Process development and optimization for CO2/O2 separation via vacuum swing adsorption

This work focuses on the bulk adsorptive separation of CO₂/O₂ mixtures. Such mixtures can evolve from electrolytic reactions for carbon dioxide (CO₂) capture and utilization processes, such as the liberation of CO₂ from carbonate-bicarbonate solutions. Typically, a CO₂/O₂ gas mixture (60–80% CO₂) arises from the anode of membrane electrode assemblies. In this work, three adsorbent materials (MSC-30 activated carbon, ZSM-5 zeolite, 13X zeolite) were evaluated for the adsorptive separation of such gas mixture. High purity (>95%) and recovery (>90%) of both components are desired, allowing storage or recycling of CO₂ as well as valorization of O₂. Breakthrough experiments confirm preferential adsorption of CO₂ over O₂ on all materials, with 13X zeolite having the highest selectivity for CO₂, followed by ZSM-5 and MSC-30. A non-isothermal process model was developed and validated by simulating the various breakthrough experiments, showing a good match with experimental data. Two vacuum swing adsorption (VSA) processes were investigated and a genetic algorithm was used for multi-objective optimization, targeting both product streams. In a three step VSA process, 13X zeolite was shown to outperform the other two materials, achieving higher purity and recovery for both CO₂ and O₂. With a more complex process cycle, including a heavy reflux step, a purity >95% and recovery >90% can be achieved for CO₂ and O₂ simultaneously with 13X and ZSM-5. With MSC-30, a maximum O₂ purity of 92% was achieved while meeting the other purity and recovery targets. For simulations in which the purity and recovery constraints were satisfied, similar CO₂ productivity was achieved with ZSM-5 and 13X, indicating that both zeolites are suitable for CO₂/O₂ separations.