PROCESS AND CATALYST FOR THE CONVERSION OF CYCLOHEXANOL TO CYCLOHEXANONE

Abstract: A catalyst and a process to convert commercial cyclohexa­ nol feed to cyclohexanone at a relatively low temperature at stable conversion levels for long periods of operation. This process and catalyst allow operation in the presence of water and high boiling side products. The process features high conversion efficiency and low by-product formation, by use of an improved CuO-ZnO catalyst promoted with an alkali-metal compound such as sodium carbonate. The catalyst is stable in the presence of water and heavy end products in the feedstock (up to 13%). The presence of water rejuvenates the catalyst, increases the conversion and decreases the phenol content in the product mixture.

Description: A catalytic process, including a new catalyst, for the catalytic dehydrogenation of cyclohexanol to cyclohexanone. Industrially, cyclohexanol is converted to cyclohexanone in the presence of a copper catalyst at temperatures of 220 to 260°C or 350 to 450°C. The low temperature conversion, in the prior art results in low throughput, and the catalyst may be subject to deactivation by the water produced as a by-product of the reaction. The hydrolysis of the catalyst by the water vapour may also fracture the catalyst and build up the pressure drop. A high temperature conversion catalyst enables nearly complete conversion of cyclohexanol to cyclohexanone; however, this often causes undesired production of phenol and cyclohexene, resulting in efficiency loss. Copper oxide-zinc oxide catalysts have been reported in several literature and patent references, namely, A Sputa et al, Czechoslovakia Patent 151,166, Dec 15, 1973 (CA 80 : 145,560); Mitsubishi Chemical Industries Co., Ltd., Japanese Kokkyo Koho 80/136,241, Oct 23, 1980 (CA 94 : 156,414); R I Belskaya et al., Inst. Fiz., Org. Khom., USSR 1981 (CA 96 : 103,707); N.P. Emelyanov et al., Dokl. Akad. Nauk Beloruss. SSR 11(3), 233 (RUSS) 1967 (CA 67 : 108,283); N.P. Emelyanov et al., Dokl. Akad. Nauk Beloruss., French Patent 2,030,602, Nov. 13 1970 (CA 75 : 48,542) U.S. Patent 3,652,460, March 28, 1972 (CA 76 : 145,400) V.S. Komarov et al., Dokl, Akad. Nauk Beloruss USSR Patent 660,701, May 5, 1979 (CA 91 : 39,009); V.S. Komarov et al., Dokl. Akad. Nauk Beloruss. SU 978,909, Dec 7, 1982 (CA 98 : 160,232). Disclosures relative to adding water to the feedstock to enhance selectivity and conversion rate appear in Ruhrchemie AG British Patent 1,444,484 and UBE Industries, Ltd. Japanese Patent Kokai 73/29,742, April 19, 1973. As mentioned above, the known types of copper oxide-zinc oxide catalysts often bring about the formation of undesirable cyclohexene and phenol. Accordingly, some of these were promoted with calcium, barium-ruthenium metals to modify the catalytic properties. The above-mentioned CS-A-151166 discloses the preparation of a catalyst for the gas phase dehydrogenation of cyclohexanol which comprises adding a solution of a copper (11) salt to a soda solution, adding powdered zinc oxide with a specific surface of 40 to 80 m²/g, heating and precipitating by adding sodium hydroxide, filtering, washing and drying. The copper oxide in the catalyst is reduced to metallic copper before use. FR-E-69954 discloses a catalyst comprising a major amount of copper oxide modified by small amounts (0.3 to 0.5%) of chromium oxide, zinc oxide or an alkali metal oxide. Preferred aspects of the present invention provide an improved process for the catalytic dehydrogenation of cyclohexanol to cyclohexanone. Further preferred aspects of the invention provide an improved catalyst for the conversion of cyclohexanol to cyclohexanone . Further aspects may provide an improved low temperature catalytic conversion process for the dehydrogenation of cyclohexanol to cyclohexanone, in which the conversion is improved and by-product formation is inhibited. Preferred aspects of the invention provide such a process and catalyst in which the conversion is improved, by use of an improved catalyst which is suitable and resistant in the presence of water and heavy end products in the feedstock (up to 13%). The invention may further provide such a process in which the CuO-ZnO catalytic agent is promoted by an alkali