Measurement and modeling of mercaptans solubility in aqueous alkanolamine solutions

International audienceNatural gas always contains contaminants such as acid gases (CO2 and H2S), mercaptans and other sulfur components. With the purpose of avoiding corrosion when water is present, safety problems and environmental issues, these impurities must be removed until an acceptable specification. According to Huguet et al. [1], the treated gas contains as maximum as 2% CO2, 2–4 ppm H2S and 5–30 ppm total sulfur (mercaptans and COS). Absorption with alkanolamines processes are commonly used for natural gas treatment. The knowledge of the mercaptans solubility in aqueous alkanolamine solutions is important in acid gas removal process simulation and design, as it allows designers to confirm their regulatory limits. In previous works done at CTP, the activity coefficients at infinite dilution and Henry's law constant of mercaptans [2] have been determined by using gas stripping method; the solubilities of n-Propyl-mercaptan, n-Butyl-mercaptan and Dimethylsulfide in loaded, and unloaded MDEA and DEA aqueous solutions [3] were measured by using static analytic method. In this work, we report the results of Vapor Liquid Equilibrium measurements of different mercaptans (methyl-and ethyl-mercaptan) in different alkanolamine solutions of MDEA. Thermodynamic models are crucial for acid gas removal process simulation and design. The association effects of water and alkanolamine have the most important role in these systems. Hence, Cubic-Plus-Association Equation of State [4] (CPA EoS) has been chosen. In previous work [5], CPA EoS was successfully applied to describe the phase equilibria of alkane-alkanolamine-water ternary systems. In the present work, CPA EoS was applied to represent mercaptans solubility in aqueous alkanolamine solutions. Satisfactory results are obtained for representing both liquid and vapor phase composition