Hydrophobic functionalized amine-impregnated resin for CO2 capture in humid air

Water vapor in air significantly affects the CO2 separation performance of solid amine sorbents. Although moisture benefits the CO2 adsorption process, the co-adsorbed H2O in amine sorbents leads to extra regeneration energy consumption, which challenges the application of solid amine sorbents for direct air capture. Reducing H2O adsorption and improving the CO2/H2O selectivity of solid amine sorbents are fundamental solutions. This work clarified the more prominent hydrophilic contribution of polyethylenimine (PEI) layers than support resins for amine-impregnated sorbents. Then, we identified the phenyl group as the preferred additive to enhance the hydrophobic properties of PEI-impregnated sorbents using an orthogonal test. The introduction of hydrophobic phenyl groups reduced the average water vapor adsorption per amine group by more than 50% and increased the CO2/H2O selectivity of the amine resin sorbents by 68%-89%, resulting in lower heat requirement caused by H2O desorption. Despite the modification reduced CO2 uptake, a modest CO2 capacity of 1.47-1.6 mmol/g was detected of BZ13.5-40%R20 in a representative air condition (28 degrees C, relative humidity 50%). In addition, BZ13.5-40%R20 showed stable CO2 capacity in 10 consecutive temperature swing adsorption cycles (desorption at 70 degrees C, N2 stripping) in laboratory.