Masaaki Teramoto

Preparation of polyethylene hollow fiber membrane via thermally induced phase separation

High-density polyethylene (HDPE) hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Two kinds of diluents such as diisodecyl phthalate (DIDP) and liquid paraffin (LP) were used in the preparation of membrane. In the case of DIDP, liquid–liquid phase separation occurred, while only the polymer crystallization occurred in the case of LP. In all cases, asymmetric structures with the smaller pores at the outer surface were obtained. Effects of polymer molecular weight, air gap distance, water bath temperature and kinds of diluents on the pore size and the water permeability were investigated. The use of the polymer with the higher molecular weight, the shorter air gap distance and the higher bath temperature were effective to obtain the higher water permeability. The membrane prepared with LP showed the lower water permeability than that with DIDP.

Effect of polypropylene molecular weight on porous membrane formation by thermally induced phase separation

Abstract The effect of the polymer molecular weight on the phase diagram and the phase separation rate was investigated in the polypropylene membrane formation via thermally induced phase separation (TIPS). The cloud point curve was shifted to the lower temperature region as the polymer molecular weight decreased, while the dynamic crystallization temperature did not change so much. The phase separation rate was measured by the light scattering method. The system with lower polymer molecular weight initially showed the smaller interphase periodic distance Λ . However, the growth rate of Λ was much larger and finally Λ exceeded the value in the case of higher molecular weight polymer. The membrane prepared with the higher molecular weight polymer showed the smaller inter-connected structure, which was in the contrast with the larger cellular pore structure in the case of the lower molecular weight polymer. The larger cellular structure was attributable to the faster phase separation rate. The polymer molecular weight can influence not only the pore size but also the pore shape.

Analysis of solute diffusion in poly(vinyl alcohol) hydrogel membrane

Abstract Measurement of diffusion and partitioning of solutes having molecular weights ranging 180–66000 in PVA gel membranes with various crosslinking degree were carried out. With increasing solute size or decreasing number of average molecular weight between crosslinks of the membranes, both the solute permeability and partition coefficient decreased. In spite of similar solute sizes, the more hydrophilic solute ribonuclease showed higher permeability and partition coefficient than the less hydrophilic α-lactalbumin, probably due to interaction with the hydrophilic PVA. The solute diffusion through swollen gel membrane was analyzed by the equation based on free volume theory. In this analysis equation, the partition coefficient, which is defined as the ratio of solute concentration in gel membrane standardized by water volume in the membrane to that in bulk solution, was introduced as the probability of a diffusing species finding a mesh with a volume of at least the solute size. The efficiency of the proposed analysis equation was confirmed by the experimental results of the effects of solute size and water volume fraction in the membrane.

Formation of porous flat membrane by phase separation with supercritical CO2

Microporous polystyrene membranes were prepared by the phase separation process using the supercritical CO2 as a nonsolvent for the polymer solution. The thin polymer solution in a laboratory dish was located inside a cell and the supercritical CO2 was introduced to induce the phase separation. The dry flat microporous membranes were obtained without collapse of the structure after the CO2 pressure was diminished. Effects of the experimental conditions such as the CO2 pressure, the polymer concentration and the temperature on the average pore size and membrane porosity were investigated.

Preparation of porous membrane by combined use of thermally induced phase separation and immersion precipitation

By immersion in the cooled nonsolvent, PMMA porous membrane was prepared by the combined use of thermally induced phase separation (TIPS) and immersion precipitation. As nonsolvent, water with low mutual affinity with cyclohexanol (diluent) and methanol with high affinity were used. In the case of water, the porous structure was formed by TIPS immediately after the immersion. Near the top surface contacted with the nonsolvent, the thin skin layer was formed due to the outflow of the diluent. After the long immersion period, macrovoids were formed near the top surface due to the penetration of the nonsolvent. Thus, TIPS and the immersion precipitation occurred serially. On the contrary, TIPS and the immersion precipitation occurred simultaneously in the case of methanol because the inflow of methanol was fast. Therefore, the membrane obtained after the short immersion period had the larger pores near the top surface due to the nonsolvent induced phase separation and the smaller pores near the bottom surface due to TIPS. These two modes of the phase separations were confirmed by the changes in light transmittance through the polymer solutions.

