A method and system for the preparation of toluene diisocyanate by a light solvent system phosgene process

Abstract

The application belongs to the technical field of organic synthesis, and provides a method and system for preparing toluene diisocyanate by a light solvent system phosgene method. Residual phosgene is removed to an extremely low level through multi-stage phosgene removal, and the occurrence of side reactions is effectively inhibited; in combination with de-focalization and toluene diisocyanate refining, the yield and purity of toluene diisocyanate product are significantly improved; at the same time, the toluene diisocyanate refining tower overhead discharge, toluene diisocyanate refining tower side line discharge and toluene diisocyanate refining tower bottom discharge obtained through toluene diisocyanate refining are specially designed, the circulation and recovery of the materials are realized, and the yield of toluene diisocyanate is improved.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and in particular to a method and system for preparing toluene diisocyanate using a phosgene method with a light solvent system. Background Technology

[0002] Toluene diisocyanate (TDI), with the molecular formula C9H6N2O2, is a colorless or pale yellow transparent liquid with a strong, pungent odor. It is highly irritating and corrosive to the eyes, skin, and respiratory mucous membranes. TDI readily changes color upon exposure to light, is insoluble in water, but miscible with organic solvents such as ether, ethanol, acetone, chlorobenzene, and carbon tetrachloride. It is chemically reactive and readily reacts with compounds containing active hydrogen. It reacts rapidly with water to form carbamic acid, which then decomposes into primary amines and CO2, easily leading to increased system pressure or foaming. Therefore, strict moisture control is necessary during production. Simultaneously, TDI can react efficiently with hydroxyl-terminated resins (such as polyester polyols and polyether polyols) to form polyurethane segments, making it a core raw material for flexible foams, coatings, adhesives, and elastomers. TDI is prone to violent exothermic reactions when in contact with strong bases or tertiary amine catalysts, posing safety hazards. At temperatures above 45°C or in the presence of catalysts such as metal salts or organotin compounds, it is prone to self-polymerization to form dimers and oligomers, reducing product purity and potentially causing equipment blockage.

[0003] TDI is the core aromatic isocyanate monomer in the polyurethane industry, with wide downstream applications and inelastic demand. It is mainly used in flexible polyurethane foams (approximately 78%), coatings (approximately 8%), adhesives (approximately 6%), and elastomers (approximately 6%), covering key applications such as residential furniture, automotive interiors, building corrosion protection, and high-end sealing components. With the advancement of policies promoting new energy vehicles and building energy conservation, the demand for TDI in high-end flexible foams and energy-saving insulation materials continues to grow, demonstrating strong industry growth momentum.

[0004] Currently, the industrial production technology of TDI is mainly divided into two major systems: the phosgene method and the non-phosgene method. Among them, the phosgene method, with its mature process route, stable product yield, and advantages of large-scale production, is the only mainstream technology for TDI industrial production at home and abroad. Toluene diamine, solvent, and fresh phosgene are first mixed and fed into a phosgenation cold reaction tower for cold reaction. The resulting product is fed into a phosgenation hot reaction tower for hot reaction. Hydrogen chloride and some phosgene are collected from the top of the phosgenation reaction tower and sent to a hydrogen chloride purification tower for separation and purification. At the same time, some phosgene and HCl are collected as a side stream into a phosgene purification tower for further recovery and utilization. The crude product containing the target product TDI is collected from the bottom of the phosgenation reaction tower. Since the crude TDI product still contains some phosgene, solvent, and tar produced in the reaction, etc., if it is directly fed into subsequent processes, it will affect the purity of the product and the stable operation of the equipment. Based on industrial production experience and relevant literature, crude TDI products require multi-step refining: First, they are sent to a phosgene removal tower to completely remove residual phosgene through a specific separation process; the material after phosgene removal enters the first desolventizing tower and the second desolventizing tower in sequence, where light solvents in the system are gradually removed using distillation separation technology; finally, the material after solvent removal enters the product refining tower, where fine separation effectively separates the tar from the TDI product, ultimately obtaining a high-purity TDI product that meets the requirements of industrial applications.

[0005] However, existing conventional TDI production methods generally suffer from low yields. Summary of the Invention

[0006] In view of this, the object of the present invention is to provide a method and system for preparing toluene diisocyanate using a phosgene method with a light solvent system. The method provided by the present invention improves the yield of toluene diisocyanate while achieving higher purity.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a method for preparing toluene diisocyanate using a phosgene method with a light solvent system, comprising the following steps: Phosgene solution and toluene diamine solution are mixed and subjected to phosgenation cold reaction and phosgenation heat reaction in a phosgenation cold reaction tower and a phosgenation heat reaction tower in sequence, respectively, to obtain the top discharge of the phosgenation heat reaction tower, the side discharge of the phosgenation heat reaction tower, and the bottom discharge of the phosgenation heat reaction tower. The phosgenation heat reaction tower bottom discharge is sequentially subjected to first phosgen removal in the first phosgen removal tower, second phosgen removal in the second phosgen removal tower, third phosgen removal in the third removal tower, first solvent removal in the first desolventizing tower, and second solvent removal in the second desolventizing tower to obtain the bottom discharge of the second desolventizing tower; The bottom product of the second desolventizing tower is sequentially decoked in a decoking tower and refined into toluene diisocyanate in a toluene diisocyanate refining tower, yielding the top product of the toluene diisocyanate refining tower, the side stream product of the toluene diisocyanate refining tower, and the bottom product of the toluene diisocyanate refining tower, respectively; the side stream product of the toluene diisocyanate refining tower is the toluene diisocyanate; the side stream product of the toluene diisocyanate refining tower enters the toluene diisocyanate finished product storage tank; The top discharge from the toluene diisocyanate refining column enters the eleventh condenser for eleventh condensation, yielding an eleventh condensate. A portion of the eleventh condensate is refluxed back to the top of the toluene diisocyanate refining column, while the remainder enters the light component removal column for light component removal, resulting in a light component removal column top discharge, a light component removal column side stream discharge, and a light component removal column bottom discharge. The top discharge from the light component removal column enters the twelfth condenser for twelfth condensation, yielding a twelfth condensate. A portion of the twelfth condensate is refluxed back to the top of the light component removal column, while the remainder is refluxed back to the first solvent removal column for first solvent removal. A portion of the light component removal column bottom discharge is refluxed back to the bottom of the light component removal column, while the remainder is refluxed back to the top of the coke removal column. A portion of the residue from the bottom of the toluene diisocyanate refining tower is refluxed back to the bottom of the toluene diisocyanate refining tower, and the remainder is refluxed back to the bottom of the second desolvation tower.

[0008] Preferably, the mass ratio of phosgene to solvent in the phosgene solution is 5-9:1, and the mass ratio of toluenediamine to solvent in the toluenediamine solution is 1:3-6. The mass ratio of phosgene in the phosgene solution to toluenediamine in the toluenediamine solution is 5.5~8:1.

[0009] Preferably, the operating pressure of the phosgenation cold reaction tower and the phosgenation heat reaction tower is independently 14~16 bar; The temperature at the top of the phosgenation thermal reaction tower is 35~45℃, the temperature at the side stream is 90~95℃, and the temperature at the bottom of the tower is 140~180℃. The total residence time of the materials in the phosgenation cold reaction tower and the phosgenation heat reaction tower is 0.25~0.64h; The residence time ratio of the materials in the phosgenation cold reaction tower and the phosgenation heat reaction tower is 1:60~154.

[0010] Preferably, the method further includes: condensing the top effluent from the phosgenation thermal reaction tower in a first condenser to obtain a first condensate and a first uncondensed gas phase; refluxing the first condensate back to the top of the phosgenation thermal reaction tower; allowing the first uncondensed gas phase to enter an HCl desorption tower to obtain the top effluent and bottom effluent of the HCl desorption tower; condensing the top effluent from the HCl desorption tower in a second condenser to obtain a second condensate and a second uncondensed gas phase; refluxing the second condensate back to the top of the HCl desorption tower, and collecting the second uncondensed gas phase; and refluxing the bottom effluent of the HCl desorption tower back to the top of the phosgenation thermal reaction tower.

[0011] Preferably, it further includes: feeding the side stream of the phosgenation thermal reaction tower into the phosgen refining tower for phosgen refining, to obtain the top output of the phosgen refining tower and the bottom output of the phosgen refining tower; The top effluent from the phosgene refining tower is condensed in a third condenser to obtain a third condensate and a third uncondensed gas phase. The third condensate is returned to the top of the phosgene refining tower, and the third uncondensed gas phase enters the phosgene absorption tower for phosgene absorption, resulting in the top effluent and bottom effluent of the phosgene absorption tower. The top effluent from the phosgene absorption tower is then condensed in a fourth condensation to obtain a fourth condensate and a fourth uncondensed gas phase. The fourth condensate is returned to the top of the phosgene absorption tower, and the fourth uncondensed gas phase is collected. A portion of the bottom effluent from the phosgene absorption tower is returned to the bottom of the phosgene absorption tower, and the remaining bottom effluent is stored in a phosgene storage tank for temporary buffering. After pressure stabilization and buffering, it is then transported to the phosgene refrigeration reaction tower. A portion of the phosgene refining tower reboiler discharge is returned to the reboiler of the phosgene refining tower, while the remaining phosgene refining tower reboiler discharge is stored in a phosgene storage tank for temporary buffering. After pressure stabilization and buffering, it is then transported to the phosgene refrigeration reaction tower. The operating pressure for phosgene refining is 0.5~2 bar; The pressure of the phosgene absorption tower is 0.8~1.5 bar, and the temperature does not exceed 165℃.

[0012] Preferably, the bottom temperature of the first phosgene removal tower, the second phosgene removal tower, and the third phosgene removal tower is independently 150~190°C; The operating pressure of the first phosgene removal tower is 3~4 bar; The operating pressure of the second phosgene removal tower is 0.9~1.5 bar; The operating pressure of the third phosgene removal tower is 20~50kPa; The first phosgene removal process yields a top effluent from the first phosgene removal tower and a bottom effluent from the first phosgene removal tower. The top effluent from the first phosgene removal tower enters a fifth condenser for fifth condensation, yielding a fifth condensate and a fifth uncondensed gas phase. A portion of the fifth condensate is returned to the top of the first phosgene removal tower, and the remainder enters the phosgene refining tower for phosgene refining. The fifth uncondensed gas phase enters the phosgene absorption tower for phosgene absorption. A portion of the bottom effluent from the first phosgene removal tower is returned to the bottom of the first phosgene removal tower, and the remainder enters the second phosgene removal tower. The second phosgene removal process yields the top effluent from the second phosgene removal tower and the bottom effluent from the second phosgene removal tower. The top effluent from the second phosgene removal tower enters the sixth condenser for sixth condensation, yielding a sixth condensate and a sixth uncondensed gas phase. A portion of the sixth condensate is returned to the top of the second phosgene removal tower, and the remainder enters the phosgene refining tower for phosgene refining. The sixth uncondensed gas phase enters the phosgene absorption tower for phosgene absorption. A portion of the bottom effluent from the second phosgene removal tower is returned to the bottom of the second phosgene removal tower, and the remainder enters the third phosgene removal tower. The third phosgene removal process yields both the top effluent and the bottom effluent of the third phosgene removal tower. The top effluent from the third phosgene removal tower enters the seventh condenser for seventh condensation, resulting in a seventh condensate and a seventh uncondensed gas phase. A portion of the seventh condensate is returned to the top of the third phosgene removal tower, while the remainder enters the phosgene refining tower for phosgene refining. The seventh uncondensed gas phase enters the phosgene absorption tower for phosgene absorption. A portion of the bottom effluent from the third phosgene removal tower is returned to the bottom of the third phosgene removal tower, while the remainder enters the first desolventizing tower.

[0013] Preferably, the operating pressure of the first desolvation tower is 1.1~1.3 bar, the bottom temperature is 150~180℃, and the top temperature is 100~110℃; The operating pressure of the second desolvation tower is 5~8 kPa, the bottom temperature is 150~170℃, and the top temperature is 35~45℃; After the first solvent is removed, the top product and bottom product of the first desolventizing tower are obtained. The top product of the first desolventizing tower enters the eighth condenser for eighth condensation, resulting in eighth condensate and eighth uncondensed gas phase. Part of the eighth condensate is refluxed to the top of the first desolventizing tower, and the remainder enters the solvent refining tower for solvent refining, resulting in the top product and bottom product of the solvent refining tower. The top product of the solvent refining tower enters the ninth condenser for ninth condensation, resulting in ninth condensate. A portion of the ninth condensate is refluxed to the top of the solvent refining tower; the remainder of the ninth condensate enters the light component removal tower for light component removal; a portion of the bottom discharge of the solvent refining tower is refluxed to the bottom of the solvent refining tower; the remainder of the bottom discharge of the solvent refining tower enters the solvent storage tank; the eighth uncondensed gas phase enters the solvent refining tower for solvent refining after heat exchange in the first heat exchanger; a portion of the bottom discharge of the first desolventizing tower is refluxed to the first desolventizing tower, and the remainder of the bottom discharge of the first desolventizing tower enters the second desolventizing tower; After the second solvent is removed, the top product of the second desolventizing tower and the bottom product of the second desolventizing tower are obtained. The top product of the second desolventizing tower enters the tenth condenser for tenth condensation, resulting in tenth condensate and tenth uncondensed gas phase. Part of the tenth condensate is returned to the top of the second desolventizing tower, and the remainder of the tenth condensate enters the solvent refining tower for solvent refining. The tenth uncondensed gas phase enters the solvent refining tower for solvent refining after heat exchange in the second heat exchanger. Part of the bottom product of the second desolventizing tower is returned to the bottom of the second desolventizing tower, and the remainder of the bottom product of the second desolventizing tower enters the decoking tower. The operating pressure of the solvent refining tower is 2~10 kPa.

