A process for the preparation of isocyanates

Abstract

The present application belongs to the technical field of preparing isocyanate, and particularly relates to a method for preparing isocyanate, comprising: 1) mixing a polyamine solution with a phosgene solution and performing a cold phosgenation reaction, and a gas-liquid-solid three-phase mixture A is generated by the reaction; 2) controlling the process conditions of the cold reaction process in stages: the mixture A is subjected to a first stage reaction, and the cold phosgenation reaction is mainly used, the cold reaction process is 50-99.9%, the hot reaction process is 0-30%, and product B is obtained; then the product B is subjected to a second stage reaction, and a mixture of phosgene and hydrogen chloride is introduced into the system at the same time; in the second stage reaction, the cold reaction process is 90-99.9%, and the hot reaction process is 3-40%; and reaction product C is obtained; 3) introducing the reaction product C into a hot reactor, and the product D obtained by the hot reaction is introduced into a refining system for refining. The method of the present application reduces the loss of L color and the generation of impurities caused by the hot reaction at high temperature, and high-quality isocyanate is obtained.

Description

Technical Field

[0001] This invention belongs to the technical field of isocyanate preparation, and particularly relates to a method for preparing isocyanates, especially a method for preparing diisocyanates. Background Technology

[0002] Polyurethane, hailed as the world's "fifth largest plastic," is widely used in aerospace, defense, construction, petrochemicals, and medical and health fields, among others. Isocyanate is the core raw material for polyurethane production, and the mainstream industrial synthesis method is currently phosgenation. Phosgenated isocyanate, as an organic reaction intermediate, is widely used in various industries such as industry, agriculture, construction, automotive, and insulation because it can be further synthesized into polyisocyanates, polyurethanes, polyureas, and spandex.

[0003] Currently, the mainstream industrial method for synthesizing isocyanates is the phosgenation method, which is based on the fact that the reaction process is divided into two stages: cold and hot. The principle is as follows:

[0004] Cold reaction stage:

[0005] RNH2 + COCl2 → RNHCOCl (carbamoyl chloride) + HCl;

[0006] RNH2 + HCl → RNH2·HCl (amino hydrochloride).

[0007] Thermal reaction stage:

[0008] RNHCOCl→RNCO+HCl;

[0009] RNH2·HCl+COCl2→RNCO+3HCl.

[0010] The cold reaction stage is relatively fast and the reaction is completed quickly; however, the hot reaction stage is characterized by the following side reactions:

[0011] RNH2·HCl→RNH2+HCl;

[0012] RNH2+RNCO→RNHCONHR (urea).

[0013] In the presence of phosgene, the higher the heating temperature, the more adducts carbodiimide and phosgene form. If HCl is not added, the adduct will decompose upon heating to form dichloroimide, resulting in a deterioration of the product's color.

[0014] The presence of byproducts such as urea, hydrochloride groups, and acyl chloride groups can significantly impact product quality and color grade. Currently, the industry primarily addresses this by controlling the amount of solvent or phosgene consumed to maintain product quality.

[0015] Chinese patent document CN1651406A discloses a tubular reactor that enhances the mixing effect at the front end of the tube through stirring in order to improve product quality, but cannot eliminate the side reactions at the back end.

[0016] Chinese patent document CN112724044B discloses a method for generating and preparing isocyanates, which mainly targets gas-phase phosgenation reactions, but does not provide guidance for liquid-phase phosgenation processes.

[0017] Chinese patent document CN 218962652U discloses a tubular reactor for producing isocyanates, which enhances the reaction through multi-stage diameter changes. However, impurities tend to accumulate at the diameter changes, affecting the operating cycle of the device.

[0018] Chinese patent document CN 102317255B improves L color by controlling the CO excess rate to an extremely low level during the production of phosgene; however, there is a high risk of overchlorination.

[0019] Patent document WO2021122625 A1 discloses the use of HCl stripping process to improve L color. Although it can improve color, it mainly targets the desolventizing process and has no significant effect on the color loss caused by the phosgenation reaction process.

[0020] From the perspective of existing technologies, the phosgenation stage of liquid-phase phosgenation reactions mainly addresses the problem of impurity generation through high phosgene and high solvent volumes, which suffers from drawbacks such as high operating costs and complex operation. Furthermore, existing reaction enhancement technologies primarily focus on the initial injection process of cold reactions, with insufficient understanding and exploration of the subsequent reaction processes.

