Further investigations of CO₂ capture using triamine-grafted pore-expanded mesoporous silica

A promising adsorbent for acid gas removal, referred to as TRI-PE-MCM-41, was produced by grafting a triamine-containing silane on an MCM-41-type mesoporous silica whose pores have been enlarged by post-synthesis hydrothermal treatment in the presence of a pore-expander. The CO₂ adsorption capacity was determined gravimetrically, and via column breakthrough measurements. The tolerance of TRI-PE-MCM-41 to moisture in the feed was substantiated by measurements under both equilibrium and dynamic conditions. Using a combination of mass spectrometry and thermogravimetry, it was corroborated that the presence of moisture enhances the CO₂ uptake at equilibrium. Adsorption measurements using fixed bed columns showed that moisture does not affect negatively the CO₂ working adsorption capacity compared to dry streams. Furthermore, since the material hardly adsorbed any N₂ or O₂, the selectivity for CO₂ over N₂ and O₂ was practically infinitely high. Cyclic measurements of pure CO₂ and CO₂:N₂ = 10:90 mixture using different regeneration modes shed light on the stability of the material and the influence of adsorption/desorption operating conditions on its performance. It was found that the temperature swing regeneration mode is suitable for desorption above 120 °C, while regeneration under temperature-vacuum swing may be attractive at lower desorption temperatures.