Process for the preparation of glutaric diisocyanate by phosgenation

Abstract

The present application relates to a method for preparing 1,5 pentylene diisocyanate, comprising the following steps: a) subjecting 1,5 pentylene diamine or its hydrochloride to a phosgenation reaction with phosgene to obtain a crude product containing 1,5 pentylene diisocyanate and phosgene; b) subjecting the crude product obtained in step a) to a phosgene removal treatment to separate and obtain a crude 1,5 pentylene diisocyanate; c) subjecting the crude 1,5 pentylene diisocyanate obtained in step b) to a refining treatment to obtain the 1,5 pentylene diisocyanate; wherein a heat treatment is performed during the process of step a) and / or step c). The PDI product obtained by the method of the present application after the heat treatment operation contains less than 10 ppm of carbamoyl chlorine compounds of hydrogenated and / or chlorinated derivatives of pyridine.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for preparing 1,5 pentamethylene diisocyanate (PDI) by reacting 1,5 pentamethylene diamine (PDA) with phosgene. BACKGROUND

[0002] 1,5-pentamethylene diisocyanate (PDI) is an aliphatic isocyanate, which has yellowing resistance, and is used in the form of biuret, trimer in the field of yellowing-resistant polyurethane coatings, inks and artificial leather. Due to the similar structure and chemical properties to HDI, and higher content of bio-based carbon, there is a possibility of replacing HDI for downstream products in the context of carbon neutralization.

[0003] In the field of isocyanate, the chlorine content in isocyanate monomer has a great influence on the application performance of isocyanate. For example, patent CN103319372A mentions controlling alcohol compounds in amine to control the chlorine content in the product, so that the product has a lower color number; patent CN109761855A also proposes to control the content of secondary amine in amine to control the chlorine content in the product, so that the product has better application performance; patent CN112592457A even proposes to control the content of alkaline chlorine in addition to hydrolysis chlorine, in order to achieve the purpose of better performance in the downstream application process.

[0004] In the aspect of PDI product, patent EP2684867A1 points out that PDI obtained by cold or hot phosgenation of bio-based 1,5 pentamethylene diamine (PDA) or its salt will contain chlorine-containing compounds (1) and (2), which will have an adverse effect on the product itself and downstream applications of PDI

[0005]

[0006] Meanwhile, EP2684867A1 also gives a technical solution to remove such compounds: that is, the crude PDI is heated to 180-245°C in the presence of inert gas, such as nitrogen, and optional phosphorus-containing compound, such as tris (tridecyl) phosphite, before distillation to reduce the content of compounds (1) and (2). Although this method is effective, it will cause PDI to stay at 180-245°C for a long time (the time length in the example is 30-60 min), and the isocyanate monomer will produce a large amount of polymer when heated at high temperature for a long time, which will cause loss of product yield, which has an adverse effect on its economic feasibility. At the same time, the phosphorus-containing catalyst needs to be removed from PDI at a high cost, otherwise it will have an adverse effect on the downstream application, which will also have an adverse effect on its economy.

[0007] Patent EP2014185564 proposes that PDI prepared by bio-based 1,5 pentanediamine (PDA) also contains chlorine-containing compounds 5-chloropentyl isocyanate and compounds (3), (4), (5), and these chlorine-containing impurities will also adversely affect the PDI product itself and its downstream applications

[0008]

[0009] EP2684867A1 also provides a technical solution to control such compounds: using a gas phase phosgenation process, the amine is preheated to 230-320℃ with phosgene, then mixed through a specific mixer and reacted to prepare PDI, and the reaction temperature is 230-320℃.

[0010] The solution provided by EP2684867A1 can only control the production of 5-chloropentyl isocyanate and compounds (3), (4), (5), and cannot control chlorine-containing compounds (1), (2). In addition, according to the inventors' research, the main reason for the production of chlorine-containing compounds (1), (2), (3), (4), (5) is that the raw material PDA contains piperidine, tetrahydropyridine, dihydropyridine and other compounds. Such compounds can be removed through relatively complex separation methods during PDA production, but during the storage of PDA, intramolecular deamination reactions still occur as follows:

[0011]

[0012] Therefore, whether using a gas phase phosgenation process or a liquid phase phosgenation process, chlorine-containing compounds (1), (2), (3), (4), (5) cannot be avoided.

