EP1805125A1

EP1805125A1 - Process for the preparation of cyclohexanol and cyclohexanone

Info

Publication number: EP1805125A1
Application number: EP05792072A
Authority: EP
Inventors: Ankie Kreuwels; Hendrik Oevering
Original assignee: DSM IP Assets BV
Current assignee: DSM IP Assets BV
Priority date: 2004-10-27
Filing date: 2005-09-30
Publication date: 2007-07-11
Also published as: EA200700950A1; EA011769B1; JP2008518001A; WO2006046852A1; UA95064C2; CN101048358B; TW200626535A; CN101048358A

Abstract

The invention relates to a process for the preparation of cyclohexanol and cyclohexanone from benzene whereby the process comprises the following steps: a. a partial hydrogenation step wherein benzene in the presence of a metal catalyst is partially hydrogenated producing a mixture comprising cyclohexene and unconverted benzene, b. a step wherein a mixture as produced in step a is hydrated producing a mixture comprising cyclohexanol and/or oxidized in the presence of a metal catalyst producing a mixture comprising cyclohexanone or a mixture comprising cyclohexanol and cyclohexanone, c. a step wherein cyclohexanol and/or cyclohexanone is separated from the mixture obtained in step b comprising unconverted benzene, cyclohexanol and/or cyclohexanone, d. a hydrogenation step wherein a mixture comprising unconverted benzene as obtained in step c is hydrogenated in the presence of a metal catalyst into cyclohexane and e. an oxidation step wherein a mixture as produced in step d comprising cyclohexane is oxidized producing a mixture comprising cyclohexanol and cyclohexanone.

Description

PROCESS FOR THE PREPARATION OF CYCLOHEXANOL AND

CYCLOHEXANONE

The invention is related to a process for the preparation of cyclohexanol and cyclohexanone from benzene.

Cyclohexanol may for instance be used for the production of adipic acid whereas cyclohexanone may be used for the production of ε-caprolactam, both nylon intermediates. For the preparation of cyclohexanol and cyclohexanone from benzene a hydrogenation as well as a hydration and/or an oxidation reaction is required. Two different processes are known to perform such a hydrogenation and a hydration and/or an oxidation.

One known process for the preparation of cyclohexanol and cyclohexanone comprises the hydrogenation of benzene into cyclohexane, followed by an oxidation of cyclohexane into cyclohexanol and cyclohexanone. Such a hydrogenation of benzene, yielding cyclohexane, may be performed in the gas phase or in the liquid phase. A gas phase process is preferred since in the gas phase the separation of cyclohexane from the catalyst is easier. Such a gas phase process is e.g. known from GB 799,396, which discloses a catalyzed hydrogenation of benzene. This hydrogenation step can be performed in such a way that a conversion of benzene of 100% can be obtained with a selectivity into cyclohexane of more than 99%. A subsequent oxidation into cyclohexanol and cyclohexanone is e.g. known from EP-A- 92867. This patent publication describes an oxidation process wherein first cyclohexane is oxidized with a gas containing molecular oxygen to form an oxidation mixture containing cyclohexyl hydroperoxide which subsequently is decomposed into cyclohexanol and cyclohexanone. The selectivity into cyclohexanol and cyclohexanone of such an oxidation process is between 86% and 91%. Thus, according to these known processes an overall selectivity into cyclohexanol and cyclohexanone of between 85 and 91% is obtained calculated from the initial amount of benzene. The disadvantage of this cyclohexane oxidation process is the low conversion of 1 - 12%, which results in a large recycle stream of unconverted cyclohexane which is separated by distillation from the mixture comprising cyclohexanol and cyclohexanone. Another process for the preparation of cyclohexanol and cyclohexanone is a process wherein benzene is partially hydrogenated into a mixture of cyclohexene, cyclohexane and unconverted benzene. Such a process is e.g. disclosed in JP-A-11 322661. In the process according to JP-A-11 322661 the mixture of cyclohexene, cyclohexane and unconverted benzene is distilled to separate cyclohexene, cyclohexane and unconverted benzene from each other. Subsequently the unconverted benzene is reused, the cyclohexene is hydrated and the cyclohexane is oxidized. The drawback of a process according to JP-A-11 322661 is the difficulty in separating cyclohexane from cyclohexene and unconverted benzene. For this reason an alternative process has been developed whereby a mixture of cyclohexene, cyclohexane and unconverted benzene is not separated first but oxidized into a mixture comprising cyclohexanol and cyclohexanone. An example of such a process is disclosed in EP-A-23379. This patent publication describes a process wherein benzene is partially hydrogenated into a mixture comprising cyclohexene, cyclohexane and unconverted benzene. Subsequently the cyclohexene is hydrated and/or oxidized into cyclohexanol and cyclohexanone. Unconverted benzene, cyclohexene and cyclohexane are recycled into the hydrogenation step after being subjected to a dehydrogenation reaction in order to reconvert unconverted cyclohexene and cyclohexane into benzene again. In this process the benzene conversion in the hydrogenation step is between 40 and 80% wherein the product mixture obtained after the hydration or oxidation step comprises 25-75 moles % of cyclohexane which has to be dehydrogenated into benzene before it can be recycled in the process. The disadvantage of this process is the production of cyclohexane which requires a dehydrogenation step in addition to the hydrogenation step in order to convert benzene with a high selectivity into cyclohexanol and cyclohexanone.

