Method for producing isocyanate, and composition

Abstract

This method for producing an isocyanate containing an isocyanate having a specific structure includes a step for obtaining the isocyanate by heating a starting material liquid containing a carbamic acid ester corresponding to the isocyanate having the specific structure to thermally decompose the carbamic acid ester. The starting material liquid contains an aromatic organic solvent that has a boiling point B1 higher than the boiling point B2 of the isocyanate having the specific structure and whose solubility of the carbamic acid ester at 180°C is 2.5 wt.% or more.

Description

Method for producing isocyanates, and compositions

[0001] This disclosure relates to a method for producing isocyanates and compositions that can be used therefor.

[0002] [Disclosure A] Isocyanates are widely used as raw materials for polyurethanes and polyureas. The conventional industrial method for producing isocyanates has been the phosgene method, which involves reacting an amine with phosgene. However, because phosgene is highly toxic, efforts have been made to develop methods for producing isocyanates without using phosgene.

[0003] As a method for producing isocyanates without using phosgene, a method of producing isocyanates by thermal decomposition of carbamic acid esters is known. Patent Document 1 discloses a method for producing xylylene diisocyanate by thermal decomposition of xylylene dicarbamate. Patent Document 2 discloses a method for producing isocyanates by thermal decomposition of a carbamate compound having a specific structure, in which the carbamate compound is thermally decomposed, the crude isocyanate solution containing the generated isocyanate and the by-product hydroxy compound are separated, the crude isocyanate solution is mixed with an extraction solvent having a lower boiling point than the isocyanate to separate it into an isocyanate phase and an extraction solvent phase, and then the extraction solvent contained in the crude isocyanate phase is separated from the obtained isocyanate phase, thereby suppressing the contamination of by-products in the purification process and producing isocyanates with high purity and yield.

[0004] [Disclosure B] Isocyanates are widely used as raw materials for polyurethanes and polyureas. The conventional industrial method for producing isocyanates has been the phosgene method, which involves reacting an amine with phosgene. However, because phosgene is highly toxic, efforts have been made to develop methods for producing isocyanates without using phosgene.

[0005] As a method for producing isocyanates without using phosgene, a method of producing isocyanates by thermal decomposition of carbamic acid esters is known. Patent Document 1 discloses a method for producing xylylene diisocyanate by thermal decomposition of xylylene dicarbamate. Patent Document 2 discloses a method for producing isocyanates by thermal decomposition of a carbamate compound having a specific structure, in which the carbamate compound is thermally decomposed, the crude isocyanate solution containing the generated isocyanate and the by-product hydroxy compound are separated, the crude isocyanate solution is mixed with an extraction solvent having a lower boiling point than the isocyanate to separate it into an isocyanate phase and an extraction solvent phase, and then the extraction solvent contained in the crude isocyanate phase is separated from the obtained isocyanate phase, thereby suppressing the contamination of by-products in the purification process and producing isocyanates with high purity and yield.

[0006] [Disclosure C] Isocyanates are widely used as raw materials for polyurethanes and polyureas. The conventional industrial method for producing isocyanates was the phosgene method, which involves reacting an amine with phosgene. However, because phosgene is highly toxic, efforts have been made to develop methods for producing isocyanates without using phosgene.

[0007] As a method for producing isocyanates without using phosgene, a method of producing isocyanates by thermal decomposition of carbamic acid esters is known. Patent Document 1 discloses a method for producing xylylene diisocyanate by thermal decomposition of xylylene dicarbamate. Patent Document 3 discloses a method for producing isocyanates by two-stage thermal decomposition of carbamate, comprising: a first thermal decomposition step in which a liquid film is formed of a raw material liquid containing carbamate and thermal decomposition is carried out while removing the by-product hydroxy compound as a gas-phase component by heating; and a second thermal decomposition step in which the liquid-phase component obtained in the first thermal decomposition step is supplied to a tank-type reactor and heated, while removing the by-product hydroxy compound as a gas-phase component from the tank-type reactor and thermal decomposing the carbamate remaining in the first thermal decomposition step.

[0008] International Publication No. 2014 / 163017, Japanese Patent Publication No. 2022-170318, Japanese Patent Publication No. 2023-91331

[0009] [Disclosure A] One aspect of this disclosure aims to provide a method for producing isocyanates from carbamic acid esters in high yield while minimizing energy consumption during production, and a composition that can be used in said production method.

[0010] [Disclosure B] One aspect of this disclosure is aimed at providing a method for obtaining high-purity isocyanates in higher yield by thermal decomposition of carbamic acid esters.

[0011] [Disclosure C] One aspect of this disclosure is aimed at providing a method for producing isocyanates that can produce isocyanates more efficiently from carbamic acid esters.

[0012] The gist of Disclosure A is as follows: [1A] A method for producing an isocyanate, wherein the isocyanate comprises an isocyanate having a structure represented by structural formula (100), and the production method comprises step A of heating a raw material solution containing a carbamic acid ester corresponding to the isocyanate having a structure represented by structural formula (100) to thermally decompose the carbamic acid ester and obtain the isocyanate, wherein the raw material solution comprises an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate having a structure represented by structural formula (100), and whose solubility at a temperature of 180°C is 2.5 wt% or more. １００ (NHCOOR １０５ ) ｐ－ｑ (NCO) ｑ (100) (In structural formula (100), R １００ This is an organic group with a valence p that contains an aromatic ring, and in structural formula (100) -NHCOOR １０５ The nitrogen atom in the group and the nitrogen atom in the -NCO group are directly bonded to the carbon atoms constituting the aromatic ring in the organic group, p is an integer of 1 or more, and q is an integer between 1 and p, R １０５ (Each of these is independently a substituted or unsubstituted hydrocarbon group.) [2A] The method for producing an isocyanate according to [1A], wherein in the structural formula (100), p is 2 or more and q is 1 or more. [3A] The method for producing an isocyanate according to [1A] or [2A], wherein the isocyanate having the structure shown in the structural formula (100) includes an isocyanate having the structure shown in the structural formula (101).

[0013]

[0014] (In structural formula (101), s and t each represent 0 or 1, provided that s + t = 1. R １０１ (This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.)

[0015] [4A] The method for producing an isocyanate according to any one of [1A] to [3A], wherein the isocyanate having the structure represented by the structural formula (101) contains an isocyanate having the structure represented by the structural formula (102).

[0016]

[0017] [5A] The method for producing an isocyanate according to any one of [1A] to [4A], wherein the organic solvent contains at least one solvent selected from the group consisting of alkyl naphthalene and dibenzyl toluene. [6A] The method for producing an isocyanate according to any one of [1] to [5], wherein the carbamate has a structure represented by the structural formula (105). R １０３ (NHCOOR １０５ ) ｐ (105) (In the structural formula (105), R １０３ is a p-valent organic group containing an aromatic ring, and R １０５ , and p are as defined in the structural formula (100))

[0018] [7A] The method for producing an isocyanate according to any one of [1A] to [6A], wherein the step A of obtaining the isocyanate further includes a step of continuously extracting from the reaction vessel a hydroxy compound by-produced by thermal decomposition of the carbamate and the isocyanate. [8A] The thermal decomposition is carried out in the presence of one or more catalysts selected from the group consisting of fatty acid metal salts and phosphoric acid metal salts, the fatty acid metal salt is a compound represented by the general formula (IA) or the general formula (IB), and the phosphoric acid metal salt is a compound represented by the general formula (IC). The method for producing an isocyanate according to any one of [1A] to [7A]: (R １１ COO) ｎ１ M １１ (IA) (In the general formula (IA), M １１ is a Group 1 metal, Group 2 metal, Group 13 metal, or lanthanoid metal in the periodic table; n1 is the valence of M １１ ; R １１ is an alkyl group having 1 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms.) (R １２ COO)ｎ２ M １２ (IB) (In general formula (IB), M １２ is a metal from groups 3 to 11 of the periodic table or zinc; n2 is M １２ The valence of; R １２ (This is an alkyl group having 10 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms.) (M １３ ) ｍ (PO ４ ) ｎ３ (IC) (In general formula (IC), M １３ m and n3 are metals from groups 1 to 11 of the periodic table, metals from group 13 of the periodic table, zinc, or lanthanide metals; m and n3 are M １３ The valence of × m = 3 × n3 is satisfied. (9A) The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), and R in the general formula (IA) １１ However, R in the general formula (IB) is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms. １２ The method for producing an isocyanate according to [8A], wherein the catalyst is an alkyl group having 12 or more carbon atoms and 40 carbon atoms or an alkenyl group having 12 or more carbon atoms and 40 carbon atoms. [10A] The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), wherein the M in the general formula (IA) １１ However, it is a metal of Group 13 of the periodic table, and M in the general formula (IB) １２ A method for producing an isocyanate according to [8] or [9A], wherein the catalyst is a metal from Group 8 to 11 of the periodic table or zinc. [11A] The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), wherein the M in the general formula (IA) １１ However, it is a metal of Group 13 of the periodic table, and M in the general formula (IB) １２A method for producing an isocyanate according to any one of [8A] to [10A], wherein the catalyst is a Group 8 metal, a Group 9 metal, or zinc. [12A] A method for producing an isocyanate according to any one of [8A] to [11A], wherein the catalyst is the fatty acid metal salt represented by the general formula (IA). [13A] A method for producing an isocyanate according to any one of [1A] to [12A], wherein the boiling point B1 of the organic solvent is 10°C or higher than the boiling point B2 of the isocyanate represented by the structural formula (100). [14A] A composition comprising a carbamic acid ester corresponding to an isocyanate having the structure represented by the structural formula (100) and an aromatic organic solvent, wherein the boiling point B1 of the organic solvent is higher than the boiling point B2 of the isocyanate having the structure represented by the structural formula (100), and the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. １００ (NHCOOR １０５ ) ｐ－ｑ (NCO) ｑ (100)

[0019] (In structural formula (100), R １００ This is an organic group with a valence p that contains an aromatic ring, and in formula (100) -NHCOOR １０５ The nitrogen atom in the group and the nitrogen atom in the -NCO group are directly bonded to the carbon atoms constituting the aromatic ring in the organic group, p is an integer of 1 or more, and q is an integer between 1 and p, R １０５ Each of these is independently a substituted or unsubstituted hydrocarbon group.

[0020] [15A] The composition according to [14A], wherein in the structural formula (100), p is 2 or more and q is 1 or more. [16A] The composition according to [14A] or [15A], wherein the isocyanate having the structure shown in the structural formula (100) comprises an isocyanate having the structure shown in the structural formula (101).

[0021]

[0022] (In structural formula (101), s and t each represent 0 or 1, provided that s + t = 1. R １０１(This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.)

[0023] [17A] The composition according to any one of [14A] to [16A], wherein the carbamic acid ester has the structure shown by structural formula (105). １０３ (NHCOOR １０５ ) ｐ (105) (In structural formula (105), R １０３ R is a p-valent organic group containing an aromatic ring, １０５ (where p is synonymous with structural formula (100)) [18A] The composition according to any one of [14A] to [17A], wherein the boiling point B1 of the organic solvent is 10°C or higher than the boiling point B2 of the isocyanate represented by structural formula (100). [19A] The composition according to any one of [14A] to [18A], wherein the organic solvent comprises at least one solvent selected from the group consisting of alkylnaphthalene and dibenzyltoluene. [20A] The composition according to any one of [14A] to [19A], wherein the content ratio of the carbamic acid ester to the composition is 1 to 25% by mass. [21A] The composition according to any one of [14A] to [20A], wherein the content ratio of the organic solvent to the composition is 75 to 99% by mass.

[0024] The gist of Disclosure B is as follows: [1B] A method for producing an isocyanate, wherein the isocyanate comprises an isocyanate having a structure represented by structural formula (1B), the production method comprising step 1B of heating a liquid containing a raw material solution containing a carbamic acid ester corresponding to the isocyanate having a structure represented by structural formula (1B) in a reaction vessel to thermally decompose the carbamic acid ester and obtain the isocyanate, the step 1B comprising step 1B-1 of continuously withdrawing the isocyanate generated in the reaction vessel by thermal decomposition of the carbamic acid ester from the reaction vessel, and step 1B-2 of continuously withdrawing a hydroxy compound produced as a by-product in the reaction vessel by thermal decomposition of the carbamic acid ester from the reaction vessel, the raw material solution comprises an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate having a structure represented by structural formula (1B), and whose solubility at a temperature of 180°C of the carbamic acid ester is 2.5 wt% or more: R ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1B) (In structural formula (1B), R ３１ R is an organic group with valency p, where p is an integer greater than or equal to 1, and q is an integer greater than or equal to 1 and less than or equal to p. ２２ (Each of these is independently a substituted or unsubstituted hydrocarbon group.) [2B] A method for producing the isocyanate according to [1B], wherein the carbamic acid ester has the structure shown in structural formula (2B): R ２１ (NHCOOR ２２ ) ｐ (2B) (In structural formula (2B), R ２１ is a p-valent organic group, R ２２ , and p are R in structural formula (1) ２２(Synonymous with p). [3B] A method for producing an isocyanate according to [1B] or [2B], wherein step 1B-1 is a step of continuously withdrawing the isocyanate from the reaction vessel as a gas phase component. [4B] A method for producing an isocyanate according to any one of [1B] to [3B], wherein step 1B-2 is a step of withdrawing the hydroxy compound from the reaction vessel as a gas phase component. [5B] In the structural formula (1B), p is 2 or more, q is 1 or more, and R ３１ However, the organic group has a valency p, and the organic group is an aliphatic hydrocarbon group having 1 or more carbon atoms, or an aromatic hydrocarbon group having 6 or more carbon atoms, provided that the aliphatic hydrocarbon group contains -CH ２ -, -O-, -S-, or -SO ２ It may be substituted with -, and the aromatic hydrocarbon group has two or more aromatic rings bonded together by a single bond, -CH ２ A method for producing an isocyanate according to any one of [1B] to [4B], which may be a group connected by at least one linking group selected from the group consisting of -, -O-, and -S-. [6B] A method for producing an isocyanate according to any one of [1] to [5], wherein the isocyanate having the structure shown in structural formula (1B) has the structure shown in the following structural formula (3-1):

[0025]

[0026] (In structural formula (3-1), s and t each represent 0 or 1, provided that s + t = 1. R ００ (This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.)

[0027] [7B] A method for producing an isocyanate according to any one of [1B] to [6B], wherein the carbamic acid ester has the structure represented by structural formula (4):

[0028]

[0029] (R ０１ , and R ０２ Each of these independently represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.

[0030] [8B] The method for producing an isocyanate according to any one of [1B] to [7B], wherein step 1B-2 is a step of removing aliphatic alcohol having 1 to 4 carbon atoms produced by the thermal decomposition as a gas phase component from the reaction vessel. [9B] The method for producing an isocyanate according to any one of [1B] to [8B], wherein the organic solvent comprises at least one solvent selected from the group consisting of alkylnaphthalene and dibenzyltoluene. [10B] The method for producing an isocyanate according to any one of [1B] to [9B], further comprising the steps of supplying the raw material liquid to the reaction vessel and removing at least a portion of the liquid from the reaction vessel. [11B] The method for producing an isocyanate according to any one of [1B] to [10B], wherein step 1B is a step of heating a liquid film containing the raw material liquid in the reaction vessel to thermally decompose the carbamic acid ester in the liquid film and produce the isocyanate.

[0031] The gist of Disclosure C is as follows: [1C] A method for producing an isocyanate, wherein the isocyanate comprises an isocyanate having the structure shown in structural formula (1C), and the production method comprises: step 1C of preparing a raw material solution containing a carbamic acid ester corresponding to the isocyanate having the structure shown in structural formula (1C), which is shown in structural formula (2C); and step 2C of heating a liquid film containing the raw material solution in a reaction vessel to thermally decompose the carbamic acid ester in the liquid film to produce the isocyanate, wherein step 2C comprises: step 2C-1 of continuously withdrawing a hydroxy compound produced as a by-product by thermal decomposition of the carbamic acid ester from the reaction vessel as a gas phase component; and step 2C-2 of continuously withdrawing the isocyanate produced by thermal decomposition of the carbamic acid ester from the reaction vessel as a gas phase component; R ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1C) R ２１ (NHCOOR ２２ ) ｐ(2C) (In structural formulas (1C) to (2C), R ２１ and R ３１ Each of these is an organic group with a valency of p, where p is an integer greater than or equal to 1, and q is an integer greater than or equal to 1 and less than or equal to p, R ２２ (Each is independently a substituted or unsubstituted hydrocarbon group). [2C] In the above structural formula (1C), p is 2 or more, q is 1 or more, and R ３１ However, the organic group has a valency p, and the organic group is an aliphatic hydrocarbon group having 1 or more carbon atoms, or an aromatic hydrocarbon group having 6 or more carbon atoms, provided that the aliphatic hydrocarbon group contains -CH ２ -, -O-, -S-, or -SO ２ It may be substituted with -, and the aromatic hydrocarbon group has two or more aromatic rings bonded together by a single bond, -CH ２ The method for producing an isocyanate according to [1C], which may be a group connected by at least one linking group selected from the group consisting of -, -O-, and -S-. [3C] The method for producing an isocyanate according to [1C] or [2C], wherein the isocyanate having the structure shown in structural formula (1C) comprises an isocyanate having the structure shown in the following structural formula (3-1), and the carbamic acid ester has the structure shown in the following structural formula (4):

[0032]

[0033] (In structural formula (3-1), s and t each represent 0 or 1, provided that s + t = 1. R ００ (This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.)

[0034]

[0035] (R ０１ , and R ０２(Each of these independently represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms). [4C] A method for producing an isocyanate according to any one of [1C] to [3C], wherein step 2C-1 and step 2C-2 are carried out simultaneously. [5C] A method for producing an isocyanate according to any one of [1C] to [4C], wherein a mixture containing the hydroxy compound and the isocyanate is withdrawn from the reaction vessel as a gas phase component by carrying out step 2C-1 and step 2C-2 simultaneously. [6C] A method for producing an isocyanate according to any one of [1C] to [5C], further comprising the step of condensing the isocyanate contained in the mixture withdrawn from the reaction vessel to separate it from the hydroxy compound contained in the mixture. [7C] A method for producing an isocyanate according to any one of [1C] to [6C], wherein the raw material liquid contains liquid paraffin. [8C] A method for producing an isocyanate according to any one of [1C] to [6C], wherein the raw material liquid comprises an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of an isocyanate having the structure shown in the structural formula (1C), and whose solubility at 180°C of the carbamic acid ester is 2.5 wt% or more. [9C] A method for producing an isocyanate according to [8C], wherein the boiling point B1 is 350°C or higher. [10C] A method for producing an isocyanate according to [8C] or [9C], wherein the organic solvent comprises at least one solvent selected from the group consisting of alkylnaphthalene and dibenzyltoluene. [11C] A method for producing an isocyanate according to any one of [1C] to [10C], wherein step 2C further comprises a step of withdrawing the liquid containing the carbamic acid ester from the reaction vessel. [12C] A method for producing an isocyanate according to [11C], wherein the liquid withdrawn from the reaction vessel is subjected to step 2C.

[0036] According to one aspect of Disclosure A, a method for producing isocyanates from carbamic acid esters in high yield while minimizing energy consumption during production is provided, and a composition used in the method for producing said isocyanates is provided.

[0037] According to one aspect of Disclosure B, a method for producing isocyanate is provided, which allows for the production of high-purity isocyanate in higher yield by thermal decomposition of carbamic acid ester.

[0038] According to one aspect of this disclosure C, a method for producing isocyanates is provided that can produce isocyanates more efficiently from carbamic acid esters.

[0039] This is an explanatory diagram of one embodiment of the method for producing isocyanate according to Disclosure A. This is an explanatory diagram of one embodiment of the method for producing isocyanate according to Disclosure B. This is an explanatory diagram of another embodiment of the method for producing isocyanate according to Disclosure B. This is an explanatory diagram of yet another embodiment of the method for producing isocyanate according to Disclosure B. This is an explanatory diagram of one embodiment of the method for producing isocyanate according to Disclosure C.

[0040] [Disclosure A] Embodiments of Disclosure A will be described below, but Disclosure A is not limited to the embodiments described below and can be implemented in various ways within the scope of its gist. In this specification, expressions representing numerical ranges, such as "XX or more," "YY or less," and "XX to YY," mean numerical ranges that include the endpoints XX and YY, unless otherwise specified. Furthermore, when numerical ranges are described in steps, any combination of the upper and lower limits of each numerical range is also disclosed. In addition, in this specification, for example, "at least one selected from the group consisting of XX, YY, and ZZ" means either XX only, YY only, ZZ only, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Furthermore, in this specification, when descriptions such as "one aspect" or "one aspect" appear multiple times, they do not necessarily refer to the same aspect, but may refer to different aspects. Furthermore, in this specification, the boiling point refers to the temperature at which 50% by mass is distilled when a distillation test is conducted under normal pressure (101.3 kPaA). If the substance being measured cannot be distilled at normal pressure, the boiling point refers to the temperature at which 50% by mass is distilled when a distillation test is conducted under a distillation-capable pressure, converted to a temperature at normal pressure (101.3 kPaA) (normal pressure equivalent boiling point).

[0041] The present inventors have been studying a method for producing an isocyanate by heating a raw material solution containing a carbamic acid ester corresponding to an isocyanate having the structure shown in structural formula (100) and thermally decomposing the carbamic acid ester. Patent Document 1 discloses a method for producing xylylene diisocyanate by thermally decomposing xylylene dicarbamate, and paragraphs

[0074] to

[0081] list solvents that can be used in the thermal decomposition of xylylene dicarbamate. In the course of the above studies, the present inventors have come to realize that the selection of a solvent used when producing an isocyanate by thermally decomposing a carbamic acid ester is important for producing isocyanate at low cost and in high yield. However, when producing an isocyanate having the structure shown in structural formula (100) by thermally decomposing the carbamic acid ester corresponding to the isocyanate, it was sometimes not possible to produce the isocyanate in high yield even when using the solvent described in Patent Document 1. The reason is unclear, but xylylene dicarbamate has a carbamate group that is a methylene group (-CH ２is bonded to the benzene ring via (-). In contrast, for the carbamate corresponding to the isocyanate corresponding to the structural formula (100), the carbamate group is directly bonded to the aromatic ring. That is, the nitrogen atom in the carbamate group is directly bonded to the carbon atom constituting the aromatic ring. Thus, the carbamate group directly bonded to the aromatic ring is considered to have weaker basicity as an amine compared to the carbamate group of xylylene dicarbamate. Therefore, the behavior during thermal decomposition of the carbamate corresponding to the isocyanate represented by the structural formula (100) is considered to be significantly different from the behavior during thermal decomposition of xylylene dicarbamate. Therefore, when the present inventors thermally decompose a carbamate in which a carbamate group is directly bonded to an aromatic ring to produce an isocyanate, in order to find a solvent that can obtain the isocyanate in a high yield while suppressing the energy consumption as much as possible, further studies were conducted. As a result, as the solvent used during thermal decomposition (hereinafter also referred to as "thermal decomposition solvent"), the boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure represented by the structural formula (100), and the solubility of the carbamate corresponding to the isocyanate at a temperature of 180 ° C. is 2.5 wt% or more. By using an aromatic organic solvent, it has been found that the isocyanate described above can be obtained in a high yield while suppressing the energy consumption during production as much as possible. That is, the method for producing an isocyanate according to the present disclosure A is a method for producing an isocyanate containing an isocyanate having the structure represented by the structural formula (100), and the production method includes a step A of heating a raw material liquid containing a carbamate corresponding to the isocyanate having the structure represented by the structural formula (100) and thermally decomposing the carbamate to obtain the isocyanate. The raw material liquid contains an aromatic organic solvent in which the boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure represented by the structural formula (100), and the solubility of the carbamate at a temperature of 180 ° C. is 2.5 wt% or more. R １００ (NHCOOR １０５ ) ｐ－ｑ (NCO) ｑ (100) (In the structural formula (100), R１００ This is an organic group with a valence p that contains an aromatic ring, and in formula (100) -NHCOOR １０５ The nitrogen atom in the group and the nitrogen atom in the -NCO group are directly bonded to the carbon atoms constituting the aromatic ring in the organic group, p is an integer of 1 or more, and q is an integer between 1 and p, R １０５ Each of these is independently a substituted or unsubstituted hydrocarbon group.

[0042] Patent Document 2 states that, as a solvent, it is preferable to use a solvent that has a higher boiling point than the hydroxy compound produced by the thermal decomposition of carbamate esters and is inert to the resulting isocyanate, and that using a solvent with a higher boiling point than the resulting isocyanate can further suppress the thermal energy required to recover the solvent. However, according to the inventors' research, even when a solvent satisfying these conditions is used in the thermal decomposition process, a large amount of by-products other than hydroxy compound are produced, and the carbamate ester cannot be efficiently converted to isocyanate in some cases. Furthermore, Patent Document 2 does not disclose the use of an aromatic organic solvent as a solvent for producing the isocyanate represented by the above structural formula (100) by thermal decomposition of the corresponding carbamic acid ester, wherein the boiling point B1 of the carbamic acid ester is higher than the boiling point B2 of the isocyanate and the solubility of the carbamic acid ester at 180°C is 2.5 wt% or more. Nor does it suggest that using such an organic solvent would have the effect of producing isocyanate in high yield while minimizing energy consumption during production.

