Method for preparing isocyanate

Abstract

The invention provides a method for preparing isocyanate. By adopting the method for preparing the isocyanate, the cost can be reduced. The method comprises the following steps: (1) carrying out cold phosgenation reaction on an amine compound, a solvent stream I and a phosgene solution to obtain a first mixed solution; (2) feeding the first mixed solution into a thermal reactor, and heating to carry out a thermal phosgenation reaction; (3) removing hydrogen chloride and phosgene from the second mixed solution to obtain a third mixed solution and a second gas mixture containing hydrogen chloride and phosgene; washing and absorbing the first gas mixture and the second gas mixture with a solvent to obtain a phosgene solution; feeding the phosgene solution into the cold reactor in the step (1); (4) carrying out solvent removal treatment on the third mixed solution to obtain an isocyanate crude product; meanwhile, the method is controlled to be carried out under the conditions that A1 is equal to 5-55 and A2 is equal to-15-50.

Description

Technical Field

[0001] The invention relates to the technical field of isocyanate preparation, and in particular to a method for preparing isocyanate which is beneficial to reducing costs. Background Art

[0002] As an organic reaction intermediate, isocyanate is widely used in various industries such as industry, agriculture, construction, automobile, and thermal insulation because it can be further synthesized into polyisocyanate, polyurethane, polyurea, spandex and other materials. At present, the mainstream isocyanate synthesis method in industry is the phosgenation method, that is, the amine corresponding to the target product is first mixed with an inert solvent and then reacted with a phosgene solution to obtain a phosgenation reaction liquid. The phosgenation reaction liquid contains isocyanate products, inert solvents, remaining phosgene and reaction product hydrogen chloride. Later, the phosgene, hydrogen chloride and solvent are removed in sequence through a separation process to finally obtain an isocyanate product.

[0003] The core of this method is that the reaction process is divided into two stages: cold and hot. The principle is as follows:

[0004] Cold reaction stage:

[0005] RNH2+COCl2→RNHCOCl(carbamoyl chloride)+HCl

[0006] RNH2+HCl→RNH2·HCl(amino hydrochloride)

[0007] Thermal reaction stage:

[0008] RNHCOCl→RNCO+HCl

[0009] RNH2·HCl+COCl2→RNCO+3HCl

[0010] Among them, the cold reaction stage has a faster reaction speed and reacts quickly and completely; while in the hot reaction stage, the following side reactions are prominent:

[0011] RNH2·HCl→RNH2+HCl

[0012] RNH2+RNCO→RNHCONHR(urea)

[0013] The presence of byproduct urea will catalyze the polymerization of products, thereby blocking equipment pipelines and affecting the yield of isocyanate, and its generation amount needs to be strictly controlled. The existing technology generally obtains higher product selectivity by making phosgene far in excess to reduce the generation of urea, but the far excess phosgene needs to be recycled and reused, and the hydrogen chloride in the phosgene recovered by condensation and absorption cannot be effectively removed. The excessive hydrogen chloride content in the circulating phosgene will lead to the formation of amine hydrochloride in the phosgenation of amines. The phosgenation of amine hydrochloride requires a long reaction residence time and a high excess of phosgene, and it is easy to react with amines and isocyanates to produce urea, which seriously affects the quality and product yield of the phosgenation reaction liquid, and a high phosgene excess rate means higher energy consumption for recycling and reuse.

[0014] Chinese patent application CN104892458A discloses a method for preparing isocyanates by reactive distillation, in which the phosgenation reaction is carried out in a distillation tower, and the excess phosgene and hydrogen chloride are separated by an external distillation tower. This method effectively reduces the content of hydrogen chloride in the circulating phosgene solution, thereby reducing the formation of amino hydrochloride and the probability of urea generation. However, it consumes a large amount of steam and cold, and it is difficult to separate hydrogen chloride from phosgene under high pressure, resulting in high process operation costs.

