Assessing Anhydrous Tertiary Alkanolamines for High-Pressure Gas Purifications

Abstract

Anhydrous tertiary alkanolamines chemically react with CO 2 and H 2 S, with greater selectivity for the latter. This is in direct contrast to aqueous amine-based solvent systems, which exhibit higher selectivity for CO 2 over H 2 S. Anhydrous tertiary alkanolamines exhibit pressure-induced chemical fixation of CO 2 to form zwitterionic ammonium alkylcarbonate ionic liquids, while the same tertiary alkanolamines react with H 2 S at atmospheric pressures to form hydrosulfide ionic liquids. This difference in capture pressure implies that certain anhydrous alkanolamines could be chemically selective for H 2 S over CO 2 . We present here the first published vapor−liquid−liquid equilibrium (VLLE) data of anhydrous ethyldiethanolamine (EDEA) with CH 4 , C 3 H 8 , H 2 S, and CO 2 at 10−50°C measured by the TPx and TPxy methods. The data are modeled in Aspen Plus using an NRTL-with-solvation model. Data trends and the underlying phenomena are discussed for each gas. We also present process simulations that compare anhydrous EDEA's performance for CO 2 and H 2 S high-pressure separations to other solvents such as Fluor Solvent (propylene carbonate), Selexol, and aqueous methyldiethanolamine (MDEA) for a representative gas-purification absorber. This work indicates that a niche for anhydrous EDEA in high-pressure gas purifications may be its stronger absorption for CO 2 and H 2 S (relative to physical solvents) and its selectivity for H 2 S over CO 2 (relative to chemical solvents). ■ INTRODUCTIONChemical solvents such as alkanolamines are well-suited for gastreating applications, such as natural gas purification and CO 2 capture, because they provide high selectivity for acid-gas components (e.g., CO 2 and H 2 S) over nonpolar species. 1,2 More than 80 years ago Bottoms 3 first recognized amines as chemical solvents, and also invented the absorption-stripping process used today. Amine scrubbing is widely expected to be the dominant technology for the low-pressure CO 2 capture from power plants, particularly for coal-fired plants. 4 Amine scrubbing is also widely used for higher-pressure gas purifications associated with gas processing. 1,2 However, chemical solvents have the disadvantage of relatively high enthalpies of solution, and in cases where the acid-gas impurities are at a significant composition of the total gas stream, the energy penalty of regenerating the solvent by application of heat may be out of proportion to the value of the treated gas. This has provided an opportunity for physical solvents, in which nonreactive organic agents are used. Here, solvent regeneration can often be accomplished by a simple reduction in pressure, without the need for heat to increase the temperature. Examples of physical solvents for gas-purification processes are Rectisol (methanol), Fluor Solvent (propylene carbonate), and Selexol (mixture of propylene glycol dimethyl ethers). 1 In this work, we present a preliminary evaluation of the niche for anhydrous tertiary alkanolamines such as EDEA (ethyldiethanolamine) for high-press...

Study of Various Aqueous and Non-Aqueous Amine Blends for Hydrogen Sulfide Removal from Natural Gas

“…TEA was the first commercially used alkanolamine for gas treating process [7]. It is now being replaced with other amines like monoethanolamine (MEA), diethanolamine (DEA), diisopropanolamine (DIPA), methyl diethanolamine (MDEA), 2-amino-2-methyl-l-L-propanol (AMP), ethyl diethanolamine (EDEA) and 2-(2-aminoethoxy) ethanol (DGA) due to its low capacity and high circulation rate [15]. MDEA based system offered advantages like selective hydrogen sulfide removal over carbon dioxide, low vapor pressure, higher thermal stability, less corrosion, lower heat of reactions and specific heat [7,13].…”

A Techno-Economic Analysis of a Novel Solvent-Based Oxycombustion CO2 Capture Process

“…N -Ethyldiethanolamine (EDEA) is a tertiary alkanolamine, which, in this study, is used as an anhydrous solvent to capture CO 2 originating from an oxycombustion process. This solvent has shown promise to capture both hydrogen sulfide H 2 S and CO 2 , making it a versatile solvent suitable for both natural gas sweetening and CO 2 capture processes . This versatility can potentiate its use across sectors, which would increase its market demand and thus reduce its unit cost.…”

“…This versatility can potentiate its use across sectors, which would increase its market demand and thus reduce its unit cost. EDEA forms a zwitterionic ammonium alkylcarbonate ionic liquid by reacting with CO 2 under pressure, and reverts back to the initial components via expansion, according to Figure …”

“…A successful simulation of this solvent-based capture process requires the knowledge of some physical and chemical properties of EDEA. The phase equilibrium data obtained by Mathias et al was used to simulate the CO 2 uptake by EDEA in the absorber, expanding upon the author’s previous work. The Aspen simulation was performed using the electrolyte NRTL property package, which is an activity-coefficient model …”

“…The phase equilibrium data obtained by Mathias et al was used to simulate the CO 2 uptake by EDEA in the absorber, expanding upon the author’s previous work. The Aspen simulation was performed using the electrolyte NRTL property package, which is an activity-coefficient model …”