[0014] Preferably, the operating pressure of the coke removal tower is 2~15 kPa and the temperature is 240~280℃; The operating pressure of the toluene diisocyanate refining column is 2~4 kPa, the top temperature is 35~55℃, the side stream temperature is 150~170℃, and the bottom temperature is 150~190℃.

[0015] This invention also provides a system for the method of preparing toluene diisocyanate using the phosgene method in a light solvent system as described above, comprising: Solvent storage tank; A drying system connected to the solvent storage tank is provided with a toluenediamine inlet on the connecting pipeline between the solvent storage tank and the drying system; the drying system is used for drying the toluenediamine solution. A phosgenation cold reaction tower connected to the drying system is also provided with a phosgenation solution inlet; A phosgene thermal reaction tower connected to the outlet of the phosgene cooling reaction tower; A first phosgene removal tower connected to the bottom outlet of the phosgenation thermal reaction tower; A second phosgene removal tower connected to the bottom outlet of the first phosgene removal tower; A third phosgene removal tower connected to the bottom outlet of the second phosgene removal tower; A first desolvation tower connected to the bottom outlet of the third phosgene removal tower; A second descaling tower connected to the bottom outlet of the first descaling tower; A decoking tower connected to the bottom outlet of the second desolventizing tower; A toluene diisocyanate refining tower connected to the top outlet of the decoking tower; An eleventh condenser is connected to the top outlet of the toluene diisocyanate refining column, and its liquid outlet is connected to the top of the toluene diisocyanate refining column and the light component removal column, respectively. A twelfth condenser is connected to the top outlet of the light component removal column, and its liquid outlet is connected to the top of the light component removal column and the feed inlet of the first desolventizing column, respectively. The bottom outlet of the light component removal column is connected to the bottom of the light component removal column and the top of the decoking column, respectively. A toluene diisocyanate finished product storage tank connected to the side outlet of the toluene diisocyanate refining tower; The outlet of the reboiler of the toluene diisocyanate refining column is connected to the reboiler of the toluene diisocyanate refining column and the reboiler of the second desolventizing column, respectively.

[0016] Preferably, the system further includes: a first condenser connected to the top outlet of the phosgenation thermal reaction tower, the liquid outlet of the first condenser being connected to the top of the phosgenation thermal reaction tower; an HCl desorption tower connected to the gas outlet of the first condenser; a second condenser connected to the top outlet of the HCl desorption tower, the liquid outlet of the second condenser being connected to the top of the HCl desorption tower; and the bottom outlet of the HCl desorption tower being connected to the top of the phosgenation thermal reaction tower. A phosgene refining tower connected to the side outlet of the phosgene thermal reaction tower; a third condenser connected to the top outlet of the phosgene refining tower, the liquid outlet of the third condenser connected to the top of the phosgene refining tower; a phosgene absorption tower connected to the gas outlet of the third condenser; a fourth condenser connected to the top outlet of the phosgene absorption tower, the liquid outlet of the fourth condenser connected to the top of the phosgene absorption tower; the bottom outlet of the phosgene absorption tower connected to the bottom of the phosgene absorption tower and a phosgene storage tank, respectively; the phosgene storage tank connected to the phosgene refrigeration reaction tower; and the bottom outlet of the phosgene refining tower connected to the bottom of the phosgene refining tower and the phosgene storage tank, respectively. A fifth condenser is connected to the top outlet of the first phosgene removal tower. The gas outlet of the fifth condenser is connected to the phosgene absorption tower, and the liquid outlet of the fifth condenser is connected to the top of the first phosgene removal tower and the phosgene refining tower, respectively. The bottom outlet of the first phosgene removal tower is connected to the bottom of the first phosgene removal tower and the second phosgene removal tower, respectively. A sixth condenser is connected to the top outlet of the second phosgene removal tower. The gas outlet of the sixth condenser is connected to the phosgene absorption tower, and the liquid outlet of the sixth condenser is connected to the top of the second phosgene removal tower and the phosgene refining tower, respectively. The bottom outlet of the second phosgene removal tower is connected to the bottom of the second phosgene removal tower and the third phosgene removal tower, respectively. A seventh condenser is connected to the top outlet of the third phosgene removal tower. The gas outlet of the seventh condenser is connected to the phosgene absorption tower, and the liquid outlet of the seventh condenser is connected to the top of the third phosgene removal tower and the phosgene refining tower, respectively. The bottom outlet of the third phosgene removal tower is connected to the bottom of the third phosgene removal tower and the first desolvation tower, respectively. An eighth condenser is connected to the top outlet of the first desolventizing tower; the gas outlet of the eighth condenser is connected to the first heat exchanger; a solvent refining tower is connected to the liquid outlet of the first heat exchanger; a ninth condenser is connected to the top outlet of the solvent refining tower; the liquid outlet of the ninth condenser is connected to the top of the solvent refining tower and the dehydrogenation component tower, respectively; the bottom outlet of the solvent refining tower is connected to the bottom of the solvent refining tower and the solvent storage tank, respectively; the liquid outlet of the eighth condenser is connected to the top of the first desolventizing tower and the solvent refining tower, respectively; the bottom outlet of the first desolventizing tower is connected to the bottom of the first desolventizing tower and the second desolventizing tower, respectively. A tenth condenser is connected to the top outlet of the second desolventizing tower, the gas outlet of the tenth condenser is connected to the second heat exchanger, and a solvent refining tower is connected to the liquid outlet of the second heat exchanger. The liquid outlet of the tenth condenser is connected to the top of the second desolventizing tower and the feed inlet of the solvent refining tower, respectively. The bottom outlet of the second desolventizing tower is connected to the bottom of the second desolventizing tower and the decoking tower, respectively.

[0017] This invention provides a method for preparing toluene diisocyanate using a phosgene method with a light solvent system.

[0018] The present invention achieves the following technical effects compared to the prior art: This invention removes residual phosgene to extremely low levels through multi-stage phosgene removal, effectively suppressing side reactions. Combined with decoking and toluene diisocyanate refining, it significantly improves the yield and purity of toluene diisocyanate. Simultaneously, the top discharge from the toluene diisocyanate refining tower enters the eleventh condenser for eleventh condensation, yielding the eleventh condensate. A portion of this eleventh condensate is refluxed back to the top of the toluene diisocyanate refining tower, and a portion enters the light component removal tower for light component removal, resulting in the top discharge, side stream discharge, and bottom discharge from the light component removal tower. The top discharge from the light component removal tower enters the twelfth condenser for twelfth condensation, yielding the... The twelfth condensate is partially refluxed to the top of the light component removal tower and partially reused in the first solvent removal tower for first solvent removal. A portion of the bottom discharge from the light component removal tower is refluxed to the top of the light component removal tower and a portion is refluxed to the top of the coke removal tower. The side stream discharge from the toluene diisocyanate refining tower enters the toluene diisocyanate finished product storage tank. A portion of the bottom discharge from the toluene diisocyanate refining tower is refluxed to the bottom of the toluene diisocyanate refining tower and a portion is refluxed to the bottom of the second solvent removal tower. This invention designs the toluene diisocyanate refining section as a circulating material recovery system, significantly improving the yield and purity of toluene diisocyanate.

[0019] Furthermore, the pressure of the phosgene absorption tower is preferably 0.8~1.5 bar, and the temperature does not exceed 165℃. Phosgene recovery utilizes an atmospheric pressure phosgene absorption tower, achieving efficient phosgene recovery with a small amount of solvent, avoiding the safety risks associated with pure phosgene distillation equipment, and significantly improving the inherent safety and operational stability of the process.

[0020] Further, after the first solvent is removed, the top product and bottom product of the first desolventizing tower are obtained; the top product of the first desolventizing tower enters the eighth condenser for eighth condensation, obtaining the eighth condensate and the eighth uncondensed gas phase. Part of the eighth condensate is refluxed back to the top of the first desolventizing tower, and the remainder of the eighth condensate enters the solvent refining tower for solvent refining, obtaining the top product and bottom product of the solvent refining tower; the top product of the solvent refining tower enters the ninth condenser for ninth condensation, obtaining the ninth condensate. Part of the ninth condensate is refluxed back to the top of the solvent refining tower; the remainder of the ninth condensate enters the light component removal tower for light component removal; part of the bottom product of the solvent refining tower is refluxed back to the bottom of the solvent refining tower; the remainder of the bottom product of the solvent refining tower enters the solvent storage tank; the eighth uncondensed gas phase... The condensed gas phase, after heat exchange in the first heat exchanger, enters the solvent refining tower for solvent refining; a portion of the bottom discharge from the first desolventizing tower is refluxed back to the first desolventizing tower, and the remainder enters the second desolventizing tower; after the second solvent is removed, the top discharge from the second desolventizing tower and the bottom discharge from the second desolventizing tower are obtained; the top discharge from the second desolventizing tower enters the tenth condenser for tenth condensation, obtaining the tenth condensate and the tenth uncondensed gas phase; a portion of the tenth condensate is refluxed back to the top of the second desolventizing tower, and the remainder enters the solvent refining tower for solvent refining; the tenth uncondensed gas phase, after heat exchange in the second heat exchanger, enters the solvent refining tower for solvent refining; a portion of the bottom discharge from the second desolventizing tower is refluxed back to the bottom of the second desolventizing tower, and the remainder enters the decoking tower. This invention simplifies the design through solvent recycling, making the process more compact, reducing equipment investment, and minimizing energy consumption. The overall technical solution is novel in design, simple in structure, and stable and reliable in operation, simultaneously meeting the multiple requirements of modern chemical production in terms of safety, environmental protection, and economy.

[0021] Compared with existing technologies, this invention significantly improves the quality and yield of toluene diisocyanate (TBD) products through multi-stage phosgene removal, decoking, toluene diisocyanate refining, and material recycling. It employs a solvent absorption phosgene recovery process to eliminate safety hazards associated with pure phosgene equipment, greatly enhancing production safety. Furthermore, through equipment integration and process optimization, it achieves a dual reduction in investment costs and operating energy consumption. The invention is novel in design, simple in structure, scientifically reliable, and meets the dual requirements of modern chemical production for environmental protection and economy. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the present invention; 1-Solvent storage tank; 2-Drying system; 3-Phosgene cold reaction tower; 4-Phosgene heat reaction tower; 5-HCl stripping tower; 6-Phosgene purification tower; 7-First phosgene removal tower; 8-Second phosgene removal tower; 9-Third phosgene removal tower; 10-First solvent removal tower; 11-Second solvent removal tower; 12-Coking tower; 13-Toluene diisocyanate (TDI) purification tower; 14-Light component removal tower; 15-Toluene diisocyanate (TDI) finished product storage tank; 16-Phosgene absorption tower; 17-Heat exchanger 1; 18-Heat exchanger 2; 19-Solvent purification tower; 20-Pump 1; 21-Pump 2; 22-Phosgene storage tank. Detailed Implementation

[0023] This invention provides a method for preparing toluene diisocyanate using a phosgene method with a light solvent system, comprising the following steps: Phosgene solution and toluene diamine solution are mixed and subjected to phosgenation cold reaction and phosgenation heat reaction in a phosgenation cold reaction tower and a phosgenation heat reaction tower in sequence, respectively, to obtain the top discharge of the phosgenation heat reaction tower, the side discharge of the phosgenation heat reaction tower, and the bottom discharge of the phosgenation heat reaction tower. The phosgenation heat reaction tower bottom discharge is sequentially subjected to first phosgen removal in the first phosgen removal tower, second phosgen removal in the second phosgen removal tower, third phosgen removal in the third removal tower, first solvent removal in the first desolventizing tower, and second solvent removal in the second desolventizing tower to obtain the bottom discharge of the second desolventizing tower; The bottom product of the second desolventizing tower is sequentially decoked in a decoking tower and refined into toluene diisocyanate in a toluene diisocyanate refining tower, yielding the top product of the toluene diisocyanate refining tower, the side stream product of the toluene diisocyanate refining tower, and the bottom product of the toluene diisocyanate refining tower, respectively; the side stream product of the toluene diisocyanate refining tower is the toluene diisocyanate; the side stream product of the toluene diisocyanate refining tower enters the toluene diisocyanate finished product storage tank; The top discharge from the toluene diisocyanate refining column enters the eleventh condenser for eleventh condensation, yielding an eleventh condensate. A portion of the eleventh condensate is refluxed back to the top of the toluene diisocyanate refining column, while the remainder enters the light component removal column for light component removal, resulting in a light component removal column top discharge, a light component removal column side stream discharge, and a light component removal column bottom discharge. The top discharge from the light component removal column enters the twelfth condenser for twelfth condensation, yielding a twelfth condensate. A portion of the twelfth condensate is refluxed back to the top of the light component removal column, while the remainder is refluxed back to the first solvent removal column for first solvent removal. A portion of the light component removal column bottom discharge is refluxed back to the bottom of the light component removal column, while the remainder is refluxed back to the top of the coke removal column. A portion of the residue from the bottom of the toluene diisocyanate refining tower is refluxed back to the bottom of the toluene diisocyanate refining tower, and the remainder is refluxed back to the bottom of the second desolvation tower.

