Covalent-organic polymers for carbon dioxide capture

Abstract

Reducing anthropogenic carbon dioxide emission has become an urgent environmental and climate issue of our age. Here, a series of covalent-organic polymers (COPs) are synthesized, and the adsorption properties of these COPs for H2, CO2, CH4, N2 and O2 are studied. The H2 uptake of COP-2 reaches 1.74 wt% at 77 K and 1 bar, which is among the highest reported uptakes in the field of microporous organic polymers under similar conditions, and CO2 and CH4 adsorption capacities are 594 mg g−1 and 78 mg g−1, respectively, at 298 K and 18 bar. Then, based on the single component isotherm, the dual-site Langmuir–Freundlich (DSLF)-based ideal adsorption solution theory (IAST) is used to predict the selectivity of the COP materials for post-combustion (CO2–N2) and pre-combustion (O2–N2) gas mixtures. The IAST predicted results indicate that COP-1 exhibits significantly higher selectivity compared to COP-2, 3 and 4, due to its smaller pore size. In particular, the adsorption selectivity of COP-1 for the CO2–N2 mixture reaches 91 at a CO2 : N2 ratio of 15 : 85 at 298 K and 1 bar, and 2.38 for the 21 : 79 O2–N2 mixture at 298 K and 1 bar. Furthermore, these COPs also show robust properties for the removal of CO2 from natural gas. The adsorption selectivity of COP-1 for CO2–CH4 is in the range of 4.1–5.0 at a CO2 : CH4 ratio of 15 : 85 at 0 < P < 40 bar.