[0015] The prior art does not have any solution that considers how to integrate and optimize the isocyanate preparation process from the perspective of the entire process to achieve good control of process operation and maintenance costs and maximize benefits. Summary of the invention

[0016] The invention provides a method for preparing isocyanate. The method of the invention is used to prepare isocyanate, which is beneficial to the control of process operation and maintenance costs and is beneficial to cost reduction.

[0017] One embodiment of the present invention provides a method for preparing isocyanate, comprising the following steps:

[0018] To achieve the purpose, the present invention provides the following technical solutions:

[0019] The present invention provides a method for preparing isocyanate, which comprises the following steps:

[0020] (1) feeding an amine compound, a solvent stream I and a phosgene solution into a cold reactor for cold phosgene gasification to obtain a first mixed solution;

[0021] In step (1), the mass ratio of the solvent in the solvent stream I to the amine compound is a, the mass ratio of the pure phosgene in the phosgene solution to the amine compound is b, and the cold phosgene gasification reaction is carried out at a temperature of c°C and a pressure of dMPaG;

[0022] (2) sending the first mixed liquid into a thermal reactor and heating it to perform a thermal phosgenation reaction to obtain a second mixed liquid containing isocyanate and a first gas mixture containing hydrogen chloride and phosgene;

[0023] In step (2), the thermal phosgenation reaction is carried out at a temperature of e°C and a pressure of gMPaG, and the residence time of the materials in the thermal phosgenation reaction system in the thermal reactor is f hours;

[0024] (3) removing hydrogen chloride and phosgene from the second mixed liquid at a temperature of h°C and a pressure of iMPaG to obtain a third mixed liquid and a second gas mixture containing hydrogen chloride and phosgene;

[0025] The first gas mixture and the second gas mixture are washed and absorbed with a solvent to obtain the phosgene solution at a temperature of j°C and the washed hydrogen chloride; the phosgene solution is fed into the cold reactor of step (1);

[0026] (4) subjecting the third mixed solution to a solvent removal treatment at a temperature of k° C. and a pressure of pMPaG to obtain a crude isocyanate;

[0027] At the same time, the method is controlled to be performed under the conditions of A1=5 to 55 and A2=-15 to 50; A1 is the cost characteristic index, dimensionless; A2 is the operation characteristic index, dimensionless; the calculation formulas of A1 and A2 are as follows:

[0028] A1=0.928×a 2 +0.239×b 2 -0.033×c-0.214×d 2 +0.022×e+0.061×f 2 +5.78×g 2 +0.0135×h+85×i 2 -0.032×j+0.027×k+99.17×p 2

[0029] A2=0.485×a 2 +0.852×b 2 -0.042×c-0.83×d 2 -0.052×e+0.192×f 2 -3.016×g 2 -0.026×h-153×i 2 +0.097×j-0.011×k+10.09×p 2 .

[0030] Furthermore, in step (1), the mass ratio a of the solvent in the solvent stream I to the amine compound is 0.5-5, the mass ratio b of the pure phosgene in the phosgene solution to the amine compound is 1-10, the temperature c°C of the cold phosgene gasification reaction is 50-180°C, and the pressure d MPa is 0.1-5 MPaG.

[0031] Furthermore, in step (2), the temperature of the thermal phosgenation reaction is e°C 50-200°C, the pressure is gMPaG 0.1-1MPaG, and the residence time of the material in the thermal phosgenation reaction system in the thermal reactor is f hours 0.5 to 12 hours.

[0032] Furthermore, in step (3), the temperature h℃ for the treatment of removing hydrogen chloride and phosgene is 100-200℃, and the pressure iMPaG is -0.05MpaG to 0.20MpaG; the temperature j℃ of the phosgene solution obtained by washing and absorbing the first gas mixture and the second gas mixture with a solvent is -50℃ to 150℃.

[0033] Furthermore, in step (4), the temperature k°C for the solvent removal treatment is 100-250°C, and the pressure pMPaG is -0.1MPaG to 0.1MPaG.

[0034] Preferably, A1 is 10-20, and A2 is -10 to 10.

