Isocyanate, and preparation method therefor and use thereof

Abstract

The present invention relates to an isocyanate, and a preparation method therefor and the use thereof. The method comprises the following steps: (1) subjecting an amine compound and phosgene to a phosgenation reaction in a solvent, so as to obtain a first mixed solution containing an isocyanate; (2) removing hydrogen chloride and phosgene from the first mixed solution, so as to obtain a second mixed solution; (3) subjecting the second mixed solution to a first solvent removal treatment, so as to obtain a crude isocyanate product; (4) subjecting the crude isocyanate product to a separation treatment, so as to obtain a polymerized isocyanate product and a third mixed solution, wherein the third mixed solution comprises the solvent and a pure isocyanate; and (5) subjecting the third mixed solution to a second solvent removal treatment, so as to obtain a pure isocyanate product. In the preparation method for an isocyanate in one embodiment of the present invention, process parameters in a plurality of steps are adjusted, and therefore the characteristic index can fall within a specific range, thereby improving the yield and chroma index of the prepared isocyanate product.

Description

Isocyanate and its preparation method and application Technical Field

[0001] The present invention relates to isocyanate, and in particular to a method for preparing isocyanate with better chroma. Background Art

[0002] Isocyanates, as organic reaction intermediates, are widely used in various industries, including industry, agriculture, construction, automotive, and thermal insulation, as they can be further synthesized into materials such as polymeric isocyanates, polyurethanes, polyureas, and spandex. Currently, the mainstream industrial synthesis method for isocyanates is phosgenation, which presents two prominent issues: First, undesirable discoloration occurs during the phosgenation process. This is due to the large amount of colored substances produced during the phosgenation reaction of diamines or polyamines. These substances cannot be removed during the subsequent separation process and remain in the isocyanate-to-polyurethane process. Second, the phosgenation reaction produces ureas as byproducts. The presence of urea can catalyze the polymerization of the products, clogging equipment pipelines, affecting the yield of isocyanates and the long-term operation of production equipment.

[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 more importantly, the by-products generated during the phosgenation process cause the product to be colored. Color treatment at the stage after the phosgenation reaction requires a large amount of engineering costs and does not significantly improve the color number. In addition, most methods of color treatment at the stage after the phosgenation reaction require the introduction of other impurities. These impurities will form undesirable by-products in the downstream applications of the isocyanate; and treatment upstream of the phosgenation reaction requires strict limits on the content of certain specific components, which is relatively costly.

[0004] On the other hand, to address the problem that the phosgenation method for preparing isocyanates easily produces urea by-products, the current more effective and convenient method is to increase the excess rate of phosgene compared to amine substances. However, an increase in the phosgene excess rate will lead to an increase in the amount of phosgene circulating in the system, which not only increases operational risks but also increases the energy consumption of phosgene evaporation.

[0005] Summary of the Invention

[0006] To overcome at least one of the above-mentioned defects of the prior art, in a first aspect, one embodiment of the present invention provides a method for preparing isocyanate, comprising the following steps:

[0007] (1) performing a phosgenation reaction on an amine compound and phosgene in a solvent to obtain a first mixed solution containing isocyanate;

[0008] (2) removing hydrogen chloride and phosgene from the first mixed solution to obtain a second mixed solution;

[0009] (3) subjecting the second mixed solution to a first solvent removal treatment to obtain a crude isocyanate;

[0010] (4) separating and treating the crude isocyanate to obtain a polymerized isocyanate product and a third mixed solution; the third mixed solution comprises the solvent and pure isocyanate; and

[0011] (5) subjecting the third mixed solution to a second solvent removal treatment to obtain a pure isocyanate product;

[0012] 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, where b is 100 to 170°C; the residence time of the materials in the phosgenation reaction system in the reaction vessel is c hours, where c is 0.5 to 12 hours;

[0013] The treatment temperature of step (2) is d°C, d is 100-200°C, and the treatment time is e hours, e is 0.01-4 hours;

[0014] The mass content f of the solvent in the second mixed liquid is 20 to 90%; the mass content g of the solvent in the crude isocyanate is 0.01 to 30%;

[0015] Where A1 and A2 are dimensionless characteristic indices; 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: A2=2.71*f 2 +99.16*g 2 +0.1228

[0017] If A1≥50, then A2 is: A2=4.08*f 2 +195.42*g 2 +0.2632

[0018] A1 is 25-80; and when A1 is less than 50, A2 is 0.5-6; when A1 is greater than or equal to 50, A2 is 0.8-7.

