Method for preparing isocyanate

Abstract

The invention belongs to the technical field of preparation of isocyanate, and particularly relates to a method for preparing isocyanate, which comprises the following steps: 1) mixing a polyamine solution and a phosgene solution, and carrying out cold phosgenation reaction to generate a gas-liquid-solid three-phase mixed material A; 2) controlling the process conditions of a cold reaction process in a segmented manner: performing a first-stage reaction on the mixed material A, mainly performing cold phosgenation reaction, with the cold reaction process being 50-99.9% and the thermal reaction process being 0-30%, so as to obtain a product B; carrying out second-stage reaction on the product B, and introducing a mixture of phosgene and hydrogen chloride into the system; in the second-stage reaction, the cold reaction process is 90-99.9%, and the thermal reaction process is 3-40%; a reaction product C is obtained; and 3) introducing the reaction product C into a thermal reactor, and refining a product D obtained by thermal reaction in a refining system. According to the method disclosed by the invention, L color loss and impurity generation caused by thermal reaction at high temperature are reduced, and high-quality isocyanate is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of preparing isocyanates, and in particular relates to a method for preparing isocyanates, in particular to a method for preparing diisocyanates. Background Art

[0002] Polyurethane is known as the world's "fifth largest plastic" and is widely used in aerospace, national defense, construction, petrochemicals, medical and health care and other fields involving international life. Isocyanate is the core raw material for the preparation of polyurethane. The mainstream synthesis method currently used in industry is phosgenation. As an organic reaction intermediate, phosgenated isocyanate can be further synthesized into polyisocyanate, polyurethane, polyurea, spandex and other materials, and is widely used in various industries such as industry, agriculture, construction, automobile, and thermal insulation.

[0003] At present, the mainstream isocyanate synthesis method in industry is the phosgenation method, the core of which is 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] Among them, the cold reaction stage has a faster reaction speed and reacts quickly and completely; while in the hot reaction stage, the following side reactions are prominent:

[0011] RNH2·HCl→RNH2+HCl;

[0012] RNH2+RNCO→RNHCONHR (urea).

[0013] When phosgene is present, the higher the heating temperature, the more carbodiimide and phosgene adducts are produced. If HCl is not added, the adducts will decompose under heat to form dichloroimide, causing the color of the product to deteriorate.

[0014] The presence of by-products such as urea, hydrochloride groups, and acyl chloride groups will have a significant impact on product quality and color. In this regard, the industry currently mainly controls product quality by using excessive solvent or phosgene consumption.

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

[0016] Chinese patent document CN112724044B discloses a method for producing isocyanate, which is mainly aimed at gas phase phosgenation reaction, but has no guiding role for liquid phase phosgenation process.

[0017] Chinese patent document CN 218962652U discloses a tubular reactor for producing isocyanate, which strengthens the reaction effect by multi-stage diameter change, but impurities tend to accumulate at the diameter change, affecting the operation cycle of the device.

[0018] Chinese patent document CN 102317255B improves L color by controlling the CO excess rate at an extremely low level during the production of phosgene, but 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 achieve the purpose of improving chromaticity, it mainly targets the desolventizing process and has no obvious effect on the chromaticity loss caused by the phosgenation reaction process.

[0020] From the existing technology, the phosgenation stage of the liquid phase phosgenation reaction mainly solves the problem of impurity generation by using high phosgene and high solvent amounts, which has the disadvantages of high operating costs and complex operations. At the same time, the existing reaction intensification technology mainly focuses on the initial injection process of the cold reaction, and the understanding and exploration of the back-end reaction process of the cold reaction is insufficient.

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

[0022] In order to solve the above problems, the purpose of the present invention is to provide a method for preparing isocyanate with low color number and low impurity content. By controlling the temperature, pressure, residence time and other parameters of the reactor, the process conditions of the cold reaction process can be controlled in stages, effectively reducing the generation of impurities; and by strengthening the cold reaction, the color loss and impurity generation caused by the thermal reaction under high temperature conditions are reduced, high-quality isocyanate is obtained, and the production cost is reduced to a certain extent.

