Apparatus and method for producing hexamethylene diisocyanate by pyrolysis of a methyl hexamethylene dicarbamate intermediate

Abstract

The present application relates to a kind of equipment and method for preparing hexamethylene diisocyanate by hexamethylene diaminoformate intermediate pyrolysis, the present application uses continuous pyrolysis reaction device, HDI can be prepared in high-boiling solvent, can completely replace the existing phosgene and phosgene derivative method for preparing HDI, solve the safety and pollution problem of phosgene method;Compared with low-boiling solvent process, the present application can greatly reduce energy consumption in product separation stage, and the energy consumption required for separating solvent in high-boiling solvent method is 1 / 10 of low-boiling solvent process, it is a green environmental protection energy-saving process;The present application uses non-toxic high-boiling solvent, compared with low-boiling solvent method, production safety is guaranteed;Compared with ordinary high-boiling solvent, the present application can avoid multiple contact between isocyanate and alcohol, and the yield of HDI can be further improved;The process flow of the present application is simple, and the operating condition is mild, it is a process that can be rapidly industrialized.

Description

Technical Field

[0001] This invention relates to an apparatus and method for preparing hexamethylene dicarboxylate via pyrolysis of a methyl hexamethylene dicarboxylate intermediate. Background Technology

[0002] Adipic diisocyanates (including HDI, IPDI, and HMDI) are key materials supporting the development of industries such as aerospace, military, high-end equipment, automobiles, and home appliances, and market demand has been rising steadily in recent years. Currently, domestic demand for ADI ester isocyanates is increasing year by year, with large quantities imported annually to meet demand, indicating a very broad application prospect. The main ADI ester isocyanate products on the market include hexamethylene diisocyanate (HDI), isoflurane diisocyanate (IPDI), and dicyclohexyl-4-4-diisocyanate (HMDI).

[0003] Currently, the main method for large-scale industrial HDI synthesis is still based on phosgene and phosgene derivatives. Phosgene is a highly toxic gas, and the synthesis process releases large amounts of phosgene and hydrogen chloride. Phosgene is also highly biotoxic, posing significant risks to production operations, corroding equipment, and causing severe environmental pollution. The government's designated system for phosgene production and application inconveniences the production of small-batch fine and specialty chemicals, thus limiting the development of this type of fine chemical industry to some extent.

[0004] The preparation of isocyanates using non-phosgene methods mainly employs low-boiling-point, medium-boiling-point, and high-boiling-point solvents. Low-boiling-point solvents are versatile and applicable to isocyanates such as MDI, TDI, and HDI, and can be used in all isocyanate processes; however, they require large equipment, significant investment, and high energy consumption. Medium-boiling-point solvents also have a wide range of applications, suitable for various isocyanate processes, but require stringent separation conditions. In non-isocyanate preparation processes, high-boiling-point solvent systems are only suitable for some isocyanates with relatively low boiling points, such as HDI and XDI, but not for MDI and NDI. However, high-boiling-point solvent systems have lower energy consumption and are simpler to operate.

[0005] Chinese patent application CN108395384A, entitled "Green Synthesis Method of Isocyanates," describes a nucleophilic reaction between an amino compound and dimethyl carbonate in an organic solvent to generate carbamate, followed by pyrolysis of the carbamate to obtain isocyanate. However, the organic solvents used in this reaction are mostly benzene-based solvents such as toluene and benzene, which are highly toxic, posing significant safety hazards to the production process and causing environmental pollution. Benzene-based solvents are low-boiling-point solvents, and their boiling points are not significantly different from those of the byproduct alcohols, making separation difficult. The HDC conversion rate is only 90.3%, and the final yield is around 83.2%. Furthermore, the process involves large investment and high energy consumption, manifested in the long reaction time (around 5 hours) and low reactant concentration, leading to a large reactor size, a large online solvent volume, and high energy consumption in the later stages.

[0006] Chinese patent application CN102964272A, entitled "A Method for Preparing Hexamethylene 1,6-Diisocyanate (HDI) by Heterogeneous Catalytic Pyrolysis in the Liquid Phase," describes a technique that requires pressures as high as 2.0 MPa during the pyrolysis of HDC to produce HDI, posing significant operational risks and demanding high-end equipment with substantial upfront investment. Because a low-boiling-point solvent is used, its boiling point is similar to that of the byproduct alcohols, making separation difficult. Therefore, an inert gas is continuously introduced into the reactor for purging during the reaction, requiring additional heat input to preheat the inert gas, resulting in additional energy consumption. This process achieves an HDC conversion rate of 96% and an HDI yield of approximately 88%.

[0007] The process of preparing isocyanates by thermal decomposition in high-boiling-point solvents (as disclosed in patent application CN103848758A) also uses high-boiling-point solution pyrolysis to produce HDI. Because the HDI vapor and alcohol vapor come into secondary contact, separation becomes difficult, reducing the purity of the HDI product.

