HK1170717A - Carbon nanotube agglomerate - Google Patents

Description

Carbon nanotube aggregate

The present invention relates to a method for producing carbon nanotubes in an aggregated form and a novel carbon nanotube aggregate obtained therefrom.

Carbon nanotubes are understood according to the prior art as being predominantly cylindrical carbon tubes, having a diameter of 3-100nm and a length which is a multiple of the diameter. These tubes are composed of one or more ordered layers of carbon atoms and have morphologically distinct cores. These carbon nanotubes are also referred to as "carbon fibrils" or "hollow carbon fibrils", for example.

Carbon nanotubes have long been known from the technical literature. Although nanotubes have been generally recognized as being found in Iijima (publication: S. Iijima, Nature 354, 56-58, 1991), these materials, particularly fibrous graphite materials having a plurality of graphite layers, have been known since the seventies or early eighties of the twentieth century. Tates and Baker (GB1469930A1, 1977 and EP56004A2) describe for the first time the deposition of very fine fibrous carbons produced by the catalytic decomposition of hydrocarbons. However, there is no more detailed characterization of the diameter of carbon filaments produced based on short chain hydrocarbons.

The conventional structure of these carbon nanotubes is these of the cylindrical type. In the case of cylindrical structures, there are a classification into single-walled single-carbon nanotubes (single-walled carbon nanotubes) and multi-walled cylindrical carbon nanotubes (multi-walled carbon nanotubes). Conventional methods for producing them are, for example, the arc method (arc discharge), laser ablation (laser ablation), chemical vapor deposition (CVD method) and catalytic chemical vapor deposition (CCVD method).

Iijima, Nature 354, 1991, 56-8 discloses forming carbon tubes in an arc discharge process that are composed of two or more graphene layers and rolled up to form seamless sealed cylinders and nested within one another. Depending on the roll-up vector, chiral and achiral arrangements of the carbon atoms with respect to the longitudinal axis of the carbon fiber are possible.

Furthermore, carbon nanotubes with the so-called fishbone morphology (j.w. Geus, EP application 198558) and other carbon nanotubes with a bamboo-like structure (z. Ren, US6911260B2) are described.

Bacon et al, j. appl. phys. 34, 1960, 283-90 describe for the first time carbon tube structures in which individual continuous graphene layers (so-called reel type) or disconnected graphene layers (so-called onion type) are the basis of the nanotube structure. This structure is called a reel type. Corresponding structures were also subsequently found by Zhou et al, Science, 263, 1994, 1744-47 and by Lavin et al, Carbon 40, 2002, 1123-30.

Another type of reel structure is recently described in patent application WO2009036877a 2. These CNT structures are composed of multiple graphene layers, which are combined in a stack and exist in a rolled form (multi-scroll type). The single graphene layer or graphite layer of these carbon nanotubes continuously continues from the center of the CNT to the outer edge, as viewed in cross section.

In the context of the present invention, all the above-described carbon nanotube structures are in the following collectively referred to simply as carbon nanotubes, filaments or CNTs or MWCNTs.

Currently known methods for producing carbon nanotubes include arc discharge, laser ablation and catalytic methods. In many of these processes, large diameter carbon black, amorphous carbon and fibers are formed as by-products. In catalytic processes, a distinction can be made between deposition on, for example, supported catalyst particles and deposition on in situ-formed metal centers having diameters in the nanometer range (the so-called Flow-Verfahren). In the case of production by catalytic deposition of carbon from a hydrocarbon which is gaseous under the reaction conditions (hereinafter referred to as CCVD; catalytic carbon vapor deposition), mention may be made, as possible carbon donors, of acetylene, methane, ethane, ethylene, butane, butene, butadiene, benzene, toluene, xylene and further carbon-containing starting materials. CNTs, which can be obtained by catalytic processes, are therefore preferably used.

The catalyst typically comprises a metal, metal oxide or decomposable or reducible metal component. As metals used in the catalysts, mention may be made in the prior art of, for example, Fe, Mo, Ni, V, Mn, Sn, Co, Cu and other elements of the subgroup. Although single metals do generally have a tendency to aid in the formation of nanotubes, the advantageous use of these metal catalysts based on the above-mentioned combinations of metals according to the prior art enables advantageously to achieve high yields and low amorphous carbon contents. CNTs that can be obtained from mixed catalysts are therefore preferably used.

