Nanoporous Organically Pillared Vermiculite for CO ₂ Capture from Humid Flue Gas

Advancing climate change and its effects require a reduction in greenhouse gas emissions, especially CO 2 . To mitigate CO 2 emissions, capturing greenhouse gas from point sources with high CO 2 concentrations is a particularly rewarding target. Here, we report on a low-cost (<$5/kg) microporous organically pillared layered silicate, MOPS-10, obtained by simple cation exchange of interlayer cations in vermiculite with diammonium ethane. In MOPSs, cationic molecules are sandwiched between silicate nanosheets, with nanopores generated between the pillar moieties. By applying the linear diammonium pillar, the pore height in MOPS-10 is adjusted to the kinetic diameter of CO 2 molecules while neither N 2 nor O 2, two gas species with larger kinetic diameters present in a typical postcombustion flue gas stream, can enter the slit pores due to effective size exclusion. Static single-gas adsorption isotherms show a strongly preferred uptake of CO 2 based exclusively on physisorption. The static single-gas isotherms are confirmed in dynamic breakthrough experiments (CO 2 /N 2 15/85), where an extremely high selectivity for CO 2 over N 2 is observed. Obviously, water molecules are small enough to enter the slit pores, and water vapor therefore plays a pivotal role for CO 2 capture from flue gas streams. With many porous materials, a preferential coordination of H 2 O is observed. With MOPS-10, however, when applying nonequilibrium conditions, no preferential adsorption of H 2 O over CO 2 is found in humid dynamic breakthrough experiments (CO 2 /H 2 O/N 2 ≈ 11/6/83 at 40 °C) mimicking a typical coal-fired power plant flue gas stream. At 1% CO 2 breakthrough, a CO 2 breakthrough capacity of 0.43 mmol/g and a CO 2 /H 2 O dynamic breakthrough selectivity of 1.2 are obtained. Additionally, MOPS-10 can be regenerated at a temperature as low as 40 °C. Regeneration thus saves costs compared to established systems, especially amine scrubbing. While cycling the adsorption material, the CO 2 /H 2 O dynamic breakthrough selectivity is even slightly increased to 1.4.