Method for producing ε-caprolactam

Abstract

The present invention synthesizes ε-caprolactam from 5-cyanovaleramide with high yield by means of the steps (A) and (B) described below. (A) a step for obtaining 5-cyanovaleramide hydrogenation reaction mixture by causing 5-cyanovaleramide to react with hydrogen in an aqueous solvent in the presence of a hydrogenation catalyst (B) a step for obtaining ε-caprolactam by heating the 5-cyanovaleramide hydrogenation reaction mixture, which has been obtained in the step (A), to a temperature of from 180°C to 300°C in an aqueous solvent

Description

Technical Field

[0001] The present invention relates to a method for producing ε-caprolactam, which is a raw material for polyamide.

Background Art

[0002] ε-Caprolactam is an important chemical raw material that serves as a raw material for polyamide. It is industrially produced worldwide and most of it is used as a raw material for nylon 6, which is mostly polyamide. As an industrial production method of ε-caprolactam, a production method using a Beckmann rearrangement reaction with fuming sulfuric acid from cyclohexanone oxime is widely adopted. However, since a large amount of ammonium sulfate is by-produced in the neutralization step of the Beckmann rearrangement reaction, the development of a production method of ε-caprolactam that does not by-produce ammonium sulfate is required. As an alternative method, a method for producing ε-caprolactam from butadiene has been studied by synthesizing adiponitrile from butadiene, subsequently synthesizing 5-cyanovaleramide from adiponitrile, and further synthesizing ε-caprolactam from 5-cyanovaleramide (Non-Patent Document 1).

[0003] In the synthesis of ε-caprolactam from 5-cyanovaleramide, which is the final step in the above alternative method using butadiene as a raw material, a method has been proposed in which 5-cyanovaleramide is hydrogenated to convert it to 6-aminocaproic acid amide, and then ε-caprolactam is synthesized by condensation of 6-aminocaproic acid amide.

[0004] For example, Patent Document 1 discloses a method in which 5-cyanovaleramide is reacted with hydrogen in the presence of a metal catalyst to obtain 6-aminocaproic acid amide, and then 6-aminocaproic acid amide is reacted by an arbitrary method to synthesize ε-caprolactam. As the solvent used in this method, liquid ammonia is preferred over an aqueous solvent, and it is shown in the examples of this document that the yield of 6-aminocaproic acid amide by hydrogenation of 5-cyanovaleramide is low in the reaction in an aqueous solvent.

[0005] Patent Document 2 discloses a method for producing ε-caprolactam by heating 6-aminocaproic acid amide in water at a temperature of 150°C or higher and lower than the critical temperature of water (374°C). In this method, when pure 6-aminocaproic acid amide reacts in water at 320°C, ε-caprolactam is quantitatively produced, but at 250°C, the yield of ε-caprolactam is as low as 79%.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0007]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0008] When carrying out a chemical conversion reaction in a solvent industrially, from the perspective of green chemistry, it is desirable to use a solvent with a lower environmental impact (specifically, an aqueous solvent), and from the perspective of reducing energy load, to carry out the reaction at as low a reaction temperature as possible (specifically, a reaction temperature of 300°C or lower). However, as described above, in the case of synthesizing ε-caprolactam from 5-cyanovaleramide, no method has been found that can synthesize ε-caprolactam in a high yield while satisfying these conditions. Therefore, an object of the present invention is to provide a method for synthesizing ε-caprolactam from 5-cyanovaleramide in a high yield at a reaction temperature of 300°C or lower in an aqueous solvent.

Means for Solving the Problems

[0009] As a result of intensive studies to solve the above problems, the present inventors have found that 5-cyanovaleramide is reacted with hydrogen in an aqueous solvent in the presence of a hydrogenation catalyst to obtain a 5-cyanovaleramide hydrogenation reaction mixture, and the 5-cyanovaleramide hydrogenation reaction mixture obtained in the above step is heated in an aqueous solvent at a temperature of 180°C or higher and 300°C or lower, whereby ε-caprolactam can be synthesized in a high yield, and thus completed the invention.