Particularly advantageous catalyst systems for the production of CNTs are based on a combination of metals or metal compounds comprising two or more elements selected from Fe, Co, Mn, Mo and Ni.

As a rule of thumb, the formation of carbon nanotubes and the properties of the tubes formed depend in a complex manner on the metal component or combination of metal components used as catalyst, the catalyst support material optionally used and the interaction between the catalyst and the support, the feed gas and its partial pressure, the incorporation of hydrogen or another gas, the reaction temperature and residence time or the reactor used.

WO2006/050903A2 discloses a particularly preferred method for producing carbon nanotubes.

In the different processes mentioned so far using different catalyst systems, carbon nanotubes of different structures are produced, which can be removed from the process mainly as carbon nanotube powder.

Further preferred carbon nanotubes suitable for the present invention are obtained by the methods described in principle in the following references:

the production of carbon nanotubes with a diameter of less than 100nm is described for the first time in EP205556B 1. For the production described, light (i.e. short-and medium-chain aliphatic or mono-or bi-nuclear aromatic) hydrocarbons and iron-based catalysts are used on which the carbon-carrying compounds are decomposed at temperatures above 800 to 900 ℃. No detailed description is given of the aggregate morphology of the carbon nanotubes.

WO86/03455a1 describes the production of carbon filaments of cylindrical structure having a constant diameter of 3.5 to 70nm, an aspect ratio (length to diameter ratio) of more than 100 and a core region. These filaments are composed of a number of sequential layers of carbon atoms arranged concentrically around the cylindrical axis of the filament. These cylindrical nanotubes are produced by a CVD process from carbon-containing compounds at temperatures of 850 ℃ to 1200 ℃ by means of metal-containing particles. The catalyst used for this reaction is obtained by impregnation of different aluminium oxides with iron salts in aqueous solution. The aluminum oxide is partially calcined prior to loading with iron salts and at temperatures up to 1100 ℃, and is calcined after loading at oxidizing conditions up to 500 ℃. Reductive calcination at temperatures up to 1100 ℃ for iron-supported alumina supports was also investigated. The produced filaments were examined under a microscope, but no information was given about the filament aggregates or their morphology. Moy and coworkers (US patent 5726116, US7198772B 2; Hyperion Catalysis International Inc.) first reported on different filament aggregate morphologies, which were formed depending on the catalyst support selected. In this case, Moy distinguishes 3 morphologies, namely a bird's nest structure (BN), a combed yarn structure (CY) and an open mesh structure (ON). In the bird's nest structure (BN), the fibrils are randomly disorganized in some form: so that filament balls intertwined with each other are formed, which resemble a bird's nest structure. Such a structure can be obtained, for example, by using alumina as a support material for an iron/molybdenum catalyst.

The combed yarn structure (CY) is composed of bundles of carbon nanotubes, most of which have the same orientation as each other. An open mesh structure (ON) is formed by an aggregation of filaments, in which the filaments are loosely woven with each other. Both structures are formed when gamma-alumina, such as ALCOA H705, or magnesia (Martin Marietta) is used as support material in the case of precipitated or impregnated catalysts. The description of morphology does not contain precise information about the size of the aggregates, the definition of the CNT arrangement in the aggregates or further physical or geometrical parameters for characterizing the structure. Aggregates formed by CY and ON structures are said to be more easily dispersed than these of BN structures.

Another method of producing CNT catalysts is co-precipitation of metal compounds, such as oxides, from solution. Spherical particles of mixed metal oxides are formed from this simultaneous precipitation. In contrast to the supported catalyst systems described above, in which the active metal is present only on the surface of the (inert) support material, in the case of co-precipitated spherical mixed oxides the catalytically active metal is distributed homogeneously throughout the catalyst particles with the other metal oxides. The loading of the active metal and thus the efficiency is increased. The catalytically inactive metal oxide acts here as a binder and a spacer. Ideally, such catalysts break open completely during the reaction and all active metal centers become accessible to the reaction. The initial catalyst particles are completely destroyed in this process. Moy et al (US 6294144; US7198772) studied catalysts based on systematic co-precipitation of iron, molybdenum and alumina for the synthesis of carbon nanotubes and obtained in all cases CNT aggregates of bird nest structure (BN).

