A jet circulation reactor and a method for synthesizing isocyanate using the same

Abstract

The present invention provides a jet circulation reactor and a method for synthesizing isocyanate using the reactor. Through the jet circulation reactor, an organic amine is efficiently mixed and reacted with a solvent mixture, hydrogen chloride or phosgene in an ejector, and then ejected through an ejector nozzle. Through continuous jet circulation reaction, the organic amine compound is completely reacted into an isocyanate product. The method provided by the present invention can make the corresponding amine and hydrogen chloride or phosgene quickly mix and react, improve the actual utilization rate of hydrogen chloride or phosgene, reduce the excess ratio of phosgene, shorten the reaction time, effectively reduce the occurrence of side reactions, and further improve the yield of organic amine hydrochloride or isocyanate.

Description

Technical Field

[0001] The invention belongs to the field of organic chemical industry, and in particular relates to a jet circulation reactor for continuous operation and a method for preparing isocyanate by using the same. Background Art

[0002] As an important class of organic chemical intermediates, isocyanates have very wide applications in industry, agriculture, medicine and health. This class of compounds is widely used in the synthesis of polyisocyanates, polyurethanes, polyureas, polymer adhesives, pesticides, herbicides, etc. The existing mainstream technology is to prepare isocyanates by reacting organic amines with phosgene in an inert solvent. The phosgene method is divided into a direct method and a salt-forming method. The direct method is to directly prepare isocyanates by reacting amines with phosgene; the salt-forming method first reacts the corresponding amines with acidic gases such as hydrogen chloride and carbon dioxide to prepare amine salts, and then reacts the amine salts with phosgene to form isocyanates. This type of reaction is a gas-liquid two-phase reaction, and phosgene needs to be excessive in the reaction. In order to reduce the excess ratio of phosgene, strong stirring must be used to enhance mass transfer and heat transfer, so that phosgene and heat are well dispersed in the liquid phase, accelerate the reaction rate, reduce the generation of by-products, and improve the reaction yield.

[0003] Patent CN206404772U reports a reactor for synthesizing isocyanate, which is provided with a mixing tank at the upper part of the inner cavity. After the raw materials react in the mixing tank first, the reaction liquid overflows to the lower part of the cavity to continue the reaction; the reactor is provided with agitators in the mixing tank and in the lower part of the cavity to enhance mixing and improve synthesis efficiency. Compared with the traditional reactor, the patent improves the mixing efficiency of phosgene and amine through secondary stirring, but the reaction between phosgene and organic amine is still an interfacial reaction, and the reaction does not reach sufficient mixing between molecules, which ultimately leads to a large excess of phosgene, a large number of by-products, and a low utilization rate of phosgene.

[0004] Patent CN103357363A reports a method for synthesizing isocyanate in a reactor with phosgene refluxed from the bottom. The reactor has a phosgene condensation reflux liquid pipeline entering from the bottom of the reactor, and a check valve is added at the inlet. All condensed liquid phosgene refluxes from the bottom of the reactor through the check valve into the reaction liquid system. The patent effectively improves the utilization rate of phosgene by condensing and recycling excess phosgene gas. However, an agitator is used to enhance the mixing of organic amine and phosgene. This method also reflects the interfacial reaction of the reaction between phosgene and organic amine, and does not achieve sufficient mixing between molecules before reaction, resulting in the generation of more by-products and reducing the yield of isocyanate.

[0005] From the above examples, it can be seen that the equipment used in the phosgenation method for synthesizing isocyanates mainly uses multi-stage stirring to enhance mass transfer and heat transfer; on the other hand, the utilization rate of phosgene is improved by reflux of phosgene into the reactor. However, no matter which method is used, the reaction between phosgene and organic amine is an interfacial reaction, and does not achieve an intermolecular mixing reaction, and does not make phosgene and heat very evenly dispersed in the liquid phase, which ultimately leads to an increase in side reaction products or insufficient phosgene utilization. Therefore, it is necessary to find an equipment and method that can achieve an intermolecular mixing reaction between phosgene and organic amine, continuously operate the process, and reduce the excess ratio of phosgene and the occurrence of side reactions. Summary of the invention

