EP2041030A2

EP2041030A2 - Method for the production of suspensions of nanoparticulate solids

Info

Publication number: EP2041030A2
Application number: EP07728909A
Authority: EP
Inventors: Frank KLEINE JÄGER; Julian PRÖLSS; Alexander BENÖHR; Thomas Breiner
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2006-05-09
Filing date: 2007-05-08
Publication date: 2009-04-01
Also published as: CA2650123A1; KR20090012347A; WO2007128821A3; US20090093553A1; WO2007128821A2; WO2007128821A9; JP2009536093A; CN101466639A

Abstract

The invention relates to a method for producing suspensions of nanoparticulate solids. Said method is characterized in that the solids contained in the suspension are provided in the form of nanoparticulate primary particles or tiny aggregates.

Description

Process for the preparation of suspensions of nanoparticulate solids

description

The invention relates to a process for the preparation of suspensions of nanoparticulate solids.

Nanoparticles are particles of the order of nanometers. With their size, they lie in the transition region between atomic or monomole-cellular systems and continuous macroscopic structures. In addition to their usually very large surface, nanoparticles are characterized by particular physical and chemical properties, which differ significantly from those of larger particles. For example, nanoparticles have a lower melting point, absorb light at shorter wavelengths, and have different mechanical, electrical, and magnetic properties than macroscopic particles of the same material. By using nanoparticles as building blocks, many of these special properties can also be used for macroscopic materials (Winnacker / Kuchler, Chemische Technik: Processes and Products, (Ed .: R. Dittmayer, W. Keim, G. Kreysa, A. Oberholz), Vol. 2: New Technologies, Chapter 9, Wiley-VCH Verlag 2004).

The production of nanoparticles can take place in the gas phase. Numerous methods for the gas-phase synthesis of nanoparticles are known in the literature, including processes in flame, plasma and hot wall reactors, inert gas condensation processes, free-jet systems and supercritical expansion (Winnacker / Kuchler, supra). A disadvantage of these methods is that the particles produced can still aggregate in the gas phase due to their high mobility and the resulting aggregates are only very poorly redispersed in fluids due to the strong van der Waals interactions and the resulting high binding forces between the particles. are gable. The problem is the bigger, the smaller the particles are. In addition to van der Waals interactions, sintering or covalent bonds can negatively affect redispersibility.

In order to obtain nanoparticles having the most uniform properties possible, it is advantageous, as is generally known to the person skilled in the art, to stabilize the gas phase conversion spatially and temporally. In this way it can be ensured that all starting materials are exposed to virtually identical conditions during the reaction and thus react to form uniform product particles.

US 20040050207 describes the production of nanoparticles by means of a burner, wherein the educts are conducted in a plurality of tubes to the reaction zone, where they are mixed and reacted. Similarly, in US 20020047110, the production of aluminum nitride powder and in JP 61-031325 the synthesis of optical glass powder are explained. DE 10243307 describes the synthesis of nano-carbon black particles. The gas phase reaction is carried out between a porous body, which serves as a non-return valve, and a baffle plate arranged above it. The educt gases are passed through the porous body into the reaction space and reacted there.

A burner and a process for producing carbon nanoparticles in the gas phase is described in US 20030044342. The educt gases are converted outside of a porous body.

In EP 1004545 a process for the pyrogenic production of metal oxides is presented, wherein the reactants are passed through a molding with through channels and reacted in a reaction space.

An object of the present invention was to provide a process for the preparation of suspensions of nanoparticulate solids, which is characterized in that the solids contained in the suspension are in the form of nanoparticulate primary particles or very small aggregates. These suspensions should allow for simplified processing of nanoparticulate solids. A further object of the invention was to provide a process for the preparation of suspensions of nanoparticulate solids of thermally unstable products, which are difficult to access by other means.

This object is achieved by a method in which the nanoparticulate solids produced in a gas-phase reaction are converted directly into a liquid phase.

