom of the brine oxidation stripping tower 400. The second heat exchanger 700 is connected to the second circulation pipe 800, the cold flow channel of the second heat exchanger 700 is connected to the second circulation pipe 800, and the hot flow channel of the second heat exchanger 700 is used to introduce steam.

[0069] In some embodiments, the extraction tower 200 is provided with an extractant interface for inputting the extractant.

[0070] In some embodiments, the brine oxidation stripping tower 400 is provided with an oxidant inlet for oxidant input, a reducing agent inlet for reducing agent input, and a stripping medium inlet for stripping medium input.

[0071] In some embodiments, the brine oxidation stripping tower 400 is provided with multiple sections of packing material loaded with at least one metal nanoparticle selected from iron, cobalt, manganese and nickel.

[0072] In some embodiments, the particle size of the metal nanoparticles is 10 nm to 50 nm. For example, the particle size of the metal nanoparticles includes, but is not limited to, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, or any range between the foregoing.

[0073] In some embodiments, the loading of metal nanoparticles in the filler is 0.5 wt% to 5 wt%. For example, the loading of metal nanoparticles in the filler includes, but is not limited to: 0.5 wt%, 0.7 wt%, 1 wt%, 1.3 wt%, 1.5 wt%, 1.8 wt%, 2 wt%, 2.3 wt%, 2.5 wt%, 2.8 wt%, 3 wt%, 3.2 wt%, 3.5 wt%, 3.7 wt%, 4 wt%, 4.2 wt%, 4.5 wt%, 4.8 wt%, 5 wt%, or any range between the foregoing.

[0074] This application also provides a method for deep treatment of MDI production waste brine according to embodiments.

[0075] A method for deep treatment of MDI production waste brine includes the following steps:

[0076] S10. Neutralize the waste brine generated during the MDI production process to obtain a mixture containing diphenylmethane polyamine and neutralized brine.

[0077] S20. Extract the mixture and obtain the extracted brine.

[0078] S30. The brine after extraction is stripped to remove diphenylmethane polyamine and extractant, thus obtaining stripped brine.

[0079] S40. The stripped brine is subjected to oxidative stripping to obtain oxidized brine.

[0080] In some embodiments, the oxidative stripping treatment includes the following steps:

[0081] The method involves a first oxidation treatment of the stripped brine using a first oxidant; a second oxidation treatment of the brine after the first oxidation treatment using a second oxidant to obtain oxidized brine; and the introduction of steam and stripping medium to remove volatile organic intermediates and ammonia generated during the first and second oxidation treatments. In this method, selective ring-opening oxidation, intermediate stripping removal, and further deep oxidation of residual organic matter are performed sequentially. The second oxidant is used to treat the brine after the first oxidation treatment to obtain oxidized brine, ensuring a gradient distribution of free radical concentration along the column sections. The catalytic effect of metal nanoparticles allows the first and second oxidants to generate a dual oxidation system of sulfate free radicals and active chlorine, oxidizing and decomposing the organic matter in the brine.

[0082] In some embodiments, the temperature of the steam introduced in this application is 100°C to 120°C. For example, the temperature of the steam introduced in this application includes, but is not limited to: 100°C, 102°C, 105°C, 108°C, 110°C, 112°C, 115°C, 117°C, 120°C, or any range between the foregoing.

[0083] In some embodiments, the stripping medium includes nitrogen.

[0084] In some embodiments, the deep treatment method for MDI production waste brine further includes the following steps: after the second oxidation treatment, a reducing agent is added to reduce the nitrate nitrogen and nitrite nitrogen generated by oxidation to ammonium ions, and then convert them into ammonia gas under alkaline high-temperature conditions.

[0085] In some of these embodiments, the reducing agent includes sodium sulfite.

[0086] In some embodiments, the mass ratio of the added reducing agent to the oxidized brine is (0.0001~0.001):1. For example, the value of the mass ratio of the added reducing agent to the oxidized brine includes, but is not limited to: 0.0001:1, 0.0002:1, 0.0003:1, 0.0004:1, 0.0005:1, 0.0006:1, 0.0007:1, 0.0008:1, 0.0009:1, 0.001:1, or any range between the foregoing.

[0087] In some embodiments, the alkaline high-temperature conditions satisfy the following conditions: in a NaOH solution and / or KOH solution with a concentration of 0.1wt% to 10wt%, the temperature is 90°C to 120°C.

[0088] In some embodiments, the mass ratio of steam introduced after the second oxidation treatment to the stripped brine is (0.05~0.1):1. For example, the mass ratio of steam introduced after the second oxidation treatment to the stripped brine includes, but is not limited to: 0.05:1, 0.055:1, 0.06:1, 0.065:1, 0.07:1, 0.075:1, 0.08:1, 0.085:1, 0.09:1, 0.095:1, 0.1:1, or a range between any two of the foregoing.

