EP1773947A1

EP1773947A1 - Method and device for producing nanoparticles

Info

Publication number: EP1773947A1
Application number: EP05759569A
Authority: EP
Inventors: Jörg HALPAP; Richard Van Gelder; Bernd Sachweh; Siegfried Welker; Norbert Wagner; Andreas Marquard; Gerhard Kasper
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 2004-07-09
Filing date: 2005-07-08
Publication date: 2007-04-18
Also published as: DE102004033320A1; KR101247838B1; CN1984967B; KR20070036173A; JP4664974B2; US20070262482A1; US7736553B2; WO2006005536A1; CN1984967A; JP2008505992A

Abstract

The invention relates to a method for producing nanoparticles, in particular, pigment particles. Said method consists of the following steps: i) a raw substance (1) is passed into the gas phase, ii) particles are produced by cooling or reacting the gaseous raw substance (1) and iii) an electric charge is applied to the particles during the production of the particles in step ii), in a device for producing nanoparticles. The invention further relates to a device for producing nanoparticles, comprising a supply line (28) which is used to transport the gas flow (29) into the device, a particle producing and charging area in order to produce and charge nanoparticles at essentially the same time, and an evacuation line (30) which is used to transport the charged nanoparticles from the particle producing and charging area.

Description

Method and device for the production of nanoparticles

The invention relates to a method and an apparatus for producing nanoparticles by substantially simultaneous generation of particles and charging of the particles from a gaseous compound contained in a gas stream.

One area where nanoparticles are made and used is in the pigments used in coloring, for example, in paints. As the size of the particles decreases, for example, the brilliance and the color intensity of the paints are improved in the case of pigments.

Another area where nanoparticles are used relates to catalysts. Thus, as the mean particle diameter decreases, the total surface area of the catalyst increases in relation to the mass, resulting in a more effective effect of the catalyst.

Furthermore, the use of nanoparticles in the field of pharmaceutical products or pesticides can increase their bioavailability.

In the case of materials which are vapor-deposited on a substrate in a production process, it is advantageous if the particles are present in very finely divided form, so that they can be converted into the gas phase more rapidly and thus the thermal load can be reduced.

Nanoparticulate solids can be prepared by various methods. These pulverulent solids are usually produced by grinding steps, reactions in the gas phase, in a flame, by crystallization, precipitation, sol-gel processes, in plasma or by desublimation. In addition to production, the subsequent formulation plays a decisive role in the targeted adjustment of product properties, such as, for example, easy redispersibility and color strength in the case of pigments. Particles with a diameter smaller than 1 .mu.m are particularly prone to agglomerate and must therefore be stabilized and put into a state from which they can be further processed (for example redispersed) as easily as possible. WO 03/039716 relates to an apparatus and a method for the production of nanoparticulate pigments in which a pigment precursor is evaporated and subsequently condensed and collected in a collecting liquid.

EP-A 0 343 796 describes a process for the preparation of pigment dispersions. For this purpose, first a pigment or an intermediate in the production of the pigment is vaporized in the presence of an inert gas stream; when using intermediates for pigment production, a further gas stream is added containing the substances which are required for the reaction of the intermediates with pigments. The gas stream is passed into a liquid in which the pigment vapor desublimates into finely divided pigment particles. The pigment particles remain in the liquid and thus form a dispersion.

A process for the preparation of quinacridone by vapor phase dehydrogenation of dihydroquinacridone is known from US 3,097,805. The resulting vaporous chinacridone is cooled by admixing a cold gas stream, so that nanoparticles form.

DE 41 211 19 A1 discloses a method for producing fine particles of a material by evaporating the material in an inert gas. The material is evaporated in an evaporation vessel and the fine particles are produced by cooling the vaporized material in the inert gas, which is blown into the vaporized material from the evaporation vessel. The fine particles are deposited on the surface of the vaporizing vessel and subsequently removed.

The agglomeration of nanoparticles can be prevented, for example, by applying a coating layer. JP 63031534 A describes a method in which an organic substance is heated and evaporated in the presence of an inert gas. The gaseous organic substance subsequently forms hyperfine particles on a solid surface. The particles are coated with a coating layer to provide easy dispersibility.

The electrostatic charging of nanoparticles as a sufficient measure to avoid the formation of agglomerates has hitherto not been considered by experts, since it was assumed that small particles can take up only very few elementary charges. From Fuchs, NA (1963) On the stationary charge distribution on aerosol particles in a bipolar ionic atmosphere, Geofisica pura e applicata 56, 185 to 193, goes forth For example, a particle with a diameter of 35 nm can absorb on average only 1.4 elementary charges.

DE 199 61 966 A1 relates to a process for the conversion of organic crude pigments into a pigment form suitable for the application by sublimation of the crude pigment and desublimation of the vaporized pigment. The crude pigment is sublimated by kurz¬ term supply of energy and, by quenching in a time of 10 ^"5 and 1 s desublimes. The temperature lowering for the desublimation is effected by admixing kälte¬ rer gaseous or liquid components. It is suggested by the specific elektrostati¬ In addition to other measures, charging of the desublimed pigment particles does not prevent aggregation of the pigment particles The electrostatic charging as an exclusive measure for preventing agglomeration is not mentioned Furthermore, the particles are charged in the already desublimed state, so that agglomerating occurs during formation The particles produced by this process therefore still contain many agglomerates.

Agglomerate formation degrades properties gained through nanoscale. Agglomerates, for example, of color pigments used in printing inks, lacquers, paints and plastics have a negative effect on the color properties, in particular on the color strength and gloss after processing of the color pigments.

The object of the present invention is to provide a method and an apparatus for the production of nanoparticles, by which an agglomeration of produced, especially by desublimation resulting nanoparticles is largely ver¬ prevented. The method and the device should be particularly suitable for large-scale application and also in the case of particle generation at high temperatures, e.g. by desublimation of the gaseous compound, with a turbulent flow and a high mass flow rate, largely prevent the agglomeration of the nanoparticles and ensure a narrow particle size distribution.

This object is achieved according to the invention by a process for the preparation of nanoparticles which comprises the following steps:

i) transferring a raw substance into the gas phase, ii) producing particles by cooling or reacting the gaseous raw material and iii) applying electrical charge to the particles during the generation of the particles in step ii).

The object is further achieved by a device for the production of nanoparticles, by substantially simultaneous generation of particles and charging of the particles from a gaseous compound contained in a gas stream comprising

A supply line for transporting the gas stream into the device,

A particle generation and charging region for generating charged nanoparticles and

A derivation for transporting the charged nanoparticles from the particle generation and charging area.

