Refining process for producing toluene diisocynate

Abstract

The invention provides a refining process for producing toluene diisocynate, and belongs to the technical field of chemical processes. The method comprises the following steps: taking toluenediamine and phosgene as raw materials, carrying out phosgenation reaction in o-dichlorobenzene, carrying out primary separation to obtain a to-be-refined material, inputting the to-be-refined material into a refining tower, and extracting primary toluene diisocynate from a tower kettle of the refining tower; wherein the number of theoretical tower plates of the refining tower is 12-18, the number of feeding tower plates is 4-12, and the reflux ratio is 1-5, so that almost no ODCB exists in a tower kettle extract of the refining tower, the requirements of a subsequent production process are met, and the finishing and refining process is low in energy consumption and high in energy utilization rate; meanwhile, the preparation process disclosed by the invention can be used for refining 70 thousand tons of toluene diisocynate and 50 thousand tons of toluene diisocynate, and is suitable for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of chemical processes, and in particular to a refining process for producing toluene diisocyanate. Background Art

[0002] Toluene diisocyanate (TDI) is an important organic chemical intermediate and an important raw material for the preparation of polyurethane. It can also be used to produce foam plastics, coatings, thermal insulation materials and medicines, etc., and has a broad market demand. At present, the industrial production of TDI mainly adopts phosgenation technology, which includes the catalytic preparation of phosgene by carbon monoxide and chlorine at a certain temperature, the reaction of toluene and nitric acid to generate dinitrotoluene (DNT), the reaction of DNT and hydrogen to generate toluenediamine (TDA) and the purification and refining of TDI. Among them, the last step of TDI purification and refining requires cold phosgenation reaction in the presence of inert solvent o-dichlorobenzene (ODCB). ODCB is the main impurity in the process of preparing TDI by phosgenation reaction. The ODCB content is an important indicator of TDI product quality. High ODCB content not only increases the difficulty of subsequent purification, but also leads to a decrease in reaction activity, a darker product color and a decrease in performance. Based on the impact of ODCB on the performance of TDI products, the ODCB content needs to be reduced during the production process.

[0003] In the prior art, Shuang Jianyong et al. simulated and simulated the entire process of the 71# tower, 73# tower, decoking tower and other distillation towers in the TDI production process. The ODCB mass fraction in the process design data of the 73# tower was 1.8E-05, and the simulation data was 1.5E-04, which met the process design requirements. The final TDI product mass fraction was 99.995%, which met the process requirements (99.99%). Tian Zhiliang et al. simulated and calculated the 71# tower, 73# tower, TDI refining tower, etc. and simulated and optimized the main equipment, and investigated the effects of the reflux ratio, feed plate position, and side line extraction position on the ODCB mass fraction. The calculated data was in good agreement with the actual operation data of the device, proving that the selected thermodynamic model was accurate and achieved the purpose of optimizing the main equipment parameters.

[0004] Although the distillation method can achieve good results in treating TDI and ODCB wastewater, the refining tower still has problems such as excessive ODCB content, high energy consumption and low energy utilization. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention discloses a refining process for producing toluene diisocyanate, which has low energy consumption and high energy utilization rate and can obtain a high-purity TDI product.

[0006] In order to achieve the above technical objectives, the present invention provides a refining process for producing toluene diisocyanate, wherein toluenediamine and phosgene are used as raw materials to undergo phosgenation reaction in o-dichlorobenzene, and the material to be refined is initially separated to obtain a material to be refined, the material to be refined is input into a refining tower, and primary toluene diisocyanate is extracted from the bottom of the refining tower; wherein the theoretical number of plates of the refining tower is 12 to 18, the number of feed plates is 4 to 12, and the reflux ratio is 1 to 5.

[0007] The research and development team of the present invention uses Aspen Plus process simulation software to perform steady-state simulation and optimization on the distillation process of TDI degradation ODCB. The physical property method in the optimization process uses the ELEC-NRTL model. The mixed liquid of TDI and ODCB to be separated is suitable for the ELEC-NRTL model. The strict distillation module is used for distillation calculation, and the sensitivity analysis module is used to investigate the theoretical plate number, feed plate number and reflux ratio. Based on a large amount of simulation experimental data, the theoretical plate number of the refining tower in the technical solution of the present invention is 12 to 18, the feed plate number is 4 to 12, and the reflux ratio is 1 to 5, and high-purity primary toluene diisocyanate can be obtained in the refining tower kettle. The embodiment of the present invention shows the technical effect of optimizing the relevant parameters of the theoretical plate number of the refining tower, the feed plate number and the reflux ratio.

