Membrane-based air dehumidification: A comparative review on membrane contactors, separative membranes and adsorptive membranes

• Membrane contactors for dehumidification focusing on its transfer resistance and liquid desiccants. • Separative membranes focusing on H 2 O/N 2 selectivity, permeance and the polymers used. • Membranes for moisture adsorption focusing on uptake capacity, kinetics and adsorbents used. • Comparative review of dehumidifying membranes on its application potential and limitations. • Proposal for next generation materials for membrane-based air dehumidification. This review compares the different types of membrane processes for air dehumidification. Three main categories of membrane-based dehumidification are identified – membrane contactors using porous membranes with concentrated liquid desiccants, separative membranes using dense membrane morphology with a pressure gradient to drive the separation of moisture from air, and adsorptive membranes using nanofibrous membranes which adsorb and capture moisture to realise dehumidification. Drawing upon the importance of dehumidification and humidity control for urban sustainability and energy efficacy, this review critically analyses and recognizes the three unique categories of membrane-based air dehumidification technologies. Essentially, the discussion is broken into three sections-one for each category-discriminating in terms of the driving force, membrane structure and properties, and its performance indicators. Readers will notice that despite having the same objective to dehumidify air, the polymers used amongst each category differs to suit the operating requirements and optimize dehumidification performance. At the end of each section, a performance table or summary of dehumidifying membranes in its class is provided. The final section concludes with a comparative review of the three categories on membrane-based air dehumidification technologies and draw inspiration from parallel research to rationalise the potential and innovative use of promising materials in membrane fabrication for air dehumidification.