Nanoparticles mean nanoparticulate solids and liquid droplets with a particle diameter <1 μm.

It has surprisingly been found that nanoparticles, in particular hot nanoparticles, can be charged electrostatically during formation from the (hot) gas phase directly with a charge sufficient to prevent agglomeration. The method according to the invention makes use of this knowledge by comprising a method step in which the application of electrical charge to the particles takes place during the generation of the particles. The device according to the invention makes use of this knowledge by comprising a particle generation and charging region, in which essentially simultaneous generation and charging of the particles can take place. The advantage of this structure and this method is that a targeted adjustment of product properties with a small range of the physical quantity to be set (for example, narrow particle size distribution, low agglomerate content) is made possible and a high quality standard is ensured. Improved product properties include brilliance, color, purity, vaporizability and solubility.

In addition to the formation of nanoparticles by cooling, in particular by desublimation, the nanoparticles can also be formed, for example, by a reaction in which a solid or liquid product is formed. For this purpose, preferably at least two precursors are fed to a furnace, which are heated in the oven to reaction temperature. The educt substances can be solid, liquid or gaseous. In the device for producing nanoparticles, the starting materials react with one another to form of nanoparticles. In order to avoid that the individual nanoparticles agglomerate with one another, they are essentially electrostatically charged in the apparatus for the production of nanoparticles at the same time as their formation.

In the context of this invention, desublimation is to be understood as the conversion of a gaseous into a solid by cooling (condensation). It is a process opposite to sublimation.

The charging of the particles is preferably carried out by addition of ions. However, the Aufla¬ tion can also be done by other methods known in the art for Teilchenaufla¬ tion, such as the electron impact ionization. In addition to the charging of the nanoparticles via the electric field, which is generated by a spray electrode, charging can also take place by supplying an ion-containing cooling gas flow. In this case, the ions contained in the cooling gas flow to the nanoparticles and thus lead to their charging. To prevent the nanoparticles from agglomerating, it is also necessary here that the ions are all unipolarly charged.

The particle generation and charging region of the device according to the invention preferably further contains an electrode arrangement suitable for corona discharge with at least one spray electrode and at least one counterelectrode. In an arrangement of electrodes, of which one (spray electrode) has a much smaller radius of curvature than the other (counter electrode) and in which the distance between the electrodes is greater than the radius of curvature of the smaller one (for example tip plate, Wire plate, wire tube), an ionization of the gas in the vicinity of the smaller Elekt¬ rode far below the breakdown field strength of the entire gap. This ionization is associated with a faint glow and is called a corona.

In a preferred embodiment of the present invention, the spray electrode is the cathode and the counter electrode is the anode. In simple terms, the ion generation then takes place in such a way that the high field strength in the immediate vicinity of the spray electrode accelerates electrons strongly present in the gas toward the counter electrode. The accelerated electrons collide with the neutral gas molecules, so that positive gas ions and other electrons are formed by impact ionization. The positive gas ions are accelerated toward the spraying electrode and release further electrons on impact there. The result is an electron avalanche, which moves towards the counter electrode. Further away from the cathode, the field strength and the energy of the electrons decrease, so that no further positive gas ions are formed. It comes to the deposition of Electrons to gas molecules and thus to the formation of negative gas ions. The negatively charged gas ions migrate to the counterelectrode and attach themselves to these in collisions with the desublimierten solid particles. The nanoparticles are charged by this process in the particle generation and charging region of the device according to the invention.

The supply line of the device according to the invention may be a tube which is flanged directly to a heating section in which the sublimation of a compound which precipitates as a nanoparticulate solid or of a starting material thereof takes place.

Preferably, the gas stream entering the device according to the invention contains, in addition to the compound to be produced as a nanoparticle, at least one carrier gas, preferably at least one carrier gas, which is inert to the compound.

The invention further relates to a process for the preparation of nanoparticles which comprises the following steps:

I) dosing a raw substance in an oven,

H) transfer of the raw substance into the gas phase,

IE) generating particles by cooling the gaseous raw substance by supplying a cooling fluid flow whose temperature is below the condensation temperature or desublimation temperature of the raw substance and

IV) applying electrical charge to the particles during the generation of the particles in step JS).

By unipolar charging of the particles is already largely avoided during the production process of the particles that agglomerate into larger particles.

In a preferred embodiment of the process according to the invention, the crude substance is metered into a carrier gas stream and fed to the furnace together with the carrier gas. Raw substance is the substance from which the nanoparticles are produced by sublimation and desublimation or by a chemical reaction. The raw substance may be present as a solid or liquid, for example. In solid form, the raw substance, for example, powder or granular.

The solid substance in raw form is, for example, with a commercially er¬ available brush dispenser, such as the brush dispenser RBG 1000 from Palas GmbH, in metered the carrier gas stream. The carrier gas used is preferably a gas which does not react with the raw substance. Suitable gases are, for example, nitrogen, carbon dioxide or noble gases.

In a further embodiment of the method according to the invention, the carrier gas is preheated. For preheating the carrier gas, heat exchangers are preferably used. Suitable heat transfer media are, for example, thermal oils, condensing steam or molten salts. In addition to the indirect heating in a heat exchanger, the carrier gas can also be heated directly, for example, in a molten metal.

When using non-preheated carrier gas, the carrier gas is heated together with the raw material in the oven.

The furnace in which the raw substance is transferred into the gas phase is preferably operated continuously. Continuous furnaces, which are flowed through by the medium to be heated, have the advantage that the medium is only subjected to thermal stress for a short time. The evaporation of the raw material can be carried out, for example, in a fluidized bed with inert fluidized material (for example quartz or aluminum oxide), wherein heating is preferably effected by heat exchangers located in the fluidized bed, or by furnaces in which the walls are heated from the outside, respectively. Furnaces in which the walls are heated from the outside are, for example, tube furnaces. The heating of the walls is usually done electrically, with flames, molten salts or molten metal. For evaporation of the raw material tube furnaces are preferably used with electrical heating.

In order to achieve a uniform temperature distribution in the furnace, the furnace is preferably divided into at least three heating zones. Depending on the degree of evaporation of the raw substance, a different amount of heat can be supplied to the individual heating zones. Thus, for example, at the furnace inlet, if no raw material has yet evaporated, a larger amount of heat is required to maintain the temperature in the furnace at the evaporation temperature than at the end of the furnace when most of the raw material has already evaporated. As soon as the raw material has evaporated, a further supply of heat causes the evaporated raw material to continue to heat up and decompose.