[0035] In some embodiments, the amine compound includes one or more of diphenylmethanediamine, polymethylene polyphenyl polyamine, diaminotoluene, isophoronediamine, hexamethylenediamine, cyclohexamethylenediamine, p-phenylenediamine, and naphthalenediamine.

[0036] In some embodiments, the solvent in the solvent stream I in step (1) and the solvent used for the washing absorption in step (3) respectively include one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene;

[0037] Preferably, the solvent in the solvent stream I in step (1) is the same as the solvent used for the wash absorption in step (3).

[0038] In some embodiments, in step (3), the mass percentage of phosgene in the phosgene solution obtained by the washing and absorption is 50 to 90%.

[0039] In some embodiments, the cold reactor in step (1) is a jet reactor or a high shear reactor;

[0040] In some embodiments, the thermal reactor in step (2) is a tank reactor or a tower reactor;

[0041] In some embodiments, the treatment for removing hydrogen chloride and phosgene in step (3) or the treatment for removing solvent in step (4) are respectively carried out in a distillation tower.

[0042] The technical solution provided by the present invention has the following beneficial effects:

[0043] The isocyanate preparation method provided by the present invention improves the operational flexibility of the isocyanate production process by regulating and controlling the characteristic indexes A1 and A2, has the advantages of simple process, convenient operation, energy saving, low cost, etc., and is beneficial to the control of process operation and maintenance costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 Schematic diagram of the isocyanate process system in some embodiments. DETAILED DESCRIPTION

[0045] 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.

[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the related listed items. The terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.

[0047] The present invention provides a method for preparing isocyanate, which comprises the following steps:

[0048] (1) feeding an amine compound, a solvent stream I and a phosgene solution into a cold reactor for cold phosgene gasification to obtain a first mixed solution;

[0049] In step (1), the mass ratio of the solvent in the solvent stream I to the amine compound is a, the mass ratio of the pure phosgene in the phosgene solution to the amine compound is b, and the cold phosgene gasification reaction is carried out at a temperature of c°C and a pressure of dMPaG;

[0050] (2) sending the first mixed liquid into a thermal reactor and heating it to perform a thermal phosgenation reaction to obtain a second mixed liquid containing isocyanate and a first gas mixture containing hydrogen chloride and phosgene;

[0051] In step (2), the thermal phosgenation reaction is carried out at a temperature of e°C and a pressure of gMPaG, and the residence time of the materials in the thermal phosgenation reaction system in the thermal reactor is f hours;

[0052] (3) removing hydrogen chloride and phosgene from the second mixed liquid at a temperature of h°C and a pressure of iMPaG to obtain a third mixed liquid and a second gas mixture containing hydrogen chloride and phosgene;

[0053] The first gas mixture and the second gas mixture are washed and absorbed with a solvent to obtain the phosgene solution at a temperature of j°C and the washed hydrogen chloride; the phosgene solution is fed into the cold reactor of step (1);

[0054] (4) subjecting the third mixed solution to a solvent removal treatment at a temperature of k° C. and a pressure of pMPaG to obtain a crude isocyanate;

[0055] At the same time, the method is controlled to be performed under the conditions of A1=5 to 55 and A2=-15 to 50; A1 is the cost characteristic index, dimensionless; A2 is the operation characteristic index, dimensionless; the calculation formulas of A1 and A2 are as follows:

[0056] A1=0.928×a 2 +0.239×b 2 -0.033×c-0.214×d 2 +0.022×e+0.061×f 2 +5.78×g 2 +0.0135×h+85×i 2 -0.032×j+0.027×k+99.17×p 2

[0057] A2=0.485×a 2 +0.852×b 2 -0.042×c-0.83×d 2 -0.052×e+0.192×f 2 -3.016×g 2 -0.026×h-153×i 2 +0.097×j-0.011×k+10.09×p 2 .

