Rectification separation method, rectification separation system and production method of 4, 4-diphenylmethane diisocyanate

Abstract

The invention relates to a rectification separation method, a rectification separation system and a production method of 4, 4-diphenylmethane diisocyanate. The rectification separation method of the 4, 4-diphenylmethane diisocyanate comprises the following steps: carrying out rectification treatment on a material containing the 4, 4-diphenylmethane diisocyanate to obtain a tower top fraction, a side-line gas-phase fraction and a tower bottom fraction, carrying out desublimation treatment on the side-line gas-phase fraction to obtain a solid-phase fraction, and carrying out desublimation treatment on the side-line gas-phase fraction to obtain the solid-phase fraction, the mass fraction of the 1, 4-diphenylmethane diisocyanate is greater than or equal to 98.5%. According to the rectification separation method of 4, 4-diphenylmethane diisocyanate, the self-polymerization capacity of 4, 4-diphenylmethane diisocyanate in the high-temperature cooling process can be effectively reduced, the finished product quality of 4, 4-diphenylmethane diisocyanate can be improved, the loss of 4, 4-diphenylmethane diisocyanate monomers can be reduced, and the rectification separation time of 4, 4-diphenylmethane diisocyanate can be prolonged. The storage time of the 1, 4-diphenylmethane diisocyanate product is prolonged, and the transportation pressure and the storage cost are reduced.

Description

Technical Field

[0001] This invention relates to the field of chemical technology, and in particular to a distillation separation method, a distillation separation system, and a production method for 4,4-diphenylmethane diisocyanate. Background Technology

[0002] A method for producing crude diisocyanates includes first obtaining a mixture of diamines and polyamines through acid-catalyzed condensation of amines and aldehydes; reacting this mixture with phosgene to synthesize the corresponding crude diisocyanates; and then separating the mixture by distillation, or by the distillation method reported in patent DE1923214B, to obtain monomeric MDI and polymeric MDI. Since diisocyanates are thermosensitive substances, during the above-mentioned distillation or distillation separation process, the reactive NCO groups in the diisocyanates readily undergo condensation reactions to generate dimers and polymers.

[0003] Typically, 4,4-diphenylmethane diisocyanate is obtained by collecting the liquid phase from the side stream of distillation or distillation, and then cooling it through a condenser. However, because diphenylmethane diisocyanate monomers or isomers are unstable at high temperatures, and the cooling time is long, diphenylmethane diisocyanate monomers are prone to self-polymerization to form dimers and polymers, resulting in a decrease in the quality of the finished diphenylmethane diisocyanate product. At the same time, the presence of dimers or polymers affects the stability of the product, resulting in a shortened storage period for the finished diphenylmethane diisocyanate product.

[0004] Patent CN101003498A reports a method of obtaining a product mixture containing 95wt%-96wt% 4,4-diphenylmethane diisocyanate through distillation, followed by static crystallization to separate a product containing at least 99.2wt% 4,4-diphenylmethane diisocyanate, thereby extending the storage period of 4,4-diphenylmethane diisocyanate. However, this static crystallization method is an intermittent operation, which is not conducive to large-scale continuous production. Furthermore, the static crystallization operation suffers from uneven film distribution, leading to poor heat transfer and affecting the quality of the crystalline product.

[0005] Patent CN109180531B reports a method to significantly reduce the formation of dimers in the high-temperature stage by controlling the ratio of 2,4-diphenylmethane diisocyanate to 2,2-diphenylmethane diisocyanate isomers in a diphenylmethane isocyanate mixture in a distillation column. Furthermore, the addition of benzoquinone stabilizers slows down the dimer production rate during storage, thus extending the shelf life. While this method controls the isomer content during distillation, it cannot solve the problem of isocyanate monomers converting to dimers and polymers during cooling. Moreover, the added polymerization inhibitors introduce new impurities into the product. Additionally, although patent CN113444022B reports improvements in the shelf life and color of MDI-50, neither method addresses the problem of dimer and polymer formation caused by high temperatures during distillation or separation. Summary of the Invention