[0089] In some embodiments, the volume ratio of the stripping medium introduced after the second oxidation treatment to the stripped brine is (0.5~2):1. For example, the volume ratio of the stripping medium introduced after the second oxidation treatment to the stripped brine includes, but is not limited to: 0.5:1, 0.6:1, 0.7:1, 0.8:1, 0.9:1, 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1, 2:1, or any range between the foregoing.

[0090] In some embodiments, the gas phase after the second oxidation treatment is controlled to be returned to the stripping step as a heat source.

[0091] In some embodiments, the effluent from the oxidized brine has a TOC ≤ 10 ppm and a TN ≤ 1 ppm, and the oxidized brine is controlled to be reused in the ion-exchange membrane caustic soda production process.

[0092] In some embodiments, the alkaline solution used for the neutralization reaction includes one or both of NaOH and KOH.

[0093] In some embodiments, the extractant used in the extraction process includes one or more of aniline, toluene, benzene, and chlorobenzene.

[0094] In some embodiments, the first oxidant includes persulfate.

[0095] In some embodiments, the first oxidant includes one or both of sodium persulfate and potassium persulfate.

[0096] In some embodiments, the second oxidant includes one or more of persulfate, sodium hypochlorite, hydrogen peroxide, and ozone.

[0097] In some embodiments, the molar ratio of the first oxidant to the TOC in the stripped brine is (0.5~4):1. Further, the molar ratio of the first oxidant to the TOC in the stripped brine is (1~3):1. For example, the molar ratio of the first oxidant to the TOC in the stripped brine includes, but is not limited to: 0.5:1, 0.6:1, 0.8:1, 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.2:1, 2.5:1, 2.7:1, 3:1, 3.1:1, 3.3:1, 3.5:1, 3.8:1, 3.9:1, 4:1, or a range between any two of the foregoing.

[0098] In some embodiments, the molar ratio of the second oxidant to the TOC in the stripped brine is (1~5):1. For example, the molar ratio of the second oxidant to the TOC in the stripped brine includes, but is not limited to: 1:1, 1.2:1, 1.5:1, 1.8:1, 2:1, 2.3:1, 2.5:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1, or a range between any two of the foregoing.

[0099] In some embodiments, the molar ratio of the first oxidant to the second oxidant is 1:(1~3). For example, the molar ratio of the first oxidant to the second oxidant may include, but is not limited to: 1:1, 1:1.2, 1:1.5, 1:1.8, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3 or any range between the foregoing.

[0100] In some embodiments, the TOC content of the stripped brine obtained after the stripping treatment is controlled to be between 20 ppm and 200 ppm. For example, the TOC content of the stripped brine obtained after the stripping treatment may include, but is not limited to, 20 ppm, 30 ppm, 40 ppm, 50 ppm, 60 ppm, 70 ppm, 80 ppm, 90 ppm, 100 ppm, 110 ppm, 120 ppm, 130 ppm, 140 ppm, 150 ppm, 160 ppm, 170 ppm, 180 ppm, 190 ppm, 200 ppm, or any range between the foregoing.

[0101] In some embodiments, the deep treatment method for MDI production waste brine adopts the MDI production waste brine deep treatment system 10 in any of the above embodiments.

[0102] The method for deep treatment of MDI production wastewater in this application utilizes the high temperature and high alkalinity of the stripped brine itself to induce free radicals generated by the first and / or second oxidants to selectively ring-open the aromatic phenols and aromatic amines in the wastewater, generating quinone or semiquinone intermediates with stripping volatility. These intermediates are then stripped away using steam and a stripping medium, thereby achieving deep removal of total organic carbon (TOC). In this method, the saline wastewater generated during MDI production undergoes sequential extraction, stripping, and oxidative stripping coupled treatment. During the oxidative stripping coupled treatment, oxidants are added stepwise to the stripped brine to form a dual oxidation system. Steam heating and the introduction of a stripping medium are used for immediate stripping to remove volatile intermediates and ammonia. After treatment, the total organic carbon (TOC) in the saline wastewater is ≤10ppm and the total nitrogen (TN) is ≤1ppm, which can be directly reused in the ion-exchange membrane caustic soda production process.

[0103] Example 1

[0104] This embodiment provides a method for deep treatment of waste brine from MDI production.

[0105] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1 The embodiment shown provides an MDI production waste brine deep treatment system 10.

