Performance evaluation of gas fraction vacuum pressure swing adsorption for CO2 capture and utilization process

Pressure swing adsorption (PSA) is widely used in various gas separation processes. Many PSA operations have been proposed that require multiple beds having a rinse step in order to obtain a product gas of high purity. This operation may cause re-adsorption of desorbed gases on the adsorbent depending on the process design, which leads to a decrease in the productivity and energy efficiency. In this work, a simple vacuum type PSA (VPSA) process without a rinse step is proposed and demonstrated experimentally for CO2 separation. The proposed VPSA process fractionates the outlet gas from the bed, which allows flexible adjustment of the purity and recovery of the product gas exploiting isotherm nonlinearity. To investigate the performance of the proposed process, a dynamic VPSA simulation was conducted. The performance of this gas fraction VPSA was evaluated also experimentally at the laboratory scale to analyse the trade-offs amongst purity, recovery, productivity and energy efficiency. In our experiment, the highest CO2 recovery of 68.7% was obtained by the newly designed 2-column gas fraction VPSA at the feed gas volume of 76 NL-feed/kg-adsorbent/cycle, which is about 60% higher than 3-column VPSA with a rinse step. The CO2 separation energy estimated from experimental results with assumptions on the efficiency of the compressor and vacuum pump also indicated the possibility of further cost reduction at moderate CO2 purity.