Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/02—Impregnation, coating or precipitation
  • B01J37/03—Precipitation; Co-precipitation
  • B01J37/031—Precipitation
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
  • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
  • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
  • B01J37/16—Reducing
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y40/00—Manufacture or treatment of nanostructures
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B32/00—Carbon; Compounds thereof
  • C01B32/15—Nano-sized carbon materials
  • C01B32/158—Carbon nanotubes
  • C01B32/16—Preparation
  • C01B32/162—Preparation characterised by catalysts
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
  • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
  • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites

Definitions

• the invention relates to a novel process for the preparation of catalysts for the production of carbon nanotubes in agglomerated form, which are characterized by a low bulk density.
• Processed carbon nanotubes with low bulk density are also subject of this invention.
• Under carbon nanotubes are understood in the prior art mainly cylindrical carbon tubes with a diameter of 3 to 100 nm and a length which is a multiple of the diameter. These tubes consist of one or more layers of ordered carbon atoms and have a different nucleus in morphology. These carbon nanotubes are for example also referred to as "carbon fibrils” or “hollow carbon fibers”.
• Carbon nanotube these materials, especially fibrous graphite materials with multiple graphite layers, since the 70s and early 80s known.
• Tates and Baker (GB 1469930A1, 1977 and EP 56004 A2) described for the first time the deposition of very fine fibrous carbon from the catalytic decomposition of hydrocarbons.
• the carbon filaments made from short-chain hydrocarbons are no longer characterized in terms of their diameter.
• Typical structures of these carbon nanotubes are those of the cylinder type. In cylindrical structures, a distinction is made between single-walled carbon nanotubes (SWCNTs) and multi-walled carbon nanotubes (MWCNTs). Common processes for their preparation are e.g. Arc discharge, laser ablation, chemical vapor deposition (CVD process) and catalytic vapor deposition (CCVD process).
• CVD process chemical vapor deposition
• CCVD process catalytic vapor deposition
• MWCNT multiwall - multi wall - CNT
• CCVD Catalytic Chemical Vapor Deposition
• the catalysts usually include metals, metal oxides or decomposable or reducible metal components.
• the metals mentioned for the catalyst are Fe, Mo, Ni, V, Mn, Sn, Co, Cu and other subgroup elements.
• the individual metals usually have a tendency to promote the formation of carbon nanotubes, according to the prior art, high yields and low levels of amorphous carbons are advantageously achieved with those metal catalysts based on a combination of the above-mentioned metals.
• Heterogeneous metal catalysts can be prepared in a variety of ways.
• the precipitation onto carrier materials the impregnation of carrier materials, the co-precipitation of the catalytically active substances in the presence of a carrier, the co-precipitation of the catalytically active metal compounds together with the carrier material or the co-precipitation of the catalytically active metal compounds together with an inert component.
• the formation of carbon nanotubes and the properties of the tubes formed thereby depend in a complex manner on the metal component used as catalyst or a combination of several metal components, the optionally used catalyst support material and the interaction between catalyst and support, the educt gas and partial pressure, a
• WO 86/03455 Al describes the production of carbon filaments, which should have a cylindrical structure with a constant diameter of 3.5 nm to 70 nm, an aspect ratio (ratio of length to diameter) greater than 100 and a core region.
• These fibrils consist of many continuous layers of ordered carbon atoms arranged concentrically about the cylindrical axis of the fibrils.
• suitable metal-containing particles are generally mentioned, but in the working examples only various iron catalysts are listed, which are obtained, for example, by impregnation of various aluminas with iron salts in aqueous solution Various methods of pretreatment are described In the case of supported catalysts, however, no catalytically active spinel structure comprising catalytically active metal constituents is formed during calcining active support is a layered doubled hydroxide (LDH) structure or a spinel structure, but is not associated with a catalytically active component (Fe, Co, Ni) e M (II) / M (III) metal ions in the carrier are exchanged for catalytically active Fe, Co or Ni ions.
• LDH layered doubled hydroxide
• the catalytically active centers are present in clusters in addition to the non-active LDH or spinel structures. At most, a small amount of Co (Fe, Ni) ( ⁇ 5%) is connected to the AI (Interface). High reduction temperatures, especially in hydrogen, therefore only accelerate the sintering of the supported Co clusters (Fe, Ni clusters), leading to thicker CNTs and further reduced activity, provided that the Co cluster size (Fe, Ni) is the maximum for CNT Synthesis exceeds suitable size.
