Method for reducing content of hydrolyzed chlorine in isocyanate

Abstract

The invention provides a method for reducing the content of hydrolyzed chlorine in isocyanate, and the isocyanate is prepared from diphenylmethane series diamine and polyamine through phosgenation reaction. The phosgenation reaction is carried out by adopting diamine and polyamine of diphenylmethane series, wherein the mass content of N-(aminobenzyl) aniline impurities in the diamine and polyamine is 0.1-1000ppm, so that the content of hydrolyzed chlorine in the prepared isocyanate can be reduced.

Description

Technical Field

[0001] The invention relates to the technical field of isocyanate preparation, and in particular to a method for reducing the hydrolysis chlorine content in isocyanate and a method for preparing isocyanate with low hydrolysis chlorine content. Background Art

[0002] As is well known in the art, isocyanates can be prepared by phosgenation reaction of DAM (diamines and polyamines of the diphenylmethane series) to obtain a mixture of diisocyanates and polyisocyanates. The hydrolyzed chlorine content is an important indicator of isocyanate products. Excessive hydrolyzed chlorine content will deepen the color of the product, and the reaction activity will be difficult to control, thereby affecting the stability and application of downstream product quality. Hydrolyzed chlorine refers to the hydrolyzable chlorine atoms present in the isocyanate product, which can be introduced by a variety of chlorine-containing by-products. How to better reduce the hydrolyzed chlorine in isocyanates, improve the quality of isocyanate products and the stability of downstream customer applications, is an important problem that needs to be solved urgently. At present, many patents in related fields have reported control methods for reducing chlorinated impurities in isocyanate products.

[0003] Patent CN 112225678 B controls the total content of methyl / acetic acid and ester in formaldehyde to 8-400ppm, and the diphenylmethane series diamines and polyamines (DAM) prepared in this way can make the hydrolyzed chlorine content in the corresponding isocyanate controllable and the activity stable during the phosgenation process of preparing isocyanate. Patent CN 112225678B reduces the free chlorine in isocyanate by controlling the formaldehyde impurity content in the raw materials used to prepare DMA, but it cannot solve the problem of impurities generated in the DAM reaction process and the generation of chlorinated impurities with downstream chlorine-containing substances.

[0004] Patent CN 116063204 B treats the liquid phosgene solution through a distillation process, which significantly reduces the content of halogen-containing impurities in the liquid phosgene solution; at the same time, a nitrogen stripping tower with a catalytic decomposition function of chlorinated impurities is used to further reduce the halogenated impurities in the crude isocyanate product. However, it is still unable to effectively separate chlorinated impurities with a boiling point close to that of isocyanate.

[0005] Patent CN 114315648 B utilizes an azidating agent to carry out a substitution reaction with chlorine-containing impurities (especially acyl chloride impurities) that introduce hydrolyzed chlorine, converting chlorine atoms into easily separable chlorides, which are separated from isocyanates by filtration or distillation, thereby achieving the purpose of reducing the hydrolyzed chlorine content in isocyanates. At the same time, the difficult-to-remove acyl chloride substances react with the azidating agent to convert into corresponding acyl azide compounds, which decompose and rearrange the molecular structure after being heated, and are finally converted into isocyanate groups. Patent CN 114315648 B inevitably introduces new impurities by introducing an azidating agent, reducing the NCO content, reducing the purity of the product, and other effects.

[0006] The existing methods mainly focus on controlling impurities in formaldehyde raw materials or converting, removing and separating chlorinated impurities in photochemical reaction liquid or isocyanate products. These methods all have certain limitations. Summary of the invention

[0007] The present invention provides a method for reducing the hydrolyzed chlorine content in isocyanate which is different from the prior art and a method for preparing isocyanate with low hydrolyzed chlorine content.

