PRODUCTION OF PULVERULENT, POROUS CRYSTALLINE METAL SILICATES BY MEANS OF FLAME SPRAY PYROLYSIS

Abstract

The present invention relates to a process for preparing a pulverulent, porous crystalline metal silicate, comprising the following steps: a) hydrothermal synthesis in an aqueous mixture comprising (A) at least one silicon source, (B) at least one metal source and (C) at least one mineralizer to obtain an aqueous suspension comprising a porous crystalline metal silicate as reaction product; and b) calcination of the reaction product, characterized in that the calcination is conducted by means of flame spray pyrolysis at an adiabatic combustion temperature within a range of 450-2200° C., wherein the suspension having a solids content of 70% by weight which is obtained in step a) is sprayed into a flame generated by combustion of a fuel in the presence of oxygen to form a pulverulent, porous crystalline metal silicate.

Claims

1-16. (canceled)

17. A process for preparing a pulverulent, porous crystalline metal silicate, comprising the steps of: a) hydrothermal synthesis in an aqueous mixture comprising: (A) at least one silicon source; (B) at least one metal source; and (C) at least one mineralizer; to obtain an aqueous suspension comprising a porous crystalline metal silicate as a reaction product and having a solids content of ≤70% by weight; and b) calcination of the reaction product, wherein the calcination is conducted by means of flame spray pyrolysis at an adiabatic combustion temperature within a range of 450-2200° C., wherein the suspension having a solids content of ≤70% by weight which is obtained in step a) is sprayed into a flame generated by combustion of a fuel in the presence of oxygen to form a pulverulent, porous crystalline metal silicate.

18. The process of claim 17, wherein the porous crystalline metal silicate has a zeolite structure.

19. The process of claim 17, wherein the porous crystalline metal silicate has a zeolite structure having a crystal structure of the LTA, MFI, FAU, MOR, MEL or MWW type.

20. The process of claim 19, wherein the metal source is a source of elements selected from the group consisting of titanium (Ti), aluminium (Al), zirconium (Zr), iron (Fe), tin (Sn), germanium (Ge), indium (In) and boron (B).

21. The process of claim 17, wherein the fuel is selected from the group consisting of: hydrogen, methane, ethane, propane, butane, natural gas and mixtures thereof.

22. The process of claim 17, wherein the mean residence time of the suspension obtained in step a) in the conversion thereof in step b) is within a range from 0.1 to 10 s.

23. The process of claim 17, wherein the ignition loss according to DIN 18128:2002-12 of the porous crystalline metal silicate is less than 5% by weight.

24. The process of claim 17, wherein the aqueous mixture in step a) additionally comprises suitable seed crystals.

25. The process of claim 17, wherein the aqueous mixture in step a) additionally comprises a template selected from the group consisting of amines, quaternary ammonium compounds, alcohols and mixtures thereof.

26. The process of claim 17, wherein step a) is conducted at a temperature of 100 to 250° C. under the autogenous pressure generated in a pressure-resistant reactor.

27. The process of claim 17, wherein, in step a), component (A) and component (B) are present together in one substance and this substance is selected from the group consisting of: amorphous mixed metal-silicon oxide; amorphous silicon dioxide doped with metal oxide; amorphous silicon dioxide impregnated with metal; metal silicate; metal-doped tetraalkyl orthosilicate; and mixtures thereof.

28. The process of claim 27, wherein component (A) is an amorphous silicon dioxide doped with metal oxide, an amorphous silicon dioxide impregnated with metal, or an amorphous mixed metal-silicon oxide.

29. The process of claim 17, wherein, in step a), component (A) is in solid form and component (B) is in liquid form.

30. The process of claim 29, wherein component (A) is selected from the group consisting of: pyrogenic silicon dioxide; precipitated silicon dioxide; silicon dioxide produced by a sol-gel process; and mixtures thereof.

31. The process of claim 30, wherein component (A) is a high-purity silicon dioxide prepared by precipitation or a pyrogenic silicon dioxide.

32. The process of claim 17, wherein step b) is followed by a shaping c) comprising the steps of: (a) adding water to obtain an aqueous suspension of the pulverulent, porous crystalline metal silicate; (b) mixing the suspension from step (a) with granulating aids; (c) compacting, granulating, spray-drying, spray granulating or extruding to obtain a porous crystalline metal silicate in the form of microgranules, spheres, tablets, solid cylinders, hollow cylinders or honeycombs.