[0043] The boiling point B1 of an aromatic organic solvent is higher than the boiling point B2 of an isocyanate having a structure represented by the structural formula (100), and the solubility of the carbamic acid ester corresponding to the isocyanate at 180 ° C is 2.5 wt% or more. The inventors of the present invention speculate the reason why the above effects can be obtained by using the following method in the thermal decomposition step. First, since the boiling point B1 is an organic solvent higher than the boiling point B2 of the isocyanate, the isocyanate can be recovered from the pyrolysis product containing the isocyanate by evaporating the isocyanate from the pyrolysis product obtained by pyrolysis. Therefore, when recovering the isocyanate from the pyrolysis product, the energy required for the evaporation of the solvent can be reduced, and as a result, the reduction of the CO ２ emission amount can be achieved. Further, since the solubility of the carbamic acid ester is a high organic solvent, the carbamic acid ester, which is the object of thermal decomposition, can be more uniformly present in the raw material liquid. Therefore, it is considered that the generation of by-products other than the hydroxy compound inevitably generated by the thermal decomposition of the carbamic acid ester can be suppressed.

[0044] [Isocyanate] The isocyanate produced in the production method according to the present disclosure A contains at least an isocyanate having a structure represented by the following structural formula (100). R １００ (NHCOOR １０５ ) ｐ－ｑ (NCO) ｑ (100) In the structural formula (100), R １００ is an organic group of valence p containing an aromatic ring, and the nitrogen atom in the -NHCOOR １０５ group and the nitrogen atom in the -NCO group in the formula (100) are each directly bonded to the carbon atom constituting the aromatic ring in the organic group. p ≧ q, p is an integer of 1 or more, preferably 2 or more, and q is an integer of 1 or more and p or less. Further, R １０５ [[ID=​​​​​It can be a group derived from R. １０３ The group derived from is R １０３ The structure may be a group that has been altered under the reaction conditions of thermal decomposition of a carbamic acid ester having the structure shown in structural formula (105) described later, and after thermal decomposition, R １０３ The group may be one in which some of the internal structure, such as the skeleton and functional groups, has been modified. Examples of such structural modifications include halogenation and nitration. Such structural modifications can be carried out, for example, by known methods or similar methods.

[0045] R １００ The organic group with a valence p containing an aromatic ring has a carbon number of typically 6 or more, preferably 8 or more, more preferably 10 or more, and also typically 30 or less, preferably 24 or less, and more preferably 20 or less. In other words, suitable ranges for the carbon number of the aromatic hydrocarbon group include 6 to 24, 8 to 30, and 10 to 20.

[0046] Examples of p-valent organic groups containing aromatic rings include groups obtained by removing any p hydrogen atoms from aromatic rings such as benzene, naphthalene, phenanthrene, anthracene, fluorene, pyrene, and triphenylene. Furthermore, these organic groups may have single bonds or -CH ２ This may also refer to a group in which two or more aromatic rings are connected by linking groups such as -, -O-, and -S-, from which p hydrogen atoms have been removed from any aromatic ring. An example of such a group is a group in which one hydrogen atom has been removed from each of the p benzene rings in poly(phenylenemethylene).

[0047] R １０５ Each of these is independently a hydrocarbon group which may have substituents. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic and may have a carbon-carbon unsaturated bond. -CH in the aliphatic hydrocarbon group ２ - stands for -O-, -S-, or -SO ２They may be substituted with -. Furthermore, the cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group, and heterocyclic group may be monocyclic, polycyclic, or fused cyclic. R １０５ The number of carbon atoms in the hydrocarbon group shown is not particularly limited, but if the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is usually 1 or more, preferably 2 or more, more preferably 3 or more, and usually 30 or less, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. In other words, suitable ranges for the number of carbon atoms in the aliphatic hydrocarbon group include 1 to 10, 1 to 8, 1 to 6, 2 to 30, and 3 to 6.

[0048] R １０５ The unsubstituted aliphatic hydrocarbon groups represented include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, isobutyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, Examples include n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclohexylmethyl group, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, 2-methylallyl group, pentenyl group, isopentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, and their isomers.

[0049] R １０５ When the hydrocarbon group represented is an aromatic hydrocarbon group, its number of carbon atoms is usually 6 or more, preferably 8 or more, and usually 30 or less, preferably 20 or less, and more preferably 10 or less. In other words, suitable ranges for the number of carbon atoms of an aromatic hydrocarbon group include 6 to 10, 6 to 20, and 8 to 30.

[0050] R １０５Examples of unsubstituted aromatic hydrocarbon groups represented by include phenyl group, 1-naphthyl group, 2-naphthyl group, 9-phenantrenyl group, 2-anthracenyl group, 9-anthracenyl group, 9-fluorenyl group, and their isomers.

[0051] R １０５ When the hydrocarbon group represented by has substituents, the substituents include: deuterium atoms; alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl groups; cycloalkyl groups having 3 to 6 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups; methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, isobutoxy, and tert-butoxy groups, etc. Examples include alkoxy groups having 1 to 4 carbon atoms; cycloalkyloxy groups having 3 to 6 carbon atoms, such as cyclopropyloxy, cyclobutoxy, cyclopentyloxy, and cyclohexyl groups; aromatic hydrocarbon groups having 6 to 12 carbon atoms, such as phenyl, 1-naphthyl, and 2-naphthyl groups; heterocyclic groups such as furanyl, thienyl, morpholino, and pyridyl groups; aralkyl groups such as benzyl and 2-phenylethyl groups; halogeno groups such as fluoro, chloro, bromo, and iodo groups; hydroxyl groups; and nitro groups.

[0052] The relationship between p and q is p ≥ q. p is an integer greater than or equal to 1, preferably greater than or equal to 2, and its upper limit is not particularly limited. p is preferably between 1 and 6, more preferably between 1 and 3, even more preferably between 1 or 2, and particularly preferably between 2, in terms of ease of manufacture and handling, and obtaining a highly versatile isocyanate. q is an integer greater than or equal to 1 and less than or equal to p, preferably between 2 and less than or equal to p. q is preferably between 1 and 6, more preferably between 1 and 3, even more preferably between 1 or 2, and particularly preferably between 2. More preferably, as a combination of p and q, p is an integer greater than or equal to 6, particularly 2 or less than or equal to 6, and q is an integer greater than or equal to 6; particularly preferably, p is an integer greater than or equal to 3, particularly 2 or less than or equal to 3, and q is an integer greater than or equal to 3; even more preferably, p is 1 or 2, and q is 1 or 2; and especially preferably, p is 2, and q is 2. Furthermore, in the manufacturing method according to this embodiment, it is preferable that all the carbamate groups of the carbamic acid ester are converted to isocyanate groups, and therefore, it is also preferable that q = p.

[0053] Examples of isocyanates produced by the manufacturing method relating to Disclosure A include monoisocyanates such as o-nitrophenyl isocyanate, m-nitrophenyl isocyanate, p-nitrophenyl isocyanate, o-methoxyphenyl isocyanate, m-methoxyphenyl isocyanate, p-methoxyphenyl isocyanate, ethyl 4-isocyanatobenzoate, 2,6-dimethylphenyl isocyanate, 3,5-dimethylphenyl isocyanate, 1-naphthyl isocyanate, and 2-naphthyl isocyanate; polyisocyanates such as 2,2'-diphenylmethane diisocyanate (2,2'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), and 4,4'-diphenylmethane diisocyanate (4,4'-MDI); and isomers thereof. The isomers include, for example, polynuclear compounds of the various MDIs mentioned above, such as polymeric MDIs.

[0054] The isocyanate produced by the manufacturing method according to Disclosure A includes an isocyanate having the structure shown in structural formula (100). The isocyanate having the structure shown in structural formula (100) preferably includes an isocyanate having the structure shown in structural formula (101), and the isocyanate having the structure shown in structural formula (100) more preferably includes a diisocyanate having the structure shown in structural formula (101). The isocyanate having the structure shown in structural formula (101) preferably includes a diisocyanate having the structure shown in structural formula (102), and more preferably is a diisocyanate having the structure shown in structural formula (102).

[0055]

[0056] In structural formula (101), s and t each represent 0 or 1, where s + t = 1. １０１ This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.

[0057]

[0058] The diisocyanate represented by structural formula (102) is generally diphenylmethane diisocyanate (hereinafter sometimes referred to as "MDI"), and includes, for example, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI.

[0059] [Carbamic Acid Ester] The isocyanate represented by structural formula (100) is obtained by converting at least one of the carbamate groups of the carbamic acid ester corresponding to the isocyanate to an isocyanate group. The carbamic acid ester corresponding to the isocyanate is not particularly limited as long as it gives an isocyanate represented by structural formula (100) by thermal decomposition, preferably an isocyanate in which p is 2 or more and q is 1 or more. Examples of such carbamic acid esters include the carbamic acid ester having the structure shown in structural formula (105). R １０３ (NHCOOR １０５ ) ｐ(105) In structural formula (105), R １０３ This is due to the thermal decomposition of the carbamic acid ester, which produces R in the structural formula (100). １００ It is a group that gives, specifically, for example, R １００ It can be the same group as p and R. １０５ This is synonymous with the structural formula (100) described above.

[0060] Furthermore, a preferred example of a carbamic acid ester having the structure shown in structural formula (105) is the carbamic acid ester shown in the following structural formula (103).

[0061]

[0062] In structural formula (103), R ０１ and R ０２ Each of these independently represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms. Specifically, R ０１ , and R ０２ Each of these can be independently selected from the group consisting of a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. Among these, R ０１ and R ０２ It is particularly preferable that it be a methyl group. ０１ and R ０２ When both are methyl groups, the hydroxy compound produced as a by-product by the thermal decomposition of the carbamic acid ester is methanol, which has a low boiling point, making it easy to remove from the reaction system as a gas. The reaction to obtain isocyanate by thermal decomposition of carbamic acid ester is an equilibrium reaction between the generated isocyanate and the by-product hydroxy compound, so isocyanate can be produced more efficiently by removing the by-product hydroxy compound from the reaction system. Furthermore, making the by-product methanol, which is easy to remove from the reaction system as a gas, allows for more efficient production of isocyanate. In addition, since methanol has a large difference in boiling point from the isocyanate shown in structural formula (101), the separation of methanol and isocyanate becomes easier.０１ , and R ０２ An example of a carbamic acid ester in which both are methyl groups is methylenediphenyl 4,4'-dimethylcarbamate (hereinafter also referred to as "MDC-Me").

[0063] [Catalyst] The thermal decomposition of carbamic acid esters is preferably carried out in the presence of at least one compound (catalyst) selected from the group consisting of fatty acid metal salts and phosphate metal salts, and more preferably in the presence of a fatty acid metal salt.

[0064] (Fatty acid metal salts) Fatty acid metal salts are compounds represented by general formula (IA) or general formula (IB). Fatty acid metal salts may also be hydrates. (R １１ COO) ｎ１ M １１ (IA) (R １２ COO) ｎ２ M １２ (IB)

[0065] In general formula (IA), M １１ These are Group 1 metals, Group 2 metals, Group 13 metals, or lanthanide metals of the periodic table. Of these, M １１ It is preferably a Group 2 metal of the periodic table, a Group 13 metal of the periodic table, or a lanthanide metal, more preferably magnesium, calcium, strontium, barium, aluminum, or cerium, and even more preferably magnesium, aluminum, or cerium. Furthermore, it is possible to more reliably suppress the generation of by-products such as allophanates and isocyanurates due to side reactions such as allophanate formation and polymerization of isocyanates, １１ It is preferably a metal from Group 13 of the periodic table, and more preferably aluminum. On the other hand, from the viewpoint of high catalytic activity, M １１ n1 is preferably a Group 2 or Group 13 metal of the periodic table, more preferably magnesium or aluminum, and even more preferably aluminum. In general formula (IA), n1 is M １１ The valence of is preferably an integer between 1 and 4.

[0066] In general formula (IA), R １１ This is an alkyl group having 1 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms, preferably an alkyl group having 1 to 40 carbon atoms. That is, the fatty acid metal salt that acts as the catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to a linear form; they may have a branched structure or a cyclic structure, but are preferably linear in that they have high catalytic activity and are readily available. Furthermore, the number, position, and bonding mode (i.e., geometric isomerism) of carbon-carbon double bonds in the alkenyl group are not particularly limited. １１ The number of carbon atoms in the alkyl group represented by is preferably 2 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １１ Preferred ranges for the number of carbon atoms in the alkyl group represented by include, for example, 1 to 36, 2 to 40, 12 to 40, 12 to 32, and 16 to 28.

[0067] R １１The alkyl groups that can be represented include, specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, isobutyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, Examples include n-henicosyl group, n-docosyl group, n-tricosyl group, n-tetracosyl group, n-pentacosyl group, n-hexacosyl group, n-heptacosyl group, n-octacosyl group, n-nonacosyl group, n-triacontyl group, n-hentriacontyl group, n-dotriacontyl group, n-tritriacontyl group, n-tetratriacontyl group, n-pentatriacontyl group, n-hexatriacontyl group, n-heptatriacontyl group, n-octatriacontyl group, n-nonatriacontyl group, n-tetracontyl group, and their isomers.

[0068] R １１ The number of carbon atoms in the alkenyl group represented by is usually between 2 and 40, and is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １１ Preferred ranges for the number of carbon atoms of the alkyl and alkenyl groups represented by the formula include, for example, 2 to 36, 8 to 40, 12 to 40, 12 to 36, 16 to 32, and 16 to 28.

[0069] R １１The alkenyl groups represented by include, specifically, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, 2-methylallyl group, pentenyl group, isopentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, undecenyl group, dodecenyl group, tridecenyl group, tetradecenyl group, pentadecenyl group, hexadecenyl group, heptadecenyl group, heptadedecenyl group, heptadedecaneyl group, heptadedecaterinyl group, octadecenyl group, nonadecenyl group, nonadedeceteraenyl group, nonadedecaterinyl group, icosenyl Examples include the yl group, henicocenyl group, henicosahexaenyl group, dococenyl group, tricocenyl group, tetracocenyl group, pentacocenyl group, hexacocenyl group, heptacocenyl group, octacocenyl group, nonacocenyl group, triacontenyl group, hentriacontenyl group, dotriacontenyl group, tritriacontenyl group, tetratriacontenyl group, pentacontenyl group, hexatriacontenyl group, heptacontenyl group, octacontenyl group, nonatriacontenyl group, tetracontenyl group, and their isomers.

[0070] In general formula (IB), M １２ These are metals from groups 3 to 11 of the periodic table or zinc. Of these, M １２ It is preferable that the catalytic activity is high, and that it is a fourth-period or fifth-period metal, more preferably scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, or silver, and even more preferably iron, cobalt, nickel, copper, or zinc. Furthermore, it is preferable that it is a metal with a good balance of high catalytic activity, low toxicity of fatty acid metal salts, and the ability to suppress the generation of by-products such as allophanates and isocyanurates due to side reactions such as allophanate formation and polymerization of isocyanates. １２ It is preferably a metal from groups 8 to 11 of the periodic table or zinc, and more preferably a metal from group 8 of the periodic table, a metal from group 9 of the periodic table, or zinc. More specifically, M １２is preferably iron, cobalt, nickel, copper, or zinc, more preferably iron, cobalt, or zinc, and even more preferably zinc. In general formula (IB), n2 is M １２ The valence of is preferably an integer between 1 and 6.

[0071] In general formula (IB), R １２ The group is an alkyl group having 10 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms, preferably an alkyl group having 10 to 40 carbon atoms. That is, the fatty acid metal salt that acts as a catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but it is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to a linear form, and may have a branched structure or a cyclic structure, but a linear form is preferred because it has high catalytic activity and is readily available. Furthermore, the number, position, and bonding mode (i.e., geometric isomerism) of carbon-carbon double bonds in the alkenyl group are not particularly limited.

[0072] R １２ The number of carbon atoms in the alkyl group represented by is preferably 12 or more, more preferably 14 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １２ Preferred ranges for the number of carbon atoms of the alkyl group represented by include, for example, 10 to 36, 12 to 40, 14 to 32, and 16 to 28. １２ The alkyl group represented by R is １１ Examples of alkyl groups represented by include those with 10 or more carbon atoms.

[0073] R １２ The number of carbon atoms in the alkenyl group represented by is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １２Preferred ranges for the number of carbon atoms in the alkenyl group represented by include, for example, 2 to 36, 8 to 40, 12 to 32, and 16 to 28. １２ The alkenyl group represented by R is １１ Examples of alkenyl groups represented by this symbol include the following:

[0074] In summary, examples of fatty acid metal salts include salts of fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, erucic acid, linoleic acid, alpha-linolenic acid, gamma-linolenic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, which are salts of the aforementioned metals.

[0075] Specific examples of fatty acid metal salts include cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, nickel laurate, copper laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, nickel stearate, copper stearate, zinc stearate, aluminum stearate, and stearyl stearate. Examples include cerium palmitate, magnesium palmitate, calcium palmitate, strontium palmitate, barium palmitate, iron palmitate, cobalt palmitate, nickel palmitate, copper palmitate, zinc palmitate, aluminum palmitate, cerium palmitate, magnesium oleate, calcium oleate, strontium oleate, barium oleate, iron oleate, cobalt oleate, nickel oleate, copper oleate, zinc oleate, aluminum oleate, and cerium oleate. Of these, the fatty acid metal salt is preferably cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, and cerium stearate, and is particularly preferably cerium acetate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, and cerium stearate.

[0076] The fatty acid metal salt may be a commercially available product, or it may be synthesized by a known manufacturing method or a similar method, for example, by a neutralization reaction between a fatty acid and a base containing the above metal.

[0077] (Metal Phosphate Salts) Metal phosphate salts used as catalysts in the thermal decomposition process are represented by the following general formula (IC). Metal phosphate salts may also be hydrates. (M １３ ) ｍ (PO ４ ) ｎ３ (IC)

[0078] In the general formula (IC), M １３ These are metals from groups 1 to 11 of the periodic table, metals from group 13 of the periodic table, zinc, or lanthanide metals. In the general formula (IC), m and n3 are M １３ The valence × m = 3 × n3 is satisfied. m and n3 are preferably the smallest values ​​among the values ​​that satisfy the above formula, for example, M １３ If it is trivalent cerium, then m is 1 and n3 is 1.

[0079] Examples of metal phosphate salts include sodium phosphate, potassium phosphate, magnesium phosphate, calcium phosphate, barium phosphate, zinc phosphate, aluminum phosphate, and cerium phosphate.

[0080] Generally, homogeneous catalysts exhibit higher catalytic activity than heterogeneous catalysts. Therefore, in this embodiment, when thermal decomposition is carried out in a solvent, it is preferable to select a catalyst that is highly soluble in the solvent and is liquid under the reaction conditions, and when thermal decomposition is carried out without a solvent, it is preferable to select a catalyst that is liquid under the reaction conditions. From this viewpoint, the catalyst used in the thermal decomposition step is preferably a fatty acid metal salt represented by general formula (IA) or general formula (IB), and is represented by general formula (IA), R １１ R is a long-chain fatty acid metal salt in which is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms, or is represented by the general formula (IB), １２ It is more preferable that the long-chain fatty acid metal salt is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms.

[0081] The catalyst may be used alone, or two or more may be used in any combination and ratio. The amount of catalyst used in the pyrolysis step should be appropriately selected depending on the type of carbamic acid ester, the type of catalyst, and the reaction conditions. When multiple types of catalysts are used, the catalyst amount refers to the total amount. Specifically, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is 100.0 mol%) is not particularly limited, but is preferably 0.01 mol% or more, more preferably 0.1 mol% or more, particularly preferably 0.3 mol% or more, preferably 20.0 mol% or less, more preferably 10.0 mol% or less, particularly preferably 5.0 mol% or less, and even more preferably 1.5 mol% or less. In other words, the range of the catalyst amount is preferably, for example, 0.01 mol% to 20.0 mol%, more preferably 0.1 mol% to 10.0 mol%, particularly preferably 0.3 mol% to 5.0 mol%, and even more preferably 0.3 mol% to 1.5 mol%.

[0082] Alternatively, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is 100% by mass) is not particularly limited, but is preferably 0.02% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.6% by mass or more, and also preferably 40.0% by mass or less, more preferably 20.0% by mass or less, particularly preferably 10.0% by mass or less, and even more preferably 3.0% by mass or less. That is, the range of the catalyst amount is, for example, preferably 0.02% by mass or more and 40.0% by mass or less, more preferably 0.2% by mass or more and 20.0% by mass or less, particularly preferably 0.6% by mass or more and 10.0% by mass or less, and even more preferably 0.6% by mass or more and 3.0% by mass or less.

[0083] [Solvent for thermal decomposition] The solvent for thermal decomposition must be an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate represented by structural formula (100), and whose solubility at 180°C of the carbamic acid ester is 2.5 wt% or more. By including such an organic solvent in the raw material solution, the carbamic acid ester dissolves well in the raw material solution, resulting in a more homogeneous reaction system. As a result, the generation of by-products other than hydroxyl compounds is suppressed. Furthermore, separation of the isocyanate from the organic solvent from the reaction product only requires the volatilization of the isocyanate, eliminating the need for energy to volatilize the thermal decomposition solvent. As a result, isocyanate can be produced more efficiently.

[0084] The boiling point B1 of the above organic solvent must be higher than the boiling point B2 of the isocyanate represented by the structural formula (100), and B1 is preferably 10°C or more higher than B2 (B1 + 10°C ≥ B2), and more preferably 40°C or more higher than B2 (B1 + 40°C ≥ B2). Furthermore, the solubility of the carbamic acid ester at a temperature of 180°C in the above organic solvent must be 2.5 wt% or more, preferably 3.0 wt% or more, and more preferably 4.0 wt% or more. The upper limit of the solubility is not particularly limited, but for example, it is preferably 30.0 wt% or less, more preferably 20.0 wt% or less, and particularly preferably 15.0 wt% or less. In other words, the solubility is preferably 2.5 wt% or more and 30.0 wt% or less, more preferably 3.0 wt% or more and 20.0 wt% or less, and particularly preferably 4.0 wt% or more and 15.0 wt% or less.

[0085] The solubility in this disclosure is measured by either Method 1 or Method 2 below. <Method 1 for measuring solubility> If the carbamate ester has a melting point of 180°C or higher, the solubility is measured using a high-temperature filtration device (manufactured by Senshu Science) and a polytetrafluoroethylene membrane filter with a pore size of 0.5 μm (model: T050A025A, manufactured by Advantec), following the steps (1) to (8) below. (1) Accurately weigh 4 g of carbamate ester and place it in a screw-cap vial. (2) Add 4 g of the solvent to be evaluated to the screw-cap vial containing the sample. (3) Heat the screw-cap vial to bring the temperature of the contents of the screw-cap vial to 180°C. (4) Add 0.1 g of carbamate ester to the screw-cap vial and shake the vial. Continue this operation until the contents of the screw-cap vial are no longer visibly transparent. (5) When the contents of the screw-cap bottle are no longer transparent, stop adding the carbamate ester, transfer the entire contents of the screw-cap bottle to a high-temperature filtration apparatus, and filter while hot. (6) Allow the residue to cool to room temperature (25°C), wash with a poor solvent (hexane, etc.), and then let stand until the poor solvent has completely evaporated. (7) Weigh the dried residue accurately and determine the mass of the residue (b). (8) Calculate the solubility of the carbamate ester in the solvent to be measured at a temperature of 180°C using the following calculation formula (1). In the calculation formula (1) below, "a" is the total amount of carbamate ester added to the screw-cap bottle until the contents of the screw-cap bottle are no longer visibly transparent. <Calculation formula (1)> Solubility (wt%) = [(a - b) / (amount of solvent + (a - b))] × 100

[0086] <Method for Measuring Solubility 2> When a carbamic acid ester has a melting point of 180°C or lower, particularly below 180°C, the solubility shall be defined as the maximum sample concentration at which the sample (carbamic acid ester) to be measured is completely dissolved by visual inspection. Here, complete dissolution means a state in which no insolubility or bilayer separation of the sample is observed by visual inspection.

[0087] The melting points of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) are 180°C, methylenediphenyl 4,4'-diethylcarbamate (MDC-Et) are 134°C, methylenediphenyl 4,4'-dibutylcarbamate (MDC-Bu) are 110°C, and hexanemethylenedimethylcarbamate (HDC-Me) is 98°C. When measuring the solubility of MDC-Me using the above measurement method 1, two-layer separation may be visually observed during the heating process depending on the solvent. In that case, the solubility should be determined according to the above measurement method 2.

[0088] The aromatic organic solvent according to Disclosure A is not particularly limited as long as its boiling point B1 is higher than the boiling point B2 of the isocyanate represented by structural formula (100), and the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. Specific examples of aromatic organic solvents include, for example, an aromatic organic solvent having the structure represented by structural formula (106). Ar-(R １０６ ) ｎ１０６ (106) In structural formula (106), Ar represents an aryl group, R １０６ is a C1-C30 hydrocarbon group which may contain an aromatic ring. n106 is an integer of 1 or more and is less than or equal to the valency of the aryl group. Here, the aryl group may be, for example, a phenyl group, a naphthyl group, or a single bond, -CH ２Examples include groups in which two or more aromatic rings are connected by linking groups such as -, -O-, and -S-, and which have p hydrogen atoms removed from any aromatic ring (e.g., a biphenyl group). Examples of C1-C30 hydrocarbon groups that may contain aromatic rings include C1-C30 linear or branched alkyl groups and benzyl groups. In particular, organic solvents containing at least two benzene rings or at least one naphthalene ring in the structure shown by structural formula (106) are preferred. Specific examples of aromatic organic solvents having the structure shown by structural formula (106) include alkylnaphthalene, dibenzyltoluene, and dialkylbenzene. The organic solvent is more preferably one selected from the group consisting of alkylnaphthalene and dibenzyltoluene, provided that the boiling point B1 and the solubility at a temperature of 180°C for the carbamic acid ester to be thermally decomposed satisfy the above requirements.

