Evaluation of diamine-appended metal-organic frameworks for post-combustion CO2 capture by vacuum swing adsorption

Five different diamine-appended metal-organic frameworks (MOFs) that show a S-shaped CO2 isotherm are evaluated for post-combustion CO2 capture from dry flue gas using a vacuum swing adsorption process. A comprehensive simulation and optimization study using a multi-objective genetic algorithm is performed. The optimization to maximize CO2 purity and recovery showed a key link between the feed temperature, evacuation pressure and process performance. The MOFs that achieve a target CO2 purity >= 95% and recovery >= 90%, namely, mmen-Mn-2(dobpdc) and mmen-Mg-2(dobpdc) were optimized to reduce parasitic energy and increase productivity. The adsorbents, mmen-Mn-2(dobpdc), mmen-Mg-2(dobpdc) and Zeolite 13X showed minimum parasitic energies of 142, 152 and 167 kWh(e)/tonne CO2 cap, respectively and maximum productivities of 0.4, 0.45 and 0.65 mol CO2 m(-1) ads s(-1), respectively while achieving CO2 purity 95% and recovery >= 90%. The possible low N-2 affinity and the unique shape of the CO2 isotherm were found to be key reasons for a lower energy consumption.