[0006] The object of the present invention is to provide a jet circulation reactor, wherein an organic amine and a solvent mixture enter a reaction kettle through a pipeline, and then is input into an ejector through a circulation pump, and hydrogen chloride or phosgene also enters the ejector, and the organic amine and phosgene or hydrogen chloride are rapidly mixed and reacted in the ejector and then ejected, and the reaction is continued through a continuous jet circulation reaction until the reaction is complete, thereby improving the actual utilization rate of hydrogen chloride or phosgene, reducing the excess ratio of phosgene, shortening the reaction time, effectively reducing the occurrence of side reactions, and further improving the yield of organic amine hydrochloride or isocyanate.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present invention is: a jet circulation reactor, which consists of an ejector 1, a reactor 5 and a circulation pump 6, the ejector 1 is connected to the reactor 5 and the circulation pump 6 through a pipeline, the ejector 1 is inserted into the reactor 5 through the top opening of the reactor 5, the bottom pipeline of the reactor 5 is connected to the circulation pump 6, and the outlet pipeline of the circulation pump 6 is connected to the inlet pipeline of the ejector 1; the ejector 1 is composed of an ejector nozzle 8, a jet zone 9, a gas-liquid mixing impact zone 10, a gas-liquid diffusion zone 11, and a suction pipe 12, and the components of the ejector 1 are coaxially connected; the reactor 5 is composed of a reactor jacket 3 and a guide tube 4, the guide tube 4 is located inside the reactor 5, and the guide tube 4 is evenly spaced on the horizontal cross section inside the reactor 5 through a fixed bracket; the raw material introduction pipe 2 is inserted into the reactor 5 through the top opening of the reactor 5, and the gas discharge pipe 7 is connected to the top of the reactor 5. The organic amine and solvent mixture enters the reactor through the reaction raw material inlet N4, and then enters the ejector 1 through the outlet pipeline of the circulation pump 6 and the active flow inlet N1. The hydrogen chloride or phosgene enters the ejector 1 through the passive flow inlet N2, and is quickly mixed and reacted in the ejector 1. Then, it is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the reaction is completed, and the completely reacted isocyanate product is discharged through the reaction product outlet N5; the hydrogen chloride or phosgene that has not participated in the reaction is discharged through the unreacted gas outlet N6.

[0008] Among them, the inner diameter of the ejector nozzle of the jet circulation reactor is 5-30mm; the inlet diameter of the jet zone pipeline is 25-30 times the inner diameter of the nozzle, the outlet diameter is 15-20 times the inner diameter of the nozzle, and the length of the jet zone pipeline is 2-3 times the inlet diameter; the diameter of the gas-liquid mixing impact zone pipeline is equal to the outlet diameter of the jet zone pipeline, and the length is 2-3 times the diameter; the inlet diameter of the gas-liquid diffusion zone pipeline is equal to the diameter of the gas-liquid mixing impact zone pipeline, the outlet diameter is 1.5-2 times the inlet diameter, and the length is 2-3 times the diameter; the diameter of the suction pipe is equal to the outlet diameter of the gas-liquid diffusion zone pipeline, and the length is 2-3 times the diameter.

[0009] 4-8 guide tubes are arranged at equal intervals on the horizontal section inside the reactor; the inner diameter of the guide tube is 15-30mm; its length is 0.3-0.4 times the total height of the reactor; each guide tube has 15-30 small holes radially opened in layers; the diameter of the small holes is 3-5mm.

[0010] The inner diameter of the raw material inlet pipe is 15-30mm; the inner diameter of the gas exhaust pipe is 20-50mm.

[0011] Another object of the present invention is to provide a method for preparing isocyanate of the general formula R(NCO)n by using the above-mentioned jet circulation reactor to synthesize isocyanate, using amine of the general formula R(NH2)n as a raw material, effectively reducing the excess ratio of phosgene, reducing the occurrence of side reactions, and further improving the yield of isocyanate. The specific technical scheme is as follows:

[0012] (1) The corresponding isocyanate is synthesized by phosgenation of organic amine salts, and the steps are as follows:

[0013] a. An amine of the general formula R(NH2)n and an inert solvent for dilution are introduced into the reaction kettle 5 through the raw material introduction pipe 2;

[0014] The organic amine and solvent mixture enters the reactor through the reaction raw material inlet N4, and then enters the ejector 1 through the outlet pipeline of the circulation pump 6 and the active flow inlet N1. The hydrogen chloride or phosgene enters the ejector 1 through the passive flow inlet N2, and is quickly mixed and reacted in the ejector 1. Then, it is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the reaction is completed, and the completely reacted isocyanate product is discharged through the reaction product outlet N5; the hydrogen chloride or phosgene that has not participated in the reaction is discharged through the unreacted gas outlet N6.

