EPOXIDATION CATALYST

Abstract

An epoxidation catalyst comprising silver, cesium, rhenium and tungsten deposited on an alumina support, wherein the catalyst comprises 20 to 50 wt.-% of silver, relative to the weight of the catalyst, an amount of cesium C.sub.cs of at least 7.5 mmol per kg of catalyst, and an amount of rhenium CR6 and an amount of tungsten Cw so as to meet the following requirements: C.sub.Re6.7 mmol per kg of catalyst; and C.sub.Re+(2c.sub.w)13.2 mmol per kg of catalyst. The epoxidation catalyst allows for a more efficient conversion of ethylene oxide by gas-phase oxidation of ethylene, particularly displaying high selectivity and high activity. The invention also relates to a process for preparing an epoxidation catalyst as defined in above, comprising i) impregnating an alumina support with a silver impregnation solution; and ii) subjecting the impregnated refractory support to a calcination process; wherein steps i) and ii) are optionally repeated, and at least one silver impregnation solution comprises rhenium, tungsten and cesium. The invention moreover relates to a process for producing ethylene oxide by gas-phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of an epoxidation catalyst according to any one of the preceding claims.

Claims

1.-13. (canceled)

14. An epoxidation catalyst comprising silver, cesium, rhenium, and tungsten deposited on an alumina support, wherein the catalyst comprises 20 to 50 wt.-% of silver, relative to the weight of the catalyst, an amount of cesium c.sub.Cs of at least 7.5 mmol per kg of catalyst, and an amount of rhenium c.sub.Re and an amount of tungsten c.sub.W so as to meet the following requirements: c.sub.Re6.7 mmol per kg of catalyst; and c.sub.Re+(2c.sub.W)13.2 mmol per kg of catalyst.

15. The catalyst according to claim 14, comprising an amount of tungsten c.sub.W of at least 3.2 mmol per kg of catalyst.

16. The catalyst according to claim 14, comprising an amount of rhenium c.sub.Re of 6.7 to 10.0 mmol per kg of catalyst.

17. The catalyst according to claim 14, comprising an amount of tungsten c.sub.W of 3.2 to 5.4 mmol per kg of catalyst.

18. The catalyst according to claim 14, comprising an amount of cesium c.sub.Cs of 7.5 to 12.4 mmol per kg of catalyst

19. The catalyst according to claim 14, comprising an amount of lithium c.sub.Li of at least 14.0 mmol per kg of catalyst.

20. The catalyst according to claim 14, comprising an amount of sulfur c.sub.S of 10.0 mmol or less per kg of catalyst.

21. The catalyst according to claim 14, comprising an amount of potassium c.sub.K of 12.0 mmol or less per kg of catalyst.

22. The catalyst according to claim 14, wherein the alumina support comprises at least 80 wt.-% alpha-alumina.

23. The catalyst according to claim 14, wherein the catalyst has a BET surface area in the range of 1.6 to 5.0 m.sup.2/g.

24. The catalyst according to claim 14, wherein the catalyst has a total Hg pore volume of 0.15 to 1.0 mL/g, as determined by mercury porosimetry.

25. A process for preparing an epoxidation catalyst as defined in claim 14, comprising i) impregnating an alumina support with a silver impregnation solution; and ii) subjecting the impregnated refractory support to a calcination process; wherein steps i) and ii) are optionally repeated, and at least one silver impregnation solution comprises rhenium, tungsten and cesium.

26. A process for producing ethylene oxide by gas-phase oxidation of ethylene, comprising reacting ethylene and oxygen in the presence of an epoxidation catalyst according to claim 14.

Description

EXAMPLES

Example 1Preparation of Shaped Catalyst Bodies

[0098] Shaped catalyst bodies according to Table 1 below were prepared by impregnating support A with a silver impregnation solution.

1.1 Production of the Silver Complex Solution

[0099] Silver complex solution was prepared according to Production Example 1 of WO 2019/154863 A1. The silver complex solution had a density of 1.529 g/mL, a silver content of 29.3 wt-% and a potassium content of 90 ppmw.

1.2. Preparation of Ag-Containing Intermediates

[0100] 315.3 g of support A were placed into a 2 L glass flask. The flask was attached to a rotary evaporator, which was set under a vacuum pressure of 80 mbar. The rotary evaporator system was set in rotation of 30 rpm. 236.2 g of silver complex solution prepared according to step 1.1 were added onto support A over 15 min under a vacuum pressure of 80 mbar. After addition of the silver complex solution, the rotary evaporator system was continued to rotate under vacuum for a further 15 min. The impregnated support was then left in the apparatus at room temperature (approximately 25 C.) and atmospheric pressure for 1 h and mixed gently every 15 min.

