WO2015010928A1 - Continuous process for the production of purified cyclohexanone - Google Patents

Continuous process for the production of purified cyclohexanone Download PDF

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Publication number
WO2015010928A1
WO2015010928A1 PCT/EP2014/064937 EP2014064937W WO2015010928A1 WO 2015010928 A1 WO2015010928 A1 WO 2015010928A1 EP 2014064937 W EP2014064937 W EP 2014064937W WO 2015010928 A1 WO2015010928 A1 WO 2015010928A1
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Prior art keywords
cyclohexanone
washing
cyclohexanol
process according
alkali metal
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PCT/EP2014/064937
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French (fr)
Inventor
Rudy Francois Maria Jozef Parton
Johan Thomas Tinge
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Dsm Ip Assets B.V.
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Priority to RU2016105997A priority Critical patent/RU2661867C2/en
Publication of WO2015010928A1 publication Critical patent/WO2015010928A1/en

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    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/48—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by oxidation reactions with formation of hydroxy groups
    • C07C29/50—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by oxidation reactions with formation of hydroxy groups with molecular oxygen only
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
    • C07C45/51—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by pyrolysis, rearrangement or decomposition
    • C07C45/53—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by pyrolysis, rearrangement or decomposition of hydroperoxides
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
    • C07C29/132—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring by reduction of an oxygen containing functional group
    • C—CHEMISTRY; METALLURGY
    • C07—ORGANIC CHEMISTRY
    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
    • C07C45/78—Separation; Purification; Stabilisation; Use of additives
    • C07C45/80—Separation; Purification; Stabilisation; Use of additives by liquid-liquid treatment

Definitions

  • the invention relates to a continuous process for the production of purified cyclohexanone.
  • Cyclohexanone, C 6 H 10 O is an intermediate in the commercial production of nylon-6.
  • cyclohexanone In general pure cyclohexanone is first converted into cyclohexanone oxime via reaction with hydroxylamine. The obtained cyclohexanone oxime is then reacted via Beckmann rearrangement into caprolactam. The Beckmann rearrangement is an acid-catalyzed rearrangement of an oxime to an amide.
  • nylon-6 is obtained via ring- opening polymerization of the caprolactam.
  • Cyclohexanone can be commercially produced from cyclohexane in a two-step chemical process followed by concentration and purification.
  • cyclohexane is oxidized by an oxygen containing gas to produce a mixture comprising the intermediate cyclohexyl hydroperoxide and the products cyclohexanol, cyclohexanone and by-products. Because the intermediate cyclohexyl hydroperoxide and the products cyclohexanol and cyclohexanone are more readily oxidized than cyclohexane, the conversion of cyclohexane is kept low.
  • the intermediate cyclohexyl hydroperoxide in the oxidized reaction mixture obtained in first step is decomposed in the presence of an aqueous phase containing basic hydroxide ions, in a decomposition section to form a decomposed reaction mixture.
  • an aqueous phase containing basic hydroxide ions Besides the desired products cyclohexanone and cyclohexanol, by-products are also formed including alkali metal salts.
  • the obtained two-phase system comprising an organic phase and an aqueous phase are separated.
  • the organic phase comprising mainly unconverted cyclohexane, cyclohexanol and cyclohexanone is worked-up further.
  • US5905173 discloses a process for decomposing a mixture containing cycloalkyl hydroperoxide with an aqueous phase containing alkali metal hydroxide where, besides the alkali metal hydroxide, there is also at least 10 wt. % of the aqueous phase of one or more alkali metal salts.
  • the alkali metal salts are preferably alkali metal carbonates, or alkali metal salts of mono- and poly-carboxylic acids, with the carboxylic acid moiety containing 1 to 24 carbon atoms.
  • US4238415 discloses a process for the preparation of cycloalkanols and cycloalkanones by the liquid phase oxidation of a cycloalkane having from 5 to 12 carbon atoms in the ring by means of a gas containing molecular oxygen to obtain an oxidation mixture containing cycloalkyl hydroperoxide and acids, and the subsequent decomposition of such cycloalkyl hydroperoxide to cycloalkanol and cycloalkanone.
  • the decomposition is carried out by means of a metal salt in the presence of an aqueous solution of an alkali metal hydroxide.
  • the improvement comprises a neutralization step wherein the acids contained in the oxidation mixture are first neutralized, forming a neutralized organic phase containing the cycloalkyl
  • hydroperoxide where after the neutralized organic phase is treated with a metal salt in the presence of an aqueous solution of an alkali metal hydroxide to decompose the cycloalkyl hydroperoxide and form an organic phase containing cycloalkanol and cycloalkanone.
  • alkali metal hydroxide entrainment A serious problem with these processes, especially when applying aqueous alkali metal hydroxides comprising solutions for the decomposition of cyclohexyl hydroperoxide, is the so-called "alkali metal hydroxide entrainment".
  • the organic phase of the two-phase system obtained after cyclohexyl hydroperoxide decomposition still contains a considerable amount of alkali metal hydroxides. Washing of this organic phase with water has been found to have little effect on the alkali metal hydroxide entrainment.
  • the main problem that occurs is loss of cyclohexanone by condensation to unwanted high-boiling by-products.
  • the alkali metal hydroxide entrainment is due to on the one hand the solubility of the alkali metal hydroxides in the organic phase, which still contains a fair amount of dissolved water, and on the other hand to incomplete phase separation, which causes very small droplets of aqueous phase containing alkali metal hydroxides to remain emulsified in the organic phase.
  • the water disappears in the later distillations, but the alkali metal hydroxides remain behind in the organic mixture.
  • US4326085 discloses a method for removal of alkali metal carboxylates from mixtures which contain a cycloalkanone and a cycloalkanol, in particular cyclohexanone and cyclohexanol, and which have been obtained in oxidation in the liquid phase of the corresponding cycloalkane with gas containing molecular oxygen.
  • Alkali metal carboxylates are removed from such mixtures containing a cycloalkanone and a cycloalkanol by washing the mixture with an aqueous acid solution, in particular an aqueous solution of carboxylic acid with 1 to 6 carbon atoms per molecule.
  • US5892122 discloses an improved method for making cyclohexanone and cyclohexanol from oxidation of cyclohexane in which a polyprotic acid is used to neutralize caustic to prevent oligomerization of cyclohexanone during fractional distillation. US5892122 also discloses that presence of caustic in a fractional distillation step may catalyse the oligomerisation of some cyclohexanone resulting in yield loss. This is solved by the installation of a water-wash upstream of the
  • cyclohexanone distillation is not necessary to have a water-wash upstream of the cyclohexanone distillation. It has been found that reducing the loss of cyclohexanone by conversion to unwanted high-boiling byproducts (such as for example oligomers) and therefore obtaining a high yield of cyclohexanone can be achieved by introducing a washing step in between the removal of cyclohexane and the recovery of the cyclohexanone. This is usually between the first distillation section and the second distillation section. At this location the flow rate of the organic phases are reduced due to removal of cyclohexane.
  • Cyclohexane is the component that is present by far in excess in the organic phases after decomposition of cyclohexyl hydroperoxide that is fed to the first distillation section. This washing step in between the removal of cyclohexane and the recovery of cyclohexanone can be done with water and thus avoids the use of acids.
  • the invention provides a solution to the various problems caused by alkali entrainment and removes the alkali metal hydroxides.
  • step IV removal of cyclohexane from the organic phase obtained in step III, resulting in a residue comprising cyclohexanone, cyclohexanol and alkali metal salts;
  • the organic phase obtained in step III contains less than 50 ppm cyclohexyl hydroperoxide and less than 25 ppm esters of cyclohexanol;
  • the residue obtained in step V after washing with water contains less than 10 ppm alkali metal salts.
  • step IV at least 75 % by weight of the cyclohexane is removed in step IV from the
  • step IV the residue obtained in step IV is not washed with an aqueous alkaline solution before being used in step VI.
  • step I which is oxidation of cyclohexane by an oxygen containing gas to produce a mixture comprising cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products is depicted here as unbalanced equation (1 ).
  • the by-products produced in reaction (1 ) comprise in general several organic acids in various quantities.
  • Air contains approximately 21 volume % of oxygen, enriched air contains more than 21 volume % of oxygen, in general from 21 volume % up to 30 volume % of oxygen; and diluted air contains less than 21 volume % of oxygen, in general from 5 volume % up to 21 volume % of oxygen.
  • cyclohexane is oxidized in a liquid phase with air.
  • Suitable oxidation temperatures are between about 120 °C and about 200 °C.
  • the reaction is carried out for 5 minutes to 6 hours and is carried out in one or more oxidation reactors which may be in series.
  • the pressure is such that a liquid phase is maintained in the system.
  • the pressure is usually between about 0.3 MPa and about 5 MPa, preferably between about 0.5 MPa and about 2 MPa.
  • this oxidation is normally conducted either uncatalyzed or catalyzed with a suitable catalyst or a mixture of catalytic compounds.
  • Suitable catalysts and reaction path modifiers are, amongst others, cobalt containing salts, chromium containing salts and NHPI (N-hydroxyphthalimide) and DEHPA
  • the degree of conversion applied is usually low, for example 1 to 12 % by weight relative to the cyclohexane supplied, so the reaction mixture obtained in the first step contains a large amount of unconverted cyclohexane.
