Isocyanate and preparation method and application thereof

Abstract

The present application relates to an isocyanate and its preparation method and application, the method comprising the following steps: (1) carrying out a phosgenation reaction of an amine compound with phosgene in a solvent to obtain a first mixed solution containing isocyanate; (2) removing hydrogen chloride and phosgene from the first mixed solution to obtain a second mixed solution; (3) carrying out a first solvent removal treatment on the second mixed solution to obtain an isocyanate crude product; (4) carrying out a separation treatment on the isocyanate crude product to obtain a polymeric isocyanate product and a third mixed solution; the third mixed solution comprises the solvent and pure isocyanate; and (5) carrying out a second solvent removal treatment on the third mixed solution to obtain a pure isocyanate product. The preparation method of the isocyanate of an embodiment of the present application can make the characteristic index be within a specific range by adjusting the process parameters in multiple steps, thereby improving the yield and color index of the prepared isocyanate product.

Description

TECHNICAL FIELD

[0001] The present application relates to isocyanate, in particular to a method capable of preparing isocyanate with better color. BACKGROUND

[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, etc. At present, the mainstream method for synthesizing isocyanate in industry is phosgenation method, which has two prominent problems: first, discoloration occurs in the phosgenation process, which is caused by a large amount of colored substances produced in the phosgenation reaction of diamines or polyamines, and these colored substances cannot be removed in the subsequent separation process and remain in the process of processing isocyanate into polyurethane. Second, the phosgenation reaction produces by-products, i.e. urea substances, which can catalyze the polymerization of products, block the equipment pipelines, and affect the yield of isocyanate and the long-period operation of production devices.

[0003] The prior art discloses some methods for treating materials after the phosgenation reaction to improve the color of isocyanate products. However, the coloring substances in isocyanate products not only come from impurity components, but also come from by-products generated in the phosgenation process. The color treatment in the stage after the phosgenation reaction requires a large amount of engineering cost and does not obviously improve the color number. In addition, the color treatment in the stage after the phosgenation reaction mostly requires the introduction of other impurities, which will form non-desired by-products in the downstream application of isocyanate; and the treatment from the upstream of the phosgenation reaction requires strict limitation of the content of certain specific components, which is relatively high in cost.

[0004] On the other hand, to solve the problem of easy production of urea by-products in the preparation of isocyanate by the phosgenation method, the prior art provides an effective and convenient method, i.e. increasing the excess ratio of phosgenation to amine substances, but the increase of the excess ratio of phosgenation will increase the circulating amount of phosgene in the system, which not only increases the operation risk, but also increases the energy consumption of evaporated phosgene. SUMMARY

[0005] To overcome at least one of the above-mentioned defects of the prior art, in a first aspect, an embodiment of the present application provides a preparation method of isocyanate, comprising the following steps:

[0006] (1) performing a phosgenation reaction of an amine compound and phosgene in a solvent to obtain a first mixed solution containing isocyanate;

[0007] (2) performing a treatment of removing hydrogen chloride and phosgene from the first mixed solution to obtain a second mixed solution;

[0008] (3) the second mixture is subjected to a first solvent removal treatment to obtain an isocyanate crude product;

[0009] (4) the isocyanate crude product is subjected to a separation treatment to obtain a polymeric isocyanate product and a third mixture; the third mixture comprises the solvent and pure isocyanate; and

[0010] (5) the third mixture is subjected to a second solvent removal treatment to obtain a pure isocyanate product;

[0011] In step (1), the mass ratio a of the phosgene to the amine compound is 1-10; the highest temperature of the phosgenation reaction is b °C, b is 100-170; the residence time of the material in the reaction vessel of the phosgenation reaction system is c hours, c is 0.5-12;

[0012] The treatment temperature of step (2) is d °C, d is 100-200, and the treatment time is e hours, e is 0.01-4;

[0013] The mass content f of the solvent in the second mixture is 20-90%, and the mass content g of the solvent in the isocyanate crude product is 0.01-30%;

[0014] A1 and A2 both represent characteristic indexes, dimensionless;

[0015] A1 = 0.164 * a 2 + 0.054 * b + 3.89 * c + 0.0007 * d 2 + 8.25 * e

[0016] If A1 < 50, then A2 is:

[0017] A2 = 2.71 * f 2 + 99.16 * g 2 + 0.1228

[0018] If A1 ≥ 50, then A2 is:

[0019] A2 = 4.08 * f 2 + 195.42 * g 2 + 0.2632

[0020] A1 is 25-80; and if A1 < 50, A2 is 0.5-6; if A1 ≥ 50, A2 is 0.8-7.