[0089] As described above, the aromatic organic solvent according to Disclosure A must have a solubility of 2.5 wt% or more of the carbamic acid ester at a temperature of 180°C. Therefore, the solvent should be appropriately selected depending on the type of carbamic acid ester used for thermal decomposition. That is, the carbamic acid ester used for thermal decomposition has the structure shown in structural formula (103), and R ０１ and R ０２When the compound is methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me), where the compound is a methyl group, specific examples of solvents that have a solubility of 2.5 wt% of MDC-Me at 180°C include alkylnaphthalenes and dibenzyltoluene. Such alkylnaphthalenes can be commercially available, for example, as "Barrel Process Oil B-28AN" (trade name, manufactured by Matsumura Petroleum Co., Ltd.). "Barrel Process Oil B-28AN" has a boiling point of 380°C, which is higher than the boiling point of methylenediphenyl 4,4'-diisocyanate (MDI) (314°C), and the solubility of methylenediphenyl 4,4'-dimethylcarbamate at 180°C is 6.9 wt%. Furthermore, dibenzyltoluene is a compound represented by structural formula (104), with a boiling point of 391°C, which is higher than the boiling point of MDI, and the solubility of the above carbamic acid ester at a temperature of 180°C is 55 wt%.

[0090]

[0091] On the other hand, for example, the boiling point of high-viscosity liquid paraffin (manufactured by Nacalai Tesque) (high-viscosity type) is 400°C or higher, and the solubility of MDC-Me is less than 1.2 wt% at 180°C and about 2.3 wt% at 230°C. Furthermore, as shown in Comparative Example 1 later, when the above liquid paraffin was used as the solvent for the thermal decomposition of MDC-Me, a large amount of by-products other than hydroxyl compounds were generated. The reason for this is thought to be that even at temperatures in the thermal decomposition process, for example, around 230°C, the solubility of carbamic acid ester in liquid paraffin is insufficient, resulting in an uneven distribution of carbamic acid ester in the raw material liquid. In addition, alkylbenzene (product name: Barrel Process Oil B-15AB, manufactured by Matsumura Petroleum Co., Ltd.) has a boiling point of 352°C, and the solubility of MDC-Me is 2.3 wt% at 180°C. Therefore, if alkylbenzene is used as the solvent for the thermal decomposition of MDC-Me, the results are likely to be similar to those of liquid paraffin.

[0092] The solvent may be used alone or in combination of two or more. Specifically, for example, the above-mentioned "Barrel Process Oil B-28AN" or dibenzyltoluene may be used alone, or a mixture thereof may be used. However, when the solvent is a mixture, the boiling point (B1) of the mixture must be higher than the boiling point B2 of the isocyanate, and the solubility of the carbamic acid ester at 180°C must be 2.5 wt% or more.

[0093] [Composition (Raw Material Liquid)] The composition used as a raw material liquid in the method for producing isocyanate according to Disclosure A comprises a carbamic acid ester corresponding to an isocyanate having the structure shown in structural formula (100) and an aromatic solvent. The boiling point B1 of the composition is higher than the boiling point B2 of the isocyanate shown in structural formula (100). The aromatic solvent has a solubility of 2.5 wt% or more of the carbamic acid ester at a temperature of 180°C. The carbamic acid ester is preferably a carbamic acid ester having the structure shown in structural formula (105), and more preferably a carbamic acid ester having the structure shown in structural formula (103).

[0094] The content ratio of the carbamic acid ester corresponding to the isocyanate having the structure shown by structural formula (100) in the composition according to Disclosure A is not particularly limited, but is preferably 1 to 25% by mass, and particularly preferably 5 to 15% by mass. The content ratio of the organic solvent in the composition is not particularly limited, but is preferably 75 to 99% by mass, and particularly preferably 85 to 95% by mass.

[0095] [Reaction Temperature] The reaction temperature in the thermal decomposition step is not particularly limited as long as it is a temperature at which the carbamic acid ester used as a raw material can be thermally decomposed and isocyanate can be produced, and is usually between 100°C and 300°C. From the viewpoint of increasing the reaction rate while suppressing side reactions, it is preferable to set the temperature between 150°C and 280°C, more preferably between 180°C and 260°C, and particularly preferably between 200°C and 240°C.

[0096] [Reaction Time] The reaction time in the thermal decomposition step is not particularly limited and can be appropriately adjusted depending on the type of catalyst, reaction temperature, and reaction scale. Specifically, the reaction time is preferably 0.5 hours or more and 60.0 hours or less, more preferably 1.0 hour or more and 48.0 hours or less, even more preferably 2.0 hours or more and 36.0 hours or less, even more preferably 3.0 hours or more and 24.0 hours or less, and particularly preferably 4.0 hours or more and 12.0 hours or less. Alternatively, the reaction time may be 0.5 hours or more and 48.0 hours or less, 1.0 hour or more and 24.0 hours or less, or 2.0 hours or more and 12.0 hours or less. By keeping the reaction time within the above range, the thermal decomposition of the carbamic acid ester can be sufficiently carried out, and side reactions such as allophanate formation and polymerization of the generated isocyanate can be suppressed.

[0097] [Operating Procedure] The method for producing isocyanate according to Disclosure A will be explained with reference to Figure 1. The isocyanate production apparatus 100 shown in Figure 1 is one embodiment of a production apparatus that can be used in the method for producing isocyanate according to Disclosure A, and is not limited to the method produced by the production apparatus embodied in Figure 1. First, a composition containing a carbamic acid ester, a catalyst, and a thermal decomposition solvent according to Disclosure A is placed as a raw material liquid 104 in a reaction vessel 103 equipped with a stirring device 102. The inside of the reaction vessel 103 may be an air atmosphere, or an inert gas atmosphere such as nitrogen and argon, but it is preferable to carry out the thermal decomposition reaction in an inert gas atmosphere. For example, it is preferable to replace the inside of the reaction vessel 103 with an inert gas atmosphere by introducing an inert gas from line 101 into the reaction vessel 103 and discharging it from line 105. Next, the obtained reaction solution is heated to a predetermined temperature to perform thermal decomposition of the carbamic acid ester. At this time, it is preferable to stir the raw material liquid 104 in the reaction vessel 103. The method of stirring the reaction solution is not particularly limited, and known stirring methods can be used. For example, a stirring device 102 using a stirring blade as shown in Figure 1, or a magnetic stirring bar (not shown) can be used. This allows the carbamate ester in the raw material solution to be uniformly dissolved by the thermal decomposition solvent.

[0098] In the thermal decomposition process, it is preferable to include a step of continuously or intermittently removing the hydroxy compounds produced as by-products by thermal decomposition from the reaction vessel 103. This can accelerate the reaction that produces isocyanates by thermal decomposition of carbamic acid esters, which is an equilibrium reaction. The method of removing the hydroxy compounds from the reaction vessel 103 is not particularly limited, but in the manufacturing apparatus 100 shown in Figure 1, a line 105 connected to a vacuum pump 109 is connected to the reaction vessel 103, and the hydroxy compounds produced as by-products in the reaction vessel 103 can be removed by reducing the pressure inside the reaction vessel 103 by the operation of the vacuum pump 109. On the other hand, a condenser 107 is connected to line 105, and even if the isocyanates produced in the reaction vessel 103 are removed from the reaction vessel 103 to line 105 as a gaseous component, they can be condensed in the condenser 107 and refluxed back into the reaction vessel 103. The hydroxy compounds extracted as gaseous components via line 105 are not condensed in condenser 107, but are condensed in condenser 111 and stored in storage tank 113. For condensers 107 and 111, for example, reflux pipes can be used. When a reflux pipe is used as condenser 107, the reflux pipe may be an air-cooled reflux pipe or a reflux pipe that uses water or the like as a refrigerant. The pressure inside the reaction vessel is not particularly limited as long as the hydroxy compounds produced as by-products in reaction vessel 103 can be extracted as gaseous components and the isocyanate can be reliably condensed in condenser 107, and can be set appropriately according to the reaction solvent type and reaction temperature. Specifically, the pressure inside the reaction vessel is preferably, for example, 0.1 kPaA or more and 20.0 kPaA or less, more preferably 0.5 kPaA or more and 20.0 kPaA or less, and particularly preferably 1.0 kPaA or more and 20.0 kPaA or less.

[0099] Furthermore, the method for producing isocyanate according to this embodiment may include any other steps besides the thermal decomposition step. An example of an optional step is a purification step to increase the purity of the isocyanate. As a method for purifying the isocyanate in the purification step, commonly used purification methods in the field of organic synthesis, such as filtration, adsorption, column chromatography, and distillation, can be employed.

[0100] [Disclosure B] The embodiments of Disclosure B will be described below, but the present invention is not limited to the embodiments described below and can be implemented in various ways within the scope of its gist. In this specification, expressions representing numerical ranges, such as "XX or more," "YY or less," and "XX to YY," mean numerical ranges that include the endpoints XX and YY, unless otherwise specified. When numerical ranges are described in steps, any combination of the upper and lower limits of each numerical range is also disclosed. Furthermore, in this specification, for example, "at least one selected from the group consisting of XX, YY, and ZZ" means either XX only, YY only, ZZ only, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Furthermore, in this specification, when descriptions such as "one aspect" or "one aspect" appear multiple times, they do not necessarily refer to the same aspect, but may refer to different aspects.

[0101] The present inventors have been conducting extensive research on a method for producing isocyanate by heating a raw material solution containing a carbamic acid ester corresponding to an isocyanate having the structure shown in structural formula (1B) and thermally decomposing the carbamic acid ester. ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1B) Note that in structural formula (1B), R ３１ R is an organic group with valency p, where p is an integer greater than or equal to 1, and q is an integer greater than or equal to 1 and less than or equal to p. ２２ Each of these is independently a substituted or unsubstituted hydrocarbon group.

[0102] As a result, it was found that high-purity diisocyanate can be efficiently obtained from carbamic acid ester by the following method. That is, a method for producing isocyanate according to one aspect of the present disclosure B is a method for producing isocyanate having the structure shown in the above structural formula (1B), comprising step 1B of obtaining the isocyanate by heating a liquid containing a raw material solution containing a carbamic acid ester corresponding to the isocyanate in a reaction vessel and thermally decomposing the carbamic acid ester, wherein step 1B comprises step 1B-1 of continuously withdrawing the isocyanate generated in the reaction vessel by thermal decomposition of the carbamic acid ester from the reaction vessel, and step 1B-2 of continuously withdrawing the hydroxy compound produced as a by-product in the reaction vessel by thermal decomposition of the carbamic acid ester from the reaction vessel, wherein the raw material solution contains an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate, and whose solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more.

[0103] As described above, in the pyrolysis process according to Disclosure B, an aromatic organic solvent is used as the solvent (hereinafter also referred to as the "thermolysis solvent"), wherein the boiling point B1 is higher than the boiling point B2 of the isocyanate, and the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. By using such a pyrolysis solvent, the isocyanate obtained from the pyrolysis product containing the isocyanate obtained by the pyrolysis of the carbamic acid ester can be recovered efficiently. That is, since the boiling point of the isocyanate is lower than the boiling point of the pyrolysis solvent, the isocyanate can be separated from the pyrolysis organic solvent by withdrawing it from the reaction vessel as a gas phase component, and there is no need to reflux the pyrolysis solvent when recovering the isocyanate, and the thermal energy required to heat the pyrolysis solvent to its boiling point is not required. As a result, CO2 is not produced during the production of the isocyanate. ２ This will make it possible to reduce emissions.

[0104] Furthermore, because the organic solvent has high solubility for carbamic acid esters, the carbamic acid esters, which are the target of thermal decomposition, can be distributed more uniformly within the raw material solution. Therefore, it is believed that the generation of by-products other than hydroxy compounds, which are inevitably produced by the thermal decomposition of the carbamic acid esters, is suppressed.

[0105] Furthermore, the above manufacturing method includes step 1B-1, in which the isocyanate generated in the reaction vessel is continuously withdrawn from the reaction vessel, and step 1B-2, in which the hydroxy compound produced as a by-product in the reaction vessel is continuously withdrawn from the reaction vessel. This allows the equilibrium to be shifted to the right in the equilibrium reaction, for example, in the equilibrium reaction shown in the following equilibrium equation (I), in which a carbamic acid ester is thermally decomposed to obtain an isocyanate, thereby enabling the isocyanate to be produced more efficiently.

[0106]

[0107] In the above equilibrium reaction equation (I), R ２１ , R ２２ , R ３１ , p, and q are R in structural formula (1B), respectively. ２２ , R ３１ It is synonymous with p and q, and also R ２１ This is R in the structural formula (2B) described later. ２１ It is synonymous with [the above].

[0108] Furthermore, according to the manufacturing method of this embodiment, the period in which the carbamic acid ester and the by-product hydroxy compound and / or isocyanate coexist in the reaction vessel can be shortened, thereby suppressing the occurrence of the reverse reaction. For these reasons, it is believed that the method for producing isocyanate according to this embodiment can convert carbamic acid ester to isocyanate more efficiently.

[0109] Here, Patent Document 2 states that, as a solvent, it is preferable to use a solvent that has a higher boiling point than the hydroxy compound produced by the thermal decomposition of carbamate esters and is inert to the isocyanate produced, and that when a thermal decomposition solvent having a higher boiling point than the isocyanate produced is used, the thermal energy required to recover the solvent can be further suppressed.

[0110] However, according to the inventors' studies, even when a solvent satisfying these conditions is used in the thermal decomposition step, a large amount of by-products other than hydroxy compounds are produced, and the carbamic acid ester cannot be efficiently converted to isocyanate in some cases. Furthermore, Patent Document 2 does not disclose the use of an aromatic organic solvent as a solvent for producing the isocyanate represented by the above structural formula (1B) by thermal decomposition of the corresponding carbamic acid ester, wherein the boiling point B1 is higher than the boiling point B2 of the isocyanate and the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. Also, Patent Document 2 does not disclose the continuous withdrawal of the isocyanate and hydroxy compounds produced in the reaction vessel from the reaction vessel. Moreover, Patent Document 2 does not suggest that using the above-mentioned specific solvent in the thermal decomposition step, along with a step of continuously withdrawing the isocyanate and hydroxy compounds from the reaction vessel in the thermal decomposition step, can yield high-purity isocyanate in high yield.

[0111] [Isocyanates and Carbamic Acid Esters] The manufacturing method according to Disclosure B relates to a method for producing an isocyanate represented by the following structural formula (1B) by thermal decomposition of a carbamic acid ester having a structure corresponding to the isocyanate. ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1B)

[0112] In structural formula (1B), R ３１ is a p-valent organic group, R ２２Each of these is independently a substituted or unsubstituted hydrocarbon group, where p ≥ q, p is an integer of 1 or more, preferably 2 or more, and q is an integer of 1 or more and less than or equal to p.

[0113] <Carbamic Acid Esters> The carbamic acid ester having a structure corresponding to the isocyanate, which is a raw material for the isocyanate having the structure shown in structural formula (1B), is not particularly limited as long as it can produce the isocyanate by thermal decomposition. Such carbamic acid esters may be commercially available products, or may be obtained by known manufacturing methods or manufacturing methods similar to known manufacturing methods. Examples of known manufacturing methods for carbamic acid esters include the methods described in Japanese Patent Publication No. 2021-191742, Japanese Patent Publication No. 2022-022652, or Japanese Patent Publication No. 2022-171090.

[0114] A specific example of a carbamic acid ester related to Disclosure B is, for example, a carbamic acid ester having the structure shown in structural formula (2B). In Disclosure B, unless otherwise specified, if a symbol in one general formula is also used in another general formula, the definition of that symbol is the same in both general formulas. R ２１ (NHCOOR ２２ ) ｐ (2B) In structural formula (2B), R ２１ is a p-valent organic group, R ２２ , and p are R in structural formula (1), respectively. ２２ It is synonymous with p.

[0115] R ２１ It may have a carbamic acid ester group (-NHCOO-), but it is preferable that it does not.

[0116] R ２１The p-valent organic group is not particularly limited, but examples include substituted or unsubstituted hydrocarbon groups, substituted or unsubstituted heterocyclic groups, etc. The hydrocarbon group may be, for example, an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic, and may have a carbon-carbon unsaturated bond. Furthermore, the -CH in the aliphatic hydrocarbon group ２ - stands for -O-, -S-, or -SO ２ It may be substituted with -. Also, the cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group, and heterocyclic group may be monocyclic, polycyclic, or fused cyclic. Of these, the organic group is preferably a hydrocarbon group, and more preferably an aromatic hydrocarbon group. The carbamic acid ester having the structure shown in structural formula (2B) is particularly R ２１ is an aromatic hydrocarbon group, that is, an organic group with a valence p containing a substituted or unsubstituted aromatic ring, and in structural formula (2B) -NHCOOR ２２ It is preferable that the nitrogen atom in the group is directly bonded to the carbon atom constituting the aromatic ring in the organic group. The reason for this will be explained later.

[0117] The number of carbon atoms in the hydrocarbon group is not particularly limited, but if the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is preferably 1 or more, more preferably 2 or more, more preferably 4 or more, and particularly preferably 6 or more. Furthermore, the upper limit is preferably 30 or less, more preferably 24 or less, particularly preferably 16 or less, and especially preferably 12 or less. In other words, the range of carbon atoms in an aliphatic hydrocarbon group is preferably 1 to 24, more preferably 2 to 30, particularly preferably 4 to 16, and particularly preferably 6 to 12. In Disclosure B, the number of carbon atoms in a hydrocarbon group or heterocyclic group includes the number of carbon atoms of the substituent if the hydrocarbon group or heterocyclic group has substituents.

[0118] Examples of unsubstituted aliphatic hydrocarbon groups include groups obtained by removing any p hydrogen atoms from alkanes such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, and n-eicosane; groups obtained by removing any p hydrogen atoms from cycloalkanes such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, and adamantane; and groups obtained by removing any p hydrogen atoms from alkenes such as ethylene, propylene, butylene, isobutylene, 1-hexene, and 1-octene.

[0119] R ２１ When the hydrocarbon group represented is an aromatic hydrocarbon group, its number of carbon atoms is usually 6 or more, preferably 8 or more, more preferably 10 or more, and usually 30 or less, preferably 24 or less, more preferably 20 or less. In other words, suitable ranges for the number of carbon atoms of an aromatic hydrocarbon group include 6 to 24, 8 to 30, and 10 to 20.

[0120] Unsubstituted aromatic hydrocarbon groups include groups obtained by removing any p hydrogen atoms from aromatic rings such as benzene, naphthalene, phenanthrene, anthracene, fluorene, pyrene, and triphenylene. Aromatic hydrocarbon groups can also be single-bonded, -CH ２ The group may be one obtained by removing any p hydrogen atoms from a compound in which multiple cyclic compounds are linked by linking groups such as -, -O-, and -S-. An example of such a group is one obtained by removing one hydrogen atom from each of the p benzene rings in poly(phenylenemethylene).

[0121] R ２１The number of carbon atoms in the heterocyclic group represented by is not particularly limited, but is usually 3 or more, preferably 5 or more, more preferably 10 or more, and also usually 30 or less, preferably 24 or less, more preferably 20 or less. In other words, suitable ranges for the number of carbon atoms in the heterocyclic group include 3 to 24, 5 to 30, and 10 to 20.

[0122] Examples of unsubstituted heterocyclic groups include groups obtained by removing any p hydrogen atoms from nitrogen-containing heterocycles such as pyrrolidone, imidazole, pyridine, pyrimidine, triazine, quinoline, phenazine, and carbazole; groups obtained by removing any p hydrogen atoms from oxygen-containing heterocycles such as tetrahydrofuran, furan, dioxane, tetrahydropyran, benzofuran, and dibenzofuran; groups obtained by removing any p hydrogen atoms from sulfur-containing heterocycles such as tetrahydrothiophene, thiophene, sulfolane, thian, trithiane, benzothiophene, and dibenzothiophene; and groups obtained by removing any p hydrogen atoms from heterocycles containing multiple heteroatoms such as oxazole, thiazole, morpholine, phenoxazine, phenothiazine, and phenoxathiin.

[0123] R ２１When a hydrocarbon group or heterocyclic group represented by has substituents, such substituents are not particularly limited as long as they do not inhibit thermal decomposition. Substituents include deuterium atoms; alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl groups; cycloalkyl groups having 3 to 6 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups; and a(C1 to 4) carbon atoms such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, isobutoxy, and tert-butoxy groups. Examples include: lucoxy groups; cycloalkyloxy groups having 3 to 6 carbon atoms, such as cyclopropyloxy, cyclobutoxy, cyclopentyloxy, and cyclohexyl groups; aromatic hydrocarbon groups having 6 to 12 carbon atoms, such as phenyl, 1-naphthyl, and 2-naphthyl groups; heterocyclic groups such as furanyl, thienyl, morpholino, and pyridyl groups; aralkyl groups such as benzyl and 2-phenylethyl groups; halogeno groups such as fluoro, chloro, bromo, and iodo groups; hydroxyl groups; and nitro groups.

[0124] In structural formula (2B), R ２２ Each of these is independently a hydrocarbon group which may have substituents. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic and may have a carbon-carbon unsaturated bond. -CH in the aliphatic hydrocarbon group ２ - stands for -O-, -S-, or -SO ２ They may be substituted with -. Also, the cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group, and heterocyclic group may be monocyclic, polycyclic, or fused cyclic.

[0125] R ２２The number of carbon atoms in the hydrocarbon group represented by is not particularly limited, but if the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is usually 1 or more, preferably 2 or more, more preferably 3 or more, and also usually 30 or less, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. In other words, suitable ranges for the number of carbon atoms in the aliphatic hydrocarbon group include 1 to 10, 1 to 8, 1 to 6, 2 to 30, and 3 to 6.

[0126] R ２２ The unsubstituted aliphatic hydrocarbon groups represented include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, isobutyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, Examples include n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclohexylmethyl group, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, 2-methylallyl group, pentenyl group, isopentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, and their isomers.

[0127] R ２２ When the hydrocarbon group represented is an aromatic hydrocarbon group, its number of carbon atoms is usually 6 or more, preferably 8 or more, and usually 30 or less, preferably 20 or less, and more preferably 10 or less. In other words, suitable ranges for the number of carbon atoms of an aromatic hydrocarbon group include 6 to 10, 6 to 20, and 8 to 30.

[0128] R ２２Examples of unsubstituted aromatic hydrocarbon groups represented by include phenyl group, 1-naphthyl group, 2-naphthyl group, 9-phenantrenyl group, 2-anthracenyl group, 9-anthracenyl group, 9-fluorenyl group, and their isomers.

[0129] R ２２ When the hydrocarbon group represented by has substituents, the substituents are R ２１ Examples of substituents include those similar to those found when a hydrocarbon group or heterocyclic group represented by has substituents.

[0130] Carbamic acid esters having the structure shown in structural formula (2B) are subjected to thermal decomposition along with isocyanates and R ２２ It generates a hydroxyl compound represented by OH. ２２ In step 1B-2, it is preferable that OH has a lower boiling point than carbamic acid esters and isocyanates, as this makes it easier to continuously extract it as a gaseous component from the reaction vessel. That is, from the viewpoint of producing a hydroxy compound with a low boiling point by thermal decomposition, R ２２ It is preferably an aliphatic hydrocarbon group having 1 to 10 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms, more preferably an aliphatic hydrocarbon group having 1 to 8 carbon atoms, or an aromatic hydrocarbon group having 6 to 10 carbon atoms, even more preferably an aliphatic hydrocarbon group having 1 to 6 carbon atoms, and particularly preferably an aliphatic hydrocarbon group having 1 to 4 carbon atoms.

[0131] In structural formula (2B), p is an integer of 1 or more, preferably an integer of 2 or more, and its upper limit is not particularly limited. p is preferably 1 to 6, more preferably 1 to 3, even more preferably 1 or 2, and particularly preferably 2, in terms of ease of manufacture and handling, and the availability of a highly versatile isocyanate. Carbamic acid esters may be used alone, or two or more may be used in any combination and ratio.

[0132] <Isocyanate> The isocyanate relating to Disclosure B is obtained by the thermal decomposition of the above carbamic acid ester and has the structure shown in the following structural formula (1B). ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1B)

[0133] In structural formula (1B), R ３１ R is a p-valent organic group. More specifically, ３１ R ２１ or R ２１ It is a group derived from R. ２１ The group derived from is R ２１ The structure of the group may be a group whose structure has changed under the conditions of thermal decomposition, and after thermal decomposition, R ２１ The group may be one in which some of the internal structure, such as the skeleton and functional groups, has been modified. Examples of structural modifications include halogenation, nitration, and hydrogenation, and can be carried out by known methods or similar methods.

[0134] In structural formula (1B), R ２２ , and p are R in structural formula (2), respectively. ２２ , and p are synonymous, and the preferred embodiment is the same.

[0135] In structural formula (1B), the relationship between p and q is p ≥ q, where q represents an integer between 1 and p. Preferably, q is between 1 and 6, more preferably between 1 and 3, even more preferably between 1 or 2, and particularly preferably between 2. More preferably, the combination of p and q is such that p is an integer between 1 and 6, particularly between 2 and 6, and q is an integer between 1 and 6; particularly preferably, p is an integer between 1 and 3, particularly between 2 and 3, and q is an integer between 1 and 3; even more preferably, p is 1 or 2, and q is 1 or 2; and especially preferably, p is 2 and q is 2. Furthermore, in the manufacturing method according to this embodiment, it is preferable that all the carbamate groups of the carbamic acid ester are converted to isocyanate groups, and therefore, it is also preferable that q = p.

