Synthesis method of n-butyl isocyanate

Abstract

The invention provides a synthesis method of n-butyl isocyanate. The synthesis method comprises the following steps: S1, introducing raw materials including an n-butylamine solution and phosgene into a tubular reactor for substitution reaction to obtain a reaction solution; s2, raw materials including the reaction liquid and protective gas are introduced into the reaction kettle for a cracking reaction, and the n-butyl isocyanate is obtained. Reaction liquid and protective gas in the step S2 enter a high-pressure reaction kettle to be subjected to cracking reaction, and hydrogen chloride can be discharged in time by introducing the protective gas, so that the content of by-products of n-chlorobutane and 1, 3-dibutyl urea can be reduced, and the purity can be improved. Meanwhile, phosgene is in a liquid state under high pressure and can continuously react with n-butylamine which does not participate in the reaction, so that the phosgene does not need to be additionally introduced, and the synthesis cost of the n-butyl isocyanate is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of organic synthesis, and in particular to a method for synthesizing n-butyl isocyanate. Background Art

[0002] n-Butyl isocyanate is mainly used to prepare benomyl, which can be prepared by the condensation reaction of n-butyl isocyanate and carbendazim. Benomyl has a good control effect on many pathogens of Ascomycetes and Deuteromycetes. The industrial preparation of n-butyl isocyanate is mainly the low-temperature and high-temperature phosgene method and the salt-first-phosgene method. The reaction formulas of the two synthesis methods are as follows:

[0003] (1) The reaction formula of low temperature and high temperature phosgene method is as follows:

[0004] Low temperature section:

[0005]

[0006] High temperature section:

[0007]

[0008] (2) The reaction formula of the salt-forming method followed by the phosgene-generating method is as follows:

[0009]

[0010] Side effects:

[0011]

[0012]

[0013] The intermediate n-butylcarbamoyl chloride in the low-temperature and high-temperature phosgene method is highly active. A part of it is decomposed into n-butyl isocyanate by heat, and a part of it is easily reacted with hydrogen chloride to form impurity n-butyl chloride, resulting in a decrease in product yield. At the same time, in order to ensure the reaction effect, a certain amount of phosgene still needs to be introduced into the high-temperature reaction process, and the phosgene utilization rate is low. The phosgene method is first used after salt formation, and the active amino group is protected, and the reaction yield is higher. However, hydrogen chloride needs to be introduced first during the salt formation reaction (high raw material cost), and 3 equivalents of hydrogen chloride are produced during the phosgenation reaction (normal reaction is 2 equivalents), which increases the difficulty of tail gas treatment. At the same time, the salt formation process is insoluble in the solvent, and the system is heterogeneous. In order to maintain good fluidity, the amount of solvent used is large, resulting in low product concentration, low production efficiency, and high energy consumption in the solvent recovery process.

[0014] The Chinese patent application with the patent application publication number CN105294498A introduces a method for synthesizing n-butyl isocyanate. It is prepared by a phosgene method at low temperature followed by high temperature. This method is a batch reaction in a kettle, and the phosgene consumption is relatively high during the reaction. The hydrogen chloride generated by the reaction is not discharged in time during the high temperature section, and there are many side reactions, resulting in a low yield of n-butyl isocyanate.

[0015] The Chinese patent application with patent application publication number CN103848759A introduces a method for synthesizing n-butyl isocyanate by first forming a salt and then passing phosgene. The reaction uses hydrogen chloride separated from tail gas and n-butylamine to form a salt, thereby realizing the resource utilization of hydrogen chloride. However, during the salt formation reaction, the system is heterogeneous, the concentration of the reaction solution is low, and the production efficiency is low. At the same time, when phosgene is passed at high temperature, phosgene is easy to overflow, the reaction efficiency is poor, and the phosgene utilization rate is low. Summary of the invention

[0016] The main purpose of the present invention is to provide a method for synthesizing n-butyl isocyanate to solve the problem that the n-butyl isocyanate prepared in the prior art has low purity.

[0017] In order to achieve the above-mentioned purpose, according to one aspect of the present invention, a method for synthesizing n-butyl isocyanate is provided, and the method comprises: step S1, introducing raw materials including n-butylamine solution and phosgene into a tubular reactor for substitution reaction to obtain a reaction liquid; step S2, introducing raw materials including the reaction liquid and protective gas into a reactor for cracking reaction to obtain n-butyl isocyanate.

