Special isocyanate rectification device and method

Abstract

The invention relates to a rectification device and method for special isocyanate, which are characterized in that a solvent removal tower, a light component removal tower, an acid separation stripping tower and a product rectification tower are respectively used for removing parts needing to be removed in each step, so that the influence caused by temperature and pressure when a single rectification tower is used for performing rectification operation is avoided. An acid stripping tower is arranged in the rectification process, and acid gas generated in the isocyanate production process is taken out from a gas phase outlet by utilizing high-temperature nitrogen, so that the acid value of a special isocyanate product is close to or even superior to that of an imported product. Technological parameters in the rectification process are adjusted through a distributed control system, and field operation is reduced, so that the danger that field personnel are in contact with toxic chemicals is avoided. The method is suitable for rectification of various isocyanate products.

Description

Technical Field

[0001] The invention belongs to the field of fine chemicals, and in particular relates to a rectification device and method for special isocyanate. Background Art

[0002] Specialty isocyanates are special chemicals that are mainly used as raw materials for the production of high-end polyurethane products. These materials are made by further processing isocyanate molecules and have better properties than ordinary isocyanates, such as better mechanical strength, lower yellowing tendency, and excellent chemical corrosion resistance. Due to these characteristics, specialty isocyanates are widely used in adhesives, coatings, elastomer materials and other fields, especially in situations where high performance and high stability are required.

[0003] The production and application of specialty isocyanates have high technical barriers, mainly because the synthesis process is complex and requires precise control of reaction conditions to ensure the quality and performance of the final product. In recent years, domestic manufacturers including Wanhua Chemical, Meirui New Materials, Shanghai Lianheng Isocyanate Co., Ltd. and Gansu Juyin have focused on independently developing the production process of specialty isocyanates. However, compared with imported products, there are still problems such as higher hydrolysis chlorine, unstable reaction activity, easy yellowing, and high product acid value. Summary of the invention

[0004] The object of the present invention is to overcome the defects of the prior art and provide a distillation device and method for special isocyanate.

[0005] To achieve the above object, the technical solution adopted by the present invention is: a special isocyanate distillation device, characterized in that it includes a crude product tank, a solvent removal tower, a light component removal tower, an acid stripping tower, and a distillation tower; the upper outlet of the crude product tank is connected to the solvent removal tower, the first-level discharge pipe at the bottom of the solvent removal tower is connected to the first reboiler through a No. 1 pump, and the first reboiler outlet is connected to the liquid phase inlet at the bottom of the solvent removal tower; the gas phase outlet at the top of the solvent removal tower is connected to the first condenser, the liquid phase outlet of the first condenser is connected to the first reflux tank, and the liquid phase outlet of the first reflux tank is connected to the solvent removal tower through a No. 2 pump through the first reflux pipe; The first discharge pipe is connected to the first delivery pipe, the first delivery pipe is connected to the light component removal tower, the second discharge pipe at the bottom of the light component removal tower is connected to the second reboiler through the third pump, the outlet of the second reboiler is connected to the liquid phase inlet at the bottom of the light component removal tower; the gas phase outlet at the top of the light component removal tower is connected to the second condenser, the liquid phase outlet at the bottom of the second condenser is connected to the second reflux tank, and the liquid phase outlet of the second reflux tank is connected to the light component removal tower through the fourth pump) through the second reflux pipe; The secondary discharge pipe is connected to the second delivery pipe, the second delivery pipe is connected to the acid stripping tower, the third delivery pipe at the bottom of the acid stripping tower is connected to the distillation tower, and the gas phase outlet at the top of the acid stripping tower is connected to The third condenser, the material outlet on the side of the third condenser is connected to the third conveying pipe, the acid liquid outlet at the bottom of the third condenser is connected to the hydrochloric acid falling film absorption tower; the lower part of the acid stripping tower is connected to the nitrogen pipe; The fourth delivery pipe at the bottom of the distillation tower is connected to the third reboiler through the No. 5 pump, the outlet of the third reboiler is connected to the distillation tower, the gas phase outlet at the top of the distillation tower is connected to the fourth condenser, and the liquid phase outlet of the fourth condenser is connected to the distillation tower through the third reflux pipe; the upper part of the distillation tower is also connected to the side line production pipe, the side line production pipe is connected to the third reflux tank, the liquid phase outlet at the bottom of the third reflux tank is connected to the fifth condenser through the No. 6 pump, and the liquid phase outlet of the fifth condenser is connected to the product tank; the fourth reflux pipe is also connected to the pipeline where the No. 6 pump outlet is located, and the fourth reflux pipe is connected to the distillation tower; the fourth delivery pipe is connected to the heavy component production pipe, and the heavy component production pipe is connected to the heavy component tank; the heavy component production pipe is connected to a branch pipe, and the branch pipe is connected to the accident tank.

[0006] The gas phase outlets at the tops of the first condenser, the second condenser and the fourth condenser are all connected to the tail gas absorption system.

[0007] The gas phase outlets at the top of the first reflux tank and the second reflux tank are both connected to the tail gas absorption system; the gas phase outlet at the top of the third reflux tank is connected to the distillation tower.

[0008] The second delivery pipe and the nitrogen pipe are both provided with heaters.

