Method for producing cyclohexanol and cyclohexanone

Abstract

The present invention relates to a method for preparing a mixture containing 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.

Description

Technical Field

[0001] Relates to a method for preparing a mixture containing cyclohexanol and cyclohexanone.

Background Art

[0002] Several different methods have been used to oxidize cyclohexane to a product mixture containing cyclohexanone and cyclohexanol. Such a product mixture is commonly referred to as a KA oil (ketone / alcohol oil) mixture. The majority of KA oil is consumed in the production of precursors for nylon 6,6 and nylon 6. The KA oil mixture can be easily oxidized to produce adipic acid, which is an important reactant in the process for preparing certain condensation polymers, particularly polyamides, especially nylon 6,6. Considering the large amount of adipic acid consumed in these and other processes, there is a need for a cost-effective method for producing adipic acid and its precursors. Further, cyclohexanol from KA oil can be dehydrogenated to obtain cyclohexanone, and the dehydrogenated products of cyclohexanone and cyclohexanol from KA oil can be reacted preferably with hydroxylamine to obtain epsilon-caprolactam via cyclohexanone oxime.

[0003] The classical method for producing a mixture containing cyclohexanone and cyclohexanol is carried out in two steps to obtain KA oil by oxidation of cyclohexane. First, cyclohexyl hydroperoxide (CyOOH) is formed by thermal auto-oxidation of cyclohexane and isolated. The second step is to obtain KA oil by decomposition of CyOOH catalyzed by using chromium ions or cobalt ions as homogeneous catalysts. Due to the worldwide restrictions, the requirement to replace environmentally unfriendly catalysts such as chromium and cobalt catalysts is becoming increasingly urgent. If the current homogeneous catalysts can be replaced with non-toxic heterogeneous catalysts, the environmental footprint and economic efficiency of this method can be significantly improved.

[0004] Various types of homogeneous catalysts have been used as catalysts for the production of KA oil by oxidizing cyclohexane with hydroperoxide. Heterogeneous catalyst processes have the advantage of being easy to separate and have been reported to catalyze the oxidation of cyclohexane with hydroperoxide. Many heterogeneous catalysts incorporate or attach transition metals or noble metals to zeolite-like carriers, or deposit transition metals on oxide carriers.

[0005] GB964,869 discloses a method for the oxidation of liquid cyclohexane to cyclohexanol and cyclohexanone with free oxygen, in which, during the oxidation process, the reaction mixture undergoes reduction, whereby cyclohexanone and cyclohexyl hydroperoxide are converted to cyclohexanol. The reduction can be carried out by catalytic hydrogenation or by a chemical (non-catalytic) reducing agent. Examples of hydrogenation catalysts include catalysts based on nickel, copper, platinum, palladium, ruthenium, and rhodium. The catalyst is preferably deposited on a solid support arranged in a fixed bed, on which the material to be hydrogenated drips countercurrently to the hydrogen. As chemical reducing agents, metals that release nascent hydrogen when contacted with the acid formed, or hydrides such as alkali borohydride or lithium aluminum hydride can be used.

[0006] U.S. Patent No. 3,479,394 discloses a process for the preparation of cyclohexanol and cyclohexanone by air-oxidizing cyclohexane, stopping the oxidation when a relatively low proportion of hydroperoxide is formed, and then converting the hydroperoxide to cyclohexanol and cyclohexanone. This conversion can be achieved by either chemical reduction with hydrogen in the presence of a catalyst, such as platinum or Raney nickel, or chemical reduction with a salt of a metal in its lowest valence state, such as ferrous sulfate.

[0007] "ε-Caprolactam: new by-product free synthesis routes" by Gerd Dahlhoff et al., Catalysis Reviews: Science and Engineering, Vol. 43, No. 4, pp. 381-441, discloses that ε-caprolactam can be produced from cyclohexanone via cyclohexanone oxime.

[0008] U.S. Patent No. 3,772,375A discloses the hydrogenation of 6-hydroxyperoxyhexanoic acid isolated from the aqueous wash of the oxidation product of cyclohexane with molecular oxygen in the liquid phase. 6-Hydroxyperoxyhexanoic acid undergoes hydrogenation in the presence of a catalyst consisting essentially of palladium, rhodium, or platinum, either by itself or as a salt contained in the aqueous phase.