In order to achieve a uniform evaporation and a uniform thermal stress, in particular of thermally sensitive raw material, the temperature in the furnace is preferably controlled so that the lowest temperature in the furnace is at most 20% lower than the highest temperature occurring in the furnace. In order to ensure only a short thermal stress, in particular of thermally sensitive Roh¬ substance, the flow rate of the raw substance enthal¬ border carrier gas stream is preferably selected so that the residence time in the oven for a maximum of 10 s, preferably at most 1 s and more preferably at most 0, 1 s. The residence time of the raw substance in the furnace is also to be adapted to the thermal stability of the raw substance.

In order to improve the flow guidance in the furnace, guide plates or guide bodies can be arranged in the furnace. The arrangement of the guide bodies or baffles reduces the flow cross section and thus increases the flow velocity. At the same time the flow is rectified by the use of baffles or guide body.

In contrast to thermally sensitive raw material, it is not necessary in the case of thermally insensitive raw material to set a uniform temperature profile and a short residence time in the furnace.

In order to be able to realize correspondingly short residence times during which the crude substance completely evaporates, it is necessary for the raw substance to be already comminuted and fed to the furnace. For comminution, for example, commercial mills, such as impact mills, ball mills, counter-jet mills, spiral jet mills or any other mills known in the art can be used. Impact mills, spiral jet mills or counter-jet mills are preferably used.

To avoid a short-term strong thermal stress on the raw material by contact with the furnace walls, in a preferred variant of the method, the carrier gas stream containing the raw substance in the furnace is surrounded by an enveloping gas stream. Suitable as the sheath gas as well as the carrier gas are gases which are inert to the raw material. The enveloping gas is preferably supplied to the furnace via gas supply nozzles distributed around the circumference of the furnace. In a preferred embodiment, the gas supply nozzles are aligned so that the enveloping gas is supplied to the furnace parallel to the furnace walls. This avoids that the enveloping gas already completely mixed at the entrance with the carrier gas containing the raw substance.

In a further preferred embodiment, the furnace walls are formed of a porous sintered material, via which the enveloping gas is supplied to the furnace. Via the porous sintered walls, a uniform supply of the enveloping gas over the entire length of the furnace is achieved. guaranteed. In this way, a contact of the raw substance with the furnace walls can be reliably avoided.

In a further embodiment, the raw substance is supplied to the furnace in the form of a suspension in a vaporizable solvent. The solvent evaporates in the oven, so that the addition of a further carrier gas can be dispensed with. In order to avoid that the raw substance reacts with the solvent, a solvent should be chosen which is inert to the raw substance even at high temperatures. A suitable solvent is, for example, water.

Also, in the evaporation of a suspension containing the raw material, it is advantageous to use a Hüllgasstrom in the oven to prevent raw material comes into contact with the furnace walls.

In one embodiment of the method according to the invention, the gaseous raw substance desublimates by sudden strong cooling to a large number of individual nanoparticles. For cooling, a cooling gas which is inert relative to the raw substance is preferably added. As the cooling gas, for example, nitrogen, carbon dioxide or a noble gas is used. Preferably, the cooling gas is the same gas as the carrier gas.

In order to obtain particles having an average particle diameter of preferably less than 0.3 μm, it is necessary for the desublimation to take place in less than 1 s, preferably in less than 0.1 s. Rapid cooling can be achieved, for example, by adding pre-cooled cooling gas. Thus, for example nitrogen for rapid cooling as the liquid nitrogen at a temperature of -195.8 ⁰ C was added with the wer¬. Also, the addition of any other inert nanoparticles inert cooling gases with temperatures below 0 ⁰ C or in their liquid form is conceivable. A further acceleration of the cooling can be achieved by greatly reducing the flow cross-section in the device for desublimation and charging and thus increasing the flow velocity.

In a further embodiment of the present invention, nanoparticles are formed from the crude substance by chemical reaction. These are preferably cooled by adding an inert cooling gas. Instead of the inert cooling gas, however, it is also possible to add a further gaseous reactant for the preparation of the nanoparticles. To avoid that the charged nanoparticles in _. In the direction of the at least one Ge counter electrode flow, it is possible to flow around the at least one counter electrode by an enveloping gas, so that the charged nanoparticles are entrained with the gas flow and do not reach the at least one counter electrode. It is also possible to arrange the at least one counterelectrode outside the device for the production of nanoparticles and to charge the walls themselves negatively. Due to the negatively charged walls, the negatively charged nanoparticles are then repelled and thus remain in the carrier gas stream.

Even with walls of electrically neutral, but electrically conductive material, a contact of the charged nanoparticles with the wall is to be avoided, since this would lead to the fact that the charges are transferred from the particle to the wall. This neutralises the nanoparticles and can then agglomerate. Such a contact can be avoided, for example, by the use of an enveloping gas.

The sheath gas is preferably supplied to the device according to the invention via gas supply nozzles distributed around the circumference of the device. In a preferred embodiment, the gas delivery nozzles are aligned so that the sheath gas is supplied to the device parallel to the walls.

In a further preferred embodiment, the walls of the device are formed of a porous sintered material. The sheath gas is then supplied uniformly over the pores of the walls of sintered metal over the circumference and the length of the particle generation and Auf¬ charge region. ^■ . ^{• ■ ■}

Accordingly, in the case of positively charged nanoparticles in a preferred embodiment, the walls of the device for the production of nanoparticles are also positively charged in order to prevent the charged nanoparticles from being attracted to the walls. Even with positively charged nanoparticles, this effect can be enhanced by the use of a Hüllgasstromes.

To increase the reliability and to avoid personal injury caused by electric shock when touching the walls, in many applications, only the use of an enveloping gas without electrical charge of the walls is possible to avoid ver¬ that nanoparticles touch the wall. The electrically charged nanoparticles are separated in a preferred embodiment of the method according to the invention in an electrostatic precipitator. In this case, any commercially available electrostatic precipitator is suitable as electrostatic precipitator. These are, for example, electrostatic precipitators from Messrs. Künzer or Lurgi.

If the nanoparticles are to be dispersed in a liquid, a wet electrostatic precipitator, in which the nanoparticles are deposited in a liquid film, is preferably used to separate the nanoparticles from the carrier gas stream. The liquid film containing the nanoparticles is collected in a collecting container. In order to concentrate the dispersion, the liquid already containing nanoparticles can be recirculated to the wet electrostatic precipitator, in which case further nanoparticles are absorbed by the liquid.

