Method for reducing TOC (total organic carbon) of waste brine generated in DAM (diacrylamide) production process

Abstract

The invention provides a method for reducing TOC (total organic carbon) of waste brine generated in a DAM (diphenylmethane) production process, which comprises the following steps: (1) in the presence of an acid catalyst, carrying out condensation reaction, transposition rearrangement reaction and acid-base neutralization reaction on aniline and formaldehyde to obtain a diamine and polyamine brine phase containing diphenylmethane series and an organic phase; (2) carrying out extraction, steam stripping and oxidation treatment on the saline water phase to obtain waste saline water; the organic phase is purified and refined to obtain diphenylmethane diamine and polyamine; wherein the content of phenol in the aniline in the step (1) is not higher than 15 ppm, and the total content of organic impurities is not higher than 200 ppm. According to the method disclosed by the invention, the TOC content in the waste brine is reduced to 10ppm, and the requirement of recycling chlor-alkali is met.

Description

Technical Field

[0001] This invention relates to the field of industrial wastewater treatment technology, specifically to a method for reducing the total organic matter (TOC) of waste brine generated during the DAM production process. Background Technology

[0002] DAM (diphenylmethane series diamines and polyamines) is an important precursor for polyurethanes, particularly for the preparation of diphenylmethane diisocyanates and polyamines.

[0003] Phenylmethane polyisocyanates (collectively known as MDI). The preparation method of DAM is well-known, typically involving the reaction of aniline with hydrochloric acid to produce benzene.

[0004] Amine hydrochloride was first produced, and then formaldehyde was added to the reactor to generate DAM hydrochloride. The resulting product was obtained through neutralization, water washing, and separation of the organic and aqueous phases.

[0005] The crude DAM and organic waste brine are used to refine the crude DAM to obtain DAM.

[0006] The neutralization process generates a large amount of waste brine, which contains organic matter such as amines, trace amounts of acids, and phenols. To achieve the reuse of this waste brine in chlor-alkali production, it is necessary to control...

[0007] The TOC content of waste brine. Currently, DAM production processes typically employ pretreatment methods such as extraction and stripping to reduce organic matter in waste brine. For example, patent ZL200710013817.2 discloses a method for continuously extracting diamines and polyamines from brine, specifically the diaminodiphenylmethane series. This extraction process removes polyamines from the brine. Additionally, some patents disclose methods for the deep reprocessing of waste brine. For instance, patent CN110743623A discloses a method for the deep catalytic oxidation treatment of MDA waste brine, where the pH of the brine is adjusted, and an oxidant is added...

[0008] The waste brine is then treated and then further oxidized by contacting a catalytic oxidation catalyst to obtain deeply treated brine.

[0009] Current literature and patent publications on advanced brine treatment processes generally require control of the content of individual impurity components at the formaldehyde and aniline feedstock levels.

[0010] Only then can the TOC of brine be stably met. However, controlling impurities at the raw material end increases costs. Therefore, it is necessary to further study the types of impurities that affect TOC content and to pretreat them before the raw materials are introduced, thereby greatly reducing the treatment cost and difficulty of waste brine. Summary of the Invention

[0011] Therefore, in order to reduce the TOC content of waste brine generated during DAM production, this invention provides a method for reducing the TOC of waste brine. This method involves controlling the phenol content in aniline to ≤15ppm, thereby reducing the refining cost of raw aniline and the difficulty of waste brine treatment, thus achieving a reduction in TOC.

[0012] The purpose of this study is to reduce the TOC content of waste brine to ≤10ppm.

[0013] To achieve this objective, the present invention adopts the following technical solution:

[0014] This invention provides a method for reducing the total organic matter (TOC) of waste brine generated during DAM production, comprising the following steps:

[0015] (1) In the presence of an acidic catalyst, aniline reacts with formaldehyde through a condensation reaction, a rearrangement reaction, and an acid-base neutralization reaction to obtain a product containing...

[0016] Diphenylmethane-based diamine and polyamine salt water phases and organic phases;

[0017] (2) The brine phase is subjected to extraction, stripping and oxidation to obtain waste brine; the organic phase is purified and refined to obtain dibenzene.

