WO2024021969A1 - 一种生产dam过程中控制废盐水中难处理苯胺类杂质的方法 - Google Patents

一种生产dam过程中控制废盐水中难处理苯胺类杂质的方法 Download PDF

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WO2024021969A1
WO2024021969A1 PCT/CN2023/103131 CN2023103131W WO2024021969A1 WO 2024021969 A1 WO2024021969 A1 WO 2024021969A1 CN 2023103131 W CN2023103131 W CN 2023103131W WO 2024021969 A1 WO2024021969 A1 WO 2024021969A1
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brine
reaction
formaldehyde
aniline
aqueous solution
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French (fr)
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徐丹
李永锋
李超群
耿文杰
王普照
吴雪峰
张宏科
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万华化学集团股份有限公司
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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
    • C07C209/68—Preparation of compounds containing amino groups bound to a carbon skeleton from amines, by reactions not involving amino groups, e.g. reduction of unsaturated amines, aromatisation, or substitution of the carbon skeleton
    • C07C209/78—Preparation of compounds containing amino groups bound to a carbon skeleton from amines, by reactions not involving amino groups, e.g. reduction of unsaturated amines, aromatisation, or substitution of the carbon skeleton from carbonyl compounds, e.g. from formaldehyde, and amines having amino groups bound to carbon atoms of six-membered aromatic rings, with formation of methylene-diarylamines
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/02—Treatment of water, waste water, or sewage by heating
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F1/00—Treatment of water, waste water, or sewage
    • C02F1/26—Treatment of water, waste water, or sewage by extraction
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C209/00—Preparation of compounds containing amino groups bound to a carbon skeleton
    • C07C209/68—Preparation of compounds containing amino groups bound to a carbon skeleton from amines, by reactions not involving amino groups, e.g. reduction of unsaturated amines, aromatisation, or substitution of the carbon skeleton
    • C07C209/74—Preparation of compounds containing amino groups bound to a carbon skeleton from amines, by reactions not involving amino groups, e.g. reduction of unsaturated amines, aromatisation, or substitution of the carbon skeleton by halogenation, hydrohalogenation, dehalogenation, or dehydrohalogenation
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
    • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
    • C07C45/29—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation of hydroxy groups
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2101/00—Nature of the contaminant
    • C02F2101/30—Organic compounds
    • C02F2101/38—Organic compounds containing nitrogen
    • C—CHEMISTRY; METALLURGY
    • C02—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F—TREATMENT OF WATER, WASTE WATER, SEWAGE, OR SLUDGE
    • C02F2103/00—Nature of the water, waste water, sewage or sludge to be treated
    • C02F2103/34—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32
    • C02F2103/36—Nature of the water, waste water, sewage or sludge to be treated from industrial activities not provided for in groups C02F2103/12 - C02F2103/32 from the manufacture of organic compounds

Definitions

  • the present invention relates to the technical field of industrial wastewater treatment, and in particular to a method for controlling refractory aniline impurities in waste brine during the production of DAM.
  • Diphenylmethane diisocyanate and polyphenylmethane polyisocyanate are one of the main raw materials in the polyurethane industry.
  • Polymethylenepolyphenylpolyamine (DAM) is first prepared by aniline and formaldehyde under acid catalysis, and then crude MDI is prepared by reacting DAM with phosgene.
  • DAM Polymethylenepolyphenylpolyamine
  • the current preparation process of DAM requires the use of alkaline solutions for neutralization.
  • the neutralization process generates a large amount of waste brine.
  • the brine contains organic matter such as amines and trace acids. It needs to be reprocessed for environmental protection discharge or subsequent applications.
  • the MDI production process usually uses pre-treatment methods such as extraction and stripping to reduce the content of organic matter in waste brine.
  • pre-treatment methods such as extraction and stripping to reduce the content of organic matter in waste brine.
  • many patents disclose methods for deep reprocessing of waste brine.
  • Chinese patent CN101143753A discloses a method of removing TOC and TN from the waste brine of aniline and diphenylmethanediamine produced in the MDI production process through oxidation reaction and adsorption treatment.
  • the treated brine TOC is ⁇ 10ppm and TN is ⁇ 3ppm.
  • Chinese patent CN101665302A discloses a waste brine treatment process that uses super gravity extraction, followed by tower extraction, and then uses a steam stripping process.
  • Chinese patent CN 112126030 A provides a method for controlling organic amines in waste brine formed by preparing MDA, by controlling the condensation reaction of anilinate and formaldehyde.
  • the turbidity of the resulting reaction liquid is used to control the content of organic amines in the final waste brine, and the turbidity is adjusted according to the main source of turbidity, preferably by condensing the macromolecular polyamine content in the reaction liquid.
  • the organic amines mentioned in the patent refer to macromolecular polyamines, which can be removed by optimizing extraction conditions such as increasing the number of extraction stages. They are not anilines that are difficult to process in brine.
  • the technology of the present invention focuses on the analysis of key components that cannot be removed by extraction and stripping in brine, and controls the generation of such components from the raw material side.
  • the process control is simple, effective, and low-cost, thereby realizing direct discharge of brine or electrolysis reuse. .
  • the purpose of the present invention is to provide a method for reducing the content of refractory aniline substances in brine, and at the same time, it is beneficial to reduce the TOC/TN of the brine. This method can reduce the difficulty and cost of the back-end treatment process of the brine.
  • the salt content in MDI waste brine is about 14 to 18%, and the pH is generally between 12 and 14.
  • the TOC contributing components are mainly formate, acetate, phenol, aminophenol, cyclohexanone and anilines.
  • pre-treatment methods such as extraction and stripping are generally used to reduce the content of these components.
  • back-end reprocessing such as oxidation or adsorption is required.
  • the applicant's research found that the important components of TOC ⁇ TN in the brine after extraction and stripping are small molecular acid salts and difficult-to-treat anilines (polar polymer amines).
  • small molecular acid salts TOC have a low contribution rate and have no impact on the ion membrane and do not affect chlor-alkali reuse;
  • the difficult-to-treat aniline substances TOC/TN contribute It has a high donation rate, and due to its high boiling point, strong polarity and aromatic ring structure, it is difficult to remove through low-cost means and has a greater impact on the ion membrane.