[0018] Furthermore, the tubular reactor is a vertical tubular reactor, which is provided with an n-butylamine solution inlet, a phosgene inlet and a reaction liquid outlet. The n-butylamine solution inlet is arranged at the top of the vertical tubular reactor, and the phosgene inlet is arranged at the side of the vertical tubular reactor. The height difference between the phosgene inlet and the n-butylamine solution inlet is denoted as h, and the total height of the vertical tubular reactor is denoted as H, then h / H=0.4~0.6; the reaction liquid outlet is arranged at the bottom of the vertical tubular reactor.

[0019] Furthermore, a stirrer is provided in the tubular reactor; preferably, the stirrer is a radial stirrer; and / or, the substitution reaction is carried out under stirring, and the stirring speed of the substitution reaction is 100 to 500 rpm, preferably 200 to 300 rpm; and / or, the temperature of the substitution reaction is 0°C to 30°C, preferably 10°C to 20°C; and / or, in step S1, the n-butylamine solution and phosgene are continuously introduced into the tubular reactor for continuous substitution reaction, and preferably the residence time of the substitution reaction is 10 to 100 min, preferably 30 to 50 min.

[0020] Furthermore, the height-to-diameter ratio of the tubular reactor is 5 to 20:1, preferably 10 to 15:1.

[0021] Furthermore, the molar ratio of the phosgene to the n-butylamine in the n-butylamine solution is 1.05 to 1.3:1, preferably 1.05 to 1.1:1.

[0022] Furthermore, the mass fraction of n-butylamine in the above n-butylamine solution is 10% to 50%, preferably 30% to 40%; and / or the solvent in the n-butylamine solution is selected from any one or more of toluene, xylene, chlorobenzene and o-dichlorobenzene; preferably, the solvent is o-dichlorobenzene.

[0023] Furthermore, the temperature of the above cracking reaction is 80-130°C, preferably 90-110°C; and / or, in step S2, the reaction liquid and the protective gas are continuously introduced into the reactor for continuous cracking reaction, and the residence time of the cracking reaction is preferably 0.5-3h, preferably 1-1.5h.

[0024] Furthermore, the above-mentioned cracking reaction is carried out under stirring, and the stirring speed of the cracking reaction is 300 to 1000 rpm, preferably 700 to 900 rpm.

[0025] Furthermore, the pressure of the above cracking reaction is 0.5 to 2.5 MPa, preferably 1 to 1.5 MPa.

[0026] Furthermore, the amount of the protective gas is 1 to 5 times, preferably 2 to 3 times, the molar equivalent of n-butylamine in the n-butylamine solution; preferably, the protective gas is selected from any one or more of nitrogen, argon and helium.

[0027] Applying the technical scheme of the present invention, in step S1 of the present application, by passing n-butylamine solution and phosgene into a tubular reactor for substitution reaction, it is helpful to make the substitution reaction proceed at a lower temperature, and the low-temperature phosgenation reaction liquid is basically liquid, which helps to avoid the problems of heterogeneous phase and large tail gas volume in the salt-forming reaction, and then helps to improve the purity and synthesis efficiency of n-butyl isocyanate. In step S2, the reaction liquid and the protective gas enter the autoclave for cracking reaction, and the introduction of the protective gas helps to achieve the timely discharge of hydrogen chloride, which is conducive to reducing the content of by-products n-butyl chloride and 1,3-dibutyl urea, and then helps to improve the purity. At the same time, phosgene is liquid under high pressure, and can continue to react with n-butylamine that does not participate in the reaction, without the need to additionally pass phosgene, which helps to reduce the synthesis cost of n-butyl isocyanate. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings constituting a part of the present application are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0029] Figure 1 A schematic diagram of the synthesis system of n-butyl isocyanate in Example 1 of the present application is shown;

[0030] Figure 2 The gas chromatogram of n-butyl isocyanate in Example 1 of the present application is shown.

[0031] The above drawings include the following reference numerals:

[0032] 1. Vertical tubular reactor; 2. Radial agitator; 3. First delivery pump; 4. Back pressure valve; 5. Reactor; 6. Second delivery pump. DETAILED DESCRIPTION

[0033] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0034] As analyzed in the background technology of the present application, the n-butyl isocyanate prepared in the prior art has the problem of low purity. In order to solve the above problem, the present application provides a method for synthesizing n-butyl isocyanate.