[0136] The isocyanates produced by the manufacturing method of this embodiment include, specifically, monoisocyanates such as n-butyl isocyanate, tert-butyl isocyanate, n-hexyl isocyanate, n-octyl isocyanate, n-octadecyl isocyanate, cyclohexyl isocyanate, adamantyl isocyanate, benzyl isocyanate, α-methylbenzyl isocyanate, phenyl isocyanate, o-tolyl isocyanate, m-tolyl isocyanate, p-tolyl isocyanate, o-nitrophenyl isocyanate, m-nitrophenyl isocyanate, p-nitrophenyl isocyanate, o-methoxyphenyl isocyanate, m-methoxyphenyl isocyanate, p-methoxyphenyl isocyanate, 4-isocyanatoethyl benzoate, 2,6-dimethylphenyl isocyanate, 3,5-dimethylphenyl isocyanate, 1-naphthyl isocyanate, and 2-naphthyl isocyanate. Anates; Hexamethylene diisocyanate (HDI), Isophorone diisocyanate (IPDI), Norbornene diisocyanate, 2,4-Tolylene diisocyanate (2,4-TDI), 2,6-Tolylene diisocyanate (2,6-TDI), 2,2'-Diphenylmethane diisocyanate (2,2'-MDI), 2,4'-Diphenylmethane diisocyanate (2,4'-MDI), 4,4'-Diphenylmethane diisocyanate (4,4'-MD I) Polyisocyanates such as m-xylylene diisocyanate (m-XDI), p-xylylene diisocyanate (p-XDI), tetramethylxylylene diisocyanate (TMXDI), 1,5-naphthalene diisocyanate (1,5-NDI), hydrogenated diphenylmethane diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate (hydrogenated XDI), and polymethylene polyphenylene polyisocyanate; and their isomers; etc. Isomers include, for example, polynuclear compounds thereof, such as polymeric MDI, when the isocyanate relating to Disclosure B is one of the above MDIs.

[0137] Furthermore, as an isocyanate relating to Disclosure B, for example, in the above structural formula (1B), p is 2 or more, q is 1 or more, and R ３１However, examples include isocyanates, which are organic groups with a valency of p, wherein the organic group is an aliphatic hydrocarbon group having 1 or more carbon atoms, or an aromatic hydrocarbon group having 6 or more carbon atoms. Here, the aliphatic hydrocarbon group is the -CH group in the aliphatic hydrocarbon group. ２ -, -O-, -S-, or -SO ２ It may be substituted with -. Also, the aromatic hydrocarbon group may have two or more aromatic rings that are single bonds, -CH ２ The group may be connected by at least one linking group selected from the group consisting of -, -O-, and -S-. Furthermore, the isocyanate according to Disclosure B is, in the above structural formula (1B), R ３１ However, it is an aromatic hydrocarbon group, that is, an organic group with a valence p containing aromatics, and in structural formula (1B) -NHCOOR ２２ It is preferable that the nitrogen atom in the group and the nitrogen atom in the -NCO group are directly bonded to the carbon atoms constituting the aromatic ring in the organic group. Particularly preferred as such isocyanates is diphenylmethane diisocyanate having the structure shown in structural formula (3-1), and even more preferably isocyanates having the structure shown in structural formula (3-2).

[0138]

[0139] In structural formula (3-1), s and t each represent 0 or 1, where s + t = 1. ００ This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.

[0140]

[0141] The isocyanates represented by structural formula (3-2) include, for example, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI.

[0142] The isocyanates represented by the above structural formulas (3-1) and (3-2) are obtained by converting the carbamate group of the corresponding carbamic acid ester to an isocyanate group. The corresponding carbamic acid ester is not particularly limited as long as it gives the isocyanate represented by structural formula (3-1) or structural formula (3-2) upon thermal decomposition, but for example, the carbamic acid ester represented by the following structural formula (4) can be cited.

[0143]

[0144] In structural formula (4), R ０１ and R ０２ Each of these independently represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms. Specifically, R ０１ , and R ０２ Each of these can be independently selected from the group consisting of a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. ０１ and R ０２ However, because each is independently an aliphatic hydrocarbon group having 1 to 4 carbon atoms, as described above, the hydroxy compound produced as a by-product by the thermal decomposition of the carbamic acid ester is a lower aliphatic alcohol with 1 to 4 carbon atoms and a low boiling point, thus making it easier to continuously extract the hydroxy compound as a gaseous component from the reaction vessel in step 1B-2.

[0145] Furthermore, R ０１ and R ０２ It is particularly preferable that it be a methyl group. ０１ and R ０２When both are methyl groups, the hydroxy compound produced as a by-product by the thermal decomposition of the carbamic acid ester is methanol, which has a particularly low boiling point, making it particularly easy to continuously extract it as a gaseous component from the reaction system. Furthermore, as shown in the equilibrium reaction equation (I), the reaction to obtain isocyanate by thermal decomposition of the carbamic acid ester is an equilibrium reaction between the generated isocyanate and the by-product hydroxy compound (alcohol). Therefore, by removing the by-product hydroxy compound from the reaction system, isocyanate can be produced more efficiently. Moreover, by using methanol as the by-product, which is easier to extract as a gaseous component from the reaction system, isocyanate can be produced more efficiently. In addition, because methanol has a large difference in boiling point from the isocyanate shown in structural formula (3-2), the separation of methanol and isocyanate after extraction from the reaction vessel can be performed more easily, contributing to the production of isocyanate of higher purity.

[0146] [Catalyst] The thermal decomposition of carbamic acid esters is preferably carried out in the presence of at least one compound (catalyst) selected from the group consisting of fatty acid metal salts and phosphate metal salts, and more preferably in the presence of a fatty acid metal salt.

[0147] (Fatty acid metal salts) Fatty acid metal salts are compounds represented by general formula (IA) or general formula (IB). Fatty acid metal salts may also be hydrates. (R １１ COO) ｎ１ M １１ (IA) (R １２ COO) ｎ２ M １２ (IB)

[0148] In general formula (IA), M １１ These are Group 1 metals, Group 2 metals, Group 13 metals, or lanthanide metals of the periodic table. Of these, M １１It is preferably a Group 2 metal, Group 13 metal, or lanthanide metal of the periodic table, more preferably magnesium, calcium, strontium, barium, aluminum, or cerium, and even more preferably magnesium, aluminum, or cerium. Furthermore, from the standpoint of being able to more reliably suppress the generation of by-products such as allophanates and isocyanurates due to side reactions such as allophanate formation and polymerization of isocyanates, M １１ It is preferably a metal from Group 13 of the periodic table, and more preferably aluminum. On the other hand, from the viewpoint of high catalytic activity, M １１ n1 is preferably a Group 2 or Group 13 metal of the periodic table, more preferably magnesium or aluminum, and even more preferably aluminum. In general formula (IA), n1 is M １１ The valence of is preferably an integer between 1 and 4.

[0149] In general formula (IA), R １１ This is an alkyl group having 1 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms, preferably an alkyl group having 1 to 40 carbon atoms. That is, the fatty acid metal salt that acts as the catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to a linear form; they may have a branched structure or a cyclic structure, but are preferably linear in that they have high catalytic activity and are readily available. Furthermore, the number, position, and bonding mode (i.e., geometric isomerism) of carbon-carbon double bonds in the alkenyl group are not particularly limited. １１ The number of carbon atoms in the alkyl group represented by is preferably 2 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １１ Preferred ranges for the number of carbon atoms in the alkyl group represented by include, for example, 1 to 36, 2 to 40, 12 to 40, 12 to 32, and 16 to 28.

[0150] R １１ The alkyl groups that can be represented include, specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, isobutyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, Examples include n-henicosyl group, n-docosyl group, n-tricosyl group, n-tetracosyl group, n-pentacosyl group, n-hexacosyl group, n-heptacosyl group, n-octacosyl group, n-nonacosyl group, n-triacontyl group, n-hentriacontyl group, n-dotriacontyl group, n-tritriacontyl group, n-tetratriacontyl group, n-pentatriacontyl group, n-hexatriacontyl group, n-heptatriacontyl group, n-octatriacontyl group, n-nonatriacontyl group, n-tetracontyl group, and their isomers.

[0151] R １１ The number of carbon atoms in the alkenyl group represented by is usually between 2 and 40, and is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １１ Preferred ranges for the number of carbon atoms of the alkyl and alkenyl groups represented by the formula include, for example, 2 to 36, 8 to 40, 12 to 40, 12 to 36, 16 to 32, and 16 to 28.

[0152] R １１The alkenyl groups represented by include, specifically, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, 2-methylallyl group, pentenyl group, isopentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, undecenyl group, dodecenyl group, tridecenyl group, tetradecenyl group, pentadecenyl group, hexadecenyl group, heptadecenyl group, heptadedecenyl group, heptadedecaneyl group, heptadedecaterinyl group, octadecenyl group, nonadecenyl group, nonadedeceteraenyl group, nonadedecaterinyl group, icosenyl Examples include the yl group, henicocenyl group, henicosahexaenyl group, dococenyl group, tricocenyl group, tetracocenyl group, pentacocenyl group, hexacocenyl group, heptacocenyl group, octacocenyl group, nonacocenyl group, triacontenyl group, hentriacontenyl group, dotriacontenyl group, tritriacontenyl group, tetratriacontenyl group, pentacontenyl group, hexatriacontenyl group, heptacontenyl group, octacontenyl group, nonatriacontenyl group, tetracontenyl group, and their isomers.

[0153] In general formula (IB), M １２ These are metals from groups 3 to 11 of the periodic table or zinc. Of these, M １２ It is preferable that the catalytic activity is high, and that it is a fourth-period or fifth-period metal, more preferably scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, or silver, and even more preferably iron, cobalt, nickel, copper, or zinc. Furthermore, it is preferable that it is a metal with a good balance of high catalytic activity, low toxicity of fatty acid metal salts, and the ability to suppress the generation of by-products such as allophanates and isocyanurates due to side reactions such as allophanate formation and polymerization of isocyanates. １２ It is preferably a metal from groups 8 to 11 of the periodic table or zinc, and more preferably a metal from group 8 of the periodic table, a metal from group 9 of the periodic table, or zinc. More specifically, M １２is preferably iron, cobalt, nickel, copper, or zinc, more preferably iron, cobalt, or zinc, and even more preferably zinc. In general formula (IB), n2 is M １２ The valence of is preferably an integer between 1 and 6.

[0154] In general formula (IB), R １２ The group is an alkyl group having 10 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms, preferably an alkyl group having 10 to 40 carbon atoms. That is, the fatty acid metal salt that acts as a catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but it is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to a linear form, and may have a branched structure or a cyclic structure, but a linear form is preferred because it has high catalytic activity and is readily available. Furthermore, the number, position, and bonding mode (i.e., geometric isomerism) of carbon-carbon double bonds in the alkenyl group are not particularly limited.

[0155] R １２ The number of carbon atoms in the alkyl group represented by is preferably 12 or more, more preferably 14 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １２ Preferred ranges for the number of carbon atoms of the alkyl group represented by include, for example, 10 to 36, 12 to 40, 14 to 32, and 16 to 28. １２ The alkyl group represented by R is １１ Examples of alkyl groups represented by include those with 10 or more carbon atoms.

[0156] R １２ The number of carbon atoms in the alkenyl group represented by is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １２Preferred ranges for the number of carbon atoms in the alkenyl group represented by include, for example, 2 to 36, 8 to 40, 12 to 32, and 16 to 28. １２ The alkenyl group represented by R is １１ Examples of alkenyl groups represented by this symbol include the following:

[0157] In summary, examples of fatty acid metal salts include salts of fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, erucic acid, linoleic acid, alpha-linolenic acid, gamma-linolenic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, which are salts of the aforementioned metals.

[0158] Specific examples of fatty acid metal salts include cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, nickel laurate, copper laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, nickel stearate, copper stearate, zinc stearate, aluminum stearate, and stearyl stearate. Examples include cerium palmitate, magnesium palmitate, calcium palmitate, strontium palmitate, barium palmitate, iron palmitate, cobalt palmitate, nickel palmitate, copper palmitate, zinc palmitate, aluminum palmitate, cerium palmitate, magnesium oleate, calcium oleate, strontium oleate, barium oleate, iron oleate, cobalt oleate, nickel oleate, copper oleate, zinc oleate, aluminum oleate, and cerium oleate. Of these, the fatty acid metal salt is preferably cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, and cerium stearate, and is particularly preferably cerium acetate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, and cerium stearate.

[0159] The fatty acid metal salt may be a commercially available product, or it may be synthesized by a known manufacturing method or a similar method, for example, by a neutralization reaction between a fatty acid and a base containing the above metal.

[0160] (Metal Phosphate Salts) Metal phosphate salts used as catalysts in the thermal decomposition process are represented by the following general formula (IC). Metal phosphate salts may also be hydrates. (M １３ ) ｍ (PO ４ ) ｎ３ (IC)

[0161] In the general formula (IC), M １３ These are metals from groups 1 to 11 of the periodic table, metals from group 13 of the periodic table, zinc, or lanthanide metals. In the general formula (IC), m and n3 are M １３ The valence × m = 3 × n3 is satisfied. m and n3 are preferably the smallest values ​​among the values ​​that satisfy the above formula, for example, M １３ If it is trivalent cerium, then m is 1 and n3 is 1.

[0162] Examples of metal phosphate salts include sodium phosphate, potassium phosphate, magnesium phosphate, calcium phosphate, barium phosphate, zinc phosphate, aluminum phosphate, and cerium phosphate.

[0163] Generally, homogeneous catalysts exhibit higher catalytic activity than heterogeneous catalysts. Therefore, in this embodiment, when thermal decomposition is carried out in a solvent, it is preferable to select a catalyst that is highly soluble in the solvent and is liquid under the reaction conditions, and when thermal decomposition is carried out without a solvent, it is preferable to select a catalyst that is liquid under the reaction conditions. From this viewpoint, the catalyst used in the thermal decomposition step is preferably a fatty acid metal salt represented by general formula (IA) or general formula (IB), and is represented by general formula (IA), R １１ R is a long-chain fatty acid metal salt in which is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms, or is represented by the general formula (IB), １２ It is more preferable that the long-chain fatty acid metal salt is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms.

[0164] The catalyst may be used alone, or two or more may be used in any combination and ratio. The amount of catalyst used in the pyrolysis step should be appropriately selected depending on the type of carbamic acid ester, the type of catalyst, and the reaction conditions. When multiple types of catalysts are used, the catalyst amount refers to the total amount. Specifically, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is 100.0 mol%) is not particularly limited, but is preferably 0.01 mol% or more, more preferably 0.1 mol% or more, particularly preferably 0.3 mol% or more, preferably 20.0 mol% or less, more preferably 10.0 mol% or less, particularly preferably 5.0 mol% or less, and even more preferably 1.5 mol% or less. In other words, the range of the catalyst amount is preferably, for example, 0.01 mol% to 20.0 mol%, more preferably 0.1 mol% to 10.0 mol%, particularly preferably 0.3 mol% to 5.0 mol%, and even more preferably 0.3 mol% to 1.5 mol%.

[0165] Alternatively, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is 100% by mass) is not particularly limited, but is preferably 0.02% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.6% by mass or more, and also preferably 40.0% by mass or less, more preferably 20.0% by mass or less, particularly preferably 10.0% by mass or less, and even more preferably 3.0% by mass or less. That is, the range of the catalyst amount is, for example, preferably 0.02% by mass or more and 40.0% by mass or less, more preferably 0.2% by mass or more and 20.0% by mass or less, particularly preferably 0.6% by mass or more and 10.0% by mass or less, and even more preferably 0.6% by mass or more and 3.0% by mass or less.

[0166] [Solvent for pyrolysis] The solvent for pyrolysis must be an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate represented by the structural formula (1B), and whose solubility at 180°C of the carbamic acid ester is 2.5 wt% or more. By using an organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate, it becomes possible to recover the isocyanate from the pyrolysis product by evaporating the isocyanate obtained by pyrolysis. Therefore, when recovering the isocyanate from the pyrolysis product, the energy required for the evaporation of the solvent can be reduced, and as a result, CO2 emissions related to the production of isocyanate can be reduced. ２ This makes it possible to reduce emissions. Furthermore, by using an organic solvent with a carbamic acid ester solubility of 2.5 wt% or more, the carbamic acid ester, which is the target of thermal decomposition, can be more uniformly present in the raw material liquid. Therefore, it is thought that the generation of by-products other than hydroxy compounds, which are inevitably produced by the thermal decomposition of the carbamic acid ester, can be suppressed. For these reasons, isocyanates can be produced more efficiently by using a thermal decomposition solvent that meets the above requirements.

[0167] Furthermore, among the carbamic acid esters having the structure shown in the above structural formula (2B), R ２１ is an organic group with a valence p that contains an aromatic ring, and the carbamate group (-NHCOOR) in structural formula (2B) ２２When thermally decomposing a carbamic acid ester in which the nitrogen atom in the organic group is directly bonded to the carbon atoms constituting the aromatic ring in the organic group, it is particularly effective to use an aromatic organic solvent as the thermal decomposition solvent, in which the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more, and the boiling point B1 is higher than the boiling point B2 of the isocyanate obtained by thermal decomposition of the carbamic acid ester, in which at least one of the carbamate groups directly bonded to the carbon atoms constituting the aromatic ring of the carbamic acid ester is converted to an isocyanate group. In other words, the inventors have recognized that when obtaining isocyanate by thermal decomposition of carbamic acid ester, the selection of the solvent used for thermal decomposition is important for producing isocyanate at low cost and in high yield. Furthermore, we found that carbamic acid esters having a carbamate group directly bonded to the aromatic ring behave differently during thermal decomposition in the same solvent as carbamic acid esters having a carbamate group bonded to the aromatic ring via a methylene group (such as xylylenedicarbamate), and the yield of the resulting isocyanate can also differ significantly. The reason for this is unclear, but it is presumed that this is due to the fact that the carbamate group directly bonded to the aromatic ring has weaker basicity as an amine compared to, for example, the carbamate group bonded to the aromatic ring via a methylene group. And, having the structure shown in the above structural formula (2B), R ２１ is an organic group with a valence p that contains an aromatic ring, and the carbamate group (-NHCOOR) in the structural formula (2B) ２２ As a solvent for the thermal decomposition of a carbamic acid ester in which the nitrogen atom in the group is directly bonded to the carbon atoms constituting the aromatic ring in the organic group, an aromatic organic solvent having a solubility of 2.5 wt% or more at 180°C and a boiling point B2 higher than that of the isocyanate obtained by the thermal decomposition of the carbamic acid is particularly suitable for obtaining isocyanate in high yield while minimizing energy consumption during production.

[0168] The boiling point B1 of the above organic solvent must be higher than the boiling point B2 of the isocyanate, and B1 is preferably 10°C or more higher than B2 (B1 + 10°C ≥ B2), and more preferably 40°C or more higher than B2 (B1 + 40°C ≥ B2). Furthermore, the solubility of the carbamic acid ester at a temperature of 180°C in the above organic solvent must be 2.5 wt% or more, and preferably 3.0 wt% or more, and more preferably 4.0 wt% or more. The upper limit of the solubility is not particularly limited, but for example, it is preferably 30.0 wt% or less, more preferably 20.0 wt% or less, and particularly preferably 15.0 wt% or less. That is, the solubility is preferably 2.5 wt% or more and 30.0 wt% or less, more preferably 3.0 wt% or more and 20.0 wt% or less, and particularly preferably 4.0 wt% or more and 15.0 wt% or less.

[0169] The solubility in Disclosure B is measured by either Method 1 or Method 2 below. <Method 1 for measuring solubility> If the carbamate ester has a melting point of 180°C or higher, it can be measured using a high-temperature filtration device (manufactured by Senshu Science) and a polytetrafluoroethylene membrane filter with a pore size of 0.5 μm (model: T050A025A, manufactured by Advantec), following the steps (1) to (8) below. (1) Accurately weigh 4 g of carbamate ester and place it in a screw-cap vial. (2) Add 4 g of the solvent to be evaluated to the screw-cap vial containing the sample. (3) Heat the screw-cap vial to bring the temperature of the contents of the screw-cap vial to 180°C. (4) Add 0.1 g of carbamate ester to the screw-cap vial and shake the vial. Continue this operation until the contents of the screw-cap vial are no longer visibly transparent. (5) When the contents of the screw-cap bottle are no longer transparent, stop adding the carbamate ester and transfer the entire contents of the screw-cap bottle to a high-temperature filtration apparatus and filter it hot. (6) Allow the residue to cool to room temperature, wash it with a poor solvent (such as hexane), and then let it stand until the poor solvent has completely evaporated. (7) Weigh the dried residue accurately and determine the mass of the residue (b). (8) Calculate the solubility of the carbamate ester in the solvent to be measured at a temperature of 180°C using the following formula (1). In the following formula (1), "a" is the total amount of carbamate ester added to the screw-cap bottle until the contents of the screw-cap bottle are no longer visibly transparent. <Formula (1)> Solubility (wt%) = [(a - b) / (amount of solvent + (a - b))] × 100

[0170] <Method for Measuring Solubility 2> When a carbamic acid ester has a melting point of 180°C or lower, particularly below 180°C, the solubility shall be defined as the maximum sample concentration at which the sample (carbamic acid ester) to be measured is completely dissolved by visual inspection. Here, complete dissolution means a state in which no insolubility or bilayer separation of the sample is observed by visual inspection.

[0171] The melting points of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) are 180°C, methylenediphenyl 4,4'-diethylcarbamate (MDC-Et) are 134°C, methylenediphenyl 4,4'-dibutylcarbamate (MDC-Bu) are 110°C, and hexanemethylenedimethylcarbamate (HDC-Me) is 98°C. When measuring the solubility of MDC-Me using the above measurement method 1, two-layer separation may be visually observed during the heating process depending on the solvent. In that case, the solubility should be determined according to the above measurement method 2.

[0172] The aromatic organic solvent according to Disclosure B is not particularly limited as long as its boiling point B1 is higher than the boiling point B2 of the isocyanate represented by structural formula (1B), and the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. Specific examples of aromatic organic solvents include, for example, aromatic organic solvents having the structure shown in structural formula (6B). Ar-(R １０６ ) ｎ１０６ (6B) In structural formula (6B), Ar represents an aryl group, and R １０６ n106 is a C1-C30 hydrocarbon group which may contain an aromatic ring. n106 is an integer of 1 or more. Examples of aryl groups include phenyl groups and naphthyl groups. Examples of C1-C30 hydrocarbon groups which may contain an aromatic ring include C1-C30 linear or branched alkyl groups and benzyl groups. In particular, organic solvents containing at least two benzene rings or at least one naphthalene ring in the structure shown in structural formula (6B) are preferred. Specific examples of aromatic organic solvents having the structure shown in structural formula (6B) include alkylnaphthalenes, dibenzyltoluene, and dialkylbenzenes. In particular, it is preferable that the organic solvent contains at least one solvent selected from the group consisting of alkylnaphthalenes and dibenzyltoluene.

[0173] As described above, the aromatic organic solvent according to Disclosure B requires that the solubility of the carbamic acid ester corresponding to the isocyanate having the structure shown in structural formula (1B) at a temperature of 180°C be 2.5 wt% or more. Therefore, the solvent can be appropriately selected depending on the carbamic acid ester species used for thermal decomposition. For example, having the structure shown in structural formula (2B), and R ０１ and R ０２ Specific examples of solvents in which methylenediphenyl 4,4'-dimethylcarbamate, whose methyl group is present, has a solubility of 2.5 wt% at 180°C include alkylnaphthalenes and dibenzyltoluene. Such alkylnaphthalenes can be commercially available, for example, as "Barrel Process Oil B-28AN" (trade name, manufactured by Matsumura Petroleum Co., Ltd.). "Barrel Process Oil B-28AN" has a boiling point of 380°C, which is higher than the boiling point of methylenediphenyl 4,4'-diisocyanate (MDI) (314°C), and the solubility of methylenediphenyl 4,4'-dimethylcarbamate at 180°C is 6.9 wt%. Dibenzyltoluene is the compound shown in structural formula (5), and its boiling point is 391°C, which is higher than the boiling point of MDI, and the solubility of the above carbamic acid ester at 180°C is 55 wt%.

[0174]

[0175] On the other hand, for example, the boiling point of high-viscosity liquid paraffin (manufactured by Nacalai Tesque) (high-viscosity type) is 400°C or higher, and the solubility of MDC-Me is less than 1.2 wt% at 180°C and about 2.3 wt% at 230°C. As shown in Comparative Example 1, when the above liquid paraffin was used as the solvent for the thermal decomposition of MDC-Me, the mass balance decreased compared to Example 1B, possibly because a large amount of by-products other than hydroxyl compounds were generated. This is thought to be due to the fact that even at temperatures in the thermal decomposition process, for example around 230°C, the solubility of the carbamate ester in the liquid paraffin was insufficient, resulting in an uneven distribution of the carbamate ester in the raw material liquid. Furthermore, dialkylbenzene (product name: Barrel Process Oil B27T, manufactured by Matsumura Oil Co., Ltd.) has a boiling point of 385°C, and its solubility in MDC-Me is 1.9 wt% at 180°C. When this dialkylbenzene was used as the thermal decomposition solvent for MDC-Me, the mass balance decreased significantly compared to Examples 1B and 2B, as shown in Comparative Example 2. Similarly, alkylbenzene (product name: Barrel Process Oil B-15AB, manufactured by Matsumura Oil Co., Ltd.) has a boiling point of 352°C, and its solubility in MDC-Me is 2.3 wt% at 180°C. When this alkylbenzene was used as the thermal decomposition solvent for MDC-Me, the mass balance decreased significantly compared to Examples 1B and 2B, as shown in Comparative Example 3B.

[0176] The solvent may be used alone or in combination of two or more. Specifically, for example, the above-mentioned "Barrel Process Oil B-28AN" or dibenzyltoluene may be used alone, or a mixture thereof may be used. However, when the solvent is a mixture, the boiling point (B1) of the mixture must be higher than the boiling point B2 of the isocyanate, and the solubility of the carbamic acid ester at 180°C must be 2.5 wt% or more.

[0177] [Reaction Temperature] The reaction temperature in the thermal decomposition step is not particularly limited as long as it is a temperature at which the carbamic acid ester used as a raw material can be thermally decomposed and isocyanate can be produced, and is usually between 100°C and 300°C. From the viewpoint of increasing the reaction rate while suppressing side reactions, it is preferable to set the temperature between 150°C and 280°C, more preferably between 180°C and 260°C, and particularly preferably between 200°C and 240°C.

