Modeling interaction of free radicals from cracking processes with asphaltene structure

Calculations with an asphaltene model were carried out by the CATIVIC program using an average asphaltene molecule that reproduces a set of physical–chemical properties of the Tia Juana Venezuelan heavy crude oil 500 + residue. The asphaltene was divided into several fragments to study the interaction of H°, CH₃°, and CH₃CH₂° radicals on the aromatic region of each fragment. Validation respect to DFT was performed. CATIVIC code gives higher adsorption energy values than DFT one. Qualitative results indicate, in both programs, that it is feasible the formation of radical species adsorbed on the asphaltene surface fragments. These adsorptions lead to surface distortions and electronic charge transfers from the adsorbate to the asphaltene surface. The adsorption energy for all fragments follows the order: H°> CH₃°> CH₃CH₂°. It is proposed that the presence of asphaltene in thermal cracking may be to act as an inhibitor of radical chain formation.