[0019] In a second aspect, an embodiment of the present invention provides a polymeric isocyanate product prepared by the above-mentioned preparation method.

[0020] In a third aspect, an embodiment of the present invention provides a pure isocyanate product prepared by the above-mentioned preparation method.

[0021] In a fourth aspect, an embodiment of the present invention provides the use of the above-mentioned polymeric isocyanate product or pure isocyanate product in the synthesis of polymeric isocyanate, polyurethane, polyurea or spandex.

[0022] In an embodiment of the isocyanate preparation method of the present invention, by adjusting the process parameters in multiple steps, the characteristic indexes A1 and A2 can be within a specific range, thereby improving the yield and color index of the prepared isocyanate product. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The accompanying drawings are only used to illustrate specific embodiments and are not to be considered as limiting the present invention.

[0024] FIG1 is a schematic structural diagram of an isocyanate preparation apparatus according to one embodiment of the present invention. DETAILED DESCRIPTION

[0025] Typical embodiments that embody the features and advantages of the present invention will be described in detail in the following description. It should be understood that the present invention is capable of various variations in different embodiments without departing from the scope of the present invention, and the descriptions herein are intended to be illustrative rather than limiting.

[0026] One embodiment of the present invention provides a method for preparing isocyanate, comprising the following steps:

[0027] (1) performing a phosgenation reaction on an amine compound and phosgene in a solvent to obtain a first mixed solution;

[0028] (2) removing hydrogen chloride and phosgene from the first mixed solution to obtain a second mixed solution;

[0029] (3) subjecting the second mixed solution to a first solvent removal treatment to obtain a crude isocyanate;

[0030] (4) separating and treating the crude isocyanate to obtain a polymerized isocyanate product and a third mixed solution; the third mixed solution includes a solvent and pure isocyanate; and

[0031] (5) subjecting the third mixed solution to a second solvent removal treatment to obtain pure isocyanate;

[0032] Wherein, in step (1), the mass ratio a of phosgene to amine compound is 1 to 10; the maximum temperature of the phosgenation reaction is b°C, where b is 100 to 170°C; the residence time of the materials in the phosgenation reaction system in the reaction vessel is c hours, where c is 0.5 to 12 hours;

[0033] The treatment temperature of step (2) is d°C, d is 100-200°C, and the treatment time is e hours, e is 0.01-4 hours;

[0034] The mass content f of the solvent in the second mixed liquid is 20 to 90%; the mass content g of the solvent in the crude isocyanate is 0.01 to 30%;

[0035] Where A1 and A2 are dimensionless characteristic indices; A1 = 0.164*a 2 +0.054*b+3.89*c+0.0007*d 2 +8.25*e

[0036] If A1<50, then A2 is: A2=2.71*f 2 +99.16*g 2 +0.1228

[0037] If A1≥50, then A2 is: A2=4.08*f 2 +195.42*g 2 +0.2632

[0038] A1 is 25-80; and when A1 is less than 50, A2 is 0.5-6; when A1 is greater than or equal to 50, A2 is 0.8-7.

[0039] In one embodiment, the mass ratio a of phosgene to amine compound is 1 to 10, such as 2, 4, 6, or 8.

[0040] In one embodiment, the maximum temperature of the phosgenation reaction may be 100-170°C, such as 110°C, 120°C, 130°C, 140°C, 150°C or 160°C. Accordingly, b may be 100-170°C, such as 110, 120, 130, 140, 150 or 160°C.

[0041] In one embodiment, the residence time of the materials in the phosgenation reaction system in the reaction vessel can be 0.5 to 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. Accordingly, c can be 0.5 to 12, for example, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, or 11 hours.

[0042] In one embodiment, the treatment temperature of step (2) is 100-200°C, for example, 110, 120, 130, 140, 150, 160 or 170.

[0043] In one embodiment, the treatment time of step (2) is 0.01 to 4 hours, such as 0.1 hour, 0.5 hour, 1 hour, 1.5 hours, 2 hours, 2.5 hours, 3 hours, or 3.5 hours. Accordingly, e is 0.01 to 4, such as 0.1, 0.5, 1, 1.5, 2, 2.5, 3, or 3.5.

[0044] In one embodiment, the mass content f of the solvent in the second mixed liquid is 20-90%, for example, 30%, 40%, 50%, 60%, 70% or 80%.

