Observations of CO2-hydrate decomposition and reformation processes

We observed CO2 hydrate decomposition and reformation (re-growth) through t emperature and pressure changes using a microscope. At pressures above CO2 vapor-liquid equilibrium P-s, decomposition from increasing temperatures le ft small liquid CO2 drops in the solution phase. Conversely, below P-s, dec omposition from increasing temperatures was more rapid due to the release o f CO2 gas that mechanically broke the hydrate apart. Similarly, hydrate dec omposition by a pressure decrease also released CO2 gas that broke the hydr ate apart. Reformation occurred more readily only by cooling, not by a pres sure increase. A barrier to CO2 nucleation can explain this memory effect b y allowing a greater concentration of CO2 to be left in the aqueous solutio n after hydrate decomposition. (C) 2000 Elsevier Science B.V. All rights re served.