Elucidation of the functional sulphur chemical structure in asphaltenes using first principles and deconvolution of mid-infrared vibrational spectra

This work aims to propose a novel methodology for the characterization of compounds such as: thiophene, benzothiophene, dibenzothiophene, naphthobenzothiophene, thioetheres and cyclic sulphides in asphaltenes. For this, quantum chemistry ab initio Hartree–Fock calculations, at the 6–31 g (d) level, were performed to produce theoretical infrared spectra (IR) of organic sulphur compounds. Based on these theoretical infrared spectra, it was possible to determine the frequency corresponding to the vibrational transition of the C―S bonds of the organic sulphur compounds in study. Finally, experimental IR spectra of these compounds were studied and the respective C―S bond frequencies were obtained. This methodology applied to Brazilian vacuum residue (VR) asphaltene allowed the elucidation of the organic sulphur constituent of the average molecule.