Process for preparing isocyanate compounds

Abstract

The present invention relates to a method of preparing an isocyanate compound. According to the present invention, there is provided a method of preparing an isocyanate compound, which can improve energy efficiency while minimizing thermal denaturation of reaction products and formation of by-products in the process of preparing an isocyanate compound using phosgene.

Description

TECHNICAL FIELD

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

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

[0003] Generally, many side reactions occur in the synthesis of isocyanate compounds, and therefore a method of reacting with anhydrous hydrochloric acid or carbonic acid to form an amine compound salt, and then reacting with phosgene is used for the production.

[0004] For example, XDI is produced by reacting XDA (hereinafter referred to as XDA) with anhydrous hydrochloric acid to form an amine hydrochloride salt, and then reacting with phosgene. More specifically, in the prior art, an isocyanate compound such as XDI is produced by reacting a liquid raw material amine, such as a solution containing XDA, with anhydrous hydrochloric acid to form an XDA-HCl hydrochloride salt, heating it to a high temperature of at least 100°C or higher, 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 continuous heating and maintaining a high temperature are required during the reaction to increase the yield.

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

[0007] As described above, since a high temperature needs to be maintained during the production of an isocyanate compound, and the high reactivity of the produced isocyanate compound such as XDI, there are more and more problems of by-products being formed or side reactions occurring due to thermal denaturation of the product, and therefore a high load often occurs even in the purification process.

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

[0009]

Technical Problem

[0010] An object of the present application is to provide a method for producing an isocyanate compound, which can improve energy efficiency while minimizing thermal denaturation of a reaction product and formation of a by-product in a process for producing an isocyanate compound using phosgene.

[0011] [Technical Solution]

[0012] According to one embodiment of the present application, there is provided a method for producing an isocyanate compound, comprising:

[0013] a 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, the solvent, and unreacted phosgene, and

[0014] a distillation step of distilling the reaction product in a dividing wall distillation column, thereby obtaining a stream containing unreacted phosgene from the top of the dividing wall distillation column, a stream containing the isocyanate compound from the bottom of the dividing wall distillation column, and a stream containing the solvent from a side stream of the dividing wall distillation column,

[0015] wherein the distillation step is performed so that the temperature at the bottom of the dividing wall distillation column is 165°C or lower.

[0016] Now, a method for producing an isocyanate compound according to one embodiment of the present application will be described.

[0017] 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.

[0018] 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.

[0019] It will be understood that the terms "comprises", "comprising", "includes" and "including" used herein are specifically intended to be interpreted as specifying 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.

[0020] While the application can be variously modified and altered, and be embodied in various alternative forms, specific embodiments thereof will be illustrated and described in detail herein. It is to be understood, however, that this application is not limited to the specific forms disclosed, but encompasses all modifications, equivalents, and alternatives falling within the spirit and scope of the application.

[0021] In describing positional relationships, for example, when the positional relationship is described as "on", "above", "below", and "next to", one or more portions can be arranged between the other two portions unless "only / just" or "directly" is used.

[0022] In describing temporal relationships, for example, when the temporal order is described as "after", "behind", "next", and "before", discontinuous cases can be included unless "only / just" or "directly" is used.

[0023] As used herein, the term "low-boiling-point substance" refers to a material having a boiling point lower than that of the isocyanate compound as the target product according to the present application, and the term "high-boiling-point substance" refers to a material having a boiling point higher than that of the isocyanate compound as the target product of the present application.

[0024] As used herein, the term "bottom" of a distillation column refers to an outlet through which a lower portion of the distillation column discharges a product to the outside of the distillation column, and the term "top" of a distillation column refers to an outlet through which an upper portion of the distillation column discharges a product to the outside of the distillation column.

[0025] According to one embodiment of the present application, there is provided a method for producing an isocyanate compound, comprising:

[0026] a 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, a solvent, and unreacted phosgene, and

[0027] a distillation step of distilling the reaction product in a dividing wall distillation column such that a stream containing unreacted phosgene is obtained from the top of the dividing wall distillation column, a stream containing the isocyanate compound is obtained from the bottom of the dividing wall distillation column, and a stream containing the solvent is obtained from a side stream of the dividing wall distillation column,

[0028] wherein the distillation step is performed such that the temperature at the bottom of the dividing wall distillation column is 165°C or lower.

[0029] The isocyanate compound is used as a raw material for fine chemical products including optical materials, and high purity is required.

[0030] However, in general, when an isocyanate compound including XDI is synthesized, there is a problem that many side reactions occur, and the purity of the isocyanate compound is reduced due to reactions between reaction products and thermal denaturation.