33. The process of claim 20, wherein the fuel is selected from the group consisting of: hydrogen; methane; ethane, propane; butane, natural gas; and mixtures thereof.

34. The process of claim 20, wherein the aqueous mixture in step a) additionally comprises a template selected from the group consisting of amines, quaternary ammonium compounds, alcohols and mixtures thereof.

35. The process of claim 20, wherein, in step a), component (A) and component (B) are present together in one substance and this substance is selected from the group consisting of: amorphous mixed metal-silicon oxide, amorphous silicon dioxide doped with metal oxide, amorphous silicon dioxide impregnated with metal, metal silicate, metal-doped tetraalkyl orthosilicate and mixtures thereof.

36. The process of claim 20, wherein step b) is followed by a shaping c) comprising the steps of: (a) adding water to obtain an aqueous suspension of the pulverulent, porous crystalline metal silicate; (b) mixing the suspension from step (a) with granulating aids; (c) compacting, granulating, spray-drying, spray granulating or extruding to obtain a porous crystalline metal silicate in the form of microgranules, spheres, tablets, solid cylinders, hollow cylinders or honeycombs.

Description

EXAMPLES

Example 1

Preparation of the Raw Suspension by Hydrothermal Synthesis

[0086] The synthesis of the titanium silicalite-1 zeolite (TS-1; MFI structure type) was conducted in a 3 m.sup.3 pressure reactor and was in accordance with the corresponding method from Example 1 of EP 0814058 B1. The silicon source used was an amorphous, high-purity silicon dioxide (manufacturer: Evonik Industries), and the titanium source used was an aqueous titanium-tetrapropylammonium hydroxide solution (Ti-TPA solution) having a content of 19.0% by weight of TiO.sub.2. The Ti-TPA solution was prepared as follows:

[0087] Mixing of 90.1 kg of deionized water, 167.3 kg of a 40% aqueous tetrapropylammonium hydroxide solution (manufacturer: Sachem) and 141.6 kg of tetraethyl orthotitanate (manufacturer: Connect Chemicals GmbH) at 40° C. in a closed vessel for one hour. The exothermicity of the reaction resulted in a temperature rise of about 25° C. This was followed by the distillative removal of the ethanol formed at 80° C. at a distillation rate of 30 l/h. The target value for the resultant Ti-TPA solution was a TiO.sub.2 content of 19.0% by weight. After cooling, the Ti-TPA solution was used in the TS-1 synthesis.

[0088] The pressure reactor was initially charged with: 500 kg of high-purity silicon dioxide (Evonik Industries), 382 kg of a 40% aqueous tetrapropylammonium hydroxide solution (manufacturer: Sachem), 193 kg of Ti-TPA solution, 10 kg of silicalite-1 seed crystals and 1800 kg of deionized water. The mixture was stirred in the closed pressure reactor at a stirrer speed of 50 rpm at 170° C. for 3 h. The heating time to 170° C. was 180 min; after a cooling time of 150 min, the synthesis was ended. The stirring at a stirrer speed of 50 rpm was continued from the start until the end of the synthesis.

[0089] The silicalite-1 seed crystals were prepared by hydrothermal synthesis of 500 kg of high-purity silicon dioxide (Evonik Industries), 400 kg of a 40% aqueous tetrapropylammonium hydroxide solution (manufacturer: Sachem) and 1800 kg of deionized water in a pressure reactor. The mixture was stirred in the closed pressure reactor at a stirrer speed of 50 rpm at 160° C. for 3 h. The heating time to 160° C. was 180 min; after a cooling time of 150 min, the synthesis was ended. The stirring at a stirrer speed of 50 rpm was continued from the start until the end of the synthesis.

Comparative Example 1

Conventional Workup after the Hydrothermal Synthesis

[0090] Acetic acid (60% by weight) was added to the raw suspension described in Example 1 up to pH=7, and the precipitate formed was filtered on a filter press and washed with distilled water. The solids obtained were dried by means of spray drying with an inlet temperature of 420° C. and with an atomizer speed of 1700 min.sup.−1 (exit temperature of 110° C.). Subsequently, the partly dried powder was calcined at a maximum of 650° C. in a rotary tube for 2 h. The product thus obtained had a BET surface area of 470 m.sup.2/g and an ignition loss (measured at 550° C.) of 0.65%. XRD analysis (FIG. 1) showed that the product has the crystal structure of TS-1 (ICDD reference code: 01-089-8099). Pore analysis with nitrogen according to BJH gave a pore volume of 0.23 ml/g.