[0058] Further, in step (1), the mass ratio a of the solvent in the solvent stream I to the amine compound is 0.5-5 (e.g., 1, 2, 3, 4, etc.), the mass ratio b of the pure phosgene in the phosgene solution to the amine compound is 1-10 (e.g., 2, 4, 6, 8, etc.), the temperature c°C of the cold phosgene gasification reaction is 50-180°C (e.g., 70°C, 90°C, 110°C, 130°C, 150°C, 170°C, etc.), and the pressure d MPaG is 0.1-5 MPaG (e.g., 1 MPaG, 2 MPaG, 3 MPaG, 4 MPaG, etc.);

[0059] In step (2), the temperature e°C of the thermal phosgenation reaction is 50-200°C (e.g., 80°C, 100°C, 120°C, 140°C, 160°C, 180°C, etc.), the pressure gMPaG is 0.1-1MPaG, and the residence time f hours of the materials in the thermal phosgenation reaction system in the thermal reactor is 0.5 to 12 hours;

[0060] In step (3), the temperature h℃ for the treatment of removing hydrogen chloride and phosgene is 100-200℃ (e.g., 120℃, 140℃, 160℃, 180℃, etc.), and the pressure iMPaG is -0.05MpaG to 0.20MpaG (e.g., 0MpaG, 0.05MpaG, 0.10MpaG, 0.15MpaG, etc.); the temperature j℃ of the phosgene solution obtained by washing and absorbing the first gas mixture and the second gas mixture with a solvent is -50℃ to 150℃ (e.g., -30℃, 0℃, 30℃, 60℃, 90℃, 120℃, etc.);

[0061] In step (4), the temperature k°C for the solvent removal treatment is 100-250°C (e.g., 120°C, 140°C, 160°C, 180°C, 200°C, 220°C, 240°C, etc.), and the pressure pMPaG is -0.1MPaG to 0.1MPaG (e.g., -0.1MpaG, 0MpaG, 0.1MpaG, etc.);

[0062] The method for preparing isocyanate of the present invention is carried out under the above-mentioned process conditions. By adjusting the above-mentioned process parameters a, b, c, d, e, f, g, h, i, j, k, and p and making the cost characteristic index A1 within the range of 5 to 55 and the operation characteristic index A2 within the range of -15 to 50, the isocyanate is prepared, which can effectively reduce the operation and maintenance costs, while also taking into account relatively good process operation stability.

[0063] In the present invention, A1 is 5 to 55, for example 5, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 55, etc., preferably 10 to 20; A2 is -15 to 50, for example -15, -10, -6, -2, 2, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, etc., preferably -10 to 10.

[0064] In some embodiments, the amine compound includes one or more of diaminodiphenylmethane, polymethylene polyphenyl polyamines, diaminotoluene, isophoronediamine, hexamethylenediamine, cyclohexanediamine, p-phenylenediamine, and naphthalenediamine.

[0065] In some embodiments, the solvent in the solvent stream I in step (1) and the solvent used for the washing absorption in step (3) respectively include one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene. Preferably, the solvent in the solvent stream I in step (1) and the solvent used for the washing absorption in step (3) are the same.

[0066] In one embodiment, the amine compound, the phosgene solution and the solvent stream I are mixed to perform a phosgenation reaction to obtain a second mixed liquid containing isocyanate and a first gas mixture containing phosgene and hydrogen chloride. The solvent in the phosgene solution can be the same as the solvent from the solvent stream I in the phosgenation reaction system.

[0067] In some embodiments, in step (3), the mass percentage of phosgene in the phosgene solution obtained by the washing and absorption is 50-90%, for example, 60%, 70%, 80%, etc. In step (3), the first gas mixture and the second gas mixture can be washed and absorbed with a solvent in a phosgene washing and absorption tower, and the obtained phosgene solution is sent to the cold reactor of step (1), that is, the phosgene solution in the cold reactor is provided by the phosgene washing and absorption tower; wherein the phosgene washing and absorption tower can be a plate tower, a packed tower, etc.

