Process for the preparation of cyclohexanol and cyclohexanone

Abstract

The invention relates to a process for preparing a mixture containing cyclohexanol and cyclohexanone, comprising the step of hydrogenating cyclohexylhydroperoxide in cyclohexane in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone.

Description

BACKGROUND

[0001] Various methods have been used to oxidize cyclohexane to a product mixture containing cyclohexanone and cyclohexanol. This product mixture is often referred to as a KA oil (ketone / alcohol oil) mixture. The vast majority of KA oil is consumed in the production of precursors to nylon 6,6 and nylon 6. The KA oil mixture can readily be oxidized to produce adipic acid, which is an important reactant in processes to make certain condensation polymers, especially polyamides, particularly nylon 6,6. Given the large consumption of adipic acid in these and other processes, there is a need for cost effective processes to produce adipic acid and its precursors. In addition, cyclohexanol from KA oil can be dehydrogenated to cyclohexanone, and cyclohexanone and dehydrogenated cyclohexanol from KA oil can be reacted, preferably with hydroxylamine via cyclohexanone oxime, to give ε-caprolactam.

[0002] A classical method is to produce a mixture containing cyclohexanone and cyclohexanol to obtain KA oil by oxidizing cyclohexane in two steps. First, thermal autoxidation of cyclohexane forms cyclohexyl hydroperoxide (CyOOH), which is isolated. In a second step, KA oil is obtained by decomposition of CyOOH, which is catalyzed by using chromium or cobalt ions as homogeneous catalysts.

[0003] With regulatory restrictions worldwide, the need to replace environmentally unfriendly catalysts, such as chromium and cobalt catalysts, is becoming more and more urgent. If a non-toxic heterogeneous catalyst could replace the current homogeneous catalyst, the environmental footprint and the economics of the process could be significantly improved.

[0004] Various types of homogeneous catalysts have been used to catalyze the oxidation of cyclohexane by hydrogen peroxide to produce KA oil. Heterogeneous catalyst methods have the advantage of easy separation, and the oxidation of cyclohexane by hydrogen peroxide has been reported. Many heterogeneous catalysts are based on zeolite-like supports, with transition metals or noble metals introduced or implemented, or on oxide supports, with transition metals deposited thereon.

[0005] GB 964,869 discloses a process for the oxidation of liquid cyclohexane to cyclohexanol and cyclohexanone by free oxygen, in which the reaction mixture is reduced during the oxidation, thus converting cyclohexanone and cyclohexyl hydroperoxide into cyclohexanol. The reduction can be carried out by catalytic hydrogenation or by means of a chemical (non-catalytic) reducing agent. As hydrogenation catalysts, there are mentioned catalysts based on nickel, copper, platinum, palladium, ruthenium and rhodium. The catalyst is preferably deposited on a solid support arranged in a fixed bed, through which the material to be hydrogenated trickles in counterflow to hydrogen. As chemical reducing agent, it is possible to use materials which, on contact with the acids formed, liberate nascent hydrogen, or hydrides such as alkali borohydrides or lithium aluminium hydride.

[0006] US 3,479,394 discloses a process for the preparation of cyclohexanol and cyclohexanone by subjecting cyclohexane to air oxidation, stopping the oxidation when a relatively low proportion of hydrogen peroxide is formed, and then converting the hydrogen peroxide to cyclohexanol and cyclohexanone. This conversion can be achieved by chemical reduction using hydrogen in the presence of a catalyst, such as platinum or Raney nickel, or using a metal salt in which the metal is in its lowest valence state, such as ferrous sulphate.

[0007] Gerd Dahlhoff et al.: "e-Caprolactam: new by-product free synthesis routes", Catalysis Reviews: Science and Engineering, Vol. 43, Chapter 4, pages 381-441 discloses that e-caprolactam can be prepared from cyclohexanone via cyclohexanone oxime.

[0008] US 3,772,375 A discloses the hydrogenation of 6-hydroxyperoxyhexanoic acid, which is isolated from the aqueous wash of the product of the oxidation of cyclohexane using molecular oxygen in the liquid phase. The 6-hydroxyperoxyhexanoic acid is hydrogenated as such or as a salt contained in an aqueous phase in the presence of a catalyst consisting essentially of metallic palladium, rhodium or platinum.

