A SAFT equation of state for the quaternary H2S–CO2–H2O–NaCl system

Abstract

Phase equilibria and thermodynamic properties of the quaternary H 2 S-CO 2 -H 2 O-NaCl system were studied using a statistical associating fluid theory (SAFT)-based equation of state (EOS) at temperatures from 0 to 200°C (373.15-473.15 K), pressures up to 600 bar (60 MPa) and concentrations of NaCl up to 6 mol/kgH 2 O. The understanding of the physical-chemical properties of this system is critical for predicting the consequences of co-injection of CO 2 and H 2 S into geological formations (geological carbon sequestration) as an option for mitigating the global warming trend. Equation of state parameters were generated from regression of available and reliable experimental data and incorporation of existing parameters for some subsystems. Densities were predicted and compared with available experimental results. Using the EOS developed in this study, we predicted equilibrium compositions in both liquid and vapor phases, fugacity coefficients of components, the equilibrium pressures at a given composition of the H 2 O-rich phase in electrolyte solutions with NaCl varying from 0 to 4 mol/ kgH 2 O, and the aqueous solution densities. These predicted values are tabulated and available as supplementary data in the electronic version online. These predictions provide information and guidance for future experiments regarding the thermodynamic properties and phase behaviors in the H 2 S-CO 2 -H 2 O-NaCl system.

A SAFT Equation of State for the H2S-CO2-H2O-NaCl System and Applications for CO2 - H2S Transportation and Geological Storage

“…Following SAFT2, the dimensionless residual Helmholtz energy is defined as the summation of terms accounting for the segment, association, chain, and ionic interactions, respectively. The detailed description was in reference [14].…”

“…To improve the model performance, two adjustable parameters can be used to adjust the cross association to account for special interactions such as hydrogen bond and, in general, one parameter is also needed to adjust the dispersion energy. These parameters (if required) are usually determined by fitting to binary or ternary data, e.g., to the gas solubility in solutions [14].…”

“…Previous modeling work in the literature has been summarized in our previous work [1,14], which reveals that for CO 2 -H 2 S-H 2 O-NaCl, the research is limited due to the lack of the experimental data. It should be mentioned here that a model based on PengRobinson (PR) EoS, TMGAS, was used to represent thermophysical properties and phase equilibria of CO 2 -H 2 S-H 2 O-NaCl [15].…”

“…However, in this model, the density of aqueous solution is independent from EoS, which we considered incorrect here. The detailed discussion on TMGAS was presented in our previous work [14].…”

“…Based on statistical associating fluid theory (SAFT) EoS, a model was developed to represent thermodynamic properties and phase equilibria for CO 2 -H 2 S-H 2 O-NaCl [1,14] and its subsystems [12,[16][17][18][19][20][21][22]. The modelling results were verified with available experimental data from their subsystems, and the phase equilibrium and aqueous solution density were investigated extensively.…”