Evaluating the emerging adsorbents for water production potential and thermodynamic limits of adsorption-based atmospheric water harvesting systems

In the context of global water scarcity, adsorption-based atmospheric water harvesting (AWH) is an emerging technology for providing potable water at anytime/anywhere. In this regard, the study evaluates silica-gel, zeolite, ionogel, polymer, membrane, and metal-organic framework based ten kinds of emerging adsorbents for the AWH systems. A thermodynamic modeling framework comprising of adsorption equilibrium models and governing steady-state equations is performed. Performance of AWH systems is always judged on water production potential (WPP), energy consumption (EC) whereas thermodynamic correctness can be measured by first (η_I) and second law (η_II) efficiencies. Thereby, the adsorbents are evaluated from perspectives of WPP, EC, η_I and η_II. As per results, ionogel based adsorbent enables maximum WPP ranging up to 1.55 kg/kg/cycle, EC of 4214.96 kJ/kg_w/cycle, η_I of 0.54, and η_II of 0.21. Whereas MIL-101(Cr) observe WPP ranging up to 0.87 kg/kg/cycle, EC of 4499.84 kJ/kg_w/cycle, η_I of 0.50, and η_II of 0.19. Parametric analyses results show that η_I of ionogel and MIL-101(Cr) can be increased up to 0.65 and 0.69 while η_II up to 0.23 and 0.25, respectively. Furthermore, η_I and η_II of dual-stage system can improve by 33% as compared to single-stage that can improve by 68-74% as compared to vapor compression system.