[0021] In a second aspect, one embodiment of the present application provides a polymeric isocyanate product prepared by the above preparation method.

[0022] In a third aspect, one embodiment of the present application provides a pure isocyanate product prepared by the above-mentioned preparation method.

[0023] In a fourth aspect, one embodiment of the present application provides an application of the above-mentioned polymeric isocyanate product or pure isocyanate product in the synthesis of polymeric isocyanate, polyurethane, polyurea or spandex.

[0024] The preparation method of isocyanate of one embodiment of the present application can make the characteristic indexes A1 and A2 be in a specific range by adjusting the process parameters in multiple steps, thereby improving the yield and color index of the prepared isocyanate product. BRIEF DESCRIPTION OF DRAWINGS

[0025] The accompanying drawings are included to provide a further understanding of the present application, and are incorporated in and constitute a part of this specification. Illustrations in the drawings are for purposes of illustrating an embodiment of the present application and are not intended to limit the present application. In the drawings:

[0026] Figure 1 FIG. 1 is a structural schematic diagram of a preparation device of isocyanate of one embodiment of the present application. DETAILED DESCRIPTION

[0027] The typical embodiments embodying the features and advantages of the present application will be described in detail in the following description. It should be understood that the present application can have various changes on different embodiments, which all do not deviate from the scope of the present application, and the description in essence is used as an illustration, not to limit the present application.

[0028] One embodiment of the present application provides a preparation method of isocyanate, comprising the following steps:

[0029] (1) performing a phosgenation reaction of an amine compound and phosgene in a solvent to obtain a first mixed solution;

[0030] (2) performing a treatment of removing hydrogen chloride and phosgene from the first mixed solution to obtain a second mixed solution;

[0031] (3) performing a first solvent removal treatment on the second mixed solution to obtain a crude isocyanate product;

[0032] (4) performing a separation treatment on the crude isocyanate product to obtain a polymeric isocyanate product and a third mixed solution; the third mixed solution comprises a solvent and a pure isocyanate; and

[0033] (5) performing a second solvent removal treatment on the third mixed solution to obtain a pure isocyanate;

[0034] In step (1), the mass ratio a of phosgene to the amine compound is 1-10; the highest temperature of the phosgenation reaction is b ℃, b is 100-170; the residence time of the material in the reaction container of the phosgenation reaction system is c hours, c is 0.5-12;

[0035] The processing temperature of step (2) is d °C, d is 100-200, and the processing time is e hours, e is 0.01-4;

[0036] The mass content of the solvent in the second mixed solution is f, f is 20-90%; the mass content of the solvent in the crude isocyanate is g, g is 0.01-30%;

[0037] Wherein, A1, A2 both represent characteristic indexes, dimensionless;

[0038] A1 = 0.164 * a 2 + 0.054 * b + 3.89 * c + 0.0007 * d 2 + 8.25 * e

[0039] If A1 < 50, then A2 is:

[0040] A2 = 2.71 * f 2 + 99.16 * g 2 + 0.1228

[0041] If A1 ≥ 50, then A2 is:

[0042] A2 = 4.08 * f 2 + 195.42 * g 2 + 0.2632

[0043] A1 is 25-80; and if A1 < 50, A2 is 0.5-6; if A1 ≥ 50, A2 is 0.8-7.

[0044] In an embodiment, the mass ratio of the phosgene to the amine compound a is 1-10, for example 2, 4, 6, 8.

[0045] In an embodiment, the highest temperature of the phosgenation reaction can be 100-170 °C, for example 110 °C, 120 °C, 130 °C, 140 °C, 150 °C or 160. Correspondingly, b can be 100-170, for example 110, 120, 130, 140, 150 or 160.