The present invention therefore provides a process for the preparation of suspensions of nanoparticulate solids, characterized in that

a) at least one feedstock and possibly further components passes through at least one reaction zone and thereby undergoes a thermal reaction in which nanoparticulate primary particles are formed,

b) subjecting the reaction product obtained in step a) to rapid cooling, and

c) initiating the cooled reaction product obtained in step b) into a liquid, wherein a suspension is formed in which the solids contained are present in the form of nanoparticulate primary particles or very small aggregates. In principle, the thermal reaction carried out according to the method of the invention may be any chemical reaction which is thermally induced and leads to the formation of nanoparticulate solids. Preferred embodiments are oxidation, reduction, pyrolysis and hydrolysis reactions. Furthermore, the reaction can be both an allothermal process in which the energy required for the reaction is supplied from the outside, as well as an autothermal process in which the required energy results from a partial conversion of a feedstock, act. Burners as well as plasma sources are suitable for initiating a spatially stable reaction.

Typical products which can be obtained as nanoparticulate solids by the process according to the invention are carbon black, oxides of at least one of the elements Si, Al, Ti, In, Zn, Ce, Fe, Nb, Zr, Sn, Cr, Mn, Co, Ni, Cu, Ag, Au, Pt, Pd, Rh, Ru, Bi, Ba, B, Y, V, La, furthermore hydrides of at least one of the elements Li, Na, K, Rb, Cs, B, Al, furthermore Sulfides such as M0S2, carbides, nitrides, chlorides, oxychlorides and elemental metals or semimetals such as Li, Na, B, Ga, Si, Ge, P, As, Sb, La and mixtures thereof.

The process according to the invention makes it possible to prepare suspensions of nanoparticulate solids starting from a large number of different starting materials and possibly further components. Suitable method embodiments for obtaining at least one of the aforementioned products are described in more detail below.

The control of the sequence of the gas phase conversion can take place, among others, via the following parameters:

Composition of the reaction gas (type and amount of starting materials, additional components, inert constituents) and

Reaction conditions in the reaction (reaction temperature, residence time, feed of the starting materials in the reaction zone, presence of catalysts).

The process according to the invention for the preparation of suspensions of nanoparticulate solids can be subdivided into the following substeps, which are described in more detail below.

Step a) According to the invention, at least one feedstock and possibly one or more further components are fed to a reaction zone and are subjected to a thermal reaction in which nanoparticulate primary particles are formed.

Suitable starting materials are any substances which can preferably be converted into the gas phase, so that they are present in gaseous form under the reaction conditions, and which can form a nanoparticulate solid by means of a thermal reaction. Depending on the desired product, the starting materials for the process according to the invention may be, for example, elemental hydrogen compounds, such as hydrocarbons, boron hydrides or hydrogen phosphides, furthermore metal oxides, metal hydrides, metal carbonyls, metal alkyls, metal halides such as fluorides, chlorides, bromides or iodides, metal sulfates, metal nitrates , Metal-olefin complexes, metal alkoxides, metal formates, metal acetates, metal oxalates, metal borates or metal acetylacetonates and elemental metals such as lithium, sodium, potassium, boron, lanthanum, tin, cerium, titanium, silicon, molybdenum, tungsten, platinum, rhodium, Ruthenium, zinc or aluminum. Preferred starting materials are elemental hydrogen compounds and the elemental metals boron, zinc, lanthanum, tin, cerium, titanium, silicon, molybdenum, tungsten, platinum, rhodium, ruthenium and aluminum.

In addition to the at least one starting material, the reaction zone can be supplied with an oxidizing agent as further component, for example molecular oxygen, oxygen-containing gas mixtures, oxygen-containing compounds and mixtures thereof. In a preferred embodiment, molecular oxygen is used as the oxygen source. This makes it possible to keep the content of inert compounds in the reaction zone low. However, it is also possible to use air or air-oxygen mixtures as the oxygen source. As oxygen-containing compounds, for example, water, preferably in the form of water vapor, and / or carbon dioxide are used. The use of carbon dioxide may be recycled carbon dioxide from the gaseous reaction product obtained in the reaction.

In a further embodiment of the invention, the reaction zone can be supplied as a further component, a reducing agent, for example, molecular hydrogen, ammonia, hydrazine, methane, hydrogen-containing gas mixtures, hydrogen-containing compounds and mixtures thereof. Particularly preferred are the reaction of aluminum in a hydrogen-argon plasma to form aluminum hydrogen (AIH3) and the reaction of lanthanum oxide with boron or boron compounds to form lanthanum hexaboride (LaBβ).

