Method for preparing isocyanate

Abstract

The present invention belongs to the technical field of isocyanate preparation, and particularly relates to a method for preparing an isocyanate. The method comprises: 1) mixing a polyamine solution with a phosgene solution, and carrying out a cold phosgenation reaction so as to generate a gas-liquid-solid three-phase mixed material A; 2) performing segmented control of process conditions of the cold reaction process: carrying out a first-stage reaction on the mixed material A, which mainly involves the cold phosgenation reaction, a cold reaction progress being 50-99.9% and a hot reaction progress being 0-30%, so as to obtain a product B; then carrying out a second-stage reaction on the product B, and introducing a mixture of phosgene and hydrogen chloride into the system at the same time, the cold reaction progress of the second-stage reaction being 90-99.9% and the hot reaction progress being 3-40%, so as to obtain a reaction product C; and 3) introducing the reaction product C into a hot reactor, performing a hot reaction to obtain a product D, and then feeding the product D to a refining system to refine same. The method disclosed by the present invention reduces the L color loss and impurities generated in hot reactions at high temperatures, thereby obtaining a high-quality isocyanate.

Description

A method for preparing isocyanate Technical Field

[0001] The present 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, known as the world's "fifth most common plastic," is widely used in a variety of fields, including aerospace, defense, construction, petrochemicals, and healthcare. Isocyanates are the core raw materials for polyurethane production, and the mainstream industrial synthesis method is phosgenation. Phosgenated isocyanates, as organic reaction intermediates, can be further synthesized into materials such as polyisocyanates, polyurethanes, polyureas, and spandex, finding widespread application in various industries, including industry, agriculture, construction, automotive, and thermal insulation.

[0003] At present, the mainstream isocyanate synthesis method in industry is the phosgenation method. Its core is that the reaction process is divided into two stages: cold and hot. The principle is as follows:

[0004] Cold reaction stage: RNH2+COCl2→RNHCOCl(carbamoyl chloride)+HCl; RNH2+HCl→RNH2·HCl(amino hydrochloride).

[0005] Thermal reaction stage: RNHCOCl→RNCO+HCl; RNH2·HCl+COCl2→RNCO+3HCl.

[0006] Among them, the reaction speed in the cold reaction stage is faster and the reaction is rapid and complete; while in the hot reaction stage, the following side reactions are prominent: RNH2·HCl→RNH2+HCl; RNH2+RNCO→RNHCONHR (urea).

[0007] In the presence of phosgene, 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.

[0008] The presence of by-products such as urea, hydrochloride groups, and acyl chloride groups can significantly impact product quality and color. Currently, the industry primarily manages product quality by controlling excess solvent or phosgene consumption.

[0009] Chinese patent document CN1651406A discloses a tubular reactor that enhances the mixing effect at the front end of the tube by stirring to improve product quality, but cannot eliminate side reactions at the back end.

[0010] 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.

[0011] Chinese patent document CN 218962652U discloses a tubular reactor for producing isocyanates. The reaction is enhanced by multiple diameter changes. However, impurities tend to accumulate at the diameter changes, affecting the operating cycle of the device.

[0012] Chinese patent document CN 102317255B improves the L color by controlling the CO excess rate to an extremely low level during the phosgene production process; however, there is a high risk of over-chlorination.

[0013] Patent document WO2021122625 A1 discloses the use of an HCl stripping process to improve L color. Although it can achieve the purpose of improving chromaticity, it mainly targets the desolvation process and has no obvious effect on the chromaticity loss caused by the phosgenation reaction process.

[0014] Existing technologies primarily address impurity generation in the phosgenation phase of liquid-phase phosgenation reactions by using high phosgene and solvent volumes, resulting in high operating costs and complex operations. Furthermore, existing reaction intensification technologies primarily focus on the initial injection process of the cold reaction, with insufficient understanding and exploration of the subsequent back-end reaction processes.

[0015] Therefore, for the liquid-phase phosgenation process, it is necessary to fundamentally avoid the generation of impurities such as urea, further improve product quality and reduce operating costs.