[0008] The present inventors unexpectedly found through extensive research that N-(aminobenzyl)aniline impurities contained in DAM (diamines and polyamines of the diphenylmethane series) have an important influence on the hydrolyzed chlorine content in the prepared isocyanate. When DAM with a mass content of N-(aminobenzyl)aniline impurities within a certain range is used to prepare isocyanates, the content of chlorinated impurities in the isocyanates can be significantly reduced. Specifically, the hydrolyzed chlorine content of the isocyanate product can be effectively reduced, thereby improving the application stability of the downstream isocyanate product.

[0009] To achieve the purpose, the present invention provides the following technical solutions:

[0010] The present invention provides a method for reducing the hydrolyzed chlorine content in isocyanate. The isocyanate is prepared by using diphenylmethane series diamines and polyamines through phosgenation reaction. The diphenylmethane series diamines and polyamines having a mass content of N-(aminobenzyl)aniline impurities of 0.1-1000ppm are used for the phosgenation reaction to reduce the hydrolyzed chlorine content in the prepared isocyanate.

[0011] Preferably, the mass content of the N-(aminobenzyl)aniline impurities is 1-1000 ppm, more preferably 5-500 ppm.

[0012] Furthermore, the N-(aminobenzyl)aniline impurities are one or more aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3):

[0013]

[0014] Furthermore, the N-(aminobenzyl)aniline impurities are substances having the following structural formula (II) and one or more of its isomers, wherein the isomers are aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3):

[0015]

[0016] Wherein, in the structural formula (II), n is a natural number ≥2; preferably, the number of benzene rings of the N-(aminobenzyl)aniline impurity is 2-3.

[0017] The present invention also provides a method for preparing isocyanate with low hydrolyzed chlorine content, wherein the isocyanate is prepared by phosgenation reaction using diphenylmethane series diamines and polyamines, and the phosgenation reaction is carried out using the diphenylmethane series diamines and polyamines having a mass content of N-(aminobenzyl)aniline impurities of 0.1-1000ppm; preferably, the mass content of the N-(aminobenzyl)aniline impurities in the diphenylmethane series diamines and polyamines is 1-1000ppm, more preferably 5-500ppm.

[0018] Furthermore, the N-(aminobenzyl)aniline impurity is an aniline compound having a structural unit represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3):

[0019]

[0020] Furthermore, the N-(aminobenzyl)aniline impurities are substances having the following structural formula (II) and one or more of its isomers, wherein the isomers are aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3):

[0021]

[0022] Wherein, in the structural formula (II), n is a natural number ≥ 2;

[0023] Preferably, the number of benzene rings of the N-(aminobenzyl)aniline impurity is 2-3.

[0024] In some embodiments, the diphenylmethane series of diamines and polyamines react with one or more of phosgene, diphosgene, and triphosgene.

[0025] In some embodiments, the phosgenation reaction is any one of a gas phase phosgenation reaction, a liquid phase phosgenation reaction, and a salt-forming phosgenation reaction.

[0026] In some embodiments, the mass content of hydrolyzed chlorine in the isocyanate is 1-15 ppm, and the isocyanate is, for example, MDI-100.

[0027] The technical solution provided by the present invention has the following beneficial effects:

[0028] The present inventors have found that by using diphenylmethane series diamines and polyamines having a mass content of N-(aminobenzyl)aniline impurities of 0.1-1000 ppm to carry out phosgenation reaction to prepare isocyanates, the hydrolyzed chlorine content in the prepared isocyanates can be reduced, thereby being able to prepare isocyanate products with low hydrolyzed chlorine content. DETAILED DESCRIPTION

[0029] 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.

[0030] 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 invention belongs. The term "and / or" as may be used herein includes any and all combinations of one or more of the associated listed items.

[0031] The invention provides a method for reducing the hydrolyzed chlorine content in isocyanate. The isocyanate is prepared by using diphenylmethane series diamines and polyamines (DAM) through a phosgenation reaction. The diphenylmethane series diamines and polyamines having a mass content of N-(aminobenzyl)aniline impurities of 0.1-1000 ppm are used for the phosgenation reaction, so that the hydrolyzed chlorine content in the prepared isocyanate can be reduced, thereby preparing an isocyanate product with a low hydrolyzed chlorine content.