If necessary, the reaction zone as a further component, a fuel gas can be supplied, which supplies the energy required for the reaction. These may be, for example, H2 / θ 2 gas mixtures, hb / air mixtures, mixtures of methane than ethane, propane, butanes, ethylene or acetylene with air or other oxygen-containing gas mixtures.

In addition to the previously mentioned constituents, which can be used both individually and jointly, at least one further component can be added to the reaction zone. These include, for example, possibly recirculated gaseous reaction products, raw synthesis gas, carbon monoxide (CO), carbon dioxide (CO2) and other gases to influence the yield and / or selectivity of certain products or particle sizes, such as hydrogen or inert gases such as nitrogen or noble gases. Furthermore, finely divided solids or liquids can be supplied as aerosols. These may be, for example, solids or liquids which are used for modification, aftertreatment or coating in the process, or which are themselves feedstock.

A preferred embodiment of the invention is characterized in that two different metals are simultaneously fed to the reaction zone. This can be done both in the form of a premix of the two metals as well as by separate supply of the two individual metals. Particularly preferred is the reaction of the metals lithium and aluminum in the presence of hydrogen in a plasma to form lithium aluminum hydride.

The feeding of solid feedstocks into the reaction zone can be carried out, for example, by means of apparatuses known to those skilled in the art, e.g. B. be accomplished by means of brush dispenser or screw conveyors, and subsequent air flow promotion. The solid starting materials are preferably used in pulverized form and form aerosols with a carrier gas in which the particle sizes of the solid starting materials can be in the same range as those of the nanoparticulate solids obtainable by the process according to the invention. The average particle or aggregate size of the solid starting materials is typically between 0.01 and 500 μm, preferably between 0.1 and 50 μm, particularly preferably between 0.1 and 5 μm. With larger average particle or aggregate sizes, there is the risk of incomplete transfer into the gas phase in the reaction zone, so that such larger particles are not or only partially available for the reaction. Optionally, incompletely vaporized particles can cause a surface reaction to passivate them.

Liquid feedstocks can be fed, for example, in gaseous form or else in the form of liquid droplet-containing steam, to the reaction zone, likewise with the aid of apparatuses known to those skilled in the art. Suitable for this purpose are evaporators, such as thin-film evaporator or flash evaporator, a combination of atomization and entrained flow evaporator or evaporation in the presence of an exothermic reaction (cold flame). An incomplete reaction of the atomized liquid As a rule, it is not to be feared that the liquid feedstock will have the aerosol dimensions of less than 50 μm.

In a preferred embodiment of the invention, the starting materials and any other components already present are already converted into the gas phase prior to their introduction into the reaction zone and mixed with one another. This is particularly suitable for low-boiling starting materials and any other components present, since they may already be present in gaseous form at temperatures at which no chemical reaction is taking place. Alternatively, however, the various starting materials and any further components present may also be transferred separately to the gas phase and fed into the reaction zone in separate gas streams, in which case their thorough mixing is advantageously carried out immediately before entry into the reaction zone.

If solid starting materials and possibly further components are used and each transported separately through a carrier gas into the reaction zone, the loading of the carrier gas is usually in each case between 0.01 and 2.0 g / l, preferably between 0.05 to 0.5 g / l , If solid starting materials and possibly other components are used and are already transported as a mixture through a carrier gas into the reaction zone, the loading of the carrier gas with the total amount of the solid starting materials is usually between 0.01 and 2.0 g / l , preferably between 0.05 and 0.5 g / l. In the case of liquid and gaseous feedstocks higher loads than previously mentioned are generally possible. The loadings suitable for the respective process conditions can usually be easily determined by appropriate preliminary tests.

As the carrier gas for transport of solid or liquid starting materials and possibly other components in the reaction zone, each of the aforementioned gases can be used, provided that it does not hinder the thermal reaction. Preference is given to using noble gases as the carrier gas.

