Method for producing metal oxides by means of spray pyrolysis

Abstract

A process for producing a metal oxide powder by flame spray pyrolysis where a) a stream of a solution containing at least one oxidizable or hydrolysable metal compound is atomized to afford an aerosol by means of an atomizer gas, b) this aerosol is brought to reaction in the reaction space of the reactor with a flame obtained by ignition of a mixture of fuel gas and air, c) the reaction stream is cooled and d) the solid product is subsequently removed from the reaction stream, wherein e) the reaction space comprises one or more successive double-walled internals, wherein the wall of the double-walled internal facing the flame-conducting region of the reaction space comprises at least one slot through which a gas or vapour is introduced into the reaction space in which the flame is burning and f) the slot is arranged such that this gas or vapour brings about a rotation of the flame.

Claims

1. A process for producing a metal oxide powder by flame spray pyrolysis, comprising the steps of: a) using an atomizer gas to atomize a stream of a solution and thereby produce an aerosol, wherein the solution comprises at least one oxidizable or hydrolysable metal compound; b) reacting the aerosol of step a) in a reaction space of a reactor with a flame obtained by ignition of a mixture of fuel gas and air to produce a reaction stream; c) cooling the reaction stream; d) removing a solid product from the cooled reaction stream of step c); wherein: i) the reaction space comprises one or more successive double-walled internals, wherein the wall of the double-walled internal facing a flame-conducting region of the reaction space comprises at least one slot through which a gas or vapour is introduced into the reaction space in which the flame is burning; and ii) the slot is arranged such that this gas or vapour brings about a rotation of the flame.

2. The process of claim 1, wherein the internal comprises at least two slots.

3. The process of claim 1, wherein slot length/slot width is 10:1-200:1.

4. The process of claim 1, wherein reaction space diameter/total slot area is 15:1-200:1.

5. The process of claim 1, wherein, when viewed in longitudinal section of an internal, an angle α of a slot to vertical is 15°≤α≤60°.

6. The process of claim 1, wherein angle β, which describes an angle between a section axis of the slot to a circle perpendicular of centre, is 30°≤β≤60°.

7. The process of claim 1, wherein the gas is a fuel gas.

8. The process of claim 1, wherein the gas is an oxygen-containing gas.

9. The process of claim 1, wherein a metal component of the metal compound is selected from the group consisting of Ag, Al, Au, B, Ba, Ca, Cd, Ce, Co, Cr, Cu, Dy, Fe, Ga, Ge, Hf, In, La, Li, Mg, Mn, Mo, Nb, Ni, Pd, Rh, Ru, Sc, Si, Sm, Sn, Sr, Ta, Ti, V, Y, Yb and Zn.

10. The process of claim 1, wherein the solution contains zinc, titanium or calcium as the metal of the metal compound.

11. The process of claim 1, wherein the solution contains Li, La and Zr as the metal of the metal compound.

12. The process of claim 1, wherein the solution contains Li and Ni as the metal of the metal compound.

13. The process of claim 1, wherein a gas supplied via a slot in an internal lengthens average residence time of the mixture of fuel gas and air in the reaction space by at least a factor of 1.2 compared to a reaction space comprising none of these internals.

14. The process of claim 1, wherein gas entry velocity from a slot of an internal into the reaction space is at least 10 Nm/s.

15. The process of claim 1, wherein the internal comprises four slots.

16. The process of claim 1, wherein angle β is 40°≤β≤50°.

17. The process of claim 2, wherein slot length/slot width is 10:1-200:1.

18. The process of claim 2, wherein reaction space diameter/total slot area is 15:1-200:1.

19. The process of claim 2, wherein the solution contains zinc, titanium or calcium as the metal of the metal compound.

20. The process of claim 2, wherein the solution contains Li, La and Zr as the metal of the metal compound.

Description

(1) FIGS. 1-3 show the process according to the invention in schematic form. FIG. 1 shows the arrangement for performing the process where A=metal solution; B=hydrogen; C=primary air; D=secondary air; R×R=reaction space; Fl=flame; I-III=internals I-III; S.sub.l, 1-4=slots in internal I, here 4 slots 1-4; representative of further internals; E-I to E-III=gas/vapour feed point.

