KR20140037844A - Method for producing carbon fillers having covalently bonded amino groups - Google Patents

Abstract

The present invention provides a process for the preparation of carbon fillers having covalently bonded amino groups, comprising a mixture containing carbon fillers and alkali metals and / or alkaline earth metals and / or amides thereof in anhydrous liquid ammonia, optionally with an inert solvent, from 35 to 500 ° C. And a method of converting at a temperature of and a pressure of 30 to 250 bar.

Description

Process for preparing carbon filler having covalently bonded amino group {METHOD FOR PRODUCING CARBON FILLERS HAVING COVALENTLY BONDED AMINO GROUPS}

The present invention relates to a process for the preparation of carbon fillers having covalently bonded amino groups.

Carbon fillers have been used for some time as fillers, especially in polymer molding compositions. Examples of such fillers are (conductive) carbon black, graphite, carbon nanotubes or graphene. Activated carbon or carbon fiber can also be used. The use is not limited to existing filler applications, but for example applications in the field of electronics and storage media, such as electrical conductors and transistors, electrode materials, storage media and the like can also be envisaged.

According to the prior art, carbon nanotubes (CNTs) are understood to mean cylindrical carbon tubes having a diameter of about 3 to 100 nm and several times the diameter. Such tubes consist of one or more layers of ordered carbon atoms and have different types of cores. It is also referred to, for example, as "carbon fibrils" or "hollow carbon fibers" and different forms (eg bamboo or onion shapes) are possible.

The general structure of such carbon nanotubes is a cylindrical structure. The cylindrical structure is distinguished between single wall single carbon nanotubes (SWCNT), double wall carbon nanotubes (DWCNT) and multiwall cylindrical carbon nanotubes (MWCNT). Conventional methods for its preparation include, for example, arc discharge machining, laser ablation, chemical vapor deposition from the vapor phase (CVD process) and catalytic chemical vapor deposition from the vapor phase (CCVD process).

Carbon nanotubes are light, have high tensile strength, and conduct current. It has especially been used up to now as an additive for polymers.

However, the advantageous properties of the CNTs are compromised by a series of disadvantages. CNTs tend to aggregate and have poor solubility in polar or nonpolar solvents. One way to compensate for this drawback consists in applying functional groups, for example amino groups, to the outer surface of the CNTs.

Numerous literature already exists regarding the functionalization of CNTs. The preparation of CNTs comprising amino groups is also well known (eg N. Karousis, N. Tagmatarchis, D. Tasis, Chem. Rev. 2010 , 110, pages 5366-5397). Generally, however, CNTs must be pretreated before the application of the amino groups.

The pretreatment may be a chemical conversion leading to a functional group, for example a carboxyl group. Only in one or more additional chemical steps, the functional group is converted to an amino group.

However, the pretreatment may also include mechanical treatment by physical means such as temperature, plasma or sonication, or decomposition of carbon compounds.

Combinations of chemical and physical treatments are likewise possible.

The aforementioned documents provide a preferred overview of the functionalization of different kinds of carbon nanotubes. Introduction of amino groups is shown, for example, in FIG. 2. It starts with an acid chloride group and involves the reaction with sodium azide. Alternatively, it may be prepared via acid amide. In addition, direct amidation of acyl chlorides is also possible.

CN-A-101774573 describes a method for amination of carbon nanotubes, wherein the carbon nanotubes are first pretreated by heat, acid and / or sonication, followed by temperatures of 340-350 ° C. and 6-11 MPa. React with ammonia or ethylenediamine at pressure. The pretreatment makes the process very expensive and inconvenient.

US 7,794,683 likewise describes the preparation of aminated carbon nanotubes, in which a carboxylic acid group is first introduced by acid treatment with sulfuric acid and nitric acid, and then reacted with diphenylphosphoryl azide to convert to acyl azide. . Further reaction leads to the formation of amino-functionalized carbon nanotubes through hydrolysis through isocyanate groups. A disadvantage of this process is that there are a number of reaction steps, some of which also require expensive reagents.

Eur. J. Org. Chem. 2008, pages 2544-2550, describes covalently bonded sidewall functionalization of single-walled carbon nanotubes by nucleophilic addition of lithium amides in THF. Lithium amides are prepared from n-butyllithium and propylamine in anhydrous THF. The reaction is carried out at room temperature. After the reaction, oxygen migrates through the reaction mixture, which gives carbon nanotubes replaced by groups of the -NH-CH ₂ -CH ₂ -CH ₃ -structure.

