Isocyanate preparation method, and isocyanate preparation system

Abstract

The present invention relates to the technical field of isocyanates. Provided are an isocyanate preparation method and an isocyanate preparation system. Using the method of the present invention for preparing an isocyanate can obviously relieve the problem of system blockage and prolong the operation cycle of reactors. The method comprises the following steps: (1) fractioning a mixed material flow obtained by means of a cold phosgenation reaction on an amine compound and phosgene in the presence of an inert solvent, so as to separate the mixed material flow into a gas phase material flow, a light liquid material flow and a heavy liquid material flow, the light liquid material flow containing light solid particles, the heavy liquid material flow containing heavy solid particles, and the density of the light solid particles being smaller than that of the heavy solid particles; and (2) feeding the light liquid material flow into the bottom of a rectifying column used for carrying out a hot phosgenation reaction, and feeding the heavy liquid material flow into the rectifying column from a position on the rectifying column between a stripping section and a rectifying section, so as to obtain an isocyanate product from the bottom of the rectifying column.

Description

Method for preparing isocyanate and isocyanate preparation system Technical Field

[0001] The present invention relates to the technical field of isocyanates, and in particular to a method for preparing isocyanates and an isocyanate preparation system. Background Art

[0002] Isocyanates all contain an -NCO functional group in their molecular structure. Phosgenation is currently the primary method used to produce these substances both domestically and internationally. Under appropriate temperature and pressure conditions, an amine compound, phosgene, and an inert solvent are mixed to produce a photochemical reaction solution containing isocyanate and hydrogen chloride. Separation of the inert solvent and phosgene from the photochemical reaction solution yields a crude isocyanate product, which is then separated to produce the final isocyanate product.

[0003] The reaction of amines with phosgene to form isocyanates requires two intermediate steps: cold phosgenation and hot phosgenation. In the first step, the amine reacts with excess phosgene at low temperatures to form isocyanate precursors, such as acyl chloride and hydrochloride. This is called cold phosgenation. In the second step, the isocyanate precursor decomposes at high temperatures to form isocyanate and hydrogen chloride. This is called hot phosgenation. Cold phosgenation typically uses lower temperatures, such as below 60°C, while hot phosgenation typically uses temperatures between 100°C and 200°C.

[0004] As is well known in the art, the reaction of amine compounds with phosgene to form isocyanates produces not only solid substances such as acyl chlorides and hydrochlorides produced in the normal cold reaction, but also some solid ureas as byproducts due to poor mass transfer. During the hot reaction, these substances not only directly deposit in the reactor but also further catalyze the formation of more solid byproducts. These solids cannot decompose and ultimately accumulate in the reaction and solvent separation systems, requiring production to be shut down for cleanup after a certain period of time, significantly increasing production costs and affecting production efficiency.

[0005] Chinese patent CN 107787318 B discloses a method for preparing isocyanates. This method involves passing the product stream obtained by reacting an amine compound with phosgene through a series of reactors. Hydrogen chloride produced during the "thermal phosgenation" reaction is separated by decompression to promote the decomposition of the isocyanate precursor. This method, which relies solely on equilibrium shifting, suffers from a low decomposition rate. Furthermore, the series of reactors requires increased equipment and operating costs.

[0006] Chinese patent application CN 114787125 A discloses a method for preparing isocyanate, in which the acyl chloride decomposition reactor is designed as a bubble tower or a plate tower.

[0007] Chinese patent CN 113831262 B discloses a method for preparing isocyanates by continuous phosgenation, which divides the phosgenation process into two levels, adds a solid separation device at the outlet of the second-stage phosgenation reaction device, separates the secondary photochemical reaction liquid into a reaction liquid free of solid matter and a reaction liquid containing solid matter, and the reaction liquid free of solid matter enters the next stage process, and the reaction liquid containing solid matter is returned to the first photochemical reaction device after crushing and dispersion. This method separates the secondary reaction liquid, which can solve the problem of solid deposition affecting long-term stable operation during post-processing such as dephosgenation and solvent separation to a certain extent. However, during the entire phosgenation reaction process, solids are mainly concentrated in the cold reaction outlet and the initial stage of the hot reaction. These solids easily cause scaling and clogging of the hot reaction system, affecting heat input and equipment operation stability. The patent does not describe the solid particle treatment scheme at this stage.

[0008] Summary of the Invention

[0009] The present invention provides a method for preparing isocyanate and an isocyanate preparation system. By preparing isocyanate using the method of the present invention, the problem of system blockage can be significantly improved, the operating cycle of a reactor in a thermal phosgenation reaction can be effectively extended, and the operating cycle of a post-processing system can be extended.