[0032] In the present invention, the mass content of the N-(aminobenzyl)aniline impurities in the diphenylmethane series of diamines and polyamines is, for example, 0.1, 0.5, 1, 5, 10, 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000 ppm, etc. Preferably, the mass content of the N-(aminobenzyl)aniline impurities is 1-1000 ppm, more preferably 5-500 ppm.

[0033] In the present invention, the N-(aminobenzyl)aniline impurities refer to one or more aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3). Specifically, the N-(aminobenzyl)aniline impurities are substances having the following structural formula (II) and one or more isomers thereof, wherein the isomers are aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3):

[0034]

[0035] Its isomers such as

[0036] wait.

[0037] Wherein, n is a natural number ≥2.

[0038] Preferably, the number of benzene rings of the N-(aminobenzyl)aniline impurities is 2-3, that is, n is 2-3; the structural unit represented by the structural formula (I-1), the structural formula (I-2) or the structural formula (I-3) may be an end group. Such impurities are, for example, N-(2-aminobenzyl)aniline and / or N-(4-aminobenzyl)aniline.

[0039] The present invention also provides a method for preparing isocyanate with low hydrolyzed chlorine content, wherein the isocyanate is prepared by phosgenation reaction using diphenylmethane series diamines and polyamines, specifically, the phosgenation reaction is carried out using diphenylmethane series diamines and polyamines having a mass content of N-(aminobenzyl)aniline impurities of 0.1-1000ppm; preferably, the mass content of the N-(aminobenzyl)aniline impurities in the diphenylmethane series diamines and polyamines is 1-1000ppm, more preferably 5-500ppm, based on the total mass of DAM.

[0040] As described above, in the present invention, the N-(aminobenzyl)aniline impurities refer to aniline compounds with structural units shown in the structural formula (I-1), structural formula (I-2) and / or structural formula (I-3). Specifically, the N-(aminobenzyl)aniline impurities are substances having the structural formula (II) and one or more of its isomers, and the isomers are aniline compounds with structural units shown in the structural formula (I-1), structural formula (I-2) and / or structural formula (I-3). For the description of N-(aminobenzyl)aniline impurities, structural formula (I-1), structural formula (I-2), structural formula (I-3), structural formula (II) and isomers of structural formula (II), please refer to the above description and will not be repeated here.

[0041] In some examples, the mass content of hydrolyzed chlorine in the isocyanate is 1-15 ppm (based on the total mass of the isocyanate), wherein the isocyanate is, for example but not limited to, 4,4-diphenylmethane diisocyanate (MDI-100) and the like.

[0042] In each step of the present invention, the solvent, monomer and other light components in each step can be removed and separated by means of techniques known in the art. In some specific embodiments, purification can be carried out by means of rectification, distillation, crystallization and the like.

[0043] In the preparation process of isocyanate, it is inevitable that a small amount of hydrolyzed chlorine will exist in the isocyanate product, especially the requirements for the hydrolyzed chlorine in isocyanate MDI-100 are more stringent. On the one hand, it will affect the color number of the isocyanate product, and on the other hand, it will cause the reaction activity in the preparation process of downstream application products to be unable to be stably controlled, resulting in unqualified products. Therefore, it is very important to reduce the content of isocyanate hydrolyzed chlorine and then control the stable and qualified performance of downstream products.