• WO 86/003455 A1 discloses that the supported catalysts described there are not or only slightly active despite hydrogen pretreatment at 900 ° C. In the case of supported catalysts, the decomposition of the catalyst particles by the growth proceeds distinctly differently from the growth of unsupported catalysts, so that the disclosure there provides no teaching for the further optimization of unsupported catalysts.
• Moy et al. (US Pat. No. 7,198,772 B2 and US Pat. No. 5,726,116 B2) report different fibril agglomerate morphologies for the first time. They distinguish between 3 different morphologies, the bird's nest structure (BN), the combed yarn structure (CY) and the open network structure (ON). In bird nest structure (BN), the fibrils are randomly entangled in a form arranged to form a ball of intertwined fibrils that resembles the structure of a bird's nest.
• the yarn structure (CY Combed Yarn) consists of bundles of carbon nanotubes, which for the most part have the same relative orientation.
• the open network structure is formed by fibril agglomerates in which the fibrils are loosely interwoven.
• the agglomerates formed from CY and ON structures should be more readily dispersible than those of the BN structure, i.
• the individual CNTs are easier to dissolve out of the agglomerate and distribute. This is to be advantageous e.g. in the manufacture of composites.
• Particularly preferred in this aspect is the CY structure.
• Moy et al. also state that the macroscopic morphology of the aggregates is determined only by the choice of catalyst support material. Generally, catalysts prepared from spherical support materials will later yield fibril agglomerates having a birdseed structure, while aggregates having CY or ON structures will only be formed if the support material has one or more readily cleavable planar surfaces. Preferred are such support materials as gamma-alumina or magnesia, which are composed of tabular, prismatic or platelet-like crystals.
• catalysts with iron as active metal which form aluminum oxide (H705® from ALCOA) or magnesium oxide from Martin Marietta Magnesia Specialties, LLC as support material, CY or ON agglomerate structures in fibril synthesis.
• aluminum oxide H705® from ALCOA
• magnesium oxide from Martin Marietta Magnesia Specialties, LLC
• CY ON agglomerate structures in fibril synthesis.
• alumina oxides C from Degussa as support material leads to fibril agglomerates with BN structure.
• catalysts described are prepared by impregnation or precipitation of the active metal on the solid support, ie, the active metal is located on the surface of a given support material. Often the carrier particle is after the Reaction at least partially unchanged.
• Moy et al. likewise co-precipitated catalysts based on iron, molybdenum and aluminum oxide for the synthesis of carbon nanotubes.
• Such mixed oxide catalysts are generally distinguished by an increased efficiency compared to supported catalysts, since the loading of active metal can be higher.
• the CNT agglomerates synthesized from these mixed oxide catalysts showed a bird's nest structure (BN).
• Carbon nanotube powder comprising carbon nanotubes having a roll-shaped structure disclosed.
• the catalysts used for this purpose are produced in a preferred embodiment by co-precipitation of the catalytically active metal compounds Co and Mn together with at least one further component.
• the text and the examples suggest conditioning in an oxidative atmosphere.
• the prior art catalysts provide CNT with values for Q in the range 2 - 3 g * L 2 / g 3 . It is an object of the present invention to provide a process for the production of carbon nanotubes which uses co-precipitated catalysts which overcome the abovementioned disadvantages of the prior art, in particular those which are frequently coupled with a high activity, ie a high yield Bulk density of the product.
• A mass CNT product (g) / dry mass catalyst (g).
• the invention thus relates to a process comprising a reduction step for the preparation of co-precipitated catalysts which can be used for the production of carbon nanotubes, which are characterized in that they are in agglomerates with low bulk densities, in high yield and in high purity.
• the invention also relates to the co-precipitated catalysts prepared by this process comprising a reduction step, and to a process for producing carbon nanotubes in which the catalysts according to the invention are used, and the carbon nanotubes with low bulk densities and high yields produced by this CNT production process in high yields Purity.
• the carbon nanotubes produced in the at least one of the initially catalytic species have a bulk density of at most 130 g / L, preferably less than 120 g / L and / or less than 110 g / L, in particular preferably less than 100 g / L and most preferably less than 90 g / L.
• the minimum settable bulk density is technically conditioned, it is about 20 g / L or 30 g / L. Bulk density is determined according to EN ISO 60.
• the carbon nanotubes have a purity of> 90% by weight, preferably a purity of> 95% by weight and very particularly preferably of> 97% by weight.
• Ig especially b Ig and> 4.5 g * L Ig and especially preferably> 5 g * L 2 3 of> 6 g * L 2 3 2 3
• even CNTs can be prepared in a ratio Q> 8, 9, 10, 11 or 12 g * L 2 / g 3 .
