Method for synthesizing n-butyl isocyanate by gas-phase salifying

Abstract

The invention provides a method for synthesizing n-butyl isocyanate by gas-phase salifying, which comprises the following steps of: mixing n-butylamine vaporized gas and hydrogen chloride gas, and performing salifying reaction on the n-butylamine vaporized gas and the hydrogen chloride gas to obtain a salifying product n-butylamine hydrochloride; mixing the obtained n-butylamine hydrochloride with a solvent to obtain a reaction suspension; mixing the reaction suspension with phosgene to obtain a reaction material, introducing the reaction material into a reactor, and sequentially carrying out reactions in a first reaction stage, a second reaction stage and a third reaction stage through temperature control to obtain a reaction mixed material; and separating impurities in the reaction mixture obtained by the phosgenation reaction to obtain the n-butyl isocyanate. By utilizing the method provided by the invention, the generation of byproducts in the preparation process of the n-butyl isocyanate can be effectively reduced, so that the reaction efficiency and the yield of the n-butyl isocyanate can be further improved. The method effectively solves the problems of low synthesis efficiency, more byproducts and high energy consumption in the synthesis process of the n-butyl isocyanate.

Description

Technical Field

[0001] This invention relates to the field of organic synthesis technology, and more specifically, to a method for gas-phase salt formation to synthesize n-butyl isocyanate. Background Technology

[0002] Benzocarb, a highly effective, broad-spectrum, systemic fungicide, plays a vital role in modern agriculture. It not only protects crops from diseases but also eradicates existing pathogens and treats crop diseases, making it the preferred agent for crop spraying, seed treatment, and soil conditioning in the agricultural industry. Benzocarb is particularly effective in controlling diseases in vegetables, fruit trees, and oilseed crops.

[0003] In the synthetic pathway of benomyl, n-butyl isocyanate (FNC) serves as a key intermediate, but its applications extend far beyond benomyl. FNC is also widely used in the pharmaceutical and pesticide industries. Thanks to the high reactivity of its isocyanate groups (-N=C=O), it can react with various compounds to introduce structural units such as urethanes, making it a powerful tool for constructing complex organic molecules. Furthermore, as an important raw material for polyurethane synthesis, FNC reacts with polyols or hydroxyl-containing compounds to form polyurethane materials with excellent physical properties, such as enhanced hardness, elasticity, and weather resistance. In the fine chemical industry, FNC is also used as a catalyst in the synthesis of sulfonylurea herbicides, in resin manufacturing, and as a softener and additive in textiles, broadening its application scope.

[0004] However, existing FNC synthesis methods have certain limitations. Industrial-scale FNC production mainly relies on batch synthesis methods, the most common being the one-step batch reaction of n-butylamine with phosgene and the low-temperature salt formation followed by high-temperature phosgenation. While these methods meet production needs to some extent, they have significant drawbacks and limitations. For example, the residues of n-butylamine and n-butylchloroamide in the reaction system inevitably lead to the formation of byproducts chlorobutane and 1,3-dibutylurea, reducing the purity and yield of FNC.

[0005] Existing attempts at continuous FNC preparation, such as the continuous tubular salt formation and reactive distillation method proposed in patent CN115677538A, while attempting to optimize the production process, have failed to fundamentally solve the problem due to the separation of the low-temperature salt formation and high-temperature reaction synthesis, which increases solvent consumption and energy usage. The circulating reactor FNC preparation technology in patent CN101735110B, employing a gas-liquid phase injection reaction, improves reaction uniformity but also faces the problems of high solvent consumption and increased byproduct formation due to n-butylamine residue, thus limiting the reaction yield.

[0006] In summary, existing FNC synthesis methods still need improvement in terms of efficiency, energy consumption, and byproduct control, especially for large-scale continuous FNC production. Therefore, developing a novel FNC synthesis process that can improve reaction efficiency and yield while reducing byproduct formation and energy consumption to meet the high standards of modern industrial production has become an urgent problem to be solved. Summary of the Invention

[0007] The main objective of this invention is to provide a method for the gas-phase salt formation synthesis of n-butyl isocyanate, in order to solve the problems of low synthesis efficiency, high energy consumption, and numerous by-products in the existing n-butyl isocyanate synthesis process. The aim is to develop a novel FNC synthesis process that can improve reaction efficiency and yield, reduce by-product formation, and lower energy consumption, so as to meet the high standards required by modern industrial production and promote the wider application of FNC in the fields of pharmaceuticals, pesticides, and fine chemicals.

[0008] This application provides a method for gas-phase salt formation synthesis of n-butyl isocyanate, the method comprising the following steps: mixing n-butylamine vapor gas and hydrogen chloride gas to carry out a salt formation reaction to obtain a salt formation reaction product; mixing the salt formation reaction product with a solvent to obtain a reaction suspension; mixing the reaction suspension with phosgene to obtain a mixed raw material; passing the mixed raw material into a reactor to carry out a phosgenation reaction to obtain a reaction mixture; wherein the phosgenation reaction includes a first reaction stage, a second reaction stage, and a third reaction stage carried out sequentially, and the reaction temperature of the second reaction stage is not lower than the reaction temperature of the first reaction stage, and the reaction temperature of the third reaction stage is not lower than the reaction temperature of the second reaction stage; removing phosgene from the reaction mixture to obtain a crude n-butyl isocyanate solution; separating the crude n-butyl isocyanate solution to obtain a crude n-butyl isocyanate and a crude solvent solution.

[0009] Further, the reaction temperature of the first reaction stage is 90–100°C, the reaction temperature of the second reaction stage is 100–110°C, and the reaction temperature of the third reaction stage is 110–130°C; preferably, the reaction temperature of the first reaction stage is 92–100°C, the reaction temperature of the second reaction stage is 100–110°C, and the reaction temperature of the third reaction stage is 110–125°C; preferably, the reaction pressure of the first, second, and third reaction stages is 0.11–0.40 MPa, and the reaction pressures of the first, second, and third reaction stages are independent of each other.

[0010] Further, the reaction time of the first reaction stage is ≥0.5h, the reaction time of the second reaction stage is ≥1.5h, and the reaction time of the third reaction stage is ≥2h; preferably, the reaction time of the first reaction stage is 0.5-5h, the reaction time of the second reaction stage is 1.5-5h, and the reaction time of the third reaction stage is 2-6h; preferably, the weight content of the salt-forming reaction product in the reaction suspension is 4-15%; more preferably, the weight content of the salt-forming reaction product in the reaction suspension is 5-8%; preferably, the molar ratio of n-butylamine vapor gas to hydrogen chloride gas is (1.02-1.8):1; preferably, the reaction pressure of the salt-forming reaction is 0.1-2MPa, and the reaction time is 0.5-3.5h.