[0023] In order to achieve the above object, the present invention provides the following technical solutions:

[0024] A method for preparing isocyanate comprises the following steps:

[0025] 1) mixing a polyamine solution with a phosgene solution and performing a cold phosgene gasification reaction to generate a gas-liquid-solid three-phase mixture material A;

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

[0027] 3) The reaction product C obtained in step 2) is subjected to a thermal reaction (i.e., an acyl chloride decomposition reaction) (such as introduced into a thermal reactor), and the product D obtained by the thermal reaction is then introduced into a refining system for refining post-treatment to ultimately obtain high-quality isocyanate.

[0028] In step 2) of the present invention, in the first stage reaction, cold reaction is mainly used, and amines are converted into acyl chlorides as much as possible 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; as the cold reaction process of the first stage continues to advance, the reaction temperature in the system continues to increase, and the thermal reaction gradually dominates; by controlling the reaction pressure, reaction temperature and the amount of the introduced COCl2 / HCl mixture in the second stage, the thermal reaction process is strengthened, and the influence of the cold reaction and the hot reaction on the color number and the generation of impurities when the cold reaction and the hot reaction are carried out simultaneously can be reduced.

[0029] According to the method provided by the present invention, in some embodiments, the isocyanate is a diisocyanate or a polyisocyanate, preferably a diisocyanate, and 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 light gasification reaction is carried out in a dynamic reactor. The reaction process in step 1) is relatively rapid, and its reaction conditions are not described in detail.

[0031] Herein, the polyamine and the solvent may be mixed in a static mixer to form a polyamine solution.

[0032] In some embodiments, 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%, 95%.

[0034] In some embodiments, the solvent in the polyamine solution is 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, in the polyamine solution, the mass ratio of polyamine to solvent 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 isophoronediamine (IPDA). Herein, the polyamine can be understood to include diamines.

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

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

[0039] In some embodiments, in step 2), the process conditions of the second stage reaction include: reaction temperature of 80-140°C (e.g., 85°C, 90°C, 92°C, 100°C, 102°C, 110°C, 120°C, 135°C), 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), cold reaction progress of 90-99.9% (e.g., 91%, 92%, 94%, 96%, 98%, 99%, 99.5%), 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 of the second stage reaction include: reaction temperature of 80-130° C., reaction pressure of 3-30 barg, cold reaction progress of 95-99.9%, and hot reaction progress of 10-40%.

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

[0042] In some embodiments, the first stage reaction and the second stage reaction of the cold reaction in step 2) are both 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 embodiments, the first stage reaction and the second stage reaction of the cold reaction in step 2) are carried out independently.

[0044] In order to further utilize the pressure change energy during the first stage reaction and the second stage reaction in step 2) and to strengthen the reaction process, in this step, the phosgene / HCl mixture can be effectively introduced into the reaction system through components such as a static ejector, an orifice plate, a regulating valve, and a variable diameter structure to strengthen the reaction and reduce the occurrence of side reactions.

[0045] In some embodiments, in step 2), a mixture of phosgene and hydrogen chloride is introduced into the reaction system by providing a static ejector, an orifice plate, a regulating valve, and a 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, and components such as a static ejector, an orifice plate, a regulating valve, and a variable diameter structure are provided between the first tubular reactor and the second tubular reactor.

[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, in the mixture of phosgene and hydrogen chloride, the mass ratio of COCl2 to HCl 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 introduced mixture of phosgene and hydrogen chloride may come from HCl refined gas, phosgene solution, thermal reactor gas phase tail gas, etc. known in the industry, and its source is not limited here.

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

[0050] For example, the thermal reaction process of step 3) can be referred to the records in patent documents (such as CN 114749116A).