[0021] Therefore, for the liquid phase phosgenation process, it is necessary to fundamentally avoid the generation of impurities such as urea in order to further improve product quality and reduce operating costs. Summary of the Invention

[0022] To address the aforementioned problems, the present invention aims to provide a method for preparing isocyanates with low color number and low impurity content. By controlling parameters such as reactor temperature, pressure, and residence time, the process conditions of the cold reaction can be controlled in stages, effectively reducing the generation of impurities. Furthermore, by enhancing the cold reaction, the loss of L color and the generation of impurities caused by the thermal reaction under high temperature conditions are reduced, resulting in high-quality isocyanates and reducing production costs to a certain extent.

[0023] To achieve the above objectives, the present invention provides the following technical solution:

[0024] A method for preparing isocyanates includes the following steps:

[0025] 1) Mix the polyamine solution with the phosgene solution and carry out a cold phosgene reaction to generate a gas-liquid-solid three-phase mixture A;

[0026] 2) As the cold reaction proceeds, the process conditions of the cold reaction are controlled in stages: The gas-liquid-solid three-phase mixture A undergoes a first-stage reaction, which is dominated by cold phosgenation, with a cold reaction progress of 50-99.9% and a hot reaction progress of 0-30%, converting amines into acyl chlorides as much as possible to obtain product B; then product B undergoes a second-stage reaction, while a mixture of phosgene and hydrogen chloride is introduced into the reaction system; in the second-stage reaction, the hot phosgenation gradually becomes dominant, with a cold reaction progress of 90-99.9% and a hot reaction progress of 3-40%; after the reaction, product C is obtained;

[0027] 3) The reaction product C obtained in step 2) is subjected to a thermal reaction (i.e., acyl chloride decomposition reaction). The product D obtained from the thermal reaction is then fed into the purification system for further purification and processing, and finally high-quality isocyanate is obtained.

[0028] In step 2) of this invention, the first stage reaction is mainly a cold reaction. By controlling the mixing effect, solvent ratio, phosgene ratio, reaction pressure, reaction temperature and other process parameters of the reactor used in the first stage, the amines are converted into acyl chlorides as much as possible. As the cold reaction process in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually takes the lead. By controlling the reaction pressure, reaction temperature and the amount of COCl2 / HCl mixture introduced in the second stage, the hot reaction process is enhanced while the impact of the simultaneous cold and hot reactions on the color and impurity generation is reduced.

[0029] In some embodiments of the method provided by the present invention, the isocyanate is a diisocyanate or a polyisocyanate, preferably a diisocyanate, more preferably selected from one or more of diphenylmethylene diisocyanate (MDI), polydiphenylmethylene diisocyanate (PMDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).

[0030] According to the method provided by the present invention, in some embodiments, in step 1), the cold photogasification reaction is carried out in a dynamic reactor. The reaction process in step 1) is relatively rapid, and its reaction conditions will not be described in detail.

[0031] In this paper, polyamines and solvents can be mixed in a static mixer to form a polyamine solution.

[0032] In some implementations, in step 1), the mass ratio of the polyamine in the polyamine solution to the phosgene in the phosgene solution is 1:(1.5-8), for example, 1:1.8, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.5, 1:4, 1:4.5, preferably 1:(2-5).

[0033] In some embodiments, the phosgene content in the phosgene solution is 40-99%, for example, 45%, 50%, 60%, 80%, 90%, or 95%.

[0034] In some embodiments, the solvent in the polyamine solution may be the same as or different from the solvent in the phosgene solution, and is selected from one or more of chlorobenzene, dichlorobenzene, toluene, and dimethyl carbonate, preferably selected from chlorobenzene and / or dichlorobenzene.

[0035] In some embodiments, the mass ratio of the polyamine to the solvent in the polyamine solution is 1:(1.5-6), for example, 1:1.6, 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, 1:3.5, 1:4, 1:5, 1:5.5, preferably 1:(1.8-4.5).

[0036] In some embodiments, the polyamine is a diamine, preferably one or more of diaminodiphenylmethane (MDA), polydiaminodiphenylmethane (DAM), diaminotoluene (TDA), hexamethylenediamine (HDA), and isophorone diamine (IPDA). In this document, the polyamine can be understood to include a diamine.