[0044] In the process of preparing DAM, various impurities are generated. The inventors have unexpectedly found through extensive research that the content of N-(aminobenzyl)aniline impurities in DAM is controlled at 0.1-1000ppm, which is conducive to obtaining isocyanates with low hydrolyzed chlorine content, while if the N-(aminobenzyl)aniline impurities in DAM exceed the above level, it will lead to a significant increase in the hydrolyzed chlorine content in the isocyanate. An exemplary reaction equation for the reaction of the above-mentioned N-(aminobenzyl)aniline impurities with phosgene to generate an isocyanate mixture containing chlorinated impurities is as follows:

[0045]

[0046] Wherein, n is a natural number ≥ 2, and in particular, when n is 2 to 3, the boiling point of N-(aminobenzyl)aniline impurities is close to that of isocyanates, in particular, close to that of diisocyanates such as 4,4-diphenylmethane diisocyanate (MDI-100), and it is impossible to effectively separate it from MDI-100. The inventors have found that when the content of N-(aminobenzyl)aniline impurities in DAM is controlled at 0.1-1000ppm, the hydrolyzed chlorine content in the prepared isocyanate can be effectively reduced. If this level is exceeded, the hydrolyzed chlorine in the isocyanate MDI-100 product will be greatly increased.

[0047] Preferably, by controlling the content of N-(aminobenzyl)aniline impurities in DAM, especially N-(aminobenzyl)aniline impurities having two benzene rings and / or three benzene rings, at 0.1-1000ppm, preferably at 1-1000ppm, more preferably at 5-500ppm, the content of isocyanate, especially the content of hydrolyzed chlorine in MDI100, can be significantly reduced.

[0048] In the art, the preparation method of DAM is well known and described in many open patents and publications, such as US-A 2009 / 0240077, EP-A-451442 and WO-A-99 / 40059. DAM is prepared by a continuous, semi-continuous or discontinuous reaction process, usually by reacting aniline with hydrochloric acid to generate aniline hydrochloride, and then adding formaldehyde in a reactor to generate DAM hydrochloride, and then obtaining crude DAM through neutralization, water washing and separation of organic phase and inorganic phase, and obtaining DAM through a refining process, and the DAM is then subjected to a phosgenation reaction to generate a mixture of diisocyanates and polyisocyanates. For example, in a preferred embodiment, the DAM preparation method specifically includes the following steps S1)-S2); thereafter, preparing isocyanate through step S3):

[0049] S1) contacting and reacting formaldehyde and aniline in the presence of an acidic catalyst to obtain a mixture of diamines and polyamines (DAM) containing the diphenylmethane series;

[0050] S2) adding a base to the mixture for neutralization, and obtaining an organic phase containing diamines and polyamines (DAM) of the diphenylmethane series after phase separation; washing the organic phase with water and distilling to obtain a refined diphenylmethane series diamine and polyamine product, i.e., a DAM product;

[0051] S3) subjecting the diphenylmethane series diamines and polyamines obtained in step S2) to phosgenation reaction to obtain crude isocyanate, which is then separated and refined, such as by vacuum distillation, to obtain an isocyanate product.

[0052] In some examples, the "contact reaction of formaldehyde and aniline in the presence of an acidic catalyst" in step S1) specifically includes the following steps: first subjecting aniline and the acidic catalyst to a salt-forming reaction, the reaction temperature is, for example, 5-95°C, and the reaction time is, for example, 1-30 min; after the reaction, adding an aqueous solution of formaldehyde (with a concentration of, for example, 15-55 wt%) for a condensation reaction, the reaction temperature is, for example, 15-95°C, and the reaction time is, for example, 5-150 min; then raising the temperature for a rearrangement reaction, the reaction temperature is, for example, 30-150°C, and the reaction time is, for example, 15-300 min.

[0053] In step S1), the molar ratio of the formaldehyde to the aniline is, for example, 0.10 to 0.80, preferably 0.20 to 0.60. In step S1), the molar ratio of the acidic catalyst to the aniline is, for example, 0.01 to 0.80, preferably 0.05 to 0.50. In step S2), when a base is added for neutralization, the base excess rate is, for example, 1.01 to 1.50, preferably 1.01-1.30. The base excess rate refers to the base (in terms of "OH - ”) and acid catalyst (in terms of “H+ ") molar ratio.