[0008] Through simulation and calculation of material balance, the invention research and development team further investigated the influence of the temperature and pressure of the refining tower on the content of ODCB in the primary toluene diisocyanate extracted from the bottom of the refining tower. According to material balance, the temperature of the refining tower can be selected to be 80-150°C, and the pressure can be selected to be 200-300kPa. The embodiment of the present invention shows the technical effect after the temperature and pressure of the refining tower are optimized.

[0009] The initial separation of the material after the phosgenation reaction in o-dichlorobenzene with toluenediamine and phosgene as raw materials is carried out in the primary separation tower. In a further example of the present invention, the temperature of the primary separation tower is 120-170°C, the pressure is 20-30kPa, and the reflux ratio is 15-20. Based on the principle that each component has a different vapor pressure at the same temperature, ODCB can be more efficiently extracted from the side line outlet of the primary separation tower and the material to be refined can be extracted from the bottom of the primary separation tower. Optionally, the reflux ratio of the primary separation tower is 18, which improves the effect of distillation separation; optionally, the material to be refined extracted from the bottom of the primary separation tower is returned to the feed port of the primary separation tower to recycle the ODCB.

[0010] Based on the above technical solution, the material to be refined extracted from the bottom of the primary separation tower contains ODCB, TDI and a small amount of tar, which is pumped to the refining tower as a raw material liquid through a feed pump for rectification, and flashed in the flash space inside the refining tower, and primary toluene diisocyanate is extracted from the bottom of the refining tower, while the rising steam is condensed by a two-stage condenser at the top of the tower and extracted from the top of the refining tower. In a further example of the present invention, a TDI recovery tower is also included, and the top extraction of the refining tower is input into the TDI recovery tower.

[0011] Furthermore, the temperature of the TDI recovery tower can be selected to be 80-160°C, the pressure can be selected to be 3-6kPa, and the top of the tower can be selected to perform full reflux operation. The top output of the refining tower includes ODCB and a small amount of TDI. Through the exploration and optimization of the TDI recovery tower, ODCB and a small amount of TDI can be separated by distillation, and the secondary toluene diisocyanate after light removal can be extracted from the bottom of the TDI recovery tower.

[0012] Furthermore, the top extraction of the TDI recovery tower is returned to the primary separation process, so that the ODCB is recycled and the process cost is reduced.

[0013] Based on the above technical scheme, it also includes decoking the primary toluene diisocyanate; further, a decoking tower is used to decoke the primary toluene diisocyanate, and when the temperature of the decoking tower is 158-164°C and the pressure is 2-5kPa, a full reflux operation can be optionally performed on the top of the tower, which can effectively remove tar impurities, and tertiary toluene diisocyanate is obtained by decoking the decoking tower.

[0014] Compared with the prior art, the invention has the following beneficial effects: in the refining process for producing toluene diisocyanate provided by the invention, by controlling the theoretical plate number, feed plate number and reflux ratio of the refining tower, the primary toluene diisocyanate extracted from the tower kettle of the refining tower is substantially free of ODCB, and the mass content of TDI is obtained to be ≥99.80%, thereby meeting the purity requirement of the subsequent production process, and the energy consumption of the finishing and refining process is low and the energy utilization rate is high; the invention can be used for the refining of 70,000 tons and 50,000 tons of toluene diisocyanate, and is suitable for industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0016] Figure 1 A flow chart showing a refining process for producing toluene diisocyanate according to the present invention is shown;

[0017] Figure 2 A flow chart showing another refining process for producing toluene diisocyanate according to the present invention;

[0018] Figure 3 The effect of the theoretical plate number of the present invention on the ODCB content in the refining tower kettle is shown;

[0019] Figure 4 The effect of the number of feed trays of the present invention on the ODCB content of the refining tower kettle is shown;

[0020] Figure 5 The effect of the reflux ratio of the present invention on the ODCB content in the bottom of the refining tower is shown.

[0021] Among them, the above drawings include the following figure marks: 1. primary separation tower, 2. refining tower, 3. TDI recovery tower, 4. decoking tower. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below, and preferred embodiments of the present invention are given. However, it should be understood that these embodiments are only used for more detailed description, and should not be understood as limiting the present invention in any form, that is, not limiting the scope of protection of the present invention. Unless otherwise defined, the technical terms used in the following examples have the same meanings as those generally understood by those skilled in the art to which the present invention belongs.

