Process for the preparation of isocyanate compounds

Abstract

The present invention relates to a method for preparing an isocyanate compound. According to the present invention, there is provided a method for preparing an isocyanate compound, which can recover and reuse materials used in the reaction in the process of preparing an isocyanate compound using phosgene, and can minimize thermal denaturation of a reaction product and formation of a by-product.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for preparing an isocyanate compound. BACKGROUND

[0002] Although xylene diisocyanate (hereinafter referred to as XDI) contains an aromatic ring in its molecule, it is classified as an aliphatic isocyanate. XDI is a very useful compound as a raw material for polyurethane-based materials, polyurea-based materials, or polyisocyanurate-based materials, etc. in the fields of chemical industry, resin industry, and coating industry.

[0003] Generally, many side reactions occur when synthesizing an isocyanate compound, and thus a method of preparing an isocyanate compound by reacting an amine compound with anhydrous hydrochloric acid or carbonic acid to form a salt, and then reacting the salt with phosgene is used.

[0004] For example, XDI is prepared by reacting xylylenediamine (hereinafter referred to as XDA) with anhydrous hydrochloric acid to form an amine hydrochloride salt, and then reacting the salt with phosgene. More specifically, in the prior art, an isocyanate compound, such as XDI, is prepared by reacting a liquid raw material amine (for example, a solution containing XDA) with anhydrous hydrochloric acid to form an XDA-HCl hydrochloride salt, heating the salt to a high temperature of at least 100°C, and then introducing gaseous phosgene to perform a gas-liquid reaction.

[0005] The reaction for forming an isocyanate compound is a typical endothermic reaction, and thus requires continuous heating and maintenance of a high temperature during the reaction to increase the yield.

[0006] Incidentally, since an isocyanate compound (such as XDI) generally has high amino reactivity, many side reactions occur during the phosgenation reaction, and the by-products formed through the side reactions affect the process in which the isocyanate compound is used as a raw material (for example, the process of producing a polyurethane resin), thereby causing deterioration of the resin quality.

[0007] As described above, due to the need for maintaining a high temperature during the preparation of an isocyanate compound, and the high reactivity of the prepared isocyanate compound (such as XDI), there is increasing concern about the formation of by-products or the occurrence of side reactions due to thermal denaturation of the product, and thus high load is often generated even during the purification process.

[0008] Due to these problems, various attempts have been made to suppress the generation of by-products or side reactions during the preparation of an isocyanate compound, but an effective technology has not yet been developed.

[0009] In addition, attempts have been made to recover and reuse compounds such as phosgene and hydrogen chloride from waste gas generated during the preparation of an isocyanate compound, but there are limitations in reducing efficiency. SUMMARY

[0010] Technical Problem

[0011] An object of the present application is to provide a method of producing an isocyanate compound, which can recover and reuse materials used in a reaction and can minimize thermal denaturation of a reaction product and formation of a by-product in producing the isocyanate compound using phosgene.

[0012] Technical Solution

[0013] According to one embodiment of the present application, there is provided a method of producing an isocyanate compound, comprising:

[0014] a phosgene reaction step of reacting a salt of an amine compound with phosgene in the presence of a solvent to obtain a reaction product containing an isocyanate compound,

[0015] a degassing step of removing a gas phase from the reaction product,

[0016] a gas compression step of compressing the gas phase obtained in the degassing step to obtain a gas phase condensate, and

[0017] a distillation step of distilling the condensate to separate phosgene from the condensate.

[0018] Now, a method of producing an isocyanate compound according to one embodiment of the present application will be described.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the present application.

[0020] As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0021] It is to be understood that the terms "including", "comprising", "having" and the like are used herein to mean the presence of stated features, regions, integers, steps, actions, elements, and / or components but do not preclude the presence or addition of one or more other features, regions, integers, steps, actions, elements, components, and / or groups thereof.

[0022] While the application can be variously modified and take on various alternative forms, specific embodiments thereof are set forth herein in detail. It should be understood, however, that the application is not limited to the particular embodiments set forth herein, but covers all modifications, equivalents, and alternatives falling within the spirit and scope of the application.

[0023] In describing a positional relationship, for example, when the positional relationship is described as "on", "above", "below", and "next to", one or more portions can be arranged between two other portions unless "only" or "directly" is used.

[0024] In describing a temporal relationship, for example, when the temporal order is described as "after", "subsequently", "next", and "before", discontinuous cases can be included unless "only" or "directly" is used.

[0025] The term "low-boiling material" as used herein means a material having a boiling point lower than that of the isocyanate compound which is the target product according to the present application, and the term "high-boiling material" means a material having a boiling point higher than that of the isocyanate compound which is the target product according to the present application.

[0026] As used herein, the term "bottom" of a distillation column means an outlet through which a lower portion of the distillation column is discharged to the outside of the distillation column, and the term "top" of a distillation column means an outlet through which an upper portion of the distillation column is discharged to the outside of the distillation column.

[0027] According to one embodiment of the present application, there is provided a method for producing an isocyanate compound, comprising:

[0028] a phosgene reaction step of reacting a salt of an amine compound with phosgene in the presence of a solvent to obtain a reaction product containing an isocyanate compound,

[0029] a degassing step of removing a gas phase from the reaction product,

[0030] a gas compression step of compressing the gas phase obtained in the degassing step to obtain a gas phase condensate, and

[0031] a distillation step of distilling the condensate to separate phosgene from the condensate.

[0032] According to another embodiment of the present application, there is provided a method for producing an isocyanate compound, comprising:

[0033] a salt formation reaction step of reacting an amine compound with hydrochloric acid in the presence of a solvent to obtain a salt of the amine compound,

[0034] a phosgene reaction step of reacting the salt of the amine compound with phosgene in the presence of a solvent to obtain a reaction product containing an isocyanate compound,

[0035] a degassing step of removing a gas phase from the reaction product,

[0036] a gas compression step of compressing the gas phase obtained in the salt formation reaction step, the phosgene reaction step, and the degassing step to obtain a gas phase condensate,

[0037] a distillation step of distilling the condensate to separate phosgene and hydrochloric acid from the condensate, and

[0038] a supply step of supplying the hydrochloric acid obtained in the distillation step to the reaction product of the salt formation reaction step, and supplying the phosgene to the reaction product of the phosgene reaction step.