[0054] In the process of preparing DAM, the content level of the N-(aminobenzyl)aniline impurities in the obtained DAM can be adjusted by adjusting reaction parameters such as the amount of the acidic catalyst used in step S1), the reaction temperature and / or the reaction time, so as to obtain a DAM product with a content level of N-(aminobenzyl)aniline impurities that meets the requirements. Specifically, DAM with an N-(aminobenzyl)aniline impurity content of 0.1-1000ppm is obtained by adjusting the above reaction parameters, and the DAM that meets this requirement is selected for use in the phosgenation reaction to prepare isocyanates with a low hydrolyzed chlorine content.

[0055] In the phosgenation reaction, the diamines and polyamines of the diphenylmethane series can react with one or more of the phosgene raw materials such as phosgene, diphosgene, and triphosgene. The phosgenation reaction can be any one of a gas phase phosgenation reaction, a liquid phase phosgenation, and a salt-forming phosgenation reaction. The phosgenation reaction can refer to the prior art such as but not limited to patents CN101811019A and CN101104595B. For example, in some examples, referring to patent CN101104595B, the mass ratio of phosgene to DAM is 3 to 6, and chlorobenzene is selected as a diluent for phosgene and DAM. The concentration of phosgene after dilution is 50 to 80wt%, the concentration of DAM after dilution is 15 to 35wt%, the reaction temperature is 65 to 95°C, and the reaction pressure is 2.5 to 4kg / cm 2 (gauge pressure), the reaction time is 2 to 4 minutes; the reaction liquid enters the downstream three-stage kettle to continue the reaction, the reaction temperatures are 85 to 95°C, 100 to 110°C, 115 to 125°C, and the reaction time is controlled at 15 to 30 minutes. After the reaction, the crude isocyanate mixture is distilled and separated in a packed tower to obtain isocyanate, for example, isocyanate MDI-100.

[0056] The present invention selects DAM with an N-(aminobenzyl)aniline impurity content of 0.1-1000 ppm as a raw material for phosgenation reaction to prepare an isocyanate product, which can effectively reduce the chlorinated impurity content of the isocyanate product, thereby reducing the hydrolyzed chlorine content of the isocyanate, especially the MDI-100 product, improving the quality of the isocyanate, especially the MDI-100 product, thereby controlling the performance of downstream products to be stable and qualified.

[0057] Herein, the mass content of "hydrolyzed chlorine" in isocyanate refers to the hydrolyzed chlorine content based on the total mass of isocyanate.

[0058] The present invention is further described below by way of examples, but it should not be understood that the present invention is limited thereto.

[0059] 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.

[0060] Some of the raw materials used in the examples and comparative examples are described as follows:

[0061] Phosgene is produced by Wanhua Chemical (Fujian) Co., Ltd. Industrial Park;

[0062] The hydrolyzed chlorine content in the isocyanate MDI-100 in the examples and comparative examples was titrated with silver nitrate using a Metron potentiometric titrator.

[0063] The N-(aminobenzyl)aniline impurity content in DAM was analyzed by Agilent 8890GC System gas chromatograph using the following parameters: injection port temperature 280°C, column box temperature 230-250°C maintained for more than 30 min, detector temperature 290°C, chromatographic column Agilent HP-5 chromatographic column (30m×0.53mm×1.5um), carrier gas flow rate 1-2ml / min, injection volume 0.2-0.5uL, split ratio 5:1, where the split ratio is the ratio of the split flow to the column flow.

