Method for producing isocyanate compounds

Abstract

The present invention relates to a method for producing an isocyanate compound. The present invention provides a method for producing an isocyanate compound that can minimize thermal degradation of a reaction product and generation of by-products and increase energy efficiency when producing an isocyanate compound using phosgene.

Description

[Technical field]

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

[0002] Xylylene diisocyanate (XDI) contains an aromatic ring in the molecule, but is classified as an aliphatic isocyanate. XDI is a very useful compound as a raw material for polyurethane-based materials, polyurea-based materials, and polyisocyanurate-based materials in the chemical, resin, and paint industries.

[0003] Generally, since isocyanate compounds undergo many side reactions during the synthesis process, they are produced by reacting them with anhydrous hydrochloric acid or carbonic acid to form a salt of an amine compound, which is then reacted with phosgene.

[0004] For example, XDI is produced by reacting xylylene diamine (hereinafter referred to as XDA) with anhydrous hydrochloric acid to form an amine hydrochloride, which is then reacted with phosgene. More specifically, in the past, a liquid raw material amine, for example, a solution containing XDA, was reacted with anhydrous hydrochloric acid to form XDA-HCl hydrochloride, which was then heated at a high temperature of at least 100°C or higher, and gas-phase phosgene was then injected to carry out a gas-liquid reaction to produce an isocyanate compound such as XDI.

[0005] The reaction for forming the isocyanate compound is a typical endothermic reaction, and in order to increase the yield, continuous heating and maintenance of a high temperature are required during the reaction.

[0006] However, since isocyanate compounds such as XDI generally have highly reactive amino groups, many side reactions occur during the phosgenation reaction, and the by-products formed by the side reactions affect processes in which the isocyanate compound is used as a raw material (for example, processes for producing polyurethane resins), resulting in a decrease in quality.

[0007] Due to the need to maintain high temperatures during the production of isocyanate compounds and the high reactivity of the generated isocyanate compounds such as XDI, the risk of by-products being generated or side reactions occurring due to thermal denaturation of the product is increased, which often places a heavy burden on the purification process.

[0008] Due to these problems, various attempts have been made to suppress side reactions and the generation of by-products during the production of isocyanate compounds, but the reality is that no effective technology has yet been developed. Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention provides a method for producing an isocyanate compound using phosgene, which can minimize thermal degradation of a reaction product and generation of by-products and increase energy efficiency. [Means for solving the problem]

[0010] According to one embodiment of the present invention, a 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, the solvent and unreacted phosgene; and distilling the reaction product in a dividing-wall distillation column to obtain a stream containing unreacted phosgene at the top of the dividing-wall distillation column, a stream containing isocyanate compounds at the bottom of the dividing-wall distillation column, and a stream containing solvent as a side stream draw of the dividing-wall distillation column; The distillation step is carried out so that the temperature at the bottom of the divided wall distillation column is 165° C. or less.

[0011] Hereinafter, a method for producing an isocyanate compound according to an embodiment of the present invention will be described. Unless otherwise defined herein, all technical and scientific terms have the same meaning as commonly understood by a person of ordinary skill in the art to which the present invention belongs. The terms used in the description of the present invention are merely for the purpose of effectively describing a specific embodiment and are not intended to limit the present invention.

[0012] As used herein, the singular forms "a," "an," and "the" include the plural forms as well, unless the context clearly indicates to the contrary. As used herein, the meaning of "comprising" is to embody certain properties, regions, integers, steps, operations, elements, components and / or components, and does not exclude the presence or addition of other certain properties, regions, integers, steps, operations, elements, components and / or groups. Since the present invention can be modified in various ways and can have various forms, specific embodiments are exemplified and described in detail below, but this is not intended to limit the present invention to the specific disclosed forms, and it should be understood that the present invention includes all modifications, equivalents, and alternatives within the above-mentioned concept and technical scope.

[0013] In this specification, when the location of two parts is described, for example, by "on," "upper," "lower," or "adjacent," one or more other parts may be located between the two parts, unless the words "immediately" or "directly" are used. In this specification, when a temporal context is described, for example, "after," "following," "next to," or "before," this can also include non-consecutive cases, unless the words "immediately" or "directly" are used.

[0014] As used herein, "low boiling point material" means a material having a lower boiling point than the isocyanate compound which is the target product of the present invention; and "high boiling point material" means a material having a higher boiling point than the isocyanate compound which is the target product of the present invention.

[0015] As used herein, the term "bottom" of a distillation column refers to an outlet through which a lower discharge from the distillation column is discharged to the outside of the distillation column, and the term "top" of a distillation column refers to an outlet through which an upper discharge from the distillation column is discharged to the outside of the distillation column.

