The invention generally relates to an improved catalytic process for decomposing alkyl or aromatic hydroperoxides to form a mixture containing the corresponding alcohol and ketone. In particular, the invention relates to decomposing a hydroperoxide by contacting it with a catalytic amount of a heterogenous catalyst of Au or Ag.

Industrial processes for the production of mixtures of cyclohexanol and cyclohexanone from cyclohexane are currently of considerable commercial significance and are well described in the patent literature. In accordance with typical industrial practice, cyclohexane is oxidized to form a reaction mixture containing cyclohexyl hydroperoxide (CHHP). The resulting CHHP is decomposed, optionally in the presence of a catalyst, to form a reaction mixture containing cyclohexanol and cyclohexanone. In the industry, such a mixture is known as a K/A (ketone/alcohol) mixture, and can be readily oxidized to produce adipic acid, which is an important reactant in processes for preparing certain condensation polymers, notably polyamides. Due to the large volumes of adipic acid consumed in these and other processes, improvements in processes for producing adipic acid and its precursors can be used to provide beneficial cost advantages.

Druliner et al., U.S. Patent No. 4,326,084, disclose an improved catalytic process for oxidizing cyclohexane to form a reaction mixture containing CHHP, and for subsequently decomposing the resulting CHHP to form a mixture containing K and A. The improvement involves the use of certain transition metal complexes of 1,3-bis(2-pyridylimino)isoindolines as catalysts for cyclohexane oxidation and CHHP decomposition. According to this patent, these catalysts demonstrate longer catalyst life, higher CHHP conversion to K and A, operability at lower temperatures (80-160°C), and reduced formation of insoluble metal-containing solids, relative to results obtained with certain cobalt(II) fatty acid salts, e.g., cobalt 2-ethylhexanoate.

Druliner et al., U.S. Patent No. 4,503,257, disclose another improved catalytic process for oxidizing cyclohexane to form a reaction mixture containing CHHP, and for subsequently decomposing the resulting CHHP to form a mixture containing K and A. This improvement involves the use of Co₃O₄, MnO₂, or Fe₃O₄ applied to a suitable solid support as catalysts for cyclohexane oxidation and CHHP decomposition at a temperature from about 80°C to about 130°C, in the presence of molecular oxygen.

Sanderon et al., U.S. Patent No. 5,414,163, discloses a process for preparing t-butyl alcohol from t-butyl hydroperoxide in the liquid phase over catalytically effective amounts of titania, zirconia, or mixtures thereof.

Sanderson et al., U.S. Patent Nos. 5,414,141, 5,399,794 and 5,401,889, disclose a process for preparing t-butyl alcohol from t-butyl hydroperoxide in the liquid phase over catalytically effective amounts of palladium with gold as a dispersing agent supported on alumina.

Druliner et al., U.S. provisional application 60/025,368 filed September 3, 1996 (now PCT US97/15332 filed September 2, 1997), disclose decomposing a hydroperoxide by contacting it with a catalytic amount of a heterogenous catalyst of Zr, Nb, Hf and Ti hydroxides or oxides. Preferably, the catalyst is supported on SiO₂, Al₂O₃, carbon or TiO₂.

US 3941845 (Voskuil et al.) discloses a process for the decomposition of cycloalkylperoxides using a heterogenous catalyst that comprises copper oxide. Preferably copper-chromium-oxide is applied as a catalyst.

EP 659726 (DSM N.V.) discloses a process for the decomposition of cycloalkylperoxides using a heterogenous catalyst that is a metal compound immobilized on a carrier material. The metal of the catalyst is selected from Mn, Fe, Co, Ni and Cu. The metal compound is usually a metal oxide compound.

Further improvements and options are needed for hydroperoxide decomposition to K/A mixtures in order to overcome the deficiencies inherent in the prior art. Other objects and advantages of the present invention will become apparent to those skilled in the art upon reference to the detailed description which hereinafter follows.

In accordance with the present invention, an improved process is provided in which a hydroperoxide is decomposed to form a decomposition reaction mixture containing a corresponding alcohol and ketone. The improvement comprises decomposing hydroperoxide by contacting a hydroperoxide with a catalytic amount of a heterogenous catalyst selected from the group consisting of Au (gold) and Ag (silver). Moreover, the catalysts are optionally supported on a suitable support member, such as SiO₂, Al₂O₃, carbon, zirconia, MgO or TiO₂.