[0016] Summary of the Invention

[0017] To solve the above problems, the purpose of the present invention is to provide a method for preparing isocyanates 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, thereby obtaining high-quality isocyanates and reducing production costs to a certain extent.

[0018] In order to achieve the above object, the present invention provides the following technical solutions:

[0019] A method for preparing isocyanate comprises the following steps:

[0020] 1) mixing a polyamine solution and a phosgene solution and performing a cold phosgene gasification reaction to generate a gas-liquid-solid three-phase mixture material A;

[0021] 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, wherein the first-stage reaction is mainly a cold phosgenation reaction, with the cold reaction progress being 50-99.9% and the hot reaction progress being 0-30%, and the amine is converted into an acyl chloride as much as possible to obtain product B; product B is then subjected to a second-stage reaction, and a mixture of phosgene and hydrogen chloride is simultaneously introduced into the reaction system; in the second-stage reaction, the hot phosgenation reaction gradually becomes dominant, with the cold reaction progress being 90-99.9% and the hot reaction progress being 3-40%; and reaction product C is obtained after the reaction;

[0022] 3) The reaction product C obtained in step 2) is subjected to a thermal reaction (i.e., an acyl chloride decomposition reaction) (e.g., introduced into a thermal reactor), and the product D obtained by the thermal reaction is then fed into a refining system for post-refining treatment to ultimately obtain high-quality isocyanate.

[0023] In step 2) of the present invention, in the first stage reaction, a cold reaction is mainly performed, and the amine is converted into the acyl chloride 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 progresses in the first stage, the reaction temperature in the system continues to increase, and the thermal reaction gradually becomes dominant; 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 while reducing the impact of the cold reaction and the hot reaction on the color number and impurity generation when the cold reaction and the hot reaction are carried out simultaneously.

[0024] 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 one or more selected from diphenylmethylene diisocyanate (MDI), polydiphenylmethylene diisocyanate (PMDI), toluene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and isophorone diisocyanate (IPDI).

[0025] 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 are not described in detail.

[0026] Herein, the polyamine and the solvent may be mixed in a static mixer to form a polyamine solution.

[0027] 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).

[0028] In some embodiments, the phosgene content in the phosgene solution is 40-99%, for example, 45%, 50%, 60%, 80%, 90%, or 95%.

[0029] 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 chlorobenzene and / or dichlorobenzene.

[0030] 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).

[0031] 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.

[0032] In some embodiments, in step 2), the process conditions of 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%);

[0033] 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%.

[0034] In some embodiments, in step 2), the process conditions of 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%);

[0035] 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%.

[0036] Herein, 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, by testing parameters known in the industry, such as load, solvent ratio, phosgene ratio, reactor pressure, etc., to achieve control of the cold reaction process and the hot reaction process.

[0037] 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.

[0038] In some embodiments, the first-stage reaction and the second-stage reaction of the cooling reaction in step 2) are carried out independently.

[0039] In order to further utilize the pressure change energy during the first and second stage reactions in step 2) and to enhance the reaction process, in this step, a 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 enhance the reaction and reduce the occurrence of side reactions.

[0040] In some embodiments, in step 2), the 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 reducing 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. The static ejector, orifice plate, regulating valve, reducing structure, and other components are provided between the first and second tubular reactors.

[0041] 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).

[0042] 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, and preferably 1:(0.005-0.7).

[0043] In step 2), the mixture of phosgene and hydrogen chloride introduced 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.

[0044] In step 3), further thermal reaction and post-refining treatment processes can be achieved using processes known in the industry.

[0045] For example, the thermal reaction process of step 3) can be referred to the records in patent documents (such as CN 114749116A).