[0035] In a typical embodiment of the present application, a method for synthesizing n-butyl isocyanate is provided, and the method comprises: step S1, introducing raw materials including n-butylamine solution and phosgene into a tubular reactor for substitution reaction to obtain a reaction liquid; step S2, introducing raw materials including the reaction liquid and protective gas into a reactor for cracking reaction to obtain n-butyl isocyanate.

[0036] In step S1 of the present application, by passing n-butylamine solution and phosgene into a tubular reactor for substitution reaction, it is helpful to make the substitution reaction proceed at a lower temperature, and the low-temperature phosgenation reaction liquid is basically liquid, which helps to avoid the problems of heterogeneous phase and large tail gas volume in the salt-forming reaction, and then helps to improve the purity and synthesis efficiency of n-butyl isocyanate. In step S2, the reaction liquid and the protective gas enter the autoclave for cracking reaction, and the introduction of the protective gas helps to achieve the timely discharge of hydrogen chloride, which is conducive to reducing the content of by-products n-butyl chloride and 1,3-dibutyl urea, and then helps to improve the purity. At the same time, phosgene is liquid under high pressure, and can continue to react with n-butylamine that does not participate in the reaction, without the need to pass phosgene additionally, thereby helping to reduce the synthesis cost of n-butyl isocyanate.

[0037] In one embodiment of the present application, the above-mentioned tubular reactor is a vertical tubular reactor, and the vertical tubular reactor is provided with an n-butylamine solution inlet, a phosgene inlet and a reaction liquid outlet. The n-butylamine solution inlet is arranged at the top of the vertical tubular reactor, and the phosgene inlet is arranged on the side of the vertical tubular reactor. The height difference between the phosgene inlet and the n-butylamine solution inlet is denoted as h, and the total height of the vertical tubular reactor is denoted as H, then h / H=0.4~0.6; the reaction liquid outlet is arranged at the bottom of the vertical tubular reactor.

[0038] When the tubular reactor is a vertical tubular reactor, the n-butylamine solution is introduced from the top of the vertical tubular reactor, and the phosgene is introduced from the side wall of the vertical tubular reactor. The n-butylamine solution flows from top to bottom, and the phosgene flows from bottom to top after being introduced. The n-butylamine solution and the phosgene form countercurrent contact, which helps to increase the contact area between the phosgene and the n-butylamine solution, thereby helping to improve the reaction efficiency of the substitution reaction. It is preferred to control the height of the phosgene inlet to the n-butylamine solution in the total length of the vertical tubular reactor within the above range, which helps to further increase the contact area between the phosgene and the n-butylamine solution, thereby helping to further improve the reaction efficiency of the substitution reaction.

[0039] In one embodiment of the present application, a stirrer is provided in the above-mentioned tubular reactor; preferably, the stirrer is a radial stirrer; and / or, the substitution reaction is carried out under stirring, and the stirring speed of the substitution reaction is 100 to 500 rpm, preferably 200 to 300 rpm; and / or, the temperature of the substitution reaction is 0°C to 30°C, preferably 10°C to 20°C; and / or, in step S1, the n-butylamine solution and phosgene are continuously introduced into the tubular reactor for continuous substitution reaction, and preferably the residence time of the substitution reaction is 10 to 100 min, preferably 30 to 50 min.

[0040] The tubular reactor is provided with an agitator, especially a radial agitator, which helps to improve the efficiency of mass transfer and heat transfer. The stirring speed of the substitution reaction is preferably controlled within the above range, which helps to increase the contact area between the n-butylamine solution and the phosgene, thereby helping to improve the reaction efficiency of the substitution reaction. The temperature and time of the substitution reaction are preferably controlled within the above range, which helps to improve the reaction efficiency of the substitution reaction while reducing the occurrence of side reactions.

[0041] In order to further improve the reaction efficiency of the substitution reaction, in one embodiment of the present application, the height-to-diameter ratio of the tubular reactor is preferably 5 to 20:1, preferably 10 to 15:1.

[0042] In one embodiment of the present application, the molar ratio of the phosgene to the n-butylamine in the n-butylamine solution is 1.05-1.3:1, preferably 1.05-1.1:1.