[0015] b. The mixture of organic amine and solvent enters the ejector 1 through the circulation pump 6 and the active flow inlet N1; hydrogen chloride enters the ejector 1 through the passive flow inlet N2 to mix and react with the mixture passing through the active flow inlet N1, and then is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the organic amine is completely reacted into organic amine hydrochloride.

[0016] c. The organic amine hydrochloride and the solvent mixture enter the ejector 1 through the circulation pump 6 and the active flow inlet N1; the phosgene enters the ejector 1 through the passive flow inlet N2 and mixes with the mixture passing through the active flow inlet N1 to react, and then is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the organic amine hydrochloride is completely reacted into the corresponding isocyanate product.

[0017] (2) Direct phosgenation of organic amines to synthesize the corresponding isocyanates, the steps are as follows:

[0018] The organic amine and solvent mixture enters the injector 1 through the circulation pump 6 and the active flow inlet N1; the phosgene enters the injector 1 through the passive flow inlet N2 and mixes with the mixture passing through the active flow inlet N1 to react, and then is ejected through the injector nozzle 8 and the intermediate product outlet N3. Through continuous injection cycle reaction, the organic amine is completely reacted into the corresponding isocyanate product.

[0019] The organic amine compound is preferably toluenediamine (TDA), diphenylmethanediamine (MDA), isophoronediamine (IPDA), 1,6-hexanediamine (HDA), 4,4'-dicyclohexylmethanediamine (HMDA), meta-xylylenediamine (XDA), trimethylhexanediamine (TMDA);

[0020] The corresponding isocyanates generated are toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), 4,4-dicyclohexylmethane diisocyanate (HMDI), meta-xylylene diisocyanate (XDI), and trimethyl hexamethylene diisocyanate (TMDI).

[0021] The inert solvents are chlorobenzene, dichlorobenzene, amyl acetate, and methyl salicylate.

[0022] The beneficial effects of the present invention are as follows: through the jet circulation reactor, the organic amine and the solvent mixture enter the reactor through the reaction raw material inlet at a certain flow rate, then enter the ejector through the circulation pump and the active flow inlet, and the hydrogen chloride or phosgene enters the ejector through the passive flow inlet, and is efficiently mixed and reacted in the ejector, and then ejected through the ejector nozzle, and the organic amine compound is completely reacted into an isocyanate product through continuous jet circulation reaction. The process method can make the corresponding amine and hydrogen chloride or phosgene quickly mix and react, improve the actual utilization rate of hydrogen chloride or phosgene, reduce the excess ratio of phosgene, shorten the reaction time, effectively reduce the occurrence of side reactions, and further improve the yield of organic amine hydrochloride or isocyanate. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Injector front view assembly drawing.

[0024] Figure 2 Front view assembly drawing of jet circulation reactor.

[0025] Figure 3 Enlarged cross-sectional view of the jet circulation reactor II.

[0026] Figure 4 A partial enlarged view of the guide tube.

[0027] Explanation of the codes in the figure: 1. Ejector; 2. Raw material inlet pipe; 3. Reactor jacket; 4. Guide tube; 5. Reactor; 6. Circulation pump; 7. Gas exhaust pipe; 8. Ejector nozzle; 9. Jet zone; 10. Gas-liquid mixing impact zone; 11. Gas-liquid diffusion zone; 12. Suction pipe; N1-active flow inlet; N2-passive flow inlet; N3-intermediate product outlet; N4-reaction raw material inlet; N5-reaction product outlet; N6-unreacted gas outlet DETAILED DESCRIPTION