• the carbon nanotubes produced are for the most part multi-walled CNTs (MWCNT) and / or multiscroll CNTs.
• the carbon nanotubes preferably have a diameter of 3 to 100 nm and a length to diameter ratio of at least 5.
• the catalysts used are prepared by co-precipitation. Suitable starting materials and processes are described, for example, in WO 2007/093337 A2 (pages 3-7) and in EP 181259 (pages 7/8).
• a particularly preferred embodiment of the catalyst preparation gives the following description:
• the metal precursors used for coprecipitation are selected so that spinel can be formed in the production by precipitation in addition to layer structures (hereinafter referred to as "LDH” as an abbreviation for "layered double hydroxides”), in particular by calcination.
• LDH layer structures
• Spinels can be described by the composition M (II) M (III) 2 O 4 , where M (II) represent divalent metals and M (III) trivalent metals.
• the precursors are present in a metal salt solution, from which the catalyst is precipitated.
• This contains in dissolved form at least one metal which catalyzes the formation of carbon nanotubes.
• Suitable catalytically active metals are, for example, all transition metals. Examples of particularly suitable catalytically active metals are Fe, Ni, Cu, W, V, Cr, Sn, Co, Mn and Mo. Very particularly suitable catalytically active metals are Co, Mn and Mo.
• the metal salt solution contains at least one further metal component which either forms a carrier material in further steps of the catalyst treatment or forms a catalytically active mixed compound together with the transition metals.
• Particularly suitable divalent metals are Mg (II), Mn (II), Co (II), Ni (II), Fe (II), Zn (II) and Cu (II).
• Examples of particularly suitable trivalent metals are Al (III), Mn (III), Co (III), Ni (III), Fe (III), V (III), Cr (III), Mo (III) and rare earth metals ,
• Preferred solvents are short chain (Cl to C6) alcohols, such as methanol, ethanol, n-propanol, i-propanol or butanol and water, and mixtures thereof. Particularly preferred are aqueous synthesis routes.
• the precipitation can be brought about, for example, by a change in the temperature, the concentration (also by evaporation of the solvent), by a change in the pH and / or by the addition of a precipitating agent or combinations thereof.
• suitable precipitating agents are solutions of ammonium carbonate, ammonium hydroxide, urea, alkali metal or alkaline earth metal carbonates and alkali metal or alkaline earth metal hydroxides in the abovementioned solvents.
• the precipitation can be carried out batchwise or continuously.
• metal salt solution and, if appropriate, the precipitation reagent and further components are mixed by means of conveying apparatuses in a mixer having a high mixing intensity.
• Preference is given to using static mixers, Y mixers, multilamination mixers, valve mixers, micromixers, (two-component jet mixers and other similar mixers known to the person skilled in the art.
• Surfactants e.g., ionic or nonionic surfactants or carboxylic acids may be added to improve the precipitation behavior and surface modification of the produced solids.
• catalyst-forming components in particular from aqueous solution, e.g. with the addition of ammonium carbonate, ammonium hydroxide, urea, alkali metal carbonates and hydroxides as
• the continuous co-precipitation of the catalytically active metal compounds is carried out together with at least one further component which forms in further steps of the catalyst treatment either a support material or a catalytically active mixed compound.
• further components are Al, Mg, Si, Zr, Ti, etc. or known to those skilled in common Mischmetalloxid- forming elements.
• the content of the other components may be between 1 and 99 wt .-% based on the total catalyst mass.
• the catalysts according to the invention preferably have a proportion of further components of 5-95% by weight.
• the solid state catalyst can be prepared by methods known to those skilled in the art such as e.g. Filtration, centrifugation, evaporation and concentration are separated from the educt solutions. Preference is given to centrifugation and filtration. The resulting solid may be further washed or used further directly as received. For improved handling of the catalyst obtained, it can be dried.
• a preferred transition metal combination is based on the components manganese and cobalt, optionally with the addition of molybdenum.
• the addition made of one or more metal components are all transition metals, preferably on the elements Fe, Ni, Cu, W, V, Cr, Sn based metal components.
• the thus-obtained, still untreated catalyst contains preferably 2-98 mol% of Mn and 2-98 mol% of Co based on the content of active components in metallic form. Particularly preferred is a content of 10-90 mol%> Mn and 10-90 mol%> Co, particularly preferred is a content of 25-75 mol%> Mn and 25-75 mol%> Co.