In addition to the separation in electrostatic precipitators or wet electrostatic precipitators, the separation of the particles from the carrier gas stream can also be effected by conventional gas filters, such as bag filters or bag filters, or by gas scrubbers, for example venturi scrubbers, to produce a dispersion.

When separated in an electrostatic filter or in a conventional gas filter, the nanoparticles can either be stored dry in powder form or further processed or dispersed in a liquid after deposition.

If the particles are dispersed in a liquid, additives are preferably added to the liquid to stabilize the dispersion. Suitable additives for stabilizing the pigment dispersion are, for example, dispersants z. As cationic oberflä¬ chenaktiven additives, or anionic surface-active additives based on sulfonates, sulfates, phosphonates or phosphates or carboxylates, or non-ionic ober¬ surface-active additives based on polyethers. Such dispersants are offered for example by the companies Lubrizol, Byk Chemie, EFKA or Tego. Mixtures of additives are also possible.

An alternative stabilization of the nanoparticles against agglomeration can be achieved by combining the charged particles with oppositely charged aerosol droplets. The aerosol droplets consist of a liquid and one or more additives which serve for stabilization. The opposite charge attracts the nanoparticles and the aerosol droplets so that they collide. Due to the still prevailing high temperature, the liquid evaporates, so that the additives from the aerosol droplets remain on the surface of the nanoparticles and thus largely prevent agglomeration of the nanoparticles.

In one embodiment of the present invention, a first particle separator is arranged between the furnace and the device for producing nanoparticles, in which parts which have not been vaporized are separated off. These are, for example, impurities which do not evaporate at the temperatures prevailing in the furnace or also crude substance which has not completely evaporated due to the short residence time in the furnace. As a particle separator, for example, a hot-electrostatic precipitator, a sintered metal filter, a plan¬ filter, a bag filter, or an absolute filter of another type can be used.

For example, the solids separated in the first particle separator may be re-supplied to the furnace for complete evaporation. In this case, the return to the oven preferably takes place after a cooling of the unvaporized raw substance. In addition to the return to the oven, the unevaporated raw material can also be returned to the mill or dosing unit. It is also possible to remove the separated solids from the process, for example to free the process of impurities.

In a further embodiment of the present invention, the device for producing nanoparticles is followed by a second particle separator in which gaseous impurities are separated off. The gaseous impurities may, for example, be supplied as gas to a gas scrubber. The not yet completely cooled off nanoparticles, which were discharged in the second particle, is in a preferred embodiment, a cold gas stream zuge¬ for further cooling zuge¬. As gas, every gas which is inert to the nanoparticles is also suitable here. Preferred gases are nitrogen, carbon dioxide or noble gases. Preferably, the same gas as the cooling gas used in the device for desublimation and charging and / or the same gas as the carrier gas.

The temperature at which the carrier gas stream containing the nanoparticles is supplied to the second particle separator for the separation of gaseous impurities is preferably below the desublimation temperature of the nanoparticles and above the sublimation or condensation temperature of the impurities.

An improved desublimation of the gaseous raw substance into nanoparticles in the device for the production of nanoparticles can be achieved in that the carrier gergas into which the raw substance is metered, non-evaporable substances or a substance with a higher desublimation temperature is added, which act as desublimation onskeime. Also, the cooling gas can already be solidified nuclei of the raw material from which the nanoparticles are formed, are added. The added germs are preferably smaller than the nanoparticles to be produced.

In a particularly preferred process variant, the crude substance is transferred to the gas phase at atmospheric pressure and desublimed.

In a preferred embodiment of the device according to the invention, the particle generation and charging region is a desublimation and charging region for generating charged nanoparticles with a gas supply for supplying a cooling fluid having a lower temperature than the gas flow. In a further preferred embodiment, the particle generation and charging region is a reaction and charging region suitable for the course of chemical reactions for producing nanoparticles.

The invention therefore also relates, in particular, to a device for producing nanoparticles, in particular nanoparticulate pigments, by substantially simultaneous desublimation and charging of a gaseous compound contained in a gas stream

A supply line for transporting the gas stream into the device,

A desublimation and charging region for generating charged nanoparticles with a gas supply for supplying a cooling fluid having a lower temperature than the gas flow and having a suitable electrode arrangement for a corona discharge, comprising a spray electrode and a counterelectrode and

• a derivative for transporting the charged nanoparticles from the Desublimati¬ ons- and charging area.

The desublimation and charging region of the device according to the invention contains a gas feed for supplying a cooling fluid having a lower temperature than the gas flow (eg a quench gas). The gas stream containing the at least one carrier gas and the gaseous compound becomes at a lower temperature than the sublimation temperature of the compound by the supply of the cooling fluid cooled and thus desublimated, so converted to the solid state. The result is very fine particles with a narrow particle size distribution.

The temperature of the supplied cooling fluid in the present invention is below the sublimation temperature of the compounds to be desublimed. Preferably, the cooling fluid has a temperature at least 10 ⁰ C, more preferably between 100 and 700 ⁰ C, most preferably between 500 and 650 ° C is lower than the Tem¬ temperature of the gas stream containing the gaseous compound. The ratio of the volume of the gas fed to the desublimation and charging region to the cooling fluid per unit time is preferably between 10: 1 and 1: 100, particularly preferably 1: 1.

The cooling fluid and / or the gas stream as carrier gas preferably contain at least one gas from the group air, carbon dioxide, noble gases and nitrogen.

In a preferred embodiment of the device according to the invention, in the sublimation and charging region, a porous tube surrounds the spray electrode concentrically, wherein the porous tube is designed such that it forms the gas feed for the cooling fluid.

The cooling fluid passes through the porous wall of the tube into the interior of the tube, in which the gas containing the compound to be desublimated is guided and in which a spray electrode for a corona discharge is arranged. If appropriate, the porous tube wall also functions as a grounded counterelectrode, against which a corona is maintained when the DC high voltage applied to the spray electrode is reached. The flowing through the porous tube wall into the tube interior cooling fluid stream serves as a cooling gas stream, which condenses the gaseous compound and thus causes particle formation. In addition, the cooling fluid flow by "blowing out" of the counter electrode (if the porous tube serves as this) prevents deposition of the charged particles on the counter electrode and the resulting unwanted particle losses in the desublimation and charging region. The charged particles can therefore reach a deposition location which can follow the desublimation and charging area.

