A modified Redlich-Kwong equation for H 2 O, CO 2 , and H 2 O-CO 2 mixtures at elevated pressures and temperatures

Carnahan and Starling's hard-sphere Redlich-Kwong equation was modified to include an attractive term (A) that is a function of pressure and temperatures. The modified equation is superior to those that assume (a) to be independent of pressure. Calculated molar volumes and fugacity coefficients for H/sub 2/O and CO/sub 2/ are in good agreement with those obtained from p-v-t data. Furthermore, this equation yields reasonably accurate fugacities for H/sub 2/O and CO/sub 2/ at p-t conditions beyond the range of experimental volumetric measurements. Using standard mixing rules for calculating a(mix) and b(mix), this equation yields z(mix) values that are consistent with those of Greenwood's p-v-t measurements. Calculated activities show significant positive nonideality of mixing at elevated pressures (p > 1 kbar and t= 400 to 800 C). Unmixing of H/sub 2/O and CO/sub 2/ is implied at lower temperatures (400 C) and at higher pressures (p > 10 kbar). 50 references.