[0178] [Reaction Time] The reaction time in the thermal decomposition step is not particularly limited and can be appropriately adjusted depending on the type of catalyst, reaction temperature, and reaction scale. Specifically, the reaction time is preferably 0.5 hours or more and 60.0 hours or less, more preferably 1.0 hour or more and 48.0 hours or less, even more preferably 2.0 hours or more and 36.0 hours or less, even more preferably 3.0 hours or more and 24.0 hours or less, and particularly preferably 4.0 hours or more and 12.0 hours or less. Alternatively, the reaction time may be 0.5 hours or more and 48.0 hours or less, 1.0 hour or more and 24.0 hours or less, or 2.0 hours or more and 12.0 hours or less. By keeping the reaction time within the above range, the thermal decomposition of the carbamic acid ester can be sufficiently carried out, and side reactions such as allophanate formation and polymerization of the generated isocyanate can be suppressed.

[0179] [Operating Procedure] The method for producing isocyanate according to Disclosure B will be explained with reference to Figure 2. Note that the manufacturing apparatus 100 shown in Figure 2 is one embodiment that can be used for producing isocyanate according to Disclosure B, and the method for producing isocyanate according to Disclosure B is not limited to the method produced by the manufacturing apparatus embodied in Figure 2.

[0180] First, the carbamic acid ester, catalyst, and solvent are supplied to the reaction vessel 101B equipped with a stirrer 101-1B. This operation may be carried out in an air atmosphere or in an inert gas atmosphere such as nitrogen and argon, but it is preferable to carry out the operation in an inert gas atmosphere because it is preferable to perform the thermal decomposition in an inert gas atmosphere. Next, with the pressure inside the reaction vessel 101B reduced to a predetermined pressure by operating the vacuum pump 113B, the raw material liquid 102B (carbamic acid ester, catalyst, solvent) inside the reaction vessel 101B is heated to the aforementioned temperature, and the carbamic acid ester in the raw material liquid 102B is thermally decomposed to form isocyanate (thermal decomposition step). During thermal decomposition, it is preferable to stir the reaction solution using the stirrer 101-1B. The method of stirring the raw material liquid is not limited to this, and for example, a method of stirring with a magnetic stirrer can also be employed. The pressure inside the reaction vessel is not particularly limited, but for example, it is preferably 0.05 kPaA to 10 kPaA, more preferably 0.1 kPaA to 5 kPaA, and particularly preferably 0.2 kPaA to 2 kPaA. Furthermore, it is particularly preferable that the thermal decomposition according to the present invention be carried out within the above-mentioned temperature range, reaction time range, and pressure range.

[0181] In the thermal decomposition process, the carbamic acid ester in the raw material liquid is thermally decomposed to produce isocyanate, and a hydroxy compound is produced as a by-product. In the method for producing isocyanate according to Disclosure B, the isocyanate and hydroxy compound are continuously withdrawn from the reaction vessel 101B (steps 1B-1 and 1B-2). The isocyanate and hydroxy compound can be withdrawn as gaseous components via line 103B, for example, by the temperature during thermal decomposition and the pressure inside the reaction vessel 101B due to the operation of the vacuum pump 113B. Figure 2 shows an example in which gaseous components containing both isocyanate and hydroxy compound are withdrawn from the reaction vessel 101B. That is, steps 1B-1 and 1B-2 are performed simultaneously (integrally).

[0182] The extracted gaseous components are introduced to the first condenser 109B via line 103B, where the isocyanate and hydroxyl compounds are separated. Specifically, the isocyanate is condensed and stored in storage tank 111B. Meanwhile, the components that were not condensed in the first condenser 109B (residual gaseous components) are introduced to the second condenser 115B via line 105B, where the residual gaseous components, specifically those containing hydroxyl compounds, are condensed and stored in storage tank 117B.

[0183] Furthermore, the method for producing isocyanate according to Disclosure B may include optional steps in addition to the thermal decomposition step. An optional step, for example, is a purification step to increase the purity of the isocyanate. As a method for purifying the isocyanate in the purification step, purification methods commonly used in the field of organic synthesis, such as filtration, adsorption, column chromatography, and distillation, can be employed.

[0184] Furthermore, when isocyanates are produced continuously, for example, the production apparatus 200B shown in Figure 3 can be used. Specifically, a storage tank 201B containing a raw material liquid 102B containing carbamic acid ester, catalyst, and solvent is connected to a reaction vessel 101B by line 203B, and the raw material liquid 102B in the storage tank 201B is configured to be supplied to the reaction vessel 101B continuously or intermittently. In addition, the liquid in the reaction vessel 101B is configured to be discharged from the reaction vessel 101B via line 205B. The raw material liquid is supplied from the storage tank 201B to the reaction vessel 101B continuously or intermittently, and while thermal decomposition and continuous extraction of diisocyanates and hydroxy compounds are carried out in the reaction vessel 101B, the liquid is discharged via line 205B so that the liquid volume in the reaction vessel 101B remains constant.

[0185] Furthermore, step 1B according to Disclosure B may include a step of heating a liquid film containing the raw material solution in a reaction vessel to thermally decompose the carbamic acid ester in the liquid film and produce isocyanate. By heating the liquid film containing the raw material solution, the carbamic acid ester can be heated rapidly. Below, a method for producing isocyanate according to one aspect of Disclosure B, which includes a step of heating a liquid film containing the raw material solution to thermally decompose the carbamic acid ester in the liquid film and produce isocyanate, will be described with reference to Figure 4. First, a raw material solution containing carbamic acid ester, a catalyst, and a solvent is prepared in a storage tank 301B (step 1B). Next, the raw material solution is supplied from the storage tank 301B to a reaction vessel 305B that has been preheated to a predetermined temperature (reaction temperature) via line 303B. Inside the reaction vessel 305B, the carbamic acid ester is thermally decomposed by heating the liquid film containing the raw material solution to produce isocyanate (step 1B). Then, the mixture containing the isocyanate produced by the thermal decomposition of the carbamic acid ester in reaction vessel 305B and the by-product hydroxy compound is continuously withdrawn as a gas phase component from line 307B (steps 1B-1 and 1B-2). The diisocyanate from the mixture containing the isocyanate and hydroxy compound withdrawn from reaction vessel 305B is condensed in condenser 309B to separate it from the hydroxy compound contained in the mixture and recovered in storage tank 311B. The hydroxy compound that has passed through condenser 309B as a gas phase component is condensed in condenser 315B and recovered in storage tank 317B. The reaction system, including the inside of reaction vessel 305B, is configured to be able to be reduced to any pressure by vacuum pump 313B. Furthermore, by reducing the pressure inside reaction vessel 305B with vacuum pump 313, it becomes possible to withdraw the isocyanate and lower aliphatic alcohol produced in the reaction vessel from reaction vessel 305B as gas phase components.The pressure within the reaction system is not particularly limited as long as it is possible to remove the isocyanate and hydroxy compound from the reaction vessel 305B as gas phase components via line 307B, and can be set appropriately according to the type of reaction solvent and reaction temperature. For example, the pressure within the reaction vessel is preferably 0.1 kPaA or more and 20.0 kPaA or less, more preferably 0.5 kPaA or more and 20.0 kPaA or less, and particularly preferably 1.0 kPaA or more and 20.0 kPaA or less. In this embodiment, the steps of removing the isocyanate as a gas phase component from the reaction vessel 305B (step 1B-1) and removing the hydroxy compound as a gas phase component (step 1B-2) are performed simultaneously (integrally), but the system is not limited to this, and the line for removing the isocyanate from the reaction vessel 305B and the line for removing the hydroxy compound may be separate.

[0186] Furthermore, even with heating in the reaction vessel 305B, at least a portion of the carbamic acid ester in the raw material liquid may not decompose and may remain unreacted (undecomposed) in the reaction vessel 305B. For this reason, it is preferable to, for example, remove the liquid containing the unreacted carbamic acid ester from the bottom of the reaction vessel 305B, return it to the storage tank 301B via line 319B, and subject it to the heating process in the reaction vessel 305B again. This can further improve the yield of isocyanate.

[0187] The above reaction may be carried out in an air atmosphere or in an inert gas atmosphere such as nitrogen and argon, but since thermal decomposition is preferable in an inert gas atmosphere, it is preferable to carry it out in an inert gas atmosphere.

[0188] In any embodiment of the method for producing isocyanate according to Disclosure B described above, any step may be included in addition to the thermal decomposition step. An example of an optional step is a purification step to increase the purity of the isocyanate. As a method for purifying the isocyanate in the purification step, a purification method commonly used in the field of organic synthesis, such as filtration, adsorption, column chromatography, or distillation, can be employed.

[0189] [Disclosure C] The embodiments of Disclosure C will be described below, but the present invention is not limited to the embodiments described below and can be implemented in various ways within the scope of its gist. In this specification, expressions representing numerical ranges, such as "XX or more," "YY or less," and "XX to YY," mean numerical ranges that include the endpoints XX and YY, unless otherwise specified. When numerical ranges are described in steps, any combination of the upper and lower limits of each numerical range is also disclosed. In this specification, for example, "at least one selected from the group consisting of XX, YY, and ZZ" means XX only, YY only, ZZ only, a combination of XX and YY, a combination of XX and ZZ, a combination of YY and ZZ, or a combination of XX, YY, and ZZ. Furthermore, in this specification, when descriptions such as "one aspect" or "one aspect" appear multiple times, they do not necessarily refer to the same aspect, but may refer to different aspects.

[0190] The present inventors have been investigating methods for producing diisocyanate using the method described in Patent Document 3, based on the understanding that the method of heating the liquid film of the raw material solution containing carbamic acid ester is a method that can more efficiently thermally decompose the carbamic acid ester. In the process, they have found that there is still room for improvement in the method of producing isocyanate described in Patent Document 3. Specifically, upon examining the examples described in Patent Document 3, it was found that insoluble matter was sometimes observed in the tank-type reactor where the second thermal decomposition step was performed, suggesting that the method of producing isocyanate described in Patent Document 3 may not always efficiently convert carbamic acid ester into isocyanate.

[0191] Therefore, the present inventors conducted further studies with the aim of obtaining a method for producing isocyanates more efficiently by suppressing the generation of by-products other than hydroxy compounds when thermally decomposing carbamic acid esters to produce isocyanates. As a result, they found that the method for producing isocyanates according to the following embodiment can successfully achieve the above objective.

[0192] That is, a method for producing an isocyanate according to one aspect of the present disclosure C is a method for producing an isocyanate comprising an isocyanate having a structure shown by structural formula (1C), comprising: step 1C of preparing a raw material solution comprising a carbamic acid ester corresponding to the isocyanate, as shown by structural formula (2C); and step 2C of heating a liquid film of the liquid containing the raw material solution in a reaction vessel to thermally decompose the carbamic acid ester in the liquid film to produce the isocyanate, wherein step 2C comprises: step 2C-1 of continuously withdrawing a hydroxy compound produced as a by-product by thermal decomposition of the carbamic acid ester from the reaction vessel as a gas phase component; and step 2C-2 of continuously withdrawing the isocyanate produced by thermal decomposition of the carbamic acid ester from the reaction vessel as a gas phase component: R ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1C) R ２１ (NHCOOR ２２ ) ｐ (2C) (In structural formulas (1C) to (2C), R ２１ and R ３１ Each of these is an organic group with a valency of p, where p is an integer greater than or equal to 1, and q is an integer greater than or equal to 1 and less than or equal to p, R ２２ (Each of these is independently a substituted or unsubstituted hydrocarbon group.)

[0193] According to the above manufacturing method, the carbamic acid ester can be rapidly heated by having a step of heating a liquid film containing a raw material solution containing the carbamic acid ester represented by structural formula (2C). Furthermore, in addition to the above step 2C-1, by having a step 2C-2 in which the isocyanate generated in the reaction vessel is continuously withdrawn from the reaction vessel as a gas phase component, the equilibrium can be shifted to the right in the thermal decomposition reaction of the carbamic acid ester represented by the following equilibrium reaction equation (I).

[0194]

[0195] In the above equilibrium reaction equation (I), R ２１, R ２２ , R ３１ p and q are R in the above structural formulas (1C) to (2C), respectively. ２１ , R ２２ , R ３１ It is synonymous with p and q.

[0196] Furthermore, according to the manufacturing method of this embodiment, by having steps 2C-1 and 2C-2, the period in which the carbamic acid ester and the by-produced hydroxy compound and / or isocyanate coexist in the reaction vessel can be shortened, thereby suppressing the occurrence of the reverse reaction. As a result, side reactions during thermal decomposition are suppressed, and consequently, the generation of by-products other than the hydroxy compound that is inevitably produced by thermal decomposition can be suppressed, making it possible to produce isocyanate more efficiently.

[0197] [Isocyanates and Carbamic Acid Esters] The method for producing isocyanates according to Disclosure C relates to a method for producing isocyanates containing an isocyanate represented by the following structural formula (1C) by thermal decomposition of a carbamic acid ester having a structure corresponding to said isocyanate. ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1C)

[0198] In structural formula (1C), R ３１ is a p-valent organic group, R ２２ Each of these is independently a substituted or unsubstituted hydrocarbon group, where p ≥ q, p is an integer of 1 or more, preferably 2 or more, and q is an integer of 1 or more and less than or equal to p.

[0199] <Carbamic Acid Esters> The carbamic acid ester having a structure corresponding to the isocyanate, which is a raw material for the isocyanate represented by the structural formula (1C), is not particularly limited as long as it can produce the isocyanate by thermal decomposition. Such carbamic acid esters may be commercially available products, or may be obtained by known manufacturing methods or manufacturing methods similar to known manufacturing methods. Examples of known manufacturing methods for carbamic acid esters include the methods described in Japanese Patent Publication No. 2021-191742, Japanese Patent Publication No. 2022-022652, or Japanese Patent Publication No. 2022-171090.

[0200] Specific examples of carbamic acid esters relating to Disclosure C include, for example, carbamic acid esters having the structure shown in structural formula (2C). In this disclosure, unless otherwise specified, if a symbol in one general formula is also used in another general formula, the definition of that symbol is the same in both general formulas. R ２１ (NHCOOR ２２ ) ｐ (2C) In structural formula (2C), R ２１ is a p-valent organic group, R ２２ , and p are R in structural formula (1C), respectively. ２２ It is synonymous with p.

[0201] R ２１ It may have a carbamic acid ester group (-NHCOO-), but it is preferable that it does not.

[0202] R ２１ The p-valent organic group is not particularly limited, but examples include substituted or unsubstituted hydrocarbon groups, substituted or unsubstituted heterocyclic groups, etc. The hydrocarbon group may be, for example, an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic, and may have a carbon-carbon unsaturated bond. Furthermore, the -CH in the aliphatic hydrocarbon group ２ - stands for -O-, -S-, or -SO ２It may be substituted with -. Also, the cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group, and heterocyclic group may be monocyclic, polycyclic, or fused cyclic. Of these, the organic group is preferably a hydrocarbon group, and more preferably an aromatic hydrocarbon group. The carbamic acid ester having the structure shown in the structural formula (2C) is particularly R ２１ is an aromatic hydrocarbon group, that is, an organic group with a valence of p containing a substituted or unsubstituted aromatic ring, and in structural formula (2C) -NHCOOR ２２ It is preferable that the nitrogen atom in the group is directly bonded to the carbon atom constituting the aromatic ring in the organic group. The reason for this will be explained later.

[0203] The number of carbon atoms in the hydrocarbon group is not particularly limited, but if the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is preferably 1 or more, more preferably 2 or more, more preferably 4 or more, and particularly preferably 6 or more. Furthermore, the upper limit is preferably 30 or less, more preferably 24 or less, particularly preferably 16 or less, and especially preferably 12 or less. In other words, the range of carbon atoms in the aliphatic hydrocarbon group is preferably 1 to 24, more preferably 2 to 30, particularly preferably 4 to 16, and particularly preferably 6 to 12. In this disclosure C, the number of carbon atoms indicated for a hydrocarbon group or heterocyclic group includes the number of carbon atoms of the substituent if the hydrocarbon group or heterocyclic group has substituents.

[0204] Examples of unsubstituted aliphatic hydrocarbon groups include groups obtained by removing any p hydrogen atoms from alkanes such as methane, ethane, propane, n-butane, isobutane, n-pentane, isopentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, n-undecane, n-dodecane, n-tridecane, n-tetradecane, n-pentadecane, n-hexadecane, n-heptadecane, n-octadecane, n-nonadecane, and n-eicosane; groups obtained by removing any p hydrogen atoms from cycloalkanes such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, and adamantane; and groups obtained by removing any p hydrogen atoms from alkenes such as ethylene, propylene, butylene, isobutylene, 1-hexene, and 1-octene.

[0205] R ２１ When the hydrocarbon group represented is an aromatic hydrocarbon group, its number of carbon atoms is usually 6 or more, preferably 8 or more, more preferably 10 or more, and usually 30 or less, preferably 24 or less, more preferably 20 or less. In other words, suitable ranges for the number of carbon atoms of an aromatic hydrocarbon group include 6 to 24, 8 to 30, and 10 to 20.

[0206] Unsubstituted aromatic hydrocarbon groups include groups obtained by removing any p hydrogen atoms from aromatic rings such as benzene, naphthalene, phenanthrene, anthracene, fluorene, pyrene, and triphenylene. Aromatic hydrocarbon groups can also be single-bonded, -CH ２ The group may be one obtained by removing any p hydrogen atoms from a compound in which multiple cyclic compounds are linked by linking groups such as -, -O-, and -S-. An example of such a group is one obtained by removing one hydrogen atom from each of the p benzene rings in poly(phenylenemethylene).

[0207] R ２１The number of carbon atoms in the heterocyclic group represented by is not particularly limited, but is usually 3 or more, preferably 5 or more, more preferably 10 or more, and also usually 30 or less, preferably 24 or less, more preferably 20 or less. In other words, suitable ranges for the number of carbon atoms in the heterocyclic group include 3 to 24, 5 to 30, and 10 to 20.

[0208] Examples of unsubstituted heterocyclic groups include groups obtained by removing any p hydrogen atoms from nitrogen-containing heterocycles such as pyrrolidone, imidazole, pyridine, pyrimidine, triazine, quinoline, phenazine, and carbazole; groups obtained by removing any p hydrogen atoms from oxygen-containing heterocycles such as tetrahydrofuran, furan, dioxane, tetrahydropyran, benzofuran, and dibenzofuran; groups obtained by removing any p hydrogen atoms from sulfur-containing heterocycles such as tetrahydrothiophene, thiophene, sulfolane, thian, trithiane, benzothiophene, and dibenzothiophene; and groups obtained by removing any p hydrogen atoms from heterocycles containing multiple heteroatoms such as oxazole, thiazole, morpholine, phenoxazine, phenothiazine, and phenoxathiin.

[0209] R ２１When a hydrocarbon group or heterocyclic group represented by has substituents, such substituents are not particularly limited as long as they do not inhibit thermal decomposition. Substituents include deuterium atoms; alkyl groups having 1 to 4 carbon atoms such as methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, isobutyl, and tert-butyl groups; cycloalkyl groups having 3 to 6 carbon atoms such as cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl groups; and a(C1 to 4) carbon atoms such as methoxy, ethoxy, n-propoxy, isopropoxy, n-butoxy, sec-butoxy, isobutoxy, and tert-butoxy groups. Examples include: lucoxy groups; cycloalkyloxy groups having 3 to 6 carbon atoms, such as cyclopropyloxy, cyclobutoxy, cyclopentyloxy, and cyclohexyl groups; aromatic hydrocarbon groups having 6 to 12 carbon atoms, such as phenyl, 1-naphthyl, and 2-naphthyl groups; heterocyclic groups such as furanyl, thienyl, morpholino, and pyridyl groups; aralkyl groups such as benzyl and 2-phenylethyl groups; halogeno groups such as fluoro, chloro, bromo, and iodo groups; hydroxyl groups; and nitro groups.

[0210] In structural formula (2C), R ２２ Each of these is independently a hydrocarbon group which may have substituents. The hydrocarbon group may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be linear, branched, or cyclic and may have a carbon-carbon unsaturated bond. -CH in the aliphatic hydrocarbon group ２ - stands for -O-, -S-, or -SO ２ They may be substituted with -. Also, the cyclic aliphatic hydrocarbon group, aromatic hydrocarbon group, and heterocyclic group may be monocyclic, polycyclic, or fused cyclic.

[0211] R ２２The number of carbon atoms in the hydrocarbon group represented by is not particularly limited. However, when the hydrocarbon group is an aliphatic hydrocarbon group, the number of carbon atoms is usually 1 or more, preferably 2 or more, more preferably 3 or more, and usually 30 or less, preferably 10 or less, more preferably 8 or less, and even more preferably 6 or less. That is, the suitable range of the number of carbon atoms in the aliphatic hydrocarbon group includes ranges of 1 to 10, 1 to 8, 1 to 6, 2 to 30, and 3 to 6.

[0212] R ２２ Examples of the unsubstituted aliphatic hydrocarbon group represented by include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, isobutyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, cyclopropyl group, cyclobutyl group, cyclopentyl group, cyclohexyl group, cycloheptyl group, cyclooctyl group, cyclohexylmethyl group, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, 2-methylallyl group, pentenyl group, isopentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, and their isomeric groups, etc.

[0213] R ２２ When the hydrocarbon group represented by is an aromatic hydrocarbon group, the number of carbon atoms is usually 6 or more, preferably 8 or more, and usually 30 or less, preferably 20 or less, more preferably 10 or less. That is, the suitable range of the number of carbon atoms in the aromatic hydrocarbon group includes ranges of 6 to 10, 6 to 20, and 8 to 30.

[0214] R ２２Examples of the unsubstituted aromatic hydrocarbon group represented by include a phenyl group, 1-naphthyl group, 2-naphthyl group, 9-phenanthrenyl group, 2-anthracenyl group, 9-anthracenyl group, 9-fluorenyl group, and isomer groups thereof.

[0215] R ２２ Examples of the substituent when the hydrocarbon group represented by has a substituent include the same groups as the substituent when the hydrocarbon group or heterocyclic group represented by has a substituent. ２１ Examples of the substituent when the hydrocarbon group or heterocyclic group represented by has a substituent include the same groups as the substituent when the hydrocarbon group represented by has a substituent.

[0216] The carbamate having the structure represented by the structural formula (2C) generates a hydroxy compound represented by R ２２ OH together with isocyanate by thermal decomposition. R ２２ OH is preferably lower in boiling point than the carbamate and isocyanate in that it can be easily withdrawn continuously as a gas-phase component from the reaction vessel in Step 2C-1. That is, from the viewpoint of generating a hydroxy compound having a low boiling point by thermal decomposition, R ２２ is preferably an aliphatic hydrocarbon group having 1 to 10 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, more preferably an aliphatic hydrocarbon group having 1 to 8 carbon atoms or an aromatic hydrocarbon group having 6 to 10 carbon atoms, still more preferably an aliphatic hydrocarbon group having 1 to 6 carbon atoms, and particularly preferably an aliphatic hydrocarbon group having 1 to 4 carbon atoms.

[0217] In the structural formula (2C), p is an integer of 1 or more, preferably an integer of 2 or more. The upper limit is not particularly limited. p is preferably 1 to 6, more preferably 1 to 3, still more preferably 1 or 2, and particularly preferably 2, in terms of ease of production and handling and obtaining a highly versatile isocyanate. The carbamate may be used alone or in combination of two or more in any combination and ratio.

[0218] <Isocyanate> The isocyanate according to Disclosure C includes an isocyanate having the structure shown in the following structural formula (1C), obtained by thermal decomposition of the above-mentioned carbamic acid ester. ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1C)

[0219] In structural formula (1C), R ３１ R is a p-valent organic group. More specifically, ３１ R ２１ or R ２１ It is a group derived from R. ２１ The group derived from is R ２１ The structure of the group may be a group whose structure has changed under the conditions of thermal decomposition, and after thermal decomposition, R ２１ The group may be one in which some of the internal structure, such as the skeleton and functional groups, has been modified. Examples of structural modifications include halogenation, nitration, and hydrogenation, and can be carried out by known methods or similar methods.

[0220] In structural formula (1C), R ２２ , and p are R in structural formula (2C), respectively. ２２ , and p are synonymous, and the preferred embodiment is the same.

[0221] In structural formula (1C), the relationship between p and q is p ≥ q. Furthermore, q is an integer between 1 and p, preferably between 2 and p. Preferably, q is between 1 and 6, more preferably between 1 and 3, even more preferably between 1 or 2, and particularly preferably between 2. More preferably, the combination of p and q is such that p is an integer between 1 and 6, particularly between 2 and 6, and q is an integer between 1 and 6; particularly preferably, p is an integer between 1 and 3, particularly between 2 and 3, and q is an integer between 1 and 3; even more preferably, p is 1 or 2, and q is 1 or 2; and especially preferably, p is 2 and q is 2. In addition, in the manufacturing method according to this embodiment, it is preferable that all carbamate groups in the carbamic acid ester are converted to isocyanate groups, and therefore, it is also preferable that q = p.

