Examining the molecular entanglement between VO complexes and their matrices in atmospheric residues by ESR

Abstract

The VO 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 VO 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 VO 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 VO complexes decreases in the order of asphaltenes > AR ≈ resins > maltenes, implying that the constraint on the mobility of the VO 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 VO complexes in the ARs and their fractions. It can be ascribed to the change in the peripheral environment of the VO complexes surrounded by the matrix molecules. A comprehensive understanding of such molecular entanglement between the VO complexes and their matrixes in ARs may give some important hints to improve the hydrodemetallization performance of AR.