[0010] To achieve its purpose, the present invention provides the following technical solutions:

[0011] The present invention provides a method for preparing isocyanate, which comprises the following steps:

[0012] (1) subjecting an amine compound and phosgene to a cold phosgene gasification reaction in the presence of an inert solvent to a graded treatment to separate the mixed stream into three parts: a gas phase stream, a light liquid stream, and a heavy liquid stream, wherein the light liquid stream contains light solid particles, the heavy liquid stream contains heavy solid particles, and the density of the light solid particles is less than the density of the heavy solid particles;

[0013] (2) feeding the light liquid stream into the bottom of a distillation tower for performing a thermal phosgenation reaction, feeding the heavy liquid stream into the distillation tower from a position between the stripping section and the distillation section of the distillation tower, and obtaining an isocyanate product in the bottom of the distillation tower.

[0014] In some embodiments, in step (1), the density of the heavy solid particles is 1.15 to 1.30 g / cm 3 , preferably 1.18 to 1.25 g / cm 3 The density of the lightweight solid particles is 0.95 to 1.12 g / cm 3 , preferably 1.02 to 1.10 g / cm 3 .

[0015] In some embodiments, in step (1), the residence time of the liquid phase stream in the mixed stream in the classification device for performing the classification treatment is 1 to 10 minutes, preferably 3 to 6 minutes;

[0016] The pressure of the classification device is, for example, 0 MPag to 0.5 MPag, preferably 0.1 MPag to 0.3 MPag.

[0017] In some embodiments, in step (1), the mass percentage of the light liquid stream in the mixed stream is 10% to 50%; the mass percentage of the heavy liquid stream in the mixed stream is 40% to 85%; and the mass percentage of the gas phase stream in the mixed stream is 1.5% to 10%.

[0018] In some embodiments, the classification process is performed in a classification device that separates light and heavy solid particles in the liquid feed based on the principle of density difference;

[0019] Preferably, the grading device includes a kettle body, the inner cavity of the kettle body is divided into a first liquid tank, a second liquid tank, a buffer area and a third liquid tank which are adjacent to each other in sequence, the first liquid tank is provided with a mixed material flow inlet, the second liquid tank is provided with an overflow port for the upper liquid in the first liquid tank to overflow into the second liquid tank, a lower liquid flow channel which can connect the first liquid tank and the buffer area is formed between the outer wall of the lower part of the second liquid tank and the inner wall of the kettle body, the third liquid tank is provided with an overflow port for the upper liquid in the buffer area to overflow into the third liquid tank; a light liquid flow outlet is provided at the bottom of the second liquid tank, and a heavy liquid flow outlet is provided at the bottom of the third liquid tank; the kettle body is provided with a gas phase outlet for discharging the gas phase flow escaping from the inner cavity of the kettle body.

[0020] In some embodiments, in step (2), the number of theoretical plates of the rectifying section of the rectifying tower is 3 to 8, preferably 4 to 5; the number of theoretical plates of the stripping section of the rectifying tower is 13 to 25, preferably 15 to 20;

[0021] Preferably, the tower body material of the distillation tower is Hastelloy or 316L.

[0022] In some embodiments, the bottom temperature of the distillation tower is 120° C. to 190° C.; the top pressure is 0 MPag to 0.5 MPag; and the reflux ratio is 0.2 to 2.0, preferably 1 to 1.2.

[0023] In some embodiments, in step (1), the inert solvent comprises one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, and diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene;

[0024] In some embodiments, the amine compound includes one or more of diaminodiphenylmethane, polymethylene polyphenyl polyamine, diaminotoluene, isophoronediamine, hexamethylenediamine, cyclohexamethylenediamine, p-phenylenediamine, and naphthalenediamine;

[0025] In some embodiments, the mass ratio of phosgene to amine compound is 1 to 10;

[0026] In some embodiments, the mass ratio of the amine compound to the inert solvent is 1:(1-6).

[0027] The present invention also provides an isocyanate preparation system for implementing the method described above, the system comprising:

[0028] a classification device for classifying a mixed stream obtained by a cold-phosgene gasification reaction to separate a gaseous phase stream, a light liquid stream containing the light solid particles, and a heavy liquid stream containing the heavy solid particles from the mixed stream; the mixed stream is obtained by a cold-phosgene gasification reaction of an amine compound and phosgene in the presence of an inert solvent;

[0029] A distillation tower is used to receive the light liquid stream and the heavy liquid stream and perform a thermal phosgenation reaction to generate isocyanate, and the light liquid stream feed position of the distillation tower is set at the bottom of the distillation tower, and the heavy liquid stream feed position of the distillation tower is set between the stripping section and the distillation section of the distillation tower.