[0064] Embodiment 1:

[0065] The preparation steps of isocyanate are as follows:

[0066] S1): Add appropriate amount of 94wt% aniline aqueous solution and 33wt% hydrochloric acid to the reactor, and react at 60°C for 10min, wherein the hydrochloric acid used has H + With the aniline -NH 2 The molar ratio of the aniline is 0.40; after the reaction, add an appropriate amount of 37wt% formaldehyde aqueous solution, react at 60°C for 30min, and increase the reaction temperature to 100°C for 240min, wherein the formaldehyde used reacts with the -NH 2 The molar ratio is 0.50; after the reaction is completed, a mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) is obtained;

[0067] S2): Neutralization, phase separation and purification. The specific steps are as follows:

[0068] Add 32 wt % sodium hydroxide aqueous solution to the mixture obtained in step S1) for neutralization (excess alkali ratio is 1.10), separate phases to obtain an organic phase after separation, and wash the organic phase with hot water at 85° C. to obtain a washed organic phase, and distill the organic phase under a pressure of 10 kPaA to remove aniline and water to obtain diaminodiphenylmethane series diamine and polyamine products, i.e., DAM products; wherein the total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and three benzene rings in DAM is 68 ppm;

[0069] S3): the DAM obtained in step S2) is diluted with chlorobenzene to 25wt% and then reacted with 65wt% phosgene (the solvent is chlorobenzene) in a reactor for phosgenation, wherein the mass ratio of DAM to phosgene is 1:4, the reaction temperature is 75°C, and the reaction pressure is 3.5kg / cm 2 (gauge pressure), the reaction time is 4min; after the reaction, the phosgene-containing mixed liquid enters the downstream three-stage kettle in series to continue the reaction, the reaction temperatures are 95°C, 110°C, and 125°C, respectively, and the reaction time is controlled at 30min. After the reaction, the crude isocyanate mixture is distilled in a packed tower, and phosgene, hydrogen chloride and chlorobenzene solvent are separated to obtain isocyanate MDI-100. The analysis results of the hydrolyzed chlorine content in the obtained isocyanate are shown in Table 1.

[0070] Embodiment 2:

[0071] The process is carried out with reference to Example 1, except that step S1) is different, and the other steps are the same as those in Example 1, and the similarities are not repeated here, and the differences are described below:

[0072] S1): Add appropriate amount of 94wt% aniline aqueous solution and 33wt% hydrochloric acid to the reactor, and react at 60°C for 10min, wherein the hydrochloric acid used has H + With the aniline -NH 2 The molar ratio of the aniline to the formaldehyde is 0.40; after the reaction is completed, an appropriate amount of 37wt% formaldehyde aqueous solution is added, the reaction is carried out at 60°C for 30min, and the reaction temperature is increased to 100°C for 120min, wherein the formaldehyde used reacts with the -NH 2 The molar ratio is 0.50; after the reaction is completed, a mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) is obtained;

[0073] The mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) obtained in step S1) is neutralized, phase-separated and purified with reference to step S2) of Example 1, and the total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and three benzene rings in the obtained DAM product is 109 ppm;

[0074] The analysis results of the hydrolyzed chlorine content in the isocyanate MDI-100 prepared in step S3) of this embodiment are shown in Table 1.

[0075] Embodiment 3:

[0076] The process is carried out with reference to Example 1, except that step S1) is different, and the other steps are the same as those in Example 1, and the similarities are not repeated here, and the differences are described below:

[0077] S1): Add appropriate amount of 94wt% aniline aqueous solution and 33wt% hydrochloric acid to the reactor, and react at 60°C for 10min, wherein the hydrochloric acid used has H + With the aniline -NH 2 The molar ratio of the aniline to the formaldehyde is 0.15; after the reaction is completed, an appropriate amount of 37wt% formaldehyde aqueous solution is added, the reaction is carried out at 60°C for 30min, and the reaction temperature is increased to 100°C for 120min, wherein the formaldehyde used reacts with the -NH 2 The molar ratio is 0.50; after the reaction is completed, a mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) is obtained;

[0078] The mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) obtained in step S1) is neutralized, phase-separated and purified with reference to step S2) of Example 1, and the total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and three benzene rings in the obtained DAM product is 317 ppm;

[0079] The analysis results of the hydrolyzed chlorine content in the isocyanate MDI-100 prepared in step S3) of this embodiment are shown in Table 1.

