Method for producing isocyanate compound

Abstract

To solve problems associated with the present technology, namely that the reduction efficiency of the tt-isomer is low, and that the isocyanate after the tt-isomer reduction is of low quality.SOLUTION: A method for producing 4,4'-diisocyanatodicyclohexylmethane in which the tt-isomer content has been reduced, the method including: a reaction and separation step a) carrying out, in a solvent, a reaction of isocyanating 4,4'-diaminodicyclohexylmethane to synthesize a solution containing 4,4'-diisocyanatodicyclohexylmethane, and thereafter, by distillation, obtaining a flowable liquid with 4,4'-diisocyanatodicyclohexylmethane as its main component; a cooling step b) cooling the flowable liquid obtained in step a) to 20°C or lower to yield a suspension liquid; and a filtration step c) filtering the suspension liquid obtained in step b) to obtain 4,4'-diisocyanatodicyclohexylmethane which is liquid at 20°C.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Isocyanate compounds are polymerized by urethanization reactions or the like and are used in applications such as elastomers, foams, resins, paints, adhesives, fibers, etc. Polyurethane elastomers are elastic materials that fill an intermediate region between rubber and plastic, and have been reported to be used in applications requiring properties such as oil resistance, abrasion resistance, chemical resistance, cold resistance, and toughness, for example, in industrial rolls or solid tires.

[0003] Polyurethane elastomers are produced by reacting a diisocyanate compound with a polyol compound. By using an aliphatic diisocyanate compound as the diisocyanate compound, polyurethane elastomers with excellent yellowing resistance and flexibility can be obtained.

[0004] An example of an aliphatic diisocyanate compound for polyurethane elastomers is 4,4'-diisocyanatodicyclohexylmethane. 4,4'-Diisocyanatodicyclohexylmethane exists as stereoisomers, such as the trans-trans isomer (hereinafter referred to as the tt isomer), the cis-trans isomer (hereinafter referred to as the ct isomer), and the cis-cis isomer (hereinafter referred to as the cc isomer), due to differences in steric structure. It is known that the performance of polyurethane elastomers produced using 4,4'-diisocyanatodicyclohexylmethane varies significantly depending on the ratio of the stereoisomers. Therefore, 4,4'-diisocyanatodicyclohexylmethane with a low ratio of the tt isomer is preferred because it can provide high-performance products. For this reason, techniques for controlling the tt isomer content of 4,4'-diisocyanatodicyclohexylmethane to a low level have been investigated (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 53-46945 Summary of the Invention [Problem to be solved by the invention]

[0006] Patent Document 1 reports a technology for controlling the stereoisomer ratio of 4,4'-diisocyanatodicyclohexylmethane by selectively precipitating the tt isomer by blowing hydrochloric acid gas into 4,4'-diisocyanatodicyclohexylmethane synthesized from 4,4'-diaminodicyclohexylmethane and phosgene, and then filtering off the precipitate. This technology had issues with the low yield of tt isomer-rich 4,4'-diisocyanatodicyclohexylmethane that was intended for precipitate removal, and with the use of hydrochloric acid gas, which increased the acidity and hydrolyzable chlorine, resulting in low-quality isocyanates. [Means for solving the problem]

[0007] As a result of extensive research into solving the above problems, the present inventors have found that the invention described below can solve the above problems, and have completed the present invention.

[0008] That is, one aspect of the present invention resides in the following [1] and [2].

[0009] [1] A method for producing 4,4'-diisocyanatodicyclohexylmethane having a reduced tt isomer content, comprising the steps of: Step a) a reaction and separation step in which 4,4'-diaminodicyclohexylmethane is reacted in a solvent to isocyanate to synthesize a 4,4'-diisocyanatodicyclohexylmethane-containing liquid, and then a fluid liquid containing 4,4'-diisocyanatodicyclohexylmethane as a main component is obtained by a distillation operation; Step b) A cooling step of cooling the fluid liquid obtained in step a) to 20°C or less to obtain a suspension; and Step c) filtering the suspension obtained in Step b) to obtain 4,4'-diisocyanatedicyclohexylmethane in a liquid state at 20°C; A method for producing 4,4'-diisocyanatedicyclohexylmethane, comprising:

[0010] [2] The method according to [1], wherein the temperature in the distillation operation in step a) is in the range of 80 to 200°C.

[0011] [3] The method according to [1], wherein the cooling temperature in step b) is in the range of -10 to 10°C.