[0039] According to still another embodiment of the present application, there is provided a method of preparing an isocyanate compound, further comprising:

[0040] a desolventizing step of removing a solvent from the reaction product from which the gas phase has been removed in the degassing step,

[0041] a low-boiler removing step of removing a low-boiler (i.e., a light substance) from the reaction product from which the solvent has been removed, and

[0042] a high-boiler removing step of removing a high-boiler (i.e., a heavy substance) from the reaction product from which the low-boiler has been removed.

[0043] In the process of preparing an isocyanate compound using phosgene, waste gas containing phosgene, hydrogen chloride, etc. is discharged in the main reaction and purification processes. According to environmental regulations, the waste gas is discharged into the atmosphere after being treated to remove harmful substances.

[0044] The present inventors have found that, when the waste gas from all processes including the gas phase obtained in the degassing step is treated by the gas compression step and the distillation step under the above conditions, phosgene and hydrogen chloride contained in the waste gas can be more effectively removed, and the recovered compounds can be supplied to the desired steps, thereby reducing costs and improving process efficiency.

[0045] Further, the present inventors have found that, when the reaction step, the degassing step, the desolventizing step, the low-boiler removing step, and the high-boiler removing step are performed to prepare an isocyanate compound, particularly when the above steps are performed under the above temperature and pressure conditions, thermal denaturation of the reaction product and formation of by-products can be minimized, and a high-purity isocyanate compound can be obtained.

[0046] Figure 1 Processes and apparatuses used in the method for preparing an isocyanate compound according to embodiments of the present application are schematically shown. Each step that can be included in the method for preparing an isocyanate compound according to embodiments of the present application will be described below with reference to Figure 1

[0047] (Phosgene Reaction Step)

[0048] The phosgene reaction step is performed in which a salt of an amine compound and phosgene are reacted in the presence of a solvent to obtain a reaction product containing an isocyanate compound, a solvent, and unreacted phosgene. ​

[0049] According to one embodiment of the present application, the amine compound is preferably used in the form of a salt of the amine compound to inhibit a rapid reaction and side reactions between the amine compound and the phosgene. For example, the salt of the amine compound can be a hydrochloride or a carbonate of the amine compound.

[0050] The salt of the amine compound can be prepared by reacting the amine compound with anhydrous hydrochloric acid or carbonic acid and performing a neutralization reaction. The neutralization reaction can be performed at a temperature of 20°C to 80°C.

[0051] The salt of the amine compound can be obtained by reacting the amine compound with anhydrous hydrochloric acid or carbonic acid in the presence of a solvent in a salt formation reactor 1. The salt of the amine compound obtained in the salt formation reactor 1 is supplied to the phosgene reactor 110 of the phosgene reaction unit 100 through an amine compound salt supply line 10. A gas phase discharged from the salt formation reactor 1 is transferred to a surge drum 251 of a gas compression unit 250 through a gas phase discharge line 9.

[0052] The supply ratio of the anhydrous hydrochloric acid or carbonic acid can be, for example, 2 to 10 moles, 2 to 6 moles, or 2 to 4 moles based on 1 mole of the amine compound.

[0053] Preferably, the amine compound can be an aliphatic amine having an aliphatic group in its molecule. Specifically, the aliphatic amine can be a chain or cyclic aliphatic amine. More specifically, the aliphatic amine can be a chain or cyclic aliphatic amine having at least two amino groups in its molecule.

[0054] For example, the amine compound can be at least one compound selected from the group consisting of hexamethylene diamine, 2,2-dimethylpentanediamine, 2,2,4-trimethylhexanediamine, butenediamine, 1,3-butadiene-1,4-diamine, 2,4,4-trimethylhexamethylenediamine, 1,6,11-undecane triamine, 1,3,6-hexamethylenetriamine, 1,8-diisocyanato-4-(isocyanatomethyl)octane, bis(aminoethyl)carbonate, bis(aminoethyl)ether, xylylenediamine, α,α,α',α'-tetramethylxylylenediamine, bis(aminoethyl) phthalate, bis(aminomethyl)cyclohexane, dicyclohexylmethane diamine, cyclohexanediamine, methylcyclohexanediamine, dicyclohexyl dimethylmethane diamine, 2,2-dimethyldicyclohexylmethane diamine, 2,5-bis(aminomethyl)bicyclo-[2,2,1]-heptane, 2,6-bis(aminomethyl)bicyclo-[2,2,1]-heptane, 3,8-bis(aminomethyl)tricyclodecane, 3,9-bis(aminomethyl)tricyclodecane, 4,8-bis(aminomethyl)tricyclodecane, 4,9-bis(aminomethyl)tricyclodecane, bis(aminomethyl)norbornene, and xylylenediamine.

[0055] Further, the amine compound can be at least one sulfur-containing aliphatic amine selected from the group consisting of bis(aminomethyl) sulfide, bis(aminoethyl) sulfide, bis(aminopropyl) sulfide, bis(aminohexyl) sulfide, bis(aminomethyl) sulfone, bis(aminomethyl) disulfide, bis(aminoethyl) disulfide, bis(aminopropyl) disulfide, bis(aminomethylthio)methane, bis(aminoethylthio)methane, bis(aminoethylthio)ethane, bis(aminomethylthio)ethane, and 1,5-diamino-2-aminomethyl-3-thiapentane.

[0056] Among the above-mentioned amine compounds, xylylenediamine (XDA) can exhibit an excellent effect when applied to the method of preparing an isocyanate compound according to an embodiment of the present application. Preferably, the amine compound can be at least one compound selected from the group consisting of m-xylylenediamine, p-xylylenediamine, and o-xylylenediamine.

[0057] According to an embodiment of the present application, the phosgene reaction step is performed in a gas-liquid-solid three-phase reaction in which the salt of the solid-phase amine compound reacts with the gas-phase phosgene in the presence of a solvent. Thus, the rapid reaction can be effectively inhibited, and the formation of by-products can be minimized.