[0009] The acid fraction stripping tower consists of a tower kettle and a tower body: the upper part of the tower body is connected to a feed pipe, the pipe mouth of the feed pipe located inside the tower body is provided with a distributor, a tower plate is provided below the distributor, and a gas phase outlet is provided at the top of the tower body; a nitrogen inlet pipe is provided in the tower kettle, the nitrogen inlet pipe extends from one side of the upper part of the tower kettle along the inner wall to the bottom of the tower kettle, and a liquid phase outlet is provided at the bottom end of the tower kettle; a tower top pressure gauge is provided at the upper part of the tower body, a tower mid-pressure gauge is provided at the bottom of the tower body, a tower bottom pressure gauge is provided at the bottom of the tower kettle, a tower mid-thermometer is provided at the upper part of the tower kettle, and a tower bottom thermometer is provided at the bottom, and a connecting piece for fixing the tower kettle is provided at one side of the tower kettle.

[0010] A method for distilling special isocyanate, characterized in that it is regulated by a distributed control system, and the specific steps are as follows: The first step is to remove solvent: the crude special isocyanate in the crude product tank is slowly introduced into the solvent removal tower, when the solvent removal tower reactor liquid level rises to 30-70%, start pump No. 1 and the first reboiler to circulate heating of the material, and the temperature and pressure of the solvent removal tower are regulated by a distributed control system, and the solvent removal tower reactor liquid level is maintained at 50%; when the first reflux tank liquid level reaches 30%, start pump No. 2, and reflux is established through the first reflux pipe, and the control solvent removal tower reflux amount is 100-500kg / h to keep the solvent removal tower reactor temperature stable; open the solvent removal tower top gas phase discharge valve, so that the solvent is evaporated from the tower top and enters the first condenser; then open the solvent removal tower reactor liquid phase discharge valve to start discharging; The second step is to remove the light components: the material from which the solvent is removed enters the light component removal tower, and when the light component removal tower kettle level rises to 30-70%, the third pump and the second reboiler are started to circulate and heat the material, so that the light component removal tower kettle level is maintained at 50%, and the temperature and pressure of the light component removal tower are adjusted by the distributed control system. When the second reflux tank level reaches 30%, the fourth pump is started, and reflux is established through the second reflux pipe, and the reflux rate of the light component removal tower is controlled to be 100-1000 kg / h, and the temperature of the light component removal tower kettle is kept stable; the light component removal tower top gas phase discharge valve is opened to allow the light component to evaporate from the top of the tower and enter the second condenser, and then the light component removal tower kettle discharge valve is opened to start discharging; The third step is to remove the acid fraction: nitrogen is introduced into the acid stripping tower, and the acid stripping tower is fed at the same time. When the acid stripping tower kettle liquid level reaches 30-70%, the temperature in the acid stripping tower is adjusted to 100-150°C through the distributed control system, and the hydrogen chloride gas generated in the isocyanate production process is passed from the gas phase port at the top of the acid stripping tower to the third condenser through hot nitrogen, and the material enters the third conveying pipe from the side outlet of the third condenser, and the acidic liquid enters the hydrochloric acid falling film absorption tower from the bottom of the third condenser; the acidity of the sample in the acid stripping tower is sampled and analyzed. When the acidity of the sample is less than 80 ppm, the discharge valve at the bottom of the acid stripping tower is opened to start discharging; The fourth step is distillation: the material with deacidification enters the distillation tower. When the liquid level in the bottom of the distillation tower reaches 30-70%, start the No. 5 pump and the third reboiler to circulate and heat the material to maintain the liquid level in the bottom of the distillation tower at 30-70%. The temperature and pressure of the distillation tower are adjusted by the distributed control system to keep the bottom temperature stable. When the liquid level in the third reflux tank reaches 30%, start the No. 6 pump to establish a side line reflux through the fourth reflux pipe, so that the side line reflux rate is 400~700 kg / h, and the reflux rate at the top of the distillation tower is controlled to be 300~2000 kg / h. After the self-circulation of the whole distillation tower is stable, the gas-liquid mixed material is condensed into liquid phase through the fifth condenser and the product is extracted.

[0011] When the side line sample is taken until the liquid level in the distillation tower kettle drops below 10%, the side line extraction valve is closed. The bottom discharge valve of the distillation tower is opened to discharge the heavy components at the bottom of the tower into the heavy component storage tank. If any process of the distillation process has a problem or exceeds the rated process parameters, the distillation product will be transferred to the accident tank; at the same time, through the distributed control system reaction process safety interlocking system, if any process has a problem or exceeds the rated process parameters, the distillation process will be forced to stop to ensure the safety and reliability of the distillation process.

[0012] Furthermore, in the first step, in the removal of solvent, the temperature of the solvent removal tower kettle is adjusted to 90~190 ℃, the pressure is -54~-81 kPa, the tower top temperature is 75~150 ℃, and the pressure is -72~-81 kPa through a distributed control system; the temperature of the first reflux tank is controlled to 40~80 ℃.

[0013] Furthermore, in the second step of removing light components, the temperature of the light component removal tower kettle is adjusted to 100~200 ℃, the pressure is -54~-81 kPa, the tower top temperature is 85~160 ℃, and the pressure is -72~-81 kPa through the distributed control system; the temperature of the second reflux tank is controlled to 40~80 ℃.

