Abstract
Membranes are increasingly replacing the traditional methods of gas separation, such as distillation and absorption. In many industrial applications, like removal of small amounts of higher hydrocarbons from natural gas or air, it is desirable from economic and operational points of view to have the larger component permeate preferentially. For such applications one must exploit the differences in solubility rather than diffusivity among the components. Either polymeric or inorganic (porous) membranes might be used for this purpose. Generally speaking, polymeric materials exhibit high selectivity at low permeation rates, while porous inorganic membranes are characterized by low selectivity factors at high permeation rates. An alternative is to produce a polymer- inorganic hybrid membrane that combines the best characteristics of both; that is the subject of this work. A procedure for the synthesis of oligomer-modified inorganic membranes and an evaluation of their ability to perform solubility-based separation are presented. Alumina membranes with average pore sizes near 5 nm and 10 run were treated with various n-alkyl trichlorosilanes. Pure gas permeation studies using nitrogen, methane, and propane were performed to investigate the effects of modification on the ideal selectivity of the membrane for these gases. After treatment, the permeation rates in the membranes decreased by 2 to 3 orders of magnitude, while the propane/nitrogen selectivity increased substantially, compared with the untreated membrane. The maximum propane/nitrogen selectivity achieved was 32, which was 16 times higher than the bare membrane. Our results clearly indicated an increase in the hydrophobic character of the membrane surface and corresponding enhancement of the solubility of propane on the membrane. Compared to some of the best results reported for pure polymeric membranes, our membranes showed superior performance in achieving solubility-based separations. This study demonstrates that synthesis of hybrid membranes with tunable free volume and surface chemistry is feasible and that high performance in solubility-based separation may be achieved.
Javaid, Asad (1999). Gas separation with oligomer-modified inorganic membranes. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1999 -THESIS -J37.