[0018] Diamines and polyamines based on methylmethane;

[0019] Wherein, the phenol content in the aniline described in step (1) is not higher than 15 ppm, preferably not higher than 12 ppm, more preferably not higher than 10 ppm; including but not limited to a range of 0.1 ppm, 0.3 ppm, 0.5 ppm, 0.8 ppm, 1 ppm, 2 ppm, 3 ppm, 4 ppm, 6 ppm, 7 ppm, 8 ppm, 9 ppm, 11 ppm, 13 ppm, 14 ppm, or any two of these ranges. Preferably, the phenol content in the aniline is within the range of

[0020] The range is 0.1ppm-15ppm. The total content of organic impurities is not higher than 200ppm, including but not limited to 10ppm, 20ppm, 40ppm, 60ppm, 80ppm, 100ppm, 120ppm, 140ppm, 160ppm, 180ppm or any combination thereof.

[0021] In the production process of DAM, the researchers of this invention discovered that the raw material aniline contains phenol impurities, which are present during the neutralization reaction.

[0022] Phenolates enter the wastewater in their phenolic form and are difficult to remove through subsequent extraction, stripping, and oxidation treatments, ultimately resulting in the discharge of wastewater...

[0023] TOC levels are elevated in aniline. Therefore, it is necessary to control the phenol content in aniline.

[0024] The phenol content in aniline can be controlled using some conventional processing methods in the art, such as distillation, adsorption with alkaline solid adsorbents or alkaline extraction. As a preferred option, aniline is first treated with an alkaline solid adsorbent or alkaline solution to obtain the raw material aniline for the production of DAM.

[0025] As a preferred embodiment, in the method of the present invention, the alkaline solid adsorbent is one or more of amino-functionalized adsorbents, alkali-activated activated carbon, and alkaline earth metal oxides, preferably amino-functionalized adsorbents, and more preferably one or more of isopropylaminopolystyrene adsorbents (ABN), amino resins, and amino silica gel adsorbents. The alkaline solution is one or more of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, and aqueous lithium hydroxide solution, preferably aqueous sodium hydroxide solution.

[0026] In some specific embodiments, an alkaline solid adsorbent may be used to adsorb and treat aniline in a fixed-bed reactor. The adsorption temperature is 5-60°C, preferably 15-35°C, including but not limited to 6°C, 10°C, 14°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, or any combination thereof. The adsorption space velocity is 0.1-2 h⁻¹. -1 Preferably 0.4-1h -1 including but not limited to 0.3h -1 0.5h -1 0.8h -1 1.2h -1 1.4h -1 1.6h -1 1.8h -1 The extraction temperature can be any range of two or more. Alternatively, phenol can be extracted by counter-current flow of alkali and aniline in an extraction tower, with a volume ratio of alkali to aniline of 0.2-2, preferably 0.4-1, including but not limited to 0.3, 0.5, 0.8, 1.2, 1.4, 1.6, 1.8, or any range of two or more thereof. The extraction temperature is 5-30°C, preferably 15-25°C, including but not limited to 6°C, 8°C, 10°C, 12°C, 14°C, 17°C, 20°C, 22°C, 24°C, 26°C, 28°C, or any range of two or more thereof. The concentration of the alkali solution is 100-5000 ppm, preferably 200-1000 ppm, including but not limited to 150 ppm, 300 ppm, 500 ppm, 700 ppm, 900 ppm, 1200 ppm, 1600 ppm, 2000 ppm, 3000 ppm, 4000 ppm, 5000 ppm, or any combination thereof. Preferably, the water source for preparing the alkali solution is selected from the wastewater produced by the plant itself, without generating any new wastewater.

[0027] Phenol reacts with the basic groups in the alkaline solid adsorbent and remains in the adsorbent. After adsorption saturation, it is regenerated using a strongly alkaline substance. Phenol reacts with the alkaline solution to separate phases. The aniline phase is used as the raw material aniline for the production of DAM, while the aqueous phase is treated using the existing wastewater treatment process.

