JPH0558611A - Method for purifying fullerenes - Google Patents

Abstract

PURPOSE:To efficiently recover a large amount of sufficiently high-purity desired fullerene from a fullerene-containing material such as a fullerene-containing soot substance prepared by arc discharge or laser abrasion of carbon such as graphite or a crude fullerene separated from the fullerene-containing soot material. CONSTITUTION:A fullerene-containing raw material is dissolved and dispersed into an aromatic compound, reacted with a hydrogen gas in the presence of a hydrogenating catalyst, then impurities and the waste catalyst are removed and the prepared hydrogenated fullerene is reacted with a dehydrogenating and dehydrogenated to give a fullerene.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying fullerenes, more specifically, a crude fullerene-containing material containing fullerenes such as fullerene C ₆₀ and fullerene C ₇₀ together with impurities (for example, High-purity soot obtained by graphite arc discharge or laser ablation, or crude fullerene powder extracted from aromatic solutes such as benzene and toluene from soot containing these fullerenes and its solution) The present invention relates to a method for purifying fullerenes, which is extremely useful in practice and can efficiently obtain fullerenes.

[0002] The purified fullerenes obtained by the method of the present invention are suitable for use in various fields of application of fullerenes including the field of electric and electronic materials, for example, as materials for conductive materials and superconductors. can do.

[0003]

2. Description of the Related Art Recently, a new type of molecular carbon material called a closed shell type carbon cluster (spherical macromolecule) having 60, 70, 84 carbon atoms has been synthesized and attracted attention. Carbon clusters with this special structure
It is also called a fullerene, and is called fullerene C ₆₀ , C ₇₀ , C ₈₄ or the like depending on the number of carbon atoms constituting the molecular skeleton (sometimes simply called C ₆₀ , C ₇₀ , C _84, etc.). Since these fullerenes are new carbon materials and are expected to show unique physical properties because they have a special molecular structure, studies on their properties and application development are being actively pursued. For example, fullerenes are expected to be used as lubricants at the molecular level such as spherical macromolecules, and because they are unsaturated macrocarbon molecules with a uniform carbon number, graphite There are great expectations as a high-performance conductive material that can replace the above. In fact, very recently, it was found that when fullerene C ₆₀ is doped with potassium, it becomes a superconductor even at an absolute temperature of 18K, and it is also shown that the addition of alkali metals such as rubidium and cesium can provide high-temperature superconductors one after another. Was
Attracting attention from various fields [Nature, 35
0 , 320-322 (1991), Nature, 35.
0 , 600-601 (1991)]. In addition, more recently, fullerene C ₆₀ has halogen (iodine and bromine).
It has also been found that the addition of Al provides a superconductor at even higher temperatures than in the case of alkali metals. In this way, fullerenes have great expectations as new materials and new materials in various fields of use including the electric and electronic fields, and therefore development of technology for mass production of high-purity materials as much as possible. Is desired.

By the way, it is known that these fullerenes are easily produced by arc discharge (resistance heating method) or laser ablation (laser evaporation method) of carbon such as graphite, but at that time, they are obtained. It is a soot-like substance containing a small amount of fullerenes. Therefore, a technology for separating (concentrating) and purifying the fullerenes from the soot-like substance is important. As a conventional technology for producing fullerenes including this separation / purification method, the soot-like substance obtained by the above-mentioned method is extracted and separated with an aromatic hydrocarbon such as benzene or toluene to obtain crude fullerenes. ,
A method of isolating and purifying this by chromatographic separation using a neutral alumina column or the like is known [Natur
e, 347 , 354-358 (1990)]. here,
Aromatic hydrocarbons are used for the extraction of fullerenes because the fullerenes are insoluble in most of the solvents but slightly soluble in the aromatic hydrocarbons.