[0031] In one example, aliphatic diisocyanates can be prepared by reacting an aliphatic diamine with phosgene. During this process, side reactions occur, producing byproducts such as monoisocyanates like benzyl (chloromethyl) isocyanate. The occurrence of these side reactions and the formation of byproducts are known to be due to the need to maintain high temperatures during the preparation of aliphatic diisocyanates and the high reactivity of the prepared aliphatic diisocyanates such as XDI. In particular, exposure of the final aliphatic diisocyanate to high temperatures for a certain period can induce side reactions or form high-molecular-weight byproducts, such as oligomers or polymers, including dimers, trimers, or higher-order oligomers.

[0032] Through continuous research, the inventors have discovered that when using a partitioned wall distillation column to distill the reaction products of the phosgenation reaction of amine compounds, energy efficiency can be improved while minimizing the thermal denaturation of the reaction products and the formation of byproducts.

[0033] The reaction products contain a mixture of various substances, including phosgene (as a raw material), solvent, and low-boiling and high-boiling substances (as byproducts). To obtain high-purity isocyanate compounds from the reaction products, an equal number of evaporators as the impurity components to be separated are required. Furthermore, when a solvent with a boiling point between that of phosgene and the isocyanate compound is used in the phosgenation reaction, remixing with other components occurs within the evaporator until the solvent is removed. Incidentally, since the solvent accounts for 80% or more of the reaction products, there is a significant decrease in energy efficiency until the solvent removal step.

[0034] In the method for preparing isocyanate compounds according to embodiments of the present invention, a partitioned-wall distillation column is used, thus allowing the solvent to be obtained from the sidestream feed of the partitioned-wall distillation column. Therefore, a separate evaporator or solvent removal process is unnecessary, and the process operating burden and energy consumption due to solvent remixing can be reduced.

[0035] Figure 1 The process and apparatus for preparing isocyanate compounds according to embodiments of the present invention are illustrated schematically.

[0036] The following will refer to Figure 1 Each step that may be included in a method for preparing isocyanate compounds according to embodiments of the present invention is described.

[0037] (Reaction steps)

[0038] First, a 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 comprising an isocyanate compound, a solvent, and unreacted phosgene.

[0039] 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.

[0040] 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 to 80°C.

[0041] 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.

[0042] 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 bifunctional or higher chain or cyclic aliphatic amine containing at least two amino groups in its molecule.

[0043] For example, the amine compound can be at least one compound selected from hexamethylene diamine, 2,2-dimethylpentanediamine, 2,2,4-trimethylhexanediamine, butylenediamine, 1,3-butadiene-1,4-diamine, 2,4,4-trimethylhexamethylenediamine, 1,6,11-undecanetriamine, 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, dicyclohexylmethanediamine, cyclohexanediamine, methylcyclohexanediamine, dicyclohexyl dimethylmethanediamine, 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, bis(aminomethyl)norbornene, and xylylenediamine.

[0044] Further, the amine compound can be at least one sulfur-containing aliphatic amine selected from 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.

[0045] Among the amine compounds described above, xylylenediamine (XDA) can exhibit an excellent effect when used in the method of producing an isocyanate compound according to one 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.

[0046] According to one embodiment of the present application, the above reaction step is performed in a gas-liquid-solid three-phase reaction in which the salt of the amine compound in the solid phase reacts with the phosgene in the gas phase in the presence of the solvent. Thus, the rapid reaction can be effectively inhibited, and the formation of side reactions and by-products can be minimized.

[0047] When the salt of the amine compound and the phosgene react in the presence of the solvent, the phosgene can be added at once or in portions. For example, a small amount of the phosgene can be first added at a relatively low temperature, which reacts with the salt of the amine compound to form an intermediate. Subsequently, the remaining amount of the phosgene can be added at a relatively high temperature, which reacts with the intermediate to obtain a reaction solution containing the isocyanate compound. For example, the xylylenediamine and a small amount of the phosgene react to form an intermediate in the form of a carbamoyl salt, and then the remaining amount of the phosgene is added thereto, which reacts with the intermediate in the form of the carbamoyl salt to form an aliphatic isocyanate, such as xylylene diisocyanate.

[0048] By such a reaction step, the time during which the final product, the 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 needs to be maintained throughout the reaction process. Furthermore, the heat 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.

[0049] The reaction step is performed in the presence of a solvent containing at least one of an aromatic hydrocarbon-based solvent and an ester-based solvent. The solvent can be selected in consideration of the temperature at which the reaction step is performed.