• the sum the proportions of Mn and Co, or Mn, Co and Mo, does not necessarily result in 100 mol%>, insofar as further elements are added as mentioned above.
• An addition of 0.2-50.0 mol% of one or more further metal components is preferred.
• Mo can be added in the range of 0-10 mol% molybdenum.
• catalysts which have similar mass fractions Mn and Co.
• Another preferred embodiment of the catalyst preferably contains 2-98 mol% Fe and 2-98 mol% Mo based on the content of active components in metallic form. Particularly preferred is a content of 5-90 mol%> Fe and 2-90 mol%> Mo, more preferably a content of 7-80 mol%> Fe and 2-75 mol%> Mo. The sum the proportions of Fe and Mo do not necessarily result in 100 mol%, inasmuch as further elements are added as mentioned above. An addition of 0.2-50 mol% of one or more further metal components is preferred.
• the mixed catalysts produced by co-precipitation are reduced according to the invention (reduction step, reductive calcination).
• the reduction (reductive calcination) is preferably carried out in a temperature range of 200-1000 ° C., more preferably in a range of 400-900 ° C., and most preferably in a range of 700-850 ° C.
• Another preferred temperature range for the reduction step is from 400 to 950 ° C, most preferably from 680 to 900 ° C, and most preferably a range from 700 to 880 ° C.
• the reduction period depends on the selected temperature range.
• a reduction time in a range of t 0.10-6.00 h, in particular 0.15-4.00 h and very particularly of 0.20-2.00 h is preferred.
• hydrogen As the reducing gas, hydrogen (H 2 ) is used. This can be used in pure form (100% by volume> H 2 ) or in a mixture with inert gases, for example in a concentration range from 5% by volume to 50% by volume of H 2 , or greater than 50% by volume. %> H 2 , especially preferably> 80% by volume H 2 .
• an inert gas for example, nitrogen or argon can be used, preferably nitrogen.
• reducing gas it is also possible to use all reducing, but not carbon-containing compounds which are gaseous under reduction conditions.
• ammonia, hydrazines or boranes can be mentioned here.
• the reducing gas contains no essential constituents of hydrocarbons ( ⁇ 10% by volume, in particular ⁇ 5% by volume).
• the reduction can be carried out at pressures of from 20 mbar to 40 bar, preferably from 1 to 20 bar, more preferably from 1 to 4 bar. Also preferred is a range of 100 mbar to normal pressure (about 1 atm or 1013 mbar).
• the catalyst is reduced by the exhaust gas from the CNT synthesis, optionally with heating to the desired temperature.
• This can be both spatially separated, e.g. in another, separated from the CNT synthesis reactor, or take place in the reactor of the CNT synthesis.
• the co-precipitated mixed catalyst is oxidatively calcined before the reduction step.
• the calcining step effects removal of the nitrate and formation of the oxides and a phase structure that is pressure and temperature dependent.
• the oxidative calcination can be carried out in air (corresponding to about 20% by volume O 2 in N 2 ), in pure oxygen, in air diluted with inert gases or in dilute oxygen.
• oxygen-containing, reducible under the appropriate conditions compounds such as nitrogen oxides, peroxides, halogen oxides, water and the like.
• the catalyst is calcined prior to the reduction step in inert gas (nitrogen, noble gases, CO 2 , more preferably N 2 and argon, most preferably N 2 ).
• inert gas nitrogen, noble gases, CO 2 , more preferably N 2 and argon, most preferably N 2 .
• this calcination at temperatures between 200 ° C and 1000 ° C, more preferably 400 ° C - 900 ° C, most preferably at 700 - 850 ° C and at pressures of 20 mbar to 40 bar, at reduced pressure, at or especially at atmospheric pressure, performed.
• a Combination of oxidative, inert and reductive calcination performed to reduce the sintering of cobalt and adjust the phase at higher temperatures.
• the conditions mentioned above for the individual steps can be set.
• the catalyst is reduced at about 700 ° C in H 2 . This temperature is sufficient for a reduction of the cobalt oxide. Subsequently, the reduced catalyst is passivated and then kept in nitrogen at higher temperatures, for example at about 850 ° C to temperature (annealed).
• the passivation (coating of the elemental Co with a thin oxide layer) protects the Co from sintering in the subsequent annealing, since the oxide layer reduces the mobility of the Co particles.
• the tempering serves to better structure the inert component or to adjust a crystallite phase (for example, conversion of gamma to theta-aluminum).
