Diamine-Anchored Polystyrene Resins for Reversible SO₂ Adsorption

Diamine-anchored Merrifield resins ([DAMR]CH₃SO₃; DA = diamine, MR = Merrifield resin, X = Cl, CH₃SO₃, and (CF₃SO₂)₂N), synthesized from the reactions of Merrifield resin with a tertiary diamine selected from N,N,N′N′-tetramethylethylenediamine (TMEDA), 1,4-dimethylpiperazine (DMP), and 1,4-diazabicyclo[2,2,2]octane (DABCO), were found to exhibit excellent performance as SO₂ adsorbents under both hydrous and dry conditions. Under dry conditions, the molar SO₂ adsorption capacity of [DAMR]X was greatly affected by the nucleophilicity of the anion but was rarely influenced by the type of diamine anchored on the cation. In contrast, under hydrous conditions, the SO₂ adsorption and desorption behaviors on [DAMR]X were strongly affected by the basicity of the diamine on the cation, [DAMR]⁺. Spectroscopic and experimental results suggest that in the presence of water SO₂ is adsorbed on [DAMR]X as a bisulfite species, and the formation and the stability of the bisulfite species increase with the increasing basicity of the diamine of [DAMR]⁺. SO₂ adsorbed on [DABCOMR]X was found to completely desorb at 80°C, irrespective of the presence of water.