FURTHER-STUDIES IN THE ELUCIDATION OF THE ABNORMAL SOLUBILITIES OF THE LOWER MOLECULAR-WEIGHT GASES IN AQUEOUS-SOLUTIONS NEAR HYDRATE FORMATION TEMPERATURES

Isobaric solubilities of pure methane and ethane gases in liquid water have been measured at different conditions including hydrate formatio n points using a ramping method in which measurements are made untradi tionally through the entire and continuous hydrate formation/decomposi tion cycle. The work was conducted for methane at 3.45 MPa (500 psia) and temperatures ranging from 17.0 to 0.0 degrees C (290.2 to 273.2 K) , and for ethane at 0.66 MPa (95 psia) and a temperature range of 17.0 to 0.0 degrees C (290.2 to 273.2 K). The isobaric solubilities obtain ed show a significant divergence from (normal) Henry's law solubilitie s as the temperature is lowered. The increase in the solubility is pre sumably the result of the onset of a sorption process that traps the g as molecules in the water structures. Several sub-processes were obser ved as the hydrate formation was taking place: (1) the dissolution of the gas in the liquid water, or interstitial solubility, (2) the onset of the sorption sub-process and build-up of the hydrate precursors, ( 3) the catastrophic formation and the existence of the solid phase wit h its slushy characteristics, and (4) the solidification of the hydrat es, therefore causing the total plugging of the experimental cell.