WO 2005/090233 describes the reductive functionalization of carbon nanotubes. For this purpose, carbon nanotubes are introduced into liquid ammonia, in which lithium is additionally introduced as metal. Alkyl halides or aryl halides are then added, which causes alkylation of the outer surface of the carbon nanotubes; See Figure 1 and Example 1. The reaction is carried out while cooling with acetone / dry ice, and at the end of the reaction while heating to room temperature. Aminated carbon nanotubes are not described.

The process of the invention described above requires chemical and / or physical pretreatment of the carbon nanotubes before any functionalization. A disadvantage of this pretreatment is that the structure of the carbon compound can be damaged by the pretreatment. For example, sonication of carbon nanotubes can cause damage, as described in WO 2005/090233 paragraph [0009]. In the case of oxidation pretreatment, the surface of the carbon nanotubes is attacked by an oxidant, which causes defect sites on the surface.

It is an object of the present invention to provide a method for preparing a carbon filler such as carbon nanotubes having covalently bonded amino groups, wherein the pretreatment of the carbon filler may not cause damage that carbon fillers such as carbon nanotubes should be avoided, The functionalization can be carried out in one reaction step with inexpensive reagents. The functionalization should preferably only impair the electrical conductivity of the carbon nanotubes to a slight extent, if any.

The object is to convert the mixture comprising carbon filler and alkali metal and / or alkaline earth metal and / or amide thereof in anhydrous liquid ammonia, optionally with an inert solvent, at a temperature of 35 to 500 ° C. and a pressure of 30 to 250 bar, It is achieved by a process for the preparation of carbon fillers having covalently bonded amino groups according to the invention.

According to the invention, it has been found that the carbon filler can be functionalized with a covalently bonded amino group by reacting with a liquid ammonia comprising an alkali metal and / or an alkaline earth metal or an amide thereof.

WO 2005/090233 discloses alkylation by reaction with alkyl halides only in the presence of lithium in liquid ammonia. Eur. J. Org. Chem. 2008, pages 2544-2550, describe the functionalization of carbon nanotubes with lithium n-propylamide, wherein the propylamino group is attached to the carbon nanotubes. The conversion was performed at room temperature in tetrahydrofuran.

In the present application, the term "carbon filler" means a particulate solid carbon material formed mainly or wholly from carbon as the sole element. Examples of such materials are carbon nanotubes, graphene, carbon black, graphite, activated carbon or carbon fibers. These can be surface-modified by the introduction of additional chemical elements. Nevertheless, its properties are derived to a critical degree from an exclusive carbon-based structure. Thus, according to the invention, the term "carbon filler" does not mean any particular application, but merely the structure of the particulate carbon material and the state of the material. In such particulate carbon materials, filler applications as well as electronics and storage media fields are possible and additionally included, such as electrical conductors and transistors, electrode materials, storage media, and the like. For example, modified conductive carbon black is considered an electrically conductive modification of the thermoplastic molding composition.

According to the invention, the use of the functionalized carbon filler is not limited to the filler. All advantageous applications are additionally included. Alternatively, the term "particulate carbon material" may be used instead of the term "carbon filler".

In the process according to the invention, no pretreatment of the carbon filler used is required. Thus, the carbon filler in one embodiment of the invention is not pretreated. More particularly, it is not pretreated at all with acid, heat, plasma and / or ultrasound, as in the prior art.

Furthermore, the reaction is preferably carried out in the absence of halogen compounds, in particular organic halides such as alkyl or aryl halides.

After the reaction, ammonia is preferably removed from the mixture, and then excess alkali metal and / or alkaline earth metal or amide thereof is reacted with alcohol and / or water, and a carbon filler having a covalently bonded amino group is removed from the reaction mixture. Remove

Preferably the excess of the alkali metal and / or alkaline earth metals or their amides are C _{1 -4} - is reacted with an alkanol.

The carbon filler used in the process is preferably selected from single- or multi-walled carbon nanotubes, graphene, carbon black, graphite, activated carbon, carbon fibers or mixtures thereof.

The carbon filler used in the process according to the invention can be selected from any suitable carbon filler. The filler ignores possible impurities and essentially includes carbon only as a chemical element.

The carbon fillers in particular have a graphite surface structure.