[0046] For example, the refining post-treatment process of step 3) can refer to the records in patent documents (such as CN115925581A). In some embodiments, the gas phase produced by the thermal reaction in step 3) is optionally condensed and then entered into a phosgene absorption tower for absorption and reuse (the condensate is refluxed to the hot phosgenation reactor), and the liquid phase produced by the thermal reaction is optionally entered into a dephosgene tower to remove phosgene and hydrogen chloride. The dephosgene tower bottom temperature can be 130°C and the tower top pressure can be 0.2 barG; the dephosgene tower top gas phase 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 gaseous phosgene, and absorbed to produce a phosgene solution. The tower bottom temperature of the phosgene absorption tower can be -5°C and the tower top pressure can be 3 barG. The liquid phase after dephosgeneation 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 tower bottom temperature can be 145°C to 185°C, and the tower top pressure can be -0.9 barG to -0.6 barG. The tower bottom solution is collected as the crude MDI product.

[0047] In the isocyanate product prepared by the method of the present invention, the mass proportion of urea impurities can be reduced to 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. This not only improves the phosgenation reaction efficiency, but also reduces the risk of equipment scaling and clogging, thereby increasing the stable operation period of the production unit.

[0048] 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, effectively ensuring the operational stability of the device and the applicability of product applications; and has simple processes, convenient operation, energy conservation, low cost, high efficiency, and is environmentally friendly.

[0049] The present invention controls parameters such as temperature, pressure, and residence time in the reaction of step 2) to segmentally distinguish and control the dominant reaction in the cold reaction process, and formulates targeted strengthening measures to effectively reduce the generation of impurities during the reaction process. In addition, a quantitative HCl / COCl2 mixture is introduced into the phosgenation reaction stage, and a cavitation mixing effect formed by structures such as an ejector / orifice plate is utilized to strengthen the cold reaction in step 2), reduce the color loss of the product and the generation of impurities caused by the thermal reaction under high temperature conditions, thereby obtaining high-quality isocyanate and reducing the production cost to a certain extent. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIG1 is a schematic diagram of the overall process flow of some embodiments of the present invention.

[0051] In the figure, the numbers are explained as follows: 1-static mixer; 2-jet reactor; 3-first tubular reactor; 4-ejector or regulating valve with pressure regulation and cavitation function; 5-second tubular reactor; 6-thermal reactor (for example, tower reactor or kettle reactor); 7-refining system. DETAILED DESCRIPTION

[0052] The embodiments of the present invention will be described in detail below with reference to specific examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the present invention. Specific conditions are not specified in the examples, and the methods are carried out according to conventional conditions or manufacturer's recommended conditions. The reagents or instruments used are not specified by manufacturer and are all commercially available conventional products.

[0053] <Source of raw materials>

[0054] In the following examples and comparative examples, the sources of some reagents or raw materials used, and those whose manufacturers are not indicated, are all conventional products that can be purchased commercially.

[0055] NCO content in isocyanate products: determined using the GB / T2009-3-2009 method;

[0056] Analysis of urea, DAM, hydrochloride, and acyl chloride content in isocyanate products: Liquid chromatography was performed using a Shimadzu LC-20A instrument, 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 developing a standard curve.

[0057] 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;

[0058] Thermal reaction progress = MDI content / (DAM + acyl chloride + hydrochloride + MDI) content; wherein the MDI content is also determined by liquid chromatography as described above;

[0059] L color test: using an integrating sphere spectrophotometer and dichloromethane as the standard.

[0060] [Example 1]

[0061] The method for preparing isocyanate, according to the process flow shown in Figure 1, includes the following steps:

[0062] (1) MDA (diphenylmethanediamine) at a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene at 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 (phosgene content of 70 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0063] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0064] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 110° C., a reaction pressure of 18 barg, a cold reaction progress of 99.2%, and a hot reaction progress of 5%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0065] 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. The mass of phosgene in this mixture is 500 kg / h and the mass of HCl is 200 kg / h.

[0066] The reaction conditions for the second stage included a reaction temperature of 98°C, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction progressed in the first stage, the reaction temperature continued to rise, and the hot reaction gradually became dominant in the second stage reaction, yielding reaction product C.

[0067] (3) The reaction liquid obtained from the second stage reaction in step 2) (i.e., reaction product C) is passed 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, the isocyanate product is obtained.

