A complete procedure for acidic gas separation by adsorption on MIL-53 (Al)

CO2 and H2S are two of the principal polluting compounds in biogas. This study focuses on these acidic gases and proposes a complete procedure based on an adsorption process for their separation from biogas. In this aim, different measurements are required like pure compound adsorption isotherms, binary mixture adsorption equilibria and breakthrough curves. Pure gas isotherms of CH4, CO2 and H2S are realized at 303.15 K on powder and shape (pellet form) industrial MIL-53 (Al), with a gravimetric technique. We also measure CO2/CH4 adsorption equilibria at 303.15 K for two pressures (1 and 4 bar) on pellet form of the adsorbent. These mixture data are in good agreement with IAST predictions. So we can compare the CH4/CO2 and CH4/H2S separation performances between powder and pellets. Although the adsorption capacities are lower for pellets than for powder the separation qualities are similar. After this test, we have concluded that the pellet form of MIL-53 (Al) is a good candidate for CO2 and H2S separations from CH4. According to the selectivity values, the limiting separation of the process is the CO2/CH4 one. So, we have performed experimentally and theoretically the breakthrough curve with this binary mixture and we have concluded that this separation is applicable. Moreover, the simulated and experimental curves are in good agreement. Finally, the last step consists in performing the simulation of a complete PSA process producing treated biogas containing more than 96% CH4 from a 60% CH4 feed gas.

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► The CO2/CH4 and H2S/CH4 separations are similar on the powder and the pellets.
► Breakthrough curve proves the applicability of the limiting CO2/CH4 separation.
► PSA simulation provides promising results: produced biogas with more than 96% CH4.
► Pellet form of MIL-53 (Al) is a good candidate for acidic gas separations from biogas.