Study On The Mechanism Of Nanofiltration Membranes With Organic Solvents

Nanofiltration (NF) is a relatively new membrane process lying between ultrafiltration (UF) and reverse osmosis (RO) and has been extensively applied in water treatment. However, transport and retention data for NF membranes in organic solvents are very limited in the literature, and the mechanism of transport through NF membranes in organic solvent environments is not well understood, which restrict the applications of NF membranes in organic solvents. The calculation of the nanofiltration model needs the liquid diffusion coefficients, but many models of liquid diffusion coefficients has their limitation. Thus it's very important to select proper model of liquid diffusion coefficients.This thesis primarily investigated the transport mechanism of nanofiltration membranes with methanol solvents by micro and macro-methods. The molecular volume in aqueous solution and in methanol solution was calculated by molecular simulation. Using molecular volume, mean pore size and standard deviation of pore size, the reflection coefficient was calculated. Moreover by macro-experiment,influences of conditions on transport flux of organic solvents permeating through nanofiltration membranes and rejection of the solute in organic solutions are also investigated. Experimental model was established in methanol solution. It will provide theories for development and application of nanofiltration membranes.First of all, in order to testify the diffusion coefficient models of alcohol, molecular dynamics simulation(MD) was employed to calculate the diffusion coefficients of alcohols in the infinite dilute aqueous solution as well as aqueous solution of different concentration of alcohols at 293.15K and 0.1 Mpa. The results show that the equations of Dullien and Asfour can be applied to calculate the diffusion coefficients of methanol and ethanol in aqueous solutions, and that the equations of Leffler and cullinan can be applied to calculate the diffusion coefficients of other alcohol in aqueous solutions.Secondly, The solvent effect of the solute molecule in experiment was simulated. It is possible that the polarity of methanol is smaller than water, and the action between molecules in methanol is smaller than that in water, and there is no hydrogen bond in methanol. Thus the repulsion between the solute molecules is small and the volume of the solute molecule in methanol is larger than that in aqueous solutions.Finally, studies established model of pure solvent permeability coefficient and these parameters. The results showed that permeating...