EP2197579A1 - Method for the production of a catalyst used for manufacturing carbon nanotubes - Google Patents

Abstract

Disclosed are a method for the production of a catalyst used for manufacturing carbon nanotubes, the use of a catalyst for manufacturing carbon nanotubes, and the carbon nanotubes manufactured according to said production method. The catalyst is produced on the basis of soluble precursor compounds of at least two metals selected from the group comprising cobalt, manganese, iron, nickel, and molybdenum by spray-drying or spray-granulating the precursor compounds that are dissolved in a solvent, followed by calcining.

Description

 Process for the preparation of a catalyst for the production of carbon nanotubes

The invention relates to a process for the preparation of a catalyst for the production of carbon nanotubes, the use of the catalyst for the production of

Carbon nanotubes and those obtained by this production method

Carbon nanotubes. The catalyst is based on at least two metals from the

Series: cobalt, manganese, iron, nickel and molybdenum from soluble precursor compounds

Spraying the dissolved in a solvent completely or partially dissolved precursor compounds and subsequent calcination.

Carbon nanotubes are understood to mean mainly cylindrical carbon tubes with a diameter between 3 and 100 nm, the length being a multiple, at least 20 times, of the diameter. Carbon nanotubes are referred to below for brevity as "CNT." These tubes consist of layers of ordered carbon atoms and have a different nucleus in morphology.These carbon nanotubes are also referred to as "carbon fibrils" or "hollow carbon fibers." The described carbon nanotubes have Due to their dimensions and their special properties, they are of technical importance for the production of composite materials, with significant potential in electronics, energy and other applications.

Carbon nanotubes are a well-known material for a long time. Although Iijima in 1991 (S. Iijima, Nature 354, 56-58, 1991) is generally referred to as the discoverer of nanotubes, these materials, especially fibrous graphite materials having multiple layers of graphite, have been known for some time. So z. B. in the 70s and early 80s, the deposition of very fine fibrous carbon from the catalytic decomposition of hydrocarbons described (GB 1469930A1, 1977 and EP 56004 A2, 1982, Tates and Baker). However, carbon filaments made from short-chain hydrocarbons are no longer characterized in terms of their diameter. The production of carbon nanotubes with diameters smaller than 100 nm is described, inter alia, also in EP 205 556 Bl or WO A 86/03455.

For the preparation here light (ie, short- and medium-chain aliphatic or mononuclear or dinuclear aromatic) hydrocarbons and an iron-based catalyst are described, are decomposed at the carbon support at temperatures above 800-900 ⁰ C. The known methods include, for example, arc, laser ablation and catalytic methods. In the catalytic process, a distinction can be made between the deposition of supported catalyst particles and the deposition of in-situ formed metal centers with diameters in the nanometer range (so-called flow processes). In many of these processes, carbon black, amorphous carbon, and large diameter (greater than 100 nm) fibers are formed as by-products.

In the production via the catalytic deposition of carbon at reaction conditions gaseous hydrocarbons (hereinafter CCVD, Catalytic Carbon Vapor Deposition) are given as possible carbon donors acetylene, methane, ethane, ethylene, butane, butene, butadiene, benzene and other carbon-containing reactants , The catalysts usually include metals, metal oxides or decomposable or reducible metal components. For example, metals such as Fe, Mo, Ni, V, Mn, Sn, Co, Cu and others are mentioned in the prior art. Although the individual metals usually have a tendency to form nanotubes, according to the prior art high yields and low proportions of amorphous carbons are advantageously achieved with metal catalysts which contain a combination of the abovementioned metals. The formation of carbon nanotubes and the properties of the tubes formed depend in complex ways on the metal component used as a catalyst or a combination of several metal components, the carrier material used and the catalyst-carrier interaction, the reactant gas and partial pressure, an admixture of hydrogen or other gases , the reaction temperature and the residence time or the reactor used.

Various processes and catalysts are known for the production of carbon nanotubes. Already EP 0205 556 A1 (Hyperion Catalysis International) describes such carbon nanotubes. The cited patent application describes an iron-containing catalyst and the reaction of various hydrocarbons at high temperatures above 800-1000 ⁰ C. Also, the use of Ni is described as a catalyst, for. Dissertation MG Nijkamp, Universiteit Utrecht, NL, 2002 "Hydrogen Storage Using Physiosorption Modified Carbon Nanofibers and Related Materials" Also Shaikhutdinov et al. (Shamil 'K. Shaikhutdinov, LB Avdeeva, OV Goncharova, DI Kochubey, BN Novgorodov , LM Plyasova, "Coprecipitated Ni-Al and Ni-Cu-Al catalysts for methane decomposition and carbon deposition L", Applied Catalysis A: General, 126, 1995, pages 125-139) Ni-based systems as active in the decomposition of Methane to Kohlenstoffhanomaterialien described. Another overview of methods for For example, Geus and DeJong report in a review (KP De Jong and JW Geus in Catal. Rev. Sci. Eng., 42 (4), 2000, pp. 481-510).