[0011] Further, the molar ratio of n-butylamine vaporized gas to phosgene is 1:(1.1-3); preferably, the molar ratio of n-butylamine vaporized gas to phosgene is 1:(1.15-2.8); preferably, the temperature of the mixture after mixing the reaction suspension and phosgene is 70-130°C.

[0012] Furthermore, the method for preparing n-butylamine vaporized gas includes the following steps: dripping liquid n-butylamine into a high-temperature solvent, and obtaining n-butylamine vaporized gas after vaporization; the temperature of the high-temperature solvent is 90-130°C; preferably, the temperature of the high-temperature solvent is 90-110°C; preferably, at least a portion of the high-temperature solvent is obtained by decoking the crude solvent product.

[0013] Further, the salt formation reaction is carried out in a gas-phase salt formation tower; preferably, the gas-phase salt formation tower is at least one of a hollow gas-phase salt formation tower, a plate-type gas-phase salt formation tower, or a packed gas-phase salt formation tower; more preferably, the gas-phase salt formation tower is a hollow gas-phase salt formation tower or a packed gas-phase salt formation tower; preferably, the gas-phase salt formation tower is provided with an overflow port for collecting the reaction suspension; preferably, the overflow port is inclined downwards; more preferably, the inclination angle of the overflow port is 25-75°; preferably, the preparation of n-butylamine vaporization gas is carried out in the gas-phase salt formation tower; Preferably, the high-temperature solvent is placed in the gas-phase salt formation tower, and a first distributor is provided above the high-temperature solvent in the gas-phase salt formation tower for introducing hydrogen chloride gas into the gas-phase salt formation tower to mix with the n-butylamine vaporized gas; preferably, the first distributor is at least one of a perforated tube distributor, a trough distributor, or a disc distributor; more preferably, the first distributor is a perforated tube distributor; preferably, the solvent is an organic solvent with a boiling point >155°C; more preferably, the solvent is selected from one or more of o-dichlorobenzene, m-dichlorobenzene, and p-dichlorobenzene.

[0014] Furthermore, the gas phase salt formation tower is provided with a second distributor, which is located in the middle and lower part of the gas phase salt formation tower and is immersed in a high-temperature solvent for dripping liquid n-butylamine into the high-temperature solvent; preferably, the second distributor is at least one of a perforated tube distributor, a trough distributor or a disc distributor; more preferably, the distributor is a perforated tube distributor.

[0015] Further, the separation process includes: pre-separating the crude n-butyl isocyanate solution in a solvent recovery tower to obtain a crude solvent solution and a primary n-butyl isocyanate solution; purifying the primary n-butyl isocyanate solution to obtain n-butyl isocyanate; purifying the crude solvent solution to obtain a high-temperature solvent; preferably, the solvent recovery tower is a first plate distillation tower; preferably, the first plate distillation tower has 25 to 40 plates; preferably, the crude n-butyl isocyanate solution is added from the 8th to 15th plates of the first plate distillation tower; preferably, the bottom temperature of the first plate distillation tower is 100 to 125°C, and the pressure is 20 to 55 kPa; preferably, the reactor is selected from at least one of a plug flow reactor or a series reactor; more preferably, the reactor is selected from a plug flow reactor; preferably, the plug flow reactor is selected from at least one of a U-tube reactor, a tubular reactor, or a combination of a U-tube reactor and a tubular reactor; more preferably, the plug flow reactor is selected from a U-tube reactor.

[0016] Furthermore, the crude solvent solution is purified in the second distillation column; preferably, the second distillation column is a second plate distillation column; preferably, the number of plates in the second plate distillation column is 15 to 25; preferably, the crude solvent solution is added from the 10th to 18th plates of the second plate distillation column; preferably, the bottom temperature of the second plate distillation column is 90 to 130°C and the pressure is 20 to 85 kPa.

[0017] Further, phosgene in the reaction mixture is removed in a phosgene removal tower; preferably, nitrogen gas is continuously introduced into the phosgene removal tower to remove phosgene from the reaction mixture; preferably, the nitrogen gas flow rate is 20–60 Nm³. 3 / h; preferably, the light-removing tower is a circulating light-removing tower; preferably, the temperature of the bottom of the light-removing tower is 60-120℃.

[0018] This invention provides a method for the gas-phase salt formation synthesis of n-butyl isocyanate. The method involves first mixing n-butylamine vaporized gas and hydrogen chloride gas to induce a salt formation reaction, yielding n-butylamine hydrochloride. The obtained n-butylamine hydrochloride is then mixed with a solvent to obtain a reaction suspension. This reaction suspension is then mixed with phosgene, and the resulting reaction mixture is introduced into a reactor for sequential reaction in three stages to obtain a reaction mixture. After separating impurities from the reaction mixture obtained from the phosgene reaction, n-butyl isocyanate is obtained. This gas-phase salt formation method for synthesizing n-butyl isocyanate effectively reduces the generation of byproducts during the n-butyl isocyanate preparation process, thereby further improving the reaction efficiency and yield of n-butyl isocyanate. This method effectively solves the problems of low synthesis efficiency, high energy consumption, and numerous byproducts in the n-butyl isocyanate synthesis process. Attached Figure Description

[0019] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0020] Figure 1 A schematic diagram of the apparatus and process for preparing n-butyl isocyanate according to the present invention is shown.

[0021] The above-mentioned figures include the following reference numerals: 1. Gas-phase salt formation tower; 2. Stirred mixer; 3. Feed pump; 4. Condenser; 5. U-tube reactor; 6. Light-removing tower; 7. Solvent recovery tower; 8. Solvent refining tower; 9. Stirrer. Detailed Implementation

[0022] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0023] As described in the background section, existing FNC synthesis methods still need improvement in terms of efficiency, energy consumption, and by-product control, especially for large-scale continuous FNC production. Therefore, developing a novel FNC synthesis process that can improve reaction efficiency and yield while reducing by-product formation and energy consumption to meet the high standards of modern industrial production has become an urgent problem to be solved.

[0024] To address the aforementioned problems, this application provides a method for the gas-phase salt formation synthesis of n-butyl isocyanate. This method includes the following steps: mixing n-butylamine vaporized gas and hydrogen chloride gas to conduct a salt formation reaction, obtaining a salt formation reaction product; mixing the salt formation reaction product with a solvent to obtain a reaction suspension; mixing the reaction suspension with phosgene to obtain a mixed raw material; passing the mixed raw material into a reactor for a phosgenation reaction to obtain a reaction mixture; wherein the phosgenation reaction includes a first reaction stage, a second reaction stage, and a third reaction stage performed sequentially, with the reaction temperature of the second reaction stage not lower than the reaction temperature of the first reaction stage, and the reaction temperature of the third reaction stage not lower than the reaction temperature of the second reaction stage; removing phosgene from the reaction mixture to obtain a crude n-butyl isocyanate solution; separating the crude n-butyl isocyanate solution to obtain a crude solvent solution and n-butyl isocyanate. The equations for the above synthesis process are shown below:

[0025]

[0026] In the above synthesis method, n-butylamine vaporized gas and hydrogen chloride gas are first mixed to carry out a salt formation reaction, yielding the salt product—n-butylamine hydrochloride. The obtained n-butylamine hydrochloride is then mixed with a solvent to obtain a reaction suspension. The reaction suspension is then mixed with phosgene, and the resulting reaction mixture is introduced into a reactor to sequentially carry out the first, second, and third reaction stages. After removing phosgene, solvent, and impurities from the reaction mixture obtained from the phosgenation reaction, n-butyl isocyanate is obtained. The preparation method provided in this application can effectively reduce the generation of by-products in the preparation of n-butyl isocyanate, improve the reaction efficiency and yield of n-butyl isocyanate, and further reduce energy consumption in the preparation process. This solves the problems of low synthesis efficiency, numerous by-products, and high energy consumption in the prior art of n-butyl isocyanate synthesis.

