Self-supported Pd-based membranes

Caravella, A., Barbieri, G. and Drioli, E., (2009) Concentration polarization analysis in self-supported Pd-based membranes. Separation and Purification Technology, in press, http //dx.doi.org/10.1016/... 

The reactor consists of 6 micro-channels 13 mm long and a section 1 mmx 1 mm, while the membranes used are self-supported Pd-based membrane thinner than 3 pm. It has been shown that in this configuration a 1.4 pm thick membrane can withstand a differential pressure > 470 kPa. 

On the contrary, Table 8.2 reports a few results in terms of glycerol conversion from GlySR reaction performed in Pd-based MRs. As shown, lulianelli et al. (lulianeUi et al., 2010, 2011) used a dense self-supported Pd—Ag membrane (50 pm membrane thickness), reaching almost 94% of glycerol conversion at 400 °C and by using a concentrated (18 wt% of dispersed Co) C0/AI2O3 catalyst. 

Arstad et al. [141] used a self-supported, Pd/(23 wt%) Ag-based MR (with a thickness of 1.6 pm) achieving 100.0% the production of pure hydrogen. Hence, the authors concluded that the low-thickness of the paUadium-based membrane can represent a fundamental step for reducing the palladium-cost and making competitive the hydrogen separation technologies by palladium-based membrane. 

Pd-Based Membranes and Membrane Reactors for Hydrogen Production 453 13.4.1 Pd-based Self-Supported Membranes... 

There are two types of membranes available for ultra-pure H2 production composite and self-supported thin ones. In both cases, the major aim of the study concerning Pd-based membranes is the reduction of their thickness. The H2 flux increases as the membrane gets thinner, therefore the overall costs decrease because of both the reduced operating and material costs. In accordance with the applications where ultra-pure H2 production is required, commercial self-supporting dense Pd-based membranes with wall thicknesses larger than 100 j.m keep a sufficient mechanical strength and assure a defect-free surface and complete H2 selectivity. However, these membranes are too thick to obtain a satisfactory Hj flux. In addition to the low H2 permeance (as customarily used for composite membranes and defined as the ratio of Pch 15), thick Pd-based membranes are too expensive. Indeed,... 

The thick-wall unsupported Pd and Pd-based alloys can also be prepared by conventional metallurgical processes. Self-supporting dense Pd-based membranes possess wall thicknesses greater than 50-100 rm to keep a sufficient mechanical strength. These membranes are too thick to obtain a... 

Finally, SINTEF has developed a technique for the manufacture of Pd-based hydrogen separation membranes based on a two-step process, allowing a reduction in membrane thickness. First, a defect-free Pd-alloy thin film is prepared by magnetron sputtering onto a silicon wafer. In the second step the film is removed from the wafer. These films may subsequently be either used self-supported or integrated with various supports of different pore size, geometry and size. This allows, for example, the preparation of... 

Nevertheless, the overall diliiisivity of hydrogen through nanocrystalhne-based membranes is commonly 10 times higher than a membrane based on polycrystalline material. Furthermore, a composite membrane based on a thin noble metal layer deposited onto a porous support makes possible the necessary mechanical strength, however superior to dense and self-standing Pd-membranes. In particular, porosity and pore size distribution of the porous support can have some influence on hydrogen flux as well as on the membrane stabUity elevated temperatures. 

Pt(IV) than Pd(n) [49], An interesting system, with asymmetric inorganic membranes, was used for selective metal ion separation. The membrane phase was a self-assembled monolayer of alkyl thiols as a hydrophobic phase for a trialkyl phosphate and phosphine oxide-based metal ion carrier. This organic mixture was attached on alumina porous supports with thin layers of gold. The thin membrane layer gave high fluxes and high selectivity, while metal ions transport was carrier limited [50]. 

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