[0043] Preferably, the molar ratio of phosgene to n-butylamine in the n-butylamine solution is controlled within the above range, which helps to improve the efficiency of the substitution reaction and thus helps to reduce the probability of side reactions.

[0044] In one embodiment of the present application, the mass fraction of n-butylamine in the above n-butylamine solution is 10% to 50%, preferably 30% to 40%; and / or the solvent in the n-butylamine solution is selected from any one or more of toluene, xylene, chlorobenzene and o-dichlorobenzene; preferably, the solvent is o-dichlorobenzene.

[0045] The mass fraction of n-butylamine in the n-butylamine solution is too high, the reaction is violent, and the heat release is large, which is not conducive to reducing the generation of side reactions. The mass fraction of n-butylamine in the n-butylamine solution is too low, which is not conducive to improving the yield of n-butyl isocyanate. It is preferred to control the mass fraction of n-butylamine in the n-butylamine solution within the above range, which helps to improve the efficiency of the substitution reaction. It is preferred to control the type of solvent in the n-butylamine solution within the above range, which helps to promote full contact between n-butylamine and phosgene, thereby helping to improve the efficiency of the substitution reaction.

[0046] In one embodiment of the present application, the temperature of the above-mentioned cracking reaction is 80-130°C, preferably 90-110°C; and / or, in step S2, the reaction liquid and the protective gas are continuously introduced into the reactor for continuous cracking reaction, and the residence time of the cracking reaction is preferably 0.5-3h, preferably 1-1.5h.

[0047] Preferably, the temperature and time of the cleavage reaction are controlled within the above ranges, which helps to improve the efficiency of the cleavage reaction while reducing the content of by-products n-butyl chloride and 1,3-dibutylurea, thereby helping to improve the purity of n-butyl isocyanate.

[0048] In order to further improve the efficiency of the cracking reaction, in one embodiment of the present application, the above-mentioned cracking reaction is preferably carried out under stirring, and the stirring speed of the cracking reaction is 300 to 1000 rpm, preferably 700 to 900 rpm.

[0049] In order to further improve the purity of n-butyl isocyanate, in one embodiment of the present application, the pressure of the above-mentioned cracking reaction is preferably 0.5 to 2.5 MPa, preferably 1 to 1.5 MPa.

[0050] In order to further improve the removal efficiency of hydrogen chloride, in one embodiment of the present application, the amount of the above-mentioned protective gas is preferably 1 to 5 times, preferably 2 to 3 times, the molar equivalent of n-butylamine in the n-butylamine solution; preferably, the protective gas is selected from any one or more of nitrogen, argon and helium.

[0051] The beneficial effects of the present application will be further illustrated below in conjunction with embodiments.

[0052] Example 1

[0053] Use Figure 1 The synthesis system shown is used for preparing n-butyl isocyanate. Specifically, step 1 is to prepare an n-butylamine solution with a mass fraction of 30% of n-butylamine, wherein the solvent in the n-butylamine solution is o-dichlorobenzene, and the n-butylamine solution and phosgene are simultaneously introduced into a vertical tubular reactor 1 for low-temperature phosgenation reaction. The vertical tubular reactor 1 is provided with an n-butylamine solution inlet, a phosgene inlet and a reaction liquid outlet. The n-butylamine solution inlet is arranged at the top of the vertical tubular reactor, and the phosgene inlet is arranged at the side of the vertical tubular reactor. The height difference between the phosgene inlet and the n-butylamine solution inlet is recorded as h, and the total height of the vertical tubular reactor is recorded as H, then h / H=0.4; the reaction liquid outlet is arranged at the bottom of the vertical tubular reactor, and a radial stirrer 2 is inserted from the top of the vertical tubular reactor 1 into the interior of the vertical tubular reactor 1 to stir the substitution reaction. The height-to-diameter ratio of the vertical tubular reactor is 15:1, the molar ratio of phosgene to n-butylamine is 1.1:1, the temperature of the substitution reaction is 10°C, the stirring speed of the substitution reaction is 300 rpm, and the residence time is 30 min; in step 2, the reaction liquid of step 1 is introduced into a reactor 5 through a first delivery pump 3 for cracking reaction, and nitrogen is introduced into the reactor 5 at the same time, the valve opening of the back pressure valve 4 is controlled to discharge the hydrogen chloride generated by the reaction in time, the system pressure is controlled by the back pressure valve 4, and the obtained step 2 reaction liquid is discharged through a second delivery pump 6, the temperature of the cracking reaction is 100°C, the reaction pressure is 1.5 MPa, the stirring speed is 800 rpm, the reaction residence time is 1 h, and the amount of nitrogen is twice the molar equivalent of n-butylamine.