[0058] When the salt of the amine compound and the phosgene are reacted in the presence of the solvent, the phosgene can be added at once or can be added in portions. For example, a small amount of the phosgene can be added at once at a lower temperature and reacted with the salt of the amine compound to form an intermediate. Subsequently, the remaining amount of the phosgene can be added at a higher temperature and reacted with the intermediate to obtain a reaction solution containing the isocyanate compound. For example, the reaction of the phenyldimethylamine and a small amount of the phosgene forms an intermediate in the form of a carbamoyl salt, and then the remaining amount of the phosgene is added thereto, and the intermediate in the form of the carbamoyl salt can be reacted with the phosgene to form an aliphatic isocyanate such as xylylene diisocyanate.

[0059] By such a phosgene reaction step, the time during which the final product isocyanate compound is exposed to high temperature can be minimized. In addition, the intermediate is formed at a relatively low temperature, thereby reducing the time during which high temperature should be maintained throughout the reaction. Further, the amount of heat charged throughout the process can be reduced. Further, the high temperature reaction time of the phosgene can be relatively shortened, and the risk of phosgene explosion vaporization can be reduced.

[0060] The phosgene reaction step is performed in the presence of a solvent containing at least one of an aromatic hydrocarbon solvent and an ester solvent. The solvent can be selected in consideration of the temperature at which the reaction step is performed.

[0061] The aromatic hydrocarbon solvent can be a halogenated aromatic hydrocarbon solvent such as monochlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, or the like.

[0062] The ester solvent can be a fatty acid ester such as pentyl formate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, methyl isopentyl acetate, methoxybutyl acetate, sec-hexyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, methylcyclohexyl acetate, benzyl acetate, ethyl propionate, n-butyl propionate, isopentyl propionate, ethyl acetate, butyl stearate, butyl lactate, pentyl lactate; or an aromatic carboxylic acid ester such as methyl salicylate, dimethyl phthalate, methyl benzoate.

[0063] According to one embodiment of the present application, the salt of the amine compound in the phosgene reaction step can be contained in the solvent at a concentration of 20 vol% or less, for example, 1 vol% to 20 vol%, or 5 vol% to 20 vol%. When the concentration of the salt of the amine compound contained in the solvent exceeds 20 vol%, a large amount of the salt is likely to be precipitated in the phosgene reaction step.

[0064] The phosgene reaction step can be performed at a temperature of 165°C or lower, preferably 80°C to 165°C.

[0065] According to one embodiment of the present application, when the phosgene is added in portions in the phosgene reaction step, it can be added in an amount of 10 to 30% by weight, or 12 to 30% by weight, or 15 to 28% by weight, based on the total amount of phosgene added, at a temperature of 80 to 100°C, or 85 to 95°C. Under such reaction conditions, the rapid reaction is suppressed and the intermediate in the form of a carbamoyl salt can be selectively and efficiently formed. Subsequently, the intermediate and the phosgene can be reacted while the remaining amount of phosgene is charged at a temperature of 110 to 165°C, or 120 to 150°C to obtain a reaction product containing an isocyanate compound.

[0066] The isocyanate compound can vary depending on the type of the amine compound used in the phosgene reaction step. For example, the isocyanate compound can be at least one compound selected from the group consisting of n-pentyl isocyanate, 6-methyl-2-heptane isocyanate, cyclopentyl isocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), di(isocyanatomethyl)cyclohexane (H6TDI), xylylene diisocyanate (XDI), cyclohexane diisocyanate (t-CHDI), and di(isocyanatocyclohexyl)methane (H12MDI).

[0067] In particular, the method for producing an isocyanate compound according to the embodiment of the present application is also useful for producing xylylene diisocyanate (XDI). XDI includes 1,2-XDI (o-XDI), 1,3-XDI (m-XDI), and 1,4-XDI (p-XDI) as structural isomers.

[0068] The phosgene reaction step can be carried out batchwise or continuously. The phosgene reaction step can be carried out in a phosgene reaction unit 100 including a reactor 110 having a rotation axis; an amine compound salt supply line 10 and a phosgene supply line 20 for supplying reactants into the reactor; a heat source for supplying heat to the reactor; a reaction product transfer line 102 for transferring the reaction product obtained in the reactor to a subsequent step; and a gas phase discharge line 109 for transferring the gas phase obtained from the reactor to a pressure regulating column 251 of a gas compression unit 250.

[0069] (Degassing step)

[0070] Then, a degassing step of removing the gas phase from the reaction product is carried out.

[0071] In the degassing step, the gas phase, such as the remaining phosgene or the by-product hydrogen chloride, is removed from the reaction product by a known degassing unit 200.

[0072] The method of removing the gas phase from the reaction product can include a method of supplying and passing a gas, or a method of separating the gas phase from the reaction product using a flash tank or a distillation column.

[0073] In particular, according to the embodiment of the present application, in order to minimize the formation of by-products in the degassing step, the degassing step is preferably performed at a temperature of 145°C to 165°C and a pressure of 100 Torr to 600 Torr.

[0074] In one example, the degassing step can be performed in a distillation column, in which the temperature at the bottom of the distillation column is set to 145°C to 165°C, and the distillation column is operated at a pressure of 100 Torr to 600 Torr at the top of the column, which can be advantageous in minimizing the formation of by-products. Here, the temperature at the bottom of the distillation column can refer to the temperature of a reboiler connected to the bottom of the distillation column. Also, the pressure at the top of the distillation column can refer to the pressure of a condenser connected to the top of the distillation column.

[0075] Preferably, the temperature at which the degassing step is performed can be 145°C to 165°C, or 150°C to 165°C, or 150°C to 160°C, or 155°C to 160°C. Also, preferably, the pressure at which the degassing step is performed can be 100 Torr to 600 Torr, or 200 Torr to 500 Torr, or 300 Torr to 450 Torr, or 350 Torr to 450 Torr.

[0076] When the temperature and pressure at which the degassing step is performed do not satisfy the above ranges, the formation of by-products in the degassing step can increase, and the removal efficiency of the gas phase can decrease, thereby reducing the concentration of the isocyanate compound in the reaction product obtained from the degassing step.

[0077] As one example, the degassing step can be performed in a degassing unit 200 including a distillation column 220 configured to be able to remove a gas phase from a reaction product supplied via a reaction product delivery line 102 of a reaction unit 100, a gas phase discharge line 209 discharging the gas phase to the top of the distillation column, and a reaction product delivery line 203 discharging the reaction product from which the gas phase is removed to the bottom of the distillation column and delivering it to a subsequent step.

