PROCESS FOR PRODUCING TUNGSTEN OXIDE AND TUNGSTEN MIXED OXIDES

Abstract

Process for producing a tungsten oxide powder or a tungsten mixed oxide powder of general formula M.sub.xWO.sub.3, wherein M=Na, K, Rb, Li and/or Cs, 0.1x0.5, comprising the consecutive steps of: a) providing a solution comprising respectively at least one tungsten compound and optionally at least one M-comprising compound in a concentration corresponding to the stoichiometry M.sub.xWO.sub.3, b) atomizing the solution, thus forming an aerosol, into a reaction space, c) reacting the aerosol in the reaction space with a hydrogen/oxygen flame for which the expression 1<O.sub.2,primary/0.5H.sub.23 applies, wherein the reaction space is configured such that it comprises two reaction zones with two different velocities of the reaction mixture v.sub.1 and v.sub.2 where v.sub.2=0.3-0.8 v.sub.1 and 0.5v.sub.110 Nm/s, d) separating the solid from vaporous or gaseous substances and e) passing a reducing gas stream over the separated solid at a temperature of 450-700 C.

Process for producing a tungsten oxide powder or a tungsten mixed oxide powder of general formula M.sub.xWO.sub.3, wherein M=Na, K, Rb, Li and/or Cs, 0.1x0.5, comprising the consecutive steps of: a) providing a solution comprising respectively at least one tungsten compound and optionally at least one M-comprising compound in a concentration corresponding to the stoichiometry M.sub.xWO.sub.3, b) atomizing the solution, thus forming an aerosol, into a reaction space, c) reacting the aerosol in the reaction space with a hydrogen/oxygen flame having a lambda value<1, wherein: lambda=total oxygen/0.5hydrogen, d) separating the solid from vaporous or gaseous substances.

Claims

1-11. (canceled)

12. A process for producing a tungsten oxide powder or a tungsten mixed oxide powder of general formula M.sub.xWO.sub.3, wherein M=Na, K, Rb, Li and/or Cs, and 0.1x0.5, comprising the consecutive steps of: a) providing a solution comprising respectively at least one tungsten compound and optionally at least one M-comprising compound in a concentration corresponding to the stoichiometry M.sub.xWO.sub.3; b) atomizing the solution, thus forming an aerosol, into a reaction space; c) reacting the aerosol in the reaction space with a hydrogen/oxygen flame for which the expression 1<O.sub.2,primary/0.5H.sub.23 applies, and wherein the reaction space is configured such that it comprises two reaction zones with two different velocities of the reaction mixture v.sub.1 and v.sub.2 where v.sub.2=0.30.8 v.sub.1 and 0.5v.sub.110 Nm/s; d) separating the solid from vaporous or gaseous substances; and e) passing a reducing gas stream over the separated solid at a temperature of 450-700 C.

13. The process of claim 12, wherein total oxygen is such that 1.5O.sub.2,ttl/0.5H.sub.25.

14. The process of claim 12, wherein t.sub.2>0.5 t.sub.1, and wherein t.sub.1 is the average residence time of the reaction mixture in reaction zone 1 and t.sub.2 is the average residence time of the reaction mixture in reaction zone 2.

15. The process of claim 12, wherein the thermal treatment is performed over a period of 1-10 hours.

16. The process of claim 12, wherein hydrogen, hydrogen/nitrogen mixtures or hydrogen/noble gas mixtures are employed as the reducing gas stream.

17. The process of claim 12, wherein the average residence time in the reaction space is 1-5 s.

18. The process of claim 17, wherein atomization is effected by means of a single- or multimaterial nozzle and the mean droplet diameter of the aerosol is less than 120 m.

19. The process of claim 18, wherein the concentration of metals in the solution is 5-60 wt %.

20. The process of claim 12, wherein atomization is effected by means of a single- or multimaterial nozzle and the mean droplet diameter of the aerosol is less than 120 m.

21. The process of claim 12, wherein the solution comprises inorganic metal compounds.

22. The process of claim 12, wherein the solution is an aqueous solution.

23. The process of claim 12, wherein the concentration of metals in the solution is 5-60 wt %.

24. A process for producing a tungsten oxide powder or a tungsten mixed oxide powder of general formula M.sub.xWO.sub.3, wherein M=Na, K, Rb, Li and/or Cs, and X is 0.1x0.5, comprising the consecutive steps of: a) providing a solution comprising respectively at least one tungsten compound and optionally at least one M-comprising compound in a concentration corresponding to the stoichiometry M.sub.xWO.sub.3; b) atomizing the solution, thus forming an aerosol, into a reaction space; c) reacting the aerosol in the reaction space with a hydrogen/oxygen flame having a lambda value<1, wherein: lambda=total oxygen/0.5hydrogen; d) separating the solid from vaporous or gaseous substances.

