Silica supported poly(propylene guanidine) as a CO2 sorbent in simulated flue gas and direct air capture

A guanidine-based oligomer/polymer, poly(propylene guanidine) (PPG), is synthesized and impregnated into mesoporous silica, SBA-15, to prepare a composite organic/inorganic CO2 sorbent. H-1 NMR and ESI-TOF MS spectra are used to characterize the structure of the synthesized oligomer/polymer. The adsorption capacities of the PPG based sorbents are measured under both simulated flue gas conditions and direct air capture conditions, and are compared to the performance of poly(ethylene imine) (PEI) based sorbents, the current state of art material among supported amine compositions. While PPG sorbents show lower pseudo-equilibrium capacities than PEI based sorbents under 400 ppm CO2 flow, they show comparable adsorption capacities using 10% CO2 streams. Furthermore, PPG sorbents were able to reach their pseudo-equilibrium capacity in a shorter time than the PEI sorbents under both 10% and 400 ppm CO2. However, due to the higher volatility of the prepared oligomeric PPG, the PPG sorbents show a fast decrease in the adsorption capacity when used over multiple cycles, suggesting that improved performance may be obtained using higher molecular weight oligomers/polymers.