Hydrate phase equilibria of the ternary CH4+NaCl plus water, CO2+NaCl plus water and CH4+CO2 plus water mixtures in silica gel pores

Abstract

Hydrate phase equilibria for the ternary CH4 + NaCl + water and CO2 + NaCl + water mixtures in 15.0 nm silica gel pores and for the ternary CH4 + CO2 + water mixtures of various CO2 vapor compositions (20, 40, 60 and 80 mol %) in silica gel pores of nominal diameters 6.0, 15.0, and 30.0 nm were experimentally 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 a higher pressure region depending on NaCl concentrations and pore sizes. A Pitzer model for electrolytes solutions and a correction term for capillary effect were adopted to estimate the activity of water in the aqueous electrolyte solutions within silica gel pores. The cage dependent C-13 NMR chemical shifts of the enclathrated CH4 molecules in 15.0 nm silica gel pores were confirmed to be identical with those of bulk CH4 hydrates (sI) and consistent through different NaCl concentrations and CO2 compositions.