(320d) Guanidine-Based Adsorbents for CO2 Capture

Over the past 200 years—correlated with the beginning of the industrial revolution—atmospheric carbon dioxide (CO₂) concentration has increased as a direct result of human activity. Current CO2 concentrations are around 420 parts-per-million (ppm). The accumulation of CO₂ and other greenhouse gases in the atmosphere has increased global average temperatures, leading to increased severity and frequency of extreme weather and climate events. To meet the Paris Agreement objective of keeping the average global temperature under 2 °C above pre-industrial temperature, removal of 10 billion metric tons per year of atmospheric CO₂ must occur before 2050 with another 20 billion metric tons per year after 2050. One of several negative emissions technologies proposed to achieve this aim is direct air capture (DAC) of CO₂. One approach to DAC that aims to lower the energy demand of the DAC process is the use of solid adsorbents.

Of the numerous solid sorbent classes proposed for CO₂ capture, such as amine-modified porous materials, zeolites, metal-organic frameworks, covalent-organic frameworks, and polymers, amine-modified materials are interesting because of their high selectivity and capacity even at DAC conditions as they have the ability to perform physisorption within the pores and chemisorption due to the acid-base interactions between amine groups and CO₂.

Here we present a series of activated carbon adsorbents functionalized with guanidine carbonate via wet impregnation with the objective of improving the CO2 adsorption capacity of activated carbon in low CO2 concentrations and in the presence of humidity. We performed CO₂ breakthrough tests under DAC conditions (420 ppm CO₂, 22 °C, 1 bar) on these adsorbents and found that the addition of guanidine carbonate at all tested loading levels improves the CO₂ adsorption capacity of activated carbon, and the presence of humidity improves CO₂ uptake further. The observed optimal guanidine carbonate loading level was 10 wt %.