Continuous production process for the synthesis of isocyanates by the salt phosgene method

Abstract

The application provides a continuous production method for synthesizing isocyanate by salt formation phosgene method. The method comprises the following steps: S1, continuously feeding an amine-containing solution and hydrogen chloride into a salt formation kettle to perform a salt formation reaction, so that part of the amine in the amine-containing solution is salted to obtain a salt formation liquid containing amine hydrochloride and unreacted amine, and the salt formation liquid is continuously discharged; S2, continuously feeding the salt formation liquid into a salt formation-phosgenation kettle to perform a reaction with phosgenation tail gas, so that the unreacted amine is salted, and the amine hydrochloride is subjected to a preliminary phosgenation reaction, to obtain phosgenation-salt formation liquid, and the phosgenation-salt formation liquid is continuously discharged; S3, continuously feeding the phosgenation-salt formation liquid and phosgene into a phosgenation kettle to perform a phosgenation reaction, to obtain phosgenation liquid and phosgenation tail gas, and the phosgenation tail gas is returned to the salt formation-phosgenation kettle; and S4, performing sedimentation separation on the phosgenation liquid to obtain isocyanate. The application solves the problems of low salt formation rate, uneven amine hydrochloride particles, and excessively high consumption of hydrogen chloride and phosgene in the synthesis of isocyanate by salt formation phosgene method.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of isocyanate synthesis, in particular to a continuous production method for synthesizing isocyanate by salt-forming phosgene method. BACKGROUND

[0002] As a method for synthesizing isocyanate, the salt-forming phosgene method has the advantages of protecting the active groups of primary amines and avoiding the generation of insoluble impurities such as urea by side reactions with product isocyanate, but in actual production process, some problems that are difficult to handle will inevitably occur, such as: 1) If the concentration of the salt-forming solution is too high, the viscosity will be too large, causing the material transfer to be inconvenient, the salt particles to wrap the amines, resulting in a low salt-forming rate, etc.; if the concentration of the salt-forming solution is too low, it will lead to insufficient production capacity of the equipment and excessive use of solvent. 2) The tail gas of phosgenation contains a large amount of hydrogen chloride and part of unreacted phosgene, which usually needs an additional set of equipment for absorption separation or rectification separation, which is high in cost. 3) The particle size of the salt particles is uneven, and the viscosity is too large, resulting in a large amount of phosgene used in the phosgenation.

[0003] CN111825572A provides a method for preparing isocyanate by salt-forming and atomized phosgene method, which atomizes the salt-forming solution by using inert gas, and then prepares isocyanate by phosgenation. This method can alleviate a series of problems caused by the excessive viscosity of the salt solution to a certain extent, but the use of a large amount of inert gas leads to excessive tail gas in the system, causing excessive pressure in the tail gas treatment system, and too much non-condensable gas also leads to a decrease in the utilization rate of phosgene, which is a disadvantage in terms of cost.

[0004] CN113181859A and CN115286535A both disclose salt-forming reactors to solve the problems of incomplete salt formation and large salt particles, but both of the two reactors described have a step divider with a small opening diameter, which is easy to be blocked by salt particles, thereby leading to a short service life of the reactor.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] The main purpose of the present application is to provide a continuous production method for synthesizing isocyanate by salt-forming phosgene method, to solve the problems of low salt-forming rate, uneven size of hydrochloride salt particles, and excessive consumption of hydrogen chloride and phosgene in the synthesis of isocyanate by salt-forming phosgene method in the prior art.

[0007] In order to achieve the above object, according to one aspect of the present application, a continuous production method for synthesizing isocyanate by salt formation phosgene method is provided, which comprises the following steps: S1, continuously feeding an amine-containing solution and hydrogen chloride into a salt formation kettle to perform a salt formation reaction, so that part of the amine in the amine-containing solution is salted to obtain a salt formation liquid containing amine hydrochloride and unreacted amine, and the salt formation liquid is continuously discharged; S2, continuously feeding the salt formation liquid into a salt formation-phosgenation kettle to react with phosgenation tail gas, so that the unreacted amine is salted and the amine hydrochloride is preliminarily phosgenated to obtain a phosgenation-salt formation liquid, and the phosgenation-salt formation liquid is continuously discharged; S3, continuously feeding the phosgenation-salt formation liquid and phosgene into a phosgenation kettle to perform a phosgenation reaction, to obtain a phosgenation liquid and phosgenation tail gas, and the phosgenation tail gas is returned to the salt formation-phosgenation kettle; and S4, performing a sedimentation separation on the phosgenation liquid to obtain isocyanate.

[0008] Further, in step S1, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.3-1.8, preferably 1:0.6-1.2.

[0009] Further, the amine in the amine-containing solution is one or more of toluene diamine, 1,6-hexanediamine, 1,5-pentanediamine, isophorone diamine, p-phenylenediamine, 1,5-naphthalenediamine, and diphenylmethane diamine; preferably, when the melting point of the amine in the amine-containing solution is higher than 80℃, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.9-1.2; when the melting point of the amine in the amine-containing solution is lower than 80℃, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.6-0.9; preferably, when the melting point of the amine in the amine-containing solution is higher than 80℃, the reaction temperature in the salt formation kettle is 60-130℃, more preferably 80-100℃; when the melting point of the amine in the amine-containing solution is lower than 80℃, the reaction temperature in the salt formation kettle is 0-60℃, more preferably 0-30℃; preferably, the residence time of the amine-containing solution in the salt formation kettle is 0.5-2h; more preferably, when the melting point of the amine in the amine-containing solution is higher than 80℃, the residence time of the amine-containing solution in the salt formation kettle is 1.2-2h; when the melting point of the amine in the amine-containing solution is lower than 80℃, the residence time of the amine-containing solution in the salt formation kettle is 0.5-1.2h; preferably, the mass concentration of the amine-containing solution is 10-40%, and the solvent thereof is one or more of chlorobenzene, dichlorobenzene, and toluene.