[0028] In the method of this invention, the molar ratio of formaldehyde to aniline, the raw material for producing DAM, is 0.3-0.6, including but not limited to 0.4, 0.45, 0.5, or any combination thereof. The formaldehyde contains organic impurities at a concentration below 500 ppm, including but not limited to 10 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 400 ppm, 450 ppm, or any combination thereof. The molar ratio of the acidic catalyst to aniline, the raw material for producing DAM, is 0.1-0.5. Preferably, the acidic catalyst is one or more of hydrochloric acid aqueous solution, phosphoric acid aqueous solution, and sulfuric acid aqueous solution, more preferably a hydrochloric acid aqueous solution with a mass percentage concentration of 25-37%. The acidic catalyst is mixed with aniline to form an aniline salt, which is then mixed with formaldehyde for a condensation reaction to obtain the condensation reaction product. In some specific embodiments, the condensation reaction is carried out at 40-80°C for 1-3 hours; then, the obtained condensation reaction product undergoes a rearrangement reaction to obtain the transposition reaction product. In some specific embodiments, the transposition rearrangement reaction is carried out at 80-120°C for 1-5 hours. The neutralization reaction is carried out at 90-110°C with a base excess ratio of 1.01-1.20, where the base excess ratio is the molar ratio of base in the alkaline solution of the neutralization reaction to the added acidic catalyst. The alkaline solution used is one or more of aqueous solutions of sodium hydroxide, potassium hydroxide, and lithium hydroxide, preferably an aqueous solution of sodium hydroxide with a mass percentage concentration of 30-55%.

[0029] In the method of this invention, the brine phase is extracted with an extractant to obtain an extracted brine phase. The extracted brine phase is then stripped to obtain a stripped brine phase. The stripped brine phase is further oxidized to obtain the waste brine. In some specific embodiments, extraction is performed at a volume ratio of extractant to brine phase of 0.2-0.8 (hereinafter referred to as the "extraction ratio"). Specifically, the brine phase and extractant are flowed counter-currently in an extraction tower to ensure sufficient extraction. The extraction temperature is 80-110°C, and the extractant is one or both of aniline and toluene, preferably aniline. The obtained extracted brine phase is then stripped in a stripping tower. The temperature of the stripping tower can be maintained at 95-110°C. As is well known to those skilled in the art, 2 kg pressure steam (hereinafter referred to as 2S steam) can be used for stripping. The obtained stripped brine phase is then oxidized in an oxidation tower for oxidation. The residence time is 20-300 min, the oxidation temperature is 40-70°C, and the pH of the waste brine to be oxidized is 4-13. The oxidant is preferably one or more of chlorine-containing oxidants, ozone, and hydrogen peroxide. Preferably, the chlorine-containing oxidant is selected from one or more of sodium hypochlorite, chlorine, and sodium perchlorate. Preferably, when the oxidant is a chlorine-containing oxidant, the molar ratio of the oxidant to the TOC in the waste brine to be oxidized is 2-5, based on available chlorine.

[0030] The above technical solution has the following beneficial effects:

[0031] The present invention provides a method for reducing the TOC (total organic carbon) content of waste brine generated during DAM production by controlling the phenol content in aniline.

[0032] By treating the waste brine to ≤15ppm, the impurity content of the upstream aniline raw material can be relaxed (for example, the phenol content in the raw aniline can be no more than 50ppm and can be used in this invention), and the treatment difficulty of the waste brine can be reduced, so that the TOC content of the waste brine is reduced to ≤10ppm, which meets the requirements for chlor-alkali reuse. Detailed Implementation

[0033] To facilitate understanding of the present invention, the invention will be further described below with reference to embodiments. It should be understood that the following embodiments are merely for illustrative purposes.

[0034] A better understanding of the present invention does not mean that the present invention is limited to the following embodiments.

[0035] Where specific experimental steps or conditions are not specified in the embodiments, the corresponding conventional experimental steps or conditions in this technical field can be followed.

[0036] This is acceptable. All reagents used in the examples are conventional reagents in the art. Unless otherwise specified, the following detection methods or experimental methods are all within the scope of the art.

[0037] Domain technicians are familiar with conventional technical means based on the existing technologies they possess.

[0038] The following columns contain information on the source of raw materials:

[0039] Isopropylaminopolystyrene adsorbent (ABN): Innocare Technology Co., Ltd.;

[0040] KOH-activated activated carbon: Yantai General Activated Carbon Co., Ltd.

[0041] Aniline: Wanhua Chemical Group Co., Ltd.;

[0042] Formaldehyde: Wanhua Chemical Group Co., Ltd.;

[0043] Hydrochloric acid: Wanhua Chemical Group Co., Ltd.;

[0044] Sodium hydroxide: Wanhua Chemical Group Co., Ltd.;

[0045] Sodium hypochlorite solution: Wanhua Chemical Group Co., Ltd.; Neutral resin XDA-1: Xi'an Lanxiao Technology New Materials Co., Ltd.