[0009] U.S. Patent No. 3,937,735 is a method for preparing cyclohexanone, comprising the steps of oxidizing cyclohexane in the liquid phase with oxygen or an oxygen-containing gas to produce an oxidation reaction product containing cyclohexyl hydroperoxide; catalytically hydrogenating this oxidation product with a hydrogen gas-containing stream in a hydrogenation zone in the presence of a catalyst containing palladium, platinum, nickel, or rhodium, thereby substantially converting cyclohexyl hydroperoxide to cyclohexanol; recovering the cyclohexanol fraction by distillation; catalytically dehydrogenating cyclohexanol to cyclohexanone and hydrogen; separating the cyclohexanone; and passing the resulting hydrogen gas-containing stream through the hydrogenation zone to effect the hydrogenation of the oxidation product. The catalyst is preferably deposited on a support such as aluminum oxide, carbon, or silica. In the examples, a fixed-bed supported palladium catalyst containing 0.1% by weight of palladium on aluminum oxide is used.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Non-Patent Document

[0011]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0012] A method for oxidizing cyclohexane to a product mixture containing cyclohexanone and cyclohexanol, which has a high conversion rate of cyclohexane and a high selectivity to KA oil, and a low-cost catalyst preparation method, is still needed. The object of the present invention is to provide such a method.

Means for Solving the Problems

[0013] This object is solved by a method for preparing a mixture containing cyclohexanol and cyclohexanone, which comprises a step of hydrogenating cyclohexyl hydroperoxide in cyclohexane in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone.

[0014] Preferably, this method a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unreacted cyclohexane; b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone; comprising. In one embodiment of the present invention, step b) is carried out in the reaction mixture obtained in step a).

[0015] In another embodiment of the present invention, prior to step b), the reaction mixture obtained in step a) is extracted with water to obtain an organic phase containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unreacted cyclohexane, and an aqueous phase containing 6-hydroxyperoxycaproic acid, and step b) is carried out in this organic phase.

[0016] In a further embodiment of the present invention, 6-hydroxyperoxycaproic acid is hydrogenated in the presence of a Raney nickel catalyst to obtain 6-hydroxycaproic acid.

[0017] In a preferred embodiment, 6-hydroxyperoxycaproic acid is hydrogenated in the aqueous phase in the presence of a Raney nickel catalyst to obtain 6-hydroxycaproic acid.

[0018] The present invention also relates to a method for preparing adipic acid, comprising: a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unreacted cyclohexane; b) hydrogenating cyclohexyl hydroperoxide 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, optionally after purification by distillation.

[0019] The present invention further relates to a method for preparing 6-hydroxycaproic acid, which comprises a step of hydrogenating 6-hydroxypeloxycaproic acid in the presence of a Raney nickel catalyst.

[0020] Preferably, the method a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxypeloxycaproic acid and unconverted cyclohexane; b1) hydrogenating 6-hydroxypeloxycaproic acid in the presence of a Raney nickel catalyst to obtain 6-hydroxycaproic acid. In one embodiment, step b1) is carried out in the reaction mixture obtained in step a).

[0021] In a further embodiment, prior to step b1), the reaction mixture obtained in step a) is extracted with water to obtain an organic phase containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane, and an aqueous phase containing 6-hydroxypeloxycaproic acid, and step b1) is carried out in this aqueous phase.

Mode for Carrying Out the Invention

[0022] Generally, in the first step a), cyclohexane is oxidized with molecular oxygen to give a reaction mixture containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxypeloxycaproic acid, unconverted cyclohexane, and optionally further by-products.

[0023] Step a) can be carried out by thermo-autoxidizing cyclohexane at a high temperature, for example, 160 to 190 ° C, under pressure (for example, 15 to 25 bar), using molecular oxygen preferably mixed with an inert gas.

[0024] In step b), cyclohexyl hydroperoxide is hydrogenated in the presence of a Raney nickel catalyst to give cyclohexanol and cyclohexanone.

[0025] In step b1), 6-hydroxyperoxycaproic acid can be hydrogenated in the presence of a Raney nickel catalyst to give 6-hydroxycaproic acid. 6-hydroxyperoxycaproic acid can be hydrogenated simultaneously with cyclohexyl hydroperoxide in the same reaction mixture, or hydroxyperoxycaproic acid can be separated from cyclohexyl hydroperoxide before hydrogenation and hydrogenated in a separate step b1).

[0026] A suitable Raney catalyst can have, for example, a BET surface of 80 - 120 m 2 / g and can contain promoter elements such as zinc or chromium.