[0045] In one embodiment, the mass content g of the solvent in the crude isocyanate is 0.01 to 30%, for example, 0.05%, 1%, 2%, 5%, 8%, 10%, 15%, 20%, or 25%.

[0046] In one embodiment, A1 is 25-80, preferably 30-60, for example 35, 40, 45, 50, 55, 65, 70 or 75.

[0047] In one embodiment, A1<50, A2 is 0.5-6, preferably 0.8-3, for example 0.5, 1, 1.5, 2, 2.5, 5.

[0048] In one embodiment, A1≥50, 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.

[0049] In one embodiment, the amine compound includes one or more of diaminodiphenylmethane, polymethylene polyphenyl polyamine, diaminotoluene, isophoronediamine, hexamethylenediamine, cyclohexamethylenediamine, p-phenylenediamine, and naphthalenediamine.

[0050] In one embodiment, the solvent includes one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene, and diethyl isophthalate, preferably chlorobenzene and / or o-dichlorobenzene.

[0051] In one embodiment, in step (1), an amine compound, a phosgene solution, and a solvent are mixed to perform a phosgenation reaction to obtain a first mixed liquid containing isocyanate and a first gaseous mixture containing phosgene and hydrogen chloride. The solvent of the phosgene solution can be the same as the solvent of the phosgenation reaction system.

[0052] 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), and more preferably 1:(3-4), for example, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5 or 1:5.5.

[0053] In one embodiment, the mass percentage of phosgene in the phosgene solution is 50-90%, for example, 60%, 70%, or 80%.

[0054] In one embodiment, the pressure of the phosgenation reaction in step (1) is 1 to 30 barg, such as 3 barg, 5 barg, 10 barg, 15 barg, 20 barg, or 25 barg. The pressures mentioned herein are all gauge pressures.

[0055] In one embodiment, the phosgenation reaction includes a cold phosgenation reaction and a hot phosgenation reaction. The cold phosgenation reaction is an exothermic reaction, while the hot phosgenation reaction is an endothermic reaction. Furthermore, the phosgenation reaction can be carried out in a reactor. The cold phosgenation reaction can be carried out in an existing jet reactor, while the hot phosgenation reaction can be carried out in an existing kettle reactor or tower reactor. 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 time of the material in the cold phosgenation reactor and the hot phosgenation reactor.

[0056] In one embodiment, the treatment for removing hydrogen chloride and phosgene in step (2) can be performed in a phosgene removal tower to obtain a second mixed liquid and a second gas mixture containing hydrogen chloride and phosgene. The treatment temperature in step (2) is the bottom temperature of the phosgene removal tower, the treatment pressure is the tower top pressure, and the treatment time refers to the residence time of the second mixed liquid in the phosgene removal tower.

[0057] In one embodiment, the processing pressure of step (2) is -0.2 to 3 barg, for example, -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.

[0058] In one embodiment, the second mixed liquid undergoes a first solvent removal treatment in a first solvent removal tower to remove a portion of the solvent, thereby obtaining a crude isocyanate product and a gaseous solvent in the bottom of the tower. The gaseous solvent can be cooled and reused. The temperature of the first solvent removal treatment is the bottom temperature of the tower, and the pressure of the first solvent removal treatment is the pressure at the top of the tower.

[0059] In one embodiment, the temperature of the first desolventizing treatment in step (3) may be 100 to 220° C., for example, 120° C., 140° C., 150° C., 160° C., 180° C., or 200° C. The pressure of the first desolventizing treatment may be -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.

[0060] In one embodiment, in step (4), the crude isocyanate product is subjected to a separation treatment (e.g., distillation) to remove the solvent and pure isocyanate therein, thereby obtaining a polymerized isocyanate product and a third gas mixture. The separated third gas mixture containing the solvent and pure isocyanate can be condensed to obtain a third mixed liquid.

[0061] In one embodiment, the separation treatment in step (4) can be performed by a distillation tower, wherein the temperature of the separation treatment is the temperature of the tower bottom, and the pressure of the separation treatment is the pressure of the tower top.

[0062] In one embodiment, the temperature of the separation treatment in step (4) can be 150-300° C., for example, 170° C., 190° C., 200° C., 210° C., 230° C., 250° C., 270° C., or 290° C. The pressure of the separation treatment can be -1-1 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.

