Krenar Shqau

Synthesis of Ultrathin Zeolite Y Membranes and their Application for Separation of Carbon Dioxide and Nitrogen Gases

Synthesis of zeolite Y membranes from submicrometer (>100 nm) and nano seed (<100 nm) crystals on alumina supports was examined and the separation characteristics of these membranes for CO(2) and N(2) were studied. Two secondary growth solutions were examined, one for a rapid growth (hours) and one for a slower growth process (days). Membranes formed from the rapid growth solution resulted in 2-2.5 microm thickness, while for the slower growth solution, a dense membrane of 350-600 nm thickness was formed, covered by a 25 microm porous zeolite layer. With the nano seeds as the seeding layer, no membrane was formed. A mechanism involving seed dissolution to initiate membrane formation is concluded. The separation characteristics of membranes for CO(2)/N(2) separation were similar, with very high selectivities for separation (alpha(CO(2),N(2)) > 500). The thicker membrane had lower permeance. By investigating both single gas and mixed gas permeances, strong evidence for a percolative type separation process is obtained.

Nanostructured Ceramic Thin Films and Membranes by Wet Chemical Processing Methods

Nanostructured ceramic thin films and membranes are used for protective or functional purposes and prepared on dense or porous substrate materials. Wet chemical methods enable cheap, low-temperature, mass-scale manufacturing routes. They produce fine-grained porous and dense micro-structures that cannot be realized otherwise. In wet-chemical processing, clean nanoparticle dispersions are deposited on the substrate at, primarily, ambient conditions. The deposition is followed by a (rapid) thermal processing treatment to remove liquids and organic additives, to convert precursors to the target composition, and to establish the final porous and dense micro-structure. In the synthesis of precursor dispersions it is very important to obtain nanoparticles with a near-isometric shape and a fairly narrow particle size distribution, without the formation of secondary (agglomerate) structures. In particular the latter requires careful control of solution and interfacial chemistry to achieve proper colloidal stability, during and after the synthesis process. Characterization of coating integrity, defect morphology and defect population is done by decoration methods, microscopy, ellipsometry and statistical methods that employ membrane transport properties.