[0106] The aniline used had a purity of 99.9 wt%, and the formaldehyde used contained 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde underwent condensation and transposition reactions sequentially, and then the waste brine was neutralized in neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture entered extraction tower 200 and underwent countercurrent extraction with aniline as the extractant. The extracted brine was then sent to the top of brine stripping tower 300, where it was stripped using steam heating to remove aniline. The steam addition ratio to the mass of the extracted brine was 0.2, and the temperature of the stripped brine was 105°C. Testing under these conditions showed that the total organic carbon (TOC) content in the stripped brine was approximately 32.6 ppm, and the total nitrogen (TN) content was approximately 3.0 ppm.

[0107] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then fed to the top of a brine oxidation stripping tower 400. The TOC molar ratio of sodium persulfate to the stripped brine is 2, and no second oxidant is added to the brine oxidation stripping tower 400. The brine oxidation stripping tower 400 is filled with packing material, consisting of upper, middle, and lower sections, and the packing material is not loaded with manganese or nickel nanoparticles. No sodium sulfite reducing agent is added above the bottom packing section of the brine oxidation stripping tower 400. The reboiler of the brine oxidation stripping tower 400 is not heated with steam, and nitrogen is not introduced into the reboiler for stripping.

[0108] After the above treatment, the final stripping brine contained approximately 9.5 ppm total organic carbon (TOC) and 2 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process, but the total nitrogen content is slightly high.

[0109] Example 2

[0110] This embodiment provides a method for deep treatment of waste brine from MDI production.

[0111] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1 The embodiment shown provides an MDI production waste brine deep treatment system 10.

[0112] The aniline used had a purity of 99.9 wt%, and the formaldehyde used contained 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde underwent condensation and transposition reactions sequentially, and then the waste brine was neutralized in neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture entered extraction tower 200 and underwent countercurrent extraction with aniline as the extractant. The extracted brine was then sent to the top of brine stripping tower 300, where it was stripped using steam heating to remove aniline. The steam addition ratio to the mass of the extracted brine was 0.2, and the temperature of the stripped brine was 105°C. Testing under these conditions showed that the total organic carbon (TOC) content in the stripped brine was approximately 32.6 ppm, and the total nitrogen (TN) content was approximately 3.0 ppm.

[0113] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then fed to the top of a brine oxidation stripping tower 400. The TOC molar ratio of sodium persulfate to the stripped brine is 2, and no second oxidant is added to the brine oxidation stripping tower 400. The brine oxidation stripping tower 400 is filled with packing material, consisting of upper, middle, and lower sections. The packing material is loaded with manganese and nickel nanoparticles, with the total loading of these nanoparticles accounting for 3 wt%. The manganese and nickel nanoparticles have the same mass, and their particle sizes are 30 nm ± 2 nm, respectively. No sodium sulfite reducing agent is added above the bottom packing section of the brine oxidation stripping tower 400. The reboiler of the brine oxidation stripping tower 400 is not heated with steam, and nitrogen is not introduced into the reboiler for stripping.

[0114] After the above treatment, the final stripping brine contained approximately 8.1 ppm total organic carbon (TOC) and 1.6 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process, but the total nitrogen content is slightly high.

[0115] Example 3

[0116] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, followed by neutralization in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0117] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then conveyed to the top of the brine oxidation stripping tower 400. The TOC molar ratio of sodium persulfate to the stripped brine is 2, and no second oxidant is added to the brine oxidation stripping tower 400. The brine oxidation stripping tower 400 is filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 3.5 wt%. The manganese and nickel nanoparticles have the same mass, and their particle sizes are 25 nm ± 2 nm, respectively. No sodium sulfite reducing agent is added above the bottom packing section of the brine oxidation stripping tower 400. Steam is introduced into the reboiler of the brine oxidation stripping tower 400 for heating. The steam addition ratio (mass ratio of steam to brine after stripping) is 0.1:1, and nitrogen is not introduced into the reboiler for stripping. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0118] After the above treatment, the final stripping brine contains approximately 6 ppm total organic carbon (TOC) and approximately 1.2 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0119] Example 4

[0120] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, followed by neutralization in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0121] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer and then fed to the top of a brine oxidation stripping tower 400. The TOC molar ratio of sodium persulfate to the stripped brine is 2, and no second oxidant is added to the brine oxidation stripping tower 400. The brine oxidation stripping tower 400 is filled with packing material loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 4 wt%, with the same mass for both manganese and nickel nanoparticles. The particle sizes of the manganese and nickel nanoparticles are 40 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added for reduction, converting the nitrate nitrogen and nitrite generated during oxidation into ammonium ions, which are further converted into ammonia gas under conditions of a 5 wt% NaOH solution at 100°C. The mass ratio of the added sodium sulfite to the oxidized brine is 0.0001:1. Steam is introduced into the reboiler of the brine oxidation stripping tower 400 for heating. The steam addition ratio (mass ratio of steam to stripped brine) is 0.05:1. Nitrogen gas is introduced into the tower bottom for stripping treatment. The volume of nitrogen introduced is the same as the volume of stripped brine, that is, the volume ratio of nitrogen to stripped brine is 1:1. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0122] After the above treatment, the final stripping brine contains approximately 6 ppm total organic carbon (TOC) and approximately 0.9 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0123] Example 5