Patent application WO2009043445a2 describes a coprecipitated catalyst based on mixed oxides of cobalt, manganese, aluminium and magnesium oxides, suitable for the production of carbon nanotubes and characterized by a very high efficiency. The carbon nanotube aggregates obtained in this way are characterized by a high degree of chaos, similar to the CNTs of a bird's nest structure, in which the individual CNTs are randomly woven with one another. As a result, the dispersion of these aggregates in, for example, polymers or low-viscosity systems, such as solvents, becomes difficult. In addition to the disintegration of the CNT aggregates, the force required for good dispersion also leads to undesired destruction of individual CNTs (e.g. shortening) and polymers (molecular weight reduction).

It would be desirable to have a process for producing CNT aggregates in which the catalyst provides high conversion and CNT yield, and the product is at the same time easily dispersible in polymer (thermoplastic) with low energy and force introduction, with the aim of avoiding the destruction of both the individual CNTs and the polymer during the disintegration of the aggregates.

The invention provides an aggregate of carbon nanotubes, the diameter of the carbon nanotubes being between 3 and 100nm and the aspect ratio being at least 5, characterized in that the aggregate comprises bundles of carbon nanotubes in the form of raised yarns of carbon nanotubes intertwined with one another, wherein the carbon nanotubes in the form of raised yarn bundles have an average distance to one another of between 20 and 100nm, preferably between 30 and 80nm, particularly preferably between 40 and 60 nm.

In a preferred embodiment of the novel aggregate, the carbon nanotubes are present in the form of CNT bump yarns, which form the aggregate, in particular in a loosely entangled form with one another. The diameter of the CNT bump yarns in the aggregate is substantially 0.1 μm to 20 μm, preferably 0.14 μm to 10 μm and particularly preferably 0.18 μm to 3 μm. The diameter of the aggregate bump yarn, as viewed through the length of the yarn, varies particularly within the ranges described above. The CNTs in the yarn are not substantially aligned with each other but have substantially disordered positions (schematically shown in figure 1) compared to the CY structure (schematically shown in figure 2).

Preference is given to novel aggregates in the form in which at least 95% by weight of the aggregate particles have an outer diameter of from 20 μm to 6000 μm, preferably from 60 μm to 4000 μm, particularly preferably from 100 μm to 1500 μm.

Preferably the aggregate has a bulk density according to EN ISO 60 of 20 to 250kg/m³Preferably 40 to 200kg/m³Particularly preferably 50 to 150kg/m³。

In a preferred variant of the novel aggregate, the aggregate comprises, in addition to the bundles of carbon nanotubes in the form of raised yarns, other bundles of carbon nanotubes in the form of bundles, in particular bundles of carbon nanotubes of the following structures: combed yarn structures, bird's nest structures, open mesh structures or fiber bundles arranged parallel to one another, in amounts of less than 30%, preferably up to 20%, particularly preferably up to 10%.

A further preferred embodiment of the aggregate is characterized in that the impurity content, in particular the metal or metal compound content, particularly preferably the metal oxide content, of the carbon nanotubes is at most 7% by weight, preferably at most 5% by weight.

Particularly preferably, the novel aggregates are constructed in such a way that the carbon nanotubes are present in the form of multi-walled carbon nanotubes, in particular in such a form that they have graphite tubes nested one inside the other (cylindrical type) or are based on wound multi-layer graphene layers (scroll type). The latter MWCNT types are described in detail in, for example, the following documents: US5747161, US4663230 and WO2009036877a 2. It is particularly preferred that the new aggregates are based on reel-type MWCNTs.

A new production method has also been developed for producing the above-described new aggregate.

The present invention therefore also provides a process for producing aggregates from carbon nanotubes, in which, in a first step, a catalyst precursor is formed from an aqueous solution as follows: from a solution of a metal salt of a metal of transition group VIII of the periodic Table, in particular of iron, cobalt or nickel, preferably of cobalt, with a metal salt of a metal of transition group VI or VII of the periodic Table, in particular with a metal salt of a metal selected from manganese, molybdenum, chromium and tungsten, preferably manganese, by precipitation of the solution onto a support, in particular to give oxides and/or hydroxides or optionally hydrates thereof, or by coprecipitation of the solution of the metal salt with one or more metal compounds selected from aluminum, magnesium, silicon, zirconium, titanium, in particular to give oxides and/or hydroxides or optionally hydrates thereof,

the solvent is removed from the catalyst precursor and,

the catalyst precursor is then subjected to a thermal post-treatment,

wherein the catalyst precursor is subjected to a high-temperature calcination at a temperature of at least 800 ℃ in the presence of a non-reducing gas, optionally under reduced pressure, in particular in the presence of air, during the thermal aftertreatment,

the catalyst obtained here is then optionally subjected to a reductive work-up,

and catalytically decomposing a carbon precursor compound, in particular a hydrocarbon, particularly preferably a compound selected from the group consisting of: acetylene, methane, ethane, ethylene, butane, butene, butadiene, benzene, alkylbenzenes, in particular toluene or xylene, particularly preferably ethylene, and separating the CNT aggregates obtained here.

