Direct Air Capture of CO₂ Using Amine/Alumina Sorbents at Cold Temperature

Abstract

Rising CO2 emissions are responsible for increasing global temperatures causing climate change. Significant efforts are underway to develop amine-based sorbents to directly capture CO2 from air (called direct air capture (DAC)) to combat the effects of climate change. However, the sorbents’ performances have usually been evaluated at ambient temperatures (25 °C) or higher, most often under dry conditions. A significant portion of the natural environment where DAC plants can be deployed experiences temperatures below 25 °C, and ambient air always contains some humidity. In this study, we assess the CO2 adsorption behavior of amine (poly(ethyleneimine) (PEI) and tetraethylenepentamine (TEPA)) impregnated into porous alumina at ambient (25 °C) and cold temperatures (−20 °C) under dry and humid conditions. CO2 adsorption capacities at 25 °C and 400 ppm CO2 are highest for 40 wt% TEPA-incorporated γ-Al2O3 samples (1.8 mmol CO2/g sorbent), while 40 wt % PEI-impregnated γ-Al2O3 samples exhibit moderate uptakes (0.9 mmol g–1). CO2 capacities for both PEI- and TEPA-incorporated γ-Al2O3 samples decrease with decreasing amine content and temperatures. The 40 and 20 wt % TEPA sorbents show the best performance at −20 °C under dry conditions (1.6 and 1.1 mmol g–1, respectively). Both the TEPA samples also exhibit stable and high working capacities (0.9 and 1.2 mmol g–1) across 10 cycles of adsorption–desorption (adsorption at −20 °C and desorption conducted at 60 °C). Introducing moisture (70% RH at −20 and 25 °C) improves the CO2 capacity of the amine-impregnated sorbents at both temperatures. The 40 wt% PEI, 40 wt % TEPA, and 20 wt% TEPA samples show good CO2 uptakes at both temperatures. The results presented here indicate that γ-Al2O3 impregnated with PEI and TEPA are potential materials for DAC at ambient and cold conditions, with further opportunities to optimize these materials for the scalable deployment of DAC plants at different environmental conditions.

Weakly Adsorbed CO2 and H2O Species on Monoethanolamine Films in a Room-Temperature CO2 and Direct Air Capture Cycle: An In Situ Infrared Study

“…Although humidity could promote CO 2 capture on amine sorbent from air, , hydrophobic environment of amine sites appears to favor the formation of carbamic acid on MEA_PPGDE. The humidity has a positive effect on CO 2 capture by the amine in a hydrophobic environment.…”

Minimal Kinetic Model of Direct Air Capture of CO2 by Supported Amine Sorbents in Dry and Humid Conditions

“…Direct air capture (DAC) of CO 2 is an important solution to control CO 2 concentration in the atmosphere in order to mitigate climate change due to the increasing CO 2 level. − The DAC process usually involves the use of liquid or solid sorbents to selectively capture CO 2 from the air via chemisorption, followed by sorbent regeneration via a temperate/pressure swing to release concentrated CO 2 for storage or utilization. Supported amine sorbents have attracted significant attention for DAC, owing to their high adsorption capacity, excellent selectivity, beneficial coadsorption with moisture, and relatively mild energy requirements for sorbent regeneration. − Physically impregnated or chemically grafted amine groups onto porous supports such as mesoporous silica, alumina, carbon, and metal–organic frameworks have been reported. − The capture capacity is dictated by the reaction stoichiometry of amine groups with CO 2 in dry or humid conditions, the temperature, and the loading of amines in the porous supports. ,− …”

Amine Sorbents for Sustainable Direct Air Capture: Long-Term Stability and Extended Aging Study

“…The era of fossil energy and the industrial revolution commenced with the introduction of the steam engine at the end of the 18th century. 1 Since then, there has been a substantial surge in energy demand driven by a burgeoning population and an overall improved quality of life. This surge has led to a significant increase in global atmospheric carbon dioxide (CO 2 ) concentrations, reaching 420 ppm in November 2023, as reported by NASA.…”

“…Class I involves physical amine impregnation into supports, offering easy preparation and higher amine loadings but suffering from stability issues due to amine leaching. 1,35,36 Class II sorbents feature chemical bonding through silane linkages, providing enhanced stability but lower CO 2 uptake and a more intricate synthesis process. 37 Class III sorbents, synthesized via in situ polymerization, combine high capacity and stability but involve the most complex synthesis process.…”

“…Subsequently, a systematic investigation was conducted to analyze the stability of the sorbents under various conditions, including thermal degradation, hydrothermal treatment, and extended operational cycles. Additionally, the study examined the impact of prolonged storage on class III sorbents, comparing the results with available literature data for class I (the only existing data , ).…”