[0027] First, this application employs a gas-phase method to prepare n-butylamine hydrochloride during the synthesis of n-butyl isocyanate. Compared to traditional liquid-phase salt formation methods, the gas-phase method used in this application effectively improves the efficiency of the salt formation reaction. This is because, under gas-phase conditions, n-butylamine gas and hydrogen chloride gas can be rapidly and uniformly mixed, greatly accelerating the salt formation reaction rate. This shortens the salt formation reaction time and further reduces the amount of hydrogen chloride gas used. Furthermore, this immediate gas-phase contact avoids reaction delays caused by uneven material dispersion, making the entire salt formation process more efficient. It also ensures a continuous supply of raw materials and continuous product output, avoiding the repeated filling and unloading steps required in traditional batch reactions. This facilitates automated control, is more conducive to continuous production processes, and better enhances production scale and flexibility.

[0028] Secondly, this application employs a segmented temperature-controlled reaction method in the phosgenation process. The temperature control in the phosgenation process comprises three stages. This segmented temperature control effectively improves the efficiency and yield of the phosgenation reaction. The reasons for this are as follows: The first stage involves the reaction of n-butylamine hydrochloride with phosgene to form an intermediate transition product. During this stage, the ionic charge in n-butylamine hydrochloride directs the reaction, allowing it to be completed at a relatively low temperature. The second stage is a deacidification reaction. During this stage, hydrogen chloride molecules need to be further removed from the intermediate transition product to form an amide transition compound. Therefore, a higher reaction temperature than the first stage is required to complete this stage. The third stage is the isocyanate formation reaction. During this stage, the resulting amide transition compound needs to further remove one molecule of hydrogen chloride to form an isocyanate group. Therefore, a higher reaction temperature than the second and third stages is required to successfully complete this stage and ultimately obtain n-butyl isocyanate. Specifically, the reaction mechanism can be represented as follows:

[0029] Phase 1:

[0030] Phase Two:

[0031] Phase Three:

[0032] This application ingeniously combines the mechanism of phosgenation reaction by segmenting and controlling the reaction temperature of the phosgenation reaction. The reaction temperature of the second stage is not lower than that of the first stage, and the reaction temperature of the third stage is not lower than that of the second stage. These conditions ensure the smooth progress of each reaction stage while reducing the formation of by-products. Conversely, if the reaction temperature of the first stage is too high, it will lead to coking of the raw materials, resulting in a low reaction yield; while if the reaction temperature of the third stage is too low, the formation of isocyanate groups will be slow, leading to the formation of side reactions. Therefore, the above-mentioned control of the reaction temperature at each stage enables a more efficient and precise synthesis of the target product, n-butyl isocyanate.

[0033] In addition, the segmented temperature control described above can effectively improve reaction efficiency while further increasing the yield of n-butyl isocyanate, enhancing the safety and economy of the production process. Compared with traditional single-stage reactions, segmented reactions exhibit several technical advantages, including: First, by precisely controlling the reaction temperature, segmented reactions can effectively adjust the selectivity of each reaction stage, reduce the formation of by-products, promote specific reaction pathways, maximize the yield of the target product n-butyl isocyanate (FNC), and suppress side reactions, thereby improving reaction efficiency. Second, segmented reactions allow each stage to proceed under optimal conditions, ensuring the full conversion of raw materials while accelerating the reaction rate, shortening the total reaction time, and improving overall reaction efficiency. Furthermore, segmented temperature control can ensure the efficiency of each stage while using the most suitable and economical heat source, reducing the overall energy consumption of the preparation process. Third, phosgene is a highly toxic gas; segmented reactions can control the phosgene concentration and contact time at each stage, reducing the risk of phosgene accumulation and accidental leakage, thus improving the safety of the entire process. Segmented reactions allow for precise monitoring and control of product formation at each stage, contributing to improved purity and quality of the final product. By minimizing side reactions, the resulting FNC exhibits higher purity and fewer impurities, meeting the requirements of high-end application markets. Segmented reaction designs are particularly suitable for continuous production models, where each reaction segment can be operated and optimized independently, forming a smooth production chain. This is a significant advantage for large-scale industrial production, enabling stable, continuous, and high-yield product output.

[0034] In summary, the method for preparing n-butyl isocyanate provided in this application involves first mixing n-butylamine vaporized gas and hydrogen chloride gas to induce a salt formation reaction, yielding n-butylamine hydrochloride as the salt product. The obtained n-butylamine hydrochloride is then mixed with a solvent to obtain a reaction suspension. The reaction suspension is then mixed with phosgene, and the resulting reaction mixture is introduced into a reactor to sequentially undergo the first, second, and third reaction stages. After removing phosgene, solvent, and impurities from the reaction mixture obtained from the phosgenation reaction, n-butyl isocyanate is obtained. Using the preparation method provided in this application, the generation of byproducts during the preparation of n-butyl isocyanate can be effectively reduced, thereby further improving the reaction efficiency and yield of n-butyl isocyanate. This method effectively solves the problems of low synthesis efficiency, numerous byproducts, and high energy consumption in the synthesis of n-butyl isocyanate.

[0035] In a preferred embodiment, the reaction temperature of the first reaction stage is 90–100°C, the reaction temperature of the second reaction stage is 100–110°C, and the reaction temperature of the third reaction stage is 110–130°C. As described above, segmented temperature control during the phosgenation reaction enables more efficient and precise synthesis of the n-butyl isocyanate product. Furthermore, the segmented temperature control effectively improves reaction efficiency and further increases the yield of the n-butyl isocyanate product, enhancing the safety and economy of the production process. Controlling the reaction temperatures of the first, second, and third reaction stages within the aforementioned ranges further enhances these effects. Preferably, the reaction temperature of the first reaction stage is 92–100°C, the reaction temperature of the second reaction stage is 100–110°C, and the reaction temperature of the third reaction stage is 110–125°C. Controlling the reaction temperatures of the three reaction stages within the aforementioned preferred ranges further improves the reaction efficiency and yield of the n-butyl isocyanate product. Preferably, the reaction pressures of the first, second, and third reaction stages are 0.11–0.40 MPa, and the reaction pressures of each stage are independent. Controlling the reaction pressures of the first, second, and third reaction stages within the above range improves the phosgenation reaction effect.