(2) FIG. 2 shows in schematic form an internal with slots 1-4 in longitudinal section along the axis A-B (FIG. 2A) and B-A (FIG. 2B). FIG. 2C shows a detailed view having regard to angle α.

(3) FIG. 3 shows the cross section through this internal with slots 1-4 and angle β.

(4) FIG. 4 shows in schematic form the rotation of the flame brought about by the introduction of gas or vapour through 4 slots. The rotation causes the flame to become narrower and longer compared to a process according to the prior art which provides no internals according to the invention.

(5) In the context of the present invention the term “internal” or “internals” is always to be understood as meaning double-walled internals. A reaction space and an internal are generally tubular. The internal is installed in the reaction space such that its outer wall is in contact with the inner wall of the reaction space. The internal is closed at top and bottom. If a plurality of internals are present these may be identical or different in terms of length or diameter for example. The successive internals may conduct identical or different gases. It is likewise possible for individual internals not to conduct gases.

(6) The process according to the invention is preferably implemented such that an internal comprises four slots. When the internal is taken to be tubular then in cross section the four slots are preferably arranged such that one slot is located in each quadrant. This is shown in FIG. 3.

(7) Usually, the length of a slot is 50-100 mm, the width thereof is 0.5-3 mm and the slot length/slot width ratio is 10:1-200:1.

(8) The angle α of a slot to the vertical is preferably 15°≤α≤60° and particularly preferably 25°≤α≤40°.

(9) The process as claimed in claims 1 to 5, characterized in that the angle β which describes the angle between the section axis of the slot to the circle perpendicular of the centre is preferably 30°≤β≤60° and particularly preferably 40°≤β≤50°.

(10) A further feature with which the flame may be varied is the ratio of the diameter of the reaction space to the total slot area. This ratio is preferably 15:1-200:1 and particularly preferably 25:1-50:1.

(11) The gas supplied via the slot in an internal may be a fuel gas. Examples of fuel gases are hydrogen, methane, ethane, natural gas and/or carbon monoxide. It is particularly preferable to employ hydrogen. A fuel gas is employed in particular for embodiments where a high crystallinity of the metal oxides to be produced is desired, for example for mixed lithium oxides for use in lithium ion batteries.

(12) The gas supplied via the slot in an internal may be an oxygen-containing gas. This is generally air or oxygen-enriched air. An oxygen-containing gas is employed in particular for embodiments where for example a high BET surface area of the metal oxide to be produced is desired.

(13) The fuel gas or oxygen-containing gas supplied via a slot in an internal is generally the same and as used for ignition of the flame in the reaction space. The total amount of oxygen is chosen such that, taken over all internals, it is sufficient at least for complete conversion of the fuel gas and the metal compounds.

(14) Furthermore, inert gases such as nitrogen or reactive vapours such as water vapour may also be supplied via a slot in an internal.

(15) In the process according to the invention the solution is introduced into the reaction space in the form of an aerosol. The fine droplets of the aerosol preferably have an average droplet size of 1-120 μm, particularly preferably of 30-100 μm. The droplets are typically produced using single- or multi-material nozzles. To increase the solubility of the metal compounds and to attain a suitable viscosity for atomization of the solution the solution may be heated.

(16) Suitable solvents include water, alkanes, alkanecarboxylic acids and/or alcohols. Preference is given to using aqueous solutions, wherein an aqueous solution is to be understood as meaning a solution in which water is the main constituent of a solvent mixture or in which water alone is the solvent. The concentration of the employed solutions is not particularly limited. If only one solution containing all mixed oxide components is present, the concentration is generally 1 to 50 wt %, preferably 3 to 30 wt %, particularly preferably 5-20 wt %, in each case based on the sum of the oxides.

(17) The metal compounds may be inorganic metal compounds, such as nitrates, chlorides, bromides, or organic metal compounds, such as alkoxides or carboxylates. The alkoxides employed may preferably be ethoxides, n-propoxides, isopropoxides, n-butoxides and/or tert-butoxides. The carboxylates used may be the compounds based on acetic acid, propionic acid, butanoic acid, hexanoic acid, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, octanoic acid, 2-ethylhexanoic acid, valeric acid, capric acid and/or lauric acid.