[0078] (Gas compression step)

[0079] Then, a gas compression step is performed, in which the gas phase obtained in the degassing step is compressed to obtain a gas phase condensate.

[0080] In the gas compression step, the gas phase obtained in the degassing step is compressed in a gas compression unit 250 to obtain a gas phase condensate.

[0081] Preferably, in the gas compression step, the gas phase obtained in the phosgene reaction step is compressed in the gas compression unit 250 together with the gas phase obtained in the degassing step to obtain a gas phase condensate.

[0082] More preferably, in the gas compression step, the gas phases obtained in the salt formation reaction step, the phosgene reaction step, and the degassing step are compressed in the gas compression unit 250 to obtain a gas phase condensate.

[0083] Preferably, in order to ensure the compression efficiency of the gas phase and the pressure of the condensate, the gas compression step can be performed in the gas compression unit 250 including three or more gas compressors. Preferably, the gas compression step can be performed in the gas compression unit 250 including three or more centrifugal compressors. Preferably, the gas compression unit 250 includes three or more sub-units including the pressure regulating column 251, the gas compressor 254, and the condenser 257.

[0084] As an example, Figure 1 A process including three sub-units connected in series is shown. Referring to Figure 1 , the gas compression unit 250 includes three gas compressors 254, 264, and 274 arranged in sequence, pressure regulating columns 251, 261, and 271 connected via the gas phase delivery lines 253, 263, and 273 in front of each gas compressor, and condensers 257, 267, and 277 connected via the compressed gas delivery lines 256, 266, and 276 after each gas compressor.

[0085] wherein the gas phase is supplied from the gas phase discharge line 209 of the degassing unit 200 to the pressure regulating column 251 of the first sub-unit. Optionally, the gas phase delivered from the gas phase discharge line 9 of the salt formation reactor 1 and the gas phase discharge line 109 of the phosgene reaction unit 100 can be further supplied to the pressure regulating column 251.

[0086] The lower part of the pressure regulating column 251 separates liquid droplets through the liquid droplet discharge line 252, thereby preventing the flow of the liquid phase into the gas compression unit 250. The gas phase is discharged to the upper part of the pressure regulating column 251, and the gas phase is supplied to the gas compressor 254 through the gas phase delivery line 253. The gas phase is compressed in the gas compressor 254. The compressed gas obtained from the gas compressor 254 is supplied to the condenser 257 through the compressed gas delivery line 256.

[0087] In order to prevent the occurrence of a surge phenomenon when the gas compressor 254 stops operating due to a power outage or the like, a part of the gas phase that is not compressed in the gas compressor 254 is supplied to the pressure regulating column 251 through the gas recirculation line 255. The compressed gas is supplied to the condenser 257 to lower its temperature, and is supplied to the pressure regulating column 261 of the second sub-unit through the delivery line 259.

[0088] In the second and third sub-units, the compression of the gas is performed in the same flow as each device corresponding to the first sub-unit.

[0089] Finally, the condensate obtained in the condenser 277 of the third unit is transported to the buffer tank 280 through the condensate transport line 279. The condensate collected in the buffer tank 280 is supplied as a feed to the distillation column 291 of the distillation unit 290.

[0090] In the gas compression unit 250, the surge drums 251, 261 and 271 are devices for preventing surge during the gas compression process. Although Figure 1 Although not shown in FIG. 2, the gas recirculation lines 255, 265 and 275 can be provided with anti-surge valves to prevent surge during the gas compression process.

[0091] In the gas compression unit 250, the gas compressors 254, 264 and 274 are devices for compressing the gas phase to form compressed gas. Preferably, in the gas compression step, in order to ensure the compression efficiency of the gas phase and the sufficient pressure of the condensate, the gas phase is preferably compressed to a pressure of 16 bar or more.

[0092] For example, it is preferable that the gas phase flowing into the first sub-unit exhibits a pressure of 16 bar or more in the last sub-unit after passing through each sub-unit.

[0093] More preferably, in the gas compression step, the gas phase can be compressed to a pressure of 16 bar to 19 bar, or 16.5 bar to 18.5 bar, or 16.5 bar to 18 bar.

[0094] (Distillation step)

[0095] Then, a distillation step is performed, in which the condensate obtained in the compression step is distilled to separate phosgene from the condensate.

[0096] In the distillation step, phosgene is separated and recovered from the condensate by the distillation unit 290 including the distillation column 291.

[0097] According to one embodiment of the present application, in order to ensure the distillation efficiency of the condensate and the energy efficiency of the entire process, the distillation step is preferably performed in the distillation column 291 having a top temperature of -15°C or more. Preferably, the distillation column 291 can have a top temperature of -15°C to 0°C, -12°C to -3°C, or -10°C to -5°C.

[0098] According to one embodiment of the present application, the overhead temperature of the distillation column 291 can be determined according to the pressure of the condensate supplied to the distillation step in the gas compression step. For example, when the final pressure of the condensate supplied from the gas compression step to the distillation step (i.e., the pressure of the condensate discharged from the last subunit of the gas compression unit 250) is 16 bar or more, the distillation column 291 can be operated at an overhead temperature of -15°C or more. The lower the column temperature that must be set during the operation of the distillation column 291, the more energy is consumed, which reduces the energy efficiency and the process efficiency.

[0099] In the distillation step, the condensate collected in the surge tank 280 is supplied as a feed to the distillation column 291. By distillation in the distillation column 291, a distillate containing phosgene separated from the condensate is discharged to the lower part of the distillation column 291 through a bottom stream line 292.

[0100] The distillate containing phosgene is supplied to a reboiler 294. In the reboiler 294, the low-boiling distillate is again supplied to the bottom of the distillation column 291, and the remaining distillate, i.e., phosgene, is recovered through a phosgene discharge line 296. The recovered phosgene is used as a reactant in the reaction step. That is, the phosgene recovered in the distillation step through the phosgene discharge line 296 is supplied to the reactor 110 through the phosgene supply line 20 of the reaction unit 100.

[0101] In the distillation step, a gas phase (e.g., a hydrochloric acid gas or a carbon dioxide gas) separated from the condensate is discharged to the top of the distillation column through an overhead stream line 293. The discharged gas phase is supplied to a condenser 295. A part of the gas phase condensed in the condenser 295 is re-supplied to the top of the distillation column 291, and the remaining part is recovered through a gas phase discharge line 297. The recovered gas phase is used as a reactant to form a salt of an amine compound.

