Exceptionally stable Bakelite-type polymers for efficient pre-combustion CO2 capture and H2 purification

Abstract

Electricity production from fossil fuels and hydrogen production from steam reformation represent two single-site large scale sources of CO₂. Separation of CO₂ from these sources via the pre-combustion capture process delivers multiple benefits – cleaner electricity, mitigates the global CO₂ concentration and generates a large stream of H₂, a clean burning fuel. This requires separation of CO₂ from high pressure gas mixtures, which is best achieved by pressure/temperature swing adsorption processes. The efficiency of such processes to a large extent relies on the performance of the solid sorbent. Both processes occur under steam-rich, high temperature and pressure conditions. Developing sorbents to capture CO₂ under such harsh conditions is challenging and rewarding. Porous organic polymers constructed from strong covalent links are promising candidates owing to their high thermal as well as chemical stability and can be tuned to adopt a microporous structure to gain substantial molecular sieving effects. Here we report Bakelite-type porous organic polymers synthesized via catalyst-free C–C bond formation reactions. These polymers exhibit high CO₂ capacity (∼15 mmol g⁻¹ at 35 bar), selectivity (S(60H₂/40CO₂) = 200 and S(80H₂/20CO₂) = 289, both at 298 K and 10 bar) and a record-breaking working capacity (∼6.8 mmol g⁻¹ for a 10 to 1 bar pressure swing). Additionally, these amorphous polymers show fast diffusion kinetics (D_c = ∼7.5 × 10⁻⁹ m² s⁻¹), comparable to highly crystalline MOFs, which explains their high CO₂ capacity (2.42 to 3.52 mmol g⁻¹) under dynamic CO₂/H₂ flow. The high surface hydrophobicity, basicity and polarity of these functionalized phenol-aldehyde frameworks make them most selective for CO₂ capture even under chemically demanding humid conditions.