The object of the present invention is to provide an alternative process for the preparation of cyclohexanol and cyclohexanone starting from benzene. It has been found that this object is achieved in providing a process comprising the following steps: a. a partial hydrogenation step wherein benzene in the presence of a metal catalyst is partially hydrogenated producing a mixture comprising cyclohexene and unconverted benzene, b. a step wherein a mixture as produced in step a is hydrated producing a mixture comprising cyclohexanol and/or oxidized in the presence of a metal catalyst producing a mixture comprising cyclohexanone or a mixture comprising cyclohexanol and cyclohexanone, c. a step wherein cyclohexanol and/or cyclohexanone is separated from the mixture obtained in step b comprising unconverted benzene, cyclohexanol and/or cyclohexanone, d. a hydrogenation step wherein a mixture comprising unconverted benzene as obtained in step c is hydrogenated in the presence of a metal catalyst into cyclohexane and e. an oxidation step wherein a mixture as produced in step d comprising cyclohexane is oxidized producing a mixture comprising cyclohexanol and cyclohexanone.

The advantage of the process according to the present invention is that it provides an alternative process for the preparation of cyclohexanol and cyclohexanone starting from benzene. This alternative process further does not include the disadvantages of the processes according to the state of the art. The process according to the present invention does not require a step wherein cyclohexane formed by hydrogenation of benzene has to be dehydrogenated again into benzene in order to be converted into cyclohexanol and cyclohexanone. In addition the process according to the present invention provides a process with a reduced recycle stream of unconverted cyclohexane when compared to the prior art. It has been found that with the process according to the present invention an overall selectivity into cyclohexanol and cyclohexanone starting from benzene of more than 91% can be obtained. An additional advantage of such an improved selectivity is that it offers an opportunity to increase the throughput through the reactors without enlarging the apparatus. Step a, a catalyzed partial hydrogenation of benzene into a mixture comprising cyclohexene may be performed by any known method. A preferred method is described e.g. in EP-A-0023379.

Preferably, the partial hydrogenation reaction of benzene is carried out in a system comprising an aqueous phase, an organic liquid phase and a gaseous phase. The organic liquid phase comprises unconverted benzene and/or cyclohexene and cyclohexane. The gaseous phase comprises hydrogen.

In general, in step a, the hydrogen pressure during the reaction has a value between 0.1 and 20 MPa and preferably between 0.5 and 10 MPa. A hydrogen pressure in these preferred ranges is favorable as it results in a favorable reaction rate. Step a can be carried out batch-wise or continuously, with the use of one or two or more reaction vessels. From an industrial point of view, the method of continuous execution is preferred.

Preferably, the amount of water of the aqueous phase is 0.1 to10 times the weight of the organic liquid phase. More preferably the amount of water in the aqueous phase is 0.1 to 5 times the weight of the organic liquid phase. Most preferred -A-

the amount of water is such that an optimum is obtained in liquid volume and reactivity of benzene.

Preferably, the partial hydrogenation of benzene is carried out under acid conditions. A preferred pH value is one between 3 and 7. More preferable the partial hydrogenation is carried out at a pH between 3.5 and 6.5, and most preferably at a pH between 4 and 6.

The aqueous phase of such a system preferable comprises a metal salt compound. Examples of metal salt compounds are sulphates, chlorides, acetates and phosphates of metals of group 1 or 2, or metals such as zinc, manganese and cobalt. The amount of metal salt usually ranges between 1x10 ^"5 and 0.2 and preferably between 1x10 ^'4 and 0.1 times the weight of the water in the aqueous phase.

The partial hydrogenation of benzene is catalyzed by using a metal catalyst. Preferred metals are group 8, 9 and 10 metals, such as ruthenium, rhodium, palladium, nickel or platinum. More preferred metals are ruthenium, rhodium and palladium. Most preferred is the use of a ruthenium catalyst. The metal catalyst may comprise more than one metal. Preferred metals to be used as an auxiliary catalyst metal, i.e. a metal in addition to the above-mentioned metals, are group 7, 8, 9, 11 and 12 metals as well as lanthanides, such as zinc, iron, cobalt, manganese, gold, copper and lanthanum. Most preferred is the use of zinc as an auxiliary catalyst metal. Preferably, the atom ratio of the auxiliary metal to the metal is between 0.001 and 20, more preferable it is between 0.005 and 10.

The catalyst may be a non-carrier type or a carrier type catalyst. In the case a carrier type catalyst is used, preferably, a metal oxide is used as carrier. Examples of such a metal oxide are silica, alumina , titania and chromina, a composite such as silica-alumina, silica-zirconia and zirconium silicate, activated carbon, a metal salt such as barium sulphate and calcium sulphate, or a hydroxide or poorly water soluble metal salt. Preferably, a carrier which has a pore diameter between 75-100.000 A and a total pore volume of 0.2-10 ml/g is used. More preferable the total pore volume of the carrier is 0.3-5 ml/g. Preferably, the pore volume with a pore diameter of 250 A or more is 50% or more of the total pore volume. More preferably it is 70% or more of the total pore volume. A too large percentage of pores with a pore diameter of less than 250 A is not preferred since that causes a decline of the selectivity of the catalyst.

The catalyst used for the partial hydrogenation reaction of benzene, may form a solid phase in addition to an aqueous phase, an organic liquid phase and a gaseous phase. The reaction temperature in step a is not critical, in general the reaction temperature is in the range of 30-500⁰C. Preferably, it is between 50-300⁰C, and more preferably between 100-250⁰C. Within these preferred ranges a favorable selectivity towards cyclohexene and a favorable reaction rate is obtained. The mixture produced in step a comprises cyclohexene and optionally cyclohexane and unconverted benzene. Varying the residence time, the reaction temperature, the hydrogen pressure and/or the catalyst concentration in step a, can be used to control final amounts of cyclohexene, cyclohexane and unconverted benzene. In general the amount of cyclohexane is between 0 and 25 mol %, preferably it is between 0 and 20 mol %. In general the amount of unconverted benzene is between 0 and 50 mol %, preferably it is between 0 and 40 mol %. In general the amount of cyclohexene is between 20 and 100 mol % or more, preferably it is between 25 and 100 mol %, more preferable it is between 30 and 100 mol %.

