Effect of surface energy on carbon dioxide hydrate formation

In this work, the effect of the surface energy between the hydrate clusters and the aqueous phase on the hydrate formation of carbon dioxide was thoroughly investigated. Our results show that the threshold pressure for hydrate formation is less sensitive to the temperatures if the surface energy is not larger than 7 mJ/m(2). However, the threshold pressure is very sensitive to the temperatures and increases significantly with the surface energy if it is over 7, 9, and 10 mJ/m(2) for the temperatures of 279, 277.45, and 276 K, respectively. The value of the surface energy for the CO(2) hydrate/water system was determined as 9.3 mJ/m(2) by comparing our results with the experimental data for stable CO(2) hydrate formation at the temperature range of 277.45-278.85 K and at pressures of 55-165 bar. This value is very close to the recently reported value of 7.5 ± 1.4 mJ/m(2) from molecular simulation. A theoretical method was proposed for computing the induction time of hydrate formation adopting a composite of the time required for critical nuclei formation and their growth to a detectable size. By using this method, the surface energy was avoided in the induction time calculation and an average crystallite volume of 0.238 mm(3) at the induction time was derived based on the experimental data. It provides an approach for predicting the induction time for gas hydrate formation.