[0050] The aromatic hydrocarbon-based solvent can be a halogenated aromatic hydrocarbon-based solvent, such as monochlorobenzene, 1,2-dichlorobenzene, and 1,2,4-trichlorobenzene.

[0051] The ester-based solvent can be a fatty acid ester, such as pentyl formate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isoamyl acetate, methyl isoamyl acetate, methoxybutyl acetate, sec-hexyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, methylcyclohexyl acetate, benzyl acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, ethyl acetate, butyl stearate, butyl lactate, and pentyl lactate; or an aromatic carboxylic acid ester, such as methyl salicylate, dimethyl phthalate, and methyl benzoate.

[0052] According to one embodiment of the present application, the salt of the amine compound in the reaction step can be contained in the solvent at a concentration of 20% by volume or less, for example, 1 to 20% by volume, or 5 to 20% by volume. When the concentration of the salt of the amine compound contained in the solvent exceeds 20% by volume, a large amount of the salt can precipitate in the reaction step.

[0053] The reaction step can be performed at a temperature of 165°C or lower, preferably 80°C to 165°C.

[0054] According to one embodiment of the present application, when the phosgene is added separately in the reaction step, the amount of the phosgene added can be 10 to 30% by weight, or 12 to 30% by weight, or 15 to 28% by weight, based on the total amount of the phosgene added at a temperature of 80°C to 100°C, or 85°C to 95°C. Under such reaction conditions, the fast reaction is inhibited and the intermediate in the form of carbamoyl salt can be selectively and efficiently formed. Subsequently, the remaining amount of the phosgene is added at a temperature of 110°C to 165°C, or 120°C to 150°C, while the intermediate can be allowed to react with the phosgene to obtain the reaction product containing the isocyanate compound.

[0055] The isocyanate compound can vary depending on the type of the amine compound used in the 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), diisocyanatomethyl cyclohexane (H6TDI), xylylene diisocyanate (XDI), diisocyanatocyclohexane (t-CHDI), and di(isocyanatocyclohexyl)methane (H12MDI).

[0056] In particular, the method for producing the isocyanate compound according to the embodiment of the present application can be further used 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.

[0057] The reaction step can be performed batchwise or continuously. The reaction step can be performed in a reaction unit 100 including a reactor 110 having a rotation shaft; a salt of an amine compound supply line 10 and a phosgene supply line 20 for supplying the reactants to the inside of the reactor; a heat source for supplying heat to the reactor; and a reaction product delivery line 102 for delivering the reaction product obtained in the reactor to a subsequent purification step.

[0058] (Distillation step)

[0059] Then, a distillation step is performed in which the reaction product is distilled in the dividing wall distillation column, whereby a stream containing unreacted phosgene is obtained from the top of the dividing wall distillation column, a stream containing the isocyanate compound is obtained from the bottom of the dividing wall distillation column, and a stream containing the solvent is obtained from the side stream of the dividing wall distillation column,

[0060] Figure 2 (a) shows the order of separation of compounds A, B and C in a conventional distillation column, Figure 2 (b) shows the order of separation of compounds A, B and C in a dividing wall distillation column. Here, it is assumed that the boiling points of compounds A, B and C are A < B < C.

[0061] Reference Figure 2 (a), in order to separate compounds A, B and C from a mixture of compounds A, B and C by a conventional distillation process, a distillation column 1 for separating compound A from the mixture and a distillation column 2 for separating compounds B and C from a mixture of compounds B and C obtained from the distillation column 1 must be continuously provided.

[0062] Meanwhile, reference Figure 2 (b), the dividing wall distillation column 30 has a structure in which a dividing wall 31 is disposed inside to integrate a pre-fractionating column side 33 and a main fractionating column side (a side stream side) 35. In the dividing wall distillation column 30, not only is it easy to operate by adjusting the pressure balance between the pre-fractionating column side 33 and the side stream side 35, but also it is possible to operate by integrating two rectifying columns into one, thereby reducing the cost burden and improving energy efficiency.

[0063] If a feed, which is a mixture of compounds A, B and C, is supplied to Figure 2 (b) shown in the dividing wall distillation column 30, in the pre-fractionating column side 33, a part of the compounds B and A rises to a rectifying section 37, and the remaining compounds B and C descend to a stripping section 39. In the rectifying section 37, the compound A is discharged to the top of the dividing wall distillation column 30. In the stripping section 39, the compound C is discharged to the bottom of the dividing wall distillation column 30. Then, the compound B having a corresponding boiling point between the compounds A and C is collected in the side stream side 35 and discharged to the side stream of the dividing wall distillation column 30.