[0013] In addition, the solution provided by EP2684867A1 can only reduce chlorine-containing compounds (3), (4), (5) to within 350 ppm, and according to the chlorine content of 24.5% in the structure of chlorine-containing compounds (3), (4), (5), the contribution of hydrolyzed chlorine is as high as 84 ppm, and according to industry recognition, high hydrolyzed chlorine will adversely affect downstream applications. SUMMARY

[0014] In view of the above problems in the prior art, the present application aims to provide a method for preparing 1,5 pentamethylene diisocyanate, which uses the method provided by the present application to obtain 1,5 pentamethylene diisocyanate with low content of pyridine hydrogenated and / or chlorinated derivatives of carbamoyl chlorine-containing compounds.

[0015] One or more embodiments of the present application provide a method for preparing 1,5-pentylene diisocyanate, comprising the following steps: a) subjecting 1,5-pentylene diamine or its hydrochloride to a phosgenation reaction with phosgene to obtain a crude product containing 1,5-pentylene diisocyanate and phosgene; b) subjecting the crude product obtained in step a) to a phosgene removal treatment to isolate a crude 1,5-pentylene diisocyanate; c) subjecting the crude 1,5-pentylene diisocyanate obtained in step b) to a purification treatment to obtain the 1,5-pentylene diisocyanate; wherein a heat treatment is performed during the process of step a) and / or step c).

[0016] In one or more embodiments, the heat treatment is heating at a temperature of 200-600 °C (e.g. 100, 150, 200, 250, 300, 350, 400 °C) for 0.1-10 s (e.g. 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 s).

[0017] In one or more embodiments, the heat treatment is heating at a temperature of 250-400 °C for 0.1-10 s.

[0018] In one or more embodiments, the heat treatment is heating at a temperature of 250-400 °C for 0.1-4 s.

[0019] In one or more embodiments, the phosgenation reaction is selected from any one of a gas phase phosgenation reaction, a liquid phase phosgenation reaction and a salt-forming phosgenation reaction.

[0020] In one or more embodiments, when the phosgenation reaction is a gas phase phosgenation reaction, a heat treatment is performed during the process of step a) and / or step c).

[0021] In one or more embodiments, when the phosgenation reaction is a liquid phase phosgenation reaction or a salt-forming phosgenation reaction, the crude product obtained in step a) is subjected to a phosgene and liquid phase solvent removal treatment in step b) to isolate a crude 1,5-pentylene diisocyanate, and a heat treatment is performed during the process of step c).

[0022] In one or more embodiments, the content of carbamoyl chlorine compounds of hydrogenated and / or chlorinated derivatives of pyridine in the 1,5-pentylene diisocyanate obtained in step c) is less than 10 ppm.

[0023] In one or more embodiments, the carbamoyl chlorine compounds of hydrogenated and / or chlorinated derivatives of pyridine are selected from one and / or more of the following structures:

[0024]

[0025] In one or more embodiments, the heat treatment is performed in the form of a gas and / or a liquid.

[0026] In one or more embodiments, the vessel for the heat treatment is selected from a pipe vessel, a kettle vessel, a tube heat exchanger, and a column vessel.

[0027] In one or more embodiments, the phosgenation reaction is a gas phase phosgenation reaction, a hot phosgenation reaction, or a salt-forming phosgenation reaction.

[0028] In one or more embodiments, the phosgenation reaction is a reaction of 1,5-pentanediamine with one or more of phosgene, diphosgene, triphosgene, fluorophosgene, or bromophosgene.

[0029] One or more embodiments of the present application provide a composition containing 1,5-pentane diisocyanate, wherein the content of carbamoyl chlorine compounds of hydrogenated and / or chlorinated derivatives of pyridine is less than 10 ppm.

[0030] In one or more embodiments, the carbamoyl chlorine compounds of hydrogenated and / or chlorinated derivatives of pyridine are selected from one and / or more of the following structures:

[0031]

[0032] The present inventors have found that the chlorine-containing compounds (1), (2), (3), (4), (5) can be decomposed at high temperature for a certain period of time, and the main products after decomposition are mainly aliphatic monoisocyanates containing no more than 5 carbon atoms other than isocyanate, including but not limited to pentyl isocyanate, pentylene isocyanate, butyl isocyanate, butylene isocyanate, propyl isocyanate, propylene isocyanate, ethyl isocyanate, ethylene isocyanate, methyl isocyanate, isocyanic acid, etc. These monoisocyanates are difficult to separate from PDI, and the separation of PDI from the decomposed monoisocyanates can be achieved.

