Research Of The Mechanism Of Nanofiltration Membranes With Organic Solvents

Nanofiltration has been proposed for uses in organic solutions. 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. We believe that research of the mechanism of NF membranes with organic solvents is interesting area, and it is significant in science and valuable for application. This thesis primarily investigated the transport mechanism of nanofiltration membranes with organic solvents by micro and macro-methods. Using atomic force microscopy (AFM), studies showed their surface morphology in organic solvents. 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 studied. Based on above experimental results, this thesis established experimental model and will provide theories for development and application of nanofiltration membranes.First of all, the stability of membranes in aqueous and organic solvents is reported. It was found that their surface morphology is obviously changed in organic solvents using atomic force microscopy (AFM). By observing flux of solvents and rejection of solute permeating through nanofiltration membranes, the results showed that flux of solvent permeating NF-SH membrane is significantly affected by membrane surface morphology, however, solvent properties mainly influence on flux of solvent permeating MPF-44 membrane. Rejections for the membranes (NF–SH, MPF–44) in organic systems are far lower than aqueous systems owing to interactions of solute-solvent.Secondly, by observing influences of pressure on transport flux of solvents permeating through nanofiltration membranes (NF-SH, Desal-DK, Les-90) and rejections in methanol solution with Brilliant Blue-G, studies showed that membrane compacting effect in methanol are more than water; in the methanol solution, a rise from 0.5Mpa to 1.5Mpa in pressure decreased rejections from 48.5% to 11.1%, which is different with result of the water solution (increased value of R=12.4%). By observing influences of temperature on the flux and rejection of the solute, studies testified the applicability of the Hagen－Poiseuille model in organic solvents and showed that a rise from 10℃ to 40℃ in temperature also decreased rejections from 31.3% to 19.7% in the methanol solution, however this result is the same as the one in the water solution (decreased value of R=13.0%). By observing influences of concentration of solute in the methanol solution on rejections, results showed that in the condition of higher pressure or temperature, concentration of solute slightly effects on rejections. Additional experiment studies the flux of some pure organic solvents and their organic solutions, results showed that due to reflect coefficient of organic solvent is far lesser than aqueous systems, when organic solvents are added with the solute, their fluxes are not changed greatly. Finally, by investigating the effects of solvent viscosity, molecular volume and solubility parameter on pure solvent permeability coefficient, studies established experimental model of pure solvent permeability coefficient and these parameters. The results showed that permeating hydrophilic membranes, the model of homogeneous and unhomogeneous solvents is A∝δ2/ Vmμ; and permeating hydrophobic membranes, the model of the above solvents is A∝1/ Vmμδ2.