Preferably the catalyst precursor is formed by means of co-precipitation of metal salt solutions of the above metals, in particular nitrates, chlorides or carboxylates, in particular acetates, of at least two metals selected from cobalt, manganese, molybdenum, aluminium and magnesium.

Preferably, the coprecipitation of the metal salts is carried out from an acidic solution of the metal salts with the aid of an alkali metal or alkaline earth metal hydroxide solution or an ammonia-based lye.

In a preferred embodiment of the process, the high temperature calcination is carried out at a temperature of 800-.

A particularly preferred variant of the novel process is characterized in that the reaction of the hydrocarbons is carried out in a fluidized bed, wherein the catalyst is added continuously or discontinuously, optionally using a (e.g. inert) carrier gas, such as nitrogen or hydrogen, and the carbon nanotube aggregates are subsequently discharged continuously from the fluidized bed.

In a preferred embodiment, the catalyst precursor used is prepared as follows: the catalytically active metal compounds of Co and Mn are Co-precipitated with at least one further component which, in a further catalyst treatment step, catalytically active mixed compounds are formed from water-soluble salts in an aqueous medium by means of an alkaline solution. Examples which can be mentioned of such further components are Al, Mg, Si, Zr, Ti, etc. and the usual elements known to the person skilled in the art which form mixed metal oxides). The precipitation is carried out in particular by adding an alkaline solution, in particular an alkali metal hydroxide solution, an alkaline earth metal hydroxide solution or an amino lye (for example ammonium hydroxide or a simple amine) (or vice versa) to the metal salt solution. The content of the further ingredient may be up to 80 wt.%, based on the total catalyst weight. Preferably, the catalyst has a further component content of from 5 to 75% by weight.

The catalyst precursor produced in solid form can be separated from the mother liquor by methods known in principle to the person skilled in the art, for example by filtration, centrifugation, evaporation and concentration. Centrifugation and filtration are preferred. The solid obtained can be further washed or used further directly in the state obtained. The obtained solid may be dried in order to improve the ease of handling. As is known in heterogeneous catalysts, additional conditioning may be advantageous. Shaping and/or classifying may also be carried out before or after the conditioning.

Particularly preferably, the catalyst used in the novel process comprises from 45 to 55mol% of Mn and from 55 to 45mol% of Co, based on the content of catalytically active components (as elements).

The high temperature calcination of the catalyst may be carried out, for example, continuously or discontinuously, where continuous or discontinuous may be associated with both the supply of dry catalyst precursor and the removal of the catalyst.

The high temperature calcination of the catalyst can be carried out in different types of reactors. By way of example and not limitation, mention may be made here of a fluidized bed reactor, a rotating tube reactor or a reactor with a stirred bed.

The high temperature calcination of the catalyst can also be carried out in steps in the same reactor in conjunction with the actual CNT production. In this process, in a first step, the catalyst precursor is first treated in an oxidizing or inert gas flow at a suitable temperature, and then, in a second step, the catalyst treated in this way is used in the same reactor under conditions suitable for the formation of CNT aggregates, after suitable gas displacement.

The invention also provides carbon nanotube aggregates obtained by the novel production method.

The novel carbon nanotube aggregates can be advantageously used in many different applications. The present invention therefore provides the use of the novel carbon nanotube aggregates as additives for polymers, rubbers, ceramics, metals, metal alloys, glass, textile fibers and composites.

The present invention further provides a mixture or composite comprising carbon nanotubes produced by adding the above-described novel carbon nanotube aggregate to a polymer, rubber, ceramic, metal alloy, glass or textile fiber.

The invention furthermore provides the use of the novel carbon nanotube aggregates as conductive additives in electrodes, in separators for separating substances, in solar cells, actuators, sensors, in inks or pastes and in energy storage devices, in particular batteries, accumulators, fuel cells or capacitors.

The invention also provides the use of the novel carbon nanotube aggregates as substrates for pharmaceutical active ingredients or for plant protection active ingredients.

