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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 aliphatic character correlates with sp3 carbon. Percentages of sp2 sites ranged between 36% and 70% for all the asphaltenes samples with values from XPS being underestimated, with respect to XAES. The splitting between the principal nonloss C 1s line and the largest plasmon loss peak, and the evolution in shape of the π → π* plasmon satellite in the energy loss spectra were in qualitative agreement with XPS and XAES data. In addition to aromatic and aliphatic hydrocarbon ion fragments, the high sensitivity of TOF−SIMS allowed the detection of several hetero-elements (such as nickel, vanadium, sulfur, and nitrogen, in the organometallic-bearing asphaltenes, or iron, chlorine, sodium, potassium, and silicon, as foreign elements). Probing the surface composition through the ΣCH x +/C2 + ratio indicated that asphaltenes were bearing more aliphatic character than the carbon blacks or graphite, presumably because of the presence of hydrogen during hydrovisbreaking. However, surface probing via the C2H-/C2 - ratio suggested that asphaltenes were less aromatic, as expected, than graphite while exhibiting an aromatic character close to that of some carbon blacks.

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This study was instigated in view of the recent commercial exploitation of the Doba oil field in landlocked Chad, which is a region from which crude oil is extracted and expected to be routed to the Atlantic shore through pipeline transportation. Thus, nonisothermal kinetic hydrovisbreaking tests of Doba crude oil were conducted in a mechanically stirred baffled autoclave reactor under various conditions to alter the rheological properties of the treated crude. The crude hydrovisbreaking kinetics was modeled based on the four-parameter reaction severity concept (ω, γ, E, β o ), as a function of the conversion in polyaromatics and polar maltenic subfractions. The hydrovisbreaking of Doba crude was observed to be a pseudo-first-order reaction (i.e., in excess of H 2 ), with respect to the polyaromatics and polar maltenic conversion. The following assortment of kinetic parameters was identified under noncatalytic hydrovisbreaking conditions: heterogeneity coefficient, γ ) 1; characteristic temperature, ω ) 29.95 K; and activation energy, E ) 140.9 kJ/mol. Four viscosity mitigation scenarios involving catalytic (FeS, MoS 2 ) and noncatalytic hydrovisbreaking of Doba heavy crude oil were investigated. It was found that the minor proportions of the fractions that distilled before 250 °C and the small asphaltene yields marginally affected the crude viscosity. It was therefore determined that it is possible to meet the viscosity specification for pipeline transportation via (noncatalytic) hydrovisbreaking, which requires neither predistillation (topping) nor post-deasphalting units. The treated crudes and the syncrudes (mixtures of untreated and treated crudes) were observed to exhibit nonelastic viscous Newtonian behavior over the temperature range typical of crude transportation via pipeline. Treated crudes at 440 °C for 25 min and syncrudes that were the result of mixing 50 wt % of untreated crudes with crudes treated at 460 °C for 15 min yielded kinematic viscosities within the pumping specifications (i.e., e 25cSt @ 50 °C). The use of catalysts led to even lessviscous maltenes subfractions; however, post-deasphalting was required, because the catalystcoke mixture, as well as asphaltenes, inflated the viscosity above the norm. An iron sulfide catalyst outperformed a molybdenum sulfide catalyst, in terms of the deasphalted crude viscosity. Aging tests over two-month periods indicated that the higher the treatment severity, the more stable the viscosity of the Doba treated crudes, which is potentially compatible with the residence times of syncrudes within the 1050-km-long transportation pipeline between Chad and Cameroon.