[0024] Unless otherwise specified, the raw materials used in this invention are preferably commercially available products.

[0025] This invention mixes a phosgene solution and a toluene diamine solution, and sequentially performs phosgenation cold reaction and phosgenation heat reaction in a phosgenation cold reaction tower and a phosgenation heat reaction tower, respectively, to obtain the top discharge, side stream discharge, and bottom discharge of the phosgenation heat reaction tower. In this invention, the mass ratio of phosgene to solvent in the phosgene solution is preferably 5-9:1, specifically preferably 5:1, 6:1, 7:1, 8:1, or 9:1. In this invention, the solvent used in the phosgene solution preferably includes chlorobenzene and / or o-dichlorobenzene. In this invention, the mass ratio of toluene diamine to solvent in the toluene diamine solution is preferably 1:3-6, specifically preferably 1:3, 1:4, 1:5, or 1:6; the solvent used in the toluene diamine solution is preferably the same type as the solvent used in the phosgene solution, and will not be elaborated further here. In this invention, the mass ratio of phosgene in the phosgene solution to toluenediamine in the toluenediamine solution is preferably 5.5 to 8:1, specifically preferably 5.5:1, 5.6:1, 5.7:1, 5.8:1, 5.9:1, 6:1, 6.1:1, 6.2:1, 6.3:1, 6.4:1, 6.5:1, 6.6:1, 6.7:1, 6.8:1, 6.9:1, 7:1, 7.1:1, 7.2:1, 7.3:1, 7.4:1, 7.5:1, 7.6:1, 7.7:1, 7.8:1, 7.9:1, or 8:1.

[0026] In this invention, the operating pressure of both the phosgenation cold reaction tower and the phosgenation heat reaction tower is preferably 14-16 bar, more preferably 14.5 bar, 15 bar, 15.5 bar, or 16 bar. In this invention, the top temperature of the phosgenation heat reaction tower is preferably 35-45°C, the side stream temperature is preferably 90-95°C, and the bottom temperature is preferably 140-180°C. In this invention, the total residence time of the materials in the phosgenation cold reaction tower and the phosgenation heat reaction tower is preferably 0.25-0.64 h. In this invention, the residence time ratio of the materials in the phosgenation cold reaction tower and the phosgenation heat reaction tower is preferably 1:60-154.

[0027] After obtaining the top product from the phosgenation thermal reaction tower, the present invention preferably further includes: first condensing the top product from the phosgenation thermal reaction tower in a first condenser to obtain a first condensate and a first uncondensed gas phase; the first condensate is refluxed back to the top of the phosgenation thermal reaction tower; the first uncondensed gas phase enters an HCl desorption tower to obtain the top product and bottom product of the HCl desorption tower; the top product of the HCl desorption tower is second condensed in a second condenser to obtain a second condensate and a second uncondensed gas phase; the second condensate is refluxed back to the top of the HCl desorption tower, and the second uncondensed gas phase is collected; the bottom product of the HCl desorption tower is refluxed back to the top of the phosgenation thermal reaction tower. In this invention, the HCl mass content in the second uncondensed gas phase is preferably 90-98%; the phosgene mass concentration in the bottom product of the HCl desorption tower is preferably 30-50%. In this invention, the operating pressure of the HCl desorption tower is preferably 15 bar. In this invention, the top temperature of the HCl desorption tower is preferably -10 to -20°C.

[0028] After obtaining the side stream output from the phosgenation thermal reaction tower, the present invention preferably further includes: feeding the side stream output from the phosgenation thermal reaction tower into a phosgen refining tower for phosgen refining, obtaining a top output and a bottom output from the phosgen refining tower; subjecting the top output from the phosgen refining tower to a third condensation in a third condenser, obtaining a third condensate and a third uncondensed gas phase; refluxing the third condensate to the top of the phosgen refining tower, and feeding the third uncondensed gas phase into a phosgen absorption tower for phosgen absorption, obtaining a top output and a bottom output from the phosgen absorption tower; subjecting the top output from the phosgen absorption tower to a fourth condensation, obtaining... The fourth condensate and the fourth uncondensed gas phase are collected; the fourth condensate is returned to the top of the phosgene absorption tower, and the fourth uncondensed gas phase is collected; a portion of the phosgene absorption tower bottom discharge is returned to the bottom of the phosgene absorption tower, and the remaining phosgene absorption tower bottom discharge is stored in a phosgene storage tank for temporary storage and buffering. After pressure stabilization and buffering, it is then transported to the phosgenation cooling reaction tower; a portion of the phosgene refining tower bottom discharge is returned to the bottom of the phosgene refining tower, and the remaining phosgene refining tower bottom discharge is stored in a phosgene storage tank for temporary storage and buffering. After pressure stabilization and buffering, it is then transported to the phosgenation cooling reaction tower.

[0029] In this invention, the mass concentration of HCl in the side stream effluent of the phosgenation thermal reaction tower is preferably 0.8-1.5%, specifically 1.1%, 1.2%, or 1.5%; the mass concentration of phosgene is preferably 95-99%, specifically 98.5%, 98.8%, or 98.9%. In this invention, the operating pressure of the phosgene refining tower is preferably 0.5-2 bar, specifically 0.5 bar, 1 bar, 1.5 bar, or 2 bar. In this invention, the pressure of the phosgene absorption tower is preferably 0.8-1.5 bar, and the temperature is preferably not exceeding 165°C.

[0030] After obtaining the phosgenation thermal reaction tower bottom product, the phosgenation thermal reaction tower bottom product of the present invention is subjected to first phosgen removal in the first phosgen removal tower, second phosgen removal in the second phosgen removal tower, third phosgen removal in the third removal tower, first solvent removal in the first desolventizing tower, and second solvent removal in the second desolventizing tower to obtain the second desolventizing tower bottom product.

[0031] In this invention, the bottom temperature of the first phosgene removal tower, the second phosgene removal tower and the third phosgene removal tower is preferably 150~190℃, and more preferably 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃ or 190℃.

[0032] In this invention, the operating pressure of the first phosgene removal tower is preferably 3 to 4 bar, specifically preferably 3 bar, 3.1 bar, 3.2 bar, 3.3 bar, 3.4 bar, 3.5 bar, 3.6 bar, 3.7 bar, 3.8 bar, 3.9 bar or 4 bar.

[0033] After the first phosgene removal, the present invention preferably obtains the top effluent and the bottom effluent of the first phosgene removal tower, respectively. The top effluent of the first phosgene removal tower preferably enters a fifth condenser for fifth condensation, yielding a fifth condensate and a fifth uncondensed gas phase. A portion of the fifth condensate is returned to the top of the first phosgene removal tower, and the remainder enters the phosgene refining tower for phosgene refining. The fifth uncondensed gas phase enters the phosgene absorption tower for phosgene absorption. A portion of the bottom effluent of the first phosgene removal tower is returned to the bottom of the first phosgene removal tower, and the remainder enters the second phosgene removal tower. In the present invention, the TDI mass concentration in the bottom effluent of the first phosgene removal tower is preferably 12-25%, the phosgene mass concentration is preferably 1.2-6%, the solvent mass concentration is preferably 80-85%, and the tar mass concentration is 0.3-0.7%.

[0034] In this invention, the operating pressure of the second phosgene removal tower is preferably 0.9~1.5 bar, and more preferably 0.9 bar, 1.0 bar, 1.1 bar, 1.2 bar, 1.3 bar, 1.4 bar or 1.5 bar.

[0035] After the second phosgene removal, the present invention preferably obtains the top discharge of the second phosgene removal tower and the bottom discharge of the second phosgene removal tower respectively; the top discharge of the second phosgene removal tower enters the sixth condenser for sixth condensation to obtain the sixth condensate and the sixth uncondensed gas phase; part of the sixth condensate is returned to the top of the second phosgene removal tower, and the remainder of the sixth condensate enters the phosgene refining tower for phosgene refining; the sixth uncondensed gas phase enters the phosgene absorption tower for phosgene absorption; part of the bottom discharge of the second phosgene removal tower is returned to the bottom of the second phosgene removal tower, and the remainder of the bottom discharge of the second phosgene removal tower enters the third phosgene removal tower.

[0036] In this invention, the operating pressure of the third phosgene removal tower is preferably 20~50 kPa, specifically preferably 20 kPa, 25 kPa, 30 kPa, 35 kPa, 40 kPa, 45 kPa or 50 kPa.

[0037] After the third phosgene removal, the present invention preferably obtains the top discharge of the third phosgene removal tower and the bottom discharge of the third phosgene removal tower respectively; the top discharge of the third phosgene removal tower enters the seventh condenser for seventh condensation to obtain the seventh condensate and the seventh uncondensed gas phase; part of the seventh condensate is returned to the top of the third phosgene removal tower, and the remainder of the seventh condensate enters the phosgene refining tower for phosgene refining; the seventh uncondensed gas phase enters the phosgene absorption tower for phosgene absorption; part of the bottom discharge of the third phosgene removal tower is returned to the bottom of the third phosgene removal tower, and the remainder of the bottom discharge of the third phosgene removal tower enters the first desolvation tower.

[0038] In this invention, the operating pressure of the first desolvation tower is preferably 1.1~1.3 bar, specifically preferably 1.1 bar, 1.2 bar or 1.3 bar; the bottom temperature is preferably 150~180℃, specifically preferably 150℃, 160℃, 170℃ or 180℃; and the top temperature is preferably 100~110℃, specifically preferably 100℃, 105℃ or 110℃.

[0039] In this invention, the solvent mass content in the system to be treated before entering the first desolventizing tower is preferably 70-85%, specifically preferably 75.6%, 76.68% or 82.03%.

[0040] After the first solvent is removed, the present invention preferably obtains the top discharge and the bottom discharge of the first solvent removal tower; the top discharge of the first solvent removal tower enters the eighth condenser for eighth condensation, obtaining the eighth condensate and the eighth uncondensed gas phase; a portion of the eighth condensate is refluxed to the top of the first solvent removal tower, and the remaining eighth condensate enters the solvent refining tower for solvent refining, obtaining the top discharge and the bottom discharge of the solvent refining tower; the top discharge of the solvent refining tower enters the ninth condenser for ninth condensation, obtaining the ninth... The condensate, a portion of which is the ninth condensate, is refluxed to the top of the solvent refining tower; the remainder of the ninth condensate enters the light component removal tower for light component removal; a portion of the bottom discharge of the solvent refining tower is refluxed to the bottom of the solvent refining tower; the remainder of the bottom discharge of the solvent refining tower enters the solvent storage tank; the eighth uncondensed gas phase, after heat exchange in the first heat exchanger, enters the solvent refining tower for solvent refining; a portion of the bottom discharge of the first desolventizing tower is refluxed to the first desolventizing tower, and the remainder of the bottom discharge of the first desolventizing tower enters the second desolventizing tower.

[0041] In this invention, the mass content of solvent in the bottom product of the first desolventizing tower is preferably 35-50%, specifically preferably 39.87%, 39.49% or 41.23%.

[0042] In this invention, the operating pressure of the solvent purification tower is preferably 2~10 kPa, specifically preferably 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa or 10 kPa.

[0043] In this invention, the operating pressure of the second desolventizing tower is preferably 5-8 kPa, specifically 5 kPa, 6 kPa, 7 kPa, or 8 kPa; the bottom temperature is preferably 150-170℃, specifically 150℃, 155℃, 160℃, 165℃, or 170℃. The top temperature of the second desolventizing tower is preferably 35-45℃, specifically 35℃, 40℃, 42℃, or 45℃.

[0044] After the second solvent is removed, the present invention preferably obtains the top discharge of the second desolventizing tower and the bottom discharge of the second desolventizing tower; the top discharge of the second desolventizing tower enters the tenth condenser for tenth condensation to obtain the tenth condensate and the tenth uncondensed gas phase; part of the tenth condensate is returned to the top of the second desolventizing tower, and the remainder of the tenth condensate enters the solvent refining tower for solvent refining; the tenth uncondensed gas phase enters the solvent refining tower for solvent refining after heat exchange in the second heat exchanger; part of the bottom discharge of the second desolventizing tower is returned to the bottom of the second desolventizing tower, and the remainder of the bottom discharge of the second desolventizing tower enters the decoking tower.