The introduced into the reaction zone feedstocks and possibly other components are subjected according to the invention a thermal reaction are formed in the nanoparticulate primary particles. This is generally carried out by heating to high temperatures, in which case in particular a flame or a thermal plasma, microwave plasma, arc plasma, induction plasma, convection and / or radiation heating, autothermal reaction or a combination of the aforementioned methods come into question.

Appropriate procedures and process conditions, by a flame or a thermal plasma, microwave plasma, arc plasma, induction plasma, convection and / or radiation heating, autothermal reaction or a combination of the abovementioned methods to bring about heating of the components in the reaction zone are sufficiently known to the person skilled in the art.

In the case of an autothermal reaction, for example, mixtures of hydrogen and halogen gas, in particular chlorine gas, are used to generate a flame. Furthermore, the flame with hydrocarbons, eg. As methane, ethane, propane, butanes, ethylene or acetylene or mixtures of the aforementioned gases on the one hand and an oxidizing agent such as oxygen or an oxygen-containing gas mixture on the other hand are generated, the latter can also be used in deficit when reducing conditions in the reaction zone a flame are preferred.

To generate a plasma, a so-called plasma spraygun is often used. It consists for example of a serving as an anode housing and a centric arranged therein, water-cooled copper cathode, wherein between the cathode and the housing, an electric arc of high energy density burns. The supplied plasma gas, for example argon or a hydrogen / argon mixture, ionizes to the plasma and leaves the gun at a high rate of vibration (about 300 to 700 m / s) at temperatures of 15,000 to 20,000 Kelvin. The starting materials are introduced directly into this plasma jet, evaporated there and then reacted in a reactive atmosphere and after prior cooling at suitable temperatures to the desired product.

As a gas or gas mixture for the production of plasmas is usually a noble gas, such as helium or argon, or noble gas mixture, for example of helium and argon, and hydrogen used.

Noble gases, such as helium or argon, or noble gas mixtures, for example of helium and argon, can also be used as inert components in the reaction zone. In the specific case, nitrogen, optionally in admixture with the noble gases mentioned above, can also be used as the inert component in the reaction zone, but at higher temperatures and depending on the nature of the feedstocks, formation of nitrides may have to be expected.

Typical powers introduced into a plasma range from a few kW up to several 100 kW. Even sources of plasma of greater power can be used in principle for the synthesis. Incidentally, the procedure for generating a stationary plasma flame is familiar to the expert, in particular with regard to introduced power, gas pressure, gas quantities for the plasma and protective gas. In addition, an inert shielding gas is usually used, which comprises a gas layer between the wall of the reactor used for the production of the plasma and the reaction zone, the latter essentially corresponding to the area in which the plasma is in the reactor.

In the course of the reaction, according to the invention, after nucleation has taken place, nanoparticulate primary particles initially form, which can undergo further particle growth through coagulation and coalescence processes. Particle formation and growth typically occur throughout the reaction zone and can continue to progress even after leaving the reaction zone until rapid cooling. If more than one solid product is formed during the reaction, the different primary particles formed may also combine with one another, resulting in nanoparticulate product mixtures, for example in the form of mixed crystals or amorphous mixtures. If, during the reaction, the formation of a plurality of different solids occurs at different times, enveloped products may also be formed in which the primary particles of a product first formed are surrounded by layers of one or more other products.

Another embodiment of the invention comprises a gradual addition of feeds to the reaction zone. In this way, if appropriate, a homogeneous coating of a core with a shell can be achieved, if u.a. It is ensured that a very fast (that is to say in a few ms) homogeneous mixing of the particles formed in the first stage takes place with the starting material added in the second stage. By means of suitable process control, a homogeneous coating of the particles from the first stage with a few nm thick layer of the product of the second stage succeeds, even if this arrangement is not thermodynamically favored (eg a silicon dioxide layer on a zinc oxide particle). ,

The control of these particle formation processes can be controlled not only by the composition of the starting materials and possibly other components and the reaction conditions but also by the type and timing of the cooling of the reaction product described in step b).

In any case, the temperature within the reaction zone must be above the boiling point of the starting materials used and any other components present. Preferably, the reaction is carried out in the reaction zone for the autothermal reaction at a temperature in the range of 600 to 1800 ° C, preferably from 800 to 1500 ° C and for plasma processes at a temperature in the range 600 to 10,000 ⁰ C, preferably from 800 up to 6000 ⁰ C.