  • the product of the uncatalyzed oxidation of cyclohexane contains at least comparable quantities, in weight percentage (wt. %), of cyclohexyl hydroperoxide and of cyclohexanol plus cyclohexanone.
  • the mixture after the oxidation reaction contains a quantity of cyclohexyl hydroperoxide that is more than twice the quantity of cyclohexanol plus cyclohexanone.
  • catalyzed oxidation produces a mixture which contains less than 50 wt. % cyclohexyl hydroperoxide compared with the weight percentage of cyclohexanol plus cyclohexanone.
  • the cyclohexyl hydroperoxide concentration in the reaction mixture as it leaves the last oxidation reactor is generally between about 0.1 wt. % and about 8.0 wt. %.
  • the cyclohexanol concentration in this mixture is generally between about 0.1 wt. % and about 10 wt. %.
  • the oxidation reaction results in a pressurized, hot and diluted solution comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and byproducts in cyclohexane.
  • the solution obtained in the first step can be used as such in the next step.
  • this oxidation mixture is allowed to expand to a lower pressure before further processing.
  • the temperature of the mixture after the oxidation reaction may be reduced before further processing.
  • this cooling is done by (partial) flashing and/or transferring heat via a heat exchanger to a coolant.
  • the oxidation mixture is concentrated by partial removal of cyclohexane before further processing.
  • an additional step lb is carried out where the oxidation reaction mixture comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products in cyclohexane is washed with water, whereby at least a fraction of the acid by-products formed during oxidation are extracted from the oxidation reaction mixture.
  • the oxidation mixture comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products in cyclohexane obtained in step I and optionally washed with water in step lb, is then treated in a separate neutralization step wherein at least a portion of the acids present in the oxidation mixture are neutralized.
  • the resulting neutralized oxidation mixture comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products in cyclohexane is then further treated in a subsequent decomposition step. If there is a step lb and a step lc, then step lc follows step lb.
  • the cyclohexyl hydroperoxide in the oxidized reaction mixture obtained in step I is decomposed in the presence of an aqueous alkaline solution to form a decomposed reaction mixture.
  • the aqueous alkaline solution is a hydroxide ion containing solution.
  • the hydroxide ions also act to neutralize acid by-products (not depicted).
  • the aqueous alkaline solution may be aqueous NaOH or KOH or a mixture thereof and preferably is aqueous NaOH.
  • the aqueous alkaline solution preferably has a pH in the range of from 1 1 to 14, more preferably 12 to 14 and especially 13 to 14.
  • the by- products produced in reaction (1 ) and in reaction (2) are in general different regarding composition, concentrations and/or quantities.
  • the aqueous alkaline solution used in step II has a hydroxide content of more than 0.01 mol per kg water.
  • a common method to introduce the required hydroxide ions is adding an aqueous solution comprising sodium hydroxide and/or potassium hydroxide to the oxidized reaction mixture.
  • an aqueous solution comprising sodium hydroxide and/or potassium hydroxide
  • sufficient alkali metal hydroxide comprising aqueous solution is added so that the concentration of hydroxide of the aqueous phase, [OH " ], on completion of decomposition is at least 0.05 N, preferably at least 0.6 N.
  • Completion of decomposition means greater than 90% conversion of the available cyclohexyl hydroperoxide. In principle [OH " ] higher than 2 N is possible, but this does not offer any advantages. Such a high concentration might result in side-reactions occurring, for instance aldol condensations of
  • the quantity of alkali metal hydroxide used is preferably such that the [OH " ] at completion is between about 0.1 N and about 2 N. More preferably, an adequate amount of hydroxide is used such that the [OH " ] at completion is between about 0.6 N and about 1 N.
  • the volume ratio between the aqueous phase and the organic phase in the decomposition step is preferably maintained at least about 0.02, and preferably between about 0.05 and 0.20. Higher volume ratios may be utilized, but they offer no particular advantage.
  • the decomposition of the cyclohexyl hydroperoxide may be carried out at a temperature in the range of, for instance, about 60 °C to about 180 °C.
  • the decomposition reaction of cyclohexyl hydroperoxide is preferably carried out in the presence of at least one catalyst, a cyclohexyl hydroperoxide decomposition-promoting metal salt.
  • a cyclohexyl hydroperoxide decomposition-promoting metal salt is generally a salt of a transition metal (e.g., Groups IB, VIB, VIIB and VI 11 B of the Periodic Table).
  • suitable transition metals are cobalt, chromium, manganese, iron, nickel, copper, or mixtures of these metals, such as for instance a mixture of cobalt and chromium.
  • the transition metal salt is water soluble.
  • the metal sulphates, metal acetates, and metal carboxylates are suitable salts.
  • transition metal salt can be about 0.1 parts per million (ppm) to about 1000 ppm, calculated as transition metal relative to the weight of the aqueous phase. However, it is also possible to use larger quantities of transition metal salt. Preferably, the transition metal salt is present between about 0.1 ppm and about 10 ppm.
  • the transition metal salt can be added, optionally in combination with the alkali metal hydroxide, as an aqueous solution to the mixture containing the cyclohexyl
  • the transition metal as an organic salt, dissolved in an organic solvent, to the reaction mixture in an amount such that the concentration of transition metal salt in the aqueous phase after phase separation is within the ranges given above.
  • the cyclohexane may be used as an organic solvent. Benzene and cyclohexene are other suitable organic solvents.
  • the decomposition reaction can be carried out either at atmospheric, at a reduced pressure or at an elevated pressure.
  • Atmospheric pressure herein is defined as a pressure in the range from about 0.08 MPa to 0.12 MPa.
  • Reduced pressure herein is defined as a pressure in the range from about 0.03 MPa to 0.08 MPa.
  • Elevated pressure herein is defined as a pressure in the range from about 0.12MPa to about 3 MPa.
  • the decomposition of cyclohexyl hydroperoxide can advantageously be carried out at a pressure that is of the same order as the pressure used for oxidation of cyclohexane; however, it may also be advantageous to evaporate part of the cycloalkane after oxidation by reducing the pressure (i.e. flashing).
  • the pressure during the decomposition reaction is then preferably about 0.03 MPa to about 1 MPa, more preferably the decomposition reaction is carried out at almost
  • the two reactions can be controlled to ensure that
  • step II comprises adding an aqueous alkaline solution to the organic phase, mixing of both phases followed by separation of an aqueous and an organic phase in step III.
  • the resulting aqueous phase may be separated from the resulting organic phase.
  • the organic phase comprises mainly cyclohexane, cyclohexanol and cyclohexanone.
  • the obtained aqueous phase can be (partially) reused in the decomposition reaction if it satisfies the above-mentioned requirements.
  • This aqueous phase already contains alkali metal salts of mono- or poly-carboxylic acids but, often, addition of alkali metal hydroxide is necessary.
  • the mono- or poly-carboxylic acids in these alkali metal salts of mono- or poly-carboxylic acids are produced in side reactions in the oxidation section and/or the decomposition reaction.
  • Reuse of the aqueous phase has the advantage that the ratio between aqueous phase and organic phase can be set and monitored in a simple manner.
  • the aqueous phase resulting from the decomposition step is (partially) recycled to the neutralization step. In this manner the consumption of the total alkali metal hydroxide consumption in the cyclohexanone production process can be reduced.
  • the obtained organic phase which comprises mainly cyclohexane, cyclohexanol and cyclohexanone is then worked up to produce purified cyclohexanone.
  • the obtained organic phase is first passed to a distillation section where preferably first cyclohexane and components that are more volatile than cyclohexane are distilled off.
  • a heavy fraction (still an organic phase) is obtained that is concentrated in cyclohexanone and cyclohexanol.
  • This heavy fraction is also called a residue comprising cyclohexanone, cyclohexanol and alkali metal salts.
  • the recovered cyclohexane is recycled back to the oxidation section.
  • this washing section comprises two or more washing steps in-series. Preferably these washing steps in-series are operated in a counter current manner.
  • a major advantage of introducing a washing section between the first distillation section and the second distillation section over prior art, where the organic phase after decomposition of cyclohexyl hydroperoxide is washed is that the concentration of alkali metal hydroxides after the first distillation section is higher and that the flow rate (expressed in m 3 /hr) of the organic phase to be washed is smaller and preferably less than 40 m 3 /hr and more preferably less than 35 m 3 /hr. It should be realized that the concentration factor due to removal of mainly cyclohexane in the first distillation section of the organic phase ranges from about 10 to 40.
  • the aqueous phase obtained in this washing section is (partly) recycled to step II where is can be used to produce the fresh aqueous solutions comprising sodium hydroxide and/or potassium hydroxide alkaline that is added to the oxidized reaction mixture.
  • At least a part of the aqueous phase obtained in step V is used to produce a fresh alkaline solution that is used in step II for the decomposition of the cyclohexyl hydroperoxide produced in step I.
  • the complete aqueous phase obtained in step V is used to produce a fresh alkaline solution that is used in step II for the decomposition of the cyclohexyl hydroperoxide produced in step I.
  • Step V may be carried out at a pressure in the range of from about 0.03 MPa to about 1 MPa, more preferably in the range of from about 0.05 MPa to about 0.5 MPa and especially in the range of from about 0.08 MPa to about 0.12 MPa (at about atmospheric pressure).
  • the amount of water that is fed in step V for removal of alkali metal salts by washing the residue obtained in step IV with water is between 5 wt. % and 300 wt. % and more preferably between 10 wt. % and 150 wt. % relative to the residue obtained in step IV.