[0045] In this invention, the mass concentration of the solvent in the bottom product of the second desolventizing tower is preferably 14-28%, specifically preferably 14.37%, 18.65% or 23.21%.

[0046] After obtaining the bottom product from the second desolventizing tower, the present invention sequentially decokes the bottom product from the second desolventizing tower in a decoking tower and refines it into toluene diisocyanate in a toluene diisocyanate refining tower, thereby obtaining the top product from the toluene diisocyanate refining tower, the side stream product from the toluene diisocyanate refining tower, and the bottom product from the toluene diisocyanate refining tower, respectively; the side stream product from the toluene diisocyanate refining tower is the toluene diisocyanate; the side stream product from the toluene diisocyanate refining tower enters the toluene diisocyanate finished product storage tank.

[0047] In this invention, the decoking tower is preferably a vacuum decoking tower, and the vacuum decoking tower is preferably an independent vacuum decoking tower. In this invention, the operating pressure of the decoking tower is preferably 2~15 kPa, specifically preferably 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, 10 kPa, 11 kPa, 12 kPa, 13 kPa, 14 kPa, or 15 kPa; the temperature is preferably 240~280℃, specifically preferably 240℃, 250℃, 260℃, 270℃, or 280℃.

[0048] In this invention, the operating pressure of the toluene diisocyanate refining tower is preferably 2-4 kPa, specifically 2 kPa, 3 kPa, or 4 kPa; the tower top temperature is preferably 35-55℃, specifically 35℃, 36℃, 37℃, 38℃, 39℃, 40℃, 41℃, 42℃, 43℃, 44℃, 45℃, 46℃, 47℃, 48℃, 49℃, 50℃, 51℃, 52℃, 53℃, 54℃, or 55℃; the side stream temperature is preferably 150-170℃, specifically 150℃, 155℃, 160℃, 165℃, or 170℃; and the tower bottom temperature is preferably 150-190℃, specifically 150℃, 155℃, 160℃, 165℃, 170℃, 175℃, 180℃, 185℃, or 190℃.

[0049] After obtaining the top product from the toluene diisocyanate refining tower, the present invention feeds the top product from the toluene diisocyanate refining tower into the eleventh condenser for eleventh condensation, obtaining the eleventh condensate. Part of the eleventh condensate is refluxed back to the top of the toluene diisocyanate refining tower, and the remainder of the eleventh condensate is fed into the light component removal tower for light component removal, resulting in the top product, side stream product, and bottom product of the light component removal tower. The top product from the light component removal tower is fed into the twelfth condenser for twelfth condensation, obtaining the twelfth condensate. Part of the twelfth condensate is refluxed back to the top of the light component removal tower, and the remainder of the twelfth condensate is refluxed back to the first solvent removal tower for first solvent removal. Part of the bottom product from the light component removal tower is refluxed back to the bottom of the light component removal tower, and the remainder of the bottom product from the light component removal tower is refluxed back to the top of the decoking tower. In this invention, the operating pressure of the light component removal tower is preferably 2-10 kPa, specifically 2 kPa, 3 kPa, 4 kPa, 5 kPa, 6 kPa, 7 kPa, 8 kPa, 9 kPa, or 10 kPa; the tower top temperature is preferably 35-45°C; the TDI mass concentration in the top discharge is preferably 3-9%, specifically 4.2%, 5.8%, or 6.15%; and the solvent mass concentration is preferably 90-96%, specifically 94.2% or 95%. The preferred concentrations are 8% or 93.85%; the side stream temperature of the light component removal tower is preferably 150~160℃, and the mass concentration of light component impurities in the test stream discharge is preferably 100%; the bottom temperature of the light component removal tower is preferably 165~175℃, and the mass concentration of TDI in the bottom discharge is preferably 85~92%, specifically preferably 87.52%, 88.75% or 89.87%; the tar mass concentration is preferably 8~15%, specifically preferably 10.13%, 11.25% or 12.48%.

[0050] After obtaining the bottom product of the toluene diisocyanate refining tower, the present invention recycles a portion of the bottom product of the toluene diisocyanate refining tower back to the bottom of the toluene diisocyanate refining tower, and the remaining bottom product of the toluene diisocyanate refining tower back to the bottom of the second desolvation tower.

[0051] This invention processes the top discharge, side discharge, and bottom discharge of the toluene diisocyanate refining tower separately, thereby forming a recycled material recovery system and improving the yield of toluene diisocyanate.

[0052] This invention also provides a system for the method of preparing toluene diisocyanate using the phosgene method in a light solvent system as described above, comprising: Solvent storage tank; A drying system connected to the solvent storage tank is provided with a toluenediamine inlet on the connecting pipeline between the solvent storage tank and the drying system; the drying system is used for drying the toluenediamine solution. A phosgenation cold reaction tower connected to the drying system is also provided with a phosgenation solution inlet; A phosgene thermal reaction tower connected to the outlet of the phosgene cooling reaction tower; A first phosgene removal tower connected to the bottom outlet of the phosgenation thermal reaction tower; A second phosgene removal tower connected to the bottom outlet of the first phosgene removal tower; A third phosgene removal tower connected to the bottom outlet of the second phosgene removal tower; A first desolvation tower connected to the bottom outlet of the third phosgene removal tower; A second descaling tower connected to the bottom outlet of the first descaling tower; A decoking tower connected to the bottom outlet of the second desolventizing tower; A toluene diisocyanate refining tower connected to the top outlet of the decoking tower; An eleventh condenser is connected to the top outlet of the toluene diisocyanate refining column, and its liquid outlet is connected to the top of the toluene diisocyanate refining column and the light component removal column, respectively. A twelfth condenser is connected to the top outlet of the light component removal column, and its liquid outlet is connected to the top of the light component removal column and the feed inlet of the first desolventizing column, respectively. The bottom outlet of the light component removal column is connected to the bottom of the light component removal column and the top of the decoking column, respectively. A toluene diisocyanate finished product storage tank connected to the side outlet of the toluene diisocyanate refining tower; The outlet of the reboiler of the toluene diisocyanate refining column is connected to the reboiler of the toluene diisocyanate refining column and the reboiler of the second desolventizing column, respectively.

[0053] Figure 1 This is a schematic diagram of the system provided by the present invention, which is described below in conjunction with... Figure 1 The system of the present invention will be described in detail.

[0054] The system provided by the present invention includes a solvent storage tank for storing solvents.

[0055] The system provided by the present invention includes a drying system connected to the solvent storage tank, and a toluene diamine inlet is provided on the connecting pipeline between the solvent storage tank and the drying system; the drying system is used for drying the toluene diamine solution; the drying system is preferably a drying tower or a molecular sieve.

[0056] The system provided by this invention includes a phosgenation cold reaction tower connected to the drying system, and the phosgenation cold reaction tower is further provided with a phosgene solution inlet. In this invention, the phosgenation cold reaction tower is preferably a device type with high-intensity mixing capacity, specifically preferably including one or more of the following structural types: jet reactor, high-shear reactor, or other structures with high-intensity mixing effect. In this invention, a pump 1 is preferably installed on the pipeline connecting the drying system and the phosgenation cold reaction tower. In this invention, the phosgene solution preferably enters the phosgenation cold reaction tower via a pump 2.

[0057] The system provided by this invention includes a phosgenation thermal reaction tower connected to the outlet of the phosgenation cooling reaction tower. Preferably, the system further includes: a first condenser connected to the top outlet of the phosgenation thermal reaction tower, the liquid outlet of the first condenser being connected to the top of the phosgenation thermal reaction tower; an HCl desorption tower connected to the gas outlet of the first condenser; a second condenser connected to the top outlet of the HCl desorption tower, the liquid outlet of the second condenser being connected to the top of the HCl desorption tower; and the bottom outlet of the HCl desorption tower being connected to the top of the phosgenation thermal reaction tower. The system provided by the present invention preferably further includes: a phosgene refining tower connected to the side outlet of the phosgene thermal reaction tower; a third condenser connected to the top outlet of the phosgene refining tower, the liquid outlet of the third condenser connected to the top of the phosgene refining tower; a phosgene absorption tower connected to the gas outlet of the third condenser; a fourth condenser connected to the top outlet of the phosgene absorption tower, the liquid outlet of the fourth condenser connected to the top of the phosgene absorption tower; the bottom outlet of the phosgene absorption tower connected to the bottom of the phosgene absorption tower and a phosgene storage tank respectively, the phosgene storage tank connected to the phosgene refrigeration reaction tower; and the bottom outlet of the phosgene refining tower connected to the bottom of the phosgene refining tower and the phosgene storage tank respectively.

[0058] The system provided by this invention includes a first phosgene removal tower connected to the bottom outlet of the phosgenation thermal reaction tower. Preferably, the system further includes a fifth condenser connected to the top outlet of the first phosgene removal tower, the gas outlet of the fifth condenser being connected to the phosgene absorption tower, and the liquid outlet of the fifth condenser being connected to the top of the first phosgene removal tower and the phosgene purification tower, respectively; the bottom outlet of the first phosgene removal tower is connected to the bottom of the first phosgene removal tower and a second phosgene removal tower, respectively.

[0059] The system provided by this invention includes a second phosgene removal tower connected to the bottom outlet of the first phosgene removal tower. Preferably, the system further includes a sixth condenser connected to the top outlet of the second phosgene removal tower, the gas outlet of the sixth condenser being connected to the phosgene absorption tower, and the liquid outlet of the sixth condenser being connected to the top of the second phosgene removal tower and the phosgene purification tower, respectively; the bottom outlet of the second phosgene removal tower is connected to the bottom of the second phosgene removal tower and a third phosgene removal tower, respectively.

[0060] The system provided by this invention includes a third phosgene removal tower connected to the bottom outlet of the second phosgene removal tower. Preferably, the system further includes a seventh condenser connected to the top outlet of the third phosgene removal tower; the gas outlet of the seventh condenser is connected to the phosgene absorption tower; the liquid outlet of the seventh condenser is connected to the top of the third phosgene removal tower and the phosgene purification tower, respectively; and the bottom outlet of the third phosgene removal tower is connected to the bottom of the third phosgene removal tower and the first desolvation tower, respectively.

[0061] The system provided by this invention includes a first desolvation tower connected to the bottom outlet of the third phosgene removal tower. Preferably, the system further includes: an eighth condenser connected to the top outlet of the first desolvation tower, the gas outlet of the eighth condenser connected to a first heat exchanger; a solvent refining tower connected to the liquid outlet of the first heat exchanger; a ninth condenser connected to the top outlet of the solvent refining tower; the liquid outlet of the ninth condenser connected to the top of the solvent refining tower and a dehydrogenation component tower, respectively; the bottom outlet of the solvent refining tower connected to the bottom of the solvent refining tower and a solvent storage tank, respectively; the liquid outlet of the eighth condenser connected to the top of the first desolvation tower and the solvent refining tower, respectively; and the bottom outlet of the first desolvation tower connected to the bottom of the first desolvation tower and a second desolvation tower, respectively.

[0062] The system provided by this invention includes a second descaling tower connected to the bottom outlet of the first descaling tower. Preferably, the system further includes: a tenth condenser connected to the top outlet of the second descaling tower, the gas outlet of the tenth condenser connected to a second heat exchanger; a solvent refining tower connected to the liquid outlet of the second heat exchanger, the liquid outlet of the tenth condenser connected to the top of the second descaling tower and the feed inlet of the solvent refining tower respectively; and the bottom outlet of the second descaling tower connected to the bottom of the second descaling tower and a decoking tower respectively.

[0063] The system provided by the present invention includes a decoking tower connected to the bottom outlet of the second desolventizing tower.

[0064] The system provided by the present invention includes a toluene diisocyanate refining tower connected to the top outlet of the decoking tower.

[0065] The system provided by this invention includes an eleventh condenser connected to the top outlet of the toluene diisocyanate refining column, a liquid outlet of the eleventh condenser connected to the top of the toluene diisocyanate refining column and a light component removal column, a twelfth condenser connected to the top outlet of the light component removal column, and a liquid outlet of the twelfth condenser connected to the top of the light component removal column and the feed inlet of the first desolventizing column; the bottom outlet of the light component removal column is connected to the bottom of the light component removal column and the top of the decoking column.

[0066] The system provided by the present invention includes a toluene diisocyanate finished product storage tank connected to the side outlet of the toluene diisocyanate refining tower.

[0067] In this invention, the outlet of the toluene diisocyanate refining tower is connected to the bottom of the toluene diisocyanate refining tower and the bottom of the second desolvation tower, respectively.

