Classifications

• • 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
  • C07C45/27—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation
  • C07C45/32—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen
  • C07C45/33—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by oxidation with molecular oxygen of CHx-moieties
• • 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

Definitions

• the invention is directed to a process for preparing a mixture comprising cyclohexanol and cyclohexanone.
• Cyclohexanol and cyclohexanone can be commercially produced from cyclohexane in a two-step process.
• the first step is oxidation of cyclohexane by an oxygen-containing gas to produce a mixture comprising cyclohexanol,
• cyclohexanone and cyclohexyl hydroperoxide Conventionally, in this first step cyclohexane is oxidized in the liquid phase with air. On an industrial scale, this oxidation is normally conducted either uncatalysed or catalysed with a soluble cobalt catalyst, in one or more reactors at temperatures in the range of 130-200 °C. The vapourised cyclohexane and other products in the gaseous effluent are condensed and recovered, and the off-gases leave the system.
• the product mixture is recovered from the liquid effluent from the reactor or reactors, and the unreacted cyclohexane is recycled (Kirk-Othmer, Encyclopedia of Chemical Technology, John Wiley & Sons, New York, 1979, 3 rd Edition, Vol. 7, pp. 410-416; and Ullmanns, Encyklopadie der Technischen Chemie, Verlag Chemie, Weinheim, 1975, 4 th Edition, Vol. 9, pp.
• the first step (oxidation) occurs in an oxidation section, wherein the reaction (I) occurs.
• the produced oxidized reaction mixture consists of cyclohexanol, cyclohexanone, cyclohexyl hydroperoxide, unreacted cyclohexane and some minor byproducts.
• this oxidized reaction mixture is decomposed in the presence of a hydroxide ion-containing phase and a cobalt catalyst, according to reaction (II) in a decomposition section to form a decomposed reaction mixture.
• the hydroxide ions also act to neutralize acid byproducts (not depicted).
• the reactions (I) and (II) are depicted here as unbalanced equations.
• the byproducts produced in reaction (I) and in reaction (II) are in general different regarding composition, concentrations and quantities.
• EP0579323 describes such a process, wherein the oxidized reaction mixture leaving the oxidation section is cooled by at least 10 °C, preferably at least 30 °C, before allowing the cyclohexyl hydroperoxide to decompose.
• Cyclohexyl hydroperoxide decomposition is effected after cooling, under the influence of a transition metal-containing catalyst. Cooling can be effected by means of heat exchangers or by expansion.
• the decomposed reaction mixture passes to a distillation section, where heat is necessarily applied to remove cyclohexane by distillation of the decomposed reaction mixture. Therefore energy is applied to the system.
• the present inventors have recognized that at least some energy removed from the system on cooling the oxidized reaction mixture prior to
• decomposition may be returned to the system via the decomposed reaction mixture prior to distillation.
• the above objective can be achieved by introducing a heat exchanger into the process so that heat is transferred from the oxidized reaction mixture to the decomposed reaction mixture.
• the heat exchanger must therefore be located between the oxidation section and the decomposition section on the one hand, and between the decomposition section and distillation section on the other hand.
• the present invention provides a continuous process for the preparation of a mixture of cyclohexanone and cyclohexanol, said process comprising:
• step b) comprises
• the present invention further provides apparatus suitable for carrying out the process described above, said apparatus comprising:
• the apparatus is configured such that a reaction mixture passes in order from a) to i) to ii) to c), back through i) to d).
• the process of the present invention is particularly beneficial, because less cooling water is required to reduce the temperature of the oxidized reaction mixture between the oxidation section and the decomposition section. Further, less heat is required from outside the process to separate the cyclohexane from the reaction mixture obtained in the decomposition section in the distillation section.
• the process of the present invention additionally has the following further unexpected benefits.
• Cooling of the reaction mixture between the oxidation section and decomposition section with cooling water can lead to the problem of fouling by crystallization of organic acids, for example adipic acid and
• hydroxycaproic acid formed as byproducts, in the oxidation unit. This is caused by localized low surface temperatures in the heat exchanger, in turn caused by the relatively low temperature of cooling water.
• a first cooling step is done with the reaction mixture originating from the decomposition section. Such reaction mixture has a higher temperature than cooling water, and as a result reduces the extent of localized cooling, and therefore fouling by crystallization of organic acids.