[0016] According to one embodiment of the invention, a 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, the solvent and unreacted phosgene; and distilling the reaction product in a dividing-wall distillation column to obtain a stream containing unreacted phosgene at the top of the dividing-wall distillation column, a stream containing isocyanate compounds at the bottom of the dividing-wall distillation column, and a stream containing solvent as a side stream draw of the dividing-wall distillation column; The distillation step is carried out so that the temperature at the bottom of the divided wall distillation column is 165° C. or less.

[0017] In order to use an isocyanate compound as a raw material for precision chemical products such as optical materials, the compound must have a high purity. However, in general, many side reactions occur during the synthesis of isocyanate compounds containing XDI, and there is a problem that the purity of the isocyanate compounds decreases due to reactions between reaction products and thermal denaturation.

[0018] For example, aliphatic diisocyanates can be produced by reacting aliphatic diamines with phosgene. During this process, side reactions occur, producing by-products such as monoisocyanates, such as (chloromethyl)benzyl isocyanate. It is known that the occurrence of such side reactions and the production of by-products are caused by the need to maintain high temperatures during the production process of aliphatic diisocyanates and the high reactivity of the produced aliphatic diisocyanates, such as XDI. In particular, when the final product, aliphatic diisocyanates, is exposed to high temperatures for a certain period of time, side reactions occur or polymeric by-products such as oligomers and polymers containing dimers or higher polymers are formed.

[0019] As a result of extensive research, the present inventors have confirmed that when a reaction product obtained by a phosgenation reaction of an amine compound is distilled using a divided wall distillation column, thermal degradation of the reaction product and the generation of by-products can be minimized and energy efficiency can be increased.

[0020] The reaction product contains a mixture of many substances, including the raw material phosgene, the solvent, and low-boiling and high-boiling by-products. In order to obtain a high-purity isocyanate compound from the reaction product, it is necessary to continuously arrange a number of distillation apparatuses equal to the number of impurity components to be separated. If a solvent having a boiling point between phosgene and the isocyanate compound is used in the phosgenation reaction, remixing with other components occurs in the distillation apparatus until the solvent is removed. However, since the solvent accounts for 80% by weight or more of the reaction product, there is a problem that the energy efficiency until the process of removing the solvent is significantly reduced.

[0021] In the method for producing an isocyanate compound according to an embodiment of the present invention, a divided wall distillation column is used, and the solvent is obtained by a side stream draw of the divided wall distillation column. Therefore, a separate distillation apparatus or process for removing the solvent is not required, and the burden of process operation and energy consumption due to remixing of the solvent can be reduced.

[0022] FIG. 1 is a diagram illustrating the steps and apparatus used in a method for producing an isocyanate compound according to one embodiment of the present invention.

[0023] Hereinafter, each step that may be included in a method for producing an isocyanate compound according to an embodiment of the present invention will be described with reference to FIG.

[0024] (Reaction Step) First, a reaction step is carried out in which a salt of an amine compound is reacted with phosgene in the presence of a solvent to obtain a reaction product containing an isocyanate compound, the solvent and unreacted phosgene.

[0025] According to an embodiment of the present invention, in order to suppress the rapid reaction and side reaction of the amine compound with phosgene, the amine compound is preferably applied as a salt of the amine compound. For example, the salt of the amine compound may be a hydrochloride or carbonate of the amine compound.

[0026] The salt of the amine compound is prepared by neutralizing the amine compound with anhydrous hydrochloric acid or carbonic acid at a temperature of 20 to 80°C. The supply ratio of the anhydrous hydrochloric acid or carbonic acid may be, for example, 2 to 10 mol, alternatively 2 to 6 mol, or alternatively 2 to 4 mol, per 1 mol of the amine compound.

[0027] Preferably, the amine compound can be an aliphatic amine having an aliphatic group in the 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 two or more functionalities and containing two or more amino groups in the molecule.

[0028] For example, the amine compound may be hexamethylenediamine, 2,2-dimethylpentanediamine, 2,2,4-trimethylhexanediamine, butenediamine, 1,3-butadiene-1,4-diamine, 2,4,4-trimethylhexamethylenediamine, 1,6,11-undecatriamine, 1,3,6-hexamethylenetriamine, 1,8-diisocyanato-4-isocyanatomethyloctane, bis(aminoethyl)carbonate, bis(aminoethyl)ether, xylylenediamine, α,α,α',α'-tetramethylxylylenediamine, bis(aminoethyl)phthalate, bis(aminomethyl)cyclohexane, dicyclohexylmethylamine, bis(aminoethyl ... The diamine may be one or more compounds selected from the group consisting of benzenediamine, 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 xylylenediamine. In the present invention, the xylylenediamine is classified as an aliphatic diamine.