[0068] The present invention achieves the following technical effects compared to the prior art: Compared with existing technologies, this invention abandons the traditional single-stage, atmospheric pressure, and extensive phosgene removal mode, and innovatively constructs a three-stage gradient phosgene removal coupling system. This system consists of a first phosgene removal tower, a second phosgene removal tower, and a third phosgene removal tower connected in series, forming an integrated degassing process of "low-pressure pre-removal - atmospheric pressure fine removal - high-vacuum deep removal". The first phosgene removal tower pre-removes most of the free phosgene in the system at an operating pressure of 3-4 bar. After collecting the light components containing phosgene and solvent at the top of the tower, the liquid phase enters the phosgene absorption tower for phosgene absorption, and the gas phase enters the phosgene refining tower for phosgene refining. The material containing solvent, TDI, and trace amounts of phosgene collected from the bottom of the first phosgene removal tower directly enters the bottom of the second phosgene removal tower. The second phosgene removal tower finely removes the remaining phosgene components under atmospheric pressure of 0.9-1.5 bar. The liquid phase at the top of the tower... Phosgene is absorbed in the phosgene absorption tower, and the gaseous phase is purified in the phosgene refining tower. The heavy components in the bottom of the second phosgene removal tower are directly fed into the feed section of the third phosgene removal tower. The third phosgene removal tower removes trace amounts of residual phosgene under a high vacuum of 20-50 kPa. The high-purity phosgene removed at the top of the tower is directly recycled in a dedicated phosgene absorption tower. The crude TDI material after phosgene removal in the bottom of the third phosgene removal tower is directly fed into an independent vacuum decoking tower. The independent vacuum decoking tower efficiently separates the heavy component tar by adjusting the appropriate bottom temperature. The decoked material is directly fed into a closed-loop material recycling system. The closed-loop material recycling system accurately captures incompletely converted toluene diamine intermediates, light solvents, and trace amounts of unreacted phosgene, and returns them to the reaction unit to participate in the photochemical reaction again. The recycled material is then reused after deep distillation, impurity removal, and dehydration in the solvent refining tower. Compared to traditional processes, this coupled system eliminates the crude distillation and coke removal, unidirectional linear material conveying, and decentralized equipment layout with simple solvent filtration and reuse. It avoids problems such as incomplete degassing, severe tar entrainment, significant material waste, low solvent purity leading to frequent side reactions, component backmixing, and loss of effective components. It also reduces mixing losses and side reaction risks caused by differences in material composition between different processes. The device features a novel design, compact structure, and scientific principle. Through optimized process flow and precise parameter control, it significantly improves product quality and raw material utilization while reducing production costs, meeting the dual requirements of environmental protection and economy in modern chemical production. Actual operation verification shows that this invention stably increases the purity of TDI products from 99.5-99.8% in traditional processes to 99.99% and above, significantly improving resource utilization efficiency and production safety, and possessing outstanding industrial application value. The method of this invention solves the core technical defects of the original single-stage degassing process, such as low yield, safety hazards caused by residual phosgene, serious material loss, and high energy consumption and investment costs during long-term operation. The slight increase in purity is only an additional effect brought about by process optimization. The entire improvement scheme has significant effects in improving TDI yield, enhancing production safety, and achieving material recycling and consumption reduction, and has clear technical progress.

[0069] The following detailed description, in conjunction with embodiments, illustrates the method and system for preparing toluene diisocyanate using the phosgene method with a light solvent system provided by the present invention. However, these descriptions should not be construed as limiting the scope of protection of the present invention.

[0070] Example 1 exist Figure 1 The system shown is used to prepare toluene diisocyanate, specifically as follows: An excess of phosgene (COCl2) solution (with phosgene in approximately 300% excess and a solution mass ratio of phosgene:solvent of approximately 6:1) is pumped into a phosgenation cold reaction tower. Toluene diamine (MTD) and solvent are mixed at a mass ratio of MTD:solvent of approximately 1:3 and then dehydrated in a drying system before being pumped back into the phosgenation cold reaction tower to react with phosgene. The operating pressure of the phosgenation cold reaction tower is 15 bar, and the mass ratio of phosgene to amine compounds is 5.6. The effluent from the phosgenation cold reaction tower is directly fed into the phosgenation heat reaction tower for further reaction. The operating pressure of the phosgenation heat reaction tower is 15 bar. The gas phase collected from the top of the phosgenation heat reaction tower is condensed and then refluxed back to the top of the tower. The temperature at the top of the phosgenation heat reaction tower is 40°C. The uncondensed gas phase contains a large amount of phosgene and enters the HCl stripping tower from the top of the phosgenation heat reaction tower to complete the separation of HCl and phosgene. The effluent from the top of the HCl stripping tower is condensed by a condenser and used as reflux. HCl is collected from the condenser gas phase and sent to the outside. The effluent from the bottom of the HCl stripping tower (phosgene solution) is refluxed back to the top of the phosgenation heat reaction tower. The concentrations of HCl sent to the outside and phosgene refluxed back to the top of the phosgenation heat reaction tower are 95% and 37.1%, respectively. Excess phosgene from the side stream of the phosgenation thermal reaction tower is sent to a phosgene refining tower for purification. The side stream temperature of the phosgenation thermal reaction tower is 92℃, and the operating pressure of the phosgene refining tower is 1 bar. The concentrations of HCl and phosgene entering the phosgene refining tower are 1.5% and 98.5%, respectively. The phosgene-containing gaseous material at the top of the phosgene refining tower is absorbed by the phosgene absorption tower. Part of the material collected from the bottom of the phosgene refining tower is refluxed, and the remainder is sent to a circulating phosgene storage tank for phosgene recycling. The bottom product of the phosgenation thermal reaction tower is a crude TDI solution containing phosgene, solvent, tar, and TDI. The bottom temperature of the phosgenation thermal reaction tower is 150℃, with a TDI concentration of 15.7%, a phosgene concentration of 41.3%, a solvent concentration of 42.96%, and a tar concentration of 0.5%, which is then sent to subsequent processing steps. The total residence time of the materials in the cold and hot reaction vessels of the phosgenation reaction system is 0.3 hours. The crude TDI solution first enters the first phosgene removal tower, which operates at a pressure of 3 bar. Most of the phosgene and a small amount of HCl are collected from the top of the first phosgene removal tower. Most of the liquid phase material is sent to the phosgene refining tower for refining, and a small amount of gaseous material containing phosgene enters the phosgene absorption tower for recovery. The temperature at the top of the first phosgene removal tower is 103°C.The HCl and phosgene concentrations entering the phosgene refining tower are 11% and 89%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 5%. The bottom product of the first phosgene removal tower is a crude TDI solution containing some phosgene, tar, and TDI. The bottom temperature of the first phosgene removal tower is 180℃, with a TDI concentration of 15.35%, a phosgene concentration of 2.1%, a solvent concentration of 82.05%, and a tar concentration of 0.5%. Subsequently, the bottom product of the first phosgene removal tower enters the second phosgene removal tower, which operates at a pressure of 0.95 bar. A portion of phosgene and a small amount of HCl are collected from the top of the second phosgene removal tower, and some liquid phase material is also sent to the phosgene refining tower for refining. A small amount of gaseous material containing phosgene is also sent to the phosgene absorption tower for recovery. The top temperature of the second phosgene removal tower is 39℃. The HCl and phosgene concentrations entering the phosgene refining tower are 8% and 92%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 4.5%. The bottom of the second phosgene removal tower yielded a crude TDI solution containing small amounts of phosgene, tar, and TDI. The bottom temperature of the second phosgene removal tower was 170℃, with a TDI concentration of 16.1%, a phosgene concentration of 1.1%, a solvent concentration of 82.03%, and a tar concentration of 0.5%. The bottom product of the second phosgene removal tower enters the third phosgene removal tower, which operates at a pressure of 20 kPa. A small amount of phosgene and HCl is collected from the top of the third phosgene removal tower. Similarly, some liquid material is sent to the phosgene refining tower for refining, and a small amount of gaseous material containing phosgene is sent to the phosgene absorption tower for recovery. The top temperature of the third phosgene removal tower is 40°C. The concentrations of HCl and phosgene entering the phosgene refining tower are 1% and 99%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 3.8%. The bottom product of the third phosgene removal tower is a crude TDI solution containing tar and TDI, with phosgene removed. The bottom temperature of the tower is 165°C, and the concentrations are as follows: TDI concentration 19.37%, phosgene concentration 0.1%, solvent concentration 80.03%, and tar concentration 0.5%. The crude TDI solution from the bottom of the third phosgene removal tower is fed into the first desolventizing tower for solvent removal. The operating pressure of the first desolventizing tower is 1.3 bar. After condensation, most of the vapor phase at the top of the first desolventizing tower is refluxed, and a small amount of uncondensed solvent is sent to the solvent refining tower for solvent refining. The top temperature of the first desolventizing tower is 105°C. The solvent mass of the small amount of uncondensed solution entering the solvent refining tower is 48% of the solvent mass of the product solution. The bottom product of the first desolventizing tower is a crude TDI solution containing some solvent, TDI, and tar. The bottom temperature of the first desolventizing tower is 160°C, with a TDI mass concentration of 58.27%, a solvent mass concentration of 41.23%, and a tar mass concentration of 0.5%. Subsequently, the bottom product of the first desolventizing tower is sent to the second desolventizing tower. The operating pressure of the second desolventizing tower is 8 kPa. After condensation, most of the vapor phase at the top of the second desolventizing tower is refluxed, and a small amount of uncondensed solvent is also sent to the solvent refining tower. The top temperature of the second desolventizing tower is 40°C.The small amount of uncondensed solution entering the solvent refining tower contains 28% of the solvent mass of the product solution. The bottom product of the second desolventizing tower is a crude TDI solution containing tar and TDI; the bottom temperature of the second desolventizing tower is 155℃, with a TDI mass concentration of 76.59%, a solvent mass concentration of 23.21%, and a tar mass concentration of 0.5%. The uncondensed vapor phases from the tops of the first and second desolventizing towers are cooled and then sent to the solvent refining tower for further processing. The crude TDI solution from the bottom of the second desolventizing tower enters the coke removal tower, which operates at a pressure of 8 kPa and a temperature of 260℃. After flash evaporation, tar is collected from the bottom of the decoking tower, containing 0.57% TDI, 0.43% solvent, and 99% tar by mass. TDI and a small amount of solvent are collected from the top of the decoking tower, condensed, and sent to the TDI refining tower, where the TDI concentration is 86.22%, the solvent concentration is 12.78%, and the tar concentration is 1%. The operating pressure of the TDI refining tower is 4 kPa. Solvent containing a small amount of TDI and light components is collected from the top of the TDI refining tower and sent to the light component removal tower for further processing. The top temperature of the TDI refining tower is 55℃, with a TDI concentration of 0.1% and a solvent concentration of 99.9%. Qualified TDI product is collected from the side stream of the TDI refining tower, cooled, and sent to the TDI finished product storage tank. The side stream temperature of the TDI refining tower is 160℃, with a TDI concentration of 99.99%. The TDI feed containing a small amount of tar in the bottom of the TDI refining tower is returned to the coke removal tower for recycling. The bottom temperature of the TDI refining tower is 175℃, with a TDI concentration of 19.87% and a tar concentration of 80.13%. The operating pressure of the light component removal tower is 6 kPa. After the vapor phase at the top of the light component removal tower is condensed, most of it is refluxed, and a small amount of liquid phase is returned to the first solvent removal tower. The top temperature of the light component removal tower is 40℃, with a TDI mass concentration of 4.2% and a solvent mass concentration of 95.8%. Light component impurities are collected from the side stream of the light component removal tower at a temperature of 160℃, with a light component impurity concentration of 100%. The TDI feed containing a small amount of solvent in the bottom of the light component removal tower is returned to the TDI refining tower for further purification, with a bottom temperature of 170℃. The TDI mass concentration is 88.75% and the tar mass concentration is 11.25%. The operating pressure of the phosgene absorption tower is 1 bar. HCl collected from the top of the phosgene absorption tower is treated as tail gas, with an HCl mass concentration of 100%. The qualified phosgene collected from the bottom of the phosgene absorption tower is returned to the phosgenation refrigeration reaction tower for recycling. The solvent purification tower operates at a pressure of 10 kPa. The solvent collected from the top of the solvent purification tower, containing a very small amount of HCl and phosgene, is sent to the light component removal tower for light component removal. The qualified solvent collected from the bottom of the solvent purification tower is sent to the solvent storage tank for recycling. All uncondensed exhaust gases from the system are collected and treated centrally, and can be used to prepare hydrochloric acid or for harmless disposal.

