PRODUCTION OF C-60 AND C-70 FULLERENES IN BENZENE OXYGEN FLAMES

Fullerenes C60 and C70 were produced in varying amounts in premixed laminar benzene/oxygen/argon flames operated under ranges of conditions including pressures of 12-100 Torr and C/O ratios from 0.717 to 1.072, the critical value for soot formation being 0.760. The fullerenes were identified in toluene extracts of condensed flame material including soot, using high-performance liquid chromatography (HPLC) with diode-array spectrophotometric detection, mass spectrometry, and infrared spectrophotometry. The yields of C60 and C70 and the C70/C60 ratio depend on temperature, pressure, carbon/oxygen ratio, and residence time in the flame. In the sooting flames, C60 and C70 first appear well after the onset of soot formation. The mass of C60 + C70 produced is in the range 0.0026-9.2% of the soot, compared to 1-14% from the conventional graphite vaporization method, and the largest C60 + C70 yield is 0.26% of the fuel carbon, observed at a pressure of 20 Torr . A C60 + C70 yield of 2 x 10(-4)% of the fuel carbon was found in a nonsooting flame. The largest rate of production of C60 + C70 WaS observed in a sooting flame at a pressure of 100 Torr. The C70/C60 molar ratio varied over the range 0.26-5.7, compared to 0.02-0.18 for the graphite vaporization method, and can be controlled by selection of flame conditions. Depending on flame conditions, the C60 + C70 fullerenes were produced with varying amounts of polycyclic aromatic hydrocarbons (PAH). The mass ratio of PAH to C60 + C70 varies roughly from 0.01 to 100 over the range of conditions studied. Also, the C60 + C70 fullerenes are accompanied by metastable C60 and C70 isomers as well as C60O, C70O, C76, C84, C90 and C94, the identification of which by liquid chromatography/mass spectrometry is described elsewhere.