Investigation of Sulfolane Addition to Heat of H2S Absorption in Aqueous MDEA Solution Using Solubility Data

Aqueous alkanolamine solutions technology is one of the most important processes in natural gas sweetening. Water provides an implicit context for alkanolamine to absorb CO2 and H2S chemically. However, apart from their advantages, aqueous alkanolamine solution is not a good solvent for mercaptan removal and due to their innate exothermic reaction, it requires high reboiler duty performance in the desorption tower. Thereby it causes some undesirable side irreversible reactions such as decomposition of solvents, degradation so on. Nowadays mixture of aqueous alkanolamine solution and physical solvents such as sulfolane so-called hybrid solvents have been used to modify conventional aqueous alkanoleamine solvents. Hybrid solvents with optimum composition may possess both advantages of physical (SFL) and chemical (aqueous alkanolamine) solvents by which, not only CO2 and H2S would be absorbed chemically, but also mercaptan would be removed up to the allowed specification limit. In this work, the differential enthalpy related to H2S dissolution in both conventional (H2O – MDEA) and hybrid solvent (H2O - SFL – MDEA) were estimated from reported solubility data in the literature using Gibbs – Helmholtz equation. The process of differentiation was done after e-Pitzer modeling of experimental solubility data. As a result, the applied model provided sound results for solubility data in quaternary hybrid systems (ARD% equal to 5.4%), and also the addition of Sulfolane in MDEA – H2O system has a marginal effect on dissolution enthalpy of H2S.