MODIFIED ORDERED MESOPOROUS SILICA MEMBRANES FOR CO 2 -N 2 SEPARATION
Reducing CO 2 emissions for addressing climate change concerns is becoming increasingly important since the CO 2 concentration in the atmosphere has increased rapidly since industrial revolution. Most currently investigated mitigation processes require CO 2 in a concentrated form. However, the CO 2 from coal-fired power plants is mixed with N 2 , water vapor, oxygen, and other impurities and present at a low ~15% concentration. Therefore, capturing CO 2 from dilute streams is an important step for many mitigation methods. Membrane separation methods are particularly promising due to potentially high CO 2 selectivities and fluxes. By a proper choice of the pore size and surface properties, the CO 2 separation and permeation across a membrane can be increased. However, current membranes for CO 2 separation suffer from a poor control over the pore size on the nanoscale and their surface properties. Mesoporous MCM-48 silica was functionalized using hindered and unhindered amine. The presence and surface concentration of the amino groups in the mesoporous MCM-48 silica upon attachment was studied by the IR, Si/CHN elemental analysis, and TGA, which confirmed that amino groups were successfully attached and their concentrations on the MCM-48 were 2.5 and 1.5 mmol/g, respectively. In addition, in-situ IR and CO 2 adsorption studies of amine-modified MCM-48 silica as potential membrane materials showed high CO 2 selectivities over N 2 . Mesoporous MCM-48 silica membranes synthesized on porous alumina supports obtained by the solution growth method and 3-aminopropylsilyl groups were attached to the surface of these silica membrane. The unsteady-state gas permeation studies using H 2 , He, N 2 , and CO 2 indicated the absence of large pinhole (>5.0 nm) in these mesoporous silica membranes. However, the aminopropyl-modified MCM-48 membrane showed no CO 2 separation in a binary gas permeation experiment due to low packing density of amino groups. In order to achieve high packing density of the amino groups on the surface of mesoporous silica membranes, surface hydration to increase silanol group concentration on MCM-48 and alternative amino functional groups was emplolyed. The polymerization of the amin-containing alkoxide and branched polyethyleneimine (PEI), which has chains with numerous CO 2 -capturing amino groups were introduced in MCM-48 membranes. The PEI-modified membranes showed high N 2 selectivity over CO 2 .
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:mesoporous silica carbon dioxide separation inorganic membrane
Date of Publication:01/01/2003