Permeation studies on oriented single-crystal ferrierite membranes

• Published in: AIChE journal 1997-01, Vol.43 (1), p.83-90
• Main Authors: Lewis Jr, John E., Gavalas, George R., Davis, Mark E.
• Format: Article
• Language: English
• Subjects: Chemistry; Colloidal state and disperse state; Exact sciences and technology; General and physical chemistry; Membranes
• ISSN: 0001-1541; 1547-5905
• DOI: 10.1002/aic.690430111

Large, high‐quality, single crystals of pure‐silica ferrierite are synthesized, and the structure is described. Selected individual crystals (approximately 600 μm X 500 μm X 20 μm) are mounted in a membrane configuration so that only the 10‐membered‐ring channels (5.4 Å X 5.4 Å X 4.2 Å) or the 8‐membered‐ring channels (4.6 Å X 3.7 Å X 3.0 Å) 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 to help select suitable probe molecules and evaluate the role of adsorption in the permeation process for 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 105 Pa are 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.