[0051] For example, the refining post-treatment process of step 3) can refer to the records in patent documents (such as CN 115925581A). In some embodiments, the gas phase produced by the thermal reaction in step 3) is optionally condensed and then enters the phosgene absorption tower for absorption and reuse (the condensate is refluxed to the thermal phosgenation reactor), and the liquid phase produced by the thermal reaction is optionally entered into the dephosgene tower to remove phosgene and hydrogen chloride. The temperature of the dephosgene tower bottom can be 130°C, and the pressure at the top of the tower can be 0.2 barG; the gas phase at the top of the dephosgene tower is first condensed and then pressurized and then sent to the bottom of the phosgene absorption tower (the condensate is refluxed to the dephosgene tower), and chlorobenzene is passed into the top of the phosgene absorption tower, countercurrently contacted with the gas phase phosgene, and absorbed to produce a phosgene solution. The bottom temperature of the phosgene absorption tower can be -5°C, and the pressure at the top of the tower can be 3 barG. The liquid phase after dephosgenesis enters the solvent removal tower for solvent removal, or the liquid phase produced by the thermal reaction directly enters the solvent removal tower for solvent removal. The bottom temperature of the tower can be 145°C to 185°C, and the top pressure of the tower can be -0.9 barG to -0.6 barG. The solution in the bottom of the tower is collected, which is the crude MDI product.

[0052] In the isocyanate product prepared by the method of the present invention, the mass proportion of urea impurities can be as low as less than 0.8%, even less than 0.05%, or even less than 0.01%; the L color of the isocyanate product can be above 80, even above 85, or even above 90. Compared with the prior art, the method of the present invention effectively reduces the content of urea substances in the isocyanate product and improves the product color number, which can not only improve the phosgenation reaction effect, but also reduce the risk of equipment scaling and clogging, and improve the stable operation cycle of the production device.

[0053] The present invention reduces the color loss of the product and the generation of impurities caused by thermal reactions under high temperature conditions without the need for new equipment or the introduction of other substances, thereby effectively ensuring the operating stability of the device and the applicability of product applications; and the process is simple, the operation is convenient, the energy consumption is saved, the cost is low, the efficiency is high, and it is environmentally friendly.

[0054] The present invention controls the temperature, pressure, residence time and other parameters in the step 2) reaction, distinguishes and controls the dominant reaction in the cold reaction process in sections, and formulates targeted strengthening measures, thereby effectively reducing the generation of impurities in the reaction process; in addition, a quantitative HCl / COCl2 mixture is introduced into the phosgenation reaction stage, and the cavitation mixing effect formed by structures such as an ejector / orifice plate is utilized to strengthen the cold reaction in step 2), reduce the L color loss of the product and the generation of impurities caused by the thermal reaction under high temperature conditions, and obtain high-quality isocyanate, while reducing the production cost to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 Schematic diagram of the overall process flow of some embodiments of the present invention.

[0056] In the figure, the descriptions of the reference numerals are as follows:

[0057] 1-static mixer; 2-jet reactor; 3-first tubular reactor; 4-ejector or regulating valve with pressure regulation and cavitation effect; 5-second tubular reactor; 6-thermal reactor (for example, tower reactor or kettle reactor); 7-refining system. DETAILED DESCRIPTION

[0058] In order to understand the technical features and content of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the embodiments, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. For those who do not specify specific conditions in the embodiments, they are carried out according to normal conditions or the conditions recommended by the manufacturer.

[0059] <Source of raw materials>

[0060] In the following examples and comparative examples, the sources of some reagents or raw materials used, without specifying the manufacturer, are all conventional products that can be purchased commercially.

[0061] <Detection method>

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

[0063] Analysis of urea content, DAM content, hydrochloride content and acyl chloride content in isocyanate products: liquid chromatography was used, the liquid chromatography instrument was Shimadzu LC-20A, SIL-20A automatic sample injector, CT0-20A column oven, SPD-M20A detector, and the chromatographic column was ODS SP (250*4.6mm) (Inertsil), 5μm; the specific content of each substance was determined by formulating a standard curve;

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

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

[0066] L color test: Use an integrating sphere spectrophotometer and dichloromethane as the standard for measurement.