• heat introduced to the reaction mixture after the decomposition section and/or in the distillation section is typically by means of steam.
• Said steam can cause localized hot spots in the heat exchanger, leading to the formation of byproducts (known as "heavies", for example
• the process of the present invention has the advantage not only of exchanging heat between reaction mixtures, but of doing so at a low temperature difference to avoid side effects which occur in the prior art processes.
• oxidized reaction mixture refers to the reaction mixture that has been oxidized in the oxidation section, but not yet
• oxidized is meant the reaction (I) described above has occurred. It will be understood that this term does not mean that the reaction mixture is completely oxidized.
• the oxidation section is typically a system of reactors arranged in series or in a pipe-reactor with compartments. Usually oxygen or oxygen containing gases are supplied to each reactor or reactor part. Oxidation may be catalysed or uncatalysed. Preferably, it is uncatalysed. Where oxidation is uncatalysed, the oxidation is typically carried out at a higher temperature than when catalysed.
• the temperature drop from oxidation to decomposition will typically be larger for a process involving an uncatalysed oxidation.
• the process of the present invention is therefore more beneficial for a process comprising such an uncatalysed oxidation reaction.
• oxygen-containing gas oxygen as such; air, rich or poor in oxygen; or oxygen mixed with nitrogen or another inert gas may be chosen. Air is preferred, but the air can be mixed with extra inert gas to eliminate the risk of explosions. In such a case usually so much oxygen containing gas is fed to the reactors, in such a way, that the oxygen concentration of the off-gas remains below the explosive limit.
• the term "without a transition metal-containing catalyst” means without an effective amount of such catalyst. Trace amounts of transition metal-containing catalyst could be present in the reaction mixture and have no appreciable effect. Therefore an amount of transition metal-containing catalyst which has substantially no effect on the cyclohexyl hydroperoxide fraction, may be present.
• the decomposition section comprises one or more decomposition units arranged in series.
• a decomposition unit is a reactor in which the reaction (II) above is carried out.
• the term decomposed reaction mixture refers to the reaction mixture that has been decomposed in the decomposition section. By decomposed is meant the reaction (II) described above has occurred. It will be understood that this term does not mean that the reaction mixture is completely decomposed. By definition the decomposed reaction mixture has already undergone oxidation as described above.
• each decomposition unit is typically between 20 °C and 150 °C; preferably between 50 °C and 130 °C.
• Cyclohexyl hydroperoxide decomposition is typically effected using a transition metal-containing catalyst, for example cobalt or chromium or a mixture thereof.
• For efficiency decomposition is typically effected at a lower temperature than oxidation. This is carried out preferably as described in EP-A-004105 or EP-A-092867.
• the decomposition section may include one or more washing units.
• the decomposition section may include one or more heat exchangers.
• embodiment of the decomposition section comprises a wash unit followed by a heat exchanger followed by a wash unit.
• Cyclohexane may be removed from the decomposed reaction mixture by techniques known to the person of skill in the art. Typically cyclohexane is distilled from the reaction mixture in a distillation section.
• the distillation section typically comprises a number of distillation columns arranged in series.
• the distillation section may be preceded by partial flash evaporation of cyclohexane from the reaction mixture.
• the presence of partial flash operation has the advantage of removal of a fraction of low boiling components, including inerts, which hamper heat transfer in
• a heat exchanger is a device for transferring heat from one fluid stream to another.
• a heat exchanger may be direct (wherein the fluid streams are mixed) or indirect (wherein the fluid streams remain separated by a dividing wall).
• An in-process heat exchanger is an indirect heat exchanger wherein a process fluid from one part of the process transfers heat to a process fluid in another part of the process.
• the temperature of the oxidized reaction mixture is higher than that of the decomposed reaction mixture. In the present invention, therefore, the oxidized reaction mixture is used to heat the decomposed reaction mixture.
• the in-process heat exchanger is configured such that the oxidized reaction mixture heats the decomposed reaction mixture and the decomposed reaction mixture cools the oxidized reaction mixture.
• Indirect heat exchangers are well-known to the person of skill in the art.
• Examples of indirect heat exchangers suitable for the present invention are shell & tube, plate, and tubular.
• the indirect heat exchanger comprises a shell & tube indirect heat exchanger.
• a shell & tube indirect heat exchanger is preferred, because it is capable of handling a large flow.