[0012] [4] 2. The method according to claim 1, wherein the cooling time in step b) is 1 to 144 hours. [Effects of the Invention]

[0013] According to one aspect of the present invention, it is possible to provide a high-quality aliphatic diisocyanate with a low acidity and in a high yield, as compared with conventionally known purification methods. DETAILED DESCRIPTION OF THE INVENTION

[0014] An embodiment of the present invention will be described in detail below. In this specification, unless otherwise specified, "A to B" representing a range of numerical values ​​means "A or more and B or less."

[0015] One aspect of the present invention relates to a method for producing 4,4'-diisocyanatodicyclohexylmethane having a reduced tt isomer content, which method comprises the following steps a, b, and c:

[0016] Step a) A reaction and separation step in which 4,4'-diaminodicyclohexylmethane is reacted in a solvent to isocyanate to synthesize a 4,4'-diisocyanatodicyclohexylmethane-containing liquid, and then a fluid liquid containing 4,4'-diisocyanatodicyclohexylmethane as the main component is obtained by a distillation operation.

[0017] Step b) A cooling step in which the flowable liquid obtained in step a) is cooled to 20°C or lower to obtain a suspension.

[0018] Step c) A filtration step of filtering the suspension obtained in step b) to obtain 4,4'-diisocyanatedicyclohexylmethane in a liquid state at 20°C.

[0019] Step a is a reaction and separation step in which 4,4'-diaminodicyclohexylmethane is reacted in a solvent to isocyanate to synthesize a 4,4'-diisocyanatodicyclohexylmethane-containing liquid, and then a fluid liquid containing 4,4'-diisocyanatodicyclohexylmethane as the main component is obtained by a distillation operation.

[0020] As described above, 4,4'-diisocyanatodicyclohexylmethane is generally synthesized by carrying out a reaction to convert 4,4'-diaminodicyclohexylmethane into an isocyanate.

[0021] The isocyanation reaction is not particularly limited, but examples thereof include an isocyanation reaction using phosgene, an isocyanation reaction using carbon dioxide and a silane compound, etc. Chemical agents used in the isocyanation reaction, such as phosgene, carbon dioxide, and a silane compound, are hereinafter referred to as isocyanation reagents.

[0022] It is known that the above-mentioned 4,4'-diaminodicyclohexylmethane exists mainly in three stereoisomers (tt, ct, and cc). 4,4'-Diisocyanatodicyclohexylmethane is produced by the isocyanation reaction of 4,4'-diaminodicyclohexylmethane, and in this process, the stereoisomer composition ratio of the raw material 4,4'-diaminodicyclohexylmethane and the stereoisomer composition ratio of the reaction product 4,4'-diisocyanatodicyclohexylmethane are, in principle, the same ratio (same substance amount (same mole) ratio).

[0023] In step a, the solvent is not particularly limited, but examples thereof include acetone, methanol, ethanol, tetrahydrofuran, toluene, normal hexane, monochlorobenzene, ortho-dichlorobenzene, meta-dichlorobenzene, and para-dichlorobenzene. Monochlorobenzene and ortho-dichlorobenzene are preferred because of their high solubility of 4,4'-diaminodicyclohexylmethane.

[0024] In step a, it is preferable that 4,4'-diaminodicyclohexylmethane is mixed with the solvent and then reacted with the isocyanation reagent.

[0025] In step a, it is preferable that the isocyanation reagent is mixed with the solvent in advance, and then mixed with 4,4'-diaminodicyclohexylmethane to cause the reaction.

[0026] In step a, the reaction can be carried out in a batch system or a flow system.

[0027] The reaction in step a is preferably carried out while mixing the reaction solution, and the mixing may be carried out using, but is not limited to, a propeller mixer, a scraping mixer, a paddle mixer, a homomixer, a disperser mixer, an ultramixer, or the like.

[0028] In step a, the reaction temperature is not particularly limited, but is preferably in the range of -20 to 200°C, more preferably in the range of -10 to 160°C.

[0029] In step a, the reaction pressure is not particularly limited, but is preferably in the range of 0 to 1,000 kPaG (gauge pressure), more preferably 0 to 300 kPaG (gauge pressure).

[0030] In step a of the present invention, the concentration of 4,4'-diaminodicyclohexylmethane in the reaction solution is not particularly limited, but is preferably 1 to 20% by mass, and more preferably 3 to 10% by mass, with the total amount of the reaction solution being 100% by mass.