[0037] In some implementations, in step 2), the process conditions for the first-stage reaction include: a reaction temperature of 50-140°C (e.g., 60°C, 80°C, 100°C, 102°C, 110°C, 120°C, 130°C, 135°C), a reaction pressure of 1-40 barg (e.g., 2 barg, 5 barg, 10 barg, 15 barg, 18 barg, 20 barg, 25 barg, 30 barg, 38 barg), a cold reaction progress of 50-99.9% (e.g., 55%, 60%, 70%, 80%, 90%, 95%, 99%, 99.1%, 99.2%, 99.5%), and a hot reaction progress of 0-30% (e.g., 1%, 2%, 4%, 5%, 6%, 8%, 10%, 15%, 20%, 25%, 28%).

[0038] Preferably, the process conditions for the first stage reaction include: a reaction temperature of 70-130°C, a reaction pressure of 8-35 barg, a cold reaction rate of 90-99.9%, and a hot reaction rate of 0-10%.

[0039] In some implementations, in step 2), the process conditions for the second-stage reaction include: a reaction temperature of 80-140°C (e.g., 85°C, 90°C, 92°C, 100°C, 102°C, 110°C, 120°C, 135°C), a reaction pressure of 3-40 barg (e.g., 4 barg, 5 barg, 8 barg, 10 barg, 12 barg, 15 barg, 20 barg, 25 barg, 35 barg, 38 barg), a cold reaction progress of 90-99.9% (e.g., 91%, 92%, 94%, 96%, 98%, 99%, 99.5%), and a hot reaction progress of 3-40% (e.g., 4%, 5%, 6%, 8%, 10%, 15%, 20%, 25%, 30%, 32%, 34%, 35%, 38%).

[0040] Preferably, the process conditions for the second-stage reaction include: a reaction temperature of 80-130°C, a reaction pressure of 3-30 barg, a cold reaction rate of 95-99.9%, and a hot reaction rate of 10-40%.

[0041] In this paper, the control of the cold reaction process and the hot reaction process in the first and second stages of step 2) can be achieved based on the test results of relevant parameters; for example, the control of the cold reaction process and the hot reaction process can be achieved by testing parameters such as load, solvent ratio, phosgene ratio, and reactor pressure through industry-known testing methods.

[0042] In some implementations, both the first and second stages of the cold reaction in step 2) are carried out in a tubular reactor. For example, the first stage reaction is carried out in a first tubular reactor, and the second stage reaction is carried out in a second tubular reactor.

[0043] In some implementations, the first and second stages of the cold reaction in step 2) are carried out independently.

[0044] To further utilize the pressure change energy and enhance the reaction process in the first and second stage reactions of step 2), the phosgene / HCl mixture can be effectively introduced into the reaction system through components such as static injectors, orifice plates, regulating valves, and variable diameter structures to enhance the reaction and reduce the generation of side reactions.

[0045] In some implementation schemes, in step 2), a mixture of phosgene and hydrogen chloride is introduced into the reaction system by means of a static injector, orifice plate, regulating valve, or variable diameter structure. For example, the first stage reaction is carried out in a first tubular reactor, and the second stage reaction is carried out in a second tubular reactor, with components such as a static injector, orifice plate, regulating valve, and variable diameter structure installed between the first and second tubular reactors.

[0046] In some embodiments, in step 2), the total mass ratio of the polyamine to the mixture of phosgene and hydrogen chloride is 1:(0.01-0.15), for example, 1:0.02, 1:0.03, 1:0.035, 1:0.04, 1:0.06, 1:0.08, 1:0.11, 1:0.12, 1:0.14, preferably 1:(0.05-0.1).

[0047] In some embodiments, the mass ratio of COCl2 to HCl in the mixture of phosgene and hydrogen chloride is 1:(0.001-0.8), for example, 1:0.002, 1:0.004, 1:0.006, 1:0.008, 1:0.01, 1:0.02, 1:0.04, 1:0.06, 1:0.08, 1:0.1, 1:0.2, 1:0.4, 1:0.5, 1:0.6, preferably 1:(0.005-0.7).

[0048] In step 2), the mixture of phosgene and hydrogen chloride introduced can be derived from HCl purification gas, phosgene solution, thermal reactor tail gas, etc., which are known in the industry, and there are no restrictions on its source.

[0049] In step 3), the further thermal reaction and refining post-treatment processes can all be achieved using known industry processes.

