Eutectic phase behavior and char yields for the pyrene dimer/trimer system

: Although considerable research has been devoted to converting petroleum and coal-tar pitches to advanced carbons, the relationship between molecular structure and the bulk properties of pitches remains ill-defined. We therefore propose a well-defined, binary system of pyrene dimer (which is isotropic) and pyrene trimer (mesogenic) to serve as a model for petroleum pitch. The effect of pyrene dimer/trimer composition on two key bulk properties of petroleum pitches, namely char yield and softening-point temperature, were investigated. For char yield, rule of mixtures was valid across the entire composition range, with the overall yield being a mass-weighted average of the two components. Thus, no interactions between the dimer and trimer species were observed as part of the carbonization process. With respect to softening points, the temperature vs composition phase diagram exhibited a eutectic at 23 mol % trimer and a temperature of 146 °C, a temperature well below the softening points for either the pure dimer or trimer. Such a large softening/melting-point depression is consistent with the isomeric nature of the dimer and trimer, as the melting-point depression for multicomponent mixtures is much larger than that predicted for a true binary. Thus, our model system exhibits softening-point behavior analogous to that observed for petroleum pitches, which are highly disperse.