In another embodiment of the present invention, the porous tube concentrically surrounding the spray electrode serves only for cooling fluid delivery and there is an additional counter electrode to the spray electrode.

Preferably, the porous tube is surrounded by an annular space for supplying the cooling fluid. The cooling fluid flows around the tube outer surface of the porous tube via the annular space and passes through the pores of the porous tube into the warm gas stream flowing around the spray electrode, which contains the compound to be desublimed, for example a pigment or a catalyst.

Examples of materials which are suitable for producing such porous tubes are porous sintered metals or sintered ceramics.

In a preferred embodiment of the present invention, the electrode arrangement comprises a bar-shaped spraying electrode which is provided with at least one radially extending wire at an end projecting into the desublimation and charging area. These are, for example, a temperature-stable platinum wire.

The at least one wire preferably has a diameter of between 20 and 200 μm. By this Sprühelektrodenanordnung an approximately punctiform discharge is achieved. The wires serve as tips on which a discharge can take place. They ensure a uniform corona discharge.

In a preferred embodiment of the device according to the invention, the latter contains at least one displacement body, which is at least partially arranged in the porous tube such that a flow gap is formed between the displacement body and the inner wall of the porous tube. The gas stream to be desublimed flows through this flow gap between the displacement body and the inner wall of the porous tube, through which the cold cooling fluid enters the flow gap. As a result, a large cooling rate and a thermodynamic homogenization are achieved in a short desublimation and charging area. The nucleation within the resulting annular gap flow leads to higher particle concentrations. Preferably, these are two displacement bodies, one of which is arranged in front of and behind the spray electrode in the flow direction of the gas flow, or a plurality of displacement bodies, which are arranged alternately with a plurality of spray electrodes in the flow direction of the gas flow.

In a preferred embodiment of the present invention, the derivative which serves to transport the charged nanoparticles from the particle generation or sublimation and charging region comprises a deposition zone or terminates in a sol¬ in which the charged nanoparticles are deposited. The nanoparticles can be deposited on a solid or in a liquid medium. The deposition into a liquid medium can be done for example by means of a wet electrostatic precipitator. The A solid medium can be deposited in a dry electrostatic precipitator or on a filter medium (fabric, felt, fleece). In order to achieve the lowest possible particle losses, the location of the particle separation should be as close as possible to the charging area.

The device according to the invention and the method according to the invention are particularly suitable for converting thermally stable organic crude pigments into a pigment form suitable for the application. Suitable classes of pigments include: phthalocyanine pigments, perylene pigments, perinone pigments, quinacridone pigments, indanthrone, flavanthrone, anthrapyrimidine, pyranthrone, isoviolanthrone pigments and lanthron- VIO, anthanthrone, anthraquinone, Chi nophthalonpigmente, te dioxazine pigments, diketopyrrolopyrrole pigments, Thioindigopigmen-, Iso indoline pigments, isoindolinone pigments and aniline black, monoazo pigments, disazo pigments, disazo condensation pigments, metal complex pigments and generally metal-organic complexes (for example for O-LEDs), pyrazolochromazolone pigments, CI. Pigment Black 1 (Aniline Black), CI. Pigment Yellow 101 (aldazeelb), beta-naphthol pigments, naphthol AS pigments, benzimidazolone pigments, triarylcarbonium pigments and CI. Pigment Brown 22.

The pigment particles obtained with the aid of the device or the method according to the invention are distinguished by their fine particle size, color strength and easy dispersibility during use.

In addition to the mentioned pigment classes, the process is also suitable for the production of very finely divided catalyst particles, which thus have a greater total surface area per mass and thus a much more effective effect. In the case of pharmaceutical products or pesticides, the fineness due to the small size of the nanoparticles can increase the bioavailability. A pharmaceutical product in which the process can be used is, for example, ephedrine, (chemical name: erythro-2-methylamino-1-hydroxy-1-phenylpropane; 2-methylamino-1-phenyl-1-propanol).

Suitable catalysts are, for example, DMPS (dimethylolpropionic acid) or TEDA (triethylenediamine) as catalysts for the preparation of polyurethane foams.

Further substances from which nanoparticles can be prepared by the process according to the invention are, for example, optical brighteners, such as Ultraphor or plant protection agents such as BAS 600 F®. In addition to the production of nanoparticles, the method is also suitable for the separation of impurities. For example, in a particle separator arranged between the furnace and the apparatus for producing nanoparticles, undiluted solid particles can be separated from the gas stream. In a separator, which is arranged behind the device for the production of nanoparticles, more easily volatile impurities, which are still gaseous at temperatures below the desublimation temperature of the product, can be discharged. In this way, a product can be obtained which is largely free of impurities. The purification is possible for substances which are solid or liquid above the vaporization temperature of the product or gaseous below the desublimation temperature of the product.

drawing

Reference to the drawings, the invention will be explained in more detail below.

It shows:

FIG. 1 shows a process flow diagram for the process according to the invention in a first embodiment,

FIG. 2 shows a process flow diagram for the method according to the invention in a second embodiment,

FIG. 3 a schematic representation of a device according to the invention for the production of nanoparticles and

FIG. 4 shows a graph with the average charge, the efficiency and the particle loss as a function of the corona voltage in a device according to the invention.

FIG. 1 shows a process flow diagram for the method according to the invention in a first embodiment.

Raw substance 1 is supplied from a supply via a metering device 2 to a carrier gas stream 3, which is preferably inert to the raw substance 1. The raw substance 1 is presented for example as a powder or granules in a storage container. Furthermore, it is possible to separate the raw substance 1 from a block, to comminute it and the carrier gas 3 to meter. In addition to the Zudosierang the raw material 1 in solid form, it is also possible to submit the raw material 1 in a suspension.

For raw substance 1 in solid form, the doser 2 is preferably a brush dispenser. However, it is also possible to use any other suitable doser 2 known to the person skilled in the art. These are, for example, dosing channels or injectors.

The carrier gas 3 to which the raw substance 1 has been metered or the raw substance 1 present in suspension is fed (preferably preheated) to a furnace 4. In a preferred embodiment, the oven 4 is heated by an electric heater 5. In order to obtain a substantially homogeneous temperature distribution in the oven 4, the oven 4 is preferably divided into several heating zones. A substantially homogeneous temperature distribution here means that the minimum temperature occurring in the furnace is at most 20% below the maximum temperature occurring in the furnace 4. In the embodiment illustrated here, the furnace 4 is heated by three electric heaters 5, which corresponds to a division of the furnace 4 into three heating zones.