[0010] That is, the present invention is composed of the following (1) to (8). (1) A method for producing ε-caprolactam, comprising the following steps (A) and (B). (A) A step of reacting 5-cyanovaleramide with hydrogen in an aqueous solvent in the presence of a hydrogenation catalyst to obtain a 5-cyanovaleramide hydrogenation reaction mixture (B) A step of heating the 5-cyanovaleramide hydrogenation reaction mixture in an aqueous solvent at a temperature of 180°C or higher and 300°C or lower to obtain ε-caprolactam (2) The method according to (1), wherein the step (A) is carried out in the absence of ammonia. (3) The method according to (1) or (2), wherein the reaction temperature in the step (A) is 50°C or higher and 200°C or lower. (4) The temperature in the step (B) is 200°C or higher and less than 280°C, (1) ~ (3) any of Crab the methods described. (5) The method according to any one of (1) to (4), wherein the step (B) is carried out in the absence of a catalyst. (6) The method according to any one of (1) to (5), wherein the proportion of 6-aminocaproic acid amide contained in the 5-cyanovaleramide hydrogenation reaction mixture is 45 mol% or more and 72 mol% or less. (7) A 5-cyanovaleramide hydrogenation reaction mixture in which the proportion of 6-aminocaproic acid amide is 45 mol% or more and 72 mol% or less. (8) An ε-caprolactam composition in which the proportion of 6-aminocaproic acid amide to ε-caprolactam is 0.1 mol% or more and 5 mol% or less. [[Effect of the Invention]]

[0011] According to the present invention, ε-caprolactam can be produced in a high yield from 5-cyanovaleramide while reducing the environmental load and energy load.

Mode for Carrying Out the Invention

[0012] Hereinafter, the present invention will be described in more detail, but the present invention is not limited to the following aspects.

[0013] [Step (A)] In the present invention, first, as step (A), 5-cyanovaleramide is reacted with hydrogen in an aqueous solvent in the presence of a hydrogenation catalyst to obtain a 5-cyanovaleramide hydrogenation reaction mixture.

[0014] 5-Cyanovaleramide is a cyano group-containing carboxylic acid amide also called 5-cyanopentanamide. 5-Cyanovaleramide can be synthesized by hydration of one cyano group of adiponitrile (for example, Bioorganic and Medicinal Chemistry, vol.7, 2239-2245 (1999)), dehydration of one amide group of adipamide (for example, US Patent No. 3331866).

[0015] The 5-cyanovaleramide used as a raw material in the present invention is not particularly limited, and 5-cyanovaleramide biologically and / or chemically synthesized from any carbon-containing raw materials such as fossil resources such as petroleum, coal, and natural gas, biomass resources, and inorganic substances containing carbon atoms such as carbon monoxide, carbon dioxide, and carbonates can be used as a raw material for ε-caprolactam.

[0016] In the present invention, the aqueous solvent means water or a water-miscible organic solvent containing water in a proportion exceeding 10% by volume. The proportion of water in the water-miscible organic solvent containing water is preferably 30% by volume or more, more preferably 50% by volume or more, still more preferably 60% by volume or more, and particularly preferably 90% or more. Specific examples of the water-miscible organic solvent that can be used in the present invention include methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, tert-butanol, 1,2-dimethoxyethane, diglyme, tetrahydrofuran, dioxane, γ-butyrolactone, N-methylpyrrolidone, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, and acetone.

[0017] The pH of the aqueous solvent is not particularly limited, but considering suppression of catalyst deterioration, suppression of by-product formation, corrosiveness to the reaction apparatus, etc., it is preferably pH 2 to 13, more preferably pH 3 to 11, and still more preferably pH 4 to 10.

[0018] In the present invention, the hydrogenation catalyst means a metal and / or an organometallic complex having hydrogenation ability. Here, having hydrogenation ability means having the ability to add hydrogen atoms to unsaturated bonds such as carbon-carbon double bonds (C=C), carbon-carbon triple bonds (C≡C), carbon-oxygen double bonds (C=O), carbon-nitrogen double bonds (C=N), and carbon-nitrogen triple bonds (C≡N) in the presence of hydrogen.

