Improved Pressure Swing Adsorption Processes for Gas Separation: By Heat Exchange Between Adsorbers and by Using High-Heat-Capacity Inert Additives

Two new pressure swing adsorption processes for bulk gas separation are proposed. The first one is by allowing heat exchange between the adsorber columns, for example, by using a shell-and-tube type heat exchanger, where the shell and the tube are two beds. By model simulations, it is shown that the new process offers substantial improvements in both product purities and recoveries over the adiabatic process, which resembles the industrial operations using large beds. A fundamental understanding for the Improvements is given through model simulations. A peculiar high-temperature plateau and cold ends in the bed are predicted for the adiabatic process. In the second process, an inert material with a high heat capacity is added into the adsorbent bed. The inert additive serves to store heat during adsorption and release it during desorption, hence reducing the magnitudes of the temperature excursions during pressure swing cycle and improving the separations. Model simulation results are presented for bulk separation of H₂/CH₄ and H₂/CO mixtures with various amounts of iron particles added In a bed of activated carbon. The results show substantial improvements in both product purities and recoveries by the inert additive. A fundamental understanding of the role played by the inert additive Is gained through a comparison of the temperature profiles in the bed and its variation with time during a steady-state cycle.