(235d) Simultaneous Separation of Fullerene C60 and C70 Solids Using a Crystallization-Based Process

The unique properties of fullerenes and their derivatives have inspired extensive research on their potential applications. However, the high cost of pure fullerenes hinders further development of such applications into products. While mixed fullerenes can be bought at US$ 4 per gram, C₆₀ and C₇₀ solids of 99% or higher purity cost several hundreds US dollars. This situation is attributed to the lack of an economical technique to separate the fullerene mixtures. Chromatography, the conventional method for fullerene isolation, suffers from the drawback of low product throughput and high capital cost arising from the requirement of large amounts of stationary and mobile phases. Crystallization, on the other hand, because of its ease to be scaled up, is a cost-effective alternative. Although previous studies had shown the capability of crystallization to separate fullerene C₆₀ and C₇₀, these works were only carried out on a trial-and-error basis in bench-scale and no account was given on the principle of separation. It is thus unclear how the process can be scaled up for the mass production of pure fullerenes.

This work presents a crystallization-based process that can simultaneously produce pure fullerene C₆₀ and C₇₀ solids in a pilot scale using o-xylene as the solvent. We began by examining the solid-liquid phase behavior of the ternary system C₆₀-C₇₀-o-xylene and measured its solid-liquid equilibrium phase diagram at several temperatures. Based on this scientific information, the flowsheet of a crystallization process was then synthesized to separate a C₆₀-C₇₀ fullerene mixture by temperature swing. To verify the practicability of the process, pilot-scale experiments were performed according to the generated flowsheet to separate a commercially available fullerene mixture. C₆₀ and C₇₀ solids of purity higher than 98% were finally obtained.