SUPERCRITICAL-FLUID EXTRACTION OF FULLERENES C-60 AND C-70 FROM CARBON SOOT

A new branch of organic chemistry has begun to emerge following the de velopment of a carbon-arc electric discharge process by Kratschmer et al. which produced a carbon soot containing a series of caged buckmins terfullerene C60,C70, and higher homologues. While these compounds are normally recovered either by sublimation in an inert atmosphere or by extraction with benzene, toluene, or a higher boiling aromatic, enhan ced selectivity can be achieved by operating at supercritical conditio ns. The ability of supercritical fluid solvents to fractionate the ext ractable material of the carbon soot by pressure and/or temperature tu ning of the solvent power appears to be possible due to the significan t molecular weight and size difference between C60 and C70 which yield different threshold solubility densities. While CO2 is unable to extr act any fullerenes, selective extraction of C60 is obtained when using a nonaromatic modifier such as cyclopentane. Quantitative recoveries are achieved by employing moderate concentrations of an aromatic solve nt modifier such as toluene at pressures imparting solvent densities g reater than 0.8 g/cm3.