Biological versus Synthetic Polymers as Templates for Calcium Oxide for CO₂ Capture

When CaO absorbs CO₂ in pre-combustion systems, it can greatly increase the H₂ yield from pyrolysis and gasification reactions. However, natural sources of CaO, such as limestone (CaCO₃), produce sorbents that quickly lose reactivity, and more stable sorbents are therefore desired. Although both synthetic and biopolymers can induce the formation of a wide variety of CaCO₃ morphologies, only a few synthetic polymers and perhaps no natural polymers have been applied to the synthesis of CO₂ sorbents. We prepared CaO precursors templated on three natural polysaccharides (chitosan, agar, and carrageenan) and three synthetic polymers [poly­(acrylic acid), poly­(ethylene glycol), and poly­(ethylene oxide-<i>b</i>-propylene oxide-<i>b</i>-ethylene oxide)] and tested these as CO₂ sorbents. The sorbents templated on biopolymer films had interesting reactivity that was affected by residual biopolymer, even after several calcination–carbonation cycles at high temperatures. However, these sorbents were not more effective than CaO derived from commercial CaCO₃. Thus, although biopolymers can direct CaCO₃ formation by binding to Ca²⁺, the biopolymer-templated CaCO₃ samples tested here were inferior CO₂ sorbents. Two of the sorbents templated on synthetic polymers, on the other hand, gave better CO₂ uptake activity and stability than CaO derived from commercial CaCO₃. These results, in combination with the vast array of existing synthetic polymers, suggest a promising future for synthetic polymers in this field