A method for treating toluenediamine tar and recovering toluenediamine

Abstract

The application provides a method for treating toluene diamine tar and recycling toluene diamine. The method comprises the following steps: mixing toluene diamine tar with water, and then heating to enter a flash evaporator; after flash evaporation, condensing the top gas phase into high-temperature water for S3 scraper separator bottom high-concentration tar transportation, and the bottom liquid phase enters the scraper separator; the toluene diamine and water mixture taken from the top of the scraper separator is sent to a toluene diamine dehydration system for further refining, and the high-concentration tar taken from the bottom is mixed with the high-temperature water condensed from the S2 gas phase in a tar tank and then sent out. In the process of treating toluene diamine tar, the method has more moderate process conditions, high toluene diamine recovery rate, and is suitable for continuous industrial production operation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of isocyanate, and particularly relates to a method for toluene diamine tar treatment and toluene diamine recovery. BACKGROUND

[0002] Toluene diamine (TDA for short) is an important polyurethane raw material, and is mainly applied to the production of toluene diisocyanate (TDI for short) or other dyes. High-boiling heavy components, called TDA tar, are produced in the process of preparing toluene diamine by hydrogenation of dinitrotoluene. In the TDA production process, after hydrogenation reaction, crude TDA dehydration, MTDA adjacent removal, and MTDA tar removal, the concentration of toluene diamine tar gradually increases. In order to ensure the flowability of the tar, the toluene diamine tar discharged usually contains 30% toluene diamine. The conventional flash evaporation recovery mode of toluene diamine can reduce the content of toluene diamine in the tar to 15wt%, but the flash evaporator temperature is high, reaching more than 200℃. In order to further recover toluene diamine in the tar, CN103896780 uses a thin film evaporator to recover toluene diamine in the tar, and the content of toluene diamine in the tar can be reduced to 2-5%, but the separation temperature of this process is high (200-240℃), and toluene diamine is easy to self-polymerize to form tar at high temperature, which reduces the recovery rate of toluene diamine and increases the viscosity of the system. CN101875614A uses molecular sieves as adsorbents for toluene diamine tar treatment, and the recovery rate of toluene diamine can reach 70.56%, and CN203222566U discloses a dinitrotoluene hydrogenation tar recovery system using resin as an adsorbent, but there are problems such as poor adsorption selectivity and complex adsorption and desorption process. CN109790104A uses Ni, Co, Pd, Pt and other supported metal-based catalysts to convert part of toluene diamine and heavy components in the tar into methylcyclohexylamine and methylcyclohexyl diamine, thereby improving the flowability or viscosity, but the tar hydrogenation process not only has harsh reaction conditions, but also has complex product composition and difficult separation. 2 + CN115246776A uses modified activated carbon to recover free toluene diamine in toluene diamine tar, and uses ultrasonic waves, Fe

[0003] Therefore, it is urgent to develop a tar treatment and toluene diamine recovery process with mild process conditions and suitable for continuous production, so as to realize high recovery rate of toluene diamine and easy treatment of tar. SUMMARY

[0004] In view of the above problems existing in the prior art, one of the main purposes of the present application is to provide a method for treating toluene diamine tar and recovering toluene diamine, which is suitable for continuous industrial production operation and has more moderate process conditions and high toluene diamine recovery rate during the treatment of toluene diamine tar.

[0005] To achieve the above-mentioned purposes of the present application, the technical scheme of the present application is as follows:

[0006] A method for treating toluene diamine tar and recovering toluene diamine, comprising the following steps:

[0007] S1: After the toluene diamine tar is mixed with water, heating is performed to enter a flash evaporator;

[0008] S2: After flashing, the top gas phase is condensed into high-temperature water for S3 scraper evaporator bottom high-concentration tar transportation, and the bottom liquid phase enters a scraper separator;

[0009] S3: The mixture of toluene diamine and water collected at the top of the scraper separator is sent to a toluene diamine dehydration system for further refining, and the high-concentration tar at the bottom is mixed with high-temperature water in a tar tank and then externally sent.

