Adsorption-based CO2 separation from gas streams: Porous adsorbents, mechanisms, and cyclic process design

Adsorption-based CO2 separation using porous solids is increasingly investigated for flue gas treatment, biogas and natural gas sweetening, hydrogen purification, direct air capture, and selected CO2-containing petrochemical streams. This review focuses on adsorption-based CO2 separation from gas streams by integrating recent findings in experimental studies, simulations and modeling works, and selected pilot and industrially relevant examples to clarify how porous adsorbents can be linked to practical cyclic CO2 capture systems. The review is organized around a structure-mechanism-process (SMP) selection logic that links the dominant adsorption mechanism required by a given gas stream to a suitable adsorbent class and cyclic process and applies it across five representative CO2-containing streams. Porous solids, including zeolites and metal-organic frameworks (MOFs), are emphasized as promising materials owing to their extensive surface area, adjustable pore structures, and selective adsorption capabilities. The study reviews the adsorption characteristics of popular zeolites (4A, 5A, 13X) under diverse conditions and assesses their reported performance in relation to industrial CO2 removal requirements. Also, key parameters such as adsorption capacity, regeneration energy, and selectivity are discussed in this review. Moreover, the performance of adsorbents in key adsorption process configurations is examined, including pressure swing adsorption (PSA), vacuum swing adsorption (VSA), temperature swing adsorption (TSA), and hybrid schemes (e.g., PVSA, TVSA). Key challenges include the absence of a practical adsorbent-selection framework, limited hydrothermal and contaminant tolerance, regeneration-energy penalties for strongly binding sorbents, shaping and mechanical robustness, and scalable synthesis. Future progress will depend on the combined optimization of adsorbent chemistry, morphology, and process configuration to achieve practical, economically viable CO2 capture solutions. By systematically linking adsorption mechanisms, materials design, and process engineering, adsorptionbased CO2 capture holds promise for advancing from laboratory-scale studies to practical, energy-efficient industrial implementation.