[0101] The impregnated material was placed on a net forming 1 to 2 layers (about 100 to 200 g per calcination run). The net was subjected to 23 Nm.sup.3/h of air flow, wherein the gas flow was pre-heated to a temperature of 305 C. The impregnated materials were heated up to a temperature of 290 C. at a heating rate of about 30 K/min and then maintained at 290 C. for 8 min to yield Ag-containing intermediate product IA according to Table 2. The temperature was measured by placing three thermocouples at 1 mm below the calcination net. Subsequently, the catalysts were cooled to ambient temperature by removing the intermediate catalyst bodies from the net using an industrial vacuum cleaner.

[0102] Ag-containing intermediate product IB was prepared in the same manner, except that support B was used instead of support A. The composition of intermediate product IB is provided in Table 2.

1.3. Preparation of Final Catalysts

[0103] An amount of Ag-containing intermediate product listed in Table 3 was placed into a 2 L glass flask. The flask was attached to a rotary evaporator, which was set under vacuum pressure of 80 mbar. The rotary evaporator system was set in rotation of 30 rpm. An amount of the silver complex solution listed in Table 3 prepared according to step 1.1 was mixed with amounts of promoter solution I, promoter solution II and promoter solution III as listed in Table 3.

[0104] Promoter solution I was obtained by dissolving lithium nitrate (FMC, 99.3%) and ammonium sulfate (Merck, 99.4%) in DI water to achieve target Li and S contents listed in Table 3.

[0105] Promoter solution II for catalysts 1-1 to 1-4, 1-7, 1-8, 1-10 and 1-11 was obtained by dissolving tungstic acid (HC Starck, 99.99%) in DI water and cesium hydroxide in water (HC Starck, 50.42%) to achieve target Cs and W contents listed in Table 3.

[0106] Promoter solution II for catalysts 1-5 and 1-6 was obtained by dissolving tungstic acid (HC Starck, 99.99%) in a mixture of cesium hydroxide in water (HC Starck, 50.42%) and an aqueous solution of ammonia (2.9 wt.-%) to achieve target Cs and W contents listed in Table 3.

[0107] Promoter solution II for catalyst 1-9 was obtained by dissolving tungstic acid (HC Starck, 99.99%) in a mixture of cesium hydroxide in water (HC Starck, 50.42%) and an aqueous solution of ammonia (4.6 wt.-%) to achieve target Cs and W contents listed in Table 3.

[0108] Promoter solution III for catalysts 1-1 and 1-2 was obtained by dissolving ammonium perrhenate (Buss & Buss Spezialmetalle GmbH, 99.9%) in deionized water (DI water) to achieve a target Re content of 3.7 wt.-%.

[0109] Promoter solution III for catalysts 1-3 to 1-11 was obtained by dissolving ammonium perrhenate (Buss & Buss Spezialmetalle GmbH, 99.9%) in a 29 wt.-% aqueous solution of ethylene diamine to achieve a target Re content of 10.0 wt.-%.

[0110] The combined impregnation solution containing silver complex solution, promoter solutions I, II, and III and an amount of DI water as listed in Table 3 was stirred for 5 min. The combined impregnation solution was added onto an amount of the silver-containing intermediate product prepared according to step 1.2 listed in Table 3 over 15 min under a vacuum pressure of 80 mbar. After addition of the combined impregnation solution, the rotary evaporator system was continued to rotate under vacuum for another 15 min. The impregnated support was then left in the apparatus at room temperature (about 25 C.) and atmospheric pressure for 1 h and gently mixed every 15 min.

[0111] The impregnated material was placed on a net forming 1 to 2 layers (about 100 to 250 g per calcination run). The net was subjected to 23 Nm.sup.3/h nitrogen flow (oxygen content: <20 ppm), wherein the gas flows were pre-heated to a temperature of 305 C. The impregnated materials were heated up to a temperature of 290 C. at a heating rate of about 30 K/min and then maintained at 290 C. for 7 min to yield catalysts according to Table 1. The temperatures were measured by placing three thermocouples at 1 mm below the calcination net. Subsequently, the catalysts were cooled to ambient temperature by removing the catalyst bodies from the net using an industrial vacuum cleaner.