[0054] Example 2

[0055] The difference from Example 1 is that the mass fraction of n-butylamine in the n-butylamine solution is 40%, and the reaction solution of step 2 is finally obtained.

[0056] Example 3

[0057] The difference from Example 1 is that the mass fraction of n-butylamine in the n-butylamine solution is 10%, and the reaction solution of step 2 is finally obtained.

[0058] Example 4

[0059] The difference from Example 1 is that the mass fraction of n-butylamine in the n-butylamine solution is 50%, and the reaction solution of step 2 is finally obtained.

[0060] Example 5

[0061] The difference from Example 1 is that the mass fraction of n-butylamine in the n-butylamine solution is 60%, and the reaction solution of step 2 is finally obtained.

[0062] Example 6

[0063] The difference from Example 1 is that the molar ratio of phosgene to n-butylamine is 1.05:1, and the reaction solution of step 2 is finally obtained.

[0064] Example 7

[0065] The difference from Example 1 is that the molar ratio of phosgene to n-butylamine is 1.3:1, and the reaction solution of step 2 is finally obtained.

[0066] Example 8

[0067] The difference from Example 1 is that the molar ratio of phosgene to n-butylamine is 1.4:1, and the reaction solution of step 2 is finally obtained.

[0068] Example 9

[0069] The difference from Example 1 is that the height-to-diameter ratio of the vertical tubular reactor is 10:1, the molar ratio of phosgene to n-butylamine is 1.05:1, the temperature of the substitution reaction is 10°C, the stirring speed of the substitution reaction is 200 rpm, the residence time of the substitution reaction is 50 min, and finally the reaction solution of step 2 is obtained.

[0070] Example 10

[0071] The difference from Example 1 is that, in step 1, an n-butylamine solution with a mass fraction of 30% of n-butylamine is prepared, the solvent in the n-butylamine solution is o-dichlorobenzene, the n-butylamine solution and phosgene are simultaneously introduced into a vertical tubular reactor 1 for low-temperature phosgenation reaction, the vertical tubular reactor 1 is provided with an n-butylamine solution inlet, a phosgene inlet and a reaction liquid outlet, the n-butylamine solution inlet is arranged at the top of the vertical tubular reactor, the phosgene inlet is arranged at the side of the vertical tubular reactor, the height difference between the phosgene inlet and the n-butylamine solution inlet is denoted as h, the total height of the vertical tubular reactor is denoted as H, then h / H=0.4; the reaction liquid outlet is arranged at the bottom of the vertical tubular reactor, and a radial stirrer 2 is inserted from the top of the vertical tubular reactor 1 into the interior of the vertical tubular reactor 1 to stir the substitution reaction. The height-to-diameter ratio of the vertical tubular reactor is 20:1, the molar ratio of phosgene to n-butylamine is 1.2:1, the temperature of the substitution reaction is 30°C, the stirring speed of the substitution reaction is 100 rpm, and the residence time is 100 min; in step 2, the reaction liquid of step 1 is introduced into a reactor 5 through a first delivery pump 3 for cracking reaction, and nitrogen is introduced into the reactor 5 at the same time, the valve opening of the back pressure valve 4 is controlled to discharge the hydrogen chloride generated by the reaction in time, the system pressure is controlled by the back pressure valve 4, and the obtained step 2 reaction liquid is discharged through a second delivery pump 6, the temperature of the cracking reaction is 130°C, the reaction pressure is 2.5 MPa, the stirring speed is 500 rpm, the reaction residence time is 0.5 h, and the amount of nitrogen is 3 times the molar equivalent of n-butylamine.