However, it is difficult to obtain fullerenes of sufficiently high purity by simply extracting from the soot-like substance with an aromatic solvent, and with this simple aromatic extraction method, fullerenes of There is also a drawback that it is necessary to use a remarkably large amount of aromatic solvent due to its low solubility. Further, the purification method by column chromatography has a problem that it is not practical for the purpose of obtaining a large amount of purified product, although it can be easily applied to a small amount of purification. Therefore, it has been strongly desired to develop a practical purification method for efficiently obtaining a large amount of high-purity fullerenes from the above-mentioned soot-like substances and fullerene-containing substances such as crude fullerenes.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. The object of the present invention is, for example, from a fullerene-containing soot-like substance obtained by arc discharge of carbon such as graphite, laser ablation or the like, or a fullerene-containing substance such as a crude fullerene separated therefrom, having a sufficiently high purity. It is an object of the present invention to provide a method for purifying fullerenes, which is extremely useful in practice and is capable of efficiently recovering the desired fullerenes in large amounts.

[0007]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned object, the present inventors have found that fullerenes are only slightly dissolved in aromatic hydrocarbons such as benzene and toluene. As far as we know, it is not soluble in other solvents, but fully hydrogenated hydrogenated fullerenes are not only soluble in aromatic hydrocarbons but also in other hydrocarbon solvents such as cycloalkanes. I focused on doing. In addition, such hydrogenated fullerene is a fullerene-containing substance (fullerene-containing soot-like substance obtained from graphite or the like or a crude fullerene which is an aromatic hydrocarbon extract thereof) is an aromatic compound such as benzene or toluene. It can be efficiently obtained by dissolving and dispersing (dissolving and / or dispersing) in a compound and reacting with hydrogen gas using a suitable hydrogenation catalyst, and in that case, the aromatic compound used as a dispersing solvent also depends on conditions. Confirmed that hydrogenation can be performed on cycloalkanes and the like. In consideration of these considerations and facts, the present inventors once changed fullerenes, which have poor solubility and are difficult to be selectively extracted and separated as they are, to hydrogenated fullerenes by the above efficient catalytic hydrogenation reaction. If the solubility is improved, the hydrogenated fullerene can be selectively and efficiently dissolved in a more suitable solvent (for example, cycloalkanes which are hydrogenated products of the aromatic solvent used). The impurities in the raw materials and solid residues such as waste catalysts can be easily removed, and the fullerenes in the raw materials can be efficiently separated and purified as high-purity hydrogenated fullerenes. The idea was that if the hydrogenated fullerenes thus obtained were successfully dehydrogenated and returned to the original fullerenes, the desired high-purity fullerenes could be recovered in high yield.

In order to realize this idea, the inventors of the present invention have conducted various studies and as a result, have found that the above-mentioned fullerene-containing soot-like substances or fullerenes such as crude fullerenes obtained by extracting the fullerene-containing soot-like substances with aromatic hydrocarbons. Disperse (dissolve and / or disperse) a substance in a specific solvent (aromatic compound)
Then, after reacting with hydrogen gas in the presence of a suitable hydrogenation catalyst, impurities are removed together with the catalyst used, and the resulting hydrogenated fullerene is reacted with a suitable dehydrogenating agent to dehydrogenate. It has been found that the method is an excellent method for purifying fullerenes that satisfies the above object.

Based on the above findings and consideration, the present inventors have completed the present invention. That is, according to the present invention, a fullerene-containing raw material is dissolved and dispersed in an aromatic compound and then reacted with hydrogen gas in the presence of a hydrogenation catalyst, and then impurities are removed together with a waste catalyst to obtain the hydrogenated fullerene. The present invention provides a method for purifying fullerenes, which comprises dehydrogenating a compound by reacting it with a dehydrogenating agent.
In the method of the present invention, examples of the fullerene-containing raw material to be subjected to the hydrogenation reaction include fullerene-containing soot-like substance obtained by arc discharge of graphite, fullerene-containing fullerene obtained by laser ablation of graphite Of soot-containing substances such as fullerene-containing soot, crude fullerene powder extracted from these soot with an aromatic hydrocarbon solvent such as benzene and toluene, or a fullerene such as a fullerene-containing extract at that time. Examples include fullerene-containing materials of various purities and forms including solutions. These various fullerene-containing materials may be used alone or in combination of two or more.

The fullerenes contained in the fullerene-containing raw material include fullerenes having various carbon numbers, for example, fullerene C ₆₀ , fullerene C ₇₀ , fullerene C _{84 and the} like, and mixed fullerenes in any proportion thereof. Can be mentioned. The fullerenes in these raw materials can be recovered as individual high-purity fullerenes or as high-purity mixed fullerenes by the purification method of the present invention, depending on the composition of the fullerenes in the raw materials.