The invention furthermore provides for the use of the novel carbon nanotube aggregates as adsorbents, in particular as adsorbents for volatile compounds, for example for gases, or biological compounds, in particular for enzymes.

The invention also provides the use of the novel carbon nanotube aggregates as a support or container for a catalyst.

The invention is explained in more detail below with the aid of examples by way of illustration.

Examples

Example 1: (preparation of catalyst 1; calcination at 400 ℃ C., comparative example)

306g of Mg (NO)₃)₂*6H₂A solution of O in water (0.35L) was mixed with 360g of Al (NO)₃)₃*9H₂A solution of O in 0.35L of water was mixed. 170g of Mn (NO) are then added₃)₂*4H₂O and 194g of Co (NO)₃)₂*6H₂O (dissolved in 0.5L of water in each case) and the pH of the entire mixture is adjusted to approximately 2 by means of addition of nitric acid with stirring for 30 min. This solution stream was mixed with 20.6% strength by weight sodium hydroxide solution in a mixer and the suspension formed was added to a container of 5L of water. The pH of the vessel was maintained at about 10 by controlled addition of sodium hydroxide solution.

The precipitated solid was separated from the suspension and washed several times.

The washed solid was then dried in a paddle dryer for 16h, the temperature of which was raised from room temperature to 160 ℃ within the first 8 hours. The solid was then calcined in the presence of air at an oven temperature of 500 ℃ for 12 hours (the final temperature measured in the sample was 400 ℃) and then cooled for 24 hours. The catalyst material was then left at room temperature for an additional 7 days for post oxidation. A total of 121.3g of catalyst material was isolated.

Example 2: (preparation of catalyst 2; calcination at 600 ℃ C. for 3 hours, comparative example)

The catalyst material was prepared analogously to example 1, but calcined in the presence of air in a muffle furnace at 600 ℃ for a further 3 h. Thereafter, the solid was cooled and weighed. 110g were isolated.

Example 3: (preparation of catalyst 3; calcination at 600 ℃ C. for 6 hours, comparative example)

The catalyst material was prepared analogously to example 1, but was calcined in the presence of air in a muffle furnace at 600 ℃ for a further 6 h. Thereafter, the solid was cooled and weighed. 109g were isolated.

Example 4: (preparation of catalyst 4; calcination at 1000 ℃ for 3 h; present invention)

The catalyst material was prepared analogously to example 1, but was calcined in the presence of air in a muffle furnace at 1000 ℃ for a further 3 h. Thereafter, the solid was cooled and weighed. 109g were isolated.

Example 5: (production of CNT1 in fluidized bed, comparative example)

The catalyst prepared in example 1 was tested in a laboratory scale fluidized bed apparatus. The catalyst 1 is first introduced into a steel reactor, the inside diameter of which is 100mm, and is heated from the outside by a heat transfer medium. The temperature of the fluidized bed is adjusted by PID regulation of the electrically heated heat transfer medium. The temperature of the fluidized bed was measured by a thermocouple. The feed gas and the inert diluent gas are fed into the reactor via an electrically controlled mass flow regulator.

The reactor was first inertized with nitrogen and heated to a temperature of 700 ℃. 18.0g of catalyst 1 prepared as in example 1 are then metered in.

Immediately thereafter, the raw material gas as a mixture of ethylene and nitrogen was turned on. The volume ratio of the raw material gas mixture is ethylene: n is a radical of₂= 90: 10. the total volume flow rate was adjusted to 40NL · min^-1(Standard L/min). The catalyst was impinged with the feed gas for a period of 31 minutes. The reaction starts in less than 2min (below the detection limit for technical reasons) and exhibits high catalyst activity (hydrogen content is measured on-line by gas chromatography). Thereafter, the reaction was stopped by interrupting the feed of the starting materials and the reactor contents were removed.

The amount of carbon deposited was measured by weighing, and the structure and morphology of the deposited carbon was measured by means of REM and TEM analysis. The amount of carbon deposited based on the catalyst used (hereinafter referred to as yield) is defined based on the weight of the catalyst after calcination (mkat, 0) and the weight increase after reaction (m total-mkat, 0): yield = (total amount of m-mkat, 0)/mkat, 0.

The test was performed 5 times in succession. The obtained products were combined to obtain a sample and analyzed. The catalyst yield was 44.7g of carbon nanotube powder per gram of catalyst used. The bulk density of the product was 146.0 g/L. The average diameter of the carbon fiber was 10.5 nm. The aspect ratio of the CNT is at least 100. The diameter of the majority (> 95% by weight) of the aggregates is 0.1-1 mm.