[0031] The reaction solution obtained in the above step a may contain the isocyanation reagent not used in the reaction, decomposition products of the isocyanation reagent, or reaction by-products (reaction products derived from the isocyanation reagent). These components usually have a lower boiling point than the target reaction product, 4,4'-diisocyanatodicyclohexylmethane.

[0032] The reaction liquid obtained in step a is then subjected to a distillation operation to obtain a fluid liquid containing 4,4'-diisocyanatedicyclohexylmethane as the main component (distillation separation operation).

[0033] As a pretreatment for the distillation separation operation, an operation for removing the isocyanation reagent and / or a reaction product derived from the isocyanation reagent from the reaction solution after completion of the isocyanation reaction may be carried out.

[0034] The operation for removing the isocyanation reagent and / or the reaction product derived from the isocyanation reagent from the reaction solution is not particularly limited, and examples thereof include expelling the isocyanation reagent and / or the reaction product derived from the isocyanation reagent by nitrogen bubbling.

[0035] The distillation separation operation is intended to separate and remove components having a boiling point lower than that of 4,4'-diisocyanatodicyclohexylmethane and / or components having a boiling point higher than that of 4,4'-diisocyanatodicyclohexylmethane contained in the reaction liquid obtained in step a.

[0036] The low-boiling point component is mainly the solvent, and the solvent can be recovered (and reused) by the distillation separation operation. In this case, the distillation separation of the low-boiling point component is preferably vacuum distillation, since it is excellent in providing a high-quality aliphatic diisocyanate in high yield.

[0037] The high-boiling components are mainly polymers of 4,4'-diisocyanatodicyclohexylmethane, which can be removed from the system by the distillation separation operation. In this case, the distillation separation operation performed to remove the high-boiling components from the system, i.e., to obtain a fluid liquid product mainly composed of 4,4'-diisocyanatodicyclohexylmethane, is preferably vacuum distillation, as this is excellent in terms of the effect of providing a high-quality aliphatic diisocyanate in high yield.

[0038] In the distillation separation operation in step a, the recovery rate of the solvent is preferably 95% by mass or more of the solvent used in the reaction, and more preferably 99% by mass or more in terms of increasing production efficiency.

[0039] The distillation separation operation in step a produces a fluid liquid containing 4,4'-diisocyanatodicyclohexylmethane as a main component, and the fluid liquid preferably has a low content of the low-boiling component and the high-boiling component. In terms of improving purification efficiency, the contents of the low-boiling component and the high-boiling component are preferably each 1% by mass or less, where the total amount of the fluid liquid is 100% by mass.

[0040] The distillation separation operation is not particularly limited, but examples thereof include vacuum distillation, atmospheric distillation, thin film distillation, and the like.

[0041] The above distillation separation operation can be carried out using one distillation apparatus or a plurality of distillation apparatuses.

[0042] The pressure of the vacuum distillation carried out during the distillation separation of the low boiling point components is preferably in the range of 0.01 to 50 kPaA (absolute pressure), more preferably in the range of 0.1 to 30 kPaA (absolute pressure), and the temperature during this distillation is preferably in the range of 80 to 200°C, more preferably in the range of 90 to 130°C.

[0043] The pressure of the reduced pressure distillation carried out during distillation separation to obtain a fluid liquid containing 4,4'-diisocyanatodicyclohexylmethane as the main component is preferably in the range of 0.01 to 100 kPaA (absolute pressure), more preferably in the range of 0.1 to 10 kPaA (absolute pressure), and the temperature during this distillation is preferably in the range of 150 to 250°C, more preferably in the range of 170 to 200°C.

[0044] By carrying out the above step a (reaction and separation step), a flowable liquid material containing 4,4'-diisocyanate dicyclohexylmethane as a main component is obtained.

[0045] Step b is a cooling step in which the fluid liquid obtained in step a is cooled to 20° C. or less to obtain a suspension.

[0046] The cooling temperature in step b is preferably in the range of −10 to 10° C., since this allows the tt isomer content to be further reduced.

[0047] The cooling time in step b is not particularly limited, but may be, for example, 0.5 to 200 hours, and is preferably 1 to 144 hours in terms of increasing production efficiency.

[0048] The pressure in step b is not particularly limited, and may be reduced pressure, atmospheric pressure, or increased pressure. The pressure does not need to be constant, and can be adjusted to an appropriate pressure depending on the individual operations performed in step b.

[0049] The atmosphere in step b is not particularly limited, and examples thereof include a nitrogen atmosphere, an argon atmosphere, and an air atmosphere. Among these, a nitrogen atmosphere is preferred in terms of its excellent industrial versatility.