[0124] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, followed by neutralization in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0125] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then conveyed to the top of the brine oxidation stripping tower 400. The molar ratio of the first oxidant, sodium persulfate, to the TOC of the stripped brine is 1. A second oxidant, sodium persulfate, is added to the brine oxidation stripping tower 400, and the molar ratio of the second oxidant, sodium persulfate, to the TOC of the stripped brine is also 1. That is, the molar ratio of the first oxidant to the second oxidant is 1:1. The brine oxidation stripping tower 400 is internally filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 5 wt%. The manganese and nickel nanoparticles have the same mass, and their particle sizes are 45 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added as a reducing agent to reduce the nitrate nitrogen and nitrite nitrogen produced during oxidation to ammonium ions, which are further converted into ammonia gas under conditions of 10 wt% NaOH solution and 90°C. The mass ratio of the added sodium sulfite to the mass of the oxidized brine is 0.0005:1. Steam is introduced into the reboiler of the brine oxidation stripping tower 400 for heating. The steam addition ratio (mass ratio of steam to brine after stripping) is 0.08:1. Nitrogen gas is introduced into the tower bottom for stripping treatment. The volume of nitrogen introduced is the same as the volume of brine after stripping, that is, the volume ratio of nitrogen to brine after stripping is 1:1. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0126] After the above treatment, the final stripping brine contains approximately 3.2 ppm total organic carbon (TOC) and 0.3 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0127] Example 6

[0128] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1 This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, followed by neutralization in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0129] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then conveyed to the top of the brine oxidation stripping tower 400. The TOC molar ratio of the first oxidant, sodium persulfate, to the stripped brine is 0.5. A second oxidant, sodium persulfate, is added to the brine oxidation stripping tower 400, and the TOC molar ratio of the second oxidant, sodium persulfate, to the stripped brine is 1.5. That is, the molar ratio of the first oxidant to the second oxidant is 1:3. The brine oxidation stripping tower 400 is internally filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles, with the total loading of these nanoparticles and nickel nanoparticles accounting for 1 wt%. The manganese and nickel nanoparticles have the same mass, and their particle sizes are 15 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added as a reducing agent to reduce the nitrate and nitrite nitrogen produced during oxidation to ammonium ions, which are further converted into ammonia gas under conditions of 1 wt% NaOH solution and 120°C. The mass ratio of the added sodium sulfite to the mass of the oxidized brine is 0.0008:1. The reboiler of the brine oxidation stripping tower 400 is heated by steam (the mass ratio of steam to stripped brine is 0.06:1), and nitrogen is introduced into the reboiler for stripping treatment, wherein the volume ratio of nitrogen to stripped brine is 0.5:1. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0130] After the above treatment, the final stripping brine contains approximately 8.5 ppm total organic carbon (TOC) and 1.2 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0131] Example 7

[0132] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1 This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, followed by neutralization in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0133] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then conveyed to the top of the brine oxidation stripping tower 400. The molar ratio of the first oxidant, sodium persulfate, to the TOC of the stripped brine is 0.5. A second oxidant, sodium persulfate, is added to the brine oxidation stripping tower 400, and the molar ratio of the second oxidant, sodium persulfate, to the TOC of the stripped brine is 1. That is, the molar ratio of the first oxidant to the second oxidant is 1:2. The brine oxidation stripping tower 400 is internally filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 2.5 wt%. The mass of the manganese nanoparticles and nickel nanoparticles is the same, and their particle sizes are 35 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added as a reducing agent to reduce the nitrate nitrogen and nitrite nitrogen produced during oxidation to ammonium ions, which are further converted into ammonia gas under conditions of 1 wt% NaOH solution and 120°C. The mass ratio of the added sodium sulfite to the mass of the oxidized brine is 0.0005:1. Steam is introduced into the reboiler of the brine oxidation stripping tower 400 for heating. The steam addition ratio (mass ratio of steam to brine after stripping) is 0.07:1. Nitrogen is introduced into the tower bottom for stripping treatment. The volume ratio of nitrogen to brine after stripping is 2:1. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0134] After the above treatment, the final stripping brine contains approximately 5.5 ppm total organic carbon (TOC) and 0.8 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0135] Example 8

