Assessing the potential of nanoporous carbon adsorbents from polyethylene terephthalate (PET) to separate CO₂ from flue gas

A series of nanoporous carbons was obtained by physical activation of polyethylene terephthalate and investigated for the separation of CO₂ from flue gas. The prepared carbons exhibited extremely low functionalization—negligible content in oxygen and other heteroatoms—accompanied by well-developed porous networks consisting of gradually increasing surface areas and micropore volumes. Such features allowed to study the role of nanopore confinement in the separation of carbon dioxide in CO₂/N₂ gas mixtures. The analysis of the adsorption isotherms of individual gases and their mixtures revealed different trends for the CO₂ uptake and the selectivity. Whereas CO₂ uptake was larger in the carbons with higher burn-off degree, the selectivity of CO₂ over N₂ was favored in the carbons with a higher fraction of narrow micropores. The differential adsorption enthalpy curves are typical of highly microporous samples reaching values close to those found in zeolites for low loadings. Data also show that the choice of the best adsorbent for cyclic gas adsorption and separation processes should consider a broad context, taking into account various parameters simultaneously such as gas selectivity, working capacity, adsorption enthalpy and energy consumption in the synthesis of the adsorbent.