A system and method for the preparation of isocyanates

Abstract

The application provides a preparation system and method of isocyanate, wherein the system comprises a cold phosgene reactor and a hot phosgene reactor connected in series, the hot phosgene reactor is used for receiving a stream output by the cold phosgene reactor, and the stream is subjected to a hot phosgene reaction to obtain isocyanate; the hot phosgene reactor comprises a rectification section, a reaction section and a stripping section, and a stream inlet is arranged between the rectification section and the reaction section; the reaction section comprises multiple layers of trays, and the overflow weirs of each layer of the reaction section trays have different inclination angles, so that the residence time of the stream on each reaction section tray is greater than a set time length. Through the scheme, the residence time of the stream in the reaction section can reach the set time length, the formamide chlorination time is adjusted, the number of generated solid particles is reduced, and thus the problem of clogging the reactor is solved.

Description

Technical Field

[0001] This application relates to the field of isocyanate preparation technology, and in particular to a system and method for preparing isocyanates. Background Technology

[0002] Isocyanates all contain -NCO functional groups in their molecular structure, and currently, the phosgenation method is mainly used to produce these substances both domestically and internationally. Under appropriate temperature and pressure conditions, a photochemical reaction solution containing isocyanate and hydrogen chloride is obtained by mixing polyamine, phosgene, and an inert solvent. After separating the inert solvent and phosgene from the photochemical reaction solution, crude isocyanate product is obtained, which is then further separated to obtain the final isocyanate product.

[0003] The phosgenation process for producing isocyanates mainly involves two intermediate steps: "cold phosgenation" and "thermal phosgenation." In cold phosgenation, polyamines react with excess phosgene at low temperatures to form the isocyanate precursor form chloroformamide. In thermal phosgenation, chloroformamide decomposes at high temperatures into isocyanate and hydrogen chloride. The cold phosgenation reaction temperature is below 60°C, while the thermal phosgenation reaction temperature reaches 100°C to 200°C. In actual production, the two reactors for cold and thermal phosgenation are connected in series. The product stream from the cold phosgenation reaction enters the thermal phosgenation reactor, where hydrogen chloride generated during the thermal phosgenation reaction is separated by depressurization to promote the decomposition of chloroformamide.

[0004] During the reaction of polyamines with phosgene to produce isocyanates, solid particles are generated. These solid particles are prone to depositing in the reactor during the thermal phosgene process of formamide decomposition to produce isocyanates, causing the reactor to become clogged and requiring shutdown for cleaning after a certain period of operation. This greatly increases production costs and affects production efficiency. Summary of the Invention

[0005] The technical problem to be solved by this application is that solid particles generated during the preparation of existing isocyanates cause reactor clogging. To address this, this application proposes an isocyanate preparation system and method.

[0006] To address the aforementioned technical problems, this application provides the following technical solution: In a first aspect, the technical solution of this application provides an isocyanate preparation system, comprising a cold phosgene reactor and a hot phosgene reactor connected in series, wherein: The thermophotogasification reactor is used to receive the feed stream output from the cold photogasification reactor and to perform a thermophotogasification reaction on the feed stream to obtain isocyanate; The thermo-photogasification reactor includes a rectification section, a reaction section, and a stripping section, with a feed inlet between the rectification section and the reaction section. The reaction section includes multiple trays, and the overflow weir of each reaction section tray has a different inclination angle so that the residence time of the feed on each reaction section tray is greater than a set time.

[0007] In some of the isocyanate preparation systems described in the schemes, the inclination angle of the outer weir of the overflow weir of the reaction section tray is determined in the following manner: ; Where s is the number of layers in the reaction section tray, the tray at the feed inlet is the first layer and increases from top to bottom, η is the inclination angle of the overflow weir of the s-th layer reaction section tray, A, B and C are all adjustment coefficients, and z is the length of the overflow weir of the s-th layer reaction section tray.

[0008] In some of the isocyanate preparation systems described in the schemes, the adjustment coefficients are: adjustment coefficient A is 0.05-1; adjustment coefficient B is 0.01-0.03; and adjustment coefficient C is 40-50.

[0009] In some embodiments of the isocyanate preparation system, the length z of the outer weir of the overflow weir is 30-120 mm.

[0010] In some schemes, the isocyanate preparation system has a total of 10-20 layers in the reaction section tray.