In general, the residence time of the starting materials and possibly other components in the reaction zone is between 0.002 s and 2 s, preferably between 0.005 s and 0.2 s. The thermal reaction of the starting materials and possibly other components for the preparation of the suspensions of nanoparticulate solids according to the invention can be carried out by the process according to the invention at any pressure, preferably in the range of 0.05 bar to 5 bar, in particular at atmospheric pressure.

Step b)

The reaction of the starting materials and possibly other components in step a) is followed, according to the invention, by a rapid cooling of the reaction product obtained in step b). Rapid cooling in the context of this invention means a temperature reduction with a cooling rate of at least 10 ⁴ K / s, preferably at least 10 ⁵ K / s, more preferably at least 10 ⁶ K / s.

This rapid cooling can take place, for example, by direct cooling, indirect cooling, expansion cooling or a combination of direct and indirect cooling. In direct cooling (quenching), a coolant is brought into direct contact with the hot reaction product to cool it. Direct cooling can be carried out, for example, by feeding quench oil, water, steam, liquid nitrogen or cold gases, if appropriate also cold recirculation gases, as coolant. For the supply of the coolant, for example, an annular gap burner can be used, which enables very high and uniform quenching rates and is known per se to those skilled in the art.

In indirect cooling, heat energy is removed from the reaction product without it coming into direct contact with a coolant. An advantage of indirect cooling is that it usually allows effective use of the heat energy transferred to the coolant. For this purpose, the reaction product can be brought into contact with the exchange surfaces of a suitable heat exchanger. The heated coolant can be used, for example, to heat the starting materials in the process according to the invention or in a different endothermic process. Furthermore, the heat removed from the reaction product can also be used, for example, for operating a steam generator.

Preferably, the process of the invention is carried out so that in step b) the resulting reaction product is cooled to a temperature in the range of 1800 ° C to 20 ° C. Depending on the process and product, cooling to a temperature of less than 650 ° C or even less than 250 ° C may be necessary to prevent further growth of particles and their aggregation or sintering.

In a preferred embodiment of the invention, the cooling is carried out in two stages, whereby a combined use of direct cooling (pre-quench) and indirect cooling is possible. This can be done by direct cooling (Vorquench) in Step a) obtained reaction product are preferably cooled to a temperature of less than 1000 ° C. The two-stage cooling is particularly suitable for thermally labile products to prevent their decomposition. In this case, the product should be cooled in the first stage with the fastest possible cooling (ie, the highest possible cooling rate of at least 10 ⁵ K / s, preferably at least 10 ⁶ K / s) to a temperature below the decomposition temperature. Preferably, in the first stage, it is rapidly cooled to a temperature which is below one third of the respective melting or decomposition temperature of the product in Kelvin in order to suppress decomposition or sintering processes as much as possible. Subsequently, it can be cooled further with a lower cooling rate. For example, the first stage may include direct cooling by adding liquid nitrogen or white oil to the gas stream, the second stage indirect cooling via a heat exchanger.

The size of the solid particles in the suspensions of nanoparticulate solids prepared by the process according to the invention is usually in the range of 1 to 500 nm, preferably 2 to 100 nm.

In a further embodiment of the method according to the invention, a further processing of the particles formed in the gas phase can take place during or immediately after the quenching, for example by coating with an organic coating and / or by modifying the surface with organic compounds. Preferably, quench gas and modifier are added simultaneously. Organic compounds suitable as modifiers are known in principle to the person skilled in the art. Preferably, those compounds are used which can be converted into the gas phase without decomposition and which can form a covalent or adhesive bond to the surface of the particles formed. For the organic coating or the organic modification, various organosilanes, for example, for metal oxide particles, such as dimethyldimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, methylcyclohexyldimethoxysilane, isooctyltrimethoxysilane, propyltrimethoxysilane, isobutyltrimethoxysilane, phenyltrimethoxysilane or octyltriethoxysilane can be used. If the particles consist of SiO 2 or are SiO 2 -coated particles, then the SiOH groups on the surface of the particles may possibly enter into a direct covalent or adhesive bond with the silane. The silanes present on the surface of the particles are expected to reduce the interactions between the particles as spacers, to facilitate the mass transfer into an organic matrix in the wet scrubber and to function as coupling sites in the event of subsequent further functionalization (possibly after concentration).