REM photographs of the obtained aggregates show the aggregate morphology of the Bird Nest (BN) structure.

Example 6: (production of CNT2, comparative example)

The catalyst prepared in example 2 was tested in a laboratory scale fluidized bed apparatus. The test was carried out analogously to example 5 and with the catalyst of example 2. The reactor was first inertized with nitrogen and heated to a temperature of 700 ℃. 18.0g of catalyst 2 prepared as in example 2 are then metered in.

Immediately thereafter, the raw material gas as a mixture of ethylene and nitrogen was turned on. The volume ratio of the raw material gas mixture is ethylene: n is a radical of₂= 90: 10. the total volume flow rate is adjusted to 40LN min^-1. The catalyst was impinged with the feed gas for a period of 31 minutes. The reaction starts in less than 2min (below the detection limit for technical reasons) and exhibits high catalyst activity (hydrogen content is measured on-line by gas chromatography). Thereafter, the reaction was stopped by interrupting the feed of the starting materials and the reactor contents were removed.

The test was performed 5 times in succession. The obtained products were combined to obtain a sample and analyzed. The catalyst yield was 53.0g of carbon nanotube powder per gram of catalyst used. The bulk density of the product was 152.4 g/L. The average diameter of the carbon fiber was 12.0 nm. The aspect ratio of the CNT is at least 100. The diameter of the majority (> 95% by weight) of the aggregates is 0.1-1 mm.

REM photographs of the obtained aggregates show the aggregate morphology of the Bird Nest (BN) structure.

Example 7: (production of CNT3, comparative example)

The catalyst prepared in example 3 was tested in a laboratory scale fluidized bed apparatus. The test was carried out analogously to example 5, the catalyst of example 3 being used. The reactor was first inertized with nitrogen and heated to a temperature of 700 ℃. 18.0g of catalyst 3 prepared as in example 3 are then metered in.

Immediately thereafter, the raw material gas as a mixture of ethylene and nitrogen was turned on. The volume ratio of the raw material gas mixture is ethylene: n is a radical of₂= 90: 10. the total volume flow rate is adjusted to 40LN min^-1. The catalyst was impinged with the feed gas for a period of 31 minutes. The reaction starts in less than 2min (below the detection limit for technical reasons) and exhibits high catalyst activity (hydrogen content is measured on-line by gas chromatography). Thereafter, the continued reaction was stopped by discontinuing the feed of starting materials and the reactor contents were removed.

The test was performed 5 times in succession. The obtained products were combined to obtain a sample and analyzed. The catalyst yield was 53.6g of carbon nanotube powder per gram of catalyst used. The bulk density of the product was 150.8 g/L. The average diameter of the carbon fiber was 12.7 nm. The aspect ratio of the CNT is at least 100. The diameter of the majority (> 95% by weight) of the aggregates is 0.1-1 mm.

REM photographs of the obtained aggregates show the aggregate morphology of the Bird Nest (BN) structure.

Example 8: (production of CNT 4; present invention)

The catalyst prepared in example 4 was tested in a laboratory scale fluidized bed apparatus. The test was carried out analogously to example 5, using the catalyst from example 4. The reactor was first inertized with nitrogen and heated to a temperature of 700 ℃. 18.0g of catalyst 4 prepared as in example 4 are then metered in.

Immediately thereafter, the raw material gas as a mixture of ethylene and nitrogen was turned on. The volume ratio of the raw material gas mixture is ethylene: n is a radical of₂= 90: 10. the total volume flow rate is adjusted to 40LN min^-1. The catalyst was impinged with the feed gas for a period of 31 minutes. The reaction was started after about 7 min. This is clearly behind the tests of examples 5-7. The catalyst activity (hydrogen content measured on-line by gas chromatography) is likewise much lower than in example 5 (about 70%). The reaction was stopped by interrupting the feed of the starting materials and the reactor contents were removed.

The test was performed 5 times in succession. The obtained products were combined to obtain a sample and analyzed. The catalyst yield was 24.3g of carbon nanotube powder per gram of catalyst used. The bulk density of the product was 141.3 g/L. The average diameter of the carbon fiber was 9.7 nm. The aspect ratio of the CNT is at least 100. The diameter of the majority (> 95% by weight) of the aggregates is 0.1-1 mm.