[0014] Furthermore, in the third step of removing the acid fraction, the flow rate of the nitrogen introduced is controlled to be 1~100 kg / h, and the temperature is 10~200 ℃; the temperature of the feed to the acid fraction stripping tower is controlled to be 10~200 ℃.

[0015] Furthermore, in the fourth step of product distillation, the distributed control system is used to adjust the distillation tower bottom temperature to 110~200 ℃, the pressure to -72~-81 kPa, and the tower top temperature to 95~175 ℃, and the pressure to -72~-81 kPa.

[0016] The beneficial effects of the present invention are: 1. The present invention adjusts the process parameters in the distillation process through a distributed control system, reduces on-site operations, and thus avoids the risk of on-site personnel being exposed to toxic chemicals. It is suitable for the distillation of a variety of isocyanate products; 2. In order to solve the problem of high acid value of special isocyanate products, the present invention sets an acid stripping tower in the distillation process, and uses high-temperature nitrogen to remove the acid gas generated in the isocyanate production process from the gas phase outlet, thereby ensuring that the acid value of the special isocyanate product is close to or even better than that of imported products.

[0017] 3. The present invention utilizes a solvent removal tower, a light component removal tower, an acid stripping tower and a product distillation tower to remove the parts that need to be removed in each step, thereby avoiding the influence of temperature and pressure when a single distillation tower performs distillation operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a diagram of a distillation device for special isocyanate of the present invention; Figure 2 A schematic diagram of an acid stripping tower according to the present invention; In the figure: 1-crude product tank, 2-solvent removal tower, 3-light component removal tower, 4-acid stripping tower, 41-tower bottom, 42-tower body, 43-feed pipe, 44-distributor, 45-tower plate, 46-nitrogen inlet pipe, 47-gas phase outlet, 48-liquid phase outlet, 49-connector, 4a-tower top pressure gauge, 4b-tower pressure gauge, 4c-tower bottom pressure gauge, 4d-tower thermometer, 4e-tower bottom thermometer; 5-rectification tower; E1-first reboiler, E2-second reboiler, E3-third reboiler; C1-first condenser, C2-second Condenser, C3-third condenser, C4-fourth condenser, C5-fifth condenser; D1-first reflux tank, D2-second reflux tank, D3-third reflux tank; B1-No. 1 pump, B2-No. 2 pump, B3-No. 3 pump, B4-No. 4 pump, B5-No. 5 pump, B6-No. 6 pump; G1-first discharge pipe, G2-second discharge pipe; L1-first conveying pipe, L2-second conveying pipe, L3-third conveying pipe, L4-fourth conveying pipe; R1-first reflux pipe, R2-second reflux pipe, R3-third reflux pipe, R4-fourth reflux pipe. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is further described in detail below in conjunction with several preferred embodiments and drawings. This embodiment is implemented on the premise of the technical solution of the invention, and a detailed implementation method and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

[0020] A special isocyanate distillation device, characterized in that it includes a crude product tank 1, a solvent removal tower 2, a light component removal tower 3, an acid stripping tower 4, and a distillation tower 5; the upper outlet of the crude product tank 1 is connected to the solvent removal tower 2, and the first-level discharge pipe G1 at the bottom of the solvent removal tower 2 is connected to the first reboiler E1 through a pump B1, and the outlet of the first reboiler E1 is connected to the lower liquid phase inlet of the solvent removal tower 2; the top gas phase outlet of the solvent removal tower 2 is connected to the first condenser C1, and the liquid phase outlet of the first condenser C1 is connected to the first reflux tank D1, and the liquid phase outlet of the first reflux tank D1 is connected to the solvent removal tower 2 through the second pump B2 through the first reflux pipe R1; The first-level discharge pipe G1 is connected to the first conveying pipe L1, and the first conveying pipe L1 is connected to the light component removal tower 3. The second-level discharge pipe G2 at the bottom of the light component removal tower 3 is connected to the second reboiler E2 through the third pump B3, and the outlet of the second reboiler E2 is connected to the liquid phase inlet of the lower part of the light component removal tower 3; the gas phase outlet at the top of the light component removal tower 3 is connected to the second condenser C2, and the liquid phase outlet at the bottom of the second condenser C2 is connected to the second reflux tank D2, and the liquid phase outlet of the second reflux tank D2 is connected to the light component removal tower 3 through the fourth pump B4 and the second reflux pipe R2; The secondary discharge pipe G2 is connected to the second delivery pipe L2, the second delivery pipe L2 is connected to the acid stripping tower 4, the third delivery pipe L3 at the bottom of the acid stripping tower 4 is connected to the distillation tower 5, the gas phase outlet at the top of the acid stripping tower 4 is connected to the third condenser C3, the material outlet at the side of the third condenser C3 is connected to the third delivery pipe L3, and the acid liquid outlet at the bottom of the third condenser C3 is connected to the hydrochloric acid falling film absorption tower; the lower part of the acid stripping tower (4) is connected to a nitrogen pipe; The fourth delivery pipe L4 at the bottom of the distillation tower 5 is connected to the third reboiler E3 through the No. 5 pump B5, the outlet of the third reboiler E3 is connected to the distillation tower 5, the gas phase outlet at the top of the distillation tower 5 is connected to the fourth condenser C4, and the liquid phase outlet of the fourth condenser C4 is connected to the distillation tower 5 through the third reflux pipe R3; the upper part of the distillation tower 5 is also connected to the side line production pipe H, the side line production pipe H is connected to the third reflux tank D3, the liquid phase outlet at the bottom of the third reflux tank D3 is connected to the fifth condenser C5 through the No. 6 pump B6, and the liquid phase outlet of the fifth condenser C5 is connected to the product tank; the fourth reflux pipe R4 is also connected to the pipeline where the No. 6 pump B6 outlet is located, and the fourth reflux pipe R4 is connected to the distillation tower 5; the fourth delivery pipe L4 is connected to the heavy component production pipe, and the heavy component production pipe is connected to the heavy component tank; the heavy component production pipe is connected to a branch pipe, and the branch pipe is connected to the accident tank.

