PROCESS FOR PRODUCING CYCLOHEXANOL AND CYCLOHEXANONE

Abstract

The invention concerns 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 give cyclohexanol and cyclohexanone.

Claims

1.-12. (canceled)

13. 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 give cyclohexanol and cyclohexanone, comprising the steps of a) oxidizing cyclohexane with molecular oxygen to give a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unconverted cyclohexane, b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to give cyclohexanol and cyclohexanone, wherein, prior to step b), the reaction mixture obtained in step a) is extracted with water to give an organic phase containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxyperoxycaproic acid, and step b) is carried out in the organic phase.

14. The method according to claim 13, wherein 6-hydroxyperoxycaproic acid is hydrogenated in the presence of a Raney nickel catalyst to give 6-hydroxycaproic acid.

15. The method according to claim 13, wherein 6-hydroxyperoxycaproic acid is hydrogenated in the aqueous phase in the presence of a Raney nickel catalyst to give 6-hydroxycaproic acid.

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

17. The method according to claim 16, wherein 6-hydroxyperoxycaproic acid is hydrogenated in the presence of a Raney nickel catalyst to give 6-hydroxycaproic acid.

18. The method according to claim 16, wherein 6-hydroxyperoxycaproic acid is hydrogenated in the aqueous phase in the presence of a Raney nickel catalyst to give 6-hydroxycaproic acid.

19. A method for preparing 6-hydroxycaproic acid, comprising the step of hydrogenating 6-hydroxyperoxycaproic acid in the presence of a Raney nickel catalyst.

20. The method according to claim 19, comprising the steps of a) oxidizing cyclohexane with molecular oxygen to give a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unconverted cyclohexane, b) hydrogenating 6-hydroxyperoxycaproic acid in the presence of a Raney nickel catalyst to give 6-hydroxycaproic acid.

21. The method according to claim 20, wherein step b1) is carried out in the reaction mixture obtained in step a).

22. The method according to claim 20, wherein, prior to step b1), the reaction mixture obtained in step a) is extracted with water to give an organic phase containing cyclohexyl hydroperoxide, cyclohexane, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxyperoxy-caproic acid, and step b) is carried out in the aqueous phase.

23. A method for preparing epsilon-caprolactam, comprising the steps a) oxidizing cyclohexane with molecular oxygen to give a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unconverted cyclohexane, b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to give 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 epsilon-caprolactam, wherein, prior to step b), the reaction mixture obtained in step a) is extracted with water to give an organic phase containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxy-peroxycaproic acid, and step b) is carried out in the organic phase.

24. The method according to claim 23 for preparing epsilon-caprolactam, comprising the steps a) oxidizing cyclohexane with molecular oxygen to give a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unconverted cyclohexane, b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to give 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 its salt to give cyclohexanonoxim, f2) reacting cyclohexanonoxim to give epsilon-caprolactam, wherein, prior to step b), the reaction mixture obtained in step a) is extracted with water to give an organic phase containing cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone and unconverted cyclohexane and an aqueous phase containing 6-hydroxy-peroxycaproic acid, and step b) is carried out in the organic phase.

Description

DETAILED DESCRIPTION

[0029] Generally, in a first step a), cyclohexane is oxidized with molecular oxygen to give a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid, unconverted cyclohexane and possibly further by-products.

[0030] Step a) can be carried out by thermal auto-oxidation of cyclohexane under pressure, e.g. at 15-25 bar, and at high temperature, e.g. at 160-190° C., with molecular oxygen, preferably in admixture with an inert gas.

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

[0032] 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 concurrently 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).

[0033] Suitable Raney catalysts can have, for example, a BET surface from 80 to 120 m.sup.2/g and can contain promotor elements, such as zinc or chromium.

[0034] The Raney catalyst used according to the present invention can be prepared in the usual manner. A Ni—Al alloy is prepared by dissolving nickel in molten aluminium followed by cooling (“quenching”). Small amounts of a third metal, such as zinc or chromium or others, can be added as promotor to enhance the activity of the resulting catalyst. The promoter changes the mixture from a binary alloy to a ternary alloy, which can lead to different quenching and leaching properties during activation.

[0035] In the activation process, the alloy, usually as a fine powder, is treated with a concentrated solution of sodium hydroxide. The formation of sodium aluminate (Na[Al(OH)4]) requires that solutions of high concentration of sodium hydroxide. Sodium hydroxide solutions with concentrations of up to 5 M are commonly used. Commonly, leaching is conducted between 70 and 110° C.