[0222] The isocyanates produced by the manufacturing method according to Disclosure C include, specifically, monoisocyanates such as n-butyl isocyanate, tert-butyl isocyanate, n-hexyl isocyanate, n-octyl isocyanate, n-octadecyl isocyanate, cyclohexyl isocyanate, adamantyl isocyanate, benzyl isocyanate, α-methylbenzyl isocyanate, phenyl isocyanate, o-tolyl isocyanate, m-tolyl isocyanate, p-tolyl isocyanate, o-nitrophenyl isocyanate, m-nitrophenyl isocyanate, p-nitrophenyl isocyanate, o-methoxyphenyl isocyanate, m-methoxyphenyl isocyanate, p-methoxyphenyl isocyanate, 4-isocyanatoethyl benzoate, 2,6-dimethylphenyl isocyanate, 3,5-dimethylphenyl isocyanate, 1-naphthyl isocyanate, and 2-naphthyl isocyanate. Cyanates; hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), norbornene diisocyanate, 2,4-tolylene diisocyanate (2,4-TDI), 2,6-tolylene diisocyanate (2,6-TDI), 2,2'-diphenylmethane diisocyanate (2,2'-MDI), 2,4'-diphenylmethane diisocyanate (2,4'-MDI), 4,4'-diphenylmethane diisocyanate (4,4'-MDI) Examples include polyisocyanates such as DI), m-xylylene diisocyanate (m-XDI), p-xylylene diisocyanate (p-XDI), tetramethylxylylene diisocyanate (TMXDI), 1,5-naphthalene diisocyanate (1,5-NDI), hydrogenated diphenylmethane diisocyanate (hydrogenated MDI), hydrogenated xylylene diisocyanate (hydrogenated XDI), and polymethylene polyphenylene polyisocyanate; and their isomers; etc. Isomers include, for example, when the isocyanate relating to this disclosure C is one of the above-mentioned MDIs, their polynuclear forms, such as polymeric MDI.

[0223] Furthermore, as an isocyanate relating to the present disclosure C, for example, in the above structural formula (1C), p is 2 or more, q is 1 or more, and R ３１ However, examples include isocyanates, which are organic groups with a valency of p, wherein the organic group is an aliphatic hydrocarbon group having 1 or more carbon atoms, or an aromatic hydrocarbon group having 6 or more carbon atoms. Here, the aliphatic hydrocarbon group is the -CH group in the aliphatic hydrocarbon group. ２ -, -O-, -S-, or -SO ２ It may be substituted with -. Also, the aromatic hydrocarbon group may have two or more aromatic rings that are single bonds, -CH ２ The group may be connected by at least one linking group selected from the group consisting of -, -O-, and -S-. Furthermore, the isocyanate according to the present disclosure C is R in the structural formula (1C) above. ３１ However, it is an aromatic hydrocarbon group, that is, an organic group with a valence p containing aromatics, and in structural formula (1C) -NHCOOR ２２ It is preferable that the nitrogen atom in the group and the nitrogen atom in the -NCO group are directly bonded to the carbon atoms constituting the aromatic ring in the organic group. Particularly preferred as such isocyanates is diphenylmethane diisocyanate having the structure shown in structural formula (3-1), and even more preferably isocyanates having the structure shown in structural formula (3-2).

[0224]

[0225] In structural formula (3-1), s and t each represent 0 or 1, where s + t = 1. ００ This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.

[0226]

[0227] The isocyanate shown in structural formula (3-2) is generally diphenylmethane diisocyanate (hereinafter sometimes referred to as "MDI"), and includes, for example, 2,2'-MDI, 2,4'-MDI, and 4,4'-MDI.

[0228] Furthermore, the isocyanates represented by structural formulas (3-1) and (3-2) above are obtained by converting the carbamate group of the corresponding carbamic acid ester to an isocyanate group. The corresponding carbamic acid ester is not particularly limited as long as it gives the isocyanate represented by structural formulas (3-1) and (3-2) upon thermal decomposition, but for example, the carbamic acid ester represented by structural formula (4) below can be cited.

[0229]

[0230] In structural formula (4), R ０１ and R ０２ Each of these independently represents an aliphatic hydrocarbon group having 1 to 4 carbon atoms. Specifically, R ０１ , and R ０２ Each of these can be independently selected from the group consisting of a methyl group, an ethyl group, an n-propyl group, an isopropyl group, an n-butyl group, an isobutyl group, a sec-butyl group, and a tert-butyl group. ０１ and R ０２ However, because each is independently an aliphatic hydrocarbon group having 1 to 4 carbon atoms, as described above, the hydroxy compound produced as a by-product by the thermal decomposition of the carbamic acid ester is a lower aliphatic alcohol with 1 to 4 carbon atoms and a low boiling point, thus making it easier to continuously extract the hydroxy compound as a gaseous component from the reaction vessel in step 2-1.

[0231] Furthermore, R ０１ and R ０２ It is particularly preferable that it be a methyl group. ０１ and R ０２When both are methyl groups, the hydroxy compound produced as a by-product by the thermal decomposition of the carbamic acid ester is methanol, which has a particularly low boiling point, making it particularly easy to continuously extract it as a gaseous component from the reaction system. Furthermore, as shown in the equilibrium reaction equation (I), the reaction to obtain isocyanate by thermal decomposition of the carbamic acid ester is an equilibrium reaction between the generated isocyanate and the by-product hydroxy compound (alcohol). Therefore, by removing the by-product hydroxy compound from the reaction system, isocyanate can be produced more efficiently. Furthermore, by making the by-product methanol, which is easier to extract as a gaseous component from the reaction system, isocyanate can be produced more efficiently. In addition, since methanol has a large difference in boiling point from the isocyanate shown in the structural formula (3-2), separation of methanol and isocyanate after extraction from the reaction vessel can be performed more easily, contributing to the production of isocyanate of higher purity. ０１ , and R ０２ An example of a carbamic acid ester in which both are methyl groups is methylenediphenyl 4,4'-dimethylcarbamate (hereinafter also referred to as "MDC-Me").

[0232] [Catalyst] The thermal decomposition of carbamic acid esters is preferably carried out in the presence of at least one compound (catalyst) selected from the group consisting of fatty acid metal salts and phosphate metal salts, and more preferably in the presence of a fatty acid metal salt.

[0233] (Fatty acid metal salts) Fatty acid metal salts are compounds represented by structural formula (IA) or structural formula (IB). Fatty acid metal salts may also be hydrates. (R １１ COO) ｎ１ M １１ (IA) (R １２ COO) ｎ２ M １２ (IB)

[0234] In structural formula (IA), M １１ These are Group 1 metals, Group 2 metals, Group 13 metals, or lanthanide metals of the periodic table. Of these, M １１It is preferably a Group 2 metal, Group 13 metal, or lanthanide metal of the periodic table, more preferably magnesium, calcium, strontium, barium, aluminum, or cerium, and even more preferably magnesium, aluminum, or cerium. Furthermore, from the standpoint of being able to more reliably suppress the generation of by-products such as allophanates and isocyanurates due to side reactions such as allophanate formation and polymerization of isocyanates, M １１ It is preferably a metal from Group 13 of the periodic table, and more preferably aluminum. On the other hand, from the viewpoint of high catalytic activity, M １１ It is preferably a Group 2 or Group 13 metal of the periodic table, more preferably magnesium or aluminum, and even more preferably aluminum. In structural formula (IA), n1 is M １１ The valence of is preferably an integer between 1 and 4.

[0235] In structural formula (IA), R １１ This is an alkyl group having 1 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms, preferably an alkyl group having 1 to 40 carbon atoms. That is, the fatty acid metal salt that acts as the catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to a linear form; they may have a branched structure or a cyclic structure, but are preferably linear in that they have high catalytic activity and are readily available. Furthermore, the number, position, and bonding mode (i.e., geometric isomerism) of carbon-carbon double bonds in the alkenyl group are not particularly limited. １１ The number of carbon atoms in the alkyl group represented by is preferably 2 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １１ Preferred ranges for the number of carbon atoms in the alkyl group represented by include, for example, 1 to 36, 2 to 40, 12 to 40, 12 to 32, and 16 to 28.

[0236] R １１ The alkyl groups that can be represented include, specifically, methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, sec-butyl group, tert-butyl group, isobutyl group, n-pentyl group, isopentyl group, neopentyl group, n-hexyl group, n-heptyl group, n-octyl group, 2-ethylhexyl group, n-nonyl group, n-decyl group, n-undecyl group, n-dodecyl group, n-tridecyl group, n-tetradecyl group, n-pentadecyl group, n-hexadecyl group, n-heptadecyl group, n-octadecyl group, n-nonadecyl group, n-icosyl group, Examples include n-henicosyl group, n-docosyl group, n-tricosyl group, n-tetracosyl group, n-pentacosyl group, n-hexacosyl group, n-heptacosyl group, n-octacosyl group, n-nonacosyl group, n-triacontyl group, n-hentriacontyl group, n-dotriacontyl group, n-tritriacontyl group, n-tetratriacontyl group, n-pentatriacontyl group, n-hexatriacontyl group, n-heptatriacontyl group, n-octatriacontyl group, n-nonatriacontyl group, n-tetracontyl group, and their isomers.

[0237] R １１ The number of carbon atoms in the alkenyl group represented by is usually between 2 and 40, and is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １２ Preferred ranges for the number of carbon atoms of the alkyl and alkenyl groups represented by the formula include, for example, 2 to 36, 8 to 40, 12 to 40, 12 to 36, 16 to 32, and 16 to 28.

[0238] R １１The alkenyl groups represented by include, specifically, vinyl group, allyl group, propenyl group, isopropenyl group, butenyl group, 2-methylallyl group, pentenyl group, isopentenyl group, hexenyl group, heptenyl group, octenyl group, nonenyl group, decenyl group, undecenyl group, dodecenyl group, tridecenyl group, tetradecenyl group, pentadecenyl group, hexadecenyl group, heptadecenyl group, heptadedecenyl group, heptadedecaneyl group, heptadedecaterinyl group, octadecenyl group, nonadecenyl group, nonadedeceteraenyl group, nonadedecaterinyl group, icosenyl Examples include the yl group, henicocenyl group, henicosahexaenyl group, dococenyl group, tricocenyl group, tetracocenyl group, pentacocenyl group, hexacocenyl group, heptacocenyl group, octacocenyl group, nonacocenyl group, triacontenyl group, hentriacontenyl group, dotriacontenyl group, tritriacontenyl group, tetratriacontenyl group, pentacontenyl group, hexatriacontenyl group, heptacontenyl group, octacontenyl group, nonatriacontenyl group, tetracontenyl group, and their isomers.

[0239] In structural formula (IB), M １２ These are metals from groups 3 to 11 of the periodic table or zinc. Of these, M １２ It is preferable that the catalytic activity is high, and that it is a fourth-period or fifth-period metal, more preferably scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, yttrium, zirconium, niobium, molybdenum, ruthenium, rhodium, palladium, or silver, and even more preferably iron, cobalt, nickel, copper, or zinc. Furthermore, it is preferable that it is a metal with a good balance of high catalytic activity, low toxicity of fatty acid metal salts, and the ability to suppress the generation of by-products such as allophanates and isocyanurates due to side reactions such as allophanate formation and polymerization of isocyanates. １２ It is preferably a metal from groups 8 to 11 of the periodic table or zinc, and more preferably a metal from group 8 of the periodic table, a metal from group 9 of the periodic table, or zinc. More specifically, M １２It is preferably iron, cobalt, nickel, copper, or zinc, more preferably iron, cobalt, or zinc, and even more preferably zinc. In structural formula (IB), n2 is M １２ The valence of is preferably an integer between 1 and 6.

[0240] In structural formula (IB), R １２ The group is an alkyl group having 10 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms, preferably an alkyl group having 10 to 40 carbon atoms. That is, the fatty acid metal salt that acts as a catalyst may be a saturated fatty acid metal salt or an unsaturated fatty acid metal salt, but it is preferably a saturated fatty acid metal salt. The alkyl group and alkenyl group are not limited to a linear form, and may have a branched structure or a cyclic structure, but a linear form is preferred because it has high catalytic activity and is readily available. Furthermore, the number, position, and bonding mode (i.e., geometric isomerism) of carbon-carbon double bonds in the alkenyl group are not particularly limited.

[0241] R １２ The number of carbon atoms in the alkyl group represented by is preferably 12 or more, more preferably 14 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １２ Preferred ranges for the number of carbon atoms of the alkyl group represented by include, for example, 10 to 36, 12 to 40, 14 to 32, and 16 to 28. １２ The alkyl group represented by R is １１ Examples of alkyl groups represented by include those with 10 or more carbon atoms.

[0242] R １２ The number of carbon atoms in the alkenyl group represented by is preferably 8 or more, more preferably 12 or more, even more preferably 16 or more, and also preferably 36 or less, more preferably 32 or less, and even more preferably 28 or less, in terms of high catalytic activity and solubility. That is, R １２Preferred ranges for the number of carbon atoms in the alkenyl group represented by include, for example, 2 to 36, 8 to 40, 12 to 32, and 16 to 28. １２ The alkenyl group represented by R is １１ Examples of alkenyl groups represented by this symbol include the following:

[0243] In summary, examples of fatty acid metal salts include salts of fatty acids such as acetic acid, propionic acid, butyric acid, valeric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, behenic acid, lignoceric acid, palmitoleic acid, oleic acid, elaidic acid, vaccenic acid, erucic acid, linoleic acid, alpha-linolenic acid, gamma-linolenic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid, which are salts of the aforementioned metals.

[0244] Specific examples of fatty acid metal salts include cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, nickel laurate, copper laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, nickel stearate, copper stearate, zinc stearate, aluminum stearate, and stearyl stearate. Examples include cerium palmitate, magnesium palmitate, calcium palmitate, strontium palmitate, barium palmitate, iron palmitate, cobalt palmitate, nickel palmitate, copper palmitate, zinc palmitate, aluminum palmitate, cerium palmitate, magnesium oleate, calcium oleate, strontium oleate, barium oleate, iron oleate, cobalt oleate, nickel oleate, copper oleate, zinc oleate, aluminum oleate, and cerium oleate. Of these, the fatty acid metal salt is preferably cerium acetate, magnesium laurate, calcium laurate, strontium laurate, barium laurate, iron laurate, cobalt laurate, zinc laurate, aluminum laurate, cerium laurate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, and cerium stearate, and is particularly preferably cerium acetate, magnesium stearate, calcium stearate, strontium stearate, barium stearate, iron stearate, cobalt stearate, zinc stearate, aluminum stearate, and cerium stearate.

[0245] The fatty acid metal salt may be a commercially available product, or it may be synthesized by a known manufacturing method or a similar method, for example, by a neutralization reaction between a fatty acid and a base containing the above metal.

[0246] The metal phosphate used as a catalyst in the thermal decomposition step is represented by the following structural formula (IC). The metal phosphate may be a hydrate. (M １３ ) ｍ (PO ４ ) ｎ３ (IC)

[0247] In the structural formula (IC), M １３ is a Group 1-11 metal in the periodic table, a Group 13 metal in the periodic table, zinc, or a lanthanoid metal. In the structural formula (IC), m and n3 satisfy M １３ valence × m = 3 × n3. m and n3 are preferably the minimum values among the values satisfying the above formula. For example, when M １３ is trivalent cerium, m is 1 and n3 is 1.

[0248] Specific examples of the metal phosphate include sodium phosphate, potassium phosphate, magnesium phosphate, calcium phosphate, barium phosphate, zinc phosphate, aluminum phosphate, and cerium phosphate.

[0249] Generally, homogeneous catalysts exhibit higher catalytic activity than heterogeneous catalysts. Therefore, as the catalyst in the present embodiment, when thermal decomposition is carried out in a solvent, it is preferably selected from those having high solubility in the solvent and those that are liquid under the reaction conditions. When thermal decomposition is carried out without a solvent, it is preferably selected from those that are liquid under the reaction conditions. From this perspective, the catalyst used in the thermal decomposition step is preferably a fatty acid metal salt represented by the structural formula (IA) or the structural formula (IB), and is represented by the structural formula (IA), where R １１ is a long-chain fatty acid metal salt having an alkyl group with 12 to 40 carbon atoms or an alkenyl group with 12 to 40 carbon atoms, or is represented by the structural formula (IB), where R １２ is a long-chain fatty acid metal salt having an alkyl group with 12 to 40 carbon atoms or an alkenyl group with 12 to 40 carbon atoms is more preferable.

[0250] The catalyst may be used alone, or two or more may be used in any combination and ratio. The amount of catalyst used in the pyrolysis step should be appropriately selected depending on the type of carbamic acid ester, the type of catalyst, and the reaction conditions. When multiple types of catalysts are used, the catalyst amount refers to the total amount. Specifically, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is 100.0 mol%) is not particularly limited, but is preferably 0.01 mol% or more, more preferably 0.1 mol% or more, particularly preferably 0.3 mol% or more, preferably 20.0 mol% or less, more preferably 10.0 mol% or less, particularly preferably 5.0 mol% or less, and even more preferably 1.5 mol% or less. In other words, the range of the catalyst amount is preferably, for example, 0.01 mol% to 20.0 mol%, more preferably 0.1 mol% to 10.0 mol%, particularly preferably 0.3 mol% to 5.0 mol%, and even more preferably 0.3 mol% to 1.5 mol%.

[0251] Alternatively, the amount of catalyst relative to the carbamic acid ester (the amount of catalyst when the amount of carbamic acid ester is 100% by mass) is not particularly limited, but is preferably 0.02% by mass or more, more preferably 0.2% by mass or more, even more preferably 0.6% by mass or more, and also preferably 40.0% by mass or less, more preferably 20.0% by mass or less, particularly preferably 10.0% by mass or less, and even more preferably 3.0% by mass or less. That is, the range of the catalyst amount is, for example, preferably 0.02% by mass or more and 40.0% by mass or less, more preferably 0.2% by mass or more and 20.0% by mass or less, particularly preferably 0.6% by mass or more and 10.0% by mass or less, and even more preferably 0.6% by mass or more and 3.0% by mass or less.

[0252] [Solvent] The organic solvent used in the thermal decomposition process (hereinafter also referred to as the "thermal decomposition solvent") is not particularly limited, but it is preferable that its boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure shown in the structural formula (1C). This is because separation of the isocyanate from the organic solvent from the reaction product only requires the volatilization of the isocyanate, thus reducing the energy required to volatilize the thermal decomposition solvent.

[0253] The boiling point B1 of the above organic solvent is preferably 10°C or more higher than B2 (B1 + 10°C ≥ B2), and more preferably 40°C or more higher than B2 (B1 + 40°C ≥ B2). More specifically, the boiling point B1 is preferably 350°C or higher. Examples of such thermal decomposition solvents include liquid paraffin.

[0254] Furthermore, as the thermal decomposition solvent according to Disclosure C, as described above, it is particularly preferable that the boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure shown in structural formula (1C), and that the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. By including such an organic solvent in the raw material liquid as the thermal decomposition solvent, the generation of by-products other than hydroxy compounds can be suppressed more reliably. This is because the carbamic acid ester can be dissolved better in the raw material liquid, resulting in a more uniform reaction system. The solubility is more preferably 3.0 wt% or more, and particularly preferably 4.0 wt% or more. The upper limit of the solubility is not particularly limited, but for example, it is preferably 30.0 wt% or less, more preferably 20.0 wt% or less, and particularly preferably 15.0 wt% or less. In other words, the solubility is preferably 2.5 wt% to 30.0 wt%, more preferably 3.0 wt% to 20.0 wt%, and particularly preferably 4.0 wt% to 15.0 wt%. Furthermore, since the boiling point B1 is higher than the boiling point B2 of the isocyanate, it is possible to recover the isocyanate from the thermal decomposition product obtained by thermal decomposition by evaporating the isocyanate from the thermal decomposition product. Therefore, when recovering the isocyanate from the thermal decomposition product, the energy required for the evaporation of the solvent can be reduced, and as a result, CO2 emissions related to the production of isocyanate can be reduced. ２ This will make it possible to reduce emissions.

[0255] Furthermore, among the carbamic acid esters having the structure shown in the above structural formula (2C), R ２１ is an organic group with a valence p that contains an aromatic ring, and the carbamate group (-NHCOOR) in structural formula (2C) ２２When thermally decomposing a carbamic acid ester in which the nitrogen atom in the organic group is directly bonded to the carbon atoms constituting the aromatic ring in the organic group, it is particularly effective to use an aromatic organic solvent as the thermal decomposition solvent, in which the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more, and the boiling point B1 is higher than the boiling point B2 of the isocyanate obtained by thermal decomposition of the carbamic acid ester, in which at least one of the carbamate groups directly bonded to the carbon atoms constituting the aromatic ring of the carbamic acid ester is converted to an isocyanate group. In other words, the inventors have recognized that when obtaining isocyanate by thermal decomposition of carbamic acid ester, the selection of the solvent used for thermal decomposition is important for producing isocyanate at low cost and in high yield. Furthermore, we found that carbamic acid esters having a carbamate group directly bonded to the aromatic ring behave differently during thermal decomposition in the same solvent as carbamic acid esters having a carbamate group bonded to the aromatic ring via a methylene group (such as xylylenedicarbamate), and the yield of the resulting isocyanate can also differ significantly. The reason for this is unclear, but it is presumed that this is due to the fact that the carbamate group directly bonded to the aromatic ring has weaker basicity as an amine compared to, for example, the carbamate group bonded to the aromatic ring via a methylene group. And, having the structure shown in the above structural formula (2C), R ２１ The organic group having a valence p and containing an aromatic ring, and the carbamate group (-NHCOOR) in the structural formula (2C) ２２ As a solvent for the thermal decomposition of a carbamic acid ester in which the nitrogen atom in the group is directly bonded to the carbon atoms constituting the aromatic ring in the organic group, an aromatic organic solvent having a solubility of 2.5 wt% or more at 180°C and a boiling point B2 higher than that of the isocyanate obtained by the thermal decomposition of the carbamic acid is particularly suitable for obtaining isocyanate in high yield while minimizing energy consumption during production.

[0256] The solubility in Disclosure C is measured by either Method 1 or Method 2 below. <Method 1 for measuring solubility> If the carbamate ester has a melting point of 180°C or higher, it can be measured using a high-temperature filtration device (manufactured by Senshu Science) and a polytetrafluoroethylene membrane filter with a pore size of 0.5 μm (model: T050A025A, manufactured by Advantec), following the steps (1) to (8) below. (1) Accurately weigh 4 g of carbamate ester and place it in a screw-cap vial. (2) Add 4 g of the solvent to be evaluated to the screw-cap vial containing the sample. (3) Heat the screw-cap vial to bring the temperature of the contents of the screw-cap vial to 180°C. (4) Add 0.1 g of carbamate ester to the screw-cap vial and shake the vial. Continue this operation until the contents of the screw-cap vial are no longer visibly transparent. (5) When the contents of the screw-cap bottle are no longer transparent, stop adding the carbamate ester and transfer the entire contents of the screw-cap bottle to a high-temperature filtration apparatus and filter it hot. (6) Allow the residue to cool to room temperature, wash it with a poor solvent (such as hexane), and then let it stand until the poor solvent has completely evaporated. (7) Weigh the dried residue accurately and determine the mass of the residue (b). (8) Calculate the solubility of the carbamate ester in the solvent to be measured at a temperature of 180°C using the following formula (1). In the following formula (1), "a" is the total amount of carbamate ester added to the screw-cap bottle until the contents of the screw-cap bottle are no longer visibly transparent. <Formula (1)> Solubility (wt%) = [(a - b) / (amount of solvent + (a - b))] × 100

[0257] <Method for Measuring Solubility 2> When a carbamic acid ester has a melting point of 180°C or lower, particularly below 180°C, the solubility shall be defined as the maximum sample concentration at which the sample (carbamic acid ester) to be measured is completely dissolved by visual inspection. Here, complete dissolution means a state in which no insolubility or bilayer separation of the sample is observed by visual inspection.

[0258] The melting points of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) are 180°C, methylenediphenyl 4,4'-diethylcarbamate (MDC-Et) are 134°C, methylenediphenyl 4,4'-dibutylcarbamate (MDC-Bu) are 110°C, and hexanemethylenedimethylcarbamate (HDC-Me) is 98°C. When measuring the solubility of MDC-Me using the above measurement method 1, two-layer separation may be visually observed during the heating process depending on the solvent. In that case, the solubility should be determined according to the above measurement method 2.

[0259] An example of an aromatic organic solvent that satisfies the above relationship between boiling point and solubility is an aromatic organic solvent having the structure shown in structural formula (6C). Ar-(R １０６ ) ｎ１０６ (6C) In structural formula (6C), Ar represents an aryl group, R １０６ n106 is a C1-C30 hydrocarbon group which may contain an aromatic ring. n106 is an integer of 1 or more. Examples of aryl groups include phenyl groups and naphthyl groups. Examples of C1-C30 hydrocarbon groups which may contain an aromatic ring include C1-C30 linear or branched alkyl groups and benzyl groups. In particular, organic solvents containing at least two benzene rings or at least one naphthalene ring in the structure shown by structural formula (6C) are preferred. Specific examples of aromatic organic solvents having the structure shown by structural formula (6C) include alkylnaphthalene, dibenzyltoluene, and dialkylbenzene. In particular, it is preferable that the organic solvent contains at least one solvent selected from the group consisting of alkylnaphthalene and dibenzyltoluene.

[0260] As a solvent for thermal decomposition, an aromatic organic solvent having a boiling point B1 higher than the boiling point B2 of an isocyanate having the structure shown in structural formula (1C), and having a solubility of the carbamic acid ester corresponding to the isocyanate at a temperature of 180°C of 2.5 wt% or more, specifically having the structure shown in structural formula (2C), and R ０１ and R０２ Specific examples of solvents in which methylenediphenyl 4,4'-dimethylcarbamate, whose methyl group is present, has a solubility of 2.5 wt% at 180°C include alkylnaphthalenes and dibenzyltoluene. Such alkylnaphthalenes can be commercially available, for example, as "Barrel Process Oil B-28AN" (trade name, manufactured by Matsumura Petroleum Co., Ltd.). "Barrel Process Oil B-28AN" has a boiling point of 380°C, which is higher than the boiling point of methylenediphenyl 4,4'-diisocyanate (MDI) (314°C), and the solubility of methylenediphenyl 4,4'-dimethylcarbamate at 180°C is 6.9 wt%. Dibenzyltoluene is the compound shown in structural formula (5), and its boiling point is 391°C, which is higher than the boiling point of MDI, and the solubility of the above carbamic acid ester at 180°C is 55 wt%.