In the method of the present invention, the fullerene-containing raw material is dissolved and dispersed (dissolved and / or dispersed) in an aromatic compound and reacted with hydrogen gas in the presence of a hydrogenation catalyst.
By this hydrogenation reaction, the fullerenes in the raw material are converted into hydrogenated fullerenes.

At this time, the aromatic compound used for dissolving and dispersing the fullerene-containing raw material is usually an aromatic hydrocarbon such as benzene, toluene, xylene and mesitylene (a single compound or a mixture of two or more thereof). Are preferably used, but not limited thereto, and other aromatic compounds other than aromatic hydrocarbons can be used. Further, these aromatic hydrocarbons and other aromatic compounds may be used as a mixture with other solvents such as other hydrocarbon solvents within a range that does not impair the object of the present invention. A cycloalkane containing a group hydrocarbon as a main component, a mixture with an alkane, and the like may be preferably used. In any case, various aromatic compound solvents (dissolution dispersion medium) can be used as long as they do not inhibit the catalytic activity of the hydrogenation catalyst.

When a raw material already dissolved or dissolved in an aromatic hydrocarbon or aromatic compound solvent such as the above-mentioned extract is used as the fullerene-containing raw material, the above-mentioned aromatic compound is not necessarily used. It does not need to be dissolved and dispersed again and can be directly used for the hydrogenation reaction.

The hydrogenation catalyst is not particularly limited,
Various hydrogenation catalysts, such as those known or used as hydrogenation catalysts for hydrocarbons or proposed, can be used. Examples of such hydrogenation catalysts include Cr and F
e, Co, Ni, Mo, Ru, Rh, Pd, W, Re,
There are various forms of catalysts made of various metals including transition metals such as Os, Ir, Pt, and the like. Representative examples of these are, for example, Pt colloid, Raney nickel, Ranel ruthenium, Raney cobalt. Metallic catalysts such as metal colloids represented by etc., metal oxide catalysts represented by platinum black, palladium black, ruthenium black, rhodium black, rhenium black, chromium oxide, molybdenum oxide, molybdenum sulfide, rhenium sulfide, etc. And metal compound catalysts such as various metal complex catalysts, and various supported catalysts (for example, supported catalysts) obtained by supporting these metals or metal compounds on various carriers. Various things such as Pd / Carbon, Ru / Carbon, Nickel / Kieselguhr, Pd / Silica are mentioned. Among these, examples that can be particularly preferably used include Pd / carbon, Ru / carbon, etc. These hydrogenation catalysts may be used alone. Two
It is also possible to use them in combination by mixing or compounding two or more species.

As the hydrogen gas used in the hydrogenation reaction, not only pure ones but also various ones having various purities or grades such as those for various industrial uses can be used, and it can also be used as the hydrogen gas-containing gas. You can The hydrogenation reaction is usually room temperature to 300 ° C., preferably 50 to 300 ° C.
It is preferably carried out at a temperature in the range of 250 ° C. The reaction time is
Since it depends on other conditions such as temperature and hydrogen gas pressure, it cannot be uniformly set, but usually 10 minutes to 10 minutes.
Time is enough. The pressure of hydrogen gas in the hydrogenation reaction is not particularly limited, but in this hydrogenation reaction, the hydrogen gas partial pressure is usually atmospheric pressure or more, preferably 1
It is suitable to carry out under the condition of 0 to 200 kg / cm ² G. When the hydrogen gas pressure is less than atmospheric pressure, the reaction rate is slow and not practical. The preferable range of hydrogen gas pressure may vary depending on the type (carbon number) of fullerenes in the raw material. For example, the hydrogenation of fullerene C ₆₀ is 1
The hydrogenation of fullerene C ₇₀ is carried out efficiently even at a relatively low hydrogen gas pressure of 0 to 100 kg / cm ² G.
Usually, it is more efficiently performed at a relatively high pressure of hydrogen gas pressure of 20 kg / cm ² G or more. By making good use of such a difference in reactivity depending on the type (carbon number) of fullerenes, only a specific fullerene is selectively hydrogenated when the raw material contains two or more types of fullerenes. It is also possible, for example, fullerene C
_In the case of a raw material containing ₆₀ and fullerene C ₇₀ , fullerene C ₆₀ can be selectively converted into hydrogenated fullerenes by controlling reaction conditions such as hydrogen gas pressure.