[0102] Meanwhile, according to another embodiment of the present application, the method for preparing an isocyanate compound can further include the following steps: a desolventizing step of removing a solvent from the reaction product from which the gas phase has been removed in the degassing step; a low-boiler removal step of removing a low-boiler (i.e., a light substance) from the reaction product from which the solvent has been removed; and a high-boiler removal step of removing a high-boiler (i.e., a heavy substance) from the reaction product from which the low-boiler has been removed.

[0103] Figure 2 The processes and apparatuses used in the method for preparing an isocyanate compound according to this embodiment are schematically shown. The steps that can be further included in the method for preparing an isocyanate compound according to the present embodiment will be described below with reference to the processes and apparatuses. Figure 2 The steps that can be further included in the method for preparing an isocyanate compound according to the present embodiment will be described below with reference to the processes and apparatuses.

[0104] (desolventizing step)

[0105] Then, a desolventizing step can be performed in which the solvent is removed from the reaction product from which the gas phase has been removed.

[0106] In the desolventizing step, the solvent is distilled from the reaction product from which the gas phase has been removed by a known desolventizing unit 300.

[0107] According to one embodiment of the present application, in order to minimize thermal denaturation and byproduct formation of the reaction product in the desolventizing step, the desolventizing step is preferably performed at a temperature of 100°C to 165°C and a pressure of 30 torr or less.

[0108] In one example, the desolventizing step can be performed in a distillation column in which the temperature at the bottom of the distillation column is set to 100°C to 165°C and the distillation column is operated at a pressure of 30 torr or less at the top of the column can be advantageous in minimizing thermal degradation and byproduct formation. Here, the temperature at the bottom of the distillation column can refer to the temperature of a reboiler connected to the bottom of the distillation column. Also, the pressure at the top of the distillation column can refer to the pressure of a condenser connected to the top of the distillation column.

[0109] Preferably, the temperature at which the desolventizing step is performed can be 100°C to 165°C, or 115°C to 165°C, or 115°C to 160°C, or 130°C to 160°C. Also, preferably, the pressure at which the desolventizing step is performed can be 5 torr to 30 torr, or 5 torr to 25 torr, or 10 torr to 20 torr, or 10 torr to 15 torr.

[0110] When the temperature and pressure at which the desolventizing step is performed do not satisfy the above ranges, thermal denaturation and byproduct formation in the desolventizing step can increase, and the solvent removal efficiency can decrease, whereby the isocyanate compound concentration in the reaction product obtained from the desolventizing step can decrease.

[0111] In one example, the desolventizing step can be performed in a desolventizing unit 300 including a distillation column 330 configured to be able to remove the solvent from the reaction product supplied via the reaction product transfer line 203 of the degassing unit 200; a solvent discharge line 309 discharging the solvent to the top of the distillation column; and a reaction product transfer line 304 discharging the reaction product from which the solvent has been removed to the bottom of the distillation column and transferring it to a subsequent step.

[0112] In order to minimize the high-temperature residence time of the reaction product in the desolventizing step, a distillation column 440 equipped with equipment such as a kettle-type reboiler, a thin-film evaporator, a forced-circulation reboiler, and a jacketed-vessel reboiler can be used.

[0113] (Low-boiling substance removal step)

[0114] Then, a low-boiler removal step can be performed in which low-boilers (i.e., light substances) are removed from the solvent-removed reaction product obtained in the desolventizing step.

[0115] In the low-boiler removal step, low-boilers (light substances) are removed from the solvent-removed reaction product by a known low-boiler removal unit 400.

[0116] Low-boilers refer to materials having a boiling point lower than that of the isocyanate compound that is the main product in the reaction step. Examples of low-boilers include materials produced by side reactions in the process of obtaining the main product. As an example, in the process of producing XDI as an isocyanate compound, low-boilers can include monoisocyanates such as (chloromethyl)benzyl isocyanate (CBI) and ethylphenyl isocyanate (EBI).

[0117] According to one embodiment of the present application, in order to minimize thermal denaturation of the reaction product and formation of by-products in the low-boiler removal step, the low-boiler removal step is preferably performed under the following conditions: the temperature at the bottom of the distillation column 440 is set to 150°C to 165°C, and the pressure at the top of the distillation column is set to 5 torr or less. Here, the temperature at the bottom of the distillation column can refer to the temperature of the reboiler connected to the bottom of the distillation column.

[0118] Preferably, the temperature at which the low-boiler removal step is performed can be 150°C to 165°C, or 155°C to 165°C, or 155°C to 162°C, or 160°C to 162°C. Also, preferably, the upper limit of the pressure at which the low-boiler removal step is performed can be 1 torr to 5 torr, or 2 torr to 5 torr, or 2 torr to 4 torr.

[0119] If the temperature and pressure at which the low-boiler removal step is performed do not satisfy the above ranges, thermal denaturation and formation of by-products in the low-boiler removal step can increase, and the removal efficiency of the low-boiler removal step can decrease, whereby the isocyanate compound concentration in the reaction product obtained in the low-boiler removal step can decrease.

[0120] In one example, the low-boiler removal step can be performed in a low-boiler removal unit 400 that includes a distillation column 440 configured to be able to remove low-boilers from the reaction product supplied through the reaction product transfer line 304 of the desolventizing unit 300; a low-boiler discharge line 409 that discharges low-boilers to the top of the distillation column; and a reaction product transfer line 405 that discharges the low-boiler-removed reaction product to the bottom of the distillation column and transfers it to a subsequent step.

[0121] To minimize the high temperature residence time of the reaction product in the low-boiler removal step, a distillation column 440 equipped with a device such as a kettle-type reboiler, a thin-film evaporator, a forced-circulation reboiler, and a jacketed-vessel reboiler can be used.

[0122] (high-boiler removal step)

[0123] Then, a high-boiler removal step can be performed in which high-boilers (i.e., heavy substances) are removed from the low-boiler-removed reaction product obtained in the low-boiler removal step.

[0124] In the high-boiler removal step, high-boilers (i.e., heavy substances) are removed from the low-boiler-removed reaction product by a known high-boiler removal unit 500.