[0064] According to one embodiment of the present application, in the distillation step, by being separated to the top, the bottom and the side stream of the dividing wall distillation column, unreacted phosgene contained in the reaction product, the isocyanate compound as a main product, the solvent, hydrogen chloride as a by-product, etc. can be obtained.

[0065] Among the components contained in the reaction product, the unreacted phosgene can be obtained as a stream corresponding to Figure 2 (b), the isocyanate compound as a main product can be obtained as a stream corresponding toFigure 2 The stream of compound C in (b) is obtained, and the solvent can be obtained as a stream corresponding to Figure 2 The stream of compound B in (c) is obtained.

[0066] Specifically, referring to Figure 1 and Figure 2 (b), the reaction product is supplied to the dividing wall distillation column 210 through the reaction product transfer line 102. In the pre-fractionator side 33 of the dividing wall distillation column 210, part of the solvent and the phosgene rise to the rectifying section 37, and the rest of the solvent and the main product isocyanate compound descend to the stripping section 39. The phosgene-rich fraction in the rectifying section 37 is discharged to the overhead stream line 293 connected to the top of the dividing wall distillation column 210. In the stripping section 39, the isocyanate compound-rich fraction is discharged to the bottom stream line 212 connected to the bottom of the dividing wall distillation column 210. Then, the solvent-rich fraction is collected in the side draw side 35 and discharged to the side stream line 251 connected to the side stream draw of the dividing wall distillation column 30.

[0067] In this way, in the method for producing an isocyanate compound according to the embodiment of the present application, the phosgene and the isocyanate compound are separated from the reaction product by using the dividing wall distillation column, and at the same time, the solvent can be obtained from the side stream draw of the dividing wall distillation column. Therefore, a separate evaporator or a process for removing the solvent is not required, and the process operation burden and energy consumption due to remixing of the solvent can be reduced.

[0068] A variety of factors affect the purity of the materials discharged through the overhead stream line 293, the bottom stream line 212, and the side stream line 251 in the dividing wall distillation column 210 and the energy efficiency of the process. For example, the total number of stages of the column, the length of the dividing wall of the dividing wall distillation column 210, the amount of reflux in the condenser 295, the amount of heat supply in the reboiler 214, the vapor split ratio, the split ratio, and the like affect the purity of the discharged materials and the energy efficiency of the process. Since a large amount of solvent is required for the distillation step according to the present application, it is preferable to perform the distillation such that the split ratio among the above factors is 15% or less from the viewpoint of energy saving.

[0069] That is, the distillation step can be performed such that the split ratio of the liquid phase that descends from the rectifying section 37 to the pre-fractionator side 33 of the dividing wall distillation column is 15% or less. The split ratio refers to the ratio of the total flow of the liquid phase that enters the pre-fractionator side 33 to the liquid phase that descends from the rectifying section 37 of the dividing wall distillation column. The split ratio can be adjusted using a liquid distributor.

[0070] According to one embodiment of the present application, the stream containing unreacted phosgene discharged to the top of the divided wall distillation column 210 is transferred through a top stream line 293 to a condenser 295. In the condenser 295, a gas phase containing phosgene is discharged through a gas phase discharge line 299, and a liquid is collected in a recovery tank 297, which is then resupplied to the upper portion of the divided wall distillation column 210. The phosgene obtained through the gas phase discharge line 299 can be recycled as a reaction product of the reaction step.

[0071] At this time, in order to improve the distillation efficiency of the divided wall distillation column 210, it is preferable to perform the distillation step so that the pressure at the top of the divided wall distillation column 210 is 20 torr or less. In one example, it is preferable to perform the distillation step so that the pressure of the condenser 295 connected to the divided wall distillation column 210 is 20 torr or less. Preferably, the distillation step can be performed so that the pressure of the condenser 295 connected to the divided wall distillation column 210 is 1 to 20 torr, 5 to 20 torr, or 10 to 20 torr.

[0072] According to one embodiment of the present application, the stream containing the isocyanate compound discharged to the bottom of the divided wall distillation column 210 is transferred through a bottom stream line 212 to a reboiler 214. In the reboiler 214, a low-boiling fraction is resupplied to the lower portion of the divided wall distillation column 210, and a fraction containing the isocyanate compound is discharged through an isocyanate discharge line 219.

