Purification and separation method, purification and separation system and preparation method of isocyanate

Abstract

The invention relates to a purification and separation method, a purification and separation system and a preparation method of isocyanate. The purification and separation method of isocyanate comprises the following steps: conveying an isocyanate reaction solution to a light component removal tower, and carrying out primary rectification to obtain an isocyanate crude product solution; directly conveying the first crude product liquid to a finished product tower, heating the second crude product liquid for partial gasification, and then conveying the second crude product liquid to the finished product tower for secondary rectification together with the first crude product liquid to obtain heavy components, isocyanate and low-boiling-point substances; heating a part of low-boiling-point substances for partial gasification, and then refluxing the low-boiling-point substances to the light component removal tower; in the processes of the first rectification and the second rectification, the inert medium is used for cleaning the trays in the light component removal tower and the finished product tower. The purification and separation method is simple to operate, the polymer generation rate is low, the yield of isocyanate is increased, meanwhile, solid waste is reduced, online self-cleaning is achieved, blockage of all equipment in the rectification process can be effectively avoided, the operation stability of the whole purification and separation system is guaranteed, and the operation cycle of the purification and separation system is greatly prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical industry, and in particular to a purification and separation method of isocyanate, a purification and separation system and a preparation method thereof. Background Art

[0002] Whether it is the gaseous phosgene method or the liquid phase phosgene method for synthesizing isocyanates, during the production process, due to the presence of N and O on the isocyanate group, it has a strong electronegativity, and is easy to self-polymerize to form dimers, trimers, cyclic polymers, etc.; for example, high-viscosity substances such as gel blocks often appear in HDI polymerization products, which are easy to clog tower plates and heat exchangers, often causing problems such as poor separation effect of distillation towers and reduced heat exchange efficiency of heat exchangers, reducing the quality and yield of finished products; at the same time, it greatly shortens the operation cycle of isocyanate production equipment, and the equipment is frequently disassembled and cleaned, which consumes a lot of man-hours and involves toxic materials, increasing safety and environmental risks.

[0003] Patent CN108744706A describes a solid automatic filtering device for phosgene solution. When a phosgene solution containing solid impurities passes through a pipeline filter, solid impurities larger than the aperture of the filter mesh are blocked by the filter mesh and deposited in a filter residue deposition bin below the pipeline filter. High-pressure nitrogen is used to blow the filter residue and filtrate in the filter residue deposition bin into a slag-liquid separation tank, and nitrogen is used to continue to push the filtrate into a filtrate collection tank. Hot nitrogen is used to displace the phosgene adsorbed on the filter residue. When the phosgene analyzer detects that there is no phosgene in the slag-liquid separation tank, the filter residue is discharged to achieve filter residue cleaning. Although this method can clean the filter residue flowing with the solution in the liquid phase pipeline, it cannot clean the tower plate in the distillation process, and fails to propose an effective anti-blocking method.

[0004] Patent CN111069203B discloses a safe cleaning method for acidic solids in a phosgenation isocyanate production device. After the device is shut down, the device is first cleaned with a solvent to heat up and decompose the acidic solids; then a deactivator solution is used to inactivate most of the acidic substances; then an alkali solution is used to inactivate the remaining acidic substances, and the solids are completely or partially dissolved and then taken out by the cleaning equipment; finally, water is used to clean the residues in the cleaning equipment. Although this method can clean the acidic solids generated in the gaseous process pipeline, it requires the introduction of cleaning liquid for cleaning after the device is shut down, and online cleaning cannot be achieved. At the same time, it cannot achieve the cleaning of isocyanate polymer solids generated in the liquid phase distillation process.

[0005] Patent CN104557613A discloses a slag removal method for continuous production of methyl isocyanate, in which a slag remover is installed under a gas-liquid separator, and the liquid phase component of the reaction liquid after passing through the gas-liquid separator enters the slag remover to automatically remove the solid residue of trimeric methyl isocyanate, and the remaining unreacted methylcarbamoyl chloride, solvent chloroform and a small amount of product methyl isocyanate are returned from the outlet of the slag remover to the mixing tank to continue to participate in the reaction. This method precipitates the solid residue at a specific location such as the gas-liquid separator, but fails to propose a cleaning method when the solid matter is blocked in the distillation process, which has obvious limitations. Summary of the invention

[0006] Based on this, it is necessary to provide a purification and separation method of isocyanate, a purification and separation system and a preparation method thereof to address the above problems. The purification and separation method is simple to operate, has a low polymer generation rate, improves the yield of isocyanate, reduces solid waste, realizes online self-cleaning, can effectively avoid blockage of various equipment during the distillation process, ensures the operating stability of the entire purification and separation system, and greatly extends the operating cycle of the purification and separation system.

[0007] A method for purifying and separating isocyanate, the method comprising the following steps:

[0008] The isocyanate reaction liquid is transported to a lightness removal tower for a first distillation to obtain a crude isocyanate liquid;

[0009] The crude isocyanate liquid is separated into a first crude liquid and a second crude liquid, the first crude liquid is directly transported to a finished product tower, the second crude liquid is heated for partial gasification, and then transported to a finished product tower for a second distillation together with the first crude liquid to obtain heavy components, isocyanate and low-boiling substances, wherein the flow rate of the first crude liquid is 38%-50% of the flow rate of the isocyanate reaction liquid, and the flow rate of the second crude liquid is 4%-7% of the flow rate of the isocyanate reaction liquid;

[0010] Heating part of the low boiling point products to partially vaporize them, and then refluxing them to the light removal tower, wherein the flow rate of the part of the low boiling point products is 3%-10% of the flow rate of the isocyanate reaction liquid;

[0011] Wherein, during the first distillation and the second distillation, an inert medium is also used to clean the trays in the lightness removal tower and the finished product tower.

