Preparation system and method for isocyanate

Abstract

A preparation system and method for an isocyanate. The preparation system comprises a cold phosgenation reactor and a hot phosgenation reactor, which are connected in series, wherein the hot phosgenation reactor is used for receiving a material flow output from the cold phosgenation reactor and allows the material flow to undergo a hot phosgenation reaction so as to obtain an isocyanate; the hot phosgenation reactor comprises a rectifying section, a reaction section and a stripping section; a material flow inlet is provided between the rectifying section and the reaction section; and the reaction section comprises a plurality of layers of trays (100), and an outer weir (102) of an overflow weir of the reaction-section tray (100) at each layer has a different angle of inclination, so as to make the residence duration of the material flow on each reaction-section tray (100) greater than a set duration. By means of the solution, the residence duration of the material flow in the reaction section can reach the set duration, and the duration of a reaction of chloroformamide can be adjusted, which can thus reduce the number of solid particles generated, thereby solving the problem of same silting up a reactor.

Description

A system and method for preparing isocyanate Technical Field

[0001] The present application relates to the technical field of isocyanate preparation, and in particular to a system and method for preparing isocyanate. 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, polyamines, 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 phosgenation process for producing isocyanates primarily involves two intermediate steps: cold phosgenation and hot phosgenation. In cold phosgenation, the isocyanate precursor, formamide chloride, is formed from polyamines and excess phosgene at low temperatures. In hot phosgenation, formamide chloride decomposes into isocyanate and hydrogen chloride at high temperatures. While the cold phosgenation reaction temperature is below 60°C, the hot phosgenation reaction temperature reaches 100°C to 200°C. In the actual production process, the cold phosgenation and hot phosgenation reactors are connected in series. The product stream from the cold phosgenation reaction enters the hot phosgenation reactor, where decompression is applied to separate the hydrogen chloride produced during the hot phosgenation reaction to promote the decomposition of formamide chloride.

[0004] Solid particles are produced during the reaction of polyamines and phosgene to form isocyanates. These solid particles are easily deposited in the reactor during the thermal phosgenation process in which formamide chloride decomposes to produce isocyanates, causing the reactor to clog and requiring shutdown and cleaning after a certain period of operation, greatly increasing production costs and affecting production efficiency.

[0005] Summary of the Invention

[0006] The technical problem to be solved by the present application is that solid particles generated in the existing isocyanate preparation process may cause reactor clogging. To this end, the present application proposes a system and method for preparing isocyanate.

[0007] In response to the above technical problems, this application provides the following technical solutions:

[0008] In a first aspect, the technical solution of the present application provides a system for preparing isocyanate, comprising a cold photogasification reactor and a hot photogasification reactor connected in series, wherein:

[0009] The hot phosgenation reactor is used to receive the material flow output by the cold phosgenation reactor for the material flow to undergo a hot phosgenation reaction to obtain isocyanate;

[0010] The thermal phosgenation reactor includes a distillation section, a reaction section, and a stripping section, with a material flow inlet between the distillation section and the reaction section. The reaction section includes multiple layers of tower trays, and the overflow weir and outer weir of each layer of reaction section tower tray have different inclination angles, so that the material flow stays on each reaction section tower tray for longer than a set time.

[0011] In some embodiments of the isocyanate preparation system, the inclination angle of the outer weir of the overflow weir of the reaction stage tray is determined as follows:

[0012] Where s is the number of reaction stage trays, 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 sth reaction stage tray, A, B, and C are adjustment coefficients, and z is the length of the overflow weir of the sth reaction stage tray.

[0013] In some embodiments of the isocyanate preparation system, among the adjustment coefficients, the adjustment coefficient A is 0.05-1; the adjustment coefficient B is 0.01-0.03; and the adjustment coefficient C is 40-50.

[0014] In some embodiments of the isocyanate preparation system, the length z of the outer weir of the overflow weir is 30-120 mm.

[0015] In some embodiments of the isocyanate preparation system, the total number of tower trays in the reaction section is 10-20.

[0016] In some embodiments of the isocyanate preparation system, the set duration is determined as follows:

[0017] A test for the residual amount of formamide chloride in a mixed product of isocyanate and an 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; and the set time 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.

[0018] In some embodiments of the isocyanate preparation system, a discharge hole is provided in a bottom setting area of ​​the outer weir of the overflow weir in the reaction section tower tray.

[0019] In some embodiments of the isocyanate preparation system, the distance between the set area and the bottom of the reaction section tray is 0-300 m.