[0072] Embodiment 11

[0073] The difference from Example 1 is that, in step 1, an n-butylamine solution with a mass fraction of 30% of n-butylamine is prepared, the solvent in the n-butylamine solution is o-dichlorobenzene, the n-butylamine solution and phosgene are simultaneously introduced into a vertical tubular reactor 1 for low-temperature phosgenation reaction, the vertical tubular reactor 1 is provided with an n-butylamine solution inlet, a phosgene inlet and a reaction liquid outlet, the n-butylamine solution inlet is arranged at the top of the vertical tubular reactor, the phosgene inlet is arranged at the side of the vertical tubular reactor, the height difference between the phosgene inlet and the n-butylamine solution inlet is denoted as h, the total height of the vertical tubular reactor is denoted as H, then h / H=0.4; the reaction liquid outlet is arranged at the bottom of the vertical tubular reactor, and a radial stirrer 2 is inserted from the top of the vertical tubular reactor 1 into the interior of the vertical tubular reactor 1 to stir the substitution reaction. The height-to-diameter ratio of the vertical tubular reactor is 5:1, the molar ratio of phosgene to n-butylamine is 1.1:1, the temperature of the substitution reaction is 0°C, the stirring speed of the substitution reaction is 500 rpm, and the residence time is 10 min; in step 2, the reaction liquid of step 1 is introduced into a reactor 5 through a first delivery pump 3 for a cracking reaction, and nitrogen is introduced into the reactor 5 at the same time, the valve opening of the back pressure valve 4 is controlled to discharge the hydrogen chloride generated by the reaction in time, the system pressure is controlled by the back pressure valve 4, and the obtained step 2 reaction liquid is discharged through a second delivery pump 6, the temperature of the cracking reaction is 80°C, the reaction pressure is 0.5 MPa, the stirring speed is 300 rpm, the reaction residence time is 3 h, and the amount of nitrogen is 5 times the molar equivalent of n-butylamine.

[0074] Example 12

[0075] The difference from Example 1 is that, in step 1, an n-butylamine solution with a mass fraction of 30% of n-butylamine is prepared, the solvent in the n-butylamine solution is o-dichlorobenzene, the n-butylamine solution and phosgene are simultaneously introduced into a vertical tubular reactor 1 for low-temperature phosgenation reaction, the vertical tubular reactor 1 is provided with an n-butylamine solution inlet, a phosgene inlet and a reaction liquid outlet, the n-butylamine solution inlet is arranged at the top of the vertical tubular reactor, the phosgene inlet is arranged at the side of the vertical tubular reactor, the height difference between the phosgene inlet and the n-butylamine solution inlet is denoted as h, the total height of the vertical tubular reactor is denoted as H, then h / H=0.4; the reaction liquid outlet is arranged at the bottom of the vertical tubular reactor, and a radial stirrer 2 is inserted from the top of the vertical tubular reactor 1 into the interior of the vertical tubular reactor 1 to stir the substitution reaction. The height-to-diameter ratio of the vertical tubular reactor is 15:1, the molar ratio of phosgene to n-butylamine is 1.1:1, the temperature of the substitution reaction is 10°C, the stirring speed of the substitution reaction is 250 rpm, and the residence time is 30 min; in step 2, the reaction liquid of step 1 is introduced into a reactor 5 through a first delivery pump 3 for cracking reaction, and nitrogen is introduced into the reactor 5 at the same time, the valve opening of the back pressure valve 4 is controlled to discharge the hydrogen chloride generated by the reaction in time, the system pressure is controlled by the back pressure valve 4, and the obtained step 2 reaction liquid is discharged through a second delivery pump 6, the temperature of the cracking reaction is 100°C, the reaction pressure is 1.0 MPa, the stirring speed is 1000 rpm, the reaction residence time is 1 h, and the amount of nitrogen is 1 times the molar equivalent of n-butylamine.

[0076] Embodiment 13

[0077] The difference from Example 1 is that the solvent is toluene, and the reaction liquid of step 2 is finally obtained.

[0078] Embodiment 14

[0079] The difference from Example 1 is that the solvent is xylene, and the reaction liquid of step 2 is finally obtained.

[0080] Embodiment 15

[0081] The difference from Example 1 is that the solvent is chlorobenzene, and the reaction solution of step 2 is finally obtained.

[0082] Example 16

[0083] The difference from Example 1 is that h / H=0.6, and the reaction solution of step 2 is finally obtained.

[0084] Embodiment 17

[0085] The difference from Example 1 is that h / H=0.8, and the reaction solution of step 2 is finally obtained.