[0010] In the process of recovering toluene diamine from toluene diamine tar according to the present application, water is added to break the gas-liquid equilibrium partial pressure between TDA and tar, thereby reducing the difficulty of separation of the two, achieving a lower temperature of the scraper separator (compared with conventional flashing and scraping), and achieving better separation effect, so as to improve the recovery rate of toluene diamine.

[0011] Meanwhile, in the process of tar treatment, the added water (pH 3-6) can limit the generation of tar by self-polymerization of toluene diamine at high temperature. The toluene diamine tar system is weakly alkaline, and the amine group self-polymerizes and condenses to form tar under high-temperature alkaline conditions. By adding water with a pH of 3-6 to reduce the pH in the system, the self-polymerization of toluene diamine is reduced, and the recovery rate of toluene diamine is also improved.

[0012] In addition, in the process of tar treatment, the heat at the top of the scraper is used to heat the raw material, heat integration is achieved to reduce energy consumption, and at the same time, the wastewater generated in the process is used to send the tar, improve the flowability of the tar, and has high economic and environmental benefits.

[0013] In an embodiment of the present application, the tar content in the toluene diamine tar in S1 is 70-80wt%.

[0014] In an embodiment of the present application, the temperature of the toluene diamine tar in S1 is 110-130°C, preferably 120-130°C; and the pressure is 2-4barA.

[0015] In an embodiment of the present application, the pH of the water in S1 is 3-6. For example, the source of acidity can be nitric acid and / or sulfuric acid contained in the water.

[0016] In one embodiment of the present application, the temperature of water in S1 is 110-130°C, preferably 120-130°C, and the pressure is 2-4 bar A.

[0017] In one embodiment of the present application, the mass ratio of toluene diamine tar to water is 4-6:1.

[0018] In one embodiment of the present application, the flash temperature in S2 is 120-130°C, and the flash pressure is 1.5-2 bar A.

[0019] In one embodiment of the present application, the flash overhead gas phase condensation temperature in S2 is 100-120°C.

[0020] In one embodiment of the present application, the temperature of the doctor blade in S3 is 170-185°C, preferably 175-185°C, and the pressure of the doctor blade is 0.04-0.06 bar A, preferably 0.05-0.06 bar A.

[0021] In one embodiment of the present application, the mass ratio of high-concentration tar to high-temperature water in S3 is 2-3:1.

[0022] In one embodiment of the present application, the toluene diamine recovery rate in the method is 70-85 wt%, and the process energy consumption is 500-600 kW / t toluene diamine.

[0023] Another object of the present application is to provide a recovered toluene diamine.

[0024] A recovered toluene diamine, which is a toluene diamine recovered by the above method, has a purity of ≥95 wt%, preferably ≥99.5 wt%, and a tar content of <0.2 wt%, preferably <0.1 wt%.

[0025] Compared with the prior art, the present application has the following beneficial effects:

[0026] (1) The temperature of the doctor blade separator is lower (compared with conventional flash and doctor blade), the separation effect is better, and the toluene diamine recovery rate is improved.

[0027] (2) The added water (pH 3-6) can effectively inhibit the self-polymerization of toluene diamine at high temperature to produce tar, and can improve the toluene diamine recovery rate.

[0028] (3) In the tar treatment process, the heat at the top of the doctor blade is used to heat the raw material, heat integration is realized to reduce energy consumption, at the same time, the wastewater produced in the process is used to send tar, the flowability of tar is improved, and the economic and environmental benefits are high. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 This is a schematic diagram of the process flow of the technical solution of the present invention.

[0030] Figure 2 This is a schematic diagram of a conventional vacuum flash evaporation process. Detailed Implementation

[0031] The technical solution and beneficial effects of the present invention will be further described below with reference to the embodiments, but the present invention is not limited to the following embodiments.

[0032] Information on the main raw material sources used in the embodiments of this invention:

[0033] Toluene diamine tar: derived from Wanhua Chemical's TDA unit, analyzed by an Agilent-7890B (DB-5, 30m*0.25mm*0.25mm) instrument, with a tar content of 70%-90%.