[0136] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1 This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, followed by neutralization in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0137] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer and then conveyed to the top of the brine oxidation stripping tower 400. The molar ratio of the first oxidant, sodium persulfate, to the TOC of the stripped brine is 1. A second oxidant, sodium hypochlorite, is added to the brine oxidation stripping tower 400, with the molar ratio of the second oxidant, sodium hypochlorite, to the TOC of the stripped brine also being 1. That is, the molar ratio of the first oxidant to the second oxidant is 1:1. The brine oxidation stripping tower 400 is internally filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 2 wt%. The manganese and nickel nanoparticles have the same mass, and their particle sizes are 20 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added as a reducing agent to reduce the nitrate nitrogen and nitrite nitrogen produced during oxidation to ammonium ions, which are further converted into ammonia gas under conditions of 3 wt% NaOH solution and 110°C. The mass ratio of the added sodium sulfite to the mass of the oxidized brine is 0.0001:1. Steam is introduced into the reboiler of the brine oxidation stripping tower 400 for heating. The steam addition ratio (mass ratio of steam to brine after stripping) is 0.1:1, and nitrogen is introduced into the tower bottom for stripping treatment. The volume of nitrogen introduced is the same as the volume of brine after stripping, that is, the volume ratio of nitrogen to brine after stripping is 1.5:1. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0138] After the above treatment, the final stripping brine contains approximately 5.1 ppm total organic carbon (TOC) and 0.7 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0139] Example 9

[0140] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, followed by neutralization in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0141] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then conveyed to the top of the brine oxidation stripping tower 400. The TOC molar ratio of the first oxidant, sodium persulfate, to the stripped brine is 1. A second oxidant, sodium hypochlorite, is added to the brine oxidation stripping tower 400, and the TOC molar ratio of the second oxidant, sodium hypochlorite, to the stripped brine is 3. That is, the molar ratio of the first oxidant to the second oxidant is 1:3. The brine oxidation stripping tower 400 is internally filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 4.5 wt%. The mass of the manganese nanoparticles and nickel nanoparticles is the same, and their particle sizes are 40 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added as a reducing agent to reduce the nitrate nitrogen and nitrite nitrogen produced during oxidation to ammonium ions, which are further converted into ammonia gas under conditions of 0.5 wt% NaOH solution and 120°C. The mass ratio of the added sodium sulfite to the mass of the oxidized brine is 0.0002:1. Steam is introduced into the reboiler of the brine oxidation stripping tower 400 for heating. The steam addition ratio (mass ratio of steam to stripped brine) is 0.075:1. Nitrogen gas is introduced into the tower bottom for stripping treatment. The volume of nitrogen introduced is the same as the volume of stripped brine, that is, the volume ratio of nitrogen to stripped brine is 0.8:1. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0142] After the above treatment, the final stripping brine contains approximately 3.5 ppm total organic carbon (TOC) and 0.5 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0143] Example 10

[0144] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1 This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.4 wt%, and the formaldehyde used contains 300 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, and the waste brine is neutralized in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 and undergoes countercurrent extraction with the extractant aniline. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam for stripping to remove aniline from the brine. The steam addition ratio is 0.2, and the temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 97.8 ppm, and the total nitrogen (TN) content is approximately 9.5 ppm.

[0145] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then conveyed to the top of the brine oxidation stripping tower 400. The TOC molar ratio of the first oxidant, sodium persulfate, to the stripped brine is 1. A second oxidant, sodium hypochlorite, is added to the brine oxidation stripping tower 400, and the TOC molar ratio of the second oxidant, sodium hypochlorite, to the stripped brine is 3. That is, the molar ratio of the first oxidant to the second oxidant is 1:3. The brine oxidation stripping tower 400 is internally filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 1 wt%. The manganese and nickel nanoparticles have the same mass, and their particle sizes are 15 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added as a reducing agent to reduce the nitrate nitrogen and nitrite nitrogen produced during oxidation to ammonium ions, which are further converted into ammonia gas under conditions of 6 wt% NaOH solution and 105°C. The mass ratio of the added sodium sulfite to the mass of the oxidized brine is 0.001:1. The reboiler of the brine oxidation stripping tower 400 is not heated by steam, but by nitrogen gas for stripping. The volume of nitrogen gas introduced is the same as the volume of the stripped brine, that is, the volume ratio of nitrogen gas to stripped brine is 1:1. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0146] After the above treatment, the final stripping brine contains approximately 12 ppm total organic carbon (TOC) and 3 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0147] Example 11

[0148] The deep treatment method for MDI production waste brine in this embodiment adopts... Figure 1 This embodiment illustrates a deep treatment system 10 for MDI production waste brine. The aniline used has a purity of 99.4 wt%, and the formaldehyde used contains 300 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, and the waste brine is neutralized in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 and undergoes countercurrent extraction with the extractant aniline. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is heated by steam to remove aniline from the brine. The steam originates from the top gas phase of the oxidative stripping tower. The temperature of the stripped brine is 105°C. Testing under these conditions shows that the total organic carbon (TOC) content in the stripped brine is approximately 97.8 ppm, and the total nitrogen (TN) content is approximately 9.5 ppm.