[0068] [Example 2]

[0069] The method for preparing isocyanate, according to the process flow shown in Figure 1, includes the following steps:

[0070] (1) MDA (diphenylmethanediamine) at a flow rate of 25 t / h and a pressure of 20 barG and chlorobenzene at 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 (phosgene content of 70 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0071] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0072] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 130° C., a reaction pressure of 30 barg, a cold reaction progress of 99.5%, and a hot reaction progress of 8%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0073] 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. The mass of phosgene in this mixture is 500 kg / h and the mass of HCl is 200 kg / h.

[0074] The reaction conditions for the second stage included a reaction temperature of 102°C, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 34%. As the cold reaction progressed in the first stage, the reaction temperature continued to rise, and the hot reaction gradually became dominant in the second stage reaction, yielding reaction product C.

[0075] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0076] [Example 3]

[0077] The method for preparing isocyanate, according to the process flow shown in Figure 1, includes the following steps:

[0078] (1) MDA (diphenylmethanediamine) at a flow rate of 10 t / h and a pressure of 30 barG and chlorobenzene at 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 (phosgene content of 70 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 63 t / h and a pressure of 25 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0079] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0080] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 102° C., a reaction pressure of 22 barg, a cold reaction progress of 99.3%, and a hot reaction progress of 6%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0081] 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. The mass of phosgene in this mixture is 800 kg / h and the mass of HCl is 300 kg / h.

[0082] The reaction conditions for the second stage included a reaction temperature of 100°C, a reaction pressure of 12 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 25%. As the cold reaction progressed in the first stage, the reaction temperature in the system continued to rise, and the hot reaction gradually became dominant in the second stage reaction, yielding reaction product C.

[0083] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0084] [Example 4]

[0085] The method for preparing isocyanate, according to the process flow shown in Figure 1, includes the following steps:

[0086] (1) MDA (diphenylmethanediamine) at a flow rate of 40 t / h and a pressure of 25 barG and chlorobenzene at 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 (phosgene content of 65 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 130 t / h and a pressure of 25 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0087] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0088] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 107° C., a reaction pressure of 22 barg, a cold reaction progress of 99.5%, and a hot reaction progress of 8%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0089] The first tubular reactor 3 and the second tubular reactor 5 are connected by a regulating valve 4. After being discharged from the first tubular reactor 3, the product B 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. The mass of phosgene in this mixture is 600 kg / h and the mass of HCl is 400 kg / h.

[0090] The reaction conditions for the second stage included a reaction temperature of 92°C, a reaction pressure of 8 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 23%. As the cold reaction progressed in the first stage, the reaction temperature continued to rise, and the hot reaction gradually became dominant in the second stage reaction, yielding reaction product C.

[0091] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0092] [Comparative Example 1]

[0093] The method for preparing isocyanate, referring to the process flow shown in FIG1 , comprises the following steps:

[0094] (1) MDA (diphenylmethanediamine) at a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene at 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 (phosgene content of 70 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0095] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0096] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 110° C., a reaction pressure of 18 barg, a cold reaction progress of 99.2%, and a hot reaction progress of 5%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0097] The first tubular reactor 3 is connected to the second tubular reactor 5. After being discharged from the first tubular reactor 3, the product B 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 progress of 99.8%, and a hot reaction progress of 30%. As the cold reaction progress of the first stage continues, the reaction temperature in the system continues to rise, and the hot reaction gradually dominates in the second stage reaction, resulting in a reaction product C.

[0098] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0099] [Comparative Example 2]

[0100] The method for preparing isocyanate, referring to the process flow shown in Figure 1, comprises the following steps:

[0101] (1) MDA (diphenylmethanediamine) at a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene at 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 (phosgene content of 70 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture 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 mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 110° C., a reaction pressure of 18 barg, a cold reaction progress of 99.2%, and a hot reaction progress of 5%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0104] 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. The mass of the introduced phosgene is 200 kg / h.

[0105] The reaction conditions for the second stage included a reaction temperature of 98°C, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction progressed in the first stage, the reaction temperature continued to rise, and the hot reaction gradually became dominant in the second stage reaction, yielding reaction product C.