The present invention provides an improved process for conducting a hydroperoxide decomposition step in an industrial process in which an alkyl or aromatic compound is oxidized to form a mixture of the corresponding alcohol and ketone. In particular, cyclohexane can be oxidized to form a mixture containing cyclohexanol (A) and cyclohexanone (K). The industrial process involves two steps: first, cyclohexane is oxidized, forming a reaction mixture containing CHHP; second, CHHP is decomposed, forming a mixture containing K and A. As previously mentioned, processes for the oxidation of cyclohexane are well known in the literature and available to those skilled in the art.

Advantages of the present heterogenous catalytic process, relative to processes employing homogenous metal catalysts, such as metal salts or metal/ligand mixtures, include longer catalyst life, improved yields of useful products, and the absence of soluble metal compounds.

The improved process can also be used for the decomposition of other alkane or aromatic hydroperoxides, for example, t-butyl hydroperoxide, cyclododecylhydroperoxide and cumene hydroperoxide.

The CHHP decomposition process can be performed under a wide variety of conditions and in a wide variety of solvents, including cyclohexane itself. Since CHHP is typically produced industrially as a solution in cyclohexane from catalytic oxidation of cyclohexane, a convenient and preferred solvent for the decomposition process of the invention is cyclohexane. Such a mixture can be used as received from the first step of the cyclohexane oxidation process or after some of the constituents have been removed by known processes such as distillation or aqueous extraction to remove carboxylic acids and other impurities.

The preferred concentration of CHHP in the CHHP decomposition feed mixture can range from about 0.5% by weight to 100% (i.e., neat). In the industrially practiced route, the preferred range is from about 0.5% to about 3% by weight.

Suitable reaction temperatures for the process of the invention range from about 80°C to about 170°C. Temperatures from about 110°C to about 130°C are typically preferred. Reaction pressures can preferably range from about 69 kPa to about 2760 kPa (10-400 psi) pressure, and pressures from about 276 kPa to about 1380 kPa (40-200 psi) are more preferred. Reaction time varies in inverse relation to reaction temperature, and typically ranges from about 2 to about 30 minutes.

The inventive process may also be performed using Au or Ag in the presence of other metals (e.g., Pd). The metal to support percentage can vary from about 0.01 to about 50 percent by weight, and is preferably about 0.1 to about 10 wt, percent. Suitable, presently preferred supports include SiO₂ (silica), Al₂O₃ (alumina), C (carbon), TiO₂ (titania), MgO (magnesia) or ZrO₂ (zirconia). Zirconia is a particularly preferred support, and Au supported on zirconia is a particularly preferred catalyst of the invention.

Some of the heterogenous catalysts of the invention can be obtained already prepared from manufacturers, or they can be prepared from suitable starting materials using methods known in the art. Supported gold catalysts can be prepared by any standard procedure known to give well-dispersed gold, such as evaporative techniques or coatings from colloidal dispersions.

In particular, ultra-fine particle sized gold is preferred. Such small particulate gold (often smaller than 10nm) can be prepared according to Haruta, M., "Size-and Support-Dependency in the Catalysis of Gold", Catalysis Today 36 (1997) 153-166 and Tsubota et al., Preparation of Catalysts V, pp. 695-704 (1991). Such gold preparations produce samples that are purple-pink in color instead of the typical bronze color associated with gold and result in highly dispersed gold catalysts when placed on a suitable support member. These highly dispersed gold particles typically are from about 3nm to about 15nm in diameter.

The catalyst solid support, including SiO₂, Al₂O₃, carbon, MgO, zirconia, or TiO₂, can be amorphous or crystalline, or a mixture of amorphous and crystalline forms. Selection of an optimal average particle size for the catalyst supports will depend upon such process parameters as reactor residence time and desired reactor flow rates. Generally, the average particle size selected will vary from about 0.005 mm to about 5 mm. Catalysts having a surface area larger than 10 m²/g are preferred since increased surface area of the catalyst has a direct correlation with increased decomposition rates in batch experiments. Supports having much larger surface areas can also be employed, but inherent brittleness of high-surface area catalysts, and attendant problems in maintaining an acceptable particle size distribution, will establish a practical upper limit upon catalyst support surface area.

In practice of the invention, the catalysts can be contacted with CHHP by formulation into a catalyst bed, which is arranged to provide intimate contact between catalysts and reactants. Alternatively, catalysts can be slurried with reaction mixtures using techniques known in the art. The process of the invention is suitable for batch or for continuous CHHP decomposition processes. These processes can be performed under a wide variety of conditions.