[0149] The stripped brine is thoroughly mixed with the first oxidant, sodium persulfate, at 105°C using a static mixer, and then conveyed to the top of the brine oxidation stripping tower 400. The TOC molar ratio of the first oxidant, sodium persulfate, to the stripped brine is 1. A second oxidant, sodium hypochlorite, is added to the brine oxidation stripping tower 400, and the TOC molar ratio of the second oxidant, sodium hypochlorite, to the stripped brine is 3. That is, the molar ratio of the first oxidant to the second oxidant is 1:3. The brine oxidation stripping tower 400 is internally filled with packing material, which consists of three sections: upper, middle, and lower. The packing material is loaded with manganese and nickel nanoparticles. The total loading of the nanoparticles and nickel nanoparticles in the packing material accounts for 0.8 wt%. The mass of the manganese nanoparticles and nickel nanoparticles is the same, and their particle sizes are 12 nm ± 2 nm, respectively. Above the bottom packing section of the brine oxidation stripping tower 400, sodium sulfite is added as a reducing agent to reduce the nitrate nitrogen and nitrite nitrogen produced during oxidation to ammonium ions, which are further converted into ammonia gas under conditions of 5.5 wt% NaOH solution and 115°C. The mass ratio of the added sodium sulfite to the mass of the oxidized brine is 0.001:1. Steam is introduced into the reboiler of the brine oxidation stripping tower 400 for heating. The steam addition ratio (mass ratio of steam to brine after stripping) is 0.1:1. Nitrogen gas is introduced into the tower bottom for stripping treatment. The volume of nitrogen introduced is the same as the volume of brine after stripping, that is, the volume ratio of nitrogen gas to brine after stripping is 1:1. Nitrogen gas is introduced into the tower bottom for stripping treatment. The gas phase at the top of the oxidation stripping tower is returned to the brine stripping tower 300 for use.

[0150] After the above treatment, the final stripping brine contains approximately 4 ppm total organic carbon (TOC) and approximately 0.5 ppm total nitrogen (TN). The TOC content of this brine meets the requirements for reuse in the ion-exchange membrane caustic soda production process.

[0151] Comparative Example 1

[0152] like Figure 1 The process flow for preparing diamines and polyamines is shown. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, and the waste brine is neutralized in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 for countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is stripped using steam heating to remove aniline from the brine. The steam addition ratio to the mass of the extracted brine is 0.2, and the temperature of the stripped brine is 105°C. Testing under these conditions revealed that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm. These values ​​do not meet the requirements for direct reuse in the ion-exchange membrane caustic soda production process.

[0153] Comparative Example 2

[0154] like Figure 1 The process flow for preparing diamines and polyamines is shown. The aniline used has a purity of 99.9 wt%, and the formaldehyde used contains 50 ppm of carboxylic acid impurities. Under hydrochloric acid catalysis, aniline and formaldehyde undergo sequential condensation and transposition reactions, and the waste brine is neutralized in a neutralization unit 100 to obtain a mixture containing diphenylmethane polyamine and neutralized brine. This mixture enters an extraction tower 200 and undergoes countercurrent extraction with aniline as the extractant. The extracted brine is then transported to the top of a brine stripping tower 300. The tower bottom is stripped using steam heating to remove aniline from the brine. The steam addition ratio to the mass of the extracted brine is 0.2, and the temperature of the stripped brine is 105°C. Testing under these conditions revealed that the total organic carbon (TOC) content in the stripped brine is approximately 32.6 ppm, and the total nitrogen (TN) content is approximately 3.0 ppm.

[0155] The stripped brine is thoroughly mixed with sodium hypochlorite at 105°C using a static mixer and then fed to the top of a brine oxidation stripping tower 400. The TOC molar ratio of sodium hypochlorite to the stripped brine is 5, and no second oxidant is added to the brine oxidation stripping tower 400. The brine oxidation stripping tower 400 is filled with packing material, which consists of upper, middle, and lower sections. No manganese or nickel nanoparticles are loaded onto the packing material. No sodium sulfite reducing agent is added above the bottom packing section of the brine oxidation stripping tower 400. The reboiler of the brine oxidation stripping tower 400 is not heated with steam, and nitrogen is not introduced into the reboiler for stripping.

[0156] After the above treatment, the final stripping brine contains approximately 25 ppm total organic carbon (TOC) and 2.5 ppm total nitrogen (TN). These brine parameters do not meet the reuse requirements and cannot be directly reused in the ion-exchange membrane caustic soda production process.

