To date, most studies describing Direct Air Capture (DAC) sorbent research have focused on the use of solid-supported amine materials. Among these studies, it has been reported that solid amine sorbents integrated on porous oxide supports are most efficient. For instance, low molecular weight, branched poly(ethylenimine) (PEI) has been employed in numerous research as a primary amine containing polymer to sorb CO2 because of its large density of amine groups and good stability. Of many physical adsorbents, one of the ordered mesoporous silica materials, MCM-41 greatly enhances CO2 adsorption capacity and separation selectivity. A chemical reaction between CO2 and the amines occurs in supported amine materials, forming strong bonds and allowing for considerable uptakes. However, the details in distribution and transport of CO2 molecules through specific capturing materials have not been completely characterized by experimental methods due to the limit of instrumental resolution. Using molecular dynamic (MD) simulation, we have discovered that the pair correlations of CO2 with the primary and secondary amines are reduced under hydrated conditions, suggesting that the carbamate formation mechanism is less prevalent compared to dry conditions. We investigated the distribution and transport of CO2 through HB-PEI-loaded MCM-41 at dry and hydrated conditions. We also investigated the binding energies between HB-PEI and MCM-41 and suggest optimal loading of the amine. To elucidate the CO2 capture mechanisms, the details of the local structures were also characterized.

CO2 adsorption in hyperbranched polyethylene imine-loaded MCM-41: Molecular dynamics simulation approach

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