X-ray Photoelectron Spectroscopy, Photoelectron Energy Loss Spectroscopy, X-ray Excited Auger Electron Spectroscopy, and Time-of-Flight−Secondary Ion Mass Spectroscopy Studies of Asphaltenes from Doba−Chad Heavy Crude Hydrovisbreaking

Abstract

The sp2-to-sp3 carbon bonding character in asphaltenes that results from heavy crude visbreaking was evaluated by means of X-ray photoelectron spectroscopy (XPS), photoelectron energy loss spectroscopy (ESCALOSS), X-ray excited Auger spectroscopy (XAES), and time-of-flight secondary ion mass spectrometry (TOF−SIMS). The asphaltenes were precipitated from virgin Doba−Chad heavy crude or from treated crudes after undergoing noncatalytic and (FeS and MoS2 mediated) catalytic hydrovisbreaking to reduce heavy crude viscosity for meeting pipeline transportation specifications. The sp2 and sp3 characters of the asphaltenes were calibrated using, respectively, highly oriented pyrolytic graphite (HOPG) and diamond. Composites of asphaltenes with polyethylene and polystyrene references were used to assess the shift from sp3- to sp2-dominated structures. It was postulated that the π aromatic character in the asphaltenes condensed polynuclear aromatic rings correlates with sp2 carbon, whereas the asphaltenes aliphati...