[0046] All other chemical reagents used in the method of this invention are conventional reagents in the art, and their purity is chemically pure or higher.

[0047] The following methods were used for detection in the following examples:

[0048] (1) Analytical method for impurities in aniline and formaldehyde: Quantitative determination was performed using external standard liquid chromatography. The analytical instrument was an Agilent LC-1200 Infinity Series. The method was as follows: 10 μL of aniline and formaldehyde sample was directly filtered and injected into the chromatographic column (Xselect RHSS T3 column).

[0049] The mobile phase consists of water and acetonitrile. The mobile phase gradient is 100% water for 0–10 min, then slowly transitions to 80% acetonitrile and 20% water for 10–40 min.

[0050] The flow rate was 1 ml / min, and the detection wavelength was 210 nm.

[0051] (2) TOC content analysis method in waste brine: The Jena N / C 2100S TOC analyzer was used for analysis. The sample was acidified and purged to remove CO2.

[0052] Example 1

[0053] In this embodiment, the phenol impurity content in aniline is 40 ppm, the total organic matter impurity content is 190 ppm, the mass concentration of formaldehyde aqueous solution is 40%, the total organic matter impurity content in formaldehyde is 400 ppm, the mass concentration of hydrochloric acid aqueous solution is 37%, and the mass concentration of sodium hydroxide aqueous solution is 30%. (1) Aniline is passed into a fixed-bed reactor containing isopropylamino polystyrene adsorbent (ABN), the adsorption temperature is 15℃, and the adsorption air...

[0054] 1 hour -1 This yields aniline, the raw material for producing DAM;

[0055] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 60°C for 1 hour. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.10, and the molar ratio of formaldehyde to aniline is 0.45.

[0056] The condensation reaction product was transferred to a transposition reactor, where a further transposition rearrangement reaction was carried out at 100°C for 1 hour under hydrochloric acid catalysis, yielding a product containing...

[0057] A mixture of diphenylmethane-based diamine hydrochloride and polyamine hydrochloride;

[0058] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.10. Then, a neutralization reaction was carried out at 100°C, and after separation, an organic phase and a brine phase were obtained.

[0059] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.2 and the temperature in the extraction tower is 110℃.

[0060] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 95°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0061] The pH of the obtained stripping brine was adjusted to 4, and then fed into the oxidation tower together with an 8% sodium hypochlorite aqueous solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 2. The oxidation temperature was 70℃ and the oxidation residence time was 150 min. The desired waste brine was obtained after oxidation.

[0062] Example 2

[0063] In this embodiment, the phenol impurity content in aniline is 40 ppm, the total organic matter impurity content is 190 ppm, the mass concentration of the formaldehyde aqueous solution is 25%, the total organic matter impurity content in formaldehyde is 400 ppm, the mass concentration of the hydrochloric acid aqueous solution is 40%, and the mass concentration of the sodium hydroxide aqueous solution is 50%. (1) Aniline is passed into a fixed-bed reactor containing KOH-activated activated carbon, the adsorption temperature is 25℃, and the adsorption space velocity is 0.7 h⁻¹. -1 This yields aniline, the raw material for producing DAM;

[0064] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 80°C for 2 hours. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.50, and the molar ratio of formaldehyde to aniline is 0.30.

[0065] The condensation reaction product was transferred to a transposition reactor and subjected to a transposition rearrangement reaction at 120°C for 5 hours under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0066] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.01. Then, a neutralization reaction was carried out at 95°C, and after separation, an organic phase and a brine phase were obtained.

[0067] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.5 and the temperature in the extraction tower is 95℃.

[0068] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 100°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0069] The pH of the obtained stripping brine was adjusted to 9, and then fed into the oxidation tower together with an 8% sodium hypochlorite aqueous solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 4. The oxidation temperature was 55℃ and the oxidation residence time was 300 min. The desired waste brine was obtained after oxidation.