[0010] Further, the molar ratio of the amine in the amine-containing solution to the phosgene fed in step S3 is 1:2-10.

[0011] Further, the molar ratio of the amine in the amine-containing solution to the phosgene fed in step S3 is 1:3-6.

[0012] Further, in step S4, the photochemical liquid is subjected to sedimentation separation in a sedimentation kettle, and the supernatant obtained is the isocyanate; the sedimentation separation also obtains a lower sedimentation slurry at the bottom of the sedimentation kettle, and the method further comprises: returning the lower sedimentation slurry to step S2 and feeding it into the salt-formation and photochemical kettle to participate in the reaction.

[0013] Further, the volume flow rate ratio of the salt-formation liquid to the returned lower sedimentation slurry is 1:0.05-0.1.

[0014] Further, in step S2, the reaction temperature in the salt-formation and photochemical kettle is 30-130℃, preferably 40-80℃; and / or, in step S3, the reaction temperature in the photochemical kettle is 80-170℃, preferably 110-160℃; and / or, the residence time of the material in the salt-formation and photochemical kettle is 0.5-2h; and / or, the residence time of the material in the photochemical kettle is 2-10h; and / or, the sedimentation separation time is 3-8h.

[0015] Further, the photochemical kettle is provided with a photochemical tail gas outlet, and a condensation reflux device is arranged at the photochemical tail gas outlet, and the condensation medium has a temperature of-30-5℃.

[0016] Further, before the photochemical liquid is subjected to sedimentation separation, step S4 further comprises: pre-quenching the photochemical liquid; preferably, the quenching temperature is 20-80℃, more preferably 40-60℃.

[0017] The technical scheme of the present application can reduce the viscosity of the salt-formation liquid, avoid the problems of low salt-formation rate and uneven particle size of the hydrochloride salt caused by too high viscosity of the salt-formation liquid, significantly improve the phosgene utilization rate and photochemical reaction efficiency, and reduce the consumption of hydrogen chloride and phosgene. BRIEF DESCRIPTION OF DRAWINGS

[0018] The drawings accompanying the specification of the present application serve to provide a further understanding of the present application, and the illustrative embodiments of the present application and their descriptions serve to explain the present application, and do not constitute an improper limitation on the present application. In the drawings:

[0019] Figure 1 Fig. 1 shows a flow chart of a continuous production method for synthesizing isocyanate by a salt-formation and phosgene method according to an embodiment of the present application;

[0020] In the above drawings, the following reference signs are used:

[0021] 10, salt-formation kettle; 20, salt-formation and photochemical kettle; 30, photochemical kettle; 40, sedimentation kettle. DETAILED DESCRIPTION

[0022] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other in the case of no conflict. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0023] As described in the background section, in the prior art, there are problems of low salting rate, uneven particle size of hydrochloride salt, and high consumption of hydrogen chloride and phosgene when isocyanate is synthesized by the salting phosgene method. In order to solve this problem, the present application provides a continuous production method for synthesizing isocyanate by the salting phosgene method, as shown in Figure 1 S1, continuously feeding an amine-containing solution a and hydrogen chloride b into a salting kettle 10 to perform a salting reaction, so that part of the amine in the amine-containing solution is salified to obtain a salting solution c containing amine hydrochloride and unreacted amine, and the salting solution c is continuously discharged; S2, continuously feeding the salting solution c into a salting-phosgenation kettle 20 to react with phosgenation tail gas d, so that the unreacted amine is salified, and the amine hydrochloride is preliminarily phosgenated to obtain phosgenation-salting solution e, and the phosgenation-salting solution e is continuously discharged; S3, continuously feeding the phosgenation-salting solution e and phosgene f into a phosgenation kettle 30 to perform a phosgenation reaction to obtain phosgenation solution g and phosgenation tail gas d, and the phosgenation tail gas d is returned to the salting-phosgenation kettle; and S4, performing sedimentation separation on the phosgenation solution to obtain isocyanate h.

