Direct air capture on amine-impregnated FAU zeolites: Exploring for high adsorption capacity and low-temperature regeneration

Abstract

To develop an efficient adsorbent for direct air capture (DAC), capturing 400 ppm of CO2 in simulated air was investigated for amine-impregnated faujasite (FAU) zeolite. Six types of amines were used: monoethanolamine (MEA), diethylenetriamine (DETA), ethylenediamine (EDA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and polyethylenimine (PEI; average molecular weight = 600). To evaluate the Si/Al ratio, FAU zeolites with different Si/Al ratios (2.75–300) were prepared by dealumination and used for impregnation. The 400 ppm CO2 adsorption under dry conditions was performed using a thermogravimetric (TG) analyzer, while humid condition test was conducted using a breakthrough measurement instrument. Under dry conditions, 40 wt% of PEI-impregnated FAU zeolite showed high CO2 adsorption capacity of 0.64 mmol g−1 and an adsorption rate of 0.035 mmol g−1 min.−1. Additionally, the capacity of DETA-impregnated samples showed a relatively high capacity of 0.40 mmol g−1. With an increase in the Si/Al ratio of FAU zeolite, the adsorption capacity of the DETA-impregnated samples increased, whereas the PEI-impregnated samples retained an adsorption capacity of approximately 0.64 mmol g−1. Under humid conditions, an enhanced adsorption capacity (1.54 mmol g−1) was observed for the PEI-impregnated FAU samples. It is noteworthy that purging at 25 °C without additional heat treatment resulted in the release of CO2 from the DETA-impregnated samples after adsorption. The amount of released CO2 after purging the DETA-impregnated samples was up to 0.27 mmol g−1. PEI- and DETA-impregnated FAU zeolites showed excellent regeneration stability over 10 adsorption cycles under humid conditions.