Separation of propane and propylene by desorbent swing adsorption using zeolite 13X and carbon dioxide

A new concept of the desorbent swing adsorption (DSA) process operating at a constant pressure is proposed. The developed process was applied to the separation of propane and propylene because propylene, a high-demand chemical, is produced from an energy-intensive and expensive process. The selection criterion of desorbent was the chemical having the adsorption affinity between propane and propylene, and carbon dioxide was selected as a case study. According to the sequential breakthrough experiments, propylene was separated from propane in the CO₂ pre-filled bed. However, the desorption step utilizing CO₂ flow played a key factor in the separation performance because a faster desorbent flowrate enhanced the desorption of adsorbed propylene and prolonged the breakthrough times of the components. A two-bed DSA process (60% propane and 40% propylene), containing rinse-out and rinse-in steps, achieved 94.427% purity for propane with 99.655% recovery and 8.816 mol/(kg·hr) productivity, and 99.999% purity for propylene with 96.644% recovery and 5.700 mol/(kg·hr) productivity. Unusual temperature variances in the DSA process (decreasing during the adsorption step and increasing during the desorption step) was opposite to that in conventional adsorptive processes. These temperature variances contributed to an enhanced separation performance and process safety (prevention of zeolite 13X poisoning and gas fires). The feasibility of the DSA process was demonstrated without further requirements for additional energy arising from compression or a vacuum. The optimization of the DSA process and subsequent desorbent recovery processes is a subject for further studies.