[0036] In the practice of the invention, the catalyst can be slurried with reaction mixtures using techniques known in the art. The process of the invention is suitable for either batch, semi-continuous or continuous cyclohexyl hydroperoxide hydrogenation. These processes can be performed under a wide variety of conditions, as will be apparent to persons of ordinary skill.

[0037] Suitable reaction temperatures for the process of the invention typically range from about 20 to about 80° C. or higher, advantageously from about 25 to about 60° C. ° C.

[0038] The process according to the invention is performed advantageously at a hydrogen pressure from 0.1 MPa (1 bar) to 10 MPa (100 bar), preferably from 0.1 MPa (1 bar) to 5 MPa (50 bar), e.g. at 2 MPa (20 bar).

[0039] At the end of the hydrogenation reaction, the compound of interest may be eventually purified by well-known methods of the technical field, such as distillation.

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

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

[0042] In further steps, cyclohexanol can be dehydrogenated to give further cyclohexanone, and cyclohexanone can be converted to epsilon-caprolactam.

[0043] Thus, the invention also concerns a method for preparing epsilon-caprolactam, comprising the steps [0044] a) oxidizing cyclohexane with molecular oxygen to give a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unconverted cyclohexane, [0045] b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to give cyclohexanol and cyclohexanone, [0046] c) optionally purifying cyclohexanol and cyclohexane by distillation, [0047] d) optionally separating cyclohexanone from cyclohexanol, [0048] e) dehydrogenating cyclohexanol to cyclohexanone, [0049] f) converting cyclohexanone to epsilon-caprolactam.

[0050] Preferably, in further steps, cyclohexanol can be dehydrogenated to give further cyclohexanone, and cyclohexanone can be reacted with hydroxylamine to give, via cyclohexanonoxim, epsilon-caprolactam. The present invention thus also concerns a method for preparing epsilon-caprolactam, comprising the steps [0051] a) oxidizing cyclohexane with molecular oxygen to give a reaction mixture comprising cyclohexyl hydroperoxide, cyclohexanol, cyclohexanone, 6-hydroxyperoxycaproic acid and unconverted cyclohexane, [0052] b) hydrogenating cyclohexyl hydroperoxide in the presence of a Raney nickel catalyst to give cyclohexanol and cyclohexanone, [0053] c) optionally purifying cyclohexanol and cyclohexanone by distillation, [0054] d) optionally separating cyclohexanone from cyclohexanol, [0055] e) dehydrogenating cyclohexanol to cyclohexanone, [0056] f1) reacting cyclohexanone with hydroxylamine or its salt to give cyclohexanonoxim,

[0057] 2) reacting cyclohexanonoxim to give epsilon-caprolactam.

[0058] Step d) is optional. The purified KA oil cantaining cyclohexanol and cyclohexanone can be subject to dehydrogenation without separation of cyclohexanone and cyclohexanol.

[0059] Step e) can be done at, for example, at 200 to 450° C., preferably about 270° C., in the presence of a zinc or copper containing dehydrogenation catalyst.

[0060] Step f) is commonly carried out with aqueous hydroxylamine sulfate or with a hydroxylamine and phosphoric acid containing buffer solution.

[0061] Step g) (Beckmann-rearrangement) is commonly carried out in the presence of concentrated sulfuric acid or oleum, at a temperature of preferably from 90 to 120° C. The formed lactam sulfate-solution is usually neutralized with ammonia to give the free lactam.

[0062] Further methods for converting cyclohexanone to epsilon-caprolactam can be found in the literature.

[0063] The present invention is further illustrated by the following examples. It should be understood that the following examples are for illustration purposes only, and are not used to limit the present invention thereto.

EXAMPLES

Analyses

[0064] Yields and selectivity was determined using gas chromatography with an internal standard. CyOOH in cyclohexane was quantified by iodometry.

[0065] Conversion=conversion of CyOOH. In the case of CyOOH decomposition, conversion is defined as the number of moles of CyOOH consumed divided by the initial number of moles of CyOOH:

Conversion=100×nCyOOH(consumed)/nCyOOH(initial)

[0066] In the case of CyOOH decomposition, selectivity is defined as the number of moles of cyclohexanol (CyOH) and cyclohexanone (CyO) produced divided by the number of moles of CyOOH consumed:

100×(nCyOH(produced)+nCyO(produced))/nCyOOH(consumed)

Yield=Conversion×Selectivity

Raw Materials

[0067] Industrial Reaction Mixture used in the Examples:

[0068] 1. Reaction mixture A, mixture of cyclohexylhydroperoxide (CyOOH) and 6-hydroxyperoxycaproic acid (HPOCap): cyclohexane is oxidized with molecular oxygen or mixtures of molecular oxygen and other gases which are inert to give a reaction mixture which comprises, as main components, CyOOH, cyclohexanol (CyOH), cyclohexanone (CyO), unconverted cyclohexane, HPOCap and other carboxylic and dicarboxilic acids having from 1 to 6 carbons.

