REACTIVITY OF ASPHALT SUPERCRITICAL FRACTIONS

The reactivities of six supercritical fractions of asphalt SHRP AAF-1 were investigated in the context of their chemical composition. The su percritical fractions were obtained using pentane as the solvent. Each fraction was aged in a pressure oxygen vessel (POV) under seven condi tions of temperature and pressure. As with whole asphalts, there is an initial rapid oxidation that slows to a constant rate. The oxidation rates for the constant rate region were measured at each of the condit ions to determine the kinetic parameters of the fractions. Arrhenius p lots were then constructed for the fractions to compare their reactivi ties. Variations in activation energy and reaction order were within e xperimental err;or. Results show that reactivity increases with fracti on number for the supercritical fractions. The heavier fractions are m ore reactive not only because they contain more polar aromatics in ter ms of Corbett analysis fractions but also because the polar aromatics of the heavier fractions are larger in molecular size and are more rea ctive. Additionally, heavier fractions contain more asphaltenes that a re larger in molecular size. Because for light fractions the reaction rates, and as previously shown the hardening rates, are very low and r emain constant with oxidation, air blowing of some light fractions wou ld be expected to produce an asphalt with a very low hardening rate. D ata explicitly show that for petroleum fractions from the same crude s ource molecular size distribution is a good indicator of reactivity. T his is not necessarily true for petroleum fractions from different cru de sources, however.