[0036] In a preferred embodiment, the reaction time of the first reaction stage is ≥0.5 h, the reaction time of the second reaction stage is ≥1.5 h, and the reaction time of the third reaction stage is ≥2 h. Controlling the reaction times of the three reaction stages within the above-mentioned ranges improves the efficiency of each reaction stage, thereby further increasing the yield of the phosgenation reaction. Preferably, the reaction time of the first reaction stage is 0.5–5 h, the reaction time of the second reaction stage is 1.5–5 h, and the reaction time of the third reaction stage is 2–6 h. Controlling the reaction times of the three reaction stages within the above-mentioned preferred ranges results in better reaction performance. Preferably, the weight content of the salt-forming reaction product in the reaction suspension is 4–15%. Controlling the mass concentration of the salt-forming reaction product in the reaction suspension within the above-mentioned range allows for better reaction between n-butylamine hydrochloride and phosgene, while also preventing the formation of byproducts (such as diurea), thereby further improving reaction efficiency. More preferably, the weight content of the salt-forming reaction product in the reaction suspension is 5–8%. Controlling the mass concentration of the salt-forming reaction product in the reaction suspension within the above-mentioned preferred range results in even better performance. More preferably, the weight content of the salt-forming reaction product in the reaction suspension is 5-7%. Controlling the mass concentration of the salt-forming reaction product in the reaction suspension within the above range allows the phosgenation reaction to proceed better. Preferably, the molar ratio of n-butylamine vapor gas to hydrogen chloride gas is (1.02-1.8):1; preferably, the pressure of the salt-forming reaction is 0.1-2 MPa, and the time is 0.5-3.5 h. Controlling the parameters of the salt-forming reaction within the above range can improve the efficiency of the salt-forming reaction, making the salt-forming reaction more complete, thereby enabling the subsequent phosgenation reaction to proceed better.

[0037] In a preferred embodiment, the molar ratio of n-butylamine vaporized gas to phosgene is 1:(1.1-3). The n-butylamine vaporized gas reacts with hydrogen chloride gas to produce n-butylamine hydrochloride, which then undergoes a further phosgenation reaction with phosgene to produce n-butyl isocyanate. Controlling the molar ratio of n-butylamine vaporized gas to phosgene within the above range allows for better phosgenation. In particular, phosgene is a relatively hazardous reactant; controlling the molar ratio of phosgene ensures complete reaction while minimizing waste, thus further improving the safety of the entire reaction process. Preferably, the molar ratio of n-butylamine vaporized gas to phosgene is 1:(1.15-2.8); controlling the molar ratio within the above range yields even better results.

[0038] Preferably, the temperature of the mixture after mixing the reaction suspension and phosgene is 70–130°C. Controlling the mixing temperature of the reaction suspension and phosgene within this range is beneficial for improving the fluidity of the salt-forming reaction product obtained by mixing the n-butylamine vaporized gas and hydrogen chloride gas in the reaction suspension, thereby facilitating the subsequent phosgenation reaction. Furthermore, the above-mentioned control of the mixing temperature also allows the subsequent reaction to proceed better and more completely. Preferably, the reaction suspension and phosgene are mixed in a mixing vessel to obtain a mixed raw material; more preferably, hydrogen chloride gas is introduced into the mixing vessel to maintain the pressure balance. The above-mentioned operation of introducing hydrogen chloride gas into the mixing vessel helps to prevent the "escape" of the n-butylamine vaporized gas in the system, thereby allowing the subsequent reaction to proceed better.

[0039] In a preferred embodiment, the method for preparing n-butylamine vaporized gas includes the following steps: dripping liquid n-butylamine into a high-temperature solvent, and obtaining n-butylamine vaporized gas after vaporization; the temperature of the high-temperature solvent is 90–130°C; preferably, at least a portion of the high-temperature solvent is obtained after decoking the crude solvent. Using the above method to prepare n-butylamine vaporized gas allows for further utilization of the heat from the high-temperature solvent obtained during the recovery process, thereby effectively reducing the use of thermal energy resources and achieving energy conservation. Preferably, the temperature of the high-temperature solvent is 90–110°C. Controlling the temperature of the high-temperature solvent within the above range also enables the rational recycling of heat and allows subsequent reactions to proceed better.

[0040] In a preferred embodiment, the salt formation reaction is carried out in a gas-phase salt formation tower; preferably, the gas-phase salt formation tower is at least one of a hollow gas-phase salt formation tower, a plate-type gas-phase salt formation tower, or a packed gas-phase salt formation tower; more preferably, the gas-phase salt formation tower is a hollow gas-phase salt formation tower or a packed gas-phase salt formation tower; preferably, the gas-phase salt formation tower is provided with an overflow port for collecting the reaction suspension; preferably, the overflow port is inclined downwards; more preferably, the inclination angle of the overflow port is 25-75°; preferably, the preparation of n-butylamine vaporization gas is carried out in the gas-phase salt formation tower; preferably, a high-temperature solvent is placed in the gas-phase salt formation tower, and a first distributor is provided above the high-temperature solvent in the gas-phase salt formation tower for introducing hydrogen chloride gas into the gas-phase salt formation tower to mix with the n-butylamine vaporization gas; preferably, the first distributor is at least one of a perforated tube distributor, a trough distributor, or a disc distributor; more preferably, the first distributor is a perforated tube distributor. Conducting the above reaction in a gas-phase salt-forming tower allows for a more efficient gas-phase salt-forming process and facilitates continuous operation in the preparation of n-butyl isocyanate. Preferably, the solvent is an organic solvent with a boiling point >155°C; more preferably, the solvent is selected from one or more of o-dichlorobenzene, m-dichlorobenzene, and p-dichlorobenzene. These organic solvents not only have suitable boiling points but also high chemical stability, making them suitable as solvents in the preparation of n-butyl isocyanate. Preferably, a spray system is provided at the overflow port to ensure that the reaction suspension is promptly discharged from the gas-phase salt-forming tower. This configuration prevents the reaction suspension from clogging the overflow port.

[0041] In a preferred embodiment, a second distributor is provided in the gas-phase salt formation tower. The second distributor is located in the lower middle part of the gas-phase salt formation tower and is immersed in a high-temperature solvent for dripping liquid n-butylamine into the high-temperature solvent. Preferably, the second distributor is at least one of a perforated tube distributor, a trough distributor, or a disc distributor; more preferably, the distributor is a perforated tube distributor. Using the above method to prepare n-butylamine vapor gas can better achieve efficient preparation of n-butylamine vapor gas and further reduce energy consumption in the preparation process. Preferably, the feed temperature of liquid n-butylamine is 0-75°C; more preferably, the feed temperature of liquid n-butylamine is 25-50°C. Controlling the feed temperature of liquid n-butylamine within the above range can not only better convert liquid n-butylamine into n-butylamine vapor gas, but also prevent liquid n-butylamine from overflowing in the reverse direction. Preferably, the feed temperature of hydrogen chloride gas is -30-15°C; more preferably, the feed temperature of hydrogen chloride gas is -15-5°C. Controlling the feed temperature of hydrogen chloride gas within the above range can ensure the gaseous state of hydrogen chloride and also allow the salt formation reaction to proceed better.

