Permeation and separation of organic liquid mixtures through liquid-crystalline polymer networks

A side-chain liquid-crystalline polymer (LCP) was synthesized by the addition of the mesogenic monomer to poly(methyl siloxane) in presence of a Pt-catalyst. When an aqueous solution of 10wt% ethanol was permeated through a LCP membrane by pervaporation at various temperatures, the permeation rate increased with increasing temperature and drastically changed at glass-nematic (Tg) and nematic-isotropic (TNI) transition temperatures of the LCP membrane. The LCP membrane exhibited the waterpermselectivity in the glassy and liquid-crystalline states. The ethanol concentration in the permeate increased with increasing permeation temperature and the LCP membrane changed from the waterpermselectivity to the ethanol-permselectivity around TNI. These results suggested that the permselectivity was influenced by the change of the LCP membrane structure, that is, its state transformation. It was found that a balance of the orientation of mesogenic groups and flexibility of siloxane chains is very important for the permeability and selectivity.     

Studies on syntheses and permeabilities of special polymer membranes. XVI. Permeation and separation characteristics of aqueous polymer solutions for acrylonitrile-styrene copolymer membranes

The permeation and separation characteristics of aqueous polymer solutions using acrylonitrile-styrene copolymer membranes were investigated under various conditions. The membranes obtained from dimethyl sulfoxide solution of acrylonitrile-styrene copolymer have not a sufficient reproducibility and stability of permeation. These lacks were improved by adding ethylene glycol or glycerol to the casting solution and treating the membranes with pressure. The permeation and separation characteristics were influenced significantly by the additional amount of above additives, the heat treatment temperature, and the operating pressure. It was found that the concentration polarization of poly(vinyl alcohol) molecules onto the surface of the acrylonitrile-styrene copolymer membranes is smaller than that onto hydrophilic polymer membranes such as membranes of cellulose acetate, cellulose nitrate, and nylon 12, etc. Moreover, the acrylonitrile-styrene copolymer membranes show better performance for separation and concentrating of aqueous polymer solutions than hydrophilic membranes.     

Studies on syntheses and permeabilities of special polymer membranes

Summary The permeation and separation characteristics of methanol/n-pentanol systems and n-propanol/n-heptane systems through nylon 12 membranes were studied by changing the feed composition of the binary organic mixtures. These characteristics were discussed from the viewpoints of physical and chemical nature of the permeating molecules and the membrane.     

pH-controlled uphill transport of ammonium ions through polymer membranes with sulfonic acid groups

Uphill transport of ammonium ions through a membrane with sulfonic acid groups were investigated with pH-controllers which keep the solution at a constant pH. A membrane with sulfonic acid groups was prepared by casting an aqueous solution containing poly(styrenesulfonic acid) and poly(vinyl alcohol) on a glass plate. When a membrane with one side alkaline and the other acidic was fixed as a diaphragm in a cell, ammonium ions were transported from the alkaline side to the acidic side through the membrane against the concentration gradient of the adjacent solutions. Uphill transport of ammonium ions with pH-controllers was more efficient than without, thus keeping the pH difference between both sides of the membrane constant, which is a driving force for the uphill transport. Furthermore, the effect of pH of the acidic side on the uphill transport was investigated and the mechanism of the pH-controlled uphill transport is discussed.     

Studies on syntheses and permeabilities of special polymer membranes

Summary The permeabilities of various cellulose ester membranes and cellulose membranes were investigated using pure water and aqueous solution of glycerol as feed. In all membranes, the permeation rate for aqueous solution of glycerol was greater than for pure water. The permeation rates of cellulose ester membranes increased with an increase in number of carbon atoms of the substituent group in cellulose ester.     

Studies on synthesis and permeability of special polymer membranes

Summary The permeation characteristics of polymer blend membranes from poly(vinylidene fluoride) and poly-(ethylene glycol) to aqueous polymer solution were investigated under carefully controlled conditions. The permeation characteristics were influenced significantly by the blend ratio, the temperature and time of heat treatment, which changed the structure of the resulting membranes.     

Characteristics of permeation and separation of dimethyl acrylamide-methyl methacrylate random and graft copolymer membranes for a benzene/cyclohexane mixture

When a benzene/cyclohexane mixture was permeated through poly(dimethyl acrylamide-random-methyl methacrylate) (DMAA-r-MMA) and poly(dimethyl acrylamide)-graft-poly(methyl methacrylate) (DMAA-g-MMA) membranes by pervaporation, the benzene-permselectivity of the DMAA-r-MMA membrane changed from the diffusivity selectivity to the solubility selectivity with increasing DMAA content but DMAA-g-MMA membranes with a high DMAA content had the higher apparent diffusivity selectivity than the apparent solubility selectivity. Furthermore, the apparent solubility selectivity for a benzene/cyclohexane mixture between the DMAA-r-MMA membrane and the DMAA-g-MMA membrane with a high DMAA content was remarkably different. These results were attributed to the difference of structure between the copolymers. Received: 27 August 1997/Revised version: 22 October 1997/Accepted: 30 October 1997     

Studies of synthesis and permeabilities of special polymer membranes. LI. Active transport of halogen ions through chitosan membranes

Anion exchange membranes containing amino groups, insoluble in acidic and alkaline aqueous solutions, were prepared from chitosan, poly(vinyl alcohol), and glutaraldehyde. Using the membrane in a diaphragm cell, one side being adjusted to be acidic and the other alkaline, it was possible to transport actively halogen ions through the membrane from the acidic side to the alkaline side against the concentration gradient between both sides of the membrane. The active transport of halogen ions through the membrane was significantly influenced by the pH difference and electric potential difference between both sides of the membrane.     

Studies on syntheses and permeabilities of special polymer membranes. 40. Formation conditions of finger-like cavities of cellulose nitrate membranes

The permeation characteristics for polymer aqueous solution and asymmetric structure of cellulose nitrate membranes, in particular the finger-like cavity in the back sponge layer of these membranes, were investigated by changing the preparation conditions of the membranes— the casting solvent, evaporation period, and gelation medium. The formation of the finger-like cavity was dependent on absorption of a water molecule into the casting mixture from the atmosphere during the solvent evaporation process and the exchange velocity between the casting solvent and the gelation medium. The mechanism and conditions for the formation of a finger-like cavity in cellulose nitrate membranes were discussed.     

Studies on syntheses and permeabilities of special polymer membranes: 30. Ultrafiltration and dialysis characteristics of cellulose nitrate-poly(vinyl pyrrolidone) polymer blend membranes

The ultrafiltration and dialysis characteristics of the semipermeable polymer blend membranes obtained from cellulose nitrate, poly(vinyl pyrrolidone), and N,N-dimethyl formamide were investigated under various conditions. The water content fraction and the ultrafiltration rate were dependent on the poly(vinyl pyrrolidone) content in the membranes, and the strengths were governed by the cellulose nitrate content in the polymer blend. If the pore radius in the membranes, calculated according to the Hagen-Poiseuilli equation for capillary model, was identical, the water content in each membrane was not identical. It was found that urea molecules broke very weak hydrogen bonds of the bound water in the membrane, but sodium chloride did not, also, the diffusion of urea through the membrane was more rapid than that of sodium chloride. The ratio of the membrane diffusion coefficient to the ultrafiltration rate was explained qualitatively by the capillary model, however, when the bound water in the water content fraction was considered, this ratio showed better agreement with the model.