Taisuke Maki

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.

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.

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.

Membrane formation via phase separation induced by penetration of nonsolvent from vapor phase. I. Phase diagram and mass transfer process

The isothermal phase diagram for poly(vinylidene fluoride)/dimethyl formamide/water system was derived. The binodal and spinodal were calculated based on the Flory–Huggins theory and the calculated binodal was approximately in agreement with the experimental data of the cloud points. The isothermal crystallization line was also obtained according to the theory of melting point depression. Mass transfer of the three components during membrane formation by the precipitation from the vapor phase has been analyzed. During this process, phase separation of the polymer solution is induced by the penetration of water vapor in the solution. The calculated result on the changes of the cast film weights indicated the good agreement with the experimental data. The time-course of the polymer concentration profile in the film was calculated for various cases of different humidity of the vapor phase and different initial polymer concentration.

Examination of relationship between coal structure and pyrolysis yields using oxidized brown coals having different macromolecular networks

Abstract Several coal samples having different structures were successfully prepared from an Australian brown coal through liquid phase oxidation with H 2 O 2 and HNO 3 . Since more than 90% of the oxidized coals were dissolved in dimethylformamide at room temperature, we could estimate the average structural parameters of the oxidized coals by spectroscopic analyses. These samples were subjected to flash pyrolysis to examine the effect of coal structure on the pyrolysis yield. The tar yield increased for the oxidized coal having a large amount of aliphatic carbon, whereas it decreased for the oxidized coal having a large amount of hydrogen bonding. It was found that the tar yield correlated well with the fraction of aliphatic carbon and the amount of hydrogen bonding determined from FT-IR spectra.

Gas separation by liquid membrane accompanied by permeation of membrane liquid through membrane physical transport

Abstract A novel liquid membrane for gas separation is proposed in which a membrane liquid is continuously supplied to the feed side (high pressure side) of a supported liquid membrane (SLM) and is forced to permeate through the membrane from the feed to the permeate side (low pressure side). The membrane liquid is circulated between the feed and the strip side of the membrane. In this mode of operation, gas permeation rate is enhanced by the convective or bulk flow of the membrane liquid dissolving gas. In addition, the fouling of membrane caused by the loss of the membrane liquid from the membrane due to drying-up and transmembrane pressure difference can be prevented. Experiments on the separation of CO 2 from CH 4 were performed using water as a membrane liquid. It was demonstrated that the convective flow of water through the membrane enhanced the gas permeabilities remarkably. For example, CO 2 permeability when the water permeation rate was 1.2 l/(m 2 min) was about 20 times that without water permeation. The effect of convective flow on the gas permeability was discussed on the basis of a simple permeation model. It was found that if the parameter (Peclet number) m = uL / D e ( u is the linear velocity of water through membrane or volumetric water flux, L the membrane thickness and D e is the effective diffusivity in membrane) is large, convective water transport considerably enhances gas permeability. Experimentally observed gas permeance was approximately simulated by the proposed model.