[0008] This study employs a continuous pyrolysis reactor. On one hand, it rapidly removes the byproduct methanol, propelling the reaction in the forward direction. On the other hand, the generated HDI can be immediately distilled off the reaction system and collected by condensation, preventing prolonged exposure of HDI to the high-temperature reaction system, which could lead to polymerization and secondary contact with byproducts, thus reducing product purity. This approach overcomes the challenges of solvent-free methods and addresses the issues of high investment and energy consumption associated with low-boiling-point solvents. Furthermore, it eliminates the problem of secondary contact between the product isocyanate and the byproduct alcohol in other high-boiling-point solvents, which reduces isocyanate yield and purity. Summary of the Invention

[0009] The technical problem to be solved by the present invention is to provide a method for preparing hexamethylene dicarboxylate by pyrolysis of hexamethylene dicarboxylate intermediate, which overcomes the difficulties of solvent-free conditions and solves the problems of high investment and high energy consumption in light boiling point solvents. It can also reduce the secondary contact between the product isocyanate and the by-product alcohol, and improve the yield and purity of the reacted isocyanate.

[0010] The technical problem to be solved by the present invention is to provide an apparatus for preparing hexamethylene dicarboxylate by pyrolysis of methyl hexamethylene dicarboxylate intermediate, in light of the current state of the art.

[0011] The technical solution adopted by the present invention to solve at least one of the above-mentioned technical problems is as follows:

[0012] An apparatus for preparing hexamethylene diisocyanate via pyrolysis of a methyl hexamethylene dicarboxylate intermediate includes an HDC synthesis unit and an HDC pyrolysis unit for preparing HDI, wherein the HDC synthesis unit comprises:

[0013] Material storage tank T-101 is used to store raw materials DMC and HDA;

[0014] The reaction vessel R-101, which contains a multiphase catalyst, is connected to the material storage tank T-101 to supply DMC and HDA for reaction.

[0015] Flash evaporator T-102 is connected to reaction vessel R-101 to separate light and heavy components from the reaction liquid;

[0016] Intermediate tank T-103 is connected to the top of flash tank T-102 and is used to receive the portion of the light component DMC that forms an azeotrope with methanol. It is also connected to the bottom of flash tank T-102 and is used to receive the filtrate of HMC after the heavy component product concentrated HDC has been crystallized and filtered by filter S-101.

[0017] Dryer E-103, connected to filter S-101, is used to dry the obtained filter cake coarse HDC;

[0018] The HDC pyrolysis to HDI preparation unit includes:

[0019] The ingredient storage tank T-201 is connected to the output end of the dryer E-103 and is used to store the dried HDC and solvent.

[0020] Reactor R-201 is connected to the feed storage tank T-201 to provide continuous pyrolysis reaction of materials and to rapidly remove methanol and HDI produced by the reaction; the bottom of reactor R-201 has a pipe for unreacted materials to flow back to the feed storage tank T-201.

[0021] Distillation column C-201 is connected to reactor R-201 and is used to input the vapor HDI, methanol, part of HMI and trace amounts of solvent and HDC generated in reactor R-201 for distillation separation of materials; the bottom of distillation column C-201 has a pipe for the solvent, HDC and part of HMI to be cooled and refluxed back into reactor R-201.

[0022] Storage tank T-202 is connected to the top of distillation column C-201;

[0023] HDI purification tower C-202 is connected to the bottom of storage tank T-202 to supply crude HDI liquid for separation and purification of materials.

[0024] Preferably, it also includes a methanol distillation column C-101, which is connected to the intermediate tank T-103 and is used to receive the solvent to be separated in the intermediate tank T-103. The top of the column is connected to the top reflux tank T-104 through the top condenser E-106, and is further connected to the inner cavity of the methanol distillation column C-101 through the top reflux pump P-106.

[0025] Preferably, the downstream of the top reflux pump P-106 is connected to the methanol storage tank T-204 via the methanol recovery condenser E-104.

[0026] Preferably, the bottom of the methanol distillation column C-101 is connected to the methanol distillation column C-101 and the material storage tank T-101 respectively via a reflux pump P-105.

[0027] Preferably, the top of the distillation column C-201 is connected to the reflux tank T-206 via the condenser E-206, and the reflux tank T-206 is connected to the distillation column C-201 and the storage tank T-202 via the reflux pump P-205.

[0028] A method for preparing hexamethylene diisocyanate via pyrolysis of methyl hexamethylene dicarboxylate intermediate includes the following steps:

[0029] Fresh DMC and HDA, along with DMC recovered from methanol distillation column C-101, enter material storage tank T-101. After being preheated by preheater E-107, they enter reaction tank R-101 to react in a multiphase catalyst.