TABLE-US-00001 TABLE 1 Catalyst composition (Ag-contents are reported in percent by weight of total catalyst, dopant values are reported in mmol/kg of total catalyst). Ag * c.sub.Re c.sub.W c.sub.Cs c.sub.Li c.sub.S IMP.sub.K ** c.sub.K *** Examples Support [wt.-%] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] 1-1 .sup.# A 27.1 6.44 3.10 7.15 67.72 1.09 2.23 5.93 1-2 A 27.1 7.52 3.64 8.65 67.72 1.09 2.23 5.93 1-3 .sup.# B 27.1 6.44 3.10 7.15 67.72 1.09 2.23 5.57 1-4 B 27.1 7.52 3.64 8.65 67.72 1.09 2.23 5.57 1-5 .sup.# B 27.1 7.52 3.64 7.15 67.72 1.09 2.23 5.57 1-6 .sup.# B 27.1 5.00 3.00 6.50 67.72 1.09 2.23 5.57 1-7 .sup.# B 27.1 5.00 3.00 8.30 67.72 1.09 2.23 5.57 1-8 B 27.1 6.68 3.26 8.30 67.72 1.09 2.23 5.57 1-9 .sup.# B 27.1 7.20 3.60 6.50 67.72 1.09 2.23 5.57 1-10 B 27.1 7.20 3.60 8.30 67.72 1.09 2.23 5.57 1-11 .sup.# B 27.1 6.00 3.60 8.30 67.72 1.09 2.23 5.57 * Ag and all promoter values are calculated values ** IMP.sub.K is understood to mean the amount of potassium added during impregnation and does not include the amount of potassium comprised in the alumina support prior to impregnation *** c.sub.K is understood to mean the total amount of potassium in the catalyst .sup.# comparative example

TABLE-US-00002 TABLE 2 Composition of Intermediate Products (Ag-contents are reported in percent by weight of total catalyst, dopant values are reported in mmol/kg of total catalyst). Intermediate Ag * IMP.sub.K ** S.sub.K **** c.sub.K *** Product Support [wt.-%] [mmol/kg] [mmol/kg] [mmol/kg] IA A 18.0 1.41 4.19 5.61 IB B 18.0 1.41 3.77 5.19 * Ag and all promoter values are calculated values ** IMP.sub.K is understood to mean the amount of potassium added during impregnation and does not include the amount of potassium comprised in the alumina support prior to impregnation * S.sub.K is understood to mean the amount of potassium contributed to the intermediate product by the alumina support **** c.sub.K is understood to mean the total amount of potassium in the catalyst

TABLE-US-00003 TABLE 3 Amounts of ingredients used for preparation of catalysts 1-1 and 1-2. Catalyst 1-1 .sup.# 1-2 1-3 .sup.# 1-4 1-5 .sup.# 1-6 .sup.# Ag-containing Intermediate IA IA IB IB IB IB Amount of Ag-containing 170.2 170.2 170.4 170.5 170.3 170.8 Intermediate [g] Amount of Ag-complex 73.532 73.574 73.619 73.703 73.600 73.760 solution [g] Amount of promoter 3.172 3.174 3.176 3.180 3.175 3.182 solution I [g] Li-/S-content in promoter 2.85/0.212 2.85/0.212 2.85/0.212 2.85/0.212 2.85/0.212 2.85/0.212 solution I [wt.-%] Amount of promoter 3.655 4.299 3.659 4.306 4.300 3.551 solution II [g] Cs-/W-content in promoter 5.0/3.0 5.149/3.0 5.0/3.0 5.149/3.0 4.254/3.0 4.696/3.0 solution II [wt.-%] Amount of promoter 6.239 7.283 2.311 2.699 2.696 1.797 solution III [g] Re-content in promoter 3.7 3.7 10.0 10.0 10.0 10.0 solution III [wt.-%] Amount of DI H.sub.2O [g] 1.785 0.0 5.72 4.66 4.67 6.39 Catalyst 1-7 .sup.# 1-8 1-9 .sup.# 1-10 1-11 .sup.# Ag-containing Intermediate IB IB IB IB IB Amount of Ag-containing 170.7 170.3 170.5 170.5 170.3 Intermediate [g] Amount of Ag-complex 73.737 73.594 73.674 73.694 73.589 solution [g] Amount of promoter 3.181 3.175 3.179 3.180 3.175 solution I [g] Li-/S-content in promoter 2.85/0.212 2.85/0.212 2.85/0.212 2.85/0.212 2.85/0.212 solution I [wt.-%] Amount of promoter 3.549 3.851 4.253 4.254 4.248 solution II [g] Cs-/W-content in promoter 5.995/3.0 5.515/3.0 3.915/3.0 4.998/3.0 4.998/3.0 solution II [wt.-%] Amount of promoter 1.796 2.393 2.585 2.585 2.150 solution III [g] Re-content in promoter 10.0 10.0 10.0 10.0 10.0 solution III [wt.-%] Amount of DI H.sub.2O [g] 6.38 5.43 4.85 4.84 5.28 .sup.# comparative example

Example 2Catalyst Testing

[0112] An epoxidation reaction was conducted in a vertically-placed test reactor constructed from stainless steel with an inner diameter of 6 mm and a length of 2.2 m. The reactor was heated using hot oil contained in a heating mantle at a specified temperature. All temperatures below refer to the temperature of the hot oil. The reactor was filled with 9 g of inert steatite balls (0.8 to 1.1 mm), onto which 26.4 g of crushed catalyst screened to a desired particle size of 1.0 to 1.6 mm were packed, and thereon an additional 29 g of inert steatite balls (0.8-1.1 mm) were packed. The inlet gas was introduced to the top of the reactor in a once-through operation mode.