[0157] Through extensive experimental research, the inventors of this application discovered that, for high-salt wastewater systems, adding an appropriate proportion of persulfate can cause organic compounds such as amines of phenols / aromatic amines to undergo only "limited ring-opening" to generate benzoquinones in high-temperature, high-alkaline brine, rather than complete mineralization. Further research revealed that these benzoquinones possess stripping properties and can be directly removed by stripping towers, reducing the total organic carbon (TOC) of the brine by approximately 30%. Conventional oxidation towers, however, cannot remove benzoquinones and must consume more oxidant to achieve partial deep mineralization. Furthermore, it was found that adding the oxidant in stages to the packing material ensures a suitable concentration of free radicals throughout the TOC oxidation process, guaranteeing mineralization efficiency and overcoming the defects of one-step oxidant addition, such as instantaneous depletion, insufficient free radical chain transfer, and incomplete oxidation in the latter half of the process. The residual organic matter in the brine after benzoquinone removal can be further decomposed into carbon dioxide by oxidants such as sodium hypochlorite. The nitrate / nitrite nitrogen generated from the oxidative decomposition of nitrogen-containing organic matter is reduced to ammonium ions by sodium sulfite. Under the alkaline environment of the brine itself, the ammonium ions are converted into ammonia gas, which is then removed through nitrogen and steam stripping in the bottom of the distillation column. Through this process, the TOC content of the brine can be reduced to below 10 ppm and the TN content to below 1 ppm, meeting the requirements of the ion-exchange membrane caustic soda production process.

[0158] Compared with the prior art, the technical solution provided in this application has the following beneficial effects:

[0159] (1) Overcoming the technical prejudice of low oxidation efficiency in high-salt environments: Through the synergistic catalysis of loaded metal nanofillers and segmented addition of oxidants, a dual oxidation system of "sulfate radicals + active chlorine" is formed. With the minimum addition of oxidants, the TOC content of the oxidized brine can be reduced by 50%.

[0160] (2) Achieving synergistic effects through the coupling of oxidation and stripping: Oxidation and stripping are integrated into the same tower. Volatile intermediates generated during oxidation are immediately stripped away by the rising steam and nitrogen from the tower bottom, breaking the equilibrium limitation of the oxidation reaction and allowing recalcitrant organic matter to be continuously oxidized and decomposed. This improves the removal efficiency of TOC from brine without increasing additional steam energy consumption.

[0161] (3) Significantly relaxed raw material requirements: Even with the purity of upstream aniline relaxed from 99.9% to 99.4% and the carboxylic acid impurities in formaldehyde relaxed from 100ppm to 500ppm, the reuse standard can still be stably met, reducing the impurity removal cost of upstream raw materials and improving the flexibility of production operations.

[0162] (4) Significantly reduce operating energy consumption: The high-temperature gas phase at the top of the oxidation stripping tower is returned to the bottom of the brine stripping tower 300 as a heat source, and the brine stripping tower 300 does not need to be supplied with additional steam.

[0163] (5) Solving the safety hazards of nitrogen-containing organic matter removal: Through the synergistic effect of sodium sulfite reduction and alkaline stripping, the entire process of "oxidation-reduction-stripping denitrification" is completed in one tower, maximizing the TN removal rate and eliminating the explosion risk of nitrogen trichloride.

[0164] (6) The brine treatment technology provided in this application has the advantages of high treatment efficiency, low operating cost and simple process flow. It is not only suitable for the treatment of waste brine generated in the MDI production process, but can also be widely used in other deep treatment scenarios of wastewater containing medium and low concentrations of organic matter.

[0165] In the above embodiments, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions in other embodiments.

[0166] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0167] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims, and the specification and drawings can be used to interpret the content of the claims.

Claims

1. A deep treatment system for MDI production waste brine, characterized in that, The system includes a neutralization unit, an extraction tower, a brine stripping tower, and a brine oxidation stripping tower. The neutralization unit is connected to the extraction tower, the extraction tower is connected to the brine stripping tower, and the brine stripping tower is connected to the brine oxidation stripping tower. The neutralization unit is used to connect to an MDI production reactor to collect waste brine generated from the MDI production reactor. The neutralization unit is also used to neutralize the waste brine to obtain a mixture containing diphenylmethane polyamine and neutralized brine. The extraction tower is used to extract the mixture to obtain extracted brine. The brine stripping tower is used to strip the extracted brine to obtain stripped brine. The brine oxidation stripping tower is used to oxidize the stripped brine to obtain oxidized brine.

2. The MDI production waste brine deep treatment system according to claim 1, characterized in that, It also meets at least one of the following conditions: (1) It also includes a first heat exchanger and a first circulation pipe. The bottom of the brine stripping tower is circulated through the first circulation pipe. The cold flow channel of the first heat exchanger is connected to the first circulation pipe. The hot flow channel of the first heat exchanger is used to introduce steam. (2) It also includes a second heat exchanger and a second circulation pipe. The bottom of the brine oxidation stripping tower is circulated through the second circulation pipe. The cold flow channel of the second heat exchanger is connected to the second circulation pipe, and the hot flow channel of the second heat exchanger is used to introduce steam.