• each of the oxidized reaction mixture and decomposed reaction mixture is mainly cyclohexane. Therefore, the specific heat capacity of each reaction mixture is approximately equal.
• the flow rate of the decomposed reaction mixture may be lower than that of the oxidized reaction mixture due to removal of byproducts of the oxidation and decomposition reaction (and optionally due to expansion of the oxidized reaction mixture before entering the decomposition section).
• a cooling unit is used to lower the temperature of the oxidized reaction mixture.
• the cooling unit preferably employs cooling by expansion, but cooling can also be effected by means of heat exchangers, for example by applying cooling water in an indirect heat exchanger. If expansion is applied, a portion of the
• cyclohexane is evaporated (typically with some Ci-C 6 components). Evaporated cyclohexane is preferably fed back to the oxidation section. On account of the expansion simultaneous concentration of the cyclohexyl hydroperoxide to be decomposed takes place.
• the present invention provides a process, further comprising, following step d), e) purifying said mixture of cyclohexanone and cyclohexanol. Purification is typically carried out by methods known in the art. In general purified mixtures of cyclohexanone and cyclohexanol are obtained by distillation. By distillation both components with boiling points lower than and boiling points higher than those of cyclohexanone and cyclohexanol can be removed. In addition cyclohexanol may be converted into cyclohexanone.
• T- is from 130 °C to 180 °C.
• T- is from 140 °C to 170 °C, for example 160 °C.
• T 3 is from 40 °C to 80 °C.
• T 3 is from 50 °C to 70 °C
• T 4 is from 80 °C to 130 °C.
• T 4 is from 90 °C to 1 10 °C.
• ⁇ ⁇ ⁇ T x - T y .
• ⁇ 1 2 is from 50 °C to 65 °C; more preferably ⁇ 1 2 is about 60 °C.
• a completely efficient in-process heat exchanger is one wherein the temperature of heated reaction mixture leaving the heat recovery unit is the same temperature as the hot reaction mixture entering the in-process heat exchanger.
• the advantage of such a completely efficient system is a reduction in cost of heating and cooling the system. In practice it is desirable that these temperatures are as close as possible.
• T 5 is as close as possible to T-i .
• ⁇ 1 5 is less than 10 °C; more preferably ⁇ 1 5 is less than 5 °C.
• step d) comprises distillation.
• step d) comprises optionally partial flash evaporation, followed by distillation in one or more distillation columns.
• the cyclohexane recovery section, d) typically comprises a partial flash evaporator followed by one or more distillation columns.
• a partial flash evaporator operates to remove part of the low boiling components (e.g. dissolved inerts) by evaporation.
• the cyclohexane recovery section, step d) comprises a series of distillation columns. More preferably there are three or four distillation columns.
• the distillation columns are preferably operated-in-effect.
• the vapours of the first distillation column are used to heat the second distillation column
• the vapours of the second distillation column are used to heat the third distillation column and optionally the vapours of the third distillation column are used to heat the fourth distillation column.
• the cyclohexane recovery section d) comprises a series of distillation columns which are integrated such that the overhead stream of a first distillation column is used as heat source of a second distillation column.
• FIG. 1 represents an embodiment of a prior art process, in which the present invention has not been implemented.
• Fresh cyclohexane is provided through feed (1 1 ) and cyclohexane removed in the cyclohexane recovery section (F) is provided through feed (16) into oxidation section (A) containing one or more oxidation reactors.
• Oxygen-containing gas is fed into (A) through feed (12).
• the oxidized reaction mixture comprising cyclohexanone, cyclohexanol, cyclohexyl hydroperoxide, byproducts and unreacted cyclohexane passes through feed (1 ) into cooling unit (C) which comprises one or more indirect heat exchangers.
• decomposition section (D) which comprises one or more decomposition reactors and one or more liquid/liquid phase separators.
• Aqueous caustic solution containing a transition metal-containing catalyst is passed into the decomposition section (D) through feed (13); separated aqueous phase is removed through feed (14).
• the decomposed reaction mixture is passed through feed (4) into cyclohexane recovery section (F) comprising one or more distillation columns.
• Removed cyclohexane is passed through feed (16) into oxidation section (A).
• a mixture comprising mainly cyclohexanone, cyclohexanol and cyclohexane exits through feed (15).
• FIG. 2 represents an embodiment of the process according to the present invention.