[0070] Example 3

[0071] In this embodiment, the phenol impurity content in aniline is 40 ppm, the total organic matter impurity content is 190 ppm, the mass concentration of formaldehyde aqueous solution is 40%, the total organic matter impurity content in formaldehyde is 400 ppm, the mass concentration of hydrochloric acid aqueous solution is 30%, and the mass concentration of sodium hydroxide aqueous solution is 55%. (1) Aniline is passed into a fixed-bed reactor containing isopropylaminopolystyrene adsorbent (ABN), the adsorption temperature is 35℃, and the adsorption space velocity is 0.4 h. -1 This yields aniline, the raw material for producing DAM;

[0072] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 40°C for 3 hours. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.30, and the molar ratio of formaldehyde to aniline is 0.60.

[0073] The condensation reaction product was transferred to a transposition reactor and the transposition rearrangement reaction was continued at 80°C for 3 hours under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0074] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.20. Then, a neutralization reaction was carried out at 110°C. After separation, an organic phase and a brine phase were obtained.

[0075] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.8 and the temperature in the extraction tower is 80℃.

[0076] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 110°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0077] The pH of the obtained stripping brine was adjusted to 13, and then fed into the oxidation tower together with an 8% sodium hypochlorite aqueous solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 5. The oxidation temperature was 40℃ and the oxidation residence time was 20 min. The desired waste brine was obtained after oxidation.

[0078] Example 4

[0079] In this embodiment, the phenol impurity content in aniline is 40 ppm, the total organic matter impurity content is 190 ppm, the mass concentration of formaldehyde aqueous solution is 40%, the total organic matter impurity content in formaldehyde is 400 ppm, the mass concentration of hydrochloric acid aqueous solution is 37%, and the mass concentration of sodium hydroxide aqueous solution is 30%. (1) Aniline is introduced into the extraction tower from the top and subjected to counter-extraction with 500 ppm sodium hydroxide aqueous solution flowing in from the bottom of the tower. The volume ratio of sodium hydroxide aqueous solution to aniline is 1. The temperature in the extraction tower is 15°C. The alkaline wastewater produced at the top of the tower is sent to the existing self-generated wastewater treatment process for treatment. The raw material aniline for producing DAM is obtained at the bottom of the tower.

[0080] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 60°C for 1 hour. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.10, and the molar ratio of formaldehyde to aniline is 0.45.

[0081] The condensation reaction product was transferred to a transposition reactor and subjected to a further transposition rearrangement reaction at 100°C for 1 hour under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0082] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.10. Then, a neutralization reaction was carried out at 100°C, and after separation, an organic phase and a brine phase were obtained.

[0083] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.2 and the temperature in the extraction tower is 110℃.

[0084] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 95°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0085] The pH of the obtained stripping brine was adjusted to 4, and then fed into the oxidation tower together with an 8% sodium hypochlorite aqueous solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 2. The oxidation temperature was 70℃ and the oxidation residence time was 150 min. The desired waste brine was obtained after oxidation.

[0086] Example 5

[0087] In this embodiment, the phenol impurity content in aniline is 40 ppm, the total organic matter impurity content is 190 ppm, the mass concentration of formaldehyde aqueous solution is 25%, the total organic matter impurity content in formaldehyde is 400 ppm, the mass concentration of hydrochloric acid aqueous solution is 40%, and the mass concentration of sodium hydroxide aqueous solution is 50%. (1) Aniline is introduced into the extraction tower from the top and subjected to counter-extraction with 200 ppm sodium hydroxide aqueous solution flowing in from the bottom of the tower. The volume ratio of sodium hydroxide aqueous solution to aniline is 0.6, the temperature in the extraction tower is 20°C, and the alkaline wastewater produced at the top of the tower is sent to the existing self-generated wastewater treatment process for treatment. The raw material aniline for producing DAM is obtained at the bottom of the tower.

[0088] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 80°C for 2 hours. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.50, and the molar ratio of formaldehyde to aniline is 0.30.

[0089] The condensation reaction product was transferred to a transposition reactor and subjected to a transposition rearrangement reaction at 120°C for 5 hours under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0090] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.01. Then, a neutralization reaction was carried out at 95°C, and after separation, an organic phase and a brine phase were obtained.

[0091] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.5 and the temperature in the extraction tower is 95℃.

[0092] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 100°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0093] The pH of the obtained stripping brine was adjusted to 9, and then fed into the oxidation tower together with an 8% sodium hypochlorite aqueous solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 4. The oxidation temperature was 55℃ and the oxidation residence time was 300 min. The desired waste brine was obtained after oxidation.