[0063] In one embodiment, the second desolventizing treatment of step (5) can be carried out in a second solvent removal tower. The temperature of the second desolventizing treatment is the temperature of the tower bottom, and the pressure of the second desolventizing treatment is the pressure of the tower top.

[0064] In one embodiment, the temperature of the second desolvation treatment may be 100 to 220° C., for example, 120° C., 140° C., 150° C., 160° C., 180° C., or 200° C. The pressure of the second desolvation treatment may be -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.

[0065] In one embodiment, the method for preparing isocyanate comprises the following steps:

[0066] (1) phosgenating an amine compound with phosgene in a solvent at a maximum reaction temperature of 100 to 170° C., a reaction pressure of 1 to 30 barg, and a reaction time of 0.5 to 12 hours to obtain a first mixed solution containing an isocyanate;

[0067] (2) removing hydrogen chloride and phosgene from the first mixed solution at 100-180° C. and -0.2-3 barg to obtain a second mixed solution; the mass percentage of the solvent in the second mixed solution is 20-90%; and in steps (1) and (2), controlling the characteristic index A1 to be 25-80;

[0068] (3) subjecting the second mixed solution to a first desolventizing treatment at 100 to 220° C. and -1 to 0 barg to remove a portion of the solvent therein to obtain a crude isocyanate having a solvent content of 0.01 to 30% by mass; and controlling the characteristic index A2 in steps (1), (2), and (3) to be 0.2 to 12.0 or 0.4 to 21;

[0069] (4) removing the solvent and pure isocyanate from the crude isocyanate product at 150 to 300° C. and -1 to 1 barg to obtain a polymerized isocyanate product and a third gas mixture; condensing the third gas mixture containing the solvent and pure isocyanate to obtain a third mixed liquid;

[0070] (5) removing the solvent from the third mixed liquid at 100-220° C. and -1-0 barg to obtain a pure isocyanate product.

[0071] One embodiment of the present invention provides a polymeric isocyanate product, which is prepared by the above-mentioned preparation method.

[0072] In one embodiment, the chromaticity of the polymeric isocyanate product is measured in L*, with higher values ​​indicating lighter product color. The L* of the polymeric isocyanate product may be greater than 60, preferably 63 to 82, more preferably 70 to 82, for example, 63, 64, 65, 67, 68, 70, 72, 74, 75, 76, 77, 80, 81, or 82.

[0073] In one embodiment, the yield of isocyanate can be measured as the mass content of isocyanate groups (-NCO) in the crude isocyanate and the polymerized isocyanate, respectively, with higher contents indicating higher yields. The mass content of isocyanate groups in the polymerized isocyanate product can be greater than 30.5%, preferably 30.5-31.6%, for example, 30.7%, 30.9%, 31.1%, 31.2%, 31.3%, 31.5%, or 31.7%.

[0074] One embodiment of the present invention provides a pure isocyanate product, which is prepared by the above-mentioned preparation method.

[0075] In one embodiment, the chromaticity of the pure isocyanate product is measured in terms of platinum cobalt color number, with lower values ​​indicating lighter product color. The platinum cobalt color number of the pure isocyanate product may be less than 10, preferably less than 8, for example, 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.

[0076] In one embodiment, the platinum cobalt color number of the pure isocyanate product is 3-9.

[0077] One embodiment of the present invention provides the use of the above-mentioned polymeric isocyanate product or the above-mentioned pure isocyanate product in the synthesis of polymeric isocyanate, polyurethane, polyurea or spandex.

[0078] 1 , an embodiment of the present invention provides an isocyanate preparation device that can be used to implement the above method. The device includes a cold reactor 10, a hot reactor 20, a phosgene removal 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.

[0079] In one embodiment, the cold reactor 10 can be a jet reactor, and the hot reactor 20 can be a kettle reactor or a tower reactor; the phosgene removal tower 30, the first solvent removal tower 40, the separation tower 50, and the second solvent removal tower 70 can all be existing distillation towers.

[0080] The inventors obtained two characteristic indices A1 and A2 by studying the coupling effect of parameters related to color number and reaction effect in the isocyanate production process, and controlled the characteristic indices within a certain range by adjusting the process parameters, so that the chromaticity and yield of the product can be within a better range.

[0081] The method for preparing isocyanate according to one embodiment of the present invention improves the operational flexibility of the isocyanate production process by regulating and controlling characteristic indices A1 and A2, and has the advantages of simple process, convenient operation, energy saving, low cost, high efficiency and environmental friendliness.