[0024] When isocyanate is synthesized by the salting phosgene method, the amine and hydrogen chloride need to be first salified to form amine hydrochloride, and then phosgenated with phosgene (carbonyl chloride). However, the amine used to prepare isocyanate usually has poor solubility, and the reaction with hydrogen chloride is very rapid. The salting reaction will rapidly change from a homogeneous reaction system to a heterogeneous reaction system, resulting in rapid increase of the viscosity of the system, poor uniformity of the particle size of the salting particles, and problems of decrease of the salting rate due to the coating of the amine by the salt particles. The present inventors have proposed the above step-by-step salting process through a large amount of research, which effectively controls the viscosity of the system and makes the salting particles uniform, thereby improving the salting rate. Specifically,

[0025] In the present application, the amine-containing solution and hydrogen chloride are continuously fed into the salting kettle to perform a salting reaction. In this process, only part of the amine is salified, and a salting solution containing amine hydrochloride and unreacted amine is obtained. In this process, because only part of the amine is salified, the viscosity of the system is greatly reduced, the uniformity of the salting particles is ensured, and the amine is not easily coated and still presents a free state. The main reaction occurring in the salting kettle is:

[0026] R-NH2+HCl→R-NH2·HCl

[0027] Secondly, the remaining unreacted amine reacts with the phosgenation tail gas in the subsequent phosgenation reaction process as the salt formation liquid enters the salt formation-phosgenation kettle. The phosgenation tail gas contains a large amount of hydrogen chloride and a small amount of phosgene, and the unreacted amine can further react with hydrogen chloride to form a salt (reaction 1 below). By stepwise salting of the amine, the viscosity of the system is effectively controlled, making material transfer convenient, enabling continuous production, and the total salting rate of the amine is relatively high, and the salted particles are uniform. In addition, because the phosgenation tail gas also carries a small amount of phosgene, the amine hydrochloride in the salted liquid and the amine hydrochloride generated by the reaction of the unreacted amine with hydrogen chloride in the tail gas can preliminarily react with the phosgene (reaction 3 below), ensuring that the amine hydrochloride in the salt formation-phosgenation kettle is in a dynamic equilibrium process, which is conducive to maintaining the viscosity of the system at a low level. Unavoidably, the unreacted amine and phosgene will also react to generate impurities (reaction 2 below), but due to the high concentration of hydrogen chloride in the salt formation-phosgenation kettle and the dynamic equilibrium state of the amine hydrochloride, the reaction 2 is effectively inhibited. Based on this, the present application can effectively utilize the phosgenation tail gas to participate in the reaction in the salt formation-phosgenation kettle, significantly improving the utilization rate of the tail gas, and maintaining a high isocyanate purity, which plays a very important role in reducing the consumption of hydrogen chloride and phosgene and the green environmental protection of the entire isocyanate production.

[0028] Reaction 1: R-NH2+HCl→R-NH2·HCl

[0029] Reaction 2: R-NH2+COCl2→R-NHCOCl+HCl

[0030] Reaction 3: R-NH2·HCl+COCl2→R-NCO+3HCl

[0031] After the reaction in the salt formation-phosgenation kettle, the amine hydrochloride in the phosgenation-salt formation liquid can react with the newly introduced phosgene in the phosgenation kettle to form a more complete phosgenation reaction (R-NH2·HCl+COCl2→R-NCO+3HCl). After the phosgenation liquid is separated by sedimentation, isocyanate is obtained. It should be noted that the size of the salt particles is an important reason for the poor phosgenation rate. It is because the stepwise salting process of the present application controls the viscosity of the system, so that the size of the salted particles is more uniform, thereby ensuring the efficient phosgenation reaction in the phosgenation kettle.

[0032] In order to better control the step-by-step salting rhythm, so that the system is stable and efficient at a lower viscosity state, in a preferred embodiment, in step S1, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.3-1.8, preferably 1:0.6-1.2. Compared with the traditional excess addition of hydrogen chloride, the above molar ratio of amine to hydrogen chloride is used in the present application, which makes the salting degree in the salting kettle more appropriate, the viscosity more stable, the total salting rate of the two-stage process higher, and the salt particles more uniform.

[0033] The amine used in the present application can be the commonly used type in the field, including but not limited to one or more of toluene diamine, 1,6-hexanediamine, 1,5-pentanediamine, isophorone diamine, p-phenylenediamine, 1,5-naphthalenediamine, and diphenylmethane diamine. Different amines have different melting points, which will cause different degrees of viscosity state during salting. In order to further maintain a lower viscosity state, improve the salting rate, salt particle uniformity and phosgenation reaction efficiency, in a preferred embodiment, when the melting point of the amine in the amine-containing solution is higher than 80℃, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.9-1.2; when the melting point of the amine in the amine-containing solution is lower than 80℃, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.6-0.9.

[0034] In actual production process, preferably, when the melting point of the amine in the amine-containing solution is higher than 80℃, the reaction temperature in the salting kettle is 60-130℃, more preferably 80-100℃; when the melting point of the amine in the amine-containing solution is lower than 80℃, the reaction temperature in the salting kettle is 0-60℃, more preferably 0-30℃; preferably, the residence time of the amine-containing solution in the salting kettle is 0.5-2h; more preferably, when the melting point of the amine in the amine-containing solution is higher than 80℃, the residence time of the amine-containing solution in the salting kettle is 1.2-2h; when the melting point of the amine in the amine-containing solution is lower than 80℃, the residence time of the amine-containing solution in the salting kettle is 0.5-1.2h. By controlling the above reaction temperature and residence time, the above beneficial effects of step-by-step salting can be further improved, and the continuous reaction is more stable. Preferably, the mass concentration of the amine-containing solution is 10-40%, and the solvent thereof is one or more of chlorobenzene, dichlorobenzene and toluene.

