Synthesis of polybenzimidazole (PBI) forward osmosis (FO) membrane and computational fluid dynamics (CFD) modeling of concentration gradient across membrane surface

The aim of this research study was to synthesize and characterize asymmetric polybenzimidazole (PBI) FO flat sheet membranes for seawater desalination applications in high temperature and high salinity regions such as in Abu Dhabi (UAE). The membrane fabrication conditions that were considered during phase inversion method were membrane casting thickness, oven temperature and duration. The impact of draw and feed solution flow rates, draw solution type and concentration were also investigated. Results showed 2 M MgCl₂ reported the highest water flux and salt rejection of 3.1 ± 0.2 LMH and 97.4 ± 1.3% when compared to NaCl and KBr (i.e. 2.6 ± 0.1 LMH and 96.9 ± 1.3%, and 2.3 ± 0.3 LMH and 95.9 ± 1.3%, respectively). Additionally, computational fluid dynamics (CFD) modeling was used to verify the experimental results and study the impact of concentration gradient across membrane film on water flux and salt rejection at different FO cell orientations. The water flux and salt rejection with 2 M MgCl₂ draw solution increased from 3.6 ± 0.1 to 21.3 ± 0.2 LMH and 89.5 ± 1.2% to 96.3 ± 1.2%, respectively when the draw solution was allowed to flow in the top compartment of the membrane cell (orientation B). CFD modeling results demonstrated that solution density, gravity and diffusion rate affected FO performance at low cross-flow velocity.