Method for preparing toluene diisocynate by phosgene method

Abstract

The invention provides a method for preparing toluene diisocynate through a phosgene method, and belongs to the technical field of toluene diisocynate preparation. According to the method, liquid phosgene is atomized into atomized phosgene through a high-pressure spraying device, the atomized phosgene is in countercurrent contact with a toluenediamine solution sprayed into a phosgenation reactor, the contact area of the atomized phosgene and the toluenediamine solution is increased, and the phosgenation reaction process is accelerated. In addition, due to the arrangement of the liquid homogenizer, the contact area between the atomized phosgene and the toluenediamine solution is increased, the reaction rate between the atomized phosgene and the toluenediamine solution is increased, and side reactions are reduced. Meanwhile, the phosgene participates in the phosgenation reaction in the form of mist droplets and is not dissolved in the solvent, so that the use of the solvent is greatly reduced, the concentration of the phosgene in the phosgenation reactor is improved, and side reactions are reduced. The liquid phosgene is subjected to high-pressure spraying treatment, so that the use of a solvent is saved, and subsequent solvent separation is facilitated. After the decomposition reaction is finished, hydrogen chloride gas and unreacted phosgene are separated in a freezing mode, phosgene recovery is achieved, and the recovery mode is simple.

Description

Technical Field

[0001] This invention belongs to the field of toluene diisocyanate preparation technology, and relates to a method for preparing toluene diisocyanate by phosgene method. Background Technology

[0002] Toluene diisocyanate (TDI) is mainly used to react with polyols to form polyurethanes and is an important chemical raw material.

[0003] Currently, the main process for producing TDI using the phosgene method involves the reaction of carbon monoxide and chlorine under specific conditions to generate phosgene; the reaction of toluene and nitric acid under acidic conditions to generate dinitrotoluene; the reaction of dinitrotoluene with hydrogen under the action of a catalyst to generate toluene diamine; the toluene diamine, after drying, reacts with phosgene under specific conditions to generate crude TDI; and the crude TDI is then purified by methods such as distillation to obtain TDI with higher purity.

[0004] In the preparation of TDI, the photochemical reaction is a vigorous and rapid process, and the concentrations of phosgene and hydrogen chloride have a significant impact on its effectiveness. Generally, higher phosgene concentrations result in fewer side reactions; the presence of hydrogen chloride increases the occurrence of side reactions and reduces the reaction yield. However, the above-mentioned preparation method requires the use of large amounts of phosgene and recycled solvent. Furthermore, to achieve the separation of phosgene and hydrogen chloride, a large amount of low-temperature light solvent is used to absorb phosgene. Therefore, the use of a large amount of solvent reduces the phosgene concentration participating in the phosgeneification reaction, and the presence of hydrogen chloride adversely affects both the reaction and subsequent solvent separation. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing toluene diisocyanate by phosgene method, so as to solve the problem of low reaction yield in the existing TDI preparation process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This application provides a method for preparing toluene diisocyanate using the phosgene method, comprising: S01: Toluene diamine is dissolved in an inert solvent to form a toluene diamine solution, and liquid phosgene is treated by high-pressure spraying to form atomized phosgene.

[0007] Toluenediamine, also known as diaminotoluene, is a colorless needle-like or rhombic crystal, mainly used in the preparation of toluene diisocyanate, and can also be used as a dye intermediate. In this application, toluenediamine is dissolved in an inert solvent at room temperature to form a toluenediamine solution. The inert solvent is one or more of monochlorobenzene, o-dichlorobenzene, p-dichlorobenzene, toluene, and p-xylene. The mass-to-volume ratio of toluenediamine to the inert solvent is 1:1-2.

[0008] Gaseous phosgene is placed at -10 to 0°C, where it condenses to form liquid phosgene. The liquid phosgene is then passed into a high-pressure spray device and subjected to high-pressure spraying at 5-10 MPa to form atomized phosgene at a pressure of 2-6 MPa. The particle size of this atomized phosgene is 100-200 μm.

[0009] S02: The toluene diamine solution is sprayed into the phosgenation reactor from the top through a homogenizer, and reacts countercurrently with the atomized phosgene entering from the bottom of the phosgenation reactor. The resulting mixture overflows from the top of the phosgenation reactor.

