Pérez Carbajo, Julio

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Pérez Carbajo
Universidad Pablo de Olavide
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Now showing 1 - 4 of 4
  • Publication
    Molecular Sieves for the Separation of Hydrogen Isotopes
    (American Chemical Society, 2019) Pérez Carbajo, Julio; Parra, José B; Ania, Conchi O; Merkling, Patrick; Calero, Sofía
    Stable molecular hydrogen isotopes, D2 and T2, are both scarce and essential in several energy, industrial, and large-scale fundamental research applications. Due to the chemical similarity of these isotopes, their extraction and purification from hydrogen has relied for decades on expensive and energy-demanding processes. However, factoring in the phenomenon of quantum sieving could provide a new route for these separations. In this work, we have explored how to separate hydrogen isotopes by adsorption taking these quantum effects into account. To this end, we have conducted adsorption measurements to test our deuterium model and performed a widespread computational screening over 210 pure-silica zeolites for D2/H2 and T2/H2 separations. Based on low-coverage adsorption properties, a reduced set of zeolites have been singled out and their performance in terms of adsorption capacity, selectivity, and dynamic behavior have been assessed. Overall, the BCT-type zeolite clearly stands out for highly selective separations of both D2 and T2 over H2, achieving the highest reported selectivities at cryogenic temperatures. We also identified other interesting zeolites for the separation of hydrogen isotopes that offer an alternative way to tackle similar isotopic separations by an aimed selection or design of porous materials.
  • Publication
    Diffusion Patterns in Zeolite MFI: The Cation Effect
    (American Chemical Society, 2018) Pérez Carbajo, Julio; Dubbeldam, David; Calero, Sofía; Merkling, Patrick
    Zeolite MFI is one of the most important stable porous materials used in catalysis and separation processes. However, some fundamental properties remain in the dark, such as the effect of different aluminum distributions on diffusion. This work, through calculations on cation probability densities, guest energy profiles, and diffusion coefficients, provides a consistent picture of accessibility and mobility for two representative adsorbates, methane and carbon dioxide, and helps to explain the stark differences in diffusion behavior among varying aluminum distributions. A distribution was identified close to the practical limit of maximum aluminum substitution and sodium cation content that actually leads to a collapse in diffusion. For all aluminum distributions studied, the diffusion properties are closely linked to the number of cations. Compensating aluminum negative charge with divalent calcium instead of monovalent sodium increases methane but decreases carbon dioxide diffusion. With respect to increasing adsorbate loading, it induces a monotonous decrease in self-diffusivities for all structures studied. This study highlights the desirability of controlling the aluminum substitution location and, more importantly, the fact that two heavily substituted MFI zeolites with identical composition reported in the literature may have very different diffusion properties.
  • Publication
    Zeolites for CO2-CO-O2 separation to obtain CO2-neutral fuels
    (American Chemical Society, 2018) Pérez Carbajo, Julio; Matito Martos, Ismael; Balestra, Salvador RG; Tsampas, Mihalis N; van de Sanden, Mauritius CM; Delgado, Jose A; Águeda, V Ismael; Merkling, Patrick; Calero, Sofía
    Carbon dioxide release has become an important global issue due to the significant and continuous rise in atmospheric CO2 concentrations and depletion of carbon-based energy resources. Plasmolysis is a very energy efficient process for reintroducing CO2 into energy and chemical cycles, by converting CO2 into CO and O2 utilizing renewable electricity. The bottleneck of the process is that CO remains mixed with O2 and residual CO2. Therefore, efficient gas separation and recuperation is essential for obtaining pure CO, which via water gas shift and Fischer-Tropsch reactions, can lead to the production of CO2 neutral fuels. The idea behind this work is to provide a separation mechanism based on zeolites to optimize the separation of carbon dioxide, carbon monoxide and oxygen at mild operational conditions. To achieve this goal, we performed a thorough screening of available zeolites based on topology and adsorptive properties using molecular simulation and Ideal Adsorption Solution Theory. FAU, BRE and MTW are identified as suitable topologies for these separation processes. FAU can be used for the separation of carbon dioxide from carbon monoxide and oxygen and BRE or MTW for the separation of carbon monoxide from oxygen. These results are reinforced by pressure swing adsorption simulations at room temperature combining adsorption columns with pure silica FAU zeolite and zeolite BRE at a Si:Al ratio of 3. These zeolites have the added advantage of being commercially available.
  • Publication
    Effect of lattice shrinking on the migration of water within zeolite LTA
    (Elsevier, 2020) Pérez Carbajo, Julio; Balestra, Salvador RG; Calero, Sofía; Merkling, Patrick
    Water adsorption within zeolites of the Linde Type A (LTA) structure plays an important role in processes of water removal from solvents. For this purpose, knowing in which adsorption sites water is preferably found is of interest. In this paper, the distribution of water within LTA is investigated in several aluminum-substituted frameworks ranging from a Si:Al ratio of 1 (maximum substitution, framework is hydrophilic) to a Si:Al ratio of 191 (almost pure siliceous framework, it is hydrophobic). The counterion is sodium. In the hydrophobic framework, water is found in the large α-cages, whereas in the most hydrophilic frameworks, water is found preferably in the small β-cages. For frameworks with moderate aluminum substitution, β-cages are populated first, but at intermediate loading water favors α-cages instead. Framework composition and pressure therefore drive water molecules selectively towards α- or β-cages.