SURFACE-TENSION OF TOLUENE-EXTRACTED BITUMENS FROM UTAH OIL SANDS AS DETERMINED BY WILHELMY PLATE AND CONTACT-ANGLE TECHNIQUES

The surface tension values for toluene-extracted bitumens from Whiterocks, Sunnyside, PR Spring, Asphalt Ridge, and Circle Cliffs oil sands were measured with the Wilhelmy plate technique and found to vary from 20.6 to 31.2 mN m-1 at 333 K. A linear relationship between the bitumen surface tension and temperature was observed in the temperature range 310-356 K, which allowed for the calculation of the temperature coefficients of surface tension. The temperature coefficients were found to vary among the bitumens from -0.063 mN m-1 deg-1 to -0.097 mN m-1 deg-1. Also, the surface tensions of these bitumens at room temperature were calculated from contact angle measurements using Neumann's equation-of-state. Satisfactory agreement between the results for bitumen surface tensions as determined from contact angle data and direct surface tension measurements with the Wilhelmy plate technique were obtained for the Whiterocks, Sunnyside, and PR Spring bitumens. However, large discrepancies, 6.4-9.4 mN m-1, were observed between the bitumen surface tension data obtained from Neumann's equation-of-state and the bitumen surface tensions determined by direct Wilhelmy plate measurements for the Asphalt Ridge and Circle Cliffs bitumens.