[0023] Example 1

[0024] A refining process for producing toluene diisocyanate, such as Figure 1 As shown, the refining process includes: using toluenediamine and phosgene as raw materials to undergo phosgenation reaction in o-dichlorobenzene, the material is initially separated to obtain the material to be refined, the material to be refined is input into a refining tower 2, and primary toluene diisocyanate is extracted from the bottom of the refining tower 2; the theoretical number of plates of the refining tower 2 is 12 to 18, the number of feed plates is 4 to 12, and the reflux ratio is 1 to 5.

[0025] According to the existing process parameters: the feed temperature of the TDI and ODCB mixed liquid to be separated in the refining tower 2 is 40°C, the feed rate is 19.22 kg / h (m 3 / h), of which the mass fraction of TDI is 64.2% and that of ODCB is 35.8%. The mass fraction of TDI extracted from the bottom of the tower is 99.7-99.8%, and that of ODCB is 0.2-0.3%. The mass content of TDI after separation is required to be ≥99.80%, and that of ODCB is ≥99.80%. Quantity ≤ 0.02%. Using Aspen Plus V11 process simulation software is used to simulate the process of reducing ODCB content in the distillation process of the refining tower 2 The ELEC-NRTL model was used for the physical property method, the strict distillation module was used for the distillation calculation, and the sensitivity analysis module was used to examine the theoretical plate number and feed plate number of the refining tower 2.

[0026] Theoretical plate number results are as follows Figure 2As shown in the figure, when the 8th to 13th trays are used, the ODCB content in the bottom of the tower decreases rapidly. Compared with the case where the theoretical tray number is 8, when the theoretical tray number is 12, the ODCB content in the bottom of the tower decreases by 90.3%, and at this time the ODCB content in the bottom of the tower is at a relatively low level (0.02%), which meets the requirements. It can be seen that when the theoretical tray number is 12, the ODCB content in the bottom of the tower can meet the requirements, but considering the need to reduce the reflux ratio, the theoretical tray number is appropriately increased to 12 to 18, at which time the ODCB content in the bottom of the tower is at a low level (0.01%).

[0027] The feed plate number result is as follows Figure 3 As shown, when the feed position is between the 2nd and 4th plates, as the number of plates increases, the ODCB content in the tower bottom shows a rapid decreasing trend; compared with the feed position of the 2nd plate, when the feed position is the 4th plate, the ODCB content in the tower bottom is reduced by 82.1%; further increasing the number of plates at the feed position, the ODCB content in the tower bottom decreases slowly, and compared with the feed position of the 4th plate, when the feed position is the 5th plate, the ODCB content in the tower bottom is reduced by 60.3%. This shows that increasing the number of plates at the feed position can effectively reduce the ODCB content in the tower bottom. At this time, the ODCB content in the tower bottom is at a relatively low level (0.02%), which meets the requirements. Therefore, the number of feed plates is 4 to 12.

[0028] The reflux ratio results are as follows Figure 4 As shown in the figure, when the reflux ratio is 0.7 to 1, the ODCB content in the tower bottom decreases rapidly. Compared with the reflux ratio of 0.7, when the reflux ratio is 1, the ODCB content in the tower bottom decreases by 80.9%. When the reflux ratio is 1, the ODCB content in the tower bottom is 0.02%, and when the reflux ratio is 1 to 5, it meets the requirements. Therefore, the reflux ratio is selected to be 1 to 5.

[0029] Furthermore, the number of theoretical plates of the refining tower 2 is 13-16, the number of feed plates is 5-8, and the reflux ratio is 1-3.

[0030] Exemplarily, the number of theoretical plates of refining tower 2 is 13, the number of feed plates is 5, and the reflux ratio is 1; or the number of theoretical plates of refining tower 2 is 14, the number of feed plates is 6, and the reflux ratio is 2; or the number of theoretical plates of refining tower 2 is 15, the number of feed plates is 7, and the reflux ratio is 3; or the number of theoretical plates of refining tower 2 is 16, the number of feed plates is 8, and the reflux ratio is 1. The range of the number of theoretical plates of refining tower 2 being 13-16, the number of feed plates being 5-8, and the reflux ratio being 1-3 all belongs to the protection scope of the present invention.

[0031] Furthermore, the temperature of the refining tower 2 is 80 to 150° C., and the pressure is 200 to 300 kPa.

