Phase Equilibrium Measurements and Modeling of Thiols + Hydrocarbon + Water Ternary Systems at 303, 335, and 365 K and Pressure Up to 9 MPa

New vapor−liquid−liquid equilibrium (VLLE) data for methanethiol + methane + water, ethanethiol + methane + water, 1-propanethiol + methane+ water, and 1-butanethiol + methane + water ternary systems have been measured at... [ view full abstract ]

New vapor−liquid−liquid equilibrium (VLLE) data for methanethiol + methane + water, ethanethiol + methane + water, 1-propanethiol + methane+ water, and 1-butanethiol + methane + water ternary systems have been measured at three temperatures (303, 335, and 365 K) and pressures up to 9 MPa. A“static-analytic” method was used for performing all the measurements. The total system pressure was maintained by CH₄. The objective of this work is to provide experimental VLLE data with thermodynamic modeling for mixtures of mercaptans (thiols) with other natural gas contents at its crude form, for which no data are available in the open literature. Such data will help the industrial modeling of processes relevant to reduction of sulfur emissions. The Cubic-Plus-Association (CPA) equation of state was applied to describe the phase behavior of the investigated systems. It is shown that the CPA EoS satisfactorily describes the solubilities of mercaptans (thiols) in all phases. It is observed from the experimental data that the solubility of CH₄ in the aqueous and organic phases increases with an increase of the total system pressure and decreases with an increase of the temperature. However, the solubility of CH₃SH in the aqueous and organic phases decreases slightly with an increase of the total system pressure and increases significantly with an increase of the temperature. The new VLLE data of ternary system were compared with predictions of the cubic-plus-association equation of state. The model tends to under predict the concentration of CH3SH in all phases, particularly the vapor phase. However, the model underestimates the water content of the vapor phase, especially at low pressures and at the highest investigated temperature, i.e., at 365 K. Only the ethanethiol + methane + water system showed significant cross-association effects. Furthermore, no cross association (solvation) was found to be significant in 1-propanethiol + methane + water and 1-butanethiol + methane +water ternary systems.