[0068] In some embodiments, the cold reactor in step (1) may be a jet reactor or a high shear reactor; the hot reactor in step (2) may be a kettle reactor or a tower reactor. The treatment for removing hydrogen chloride and phosgene in step (3) or the solvent removal treatment in step (4) may be carried out in a distillation tower; specifically, the treatment for removing hydrogen chloride and phosgene in step (3) is carried out in a light removal tower, such as a plate tower, a packed tower, etc.; the solvent removal treatment in step (4) may be carried out in a solvent removal tower, such as a plate tower, a packed tower, etc.

[0069] The inventors obtained two characteristic indexes A1 and A2 by studying the coupling effect of parameters related to production cost and operation cycle in the isocyanate production process, and controlled the characteristic indexes within a certain range by adjusting the process parameters, thereby ensuring lower operating costs. Moreover, on the basis of ensuring lower operating costs, relatively good process operation stability can also be taken into account, thereby maximizing profits.

[0070] The isocyanate preparation method provided by the present invention improves the operational flexibility of the isocyanate production process by regulating and controlling the characteristic indexes A1 and A2, and has the advantages of simple process, convenient operation, energy saving, low cost, etc.

[0071] The technical solution of the present invention is further illustrated by the following examples, but it should not be understood that the present invention is limited thereto.

[0072] 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. The reagents or instruments used without specifying the manufacturer are all conventional products that can be purchased commercially.

[0073] See the schematic diagram of the process system for preparing isocyanate in the following examples. Figure 1 The process system includes a cold reactor 1 (adopting a jet reactor), a hot reactor 2 (adopting a kettle reactor), a phosgene removal tower 3 (a plate tower), a solvent removal tower 4 (a plate tower), and a phosgene washing absorption tower 5 (a plate tower).

[0074] In the embodiments and comparative examples, when the system device has been running for a long period of time, the system is severely scaled and blocked, resulting in reduced heat exchange efficiency and transportation efficiency, and cannot meet the normal operation requirements, it is necessary to stop the system to clean it and overhaul the device. In each embodiment and comparative example, the other time except the cumulative overhaul time during the three-year operation period is the stable operation time.

[0075] Operation and maintenance costs include utility costs during operation and equipment replacement, maintenance and labor costs during maintenance. Specifically, the average operation and maintenance cost = operation cost + maintenance cost, where:

[0076] Operating cost = three-year utility cost (including steam, electricity, circulating water, chilled water, etc.) / three-year crude isocyanate output, in yuan / t.

[0077] In each embodiment and comparative example, in the calculation of operation and maintenance costs, the unit prices of steam, electricity, circulating water, chilled water, etc. are all calculated according to a unified standard.

[0078] Maintenance cost = all maintenance costs within three years / three years' crude isocyanate production, in Yuan / t.

[0079] Example 1

[0080] (1) diphenylmethanediamine (amine compound) with a flow rate of 30 t / h and chlorobenzene (solvent stream I) with a flow rate of 48 t / h are mixed and introduced into a cold reactor 1, and a phosgene solution is introduced into the cold reactor 1 at the same time; the flow rate of the phosgene solution is 100 t / h, and the mass percentage of phosgene in the phosgene solution is 90%; diphenylmethanediamine and phosgene undergo cold phosgenation reaction in the cold reactor 1 to obtain a first mixed solution;

[0081] (2) Then, the first mixed liquid is introduced into the thermal reactor 2 for thermal phosgenation reaction to obtain a second mixed liquid containing isocyanate and a first gas mixture containing phosgene and hydrogen chloride.

[0082] (3) The second mixed liquid is passed into a phosgene removal tower 3 to remove hydrogen chloride and phosgene, thereby obtaining a third mixed liquid located in the bottom of the tower and a second gas mixture containing hydrogen chloride and phosgene. The second gas mixture is discharged from the top of the tower and enters a phosgene washing and absorption tower 5 together with the first gas mixture. A solvent, chlorobenzene, is passed into the phosgene washing and absorption tower 5 to wash and absorb the phosgene in the first and second gas mixtures to obtain a phosgene solution, and hydrogen chloride is extracted from the top of the tower. The phosgene solution is fed into the cold reactor 1 of step (1) to participate in the cold phosgenation reaction.

