Chemical structure of bitumen-derived asphaltenes by nuclear magnetic resonance spectroscopy and X-ray diffractometry

Asphaltene samples obtained from bitumen processed at three Indian refineries were characterized for chemical composition and structure by nuclear magnetic resonance (n.m.r.) spectroscopy and X-ray diffractometry (XRD). The average structural parameters were obtained by combined H-1, C-13 and DEPT spectral editing techniques. New equations were used for the estimation of n.m.r. average structure parameters. The macrostructure and crystalline parameters of these samples were obtained by XRD. A combined n.m.r. and XRD procedure was used to estimate the size of the average aromatic structural unit. Asphaltenes from one of the bitumens (ASP-D) was found to have different structural parameters from those of the asphaltenes from the other two bitumens. The number of aromatic rings per unit sheet in ASP-D was eight, compared with 13 for both ASP-M and ASP-H. XRD data indicated that the aromatic sheets are randomly oriented in ASP-D. The structural parameters allowed a model structure of the asphaltenes to be constructed. (C) 1996 Elsevier Science Ltd.