  • the washing in step V for removal of alkali metal salts by washing the residue obtained in step IV consists of one or more washing steps in- series.
  • step V for removal of alkali metal salts by washing the residue obtained in step IV consists of 2 or more washing steps in- series.
  • step V for removal of alkali metal salts by washing the residue obtained in step IV consists of 2 washing steps in-series.
  • the washing in step V is performed in one or more mixer- settlers in-series and/or in a washing column.
  • the washing column might contain trays and/or packing.
  • step V for removal of alkali metal salts by washing the residue obtained in step IV is performed in a counter current mode.
  • any type of water can be used.
  • water with a low salt content is used.
  • demineralized water or steam condensate is used.
  • step V Preferably more than 90% of the amount of alkali metal salts in the residue obtained in step IV is removed in step V.
  • the washed fraction obtained in step V that is concentrated in cyclohexanone is then passed to a second distillation section where components that are more volatile than cyclohexanone are distilled off as top product(s). More preferably, the second distillation section is divided into at least two sub-sections. In the first sub-section components that are more volatile than cyclohexanone (e.g.
  • cyclohexane and might be recycled back into the first distillation section are distilled off as top product. While in the last sub-section components that are more volatile than cyclohexanone (e.g. pentanol and heptanone) and which are not recycled back into the first distillation section are distilled off as top product.
  • the heavier fraction obtained in the second distillation section is passed to a third distillation section wherein cyclohexanone is distilled off.
  • a heavier fraction of the third distillation section a fraction concentrated in cyclohexanol is obtained.
  • This heavier fraction obtained in step VI is fed to a fourth distillation section.
  • a heavier fraction a mixture comprising oligomers of cyclohexanone is obtained.
  • cyclohexanol is distilled off.
  • the distilled off cyclohexanol is fed to a dehydrogenation unit where an additional amount of cyclohexanone is obtained.
  • hydrogen gas is separated from the reaction mixture leaving the dehydrogenation unit and the remaining mixture is fed to the second distillation section.
  • the cyclohexanone recovered in step VII is pure.
  • Pure is defined in the present invention as comprising less than 1 wt. % of impurities, more preferably less than 0.5 wt. % and especially comprising less than 0.2 wt. % of impurities.
  • Figure 1 schematically represents a suitable process configuration for carrying out a preferred embodiment of the present invention.
  • Figure 1 shows oxidation section [A] where cyclohexane is introduced via line [1 ] and air is introduced via line [2].
  • the oxidation mixture leaves this section via line [3] and is fed to decomposition section [B].
  • An aqueous NaOH solution is introduced via line [4].
  • An aqueous phase leaves section [B] via line [5].
  • the decomposed reaction mixture leaves section [B] via line [6] and is fed to washing section [C].
  • washing section [C] the decomposed reaction mixture is washed with water that is fed via line [7].
  • the aqueous phase that is produced in the washing section [C] leaves this section via line [8].
  • the obtained washed decomposed reaction mixture leaves the washing section [C] via line [9] and is fed to the first distillation section [D].
  • the decomposed reaction mixture leaves section [B] via line [6] and is directly fed to the first distillation section [D], thereby by-passing washing section [C] (not shown in Figure 1 ).
  • the recovered cyclohexane leaves the first distillation section [D] via line [10] and is reused in oxidation section [A].
  • the solution that is formed in the first distillation section [D] exits via line [1 1 ] and is fed to washing section [E]. In washing section [E] the solution is washed with water that enters via line [12].
  • cyclohexane is added to washing section [E] in order to improve the separation of the water phase and the organic phase (not shown in figure 1 ).
  • the resulting water phase exits via line [13].
  • the washed organic solution exits via line [14] and is fed to the second distillation section [F].
  • Components that are re-used in the cyclohexanone production process e.g. cyclohexane, are removed overhead via line [15].
  • cyclohexanone and that are not re-used in the cyclohexanone production process are removed overhead via line [16].
  • the bottom product of this column is fed to the third distillation section [G] via line [17].
  • cyclohexanone is recovered as top product and exits via line [18].
  • the heavy phase obtained in the third distillation section [G] is discharged via line [19] and is fed to the fourth distillation section [H].
  • a flow comprising mainly cyclohexanol and a residue flow exit this section via lines [21] and line [20], respectively.
  • the flow that comprises mainly cyclohexanol is fed to dehydrogenation section [I].
  • a hydrogen gas comprising flow exits the dehydrogenation section [I] via line [22].
  • the remaining reaction mixture exits the dehydrogenation section [I] via line [23] and is fed the second distillation section [F].
  • This Comparative Example 1 describes an embodiment of the prior art as depicted in Figure 1 , except that both water washing section [C] and washing section [E] would be absent from Figure 1 for Comparative Example 1 .
  • oxidation section [A] which consists of six reactors in-series, liquefied cyclohexane that was introduced via line [1 ] was oxidized with air that was introduced via line [2].
  • the temperature and pressure in this oxidation section were about 165 °C and 1 .2 MPa respectively.
  • no catalyst was added to the reaction mixture.
  • the obtained oxidation mixture comprised cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and as a by-products cyclohexane. This was cooled down via heat exchangers and neutralized. The obtained cooled down and neutralized oxidation mixture left this section via line [3] and was fed to the
  • decomposition section [B] where the cyclohexyl hydroperoxide was decomposed.
  • An aqueous NaOH solution was fed to the decomposition section [B].
  • the resulting aqueous phase was separated from the decomposed reaction mixture which comprised mainly cyclohexane, cyclohexanol and cyclohexanone.
  • the sum of the concentrations of cyclohexanone and cyclohexanol in this decomposed reaction mixture was about 3.5 wt.
  • the organic phase obtained contained less than 50 ppm cyclohexyl hydroperoxide and less than 25 ppm esters of cyclohexanol.
  • the decomposed reaction mixture having an average flow rate of about 350 m 3 /hr, left the decomposition section [B] via line [6].
  • the resulting aqueous phase with a pH value in the range of 13 to 14 (at 25 °C) was separated from the decomposed reaction mixture and was partially reused for decomposition of cyclohexyl hydroperoxide and was partially reused for the neutralization of carboxylic acids.
  • An aqueous phase comprising neutralized organic acids left the decomposition section [B] via line [5].
  • Line [6] continued as line [9] due to absence of water washing section [C].
  • the decomposed reaction mixture that was transported via line [9] was after being heated up fed to the first distillation section [D], in which cyclohexane was recovered from the washed decomposed reaction mixture.
  • the recovered cyclohexane left the first distillation section [D] via line [10] and was reused in oxidation section [A].
  • the residue comprising cyclohexanone, cyclohexanol and alkali metal salts, having an average flow rate of about 20 m 3 /hr, that was formed in the first distillation section [D] exits via line [1 1 ].
  • Line [1 1] continued as line [14] due to absence of washing section [E].
  • the residue comprising cyclohexanone, cyclohexanol and alkali metal salts was transported via line [14] and was fed to the second distillation section [F], in which components that are more volatile than cyclohexanone were distilled off.
  • the second distillation section [F] consists of two distillation columns that are operated in series. In the first distillation column of the second distillation section [F] components that are reused in the cyclohexanone production process, e.g. cyclohexane, were removed overhead via line [15]. The bottom product of this column was fed to the second distillation column of the second distillation section [F]. In the second distillation column of the second distillation section [F] components that are more volatile than
  • cyclohexanone and that are not re-used in the cyclohexanone production process were removed overhead via line [16].
  • the bottom product of this column was fed to the third distillation section [G] via line [17].
  • cyclohexanone was recovered as top product and exits via line [18].
  • the heavy phase obtained in the third distillation section [G] that comprises cyclohexanol, cyclohexanone and heavies were discharged via line [19] and was fed to the fourth distillation section [H].
  • the flow that comprised mainly cyclohexanol was fed to dehydrogenation section [I] in which part of the cyclohexanol was converted into cyclohexanone and hydrogen gas.
  • a hydrogen gas comprising flow exits the dehydrogenation section [I] via line [22].
  • the remaining reaction mixture exits the dehydrogenation section [I] via line [23] and was fed the second distillation column of the second distillation section [F].
  • the residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D] and exited via line [1 1] comprised: Cyclohexanone ca. 42 wt. %
  • This Comparative Example 2 utilizes an embodiment of the prior art as depicted in Figure 1 except that washing section [E] would be absent from Figure 1 for Comparative Example 2.
  • washing section [C] the decomposed reaction mixture was washed with water that was fed via line [7] at a pressure of about 0.7 MPa.
  • the obtained washed decomposed reaction mixture left the washing section [C] via line [9] and is after being heated up was fed to the first distillation section [D], in which cyclohexane is was recovered from the washed decomposed reaction mixture.
  • the content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was on average about 27 ppm (only Na).
  • EXAMPLE 1 This example 1 describes an embodiment of the invention as depicted in Figure 1 except that water washing section [C] is absent from Figure 1 for Example 1.
  • washing section [E] comprised a packed column.
  • Residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D] was fed to washing section [E] via line [1 1].
  • the residue comprising cyclohexanone, cyclohexanol and alkali metal salts was fed to the bottom section of the packed column for a washing step.
  • To the top section of the packed column about 50 wt. % water relative to the residue comprising cyclohexanone, cyclohexanol and alkali metal salts was fed via line [12] at atmospheric pressure.