[0006] Therefore, it is necessary to provide a distillation separation method, a distillation separation system, and a production method for 4,4-diphenylmethane diisocyanate to address the aforementioned problems. This distillation separation method for 4,4-diphenylmethane diisocyanate not only effectively reduces the self-polymerization ability of 4,4-diphenylmethane diisocyanate during high-temperature cooling, improves the quality of the finished product, and reduces the loss of 4,4-diphenylmethane diisocyanate monomers, but also extends the storage time of 4,4-diphenylmethane diisocyanate products, reducing transportation pressure and storage costs.

[0007] A method for distilling and separating 4,4-diphenylmethane diisocyanate includes distilling a material containing 4,4-diphenylmethane diisocyanate to obtain a top fraction, a side vapor fraction, and a bottom fraction; and sublimating the side vapor fraction to obtain a solid fraction, wherein the mass fraction of 4,4-diphenylmethane diisocyanate in the side vapor fraction is greater than or equal to 98.5%.

[0008] In one embodiment, in the step of sublimating the sidestream vapor fraction, the sidestream vapor fraction at a temperature of 195°C-240°C is directly converted into the solid fraction at a temperature of -10°C to 0°C.

[0009] In one embodiment, in the step of sublimating the sidestream vapor fraction, and / or, the temperature of the condensing medium used is 48°C-240°C lower than the freezing point of the sidestream vapor fraction.

[0010] In one embodiment, the temperature of the condensing medium is -195°C to -10°C, and the sublimation time is 3s to 25s;

[0011] And / or, the condensing medium is selected from at least one of liquid nitrogen, liquid ammonia, ethylene glycol, dry ice and ethanol.

[0012] In one embodiment, the material containing 4,4-diphenylmethane diisocyanate is derived from a diphenylmethane diisocyanate reaction solution or a mixture of diphenylmethane diisocyanate isomers.

[0013] In one embodiment, before distilling the material containing 4,4-diphenylmethane diisocyanate, the material is further subjected to a preheating treatment.

[0014] And / or, the distillation separation method further includes encapsulating the solid fraction in a container filled with an inert medium, wherein the inert medium is selected from nitrogen and / or an inert gas.

[0015] A method for producing 4,4-diphenylmethane diisocyanate, the method further comprising the distillation separation method for isocyanate as described above.

[0016] A distillation separation system for the distillation separation method of 4,4-diphenylmethane diisocyanate as described above, comprising:

[0017] Distillation column;

[0018] A condenser, wherein the feed inlet of the condenser is connected to the side vapor phase outlet of the distillation column, wherein the temperature of the condensing medium in the condenser is lower than the freezing point of the side vapor phase fraction collected from the side vapor phase outlet.

[0019] In one embodiment, the distillation separation system further includes a preheater connected to the feed inlet of the distillation column for preheating the material containing 4,4-diphenylmethane diisocyanate.

[0020] In one embodiment, the distillation separation system further includes a conveying device and a storage device. The conveying device is connected to the outlet of the condenser, and the storage device is connected to the outlet of the conveying device for storing solid fractions. The storage device is filled with nitrogen and / or inert gas.

[0021] In the distillation separation method for 4,4-diphenylmethane diisocyanate of the present invention, the side-stream vapor fraction is subjected to sublimation treatment, so that the 4,4-diphenylmethane diisocyanate in the side-stream vapor fraction is directly transformed from the gas phase to the solid phase, achieving rapid cooling of 4,4-diphenylmethane diisocyanate without the need for a long liquid phase cooling time. This reduces the self-polymerization ability of 4,4-diphenylmethane diisocyanate during high-temperature cooling, reduces the loss of 4,4-diphenylmethane diisocyanate monomers, improves the quality of the finished 4,4-diphenylmethane diisocyanate product, and extends the storage time of 4,4-diphenylmethane diisocyanate products, reducing transportation pressure and storage costs. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the distillation and separation system for 4,4-diphenylmethane diisocyanate according to an embodiment of the present invention. In the figure, F represents the material containing 4,4-diphenylmethane diisocyanate, P1 represents the top fraction, P2 represents the solid fraction, and P3 represents the bottom fraction.