The hydration of cyclohexene, produced in step a, to cyclohexanol can be effected by any known method. A suitable method as well as further references is described in EP-A-23379 which are incorporated herein by reference.

The hydration of cyclohexene may be effected in the presence of benzene and cyclohexane. Thus, there is no need for separating cyclohexene from the reaction mixture produced in step a, prior to the hydration step. As a result of this, the reaction product obtained after hydration of cyclohexene in general may comprise an aqueous phase, and an organic phase comprising cyclohexanol, benzene, cyclohexane, and unconverted cyclohexene.

Preferably, an acid catalyst is used in the hydration process. Examples of acid catalysts are strongly acid ion exchangers, such as a cross-linked polystyrene resin containing sulphonic acid groups, sulphuric acid and phosphoric acid. Sulphuric acid can be mentioned as a preferred catalyst for the hydration reaction, wherein ferrous sulphate may be used as a co-catalyst.

Preferably, the hydration process of cyclohexene is carried out in a sequence of process steps involving (1) the addition of the acid to the double bond of the cyclohexene, thus forming an ester of cyclohexanol and the acid, for example, cyclohexyl hydrogen sulphate, and (2) hydrolysis of the cyclohexyl ester to cyclohexanol and the acid. The ester forming step can be carried out at temperatures in the range of e.g. between -50 ⁰C. and +100 ⁰C. Temperatures in the range of 30 ⁰C to 100⁰C are preferred. The hydrolysis step, the second step, can be suitably carried out at a temperature in the range of between about 50 ⁰C and 150 ⁰C. The oxidation of cyclohexene, produced in step a, into cyclohexanone or into a mixture comprising cyclohexanol and cyclohexanone can be effected by any of the known methods. A suitable method is described in EP-A-23379 which is incorporated herein by reference. In addition EP-A-23379 comprises further references for suitable methods.

The oxidation of cyclohexene may be effected in the presence of benzene and cyclohexane or in the presence of benzene and cyclohexane and any further solvent, to be used as a co-solvent. Therefore, prior to the oxidation step, it is not necessary to separate cyclohexene from the hydrogenation reaction mixture, comprising unreacted benzene and/or cyclohexane, and optionally comprising a co- solvent.

A co-solvent may be any organic solvent. A person skilled in the art knows which solvents can be used as such a co-solvent. Non-limiting examples of such co-solvents are acetic acid, acetone, anisole, 1 ,2-dichlorobenzene, dimethylacetamid, dimethylcarbomate, dimethylformamide, dimethylphtalaat, diphenylether, any polyhydric alcohol and any nitrile. Preferred polyhydric alcohol are dihydric, trihydric and tetrahydric alcohols. Preferably diols having 2 or more carbon atoms are used. Preferred examples are ethylene glycol, 1 ,3-propanediol, 1 ,2-dihydroxybutane, 1 ,2- dihydroxypropane, 1 ,4-butanediol, 1 ,4-cyclohexanedimethanol, 1 ,2- cyclohexanedimethanol, diethylene glycol, 1 ,2-transcyclopentanediol, 2,4-pentanediol, styrene glycol, or mixtures comprising two or more of such diols. Preferred nitriles are acetonitril, 2-cyanopyridine, 3-cyanopyridine, 4-cyanopyridine, benzonitril, adiponitril, butyronitril, aminobenzonitril, 2-cyanoethylether.

The oxidation process is catalyzed by a metal and preferably carried out in a sequence of process steps involving (1) oxidation of cyclohexene to cyclohexanone by reaction of cyclohexene with the catalyst solution in which the catalyst is reduced, (2) separating the organic phase from the reaction mixture, (3) bringing the catalyst back in the oxidated state by means of an oxygen containing gas, e.g. air, (4) recirculating the catalyst to the first step. The first step may be carried out at a temperature of between 0 ⁰C and 150 ⁰C and a pressure of between 0.05 and 5 MPa. The third step may be carried out at a temperature of between 0 ⁰C and 250 ⁰C, and at a pressure of between 0.05 and 200 MPa.

Preferably a palladium catalyst system is used for the oxidation of cyclohexene. Examples of such a catalyst and its use in the oxidation of an olefin are described in US 4720474 as well as in an article of Kim et al. in "Applied Catalysis A: General, 155 (1997)", pages 15-26. Such a catalyst system may comprise (a) palladium, (b) at least one further metal chosen from group 8, 9, 10 or 14 of the periodic system, and (c) a heteropolyacid or halogen. All components may be present in a form such as a dissociated ion. Preferably palladium is present in a divalent or tetravalent form. Suitable palladium sources are palladium halogenides such as palladium chloride and palladium bromide, palladium salts of inorganic acids or organic acids such as palladium nitrate, palladium sulphate, palladium acetate, palladium trifluoroacetate and palladium acetylacetonate, and inorganic palladium such as palladium oxide and palladium hydroxide. In addition, palladium compounds with base ligands which have been derived from these metal salts can be used as palladium source. Examples of such palladium ligands are [Pd(en)₂]CI₂, [Pd(phen)₂]CI₂ [Pd(CH₃CN)₂]CI₂, [Pd(C₆H₅CN)₂]CI₂, [Pd(C₂O₄)₂]₂, [PdCI₂(NH₃)₂] and, [Pd(NOa)₂(NHs)₂]. Preferably, palladium (a) is present in an amount between 0.001 wt% and 10wt% (calculated as the weight of [Pd²⁺] divided by the total weight of the reaction liquid). More preferable palladium is present in an amount between 0.1 wt% and 5 wt. %.