• the catalyst after the reduction step is again mixed with a thin oxide layer, e.g. passivated with oxygen gas or an oxygen-containing gas or gas mixture.
• a thin oxide layer e.g. passivated with oxygen gas or an oxygen-containing gas or gas mixture.
• This passivation is preferably carried out by passing over up to 5% by volume of oxygen, preferably 0.001-5,000% by volume, of oxygen-containing gas or gas mixture at room temperature for at least 10 minutes, for example about or at least 15 minutes. and then gradually increasing the oxygen content in the gas mixture to 20 vol .-% oxygen.
• the time to increase the oxygen content to 20% by volume can also be chosen longer, without damaging the catalyst.
• the temperature of the catalyst is monitored and prevents heating by the resulting hydrogenation by controlling the gas flow.
• the passivation can also be carried out by means of oxygen-containing compounds reducible under the appropriate conditions, e.g. Nitrogen oxides, peroxides, halogen oxides, water and the like take place.
• the passivation takes place at temperatures ⁇ 100 ° C, preferably ⁇ 50 ° C, more preferably ⁇ 30 ° C. Passivation is particularly preferably carried out with air diluted in nitrogen.
• the reduction step, calcination and passivation steps are advantageously carried out in suitable furnaces, for example tube or muffle furnaces, or in a suitable reactor.
• the steps can also take place in fluidized bed and moving bed reactors, as well as rotary kilns and in the synthesis reactor used for the production of the CNT.
• the catalysts of the invention can be used advantageously for the production of carbon nanotubes.
• Another object of the present invention is the production of carbon nanotubes using the catalyst according to the invention.
• the production of carbon nanotubes can be carried out in different reactor types. Examples include solid-bed reactors, tubular reactors, rotary tubular reactors, moving bed reactors, reactors with a bubbling, turbulent or irradiated fluidized bed, called internally or externally circulating fluidized beds. It is also possible to place the catalyst in a particle-filled reactor falling, for example, under the above classes. These particles may be inert particles and / or consist entirely or partially of a further catalytically active material. These particles can also be agglomerates of carbon nanotubes.
• the process can be carried out, for example, continuously or batchwise, with continuous or discontinuous reference to both the supply of the catalyst and the removal of the carbon nanotubes formed with the spent catalyst.
• Suitable starting materials are light hydrocarbons such as aliphates and olefins.
• alcohols, carbon oxides, in particular CO aromatic compounds with and without heteroatoms and functionalized hydrocarbons, for example aldehydes or ketones, as long as these are decomposed on the catalyst.
• mixtures of the abovementioned hydrocarbons are, for example, methane, ethane, propane, butane or higher aliphatics, ethylene, propylene, butene, butadiene or higher olefins or aromatic hydrocarbons or carbon oxides or alcohols or hydrocarbons with heteroatoms.
• the carbon donating educt may be supplied in gaseous form or vaporized in the reaction space or a suitable upstream apparatus. Hydrogen or an inert gas, for example noble gases or nitrogen, may be added to the educt gas. It is possible to carry out the process according to the invention for the production of carbon nanotubes with the addition of an inert gas or a mixture of several inert gases with and without hydrogen in any desired combination.
• the reaction gas preferably consists of carbon support, hydrogen and optionally an inert component Setting of advantageous reactant partial pressures. It is also conceivable to add an inert component in the reaction as an internal standard for the analysis of the educt or product gas or as a detection aid in process monitoring.
• the preparation can be carried out at pressures above and below the atmospheric pressure.
• the process can be carried out at pressures of from 0.05 bar to 200 bar, pressures of from 0.1 to 100 bar are preferred, and pressures of from 0.2 to 10 bar are particularly preferred.
• the temperature can be varied in the temperature range from 300 ° C to 1600 ° C. However, it must be so high that the deposition of carbon by decomposition takes place with sufficient speed and must not lead to a significant self-pyrolysis of the hydrocarbon in the gas phase. This would result in a high level of non-preferred amorphous carbon in the resulting material.
• the advantageous temperature range is between 500 ° C and 800 ° C. Preferred is a decomposition temperature of 550 ° C to 750 ° C.
• the catalyst can be batchwise or continuously brought into the reaction space.
• the catalyst is used in dilute driving mode (lower HC content) for converting hydrocarbons (HC) into carbon nanotubes, which still allows lower bulk densities under otherwise identical reaction conditions.
• a hydrocarbon content of 30 to 90% by volume is used, preferably from 50 to 90% by volume.
• inert gases such as nitrogen, as well as gases such as Kohlenstoffitnonoxid or hydrogen can be added.