[0011] In some of the isocyanate preparation systems described in the schemes, the set time is determined by the following method: The residual amount of formamide chloride in the mixture of isocyanate and inert solvent was tested in a reactor adapted to the scale of the reaction section; the relationship between time and residual amount was recorded during the test; the set time corresponding to the target residual amount was determined according to the relationship; wherein the target residual amount is the minimum residual amount that will not cause clogging.

[0012] In some of the isocyanate preparation systems described in the scheme, a vent hole is provided at the bottom of the overflow weir in the reaction section tray.

[0013] In some embodiments of the isocyanate preparation system, the distance between the designated area and the bottom of the reaction section tray is 0-300 mm.

[0014] In some embodiments of the isocyanate preparation system, the vent hole has a diameter larger than a set diameter, which is determined based on the diameter of the solid particles generated during the phosgene reaction.

[0015] Secondly, the present application provides a method for preparing isocyanate using the isocyanate preparation system described in any one of the first aspects, comprising: Polyamine, phosgene, and inert solvent are placed in a cold phosgene reactor to undergo a cold phosgene reaction to obtain a mixed feed stream; The feed stream is fed into a thermophotogasification reactor, and the reaction section temperature, top pressure, top temperature, reflux ratio, and bottom temperature of the thermophotogasification reactor are adjusted to create a reaction environment suitable for the feed stream to undergo thermophotogasification to obtain isocyanate. The top of the thermophotogasification reactor yields hydrogen chloride and an inert solvent, while the bottom of the thermophotogasification reactor yields a mixture of isocyanate and inert solvent. Isocyanates were extracted from the mixture.

[0016] In the above scheme, the inert solvent is a conventional solvent in the art, selected from one or more of m-toluene, xylene, chlorobenzene and o-dichlorobenzene, ethyl acetate, and diethyl carbonate, preferably chlorobenzene and o-dichlorobenzene, and more preferably chlorobenzene. The suitable isocyanate raw material monomer is selected from diisocyanates, preferably diphenylmethylene diisocyanate, polydiphenylmethylene diisocyanate, toluene diisocyanate, isophthalimethylene diisocyanate, or isophorone diisocyanate.

[0017] The technical solution of this application has the following technical advantages over the prior art: This application provides a system and method for preparing isocyanates. The system includes a cold phosgene reactor and a hot phosgene reactor connected in series. The hot phosgene reactor receives the feed stream output from the cold phosgene reactor and performs a hot phosgene reaction to obtain isocyanates. The hot phosgene reactor includes a rectification section, a reaction section, and a stripping section, with the feed stream inlet located between the rectification section and the reaction section. The reaction section includes multiple trays, each tray having an overflow weir with a different inclination angle to ensure that the residence time of the feed stream on each tray exceeds a set time. This method achieves the set residence time of the feed stream in the reaction section, allowing for adjustment of the formamide chlorine reaction time and thus reducing the amount of solid particles generated, thereby solving the problem of reactor clogging. Attached Figure Description

[0018] The preferred embodiments of this application will be described in detail below with reference to the accompanying drawings, which will help to understand the purpose and advantages of this application, wherein: Figure 1 This is a schematic diagram of the structure of a single-layer tray according to one embodiment of this application; Figure 2 This is a schematic diagram illustrating the arrangement of the vent holes according to one embodiment of this application; Figure 3This is a process flow diagram of the isocyanate preparation method according to one embodiment of this application. Detailed Implementation

[0019] The technical solutions of this application will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0021] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "joining" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0022] Furthermore, the technical features involved in the different embodiments of this application described below can be combined with each other as long as they do not conflict with each other.

[0023] One embodiment of this application provides an isocyanate preparation system, including a cold phosgene reactor and a hot phosgene reactor connected in series. The hot phosgene reactor receives the feed stream output from the cold phosgene reactor and performs a hot phosgene reaction to obtain isocyanate. The hot phosgene reactor includes a rectification section, a reaction section, and a stripping section, with a feed inlet between the rectification section and the reaction section. The reaction section includes multi-layer trays. Figure 1 As shown, each reaction section tray 100 includes a bottom 101 and an overflow weir 102 with different inclination angles, so that the residence time of the material flow on each reaction section tray is longer than a set time.

[0024] The above-described solution of this application enables the material flow to maintain a set residence time in the reaction section 200, thereby extending the residence time of formamide chlorine in the reaction section 200 and reducing the amount of solid particles generated, thus solving the problem of reactor clogging.