Examples of one further metal chosen from group 8, 9, 10 or 14 of the periodic system are iron, copper, cobalt, nickel, ruthenium and tin. Preferably, copper is used as a further metal. Such a further metal is used to suppress precipitation of palladium. Suitable copper sources are copper compounds in the divalent state. Examples of such copper compounds are copper (II) chloride, copper (II) bromide, copper (II) sulphate, copper (II) nitrate, copper (II) acetate, copper (II) formiate and copper (II) acetylacetonate.

In general these further metal compounds are present in the divalent, trivalent or tetravalent state. Preferably, their halogenides such as chlorides and bromides, salts of inorganic acids such as sulphates and nitrates, and various salts such as acetates, oxalates, formiates and acetylacetonates are being used.

The preferred concentration of (b) the further metal, can be described with a relative concentration to palladium (a): mole (b)/mole (a). Preferably this molar ratio is between 0.1 and 100, more preferred between 0.1 and 10.

An example of a heteropolyacid is a heteropolyoxianion with a countercation. This heteropolyoxianion may be presented by the following general formula [X_xM_aM^J _bM"_cO_z]^m" wherein X is a member selected from the group consisting of boron, silicon, germanium, phosphorus, arsenic, selenium, tellurium, iodine, cobalt, manganese, copper and M, M' and M" are members independently selected from the group consisting of tungsten, molybdenum, vanadium, niobium, tantalum, rhenium. More preferred, X is silicon, germanium, phosphorus or arsenic and M, M' and M" are chosen from the group consisting of tungsten, molybdenum and vanadium. Integers a, x, z and m are >0, integers b and c are > 0, whereby a+b+c > 2. Examples of countercations are: protons, alkali metal cations, alkaline earth cations, transition metal cations, including cations of Pd, Cu, Co and Mn and organic cations. Most preferred heteropolyacids are H(3_+V)PMθ₍i₂-_V)V_v0₄o whereby v is 0>12.

Chlorine (Cl) and bromine (Br) are preferred halogens. The source of these halogens may be HCI, HBr or a metal catalyst having a halogen as counterion, provided that the halogen is present in the ion form.

The concentration of (c) a heteropolyacid or a halogen, can also be described with a relative concentration to palladium (a), i.e. mole (c)/mole (a). Preferably, in the case of heteropolyacids this molar ratio is between 0.1 and 100, more preferred between 0.1 and 10. In the case of halogens preferred molar ratios are between 0.3 and 100, more preferable between 1 and 50. High halogen concentrations are not preferred due to a high risk for corrosion of the reactor which in general occurs at high halogen concentrations in an aqueous solution.

The conversion of cyclohexene is preferably >50% and more preferably >75%. This conversion can be controlled by varying the catalyst concentration but also by varying the residence time, the reaction temperature and/or the partial oxygen pressure during the oxidation step. The residence time is between 5 seconds and 20 hours. Preferably, the residence time in the oxidation step is between 10 seconds and 10 hours. The reaction temperature during this oxidation step, in general, is 0⁰C or higher. Preferably, it is between 20-200⁰C, and more preferably between 40-100⁰C. In general, the partial oxygen pressure during the oxidation reaction has a value of 0.001 MPa or more. Preferably the partial oxygen pressure has a value between 0.01 and 10 MPa, more preferable between 0.05 and 5 MPa. For the supply of oxygen, any technique is applicable. Preferably a technique is applied wherein a gas that contains oxygen is introduced as fine bubbles by stirring wings, and the technique wherein a barrier plate is established inside the reactor and the oxygen gas is converted to fine bubbles.

Step b may be performed batch-wise or continuously. The reaction mixture produced in the oxidation and/or hydration reactor generally comprises an aqueous phase, and an organic phase comprising cyclohexanol and/or cyclohexanone, unconverted benzene, cyclohexane, and cyclohexene.

After separation of the aqueous phase from the oxidation and/or hydration reaction mixture, cyclohexanol and/or cyclohexanone can be recovered from the organic phase, by any known separation method, for example by a distillation. This separation step is referred to as step c.

The mixture comprising unconverted benzene, unconverted cyclohexene as well as cyclohexane is subjected to a hydrogenation step, step d, wherein benzene as well as cyclohexene are hydrogenated into cyclohexane. In general this hydrogenation step may be performed by any known hydrogenation process for benzene and/or cyclic olefins. It may be performed in the liquid phase as well as in the gas phase. Preferably, the hydrogenation is performed in the gas phase.

Examples of hydrogenation processes are described in GB 799,396 and GB 835,394. Optionally, an additional amount of benzene may be added to a reaction mixture obtained in step c comprising unconverted benzene, unconverted cyclohexene as well as cyclohexane, before it is subjected to a step d. Any amount of benzene may be added to this mixture. Preferably, an amount is added equal to or less than the amount of unconverted benzene present in the mixture obtained from step c as unconverted benzene.

The hydrogenation of benzene is catalyzed by means of a metal catalyst. Preferred metal catalysts are group 8, 9 and 10 metal catalysts. Nickel, iron, palladium, platinum, ruthenium and rhodium based catalyst are more preferred, whereas a platinum based catalyst is most preferred.