• Fresh cyclohexane is provided through feed (1 1 ) and cyclohexane removed in the cyclohexane recovery section (F) is provided through feed (16) into oxidation section (A) containing one or more oxidation reactors.
• Oxygen-containing gas is fed into (A) through feed (12).
• the oxidized reaction mixture comprising
• cyclohexanone, cyclohexanol, cyclohexyl hydroperoxide, byproducts and unreacted cyclohexane passes through feed (1 ) into in-process heat exchange unit (B), which comprises one or more in-process heat exchangers, where it is cooled.
• the cooled oxidized reaction mixture then passes through feed (2) to cooling unit (C), which comprises one or more indirect heat exchangers, where it is further cooled.
• the further cooled oxidized reaction mixture is then passed into decomposition section (D) which comprises one or more decomposition reactors and one or more liquid/liquid phase separators.
• Aqueous caustic solution containing a transition metal-containing catalyst is passed through feed (13) into the decomposition section (D); separated aqueous phase is removed through feed (14).
• the decomposed reaction mixture is passed through feed (4) into in-process heat exchange unit (B) where it is heated.
• the heated decomposed reaction mixture is passed through feed (5) into partial flash evaporation section (E), which comprises one or more flash evaporators, where a portion of low boiling components is removed by flash evaporation.
• the decomposed flashed reaction mixture is then passed through feed (6) into cyclohexane recovery section (F) comprising one or more distillation columns. Removed cyclohexane is passed through feed (16) into oxidation section (A).
• flash evaporation section (E) is bypassed and the heated decomposed reaction mixture is passed through feed (5) directly into cyclohexane recovery section (F) (Not shown in Figure 2).
• a mixture comprising mainly cyclohexanone, cyclohexanol and cyclohexane exits through feed (15).
• T-i to T 5 correspond to the following points.
• T-i is the temperature of oxidized reaction mixture leaving oxidation section (A);
• T 2 is the temperature of cooled oxidized reaction mixture leaving in-process heat exchanger (B);
• T 3 is the temperature of cooled oxidized reaction mixture leaving cooling unit (C);
• T 4 is the temperature of decomposed reaction mixture leaving decomposition section (D);
• T 5 is the temperature of heated decomposed reaction mixture leaving in-process heat exchanger (B).
• the Example was carried out in an operating cyclohexanone plant.
• the data for the Comparative Example was calculated by modeling a cyclohexanone plant having the same capacity as the plant of the Example.
• a cyclohexanone plant consisting of an uncatalysed cyclohexane oxidation reaction section, a cooling unit, a decomposition section, a cyclohexane recovery section, and a cyclohexanone purification section, as described above with reference to Figure 1 , directly after cleaning of the whole plant including the reboiler of the first distillation column in the cyclohexane recovery section, is operated at an hourly mass flow of the decomposed reaction mixture leaving the decomposition section of 500 metric tons.
• the sum of weight fractions of cyclohexanol and cyclohexanone in the organic flow obtained after decomposition is maintained at 3.4 per cent.
• the oxidation section consists of five oxidation reactors in-series with air as oxygen source.
• the cooling section consists of a series of 6 shell-and-tube type indirect heat exchangers.
• the oxidized reaction mixture leaving the uncatalysed cyclohexane oxidation reaction section has a temperature of about 165 °C and a pressure of about 1 .2 MPa and flows through the inside of the tubes of the heat exchangers. Water is used as coolant and flows on the outside of the tubes of the heat exchangers of the cooling section.
• the cooled down oxidized reaction mixture leaving the cooling section is fed to the decomposition section.
• the decomposition section consists of a pre-neutralization section and a biphasic decomposition section.
• the incoming oxidized reaction mixture is washed with aqueous spent caustic recovered from the decomposition section.
• the biphasic decomposition section the washed organic phase is decomposed with an aqueous caustic solution in the presence of a Co- containing homogeneous catalyst, followed by phase separation of the obtained organic phase and aqueous spent caustic.
• the aqueous caustic flow recovered after the washing in the pre-neutralization is disposed of.
• the temperature of the organic phase increases due to the release of reaction heat of neutralization reactions and decomposition of cyclohexyl hydroperoxide.
• the temperature of the organic flow, the decomposed reaction mixture, leaving the decomposition section is maintained at about 94 °C by adjusting the water flow in the cooling section.