[0030] In some embodiments, the classification device is a classification device that separates light and heavy solid particles in a liquid feed based on the principle of density difference.

[0031] The technical solution provided by the present invention has the following beneficial effects:

[0032] The present invention adds a classification process of solid particles in the mixed liquid obtained by cold phosgenation reaction to the process of preparing isocyanate by traditional phosgenation reaction, separates urea substances that are prone to clogging and aggravate side reactions, and reduces their residence time on the tower tray. On the one hand, it reduces the risk of clogging of the reaction liquid during the heat treatment process and can extend the stable operation period of the reaction device. On the other hand, it is beneficial to improve the quality of the isocyanate product.

[0033] The method of the present invention is used to prepare isocyanate, wherein the mixed liquid obtained by the cold phosgenation reaction is first subjected to a graded treatment, and then the heavy liquid stream and the light liquid stream obtained by the graded treatment are fed into a reaction distillation tower through a specific feed position for a hot phosgenation reaction. This can effectively solve the clogging problem of the tower reactor. Compared with the prior art, not only is the process simpler and the production process can be effectively shortened, but it is also beneficial to improving the raw material conversion rate, extending the operation cycle of the tower reactor, and reducing the pressure drop of the entire tower, thereby helping to reduce production costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG1 is a schematic diagram of an isocyanate preparation system in one embodiment;

[0035] FIG. 2 is a schematic diagram of a classification device in one embodiment.

[0036] Explanation of the accompanying drawings: mixed material flow inlet 1, gas phase outlet 2, light liquid material flow outlet 3, heavy liquid material flow outlet 4, mixed material flow 5, gas phase material flow 6, heavy liquid material flow 7, light liquid material flow 8, tower bottom 11, distillation section 12, distillation section 13, first partition plate 14, second partition plate 15, third partition plate 16, first feed liquid tank 17, second feed liquid tank 18, buffer area 19, third feed liquid tank 20, kettle body 100, grading device 200, distillation tower 300. DETAILED DESCRIPTION

[0037] In order to facilitate the understanding of the present invention, the present invention will be further described below in conjunction with examples. It should be understood that the following examples are only for a better understanding of the present invention and do not mean that the present invention is limited to the following examples.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which the present invention pertains. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0039] Where specific experimental steps or conditions are not specified in the examples, the corresponding conventional experimental steps or conditions in the art can be used. Reagents or instruments used without specifying the manufacturer are all commercially available conventional products.

[0040] Directional terms such as "up," "down," "left," "right," "front," "rear," "front," "back," "top," and "bottom" mentioned or potentially mentioned in this specification are defined relative to the configurations shown in the accompanying drawings. These terms are relative and may vary depending on the location and usage of the component. The words "inward" and "outward" refer to directions toward or away from the geometric center of a particular component, respectively. Furthermore, the terms "first," "second," and "third," etc., are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

[0041] One aspect of the present invention provides a method for preparing isocyanate, comprising the steps of:

[0042] (1) subjecting an amine compound and phosgene to a cold phosgene gasification reaction in the presence of an inert solvent to obtain a mixed stream 5 (a reaction liquid containing acyl chloride and hydrochloride substances) to a graded treatment, so that the mixed stream 5 is divided into three parts: a gas phase stream 6, a light liquid stream 8, and a heavy liquid stream 7, wherein the light liquid stream 8 contains light solid particles, and the heavy liquid stream 7 contains heavy solid particles, and the density of the light solid particles is less than that of the heavy solid particles; wherein the main components of the gas phase stream 6 are HCl and phosgene;

[0043] (2) The light liquid stream 8 is fed into the bottom 11 of a distillation tower 300 for performing a thermal phosgenation reaction, and the heavy liquid stream 7 is fed into the distillation tower 300 from a position between the stripping section 12 and the distillation section 13 of the distillation tower 300. An isocyanate product is obtained in the bottom 11 of the distillation tower 300, which is mainly a mixed product of isocyanate and an inert solvent.