• the catalysts according to the invention retain a high surface area during the production of carbon nanotubes, even at high calcining temperatures, and thus rapidly start up in the CNT reactor, ie. do not have to go through an activation phase.
• the reduction step further succeeds in reactivating catalysts which have been calcined and inactivated by high temperatures in an oxidative atmosphere, i. With the reduction can be activated "dead glow" catalyst again.
• the percolation curve corresponds to the curve that results from the application of specific resistance of a composite as a function of the degree of filling of the matrix (for example, a polymer) with CNT.
• the resistance is usually very high for non-conductive Matrice initially. As the degree of filling increases, guide paths of CNT in the composite increasingly form.
• the resistance decreases rapidly (percolation threshold). After reaching the percolation threshold, the resistance decreases only very slowly, even with a strong increase in fill level.
• percolation threshold the resistance decreases rapidly (percolation threshold).
• the resistance decreases only very slowly, even with a strong increase in fill level.
• oxidative pretreatment in particular by high oxidative pretreatment temperatures, and subsequent (re) activation by reductive calcination, a targeted increase in the CNT diameters is achieved.
• the larger diameter CNTs cause a shift in the percolation threshold towards higher CNT mass fractions in the composite. The effect can therefore be used to precisely set this threshold.
• the thickness of the CNT resulting from CNT production increases with a reductive calcination temperature of the present invention in a Co-containing catalyst (possibly by sintering the cobalt formed).
• the thickness of the CNT in the range of about 10 to 50 nm, in particular 10 to 40 nm and especially 10 to 30 nm and 1 1 to 20 nm, in another embodiment in a range of 16 to 50 nm and thus adjust the Percolation curve of a CNT polymer composite also targeted to eg move higher CNT levels.
• the width of the diameter distribution of the CNT can be adjusted in a targeted manner.
• this treatment should preferably be carried out at higher temperatures under inert conditions, if not simultaneously an influence on the thickness of the CNT is desired.
• a reductive calcination at about 700 ° C is already sufficiently fast to reduce the active component in a short time. It is also advantageous that the process according to the invention is carried out in the last part of the catalyst preparation. This makes it possible, when using the same Katalysatorprecursors by different embodiments of the reduction step targeted to obtain different product qualities with otherwise identical CNT- manufacturing process conditions.
• agglomerates with a so-called BN structure are preferably formed.
• the carbon nanotubes may also have mixed structures. They have a structure different from the structure obtained with the unreduced catalyst.
• the invention makes it possible for the first time to produce CNT agglomerates with low bulk density and high yield (based on catalyst) with simultaneously high catalyst-specific activity.
• An advantage of the low bulk density C NT agglomerates is the improved dispersibility of the CNT agglomerates, as evidenced, for example, by simplified intrusion of a polymer melt and concomitant better wetting of the CNT. Improved dispersibility generally improves the mechanical, haptic, and optical properties of CNT composites (polymers, coatings, and metals), as undispersed agglomerate residues both exhibit stress fracture upon mechanical stress and cause a dull and scarred composite surface.
• the low bulk density CNT agglomerates so produced can be incorporated into thermoplastic polymers, thermosetting polymers, rubbers, coatings, low and medium viscosity media such as water, solvents, oils, resins and metals in a simplified manner.
• finely distributed CNTs are imperative for the realization of the thin layer as well as for any desired transparency.
• the better dispersing properties of the loose CNT agglomerates have a shortened incorporation time as well as a reduction in dispersion energy and forces, e.g.
• the inventive method provides catalysts which are particularly suitable for the production of CNT agglomerates with low bulk density ( ⁇ 90 g / L) and good flowability (flow rate> 20 mL / s, measured with the flowability device from Karg-Industrietechnik (code no 1012,000) model PM and a 15 mm nozzle according to standard ISO 6186) in high yield (> 20 g / g, preferably> 30 g / g and very particularly preferably> 40 g / g) and high purity.
• the carbon nanotubes produced in this way can usually be used in the end product without prior workup because of the low catalyst content.
• the materials may be purified, e.g. by chemical dissolution of the catalyst and carrier residues, by oxidation of the amounts of amorphous carbon formed in very small amounts or by a thermal aftertreatment in an inert or reactive gas. It is possible to chemically functionalize the manufactured carbon nanotubes, e.g. to obtain improved incorporation into a matrix or to adapt the surface properties specifically to the desired application.
• the carbon nanotubes produced according to the invention are suitable for use as additives in polymers, in particular for mechanical reinforcement and for increasing the electrical conductivity.