  • the applicant was surprised to find that the generation of difficult-to-treat aniline substances is related to acrylic acid, maleic acid, and acrolein in formaldehyde.
  • reaction products in formulas I, II, and III also contain amino, carboxyl, or aldol groups, they become ionic in alkaline brine, making them unable to be removed by organic solvent extraction or stripping. Based on the above research findings, it is To achieve the aforementioned objects of the present invention, the present invention provides the following technical solutions:
  • the present invention provides a control method for reducing the content of refractory anilines in brine in the MDI production process.
  • the method includes the following steps: (1) reacting methanol with fresh air in the presence of an iron-molybdenum catalyst The reaction gas containing formaldehyde is prepared, and after cooling, pure water is used to absorb it to obtain a formaldehyde aqueous solution, the raw material for DAM production;
  • the prepared formaldehyde aqueous solution and aniline are subjected to a condensation reaction, a translocation rearrangement reaction, and an acid-base neutralization reaction to obtain a brine containing diphenylmethane-based diamines and polyamines. phase and organic phase;
  • step (1) the ethanol content in the methanol is less than or equal to 100 ppm, the molar ratio of oxygen to alcohol is 0.9 to 1.3, and the reaction pressure is ⁇ 1.9 bara.
  • step (1) in the presence of an iron-molybdenum catalyst, methanol is reacted with fresh air to prepare a reaction gas containing formaldehyde, also known as the "iron-molybdenum method", which is a common formaldehyde production process.
  • the reaction operates at the lower explosion limit of methanol-air, see Reaction Formula IV, which is well known in the industry and will not be described again here.
  • Iron-molybdenum catalysts are well known to those skilled in the art as catalysts for the production of formaldehyde, such as commercially available iron-molybdenum catalysts.
  • formaldehyde In the process of preparing formaldehyde using the iron-molybdenum method, formaldehyde inevitably contains other impurities: formic acid, acetic acid, methyl formate, ethyl formate and other impurities. These acidic impurities such as formic acid can react with amines to form amide impurities, but the above amide impurities can be removed during the extraction or stripping stage.
  • the impurity ethanol will react with formaldehyde in the form of acetaldehyde or acetic acid as the oxidation product as shown below. It can be seen that controlling the content of ethanol impurities can control the content of acrylic acid, maleic acid, and acrolein in formaldehyde.
  • the formation amount is controlled to control the amount of bipolar, high-boiling point and difficult-to-handle aniline substances produced by the reaction of acrylic acid, maleic acid, acrolein and amines.
  • the ethanol content in methanol in step (1) when the ethanol content in methanol in step (1) is high, the contents of acetaldehyde and acetic acid in formaldehyde are both high, resulting in an increase in the contents of acrylic acid and acrolein, the products of the condensation reaction between the two and formaldehyde. It was found that in order to control the refractory aniline substances in MDI brine to a content that meets the needs of chlor-alkali electrolysis, the ethanol content in methanol needs to be controlled to be equal to or ⁇ 100ppm, preferably ⁇ 100ppm. The specific ethanol content that meets this content requirement is not specified. Limits such as 90ppm, 80ppm, 70ppm, 60ppm, 50ppm, 40ppm, 30ppm, 20ppm, 10ppm.
  • the technology of the present invention also needs to control the oxygen-alcohol molar ratio between 0.9 and 1.3.
  • the oxygen-alcohol molar ratio is 0.9, 1, 1.1, 1.2, and 1.3.
  • the present invention further explored and found that the greater the reaction pressure, the more conducive to the side reaction process in Formula V.
  • the oxidation reaction pressure in the formaldehyde preparation process needs to be controlled to 1.9 below bara.
  • the oxygen-alcohol molar ratio of the formaldehyde reaction is 0.9-1.3, and the reaction pressure is ⁇ 1.9 bara
  • the acrylic acid and propylene in the formaldehyde solution are
  • the total amount of aldehyde and maleic acid impurities is ⁇ 20ppm, preferably ⁇ 8ppm.
  • hydrochloric acid is used as an acidic catalyst in step (2), and its molar ratio to aniline is 0.1-0.5, preferably 0.15-0.35; wherein, the hydrochloric acid catalyst preferably has a mass concentration of 25%-37% of hydrochloric acid aqueous solution.
  • the molar ratio of formaldehyde to aniline in step (2) is 0.30-0.60, and the mass concentration of the formaldehyde aqueous solution is 30%-50%, in which there are three types of formaldehyde aqueous solution: acrylic acid, maleic acid, and acrolein.
  • the total amount of impurities is ⁇ 20ppm, preferably ⁇ 8ppm.
  • the hydrochloric acid aqueous solution is mixed with aniline to form an aniline salt, and then mixed with formaldehyde to perform a condensation reaction to obtain a condensation reaction product.
  • the condensation reaction is performed at 50-70°C for 1-3 hours; the resulting condensation
  • the reaction product continues to undergo translocation rearrangement reaction to obtain a mixture containing DAM salt; the translocation rearrangement reaction is carried out at 75-110°C for 1-5h; the acid-base neutralization reaction is carried out at 100-110°C. It is carried out at 120°C.
  • the alkali liquid used for the acid-base neutralization reaction is selected from a sodium hydroxide aqueous solution or a potassium hydroxide aqueous solution, preferably a sodium hydroxide aqueous solution with a mass percentage concentration of 30%-55%.
  • the alkali liquid is added
  • the molar ratio of the amount relative to the hydrochloric acid catalyst is 1.03-1.08.
  • the extraction agent used to extract the brine phase is selected from aniline or toluene, and the extraction is performed according to the volume ratio of the brine phase to the extraction agent of 0.1-0.4 (referred to as "extraction ratio").
  • extraction ratio the volume ratio of the brine phase to the extraction agent of 0.1-0.4
  • the brine phase and the extraction agent flow countercurrently in the extraction tower to fully perform extraction; the extraction temperature is 95-105°C.
  • the stripping in step (3) is carried out in a stripping tower, and the stripping temperature is controlled at 95-110°C to obtain the waste brine.
  • the conventional organic amine substances such as extraction agent, aniline and MDA in the waste brine obtained after the above treatment are ⁇ 0.1ppm, and the refractory aniline substances are ⁇ 0.3ppm.