Adding air or a mixture of air and inert gases to CHHP decomposition mixtures provides higher conversions of process reactants to K and A, since some cyclohexane is oxidized directly to K and A, in addition to K and A being formed by CHHP decomposition. This ancillary process is known as "cyclohexane participation", and is described in detail in Druliner et al., U.S. Patent No. 4,326,084, the entire contents of which are incorporated by reference herein.

The process of the present invention is further illustrated by the following non-limiting examples. In the examples, all temperatures are in degrees Celsius and all percentages are by weight unless otherwise indicated.

5 g of 20-35 mesh (0.5-0.85 mm) charcoal carbon (EM Science, Cherry Hill, NJ) was calcined in flowing helium (100 mL/min) at 400°C for 1 hour. This material was then slurried into a solution of 0.1 g gold trichloride in 10 mL water containing 1 mL concentrated HCI. The slurry was stirred for 15 minutes at room temperature and then evaporated to dryness on a rotary evaporator. The recovered solid was calcined in flowing nitrogen (100 mL/min) at 400°C for 1 hour, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

5 g of + 8 mesh silica gel with surface area 300 m²/g and pore volume 1 cc/g (Alfa Aesar, Ward Hill, MA) was calcined in flowing helium (100 mL/min) at 400°C for 1 hour. This material was then slurried into a solution of 0.1 g gold trichloride in 10 mL water containing 1 mL concentrated HCI. The slurry was stirred for 15 minutes at room temperature and then evaporated to dryness on a rotary evaporator. The recovered solid was calcined in flowing nitrogen (100 mL/min) at 400°C for 1 hour, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

5 g of <2 micron silica gel with surface area 450 m²/g and pore volume 1.6 cc/g (Alfa Aesar, Ward Hill, MA) was calcined in flowing helium (100 mL/min) at 400°C for 1 hour. This material was then slurried into a solution of 1.0 g gold trichloride in 10 mL water containing 1 mL concentrated HCl. The slurry was stirred for 15 minutes at room temperature and then evaporated to dryness on a rotary evaporator. The recovered solid was calcined in flowing nitrogen (100 mL/min) at 400°C for 1 hour, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

5 g of + 8 mesh silica gel with surface area 300 m²/g and pore volume 1 cc/g (Alfa Aesar, Ward Hill, MA) was calcined in flowing helium (100 mL/min) at 400°C for 1 hour. This material was then slurried into a solution of 10 mL water containing 1 mL concentrated HCl. The slurry was stirred for 15 minutes at room temperature and then evaporated to dryness on a rotary evaporator. The recovered solid was calcined in flowing nitrogen (100 mL/min) at 400°C for 1 hour, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

5 g of 6-12 mesh α-alumina spheres (Calsicat, Erie, PA) was slurried into a solution of 0.1 g gold trichloride in 10 mL water containing 1 mL concentrated HCl. The slurry was stirred for 15 minutes at room temperature and then evaporated to dryness on a rotary evaporator. The recovered solid was calcined in flowing nitrogen (100 mL/min) at 400°C for 1 hour, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

5 g of + 8 mesh silica gel with surface area 300 m²/g and pore volume 1 cc/g (Alfa Aesar, Ward Hill, MA) was calcined in flowing helium (100 mL/min) at 400°C for 1 hour. This material was then slurried into a solution of 1.0 g silver nitrate in 10 mL water containing 1 mL concentrated HNO3. The slurry was stirred for 15 minutes at room temperature and then evaporated to dryness on a rotary evaporator. The recovered solid was calcined in flowing nitrogen (100 mL/min) at 400°C for 1 hour, cooled to 200°C and calcined another 1 hour in flowing hydrogen (100 mL/min) and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

10 g of powdered- 200 mesh MgO (Alfa Aesar, Ward Hill, MA) was slurried into a solution of 0.2 g gold trichloride in 50 mL water containing 1 mL concentrated HCl. The pH of the slurry was adjusted to 9.6 with sodium carbonate solution and then 0.69 g sodium citrate was added. After stirring for 2 hours at room temperature the solid was recovered by filtration and washed well with distilled water. The recovered solid was calcined in flowing air (100 mL/min) at 250°C for 5 hour, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

10 g of powdered - 60 mesh γ-alumina (Alfa Aesar, Ward Hill, MA) was slurried into a solution of 0.2 g gold trichloride in 50 mL water containing 1 mL concentrated HCI. The pH of the slurry was adjusted to 9.6 with sodium carbonate solution and then 0.69 g sodium citrate was added. After stirring for 2 hours at room temperature the solid was recovered by filtration and washed well with distilled water. The recovered solid was calcined in flowing air (100 mL/min) at 250°C for 5 hours, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst. The resulting catalyst was purple/pink in color and had a gold particle size of 8nm as determined by x-ray diffraction (XRD).