[0082] The method for preparing isocyanate according to one embodiment of the present invention can improve the yield and extend the stable operation period of the production device while preparing light-colored isocyanate.

[0083] In this study, the mass percentage of the solvent in the mixed solution was determined and calculated using gel permeation chromatography (GPC). The analysis method was as follows: 10 μL of the mixed solution was injected directly into the sample. The columns used were Waters HR01*1 and Waters HR01*3, and the column oven temperature was 35°C. The detector type was an FID detector, the detector temperature was 35°C, and the mobile phase was tetrahydrofuran at a flow rate of 1 mL / min. The mass percentage of the solvent in the mixed solution was obtained by integrating the chromatogram: the mass percentage of the solute was 100% - the mass percentage of the solvent.

[0084] The following further describes the preparation method of isocyanate according to one embodiment of the present invention in conjunction with the accompanying drawings and specific examples. The relevant performance testing methods are as follows:

[0085] 1. The platinum-cobalt color number of pure isocyanate products is measured according to the test method of GB / T 3143-1982.

[0086] 2. Determination of L* of Polyisocyanate Products

[0087] The colorimeter was measured using a VTS spectrophotometer from Hunterlab. The specific process was as follows: a colorimetric cell was placed in the instrument's detection tank for blank calibration. After the calibration was complete, the sample to be tested was placed in the colorimetric cell and placed in the instrument's detection tank for reading.

[0088] 3. The content of isocyanate groups (-NCO) is measured using the method of GB / T 12009.4-1989.

[0089] Example 1

[0090] (1) Diphenylmethanediamine with a flow rate of 30 t / h and chlorobenzene with a flow rate of 25 t / h are mixed and introduced into a cold reactor 10, and a phosgene solution is simultaneously 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%; diphenylmethanediamine and phosgene react in the cold reactor 10, and then the mixture is introduced into a hot reactor 20 for reaction to obtain a first mixed liquid containing isocyanate and a first gas mixture containing phosgene and hydrogen chloride.

[0091] (2) The first mixed liquid is passed into a phosgene removal tower 30 to remove hydrogen chloride and phosgene, thereby obtaining a second 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.

[0092] (3) The second mixed liquid is passed into the first solvent removal tower 40 to remove part of the chlorobenzene, and the solution in the bottom of the tower is collected to obtain a crude isocyanate; the removed chlorobenzene is discharged from the top of the tower.

[0093] (4) The crude isocyanate product is passed into a separation tower 50 for component separation to obtain a polymerized isocyanate product and a third gas mixture; the polymerized isocyanate product is extracted from the bottom of the tower, and the third gas mixture is discharged from the top of the tower into a condenser 60 for condensation to obtain a third mixed liquid, which includes pure isocyanate and a small amount of chlorobenzene.

[0094] (5) The third mixed liquid is passed into a second solvent removal tower 70 to remove chlorobenzene. The removed chlorobenzene is extracted from the top of the tower, and a pure isocyanate product is obtained from the bottom of the tower.

[0095] Wherein, in step (1), the mass ratio a of phosgene to diphenylmethanediamine is 1.5, the maximum temperature of the phosgenation reaction is 135°C (b=135), and the phosgenation reaction time is 2.1 hours (c=2.1). In step (2), the temperature of the tower 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 mixed liquid is 75% by regulating the tower top pressure of the phosgenation tower. In step (3), the mass content g of the solvent in the crude isocyanate product is 4.5% by regulating the tower bottom temperature and tower top pressure of the first solvent removal tower 40. The characteristic index A1 is 32.20 and A2 is 1.85.

[0096] The isocyanates of Examples 2 to 11 and Comparative Examples 1 to 8 were prepared using substantially the same raw materials and processes as in Example 1, with the only difference being that the process parameters a, b, c, e, d, f, g and characteristic indices A1 and A2 used were different. See Table 1 for details.

[0097] Table 1

[0098] The pure isocyanate products and polymerized isocyanate products prepared in each embodiment and comparative example were tested according to the aforementioned test method. The test results are shown in Table 2.