  • the waste brine produced in step (3) can be directly sent to the ion membrane electrolysis alkali production device for use.
  • the voltage of the electrolytic cell is stably lower than 3.1V, and the current efficiency is continuously higher than 95%.
  • the invention provides a method for controlling the generation of refractory aniline substances in brine during the production of MDI.
  • the molar ratio of oxygen to alcohol in the formaldehyde production reaction is 0.9 ⁇ 1.3, reaction pressure ⁇ 1.9 bara, which greatly reduces the amount of difficult-to-treat aniline impurities generated by the reaction of acrylic acid, maleic acid, acrolein and amines, making the extracted waste brine, aniline and MDA, etc.
  • Conventional organic amine substances are ⁇ 0.1ppm, and difficult-to-treat aniline substances are ⁇ 0.3ppm, meeting the requirements for subsequent processing.
  • reagents used in the examples are all conventional reagents in this field. Unless otherwise specified, the following detection methods or experimental methods are conventional technical means known to those skilled in the art based on the prior art they have mastered.
  • Formaldehyde Wanhua Chemical Co., Ltd.;
  • the American Agilent LC-1200 Infinity Series LC was used for quantitative determination through external standard. The method is as follows: directly take the formaldehyde sample, filter it and inject 10ul, and use the chromatographic column XSelect RHSS T3 column.
  • the American Agilent GC 8890 GC was used for quantitative determination by external standard. The method is as follows. Directly take the methanol sample and filter it for injection. The injection volume is 1ul, the split ratio is 50:1, and the chromatographic column is Agilent J&W DB-wax 30m*0.32mm*0.5um.
  • the ethanol content in methanol is 100 ppm
  • the molar ratio of oxygen to alcohol in the formaldehyde preparation reaction is 1.2
  • the reaction pressure is 1.4 bara.
  • Formaldehyde preparation process 14.67t of the overhead gas of the formaldehyde absorption tower is used to produce formaldehyde with 5.45t/h fresh air at 25°C and 1.01bara (the mass concentration of oxygen is 22.9%, and the rest is nitrogen and water) and reaction gas. /h (the mass concentration of oxygen is 8% and the mass fraction of water is 2.8%), use a fan to raise the pressure to 1.7 bara, mix it with 2.02t/h methanol, preheat the mixed material to 195°C, and then send it to the charging station.
  • methanol is oxidized by oxygen in the reactor at 268°C and 1.4 bara, and converted into formaldehyde and water. Then, after cooling to 130°C, the reaction gas is sent to the formaldehyde absorption tower, where it is heated at 1.95t/ h Under the capture of process water at 25°C, a formaldehyde aqueous solution of 4.76t/h 50°C and 37% mass concentration was obtained, which was used as a raw material for preparing DAM in the second step.
  • the total content of acrylic acid, maleic acid, and acrolein in the formaldehyde aqueous solution was (Corresponding to "Content of three impurities in formaldehyde" in Table 1) See Table 1 for details.
  • the above brine is sent to the chlor-alkali ion membrane alkali production device.
  • the cell voltage and current efficiency data are detailed in Table 1.
  • the ethanol content in methanol is 80 ppm
  • the molar ratio of oxygen to alcohol in the formaldehyde preparation reaction is 0.9
  • the reaction pressure is 1.7 bara.
  • Formaldehyde preparation process 11.00t of top gas from the formaldehyde absorption tower that produces formaldehyde with 4.09t/h fresh air at 25°C and 1.01bara (mass concentration of oxygen is 22.9%, the rest is nitrogen and water) and reaction gas /h (the mass concentration of oxygen is 8% and the mass fraction of water is 2.8%), use a fan to raise the pressure to 1.9 bara, mix it with 2.02t/h methanol, preheat the mixed material to 195°C, and then send it to the charging station.
  • methanol is oxidized by oxygen in the reactor at 268°C and 1.7 bara, and converted into formaldehyde and water.
  • the mass concentration of the prepared formaldehyde aqueous solution is 45%.
  • the rest of the process is the same as in Example 1.
  • the mass concentration of the hydrochloric acid aqueous solution used in step (2) is 37%
  • the mass concentration of the sodium hydroxide aqueous solution used is 35%
  • the molar ratio of hydrochloric acid to aniline during the preparation of DAM is 0.35
  • the molar ratio of formaldehyde to aniline is 0.50.
  • the ethanol content in methanol is 40 ppm
  • the molar ratio of oxygen to alcohol in the formaldehyde preparation reaction is 1.0
  • the reaction pressure is 1.3 bara.
  • Formaldehyde preparation process 12.23t of the overhead gas of the formaldehyde absorption tower is used to produce formaldehyde with 4.54t/h fresh air at 25°C and 1.01bara (mass concentration of oxygen is 22.9%, the rest is nitrogen and water) and reaction gas. /h (the mass concentration of oxygen is 8% and the mass fraction of water is 2.8%), use a fan to raise the pressure to 1.5 bara, mix it with 2.02t/h methanol, preheat the mixed material to 195°C, and then send it to the charging station. In a reactor with an iron-molybdenum catalyst, methanol is oxidized by oxygen in the reactor at 268°C and 1.3 bara, and converted into formaldehyde and water. The mass concentration of the prepared formaldehyde aqueous solution is 35%.
  • the rest of the process is the same as in Example 1.
  • the mass concentration of the hydrochloric acid aqueous solution used in step (2) is 34%
  • the mass concentration of the sodium hydroxide aqueous solution used is 45%
  • the molar ratio of hydrochloric acid to aniline during the preparation of DAM is 0.20
  • the molar ratio of formaldehyde to aniline is 0.40.
  • the ethanol content in methanol is 60 ppm
  • the molar ratio of oxygen to alcohol in the formaldehyde preparation reaction is 1.3
  • the reaction pressure is 1.9 bara.
  • Formaldehyde preparation process 15.89t of the overhead gas of the formaldehyde absorption tower is used to produce formaldehyde with 5.90t/h fresh air at 25°C and 1.01bara (mass concentration of oxygen is 22.9%, the rest is nitrogen and water) and reaction gas. /h (the mass concentration of oxygen is 8% and the mass fraction of water is 2.8%), use a fan to raise the pressure to 2.1 bara, mix it with 2.02t/h methanol, preheat the mixed material to 195°C, and then send it to the charging station.