[0020] In some embodiments of the isocyanate preparation system, the pore size of the vent hole is larger than a set pore size, and the set pore size is determined according to the diameter of solid particles generated during the phosgene reaction.

[0021] In a second aspect, the technical solution of the present application provides a method for preparing isocyanate using the isocyanate preparation system according to any one of the first aspects, comprising:

[0022] placing polyamine, phosgene and an inert solvent in a cold photogasification reactor to carry out a cold photogasification reaction to obtain a mixed material stream;

[0023] The material stream is fed into a thermal phosgenation reactor, and the reaction zone temperature, tower top pressure, tower top temperature, reflux ratio, and tower bottom temperature of the thermal phosgenation reactor are adjusted to form a reaction environment suitable for the material stream to undergo a thermal phosgenation reaction to obtain isocyanate;

[0024] The top of the thermal phosgenation reactor obtains hydrogen chloride and an inert solvent, and the bottom of the thermal phosgenation reactor obtains a mixed product of isocyanate and an inert solvent;

[0025] Isocyanate is extracted from the mixed product.

[0026] In the above embodiment, the inert solvent is a conventional solvent in the art, selected from one or more of m-toluene, xylene, chlorobenzene, o-dichlorobenzene, ethyl acetate, and diethyl carbonate, preferably chlorobenzene and o-dichlorobenzene, more preferably chlorobenzene. Suitable isocyanate raw material monomers are selected from diisocyanates, preferably diphenylmethylene diisocyanate, polydiphenylmethylene diisocyanate, toluene diisocyanate, m-xylylene diisocyanate, or isophorone diisocyanate.

[0027] The technical solution of this application has the following technical effects compared with the existing technology:

[0028] The preparation system and method of isocyanate provided by the present application, wherein the system includes a cold photogasification reactor and a hot photogasification reactor connected in series, the hot photogasification reactor is used to receive the feed stream output by the cold photogasification reactor, and the feed stream is subjected to hot photogasification reaction to obtain isocyanate; the hot photogasification reactor includes a rectifying section, a reaction section and a stripping section, and the rectifying section and the reaction section are connected to form a feed stream inlet; the reaction section includes a multi-layer tower plate, and the overflow weir outer weir of each layer of the reaction section tower plate has a different inclination angle so that the residence time of the feed stream on each reaction section tower plate is greater than the set duration. Through the scheme of the present application, it is possible to achieve a set residence time of the feed stream in the reaction section, adjust the reaction time of methylamide chloride, thereby reducing the number of solid particles generated, thereby solving the problem of clogging the reactor. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The preferred embodiments of the present application will be described in detail below with reference to the accompanying drawings, which will help to understand the objects and advantages of the present application.

[0030] FIG1 is a schematic structural diagram of a single-layer tower tray according to an embodiment of the present application;

[0031] FIG2 is a schematic diagram of the arrangement of the discharge holes according to an embodiment of the present application;

[0032] FIG3 is a process flow chart of a method for preparing isocyanate according to an embodiment of the present application. DETAILED DESCRIPTION

[0033] The following will clearly and completely describe the technical solution of this application in conjunction with the accompanying drawings. Obviously, the embodiments described are only part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making any creative efforts are within the scope of protection of this application.

[0034] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate the description of this application and simplify the description. They do not indicate or imply that the devices or components referred to must have a specific orientation, be constructed, or operate 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.

[0035] In the description of this application, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to direct connections, indirect connections through an intermediate medium, or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in this application based on the specific circumstances.

[0036] In addition, the technical features involved in the different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0037] One embodiment of the present application provides a system for preparing isocyanate, comprising a cold phosgenation reactor and a hot phosgenation reactor connected in series. The hot phosgenation reactor is used to receive the stream output by the cold phosgenation reactor for the stream to undergo a hot phosgenation reaction to obtain isocyanate; the hot phosgenation reactor comprises a rectifying section, a reaction section, and a stripping section, with a stream inlet between the rectifying section and the reaction section, and the reaction section comprises multiple layers of trays. As shown in FIG1 , each layer of reaction section tray 100 comprises a bottom 101 and an overflow weir 102 having different inclination angles, so that the residence time of the stream on each reaction section tray is greater than the set time.

[0038] Through the above-mentioned scheme of the present application, the residence time of the material flow in the reaction section can be achieved to a set time, and the residence time of chlorinated formamide in the reaction section can be extended, thereby reducing the amount of solid particles generated, thereby solving the problem of clogging the reactor.

