Characterization and permeation studies on oriented single-crystal ferrierite membranes
NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Single-crystals (up to 650 x 550 x 20 [...]) of highly silicious ferrierite (Si-FER, 1), suitable for single-crystal X-ray investigations, are synthesized under organothermal conditi...
| Summary: | NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document.
Single-crystals (up to 650 x 550 x 20 [...]) of highly silicious ferrierite (Si-FER, 1), suitable for single-crystal X-ray investigations, are synthesized under organothermal conditions. The structures of the as-synthesized (1a) and the calcined (1b) Si-FER are determined at room temperature. Both structures are refined in the orthorhombic space group Pnnm (No.58, standard setting) with a = 743.0(1), b = 1409.2(2), c = 1882.0(2)pm, V = 1970.5(4)[...], Z = 1,R = 0.041 (la) and a = 741.8(1), b = 1407.0(2), c = 1871.3(2) pm, V = 1953.1(5)[...], Z = 1, R = 0.037 (lb). The structure solution when combined with chemical analysis and [...] and [...] MAS NMR, give a unit cell content of [...] (x = 0 - 1, py = pyridine, ap = 1-amino-n-propane) and [...] for 1a and 1b, respectively. The structure of 1a shows only weak host-guest interactions between the [...] framework and the occluded, orientationally disordered pyridine molecules by means of relatively long organic-to-framework distances,d[...] [...] 354(2) pm. [...] MAS NMR spectra from the organic-containing Si-FER 1a and the organic-free form 1b are in good agreement with the crystallographic results in that they conform to the well-known linear relationship between the cosine expression of the T-O-T angles and the chemical shift of the respective tetrahedral sites (T-sites). A new modification of this relationship is presented here and offers an improved linear correlation between the X-ray and NMR data for 1a and 1b, as well as for other high-silica microporous materials. Application of this new correlation to denser SiO2 compounds is discussed.
Selected individual crystals of the calcined Si-FER are mounted in a membrane configuration so that only the 10-membered ring channels (5.4 [...] x 5.4 [...] x 4.2 [...]) or the 8-membered ring channels (4.6 [...] x 3.7 [...] x 3.0 [...]) are accessible for gas molecule permeation. The first examples of transport exclusively through 8- or 10-membered ring channel systems are reported and obtained through crystal orientation in the membrane. A series of adsorption experiments are conducted in order to assist the selection of suitable probe molecules and evaluate the role of adsorption in the permeation process for the single-crystal membranes. Methane, n-butane, isobutane and nitrogen probe molecules are used to study intracrystalline sorption and transport effects for different crystal orientations, pressures and temperatures. Both pure gas selectivities and mixed gas separation factors are reported. A mixed gas separation factor of n-butane/isobutane = 116 for the 10-membered ring orientation of the crystal at 383 K and a transmembrane pressure difference of 1.01 x [...] Pa is found using this technique. In addition, molecular sieving is observed for the 8-membered ring orientation of the crystal since methane, but not butane, transport is observed for this crystal orientation.
|
|---|