Gas Hydrates of Carbon Dioxide-Methane Mixtures

Abstract

Abstract Experimental data are presented for hydrate formation conditions for gasmixtures of carbon dioxide and methane. Equilibrium constants for carbondioxide, defined as the mole fraction of carbon dioxide in the gas phase (drybasis) divided by the mole fraction of carbon dioxide in the hydrate (drybasis), were calculated using the equilibrium constants for methane developedin an earlier paper. Introduction A series of papers have been written on gas hydrates, giving temperaturesand pressures at which hydrates would form. Vapor-solid equilibrium constantshave been developed for methane, ethane, propane and iso-butane by which it ispossible to compute for a specific gas mixture the temperature and pressure atwhich hydrates will form. Carbon dioxide is present in many natural gases in concentrations usuallyfrom 0.1 to 2.0 per cent. It also forms a gas hydrate with water and presumablyenters the solid solution when present with a natural gas which is forming ahydrate. The equilibrium constant giving the ratio of the concentration ofcarbon dioxide in the gas phase to the concentration in the solid phase isrequired for including the effect of the carbon dioxide when computing theconditions for hydrate formation. Direct determination of the concentration of carbon dioxide in solid hydraterequires a difficult separation to be made. Therefore, this research resortedto the measurement of the temperature and pressure at which specific mixturesof methane and carbon dioxide would form hydrates. From the equilibriumconstants previously mentioned for methane, it is possible to compute theequilibrium constant for carbon dioxide, without measurement of the compositionof the solid phase. Fig. 1 shows the conditions at which methane and carbon dioxide formhydrates. T.P. 2578