Liquid composition-total pressure and liquid composition-liquid density data for the carbon dioxide-ethane system were measured at -31.7', -17.8O, -3.9O, and 10.O°C (-25O, Oo, 25O, and 50°F +0.02OF), from 0 to 80 mole yo COz at 10°C and 0 to 10Wj' o COz for the other isotherms. TheBenedict-Webb-Rubin equation of state with a modsed A0 mixing rule was used to correlate the composition-pressure data, with deviations in predicted pressures of only 0.8t70 average and 2% maximum. Vapor-liquid equilibrium compositions and component K values y/x were then predicted for this minimum boiling azeotrope system from loo down to -56.7OC(50' to -70OF). The objective of this study was to obtain sufficient experimental data on the behavior of the minimum boiling azeotrope system, carbon dioxideethane, to develop mathematical correlations which can be used for reliable predictions of vapor-liquid equilibrium compositions and vaporization equilibrium constants for designing the most efficient distillation towers for the cryogenic processing of natural gas. The importance of the carbon dioxideethane system results primarily from the fact that most natural gases contain sufficient carbon dioxide to warrant concern in processing plants, where solidified carbon dioxide can dangerously plug low-temperature equipment. Carbon dioxide also lowers the heating value of natural gas. R.To remove the carbon dioxide, either absorption in amine solutions or adsorption by molecular sieves has commonly been used, but low temperature distillation offers both operating and economic advantages. The accurate phase equilibrium data required for design of the most efficient cryogenic distillation towers were not available from the literature, however. Therefore, experimental measurements of total vapor pressure versus liquid composition were made as a basis for developing correlations for calculating the needed phase equilibrium data, and liquid density data were determined in the same runs for use in other design calculations.A modified mixing rule with the Benedict-Webb-Rubin equation of state was then used to correlate the pressurecomposition data. Finally, the resulting equations were employed to predict vapor-liquid compositions, and equilibrium constants for both components, over the temperature range of interest. CONCLUSIONS AND SIGNIFICANCEThe experimental values obtained for total vapor pressure and liquid density as a function of saturated liquid phase composition at -31.7O, -17.8O, -3.9O, and 10.O°C (-25O, Oo, 25O, and SOOF) are presented in Table 1. The range of liquid compositions covered was 0 to 80 mole yo C 0 2 at 10°C and 0 to 100% at each of the other isotherms.The Benedict-Webb Rubin equation of state with a modified A. mixing rule, presented in Table 2, very successfully correlated the experimental pressure-composition data, with an average deviation in predicted pressure of only O.8Y0 and a maximum deviation of 2y0. These correlation curves are shown in Figures 4 and 5. The vaporliquid equilibrium compositians, and the equilibrium ...

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