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

Abstract

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 (ηI) and second law (ηII) efficiencies. Thereby, the adsorbents are evaluated from perspectives of WPP, EC, ηI and ηII. As per results, ionogel based adsorbent enables maximum WPP ranging up to 1.55 kg/kg/cycle, EC of 4214.96 kJ/kgw/cycle, ηI of 0.54, and ηII of 0.21. Whereas MIL-101(Cr) observe WPP ranging up to 0.87 kg/kg/cycle, EC of 4499.84 kJ/kgw/cycle, ηI of 0.50, and ηII of 0.19. Parametric analyses results show that ηI of ionogel and MIL-101(Cr) can be increased up to 0.65 and 0.69 while ηII up to 0.23 and 0.25, respectively. Furthermore, ηI and ηII 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.