[0073] At this time, in order to improve the distillation efficiency of the divided wall distillation column 210, it is preferable to perform the distillation step so that the temperature at the bottom of the divided wall distillation column is 165°C or less. As one example, it is preferable to perform the distillation step so that the temperature of the reboiler 214 connected to the divided wall distillation column 210 is 165°C or less. Preferably, the distillation step can be performed so that the temperature of the reboiler 214 connected to the distillation column 210 is 100°C to 165°C, 120°C to 165°C, or 130°C to 160°C.

[0074] Further, in order to minimize the high-temperature residence time of the reaction product in the distillation step, as the reboiler 214, it is preferable to apply a device such as a kettle-type reboiler, a thin-film evaporator, a forced circulation reboiler, a jacketed vessel-type reboiler, and the like.

[0075] According to one embodiment of the present application, the solvent-containing stream discharged to the side stream draw of the divided wall distillation column 210 is transferred through a side stream line 251 and then through a condenser 253 to a recovery tank 255. The solvent-containing stream collected in the recovery tank 255 is discharged through a solvent discharge line 259. The solvent obtained through the solvent discharge line 259 can be recycled to the reaction step.

[0076] The fraction containing the isocyanate compound discharged through the isocyanate discharge line 219 can contain a trace amount of solvent, high-boiling substances, and the like. If necessary, a step of further purifying the fraction containing the isocyanate compound can be performed to obtain a high-purity isocyanate compound.

[0077] As one non-limiting example, a low-boiling substance removal step can be performed in which low-boiling substances (i.e., light-ends) are removed from the fraction containing the isocyanate compound. In the low-boiling substance removal step, low-boiling substances (light-ends) can be removed from the fraction containing the isocyanate compound by a well-known low-boiling substance removal unit.

[0078] Low-boiling substances refer to substances having a boiling point lower than that of the isocyanate compound as the main product in the reaction step. Examples of low-boiling substances include substances produced by side reactions in the process of obtaining the main product. For example, in the process of producing XDI as the isocyanate compound, low-boiling substances can include monoisocyanates such as (chloromethyl)benzyl isocyanate (CMBI) and ethylphenyl isocyanate (EBI).

[0079] 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-boiling substance removal step, the low-boiling substance removal step is preferably performed at a temperature of 150°C to 165°C. Also, the low-boiling substance removal step is preferably performed at a pressure of 5 torr or less.

[0080] In one example, the low-boiling substance removal step can be performed in a distillation column in which the temperature at the bottom of the distillation column is set to 150°C to 165°C and the distillation column is operated at a pressure of 5 torr or less at the top of the column can be advantageous in minimizing thermal degradation and 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.

[0081] Preferably, the temperature at which the low-boiling substance 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-boiling substance removal step is performed can be 1 torr to 5 torr, or 2 torr to 5 torr, or 2 torr to 4 torr.

[0082] If the temperature and pressure at which the low-boiling substance removal step is performed do not satisfy the above ranges, thermal denaturation and formation of by-products in the low-boiling substance removal step can increase, and the removal efficiency of the low-boiling substances can decrease, thereby reducing the concentration of the isocyanate compound in the reaction product obtained from the low-boiling substance removal step.

[0083] In one example, the low-boiling substance removal step can be performed in a low-boiling substance removal unit including a distillation column configured to remove a low-boiling substance from the isocyanate compound-containing fraction supplied through the isocyanate compound discharge line 219 of the distillation unit 200; a low-boiling substance discharge line discharging the low-boiling substance to the top of the distillation column; and a reaction product delivery line discharging the low-boiling substance-removed reaction product to the bottom of the distillation column and delivering to a subsequent process.

[0084] To minimize the high-temperature residence time of the reaction product in the low-boiling substance removal step, a distillation column 440 equipped with devices such as a kettle-type reboiler, a thin-film evaporator, a forced circulation reboiler, and a jacketed vessel-type reboiler can be used.

[0085] As a non-limiting example, a high-boiling substance removal step can be performed in which a high-boiling substance (i.e., heavies) is removed from the low-boiling substance-removed reaction product. In the high-boiling substance removal step, the high-boiling substance (i.e., heavies) can be removed from the low-boiling substance-removed reaction product by a known high-boiling substance removal unit.

[0086] A high-boiling substance refers to a substance having a boiling point higher than that of the isocyanate compound that is the main product in the reaction step. Examples of the high-boiling substance include high-molecular weight by-products such as oligomers or polymers of the isocyanate compound formed in the step of obtaining the main product, including dimers, trimers, or higher polymers.

[0087] According to one embodiment of the present application, to minimize thermal denaturation of the reaction product and formation of by-products in the high-boiling substance removal step, the high-boiling substance removal step can preferably be performed at a temperature of 145°C to 165°C and a pressure of 1 torr or less.