Examples of single or multiwalled carbon nanotubes are, for example, single-walled, double-walled or multi-walled carbon nanotubes (SWCNT, DWCNT, MWCNT), as described above.

Suitable carbon nanotubes and graphene are well known in the art. In the description of suitable carbon nanotubes (CNTs), reference may be made to DE-A-102 43 592, in particular paragraphs [0025]-[0027] and also WO 2008/012233, in particular page 16, 11-41. Line 8, or DE-A-102 59 498, paragraphs [0131]-[0135]. Suitable carbon nanotubes are also described in WO 2006/026691, paragraphs [0069]-[0074]. In addition, suitable carbon nanotubes are described in WO 2009/000408, page 2, line 28-page 3, line 11.

In the context of the present invention, carbon nanotubes are understood to mean carbon-containing macromolecules in which carbon has a (mainly) graphite structure and each graphite layer is arranged in the form of a tube. Nanotubes and their synthesis are already known in the literature (eg, J. Hu et al., Acc. Chem. Res. 32 (1999) 435-445). In the context of the invention, in principle any kind of nanotubes can be used.

The diameter of the individual tubular graphite layers (graphite tubes) is preferably 0.3 to 100 nm, in particular 0.3 to 30 nm. Nanotubes can in principle be divided into single-walled nanotubes (SWCNTs) and multi-walled nanotubes (MWCNTs). Thus, there are several concentric graphite tubes in the MWCNT.

In addition, the outer shape of the tube may vary; It can have the same diameter for the inside and the outside, and can also be made into a nodular tube and a worm-shaped structure.

The aspect ratio (length of the particulate graphite tube to its diameter) is> 10, preferably> 5. The nanotubes have a length of at least 10 nm. In the context of the present invention, preferred component B) is MWCNT. More particularly, the MWCNTs have an aspect ratio of approximately 500: 1 and an average length in the range of 1-500 μm.

The BET specific surface area is generally from 50 to 2000 m ² / g, preferably from 130 to 1200 m ² / g. Impurities formed during catalyst preparation are generally from 0.1 to 12%, preferably from 0.2 to 10%, depending on the HRTEM.

Suitable nanotubes sold under the name “multiwall” of Hyperion Catalysis Int., Cambridge, MA (USA) (see also EP 205 556, EP 969 128, EP 270 666, US 6,844,061) and also Bayer Material Science, Nanocyl, Arkema And FutureCarbon.

In the preparation of the present invention, carbon nanotubes do not require any pretreatment or surface modification.

Suitable graphene is described, for example, in Macromolecules 2010, 43, pages 6515-6530.

Alternatively, (conductive) carbon black, graphite or mixtures thereof are used. Suitable carbon blacks and graphites are known to those skilled in the art.

The carbon black is in particular conductive carbon black or conductive carbon black, for example acetylene carbon. The conductive carbon black used can be any common carbon black, a suitable example of which is Ketjenblack 300 from Akzo.

For conductivity modification, conductive carbon black can also be used. As a result of the inclusion of the graphite layer in amorphous carbon, carbon black transfers electrons (F. Camona, Ann. Chim. Fr. 13, 395 (1988)). The electric current is conducted in the aggregate composed of carbon black particles and between the aggregates when the distance between the aggregates is sufficiently small. In order to achieve conductivity at the minimum dosage, preference is given to using carbon black with an anisotropic structure (G. Wehner, Advances in Plastics Technology, APT 2005, Paper 11, Katowice 2005). In the case of the carbon black as described above, since the main particles are combined to form an anisotropic structure, separation of the carbon black particles is required to achieve conductivity at a relatively low load in the compound (C. Van Bellingen, N. Probst, E. Grivei, Advances in Plastics Technology, APT 2005 Paper 13, Katowice 2005).

Suitable types of carbon black have, for example, oil absorption (measured according to ASTM D 2414-01) of at least 60 ml / 100g, preferably greater than 90 ml / 100g. The BET surface area of suitable products is greater than 50 and preferably greater than 60 m ² / g (measured according to ASTM D 3037-89). Various functional groups can be present on the carbon black surface. Conductive carbon black can be prepared by a variety of methods (G. Wehner, Advances in Plastics Technology, APT 2005 Paper 11, Katowice 2005).

