CO2 capture on easily regenerable hybrid adsorbents based on polyamines and mesocellular silica foam. Effect of pore volume of the support and polyamine molecular weight

Abstract

Mesocellular foams (MCFs) with a wide range of pore volumes and pore sizes were prepared by varying a number of synthesis parameters such as ammonium fluoride concentration, effect of swelling agent trimethylbenzene (TMB), equilibration time and calcination heating rate. The obtained MCFs with pore volumes from 0.98 cm³ g⁻¹ to 4.17 cm³ g⁻¹ were impregnated with polyethylenimine (PEI) having molecular weights of 800 g mol⁻¹ to 25 000 g mol⁻¹. These organic/inorganic hybrid materials with PEI loadings of 50 to 83% were tested for CO₂ adsorption capacity, kinetics, stability and regenerability. Increasing pore volume and size in MCFs allowed the loading of higher amounts of PEI and a better distribution of PEI in the pores. Access to the active amino sites by CO₂ was consequently facilitated. Adsorption of up to 6 mmol CO₂ per g adsorbent (265 mg g⁻¹) was obtained at 85 °C with the adsorbent containing PEI with a molecular weight of 800 g mol⁻¹ loaded on the support with the highest pore volume. Contrary to expectation, the adsorbents based on PEI with the highest molecular weight had faster desorption kinetics than the ones loaded with lower molecular weight PEIs. On the other hand the CO₂ adsorption kinetics for a given concentration were very similar for all PEIs, regardless of molecular weights. The adsorption capacity of the adsorbents did not decrease over 100 adsorption/desorption cycles at 75 °C. The CO₂ adsorption results obtained here were in the top tier compared to the ones reported in the literature. Preparation of PEI based adsorbents clearly benefited from the utilization of supports with larger pore volume and diameter which in turn led to significantly improved CO₂ adsorption characteristics.