(18) The metal component is preferably selected from the group consisting of Ag, Al, Au, B, Ba, Ca, Cd, Ce, Co, Cr, Cu, Dy, Fe, Ga, Ge, Hf, In, La, Li, Mg, Mn, Mo, Nb, Ni, Pd, Rh, Ru, Sc, Si, Sm, Sn, Sr, Ta, Ti, V, Y, Yb and Zn. In the context of the invention silica and boron are to be regarded as metals.

(19) In a particular embodiment the solution contains Zn, Ti or Ca as the metal of the metal compound.

(20) In a further particular embodiment the solution contains Li, La and Zr as the metal of the metal compound. In addition to these the solution may further contain Al, Au, Ba, Ca, Ce, Dy, Ga, Ge, Hf, Mg, La, Nb, Sc, Si, Sm, Sn, Sr, Ta, Ti, V, Yb or Zn.

(21) In a further particular embodiment the solution contains Li and Ni as the metal of the metal compound. In addition to these the solution may further contain Co and Mn.

(22) On account of the rotating flame the average residence time of the particles in the flame is lengthened. The rotational movement causes the flame itself to become narrower but also substantially longer compared to a flame burning in a reaction space without internals. The process according to the invention is preferably implemented such that gas supplied via a slot in an internal lengthens the average residence time of the reaction mixture in the reaction space by at least a factor of 1.2, particularly preferably 1.2-5, compared to a reaction space comprising none of these internals.

(23) It is likewise possible to influence the rotation of the flame via the gas entry velocity from a slot in an internal into the reaction space. The gas entry velocity is preferably at least 10 Nm/s, particularly preferably 10-50 Nm/s.

EXAMPLES

(24) In the comparative examples the cylindrical reaction space comprises no internals. FIG. 1A shows in schematic form the input materials and the feed point thereof for the comparative examples.

(25) In the inventive examples the reaction space 3 comprises successive tubular internals, internal I-III, of 50 cm in length respectively. These are affixed in the reaction space. The internals comprise four slots having a length of 10 cm and a width of 0.15 cm. The arrangement of the slots is as shown in FIG. 2 and FIG. 3, where α=33° and β=45°. The slot length/slot width ratio is 67:1.

(26) FIG. 1B shows in schematic form the input materials and the feed point thereof for the inventive examples.

(27) The ratio of the diameter of the reaction space to the total slot area is 31.4:1.

Example 1.1 (Comparative)

(28) Solution Employed:

(29) Calcium octoate solution, Octa-Soligen Calcium 10, a mixture of calcium salts of C6-C19-fatty acids and naphtha (petroleum), OMG Borchers, containing 10 wt % of calcium.

(30) 2.5 kg/h of the solution are atomized into the tubular reaction space with 3.5 Nm.sup.3/h of atomization air by means of a two-material nozzle.

(31) The reaction space comprises no internals.

(32) The flame is formed by the reaction of 5 Nm.sup.3/h of hydrogen, 13 Nm.sup.3/h of primary air and 15 Nm.sup.3/h of secondary air. Further reaction parameters are reported in the table.

(33) The obtained powder has a BET surface area according to DIN ISO 9277 of 20 m.sup.2/g.

Example 1.2 (According to the Invention)

(34) As per example 1 but via internal 115 Nm.sup.3/h of air are introduced into the reaction space.

(35) The obtained powder has a BET surface area of 38 m.sup.2/g.

Example 2.1 (Comparative)

(36) Zinc octoate solution, Octa-Soligen Zink 29, a mixture of zinc salts of C6-C19-fatty acids and naphtha (petroleum), TIB, containing 29 wt % of zinc.

(37) 1.5 kg/h of the solution are atomized into the tubular reaction space with atomization air (4 Nm.sup.3/h) by means of a two-material nozzle. The reaction space comprises no internals.

(38) The flame is formed by the reaction of 5 Nm.sup.3/h of hydrogen and 24 Nm.sup.3/h of primary air. Further reaction parameters are reported in the table

(39) The obtained powder has a BET surface area according to DIN ISO 9277 of 11 m.sup.2/g.