• the decomposed reaction mixture is fed to the cyclohexane recovery section.
• the cyclohexane recovery section consists of 3 distillation columns that are operated-in-effect.
• the vapours of the first distillation column are used to heat the second distillation column
• the vapours of the second distillation column are used to heat the third distillation column.
• the decomposed reaction mixture is fed to the first cyclohexane distillation column, which is equipped with a steam driven reboiler.
• the head pressures of these three distillation columns are approx. 0.5 MPa, 0.3 MPa, and 0.1 MPa, respectively. All these distillation columns are operated with reflux in order to recover overheads, mainly cyclohexane, with low concentrations of cyclohexanone and cyclohexanol.
• the recovered overheads are re-used in the oxidation section.
• the bottom flow of the last distillation column contains about 66% by weight cyclohexane, while the remainder mainly being cyclohexanone, cyclohexanol, lights and heavies.
• the bottom flow of the last distillation column is sent to the cyclohexanone purification section for further purification and for converting
• On/OI/CHHP sum of cyclohexanone, cyclohexanol, and cyclohexyl hydroperoxide
• the steam consumption of the reboiler of the first cyclohexane distillation column is 121.5 GJ/hr.
• fouling of this reboiler is predicted, causing energy transfer to deteriorate over time.
• the plant In order to maintain adequate operation of the plant, the plant is expected to require shutting down for approximately three weeks in every year to remove fouling from the reboiler. As a consequence of the shut downs to remove fouling a loss in the actual annual production capacity of the cyclohexanone plant of approximately 8,250 metric tons per year can be calculated.
• the amount of heat that is transferred to cooling water in the cooling section is 133.2 GJ/hr.
• a cyclohexanone plant consisting of an uncatalysed cyclohexane oxidation reaction section, an in-process heat exchanger, a cooling unit, a
• each of the in-process heat exchanger and the cooling section consist of a series of 3 shell-and-tube type indirect heat exchangers.
• the oxidized reaction mixture leaving the uncatalysed cyclohexane oxidation reaction section had a temperature of about 165 °C and a pressure of about 1 .2 MPa.
• the oxidized reaction mixture leaving the uncatalysed cyclohexane oxidation reaction section flowed around the outside of the tubes of the heat exchangers in the in-process heat exchanger.
• the decomposed reaction mixture leaving the decomposition section flowed through the inside of the tubes of the heat exchangers of the in-process heat exchanger.
• water is used as coolant and flowed on the outside of the tubes of the heat exchanger of the cooling section.
• the oxidized reaction mixture leaving the heat recovery section flowed through the inside of the tubes of the heat exchangers.
• the decomposition section consists of a pre-neutralization section and a biphasic decomposition section.
• the pre-neutralization section the incoming oxidized reaction mixture was washed with aqueous spent caustic recovered from the decomposition section.
• the biphasic decomposition section the washed organic phase was decomposed with an aqueous caustic solution in the presence of a Co- containing homogeneous catalyst, followed by phase separation of the obtained organic phase and aqueous spent caustic. The aqueous caustic flow recovered after the washing in the pre-neutralization was disposed of.
• the temperature of the organic phase increases due to the release of reaction heat of neutralization reactions and decomposition of cyclohexyl hydroperoxide.
• the temperature of the organic flow, the decomposed reaction mixture, leaving the decomposition section was maintained constant by adjusting the water flow in the cooling section.
• the decomposed reaction mixture is fed to the cyclohexane recovery section.
• the cyclohexane recovery section consists of 3 distillation columns that are operated-in-effect.
• the vapours of the first distillation column were used to heat the second distillation column, and the vapours of the second distillation column were used to heat the third distillation column.
• the decomposed reaction mixture was fed to the first cyclohexane distillation column, which is equipped with a steam driven reboiler.
• the head pressures of these three distillation columns were approx. 0.5 MPa, 0.3 MPa, and 0.1 MPa, respectively. All these distillation columns were operated with reflux in order to recover overheads, mainly cyclohexane, with low concentrations of cyclohexanone and cyclohexanol.
• the recovered overheads were re-used in the oxidation section.
• the bottom flow of the last distillation column contains about 66% by weight cyclohexane, while the remainder mainly being cyclohexanone, cyclohexanol, lights and heavies.
• the bottom flow of the last distillation column was sent or further purification and for converting cyclohexanol into

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