[0050] For example, the thermal reaction process in step 3) can be found in patent literature (such as CN 114749116A).

[0051] For example, the post-refining process in step 3) can be referred to in patent literature (such as CN 115925581A). In some embodiments, optionally, the gas phase generated by the thermal reaction in step 3) is condensed and then absorbed and reused in a phosgene absorption tower (the condensate is returned to the thermophosgene reactor). Optionally, the liquid phase generated by the thermal reaction is introduced into a phosgene removal tower to remove phosgene and hydrogen chloride. The bottom temperature of the phosgene removal tower can be 130°C, and the top pressure can be 0.2 barG. The gas phase at the top of the phosgene removal tower is first condensed and then pressurized before being sent to the bottom of the phosgene absorption tower (the condensate is returned to the phosgene removal tower). Chlorobenzene is introduced into the top of the phosgene absorption tower and comes into countercurrent contact with the gas phase phosgene to absorb and generate a phosgene solution. The bottom temperature of the phosgene absorption tower can be -5°C, and the top pressure can be 3 barG. The liquid phase after phosgene removal enters the solvent removal tower for solvent removal, or the liquid phase generated by the thermal reaction directly enters the solvent removal tower for solvent removal. The tower bottom temperature can be 145℃ to 185℃, and the tower top pressure can be -0.9 barG to -0.6 barG. The solution collected from the tower bottom is the crude MDI product.

[0052] The isocyanate products prepared by the method of this invention have a urea impurity content as low as 0.8%, even 0.05%, or even 0.01%; the L color of the isocyanate products can be above 80, even 85, or even 90. Compared with the prior art, the method of this invention effectively reduces the urea content in isocyanate products and improves the product color, which not only improves the phosgenation reaction effect but also reduces the risk of equipment scaling and clogging, and increases the stable operation cycle of the production equipment.

[0053] This invention reduces the loss of product color and the generation of impurities caused by thermal reactions under high-temperature conditions, without requiring additional moving equipment or the introduction of other substances, effectively ensuring the stability of the device operation and the applicability of the product; moreover, the process is simple, easy to operate, energy-saving, low-cost, highly efficient, and environmentally friendly.

[0054] This invention controls the temperature, pressure, residence time, and other parameters in step 2) of the reaction process, segmenting and controlling the dominant reaction in the cold reaction process, and formulates targeted enhancement measures to effectively reduce the generation of impurities during the reaction. In addition, by introducing a quantitative HCl / COCl2 mixture in the phosgenation reaction stage, and utilizing the cavitation mixing effect formed by structures such as ejectors / orifice plates, the cold reaction in step 2) is enhanced, reducing the loss of product L color and the generation of impurities caused by the hot reaction under high temperature conditions. This results in high-quality isocyanates and reduces production costs to a certain extent. Attached Figure Description

[0055] Figure 1 This is a schematic diagram of the overall process flow for some embodiments of the present invention.

[0056] The labels in the diagram are explained as follows:

[0057] 1-Static mixer; 2-Ejector reactor; 3-First tubular reactor; 4-Ejector or regulating valve with pressure regulation and cavitation function; 5-Second tubular reactor; 6-Thermal reactor (e.g., tower reactor or batch reactor); 7-Refining system. Detailed Implementation

[0058] To provide a detailed understanding of the technical features and content of this invention, preferred embodiments will be described in more detail below. While preferred embodiments are described in the examples, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer shall apply.

[0059] <Source of Raw Materials>

[0060] In the following examples and comparative examples, the sources of some reagents or raw materials used, unless otherwise specified, are all conventional products that can be purchased commercially.

[0061] <Detection Method>

[0062] NCO content in isocyanate products: determined according to GB / T2009-3-2009 method;

[0063] Analysis of urea, DAM, hydrochloride, and acyl chloride content in isocyanate products: Liquid chromatography was used. The HPLC instrument was a Shimadzu LC-20A, with a SIL-20A autosampler, a CTO-20A column oven, an SPD-M20A detector, and an ODS SP (250*4.6mm) (Inertsil) 5μm column. The specific content of each substance was determined by establishing a standard curve.