[0024] Figure 2 For the present invention Figure 1 A schematic diagram of the structure of the condenser in conjunction with the conveying and storage devices.

[0025] Figure descriptions: 1. Distillation column; 2. Top condenser; 3. Bottom reboiler; 4. Condenser; 5. Preheater; 6. Packing; 7. Vacuum system; 8. Shell; 9. Condensation chamber; 10. Scraper drive motor; 11. Conveying device; 12. Storage device; 13. Scraper; 14. Condensing medium inlet; 15. Condensing medium outlet; 16. Material outlet; 17. Gas phase inlet; 18. Solid phase outlet. Detailed Implementation

[0026] To facilitate understanding of the present invention, it 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. Rather, these embodiments or examples are provided to make the disclosure of the present invention more thorough and complete.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification of this invention is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional scope of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0028] The distillation separation method for 4,4-diphenylmethane diisocyanate provided by this invention is mainly used for the distillation separation of diphenylmethane diisocyanate reaction solution or a mixture of diphenylmethane diisocyanate isomers to obtain a target 4,4-diphenylmethane diisocyanate product with high purity, good quality, and long shelf life. The diphenylmethane diisocyanate reaction solution can be derived from a diphenylmethane diisocyanate reaction solution prepared by a gas-phase or liquid-phase method; the diphenylmethane diisocyanate isomer mixture can be a crude product obtained by pretreatment of the diphenylmethane diisocyanate reaction solution to remove the solvent.

[0029] In this invention, a diphenylmethane diisocyanate reaction solution, or a crude diphenylmethane diisocyanate mixture obtained by pretreatment and solvent removal of the diphenylmethane diisocyanate reaction solution, is used as the material containing 4,4-diphenylmethane diisocyanate for distillation to obtain a top fraction, a side vapor fraction, and a bottom fraction. The mass fraction of 4,4-diphenylmethane diisocyanate in the side vapor fraction is greater than or equal to 98.5%, preferably greater than or equal to 99%. It can be understood that the top fraction is the light component collected from the top of the column, the bottom fraction is the heavy component collected from the bottom of the column, and the side vapor fraction is the finished 4,4-diphenylmethane diisocyanate product collected from the side of the column.

[0030] The sidestream vapor fraction obtained above is subjected to sublimation treatment to obtain a solid fraction, namely, the solid-phase 4,4-diphenylmethane diisocyanate product. This allows the 4,4-diphenylmethane diisocyanate in the sidestream vapor fraction to directly transform from the gas phase to the solid phase, achieving rapid cooling of the 4,4-diphenylmethane diisocyanate without the need for a long liquid phase cooling time. This reduces the self-polymerization ability of 4,4-diphenylmethane diisocyanate during high-temperature cooling, reduces the loss of 4,4-diphenylmethane diisocyanate monomers, improves the quality of the finished 4,4-diphenylmethane diisocyanate product, and extends the storage time of 4,4-diphenylmethane diisocyanate products, reducing transportation pressure and storage costs.

[0031] It should be noted that sublimation refers to the phenomenon where a substance skips the liquid state and changes directly from a gaseous state to a solid state. It is a change of state that occurs when the temperature and pressure are below the triple point.

[0032] It is understandable that, compared to traditional cooling and heat exchange methods, which involve the transformation of 4,4-diphenylmethane diisocyanate from a gaseous state to a liquid state, or vice versa, the cooling and heat exchange time for 4,4-diphenylmethane diisocyanate is relatively long. This makes it highly susceptible to self-polymerization, leading to the formation of dimers and polymers. Consequently, the purity of the finished 4,4-diphenylmethane diisocyanate product decreases, monomer loss increases, and the storage period is shortened, increasing transportation pressure and storage costs. In this invention, sublimation is used to directly transform gaseous 4,4-diphenylmethane diisocyanate into a solid state across phases, achieving rapid cooling. This effectively reduces the self-polymerization ability of 4,4-diphenylmethane diisocyanate, improving its purity and quality, and extending its storage period.