[0083] (4) The third mixed solution is passed into a solvent removal tower 4 to remove chlorobenzene, and the solution in the bottom of the tower is collected to obtain a crude isocyanate; and the removed chlorobenzene is discharged from the top of the tower.

[0084] Wherein, in step (1), the mass ratio a of the solvent chlorobenzene to the amine compound in the solvent stream I is 1.6, the mass ratio b of the pure phosgene in the phosgene solution to the amine compound is 3, the temperature of the cold phosgene gasification reaction is 100°C (i.e. c=100), and the pressure of the cold phosgene gasification reaction is 3MpaG (i.e. d=3).

[0085] In step (2), the temperature of the thermal phosgenation reaction is 160°C (ie, e=160), the residence time of the materials in the thermal phosgenation reaction system in the reaction vessel is 4 hours (ie, f=4), and the pressure of the thermal phosgenation reaction is 0.6 MpaG (ie, g=0.6).

[0086] In step (3), the temperature condition for removing hydrogen chloride and phosgene is 135°C (i.e., h=135), the pressure condition for removing hydrogen chloride and phosgene is 0.02MpaG (i.e., i=0.02), and the temperature of the phosgene solution obtained by washing and absorbing the first gas mixture and the second gas mixture in the phosgene washing and absorption tower 5 with the solvent is 80°C (i.e., j=80).

[0087] In step (4), the temperature condition for removing the solvent chlorobenzene in the solvent removal tower 4 is 200° C. (ie, k=200), and the pressure condition for removing the solvent chlorobenzene is -0.07 MpaG (ie, p=-0.07).

[0088] Calculated by the above formula, the cost characteristic index A1 is 11.06, and the operation characteristic index A2 is -7.81. The above process has been in operation for three years and the cumulative maintenance time is 68 days. The average cost of operation and maintenance in three years is 1572 yuan / t (crude isocyanate).

[0089] Embodiment 2-6

[0090] The method is carried out with reference to Example 1, except that the process parameters a, b, c, d, e, f, g, h, i, j, k, and p are adjusted to achieve the regulation of A1 and A2. For the relevant data of different embodiments, see Table 1. For the parts not explained, refer to Example 1:

[0091] Table 1

[0092]

[0093] Note: If the description of the parameters in the examples is inconsistent with that in Table 1, the data in Table 1 shall prevail.

[0094] Comparative Example 1

[0095] (1) diphenylmethanediamine (amine compound) with a flow rate of 30 t / h and chlorobenzene (solvent stream I) with a flow rate of 45 t / h are mixed and introduced into a cold reactor 1, and a phosgene solution is introduced into the cold reactor 1 at the same time; the flow rate of the phosgene solution is 64 t / h, and the mass percentage of phosgene in the phosgene solution is 95%; diphenylmethanediamine and phosgene react in the cold reactor 1 to obtain a first mixed solution;

[0096] (2) Then, the first mixed liquid is introduced into the thermal reactor 2 for thermal phosgenation reaction to obtain a second mixed liquid containing isocyanate and a first gas mixture containing phosgene and hydrogen chloride.

[0097] (3) The second mixed liquid is passed into a phosgene removal tower 3 to remove hydrogen chloride and phosgene, thereby obtaining a third mixed liquid located in the bottom of the tower and a second gas mixture containing hydrogen chloride and phosgene. The second gas mixture is discharged from the top of the tower and enters a phosgene washing and absorption tower 5 together with the first gas mixture. A solvent, chlorobenzene, is passed into the phosgene washing and absorption tower 5 to wash and absorb the phosgene in the first and second gas mixtures to obtain a phosgene solution, and hydrogen chloride is extracted from the top of the tower. The phosgene solution is fed into the cold reactor 1 of step (1) to participate in the cold phosgenation reaction.

[0098] (4) The third mixed solution is passed into a solvent removal tower 4 to remove chlorobenzene, and the solution in the bottom of the tower is collected to obtain a crude isocyanate; and the removed chlorobenzene is discharged from the top of the tower.

