PROCESS FOR PRODUCING A SILVER-BASED EPOXIDATION CATALYST

Abstract

A process for producing a silver-based epoxidation catalyst, comprising i) impregnating a particulate porous refractory support with a first aqueous silver impregnation solution comprising silver ions and an aminic complexing agent selected from amines, alkanolamines and amino acids; ii) converting at least part of the silver ions impregnated on the refractory support to metallic silver by heating while directing a stream of a first gas over the impregnated refractory support to obtain an intermediate catalyst, wherein the first gas comprises at least 5 vol.-% oxygen; iii) impregnating the intermediate catalyst with a second aqueous silver impregnation solution comprising silver ions, an aminic complexing agent selected from amines, alkanolamines and amino acids, and one or more transition metal promoters, in particular rhenium; and iv) converting at least part of the silver ions impregnated on the intermediate catalyst to metallic silver by heating while directing a stream of a second gas over the impregnated intermediate catalyst to obtain the epoxidation catalyst, wherein the second gas comprises at most 2.0 vol.-% oxygen, wherein the impregnated refractory support and the impregnated intermediate catalyst are each heated to a temperature of 200 to 800° C. The process of the invention surprisingly allows for obtaining a catalyst with high selectivity in a cost-efficient manner. The invention also relates to a silver-based epoxidation catalyst obtainable by such a process, and to a process for producing an alkylene oxide by gas-phase oxidation of an alkylene, comprising reacting an alkylene and oxygen in the presence of a silver-based epoxidation catalyst obtainable by the above process.

Claims

1.-18. (canceled)

19. A process for producing a silver-based epoxidation catalyst, comprising i) impregnating a particulate porous refractory support with a first aqueous silver impregnation solution comprising silver ions and an aminic complexing agent selected from amines, alkanolamines and amino acids; ii) converting at least part of the silver ions impregnated on the refractory support to metallic silver by heating while directing a stream of a first gas over the impregnated refractory support to obtain an intermediate catalyst, wherein the first gas comprises at least 5 vol.-% oxygen; iii) impregnating the intermediate catalyst with a second aqueous silver impregnation solution comprising silver ions, an aminic complexing agent selected from amines, alkanolamines and amino acids, and one or more transition metal promoters, in particular rhenium; and iv) converting at least part of the silver ions impregnated on the intermediate catalyst to metallic silver by heating while directing a stream of a second gas over the impregnated intermediate catalyst to obtain the epoxidation catalyst, wherein the second gas comprises at most 2.0 vol.-% oxygen; wherein the impregnated refractory support and the impregnated intermediate catalyst are each heated to a temperature of 200 to 800° C.

20. The process according to claim 19, additionally comprising ii′) subsequent to ii) and prior to iii), cooling the intermediate catalyst; and/or iv′) subsequent to iv), cooling the catalyst.

21. The process according to claim 20, wherein in step iv′) the catalyst is cooled while directing a stream of the second gas over the impregnated intermediate catalyst to obtain the epoxidation catalyst until the temperature of the catalyst is 100° C. or lower.

22. The process according to claim 19, wherein the first gas comprises at least 10 vol.-% oxygen.

23. The process according to claim 22, wherein the first gas is air.

24. The process according to claim 19, wherein the second gas comprises at least 98 vol.-% nitrogen.

25. The process according to claim 19, wherein the first aqueous silver impregnation solution and/or the second aqueous silver impregnation solution comprise a carboxylate anion.

26. The process according to claim 19, wherein the aminic complexing agent in the first and second impregnation solution comprises a vicinal C.sub.2-C.sub.6-alkylenediamine.

27. The process according to claim 19, wherein the first aqueous silver impregnation solution is free of transition metal promoters.

28. The process according to claim 19, wherein the first aqueous silver impregnation solution and/or the second aqueous silver impregnation solution comprises one or more alkali metal promoters.

29. The process according to claim 19, wherein the impregnated refractory support and the impregnated intermediate catalyst are each heated to a temperature of 210 to 650° C.

30. The process according to claim 19, wherein the heating rate in the temperature range of 40 to 200° C. is at least 20 K/min.

31. The process according to claim 19, wherein the impregnated refractory support and the impregnated intermediate catalyst are each heated for a total period of 5 to 60 min.

32. The process according to claim 19, wherein the impregnated refractory support and the impregnated intermediate catalyst are each heated at an absolute pressure in the range of 0.9 to 1.1 bar.

33. The process according to claim 19, wherein the porous refractory support comprises at least 90 wt.-% alpha-alumina.

34. The process according to claim 19, wherein the intermediate catalyst is impregnated with the second aqueous silver impregnation solution in step iii) sufficient so as to obtain an epoxidation catalyst comprising 15 to 50 wt.-% silver, relative to the total weight of the catalyst.

35. A silver-based epoxidation catalyst obtained by the process according to claim 19.

36. A process for producing an alkylene oxide by gas-phase oxidation of an alkylene, comprising reacting an alkylene and oxygen in the presence of a silver-based epoxidation catalyst obtained by the process according to claim 19.

Description

EXAMPLES

Example 1—Preparing Shaped Catalyst Bodies

[0133] Shaped catalyst bodies according to Table 1 below were prepared by impregnating support A with a silver impregnation solution. The catalyst composition is shown in Table 1 below.