[0035] Considering the reaction rate of phosgene and the suitability of phosgene in the tail gas in the continuous production process, in a preferred embodiment, the molar ratio of the amine in the above amine-containing solution to the phosgene introduced in step S3 is 1:2-10, preferably 1:3-6. Controlling the molar ratio of phosgene to amine within the above range is beneficial to the dynamic balance of the reactions in the salting kettle, the salting-phosgenation kettle and the phosgenation kettle, and has a better promoting effect on the stability and material balance of the continuous production.

[0036] In the phosgenation reaction process, the amine hydrochloride salt reacts with phosgene to form isocyanate, but inevitably, a part of the salt particles does not complete the reaction, and some small amount of polymer impurities similar to isocyanate biuret, uretdione, carbodiimide, etc. are inevitably produced during the reaction. In a preferred embodiment, as shown in Figure 1 In the above step S4, the phosgenation liquid is subjected to sedimentation separation in the sedimentation kettle 40, and the supernatant obtained is the isocyanate h; the lower sedimentation slurry i at the bottom of the sedimentation kettle is also obtained, and the method further comprises: returning the lower sedimentation slurry i to step S2 and introducing it into the salt-phosgenation kettle to participate in the reaction. Through sedimentation separation, the isocyanate is separated in the supernatant, and the unreacted salt particles and a small amount of impurities are at the bottom of the sedimentation kettle, which are returned to the salt-phosgenation kettle, which is beneficial to the continuous reaction of the unreacted salt particles, so as to further improve the conversion rate and product yield. At the same time, it needs to be emphasized that compared with directly returning the lower sedimentation slurry to the phosgenation kettle, returning it to the salt-phosgenation kettle is also beneficial to the discharge of the total tail gas j of the reaction, and further improves the purity of the product.

[0037] In order to make the continuous production more stable, in a preferred embodiment, the volume flow ratio of the salted liquid to the returned lower sedimentation slurry is 1:0.05-0.1.

[0038] In the specific implementation process, a plurality of sedimentation kettles 40 are preferably connected in parallel, such as two, and the phosgenation liquid can first enter one sedimentation kettle 40, and after a certain time, the phosgenation liquid reaches the specified liquid level of the sedimentation kettle, at which time the phosgenation liquid pipeline is switched to discharge the phosgenation liquid to another sedimentation kettle 40.

[0039] In a preferred embodiment, in the above step S2, the reaction temperature in the salt-phosgenation kettle is 30-130°C, preferably 40-80°C; and / or, in step S3, the reaction temperature in the phosgenation kettle is 80-170°C, preferably 110-160°C; and / or, the residence time of the material in the salt-phosgenation kettle is 0.5-2h; and / or, the residence time of the material in the phosgenation kettle is 2-10h; and / or, the sedimentation separation time is 3-8h. Controlling the reaction temperature and residence time of the material in each kettle within the above range is beneficial to further improve the stability and efficiency of the continuous reaction.

[0040] Preferably, the phosgenation kettle is provided with a phosgenation tail gas outlet, and a condensation reflux device is arranged at the phosgenation tail gas outlet, and the condensation medium thereof has a temperature of-30-5°C. By using the condensation reflux device, the phosgene in the phosgenation tail gas can be returned to the phosgenation kettle as much as possible to participate in the reaction, reducing the proportion of phosgene in the phosgenation tail gas, so as to better position the balance of each reaction in the salt-phosgenation kettle and inhibit the above-mentioned side reaction 2 as much as possible.

[0041] To make the reaction product more stable, in a preferred embodiment, before the photochemical liquid is subjected to settling separation, step S4 further comprises, pre-quenching the photochemical liquid; preferably, the quenching temperature is 20-80℃, more preferably 40-60℃.

[0042] The application will be further described in conjunction with specific examples, which should not be construed as limiting the scope of the application.

[0043] Example 1

[0044] A continuous production method for synthesizing isocyanate by salt formation and phosgene method is provided in this example, as shown in Figure 1 which comprises the following steps:

[0045] S1, continuously pass a 10% mass concentration p-phenylenediamine (melting point ≈ 138℃) solution in o-dichlorobenzene and hydrogen chloride gas into a salt formation kettle with a volume of 50L to perform a salt formation reaction, control the reaction temperature in the salt formation kettle to be 100℃, the flow rate of the amine-containing solution to be 16.25L / h, the volumetric flow rate of the hydrogen chloride gas to be 525.78L / h, the molar ratio of the amine to the hydrogen chloride to be 1:1.2, and the residence time of the material in the salt formation kettle to be 2h; the salt formation liquid obtained after the salt formation reaction contains amine hydrochloride and unreacted amine, which is continuously discharged (viscosity about 83mpa·s); after detection, the salt formation rate of the amine in the salt formation kettle is 48%;

[0046] S2, continuously pass the salt formation liquid into a salt formation-photochemical kettle with a volume of 60L to react with photochemical tail gas, wherein the flow rate of the salt formation liquid is 17.89L / h, the volumetric flow rate of the photochemical tail gas is 3945.15L / h, the reaction temperature in the salt formation-photochemical kettle is 80℃, and the residence time is 2h, to obtain a photochemical-salt formation liquid; after detection, the total salt formation rate of the amine in the salt formation kettle and the salt formation-photochemical kettle is 96.8%, and the median particle size D50 is 9.33 microns;

