EP3596006A1

EP3596006A1 - Method for producing nanoparticles from a liquid mixture

Info

Publication number: EP3596006A1
Application number: EP18714986.9A
Authority: EP
Inventors: Sebastian Schimek; Christian Oliver Paschereit; Moritz SIEBER
Original assignee: Technische Universitaet Berlin
Current assignee: Technische Universitaet Berlin
Priority date: 2017-03-17
Filing date: 2018-03-16
Publication date: 2020-01-22
Also published as: CN110418764B; US11299394B2; WO2018167281A1; US20200231438A1; CN110418764A; DE102017204488A1

Abstract

The invention relates to a method for producing nanoparticles from a liquid mixture of at least one precursor and at least one solvent in a continuous flow reactor, having the following steps: a) introducing at least one oxygen-containing gas inlet flow (E) at a temperature (T_E) into the at least one reactor, b) adding at least one fuel (B) at a temperature (T_B) into the oxygen-containing gas inlet flow, wherein the fuel and the oxygen-containing gas inlet flow form a homogeneous ignitable mixture (ZM) at a temperature (T_ZM), the temperature of the homogeneous ignitable mixture (T_ZM) lying above the spontaneous ignition temperature (T_EntzZM) of the homogeneous ignitable mixture; c) introducing at least one precursor/solvent mixture into the homogenous ignitable mixture (ZM); d) spontaneously combusting the ignitable mixture (ZM) of the oxygen-containing gas and the fuel after an ignition delay time (t_vz), thereby forming a stabilized flame, and converting the precursor/solvent mixture in the stabilized flame, thereby forming nanoparticles from the precursor; and e) removing the formed nanoparticles from the reactor.

Description

Process for the preparation of nanoparticles from a liquid mixture

The present invention relates to a process for the preparation of nanoparticles from a liquid mixture of a precursor and a solvent and to a reactor for carrying out such a process.

description

The synthesis of specific nanomaterials by the atomization of solutions of suitable precursor mixtures and subsequent combustion of the spray has a high potential. It makes it possible to produce complex and high-purity nanomaterials in the exhaust gas of the flame in the gas phase in a continuous process based on low-cost starting materials. Through the spray process, a wide variety of chemical elements can be used and combined. This distinguishes the spray flame process significantly from industrially established particle production in gas flames.

With suitable process control, the production of materials with defined composition, particle size and morphology succeeds - even beyond the thermodynamic stability limits and thus outside the achievable material spectrum of synthesis processes in the liquid phase. Likewise, when spraying a spray, nanoscopic mixtures and composites of different material systems can be achieved. Such materials are of great practical and commercial interest in a wide range of applications, e.g. technical catalysis, battery storage and photovoltaics.

For example, US 2006/0162497 A1 describes the production of nanoparticles in a flame spraying system in which a precursor medium comprising a liquid phase (organic, aqueous or mixture thereof) and a non-gaseous component are introduced into a flame reactor, e.g. is introduced by spraying. The populations of

Nanoparticles have a narrow particle size distribution.

The principal feasibility of spray flame synthesis has been demonstrated in a variety of experiments and publications (see Teoh et al., Flame spray pyrolysis, Nanoscale, 2010, 2, 1324-1347). In addition, the investigations show great potential for previously unexplored materials. A transfer to the technical However, the scale and the associated use of highly attractive materials in large-area products has only partially begun.

A challenge in the synthesis of nanoparticles by means of spray flames is that for practical applications the smallest possible distribution of particle size and morphology is necessary (monodispersibility). This can only be achieved in the production process if very homogeneous conditions exist. In particular, the temperature-time history must have a high similarity for all particles. On a laboratory scale, this is usually achieved with the help of laminar flames.

