C60, C60O, C70 and C70O fullerene formations in premixed benzene-oxygen flames

The use of hydrocarbons for fullerenes synthesis has been described in the literature. In this study, the formation of fullerenes C₆₀, C₆₀O, C₇₀, and C₇₀O is investigated in premixed benzene-oxygen flames operated under a pressure of 7.5 kPa by systematically varying two physicochemical parameters: the initial velocity of the fresh gas mixture (at 298 K) at the burner, which is varied between 40 and 50 cm s⁻¹, and the atomic C/O ratio, which is varied from 0.7 to 1.15. The objective of running each flame at different sets of conditions is to assess the sensitivity of reaching an optimum in the process of fullerenes production in flames.

A higher production rate of fullerenes C_n under different conditions is achieved at an optimal level of C/O ratio of 1.05 and 45 cm s⁻¹ of gas velocity. In addition, the highest production rate of fullerenes is 786.7 mg/h, and the highest yield of carbon transformed to fullerenes, obtained is 0.22%. Flame synthesis of fullerenes would seem to offer potential for large-scale production. Different patterns for the production of fullerene and fullerenes oxide are obtained. This result seems to challenge the notion of complexity of the combustion, which accompanies the formation of these carbon molecules in flames. The mass spectrometer shows that heavy fullerenes containing more than 150 atoms are present in the production process. Peaks of PAH at m/e smaller than 500 amu suggest that the reaction of combining the polycyclic aromatic hydrocarbons in burned gases may play an important role in the formation of fullerenes in burned gas flames.