[0125] High-boilers refer to materials having a boiling point higher than that of the main product isocyanate compound in the reaction step. Examples of high-boilers include high-molecular-weight by-products formed in the step of obtaining the main product, such as oligomers or polymers of the isocyanate compound, including dimers, trimers, or higher multimers.

[0126] According to one embodiment of the present application, to minimize thermal denaturation of the reaction product and formation of by-products in the high-boiler removal step, the high-boiler removal step can preferably be performed at a temperature of 145°C to 165°C and a pressure of 1 torr or less.

[0127] In one example, the high-boiler removal step can be performed in a thin-film evaporator, in which the temperature at the bottom of the thin-film evaporator is set to 145°C to 165°C and the thin-film evaporator is operated at an evaporator bottom pressure of 1 torr or less can be advantageous to minimize thermal degradation and formation of by-products.

[0128] Preferably, the temperature at which the high-boiler removal step is performed can be 145°C to 165°C, or 150°C to 165°C, or 150°C to 160°C, or 155°C to 160°C. Also, preferably, the pressure at which the high-boiler removal step is performed can be 0.1 torr to 1 torr, or 0.5 torr to 1 torr.

[0129] If the temperature and pressure at which the high-boiler removal step is performed do not satisfy the above ranges, thermal denaturation and formation of by-products in the high-boiler removal step can increase, and the removal efficiency of the high-boiler removal step can decrease, whereby the concentration of the isocyanate compound obtained in the high-boiler removal step can decrease.

[0130] In one example, the high-boiler removal step can be performed in a high-boiler removal unit 500 including a thin film evaporator 550 configured to be capable of removing high-boilers from the reaction product supplied through the reaction product delivery line 405 of the low-boiler removal unit 400; an isocyanate compound discharge line 509 discharging isocyanate compounds to a condensing section of the thin film evaporator; and a high-boiler discharge line 506 discharging high-boilers to a bottom section of the thin film evaporator.

[0131]

Advantages

[0132] According to the present application, there is provided a method of preparing an isocyanate compound, which can recover and reuse materials used in the reaction and can minimize thermal denaturation of the reaction product and formation of by-products in the process of preparing the isocyanate compound using phosgene. BRIEF DESCRIPTION OF DRAWINGS

[0133] Figure 1 and Figure 2 Processes and apparatuses used in a method of preparing an isocyanate compound according to an embodiment of the present application are schematically shown.

[0134] <EXPLANATION OF REFERENCE NUMERALS>

[0135] 1: salt formation reactor

[0136] 9: gas phase discharge line

[0137] 10: amine compound salt supply line

[0138] 20: phosgene supply line

[0139] 100: phosgene reaction unit

[0140] 110: phosgene reactor

[0141] 102: reaction product delivery line

[0142] 109: gas phase discharge line

[0143] 200: degassing unit

[0144] 220: distillation column

[0145] 209: gas phase discharge line

[0146] 203: reaction product delivery line

[0147] 250: gas compression unit

[0148] 251, 261, 271: pressure regulating column

[0149] 252, 262, 272: droplet discharge line

[0150] 253, 263, 273: gas phase delivery line

[0151] 254, 264, 274: gas compressor

[0152] 255, 265, 275: gas recirculation line

[0153] 256, 266, 276: compressed gas delivery line

[0154] 257, 267, 277: condenser

[0155] 259, 269, 279: condensate delivery line

[0156] 280: buffer tank

[0157] 290: distillation unit

[0158] 291: distillation column

[0159] 293: overhead stream line

[0160] 295: condenser

[0161] 297: gas phase discharge line

[0162] 292: bottoms stream line

[0163] 294: reboiler

[0164] 296: phosgene discharge line

[0165] 300: desolvation unit

[0166] 330: distillation column

[0167] 309: solvent discharge line

[0168] 304: reaction product delivery line

[0169] 400: low boiler removal unit

[0170] 440: distillation column

[0171] 409: low boiler discharge line

[0172] 405: reaction product delivery line

[0173] 500: high boiler removal unit

[0174] 550: thin film evaporator

[0175] 506: high boiler discharge line

[0176] 509: isocyanate compound discharge line DETAILED DESCRIPTION

[0177] Hereinafter, the effects and advantages of the present application will be described in more detail through specific examples of the present application. However, these examples are given only to illustrate the present application and do not thereby determine the scope of the present application.

[0178] Example 1

[0179] Using Figure 1 and 2 The 1,3-XDI (m-XDI) was prepared by the following process using the apparatus shown in FIG. 1.

[0180] (Phosgene reaction step)

[0181] At normal temperature and pressure, 500 kg of hydrochloric acid was reacted with 560 kg of m-xylylenediamine (m-XDA) in 6500 kg of 1,2-dichlorobenzene (o-DCB) solvent for 4 hours to produce 870 kg of hydrochloride of m-xylylenediamine. At this time, the unreacted hydrochloric acid gas discharged through the gas phase discharge line 9 was transferred to the pressure regulating column 251 of the gas compression unit 250.

[0182] The 870 kg of hydrochloride of m-xylylenediamine was added to the reactor 110 through the supply line 10, and the temperature of the reactor was raised to 125°C. During the reaction, a total of 1359 kg of phosgene was introduced into the reactor through the supply line 20 and stirred. A dry ice-acetone condenser was used from the time of phosgene addition to the time of completion of the reaction to prevent leakage of phosgene to the outside. The reaction was performed at a temperature of 90°C for 1.5 hours.

[0183] After that, the internal temperature of the reactor was heated to 125°C, and further 6000 kg of phosgene was added. The temperature of the reactor was maintained at 125°C, and further stirred for 4.5 hours until the reaction solution became clear. The heating was stopped after the reaction solution became clear. The reaction product obtained by the above method was transported to the degassing unit 200 through the transport line 102. At this time, the unreacted phosgene and hydrochloric acid gas discharged through the gas phase discharge line 109 were transported to the pressure regulating column 251 of the gas compression unit 250.

[0184] (Degassing step)

[0185] The distillation column 220 of the degassing unit 200 was configured to be able to remove the gas phase from the reaction product supplied through the transport line 102.

[0186] Specifically, the distillation column 220 used was a packed column filled with Mellapak, a structured packing, and had a height of about 6 m.

[0187] The temperature at the bottom of the distillation column 220 was set to 155 °C and the distillation column 220 was operated at a top pressure of 400 Torr.