As described above, fullerenes in raw materials (specific fullerenes in fullerenes in some cases)
Can be efficiently hydrogenated and converted into the corresponding hydrogenated fullerenes.

The hydrogenated fullerenes thus obtained generally have the same degree of hydrogenation (H / C) even if they have the same carbon number.
There are various hydrogenated fullerenes with different ratios. According to the above-mentioned catalytic hydrogenation method, for example, from fullerene C ₆₀ to C
It is possible to efficiently obtain hydrogenated fullerenes having a sufficiently high degree of hydrogenation, such as a mixture of hydrogenated fullerenes represented by ₆₀ H _n (n is an even number of about 36 to 44). On the other hand, from fullerene C ₇₀ , C ₇₀ H _m
(M is, for example, an even number of about 30 to 46.) It is possible to efficiently obtain hydrogenated fullerenes having a sufficiently high degree of hydrogenation, such as a mixture of hydrogenated fullerenes.

It is possible to selectively obtain hydrogenated fullerenes having a specific degree of hydrogenation by precisely controlling the reaction conditions of the hydrogenation reaction (for example, hydrogen gas pressure, reaction temperature, reaction time, etc.). It is much easier to obtain a mixture of hydrogenated fullerenes with a distribution in the degree of hydrogenation, and the yield is also likely to be large enough. For the purpose of the purification method of the present invention, even if there is a distribution in the degree of hydrogenation, there is no problem, and it is usually sufficient to use a mixture of hydrogenated fullerenes having different degrees of hydrogenation.

What range of hydrogenation degree is suitable for the hydrogenated fullerenes may be determined in consideration of the efficiency of the subsequent step of separating impurities and dehydrogenation step. Usually, for example, hydrogenation to a sufficiently high degree of hydrogenation may be sufficient to sufficiently improve the solubility in a solvent such as cyclohexane described below, while the efficiency of the dehydrogenation step such as saving the dehydrogenating agent may be improved. Considering the points, it is preferable not to increase the hydrogenation degree more than necessary. Considering such points and the efficiency of hydrogenation reaction, for example, for fullerene C ₆₀ , a method of preparing a mixture of hydrogenated fullerenes C ₆₀ H _n having _{n in} the range of 36 to 44 is preferable. On the other hand, in the case of hydrogenating fullerene C ₇₀ , a method of mainly using a mixture of hydrogenated fullerenes C ₇₀ H _m having _m in the range of about 30 to 46 is preferably adopted.

In some cases, aromatic compounds such as aromatic hydrocarbons used as a dispersion solvent in the hydrogenation reaction are hydrogenated together with fullerenes to give hydrogenated products of aromatic compounds such as cyclohexanes. The method of converting into Aromatic hydrogenated products such as cyclohexanes hydrogenated in this way directly serve as good solvents for the obtained hydrogenated fullerenes, while they are poor against impurities in raw materials, waste catalysts and unreacted fullerenes. This is because it becomes a solvent or an insoluble solvent and is suitable for selective separation of hydrogenated fullerenes.

In the method of the present invention, after carrying out the hydrogenation reaction, impurities and waste catalyst are removed from the reaction mixture (or the mixture obtained by subjecting the reaction mixture to an appropriate treatment). Removal of these impurities and waste catalyst can be carried out by various methods, but usually,
It is preferably carried out by a separation means by selective dissolution of hydrogenated fullerenes using a suitable solvent such as a cycloalkane-based solvent. One of the important points here is that the hydrogenated fullerenes having a sufficiently high degree of hydrogenation obtained in the hydrogenation reaction are not only the aromatic compounds used but also many other than the fullerenes in the raw material. It is also easily dissolved in the organic solvent (for example, hydrogenated product of aromatic compound such as cycloalkane). In addition, carbons other than fullerenes in the raw material (soot-like substances other than fullerenes) are generally less hydrogenated than fullerenes, and even if hydrogenated, they are much more soluble than hydrogenated fullerenes. It is also important that it is poor in solubility and does not substantially dissolve in many solvents such as cycloalkanes. Further, the catalyst used is also insoluble in the solvent in the case of a solid catalyst as it is, and even if a complex catalyst is used, it can be easily converted into an insoluble solid residue by decomposing it well. From such a point, the highly hydrogenated fullerenes obtained by the hydrogenation reaction,
By utilizing such high solubility, it is possible to selectively and efficiently separate impurities (insoluble soot in the raw material) and used catalyst (waste catalyst).