For large-scale use, in which large quantities of a few 100 kg per day of particles are to be produced inexpensively, the use of laminar spray flames is not realistic. The necessary high substance conversions due to one or a small number (<1000) of nozzles in a reactor ensure that relatively high Reynolds numbers are unavoidable, thereby creating a turbulent flow field. Turbulence, but also high velocities lead to increased mass transfer (turbulent diffusion), which fundamentally changes the combustion kinetics and flow dynamics. For example, the turbulent flame velocity is usually an order of magnitude higher than the laminar flame velocity, and the flow field characterized by turbulent viscosity differs significantly from the previously considered laminar flow. The objective of the present invention is that despite these boundary conditions an approximately one-dimensional flow is present in the reactor, which also allows the stable process conditions described below. A major difficulty in the large-scale application of this technology is to stabilize the flame. With large material flows inevitably high velocities in the reactor are associated. In industrial combustion systems for other applications, powerful flames are often spin-stabilized. This means that so-called recirculation zones or backflow areas are formed by the swirl of the flow. These ensure that the fresh educts are mixed with recirculating exhaust gas, which on the one hand has a very high temperature and the second still contains reaction intermediates, such as radicals. This recirculation leads to the ignition of the fresh educts and thus to a stabilization of the flame by the spin. This approach is unsuitable for the spray flame synthesis of nanoparticles since the recirculation of parts of the exhaust gas would result in a strong inhomogeneity in the residence time distribution of the precursor material in the immediate vicinity of the hot reaction zone. This would lead to a strong dispersion in the temperature-time history and thus in the size distribution of the particles produced.

The various ignition mechanisms are summarized below: i) In a laminar flame, the reactants are essentially chemically reacted by reacting the temperature and active intermediates (radicals) upstream of the reaction zone, i. diffuse into the unburned fuel-oxidizer mixture. ii) In turbulent flames or flames with exhaust gas recirculation, the reactants also ignite by mixing the educts with the hot exhaust gas (high temperature and active intermediates). In this case, however, the mixing is based not only on the tough diffusion, but also on turbulent transport processes (turbulent diffusion). iii) Another way of igniting a fuel-oxidizer mixture is to heat this mixture beyond the autoignition temperature. Depending on the temperature and exact mixture composition, the chemical reaction (auto-ignition) begins after a characteristic ignition delay time.

The process of auto-ignition can be explained as follows. When a fuel-oxidizer mixture is heated above the auto-ignition temperature, first intermediates begin to form from the combustion educts, which in turn initiate further reactions and release additional heat as combustion products form. The temperature increases exponentially until a large part of the combustion products has reacted and the maximum temperature is set. The time scale on which this chain reaction takes place is characterized by the ignition delay time, which is the time from reaching the autoignition temperature to the observation of luminescence of the flame. The Zündverzugszeit reduces with higher temperatures and also depends on the composition of the mixture. The ignition delay time can be in the range of microseconds to seconds. Auto-ignition finds widespread technical application in diesel engines, the ignition temperature being achieved by the heating during the compression of the fuel-air mixture in the piston. In gasoline engines, however, it is responsible for the undesirable knocking of the engine, which in turn is prevented by adjusting the octane number of the fuel.

The use of autoignition of mixtures of a fuel and a suitable precursor to produce metal nitride and metal oxide powders is e.g. in US 2008/0131350 A1. However, this method is not suitable for large-scale industrial use, since the apparatus described does not allow large throughputs.

The object of the present invention is therefore to overcome the disadvantages described and to provide a process for the preparation of monodisperse nanoparticles, which is suitable for large-scale industrial production.

This object is achieved by a method for producing nanoparticles according to claim 1 and a reactor for carrying out such a method having the features of claim 12. Accordingly, a method is provided for producing nanoparticles from at least one precursor and at least one solvent in a continuously flow-through reactor, comprising the following steps: a) introduction of at least one oxygen-containing gas input stream (E) with a temperature TE into the at least one reactor, b) adding at least one fuel (B) having a temperature TB to the oxygen-containing gas input stream, wherein fuel and oxygen-containing gas input stream form a homogeneous ignitable mixture (ZM) having a temperature TZM, the temperature of the homogeneous ignitable mixture T _Z M above the autoignition temperature T _En tzZM the homogeneous explosive mixture is located, c) introducing at least one precursor-solvent mixture in the homogeneous combustible mixture (ZM); d) spontaneously igniting the combustible mixture (ZM) of oxygen-containing gas and fuel after an ignition delay time tvz to form a stabilized flame and evaporating / burning the precursor-solvent mixture in the stabilized flame to form nanoparticles from the precursor, and e) removing the formed nanoparticles from the reactor.