[0039] In some embodiments, as shown in FIG1 , the inclination angle of the overflow weir 102 of the reaction stage tray 100 is determined by:

[0040] Wherein, s is the number of layers of the reaction stage tray 100, the tray at the material flow 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 of the reaction stage tray, A, B and C are all adjustment coefficients, and z is the length of the overflow weir 102 of the s-th layer of the reaction stage tray.

[0041] Among the adjustment coefficients, the adjustment coefficient A is 0.05-1; the adjustment coefficient B is 0.01-0.03; and the 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 outer weir 102 of the s-th layer reaction stage tray is preferably determined by the following formula:

[0042] Further preferably, the length Z of the outer weir of the overflow weir is 30-120 mm, preferably 40-75 mm. In addition, the length of the outer weir of the overflow weir can also be gradually increased as the value of s increases. The above-mentioned angle in the solution of the present application is determined according to the set time, and the set time is determined as follows: conducting a residual amount test of formamide chloride in a mixed product of isocyanate and inert solvent in a reactor adapted to the scale of the reaction section; recording the relationship between time and residual amount during the test; and determining the set time corresponding to the target residual amount based on the relationship; wherein the target residual amount is the minimum residual amount that will not cause clogging. Based on the reaction section tray structure set in the above embodiment of the present application, in the thermal phosgenation reactor, the number of trays in the rectifying section is 3 to 8, preferably 4 to 5; the number of trays in the reaction section is 10 to 20, preferably 12 to 15; and the number of trays in the stripping section is 3 to 5, preferably 4. In specific implementation, the thermal phosgenation reactor can be implemented using a rectifying tower with a tower body material of Hastelloy or 316L.

[0043] By setting the above-mentioned inclination angle, the reaction section tray has an inclined outer weir design, which helps solid particles overflow from the liquid layer of the reaction section tray and avoids solid particles from accumulating at the bottom of the outer weir of the reaction section tray.

[0044] In some embodiments, in the reaction stage tray of the isocyanate preparation system, a discharge hole 103 is provided in a set area at the bottom 101 of the outer weir of the overflow weir. The discharge hole 103 allows solid particles to be discharged to avoid being retained in the reactor. The set area is preferably within a distance of 0-300 mm, preferably 200 mm, for example, 180 mm from the connection point of the reaction stage tray. Accumulation is likely to occur in this area, so the discharge holes 103 can be arranged in this area. The discharge holes 103 can be evenly distributed, and the center spacing between different discharge holes 103 is 100-300 mm, preferably 150-180 mm, for example, 160 mm or 170 mm.

[0045] In some embodiments, in the isocyanate preparation system, the aperture of the discharge hole 103 is larger than the set aperture. The set aperture is determined according to the diameter of the solid particles produced during the phosgene reaction. The size of the set aperture can be determined based on empirical values. Furthermore, the aperture of the discharge hole 103 is 8-20 mm, preferably 10-12 mm, for example, 11 mm.

[0046] The isocyanate preparation system provided in the embodiments of the present application optimizes the average residence time of the tower plates during the distillation process, effectively shortens the total residence time of the decomposition of formamide chloride, and simultaneously utilizes the distillation effect to continuously separate the product from the reaction system, prompting the equilibrium to shift toward the product, significantly improving the equilibrium conversion rate of the isocyanate precursor, and reducing the loss of isocyanate during the production process. Moreover, the reaction and separation are carried out in the same equipment, which can save equipment costs and operating costs, reduce the risks of corrosion and blockage of materials during transportation and storage, extend the stable operation time of the reaction device, and improve the quality of the isocyanate product.

[0047] The present invention also provides a method for preparing isocyanate using the above-mentioned isocyanate preparation system, as shown in FIG3 , comprising:

[0048] S10: placing polyamine, phosgene and an inert solvent in a cold phosgene gasification reactor to perform a cold phosgene gasification reaction to obtain a mixed material stream.

[0049] S20: The material stream is fed into a thermal phosgenation reactor, and the reaction section temperature, reflux ratio, tower top temperature, and tower bottom temperature of the thermal phosgenation reactor are adjusted to form a reaction environment suitable for the material stream to undergo a thermal phosgenation reaction to obtain isocyanate. Preferably, the reaction section temperature of the thermal phosgenation reactor is 100°C to 150°C, and further, the reaction section temperature is 110°C to 135°C; preferably, the tower top pressure is 0MPag to 0.5MPag, and further, the tower top pressure is 0.2MPag to 0.4MPag; preferably, the tower top temperature is 65°C to 95°C, and further, the tower top temperature is 65°C to 80°C; preferably, the tower bottom temperature is 100°C to 180°C, and further, the tower bottom temperature is 140°C to 155°C; preferably, the reflux ratio is 0.2 to 2.0, and further, the reflux ratio is 1 to 1.2.

