(758e) Theory and Experiment for Thermodynamics of the CO2/H2O System

Mixtures containing CO₂ and H₂O are important in many applications. In the electric power industry, they are two of the primary components of combustion gases. In advanced power cycles that facilitate CO₂ sequestration, these components may appear in synthesis gas, and they will certainly appear in CO₂-rich streams being compressed and transported for sequestration. Of key importance in many of these applications is the vapor-phase thermodynamic properties, which determine, for example, the dew point where liquid water will condense out of a CO₂ stream being compressed for sequestration.

We have undertaken a comprehensive program to study the gas-phase thermodynamics of this mixture, particularly at high temperatures where experimental data are scarce and scattered. We have used ab initio quantum mechanics to develop an intermolecular potential-energy surface of low uncertainty for the CO₂/H₂O pair; this surface has been used to calculate the cross second virial coefficient B₁₂ as a function of temperature. In addition, we have constructed a high-temperature, single-sinker magnetic suspension densimeter and used it to make density measurements on CO₂/H₂O mixtures at temperatures from 500 K to 620 K and pressures up to 17 MPa. Values of B₁₂ derived from the mixture density measurements agree within mutual uncertainties with those derived from theory. Similar agreement between theory and experiment has been obtained for the N₂/H₂O system, which is also of interest in energy applications.