THE DIFFUSION COEFFlCIENT OF HEHEHP IN HEPTANE MEASURED BY THE MODIFIED STOKES CELL TECHNIQUE AT TEMPERATURES BETWEEN 25 AND 55°C.

ABSTRACT The diffusion coefficient of HEHEHP in heptane has been measured by the modified Stokes cell technique at temperatures between 25 and 55°C. The Stokes cell was calibrated by measuring acetic acid diffusion with the pH-stat technique. The average diffusion coefficient of HEHEHP in heptane was determined to be 0.97 × 10 −9 m2/s at 25 °C for HEHEHP concentrations of 0 - 0.1 kmol/m3. The diffusion coefficient did not vary significantly with HEHEHP concentration. The Wilke-Chane relationship was used to predict D values of 1.53 × lO−9m2/s and 1.01 × 10 −9m2/s for the monomelic and dimeric species respectively. Comparison of the measured and predicted diffusion coefficients led to the conclusion that the HEHEHP was substantially dimenzed over the concentration range studied An activation energy of 6.90 kJ/mol was calculated from the diffusion coefficient measurements at elevated temperature.