Fullerene reactor

Bora- and further heterofuUerenes (C Si, C Ge) may be produced, among others, by arc discharge methods. To this end, suitably impregnated rods of graphite are employed in typical fullerene reactors. For the preparation of phosphafuUerenes, the simultaneous vaporization of carbon and phosphorus in a radio frequency oven proved its worth. The vaporization of both elements at different positions in the oven, corresponding to different temperatures, was found to be crucial in this... 

MWCNT grows only inside the cathode deposit and does not exist in other places in the reactor. Quantity of MWCNT obtained depends on the pressure of He atmosphere in the reactor, which is the most important parameter. The highest quantity of MWCNT is obtained when the pressure of He is ca. 500 Torr. When this value becomes below 100 Torr, almost no MWCNT grow. This contrasts to that the highest quantity of fullerene is obtained when the pressure becomes 100 Torr or less. 

Continuous production of fullerenes was possible by pyrolysis of acetylene vapor in a radio-frequency induction heated cylinder of glassy polymeric carbon having multiple holes through which the gas mixture passes [44]. Fullerene production is seen at temperatures not exceeding 1500 K. The yield of fullerenes, however, generated by this method is less than 1%. A more efficient synthesis (up to 4.1% yield) was carried out in an inductively coupled radio-frequency thermal plasma reactor [45]. 

Fig. 4 Arc discharge reactor for the production of fullerenes. (Reprinted with permission from [25])...

A 70-ml stainless steel reactor was charged with C ) fullerene (50 mg), 20 ml of 1,2,4-trichlorobenzene, and perfluoro(3-oxo-penta-4-ene)sulfonyl fluoride (3 g) and cooled to 50°C and then evacuated and filled with nitrogen and the mixture heated to 200°C for 18 hours. The solvent was then removed and the product isolated as a brown solid. 

All samples were obtained in the setup for fullerene synthesis by the technique described earlier [4-5], Novelty of this technique was that materials were produced in plasma-chemical reactor without air access and they shifted to the chamber for the sample investigation, see Fig. 1. 

Any kind of carbon, such as natural graphite, petroleum coke, carbon black, carbon fiber, exfoliated graphite, natural or synthetic graphite and fullerenes can be fluorinated under controlled conditions. Each carbon has unique crystalline properties. To achieve a desired degree of fluorination — or carbon fluorine ratio — numerous experiments are conducted in specialized TGFA reactors to determine the operating conditions such as fluorination temperature, fluorine flow rate, and fluorination duration. 

Figure 6.20. Cross-section schematics of reactors used for fullerene synthesis. Shown are (a) a reduced-pressure fuel-rich pyrolytic chamber, and (b) a benchtop modified arc evaporation system. Reproduced with permission from (a) Hebgen, R Goel, A. Howard, J. B. Rainey, L. C. Vander Sande, J. B. Proc. Combust. Inst 2000,28,1397, Copyright 2000 Elsevier, and (b) Scrivens, W. A. Tour, J. A. J. Org. Chem. 1992,57, 6932. Copyright 1992 American Chemical Society.

We conclude this chapter with a few brief notes about the availability of fullerenes for research applications. The Budty bibliography database, described in the introduction, lists several commercial suppliers of fullerenes. As of this writing, the quoted price is around 250 per gram of purified Ceo- There are also several detailed descriptions of the construction and operation of fullerene soot reactors and solvent-reflux purification systems in the literature.[Ko91, Kh92]. 

Ko91 A. S. Koch, K. C. Khemani and F. Wudl, Preparation of Fullerenes with a Simple Benchtop Reactor, J. Org. Chem. 56, 4543-4545 (1991). Sa93... 

Krestinin AV, Moravsky AP. Mechanism of fullerene synthesis in the arc reactor. Chem. Phys. Lett. 1998, 286. 479. 

The arc-method uses the same procedure as successfully employed to produce empty fullerenes (refer to Section 2.3.3), with the sole difference that the anodes of graphite evaporated in a classical arc-apparatus are impregnated with metal oxides or carbides. (In the graphitic rods treated with metal oxides, the respective carbides will be generated, too, when heated to >1600 °C.) Besides empty species, the soot deposited on the cooler reactor walls contains various metaUofuUerenes. 

---