The solution of hydrogenated fullerenes and the insoluble components such as impurities and waste catalysts can be easily separated by various methods known in the art, for example, filtration, centrifugation and other precipitation methods. Of these, usually, a method such as filtration is preferably used. Of course, the insoluble matter separated by filtration is washed with a suitable washing solvent,
An ordinary method of collecting hydrogenated fullerenes remaining in the insoluble matter together with the filtrate is also suitably used.

As the appropriate separating solvent and washing solvent, a solvent (single solvent or mixed solvent) capable of selectively and sufficiently dissolving the obtained hydrogenated fullerenes is used. Include, for example, cyclohexane, methylcyclohexane, dimethylcyclohexane,
Cyclohexanes such as trimethylcyclohexane, or hydrogenated products of other aromatic hydrocarbons, further cyclopentanes, cycloalkanes such as cyclooctanes, etc., or a mixture thereof or a mixed solvent containing these as the main components. Are preferably used. Of these, cyclohexanes such as cyclohexane, methylcyclohexane, dimethylcyclohexane and trimethylcyclohexane are particularly preferably used. In addition, these solvents are
They may be used alone or in combination of two or more as a mixed solvent or the like.

By the way, such a separating solvent such as a cyclohexane-based solvent may be prepared and used separately, but as described above, the aromatic compound used in the hydrogenation reaction is the hydrogenation reaction. In this case, if hydrogenated with fullerenes as appropriate, hydrogenated fullerenes are automatically obtained in the form of being dissolved in a hydrogenated product of an aromatic compound such as cyclohexane, so in this case, it is not always necessary to separate it. The insoluble impurities and the waste catalyst can be easily removed by simply filtering the reaction mixture without using a solvent.

As described above, highly pure hydrogenated fullerenes from which impurities such as raw materials and impurities such as spent catalyst are sufficiently removed can be efficiently obtained in high yield (usually as a solution thereof). ..

In the method of the present invention, the hydrogenated fullerene thus obtained is reacted with a suitable dehydrogenating agent to dehydrogenate the hydrogenated fullerene to obtain a desired highly purified fullerene (for example, fullerene). A single compound such as C ₆₀ and fullerene C ₇₀ , or a mixture thereof is obtained.

This dehydrogenation reaction may be carried out as it is on the solution of the hydrogenated fullerenes obtained above, but usually, after the dehydrogenation reaction is changed to a suitable form (concentration, solvent, etc.), A method of subjecting to a dehydrogenation reaction is preferably adopted. For example, for hydrogenated fullerenes separated and recovered as a solution of a cyclohexane solvent, the solvent is evaporated to sufficiently concentrate the solution, and then an aromatic hydrocarbon solvent such as benzene, toluene and xylene is added, A method in which an aromatic hydrocarbon solution of hydrogenated fullerenes is used and then this is subjected to the dehydrogenation reaction can also be suitably adopted.

As the dehydrogenating agent, any one can be used as long as it can dehydrogenate hydrogenated fullerenes to fullerenes, but usually, the efficiency for this dehydrogenation reaction is It is preferable to select in consideration of (reactivity or activity, selectivity, etc.).

There are various dehydrogenating agents, such as stoichiometric, repetitive, catalytic, and combinations thereof, and according to other classifications, for example, hydrogen. There are various types such as a receptive type, an oxidative dehydrogenation type, a simple dehydrogenation type, and a combination type thereof, and any of them can be used.