Modeling of the Permeation of Copper through Liquid Surfactant Membranes

Abstract A general permeation model for the extraction of copper by liquid surfactant membranes using a chelating agent as a carrier is presented in which the internal mass transfer in the W/O emulsion drop, the external mass transfer around the drop, the rates of the formation and decomposition of the complex at the aqueous-organic interface, and the leakage of the internal aqueous phase to the external phase due to the membrane breakup are taken into account. The batch extraction of copper using SME529 as a carrier was carried out under various experimental conditions. It is shown that the extraction rates can be satisfactorily simulated by the present model.

Selective permeation of CO2 through poly 2-(N,N-dimethyl)aminoethyl methacrylate membrane prepared by plasma-graft polymerization technique

A membrane having an amine moiety was prepared by plasma-grafting 2-(N,N-dimethyl)aminoethyl methacrylate (DAMA) onto a microporous polyethylene substrate. Permselectivity of the membrane for CO2 over N2 was achieved in both dry and water swollen conditions. When the CO2 partial pressure in the feed gas was 0.047 atm, the selectivity of CO2 over N2 reached 130 for the highly swollen water containing membrane. This value was found to agree with that obtained with a mobile carrier membrane (supported liquid membrane) using DAMA as the carrier. The effects of several experimental conditions such as degree of grafting, feed partial pressure and temperature on the membrane performance were studied. It was suggested that the membrane acted as a fixed carrier membrane for CO2 facilitated transport in under the dry condition and acted as a fixed reaction site membrane in the water swollen condition. The carrier transport mechanism is discussed for dry and aqueous membranes.

An attempt for the stabilization of supported liquid membrane

As a part of the investigation on the treatment of low-level radioactive wastewater using supported liquid membranes, a method for stabilizing a supported liquid membrane (SLM) is proposed. Aqueous Ce(III) solutions containing sodium nitrate and nitric acid were used as the simulated low level radioactive wastewater. The SLM consisted of octyl(phenyl)-N,N-diisobutylcarbamoylmethylphosphine oxide (CMPO) as a carrier of Ce(III), tributyl phosphate (TBP) as a modifier and dodecane as a solvent. The strip solutions were aqueous solutions of chelating agents such as trisodium citrate and disodium hydrogen citrate. A small plate-and-frame type SLM module was used and circulation mode for both the feed and the strip solutions was adopted. The SLM was unstable and water permeation through the SLM occurred, suggesting replacement of the organic membrane solution in the pores of a support membrane by the aqueous feed solution. However, the SLM was stabilized by adding an organic membrane solution to the reservoir of the strip solution and by circulating the membrane solution through the strip side of the SLM module so that the SLM could frequently contact the membrane solution dispersed as droplets in the strip solution. By this method, the SLM was not degraded by repeated replacements of both the feed and the strip solutions. The effect of chelating agent in the strip solution on the permeation rate of Ce(III) was also investigated.

Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. II. Membrane morphology

Phase separation of poly(vinylidene fluoride) dimethylformamide solution was induced by the penetration of water vapor, and the porous membrane was formed. As the humidity in the gas phase increased, membrane morphology changed in the order of dense, porous (cellular), and lacy-like structures. At the higher humidity condition, spherical bead structure was observed, which is likely to be crystalline spherulite. With the increase of the initial polymer concentration, less pores were formed in the case of the lower humidity of 20%, whereas more distinguished spherical structures were formed in the case of higher humidity of 40%. The obtained membrane morphologies were discussed based on both the calculated composition paths during the process and the phase diagram.

Effect of organic solvents on membrane formation by phase separation with supercritical CO2

Porous cellulose acetate membranes were prepared by phase separation with supercritical CO2 as a non-solvent. Four kinds of organic solvents were used and the effect of the solvent on the membrane structure was investigated. As the mutual affinity between solvent and supercritical CO2 decreased, the membrane porosity and the average pore size near the center position increased. In all cases, macrovoid was not formed, although the phase separation occurred instantaneously after CO2 was introduced. The membrane performances such as solute rejection coefficient and water permeability were measured for the obtained porous membrane.