[0012] In one embodiment, before the isocyanate reaction liquid is transported to the lightness removal tower, the isocyanate reaction liquid is also preheated.

[0013] In one embodiment, the inert medium is selected from a gaseous medium or a liquid medium;

[0014] And / or, the inert medium is sprayed toward the tower tray through a nozzle.

[0015] In one embodiment, the spray angle of the nozzle is 45°-120°;

[0016] And / or, the nozzle is arranged on one side of the tower tray, and the center line of the nozzle is arranged perpendicular to the overflow weir of the tower tray and passes through the center of the tower tray;

[0017] And / or, the nozzle has a plurality of nozzle holes, and the flow rate of the inert medium sprayed from each nozzle hole is 0.5Nm 3 / h-10Nm 3 / h.

[0018] In one embodiment, the gaseous medium is selected from nitrogen and / or an inert gas;

[0019] Alternatively, the temperature of the liquid medium is 100° C.-190° C., and the liquid medium is selected from isocyanate finished products.

[0020] A method for preparing isocyanate, the preparation method also includes the isocyanate purification and separation method as described above.

[0021] A purification and separation system for the above-mentioned purification and separation method of isocyanate, the purification and separation system comprising:

[0022] Light-removal tower;

[0023] A finished product tower, wherein the bottom discharge port of the light-removing tower is connected to the finished product tower through a pipeline, and is used to directly transport the first crude product liquid to the finished product tower. The bottom discharge port of the light-removing tower is connected to a first reboiler through a pipeline, and the discharge port of the first reboiler is connected to the finished product tower, and is used to heat the second crude product liquid for partial vaporization, and then transport it to the finished product tower for rectification together with the first crude product liquid. The top discharge port of the finished product tower is connected to a second reboiler through a pipeline, and the discharge port of the second reboiler is connected to the light-removing tower, and is used to heat part of the low-boiling substances for partial vaporization, and then transport them to the light-removing tower;

[0024] Wherein, the light-removing tower and the finished product tower are both provided with a spray cleaning device, and the spray cleaning device cleans the tower plates in the light-removing tower and the finished product tower by spraying an inert medium.

[0025] In one embodiment, the purification and separation system further comprises a preheater, the discharge port of the preheater is connected to the feed port of the light removal tower, and is used to preheat the isocyanate reaction liquid;

[0026] And / or, the purification and separation system also includes a filter, the feed port of the filter is connected to the bottom discharge port of the finished product tower, the discharge port of the filter is connected to the first reboiler through a pipeline for reflux, and the discharge port of the filter is connected to the outside through a pipeline for extracting heavy components.

[0027] In one embodiment, the spray cleaning device includes a spray head, and the spray angle of the spray head is 45°-120°;

[0028] And / or, the inert medium is selected from a gaseous medium or a liquid medium, and the gaseous medium is selected from nitrogen and / or an inert gas.

[0029] In one of the embodiments, the nozzle is disposed on one side of the tower tray, and the center line of the nozzle is vertically arranged to the overflow weir of the tower tray.

[0030] In the method for purifying and separating isocyanate of the present invention, part of the crude isocyanate liquid with a specific flow rate is applied to the finished product tower in a gaseous state, which can reduce the partial pressure of the heavy components in the finished product tower, reduce the temperature of the finished product tower, thereby avoiding the polymerization of isocyanate, reducing the polymer formation rate, reducing the blockage in the second distillation, and improving the yield of isocyanate; at the same time, part of the low-boiling substances with a specific flow rate is applied to the light-removing tower in a gaseous state, and the low-boiling substances have the characteristics of low viscosity and good fluidity, so as to reduce the adhesion of the materials in the light-removing tower to a certain extent, and avoid the polymerization of isocyanate caused by long-term local high temperature residence. The isocyanate used in the light-removal tower and the finished product tower will dilute the isocyanate content in the light-removal tower and the finished product tower to a certain extent, thereby reducing the self-polymerization rate of isocyanate and further reducing the blockage in the distillation process. In addition, the use of inert media to clean the trays in the light-removal tower and the finished product tower can achieve online cleaning of blockages on the trays and avoid tray blockage, thereby ensuring the operating stability of the entire purification and separation system, greatly extending the operating cycle of the entire purification and separation system, and reducing cleaning and maintenance costs.

[0031] Therefore, the isocyanate purification and separation method of the present invention is simple to operate, has a low polymer formation rate, improves the isocyanate yield, reduces solid waste, realizes online self-cleaning, can effectively avoid the blockage of various equipment in the distillation process, ensures the operating stability of the entire purification and separation system, and greatly extends the operating cycle of the purification and separation system. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0033] Figure 1 Schematic diagram of the structure of a purification and separation system according to one embodiment of the present invention, wherein, in the figure, Fa represents part of low-boiling substances, Fb represents the second crude liquid, F2 represents the first crude liquid, and A represents isocyanate;

[0034] Figure 2 Schematic diagram of a top view of a tray in a light-removal tower and a finished product tower according to an embodiment of the present invention, wherein in the figure, B represents a horizontal liquid flow;

[0035] Figure 3 It is a cross-sectional schematic diagram of a nozzle according to one embodiment of the present invention.