[0033] In one or more embodiments, the heat treatment is performed at a temperature of 200-600°C for 0.1-10s.

[0034] In one or more embodiments, the heat treatment is performed at a temperature of 250-400°C for 0.1-10s.

[0035] In one or more embodiments, the heat treatment is performed at a temperature of 250-400°C for 0.1-4s.

[0036] In one or more embodiments, the heat treatment operation mode is not limited, and any mode capable of achieving the effect of the present application can be used, such as heat treatment in the form of gas and / or liquid, and the heat treatment container used can be, but is not limited to, the following modes: tubular container, kettle type container, tube type heat exchanger, tower type container.

[0037] In one or more embodiments, the phosgenation reaction in step a) can be any one of a gas phase phosgenation reaction, a hot phosgenation reaction, a salt-forming phosgenation reaction. Among them, the phosgenation reaction is the reaction of pentanediamine with one or more of phosgene, diphosgene, triphosgene, fluorophosgene or bromophosgene.

[0038] In one or more embodiments, the above-mentioned phosgenation reaction can be carried out in the gas phase, and the specific method is described in Chinese patent CN105214568A, which is incorporated by reference into the present application. Specifically, a) gasification of amine to form an amine gas stream containing amine droplets; b) removing the amine droplets contained in the amine gas stream to obtain an amine gas stream substantially free of amine droplets; c) carrying out a gas phase phosgenation reaction of the amine gas stream substantially free of amine droplets with phosgene to obtain isocyanate; at the same time, using a heater to remove the amine droplets contained in the amine gas stream. The specific structure of the above-mentioned heater can be found in patent document CN105214568A.

[0039] In one or more embodiments, the reaction temperature is 200-550°C.

[0040] In one or more embodiments, the reaction temperature is 250-400°C, such as 300°C, 320°C.

[0041] In one or more embodiments, the reaction pressure is 0.01-1 MPa.

[0042] In one or more embodiments, the reaction pressure is 0.03-0.3 MPa, such as 0.08 MPa, 0.2 MPa.

[0043] In one or more embodiments, the mixed gas after the reaction of phosgene with 1,5-pentanediamine needs to be absorbed and cooled with a liquid inert medium or / and a mixture of inert medium and isocyanate.

[0044] In one or more embodiments, the inert gas is nitrogen or argon or steam of toluene, xylene, chlorobenzene, o-dichlorobenzene.

[0045] In one or more embodiments, the liquid inert medium is selected from all inert liquids suitable for the preparation of isocyanate.

[0046] In one or more embodiments, the inert liquid is chlorobenzene, dichlorobenzene, o-dichlorobenzene, toluene, chlorotoluene, xylene and / or a mixture thereof.

[0047] In one or more embodiments, the above-mentioned phosgenation reaction can be carried out in liquid phase, and the specific method is described in Chinese patent CN103319372B, which is incorporated herein by reference. Specifically, a) cold reaction, temperature is 0-130℃, for example 40-70℃; pressure is 0.1-1 MPa; with toluene, chlorobenzene, benzene, dichlorobenzene, cyclohexane, xylene or a mixture thereof as solvent, preferably chlorobenzene, dichlorobenzene as solvent; with super stoichiometric phosgene, reaction residence time is 2-120 min, preferably 5-45 min; b) is a hot reaction, temperature is 60-190℃, preferably 110-165℃; pressure is 0.1-1 MPa; with toluene, chlorobenzene, benzene, dichlorobenzene, cyclohexane, xylene or a mixture thereof as solvent, preferably chlorobenzene, dichlorobenzene as solvent, with super stoichiometric phosgene, reaction residence time is 0.5-5h, preferably 1-4h.