Example 2.2 (According to the Invention)

(40) As per example 1 but via

(41) internal I 20 Nm.sup.3/h of air and 1 Nm.sup.3/h of water vapour

(42) internal II 10 Nm.sup.3/h of air and 1 Nm.sup.3/h of water vapour and

(43) internal III 10 Nm.sup.3/h of air

(44) are introduced into the reaction space.

(45) The obtained powder has a BET surface area of 70 m.sup.2/g.

Example 3.1 (Comparative)

(46) Solution used: 5.21 wt % of lithium nitrate, 15.66% wt % of lanthanum nitrate, 10.35 wt % of zirconium nitrate, wt % of aluminium nitrate, remainder water. The concentration based on the oxide Li.sub.6.27La.sub.3Zr.sub.2Al.sub.0.24O.sub.12 is 10.26 wt %.

(47) 8 kg/h of the solution are atomized into the tubular reaction space with an atomization gas consisting of 15 Nm.sup.3/h of air and 0.05 kg of ammonia gas/Nm.sup.3 of air by means of a two-material nozzle.

(48) The reaction space comprises no internals.

(49) The flame is formed by the reaction of 13 Nm.sup.3/h of hydrogen, 75 Nm.sup.3/h of primary air and 25 Nm.sup.3/h of secondary air. Further reaction parameters are reported in the table.

(50) The mixed oxide powder has a composition of Li.sub.6.27La.sub.3Zr.sub.2Al.sub.0.24O.sub.12. The BET surface area is 5 m.sup.2/g.

Example 3.2 (According to the Invention)

(51) As per example 5 but via internal I and internal II 3 Nm.sup.3/h respectively of hydrogen are introduced into the reaction space.

(52) The mixed oxide powder has a composition of Li.sub.6.27La.sub.3Zr.sub.2Al.sub.0.24O.sub.12. The BET surface area is <1 m.sup.2/g.

Example 3.3 (According to the Invention)

(53) As per example 5 but via internal II 20 Nm.sup.3/h of air and via internal III 30 Nm.sup.3/h of air are introduced into the reaction space.

(54) The mixed oxide powder has a composition of Li.sub.6.27La.sub.3Zr.sub.2Al.sub.0.24O.sub.12. The BET surface area is 20 m.sup.2/g.

Example 4.1 (Comparative)

(55) Employed solution consisting of 13.3 wt % of lithium nitrate, 3.8 wt % of nickel(II) nitrate, 15.6 wt % of manganese(II) nitrate, 3.7 wt % of cobalt(II) nitrate and 0.05 wt % of boric acid, remainder water. Sum of metal is 8.6wt %.

(56) 10 kg/h of the solution are atomized into the tubular reaction space with an atomization gas consisting of 15 Nm.sup.3/h of air and 1.5 kg of ammonia gas/Nm.sup.3 of air by means of a two-material nozzle.

(57) The reaction space comprises no internals.

(58) The flame is formed by the reaction of 13.9 Nm.sup.3/h of hydrogen and 45 Nm.sup.3/h of primary air. Further reaction parameters are reported in the table.

(59) The mixed oxide powder has the composition Li.sub.1.2(Ni.sub.0.13Co.sub.0.125Mn.sub.0.54B.sub.0.05)O.sub.2. The BET surface area is 14 m.sup.2/g, the crystallite diameter d.sub.XRD=750 nm.

Example 4.2 (According to the Invention)

(60) As per example 7 but via internal I 40 Nm.sup.3/h of air and via internal II 10 Nm.sup.3/h of air are introduced into the reaction space.

(61) The mixed oxide powder has the composition Li.sub.1.2(Ni.sub.0.13Co.sub.0.125Mn.sub.0.54B.sub.0.05)O.sub.2. The BET surface area is 5 m.sup.2/g, the crystallite diameter d.sub.XRD=5500 nm.

(62) Examples 1 and 2 show how the BET surface areas of a metal oxide powder may be increased by means of the process according to the invention compared to a process comprising no internals in the reaction space.

(63) Examples 3 show that by means of the process according to the invention the BET surface area of the metal oxide powder may be both reduced (example 3.2) and increased (example 3.3) in each case compared to a process comprising no internals in the reaction space. The method oxide powder from example 3.2 also exhibits a high crystallinity.

