Process for the preparation of pulverulent heterogeneous substances

Abstract

A suspension, dispersion or emulsion is introduced into a burner. An optionally two-stage after-treatment is then carried out. The resulting powder can be employed as a catalyst.

Description

[0001] The invention relates to a process for the preparation of pulverulent heterogeneous substances.

[0002] It is known to prepare pulverulent heterogeneous substances from oxides and salts starting from a suspension, dispersion or emulsion.

[0003] Spray driers (or similar) are usually employed for drying for suspensions, dispersions or emulsions. This is followed by a rotary tube for calcining (or similar). The losses of powder by cleaning and handling, and also during operation of the plant are or can be considerable, and/or the expenditure on personnel is high.

[0004] Drying and calcining in batches (for example in vessels in a muffle furnace) is used as an alternative. However, there is the risk here of a very wide range of product quality due to diffusion processes and temperature gradients in the powder.

[0005] There is thus the object of developing a process for the preparation of pulverulent heterogeneous substances which does not have these disadvantages.

[0006] The invention provides a process for the preparation of pulverulent heterogeneous substances, characterized in that a dispersion, suspension or emulsion is introduced into a turbulent or laminar burner, this dispersion, suspension or emulsion is treated there under the conditions established there, the resulting reaction mixture is introduced into a downstream flow-through tube, the powder is treated further there, the powder is subsequently fed, optionally, to a washer, a separator or a filter, subjected, optionally, to a further treatment there, and subsequently transported further via an appropriate device.

[0007] In the high temperature flow reactor, the dispersion, suspension or emulsion can be present as a gas-borne group of particles.

[0008] The high temperature flow reactor can be heated by feeding in non-combustible hot gases.

[0009] The high temperature flow reactor can be heated indirectly by heating up the walls adjacent to the reaction space.

[0010] Heating can be achieved here by electrical plasma and/or inductive plasma.

[0011] A high-energy laser light beam and/or microwave energy can additionally be fed to the high temperature flow reactor.

[0012] In addition to the dispersion, suspension or emulsion, non-combustible reactive gases or vapours can be fed to the high temperature flow reactor, it being possible for the reaction product to be a highly disperse nanostructured solid which adds on to the surface of the particles of the dispersion, emulsion or suspension.

[0013] The reaction product can form homogeneous molecular layers on the particles of the dispersion, emulsion or suspension, the particles of the dispersion, emulsion or suspension being coated with a mono- or multimolecular layer.

[0014] The non-combustible reactive gases or vapours can be metal chlorides and/or organometallic compounds, as well as mixtures of these compounds.

[0015] The temperature in the reaction space can be above 1000.degree. C.

[0016] The suspension, dispersion or emulsion can be fed to the reaction space axially in co- or countercurrent or radially.

[0017] The dispersion, emulsion or suspension can be fed to the reaction space radially.

[0018] The dispersion, emulsion or suspension can be a solids suspension, a solution, powder, pastes, melts or granules with or without dissolved "salts". The dispersion, emulsion or suspension is metered into the space in finely divided form by atomizing, wave-breaking, as a mist or jet.

[0019] The secondary gas mentioned in the FIGURE can be air, ambient air with oxygen contents of between 0 and 100%, dry or humid, water vapour, other vapours or gases, nitrogen and the like.

[0020] The burner can be of a known design with pulsatory combustion. Such a burner is described in the document DD 114 454.

[0021] A burner of high turbulence can preferably be employed to improve the transportation of material. In particular, a spinning burner, possibly with an overlaid pulsation, can be employed.

[0022] The liquid phase of the suspension, dispersion or emulsion can be water, alcohol, liquid organic hydrocarbons or organic solvents.

[0023] The components present as the solid in the suspension, dispersion or emulsion can be, individually or as a mixture: oxides, nitrides or carbides of aluminium, silicon, cerium, zirconium, titanium, crystallized-out salts of aluminium, silicon, cerium, zirconium, lanthanum, barium, metals such as, for example, nickel, silver, palladium, gold, rhodium, platinum, carbon black, organic compounds.