  • methanol is oxidized by oxygen in the reactor at 268°C and 1.9 bara, and converted into formaldehyde and water.
  • the mass concentration of the prepared formaldehyde aqueous solution is 50%.
  • the rest of the process is the same as in Example 1.
  • the mass concentration of the hydrochloric acid aqueous solution used in step (2) is 30%;
  • the mass concentration of the sodium hydroxide aqueous solution is 40%.
  • the molar ratio of hydrochloric acid to aniline is 0.25, and the molar ratio of formaldehyde to aniline is 0.35.
  • the ethanol content in methanol is 30 ppm
  • the molar ratio of oxygen to alcohol in the formaldehyde preparation reaction is 1.1
  • the reaction pressure is 1.8 bara.
  • Formaldehyde preparation process 13.45t of the overhead gas of the formaldehyde absorption tower is used to produce formaldehyde with 5.00t/h fresh air at 25°C and 1.01bara (mass concentration of oxygen is 22.9%, the rest is nitrogen and water) and reaction gas. /h (the mass concentration of oxygen is 8% and the mass fraction of water is 2.8%), use a fan to raise the pressure to 2.0 bara, mix it with 2.02t/h methanol, preheat the mixed material to 195°C, and then send it to the charging station. In a reactor with an iron-molybdenum catalyst, methanol is oxidized by oxygen in the reactor at 268°C and 1.8 bara, and converted into formaldehyde and water. The mass concentration of the prepared formaldehyde aqueous solution is 30%.
  • the rest of the process is the same as in Example 1.
  • the mass concentration of the hydrochloric acid aqueous solution used in step (2) is 35%
  • the mass concentration of the sodium hydroxide aqueous solution used is 50%
  • the molar ratio of hydrochloric acid to aniline during the preparation of DAM is 0.20
  • the molar ratio of formaldehyde to aniline is 0.55.
  • the ethanol content in methanol is 110 ppm.
  • Example 1 The remaining processes are consistent with Example 1.
  • the relevant data of this comparative example are detailed in Table 1.
  • the reaction pressure for preparing formaldehyde in this comparative example is 2.0 bara.
  • Example 2 The rest are consistent with Example 2.
  • the relevant data of this comparative example are detailed in Table 1.
  • step (1) the flow rate of fresh air is 6.81t/h, the top gas flow rate of the formaldehyde absorption tower is 18.34t/h; the molar ratio of oxygen to alcohol in the formaldehyde preparation reaction is 1.5.
  • Example 3 The rest are consistent with Example 3.
  • the relevant data of this comparative example are detailed in Table 1.
  • the three impurities in formaldehyde are the total amount of acrylic acid, maleic acid, and acrolein.
  • Comparative Example 2 adopted a higher reaction pressure.