[0071] Example 2 Except for the following features, the technical features of this example are the same as those in Example 1: An excess phosgene (COCl2) solution (approximately 400% excess phosgene; the mass ratio of phosgene to solvent is approximately 7:1) is pumped into a phosgenation cold reaction tower. Toluene diamine (MTD) and solvent are mixed at a mass ratio of approximately 1:4 (MTD:solvent) and then dehydrated in a drying system before being pumped back into the phosgenation cold reaction tower to react with the phosgene. The operating pressure of the phosgenation cold reaction tower is 14.5 bar, and the mass ratio of phosgene to the amine compound is 7.8. The effluent from the phosgenation cold reaction tower is directly fed into a phosgenation hot reaction tower for further reaction. The operating pressure of the phosgenation hot reaction tower is 14.5 bar. The vapor phase collected from the top of the phosgenation hot reaction tower is condensed and refluxed back to the top of the tower. The temperature at the top of the phosgenation hot reaction tower is 40°C. The uncondensed gas phase contains a large amount of phosgene. It enters the HCl stripping tower from the top of the phosgenation heat reaction tower to complete the separation of HCl and phosgene. The top effluent from the HCl stripping tower is partially condensed by the condenser and used as reflux. The HCl is collected from the condenser gas phase and sent to the outside. The phosgene solution in the bottom of the HCl stripping tower is refluxed to the top of the phosgenation heat reaction tower. The concentrations of HCl sent to the outside and phosgene refluxed to the top of the phosgenation heat reaction tower are 93% and 34.1%, respectively. Excess phosgene from the side stream of the phosgenation thermal reaction tower is sent to a phosgene refining tower for purification. The side stream temperature of the phosgenation thermal reaction tower is 93℃, and the operating pressure of the phosgene refining tower is 0.8 bar. The concentrations of HCl and phosgene entering the phosgene refining tower are 1.2% and 98.8%, respectively. The phosgene-containing gaseous material at the top of the phosgene refining tower is absorbed by the phosgene absorption tower. The phosgene collected from the bottom of the phosgene refining tower is recycled into a circulating phosgene storage tank. The bottom product of the phosgenation thermal reaction tower is a crude TDI solution containing phosgene, solvent, tar, and TDI. The bottom temperature of the phosgenation thermal reaction tower is 155℃, with a TDI concentration of 16.66%, a phosgene concentration of 42.23%, a solvent concentration of 41.11%, and a tar concentration of 0.4%. This solution is then sent to subsequent processing steps. The total residence time of the materials in the cold and hot reaction vessels of the phosgenation reaction system is 0.4 hours. The crude TDI solution discharged from the bottom of the phosgenation thermal reaction tower first enters the first phosgene removal tower, which operates at a pressure of 3 bar. Most of the phosgene and a small amount of HCl are collected from the top of the first phosgene removal tower. Most of the liquid phase material is sent to the phosgene refining tower for purification, and a small amount of phosgene-containing gaseous material is sent to the phosgene absorption tower for recovery. The top temperature of the first phosgene removal tower is 105°C. The concentrations of HCl and phosgene entering the phosgene refining tower are 13.5% and 86.5%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 4.5%. The bottom discharge from the first phosgene removal tower is a crude TDI solution containing some phosgene, tar, and TDI. The bottom temperature of the first phosgene removal tower is 170°C, with a TDI concentration of 16.32%, a phosgene concentration of 1.9%, a solvent concentration of 81.38%, and a tar concentration of 0.4%.Subsequently, the feed from the bottom of the first phosgene removal tower enters the second phosgene removal tower, which operates at a pressure of 0.90 bar. A portion of phosgene and a small amount of HCl are collected from the top of the second phosgene removal tower, while a portion of the liquid phase is also sent to a phosgene refining tower for further refining. A small amount of phosgene-containing gaseous material is also sent to a phosgene absorption tower for recovery. The top temperature of the second phosgene removal tower is 41°C. The concentrations of HCl and phosgene entering the phosgene refining tower are 6.5% and 93.5%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 3.5%. The bottom of the second phosgene removal tower yields a crude TDI solution containing small amounts of phosgene, tar, and TDI. The bottom temperature of the second phosgene removal tower is 175°C, with a TDI concentration of 18.33%, a phosgene concentration of 1.4%, a solvent concentration of 79.77%, and a tar concentration of 0.4%. The feed from the bottom of the second phosgene removal tower enters the third phosgene removal tower, which operates at a pressure of 20 kPa. A small amount of phosgene and HCl is collected from the top of the third phosgene removal tower. Similarly, some liquid material is sent to a phosgene refining tower for purification, and a small amount of phosgene-containing gaseous material is sent to a phosgene absorption tower for recovery. The top temperature of the third phosgene removal tower is 40°C. The concentrations of HCl and phosgene entering the phosgene refining tower are 0.03% and 99.97%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 3.8%. The bottom of the third phosgene removal tower yields a crude TDI solution containing tar and TDI, after phosgene removal. The bottom temperature of the third phosgene removal tower is 165°C, with a TDI concentration of 22.77%, a phosgene concentration of 0.05%, a solvent concentration of 76.68%, and a tar concentration of 0.4%. The crude TDI solution from the bottom of the third phosgene removal tower is fed into the first desolventizing tower for solvent removal. The operating pressure of the first desolventizing tower is 1.2 bar. Most of the vapor phase from the top of the first desolventizing tower is refluxed after condensation, with a small amount of condensed solvent sent to the solvent refining tower for solvent purification. The top temperature of the first desolventizing tower is 103°C. The small amount of uncondensed solution entering the solvent refining tower contains 45% of the solvent mass of the product solution. The bottom of the first desolventizing tower yields a crude TDI solution containing some solvent, TDI, and tar. The bottom temperature of the first desolventizing tower is 165°C, with a TDI concentration of 59.63%, a solvent concentration of 39.87%, and a tar concentration of 0.4%. The liquid from the bottom of the first desolventizing tower is then fed into the second desolventizing tower, which operates at 7 kPa. Most of the vapor phase from the top of the second desolventizing tower is refluxed after condensation, with a small amount of condensed solvent also sent to the solvent refining tower. The top temperature of the second desolventizing tower is 40°C. The small amount of uncondensed solution entering the solvent refining tower contains 30% of the solvent mass of the product solution. The bottom product of the second desolventizing tower yields a crude TDI solution containing tar and TDI; the bottom temperature of the second desolventizing tower is 153℃, with a TDI concentration of 80.85%, a solvent concentration of 18.65%, and a tar concentration of 0.4%. The uncondensed vapor phases from the tops of the first and second desolventizing towers are cooled and then sent to the solvent refining tower for further processing.The crude TDI solution from the bottom of the second desolventizing tower enters the coke removal tower, which operates at a pressure of 5 kPa and a temperature of 255°C. After flash evaporation, tar is collected from the bottom of the coke removal tower, containing 0.33% TDI, 0.67% solvent, and 99% tar. TDI and a small amount of solvent are collected from the top of the coke removal tower, condensed, and sent to the TDI refining tower, where the TDI concentration is 88.98%, the solvent concentration is 10.32%, and the tar concentration is 0.7%. The TDI refining tower operates at a pressure of 3 kPa. Solvent containing a small amount of TDI and light components is collected from the top of the TDI refining tower and sent to the light component removal tower for further processing. The top temperature of the TDI refining tower is 53°C, with a TDI concentration of 0.08% and a solvent concentration of 99.92%. Qualified TDI product is collected from the side stream of the TDI refining tower, cooled, and sent to the TDI finished product storage tank. The side stream temperature of the TDI refining tower is 165°C, with a TDI concentration of 99.98%. The TDI material containing a small amount of tar in the TDI refining tower bottom is returned to the coke removal tower for recycling. The TDI refining tower bottom temperature is 180℃, with a TDI concentration of 18.87% and a tar concentration of 81.13%. The light component removal tower operates at a pressure of 5 kPa. Most of the vapor phase condensed at the top of the light component removal tower is refluxed, with a small amount of liquid phase returned to the first solvent removal tower. The light component removal tower top temperature is 40℃, with a TDI concentration of 5.8% and a solvent concentration of 94.2%. Light component impurities are collected from the side stream of the light component removal tower at a temperature of 158℃, with a light component impurity concentration of 100%. The TDI material containing a small amount of solvent in the light component removal tower bottom is returned to the TDI refining tower for further purification, with a tower bottom temperature of 173℃. The TDI concentration is 87.52%, and the tar concentration is 12.48%. The phosgene absorption tower operates at a pressure of 1 bar. HCl collected from the top of the phosgene absorption tower is treated as tail gas, with an HCl concentration of 100%. The qualified phosgene collected from the bottom of the phosgene absorption tower is returned to the phosgenation refrigeration reaction tower for recycling. The solvent purification tower operates at a pressure of 9 kPa. The solvent collected from the top of the solvent purification tower, containing a very small amount of HCl and phosgene, is sent to the light component removal tower for light component removal. The qualified solvent collected from the bottom of the solvent purification tower is sent to the solvent storage tank for recycling. All uncondensed exhaust gases from the system are collected and treated centrally, and can be used to prepare hydrochloric acid or for harmless disposal.

[0072] Example 3 Except for the following features, the technical features of this example are the same as those in Example 1: An excess phosgene (COCl2) solution (approximately 500% excess phosgene; solution mass ratio of phosgene:solvent approximately 8:1) is pumped into a phosgenation cold reaction tower. Toluene diamine (MTD) and solvent are mixed at a mass ratio of MTD:solvent approximately 1:5 and then dehydrated in a drying system before being pumped back into the phosgenation cold reaction tower to react with the phosgene. The operating pressure of the phosgenation cold reaction tower is 15.5 bar, and the mass ratio of phosgene to the amine compound is 6.2. The effluent from the phosgenation cold reaction tower is directly fed into a phosgenation hot reaction tower for further reaction. The operating pressure of the phosgenation hot reaction tower is 15.5 bar. The vapor phase collected from the top of the phosgenation hot reaction tower is condensed and refluxed back to the top of the tower. The temperature at the top of the phosgenation hot reaction tower is 40°C. The uncondensed gas phase contains a large amount of phosgene and enters the HCl stripping tower from the top of the phosgenation thermal reaction tower to complete the separation of HCl and phosgene. The top effluent from the HCl stripping tower is partially condensed in a condenser and used as reflux. HCl is collected from the condenser gas phase and sent to the outside. The phosgene solution in the bottom of the HCl stripping tower is refluxed back to the top of the phosgenation thermal reaction tower. The concentrations of HCl sent to the outside and phosgene refluxed to the top of the phosgenation thermal reaction tower are 92% and 33.1%, respectively. Excess phosgene collected from the side stream of the phosgenation thermal reaction tower is sent to the phosgene purification tower for purification. The side stream temperature of the phosgenation thermal reaction tower is 95℃, and the operating pressure of the phosgene purification tower is 1.3 bar. The concentrations of HCl and phosgene entering the phosgene purification tower are 1.1% and 98.9%, respectively. The phosgene-containing gas phase material at the top of the phosgene purification tower is absorbed in the phosgene absorption tower, and the phosgene collected from the bottom of the phosgene purification tower is sent to the circulating phosgene storage tank for phosgene recycling. The phosgenation thermal reaction tower produces a crude TDI solution containing phosgene, solvent, tar, and TDI at its bottom. The bottom temperature of the phosgenation thermal reaction tower is 150℃. The TDI concentration is 15.21%, the phosgene concentration is 43.53%, the solvent concentration is 41.26%, and the tar concentration is 0.6%, which is then fed into subsequent processing steps. The total residence time of the materials in the cold and hot reaction vessels of the phosgenation reaction system is 0.55 hours. The crude TDI solution from the bottom of the phosgenation thermal reaction tower first enters the first phosgene removal tower. The operating pressure of the first phosgene removal tower is 3 bar. Most of the phosgene and a small amount of HCl are collected from the top of the first phosgene removal tower. Most of the liquid phase material is sent to the phosgene refining tower for refining, and a small amount of phosgene-containing gaseous material is sent to the phosgene absorption tower for recovery. The top temperature of the first phosgene removal tower is 107℃. The HCl and phosgene concentrations entering the phosgene refining tower are 12.2% and 87.8%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 2.5%. The bottom product of the first phosgene removal tower is a crude TDI solution containing some phosgene, tar, and TDI; the bottom temperature of the first phosgene removal tower is 170℃, with a TDI concentration of 14.32%, a phosgene concentration of 1.5%, a solvent concentration of 83.58%, and a tar concentration of 0.6%.Subsequently, the bottom product of the first phosgene removal tower enters the second phosgene removal tower. At the top of the second phosgene removal tower, some phosgene and a small amount of HCl are collected, while some liquid material is also sent to the phosgene refining tower for purification. A small amount of gaseous material containing phosgene is also sent to the phosgene absorption tower for recovery. The top temperature of the second phosgene removal tower is 42°C. The concentrations of HCl and phosgene entering the phosgene refining tower are 5.5% and 94.5%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 1.5%. The bottom product of the second phosgene removal tower is a crude TDI solution containing small amounts of phosgene, tar, and TDI. The bottom temperature of the second phosgene removal tower is 175°C, with a TDI concentration of 20.66%, a phosgene concentration of 1.2%, a solvent concentration of 77.64%, and a tar concentration of 0.6%. The feed from the bottom of the second phosgene removal tower enters the third phosgene removal tower, which operates at a pressure of 20 kPa. A small amount of phosgene and HCl is collected from the top of the third phosgene removal tower. Similarly, some liquid material is sent to a phosgene refining tower for purification, and a small amount of phosgene-containing gaseous material is sent to a phosgene absorption tower for recovery. The top temperature of the third phosgene removal tower is 40°C. The concentrations of HCl and phosgene entering the phosgene refining tower are 0.02% and 99.98%, respectively, while the concentration of uncooled phosgene entering the phosgene absorption tower is 1.1%. The bottom of the third phosgene removal tower yields a crude TDI solution containing tar and TDI, after phosgene removal. The bottom temperature of the third phosgene removal tower is 165°C, with a TDI concentration of 23.88%, a phosgene concentration of 0.02%, a solvent concentration of 75.6%, and a tar concentration of 0.6%. The crude TDI solution from the bottom of the third phosgene removal tower is fed into the first desolventizing tower for solvent removal. The operating pressure of the first desolventizing tower is 1.1 bar. Most of the vapor phase from the top of the first desolventizing tower is refluxed after condensation, with a small amount of uncondensed solvent sent to the solvent refining tower for solvent purification. The top temperature of the first desolventizing tower is 102°C. The solvent mass of the small amount of uncondensed solution entering the solvent refining tower accounts for 41% of the solvent mass of the product solution. The bottom of the first desolventizing tower yields a crude TDI solution containing some solvent, TDI, and tar. The bottom temperature of the first desolventizing tower is 165°C, with a TDI concentration of 60.51%, a solvent concentration of 39.49%, and a tar concentration of 0.6%. The liquid from the bottom of the first desolventizing tower is then fed into the second desolventizing tower, which operates at 5 kPa. Most of the vapor phase from the top of the second desolventizing tower is refluxed after condensation, with a small amount of uncondensed solvent also sent to the solvent refining tower. The top temperature of the second desolventizing tower is 40°C. The small amount of uncondensed solution entering the solvent refining tower contains 26% of the solvent mass of the product solution. The bottom of the second desolventizing tower yields a crude TDI solution containing tar and TDI; the bottom temperature of the second desolventizing tower is 158℃, with a TDI concentration of 85.13%, a solvent concentration of 14.37%, and a tar concentration of 0.6%. The uncondensed vapor phases from the tops of the first and second desolventizing towers are cooled and then sent to the solvent refining tower for further processing. The crude TDI solution enters the decoking tower, which operates at a pressure of 3 kPa and a temperature of 245℃.After flash evaporation, tar is collected from the bottom of the decoking tower, containing 0.23% TDI, 0.77% solvent, and 99% tar. TDI and a small amount of solvent are collected from the top of the decoking tower, condensed, and sent to the TDI refining tower. The TDI concentration there is 89.21%, the solvent concentration is 9.99%, and the tar concentration is 0.8%. The operating pressure of the TDI refining tower is 2 kPa. Solvent containing a small amount of TDI and light components is collected from the top of the TDI refining tower and sent to the light component removal tower for further processing. The top temperature of the TDI refining tower is 52℃, with a TDI concentration of 0.03% and a solvent concentration of 99.97%. Qualified TDI product is collected from the side stream of the TDI refining tower, cooled, and sent to the TDI finished product storage tank. The side stream temperature of the TDI refining tower is 167℃, with a TDI concentration of 99.95%. The TDI material containing a small amount of tar in the bottom of the TDI refining tower is returned to the coke removal tower for recycling. The bottom temperature of the TDI refining tower is 178℃, with a TDI concentration of 21.52% and a tar concentration of 78.48%. The operating pressure of the light component removal tower is 3 kPa. After the vapor phase at the top of the light component removal tower is condensed, most of it is refluxed, and a small amount of liquid phase is returned to the first solvent removal tower. The top temperature of the light component removal tower is 40℃, with a TDI concentration of 6.15% and a solvent concentration of 93.85%. Light component impurities are collected from the side stream of the light component removal tower at a temperature of 154℃, with a light component impurity mass concentration of 100%. The TDI material containing a small amount of solvent in the bottom of the light component removal tower is returned to the TDI refining tower for further purification. The bottom temperature of the light component removal tower is 172℃, with a TDI mass concentration of 89.87% and a tar mass concentration of 10.13%. The phosgene absorption tower operates at a pressure of 1 bar. HCl, with a concentration of 100%, is collected from the top of the tower as tail gas for treatment. Qualified phosgene from the bottom of the phosgene absorption tower is returned to the phosgenation refrigeration reaction tower for recycling. The solvent purification tower operates at a pressure of 5 kPa. Solvent containing a very small amount of HCl and phosgene is collected from the top of the solvent purification tower and sent to the light component removal tower for light component removal. Qualified solvent from the bottom of the solvent purification tower is sent to the solvent storage tank for recycling. All uncondensed tail gas from the system is collected and treated centrally, and can be used to prepare hydrochloric acid or for harmless disposal.