For the production of a special modification of carbon nanotubes especially for use in polymers is also z. No. 6,358,878 B1 (Hyperion Catalysis International Inc.) reports the use of supports of well-defined structure. Partial parallel alignment of the long nanotubes and fibers into bundles is achieved by the use of support materials having a structure of fissile planar surfaces or consisting of crystallites with just such fissile surfaces. Although these materials provide a material that is particularly suitable for polymer application, the active components are preferably applied by impregnation and impregnation methods. However, as is generally known in the literature for the preparation of heterogeneous catalysts, the amount of catalyst loading is limited with simultaneously high dispersion. However, very high dispersions or small diameters of the active catalyst components are advantageous for the growth of carbon nanotubes. Low active component diameters are achieved in the case of impregnations or precipitations on catalyst supports only at low loadings and high dispersion. This greatly limits the performance of the catalysts used. In US Pat. No. 6,358,878 Bl typical yields of the order of magnitude of 20-25 times the catalyst mass used are mentioned. Higher yields are not disclosed. In the catalysts described, the content of catalyst and carrier residues is so high that these residues must be removed for further use. This results in an increased technical complexity, which entails several further process steps. Furthermore, the workup and purification may influence the morphology and properties of the carbon nanotubes depending on the chosen procedure.

An easy removal of the catalyst residues from the CNT is, for example, also the aim of the application WO 03/004410 A1. As a solution to this problem, the use of soluble carriers such as hydroxides and / or carbonates of Ca, Mg, Al, Ce, Ti, La is called as a carrier. Their preparation by intensive mixing of the catalytically active components with the alkaline carrier components is virtually in the dry state (possibly pasty

State) in mixing apparatus such as. Ball mill, kneader, etc. The micro-mixing of the powder thus produced is sub-optimal and leads to large variations in the diameter of the

Metal cluster and thus the CNT.

Basically, the catalysts described in the prior art have the disadvantage that the expenses for the preparation of the heterogeneous catalyst are relatively high. at In the preparation of supported catalysts, sufficient dispersion of the primary crystallites contributing to growth must be ensured. This can be done, for example, as known in heterogeneous catalysis, by impregnation with comparatively low contents of active metals [Handbook of Heterogeneous Catalysis, Vol. 1, 1997, Chap. 2.2.]. Here is ensured by the comparatively low surface concentration of catalytically active metal sufficient dispersion and thus the small diameter of the active metal cluster. When precipitating the active components on submitted carriers of a certain particle size or on a suspension of small-sized catalyst supports (typically aluminum, magnesium, silicon, zirconium oxides and others) is usually a change in conditions needed, this can eg temperature jumps, concentration jumps and the Addition of a precipitating agent [Handbook of Heterogeneous Catalysis, Vol. 1, 1997, chap. 2.1.3.]. In this case, an additional component is introduced into the system and, in particular in the case of using a precipitating agent, additional waste and by-product streams are produced. In addition, the secondary components resulting from the precipitation, such as alkali oxides or halides, can impair the catalytic properties. As a result, time-consuming washes of the catalyst solid obtained are necessary in many cases. For example. WO 2006/050903 A2 has disclosed a process for preparing a catalyst for the production of CNT, in which the precursor compounds for the catalyst are subjected to an alkaline precipitation reaction and the catalyst is elaborately prepared further from the precipitated mixed hydroxides. Because of the numerous local parameters in the precipitates and impregnations, it is further known that scale-up of production is associated with great difficulty, so that in practice catalysts having a broad distribution of metal cluster diameters are usually obtained.

Particularly in the case of the production of carbon nanotubes, a narrow particle diameter distribution is important in order to reproducibly obtain the desired diameter of the carbon nanomaterials in the product. WO 2007/093337 A2 describes the preparation of a catalyst by means of a continuous precipitation in a micromixer. Although very small metal cluster diameter or at the same time a very narrow distribution of the diameters are achieved, but the process requires complex filtration and washing steps to produce a highly active catalyst.

A further disadvantage in the preparation of the catalysts of the prior art is that by wet-chemical preparation as precipitation or a loss of active components must be accepted. Most of the solutions are difficult to work up due to the high dilutions in which the catalytically active metals are produced.

A complicated further problem is the shape of the resulting catalysts. Should these be used in a process in which the catalyst particles or catalyst / Kohlenstoffhanomaterialagglomerate or carbon agglomerates are moved by the flow of a fluid within the reactor or the solids content of the reactor is moved, so a defined particle size distribution is necessary, often only within narrow limits allowed a failure-prone and efficient reactor operation. The particle size here denotes the size of an occupied carrier or the mixture of carrier and active metals used in the reaction. In the case of a classical catalyst, therefore, additional process steps such as e.g. Comminution or agglomeration and classification necessary. In the latter case, the yield of catalyst from precipitation reactions can be significantly reduced. There is also a risk that impurities, e.g. from equipment or other batches affect the quality of the material.

In particular, CNT catalysts having a defined particle size are required when using the catalysts for the reaction in a fluidized bed, a circulating fluidized bed, a moving bed, as well as for other reasons in the fixed bed (to reduce the pressure loss across the catalyst bed), in the floating reactor, Dust / cloud cloud reactor, downer or riser. In the case of the reactors mentioned, the particle velocity and thus, as a rule, the mixing or residence time in the reactor depend on the particle diameter, therefore the narrowest possible particle size distribution is of technical advantage.

The object of the present invention, starting from the prior art, is to develop a process for the preparation of catalysts for CNT production, which avoids the disadvantages of the known processes and in particular works in an energy-efficient manner, in an efficient manner, the starting materials in catalyst preparation exploited, preferably the waste produced in the catalyst production or wastewater to be treated and thus minimized the steps in the production of the solid catalyst and in particular allows adjustment of an advantageous particle size of the catalyst.