[0025] In some schemes, such as Figure 1 As shown, the inclination angle of the outer weir 102 of the overflow weir of the reaction section tray 100 is determined in the following manner: ; Where s is the number of layers in the reaction section tray 100, the tray at the material inlet is the first layer and increases from top to bottom, η is the inclination angle of the overflow weir 102 of the s-th layer reaction section tray, A, B and C are all adjustment coefficients, and z is the length of the overflow weir 102 of the s-th layer reaction section tray.

[0026] Wherein, the adjustment coefficients are: adjustment coefficient A is 0.05-1; adjustment coefficient B is 0.01-0.03; and adjustment coefficient C is 40-50. Preferably, A is 0.08, B is 0.02, and C is 42.0. That is, the inclination angle of the overflow weir 102 of the tray in the s-th reaction section is preferably determined by the following formula: .

[0027] More preferably, the length Z of the outer overflow weir is 30-120 mm, preferably 40-75 mm. Furthermore, the length of the outer overflow weir can gradually increase with the increase of the s value. The aforementioned angle in this application is determined based on a set duration, which is determined as follows: a residual amount test of formamide chloride in a mixture of isocyanate and inert solvent is conducted in a reactor adapted to the scale of the reaction section; the relationship between time and residual amount is recorded during the test; the set duration corresponding to the target residual amount is determined based on the relationship; wherein the target residual amount is the minimum residual amount that will not cause clogging. Through the reaction section tray structure set in the above embodiments of this application, in the thermophotogasification reactor, the number of trays in the rectification section is 3-8, preferably 4-5; the number of trays in the reaction section is 10-20, preferably 12-15; and the number of trays in the stripping section is 3-5, preferably 4. Specifically, the thermophotogasification reactor can be implemented using a rectification column with a Hastelloy or 316L column body material.

[0028] By setting the above-mentioned tilt angle, the reaction section tray has a tilted external weir design, which helps solid particles to overflow from the liquid layer of the reaction section tray and avoids solid particles accumulating at the bottom of the external weir of the reaction section tray.

[0029] In some embodiments, in the reaction section tray of the isocyanate preparation system, a vent hole 103 is provided in a designated area 104 at the bottom 101 of the overflow weir. The vent hole 103 allows solid particles to be released, preventing them from remaining in the reactor. The distance x between the designated area 104 and the bottom of the reaction section tray is 0-300 mm, preferably 200 mm, for example, within 180 mm. Accumulation easily occurs in this area, therefore the vent holes 103 can be arranged within this area. The vent holes 103 can be evenly distributed, and the center-to-center distance between different vent holes 103 is 100-300 mm, preferably 150-180 mm, for example, 160 mm or 170 mm.

[0030] In some embodiments, in the isocyanate preparation system, the pore size of the vent 103 is larger than a set pore size, which is determined based on the diameter of the solid particles generated during the phosgene reaction. The size of the set pore size can be determined based on empirical values. Further, the pore size of the vent 103 is 8-20 mm, preferably 10-12 mm, for example 11 mm.

[0031] The isocyanate preparation system provided in this application optimizes the average residence time of the trays during distillation, effectively shortening the total residence time of formamide chlorination. Simultaneously, the distillation process continuously separates the product from the reaction system, shifting the equilibrium towards the products and significantly increasing the equilibrium conversion rate of the isocyanate precursor. This reduces isocyanate losses during production. Furthermore, the reaction and separation are carried out in the same equipment, saving equipment and operating costs. It also reduces the risk of corrosion and blockage during material transport and storage, extends the stable operating time of the reaction unit, and improves the quality of the isocyanate product.

[0032] This application also provides an isocyanate preparation method utilizing the above-described isocyanate preparation system, such as... Figure 3 As shown, it includes: S10: Polyamine, phosgene, and inert solvent are placed in a cold phosgene reactor to undergo a cold phosgene reaction to obtain a mixed feed stream.

[0033] S20: The feed stream is fed into a thermophotogasification reactor, and the reaction section temperature, reflux ratio, top temperature, and bottom temperature of the thermophotogasification reactor are adjusted to create a suitable reaction environment for the feed stream to undergo thermophotogasification to obtain isocyanate. Preferably, the reaction section temperature of the thermophotogasification reactor is 100℃~150℃, further, the reaction section temperature is 110℃~135℃; preferably, the top pressure is 0MPag~0.5MPag, further, the top pressure is 0.2MPag~0.4MPag; preferably, the top temperature is 65℃~95℃, further, the top temperature is 65℃~80℃; preferably, the bottom temperature is 100℃~180℃, further, the bottom temperature is 140℃~155℃; preferably, the reflux ratio is 0.2~2.0, further, the reflux ratio is 1~1.2.