[0094] Example 6

[0095] In this embodiment, the phenol impurity content in aniline is 40 ppm, the total organic matter impurity content is 190 ppm, the mass concentration of formaldehyde aqueous solution is 40%, the total organic matter impurity content in formaldehyde is 400 ppm, the mass concentration of hydrochloric acid aqueous solution is 30%, and the mass concentration of sodium hydroxide aqueous solution is 55%. (1) Aniline is introduced into the extraction tower from the top and subjected to counter-extraction with 1000 ppm sodium hydroxide aqueous solution flowing in from the bottom of the tower. The volume ratio of sodium hydroxide aqueous solution to aniline is 0.4, the temperature in the extraction tower is 25°C, and the alkaline wastewater produced at the top of the tower is sent to the existing self-generated wastewater treatment process for treatment. The raw material aniline for producing DAM is obtained at the bottom of the tower.

[0096] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 40°C for 3 hours. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.30, and the molar ratio of formaldehyde to aniline is 0.60.

[0097] The condensation reaction product was transferred to a transposition reactor and the transposition rearrangement reaction was continued at 80°C for 3 hours under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0098] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.20. Then, a neutralization reaction was carried out at 110°C. After separation, an organic phase and a brine phase were obtained.

[0099] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.8 and the temperature in the extraction tower is 80℃.

[0100] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 110°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0101] The pH of the obtained stripping brine was adjusted to 13, and then fed into the oxidation tower together with an 8% sodium hypochlorite aqueous solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 5. The oxidation temperature was 40℃ and the oxidation residence time was 20 min. The desired waste brine was obtained after oxidation.

[0102] Example 7

[0103] In this embodiment, the phenol impurity content in aniline is 40 ppm, the total organic matter impurity content is 190 ppm, the mass concentration of formaldehyde aqueous solution is 40%, the total organic matter impurity content in formaldehyde is 400 ppm, the mass concentration of hydrochloric acid aqueous solution is 30%, and the mass concentration of sodium hydroxide aqueous solution is 55%. (1) Aniline is fed into a distillation column, the pressure at the top of the column is controlled at 10 kPaA, the temperature at the top of the column is controlled at 112°C, the reflux ratio is controlled at 2.5, and the gas phase at the top of the column is cooled into a liquid phase by the top condenser and distilled out to obtain aniline as the raw material for producing DAM;

[0104] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 40°C for 3 hours. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.30, and the molar ratio of formaldehyde to aniline is 0.60.

[0105] The condensation reaction product was transferred to a transposition reactor and the transposition rearrangement reaction was continued at 80°C for 3 hours under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0106] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.20. Then, a neutralization reaction was carried out at 110°C. After separation, an organic phase and a brine phase were obtained.

[0107] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.8 and the temperature in the extraction tower is 80℃.

[0108] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 110°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0109] The pH of the obtained stripping brine was adjusted to 13 and then fed into the oxidation tower together with the sodium hypochlorite aqueous solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 5. The oxidation temperature was 40℃ and the oxidation residence time was 20 min. The desired waste brine was obtained after oxidation.

[0110] Comparative Example 1

[0111] In this comparative example, the phenol impurity content in aniline was 40 ppm, the total organic matter impurity content was 190 ppm, the mass concentration of formaldehyde aqueous solution was 25%, the total organic matter impurity content in formaldehyde was 400 ppm, the mass concentration of hydrochloric acid aqueous solution was 40%, and the mass concentration of sodium hydroxide aqueous solution was 50%. (1) Aniline was passed into a fixed-bed reactor containing XDA-1 resin, the adsorption temperature was 25℃, and the adsorption space velocity was 0.7 h⁻¹. -1 This yields aniline, the raw material for producing DAM;

[0112] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 80°C for 2 hours. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.50, and the molar ratio of formaldehyde to aniline is 0.30.

[0113] The condensation reaction product was transferred to a transposition reactor and subjected to a transposition rearrangement reaction at 120°C for 5 hours under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0114] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.01. Then, a neutralization reaction was carried out at 95°C, and after separation, an organic phase and a brine phase were obtained.

[0115] (3) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the extract brine phase; wherein the volume ratio of aniline to brine phase is 0.5 and the temperature in the extraction tower is 95℃.