[0099] Table 2

[0100] Referring to Table 1, it can be seen that although the process parameters a to g of Comparative Examples 1 to 8 are all within the aforementioned defined ranges, one or both of their characteristic parameters A1 and A2 are not within the scope of the claims. According to the results in Table 2, it can be seen that the chromaticity and yield of the products obtained in Comparative Examples 1 to 8 are significantly worse than the chromaticity and yield of the products obtained in Examples 1 to 11. It can be seen that characteristic parameters exceeding the aforementioned ranges will lead to increased losses in the chromaticity, -NCO groups, etc. of the product during the isocyanate production process, affecting the chromaticity and yield of the product and the stable operation cycle. The embodiments of the present invention effectively reduce the chromaticity loss generated in the production process by precisely controlling the characteristic indices A1 and A2 in the isocyanate production process, reduce the color depth of the isocyanate product, improve the reaction yield, and enhance the stable operation cycle of the production device.

[0101] Specifically, according to the results in Table 2, the platinum-cobalt color number of the pure isocyanate products prepared in Examples 1 to 11 ranged from 3.2 to 8.6#, the L* of the polymerized isocyanate products ranged from 63 to 82, the mass fraction of -NCO groups in the polymerized isocyanate was 30.89 to 31.54%, and the cleaning cycle of the inlet filter of the polymerized isocyanate feed tank was 45 to 80 days. These results were superior to the corresponding results of the products of Comparative Examples 1 to 8. Thus, by controlling process parameters and characteristic indices such as the phosgenation reaction time during the isocyanate preparation process within a certain range, the color and yield of the product can be improved.

[0102] Unless otherwise defined, the terms used in the present invention have the same meanings as those commonly understood by those skilled in the art.

[0103] The embodiments described in the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. Those skilled in the art may make various other substitutions, changes and improvements within the scope of the present invention. Therefore, the present invention is not limited to the above-mentioned embodiments, but is only limited by the claims.

Claims

1. A method for preparing isocyanate, comprising the following steps: (1) subjecting an amine compound and phosgene to a phosgenation reaction 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) subjecting the second mixed solution to a first solvent removal treatment to obtain a crude isocyanate; (4) separating and treating the crude isocyanate to obtain a polymerized isocyanate product and a third mixed solution; the third mixed solution comprises the solvent and pure isocyanate; as well as (5) subjecting the third mixed solution 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, where b is 100 to 170°C; the residence time of the materials in the phosgenation reaction system in the reaction vessel is c hours, where c is 0.5 to 12 hours; 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; The mass content f of the solvent in the second mixed liquid is 20 to 90%; the mass content g of the solvent in the crude isocyanate is 0.01 to 30%; Among them, A1 and A2 both represent characteristic indices and are dimensionless; 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 If A1≥50, then A2 is: A2=4.08*f 2 +195.42*g 2 +0.2632 A1 is 25-80; and when A1 is less than 50, A2 is 0.5-6; when A1 is greater than or equal to 50, A2 is 0.8-7.

2. The preparation method according to claim 1, wherein A1 is 30 to 60; and / or, A1<50, A2 is 0.8~3; and / or, A1≥50, A2 is 1.2~5.

3. The preparation method according to claim 1, wherein The amine compound includes one or more of diaminodiphenylmethane, polymethylene polyphenyl polyamines, diaminotoluene, isophoronediamine, hexamethylenediamine, cyclohexamethylenediamine, p-phenylenediamine, and naphthalenediamine; and / or, The solvent includes one or more of chlorobenzene, dichlorobenzene, trichlorobenzene, toluene, xylene, benzene and diethyl isophthalate.

4. The preparation method according to claim 1, wherein The pressure of the phosgenation reaction in step (1) is 1 to 30 barg; and / or, The treatment pressure of step (2) is -0.2 to 3 barg; and / or, The temperature of the first solvent removal treatment in step (3) is 100 to 220° C. and the pressure is -1 to 0 barg; and / or, The temperature of the separation treatment in 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 in step (5) is 100 to 220° C. and the pressure is -1 to 0 barg.

5. The preparation method according to claim 1, wherein The treatment for removing hydrogen chloride and phosgene, the first treatment for removing solvent, the separation treatment, and the second treatment for removing solvent are all carried out in a distillation tower.

6. A polymeric isocyanate product obtained by the preparation method according to any one of claims 1 to 5.

7. The product according to claim 6, wherein L* is greater than 60, preferably 70 to 82.

8. A pure isocyanate product obtained by the preparation method according to any one of claims 1 to 5.

9. The product according to claim 8, which has a platinum cobalt color number of less than 10.

10. Use of the polymeric isocyanate product according to claim 6 or 7 or the pure isocyanate product according to claim 8 or 9 in the synthesis of polymeric isocyanate, polyurethane, polyurea or spandex.

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