Impacts of spiral-wound membrane modules in organic solvent nanofiltration applications

Abstract

In recent years organic solvent nanofiltration has showed great potential in a number of industrial fields. A growing number of studies have been reported on development of new membrane materials, optimisation of membrane manufacturing conditions, enhancement of membrane performance and fundamental understanding of molecular transport through membranes. However, studies on spiral-wound membrane modules which are almost exclusively applied in industry are few. In this research project, experimental data on spiral-wound membrane modules of different sizes (from 1.8"x12" to 4.0"x40") in solutions covering a wide range of solute concentrations were collected under steady state operation. Then a procedure to obtain correlations describing fluid dynamics and mass transfer characteristics in the modules was developed using a limited number of experimental data for flat sheets and a 1.8"x12" module only. Furthermore, a multi-scale model for simulating the performance of processes using the modules was developed, considering the molecular transport through the membranes (membrane scale), the fluid dynamics and mass transfer characteristics in the modules (module scale) and the thermodynamic and physical properties of the solutions as a function of operating conditions (process scale). This model was used to simulate the performance of a batch concentration process using different modules under various operating conditions, and good agreement between simulation and experiments was found. In addition, the impact of ultra-high membrane permeance on process efficiency is examined in organic solvent nanofiltration and reverse osmosis as case studies via simulation, considering both concentration polarisation and pressure drops in modules. The key conclusion is that ultra-high permeance membranes will not be able to make a significant impact on process efficiency with current module designs; and the recommendation is that fresh research into module and process design is required.