  • the water phase that was obtained after this washing exited from the bottom of the packed column via line [13] and was partly used for the preparation of aqueous NaOH solution that was charged to the decomposition section [B].
  • the obtained washed residue comprising cyclohexanone, cyclohexanol and alkali metal salts exited from the top section of the packed column and was fed to the first distillation column in the second distillation section [F] via line [14].
  • the content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was on average about 12 ppm (only Na).
  • the amount of water used for the washing step in washing section [E] was 0.71 kg water / kg cyclohexanone and cyclohexanol in the residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D].
  • Example 1 in comparison to Comparative Example 1 clearly shows that by introducing washing section [E] containing a single washing step the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was reduced from on average about 190 ppm to on average about 12 ppm (only Na). So, due to the introduction of washing section [E] the reduction of the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was more than 93%.
  • the content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section was on average about 2 ppm (only Na).
  • the amount of water used for the washing step in washing section [E] was 0.71 kg water / kg cyclohexanone and cyclohexanol in the residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D].
  • Example 2 in comparison to Comparative Example 2 clearly shows that by introducing washing section [E] containing a single washing step the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was reduced from on average about 27 ppm to on average about 2 ppm (only Na). So, due to the introduction of washing section [E] the reduction of the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was more than 92%.
  • This example 3 describes an embodiment of the invention as depicted in Figure 1 .
  • Example 2 The experiment described in Example 2 was repeated, the sole difference being that now the washing section [E] contained two washing steps in- series.
  • the first washing step comprised a mixer-settler and the second washing step comprised a packed column.
  • Residue comprising cyclohexanone, cydohexanol and alkali metal salts that were formed in the first distillation section [D] were fed to washing section [E] via line [1 1 ].
  • first washing step about 27 wt. % water relative to the amount of residue comprising cyclohexanone, cydohexanol and alkali metal salts that was formed in the first distillation section [D] was fed via line [12] at atmospheric pressure.
  • the water phase that was obtained after separating of the water phase and the washed residue comprising cyclohexanone, cydohexanol and alkali metal salts was exited.
  • the washed residue comprising cyclohexanone, cydohexanol and alkali metal salts obtained in the first washing step was fed to the bottom section of the packed column for a second washing step.
  • To the top section of this packed column about 50 wt. % water relative to the residue comprising cyclohexanone, cydohexanol and alkali metal salts was fed via line [12] at atmospheric pressure.
  • the water phase that is obtained after this washing exited from the bottom of the packed column. Both water phases that were obtained after the washings were exited via line [13] and were partly used for the preparation of aqueous NaOH solution that was charged to the decomposition section [B].
  • the obtained washed residue comprising cyclohexanone, cydohexanol and alkali metal salts exited from the top section of the packed column and was fed to the first distillation column in the second distillation section [F] via line [14].
  • the content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was on average less than 1 ppm (only Na).
  • the amounts of water used for the first and second washing step in washing section [E] were about 0.39 and 0.71 kg water / kg cyclohexanone and cyclohexanol in the residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D], respectively.
  • Example 3 in comparison to Comparative Example 2 clearly shows that by introducing washing section [E] contained two washing steps in- series the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was reduced from on average about 27 ppm to on average less than 1 ppm (only Na). So, due to the introduction of washing section [E] the reduction of the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was more than 96%.

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Abstract

A continuous process for the production of purified cyclohexanone which comprises at least the following steps: oxidation of cyclohexane; decomposition of cyclohexyl hydroperoxide; separation of an organic phase and aqueous phase; removal of cyclohexane from the organic phase; removal of alkali metal salts by washing with water; distillation and recovery of cyclohexanonewherein any residue obtained after washing contains less than 10 ppm alkali metal salts.

Description

CONTINUOUS PROCESS FOR THE PRODUCTION OF PURIFIED
CYCLOHEXANONE
The invention relates to a continuous process for the production of purified cyclohexanone.
Cyclohexanone, C6H10O, is an intermediate in the commercial production of nylon-6.
In general pure cyclohexanone is first converted into cyclohexanone oxime via reaction with hydroxylamine. The obtained cyclohexanone oxime is then reacted via Beckmann rearrangement into caprolactam. The Beckmann rearrangement is an acid-catalyzed rearrangement of an oxime to an amide.
After purification of the caprolactam, nylon-6 is obtained via ring- opening polymerization of the caprolactam.
Cyclohexanone can be commercially produced from cyclohexane in a two-step chemical process followed by concentration and purification. In the first chemical step cyclohexane is oxidized by an oxygen containing gas to produce a mixture comprising the intermediate cyclohexyl hydroperoxide and the products cyclohexanol, cyclohexanone and by-products. Because the intermediate cyclohexyl hydroperoxide and the products cyclohexanol and cyclohexanone are more readily oxidized than cyclohexane, the conversion of cyclohexane is kept low. In the second step, the intermediate cyclohexyl hydroperoxide in the oxidized reaction mixture obtained in first step is decomposed in the presence of an aqueous phase containing basic hydroxide ions, in a decomposition section to form a decomposed reaction mixture. Besides the desired products cyclohexanone and cyclohexanol, by-products are also formed including alkali metal salts. After decomposing the intermediate cyclohexyl hydroperoxide the obtained two-phase system comprising an organic phase and an aqueous phase are separated. The organic phase comprising mainly unconverted cyclohexane, cyclohexanol and cyclohexanone is worked-up further. From this organic phase the unconverted cyclohexane is recovered and recycled back to the oxidation section. Then desired products are separated out and purified. Optionally, in a third step the obtained cyclohexanol is dehydrogenated into cyclohexanone. The steps are operated in a continuous process.
US5905173 discloses a process for decomposing a mixture containing cycloalkyl hydroperoxide with an aqueous phase containing alkali metal hydroxide where, besides the alkali metal hydroxide, there is also at least 10 wt. % of the aqueous phase of one or more alkali metal salts. The alkali metal salts are preferably alkali metal carbonates, or alkali metal salts of mono- and poly-carboxylic acids, with the carboxylic acid moiety containing 1 to 24 carbon atoms.
US4238415 discloses a process for the preparation of cycloalkanols and cycloalkanones by the liquid phase oxidation of a cycloalkane having from 5 to 12 carbon atoms in the ring by means of a gas containing molecular oxygen to obtain an oxidation mixture containing cycloalkyl hydroperoxide and acids, and the subsequent decomposition of such cycloalkyl hydroperoxide to cycloalkanol and cycloalkanone. The decomposition is carried out by means of a metal salt in the presence of an aqueous solution of an alkali metal hydroxide. The improvement comprises a neutralization step wherein the acids contained in the oxidation mixture are first neutralized, forming a neutralized organic phase containing the cycloalkyl
hydroperoxide, where after the neutralized organic phase is treated with a metal salt in the presence of an aqueous solution of an alkali metal hydroxide to decompose the cycloalkyl hydroperoxide and form an organic phase containing cycloalkanol and cycloalkanone.
A serious problem with these processes, especially when applying aqueous alkali metal hydroxides comprising solutions for the decomposition of cyclohexyl hydroperoxide, is the so-called "alkali metal hydroxide entrainment". The organic phase of the two-phase system obtained after cyclohexyl hydroperoxide decomposition still contains a considerable amount of alkali metal hydroxides. Washing of this organic phase with water has been found to have little effect on the alkali metal hydroxide entrainment. The main problem that occurs is loss of cyclohexanone by condensation to unwanted high-boiling by-products. Another problem that is observed, is fouling in distillation columns and auxiliary equipment such as reboilers which is caused by these produced high-boiling by-products. The condensation tends to occur under conditions of high temperature in combination with relatively high cyclohexanone concentrations. These conditions are mainly observed after the majority of the non- converted cycloalkanes present in the organic phase are removed. Besides fouling in distillation columns and auxiliary equipment caused by high-boiling by-products, also fouling comprising alkali metal salts was observed in distillation columns and auxiliary equipment such as reboilers. The alkali metal hydroxide entrainment is due to on the one hand the solubility of the alkali metal hydroxides in the organic phase, which still contains a fair amount of dissolved water, and on the other hand to incomplete phase separation, which causes very small droplets of aqueous phase containing alkali metal hydroxides to remain emulsified in the organic phase. The water disappears in the later distillations, but the alkali metal hydroxides remain behind in the organic mixture. The fact that on an industrial production scale the flows of these organic phases after decomposition of cyclohexyl hydroperoxide are very large, due to the low degree of conversion in the oxidation section, makes the problem on large scale production even more complex.
US4326085 discloses a method for removal of alkali metal carboxylates from mixtures which contain a cycloalkanone and a cycloalkanol, in particular cyclohexanone and cyclohexanol, and which have been obtained in oxidation in the liquid phase of the corresponding cycloalkane with gas containing molecular oxygen. Alkali metal carboxylates are removed from such mixtures containing a cycloalkanone and a cycloalkanol by washing the mixture with an aqueous acid solution, in particular an aqueous solution of carboxylic acid with 1 to 6 carbon atoms per molecule.
