Separation of fullerenes C₆₀ and C₇₀ using a crystallization‐based process

A crystallization‐based process that separates pure fullerenes C 60 and C 70 from their mixture using o‐xylene as the solvent has been developed. Isothermal solid–liquid equilibrium phase diagrams of the C 60 ‐C 70 ‐o‐xylene ternary system for a number of temperatures were first determined at 1 atm. Taking advantage of the shift in solvent‐free composition of the C 60 ‐C 70 double saturation point with temperature and based on the solid solution‐forming phase behavior between C 60 and C 70 , the flowsheet of a general crystallization process was then synthesized. It involved the fractionation of a C 60 ‐C 70 fullerene mixture into C 60 ‐rich and C 70 ‐rich solid solutions using temperature‐swing crystallization, followed by purification of the solid solutions with multistage crystallization into pure C 60 and C 70 solids. To demonstrate process feasibility, bench‐scale batch experiments were performed using a commercially available fullerene mixture that was pretreated by adsorption to remove higher fullerenes. C 60 and C 70 solids of purity higher than 99 wt % were obtained.