[0064] Cold reaction progress = 1 - DAM content / (hydrochloride + acyl chloride + DAM + MDI) content; wherein, the MDI content is also determined by liquid chromatography as described above;

[0065] Thermal reaction progress = MDI content / (DAM + acyl chloride + hydrochloride + MDI) content; wherein, the MDI content is also determined by liquid chromatography as described above;

[0066] L-color test: The test was performed using an integrating sphere spectrophotometer with dichloromethane as the standard.

[0067]

Example 1

[0068] The method for preparing isocyanates is as follows: Figure 1 The process flow shown includes the following steps:

[0069] (1) MDA (diphenylmethane diamine) with a flow rate of 20 t / h and a pressure of 20 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG in static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution (phosgene content in phosgene solution is 70 wt%, solvent is chlorobenzene) with a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene reaction is carried out in jet reactor 2 to obtain gas-liquid-solid three-phase mixture A;

[0070] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0071] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: reaction temperature of 110℃, reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0072] The first tubular reactor 3 and the second tubular reactor 5 are connected by an ejector 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, a mixture of phosgene and hydrogen chloride is introduced into the system through the ejector 4. In this mixture, the mass of phosgene is 500 kg / h and the mass of HCl is 200 kg / h.

[0073] The reaction conditions in the second stage include: a reaction temperature of 98℃, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction process in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage reaction, yielding reaction product C.

[0074] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a tower reactor) and heated to 135°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 185°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0075]

Example 2

[0076] The method for preparing isocyanates is as follows: Figure 1 The process flow shown includes the following steps:

[0077] (1) MDA (diphenylmethane diamine) with a flow rate of 25 t / h and a pressure of 20 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG in a static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution with a flow rate of 63 t / h and a pressure of 20 barG (phosgene content in the phosgene solution is 70 wt%, and the solvent is chlorobenzene), and a cold phosgene reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture A;

[0078] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0079] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: reaction temperature of 130℃, reaction pressure of 30 barg, cold reaction progress of 99.5%, and hot reaction progress of 8%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0080] The first tubular reactor 3 and the second tubular reactor 5 are connected by an ejector 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, a mixture of phosgene and hydrogen chloride is introduced into the system through the ejector 4. In this mixture, the mass of phosgene is 500 kg / h and the mass of HCl is 200 kg / h.

[0081] The reaction conditions in the second stage include: a reaction temperature of 102℃, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 34%. As the cold reaction process in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage reaction, yielding reaction product C.

[0082] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 140°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0083]

Example 3

[0084] The method for preparing isocyanates is as follows: Figure 1 The process flow shown includes the following steps:

[0085] (1) MDA (diphenylmethane diamine) with a flow rate of 10 t / h and a pressure of 30 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 30 barG in static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution with a flow rate of 63 t / h and a pressure of 25 barG (phosgene content in phosgene solution is 70 wt%, solvent is chlorobenzene) and carried out in jet reactor 2 for cold phosgene reaction to obtain gas-liquid-solid three-phase mixture A;

[0086] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0087] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: reaction temperature of 102℃, reaction pressure of 22 barg, cold reaction progress of 99.3%, and hot reaction progress of 6%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0088] The first tubular reactor 3 and the second tubular reactor 5 are connected by a regulating valve 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, a mixture of phosgene and hydrogen chloride is introduced into the system through the regulating valve 4. In this mixture, the mass of phosgene is 800 kg / h and the mass of HCl is 300 kg / h.

[0089] The reaction conditions in the second stage include: a reaction temperature of 100℃, a reaction pressure of 12 barg, a cold reaction rate of 99.9%, and a hot reaction rate of 25%. As the cold reaction in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage, yielding reaction product C.

[0090] (3) The reaction liquid (i.e., reaction product C) obtained in the second stage of the reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 130°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.65 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0091]

Example 4

[0092] The method for preparing isocyanates is as follows: Figure 1 The process flow shown includes the following steps:

[0093] (1) MDA (diphenylmethane diamine) with a flow rate of 40 t / h and a pressure of 25 barG is mixed with chlorobenzene with a flow rate of 80 t / h and a pressure of 25 barG in a static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution (phosgene content in the phosgene solution is 65 wt%, and the solvent is chlorobenzene) with a flow rate of 130 t / h and a pressure of 25 barG, and a cold phosgene reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture A;

[0094] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0095] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: a reaction temperature of 107℃, a reaction pressure of 22 barg, a cold reaction progress of 99.5%, and a hot reaction progress of 8%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0096] The first tubular reactor 3 and the second tubular reactor 5 are connected by a regulating valve 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, a mixture of phosgene and hydrogen chloride is introduced into the system through the regulating valve 4. In this mixture, the mass of phosgene is 600 kg / h and the mass of HCl is 400 kg / h.

