Cyclic adsorption of water vapour on CuBTC MOF: Sustaining the hydrothermal stability under non-equilibrium conditions

Metal organic frameworks (MOFs) based adsorption processes for gas separation from humid streams are limited by the hydrothermal stability of MOFs. This work presents a comprehensive study of the hydrothermal stability of CuBTC (BTC=benzene-1,3,5-tricarboxylate) MOF when exposed to humid streams in cyclic operations. We show that water uptake is slow, and that adsorption processes will most likely operate under non-equilibrium conditions. CuBTC does not show signs of decomposition when exposed to low water concentration and room temperature (up to water partial pressures of 6 mbar and 25 degrees C) for up to 48 h of cyclic operation. Nevertheless, short cycles (of less than 15 min per pressure stage) are required when exposed to high water vapour content (up to 70 mbar, 50 degrees C). This work demonstrates the need of tailoring the length of water exposure to avoid the equilibrium adsorption of water vapour on CuBTC and maintain the adsorbent integrity.