[0069] The reaction mixture A, after adding water in a washing column, is separated into an organic phase (reaction mixture B) and an aqueous phase (reaction mixture C).

[0070] 2. Reaction mixture B, CyOOH: After washing reaction mixture A with water, the organic phase is mainly composed of cyclohexane, cyclohexanone, cyclohexanol, CyOOH and other carboxylic and dicarboxilic acids having from 1 to 6 carbons.

[0071] 3.

[0072] 4. Reaction mixture C, HPOCap: After washing reaction mixture A with water, the aqueous phase is mainly composed of HPOCap and other carboxylic and dicarboxilic acids having from 1 to 6 carbons.

Example 1: Conversion of Reaction Mixture B using the Current Industrial Chromium Based Catalyst

[0073] A reference experiment was conducted batchwise with the current industrial catalyst based on chromium, used for the conversion of reaction mixture B to KA oil. 42.7 g of reaction mixture B, containing approximatively 6% of cyclohexylhydroperoxide in cyclohexane, were poured in a glass reactor equipped with a Dean Stark filled with cyclohexane. The temperature was raised at 80° C. and 0.1 g solution containing 0.5% of chromium catalyst was added to the reaction mixture B. The results obtained are reported in the following table.

[0074] Conversion=conversion of CyOOH. In the case of CyOOH decomposition, conversion is defined as the number of moles of CyOOH consumed divided by the initial number of moles of CyOOH:

Conversion=100×nCyOOH(consumed)/nCyOOH(initial)

[0075] In the case of CyOOH decomposition, selectivity is defined as the number of moles of cyclohexanol (CyOH) and cyclohexanone (CyO) produced divided by the number of moles of CyOOH consumed:

100×(nCyOH(produced)+nCyO(produced))/nCyOOH(consumed)

Yield=Conversion×Selectivity

TABLE-US-00001 Conversion Yield (%) (%) Total Cyclohexanol Cyclohexanone By-products 99 98.8 20.5 78.3 1.7

[0076] Molar percentages of the main by-products in the crude reaction mixture are reported below:

TABLE-US-00002 % Propionic acid 0.56 Valeric acid 0.43 Caproic acid 0.18 1,2-t-cyclohexanediol 0.09 6-hydroxycaproic acid 0.28 peroxydicyclohexane 0.32 Unknown 2.02

Example 2: General Procedure for Reaction Mixture B Batchwise Hydrogenation over Nickel Raney Catalyst

[0077] In a dry atmosphere of N.sub.2, 0.3 g of nickel Raney catalyst were stirred in the hydrogenation autoclave with 68 g of reaction mixture B, containing approximately 6% of cyclohexylhydroperoxide in cyclohexane. The temperature was raised at 60° C. and 20 bar of hydrogen overall pressure. After 2 hours, the crude reaction mixture produced was analyzed by gas chromatography. The results obtained are reported in the following table.

TABLE-US-00003 Conversion Yield (%) (%) Total Cyclohexanol Cyclohexanone By-products 100 102 86.9 15.3 −0.5

[0078] Since the starting reaction mixture B already contains impurities, the hydrogenation of reaction mixture B leads to a decrease of those impurities in the reaction medium. Thus, the amount of impurities is lower after hydrogenation than before.

[0079] Molar percentages of the main by-products in the crude reaction mixture are reported below:

TABLE-US-00004 % Propionic acid 0.58 Valeric acid 0.36 Caproic acid 0.17 1,2-t-cyclohexanediol 0.26 6-hydroxycaproic acid 0.13 peroxydicyclohexane 0.12 Unknown 1.24

[0080] The overall performances of reaction mixture B conversion into KA oil were improved with batchwise hydrogenation over nickel Raney catalyst compared to those obtained with chromium catalyst. The cyclohexylhydroperoxide transformation rate (or conversion) and KA oil yield are higher and by-products formation is lower than those obtained with chromium catalyst. The yield in by-products is negative because the initial reaction mixture B already contained by-products before hydrogenation reaction. Cyclohexanol is the main product of CyOOH hydrogenation.

