Preparation of urea- and isocyanurate-containing polysilsesquioxane membranes for CO2 separation

Urea-and isocyanurate-containing polysilsesquioxane (PSQ) membranes were prepared and their CO2 separation performance was investigated. Applying the sol-gel process to N,N'-bis(triethoxysilylpropyl)urea (BTESPU) gave a urea containing PSQ membrane on an inorganic support, which showed good CO2/N2 permselectivity of 12 with CO2 permeance of 3.8 x 10(-9) mol/(m2 s Pa). The copolymerization of BTESPU with bis(triethoxysilyl)alkanes (EtO)3Si(CH2)xSi(OEt)3 (x = 1-3) produced membranes with improved performance, and the membrane prepared with bis(triethoxysilyl)ethane (BTESE, x = 2) showed CO2/N-2 permselectivity of 13 and CO2 permeance of 2.2 x 10(-7) mol/(m(2) s Pa). The homopolymerization of isocyanurate-containing precursors, tris(triethoxysilylpropyl) isocyanurate (TTESPI), tris(triethoxysilylmethyl) isocyanurate (TTESMI), and bis(triethoxysilylpropyl) isocyanurate (BTESPI), was found to yield membranes that have higher performance than the BTESPU homopolymer membrane. Of these, the membrane prepared from TTESPI showed the highest CO2 permeance of 3.2 x 10(-7) mol/(m(2) s Pa) and the highest CO2/N-2 permselectivity of 18. The copolymerization of TTESPI with BTESE resulted in the increase of CO2 permeance by 1.7 times, although CO2/N-2 permselectivity was slightly decreased to 12. The CO2-philicity of the urea units, which was estimated by density functional theory calculations on model systems, suggested a relationship between urea structure and membrane performance.