Investigation on the structure of low-temperature coal tar asphaltene precipitated with different n-alkane solvents

To study the effects of deasphalting solvents on asphaltene, n-pentane asphaltene (As-5), n-heptane asphaltene (As-7), and soluble in n-heptane but insoluble in n-pentane asphaltene (As-(5–7)) were precipitated from low-temperature coal tar. Gel Permeation Chromatography (GPC), nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) are used to analyze their structure. The results show that As-(5–7) is composed of the aromatic layer periphery of As-5, so the aromatic degree of As-(5–7) is lower and the content of alkyl and naphthenic base groups is larger. What is more, the aromatic ring consistency and condensation degree of As-(5–7), As-5, and As-7 increase gradually, so their coking potential and hydrogenating difficulty increase.