[0019] The hydrogenation catalyst preferably contains a transition metal element. Specifically, it preferably contains one or more selected from the group consisting of palladium, platinum, ruthenium, rhodium, rhenium, nickel, cobalt, iron, iridium, osmium, copper, and chromium, and more preferably contains one or more selected from the group consisting of palladium, platinum, ruthenium, rhodium, nickel, cobalt, iron, copper, and chromium.

[0020] The hydrogenation catalyst may be a homogeneous hydrogenation catalyst or a heterogeneous hydrogenation catalyst. Any hydrogenation catalyst can be used in the present invention. The hydrogenation catalyst used in the present invention is preferably a heterogeneous hydrogenation catalyst because, in addition to being easily separable from the 5-cyanovaleramide hydrogenation reaction mixture described later, the recovery and reuse of the hydrogenation catalyst after the reaction are simple.

[0021] The homogeneous hydrogenation catalyst means a hydrogenation catalyst dissolved in an aqueous solvent, and more specifically, an organometallic complex having hydrogenation ability. Examples of such catalysts include Wilkinson catalyst, Crabtree catalyst, Shvo catalyst, Schrock-Osborn catalyst, chiral phosphine-rhodium complex, phosphine-ethylenediamine-ruthenium complex, iridium PNP complex, and the like.

[0022] The heterogeneous hydrogenation catalyst means a substance having hydrogenation ability that is insoluble in an aqueous solvent. Examples of such catalysts include particulate metal catalysts, sponge (porous) metal catalysts, supported organometallic complex catalysts, platinum oxide (Adams catalyst), palladium oxide, palladium hydroxide (Pearlman catalyst), and the like.

[0023] The particulate metal catalyst is a solid catalyst of minute size composed of a metal element. The particle size of the particulate metal catalyst is not particularly limited and may be any of the sub-nanometer level, nanometer level, and micrometer level. From the viewpoints of saving the amount of metal used due to an increase in the active surface, improving stability by suppressing aggregation of metal fine particles by being supported, and improving the ease of separation, recovery, and reuse of the catalyst, when using a particulate metal catalyst as the hydrogenation catalyst, it is preferable to use a supported metal catalyst having a structure in which metal fine particles are supported on a carrier.

[0024] The supported metal catalyst can be prepared by known methods such as the impregnation method, precipitation method, ion exchange method, and vapor phase loading method. Examples of carriers that can be used in the preparation of the supported metal catalyst include carbon, polymers, metal oxides, metal sulfides, zeolites, clays, heteropolyacids, solid phosphoric acid, hydroxyapatite, and the like.

[0025] The sponge (porous) metal catalyst is a porous metal catalyst obtained by eluting an amphoteric metal such as aluminum, zinc, or silicon from an alloy composed of a metal having hydrogenation catalytic activity and an amphoteric metal. Specifically, examples include sponge cobalt catalysts, sponge nickel catalysts, sponge copper catalysts, and sponge iron catalysts obtained by developing alloys of metals such as nickel, cobalt, copper, and iron with aluminum using an alkali. These are also widely known as "Raney cobalt", "Raney nickel", "Raney copper", and "Raney iron" (all registered trademarks of W.R. Grace & Co.).

[0026] The supported organometallic complex catalyst is a catalyst in which an organometallic complex is fixed to a carrier via a linker ligand. Examples of carriers that can be used in the preparation of the supported organometallic complex catalyst include polymers and metal oxides.

[0027] For the purpose of improving the catalytic activity and stability of the hydrogenation catalyst, a promoter may be added to the hydrogenation catalyst. Examples of the promoter include molybdenum, sulfur, and bismuth.

[0028] In the present invention, hydrogen refers to molecular hydrogen (H2) unless otherwise specified.

[0029] The hydrogen to be reacted with 5-cyanovaleramide may be added to the reactor all at once or sequentially.

