New cycle configuration to enhance performance of kinetic PSA processes

This work shows a new column arrangement to improve the utilization of the adsorbent in multi-column Pressure Swing Adsorption (PSA) processes. This cycle was specifically designed to increase the unit productivity for gas separations using adsorbents with slow diffusion kinetics where mass transfer zone (MTZ) inside the column is important. In this column arrangement, when the heavy (most adsorbed) gas breaks through one column, the exit of this column is connected to a second column (trim bed) where more heavy gas can be adsorbed. In this way, also more heavy gas will be adsorbed in the first (lead) column. The increase of process performance is directly related to the length of the MTZ: the larger the MTZ, the better will perform using the lead-trim beds concept. The cycle performance was tested for biogas upgrading to obtain high purity bio-methane (purity >98%) that can be used as renewable fuel. Two different adsorbents were employed in the process simulations: zeolites 13X (fast diffusion) and carbon molecular sieve (slow diffusion). Furthermore, the possibility of using less power in the purge step was considered. Using this process, it was possible to obtain unit productivity of 5.5 mol CH4 per hour per kilogram of adsorbent.