[0029] The amine compound may be one or more sulfur-containing aliphatic amines 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.

[0030] Among the amine compounds, xylylenediamine (XDA) can show more excellent effects when applied to the method for producing an isocyanate compound according to one embodiment of the present invention. Preferably, the amine compound may be one or more compounds selected from the group consisting of m-xylylenediamine, p-xylylenediamine, and o-xylylenediamine.

[0031] According to one embodiment of the present invention, the reaction step is carried out as a gas-liquid-solid three-phase reaction in which a solid amine salt is reacted with gas-phase phosgene in the presence of a solvent, thereby effectively suppressing a rapid reaction and minimizing the generation of side reactions and by-products.

[0032] When the salt of the amine compound and phosgene are reacted in a solvent, the phosgene can be added at once or in portions. For example, a small amount of phosgene is first added at a relatively low temperature to react with the salt of the amine compound to produce an intermediate. Then, the remaining amount of phosgene is secondly added at a relatively high temperature to react with the intermediate, thereby obtaining a reaction liquid containing an isocyanate compound. For example, a small amount of phosgene is reacted with xylylenediamine to produce an intermediate in the form of a carbamoyl salt, and the remaining amount of phosgene is then added to react the intermediate in the form of a carbamoyl salt with phosgene to form an aliphatic isocyanate such as xylylenediisocyanate.

[0033] This reaction step can minimize the time that the final product, the isocyanate compound, is exposed to high temperatures. Furthermore, by forming the intermediate at a relatively low temperature, the time required to maintain high temperatures in the entire reaction process can be reduced. This reduces the amount of heat input to the entire process. In addition, the high-temperature reaction time of phosgene can be relatively shortened, reducing the risk of explosive vaporization of phosgene.

[0034] The reaction step is carried out in a solvent including at least one of an aromatic hydrocarbon solvent and an ester solvent, and the solvent may be selected in consideration of the temperature at which the reaction step is carried out. The aromatic hydrocarbon solvent may be a halogenated aromatic hydrocarbon solvent such as monochlorobenzene, 1,2-dichlorobenzene, and 1,2,4-trichlorobenzene.

[0035] The ester solvent may be a fatty acid ester such as 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, methylcyclohexyl acetate, benzyl acetate, ethyl propionate, n-butyl propionate, isoamyl propionate, ethyl acetate, butyl stearate, butyl lactate, and amyl lactate; or an aromatic carboxylic acid ester such as methyl salicylate, dimethyl phthalate, and methyl benzoate.

[0036] According to one embodiment of the present invention, the salt of the amine compound may 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, in the reaction step. If the concentration of the salt of the amine compound contained in the solvent exceeds 20% by volume, a large amount of salt may be precipitated in the reaction step.

[0037] The reaction step is carried out at a temperature of 165°C or less, preferably 80°C to 165°C.

[0038] According to one embodiment of the present invention, when phosgene is added in portions in the reaction step, 10-30 wt%, 12-30 wt%, or 15-28 wt% of the total amount of phosgene is added at a temperature of 80°C to 100°C or 85°C to 95°C. Such reaction conditions suppress a rapid reaction, and an intermediate in the form of a carbamoyl salt can be selectively and effectively formed. Next, the intermediate is reacted with phosgene while adding the remaining amount of phosgene at a temperature of 110°C to 165°C or 120°C to 150°C to obtain a reaction product containing an isocyanate compound.

[0039] The isocyanate compound varies depending on the type of the amine compound used in the reaction step. For example, the isocyanate compound may be one or more compounds selected from the group consisting of n-pentyl isocyanate, 6-methyl-2-heptane isocyanate, cyclopentyl isocyanate, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), diisocyanatomethylcyclohexane (H6TDI), xylylene diisocyanate (XDI), diisocyanatocyclohexane (t-CHDI), and di(isocyanatocyclohexyl)methane (H12MDI).

[0040] In particular, the method for producing an isocyanate compound according to an embodiment of the present invention is useful for producing xylylene diisocyanate (XDI). XDI includes structural isomers such as 1,2-XDI (o-XDI), 1,3-XDI (m-XDI), and 1,4-XDI (p-XDI).

[0041] The reaction step can be carried out either by batch or continuous. The reaction step can be carried out in a reaction unit 100 including a reactor 110 having a rotating shaft, an amine compound salt supply line 10 and a phosgene supply line 20 for supplying reactants to the inside of the reactor, a heat source for supplying heat to the reactor, and a reaction product transfer line 102 for transferring the reaction product obtained in the reactor to a subsequent purification process.

