Investigation on the formation kinetics and equilibrium of carbon dioxide hydrate in soil and soil mineral suspensions

Abstract

In this research, $CO_2$ hydrate formation kinetics and equilibrium in soil and soil mineral suspensions were investigated to provide a fundamental knowledge related to clathrate hydrate technology for $CO_2$ storage. In the first chapter, stochastic nature of $CO_2$ hydrate induction time in Na-montmorillonite (Na-MMT) suspension was shown and the patterns of stochastic induction times were identified by varying environmental factors (pressure, temperature, electrolyte, and soil mineral). Probability density functions of the induction time were analyzed. Goodness-of-fit tests (e.g. Kolmo-gorov-Smirnov and Chi-squared tests) showed that the probability distribution functions of $CO_2$ hydrate induction time can be properly fit to lognormal distribution. As pressure increased and temperature decreased, mean and standard deviation (arithmetic and geometric) of the lognormal distribution significantly decreased in general due to super-cooling effect. Geometric mean $(μ^*)$ indicates a quantitative acceleration factor while geometric standard deviation $(σ^*)$ suggest qualitative criteria for data consistency. Addition of NaCl (3.5%) into the Na-MMT suspension accelerated the hydrate formation kinetic 1.7 times in terms of $μ^*$ and also $σ^*$ slightly increased probably due to the nucleation site heterogeneity by creation of different Na-MMT surfaces. $CO_2$ hydrate nucleation in Ulleung-basin sediment suspension was remarkably faster approximately 1.4 times and showed more consistent induction time. It is speculated that organic matter component in Ulleung-basin sediment may help to promote the hydrate nucleation. In the second chapter, $CO_2$ hydrate equilibrium in soil mineral and organic matter suspensions was investigated. $CO_2$ hydrate equilibrium measured in deionized water and alkaline electrolyte solutions as controls and the data were in agreement with other previous researches. No significant equilibrium shift was observed in pyrite and illite suspensi...