[0047] S3, continuously pass the photochemical-salt formation liquid into a photochemical kettle with a volume of 180L to perform a phosgenation reaction with fresh phosgene, control the flow rate of the photochemical-salt formation liquid to be 20.16L / h, the volumetric flow rate of the phosgene to be 1753L / h, the molar ratio of the amine in the amine-containing solution to the phosgene to be 1:4, the reaction temperature in the photochemical kettle to be 140℃, and the residence time of the material to be 6h; the obtained photochemical liquid is continuously discharged, and the photochemical tail gas is returned to step S2; a condensing device with cooling medium at -20℃ is arranged at the outlet of the photochemical tail gas to make most of the phosgene in the photochemical tail gas return to the photochemical kettle for reaction;

[0048] S4, prepare two switchable settling tanks, after the photochemical solution is quenched at 55°C, continuously input into one of the settling tanks, switch the photochemical solution pipeline after a certain time to reach the specified liquid level, and discharge the photochemical solution to the other settling tank. After 4.5h of settling separation in the settling tank, the supernatant containing isocyanate is discharged, and the lower layer of the settling slurry in the tank is returned to the salt-forming-phosgene tank in step S2 at a flow rate of 0.63L / h for continuous reaction.

[0049] According to the detection calculation, the yield of isocyanate in the above continuous production is 98.9%.

[0050] Example 2

[0051] A continuous production method for synthesizing isocyanate by salt-forming phosgene method is provided in this example, as shown in Figure 1 , which includes the following steps:

[0052] S1, continuously input the solution of p-phenylenediamine (melting point ≈ 138℃) with a mass concentration of 10% in o-dichlorobenzene and hydrogen chloride gas into a salt-forming tank with a volume of 50L for salt-forming reaction, control the reaction temperature in the salt-forming tank to be 80℃, the flow rate of the amine-containing solution to be 16.25L / h, the volume flow rate of hydrogen chloride gas to be 328L / h, the molar ratio of amine to hydrogen chloride to be 1:0.75, and the residence time of the material in the salt-forming tank to be 1.2h; the salt-forming liquid obtained after the salt-forming reaction contains amine hydrochloride and unreacted amine, which is continuously discharged (viscosity about 79mpa·s); according to the detection, the salt-forming rate of amine in the salt-forming tank is 41%;

[0053] S2, continuously input the salt-forming liquid into a salt-forming-phosgene tank with a volume of 60L for reaction with phosgene tail gas, wherein the flow rate of the salt-forming liquid is 17.91L / h, the volume flow rate of the phosgene tail gas is 4293L / h, the reaction temperature in the salt-forming-phosgene tank is 40℃, and the residence time is 2h, to obtain a phosgene-salt-forming liquid; according to the detection, the total salt-forming rate of amine in the salt-forming tank and the salt-forming-phosgene tank is 96.3%, and the median particle size D50 is 9.25 microns;

[0054] S3, continuously input the phosgene-salt-forming liquid into a phosgene tank with a volume of 180L for phosgenation reaction with fresh phosgene, control the flow rate of the phosgene-salt-forming liquid to be 21.22L / h, the volume flow rate of the phosgene to be 2629L / h, the molar ratio of amine in the amine-containing solution to the phosgene to be 1:6, the reaction temperature in the phosgene tank to be 130℃, and the residence time of the material to be 6h; the obtained phosgene liquid is continuously discharged, and the phosgene tail gas is returned to step S2; a condensing device with cooling medium at -30℃ is arranged at the outlet of the phosgene tail gas to make most of the phosgene in the phosgene tail gas return to the phosgene tank for reaction;

[0055] S4, prepare two switchable settling tanks, after the photochemical solution is quenched at 40°C, continuously input into one of the settling tanks, switch the photochemical solution pipeline after a certain time to reach the specified liquid level, and make the photochemical solution discharge to the other settling tank. After 8h of settling separation in the settling tank, the supernatant containing isocyanate is discharged, and the lower layer of the settling slurry in the tank is returned to the salt-forming-phosgene tank in step S2 at a flow rate of 0.35L / h for continuous reaction.

[0056] According to the detection calculation, the yield of isocyanate in the above continuous production is 98.5%.

[0057] Example 3

[0058] A continuous production method for synthesizing isocyanate by salt-forming phosgene method is provided in this example, as shown in Figure 1 , which includes the following steps:

[0059] S1, continuously input the o-dichlorobenzene solution of p-phenylenediamine with a mass concentration of 20% (melting point ≈ 138℃) and hydrogen chloride gas into a salt-forming tank with a volume of 50L for salt-forming reaction, control the reaction temperature in the salt-forming tank to be 130℃, the flow rate of the amine-containing solution to be 16.25L / h, the volume flow rate of hydrogen chloride gas to be 876.3L / h, the molar ratio of amine to hydrogen chloride to be 1:1.0, and the residence time of the material in the salt-forming tank to be 0.5h; the salt-forming liquid obtained after the salt-forming reaction contains amine hydrochloride and unreacted amine, which is continuously discharged (viscosity about 116mpa·s); according to the detection, the salt-forming rate of amine in the salt-forming tank is 52.5%;

[0060] S2, continuously input the salt-forming liquid into a salt-forming-phosgene tank with a volume of 50L for reaction with phosgene tail gas, wherein the flow rate of the salt-forming liquid is 18.58L / h, the volume flow rate of the phosgene tail gas is 5082L / h, the reaction temperature in the salt-forming-phosgene tank is 60℃, and the residence time is 1.0h, to obtain a phosgene-salt-forming liquid; according to the detection, the total salt-forming rate of amine in the salt-forming tank and the salt-forming-phosgene tank is 92.5%, and the median particle size D50 is 11.63 microns;