Specific examples of the dehydrogenating agent which is usually preferably used include, for example, organic dehydrogenating agents such as 2,3-dichloro-5,6-dicyano-1,4-benzoquinone, lead tetraacetate and acetic acid. Inorganic dehydrogenating agent such as mercury (II), platinum catalyst,
Dehydrogenation active catalysts such as metal catalysts such as palladium catalysts,
Further, a combination of such a catalyst having a dehydrogenation function and a suitable hydrogen acceptor can be mentioned. These dehydrogenating agents may be used alone or in combination of two or more. The amount of the dehydrogenating agent used varies depending on the type of the dehydrogenating agent and also depends on other conditions such as the degree of hydrogenation of the hydrogenated fullerenes to be dehydrogenated and the reaction temperature, so it cannot be expressed uniformly. Use can be easily determined by preliminary experiments, calculations and the like.

This dehydrogenation reaction can be carried out in various solvents that do not hinder the dehydrogenation reaction. For example, cyclohexanes such as hydrogenated products of aromatic compounds used in the hydrogenation reaction, benzene, Aromatic hydrocarbons such as toluene and xylene, etc., and further various kinds of single or mixed solvents such as mixed solvents of cyclohexanes and aromatic hydrocarbons can be used. Of these, aromatic hydrocarbon solvents such as benzene, toluene and xylene, or mixed solvents containing these as the main components are preferably used from the viewpoint of the efficiency of the dehydrogenation reaction. Such aromatic hydrocarbons are
It has the advantages of increasing the contact efficiency of the reaction and not being dehydrogenated by a dehydrogenating agent, and is also suitable for the subsequent separation and recovery of fullerenes.

The reaction temperature of the dehydrogenation reaction is usually room temperature to 300 ° C., preferably 50 to 250 ° C. At that time, a method of controlling the reaction temperature by refluxing the solvent is also suitably adopted. If the temperature is lower than room temperature, the reaction generally proceeds slowly or requires cooling, which is disadvantageous in terms of process. On the other hand, if the temperature exceeds 300 ° C., it is difficult to control the reaction because side reactions occur simultaneously. It is easy to cause problems such as. The reaction time varies depending on other conditions such as the reaction temperature and the type of dehydrogenating agent, but is usually 10 minutes to 10 hours.

As described above, a reaction mixture (solution, or in some cases, containing high-purity fullerenes)
A dissolved dispersion, etc.) can be obtained. Separation and recovery of desired fullerenes from the reaction mixture thus obtained can be easily achieved by various methods such as known separation methods.

For example, when a sufficient amount of aromatic hydrocarbon is used as a solvent for dehydrogenation and the fullerenes, the dehydrogenating agent and the decomposition products thereof are also dissolved, the solution as it is,
Alternatively, the dehydrogenating agent and its decomposed product are washed with water and transferred to an aqueous phase, or when these are solids, they are separated by filtration and the like, and then the solution is appropriately concentrated to give fullerene having the lowest solubility. A method of selectively precipitating the compounds and separating them by, for example, filtration, or a method of separating the fullerene as its evaporation residue by sufficiently distilling off low boiling substances such as solvents is preferable. However, the present invention is not limited to these, and various methods can be used.

On the other hand, when the solvent for dehydrogenation used has low solubility only in fullerenes, for example, directly from the reaction mixture or after appropriate concentration, the dehydrogenating agent and its decomposition may be used as necessary. A method in which a desired fullerene precipitate is separated by, for example, filtration after the material is removed by washing with water is also preferably used. The fullerenes thus separated are, if necessary, washed with a suitable solvent, extracted, recrystallized, or subjected to a further purification separation operation to recover higher fullerenes. You can also

In the separation and recovery step after the dehydrogenation, even when the raw material used for the hydrogenation reaction contains impurities having higher solubility than fullerenes, these are selectively removed. It should be noted that it can be done. That is, according to the purification method of the present invention, first, the desired fullerenes are converted into highly soluble hydrogenated fullerenes by the hydrogenation reaction step of the fullerene-containing raw material, so that a high-purity hydrogenation from the reaction mixture is performed. Separation and recovery of fullerenes as a solution becomes extremely easy, and at that time, all impurities with lower solubility than hydrogenated fullerenes (for example, soot-like carbon other than the desired fullerenes in the raw material, waste catalyst, etc.) are efficiently treated. In addition to the dehydrogenating agent and its decomposition products used in the separation process of the fullerenes returned by the dehydrogenation reaction, all impurities that are more soluble than the fullerenes are removed. Therefore, as a result, it is possible to efficiently obtain a desired fullerene having extremely high purity. Further, when the raw materials contain different fullerenes such as fullerene C ₆₀ and fullerene C _70, only the desired fullerenes (eg, fullerene C ₆₀ ) are selectively soluble by controlling the reaction conditions. Since it is possible to change to a good hydrogenated fullerene, unnecessary fullerenes (for example, fullerenes other than fullerene C ₆₀ such as fullerene C ₇₀ ) can be easily separated by utilizing their low solubility. You can
As a result, only desired fullerenes (for example, fullerene C ₆₀ ) can be efficiently recovered in high purity.