[0050] Step b can also be carried out in the presence of seed crystals.

[0051] The seed crystal is not particularly limited, but examples thereof include single crystals of the tt isomer of 4,4'-diisocyanatodicyclohexylmethane, or the solid separated in the above step c.

[0052] When the seed crystals are used, they are added to the flowable liquid obtained in step a. The timing of the addition is preferably when the temperature of the flowable liquid has reached 50°C or less, more preferably when the temperature has reached 20°C or less.

[0053] By using the seed crystals, it is possible to increase the purity of the tt isomer in the solid produced in the suspension obtained in step c, and it is expected that the amount of the target product finally obtained can be increased or the concentration of the tt isomer in the target product can be reduced.

[0054] By carrying out such a heating operation (heating in step a or step b) and cooling operation (step b), a suspension containing 4,4'-diisocyanate dicyclohexylmethane as the main component is obtained.

[0055] If the fluid liquid material obtained in step a loses its fluidity for some reason, or if the fluid liquid material obtained in step a is not cooled to 20° C. or below and is left at a temperature range of more than 20° C. and less than 50° C. for 3 hours or more and therefore is unable to form a suspension, it is preferable to once heat the material to a temperature of 50° C. or above. By carrying out such a heating operation, it is possible to regenerate a fluid liquid material equivalent to the fluid liquid material obtained in step a, even if the fluidity has once been lost or a suspension could not be formed from the fluid liquid material.

[0056] The heating time at this time is not particularly limited, but may be, for example, 0.5 to 6 hours, and is preferably 0.5 to 2 hours in terms of increasing production efficiency.

[0057] Step c relates to a filtration step in which the suspension obtained in step b above is filtered to obtain 4,4'-diisocyanatedicyclohexylmethane in a liquid state at 20°C.

[0058] In step c, the method for filtering the suspension obtained in step b is not particularly limited, but examples thereof include vacuum filtration, pressure filtration, and centrifugation.

[0059] The temperature for the filtration is not particularly limited, but is preferably in the range of -10 to 50°C, more preferably in the range of 0 to 50°C, and even more preferably in the range of 10 to 30°C.

[0060] Of the three isomers contained in 4,4'-diisocyanatodicyclohexylmethane, the tt isomer has higher crystallinity than the other isomers. Therefore, the solid component in the suspension obtained in step b is mainly produced by solidification of the highly crystalline tt isomer, and contains a higher concentration of the tt isomer. Therefore, the liquid component in the suspension has a relatively low concentration of the tt isomer.

[0061] The 4,4'-diisocyanate dicyclohexylmethane obtained by carrying out step c has a reduced tt isomer content (lower than the tt isomer content in the raw material) and remains liquid at 20°C.

[0062] The quality evaluation of 4,4'-diisocyanatodicyclohexylmethane is not particularly limited, but examples thereof include GC purity evaluation by gas chromatography measurement, acidity evaluation by acid content measurement, and chlorine content evaluation by hydrolyzable chlorine measurement.

[0063] In particular, the acidity must be less than 10 ppm, since if it is 10 ppm or more, the reactivity with polyurethane will be significantly reduced.

[0064] The gas chromatography measurement can be performed under the following conditions, for example, but is not particularly limited to these.

[0065] Measuring device: Shimadzu GC-2030 Measurement method: Column DB-1701 (0.25 mm x 30 m, 1.0 μm) Column temperature: 180°C (3°C / min) → 240°C (10°C / min) →320℃(5min) INJ: 280℃, DET: 3200℃ The method for measuring the acid content is not particularly limited, but for example, the acid content can be measured by the method described in JIS K 1603-2.

[0066] The chlorine content measurement by the hydrolyzable chlorine measurement is not particularly limited, but can be performed, for example, under the following conditions.

[0067] Measuring device Automatic titration device set (electrode silver electrode M-211, silver nitrate reference electrode R-211) Measurement method (1) Accurately weigh 0.1 to 1.0 g of the sample to be measured into a 200 mL beaker.

[0068] (2) Place a stir bar in a beaker, add 15 mL of toluene, 50 mL of methanol, 2 mL of 30% sodium hydroxide-methanol solution, and 50 mL of pure water, and quickly cover with a watch glass.

[0069] (3) Heat on a hot plate until the methanol gently refluxes.

[0070] (4) When the liquid volume in the beaker reaches 50 mL, cool it.

