Preparation of amine- and ammonium-containing polysilsesquioxane membranes for CO2 separation

Amine-containing polysilsesquioxane (PSQ) membranes were studied with regard to their CO2 separation ability. PSQ membranes were prepared by the sol–gel process using three amine-containing monomers, bis(triethoxysilylpropyl)amine (BTESPA), (aminopropyl)triethoxysilane (APTES), and (aminoethylaminopropyl)triethoxysilane (AEAPTES), to examine the relationship between precursor structure and membrane performance. The CO2 permeances of the membranes prepared by 1:1 copolymerization with bis(triethoxysilyl)ethane increased in the order of AEAPTES-derived membranes < APTES-derived membranes < BTESPA-derived membranes, and their CO2/N2 permselectivities decreased in the same order. On the basis of density functional theory calculations on model systems and nitrogen adsorption-desorption experiments of the PSQ gels, it was found that CO2 affinity and porosity of the membranes were important factors affecting CO2 separation performance. Copolymerization under acidic conditions resulted in the formation of ammonium-containing membranes with improved CO2 permeances and acceptable CO2/N2 permselectivities.