[0048] In one or more embodiments, the above-mentioned phosgenation reaction can be carried out in hydrogen chloride and / or carbon dioxide salt phosgenation reaction, and the specific method is described in Chinese patents CN105218422B, CN107337615A, which are incorporated herein by reference. Specifically, a) hydrogen chloride or / and carbon dioxide and amine are reacted in an inert solvent to form a salt, the molar equivalent ratio of the hydrogen chloride to the amino group of the amine is 1-2.5:1, preferably 1.2-2:1, the molar equivalent ratio of the carbon dioxide to the amino group of the amine is 0.5-5:1, preferably 0.6-3:1, the mass ratio of the solvent to the amine is 25-5:1, preferably 20-5:1; the salt formation reaction temperature is 0-50℃, preferably 5-30℃, the pressure is 0.1-1 MPa, preferably 0.2-0.5 MPa; the reaction residence time is 1-15 min, preferably 5-10 min; the reaction pressure is 0.1-1 MPa, preferably 0.2-0.5 MPa. The reaction liquid of the hydrochloride or carbonate salt obtained after a) salt formation reaction enters b) for phosgenation reaction, the temperature is 100-170℃, preferably 110-165℃; the pressure is 0.1-1 MPa, preferably 0.2-0.5 MPa; with super stoichiometric phosgene, reaction residence time is 1-5h, preferably 1.5-4h. Among them, the inert solvent is toluene, chlorobenzene, benzene, dichlorobenzene, cyclohexane, xylene or a mixture thereof, preferably chlorobenzene, dichlorobenzene.

[0049] In one or more embodiments, the process of removing phosgene and solvent from the obtained crude product is a routine operation in the art.

[0050] In one or more embodiments, the process of removing the obtained crude product from phosgene and aromatic solvent in step b) can use the method disclosed in Chinese patent application CN107652208A; preferably at 50-180°C, more preferably at 60-150°C, under an absolute pressure of 0.01-0.1 MPa.

[0051] In one or more embodiments, the process of purifying the crude 1,5-pentane diisocyanate is a conventional operation in the art.

[0052] In one or more embodiments, the process of purifying the crude polyisocyanate obtained in step b) without phosgene in step c) can use the technology known in the art to remove small molecules such as solvents and monomers in each step; for example, purification and purification can be carried out by rectification, distillation, crystallization, etc.

[0053] In one or more embodiments, if the phosgenation reaction is a gas phase phosgenation process, the heat treatment operation can be carried out in step a). If the heat treatment is carried out after the reaction, the heat treatment is carried out after the phosgenation reaction is completed, and before the reaction liquid is absorbed by the inert solvent, at this time the mixed gas after the reaction can be heat treated by the heat treatment scheme provided by the present application.

[0054] In one or more embodiments, the heat treatment operation can be carried out after the gas phase phosgenation reaction is completed and before the reaction liquid is absorbed by the solvent.

[0055] In one or more embodiments, if the liquid phase phosgenation method and the salt-forming phosgenation method are used, although the heat treatment of the reaction liquid can achieve the same effect, the liquid phase phosgenation method and the salt-forming phosgenation method contain more solvents. As mentioned in patent CN110511163A, the inert solvent and phosgene will react to generate benzophenone compounds under high temperature heating, which is not conducive to the downstream application of isocyanate. Therefore, if the liquid phase phosgenation method and the salt-forming phosgenation method are used, it is not recommended to carry out heat treatment in step a), and heat treatment can be carried out in the process of step c). If the gas phase phosgenation reaction is used, heat treatment can be carried out in the process of step a) and / or step c).

[0056] In one or more embodiments, the heat treatment operation is not recommended in step b), because this process involves the separation of phosgene and solvent, and in order to avoid the generation of benzophenone compounds mentioned in patent CN110511163A, it is not recommended to carry out in the phosgene removal stage. It is recommended to carry out after the phosgene in the reaction liquid is completely removed, at this time there is no phosgene in the stream, although there is high temperature heating, but benzophenone compounds will not be generated.

[0057] In one or more embodiments, the high-temperature heat treatment process decomposes the chlorine-containing compounds (1), (2), (3), (4), (5) into aliphatic monoisocyanates. If the heat treatment is performed before the solvent is completely removed from the reaction solution, the aliphatic monoisocyanates produced will partially or completely enter the solvent stream during the desolvation process. In the conventional operation in the art, the solvent is recycled for use, as mentioned in CN110511163A. If the solvent contains a large amount of isocyanates, it will adversely affect the phosgenation process.