[0088] In one example, the high-boiling substance removal step can be performed under a thin-film evaporator in which the bottom temperature of the thin-film evaporator is set to 145°C to 165°C, and operating the thin-film evaporator at an evaporator bottom pressure of 1 torr or less can be advantageous in minimizing thermal degradation and formation of by-products.

[0089] Preferably, the temperature at which the high-boiling substance 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-boiling substance removal step is performed can be 0.1 torr to 1 torr, or 0.5 torr to 1 torr.

[0090] If the temperature and pressure during the high-boiling-point substance removal step do not meet the above range, the thermal denaturation and byproduct formation in the high-boiling-point substance removal step may increase, and the removal efficiency of high-boiling-point substances may decrease, thereby reducing the concentration of isocyanate compounds obtained from the high-boiling-point substance removal step.

[0091] In one example, the high-boiling-point substance removal step can be carried out in a high-boiling-point substance removal unit, which includes a thin-film evaporator configured to remove high-boiling-point substances from reaction products supplied by a reaction product delivery line through a low-boiling-point substance removal unit; an isocyanate compound discharge line that discharges isocyanate compounds into the condenser section of the thin-film evaporator; and a high-boiling-point substance discharge line that discharges high-boiling-point substances to the bottom of the thin-film evaporator.

[0092] [Beneficial Effects]

[0093] According to the present invention, a method for preparing isocyanate compounds is provided, which can improve energy efficiency during the preparation of isocyanate compounds using phosgene, while minimizing the thermal denaturation of reaction products and the formation of byproducts. Attached Figure Description

[0094] Figure 1 The process and apparatus for preparing isocyanate compounds according to one embodiment of the present invention are illustrated schematically.

[0095] Figure 2 (a) shows the sequence of separation of compounds A, B, and C in a conventional distillation column. Figure 2 (b) shows the sequence of separation of compounds A, B and C in a partitioned wall distillation column.

[0096] <Explanation of Figure Markers>

[0097] 10: Salt supply line for amine compounds; 20: Phosgene supply line.

[0098] 100: Reaction Unit; 110: Reactor

[0099] 102: Reaction product delivery line; 200: Distillation unit.

[0100] 210: Divider wall distillation column; 212: Bottom feed line

[0101] 214: Reboiler; 219: Isocyanate compound discharge line

[0102] 251: Side flow line; 253: Condenser

[0103] 255: Recovery tank; 259: Solvent discharge line

[0104] 293: Top feed line 295: Condenser

[0105] 297: Recycling tank; 299: Gas phase emission pipeline

[0106] A, B, C: Compounds 1 and 2: Distillation column

[0107] 30: Distillation column with partition wall; 31: Partition wall

[0108] 33: Pre-fractionation tower side

[0109] 35: Main fractionation tower side (feed intake side)

[0110] 37: Rectifying section

[0111] 39: Steam stripping section Detailed Implementation

[0112] The effects and functions of the present invention will be described in more detail below through specific embodiments. However, these embodiments are provided merely as illustrative purposes and do not define the scope of the invention.

[0113] Example 1

[0114] use Figure 1 The apparatus shown is used to prepare 1,3-XDI (m-XDI) as follows.

[0115] (Reaction steps)

[0116] Under normal temperature and pressure conditions, 500 kg of hydrochloric acid and 560 kg of m-phenylenediamine (m-XDA) reacted in 6500 kg of 1,2-dichlorobenzene (o-DCB) solvent for 4 hours to produce 870 kg of m-phenylenediamine hydrochloride.

[0117] 870 kg of m-phenylenediamine hydrochloride was added to reactor 110 via supply line 10, and the reactor temperature was raised to 125°C. During the reaction, a total of 1359 kg of phosgene was introduced into the reactor via supply line 20, and the mixture was stirred. A dry ice-acetone condenser was used from the time the phosgene was introduced until the reaction was completed to prevent phosgene leakage to the outside. The reaction was carried out at 90°C for 1.5 hours.

[0118] Next, the internal temperature of the reactor was heated to 125°C, and 6000 kg of phosgene was added. The reactor temperature was maintained at 125°C, and the mixture was stirred for 4.5 hours until the reaction solution became clear. Heating was stopped after the reaction solution became clear. The reaction product obtained by the above method was transported to the distillation unit 200 through the delivery line 102.

[0119] (Distillation step)

[0120] The dividing wall distillation column 210 of the distillation unit 200 is configured such that a stream containing unreacted phosgene from the reaction product supplied through the feed line 102 is obtained from the top of the dividing wall distillation column, a stream containing 1,3-XDI is obtained from the bottom of the dividing wall distillation column, and a stream containing solvent is obtained from the side draw of the dividing wall distillation column.