However it has been found that a disadvantage of using an acid wash as described above, in existing industrial scale production units results in the corrosion of equipment due to the acidic nature of the various process flows after the addition of the aqueous acid solution. Replacement of these pieces of equipment with acid resistant pieces of equipment is very expensive. In addition variable costs of the used aqueous acid solutions should not be neglected. Furthermore it was observed that by washing the mixture with an aqueous acid solution the alkali metal hydroxides entrainment was hidden due to neutralization of the alkali metal hydroxides with the aqueous acid solution rather than actually removing them from the mixtures containing cycloalkanone and cycloalkanol. Thus fouling as a result of the presence of alkali metal salts in downstream process equipment could still be observed.
Furthermore this process requires the treatment of large flow rates of mixtures which contain a cycloalkanone and a cycloalkanol, because these mixtures are still diluted with substantial amounts of unreacted cycloalkane. In addition the washing with aqueous acid solutions is performed at high pressure. Thus for this type of aqueous acid wash large volume flows of the aqueous acid solutions are required. A large flow rate is usually defined as a flow of more than 50 m3/hr. However the relative flow rates are also relative to the scale of the industrial production process.
US5892122 discloses an improved method for making cyclohexanone and cyclohexanol from oxidation of cyclohexane in which a polyprotic acid is used to neutralize caustic to prevent oligomerization of cyclohexanone during fractional distillation. US5892122 also discloses that presence of caustic in a fractional distillation step may catalyse the oligomerisation of some cyclohexanone resulting in yield loss. This is solved by the installation of a water-wash upstream of the
cyclohexanone distillation. However it has surprisingly been found that it is not necessary to have a water-wash upstream of the cyclohexanone distillation. It has been found that reducing the loss of cyclohexanone by conversion to unwanted high-boiling byproducts (such as for example oligomers) and therefore obtaining a high yield of cyclohexanone can be achieved by introducing a washing step in between the removal of cyclohexane and the recovery of the cyclohexanone. This is usually between the first distillation section and the second distillation section. At this location the flow rate of the organic phases are reduced due to removal of cyclohexane. Cyclohexane is the component that is present by far in excess in the organic phases after decomposition of cyclohexyl hydroperoxide that is fed to the first distillation section. This washing step in between the removal of cyclohexane and the recovery of cyclohexanone can be done with water and thus avoids the use of acids.
Another advantage is that the concentration of alkali metal hydroxides after the first distillation section is higher than in the organic phases after
decomposition of cyclohexyl hydroperoxide, which makes the washing process more efficient.
In addition investments related to washing of the organic phase after removal of most of the cyclohexane in the first distillation section will be much lower than investments related to washing of the organic phase before removal of most of the cyclohexane in the first distillation section (directly after decomposition of cyclohexyl hydroperoxide) due to much smaller dimensions of the equipment needed as the flow rates can then be much lower. Furthermore washing equipment needed for washing between the first distillation section and the second distillation section can be designed for use at atmospheric pressure, while washing equipment installed directly after the decomposition of cyclohexyl hydroperoxide might be expensive super-atmospheric or sub-atmospheric equipment. In general washing of the organic phase directly after decomposition of cyclohexyl hydroperoxide is performed at a pressure between 0.5 and 1.5 MPa.
Therefore, the invention provides a solution to the various problems caused by alkali entrainment and removes the alkali metal hydroxides.
According to the invention there is provided a continuous process for the production of purified cyclohexanone which comprises the following steps:
I. oxidation of cyclohexane in a liquid phase with an oxygen containing gas
forming cyclohexyl hydroperoxide, cyclohexanone, cyclohexanol, esters of cyclohexanol and carboxylic acids;
II. decomposition of the cyclohexyl hydroperoxide produced in step I in the
presence of an aqueous alkaline solution resulting in an organic phase comprising cyclohexane, cyclohexanone and cyclohexanol and an aqueous phase;
III. separation of the organic phase and the aqueous phase produced in step II;
IV. removal of cyclohexane from the organic phase obtained in step III, resulting in a residue comprising cyclohexanone, cyclohexanol and alkali metal salts;
V. removal of alkali metal salts by washing the residue obtained in step IV with water:
VI. removal of components with a boiling point lower than that of cyclohexanone from the residue obtained in step V, resulting in a residue comprising cyclohexanone and cyclohexanol;
VII. recovery of cyclohexanone from the residue obtained in step VI, resulting in a residue comprising cyclohexanol;
wherein
a) the organic phase obtained in step III contains less than 50 ppm cyclohexyl hydroperoxide and less than 25 ppm esters of cyclohexanol;
b) the residue obtained in step V after washing with water contains less than 10 ppm alkali metal salts.
c) at least 75 % by weight of the cyclohexane is removed in step IV from the
organic phase; and
d) the residue obtained in step IV is not washed with an aqueous alkaline solution before being used in step VI.
STEP I
For simplicity the first step, step I, which is oxidation of cyclohexane by an oxygen containing gas to produce a mixture comprising cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products is depicted here as unbalanced equation (1 ).
C6H12 + 02→ C6H10O + C6HnOH + C6HnOOH + by-products (1 )
The by-products produced in reaction (1 ) comprise in general several organic acids in various quantities.
As the oxygen containing gas source mostly air, enriched air or diluted air are applied. Air contains approximately 21 volume % of oxygen, enriched air contains more than 21 volume % of oxygen, in general from 21 volume % up to 30 volume % of oxygen; and diluted air contains less than 21 volume % of oxygen, in general from 5 volume % up to 21 volume % of oxygen. In general, in industrial processes, in this first step cyclohexane is oxidized in a liquid phase with air.
Suitable oxidation temperatures are between about 120 °C and about 200 °C. The reaction is carried out for 5 minutes to 6 hours and is carried out in one or more oxidation reactors which may be in series. The pressure is such that a liquid phase is maintained in the system. The pressure is usually between about 0.3 MPa and about 5 MPa, preferably between about 0.5 MPa and about 2 MPa. On an industrial scale, this oxidation is normally conducted either uncatalyzed or catalyzed with a suitable catalyst or a mixture of catalytic compounds. Suitable catalysts and reaction path modifiers are, amongst others, cobalt containing salts, chromium containing salts and NHPI (N-hydroxyphthalimide) and DEHPA
(di-(2-ethylhexyl)phosphoric acid) and are well known. The degree of conversion applied is usually low, for example 1 to 12 % by weight relative to the cyclohexane supplied, so the reaction mixture obtained in the first step contains a large amount of unconverted cyclohexane.
Usually the product of the uncatalyzed oxidation of cyclohexane contains at least comparable quantities, in weight percentage (wt. %), of cyclohexyl hydroperoxide and of cyclohexanol plus cyclohexanone. Often, the mixture after the oxidation reaction contains a quantity of cyclohexyl hydroperoxide that is more than twice the quantity of cyclohexanol plus cyclohexanone. In contrast, catalyzed oxidation produces a mixture which contains less than 50 wt. % cyclohexyl hydroperoxide compared with the weight percentage of cyclohexanol plus cyclohexanone. Often, there is even less than 40 wt. % cyclohexyl hydroperoxide compared with the weight percentage of cyclohexanol plus cyclohexanone.
The cyclohexyl hydroperoxide concentration in the reaction mixture as it leaves the last oxidation reactor is generally between about 0.1 wt. % and about 8.0 wt. %. The cyclohexanol concentration in this mixture is generally between about 0.1 wt. % and about 10 wt. %.
The oxidation reaction results in a pressurized, hot and diluted solution comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and byproducts in cyclohexane. The solution obtained in the first step can be used as such in the next step. However, optionally, this oxidation mixture is allowed to expand to a lower pressure before further processing. Furthermore, the temperature of the mixture after the oxidation reaction may be reduced before further processing. Preferably, this cooling is done by (partial) flashing and/or transferring heat via a heat exchanger to a coolant. Optionally, the oxidation mixture is concentrated by partial removal of cyclohexane before further processing. STEP IB
Optionally, before performing step II, an additional step lb is carried out where the oxidation reaction mixture comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products in cyclohexane is washed with water, whereby at least a fraction of the acid by-products formed during oxidation are extracted from the oxidation reaction mixture.
STEP IC
Preferably, the oxidation mixture comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products in cyclohexane obtained in step I and optionally washed with water in step lb, is then treated in a separate neutralization step wherein at least a portion of the acids present in the oxidation mixture are neutralized. The resulting neutralized oxidation mixture comprising of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and by-products in cyclohexane is then further treated in a subsequent decomposition step. If there is a step lb and a step lc, then step lc follows step lb.
STEP II
In the second step, the cyclohexyl hydroperoxide in the oxidized reaction mixture obtained in step I is decomposed in the presence of an aqueous alkaline solution to form a decomposed reaction mixture.
Besides the desired products cyclohexanone and cyclohexanol also by-products are formed.
For simplicity this reaction is depicted here as unbalanced equation
(2).
C6H„OOH υΗ > C6H10O + C6HnOH + by - products
(2)
Preferably the aqueous alkaline solution is a hydroxide ion containing solution. The hydroxide ions also act to neutralize acid by-products (not depicted). The aqueous alkaline solution may be aqueous NaOH or KOH or a mixture thereof and preferably is aqueous NaOH. The aqueous alkaline solution preferably has a pH in the range of from 1 1 to 14, more preferably 12 to 14 and especially 13 to 14. The by- products produced in reaction (1 ) and in reaction (2) are in general different regarding composition, concentrations and/or quantities.
Preferably the aqueous alkaline solution used in step II has a hydroxide content of more than 0.01 mol per kg water.