[0024] The dissolved or non-dissolved salts can be nitrates, acetates, carbonates, chlorides of aluminium, cerium, silicon, zirconium, titanium, lanthanum, barium, platinum, rhodium, palladium, iridium, potassium, calcium and ammonium and mixtures of these components.

[0025] A combustible gas, such as, for example, hydrogen and/or methane, can be used as the fuel.

[0026] The temperature in the burner can be 500 to 2000.degree. C.

[0027] The temperature after the burner and the reducing or oxidizing atmosphere in the flow-through tube can be established via the ratio of oxygen (from the combustion air) to hydrogen and the flow rates. Moreover, further reactive or inert gases and vapours can be fed into the tube.

[0028] The dispersion, emulsion or suspension of the solid can be sprayed or dripped into the flame of the burner.

[0029] The water or the solvent evaporates and the powder formed is calcined, oxidized or reduced and sintered at high temperatures in the gas atmosphere present. The residence time of the powder in the hot gas phase can be varied in the range from 0.01 second up to minutes by the separating device (cyclone, high temperature filter). The mass and heat transfer is significantly better than in a rotary tube or in a muffle furnace.

[0030] With spray calcining, the surfaces to be cleaned are considerably smaller compared with a spray drier with subsequent calcining in a rotary tube and the losses of substance are low. Due to the use of a continuous process, the range of product quality is narrow. Compared with the rotary tube, the losses during start-up and shut-down are very low.

[0031] The powder in the waste air filters/cyclone of a rotary tube has a wide range of product quality and often cannot be used, while in the process according to the invention the range of product quality in the waste air filter/cyclone is a very narrow range.

[0032] The in situ treatment of the waste air can have an effect as a further advantage. The salts are often nitrates, acetates and ammonium compounds, the decomposition products of which, NO, NH.sub.3 and CHNO, can be reduced in amount by adjusting the composition of the hot waste gases or can be treated in a downstream catalyst without additional heating up.

[0033] The products which can be prepared are heterogeneous powders/granules:

[0034] 1. Mixed agglomerates and/or mixed aggregates of different oxides/metals/nitrides/carbides/carbon black.

[0035] 2. Base substances (support material) (possibly in shell form) impregnated/covered/coated with oxides/metals/nitrides/carbides.

[0036] 3. Combination of 1. and 2.

[0037] The substances prepared according to the invention can be employed as a catalyst, for the production of ductile ceramic components, for the production of components with a quantum mechanics activity, in particular sensors and photoelectrically active emitters, and as oxygen stores, NO.sub.x stores, C.sub.nH.sub.m stores for catalysis and adsorbents.

[0038] The process according to the invention is shown and explained in more detail in the drawing:

[0039] FIG. 1 shows a burner 1, to which the flow-through tube 2 is connected. The washer 3, the separator 4, the filter 5 and the fan 6 are connected to the flow-through tube 2.

[0040] In the process according to the invention, a dispersion, suspension or emulsion, a secondary gas, combustion air and fuel are introduced into the burner 1. The reaction mixture reacted in the burner 1 is introduced into the flow-through tube 2. A reducing or oxidizing gas atmosphere can be established in the flow-through tube 2. The reacted reaction mixture can be treated in the flow-through tube 2 such that

[0041] a) the dispersion, suspension or emulsion is dried,

[0042] b) the water of crystallization is driven off,

[0043] c) the powder is calcined, substances such as nitrates, acetates, carbonates being decomposed to gases,

[0044] d) the powder is oxidized or reduced,

[0045] e) the powder is sintered,

[0046] f) the specific surface area of the powder is decreased.

[0047] After passage through the flow-through tube 2, the powder can be treated in the washer 3 if a dispersion is to be prepared or contact with air is to be avoided.

[0048] Alternatively, after leaving the flow-through tube 2, the powder can be separated off via the separating device 4, for example for brief treatment at high temperatures.

[0049] In another alternative, the powder can be separated off by means of the filter 5 for a longer treatment at high temperatures.

[0050] The waste gas can be discharged by means of the fan 6.

EXAMPLE 1

[0051] A aluminium oxide/water suspension with dissolved platinum nitrate is introduced into the burner 1. The suspension comprises

[0052] 400 g/l aluminium oxide

[0053] 10 g/l platinum nitrate

[0054] 800 g/l water.