[0071] (5) Wash the watch glass and the walls of the beaker with pure water, and add pure water up to the 100 mL mark on the beaker.

[0072] (6) Add 3 mL of nitric acid (7) Perform potentiometric titration with 0.01 mol / L silver nitrate solution.

[0073] (8) Perform the measurement procedures (1) to (7) twice and take the average value.

[0074] (9) Substitute the obtained average value into the calculation formula to calculate the hydrolyzable chlorine. [Example]

[0075] The present invention will be described in detail below with reference to examples, but the present invention should not be construed as being limited thereto.

[0076] Example 1 A 400 L reaction vessel was charged with 329 kg of orthodichlorobenzene and 9.9 kg of 4,4'-diaminodicyclohexylmethane to prepare a mixed solution. The temperature inside the reaction vessel was adjusted to 130°C, and phosgene was blown into the mixed solution for 6 hours while stirring (injection rate: 13 kg / hour).

[0077] After dephosgenation with nitrogen, the reaction vessel was adjusted to 130°C and a pressure of 15 kPaA to distill off low-boiling components from the reaction mixture. The temperature was then adjusted to 180°C and a pressure of 15 kPaA to obtain 12 kg of a fluid liquid primarily composed of 4,4'-diisocyanatodicyclohexylmethane. Gas chromatography analysis confirmed that the concentration of 4,4'-diisocyanatodicyclohexylmethane in the fluid liquid was 99% by mass or higher. Gas chromatography analysis also confirmed that the concentration of the tt isomer of 4,4'-diisocyanatodicyclohexylmethane in the fluid liquid was 28% by mass.

[0078] 100.3 g of the fluid liquid was cooled at 0°C for 20 hours to obtain a suspension. The suspension was filtered to separate 52.1 g (52% yield) of liquid and 45.9 g (46% yield) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 17% by mass. The acid content and hydrolyzable chlorine concentration in the liquid were 6 ppm and 27 ppm, respectively.

[0079] Example 2 100.2 g of the fluid liquid obtained in Example 1 was cooled at 6°C for 144 hours to obtain a suspension. The obtained suspension was filtered to obtain 52.4 g (yield 52%) of liquid and 45.0 g (yield 45%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 14 mass%. The acidity and hydrolyzable chlorine in the liquid were 6 ppm and 27 ppm, respectively.

[0080] The results obtained so far are summarized in Table 1. The results of the prior art (JP 53-46945 A) are also shown as Comparative Example 1.

[0081] [Table 1]

[0082] Example 3 A 50 L reaction vessel was charged with 14 kg of monochlorobenzene and the temperature was adjusted between 0 and 10°C. Then, 1.2 kg of phosgene was blown into the reaction vessel (injection rate: 2.4 kg / hr) to prepare a phosgene solution. An amine solution consisting of 1.2 kg of 4,4'-diaminodicyclohexylmethane and 15 kg of monochlorobenzene was added dropwise to the prepared phosgene solution (injection rate: 5.1 kg / hr). After the dropwise addition was completed, the temperature of the reaction vessel was increased to 120°C at a rate of 40°C / hr. After the temperature increase, the reaction vessel was heated between 110 and 120°C for 4 hours while blowing in a total of 1.6 kg of phosgene. Nitrogen was blown into the reaction solution to remove unreacted phosgene from the reaction solution (dephosgenation), and 30 kg of reaction solution was obtained. At this time, the temperature of the reaction solution was lowered to 20°C. The resulting reaction mixture was then heated from 20°C to 90°C while maintaining a pressure range of 10 to 15 kPaA to distill off monochlorobenzene, yielding 1.4 kg of reaction mixture. The resulting reaction mixture was then reduced in pressure from an initial pressure of 10 kPaA to a final pressure of 0.2 kPaA while adjusting the temperature to 90°C to separate low-boiling components by distillation. The temperature was then raised to 200°C at 0.2 kPaA to yield 1.4 kg (93% yield) of a fluid liquid composed primarily of 4,4'-diisocyanatodicyclohexylmethane. Gas chromatography analysis confirmed that the concentration of 4,4'-diisocyanatodicyclohexylmethane in the fluid liquid was 99% by mass or higher. Gas chromatography analysis also confirmed that the concentration of the tt isomer of 4,4'-diisocyanatodicyclohexylmethane in the fluid liquid was 26% by mass.