A common method to introduce the required hydroxide ions is adding an aqueous solution comprising sodium hydroxide and/or potassium hydroxide to the oxidized reaction mixture. For the decomposition of cyclohexyl hydroperoxide, sufficient alkali metal hydroxide comprising aqueous solution is added so that the concentration of hydroxide of the aqueous phase, [OH"], on completion of decomposition is at least 0.05 N, preferably at least 0.6 N. Completion of decomposition means greater than 90% conversion of the available cyclohexyl hydroperoxide. In principle [OH"] higher than 2 N is possible, but this does not offer any advantages. Such a high concentration might result in side-reactions occurring, for instance aldol condensations of
cyclohexanone. Therefore, the quantity of alkali metal hydroxide used is preferably such that the [OH"] at completion is between about 0.1 N and about 2 N. More preferably, an adequate amount of hydroxide is used such that the [OH"] at completion is between about 0.6 N and about 1 N.
In order to efficiently and effectively carry out the available cyclohexyl hydroperoxide decomposition, the volume ratio between the aqueous phase and the organic phase in the decomposition step is preferably maintained at least about 0.02, and preferably between about 0.05 and 0.20. Higher volume ratios may be utilized, but they offer no particular advantage.
The decomposition of the cyclohexyl hydroperoxide may be carried out at a temperature in the range of, for instance, about 60 °C to about 180 °C.
The decomposition reaction of cyclohexyl hydroperoxide is preferably carried out in the presence of at least one catalyst, a cyclohexyl hydroperoxide decomposition-promoting metal salt. This is generally a salt of a transition metal (e.g., Groups IB, VIB, VIIB and VI 11 B of the Periodic Table). Examples of suitable transition metals are cobalt, chromium, manganese, iron, nickel, copper, or mixtures of these metals, such as for instance a mixture of cobalt and chromium. Preferably, the transition metal salt is water soluble. The metal sulphates, metal acetates, and metal carboxylates (e.g., benzoate) are suitable salts. Besides sulphates, nitrates and chlorides can be used, although they have the disadvantage of often being corrosive. Complex salts such as, for example, potassium chromate can, in principle, be used. The quantity of transition metal salt can be about 0.1 parts per million (ppm) to about 1000 ppm, calculated as transition metal relative to the weight of the aqueous phase. However, it is also possible to use larger quantities of transition metal salt. Preferably, the transition metal salt is present between about 0.1 ppm and about 10 ppm.
The transition metal salt can be added, optionally in combination with the alkali metal hydroxide, as an aqueous solution to the mixture containing the cyclohexyl
hydroperoxide. It is also possible to add the transition metal as an organic salt, dissolved in an organic solvent, to the reaction mixture in an amount such that the concentration of transition metal salt in the aqueous phase after phase separation is within the ranges given above. For example, the cyclohexane may be used as an organic solvent. Benzene and cyclohexene are other suitable organic solvents.
The decomposition reaction can be carried out either at atmospheric, at a reduced pressure or at an elevated pressure. Atmospheric pressure herein is defined as a pressure in the range from about 0.08 MPa to 0.12 MPa. Reduced pressure herein is defined as a pressure in the range from about 0.03 MPa to 0.08 MPa. Elevated pressure herein is defined as a pressure in the range from about 0.12MPa to about 3 MPa. The decomposition of cyclohexyl hydroperoxide can advantageously be carried out at a pressure that is of the same order as the pressure used for oxidation of cyclohexane; however, it may also be advantageous to evaporate part of the cycloalkane after oxidation by reducing the pressure (i.e. flashing). The pressure during the decomposition reaction is then preferably about 0.03 MPa to about 1 MPa, more preferably the decomposition reaction is carried out at almost
atmospheric pressure. The two reactions can be controlled to ensure that
decomposition is not completed before oxidation is completed.
Thus step II comprises adding an aqueous alkaline solution to the organic phase, mixing of both phases followed by separation of an aqueous and an organic phase in step III.
STEP III
After completion of the decomposition reaction, the resulting aqueous phase may be separated from the resulting organic phase. The organic phase comprises mainly cyclohexane, cyclohexanol and cyclohexanone. The obtained aqueous phase can be (partially) reused in the decomposition reaction if it satisfies the above-mentioned requirements. This aqueous phase already contains alkali metal salts of mono- or poly-carboxylic acids but, often, addition of alkali metal hydroxide is necessary. The mono- or poly-carboxylic acids in these alkali metal salts of mono- or poly-carboxylic acids are produced in side reactions in the oxidation section and/or the decomposition reaction. Reuse of the aqueous phase has the advantage that the ratio between aqueous phase and organic phase can be set and monitored in a simple manner. Preferably, the aqueous phase resulting from the decomposition step is (partially) recycled to the neutralization step. In this manner the consumption of the total alkali metal hydroxide consumption in the cyclohexanone production process can be reduced.
The obtained organic phase which comprises mainly cyclohexane, cyclohexanol and cyclohexanone is then worked up to produce purified cyclohexanone.
STEP IV
Preferably, the obtained organic phase is first passed to a distillation section where preferably first cyclohexane and components that are more volatile than cyclohexane are distilled off. Thus a heavy fraction (still an organic phase) is obtained that is concentrated in cyclohexanone and cyclohexanol. This heavy fraction is also called a residue comprising cyclohexanone, cyclohexanol and alkali metal salts. The recovered cyclohexane is recycled back to the oxidation section.
STEP V
Optionally this washing section comprises two or more washing steps in-series. Preferably these washing steps in-series are operated in a counter current manner. A major advantage of introducing a washing section between the first distillation section and the second distillation section over prior art, where the organic phase after decomposition of cyclohexyl hydroperoxide is washed, is that the concentration of alkali metal hydroxides after the first distillation section is higher and that the flow rate (expressed in m3/hr) of the organic phase to be washed is smaller and preferably less than 40 m3/hr and more preferably less than 35 m3/hr. It should be realized that the concentration factor due to removal of mainly cyclohexane in the first distillation section of the organic phase ranges from about 10 to 40.
Preferably the aqueous phase obtained in this washing section is (partly) recycled to step II where is can be used to produce the fresh aqueous solutions comprising sodium hydroxide and/or potassium hydroxide alkaline that is added to the oxidized reaction mixture.
In an embodiment of the invention at least a part of the aqueous phase obtained in step V is used to produce a fresh alkaline solution that is used in step II for the decomposition of the cyclohexyl hydroperoxide produced in step I.
In another embodiment of the invention the complete aqueous phase obtained in step V is used to produce a fresh alkaline solution that is used in step II for the decomposition of the cyclohexyl hydroperoxide produced in step I. Step V may be carried out at a pressure in the range of from about 0.03 MPa to about 1 MPa, more preferably in the range of from about 0.05 MPa to about 0.5 MPa and especially in the range of from about 0.08 MPa to about 0.12 MPa (at about atmospheric pressure).
Preferably the amount of water that is fed in step V for removal of alkali metal salts by washing the residue obtained in step IV with water is between 5 wt. % and 300 wt. % and more preferably between 10 wt. % and 150 wt. % relative to the residue obtained in step IV.
Preferably the washing in step V for removal of alkali metal salts by washing the residue obtained in step IV consists of one or more washing steps in- series.
More preferably the washing in step V for removal of alkali metal salts by washing the residue obtained in step IV consists of 2 or more washing steps in- series.
Most preferably the washing in step V for removal of alkali metal salts by washing the residue obtained in step IV consists of 2 washing steps in-series.
Preferably, the washing in step V is performed in one or more mixer- settlers in-series and/or in a washing column. The washing column might contain trays and/or packing.
Preferably the washing in step V for removal of alkali metal salts by washing the residue obtained in step IV is performed in a counter current mode.
For washing in step V any type of water can be used. Preferably, water with a low salt content is used. More preferably, demineralized water or steam condensate is used.
Preferably more than 90% of the amount of alkali metal salts in the residue obtained in step IV is removed in step V.
STEP VI
The washed fraction obtained in step V that is concentrated in cyclohexanone is then passed to a second distillation section where components that are more volatile than cyclohexanone are distilled off as top product(s). More preferably, the second distillation section is divided into at least two sub-sections. In the first sub-section components that are more volatile than cyclohexanone (e.g.
cyclohexane) and might be recycled back into the first distillation section are distilled off as top product. While in the last sub-section components that are more volatile than cyclohexanone (e.g. pentanol and heptanone) and which are not recycled back into the first distillation section are distilled off as top product. The heavier fraction obtained in the second distillation section is passed to a third distillation section wherein cyclohexanone is distilled off. As a heavier fraction of the third distillation section a fraction concentrated in cyclohexanol is obtained.
STEP VII
This heavier fraction obtained in step VI is fed to a fourth distillation section. As a heavier fraction a mixture comprising oligomers of cyclohexanone is obtained. In the fourth distillation section cyclohexanol is distilled off. Optionally the distilled off cyclohexanol is fed to a dehydrogenation unit where an additional amount of cyclohexanone is obtained. Preferably hydrogen gas is separated from the reaction mixture leaving the dehydrogenation unit and the remaining mixture is fed to the second distillation section.
In order to minimize impurities like aldehydes in the produced cyclohexanone small quantities of amines or alkaline compounds might be added in the second distillation section.
Preferably the cyclohexanone recovered in step VII is pure. Pure is defined in the present invention as comprising less than 1 wt. % of impurities, more preferably less than 0.5 wt. % and especially comprising less than 0.2 wt. % of impurities.