[0121] Specifically, the dividing wall distillation column 210 is composed of a dividing wall located at the center of the column, a liquid distributor, a packing support, a grid, and the like. The pre-fractionation column side, the main fractionation column side, the rectification section, and the stripping section employ Mellapak packing which is a kind of structured packing.

[0122] * Total number of columns: 20

[0123] * Vapor split ratio = 50:50

[0124] * Split ratio = 10:90

[0125] In the distillation step, the pressure of the condenser 295 connected to the dividing wall distillation column 210 is set to 15 torr, and the temperature of the reboiler 214 connected to the dividing wall distillation column 210 is set to 160°C.

[0126] The reflux stream of about 1350 kg / hr from the top of the dividing wall distillation column 210 is recharged to the dividing wall distillation column 210, which corresponds to a reflux ratio of about 39.5 with respect to the column top outflow.

[0127] The gas phase containing phosgene in the condenser 295 is discharged through the gas phase discharge line 299, the liquid is collected in the recovery tank 297, and then is re-supplied to the top of the dividing wall distillation column 210. The phosgene obtained through the gas phase discharge line 299 is recycled as a reactant of the reaction step.

[0128] The low-boiling fraction in the reboiler 214 is re-supplied to the lower portion of the dividing wall distillation column 210, and the fraction containing 1,3-XDI is discharged through the isocyanate discharge line 219.

[0129] The solvent-containing stream discharged to the side draw of the dividing wall distillation column 210 is transported through the side stream line 251 and then through the condenser 253 to the recovery tank 255. The solvent-containing stream collected in the recovery tank 255 is discharged through the solvent discharge line 259. The solvent obtained through the solvent discharge line 259 is recycled to the reaction step.

[0130] Example 2

[0131] An isocyanate compound containing 1,3-XDI (m-XDI) was obtained in the same manner as in Example 1, except that the divided wall distillation column 210 was operated so that the temperature of the reboiler 214 connected thereto was 120°C in the distillation step.

[0132] Example 3

[0133] An isocyanate compound containing 1,3-XDI (m-XDI) was obtained in the same manner as in Example 1, except that the divided wall distillation column 210 was operated so that the temperature of the reboiler 214 connected thereto was 120°C in the distillation step.

[0134] Comparative Example 1

[0135] Using Figure 2 An isocyanate compound containing 1,3-XDI (m-XDI) was prepared in the following manner using the apparatus shown in (a).

[0136] (Reaction step)

[0137] The reaction product was prepared in the same manner as in Example 1. The reaction product was supplied to the first distillation column 1 through a transfer line.

[0138] (First distillation step)

[0139] The first distillation column 1 was configured so as to be able to remove a gas phase containing phosgene from the reaction product supplied through the transfer line.

[0140] Specifically, the first distillation column 1 used was a packed column packed with Mellapak as a kind of structured packing, and had a height of about 6 m.

[0141] The bottom temperature of the first distillation column 1 was set to 155°C, and the first distillation column 1 was operated at a column top pressure of 400 torr.

[0142] A reflux stream of about 150 kg / hr was recharged to the first distillation column 1, which corresponds to a reflux ratio of about 3.2 with respect to the column top outflow.

[0143] A gas phase containing phosgene was discharged through a gas phase discharge line connected to the top of the first distillation column 1. The reaction product from which the gas phase was removed was transferred to the next process through a transfer line connected to the bottom of the first distillation column 1.

[0144] (Second distillation step)

[0145] The second distillation column 2 was configured so as to be able to remove the solvent from the reaction product supplied through the transfer line.

[0146] Specifically, the second distillation column 2 used is a packed column filled with Mellapak as a structural packing material, and its height is approximately 7m.

[0147] The temperature at the bottom of the second distillation column 2 is set to 160°C, and the second distillation column 2 operates at a top pressure of 15 Torr.

[0148] Approximately 600 kg / hr of reflux feed is re-charged into the second distillation column 2, which corresponds to a reflux ratio of approximately 0.5 relative to the column top effluent.

[0149] The solvent containing 1,2-dichlorobenzene (o-DCB) is discharged through a solvent discharge line connected to the top of the second distillation column 2. The reaction products, after solvent removal, are discharged through a delivery line connected to the bottom of the second distillation column 2.

