Development of a new clay supported polyethylenimine composite for CO₂ capture

A new inexpensive inorganic-organic composite sorbent for CO₂ capture was prepared by the immobilization of a branched polyethyleneimine (PEI) onto porosity-enhanced clays using the wet impregnation method. In the composite, a low cost and naturally abundant clays (e.g. kaolinite and montmorillonite) was used as the supporting material, which was pre-modified by acid- or alkaline-treatment to improve its textural properties, i.e. pore volume and surface area, for accommodating the CO₂-philic PEI. Among the modified clays, the montmorillonite modified by 6M HCl (Mon_HCl_6M) showed the highest porosity with the pore volume of 0.71cm³/g from 0.16cm³/g, and BET surface area of 253m²/g from 72m²/g. The cost of the Mon_HCl_6M was estimated as $0.14/kg, which was significantly lower than reported supporting materials for the amine-based sorbents for CO₂ capture. At the optimal PEI loading of 50 wt% on the Mon_HCl_6M support, the CO₂ sorption capacity reached 112mg CO₂/g-sorbent at 75°C under dry condition, which can be further enhanced to 142mg CO₂/g-sorbent with the moisture addition (ca. 3vol%) due to the change in the interaction mechanism between CO₂ and amine in the presence of moisture. Moreover, the PEI/Mon_HCl_6M sorbent showed a good regenerability for 10 sorption-desorption cycles tested and a good thermal stability in the temperature range of CO₂ sorption (75°C) and desorption (100°C).