Accordingly, a method for the synthesis of nanoparticles is provided in which a flame is stabilized at a fixed position in a continuously flow-through reactor by precise adjustment of the process parameters. The stabilization of the flame is based on the principle of auto-ignition and can be controlled by the Zündverzugszeit.

For this purpose, an oxygen-containing gas is initially introduced at a reactor inlet (step a), which has been preheated to a predetermined temperature TE. The nature of the preheating of the gas at the inlet is not an essential part of the process and may be e.g. by a pre-flame, electric heater, heat exchanger or the like.

The hot oxygen-containing gas stream is blended in step b) with a fuel, e.g. a gaseous fuel added, which is introduced so that the fuel mixes very quickly with the gas to form a homogeneous mixture. It is always important that after a short time or short run length in the reactor, a homogeneous mixture of oxygen-containing gas and fuel is present.

The resulting homogeneous mixture of oxygen-containing gas and fuel forms an ignitable mixture. The temperature of the resulting ignition mixture is also above the

Autoignition temperature of the mixture, but a burning of the mixture takes place only after the lapse of a Zündverzugszeit tzv. The Zündverzugszeit results essentially by composition of the mixture and its temperature. By a suitable choice of the fuel-oxygen ratio and the temperature, this can be controlled.

In step e), the introduction is carried out, for example, injecting the precursor-solvent mixture into the homogeneous ignitable mixture (ZM). The spontaneous ignition of the ignitable mixture (ZM) from oxygen-containing gas and fuel in step d) takes place after an ignition delay time tvz to form a stabilized flame. The ignition delay time tvz depends on the chemical properties of the fuel. The reaction rates and heat release of the individual reaction paths are decisive for the time in which the reactions take place. In addition, the ignition delay time is influenced by the properties of the oxygen-containing gas inlet flow, in particular temperature, composition (such as existing radicals from a pre-flame, inert gas components by pre-flame, such as H ₂ O, CO2 content) and / or pressure. These parameters of the gas inlet flow are matched to one another such that the product of ignition delay time and flow velocity defines a fixed distance between fuel injection and the position in the reactor at which the flame is stabilized by autoignition. The essential control variables which are used for setting the ignition delay time and thus a stable operating point of the reactor are mass flows and temperatures of the input currents. In particular, the choice of the fuel gas, temperature of the mixture, and the oxygen-fuel ratio are essential. The process of auto-ignition is very complex. Thus, when burning mixtures, hundreds of reaction paths of intermediates are possible. By varying parameters such as temperature, pressure or the proportion of inert gases, this not only changes the reaction rate, but under certain circumstances also the preferred reaction path. Trends such as the reduction of the ignition delay time with increasing temperature can sometimes be reversed. Accordingly, every possible mixture must be considered separately

Accordingly, in one embodiment of the present method, the auto-ignition of the ignition mixture of oxygen-containing gas and fuel with a dependent of the flow velocity v and temperature of the input flow T _G Zündverzugszeit tvz. The ignition delay time t _vz can be in a range between 1 με to 1 s, preferably 1 ms to 200 ms, in particular 10 ms to 100 ms. Thus, a stoichiometric air-hydrogen mixture having a temperature of 860K has an ignition delay of 10ms. A stoichiometric mixture of air and methane already has an ignition delay of a few seconds at the same temperature. In the methane embodiment, a temperature of 1700K is required to achieve an ignition delay of 10ms. Another important point is that the flow rate (resulting from the cross-section, density of the mixture, and sum of the mass flows of oxygen-containing gas and fuel), which sets in the reactor is greater than the turbulent flame velocity of the mixture. This prevents a flashback of the flame to the fuel addition location.

Accordingly, in one embodiment of the present method, the homogeneous ignitable mixture (ZM) has a flow velocity VZM in the reactor that is greater than the turbulent flame velocity v _F resulting from the ignitable mixture (ZM) in step d ) flame formed by spontaneous combustion.

The flow velocity V _Z M of the oxygen-containing gas input stream may be in a range between 5 and 200 m / s, preferably between 10 and 1 00 m / s

The turbulent flame velocity VF for lean combustion in air at 300K with e.g. Hydrogen is between 1 and 150 m / s or with methane between 9 and 35 m / s. It scales with the degree of turbulence, pressure and temperature of the flow and can sometimes vary even more.

