Thermal conversion of polynuclear aromatics to carbon

Polynuclear aromatics can be transformed thermally into carbonaceous residues and ultimately to carbon and graphite by a process called carbonization. The chemistry of carbonization is exceedingly complex and encompasses a wide variety of reaction types including: bond cleavage, polymerization, molecular rearrangement, and hydrogen transfer. It has been shown that even with a single aromatic hydrocarbon starting material, pyrolysis leads initially to a diversity of products. Detailed thermal reaction studies have been carried out on a number of polynuclear aromatic compounds. A variety of experimental as well as theoretical techniques have been used in attempting to clarify the nature of these reactions. There is also extensive literature on the thermal reactions of polynuclear aromatic mixtures as they occur naturally in petroleum and coal derived products. It has not been possible to provide a complete reaction mechanism from any of these studies. However, it has been highly useful to propose generalized schemes which describe the main reactions occurring during the conversion of polynuclear aromatics to carbon. This approach has been facilitated through the use of model compound starting materials and advanced analytical techniques. These studies are reviewed in this paper with the objective of clarifying the chemistry of the carbonization process.