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Teses de Mestrado ESTiG

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  • Separation of methane and hydrogen in a 3D-printed porous carbon monolith
    Publication . Junqueira, Matheus Raphael Diniz; Silva, José A.C.; Dumont, Marcello Rosa
    The efficient separation of methane (CH4) and hydrogen (H2) is a key challenge in industrial processes such as steam methane reforming (SMR), which is the primary technology used for hydrogen production; however, the generated gas contains impurities such as carbon monoxide (CO), carbon dioxide (CO2), and unreacted methane, which must be removed to ensure high-purity H2. The separation of these gases is commonly performed through pressure swing adsorption (PSA) using adsorbent materials such as zeolites (e.g., zeolite 13X) and activated carbons. However, these adsorbents often present challenges, including high pressure drop and limited control over pore structure. In this context, this study investigates a 3D-printed porous carbon monolith with tetragonal cubic centred unit cells, designed to maximize CH4 selectivity over H2 while reducing pressure drop due to its highly controllable structural design. The material was characterized using fixed-bed adsorption experiments analyzed via flow gas chromatography, including single-component (H2 and CH4) and binary adsorption (CH4/H2 mixtures) at 303 K, 313 K, and 343 K, with pressures up to 30 bar. Adsorption equilibrium modelling was conducted using the Dual-Site Langmuir (DSL) isotherm, accurately describing an experimental 76/24 (% vol.) CH4/H2 mixture, reinforcing the material’s selectivity, closely matching the values predicted by the isotherm from single component experiments. These findings highlight the potential of 3D-printed porous carbon monoliths for selective CH4 separation in PSA processes applied to SMR, offering a promising alternative with lower pressure drop and greater structural control compared to conventional adsorbents. the gas-monolith interactions. Results showed that H2 adsorption was negligible under all tested conditions. For CH4, the maximum adsorption experimental capacity was 3.25 mol.kg−1 at 303 K and 30 bar. Equilibrium isotherms confirmed material heterogeneity, with two distinct adsorption sites, each with its own adsorption capacity. The isosteric heat of adsorption ranged from 17.5 to 17.1 kJ.mol−1, indicating a moderate physisorption mechanism. In binary adsorption experiments at 303 K and 5 bar, CH4 adsorption reached 2.10 mol.kg−1 for an experimental 76/24 (% vol.) CH4/H2 mixture, reinforcing the material’s selectivity, closely matching the values predicted by the isotherm from single component experiments. These findings highlight the potential of 3D-printed porous carbon monoliths for selective CH4 separation in PSA processes applied to SMR, offering a promising alternative with lower pressure drop and greater structural control compared to conventional adsorbents.
    2025Master thesis Embargoed access Show more