10 g of silica + 8 mesh granules (Alfa Aesar, Ward Hill, MA) was slurried into a solution of 0.2 g gold trichloride in 50 mL water containing 1 mL concentrated HCI. The pH of the slurry was adjusted to 9.6 with sodium carbonate solution and then 0.69 g sodium citrate was added. After stirring for 2 hours at room temperature the solid was recovered by filtration and washed well with distilled water. The recovered solid was calcined in flowing air (100 mL/min) at 250°C for 5 hours, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

10 g of powdered - 325 mesh titania (Alfa Aesar, Ward Hill, MA) was slurried into a solution of 0.2 g gold trichloride in 50 mL water containing 1 mL concentrated HCI. The pH of the slurry was adjusted to 7.0 with sodium carbonate solution and then 1.5 g sodium citrate was added. After stirring for 2 hours at room temperature the solid was recovered by filtration and washed well with distilled water. The recovered solid was calcined in flowing air (100 mL/min) at 400°C for 5 hours, cooled and then stored in tightly capped vial for testing as a CHHP decomposition catalyst.

10g - 325 mesh zirconia (Calsicat #96F-88A, Erie, PA) was slurried into a solution of 0.2g gold chloride in 50mL water and 1 drop conc. HCI. The slurry was stirred gently as the pH was adjusted to 9.6 with 0.1M sodium carbonate solution. The slurry was stirred gently while 0.69g sodium citrate solid was slowly added and then stirred for 2 further hours. After filtering and washing well with distilled water, the solid was calcined in flowing air for 5 hours at 250°C.

10g - 60 mesh γ-alumina was slurried into a solution of 0.2g gold and 0.02g palladium tetraamine chloride in 50mL water and one drop of conc. HCl. The slurry was stirred gently as the pH was adjusted to 9.6 with 0.1M sodium carbonate solution. The slurry was again stirred gently while 0.69g sodium citrate solid was slowly added and then stirred for 2 further hours. After filtering and washing well with distilled water, the solid was calcined in flowing air for 5 hours at 250°C.

All reactions were run in batch reactor mode, in stirred 3.5 mL glass vials, sealed with septa and plastic caps. Vials were inserted into a block aluminum heater/stirrer apparatus that holds up to 8 vials. Stirring was done using Teflon®-coated stir bars. Each vial was first charged with 1.5 mL of n-octane or undecane solvent, approximately 0.005 or 0.01 g of a given crushed catalyst, a stir bar and the vial was sealed. Vials were stirred and heated approximately 10 minutes to assure that the desired reaction temperature of 125°C had been attained. Next, at the start of each example, 30 µL of a stock solution of CHHP and TCB(1,2,4-trichlorobenzene) or CB (chlorobenzene), GC (gas chromatograph) internal standard, were injected. Stock solutions consisted of mixtures of about 20 wt% TCB or CB in CHHP. The CHHP source contained up to 2.0 wt% of combined cyclohexanol and cyclohexanone. Vials were removed from the aluminum heater/stirrer after a 0.5 to 10 minute period and were allowed to cool to ambient temperature.

In Examples 1-9 (Table I) vials were analyzed directly for the amount of CHHP remaining, using a 15 m DB-17 capillary column with a 0.32 mm internal diameter. The liquid phase of the column was comprised of (50 wt% phenyl) methyl polysiloxane. The column was obtained from J. and W. Scientific, Folsum, California.

GC analyses for the amounts of CHHP in each solution were calculated using the equation:$${\text{wt. \% CHHP = (area \% CHHP/area \% TCB) x wt. \% TCB x R.F.}}_{\text{CHHP}}$$

R.R._CHHP (GC response factor for CHHP) was determined from calibration solutions containing known amounts of CHHP and TCB, and was calculated from the equation:$${\text{R.F.}}_{\text{CHHP}}\text{=}\frac{\text{wt. \% CHHP/area \% CHHP}}{\text{wt. \% TCB/are \% TCB}}$$$$\begin{gathered} \text{\% CHHP Decomp. = 100 x [1-(area \% CHHP/area \% TCB) final/} \\ \text{(area \% CHHP/area \% TCB initial]} \end{gathered}$$

In Examples 1-9 (Table I) the initial concentrations of CHHP in each vial were approximately 2.2 wt %. The GC wt % CHHP_initial and CHHP_final numbers are only approximate because the amount of TCB per g solution ratios used in GC calculations were arbitrarily all made equal to 0.25 mg TCB/ g solution. Since an unheated sample of 1.5 mL n-octane and 30 µL CHHP/TCB solution was analyzed with each set of CHHP decomposition product vials made from the same CHHP/TCB solution, accurate changes in CHHP/TCB ratios could be calculated.

