Investigation of chemical transformations by NMR and GPC during the laboratory aging of Arabian asphalt

In this work, the chemical properties of a commercial grade Saudi Arabian a sphalt procured from Ras Tanura refinery were evaluated. The rolling thin f ilm oven (RTFO), termed as short-term aging, and pressurized aging vessel ( PAV), termed as long-term aging, tests were used to simulate the laboratory aging of this asphalt. It was found that PAV has more severe effects on th e chemical properties of asphalt than RTFO method. The Corbett fractionatio n procedure was used to separate fresh and aged asphalts into four generic fractions namely; asphaltenes, polar aromatics, naphthene aromatics, and sa turates and various analytical techniques were applied to evaluate the chem ical changes that occurred during the aging processes. High pressure-gel pe rmeation chromatography (HP-GPC) molecular weight and size distributions su ggested that molecular rearrangement occurs predominantly on aging. Carbon and proton NMR measurements of generic fractions showed that isomerization, internal cross-linking, and dehydrogenation were the main chemical reactio ns of hydrocarbon groups following aging. Coupling the results from the GPC and NMR techniques have led to some interesting information concerning the chemical reaction types during the aging processes. Significant difference s were observed between the structure and composition of fresh and aged gen eric fractions of Ras Tanura asphalt. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.