Example 2

Spray Calcination after the Hydrothermal Synthesis (600° C.)

[0091] The raw suspension (16 kg/h) described in Example 1 was sprayed in a pilot plant with 18 m.sup.3/h of nitrogen for atomization through a two-phase nozzle with internal diameter 2 mm and gap 1 mm. The hydrogen/air flame was operated with 10 m.sup.3/h of hydrogen and 45 m.sup.3/h of primary air. For avoidance of material deposits, 25 m.sup.3/h of secondary air were injected tangentially. The temperature measured 1.5 m below the ignition site was adjusted to 600° C. by slight variation of the hydrogen. The adiabatic combustion temperature in the reactor was about 680° C. The residence time in the reactor was about 1.1 s. The offgases, including calcined zeolite, were guided through a water-cooled cooling zone (coolant temperature: 25° C.) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250° C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product (4.35 kg/h). The product thus obtained had a BET surface area of 499 m.sup.2/g and an ignition loss (measured at 550° C.) of 1.35%. XRD analysis (FIG. 2) showed that the product has the crystal structure of TS-1 (ICDD reference code: 01-089-8099). Pore analysis with nitrogen according to BJH gave a pore volume of 0.3 ml/g.

Comparative Example 2 (Negative Example)

Spray Calcination after the Hydrothermal Synthesis (400° C.)

[0092] The raw suspension (15 kg/h) described in Example 1 was sprayed in a pilot plant with 18 m.sup.3/h of nitrogen for atomization through a two-phase nozzle with internal diameter 2 mm and gap 1 mm. The hydrogen/air flame was operated with 8 m.sup.3/h of hydrogen and 45 m.sup.3/h of primary air. The temperature measured 1.5 m below the ignition site was adjusted to 400° C. by slight variation of the hydrogen. The adiabatic combustion temperature in the reactor was about 544° C. The residence time in the reactor was 1.35 s. The offgases, including calcined zeolite, were guided through a water-cooled cooling zone (coolant temperature: 25° C.) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250° C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product (4.4 kg/h). The product thus obtained had a BET surface area of 240 m.sup.2/g and an ignition loss (measured at 550° C.) of 9.0%. Owing to the high ignition loss, the product obtained is unsuitable for further processing to give the end product and use in the HPPO test reaction.

Example 3

Spray Calcination After the Hydrothermal Synthesis (700° C.)

[0093] The raw suspension (30 kg/h) described in Example 1 was sprayed in a pilot plant with 18 m.sup.3/h of air for atomization through a two-phase nozzle with internal diameter 2 mm and gap 1 mm. The hydrogen/air flame was operated with 9.1 m.sup.3/h of hydrogen and 27 m.sup.3/h of primary air. The temperature measured 1.5 m below the ignition site was adjusted to 700° C. by slight variation of the hydrogen. The adiabatic combustion temperature in the reactor was about 750° C. The residence time in the reactor was about 1.1 s. The offgases, including calcined zeolite, were guided through a quench gas-cooled cooling zone (10 l/h of H.sub.2O, 4 m.sup.3/h of air) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250° C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product (8.7 kg/h). The product thus obtained had a BET surface area of 506 m.sup.2/g and an ignition loss (measured at 550° C.) of 1.1%. XRD analysis (FIG. 3) showed that the product has the crystal structure of TS-1 (ICDD reference code: 01-089-8099). Pore analysis with nitrogen according to BJH gave a pore volume of 0.3 ml/g.

Example 4

Spray Calcination After the Hydrothermal Synthesis (800° C.)

[0094] The raw suspension (14 kg/h) described in Example 1 was sprayed in a pilot plant with 18 m.sup.3/h of nitrogen for atomization through a two-phase nozzle with internal diameter 2 mm and gap 1 mm. The hydrogen/air flame was operated with 12.2 m.sup.3/h of hydrogen and 40 m.sup.3/h of primary air. The temperature measured 1.5 m below the ignition site was adjusted to 800° C. by slight variation of the hydrogen. The adiabatic combustion temperature in the reactor was about 830° C. The residence time in the reactor was 0.85 s. The offgases, including calcined zeolite, were guided through a water-cooled cooling zone (coolant temperature: 25° C.) having a diameter of 100 mm and a length of 6 m and then collected at filter candles at max. 250° C. By sequential cleaning of the filter candles, it was possible to collect the ready-calcined product (4.2 kg/h). The product thus obtained had a BET surface area of 477 m.sup.2/g and an ignition loss (measured at 550° C.) of 0.87%. XRD analysis (FIG. 4) showed that the product has the crystal structure of TS-1 (ICDD reference code: 01-089-8099). Pore analysis with nitrogen according to BJH gave a pore volume of 0.3 ml/g.