[0010] A liquid equalizer is provided in the upper middle part of the phosgenation reactor. This equalizer includes a liquid equalizer plate and vents and spray heads evenly distributed on the plate. The vents are through holes on the equalizer plate, allowing unreacted atomized phosgene and the mixture formed by the reaction-generated carbamoyl chloride to pass through and overflow from the top of the phosgenation reactor. In this application, the vent diameter is 1-3 mm. The spray heads face the bottom of the phosgenation reactor to ensure that the toluene diamine solution droplets sprayed by the spray heads are evenly distributed into the interior of the phosgenation reactor.

[0011] The toluenediamine solution entering from the top of the phosgenation reactor is sprayed through a spray nozzle. The fine droplets then come into countercurrent contact with the atomized phosgene entering from the bottom of the reactor, increasing the contact area and accelerating the reaction rate while reducing side reactions. Furthermore, because the phosgene participates in the phosgenation reaction as atomized droplets without dissolving in the solvent, solvent usage is significantly reduced, increasing the phosgene concentration in the reactor and minimizing side reactions.

[0012] Furthermore, to increase the contact area between the atomized phosgene and the toluenediamine solution, the pores and spray heads are arranged in a circular, spaced pattern on the liquid distribution plate. As the atomized phosgene passes through the pores, it can quickly come into contact with the toluenediamine solution sprayed by the adjacent nozzles, shortening the contact time and increasing the reaction rate.

[0013] A solution of toluene diamine in fine droplets reacts with atomized phosgene at 100-120°C and 2.5-4 MPa to produce carbamoyl chloride. The generated carbamoyl chloride passes through pores and overflows from the top of the phosgene reactor.

[0014] In this application, to ensure the concentration of phosgene in the phosgenation reactor, the content of liquid phosgene in the phosgenation reactor must be greater than the content of toluenediamine solution. Based on this, the toluenediamine solution and atomized phosgene can be introduced into the phosgenation reactor simultaneously; alternatively, the atomized phosgene can be introduced into the phosgenation reactor first, followed by the toluenediamine solution.

[0015] When the simultaneous entry method is adopted, the atomized phosgene and toluene diamine solution are simultaneously entered into the phosgenation reactor at a feed flow ratio of (3-10):1.

[0016] When a stepwise injection method is adopted, after atomized phosgene is injected into the phosgenation reactor for 2-3 minutes, the toluene diamine solution is then sprayed into the phosgenation reactor. The molar ratio of atomized phosgene to toluene diamine is 3-5:1. More preferably, the molar ratio of atomized phosgene to toluene diamine is 4:1.

[0017] S03: The mixture is heated to 150-160℃ and decomposed into a gaseous mixture and crude TDI. The gaseous mixture is then frozen to obtain hydrogen chloride gas and unreacted liquid phosgene. The crude TDI is then distilled to remove the inert solvent and obtain TDI.

[0018] The mixture overflowing from the top of the phosgenation reactor is heated to 150-160°C, causing carbamoyl chloride in the mixture to decompose into hydrogen chloride gas and crude TDI. Unreacted liquid phosgene and hydrogen chloride gas form a gaseous mixture. This gaseous mixture is passed through a refrigeration unit at -10 to 0°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. The crude TDI is distilled to remove the inert solvent, yielding TDI.

[0019] The present invention has the following beneficial effects: (1) In this application, liquid phosgene is atomized by a high-pressure spray device, which can better contact and mix with the toluene diamine solution sprayed into small droplets, thus accelerating the phosgenation reaction process. At the same time, the high-pressure spray treatment of liquid phosgene saves the use of solvent and is beneficial to the subsequent solvent separation.

[0020] (2) In the phosgenation reactor, the concentration of atomized phosgene is much greater than that of toluene diamine solution, which greatly reduces side reactions and improves the purity of TDI.

[0021] (3) In this application, the setting of the homogenizer increases the contact area between the atomized phosgene and the toluene diamine solution, accelerates the reaction rate between the two, and reduces side reactions.

[0022] (4) Phosgene participates in the phosgenation reaction in the form of mist droplets and does not dissolve in the solvent, thus greatly reducing the use of solvent, increasing the concentration of phosgene in the phosgenation reactor, and reducing side reactions.

[0023] (5) After the decomposition reaction is completed, hydrogen chloride gas and unreacted phosgene are separated by freezing to achieve phosgene recovery, and the recovery method is simple.