REM photographs of the obtained aggregates show that the aggregates are composed of a number of expanded shaped CNT yarns, in which the individual CNTs are loosely woven with each other and are not substantially aligned or parallel to each other (see fig. 1 and 2).

Example 9: (mixing CNT1 into PC, comparative example)

Because of the high surface area of the carbon nanotubes, the singulation is advantageous only in combination with the stabilization of the individual states (immobilization in a matrix, addition of substances acting as stabilizers), since otherwise a fast re-agglomeration of the carbon nanotubes would occur, which is due to the high van der waals forces or thermal movements of the singulated carbon nanotubes.

The carbon nanotube powder CNT1 produced in example 5 was introduced into the main inlet of a co-rotating twin-screw extruder (ZSK 26Mc, L/D36) together with polycarbonate (Makrolon 2805). The temperature of the extruder was 280 ℃. The throughput of the composite material was adjusted to 26 kg/h at 400 rpm. The mass ratio of the carbon nanotube powder to the polycarbonate is 3: 97. the strands emerging from the extruder were cooled in a water bath and then pelletized. TEM photographs of the part prepared from the composite show that the carbon nanotubes are still partly present in aggregated form in the polycarbonate. The composite was then injection molded on an Arburg 370S 800-150 injection molding machine to produce disks 80mm in diameter and 2mm in thickness. The injection port is on the side. The injection molding conditions were a mold temperature of 90 ℃, a material temperature of 340 ℃ and a feed rate of 10 mm/s. The surface resistance was then measured with a ring electrode (Monroe model 272, 100V). The surface resistance of the sample was shown to be greater than 10¹²Ohm. Polymer degradation was also measured by means of GPC. PC showed an Mw of 27027g/mol (formerly 28000 g/mol).

Example 10: (mixing CNT4 into PC, present invention)

The carbon nanotube powder CNT4 produced in example 8 was introduced into the main inlet of a co-rotating twin-screw extruder (ZSK 26Mc, L/D36, screw configuration same as in example 9) together with polycarbonate (Makrolon 2805). The temperature of the extruder was 280 ℃. The throughput of the composite material was adjusted to 26 kg/h at 400 rpm. The carbon nanotube powder andthe mass ratio of the polycarbonate is 3: 97. the strands emerging from the extruder were cooled in a water bath and then pelletized. TEM photographs of sections prepared from the composite show that the carbon nanotubes are predominantly in singulated form in the polycarbonate. The composite was then injection molded on an Arburg 370S 800-150 injection molding machine to produce disks 80mm in diameter and 2mm in thickness. The injection port is on the side. The injection molding conditions were a mold temperature of 90 ℃, a material temperature of 340 ℃ and a feed rate of 10 mm/s. The surface resistance was then measured with a ring electrode (Monroe model 272, 100V). The surface resistance of the sample was expressed as 2.10⁸Ohm. Polymer degradation was also measured by means of GPC. PC showed an Mw of 27543g/mol (formerly 28000 g/mol). The reduction in molecular weight of the polymer is significantly reduced compared to the material shown in example 9 (comparative).

Claims (20)

1. Aggregate of carbon nanotubes, the diameter of the carbon nanotubes being between 3 and 100nm and the aspect ratio being at least 5, characterized in that the aggregate comprises bundles of carbon nanotubes in the form of raised yarns of carbon nanotubes intertwined with each other, wherein the average distance of the carbon nanotubes in the raised yarns from each other is between 20 and 100nm, preferably between 30 and 80nm, particularly preferably between 40 and 60 nm.

2. Aggregate according to claim 1, characterized in that at least 95% by weight of the aggregate particles have an outer diameter of 20 μm to 6000 μm, preferably 60 μm to 4000 μm, particularly preferably 100 μm to 1500 μm.

3. Aggregate according to claim 1 or 2, characterized in that its bulk density according to EN ISO 60 is from 20 to 250kg/m³Preferably 40 to 200kg/m³Particularly preferably 50 to 150kg/m³。

4. Aggregate according to any of claims 1 to 3, characterized in that the carbon nanotubes are present in the form of raised yarns twisted around each other and not substantially aligned with each other.

5. Aggregate according to any of claims 1 to 4, characterised in that the diameter of the carbon nanotube bump yarn is substantially between 0.1 μm and 20 μm, preferably between 0.14 μm and 10 μm and particularly preferably between 0.18 μm and 3 μm.

