Experimental characterization of the difference in induction period between CH4 and CO2 hydrates: Motivations and possible consequences on the replacement process

Abstract

The present research explores the differences in induction time between methane and carbon dioxide hydrates. This parameter was calculated by considering the heat released during the formation of hydrates. Being the process exothermic, the heat released, in conjunction with the enthalpy of formation, allowed to calculate the quantity of hydrates formed as soon as the process became detectable. This information was then combined with the measure of time to define the induction period. The procedure was selected in order to avoid possible errors related to the dissolution of carbon dioxide in water, which may affect the accuracy of detection. It was found that the induction time is significantly longer for carbon dioxide hydrates. It can be explained with the non-hydrophobicity of the molecule and with the higher Gibbs free energy barrier which must be overcome to produce the first nuclei of CO₂ hydrates. The reliability of the proposed method was verified by evaluating the gas absorption over time for methane, whose dissolution in water can be considered negligible. Finally, it was proved that, after the formation of the first conglomerates, the growth of carbon dioxide hydrates is faster than that of methane hydrates, due to the higher degree of mixing between water and gas molecules within the whole formation environment.