Permeability zeolite-based membranes

With appropriate membrane pore size and a narrow distribution, membrane selectivity for smaller gas molecules can be high but the overall permeability is generally low due to a high flow resistance in fine pores. Several studies are being conducted to develop molecular sieve-type membranes using different inorganic materials, for example, those based on carbon (Liu, 2007), silica (Pex and van Delft, 2005), and zeolites (Lin, 2007). 

In asymmetric supported membranes the use of permeability data can give rise to much confusion and erroneous conclusions for several reasons. In most cases the layer thickness is not precisely known and usually it is not known whether this layer is homogeneous or has property gradients (e.g. a "skin" and a more porous part). In many cases the material of the layer penetrates the support to some extent and so it is not possible to separate properties of separation layer and support without giving account of the interface effect. Finally, even if all these complications can be avoided, a comparison based on separation layer properties expressed in terms of permeabilities can give a completely wrong impression of the practical possibilities (as done in e.g. Ref. [109]). This is illustrated by comparison of hydrogen permeabilities of ultra-thin silica layers (see Tables 9.14-9.16) with other materials such as zeolites and metals. The "intrinsic" material properties of these silica layers are not impressive ... 

The manufacture of DPMs based on infiltrated molten carbonates in the porosity of perovskite membranes constitutes the most recent and innovative application of perovskites for CO2 capture. Since the first studies reported by Wade and coworkers [33] and Lin and coworkers [34], many efforts have been made to develop stable high-flux membranes for CO2 separation. Table 39.5 collects the most remarkable results, whereas Figvue 39.12 plots the permeance versus permeability plots for dual-phase perovskite-carbonate materials compared with low-temperature CO2 separating membranes (zeolites and MOFs/ZIFs). 

Gas separation membranes combining the desirable gas transport properties of molecular sieving media and the attractive mechanical and low cost properties of polymers are considered. A fundamental analysis of predicted mixed matrix membrane performance based on intrinsic molecular sieve and polymer matrix gas transport properties is discussed. This assists in proper materials selection for the given gas separation. In addition, to explore the practical applications of this concept, this paper describes the experimental incorporation of 4A zeolites and carbon molecular sieves in a Matrimid matrix with subsequent characterization of the gas transport properties. There is a discrepancy between the predicted and the observed permeabilities of O2/N2 in the mixed matrix membranes. This discrepancy is analyzed. Some conclusions are drawn and directions for further investigations are given. 

Tricoli and Nanetti [17] prepared a novel zeolite-Naflon composite manbrane by embedding zeolite fillers in Nafion. The zeolites used in this study were chabazite and clinoptilolite. The presence of zeolites in the membranes caused notable changes in conductivity, methanol permeability, and selectivity with respect to pure Nafion. In another interesting study, Holmberg et al. synthesized and characterized zeolite-Y nanocrystals for Nafion-zeolite-Y composite proton exchange membranes. The composite membranes were found to be more hydrophilic and proton conductive than the base-unmodified membranes at high temperatures [18]. 

Guiver et al, 2002). An increase in H2/CO2 separation factor from 1.53 to 3.57 has been observed for membranes containing 40% zeolite (Khan et aL, 2010,2011). Enhanced performance has been achieved for nanocomposites based on Multiwalled Carbon Nanotubes (MWCNTs) in poly(bisphenol A-co-4-nitrophthalicanhydride-co-l,3-phenylene diamine) (PBNPI). Reduced d-spacing compared to the pure polymer has yielded H2 permeability of 14 Barrer, H2/CH4 selectivity of 8, and H2/CO2 selectivity of 6 at 15% of CNT(Wengeffl/.,2009). 

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