[0036] Description of the drawings: 1. Light-removal tower; 2. Second reboiler; 3. Finishing tower; 4. First reboiler; 5. First condenser; 6. Preheater; 7. Second condenser; 8. Filter; 9. Storage device; 10. First pump; 11. Second pump; 12. Third pump; 13. Nozzle; 14. Overflow weir; 15. Tower plate; 16. Downcomer; 17. Base; 18. Spray body; 19. Spray core; 20. Spray hole. DETAILED DESCRIPTION

[0037] For ease of understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by those skilled in the art of the present invention. The terms used herein in the specification of the present invention are only for the purpose of describing specific implementation methods or embodiments, and are not intended to limit the present invention. The optional scope of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of related listed items, and the combinations include any two related listed items, any more related listed items, or all related listed items.

[0039] The method for purifying and separating isocyanate provided by the present invention is mainly used for rectifying the isocyanate reaction liquid obtained after gas-liquid separation in a gas-liquid separator in a gas-phase method or liquid-phase method reaction system to obtain a target isocyanate finished product. In the present invention, the preparation of isocyanate by the gas-phase method is taken as an example, and the liquid phase obtained by the gas-liquid separation treatment, i.e., the isocyanate reaction liquid, is transported to a light-removal tower for the first rectification to remove light components such as phosgene, HCl, and solvents, and obtain a crude isocyanate liquid.

[0040] The crude isocyanate liquid obtained above is divided into a first crude liquid and a second crude liquid, the first crude liquid is directly transported to the finished product tower, the second crude liquid is heated for partial gasification, and then transported to the finished product tower for a second distillation together with the first crude liquid to obtain heavy components, isocyanates and low boiling substances, wherein the flow rate of the first crude liquid is 38%-50% of the flow rate of the isocyanate reaction liquid, and the flow rate of the second crude liquid is 4%-7% of the flow rate of the isocyanate reaction liquid. In this way, the first crude liquid (isocyanate) with a specific flow rate is introduced into the finished product tower, which can reduce the partial pressure of the heavy components of the finished product tower, reduce the temperature of the finished product tower, and thus avoid the polymerization of isocyanate, reduce the polymer formation rate, reduce the blockage in the second distillation, and improve the yield of isocyanate; and the isocyanate applied to the finished product tower will dilute the content of isocyanate in the finished product tower to a certain extent, thereby reducing the self-polymerization reaction rate of isocyanate and further reducing the blockage in the distillation process.

[0041] It should be noted that, in the present invention, a valve may be used for flow control, so as to separate the crude isocyanate liquid obtained above into a first crude liquid and a second crude liquid.

[0042] Part of the low boiling point matter is heated for partial vaporization and then refluxed to the lightness removal tower, wherein the flow rate of part of the low boiling point matter is 3%-10% of the flow rate of the isocyanate reaction liquid. With such arrangement, since the low boiling point matter mainly comprises chlorinated organic matter containing a low content of isocyanate, chlorinated organic matter not containing isocyanate and solvent, and has the characteristics of low viscosity and good fluidity, the adhesion of the material in the lightness removal tower is reduced to a certain extent, and the polymerization and coking of isocyanate caused by long-term local high temperature residence is avoided, thereby reducing the blockage in the first distillation process. Moreover, the low boiling point matter applied to the lightness removal tower will dilute the content of isocyanate in the lightness removal tower to a certain extent, thereby reducing the self-polymerization reaction rate of isocyanate and further reducing the blockage in the distillation process.

[0043] During the operation of the light-removal tower and the finished product tower, when the actual operating temperature of the tower plates of the light-removal tower and the finished product tower is greater than 100°C and the mass fraction of isocyanate in the material on the tower plates is greater than 47%, it is very easy for isocyanate to polymerize and coke to cause the tower plates to be blocked. For this reason, in the present invention, during the first distillation and the second distillation, an inert medium is also used to clean the tower plates in the light-removal tower and the finished product tower, so that blockages on the tower plates can be cleaned online to avoid blockage of the tower plates, thereby ensuring the operating stability of the entire purification and separation system, greatly extending the operating cycle of the entire purification and separation system, and reducing the cleaning and maintenance costs; moreover, in addition to having the function of cleaning the tower plates, the inert medium can also promote the rapid flow of the lateral liquid flow on the tower plates, avoiding the lateral flow of the liquid flow on the tower plates from being retained in the eddy current zone for a long time, resulting in polymerization and the generation of solids, and at the same time can evenly distribute the liquid phase to improve the gas-liquid mass transfer effect of the tower plates.

[0044] In addition, in the present invention, by regulating the flow rate of the first crude product liquid, the flow rate of the second crude product liquid and the flow rate of some low-boiling substances, it is possible to effectively reduce the gas partial pressure, temperature and adhesion in the light-removal tower and the finished product tower while ensuring the feed balance between the light-removal tower and the finished product tower, thereby better reducing the polymer formation rate of isocyanate, reducing blockage in the distillation process, and improving the yield of isocyanate.

[0045] Therefore, in the present invention, part of the crude isocyanate liquid jacket is used for the finished product tower and part of the low-boiling-point jacket is used for the light-removal tower, and an inert medium is used in coordination for cleaning the tower plate, so that the purification and separation method of the present invention is simple to operate, the polymer formation rate is low, the isocyanate yield is improved, and solid waste is reduced. Online self-cleaning is achieved, and blockage of various equipment in the distillation process can be effectively avoided, the operating stability of the entire purification and separation system is guaranteed, and the operating cycle of the purification and separation system is greatly extended.