[0042] (Distillation step) Next, the reaction product is distilled in a dividing-wall distillation column, a stream containing the unreacted phosgene is obtained at the top of the dividing-wall distillation column, a stream containing the isocyanate compound is obtained at the bottom of the dividing-wall distillation column, and a distillation step is performed to obtain a stream containing the solvent by side stream draw of the dividing-wall distillation column.

[0043] Figure 2(a) is a diagram showing a sequence for separating compounds A, B, and C in a normal distillation column, and Figure 2(b) is a diagram showing a sequence for separating compounds A, B, and C in a dividing-wall distillation column. Here, it is assumed that the boiling points of the compounds A, B, and C are A < B < C.

[0044] Referring to Figure 2(a), in order to separate A, B, and C from a mixture of compounds A, B, and C by a normal distillation process, a distillation column 1 for separating compound A from the mixture and a distillation column 2 for separating B and C from the mixture of compounds B and C obtained from the distillation column 1 must be continuously arranged.

[0045] On the other hand, referring to Figure 2(b), the dividing-wall distillation column 30 has a structure in which a dividing wall 31 is placed inside to integrate the prefractionator side 33 and the draw side 35. In the dividing-wall distillation column 30, not only is the operation easy by adjusting the pressure balance between the prefractionator side 33 and the draw side 35, but also two distillation columns can be integrated and operated as one, reducing the cost burden and increasing the energy efficiency.

[0046] When a feed mixture of compounds A, B, and C is supplied to the divided wall distillation column 30 shown in FIG. 2(b), a part of compound B and compound A rise to the rectification section 37 on the preliminary separator side 33, and the remaining compound B and compound C fall to the stripping section 39. In the rectification section 37, compound A is discharged from the top of the divided wall distillation column 30. In the stripping section 39, compound C is discharged from the bottom of the divided wall distillation column 30. Compound B, which has a boiling point between compounds A and C, is collected on the main separator side 35 and discharged from the side stream draw of the divided wall distillation column 30.

[0047] According to an embodiment of the present invention, in the distillation step, unreacted phosgene, the main product isocyanate compound, the solvent, the by-product hydrogen chloride, etc. contained in the reaction product are separated at the top, bottom, and side stream draw of the divided wall distillation column.

[0048] Among the components contained in the reaction product, unreacted phosgene is obtained from a stream corresponding to compound A in (b) of Figure 2, the main product, the isocyanate compound, is obtained from a stream corresponding to compound C in (b) of Figure 2, and the solvent is obtained from a stream corresponding to compound B in (c) of Figure 2.

[0049] Specifically, referring to FIG. 1 and FIG. 2(b), the reaction product is supplied to the divided wall distillation column 210 via the reactant transfer line 102. At the pre-separator side 33 of the divided wall distillation column 210, a part of the solvent and phosgene rise to the rectification section 37, and the remaining solvent and the main product, the isocyanate compound, fall to the stripping section 39. At the rectification section 37, the phosgene-rich fraction is discharged from the top streamline 293 connected to the top of the divided wall distillation column 210. At the stripping section 39, the isocyanate compound-rich fraction is discharged from the bottom streamline 212 connected to the bottom of the divided wall distillation column 210. Then, the solvent-rich fraction is collected at the main separator side 35 and discharged from the side stream line 251 connected to the side stream draw of the divided wall distillation column 30.

[0050] In this manner, in the method for producing an isocyanate compound according to an embodiment of the present invention, phosgene and an isocyanate compound are separated from the reaction product using a divided wall distillation column, and the solvent can be obtained from a side stream draw of the divided wall distillation column at the same time. Therefore, a separate distillation device or process for removing the solvent is not required, and the burden of process operation and energy consumption due to remixing of the solvent can be reduced.

[0051] There are various factors that affect the purity of the material discharged from the divided wall distillation column 210 through the top streamline 293, bottom streamline 212, and side streamline 251, and the energy efficiency of the process. For example, the number of stages in the divided wall distillation column 210, the length of the dividing wall, the reflux amount in the condenser 295, the amount of heat supplied to the reboiler 214, the vapor split ratio, the liquid split ratio, etc., can affect the purity of the material discharged and the energy efficiency of the process. Since the distillation step according to the present invention uses a large amount of solvent, it is preferable from the viewpoint of energy saving that the liquid split ratio is 15% or less among the above factors.

[0052] That is, the distillation step can be performed such that the division ratio of the liquid phase flow divided from the rectification section 37 of the divided wall distillation column to the preliminary separator side 33 is 15% or less. The division ratio of the liquid phase flow means the ratio of the liquid phase input to the preliminary separator side 33 to the total flow rate of the liquid phase from the rectification section 37 of the divided wall distillation column. The division ratio of the liquid phase flow can be adjusted using a liquid distributor.

