Investigation of flux dependence on viscosity in ultrafiltration

Abstract: This project aims to compare the effect of viscosity on flux for high viscosity liquids. The performance of two different viscous solutions was studied in a plate-and-frame membrane module. The solutions used were based on molasses, which is a liquid containing mainly low-molar mass components and konjac glucomannan (KGM) which is a substance with high molar mass. The change of the mass transport through the membrane (flux) during ultrafiltration of molasses and KGM as concentration (dry matter) was increased was investigated. The Alfa Laval RC70PP membrane and the Alfa Laval LabStak M39 equipment were used in the experiments. Additionally, this study also aims to model and simulate the concentration and viscosity gradient in proximity to the membrane and its effect on the flux by using COMSOL Multiphysics. Simulation of the concentration at the membrane surface is to be used to study different operational parameters effect on the flux at varying viscosities. In this case, a clear dependence of flux on viscosity was established. For the molasses, there was little retention and the flux was mainly influenced by permeate viscosity. The KGM experiments resulted in permeate viscosity values independent of feed viscosity, the flux was however greatly influenced by increasing hydraulic membrane resistance with higher feed viscosity. The viscosity effect on flux for molasses was successfully modelled in COMSOL. In the simulation, the concentration gradient in this case was found to have little effect on the flux.