[0024] (6) TDI can be produced continuously in this application. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the structure of the phosgene method for preparing toluene diisocyanate provided in the embodiments of this application; Figure 2 A top view of the homogenizer provided in an embodiment of this application; Figure 3 Provided for the embodiments of this application Figure 2 Sectional view at point AA; Symbolic representation: 1-High-pressure spray device, 2-Phosgenesis reactor, 3-Thermal decomposition device, 4-Freezing device, 5-Equalizer, 6-Air hole, 7-Spray head. Detailed Implementation

[0026] This application provides a method for preparing toluene diisocyanate using a phosgene method, and the corresponding system is shown in the attached figure. Figure 1 As shown, the system for preparing toluene diisocyanate by the phosgene method includes a high-pressure spray device 1, a phosgenation reactor 2, a thermal decomposition device 3, and a refrigeration device 4 connected in series. The high-pressure spray device 1 is connected to both the device for holding liquefied phosgene and the bottom of the phosgenation reactor 2, so that the liquefied phosgene is atomized into atomized phosgene and then discharged from the bottom of the phosgenation reactor 2.

[0027] The top of the phosgenation reactor 2 is connected to both a device for holding toluene diamine solution and a thermal decomposition device 3. The reactor 2 also contains a liquid equalizer 5, which has vent holes 6 and spray heads 7, as shown in the attached diagram. Figure 2 , 3 As shown, toluenediamine solution enters from the top of phosgenation reactor 2 and is sprayed into the interior of phosgenation reactor 2 through spray head 7 on the equalizer 5, forming small droplets. Toluenediamine solution and atomized phosgene react countercurrently in phosgenation reactor 2 to form carbamoyl chloride. Carbamoyl chloride and unreacted atomized phosgene pass through pore 6 and are discharged from the top of phosgenation reactor 2 into thermal decomposition device 3.

[0028] In thermal decomposition apparatus 3, carbamoyl chloride decomposes at 150-160°C into hydrogen chloride gas and crude TDI. Unreacted liquid phosgene and hydrogen chloride gas form a gaseous mixture. This gaseous mixture is passed into a refrigeration apparatus 4 at a temperature of -10 to 0°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. Crude TDI is distilled to remove the inert solvent, yielding TDI.

[0029] The technical solution of the present invention will be further explained and described below through specific embodiments.

[0030] Example 1 This application provides a method for preparing toluene diisocyanate using the phosgene method, comprising: S101: Toluenediamine is dissolved in monochlorobenzene at a mass-to-volume ratio of 1:1.5 to form a toluenediamine solution. Gaseous phosgene is placed at -8°C to condense and form liquid phosgene. The liquid phosgene is then subjected to high-pressure spraying using a high-pressure spraying device with a spray pressure of 8 MPa to form atomized phosgene.

[0031] S102: Atomized phosgene is injected into the phosgenation reactor from the bottom; simultaneously, toluenediamine solution is injected into the phosgenation reactor from the top through a spray nozzle on a homogenizer. The feed flow ratio of atomized phosgene to toluenediamine solution is (3-10):1. The atomized phosgene and toluenediamine solution undergo a phosgenation reaction at 110℃ and 3MPa to obtain a mixture. This mixture overflows from the top of the phosgenation reactor through the vents on the homogenizer.

[0032] S103: The mixture overflowing from the top of the phosgenation reactor is heated to 155°C, causing the carbamoyl chloride in the mixture to decompose into a gaseous mixture and crude TDI. The gaseous mixture includes hydrogen chloride gas produced in the reaction and unreacted phosgene. The gaseous mixture is passed into a freezer at -8°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. The crude TDI is distilled to remove monochlorobenzene, yielding TDI.

[0033] Example 2 This application provides a method for preparing toluene diisocyanate using the phosgene method, comprising: S201: Toluenediamine is dissolved in monochlorobenzene at a mass-to-volume ratio of 1:1.5 to form a toluenediamine solution. Gaseous phosgene is placed at -8°C to condense and form liquid phosgene. The liquid phosgene is then subjected to high-pressure spraying using a high-pressure spraying device with a spray pressure of 8 MPa to form atomized phosgene.

[0034] S202: After atomized phosgene is injected into the phosgenation reactor from the bottom for 3 minutes, a toluenediamine solution is injected into the phosgenation reactor from the top through a spray nozzle on a homogenizer. The molar ratio of atomized phosgene to toluenediamine is 4:1. The atomized phosgene and toluenediamine solution undergo a phosgenation reaction at a temperature of 110℃ and a pressure of 3MPa to obtain a mixture. This mixture overflows from the top of the phosgenation reactor through the vents on the homogenizer.

