The coking mechanism of conjugated radicals and its inhibition by additives: ReaxFF simulations and quantum chemical calculations

To investigate the aggregation behavior of conjugated radicals and the impact of additives on coking growth, 17 conjugated radicals are simulated as initial species in the dynamic formation of coke, with water (H2O), methanol (CH3OH), and formaldehyde (CH2O) considered as inhibitory additives. After 6.0 ns of ReaxFF simulations, coking phenomena emerge in all initial systems of conjugated radicals. A coking mechanism, referred to as the "Ring Duplication - Open Ring - Chain into Ring" (RDORCR), is identified in these simulations. The addition of inhibitory additives reveals that H2O exerts the strongest inhibition effect on coke formation by directly capturing conjugated radicals. Quantum chemical calculations are employed to study the inhibitory reactions involving H2O. Potential energy profiles indicate that reaction barriers range from 36 to 71 kcal/mol for conjugated radicals reacting with the OH part of H2O, while reactions with the H atom of H2O exhibit lower barriers of 11–46 kcal/mol. Because H2O can react efficiently by transferring its H atoms, present work elucidates the primary reasons for H2O as an excellent inhibitor. Furthermore, high temperatures enable H2O to exert a stronger inhibitory effect. Various wave function analysis methods are applied to analyze the conjugation strength and reactivity of conjugated radicals, as well as electron transfer in transition states involving H2O.