[0009] US 3,593,735 discloses a process for the preparation of cyclohexanone comprising the oxidation of cyclohexane in the liquid phase using oxygen or an oxygen-containing gas to produce an oxidation product containing cyclohexyl hydroperoxide, the catalytic hydrogenation of said oxidation product in the presence of a catalyst containing palladium, platinum, nickel or rhodium using a gas stream containing hydrogen in a hydrogenation zone to thereby effect the conversion of said cyclohexyl hydroperoxide substantially to cyclohexanol, the recovery of said cyclohexanol fraction by distillation and the catalytic dehydrogenation of said cyclohexanol to cyclohexanone and hydrogen, the separation of said cyclohexanone and the delivery of the resulting hydrogen-containing gas stream to said hydrogenation zone to thereby effect the hydrogenation of said oxidation product. The catalyst is preferably deposited on a support such as alumina, carbon or silica. In the examples, a supported palladium catalyst containing 0.1 wt% palladium in a fixed bed on alumina is used.

[0010] There is still a need for a process for the oxidation of cyclohexane to a product mixture containing cyclohexanone and cyclohexanol with a high conversion of cyclohexane and a high selectivity to KA oil, while having a low catalyst preparation cost. It is an object of the present invention to provide such a process. SUMMARY

[0011] This object is solved by a process for the preparation of a mixture comprising cyclohexanol and cyclohexanone, comprising the step of hydrogenating cyclohexyl hydroperoxide in cyclohexane in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone.

[0012] Preferably, the process comprises the following steps:

[0013] a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane,

[0014] b) hydrogenating the cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone.

[0015] In one embodiment of the present application, step b) is carried out in the reaction mixture obtained in step a).

[0016] In another embodiment of the present application, the reaction mixture obtained in step a) is extracted with water before step b) to obtain an organic phase containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxyperoxyhexanoic acid, and step b) is carried out in the organic phase.

[0017] In further embodiments of the present application, the 6-hydroxyperoxyhexanoic acid is hydrogenated in the presence of a Raney nickel catalyst to obtain 6-hydroxyhexanoic acid.

[0018] In preferred embodiments, the 6-hydroxyperoxyhexanoic acid is hydrogenated in the presence of a Raney nickel catalyst in the aqueous phase to obtain 6-hydroxyhexanoic acid.

[0019] The present application also relates to a process for preparing adipic acid, comprising the following steps:

[0020] a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane,

[0021] b) hydrogenating the cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone, and

[0022] c) optionally oxidizing the cyclohexanol and the cyclohexanone with nitric acid after purification by distillation to obtain adipic acid.

[0023] The present application also relates to a process for preparing 6-hydroxyhexanoic acid, comprising the step of hydrogenating the 6-hydroxyperoxyhexanoic acid in the presence of a Raney nickel catalyst.

[0024] Preferably, the process comprises the following steps:

[0025] a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane, and

[0026] b1) hydrogenating the 6-hydroxyperoxyhexanoic acid in the presence of a Raney nickel catalyst to obtain 6-hydroxyhexanoic acid.

[0027] In one embodiment, step b1 ) is carried out in the reaction mixture obtained in step a).

[0028] In another embodiment, prior to step b1 ), the reaction mixture obtained in step a) is extracted with water to obtain an organic phase containing cyclohexylhydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxyperoxyhexanoic acid, and step b1 ) is carried out in the aqueous phase. DETAILED DESCRIPTION

[0029] Generally, in the first step a), cyclohexane is oxidized with molecular oxygen to obtain a reaction mixture comprising cyclohexylhydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid, unconverted cyclohexane and other possible by-products.

[0030] Step a) can be carried out by thermal autoxidation of cyclohexane with molecular oxygen, preferably admixed with an inert gas, at a pressure of, for example, 15 to 25 bar and at a high temperature of, for example, 160 to 190 °C.

[0031] In step b), the cyclohexylhydroperoxide is hydrogenated in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone.