[0053] According to one embodiment of the present invention, the stream containing the unreacted phosgene discharged from the top of the divided wall distillation column 210 is transferred to a condenser 295 via a top streamline 293. The gas phase containing phosgene is discharged from the condenser 295 via a gas phase discharge line 299, and the liquid phase is collected in a recovery drum 297 and then re-fed to the top of the divided wall distillation column 210. The phosgene obtained via the gas phase discharge line 299 is recycled as a reactant for the reaction step.

[0054] In this case, in order to improve the distillation efficiency in the divided wall distillation column 210, the distillation step is preferably performed so that the pressure at the top of the divided wall distillation column 210 is 20 torr or less. As an example, the distillation step is preferably performed 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 is 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.

[0055] According to one embodiment of the present invention, the stream containing the isocyanate compounds discharged from the bottom of the divided wall distillation column 210 is transferred to a reboiler 214 via a bottom streamline 212. In the reboiler 214, the low boiling point fraction is fed back to the lower part of the divided wall distillation column 210, and the fraction containing the isocyanate compounds is discharged via an isocyanate discharge line 219.

[0056] In this case, in order to improve the distillation efficiency in the divided wall distillation column 210, the distillation step is preferably performed so that the temperature of the bottom of the divided wall distillation column is 165° C. or less. As an example, the distillation step is preferably performed 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 is performed so that the temperature of the reboiler 214 connected to the distillation column 210 is 100° C. to 165° C., or 120° C. to 165° C., or 130° C. to 160° C.

[0057] In order to minimize the residence time of the reaction product at high temperature during the distillation step, it is preferable to use, as the reboiler 214, a device such as a kettle type reboiler, a thin film evaporator, a force circulated reboiler, or a jacketed vessel type reboiler.

[0058] According to one embodiment of the present invention, the solvent-containing stream discharged from the side stream draw of the divided wall distillation column 210 is transferred via a side stream line 251 through a condenser 253 to a recovery drum 255. The solvent-containing stream collected in the recovery drum 255 is discharged via a solvent discharge line 259. The solvent obtained via the solvent discharge line 259 can be recycled to the reaction step.

[0059] The fraction containing the isocyanate compound discharged through the isocyanate discharge line 219 may contain a trace amount of solvent, high boiling point substance, etc. If necessary, a step of purifying the fraction containing the isocyanate compound to obtain a high purity isocyanate compound may be further carried out.

[0060] As a non-limiting example, a low boiler removal step may be performed to remove low boiling lights from the fraction containing the isocyanate compound. In the low boiler removal step, low boiling lights may be removed from the fraction containing the isocyanate compound by a known low boiler removal unit.

[0061] The low boiling point substance refers to a substance having a boiling point lower than that of the isocyanate compound, which is the main product in the reaction step. The low boiling point substance may be a substance produced by a side reaction in the process of obtaining the main product. For example, in the process of producing XDI from the isocyanate compound, the low boiling point substance may include monoisocyanates such as (chloromethyl)benzyl isocyanate (CBI) and ethylphenyl isocyanate (EBI).

[0062] According to an embodiment of the present invention, in order to minimize thermal denaturation of the reaction product and generation of by-products in the low boiler removal step, the low boiler removal step is preferably performed at a temperature of 150° C. to 165° C. And, the low boiler removal step is preferably performed under a pressure of 5 torr or less.

[0063] For example, the low boiling point removal step is performed in a distillation tower, and it is advantageous to operate the distillation tower at a bottom temperature of 150°C to 165°C and a top pressure of 5 torr or less in order to minimize the thermal degradation and the generation of by-products. Here, the temperature at the bottom of the distillation tower refers to the temperature of a reboiler connected to the bottom of the distillation tower.

[0064] Preferably, the low boiler removal step is performed at a temperature of 150° C. to 165° C., alternatively 155° C. to 165° C., alternatively 155° C. to 162° C., alternatively 160° C. to 162° C. And preferably, the upper pressure at which the low boiler removal step is performed is 1 torr to 5 torr, alternatively 2 torr to 5 torr, alternatively 2 torr to 4 torr.

[0065] If the operating temperature and pressure of the low boiler removal step do not satisfy the above ranges, the amount of thermal degradation and by-products produced in the low boiler removal step increases, and the efficiency of removing low boiling materials decreases, thereby decreasing the concentration of isocyanate compounds in the reaction product obtained from the low boiler removal step.