[0044] During their research, the inventors discovered that the solid particles produced by the reaction of amine compounds and phosgene can be divided into two categories based on their density: lightweight solid particles with a lower density and heavy solid particles with a higher density. The density of the lightweight solid particles is lower than the liquid phase density of the mixed stream, while the density of the heavy solid particles is higher than the liquid phase density of the mixed stream. In the present invention, the mixed stream 5 obtained by the cold phosgenation reaction is first subjected to a graded treatment before entering the hot phosgenation reaction stage to separate it into three parts: a gas phase stream 6, a light liquid stream 8, and a heavy liquid stream 7. The light liquid stream 8 is a liquid enriched with light solid particles (mainly containing urea by-products, the main component of which is an isocyanate-amine complex containing urea groups), and the heavy liquid stream 7 is a liquid enriched with heavy solid particles (mainly composed of acyl chloride, hydrochloride, and a complex of the two). The inventors have found that by feeding the light liquid stream 8 into the bottom 11 of the distillation tower 300 in the hot phosgenation reaction stage and feeding the heavy liquid stream 7 into the position between the stripping section 12 and the distillation section 13 of the distillation tower 300, problems such as clogging and scaling of the distillation tower can be significantly improved, the raw material conversion rate can be improved, and the operating cycle of the distillation tower can be effectively extended, which will also be beneficial to extending the operating cycle of the downstream post-processing system.

[0045] Preferably, in step (1), the density of the heavy solid particles is 1.15 to 1.30 g / cm 3 , for example 1.15 g / cm 3 , 1.16g / cm 3 , 1.18g / cm 3 , 1.20g / cm 3 , 1.23g / cm 3 , 1.25g / cm 3 , 1.28g / cm 3 or 1.30g / cm 3etc., preferably 1.18 to 1.25 g / cm 3 The density of the lightweight solid particles is 0.95 to 1.12 g / cm 3 , for example 0.95g / cm 3 , 0.98g / cm 3 , 1.00g / cm 3 , 1.02g / cm 3 , 1.05g / cm 3 , 1.10g / cm 3 or 1.12 g / cm 3 etc., preferably 1.02 to 1.10 g / cm 3 By subjecting the mixed stream 5 to graded treatment to obtain a heavy liquid stream 7 enriched with heavy solid particles of the above-mentioned preferred density and a light liquid stream 8 enriched with light solid particles of the above-mentioned preferred density, urea by-products are more thoroughly separated from other solid particles, wherein urea by-products are enriched in the light liquid stream 8, and heavy solid particles (mainly composed of acyl chloride, hydrochloride and a complex thereof) are enriched in the heavy liquid stream 7. The light liquid stream 8 enriched with light solid particles of the above-mentioned density and the heavy liquid stream 7 enriched with heavy solid particles of the above-mentioned density are fed into the distillation tower 300 according to the specific feed position of the present invention to carry out a thermal phosgenation reaction, which is beneficial to further enhance the anti-clogging effect of the reaction device and further improve the quality of the isocyanate product.

[0046] The inventors have found that the light solid particles contained in the mixed stream obtained by the cold phosgenation reaction are the main cause of clogging and scaling of the tower reactor in the hot phosgenation reaction. The main component of the light solid particles is an isocyanate-amine complex containing urea groups. During the hot phosgenation reaction, due to the strong hydrogen bond interaction between the urea groups, it is difficult to dissolve in an inert solvent. In the present invention, the light liquid stream 8 rich in light solid particles is fed into the bottom 11 of the distillation tower 300 to enter the hot phosgenation reaction stage, which can greatly reduce the Light solid impurity particles may cause clogging and scaling of the reactor; in the present invention, a heavy liquid stream 7 rich in heavy solid particles is fed into the distillation tower 300 between the distillation section 13 and the stripping section 12, and the heavy solid particles are mainly composed of acyl chloride, hydrochloride and a complex of the two, which will be gradually dissolved and completely dissolved in the mixed stream during the thermal phosgenation reaction; through the specific feeding method of the light liquid stream 8 and the heavy liquid stream 7 in the thermal phosgenation reaction stage of the present invention, not only can the problem of tower reactor clogging be effectively solved, but also it is beneficial to improve the conversion rate of the raw materials.

[0047] Preferably, in step (1), when the classification treatment is performed, the residence time of the liquid phase stream in the mixed stream 5 in the classification device 200 is 1 to 10 minutes, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 minutes, and preferably 3 to 6 minutes. The preferred residence time is advantageous for enriching light solid particles of target density in the light liquid stream 8 and enriching heavy solid particles of target density in the heavy liquid stream 7 during the classification process, which is advantageous for further extending the reactor operation cycle and further improving the quality of the isocyanate product. The operating pressure of the classification device 200 is, for example, 0 MPag to 0.5 MPag, for example, 0.1, 0.2, 0.3, 0.4, 0.5 MPag, and preferably 0.1 MPag to 0.3 MPag.