[0033] It is understood that in this invention, since the distillation column has two vapor phase fraction outlets on the side stream, the side stream vapor phase fraction usually includes a first side stream vapor phase fraction and a second side stream vapor phase fraction. Considering that the mass fraction of isocyanate in the second side stream vapor phase fraction is relatively high, the second side stream vapor phase fraction is preferred in this invention. Specifically, in this invention, when the diphenylmethane diisocyanate reaction solution or the crude diphenylmethane diisocyanate isomer mixture obtained by pretreatment of the diphenylmethane diisocyanate reaction solution to remove solvent and polymer is used as the material containing 4,4-diphenylmethane diisocyanate for distillation, the first side stream vapor phase fraction is a mixture of 2,4-diphenylmethane diisocyanate and 4,4-diphenylmethane diisocyanate isomers, the bottom fraction is the heavy fraction collected from the bottom of the column, and the second side stream vapor phase fraction is the 4,4-diphenylmethane diisocyanate finished product collected from the side stream of the column, with a mass fraction greater than or equal to 98.5%, preferably greater than or equal to 99%.

[0034] Optionally, in the step of sublimating the sidestream vapor fraction, the sidestream vapor fraction at a temperature of 195℃-240℃ is directly converted into the solid fraction at a temperature of -10℃ to 0℃. This configuration can further reduce the occurrence of self-polymerization of 4,4-diphenylmethane diisocyanate while also reducing energy consumption.

[0035] Optionally, in the step of sublimating the sidestream vapor fraction, the temperature of the condensing medium used is 48°C-240°C lower than the freezing point of the sidestream vapor fraction, preferably 48°C-65°C. This setting can further ensure that the vapor fraction is quickly converted into a solid fraction, shorten the sublimation treatment time, better reduce the self-polymerization ability of 4,4-diphenylmethane diisocyanate, and improve the quality of 4,4-diphenylmethane diisocyanate.

[0036] Optionally, the temperature of the condensing medium is -195℃ to -10℃, and the sublimation time is 3s to 25s. Preferably, the temperature of the condensing medium is -30℃ to -25℃, and the sublimation time is 5s to 25s. This setting allows for better rapid cooling of the gas phase fraction at 195℃-240℃ into a solid phase fraction at -10℃ to 0℃.

[0037] Furthermore, the condensing medium is selected from at least one of liquid nitrogen, liquid ammonia, ethylene glycol, dry ice and ethanol, preferably ethylene glycol.

[0038] In this invention, the material containing 4,4-diphenylmethane diisocyanate is selected from diphenylmethane diisocyanate reaction solution or a mixture of diphenylmethane diisocyanate isomers, preferably a mixture of diphenylmethane diisocyanate isomers. Specifically, the mixture of diphenylmethane diisocyanate isomers is obtained by removing the solvent from the diphenylmethane diisocyanate reaction solution, and then removing some of the light components and the polymerized diphenylmethane diisocyanate product by passing it through a distillation column.

[0039] In one embodiment, before distilling the material containing 4,4-diphenylmethane diisocyanate, the material is further subjected to a preheating treatment.

[0040] Furthermore, the temperature of the preheated material containing 4,4-diphenylmethane diisocyanate is 165℃-180℃, which helps to reduce energy consumption during the distillation process.

[0041] In one embodiment, in the step of distilling the material containing 4,4-diphenylmethane diisocyanate, the top temperature of the column is controlled at 181°C-220°C, the bottom temperature at 200°C-245°C, the pressure in the column at 100 Pa-800 Pa, and the side temperature at 195°C-230°C.

[0042] In this invention, the distillation separation method further includes encapsulating the solid fraction in a container filled with an inert medium, wherein the inert medium is selected from nitrogen and / or an inert gas.

