A unified thermodynamic framework to compute the hydrate formation conditions of acidic gas/water/alcohol/electrolyte mixtures up to 186.2 MPa

The coexistence of acid gas/water/alcohol/electrolyte mixtures is common during the gas production process. Traditional methods have difficulty accurately predicting hydrate formation temperatures and pressures because of complicated molecular and ionic interactions in such mixture components. Based on the electrolyte Cubic-Plus-Association (e-CPA) equation of state (EoS) and the Parrish-Prausnitz model, this paper proposed a unified thermodynamic model to describe the multiple interactions of acid gas/water/alcohol/electrolyte components on gas, liquid, and hydrate phases by using the advantages of the e-CPA EoS to characterize the hydrogen bond association, solvation, ion electrostatic interaction, and ionic solvation. This work has achieved an accurate and flexible way to compute the hydrate formation conditions with or without acid gases, alcohols, and electrolytes. A total of 281 groups of experimental data at pressures from 0.068 MPa to 186.2 MPa are applied to validate this model. The results show that the average relative deviations (ARDs) of predicted temperatures and pressures are 0.13% and 6.52%, respectively. For nonelectrolyte systems, the ARD between the experimental and calculated hydrate formation temperatures is 0.19%, which is reduced by 0.24% and 0.34% in comparison with traditional Soave–Redlich–Kwong and Peng–Robinson EoSs. For mixtures containing alcohol and/or electrolytes, the ARD of predicted hydrate temperatures is 0.12%. Particularly, for harsh systems with ultrahigh pressure (186.2 MPa), the sour gas content of 24.52 mol%, MeOH concentration of 50% by mass, and salinity of 31% by mass, the deviations are less than 2.2 K. More cases demonstrate the performance and synergistic effect of alcohol and electrolytes in inhibiting hydrate formation.