[0042] In a preferred embodiment, the separation process includes: pre-separating the crude n-butyl isocyanate solution in a solvent recovery tower to obtain a crude solvent solution and a preliminary n-butyl isocyanate solution; purifying the preliminary n-butyl isocyanate solution to obtain n-butyl isocyanate; and purifying the crude solvent solution to obtain a high-temperature solvent. This separation process not only separates the n-butyl isocyanate but also achieves further recovery of the solvent and the heat carried by the solvent, which is beneficial for saving energy and reducing energy consumption.

[0043] Preferably, the solvent recovery tower is a first plate distillation column; preferably, the first plate distillation column has 25 to 40 plates; preferably, the crude n-butyl isocyanate solution is added from the 8th to 15th plates of the first plate distillation column; preferably, the reboiler temperature of the first plate distillation column is 100 to 125°C, and the pressure is 20 to 55 kPa. Controlling the parameters during the pre-separation process of the crude n-butyl isocyanate solution within the above ranges results in high separation efficiency. This not only allows for the preparation of higher purity n-butyl isocyanate but also enables further recovery of the solvent and utilization of the heat from the recovered solvent, thus better reducing energy consumption. Preferably, the reactor is selected from at least one of a plug flow reactor or a series reactor; in the phosgenation reaction process, using a series reactor or a plug flow reactor can effectively control the reaction temperature of the staged reaction. Preferably, the reactor is selected from a plug flow reactor; more preferably, the plug flow reactor is selected from at least one of a U-tube reactor, a tubular reactor, or a combination of a U-tube reactor and a tubular reactor; more preferably, the plug flow reactor is selected from a U-tube reactor. Selecting a plug flow reactor for the phosgenation reaction can further improve the reaction efficiency.

[0044] In a preferred embodiment, the crude solvent solution is purified in a second distillation column; preferably, the second distillation column is a second plate distillation column; preferably, the second plate distillation column has 15 to 25 plates; preferably, the crude n-butyl isocyanate is added from the 10th to 18th plates of the second plate distillation column; preferably, the bottom temperature of the second plate distillation column is 90 to 130°C, and the pressure is 20 to 85 kPa. Controlling the parameters during the purification process within the above ranges allows for better recovery of the solvent and the heat carried by the solvent during the preparation of n-butyl isocyanate.

[0045] In a preferred embodiment, phosgene in the reaction mixture is removed in a phosgene removal tower; preferably, nitrogen gas is continuously introduced into the phosgene removal tower to remove phosgene from the reaction mixture; preferably, the nitrogen gas flow rate is 20–60 Nm³. 3 / h; preferably, the phosgene removal tower is a circulating phosgene removal tower; preferably, the temperature of the bottom of the phosgene removal tower is 60-120℃. Controlling the parameters in the process of removing phosgene from the reaction mixture within the above range makes the purification efficiency of n-butyl isocyanate higher and also realizes the recycling of phosgene.

[0046] In a preferred embodiment, this application also provides an apparatus and process flow diagram for the preparation of n-butyl isocyanate, such as... Figure 1 As shown. Specifically, liquid n-butylamine A is passed into a high-temperature solvent in a gas-phase salt-forming tower 1, and after vaporization, n-butylamine vaporized gas is obtained. Hydrogen chloride gas B is condensed by condenser 4 and then passed into the gas-phase salt-forming tower 1 to react with the n-butylamine vaporized gas to obtain the salt-forming reaction product. The obtained gas-phase salt-forming product is then mixed with a high-temperature solvent and fed into a stirred mixer 2 from the overflow port of the gas-phase salt-forming tower 1. Under the full stirring action of the stirrer 9, a reaction suspension is obtained. During this process, hydrogen chloride gas B condensed by condenser 4 is passed into the stirred mixer 2 to maintain the pressure balance in the system of the stirred mixer 2. Then, the reaction suspension is fed into a U-tube reactor 5 through a feed pump 3, and phosgene C is also passed into the U-tube reactor 5 to mix with the reaction suspension for a segmented temperature-controlled phosgenation reaction. After the phosgenation reaction is completed, the reaction mixture is fed into the phosgenation tower 6 for phosgenation treatment. The tail gas D, which includes gases such as phosgene and hydrogen chloride, generated during the phosgenation treatment, is discharged from the system for further processing. The resulting crude n-butyl isocyanate solution is then fed into the solvent recovery tower 7 for further processing. After processing in the solvent recovery tower 7, the resulting initial n-butyl isocyanate solution is discharged from the solvent recovery tower 7 and further purified to obtain n-butyl isocyanate. The resulting crude solvent solution is then fed into the solvent purification tower 8 for decoking and purification. The resulting heavy components E (such as tar) are discharged from the solvent purification tower 8 for further processing. The high-temperature solvent obtained after purification is fed into the gas phase salt formation tower 1 to continue participating in the above reaction.

[0047] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0048] Example 1

[0049] use Figure 1 The process unit in the middle synthesizes n-butyl isocyanate, specifically:

[0050] The recovered o-dichlorobenzene high-temperature solvent at 100℃ was introduced into the gas-phase salt-forming tower 1 at a rate of 285 kg / h. Liquid n-butylamine was introduced into the high-temperature solvent in the gas-phase salt-forming tower 1 at a rate of 22 kg / h to form n-butylamine vaporized gas. Hydrogen chloride gas cooled by condenser 4 was introduced into the gas-phase salt-forming tower at a controlled temperature of 5℃ and a rate of 8622 L / h, with the tower pressure controlled at 0.14 MPa. The hydrogen chloride gas and n-butylamine vaporized gas underwent a salt-forming reaction in the upper cavity of the tower to generate salt-forming reaction products. The salt-forming reaction time was 1 hour, and the molar ratio of hydrogen chloride gas to n-butylamine vaporized gas was 1.28:1. The generated salt-forming reaction products were mixed with the solvent and then introduced from the overflow port of the gas-phase salt-forming tower into a stirred mixer 2. After thorough stirring by a stirrer 9, a reaction suspension was obtained. The reaction suspension was sampled and tested. The weight content of the salt-forming reaction product in the reaction suspension was 10.36%, and the weight content of the non-salted n-butylamine was 0%.