[0043] Specifically, the solid fraction can be first encapsulated in a container filled with an inert medium, and then stored in an ice storage facility.

[0044] The inert medium is selected from nitrogen and / or inert gases, preferably nitrogen.

[0045] Meanwhile, the present invention also provides a method for producing 4,4-diphenylmethane diisocyanate, the method further comprising the distillation separation method of 4,4-diphenylmethane diisocyanate as described above.

[0046] Specifically, in the preparation of 4,4-diphenylmethane diisocyanate by the gas-phase method, aniline and formaldehyde are first subjected to acid-catalyzed condensation. The resulting diamine reacts with phosgene to generate a diphenylmethane diisocyanate reaction solution. This reaction solution is then subjected to distillation. Alternatively, the obtained diphenylmethane diisocyanate reaction solution is pretreated to remove solvents and polymers to obtain a mixture of diphenylmethane diisocyanate isomers. This mixture of diphenylmethane diisocyanate isomers is then subjected to distillation to obtain a side-stream gas fraction. This side-stream gas fraction is then subjected to sublimation to obtain a solid fraction, i.e., the solid-phase 4,4-diphenylmethane diisocyanate product.

[0047] Furthermore, the present invention also provides a distillation separation system for the distillation separation method of 4,4-diphenylmethane diisocyanate as described above, such as... Figures 1-2 As shown, the system includes a distillation column 1, a top condenser 2, a bottom reboiler 3, and a sublimator 4. The bottom outlet of the distillation column 1 is connected to the inlet of the bottom reboiler 3 via a pipe. The outlet of the bottom reboiler 3 is connected to the distillation column 1. The bottom outlet of the distillation column 1 is connected to the outside via another pipe for collecting the bottom fraction P3. The top outlet of the distillation column 1 is connected to the inlet of the top condenser 2. The outlet of the top condenser 2 is connected to the distillation column 1 via a pipe. The outlet of the top condenser 2 is connected to the outside via another pipe for collecting the top fraction P1. The inlet of the sublimator 4 is connected to the side vapor phase outlet of the distillation column 1. The temperature of the condensing medium in the sublimator 4 is lower than the freezing point of the side vapor phase fraction P2 collected from the side vapor phase outlet.

[0048] In one embodiment, the distillation column is a distillation column with vertical partition walls, and along the height direction of the distillation column, the interior of the distillation column is divided into an interconnected preliminary fractionation zone, a rectification zone, a stripping zone, and a side zone.

[0049] Furthermore, to better increase the contact area between the gas and liquid phases within the distillation column 1, and to achieve sufficient gas-liquid exchange and better mass transfer, the distillation column 1 is filled with packing material 6, wherein the total height of the packing material 6 is 7.5m-13.5m. Specifically, the packing height in the preliminary fractionation zone is 6.5m-7m, the packing height in the rectification zone is 1.5m-2.2m, the packing height in the stripping zone is 1.0m-1.8m, and the packing height in the side zone is 6.2m-6.9m.

[0050] Optionally, the distillation column 1 has a feed inlet through which material containing 4,4-diphenylmethane diisocyanate enters the distillation column 1.

[0051] Optionally, the distillation separation system further includes a preheater 5, which is connected to the feed inlet of the distillation column 1 and is used to preheat the material containing 4,4-diphenylmethane diisocyanate. Specifically, in conjunction with Figure 1 As shown, the material containing 4,4-diphenylmethane diisocyanate is first fed into the preheater 5 for heating, and then enters the distillation column 1 through the feed inlet of the distillation column 1.

[0052] Optionally, combined Figure 2 It is understood that the distillation separation system also includes a conveying device 11 and a storage device 12. The conveying device 11 is connected to the outlet of the condenser 4, and the storage device 12 is connected to the outlet of the conveying device 11 for storing solid fractions. The storage device 12 is filled with nitrogen and / or inert gas.

[0053] In one embodiment, the conveying device 11 is a screw conveyor.

[0054] In one embodiment, the storage device 12 is a container, which may be a bucket.

