Air separation is currently one of the most important gas operations in the chemical industry [1,2]. It is performed typically at large-scale by cryogenic distillation to produce high-purity product streams. Adsorption processes have the potential to substitute the energy- and capital-intensive distillation operations with the right adsorbent and process technology for several applications. Currently, commercial adsorption technologies of different production scales, i.e., PSA & VPSA, exist to realize this separation to generate oxygen-rich streams as well as nitrogen-rich streams, which are useful in a variety of industries [1,2]. Traditionally, adsorption-based air separation employs materials that selectively adsorb nitrogen in order to recover high-purity oxygen as light-product, e.g., commercial LiX zeolites [2]. Nitrogen-rich product streams may also be generated by applying carbon molecular sieves (CMS), modifying cycle configuration & process operating conditions [1]. In the last decades, novel classes of materials have been developed & investigated to alternatively reverse the adsorptive selectivity, i.e., adsorbing preferentially the oxygen species, thus enabling its recovery as heavy-product stream of pressure-swing operations, whilst rejecting nitrogen as light-productâsee e.g., Hutson & Yang [3] among others. In this contribution, we investigate vacuum pressure-swing adsorption (VPSA) cycle configurations via process modeling; these cycle designs target specifically high-purity recovery of oxygen. We parametrize single component adsorption equilibria from experimental measurements for nitrogen and oxygen species, adsorbed by a tailored oxygen-binding adsorbent. We feed a full-order VPSA process solver with this equilibrium information, as well as appropriate mass & heat transfer approximations. We apply a state-of-the-art multi-objective optimization strategy developed recently [4], in order to determine optimal trade-offs between performance variables relevant to these cyclic processes. These modeling efforts allow us to better evaluate the potential of oxygen-binding adsorbents, as well as assisting in the design of efficient adsorption-based air separation processes for oxygen production.
References
[1] Böcker, N.; Grahl, M.; Tota, A.; Häussinger, P.; Leitgeb, P.; Schmücker, B. Ullmannâs Encyclopedia of Industrial Chemistry; Wiley-VCH Verlag GmbH & Co. KGaA, 2013; pp. 1â27.
[2] Kirschner, M. J.; Alekseev, A.; Dowy, S.; Grahl, M.; Jansson, L.; Keil, P.; Lauermann, G.; Meilinger, M.; Schmehl, W.; Weckler, H.; Windmeier, C. Ullmannâs Encyclopedia of Industrial Chemistry; Wiley-VCH Verlag GmbH & Co. KGaA, 2017; pp. 1â32.
[3] Hutson, N. D.; Yang, R. T. Synthesis and Characterization of the Sorption Properties of Oxygen-Binding Cobalt Complexes Immobilized in Nanoporous Materials. Industrial & Engineering Chemistry Research 2000, 39, 2252â2259.
[4] Rubiera Landa, H. O.; Kawajiri, Y.; Realff, M. J. Efficient evaluation of vacuum pressure-swing cycle performance using surrogate-based, multi-objective optimization algorithm. Proceedings of the 30th European Symposium on Computer Aided Process Engineering (ESCAPE30), 2020 (accepted).