[0048] In some preferred embodiments, in step (1), the density of the heavy solid particles is 1.15 to 1.30 g / cm 3 The density of the light solid particles is 0.95 to 1.12 g / cm 3 , and the residence time of the liquid phase stream in the classification device 200 is 1 to 10 minutes, which can further extend the operation cycle of the distillation tower 300 and improve the product quality. In a more preferred embodiment, in step (1), the density of the heavy solid particles is 1.18 to 1.25 g / cm 3 The density of the lightweight solid particles is 1.02 to 1.10 g / cm 3 , and the residence time of the liquid phase stream in the classification device 200 is preferably 3 to 6 minutes, which is conducive to more significantly improving the operating cycle of the distillation tower 300 and the product quality.

[0049] In some embodiments, in step (1), after the classification process by the classification device 200, the mass percentage of the light liquid stream 8 in the mixed stream 5 is 10% to 50%, for example, 10%, 20%, 30%, 40% or 50%, etc.;

[0050] After the classification process by the classification device 200 , the mass percentage of the heavy liquid stream 7 in the mixed stream 5 is 40% to 85%, such as 40%, 50%, 60%, 70%, 80% or 85%, for example, 50% to 85%;

[0051] The mass percentage of the gas phase stream 6 in the mixed stream 5 is 1.5% to 10%, for example, 1.5%, 2%, 4%, 6%, 8% or 10%.

[0052] In step (1), the mixed material stream 5 can be transported to the classification device 200 by a pump for classification treatment. Furthermore, the classification treatment is carried out in a classification device that separates light and heavy solid particles based on the density difference principle. The classification treatment of the mixed material stream can be directly carried out by using a device known in the art that can classify light and heavy solid particles in a liquid feed based on the density difference principle.

[0053] In some embodiments, a grading device 200 as shown in FIG2 can be used to perform grading of the mixed material flow. Specifically, for example, the grading device 200 includes a kettle body 100, and the inner cavity of the kettle body 100 is divided into a first liquid tank 17, a second liquid tank 18, a buffer area 19 and a third liquid tank 20 adjacent to each other in sequence. The first liquid tank 17 is provided with a mixed material inlet 1, and the second liquid tank 18 is provided with an overflow port for the upper liquid in the first liquid tank 17 to overflow into the second liquid tank 18. The outer wall of the lower part of the second liquid tank 18 and the inner wall of the kettle body 100 are connected. A lower liquid flow channel is formed between the first liquid tank 17 and the buffer area 19, that is, the liquid in the lower part or bottom of the first liquid tank 17 can enter the buffer area 19 through the lower liquid flow channel indicated by the dotted arrow in Figure 1, and the third liquid tank 20 is provided with an overflow port for the upper liquid in the buffer area 19 to overflow into the third liquid tank 20; a light liquid flow outlet 3 is provided at the bottom of the second liquid tank 18, and a heavy liquid flow outlet 4 is provided at the bottom of the third liquid tank 20; the kettle body 100 is provided with a gas phase outlet 2 for discharging the gas phase flow escaping from the inner cavity of the kettle body 100. Specifically, for example, the inner cavity of the kettle body is divided into a first liquid tank 17, a second liquid tank 18, a buffer area 19, and a third liquid tank 20, which are adjacent to each other in sequence, by a plurality of partitions. Taking FIG1 as an example, these partitions include a first partition 14, a second partition 15, and a third partition 16. Specifically, for example, the lower portion of the second liquid tank 18 is narrower than the upper portion, thereby forming a free space between the lower outer wall of the second liquid tank 18 and the lower inner wall of the kettle body 100, thereby serving as a lower liquid flow channel for the lower liquid flow. A gap is formed between the top of the second partition 15 and the top of the kettle body 100, thereby allowing the gas phase to pass through and enter the gas phase outlet 2. In the example of FIG2, the height of the third partition 16 is less than that of the first partition 14. FIG2 shows only an example of a classification device 200. Other devices that can classify light and heavy solid particles in the liquid feed based on the principle of density difference can also be used to classify the mixed material flow 5.

[0054] In a preferred embodiment, in step (2), the number of theoretical plates of the rectifying section 13 of the rectifying tower 300 is 3 to 8, preferably 4 to 5; the number of theoretical plates of the stripping section 12 of the rectifying tower 300 is 13 to 25, preferably 15 to 20. The stripping section 12 of the rectifying tower 300 simultaneously performs the functions of reaction and stripping. The use of the above-mentioned preferred rectifying tower parameters is conducive to further improving the reaction effect and anti-clogging effect, and is conducive to obtaining a longer equipment operation cycle.