[0055] In one embodiment, the storage device 12 may also be a packaging storage device.

[0056] In one embodiment, the distillation separation system further includes a vacuum system 7, which is connected to the outlet of the top condenser 2 via a pipeline.

[0057] Specifically, in combination Figure 2As shown, the condenser 4 includes a shell 8, a condensation chamber 9, and a scraper drive motor 10. The shell 8 has a condensing medium inlet 14, a condensing medium outlet 15, and a material outlet 16. The condensation chamber 9 is located inside the shell 8 and has a gas phase inlet 17 and a solid phase outlet 18. The solid phase outlet 18 is connected to the material outlet 16. A scraper 13 is provided inside the condensation chamber 9 and is driven by the scraper drive motor 10. The material outlet 16 is connected to the inlet of the conveying device 11, and the outlet of the conveying device 11 is connected to the storage device 12. It is understood that the side vapor fraction collected from the side vapor phase outlet of the distillation column enters the condensation chamber 9 through the vapor phase inlet 17 and is condensed to form a solid phase fraction. Under the action of the scraper drive motor 10, the scraper 13 quickly scrapes off the solid phase fraction formed on the inner wall of the condensation chamber 9. The scraped solid phase fraction enters the conveying device 11 through the solid phase outlet 18 of the condensation chamber 9 and the material outlet 16 of the shell 8. Then, it is conveyed to the storage device 12 through the conveying device 11, that is, the isocyanate product is stored in the storage device 12.

[0058] It should be noted that the specific structure of the condenser 4 in this invention belongs to the prior art, so it will not be described in detail here.

[0059] The following specific examples will further illustrate the distillation separation method, distillation separation system, and production method of 4,4-diphenylmethane diisocyanate. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the examples were performed under conventional conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products.

[0060] Example 1

[0061] A mixture of diphenylmethane diisocyanate isomers is fed to a preheater and heated to 173°C, then fed into a distillation column. The column pressure is controlled at approximately 150 Pa, and the packing height is approximately 9 m. After heating in a reboiler at the bottom of the column, the temperature inside the distillation column reaches approximately 210°C. The gaseous material rises countercurrently from the bottom of the column and undergoes thorough gas-liquid exchange with the liquid material after heat exchange in the condenser at the top of the column. The top fraction is collected at approximately 185°C, the first sidestream gaseous fraction is collected at approximately 192°C, and the second sidestream fraction is collected at approximately 200°C. In vapor-phase distillation, the bottom fraction is collected at the bottom of the distillation column. The top fraction includes 0.85% solvent, 4.12% 2,2-diphenylmethane diisocyanate, 38.96% 2,4-diphenylmethane diisocyanate, and 60.25% 4,4-diphenylmethane diisocyanate. The first side stream vapor-phase fraction includes 54% 2,4-diphenylmethane diisocyanate and 45% 4,4-diphenylmethane diisocyanate. The second side stream vapor-phase fraction includes 99.4% diisocyanate. The bottom fraction includes 33% diphenylmethane diisocyanate and 68% dimers and polymers.

[0062] The second side-stream vapor fraction obtained above is fed into a scraped condenser and subjected to condensation treatment at -30°C for 10 seconds to obtain a solid fraction at -10°C, which is the solid diisocyanate product. The condensing medium in the scraped condenser is ethylene glycol, and the mass fraction of dimer in the solid fraction is 43 ppm.

[0063] The obtained solid fraction was sealed in a nitrogen-filled container and stored in an ice cellar.

[0064] Example 2

[0065] The only difference between Example 2 and Example 1 is that the side-stream vapor fraction obtained above was fed into a scraped condenser and condensed at -10°C for 25 seconds to obtain a solid fraction at 0°C. The mass fraction of dimers in the solid fraction was found to be 72 ppm.

[0066] Example 3

[0067] The only difference between Example 3 and Example 1 is that the side-stream vapor fraction obtained above was fed into a scraped condenser and condensed at -20°C for 10 seconds to obtain a solid fraction at -5°C. The mass fraction of dimers in the solid fraction was found to be 64 ppm.