[0046] It should be noted that, in the present invention, the crude isocyanate liquid obtained after treatment with the lightness removal tower does not include part of the crude isocyanate liquid discharged from the bottom of the lightness removal tower and refluxed into the lightness removal tower after being heated in the bottom reboiler; at the same time, after the first crude liquid and the second crude liquid are treated with the finished product tower, the low-boiling substances obtained do not include part of the low-boiling substances refluxed into the finished product tower through the top condenser of the finished product tower, and the heavy components obtained do not include part of the heavy components refluxed into the finished product tower after being heated in the bottom reboiler of the finished product tower.

[0047] In one embodiment, the remaining portion of the low boilers is directly discharged.

[0048] In one embodiment, the purification and separation method further comprises recovering the heavy component to recover the isocyanate product in the heavy component to improve the product yield.

[0049] It can be understood that when the isocyanate is prepared by the gas phase method in the present invention, the components of the crude isocyanate liquid mainly include the content of precursor impurities, solvent, isocyanate and heavy components, wherein the precursor impurities are mainly chlorinated organic matter containing low content of isocyanate, chlorinated organic matter without isocyanate and solvent; the solvent is selected from at least one of toluene, xylene, chlorobenzene, o-dichlorobenzene or p-chlorotoluene; and the heavy components are mainly polymers of isocyanate.

[0050] In one embodiment, the flow rate of the isocyanate reaction liquid is 50 kg / h-500 kg / h.

[0051] Optionally, before conveying the isocyanate reaction liquid to the lightness removal tower, the isocyanate reaction liquid is also preheated. Furthermore, the temperature of the isocyanate reaction liquid after the preheating treatment is 150°C-170°C. Such a setting is beneficial to improving the distillation treatment efficiency of the isocyanate reaction liquid in the lightness removal tower.

[0052] Optionally, the temperature of the second crude liquid after heating treatment is 150°C-200°C; such a setting is conducive to allowing the second crude liquid to fully form a gas before refluxing into the finished product tower, thereby better reducing the partial pressure and temperature of the heavy components in the finished product tower, thereby reducing the isocyanate polymerization rate and improving the isocyanate yield.

[0053] In one embodiment, the isocyanate is selected from toluene diisocyanate (2,4-TDI, 2,6-TDI or a mixture thereof), isomers of xylylene diisocyanate (XDI), p-phenylene diisocyanate (PPDI) or its isomers, tetramethylxylene diisocyanate (TMXDI), 1,3-dimethyl isocyanate cyclohexane (H6XDI), 2,6-xylene isocyanate, 1,5-naphthalene diisocyanate (1,5-NDI), 1,4-butane diisocyanate, 1,5-pentane diisocyanate (PDI), 1,6-hexane diisocyanate (HDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), 2,4'-dicyclohexylmethane diisocyanate, 1,8-octane diisocyanate, 1,9-nonane diisocyanate, 1,10-decane diisocyanate, 2,2-dimethylpentane-1,5-diisocyanate, 2-methyl-1,5-pentane diisocyanate (MPDI), 2,4,4 (or 2,2,4)- trimethyl-1,6-hexane diisocyanate (TMDI), 1,3- and 1,4-cyclohexane diisocyanate, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (IPDI), 2,4- or 2,6-diisocyanato-1-methylcyclohexane (H6-TDI), 1-isocyanato-1-methyl-4(3)-isocyanatomethylcyclohexane (AMCI), 1,3 (and / or 1,4)-bis(isocyanatomethyl)cyclohexane, Bis(isocyanatomethyl)norbornane (NBDI), triisocyanatocyclohexane, tri(isocyanatomethyl)cyclohexane, triisocyanato-methylcyclohexane, 1,8-diisocyanato-4-(isocyanatomethyl)octane, 1,6,11-undecane triisocyanate, 1,7-diisocyanato-4-(3-isocyanatopropyl)heptane, 1,6-diisocyanato-3-(isocyanatomethyl)hexane, 1,3,5-tris(isocyanatomethyl)cyclohexane.

[0054] Optionally, the inert medium is selected from a gaseous medium or a liquid medium.

[0055] Furthermore, the gaseous medium is selected from nitrogen and / or an inert gas, wherein the inert gas is selected from at least one of helium, neon, argon or krypton. Such an arrangement can effectively clean the tray and avoid tray blockage, and can also play a role in stripping, thereby reducing the hydrolysis chlorine and acid value of the product and improving the product quality of isocyanate. Therefore, the gaseous medium is preferably used in the present invention.

[0056] When the inert medium is selected from a liquid medium, the temperature of the liquid medium is 100° C.-190° C., and the liquid medium is selected from an isocyanate product. In this way, by intermittently spraying the isocyanate product to flush the vortex area of ​​the tray, the tray cleaning effect can be ensured, the tray blockage can be prevented, and the distillation effect can be avoided and impurities can be avoided.

[0057] It should be noted that the isocyanate product of the present invention can be purchased from the market, or can be obtained from the isocyanate obtained after the second distillation treatment of the present invention. The present invention preferably uses the isocyanate obtained after the second distillation treatment, so that the cost can be reduced.

[0058] Optionally, the inert medium is sprayed toward the tower tray through a nozzle. It can be understood that the spraying area of ​​the nozzle is the tower tray.