[0021] The top gas phase outlets of the first condenser C1, the second condenser C2 and the fourth condenser C4 are all connected to the tail gas absorption system.

[0022] The top gas phase outlets of the first reflux tank D1 and the second reflux tank D2 are both connected to the tail gas absorption system; the top gas phase outlet of the third reflux tank D3 is connected to the distillation tower 5.

[0023] The second delivery pipe L2 and the nitrogen pipe are both provided with heaters.

[0024] The acid fraction stripping tower 4 consists of a tower kettle 41 and a tower body 42: the upper part of the tower body 42 is connected to a feed pipe 43, and a distributor 44 is provided at the pipe mouth of the feed pipe 43 located inside the tower body 42, a tower plate 45 is provided below the distributor 44, and a gas phase outlet 47 is provided at the top of the tower body 42; a nitrogen inlet pipe 46 is provided in the tower kettle 41, and the nitrogen inlet pipe 46 extends from one side of the upper part of the tower kettle 41 along the inner wall to the bottom of the tower kettle 41, and a liquid phase outlet 48 is provided at the bottom of the tower kettle 41; a tower top pressure gauge 4a is provided at the upper part of the tower body 42, a tower mid-pressure gauge 4b ​​is provided at the bottom of the tower body 42, a tower bottom pressure gauge 4c is provided at the bottom of the tower kettle 41, a tower mid-thermometer 4d is provided at the upper part of the tower kettle 41, and a tower bottom thermometer 4e is provided at the bottom, and a connecting piece 49 for fixing the tower kettle 41 is provided at one side of the tower kettle 41.

[0025] The working principle of the acid stripping tower is: hot nitrogen and materials are contacted on the tower plate 45, and the volatile hydrogen chloride gas is separated from the materials through the stripping process. In the acid stripping tower, the materials enter from the feed pipe 43 and are dispersed through the distributor 44. The heated N2 extends from the nitrogen inlet pipe 46 from the upper side of the tower kettle 41 along the inner wall to the bottom of the tower kettle 41. The hot nitrogen contacts the multiple streams of materials dispersed by the distributor 44 on the tower plate 45, and the volatile hydrogen chloride gas is taken out from the gas phase outlet 47 by the hot nitrogen, and the materials enter the tower kettle 41 along the tower plate 45.

[0026] The trial raw materials and industrial production equipment used in the following examples, unless otherwise specified, can all be purchased from conventional biochemical reagent companies, the chemical production equipment is provided by domestic manufacturers, and the distributed control system is also provided by Zhejiang University Supcon, thus realizing domestic independent research and development.

[0027] Example 1 takes the distillation of hexamethylene diisocyanate as an example.

