Synthesis of microporous organic polymers with high CO2-over-N2 selectivity and CO2 adsorption

Abstract

A series of microporous organic polymers (MOPs) were synthesized by Schiff base condensation of 1,3,5-tris(4-aminophenyl)benzene and a number of dialdehyde monomers. The polymers were structurally characterized by in situ infrared and ex situ solid state ¹³C{¹H} nuclear magnetic resonance (NMR) spectroscopy. Synthesis conditions were optimized to enhance CO₂ uptake by the MOPs. Synthesis at low temperatures results in the MOPs being linked by imine groups. Heating of the MOPs reduces the number of imine groups and after heating to >300 °C nitrile groups were found to be present in the MOPs. The MOPs have specific surface areas up to 614 m² g⁻¹ and narrow pore size distributions of ∼4 to 8 Å. The selectivity of CO₂-over-N₂ at 273 K and 1 bar was 56–77, which requires either an influence of chemisorption on CO₂ or a molecular sieving (or kinetic selection) of CO₂-over-N₂. The materials had also heats of adsorption typical for physisorption of CO₂.