[0113] The catalysts were charged into the reactor at a reactor temperature of 90 C. under nitrogen flow of 130 NL/h at a pressure of 1.5 bar absolute. Then, the reactor temperature was ramped up to 210 C. at a heating rate of 50 K/h and the catalysts were maintained under these conditions for 15 h. Subsequently, the nitrogen flow was substituted by a flow of 114 NL/h methane and 1.5 NL/h CO.sub.2. The reactor was pressurized to 16 bar absolute. Subsequently, 30.4 NL/h ethylene and 0.8 NL/h of a mixture of 500 ppm ethylene chloride in methane were added. Then, oxygen was introduced stepwise to reach a final flow of 6.1 NL/h. At this point, the inlet composition consisted of 20 vol.-% ethylene, 4 vol.-% oxygen, 1 vol.-% carbon dioxide, and ethylene chloride (EC) moderation of 2.5 parts per million by volume (ppmv), with methane used as a balance at the total gas flow rate of 152.7 NL/h.

[0114] The reactor temperature was ramped up to 225 C. at a heating rate of 5 K/h, and afterwards to 240 C. at a heating rate of 2.5 K/h. The catalysts were maintained under these conditions for 135 hours. Afterwards, EC concentration was decreased to 2.2 ppmv, and the temperature was decreased to 225 C. Subsequently, the inlet gas composition was gradually changed to 35 vol.-% ethylene, 7 vol.-% oxygen, 1 vol.-% carbon dioxide with methane used as a balance and a total gas flow rate of 147.9 NL/h. The temperature was adjusted to achieve an ethylene oxide (EO) concentration in the outlet gas of 3.05%. The EC concentration was adjusted to optimize the selectivity. Results of the catalyst tests are summarized in Table 4.

TABLE-US-00004 TABLE 4 Summary of catalyst tests. time on stream .sup. 11 days 28 days Heating Heating EO- Oil EO- Oil Selec- Temper- Selec- Temper- tivity ature tivity ature Test Catalyst [%] [ C.] [%] [ C.] 2-1 1-1 .sup.# n. d. * n. d. * 88.8 237.0 2-2 1-2.sup. n. d. * n. d. * 89.2 236.0 2-3 1-3 .sup.# 86.8 230 87.7 232 2-4 1-4.sup. 87.1 232 88.0 234 2-5 1-5 .sup.# 86.1 234 87.1 234 2-6 1-6 .sup.# 86.9 231 87.7 231 2-7 1-7 .sup.# 83.3 228 85.2 234 2-8 1-8.sup. 87.8 234 88.3 234 2-9 1-9 .sup.# 85.3 227 85.9 228 2-10 1-10.sup. 87.6 235 88.4 236 2-11 1-11 .sup.# 85.4 229 n. d. * n. d. * .sup.# comparative example * n. d. = not determined .sup. time on stream: determined from the point of time of oxygen introduction

[0115] It is evident that inventive catalysts exhibit a higher ethylene oxide selectivity than comparative catalysts based on the same support.

Example 3

[0116] Further catalyst compositions can be prepared by varying the amounts of silver, rhenium, tungsten, lithium or sulfur within the ranges disclosed above. The properties of catalyst compositions 2-1 to 2-8, all of which are based on support A and which are illustrated in Table 5 below, are expected to be substantially equally beneficial as those of the inventive catalyst compositions of example 2.

TABLE-US-00005 TABLE 5 Further catalyst compositions (Ag-contents are reported in percent by weight of total catalyst, dopant values are reported in mmol/kg of total catalyst). Ag c.sub.Re c.sub.W c.sub.Cs c.sub.Li c.sub.S IMP.sub.K * c.sub.K ** Examples [wt.-%] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] [mmol/kg] 2-1 29.5 7.09 3.35 7.71 68.00 1.00 2.28 5.86 2-2 29.5 7.09 3.35 7.71 68.00 1.40 2.28 5.86 2-3 29.5 7.09 3.35 7.71 68.00 0.60 2.28 5.86 2-4 29.5 7.09 3.35 7.71 75.00 1.00 2.28 5.86 2-5 29.5 7.09 3.35 7.71 61.00 1.00 2.28 5.86 2-6 29.5 7.09 3.35 7.71 68.00 1.00 3.32 6.90 2-7 29.5 7.09 3.35 7.71 68.00 1.00 1.32 4.90 2-8 29.5 7.52 3.86 8.65 68.00 1.00 2.28 5.86 * IMP.sub.K is understood to mean the amount of potassium added during impregnation and does not include the amount of potassium comprised in the alumina support prior to impregnation ** c.sub.K is understood to mean the total amount of potassium in the catalyst