[0188] A reflux stream of about 150 kg / hr was recharged to the distillation column 220, which corresponds to a reflux ratio of about 3.2 relative to the top outflow.

[0189] The gas phase containing phosgene was discharged through a gas phase discharge line 209 connected to the top of the distillation column 220. The gas phase discharged via the gas phase discharge line 209 was transferred to a pressure regulating column 251 of a gas compression unit 250. The reaction product from which the gas phase had been removed was transported through a transport line 203 connected to the bottom of the distillation column 220 to a desolventizing unit 300.

[0190] (gas compression step)

[0191] The gas phase supplied to the pressure regulating column 251 of the first subunit supplied to the gas compression unit 250 was supplied through a transport line 253 to a gas compressor 254. In the gas compressor 254, the gas phase was compressed at a pressure of 2.7 bar. The compressed gas obtained from the gas compressor 254 was supplied through a transport line 256 to a condenser 257. The temperature of the compressed gas supplied to the condenser 257 was reduced to 15 °C and the compressed gas was supplied through a transport line 259 to the pressure regulating column 261 of the second subunit.

[0192] The compressed gas supplied to the pressure regulating column 261 of the second subunit was supplied through a transport line 263 to a gas compressor 264. In the gas compressor 264, the compressed gas was further compressed at a pressure of 7.6 bar. The compressed gas obtained from the gas compressor 264 was supplied through a transport line 266 to a condenser 267. The temperature of the compressed gas supplied to the condenser 267 was reduced to 41 °C and the compressed gas was supplied through a transport line 269 to the pressure regulating column 271 of the third subunit.

[0193] The compressed gas supplied to the pressure regulating column 271 of the third subunit was supplied through a transport line 273 to a gas compressor 274. In the gas compressor 274, the compressed gas was further compressed at a pressure of 16.86 bar (12644 Torr). The compressed gas obtained from the gas compressor 274 was supplied through a transport line 276 to a condenser 277. The temperature of the condensate supplied to the condenser 277 was reduced to -5 °C to form a condensate. The condensate was transported through a transport line 279 to a buffer tank 280.

[0194] (distillation step)

[0195] The condensate collected in the buffer tank 280 is supplied as a feed to a distillation column 291 of a distillation unit 290. The distillation column 291 is configured to be able to separate phosgene from the condensate.

[0196] Specifically, the distillation column 291 is a column of about 8 m consisting of 12 bubble cap trays. A reflux stream of about 710 kg / hr is recharged to the distillation column 291, which corresponds to a reflux ratio of about 3 with respect to the column top outflow.

[0197] When the condensate from the gas compression step is supplied to the distillation column 291 at a pressure of 16.86 bar, the condenser 295 connected to the top of the distillation column 291 is operated at a temperature of -15°C.

[0198] The phosgene-containing fraction separated from the condensate is discharged to the bottom of the distillation column 291 through a column bottom stream line 292. The phosgene-containing fraction is supplied to a reboiler 294. The low-boiling fraction within the reboiler 294 is again supplied to the bottom of the distillation column 291, and the remaining fraction, i.e., phosgene, is recovered through a phosgene discharge line 296. The recovered phosgene is supplied to the reactor 110 through the phosgene supply line 20 of the reaction unit 100.

[0199] The fraction containing hydrochloric acid gas separated from the condensate is discharged to the top of the distillation column 291 through a column top stream line 293. The discharged fraction containing hydrochloric acid gas is supplied to the condenser 295. A part of the fraction condensed in the condenser 295 is again supplied to the top of the distillation column 291, and the remaining hydrochloric acid gas is recovered through a gas phase discharge line 297. The recovered hydrochloric acid gas is supplied to the reaction step as a reactant for forming a salt of an amine compound.

[0200] (desolvation step)

[0201] The distillation column 330 of the desolvation unit 300 is configured to be able to remove the solvent from the reaction product supplied through the transfer line 203.

[0202] Specifically, the distillation column 330 used is a packed column packed with Mellapak, a structured packing, and has a height of about 7 m.

[0203] The temperature at the bottom of the distillation column 330 is set to 160°C, and the distillation column 330 is operated at a column top pressure of 15 torr.

[0204] A reflux stream of about 600 kg / hr is recharged to the distillation column 330, which corresponds to a reflux ratio of about 0.5 with respect to the column top outflow.

[0205] Solvent comprising 1,2-dichlorobenzene (o-DCB) is discharged through a solvent discharge line 309 connected to the top of the distillation column 330. The reaction product from which the solvent has been removed is transported through a transport line 304 connected to the bottom of the distillation column 330 to the low-boiler removal unit 400.

[0206] (low-boiler removal step)

[0207] The distillation column 440 of the low-boiler removal unit 400 is configured to be able to remove low-boilers from the reaction product supplied through the transport line 304.

[0208] Specifically, the distillation column 440 used is a packed column packed with Mellapak, a structured packing, and has a height of about 13 m.

[0209] The temperature at the bottom of the distillation column 440 is set to 160°C, and the distillation column 440 is operated at a column top pressure of 5 torr.

[0210] A reflux stream of about 40 kg / hr is recharged to the distillation column 440, which corresponds to a reflux ratio of about 2.0 with respect to the column top outflow.

[0211] Low-boilers including (chloromethyl)benzyl isocyanate (CBI) are discharged through a low-boiler discharge line 409 connected to the top of the distillation column 440. The reaction product from which the low-boilers have been removed is transported through a transport line 405 connected to the bottom of the distillation column 440 to the high-boiler removal unit 500.

[0212] (high-boiler removal step)

[0213] The thin-film evaporator 550 of the high-boiler removal unit 500 is configured to be able to remove high-boilers from the reaction product supplied through the transport line 405.

[0214] Specifically, the thin-film evaporator 550 used is an evaporator in the form of a short-path evaporator in which a condenser is installed.

[0215] The bottom temperature of the thin-film evaporator 550 is set to 160°C, and the thin-film evaporator 550 is operated at an evaporator bottom pressure of 0.5 torr.

[0216] A high-boiling condensate of about 13 kg / hr is separated from the bottom of the thin-film evaporator.

[0217] Isocyanate compounds including 1,3-XDI (m-XDI) are discharged through a discharge line 509 connected to the top of the thin-film evaporator 550. The high-boilers separated from the reaction product are discharged through a discharge line 506 connected to the bottom of the thin-film evaporator 550.