[0150] Comparative Example 2

[0151] Except that during the distillation step, the partitioned wall distillation column 210 is operated such that the pressure of the condenser 295 connected thereto is 30 Torr, the isocyanate compound containing 1,3-XDI (m-XDI) is obtained in the same manner as in Example 1.

[0152] Comparative Example 3

[0153] Except that during the distillation step, the partitioned wall distillation column 210 is operated such that the temperature of the reboiler 214 connected thereto is 170°C, an isocyanate compound containing 1,3-XDI (m-XDI) is obtained in the same manner as in Example 1.

[0154] Test Example

[0155] A portion of the fractions obtained from each outlet of the Examples and Comparative Examples was recovered and analyzed by gel permeation chromatography. The contents of the major components determined by the above analysis are shown in Tables 1 to 6 below.

[0156] In addition, the energy per unit time (kcal / hr) of the injection process performance according to the embodiments and comparative examples was measured and is shown in Tables 1 to 6 below.

[0157] In Tables 1 to 6 below, “heavy” refers to the fraction containing m-XDI obtained through isocyanate compound discharge line 219.

[0158] Table 1

[0159]

[0160] Table 2

[0161]

[0162] [Table 3]

[0163]

[0164] [Table 4]

[0165]

[0166] [Table 5]

[0167]

[0168] [Table 6]

[0169]

[0170] Referring to Tables 1 to 6, it is confirmed that the method of preparing an isocyanate compound according to the example can improve energy efficiency while obtaining a high-purity isocyanate compound.

[0171] In contrast, it is confirmed that in the comparative example, thermal denaturation and by-product formation increase, and the concentration and energy efficiency of the final isocyanate compound are low.

Claims

1. A method for preparing isocyanate compounds, comprising: Reaction steps: The salt of the amine compound is reacted with phosgene in the presence of a solvent to yield a reaction product containing an isocyanate compound, a solvent, and unreacted phosgene. Distillation steps: The reaction products are distilled in a partitioned-wall distillation column, thereby obtaining a stream containing unreacted phosgene from the top of the partitioned-wall distillation column, a stream containing isocyanate compounds from the bottom of the partitioned-wall distillation column, and a stream containing solvent from the side stream of the partitioned-wall distillation column. The distillation step is performed to bring the pressure at the top of the partitioned wall distillation column to 5 to 20 Torr. The distillation step is performed such that the temperature at the bottom of the partition wall distillation column is 165°C or lower and the temperature of the reboiler connected to the partition wall distillation column is 120°C to 165°C.

2. The method of claim 1, wherein the distillation step is performed such that the fractionation rate from the rectification section of the dividing wall distillation column to the pre-fractionation column side is less than 15%.

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

4. The method according to claim 1, wherein the amine compound is selected from 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, α,α,α',α'-tetramethylphenylenediamine, bis(aminoethyl) phthalate, bis(aminomethyl)cyclohexane, dicyclohexane The compound is selected from at least one of the following: methyl hexanediamine, 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, bis(aminomethyl)norbornene, and phenylenediamine.

5. The method according to claim 1, wherein the amine compound is at least one sulfur-containing aliphatic amine selected from 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(aminomethylthio)ethane, and 1,5-diamino-2-aminomethyl-3-thiapentane.

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

7. The method according to claim 1, wherein the salt of the amine compound is a hydrochloride or carbonate of the amine compound.

8. The method of claim 1, wherein the reaction step is carried out in the presence of a solvent comprising at least one of aromatic solvents and ester solvents.

9. The method according to claim 8, wherein the solvent is at least one compound selected from monochlorobenzene, 1,2-dichlorobenzene, 1,2,4-trichlorobenzene, amyl formate, n-butyl acetate, isobutyl acetate, n-amyl acetate, isoamyl acetate, methyl isoamyl acetate, methoxybutyl acetate, sec-hexyl acetate, 2-ethylbutyl acetate, 2-ethylhexyl acetate, cyclohexyl acetate, methyl cyclohexyl acetate, benzyl acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, ethyl acetate, butyl stearate, butyl lactate, amyl lactate, methyl salicylate, dimethyl phthalate, and methyl benzoate.

10. The method of claim 1, further comprising a low-boiling-point substance removal step for removing low-boiling-point substances from a feed stream containing an isocyanate compound, wherein low-boiling-point substances refer to substances whose boiling point is lower than that of the isocyanate compound, which is the main product in the reaction step.

11. The method of claim 1, further comprising a high-boiling-point substance removal step of removing high-boiling-point substances from a feed stream containing isocyanate compounds, wherein high-boiling-point substances refer to substances whose boiling point is higher than that of the isocyanate compound, which is the main product in the reaction step.

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