[0028] A distillation method for special isocyanate, the specific steps are: The first step is to remove the solvent: the crude hexamethylene diisocyanate in the crude product tank 1 is slowly introduced into the solvent removal tower 2. When the liquid level of the bottom of the solvent removal tower 2 rises to 50%, the first pump B1 and the first reboiler E1 are started to heat the material in a cycle. The temperature of the bottom of the solvent removal tower 2 is adjusted to 125°C and the pressure is -81 kPa through the distributed control system. The temperature of the top of the solvent removal tower 2 is 100°C and the pressure is -81 kPa, and the liquid level of the bottom of the solvent removal tower 2 is maintained at 50%; when the liquid level of the first reflux tank D1 reaches 30%, the second pump B2 is started, and reflux is established through the first reflux pipe R1. The reflux amount is controlled to 600 kg / h to keep the temperature of the bottom of the solvent removal tower 2 stable; the gas phase discharge valve at the top of the solvent removal tower 2 is opened to allow the solvent to evaporate from the top of the tower and enter the first condenser C1; and the liquid phase discharge valve of the bottom of the solvent removal tower 2 is opened to start discharging; The second step is to remove light components: the material from which the solvent has been removed enters the light component removal tower 3. When the liquid level in the bottom of the light component removal tower 3 rises to 50%, the third pump B3 and the second reboiler E2 are started to heat the material in a cycle. The temperature of the bottom of the light component removal tower 3 is adjusted to 135 ° C and the pressure is -81 kPa through the distributed control system. The temperature of the top of the light component removal tower 3 is 110 ° C and the pressure is -81 kPa. The liquid level of the bottom of the light component removal tower 3 is maintained at 50%; when the liquid level of the second reflux tank D2 reaches 30%, the fourth pump B4 is started, and reflux is established through the second reflux pipe R2. The reflux rate of the light component removal tower 3 is controlled to be 600 kg / h, and the temperature of the bottom of the light component removal tower 3 is kept stable; the gas phase discharge valve at the top of the light component removal tower 3 is opened to allow the light component to evaporate from the top of the tower and enter the second condenser C2, and then the discharge valve of the bottom of the light component removal tower 3 is opened to start discharging; The third step is to remove the acid fraction: nitrogen is introduced into the acid stripping tower 4, and material is fed into the acid stripping tower 4 at the same time. When the liquid level in the bottom of the acid stripping tower 4 reaches 30%, the temperature in the acid stripping tower 4 is adjusted to 150°C through the distributed control system, and the hydrogen chloride gas generated in the isocyanate production process is passed from the gas phase port at the top of the acid stripping tower 4 to the third condenser C3 through hot nitrogen, and the material enters the third conveying pipe L3 from the side outlet of the third condenser C3, and the acidic liquid enters the hydrochloric acid falling film absorption tower from the bottom of the third condenser C3; the acidity of the sample in the acid stripping tower 4 is sampled and analyzed, and when the acidity of the sample is less than 80 ppm, the discharge valve at the bottom of the acid stripping tower 4 is opened to start discharging; Step 4: distillation: the material with the acid removed enters distillation tower 5. When the liquid level in the bottom of distillation tower 5 reaches 50%, start pump No. 5 B5 and the third reboiler E3 to heat the material in a cycle. The temperature of the bottom of distillation tower 5 is adjusted to 150 ℃ and the pressure is -81 kPa through the distributed control system. The temperature of the top of distillation tower 5 is 120 ℃ and the pressure is -81 kPa. Maintain the liquid level in the bottom of distillation tower 5 at 50%; when the liquid level of the third reflux tank D3 reaches 30%, start pump No. 6 B6, establish side line reflux through the fourth reflux pipe R4, make the side line reflux amount 500 kg / h, control the reflux amount at the top of distillation tower 5 to 700 kg / h, and after the self-circulation of the whole tower of distillation tower 5 is stable, the gas-liquid mixed material is condensed into liquid phase through the fifth condenser C5, and the special hexamethylene diisocyanate product is extracted.

[0029] Example 2, taking the distillation of pentamethylene diisocyanate as an example.

[0030] A distillation method for special isocyanate, the specific steps are: The first step is to remove the solvent: the crude pentamethylene diisocyanate in the crude product tank 1 is slowly introduced into the solvent removal tower 2. When the liquid level of the bottom of the solvent removal tower 2 rises to 50%, the first pump B1 and the first reboiler E1 are started to heat the material in a circulation manner. The temperature of the bottom of the solvent removal tower 2 is adjusted to 140°C and the pressure is -81 kPa through the distributed control system. The temperature of the top of the solvent removal tower 2 is 115°C and the pressure is -81 kPa, and the liquid level of the bottom of the solvent removal tower 2 is maintained at 50%; when the liquid level of the first reflux tank D1 reaches 30%, the second pump B2 is started, and reflux is established through the first reflux pipe R1. The reflux amount is controlled to 400 kg / h to keep the temperature of the bottom of the solvent removal tower 2 stable; the gas phase discharge valve at the top of the solvent removal tower 2 is opened to allow the solvent to evaporate from the top of the tower and enter the first condenser C1; and the liquid phase discharge valve at the bottom of the solvent removal tower 2 is opened to start discharging; The second step is to remove the light components: the material after the solvent removal enters the light component removal tower 3. When the liquid level in the bottom of the light component removal tower 3 rises to 50%, the third pump B3 and the second reboiler E2 are started to heat the material in a circulation manner. The temperature of the bottom of the light component removal tower 3 is adjusted to 150°C and the pressure is -81 kPa through the distributed control system. The temperature of the top of the light component removal tower 3 is 120°C and the pressure of the top of the light component removal tower 3 is -81 kPa. The liquid level in the bottom of the light component removal tower (3) is maintained at 50%; when the liquid level in the second reflux tank D2 reaches 30%, the fourth pump B4 is started to establish reflux through the second reflux pipe R2, and the reflux rate of the light component removal tower 3 is controlled to be 400 kg / h, and the temperature of the bottom of the light component removal tower 3 is kept stable; the gas phase discharge valve at the top of the light component removal tower 3 is opened to allow the light components to evaporate from the top of the tower and enter the second condenser C2, and then the discharge valve of the bottom of the light component removal tower 3 is opened to start discharging; The third step is to remove the acid fraction: nitrogen is introduced into the acid stripping tower 4, and material is fed into the acid stripping tower 4 at the same time. When the liquid level in the bottom of the acid stripping tower 4 reaches 30%, the temperature in the acid stripping tower 4 is adjusted to 150°C through the distributed control system, and the hydrogen chloride gas generated in the isocyanate production process is passed from the gas phase port at the top of the acid stripping tower 4 to the third condenser C3 through hot nitrogen, and the material enters the third conveying pipe L3 from the side outlet of the third condenser C3, and the acidic liquid enters the hydrochloric acid falling film absorption tower from the bottom of the third condenser C3; the acidity of the sample in the acid stripping tower 4 is sampled and analyzed, and when the acidity of the sample is less than 80 ppm, the discharge valve at the bottom of the acid stripping tower 4 is opened to start discharging; The fourth step is distillation: the material after the removal of acid content enters the distillation tower 5. When the liquid level in the bottom of the distillation tower 5 reaches 50%, the fifth pump B5 and the third reboiler E3 are started to circulate and heat the material. The temperature of the bottom of the distillation tower 5 is adjusted to 160°C and the pressure is -81 kPa through the distributed control system, and the temperature of the top of the distillation tower 5 is adjusted to 125°C and the pressure is -81 kPa; the liquid level in the bottom of the distillation tower 5 is maintained at 50%; when the liquid level of the third reflux tank D3 reaches 30%, the sixth pump B6 is started, and a side line reflux is established through the fourth reflux pipe R4, so that the side line reflux rate is 600 kg / h, and the reflux rate at the top of the distillation tower 5 is controlled to be 380 kg / h. After the self-circulation of the whole tower of the distillation tower 5 is stable, the gas-liquid mixed material is condensed into a liquid phase through the fifth condenser C5, and the special pentamethylene pentamethylene diisocyanate product is extracted.