[0050] S30: Hydrogen chloride and an inert solvent are obtained at the top of the thermal phosgenation reactor, and a mixed product of isocyanate and an inert solvent is obtained at the bottom of the thermal phosgenation reactor.

[0051] S40: extracting isocyanate from the mixed product.

[0052] It has been verified that the above-mentioned scheme of the present application can effectively reduce the residual isocyanate precursor, and reduce the total content of isocyanate precursor in the mixed stream of isocyanate and inert solvent (calculated as the remaining amount after deducting the inert solvent from the isocyanate and mixed solvent stream) to 15-30 ppm, which can effectively extend the operating life of the thermal phosgenation reactor by 750-800 days, and the pressure drop of the entire tower is 5-10 kPa.

[0053] The above-mentioned solution of the present application reduces the risks of corrosion and blockage of the reaction materials during transportation and storage, prolongs the stable operation time of the reaction device, and improves the quality of the isocyanate product.

[0054] The following describes the implementation process and effects of the above solution in detail with reference to a specific example:

[0055] raw material:

[0056] Phosgene: Produced by the Yantai MDI unit in Yantai Wanhua Industrial Park, industrial product;

[0057] Polyphenylmethane series diamine / polyamine: Produced by Yantai MDI unit in Yantai Wanhua Industrial Park, industrial products;

[0058] Chlorobenzene: selected from Jiangsu Longchang Chemical Co., Ltd., industrial product, 99%;

[0059] Main instruments and test methods:

[0060] The determination method of isocyanate precursors in the mixed stream of isocyanate and inert solvent is carried out by liquid chromatography derivatization method, and the analytical instrument is Agilent 1260.

[0061] First, a method for preparing a reaction solution by reacting polyamines and phosgene in a solvent of chlorobenzene is described: the solvent chlorobenzene and a methylene-crosslinked polyphenylmethane series of diamines / polyamines are mixed in a static mixer at a mass ratio of 3:1 to generate a mixed solution, and the phosgene and the mixed solution are mixed in a dynamic mixer at a mass ratio of phosgene to diamines / polyamines of 4:1. After mixing, the mixture enters a cold phosgenation reactor, and the cold reaction temperature is controlled at 70°C and the pressure is 270 kPaG. After the reaction, a mixed stream can be obtained for use in subsequent embodiments.

[0062] The above-mentioned material flow is conveyed to the hot phosgene reactor, and the material flow enters between the distillation section and the reaction section of the reactor. The number of trays in the distillation section is 5, and the number of trays in the reaction section is 17; the number of trays in the stripping section is 4, and the tower body material is 316L. The outer weir of the overflow weir of each tray is 74 mm long, and the inclination angle of the outer weir of the overflow weir of each tray is arranged according to the 1-15 theoretical plates, 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°, and 84.0°. The reaction zone temperature is 135°C; the tower top pressure is 0 MPag to 0.5 MPag, preferably 0.4 MPag; the tower top temperature is 95°C, the tower bottom temperature is 155°C, and the reflux ratio is 1.2. Solid particle discharge holes are provided within a 200m area along the tower tray, measured from the junction of the overflow weir and the tower tray. The discharge holes have a diameter of 12mm and a center-to-center spacing of 180mm.

[0063] In the above example, the total content of isocyanate precursors in the mixed stream of isocyanate and inert solvent (measured as the amount remaining after deducting the inert solvent from the isocyanate and mixed solvent stream) was reduced to 15 ppm. This effectively extended the operating life of the hot phosgene reactor in the isocyanate production system to 779 days, with a total pressure drop of 7.5 kPa. This embodiment significantly improves the equilibrium conversion rate of isocyanate precursors, effectively shortening the existing production process, improving raw material conversion, and simplifying the process with low operating costs.

[0064] Comparative Example 1

[0065] Referring to the scheme in the previous example, this comparative example differs only in that the overflow weirs on theoretical trays 1-15 are tilted at a 90° angle, perpendicular to the tray plane. After distillation using the above-described apparatus, the total isocyanate precursor content in the mixed stream of isocyanate and inert solvent (calculated as the residual amount after deducting the inert solvent from the isocyanate and mixed solvent stream) in this example is 120 ppm. The hot phosgene reactor in the isocyanate production system has an operating life of 220 days, with a pressure drop of 19 kPa across the entire column.