[0261]

[0262] On the other hand, for example, the boiling point of high-viscosity liquid paraffin (manufactured by Nacalai Tesque) (high-viscosity type) is 400°C or higher, and the solubility of MDC-Me is less than 1.2 wt% at 180°C and about 2.3 wt% at 230°C. Furthermore, when the above liquid paraffin is used as the solvent for the thermal decomposition of MDC-Me, the mass balance may decrease compared to when the above "barrel process oil B-28AN" or "dibenzyltoluene" is used.

[0263] The solvent may be used alone or in combination of two or more. Specifically, for example, the above-mentioned "Barrel Process Oil B-28AN" or dibenzyltoluene may be used alone, or a mixture thereof may be used. However, when the solvent is a mixture, it is preferable that the boiling point (B1) of the mixture is higher than the boiling point B2 of the isocyanate, and that the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. Furthermore, it is preferable to use a solvent for thermal decomposition that has been dehydrated by a known method, for example. Specifically, for example, a method can be used in which heated and dried molecular sieves are added to the thermal decomposition solvent and left to stand for about 12 to 24 hours.

[0264] [Reaction Temperature] The reaction temperature in the thermal decomposition step is not particularly limited as long as it is a temperature at which the carbamic acid ester used as a raw material can be thermally decomposed and isocyanate can be produced, and is usually between 100°C and 300°C. From the viewpoint of increasing the reaction rate while suppressing side reactions, it is preferable to set the temperature between 150°C and 280°C, more preferably between 180°C and 260°C, and particularly preferably between 200°C and 240°C.

[0265] [Reaction Time] The reaction time in the thermal decomposition step is not particularly limited and can be appropriately adjusted depending on the type of catalyst, reaction temperature, and reaction scale. Specifically, the reaction time is preferably 0.5 hours or more and 60.0 hours or less, more preferably 1.0 hour or more and 48.0 hours or less, even more preferably 2.0 hours or more and 36.0 hours or less, even more preferably 3.0 hours or more and 24.0 hours or less, and particularly preferably 4.0 hours or more and 12.0 hours or less. Alternatively, the reaction time may be 0.5 hours or more and 48.0 hours or less, 1.0 hour or more and 24.0 hours or less, or 2.0 hours or more and 12.0 hours or less. By keeping the reaction time within the above range, the thermal decomposition of the carbamic acid ester can be sufficiently carried out, and side reactions such as allophanate formation and polymerization of the generated isocyanate can be suppressed.

[0266] [Operating Procedure] One embodiment of the method for producing isocyanate according to Disclosure C will be explained with reference to Figure 5. First, a raw material liquid containing carbamic acid ester, catalyst, and solvent is prepared in a storage tank 101C (Step 1C). Next, the raw material liquid is supplied from the storage tank 101C to a reaction vessel 105C that has been preheated to a predetermined temperature (reaction temperature) via line 103C. Inside the reaction vessel 105C, the carbamic acid ester is thermally decomposed by heating the liquid film containing the raw material liquid (Step 2C). Then, the mixture containing isocyanate produced by the thermal decomposition of the carbamic acid ester and the by-product hydroxy compound is continuously withdrawn as a gas phase component from line 107C (Steps 2C-2, Step 2C-1). The diisocyanate from the mixture containing isocyanate and hydroxy compound withdrawn from the reaction vessel 105C is condensed in a condenser 109C to separate it from the hydroxy compound contained in the mixture and recovered in a storage tank 111C. Furthermore, the hydroxy compounds that have passed through condenser 109C as gas-phase components are condensed in condenser 115C and recovered in storage tank 117C. The reaction system, including the reaction vessel 105C, is configured to be able to be reduced to any pressure by vacuum pump 113C. By reducing the pressure inside reaction vessel 105C with vacuum pump 113C, the isocyanates and lower aliphatic alcohols generated in the reaction vessel can be extracted from reaction vessel 105C as gas-phase components. The pressure within the reaction system is not particularly limited as long as the isocyanate and hydroxy compound in the reaction vessel can be removed from the reaction vessel 105C via line 107C as gas phase components, and can be set appropriately according to the type of reaction solvent and reaction temperature. For example, the pressure inside the reaction vessel is preferably 0.1 kPaA or more and 20.0 kPaA or less, more preferably 0.5 kPaA or more and 20.0 kPaA or less, and particularly preferably 1.0 kPaA or more and 20.0 kPaA or less.In this embodiment, the steps of extracting the isocyanate as a gas phase component from the reaction vessel 105C (step 2C-2) and extracting the hydroxy compound as a gas phase component (step 2C-1) are performed simultaneously (integrally). However, the embodiment is not limited to this, and the line for extracting the isocyanate from the reaction vessel 105C and the line for extracting the hydroxy compound may be separate.

[0267] Furthermore, even with heating in the reaction vessel 105C, at least a portion of the carbamic acid ester in the raw material liquid may not decompose and may remain unreacted (undecomposed) in the reaction vessel 105C. For this reason, it is preferable to, for example, remove the liquid containing the unreacted carbamic acid ester from the bottom of the reaction vessel 105C, return it to the storage tank 101C via line 119C, and then subject it to the heating step (step 2C) in the reaction vessel 105C again. This can further improve the yield of isocyanate.

[0268] The above reaction may be carried out in an air atmosphere or in an inert gas atmosphere such as nitrogen and argon, but since thermal decomposition is preferable in an inert gas atmosphere, it is preferable to carry it out in an inert gas atmosphere.

[0269] Furthermore, the method for producing isocyanate according to this embodiment may include optional steps in addition to the thermal decomposition step. An optional step, for example, is a purification step to increase the purity of the isocyanate. As a method for purifying the isocyanate in the purification step, purification methods commonly used in the field of organic synthesis, such as filtration, adsorption, column chromatography, and distillation, can be employed.

[0270] [Disclosure A] Disclosure A will be described in more detail below with reference to examples, but Disclosure A is not limited to the embodiments embodied in the following examples, unless it deviates from its gist. In the examples, "room temperature" means a temperature range of 15°C to 35°C.

[0271] (Analysis method) ・ １ H-NMR analysis method １The 1H-NMR analysis was performed using a nuclear magnetic resonance spectrometer (product name: ULTRASHIELD AVANCE-III, Bruker) under the following conditions: Frequency: 400 MHz, Measurement solvent: Deuterated tetrahydrofuran. The deuterated tetrahydrofuran was dehydrated overnight using molecular sieves 3A1 / 16 (Fujifilm Wako Pure Chemical Industries, Ltd.) which had been activated by heating with a heat gun for more than 25 minutes.

[0272] <Example 1A> Alkylnaphthalene (product name: Barrel Process Oil B-28AN, manufactured by Matsumura Oil Co., Ltd.) was prepared as the solvent for thermal decomposition. The alkylnaphthalene was dehydrated overnight using molecular sieves 3A1 / 16 that had been activated by heating with a heat gun for 25 minutes or more.

[0273] Inside the glove box, 3.0 g (9.54 mmol) of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) and 0.036 g (0.0569 mmol) of zinc stearate were placed in a 100 mL two-necked pear-shaped flask corresponding to reaction vessel 103 in Figure 1. Next, the two-necked flask was sealed tightly and removed from the glove box. While argon gas was flowing through the flask, an air-cooled reflux tubing corresponding to condenser 107 in Figure 1 was attached to one neck, and a three-way stopcock was attached to the other neck. Then, while argon gas was flowing into the flask through the three-way stopcock, 30 mL of the alkylnaphthalene was added. A vacuum pump and a trap tube were also connected to the reflux tubing. The vacuum pump corresponds to vacuum pump 109 in Figure 1, and the trap tube corresponds to condenser 111 and storage tank 113 in Figure 1.

[0274] Next, the vacuum pump was activated to reduce the pressure inside the reaction vessel to the pressure shown in Table 1. The stirring blade was rotated at 700 rpm to stir the raw material solution inside the reaction vessel, and the temperature was raised to 230°C using an aluminum block. When the pressure inside the reaction vessel dropped to the pressure shown in Table 1, the trap tube was placed in a Dewar flask containing acetone / dry ice. Heating and stirring were continued for 5 hours from the time the temperature reached 230°C to carry out the thermal decomposition reaction. After the reaction was complete, the heating with the aluminum block and the operation of the vacuum pump were stopped, and the mixture was left at room temperature for 1 hour. Then, anhydrous tetrahydrofuran (82.5 mL, 3.9 wt%) and mesitylene (0.1 eq, 0.115 g) as an internal standard substance were added while stirring in a glove box. Next, the two-necked flask was capped and removed from the glove box, and stirred with an aluminum block at room temperature for 20 minutes at 700 rpm. Subsequently, 0.1 mL of the liquid in the two-necked flask was collected with a syringe while performing argon flow, added to an NMR tube, and then 0.5 mL of deuterated tetrahydrofuran was added to prepare an NMR sample. Using this NMR sample, NMR measurements were performed according to the method described above to calculate the molar ratios (based on mesitylene) of MDC-Me, diisocyanate (methylenediphenyl 4,4'-diisocyanate), and the unilateral compound in the liquid in the two-necked flask after the reaction. The results are shown in Table 1. Note that the unilateral compound refers to the two CH groups present in MDC-Me. ３ This compound has only one of the COONH- groups converted to a -N=C=O group. Visual observation of the liquid in the reaction vessel revealed that it remained homogeneous throughout the thermal decomposition reaction and did not undergo phase separation. The boiling point of methylenediphenyl 4,4'-diisocyanate, which is produced by the decomposition of the two carbamate groups of MDC-Me, is 314°C.

[0275] <Comparative Example 1A> Thermal decomposition of MDC-Me was carried out in the same manner as in Example 1A, except that the solvent used for thermal decomposition was changed from alkylnaphthalene to liquid paraffin (high viscosity type) (manufactured by Nacalai Tesque). Then, NMR measurement of the liquid in the two-necked flask was performed in the same manner as in Example 1A. Visual observation of the liquid in the reaction vessel revealed that it had separated into two layers from the start of the reaction, and MDC-Me was not dissolved in the liquid paraffin. The boiling point of the liquid paraffin is 400°C or higher, and the solubility of MDC-Me at a temperature of 180°C is less than 1.2 wt%.

[0276] <Comparative Example 2A> The thermal decomposition of MDC-Me was carried out in the same manner as in Example 1A, except that the solvent used for thermal decomposition was changed from alkylnaphthalene (B-28AN) to decalin (decahydronaphthalene). However, since the liquid (raw material solution) rose to the top of the reflux tube during the reaction, the reaction was stopped after 1.5 hours from the start of the reaction. Then, NMR measurement of the liquid in the two-necked flask was performed in the same manner as in Example 1A. The boiling point of decalin is 190°C, and the solubility of MDC-Me at a temperature of 180°C is 22 wt%. Visual observation of the raw material solution in the reaction vessel immediately after the start of the reaction revealed that MDC-Me was insoluble in the solvent. MDC-Me was also observed in the reaction vessel one hour after the start of the reaction. Furthermore, a large amount of deposits were observed on the reflux tube immediately after the start of the reaction, and a large amount of deposits were also observed on the reflux tube one hour after the start of the reaction. These phenomena are thought to be due to the evaporation of decalin from the reaction vessel during the reaction, as decalin has a low boiling point.

[0277] <Examples 2A-3A> Except for changing the pressure inside the reaction vessel as shown in Table 1, the thermal decomposition of MDC-Me was carried out in the same manner as in Example 1A. Then, the NMR measurement of the liquid in the two-necked flask was performed in the same manner as in Example 1A.

[0278] <Comparative Examples 3A-4A> Except for changing the solvent used for thermal decomposition from alkylnaphthalene to liquid paraffin (special grade) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.), thermal decomposition of MDC-Me was carried out in the same manner as in Example 2A or Example 3A. Then, NMR measurement of the liquid in the two-necked flask was performed in the same manner as in Example 1A. The above liquid paraffin has a boiling point of 400°C or higher, and the solubility of MDC-Me at a temperature of 180°C is 1.2 wt%. Liquid paraffin (special grade) (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) has a lower viscosity than liquid paraffin (high viscosity type) (manufactured by Nacalai Tesque) used in Comparative Example 1A.

[0279] <Example 4A> Thermal decomposition of MDC-Me was carried out in the same manner as in Example 1A, except that the solvent for thermal decomposition was changed from alkylnaphthalene (product name: Barrel Process Oil B-28AN, manufactured by Matsumura Oil Co., Ltd.) to dibenzyltoluene (product name: Barreltherm 400, manufactured by Matsumura Oil Co., Ltd.). Then, NMR measurement of the liquid in the two-necked flask was performed in the same manner as in Example 1A. The boiling point of dibenzyltoluene is 391°C, and the solubility of MDC-Me at a temperature of 180°C is 55 wt%.

[0280] <Example 5A> MDC-Et was thermally decomposed in the same manner as in Example 1A, except that methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) was replaced with methylenediphenyl 4,4'-diethylcarbamate (MDC-Et). Then, the liquid in the two-necked flask was measured by NMR in the same manner as in Example 1A. Note that the solubility of MDC-Et at a temperature of 180°C for "B-28AN" is 50 wt%.

[0281] <Example 6A> MDC-Bu was thermally decomposed in the same manner as in Example 1A, except that methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) was replaced with methylenediphenyl 4,4'-dibutylcarbamate (MDC-Bu). Then, the liquid in the two-necked flask was measured by NMR in the same manner as in Example 1A. Note that the solubility of MDC-Bu in "B-28AN" at a temperature of 180°C is 50 wt% or more.

[0282] <Comparative Example 5A> Thermal decomposition of HDC-Me was carried out in the same manner as in Example 1A, except that methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) was replaced with hexanemethylenedimethylcarbamate (HDC-Me). Then, NMR measurement of the liquid in the two-necked flask was performed in the same manner as in Example 1A. Note that "B-28AN" indicates that the solubility of HDC-Me at a temperature of 180°C is 50 wt% or more. Furthermore, the boiling point of hexamethylene diisocyanate (HDI), which is produced by the decomposition of the two carbamate groups of HDC-Me, is 255°C.

[0283] Table 1A shows the evaluation results for Examples 1A to 6A and Comparative Examples 1A to 5A. In Table 1A, the material balance is the sum of the proportions of unreacted carbamic acid ester, diisocyanate produced by thermal decomposition, and unilateral product. The solubility values ​​listed in Table 1A are those obtained by solubility measurement method 1 for Examples 1A to 4A and Comparative Examples 1A to 4A. On the other hand, the values ​​for Examples 5A to 6A and Comparative Example 5A are those obtained by solubility measurement method 2.

[0284]

[0285] From the results in Table 1A, it can be seen that in Example 1A, the proportion (material balance) of the three components in the reaction product—diisocyanate, unilateral product, and the raw material carbamic acid ester—was approximately three times higher than in Comparative Example 1A, indicating that the generation of by-products other than the three components mentioned above was significantly suppressed. The comparison between Example 2A and Comparative Example 3A, and between Example 3A and Comparative Example 4A, also shows that diisocyanate could be obtained more efficiently by using a specific solvent as the thermal decomposition solvent. Furthermore, the comparison between Example 2A and Comparative Example 5A shows that even when using the same thermal decomposition solvent ("B-28AN"), MDC-Me, which has a carbamate group directly bonded to the aromatic ring, can produce diisocyanate more efficiently than HDC-Me, in which the carbamate group is not directly bonded to the aromatic ring.

[0286] [Disclosure B] Disclosure B will be described in more detail below with reference to examples, but Disclosure B is not limited to the embodiments embodied in the following examples without departing from its gist. In the examples, "room temperature" means a temperature range of 15°C to 35°C.

[0287] <Analysis method> ・ １ H-NMR analysis method １ The 1H-NMR analysis was performed using a nuclear magnetic resonance spectrometer (product name: ULTRASHIELD AVANCE-III, Bruker) under the following conditions: Frequency: 400 MHz, Measurement solvent: Deuterated tetrahydrofuran. The deuterated tetrahydrofuran used as the measurement solvent was activated by heating it with a heat gun for more than 25 minutes and then dehydrated overnight using molecular sieves 3A1 / 16 (Fujifilm Wako Pure Chemical Industries, Ltd.).

[0288] (Example 1B) Alkylnaphthalene (trade name: Barrel Process Oil B-28AN, manufactured by Matsumura Oil Co., Ltd.) was prepared as the solvent for thermal decomposition. The alkylnaphthalene used was dehydrated overnight using molecular sieves 3A1 / 16 that had been activated by heating with a heat gun for 25 minutes or more. Other reagents were used as commercially available products.

[0289] In a glove box filled with nitrogen, 0.3 mol% zinc stearate as catalyst, 4 g of methylenediphenyl 4,4'-dimethylcarbamate (MDC-Me) as substrate, and 22.5 g of the above-mentioned dehydrated alkylnaphthalene as thermal decomposition solvent were placed in a 100 mL pear-shaped flask (corresponding to reaction vessel 101B). After sealing the pear-shaped flask, it was removed from the glove box, and a U-shaped glass tube (corresponding to line 103B) was connected to it. A 100 mL two-necked flask (corresponding to storage tank 111B) with a stopcock attached was connected to the other end of the U-shaped glass tube. A condenser (corresponding to second condenser 115B) and an oil pump (corresponding to vacuum pump 113B) were attached to this stopcock. A temperature-controlled ribbon heater (not shown) was also wrapped around the U-shaped glass tube.

[0290] The internal pressure of the reaction vessel was reduced to 0.2 kPaA by operating an oil pump. To prevent the precipitation of isocyanate inside the U-shaped glass tube, the U-shaped glass tube was heated to 230°C. At the same time, the round-necked flask was heated to 230°C in an oil bath, and the thermal decomposition reaction was carried out for 30 minutes. During the reaction, the two-necked flask was cooled in a water bath (corresponding to the first condenser 109B), and the isocyanate (methylenediphenyl 4,4'-diisocyanate (4,4'-MDI) and its unilateral component) and the methanol-containing gas phase component, which had been withdrawn from the round-necked flask via the U-shaped glass tube, were condensed and recovered in the two-necked flask. The unilateral component refers to the two CH groups present in MDC-Me. ３ This compound is formed in which only one of the COONH- groups is converted to a -N=C=O group, and will hereafter be referred to as H-MDI. The boiling point of 4,4'-MDI, which is produced by the decomposition of the two carbamate groups of MDC-Me, is 314°C. Barrel Process Oil B-28AN has a boiling point of 380°C, which is higher than the boiling point of 4,4'-MDI (314°C), and the solubility of MDC-Me at 180°C is 6.9 wt%. This solubility is the value obtained by the solubility measurement method 1 described above.

[0291] After the reaction was complete, the entire reaction vessel was cooled to room temperature, and the round-bottom flask and two-neck flask were sealed and placed in a glove box filled with nitrogen. 20 mL of tetrahydrofuran and 800 mg of trimethoxybenzene as an internal standard were added to each flask and mixed thoroughly. After filtering off the solids, tetrahydrofuran-d8 was used as the solvent. １ ¹H NMR measurements were performed to calculate the molar ratios of 4,4'-MDI, ¹H-MDI, and MDC-Me in the contents of the two-necked flask (distillation recovery) and the contents of the round-bottom flask (residual in the reaction vessel). The results are shown in Table 1B. In Table 1B, 4,4'-MDI is abbreviated as "MDI".

[0292] (Comparative Example 1B) The thermal decomposition reaction was carried out in the same manner as in Example 1B, except that the thermal decomposition solvent was changed from alkylnaphthalene to liquid paraffin (high viscosity type) (manufactured by Nacalai Tesque). The MDI, the yield of one side, and the recovery rate of MDC-Me were calculated for the contents of the two-necked flask (distillation recovery) and the contents of the pear-shaped flask (residual in the reaction vessel). The results are shown in Table 1B. The liquid paraffin has a boiling point of 400°C or higher, and the solubility of MDC-Me at a temperature of 180°C is less than 1.2 wt%. The solubility is the value obtained by the solubility measurement method 1 described above.

[0293]

[0294] As shown in Table 1B, Example 1B, which used alkylnaphthalene as the thermal decomposition solvent, is an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of 4,4'-MDI and whose solubility of MDC-Me at 180°C is 2.5 wt% or more. Compared to Comparative Example 1B, which used liquid paraffin that is not an organic solvent, the mass balance was improved and the carbamic acid ester was converted to diisocyanate with higher efficiency.

[0295] (Example 2B) The thermal decomposition reaction was carried out in the same manner as in Example 1B, except that the thermal decomposition solvent was changed from alkylnaphthalene to dibenzyltoluene. Then, in the same manner as in Example 1B, the yields of diisocyanate (4,4'-MDI) and the unilateral product (H-MDI), as well as the recovery rate of the raw material carbamic acid ester (MDC-Me), were calculated from the contents of the two-necked flask (distillation recovery) and the contents of the round-bottom flask (residual in the reaction vessel). The results are shown in Table 2B. Note that dibenzyltoluene has a boiling point of 391°C, and the solubility of carbamic acid ester (MDC-Me) at 180°C is 55 wt%.

[0296] (Comparative Examples 2B-3B) The thermal decomposition reaction was carried out in the same manner as in Example 1B, except that alkylnaphthalene (product name: Barrel Process Oil B27T, manufactured by Matsumura Petroleum Co., Ltd.) or alkylnaphthalene (product name: Barrel Process Oil B-15AB) was used as the solvent for thermal decomposition. Then, in the same manner as in Example 1B, the yields of diisocyanate (4,4'-MDI) and the unilateral product (H-MDI), as well as the recovery rate of the raw material, carbamic acid ester (MDC-Me), were calculated from the contents of the two-necked flask (distillation recovered) and the contents of the pear-shaped flask (residual in the reaction vessel). Note that "Barrel Process Oil B27T" has a boiling point of 385°C, and the solubility of carbamic acid ester (MDC-Me) at 180°C is 1.9 wt%. Furthermore, "Barrel Process Oil B-15AB" has a boiling point of 352°C, and the solubility of carbamate ester (MDC-Me) at 180°C is 2.3 wt%. The results are shown in Table 2B.

[0297] (Examples 3B-4B) The pyrolysis reaction was carried out in the same manner as in Example 1B, except that the temperature of the U-shaped glass tube and the pear-shaped flask was changed to 250°C or 260°C, and the internal pressure of the reaction vessel was changed to 0.7 kPaA. Then, in the same manner as in Example 1B, the yields of diisocyanate (4,4'-MDI), the unilateral product (H-MDI), and the recovery rate of the raw material, carbamic acid ester (MDC-Me), were calculated from the contents of the two-necked flask (distillation recovered) and the contents of the pear-shaped flask (residual in the reaction vessel). The results are shown in Table 2B. In this example, the degree of reduced pressure in the reaction vessel was relaxed compared to Example 1B, while the reaction temperature was increased. In this example, by relaxing the degree of reduced pressure in the reaction vessel compared to Example 1, the volatilization of the pyrolysis solvent from the reaction vessel was suppressed. Furthermore, by increasing the reaction temperature, the formation of the unilateral product was suppressed, and the yield of 4,4'-MDI was improved compared to Example 1B.

[0298] (Examples 5B-6B) The thermal decomposition reaction was carried out in the same manner as in Example 1B, except that the substrate was changed to methylenediphenyl 4,4'-diethylcarbamate (MDC-Et) or methylenediphenyl 4,4'-dibutylcarbamate (MDC-Bu). Then, in the same manner as in Example 1B, the yields of diisocyanate (4,4'-MDI), the unilateral product (H-MDI), and the recovery rate of the raw material carbamic acid ester (MDC-Et or MDC-Bu) were calculated from the contents of the two-necked flask (distillation recovery) and the contents of the round-bottom flask (residual in the reaction vessel). The results are shown in Table 2B.

[0299] (Example 7B) The thermal decomposition reaction was carried out in the same manner as in Example 1B, except that the substrate was changed to N,N'-hexamethylenebis(methyl carbamate) (HDC-Me). Then, in the same manner as in Example 1B, the yields of diisocyanate (HDI), the unilateral product (H-HDI), and the recovery rate of the raw material, carbamate ester (HDC-Me), were calculated for the contents of the two-necked flask (distillation recovery) and the contents of the round-bottom flask (residual in the reaction vessel). Note that the solubility of carbamate ester (HDC-Me) in "Barrel Process Oil B-28AN" at 180°C is 50 wt% or more. The boiling point of hexamethylene diisocyanate (HDI), which is produced by the decomposition of the two carbamate groups of HDC-Me, is 255°C. The results are shown in Table 2B.

[0300] (Example 8B) The thermal decomposition reaction was carried out in the same manner as in Example 7B, except that the internal pressure in the reaction vessel was changed to 2 kPaA. Then, in the same manner as in Example 1B, the yields of diisocyanate (HDI), the unilateral product (H-HDI), and the recovery rate of the raw material, carbamic acid ester (HDC-Me), were calculated from the contents of the two-necked flask (distillation recovered) and the contents of the pear-shaped flask (residual in the reaction vessel). The results are shown in Table 2B. Note that the solubility values ​​listed in Table 2B are the values ​​obtained by the solubility measurement method 1 described above for Example 2B and Comparative Examples 2B to 3B. On the other hand, the values ​​for Examples 5B to 7B are the values ​​obtained by the solubility measurement method 2 described above.

[0301]

[0302] [Disclosure C] Disclosure C will be described in more detail below with reference to examples, but Disclosure C is not limited to the embodiments embodied in the following examples without departing from its gist. In the examples, "room temperature" means a temperature range of 15°C to 35°C.