[0030] The reaction liquid enters the flash tank T-102 through pressure difference. The light component DMC and methanol form an azeotrope and are partially evaporated, entering the intermediate tank T-103 through the condenser E-101. The heavy component product, concentrated HDC, is filtered through the crystallization filter S-101, and the filtrate containing HMC is transported to the intermediate tank T-103. The filter cake coarse HDC is further purified by steam drying in the HDC dryer E-103. The dried pure HDC is then transported to the HDI section.

[0031] The solvent to be separated in intermediate tank T-103 enters methanol distillation column C-101 via P-103. The light component methanol is discharged from the top of the column, cooled by the top condenser E-106, and enters the top reflux tank T-104. After being transported by the top reflux pump P-106, it is divided into two streams: one stream is returned to methanol distillation column C-101, and the other stream is cooled by the methanol recovery condenser E-104 and then sent to methanol storage tank T-204. Meanwhile, the heavy component mixture of DMC, HMC, and methanol is discharged from the bottom of methanol distillation column C-101. It is divided into two streams by the bottom reflux pump P-105: one stream is returned to methanol distillation column C-101 via the bottom reboiler E-105, and the other stream is returned to the material storage tank T-101 for recycling.

[0032] The HDC, fresh solvent, and solvent recycled from the bottom of reactor R-201 output from the first-stage dryer E-103 enter the feed storage tank T-201. The material is then transported to reactor R-201 for pyrolysis. Reactor R-201 is a continuous pyrolysis reactor that rapidly removes methanol and HDI. Vaporized HDI, methanol, a portion of HMI, and trace amounts of solvent and HDC enter the distillation column C-201 from the top steam pipe of the reactor. The remaining solvent, unreacted HDC, and intermediate HMI are recycled from the bottom of the reactor to the feed storage tank T-201 for further reaction.

[0033] Solvent, HDC, and part of HMI are cooled and refluxed from the bottom of the distillation column to reactor R-201 to continue the reaction. Meanwhile, vaporized HDI, HMI, and methanol are discharged from the top of distillation column C-201, cooled by the top HDI and methanol condenser E-206, and enter the HDI and methanol reflux tank T-206. After being transported by the HDI and methanol reflux pump P-205, they are divided into two streams: one stream refluxes back to distillation column C-201, and the other stream is cooled by the HDI and methanol condenser E-201 and enters the HDI and HMI storage tank T-202.

[0034] The methanol, HDI, and HMI in HDI and HMI storage tanks T-202 require further separation. Firstly, vaporized methanol and small amounts of HDI and HMI undergo a two-stage series cooling separation process to separate methanol and light components. The methanol can then be pumped to the methanol tank area via methanol transfer pump P-204. Secondly, crude HDI liquid is transported from the bottom to the HDI refining tower C-202 for separation and purification. The light HDI component is discharged from the top of the tower, cooled by the top condenser E-206, and then enters the top HDI reflux tank T-207. After being conveyed by the HDI refining tower top reflux pump P-206, it is divided into two streams. One stream flows back to the HDI refining tower C-202, and the other stream is cooled by the HDI quench cooler E-204 and then sent to the HDI product tank area by the HDI product transfer pump P-202. Meanwhile, the heavy components in the HDI refining tower C-202 are discharged from the bottom of the tower and conveyed by the HDI refining tower bottom circulation pump P-207. They can be divided into two streams. One stream returns to the HDI refining tower C-202 via the reboiler E-207, and the other stream is the reboiler residue, which is incinerated.

[0035] The process of preparing HDI by pyrolysis of carbamate (HDC) has gradually become a key research focus in the alternative to the traditional phosgene method for isocyanate preparation due to its advantages such as mild reaction conditions, high conversion rate, and environmental friendliness. This process mainly consists of two steps: the first step is the synthesis of carbamate, and the second step is the thermal decomposition of carbamate to generate HDI.

[0036] The first step in HDC synthesis involves dimethyl carbonate (DMC), an important chemical intermediate that is highly reactive, easy to store and transport, low in toxicity, and pollution-free. Its molecular structure contains carbonyl, methyl, and methoxy groups, allowing it to replace highly toxic substances such as phosgene, dimethyl sulfate, and methyl chloroformate in organic synthesis reactions such as carbonylation, methylation, methoxylation, and carbonyl methylation. The preparation of HDC using DMC and 1,6-hexanediamine (HDA) as raw materials has attracted widespread attention, especially with the increasing maturity of DMC preparation processes. Carbonate carbonylation has become the most promising method for HDC synthesis. DMC can undergo a carbonylation reaction to generate the target product, carbamate (HDC), and the intermediate, methyl 1-(6-amino)-hexamethylene monocarbamate (HMC). In this reaction, DMC serves as both a reactant and a solvent.

[0037] The reaction equation is as follows:

[0038] H2N(CH2)6NH2+2CH3OCOOCH3

[0039] →H3COCONH(CH2)6NHCOOCH3+2CH3OH

[0040] The reaction intermediate equation is as follows:

[0041]

[0042]

[0043] The reaction principle is as follows: Under the action of a catalyst, HDA, an amine, acts as a nucleophile to attack the carbonyl C atom in an addition-elimination reaction to obtain the intermediate HMC and the product HDC, while methanol is generated as a byproduct.