[0032] In step b1 ), the 6-hydroxyperoxyhexanoic acid can be hydrogenated in the presence of a Raney nickel catalyst to obtain 6-hydroxyhexanoic acid. The 6-hydroxyperoxyhexanoic acid can be hydrogenated simultaneously with the cyclohexylhydroperoxide in the same reaction mixture, or the hydroxyperoxyhexanoic acid is separated from the cyclohexylhydroperoxide before hydrogenation and hydrogenated in a separate step b1 ).

[0033] Suitable Raney catalysts can have a BET surface area of, for example, 80 to 120 m 2 / g and can comprise a promoter element such as zinc or chromium.

[0034] The Raney catalysts used in the present application can be prepared in the usual way. A Ni-Al alloy is prepared by dissolving the nickel in molten aluminium and then cooling ("quenching"). A small amount of a third metal such as zinc or chromium etc. can be added as a promoter to enhance the activity of the resulting catalyst. The promoter changes the mixture from a binary to a ternary alloy which gives different quenching and leaching characteristics during activation.

[0035] In the activation process, the alloy, usually in the form of a fine powder, is typically treated with a concentrated solution of sodium hydroxide. The formation of sodium aluminate (Na[AI(OH)4]) requires a high concentration of the sodium hydroxide solution. Typically, a sodium hydroxide solution with a concentration of up to 5 M is used. Typically, the leaching is carried out at 70 to 1 10 °C.

[0036] In the practice of the present application, the catalyst can be slurried using reaction mixtures using techniques known in the art. The processes of the present application are suitable for batch, semi-continuous or continuous cyclohexylhydroperoxide hydrogenation. These processes can be carried out under a wide variety of conditions, as will be apparent to the ordinarily skilled artisan.

[0037] Suitable reaction temperatures for the processes of the present application are generally from about 20 to about 80°C or higher, advantageously from about 25 to about 60°C.

[0038] The processes of the present application are advantageously carried out at hydrogen pressures from 0.1 MPa (1 bar) to 10 MPa (100 bar), preferably from 0.1 MPa (1 bar) to 5 MPa (50 bar), for example 2 MPa (20 bar).

[0039] At the end of the hydrogenation reaction, the target compound can be finally purified by methods well known in the art, for example distillation.

[0040] In a further step c), the cyclohexanol and cyclohexanone can be oxidized with nitric acid to obtain adipic acid.

[0041] Step c) can be carried out by nitric acid oxidation of KA oil in concentrated nitric acid at atmospheric pressure or at elevated pressure. The reaction temperature is from 70 to 100°C. Homogeneous transition metals can catalyze the reaction. Adipic acid and by-products can be purified by a series of crystallizations.

[0042] In a further step, the cyclohexanol can be dehydrogenated to obtain further cyclohexanone, which can be converted to ε-caprolactam.

[0043] The present application therefore also relates to a process for the preparation of ε-caprolactam, comprising the following steps:

[0044] a) oxidation of cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexylhydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane,

[0045] b) hydrogenation of the cyclohexylhydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone,

[0046] c) optionally purification of the cyclohexanol and cyclohexane by distillation,

[0047] d) optionally separation of the cyclohexanone from the cyclohexanol,

[0048] e) dehydrogenation of the cyclohexanol to cyclohexanone,

[0049] f) conversion of the cyclohexanone to ε-caprolactam.

[0050] Preferably, in a further step, the cyclohexanol can be dehydrogenated to give further cyclohexanone, which can be reacted with hydroxylamine to give ε-caprolactam via cyclohexanone oxime.

[0051] The present application therefore also relates to a process for the preparation of ε- caprolactam, comprising the following steps:

[0052] a) oxidation of cyclohexane with molecular oxygen to give a reaction mixture comprising cyclohexylhydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane,

[0053] b) hydrogenation of the cyclohexylhydroperoxide in the presence of a Raney nickel catalyst to give cyclohexanol and cyclohexanone,

[0054] c) optional purification of the cyclohexanol and cyclohexanone by distillation,

[0055] d) optional separation of the cyclohexanone from the cyclohexanol,

[0056] e) dehydrogenation of the cyclohexanol to cyclohexanone,

[0057] f1) reaction of the cyclohexanone with hydroxylamine or a salt thereof to give cyclohexanone oxime,

[0058] 2) reaction of the cyclohexanone oxime to give ε-caprolactam.

