CO ₂ Capture from Air Using Pelletized Polyethylenimine Impregnated MCF Silica

Two polyethylenimine impregnated mesocellular foam silica sorbents (PEI-80a and PEI-80b) were evaluated for capturing CO ₂ from 420 ppm of CO ₂ in N ₂ under both dry and humid conditions. A fixed bed adsorption setup was used to evaluate the CO ₂ uptake under isothermal conditions between 33 and 81 °C with a gas flow of 200 mL/min. Under dry conditions, the highest capacity was observed at 46 and 52 °C for PEI-80a (1.29 mmol/g) and at 46 °C for PEI-80b (1.94 mmol/g). There was negligible uptake of CO ₂ at 81 °C, indicating possible regeneration at relatively low temperatures. For PEI-80b, the introduction of moisture (0.5 and 2% mol-H ₂ O in feed gas) yielded up to 53% enhancement in capacity. Higher moisture levels (3% mol-H ₂ O) appeared to be detrimental to the CO ₂ uptake. The highest capacity of 2.52 mmol/g was achieved at a temperature of 46 °C and a moisture level of 2% mol-H ₂ O.