Alkyl-Aryl Amine-Rich Molecules for CO2 Removal via Direct Air Capture

• Published in: ACS sustainable chemistry & engineering Vol. 8; no. 29; pp. 10971 - 10982
• Main Authors: Kumar, Dharam Raj, Rosu, Cornelia, Sujan, Achintya R, Sakwa-Novak, Miles A, Ping, Eric W, Jones, Christopher W
• Format: Journal Article
• Language: English
• Published: American Chemical Society 27.07.2020
• Subjects: Direct air capture (DAC); CO2 capture; Amine-based sorbents; CO2 separation
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.0c03706

Alkyl-aryl amine-rich small molecules (Ph-X-YY) are prepared by one-step nucleophilic substitution from tri- (X = 3) and hexa-bromine-substituted (X = 6) aromatic cores with two different aliphatic diamines, ethylenediamine (YY = ED) and propylenediamine (YY = PD). The resulting Ph-X-YY molecules are impregnated into mesoporous silica support materials (SBA-15) at predetermined organic loadings (20%–60%). TGA and DSC analyses suggest that these sorbent materials have good thermal stability. An increase in the amine loading led to an increase in CO2 adsorption capacity measured under simulated dry direct air capture (DAC) conditions. The Ph-3-YY based sorbents show superior CO2 adsorption capacities compared to the Ph-6-YY-based sorbent homologues, likely due to the bulkier molecular structure of the Ph-6-YY family. The highest CO2 capacity was demonstrated with the Ph-3-ED-based sorbent, 1.9 mmol/gSiO2, and an amine efficiency of 0.13 mmol CO2/mmol N at 35 °C under dry conditions. Temperature-swing adsorption/desorption cycles showed that the Ph-X-YY/SBA-15 had relatively stable performance that is comparable to that of the benchmark poly­(ethyleneimine) (PEI) and linear poly­(propyleneimine) (PPI) supported SBA-15 sorbents. The 60% Ph-3-ED/SBA-15 sample showed a 2-fold increase in the CO2 adsorption capacity under humid conditions (2.9 mmol/gSiO2 @ 30%, RH) and a 70% increase in amine efficieny (0.17 mmol CO2/mmol N). Thus, these aromatic-based polyamine molecules offer good potential for incorporation into practical CO2 sorbents targeting DAC technologies, and their structures expand the library of the amine-rich molecules that have been explored for DAC.