In addition, a distance x = VZM * tvz from the flow velocity and the ignition delay time results at the location at which the mixture burns off and the flame correspondingly stabilizes by self-ignition. This distance x is preferably in the range 0.01 m to 10 m, particularly preferably in a range between 0.1 m to 2 m.

In a variant of the present method, the oxygen-containing gas used is air or a mixture of oxygen with at least one inert gas, in particular nitrogen, carbon dioxide, argon. The oxygen-containing gas is preheated, with suitable heat sources may be a pre-flame, electric heater, heat exchanger or the like. Preference is given to the use of a pre-flame (eg a lean swirl-stabilized natural gas flame) or the use of plasma generated by high voltage for this purpose, since not only a high temperature can be achieved, but also active reaction intermediates (radicals) are included in the mass flow, which In addition, self-ignition positively influence It is also possible to add a catalyst to the oxygen-containing gas or the fuel or to selectively vary the gas mixture, which allows additional adjustment of the ignition delay time. For example, when methane is used as the fuel, dimethyl ether or long chain isoalkanes can be used to reduce ignition delay time. An increase in the ignition delay time can be achieved, for example, by supplying inert gases, for example nitrogen, to the acid-containing gas. The associated reduction of the oxygen content in the ignitable mixture increases the ignition delay time. Furthermore, a mixture of different fuel gases such as hydrogen and methane allows a continuous variation of the ignition delay time between the values of the two individual gases.

The volume ratios in the addition of inert gases are limited by the ignitability of the mixture. The temperature T _{E of} the oxygen-containing gas inlet flow is in a range between 500-1500 K, preferably between 900-1400 K. Depending on the used fuel (or solvent), enthalpy of vaporization, ignition temperature, equivalence ratio and / or pressure, the temperature of the gas inlet flow can also above or below. For example, long-chain hydrocarbons can ignite even at temperatures below 900K, which would allow operation at lower temperatures, for example.

The fuel used may be a gaseous fuel and / or a liquid fuel. As gaseous fuels, gases such as hydrogen, natural gas, methane, propane, butane or other hydrocarbons are used. As liquid fuels are those substances that either evaporate immediately or can be very finely dusted.

In a further variant of the present method can be used as fuel, an organic fuel which is preferably selected from the group comprising methanol, ethanol, isopropanol, other alcohols, tetrahydrofuran, 2-ethylhexanoic acid,

Acetonitrile, acetic acid, acetic anhydride, urea, N-methyl urea, glycine, citric acid, stearic acid and simple non-aliphatic hydrocarbons such as pentane, hexane, heptane, octane, nonane, decane, undecane, dodecane or aromatic hydrocarbons such as xylene. But it is also generally possible to use other fuels. The fuel is introduced at a temperature TB in a range between 250 and 1500 K, preferably between 300 and 500 K in the oxygen-containing gas stream. The resulting temperature T _Z M of the ignitable mixture is correspondingly below the temperature T _{E of} the oxygen-containing gas input stream.

In one variant, for example, hydrogen is added as a fuel at a temperature of 300 K into the air inlet flow at a temperature of 1000 K, wherein the forming ignitable mixture has a temperature T _Z M of about 890K. The auto-ignition temperature Τ _ΕΠ ergeben for the ignition mixture is 770K.

The air ratio λ of the ignitable mixture indicates the amount of oxygen of the gas inlet flow relative to the amount of oxygen required for the oxidation of the fuel, wherein a value of λ greater than 1 refers to an excess of air, and a value of λ less than 1 refers to an air deficiency. The range of possible air numbers is limited by the ignitability of the fuel-oxygen mixture and may be in a range between 0.1 and 25, preferably in a range between 0.5 and 10, particularly preferably between 1 and 3.

As precursors metal salts or organometallic compounds can be used.

When a metal salt is used as the precursor, the metal salt used is selected from the group consisting of salts of aluminum, barium, bismuth, calcium, cerium, iron, magnesium, platinum, palladium, strontium, titanium, zirconium, manganese, chromium, zinc, copper , Nickel, cobalt, yttrium, silver, vanadium, molybdenum or other metals. In one variant, among other ferric nitrate, Aluminiumtnisopropanolat, zinc naphthenate or

Manganese nitrate used as a precursor. Also, the use of semi-metal salts, e.g. Salts of silicon generally conceivable. Again, the use of other metal salts or semi-metal salts is conceivable. In the case of using organometallic compounds as precursor alkylated

Silicon compounds, e.g. Tetraethyl orthosilicate or alkylated titanium compounds, e.g. Tetraisopropylorthotitanate be used.