In addition, graphite may be used as the filler. Graphite is, for example, A.F. Hollemann, E. Wiberg "Lehrbuch der anorganischen Chemie" [Inorganic Chemistry], 91-100, pph. It is understood to mean a polymorph of carbon as described in 701-702. Graphite consists of a planar carbon layer arranged on top of another layer. Graphite can be broken down by grinding. The particle size is in the range of 0.01 μm to 1 mm, preferably in the range of 1 to 250 μm.

Carbon black and graphite are described, for example, in Donnet, J. B. et al., Carbon Black Science and Technology, Second Edition, Marcel Dekker, Inc., New York 1993. It is also possible to use conductive carbon blacks based on highly ordered carbon blacks. This is for example DE-A-102 43 592, especially in [0028]-[0030], EP-A-2 049 597, in particular on page 17, line 1-23, DE-A-102 59 498, in particular Paragraphs [0136]-[0140] and EP-A-1 999 201, in particular page 3, lines 10-17.

The particle size depends on the particular carbon material, which is preferably in the range of 1 nm to 1 mm, more preferably 2 nm to 250 μm. The carbon fibers preferably have a diameter in the range of 1 to 20 μm, more preferably 5 to 10 μm. The fibers may also be in the form of fiber bundles.

The reaction is carried out in the presence of alkali metals and / or alkaline earth metals or amides thereof. The alkaline earth metal is preferably Ca or Mg. The alkali metal is preferably selected from Li, Na, K and mixtures thereof. Especially preferably, Li or Na, in particular Na, is used.

Instead of alkali metals and alkaline earth metals, the corresponding amides prepared in independent reaction steps may also be used. Suitable among these are lithium amide, sodium amide, potassium amide, calcium amide and magnesium amide, preferably lithium amide, sodium amide and calcium amide, particularly preferably lithium amide and sodium amide, very particularly preferably sodium Amide.

Alkali metal and alkaline earth metal amides can be prepared by converting the metal in liquid ammonia, optionally in the presence of a catalyst. Sodium amide is synthesized industrially by passing gaseous ammonia over molten sodium (Ullmanns Encyclopedia of Technical Chemistry, 5th edition, A 2, pages 151-161).

Ammonia is used in the form of anhydrous liquid ammonia. "Anhydrous" is understood to mean a moisture content of less than 1000 ppm.

The conversion can be carried out in anhydrous liquid ammonia. Alternatively, it is additionally possible to use solvents or diluents which are inert under the reaction conditions.

Useful solvents which are inert under these reaction conditions include ethers such as tetrahydrofuran, dioxane, methyl tert-butyl ether, and aliphatic, cycloaliphatic, aromatic hydrocarbons such as hexane, cyclohexane and toluene, dimethylformamide or mixtures of these solvents. This includes.

The amount of solvent mentioned above is 0 to 20 000% by weight, in particular 0 to 2000% by weight, based on the carbon compound used.

The carbon filler may be introduced into the reactor suspended in the solvents mentioned above. After amination, it can be obtained after ammonia removal, suspended or dissolved in a solvent. As a result of using the solvent, dust is generated only to a very small degree. This allows for safe operation.

The weight ratio of carbon filler to ammonia is preferably 1: 200, more preferably 1:20 to 1:90.

The molar ratio of alkali metal and alkaline earth metal or alkali metal amide and alkaline earth metal amide to ammonia is preferably 1: 1000, more preferably 1:50 to 1: 400.

The carbon compound is aminated at 35 to 500 ° C, preferably 50 to 250 ° C, more preferably 80 to 180 ° C.

The total pressure used is the pressure where ammonia is in liquid form. The pressure is 30 to 250 MPa (bar), in particular 70 to 150 MPa (bar).

The conversion can be carried out in any suitable reactor capable of withstanding the abovementioned pressures and the abovementioned temperatures. During the conversion, the reaction mixture in the reactor is preferably mixed or stirred.

The reaction mixture is stirred vigorously in the reactor, preferably under the reaction conditions mentioned above. The stirrer speed is 50 to 1000 rpm, in particular 250 to 350 rpm. Before use, the reactor is purged with an inert gas, preferably nitrogen or argon.

The conversion of the invention is preferably carried out for 2 to 24 hours, more preferably for 4 to 8 hours, preferably batchwise or continuously.

For workup, the reaction mixture is preferably depressurized and cooled to 20-40 ° C. During reduced pressure, ammonia can be recovered by evaporation and cooling. It is also possible to remove ammonia in the distillation column.