[0073] Comparative Example 1 An excess of phosgene (COCl2) solution (wherein, phosgene is approximately 400% in excess; the mass ratio of phosgene to solvent is approximately 8:1) is pumped into a phosgenation cold reaction tower. Toluene diamine (MTD) and solvent are mixed at a mass ratio of MTD:solvent of approximately 1:7 and then dehydrated in a drying system before being pumped into the phosgenation cold reaction tower to react with phosgene. The operating pressure of the phosgenation heat reaction cold reaction tower is 15 bar, and the mass ratio of phosgene to the amine compound is 7.1. The effluent from the phosgenation cold reaction tower is directly fed into the phosgenation heat reaction tower for further reaction. The operating pressure of the phosgenation heat reaction tower is 15 bar. The gas phase collected from the top of the phosgenation heat reaction tower is condensed and refluxed back to the top of the tower. The temperature at the top of the phosgenation heat reaction tower is 40°C. The uncondensed gas phase contains a large amount of phosgene and enters the HCl stripping tower from the top to complete the separation of HCl and phosgene. The effluent from the top of the HCl stripping tower is partially condensed by the condenser and used as reflux. HCl is collected from the condenser gas phase and sent to the outside. The phosgene solution in the bottom of the HCl stripping tower is refluxed back to the top of the phosgenation heat reaction tower. The concentrations of HCl sent to the outside and phosgene refluxed to the top of the phosgenation heat reaction tower are 91% and 32.1%, respectively. Excess phosgene collected from the side stream of the phosgenation heat reaction tower is sent to the phosgene purification tower for purification. The side stream temperature is 92°C. The operating pressure of the phosgene purification tower is 1 bar. The concentrations of HCl and phosgene entering the phosgene purification tower are 1.2% and 98.8%, respectively. HCl is collected from the top of the phosgene refining tower; phosgene is collected from the bottom of the phosgene refining tower. The bottom product of the phosgenation thermal reaction tower is a crude TDI solution containing phosgene, solvent, tar, and TDI. The bottom temperature of the phosgenation thermal reaction tower is 150℃, with a TDI concentration of 12.21%, a phosgene concentration of 46.53%, and a solvent concentration of 41.26%, which enters subsequent processing steps. The total residence time of the materials in the cold and hot reaction vessels of the phosgenation reaction system is 0.35 hours. The crude TDI solution from the bottom of the phosgenation thermal reaction tower enters the phosgene removal tower, which operates at a pressure of 3 bar. Most of the phosgene and a small amount of HCl are collected from the top of the phosgene removal tower and sent to the phosgene refining tower for further refining. The top temperature of the phosgene removal tower is 40℃. The HCl and phosgene concentrations entering the phosgene refining tower are 13.2% and 86.8%, respectively. The bottom product of the phosgene removal tower is a crude TDI solution containing some phosgene, tar, and TDI. The bottom temperature of the phosgene removal tower is 170℃, with a TDI concentration of 13.32%, a phosgene concentration of 1.5%, a solvent concentration of 84.68%, and a tar concentration of 0.5%. This crude TDI solution then enters the first solvent removal tower for solvent removal. The operating pressure of the first solvent removal tower is 1.2 bar. Most of the vapor phase at the top of the first solvent removal tower is refluxed after condensation, and a small amount of uncondensed solvent is sent to the solvent refining tower for solvent purification. The top temperature of the first solvent removal tower is 102℃. The bottom product of the first solvent removal tower is a crude TDI solution containing some solvent, TDI, and tar, with a bottom temperature of 165℃. The TDI concentration is 60.51%, the solvent concentration is 39.49%, and the tar concentration is 0.5%.The solvent is then fed into a second desolventizing tower, operating at 3 kPa. Most of the vapor condensation at the top of the second desolventizing tower is refluxed, with a small amount of uncondensed solvent also fed into a solvent refining tower; the top temperature is 40°C. The bottom of the second desolventizing tower yields a crude TDI solution containing tar and TDI; the bottom temperature is 158°C, with a TDI concentration of 88.13%, a solvent concentration of 17.37%, and a tar concentration of 0.5%. This crude TDI solution is then fed into a TDI refining tower. The TDI refining tower operates at 3 kPa. The top of the TDI refining tower yields a solvent containing a small amount of TDI and light components; the top temperature is 52°C, with a TDI concentration of 0.02% and a solvent concentration of 99.98%. A qualified TDI product is collected from the side stream of the TDI refining tower at 163°C, with a TDI purity of 99.92%. A TDI material containing a small amount of tar is collected from the bottom of the TDI refining tower at 173°C. The TDI concentration was 20.52%, and the tar concentration was 79.48%.

[0074] In Comparative Example 1, the lack of a multi-stage gradient degassing, vacuum decoking, and material recycling system resulted in a reduced TDI yield. Furthermore, the absence of a phosgene absorption tower and solvent refining tower for subsequent processing reduced production safety. Ultimately, this led to a double increase in investment costs and operating energy consumption. The single-stage phosgene removal process in Comparative Example 1 had limited separation efficiency, and residual phosgene within the system could not be fully removed and recovered. This not only resulted in continuous side reactions that damaged TDI products, but also caused a large amount of target products to be carried in the tar. Additionally, the lack of solvent refining and material recycling units made it difficult to reuse solvents and unconverted intermediates, leading to high overall operating costs in terms of long-term raw material consumption, hazardous waste treatment, and tail gas safety management. This invention upgrades single-stage phosgene removal to a three-stage gradient degassing process, incorporating a vacuum decoking tower, material recycling tower, phosgene absorption tower, and solvent refining tower. While the addition of new equipment increases initial investment, and the multi-stage vacuum and recycling processes slightly increase operating energy consumption, the entire system efficiently removes residual phosgene in stages, recovers entrained TDI from tar, and enables solvent recycling, significantly improving overall product yield. It also reduces the risk of phosgene leakage at the source, minimizing ongoing costs for safety maintenance and hazardous waste disposal. The core innovation of this invention is not a significant increase in product purity, but rather addressing the shortcomings of the original single-stage removal process, such as poor material recovery and weak safety control. Considering the entire production cycle, the benefits of raw material savings and increased capacity fully cover the increased energy consumption from the new equipment, demonstrating significant technological advancement value.

[0075] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing toluene diisocyanate using a light solvent system via phosgene, characterized in that, Includes the following steps: Phosgene solution and toluene diamine solution are mixed and subjected to phosgenation cold reaction and phosgenation heat reaction in a phosgenation cold reaction tower and a phosgenation heat reaction tower in sequence, respectively, to obtain the top discharge of the phosgenation heat reaction tower, the side discharge of the phosgenation heat reaction tower, and the bottom discharge of the phosgenation heat reaction tower. The phosgenation heat reaction tower bottom discharge is sequentially subjected to first phosgen removal in the first phosgen removal tower, second phosgen removal in the second phosgen removal tower, third phosgen removal in the third removal tower, first solvent removal in the first desolventizing tower, and second solvent removal in the second desolventizing tower to obtain the bottom discharge of the second desolventizing tower; The bottom product of the second desolventizing tower is sequentially decoked in a decoking tower and refined into toluene diisocyanate in a toluene diisocyanate refining tower, yielding the top product of the toluene diisocyanate refining tower, the side stream product of the toluene diisocyanate refining tower, and the bottom product of the toluene diisocyanate refining tower, respectively; the side stream product of the toluene diisocyanate refining tower is the toluene diisocyanate; the side stream product of the toluene diisocyanate refining tower enters the toluene diisocyanate finished product storage tank; The top discharge from the toluene diisocyanate refining column enters the eleventh condenser for eleventh condensation, yielding an eleventh condensate. A portion of the eleventh condensate is refluxed back to the top of the toluene diisocyanate refining column, while the remainder enters the light component removal column for light component removal, resulting in a light component removal column top discharge, a light component removal column side stream discharge, and a light component removal column bottom discharge. The top discharge from the light component removal column enters the twelfth condenser for twelfth condensation, yielding a twelfth condensate. A portion of the twelfth condensate is refluxed back to the top of the light component removal column, while the remainder is refluxed back to the first solvent removal column for first solvent removal. A portion of the light component removal column bottom discharge is refluxed back to the bottom of the light component removal column, while the remainder is refluxed back to the top of the coke removal column. A portion of the residue from the bottom of the toluene diisocyanate refining tower is refluxed back to the bottom of the toluene diisocyanate refining tower, and the remainder is refluxed back to the bottom of the second desolvation tower.