The metal catalyst may be a supported catalyst or a non-supported catalyst. In the case it is a supported one it may be supported on a carrier such as silica, zirconia, titania, alumina, thoria, silicon carbide, clay and diatomaceous earth. In general oxides of silica, zirconia, titania, alumina, thoria and silicon carbide are used as carrier. Preferably, oxides of silica, zirconia, titania and alumina are used as carrier.

Aluminium oxide is most preferred as a carrier. The most preferred supported metal catalyst is a platinum catalyst supported on aluminium oxide. The concentration of the catalyst can be expressed in wt% calculated on the weight of the support. Preferably this is between 0.01 and 10%, more preferred between 0.01 and 1% and most preferred between 0.1 and 0.5 wt%.

The partial hydrogen pressure at the outlet of the benzene hydrogenation reactor preferably is at least between 0.1 and 35 MPa at a temperature ranging from about 350-400 ⁰C at the reactor inlet to about 225 ⁰C at the reactor outlet. More preferable this partial pressure is between 0.5 and 10 MPa. Most preferable it is between 0.8 and 2 MPa.

The mixture obtained after the hydrogenation step, comprising cyclohexane is subjected to an oxidation step, step e, to yield a mixture comprising cyclohexanol and cyclohexanone. In general this oxidation step may be performed by any known method. A suitable method is e.g. described in EP-A-579323, EP-A- 0092867 and EP-A-4105. According to these known methods cyclohexane is first converted into cyclohexyl hydroperoxide. This cyclohexyl hydroperoxide is subjected to a decomposition reaction to convert the obtained cyclohexyl hydroperoxide into cyclohexanol and cyclohexanone.

The conversion of cyclohexane into cyclohexyl hydroperoxide may be performed in the liquid phase in the presence of a gas comprising molecular oxygen. Examples of a gas comprising molecular oxygen are oxygen, air and mixtures of oxygen with an inert gas such as nitrogen, helium, neon and argon. The pressure during the oxidation process is not critical, in general it is between 0.1 and 5 MPa. Preferably, the pressure is between 1 and 2 MPa.

The temperature during the oxidation process is not critical but in general has a value between 70 and 115 ⁰C.

The oxidation process may be performed during a period of time of between 5 seconds and 20 hours. Preferably, at least 10 seconds and at most 14 hours.

Preferably, the oxidation process is performed without a catalyst in order to prevent an immediately decomposition of the cyclohexyl hydroperoxide formed. In the case a catalyst is used, only a very small amount is used, preferably an amount between 0,1 and 10 ppm. More preferred is an amount between 0.2 and 2 ppm. Examples of suitable oxidation catalysts are cobalt, chromium, manganese, iron, nickel or copper. Preferred catalysts are salts of cobalt such as cobaltous naphthenate and cobalt-2-ethyl-hexanoate.

The decomposition of the cyclohexyl hydroperoxide in the oxidation mixture may be effected by means of metal salts, for instance salts of transition metals such as cobalt, nickel, iron, chromium, manganese and copper. Preferably, a salt of cobalt and/or of chromium is used, for example cobalt sulphate, cobalt nitrate, chromium sulphate or chromium nitrate. The metal salt may be used in an amount of 0.1-1000 parts by weight per million (calculated as the weight of the metal on the total weight of the aqueous phase). Preferably, the amount of metal salt is 1-200 parts by weight per million.

The decomposition of the cyclohexyl hydroperoxide may be carried out in a stirred tank reactor or in a plug flow reactor.

Preferably, the decomposition is performed at a temperature within the range of 70-115 ⁰C.

The cyclohexanol and cyclohexanone obtained after the decomposition may be separated from this mixture by any known separation method.

Preferably, the organic phase is subjected to a distillation step to separate cyclohexane from the mixture comprising cyclohexanol and cyclohexanone, after the organic phase has been separated from the aqueous phase. The separated cyclohexane may be recycled into the oxidation step.

Brief Description of the Drawing

Fig. 1 is a schematic diagram of an embodiment of the process according to the present invention.

Description of an embodiment

Referring to Fig. 1, A represents a hydrogenation reactor, which contains an aqueous solution of the hydrogenation catalyst supported on a carrier. Benzene is fed through line 1 , and hydrogen is fed through line 2 to this hydrogenation reactor. Unreacted hydrogen is discharged through line 3. The hydrogenated reaction mixture is fed through line 4 to a separator B, wherein the organic layer comprising unreacted benzene, cyclohexene and cyclohexane, is separated from the aqueous layer comprising the catalyst. The aqueous layer is discharged through line 5 and recycled into the hydrogenation reactor, whereas the organic layer is fed through line 6 to an oxidation reactor, represented by C, containing a solvent. After the oxidation catalyst is fed to this reactor through line 7 air is blown in into this reactor through line 8. Unreacted air is discharged through line 9. The oxidized reaction mixture, is discharged and fed to a separator, represented by D, through line 10. In the separator cyclohexanol and cyclohexanone, are separated from cyclohexane and unconverted benzene, and discharged through line 11. Subsequently the residual mixture comprising cyclohexane and unconverted benzene is fed through line 12 to a hydrogenation reactor E. Optionally an additional amount of benzene is fed to this hydrogenation reactor through line 27. To this hydrogenation reactor, which contains a hydrogenation catalyst, hydrogen is fed through line 13. Unreacted hydrogen is discharged through line 14. The hydrogenated reaction mixture is fed through line 15 to a separator F, a distillation tower wherein cyclohexane is distilled off from the reaction mixture. The residual aqueous solution is recycled into the hydrogenation reactor E, through line 16 whereas the distilled cyclohexane is fed through line 17 to oxidation reactor G. Through line 18 air is blown in into this reactor, whereas unreacted air is discharged from the reactor through line 19. The oxidized reaction mixture, is fed to a decomposition reactor, represented by H, through line 20, which contains an aqueous solution comprising a decomposition catalyst. Subsequently, an aqueous sodium hydroxide solution was fed to this reactor through line 21. The decomposed reaction mixture comprising two layers an organic layer comprising unreacted cyclohexane, cyclohexanol and cyclohexanone, and an aqueous layer comprising the catalyst, was fed to a separator I via line 22, to separate those two layers from each other. Subsequently, the aqueous layer is recycled into oxidation reactor G through line 23 whereas the organic layer is fed through line 24 to a distillation tower K to distil off unreacted cyclohexane from cyclohexanol and cyclohexanone, in order to recycle the cyclohexane into oxidation reactor G, through line 25, and to isolate cyclohexanol and cyclohexanone through line 26.

