Macro and micro approaches: Hydrate phase equilibria

To describe the phase equilibria of gas hydrate by means of a macroscopic approach, hydrate phase equilibria for the CH4 + water, CO2 + water and CH4 + CO2 + water mixtures in silica gel pores were measured and compared with the calculated results based on van der Waals and Platteeuw model. At a specified temperature, three phase H-L-W-V equilibrium curves of pore hydrates were shifted to higher pressure region depending on pore sizes when compared with those of bulk hydrates. The activities of water in porous silica gels were expressed with a correction term to account for both capillary effect and activity decrease. In microscopic analysis of gas hydrates, the CH4 + CO2 and CO2 + N-2 mixed gas hydrate were measured by spectroscopic methods such as NMR and XRD. With these measurements, we can analyze and obtain some critical information on gas hydrates such as hydration number and cage occupancy. Accordingly, it becomes important to interconnect various physicochemical properties determined from both macroscopic and microscopic methods.