25. The process of claim 24, wherein atomization is effected by means of a single- or multimaterial nozzle and the mean droplet diameter of the aerosol is less than 120 m.

26. The process of claim 24, wherein the average residence time in the reaction space is 1-5 s.

27. The process of claim 26, wherein atomization is effected by means of a single- or multimaterial nozzle and the mean droplet diameter of the aerosol is less than 120 m.

28. The process of claim 27, wherein the concentration of metals in the solution is 5-60 wt %.

29. The process of claim 24, wherein the solution comprises inorganic metal compounds.

30. The process of claim 24, wherein the solution is an aqueous solution.

31. The process of claim 24, wherein the concentration of metals in the solution is 5-60 wt %.

Description

EXAMPLES

[0037] Examples 1-5 show the production of alkali metal-tungsten mixed oxide powders by the two-stage process according to the invention. Example 6 shows a comparative example of a two-stage process. Examples 7-11 show the production of potassium-tungsten mixed oxide powders by the single-stage process according to the invention.

Example 1

[0038] A solution of 2165 g of ammonium metatungstate, 335 g of caesium nitrate and 12 020 g of water is produced. The total concentration of W and Cs, as metal in each case, is 12.7 wt %.

[0039] Reaction zone 1: Jetting 2500 g/h of this solution with 5 Nm.sup.3/h of air as jetting gas by means of a two-material nozzle at room temperature (23 C.) affords an aerosol. This is brought to reaction with 8 Nm.sup.3/h (0.357 kmol/h) of hydrogen and 30 Nm.sup.3/h of air (0.281 kmol 02/h). The temperature 50 cm below the burner mouth is 527 C.

[0040] The residence time in reaction zone 1 is 0.48 seconds at a gas velocity of 2.89 Nm/s.

[0041] Reaction zone 2: 15 Nm.sup.3/h of secondary air (0.141 kmol 02/h) are additionally introduced into the reactor outside reaction zone 1.

[0042] The residence time in reaction zone 2 is 0.36 seconds at a gas velocity of 1.65 Nm/s. Subsequently, the reaction mixture is cooled and the obtained solid separated from the gaseous materials on a filter.

[0043] The solid has a BET surface area of 7.2 m.sup.2/g.

[0044] The solid from the FSP is heated under a nitrogen atmosphere at a heating rate of 8.0 C./min to an end temperature of 500 C. and there treated in a forming gas atmosphere (70/30 vol % N.sub.2/H.sub.2,volume flow 100 NI/h) over a period of 2 hours at a temperature of 500 C.

[0045] The obtained reduced solid has a BET surface area of 5.4 m.sup.2/g. A dispersion of the solid, 18 wt % in 1-methoxy-2-propanol, is deep blue in colour.

[0046] Examples 2 to 6 are performed analogously. Example 6 is a comparative example where the average velocities in both reaction zones are identical. Starting materials and reaction conditions may be found in table 1. Table 2 shows calculated values.

[0047] The two-stage process according to the invention is directed at obtaining in a flame pyrolytic process a material having a low BET surface area coupled with a rather high crystallinity. In the subsequent reduction step the BET surface area is reduced only to a small extent while the reduction proceeds rapidly under moderate conditions without appreciable sintering. This material is correspondingly readily dispersible.

[0048] In comparative example 6 a material having an increased BET surface area is obtained from the FSP. This material is more difficult to reduce. The reduced material itself is more difficult to disperse.

Example 7

[0049] A solution of 4316 g of ammonium metatungstate, 502 g of potassium acetate, 64 g of glacial acetic acid and 4831 g of water is produced. The total concentration of W and K, in each case as metal, is 34.2 wt %.

[0050] Jetting 9.0 kg/h of this solution with 9.2 Nm.sup.3/h of air as jetting gas by means of a two-material nozzle at room temperature (23 C.) affords an aerosol. This is brought to reaction with 10 Nm.sup.3/h of hydrogen and 13.5 Nm.sup.3/h of air. The temperature 50 cm below the burner mouth is 464 C. Lambda is 0.87. The residence time is 1.9 seconds.

[0051] The solid has a BET surface area of 2.4 m.sup.2/g. A dispersion of the solid, 18 wt % in 1-methoxy-2-propanol, is deep blue in colour. X-ray structural analysis shows a hexagonal potassium-tungsten mixed oxide.