[0059] Furthermore, the spray angle of the nozzle is 45°-120°, preferably 60°-100°. Such a setting is conducive to better spraying the inert medium to the vortex areas on both sides of the tower plate, avoiding the long-term retention of the lateral liquid flow in the vortex area of ​​the tower plate, and thus better avoiding the production of polymers.

[0060] Optionally, the nozzle is arranged on one side of the tray, and the center line of the nozzle is arranged perpendicular to the overflow weir of the tray and passes through the center of the tray. Such arrangement can further ensure that the inert medium sprayed by the nozzle is sprayed more accurately to the vortex area of ​​the tray, further avoid the clogging of the tray, improve the cleaning effect of the tray, and better improve the gas-liquid mass transfer effect of the tray, thereby improving the distillation efficiency.

[0061] Optionally, the nozzle has a plurality of nozzle holes, and the flow rate of the inert medium sprayed from each nozzle hole is 0.5 Nm 3 / h-10Nm 3 It can be understood that each nozzle can have two nozzle holes, three nozzle holes or four nozzle holes, and two nozzle holes are preferred in the present invention.

[0062] At the same time, the present invention also provides a method for preparing isocyanate, the preparation method also includes the purification and separation method of isocyanate as described above. The preparation method of isocyanate can improve the overall yield of the target product isocyanate, while ensuring the operating stability of the entire isocyanate production device, thereby extending the operating cycle of the entire isocyanate production device.

[0063] In addition, the present invention also provides a purification and separation system for the above-mentioned purification and separation method of isocyanate, such as Figure 1 As shown, the purification and separation system comprises:

[0064] Light removal tower 1;

[0065] The finished product tower 3, the bottom discharge port of the de-lightening tower 1 is connected with the finished product tower 3 through a pipeline, and is used to directly transport the first crude product liquid to the finished product tower 3, the bottom discharge port of the de-lightening tower is connected with the first reboiler 4 through a pipeline, and the discharge port of the first reboiler 4 is connected with the finished product tower 3, and is used to heat the second crude product liquid for partial vaporization, and then transport it to the finished product tower 3 together with the first crude product liquid for distillation, the top discharge port of the finished product tower 3 is connected with the second reboiler 2 through a pipeline, and the discharge port of the second reboiler 2 is connected with the de-lightening tower 1, and is used to heat part of the low-boiling substances for partial vaporization, and then transport them to the de-lightening tower 1.

[0066] Wherein, both the light-removal tower 1 and the finished product tower 3 are provided with a spray cleaning device (not shown in the figure), and the spray cleaning device cleans the trays in the light-removal tower 1 and the finished product tower 3 by spraying an inert medium.

[0067] Specifically, Figure 1 As shown, the purification and separation system also includes a first condenser 5 and a second condenser 7. The top outlet of the light-removing tower 1 is connected to the feed port of the first condenser 5 for condensation. The discharge port of the first condenser 5 is connected to the light-removing tower 1 through a pipeline for reflux. The discharge port of the first condenser 5 is connected to the outside through a pipeline for extracting light components. The bottom discharge port of the light-removing tower 1 is also connected to the feed port of the second reboiler 2 through a pipeline. The discharge port of the second reboiler 2 is connected to the light-removing tower 1 for reflux. for reflux; the top outlet of the finished product tower 3 is connected with the feed port of the second condenser 7 for condensation, the discharge port of the second condenser 7 is connected with the finished product tower 3 through a pipeline for reflux, the discharge port of the second condenser 7 is connected with the second reboiler 2 through a pipeline for partially vaporizing part of the low-boiling substances, the bottom discharge port of the finished product tower 3 is connected with the feed port of the first reboiler 4 through a pipeline for reflux, and the bottom discharge port of the finished product tower 3 is connected with the outside through a pipeline for extracting heavy components.

[0068] It can be understood that in the present invention, the low-boiling substances taken out from the top outlet of the finished product tower 3 are actually the condensate taken out from the outlet of the second condenser 7 .

[0069] Optionally, the purification and separation system further comprises a preheater 6, the discharge port of the preheater 6 is connected to the feed port of the lightness removal tower 1, and is used to preheat the isocyanate reaction liquid. In this way, the isocyanate reaction liquid from the gas-liquid separation device is input into the preheater 6 for preheating treatment and then input into the lightness removal tower 1 for the first distillation treatment.

[0070] In one embodiment, a first pump 10 is provided on a pipeline through which a bottom outlet of the light removal tower 1 is respectively connected to the second reboiler 2 , the finished product tower 3 and the first reboiler 4 .

[0071] In one embodiment, the purification and separation system further includes a storage device 9, the discharge port of the second condenser 7 is connected to the storage device 9 for storing low-boiling substances, and the discharge port of the storage device 9 is connected to the second reboiler 2 for heating part of the low-boiling substances into a gaseous state.

[0072] In one embodiment, a third pump 12 is provided on a pipeline connecting the discharge port of the storage device 9 and the second reboiler 2 .

[0073] Optionally, the purification and separation system also includes a filter 8, the feed port of the filter 8 is connected to the bottom discharge port of the finished product tower 3, the discharge port of the filter 8 is connected to the first reboiler 4 through a pipeline for reflux, and the discharge port of the filter 8 is connected to the outside through a pipeline for extracting heavy components.

[0074] Furthermore, the purification and separation system further comprises a heavy component recovery device, which is connected to the discharge port of the filter 8 and is used for recovering the isocyanate product in the heavy component to improve the product yield.