[0027] The Raney catalyst used according to the present invention can be prepared by conventional methods. The Ni - Al alloy can be prepared by dissolving nickel in molten aluminum and then cooling (quenching). A small amount of a third metal such as zinc or chromium or others can be added as a promoter to enhance the activity of the resulting catalyst. This promoter changes the mixture from a binary alloy to a ternary alloy, which can result in various quenching and leaching characteristics upon activation.

[0028] In the activation process, the alloy, usually in the form of a fine powder, is treated with a concentrated solution of sodium hydroxide. A high - concentration solution of sodium hydroxide is required for the formation of sodium aluminate (Na[Al(OH)4]). Sodium hydroxide solutions with a concentration up to 5M are generally used. Generally, the leaching is carried out between 70 - 110 °C.

[0029] In the practice of the present invention, the catalyst can be slurried with the reaction mixture using techniques known in the art. The process of the present invention is suitable for any of batch, semi - continuous, or continuous cyclohexyl hydroperoxide hydrogenation. These processes can be carried out under various conditions, as will be apparent to those skilled in the art.

[0030] The reaction temperature suitable for the process of the present invention is typically in the range of about 20 to about 80 °C or higher, preferably about 25 to about 60 °C.

[0031] The process according to the present invention can advantageously be carried out at a hydrogen pressure of 0.1 MPa (1 bar) to 10 MPa (100 bar), preferably 0.1 MPa (1 bar) to 5 MPa (50 bar), for example, 2 MPa (20 bar).

[0032] At the end of the hydrogenation reaction, the target compound can be finally purified by methods well - known in the art such as distillation.

[0033] In a further step c), cyclohexanol and cyclohexanone can be oxidized with nitric acid to obtain adipic acid.

[0034] Step c) can be carried out by the nitric acid oxidation of KA oil in concentrated nitric acid under atmospheric or high pressure. The reaction temperature is between 70 and 100 °C. A homogeneous transition metal can catalyze this reaction. Adipic acid and by - products can be purified by continuous crystallization.

[0035] In a further step, cyclohexanol can be dehydrogenated to give further cyclohexanone, and cyclohexanone can be converted to epsilon - caprolactam.

[0036] Accordingly, the present invention also relates to a process for preparing epsilon - caprolactam, comprising a) Oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid, and unconverted cyclohexane; b) Hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone; c) Optionally purifying cyclohexanol and cyclohexanone by distillation; d) Optionally separating cyclohexanone from cyclohexanol; e) Dehydrogenating cyclohexanol to cyclohexanone; f) Converting cyclohexanone to epsilon-caprolactam; relates to a method comprising.

[0037] Preferably, in a further step, cyclohexanol is dehydrogenated to obtain further cyclohexanone, and cyclohexanone is reacted with hydroxylamine to obtain epsilon-caprolactam via cyclohexanone oxime. Accordingly, the present invention also relates to a method for preparing epsilon-caprolactam, comprising: a) Oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid, and unconverted cyclohexane; b) Hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone; c) Optionally purifying cyclohexanol and cyclohexanone by distillation; d) Optionally separating cyclohexanone from cyclohexanol; e) Dehydrogenating cyclohexanol to cyclohexanone; f1) Reacting cyclohexanone with hydroxylamine or a salt thereof to obtain cyclohexanone oxime; f2) reacting cyclohexanone oxime to obtain ε-caprolactam, and, a method related thereto. Step d) is optional. The purified KA oil containing cyclohexanol and cyclohexanone can be dehydrogenated without separating cyclohexanone and cyclohexanol. 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. Step f) is usually carried out using an aqueous solution of hydroxylamine sulfate or using a buffer solution containing hydroxylamine and phosphoric acid. Step g) (Beckmann rearrangement) is usually carried out in the presence of concentrated sulfuric acid or fuming sulfuric acid, preferably at a temperature of 90 to 120 ° C. The formed lactam sulfate solution is usually neutralized with ammonia to obtain the free lactam.

[0038] A further method for converting cyclohexanone to ε-caprolactam is described in the literature.

[0039] The present invention will be further described by the following examples. It should be understood that the following examples are for illustrative purposes only and are not used to limit the present invention.

Example

[0040] Analysis The yield and selectivity were determined using gas chromatography with an internal standard. CyOOH in cyclohexane was quantified by iodometry.

[0041] Conversion rate = conversion rate of CyOOH. In the case of CyOOH decomposition, the conversion rate is the number of moles of consumed CyOOH divided by the initial number of moles of CyOOH: Conversion rate = 100 × nCyOOH (consumed) / nCyOOH (initial) as defined.