[0030] The partial pressure of hydrogen during the reaction is not particularly limited. However, if it is too low, the reaction time will be prolonged, while if it is too high, it is not desirable from the perspective of equipment safety. Therefore, at the start of the reaction, it is preferably not less than atmospheric pressure and not more than 10 MPa (gauge pressure) at normal temperature, more preferably not less than atmospheric pressure and not more than 3 MPa (gauge pressure) at normal temperature, and even more preferably not less than atmospheric pressure and not more than 1 MPa (gauge pressure) at normal temperature.

[0031] The reaction mode is not particularly limited, and it can be carried out in any form using a batch tank reactor, semi-batch tank reactor, continuous tank reactor, continuous tubular reactor, or trickle bed reactor. When the reaction is carried out using a heterogeneous catalyst, the reaction can be carried out in any of the suspension bed, fixed bed, moving bed, or fluidized bed modes.

[0032] The reaction temperature is not particularly limited. However, if it is too low, the reaction rate will be slow, and if it is too high, not only will the energy consumption increase, but the final ε-caprolactam selectivity will also be low, which is not preferable. From this perspective, the reaction temperature is preferably 25 to 250 °C, more preferably 50 to 200 °C, and even more preferably 80 to 150 °C.

[0033] In the reactor, in addition to hydrogen, inert gases such as nitrogen, helium, and argon may coexist.

[0034] On the other hand, since it may lead to the deterioration of the hydrogenation catalyst and the generation of explosive gas, it is preferable that the oxygen concentration in the reactor is low. Specifically, it is preferably 5% by weight or less based on the charged amount of 5-cyanovaleramide, more preferably 1% by weight or less, and even more preferably 0% by weight (i.e., in the absence of oxygen).

[0035] Also, from the perspective of the reaction selectivity to ε-caprolactam, the amount of ammonia relative to the aqueous solvent is preferably 3% by weight or less, more preferably 1% by weight or less, and even more preferably 0% by weight (i.e., in the absence of ammonia).

[0036] The charged amount of 5-cyanovaleramide with respect to the aqueous solvent is not particularly limited, but if the charged amount is small, it is not industrially preferable. From such a viewpoint, the charged amount of 5-cyanovaleramide with respect to the aqueous solvent is preferably 0.01% by weight or more, more preferably 0.1% by weight or more, and still more preferably 1.0% by weight or more.

[0037] The 5-cyanovaleramide hydrogenation reaction mixture, which is the product of step (A), means a mixture of a plurality of products generated by reacting 5-cyanovaleramide with hydrogen in the presence of a hydrogenation catalyst in an aqueous solvent as described in the above-described embodiment. That is, the 5-cyanovaleramide hydrogenation reaction mixture contains 6-aminocaproic acid amide as a main component, and in addition, contains a dimer, an oligomer, ε-caprolactam, unreacted 5-cyanovaleramide, etc. of 6-aminocaproic acid amide. Therefore, pure 6-aminocaproic acid amide does not coincide with the 5-cyanovaleramide hydrogenation reaction mixture.

[0038] When step (A) is carried out in the presence of a homogeneous hydrogenation catalyst, the catalyst can be used in step (B) without being separated and without taking out the 5-cyanovaleramide hydrogenation reaction mixture generated in the aqueous solvent from the aqueous solvent.

[0039] When step (A) is carried out by suspending a heterogeneous hydrogenation catalyst in an aqueous solvent, the 5-cyanovaleramide hydrogenation reaction mixture generated in the aqueous solvent may be used in step (B) without taking it out of the aqueous solvent while the catalyst is suspended. After separating the catalyst by a simple solid-liquid separation operation (filtration, centrifugation, decantation, etc.), the 5-cyanovaleramide hydrogenation reaction mixture may be used in step (B) without taking it out of the aqueous solvent.

[0040] In step (A), the 5-cyanovaleramide hydrogenation reaction mixture produced in an aqueous solvent may be taken out from the aqueous solvent in the previous stage of step (B), or the 5-cyanovaleramide hydrogenation reaction mixture taken out from the aqueous solvent may be crude or purified. The crude or purification of the 5-cyanovaleramide hydrogenation reaction mixture can be carried out by ordinary separation operations such as filtration, extraction, distillation, and crystallization.