[0067] [Example 1]

[0068] A method for preparing isocyanates according to Figure 1 The process flow shown includes the following steps:

[0069] (1) MDA (diphenylmethanediamine) with a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 63 t / h and a pressure of 20 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 110° C., reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%; the first stage is mainly cold reaction, and amines are converted 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. The product B is discharged from the first tubular reactor 3 and 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. The mass of phosgene in the mixture is 500 kg / h, and the mass of HCl is 200 kg / h.

[0073] The reaction conditions of the second stage include: reaction temperature of 98°C, reaction pressure of 10 barg, cold reaction progress of 99.9%, and hot reaction progress of 32%. As the cold reaction progress of 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, obtaining the reaction product C.

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

[0075] [Example 2]

[0076] A method for preparing isocyanates according to Figure 1 The process flow shown includes the following steps:

[0077] (1) MDA (diphenylmethanediamine) with a flow rate of 25 t / h and a pressure of 20 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 63 t / h and a pressure of 20 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 130° C., reaction pressure of 30 barg, cold reaction progress of 99.5%, and hot reaction progress of 8%; the first stage is mainly cold reaction, and amines are converted 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. The product B is discharged from the first tubular reactor 3 and 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. The mass of phosgene in the mixture is 500 kg / h, and the mass of HCl is 200 kg / h.

[0081] The reaction conditions of the second stage include: reaction temperature of 102°C, reaction pressure of 10 barg, cold reaction progress of 99.9%, and hot reaction progress of 34%. As the cold reaction progress of 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, obtaining the reaction product C.

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

[0083] [Example 3]

[0084] A method for preparing isocyanates according to Figure 1 The process flow shown includes the following steps:

[0085] (1) MDA (diphenylmethanediamine) with a flow rate of 10 t / h and a pressure of 30 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 30 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 63 t / h and a pressure of 25 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 for the first stage reaction; the first stage reaction conditions include: reaction temperature of 102°C, reaction pressure of 22 barg, cold reaction progress of 99.3%, and hot reaction progress of 6%; the first stage is mainly cold reaction, and amines are converted 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. The product B is discharged from the first tubular reactor 3 and 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 the mixture, the mass of phosgene is 800 kg / h, and the mass of HCl is 300 kg / h.

[0089] The reaction conditions of the second stage include: reaction temperature of 100°C, reaction pressure of 12 barg, cold reaction progress of 99.9%, and hot reaction progress of 25%. As the cold reaction progress of 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, obtaining the reaction product C.

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

[0091] [Example 4]

[0092] A method for preparing isocyanates according to Figure 1 The process flow shown includes the following steps:

[0093] (1) MDA (diphenylmethanediamine) with a flow rate of 40 t / h and a pressure of 25 barG and chlorobenzene with a flow rate of 80 t / h and a pressure of 25 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 130 t / h and a pressure of 25 barG (the phosgene content in the phosgene solution is 65 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 107°C, reaction pressure of 22 barg, cold reaction progress of 99.5%, and hot reaction progress of 8%; the first stage is mainly cold reaction, and amines are converted 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. The product B is discharged from the first tubular reactor 3 and 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 the mixture, the mass of phosgene is 600 kg / h, and the mass of HCl is 400 kg / h.

[0097] The reaction conditions of the second stage include: reaction temperature of 92°C, reaction pressure of 8 barg, cold reaction progress of 99.9%, and hot reaction progress of 23%. As the cold reaction progress of 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, obtaining the reaction product C.

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

[0099] [Comparative Example 1]

[0100] Method for preparing isocyanate, referring to Figure 1 The process flow shown includes the following steps:

[0101] (1) MDA (diphenylmethanediamine) with a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 63 t / h and a pressure of 20 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 110° C., reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%; the first stage is mainly cold reaction, and amines are converted 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, and the product B is discharged from the first tubular reactor 3 and enters the second tubular reactor 5 for a second stage reaction; the reaction conditions of the second stage include: a reaction temperature of 200°C, a reaction pressure of 10 barg, a cold reaction process of 99.8%, and a hot reaction process of 30%; as the cold reaction process of 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, obtaining a reaction product C;

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

[0106] [Comparative Example 2]

[0107] Method for preparing isocyanate, referring to Figure 1 The process flow shown includes the following steps:

[0108] (1) MDA (diphenylmethanediamine) with a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 63 t / h and a pressure of 20 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 110° C., reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%; the first stage is mainly cold reaction, and amines are converted 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. The product B is discharged from the first tubular reactor 3 and 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. The mass of the introduced phosgene is 200 kg / h.