[0116] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 100°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0117] The pH of the obtained stripping brine was adjusted to 9 and then introduced into the oxidation tower along with an aqueous sodium hypochlorite solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 4. The oxidation temperature was 55℃ and the oxidation residence time was 300 min. The desired waste brine was obtained after oxidation.

[0118] Comparative Example 2

[0119] In this comparative example, the phenol impurity content in aniline was 40 ppm, the total organic matter impurity content was 190 ppm, the mass concentration of formaldehyde aqueous solution was 25%, the total organic matter impurity content in formaldehyde was 400 ppm, the mass concentration of hydrochloric acid aqueous solution was 40%, and the mass concentration of sodium hydroxide aqueous solution was 50%. (1) Aniline was used directly as a raw material for the production of DAM without any treatment;

[0120] (2) The raw material for producing DAM, aniline, is mixed with hydrochloric acid aqueous solution in a static mixer to form aniline hydrochloride. Formaldehyde is then added to the mixture, and a condensation reaction is carried out in a reactor at 80°C for 2 hours. The molar ratio of hydrochloric acid aqueous solution (based on the molar amount of hydrochloric acid) to aniline is 0.50, and the molar ratio of formaldehyde to aniline is 0.30.

[0121] The condensation reaction product was transferred to a transposition reactor and subjected to a transposition rearrangement reaction at 120°C for 5 hours under hydrochloric acid catalysis to obtain a mixture containing diphenylmethane-based diamine hydrochloride and polyamine hydrochloride.

[0122] An aqueous solution of sodium hydroxide was added to the mixture above, with an alkali excess of 1.01. Then, a neutralization reaction was carried out at 95°C, and after separation, an organic phase and a brine phase were obtained.

[0123] (2) The brine phase is introduced into the extraction tower from the top and is counter-extracted with the aniline flowing in from the bottom of the tower to obtain the brine phase; wherein the volume ratio of aniline to brine phase is 0.5 and the temperature in the extraction tower is 95℃.

[0124] The resulting brine phase was passed into a stripping column and stripped under 2S steam (stripping ratio of 0.12). The top temperature of the stripping column was 100°C. Aniline was removed from the top of the column, and the stripped brine phase was produced at the bottom.

[0125] The pH of the obtained stripping brine was adjusted to 9 and then introduced into the oxidation tower along with an aqueous sodium hypochlorite solution. The molar ratio of available chlorine in the added sodium hypochlorite to TOC in the stripping brine was 4. The oxidation temperature was 55℃ and the oxidation residence time was 300 min. The desired waste brine was obtained after oxidation.

[0126] The content of aniline impurities in the raw material for DAM production obtained in step (1) and the content of TOC in the waste brine obtained in step (3) of the above embodiments and comparative examples are shown in Table 1 below.

[0127] Table 1. Results of Examples and Comparative Examples

[0128] Table 1

[0129]

[0130] As can be seen from the data in the table above, in the aniline mixture obtained in step (1) of each example for producing DAM, the phenol impurities in the aniline can be treated to a minimum.

[0131] <15ppm, so that the TOC content in the resulting waste brine is less than 10ppm.

[0132] As can be seen from the comparative examples, in Comparative Example 1, the use of neutral resin to treat aniline resulted in poor treatment of phenol impurities, leading to a TOC content in the resulting waste brine exceeding 10 ppm; in Comparative Example 2, aniline was not treated in any way, resulting in a TOC content in the resulting waste brine far exceeding 10 ppm.

[0133] The waste brine obtained in the comparative examples could not be reused in chlor-alkali systems.

[0134] Therefore, it can be seen that phenol in aniline is difficult to remove in subsequent processing steps, and the refining cost of aniline is relatively high. The treatment scheme of the present invention effectively reduces the difficulty of treating waste brine and can relax the impurity content of upstream aniline raw materials, thereby reducing the production cost of aniline. Finally, it should be noted that the above embodiments are only used to describe preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that various modifications and improvements made to the technical solutions of the present invention or equivalent substitutions should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for reducing the total organic matter (TOC) of waste brine generated during DAM production, characterized in that, Includes the following steps: (1) In the presence of an acidic catalyst, aniline and formaldehyde undergo condensation reaction, repositioning reaction, and acid-base neutralization reaction to obtain a diamine and polyamine salt water phase and an organic phase containing diphenylmethane. (2) The brine phase is subjected to extraction, stripping and oxidation to obtain waste brine; the organic phase is purified and refined to obtain diphenylmethane-based diamines and polyamines; Wherein, the phenol content in the aniline in step (1) is ≤15ppm, preferably, the phenol content in the aniline is in the range of 0.1ppm-15ppm, and the total content of organic impurities is ≤200ppm.