[0106] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0107] [Comparative Example 3]

[0108] The method for preparing isocyanate, referring to the process flow shown in Figure 1, comprises the following steps:

[0109] (1) MDA (diphenylmethanediamine) at a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene at 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 (phosgene content of 70 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0110] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0111] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 110° C., a reaction pressure of 18 barg, a cold reaction progress of 99.2%, and a hot reaction progress of 5%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0112] 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 at a mass of 200 kg / h.

[0113] The reaction conditions for the second stage included a reaction temperature of 98°C, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction progressed in the first stage, the reaction temperature continued to rise, and the hot reaction gradually became dominant in the second stage reaction, yielding reaction product C.

[0114] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0115] [Comparative Example 4]

[0116] The method for preparing isocyanate, referring to the process flow shown in FIG1 , comprises the following steps:

[0117] (1) MDA (diphenylmethanediamine) at a flow rate of 20 t / h and a pressure of 20 barG and chlorobenzene at 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 (phosgene content 70 wt% in the phosgene solution, the solvent is chlorobenzene) at a flow rate of 63 t / h and a pressure of 20 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0118] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0119] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 110° C., a reaction pressure of 18 barg, a cold reaction progress of 99.2%, and a hot reaction progress of 5%. The first stage is primarily a cold reaction, converting the amines into acyl chlorides as much as possible to obtain product B.

[0120] 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. The mass of phosgene in this mixture is 200 kg / h, and the mass of HCl is 200 kg / h.

[0121] The reaction conditions for the second stage included a reaction temperature of 98°C, a reaction pressure of 10 barg, a cold reaction progress of 99.9%, and a hot reaction progress of 32%. As the cold reaction progressed in the first stage, the reaction temperature continued to rise, and the hot reaction gradually became dominant in the second stage reaction, yielding reaction product C.

[0122] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0123] [Comparative Example 5]

[0124] The method for preparing isocyanate, referring to the process flow shown in Figure 1, comprises the following steps:

[0125] (1) MDA (diphenylmethanediamine) at a flow rate of 20 t / h and a pressure of 35 barG and chlorobenzene at 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 (phosgene content of 70 wt% in the phosgene solution, the solvent being chlorobenzene) at a flow rate of 40 t / h and a pressure of 20 barG, and a cold phosgene gasification reaction is carried out in a jet reactor 2 to obtain a gas-liquid-solid three-phase mixture material A;

[0126] (2) As the cold photogasification reaction proceeds, the process conditions of the cold reaction process are controlled in stages:

[0127] The gas-liquid-solid three-phase mixture A is introduced into the first tubular reactor 3 for a first-stage reaction. The first-stage reaction conditions include: a reaction temperature of 140° C., 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, a product B is obtained.

[0128] 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. The mass of phosgene in this mixture is 200 kg / h, and the mass of HCl is 200 kg / h.

[0129] The reaction conditions for the second stage include: a reaction temperature of 125°C, 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, a reaction product C is obtained;

[0130] (3) The reaction liquid (i.e., reaction product C) obtained from the second stage reaction in step 2) is passed into a thermal reactor 6 (e.g., a tank 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, the isocyanate product is obtained.

[0131] Table 1 Performance test results of the products obtained in each embodiment and comparative example

[0132] 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.

[0133] The test results in Table 1 show 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 cycle of the device is maintained at more than 36 months.

[0134] Compared with the embodiment, in step 2) of the comparative example, the mixture of phosgene and hydrogen chloride was not introduced, 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, which would have an adverse effect on the content of urea impurities in the product, L color, and the operating cycle of the device.

[0135] Unless otherwise defined, the terms used in the present invention have the same meanings as those commonly understood by those skilled in the art.

[0136] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above-mentioned embodiments, but is only limited by the claims.

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 of diaminodiphenylmethane, polydiaminodiphenylmethane, diaminotoluene, hexamethylenediamine and isophoronediamine. or more.

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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