Furthermore, the combustion of the substance mixture can be carried out in the presence of nitrogen and / or in the presence of additives such as sodium azide or lithium nitride. This allows not only the production of oxides but also the production of nitrides. Other additives which may be added to the mixture viscosity modifiers (such as methanol, ethanol, isopropanol), surface modifiers (such as alkyl sulfates, alkyl sulfonates, fatty acids), emulsifiers (such as monoglycerides, polysaccharides) or stabilizers (such as polyalcohols, polyamines, polyacrylates, polyoxides) become.

In a further embodiment of the present method, the precursor-solvent mixture is injected or sprayed into the gas stream via at least one nozzle or atomizer. The mixture is finely atomized by the injection and the distance of the injection to the flame is chosen so that the mixture is not completely evaporated. Otherwise, it may be the case that at high temperature of the gas stream, only the solvent evaporates, the precursor precipitates and thereby forms large particles (spray drying). The precursor-solvent mixture is preferably added at room temperature (300K). However, in order to adjust the viscosity of the mixture to the technical limitations of the injector (e.g., die cross section), the temperature may be varied, in particular increased (e.g., 500 K).

For the injection of the precursor-solvent mixture, for example, an ultrasonic atomizer or a pressure-controlled injection nozzle can be used. Ultrasonic nebulizers generate liquid droplets using a piezoelectric material that vibrates at ultrasonic frequencies to break up the liquid into small droplets. It is also possible to use pressure-controlled injection nozzles or other injector systems.

Injectors are preferably used, which can produce a droplet size of 10-100μηι.

The solvent of the precursor-solvent mixture is preferably water or an organic solvent such as, for example, alcohols (methanol, ethanol, isopropanol, etc.) or xylene. The choice of solvent depends primarily on the solubility of the precursor. It may be a solvent such as water, which does not react further after the evaporation and is not directly involved in the combustion as an inert gas or solvents from the group of the above-mentioned liquid fuels which burn when burned together with the gaseous fuel , The concentration of the precursor in the precursor-solvent mixture results from the respective solubility limits of the precursor in the solvent used. Thus, the concentration of metal salts in water as a solvent in a range between 0, 1 molar and 1 molar. However, this depends on the specific precursor-solvent mixture as stated.

In the stabilized flame, the liquid precursor-solvent solution evaporates, resulting in the formation of nanoparticles due to the high temperature in the stabilized flame. The nanoparticles produced are quenched using suitable techniques (e.g., quenching), collected, and discharged from the manufacturing process.

The present process allows the preparation of the nanoparticles, in amounts above a few grams per hour (and thus above the laboratory scale). The nanoparticles produced have a particle diameter with a d95 value of less than 1000 nm, preferably of less than 800 nm, particularly preferably of less than 500 nm. In the context of the present invention, the value d95 of e.g. 10,000 nanometers, that 95% of the particles of a population have a diameter of less than 1000 nm.

The nanoparticles formed have a unimodal size distribution, the shape of the nanoparticles being mostly, but not necessarily spherical, uniform and homogeneous. The nanoparticles are characterized by a narrow size distribution with low standard deviation. Thus, in one embodiment, the generated population of nanoparticles has a standard deviation of less than 2.2, preferably less than 2.0, more preferably less than 1.8.

The nanoparticles produced by the present process can be used in a variety of ways. Depending on their properties (such as transparent, electrically conductive, electrically insulating, thermally conductive, or catalytically active), the nanoparticles can be used as a coating material, in electrical appliances, for heat conduction or thermal insulation or as a catalyst, etc.

The process of the invention is carried out in a reactor comprising: a first section A having at least one means for introducing an oxygen-containing gas stream;

- A second, downstream of the first section A, provided section B with at least one means for introducing at least one

Fuel in the reactor;

a third section C provided downstream of the first section A and having at least one means for injecting the at least one precursor-solvent mixture into the reactor;

a fourth section D provided downstream of the second section B and third section C for spontaneously igniting the combustible mixture of oxygen-containing gas and fuel; and

- A fifth, provided downstream of the section D section E for the formation and removal of the nanoparticles formed from the reactor.