2. The method according to claim 1, characterized in that, In step (1), aniline is treated with an alkaline solid adsorbent or alkaline solution before reacting with formaldehyde.

3. The method according to claim 2, characterized in that, The alkaline solid adsorbent is one or more of amino-functionalized adsorbents, alkali-activated activated carbon, and alkaline earth metal oxides, preferably amino-functionalized adsorbents, more preferably isopropylaminopolystyrene adsorbents, amino resins, and amino silica gel adsorbents; and / or, the alkaline solution is one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and lithium hydroxide aqueous solution, preferably sodium hydroxide aqueous solution.

4. The method according to claim 2 or 3, characterized in that, The alkaline solid adsorbent is placed in a fixed-bed reactor, the adsorption temperature is 5-60℃, preferably 15-35℃, and the adsorption space velocity is 0.1-2 h⁻¹. -1 Preferably 0.4-1h -1 ; and / or, the alkali solution and aniline flow counter-currently in an extraction tower to extract phenol, wherein the volume ratio of the alkali solution to the aniline is 0.2-2, preferably 0.4-1, the extraction temperature is 5-30°C, preferably 15-25°C, and the concentration of the alkali solution is 100-5000 ppm, preferably 200-1000 ppm.

5. The method according to any one of claims 1-4, characterized in that, The molar ratio of formaldehyde to aniline in step (1) is 0.3-0.6; The formaldehyde contains less than 500 ppm of organic impurities.

6. The method according to any one of claims 1-5, characterized in that, The molar ratio of the acidic catalyst to aniline in step (1) is 0.1-0.5; wherein the acidic catalyst is one or more of hydrochloric acid aqueous solution, phosphoric acid aqueous solution, and sulfuric acid aqueous solution, preferably hydrochloric acid aqueous solution with a mass percentage concentration of 25-37%.

7. The method according to any one of claims 1-6, characterized in that, The condensation reaction in step (1) is carried out at 40-80°C for 1-3 hours, and / or the rearrangement reaction is carried out at 80-120°C for 1-5 hours, and / or the neutralization reaction is carried out at 90-110°C, with an alkali excess rate of 1.01-1.20, wherein the alkali excess rate is the molar ratio of alkali in the alkali solution of the neutralization reaction to the added acidic catalyst. Preferably, the alkali solution is one or more of sodium hydroxide aqueous solution, potassium hydroxide aqueous solution, and lithium hydroxide aqueous solution, more preferably a sodium hydroxide aqueous solution with a mass percentage concentration of 30-55%.

8. The method according to any one of claims 1-7, characterized in that, In step (2), the brine phase is extracted with an extractant to obtain an extracted brine phase. The extracted brine phase is then subjected to stripping to obtain a stripped brine phase. The stripped brine phase is then subjected to oxidation to obtain the waste brine.

9. The method according to claim 8, characterized in that, The extractant is one or both of aniline and toluene, preferably aniline. The extractant and the brine phase flow counter-currently in the extraction tower for extraction. The volume ratio of the extractant to the brine phase is 0.2-0.

8. The extraction temperature is 80-110℃. And / or, the stripping process is carried out in a stripping tower. The top temperature of the stripping tower is preferably 95-110℃.

10. The method according to any one of claims 1-9, characterized in that, The oxidation treatment is carried out in an oxidation tower, the residence time is 20-300 min, and the temperature is 40-70℃; the pH of the waste brine to be oxidized is 4-13; the oxidant is preferably one or more of chlorine-containing oxidants, ozone, and hydrogen peroxide, and preferably, the chlorine-containing oxidant is selected from one or more of sodium hypochlorite, chlorine, and sodium perchlorate. Preferably, when the oxidant is a chlorine-containing oxidant, the oxidant is calculated as available chlorine, and the molar ratio of the oxidant to the TOC in the waste brine to be oxidized is 2-5.

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