metal compound such as sodium carbonate, bicarbonate or carboxylate. Still further aspects may provide an improved catalyst for and a process which is compatible with water. It have been discovered that a catalyst composed of copper oxide and zinc oxide promoted with an alkali metal compound such as sodium carbonate is capable of producing high conversions of cyclohexanol to cyclohexanone at a relatively low reaction temperature, without a large increase of phenol by-product and aldol condensation products. According to the present invention, there is provided a process for the catalytic dehydrogenation of cyclohexanol to cyclohexanone comprising contacting a cyclohexanol-containing feedstream with a calcined copper oxide - zinc oxide catalyst and recovering an effluent containing cyclohexanone, characterised in that the catalyst comprises copper oxide and zinc oxide which has been treated after calcination with from 0.05 to 5.0 wt.% of an alkali metal compound and in that said contacting takes place at a temperature from 200 to 320°C. The catalyst is not only stable thermally during the operation, but is also resistant to the poisonous effect of large amounts of water and high boiling products which are present in industrial cyclohexanol feedstock. Furthermore, two beneficial effects of water have been found by using the subject catalyst in a large scale pilot plant test for converting cyclohexanol into cyclohexanone. Firstly, the incorporation of the proper amount of water unexpectedly increases the conversion and decreases the phenol content in the reaction produce. Secondly, an increase of catalyst activity is observed by the addition of a large amount of water for a short period, and this increase of activity was kept unchanged even after the water concentration decreased to the normal level. This rejuvenation effect of water occurred repeatedly in plant tests to maintain a constant level of conversion without the need significantly to increase the reaction temperature. The product cyclohexanone is used, inter alia , in the manufacture of caprolactam, and constitutes a caprolactam precursor. The process features high conversion efficiency and low by-product formation, due to the improved catalyst of CuO-ZnO promoted by an alkali metal compound such as sodium carbonate. The catalyst is stable and resistant to water and heavy end products in the feedstock (up to 13%). The presence of water serves to rejuvenate the catalyst in the product mixture. The modified CuO-ZnO catalyst retains its activity, is fast, and selective. The process achieves a selectivity of form 97 to 99% at a conversion level of 50 to 60%. The copper oxide-zinc oxide catalyst is promoted with a small but effective amount if alkali metal compound. The alkali metal compound is present in the range of 0.05 to 5.0. wt%. The alkali metal compound is typically a salt such as sodium carbonate, bicarbonate or alkali metal salt of an organic acid, e.g., acetate, citrates, naphthanate or octate, which decomposes to the oxide slowly upon heating. The alkali metal may be sodium, potassium, lithium, cesium or rubidium. With the catalyst of the invention the presence of water has a salutary effect. Generally, the feedstream may contain up to 10 wt% of water, and up to 14 wt% of regular industrial side products. Typically, the catalyst, when partially deactivated, is rejuvenated by the incorporation of water in the process environment. The conversion usually takes place in a tube and shell reactor. It takes place at an elevated temperature in the range of 200°C to 320°C, preferably 220°C to 260°C. The space velocity in the reactor is generally in the range of 0.1 to 3.0, preferably, from 0.5 to 1.5. Fig 1 shows the effect of water in the cyclohexanol feed on the conversion to cyclohexanone over the promoted copper oxide-zinc oxide catalyst of the invention; Fig 2 is a process flow diagram of the cyclohexanol conversion system; and Fig 3 shows the results of a continuous aging test using the catalyst in the process of the invention. Following are examples which illustrate various aspects of the invention, as well as comparative examples showing the advantages of the present catalyst. EXAMPLE 1. The catalyst of the invention is prepared as