[0218] Example 2

[0219] The isocyanate compound containing 1,3-XDI (m-XDI) was obtained in the same manner as in Example 1, except that, in the gas compression step, compression was performed at a pressure of 20 bar in the gas compressor 274 of the last subunit.

[0220] When the condensate from the gas compression step was supplied to the distillation column 291 at a pressure of 20 bar, the condenser 295 connected to the top of the distillation column 291 was operated at a temperature of -9.2°C.

[0221] Reference Example

[0222] The isocyanate compound containing 1,3-XDI (m-XDI) was prepared in the same manner as in Example 1, except that, in the gas compression step, compression was performed at a pressure of 10 bar in the gas compressor 274 of the last subunit.

[0223] When the condensate from the gas compression step was supplied to the distillation column 291 at a pressure of 10 bar, the condenser 295 connected to the top of the distillation column 291 was operated at a temperature of -32°C.

[0224] Test Example

[0225] The part streams of the gas phase discharge line 297 and the phosgene discharge line 296 of the distillation unit 290 in the examples and reference examples were recovered and subjected to gel permeation chromatography analysis. The contents of the main components identified by the above analysis are shown in Tables 1 to 3 below.

[0226] In addition, the energy per unit time (kcal / hr) injected into the gas compression step and the distillation step in the examples and reference examples was measured and is shown in Tables 1 to 3 below.

[0227] [Table 1]

[0228]

[0229] [Table 2]

[0230]

[0231] [Table 3]

[0232]

[0233] Referring to Tables 1 to 3, it was confirmed that the method of producing an isocyanate compound according to the examples can efficiently recover and reuse the phosgene and hydrochloric acid used in the reaction step with relatively low energy consumption.

[0234] Even in the reference example, the phosgene and hydrochloric acid can be recovered from the distillation unit through the gas compression step, but in the gas compression step, sufficient pressure of the compressed gas cannot be ensured, and thus a large amount of energy is consumed per unit time. In particular, in the reference example, since a large amount of expensive refrigerant must be used to keep the overhead temperature low during the distillation column operation, the economic benefit is greatly different compared to the example.

Claims

1. A method for preparing isocyanate compounds, comprising: Salt formation reaction steps: The amine compound is reacted with hydrochloric acid in the presence of a solvent to obtain the salt of the amine compound. Phosgene reaction step: The salt of the amine compound is reacted with phosgene in the presence of a solvent to obtain a reaction product containing an isocyanate compound. Degassing step: Remove the gaseous phase from the reaction products. Gas compression step: The gas phase obtained in the salt formation reaction step, the phosgene reaction step, and the degassing step is compressed to obtain a gas phase condensate. Distillation step: Distill the condensate to separate phosgene and hydrochloric acid from the condensate, and Supply steps: Supplying hydrochloric acid obtained in the distillation step to the reaction product of the salt formation step, and supplying phosgene to the reaction product of the phosgene reaction step. In the gas compression step, the gas phase is compressed to a pressure of 16 bar or higher.

2. The method according to claim 1, wherein, The degassing step is carried out at a temperature of 145°C to 165°C and a pressure of 100 Torr to 600 Torr.

3. The method according to claim 1, wherein, The gas compression step is carried out in a gas compression unit comprising three or more gas compressors.

4. The method according to claim 1, wherein, The distillation process is carried out in a distillation column with a top temperature of -15°C or higher.

5. The method according to claim 1, further comprising: Solvent removal step: The solvent is removed from the reaction product obtained in the degassing step, from which the gas phase has been removed. Low-boiling-point removal step: Removing low-boiling-point substances from the reaction product after solvent removal, and High-boiling-point removal step: Remove high-boiling-point substances from the reaction products from which low-boiling-point substances have been removed.

6. The method according to claim 5, wherein, The degassing step, the solvent removal step, the low-boiling-point substance removal step, and the high-boiling-point substance removal step are each carried out at a temperature below 165°C.

7. The method according to claim 1, wherein, The amine compound is an aliphatic amine having an aliphatic group in its molecule.

8. The method according to claim 1, wherein, The amine compound is a chain or cyclic aliphatic amine containing two or more amino groups, or bifunctional groups, in its molecule.

9. The method according to claim 1, wherein, The amine compound is selected from at least one of the following: hexamethylenediamine, 2,2-dimethylpentanediamine, 2,2,4-trimethylhexanediamine, butenediamine, 1,3-butadiene-1,4-diamine, 2,4,4-trimethylhexamethylenediamine, 1,6,11-undecanetriamine, 1,3,6-hexamethylenetriamine, bis(aminoethyl) carbonate, bis(aminoethyl) ether, phenylenediamine, α,α,α',α'-tetramethylphenylenediamine, bis(aminoethyl) phthalate, bis(aminomethyl) Cyclohexane, dicyclohexylmethanediamine, cyclohexanediamine, methylcyclohexanediamine, dicyclohexyldimethylmethanediamine, 2,2-dimethyldicyclohexylmethanediamine, 2,5-bis(aminomethyl)bicyclo-[2,2,1]-heptane, 2,6-bis(aminomethyl)bicyclo-[2,2,1]-heptane, 3,8-bis(aminomethyl)tricyclodecane, 3,9-bis(aminomethyl)tricyclodecane, 4,8-bis(aminomethyl)tricyclodecane, 4,9-bis(aminomethyl)tricyclodecane and bis(aminomethyl)norbornene.

10. The method according to claim 1, wherein, The amine compound is at least one sulfur-containing aliphatic amine selected from the following: bis(aminomethyl) sulfide, bis(aminoethyl) sulfide, bis(aminopropyl) sulfide, bis(aminohexyl) sulfide, bis(aminomethyl) sulfone, bis(aminomethyl) disulfide, bis(aminoethyl) disulfide, bis(aminopropyl) disulfide, bis(aminomethylthio)methane, bis(aminoethylthio)methane, bis(aminoethylthio)ethane, bis(aminomethylthio)ethane, and 1,5-diamino-2-aminomethyl-3-thiapentane.

11. The method according to claim 1, wherein, The amine compound is selected from at least one compound chosen from m-phenylenediamine, p-phenylenediamine, and o-phenylenediamine.

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