Interaction of Vanadyl Complexes in Atmospheric Residue with Their Matrixes: An ESR Study in a Temperature Range up to 170 °C

It is important to understand the interaction of vanadyl complexes in atmospheric residue (AR) with their matrixes at different conditions for demetallization processes of AR and heavy oil. An ESR study in rotational mobility of vanadyl complexes in AR was conducted at a temperature range from 20 to 170 °C with and without 1-methylnaphthalene as solvent. A complete transformation of the ESR spectrum from anisotropy to isotropy was observed at a temperature of 170 °C with decreasing AR concentration in 1-methylnaphthalene from 100 to 20 wt %, which corresponds to a transformation of the vanadyl complexes from a rigid status constrained by the surrounding matrixes to a free status. Both increase in the temperature and decrease in the AR concentration are beneficial to such transformation. The study showed that dependency of the rotational mobility of vanadyl complexes on the temperature and concentration can be classified into three domains: isotropic, transitional, and anisotropic domains. In the anisotropic domain, effects of the temperature and concentration on the B parameter can be estimated quantitatively through a model with a standard error of 0.0351. According to this study, a B contour map as a function of temperature and concentration was obtained, which provides a deeper and more comprehensive insight into the constraint on the rotational mobility of vanadyl complexes by their surrounding matrixes in AR and thus is useful for improving the demetallization process of AR and heavy oil.