At equilibrium the fugacity of each component in the vapor phase is the same as that in the liquid phase. The vapor phase fugacity of component i in a mixture can be calculated f_i^(vap-mixt.)=P* y_(i )* ∅_iWhere p is the total pressure, yi is the mole fraction of the component in the vapor phase and ϕi is the fugacity coefficient which is a correction factor to take into account the non-ideality of the vapor phase. The liquid phase fugacity of component i in a mixture can be calculated with f_i^(Liq-mixt.)= f_i^Liq* X_i* γ_i, filiq is the fugacity of pure i in the liquid phase, Xi is the mass fraction of component in the liquid mixture and ϒi is the activity coefficient of component i at the temperature and pressure of the system. For water (the solvent) filiq is calculated according to f_i^Liq=P_w^sat* ∅_w^sat* Exp [ (V_w^L*(P- P_w^sat ))/(R*T)]Where Pwsat is the saturation of water vapor pressure at the system temperature, ϕwsat is the fugacity coefficient of water at T, Psat, VwL is the liquid molar volume of water and R is the universal gas constant. The exponential function is called the Poynting correction factor which is significant for high pressure applications. For components such as acid gases, the infinite dilution approach can be used where f_i^(Liq-mixt.)= - P_w^sat ))/(R*T) ]Where ϒi* is the activity coefficient of component i normalized to infinite dilution (=ϒi / ϒi∞ ), ϒi∞ is the infinite dilution activity coefficient and Hi is the Henry coefficient at infinite dilution. Vi,wL is the partial molar volume of the molecule in the solvent at the temperature of the system.2.1.2 Chemical equilibrium To study the chemical equilibrium, it is necessary to specify the set of reactions that occur in the liquid phase. For example, the main reactions of a… half of the paper… and the concentration dependence of the apparent equilibrium constants (Deshmukh and Mather 1981). A similar approach is the work of (Atwood, Arnold and Kindrick 1957) who used the “average ionic activity coefficient” to study the solubility of H2S in MEA, DEA and TEA. Although the model was simple, their approach can be considered good only for low ionic strength solutions, which is not the case for alkanolamine solutions (Deshmukh and Mather 1981 (SD Klyamer and TL 1972) followed the same approach as ( Atwood, Arnold and Kindrick 1957) to model CO2-amine-water systems (Solbraa 2002) and then generalized their approach to the model of H2S-CO2-amine-water systems (SD Klyamer, Kolesnikova and Rodin 1973) (Yu). , Astarita and Savage 1985) presented a model in which the apparent equilibrium constant is a function of the liquid species composition for the CO2-MDEA-H2O system.