[0028] The present invention provides a jet circulation reactor, which consists of an ejector 1, a reactor 5 and a circulation pump 6. The ejector 1 is connected with the reactor 5 and the circulation pump 6 through a pipeline. The ejector 1 is inserted into the reactor 5 through an opening at the top of the reactor 5. The pipeline at the bottom of the reactor 5 is connected with the circulation pump 6. The outlet pipeline of the circulation pump 6 is connected with the inlet pipeline of the ejector 1. The ejector 1 consists of an ejector nozzle 8, a jet zone 9, a gas-liquid mixing impact zone 10, a gas-liquid diffusion zone 11 and a suction pipe 12. The components of the ejector 1 are coaxially connected. The reactor 5 consists of a reactor jacket 3 and a guide tube 4. The guide tube 4 is located inside the reactor 5. The guide tube 4 is evenly spaced on a horizontal cross section inside the reactor 5 through a fixed bracket. A raw material introduction pipe 2 is inserted into the reactor 5 through an opening at the top of the reactor 5. A gas discharge pipe 7 is connected to the top of the reactor 5. The organic amine and solvent mixture enters the reactor through the reaction raw material inlet N4, and then enters the ejector 1 through the outlet pipeline of the circulation pump 6 and the active flow inlet N1. The hydrogen chloride or phosgene enters the ejector 1 through the passive flow inlet N2, and is quickly mixed and reacted in the ejector 1. Then, it is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the reaction is completed, and the completely reacted isocyanate product is discharged through the reaction product outlet N5; the hydrogen chloride or phosgene that has not participated in the reaction is discharged through the unreacted gas outlet N6.

[0029] Among them, the inner diameter of the ejector nozzle of the jet circulation reactor is 5-30mm; the inlet diameter of the jet zone pipeline is 25-30 times the inner diameter of the nozzle, the outlet diameter is 15-20 times the inner diameter of the nozzle, and the length of the jet zone pipeline is 2-3 times the inlet diameter; the diameter of the gas-liquid mixing impact zone pipeline is equal to the outlet diameter of the jet zone pipeline, and the length is 2-3 times the diameter; the inlet diameter of the gas-liquid diffusion zone pipeline is equal to the diameter of the gas-liquid mixing impact zone pipeline, the outlet diameter is 1.5-2 times the inlet diameter, and the length is 2-3 times the diameter; the diameter of the suction pipe is equal to the outlet diameter of the gas-liquid diffusion zone pipeline, and the length is 2-3 times the diameter.

[0030] 4-8 guide tubes are arranged at equal intervals on the horizontal section inside the reactor; the inner diameter of the guide tube is 15-30mm; its length is 0.3-0.4 times the total height of the reactor; each guide tube has 15-30 small holes radially opened in layers; the diameter of the small holes is 3-5mm.

[0031] The inner diameter of the raw material inlet pipe is 15-30mm; the inner diameter of the gas exhaust pipe is 20-50mm.

[0032] Another object of the present invention is to provide a method for preparing isocyanate of the general formula R(NCO)n by using the above-mentioned jet circulation reactor to synthesize isocyanate, using amine of the general formula R(NH2)n as a raw material, effectively reducing the excess ratio of phosgene, reducing the occurrence of side reactions, and further improving the yield of isocyanate. The specific technical scheme is as follows:

[0033] (1) The corresponding isocyanate is synthesized by phosgenation of organic amine salts, and the steps are as follows:

[0034] a. An amine of the general formula R(NH2)n and an inert solvent for dilution are introduced into the reaction kettle 5 through the raw material introduction pipe 2;

[0035] The organic amine and solvent mixture enters the reactor through the reaction raw material inlet N4, and then enters the ejector 1 through the outlet pipeline of the circulation pump 6 and the active flow inlet N1. The hydrogen chloride or phosgene enters the ejector 1 through the passive flow inlet N2, and is quickly mixed and reacted in the ejector 1. Then, it is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the reaction is completed, and the completely reacted isocyanate product is discharged through the reaction product outlet N5; the hydrogen chloride or phosgene that has not participated in the reaction is discharged through the unreacted gas outlet N6.

[0036] b. The mixture of organic amine and solvent enters the ejector 1 through the circulation pump 6 and the active flow inlet N1; hydrogen chloride enters the ejector 1 through the passive flow inlet N2 to mix and react with the mixture passing through the active flow inlet N1, and then is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the organic amine is completely reacted into organic amine hydrochloride.