Comparative Example 3

Shaping of the Zeolite Powder from Comparative Example 1

[0095] The powder from Comparative Example 1 (1200 g) was mixed with 75 g of methyl hydroxyethyl cellulose (Tylose MH1000), 75 g of Licowax C, 1000 g of silica sol solution (Koestrosol 0830 AS) and 350 g of deionized water in an Eirich mixer. The mass obtained was extruded with an extruder (HB-Feinmechanik LTW 63) through a perforated plate with diameter 3.2 mm. The extrudates were then dried in a drying cabinet at 80° C. for one hour and calcined in a muffle furnace at 570° C. for 12 h.

Example 5

Shaping of the Zeolite Powder from Example 2

[0096] The powder from Example 2 (1200 g) was mixed with 75 g of methyl hydroxyethyl cellulose (Tylose MH1000), 75 g of Licowax C, 1000 g of silica sol solution (Koestrosol 0830 AS) and 350 g of deionized water in an Eirich mixer. The mass obtained was extruded with an extruder (HB-Feinmechanik LTW 63) through a perforated plate with diameter 3.2 mm. The extrudates were then dried in a drying cabinet at 80° C. for one hour and calcined in a muffle furnace at 570° C. for 12 h.

Example 6

Catalytic Test with the Catalyst from Comparative Example 3

[0097] The epoxidation of propene by means of hydrogen peroxide (60%) was effected over two fixed bed reactors, each of which contained 9 g of catalyst from Comparative Example 3 in the form of extrudates. The reactors were arranged in series (reactor 1.fwdarw.reactor 2) and were operated in upward flow. The first feed stream with a total flow rate of 20 g/h, consisting of methanol, hydrogen peroxide and water, and a second feed stream consisting of 20 g/h of propene were both fed to the first reactor. The reaction pressure was kept at 25 bar by means of a pressure-retaining valve downstream of the second reactor. The reaction mixture exiting from the second fixed bed reactor was expanded to ambient pressure. The resulting gas phase was analysed for propene, propylene oxide and oxygen, and the resulting liquid phase was analysed for propylene oxide and hydrogen peroxide. The initial selectivity for propylene oxide after a reaction run time of 23 h was 91.1%. After 480 h, the selectivity for propylene oxide was 97.7%.

Example 7

Catalytic Test with the Catalyst from Example 5

[0098] The catalytic epoxidation of propene was effected according to Example 6, but with the catalyst prepared in Example 5.

[0099] The initial selectivity for propylene oxide after a reaction run time of 25 h was 93.5%. After 480 h, the selectivity for propylene oxide was 98.6%.

TABLE-US-00001 TABLE 1 Comparison of the results of catalytic test reactions S(PO), % Space-time yield, after 480 h kg PO/kg cat-h Example 6: 97.7 0.21 Conventionally prepared catalyst (Comparative Example 3) Example 7: 98.6 0.21 Inventive catalyst (Example 5)

[0100] As shown by Examples 2-4 by comparison with Comparative Example 1, the process according to the invention contains much fewer process steps than the conventional process. Moreover, this dispenses with the problems of disposing of the wastewaters that typically arise during the filtration and cleaning of the product after the hydrothermal synthesis. Surprisingly, the titanium silicalites obtained, after the flame spray pyrolysis, have a porosity comparable to the conventionally prepared titanium silicalite.

[0101] As apparent from Examples 6 and 7 and from Table 1, both the conventionally prepared catalyst (Comparative Example 3) and the catalyst which has been obtained from the metal silicate prepared in accordance with the invention (Example 5), after an operating time of 480 h in the epoxidation of propylene to propylene oxide (PO), are highly active and selective. The catalyst which has been obtained from the metal silicate prepared in accordance with the invention actually shows a higher selectivity for propylene oxide by 0.9% than the conventional catalyst with a comparable space-time yield. Wth a catalyst which has been obtained from a titanium silicalite prepared in accordance with the invention, based on unit time and reactor volume, it is thus possible to distinctly increase the product yield of propylene oxide.