[0051] The reaction suspension was introduced into U-tube reactor 5 at a rate of 318 kg / h, and phosgene (85% by weight) was introduced at a rate of 9910 L / h to carry out the phosgenation reaction (at this point, the molar ratio of n-butylamine to phosgene was 1.25:1). The reaction temperature was controlled at 98℃ for 1 h in the first stage; the reaction temperature at 105℃ for 2.5 h in the second stage; and the reaction temperature at 115℃ for 2 h in the third stage. After the reaction was completed, the reaction mixture was obtained. Nitrogen gas was then introduced at a rate of 50 Nm³. 3 The mixture is fed into a phosgene-removing tower 6 to remove phosgene from the reaction mixture, yielding a crude n-butyl isocyanate solution. This crude n-butyl isocyanate solution is then fed into a solvent recovery tower 7 for further pre-separation (the solvent recovery tower is a plate distillation tower with 22 plates; the crude n-butyl isocyanate solution is added from the 16th plate; the reboiler temperature is 115°C and the pressure is 28 kPa). After pre-separation in the solvent recovery tower, the initial n-butyl isocyanate solution is discharged from the solvent recovery tower 7 for further purification to obtain n-butyl isocyanate. The resulting crude solvent solution is then fed into a solvent purification tower 8 for decoking and purification (the solvent purification tower 8 is a plate distillation tower with 15 plates; the crude solvent solution is added from the 10th plate; the reboiler temperature is 118°C and the pressure is 8 kPa), yielding a high-temperature solvent. This high-temperature solvent is then fed into a gas-phase salt-forming tower 1 to continue participating in the above reactions.

[0052] Example 2

[0053] use Figure 1 The process unit in the middle synthesizes n-butyl isocyanate, specifically:

[0054] The recovered 90°C o-dichlorobenzene high-temperature solvent was introduced into the gas-phase salt-forming tower 1 at a rate of 285 kg / h. Liquid n-butylamine was introduced into the high-temperature solvent in the gas-phase salt-forming tower 1 at a rate of 22 kg / h to form n-butylamine vaporized gas. Hydrogen chloride gas cooled by condenser 4 was introduced into the gas-phase salt-forming tower at a controlled temperature of 5°C and a rate of 7425 L / h, with the tower pressure controlled at 2 MPa. The hydrogen chloride gas and n-butylamine vaporized gas underwent a salt-forming reaction in the upper cavity of the tower, generating salt-forming reaction products. The salt-forming reaction time was 0.5 h, and the molar ratio of hydrogen chloride gas to n-butylamine vaporized gas was 1.08:1. The generated salt-forming reaction products were mixed with the solvent and then introduced from the overflow port of the gas-phase salt-forming tower into a stirred mixer 2. After thorough stirring by a stirrer 9, a reaction suspension was obtained. The reaction suspension was sampled and tested. The weight content of the salt-forming reaction product in the reaction suspension was 10.29%, and the weight content of the non-salted n-butylamine was 0.28%.

[0055] The reaction suspension was introduced into U-tube reactor 5 at a rate of 318 kg / h, and phosgene (85% by weight) was introduced at a rate of 9720 L / h to carry out the phosgenation reaction (at this point, the molar ratio of n-butylamine to phosgene was 1:1.22, and the temperature of the reaction suspension after mixing with phosgene was 130℃). The reaction temperature was controlled at 98℃ for 1 h in the first reaction stage; the reaction temperature was controlled at 105℃ for 2.5 h in the second reaction stage; and the reaction temperature was controlled at 115℃ for 2 h in the third reaction stage. After the reaction was completed, the reaction mixture was obtained. Nitrogen gas was then introduced at a rate of 50 Nm³. 3 The mixture is fed into a phosgene-removing tower 6 to remove phosgene from the reaction mixture, yielding a crude n-butyl isocyanate solution. This crude n-butyl isocyanate solution is then fed into a solvent recovery tower 7 for further pre-separation (the solvent recovery tower is a plate distillation tower with 22 plates; the crude n-butyl isocyanate solution is added from the 16th plate; the reboiler temperature is 115°C and the pressure is 28 kPa). After pre-separation in the solvent recovery tower, the initial n-butyl isocyanate solution is discharged from the solvent recovery tower 7 for further purification to obtain n-butyl isocyanate. The resulting crude solvent solution is then fed into a solvent purification tower 8 for decoking and purification (the solvent purification tower 8 is a plate distillation tower with 15 plates; the crude solvent solution is added from the 10th plate; the reboiler temperature is 118°C and the pressure is 8 kPa), yielding a high-temperature solvent. This high-temperature solvent is then fed into a gas-phase salt-forming tower 1 to continue participating in the above reactions.

[0056] Example 3

[0057] use Figure 1 The process unit in the middle synthesizes n-butyl isocyanate, specifically:

[0058] The recovered o-dichlorobenzene high-temperature solvent at 140℃ was introduced into the gas-phase salt-forming tower 1 at a rate of 285 kg / h. Liquid n-butylamine was introduced into the high-temperature solvent in the gas-phase salt-forming tower 1 at a rate of 22 kg / h to form n-butylamine vaporized gas. Hydrogen chloride gas cooled by condenser 4 was introduced into the gas-phase salt-forming tower at a controlled temperature of 5℃ and a rate of 12123 L / h, with the tower pressure controlled at 0.15 MPa. The hydrogen chloride gas and n-butylamine vaporized gas underwent a salt-forming reaction in the upper cavity of the tower to generate salt-forming reaction products. The salt-forming reaction time was 3.5 h, and the molar ratio of hydrogen chloride gas to n-butylamine vaporized gas was 1.8:1. The generated salt-forming reaction products were mixed with the solvent and then introduced from the overflow port of the gas-phase salt-forming tower into a stirred mixer 2. After thorough stirring by a stirrer 9, a reaction suspension was obtained. The reaction suspension was sampled and tested. The weight content of the salt-forming reaction product in the reaction suspension was 10.32%, the weight content of the non-salted n-butylamine was 0.6%, and n-butylamine escape was detected in the tail gas.

[0059] The reaction suspension was introduced into U-tube reactor 5 at a rate of 318 kg / h, and phosgene (85% by weight) was introduced at a rate of 23780 L / h to carry out the phosgenation reaction (at this point, the molar ratio of n-butylamine to phosgene was 1:3, and the temperature of the reaction suspension after mixing with phosgene was 70℃). The reaction temperature was controlled at 98℃ for 1 h in the first reaction stage; the reaction temperature was controlled at 105℃ for 2.5 h in the second reaction stage; and the reaction temperature was controlled at 115℃ for 2 h in the third reaction stage. After the reaction was completed, the reaction mixture was obtained. Nitrogen gas was then introduced at a rate of 50 Nm³. 3 The mixture is fed into a phosgene-removing tower 6 to remove phosgene from the reaction mixture, yielding a crude n-butyl isocyanate solution. This crude n-butyl isocyanate solution is then fed into a solvent recovery tower 7 for further pre-separation (the solvent recovery tower is a plate distillation tower with 22 plates; the crude n-butyl isocyanate solution is added from the 16th plate; the reboiler temperature is 115°C and the pressure is 28 kPa). After pre-separation in the solvent recovery tower, the initial n-butyl isocyanate solution is discharged from the solvent recovery tower 7 for further purification to obtain n-butyl isocyanate. The resulting crude solvent solution is then fed into a solvent purification tower 8 for decoking and purification (the solvent purification tower 8 is a plate distillation tower with 15 plates; the crude solvent solution is added from the 10th plate; the reboiler temperature is 118°C and the pressure is 8 kPa), yielding a high-temperature solvent. This high-temperature solvent is then fed into a gas-phase salt-forming tower 1 to continue participating in the above reactions.