follows: Zinc nitrate trihydrate (244 g) and copper nitrate trihydrate (483 g) are dissolved in distilled water (1500 ml) at 25°C. The solution is rapidly agitated while 10% ammonium bicarbonate solution (3800 ml) is added over a period of 30 minutes at 25°C. Agitation is continued for 30 minutes. The slurry is filtered, washed with distilled water (1500 ml), and the filter cake dried at 110°C for 4 hours. After drying, the cake is calcined at 400°C for 2 hours. After cooling, sodium carbonate (0.76 g) is added to the calcined product with sufficient distilled water to produce a paste. The paste is dried and shaped into tablets (6 mm O.D. *3mm H). the BET surface area is found to be 40 m²/g. typically, the catalyst is initially reduced with hydrogen and has a BET surface area of about 42 m²/g, a pore volume of 0.23 cc/g, a bulk density of 1.15 g/cc, and a side crush strength (dead weight load) of 7.3 kg (minimum, 6kg) when in a fresh condition, and 8.3 kg (minimum, 4 kg) after 180 days on-stream. COMPARATIVE EXAMPLE 2 . In a 25mm (one inch) (ID) tubular reactor, cyclohexanol is converted to cyclohexanone at a weight hourly space velocity, (WHSV) of 0.6. The effect of molar ratio of copper oxide to zinc oxide on catalyst activity is shown in Table 1. Molar ratio of CuO/ZnO Temperature, °C Conversion, % 2.0 214 36 228 40 0.5 212 42 218 47 The results shown in the above table are for steady state operation after eight hour runs. EXAMPLE 3 . As in Example 2, the copper oxide-zinc oxide catalyst is modified with different amounts of sodium carbonate by an impregnation method. The effect of sodium level on the activity of catalyst is shown in Table 2. Na₂CO₃ in CuO-ZnO (1/2) % by weight Reaction time, Hr 8 50 Temp °C Conv % Temp °C Conv % 5 216 45 224 51 1.7 216 47 224 54 0.34 213 40 226 51 0 212 42 218 47 EXAMPLE 4 . As in Example 2, a copper oxide-zinc oxide catalyst is promoted with a small amount of Group 1A metals by the impregnation method. The effect of Group 1A metals in the conversion of cyclohexanol to cyclohexanone is shown in Table 3. Catalyst Temp °C WHSV Conversion % CuO/ZnO(1/2) 280 1.0 82 CuO/ZnO(1/2) + 0.2%Na 280 1.0 87 CuO/ZnO(1/2) + 0.2%Rb 280 1.0 88 CuO/ZnO(1/2) + 0.2%Cs 280 1.0 83 CuO/ZnO(1/2) + 0.2%K 217 0.6 39 EXAMPLE 5. As in Example 2, a copper oxide-zinc oxide catalyst is promoted with 1% sodium and with 1% barium, respectively, by the impregnation method. The results for the reactions at 235°C and 0.6 WHSV are shown in Table 4. The differences between an alkaline metal and an alkaline earth promoted catalyst are also shown. Catalyst % Conversion on Cyclohexanol % Selectivity to Cyclohexanol ppm Phenol in Product CuO/ZnO (1/2)+1%Na 58 100 390 CuO/ZnO (1/2)+1%Ba 56 99 1600 COMPARATIVE EXAMPLE 6 . 6 g of CuO\ZnO catalyst modified with 0.2 wt& Zr (prepared by impregnation of 0.565 g Zr(No₃)₂H₂O on 96.28 g of CuO/ZnO catalyst) was used to convert cyclohexanol to cyclohexanone at 300°C at 1.0 WHSV. The products were found to contain 62% of cyclohexanone, 32% of 2-cyclohexyl-cyclohexanone and 5% of phenol. The conversion was calculated to be 70mol%. EXAMPLE 7. The interaction of sodium carbonate on copper oxide-zinc oxide and water in the cyclohexanol feed was determined at 215°C. Table 5 shows that adding water alone is not always beneficial. Only when water was added with a specific catalyst, viz, copper oxide-zinc oxide promoted by sodium carbonate, was a better conversion and lower by-product formation obtained. Catalyst % Na₂CO₃ by weight % H₂O in feed % Conversion ppm phenol in product 0 0 38.5 1400 0.2 0 40.1 600 0 2 34.4 900 0.2 2 41.1 500 EXAMPLE 8. As in Example 2, cyclohexanol feed containing different amounts of water was converted to cyclohexanone over promoted copper oxide-zinc oxide at 242 - 245°C. The results are shown in Fig 1. EXAMPLE 9. In a pilot plant reactor composed of 103 carbon steel tubes of 105 BWG*6 ft, cyclohexanol, (WHSV = 0.6, T = 240°C, p = 1.7 kg/cm² abs.) was converted to cyclohexanone at 60% constant conversion level. The flow diagram of the conversion system and the results of a continuous test for 180 days are shown in Fig 2 and Fig 3. EXAMPLE 10. In Fig 3 of Example 9, the partially deactivated catalyst, after 87 days, was rejuvenated with 10% water