2. The method according to claim 1, characterized in that, The mass ratio of phosgene to solvent in the phosgene solution is 5-9:1, and the mass ratio of toluenediamine to solvent in the toluenediamine solution is 1:3-6. The mass ratio of phosgene in the phosgene solution to toluenediamine in the toluenediamine solution is 5.5~8:

1.

3. The method according to claim 1, characterized in that, The operating pressures of the phosgenation cold reaction tower and the phosgenation heat reaction tower are independently 14~16 bar; The temperature at the top of the phosgenation thermal reaction tower is 35~45℃, the temperature at the side stream is 90~95℃, and the temperature at the bottom of the tower is 140~180℃. The total residence time of the materials in the phosgenation cold reaction tower and the phosgenation heat reaction tower is 0.25~0.64h; The residence time ratio of the materials in the phosgenation cold reaction tower and the phosgenation heat reaction tower is 1:60~154.

4. The method according to claim 1, characterized in that, Also includes: The top effluent from the phosgenation thermal reaction tower is first condensed in a first condenser to obtain a first condensate and a first uncondensed gas phase. The first condensate is refluxed back to the top of the phosgenation thermal reaction tower. The first uncondensed gas phase enters an HCl stripping tower to obtain the top effluent and bottom effluent of the HCl stripping tower. The top effluent from the HCl stripping tower is second condensed in a second condenser to obtain a second condensate and a second uncondensed gas phase. The second condensate is refluxed back to the top of the HCl stripping tower, and the second uncondensed gas phase is collected. The bottom effluent from the HCl stripping tower is refluxed back to the top of the phosgenation thermal reaction tower.

5. The method according to claim 1, characterized in that, Also includes: The side stream of the phosgenation thermal reaction tower is fed into the phosgen refining tower for phosgen refining, resulting in the top discharge and bottom discharge of the phosgen refining tower. The top effluent from the phosgene refining tower is condensed in a third condenser to obtain a third condensate and a third uncondensed gas phase. The third condensate is returned to the top of the phosgene refining tower, and the third uncondensed gas phase enters the phosgene absorption tower for phosgene absorption to obtain the top effluent from the phosgene absorption tower and the bottom effluent from the phosgene absorption tower. The top effluent from the phosgene absorption tower undergoes a fourth condensation to obtain a fourth condensate and a fourth uncondensed gas phase. The fourth condensate is returned to the top of the phosgene absorption tower, and the fourth uncondensed gas phase is collected. A portion of the bottom effluent from the phosgene absorption tower is returned to the bottom of the phosgene absorption tower, and the remaining bottom effluent is stored in a phosgene storage tank for temporary buffering. After pressure stabilization and buffering, it is then transported to the phosgene refrigeration reaction tower. A portion of the phosgene refining tower reboiler discharge is returned to the reboiler of the phosgene refining tower, while the remaining phosgene refining tower reboiler discharge is stored in a phosgene storage tank for temporary buffering. After pressure stabilization and buffering, it is then transported to the phosgene refrigeration reaction tower. The operating pressure for phosgene refining is 0.5~2 bar; The pressure of the phosgene absorption tower is 0.8~1.5 bar, and the temperature does not exceed 165℃.

6. The method according to claim 1, characterized in that, The bottom temperature of the first phosgene removal tower, the second phosgene removal tower, and the third phosgene removal tower is independently 150~190℃; The operating pressure of the first phosgene removal tower is 3~4 bar; The operating pressure of the second phosgene removal tower is 0.9~1.5 bar; The operating pressure of the third phosgene removal tower is 20~50kPa; The first phosgene removal yields the top discharge of the first phosgene removal tower and the bottom discharge of the first phosgene removal tower. The top discharge from the first phosgene removal tower enters the fifth condenser for fifth condensation, resulting in a fifth condensate and a fifth uncondensed gas phase. Part of the fifth condensate is returned to the top of the first phosgene removal tower, and the remainder enters the phosgene refining tower for phosgene refining. The fifth uncondensed gas phase enters the phosgene absorption tower for phosgene absorption. Part of the bottom discharge from the first phosgene removal tower is returned to the bottom of the first phosgene removal tower, and the remainder enters the second phosgene removal tower. The second phosgene removal process yields the top effluent from the second phosgene removal tower and the bottom effluent from the second phosgene removal tower. The top effluent from the second phosgene removal tower enters the sixth condenser for sixth condensation, yielding a sixth condensate and a sixth uncondensed gas phase. A portion of the sixth condensate is returned to the top of the second phosgene removal tower, and the remainder enters the phosgene refining tower for phosgene refining. The sixth uncondensed gas phase enters the phosgene absorption tower for phosgene absorption. A portion of the bottom effluent from the second phosgene removal tower is returned to the bottom of the second phosgene removal tower, and the remainder enters the third phosgene removal tower. The third phosgene removal yields the top discharge of the third phosgene removal tower and the bottom discharge of the third phosgene removal tower, respectively. The top discharge from the third phosgene removal tower enters the seventh condenser for seventh condensation, resulting in a seventh condensate and a seventh uncondensed gas phase. Part of the seventh condensate is returned to the top of the third phosgene removal tower, and the remainder enters the phosgene refining tower for phosgene refining. The seventh uncondensed gas phase enters the phosgene absorption tower for phosgene absorption. Part of the bottom discharge from the third phosgene removal tower is returned to the bottom of the third phosgene removal tower, and the remainder enters the first desolventizing tower.

7. The method according to claim 1, characterized in that, The first desolventizing tower operates at a pressure of 1.1~1.3 bar, a bottom temperature of 150~180℃, and a top temperature of 100~110℃. The operating pressure of the second desolvation tower is 5~8 kPa, the bottom temperature is 150~170℃, and the top temperature is 35~45℃; After the first solvent is removed, the top product and bottom product of the first desolventizing tower are obtained. The top product of the first desolventizing tower enters the eighth condenser for eighth condensation, resulting in eighth condensate and eighth uncondensed gas phase. Part of the eighth condensate is refluxed to the top of the first desolventizing tower, and the remainder enters the solvent refining tower for solvent refining, resulting in the top product and bottom product of the solvent refining tower. The top product of the solvent refining tower enters the ninth condenser for ninth condensation, resulting in ninth condensate. A portion of the ninth condensate is refluxed to the top of the solvent refining tower; the remainder of the ninth condensate enters the light component removal tower for light component removal; a portion of the bottom discharge of the solvent refining tower is refluxed to the bottom of the solvent refining tower; the remainder of the bottom discharge of the solvent refining tower enters the solvent storage tank; the eighth uncondensed gas phase enters the solvent refining tower for solvent refining after heat exchange in the first heat exchanger; a portion of the bottom discharge of the first desolventizing tower is refluxed to the first desolventizing tower, and the remainder of the bottom discharge of the first desolventizing tower enters the second desolventizing tower; After the second solvent is removed, the top product of the second desolventizing tower and the bottom product of the second desolventizing tower are obtained. The top product of the second desolventizing tower enters the tenth condenser for tenth condensation, resulting in tenth condensate and tenth uncondensed gas phase. Part of the tenth condensate is returned to the top of the second desolventizing tower, and the remainder of the tenth condensate enters the solvent refining tower for solvent refining. The tenth uncondensed gas phase enters the solvent refining tower for solvent refining after heat exchange in the second heat exchanger. Part of the bottom product of the second desolventizing tower is returned to the bottom of the second desolventizing tower, and the remainder of the bottom product of the second desolventizing tower enters the decoking tower. The operating pressure of the solvent refining tower is 2~10 kPa.

8. The method according to claim 1, characterized in that, The operating pressure of the coke removal tower is 2~15 kPa, and the temperature is 240~280℃; The operating pressure of the toluene diisocyanate refining column is 2~4 kPa, the top temperature is 35~55℃, the side stream temperature is 150~170℃, and the bottom temperature is 150~190℃.

9. The system used in the method for preparing toluene diisocyanate using the phosgene method with a light solvent system according to any one of claims 1 to 8, characterized in that, include: Solvent storage tank; A drying system connected to the solvent storage tank is provided with a toluenediamine inlet on the connecting pipeline between the solvent storage tank and the drying system; the drying system is used for drying the toluenediamine solution. A phosgenation cold reaction tower connected to the drying system is also provided with a phosgenation solution inlet; A phosgene thermal reaction tower connected to the outlet of the phosgene cooling reaction tower; A first phosgene removal tower connected to the bottom outlet of the phosgenation thermal reaction tower; A second phosgene removal tower connected to the bottom outlet of the first phosgene removal tower; A third phosgene removal tower connected to the bottom outlet of the second phosgene removal tower; A first desolvation tower connected to the bottom outlet of the third phosgene removal tower; A second descaling tower connected to the bottom outlet of the first descaling tower; A decoking tower connected to the bottom outlet of the second desolventizing tower; A toluene diisocyanate refining tower connected to the top outlet of the decoking tower; An eleventh condenser is connected to the top outlet of the toluene diisocyanate refining column, and its liquid outlet is connected to the top of the toluene diisocyanate refining column and the light component removal column, respectively. A twelfth condenser is connected to the top outlet of the light component removal column, and its liquid outlet is connected to the top of the light component removal column and the feed inlet of the first desolventizing column, respectively. The bottom outlet of the light component removal column is connected to the bottom of the light component removal column and the top of the decoking column, respectively. A toluene diisocyanate finished product storage tank connected to the side outlet of the toluene diisocyanate refining tower; The outlet of the reboiler of the toluene diisocyanate refining column is connected to the reboiler of the toluene diisocyanate refining column and the reboiler of the second desolventizing column, respectively.

10. The system according to claim 9, characterized in that, Also includes: A first condenser is connected to the top outlet of the phosgenation thermal reaction tower, and the liquid outlet of the first condenser is connected to the top of the phosgenation thermal reaction tower; an HCl desorption tower is connected to the gas outlet of the first condenser; a second condenser is connected to the top outlet of the HCl desorption tower, and the liquid outlet of the second condenser is connected to the top of the HCl desorption tower; the bottom outlet of the HCl desorption tower is connected to the top of the phosgenation thermal reaction tower. A phosgene refining tower connected to the side outlet of the phosgene thermal reaction tower; a third condenser connected to the top outlet of the phosgene refining tower, the liquid outlet of the third condenser connected to the top of the phosgene refining tower; a phosgene absorption tower connected to the gas outlet of the third condenser; a fourth condenser connected to the top outlet of the phosgene absorption tower, the liquid outlet of the fourth condenser connected to the top of the phosgene absorption tower; the bottom outlet of the phosgene absorption tower connected to the bottom of the phosgene absorption tower and a phosgene storage tank, respectively; the phosgene storage tank connected to the phosgene refrigeration reaction tower; and the bottom outlet of the phosgene refining tower connected to the bottom of the phosgene refining tower and the phosgene storage tank, respectively. A fifth condenser is connected to the top outlet of the first phosgene removal tower. The gas outlet of the fifth condenser is connected to the phosgene absorption tower, and the liquid outlet of the fifth condenser is connected to the top of the first phosgene removal tower and the phosgene refining tower, respectively. The bottom outlet of the first phosgene removal tower is connected to the bottom of the first phosgene removal tower and the second phosgene removal tower, respectively. A sixth condenser is connected to the top outlet of the second phosgene removal tower. The gas outlet of the sixth condenser is connected to the phosgene absorption tower, and the liquid outlet of the sixth condenser is connected to the top of the second phosgene removal tower and the phosgene purification tower, respectively. The bottom outlet of the second phosgene removal tower is connected to the bottom of the second phosgene removal tower and the third phosgene removal tower, respectively. A seventh condenser is connected to the top outlet of the third phosgene removal tower. The gas outlet of the seventh condenser is connected to the phosgene absorption tower, and the liquid outlet of the seventh condenser is connected to the top of the third phosgene removal tower and the phosgene refining tower, respectively. The bottom outlet of the third phosgene removal tower is connected to the bottom of the third phosgene removal tower and the first desolvation tower, respectively. An eighth condenser is connected to the top outlet of the first desolventizing tower; the gas outlet of the eighth condenser is connected to the first heat exchanger; a solvent refining tower is connected to the liquid outlet of the first heat exchanger; a ninth condenser is connected to the top outlet of the solvent refining tower; the liquid outlet of the ninth condenser is connected to the top of the solvent refining tower and the dehydrogenation component tower, respectively; the bottom outlet of the solvent refining tower is connected to the bottom of the solvent refining tower and the solvent storage tank, respectively; the liquid outlet of the eighth condenser is connected to the top of the first desolventizing tower and the solvent refining tower, respectively; the bottom outlet of the first desolventizing tower is connected to the bottom of the first desolventizing tower and the second desolventizing tower, respectively. A tenth condenser is connected to the top outlet of the second desolventizing tower, the gas outlet of the tenth condenser is connected to the second heat exchanger, and a solvent refining tower is connected to the liquid outlet of the second heat exchanger. The liquid outlet of the tenth condenser is connected to the top of the second desolventizing tower and the feed inlet of the solvent refining tower, respectively. The bottom outlet of the second desolventizing tower is connected to the bottom of the second desolventizing tower and the decoking tower, respectively.

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