[0099] Wherein, in step (1), the mass ratio a of the solvent chlorobenzene to the amine compound in the solvent stream I is 1.5, the mass ratio b of the pure phosgene in the phosgene solution to the amine compound is 2, the temperature of the cold phosgene gasification reaction is 160°C (i.e. c=160), and the pressure of the cold phosgene gasification reaction is 4Mpag (i.e. d=4).

[0100] In step (2), the temperature of the thermal phosgenation reaction is 120° C. (ie, e=120), the residence time of the materials in the thermal phosgenation reaction system in the reaction vessel is 2 hours (ie, f=2), and the pressure of the thermal phosgenation reaction is 0.1 Mpag (ie, g=0.1).

[0101] In step (3), the temperature condition for removing hydrogen chloride and phosgene is 115°C (i.e., h=115), the pressure condition for removing hydrogen chloride and phosgene is -0.07Mpag (i.e., i=-0.07), and the temperature of the phosgene solution obtained by washing and absorbing the first gas mixture and the second gas mixture in the phosgene washing absorption tower 5 after solvent washing is 100°C (i.e., j=100).

[0102] In step (4), the temperature condition for removing the solvent chlorobenzene in the solvent removal tower 4 is 220° C. (ie, k=220), and the pressure condition for removing the solvent chlorobenzene is -0.1 Mpag (ie, p=-0.1).

[0103] According to the above formula, the cost characteristic index A1 is 2.98 and the operation characteristic index A2 is -18.47. The three-year cumulative maintenance time, three-year operation and maintenance average cost of the above process are shown in Table 2.

[0104] Comparative Examples 2-5

[0105] Refer to Comparative Example 1, except that the process parameters a, b, c, d, e, f, g, h, i, j, k, and p are adjusted to achieve the regulation of A1 and A2. For the relevant data of different comparative examples, see Table 2. For the parts not explained, refer to Comparative Example 1:

[0106] Table 2

[0107]

[0108]

[0109] Note: If the description of the parameters in the comparison ratio is inconsistent with that in Table 2, the data in Table 2 shall prevail.

[0110] It can be seen from the results of the comparative examples that by controlling the cost characteristic index A1 and the operation characteristic index A2 within a reasonable range, the operation and maintenance costs can be significantly reduced. On this basis, relatively good process operation stability can be taken into account at the same time (for example, during the three-year operation, the shutdown and maintenance time will not be too long, for example, the shutdown and maintenance time will not exceed 130 days, and there is a relatively long cumulative stable operation time). On the basis of controlling lower costs, a good balance can be achieved in terms of process operation stability to maximize benefits. In the comparative examples, there are significantly higher operation and maintenance costs; although the shutdown and maintenance time in comparative examples 2 and 3 is short, the operation and maintenance costs are greatly increased. It is difficult to achieve lower operation and maintenance costs in the comparative examples, and it is also difficult to strike a good balance between low cost and process operation stability.

[0111] It is easy to understand that the above embodiments are only examples for clear explanation and do not mean that the present invention is limited thereto. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from this are still within the protection scope of the present invention.