The unconverted alkali metal or alkaline earth metal or the corresponding amides present in the reaction product are preferably converted into compounds which can be removed in a non-hazardous manner. Examples of suitable compounds for the conversion are alcohol or water, preferably linear or branched alkyl alcohols having 1 to 4 carbon atoms, more preferably methanol or ethanol, most preferably methanol. The alkoxide formed as the reaction product can be removed from the aminated carbon compound with the corresponding excess alcohol and any solvent. Preferably the carbon compound is removed by suction on a suction filter, for example a glass suction filter. The pore size of the suction filter is preferably 10 to 16 μm. The carbon filler can be washed with alcohol until the filtrate is no longer alkaline.

If a dry carbon compound is desired, it can be dried, for example under reduced pressure, at a constant weight of from 50 to 100 ° C. until reaching a certain weight.

The invention is illustrated in detail by the following examples.

Example

After preparation, the obtained aminated carbon filler was analyzed via XPS analysis to determine the nitrogen content.

A method description for XPS for the study of CNT functionalization levels is described below:

Functionalization was measured via XPS on a standard laboratory spectrometer with monochromatic aluminum K alpha radiation (eg, Phi 5600 LS, Phi VersaProbe or Kratos Axis Nova) using conventional charge neutralization methods. Elemental composition was quantified through a spectral scheme (1350 eV to -5 eV, step width 0.5 eV, pass energy 112-160 eV). For this quantification, Relative Sensitivity Factor (RSF) measured for a particular instrument was used, and Shirley background removal was performed.

The functionalization is derived from the detailed spectra (measurement range: ± 5-10 eV from maximum peak, energy resolution 0.1 eV, pass energy 20-30 eV) from known comparable data (eg, Beamson G., Briggs D. The high resolution XPS of Organic Polymers: the Scienta ESCA300 Database (1992) was used to compare the peak peaks of heteroatoms and carbons.

For this quantification, carbon linears of the reactants were measured under the same measurement conditions, on the same spectrometer, as measured for the product (detailed spectra, Shirley background removal).

The peak maximum of carbon was corrected to 284.5 eV (aromatic carbon), and the change in the functionalization was determined by fitting the line of reactants and various reference peaks against the measured spectrum of the product.

Example  One

Amination of MWCNTs in the Presence of Sodium in Liquid Ammonia

The conversion was carried out in a stirred autoclave (reaction volume 3.5 L, equipped with disc stirrer). The autoclave was purged with argon. 30 g of sodium Baytubes ^® C 150 P MWCNT (wetted with 140 ml of tetrahydrofuran hwadoem) and 8 g of was introduced. After closing the autoclave, 1200 ml (720 g) of ammonia was metered in liquid form. The autoclave was heated to 120 ° C. at a stirrer speed of 300 rpm. A pressure of 84 bar was formed. After 3 hours, the autoclave was cooled to 40 ° C. 0.5 L of methanol was pumped to convert any residual sodium and sodium amide. The autoclave was gradually depressurized and maintained at 40 ° C. for 1 hour for degassing. After again pumping 0.5 L of methanol, the autoclave was emptied through a riser line.

The reaction product was filtered through a glass suction filter (10-16 μm) and washed with 1 L of methanol. After transferring the CNTs to a 1 L Erlenmeyer flask, it was stirred with 1 L of methanol for 15 minutes and again filtered by suction. The operation was repeated three times. Thereafter, the CNTs were dried under reduced pressure at 70 ° C. until constant weight was reached.

Detailed spectra of nitrogen from XPS analysis showed amines at 400.6 eV. The nitrogen content was measured at 0.6% (average from three measuring points).

Example  2

Amination of Graphene in the Presence of Sodium in Liquid Ammonia

Similar to Example 1, 100 mg of graphene (Vor-X) is suspended in 10 ml of tetrahydrofuran and in the 300 ml autoclave, the presence of 120 ml (72 g) of ammonia and 800 mg of sodium Under stirring at 120 ° C. and 300 rpm for 5 hours. A total pressure of 100 bar was formed.

The autoclave was cooled to 40 ° C. Aminated graphene was washed with methanol outside the autoclave and filtered by suction using a 0.5 μm Teflon membrane. The graphene was then suspended in 100 ml of methanol, stirred for 30 minutes and filtered again by suction.

After repeating the operation once more, the graphene was dried under reduced pressure, at 70 ° C., until reaching a constant weight.