In particular, the recycling of such catalyst material into the production process should be possible, which does not occur, for example, in the range of the desired particle size distribution. Of the The catalyst obtained should also preferably be usable in the reactor types described above, especially in moving beds such as fluidized beds.

It has surprisingly been found in studies that suitable catalysts can be prepared in an unexpectedly simple manner by spray drying or spray agglomeration from salt solutions of the active metals and support materials in predominantly or completely dissolved form.

The present invention relates to a process for preparing a catalyst based on at least two catalytically active metals from the series: cobalt, manganese, iron, nickel and molybdenum for the production of carbon nanotubes with the steps:

a) dissolving at least two thermally decomposable precursor compounds of the catalyst selected from the series of the salts of: cobalt, manganese, iron, nickel and molybdenum in a solvent to form a solution, optionally with suspended undissolved precursor compounds, preferably an aqueous solvent,

b) removing the solvent by spray granulation or spray drying with a drying gas at a temperature of 150 to 600 ⁰ C, preferably by means of nozzle or disc atomizer, in particular to obtain an outlet temperature of the exhaust gas (= mixture of drying gas and solvent vapor) of at least 70 ⁰ C, preferably 70-200 ⁰ C, most preferably 80- 120 ⁰ C,

c) optionally grinding the mixture obtained from step b) and, optionally, post-drying the mixture obtained from step b) at a temperature of 60 to 500 ^° C.,

d) if appropriate, classifying the mixture obtained from step b) or c) to obtain a granulate having a particle diameter in the range from 30 to 100 μm, preferably from 40 to 70 μm,

e) optionally further drying of the granules obtained from step d) at a temperature of 60 to 500 ^° C.,

f) calcination of the granules obtained from step e) in the presence of an oxygen-containing gas, in particular in the presence of air, at a temperature of 200 to 900 ⁰ C, preferably 250 to 800 ⁰ C, particularly preferably 300 to 700 ⁰ C, in a Treatment time of at least 0.5 h, preferably 1 to 24 h, more preferably 2 to 16 h, with removal of the decomposition gases and obtaining the catalyst,

g) optionally subsequent reduction of the catalyst from step f) by means of reducing gases, in particular with hydrogen, in particular at a temperature of 250 to 750 ^° C.,

The new method will be described in general again below.

In a first step, the catalytically active materials and the carrier substances are dissolved in a solvent and possibly suspended particles no longer suspended. Suitable solvents for this purpose are, for example, water, alcohols, low-boiling aliphatic and aromatic hydrocarbons, generally carbon-containing solvents, for example nitromethane or supercritical CO ₂ . Due to the ease of use of known techniques, preference is given to alcoholic or aqueous solvents or mixtures thereof. Particularly preferred are aqueous solvents.

Suitable precursors for the catalytically active materials and vehicles are preferably those compounds which can be dissolved in the solvent or solvent mixture used and which, after removal of the solvent, can be thermally decomposed to the corresponding catalyst compound (i.e., metal oxides). Suitable compounds are, for example, inorganic salts, for example: the hydroxides, carbonates, nitrates and the like, as well as oxalates or salts of the lower carboxylic acids, in particular acetates or derivatives, and organometallic compounds, e.g. Acetylacetonate, the metals cobalt, manganese, iron, molybdenum and nickel, wherein the metals may be present in any possible oxidation state. Optionally, one or more carrier components may also be added to the solution as a non-soluble solid to obtain suspensions. The particle size of the solid is advantageously smaller than the particle diameter of the catalyst agglomerates obtained by the overall process. In a further preferred variant of the first method step, particulate matter from the classification in step d) (ie particles whose diameter is below a specified specification range) is additionally added to the solution / suspension, the particulate matter particles acting as nucleation nuclei and the overall yield being recycled by recycling the particulate matter of the method is increased.

The maximum temperature of the gaseous mixture of drying gas discharged from the dryer used for the treatment during spray granulation or spray drying Solvent is chosen so that it does not come in the exit from the dryer to form sticky phases of the resulting in the spray granulation or spray drying solid.

The gas inlet temperature of the drying gas for drying should be as high as possible in order to achieve the highest possible drying performance. The gas inlet temperature can be selected in the range 150 - 600 ⁰ C. If no safety concerns or

Quality losses are to be feared by thermal decomposition of zurückgewehtem dry matter or caking in the gas inlet region, the preferred drying gas inlet temperature in the range 300-500 ⁰ C. As the drying gas is preferably air or inert gas, in particular nitrogen used.

In spray drying [see: K. Masters, "Spray Drying Handbook", Longman Scientific & Technical 1991, 725 pages, ISBN 0-582-06266-7] is liquid wet material ("slurry"), for example, a solution or suspension, in More or less small droplets are broken up and dried by contact with a hot gas stream to obtain a powder whose particle size distribution can be set decisively by the droplet size distribution, since spray drying is a short-term drying process with a residence time of just under 1 sec 30 seconds, the drops are usually below 500 .mu.m, in laboratory apparatus with correspondingly small residence times <50 .mu.m.Da at least for longer spray towers with particle diameters above 100-200μm coarse dry material can be generated, as it is known from granulation technologies speaks One also frequently uses spray granulation, but also downstream agglomeration pr ozesse, which may also be integrated in the cone area of the spray tower, possible [cf. Gehrmann et al., "Dryer", Chem.Ing. Tech. (75) 2003, 1706-1714.]