[0086] Embodiment 18

[0087] The difference from Example 1 is that the stirring speed of the substitution reaction is 200 rpm, the temperature of the substitution reaction is 20° C., the residence time of the substitution reaction is 50 min, and finally the reaction solution of step 2 is obtained.

[0088] Embodiment 19

[0089] The difference from Example 1 is that the stirring speed of the substitution reaction is 100 rpm, the temperature of the substitution reaction is 0° C., the residence time of the substitution reaction is 10 min, and finally the reaction solution of step 2 is obtained.

[0090] Embodiment 20

[0091] The difference from Example 1 is that the stirring speed of the substitution reaction is 500 rpm, the temperature of the substitution reaction is 30° C., the residence time of the substitution reaction is 100 min, and finally the reaction solution of step 2 is obtained.

[0092] Embodiment 21

[0093] The difference from Example 1 is that the height-to-diameter ratio of the vertical tubular reactor is 5:1, and the reaction liquid of step 2 is finally obtained.

[0094] Embodiment 22

[0095] The difference from Example 1 is that the height-to-diameter ratio of the vertical tubular reactor is 20:1, and the reaction liquid of step 2 is finally obtained.

[0096] Embodiment 23

[0097] The difference from Example 1 is that the temperature of the cracking reaction is 90° C., the residence time of the cracking reaction is 1.5 h, the stirring speed of the cracking reaction is 700 rpm, the pressure of the cracking reaction is 1.5 MPa, and the amount of nitrogen used is 3 times the molar equivalent of n-butylamine, and finally the reaction solution of step 2 is obtained.

[0098] Embodiment 24

[0099] The difference from Example 1 is that the temperature of the cracking reaction is 110° C., the residence time of the cracking reaction is 1 h, the stirring speed of the cracking reaction is 900 rpm, the pressure of the cracking reaction is 1 MPa, and the amount of nitrogen used is 2 times the molar equivalent of n-butylamine, and finally the reaction solution of step 2 is obtained.

[0100] Embodiment 25

[0101] The difference from Example 1 is that the temperature of the cracking reaction is 80° C., the residence time of the cracking reaction is 0.5 h, the stirring speed of the cracking reaction is 1000 rpm, the pressure of the cracking reaction is 2.5 MPa, and the amount of nitrogen used is 1 times the molar equivalent of n-butylamine, and finally the reaction solution of step 2 is obtained.

[0102] Embodiment 26

[0103] The difference from Example 1 is that the temperature of the cracking reaction is 130° C., the residence time of the cracking reaction is 3 h, the stirring speed of the cracking reaction is 300 rpm, the pressure of the cracking reaction is 0.5 MPa, and the amount of nitrogen used is 5 times the molar equivalent of n-butylamine, and finally the reaction solution of step 2 is obtained.

[0104] Comparative Example 1

[0105] Step 1, preparing an n-butylamine solution with a mass fraction of 30% of n-butylamine, wherein the solvent in the n-butylamine solution is o-dichlorobenzene, placing the n-butylamine solution in a reactor, introducing phosgene for low-temperature phosgenation reaction, wherein the molar ratio of phosgene to n-butylamine is 1.1:1, the reaction temperature is 10° C., the stirring speed is 300 rpm, and the reaction time is 30 min; Step 2, after the low-temperature phosgenation reaction is completed, heating the reactor to 100° C. and performing high-temperature cracking, the stirring speed is 800 rpm, and the reaction time is 1 h, to obtain the reaction solution of step 2.

[0106] The reaction liquid of step 2 prepared in the embodiment and the comparative example was drained away and analyzed by gas chromatography. The analysis results are shown in Table 1.

[0107] Table 1

[0108]

[0109]

[0110] Figure 2 is the gas chromatogram of n-butyl isocyanate in Example 1 of the present application, Figure 2 The peak with a retention time of 5.706 min is that of n-butyl isocyanate, the peak with a retention time of 3.135 min is that of n-butyl chloride, and the peak with a retention time of 13.663 min is that of 1,3-dibutylurea. Figure 2 It can be seen that the content of n-butyl isocyanate in the reaction solution of step 2 is relatively high.