[0068] Example 4

[0069] Example 4 differs from Example 1 only in that liquid nitrogen is used instead of ethylene glycol as the condensing medium. The side-stream vapor fraction obtained above is fed into a scraped condenser and condensed at -195°C for 3 seconds to obtain a solid fraction at -10°C. The mass fraction of dimers in the solid fraction is 43 ppm.

[0070] Example 5

[0071] Compared with Example 1, Example 5 differs only in that liquid ammonia is used instead of ethylene glycol as the condensing medium. The side-stream vapor fraction obtained above is fed into a scraped condenser and condensed at -33°C for 5 seconds to obtain a solid fraction at -5°C. The mass fraction of dimers in the solid fraction is 44 ppm.

[0072] Example 6

[0073] Example 6 differs from Example 1 only in that a mixture of dry ice and ethanol is used instead of ethylene glycol as the condensing medium, wherein the mass ratio of dry ice to ethanol is 1:3. The side-stream vapor fraction obtained above is fed into a scraped condenser and condensed at -78°C for 4 seconds to obtain a solid fraction at -8°C, wherein the mass fraction of dimers in the solid fraction is 43 ppm.

[0074] Example 7

[0075] Example 7 differs from Example 1 only in that a diphenylmethane diisocyanate reaction solution is used instead of the diphenylmethane diisocyanate isomer mixture as the feed material containing 4,4-diphenylmethane diisocyanate, which is then heated to 165°C in the preheater. The overhead fraction comprises 45.4% solvent, 1.8% 2,2-diphenylmethane diisocyanate, 4.5% 2,4-diphenylmethane diisocyanate, and 48.3% 4,4-diphenylmethane diisocyanate. 4-Diphenylmethane diisocyanate, the first side stream vapor phase fraction includes 0.1% 2,2-diphenylmethane diisocyanate, 53.5% 2,4-diphenylmethane diisocyanate and 48% 4,4-diphenylmethane diisocyanate, the second side stream vapor phase fraction includes more than 98.5% diisocyanate, the bottoms fraction includes 35% diphenylmethane diisocyanate and 65% dimers and polymers, and the solid phase fraction contains 83 ppm of dimers.

[0076] Example 8

[0077] The only difference between Example 8 and Example 1 is that the obtained solid fraction is encapsulated in a barrel and stored in an ice room at a temperature of -5°C, wherein the barrel is not filled with nitrogen.

[0078] Comparative Example 1

[0079] The only difference between Comparative Example 1 and Example 1 is that the second side-stream vapor fraction obtained above was fed into a shell-and-tube heat exchanger and cooled at 40°C for 15 minutes to obtain a liquid fraction at 45°C. The liquid fraction was added to a crystallizer and cooled to solid state at -10°C. The condensing medium in the shell-and-tube heat exchanger was water, the cooling medium in the crystallizer was ethylene glycol, and the mass fraction of dimer in the solid fraction was 110 ppm.

[0080] Comparative Example 2

[0081] Compared with Example 1, Comparative Example 2 differs only in that the second side-stream vapor fraction obtained above is fed into a shell-and-tube heat exchanger and cooled at 40°C for 25 minutes to obtain a liquid fraction at 50°C. The condensing medium in the shell-and-tube heat exchanger is water, and the mass fraction of dimer in the liquid fraction is 174 ppm.

[0082] After storing the barrels containing solid fractions (i.e., 4,4-diphenylmethane diisocyanate product) in Examples 1-8 and Comparative Example 1, and the barrel containing liquid fractions (i.e., 4,4-diphenylmethane diisocyanate product) in Comparative Example 2 in an ice storage for 15 days, the content of dimers in the 4,4-diphenylmethane diisocyanate product in the barrels of Examples 1-8 and Comparative Example 1, and the content of dimers in the 4,4-diphenylmethane diisocyanate product in the barrel of Comparative Example 2 were measured respectively.

