THE INFLUENCE OF CARBOXYLIC-ACID CONTENT ON BITUMEN VISCOSITY

Bitumens from six diverse tar sand deposits were obtained by toluene e xtraction. The viscosities of each of the bitumens were determined in the temperature range 60 to 90 degrees C and were found to be Newtonia n in character. All bitumen samples were fractionated using a modified SARA (saturates, aromatics, resins and asphaltenes) type analysis. Th e separated fractions were examined by transmission and specular refle ctance FT-i.r. spectrsocopy (SR-FT-i.r.). The FT-i.r. analysis indicat ed that carboxylic acid present in the bitumen accumulated in the pola r fractions, particularly in the resin fraction. The carboxylic acid c oncentration was estimated from its characteristic FT-i.r. absorbance band by the band-fit method. The carboxylic acid in the resin fraction s was also estimated by a potentiometric titration method using a mixe d solvent. Although it was clearly indicated from the infrared analysi s of the bitumen fractions that bitumens with higher viscosity general ly 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 vis cous nature of the bitumen is principally attributed to the internally suspended asphaltene particles. The fractional compositions of the va rious bitumens clearly indicated that the viscosity of a given bitumen cannot always be correlated with its asphaltene content alone. Howeve r, the introduction of another variable, namely the carboxylic acid co ntent of the bitumen, together with asphaltene content can better acco unt for the property of viscosity. The Athabasca sample was the least viscous of all the bitumens under study, although it contained an inte rmediate amount of asphaltenes. FT-i.r. analysis indicated that the At habasca resin fraction contained only a small amount of acid and was e xplained to be inadequate to optimally engage the asphaltenes in suspe nsion through hydrogen bonding. In addition, it was shown that the maj or oxygen functional group in Athabasca bitumen is an ester which was believed to be not as efficient as an acid in the hydrogen bond format ion. The presence of esters in the Athabasca resin fraction was confir med by the hydrolysis of the resin fraction and analysis of the hydrol ysis products by SR-FT-i.r.. The influence of carboxylic acid and asph altene contents on bitumen viscosity is discussed with reference to th e structural model developed by Nellensteyn.