[0066] As an example, the low boiler removal step can be performed in a low boiler removal unit including a distillation column configured to remove low boiling materials from the isocyanate compound-containing fraction supplied via the isocyanate compound discharge line 219 of the distillation unit 200; a low boiler discharge line for discharging the low boiling materials from the top of the distillation column; and a reaction product transfer line for discharging the reaction product from which the low boiling materials have been removed from the bottom of the distillation column and transferring it to a subsequent step.

[0067] In order to minimize the residence time of the reaction product at high temperatures in the low boiler removal step, a distillation column 440 equipped with devices such as a kettle type reboiler, a thin film evaporator, a force circulated reboiler, and a jacketed vessel type reboiler is used.

[0068] As a non-limiting example, a high boiler removal step is performed to remove high boilers from the reaction product from which the low boilers have been removed, in which high boilers are removed from the reaction product from which the low boilers have been removed by a known high boiler removal unit.

[0069] The high boiling point substance means a substance having a boiling point higher than that of the isocyanate compound which is the main product in the reaction step, and examples of the high boiling point substance include by-products in the form of high molecular weight such as oligomers including dimers or trimers or higher polymers of the isocyanate compound formed in the process of obtaining the main product.

[0070] According to an embodiment of the present invention, in order to minimize thermal denaturation of the reaction product and generation of by-products in the high boiler removal step, the high boiler removal step is preferably carried out at a temperature of 145° C. to 165° C. and under a pressure of 1 torr or less.

[0071] For example, the high boiling point removal step is carried out in a thin-film evaporator, and it is advantageous to operate the thin-film evaporator at a bottom temperature of 145°C to 165°C and a bottom pressure of 1 torr or less in order to minimize the thermal denaturation and the generation of by-products.

[0072] Preferably, the high boiler removal step may be performed at a temperature of 145° C. to 165° C., alternatively 150° C. to 165° C., alternatively 150° C. to 160° C., alternatively 155° C. to 160° C. And preferably, the high boiler removal step may be performed at a pressure of 0.1 torr to 1 torr, alternatively 0.5 torr to 1 torr.

[0073] If the operating temperature and pressure of the high boiler removal step do not satisfy the above ranges, the amount of thermal degradation and by-products produced in the high boiler removal step increases, and the efficiency of removing high boiling materials decreases, thereby decreasing the concentration of isocyanate compounds obtained from the high boiler removal step.

[0074] As an example, the high boiler removal step can be performed in a high boiler removal unit including a thin film distillation apparatus configured to remove high boiling materials from the reaction product supplied through a reaction product transfer line of the low boiler removal unit; an isocyanate compound discharge line for discharging an isocyanate compound to a condensation section of the thin film distillation apparatus; and a high boiler discharge line for discharging the high boiling materials from the bottom of the thin film distillation apparatus. Effect of the Invention

[0075] According to the present invention, there is provided a method for producing an isocyanate compound, which can minimize thermal denaturation of a reaction product and generation of by-products and can increase energy efficiency when producing an isocyanate compound using phosgene. [Brief description of the drawings]

[0076] [Figure 1]FIG. 1 is a diagram illustrating a process and an apparatus used in a method for producing an isocyanate compound according to one embodiment of the present invention. [Diagram 2] FIG. 1A is a diagram showing a sequence for separating compounds A, B, and C in a conventional distillation column; FIG. 1B is a diagram showing a sequence for separating compounds A, B, and C in a divided wall distillation column. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0077] The functions and effects of the present invention will be described in more detail below with reference to specific embodiments of the present invention, however, these are presented as examples to aid in understanding the invention and are not intended to limit the scope of the invention in any way.

[0078] Example 1 1,3-XDI (m-XDI) was produced using the apparatus shown in FIG. 1 and the following steps.

[0079] (Reaction Step) Under normal temperature and pressure conditions, 500 kg of hydrochloric acid and 560 kg of m-xylylenediamine (m-XDA) were reacted in a solvent of 6,500 kg of 1,2-dichlorobenzene (o-DCB) for 4 hours to form 870 kg of m-xylylenediamine hydrochloride.

[0080] 870 kg of the m-xylylenediamine hydrochloride was fed into the reactor 110 through the feed line 10, and the temperature of the reactor was raised to 125° C. During the reaction time, a total of 1,359 kg of phosgene was fed into the reactor through the feed line 20 and stirred. A dry ice-acetone condenser was used from the time of feeding phosgene until the end of the reaction to prevent phosgene from leaking outside. The reaction was carried out at a temperature of 90° C. for 1.5 hours.

[0081] Then, the reactor was heated to an internal temperature of 125° C., and 6,000 kg of phosgene was further added. The temperature of the reactor was maintained at 125° C., and the reaction solution was further stirred for 4.5 hours until it became transparent. After the reaction solution became transparent, heating was discontinued. The reaction product obtained by the above method was transferred to the distillation unit 200 via the transfer line 102.