[0111] From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:

[0112] In step S1 of the present application, by passing n-butylamine solution and phosgene into a tubular reactor for substitution reaction, it is helpful to make the substitution reaction proceed at a lower temperature, and the low-temperature phosgenation reaction liquid is basically liquid, which helps to avoid the problems of heterogeneous phase and large tail gas volume in the salt-forming reaction, and then helps to improve the purity and synthesis efficiency of n-butyl isocyanate. In step S2, the reaction liquid and the protective gas enter the autoclave for cracking reaction, and the introduction of the protective gas helps to achieve the timely discharge of hydrogen chloride, which is conducive to reducing the content of by-products n-butyl chloride and 1,3-dibutyl urea, and then helps to improve the purity. At the same time, phosgene is liquid under high pressure, and can continue to react with n-butylamine that does not participate in the reaction, without the need to pass phosgene additionally, thereby helping to reduce the synthesis cost of n-butyl isocyanate.

[0113] The above are only embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for synthesizing n-butyl isocyanate, characterized in that: The synthesis method comprises: Step S1, introducing raw materials including n-butylamine solution and phosgene into a tubular reactor for substitution reaction to obtain a reaction solution; Step S2, introducing the raw materials including the reaction solution and the protective gas into a reactor for cracking reaction to obtain the n-butyl isocyanate.

2. The synthesis method according to claim 1, characterized in that The tubular reactor is a vertical tubular reactor, and is provided with an n-butylamine solution inlet, a phosgene inlet and a reaction liquid outlet. The n-butylamine solution inlet is arranged at the top of the vertical tubular reactor, and the phosgene inlet is arranged at the side of the vertical tubular reactor. The height difference between the phosgene inlet and the n-butylamine solution inlet is denoted as h, and the total height of the vertical tubular reactor is denoted as H, then h / H=0.4-0.6; the reaction liquid outlet is arranged at the bottom of the vertical tubular reactor.

3. The synthesis method according to claim 1 or 2, characterized in that The tubular reactor is provided with an agitator; preferably, the agitator is a radial agitator; And / or, the substitution reaction is carried out under stirring, and the stirring speed of the substitution reaction is 100 to 500 rpm, preferably 200 to 300 rpm; and / or, the temperature of the substitution reaction is 0°C to 30°C, preferably 10°C to 20°C; And / or, in the step S1, the n-butylamine solution and the phosgene are continuously introduced into the tubular reactor to carry out the continuous substitution reaction, and the residence time of the substitution reaction is preferably 10 to 100 minutes, preferably 30 to 50 minutes.

4. The synthesis method according to any one of claims 1 to 3, characterized in that The height-to-diameter ratio of the tubular reactor is 5 to 20:1, preferably 10 to 15:

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5. The synthesis method according to any one of claims 1 to 4, characterized in that The molar ratio of the phosgene to the n-butylamine in the n-butylamine solution is 1.05 to 1.3:1, preferably 1.05 to 1.1:

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6. The synthesis method according to any one of claims 1 to 5, characterized in that The mass fraction of n-butylamine in the n-butylamine solution is 10% to 50%, preferably 30% to 40%; and / or the solvent in the n-butylamine solution is selected from any one or more of toluene, xylene, chlorobenzene and o-dichlorobenzene; preferably, the solvent is o-dichlorobenzene.

7. The synthesis method according to any one of claims 1 to 6, characterized in that The temperature of the cleavage reaction is 80-130°C, preferably 90-110°C; And / or, in the step S2, the reaction liquid and the protective gas are continuously introduced into the reactor to perform the continuous cracking reaction, and the residence time of the cracking reaction is preferably 0.5 to 3 hours, preferably 1 to 1.5 hours.

8. The synthesis method according to any one of claims 1 to 7, characterized in that The cleavage reaction is carried out under stirring, and the stirring speed of the cleavage reaction is 300 to 1000 rpm, preferably 700 to 900 rpm.

9. The synthesis method according to any one of claims 1 to 8, characterized in that The pressure of the cracking reaction is 0.5-2.5 MPa, preferably 1-1.5 MPa.

10. The synthesis method according to any one of claims 1 to 9, characterized in that The amount of the protective gas is 1 to 5 times, preferably 2 to 3 times, the molar equivalent of n-butylamine in the n-butylamine solution; preferably, the protective gas is selected from any one or more of nitrogen, argon and helium.

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