Calorimetric and Rheological Studies on Cyclopentane Hydrate-Forming Water-in-Kerosene Emulsions

The effect of salt, a thermodynamic inhibitor of hydrate, on a density-matched cyclopentane hydrate-forming water-in-kerosene emulsion with a fixed aqueous phase mass fraction of 0.4 is presented, based on studies by microdifferential scanning calorimetry (mu DSC) and rheometry. Kerosene is a candidate material for flow loop studies. Microdifferential scanning calorimetry data are presented on the equilibrium temperature (liquidus line); water-to-hydrate conversions are computed using the liquidus line. Mechanical properties obtained using a stress controlled rheometer are correlated to thermodynamic properties. Effects of subcooling, salt concentration, and shear rate dependence are studied and presented along with oscillatory rheometric and yield stress measurements. Critical time is defined as the onset of a viscosity jump, and the viscosity evolution time is the time from the initial jump to 90 % attainment of the final viscosity; both times are shortened by higher subcooling. The final viscosity, storage modulus and yield stress achieve a peak between 0.85 to 0.95 (mass fraction) water-to-hydrate conversion indicating a mechanical influence of capillary bridge formation. The hydrate slurry exhibits a shear thinning behavior when cycled up and down in shear rate, showing negligible hysteresis in the rate dependence.