Example 3: General Procedure for Semi-Continuous Reaction Mixture B Hydrogenation over Nickel Raney Catalyst

[0081] In a dry atmosphere of N.sub.2, 0.1 g of nickel Raney catalyst were stirred in the hydrogenation autoclave with 5.6 g of cyclohexane. The temperature was raised at 60° C. and 20 bar of hydrogen overall pressure. 19 g of reaction mixture B were added dropwise at a mass flow of 15 g/h and were hydrogenated. After 1.5 hours, the crude reaction mixture produced was analyzed by gas chromatography. The results obtained are reported in the following table.

TABLE-US-00005 Conversion Yield (%) (%) Total Cyclohexanol Cyclohexanone By-products 99.6 95.0 80.8 14.2 −1.9

[0082] Molar percentages of the main by-products in the crude reaction mixture are reported below:

TABLE-US-00006 % Propionic acid 0.54 Valeric acid 0.17 Caproic acid 0.12 1,2-t-cyclohexanediol 0.27 6-hydroxycaproic acid 0.02 peroxydicyclohexane 0.10 Unknown 0.92

[0083] The by-products yield is lower in semi continuous hydrogenation than that obtained batchwise.

Example 4: Effect of Temperature

[0084] In a dry atmosphere of N.sub.2, 0.054 g of nickel Raney catalyst were stirred in the autoclave with 5.6 g of cyclohexane. The temperature was raised at the set point value and 20 bar of hydrogen overall pressure. 12.32 g of reaction mixture B were added in one time and were hydrogenated. The crude reaction mixture produced was analyzed by gas chromatography. The results obtained are reported in the following table.

TABLE-US-00007 Yield (%) Conversion By- T (° C.) (%) Total Cyclohexanol Cyclohexanone products 25 98 97.7 83.1 14.6 −0.84 45 100 104.0 94.0 10.0 — 60 100 104.3 99.8 4.5 −0.50

[0085] Molar percentages of the main by-products in the crude reaction mixture are reported below:

TABLE-US-00008 25 45 60 Temperature (° C.) % Propionic acid 0.39 0.40 0.40 Valeric acid 0.24 0.25 0.25 Caproic acid 0.10 0.11 0.12 1,2-t-cyclohexanediol 0.14 0.18 0.19 6-hydroxycaproic acid 0.07 0.17 0.17 peroxydicyclohexane 0.00 0.00 0.00

[0086] The catalytic activity was measured at each reaction temperature:

TABLE-US-00009 Catalytic activity T (° C.) (10.sup.−5 mol H.sub.2/g/s) 25 6.9 45 7.7 60 8.6

[0087] More cyclohexanone was obtained at lower temperature meaning that hydrogenation of cyclohexanone to cyclohexanol is the main side reaction.

Example 5: Re-Use of the Catalyst

[0088] The procedure of example 2 was followed. Then the recovered nickel Raney catalyst was added again to the system and the hydrogenation was carried out cyclically at 60° C. The results obtained are reported in the following table.

TABLE-US-00010 Conversion Yield KA oil Cycle No. of the catalyst (%) (%) Fresh catalyst 100 99.9 1 100 99.6 2 100 99.9

Example 6: Hydrogenation of Reaction Mixture C

[0089] The procedure of example 2 was followed except that the reaction mixture C was hydrogenated. In a dry atmosphere of N.sub.2, 0.43 g of nickel Raney catalyst were stirred with 26 g of reaction mixture C, containing approximately 10% of 6-hydroxyperoxycaproic acid (HPOCap). The temperature was raised at 60° C. and 20 bar of hydrogen overall pressure. After 1 hour, the transformation rate of HPOCap was 100%.

Example 7: Hydrogenation of Reaction Mixture A

[0090] The procedure of example 4 was followed except that the reaction mixture A was hydrogenated. In a dry atmosphere of N.sub.2, 0.061 g of nickel Raney catalyst were stirred with 5.7 g of cyclohexane. The temperature was raised at 60° C. and 20 bar of hydrogen overall pressure. 12.7 g of reaction mixture A, containing approximately 6.5% of hydroperoxides (CyOOH+HPOCap) were added in one time in the autoclave and were hydrogenated. The crude reaction mixture produced was analyzed by gas chromatography. The results obtained are reported in the following table.

TABLE-US-00011 Yield (%) TT.sub.HPOCap* Conversion By- (%) (%) Total Cyclohexanol Cyclohexanone products 85.1 85.3 80.0 54.5 25.5 −0.2 *TT.sub.HPOCap = Conversion of HPOCap