A bitumen fractionation procedure was developed based on the Iatroscan device. Asphaltenes are precipitated conventionally then maltenes are separated using Iatroscan thin layer chromatography and the proportions of each maltenes fraction measured using a flame ionisation detector. The procedure is comparatively rapid, and a control bitumen is included in every run to improve reproducibility. Testing of bitumens from the ARRB library covering the half century from 1956 to 2004 indicated that there had been a change in chemical composition over the period. Field performance problems were associated with low asphaltenes content or high saturates content. A single parameter, the Gaestel Index, indicated regions of poor performance. Colloidally unstable and temperature susceptible bitumens had high Gaestel values while tender bitumens had a low Gaestel Index. Multigrade bitumens had a much higher Gaestel Index than other bitumens but have not shown colloidal instability in service due, in part, to the different nature of their asphaltenes. This indicates that a number of factors must be taken into account when interpreting compositional data. The analysis technique should be useful for assessing future Australian and overseas bitumens. Chemical specification of bitumens is probably impractical at present. (a) For the covering entry of this conference, please see ITRD abstract no. 0612AR242E.
Abstract