Browsing by Author "Brencio, Camilla"
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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.Item Tailoring pore structure and surface chemistry of microporous Alumina-Carbon Molecular Sieve Membranes (Al-CMSMs) by altering carbonization temperature for optimal gas separation performance: An investigation using low-field NMR relaxation measurements: An investigation using low-field NMR relaxation measurements(2021-11-15) Forster, Luke; D'Agostino, Carmine; Anabell Llosa-Tanco, Margot; Spallina, Vincenzo; Brencio, Camilla; Gallucci, Fausto; Lindley, Matthew; Haigh, Sarah J.; Alfredo Pacheco-Tanaka, David; Tecnalia Research & Innovation; TECNOLOGÍA DE MEMBRANAS E INTENSIFICACIÓN DE PROCESOSIn this work we applied low-field, NMR spin-lattice measurements to evaluate for the first time the effect of carbonization temperature (range 600 - 1000 ℃) on the preparation of Alumina-Carbon Molecular Sieve Membranes (Al-CMSMs), providing new insights into intra-pore fluid interactions. The results show that the average Al-CMSM pore size generally increases with carbonization temperature whilst the hydrophilicity of the pore surface, and the amount of strongly adsorbed H2O, decreases with an increasing carbonization temperature. As such, lower carbonization temperatures produce more hydrophilic membranes, with further evidence provided by FTIR measurements demonstrating the presence of polar functional groups on the surface, with water interacting more strongly with the membrane surface, as evidenced by NMR. It was found that the Al-CMSM carbonization temperature significantly affected permeance and H2O/CH4 permselectivity by altering the membrane pore size distribution and pore hydrophilicity. H2O permeance values are seen to be up to 100 times larger than respective CH4 permeance values. The greater permeance of H2O is attributed to the larger kinetic diameter of CH4 relative to H2O and the adsorption of water in the hydrophilic pores enhancing the adsorption-diffusion transport mechanism. Optimal water permeation temperatures are thus higher for the more hydrophilic membranes, obtained at lower carbonization temperatures, as more energy is required to remove strongly adsorbed water blocking the pores. At higher carbonization temperatures, the Knudsen diffusion mechanism of permeance dominates over the adsorption-diffusion mechanism thereby reducing permeance as diffusion slows due to collisions between gas molecules and the pore walls. CH4 permeation always occurs via Knudsen diffusion with CH4 permeance increasing with permeation temperature due to the increased rate of CH4 diffusion.