[0046] In an embodiment, the residence time of the phosgenation reaction system in the reaction vessel can be 0.5-12 hours, for example 1 hour, 2 hours, 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, 10 hours or 11 hours. Correspondingly, c can be 0.5-12, for example 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11.

[0047] In one embodiment, the processing temperature of step (2) is 100-200°C, for example 110, 120, 130, 140, 150, 160 or 170.

[0048] In one embodiment, the processing time of step (2) is 0.01-4 hours, for example 0.1 hour, 0.5 hour, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, 3.5 hours. Correspondingly, e is 0.01-4, for example 0.1, 0.5, 1, 1.5, 2, 2.5, 3 or 3.5.

[0049] In one embodiment, the mass content f of the solvent in the second mixture is 20-90%, for example 30%, 40%, 50%, 60%, 70% or 80%.

[0050] In one embodiment, the mass content g of the solvent in the crude isocyanate is 0.01-30%, for example 0.05%, 1%, 2%, 5%, 8%, 10%, 15%, 20%, 25%.

[0051] In one embodiment, A1 is 25-80, preferably 30-60, for example 35, 40, 45, 50, 55, 65, 70 or 75.

[0052] In one embodiment, A1 < 50 and A2 is 0.5-6, preferably 0.8-3, for example 0.5, 1, 1.5, 2, 2.5, 5.

[0053] In one embodiment, A1 > 50 and A2 is 0.8-7, preferably 1.2-5, for example 0.8, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 6.

[0054] In one embodiment, the amine compound includes one or more than two of diaminodiphenylmethane, polymethylene polyphenyl polyamine, diaminotoluene, isophorone diamine, hexamethylene diamine, cyclohexane diamine, p-phenylene diamine, naphthalene diamine.

[0055] In one embodiment, the solvent includes one or more than two of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene.

[0056] In one embodiment, in step (1), the amine compound, the phosgene solution and the solvent are mixed to carry out the phosgenation reaction to obtain the first mixture containing isocyanate and the first gas mixture containing phosgene and hydrogen chloride. The solvent of the phosgene solution can be the same as the solvent of the phosgenation reaction system.

[0057] In one embodiment, the mass ratio of the amine compound to the solvent in step (1) is 1 : (2-6), preferably 1 : (2.5-5), more preferably 1 : (3-4), such as 1 :2.5, 1 :3, 1 :3.5, 1 :4, 1 :4.5, 1 :5 or 1 :5.5.

[0058] In one embodiment, the mass percentage of phosgene in the phosgene solution is 50-90%, such as 60%, 70%, 80%.

[0059] In one embodiment, the pressure of the phosgenation reaction in step (1) is 1-30 barg, such as 3 barg, 5 barg, 10 barg, 15 barg, 20 barg, 25 barg. In this context, the pressure is always gauge pressure.

[0060] In one embodiment, the phosgenation reaction comprises a cold phosgenation reaction and a hot phosgenation reaction, the cold phosgenation reaction is an exothermic reaction, and the hot phosgenation reaction is an endothermic reaction. Further, the phosgenation reaction can be carried out in a reactor, the cold phosgenation reaction can be carried out in an existing jet reactor, and the hot phosgenation reaction can be carried out in an existing tank reactor or column reactor. In this context, the maximum temperature of the phosgenation reaction is the maximum temperature of the cold phosgenation reaction and the hot phosgenation reaction, and the residence time of the phosgenation reaction is the sum of the residence times of the material in the reactor of the cold phosgenation reaction and the reactor of the hot phosgenation reaction.

[0061] In one embodiment, the treatment for removing hydrogen chloride and phosgene in step (2) can be carried out in a dephosgenation column to obtain a second mixture and a second gas mixture comprising hydrogen chloride and phosgene. In this context, the treatment temperature of step (2) is the temperature of the column bottom of the dephosgenation column, the treatment pressure is the pressure at the column top, and the treatment time refers to the residence time of the second mixture in the dephosgenation column.