[0058] In one or more embodiments, the heat treatment operation is not suitable to be performed in the presence of a solvent.

[0059] In one or more embodiments, the heat treatment operation can be performed in step a) or c). In order to obtain qualified PDI products, the isocyanate crude product after removal of phosgene and solvent needs to be further subjected to removal of heavy components and light components. For example, the removal of solvent is performed first, and then the removal of heavy components and light components is performed. There is no particular requirement for the order of removal of heavy components and removal of light components, and they can even be removed simultaneously by distillation.

[0060] In one or more embodiments, the technical solution adopted is high-temperature heat treatment. On the one hand, the high-temperature heat treatment decomposes the chlorine-containing compounds (1), (2), (3), (4), (5) into aliphatic monoisocyanates, which are light components relative to PDI. On the other hand, the high-temperature heat treatment process also causes the polymerization of PDI monomers. Although the heat treatment time is short, a small amount of polymer heavy components will also be formed. Therefore, in some embodiments, the heat treatment process can be performed before the removal of heavy components and / or the removal of light components. In this way, the removal of heavy components and / or the removal of light components can be avoided.

[0061] In one or more embodiments, compared with the prior art, the present application has the following advantages: after the heat treatment operation of the method of the present application, the content of the carbamoyl chlorine-containing compound containing hydrogenated and / or chlorinated derivatives of pyridine in the obtained PDI product is less than 10 ppm. DETAILED DESCRIPTION

[0062] The method for analyzing the chlorine-containing compounds (1), (2) in PDI in the present application adopts the method provided in patent CN103347852A;

[0063] The method for analyzing the chlorine-containing compounds (3), (4), (5) in PDI in the present application adopts the method provided in patent CN106715384A;

[0064] The analysis of the hydrolytic chlorine content in PDI is performed by the method mentioned in the national standard GB / T 12009.2-1989.

[0065] The analysis of the color index in PDI is performed by the method mentioned in the national standard GB / T 605-2006.

[0066] Example 1

[0067] a) The 1,5-pentanediamine (PDA) is vaporized and heated to 325℃ by using the heater disclosed in Example 1 of Chinese patent application CN105214568A, and is continuously added into a reactor with gaseous phosgene heated to 325℃ via respective feeding pipes under the protection of nitrogen; the reaction pressure is 0.05 MPa, and the reaction temperature is 330℃; wherein the feeding amount of PDA is 390 Kg / h, and the feeding amount of gaseous phosgene is 3000 Kg / h;

[0068] The mixed gas obtained after the reaction is rapidly cooled to 100℃ by using the o-dichlorobenzene solution through a gas jet absorption device to obtain a crude product containing the product PDI, phosgene and o-dichlorobenzene solution.

[0069] b) The crude product obtained in step a) is treated to remove phosgene and o-dichlorobenzene solution, and the o-dichlorobenzene solution and excess phosgene in the crude product are removed at 168℃ and 0.1 MPa absolute pressure to obtain a PDI crude product without phosgene;

[0070] c) The PDI crude product without phosgene obtained in step b) is purified by rectification to obtain the PDI product at 0.5 KPa absolute pressure and 120-140℃ distillation range.

[0071] The obtained PDI product is analyzed for color number, purity, chlorine-containing compounds, hydrolytic chlorine and other indexes.

[0072] Before the step a) of rapidly cooling the mixed gas obtained after the reaction to 100℃ by using the o-dichlorobenzene solution through a gas jet absorption device, the mixed gas containing phosgene, hydrogen chloride and PDI obtained from the gas phase phosgenation reaction is introduced into a heat treatment reactor for heat treatment, the treatment temperature is 340℃, the treatment time is 0.5 s, and the heat treatment reactor is in the form of a tubular reactor.

[0073] Example 2

[0074] This example was carried out with reference to the procedure described in Example 1 above. In the method for preparing PDI, the difference is that the thermal treatment process taken in Example 2 is not in step a), but before the crude product of PDI without phosgene is purified by rectification in step c), the crude product of PDI without phosgene is introduced into the thermal treatment reactor for thermal treatment, the treatment temperature is 320°C, the treatment time is 1 s, and the reactor form is a kettle type reactor.

