(267e) Increasing the Yield of High-Value, Liquid-Crystalline-Forming Pyrene Pitch Oligomers

Carbonaceous pitch, an underutilized byproduct of fossil-fuel processing, is comprised primarily of polycyclic aromatic hydrocarbons (PAHs). These high-carbon materials are of great interest in the aerospace, automotive, and construction industries. Pitch itself can be derived from both coal tar and petroleum processing; however, both pitches are difficult to characterize and thus most effectively utilize. The molecular composition of fossil-fuel-derived pitch is broad and consists of hundreds of different compounds. Nevertheless, pitches are still useful for the synthesis of advanced carbon materials. Their char yields have been shown to have a direct correlation to many of the mechanical properties of the pitch-based advanced carbon materials. Previous workers (including the recently deceased pioneer giant of synthetic pitches, Isao Mochida) have oligomerized naphthalene and anthracene to create model pitches. Although these compounds, and in particular naphthalene pitches, have excellent properties for materials application, they fragment easily during synthesis and thus also have broad molecular weight distributions.

Our research has focused primarily on pitches derived from pyrene, a relatively new model pitch that recent work from Chen et al. 2020 shows as an excellent analogy to petroleum pitch systems. Pyrene addresses many of the problems from other model pitches because it essentially does not fragment; thus, it has a narrow molecular weight distribution. However, controlling the degree of oligomerization of pyrene pitches is of significant interest because of its impact on the mesophase content (i.e., liquid crystallinity) of these pitches. This work explores utilizing a new reagent (to be presented) for increasing the degree of oligomerization of pyrene-derived pitches. In this study, reaction conditions are held constant to allow direct comparison between pitch derived via this new reagent and that derived via the existing technique. We have observed that pyrene pitches synthesized from this new reagent have a softening point and char yield over twice that of standard pyrene-derived pitch, with similar increases in composition increases of the liquid-crystalline trimer.

We also explored the effects of the reaction conditions (reaction time, pressure, and temperature) on the kinetics of the Scholl reaction – and thus the properties of the derived pitch. By using a combination of supercritical extraction (SCE) and gel permeation chromatography (GPC), oligomeric compositions of each of the synthesized pyrene pitches are being obtained. Another encouraging result is that the new synthesis technique requires less than a quarter of the time to produce the desired product. In summary, our new reagent allows us to synthesize a pyrene pitch that is a more useful model for the development of advanced carbon materials where softening point, char yield, and liquid crystallinity are all of primary importance.