Preferably, the process of modification is carried out by the supply of the quench gas or a controlled heat extraction after supply of the Quenchgases a targeted condensation of the modifier takes place on the particles. In addition, in a subsequent step, further aqueous or organic modifiers for condensation support can be added. Particularly preferred is the use of a modifier, which is also included in the liquid used in step c).

Step c)

In the process according to the invention, the cooled reaction product obtained in step b) is introduced into a liquid, a suspension being formed in which the solids present are present in the form of nanoparticulate primary particles or very small aggregates thereof. As a result, the still isolated nanoparticulate primary particles or very small aggregates are protected from further agglomeration by being introduced directly into a liquid phase.

According to the invention, the liquid may be aqueous or non-aqueous, organic or inorganic liquids or mixtures of at least two of these liquids. Furthermore, ionic liquids can also be used. Preferred liquids are white oil, tetrahydrofuran, diglyme, solvent naphtha, water or 1,4-butanediol. In the liquids, other ingredients may be dissolved, for example salts, surfactants or polymers which u. a. serve as a modifier and can increase the stability of the suspensions. Preference is given to using aqueous or organic liquids, especially water.

To carry out the process step c) according to the invention, it is possible to use customary apparatus known to the person skilled in the art, for example wet electrostatic precipitators or venturi scrubbers. Optionally, the formed nanoparticulate solids may be fractionated during deposition, for example by fractional deposition. The deposition may possibly be intensified by condensation support and the suspension formed by modifying further stabilized. Suitable substances for the surface modification are anionic, cationic, amphoteric or nonionic surfactants, for example Lutensol ^® - or Sokalan ^® brands from BASF Aktiengesellschaft..

In a preferred embodiment of the invention, a surfactant-containing liquid is continuously metered into the upstream part of a wet electrostatic precipitator. Due to the usually vertical arrangement of the wet electrostatic precipitator, a closed liquid film forms on its wall within its tubular separating vessel. The continuously circulated liquid is collected in the downstream part of the wet electrostatic precipitator and conveyed by a pump. Preferably, in countercurrent to the liquid flows laden with the nanoparticulate solid gas stream through the wet electrostatic precipitator. In the tubular separating vessel is a centrally arranged wire, which acts as a spray electrode. A voltage of approximately 50 to 70 kV is applied between the container wall serving as counterelectrode and the discharge electrode. The gas stream loaded with the nanoparticulate solid flows from the top into the separation vessel, wherein the gas-borne particles are electrically charged by the spray electrode and thus the deposition of the particles at the counterelectrode (ie the wall of the wet electrostatic precipitator) is induced. Due to the liquid film flowing along the wall, the particles are deposited directly in the film. The charging of the particles simultaneously causes an avoidance of unwanted particle agglomeration. The surfactant leads to the formation of a stable suspension. The degree of separation is usually above 95%.

In a further preferred embodiment of the invention, a venturi scrubber is used for deposition. Due to the high turbulence in the area of the Venturi throat, a very efficient separation of nanoparticulate solids occurs. By adding surfactants to the circulating separation medium (for example water, white oil, THF), the agglomeration of separated particles can be avoided. Preferably, a pressure difference across the throat of the Venturi scrubber in the range 20 to 1000 mbar, more preferably adjusted from 150 to 300 mbar. With this method, nanoparticles with particle diameters smaller than 50 nm can be deposited with a separation efficiency greater than 90%.

For workup, the reaction product obtained in step b) may be subjected to at least one separation and / or purification step prior to introduction into a liquid. The nanoparticulate solids formed are separated from the other constituents of the reaction product.

