Water vapor permeation and dehumidification performance of poly(vinyl alcohol)/lithium chloride composite membranes

Abstract

a b s t r a c tThin and robust composite membranes comprising stainless steel scaffold, fine and porous TiO 2 and polyvinyl alcohol/lithium chloride were fabricated and studied for air dehumidification application. Higher hydrophilicity, sorption and permeation were observed for membranes with increased lithium chloride content up to 50%. The permeation and sorption properties of the membranes were investigated under different temperatures. The results provided a deeper insight into the membrane water vapor permeation process. It was specifically noted that lithium chloride significantly reduces water diffusion energy barrier, resulting in the change of permeation energy from positive to negative values. Higher water vapor permeance was observed for the membrane with higher LiCl content at lower temperature. The isothermal air dehumidification tests show that the membrane is suitable for dehumidifying air in high humid condition. Additionally, results also indicate a trade-off between the humidity ratio drop with the water vapor removal rate when varying air flowrate.

Next-generation HVAC: Prospects for and limitations of desiccant and membrane-based dehumidification and cooling

“…This assumption presents a reasonable approximation as recent membranes developed by researchers have been reported to achieve a selectivity, or a water/air permeance ratio, of around 10,000. 20 Membranes with lower selectivity tend to require higher transmembrane pressures or larger areas to achieve the desired dehumidification effect. In addition, separation across the membrane is assumed to be isothermal and hydraulic losses are ignored for simplicity.…”

“…In recent reviews, Woods 15 and Zhang 16 provided overviews of the latest membrane developments in HVAC and a summary of potential avenues for future research, while another review by Yang et al 17 highlighted the major advances membrane technology has made in air dehumidification. In search of membranes with the greater selectivity necessary to make this process viable, Zhang et al 18 developed a novel membrane using a polyethersulfone (PES) support layer coupled with a polyvinylalcohol (PVA) active layer, while Bui et al 19,20 later reported the fabrication of a robust hydrophilic PVA/LiCl composite membrane. Other studies explored boosting air-conditioning performance through incorporating membrane-based total heat recovery, 21,22 enabling heat and mass exchange across air streams.…”

Effect of hygroscopic materials on water vapor permeation and dehumidification performance of poly(vinyl alcohol) membranes

“…Membranes can be employed to dehumidify air by simply passing a humid air stream on one side of the membrane and passing a dry air stream or applying a vacuum on the other side . The use of membranes for air dehumidification has higher energy efficiency compared with other conventional technologies.…”

“…Therefore, polymer membranes have high water vapor selectivity over air. For low temperature applications, such as ventilation and air conditioning, stable performances can be achieved from polymeric membranes …”

“…The unique properties of Nafion are due to highly hydrophilic perfluorovinyl ether groups terminated with sulfonate groups incorporated onto its hydrophobic tetrafluoroethylene backbone. Therefore, to improve the water vapor permeability of a poorly permeable polymer, strong hydrophilic components are usually incorporated in the polymer matrix either under chemical (such as sulfonation, fluorination, block co‐polymer formation) or physical blending processes . Of these processes, physical blending processes are more preferable because they are more controllable, environmental friendly and inexpensive.…”