[0044] Under optimal process conditions, the HDA conversion rate can reach 100%, and the HDC yield reaches 98.0%. The reaction exhibits extremely high selectivity, virtually no side reactions, and the catalyst demonstrates high stability, maintaining its activity even after prolonged repeated use.

[0045] The second step, HDI synthesis, involves the non-phosgene liquid-phase pyrolysis method, where HDC undergoes thermal decomposition under the action of a catalyst to generate HDI. This reaction is achieved primarily through two steps: HDC loses one molecule of methanol to generate the intermediate hexamethylene monocarbamate monoisocyanate (HMI), and HMI further loses another molecule of methanol to generate HDI. The reaction equation is shown below:

[0046] H3CCOONH(CH2)6NHCOOCH3→OCN(CH2)6NCO+2CH3OH

[0047] The reaction intermediate equation is as follows:

[0048]

[0049] The reaction principle is as follows: HDC undergoes a thermal decomposition reaction in a high-boiling-point solvent, first releasing methanol from one end to generate the intermediate HMI, and then releasing methanol from the other end to generate the final product HDI.

[0050] Under optimal pyrolysis conditions, the conversion rate of HDC reached 100.0%, the yield of HDI reached 90.8%, and the yield of HMI reached 9.2%. The reaction exhibits extremely high selectivity, few basic side reactions, and the catalyst has high stability, while the solvent can be recycled.

[0051] In this invention, dimethyl carbonate and 1,6-hexanediamine are reacted in a fixed-bed reactor packed with a multiphase catalyst to produce HDC. The reactor is equipped with a stirring shaft, on which a frame for loading the catalyst is fixed, and it has an external jacket for heating. The crude HDC reaction solution is purified in three steps—flash evaporation, crystallization filtration, and drying—to obtain pure HDC product. HDC and high-boiling-point solvents are thermally cracked using a continuous pyrolysis distillation reactor to rapidly remove methanol and HDI, driving the reaction in the forward direction. The reaction byproduct methanol is purified through multi-stage condensation to obtain methanol byproduct with a purity of over 99%. The HDI product is separated from the polymer by vacuum distillation in a distillation column.

[0052] In the HDC section, DMC and HAD are reacted in a fixed-bed reactor stirred by a stirrer with a catalyst frame. The reactor is equipped with an external jacket and a steam heat source is provided. The HDC reactor is operated at a slightly positive pressure to promote the reaction in both forward and reverse directions. In the methanol distillation column, methanol and unreacted DMC form an azeotrope, thus ensuring the DMC content in the bottom reflux is maintained, keeping the feed at the optimal reactant ratio. Connecting three reactors in parallel ensures continuous downstream operation, improving operational management convenience and facilitating industrialization.

[0053] In the HDI section, the HDI cracking reactor and distillation column are connected in series for continuous reactive distillation, which significantly reduces the secondary contact time between HDI vapor and methanol vapor. The cracking reactor operates under negative pressure, further promoting the reaction in the forward direction and allowing control of the cracking reaction temperature to prevent high-temperature polymerization of HDI. The HDI distillation column operates under high vacuum and low temperature, reducing the polymerization reaction of polymeric HDI and improving product purity.

[0054] Compared with existing technologies, the advantages of this invention are as follows: This invention uses a continuous pyrolysis reaction device to prepare HDI in a high-boiling-point solvent, which can completely replace the existing phosgene and phosgene derivative methods for HDI preparation, solving the safety and pollution problems of the phosgene method; compared with low-boiling-point solvent processes, this invention can significantly reduce energy consumption in the product separation stage. The energy consumption required for solvent separation using high-boiling-point solvent methods is only 1 / 10 of that required by low-boiling-point solvent processes, making it a green, environmentally friendly, and energy-saving process; this invention uses non-toxic high-boiling-point solvents, ensuring production safety compared to low-boiling-point solvent methods; compared with ordinary high-boiling-point solvents, this invention can avoid multiple contacts between isocyanates and alcohols, further improving the yield of HDI; the process flow of this invention is simple, the operating conditions are mild, and it is a process that can be rapidly industrialized. Attached Figure Description

[0055] Figure 1 This is a flowchart of the HDC synthesis unit in an embodiment of the present invention;

[0056] Figure 2 This is a flowchart illustrating the preparation of HDI units from HDC pyrolysis in an embodiment of the present invention. Detailed Implementation

[0057] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0058] like Figure 1 , 2As shown, the equipment for preparing hexamethylene dicarboxylate via pyrolysis of methyl hexamethylene dicarboxylate intermediate in this embodiment includes an HDC synthesis unit and an HDC pyrolysis unit for preparing HDI. The HDC synthesis unit includes:

[0059] Material storage tank T-101 is used to store raw materials DMC and HDA;

[0060] The reaction vessel R-101, which contains a multiphase catalyst, is connected to the material storage tank T-101 to supply DMC and HDA for reaction.