The atomization of the moist material can be done with so-called. Two-fluid nozzles, which are preferably used at low throughput and to obtain small drops. This atomizing gas, usually compressed air or nitrogen, abandoned. Depending on the supply, a distinction is made between two-fluid nozzles with external or internal admixture. The former is usually operated with larger gas volumes up to gas throughputs of 2 kg of gas per kg wet material, in order to achieve droplet sizes below 50 microns. In the case of two-substance nozzles with internal mixing, smaller gas throughputs of about 0.1 kg of gas per kg of moist material usually suffice. Alternatively, for the intended use case with relatively small particle sizes below 100 μm, it is also possible to use disk atomizers which are operated at a speed in the region of 20,000 rpm and peripheral speeds of 100 m / s and more. Both technologies, Two-fluid nozzle and disc, are particularly suitable for smaller droplet diameter <100μm. Although coarser droplets can be produced by corresponding reduction of gas quantity or speed, but a fine fraction is unavoidable. Narrower droplet distributions can usually be achieved by single-fluid nozzles in which the atomization energy is provided by increased pre-pressure of the moist material. At a pressure of approx. 5 to 20 bar, coarser drops with a diameter d ₅₀ > 100 μm can be set. At a higher pressure of 50-100 bar, in exceptional cases up to 300 bar, depending on the viscosity and surface tension of the moist material, finer droplet diameters can also be set. The single-fluid nozzle is particularly suitable for high throughputs, as it dispenses with the relatively expensive compressed gas, but is sensitive to throughput fluctuations. For large-scale use, the single-fluid nozzle seems advantageous. On the development scale, however, the two-fluid nozzles have prevailed rather.

The residual moisture of the spray-dried product can be adjusted within certain limits, depending on the product-specific drying behavior, by the exhaust gas temperature of the dryer The gas inlet temperature, however, is set as high as possible, since the temperature difference in the dryer also determines the throughput. The product takes during drying due to the evaporative cooling to the gas temperature significantly lower steady-state, usually from 40-100 ⁰ C, depending on the solvent loading in the drying gas. The dry material then very quickly assumes the local gas temperature, so that the product leaves the dryer at approximately exhaust gas temperature. If overdrying does not need to be feared and gluing of the dry material through higher temperatures and the associated melting processes need not be feared, a higher exhaust gas temperature can be tolerated in order to temper the product at the same time. However, a corresponding reduction in throughput must be accepted. Therefore, if necessary, any necessary tempering is followed in suitable apparatuses. A use of the waste heat from the heat treatment for the drying is conceivable and can reduce the total energy consumption.

Depending on the process procedure, the solid material obtained in step b) has little or no residual moisture remaining and is classified as described in step d). In the classification, unwanted coarse material or fine material can be sorted out and fed back into the processes according to step a) or b). Furthermore, a shaping treatment is exceptionally possible in addition, for example by pressing, tableting or agglomeration of the intermediate product, if the desired shape in the subsequent CNT production process has not yet been achieved. However, this is usually not necessary. It is possible to insert further procedural steps, eg dedusting, compaction or especially drying and milling of the intermediate before classification. The milling and drying (optional step c)) can usually be dispensed with, since the intermediate product is usually obtained in the desired particle size from the spray-drying process after step b). Preference is given to a classification and reuse of the fraction of the intermediate product which has a size outside the desired particle size range, without additional solids treatment or shaping. In the case of fine dust (ie the proportion of particles whose diameter is below the specification limit), this reuse is possible and preferred without further treatment by recycling to the preparation of the solution (step a)); for the coarse material (ie particles whose diameter is above the specifcation limit) a comminution step before reuse will generally not be avoidable.

The optionally classified catalytically active intermediate from step c) or b) is then optionally after-dried (step e)) and then calcined (step f)). For this purpose, batchwise or continuous methods can be used. Depending on the educts used, decomposition products (for example NO _x ) are formed which have to be separated off in the process, methods for which are known to the person skilled in the art from the technical preparation of catalysts. The drying according to step e) is preferably carried out at a temperature of 150 to 300 ⁰ C with temperature-stable catalyst intermediates which do not form adhesive phases by melting operations, and is preferably in the range 80-120 ⁰ C in temperature-sensitive catalyst intermediates, which tend to form adhesive phases.

Depending on the reactants used, the calcination temperature can be increased or decreased continuously or stepwise.

Depending on the calcination temperature required, the step of drying and calcination in step b) can be combined and directly spray-pyrolyzed material obtained. It may also be necessary due to the moisture levels to be set and Abreaktionsgrade to be decomposed precursors, downstream of a further calcining behind a Sprühpyrolyseteil whose waste heat can be used in the spray drying.

The described thermal treatment (calcination according to step f)) can be carried out, for example, in fixed beds, tray ovens, fluidized beds and moving beds, rotary kilns, risers, downers, circulating systems. The calcination time is also dependent on the choice of the reactor and is adjusted accordingly. Depending on the catalytically active metals used, a reduction may optionally be advantageous. This can be carried out separately or in situ by adding a fluid containing a reducing agent, in particular hydrogen, in the reactors described above for step e).

In the following preferred embodiments of the invention are shown:

The solvent for step a) is preferably selected from at least one solvent of the series: water, alcohols, low-boiling, aliphatic and aromatic hydrocarbons, nitromethane or supercritical CO ₂ , preferably water and alcohols, or possible mixtures thereof.

