DE4129718A1 - Fullerene prodn. - by evaporating and condensing carbon@ at 0.05-0.5 bar in oxygen-contg. gas extracting with solvent - Google Patents

Abstract

Prodn. of a C60/C70 mixt. (fullerene) (I), comprises evaporating carbon at 0.05-0.5 bar, condensing the vapour on a cool surface to give a mixt. of (I) and carbon black, and extracting (I) with organic solvent. Evapn. and condensation are preformed in an oxygen-contg. gas i.e. CO, CO2, oxygen or a mixt. thereof, opt. with addn. of inert gas. USE/ADVANTAGE - The above gases are much cheaper than He which is normally used and their use enables a much higher evapn. rate from carbon electrodes for the same current density. (I) is useful as a starting material for new syntheses and materials. In an example, the process was performed in a metal vessel fitted with an EK 78 graphite (RTM) rod as cathode and an EK 86 graphite (RTM) rod as anode 2 mm. apart. The vessel was evacuated to 10 power (-5) bar, and then CO was passed through the system at 0.5 l/hr. at a constant pressure of 0.2 bar, while an arc was produced between the electrodes with I = 120 A (43 V) and maintained at 1-10 mm. by advancing the evaporating anode. The anode lost 104 mm. in 8.8 mins., corresp. to 5.93 g. graphite, and 4.33 g. carbon/fullerene mixt. (II) was collected from the water-cooled walls of the reactor, this mixt. contained 7.1% crude (I) as determined by exhaustive extn. with toluene and drying at 150 deg.C. With He instead of CO, the anode lost 105 mm. (6.53 g.) in 15 mins., and the yield was 3.28 g. (II) contg. 7.4 g. (I)

Description

The invention relates to a method for producing a fullerene called C ₆₀ / C ₇₀ mixture by vaporization of carbon.

Fullerene are carbon cage molecules of the formula C ₆₀ , C ₇₀ , C ₈₄ and others. The prototype C _{60 was} given the name Buckminsterfulleren. The fullerenes are sublimable solids and are soluble in organic solvents to a limited extent to strongly red / brown colored solutions; they are clearly characterized by mass, NMR, IR, UV / Vis and X-ray spectra.

The C ₆₀ / C ₇₀ mixture (approx. 15 mol% of C ₇₀ in the mixture) was only produced in tangible quantities in 1990 and isolated as a solid substance (W. Kratschmer et al. "Solid C ₆₀ : a new form of carbon ", Nature, Vol. 347 (1990), 354-358). Since then, a large number of publications have appeared on the production, cleaning and properties of fullerenes, which serve as the starting point for new classes of synthesis and substances (RM Baum, "Research on Buckminsterfullerene continues to proliferate", Chem. And Eng. News, 10. June 1991, pp. 31-33).

Fullerenes are formed by rapid cooling from carbon vapor. According to RE Haufler et al., J. Phys. Chem. 94 (1990), 8634-6 an arc with high current density is generated in a closed vessel with cooled walls between 2 carbon (graphite) electrodes; alternatively, according to H. Ajie et al., J. Phys. Chem. 94 (1990) 8630-3 a thin graphite rod heated very high by resistance heating. The carbon vapor formed cools rapidly in the surrounding helium atmosphere (pressure 0.067-0.30 bar) and forms a C ₆₀ / C ₇₀ mixture, the rest being soot; both components deposit as a coating on the vessel wall. After cooling, the deposit is removed mechanically and extracted with benzene or toluene. From the dark red colored solution 1-15% crude fullerene (C ₆₀ / C ₇₀ - mixture with a small amount of solvent) is obtained as a black solid by evaporation.

In all known processes, the C ₆₀ / C ₇₀ mixture is formed in the presence of helium or argon. No other gases are mentioned anywhere.

In contrast, it is an object of the invention, a manufacturer drive to indicate that on the use of expensive helium waived.

It has been found that fullerenes form in the arc in comparable yield if CO, CO ₂ or O _{2 form} the gas atmosphere of the reaction vessel instead of helium. An advantage of using these oxygen-containing gases is further that the evaporation rate of the graphite electrodes is greatly increased at the same current density.