[0075] Specifically, the discharge port of the filter 8 is connected to the heavy component recovery device and the first reboiler 4 through pipelines, and a second pump 11 is provided on the pipeline.

[0076] Optionally, the inert medium is selected from a gaseous medium or a liquid medium, and the gaseous medium is selected from nitrogen and / or an inert gas.

[0077] In one embodiment, the spray washing device is disposed on one side of a tray in the light-removal tower 1 or the finished product tower 3 .

[0078] like Figure 2 As shown, the direction of the arrow is the direction of the lateral flow of the material liquid flow in the tower plate, and the tower plate includes a tower plate 15, an overflow weir 14 and a downcomer 16. The overflow weir 14 is arranged at one end of the tower plate 15, and the downcomer 16 is arranged on one side above the tower plate 15. The overflow weir 14 and the downcomer 16 are arranged opposite to each other.

[0079] Optionally, the spray cleaning device includes a spray head 13, and a spray angle of the spray head 13 is 45°-120°.

[0080] Furthermore, the nozzle 13 is arranged on one side of the tray, such as Figure 2As shown, the center line of the nozzle 13 is arranged perpendicular to the overflow weir 14 of the tower plate and passes through the center of the tower plate. It should be noted that the center line of the nozzle 13 in the present invention refers to the center line of the nozzle outlet in the horizontal direction.

[0081] like Figure 3 As shown, in one embodiment, the direction indicated by the arrow in the figure represents the inlet of the inert medium, and the nozzle 13 includes a base 17 and a cylindrical spray body 18 installed on the base 17, and a spray core 19 is provided in the spray body 18, and a spray hole is provided at one end of the spray core 19.

[0082] It is understood that the nozzle 13 may have one nozzle hole 20, or may have multiple nozzle holes 20, such as two nozzle holes 20, or three nozzle holes 20, or four nozzle holes 20. In the present invention, two nozzle holes 20 are preferred, such as Figure 3 shown.

[0083] In one embodiment, when the nozzle 13 has a plurality of nozzle holes 20, the angle between adjacent nozzle holes 20 is 45°-120°.

[0084] Optionally, the flow rate of the inert medium sprayed from each spray hole 20 is 0.5 Nm 3 / h-10Nm 3 / h.

[0085] Hereinafter, the purification and separation method, purification and separation system and preparation method of the isocyanate will be further described by the following specific examples. However, it will be understood by those skilled in the art that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be obtained commercially.

[0086] Example 1

[0087] The gas-phase reaction system is subjected to gas-liquid separation in a gas-liquid separator to obtain a hexamethylene diisocyanate reaction liquid, the hexamethylene diisocyanate reaction liquid is transported to a preheater for preheating, and then transported to a lightness removal tower at a flow rate of 100 kg / h for a first distillation treatment. In the distillation process, phosgene, HCl, solvent, etc. are removed from the top of the lightness removal tower, and the hexamethylene diisocyanate crude liquid is produced at the bottom of the tower. The hexamethylene diisocyanate crude liquid is divided into a first crude liquid and a second crude liquid, the first crude liquid is directly transported to a finished product tower at a flow rate of 43 kg / h, the second crude liquid is first transported to a reboiler of the finished product tower at a flow rate of 6 kg / h for heating and partial vaporization, and then transported to the finished product tower for a second distillation treatment together with the first crude liquid. In the distillation process, a low-boiling substance is produced from a top condenser of the finished product tower, and part of the low-boiling substance is produced. The boiling materials are first transported to the reboiler of the light removal tower at a flow rate of 8kg / h for heating and partial vaporization, and then transported to the light removal tower, and the remaining low-boiling materials are discharged as pre-miscellaneous scraps; the finished hexamethylene diisocyanate product is extracted from the tower of the finished product tower; the heavy components are extracted from the bottom of the tower of the finished product tower, and the heavy components are processed by the heavy component recovery unit to recover the products in the heavy components, and the remaining heavy components are scraps, and the scrap rate is calculated; wherein, the trays with a temperature higher than 110°C in the light removal tower and the finished product tower are provided with corresponding nozzles, and during the first distillation treatment and the second distillation treatment, the nozzle is used to spray an inert medium to clean the corresponding tray, the center line of the nozzle is perpendicular to the overflow weir of the tray and passes through the center of the tray, the inert medium is nitrogen, the nozzle has two nozzles, and the spray angle of the nozzle is 75°, and the inert medium flow rate of each nozzle is 1Nm 3 / h.

[0088] Example 2

[0089] The only difference between Example 2 and Example 1 is that the first crude liquid is directly transported to the finished product tower at a flow rate of 38 kg / h for a second distillation treatment, and part of the low-boiling substances are first transported to the light removal tower reboiler at a flow rate of 3 kg / h for heating and partial vaporization.

[0090] Example 3

[0091] The only difference between Example 3 and Example 1 is that the first crude product liquid is directly transported to the finished product tower at a flow rate of 45 kg / h for a second distillation treatment, and part of the low-boiling substances are first transported to the light removal tower reboiler at a flow rate of 10 kg / h for heating and partial vaporization.

[0092] Example 4

[0093] The only difference between Example 4 and Example 1 is that the second crude liquid is first transported to the reboiler of the finished product tower at a flow rate of 4 kg / h for heating and partial vaporization.

[0094] Example 5

[0095] The only difference between Example 5 and Example 1 is that the second crude product liquid is first transported to the reboiler of the finished product tower at a flow rate of 5 kg / h for heating and partial vaporization.