[0061] Flash evaporator T-102 is connected to reaction vessel R-101 to separate light and heavy components from the reaction liquid;

[0062] Intermediate tank T-103 is connected to the top of flash tank T-102 and is used to receive the portion of the light component DMC that forms an azeotrope with methanol. It is also connected to the bottom of flash tank T-102 and is used to receive the filtrate of HMC after the heavy component product concentrated HDC has been crystallized and filtered by filter S-101.

[0063] Dryer E-103, connected to filter S-101, is used to dry the obtained filter cake coarse HDC;

[0064] The HDC pyrolysis to HDI preparation unit includes:

[0065] The ingredient storage tank T-201 is connected to the output end of the dryer E-103 and is used to store the dried HDC and solvent.

[0066] Reactor R-201 is connected to the feed storage tank T-201 to provide continuous pyrolysis reaction of materials and to rapidly remove methanol and HDI produced by the reaction; the bottom of reactor R-201 has a pipe for unreacted materials to flow back to the feed storage tank T-201.

[0067] Distillation column C-201 is connected to reactor R-201 and is used to input the vapor HDI, methanol, part of HMI and trace amounts of solvent and HDC generated in reactor R-201 for distillation separation of materials; the bottom of distillation column C-201 has a pipe for the solvent, HDC and part of HMI to be cooled and refluxed back into reactor R-201.

[0068] Storage tank T-202 is connected to the top of distillation column C-201;

[0069] HDI purification tower C-202 is connected to the bottom of storage tank T-202 to supply crude HDI liquid for separation and purification of materials.

[0070] The HDC synthesis unit also includes a methanol distillation column C-101, connected to the intermediate tank T-103, for receiving the solvent to be separated in the intermediate tank T-103. The top of the column is connected to the top reflux tank T-104 via a top condenser E-106, and further connected to the inner cavity of the methanol distillation column C-101 via a top reflux pump P-106. Downstream of the top reflux pump P-106 is connected to the methanol storage tank T-204 via a recoverable methanol condenser E-104. The bottom of the methanol distillation column C-101 is connected to both the methanol distillation column C-101 and the material storage tank T-101 via a reflux pump P-105.

[0071] The top of distillation column C-201 is connected to reflux tank T-206 via condenser E-206. Reflux tank T-206 is connected to distillation column C-201 and storage tank T-202 via reflux pump P-205.

[0072] In this embodiment, the method for preparing hexamethylene dicarboxylate via pyrolysis of the methyl hexamethylene dicarboxylate intermediate includes the following steps:

[0073] Fresh DMC and HDA, along with DMC recovered from methanol distillation column C-101, enter material storage tank T-101. After being preheated by preheater E-107, they enter reaction tank R-101 to react in a multiphase catalyst.

[0074] The reaction liquid enters the flash tank T-102 through pressure difference. The light component DMC and methanol form an azeotrope and are partially evaporated, entering the intermediate tank T-103 through the condenser E-101. The heavy component product, concentrated HDC, is filtered through the crystallization filter S-101, and the filtrate containing HMC is transported to the intermediate tank T-103. The filter cake coarse HDC is further purified by steam drying in the HDC dryer E-103. The dried pure HDC is then transported to the HDI section.

[0075] The solvent to be separated in intermediate tank T-103 enters methanol distillation column C-101 via P-103. The light component methanol is discharged from the top of the column, cooled by the top condenser E-106, and enters the top reflux tank T-104. After being transported by the top reflux pump P-106, it is divided into two streams: one stream is returned to methanol distillation column C-101, and the other stream is cooled by the methanol recovery condenser E-104 and then sent to methanol storage tank T-204. Meanwhile, the heavy component mixture of DMC, HMC, and methanol is discharged from the bottom of methanol distillation column C-101. It is divided into two streams by the bottom reflux pump P-105: one stream is returned to methanol distillation column C-101 via the bottom reboiler E-105, and the other stream is returned to the material storage tank T-101 for recycling.

[0076] The HDC, fresh solvent, and solvent recycled from the bottom of reactor R-201 output from the first-stage dryer E-103 enter the feed storage tank T-201. The material is then transported to reactor R-201 for pyrolysis. Reactor R-201 is a continuous pyrolysis reactor that rapidly removes methanol and HDI. Vaporized HDI, methanol, a portion of HMI, and trace amounts of solvent and HDC enter the distillation column C-201 from the top steam pipe of the reactor. The remaining solvent, unreacted HDC, and intermediate HMI are recycled from the bottom of the reactor to the feed storage tank T-201 for further reaction.

