Separation Characteristics of Tetrapropylammoniumbromide Templating Silica/Alumina Composite Membrane in CO_2/N_2, CO_2/H_2 and CH_4/H_2 Systems

摘要

Nanoporous silica membrane without any pinholes and cracks was synthesized by organic templating method. The tetrapropylammoniumbromide (TPABr)-templating silica sols were coated on tubular alumina composite support (γ-Al_2O_3/α-Al_2O_3 composite) by dip coating and then heat-treated at 550℃. By using the prepared TPABr templating silica/alumina composite membrane, adsorption and membrane transport experiments were performed on the CO_2/N_2, CO_2/H_2 and CH/H_2 systems. Adsorption and permeation by using single gas and binary mixtures were measured in order to examine the transport mechanism in the membrane. In the single gas systems, adsorption characteristics on the α-Al_2O_3 support and nanoporous unsupport (TPABr templating SiO_2/γ-Al_2O_3 composite layer without α-Al_2O_3 support) were investigated at 20-40℃ conditions and 0.0-1.0 atm pressure range. The experimental adsorption equilibrium was well fitted with Langmuir or/and Langmuir-Freundlich isotherm models. The α-Al_2O_3 support had a little adsorption capacity compared to the unsupport which had relatively larger adsorption capacity for CO_2 and CH_4. While the adsorption rates in the unsupport showed in the order of H_2>CO_2>N_2>CH_4 at low pressure range, the permeate flux in the membrane was in the order of H_2N_2>CH_4>CO_2. Separation properties of the unsupport could be confirmed by the separation experiments of adsorbableon-adsorbable mixed gases, such as CO_2/H_2 and CH_4/H_2 systems. Although light and non-adsorbable molecules, such as H_2, showed the highest permeation in the single gas permeate experiments, heavier and strongly adsorbable molecules, such as CO_2 and CH_4, showed a higher separation factor (CO_2/H_2=5-7, CH_4/H_2=4-9). These results might be caused by the surface diffusion or/and blocking effects of adsorbed molecules in the unsupport. And these results could be explained by surface diffusion.