In particular, the process for the preparation of a full C ₆₀ / C ₇₀ mixture by vaporization of carbon at pressures of 0.05 to 0.5 bar, condensation of the gaseous carbon in cooled zones to form a fullerene / carbon black mixture and extraction of the fullerene from this mixture with organic solvents according to the inven tion now characterized in that the evaporation and condensation in oxygen-containing gases from the group Koh lenmonoxid (CO), carbon dioxide (CO ₂ ), oxygen (O ₂ ) or mixtures thereof becomes.

According to the invention, it is also possible to use evaporation and Condensation of carbon in a mixture or several of the above-mentioned oxygen-containing gases with noble gases perform.

Example 1 (CO)

In an evacuable metal container with a sight glass of 150 mm inner diameter and 170 mm inner height with water-cooled walls, an 8 mm diameter rod made of graphite EK 78 (Ringsdorff) as the cathode and a rod with 6 mm diameter made of graphite EK 86 ( Ringsdorff) arranged as an anode. Both electrodes are provided with external power leads; the power supply to the anode is axially displaceable to compensate for the anode consumption. The container is evacuated to 10 ^-5 bar and filled with CO to 0.2 bar; During the arc operation, the pressure is kept constant at 0.20 bar by means of a pressure regulator at a flow of 0.5 l CO / h. The electrode gap is brought to approx. 2 mm; an arc is then ignited and regulated to I = 120 A (U = 43 V). The anode evaporates quickly and is adjusted accordingly so that the length of the arc remains in the range 1-10 mm. After 8.8 minutes, 104 mm of the anode rod corresponding to 5.93 g of graphite evaporated; the power is turned off. After cooling, 4.33 g are isolated from the soot / fullerene mixture deposited on the cooled surfaces and therein the content of crude fullerene (C ₆₀ / C ₇₀ mixture) by exhaustive extraction with toluene, evaporation of the solvent and drying determined at 150 ° C to 7.1%.

Example 2 (comparative example with helium)

With the same application as in Example 1, helium is used le used by CO. Pressure: 0.2 bar; Flow: 0.44 l He / l; Current: 142 A; Voltage: 33.5 V; Duration: 15 min; Anode Consumption: 105 mm corresponds to 6.53 g. There will be 3.28 g of soot / fullness Ren mixture with 7.4% crude fullerene obtained.

Example 3 (CO ₂ )

With the same arrangement as in Example 1, the container is filled with 0.11 bar of CO ₂ and the pressure is set to 0.20 bar during the experiment. With an arc current of 85 A (voltage 37 V), the evaporation of the anode rod is carried out for 15 minutes. Despite a considerably reduced current compared to example 2, the anode consumption is 110 mm / 6.89 g. 8.5% of crude fullerene are obtained from 2.90 g of the soot deposited on the container wall.

Example 4 (O ₂ )

With the same arrangement as in Example 1, the container is filled with 0.10 bar O ₂ and sealed. During arc operation, a pressure of 0.41 bar is set, which drops to 0.185 bar after cooling and temperature compensation. At a current of 80 A (voltage 40 V), 110 mm / 6.80 g are evaporated from the anode in 17 minutes. 6.9% crude fullerene are obtained from 4.41 g of the deposited carbon black. The pressure increase from 0.10 to 0.185 bar shows that 85% of the O _{2 introduced are converted} to CO.

Claims (2)

1. Process for the preparation of a fullerene called C ₆₀ / C ₇₀ mixture by vaporization of carbon at pressures from 0.05 to 0.5 bar, condensation of the gaseous carbon in cooled zones to form a fullerene / carbon black mixture and extraction of the Fullerene from this mixture with organic solvents, characterized in that the evaporation and condensation is carried out in oxygen-containing gases from the group CO, CO ₂ , O ₂ or mixtures thereof. 2. The method according to claim 1, characterized in that the evaporation and condensation in a mixture of one or more of the oxygen-containing gases mentioned Noble gases is carried out.