PNNL

Abstract

Anhydrous tertiary alkanolamines chemically react with CO2 and H2S, with greater selectivity for the latter. This is in direct contrast to aqueous amine-based solvent systems, which exhibit higher selectivity for CO2 over H2S. Anhydrous tertiary alkanolamines exhibit pressure-induced chemical fixation of CO2 to form zwitterionic ammonium alkylcarbonate ionic liquids, while the same tertiary alkanolamines react with H2S at atmospheric pressures to form hydrosulfide ionic liquids. This difference in capture pressure implies that certain anhydrous alkanolamines could be chemically selective for H2S over CO2. We present here the first vapor-liquid equilibrium (VLE) data of anhydrous ethyldiethanolamine (EDEA) with CH4, C3H8, H2S and CO2 at 10 to 50 °C measured by the PTx and PTxy methods. The data are modeled in Aspen Plus® using an NRTL-with-solvation model. Data trends and phenomena are discussed for each gas. We also present simulations that compare anhydrous EDEA’s performance for CO2 and H2S high-pressure separations to other solvents such as Fluor Solvent, Selexol®, and aqueous methyldiethanolamine (MDEA) for a representative gas-purification absorber.