The inventive method is thus suitable for the continuous or discontinuous production of suspensions of nanoparticulate solids. Important features of this process are a rapid supply of energy at a high temperature level, usually short and uniform residence times under the reaction conditions and a rapid cooling ("quenching") of the reaction products with subsequent transfer of the particles into a liquid phase, thereby agglomerating the formed nanoparticulate The products obtainable by the process according to the invention can be easily further processed and allow the simple achievement of new material properties which are attributable to nanoparticulate solids.

The invention is explained in more detail by the following examples. Examples 1 to 3: Preparation of suspension of nanoparticulate zinc oxide

Elemental zinc was fed with a brush dispenser with a mass flow of 10 to 40 g / h together with a nitrogen carrier gas stream (1 Nm ³ / h) in a tube furnace and evaporated there at about 1000 ° C, then gaseous into the reaction zone of a Burner introduced and reacted there with atmospheric oxygen (4 Nm ³ / h) at temperatures in the range of 950 to 1200 ° C to the zinc oxide. In order to maintain or moderate the reaction temperature, additional hydrogen (1 Nm ³ / h) and air (6 Nm ³ / h) were metered into the reaction zone. After a residence time in the reaction zone of 20 ms to 50 ms, the reaction product is passed through an annular gap with air as

Quench medium (100 to 150 Nm ³ / h) cooled to about 150 ° C, wherein the cooling rate is at least 10 ⁵ K / s. For surface modification, evaporated hexamethyldisiloxane was added.

Subsequently, the gas-borne particles of zinc oxide and 2 wt .-% Lutensol ^® AO5 (Ex.2) or Solvent Naphtha separator by a Nasselektroab-, in the 1, 3-butanediol with 2 wt .-% of hexamethyldisiloxane (HMDS 1, Ex.) with 2 wt .-% HMDS (Ex 3) was promoted as a separation medium via a pump in a circle, deposited. The application of electrical charges to the zinc oxide particles entering the wet electrostatic precipitator was effected by means of a spray electrode, which is arranged centrally in the wet electrostatic precipitator. The applied voltage was 60 kV.

Figures 1 to 3 show the particle size distributions of the suspensions obtained.

These results show that the samples prepared are dispersing soft and the particle size distribution strongly depends on the formulation.

Example 4: Preparation of a suspension of nanoparticulate aluminum hydride in white oil

Using a plasma system (Sulzer Metco), an arc plasma with an electric power of 45 kW was provided, whereby due to the introduced thermal power temperatures of T ~ 10000 K were reached. The plasma gases used were argon with a volumetric flow rate of \ r = 50 Nl / min and hydrogen with \ r = 20 Nl / min. Furthermore, aluminum particles with an average size of dδo = 9 μm as feedstock were conveyed into the reaction zone of the plasma with the aid of an argon carrier gas flow of \ r = 14 Nl / min. Before entering the reactor, hydrogen was metered in as the reaction gas at up to $ = 35 Nm ³ / h in order to react with alumina as the reactant with the aluminum hydride. After a few μs, an argon was added in the reaction zone via an annular gap (up to $ = 330 Nm ³ / h). quenched. The temperature was after the quench at about 350 K, the quench rate was 10 ⁶ K / s.

In a Venturi scrubber with a throat diameter of 14 mm, the particles were precipitated in white oil ($ = 125 l / h), which in turn was separated in a cyclone and collected in a receiver. The exhaust gas was passed through a spray washer. The process pressure in the scrubber was approx. 1.5 bar (abs). Downstream of the scrubber, the solids-free process gas, consisting essentially of argon and hydrogen, was recycled by repeatedly using it as the quench medium.

The particle size distribution of the product obtained showed an average particle size of about 30 to 50 nm. FIG. 4 shows a transmission electron microscopic (TEM) image of the solid isolated from the product.

Example 5: Preparation of a suspension of nanoparticulate lanthanum hexaboride in white oil

20 g / h of a highly dispersed mixture of 40% by weight of amorphous boron and 60% by weight of La2Ü3 (molar ratio B: La = 10: 1) were introduced into the reaction zone of an induction plasma with an argon carrier gas stream (180 l / h) a temperature of above 5000 K metered. In addition, a current of 3.6 Nm ³ / h of a gas mixture of 75% by volume of Ar, 10% by volume of hydrogen and 15% by volume of He was added to the induction plasma. The

Plasma was stimulated with a power of 30 kW. After a rapid quench, the particle-laden gas stream was passed into a Venturi scrubber in which white oil was circulated as a precipitating medium. The formed nanoparticulate product from LaBβ had almost no agglomerates due to the rapid quenching and direct deposition of the LaBβ particles in white oil. The primary particles obtained had a size of 25 to 50 nm. The particle size distribution measured in the suspension by means of dynamic light scattering showed a D ₅ o value of 50 nm and a Dgo value of 85 nm.