[0080] Embodiment 4:

[0081] The process is carried out with reference to Example 1, except that step S1) is different, and the other steps are the same as those in Example 1, and the similarities are not repeated here, and the differences are described below:

[0082] S1): Add appropriate amount of 94wt% aniline aqueous solution and 33wt% hydrochloric acid to the reactor, and react at 60°C for 10min, wherein the hydrochloric acid used has H + With the aniline -NH 2 The molar ratio of the aniline to the formaldehyde is 0.05; after the reaction is completed, an appropriate amount of 37wt% formaldehyde aqueous solution is added, the reaction is carried out at 60°C for 30min, and the reaction temperature is increased to 100°C for 120min, wherein the formaldehyde used reacts with the -NH 2 The molar ratio is 0.50; after the reaction is completed, a mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) is obtained;

[0083] The mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) obtained in step S1) is neutralized, phase-separated and purified with reference to step S2) of Example 1, and the total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and three benzene rings in the obtained DAM product is 493ppm;

[0084] The analysis results of the hydrolyzed chlorine content in the isocyanate MDI-100 prepared in step S3) of this embodiment are shown in Table 1.

[0085] Comparative Example 1:

[0086] The process is carried out with reference to Example 1, except that step S1) is different, and the other steps are the same as those in Example 1, and the similarities are not repeated here, and the differences are described below:

[0087] S1) Add appropriate amount of 94wt% aniline aqueous solution and 33wt% hydrochloric acid to the reactor, and react at 60°C for 10min, wherein the hydrochloric acid used has H + With the aniline -NH 2 The molar ratio of 0.15 is 0.15; after the reaction is completed, add an appropriate amount of 37wt% formaldehyde aqueous solution, react at 60°C for 30min, and increase the reaction temperature to 80°C for 60min, wherein the formaldehyde used is 2 The molar ratio is 0.50; after the reaction is completed, a mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) is obtained;

[0088] The mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) obtained in step S1) is neutralized, separated and purified with reference to step S2) of Example 1. The total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and three benzene rings in the obtained DAM product is 2075ppm.

[0089] The analysis results of the hydrolyzed chlorine content in the isocyanate MDI-100 prepared in step S3) of this embodiment are shown in Table 1.

[0090] Comparative Example 2:

[0091] The process is carried out with reference to Example 1, except that step S1) is different, and the other steps are the same as those in Example 1, and the similarities are not repeated here, and the differences are described below:

[0092] S1): Add appropriate amount of 94wt% aniline aqueous solution and 33wt% hydrochloric acid to the reactor, and react at 60°C for 10min, wherein the hydrochloric acid used has H + With the aniline -NH 2The molar ratio of the aniline is 0.40; after the reaction, add an appropriate amount of 37wt% formaldehyde aqueous solution, react at 60°C for 30min, and raise the reaction temperature to 65°C for 60min, wherein the formaldehyde used is reacted with the -NH 2 The molar ratio is 0.50; after the reaction is completed, a mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) is obtained;

[0093] The mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) obtained in step S1) is neutralized, separated and purified with reference to step S2) of Example 1. In the obtained DAM product, the total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and three benzene rings is 1893ppm.

[0094] The analysis results of the hydrolyzed chlorine content in the isocyanate MDI-100 prepared in step S3) of this embodiment are shown in Table 1.

[0095] Comparative Example 3

[0096] The process is carried out with reference to Example 1, except that step S1) is different, and the other steps are the same as those in Example 1, and the similarities are not repeated here, and the differences are described below:

[0097] S1): Add appropriate amount of 94wt% aniline aqueous solution and 33wt% hydrochloric acid to the reactor, and react at 60°C for 10min, wherein the hydrochloric acid used has H + With the aniline -NH 2 The molar ratio of the aniline is 0.45; after the reaction is completed, add an appropriate amount of 37wt% formaldehyde aqueous solution, react at 60°C for 30min, and increase the reaction temperature to 65°C for 60min, wherein the formaldehyde used is 2 The molar ratio is 0.50; after the reaction is completed, a mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) is obtained;

[0098] The mixture containing diaminodiphenylmethane series diamines and polyamines (DAM) obtained in step S1) is neutralized, separated and purified with reference to step S2) of Example 1. In the obtained DAM product, the total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and three benzene rings is 1136ppm.