[0034] Other substances, such as nitric acid and sulfuric acid, are all obtained through commercial channels unless otherwise specified, and are all of chemical purity.

[0035] Example 1

[0036] a) After the toluene diamine tar and water are thoroughly mixed in a mixer, the mixture is heated to 120°C by a heater and then enters a flash evaporator. The toluene diamine tar content is 70 wt%, the temperature is 110°C, and the pressure is 3 barA. The water is a nitric acid aqueous solution with a pH of 5, a temperature of 130°C, and a pressure of 3 barA. The mass ratio of toluene diamine tar to water is 4:1.

[0037] b) After flash evaporation, the top vapor phase condenses into high-temperature water for the next step of conveying high-concentration tar, while the bottom liquid phase enters the scraper separator. The flash evaporation temperature is 120°C, the flash evaporation pressure is 1.5 barA, and the top vapor phase condensation temperature is 100°C.

[0038] c) The toluene diamine and water mixture collected from the top of the scraper separator is sent to the TDA dehydration system for further refining (the crude TDA material generated by the hydrogenation unit and after the catalyst is removed by the catalyst filtration unit is dehydrated in three stages to reduce the water content of the TDA material so that the water content of the TDA material meets the requirements of the photochemical unit). The high-concentration tar collected from the bottom is mixed with high-temperature water at a ratio of 2:1 in the tar tank to improve the fluidity of the high-concentration tar before being sent out. The scraper temperature is 170°C and the scraper pressure is 0.04 barA.

[0039] Test results show that the recovery rate of toluene diamine can reach 79.5%, the energy consumption of the process is 545 kW / t toluene diamine, the purity of the recovered toluene diamine is 99.5%, and the tar content is 0.15%.

[0040] Example 2

[0041] a) The toluenediamine tar and water are mixed in a mixer, then heated to 125°C by a heater, and then enter the flasher, wherein the toluenediamine tar content is 80wt%, the temperature is 120°C, and the pressure is 2.3barA; the water is nitric acid aqueous solution, the pH is 3, the temperature is 120°C, and the pressure is 2.3barA; the mass ratio of toluenediamine tar to water is 6:1.

[0042] b) After the flasher, the top gas phase is condensed into high-temperature water for transporting high-concentration tar in the next step, and the bottom liquid phase enters the scraper separator, wherein the flash temperature is 125°C, the flash pressure is 1.5barA, and the condensation temperature of the top gas phase of the flasher is 120°C.

[0043] c) The mixture of toluenediamine and water taken from the top of the scraper separator is sent to the TDA dehydration system for further refining (the crude TDA material generated by the hydrogenation unit and removed from the catalyst after passing through the catalyst filter unit is subjected to three-stage dehydration to reduce the water content of the TDA material, so that the water content of the TDA material meets the requirements of the photochemical unit), and the high-concentration tar and high-temperature water 3:1 are mixed in the tar tank to improve the flowability of the high-concentration tar before being sent out, wherein the scraper temperature is 180°C, and the scraper pressure is 0.05barA.

[0044] The results show that the toluenediamine recovery rate can reach 73.5%, the process energy consumption is 502kW / t toluenediamine, the purity of the recovered toluenediamine is 99.7%, and the tar content is 0.18%.

[0045] Example 3

[0046] a) The toluenediamine tar and water are mixed in a mixer, then heated to 130°C by a heater, and then enter the flasher, wherein the toluenediamine tar content is 75%, the temperature is 130°C, and the pressure is 3.3barA; the water is sulfuric acid aqueous solution, the pH is 6, the temperature is 110°C, and the pressure is 3.3barA; the mass ratio of toluenediamine tar to water is 5:1.

[0047] b) After the flasher, the top gas phase is condensed into high-temperature water for transporting high-concentration tar in the next step, and the bottom liquid phase enters the scraper separator, wherein the flash temperature is 130°C, the flash pressure is 2barA, and the condensation temperature of the top gas phase of the flasher is 120°C.