[0303] <Example 1C> Isocyanate was produced from carbamic acid ester using the manufacturing apparatus 100C shown in Figure 5. In this example, a 1 L round-bottom flask was used as the storage tank 101C in Figure 5, and a reaction vessel 105C with a heat transfer area of ​​0.05 m² was used. ２A thin-film evaporator (product name: DN60, manufactured by Asahi Seisakusho Co., Ltd.) was used. First, with the line 103C connecting the storage tank 101C and the reaction vessel 105C closed, 24.8 g of MDC-Me, 0.30 g of zinc stearate, and 474.0 g of alkylnaphthalene (product name: Barrel Process Oil B-28AN; manufactured by Matsumura Petroleum Co., Ltd.) were placed in the storage tank 101C and heated to 60°C to prepare the raw material solution. Next, the reaction vessel 105C was heated to 230°C, and the pressure inside the reaction vessel 105C was set to 0.25 kPaA by operating the vacuum pump 113C, and the rotation speed of the wiper (not shown) on the reaction vessel 105C was set to 300 rpm. Furthermore, a temperature-controlled ribbon heater (not shown) was wrapped around the section of line 107C from reaction vessel 105C to condenser 109C and heated to a temperature of 230°C. Next, line 103C was opened, and the raw material liquid from storage tank 101C was supplied to the top of reaction vessel 105C at a rate of 8 g / min. While the liquid flowed down inside reaction vessel 105C, a liquid film of the raw material liquid was formed on the inner wall of reaction vessel 105C using a wiper. Then, the liquid film of the raw material liquid formed on the inner wall of reaction vessel 105C was heated to thermally decompose the carbamic acid ester in the liquid film. The reaction was terminated when the entire amount of prepared raw material liquid had flowed down inside reaction vessel 105C. During the thermal decomposition process in reaction vessel 105C, the vacuum pump 113C was in operation, allowing the gaseous components, including the isocyanate and its halved counterpart produced by the thermal decomposition of the carbamic acid ester, methanol as a by-product, and a portion of the raw material MDC-Me, to be continuously withdrawn from reaction vessel 105C via line 107C. Of the withdrawn gaseous components, the isocyanate, its halved counterpart, and MDC-Me were condensed in an air-cooled cooling tube (corresponding to condenser 109C) connected to line 107C and stored in storage tank 111C. The methanol, as a gaseous component, was guided to condenser 115C via line 110C, where it was condensed and stored in storage tank 117C. A chiller heat exchanger was used as the condenser 115C, and the temperature was adjusted to -50 to -55°C. In this embodiment, line 119C was kept closed.Therefore, at the end of the reaction, a liquid containing the thermal decomposition solvent (reaction residue) accumulated at the bottom of reaction vessel 105C. Visual inspection revealed no insoluble matter in the reaction residue. The amount of liquid accumulated in storage tank 111C was 42.2 g.

[0304] Next, the contents of storage tank 111C and the reaction residue accumulated at the bottom of reaction vessel 105C were analyzed using high-performance liquid chromatography (hereinafter also referred to as "HPLC"), and the molar ratios of MDI, unilateral compound, and MDC-Me in the contents and reaction residue were calculated. Note that unilateral compound refers to the two CH groups present in MDC-Me. ３ This compound has one COONH- group converted to an -N=C=O group. The boiling point of methylenediphenyl 4,4'-diisocyanate (4,4'-MDI), which is produced by the decomposition of the two carbamate groups of MDC-Me, is 314°C. Barrel Process Oil B-28AN has a boiling point of 380°C, which is higher than the boiling point of methylenediphenyl 4,4'-diisocyanate (4,4'-MDI) (314°C), and the solubility of MDC-Me at 180°C is 6.9 wt%. This solubility is the value obtained by the solubility measurement method 1 described above.

[0305] Specifically, first, 10 mg of sample was taken from both the reservoir and the reaction residue, and 1 mL of 20 mM phenylpiperazine / acetonitrile solution was added. This would form a derivative of the isocyanate if it was present in the sample. After confirming that no insoluble matter had formed in the sample, HPLC analysis was performed. The HPLC analysis conditions were as follows.

[0306] (HPLC analysis conditions) • Instrument: Liquid chromatograph (product name: LC-2050, manufactured by Shimadzu Corporation) • Column: TSKgel ODS-100V (5 μm, 4.6 mm x 25 cm) • Eluent: CH ３ CN-1 wt% phosphoric acid aqueous solution (see Table 1 below) • Flow rate: 1 mL / min • Injection volume: 1 μL • Detection conditions: UV (220 nm) • Column temperature: 40°C

[0307] Furthermore, the eluent changes over time, CH ３ The ratio of CN to 1 wt% phosphoric acid aqueous solution was varied as shown in Table 1C below.

[0308]

[0309] <Example 2C> The thermal decomposition of MDC-Me was carried out in the same manner as in Example 1C, except that the temperature of reaction vessel 105C was changed to 250°C. As a result, 175.5 g of material accumulated in storage tank 111C. In addition, no insoluble material was observed visually in the reaction residue at the bottom of reaction vessel 105C. The material in storage tank 111C and the reaction residue accumulated at the bottom of reaction vessel 105C were then subjected to HPLC analysis in the same manner as in Example 1C to determine the molar ratios of 4,4'-MDI, unilateral, and MDC-Me.

[0310] Table 2C shows the molar ratios of 4,4'-MDI, unilateral, and MDC-Me contained in the reservoir and reaction residue for Examples 1C to 2C. In Table 2C, 4,4'-MDI is denoted as "MDI".

[0311]

[0312] <Example 3C> In the same manner as in Example 2C, MDC-Me was thermally decomposed (hereinafter also referred to as "first thermal decomposition") to obtain 175.5 g of a deposit (hereinafter also referred to as "deposit A1") in storage tank 111C. Meanwhile, the amount of reaction residue (hereinafter also referred to as "reaction residue A1") accumulated at the bottom of reaction vessel 105C was 307.5 g. Deposit A1 was removed from storage tank 111C. Next, the reaction residue A1 accumulated at the bottom of reaction vessel 105C was returned to storage tank 101C via line 119C and introduced back into reaction vessel 105C, where the reaction residue A1 was subjected to thermal decomposition (hereinafter also referred to as "second thermal decomposition") under the same conditions as the first thermal decomposition. As a result of the second thermal decomposition, 188.8 g of a deposit (hereinafter also referred to as "deposit A2") was newly accumulated in storage tank 111C. Furthermore, 123.1 g of reaction residue (hereinafter also referred to as "reaction residue A2") accumulated at the bottom of reaction vessel 105C. The stored material A2 was removed from storage tank 111C. Next, the reaction residue A2 accumulated at the bottom of reaction vessel 105C was returned to storage tank 101C via line 119C and introduced back into reaction vessel 105C, where it was subjected to thermal decomposition (hereinafter also referred to as "third thermal decomposition") under the same conditions as the first thermal decomposition. As a result of the third thermal decomposition, 36.6 g of stored material (hereinafter also referred to as "stored material A3") newly accumulated in storage tank 111C. Furthermore, reaction residue accumulated at the bottom of reaction vessel 105C after the third thermal decomposition (hereinafter also referred to as "reaction residue A3").

[0313] Each of the deposits A1-A3 and reaction residues A1-A3 obtained from the first to third thermal decompositions described above was subjected to HPLC analysis in the same manner as in Example 1C, and the molar ratios of 4,4'-MDI, the unilateral, and MDC-Me were calculated. The results are shown in Table 3C. In Table 3C, 4,4'-MDI is denoted as "MDI".

[0314]

[0315] <Comparative Example 1C> The same reaction apparatus used in Example 1C was prepared. First, with the line 103C connecting the storage tank 101C and the reaction vessel 105C closed, 6.0 g of MDC-Me, 0.072 g of zinc stearate, and 195.3 g of alkylnaphthalene (product name: Barrel Process Oil B-28AN; manufactured by Matsumura Petroleum Co., Ltd.) were placed in the storage tank 101C and heated to 60°C to prepare the raw material solution. Next, the reaction vessel 105C was heated to 230°C, and the pressure inside the reaction vessel 105C was set to 2.0 kPaA by operating the vacuum pump 113C, and the rotation speed of the wiper on the reaction vessel 105C was set to 300 rpm. Next, line 103C was opened, and the raw material liquid from storage tank 101C was supplied to the top of reaction vessel 105C at a rate of 8 g / min. While the liquid flowed down inside reaction vessel 105C, a liquid film of the raw material liquid was formed on the inner wall of reaction vessel 105C by a wiper. Then, the liquid film of the raw material liquid formed on the inner wall of reaction vessel 105C was heated (first thermal decomposition step). As a result, no liquid accumulated in storage tank 111C. The reason for this is thought to be that, although the vacuum pump 113C was operated during the thermal decomposition step inside reaction vessel 105C, the degree of reduced pressure was lower compared to Example 1C, so the isocyanate and unilateral components produced by the thermal decomposition of carbamic acid ester were not extracted from reaction vessel 105C as gaseous components.

[0316] Next, the reaction residue accumulated at the bottom of reaction vessel 105C (hereinafter also referred to as "reaction residue C11") was returned to storage tank 101C via line 119C and introduced into reaction vessel 105C to subject reaction residue C1 to thermal decomposition (second thermal decomposition step). No liquid accumulated in storage tank 111C even after the second thermal decomposition step. Next, the reaction residue accumulated at the bottom of reaction vessel 105C (hereinafter also referred to as "reaction residue C12") was returned to storage tank 101C and introduced into reaction vessel 105C to subject reaction residue C2 to thermal decomposition (third thermal decomposition step). No liquid accumulated in storage tank 111C even after the third thermal decomposition step. Next, the reaction residue accumulated at the bottom of reaction vessel 105C (hereinafter also referred to as "reaction residue C13") was returned to storage tank 101C and introduced into reaction vessel 105C to subject reaction residue C3 to thermal decomposition (fourth thermal decomposition step). No liquid accumulated in storage tank 111C even after the fourth thermal decomposition step. On the other hand, reaction residue (hereinafter also referred to as "reaction residue C14") had accumulated at the bottom of reaction vessel 105C. Insoluble matter was visually observed in all of reaction residues C11 to C14.

[0317] Each of the liquid portions of reaction residues C11 to C14 was subjected to HPLC analysis in the same manner as in Example 1C, and the molar ratios of 4,4'-MDI, the unilateral, and MDC-Me were calculated. The results are shown in Table 4C. In Table 4C, 4,4'-MDI is abbreviated as "MDI".

[0318]

[0319] <Comparative Example 2C> The raw material solution was prepared in the same manner as in Comparative Example 1C, except that the amount of MDC-Me added to storage tank 101C was 3.0 g, the amount of alkylnaphthalene was 100.1 g, and zinc stearate was not added. The raw material solution was subjected to four thermal decomposition steps in the same manner as in Comparative Example 2C, except that the above raw material solution was used and the temperature of reaction vessel 105C was set to 250°C. After each thermal decomposition step, no liquid accumulated in storage tank 111C. Furthermore, insoluble matter was visually observed in the reaction residue (hereinafter also referred to as reaction residues C21, C22, C23, and C24) that accumulated at the bottom of reaction vessel 105C after each thermal decomposition step.

[0320] Each of the liquid portions of reaction residues C21 to C24 was subjected to HPLC analysis in the same manner as in Example 1C, and the molar ratios of 4,4'-MDI, the unilateral, and MDC-Me were calculated. The results are shown in Table 5C. In Table 5C, 4,4'-MDI is abbreviated as "MDI".

[0321]

[0322] 101, 105: Line 102: Agitator 103: Reaction vessel 104: Raw material liquid 107, 111: Condenser 109: Vacuum pump 113: Storage tank 101B: Reaction vessel 101-1B: Agitator 102B: Liquid containing raw material liquid 103B, 105B, 203B, 205B: Line 111B, 117B, 201B: Storage tank 109B, 115B: Condenser 113B: Vacuum pump 101C, 111C, 117C: Storage tank 103C, 107C, 119C: Line 105C: Reaction vessel 109C, 115C: Condenser 113C: Vacuum pump

Claims

A method for producing isocyanates, The isocyanate includes an isocyanate having the structure shown in structural formula (100). The above manufacturing method includes step A, which involves heating a raw material solution containing a carbamic acid ester corresponding to an isocyanate having the structure shown in the structural formula (100) to thermally decompose the carbamic acid ester and obtain the isocyanate. A method for producing an isocyanate, wherein the raw material solution contains an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure shown in the structural formula (100), and whose solubility at a temperature of 180°C of the carbamic acid ester is 2.5 wt% or more. R １００ (NHCOOR) １０５ ) ｐ－ｑ (NCO) ｑ (100) (In structural formula (100), R １００ This is an organic group with a valence p that contains an aromatic ring, and in formula (100) -NHCOOR １０５ The nitrogen atom in the group and the nitrogen atom in the -NCO group are directly bonded to the carbon atoms constituting the aromatic ring in the organic group, p is an integer of 1 or more, and q is an integer between 1 and p, R １０５ Each of these is independently a substituted or unsubstituted hydrocarbon group. 　 The method for producing an isocyanate according to claim 1, wherein in the structural formula (100), p is 2 or more and q is 1 or more. 　 The method for producing an isocyanate according to claim 1, wherein the isocyanate having the structure represented by structural formula (100) includes an isocyanate having the structure represented by structural formula (101). (In structural formula (101), s and t each represent 0 or 1, provided that s + t = 1. R １０１ (This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.) 　 The method for producing an isocyanate according to claim 3, wherein the isocyanate having the structure represented by structural formula (101) includes an isocyanate having the structure represented by structural formula (102). The method for producing an isocyanate according to claim 1, wherein the organic solvent comprises at least one solvent selected from the group consisting of alkylnaphthalenes and dibenzyltoluene. 　 A method for producing an isocyanate according to claim 1, wherein the carbamic acid ester has the structure shown in structural formula (105): R １０３ (NHCOOR １０５ ) ｐ (105) (In structural formula (105), R １０３ R is a p-valent organic group containing an aromatic ring, １０５ , and p are synonymous with structural formula (100) above. 　 The method for producing an isocyanate according to claim 1, wherein step A for obtaining the isocyanate further includes a step of continuously withdrawing a hydroxy compound produced as a by-product by the thermal decomposition of the carbamic acid ester and the isocyanate from the reaction vessel. 　 The method for producing an isocyanate according to claim 1, wherein the thermal decomposition is carried out in the presence of one or more catalysts selected from the group consisting of fatty acid metal salts and phosphate metal salts, the fatty acid metal salt is a compound represented by general formula (IA) or general formula (IB), and the phosphate metal salt is a compound represented by general formula (IC): (R １１ COO) ｎ１ M １１ (IA) (In general formula (IA), M １１ n1 is a Group 1 metal, Group 2 metal, Group 13 metal, or lanthanide metal, and n1 is M １１ The valence of R １１ (This refers to an alkyl group having 1 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms.) (R １２ COO) ｎ２ M １２ (IB) (In general formula (IB), M １２ is a metal from groups 3 to 11 of the periodic table or zinc; n2 is M １２ The valence of; R １２ (This refers to an alkyl group having 10 to 40 carbon atoms or an alkenyl group having 2 to 40 carbon atoms.) (M １３ ) ｍ (PO ４ ) ｎ３ (IC) (In the general formula (IC), M １３ is a metal from groups 1 to 11 of the periodic table, a metal from group 13 of the periodic table, zinc, or a lanthanide metal, and m and n3 are M １３ The valence × m = 3 × n³ is satisfied. 　 The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), In the above general formula (IA), R １１ However, it is an alkyl group having 12 to 40 carbon atoms or an alkenyl group having 12 to 40 carbon atoms. In the above general formula (IB), R １２ The method for producing an isocyanate according to claim 8, wherein the alkyl group has 12 to 40 carbon atoms or an alkenyl group has 12 to 40 carbon atoms. 　 The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), M in the above general formula (IA) １１ However, it is a metal of Group 13 of the periodic table. In the above general formula (IB), M １２ The method for producing an isocyanate according to claim 8, wherein the isocyanate is a metal from group 8 to 11 of the periodic table or zinc. 　 The catalyst is the fatty acid metal salt represented by the general formula (IA) or the general formula (IB), M in the above general formula (IA) １１ However, it is a metal of Group 13 of the periodic table. In the above general formula (IB), M １２ The method for producing an isocyanate according to claim 8, wherein the isocyanate is a Group 8 metal of the periodic table, a Group 9 metal of the periodic table, or zinc. 　 The method for producing an isocyanate according to claim 8, wherein the catalyst is the fatty acid metal salt represented by the general formula (IA). 　 The method for producing an isocyanate according to claim 1, wherein the boiling point B1 of the organic solvent is 10°C or higher than the boiling point B2 of the isocyanate represented by the structural formula (100). 　 A composition comprising a carbamic acid ester corresponding to an isocyanate having the structure shown in structural formula (100), and an aromatic organic solvent, The organic solvent is a composition in which the boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure shown in the structural formula (100), and the solubility of the carbamic acid ester at a temperature of 180°C is 2.5 wt% or more. R １００ (NHCOOR) １０５ ) ｐ－ｑ (NCO) ｑ (100) (In structural formula (100), R １００ This is an organic group with a valence p that contains an aromatic ring, and in formula (100) -NHCOOR １０５ The nitrogen atom in the group and the nitrogen atom in the -NCO group are directly bonded to the carbon atoms constituting the aromatic ring in the organic group, p is an integer of 1 or more, and q is an integer between 1 and p, R １０５ Each of these is independently a substituted or unsubstituted hydrocarbon group. 　 The composition according to claim 14, wherein in the structural formula (100), p is 2 or more and q is 1 or more. The composition according to claim 14, wherein the isocyanate having the structure represented by structural formula (100) includes an isocyanate having the structure represented by structural formula (101). (In structural formula (101), s and t each represent 0 or 1, provided that s + t = 1. R １０１ (This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.) The composition according to claim 14, wherein the carbamic acid ester has the structure shown in structural formula (105). R １０３ (NHCOOR １０５ ) ｐ (105) (In structural formula (105), R １０３ R is a p-valent organic group containing an aromatic ring, １０５ (, and p are synonymous with structural formula (100) above.) The composition according to claim 14, wherein the boiling point B1 of the organic solvent is 10°C or higher than the boiling point B2 of the isocyanate represented by the structural formula (100). 　 The composition according to claim 14, wherein the organic solvent comprises at least one solvent selected from the group consisting of alkylnaphthalenes and dibenzyltoluene. 　 The composition according to claim 14, wherein the content ratio of the carbamic acid ester to the composition is 1 to 25% by mass. 　 The composition according to claim 14, wherein the content ratio of the organic solvent to the composition is 75 to 99% by mass. 　 A method for producing isocyanates, The isocyanate includes an isocyanate having the structure shown in structural formula (1B). The above-mentioned manufacturing method includes step 1B, in which a liquid containing a raw material solution containing a carbamic acid ester corresponding to an isocyanate having the structure shown in the structural formula (1B) is heated in a reaction vessel to thermally decompose the carbamic acid ester and obtain the isocyanate, The aforementioned step 1B is, Step 1B-1 involves continuously withdrawing the isocyanate generated in the reaction vessel by thermal decomposition of the carbamic acid ester from the reaction vessel, and The process includes step 1B-2, in which the hydroxy compound produced as a by-product in the reaction vessel by thermal decomposition of the carbamic acid ester is continuously withdrawn from the reaction vessel. A method for producing an isocyanate, wherein the raw material liquid contains an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure shown in the structural formula (1B), and whose solubility at 180°C of the carbamic acid ester is 2.5 wt% or more: R ３１ (NHCOOR) ２２ ) ｐ－ｑ (NCO) ｑ (1B) (In structural formula (1B), R ３１ R is an organic group with valency p, where p is an integer greater than or equal to 1, and q is an integer greater than or equal to 1 and less than or equal to p. ２２ (Each of these is independently a substituted or unsubstituted hydrocarbon group.) 　 The method for producing an isocyanate according to claim 22, wherein the carbamic acid ester has the structure shown in structural formula (2B): R ２１ (NHCOOR ２２ ) ｐ (2B) (In structural formula (2B), R ２１ is a p-valent organic group, R ２２ , and p are R in structural formula (1B) ２２ , and are synonymous with p. 　 The method for producing an isocyanate according to claim 22, wherein step 1B-1 comprises a step of continuously withdrawing the isocyanate as a gas phase component from the reaction vessel. 　 The method for producing an isocyanate according to claim 24, wherein step 1B-2 comprises a step of withdrawing the hydroxy compound from the reaction vessel as a gas phase component. 　 In the above structural formula (1B), p is 2 or more, q is 1 or more, and R ３１ However, the organic group has a valency p, and the organic group is an aliphatic hydrocarbon group having 1 or more carbon atoms, or an aromatic hydrocarbon group having 6 or more carbon atoms, provided that the aliphatic hydrocarbon group contains -CH ２ -, -O-, -S-, or -SO ２ It may be substituted with -, and the aromatic hydrocarbon group has two or more aromatic rings bonded together by a single bond, -CH ２ The method for producing an isocyanate according to claim 22, which may be a group connected by at least one linking group selected from the group consisting of -, -O-, and -S-. 　 The method for producing an isocyanate according to claim 22, wherein the isocyanate having the structure shown in structural formula (1B) includes an isocyanate having the structure shown in structural formula (3-1). The method for producing an isocyanate according to claim 22, wherein the carbamic acid ester has a structure represented by structural formula (4): (R ０１ , and R ０２ Each of these independently represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms. 　 The method for producing an isocyanate according to claim 22, wherein step 1B-2 comprises a step of removing aliphatic alcohols having 1 to 4 carbon atoms, which are by-products of the thermal decomposition, from the reaction vessel as a gas phase component. 　 The method for producing an isocyanate according to claim 22, wherein the organic solvent comprises at least one solvent selected from the group consisting of alkylnaphthalenes and dibenzyltoluene. 　 The method for producing an isocyanate according to claim 22, further comprising the steps of supplying the raw material liquid to the reaction vessel and withdrawing at least a portion of the liquid from the reaction vessel. 　 The method for producing an isocyanate according to claim 22, wherein step 1B includes heating a liquid film containing the raw material liquid in the reaction vessel to thermally decompose the carbamic acid ester in the liquid film to produce the isocyanate. 　 A method for producing isocyanates, The isocyanate includes an isocyanate having the structure shown in structural formula (1C), The above manufacturing method includes step 1C, which involves preparing a raw material solution containing a carbamic acid ester corresponding to an isocyanate having the structure shown in structural formula (2C) and structural formula (1C), and The process includes step 2C, in which a liquid film containing the raw material liquid is heated in a reaction vessel to thermally decompose the carbamic acid ester in the liquid film and produce the isocyanate, The aforementioned step 2C is, Step 2C-1 involves continuously extracting the hydroxy compound produced as a by-product by thermal decomposition of the carbamic acid ester from the reaction vessel as a gas-phase component. A method for producing an isocyanate, comprising step 2C-2 of continuously withdrawing the isocyanate produced by thermal decomposition of the carbamic acid ester from the reaction vessel as a gas phase component: R ３１ (NHCOOR ２２ ) ｐ－ｑ (NCO) ｑ (1C) R ２１ (NHCOOR ２２ ) ｐ (2C) (In structural formulas (1C) to (2C), R ２１ and R ３１ Each of these is an organic group with a valency of p, where p is an integer greater than or equal to 1, and q is an integer greater than or equal to 1 and less than or equal to p, R ２２ (Each of these is independently a substituted or unsubstituted hydrocarbon group.) 　 In the above structural formula (1C), p is 2 or more, q is 1 or more, and R ３１ However, the organic group has a valency p, and the organic group is an aliphatic hydrocarbon group having 1 or more carbon atoms, or an aromatic hydrocarbon group having 6 or more carbon atoms, provided that the aliphatic hydrocarbon group contains -CH ２ -, -O-, -S-, or -SO ２ It may be substituted with -, and the aromatic hydrocarbon group has two or more aromatic rings bonded together by a single bond, -CH ２ The method for producing an isocyanate according to claim 33, which may be a group connected by at least one linking group selected from the group consisting of -, -O-, and -S-. 　 A method for producing an isocyanate according to claim 33, wherein the isocyanate having the structure shown in structural formula (1C) comprises an isocyanate having the structure shown in structural formula (3-1) below, and the carbamic acid ester has the structure shown in structural formula (4) below: (In structural formula (3-1), s and t each represent 0 or 1, provided that s + t = 1. R ００ (This represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms.) (In structural formula (4), R ０１ , and R ０２ Each of these independently represents an aliphatic hydrocarbon group with 1 to 4 carbon atoms. 　 A method for producing an isocyanate according to claim 33, wherein the above steps 2C-1 and 2C-2 are performed simultaneously. 　 The method for producing an isocyanate according to claim 33, wherein the steps 2C-1 and 2C-2 are carried out simultaneously to extract the mixture containing the hydroxy compound and the isocyanate from the reaction vessel as a gas phase component. 　 The method for producing an isocyanate according to claim 37, further comprising the step of condensing the isocyanate contained in the mixture withdrawn from the reaction vessel to separate it from the hydroxy compound contained in the mixture. 　 The method for producing an isocyanate according to claim 33, wherein the raw material liquid includes liquid paraffin. 　 The method for producing an isocyanate according to claim 33, wherein the raw material liquid contains an aromatic organic solvent whose boiling point B1 is higher than the boiling point B2 of the isocyanate having the structure shown in the structural formula (1C), and whose solubility at a temperature of 180°C of the carbamic acid ester is 2.5 wt% or more. 　 The method for producing an isocyanate according to claim 40, wherein the boiling point B1 is 350°C or higher. 　 The method for producing an isocyanate according to claim 40, wherein the organic solvent comprises at least one solvent selected from the group consisting of alkylnaphthalene and dibenzyltoluene. 　 The method for producing an isocyanate according to claim 33, wherein step 2C further comprises a step of withdrawing the liquid containing the carbamic acid ester from the reaction vessel. 　 The method for producing an isocyanate according to claim 43, wherein the liquid withdrawn from the reaction vessel is subjected to step 2C.

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