Hydrogen abstraction of alkyl radicals from polycyclic aromatic hydrocarbons and heterocyclic aromatic hydrocarbons.

The difficulty of the H-abstraction of alkyl radicals from PAHs or hetero-PAHs follows the order: S-containing heterocycles > PAHs > N-containing heterocycles. • H-abstraction of CH 3 or C 2 H 5 from PAHs or hetero-PAHs was investigated. • CH 3 instead of C 2 H 5 is responsible for aromatic C radical formation on PAHs. • Activation entropy determines the difference in k T S T of H-abstraction on PAHs. • H-abstraction difficulty: S-containing heterocycles > PAHs > N-containing heterocycles. To understand the condensation during heavy oil thermal processing, the formation of aromatic carbon radicals by H-abstraction of methyl radicals (CH 3) or ethyl radicals (C 2 H 5) from polycyclic aromatic hydrocarbons (PAHs) or heterocyclic aromatic hydrocarbons (hetero-PAHs) was studied by density functional calculation. The H-abstraction from different PAHs all has a positive standard state Gibbs free energy change, while increasing reaction temperature or radical concentration promotes the reaction to proceed spontaneously. CH 3 mainly contributes to the formation of aromatic carbon radicals on PAHs, and the activation entropy of H-abstraction determines the difference in reaction rate constants. The particularity of H-abstraction from hetero-PAHs is reflected at the α-site of heterocycles. The H-abstraction from N-containing hetero-PAHs occurs preferentially at the α-site of heterocycles, and both CH 3 and C 2 H 5 could participate in abstracting the α-H. The H-abstraction from S-containing hetero-PAHs occurs preferentially on coupled aromatic rings, showing reaction behavior similar to the H-abstraction on PAHs. [ABSTRACT FROM AUTHOR]