[0062] In one embodiment, the treatment pressure of step (2) is -0.2-3 barg, such as -0.15 barg, -0.1 barg, -0.05 barg, 0 barg, 0.05 barg, 0.1 barg, 0.15 barg, 0.5 barg, 1 barg, 1.5 barg, 2 barg, 2.5 barg.

[0063] In one embodiment, the second mixture is subjected to a first solvent removal treatment in a first solvent removal column to remove part of the solvent and obtain an isocyanate crude product and a gaseous solvent at the column bottom, and the gaseous solvent can be recycled after being cooled. In this context, the temperature of the first solvent removal treatment is the temperature of the column bottom, and the pressure of the first solvent removal treatment is the pressure at the column top.

[0064] In one embodiment, the first solvent removal treatment of step (3) can be at a temperature of 100 to 220 °C, for example 120 °C, 140 °C, 150 °C, 160 °C, 180 °C or 200 °C. The first solvent removal treatment can be at a pressure of -1 to 0 barg, for example -0.9 barg, -0.8 barg, -0.7 barg, -0.6 barg, -0.5 barg, -0.4 barg, -0.3 barg, -0.2 barg or -0.1 barg.

[0065] In one embodiment, the separation treatment of step (4) is performed by subjecting the crude isocyanate to a separation treatment, for example distillation, to remove solvent and pure isocyanate therefrom, to obtain a polymeric isocyanate product and a third gaseous mixture. The third gaseous mixture comprising solvent and pure isocyanate separated therefrom can be condensed to obtain a third mixture liquid.

[0066] In one embodiment, the separation treatment of step (4) can be performed by a distillation column, wherein the temperature of the separation treatment is the temperature of the column bottom and the pressure of the separation treatment is the pressure of the column top.

[0067] In one embodiment, the separation treatment of step (4) can be at a temperature of 150 to 300 °C, for example 170 °C, 190 °C, 200 °C, 210 °C, 230 °C, 250 °C, 270 °C or 290 °C. The separation treatment can be at a pressure of -1 to 1 barg; for example -0.8 barg, -0.6 barg, -0.4 barg, -0.2 barg, 0 barg, 0.2 barg, 0.4 barg, 0.6 barg or 0.8 barg.

[0068] In one embodiment, the second solvent removal treatment of step (5) can be performed in a second solvent removal column. The temperature of the second solvent removal treatment is the temperature of the column bottom and the pressure of the second solvent removal treatment is the pressure of the column top.

[0069] In one embodiment, the second solvent removal treatment can be at a temperature of 100 to 220 °C, for example 120 °C, 140 °C, 150 °C, 160 °C, 180 °C or 200 °C. The second solvent removal treatment can be at a pressure of -1 to 0 barg, for example -0.9 barg, -0.8 barg, -0.7 barg, -0.6 barg, -0.5 barg, -0.4 barg or -0.2 barg.

[0070] In one embodiment, the method of preparing isocyanate comprises the steps of:

[0071] (1) reacting the amine compound with phosgene in a solvent, the highest reaction temperature being 100-170°C, the reaction pressure being 1-30 barg, and the reaction time being 0.5-12 h to obtain a first mixture containing isocyanate;

[0072] (2) removing hydrogen chloride and phosgene from the first mixture at 100-180°C and -0.2-3 barg to obtain a second mixture; the mass percentage of the solvent in the second mixture being 20-90%; and in steps (1) and (2), the characteristic index A1 being controlled to be 25-80;

[0073] (3) subjecting the second mixture to a first solvent removal treatment at 100-220°C and -1-0 barg to remove part of the solvent therefrom to obtain an isocyanate crude product having a solvent mass percentage of 0.01-30%; and in steps (1), (2) and (3), the characteristic index A2 being controlled to be 0.2-12.0 or 0.4-21;

[0074] (4) removing the solvent and pure isocyanate from the isocyanate crude product at 150-300°C and -1-1 barg to obtain a polymeric isocyanate product and a third gaseous mixture; and condensing the third gaseous mixture containing the solvent and pure isocyanate to obtain a third mixture;

[0075] (5) removing the solvent from the third mixture at 100-220°C and -1-0 barg to obtain a pure isocyanate product.

