Cellulose Acetate Hollow Fiber Membranes for Forward Osmosis Using the Green Solvent Agnique AMD 3 L
Tobias Götz, B. Achenbach, Thomas Schiestel
Abstract
A set of cellulose acetate (CA) hollow fiber membranes is manufactured by using a variation of CA (20–25 wt %) and different weight ratios of acetone and the green solvent Agnique AMD 3 L (3:2, 1:1, 2:3) in dope solutions (DS). The DSs are spun combining an evaporation and non-solvent-induced phase separation (EIPS–NIPS) process. The obtained hollow fibers (HF) annealed in either water (95 °C) or humid air (95 °C, 98% relative humidity) reveal an asymmetric membrane structure with a dense layer on the shell side and a molecular weight cutoff down to 100 g mol –1 . Regarding the use of forward osmosis (FO), the hollow fibers are tested with aqueous NaCl (1 M) as draw solution in the lumen of the fibers and ultra-pure water as feed at the shell side. With a decreasing amount of acetone in the DSs, an increase in water flux from 2.0 L m –2 h –1 (LMH) to 6.2 LMH and a reverse salt flux from 0.5 g m –2 h –1 (GMH) to 13.3 GMH of the HF annealed in water are found. When annealing in humid air, the water flux of the HF increases from 2.0 to 4.5 LMH and a reverse salt flux from 0.5 to 4.1 GMH occurs, compared to annealing in water. Decreasing the NaCl concentration to 0.5 M, an increase in the performance ratio up to 17.9% is given, which is in the same range of commercially available cellulose ester-based HFs for FO.