[0055] Preferably, the tower body material of the distillation tower 300 is Hastelloy or 316L.

[0056] In a preferred embodiment, the bottom temperature of the distillation tower 300 is 120°C to 190°C, for example, 120, 130, 150, 170, 190°C, etc.; the top pressure is 0 MPag to 0.5 MPag, for example, 0.1, 0.3, 0.5 MPag, etc.; the reflux ratio is 0.2 to 2.0, for example, 0.2, 0.5, 1, 1.5, 2.0, etc., preferably 1 to 1.2.

[0057] In some embodiments, preparing the isocyanate under a combination of the above-mentioned preferred conditions will facilitate obtaining better implementation results.

[0058] In some embodiments, the amine compound includes one or more of diaminodiphenylmethane, polymethylene polyphenyl polyamines, diaminotoluene, isophoronediamine, hexamethylenediamine, cyclohexamethylenediamine, p-phenylenediamine, and naphthalenediamine.

[0059] In some embodiments, the inert solvent includes one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, and diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene. The mass ratio of the amine compound to the inert solvent is, for example, 1:(1-6), preferably 1:(2.5-5), more preferably 1:(3-4), such as 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, or 1:5.5. In some embodiments, the mass ratio of phosgene to the amine compound is 1-10, such as 1, 2, 4, 6, 8, 10, etc.

[0060] In the present invention, the cold phosgene vaporization reaction in step (1) can be carried out using conventional processes in the art, without particular limitation. For example, the amine compound is mixed with a solvent in a static mixer, and then mixed with a mixed solution of phosgene and solvent in a dynamic mixer for an adiabatic reaction to obtain a cold phosgene vaporization reaction product. Preferably, the temperature of the cold phosgene vaporization reaction product is 60 to 140°C; preferably, the pressure of the cold phosgene vaporization reaction is 1 to 30 barg.

[0061] The reaction process of the cold phosgenation reaction can be described with reference to patent application CN115925581A. The main improvement of the present invention over the prior art is that the mixed stream obtained from the cold phosgenation reaction is subjected to a graded treatment before entering the hot phosgenation reaction.

[0062] The present invention provides an isocyanate preparation system for implementing the method described above. Referring to FIG1 , the system comprises:

[0063] The classification device 200 is used to classify the mixed stream 5 obtained by the cold phosgene gasification reaction to separate the mixed stream 5 into a gas phase stream 6, a light liquid stream 8 containing the light solid particles, and a heavy liquid stream 7 containing the heavy solid particles; wherein the mixed stream 5 is obtained by the cold phosgene gasification reaction of an amine compound and phosgene in the presence of an inert solvent;

[0064] The distillation tower 300 is used to receive the light liquid stream 8 and the heavy liquid stream 7 and perform a thermal phosgenation reaction to generate isocyanate, and the feeding position of the light liquid stream 8 of the distillation tower 300 is set at the bottom 11 of the distillation tower 300, and the feeding position of the heavy liquid stream of the distillation tower 300 is set between the distillation section 12 and the distillation section 13 of the distillation tower 300.

[0065] Furthermore, the classification device 200 is a classification device that separates light and heavy solid particles based on the density difference principle. In some embodiments, the classification device is, for example, the device shown in FIG2 . The description of the classification device shown in FIG2 is referred to the above description and will not be repeated here.

[0066] The present invention is further illustrated below by means of specific examples, but it should not be understood that the protection scope of the present invention is limited thereto.

[0067] In the following examples and comparative examples, the density of heavy solid particles in the heavy liquid stream 7 and the density of light liquid solid particles in the light liquid stream 8 are detected by filtering a sample of the heavy liquid stream 7 or the light liquid stream 8 and measuring the density using the drainage method.

[0068] In the following examples and comparative examples, the reaction effect is characterized by the content of the by-product urea compound in the bottom liquid of the distillation tower (the lower the content of the urea compound, the better the reaction quality).

[0069] The determination method of urea compounds is as follows: liquid chromatography is used for determination, the liquid chromatography instrument is Shimadzu LC-20A, using SIL-20A automatic sampler, CTO-20A column oven, SPD-M20A detector, and the chromatographic column is ODS SP (250*4.6mm) (Inertsil), 5μm.