[0035] S203: The mixture overflowing from the top of the phosgenation reactor is heated to 155°C, causing the carbamoyl chloride in the mixture to decompose into a gaseous mixture and crude TDI. The gaseous mixture includes hydrogen chloride gas produced in the reaction and unreacted phosgene. The gaseous mixture is passed into a freezer at -8°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. The crude TDI is distilled to remove monochlorobenzene, yielding TDI.

[0036] Example 3 This application provides a method for preparing toluene diisocyanate using the phosgene method, comprising: S301: Toluenediamine is dissolved in o-dichlorobenzene at a mass-to-volume ratio of 1:1 to form a toluenediamine solution. Gaseous phosgene is placed at -10℃ to condense into liquid phosgene. Atomized phosgene is injected into the phosgenation reactor from the bottom; simultaneously, the toluenediamine solution is injected into the phosgenation reactor from the top through a spray nozzle on a liquid leveler. The feed flow ratio of atomized phosgene to toluenediamine solution is (3-10):1. The atomized phosgene and toluenediamine solution undergo a phosgenation reaction at a temperature of 100℃ and a pressure of 2.50 MPa to obtain a mixture. This mixture overflows from the top of the phosgenation reactor through the vents on the liquid leveler.

[0037] S303: The mixture overflowing from the top of the phosgenation reactor is heated to 150°C, causing the carbamoyl chloride in the mixture to decompose into a gaseous mixture and crude TDI. The gaseous mixture includes hydrogen chloride gas produced in the reaction and unreacted phosgene. The gaseous mixture is passed into a freezer at -10°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. Crude TDI is distilled to remove o-dichlorobenzene, yielding TDI.

[0038] Example 4 This application provides a method for preparing toluene diisocyanate using the phosgene method, comprising: S401: Toluenediamine is dissolved in p-dichlorobenzene at a mass-to-volume ratio of 1:2 to form a toluenediamine solution. Gaseous phosgene is placed at 0°C and condensed to form liquid phosgene. The liquid phosgene is then subjected to high-pressure spraying using a high-pressure spraying device with a spray pressure of 5 MPa to form atomized phosgene.

[0039] S402: After atomized phosgene is injected into the phosgenation reactor from the bottom for 2 minutes, a toluenediamine solution is injected into the phosgenation reactor from the top through a spray nozzle on a homogenizer. The molar ratio of atomized phosgene to toluenediamine is 3:1. The atomized phosgene and toluenediamine solution undergo a phosgenation reaction at a temperature of 100℃ and a pressure of 2.50 MPa to obtain a mixture. This mixture overflows from the top of the phosgenation reactor through the vent on the homogenizer.

[0040] S403: The mixture overflowing from the top of the phosgenation reactor is heated to 150°C, causing the carbamoyl chloride in the mixture to decompose into a gaseous mixture and crude TDI. The gaseous mixture includes hydrogen chloride gas produced in the reaction and unreacted phosgene. The gaseous mixture is passed into a freezer at -10°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. The crude TDI is distilled to remove p-dichlorobenzene, yielding TDI.

[0041] Example 5 This application provides a method for preparing toluene diisocyanate using the phosgene method, comprising: S501: Toluene diamine is dissolved in toluene at a mass-to-volume ratio of 1:2 to form a toluene diamine solution. Gaseous phosgene is placed at 0°C and condensed to form liquid phosgene. The liquid phosgene is then subjected to high-pressure spraying using a high-pressure spraying device with a spray pressure of 10 MPa to form atomized phosgene.

[0042] S502: Atomized phosgene is injected into the phosgenation reactor from the bottom; simultaneously, toluenediamine solution is injected into the phosgenation reactor from the top through a spray nozzle on a homogenizer. The feed flow ratio of atomized phosgene to toluenediamine solution is (3-10):1. The atomized phosgene and toluenediamine solution undergo a phosgenation reaction at 120℃ and 4MPa to obtain a mixture. This mixture overflows from the top of the phosgenation reactor through the vents on the homogenizer.

[0043] S503: The mixture overflowing from the top of the phosgenation reactor is heated to 160°C, causing the carbamoyl chloride in the mixture to decompose into a gaseous mixture and crude TDI. The gaseous mixture includes hydrogen chloride gas produced in the reaction and unreacted phosgene. The gaseous mixture is passed into a freezer at 0°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. The crude TDI is distilled to remove toluene, yielding TDI.