[0032] For example, when the optimal feed position of the 70,000-ton refining tower 2 is selected as the 5th tray, the theoretical number of trays is 13 trays, the reflux ratio is 1, the feed temperature is 145°C, the tower top temperature is 81.1-103.1°C, the tower bottom extraction temperature is 148.5°C, and the feed pressure is 200kPa, after simulation calculation of material balance, the results are shown in Table 1. The total mass flow rate of TDI product in the tower bottom of refining tower 2 is 12549.72kg / h, the TDI sub-mass flow rate is 12549.71kg / h, and the ODCB sub-mass flow rate is 0. It shows that there is basically no ODCB in the tower bottom, and the ODCB is all at the top of the tower. The total mass flow rate of the top extraction is 8740.00kg / h, the TDI sub-mass flow rate is 1118.28kg / h, and the ODCB sub-mass flow rate is 7621.71kg / h. The required tower top TDI content is ≥99.80%, and the ODCB content is ≤0.02%.

[0033] Table 1 Material balance table for simulation calculation of 70,000-ton refining tower

[0034]

[0035] For example, when the optimal feed position of the 50,000-ton refining tower 2 is the 5th tray, the theoretical tray number is 13 trays, the reflux ratio is 1, the feed temperature is 145°C, the tower top temperature is 80.9-103.2°C, the tower bottom extraction temperature is 150.8°C, and the feed pressure is 300kPa, after simulation calculation of material balance, the results are shown in Table 2, the total mass flow rate of TDI product in the tower bottom is 10751.99kg / h, the TDI sub-mass flow rate is 10751.99kg / h, and the ODCB sub-mass flow rate is 0. This indicates that there is basically no ODCB in the tower bottom, and the ODCB is all at the top of the tower, which meets the production requirements.

[0036] Table 2 Material balance table for simulation calculation of 50,000-ton refining tower

[0037]

[0038] Furthermore, hydraulic calculation is performed on the refining tower 2. The main purpose of the hydraulic calculation is to evaluate the hydraulic performance of the gas-liquid two-phase flow in the tower, including key parameters such as flooding rate, spray density and packing pressure drop, so as to ensure that the tower equipment can meet the process requirements under the designed operating conditions and avoid abnormal operation phenomena such as flooding and leakage.

[0039] For example, hydraulic calculation is performed on a 70,000-ton refining tower 2, with specific parameters as follows: tower diameter is 2450 mm, packing type is M 250Y, and packing height is 2.31 m; or tower diameter is 2450 mm, packing type is M 250Y, and packing height is 3.99 m. After hydraulic calculation, its flooding rate, spray density, and packing pressure drop are all within the normal working range.

[0040] For example, hydraulic calculation is performed on a 50,000-ton refining tower 2, with specific parameters as follows: tower diameter is 2450 mm, packing type is M 250Y, and packing height is 2.31 m; or tower diameter is 2450 mm, packing type is M 250Y, and packing height is 3.99 m. After hydraulic calculation, its flooding rate, spray density, and packing pressure drop are all within the normal working range.

[0041] Example 2

[0042] The preferred embodiment of the present invention is as follows Figure 2 As shown, on the basis of Example 1, the initial separation is carried out in the primary separation tower 1, and the temperature of the primary separation tower 1 is 120°C, the pressure is 20kPa, and the reflux ratio is 18. Therefore, according to the principle that each component has a different vapor pressure at the same temperature, ODCB is more efficiently extracted from the side line outlet of the primary separation tower, thereby removing most of the ODCB in the mixed solution of TDI and ODCB, and ODCB can be returned to the distillation tower for recycling. The tower bottom outlet extracts the material to be refined, and the material to be refined contains ODCB, TDI and a small amount of tar. Under the process conditions of Example 2, there is basically no ODCB in the tower bottom of the refining tower 2, and the ODCB is all at the top of the tower, which meets the production requirements.