In one embodiment of the present reactor, the distance x between the section B, in which the fuel is introduced, and the section D, in which the self-ignition of the ignitable mixture takes place, the equation x = V _Z M * tvz.

In the following, the present invention will be explained in more detail by means of embodiments with reference to the figures. It shows:

Figure 1 is a schematic representation of a first embodiment of the present invention

Process.

FIG. 1 shows a schematic structure for a self-ignition-stabilized flame for nanoparticle synthesis from a liquid spray.

In a first section A, a heated, preconditioned, oxygen-containing gas inlet flow having the temperature T _{E is} provided in step 1. The preconditioning of the input flow can be done for example by an electric heater. Other options are to use a lean pre-flame, for example, a lean spin-stabilized natural gas flame or plasma generated by high voltage. Not only the resulting temperature of the inlet flow plays a role here. Also, changing the concentration of oxygen through a preignition flame may cause an increase in the ignition delay time, whereas radicals due to combustion or plasma in the flow may drastically reduce the ignition delay time.

In Section B, a preferably gaseous fuel is added in step 2 to the hot gas stream, which is added so that the fuel mixes very quickly with the gas to form a homogeneous mixture. Suitable fuels are hydrogen, natural gas, methane, propane, butane but also liquid fuels. It is always important that after a short time or short run length in the reactor is a homogeneous mixture.

In step 3, an ignitable mixture is formed from the homogeneous mixture of oxygen-containing gas and fuel. The temperature of the resulting mixture is above the autoignition temperature of the mixture, but instantaneous burning of the mixture does not occur. This begins only after the ignition delay time tvz has elapsed, ie when section D. is reached.

In section C of the reactor, in step 4, the liquid precursor-solvent mixture is introduced through a sputtering die. The distance to the flame in section D of the

Reactor is chosen so that the liquid is not completely evaporated before reaching the flame. In the figure, section C is shown downstream of section B, depending on the process, section C may also be upstream of section B. The solvent used does not necessarily have to be flammable.

Thus, in section D, when the characteristic ignition delay time has elapsed, auto-ignition of the ignitable mixture of oxygen-containing gas and fuel takes place (step 5). In section D burn fuel and possibly solvent. The precursor for the nanoparticles is preferably converted to the gas phase. In this case, the precursor can undergo a reaction (oxidation, reduction, pyrolysis, hydrolysis) and, if appropriate, the solvent can liberate additional thermal energy by burning, as a result of which locally very high temperatures are achieved. Supercritical heating of liquid droplets and resulting explosive evaporation is also possible (Rosebrock et al., AIChE Journal, 2016, Vol. 62, 381-391). This mechanism also allows the formation of droplets of the precursor-solvent mixture which are smaller than one micrometer and thus the formation of nanoparticles without prior transition to the gas phase. To ensure this process flow, precise preconditioning of the inlet flow is necessary. The temperatures and mass flows of the supplied substances must be very stable regulated to a value to keep the flame stable in one position. To set the flame position at defined process conditions, the theoretical ignition delay times may provide orientation, but optical access to the reactor to adjust and control the flame position has been found to be helpful in laboratory implementation. In section E of the reactor, nanoparticles are formed in step 6, preferably by condensation from the gaseous phase during and after the combustion, which are subsequently removed from the reactor accordingly. However, formation of particles directly from the liquid phase is also possible. Embodiment 1:

An air inlet flow at a temperature of 1000K is introduced into the reactor. Hydrogen is added in an air ratio of 2 and a temperature of 300K. This results in the reactor an air-hydrogen mixture with a temperature of 890K. This mixture has an ignition delay of approx. 10 ms and a turbulent flame velocity of approx. 40 m / s. The flow rate in the reactor now results from the total mass flow and the cross section and is set in the following to 80 m / s. This results in run length x of 800mm from the fuel injection (2) to the position of the flame (5). At a distance of 100 mm upstream of the flame, a 0.1 molar solution of iron (III) nitrate in ethanol is sprayed in at 300 K (4). This reaches the flame after about 1 ms, which means the drops have not yet evaporated. In the flame, the liquid solution evaporates and the solvent burns, resulting in the high temperatures to the formation of Fe203 nanoparticles. Embodiment 2:

An air inlet flow at a temperature of 1000K is introduced into the reactor. Hydrogen is added in an air ratio of 1, 7 and a temperature of 300K. This results in the reactor an air-hydrogen mixture with a temperature of 870K. This mixture has an ignition delay of approx. 1 ms and a turbulent flame velocity of approx. 56 m / s. The flow rate in the reactor results now from the total mass flow and the cross section and is set in the following to 100 m / s. This results in run length x of 1 100mm from the fuel injection (2) to the position of the flame (5). At a distance of 100 mm upstream of the flame, a 0.1 molar solution of manganese (II) nitrate is sprayed in isopropanol at 300 K (4). This reaches the flame after about 1 ms, which means the drops have not yet evaporated. In the flame, the liquid solution evaporates and the solvent burns, whereby the high temperatures lead to the formation of Mn ₂ O ₃ nanoparticles.

Embodiment 3:

An air inlet flow at a temperature of 1000K is introduced into the reactor. Hydrogen is added in an air ratio of 2.5 and a temperature of 300K. This results in the reactor, an air-hydrogen mixture with a temperature of 91 OK. This mixture has an ignition delay of approx. 8 ms and a turbulent flame velocity of approx. 24 m / s. The flow rate in the reactor now results from the total mass flow and the cross section and is set in the following to 50 m / s. This results in barrel length x of 400mm from the fuel injection (2) to the position of the flame (5). At a distance of 100 mm upstream of the flame, a 0.1 molar solution of zinc naphthenate in ethanol is sprayed in at 300 K (4). This reaches the flame after about 2ms, so that the drops have not yet evaporated. In the flame, the liquid solution evaporates and the solvent burns, where the high temperatures lead to the formation of ZnO nanoparticles.

Embodiment 4:

An air inlet flow at a temperature of 900K is introduced into the reactor. Hydrogen is added in an air ratio of 2.5 and a temperature of 300K. This results in the reactor an air-hydrogen mixture with a temperature of 830K. This mixture has an ignition delay of approx. 48 ms and a turbulent flame velocity of approx. 23 m / s. The flow rate in the reactor now results from the total mass flow and the cross section and is set in the following to 50 m / s. This results in barrel length x of 2400mm from the fuel injection (2) to the position of the flame (5). At a distance of 100 mm upstream of the flame, a 0.1 molar solution of aluminum triisopropoxide in isopropanol is sprayed in at 300 K (4). This reaches the flame after about 2ms, which does not evaporate the drops yet are. In the flame, the liquid solution evaporates and the solvent burns, whereby the high temperatures lead to the formation of Al ₂ O ₃ nanoparticles.

Embodiment 5:

An air inlet flow at a temperature of 1400K is introduced into the reactor. It is added methane in an air ratio of 1, 7 and a temperature of 300K. This results in the reactor an air-methane mixture with a temperature of 1330K. This mixture has an ignition delay of approx. 25 ms and a turbulent flame velocity of approx. 1 6 m / s. The flow rate in the reactor now results from the total mass flow and the cross section and is set in the following to 30 m / s. This results in run length x of 750mm from the fuel injection (2) to the position of the flame (5). At a distance of 1 00 mm upstream of the flame, a 0, 1 molar solution of tetraisopropyl orthotitanate in xylene is sprayed at 300 K (4). This reaches the flame after about 3ms so that the drops have not yet evaporated. In the flame, the liquid solution evaporates and the solvent burns, resulting in the formation of Ti0 ₂ nanoparticles due to the high temperatures.

Embodiment 6:

An air inlet stream at a temperature of 1,300K is introduced into the reactor. It is added methane in an air ratio of 1, 7 and a temperature of 300K. This results in the reactor an air-methane mixture with a temperature of 1230K. This mixture has an ignition delay time of approximately 70 ms and a turbulent flame velocity of approximately 14 m / s. The flow rate in the reactor now results from the total mass flow and the cross section and is set in the following to 30 m / s. This results in run length x of 2100mm from the fuel injection (2) to the position of the flame (5). At a distance of 1 00 mm upstream of the flame, a 0, 1 molar solution of tetraethyl orthosilicate in isopropanol is sprayed at 300 K (4). This reaches the flame after about 3ms so that the drops have not yet evaporated. In the flame, the liquid solution evaporates and the solvent burns, whereby the high temperatures lead to the formation of S1O2 nanoparticles.