  • the contents of acrylic acid, maleic acid, and acrolein in formaldehyde increased significantly, and the final content of waste brine was Difficult-to-treat aniline impurities increased significantly, resulting in an increase in tank voltage during chlor-alkali recycling.
  • Example 3 Through the comparison between Example 3 and Comparative Example 3, it can be clearly found that when the ethanol content in methanol is constant, the higher the molar ratio of oxygen to alcohol, the higher the content of acrylic acid, maleic acid, and acrolein in formaldehyde, and finally the content of acrylic acid, maleic acid, and acrolein in the waste brine.
  • Example 2 the ethanol content is 80 ppm, and almost no refractory amines are detected in the final waste brine, which can be directly used in chlor-alkali.
  • the molar ratio of oxygen to alcohol in the formaldehyde production reaction is 0.9 to 1.3, and the reaction pressure is ⁇ 1.9 bara, which greatly reduces the reaction between acrylic acid, maleic acid, acrolein and amines.
  • the amount of refractory aniline impurities generated is such that the extraction agent, aniline, MDA and other conventional organic amine substances in the waste brine after treatment are ⁇ 0.1ppm, and the refractory aniline substances are ⁇ 0.3ppm, meeting the requirements for subsequent treatment.

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Abstract

本发明提供了一种生产DAM过程中控制废盐水中难处理苯胺类杂质的方法，包含如下步骤：(1)在铁钼催化剂存在下，采用甲醇与新鲜空气反应制得含甲醛的反应气，冷却后采用纯水吸收，得到生产DAM的原料-甲醛水溶液；(2)在酸性催化剂存在下，采用制得的甲醛水溶液与苯胺经缩合反应、转位重排反应、酸碱中和反应后，得到含有二苯基甲烷系的二胺与多胺盐水相和有机相；(3)将盐水相进行萃取、汽提处理后得到废盐水；有机相经纯化、精制处理后得到二苯基甲烷系的二胺与多胺，其中步骤(1)中，甲醇中的乙醇含量低于或等于100ppm，氧醇摩尔比为0.9～1.3，反应压力≤1.9bara。本发明的方法使得生产DAM过程中废盐水中难处理苯胺类杂质降至0.3ppm以下，满足后续处理的要求。

Description

一种生产DAM过程中控制废盐水中难处理苯胺类杂质的方法 技术领域
本发明涉及工业废水处理技术领域，尤其涉及一种生产DAM过程中控制废盐水中难处理苯胺类杂质的方法。
背景技术
二苯甲烷二异氰酸酯与多苯基甲烷多异氰酸酯(统称MDI)是聚氨酯行业主要原料之一。先通过苯胺与甲醛在酸催化下制备多亚甲基多苯基多胺(DAM)，再以DAM与光气反应制备粗MDI。目前的制备DAM过程，需要用到碱溶液进行中和，中和过程产生大量废盐水，盐水中含胺类、微量酸类等有机物，为实现环保排放或后续应用都需要再处理。
目前MDI生产过程通常采用萃取、汽提等前处理方式降低废盐水中有机物的含量，另外很多专利公开了废盐水深度再处理的方法。中国专利CN101143753A公开了一种MDI生产过程中产生的苯胺和二苯基甲烷二胺废盐水通过氧化反应和吸附处理脱除盐水中TOC和TN，处理后的盐水TOC＜10ppm，TN＜3ppm。中国专利CN101665302A公开了一种废盐水处理工艺，采用超重力萃取，然后进行塔式萃取，再以蒸汽汽提工艺，汽提塔排出的废盐水和化学氧化剂进行氧化反应，之后进行吸附处理，控制废盐水TOC＜8ppm，TN＜2.5ppm，以达到氯碱回用要求。中国专利CN110743623A公开了一种将MDI盐水采用催化氧化法深度处理的方法，对MDI盐水的pH值进行调节，并加入氧化剂进行处理；再将处理后的MDI盐水与催化氧化催化剂接触进行催化氧化反应，得到深度处理后的盐水。目前文献报道的及专利公开的MDI盐水深度处理工艺流程长、成本高，如果从源头控制MDI废盐水中难处理的胺类有机物的生成，保证在萃取、汽提处理后盐水TOC\TN稳定可控，即可实现直接回用氯碱，从经济 和效率方面实现显著提升。中国专利CN112094194A提供了一种生产DAM过程中控制废盐水中TOC的方法，通过对制备方法中碱过剩率的严格控制，达到降低废盐水中TOC含量的目的。这种方法降低的是甲酸、乙酸对TOC的影响，无法降低TN；中国专利CN 112126030 A提供了一种制备MDA形成的废盐水中有机胺的控制方法，通过控制苯胺酸盐与甲醛发生缩合反应后所得反应液的浊度来控制最终的废盐水中的有机胺的含量，并根据浊度的主要来源优选通过缩合反应液中大分子多胺含量对浊度进行调节。该专利提到的有机胺指的是大分子多胺，可以通过优化萃取条件如增加萃取级数来脱除，并不属于盐水中难处理的苯胺类物质。