In the oven 4, the raw material 1 is transferred to the gas phase. The carrier gas 3 containing the gaseous raw substance 1 is fed to a device for producing nanoparticles 9. For the sudden cooling of the gaseous raw substance 1 containing Trä¬ gergases the device 9, a cooling gas 6 is supplied to desublimate the raw material 1 from the carrier gas 3 to nanoparticles or by chemical reaction and subsequent closing cooling nanoparticles to form. As the cooling gas 6, any gas which is inert to the raw substance 1 is suitable.

The cooling gas 6 is supplied to the device for producing nanoparticles 9, for example via nozzles distributed around the circumference of the device 9. However, the feed preferably takes place via porous walls of the device for the production of nanoparticles 9. During the supply of the cooling gas 6 via porous walls, the cooling gas 6 simultaneously acts as sheathing gas and thus prevents nanoparticles formed from coming into contact with the walls and against them be liable.

In order to avoid that individual nanoparticles agglomerate with each other, they are electrostatically charged upon formation. For this purpose, within the apparatus for producing nanoparticles 9, in a preferred embodiment, a spray electrode 7 is accommodated. Counter electrodes 8 are arranged between the spray electrode 7 and along the wall of the device for the production of nanoparticles 9. Between the spray Electrode 7 and the counter electrodes 8 form an electric field in which the gas is ionized between the spray electrode 7 and the counter electrodes 8 by emission of Elekt¬ rons from the spray electrode 7. When the nanoparticle-containing gas stream flows through the electric field, charges are deposited by diffusion charging on the nanoparticles, so that they are charged electrostatically. With unipolar charge, the individual nanoparticles repel each other, so that agglomeration is prevented.

The temperature and the amount of the supplied cooling gas is chosen so that, for example, for organic pigments within the cooling section a cooling of vor¬ preferably 300 ° C per 10 mm to 10 ° C per 10 mm sets. The cooling rate can be increased by improved isolation (for example with quartz disks) between the furnace and the quench. In addition, the cooling rate can be significantly increased by adiabatic relaxation, for example by means of a Laval nozzle.

By charging the nanoparticles already during formation, it is prevented that individual nanoparticles agglomerate into larger particles.

In addition to the charging of the nanoparticles by electrons emitted by a spray electrode 7, the charging can also take place by adding ion-containing cooling gas to the device for the production of nanoparticles 9.

The particle-containing gas stream is fed from the device for producing nanoparticles 9 to an electrostatic precipitator 10. In the electrostatic filter 10, the charged nanoparticles are separated from the gas stream. The charged nanoparticles are withdrawn as a product 12 from the e lektrofilter 10 and can be fed to a further processing. The gas stream, as the exhaust gas 11, is preferably supplied to an exhaust gas purification unit, not shown here, and discharged to the environment after cleaning.

In addition to the electrostatic precipitator 10, a wet electrostatic filter in which the nanoparticles are dispersed in a liquid film or a gas filter, for example a bag filter, in which the charged nanoparticles are retained by the filter bags is suitable for separating the charged nanoparticles from the gas stream and later be cleaned from the filter tubes. A combination of different apparatuses (for example a series connection) for improving the degree of separation (for example Venturi scrubber in front of an electrostatic precipitator) is conceivable. FIG. 2 shows a process flow diagram of the method according to the invention in a second embodiment variant.

As in the case of the method variant shown in FIG. 1, the raw substance 1 is also metered into a carrier gas 3 via a metering device 2 and fed to the carrier gas 3 into a furnace 4. The oven 4 is preferably heated by electric heaters 5, but can also be heated by heat transfer, such as molten salts or molten metal.

In the case of the embodiment variant shown in FIG. 2, the oven 4 is divided into three heating zones, which are each heated with their own electric heater 5. By dividing the furnace 4 into individual heating zones, it is possible to realize a largely homogeneous temperature distribution in the furnace 4.

In the oven 4, so much heat is supplied that the raw material 1 evaporates. After the opening, the carrier gas stream 3 containing the evaporated raw material 1 is fed to a first particle separator 13. In the first particle separator 13, non-evaporated substances are separated off. Unvaporized substances may, for example, be contaminants that evaporate at a higher temperature than that prevailing in the oven 4. Also, the non-evaporated substance may be raw substance 1, which is not completely evaporated in the furnace 4 due to the particle size during the residence time of the raw substance 1. In the first particle separator 13 separated solid 21 is discharged from the first particle 13. When the discharged solid 21 contains unvaporized raw material 1, the solid 21 is preferably returned to the furnace 4 via a solids return 22. For this purpose, the solids return 22 can open directly into the furnace 4 or into the supply of carrier gas 3 containing the raw substance 1. The solids return 22 can be cooled in order to prevent thermal decomposition with a high residence time and temperature.

The gas stream purified in the first particle separator 13 of solid 21 is fed to the device for producing nanoparticles 9. In the device 9 1 nanoparticles are formed from the gaseous raw material. During formation, the resulting particles are electrostatically charged to prevent agglomeration. The electrostatic charging takes place, as shown in Figure 2, via a corona discharge at the spray electrode 7. The charging mechanism of the particles corresponds to that of the method described in Figure 1. In order to prevent a purification during cleaning, any impurities present in the gas stream are desublimed or condensed out in the apparatus 9, the gas stream is cooled to a temperature below the desublimation temperature of the raw substance 1 and above the desublimation or condensation temperature of the contaminants ¬ lies lies. The gas stream containing the product in the form of nanoparticles is fed to a second particle separator 14, in which the nanoparticles are separated from the gas stream. With the gas stream exiting the second particle separator 14 as waste gas 11, any gaseous impurities present are removed. The product present in the form of nanoparticles is fed to a cooling device 15 for further cooling. The cooling device 15 is supplied with a cooling gas 20, which is inert to the product. As a cooling gas is, for example, nitrogen or carbon dioxide, but it can also noble gases such as argon or water, which is evaporated to steam, are used. From the cooling device 15, the gas stream containing the product is supplied to a wet electrostatic precipitator 16. In wet electrostatic precipitators 16, the charged nanoparticles are dispersed in a liquid film. The dispersion 17 containing the nanoparticles is fed to a collecting container 18. In order to concentrate the dispersion 17, that is to disperse further nanoparticles into the dispersion, the dispersion 17 is supplied to the electrostatic precipitator 16 again via a circulating stream 19. In the electrostatic precipitator 16 then separate more particles in the dispersion. The purified in the wet electrostatic precipitator 16 of the nanoparticles gas is discharged as exhaust gas 11. The exhaust gas 11 can be supplied for further treatment of an exhaust gas purification, before it is discharged to the environment.