[0042] In the case of CyOOH decomposition, the selectivity is defined as the ratio of the number of moles of the produced cyclohexanol (CyOH) and cyclohexanone (CyO) to the number of moles of the consumed CyOOH: 100×(nCyOH(produced)+nCyO(produced) / nCyOOH(consumed) Yield = Conversion rate × Selectivity as defined by

[0043] Raw material Industrial reaction mixture used in the examples 1. Mixture of reaction mixture A, cyclohexyl hydroperoxide (CyOOH) and 6-hydroxyperoxycaproic acid (HPOCap): Cyclohexane is oxidized with molecular oxygen or a mixture of molecular oxygen and other inert gases to obtain a reaction mixture mainly containing CyOOH, cyclohexanol (CyOH), cyclohexanone (CyO), unreacted cyclohexane, HPOCap, and other carboxylic acids and dicarboxylic acids having 1 to 6 carbon atoms. After adding water to the washing column to this reaction mixture A, it is separated into an organic phase (reaction mixture B) and an aqueous phase (reaction mixture C). 2. Reaction mixture B, CyOOH: After washing reaction mixture A with water, the organic phase mainly consists of cyclohexane, cyclohexanone, cyclohexanol, CyOOH and other carboxylic acids and dicarboxylic acids having 1 to 6 carbon atoms. 3. 4. Reaction mixture C, HPOCap: After washing reaction mixture A with water, the aqueous phase mainly consists of HPOCap and other carboxylic acids and dicarboxylic acids having 1 to 6 carbon atoms.

[0044] (Example 1) Conversion of reaction mixture B using the current industrial chromium-based catalyst The reference experiment was carried out batchwise using the current industrial chromium-based catalyst to convert reaction mixture B into KA oil. 42.7 g of reaction mixture B containing about 6% cyclohexyl hydroperoxide in cyclohexane was 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% chromium catalyst was added to reaction mixture B. The results obtained are shown in the following table.

[0045] [Table 1]

[0046] The molar percentages of the main by-products in the crude reaction mixture are shown below.

[0047] [Table 2]

[0048] (Example 2) General procedure for batch hydrogenation of reaction mixture B over Raney nickel catalyst In a dry atmosphere of N2, 0.3 g of Raney nickel catalyst was stirred in a hydrogenation autoclave together with 68 g of reaction mixture B containing about 6% cyclohexyl hydroperoxide in cyclohexane. The temperature was raised to 60 °C at a total hydrogen pressure of 20 bar. After 2 hours, the resulting crude reaction mixture was analyzed by gas chromatography. The results obtained are shown in the following table.

[0049] [Table 3]

[0050] Since the starting reaction mixture B already contains impurities, the hydrogenation of reaction mixture B reduces these impurities in the reaction medium. Therefore, the amount of impurities after hydrogenation is less than before hydrogenation.

[0051] The molar percentages of the main by-products in the crude reaction mixture are shown below.

[0052]

Table 4

[0053] The overall performance of reaction mixture B to KA oil was improved by batch hydrogenation on a Raney nickel catalyst compared to that obtained with a chromium catalyst. The conversion rate of cyclohexyl hydroperoxide and the yield of KA oil were higher than those obtained with a chromium catalyst, and the formation of by-products was less. Since the initial reaction mixture B already contained by-products before the hydrogenation reaction, the yield of by-products was negative. Cyclohexanol is the main product of CyOOH hydrogenation.

[0054] (Example 3) General procedure for hydrogenation of reaction mixture B on a semi-continuous Raney nickel catalyst In a dry atmosphere of N2, 0.1 g of Raney nickel catalyst was stirred in a hydrogenation autoclave together with 5.6 g of cyclohexane. The temperature was raised to 60 °C at a total hydrogen pressure of 20 bar. 19 g of reaction mixture B was added dropwise at a mass flow rate of 15 g / h and hydrogenated. After 1.5 h, the resulting crude reaction mixture was analyzed by gas chromatography. The results obtained are shown in the following table.

[0055]

Table 5

[0056] The molar percentages of the main by-products in the crude reaction mixture are shown below.

[0057]

Table 6

[0058] The yield of by-products is lower for semi-continuous hydrogenation than for batch hydrogenation.

[0059] (Example 4) Effect of temperature In a dry atmosphere of N2, 0.054 g of Raney nickel catalyst was stirred in an autoclave together with 5.6 g of cyclohexane. At a total hydrogen pressure of 20 bar, the temperature was raised to the set point value. 12.32 g of reaction mixture B was added all at once and hydrogenated. The resulting crude reaction mixture was analyzed by gas chromatography. The results obtained are shown in the following table.