By the above-described purification method of the present invention, it is possible to recover a desired high-purity fullerene from a raw material containing a fullerene containing impurities in a high yield. In addition, the method of the present invention does not necessarily require column chromatographic separation, which is a poorly productive separation / purification method, to have extremely high-purity fullerenes (fullerene C ₆₀ , fullerene C _70, etc.), or a mixture thereof. Since it is possible to obtain a solution or the like), it is suitable for mass production and is an extremely advantageous method in practical use.

The fullerenes obtained by the method of the present invention can be suitably used in the field of electric / electronic materials, for example, as various conductive materials, superconductive materials, etc. It can be suitably used for various applications such as a type of lubricating member (lubricating oil additive, solid lubricant, etc.).

[0039]

The present invention will be described in more detail below with reference to examples of the present invention, but the present invention is not limited to these examples. Example 1 A soot-like substance obtained by arc discharge of graphite was used as a fullerene-containing raw material.
g was extracted with 800 ml of toluene using a Soxhlet extractor to obtain an extract. The whole amount of the obtained extract was concentrated by removing 1 part of toluene to give a solution of 500 ml, and the whole amount of the solution was evacuated inside together with 5.00 g of 5% ruthenium / carbon (50% wet) which was a hydrogenation catalyst. I put it in the autoclave. Hydrogen gas was introduced into the autoclave at a hydrogen pressure of 70 Kg / cm ² (absolute pressure: the same applies hereinafter), and the temperature rise was started. The pressure starts to drop when the temperature rises to about 50 ° C and 10 kg / cm.
Hydrogen gas was newly added when the pressure dropped below ² . When this operation was repeated several times, the pressure drop of hydrogen disappeared, and the internal temperature had risen to 180 ° C. at that time. At this time, the reaction was carried out for 2 hours while maintaining the hydrogen pressure at 80 Kg / cm ² and the temperature at 180 ° C. After the obtained reaction mixture is cooled, it is filtered to separate the waste catalyst and solid matter such as solid matter adhered thereto by filtration, and then the solid matter (filter residue) is washed several times with a small amount of solvent (methylcyclohexane). After washing, the washing solution was transferred to the filtrate. The filtrate thus obtained was concentrated to sufficiently remove the solvent, and then the concentrate was dissolved in 800 ml of toluene. Then, this solution was added with a few dehydrogenating agents.
-Dichloro-5,6-dicyano-1,4-benzoquinone (7.0 g) was added and reacted under reflux for 5 hours. After completion of the reaction, an appropriate amount of water was added to the reaction mixture and the mixture was washed with water, and the aqueous layer was separated and removed from the organic layer (toluene layer).
The solvent (toluene or the like) was distilled off from the recovered toluene layer to obtain a desired purified product (yield 0.65 g).

A part of this purified product was dissolved in toluene and mass spectrum analysis was performed. As a result, in addition to toluene as a solvent, a peak based on C ₆₀ (that is, fullerene C ₆₀ ) [M ⁺ = 720 ( ¹² C ₆₀ ), M ⁺ +1 = 721 ( ¹² C
₅₉ ¹³ C ₁ ), M ⁺ + 2 = 722 ( ¹² C ₅₈ ¹³ C ₂ ), M ²⁺
= 360 etc.] was observed. Further, as a result of dissolving a part of the purified product in deuterated benzene and performing ¹³ C-NMR analysis, only a peak of 143 ppm peculiar to fullerene C ₆₀ was observed. From these results, it was confirmed that the purified product was almost pure fullerene C ₆₀ .