[0041] In step (A), when unreacted 5-cyanovaleramide remains, the unreacted 5-cyanovaleramide can be separated by the above separation operation and reused in step (A) to further improve the yield of ε-caprolactam.

[0042] From the viewpoint of obtaining ε-caprolactam in a high yield in the subsequent step (B), the proportion of 6-aminocaproic acid amide contained in the 5-cyanovaleramide hydrogenation reaction mixture obtained in step (A) is preferably 45 mol% or more and 72 mol% or less, more preferably 50 mol% or more and 71 mol% Below and even more preferably 60 mol% or more and 70 mol% or less. The proportion of 6-aminocaproic acid amide referred to here is the molar ratio of 6-aminocaproic acid amide to the substances contained in the 5-cyanovaleramide hydrogenation reaction mixture (including unreacted 5-cyanovaleramide). Since all the substances contained in the 5-cyanovaleramide hydrogenation reaction mixture can be regarded as derived from 5-cyanovaleramide before the hydrogenation reaction, the molar ratio of 6-aminocaproic acid amide to 5-cyanovaleramide charged in step (A) can be regarded as the proportion of 6-aminocaproic acid amide contained in the 5-cyanovaleramide hydrogenation reaction mixture.

[0043] [Step (B)] In step (B), the 5-cyanovaleramide hydrogenation reaction mixture obtained from step (A) is heated to a temperature of 180 to 300 °C in an aqueous solvent to obtain ε-caprolactam.

[0044] In step (B), ε-caprolactam can be obtained in a high yield by heating the 5-cyanovaleramide hydrogenation reaction mixture in an aqueous solvent at a temperature of 180 to 300 °C. The temperature range is more preferably 200 to 280 °C, and even more preferably 220 to 260 °C. As the aqueous solvent, the aforementioned solvents are used, but the aqueous solvent used in step (A) and the aqueous solvent used in step (B) do not have to be the same solvent.

[0045] The reaction form is not particularly limited, and it can be carried out in any form using a batch tank reactor, a semi-batch tank reactor, a continuous tank reactor, a continuous tubular reactor, or a trickle bed reactor. When the reaction is carried out using a heterogeneous catalyst, the reaction can be carried out in any of the suspension bed type, fixed bed type, moving bed type, or fluidized bed type.

[0046] An inert gas such as nitrogen, helium, or argon may be present in the reactor.

[0047] In order to suppress the sequential oxidation of ε-caprolactam, the oxygen concentration in the reactor is preferably low. Specifically, it is preferably 5% by weight or less, more preferably 1% by weight or less, and even more preferably 0% by weight (i.e., in the absence of oxygen) based on the charged amount of 5-cyanovaleramide.

[0048] In order to suppress the sequential hydrogenation of ε-caprolactam, the hydrogen concentration in the reactor is preferably low. Specifically, it is preferably 5% by weight or less, more preferably 1% by weight or less, and even more preferably 0% by weight (i.e., in the absence of hydrogen) based on the charged amount of 5-cyanovaleramide. Therefore, when step (B) is continuously carried out from step (A), it is preferable to purge the hydrogen present in step (A) out of the reaction system in the previous stage of step (B).

[0049] From the viewpoint of the reaction selectivity to ε-caprolactam, the amount of ammonia relative to the aqueous solvent is preferably 3% by weight or less, more preferably 1% by weight or less, and even more preferably 0% by weight (i.e., in the absence of ammonia).

[0050] Step (B) can usually be carried out in the absence of a catalyst, but it may also be carried out in the presence of a catalyst. When using a catalyst, it is preferable to use an acid catalyst, and more preferably a heterogeneous acid catalyst. Specific examples of the heterogeneous acid catalyst include polymers, metal oxides, metal sulfides, zeolites, clays, heteropolyacids, solid phosphoric acid, hydroxyapatite, and the like.

[0051] Examples of the polymer having acid catalyst activity include acidic ion exchange resins. Specifically, styrene-based sulfonic acid type ion exchange resins and phenol-based sulfonic acid type ion exchange resins can be used.