[0112] The reaction conditions of the second stage include: reaction temperature of 98°C, reaction pressure of 10 barg, cold reaction progress of 99.9%, and hot reaction progress of 32%. As the cold reaction progress of 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, obtaining the reaction product C.

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

[0114] [Comparative Example 3]

[0115] Method for preparing isocyanate, referring to Figure 1 The process flow shown includes the following steps:

[0116] (1) MDA (diphenylmethanediamine) with a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 63 t / h and a pressure of 20 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 110° C., reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%; the first stage is mainly cold reaction, and amines are converted 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. The product B is discharged from the first tubular reactor 3 and 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. The mass of the introduced HCl is 200 kg / h.

[0120] The reaction conditions of the second stage include: reaction temperature of 98°C, reaction pressure of 10 barg, cold reaction progress of 99.9%, and hot reaction progress of 32%. As the cold reaction progress of 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, obtaining the reaction product C.

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

[0122] [Comparative Example 4]

[0123] Method for preparing isocyanate, referring to Figure 1 The process flow shown includes the following steps:

[0124] (1) MDA (diphenylmethanediamine) with a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 63 t / h and a pressure of 20 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 110° C., reaction pressure of 18 barg, cold reaction progress of 99.2%, and hot reaction progress of 5%; the first stage is mainly cold reaction, and amines are converted 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. The product B is discharged from the first tubular reactor 3 and 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. The mass of phosgene in the mixture is 200 kg / h, and the mass of HCl is 200 kg / h.

[0128] The reaction conditions of the second stage include: reaction temperature of 98°C, reaction pressure of 10 barg, cold reaction progress of 99.9%, and hot reaction progress of 32%. As the cold reaction progress of 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, obtaining the reaction product C.

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

[0130] [Comparative Example 5]

[0131] Method for preparing isocyanate, referring to Figure 1 The process flow shown includes the following steps:

[0132] (1) MDA (diphenylmethanediamine) with a flow rate of 20 t / h and a pressure of 35 barG and chlorobenzene with a flow rate of 40 t / h and a pressure of 20 barG are mixed in a static mixer 1 to form a polyamine solution; the polyamine solution is then mixed with a phosgene solution with a flow rate of 40 t / h and a pressure of 20 barG (the phosgene content in the phosgene solution is 70 wt %, and the solvent is chlorobenzene), and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixed material 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 mixed material A enters the first tubular reactor 3 to carry out the first stage reaction; the first stage reaction conditions include: reaction temperature of 140°C, reaction pressure of 30 barg, cold reaction progress of 99.2%, and 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. The product B is discharged from the first tubular reactor 3 and 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. The mass of phosgene in the mixture is 200 kg / h, and the mass of HCl is 200 kg / h.

[0136] The reaction conditions of the second stage include: reaction temperature of 125°C, reaction pressure of 20 barg, cold reaction progress of 99.9%, hot reaction progress of 45%, and after the second stage reaction, reaction product C is obtained;

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

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

[0139] Product Category Urea content NCO content L color Device 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 months Comparative Example 3 MDI 1.1％ 31.8％ 78 19th Comparative Example 4 MDI 0.8％ 32％ 80 22 months Comparative Example 5 MDI 1.3％ 31.6％ 73 December

[0140] Note: The determination of the device operating cycle can be achieved through conventional test operations in this field; for example, when the steam valve of the thermal reactor is fully open and the temperature of the reactor cannot be maintained at the target temperature, the operating cycle is reached.

