Examining the molecular entanglement between V=O complexes and their matrices in atmospheric residues by ESR

The V=O complexes in atmospheric residues (ARs) and their maltene, resin and asphaltene fractions have been investigated using ESR to examine the effects of the surrounding matrices, measurement temperature, pre-heat-treatment of AR as well as addition of toluene on the electron structure and mobility of the V=O ion. The B parameter calculated on the basis of the ESR spectrum has been found to be a good index to reflect the molecular entanglement between the V=O complexes and their matrixes in ARs and their fractions, and to indicate the effects of the measurement temperature, pre-heat-treatment as well as the solvent on such interactions. The B parameter value for the V=O complexes decreases in the order of asphaltenes > AR ≈ resins > maltenes, implying that the constraint on the mobility of the V=O complexes in the samples decreases in the same trend. Increasing temperature, pre-heat-treatment and the addition of toluene reduce the B parameter value, thus, favoring the mobility of the V=O complexes in the ARs and their fractions. It can be ascribed to the change in the peripheral environment of the V=O complexes surrounded by the matrix molecules. A comprehensive understanding of such molecular entanglement between the V=O complexes and their matrixes in ARs may give some important hints to improve the hydrodemetallization performance of AR.