[0037] c. The organic amine hydrochloride and the solvent mixture enter the ejector 1 through the circulation pump 6 and the active flow inlet N1; the phosgene enters the ejector 1 through the passive flow inlet N2 and mixes with the mixture passing through the active flow inlet N1 to react, and then is ejected through the ejector nozzle 8 and the intermediate product outlet N3. Through continuous ejection cycle reaction, the organic amine hydrochloride is completely reacted into the corresponding isocyanate product.

[0038] (2) Direct phosgenation of organic amines to synthesize the corresponding isocyanates, the steps are as follows:

[0039] The organic amine and solvent mixture enters the injector 1 through the circulation pump 6 and the active flow inlet N1; the phosgene enters the injector 1 through the passive flow inlet N2 and mixes with the mixture passing through the active flow inlet N1 to react, and then is ejected through the injector nozzle 8 and the intermediate product outlet N3. Through continuous injection cycle reaction, the organic amine is completely reacted into the corresponding isocyanate product.

[0040] The organic amine compound is one of toluene diamine (TDA), diphenylmethane diamine (MDA), isophorone diamine (IPDA), 1,6-hexanediamine (HDA), 4,4'-dicyclohexylmethane diamine (HMDA), meta-xylylenediamine (XDA), and trimethylhexanediamine (TMDA);

[0041] The corresponding isocyanates generated are toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), isophorone diisocyanate (IPDI), hexamethylene diisocyanate (HDI), 4,4-dicyclohexylmethane diisocyanate (HMDI), meta-xylylene diisocyanate (XDI), and trimethyl hexamethylene diisocyanate (TMDI).

[0042] The inert solvent is one of chlorobenzene, dichlorobenzene, amyl acetate and methyl salicylate.

[0043] The internal structure of the jet reactor in each embodiment and the process parameters in the method for preparing isocyanate are shown in the following table

[0044]

[0045]

Claims

1. A jet circulation reactor, characterized in that: The reactor is composed of an ejector (1), a reactor (5) and a circulation pump (6); the ejector (1), the reactor (5) and the circulation pump (6) are connected via pipelines; the ejector (1) is inserted into the reactor (5) through the top opening of the reactor (5); the bottom pipeline of the reactor (5) is connected to the circulation pump (6); the outlet pipeline of the circulation pump (6) is connected to the inlet pipeline of the ejector (1); the ejector (1) is composed of an ejector nozzle (8), a jet zone (9), a gas-liquid mixing impact zone (10), a gas-liquid diffusion zone (11), and a suction pipe (12); the components of the ejector (1) are coaxially connected; the reactor (5) is composed of a reactor jacket (3) and a flow guide tube (4); the flow guide tube (4) is located inside the reactor (5); the flow guide tube (4) is horizontally fixed inside the reactor (5) by a fixed bracket. The raw material introduction pipe (2) is inserted into the reactor (5) through the top opening of the reactor (5), and the gas discharge pipe (7) is connected to the top of the reactor (5); the organic amine and the solvent mixture enter the reactor through the reaction raw material inlet (N4), and then enter the ejector (1) through the outlet pipeline of the circulation pump (6) and the active flow inlet (N1); the hydrogen chloride or phosgene enters the ejector (1) through the passive flow inlet (N2), and is rapidly mixed and reacted in the ejector (1), and then ejected through the ejector nozzle (8) and the intermediate product outlet (N3); the reaction is carried out through a continuous ejection cycle until the reaction is complete, and the completely reacted isocyanate product is discharged through the reaction product outlet (N5); the hydrogen chloride or phosgene that has not participated in the reaction is discharged through the unreacted gas outlet (N6); 4-8 guide tubes (4) are arranged at equal intervals on the horizontal cross section inside the reactor (5); the inner diameter of the guide tube (4) is 15-30 mm; its length is 0.3-0.4 times the total height of the reactor (5); each guide tube (4) is radially provided with 15-30 small holes in layers; the diameter of the small holes is 3-5 mm; The inner diameter of the raw material introduction pipe (2) is 15-30 mm; the inner diameter of the gas discharge pipe (7) is 20-50 mm.