[0052] Examples of metal oxides having acid catalyst activity include oxides containing one or more metal elements selected from the group consisting of Sc, Y, Ce, Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Fe, Zn, Cd, Al, Ga, In, Si, Ge, Sn, and Pb. More specifically, scandium oxide (Sc2O3), cerium oxide (CeO2), anatase titanium oxide (A-TiO2), rutile titanium oxide (R-TiO2), zirconium oxide (ZrO2), vanadium oxide (V2O5), niobium oxide (Nb2O5), tantalum oxide (Ta2O5), chromium oxide (Cr2O3), molybdenum oxide (MoO3), tungsten oxide (WO3), manganese oxide (MnO2), iron oxide (Fe2O3, Fe3O4), zinc oxide (ZnO), aluminum oxide (Al2O3), gallium oxide (Ga2O3), indium oxide (In2O3), silicon dioxide (SiO2), germanium oxide (GeO2), tin oxide (SnO2), lead oxide (PbO), silica-alumina (SiO2-Al2O3), etc. can be exemplified. For these metal oxides, porous ones with a large specific surface area may be used. For example, mesoporous silica, mesoporous titania, etc. can be preferably used.

[0053] Examples of zeolites having acid catalyst activity include zeolites given a three-letter alphabetic structure code in the database of the International Zeolite Association. More specifically, zeolites given structure codes such as LTA, FER, MWW, MFI, MOR, LTL, FAU, BEA, CHA, CON, etc. can be exemplified.

[0054] Examples of clays having acid catalyst activity include kaolin, montmorillonite, bentonite, saponite, acid clay, etc.

[0055] The ε-caprolactam obtained in Step (B) is an ε-caprolactam composition containing a small amount of 6-aminocaproic acid amide in addition to ε-caprolactam. In the ε-caprolactam composition, if the ratio of 6-aminocaproic acid amide to ε-caprolactam is 0.1 mol% or more and 5 mol% or less, it is preferable from the viewpoint of process efficiency, more preferably 0.2 mol% or more and 4 mol% or less, and even more preferably 0.5 mol% or more and 3 mol% or less. If it is less than 0.1 mol%, the progress of the subsequent polyamide polymerization will be slow, while if it exceeds 5 mol%, the load on the recovery process tends to increase.

[0056] [Recovery of ε-caprolactam] The ε-caprolactam produced by the method for producing ε-caprolactam of the present invention can be recovered by ordinary separation and purification operations such as filtration, extraction, distillation, and crystallization after the reaction is completed.

[0057] [Polyamide polymerization] The ε-caprolactam obtained by the method for producing ε-caprolactam of the present invention can be used as a raw material for the production of polyamide. As a method for producing polyamide, a known method of ring-opening polymerization of ε-caprolactam can be applied (see Osamu Fukumoto, "Polyamide Resin Handbook", Nikkan Kogyo Shimbun, Ltd. (January 1998)).

Examples

[0058] Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to the following examples. The reaction results are defined by the following formula.

[0059] Product yield (mol%) = Amount of product produced (mol) / Amount of 5-cyanovaleramide charged (mol) × 100.

[0060] Ratio of 6-aminocaproic acid amide in 5-cyanovaleramide hydrogenation reaction mixture (product of Step (A)) (mol%) = Amount of 6-aminocaproic acid amide produced after Step (A) (mol) / Amount of 5-cyanovaleramide charged (mol) × 100.

[0061] Ratio of 6-aminocaproic acid amide to ε-caprolactam (mol %)=amount of 6-aminocaproic acid amide produced after step (B) (mol) / amount of ε-caprolactam produced after step (B) (mol)×100.

[0062] The reaction solutions were analyzed by high performance liquid chromatography (HPLC). The quality and quantity of the products were determined by an absolute calibration curve prepared using standard samples. The HPLC analysis conditions are as follows:

[0063] [HPLC analysis conditions] HPLC equipment: Prominence (Shimadzu Corporation) Column: Synergi hydro-RP (Phenomenex), length 250 mm, inner diameter 4.60 mm, particle size 4 μm Mobile phase: 0.1% by weight phosphoric acid aqueous solution / acetonitrile = 95 / 5 (volume ratio) Flow rate: 1.0mL / min Detector: UV (210 nm) Column temperature: 40°C.