[0076] One embodiment of the present application provides a polymeric isocyanate product prepared by the above-mentioned preparation method.

[0077] In one embodiment, the color of the polymeric isocyanate product is measured by L*; the higher the value, the lighter the color of the product. The L* of the polymeric isocyanate product can be greater than 60, preferably 63-82, more preferably 70-82, such as 63, 64, 65, 67, 68, 70, 72, 74, 75, 76, 77, 80, 81, 82.

[0078] In one embodiment, the yield of isocyanate can be measured by the mass content of isocyanate group (-NCO) in the isocyanate crude product and the polymeric isocyanate, respectively; the higher the content, the higher the yield. The mass content of isocyanate group in the polymeric isocyanate product can be higher than 30.5%, preferably 30.5-31.6%, such as 30.7%, 30.9%, 31.1%, 31.2%, 31.3%, 31.5% or 31.7%.

[0079] One embodiment of the present application provides a pure isocyanate product prepared by the above-mentioned preparation method.

[0080] In one embodiment, the color of the pure isocyanate product is measured in terms of platinum-cobalt color number, and the lower the number, the lighter the color of the product. The platinum-cobalt color number of the pure isocyanate product can be less than 10, preferably 8 or less, such as 1, 2, 3, 3.2, 3.6, 3.8, 4, 5, 5.1, 5.9, 6, 6.2, 6.3, 6.8, 7, 8, 8.2, 8.3, 8.6, or 9.

[0081] In one embodiment, the platinum-cobalt color number of the pure isocyanate product is 3-9.

[0082] One embodiment of the present application provides the use of the above-mentioned polymeric isocyanate product or the above-mentioned pure isocyanate product in the synthesis of polyisocyanate, polyurethane, polyurea, or spandex.

[0083] Reference Figure 1 One embodiment of the present application provides an isocyanate preparation device for implementing the above-mentioned method, which comprises a cold reactor 10, a hot reactor 20, a dephotor tower 30, a first solvent removal tower 40, a separation tower 50, a condenser 60, and a second solvent removal tower 70 connected in sequence.

[0084] In one embodiment, the cold reactor 10 can be a jet reactor, and the hot reactor 20 can be a kettle reactor or a column reactor; the dephotor tower 30, the first solvent removal tower 40, the separation tower 50, and the second solvent removal tower 70 can all be existing rectification towers.

[0085] The inventors have found that the coupling of parameters related to color number and reaction effect in the isocyanate production process can result in two characteristic indexes A1 and A2, and by controlling the process parameters to control the characteristic indexes within a certain range, the color and yield of the product can be within a better range.

[0086] The isocyanate preparation method of one embodiment of the present application controls the characteristic indexes A1 and A2, improves the operation flexibility of the isocyanate production process, and has the advantages of simple process, easy operation, energy saving, low cost, high efficiency, and environmental friendliness.

[0087] The isocyanate preparation method of one embodiment of the present application can produce light-colored isocyanate while improving the yield and prolonging the stable operation period of the production device.

[0088] In the present application, the mass percentage of the solvent in the mixed solution is determined by gel permeation chromatography (GPC) and calculated, and the analysis method is as follows: the mixed solution is directly injected for analysis, and the injection amount is 10 uL. The chromatographic column used is Waters HR01*1 and Waters HR01*3, the column oven temperature is 35℃; the detector type is FID detector, the detector temperature is 35℃, and the mobile phase is tetrahydrofuran with a flow rate of 1 ml / min. The mass percentage of the solvent in the mixed solution can be obtained by integrating the chromatogram, and the mass content of the solute is: 100%-the mass percentage of the solvent.

[0089] The preparation method of the isocyanate according to one embodiment of the present application will be further described below in combination with the drawings and specific examples. The relevant performance test methods are as follows:

[0090] 1. The platinum-cobalt color number of the pure isocyanate product is measured according to the test method of GB / T 3143-1982.