[0141] It can be seen from the test results in Table 1 that 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 operation period of the device is maintained at more than 36 months.

[0142] Compared with the embodiment, in step 2) of the comparative example, the mixture of phosgene and hydrogen chloride is not introduced, or the ratio of phosgene to hydrogen chloride in the mixture is not within a reasonable range, or the thermal reaction process of the first stage and the second stage is too high, which will have an adverse effect on the content of urea impurities in the product, L color and the operation cycle of the device.

[0143] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for preparing isocyanate, characterized in that: The following steps are involved: 1) mixing a polyamine solution with a phosgene solution and performing a cold phosgene gasification reaction to generate a gas-liquid-solid three-phase mixture material A; 2) As the cold reaction proceeds, the process conditions of the cold reaction process are controlled in stages: the gas-liquid-solid three-phase mixture A is subjected to a first-stage reaction, in which the first-stage reaction is mainly a cold phosgenation reaction, the cold reaction progress is 50-99.9%, and the hot reaction progress is 0-30%, and the amines are converted into acyl chlorides as much as possible to obtain product B; the product B is then subjected to a second-stage reaction, and at the same time, a mixture of phosgene and hydrogen chloride is introduced into the reaction system; in the second-stage reaction, the hot phosgenation reaction gradually dominates, the cold reaction progress is 90-99.9%, and the hot reaction progress is 3-40%; after the reaction, a reaction product C is obtained; 3) The reaction product C obtained in step 2) is subjected to a thermal reaction, and the product D obtained by the thermal reaction is then sent to a refining system for refining post-treatment to finally obtain high-quality isocyanate.

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

3. The method according to claim 1 or 2, characterized in that: In step 1), the cold light gasification reaction is carried out in a dynamic reactor; Preferably, 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), preferably 1:(2-5); Preferably, the phosgene content in the phosgene solution is 40-99%; Preferably, the solvent in the polyamine solution is 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; Preferably, in the polyamine solution, the mass ratio of polyamine to solvent is 1:(1.5-6), preferably 1:(1.8-4.5); Preferably, the polyamine is a diamine, more preferably one or more of diaminodiphenylmethane, polydiaminodiphenylmethane, diaminotoluene, hexamethylenediamine and isophoronediamine.

4. The method according to any one of claims 1 to 3, characterized in that In step 2), the process conditions of the first stage reaction include: reaction temperature of 50-140°C, reaction pressure of 1-40 barg, cold reaction progress of 50-99.9%, and hot reaction progress of 0-30%; Preferably, the process conditions of the first stage reaction include: reaction temperature of 70-130° C., reaction pressure of 8-35 barg, cold reaction progress of 90-99.9%, and hot reaction progress of 0-10%.

5. The method according to any one of claims 1 to 4, characterized in that In step 2), the process conditions of the second stage reaction include: reaction temperature of 80-140°C, reaction pressure of 3-40 barg, cold reaction progress of 90-99.9%, and hot reaction progress of 3-40%; Preferably, the process conditions of the second stage reaction include: reaction temperature of 80-130° C., reaction pressure of 3-30 barg, cold reaction progress of 95-99.9%, and hot reaction progress of 10-40%.

6. The method according to any one of claims 1 to 5, characterized in that The first stage reaction and the second stage reaction of the cooling reaction in step 2) are both carried out in a tubular reactor.

7. The method according to any one of claims 1 to 6, characterized in that The first stage reaction and the second stage reaction of the cold reaction in step 2) are carried out independently.

8. The method according to any one of claims 1 to 7, characterized in that In step 2), a mixture of phosgene and hydrogen chloride is introduced into the reaction system by providing a static injector, an orifice plate, a regulating valve, and a variable diameter structure.

9. The method according to any one of claims 1 to 8, 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), preferably 1:(0.05-0.1).

10. The method according to any one of claims 1 to 9, characterized in that In the mixture of phosgene and hydrogen chloride, the mass ratio of COCl2 to HCl is 1:(0.001-0.8), preferably 1:(0.005-0.7).

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