Structure characteristics and association behavior of coal and petroleum C7-asphaltenes

Abstract

The structural characteristics and differences of coal tar and petroleum C7-asphaltenes were studied, such as chemical composition, functional groups and molecular structure, using nuclear magnetic resonance (NMR), small angle X-ray scattering (SAXS), X-ray photoelectron spectroscopy (XPS), improved B-L method and other methods. Furthermore, the association behavior and aggregation size of two different types of asphaltenes as well as the hydrogen bonds and acidic-basic interaction were analyzed by asphaltenes solubility parameters in polar solvents. The experiment results showed that the coal tar asphaltenes (CT-asp) was mainly composed of less aromatic rings with short alkyl branched chains and possessed a high aromaticity degree. The higher content oxygen heteroatoms of CT-asp were mostly presented as aromatic ether bonds and phenolic hydroxyl groups. The aromatic nucleus size and the average relative molecular weight of petroleum asphaltenes (M-asp) were larger than that of CT-asp. The M-asp consisted primarily of more aromatic rings with long alkyl branched chains and possessed a low aromaticity degree. The association and aggregation degree between CT-asp and M-asp was associated with the amount of substance ratio (nCT-asp/nM-asp) and their molecular structure characteristics. The association force of two types mainly was the hydrogen bonds and the acidic-basic interaction from heteroatomic functional groups.