Adsorption selectivity of CO₂ over CH₄, N₂ and H₂ in melamine-resorcinol-formaldehyde xerogels

Sorptive selectivity of melamine-resorcinol-formaldehyde xerogels, towards CO₂, CH₄, N₂ and H₂, is reported, where all systems demonstrate potential for selective adsorption of CO₂ from corresponding binary gas mixtures. Selected gas mixtures represent important gas separation applications found in industry, i.e. CO₂ removal from power plant flue gases (CO₂-N₂), sour gas sweetening (CO₂-CH₄), and separation of species in the water-gas shift reaction (CO₂-H₂). All materials tested exhibit microporous character, enhancing adsorption of small molecules, however, it is the inclusion of a nitrogen-rich material into the gel matrix that results in enhanced selectivities for these systems. Despite the porous character of the gels, under the test conditions used to simulate industrial parameters, all three balance gases, i.e. H₂, N₂ and CH₄, showed low affinities for the xerogels, while CO₂ adsorption was notably higher and increased with the inclusion and increased concentration of melamine. Ideal Adsorbed Solution Theory was used to demonstrate significant differences in adsorption uptake, especially for CO₂-CH₄, and high selectivities for CO₂ over N₂. In all cases, selected xerogels exhibited industrially relevant adsorption timescales for CO₂ over competitor gases, demonstrating the potential of these materials for the selective adsorption of CO₂ from process streams.