The invention will be further elucidated by means of the following non-restrictive examples.

Examples

Calculation of selectivity

A selectivity towards a certain compound is calculated by dividing the amount of this compound expressed in mole by the total amount of compounds expressed in moles and multiplying the result with 100%.

The overall selectivity from benzene towards cyclohexanol and/or cyclohexanone is calculated by means of the following formula:

(Yield of cyclohexene in mole% divided by 100%) * (conversion of cyclohexene in mole% divided by 100%) ^* (selectivity towards cyclohexene oxidation in mole% divided by 100%) + (yield of cyclohexane in mole% divided by 100%) * (1 - (conversion of benzene in mole% divided by 100%)) + (yield of cyclohexene in mole% divided by 100%) * (1- (conversion of cyclohexene in mole% divided by 100%)) * (selectivity towards cyclohexene oxidation in mole% divided by 100%) Preparation of the catalyst

2.5 g of RuCI₃.3H₂O and 6.7 g of ZnCI₂ were dissolved in 250 ml of water. To this solution 35 ml of a 30% aqueous NaOH solution was added under continuous stirring. After the mixture was heated for 2.5 hours at 80 ⁰C, stirring was stopped and the mixture was allowed to cool to room temperature. The precipitate formed was twice washed with a 1 N aqueous NaOH solution. Subsequently the precipitated product was heated together with 250 ml of a 5% aqueous NaOH solution in an autoclave for 17 hours at 150 ⁰C in a hydrogen atmosphere at a pressure of 5 MPa under continuous stirring. After the reactor was cooled to room temperature and the product was brought under an argon atmosphere the product was washed first with a 30% aqueous NaOH solution and then with water. The obtained product, a Ruthenium/Zinc hydrogenation catalyst, was dried under vacuum.

Comparative Experiment A

Hydrogenation of benzene

Per hour 100 g of benzene and 300 NI of hydrogen were fed into a tubular hydrogenation reactor, containing 50 mL of a platinum on aluminium oxide catalyst (0.3 wt% Pt). The hydrogenation reaction was performed at a pressure of about 3.1 MPa and a maximum temperature in the reactor of 390⁰C, obtained by removing reaction heat by cooling the reactor with oil to about 225°C. All organic compounds were condensed and a gas chromatographic analysis showed that the content of impurities in cyclohexane was less than 0.05 wt%. This indicates a cyclohexane selectivity of at least 99.9%.

Oxidation of cyclohexane

170 g cyclohexane obtained by hydrogenation of benzene was charged to a batch reactor with a reflux condenser. The cyclohexane mixture was stirred at 1300 rpm and heated to 16O⁰C under a continuous flow of 8% O₂ in N₂ at a reactor pressure 1.5 MPa. After 1 hour of supplying oxygen as a mixture of 8% O₂ in N₂ , in an amount of 80 Nl/hr nitrogen was supplied and the reactor was cooled to room temperature. After releasing the pressure 35 ml of a 1 N aqueous NaOH solution, comprising 20 ppm cobalt, added as cobaltous sulphate, was added to the reaction mixture. Subsequently the reactor was pressurized with nitrogen to 1 MPa and stirred for one hour at 1000 rpm at a temperature of 95 ⁰C. After cooling down the reaction mixture and release of the pressure the reaction mixture was acidified with diluted sulphuric acid. Subsequently the organic layer was separated off. Analysis by gas chromatography of the separated organic layer shows the presence of 43.1 mMoles of cyclohexanone, 33.2 mMoles of cyclohexanol and 8.9 mMoles of C6 type by-products.

This relates to a selectivity towards cyclohexanone and cyclohexanol from cyclohexane of 89.6% (=100%*(43.1+33.2)/(43.1+33.2+8.9)).

The overall selectivity into cyclohexanol and cyclohexanone, calculated on the initial amount of benzene is 89,5%.

Example 1

Partial Hydrogenation of benzene

To a mixture of 80 ml of benzene and 320 ml of water in a titanium autoclave, 0.4 g of a Ruthenium/Zinc hydrogenation catalyst together with 14.4 g of ZnSO₄.7H₂O, and 2 g OfZrO₂ was added. This mixture was stirred at 1500 rpm and heated to 145 ⁰C under a 5 MPa hydrogen atmosphere. After 65 minutes the reaction mixture was cooled to room temperature. Analysis of the organic layer with gas chromatography demonstrated that the resulting reaction mixture of benzene, cyclohexene and cyclohexane contained less then 0.05% of impurities and had a benzene/cyclohexene/cyclohexane molar ratio of 29.9/54.8/15.2.

