A simple model for estimating hydrogen sulfide solubility in aqueous alkanolamines in the high pressure-high gas loading region

Abstract

Hydrogen sulfide is essentially removed from the raw natural gas to meet the process, health, safety and environmental standards. Alkanolamine based absorption process remains the prevalent technique for hydrogen sulfide removal due to ease of operation and economic considerations. The design of such gas separation systems is a critical factor in meeting the stringent process requirements and optimizing operations. To achieve precise design, determination of vapor–liqid equilibrium for the system is indispensable while maintaining efficacy and simplicity. This study presents a simple model for estimating hydrogen sulfide solubility in aqueous alkanolamines and their blends in the high pressure-high gas loading region. The model equation is developed by considering and combining amine protonation and bi-sulfide formation reactions, assuming ideal liquid properties. Satisfactory correlated values of hydrogen sulfide loadings (0.21–3.15 mol gas/mole solvent) are obtained over a wide range of temperature (298.15–393.15 K), pressure (60–7027 kPa) and alkanolamine concentration (1.12–14.27 molal). Parameters are given for the hydrogen sulfide solubility in aqueous solutions of monoethanolamine, diethanolamine, N-methyldiethanolamine, 2-amino-2-methyl-1-propanol, piperazine, diglycolamine, di-isopropylamine, 1-amino-2-propanol and their selected blends. The model shall be useful for the design of alkanolamine based natural gas sweetening systems, operating at high pressure and high hydrogen sulfide gas loadings.