[0082] (Distillation stage) The divided wall distillation column 210 of the distillation unit 200 is configured to obtain a stream containing unreacted phosgene from the reaction product supplied via transfer line 102 at the top of the divided wall distillation column, a stream containing 1,3-XDI from the bottom of the divided wall distillation column, and a stream containing the solvent from a side stream draw of the divided wall distillation column.

[0083] Specifically, the divided wall distillation column 210 is composed of a dividing wall located in the center of the column, a liquid distributor, a packing support, a grid, etc., and the pre-separator side, main separator side, rectifying section, and stripping section are packed with Mellapak, a type of structured packing. * Total number of columns: 20 * Vapor split ratio = 50:50 * Liquid split ratio=10:90

[0084] In this distillation step, the pressure of the condenser 295 connected to the divided wall distillation column 210 was set to 15 torr, and the temperature of the reboiler 214 connected to the divided wall distillation column 210 was set to 160°C.

[0085] At the top of fractional distillation column 210, a reflux stream of about 1350 kg / hr was recharged to fractional distillation column 210, corresponding to a reflux ratio to overhead output of about 39.5.

[0086] The gas phase containing phosgene was discharged from the condenser 295 via a gas phase discharge line 299, and the liquid phase was collected in a recovery drum 297 and then re-supplied to the upper part of the divided wall distillation column 210. The phosgene obtained via the gas phase discharge line 299 was recycled as a reactant for the above reaction step.

[0087] The low boiling fraction was re-fed to the bottom of the dividing wall distillation column 210 in reboiler 214 and the fraction containing 1,3-XDI was discharged via isocyanate discharge line 219 .

[0088] The solvent-containing stream discharged from the side stream draw of the divided wall distillation column 210 was transferred via side stream line 251 through condenser 253 to recovery drum 255. The solvent-containing stream collected in the recovery drum 255 was discharged via solvent discharge line 259. The solvent obtained via solvent discharge line 259 was recycled to the reaction step.

[0089] Example 2 In the distillation step, the pressure of the condenser 295 connected to the divided wall distillation column 210 was operated to 5 torr, and an isocyanate compound including 1,3-XDI (m-XDI) was obtained in the same manner as in Example 1.

[0090] Example 3 In the distillation step, an isocyanate compound including 1,3-XDI (m-XDI) was obtained in the same manner as in Example 1, except that the temperature of the reboiler 214 connected to the divided wall distillation column 210 was 120°C.

[0091] Comparative Example 1 1,3-XDI (m-XDI) was produced using the apparatus shown in FIG. 2(a) through the following steps. (Reaction Step) A reaction product was prepared in the same manner as in Example 1. The reaction product was supplied to a first distillation column 1 via a transfer line.

[0092] (First distillation stage) The first distillation column 1 was configured so as to allow the removal of a gas phase containing phosgene from the reaction product fed via a transfer line. Specifically, the first distillation column 1 uses a packing tower packed with Mellapak, which is a type of structured packing, and has a height of about 6 m. The temperature at the bottom of the first distillation column 1 was set to 155° C., and the pressure at the top of the first distillation column 1 was operated at 400 torr. 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 relative to the overhead output. 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 step through a transfer line connected to the bottom of the first distillation column 1.

[0093] (Second distillation stage) The second distillation column 2 was configured to remove the solvent from the reaction product fed via a transfer line. Specifically, the second distillation column 2 uses a packing tower packed with Mellapak, which is a type of structured packing, and has a height of about 7 m. The temperature at the bottom of the second distillation column 2 was set to 160° C., and the pressure at the top of the second distillation column 2 was operated at 15 torr. A reflux stream of about 600 kg / hr was recharged to the second distillation column 2, which corresponds to a reflux ratio of about 0.5 to the overhead output. A solvent containing 1,2-dichlorobenzene (o-DCB) was discharged through a solvent discharge line connected to the top of the second distillation column 2. The reaction product from which the solvent had been removed was discharged through a transfer line connected to the bottom of the second distillation column 2.

[0094] Comparative Example 2 In the distillation step, the pressure of the condenser 295 connected to the divided wall distillation column 210 was operated to be 30 torr, and an isocyanate compound including 1,3-XDI (m-XDI) was obtained in the same manner as in Example 1.

[0095] Comparative Example 3 In the distillation step, an isocyanate compound including 1,3-XDI (m-XDI) was obtained in the same manner as in Example 1, except that the temperature of the reboiler 214 connected to the divided wall distillation column 210 was 170°C.