BRIEF DESCRIPTION OF THE DRAWING
Figure 1 schematically represents a suitable process configuration for carrying out a preferred embodiment of the present invention.
Figure 1 shows oxidation section [A] where cyclohexane is introduced via line [1 ] and air is introduced via line [2]. The oxidation mixture leaves this section via line [3] and is fed to decomposition section [B]. An aqueous NaOH solution is introduced via line [4]. An aqueous phase leaves section [B] via line [5]. The decomposed reaction mixture leaves section [B] via line [6] and is fed to washing section [C]. In washing section [C] the decomposed reaction mixture is washed with water that is fed via line [7]. The aqueous phase that is produced in the washing section [C] leaves this section via line [8]. The obtained washed decomposed reaction mixture leaves the washing section [C] via line [9] and is fed to the first distillation section [D]. Optionally the decomposed reaction mixture leaves section [B] via line [6] and is directly fed to the first distillation section [D], thereby by-passing washing section [C] (not shown in Figure 1 ). The recovered cyclohexane leaves the first distillation section [D] via line [10] and is reused in oxidation section [A]. The solution that is formed in the first distillation section [D] exits via line [1 1 ] and is fed to washing section [E]. In washing section [E] the solution is washed with water that enters via line [12]. Optionally additional cyclohexane is added to washing section [E] in order to improve the separation of the water phase and the organic phase (not shown in figure 1 ). After phase separation the resulting water phase exits via line [13]. The washed organic solution exits via line [14] and is fed to the second distillation section [F]. Components that are re-used in the cyclohexanone production process, e.g. cyclohexane, are removed overhead via line [15]. Components that are more volatile than
cyclohexanone and that are not re-used in the cyclohexanone production process are removed overhead via line [16]. The bottom product of this column is fed to the third distillation section [G] via line [17]. In the third distillation section [G] cyclohexanone is recovered as top product and exits via line [18]. The heavy phase obtained in the third distillation section [G] is discharged via line [19] and is fed to the fourth distillation section [H]. In the fourth distillation section [H] a flow comprising mainly cyclohexanol and a residue flow, exit this section via lines [21] and line [20], respectively. The flow that comprises mainly cyclohexanol is fed to dehydrogenation section [I]. A hydrogen gas comprising flow exits the dehydrogenation section [I] via line [22]. The remaining reaction mixture exits the dehydrogenation section [I] via line [23] and is fed the second distillation section [F].
MEASUREMENTS:
1 ) For determination of the ester number of products from the cyclohexane oxidation a titrimetric method was used. The principle of the method includes saponification of the ester by boiling after neutralization with a known amount of ethanolic sodium hydroxide solution and the subsequent titration of the excess of the latter. This method determines the total ester number and therefore also any esters of cyclohexanol that may be produced. Thus, the amount of esters of cyclohexanol is equal or smaller than the result given by this method.
2) For determination of reactive peroxides a titrimetric method was used. The principle of the method is that in acetic acid-chloroform media and at room temperature, the peroxide reacts with potassium iodide, with formation of an equivalent amount of iodine. The iodine was then titrated with sodium thiosulphate.
3) For describing the alkali metal salt content of various flows only the alkali metal content is determined. For the determination of Na ions in samples from the oxidation of cyclohexane, atomic absorption spectroscopy was used. 4) For the determination of the cyclohexanol content, the
cyclohexanone content and the cyclohexane content of products from the cyclohexane oxidation, gas chromatography was used.
The invention is now demonstrated by the following non-limiting set of Examples and Comparative Examples.
The numbers in the following examples are with reference to the Figure 1. It should be understood that examples are illustrative only, and other process configurations and parameters may be suitably utilized within the scope of the invention.
In none of the examples or comparative examples was the residue obtained in step IV washed with an aqueous alkaline solution before being used in step VI.
COMPARATIVE EXAMPLE 1
This Comparative Example 1 describes an embodiment of the prior art as depicted in Figure 1 , except that both water washing section [C] and washing section [E] would be absent from Figure 1 for Comparative Example 1 .
In oxidation section [A], which consists of six reactors in-series, liquefied cyclohexane that was introduced via line [1 ] was oxidized with air that was introduced via line [2]. The temperature and pressure in this oxidation section were about 165 °C and 1 .2 MPa respectively. In the oxidation section no catalyst was added to the reaction mixture. The obtained oxidation mixture comprised cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide and as a by-products cyclohexane. This was cooled down via heat exchangers and neutralized. The obtained cooled down and neutralized oxidation mixture left this section via line [3] and was fed to the
decomposition section [B], where the cyclohexyl hydroperoxide was decomposed. An aqueous NaOH solution was fed to the decomposition section [B]. After completion of the decomposition reaction, the resulting aqueous phase was separated from the decomposed reaction mixture which comprised mainly cyclohexane, cyclohexanol and cyclohexanone. The sum of the concentrations of cyclohexanone and cyclohexanol in this decomposed reaction mixture was about 3.5 wt. The organic phase obtained contained less than 50 ppm cyclohexyl hydroperoxide and less than 25 ppm esters of cyclohexanol.
The decomposed reaction mixture, having an average flow rate of about 350 m3/hr, left the decomposition section [B] via line [6]. The resulting aqueous phase with a pH value in the range of 13 to 14 (at 25 °C) was separated from the decomposed reaction mixture and was partially reused for decomposition of cyclohexyl hydroperoxide and was partially reused for the neutralization of carboxylic acids. An aqueous phase comprising neutralized organic acids left the decomposition section [B] via line [5].
Line [6] continued as line [9] due to absence of water washing section [C]. The decomposed reaction mixture that was transported via line [9] was after being heated up fed to the first distillation section [D], in which cyclohexane was recovered from the washed decomposed reaction mixture. The recovered cyclohexane left the first distillation section [D] via line [10] and was reused in oxidation section [A]. The residue comprising cyclohexanone, cyclohexanol and alkali metal salts, having an average flow rate of about 20 m3/hr, that was formed in the first distillation section [D] exits via line [1 1 ].
Line [1 1] continued as line [14] due to absence of washing section [E]. The residue comprising cyclohexanone, cyclohexanol and alkali metal salts was transported via line [14] and was fed to the second distillation section [F], in which components that are more volatile than cyclohexanone were distilled off. The second distillation section [F] consists of two distillation columns that are operated in series. In the first distillation column of the second distillation section [F] components that are reused in the cyclohexanone production process, e.g. cyclohexane, were removed overhead via line [15]. The bottom product of this column was fed to the second distillation column of the second distillation section [F]. In the second distillation column of the second distillation section [F] components that are more volatile than
cyclohexanone and that are not re-used in the cyclohexanone production process, e.g. pentanol and heptanone, were removed overhead via line [16]. The bottom product of this column was fed to the third distillation section [G] via line [17]. In the third distillation section [G] cyclohexanone was recovered as top product and exits via line [18]. The heavy phase obtained in the third distillation section [G] that comprises cyclohexanol, cyclohexanone and heavies were discharged via line [19] and was fed to the fourth distillation section [H]. In the fourth distillation section [H] a flow comprising mainly cyclohexanol and a residue flow, in which the heavies are concentrated, was obtained, which exited this section via lines [21] and line [20], respectively. The flow that comprised mainly cyclohexanol was fed to dehydrogenation section [I] in which part of the cyclohexanol was converted into cyclohexanone and hydrogen gas. A hydrogen gas comprising flow exits the dehydrogenation section [I] via line [22]. The remaining reaction mixture exits the dehydrogenation section [I] via line [23] and was fed the second distillation column of the second distillation section [F].
The residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D] and exited via line [1 1] comprised: Cyclohexanone ca. 42 wt. %
Cyclohexanol ca. 28 wt. %
Cyclohexane ca. 29 wt. %
Sodium salts ca. 150 ppm (only Na)
The content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was on average about 190 ppm (only Na). COMPARATIVE EXAMPLE 2
This Comparative Example 2 utilizes an embodiment of the prior art as depicted in Figure 1 except that washing section [E] would be absent from Figure 1 for Comparative Example 2.
The experiment described in Comparative Example 1 was repeated, the sole difference being that now water washing section [C] was in operation.
The decomposed reaction mixture left the decomposition section [B] via line [6] and was fed to washing section [C]. In washing section [C] the decomposed reaction mixture was washed with water that was fed via line [7] at a pressure of about 0.7 MPa. The aqueous phase that was produced in the washing section [C] left this section via line [8]. The obtained washed decomposed reaction mixture left the washing section [C] via line [9] and is after being heated up was fed to the first distillation section [D], in which cyclohexane is was recovered from the washed decomposed reaction mixture.
The residue comprising cyclohexanone, cyclohexanol and alkali metal salts, that was formed in the first distillation section [D] and exited via line [1 1] comprised:
Cyclohexanone ca. 42 wt. %
Cyclohexanol ca. 28 wt. %
Cyclohexane ca. 29 wt. %
Sodium salts ca. 20 ppm (only Na)
The content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was on average about 27 ppm (only Na).
EXAMPLE 1 This example 1 describes an embodiment of the invention as depicted in Figure 1 except that water washing section [C] is absent from Figure 1 for Example 1.
The experiment described in Comparative Example 1 was repeated, the sole difference being that now washing section [E] was in operation. Washing section [E] comprised a packed column.
Residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D] was fed to washing section [E] via line [1 1]. The residue comprising cyclohexanone, cyclohexanol and alkali metal salts was fed to the bottom section of the packed column for a washing step. To the top section of the packed column about 50 wt. % water relative to the residue comprising cyclohexanone, cyclohexanol and alkali metal salts was fed via line [12] at atmospheric pressure. The water phase that was obtained after this washing exited from the bottom of the packed column via line [13] and was partly used for the preparation of aqueous NaOH solution that was charged to the decomposition section [B]. The obtained washed residue comprising cyclohexanone, cyclohexanol and alkali metal salts exited from the top section of the packed column and was fed to the first distillation column in the second distillation section [F] via line [14].
In the first distillation section [D] about 98 % by weight of the cyclohexane is removed from the organic phase resulting from the decomposition section [B].
The residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D] and exited via line [1 1] comprised:
Cyclohexanone ca. 42 wt. %
Cyclohexanol ca. 28 wt. %
Cyclohexane ca. 29 wt. %
Sodium salts ca. 150 ppm (only Na) The obtained washed residue comprising cyclohexanone,
cyclohexanol and alkali metal salts exited from the top section of the packed column contained on average less than 10 ppm alkali metal salts.
The content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was on average about 12 ppm (only Na).
The amount of water used for the washing step in washing section [E] was 0.71 kg water / kg cyclohexanone and cyclohexanol in the residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D].
Example 1 in comparison to Comparative Example 1 clearly shows that by introducing washing section [E] containing a single washing step the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was reduced from on average about 190 ppm to on average about 12 ppm (only Na). So, due to the introduction of washing section [E] the reduction of the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was more than 93%.
Figure imgf000019_0001
cyclohexane is removed from the organic phase resulting from the decomposition section [B].
The residue comprising cyclohexanone, cyclohexanol and alkali metal salts, that was formed in the first distillation section [D] and exited via line [1 1] comprised:
Cyclohexanone ca. 42 wt. %
Cyclohexanol ca. 28 wt. %
Cyclohexane ca. 29 wt. %
Sodium salts ca. 20 ppm (only Na)
The obtained washed residue comprising cyclohexanone,
cyclohexanol and alkali metal salts exited from the top section of the packed column contained on average less than 10 ppm alkali metal salts.
The content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section was on average about 2 ppm (only Na).
The amount of water used for the washing step in washing section [E] was 0.71 kg water / kg cyclohexanone and cyclohexanol in the residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D]. Example 2 in comparison to Comparative Example 2 clearly shows that by introducing washing section [E] containing a single washing step the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was reduced from on average about 27 ppm to on average about 2 ppm (only Na). So, due to the introduction of washing section [E] the reduction of the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was more than 92%.
EXAMPLE 3
This example 3 describes an embodiment of the invention as depicted in Figure 1 .
The experiment described in Example 2 was repeated, the sole difference being that now the washing section [E] contained two washing steps in- series. The first washing step comprised a mixer-settler and the second washing step comprised a packed column.
Residue comprising cyclohexanone, cydohexanol and alkali metal salts that were formed in the first distillation section [D] were fed to washing section [E] via line [1 1 ]. In the first washing step about 27 wt. % water relative to the amount of residue comprising cyclohexanone, cydohexanol and alkali metal salts that was formed in the first distillation section [D] was fed via line [12] at atmospheric pressure. The water phase that was obtained after separating of the water phase and the washed residue comprising cyclohexanone, cydohexanol and alkali metal salts was exited. The washed residue comprising cyclohexanone, cydohexanol and alkali metal salts obtained in the first washing step was fed to the bottom section of the packed column for a second washing step. To the top section of this packed column about 50 wt. % water relative to the residue comprising cyclohexanone, cydohexanol and alkali metal salts was fed via line [12] at atmospheric pressure. The water phase that is obtained after this washing exited from the bottom of the packed column. Both water phases that were obtained after the washings were exited via line [13] and were partly used for the preparation of aqueous NaOH solution that was charged to the decomposition section [B]. The obtained washed residue comprising cyclohexanone, cydohexanol and alkali metal salts exited from the top section of the packed column and was fed to the first distillation column in the second distillation section [F] via line [14].
In the first distillation section [D] about 98 % by weight of the cyclohexane is removed from the organic phase resulting from the decomposition section [B]. The residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D] and exited via line [1 1] comprised:
Cyclohexanone ca. 42 wt. %
Cyclohexanol ca. 28 wt. %
Cyclohexane ca. 29 wt. %
Sodium salts ca. 20 ppm (only Na)
The obtained washed residue comprising cyclohexanone,
cyclohexanol and alkali metal salts exited from the top section of the packed column contained on average less than 10 ppm alkali metal salts.
The content of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was on average less than 1 ppm (only Na).
The amounts of water used for the first and second washing step in washing section [E] were about 0.39 and 0.71 kg water / kg cyclohexanone and cyclohexanol in the residue comprising cyclohexanone, cyclohexanol and alkali metal salts that was formed in the first distillation section [D], respectively.
Example 3 in comparison to Comparative Example 2 clearly shows that by introducing washing section [E] contained two washing steps in- series the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was reduced from on average about 27 ppm to on average less than 1 ppm (only Na). So, due to the introduction of washing section [E] the reduction of the amount of sodium salts in the bottom flow that exited the first distillation column in the second distillation section [F] was more than 96%.

Claims

A continuous process for the production of purified cyclohexanone which comprises the following steps:
I. oxidation of cyclohexane in a liquid phase with an oxygen containing gas forming cyclohexyl hydroperoxide, cyclohexanone, cyclohexanol, esters of cyclohexanol and carboxylic acids;
II. decomposition of the cyclohexyl hydroperoxide produced in step I in the presence of an aqueous alkaline solution resulting in an organic phase comprising cyclohexane, cyclohexanone and cyclohexanol and an aqueous phase;
III. separation of the organic phase and the aqueous phase produced in step II;
IV. removal of cyclohexane from the organic phase obtained in step III, resulting in a residue comprising cyclohexanone, cyclohexanol and alkali metal salts;
V. removal of alkali metal salts by washing the residue obtained in step IV with water:
VI. removal of components with a boiling point lower than that of
cyclohexanone from the residue obtained in step V, resulting in a residue comprising cyclohexanone and cyclohexanol;
VII. recovery of cyclohexanone from the residue obtained in step VI,
resulting in a residue comprising cyclohexanol;
wherein
a) the organic phase obtained in step III contains less than 50 ppm
cyclohexyl hydroperoxide and less than 25 ppm esters of cyclohexanol; b) the residue obtained in step V after washing with water contains less than 10 ppm alkali metal salts.
c) at least 75 % by weight of the cyclohexane is removed in step IV from the organic phase; and
d) the residue obtained in step IV is not washed with an aqueous alkaline solution before being used in step VI.
Process according to claim 1 wherein the oxygen containing gas is air, enriched air or diluted air.
Process according to anyone of the preceding claims comprising an additional step lb where the liquid phase obtained in step I is washed with water. Process according to claim 3 comprising an additional step lc where the liquid phase obtained in step I is then treated in a separate neutralization step wherein at least a portion of the acids present in the oxidation mixture are neutralized.
Process according to anyone of the preceding claims, wherein the aqueous alkaline solution used in step II has a hydroxide content of more than 0.01 mol per kg water.
Process according to anyone of the preceding claims wherein the removal of cyclohexane from the organic phase in step IV is done by distillation.
Process according to anyone of the preceding claims wherein the amount of water that is fed in step V for removal of alkali metal salts by washing the residue obtained in step IV with water is between 5 wt. % and 300 wt. % relative to the residue obtained in step IV.
Process according to anyone of the preceding claims wherein the washing in step V for removal of alkali metal salts by washing the residue obtained in step IV consists of 2 washing steps in-series.
Process according to claim 6 wherein the washing in step V for removal of alkali metal salts by washing the residue obtained in step IV is performed in a counter current mode.
Process according to anyone of the preceding claims wherein at least 90 % by weight of the alkali metals salts in the residue obtained in step IV are removed in step V by washing the residue obtained in step IV with water.
Process according to anyone of the preceding claims wherein step V is carried out at a pressure in the range of from about 0.05 MPa to about 0.5 MPa. Process according to anyone of the preceding claims wherein step V is carried out at atmospheric pressure.
Process according to anyone of the preceding claims wherein at least a part of the aqueous phase obtained in step V is used to produce a fresh alkaline solution that is used in step II for the decomposition of the cyclohexyl hydroperoxide produced in step I.
Process according to anyone of the claims 1 to 10, wherein the complete aqueous phase obtained in step V is used to produce a fresh alkaline solution that is used in step II for the decomposition of the cyclohexyl hydroperoxide produced in step I.
Process according to anyone of the preceding claims wherein the removal of components with a boiling point lower than that of cyclohexanone from the washed residue obtained in step V is done by distillation. Process according to anyone of the preceding claims wherein the recovery of cyclohexanone from the residue obtained in step VI is done by distillation. Process according to anyone of the preceding claims wherein the
cyclohexanone recovered in step VII is pure.
PCT/EP2014/064937 2013-07-22 2014-07-11 Continuous process for the production of purified cyclohexanone WO2015010928A1 (en)

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EP3388409A4 (en) * 2015-12-07 2019-07-24 UBE Industries, Ltd. Ketone and/or alcohol production method, and system for same
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