[0097] The reaction conditions in the second stage include: a reaction temperature of 92℃, a reaction pressure of 8 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 23%. As the cold reaction process in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage reaction, yielding reaction product C.

[0098] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 140°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0099] Comparative Example 1

[0100] For the method of preparing isocyanates, refer to Figure 1 The process flow shown includes the following steps:

[0101] (1) MDA (diphenylmethane diamine) with a flow rate of 20 t / h and a pressure of 20 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG in static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution (phosgene content in phosgene solution is 70 wt%, solvent is chlorobenzene) with a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene reaction is carried out in jet reactor 2 to obtain gas-liquid-solid three-phase mixture A;

[0102] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0103] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: reaction temperature of 110℃, reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0104] The first tubular reactor 3 is connected to the second tubular reactor 5. After product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. The reaction conditions of the second stage include: reaction temperature 200℃, reaction pressure 10 barg, cold reaction progress 99.8%, and hot reaction progress 30%. As the cold reaction process of the first stage continues to advance, the reaction temperature in the system continues to rise. In the second stage reaction, the hot reaction gradually dominates, and reaction product C is obtained.

[0105] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 140°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0106] Comparative Example 2

[0107] For the method of preparing isocyanates, refer to Figure 1 The process flow shown includes the following steps:

[0108] (1) MDA (diphenylmethane diamine) with a flow rate of 20 t / h and a pressure of 20 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG in static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution (phosgene content in phosgene solution is 70 wt%, solvent is chlorobenzene) with a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene reaction is carried out in jet reactor 2 to obtain gas-liquid-solid three-phase mixture A;

[0109] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0110] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: reaction temperature of 110℃, reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0111] The first tubular reactor 3 and the second tubular reactor 5 are connected by an ejector 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, phosgene is introduced into the system through the ejector 4, and the mass of the introduced phosgene is 200 kg / h.

[0112] The reaction conditions in the second stage include: a reaction temperature of 98℃, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction process in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage reaction, yielding reaction product C.

[0113] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 140°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0114] Comparative Example 3

[0115] For the method of preparing isocyanates, refer to Figure 1 The process flow shown includes the following steps:

[0116] (1) MDA (diphenylmethane diamine) with a flow rate of 20 t / h and a pressure of 20 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG in static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution (phosgene content in phosgene solution is 70 wt%, solvent is chlorobenzene) with a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene reaction is carried out in jet reactor 2 to obtain gas-liquid-solid three-phase mixture A;

[0117] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0118] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: reaction temperature of 110℃, reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0119] The first tubular reactor 3 and the second tubular reactor 5 are connected by an ejector 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, HCl is introduced into the system through the ejector 4, and the mass of HCl introduced is 200 kg / h.

[0120] The reaction conditions in the second stage include: a reaction temperature of 98℃, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction process in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage reaction, yielding reaction product C.

[0121] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 140°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0122] Comparative Example 4

[0123] For the method of preparing isocyanates, refer to Figure 1 The process flow shown includes the following steps:

[0124] (1) MDA (diphenylmethane diamine) with a flow rate of 20 t / h and a pressure of 20 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG in static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution (phosgene content of 70 wt% and solvent of chlorobenzene) with a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene reaction is carried out in jet reactor 2 to obtain gas-liquid-solid three-phase mixture A;

[0125] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0126] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: reaction temperature of 110℃, reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%. The first stage is mainly a cold reaction, which aims to convert amines into acyl chlorides as much as possible to obtain product B.

[0127] The first tubular reactor 3 and the second tubular reactor 5 are connected by an ejector 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, a mixture of phosgene and hydrogen chloride is introduced into the system through the ejector 4. In this mixture, the mass of phosgene is 200 kg / h and the mass of HCl is 200 kg / h.

[0128] The reaction conditions in the second stage include: a reaction temperature of 98℃, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction process in the first stage continues to advance, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage reaction, yielding reaction product C.