[0077] Solvent, HDC, and part of HMI are cooled and refluxed from the bottom of the distillation column to reactor R-201 to continue the reaction. Meanwhile, vaporized HDI, HMI, and methanol are discharged from the top of distillation column C-201, cooled by the top HDI and methanol condenser E-206, and enter the HDI and methanol reflux tank T-206. After being transported by the HDI and methanol reflux pump P-205, they are divided into two streams: one stream refluxes back to distillation column C-201, and the other stream is cooled by the HDI and methanol condenser E-201 and enters the HDI and HMI storage tank T-202.

[0078] The methanol, HDI, and HMI in HDI and HMI storage tanks T-202 require further separation. Firstly, vaporized methanol and small amounts of HDI and HMI undergo a two-stage series cooling separation process to separate methanol and light components. The methanol can then be pumped to the methanol tank area via methanol transfer pump P-204. Secondly, crude HDI liquid is transported from the bottom to the HDI refining tower C-202 for separation and purification. The light HDI component is discharged from the top of the tower, cooled by the top condenser E-206, and then enters the top HDI reflux tank T-207. After being conveyed by the HDI refining tower top reflux pump P-206, it is divided into two streams. One stream flows back to the HDI refining tower C-202, and the other stream is cooled by the HDI quench cooler E-204 and then sent to the HDI product tank area by the HDI product transfer pump P-202. Meanwhile, the heavy components in the HDI refining tower C-202 are discharged from the bottom of the tower and conveyed by the HDI refining tower bottom circulation pump P-207. They can be divided into two streams. One stream returns to the HDI refining tower C-202 via the reboiler E-207, and the other stream is the reboiler residue, which is incinerated.

[0079] The following is a detailed implementation example to illustrate the solution of the present invention:

[0080] Fresh DMC (189 kg / h) and HDA (122 kg / h) mixed with DMC and methanol recovered from methanol distillation column C-101 are fed into material storage tank T-101, and the molar ratio of DMC to HDA ​​is controlled at 4:1. Then, the mixture is transported to preheater E-107 by material transfer pump P-101 and then fed into reaction tank R-101. The multiphase catalyst loading is 7% of the mass of HDA. The reaction temperature is maintained at <100℃, the pressure is 0.1~0.3MPaa, and the reaction time is 5~7h.

[0081] The reaction liquid (656 kg / h) enters the flash tank T-102 (temperature 88℃, pressure 0.1 MPaa) through pressure differential. The light component DMC and methanol form an azeotrope, which is partially distilled off and cooled to 25℃ by the condenser E-101 before entering the intermediate tank T-103. The heavy component product, concentrated HDC, is transported to the HDC filter S-101 for crystallization filtration by the slurry pump P-102. The azeotrope containing DMC and methanol is transported to the intermediate tank T-103 (temperature 29℃, pressure 0.1 MPaa). The filter cake coarse HDC is transported to the HDC dryer E-103 for further drying and purification by the HDC transfer pump P-104. The vapor generated during the drying process is cooled by the condenser E-102 and then enters the intermediate tank T-103 (temperature 29℃, pressure 0.1 MPaa). The dried pure HDC is then transported to the second stage via the HDC transfer pump.

[0082] The solvent to be separated in intermediate tank T-103 enters methanol distillation column C-101 (top temperature 64℃, bottom temperature 77℃, operating pressure 0.1MPaa) via methanol solution transfer pump P-103. The light methanol component is discharged from the top of the column, cooled by the top condenser E-106, and enters the top reflux tank T-104 (temperature 64℃). After being pumped by the top reflux pump P-106, it is divided into two streams: one stream returns to methanol distillation column C-101, and the other stream passes through the methanol recovery condenser. After cooling, E-104 (67.1 kg / h, temperature 25℃, pressure 0.1 MPaa) goes to methanol storage tank T-204; while the heavy components DMC, HMC and methanol mixture at the bottom of methanol distillation column C-101 are discharged from the bottom of the column and divided into two streams by bottom reflux pump P-105. One stream returns to methanol distillation column C-101 via bottom reboiler E-105, and the other stream (1275.2 kg / h, temperature 65℃) returns to material storage tank T-101 for recycling.

[0083] HDC (243 kg / h) from the first-stage dryer and high-boiling-point solvent, pumped back from the bottom of reactor R-201 (temperature 255°C, pressure evacuated) by a transfer pump, enter the feed storage tank T-201 (temperature 25°C, pressure 0.1 MPaa). The HDC mass fraction is controlled at 10%. Using pressure differential, the material is transported to reactor R-201 for pyrolysis. The reactor is characterized by a continuous pyrolysis reaction device, rapidly removing methanol and HDI to drive the reaction in the forward direction and prevent HDI from remaining in the high-temperature reaction system for extended periods, which could lead to polymerization. In reactor R-201, the heterogeneous catalyst is packed at 5% of the HDC mass. Vaporized HDI, methanol, some HMI, and high-boiling-point solvent, along with HDC, enter the distillation column C-201 from the top steam pipe of the reactor. The liquid solvent, unreacted HDC, and intermediate HMI are circulated from the bottom of the reactor to the feed storage tank T-201 for continued reaction.

