Zeolite Membranes for Gas and Liquid Separations

Metal–organic framework membranes: from synthesis to separation application

“…In general, the synthesis of zeolite membranes follows one of two approaches: in situ growth or seeded-assisted (secondary) growth. 21 The fabrication of an MOF film or membrane involves processing a known porous MOF with interesting properties on top of a substrate. 22,23 In 2005, Fischer et al successfully prepared the first MOF film anchoring a typical MOF-5 building unit to a carboxylic acid-terminated, self-assembled monolayer (SAM) on an Au (111) substrate.…”

Characterization of Natural Zeolite Membranes for H2/CO2 Separations by Single Gas Permeation

“…Zeolite molecular sieves have uniform pore sizes which could make them promising for this separation. Zeolite membranes are capable of separating compounds by a combination of molecular sieving, selective adsorption, and differences in diffusion rates. − Synthetic molecular sieve membranes for hydrogen separation have also been studied intensively; however, their applications have been limited by both high production costs and lack of mechanical integrity including cracks or defects, and poor physical and chemical compatibility between the sieves and the supports on which they are grown. , While extensive research has been performed on the potential for hydrogen purification by synthetic molecular membranes, − very little attention has been paid to the natural zeolite-based membranes and their potential applications for purification.…”

Cellulose Nanofibrils Films: Molecular Diffusion through Elongated Sub-Nano Cavities

“…Diffusion occurs by jumps between these sites and has thermally activated character because the jump occurs after the penetrant has accumulated enough thermal energy to overcome a potential barrier E D . The diffusivity D conf of a molecule can be expressed by the relation: where 1/ z is the probability that a molecule jumps into one of the z adjacent diffusional sites and l s the average distance between these sites. − …”

“…When the cavity size d p is comparable to the kinetic diameter σ k of the diffusing molecules, as in the present CNF film samples, diffusion occurs in Knudsen or in configurational regime depending on the value of the σ k / d p ratio. − When σ k / d p < 0.5, diffusion occurs in Knudsen regime. Penetrant molecules maintain their gaseous characteristics and travel at thermal velocity , where M is the penetrant molecular weight.…”

“…When σ k / d p > 0.8, diffusion occurs in configurational regime and the penetrant diffusion process shows similarities with the surface diffusion process. Modeling of configurational regime assumes that penetrant molecules in empty regions interact with the host matrix and lose their gaseous state residing in a periodic potential at thermal equilibrium with the host matrix. − In the case of strongly corrugated potential with respect to K B T , the particles vibrate at frequency ν e within a bound state. Diffusion occurs by jumps between these sites and has thermally activated character because the jump occurs after the penetrant has accumulated enough thermal energy to overcome a potential barrier E D .…”