[0129] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 140°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0130] Comparative Example 5

[0131] For the method of preparing isocyanates, refer to Figure 1 The process flow shown includes the following steps:

[0132] (1) MDA (diphenylmethane diamine) with a flow rate of 20 t / h and a pressure of 35 barG is mixed with chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG in a static mixer 1 to form a polyamine solution; then it is mixed with phosgene solution with a flow rate of 40 t / h and a pressure of 20 barG (phosgene content in the phosgene solution is 70 wt%, and the solvent is chlorobenzene), and a cold phosgene reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture A;

[0133] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0134] The gas-liquid-solid three-phase mixture A is fed into the first tubular reactor 3 for the first stage reaction. The first stage reaction conditions include: a reaction temperature of 140℃, a reaction pressure of 30 barg, a cold reaction progress of 99.2%, and a hot reaction progress of 25%. After the first stage reaction, product B is obtained.

[0135] The first tubular reactor 3 and the second tubular reactor 5 are connected by an ejector 4. After the product B is discharged from the first tubular reactor 3, it enters the second tubular reactor 5 for the second stage reaction. At the same time, a mixture of phosgene and hydrogen chloride is introduced into the system through the ejector 4. In this mixture, the mass of phosgene is 200 kg / h and the mass of HCl is 200 kg / h.

[0136] The second-stage reaction conditions include: a reaction temperature of 125℃, a reaction pressure of 20 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 45%. After the second-stage reaction, reaction product C is obtained.

[0137] (3) The reaction liquid (i.e. reaction product C) obtained in the second stage reaction in step 2) is passed into the thermal reactor 6 (such as a batch reactor) and heated to 140°C for thermal reaction. The product D obtained from the thermal reaction is then sent to the purification system 7 (such as a desolventizing tower) for purification. The bottom temperature of the desolventizing tower is 180°C and the top pressure is 0.6 barg. After removing phosgene and chlorobenzene, isocyanate product is obtained.

[0138] Table 1. Performance test results of the products obtained from each embodiment and comparative example.

[0139] Product Categories Urea content NCO content L color Equipment operation cycle Example 1 MDI 0.3％ 32.3％ 89 36 months Example 2 MDI 0.4％ 32.1％ 87 33 months Example 3 MDI 0.28％ 32.3％ 90 37 months Example 4 MDI 0.32％ 32.2％ 88 36 months Comparative Example 1 MDI 1.2％ 31.7％ 75 15 months Comparative Example 2 MDI 1.0％ 31.9％ 77 21 Comparative Example 3 MDI 1.1％ 31.8％ 78 September Comparative Example 4 MDI 0.8％ 32％ 80 February Comparative Example 5 MDI 1.3％ 31.6％ 73 December

[0140] Note: The determination of the device's operating cycle can be achieved through conventional testing operations in this field; for example, if the temperature of the reactor cannot be maintained at the target temperature even with the steam valve of the thermal reactor fully open, then the operating cycle has been reached.

[0141] As can be seen from the test results in Table 1, the urea impurity content in the isocyanate products prepared in Examples 1-4 is 0.4% or less, the L color is above 86, and the operating cycle of the device is maintained at more than 36 months.

[0142] Compared with the examples, the comparative example did not introduce a mixture of phosgene and hydrogen chloride in step 2), or the ratio of phosgene to hydrogen chloride in the mixture was not within a reasonable range, or the thermal reaction process in the first and second stages was too high, all of which would have an adverse effect on the content of urea impurities in the product, the L color, and the operating cycle of the device.

[0143] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the spirit of the invention.

Claims

1. A method for preparing isocyanate, characterized in that, Includes the following steps: 1) Mix the polyamine solution with the phosgene solution and carry out a cold phosgene reaction to generate a gas-liquid-solid three-phase mixture A; 2) As the cold reaction proceeds, the process conditions of the cold reaction are controlled in stages: The gas-liquid-solid three-phase mixture A undergoes a first-stage reaction, which is dominated by cold phosgenation, with a cold reaction progress of 50-99.9% and a hot reaction progress of 0-30%, converting amines into acyl chlorides as much as possible to obtain product B; then product B undergoes a second-stage reaction, while a mixture of phosgene and hydrogen chloride is introduced into the reaction system; in the second-stage reaction, the hot phosgenation gradually becomes dominant, with a cold reaction progress of 90-99.9% and a hot reaction progress of 3-40%; after the reaction, reaction product C is obtained; In the mixture of phosgene and hydrogen chloride, the mass ratio of COCl2 to HCl is 1:(0.001-0.8). 3) The reaction product C obtained in step 2) is subjected to thermal reaction, and the product D obtained from the thermal reaction is then fed into the purification system for further purification and processing, finally obtaining high-quality isocyanate.