[0084] After separation, the vapor entering distillation column C-201 is cooled and refluxed from the bottom of the column (1410 kg / h, temperature 255℃) to reactor R-201 for further reaction. Meanwhile, the vapors of HDI, HMI, and methanol are discharged from the top of distillation column C-201, cooled by the top HDI and methanol condenser E-205, and enter the HDI and methanol reflux tank T-206. After being transported by the HDI and methanol reflux pump P-205, it is divided into two streams. One stream refluxes back to distillation column C-201 (top temperature 140℃, bottom temperature 250℃, pressure is vacuum), and the other stream is cooled by the HDI and methanol condenser E-201 (243 kg / h, temperature 60℃) and enters the HDI and HMI storage tank T-202 (temperature 60℃).

[0085] Methanol, HDI, and HMI in HDI and HMI storage tank T-202 require further separation. Firstly, vaporized methanol and a small amount of HDI and HMI are cooled by HDI and methanol condenser E-202. The condensed HDI and HMI enter HDI and methanol storage tank T-203 (temperature 30℃), and are then pumped back to HDI and HMI storage tank T-202 by HDI transfer pump P-203. Methanol vapor, on the other hand, is discharged from the top of HDI and methanol storage tank T-203, cooled by methanol condenser E-203, and enters methanol storage tank T-204 (temperature -10℃). Methanol can then be delivered to the methanol tank area via methanol transfer pump P-204. Secondly, the crude HDI liquid in the HDI and HMI storage tank T-202 is transported from the bottom to the HDI refining tower C-202 (bottom temperature 130℃, top temperature 100℃, pressure ultra-vacuum) for separation and purification. The light HDI component is discharged from the top of the tower, cooled by the top condenser E-206, and enters the top HDI reflux tank T-207. After being transported by the HDI refining tower top reflux pump P-206, it is divided into two streams, one of which flows back to the HDI refining tower C-202. One stream, cooled by the HDI quencher E-204, enters the HDI storage tank T-205 (161 kg / h, temperature 8℃). The HDI product can be sent to the HDI product tank area by the HDI product transfer pump P-202. Meanwhile, the heavy components of the HDI refining tower C-202 are discharged from the bottom of the tower and, after being transported by the HDI refining tower reboiler circulation pump P-207, can be divided into two streams. One stream returns to the HDI refining tower C-202 via the reboiler E-207, and the other stream is the reboiler residue, which is incinerated.

Claims

1. An apparatus for preparing hexamethylene diisocyanate via pyrolysis of a methyl hexamethylene dicarboxylate intermediate, characterized in that: The system includes an HDC synthesis unit and an HDC pyrolysis unit for preparing HDI, wherein the HDC synthesis unit includes: Material storage tank T-101 is used to store raw materials DMC and HDA; The reaction vessel R-101, which contains a multiphase catalyst, is connected to the material storage tank T-101 to supply DMC and HDA for reaction. Flash evaporator T-102 is connected to reaction vessel R-101 to separate light and heavy components from the reaction liquid; Intermediate tank T-103 is connected to the top of flash tank T-102 and is used to receive the portion of the light component DMC that forms an azeotrope with methanol. It is also connected to the bottom of flash tank T-102 and is used to receive the filtrate of HMC after the heavy component product concentrated HDC has been crystallized and filtered by filter S-101. Dryer E-103, connected to filter S-101, is used to dry the obtained filter cake coarse HDC; The HDC pyrolysis to HDI preparation unit includes: The ingredient storage tank T-201 is connected to the output end of the dryer E-103 and is used to store the dried HDC and solvent. Reactor R-201 is connected to the feed storage tank T-201 to provide continuous pyrolysis reaction of materials and to rapidly remove methanol and HDI produced by the reaction; the bottom of reactor R-201 has a pipe for unreacted materials to flow back to the feed storage tank T-201. Distillation column C-201 is connected to reactor R-201 and is used to input the vapor HDI, methanol, part of HMI and trace amounts of solvent and HDC generated in reactor R-201 for distillation separation of materials; the bottom of distillation column C-201 has a pipe for the solvent, HDC and part of HMI to be cooled and refluxed back into reactor R-201. Storage tank T-202 is connected to the top of distillation column C-201; HDI purification tower C-202 is connected to the bottom of storage tank T-202 to supply crude HDI liquid for separation and purification of materials.

2. The apparatus for preparing hexamethylene diisocyanate by pyrolysis of methyl hexamethylene dicarboxylate intermediate according to claim 1, characterized in that: It also includes a methanol distillation column C-101, which is connected to the intermediate tank T-103 to receive the solvent to be separated in the intermediate tank T-103. The top of the column is connected to the top reflux tank T-104 through the top condenser E-106, and further connected to the inner cavity of the methanol distillation column C-101 through the top reflux pump P-106.