In a preferred method, for a product liable to form sticky phases, the final drying e) is carried out at a temperature of 80 to 120 ^° C. in order to prevent melting. In the case of the preceding spray drying, low exhaust gas temperatures and high residual moistures must already be used for such products to avoid melting processes and the corresponding formation of sticky phases, so that after-drying is generally unavoidable.

In a further preferred alternative method, the drying e) is carried out at a temperature of 150 to 300 ⁰ C to remove bound water in the form of Hydrathüllen already before calcination. This is possible if the material does not tend to stick as described above.

The classification d) is particularly preferably carried out so that a granulate having a particle size in the range of 40 to 70 microns is obtained. The mean catalyst particle diameter is chosen according to the desired size of the CNT agglomerates to be produced. The narrowest possible particle size distribution is particularly advantageous for the use of the catalyst in a fluidized bed, since usually only a relatively narrow speed window exists in which the heavier large CNT agglomerates in the reactor are not yet defluidized and at the same time the fine catalyst particles are not upwardly out of the reactor Bed be discharged, a stationary operation of the reactor is thus possible without special repatriation measures.

In a preferred method, the precursor compounds are selected from hydroxides, carbonates, nitrates, oxalates or other salts of lower carboxylic acids, in particular acetates, the metals Co, Mn, Fe, Ni and Mo. More preferably, the precursor compounds comprise hydroxides, carbonates or nitrates, in particular nitrates at least of cobalt and manganese. In a particularly preferred variant of the novel process, together with the precursor compounds for the catalyst, precursor compounds for a catalyst support selected from the group of metal compounds of: alkaline earth metals (eg magnesium, calcium), aluminum, silicon, titanium, cerium and lanthanum are preferred Hydroxides, carbonates or nitrates of alkaline earth metals, aluminum, silicon, titanium and titanium, in step a) dissolved in the solvent and / or suspended.

Particularly energy-efficient works a preferred method in which the final drying e) and the calcination f) are carried out in a common reaction space.

The spray granulation or spray drying according to step b) is preferably carried out using a single-substance atomizing nozzle or a two-component atomizing nozzle with the addition of inert gas or air during the atomization. In the case of single-substance atomization, the energy required to produce the droplets (surface energy) is obtained only from the liquid which is conveyed with a high pre-pressure and a correspondingly high speed through a small nozzle opening. By skillful choice of the form and nozzle diameter and depending on the material properties of other parameters such. B. the geometry of the upstream Dralloder mixing chamber, the average diameter and the width of the diameter distribution of the resulting droplets can be set in the desired manner. In the two-component atomization, the energy required to produce the drops is not or not exclusively obtained from the liquid, but additionally, under high pressure, a gas is brought into contact with the liquid jet. The liquid pre-pressure can then be considerably lower than in the case of single atom atomization or completely eliminated. The choice of the appropriate method for a given atomization task also depends on the desired throughput rates. The exact operating parameters can usually be determined after carrying out appropriate preliminary tests, since the mutual dependencies of the parameters are complex.

In the case where spray granulation or spray drying is performed using a single atom atomizing nozzle, the pressure difference across the nozzle is from 5 * 10 ⁵ to 300 * 10 ⁵ Pa (5 to 300 bar), preferably 20 * 10 ⁵ to 100 * 10 ⁵ Pa (20 to 100 bar), more preferably 40 * 10 ⁵ to 70 * 10 ⁵ Pa (40 to 70 bar).

In the case where spray granulation or spray drying b) is preferably carried out using a two-component atomizing nozzle, this step is carried out with the addition of inert gas or air, wherein the ratio of gas mass flow to liquid mass flow is from 0.1 to 1 to 2 to 1. The smaller amounts of air can be achieved mainly in two-fluid nozzles with internal mixing and liquid pre-pressure and save in addition to the savings of compressed gas the risk of nozzle clogging. In two-fluid nozzles with external mixing, the risk of blockage of the nozzle is lower, but more atomizing gas must normally be used.

An alternative further preferred method is characterized in that to remove the solvent in step b) a disc atomizer is used, which is operated at a speed of the atomizer disk in the range of 2000 to 20,000 rpm, in particular depending on the diameter of the disc, with a peripheral speed of 50 - 150m / s. The advantage of disk atomization is the saving of compressed gas and liquid pressure as well as a broad local distribution of the droplet spray in the spray tower with only one atomizing device.

Also very advantageous is a preferred variant of the new process in which the exhaust gases and / or heating gases resulting from the final drying e) and / or the calcination f) are recycled for heat exchange when the spray drying is carried out.

The invention also provides a catalyst for the production of carbon nanotubes, which is obtained from the process according to the invention.

The catalyst material obtained by the catalyst preparation method according to the invention can in principle for the production of nanostructured, at least in one spatial direction also nanoscale carbon materials, in particular carbon nanotubes, by decomposition of carbonaceous gases or mixtures thereof at elevated temperature in the presence or absence of inert gases, that is the decomposition reaction not chemically directly involved gases are used in the described reactor types. Since the catalyst preparation process of the present invention makes available active catalytic materials for a wide range of applications, a wide range of reaction parameters, e.g. Reaction temperature (T = 300 ° C-2500 ° C), concentrations (one or more carbon-containing educt gases which form nanoscale carbon materials under the selected conditions) and residence time (residence time of the catalytically active material, the mixtures of catalytically active material and nanoscale carbon materials and the carbon nanotubes consisting mainly of carbon) in the range of 0.01 s <t <36000 s (10 h).