[0059] Step d) is optional. The purified KA oil containing cyclohexanol and cyclohexanone can be dehydrogenated without separation of the cyclohexanone and the cyclohexanol.

[0060] Step e) can be carried out, for example, at 200 to 450°C, preferably at about 270°C, in the presence of a dehydrogenation catalyst containing zinc or copper.

[0061] Step f) is usually carried out with aqueous hydroxylamine sulfate or a buffer solution containing hydroxylamine and phosphoric acid.

[0062] Step g) the Beckmann rearrangement is usually carried out in the presence of concentrated sulfuric acid or fuming sulfuric acid at a temperature of preferably 90 to 120°C. The formed lactam sulfate solution is usually neutralized with ammonia to give the free lactam.

[0063] Other processes for the conversion of cyclohexanone to ε-caprolactam can be found in the literature.

[0064] The present application is further illustrated by the following examples. It is to be understood that the following examples are for illustrative purposes only and do not limit the present application thereto.

[0065] Example

[0066] Analysis

[0067] Yield and selectivity were determined using gas chromatography with internal standard. CyOOH in cyclohexane was quantified by iodometric titration.

[0068] Conversion = Conversion of CyOOH. In case of CyOOH decomposition, the conversion is defined as the number of moles of CyOOH consumed divided by the initial number of moles of CyOOH:

[0069] Conversion = 100 x n CyOOH(consumed) / n CyOOH(initial)

[0070] Selectivity = Selectivity of CyOOH. In case of CyOOH decomposition, the selectivity is defined as the number of moles of cyclohexanol (CyOH) and cyclohexanone (CyO) produced divided by the number of moles of CyOOH consumed.

[0071] Selectivity = 100 x (n CyOH (produced)) + nCyO (produced)) / n CyOOH (consumed)

[0072] Yield = Conversion x Selectivity

[0073] Tap

[0074] Raw materials

[0075] Industrial reaction mixture used in the examples

[0076] 1. Reaction mixture A, mixture of cyclohexylhydroperoxide (CyOOH) and 6-hydroxyperoxycaproic acid (HPOCap): Cyclohexane is oxidized with molecular oxygen or a mixture of molecular oxygen and other gas that is inert to obtain a reaction mixture comprising CyOOH as the main component, cyclohexanol (CyOH), cyclohexanone (CyO), unconverted cyclohexane, HPOCap and other carboxylic and dicarboxylic acids with 1 to 6 carbons.

[0077] After addition of water in the scrubbing column, reaction mixture A is separated into an organic phase (reaction mixture B) and an aqueous phase (reaction mixture C).

[0078] 2. Reaction mixture B, CyOOH: After washing reaction mixture A with water, the organic phase consists mainly of cyclohexane, cyclohexanone, cyclohexanol, CyOOH and other carboxylic and dicarboxylic acids with 1 to 6 carbons. 3.

[0080] 4. Reaction mixture C, HPOCap: After washing reaction mixture A with water, the aqueous phase consists mainly of HPOCap and other carboxylic and dicarboxylic acids with 1 to 6 carbons.

[0081] Example 1 : Conversion of reaction mixture B using a chromium catalyst based on current industry

[0082] The reference experiment was carried out in batch based on current industry chromium catalysts for the conversion of reaction mixture B into KA oil. 42.7 g of reaction mixture B, containing about 6% of cyclohexylhydroperoxide in cyclohexane, were poured into a glass reactor equipped with a Dean Stark filled with cyclohexane. The temperature was raised to 80°C and 0.1 g of a solution containing 0.5% of chromium catalyst was added to the reaction mixture B. The results obtained are reported in the table below.

[0083] Conversion = conversion of CyOOH. In case of CyOOH decomposition, the conversion is defined as the number of moles of CyOOH consumed divided by the initial number of moles of CyOOH:

[0084] Conversion = 100 x n CyOOH(consumed) / n CyOOH(initial)

[0085] In case of CyOOH decomposition, the selectivity is defined as the number of moles of cyclohexanol (CyOH) and cyclohexanone (CyO) produced divided by the number of moles of CyOOH consumed.