[0031] Example 3 takes the distillation of m-xylylene diisocyanate as an example.

[0032] A distillation method for special isocyanate, the specific steps are: The first step is to remove the solvent: the crude meta-xylylene diisocyanate in the crude product tank 1 is slowly introduced into the solvent removal tower 2. When the liquid level of the bottom of the solvent removal tower 2 rises to 60%, the first pump B1 and the first reboiler E1 are started to heat the material in a circulation manner. The temperature of the bottom of the solvent removal tower 2 is adjusted to 170°C and the pressure is -72 kPa through the distributed control system. The temperature of the top of the solvent removal tower 2 is 130°C and the pressure is -72 kPa, and the liquid level of the bottom of the solvent removal tower 2 is maintained at 50%; when the liquid level of the first reflux tank D1 reaches 30%, the second pump B2 is started, and reflux is established through the first reflux pipe R1. The reflux amount is controlled to 800 kg / h, and the temperature of the bottom of the solvent removal tower 2 is kept stable; the gas phase discharge valve at the top of the solvent removal tower 2 is opened to allow the solvent to evaporate from the top of the tower and enter the first condenser C1; and the liquid phase discharge valve of the bottom of the solvent removal tower 2 is opened to start discharging; The second step is to remove light components: the material from which the solvent has been removed enters the light component removal tower 3. When the liquid level in the bottom of the light component removal tower 3 rises to 50%, the third pump B3 and the second reboiler E2 are started to heat the material in a cycle. The temperature of the bottom of the light component removal tower 3 is adjusted to 180 ° C by the distributed control system, the pressure of the light component removal tower 3 is -72 kPa, the top temperature of the light component removal tower 3 is 135 ° C, and the pressure is -72 kPa, and the liquid level of the bottom of the light component removal tower 3 is maintained at 50%; when the liquid level of the second reflux tank D2 reaches 30%, the fourth pump B4 is started, and reflux is established through the second reflux pipe R2, and the reflux rate of the light component removal tower 3 is controlled to be 600kg / h, and the temperature of the bottom of the light component removal tower 3 is kept stable; the gas phase discharge valve at the top of the light component removal tower 3 is opened to allow the light component to evaporate from the top of the tower and enter the second condenser C2, and then the discharge valve of the bottom of the light component removal tower 3 is opened to start discharging; The third step is to remove the acid fraction: nitrogen is introduced into the acid stripping tower 4, and material is fed into the acid stripping tower 4 at the same time. When the liquid level in the bottom of the acid stripping tower 4 reaches 30%, the temperature in the acid stripping tower 4 is adjusted to 150°C through the distributed control system, and the hydrogen chloride gas generated in the isocyanate production process is passed from the gas phase port at the top of the acid stripping tower 4 to the third condenser C3 through hot nitrogen, and the material enters the third conveying pipe L3 from the side outlet of the third condenser C3, and the acidic liquid enters the hydrochloric acid falling film absorption tower from the bottom of the third condenser C3; the acidity of the sample in the acid stripping tower 4 is sampled and analyzed, and when the acidity of the sample is less than 80 ppm, the discharge valve at the bottom of the acid stripping tower 4 is opened to start discharging; Step 4: distillation: the material with the acid removed enters distillation tower 5. When the liquid level in the bottom of distillation tower 5 reaches 50%, start pump No. 5 B5 and the third reboiler E3 to heat the material in a cycle. The temperature of the bottom of distillation tower 5 is adjusted to 185 ℃ and the pressure is -81 kPa through the distributed control system. The temperature of the top of distillation tower 5 is 140 ℃ and the pressure is -81 kPa. Maintain the liquid level in the bottom of distillation tower 5 at 50%; when the liquid level of the third reflux tank D3 reaches 30%, start pump No. 6 B6, establish side line reflux through the fourth reflux pipe R4, make the side line reflux amount 600 kg / h, control the reflux amount at the top of distillation tower 5 to 600 kg / h, wait for the self-circulation of the whole tower of distillation tower 5 to be stable, and the gas-liquid mixed material is condensed into liquid phase through the fifth condenser C5, and the special m-xylylene diisocyanate product is extracted.