[0075] Example 3

[0076] The phosgenation reaction of step a) is a liquid phase phosgenation reaction, which is carried out in a reaction kettle with reference to the reaction kettle disclosed in Chinese patent document CN103319372A by using the following steps:

[0077] 1) Cold reaction: PDA is configured into a solution with a mass content of 15% with o-dichlorobenzene as the solvent, and preheated to 40°C, and introduced into the reaction kettle containing the o-dichlorobenzene solution at the same time with liquid phosgene at -5°C to carry out the liquid phase phosgenation reaction; wherein the feeding amount of PDA is 195 Kg / h, the feeding amount of cold reaction phosgene is 1500 kg / h, the cold reaction temperature is controlled at 60°C, and the residence time is 5 min;

[0078] 2) Hot reaction: the temperature is controlled at 155°C and the residence time is 2 h, and the reaction is carried out in the presence of o-dichlorobenzene solution and excess phosgene to obtain a reaction liquid (crude product) containing product PDI, phosgene and o-dichlorobenzene solution;

[0079] b) The crude product obtained in step a) is treated to remove phosgene and o-dichlorobenzene solution, and the o-dichlorobenzene solution and excess phosgene in the crude product are removed at 168°C and 0.1 MPa absolute pressure to separate the crude product of PDI without phosgene;

[0080] c) The crude product of PDI without phosgene obtained in step b) is purified by rectification to obtain the PDI product at 0.5 KPa absolute pressure, 120-140°C distillation range.

[0081] The PDI product obtained is analyzed for color number, purity, chlorine-containing compounds, hydrolytic chlorine and other indicators.

[0082] In which, before the crude product of PDI without phosgene is purified by rectification in step c), the crude product of PDI without phosgene is introduced into the thermal treatment reactor for thermal treatment, the treatment temperature is 360°C, the treatment time is 4 s, and the reactor form is a tube type heat exchanger.

[0083] Example 4

[0084] The phosgenation reaction of step a) is carried out by a salt-forming phosgenation reaction, which is carried out in a kettle reactor as disclosed in Example 1 of Chinese patent document CN105218422B by using the following steps:

[0085] 1) 1000 Kg of o-dichlorobenzene is pre-added as a reaction solvent in a salt-forming reaction kettle, a circulating pump and stirring are started, and hydrogen chloride compressed gas is introduced into the reactor at a speed of 50 mol / min through a pre-mixer. After stirring for 15 min, the mixture of PDA and o-dichlorobenzene is heated to 30°C through a raw material pre-heater, and after being fully contacted with the hydrogen chloride gas at a flow rate of 335 Kg / h, the salt-forming reaction is carried out. External circulating cooling water is used for cooling, and part of the reaction heat is removed, the circulating liquid flow rate is about 5 m3 / h, and the reaction liquid temperature is maintained at 30-45°C. After 3 h of feeding, the feeding of the mixture of PDA and o-dichlorobenzene is stopped, and the HCl gas is continuously introduced for 30 min.

[0086] 2) The PDA hydrochloride slurry obtained in step 1) is transferred to a phosgenation reaction kettle, which has a phosgene gas inlet pipe, a gas phase condensation reflux and stirring. The phosgenation reaction kettle is heated, and stirring is started at the same time. After the temperature reaches 60°C, phosgene is introduced, the phosgene feeding speed is 50 mol / min, the reaction temperature is 145°C, and after the reaction liquid is clarified, the phosgene feeding is stopped, and a salt-forming phosgenation reaction liquid (crude product) containing the product PDI, phosgene and o-dichlorobenzene is obtained.

[0087] b) The crude product obtained in step a) is treated by removing the phosgene and o-dichlorobenzene solution, and the o-dichlorobenzene solution and excess phosgene in the crude product are removed at 168°C and an absolute pressure of 0.1 MPa, and the PDI crude product without phosgene is separated;

[0088] c) The PDI crude product without phosgene obtained in step b) is purified by rectification at an absolute pressure of 0.5 KPa and a distillation range of 120-140°C, and the PDI product is obtained.

[0089] The obtained PDI product is analyzed for color number, purity, chlorine-containing compounds, hydrolytic chlorine and other indicators.

