# Effect of Fuel Composition on Carbon Black Formation Pathways
## 4 Summary  
Two feedstocks, CT and FCC form carbon black using similar reactor conditions. The main compositional difference is the prevalent content of methylated aromatics, heavy to light in the CT. This difference is postulated to be the driver in early particle inception and growth for the CT feed. With resonance stabilized radicals propagating molecular growth by radical addition reactions, inception begins at earlier times, higher feedstock  
Figure 10: HRTEM images of laser heated (**A–C**) CT- and (**D–F**) FCC-CB blacks.  
concentrations, and lower temperatures. Collectively these conditions result in rapid nuclei formation, high number concentrations, and early particle growth by nuclei coalescence and PAH addition. Primary particle cores typically show multiple nuclei.  
For the FCC feedstock, higher hydrogen content serves to terminate radicals by H-abstraction reactions while saturating pyrolysis products (H-atoms and alkyl radicals) can similarly cap aromatic radicals to inhibit their clustering via resonance-stabilized radical (RSR) reactions--both mechanisms delaying particle inception and growth. The lower aromatic content and resulting increased chemical kinetic time allows turbulence induced mixing to lower feed concentration while increasing temperature. With inception occurring under diluted conditions, nuclei concentration is lower and primary particles generally contain but one identifiable center. Smaller pyrolysis species contributing to growth at higher temperatures lead to a more radially uniform nanostructure.  
Differences in growth conditions result in different nanostructure and chemistry--as measured by the sp\({}^{2}\) content. The comparative sp\({}^{2}\) content for the FCC-CB is 3.5 times that of the CT-CB-consistent with early nucleation and growth for the CT derived particles and delayed nucleation and growth for the FCC derived particles reflecting preceding pyrolysis. Different particle sizes are consistent with this view.  
To better illustrate the chemistry and nanostructure differences between the two carbon blacks, pulsed laser annealing is applied. Collectively chemistry, nanostructure, and nuclei differences are magnified. Core-shell structure is observed for the CT-CB while intertwined ribbons comprise the particle interior of the FCC-CB after laser heating. The distinctly different structures support the postulate of different formation conditions for the two carbon blacks. In further support of the postulate and as further illustration of their different chemistry--oxidative reactivity is assessed using a TGA. Disordered carbon reacts faster--with interior burnout observed for the CT-CB material whereas the FCC-CB exhibits mixed surface and internal burnout as observed by TEM.  
Conceptualization, R.L.V.W. and C.R.H.; methodology, R.L.V.W. and C.R.H.; validation, R.L.V.W., J.K. and C.R.H.; formal analysis, M.S. and A.G.; investigation, M.S., A.G., R.L.V.W., J.K. and C.R.H.; resources, R.L.V.W. and C.R.H.; data curation, M.S., A.G., R.L.V.W. and C.R.H.; writing--original draft preparation, M.S., A.G. and R.L.V.W.; writing--review and editing. M.S., A.G., R.L.V.W., J.K. and C.R.H.; visualization, R.L.V.W. and C.R.H.; supervision, R.L.V.W. and C.R.H.; project administration, R.L.V.W. and C.R.H.; funding acquisition, R.L.V.W. and C.R.H. All authors have read and agreed to the published version of the manuscript.  
This work was supported by Birla Carbon, c/o Columbian Chemicals through sponsored agreement number 225973 with the Pennsylvania State University. The APC was funded by MDPI.  
Not applicable.  
The authors declare no conflict of interest.