Claims

1. A distillation device for special isocyanate, characterized in that: It comprises a crude product tank (1), a solvent removal tower (2), a light component removal tower (3), an acid stripping tower (4), and a distillation tower (5); the upper outlet of the crude product tank (1) is connected to the solvent removal tower (2); the first-level discharge pipe (G1) at the bottom of the solvent removal tower (2) is connected to the first reboiler (E1) through a No. 1 pump (B1); the outlet of the first reboiler (E1) is connected to the lower liquid phase inlet of the solvent removal tower (2); the top gas phase outlet of the solvent removal tower (2) is connected to the first condenser (C1); the liquid phase outlet of the first condenser (C1) is connected to the first reflux tank (D1); the liquid phase outlet of the first reflux tank (D1) is connected to the solvent removal tower (2) through a No. 2 pump (B2) and a first reflux pipe (R1); The first discharge pipe (G1) is connected to the first delivery pipe (L1), the first delivery pipe (L1) is connected to the light component removal tower (3), the second discharge pipe (G2) at the bottom of the light component removal tower (3) is connected to the second reboiler (E2) through the third pump (B3), the outlet of the second reboiler (E2) is connected to the lower liquid phase inlet of the light component removal tower (3); the gas phase outlet at the top of the light component removal tower (3) is connected to the second condenser (C2), the liquid phase outlet at the bottom of the second condenser (C2) is connected to the second reflux tank (D2), and the liquid phase outlet of the second reflux tank (D2) is connected to the light component removal tower (3) through the fourth pump (B4) and the second reflux pipe (R2); The secondary discharge pipe (G2) is connected to the second delivery pipe (L2), the second delivery pipe (L2) is connected to the acid stripping tower (4), the third delivery pipe (L3) at the bottom of the acid stripping tower (4) is connected to the distillation tower (5), the gas phase outlet at the top of the acid stripping tower (4) is connected to the third condenser (C3), the material outlet at the side of the third condenser (C3) is connected to the third delivery pipe (L3), and the acid liquid outlet at the bottom of the third condenser (C3) is connected to the hydrochloric acid falling film absorption tower; the lower part of the acid stripping tower (4) is connected to the nitrogen pipe; The fourth delivery pipe (L4) at the bottom of the distillation tower (5) is connected to the third reboiler (E3) through the fifth pump (B5), the outlet of the third reboiler (E3) is connected to the distillation tower (5), the gas phase outlet at the top of the distillation tower (5) is connected to the fourth condenser (C4), and the liquid phase outlet of the fourth condenser (C4) is connected to the distillation tower (5) through the third reflux pipe (R3); the upper part of the distillation tower (5) is also connected to the side line extraction pipe (H), and the side line extraction pipe (H) is connected to the third reflux tank (D3) The liquid phase outlet at the bottom of the third reflux tank (D3) is connected to the fifth condenser (C5) through the sixth pump (B6), and the liquid phase outlet of the fifth condenser (C5) is connected to the product tank; the pipeline where the sixth pump (B6) is located is also connected to the fourth reflux pipe (R4), and the fourth reflux pipe (R4) is connected to the distillation tower (5); the fourth delivery pipe (L4) is connected to the heavy component extraction pipe, and the heavy component extraction pipe is connected to the heavy component tank; the heavy component extraction pipe is connected to the branch pipe, and the branch pipe is connected to the accident tank.

2. A special isocyanate distillation device as claimed in claim 1, characterized in that: The top gas phase outlets of the first condenser (C1), the second condenser (C2) and the fourth condenser (C4) are all connected to the tail gas absorption system.

3. A special isocyanate distillation device as claimed in claim 1, characterized in that: The gas phase outlets at the top of the first reflux tank (D1) and the second reflux tank (D2) are both connected to the tail gas absorption system; and the gas phase outlet at the top of the third reflux tank (D3) is connected to the distillation tower (5).

4. A special isocyanate distillation device as claimed in claim 1, characterized in that: The second delivery pipe (L2) and the nitrogen pipe are both provided with heaters.

5. A special isocyanate distillation device as claimed in claim 1, characterized in that: The acid stripping tower (4) is composed of a tower kettle (41) and a tower body (42). The upper part of the tower body (42) is connected to a feed pipe (43). A distributor (44) is provided at the pipe mouth of the feed pipe (43) located inside the tower body (42). A tower plate (45) is provided below the distributor (44). A gas phase outlet (47) is provided at the top of the tower body (42). A nitrogen inlet pipe (46) is provided in the tower kettle (41). The nitrogen inlet pipe (46) extends from one side of the upper part of the tower kettle (41) along the inner wall into the tower body (42). To the bottom of the tower kettle (41), a liquid phase outlet (48) is provided at the bottom of the tower kettle (41); a tower top pressure gauge (4a) is provided at the top of the tower body (42), a tower mid-pressure gauge (4b) is provided at the bottom of the tower body (42), a tower bottom pressure gauge (4c) is provided at the bottom of the tower kettle (41), a tower mid-temperature gauge (4d) is provided at the top of the tower kettle (41), and a tower bottom temperature gauge (4e) is provided at the bottom; and a connecting piece (49) for fixing the tower kettle (41) is provided at one side of the tower kettle (41).