[0061] S3, continuously input the phosgene-salt-forming liquid into a phosgene tank with a volume of 150L for phosgenation reaction with fresh phosgene, control the flow rate of the phosgene-salt-forming liquid to be 23.68L / h, the volume flow rate of the phosgene to be 2629L / h, the molar ratio of amine in the amine-containing solution to the phosgene to be 1:3, the reaction temperature in the phosgene tank to be 160℃, and the residence time of the material to be 3h; the obtained phosgene liquid is continuously discharged, and the phosgene tail gas is returned to step S2; a condensing device with cooling medium at 5℃ is arranged at the outlet of the phosgene tail gas to make most of the phosgene in the phosgene tail gas return to the phosgene tank for reaction;

[0062] S4, prepare two switchable settling tanks, after the photochemical solution is quenched at 60°C, continuously input into one of the settling tanks, switch the photochemical solution pipeline after a certain time to reach the specified liquid level, and make the photochemical solution discharge to the other settling tank. After 3h of settling separation in the settling tank, the supernatant containing isocyanate is discharged, and the lower layer of the settling slurry at the bottom is returned to the salt-forming-phosgene reactor in step S2 at a flow rate of 1.35L / h for continuous reaction.

[0063] According to the detection calculation, the yield of isocyanate in the above continuous production is 96.2%.

[0064] Example 4

[0065] A continuous production method for synthesizing isocyanate by salt-forming phosgene method is provided in this example, as shown in Figure 1 , which includes the following steps:

[0066] S1, continuously input the chlorobenzene solution of 1,6-hexanediamine with a mass concentration of 40% (melting point ≈ 42-46°C) and hydrogen chloride gas into a salt-forming reactor with a volume of 50L for salt-forming reaction, control the reaction temperature in the salt-forming reactor to be 30°C, the flow rate of the amine-containing solution to be 16.25L / h, the volume flow rate of hydrogen chloride gas to be 1240L / h, the molar ratio of amine to hydrogen chloride to be 1:0.9, and the residence time of the material in the salt-forming reactor to be 1.2h; the salt-forming solution obtained after the salt-forming reaction contains amine hydrochloride and unreacted amine, which is continuously discharged (viscosity about 128mpa·s); according to the detection, the salt-forming rate of amine in the salt-forming reactor is 45%;

[0067] S2, continuously input the salt-forming solution into a salt-forming-phosgene reactor with a volume of 60L for reaction with phosgene tail gas, wherein the flow rate of the salt-forming solution is 21.63L / h, the volume flow rate of the phosgene tail gas is 9610L / h, the reaction temperature in the salt-forming-phosgene reactor is 50°C, and the residence time is 1.5h, to obtain a phosgene-salt-forming solution; according to the detection, the total salt-forming rate of amine in the salt-forming reactor and the salt-forming-phosgene reactor is 96.6%, and the median particle size D50 is 9.12 microns;

[0068] S3, continuously input the phosgene-salt-forming solution into a phosgene reactor with a volume of 200L for phosgenation reaction with fresh phosgene, control the flow rate of the phosgene-salt-forming solution to be 25.63L / h, the volume flow rate of the phosgene to be 8265.6L / h, the molar ratio of amine in the amine-containing solution to the phosgene to be 1:6, the reaction temperature in the phosgene reactor to be 110°C, and the residence time of the material to be 6h; the obtained phosgene solution is continuously discharged, and the phosgene tail gas is returned to step S2; a condensing device with cooling medium at -30°C is arranged at the outlet of the phosgene tail gas to make most of the phosgene in the phosgene tail gas return to the phosgene reactor for reaction;

[0069] S4, prepare two switchable settling tanks, after the photochemical solution is quenched at 40°C, continuously input into one of the settling tanks, after a certain time to reach the specified liquid level, switch the photochemical solution pipeline to make the photochemical solution discharge to another settling tank. After 4.5h of settling separation in the settling tank, the supernatant containing isocyanate is discharged, and the lower layer of the settling slurry at the bottom is returned to the salt-forming-phosgenation reactor in step S2 at a flow rate of 1.5L / h for continuous reaction.

[0070] According to the detection calculation, the yield of isocyanate in the above continuous production is 98.7%.

[0071] Example 5

[0072] A continuous production method for synthesizing isocyanate by salt-forming-phosgenation method is provided in this example, as shown in Figure 1 , which comprises the following steps:

[0073] S1, continuously input the chlorobenzene solution of 1,6-hexanediamine with a mass concentration of 20% (melting point ≈ 42-46°C) and hydrogen chloride gas into a salt-forming reactor with a volume of 50L for salt-forming reaction, control the reaction temperature in the salt-forming reactor to be 0°C, the flow rate of the amine-containing solution to be 39.93L / h, the volume flow rate of hydrogen chloride gas to be 1016L / h, the molar ratio of amine to hydrogen chloride to be 1:0.6, and the residence time of the material in the salt-forming reactor to be 0.5h; the salt-forming liquid obtained after the salt-forming reaction contains amine hydrochloride and unreacted amine, which is continuously discharged (viscosity about 58mpa·s); according to the detection, the salt-forming rate of amine in the salt-forming reactor is 44%;