2. The method according to claim 1, characterized in that, The isocyanate is a diisocyanate or a polyisocyanate.

3. The method according to claim 1, characterized in that, The isocyanate is a diisocyanate.

4. The method according to claim 1, characterized in that, The isocyanate is selected from one or more of diphenylmethylene diisocyanate, polydiphenylmethylene diisocyanate, toluene diisocyanate, hexamethylene diisocyanate, and isophorone diisocyanate.

5. The method according to claim 1, characterized in that, In step 1), the cold photogasification reaction is carried out in a dynamic reactor.

6. The method according to claim 1, characterized in that, In step 1), the mass ratio of polyamine in the polyamine solution to phosgene in the phosgene solution is 1:(1.5-8).

7. The method according to claim 1, characterized in that, In step 1), the mass ratio of the polyamine in the polyamine solution to the phosgene in the phosgene solution is 1:(2-5).

8. The method according to claim 1, characterized in that, The phosgene solution contains 40-99% phosgene.

9. The method according to claim 1, characterized in that, The solvent in the polyamine solution may be the same as or different from the solvent in the phosgene solution, and may be selected from one or more of chlorobenzene, dichlorobenzene, toluene, and dimethyl carbonate.

10. The method according to claim 1, characterized in that, The solvent in the polyamine solution may be the same as or different from the solvent in the phosgene solution, and may be selected from chlorobenzene and / or dichlorobenzene.

11. The method according to claim 1, characterized in that, In the polyamine solution, the mass ratio of polyamine to solvent is 1:(1.5-6).

12. The method according to claim 1, characterized in that, In the polyamine solution, the mass ratio of polyamine to solvent is 1:(1.8-4.5).

13. The method according to claim 1, characterized in that, The polyamine is a diamine.

14. The method according to claim 1, characterized in that, The polyamine is one or more of diaminodiphenylmethane, polydiaminodiphenylmethane, diaminotoluene, hexamethylenediamine, and isophoronediamine.

15. The method according to any one of claims 1-14, characterized in that, In step 2), the process conditions for the first stage reaction include: reaction temperature of 50-140℃, reaction pressure of 1-40 barg, cold reaction progress of 50-99.9%, and hot reaction progress of 0-30%.

16. The method according to claim 15, characterized in that, In step 2), the process conditions for the first stage reaction include: reaction temperature of 70-130℃, reaction pressure of 8-35 barg, cold reaction progress of 90-99.9%, and hot reaction progress of 0-10%.

17. The method according to any one of claims 1-14, characterized in that, In step 2), the process conditions for the second stage reaction include: reaction temperature of 80-140℃, reaction pressure of 3-40 barg, cold reaction progress of 90-99.9%, and hot reaction progress of 3-40%.

18. The method according to claim 17, characterized in that, In step 2), the process conditions for the second stage reaction include: reaction temperature of 80-130℃, reaction pressure of 3-30 barg, cold reaction progress of 95-99.9%, and hot reaction progress of 10-40%.

19. The method according to any one of claims 1-14, 16, and 18, characterized in that, Step 2) The first and second stages of the intermediate cooling reaction are both carried out in a tubular reactor.

20. The method according to any one of claims 1-14, 16, and 18, characterized in that, In step 2), the first and second stages of the cold reaction are carried out independently.

21. The method according to any one of claims 1-14, 16, and 18, characterized in that, In step 2), a mixture of phosgene and hydrogen chloride is introduced into the reaction system by setting up a static injector, orifice plate, regulating valve, and variable diameter structure.

22. The method according to any one of claims 1-14, 16, and 18, characterized in that, In step 2), the total mass ratio of the polyamine to the mixture of phosgene and hydrogen chloride is 1:(0.01-0.15).

23. The method according to claim 22, characterized in that, In step 2), the total mass ratio of the polyamine to the mixture of phosgene and hydrogen chloride is 1:(0.05-0.1).

24. The method according to any one of claims 1-14, 16, 18, and 23, characterized in that, In the mixture of phosgene and hydrogen chloride, the mass ratio of COCl2 to HCl is 1:(0.005-0.7).

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