6. Aggregate according to any of claims 1 to 5, characterized in that the aggregate comprises, in addition to carbon nanotube bundles in the form of raised yarns, other structural bundle forms of carbon nanotubes, in particular carbon nanotube bundles of the following structures: combed yarn structures, bird's nest structures, open mesh structures or filament bundles arranged parallel to one another, in amounts of less than 30%, preferably up to 20%, particularly preferably up to 10%.

7. Aggregate according to any of claims 1 to 6, characterized in that the content of impurities, in particular metals or metal compounds, particularly preferably the content of metal oxides is at most 7 wt.%, preferably at most 5 wt.%, of the carbon nanotubes.

8. Aggregate according to any of claims 1 to 7, characterized in that the carbon nanotubes are present in the form of multi-walled carbon nanotubes, in particular in the form of tubes with graphite nested inside each other, or based on a rolled up multi-layered graphene layer.

9. Method for producing carbon nanotube aggregates, in which in a first step a catalyst precursor is formed from an aqueous solution as follows: from a solution of a metal salt of a metal of transition group VIII of the periodic table, in particular of iron, cobalt or nickel, with a metal salt of a metal of transition group VI or VII of the periodic table, in particular with a metal selected from manganese, molybdenum, chromium and tungsten, by precipitation of the solution onto a support, in particular in the form of an oxide and/or hydroxide or optionally a hydrate thereof; or the metal salt solution is coprecipitated with one or more metal compounds selected from the group consisting of aluminium, magnesium, silicon, zirconium, titanium, in particular to produce oxides and/or hydroxides or optionally hydrates thereof,

the solvent is removed from the catalyst precursor and,

the catalyst precursor is then subjected to a thermal post-treatment,

wherein the catalyst precursor is subjected to a high-temperature calcination at a temperature of at least 800 ℃ in the presence of a non-reducing gas, optionally under reduced pressure, in particular in the presence of air, during the thermal aftertreatment,

the catalyst obtained here is then optionally subjected to a reductive work-up,

and catalytically decomposing a carbon precursor compound, in particular a hydrocarbon, particularly preferably a compound selected from the group consisting of: acetylene, methane, ethane, ethylene, butane, butene, butadiene, benzene, alkylbenzenes, in particular toluene or xylene, particularly preferably ethylene, and separating the CNT aggregates obtained here.

10. A process according to claim 9, characterized in that the catalyst precursor is formed by means of co-precipitation of the following components: a metal salt solution, in particular a nitrate, chloride or carboxylate, in particular an acetate, of at least two metals selected from cobalt, manganese, molybdenum, aluminum and magnesium.

11. Process according to claim 9 or 10, characterized in that the coprecipitation of the metal salts is carried out from an acidic solution of the metal salts with the aid of an alkali metal hydroxide solution.

12. Process according to one of claims 9 to 11, characterized in that the high-temperature calcination is carried out at a temperature of 800-.

13. Process according to one of claims 9 to 12, characterized in that the reaction of the hydrocarbons is carried out in a fluidized bed, wherein the catalyst is added continuously or discontinuously, optionally using a carrier gas, preferably nitrogen or hydrogen, and subsequently the carbon nanotube aggregates are continuously discharged from the fluidized bed.

14. Carbon nanotube aggregates obtained by the process according to one of claims 9 to 13.

15. Mixture or composite material comprising carbon nanotubes, produced by adding an aggregate according to any of claims 1 to 8 or claim 14 to a polymer, rubber, ceramic, metal alloy, glass or textile fibre.

16. Use of carbon nanotube aggregates according to one of claims 1 to 8 and claim 14 as additives for polymers, rubbers, ceramics, metals, metal alloys, glass, textile fibers and composites.

17. Use of carbon nanotube aggregates according to one of claims 1 to 8 or claim 14 as conductive additive in electrodes, in separators for separating substances, in solar cells, actuators, sensors, inks or pastes and in energy storage devices, in particular batteries, accumulators, fuel cells or capacitors.

18. Use of carbon nanotube aggregates according to one of claims 1 to 8 or claim 14 as a substrate for pharmaceutical active ingredients or for plant protection active ingredients.

19. Use of carbon nanotube aggregates according to one of claims 1 to 8 or claim 14 as adsorbents, in particular as adsorbents for volatile compounds, for example for gases, or biological compounds, in particular for enzymes.

20. Use of carbon nanotube aggregates according to one of claims 1 to 8 or claim 14 as a support or container for a catalyst.