[0096] Example 6

[0097] The only difference between Example 6 and Example 1 is that the second crude liquid is first transported to the reboiler of the finished product tower at a flow rate of 7 kg / h for heating and partial vaporization.

[0098] Example 7

[0099] The only difference between Example 7 and Example 1 is that the spray angle of the nozzle is 45°.

[0100] Example 8

[0101] The only difference between Example 8 and Example 1 is that the spray angle of the nozzle is 30°.

[0102] Example 9

[0103] The only difference between Example 9 and Example 1 is that the spray angle of the nozzle is 120°.

[0104] Example 10

[0105] The only difference between Example 10 and Example 1 is that the inert medium flow rate of each nozzle is 0.5 Nm 3 / h.

[0106] Embodiment 11

[0107] The difference between Example 11 and Example 1 is that the inert medium flow rate of each nozzle is 5Nm 3 / h.

[0108] Example 12

[0109] The difference between Example 12 and Example 1 is that the inert medium flow rate of each nozzle is 10Nm 3 / h.

[0110] Embodiment 13

[0111] Compared with Example 1, Example 13 differs only in that the first crude product liquid is transported to the light-removing tower at a flow rate of 50 kg / h for the first distillation treatment, the first crude product liquid is directly transported to the finished product tower at a flow rate of 20 kg / h, the second crude product liquid is first transported to the finished product tower reboiler at a flow rate of 2.5 kg / h for heating and partial vaporization, and then transported to the finished product tower together with the first crude product liquid for the second distillation treatment, and some low-boiling substances are first transported to the light-removing tower reboiler at a flow rate of 4.5 kg / h for heating and partial vaporization; the inert medium is helium, and the nozzle has 1 spray hole.

[0112] Embodiment 14

[0113] Compared with Example 1, Example 14 differs only in that the first crude product liquid is transported to the light-removing tower at a flow rate of 500 kg / h for the first distillation treatment, the first crude product liquid is directly transported to the finished product tower at a flow rate of 200 kg / h, the second crude product liquid is first transported to the finished product tower reboiler at a flow rate of 27 kg / h for heating and partial vaporization, and then transported to the finished product tower for the second distillation treatment together with the first crude product liquid, and some low-boiling substances are first transported to the light-removing tower reboiler at a flow rate of 45 kg / h for heating and partial vaporization; the inert medium is a cyanate ester liquid.

[0114] Embodiment 15

[0115] The only difference between Example 15 and Example 1 is that the center line of the nozzle and the overflow weir of the tower plate are not arranged perpendicularly, that is, the angle between the center line of the nozzle and the overflow weir of the tower plate is 75° and passes through the center of the tower plate.

[0116] Comparative Example 1

[0117] The only difference between Comparative Example 1 and Example 1 is that the crude isocyanate liquid taken out from the bottom of the light removal tower is directly transported to the finished product tower at a flow rate of 49 kg / h for the second distillation treatment.

[0118] Comparative Example 2

[0119] The only difference between Comparative Example 2 and Example 1 is that the first crude isocyanate liquid is directly transported to the finished product tower at a flow rate of 55 kg / h, and the second crude isocyanate liquid is first transported to the finished product tower reboiler at a flow rate of 3 kg / h for heating and partial vaporization, and then input into the finished product tower for a second distillation treatment together with the first crude liquid.

[0120] Comparative Example 3

[0121] The only difference between Comparative Example 3 and Example 1 is that the first crude product liquid is directly transported to the finished product tower at a flow rate of 36 kg / h, and the second crude product liquid is first transported to the finished product tower reboiler at a flow rate of 8 kg / h for heating and partial vaporization, and then transported to the finished product tower for a second distillation treatment together with the first crude product liquid.

[0122] Comparative Example 4

[0123] The only difference between Comparative Example 4 and Example 1 is that all the low-boiling substances taken out from the top of the finished product tower are discharged as pre-waste materials.

[0124] Comparative Example 5

[0125] The only difference between Comparative Example 5 and Example 1 is that the first crude product liquid is directly transported to the finished product tower at a flow rate of 37 kg / h for a second distillation treatment, low boiling points are extracted from the top of the finished product tower, and part of the low boiling points are first transported to the light removal tower reboiler at a flow rate of 2 kg / h for heating and partial vaporization, and then transported to the light removal tower, and the remaining low boiling points are discharged as front scraps.

[0126] Comparative Example 6

[0127] The only difference between Comparative Example 6 and Example 1 is that the first crude product liquid is directly transported to the finished product tower at a flow rate of 46 kg / h for a second distillation treatment, low boiling points are extracted from the top of the finished product tower, and part of the low boiling points are first transported to the light removal tower reboiler at a flow rate of 11 kg / h for heating and partial vaporization, and then transported to the light removal tower, and the remaining low boiling points are discharged as front scraps.

[0128] Comparative Example 7

[0129] The only difference between Comparative Example 7 and Example 1 is that the crude isocyanate liquid taken out from the bottom of the light removal tower is directly transported to the finished product tower at a flow rate of 49 kg / h for a second distillation treatment; and the low-boiling substances taken out from the top of the finished product tower are all discharged as pre-waste materials.

[0130] Comparative Example 8

[0131] The only difference between Comparative Example 8 and Example 1 is that, during the first distillation treatment and the second distillation treatment, the nozzle is not used to spray the inert medium to clean the corresponding tower plates.