In addition to the method variant shown here, in which the nanoparticles are dispersed in a wet electrostatic precipitator 16 in a liquid, the charged nanoparticles can also be in an electrostatic filter or in a gas filter, for example a pocket filter, as already shown in the method in FIG be separated from the gas stream. Furthermore, a separation of the nanoparticles with a wet scrubber is possible.

If the nanoparticles are not deposited in a dispersion, it is possible, in order to permit long-term storage, without the nanoparticles agglomerating, to coat the nanoparticles with a surface-active substance after separation from the gas stream. This is necessary in particular because the nanoparticles recharge and thus no longer repel each other.

FIG. 3 shows schematically a device according to the invention for the production of nanoparticles. The device comprises a stovepipe serving as a supply line 28, a desublimation and charging region 31 and an exhaust pipe serving as a discharge 30. Into the supply line 28 flows a compound containing gas stream 29 (eg 40 L / min). The desublimation and charging region 31 contains an electrode arrangement 23, 25 with a spray electrode 23 and a counterelectrode 25. The counterelectrode 25 is formed by a porous tube 32, which consists of a grounded sintered metal. The diameter of the Roh¬ res 32 is for example 40 mm, the length, for example, 20 mm. The spray electrode 23 consists of a thin rod whose end ver¬ at the height of the porous tube 32 in which it is centrally located, with (eg six) radially clamped fine platinum wires 33 (diameter 40 microns) ver¬ is seen.

A cooling fluid 27 enters the annular space 26 (eg 40 L / min) and flows around the porous tube 32. Through the pores of the porous tube 32, the cooling fluid 27 enters the desublimation and charging region 31, where it acts as a cooling gas acts, which condenses a gaseous compound in the gas stream 29 of hot gas and thus causes the formation of nanoparticles. Furthermore, the cooling fluid 27 serves for blowing out the porous tube 32 serving as a counterelectrode 25 in order to avoid particle losses due to deposition on the inner side of the tube. Furthermore, with the cooling fluid 27, a further vaporous substance can be supplied (for example a coating substance) which condenses heterogeneously on the nanoparticles on the way of the particles to the deposition zone (not shown) at suitable condensation temperatures.

Furthermore, the device according to the invention comprises two displacement bodies 24, 34, of which the first 24 is arranged in the flow direction of the gas flow 7 in front of the spray electrode 23 and the second 34 behind the spray electrode 23. As a result, a flow gap 35 forms between the displacement bodies 24, 34 and the inner wall of the porous tube 32, through which the gas flow 7 flows through the cooling fluid 27 during its cooling by charging the desublimed particles through the negative corona discharge. The flow gap 35 has e.g. a width of 15 mm.

FIG. 4 shows a graph with the average particle charge and the efficiency as a function of the corona voltage in a device according to the invention.

For this purpose, nanoscale Heliogenblau® particles (copper phthalocyanines from BASF AG) were investigated in low concentrations at 25 ^° C. in the apparatus (without the desublimation step). Two variables determined as a function of the corona voltage were calculated as follows: 1. Efficiency:

_* C ^v ^ off, neutral

C ^ out, totally

With

C _aus , _ne ut _ta i the concentration of neutral particles that pass through an electrical separator connected to the device when high voltage is applied and

C _uus , _tota i the particle concentration emerging from the desublimation and charging area.

and

2. Medium charge:

q = ¹ FCE ^{β '} C out, total y FCE

With

I _FCE the particle charge current measured in a Faradaycup electrometer,

e of the elementary charge and

V _FCE the volume flow through the Faradaycup electrometer.

In FIG. 4, the efficiency values ε calculated from measured values are shown as small dark triangles and the average charge q as black diamonds. The height of the efficiency values / loss values is readable from the right, the height of the values of the average charge from the left ordinate.

The polydisperse Heliogenblau® particles (d = 35 nm, σ _g = 1.5, c = 10 # / cm) were aspirated about 20 cm after the charging zone. The charge in the figure (average charge and efficiency) starts with 8 kV with increasing corona voltage, then rises steeply until it finally saturates at 14 kV.

Despite a short residence time in the charging zone (about 0.5 s) and a mean Teilchen¬ size of 35 nm very high values are achieved with just under four charges per particle, according to the rule of thumb of Batel (1972) of the expected saturation charge at theoretically approaching an infinitely long residence time during diffusion charging. It was thus shown that in the device according to the invention a faster charging of nanoparticles can be achieved than expected. This charge is used in the production of nanoparticles to avoid agglomeration. With the apparatus according to the invention, experiments were carried out to influence the agglomeration by the charging. The experiments carried out at about 290 ° C. and particle concentration of about 4 × 10 5 / cm documented a significant inhibition of the agglomeration. The greater the charge, the higher the concentration and the smaller the average particle size _r. In addition, the measured particle size distribution approached the shape of a Gaussian distribution with increasing stabilization.

Examples

example 1

The formulation of the nanoscale pigment Red 179 is carried out by applying a milled crude pigment having an average particle size of 15 μm by means of a commercially available brush dispenser into an N ₂ solution of 1 m / h. The N ₂ stream containing the ground crude pigment is heated to 600 ° C. in a 3-zone oven, the pigment being completely sublimed. Subsequently, the sublimate is m by coaxial injection of 1 ³ / h N _2, which has a temperature of 2O ⁰ C, cooled, wherein the pigment desublimes tikeln to Nanopar¬. At the same time, the resulting particles are charged via a high-voltage electrode arranged centrally in the region of the injection nozzles of the nitrogen. The gas stream is cooled to a temperature below 100 ° C and passed into a wet electrostatic precipitator. In the wet electrostatic precipitator, fully desalinated water is circulated and concentrated by separation of the resulting charged nanoparticles. For stabilization, Solsperse 27000 from Lubrizol is added to the fully desalted water as a dispersing additive. Example 2

The purification of a pigment raw material based on PB 15: 1, which contains conventional impurities from the synthesis, is effected by applying the ground crude pigment (X ₅₀ = 15 μm) to an N ₂ stream (1 mVh i.N) by means of brush dispensers (RBG 1000, Fa. Lasas). Of the crude pigment-containing stream of N ₂ is heated in an oven at 3 -zonigen a narrow temperature profile to 600 ⁰ C, wherein the material completely sublimated. Thereafter, the sublimate is passed over a plan filter leaving solid impurities on the filter. Subsequently, the sublimate is cooled by coaxial injection of N ₂ (1 m ³ / h LN., 20 ⁰ C). This leads to the desublimation of the desired product. This valuable product is abgeschie¬ in an electrostatic precipitator (Delta Profimat, Fa. Künzer) at 200 ° C. Provisions of the values have shown that a significant increase of the value content of the raw material by up to 6% is possible.

