CO2 Adsorption on Chitosan Aerogel Beads

Abstract

Direct CO2 capture from air or CO2 separation are key strategies to control the carbon dioxide concentration of the atmosphere. Highly porous solid amine bearing adsorbents promise applicability in this respect. Open porous aerogel beads prepared from sustainable sources like chitosan combine important features for selective CO2 separation. Macropores in a mixed bed of aerogel beads and internal mesopores guarantee good substance transport. Primary amine groups of chitosan selectively adsorb CO2 via chemisorption. Scalable methods as the JetCutter technology and supercritical drying were employed to develop chitosan aerogel beads. The aerogel structure was investigated with scanning electron microscopy and nitrogen physisorption experiments. Static and dynamic sorption experiments were performed to determine CO2 adsorption capacity. The chitosan aerogel structure is defined by 15 nm wide fibrils that create an open porous cellular network with 50 nm cell width. The specific surface area was measured at 240 m2/g and the volume porosity above 90 %. CO2 isotherms recorded at different temperatures begin with a convex incline and transition into a linear region between 30 and 100 kPa CO2. The desorption isotherm does not match the adsorption branch but span a hysteresis with a delay up to 30 kPa. The maximum CO2 adsorption capacity at 100 kPa and 0 °C was recorded at 1 mmol/g. An isotherm separation indicates that the adsorption capacity stems from 40 % chemisorption and 60 % physisorption. Dynamic breakthrough experiments on chitosan aerogel beads prepared from sustainable sources confirm selective CO2 separation from N2/CO2 mixtures.