Effect of Fuel Composition on Carbon Black Formation Pathways

Abstract

Differences in lamellae length, stacking, and particularly a difference in the core-to-shell radial structure are observed for carbon blacks produced using different feedstocks. Carbon black (CB) produced using a coal tar (CT) feedstock formed particles with amorphous cores exhibiting a sharp transition to extended lamellae oriented about the periphery of the particle. In contrast, the carbon black produced from fluidized catalytic cracker (FCC) decant oil as feedstock formed particles with a single nucleated core possess a rather uniform radial transition—reflecting the presence of ordered, concentric lamellae across most of the particle radius. Minimal disorder was observed in the core while the undulations in perimeter lamellae were fewer. Our interpretation for these structural dissimilarities is premised on differences in fuel composition, specifically component classes as found by saturate, aromatic, resin, asphaltene (SARA) analysis. These in turn lead to variation in the relative rates of particle nucleation and particle growth by pyrolysis products, moderated by temperature. Electron energy loss spectroscopy reveals radial variation in the sp2 content between the different feedstocks consistent with observed nanostructures. Collectively these results are interpreted in terms of an offset in nucleation and growth—dependent upon the relative contributions of feedstock aromatic content and pyrolysis processes to particle nucleation and growth. To further test the postulate of different formation conditions for the two carbon blacks pulsed laser annealing was applied. The high temperature heating accentuated the dissimilarities in nanostructure and chemistry—leading to stark dissimilarities. These differences were also manifested by comparing oxidative reactivity.