Claims

claims

1 . A process for the production of nanoparticles from a liquid mixture of at least one precursor and at least one solvent in a continuous flow reactor comprising the steps of: a) introducing at least one oxygen-containing gas input stream (E) at a temperature TE into the at least one reactor, b) adding of at least one fuel (B) having a temperature TB in the oxygen-containing gas input stream, wherein fuel and oxygen-containing gas input stream form a homogeneous ignitable mixture (ZM) having a temperature TZM, wherein the temperature of the homogeneous ignitable mixture T _Z M above the autoignition temperature T _En tzZM the homogeneous ignitable mixture is, c) introducing at least one precursor-solvent mixture into the homogeneous ignitable mixture (ZM); and d) autoignition of the flammable mixture (ZM) of oxygen-containing gas and fuel after an ignition delay time tvz to form a stabilized flame and reacting the precursor-solvent mixture in the stabilized flame to form nanoparticles from the metal salt precursor, and e) removing the formed nanoparticles from the reactor.

2. The method according to claim 1, characterized in that the homogeneous ignitable mixture (ZM) has a flow velocity V _Z M in the reactor which is greater than the turbulent flame velocity VF from the ignitable mixture (ZM) in step d) formed by auto-ignition Flame.

3. The method according to any one of the preceding claims, characterized in that the flow velocity V _Z M of the oxygen-containing gas inlet stream in a range between 5 and 200 m / s, preferably between 10 and 100 m / s.

4. The method according to any one of the preceding claims, characterized in that is used as the oxygen-containing gas is air or a mixture of oxygen with at least one inert gas, in particular nitrogen, carbon dioxide, argon.

5. The method according to any one of the preceding claims, characterized in that the temperature T _{E of} the oxygen-containing gas inlet stream in a range between 500 - 1500 K, preferably between 900 - 1400 K.

6. The method according to any one of the preceding claims, characterized in that the at least one fuel (B) is a gaseous fuel and / or a liquid fuel.

7. The method according to any one of the preceding claims, characterized in that the air ratio λ of the ignitable mixture in a range between 0.1 and 25, preferably in a range between 0.5 to 10, more preferably in a range between 1 to 3 ,

8. The method according to any one of the preceding claims, characterized in that the at least one precursor is a metal salt selected from the group of aluminum, barium, bismuth, calcium, cerium, iron, magnesium, platinum, palladium, strontium, titanium, zirconium, manganese, Chromium, zinc, copper, nickel, cobalt, yttrium, silver, vanadium, molybdenum or other metals or semi-metals.

9. The method according to any one of the preceding claims, characterized in that the precursor-solvent mixture is injected or sprayed via at least one nozzle or atomizer in the homogeneous ignition mixture.

10. The method according to claim 9, characterized in that for the injection of the precursor solvent mixture, an ultrasonic atomizer or a pressure-controlled injection nozzle is used.

1 1. Method according to one of the preceding claims, characterized in that the solvent of the metal salt precursor solvent mixture is selected from a group containing water or an organic solvent.

1 2. The method according to any one of the preceding claims, characterized in that the Zündverzugszeit t _vz in a range between 1 microseconds to 1 s, preferably 1 ms to 200ms, in particular 10 ms to 100 ms.

13. The method according to any one of the preceding claims, characterized in that the nanoparticles produced have a particle diameter with a d95 value of less than 1000 nm, preferably less than 800 nm, more preferably less than 500 nm.

14. Reactor for carrying out a method according to one of the preceding

Claims characterized by

a first section A having at least one means for introducing an oxygen-containing gas stream into the reactor;

a second section B provided downstream of the first section A and having at least one means for introducing at least one fuel into the reactor;

a third section downstream of the first section A, having at least one means for injecting the at least one precursor-solvent mixture into the reactor;

1 5. A reactor according to claim 14, characterized in that the distance x between the section B, in which the fuel is introduced, and the section D, in which the self-ignition of the ignitable mixture takes place, the equation x = VZM * tvz corresponds.