[0043] Example 3

[0044] The preferred embodiment of the present invention is as follows Figure 2 As shown, on the basis of Example 1, the material to be refined extracted from the bottom of the primary fractionation tower 1 contains ODCB, TDI and a small amount of tar, and this part of the material is pumped to the refining tower 2 as a raw material liquid through a feed pump for distillation, and flashed in the flash space inside the refining tower 2, and primary toluene diisocyanate is extracted from the bottom of the refining tower 2, and the rising steam is condensed through the two-stage condenser at the top of the tower and extracted from the top of the refining tower 2, and the top extraction of the refining tower 2 is input to the TDI recovery tower 3. The top extraction of the refining tower 2 includes ODCB and a small amount of TDI. When the temperature of the TDI recovery tower 3 is 80°C, the pressure is 3kPa, and the total reflux operation is performed, ODCB and a small amount of TDI are separated by distillation, and secondary toluene diisocyanate is extracted from the bottom of the TDI recovery tower 3. Optionally, the top extraction of TDI recovery tower 3 is ODCB which is returned to primary separation tower 1, so as to recycle ODCB and reduce process cost. In addition, there is basically no ODCB in the bottom of refining tower 2, and ODCB is all at the top of the tower, meeting production requirements.

[0045] Example 4

[0046] The preferred embodiment of the present invention is as follows Figure 2As shown, on the basis of Example 1, the primary toluene diisocyanate is decoked, the primary toluene diisocyanate is extracted from the bottom of the refining tower 2, the primary toluene diisocyanate includes toluene diisocyanate and tar, the primary toluene diisocyanate is decoked by the decoking tower 4, and the tertiary toluene diisocyanate is obtained after decoking by the decoking tower 4. The temperature of the decoking tower 4 is 158°C, the pressure is 2kPa, and the full reflux operation is performed, which can efficiently remove tar impurities, and there is basically no ODCB in the bottom of the refining tower 2, and the ODCB is all at the top of the tower, which meets the production requirements.

[0047] Example 5

[0048] A refining process for producing toluene diisocyanate, such as Figure 2 As shown, the material after phosgenation reaction in o-dichlorobenzene with toluenediamine and phosgene as raw materials is initially separated by a primary separation tower 1. The temperature of the primary separation tower 1 is 150°C, the pressure is 25 kPa, and the reflux ratio is 18. Most of the ODCB is produced from the side line production outlet of the primary separation tower 1, and the ODCB can be returned to the primary separation tower 1 for recycling. The material to be refined is produced from the bottom of the primary separation tower 1. The material to be refined includes ODCB, TDI and tar. The material to be refined is sent to the refining tower 2 for further refining and separation. The theoretical number of plates of the refining tower 2 is 13, the number of feed plates is 5, the reflux ratio is 1, and the feed ratio is 1. When the material temperature is 145°C, the tower top temperature is 81.1-103.1°C, the tower bottom extraction temperature is 148.5°C, and the feed pressure is 200kPa, after distillation and separation in refining tower 2, o-dichlorobenzene and a small amount of toluene diisocyanate are extracted from the top of refining tower 2 and input into TDI recovery tower 3. When the temperature of TDI recovery tower 3 is 100°C, the pressure is 4kPa, and full reflux operation is performed, secondary toluene diisocyanate is extracted from the tower bottom of TDI recovery tower 3, and o-dichlorobenzene extracted from the top of TDI recovery tower 3 is sent to primary separation tower 1, so that primary separation tower 1, refining tower 2 and TDI recovery tower 3 form an external circulation. The first-grade toluene diisocyanate is extracted from the bottom of the refining tower 2, and the first-grade toluene diisocyanate includes toluene diisocyanate and tar, and then sent to the decoking tower 4 for decoking treatment. When the temperature of the decoking tower 4 is 160°C, the pressure is 4kPa and the total reflux state, the first-grade toluene diisocyanate is decoked by the decoking tower 4 to obtain the tertiary toluene diisocyanate. Under the process conditions of Example 5, there is basically no ODCB in the bottom of the refining tower 2, and the ODCB is all at the top of the tower, which meets the production requirements.