• the carbon nanotubes produced can also be used as material for gas and energy storage, for coloring and as flame retardants. Due to the good electrical conductivity, the carbon nanotubes produced according to the invention can be used as electrode material or for the production of printed conductors and conductive structures. It is also possible to use the carbon nanotubes produced according to the invention as emitters in displays.
• the carbon nanotubes 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, sensors, capacitors, displays (eg Fiat Screen Displays) or light sources, as a field effect transistor, as storage medium eg for hydrogen or lithium, in membranes eg for the Purification of gases, as a catalyst or as a carrier material for example for catalytically active components in chemical reactions, in fuel cells, in the medical field, for example as a scaffold for growth control of cell tissue, in the diagnostic field, for example as a marker, as well as in chemical and physical analysis (eg in atomic force microscopes ) used.
• the precipitated solid was separated from the suspension and washed several times.
• the washed solid was then dried in a paddle dryer over 16 hours, with the temperature of the dryer increasing from room temperature to 160 ° C within the first eight hours.
• the solid was milled in a laboratory mill to an average particle size of 50 ⁇ and the average fraction in the range of 30 ⁇ to 100 ⁇ particle size taken to facilitate the subsequent calcination, especially to improve the fluidization in the fluidized bed and a high yield to achieve product.
• the solid was calcined for 12 hours in an oven of 500 ° C with air access and then cooled for 24 hours.
• the catalyst material was then allowed to stand at room temperature for a further 7 days for post-oxidation. A total of 121.3 g of catalyst material were isolated.
• Example 1 The catalyst prepared in Example 1 was tested in a laboratory scale fluid bed apparatus. For this purpose, a defined amount of catalyst in a heated from the outside by a heat transfer steel reactor with an inner diameter of
• the temperature of the fluidized bed was controlled by a PID control of regulated electrically heated heat carrier.
• the temperature of the fluidized bed was determined by a thermocouple. Feed gases and inert diluent gases were fed into the reactor via electronically controlled mass flow controllers.
• a CNT bed template of about 30 cm unexpanded height was first introduced to ensure good mixing.
• the reactor was then made inert with nitrogen and heated to a temperature of 650 ° C.
• An amount of 24 g of catalyst 1 according to Example 1 was then metered in.
• the reactant gas was switched on directly as a mixture of ethene and nitrogen.
• the total flow rate was set at 40 NL-min '1.
• the amount of carbon deposited was determined by weighing and the structure and morphology of the deposited carbon was determined by SEM and TEM analyzes.
• the carbon nanotube powder had a BET surface area of 260 m 2 / g.
• the catalyst was precipitated as described in Comparative Example 1, step a), separated, washed, dried and ground. Step b) of Example 1, oxidative calcination, was not performed.
• the uncalcined, dried catalyst of Example 3 was oxidatively calcined in a muffle furnace in air under the conditions given below.
• Example 4a Calcination in air for 6 h at 400 ° C at a pressure of 1 atm.
• Example 4b Calcination in air for 2 h at 900 ° C at a pressure of 1 atm.
• Example 5 Preparation of a catalyst according to the invention by reductive calcination
• the uncalcined, dried catalyst from Example 3 was in a tube furnace in a
• the air-calcined catalyst from Example 4 was reductively calcined in a tubular furnace in a hydrogen-nitrogen mixture or pure hydrogen under the conditions listed below and after cooling to room temperature directly in the CNT
• Example 7 Preparation of a catalyst according to the invention by inert calcination with previous reductive calcination
• the uncalcined, dried catalyst of Example 3 was subjected to the following calcining series in a tube furnace: i) reductive calcination in H 2 at 700 ° C for 1 h, ii) inert calcination in N 2 at 850 ° C for 2 h and after cooling to Room temperature used directly in the CNT synthesis.
• Example 8 Preparation of a catalyst according to the invention by inert calcination with previous oxidative calcination
• the reduced catalyst from Example 6a) was passivated on the surface by treatment with air.
• the passive layer was removed in the subsequent CNT synthesis in the CNT synthesis reactor at a temperature of 700 ° C (duration: 15 min) again.
• Example 10 Reactivation of a "dead-glowed" catalyst
• Example 4b The catalyst from Example 4b calcined in air at 900 ° C. was reductively calcined in a H 2 / N 2 mixture with 5% by volume of H 2 at 825 ° C. for 2 h and, after cooling to room temperature, used directly in the CNT synthesis ,
• Example 11 Production of carbon nanotubes with the catalysts according to the invention
• the above-mentioned catalysts were used in a fluidized bed for the production of carbon nanotubes analogously to Example 2.
