(694i) Nexar Block Copolymer Coated Composite Hollow Fiber Membrane for Liquid Desiccant Membrane Air Dehydration

In this work, a hollow-fiber membrane in a shell-and-tube configuration was developed to deal with corrosion and crossover contamination of liquid desiccant for air dehydration application. Without involving any phase change, membrane-based dehumidification is an energy-efficient system compared with traditional vapor compression that reduces air temperature below its dew point. The novelty of this work lies in the fabrication of a composite hollow-fiber membrane coated with NEXAR^TM, a commercial pentablock copolymer in tetrahydrofuran on polyetherimide hollow fiber support. Coating of the membrane with 2 wt% block copolymer and a subsequent solvent vapor annealing formed a lamellar/parallel cylindrical structure separated by equidistance during the morphological transformation process (shown in figure 1). At the optimum self-assembly conditions, the formed coating gave an excellent structure that supports easy water vapor separation from air.

We determine the characteristics of counterflow configurations under various air and liquid side hydrodynamics, packing density, temperature, and contact length. The absorption of water vapor from the shell side air into the lumen side liquid desiccant was weakly increased by the liquid desiccant flow rate. Varying the desiccant temperature, however, has a huge impact. The air to be humidified was kept at a typical dry bulb temperature of 35°C, while the desiccant solutions were at 35°C, 28°C and 22°C. A low desiccant temperature implies a lower vapor pressure at the lumen side i.e., increased driving force across the membrane. When the desiccant temperature was reduced from 35°C to 22°C, the vapor pressure difference across the membrane increase from 0.85 kPa to 3.25 kPa (4x). As a result, the water vapor flux increased from 0.19 to 0.75 kg/m² h; and from 0.23 to 0.92 kg/m² h using 30 wt% CalCl₂ and LiCl desiccant solutions respectively.

The fabricated composite membrane with the lamellar morphology promoted a great water vapor flux. Dehumidification at 22°C and 28°C, which mimics an internally cooled system, was generally higher than the isothermal condition. A 15 cm effective membrane length was enough to achieve fast water vapor absorption by the liquid desiccant with a coefficient of performance (COP) 1, guiding us towards future system design for a broad scope of dehydration.