[0066] Comparative Example 2

[0067] Referring to the scheme in the previous example, this comparative example differs in that the overflow weirs on the theoretical plates 1-15 are inclined at an angle of 70°. After distillation using the above-described apparatus, the total isocyanate precursor content in the mixed stream of isocyanate and inert solvent (calculated as the residual amount after deducting the inert solvent from the isocyanate and mixed solvent stream) in this example is 690 ppm. The hot phosgene reactor in the isocyanate production system has an operating life of 350 days, with a pressure drop of 16 kPa across the entire column.

[0068] Comparative Example 3

[0069] Referring to the scheme in the previous example, this comparative example differs only in that no drain holes for solid particulate discharge are provided at the junction between the overflow weir and the column tray. After distillation treatment using the above-described apparatus, the total isocyanate precursor content in the mixed stream of isocyanate and inert solvent (calculated as the residual amount after deducting the inert solvent from the isocyanate and mixed solvent stream) in this example was reduced to 18 ppm. The hot phosgene reactor in the isocyanate production system had an operating life of 156 days, with a pressure drop of 35 kPa across the column.

[0070] After comparison with the above three comparative examples, the scheme in the embodiment of the present application can greatly improve the equilibrium conversion rate of the isocyanate precursor, effectively shorten the production process, improve the raw material conversion rate, increase the operating life of the reactor, and improve the pressure drop of the entire tower.

[0071] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will readily appreciate that other variations or modifications based on the above descriptions are possible. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A system for preparing isocyanate, characterized in that: It comprises a cold photogasification reactor and a hot photogasification reactor connected in series, wherein: The thermal phosgenation reactor is used to receive the material flow output by the cold phosgenation reactor for the material flow to undergo a thermal phosgenation reaction to obtain isocyanate; The thermal phosgenation reactor comprises a distillation section, a reaction section and a stripping section, wherein a material flow inlet is located between the distillation section and the reaction section; the reaction section comprises multiple layers of tower plates, and the overflow weir and outer weir of each layer of the reaction section tower plates have different inclination angles, so that the residence time of the material flow on each reaction section tower plate is greater than a set time.

2. The isocyanate preparation system according to claim 1, characterized in that: The inclination angle of the outer weir of the overflow weir of the reaction stage tower tray is determined by the following method: Wherein, s is the number of layers of the reaction stage tray, the tray at the material flow inlet is the first layer and increases from top to bottom, η is the inclination angle of the overflow weir outer weir of the s-th layer of the reaction stage tray, A, B and C are all adjustment coefficients, and z is the length of the overflow weir outer weir of the s-th layer of the reaction stage tray.

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

4. The system for preparing isocyanate according to claim 2, characterized in that: The length z of the outer weir of the overflow weir is 30-120 mm.

5. The system for preparing isocyanate according to claim 4, characterized in that: The total number of layers of the reaction stage trays is 10-20.

6. The system for preparing isocyanate according to claim 1, characterized in that: The set duration is determined by: The residual amount of formamide chloride in the mixed product of isocyanate and inert solvent was tested in a reactor suitable for the scale of the reaction section; the time and residual amount were recorded during the test. The relationship between the target residual amount and the set time length corresponding to the target residual amount is determined according to the relationship; wherein the target residual amount is the minimum residual amount that will not cause clogging.

7. The system for preparing isocyanate according to any one of claims 1 to 6, characterized in that: In the reaction stage tower plate, a discharge hole is provided in a bottom setting area of ​​the outer weir of the overflow weir.

8. The system for preparing isocyanate according to claim 7, characterized in that: The distance between the set area and the bottom of the reaction stage tray is 0-300m.

9. The system for preparing isocyanate according to claim 8, characterized in that: The aperture of the discharge hole is larger than the set aperture, and the set aperture is determined according to the diameter of the solid particles generated during the phosgene reaction.

10. A method for preparing isocyanate using the isocyanate preparation system according to any one of claims 1 to 9, characterized in that: include: placing polyamine, phosgene and an inert solvent in a cold photogasification reactor to carry out a cold photogasification reaction to obtain a mixed material stream; The material stream is fed into a thermal phosgenation reactor, and the reaction section temperature, tower top pressure, tower top temperature, reflux ratio and tower bottom temperature of the thermal phosgenation reactor are adjusted to form a reaction environment suitable for the material stream to undergo a thermal phosgenation reaction to obtain isocyanate; The top of the thermal phosgenation reactor obtains hydrogen chloride and an inert solvent, and the bottom of the thermal phosgenation reactor obtains a mixed product of isocyanate and an inert solvent; Isocyanate is extracted from the mixed product.

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