Example 6: Preparation of a suspension of nanoparticulate molybdenum disulfide in white oil

In a hot wall reactor with an electric power of 30 kW, a temperature of 800 ° C was provided. As purge gases for the heated tube nitrogen with v ^ = 0.5 Nm ³ / h and hydrogen with ^ = 0.1 Nm ³ / h were used. The purge gases were preheated to 175 ° C and heated to 175 ° C template with molybdenum chloride directed. Molybdenum chloride volatilized here until a saturation of the purge gases was achieved. The mixture was mixed just before entering the hot wall reactor with 30 Nl / h of hydrogen sulfide. In the reaction zone, molybdenum chloride reacted with hydrogen sulfide to form molybdenum disulfide. After a residence time of about 150 ms nitrogen was passed with a volume flow of 10 Nm ³ / h in the hot gas as a quench. The temperature after the quench was about 350 K, the process pressure was 980 mbar absolute. In the downstream Venturi scrubber, the particles were deposited with particle sizes 20 to 50 nm in white oil (»= 250 l / h), which in turn was deposited in a cyclone and collected in a storage container. The exhaust gas was supplied to an afterburner. FIG. 5 shows a transmission electron microscopic (TEM) image of the solid isolated from the product.

Claims

claims

1. A process for the preparation of suspensions of nanoparticulate solids, characterized in that

b) subjecting the reaction product obtained in step a) to rapid cooling, and

c) initiating the cooled reaction product obtained in step b) into a liquid, wherein a suspension is formed in which the solids contained are present in the form of nanoparticulate primary particles or very small aggregates.

2. Process according to claim 1, characterized in that the starting material is an elemental hydrogen compound or an elemental metal selected from the group consisting of boron, zinc, lanthanum, tin, cerium,

Titanium, silicon, molybdenum, tungsten, platinum, rhodium, ruthenium and aluminum.

3. The method according to any one of claims 1 or 2, characterized in that are used as the starting material aluminum and hydrogen as another component, which react in the reaction zone to aluminum hydrogen.

4. The method according to any one of claims 1 or 2, characterized in that as starting materials lanthanum oxide and boron or boron compounds are used, which react in the reaction zone to lanthanum hexaboride.

5. The method according to any one of claims 1 or 2, characterized in that are used as starting materials lithium and aluminum and as a further component hydrogen, which react in the reaction zone to Lithiumalumini- umhydrid.

6. The method according to any one of claims 1 to 5, characterized in that the particle size of the nanoparticulate solids in the range of 1 to 500 nm.

7. The method according to any one of claims 1 to 6, characterized in that the residence time of the feedstocks and possibly other components in the reaction zone is between 0.002 s and 2 s.

8. The method according to any one of claims 1 to 7, characterized in that the thermal reaction of the reaction gas takes place at a pressure in the range of 0.05 bar to 5 bar.

9. The method according to any one of claims 1 to 8, characterized in that the rapid cooling in step b) with a cooling rate of at least 10 ^4th

K / s takes place.

10. The method according to any one of claims 1 to 9, characterized in that the rapid cooling in step b) to a temperature which is below one third of the melting or decomposition temperature of the product in

Kelvin lies.

1 1. A method according to any one of claims 1 to 10, characterized in that it is the white liquid used in step c), tetrahydrofuran, diglyme, solvent naphtha, water or 1, 4-butanediol.

12. The method according to any one of claims 1 to 11, characterized in that in step c) a wet electrostatic precipitator or a Venturi scrubber can be used.

13. The method according to claim 1, characterized in that step b) comprises the addition of a modifying agent.

14. The method according to claim 13, characterized in that quenching gas and modifier are added simultaneously.