(64) Examples 4 show how the crystallinity of a metal oxide powder may be increased by means of the process according to the invention compared to a process comprising no internals in the reaction space.

(65) Key to Table: v=Gas entry velocity in internals I-III; v.sub.in=Gas velocity of the gases or vapours introduced into internals I-III; t=average residence time in internal I-III; t.sup.ttl=average residence time via internals I-III; v.sup.ttl=average gas velocity via internals I-III; a) atomization gas contains NH.sub.3; b) N.sub.2 instead of air in example 3.3; c) Nm/s=normalized velocity calculated from normal volume and cross section; d) T.sub.flame=flame temperature; measured 10 cm below feed point for aerosol, H.sub.2 and air into the reaction space; e) T.sub.flame.sup.(I)-(III)=flame temperature; measured 10 cm below internal;

(66) TABLE-US-00001 TABLE Input materials and reaction conditions Example 1.1 1.2 2.1 2.2 3.1 3.2 3.3 4.1 4.2 {dot over (m)}.sub.solution kg/h 2.5 2.5 1.5 1.5  8  8  8  10  10 c.sub.metal wt % 7 7 16 16    10.17    10.17    10.17    8.6    8.6 {dot over (V)}.sub.atomization air Nm.sup.3/h 3.5 3.5 4 4  15.sup.a)  15.sup.a)   15.sup.a) b)  15.sup.a)  15.sup.a) {dot over (V)}.sub.primary air Nm.sup.3/h 13 13 24 24  75  75  75  45  5 {dot over (V)}.sub.secondary air Nm.sup.3/h 15 15 — —  25  25  25 — — {dot over (V)}.sub.hydrogen Nm.sup.3/h 5 5 1.8 1.8  13  13  13   13.9   13.9 T.sub.flame.sup.d) ° C. 788 788 1244 1244 517 517 515 789 979 Internal I {dot over (V)}.sub.hydrogen.sup.(I) Nm.sup.3/h — — — — —  3 — — — {dot over (V)}.sub.air.sup.(I) Nm.sup.3/h — 15 — 20 — — — —  40 {dot over (V)}.sub.water vapour.sup.(I) kg/h — — — 1 — — — — — v.sub.in.sup.(I) Nm/s — 17.6 — 19.4   10.2 — —   15.4 v.sup.(I) Nm/s 1.40 1.84 1.65 2.55    3.34    4.56    3.34    2.83    3.24 t.sup.(I) ms 357 1.360 303 980 150 550 150 177 772 T.sub.flame.sup.(I) e) ° C. 751 686 1023 643 498 681 498 723 983 Internal II {dot over (V)}.sub.air.sup.(II) Nm.sup.3/h — — — 10 — —  30 —  10 {dot over (V)}.sub.water vapour.sup.(II) kg/h — — — 1 — — — — — v.sub.in.sup.(II) Nm/s.sup.c) — — — 14.1 — —   27.8 — — v.sup.(II) Nm/s 1.15 1.75 1.47 2.89    2.49    4.83    3.86    2.17    2.61 t.sup.(II) ms 435 286 340 865    2.01 104 650 230 958 T.sub.flame.sup.(II) e) ° C. 723 657 917 491 463 719 372 697 927 Internal III {dot over (V)}.sub.hydrogen.sup.(III) Nm.sup.3/h — — — — —  3 — — — {dot over (V)}.sub.air.sup.(III) Nm.sup.3/h — — — 10 — —  20 — — v.sub.in.sup.(III) Nm/s — — — 12.4 —   10.2   18.5 — — v.sup.(III) Nm/s 0.94 1.63 1.33 3.34    2.03    5.62    4.02    2.03    2.26 t.sup.(III) ms 532 307 376 750    2.46 445 620 246 221 T.sub.flame .sup.(III) e) ° C. 710 611 821 383 426 839 302 681 871 Sum internals I-III v.sup.(ttl) Nm/s 1.13 1.73 1.47 2.89    2.51    4.95    3.71    2.34    2.70 t.sup.(ttl) ms 1324 1953 1019 2595 597 699 1420  653 1951