LIST OF REFERENCE NUMBERS

crude

doser

carrier gas

Oven electric heating

cooling gas

spray electrode

counter electrode

Device for producing nanoparticles

electrostatic precipitator

exhaust

Product first particle separator second particle separator

cooler

Wet Electrostatic Precipitator

dispersion

receptacle

loop current

cooling gas

solid fuel

Solid rear vehicle

Spray electrode first displacement body

counter electrode

annulus

Cooling fluid heated supply line

gas flow

derivation

Desublimation and charging area of porous pipe

Platinum wires second displacement body

flow gap

Claims

claims

1. A process for the preparation of nanoparticles, in particular of pigment particles, comprising the following steps:

i) transfer of a raw substance (1) into the gas phase, ii) production of particles by cooling or reaction of the gaseous raw substance (1) and iii) application of electrical charge to the particles during the production of the particles in step ii) in one Device for producing nanoparticles.

2. The method according to claim 1, characterized in that the generation of particles by cooling the gaseous raw substance (1) takes place by a cooling fluid stream (6) is supplied, the temperature of which is below the condensation temperature or sublimation temperature of the raw material (1)

3. The method according to claim 1 or 2, characterized in that the raw substance (1) in a relation to the raw material (1) inert carrier gas stream (3) is metered, which is fed to a furnace (4) for transferring a raw substance (1 ) into the gas phase.

4. The method according to claim 3, characterized in that the carrier gas stream (3) is heated vor¬.

5. The method according to claim 3 or 4, characterized in that the furnace (4) is divided into at least three heating zones.

6. The method according to any one of claims 3 to 5, characterized in that the minima¬ le temperature in the oven (4) is at most 20% below the highest temperature in the O- fen (4) and that the residence time of the raw material (1) in Furnace (4) for a maximum of 10 s be¬ contributes.

7. The method according to any one of claims 3 to 6, characterized in that the raw substance (1) containing carrier gas stream (3) in the oven (4) is enclosed by a Hüllgasstrom.

8. The method according to any one of claims 1 to 7, characterized in that the charge is applied to the nanoparticles by corona discharge or by supplying an ion-containing cooling gas stream.

9. The method according to any one of claims 1 to 8, characterized in that the walls of the apparatus for producing nanoparticles (9) and the particles are unipolar charged or that along the walls of the apparatus for producing nanoparticles (9) flows an inert sheath gas ,

10. The method according to any one of claims 1 to 9, characterized in that the elektro¬ statically charged nanoparticles are separated in a Elektrofiltef (10).

11. The method according to claim 10, characterized in that the particles are deposited in a wet electrostatic precipitator (16) in a liquid. ^''

12. The method according to any one of claims 3 to 11, characterized in that between the furnace (4) and the device for producing nanoparticles (9) a first Par¬ is tikelabscheider (13) is arranged, in which unvaporized substance is separated.

13. The method according to any one of claims 1 to 12, characterized in that the produ¬ th nanoparticles are dispersed in a liquid.

14. The method according to claim 13, characterized in that the dispersion for Stabili¬ sation additives are added and the dispersion ^* , is driven to the concentration in the circulation.

15. The method according to any one of claims 1 to 14, characterized in that the generated nanoparticles n are combined with oppositely charged, additive-containing Aerosoltröpf¬ chen.

16. The method according to any one of claims 1 to 15, characterized in that the Vor¬ direction for the production of nanoparticles (9) is followed by a second Partikelabscheider (14), in which gaseous impurities at a temperature below the desublimation of the raw material and above the desublimati- on temperature / condensation temperature of the impurities are separated from the product stream.

17. An apparatus for producing nanoparticles, in particular of nanoparticulate pigments, by substantially simultaneous desublimation and charging a gaseous compound contained in a gas stream comprising

A supply line (28) for transporting the gas flow (29) into the device,

A particle generation and charging region for generating and charging nanoparticles substantially simultaneously

A discharge line (30) for transporting the charged nanoparticles from the particle generation and charging area.

18. The device according to claim 17, characterized in that the Partikelerzeugungs¬ and charging region contains a suitable for a corona discharge electrode assembly with at least one spray electrode (23) and at least one counter electrode (25).

19. The apparatus of claim 17 or 18, characterized in that the Partikeler¬ generating and charging a desublimation and charging area (31) with a gas supply for supplying a relative to the gas flow (29) having a lower temperature cooling fluid or a for the flow chemical reaction is suitable for generating nanoparticles suitable reaction and charging area.

20. The apparatus according to claim 19, characterized in that in the desublimation and charging region (31), a porous tube (32) surrounding the spray electrode (23) concentrically, wherein the porous tube (32) is designed so that it the gas supply for the Cooling fluid (27) forms.

21. The device according to claim 20, characterized in that the porous tube (32) is designed so that it forms the counter electrode (25) to the spray electrode (23).

22. Device according to one of claims 20 or 21, characterized in that the porous tube (32) by an annular space (26) for supplying the cooling fluid (27) is surrounded.

23. Device according to one of claims 20 to 22, characterized in that the porous tube (32) is a sintered metal or a sintered ceramic tube.

24. The device according to one of claims 19 to 23, characterized in that the cooling fluid and / or the gas stream contains as carrier gas at least one gas from the group air, carbon dioxide, noble gases and nitrogen.

25. Device according to one of claims 18 to 24, characterized in that the electrode arrangement comprises a rod-shaped spray electrode (23) which projects at an end projecting into the particle generation and charging region (31) with at least one radially extending electrically conductive wire (33 ) is provided.

26. Device according to one of claims 20 to 25, characterized by at least one displacement body (24, 34) which is at least partially disposed in the porous tube (32), so that between the displacement body (24, 34) and the Innen¬ wall of the porous tube (32) forms a flow gap (35).

27. Apparatus according to claim 26, characterized by two displacement bodies (24, 34), one of which is arranged in front of and behind the spray electrode (23) in the flow direction of the gas flow (29).

28. Device according to one of claims 17 to 27, characterized in that the discharge line (30) contains a separation zone or opens into a deposition zone in which the charged nanoparticles can be deposited on a solid or in a liquid medium.