[0060] Example 4

[0061] The difference between Example 4 and Example 1 is that the feed rate of liquid n-butylamine is 8 kg / h, the molar ratio of hydrogen chloride gas and n-butylamine vapor is 1.5:1, the weight content of the salt-forming reaction product in the resulting reaction suspension is 4%, and the weight content of unsalted n-butylamine is 0%.

[0062] Example 5

[0063] The difference between Example 5 and Example 1 is that the feed rate of liquid n-butylamine is 10 kg / h, the molar ratio of hydrogen chloride gas to n-butylamine vapor is 1.5:1, the weight content of the salt-forming reaction product in the resulting reaction suspension is 5%, and the weight content of unsalted n-butylamine is 0%.

[0064] Example 6

[0065] The difference between Example 6 and Example 1 is that the feed rate of liquid n-butylamine is 15 kg / h, the molar ratio of hydrogen chloride gas to n-butylamine vapor is 1.5:1, the weight content of salt-forming reaction product in the resulting reaction suspension is 7.3%, and the weight content of unsalted n-butylamine is 0%.

[0066] Example 7

[0067] The difference between Example 7 and Example 1 is that the feed rate of liquid n-butylamine is 25 kg / h, the molar ratio of hydrogen chloride gas to n-butylamine vapor is 1.5:1, the weight content of the salt-forming reaction product in the resulting reaction suspension is 11.6%, and the weight content of unsalted n-butylamine is 0.72%.

[0068] Example 8

[0069] The difference between Example 8 and Example 1 is that in the phosgenation reaction process, the reaction temperature of the first reaction stage is 100°C, the reaction temperature of the second reaction stage is 105°C, and the reaction temperature of the third reaction stage is 115°C.

[0070] Example 9

[0071] The difference between Example 9 and Example 1 is that in the phosgenation reaction process, the reaction temperature of the first reaction stage is 90°C, the reaction temperature of the second reaction stage is 100°C, and the reaction temperature of the third reaction stage is 110°C.

[0072] Example 10

[0073] The difference between Example 10 and Example 1 is that in the phosgenation reaction process, the reaction temperature of the first reaction stage is 100°C, the reaction temperature of the second reaction stage is 110°C, and the reaction temperature of the third reaction stage is 130°C.

[0074] Example 11

[0075] The difference between Example 11 and Example 1 is that the reaction temperature of the first reaction stage in the phosgenation reaction process is 92°C, the reaction temperature of the second reaction stage is 110°C, and the reaction temperature of the third reaction stage is 125°C.

[0076] Example 12

[0077] The difference between Example 12 and Example 1 is that the reaction temperature of the first reaction stage in the phosgenation reaction process is 85°C, the reaction temperature of the second reaction stage is 95°C, and the reaction temperature of the third reaction stage is 105°C.

[0078] Example 13

[0079] The difference between Example 13 and Example 1 is that the reaction temperature of the first reaction stage in the phosgenation reaction process is 105°C, the reaction temperature of the second reaction stage is 115°C, and the reaction temperature of the third reaction stage is 130°C.

[0080] Example 14

[0081] The difference between Example 14 and Example 1 is that the feed rate of liquid n-butylamine is 36 kg / h, the molar ratio of hydrogen chloride gas to n-butylamine vapor is 1.5:1, the weight content of salt-forming reaction product in the resulting reaction suspension is 15.11%, and the weight content of unsalted n-butylamine is 1.96%.

[0082] Comparative Example 1

[0083] 3200 kg of o-dichlorobenzene at 100°C was fed into a batch synthesis reactor. After cooling with a refrigerant for 5.5 h, 300 kg of n-butylamine was added, ensuring the temperature of o-dichlorobenzene in the reactor remained ≤30°C. Hydrogen chloride gas was introduced at a rate of 40 kg / h to maintain a slight negative pressure in the reactor, and the reaction was carried out for 6 h. A sample was taken, and the n-butylamine content was found to be 0%. Phosgene was then added, maintaining a molar ratio of n-butylamine to phosgene of 1:2.2. The temperature was slowly increased to 105°C, and the reaction was carried out for 4.5 h to obtain the reaction solution.

[0084] Comparative Example 2

[0085] The difference between Comparative Example 2 and Example 1 is that in the phosgenation reaction process, the reaction temperature of the first reaction stage is 90°C and the time is 2 hours; the reaction temperature of the second reaction stage is 115°C and the time is 3 hours.

[0086] The reaction conditions and results of some of the above examples and comparative examples are summarized in Table 1.

[0087] Table 1

[0088]

[0089] As can be seen from the above description, the embodiments of the present invention achieve the following technical effects:

[0090] This application provides a method for the gas-phase salt formation synthesis of n-butyl isocyanate. As shown in Table 1, the method provided in this application effectively improves the yield of n-butyl isocyanate. In particular, controlling the parameters during the preparation process within the preferred range results in an even better yield. In Comparative Example 1, a conventional batch reactor method was used to prepare n-butyl isocyanate. In Comparative Example 2, two-stage temperature control was implemented during the phosgenation reaction, and the yields of the prepared n-butyl isocyanate were significantly lower than those of this application.

[0091] In summary, the method for preparing n-butyl isocyanate provided in this application first involves a salt-forming reaction between n-butylamine vapor gas and hydrogen chloride gas. The resulting salt-forming product is then mixed with a solvent to obtain a reaction suspension. During the phosgenation reaction, by controlling the temperature, the hydrochloride salt formed from the n-butylamine vapor gas and hydrogen chloride gas reacts with phosgene in the first, second, and third reaction stages sequentially. Finally, the resulting reaction solution is separated to obtain n-butyl isocyanate. Using the preparation method provided in this application, the generation of byproducts during the preparation of n-butyl isocyanate can be effectively reduced, thereby further improving the reaction efficiency and yield of n-butyl isocyanate. Furthermore, this method is continuous, easy to operate, has high reaction safety and stability, and is easily automated. This method effectively solves the problems of low synthesis efficiency, numerous byproducts, and high energy consumption in the synthesis of n-butyl isocyanate.