in the cyclohexanol feed for 3 days. The results in Table 6 show that adding the proper amount of water to the feedstock will restore the conversion rate and rejuvenate partially deactivated catalyst. The data also show that withdrawing water is not required, for it will not cause a detrimental effect to the catalyst. It is known that adding water to a commercial copper-magnesium dehydrogenation catalyst often leads to the hydrolysis of the catalyst. Time days Temp. °C Water in feed % Conversion % Phenol in product % 78 246 0.26 50.9 0.05 79 246 0.26 55.2 0.05 80 246 0.26 57.0 0.03 81 247 0.26 55.0 0.03 82 247 0.31 51.4 0.02 83 248 0.31 55.0 0.02 84 248 0.31 56.0 0.02 85 248 0.31 55.0 0.02 86 246 0.50 59.2 0.02 87 245 1.00 60.4 0.02 88 246 10.50 64.8 0.02 89 245 10.50 64.7 0.06 90 246 10.50 68.2 0.07 91 243 1.00 61.5 0.04 92 242 0.20 59.2 0.04 93 243 0.20 59.2 0.04 94 242 0.60 59.2 0.04 95 242 0.60 58.6 0.07 96 243 0.60 59.2 0.07 97 243 0.10 59.2 0.06 EXAMPLE 11. While it is generally known to add water to the cyclohexanol feedstock to enhance selectivity and conversion rate, there are differences between its use in the present invention and existing prior art. For example, in British Patent 1,444,484, a patent granted to Ruhrchemie AG, water was added to feedstock to give a higher selectivity. The catalyst used was copper, whereas in the present invention a copper oxide-zinc oxide catalyst promoted by sodium carbonate is used. In a patent granted to Ube Industries, Ltd. (Japan Kokai 73/29,742), 2% Of water was added to feedstock for 48 hours after the conversion rate deteriorated to 70% after 150 days. By adding water, the conversion rate was restored to 80%. In comparing this prior art with the present invention, differences, shown in Table 7, are apparent. Conversion temperature Catalyst used Withdraw of water Japan Kokai 370-380°C High temperature erature process ZnO-CaO (1:1 mol) a catalyst that is inactive under lower temperature Immediate withdraw of water after 48 hours, or detrimental effect will occur to catalyst Present invention 220-260°C Low temperature process Copper oxide-zinc oxide promoted by sodium carbonate Withdraw of water not required

Claims: A process for the catalytic dehdrogenation of cyclohexanol to cyclohexanone comprising contacting a cyclohexanol-containing feedstream with a calcined copper oxide-zinc oxide catalyst and recovering an effluent containing cyclohexanone, characterised in that the catalyst comprises copper oxide and zinc oxide which has been treated after calcination with from 0.05 to 5.0 wt.% of an alkali metal compound and in that said contacting takes place at a temperature from 200 to 320°C. A process according to Claim 1 characterised in that the temperature is from 220°C to 260°C. A process according to any of the preceding claims characterised in that the hourly space velocity in the reactor is from 0.1 to 3.0. A process according to any one of Claims 1 to 3 characterised in that the alkali metal compound is an alkali metal salt. A process according to Claim 4 characterised in that the alkali metal salt is sodium carbonate, bicarbonate or carboxylate. A process according to any one of Claims 1 to 4 characterised in that the alkali metal is sodium, potassium, cesium or rubidium. A process according to any of Claims 1 to 6 characterised in that the amount of alkali metal in the catalyst is from 0.1 to 5.0 wt.%. A process according to any one of Claims 1 to 7 characterised in that the cyclohexanol feedstream contains up to 10 wt.% of water. A process according to any one of Claims 1 to 8 characterised in that the cyclohexanol feedstream contains up to 14 wt.% of industrial side products. A process according to any one of Claims 1 to 9 characterised in that the catalyst, when partially deactivated, is rejuvenated by the incorporation of water in the process environment. A process as claimed in any preceding claim, wherein the copper oxide and zinc oxide are in a molar ratio of 0.1:1 to 4:1. A process as claimed in Claim 11, wherein the molar ratio is 0.5:1 to 2:1.

Inventors: CHIU, HORN-MING, REI, MIN-HON
Applicants: INDUSTRIAL TECHNOLOGY RESEARCH INSTITUTE
Application year: 1985
Main classification: C07C45
IPC codes: C07C67, C07B61, C07C49, B01J23, C07C45