[0074] S2, continuously input the salt-forming liquid into a salt-forming-phosgenation reactor with a volume of 150L for reaction with phosgenation tail gas, wherein the flow rate of the salt-forming liquid is 43.38L / h, the volume flow rate of the phosgenation tail gas is 15108L / h, the reaction temperature in the salt-forming-phosgenation reactor is 30°C, and the residence time is 2h, to obtain a phosgenation-salt-forming liquid; according to the detection, the total salt-forming rate of amine in the salt-forming reactor and the salt-forming-phosgenation reactor is 96.0%, and the median particle size D50 is 9.08 microns;

[0075] S3, continuously input the phosgenation-salt-forming liquid into a phosgenation reactor with a volume of 400L for phosgenation reaction with fresh phosgene, control the flow rate of the phosgenation-salt-forming liquid to be 46.95L / h, the volume flow rate of phosgene to be 10160L / h, the molar ratio of amine in the amine-containing solution to phosgene to be 1:6, the reaction temperature in the phosgenation reactor to be 80°C, and the residence time of the material to be 6h; the obtained phosgenation liquid is continuously discharged, and the phosgenation tail gas is returned to step S2; a condensing device with cooling medium at -20°C is arranged at the outlet of the phosgenation tail gas to make most of the phosgene in the phosgenation tail gas return to the phosgenation reactor for reaction;

[0076] S4, prepare two switchable settling tanks, after the photochemical solution is quenched at 55°C, continuously input into one of the settling tanks, switch the photochemical solution pipeline after a certain time to reach the specified liquid level, and discharge the photochemical solution to the other settling tank. After 4.5h of settling separation in the settling tank, the supernatant containing isocyanate is discharged, and the lower layer of the settling slurry at the bottom is returned to the salt-forming-phosgene reactor of step S2 at a flow rate of 1.83L / h for continuous reaction.

[0077] According to the detection calculation, the yield of isocyanate in the above continuous production is 97.6%.

[0078] Example 6

[0079] A continuous production method for synthesizing isocyanate by salt-forming phosgene method is provided in this example, as shown in Figure 1 , which includes the following steps:

[0080] S1, continuously input the chlorobenzene solution of 1,5-pentanediamine (melting point ≈ 9°C) with a mass concentration of 30% and hydrogen chloride gas into a salt-forming reactor with a volume of 50L for salt-forming reaction, control the reaction temperature in the salt-forming reactor to be 30°C, the flow rate of the amine-containing solution to be 16.25L / h, the volume flow rate of hydrogen chloride gas to be 1531L / h, the molar ratio of amine to hydrogen chloride to be 1:1.3, and the residence time of the material in the salt-forming reactor to be 3h; the salt-forming liquid obtained after the salt-forming reaction contains amine hydrochloride and unreacted amine, which is continuously discharged (viscosity about 63mpa·s); according to the detection, the salt-forming rate of amine in the salt-forming reactor is 38%;

[0081] S2, continuously input the salt-forming liquid into a salt-forming-phosgene reactor with a volume of 60L for reaction with phosgene tail gas, wherein the flow rate of the salt-forming liquid is 17.55L / h, the volume flow rate of the phosgene tail gas is 11541L / h, the reaction temperature in the salt-forming-phosgene reactor is 30°C, and the residence time is 2h, to obtain a phosgene-salt-forming liquid; according to the detection, the total salt-forming rate of amine in the salt-forming reactor and the salt-forming-phosgene reactor is 88.3%, and the median particle size D50 is 11.38 microns;

[0082] S3, continuously input the phosgene-salt-forming liquid into a phosgene reactor with a volume of 150L for phosgenation reaction with fresh phosgene, control the flow rate of the phosgene-salt-forming liquid to be 19.35L / h, the volume flow rate of the phosgene to be 7066L / h, the molar ratio of amine in the amine-containing solution to the phosgene to be 1:6, the reaction temperature in the phosgene reactor to be 80°C, and the residence time of the material to be 4h; the obtained phosgene liquid is continuously discharged, and the phosgene tail gas is returned to step S2; a condensing device with cooling medium at -20°C is arranged at the outlet of the phosgene tail gas to make most of the phosgene in the phosgene tail gas return to the phosgene reactor for reaction;

[0083] S4, prepare two switchable settling tanks, after the photochemical solution is quenched at 55℃, continuously input into one of the settling tanks, switch the photochemical solution pipeline after a certain time to reach the specified liquid level, so that the photochemical solution is discharged to the other settling tank. After 4.5h of settling separation in the settling tank, the supernatant containing isocyanate is discharged, and the lower layer of the settling slurry at the bottom is returned to the salt-forming-photoreactor of step S2 at a flow rate of 0.93L / h for continuous reaction.

[0084] According to the detection calculation, the yield of isocyanate in the above continuous production is 98.9%.