[0132] Comparative Example 9

[0133] The only difference between Comparative Example 9 and Example 1 is that the crude isocyanate liquid taken out from the bottom of the light removal tower is directly transported to the finished product tower at a flow rate of 49 kg / h for the second distillation treatment; the low-boiling products taken out from the top of the finished product tower are all discharged as pre-waste materials, and during the first distillation treatment and the second distillation treatment, the nozzle is not used to spray inert medium to clean the corresponding tower plates.

[0134] The isocyanate content and viscosity of the light removal tower in Examples 1-15 and Comparative Examples 1-9, as well as the temperature, viscosity and heap rate in the finished product tower were tested respectively. The test results are shown in Table 1.

[0135] Table 1

[0136]

[0137] In addition, it has been verified that the purification and separation system of isocyanate used in Examples 1-15 can stably operate for more than 185 days, while the purification and separation system of isocyanate used in Comparative Examples 1-6 can stably operate for less than 140 days, and the purification and separation system of isocyanate used in Comparative Examples 7-9 can stably operate for less than 120 days. Therefore, the purification and separation method of isocyanate of the present invention can ensure the operating stability of the entire purification and separation system, greatly extending the operating cycle of the purification and separation system.

[0138] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0139] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A method for purifying and separating isocyanate, characterized in that: The purification and separation method comprises the following steps: The isocyanate reaction liquid is transported to a lightness removal tower for a first distillation to obtain a crude isocyanate liquid; The crude isocyanate liquid is separated into a first crude liquid and a second crude liquid, the first crude liquid is directly transported to a finished product tower, the second crude liquid is heated for partial gasification, and then transported to a finished product tower for a second distillation together with the first crude liquid to obtain heavy components, isocyanate and low-boiling substances, wherein the flow rate of the first crude liquid is 38%-50% of the flow rate of the isocyanate reaction liquid, and the flow rate of the second crude liquid is 4%-7% of the flow rate of the isocyanate reaction liquid; Heating part of the low boiling point products to partially vaporize them, and then refluxing them to the light removal tower, wherein the flow rate of the part of the low boiling point products is 3%-10% of the flow rate of the isocyanate reaction liquid; Wherein, during the first distillation and the second distillation, an inert medium is also used to clean the trays in the lightness removal tower and the finished product tower.

2. The method for purifying and separating isocyanate according to claim 1, characterized in that: Before the isocyanate reaction liquid is transported to the lightness removal tower, the isocyanate reaction liquid is also preheated.

3. The method for purifying and separating isocyanate according to claim 1, characterized in that: The inert medium is selected from a gaseous medium or a liquid medium; And / or, the inert medium is sprayed toward the tower tray through a nozzle.

4. The method for purifying and separating isocyanate according to claim 3, characterized in that: The spray angle of the nozzle is 45°-120°; And / or, the nozzle is arranged on one side of the tower tray, and the center line of the nozzle is arranged perpendicular to the overflow weir of the tower tray and passes through the center of the tower tray; And / or, the nozzle has a plurality of nozzle holes, and the flow rate of the inert medium sprayed from each nozzle hole is 0.5Nm 3 / h-10Nm 3 / h.

5. The method for purifying and separating isocyanate according to claim 4, characterized in that: The gaseous medium is selected from nitrogen and / or an inert gas; Alternatively, the temperature of the liquid medium is 100° C.-190° C., and the liquid medium is selected from isocyanate finished products.

6. A method for preparing isocyanate, characterized in that: The preparation method also includes the method for purifying and separating the isocyanate as described in any one of claims 1 to 5.

7. A purification and separation system for the isocyanate purification and separation method according to any one of claims 1 to 5, characterized in that: The purification and separation system comprises: Light-removal tower; A finished product tower, wherein the bottom discharge port of the light-removing tower is connected to the finished product tower through a pipeline, and is used to directly transport the first crude product liquid to the finished product tower. The bottom discharge port of the light-removing tower is connected to a first reboiler through a pipeline, and the discharge port of the first reboiler is connected to the finished product tower, and is used to heat the second crude product liquid for partial vaporization, and then transport it to the finished product tower for rectification together with the first crude product liquid. The top discharge port of the finished product tower is connected to a second reboiler through a pipeline, and the discharge port of the second reboiler is connected to the light-removing tower, and is used to heat part of the low-boiling substances for partial vaporization, and then transport them to the light-removing tower; Wherein, the light-removing tower and the finished product tower are both provided with a spray cleaning device, and the spray cleaning device cleans the tower plates in the light-removing tower and the finished product tower by spraying an inert medium.

8. The purification and separation system according to claim 7, characterized in that: The purification and separation system further comprises a preheater, the discharge port of the preheater is connected to the feed port of the light removal tower, and is used for preheating the isocyanate reaction liquid; And / or, the purification and separation system also includes a filter, the feed port of the filter is connected to the bottom discharge port of the finished product tower, the discharge port of the filter is connected to the first reboiler through a pipeline for reflux, and the discharge port of the filter is connected to the outside through a pipeline for extracting heavy components.

9. The purification and separation system according to claim 7, characterized in that: The spray cleaning device comprises a spray head, and the spray angle of the spray head is 45°-120°; And / or, the inert medium is selected from a gaseous medium or a liquid medium, and the gaseous medium is selected from nitrogen and / or an inert gas.

10. The purification and separation system according to claim 9, characterized in that: The nozzle is arranged on one side of the tower plate, and the center line of the nozzle is perpendicular to the overflow weir of the tower plate and passes through the center of the tower plate.

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