At a benzene conversion of 70.1 % a cyclohexane yield of 15.2% and a cyclohexene yield of 54.8% was obtained.

Example 2 Oxidation of the mixture of benzene, cyclohexene and cyclohexane

54 ml of a mixture of benzene, cyclohexene and cyclohexane with a molar ratio of 29.9/54.8/15.2 was added to an autoclave together with 80 ml of an 3% aqueous sulphuric acid solution, 40 ml of acetonitrile, 199 mg of Pd(NO₃)₂, 746 mg OfCuSO₄ and 6.99 g of H₃PMo₁₂O₄₀. This reaction mixture was stirred at 1500 rpm under a constant flow 80 NI of 5% oxygen in nitrogen per hour at a pressure of 5 MPa at a temperature of 80⁰C. After 8 hours the reaction mixture was cooled to room temperature. Analysis of the products by gas chromatography showed 29.9 Mol% benzene, 3.6 Mol% cyclohexene, 15.2 Mol% cyclohexane, 50.1 Mol% cyclohexanone, 0.5 Mol% cyclohexanol and 0.6 Mol% C6 impurities. At 93.4% conversion of cyclohexene a cyclohexanol and cyclohexanone selectivity of 98.8% is obtained.

Example 3 Hydrogenation of benzene/cyclohexene/cyclohexane mixture

Per hour 100 gram of a mixture of 61.4 gram benzene, 7.4 gram cyclohexene and 31.2 gram cyclohexane was fed into a tubular hydrogenation reactor, containing 50 ml of a platinum on aluminum oxide catalyst (0.3 wt% Pt), together with 300 NI hydrogen. The hydrogenation reaction was performed at a pressure of about 3.0 MPa. The reaction heat was removed by cooling the reactor with oil to about 225°C whereby the maximum temperature in the reactor was 370°C. All organic compounds were condensed and a gas chromatographic analysis showed that the content of impurities in cyclohexane was less than 0.03%.

This indicates a hydrogenation selectivity towards cyclohexane of at least 99.9%.

Example 4

Oxidation of cyclohexane 165 g of cyclohexane was charged to a batch reactor with a reflux condenser. The cyclohexane was stirred at 1300 rpm and heated to 160⁰C under a continuous flow of 80 Nl/hr of 8% O₂ in N₂ at a pressure of 1.5 MPa. After 1 hour the oxygen supply was replaced by nitrogen and the reactor was cooled to room temperature. After releasing the pressure 35 ml of a 1 N aqueous NaOH solution, comprising 20 ppm cobalt, added as cobaltous sulphate, was added to the reaction mixture in order to decompose the cyclohexyl hydroperoxide formed in the oxidation reaction. Therefore the reactor was pressurized with nitrogen to 1 MPa and the reaction mixture was stirred at 1000 rpm for one more hour at 95°C. After cooling down the reaction mixture was acidified with diluted sulphuric acid the organic layer was separated. Gas chromatographic analysis showed that 42.7 mMoles cyclohexanone, 32.6 mMoles cyclohexanol and 8.2 mMoles C6 type by-products were obtained. This relates to a selectivity towards cyclohexanone and cyclohexanol from cyclohexane of 90.2%.

From Examples 1 to 4 it can be calculated that the overall selectivity into cyclohexanol and cyclohexanone, calculated on the initial amount of benzene, is 94.5 %. Example 5

Partial Hydrogenation of benzene

Example 1 was repeated whereby the reaction mixture after being stirred at 1500 rpm and heated to 145°C under a 5 MPa hydrogen atmosphere was cooled down to room temperature. Analysis of the organic layer with gas chromatography showed that the mixture of benzene, cyclohexene and cyclohexane contained less then 0.05% of impurities and a benzene/cyclohexene/cyclohexane molar ratio of 56.2/37.3/6.5. At 43.8 % benzene conversion a cyclohexane yield of 6.5 % and a cyclohexene yield of about 37.3% is obtained.

Example 6

Oxidation of the mixture of benzene, cyclohexene and cyclohexane Example 2 was repeated with the mixture obtained from Example 5, a mixture of benzene, cyclohexene and cyclohexane with a molar ratio of 56.2/37.3/6.5. Analysis of the resulting oxidized mixture by gas chromatography showed the presence of 56.2 mol% benzene, 3.2 mol% cyclohexene, 6.5 mol% cyclohexane, 33.4 mol% cyclohexanone, 0.4 mol% cyclohexanol and 0.3 mol% C6 impurities. At a conversion of cyclohexene of 91.4% a cyclohexanol and cyclohexanone selectivity of 99.1% is obtained.

Example 7

Hydrogenation ofbenzene/cyclohexene/cyclohexane mixture

100 gram/hour of a mixture of 85.3 gram benzene, 4.9 gram cyclohexene and 9.9 gram cyclohexane was fed into a tubular hydrogenation reactor, containing 50 ml of a platinum on aluminum oxide catalyst (0.3 wt% Pt), together with 300 Nl/hr hydrogen. The hydrogenation reaction was performed at a pressure of about 3.0 MPa and the reaction heat was removed by cooling the reactor with oil to about 225°C whereby the maximum temperature in the reactor was 37O⁰C. All organic compounds were condensed and a gas chromatographic analysis showed that the content of impurities in cyclohexane was less than 0.03%.

This corresponds to a hydrogenation selectivity into cyclohexane of at least 99.9%.