[0091] 2. The determination method of L* of the polymeric isocyanate product

[0092] The determination is performed by using a VTS spectrophotometer of Hunterlab Company, and the specific process is as follows: the colorimetric cell is placed into the instrument detection slot for blank calibration, after the calibration is completed, the sample to be measured is loaded into the colorimetric cell, and then the reading is obtained by placing the colorimetric cell into the instrument detection slot.

[0093] 3. The content of isocyanate group (-NCO) is measured by the method of GB / T 12009.4-1989.

[0094] Example 1

[0095] (1) Diphenylmethane diamine with a flow rate of 30 t / h is mixed with chlorobenzene with a flow rate of 25 t / h, and then introduced into a cold reactor 10, and at the same time, phosgene solution is introduced into the cold reactor 10; the flow rate of the phosgene solution is 40 t / h, and the mass percentage of phosgene is 70%; the diphenylmethane diamine and the phosgene are reacted in the cold reactor 10, and then the mixture is introduced into a hot reactor 20 for reaction, to obtain a first mixed solution containing isocyanate and a first gas mixture containing phosgene and hydrogen chloride.

[0096] (2) The first mixed solution is introduced into a dephosgenation tower 30 to remove hydrogen chloride and phosgene, to obtain a second mixed solution in the tower kettle and a second gas mixture containing hydrogen chloride and phosgene, which is discharged from the top of the tower.

[0097] (3) The second mixed solution is introduced into a first solvent removal tower 40 to remove part of the chlorobenzene, and the solution in the tower kettle is collected to obtain a crude isocyanate product; and the removed chlorobenzene is discharged from the top of the tower.

[0098] (4) The crude isocyanate is passed into a separation column 50 to separate the components and obtain a polymeric isocyanate product and a third gas mixture; the polymeric isocyanate product is withdrawn from the column bottom, and the third gas mixture is discharged from the column top into a condenser 60 to be condensed and obtain a third mixture liquid, which includes pure isocyanate and a small amount of chlorobenzene.

[0099] (5) The third mixture liquid is passed into a second solvent removal column 70 to remove chlorobenzene, which is withdrawn from the column top, and pure isocyanate product is obtained from the column bottom.

[0100] In step (1), the mass ratio a of phosgene to diphenylmethane diamine is 1.5, the highest temperature of the phosgenation reaction is 135°C (b=135), and the time of the phosgenation reaction is 2.1 hours (c=2.1). In step (2), the temperature of the column bottom is 145°C (d=145), the treatment time is 0.2 hours (e=0.2), and the mass content f of the solvent in the second mixture liquid is 75% by adjusting the column top pressure of the de-phosgenation column. In step (3), the mass content g of the solvent in the crude isocyanate is 4.5% by adjusting the column bottom temperature and the column top pressure of the first solvent removal column 40. The characteristic index A1 is 32.20, and the characteristic index A2 is 1.85.

[0101] Examples 2 to 11 and Comparative Examples 1 to 8 are prepared by using the same raw materials and process as in Example 1, except that the process parameters a, b, c, e, d, f, g and the characteristic indexes A1 and A2 are different. See Table 1 for details.

[0102] Table 1

[0103]

[0104]

[0105] The pure isocyanate product and the polymeric isocyanate product prepared in each example and comparative example are tested according to the aforementioned test methods, and the test results are shown in Table 2.

[0106] Table 2

[0107]

[0108] As can be seen from Table 1, although the process parameters a to g of Comparative Examples 1 to 8 are within the aforementioned limited ranges, one or both of the characteristic parameters A1 and A2 are not within the scope of the claims. As can be seen from the results in Table 2, the color and yield of the products prepared in Comparative Examples 1 to 8 are significantly poorer than those of the products prepared in Examples 1 to 11. Therefore, exceeding the aforementioned ranges of the characteristic parameters can result in increased loss of color and -NCO groups of the isocyanate product during production, affecting the color and yield of the product and the stable operation period of the production device. The Examples of the present application effectively reduce the loss of color during production by precisely controlling the characteristic parameters A1 and A2 during isocyanate production, reduce the color depth of the isocyanate product, increase the reaction yield, and improve the stable operation period of the production device.