[0102] Crystallographic Data of Titanium Silicalite-1 (Source: ICDD Database)

[0103] Reference code: 01-089-8099

[0104] Name of the compound: silicon titanium oxide

[0105] ICSD code: 88413

[0106] Reference: Lamberti, C., Bordiga, S., Zecchina, A., Carati, A., Fitch, A. N., Artioli, G., Petrini, G., Salvalaggio, M., Marra, G. L., J. Catal., 183, 222, (1999)

[0107] List of Reflections:

TABLE-US-00002 Number h k l d [Å] 2θ [°] l [%] 1 0 1 1 11.17140 7.908 100.0 2 1 0 1 11.17140 7.908 100.0 3 2 0 0 10.07340 8.771 33.7 4 0 2 0 9.97825 8.855 36.2 5 1 1 1 9.74800 9.065 17.1 6 2 1 0 8.99270 9.828 1.3 7 2 0 1 8.05720 10.972 0.5 8 1 2 1 7.44190 11.882 1.1 9 2 1 1 7.44190 11.882 1.1 10 2 2 0 7.08909 12.476 0.3 11 0 0 2 6.71210 13.180 4.1 12 1 0 2 6.36799 13.896 8.3 13 1 1 2 6.06662 14.589 1.0 14 3 0 1 6.00599 14.738 9.2 15 0 3 1 5.96048 14.851 6.0 16 1 3 1 5.71559 15.491 5.5 17 0 2 2 5.58570 15.853 5.7 18 2 0 2 5.58570 15.853 5.7 19 2 1 2 5.36799 16.501 1.9 20 1 2 2 5.36799 16.501 1.9 21 2 3 1 5.14575 17.219 0.8 22 3 2 1 5.14575 17.219 0.8 23 4 0 0 5.03670 17.594 2.4 24 0 4 0 4.98912 17.764 3.4 25 4 1 0 4.88356 18.151 0.4 26 2 2 2 4.88356 18.151 0.4 27 4 0 1 4.71570 18.803 0.1 28 3 1 2 4.61852 19.202 2.4 29 1 4 1 4.55547 19.470 0.3 30 4 2 0 4.49635 19.729 0.2 31 2 4 0 4.45787 19.901 0.5 32 3 3 1 4.45787 19.901 0.5 33 0 1 3 4.36632 20.322 3.0 34 1 0 3 4.36632 20.322 3.0 35 4 2 1 4.26355 20.818 5.0 36 1 1 3 4.26355 20.818 5.0 37 2 0 3 4.08941 21.715 1.1 38 4 3 0 4.01553 22.119 1.9 39 2 1 3 4.01553 22.119 1.9 40 4 1 2 3.94894 22.497 0.3 41 4 3 1 3.85926 23.027 30.6 42 5 0 1 3.85926 23.027 30.6 43 3 4 1 3.82578 23.231 23.6 44 0 5 1 3.82578 23.231 23.6 45 1 5 1 3.75861 23.652 10.4 46 3 0 3 3.72380 23.877 15.6 47 0 3 3 3.72380 23.877 15.6 48 3 1 3 3.65139 24.357 12.3 49 1 3 3 3.65139 24.357 12.3 50 5 2 1 3.59942 24.714 1.2 51 4 4 0 3.54454 25.103 0.1 52 3 2 3 3.48877 25.511 1.8 53 2 3 3 3.48877 25.511 1.8 54 4 3 2 3.44594 25.834 4.1 55 3 4 2 3.44594 25.834 4.1 56 5 1 2 3.40404 26.157 1.0 57 1 5 2 3.38191 26.332 0.8 58 0 0 4 3.35780 26.524 2.2 59 6 0 0 3.35780 26.524 2.2 60 5 3 1 3.34523 26.626 1.1 61 4 0 3 3.34523 26.626 1.1 62 0 6 0 3.32608 26.782 2.1 63 3 5 1 3.32608 26.782 2.1 64 6 1 0 3.31043 26.911 3.6 65 1 0 4 3.31043 26.911 3.6 66 5 2 2 3.26581 27.286 0.6 67 1 1 4 3.26581 27.286 0.6 68 6 0 1 3.25744 27.357 0.7 69 3 3 3 3.24744 27.443 1.2 70 2 5 2 3.24744 27.443 1.2 71 6 1 1 3.21490 27.726 0.1 72 2 0 4 3.18399 28.001 0.7 73 6 2 0 3.18399 28.001 0.7 74 4 2 3 3.17173 28.111 0.4 75 1 2 4 3.14203 28.383 1.2