[0055] Hydrogen is employed as the fuel.

[0056] The burner temperature is 1,200.degree. C., and the residence time is approx. 1 sec.

[0057] The powder separated off in the cyclone is dry and no longer contains nitrate ions. The platinum is deposited in a finely disperse form on the surface of the aluminium oxide.

EXAMPLE 2

[0058] An aqueous suspension which comprises

[0059] 400 g/l aluminium oxide,

[0060] 100 g/l cerium acetate,

[0061] 100 g/l zirconium nitrate and

[0062] 800 g/l water

[0063] is introduced into the burner 1. Natural gas is employed as the fuel. The burner temperature is 1,000.degree. C. The powder separated off in the cyclone is dry and contains neither acetate ions nor nitrate ions. The cerium oxide and the zirconium oxide are deposited in a finely divided form on the surface of the aluminium oxide.

EXAMPLE 3

[0064] A moist powder comprising

[0065] 78 wt. % aluminium oxide

[0066] 20 wt. % water

[0067] 2 wt. % platinum nitrate

[0068] is treated with natural gas at a burner temperature of 900.degree. C.

[0069] The powder separated off in the cyclone is dry and contains no nitrate ions. The platinum is deposited in a finely divided form on the surface of the aluminium oxide.

Claims

1. A process for the preparation of pulverulent heterogeneous substances, characterised in that a dispersion, suspension or emulsion is introduced into a turbulent or laminar burner, this dispersion, suspension or emulsion is treated there under the conditions established there, the resulting reaction mixture is introduced into a downstream flow-through tube, the powder is treated further there, the powder is subsequently fed, optionally, to a washer, a separator or a filter, subjected, optionally, to a further treatment there, and subsequently transported further via an appropriate device

2. A process and device according to claim 1, characterised in that the dispersion, suspension or emulsion is present in the high temperature flow reactor as a gas-borne group of particles.

3. A process and device according to claim 1 and 2, characterised in that the high temperature flow tube is heated by an exothermic combustion reaction which takes place in the tube.

4. A process and device according to claim 1 and 2, characterised in that the high temperature flow tube is heated by feeding in non-combustible hot gases.

5. A process and device according to claim 1 and 2, characterised in that the high temperature flow reactor is heated indirectly by heating up the walls adjacent to the reaction space.

6. A process and device according to claim 1 and 2, characterised in that the high temperature flow tube is heated by electrical plasma and/or inductive plasma.

7. A process and device according to claim 1 to 6, characterised in that a high-energy laser light beam and/or microwave energy is additionally fed to the high temperature flow reactor.

8. A process and device according to claim 7, characterised in that, in addition to the dispersion, suspension or emulsion, non-combustible reactive gases or vapours are fed to the high temperature flow reactor, the reaction product being a highly disperse nanostructured solid which adds on to the surface of the particles of the dispersion or suspension.

9. A process and device according to claim 8, characterised in that the reaction product forms homogeneous molecular layers on the particles of the dispersion or suspension, the particles of the dispersion or suspension thus being coated with a mono- or multimolecular layer.

10. A process and device according to claim 8, characterised in that the non-combustible reactive gases or vapours are metal chlorides and/or organometallic compounds, as well as mixtures of these compounds.

11. A process and device according to claim 1-10, characterised in that the temperature in the reaction space is above 1000.degree. C.

12. A process and device according to claim 1-10, characterised in that the suspension is fed to the reaction space axially in co- or countercurrent or radially.

13. A process and device according to claim 1-10, characterised in that the dispersion or suspension is fed to the reaction space radially.

14. A pulverulent substance obtainable by a process according to claim 1-13.

15. The use of a pulverulent substance according to claim 14 as a catalyst.

16. The use of a pulverulent substance according to claim 14 as an oxygen store, NO.sub.x store, C.sub.nH.sub.m store for catalysis and adsorbents.

17. The use of a pulverulent substance according to claim 14 for the production of ductile ceramic components.

18. The use of a pulverulent substance according to claim 14 for the production of components with a quantum mechanics activity, in particular sensors, and photoelectrically active emitters.

19. The use of a pulverulent substance according to claim 14 for the production of glasses and glass ceramic.