[0109] Specifically, as can be seen from the results in Table 2, the platinum-cobalt color number of the pure isocyanate product prepared in Examples 1 to 11 is 3.2 to 8.6, the L* of the polymeric isocyanate product is 63 to 82, the mass fraction of -NCO groups of the polymeric isocyanate product is 30.89 to 31.54%, and the cleaning period of the inlet filter of the polymeric isocyanate feed tank is 45 to 80 days. These results are all better than the corresponding results of the products of Comparative Examples 1 to 8. Therefore, by controlling the process parameters such as the phosgenation reaction time and the characteristic parameters during isocyanate production within a certain range, the color and yield of the product can be improved.

[0110] Unless specifically defined, the terms used in the present application are understood by those skilled in the art in the usual sense.

[0111] The embodiments described in the present application are for illustrative purposes only and are not intended to limit the scope of protection of the present application, and those skilled in the art can make various other replacements, changes and improvements within the scope of the present application, and therefore the present application is not limited to the above-described embodiments, but is limited only by the claims.

Claims

1. A method for preparing isocyanate, comprising the steps of: (1) subjecting an amine compound to a phosgenation reaction with phosgene in a solvent to obtain a first mixture containing isocyanate; (2) subjecting the first mixture to a treatment for removing hydrogen chloride and phosgene to obtain a second mixture; (3) subjecting the second mixture to a first solvent removal treatment to obtain a crude isocyanate product; (4) subjecting the crude isocyanate product to a separation treatment to obtain a polymeric isocyanate product and a third mixture; the third mixture comprising the solvent and pure isocyanate; and (5) subjecting the third mixture to a second solvent removal treatment to obtain a pure isocyanate product; wherein, in step (1), the mass ratio a of the phosgene to the amine compound is 1 to 10; the maximum temperature of the phosgenation reaction is b°C, b being 100 to 170; and the residence time of the materials in the phosgenation reaction system in the reaction vessel is c hours, c being 0.5 to 12; the treatment temperature of step (2) is d°C, d being 100 to 200, and the treatment time is e hours, e being 0.01 to 4; the mass content f of the solvent in the second mixture is 20 to 90%; and the mass content g of the solvent in the crude isocyanate product is 0.01 to 30%; wherein, A1 and A2 each represent a characteristic index, dimensionless; if A1 < 50, then A2 is: A1 = 0.164 * a 2 + 0.054 * b + 3.89 * c + 0.0007 * d 2 + 8.25 * e if A1 ≥ 50, then A2 is: A2 = 2.71 * f 2 + 99.16 * g 2 + 0.1228 A1 is 25 to 80; and A1 < 50, A2 is 0.5 to 6; and A1 ≥ 50, A2 is 0.8 to 7. A2 = 4.08 * f 2 + 195.42 * g 2 + 0.2632 A1 is 30 to 60; and / or, 2. The production method according to claim 1, wherein A1 < 50, A2 is 0.8 to 3; and / or, A1 ≥ 50, A2 is 1.2 to 5. the amine compound is selected from one or more than two of diaminodiphenylmethane, polymethylene polyphenyl polyamine, diaminotoluene, isophorone diamine, hexamethylene diamine, cyclohexane diamine, p-phenylene diamine, naphthalene diamine; and / or, 3. The production method according to claim 1, wherein the solvent is selected from one or more than two of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, diethyl isophthalate. the pressure of the phosgenation reaction of step (1) is 1 to 30 barg; and / or, 4. The production method according to claim 1, wherein the treatment pressure of step (2) is -0.2 to 3 barg; and / or, the temperature of the first solvent removal treatment of step (3) is 100 to 220°C, and the pressure is -1 to 0 barg; and / or, the temperature of the separation treatment of step (4) is 150 to 300°C, and the pressure is -1 to 1 barg; and / or, the temperature of the second solvent removal treatment of step (5) is 100 to 220°C, and the pressure is -1 to 0 barg. the treatment for removing hydrogen chloride and phosgene, the first solvent removal treatment, the separation treatment, and the second solvent removal treatment are each carried out in a rectifying column.

5. The production method according to claim 1, wherein ​

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