[0064] Example 1 [Process (A)] 0.1g of 5-cyanovaleramide (Enamine), 100mL of water, and 0.035g of powdered sponge cobalt catalyst R-401 (Nikko Rica Corporation) were added to a 0.2L stainless steel autoclave (Taiatsu Glass Industry Co., Ltd.). The autoclave was purged with nitrogen while stirring at a stirring speed of 1000 rpm, and hydrogen gas was introduced so that the hydrogen partial pressure in the autoclave was 3.5MPa (gauge pressure). The temperature in the autoclave was then raised to 100°C. After being held at 100°C for 5 hours, the autoclave was allowed to cool to room temperature, the gas in the autoclave was released, and the pressure was returned to normal, after which the reaction solution was recovered. The supernatant from which the catalyst had been removed by filtration was analyzed by HPLC. The results are shown in Table 1-1.

[0065] [Process (B)] The aqueous solution containing the 5-cyanovaleramide hydrogenation reaction mixture obtained in step (A) was again added to a stainless steel autoclave (manufactured by Taiatsu Glass Industry Co., Ltd.) with a capacity of 0.2 L. After purging the inside of the autoclave with nitrogen, nitrogen gas was introduced so that the nitrogen partial pressure in the autoclave was 0.5 MPa (gauge pressure). The temperature in the autoclave was then raised to 250°C. After holding at 250°C for 1 hour, the autoclave was allowed to cool to room temperature, the gas in the autoclave was released to return to normal pressure, and the reaction solution was collected and analyzed by HPLC. The results are shown in Table 1-1.

[0066] Example 2 The reaction was carried out in the same manner as in Example 1, except that in step (A), the hydrogen partial pressure was kept at 1.0 MPa (gauge pressure) and the temperature was kept at 100° C. for 3 hours. The results are shown in Table 1-1.

[0067] Example 3 The reaction was carried out in the same manner as in Example 2, except that "Raney Nickel" (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) was used as the catalyst. The results are shown in Table 1-1.

[0068] Comparative Example 1 Except for using t-butanol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as the solvent, the reaction was carried out in the same manner as in Example 1. The results are shown in Table 1-1.

[0069] Comparative Example 2 Except for using methanol (manufactured by FUJIFILM Wako Pure Chemical Industries, Ltd.) as the solvent, the reaction was carried out in the same manner as in Example 1. The results are shown in Table 1-1.

[0070] Comparative Example 3 Except for using dioxane (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.) as the solvent, the reaction was carried out in the same manner as in Example 1. The results are shown in Table 1-1.

[0071] Example 4 Except for changing the reaction time in step (A) to 1 hour, the reaction was carried out in the same manner as in Example 1. The results are shown in Table 1-2.

[0072] Example 5 The reaction was carried out in the same manner as in Example 1, except that the reaction temperature in step (A) was 120 °C and the reaction temperature in step (B) was 260 °C. The results are shown in Table 1-2.

[0073] (Example 6) [Step (A)] To a 0.1 L stainless steel autoclave (manufactured by Pressure Glass Industry Co., Ltd.), 0.1 g of 5-cyanovaleramide (manufactured by Enamine), 30 mL of water, and 0.033 g of ruthenium-supported aluminum oxide (manufactured by N.E. Chemcat Corporation) were added. While stirring at a stirring speed of 500 rpm, the inside of the autoclave was purged with nitrogen, and then hydrogen gas was introduced so that the hydrogen partial pressure inside the autoclave became 0.9 MPa (gauge pressure). Next, the temperature inside the autoclave was raised to 80 °C. After maintaining at 80 °C for 5 hours, it was allowed to cool to room temperature, the gas inside the autoclave was released, and the pressure was returned to normal pressure. The supernatant from which the catalyst was removed by filtration was analyzed by HPLC. The results are shown in Table 1-2.

