Effect of inter-molecular association on bitumen oxidation

The hypothesis that inter-molecular associations between species in petroleum bitumens affects the rate of air oxidation of the bitumens was examined using infrared spectroscopy, gel permeation chromatography and viscosity measurements. Experiments were carried out in which the rate of oxidation of two different bitumens and their fractions (maltenes, resins, asphaltenes) were measured in terms of carbonyl group formation. In THF solution at 30 °C the rates of reaction of the maltene and asphaltene fractions were the same when oxidized separately or as a mixture. Although the presence of inter-molecular associations were confirmed by gel permeation chromatography, the results indicated that such effects were unimportant to the rate of the reaction. Further experiments were performed in which neat bitumen, resin and maltene (n-heptane) factors and reconstituted mixtures were oxidized under 2069 kPa of oxygen or air at 40 °C or 60 °C. Again, no evidence for the effect of inter-molecular association on oxidation rate was obtained. Another experiment in which a bitumen, rejuvenating oil (RO), and a mixture of the two was oxidized (2069 kPa air, 60 °C) again showed that the reaction rate of the bitumen and RO were the same when oxidized separately or in the mixture. However, in contrast, the rate of increase of viscosity of the bitumen was significantly affected by the RO and was attributed to dispersal of polar oxidation products by the RO.