Microfluidic preparation of thin film composite hollow fiber membrane modules for water nanofiltration: Up-scaling, reproducibility and MOF based layers

The commercialization of thin film composite (TFC) hollow fiber (HF) membranes remains challenging owing to issues associated with membrane manufacturing. TFC membranes were synthesized by microfluidic interfacial polymerization of polyamide (PA) on polysulfone hollow fiber (HF) membrane modules. A total of 33 HF membrane modules were prepared with different number of HFs (from 1 to 25) and different lengths (from 10 to 50 cm). They were evaluated in a nanofiltration operation in terms of water permeance and rose Bengal (RB) and MgSO4 rejections. Among the 33 modules, 73% showed RB rejections higher than 95%, while 36% of the modules reached rejections above 99%. During the membrane synthesis, different parameters, such as PA monomer concentration, residence time and reaction time, were studied. As a result, the amount of monomer was reduced by ca. 80%. The versatility of microfluidics allowed incorporating hydrophilic metal-organic framework (MOF) ZIF-93 to produce HF modules with PA/MOF bilayered membranes (a continuous layer of MOF between the support and the PA film) which led to an important enhancement of the water permeance from 1.3 (bare PA membrane) to 5.3 L·m−2·h−1·bar−1 (PA/ZIF-93 HF membrane), maintaining RB rejection above 95%.