3. The apparatus for preparing hexamethylene diisocyanate by pyrolysis of methyl hexamethylene dicarboxylate intermediate according to claim 2, characterized in that: The downstream of the top reflux pump P-106 is connected to the methanol storage tank T-204 via the methanol recovery condenser E-104.

4. The apparatus for preparing hexamethylene diisocyanate by pyrolysis of methyl hexamethylene dicarboxylate intermediate according to claim 2, characterized in that: The bottom of the methanol distillation column C-101 is connected to the methanol distillation column C-101 and the material storage tank T-101 via a reflux pump P-105.

5. The apparatus for preparing hexamethylene dicarboxylate via pyrolysis of a methyl hexamethylene dicarboxylate intermediate according to claim 1, 2, 3, or 4, characterized in that: The top of the distillation column C-201 is connected to the reflux tank T-206 via the condenser E-206. The reflux tank T-206 is connected to the distillation column C-201 and the storage tank T-202 via the reflux pump P-205.

6. A method for preparing hexamethylene diisocyanate via pyrolysis of a methyl hexamethylene dicarboxylate intermediate, characterized in that, The apparatus for preparing hexamethylene diisocyanate by pyrolysis of methyl hexamethylene dicarboxylate intermediate according to any one of claims 1 to 5 includes the following steps: Fresh DMC and HDA, along with DMC recovered from methanol distillation column C-101, enter material storage tank T-101. After being preheated by preheater E-107, they enter reaction tank R-101 to react in a multiphase catalyst. The reaction liquid enters the flash tank T-102 through pressure difference. The light component DMC and methanol form an azeotrope and are partially evaporated, entering the intermediate tank T-103 through the condenser E-101. The heavy component product, concentrated HDC, is filtered through the crystallization filter S-101, and the filtrate containing HMC is transported to the intermediate tank T-103. The filter cake coarse HDC is further purified by steam drying in the HDC dryer E-103. The dried pure HDC is then transported to the HDI section. The solvent to be separated in intermediate tank T-103 enters methanol distillation column C-101 via P-103. The light component methanol is discharged from the top of the column, cooled by the top condenser E-106, and enters the top reflux tank T-104. After being transported by the top reflux pump P-106, it is divided into two streams: one stream is returned to methanol distillation column C-101, and the other stream is cooled by the methanol recovery condenser E-104 and then sent to methanol storage tank T-204. Meanwhile, the heavy component mixture of DMC, HMC, and methanol is discharged from the bottom of methanol distillation column C-101. It is divided into two streams by the bottom reflux pump P-105: one stream is returned to methanol distillation column C-101 via the bottom reboiler E-105, and the other stream is returned to the material storage tank T-101 for recycling. The HDC, fresh solvent, and solvent recycled from the bottom of reactor R-201 output from the first-stage dryer E-103 enter the feed storage tank T-201. The material is then transported to reactor R-201 for pyrolysis. Reactor R-201 is a continuous pyrolysis reactor that rapidly removes methanol and HDI. Vaporized HDI, methanol, a portion of HMI, and trace amounts of solvent and HDC enter the distillation column C-201 from the top steam pipe of the reactor. The remaining solvent, unreacted HDC, and intermediate HMI are recycled from the bottom of the reactor to the feed storage tank T-201 for further reaction. Solvent, HDC, and part of HMI are cooled and refluxed from the bottom of the distillation column to reactor R-201 to continue the reaction. Meanwhile, vaporized HDI, HMI, and methanol are discharged from the top of distillation column C-201, cooled by the top HDI and methanol condenser E-206, and enter the HDI and methanol reflux tank T-206. After being transported by the HDI and methanol reflux pump P-205, they are divided into two streams: one stream refluxes back to distillation column C-201, and the other stream is cooled by the HDI and methanol condenser E-201 and enters the HDI and HMI storage tank T-202. The methanol, HDI, and HMI in HDI and HMI storage tanks T-202 require further separation. Firstly, vaporized methanol and small amounts of HDI and HMI undergo a two-stage series cooling separation process to separate methanol and light components. The methanol can then be pumped to the methanol tank area via methanol transfer pump P-204. Secondly, crude HDI liquid is transported from the bottom to the HDI refining tower C-202 for separation and purification. The light HDI component is discharged from the top of the tower, cooled by the top condenser E-206, and then enters the top HDI reflux tank T-207. After being conveyed by the HDI refining tower top reflux pump P-206, it is divided into two streams. One stream flows back to the HDI refining tower C-202, and the other stream is cooled by the HDI quench cooler E-204 and then sent to the HDI product tank area by the HDI product transfer pump P-202. Meanwhile, the heavy components in the HDI refining tower C-202 are discharged from the bottom of the tower and conveyed by the HDI refining tower bottom circulation pump P-207. They can be divided into two streams. One stream returns to the HDI refining tower C-202 via the reboiler E-207, and the other stream is the reboiler residue, which is incinerated.

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