• dry matter 0.5 g, dry matter is the mass that the catalyst still has after annealing in air at 650 ° C for 6 h after loss of precursor residues and water
• the temperature of the fluidized bed was controlled by a PID control of the electrically heated heat carrier.
• the temperature of the fluidized bed was determined by a thermocouple. Feed gases and inert Diluent gases were fed into the reactor via electronically controlled mass flow controllers.
• the reactor was then rendered inert with nitrogen and heated to a temperature of 700 ° C. within 15 minutes.
• the reactant gas was switched on directly as a mixture of ethene and nitrogen.
• the total volume flow was adjusted to 10 ⁇ * ⁇ -1 .
• the admission of the catalyst with the educt gases took place for a period of standard 34 minutes. Thereafter, the current reaction was stopped by interrupting the educt feed and the reactor contents were cooled in N 2 within 30 min and removed.
• the amount of carbon deposited was determined by weighing.
• the amount of carbon deposited in relation to the catalyst used, hereinafter referred to as yield, was defined on the basis of the dry mass of catalyst (mKat., Tr.) And the weight gain after reaction (mg all -mKat, Tr.): Yield ( mg all - niKat r.) / m cat . , Tr.
• Examples I Ib to I le show that the reductive calcination of dried catalyst with increasing treatment temperature and treatment time increasingly better Q values are achieved, which also significantly exceed the state of the art (Example 2, I Ia).
• the average diameters of the carbon nanotubes prepared in Experiments 11g-I (ii) were determined by measuring> 200 single CNT on transmission electron microscopy (TEM) scans.
• TEM transmission electron microscopy
• the diameter decreases with increasing partial pressure.
• the width of the diameter distribution is reduced with increasing H 2 - partial pressure, which is advantageous for the product quality.
• Example 11k) to l im) show that the catalyst is effectively protected by passivation.
• Example 11k shows the result for passivated catalyst, which was used immediately after passivation,
• Example 111) shows results of the same catalyst after 1 week storage in air, Example 1 after 8 weeks of storage in air. There are no significant differences. Temperatures of 300 to 400 ° C are sufficient to remove the passive layer.
• Example I ln-1) shows the result of carbon nanotube production with a catalyst calcined at 900 ° C in air. This was inactive within the reaction time, so that no yield and bulk density could be determined. By a reductive calcination of this catalyst, the catalyst could be reactivated (Example 1 ln-2).
• oxidative pretreatment for example by the high oxidative pretreatment temperature set here and subsequent (re) activation by reductive calcination, a targeted increase in the CNT diameter could thus be achieved.
• the yield was not significantly deteriorated compared to a prior art catalyst (Example 2).
• the larger diameter CNTs cause a shift in the percolation threshold towards higher CNT mass fractions in the composite. The effect can therefore be used to precisely set this threshold.
• Example I lo shows that both the yield and the Q value for an inert calcination without previous reductive calcination are far below the values of the comparative examples.
• Example 12 (comparison): The CNTs produced with the catalyst from Example 4 under standard conditions (Example 11) were introduced by hopper-feeding onto a twin-screw extruder from Coperion / Wemer & Pfleiderer (ZSK MC 26, L / D 36) and with 3 wt .-% in polyoxymethylene (POM, Hostaform ® C13031 Fa. Ticona) incorporated. The composite was then injection molded into standard test specimens on an Arburg 370 S 800-150 injection molding machine. The throughput was 15 kg / h, the melt temperature 200 ° C at 300 rpm.
• POM polyoxymethylene
• the conditions were 340 ° C melt temperature, 90 ° C mold temperature and 10 mm / s feed.
• the composite was then injection molded on an Arburg 370 S 800 - 150 injection molding machine into 80 mm diameter round plates with a thickness of 2 mm. The sprue was laterally.
• the injection molding conditions were mold temperature 90 ° C, melt temperature 340 ° C and feed 10 mm / s.
• the surface resistance was measured with a ring electrode (Monroe Model 272, 100V).
• the sample with 3 wt% CNT showed a surface resistance of c a. 1 0 10 ohms / sq, the sample with 5 wt .-%, a surface resistance of ⁇ 10 6 ohms / sq.
• a surface resistance of about 10 12 ohms / sq was found at a concentration of 3 wt% CNT, and a surface resistance of 10 7 - 10 8 ohms / sq for 5 wt%.

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