(173i) Fabrication and Characterization of Silicalite Membranes Subject to Knudsen and Surface Diffusion Transportation Regimes
AIChE Annual Meeting
2017
2017 Annual Meeting
Separations Division
Rapid Fire Session: TED-Sep Separations Division
Monday, October 30, 2017 - 1:40pm to 1:46pm
To demonstrate this characterization model, several batches of silicalite membranes have been hydrothermally synthesized using ceramic membrane supports with active layers whose pore sizes are 0.45 and 0.8 µm. Pure gas permeation experiments were then conducted using these membranes with He, N2, and CH4 gases in turn. The transport of these gases through membranes of this type proceed according to the regimes of Knudsen diffusion through defects, and surface diffusion through silicalite crystals (excepting He, which is sufficiently small that it is predominantly transported by Knudsen diffusion through silicalite crystals at standard conditions). The results of these permeation experiments, in combination with previously reported diffusion data and adsorption isotherms have then been used to determine the effective silicalite channel path length, and defect size to length ratio that are unique to each membrane. Through the application of the proposed model, effective silicalite channel lengths and defect ratios for membranes that were fabricated in different batches at similar conditions have been found to vary up to 20% and 700% respectively.
Given these results, characteristic values such as permselectivity can be determined that are normalized to exclude the defect transport of gases, and are therefore expected to be more comparable. Furthermore, this model can be applied to many different inorganic type membranes, and enable more reliable simulations of scaled up membrane processes.