Example 2 10 g of soot-like substance obtained by arc discharge of graphite, which is the same fullerene-containing raw material as that used in Example 1, was directly used in 500 ml without extraction treatment.
Was carried out in the same manner as in Example 1 except that this was dispersed in toluene and subjected to hydrogenation reaction.
54 g was obtained.

When this purified product was subjected to mass spectrum analysis and ¹³ C-NMR analysis in the same manner as in Example 1, the same results as in Example 1 were obtained, and the purified product was almost pure fullerene C _60. Was confirmed.

Comparative Example 1 1 g of soot-like substance obtained by arc discharge of graphite, which is the same fullerene-containing raw material as used in Example 1, was subjected to extraction treatment with toluene in the same manner as in Example 1 to obtain an extract. Obtained. The extract was concentrated to 100 ml, column chromatographic separation was performed using neutral alumina as a separating agent and a 5% toluene / hexane mixed solution as a developing solvent, and a fraction corresponding to fullerene C ₆₀ was collected. The solvent was distilled off from this separated liquid to obtain a purified product. The purified product had the same mass spectrum and ¹³ C- as the purified product obtained in Example 1.
NMR results were given and confirmed to be almost pure fullerene C ₆₀ . The yield was 0.072 g.

The amount of neutral alumina used in the above column chromatography separation was 500 g, and the amount of developing solvent used was about 2
It was 0, and the development time was about 20 hours. As described above, in the case of the conventional purification method by column chromatography separation, a large amount of separating agent and developing solvent are required even for a small amount of purification, and the operation time is long. It was confirmed that it is unsuitable for mass production and industrially disadvantageous.

On the other hand, as can be easily understood from the above Examples 1 and 2, the purification method of the present invention enables hydrogenation reaction and dehydrogenation which can be carried out in a large amount and can be easily carried out industrially. High-purity fullerenes can be obtained in high yield by utilizing the reaction and the usual separation method, and therefore, their industrial value is remarkably large as compared with the conventional methods.

[0046]

According to the method of the present invention, soot-like substances containing fullerenes obtained by arc discharge of carbon such as graphite, laser ablation, etc., and impurities such as powders and solutions of crude fullerenes separated therefrom By converting a desired fullerene in the raw material into a highly soluble hydrogenated fullerene by subjecting a raw material containing a fullerene and a fullerene to a catalytic hydrogenation reaction, impurities and waste catalysts are removed, and then obtained. Since a specific method of dehydrogenating the hydrogenated fullerenes thus obtained to return them to the original fullerenes, the desired fullerenes can be efficiently separated as a solution of highly pure hydrogenated fullerenes. At that time, not only the waste catalyst but also the impurities such as impurities in the raw material having a lower solubility than the hydrogenated fullerene can be efficiently separated. Moreover, when separating and recovering fullerenes that have been restored by dehydrogenation, not only the dehydrogenating agent used and its decomposition products, but also impurities that are more soluble than the fullerenes (such as those in the raw materials) It can be efficiently removed, and thus high-purity desired fullerenes can be recovered in high yield from the above-mentioned various fullerene-containing raw materials.

Further, the method of the present invention comprises industrially easy steps such as catalytic hydrogenation reaction with hydrogen gas, dehydrogenation reaction and separation operation using a usual solvent. Since it can be purified to high-purity fullerenes without using it, it also has practical advantages such as easy mass production.

That is, according to the present invention, for example, fullerene-containing soot-like substances obtained by arc discharge of carbon such as graphite, laser ablation, etc. and fullerene-containing substances such as crude fullerenes separated therefrom are obtained. It is possible to provide a method for purifying fullerenes, which is extremely useful in practice and is capable of efficiently recovering a desired fullerene of sufficiently high purity in a large amount.

Claims (1)

[Claims] 1. A hydrogenated fullerene obtained by dissolving and dispersing a fullerene-containing raw material in an aromatic compound and then reacting it with hydrogen gas in the presence of a hydrogenation catalyst, and then removing impurities together with a waste catalyst. A method for purifying fullerenes, which comprises dehydrogenating by reacting hydrogen peroxide with a dehydrogenating agent.