[0086] 100 x (n CyOH (produced)) + nCyO (produced)) / n CyOOH (consumed)

[0087] Yield = Conversion x Selectivity

[0088]

[0089] The molar percentage of the main by-products in the crude reaction mixture is reported as follows:

[0090] ％ Propionic acid 0.56 Valeric acid 0.43 Caproic acid 0.18 1,2-tert-hexanediol 0.09 6-hydroxyhexanoic acid 0.28 peroxydicyclohexane 0.32 unknown 2.02

[0091] Example 2: General procedure for the batch hydrogenation of reaction mixture B over a Raney nickel catalyst

[0092] 0.3 g of Raney nickel catalyst and 68 g of reaction mixture B, containing about 6% of cyclohexylhydroperoxide in cyclohexane, were stirred in a hydrogenation autoclave under a dry atmosphere of N2. The temperature was raised at 60°C and 20 bar of total hydrogen pressure. After 2 hours, the crude reaction mixture produced was analyzed by gas chromatography. The results obtained are reported in the table below.

[0093]

[0094] Since the starting reaction mixture B already contains impurities, the hydrogenation of reaction mixture B allows to reduce those impurities in the reaction medium. Therefore, the amount of impurities after hydrogenation is lower than the amount of impurities before.

[0095] The molar percentage of the main by-products in the crude reaction mixture is reported as follows:

[0096] ％ Propionic acid 0.58 Valeric acid 0.36 Caproic acid 0.17 1,2-tert-hexanediol 0.26 6-hydroxyhexanoic acid 0.13 peroxydicyclohexane 0.12 unknown 1.24

[0097] The batch hydrogenation over Raney nickel catalyst improves the overall performance of the conversion of the reaction mixture B to KA oil compared to those obtained with chromium catalysts. The cyclohexyl hydrogen peroxide conversion (or conversion) and the KA oil yield are higher and the by-product formation is lower than those obtained with chromium catalysts. The yield in by-products is negative because the initial reaction mixture B already contains by-products before the hydrogenation reaction. Cyclohexanol is the main product of the hydrogenation of CyOOH.

[0098] Example 3: General procedure for the semi-continuous hydrogenation of reaction mixture B over a Raney nickel catalyst

[0099] In a dry atmosphere of N2, 5.6 g of cyclohexane and 0.1 g of Raney nickel catalyst were stirred together in a hydrogenation autoclave. The temperature was raised at 60 °C and a total hydrogen pressure of 20 bar. 19 g of reaction mixture B were added dropwise at a mass flow of 15 g / h and hydrogenated. After 1.5 hours, the resulting crude reaction mixture was analyzed by gas chromatography. The obtained results are reported in the table below.

[0100]

[0101] The molar percentages of the main by-products in the crude reaction mixture are reported as follows:

[0102] ％ Propionic acid 0.54 Valeric acid 0.17 Caproic acid 0.12 1,2-tert-hexanediol 0.27 6-hydroxyhexanoic acid 0.02 peroxydicyclohexane 0.10 unknown 0.92

[0103] The by-product yield obtained in semi-continuous hydrogenation is lower than the by-product yield obtained in batch.

[0104] Example 4: Influence of temperature

[0105] In a dry atmosphere of N2, 0.054 g of Raney nickel catalyst and 5.6 g of cyclohexane were stirred together in an autoclave. The temperature was raised at the set point value and a total hydrogen pressure of 20 bar. 12.32 g of reaction mixture B were added in one shot and hydrogenated. The resulting crude reaction mixture was analyzed by gas chromatography. The obtained results are reported in the table below.

[0106]

[0107] The molar percentages of the main by-products in the crude reaction mixture are reported as follows:

[0108]

[0109] The catalytic activity was measured at each reaction temperature:

[0110]

[0111] More cyclohexanone is obtained at lower temperatures, which means that the hydrogenation of cyclohexanone to cyclohexanol is the main side reaction.

[0112] Example 5: Reuse of catalyst

[0113] The procedure of Example 2 was followed, then the recovered Raney nickel catalyst was added again to the system and the hydrogenation was carried out in cycles at 60°C. The results obtained are reported in the table below.