[0034] S30: Hydrogen chloride and an inert solvent are obtained at the top of the thermophotogasification reactor, and a mixture of isocyanate and inert solvent is obtained at the bottom of the thermophotogasification reactor.

[0035] S40: Extract isocyanate from the mixture.

[0036] Verification has shown that the above-mentioned scheme of this application can effectively reduce the residue of isocyanate precursors, reducing the total content of isocyanate precursors in the isocyanate and inert solvent mixture (calculated as the amount remaining after deducting the inert solvent from the isocyanate and mixed solvent mixture) to 15-30 ppm, effectively extending the operating life of the thermo-photogasification reactor by 750-800 days and reducing the overall pressure drop of the tower by 5-10 kPa.

[0037] The above-mentioned solution in this application reduces the risk of corrosion and blockage of reactants during transportation and storage, extends the stable operation time of the reaction device, and improves the quality of isocyanate products.

[0038] The implementation process and effects of the above solution will be described in detail below with a specific example: raw material: Phosgene: Produced using the Yantai MDI unit within the Yantai Wanhua Industrial Park; industrial product. Polyphenylmethane series diamines / polyamines: produced using the Yantai MDI unit within the Yantai Wanhua Industrial Park; industrial products. Chlorobenzene: Selected from Jiangsu Longchang Chemical Co., Ltd., industrial grade, 99%; Main instruments and testing methods: The determination of isocyanate precursors in a mixture of isocyanate and inert solvent was performed using liquid chromatography derivatization, with an Agilent 1260 instrument selected for analysis.

[0039] First, the method for preparing the reaction solution by reacting polyamines and phosgene in solvent chlorobenzene is described: chlorobenzene and a methylene crosslinked polyphenylmethane series diamine / polyamine are mixed in a static mixer at a mass ratio of 3:1 to generate a mixed solution. Phosgene and the mixed solution are then mixed in a dynamic mixer at a mass ratio of phosgene to diamine / polyamine of 4:1. The mixture is then fed into a cold phosgenation reactor, where the cold reaction temperature is controlled at 70°C and the pressure at 270 kPaG. The resulting mixture is used in subsequent examples.

[0040] The above-mentioned feed stream is transported to the thermoluminescent reactor. The feed stream enters between the rectification section and the reaction section of the reactor. The rectification section has 5 trays, the reaction section has 17 trays, and the stripping section has 4 trays. The column body material is 316L. The overflow weir of each tray is 74mm long. The inclination angle of the overflow weir of each tray is arranged according to the theoretical plate order of 1-15, which can be the following sequence: 37.2°, 38.2°, 39.3°, 40.7°, 42.2°, 44.0°, 46.0°, 48.3°, 50.9°, 53.8°, 57.1°, 61.1°, 65.9°, 72.3°, 84.0°. The reaction section temperature is 135℃; the column top pressure is 0MPag~0.5MPag, preferably 0.4MPag; the column top temperature is 95℃, and the column bottom temperature is 155℃; the reflux ratio is 1.2. Within a 200m range along the column tray direction, from the connection point between the overflow weir and the tray, there are vent holes for solid particles. The diameter of the vent holes is 12mm, and the center-to-center distance between the circular holes is 180mm.

[0041] In the above example, the total content of isocyanate precursor in the isocyanate and inert solvent mixture (calculated as the amount remaining after deducting the inert solvent from the isocyanate and mixed solvent stream) is reduced to 15 ppm. This effectively extends the operating life of the thermophosgene reactor in the isocyanate preparation system to 779 days, with a total tower pressure drop of 7.5 kPa. The above embodiment significantly improves the equilibrium conversion rate of isocyanate precursor, effectively shortens the existing production process, increases the raw material conversion rate, and simplifies the process with low operating costs.

[0042] Comparative Example 1 Referring to the scheme in the foregoing embodiments, the only difference in this comparative example is that in the 1-15 theoretical trays, the overflow weir of each tray has an inclination angle of 90°, perpendicular to the tray plane. After distillation processing using the above apparatus, in the above example, the total content of isocyanate precursor in the isocyanate and inert solvent mixture (calculated as the amount remaining after deducting the inert solvent from the isocyanate and mixed solvent stream) is 120 ppm. The thermal phosgene reactor in the isocyanate preparation system has an operating life of 220 days, and the overall pressure drop is 19 kPa.