而本发明的技术是重点剖析盐水中萃取、汽提无法脱除的关键组分，从原料端控制这类组分的生成，工艺控制简单有效，成本低，从而实现盐水直接排放或电解回用。
发明内容
本发明的目的是提供一种降低盐水中难处理苯胺类物质含量的方法，同时利于降低盐水的TOC/TN，通过该方法可以降低盐水后端处理工艺的难度和成本。
目前MDI废盐水中盐含量约在14～18％，pH一般在12～14之间，含有的TOC贡献组分主要为甲酸盐、乙酸盐、苯酚、氨基酚、环己酮和苯胺类有机物，一般工艺上采用萃取、汽提的前处理方式来降低这些组分的含量，如果处理后的MDI废盐水需要再去氯碱回用，则需要进行氧化或吸附等后端再处理。通过申请人研究发现，经过萃取、汽提后的盐水，其中的TOC\TN的重要组成为小分子酸盐和难处理的苯胺类物质(极性高分子的胺)。其中，小分子酸盐TOC贡献率低，且对离子膜无影响，不影响氯碱回用；难处理的苯胺类物质TOC/TN贡 献率高，且因沸点高、极性强以及含有芳环结构，难以通过低成本方式去除，而且对离子膜影响较大。申请人惊奇的发现，难处理的苯胺类物质的生成与甲醛中的丙烯酸、马来酸、丙烯醛相关，当甲醛中丙烯酸、马来酸、丙烯醛较高时，会导致萃取和汽提后的盐水中TOC＞15ppm，苯胺类物质＞3ppm，这样的盐水需要大量水去稀释才能达到废水排放标准，或需研究非常有效的深度处理工艺进行处理后才能回用至氯碱装置，目前已公开的专利技术对此类难处理苯胺类物质的处理效果均不理想。下面以反应式Ⅰ、Ⅱ、Ⅲ为例说明丙烯酸、马来酸、丙烯醛与二苯基甲烷二胺反应生成难处理的苯胺类物质的过程，如下：
因式Ⅰ、Ⅱ、Ⅲ中的反应产物同时含有氨基、羧基或羟醛基，在碱性盐水中成离子态，从而导致其无法被有机溶剂萃取或汽提脱除，基于以上研究发现，为实现本发明的前述目的，本发明提供如下技术方案：
一方面，本发明提供了一种降低MDI生产过程的盐水中难处理苯胺类物质含量的控制方法，所述方法包含以下步骤：(1)在铁钼催化剂的存在下，采用甲醇与新鲜空气反应制得含甲醛的反应气，冷却后采用纯水吸收，得到生产DAM的原料-甲醛水溶液；
(2)在酸性催化剂的存在下，采用制得的甲醛水溶液与苯胺经缩合反应、转位重排反应、酸碱中和反应后，得到含有二苯基甲烷系的二胺与多胺的盐水相和有机相；
(3)将盐水相进行萃取、汽提处理后得到废盐水；有机相经纯化、精制处理后得到二苯基甲烷系的二胺与多胺。
其中步骤(1)中，所述甲醇中的乙醇含量低于或等于100ppm，氧醇摩尔比为0.9～1.3，反应压力≤1.9bara。
本发明中，步骤(1)中所述在铁钼催化剂的存在下，采用甲醇与新鲜空气反应制得含甲醛的反应气又称“铁钼法”，是一种常见的甲醛生产工艺，其反应是在甲醇-空气爆炸下限操作，见反应式IV，为行业熟知，此处不再赘述。
CH3OH+1/2O2→CH2O+H2O   式IV
铁钼催化剂为本领域技术人员所熟知的用于制甲醛的催化剂，例如可商业购得的铁钼催化剂。
铁钼法工艺制备甲醛过程，甲醛中不可避免的会含有其他杂质：甲酸、乙酸、甲酸甲酯、甲酸乙酯等杂质。这些甲酸等酸性杂质可以和胺生成酰胺类杂质，但上述酰胺类杂质可以在萃取或汽提阶段脱除。但申请人发现当甲醇中乙醇杂质含量较高时，最终会导致盐水中难脱除苯胺类物质含量较高。上述原因是杂质乙醇在氧化过程中会以氧化产物乙醛或乙酸的形式再与甲醛发生如下式Ⅴ的反应，可知控制乙醇杂质的含量，即可控制甲醛中丙烯酸、马来酸、丙烯醛的形成量，从而控制丙烯酸、马来酸、丙烯醛与胺的反应生成的双极性、高沸点难处理的苯胺类物质的量。
本发明的方法中，当步骤(1)中甲醇中乙醇含量较高时，甲醛中的乙醛、乙酸含量都高，导致两者与甲醛的缩合反应产物丙烯酸、丙烯醛的含量增加，本发明人发现，为了将MDI盐水中难处理苯胺类物质控制在满足氯碱电解需求的含量，则需控制甲醇中乙醇含量等于或＜100ppm，优选＜100ppm，满足该含量要求的乙醇的具体含量没有特别的限制，如90ppm、80ppm、70ppm、60ppm、50ppm、40ppm、30ppm、20ppm、10ppm。
此外，甲醛制备中甲醇在铁钼催化剂作用下被空气氧化，当氧醇摩尔比＞1.3，氧化产生的丙烯酸含量显著升高；当氧醇摩尔比＜0.9，甲醛的收率降低、装置成本高，为此本发明的技术还需控制氧醇摩尔比在0.9～1.3之间，如氧醇摩尔比为0.9、1、1.1、1.2、1.3，通过控制氧醇摩尔比在上述范围，降低致使MDI盐水处理难度较大的甲醛中丙烯酸等杂质含量的同时，兼顾甲醛生产的经济性。
除上述的方法外，本发明进一步深入探究，发现反应压力越大越利于式Ⅴ中的副反应过程，为进一步提升本发明技术的可靠性及稳定性，甲醛制备过程中的氧化反应压力需控制1.9bara以下。因此本发明的方法中，通过控制步骤(1)中所述甲醇中乙醇含量低于或等于100ppm，甲醛反应的氧醇摩尔比0.9～1.3，反应压力≤1.9bara来使得甲醛溶液中丙烯酸、丙烯醛、马来酸三种杂质总量≤20ppm，优选≤8ppm。使得步骤(2)中丙烯酸、丙烯醛、马来酸与胺的反应产物难处理苯胺类物质(见式I\II\III)含量≤0.3ppm。
本发明中，所述步骤(2)中采用盐酸作为酸性催化剂，其与苯胺的摩尔比为0.1-0.5，优选为0.15-0.35；其中，所述盐酸催化剂优选为质量浓度为25％-37％ 的盐酸水溶液。
本发明中，所述步骤(2)中甲醛与苯胺的摩尔比为0.30-0.60，所述甲醛水溶液的质量浓度为30％-50％，其中甲醛水溶液中丙烯酸、马来酸、丙烯醛三种杂质总量≤20ppm，优选≤8ppm。
本发明中，所述步骤(2)中盐酸水溶液与苯胺混合形成苯胺盐，再与甲醛混合进行缩合反应得到缩合反应产物，所述缩合反应在50-70℃下进行1-3h；所得的缩合反应产物继续进行转位重排反应，得到含有DAM盐的混合物；所述转位重排反应在75-110℃下进行转位重排反应1-5h；所述酸碱中和反应在100-120℃下进行，进行所述酸碱中和反应所用的碱液选自氢氧化钠水溶液或氢氧化钾水溶液，优选为质量百分浓度为30％-55％的氢氧化钠水溶液，碱液加入量相对于盐酸催化剂摩尔比为1.03-1.08。
本发明中，所述步骤(3)中，对盐水相进行萃取所用萃取剂选自苯胺或甲苯，按照盐水相与萃取剂的体积比0.1-0.4的比例(简称为“萃取比”)进行萃取，萃取过程盐水相和萃取剂在萃取塔中逆向流动，以充分进行萃取；萃取温度在95-105℃。