3. The MDI production waste brine deep treatment system according to claim 1, characterized in that, The top of the brine oxidation stripping tower is connected to the bottom of the brine stripping tower, and is used to reflux the gas phase in the brine oxidation stripping tower back into the brine stripping tower.

4. The MDI production waste brine deep treatment system according to any one of claims 1 to 3, characterized in that, It also satisfies at least one of the following conditions: (1) The extraction tower is provided with an extractant interface for inputting extractant; (2) The brine oxidation stripping tower is provided with an oxidant interface for oxidant input, a reducing agent interface for reducing agent input, and a stripping medium interface for stripping medium input.

5. The MDI production waste brine deep treatment system according to any one of claims 1 to 3, characterized in that, The brine oxidation stripping tower is equipped with multiple sections of packing material loaded with at least one metal nanoparticle selected from iron, cobalt, manganese, and nickel. Optionally, the particle size of the metal nanoparticles is 10 nm to 50 nm; Optionally, the loading of the metal nanoparticles in the filler is 0.5wt% to 5wt%.

6. A method for deep treatment of MDI production waste brine, characterized in that, Includes the following steps: The waste brine generated during the MDI production process was neutralized to obtain a mixture containing diphenylmethane polyamine and neutralized brine; The mixture is subjected to extraction treatment to obtain extractable brine; The extracted brine is subjected to stripping treatment to remove diphenylmethane polyamine and extractant from the extracted brine, resulting in stripped brine. Furthermore, the stripped brine is subjected to oxidative stripping treatment to obtain oxidized brine.

7. The method for deep treatment of MDI production waste brine according to claim 6, characterized in that, The oxidative stripping treatment includes the following steps: The stripped brine is subjected to a first oxidation treatment using a first oxidant; the brine subjected to the first oxidation treatment is subjected to a second oxidation treatment using a second oxidant to obtain oxidized brine. In addition, steam and stripping media are introduced to remove volatile organic intermediates and ammonia generated by the first oxidation treatment and the second oxidation treatment.

8. The method for deep treatment of MDI production waste brine according to claim 7, characterized in that, It also satisfies at least one of the following conditions: (1) It also includes the following steps: after the second oxidation treatment, a reducing agent is added to reduce the nitrate nitrogen and nitrite nitrogen generated by oxidation to ammonium ions, and convert them into ammonia gas under alkaline high temperature conditions; Optionally, the alkaline high-temperature conditions satisfy the following conditions: in a NaOH solution and / or KOH solution with a concentration of 0.1wt%~10wt%, the temperature is 90℃~120℃; Optionally, the reducing agent includes sodium sulfite; Optionally, the mass ratio of the added reducing agent to the oxidized brine is (0.0001~0.001):1; (2) The mass ratio of steam introduced after the second oxidation treatment to the brine after stripping is (0.05~0.1):1; (3) The volume ratio of the stripping medium introduced after the second oxidation treatment to the stripped brine is (0.5~2):1; (4) Control the gas phase after the second oxidation treatment to return to the stripping treatment step as a heat source; (5) Control the TOC of the effluent after oxidation to be ≤10ppm and TN to be ≤1ppm, and control the effluent after oxidation to be recycled to the ion-exchange membrane caustic soda production process.

9. The method for deep treatment of MDI production waste brine according to claim 7 or 8, characterized in that, It also satisfies at least one of the following conditions: (1) The alkaline solution used in the neutralization reaction includes one or both of NaOH and KOH; (2) The extractant used in the extraction process includes one or more of aniline, toluene, benzene, and chlorobenzene; (3) The first oxidant includes persulfate; (4) The second oxidant includes one or more of persulfate, sodium hypochlorite, hydrogen peroxide, and ozone; (5) The molar ratio of the first oxidant to the TOC in the stripped brine is (0.5~4):1; Optionally, the molar ratio of the first oxidant to the TOC in the stripped brine is (1~3):1; (6) The molar ratio of the second oxidant to the TOC in the stripped brine is (1~5):1; (7) The molar ratio of the first oxidant to the second oxidant is 1:(1~3).

10. The method for deep treatment of MDI production waste brine according to any one of claims 7 to 9, characterized in that, It also satisfies at least one of the following conditions: (1) The TOC content of the stripped brine obtained after the stripping treatment is controlled to be 20ppm~200ppm; (2) The deep treatment method for MDI production waste brine adopts the deep treatment system for MDI production waste brine as described in any one of claims 1 to 5.

Images