An admixed inert gas, hydrogen or the carbon-containing educt gas can be recycled in the process. The carbon-containing educt gas may be compounds with any

Heteroatoms such as nitrogen, sulfur, included. There may be certain, in the deposition incorporation of heteroatoms into the carbon structure of the nanomaterials generating substances are separately added to the process.

Furthermore, the invention relates to the process for the production of fibrous

Carbon materials, in particular of carbon nanotubes with an average single diameter of 2-60 nm and an aspect ratio length: diameter (L: D)> 10 by decomposition of hydrocarbons with and without heteroatoms, in particular C 1 - to C ₅ -

Alkane or C ₂ - to C ₅ alkenes, on a catalyst in the presence of inert gas and optionally hydrogen at a temperature of 450 to 1200 ° C in a fixed bed or a fluidized bed, preferably a fluidized bed, as well as workup and purification of the resulting carbon nanotubes, characterized characterized in that a catalyst is used which is obtained from the catalyst preparation process according to the invention.

The invention also relates to the use of the catalyst obtained from the catalyst preparation process according to the invention for the production of carbon nanotubes or agglomerates of carbon nanotubes.

The separation of the nanoscale carbon materials from the catalyst used and, if appropriate, purification takes place according to physical and / or chemical methods known in principle from the prior art. The recycling of the catalytically active metals and the carrier materials obtained during the purification takes place in a preferred embodiment of the invention.

The carbon nanotubes obtained by the processes according to the invention consist essentially of largely concentric graphite layers with low-defect tube sections or have a herringbone or helix structure and have an unfilled or filled core.

The carbon nanotubes are particularly preferably obtained in the form of agglomerates, the agglomerates in particular having a mean diameter in the range of 0.5 to 2 mm. A further preferred method is characterized in that the carbon nanotubes have an average diameter of 3 to 100 nm, preferably 3 to 80 nm, particularly preferably 5 to 25 nm.

The carbon nanomaterials obtainable by the CNT preparation process according to the invention are suitable for use as additives in polymers, in particular for mechanical

Amplification and to increase the electrical conductivity. The described

Carbon hemp materials can also be used as gas and energy storage material, for Coloring and used as a flame retardant. Due to the good electrical conductivity, the carbon nanomaterials produced according to the invention can be used as electrode material or for the production of conductor tracks and conductive structures. It is also possible to use the carbon nanotubes according to the invention as emitters in displays. The carbon nanomaterials are preferred in polymer composite materials, ceramic or metal composite materials for improving the electrical or thermal conductivity and mechanical properties, for the production of conductive coatings and composite materials, as a dye, in batteries, capacitors, displays (eg Fiat Screen Displays) or Light sources, as a field effect transistor, as a storage medium z. As for hydrogen or lithium, in membranes z. B. for the purification of gases, as a catalyst or as a carrier material z. B. for catalytically active components in chemical reactions, in fuel cells, in the medical field z. B. as a scaffold for the growth control of cell tissue, in the diagnostic area z. As a marker, and in chemical and physical analysis (eg., In atomic force microscopes) used.

In the following, the invention will be explained in more detail by way of example with reference to embodiments and figures. Show it

Fig.l a transmission electron micrograph of

Carbon nanomaterial which was prepared using catalyst prepared according to the invention according to Example 2 (TEM: FA.

FEI / Philips Tecnai 20 LaB ₆ cathode, camera Tietz F114T IxIK, method after

Manufacturer's instructions)

2 shows a high-resolution transmission electron micrograph of

Carbon nanomaterial which was prepared using catalyst prepared according to the invention according to Example 2 (TEM: FA.

FEI / Philips Tecnai 20 LaB ₆ cathode, camera Tietz F114T Ix IK, method after

Manufacturer's instructions)

3 shows a scanning electron microscope photograph of carbon nanomaterial which was produced using catalyst prepared according to the invention according to Example 3 (REM: FA, FEI SFEGSEM Sirion 100 T, method according to FIG

Manufacturer's instructions) Examples

Example 1 Preparation of a Catalyst by Spray Drying and Subsequent Calcination

Four solutions were prepared from 213.2 g Co (NO ₃ ) ₂ * 6H ₂ O in 549.5 mL deionized water, 186.8 g Mn (NO ₃ ) ₂ .4H ₂ O in 549.5 mL deionized water, 395.6 g of A1 (NO ₃ ) ₃ .9H ₂ O in 384.6 ml of deionized water and 336.3 g of Mg (NO ₃ ) _{2 *} 6H ₂ O in 384.6 ml of deionized water. The Mn- and Co-containing solutions or the Al and Mg-containing solutions were combined and stirred at room temperature for 5 min. The two solutions obtained were then also combined and stirred for 5 min. Possibly existing purges were solved by dropwise addition of dilute HNO ₃ . From this solution, 2.84 kg of a Nubilosa spray dryer (d = 0.8 m, H _Zyhnder = lm, Nubilosa two-fluid nozzle, product separation via cyclone) Ih long dosed. The inlet temperature was 180 ⁰ C, while the outlet temperature (behind cyclone) was 92 ° C. N _{2 was} metered in at a flow rate of 100 Nm ³ / h. From the cyclone about 282 g of solids were removed. The solid had a Pπmär- grain size (diameter) in the range of 5 to 50 microns; in the discharge of the dryer, the product tended to agglomerate, which leads to a coarsening of the grain size. The solid was subsequently dried at 180 ^° C. overnight and subsequently calcined at 400 ^° C. in air for 4 hours. The yield after calcination was 55%. The theoretical ratio of the active metals used based on the Trägermateπal is Mn: Co: Al ₂ O ₃ : MgO = 17: 18: 44: 22.