[0044] Example 6 This application provides a method for preparing toluene diisocyanate using the phosgene method, comprising: S601: Toluene diamine is dissolved in p-xylene at a mass-to-volume ratio of 1:1.2 to form a toluene diamine solution. Gaseous phosgene is placed at 0°C and condensed to form liquid phosgene. The liquid phosgene is then subjected to high-pressure spraying using a high-pressure spraying device with a spray pressure of 10 MPa to form atomized phosgene.

[0045] S602: Atomized phosgene is injected into the phosgenation reactor from the bottom; simultaneously, toluenediamine solution is injected into the phosgenation reactor from the top through a spray nozzle on a homogenizer. The feed flow ratio of atomized phosgene to toluenediamine solution is (3-10):1. The atomized phosgene and toluenediamine solution undergo a phosgenation reaction at 120℃ and 4MPa to obtain a mixture. This mixture overflows from the top of the phosgenation reactor through the vents on the homogenizer.

[0046] S603: The mixture overflowing from the top of the phosgenation reactor is heated to 160°C, causing the carbamoyl chloride in the mixture to decompose into a gaseous mixture and crude TDI. The gaseous mixture includes hydrogen chloride gas produced in the reaction and unreacted phosgene. The gaseous mixture is passed into a freezer at 0°C to obtain hydrogen chloride gas and unreacted liquid phosgene frozen into a liquid state. The unreacted liquid phosgene is reused as a reaction feedstock. The hydrogen chloride gas is absorbed by water and used as hydrochloric acid. The crude TDI is distilled to remove p-xylene, yielding TDI.

[0047] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for preparing toluene diisocyanate via phosgene, characterized in that, include: Toluenediamine is dissolved in an inert solvent to form a toluenediamine solution, and liquid phosgene is treated by high-pressure spraying to form atomized phosgene; The toluene diamine solution is sprayed into the phosgenation reactor from the top through a homogenizer and reacts countercurrently with the atomized phosgene that enters from the bottom of the phosgenation reactor. The resulting mixture overflows from the top of the phosgenation reactor. The mixture is heated to 150-160℃ and decomposed into a gaseous mixture and crude TDI. The gaseous mixture is then frozen to obtain hydrogen chloride gas and unreacted liquid phosgene. The crude TDI is then distilled to remove the inert solvent, yielding TDI.

2. The method for preparing toluene diisocyanate by the phosgene method according to claim 1, characterized in that, The mass-to-volume ratio of the toluene diamine to the inert solvent is 1:1-2.

3. The method for preparing toluene diisocyanate by the phosgene method according to claim 1, characterized in that, The atomized phosgene and the toluene diamine solution are simultaneously introduced into the phosgenation reactor at a feed flow ratio of (3-10):

1.

4. The method for preparing toluene diisocyanate by the phosgene method according to claim 1, characterized in that, After the atomized phosgene is injected into the phosgenation reactor for 2-3 minutes, the toluene diamine solution is then sprayed into the phosgenation reactor through a homogenizer.

5. The method for preparing toluene diisocyanate by the phosgene method according to claim 4, characterized in that, The molar ratio of the liquid phosgene to the toluene diamine is (3-5):

1.

6. The method for preparing toluene diisocyanate by the phosgene method according to claim 1, characterized in that, The temperature of the countercurrent contact reaction is 100-120℃, and the pressure is 2.5-4MPa.

7. The method for preparing toluene diisocyanate by the phosgene method according to claim 1, characterized in that, The spray pressure of the high-pressure spray is 5-10 MPa.

8. The method for preparing toluene diisocyanate by the phosgene method according to claim 1, characterized in that, The liquid equalizer includes a liquid equalizer plate and air holes and spray heads evenly distributed on the liquid equalizer plate, with the spray heads facing the bottom of the phosgenation reactor.

9. The method for preparing toluene diisocyanate by the phosgene method according to claim 8, characterized in that, The air holes and the spray head are distributed in a ring at intervals on the liquid equalization plate, and the diameter of the air holes is 1-3mm.

10. The method for preparing toluene diisocyanate by the phosgene method according to claim 1, characterized in that, The freezing temperature of the gaseous mixture is -10 to 0°C.

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