Determination of Mutual Solubility between CO2 and Water by Using the Peng–Robinson Equation of State with Modified Alpha Function and Binary Interaction Parameter

Abstract

Techniques have been developed to determine mutual solubility between CO2 and water by using the Peng–Robinson equation of state (PR EOS) with a modified alpha function and a new binary interaction parameter (BIP) correlation in the presence and absence of hydrocarbons. More specifically, the alpha function for the water compound is modified by improving its prediction for water vapor pressure in the full temperature range of 273.16 to 647.10 K with an overall absolute average relative deviation (AARD) of 0.07%. Also, the polynomial temperature-dependent BIP correlation for the CO2–water pair in the aqueous phase is proposed by matching CO2 solubility in water at temperatures from 273.15 to 448.15 K and pressures up to 100 MPa. It is found that the newly modified alpha function together with the proposed BIP correlation provides more accurate prediction of the CO2 solubility in water with an overall AARD of 6.12%, compared with 8.67% from the previous exponential BIP correlation. As for the nonaqueous phase of the binary CO2–water system, it is found that a constant BIP for the CO2–water pair generally results in a good agreement between the reported and predicted compositions of the CO2-rich phase. Furthermore, the accurate solubility prediction of either CH4 or CO2 in the water-rich phase of the ternary CH4–CO2–water systems has been achieved with an overall AARD of 6.15% at a temperature of 344.15 K and pressures of 10, 20, 50, and 75 MPa, respectively.