[0048] c) The toluene diamine and water mixture collected from the top of the scraper separator is sent to the TDA dehydration system for further refining (the crude TDA material generated by the hydrogenation unit and after the catalyst is removed by the catalyst filtration unit is dehydrated in three stages to reduce the water content of the TDA material so that the water content of the TDA material meets the requirements of the photochemical unit). The high-concentration tar collected from the bottom is mixed with high-temperature water at a ratio of 2.5:1 in the tar tank to improve the fluidity of the high-concentration tar before being sent out for processing. The scraper temperature is 185°C and the scraper pressure is 0.06 barA.

[0049] The results showed that the recovery rate of toluene diamine could reach 80.9%, the energy consumption of the process was 598 kW / t toluene diamine, the purity of the recovered toluene diamine was 99.6%, and the tar content was 0.17%.

[0050] Comparative Example 1

[0051] Toluene diamine tar is simply flash-evaporated under reduced pressure.

[0052] according to Figure 2 As shown in the process flow, after the toluene diamine tar enters the flash evaporator and is flashed, the toluene diamine is collected from the top and the high-concentration tar is collected from the bottom liquid phase. The toluene diamine tar content is 80%, the temperature is 130℃, and the pressure is 3 barA. The flash evaporation temperature is 240℃ and the flash evaporation pressure is 0.05 barA.

[0053] The results showed that the recovery rate of toluene diamine was 51.2%, and the energy consumption of the process was 860 KW / t toluene diamine.

[0054] Comparative Example 2

[0055] A mixture of toluene diamine tar and water is simply subjected to vacuum flash evaporation.

[0056] according to Figure 2 As shown in the process flow, the mixture of toluene diamine tar and water enters the flash evaporator for flash evaporation. The top of the flash evaporator collects toluene diamine and water and sends them to the TDA dehydration system for further purification. The bottom liquid phase collects high-concentration tar. The toluene diamine tar and water mixture contains 64% tar and 20% water, at a temperature of 130°C and a pressure of 3 barA. The flash evaporation temperature is 180°C and the flash evaporation pressure is 0.05 barA.

[0057] The results showed that the recovery rate of toluene diamine was 43%, and the energy consumption of the process was 800 KW / t toluene diamine.

Claims

1. A method for recovering toluenediamine from toluenediamine tar, characterized in that, The method includes the following steps: S1: Toluene diamine tar is mixed with water, heated, and then fed into a flash evaporator; S2: After flash evaporation, the top gas phase condenses into high-temperature water for conveying high-concentration tar at the bottom of the S3 scraper separator, while the bottom liquid phase enters the scraper separator. S3: The mixture of toluene diamine and water collected from the top of the scraper separator is sent to the toluene diamine dehydration system for further refining. The high-concentration tar collected from the bottom is mixed with the high-temperature water condensed from the S2 gas phase in the tar tank and then sent out. The pH of the water in S1 is 3-6.

2. The method according to claim 1, characterized in that, The toluene diamine tar in S1 has a tar content of 70-80 wt%; And / or, the temperature of the toluene diamine tar in S1 is 110-130℃; the pressure is 2-4 barA; And / or, the temperature of the water in S1 is 110-130℃ and the pressure is 2-4 barA.

3. The method according to claim 2, characterized in that, The temperature of toluene diamine tar in S1 is 120-130℃; And / or, the temperature of the water in S1 is 120-130℃; The mass ratio of toluene diamine tar to water in S1 is 4-6:

1.

4. The method according to claim 1 or 2, characterized in that, The flash temperature in S2 is 120-130℃; the flash pressure is 1.5-2 barA. And / or, the condensation temperature of the vapor phase extracted from the top of the flash evaporator in S2 is 100-120℃.

5. The method according to claim 1 or 2, characterized in that, In S3, the scraper temperature is 170-185℃; the scraper pressure is 0.04-0.06 barA. And / or, the mass ratio of high-concentration tar to high-temperature water in S3 is 2-3:

1.

6. The method according to claim 5, characterized in that, In S3, the scraper temperature is 175-185℃; the scraper pressure is 0.05-0.06 barA.

7. The method according to claim 1 or 2, characterized in that, The recovery rate of toluene diamine in the method is 70-85 wt%, and the energy consumption of the process is 500-600 kW / t toluene diamine.

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