Claims

1. A method for preparing isocyanate, characterized in that: The method comprises the following steps: (1) feeding an amine compound, a solvent stream I and a phosgene solution into a cold reactor for cold phosgene gasification to obtain a first mixed solution; In step (1), the mass ratio of the solvent in the solvent stream I to the amine compound is a, the mass ratio of the pure phosgene in the phosgene solution to the amine compound is b, and the cold phosgene gasification reaction is carried out at a temperature of c°C and a pressure of d MPaG; (2) sending the first mixed liquid into a thermal reactor and heating it to perform a thermal phosgenation reaction to obtain a second mixed liquid containing isocyanate and a first gas mixture containing hydrogen chloride and phosgene; In step (2), the thermal phosgenation reaction is carried out at a temperature of e°C and a pressure of gMPaG, and the residence time of the materials in the thermal phosgenation reaction system in the thermal reactor is f hours; (3) removing hydrogen chloride and phosgene from the second mixed liquid at a temperature of h°C and a pressure of iMPaG to obtain a third mixed liquid and a second gas mixture containing hydrogen chloride and phosgene; The first gas mixture and the second gas mixture are washed and absorbed with a solvent to obtain the phosgene solution at a temperature of j°C and the washed hydrogen chloride; the phosgene solution is fed into the cold reactor of step (1); (4) subjecting the third mixed solution to a solvent removal treatment at a temperature of k° C. and a pressure of pMPaG to obtain a crude isocyanate; Meanwhile, the method is controlled to be performed under the conditions of A1=5 to 55, and A2=-15 to 50; A1 is a cost characteristic index, dimensionless; A2 is the operating characteristic index, dimensionless; the calculation formulas for A1 and A2 are as follows: A1=0.928×a 2 +0.239×b 2 -0.033×c-0.214×d 2 +0.022×e+0.061×f 2 +5.78×g 2 +0.0135×h+85×i 2 -0.032×j+0.027×k+99.17×p 2 <h2 style=";text-align:left;direction:ltr">A2 = 0.485×a<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> +0.852×b<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -0.042×c-0.83×d<h2 style=";text-align:left;direction:ltr"> 2 <h2 style=";text-align:left;direction:ltr"> -0.052×e+ 0.192×f 2 -3.016×g 2 -0.026×h-153×i 2 +0.097×j- 0.011×k+10.09×p 2 。 2. The method for preparing isocyanate according to claim 1, characterized in that: In step (1), the mass ratio a of the solvent in the solvent stream I to the amine compound is 0.5-5, the mass ratio b of the pure phosgene in the phosgene solution to the amine compound is 1-10, the temperature c°C of the cold phosgene gasification reaction is 50-180°C, and the pressure d MPa is 0.1-5 MPaG.

3. The method for preparing isocyanate according to claim 2, characterized in that: In step (2), the temperature e°C of the thermal phosgenation reaction is 50-200°C, the pressure gMPaG is 0.1-1MPaG, and the residence time f hours of the materials in the thermal phosgenation reaction system in the thermal reactor is 0.5 to 12 hours.

4. The method for preparing isocyanate according to claim 3, characterized in that: In step (3), the temperature h℃ for the treatment of removing hydrogen chloride and phosgene is 100-200℃, and the pressure iMPaG is -0.05MpaG to 0.20MpaG; the temperature j℃ of the phosgene solution obtained by washing and absorbing the first gas mixture and the second gas mixture with a solvent is -50℃ to 150℃.

5. The method for preparing isocyanate according to claim 4, characterized in that: In step (4), the temperature k°C for the solvent removal treatment is 100-250°C, and the pressure pMPaG is -0.1MPaG to 0.1MPaG.

6. The method for preparing isocyanate according to any one of claims 1 to 5, characterized in that: A1 is 10~20, A2 is -10 to 10.

7. The method for preparing isocyanate according to any one of claims 1 to 6, characterized in that: The amine compound includes one or more of diphenylmethanediamine, polymethylene polyphenyl polyamine, diaminotoluene, isophoronediamine, hexamethylenediamine, cyclohexamethylenediamine, p-phenylenediamine, and naphthalenediamine.

8. The method for preparing isocyanate according to any one of claims 1 to 7, characterized in that: The solvent in the solvent stream I in step (1) and the solvent used for the washing absorption in step (3) respectively include one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene; Preferably, the solvent in the solvent stream I in step (1) is the same as the solvent used for the wash absorption in step (3).

9. The method for preparing isocyanate according to any one of claims 1 to 8, characterized in that: In step (3), the mass percentage of phosgene in the phosgene solution obtained by the washing and absorption is 50 to 90%.

10. The method for preparing isocyanate according to any one of claims 1 to 9, characterized in that: The cold reactor in step (1) is a jet reactor or a high shear reactor; And / or, the thermal reactor in step (2) is a kettle reactor or a tower reactor; And / or, the treatment for removing hydrogen chloride and phosgene in step (3) or the treatment for removing solvent in step (4) are respectively carried out in a distillation tower.

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