[0043] Comparative Example 2 Referring to the scheme in the foregoing embodiments, the difference in this comparative example is that the overflow weir of each of the 1-15 theoretical plate trays has an inclination angle of 70°. After distillation processing using the above apparatus, in the above example, the total content of isocyanate precursor in the isocyanate and inert solvent mixture (calculated as the amount remaining after deducting the inert solvent from the isocyanate and mixed solvent stream) is 690 ppm. The thermal phosgene reactor in the isocyanate preparation system has an operating life of 350 days, and the overall pressure drop of the column is 16 kPa.

[0044] Comparative Example 3 Referring to the scheme in the foregoing embodiments, the only difference in this comparative example is that no vent hole for discharging solid particles is provided at the connection between the overflow weir and the tray. After distillation treatment using the aforementioned apparatus, in the above example, the total content of isocyanate precursor in the isocyanate and inert solvent mixture (calculated as the amount remaining after deducting the inert solvent from the isocyanate and mixed solvent mixture) is 18 ppm. The thermal phosgene reactor in the isocyanate preparation system has an operating life of 156 days, and the overall pressure drop of the tower is 35 kPa.

[0045] Compared with the three comparative examples above, the solution in this application embodiment can significantly improve the equilibrium conversion rate of isocyanate precursor, effectively shorten the production process, improve the raw material conversion rate, increase the reactor operating life, and improve the overall tower pressure drop.

[0046] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. A system for preparing isocyanate, characterized in that, It includes a cold phosgene reactor and a hot phosgene reactor connected in series, wherein: The thermophotogasification reactor is used to receive the feed stream output from the cold photogasification reactor and to perform a thermophotogasification reaction on the feed stream to obtain isocyanate; The thermophotogasification reactor includes a rectification section, a reaction section, and a stripping section, with a feed inlet between the rectification section and the reaction section. The reaction section includes multiple trays, each tray having an overflow weir with a different inclination angle to ensure that the residence time of the feed on each tray is greater than a set time. The inclination angle of the overflow weir of the reaction section tray is determined as follows: ； Where s is the number of layers in the reaction section tray, the tray at the feed inlet is the first layer and increases from top to bottom, η is the inclination angle of the overflow weir of the s-th layer reaction section tray, A, B and C are all adjustment coefficients, and z is the length of the overflow weir of the s-th layer reaction section tray.

2. The isocyanate preparation system according to claim 1, characterized in that: Among the adjustment coefficients, adjustment coefficient A is 0.05-1; adjustment coefficient B is 0.01-0.03; and adjustment coefficient C is 40-50.

3. The isocyanate preparation system according to claim 1, characterized in that: The length z of the outer weir of the overflow weir is 30-120mm.

4. The isocyanate preparation system according to claim 3, characterized in that: The total number of trays in the reaction section is 10-20.

5. The isocyanate preparation system according to claim 1, characterized in that, The set duration is determined in the following way: The residual amount of formamide chloride in the mixture of isocyanate and inert solvent was tested in a reactor adapted to the scale of the reaction section; the relationship between time and residual amount was recorded during the test; the set time corresponding to the target residual amount was determined according to the relationship; wherein the target residual amount is the minimum residual amount that will not cause clogging.

6. The isocyanate preparation system according to any one of claims 1-5, characterized in that: In the reaction section tray, a vent hole is provided at the bottom of the outer weir of the overflow weir in a designated area.

7. The isocyanate preparation system according to claim 6, characterized in that: The distance between the designated area and the bottom of the reaction section tray is 0-300mm.

8. The isocyanate preparation system according to claim 7, characterized in that: The diameter of the vent hole is larger than the set diameter, which is determined based on the diameter of the solid particles generated during the phosgene reaction.

9. A method for preparing isocyanate using the isocyanate preparation system according to any one of claims 1-8, characterized in that, include: Polyamine, phosgene, and inert solvent are placed in a cold phosgene reactor to undergo a cold phosgene reaction to obtain a mixed feed stream; The feed stream is fed into a thermophotogasification reactor, and the reaction section temperature, top pressure, top temperature, reflux ratio, and bottom temperature of the thermophotogasification reactor are adjusted to create a reaction environment suitable for the feed stream to undergo thermophotogasification to obtain isocyanate. The top of the thermophotogasification reactor yields hydrogen chloride and an inert solvent, while the bottom of the thermophotogasification reactor yields a mixture of isocyanate and inert solvent. Isocyanates were extracted from the mixture.

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