Characterization of a New Ionic Liquid and Its Use for CO2 Capture from Ambient Air: Studies on Solutions of Diethylenetriamine (DETA) and [DETAH]NO3 in Polyethylene Glycol

The development of effective CO2 capture technologies with low environmental impacts has been the focus of much recent research. Additionally, consideration is being given as to how CO2 sorbent systems may be applied to small-scale CO2 capture. After developing a useful CO2 capture system using the simple amine diethylenetriamine (DETA), we decided to investigate how the nitrate salt of DETA, [DETAH]NO3, with a reported high affinity for CO2 and exhibiting many of the ideal characteristics of an ionic liquid, would compare to DETA in terms of its performance as a CO2 sorbent. As a first step, [DETAH]NO3 was prepared and characterized using X-ray crystallography. For the CO2 capture studies, polyethylene glycol (PEG 200) was chosen as the solvent because of its nonreactivity toward the sorbent and CO2 as well as its low volatility and toxicity. Solutions of both DETA and [DETAH]NO3 in PEG 200 were found to perform optimally at a concentration of roughly 10% (v/v). [DETAH]NO3 proved slightly better for CO2 uptake at lower concentrations (5% v/v), while DETA performed better at higher concentrations. However, [DETAH]NO3 was calculated to have a vapor pressure considerably lower than that of DETA over the entire temperature range studied. Both the DETA and [DETAH]NO3 solutions could be regenerated, with no observed degradation, over several heating and cooling cycles. These results, paired with the many favorable physical characteristics of ionic liquids, make [DETAH]NO3 a viable alternative for CO2 capture and ideal for application in small-scale CO2 capture from ambient air.