Evaluation of Polyethylenimine Grafted and Polyallylamine Dendrimer Grafted Mesocellular Silica Foam Promoted By Surfactants for Post-Combustion CO2 Capture

Amino polymer-based adsorbents can significantly reduce the energy penalty for CO₂ capture as compared to amine solutions and offer high CO₂ capture capacities (>2 mmole per g adsorbent).  However many amino polymers degrade at low temperatures of 90-110°C, which makes it difficult for desorption.

In this presentation, the technical issues associated with previously reported sorbents such as 1) thermal stability, 2) mechanical stability and 3) resistance to CO₂ diffusion will be addressed.  In this study, mesocellular silica foam (MCF) with a pore size range of 20-40 nm and a pore volume 1-2 cm³/g was synthesized.  The control of silica substrate pore sizes is critical to keeping the CO₂ diffusion resistance as small as possible.  Adsorbents were synthesized using a double grafting method where anchor agents such as γ-chloropropyltrimethoxysilane help in covalent bond formation between poly-allylamine dendrimer, polyethylenimine and MCF. The thermal stability and CO₂ capture capacities of the sorbent were found to increase by the adding a surfactant.  The CO₂ adsorption capacity obtained at 75°C for  a surfactant promoted sorbent is 2.3 mmol of CO₂/g adsorbent.  The as-synthesized adsorbents with amino polymer (30-50% by weight) and surfactant (5-10% by weight) were evaluated for CO₂ adsorption and desorption.  The characterization of the fresh and spent sorbents using BET, SEM, TEM, FTIR, and TGA- will be presented.

An adsorption-desorption study was performed by temperature swing adsorption between 75-85°C using 99.9% CO₂ gas and desorption at 90 °C in 100% N₂ atmosphere using TGA-MS. For desorption, the pressure was reduced from 1 atm to 0.1 – 0.5 atm at 90°C to desorb 99% of the adsorbed CO₂ gas.  The equilibrium studies and cyclic performance results of the sorbents for 10 adsorption – desorption cycles will be presented.