[0099] The analysis results of the hydrolyzed chlorine content in the isocyanate MDI-100 prepared in step S3) of this embodiment are shown in Table 1.

[0100] Table 1 Experimental results of embodiments and comparative examples

[0101]

[0102] In Table 1, N-(aminobenzyl)aniline impurities refer to the total mass content of N-(aminobenzyl)aniline impurities with two benzene rings and N-(aminobenzyl)aniline impurities with three benzene rings.

[0103] By comparing the above embodiments and comparative examples, it can be seen that when preparing isocyanate by phosgenation reaction, using DAM with an N-(aminobenzyl)aniline impurity content in the range of 0.1-1000 ppm can significantly reduce the hydrolyzed chlorine content in the obtained isocyanate compared to DAM with an impurity content of such impurities higher than 1000 ppm.

[0104] 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 reducing the hydrolyzed chlorine content in isocyanate, wherein the isocyanate is prepared by phosgenation reaction using diamines and polyamines of the diphenylmethane series, characterized in that: The phosgenation reaction is carried out by using diamines and polyamines of the diphenylmethane series having a mass content of N-(aminobenzyl)aniline impurities of 0.1-1000 ppm to reduce the hydrolyzed chlorine content in the prepared isocyanate; Preferably, the mass content of the N-(aminobenzyl)aniline impurities is 1-1000 ppm, more preferably 5-500 ppm.

2. The method according to claim 1, characterized in that The N-(aminobenzyl)aniline impurities are one or more aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3):

3. The method according to claim 1 or 2, characterized in that: The N-(aminobenzyl)aniline impurities are substances having the following structural formula (II) and one or more of its isomers, wherein the isomers are aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3): Wherein, in the structural formula (II), n is a natural number ≥2; preferably, the number of benzene rings of the N-(aminobenzyl)aniline impurity is 2-3.

4. A method for preparing isocyanate with low hydrolyzed chlorine content, using diphenylmethane series diamines and polyamines to prepare the isocyanate through phosgenation reaction, characterized in that: The phosgenation reaction is carried out using diphenylmethane series diamines and polyamines having a mass content of N-(aminobenzyl)aniline impurities of 0.1-1000 ppm; preferably, the mass content of N-(aminobenzyl)aniline impurities in the diphenylmethane series diamines and polyamines is 1-1000 ppm, more preferably 5-500 ppm.

5. The preparation method according to claim 4, wherein the N-(aminobenzyl)aniline impurities are one or more aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3):

6. The preparation method according to claim 4 or 5, characterized in that: The N-(aminobenzyl)aniline impurities are substances having the following structural formula (II) and one or more of its isomers, wherein the isomers are aniline compounds having structural units represented by the following structural formula (I-1), structural formula (I-2) and / or structural formula (I-3): Wherein, in the structural formula (II), n is a natural number ≥ 2; Preferably, the number of benzene rings of the N-(aminobenzyl)aniline impurity is 2-3.

7. The preparation method according to any one of claims 4 to 6, characterized in that: In the phosgenation reaction, the diphenylmethane series of diamines and polyamines react with one or more of phosgene, diphosgene, and triphosgene.

8. The preparation method according to any one of claims 4 to 7, characterized in that: The phosgenation reaction is any one of a gas phase phosgenation reaction, a liquid phase phosgenation reaction, and a salt-forming phosgenation reaction.

9. The preparation method according to any one of claims 4 to 8, characterized in that: The mass content of hydrolyzed chlorine in the isocyanate is 1-15 ppm.

10. The preparation method according to any one of claims 4 to 9, characterized in that: The isocyanate is MDI-100.

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