[0090] Before step c) of purifying the PDI crude product without phosgene by rectification, the PDI crude product without phosgene is introduced into a heat treatment reactor for heat treatment, the treatment temperature is 380°C, the treatment time is 3 s, and the reactor is a tube heat exchanger.

[0091] Comparative Example 1:

[0092] This comparative example is carried out by referring to the process described in Example 1 above. In the method for preparing PDI, the difference is that no heat treatment measures are taken in this comparative example.

[0093] Comparative Example 2:

[0094] The comparative example was carried out according to the procedure described above in Example 3. The difference in the method of preparing PDI was that no heat treatment was taken in the comparative example.

[0095] Comparative Example 3:

[0096] The comparative example was carried out according to the procedure described above in Example 4. The difference in the method of preparing PDI was that no heat treatment was taken in the comparative example.

[0097] The results of the analysis of the PDI products obtained in the examples and comparative examples are summarized as follows:

[0098]

[0099] The results in the above table show that the PDI prepared in Examples 1-4 has significantly lower total amount of chlorine-containing compounds in 1, 2, 3, 4 and 5 than the PDI prepared in Comparative Examples 1-3, which leads to obvious advantages in color number, purity and hydrolytic chlorine index. Although there is a 0.1% loss in yield in the heat treatment process, the quality of the PDI is improved significantly. This shows that the process for preparing PDI provided in the present application has obvious advantages over other processes.

[0100] The above examples are used to illustrate the detailed method of the present application, but the present application is not limited to the above detailed method, i.e. it does not mean that the present application must rely on the above detailed method to be implemented. It should be understood by those skilled in the art that any improvement on the present application, equivalent replacement of each raw material of the product of the present application, addition of auxiliary ingredients, selection of specific methods, etc. all fall within the protection scope and disclosure scope of the present application.

Claims

1. A method for preparing 1,5-pentanediisocyanate, comprising the following steps: a) 1,5-pentanediamine or its hydrochloride is reacted with phosgene to obtain a crude product containing 1,5-pentanediisocyanate and phosgene. b) The crude product obtained in step a) is subjected to phosgene removal treatment to separate crude 1,5-pentanediisocyanate; c) The crude 1,5-pentanediisocyanate obtained in step b) is purified to obtain the 1,5-pentanediisocyanate. Heat treatment is performed during steps a) and / or c); the heat treatment is heating at 250-400℃ for 0.1-10s.

2. The method according to claim 1, wherein, The heat treatment involves heating at 250-400℃ for 0.1-4 seconds.

3. The method according to claim 1, wherein, The phosgenation reaction is selected from any one of gas-phase phosgenation, liquid-phase phosgenation, and salt-forming phosgenation.

4. The method according to claim 3, wherein, When the phosgenation reaction is a gas-phase phosgenation reaction, heat treatment is performed during step a) and / or step c).

5. The method according to claim 3, wherein, When the phosgenation reaction is a liquid-phase phosgenation reaction or a salt-forming phosgenation reaction, in step b), the crude product obtained in step a) is treated to remove phosgene and liquid solvent to separate crude 1,5-pentanediisocyanate, and heat treatment is performed in step c).

6. The method according to claim 1, wherein, The content of carbamoyl chloride compounds of hydrogenated and / or chlorinated derivatives of pyridine in the 1,5-pentanediisocyanate obtained in step c) is less than 10 ppm.

7. The method according to claim 6, wherein, The carbamoyl chloride compounds of the hydrogenated and / or chlorinated derivatives of pyridine are selected from one and / or more of the following structures: 。 8. The method according to claim 1, wherein, The heat treatment is carried out in the form of gas and / or liquid.

9. The method according to claim 8, wherein, The container used for heat treatment is selected from tubular containers, autoclaves, shell-and-tube heat exchangers, and tower containers.

10. The method according to claim 1, wherein, The phosgenation reaction is a gas-phase phosgenation reaction, a cold-thermal phosgenation reaction, or a salt-forming phosgenation reaction.

11. The method according to claim 10, wherein, The phosgenation reaction is a reaction of 1,5-pentanediamine with one or more of phosgene, diphosgene, triphosgene, fluorophosgene, or bromophosgene.

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