[0060] [Table 7]

[0061] The molar percentages of the main by-products in the crude reaction mixture are shown below.

[0062] [Table 8]

[0063] The catalytic activity was measured at each reaction temperature.

[0064] [Table 9]

[0065] The fact that more cyclohexanone was obtained at lower temperatures means that the hydrogenation of cyclohexanone to cyclohexanol is the main side reaction.

[0066] (Example 5) Reuse of catalyst The procedure of Example 2 was followed. Next, the recovered Raney nickel catalyst was added to this system again, and hydrogenation was carried out periodically at 60 °C. The results obtained are shown in the following table.

[0067] [Table 10]

[0068] (Example 6) Hydrogenation of reaction mixture C The procedure of Example 2 was followed except that reaction mixture C was hydrogenated. In a dry atmosphere of N2, 0.43 g of Raney nickel catalyst was stirred with 26 g of reaction mixture C containing about 10% 6-hydroxyperoxycaproic acid (HPOCap). The temperature was raised to 60 °C at a total hydrogen pressure of 20 bar. After 1 hour, the conversion rate of HPOCap was 100%.

[0069] (Example 7) Hydrogenation of reaction mixture A The procedure of Example 4 was followed except that reaction mixture A was hydrogenated. In a dry atmosphere of N2, 0.061 g of Raney nickel catalyst was stirred with 5.7 g of cyclohexane. The temperature was raised to 60 °C at a total hydrogen pressure of 20 bar. 12.7 g of reaction mixture A containing about 6.5% hydroperoxides (CyOOH + HPOCap) was added to the autoclave all at once and hydrogenated. The resulting crude reaction mixture was analyzed by gas chromatography. The results obtained are shown in the following table.

[0070] [Table 11]

Claims

1. A method for preparing 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, a) a step of oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unreacted cyclohexane; b) a step of hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone; comprising prior to step b), the reaction mixture obtained in step a) is extracted with water to obtain an organic phase comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unreacted cyclohexane, and an aqueous phase comprising 6-hydroxyperoxycaproic acid, and step b) is carried out in the organic phase.

2. The method according to claim 1, wherein 6-hydroxyperoxycaproic acid is hydrogenated in an aqueous phase in the presence of a Raney nickel catalyst to obtain 6-hydroxycaproic acid.

3. A method for preparing adipic acid, comprising a) a step of oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unreacted cyclohexane; b) a step of hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone; c) a step of oxidizing cyclohexanol and cyclohexanone with nitric acid to obtain adipic acid; comprising prior to step b), the reaction mixture obtained in step a) is extracted with water to obtain an organic phase comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unreacted cyclohexane, and an aqueous phase comprising 6-hydroxy-peroxycaproic acid, and step b) is carried out in the organic phase.

4. The method according to claim 3, wherein 6-hydroxyperoxycaproic acid is hydrogenated in an aqueous phase in the presence of a Raney nickel catalyst to obtain 6-hydroxycaproic acid.

5. A method for preparing epsilon - caprolactam, comprising: a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6 - hydroxyperoxycaproic acid and unreacted cyclohexane; b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone; c) optionally purifying cyclohexanol and cyclohexanone by distillation; d) optionally separating cyclohexanone from cyclohexanol; e) dehydrogenating cyclohexanol to cyclohexanone; f) converting cyclohexanone to epsilon - caprolactam; wherein prior to step b), the reaction mixture obtained in step a) is extracted with water to obtain an organic phase comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unreacted cyclohexane and an aqueous phase comprising 6 - hydroxy - peroxycaproic acid, and step b) is carried out in the organic phase. A method as claimed in claim 6 for preparing epsilon - caprolactam, comprising: a) oxidizing cyclohexane with molecular oxygen to obtain a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6 - hydroxyperoxycaproic acid and unreacted cyclohexane; b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to obtain cyclohexanol and cyclohexanone; c) optionally purifying cyclohexanol and cyclohexanone by distillation; d) optionally separating cyclohexanone from cyclohexanol; e) dehydrogenating cyclohexanol to cyclohexanone; f1) reacting cyclohexanone with hydroxylamine or a salt thereof to obtain cyclohexanone oxime; f2) reacting cyclohexanone oxime to obtain epsilon - caprolactam. ​ ​ A method in which step b) is carried out in the organic phase by extracting the reaction mixture obtained in step a) with water prior to step b) to obtain an organic phase containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unreacted cyclohexane and an aqueous phase containing 6-hydroxy-peroxycaproic acid.

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