本发明中，所述步骤(3)中汽提在汽提塔中进行，汽提的温度控制在95-110℃，得到所述废盐水。上述处理后得到的废盐水中萃取剂、苯胺及MDA等常规有机胺物质≤0.1ppm，难处理苯胺类物质≤0.3ppm。
本发明中，所述步骤(3)中制得的废盐水可直接送至离子膜电解制碱装置进行使用，电解槽电压稳定低于3.1V，电流效率持续高于95％。
采用上述的技术方案，具有如下的有益效果：
本发明提供的生产MDI过程中控制盐水中难处理苯胺类物质生成的方法，通过控制甲醇中的乙醇含量低于或等于100ppm，制甲醛反应的氧醇摩尔比为 0.9～1.3，反应压力≤1.9bara，大大降低了由丙烯酸、马来酸、丙烯醛与胺类反应而生成的难处理苯胺类杂质的量，使得处理后废盐水中萃取剂、苯胺及MDA等常规有机胺物质≤0.1ppm，难处理的苯胺类物质≤0.3ppm，满足后续处理的要求。
具体实施方式
为了更好的理解本发明的技术方案，下面结合实施例进一步阐述本发明的内容，但本发明的内容并不仅仅局限于以下实施例。
实施例中所用试剂均为本领域常规试剂。以下检测方法或实验方法若未特别说明，均为本领域技术人员根据其所掌握的现有技术所能知晓的常规技术手段。
下述各例中原料来源信息：
苯胺：万华化学有限公司；
甲醇：万华化学有限公司；
甲醛：万华化学有限公司；
盐酸：万华化学有限公司；
氢氧化钠：万华化学有限公司。
本发明方法中用到的其他化学试剂，均采用本领域常规试剂，纯度为化学纯以上。
下文中的百分含量“％”均指“wt％”。
以下实验过程涉及的测试方法说明如下：
1、废盐水中苯胺类物质
方法：GB/T 11889N-(1-萘基)乙二胺偶氮分光光度法。
2、甲醛中丙烯酸、马来酸、丙烯醛含量的分析
采用美国安捷伦LC-1200 Infinity Series LC通过外标定量进行测定，方法如下：直接取甲醛样品过滤进样，10ul，色谱柱XSelect RHSS T3柱。
3、废盐水中TOC含量分析方法：采用耶拿N/C 2100S TOC仪进行分析。
4、甲醇中乙醇含量的分析
采用美国安捷伦GC 8890 GC通过外标定量进行测定，方法如下，直接取甲醇样品过滤进样，进样量1ul，分流比50：1，色谱柱Agilent J&W DB-wax 30m*0.32mm*0.5um。
实施例1：
该实施例中甲醇中乙醇含量为100ppm，制备甲醛反应的氧醇摩尔比为1.2，反应压力为1.4bara。
(1)甲醛制备过程：将25℃、1.01bara的5.45t/h新鲜空气(氧的质量浓度为22.9％，其余为氮气和水)与反应气制甲醛的甲醛吸收塔的塔顶气14.67t/h(氧的质量浓度为8％、水的质量分数为2.8％)混合，采用风机提压至1.7bara，与2.02t/h甲醇混合，将混合物料预热至195℃，然后送入装有铁钼催化剂的反应器，在268℃、1.4bara下甲醇在反应器中被氧气氧化，转化为甲醛和水，然后冷却至130℃后，将反应气送入甲醛吸收塔，在1.95t/h 25℃工艺水的捕集下，得到4.76t/h 50℃、37％质量浓度的甲醛水溶液，用作第二步制备DAM的原料，该甲醛水溶液中丙烯酸、马来酸、丙烯醛总含量(对应表1中“甲醛中三种杂质的含量”)详见表1。
(2)含DAM有机相与盐水相的制备：将12t/h质量浓度为99.9％苯胺与3.83t/h质量浓度为32％的盐酸水溶液(盐酸相对于苯胺的摩尔比为0.26)在静态混合器内混合形成苯胺盐酸盐，向其中加入4.71t/h质量浓度为37％的甲醛水溶液(甲醛相对于苯胺的摩尔比为0.45)，之后在70℃下于反应器中进行缩合 反应2h；随后继续在110℃下发生转位重排反应3h，得到含有DAM盐酸盐的混合物；采用2.84t/h质量浓度为50％的氢氧化钠水溶液中和含有DAM盐酸盐的混合物，分相得到含DAM的有机相13.2t/h和盐水相10.2t/h，将有机相进行洗涤、精制即可得到符合下游光气化制备MDI需求的DAM。
(3)盐水的处理：将10.2t/h盐水相与2.5t/h苯胺送入萃取塔中在100℃下逆流萃取，得到萃取后盐水相；然后将所得萃取盐水相通入汽提塔中，在塔底再沸器中按0.2的汽提比通入2barg蒸汽进行汽提处理，汽提塔的塔顶温度为101℃；苯胺从塔顶被除去后，塔底产出的盐水即为处理完成的盐水8t/h，处理后盐水(即，表1中的“废盐水”)中的难处理苯胺类物质及TOC含量数据详见表1。
将上述盐水送至氯碱离子膜制碱装置，槽电压及电流效率数据详见表1。
实施例2：
该实施例中甲醇中乙醇含量为80ppm，制备甲醛反应的氧醇摩尔比为0.9，反应压力为1.7bara。
(1)甲醛制备过程：将25℃、1.01bara的4.09t/h新鲜空气(氧的质量浓度为22.9％，其余为氮气和水)与反应气制甲醛的甲醛吸收塔的塔顶气11.00t/h(氧的质量浓度为8％、水的质量分数为2.8％)混合，采用风机提压至1.9bara，与2.02t/h甲醇混合，将混合物料预热至195℃，然后送入装有铁钼催化剂的反应器，在268℃、1.7bara下甲醇在反应器中被氧气氧化，转化为甲醛和水，制备的甲醛水溶液的质量浓度为45％。
其余过程同实施例1，步骤(2)中所用的盐酸水溶液的质量浓度为37％，所用的氢氧化钠水溶液的质量浓度为35％，制备DAM过程中盐酸相对于苯胺的摩尔比为0.35、甲醛相对于苯胺的摩尔比为0.50。
实施例的相关数据详见表1。
实施例3：
该实施例中甲醇中乙醇含量为40ppm，制备甲醛反应的氧醇摩尔比为1.0，反应压力为1.3bara。
(1)甲醛制备过程：将25℃、1.01bara的4.54t/h新鲜空气(氧的质量浓度为22.9％，其余为氮气和水)与反应气制甲醛的甲醛吸收塔的塔顶气12.23t/h(氧的质量浓度为8％、水的质量分数为2.8％)混合，采用风机提压至1.5bara，与2.02t/h甲醇混合，将混合物料预热至195℃，然后送入装有铁钼催化剂的反应器，在268℃、1.3bara下甲醇在反应器中被氧气氧化，转化为甲醛和水，制备的甲醛水溶液的质量浓度为35％。
其余过程同实施例1，步骤(2)中所用的盐酸水溶液的质量浓度为34％，所用的氢氧化钠水溶液的质量浓度为45％，制备DAM过程中盐酸相对于苯胺的摩尔比为0.20、甲醛相对于苯胺的摩尔比为0.40。
实施例的相关数据详见表1。
实施例4：
该实施例中甲醇中乙醇含量为60ppm，制备甲醛反应的氧醇摩尔比为1.3，反应压力为1.9bara。