[0074] [Step (B)] An aqueous solution containing the 5-cyanovaleramide hydrogenation reaction mixture obtained in step (A) was added again to a 0.1 L stainless steel autoclave (manufactured by Pressure Glass Industry Co., Ltd.). After purging the inside of the autoclave with nitrogen, nitrogen gas was introduced so that the nitrogen partial pressure inside the autoclave became 0.5 MPa (gauge pressure). Next, the temperature inside the autoclave was raised to 240 °C. After maintaining at 240 °C for 1 hour, it was allowed to cool to room temperature, the gas inside the autoclave was released, and the pressure was returned to normal pressure. Then the reaction solution was recovered and analyzed by HPLC. The results are shown in Table 1-2.

[0075] (Example 7) The reaction was carried out in the same manner as in Example 6, except that the catalyst in step (A) was nickel-supported silicon dioxide-aluminum oxide (manufactured by Alfa Aesar), the reaction temperature in step (A) was 100 °C, and the reaction temperature in step (B) was 250 °C. The results are shown in Table 1-2.

[0076] (Example 8) The reaction was carried out in the same manner as in Example 6, except that a water / methanol mixed solvent (90% by volume of water) was used instead of water as the solvent, and the reaction temperature in Step (B) was set to 250°C. The results are shown in Table 1-2.

[0077] (Example 9) The reaction was carried out in the same manner as in Example 8, except that a water / methanol mixed solvent (60% by volume of water) was used as the solvent. The results are shown in Table 1-2.

[0078] (Example 10) The reaction was carried out in the same manner as in Example 8, except that a water / dioxane mixed solvent (90% by volume of water) was used as the solvent. The results are shown in Table 1-2.

[0079] (Example 11) The reaction was carried out in the same manner as in Example 8, except that a water / t-butanol mixed solvent (90% by volume of water) was used as the solvent. The results are shown in Table 1-2.

[0080] (Comparative Example 4) The reaction was carried out in the same manner as in Example 1, except that a water / t-butanol mixed solvent (10% by volume of water) was used as the solvent. The results are shown in Table 1-2.

[0081]

Table 1-1

[0082]

Table 1-2

[0083] From Examples 1 to 3, a 5-cyanovaleramide hydrogenation reaction mixture having 6-aminocaproic acid amide as a main product was obtained by a step of reacting 5-cyanovaleramide with hydrogen in an aqueous solvent in the presence of a hydrogenation catalyst (Step (A)), and ε-caprolactam could be synthesized in a high yield by heating the 5-cyanovaleramide hydrogenation reaction mixture obtained in Step A in an aqueous solvent at 180 to 300°C (Step (B)). Further, from the comparison between Examples 1 to 3 and Comparative Examples 1 to 3, it was shown that using an aqueous solvent in Steps (A) and (B) was important for synthesizing ε-caprolactam in a high yield.

[0084] From Examples 4 to 7, it was shown that Steps (A) and (B) could be carried out with various reaction temperatures, reaction times, and catalysts. From Examples 8 to 11 and Comparative Example 4, it was shown that it was preferable to use a water-containing water-miscible organic solvent containing more than 10% by volume of water as a solvent.

Claims

Claim 1 A method for producing ε-caprolactam, comprising the following steps (A) and (B). (A) A step of reacting 5-cyanovaleramide with hydrogen in an aqueous solvent in the presence of a hydrogenation catalyst to obtain a 5-cyanovaleramide hydrogenation reaction mixture (B) A step of heating the 5-cyanovaleramide hydrogenation reaction mixture in an aqueous solvent at a temperature of 180°C or higher and 300°C or lower to obtain ε-caprolactam Claim 2 The method according to claim 1, wherein step (A) is carried out in the absence of ammonia. Claim 3 The method according to claim 1 or 2, wherein the reaction temperature of step (A) is 50°C or higher and 200°C or lower. Claim 4 The method according to any one of claims 1 to 3, wherein the temperature of step (B) is 200°C or higher and less than 280°C. Claim 5 The method according to any one of claims 1 to 4, wherein step (B) is carried out in the absence of a catalyst. Claim 6 The method according to any one of claims 1 to 5, wherein the proportion of 6-aminocaproic acid amide contained in the 5-cyanovaleramide hydrogenation reaction mixture is 45 mol% or more and 72 mol% or less.

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