Examples 10-12 (Table II), and Examples 13-15 (Table III), give batch % t-butylhydroperoxide (t-BuOOH) and % cumenehydroperoxide (CumeneOOH) decomposition results, respectively for 1 % Au/Carbon and 10 % Au/SiO₂ catalysts. Analyses for t-BuOOH and CumeneOOH were done using a well known iodometric titration procedure, described in Comprehensive Analytical Chemistry, Elsevier Publishing Company, New York, Eds. C. L. Wilson, p. 756, 1960. Starting and product solutions of t-BuOOH and CumeneOOH in n-octane, followed by adding excess KI/ acetic acid solution, were stirred in sealed vials at ambient temperature for 10 minutes and were titrated with 0.1 M Na₂S₂O₃ solution for amounts of I₂ liberated by the t-BuOOH and CumeneOOH present.

Examples 16-21 (Table IV) were run as described for Examples 1-9 except that the reaction was run at 150°C and chlorobenzene was used as a GC internal standard in place of TCB and undecane was used in place of n-octane solvent. In Table IV, the amount of initial CHHP and final CHHP in the reaction was determined by calculating the area of the CHHP GC peak divided by the area of the chlorobenzene GC peak (area % CHHP/area % CB). EX. Catalyst Method of Prep Approx. Wt% CHHP Reaction Temp., °C Time, min. Wt% CHHP initial Wt% CHHP final % CHHP Decomp. 1 1.4% Au/Carbon, 0.0100 Exp. 1 2.2 125 10 0.407 0.221 45.7 2 1.4% Au/Carbon, 0.0103 Exp. 1 2.2 125 10 0.537 0.281 47.7 3 1.4% Au/SiO₂, 0.0101 Exp. 2 2.2 125 10 0.407 0.391 3.9 4 1.4% Au/SiO₂, 0.0101 Exp. 2 2.2 125 10 0.537 0.430 19.9 5 14% Au/SiO₂, 0.0102 Exp. 3 2.2 125 10 0.407 0.154 62.2 6 14% Au/SiO₂, 0.0104 Exp. 3 2.2 125 10 0.407 0.131 67.8 7 0% Au/SiO₂, 0.0103 Exp. 4 2.2 125 10 0.407 0.379 6.9 8 1.4% Au/Al₂O₃, 0.0102 Exp. 5 2.2 125 10 0.537 0.449 16.4 9 13% Ag/SiO₂,0.0102 Exp. 6 2.2 125 10 0.407 0.245 39.8 EX. Catalyst, g Method of prep. Reaction Temp., °C Time, min. Wt% t-BuOOH initial Wt% t-BuOOH final % t-BuOOH Decomp. 10 1.4% Au/Carbon, 0.0102 Exp. 1 125 10 0.35 0.20 44 11 14%Au/SiO₂, 0.0102 Exp. 3 125 10 0.35 0.18 48 12 none 125 10 0.35 0.33 5 EX. Catalyst, g Method of prep. Reaction Temp., °C Time, min. Wt% t-Cumene-(OOH) initial Wt% t-Cumene-(OOH) final % t-Cumene-(OOH) Decomp. 13 1.4% Au/Carbon, 0.0103 Exp. 1 125 10 0.55 0.32 42 14 14% Au/SiO₂, 0.0103 Exp. 3 125 10 0.55 0.30 45 15 none 125 10 0.55 0.54 2 EX. Catalyst Method of Prep Approx. Wt% CHHP Reaction Temp., °C Time, min. CHHP/ CB initial CHHP/ CB final % CHHP Decomp. 16 1%Au/MgO, 0.0102 Exp.8 2.2 150 5 3.41 329 3.5 17 1%Au/γ-Al₂O₃, 0.0120 Exp.9 2.2 150 5 3.41 0 100 18 1%Au/SiO₂, 0.0101 Exp. 10 2.2 150 5 3.41 0.91 73.3 19 1%Au/TiO₂, 0.0106 Exp. 11 2.2 150 5 3.41 2.16 33.6 20 1% Au/ZrO₂, 0.0054 Exp. 12 2 150 0.5 5.26 4.68 11.1 21 1% Au, 0.1% Pd/Al₂O₃, 0.0051 Exp. 13 2 150 0.5 4.82 3.01 37.5