Browsing by Keyword "Pd membranes"
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Item Attrition-resistant membranes for fluidized-bed membrane reactors: Double-skin membranes: Double-skin membranes(2018-10-01) Arratibel, Alba; Medrano, Jose Antonio; Melendez, Jon; Pacheco Tanaka, D. Alfredo; van Sint Annaland, Martin; Gallucci, Fausto; TECNOLOGÍA DE MEMBRANAS E INTENSIFICACIÓN DE PROCESOS; Tecnalia Research & InnovationPd-Ag supported membranes have been prepared by coating a ceramic interdiffusion barrier onto a Hastelloy X (0.2 µm media grade) porous support followed by deposition of the hydrogen selective Pd-Ag (4–5 µm) layer by electroless plating. To one of the membranes an additional porous Al2O3-YSZ layer (protective layer with 50 wt% of YSZ) was deposited by dip-coating followed by calcination at 550 °C on top of the Pd-Ag layer, and this membrane is referred to as a double-skin membrane. Both membranes were integrated at the same time in a single reactor in order to assess and compare the performance of both membranes under identical conditions. The membranes have first been tested in an empty reactor with pure gases (H2 and N2) and afterwards in the presence of a catalyst (rhodium onto promoted alumina) fluidized in the bubbling regime. The membranes immersed in the bubbling bed were tested at 400 °C and 500 °C for 115 and 500 h, respectively. The effect of the protective layer on the permeation properties and stability of the membranes were studied. The double-skinned membraned showed a H2 permeance of 1.55·10−6 mol m−2 s−1 Pa−1 at 500 °C and 4 bar of pressure difference with an ideal perm-selectivity virtually infinite before incorporation of particles. This selectivity did not decay during the long term test under fluidization with catalyst particles.Item Kinetic model for Pd-based membranes coking/deactivation in propane dehydrogenation processes(Elsevier B.V., 2023-01-15) Brencio, Camilla; Gough, Robin; de Leeuw den Bouter, Anouk; Arratibel, Alba; Di Felice, Luca; Gallucci, FaustoThis work aims at providing insight into the deactivation mechanism of Pd-based membranes in propane dehydrogenation processes. Thermogravimetric analysis (TGA) experiments were conducted to study the adsorption and coking of propylene over conventional thin layer (TL) and double-skinned (DS) Pd-based membranes under several operating conditions. A mechanistic monolayer-multilayer coke growth model was selected to mathematically describe the membrane coking observed during TGA experiments. In addition, the reaction rate of coke formation and its influence on membranes deactivation has been studied. The deactivation model able to describe the hydrogen flux decay over time suggests that monolayer coke is the main responsible for the membrane deactivation. Multilayer coke also causes deactivation but with a smaller order than monolayer coke, for both the TL and the DS membranes. Among the two membrane types, DS membrane deactivates faster, i.e. with a higher order than the TL membrane, which is equal to 1.55 for the former and 0.51 for the latter. This is related to the higher number of active sites available in the controlling step of the deactivation reaction, which are most probably given by the addition of the ceramic Al2O3 protective layer. XPS spectra further confirms that, in the presence of Pd, Al2O3 sites contribute to carbon formation by evidencing a different nature of carbon formed on the two membranes. Finally, the experimental results of hydrogen permeation over time conducted on different membranes types and operative conditions confirmed the validity of the derived and parametrized kinetic models for coke formation and membrane deactivation. The experimental findings and the kinetic model derived in this work provide essential tools for the design and optimization of membrane reactors for dehydrogenation processes.