[0070] The schematic diagram of the isocyanate preparation system in the following examples is shown in FIG1 , and the classification device 200 used is shown in FIG2 . In the following examples and comparative examples, the method for generating a mixed stream by cold phosgene gasification reaction of an amine compound with phosgene in chlorobenzene solvent is described as follows:

[0071] Chlorobenzene solvent and a methylene-crosslinked polyphenylmethane series polyamine (hereinafter referred to as polyamine) are mixed in a static mixer to form a mixed solution. Phosgene and the mixed solution are then mixed in a dynamic mixer and subjected to an adiabatic cold phosgenation reaction at a pressure of 1 to 30 barg and a cold reaction product temperature of 60 to 140°C. After the reaction, a mixed stream, i.e., mixed stream 5 in Figure 1, is obtained and used in subsequent examples and comparative examples.

[0072] The methylene-crosslinked polyphenylmethane series polyamines are produced by the Yantai MDI unit in the Yantai Wanhua Industrial Park. The mass ratio of chlorobenzene to the methylene-crosslinked polyphenylmethane series polyamines is 1.0-4.0. The mass ratio of phosgene to the polyamines is 1.0-5.0.

[0073] Example 1

[0074] The mixed material flow 5 is pumped from the mixed material inlet 1 to the grading device 200 for grading treatment. The pressure in the inner cavity of the grading device 200 is 0.12 MPag, and the residence time of the liquid phase flow in the mixed material flow 5 in the grading device 200 is 5 minutes. The light liquid flow 8 flows out from the light liquid flow outlet 3, the heavy liquid flow 7 flows out from the heavy liquid flow outlet 4, and the gas phase flow 6 is discharged from the gas phase outlet 2. The mass proportion of the light liquid flow 8 obtained after grading in the mixed material flow 5 is 35%, the mass proportion of the heavy liquid flow 7 obtained after grading in the mixed material flow 5 is 62%, and the mass proportion of the gas phase flow 6 obtained after grading in the mixed material flow 5 is 3%. Among them, the density of heavy solid particles in the heavy liquid flow 7 is 1.23 g / cm 3 The density of light solid particles in the light liquid stream 8 is 1.05 g / cm 3 Referring to Figure 1 , the light liquid stream 8 obtained in the above steps is fed into the bottom 11 of the distillation tower 300 , and the heavy liquid stream 7 is fed into the first theoretical stage between the rectifying section 13 and the stripping section 12 of the distillation tower 300 . The rectifying section 13 has 5 theoretical stages, while the stripping section 12 has 21 theoretical stages. The tower body of the distillation tower 300 is made of 316L.

[0075] The temperature of the bottom 11 of the distillation tower 300 was 155° C.; the pressure at the top of the tower was 0.4 MPag; the temperature at the top of the tower was 95° C.; and the reflux ratio was 1.2.

[0076] According to this embodiment, the preparation of isocyanate was carried out, and the operating life of the distillation tower 300 reached 779 days (during which no clogging or scaling occurred, resulting in the need to stop production for desilting or clearing).

[0077] Examples 2-3 and Comparative Examples 1-2

[0078] Examples 2-3 and Comparative Examples 1-2 were carried out with reference to Example 1, with the only difference being the density of the light solid particles in the light liquid stream 8 obtained after classification, the density of the heavy solid particles in the heavy liquid stream 7 obtained after classification, and the residence time of the liquid phase stream in the mixed stream 5 in the classification device 200 when the mixed stream 5 is classified in the classification device 200. For details of the differences, please refer to Table 1.

[0079] Table 1

[0080] Note: The “distillation tower operation cycle” mentioned in Table 1 refers to the duration of continuous operation of the distillation tower, during which no siltation or scaling occurs, resulting in the need to stop production for desilting or clearing.

[0081] Comparative Example 3

[0082] The process was carried out with reference to Example 1, except that in Comparative Example 3, the mixed stream produced in the cold-light gasification reaction was directly pumped into the first theoretical plate between the rectifying section and the stripping section of the distillation tower.

[0083] When isocyanate was prepared according to this comparative example, the operating life of the distillation tower was shortened to 274 days, and the urea content in the bottom liquid of the distillation tower was 2634 ppm.

[0084] It will be readily understood that the above embodiments are merely examples for clarity of description and are not intended to limit the present invention to these examples. Those skilled in the art will readily appreciate that other variations or modifications based on the above description are possible. It is not necessary and impossible to provide an exhaustive list of all possible implementations. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A method for preparing isocyanate, characterized in that, The method comprises the following steps: (1) Classify the mixed material stream obtained by subjecting an amine compound and phosgene to a cold phosgenation reaction in the presence of an inert solvent, so that the mixed material stream is divided into three parts: a gas-phase material stream, a light liquid material stream, and a heavy liquid material stream. The light liquid material stream contains light solid particles, the heavy liquid material stream contains heavy solid particles, and the density of the light solid particles is less than that of the heavy solid particles; (2) Feed the light liquid material stream into the bottom of a distillation column for a thermal phosgenation reaction, and feed the heavy liquid material stream into the distillation column at a position between the stripping section and the rectifying section of the distillation column, and obtain an isocyanate product at the bottom of the distillation column.