Example 2: Use of the catalyst described in Example 1 in the synthesis of carbonaceous nanomaterials in a fixed bed reactor

The catalysts were tested in a fixed bed apparatus on a laboratory scale. For this purpose, a defined amount of catalyst from Example 1 in a heated from the outside by a heat transfer quartz tube was presented with an inner diameter of 9 mm. The temperature of the solid beds was controlled by a PID control of the electrically heated heat carrier. The temperature of the catalyst bed or of the catalyst / nanotube mixture was determined by a thermocouple surrounded by an inert quartz capillary. Feed gases and inert diluent gases were fed into the reactor via electronically controlled mass flow controllers. The catalyst samples were first heated in a stream of hydrogen and inert gas to the reaction temperature of 650 ⁰ C. After reaching the reaction temperature, the educt gas ethene was switched on. The volume ratio of Ethylene gas mixture was ethene: hydrogen: Ar = 45: 60: 5. The total volume flow was adjusted to 110 mLN min-1. The loading of the catalyst with the educt gases was carried out for a period of 100-120 minutes usually until complete deactivation of the catalyst. Thereafter, the amount of deposited carbon was determined by weighing. The structure and morphology of the deposited carbon was determined by means of SEM and / or TEM analyzes. The amount of carbon deposited in relation to the catalyst used, hereinafter referred to as yield, was defined on the basis of the mass of catalyst after calcination (mkat, 0) and the weight gain after reaction (m-total mkat, 0): Yield = (total) mcat, 0) / mCat, 0th The yield of the catalyst prepared in Example I was 25.385 gCNT / gKAT.

Example 3: Use of the catalyst described under Example 1 in the synthesis of carbonaceous nanomaterials in a fluidized bed

The catalysts were tested batchwise in a pilot plant fluidized bed apparatus. The apparatus consists of a stainless steel reactor with a diameter of ID = 100 mm and a

Height of approx. 1200 mm, equipped with extended head. Product removal took place in the lower one

Third with a clear distance to the gas distributor. In the upper part below the reactor head, the catalyst can be added via a lock system. The supply of catalyst and removal of product or product and catalyst can be carried out batchwise or quasi-continuously. The reactor is electrically heated and equipped with commercial mass flow controllers

Provided reactant gas supply. The bed temperature of the bed located in the reactor can with

Help of several thermocouples are measured and regulated.

In the experiment, a grain fraction of 32-80 μm was produced by sieving from the material produced in Example 1. The temperature was set within the reactor to T = 650 ⁰ C (heating in N ₂ ) and controlled during the experiment. Once 20 g and once 25 g of catalyst were added in 2 consecutive experiments. For better metering on a laboratory scale, the catalyst was mixed with a small amount of carbon nanotubes. Each time after the addition, a reactant stream of 4 LN / min of nitrogen and 36 LN / min of ethylene was adjusted and the reaction was continued until an incipient decline in the conversion was observed. The initial conversions were between Xc _2H4 = 67% and Xc _2H4 ⁼ 72%. After the reaction time of each experiment, the reaction space was rendered inert and the material removed and fed new catalyst. From a total of 45 g of added catalyst so 1514 g carbon nanotubes were prepared, this corresponds to a yield of 33.64 g Carbon dioxide tubes per gram of catalyst added to the reactor. The carbon footprint error was less than 4%. As gaseous by-products small amounts (selectivity in each case less than 8%) ethane and methane were detected by gas chromatography.

The catalyst prepared by the spraying process according to the invention is distinguished from the prior art by a simple, time-saving and cost-saving preparation and a high activity of the catalyst according to the invention and by a high quality of the carbon nanotubes produced therewith.

Claims

claims

1. A process for the preparation of a catalyst based on at least two metals from the series: cobalt, manganese, iron, nickel and molybdenum for the production of carbon nanotubes with the steps:

a) dissolving at least two thermally decomposable precursor compounds of the catalyst selected from the series of the salts of: cobalt, manganese, iron, nickel and molybdenum in a solvent to form a solution optionally with suspended undissolved precursor compounds, preferably an aqueous solvent,

b) removing the solvent by spray granulation or spray drying with a drying gas having a temperature of 150-600 ⁰ C, preferably 300 -

500 ⁰ C, preferably by means of nozzle or disc atomizer, in particular to obtain an outlet temperature of the exhaust gas (mixture of drying gas and solvent vapor) of at least 70 ⁰ C, preferably 70 - 200 ⁰ C, particularly preferably 80-120 ⁰ C ,.

c) optionally grinding the mixture obtained from step b) and, if appropriate, post-drying the mixture obtained from step b) at a temperature of 60 to 500 ^° C., preferably 150 to 300 ^° C., if the product does not tend to stick in the temperature range, or preferably of 60-120 ⁰ C to avoid the adhesive properties of the dry material.