[0096] Test Example A part of the fractions obtained from each outlet of the Examples and Comparative Examples was collected and analyzed by gel permeation chromatography. The contents of the main components confirmed by the above analysis are shown in Tables 1 to 6 below.

[0097] The energy per unit time (kcal / hr) input during the processes according to the examples and comparative examples was measured and is shown in Tables 1 to 6 below. In the following Tables 1 to 6, "Heavys" refers to the m-XDI-containing fraction obtained via the discharge line 219 for the isocyanate compound.

[0098] [Table 1]

[0099] [Table 2]

[0100] [Table 3]

[0101] [Table 4]

[0102] [Table 5]

[0103] [Table 6]

[0104] Referring to Tables 1 to 6 above, it was confirmed that the method for producing an isocyanate compound according to the above examples can obtain a high-purity isocyanate compound and increase energy efficiency. In contrast, in the comparative example, it was confirmed that the amount of thermal denaturation and by-products produced increased, and the concentration of the isocyanate compound finally obtained and the energy efficiency were low. [Explanation of symbols]

[0105] 10. Amine compound salt supply line 20 Phosgene supply line 100 reaction units 110 Reactor 102 Reaction product transfer line 200 Distillation Unit 210 Dividing Wall Distillation Column 212 Tower Bottom Streamline 214 Reboiler 219 Isocyanate compound discharge line 251 Sidestream Line 253 Condenser 255 recovery drum 259 Solvent Discharge Line 293 Tower Top Streamline 295 Condenser 297 Recovery drum 299 Gas Phase Discharge Line A, B, C compounds 1. 2 Steaming and Retention Tower 30 Split wall distillation tower 31 dividing wall 33 Prefractionator side 35 Main separator side (draw side) 37 Rectifying section 39 stripping section

Claims

1. a 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, the solvent and unreacted phosgene; and distilling the reaction product in a dividing-wall distillation column to obtain a stream containing unreacted phosgene at the top of the dividing-wall distillation column, a stream containing isocyanate compounds at the bottom of the dividing-wall distillation column, and a stream containing solvent at a side stream draw of the dividing-wall distillation column; The distillation step is carried out so that the temperature of the reboiler connected to the divided wall distillation column is 100° C. to 165° C.; The method for producing an isocyanate compound, wherein the pressure at the top of the divided wall distillation column is kept at 20 torr or less.

2. The method for producing an isocyanate compound according to claim 1, wherein the distillation step is performed so that a liquid split ratio of the liquid phase flow separated from the rectification section of the divided wall distillation column to the preliminary separator side is 15% or less.

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

4. The method for producing an isocyanate compound according to claim 1, wherein the amine compound is a difunctional or more functional chain or cyclic aliphatic amine containing two or more amino groups in the molecule.

5. The amine compound is, for example, hexamethylenediamine, 2,2-dimethylpentanediamine, 2,2,4-trimethylhexanediamine, butenediamine, 1,3-butadiene-1,4-diamine, 2,4,4-trimethylhexamethylenediamine, 1,6,11-undecatriamine, 1,3,6-hexamethylenetriamine, 1,8-diisocyanato-4-isocyanatomethyloctane, bis(aminoethyl)carbonate, bis(aminoethyl)ether, xylylenediamine, α,α,α',α'-tetramethylxylylenediamine, bis(aminoethyl)phthalate, bis(aminomethyl)cyclohexane, dicyclohexylmethanediamine, cyclohexamethyl ...

2. The method for producing an isocyanate compound according to claim 1, wherein the isocyanate is one or more compounds selected from the group consisting of 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.

6. The method for producing an isocyanate compound according to claim 1, wherein the amine compound is one or more sulfur-containing aliphatic amines 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.

7. The method for producing an isocyanate compound according to claim 1, wherein the amine compound is one or more compounds selected from the group consisting of m-xylylenediamine, p-xylylenediamine, and o-xylylenediamine.

8. The method for producing an isocyanate compound according to claim 1 , wherein the salt of the amine compound is a hydrochloride or a carbonate of the amine compound.

9. The method for producing an isocyanate compound according to claim 1, wherein the reaction step is carried out in a solvent containing at least one of an aromatic hydrocarbon solvent and an ester solvent.

10. The solvent is one or more compounds selected from the group consisting of 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, methylcyclohexyl 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. The method for producing an isocyanate compound according to claim 9.

11. 2. The method for producing an isocyanate compound according to claim 1, further comprising a low boiler removal stage for removing low boilers from the stream containing the isocyanate compound.

12. 2. The method of claim 1 further comprising a high boiler removal stage for removing heavies from the stream containing the isocyanate compound.

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