[0049] Example 6

[0050] A refining process for producing toluene diisocyanate, such as Figure 2As shown, the material after phosgenation reaction in o-dichlorobenzene with toluenediamine and phosgene as raw materials is initially separated in a primary separation tower 1. The temperature of the primary separation tower 1 is 170°C, the pressure is 30 kPa, and the reflux ratio is 18. Most of the ODCB is produced from the side line production outlet of the primary separation tower 1, and the ODCB can be returned to the primary separation tower 1 for recycling. The material to be refined is produced from the bottom of the primary separation tower 1. The material to be refined includes ODCB, TDI and tar. The material to be refined is sent to the refining tower 2 for further refining and separation. The theoretical number of plates of the refining tower 2 is 14, the number of feed plates is 6, the reflux ratio is 1, and the feed ratio is 1. When the material temperature is 145°C, the tower top temperature is 81.1-103.1°C, the tower bottom extraction temperature is 148.5°C, and the feed pressure is 200kPa, after distillation and separation in refining tower 2, o-dichlorobenzene and a small amount of toluene diisocyanate are extracted from the top of refining tower 2 and input into TDI recovery tower 3. When the temperature of TDI recovery tower 3 is 160°C, the pressure is 6kPa, and full reflux operation is performed, secondary toluene diisocyanate is extracted from the tower bottom of TDI recovery tower 3, and o-dichlorobenzene is extracted from the top of TDI recovery tower 3 and sent to primary separation tower 1, so that primary separation tower 1, refining tower 2 and TDI recovery tower 3 form an external circulation. The first-grade toluene diisocyanate is extracted from the bottom of the refining tower 2, and the first-grade toluene diisocyanate includes toluene diisocyanate and tar, and then sent to the decoking tower 4 for decoking treatment. When the temperature of the decoking tower 4 is 164° C., the pressure is 5 kPa and the total reflux state, the first-grade toluene diisocyanate is decoked by the decoking tower 4 to obtain the tertiary toluene diisocyanate. Under the process conditions of Example 6, there is basically no ODCB in the bottom of the refining tower 2, and the ODCB is all at the top of the tower, which meets the production requirements.

[0051] Example 7

[0052] The actual transformation of the 70,000-ton and 50,000-ton refining towers showed that when the theoretical number of plates of the 70,000-ton and 50,000-ton refining towers was 13, the number of feed plates was 5, and the reflux ratio was 1, the TDI mass content after separation of the 70,000-ton and 50,000-ton refining towers was ≥99.80%, and the ODCB content was ≤0.02%. After starting up, the towers operated stably for three consecutive months.

[0053] It should be noted that the above contents are further detailed descriptions of the present invention in combination with specific implementation methods, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple improvements and modifications can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A refining process for producing toluene diisocyanate, It is characterized in that The material to be refined is obtained by phosgenation reaction of toluenediamine and phosgene in o-dichlorobenzene after initial separation. The material to be refined is input into a refining tower (2), and primary toluene diisocyanate is extracted from the bottom of the refining tower (2); wherein the theoretical number of plates of the refining tower (2) is 12 to 18, the number of feed plates is 4 to 12, and the reflux ratio is 1 to 5.

2. A refining process for producing toluene diisocyanate according to claim 1, It is characterized in that The number of theoretical plates of the refining tower (2) is 13 to 16, the number of feed plates is 5 to 8, and the reflux ratio is 1 to 3.

3. A refining process for producing toluene diisocyanate according to claim 1, It is characterized in that The temperature of the refining tower (2) is 80-150°C, and the pressure is 200-300 kPa.

4. A refining process for producing toluene diisocyanate according to claim 1, It is characterized in that The primary separation is carried out in a primary separation tower (1), and the material to be refined is taken out from the tower bottom outlet of the primary separation tower (1). The temperature of the primary separation tower (1) is 120-170°C, the pressure is 20-30 kPa, and the reflux ratio is 15-20.

5. A refining process for producing toluene diisocyanate according to claim 4, It is characterized in that The primary separation tower (1) is provided with a side line extraction port, and the material extracted from the side line extraction port is returned to the feed port of the primary separation tower (1).

6. A refining process for producing toluene diisocyanate according to claim 1, It is characterized in that It also includes a TDI recovery tower (3); the top product of the refining tower (2) is input into the TDI recovery tower (3), and the secondary toluene diisocyanate after light removal is extracted from the bottom of the TDI recovery tower (3).

7. A refining process for producing toluene diisocyanate according to claim 6, It is characterized in that The top extraction of the TDI recovery tower (3) is returned to the primary separation step.

8. A refining process for producing toluene diisocyanate according to claim 6, It is characterized in that The temperature of the TDI recovery tower (3) is 80-160°C, the pressure is 3-6 kPa, and a total reflux operation is performed at the top of the tower.

9. A refining process for producing toluene diisocyanate according to claim 1, It is characterized in that The method also includes decoking the primary toluene diisocyanate.

10. A refining process for producing toluene diisocyanate according to claim 9, It is characterized in that The decoking treatment is carried out in a decoking tower (4), the temperature of the decoking tower (4) is 158-164°C, the pressure is 2-5 kPa, and a total reflux operation is carried out at the top of the tower.

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