Bitumens from six diverse tar sand deposits were obtained by toluene extraction. The viscosities of each of the bitumens were determined in the temperature range 60 to 90 degrees C and were found to be Newtonian in character. All bitumen samples were fractionated using a modified SARA (saturates, aromatics, resins and asphaltenes) type analysis. The separated fractions were examined by transmission and specular reflectance FT-i.r. spectrsocopy (SR-FT-i.r.). The FT-i.r. analysis indicated that carboxylic acid present in the bitumen accumulated in the polar fractions, particularly in the resin fraction. The carboxylic acid concentration was estimated from its characteristic FT-i.r. absorbance band by the band-fit method. The carboxylic acid in the resin fractions was also estimated by a potentiometric titration method using a mixed solvent. Although it was clearly indicated from the infrared analysis of the bitumen fractions that bitumens with higher viscosity generally contained larger amounts of carboxylic acid, a simple quantitative relationship between these two variables to the exclusion of others in a complex material such as bitumen was found to be difficult. The viscous nature of the bitumen is principally attributed to the internally suspended asphaltene particles. The fractional compositions of the various bitumens clearly indicated that the viscosity of a given bitumen cannot always be correlated with its asphaltene content alone. However, the introduction of another variable, namely the carboxylic acid content of the bitumen, together with asphaltene content can better account for the property of viscosity. The Athabasca sample was the least viscous of all the bitumens under study, although it contained an intermediate amount of asphaltenes. FT-i.r. analysis indicated that the Athabasca resin fraction contained only a small amount of acid and was explained to be inadequate to optimally engage the asphaltenes in suspension through hydrogen bonding. In addition, it was shown that the major oxygen functional group in Athabasca bitumen is an ester which was believed to be not as efficient as an acid in the hydrogen bond formation. The presence of esters in the Athabasca resin fraction was confirmed by the hydrolysis of the resin fraction and analysis of the hydrolysis products by SR-FT-i.r.. The influence of carboxylic acid and asphaltene contents on bitumen viscosity is discussed with reference to the structural model developed by Nellensteyn.