(1)甲醛制备过程：将25℃、1.01bara的5.90t/h新鲜空气(氧的质量浓度为22.9％，其余为氮气和水)与反应气制甲醛的甲醛吸收塔的塔顶气15.89t/h(氧的质量浓度为8％、水的质量分数为2.8％)混合，采用风机提压至2.1bara，与2.02t/h甲醇混合，将混合物料预热至195℃，然后送入装有铁钼催化剂的反应器，在268℃、1.9bara下甲醇在反应器中被氧气氧化，转化为甲醛和水，制备的甲醛水溶液的质量浓度为50％。
其余过程同实施例1，步骤(2)中所用盐酸水溶液的质量浓度为30％；所用 的氢氧化钠水溶液的质量浓度为40％，制备DAM过程中盐酸相对于苯胺的摩尔比为0.25、甲醛相对于苯胺的摩尔比为0.35。
实施例的相关数据详见表1。
实施例5：
该实施例中甲醇中乙醇含量为30ppm，制备甲醛反应的氧醇摩尔比为1.1，反应压力为1.8bara。
(1)甲醛制备过程：将25℃、1.01bara的5.00t/h新鲜空气(氧的质量浓度为22.9％，其余为氮气和水)与反应气制甲醛的甲醛吸收塔的塔顶气13.45t/h(氧的质量浓度为8％、水的质量分数为2.8％)混合，采用风机提压至2.0bara，与2.02t/h甲醇混合，将混合物料预热至195℃，然后送入装有铁钼催化剂的反应器，在268℃、1.8bara下甲醇在反应器中被氧气氧化，转化为甲醛和水，制备的甲醛水溶液的质量浓度为30％。
其余过程同实施例1，步骤(2)中所用的盐酸水溶液的质量浓度为35％，所用的氢氧化钠水溶液的质量浓度为50％，制备DAM过程中盐酸相对于苯胺的摩尔比为0.20、甲醛相对于苯胺的摩尔比为0.55。
实施例的相关数据详见表1。
对比例1：
该对比例中甲醇中乙醇含量为110ppm。
其余过程均与实施例1一致，该对比例的相关数据详见表1。
其余反应过程同实施例1。
对比例2：
该对比例中制备甲醛的反应压力为2.0bara。
其余均与实施例2一致，该对比例的相关数据详见表1。
对比例3：
该对比例中，步骤(1)中，新鲜空气的流量为6.81t/h，甲醛吸收塔的塔顶气流量为18.34t/h；制备甲醛反应的氧醇摩尔比为1.5。
其余均与实施例3一致，该对比例的相关数据详见表1。
表1实施例及对比例条件下甲醛、废盐水中杂质含量及离子膜电槽运行参数情况
备注：甲醛中三种杂质为丙烯酸、马来酸、丙烯醛三种杂质的总量。
通过实施例1和对比例1的对比可见，在制甲醛反应中，氧醇摩尔比和反应压力一定时，甲醇中乙醇含量超过100ppm的对比例1中，甲醛中的丙烯酸、马来酸、丙烯醛含量明显增加，最终废盐水中的难处理苯胺类杂质明显增加，导致在氯碱回用中槽电压增高。
通过实施例2与对比例2的对比可见，在制甲醛反应中，对比例2采用了较高的反应压力，结果甲醛中的丙烯酸、马来酸、丙烯醛含量明显增加，最终废盐水中的难处理苯胺类杂质明显增加，导致在氯碱回用中槽电压增高。
通过实施例3与对比例3的对比可以很清晰的发现，甲醇中乙醇含量一定时，氧醇摩尔比越高，甲醛中的丙烯酸、马来酸、丙烯醛含量越高，最终废盐水中的难处理苯胺类杂质含量越高，导致在氯碱回用中槽电压增高。
实施例2中，乙醇含量为80ppm，最终废盐水中的难处理胺类几乎未检出，可以直接应用于氯碱。
因此，通过控制甲醇中的乙醇总含量低于或等于100ppm，制甲醛反应的氧醇摩尔比为0.9～1.3，反应压力≤1.9bara，大大降低了丙烯酸、马来酸、丙烯醛与胺类反应生成的难处理苯胺类杂质的量，使得处理后废盐水中萃取剂、苯胺及MDA等常规有机胺物质≤0.1ppm，难处理苯胺类物质≤0.3ppm，满足后续处理的要求。
尽管本发明的内容已经通过上述优选实施例作了详细介绍，但应当认识到上述的描述不应被认为是对本发明的限制。本领域技术人员可以理解，在本说明书的教导之下，可对本发明做出一些修改或调整。这些修改或调整也应当在本发明权利要求所限定的范围之内。

Claims (9)

  1. 一种降低MDI生产过程的盐水中难处理苯胺类物质的控制方法，其特征在于，所述方法包含以下步骤：(1)在铁钼催化剂的存在下，采用甲醇与新鲜空气反应制得含甲醛的反应气，冷却后采用纯水吸收，得到生产DAM的原料-甲醛水溶液；
    (2)在酸性催化剂的存在下，采用制得的甲醛水溶液与苯胺经缩合反应、转位重排反应、酸碱中和反应后，得到含有二苯基甲烷系的二胺与多胺的盐水相和有机相；
    (3)将盐水相进行萃取、汽提处理后得到废盐水；有机相经纯化、精制处理后得到二苯基甲烷系的二胺与多胺；
    其中步骤(1)中，所述甲醇中的乙醇含量低于或等于100ppm，氧醇摩尔比为0.9～1.3，优选为1.0-1.2，反应压力≤1.9bara。
  2. 如权利要求1所述的方法，其特征在于，所述步骤(2)中采用盐酸作为酸性催化剂，其与苯胺的摩尔比为0.1-0.5，优选为0.15-0.35；其中，所述酸性催化剂优选为质量浓度为25％-37％的盐酸水溶液。
  3. 如权利要求1或2所述的方法，其特征在于，所述步骤(2)中甲醛与苯胺的摩尔比为0.30-0.60，所述甲醛水溶液的质量浓度为30％-50％，其中甲醛水溶液中丙烯酸、马来酸、丙烯醛三种杂质总量≤20ppm，优选≤8ppm。
  4. 如权利要求1-3任一项所述的方法，其特征在于，所述步骤(2)中缩合反应在50-70℃下进行1-3h。
  5. 如权利要求1-4任一项所述的方法，其特征在于，所述步骤(2)中转位重排反应在75-110℃下进行转位重排反应1-5h。
  6. 如权利要求1-5任一项所述的方法，其特征在于，所述步骤(2)中酸碱 中和反应在100-120℃下进行，进行所述酸碱中和反应所用的碱液选自氢氧化钠水溶液或氢氧化钾水溶液，优选为质量百分浓度为30％-55％的氢氧化钠水溶液，碱液加入量相对于盐酸催化剂摩尔比为1.03-1.08。
  7. 如权利要求1-6任一项所述的方法，其特征在于，所述步骤(3)中，对所述盐水相进行所述萃取所用的萃取剂选自苯胺或甲苯，按照盐水相与萃取剂的体积比0.1-0.4的比例进行萃取，萃取过程在萃取塔中逆向流动；萃取温度为95-105℃。
  8. 如权利要求1-7任一项所述的方法，其特征在于，所述步骤(3)中所述汽提在汽提塔中进行，汽提的温度控制在95-110℃。
  9. 如权利要求1-8任一项所述的方法，其特征在于，所述步骤(3)中制得的废盐水可直接送至离子膜电解制碱装置进行使用，电解槽电压稳定低于3.1V，电流效率持续高于95％。
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