TABLE-US-00001 TABLE 1 Catalyst composition (Ag-contents are reported in percent by weight of total catalyst, dopant values are reported in parts per million by weight of total catalyst) Ag.sub.CAT * Li.sub.CAT S.sub.CAT W.sub.CAT Cs.sub.CAT Re.sub.CAT K.sub.ADD ** K.sub.CAT *** [wt.-%] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] [ppm] 28.9 470 35 570 950 1200 93 213 * Ag and all promoter values are calculated values; ** K.sub.ADD 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; *** K.sub.CAT is understood to mean the total amount of potassium in the catalyst

[0134] 1.1 Production of the Silver Complex Solution

[0135] 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 ppm.

[0136] 1.2. Preparation of Intermediate Catalysts 315.2 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. 251.7 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.

[0137] The impregnated material was placed on a net forming 1 to 2 layers (about 100 to 200 g per heating run). The net was subjected either to 23 Nm.sup.3/h nitrogen flow (oxygen content: <20 ppm) (intermediates 1.1, 1.3) or 23 Nm.sup.3/h of air flow (intermediates 1.2, 1.4), 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 8 min to yield Ag-containing intermediate products according to Table 2. The temperatures were measured by placing three thermocouples at 1 mm below the net. Subsequently, the catalysts were cooled to ambient temperature by removing the intermediate catalyst bodies from the net using an industrial vacuum cleaner.

TABLE-US-00002 TABLE 2 Ag containing intermediate catalysts (Ag-contents are reported in percent by weight of total catalyst, dopant values are reported in parts per million by weight of total intermediate catalyst) Ag.sub.CAT * K.sub.ADD ** K.sub.INT *** Heating Intermediate Support [wt.-%] [ppm] [ppm] Inlet Gas 1.1 A 19.0 58 138 Nitrogen 1.2 A 19.0 58 138 Air 1.3 A 19.0 58 138 Nitrogen 1.4 A 19.0 58 138 Air * Ag and all promoter values are calculated values; ** K.sub.ADD 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; *** K.sub.INT is understood to mean the total amount of potassium in the intermediate

[0138] 1.3. Preparation of Catalysts 170.7 g of Ag-containing intermediate products 1.1 to 1.4 as prepared according to step 1.2 were each 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. 82.09 g of the silver complex solution prepared according to step 1.1 was mixed with 3.22 g of promoter solution I, 3.71 g of promoter solution II, and 6.34 g of promoter solution III.

[0139] Promoter solution I was obtained by dissolving lithium nitrate (FMC, 99.3%) and ammonium sulfate (Merck, 99.4%) in DI water to achieve a Li content of 2.85 wt.-% and a S content of 0.21 wt.-%. Promoter solution II was obtained by dissolving tungstic acid (HC Starck, 99.99%) in DI water and cesium hydroxide in water (HC Starck, 50.42%) to achieve a target Cs content of 5.0 wt.-% and a W content of 3.0 wt.-%. Promoter solution III was obtained by dissolving ammonium perrhenate (Engelhard, 99.4%) in DI water to achieve a Re content of 3.7 wt.-%.

[0140] The combined impregnation solution containing silver complex solution and promoter solutions I, II, and III was stirred for 5 minutes. The combined impregnation solution was added onto each of the silver-containing intermediate products 1.1 to 1.4 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 mixed gently every 15 min.

[0141] The impregnated material was placed on a net forming 1 to 2 layers (about 100 to 250 g per heating run). The net was subjected either to 23 Nm.sup.3/h nitrogen flow (oxygen content: <20 ppm) (catalysts C1.1, C1.2) or 23 Nm.sup.3/h of air flow (catalysts C1.3, C1.4), 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 Ag-containing intermediate products according to Table 1. The temperatures were measured by placing three thermocouples at 1 mm below the net. Subsequently, the catalysts were cooled to ambient temperature by removing the catalyst bodies from the net using an industrial vacuum cleaner.

Example 2—Catalyst Testing

[0142] 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 mantel at a specified temperature. All temperatures below refer to the temperature of the hot oil. The reactor was heated to a temperature of 90° C. under nitrogen. The reactor was then charged 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 to 1.1 mm) were packed. An inlet gas was introduced to the top of the reactor in a “once-through” operation mode. The inlet gas was a nitrogen flow of 130 NL/h, at a pressure of 1.5 bar absolute and a temperature of 90° C. 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.

[0143] Subsequently, the nitrogen flow was changed to a flow of 114 NL/h methane and 1.5 NL/h CO.sub.2. The reactor was pressurized to 16 bar absolute. Then, 30.4 NL/h ethylene and 0.8 NL/h of a mixture of 500 ppm ethylene chloride in methane were added. Subsequently, oxygen was introduced in a stepwise manner 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 152.8 NL/h.

[0144] 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 at this condition for 135 h. Afterwards, EC concentration was decreased to 2.0 ppmv, and the temperature was decreased to 225° C. Then, 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 3.

TABLE-US-00003 TABLE 3 Summary of Catalyst Tests C1.1 C1.2 C1.3 C1.4 Catalyst Comparative Inventive Comparative Comparative Heating inlet Nitrogen Air Nitrogen Air gas after 1.sup.st impregnation Heating inlet Nitrogen Nitrogen Air Air gas after 2.sup.nd impregnation Time-on- stream [h] Performance 600 Catalyst 232 233 234 234 temperature [° C.] Selectivity 89.3 89.5 88.6 88.4 [%]

[0145] It is evident that catalyst C1.2, which was obtained by a first heating step under air and a second heating step under nitrogen, displays a selectivity equivalent to or even better than that of catalyst C1.1, which was obtained by two heating steps under nitrogen. Catalyst C1.2 also has a higher selectivity than catalyst C1.3, which was obtained by a first heating step under nitrogen and a second heating step air, and catalyst C1.4, which was obtained by two heating steps under air.