[0092] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for gas-phase salt formation synthesis of n-butyl isocyanate, characterized in that, The synthesis method includes the following steps: The vaporized gas of n-butylamine and hydrogen chloride gas are mixed to carry out a salt formation reaction to obtain a salt formation reaction product; the salt formation reaction product is then mixed with a solvent to obtain a reaction suspension. The reaction suspension is mixed with phosgene to obtain a mixed raw material; the mixed raw material is passed into a reactor to carry out a phosgenation reaction to obtain a reaction mixture; wherein the phosgenation reaction includes a first reaction stage, a second reaction stage and a third reaction stage carried out in sequence, and the reaction temperature of the second reaction stage is not lower than the reaction temperature of the first reaction stage, and the reaction temperature of the third reaction stage is not lower than the reaction temperature of the second reaction stage. Remove the phosgene from the reaction mixture to obtain a crude n-butyl isocyanate solution; separate the crude n-butyl isocyanate solution to obtain a crude n-butyl isocyanate and solvent solution.

2. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to claim 1, characterized in that, The reaction temperature of the first reaction stage is 90-100℃, the reaction temperature of the second reaction stage is 100-110℃, and the reaction temperature of the third reaction stage is 110-130℃. Preferably, the reaction temperature of the first reaction stage is 92-100°C, the reaction temperature of the second reaction stage is 100-110°C, and the reaction temperature of the third reaction stage is 110-125°C. Preferably, the reaction pressures of the first reaction stage, the second reaction stage, and the third reaction stage are 0.11 to 0.40 MPa, and the reaction pressures of the first reaction stage, the second reaction stage, and the third reaction stage are independent of each other.

3. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to claim 1, characterized in that, The reaction time of the first reaction stage is ≥0.5h, the reaction time of the second reaction stage is ≥1.5h, and the reaction time of the third reaction stage is ≥2h. Preferably, the reaction time of the first reaction stage is 0.5 to 5 hours, the reaction time of the second reaction stage is 1.5 to 5 hours, and the reaction time of the third reaction stage is 2 to 6 hours. Preferably, the weight content of the salt-forming reaction product in the reaction suspension is 4-15%; more preferably, the weight content of the salt-forming reaction product in the reaction suspension is 5-8%. Preferably, the molar ratio of the n-butylamine vaporized gas to the hydrogen chloride gas is (1.08~1.8):1; Preferably, the reaction pressure of the salt formation reaction is 0.1-2 MPa, and the reaction time is 0.5-3.5 h.

4. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to any one of claims 1 to 3, characterized in that, The molar ratio of the n-butylamine vaporized gas to the phosgene is 1:(1.1-3); Preferably, the molar ratio of the n-butylamine vaporized gas to the phosgene is 1:(1.15-2.8); Preferably, the temperature of the mixture after the reaction suspension and the phosgene are mixed is 70-130°C.

5. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to any one of claims 1 to 3, characterized in that, The method for preparing the n-butylamine vaporized gas includes the following steps: Liquid n-butylamine is dropped into a high-temperature solvent and vaporized to obtain the n-butylamine vapor gas; the temperature of the high-temperature solvent is 90-130°C; preferably, the temperature of the high-temperature solvent is 90-110°C. Preferably, at least a portion of the high-temperature solvent is obtained by decoking the crude solvent.

6. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to claim 5, characterized in that, The salt-forming reaction is carried out in a gas-phase salt-forming tower; Preferably, the gas phase salt formation tower is at least one of a hollow gas phase salt formation tower, a plate gas phase salt formation tower, or a packed gas phase salt formation tower; more preferably, the gas phase salt formation tower is the hollow gas phase salt formation tower or the packed gas phase salt formation tower. Preferably, the gas-phase salt-forming tower is provided with an overflow port for collecting the reaction suspension; preferably, the overflow port is inclined downwards; more preferably, the inclination angle of the overflow port is 25-75°. Preferably, the n-butylamine vaporization gas is prepared in the gas-phase salt-forming tower; Preferably, the high-temperature solvent is placed in the gas-phase salt-forming tower, and a first distributor is provided above the high-temperature solvent in the gas-phase salt-forming tower for introducing the hydrogen chloride gas into the gas-phase salt-forming tower to mix with the n-butylamine vaporized gas; Preferably, the first distributor is at least one of a perforated tube distributor, a slotted distributor, or a disc distributor; more preferably, the first distributor is a perforated tube distributor. Preferably, the solvent is an organic solvent with a boiling point >155°C; more preferably, the solvent is selected from one or more of o-dichlorobenzene, m-dichlorobenzene and p-dichlorobenzene.

7. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to claim 6, characterized in that, The gas-phase salt formation tower is equipped with a second distributor, which is located in the lower middle part of the gas-phase salt formation tower and is immersed in the high-temperature solvent, for dripping the liquid phase n-butylamine into the high-temperature solvent; Preferably, the second distributor is at least one of a perforated tube distributor, a slotted distributor, or a disc distributor; more preferably, the distributor is a perforated tube distributor.

8. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to any one of claims 5 to 7, characterized in that, The separation process includes: pre-separating the crude n-butyl isocyanate solution in a solvent recovery tower to obtain the crude solvent solution and the initial n-butyl isocyanate solution; purifying the initial n-butyl isocyanate solution to obtain the n-butyl isocyanate; and purifying the crude solvent solution to obtain the high-temperature solvent. Preferably, the solvent recovery tower is a first plate distillation separation tower; Preferably, the first plate distillation column has 25 to 40 trays; Preferably, the crude n-butyl isocyanate solution is added from the 8th to 15th trays of the first plate distillation column; Preferably, the bottom temperature of the first plate distillation column is 100-125°C and the pressure is 20-55 kPa. Preferably, the reactor is selected from at least one of a plug flow reactor or a series reactor; more preferably, the reactor is selected from a plug flow reactor. Preferably, the plug flow reactor is selected from at least one of a U-tube reactor, a tubular reactor, or a combination of the U-tube reactor and the tubular reactor; more preferably, the plug flow reactor is selected from a U-tube reactor.

9. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to claim 8, characterized in that, The crude solvent solution is subjected to the purification process in a second distillation column. Preferably, the second distillation column is a second plate distillation column; Preferably, the second plate distillation column has 15 to 25 plates. Preferably, the crude solvent solution is added from the 10th to 18th trays of the second plate distillation column; Preferably, the bottom temperature of the second plate distillation column is 90–130°C and the pressure is 20–85 kPa.

10. The method for gas-phase salt formation synthesis of n-butyl isocyanate according to any one of claims 1 to 9, characterized in that, The phosgene in the reaction mixture is removed in a phosgene removal tower; Preferably, nitrogen gas is continuously introduced into the phosgene tower to remove the phosgene from the reaction mixture. Preferably, the nitrogen flow rate is 20–60 Nm³. 3 / h; Preferably, the light-driving tower is a circulating light-driving tower; Preferably, the temperature of the bottom of the light-generating tower is 60–120°C.

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