2. The method according to claim 1, characterized in that, In step (1), the density of the heavy solid particles is 1.15 to 1.30 g / cm 3 , preferably 1.18 to 1.25 g / cm 3 ; the density of the light solid particles is 0.95 to 1.12 g / cm 3 , preferably 1.02 to 1.10 g / cm 3 .

3. The method according to claim 2, wherein In step (1), the residence time of the liquid-phase material stream in the mixed material stream in the classification device for the classification treatment is 1 to 10 minutes, preferably 3 to 6 minutes; The pressure of the classification device is, for example, 0 MPag to 0.5 MPag, preferably 0.1 MPag to 0.3 MPag.

4. The method according to claim 2, characterized in that, In step (1), the mass percentage of the light liquid material stream in the mixed material stream is 10% to 50%; The mass percentage of the heavy liquid material stream in the mixed material stream is 40% to 85%; The mass percentage of the gas-phase material stream in the mixed material stream is 1.5% to 10%.

5. The method according to any one of claims 1 to 4, characterized in that, The classification treatment is carried out in a classification device that separates light and heavy solid particles in the feed liquid based on the principle of density difference; Preferably, the classification device includes a kettle body. The inner cavity of the kettle body is divided into an adjacent first liquid material tank, a second liquid material tank, a buffer area, and a third liquid material tank in sequence. A mixed material stream inlet is provided in the first liquid material tank, and an overflow port for the upper-layer liquid in the first liquid material tank to overflow into the second liquid material tank is provided in the second liquid material tank. A lower liquid flow channel capable of connecting the first liquid material tank and the buffer area is formed between the outer wall of the lower part of the second liquid material tank and the inner wall of the kettle body. An overflow port for the upper-layer liquid in the buffer area to overflow into the third liquid material tank is provided in the third liquid material tank; a light liquid material stream outlet is provided at the bottom of the second liquid material tank, and a heavy liquid material stream outlet is provided at the bottom of the third liquid material tank; a gas-phase outlet for discharging the gas-phase material stream escaping from the inner cavity of the kettle body is provided on the kettle body.

6. The method according to any one of claims 1-4, characterized in that, In step (2), the number of theoretical plates in the rectifying section of the distillation column is 3 to 8, preferably 4 to 5; the number of theoretical plates in the stripping section of the distillation column is 13 to 25, preferably 15 to 20; Preferably, the tower body material of the distillation column is Hastelloy or 316L.

7. The method according to claim 6, characterized in that The temperature at the bottom of the distillation column is 120 °C to 190 °C; the pressure at the top of the tower is 0 MPag to 0.5 MPag; the reflux ratio is 0.2 to 2.0, preferably 1 to 1.

2.

8. The method according to any one of claims 1-4, characterized in that, In step (1), the inert solvent includes one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, and diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene; And / or, the amine compound includes one or more of diaminodiphenylmethane, polymethylenepolyphenyl polyamine, diaminotoluene, isophorone diamine, hexamethylenediamine, cyclohexanediamine, p-phenylenediamine, naphthalenediamine; And / or, the mass ratio of the phosgene to the amine compound is 1 to 10; And / or, the mass ratio of the amine compound to the inert solvent is 1:(1 to 6).

9. An isocyanate preparation system for implementing the method according to any one of claims 1-8, characterized in that, The system includes: A classification device for classifying the mixed material flow obtained from the cold phosgenation reaction to separate a gas-phase material flow, a light liquid material flow containing the light solid particles, and a heavy liquid material flow containing the heavy solid particles from the mixed material flow; the mixed material flow is obtained by the cold phosgenation reaction of an amine compound and phosgene in the presence of an inert solvent; A rectification column for receiving the light liquid material flow and the heavy liquid material flow and performing a thermal phosgenation reaction to generate isocyanate, and the feeding position of the light liquid material flow of the rectification column is arranged at the bottom of the rectification column, and the feeding position of the heavy liquid material flow of the rectification column is arranged between the stripping section and the rectification section of the rectification column.

10. The isocyanate preparation system according to claim 9, characterized in that, The classification device is a classification device that separates the light and heavy solid particles in the liquid material based on the principle of density difference.

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