[0083] Table 1

[0084]

[0085] As can be seen from the data in the examples and comparative examples in Table 1, the sublimation treatment of the side-stream gaseous fraction in this invention can directly and rapidly convert the side-stream gaseous fraction into a solid-phase fraction, that is, convert the gaseous 4,4-diphenylmethane diisocyanate into the solid-phase 4,4-diphenylmethane diisocyanate. This effectively reduces the self-polymerization ability of the 4,4-diphenylmethane diisocyanate product, significantly reduces the content of dimers and polymers in the 4,4-diphenylmethane diisocyanate product, and improves the finished quality of 4,4-diphenylmethane diisocyanate. At the same time, the content of dimers and polymers in the 4,4-diphenylmethane diisocyanate product does not increase after 15 days of storage.

[0086] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above 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.

[0087] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for distilling and separating 4,4-diphenylmethane diisocyanate, comprising distilling a material containing 4,4-diphenylmethane diisocyanate to obtain a top fraction, a side stream vapor fraction, and a bottom fraction, characterized in that, The sidestream vapor fraction is subjected to sublimation treatment to obtain a solid fraction, wherein the mass fraction of 4,4-diphenylmethane diisocyanate in the sidestream vapor fraction is greater than or equal to 98.5%.

2. The distillation separation method for 4,4-diphenylmethane diisocyanate according to claim 1, characterized in that, In the step of sublimation treatment of the side-stream vapor fraction, the side-stream vapor fraction at a temperature of 195℃-240℃ is directly converted into the solid fraction at a temperature of -10℃ to 0℃.

3. The distillation separation method for 4,4-diphenylmethane diisocyanate according to claim 1, characterized in that, In the step of sublimating the sidestream vapor fraction, the temperature of the condensing medium used is 48°C-240°C lower than the freezing point of the sidestream vapor fraction.

4. The distillation separation method for 4,4-diphenylmethane diisocyanate according to claim 3, characterized in that, The temperature of the condensing medium is -195℃ to -10℃, and the sublimation time is 3s to 25s. And / or, the condensing medium is selected from at least one of liquid nitrogen, liquid ammonia, ethylene glycol, dry ice and ethanol.

5. The distillation separation method for 4,4-diphenylmethane diisocyanate according to claim 1, characterized in that, The material containing 4,4-diphenylmethane diisocyanate is derived from a diphenylmethane diisocyanate reaction solution or a mixture of diphenylmethane diisocyanate isomers.

6. The distillation separation method for 4,4-diphenylmethane diisocyanate according to claim 1, characterized in that, Before distilling the material containing 4,4-diphenylmethane diisocyanate, the process also includes preheating the material containing 4,4-diphenylmethane diisocyanate. And / or, the distillation separation method further includes encapsulating the solid fraction in a container filled with an inert medium, wherein the inert medium is selected from nitrogen and / or an inert gas.

7. A method for producing 4,4-diphenylmethane diisocyanate, characterized in that, The production method further includes a distillation separation method for 4,4-diphenylmethane diisocyanate as described in any one of claims 1-6.

8. A distillation separation system for the distillation separation method of 4,4-diphenylmethane diisocyanate as described in any one of claims 1-6, characterized in that, include: Distillation column; A condenser, wherein the feed inlet of the condenser is connected to the side vapor phase outlet of the distillation column, wherein the temperature of the condensing medium in the condenser is lower than the freezing point of the side vapor phase fraction collected from the side vapor phase outlet.

9. The distillation and separation system for 4,4-diphenylmethane diisocyanate according to claim 8, characterized in that, The distillation separation system also includes a preheater connected to the feed inlet of the distillation column for preheating materials containing 4,4-diphenylmethane diisocyanate.

10. The distillation and separation system for 4,4-diphenylmethane diisocyanate according to claim 8 or claim 9, characterized in that, The distillation separation system further includes a conveying device and a storage device. The conveying device is connected to the outlet of the condenser, and the storage device is connected to the outlet of the conveying device for storing solid fractions. The storage device is filled with nitrogen and / or inert gas.

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