Detailed spectra of nitrogen from XPS analysis showed amines at 400.7 eV and imines at 398.9 eV. The amine nitrogen content was measured at 0.6% and the imine nitrogen content at 0.9% (each average from five measurement points).

Injection of nitrogen was not absolutely required.

Example  3

Amination of MWCNTs in the Presence of Sodium Amides in Liquid Ammonia

Example 2 In analogy, was converted to Baytubes ^® C 150 P MWCNT of 500 mg under a tetrahydrofuran, 250 mg of sodium amide and liquid ammonia in the presence of 120 ml 10 ml. After workup and drying as described in Example 2, XPS analysis was performed.

Detailed spectra of nitrogen from XPS analysis showed amines at 400.4 eV and imines at 398.9 eV. The amine nitrogen content was measured at 1.1% and the imine nitrogen content at 0.9% (each average from five measurement points).

Example  4

Similar to Example 1, 10 g Nanocyl 7000 MWCNTs were converted in the presence of 140 ml tetrahydrofuran, 5 g sodium and 1200 ml (720 g) ammonia. Post-treatment and drying as described in Example 1.

Detailed spectra of nitrogen from XPS analysis showed amines at 400.7 eV. The nitrogen content was measured at 1.1% (average from three measurements).

Example  5

Similar to Example 1, 30 g of Arkema C100 MWCNTs were converted in the presence of 140 ml tetrahydrofuran, 15 g sodium and 1200 ml (720 g) ammonia. Post-treatment and drying as described in Example 1.

Detailed spectra of nitrogen from XPS analysis showed amines at 400.5 eV. The nitrogen content was measured at 1.0% (average from five measurements).

Example  6

Similar to Example 2, 500 mg of acetylene carbon (ABCR-50% compressed, average particle size: 0.042 μm, density: 0.100 g / cm ³ , surface area 80 m ² / g) was added to 10 ml of tetrahydrofuran, Conversion was carried out in the presence of 500 mg sodium and 120 ml (72 g) of liquid ammonia and after 30 bar nitrogen injection. Post-treatment and drying as described in Example 2.

Detailed spectra of nitrogen from XPS analysis showed amines at 399.7 eV. The nitrogen content was measured at 1.1% (average from five measurements).

Example  7

Similar to Example 2, 500 mg of SWCNT (for example from Nanocyl) was added in the presence of 10 ml of tetrahydrofuran, 500 mg of sodium and 120 ml (72 g of liquid ammonia) and 30 bar. Switching after nitrogen injection. Post-treatment and drying as described in Example 2.

Detailed spectra of nitrogen from XPS analysis showed amines at 399.7 eV. The nitrogen content was measured at 0.9% (average from five measurements).

Claims (10)

A process for the preparation of carbon fillers having covalently bonded amino groups, comprising: a mixture comprising a carbon filler and an alkali metal and / or an alkaline earth metal and / or an amide thereof in anhydrous liquid ammonia, optionally with an inert solvent, at a temperature of 35 to 500 ° C and Method of switching at a pressure of 30 to 250 bar. The process according to claim 1, wherein said conversion is followed by removal of ammonia from said mixture, reaction of excess alkali metal and / or alkaline earth metal or amide thereof with alcohol and / or water and having an amino group covalently bonded from said reaction mixture. Removing carbon filler. The process according to claim 2, characterized in that the excess alkali metal and / or alkaline earth metal or amide thereof is reacted with C _{1-4 -} alkanol. The method of claim 1, wherein the carbon filler is selected from single- or multi-walled carbon nanotubes, graphene, carbon black, graphite, activated carbon, carbon fibers and mixtures thereof. . The process according to claim 1, wherein the reaction is carried out in the presence of an alkali metal selected from Li, Na, K and mixtures thereof. The process according to claim 1, wherein the conversion is carried out at a temperature of 50 to 250 ° C. 7. 7. Process according to any one of the preceding claims, characterized in that the conversion is carried out at a pressure of 30 to 250 bar. 8. Process according to any one of the preceding claims, characterized in that the conversion is carried out in the absence of halogen compounds, in particular organic halides such as alkyl or aryl halides. 9. The process according to claim 1, wherein the used carbon filler is not pretreated. 10. The method of claim 9, wherein the carbon filler used is not pretreated with acid, heat, plasma, and / or ultrasonic waves.