[0085] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A continuous process for the synthesis of isocyanates by salt-forming phosgene method, characterized in that, The method comprises the following steps: S1, continuously feeding an amine-containing solution and hydrogen chloride into a salting kettle to perform a salting reaction, so that part of the amine in the amine-containing solution is salified to obtain a salting solution containing amine hydrochloride and unreacted amine, and the salting solution is continuously discharged; S2, continuously feeding the salting solution into a salting-photolysis kettle to react with photolysis tail gas, so that the unreacted amine is salified, and the amine hydrochloride is preliminarily photolyzed to obtain a photolysis-salting solution, and the photolysis-salting solution is continuously discharged; S3, continuously feeding the photolysis-salting solution and phosgene into a photolysis kettle to perform a phosgenation reaction to obtain a photolysis solution and the photolysis tail gas, and returning the photolysis tail gas to the salting-photolysis kettle; S4, performing a sedimentation separation on the photolysis solution to obtain an isocyanate; The amine in the amine-containing solution is one or more of toluene diamine, 1,6-hexanediamine, 1,5-pentanediamine, isophorone diamine, p-phenylenediamine, 1,5-naphthalenediamine, and diphenylmethane diamine; The mass concentration of the amine-containing solution is 10-40%, and the solvent is one or more of chlorobenzene, dichlorobenzene, and toluene; In step S1, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.3-1.

8.

2. The continuous production process for the synthesis of isocyanates by the salt-forming phosgene method according to claim 1, characterized in that, In step S1, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.6-1.

2.

3. The continuous production method of synthesizing an isocyanate by a salting phosgenation method according to claim 2, characterized in that, when the melting point of the amine in the amine-containing solution is higher than 80℃, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.9-1.2; when the melting point of the amine in the amine-containing solution is lower than 80℃, the molar ratio of the amine in the amine-containing solution to hydrogen chloride is 1:0.6-0.9; when the melting point of the amine in the amine-containing solution is higher than 80℃, the reaction temperature in the salting kettle is 60-130℃; when the melting point of the amine in the amine-containing solution is lower than 80℃, the reaction temperature in the salting kettle is 0-60℃; The residence time of the amine-containing solution in the salting kettle is 0.5-2h.

4. The continuous production method of synthesizing an isocyanate by a salting phosgenation method according to claim 3, characterized in that, when the melting point of the amine in the amine-containing solution is higher than 80℃, the reaction temperature in the salting kettle is 80-100℃; when the melting point of the amine in the amine-containing solution is lower than 80℃, the reaction temperature in the salting kettle is 0-30℃.

5. The continuous production method of synthesizing an isocyanate by a salting phosgenation method according to claim 3, characterized in that, when the melting point of the amine in the amine-containing solution is higher than 80℃, the residence time of the amine-containing solution in the salting kettle is 1.2-2h; when the melting point of the amine in the amine-containing solution is lower than 80℃, the residence time of the amine-containing solution in the salting kettle is 0.5-1.2h.

6. The continuous production process of isocyanate by salt-forming phosgene method according to claim 1 or 2, characterized in that, The molar ratio of the amine in the amine-containing solution to the phosgene fed in step S3 is 1:2-10.

7. The continuous production process of isocyanate by salt-forming phosgene method according to claim 6, characterized in that, The molar ratio of the amine in the amine-containing solution to the phosgene fed in step S3 is 1:3-6.

8. The continuous production process of isocyanate by salt-forming phosgene method according to claim 1 or 2, characterized in that, In step S4, the photochemical liquid is subjected to the sedimentation separation in a sedimentation kettle, and the supernatant obtained is the isocyanate; the sedimentation separation also obtains a lower sedimentation slurry at the bottom of the sedimentation kettle, and the method further comprises: The lower sedimentation slurry is returned to step S2 and introduced into the salt-formation and photochemical kettle to participate in the reaction.

9. The continuous production process of isocyanate by salt-forming phosgene method according to claim 8, characterized in that, The volume flow rate ratio of the introduction of the salt-formation liquid to the returned lower sedimentation slurry is 1:0.05-0.

1.

10. The continuous production method for synthesizing isocyanate by salt-formation and phosgene method according to claim 1 or 2, characterized in that, In step S2, the reaction temperature in the salt-formation and photochemical kettle is 30-130°C; and / or, In step S3, the reaction temperature in the photochemical kettle is 80-170°C; and / or, The residence time of the material in the salt-formation and photochemical kettle is 0.5-2h; and / or, The residence time of the material in the photochemical kettle is 2-10h; and / or, The time for the sedimentation separation is 3-8h.

11. The continuous production method for synthesizing isocyanate by salt-formation and phosgene method according to claim 10, characterized in that, In step S2, the reaction temperature in the salt-formation and photochemical kettle is 40-80°C; In step S3, the reaction temperature in the photochemical kettle is 110-160°C.

12. The continuous production process of isocyanate by salt-forming phosgene method according to claim 1 or 2, characterized in that, The photochemical kettle is provided with a photochemical tail gas outlet, and the photochemical tail gas outlet is provided with a condensation reflux device, and the temperature of the condensing medium is -30-5°C.

13. The continuous production process of isocyanate by salt-forming phosgene method according to claim 1 or 2, characterized in that, Before the photochemical liquid is subjected to the sedimentation separation, step S4 further comprises pre-quenching the photochemical liquid.

14. The continuous production process for the synthesis of isocyanates by the salt-forming phosgene method according to claim 13, characterized in that, The temperature for the quenching is 20-80°C.

15. The continuous production process for the synthesis of isocyanates by the salt-forming phosgene method according to claim 14, characterized in that, The temperature for the quenching is 40-60°C.

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