d) if appropriate, classifying the mixture obtained from step b) or c) to obtain a granulate having a particle diameter in the range from 30 to 100 μm,

e) optionally further drying of the granules obtained from step d) at a temperature of 60 to 500 ^° C.,

f) calcination of the granules obtained from step e) in the presence of an oxygen-containing gas, in particular in the presence of air, at a temperature of 200 to 900 ⁰ C, preferably 250 to 800 ⁰ C, particularly preferably 300 to 700 0C, at a treatment time of at least 0.5 h, preferably 1 to 24 h, more preferably 2 to 16 hours with removal of the decomposition gases and obtaining the catalyst.

g) optionally subsequent reduction of the granulate material by means of reducing gases, in particular with hydrogen, in particular at a temperature of 200 to 750 ^° C.,

2. The method according to claim 1, characterized in that the solvent for step a) is selected from at least one solvent of the series: water, alcohols, low-boiling, aliphatic and aromatic hydrocarbons, nitromethane or supercritical CO ₂ , preferably water and alcohols or possible Mixtures thereof.

3. The method according to claim 1 or 2, characterized in that the drying e) for a prone to the formation of sticky phases product at a temperature of 80 to 120 ⁰ C and for a not prone to the formation of sticky phases product at a temperature of 150 to 300 ⁰ C is performed.

4. The method according to any one of claims 1 to 3, characterized in that the classification d) is carried out to obtain a granulate having a particle diameter in the range of 40 to 70 microns.

5. The method according to any one of claims 1 to 4, characterized in that the precursor compounds are selected from hydroxides, carbonates, nitrates, oxalates or other salts of lower carboxylic acids, in particular acetates of the metals cobalt, manganese, iron, molybdenum and nickel.

6. The method according to any one of claims 1 to 5, characterized in that the precursor compounds include hydroxides, carbonates or nitrates, in particular nitrates, at least of the cobalt, manganese, iron, molybdenum or nickel.

7. The method according to any one of claims 1 to 6, characterized in that, together with the precursor compounds for the catalyst precursor compounds for a

Catalyst support selected from the group of metal compounds of: aluminum, magnesium, calcium, titanium, cerium and lanthanum, preferably hydroxides, carbonates or nitrates of aluminum, magnesium, calcium and titanium, are dissolved and / or suspended in step a) in the solvent.

8. The method according to any one of claims 1 to 7, characterized in that in step a) additionally recycled particulate matter from catalyst material from the classification in step d) is added to the solution or suspension.

9. The method according to any one of claims 1 to 8, characterized in that the drying e) and the calcination f) are carried out in a common reaction space.

10. The method according to any one of claims 1 to 9, characterized in that the spray granulation or spray drying b) using a

Einstoffzerstäubungsdüse or Zweistoffzerstäubungsdüse under addition of inert gas or air during atomization takes place.

11. The method according to claim 10, characterized in that the spray granulation or spray drying using a Einstoffzerstäubungsdüse in a

Pressure difference across the nozzle of 5 * 10 ⁵ to 300 * 10 ⁵ Pa (5 to 300 bar), preferably 20 * 10 ⁵ to 100 * 10 ⁵ Pa (20 to 100 bar), more preferably 40 * 10 ⁵ to 70 * 10 ⁵ Pa (40 to 70 bar), takes place.

12. The method according to claim 10, characterized in that the spray granulation or spray drying using a Zweistoffzerstäubungsdüse with the addition of inert gas or air, wherein the ratio of gas mass flow to liquid mass flow of 0, 1 to 1 to 2 to 1.

13. The method according to any one of claims 1 to 9, characterized in that the removal of the solvent in step b) a disc atomizer is used, which is operated at a rotational speed of the atomizer disk in the range of 2000 to 20,000 rpm.

14. The method according to any one of claims 1 to 13, characterized in that in the drying e) and / or calcination g) resulting exhaust gases and / or heating gases are recycled to the heat exchange in carrying out the spray drying.

15. A catalyst for the production of carbon nanotubes obtained from a process according to one of claims 1 to 14.

16. A process for the production of fibrous carbon materials, in particular of carbon nanotubes with an average single diameter of 2-60 nm and an aspect ratio length: diameter (L: D)> 10 by decomposition of hydrocarbons with and without heteroatoms, in particular Ci - to C ₅ - Alkanes or C ₂ - to C ₅ -alkenes, on a catalyst optionally in the presence of inert gas and / or hydrogen at a temperature of 450 to 1200 ⁰ C in a fixed bed or a fluidized bed, preferably a fluidized bed, working up and purification of the resulting carbon nanotubes, characterized in that a catalyst obtained from a production process according to any one of claims 1 to 14 is used.

17. Use of the catalyst according to claim 15 for the production of carbon nanotubes or agglomerates of carbon nanotubes.

18. Use of the carbon nanotubes obtained from a method according to claim 16 in polymer composite materials, ceramic or Metallkompositmaterialien to improve the electrical or thermal conductivity and mechanical properties, for the production of conductive coatings and composite materials, as a dye in batteries, capacitors, displays (eg Fiat Screen Displays) or bulbs, as a field effect transistor, as a storage medium eg for hydrogen or lithium, in membranes e.g. for the purification of gases, as catalyst or as carrier material e.g. for catalytically active components in chemical reactions, in fuel cells, in the medical field e.g. as a framework for growth control of

Cell tissue, in the diagnostic range e.g. as a marker, as well as in chemical and physical analysis (for example in atomic force microscopes).