2. A jet circulation reactor according to claim 1, characterized in that The inner diameter of the ejector nozzle (8) of the jet circulation reactor is 5-30 mm; the inlet diameter of the jet zone (9) pipe is 25-30 times the inner diameter of the ejector nozzle (8), the outlet diameter is 15-20 times the inner diameter of the ejector nozzle (8), and the length of the jet zone (9) pipe is 2-3 times the inlet diameter; the diameter of the gas-liquid mixing impact zone (10) pipe is equal to the outlet diameter of the jet zone (9) pipe, and the length is 2-3 times the diameter; the inlet diameter of the gas-liquid diffusion zone (11) pipe is equal to the diameter of the gas-liquid mixing impact zone (10) pipe, the outlet diameter is 1.5-2 times the inlet diameter, and the length is 2-3 times the diameter; the diameter of the suction pipe (12) is equal to the outlet diameter of the gas-liquid diffusion zone (11) pipe, and the length is 2-3 times the diameter.

3. A method for preparing an isocyanate of the general formula R(NCO)n using a jet circulation reactor as described in any one of claims 1 to 2, characterized in that: The method comprises: (1) The corresponding isocyanate is synthesized by phosgenation of organic amine salts, and the steps are as follows: a. An amine of the general formula R(NH2)n and an inert solvent for dilution are introduced into a reaction kettle (5) through a raw material introduction pipe (2); an organic amine and a solvent mixture are introduced into the reaction kettle through a reaction raw material inlet (N4), and then introduced into an ejector (1) through an outlet pipeline of a circulation pump (6) and an active flow inlet (N1); hydrogen chloride or phosgene is introduced into the ejector (1) through a passive flow inlet (N2), and is rapidly mixed and reacted in the ejector (1), and then ejected through an ejector nozzle (8) and an intermediate product outlet (N3); a continuous ejection cycle reaction is performed until the reaction is complete, and a completely reacted isocyanate product is discharged through a reaction product outlet (N5); hydrogen chloride or phosgene that has not participated in the reaction is discharged through an unreacted gas outlet (N6); b. The organic amine and the solvent mixture enter the ejector (1) through the circulation pump (6) and the active flow inlet (N1); the hydrogen chloride enters the ejector (1) through the passive flow inlet (N2) and mixes with the mixture passing through the active flow inlet (N1) for reaction, and then is ejected through the ejector nozzle (8) and the intermediate product outlet (N3). Through continuous ejection cycle reaction, the organic amine is completely reacted into organic amine hydrochloride; c. The organic amine hydrochloride and the solvent mixture enter the ejector (1) through the circulation pump (6) and the active flow inlet (N1); the phosgene enters the ejector (1) through the passive flow inlet (N2) and mixes with the mixture passing through the active flow inlet (N1) for reaction, and then is ejected through the ejector nozzle (8) and the intermediate product outlet (N3). Through continuous ejection cycle reaction, the organic amine hydrochloride is completely reacted into the corresponding isocyanate product; (2) Direct phosgenation of organic amines to synthesize the corresponding isocyanates, the steps are as follows: The organic amine and solvent mixture enters the ejector (1) through a circulation pump (6) and an active flow inlet (N1); phosgene enters the ejector (1) through a passive flow inlet (N2) and is mixed with the mixture passing through the active flow inlet (N1) for reaction, and then ejected through an ejector nozzle (8) and an intermediate product outlet (N3). Through continuous ejection cycle reaction, the organic amine is completely reacted into a corresponding isocyanate product.

4. The method according to claim 3, characterized in that The organic amine compound is one of toluenediamine, diphenylmethanediamine, isophoronediamine, 1,6-hexanediamine, 4,4'-dicyclohexylmethanediamine, meta-xylylenediamine, and trimethylhexanediamine; The corresponding isocyanates generated are toluene diisocyanate, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 4,4-dicyclohexylmethane diisocyanate, meta-xylylene diisocyanate, and trimethyl hexamethylene diisocyanate.

5. The method according to claim 3, characterized in that The inert solvent is one of chlorobenzene, dichlorobenzene, amyl acetate and methyl salicylate.

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