[0114]

[0115] Example 6: Hydrogenation of reaction mixture C

[0116] The procedure of Example 2 was followed, except that reaction mixture C was hydrogenated. 0.43 g of Raney nickel catalyst was stirred with 26 g of reaction mixture C containing about 10% of 6-hydroxyperoxycaproic acid (HPOCap) under a dry atmosphere of N2. The temperature was raised at 60°C and 20 bar of total hydrogen pressure. After 1 hour the conversion of HPOCap was 100%.

[0117] Example 7: Hydrogenation of reaction mixture A

[0118] The procedure of Example 4 was followed, except that reaction mixture A was hydrogenated. 0.061 g of Raney nickel catalyst was stirred with 5.7 g of cyclohexane under a dry atmosphere of N2. The temperature was raised at 60°C and 20 bar of total hydrogen pressure. 12.7 g of reaction mixture A containing about 6.5% of hydrogen peroxide (CyOOH + HPOCap) were added in one portion in the autoclave and hydrogenated. The resulting crude reaction mixture was analyzed by gas chromatography. The results obtained are reported in the table below.

[0119]

[0120] * TT HPOCap = conversion of HPOCap

Claims

1. Process for the preparation of a mixture containing cyclohexanol and cyclohexanone, comprising hydrogenating cyclohexylhydroperoxide in cyclohexane in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone, which process comprises the steps of: a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexylhydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane, b) hydrogenating the cyclohexylhydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone, before step b) the reaction mixture obtained in step a) is extracted with water to obtain an organic phase containing cyclohexylhydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxyperoxyhexanoic acid and step b) is carried out in the organic phase.

2. Process according to claim 1, wherein the hydrogenation of cyclohexylhydroperoxide is a semi-continuous process.

3. Process according to claim 1, wherein 6-hydroxyperoxyhexanoic acid is hydrogenated in the aqueous phase in the presence of a Raney nickel catalyst to obtain 6-hydroxyhexanoic acid. wherein 4. Process for the preparation of adipic acid, comprising the steps of: a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexylhydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane, b) hydrogenating the cyclohexylhydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone, c) oxidizing cyclohexanol and cyclohexanone with nitric acid to obtain adipic acid, before step b) the reaction mixture obtained in step a) is extracted with water to obtain an organic phase containing cyclohexylhydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxyperoxyhexanoic acid and step b) is carried out in the organic phase.

5. Process according to claim 4, wherein the hydrogenation of cyclohexylhydroperoxide is a semi-continuous process.

6. Process according to claim 4, wherein 6-hydroxyperoxyhexanoic acid is hydrogenated in the aqueous phase in the presence of a Raney nickel catalyst to obtain 6-hydroxyhexanoic acid.

7. Process for the preparation of ε-caprolactam, comprising the steps of: a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexylhydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane, b) hydrogenating the cyclohexylhydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone, c) optionally purifying cyclohexanol and cyclohexane by distillation, d) optionally separating cyclohexanone from cyclohexanol, e) dehydrogenating cyclohexanol to cyclohexanone, f) converting cyclohexanone to ε-caprolactam, before step b) the reaction mixture obtained in step a) is extracted with water to obtain an organic phase containing cyclohexylhydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxyperoxyhexanoic acid and step b) is carried out in the organic phase.

8. Process for the preparation of ε-caprolactam according to claim 7, comprising the steps of: a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexylhydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxyhexanoic acid and unconverted cyclohexane, ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ wherein ​ ​ ​ b) hydrogenation of the cyclohexylhydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone, c) optionally purifying the cyclohexanol and cyclohexanone by distillation, d) optionally separating the cyclohexanone from the cyclohexanol, e) dehydrogenation of the cyclohexanol to cyclohexanone, fl) reacting the cyclohexanone with hydroxylamine or a salt thereof to obtain cyclohexanone oxime, f2) reacting the cyclohexanone oxime to obtain ε-caprolactam, wherein Before step b), the reaction mixture obtained in step a) is extracted with water to obtain an organic phase containing cyclohexylhydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxy-peroxyhexanoic acid and step b) is performed in the organic phase.

9. The process according to claim 7, wherein the hydrogenation of the cyclohexylhydroperoxide is a semi-continuous process.

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