Example 8

Oxidation of cyclohexane Example 4 was repeated with 167 g obtained from example 7. Gas chromatographic analysis showed that 43.0 mMoles cyclohexanone, 32.8 mMoles cyclohexanol and 8.6 mMoles C6 type by-products were obtained. This relates to a selectivity towards cyclohexanone and cyclohexanol from cyclohexane of 89.9%

From Examples 5 to 8 it can be calculated that the overall selectivity into cyclohexanol and cyclohexanone, calculated on the initial amount of benzene, is 93 %.

Example 9 Oxidation of the mixture of benzene, cyclohexene and cyclohexane

54 ml of a mixture of benzene, cyclohexene and cyclohexane with a molar ratio of 29.9/54.8/15.2 as prepared in example 1 , was added to an autoclave and subjected to an oxidation according to Example 2, with the difference that the reaction mixture was cooled to room temperature after 3.5 hours. Analysis of the products by gas chromatography showed 29.9 Mol% benzene, 21.3 Mol% cyclohexene, 15.2 Mol% cyclohexane, 32.9 Mol% cyclohexanone, 0.4 Mol% cyclohexanol and 0.2 Mol% C6 impurities. At 61.1 % conversion of cyclohexene a cyclohexanol and cyclohexanone selectivity of 99.4% is obtained.

Example 10

Hydrogenation ofbenzene/cyclohexene/cyclohexane mixture 100 gram/hour of a mixture of 45.0 gram benzene, 32.1 gram cyclohexene and 22.9 gram cyclohexane was fed into a tubular hydrogenation reactor, containing 50 ml of a platinum on aluminum oxide catalyst (0.3 wt% Pt), together with 300 Nl/hr hydrogen. The hydrogenation reaction was performed at a pressure of about 3.0 MPa and the reaction heat was removed by cooling the reactor with oil to about 225°C whereby the maximum temperature in the reactor was 37O⁰C. All organic compounds were condensed and a gas chromatographic analysis showed that the content of impurities in cyclohexane was less than 0.03%. This indicates a hydrogenation selectivity towards cyclohexane of at least 99.9%.

Example 11

Oxidation of cyclohexane Example 4 was repeated with 170 g cyclohexane obtained from example 10. Gas chromatographic analysis showed that 42.9 mMoles cyclohexanone, 32.8 mMoles cyclohexanol and 8.1 mMoles C6 type by-products were obtained.

From Examples 8 to 11 it can be calculated that the overall selectivity into cyclohexanol and cyclohexanone, calculated on the initial amount of benzene, is 93.1 %.

Claims

1. Process for the preparation of cyclohexanol and/or cyclohexanone from benzene characterized in that the process comprises the following steps: a. a partial hydrogenation step wherein benzene in the presence of a metal catalyst is partially hydrogenated producing a mixture comprising cyclohexene and unconverted benzene, b. a step wherein a mixture as produced in step a is hydrated producing a mixture comprising cyclohexanol and/or oxidized in the presence of a metal catalyst producing a mixture comprising cyclohexanone or a mixture comprising cyclohexanol and cyclohexanone, c. a step wherein cyclohexanol and/or cyclohexanone is separated from the mixture obtained in step b comprising unconverted benzene, cyclohexanol and/or cyclohexanone, d. a hydrogenation step wherein a mixture comprising unconverted benzene as obtained in step c is hydrogenated in the presence of a metal catalyst into cyclohexane and e. an oxidation step wherein a mixture as produced in step d comprising cyclohexane is oxidized producing a mixture comprising cyclohexanol and cyclohexanone.

2. Process according to claim 1 characterized in that step a is catalyzed by means of a ruthenium catalyst.

3. Process according to claim 1 or 2 characterized in that a hydration step in step b is catalyzed by means of a strongly acid ion exchanger, sulphuric acid or phosphoric acid.

4. Process according to any one of claims 1 to 3 characterized in that the metal catalyst mentioned in step b for oxidizing a mixture as produced in step a is a palladium catalyst system comprising (a) palladium, (b) at least one further metal chosen from group 8, 9, 10 or 14 of the periodic system, and (c) a heteropolyacid or halogen.

5. Process according to any one of claims 1 to 4 characterized in that step d is catalyzed by means of a platinum catalyst supported on aluminum oxide. CLAIMS (continued)

6. Process according to any one of claims 1 to 5 characterized in that in step e cyclohexane is converted into cyclohexyl peroxide and this cyclohexyl peroxide is subjected to a decomposition into cyclohexanol and cyclohexanone.

7. Process according to claim 6 characterized in that the decomposition is catalyzed by means of a metal salt.

8. Process according to any one of claims 1-7 characterized in that the mixture produced in step a comprises cyclohexene, cyclohexane and benzene and that this mixture is subjected to an oxidation in the presence of a metal catalyst producing an oxidation reaction mixture comprising cyclohexane, benzene, cyclohexanol and cyclohexanone.

9. Process according to claim 8 characterized in that cyclohexanol and cyclohexanone are separated from the oxidation reaction mixture comprising cyclohexane, benzene, cyclohexanol and cyclohexanone and the resulting mixture comprising cyclohexane and benzene is subjected to a metal catalyzed hydrogenation producing a hydrogenation reaction mixture comprising cyclohexane which is oxidized into a mixture comprising cyclohexyl peroxide which in a further step is decomposed into cyclohexanol and cyclohexanone.

10. Process according to claim 9 characterized in that an additional amount of benzene is fed to the resulting mixture comprising cyclohexane and benzene which is fed to the metal catalyzed hydrogenation whereby this additional amount of benzene is equal to or less than the amount of benzene fed to the partial hydrogenation step, step a.