6. A method for distilling special isocyanates, characterized in that: Through the distributed control system adjustment, the specific steps are as follows: The first step is to remove the solvent: the crude special isocyanate in the crude product tank (1) is slowly introduced into the solvent removal tower (2); when the liquid level in the bottom of the solvent removal tower (2) rises to 30-70%, the first pump (B1) and the first reboiler (E1) are started to circulate and heat the material; the temperature and pressure of the solvent removal tower (2) are adjusted by a distributed control system to maintain the liquid level in the bottom of the solvent removal tower (2) at 50%; when the liquid level in the first reflux tank (D1) reaches 30%, the second pump (B2) is started to establish reflux through the first reflux pipe (R1); the reflux rate of the solvent removal tower (2) is controlled to be 100-500 kg / h to keep the temperature of the bottom of the solvent removal tower (2) stable; the gas phase discharge valve at the top of the solvent removal tower (2) is opened to allow the solvent to evaporate from the top of the tower and enter the first condenser (C1); and the liquid phase discharge valve at the bottom of the solvent removal tower (2) is opened to start discharging; The second step is to remove the light components: the material from which the solvent has been removed is fed into the light component removal tower (3). When the liquid level in the bottom of the light component removal tower (3) rises to 30-70%, the third pump (B3) and the second reboiler (E2) are started to heat the material in a circulation manner, so that the liquid level in the bottom of the light component removal tower (3) is maintained at 50%. The temperature and pressure of the light component removal tower (3) are adjusted by a distributed control system. When the liquid level in the second reflux tank (D2) reaches 30%, the fourth pump (B4) is started to establish reflux through the second reflux pipe (R2), and the reflux rate of the light component removal tower (3) is controlled to be 100-1000 kg / h, so that the bottom temperature of the light component removal tower (3) is kept stable. The gas phase discharge valve at the top of the light component removal tower (3) is opened to allow the light components to evaporate from the top of the tower and enter the second condenser (C2), and then the discharge valve at the bottom of the light component removal tower (3) is opened to start discharging. The third step is to remove the acid fraction: nitrogen is introduced into the acid fraction stripping tower (4), and material is fed into the acid fraction stripping tower (4) at the same time. When the bottom liquid level of the acid fraction stripping tower (4) reaches 30-70%, the temperature in the acid fraction stripping tower (4) is adjusted to 100-150° C. through a distributed control system. The hydrogen chloride gas generated in the isocyanate production process is passed from the gas phase port at the top of the acid fraction stripping tower (4) into the third condenser (C3) through hot nitrogen. The material enters the third conveying pipe (L3) from the side outlet of the third condenser (C3). The acidic liquid enters the hydrochloric acid falling film absorption tower from the bottom of the third condenser (C3); the acidity of the sample in the acid fraction stripping tower (4) is sampled and analyzed. When the acidity of the sample is less than 80 ppm, the bottom discharge valve of the acid fraction stripping tower (4) is opened to start discharging the material; The fourth step is distillation: the material after the acid is removed enters the distillation tower (5). When the liquid level in the bottom of the distillation tower (5) reaches 30-70%, the fifth pump (B5) and the third reboiler (E3) are started to circulate and heat the material to maintain the liquid level in the bottom of the distillation tower (5) at 30-70%. The temperature and pressure of the distillation tower (5) are adjusted by the distributed control system to keep the bottom temperature stable. When the liquid level in the third reflux tank (D3) reaches 30%, the sixth pump (B6) is started to establish a side line reflux through the fourth reflux pipe (R4) to make the side line reflux rate 400-700 kg / h. The reflux rate at the top of the distillation tower (5) is controlled to be 300-2000 kg / h. After the self-circulation of the whole tower of the distillation tower (5) is stable, the gas-liquid mixed material is condensed into a liquid phase through the fifth condenser (C5) and the product is extracted.

7. The method for distilling a special isocyanate according to claim 6, characterized in that: In the first step, during the solvent removal, the temperature of the bottom of the solvent removal tower (2) is adjusted to 90~190°C and the pressure is -54~-81 kPa, and the temperature of the top of the tower is adjusted to 75~150°C and the pressure is -72~-81 kPa through a distributed control system; the temperature of the first reflux tank (D1) is controlled to 40~80°C.

8. The method for distilling a special isocyanate according to claim 6, characterized in that: In the second step, in removing the light components, the distributed control system is used to adjust the bottom temperature of the light component removal tower (3) to 100~200°C, the pressure to -54~-81 kPa, the top temperature to 85~160°C, and the pressure to -72~-81 kPa; the temperature of the second reflux tank (D2) is controlled to 40~80°C.

9. The method for distilling a special isocyanate according to claim 6, characterized in that: In the third step, during the acid removal, the flow rate of nitrogen is controlled to be 1-100 kg / h and the temperature is controlled to be 10-200 °C; the temperature of the feed to the acid stripping tower (4) is controlled to be 10-200 °C.

10. The method for distilling a special isocyanate according to claim 6, characterized in that: In the fourth step, during the product distillation, the temperature of the bottom of the distillation tower (5) is adjusted to 110~200°C and the pressure is adjusted to -72~-81 kPa through the distributed control system, and the temperature of the top of the tower is adjusted to 95~175°C and the pressure is adjusted to -72~-81 kPa.

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