[0052] Examples 8 to 11 are performed analogously with the same solution. The reaction conditions may be found in table 3.

[0053] Examples 7 to 11 show that reduced powders are producible by means of a single-stage process, namely a flame-spray pyrolysis.

TABLE-US-00001 TABLE 1 Two-stage process - starting materials - BET surface area of the powders Example 1 2 3 4 5 6 (comp.) solution ammonium g/h 216.5 241.5 143.8 145.3 144.9 216.5 metatungstate caesium nitrate g/h 33.5 33.5 potassium nitrate g/h 8.5 3.2 sodium nitrate g/h 6.2 47.4 1.9 concentration.sup.a) wt % 12.7 13.0 13.0 13.0 13.0 12.7 gases atomizer air Nm.sup.3/h 5 5 5 5 5 5 hydrogen Nm.sup.3/h 8 6 6 6 6 8 primary air Nm.sup.3/h 30 30 30 30 30 30 secondary air Nm.sup.3/h 15 15 15 15 15 53 temperature.sup.b) C. 527 531 525 528 524 524 red. atmosphere vol % 70:30 N.sub.2/H.sub.2.sup.c) T.sub.reduction/t.sub.reduction C./h 500/2 BET.sub.FSP m.sup.2/g 7.2 3.9 2.0 2.1 2.1 16.2 BET.sub.reduced m.sup.2/g 5.4 3.5 1.8 1.8 2.0 5.8 BET.sub.reduced/BET.sub.FSP 0.75 0.90 0.90 0.86 0.95 0.36 .sup.a)based on metals; .sup.b)reaction zone 1; 50 cm below reactor inlet; .sup.c)volume flow 100 Nl/h

TABLE-US-00002 TABLE 2 Two-stage process - calculated values 6 example 1 2 3 4 5 (comp.) H.sub.2 kmol/h 0.357 0.268 0.268 0.268 0.268 0.357 O.sub.2, primary kmol/h 0.281 0.281 0.281 0.281 0.281 0.281 O.sub.2, secondary kmol/h 0.141 0.141 0.141 0.141 0.141 0.496 O.sub.2, atomiz. kmol/h 0.047 0.047 0.047 0.047 0.047 0.047 O.sub.2, ttl kmol/h 0.469 0.469 0.469 0.469 0.469 0.824 O.sub.2, primary/0.5H.sub.2 1.57 2.10 2.10 2.10 2.10 1.57 O.sub.2, primary+atomiz./ 1.84 2.45 2.45 2.45 2.45 1.84 0.5H.sub.2 O.sub.2, ttl/0.5H.sub.2 2.63 3.50 3.50 3.50 3.50 4.62 v.sub.1.sup.a) Nm/s 2.89 2.77 2.74 2.75 2.74 2.89 v.sub.2.sup.a) Nm/s 1.65 1.61 1.45 1.59 1.57 2.89 t1.sup.b) s 0.48 0.51 0.51 0.51 0.51 0.48 t2.sup.b) s 0.36 0.37 0.41 0.38 0.38 0.21 v.sub.2/v.sub.1 0.57 0.58 0.53 0.58 0.57 1.00 t.sub.2/t.sub.1 0.75 0.74 0.81 0.74 0.75 0.43 .sup.a)v.sub.1, v.sub.2 = average gas velocity reaction zone 1, 2; .sup.b)average residence time reaction zone 1, 2;

TABLE-US-00003 TABLE 3 single-stage process - starting materials - BET surface area of the powders example 7 8 9 10 11 solution ammonium g/h 4316 metatungstate potassium g/h 502 acetate solution.sup.a) wt % 34.2 34.2 34.2 34.2 42.8 throughput kg/h 9.0 6.0 6.0 9.0 12.0 gases air Nm.sup.3/h 13.5 13.5 13.5 13.5 13.5 atomizer air Nm.sup.3/h 9.2 9.2 9.4 9.5 9.5 total oxygen Nm.sup.3/h 4.77 4.77 4.81 4.83 4.83 hydrogen Nm.sup.3/h 10.0 10.0 12.0 12.0 12.0 lambda.sup.b) 0.87 0.87 0.80 0.81 0.81 temperature.sup.c) C. 464 449 587 566 590 BET surface m.sup.2/g 2.4 2.0 1.3 1.7 1.5 area .sup.a)based on metals; .sup.b)lambda = total oxygen/0.5 hydrogen; .sup.c)reaction zone 1; 50 cm below reactor inlet