Separation of Methane, Nitrogen, and Helium Using a Layered Triple-Reflux Pressure Swing Adsorption

The industrial gas separation poses significant challenges to achieve the simultaneous recovery of multiple valuable product gases via a one-stage separation process. To address this issue, we previously introduced the concept of a triple-reflux pressure swing adsorption (TR-PSA) process consisting of three reflux and product streams, which was demonstrated to separate ternary methane (CH4), nitrogen (N2), and helium (He) gaseous mixtures using activated carbon. In this work, we have modified the adsorption column packing method from a single uniform adsorbent layer to two distinct layers of adsorbents, aiming to optimize the separation performance of each column section, i.e., the CH4 enrichment and He purification sections. The adsorbents packed within each bed section are particularly suitable to improve the selectivity and efficiency of each separation section and thus enhance the purity and recovery of three product gases. A nonisothermal dynamic model was built to conduct the parametric studies and to complete the optimization of separation performance by varying the filling height of different adsorbent species in the beds. Results show that the feed gas containing 10% helium, 20% methane, and 70% nitrogen can be enriched to 93.22%, 79.92%, and 96.13%, respectively, via a single-stage layered TR-PSA process. This work provides an effective approach for crude helium purification and methane enrichment from raw natural gas and boil-off gas in the LNG industry.