[0083] With the vacuum released, 100 g of the fluid liquid was cooled to -10°C for 1 hour to obtain a suspension. The suspension was filtered to separate 60 g (60% yield) of liquid and 40 g (40% yield) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 20% by mass. The acidity and hydrolyzable chlorine concentration in the liquid were 5 ppm and 20 ppm, respectively.

[0084] Example 4 95 g of the fluid liquid obtained in Example 3 was cooled at -10°C for 5 hours to obtain a suspension. The obtained suspension was filtered to obtain 40 g (yield 42%) of liquid and 53 g (yield 56%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 19 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0085] Example 5 99 g of the fluid liquid obtained in Example 3 was cooled at -5°C for 1 hour to obtain a suspension. The obtained suspension was filtered to obtain 68 g (yield 69%) of liquid and 28 g (yield 28%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 20 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0086] Example 6 100 g of the fluid liquid obtained in Example 3 was cooled at -5°C for 5 hours to obtain a suspension. The obtained suspension was filtered to obtain 39 g (yield 39%) of liquid and 59 g (yield 59%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 18 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0087] Example 7 100 g of the fluid liquid obtained in Example 3 was cooled at 0°C for 5 hours to obtain a suspension. The obtained suspension was filtered to obtain 61 g (yield 61%) of liquid and 39 g (yield 39%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 20 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0088] Example 8 92 g of the fluid liquid obtained in Example 3 was cooled at 0°C for 16 hours to obtain a suspension. The obtained suspension was filtered to obtain 46 g (yield 50%) of liquid and 43 g (yield 47%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 17 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0089] Example 9 98 g of the fluid liquid obtained in Example 3 was cooled at 5°C for 16 hours to obtain a suspension. The obtained suspension was filtered to obtain 58 g (yield 59%) of liquid and 39 g (yield 40%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 18 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0090] Example 10 100 g of the fluid liquid obtained in Example 3 was cooled at 10°C for 16 hours to obtain a suspension. The obtained suspension was filtered to obtain 66 g (yield 66%) of liquid and 32 g (yield 32%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 19 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0091] Example 11 96 g of the fluid liquid obtained in Example 3 was cooled at 0°C for 20 hours to obtain a suspension. The obtained suspension was filtered to obtain 53 g (yield 55%) of liquid and 39 g (yield 41%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 16 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0092] Example 12 100 g of the fluid liquid obtained in Example 3 was cooled at 6°C for 144 hours to obtain a suspension. The obtained suspension was filtered to obtain 52 g (yield 52%) of liquid and 45 g (yield 45%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 14 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0093] Example 13 When the temperature of the fluid liquid obtained in Example 3 was 0°C, 0.1 g of the solid obtained in Example 6 (tt isomer concentration 29%) was added as seed crystals to 96 g of the fluid liquid, and the mixture was cooled at 0°C for 7 hours to obtain a suspension. The resulting suspension was filtered to obtain 82 g (yield 85%) of liquid and 12 g (yield 13%) of solid. The stereoisomer content of the liquid was analyzed by gas chromatography, and the tt isomer concentration was found to be 20 mass%. The acidity and hydrolyzable chlorine in the liquid were 5 ppm and 20 ppm, respectively.

[0094] [Table 2]

[0095] As can be seen from the above results, the production method of the present invention is extremely useful industrially as a production method that can obtain high-quality 4,4'-diisocyanatedicyclohexylmethane with a low tt isomer content and low acidity in high yield.

Claims

1. A method for producing 4,4'-diisocyanatodicyclohexylmethane having a reduced tt-isomer content, comprising the steps of: Step a) a reaction and separation step in which 4,4'-diaminodicyclohexylmethane is reacted in a solvent to isocyanate to synthesize a 4,4'-diisocyanatodicyclohexylmethane-containing liquid, and then a fluid liquid containing 4,4'-diisocyanatodicyclohexylmethane as a main component is obtained by a distillation operation; Step b) A cooling step of cooling the fluid liquid obtained in step a) to 20°C or less to obtain a suspension; and Step c) A filtration step of filtering the suspension obtained in Step b) to obtain 4,4'-diisocyanatedicyclohexylmethane in a liquid state at 20°C. A method for producing 4,4'-diisocyanate dicyclohexylmethane, comprising:

2. The method according to claim 1, wherein the temperature in the distillation operation of step a) is in the range of 80 to 200°C.

3. The method according to claim 1, wherein the cooling temperature in step b) is in the range of -10 to 10°C.

4. The method according to claim 1, wherein the cooling time in step b) is 1 to 144 hours.

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