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The effects of membrane porosity and pore size on CO 2 absorption performance and long-term stability were investigated using asymmetric poly(vinylidene fluoride) hollow fiber membrane contactors, prepared with differing inner surface structures by thermally induced phase separation. Membranes prepared using nitrogen gas as the bore fluid had lower inner surface porosity than membranes prepared with solvent. Monoethanolamine (MEA) solutions were used as absorbents on the tube side, while pure CO 2 was supplied to the shell side. Gas absorption performance and long-term stability of the synthesized membranes were compared with those of a commercial poly(tetrafluoroethylene) membrane. The effect of surface properties on gas absorption performance depended on MEA concentration. A membrane with lower porosity and small pore diameter at the inner surface was stable for 200 h, while a membrane with high porosity and larger pore size was completely wetted within 100 h and flux rate decreased sharply. A mathematical model for pure CO 2 absorption was developed by considering partial wetting of the membrane. The simulation results were discussed in light of the results from long-term stability tests of membranes.

Five kinds of asymmetric poly(vinylidene fluoride) (PVDF) hollow fiber membranes with considerable different porosities at the inner and outer surfaces of the membrane were prepared via thermally induced phase separation (TIPS) method and applied for propylene absorption as gas–liquid membrane contactors. A commercial microporous poly(tetrafluoroethylene) (PTFE) hollow fiber membrane was also used as a highly hydrophobic membrane. Experiments on the absorption of pure propylene into silver nitrate solutions were performed and the effects of membrane structure, inner diameter, silver nitrate concentration and absorbent liquid flow rate were investigated at 298 K. PVDF membranes prepared by using nitrogen as bore fluid had lower inner surface porosity than the membranes prepared with solvent as bore fluid. Except the membrane with a skin layer at the outer surface, propylene absorption flux was inversely proportional to the inner diameter of the hollow fiber membrane, and propylene absorption rate per fiber was almost the same. Propylene flux increased with increasing the silver nitrate concentration and also with increasing the absorbent flow rate. A mathematical model for pure propylene absorption in a membrane contactor, which assumes that the membrane resistance is negligibly small and the total membrane area is effective for gas absorption, was proposed to simulate propylene absorption rates. Experimental results were satisfactorily simulated by the model except for the membrane having a skin layer. The model also suggested that propylene is absorbed in silver nitrate solutions accompanied by the instantaneous reversible reaction. This paper may be the first experimental and theoretical study on propylene absorption in membrane contactors.

The facilitated transport mechanism of cerium(III) ions through polymer inclusion membrane (PIM) consisting of cellulose triacetate (CTA) as a polymer matrix, 2-nitrophenyl n -octyl ether (NPOE) as a solvent and N , N , N ′, N ′-tetraoctyl-3-oxapentanediamide (TODGA) as a carrier was studied. In order to evaluate the mass transport phenomena in the PIM, a mathematical model was derived from the Fick's first law and the equations for the extraction and the material balance. Methods to determine the values of the transport parameters such as the diffusion coefficient are described, and the dependency of the flux on the experimental condition was calculated. The model is very useful as a design tool to analyze and optimize the concentration process of low level radioactive wastewater using the PIM.

Poly(ethylene-co-vinyl alcohol) (EVOH) is a copolymer of ethylene and vinyl alcohol with an excellent combination of chemical, thermal and mechanical properties. EVOH hollow fiber membranes were successfully prepared by adding solvent (glycerol) to the cooling water bath in thermally induced phase separation (TIPS) process. The effect of glycerol:water ratio on membrane structures and properties including water permeability, solute rejection, and membrane strength were studied. EVOH crystallization is so slow that glycerol in the quench bath was allowed to flow into the membrane, thereby achieving high porosity at the outer surface. Therefore, adding solvent (glycerol) and increasing its content brings about an increase in the water permeability and a decrease in solute rejection. However, the membrane becomes more symmetric and weaker with increasing glycerol:water ratio due to the higher porosity.

Hydrophilic microporous hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Poly(vinyl butyral) (PVB) and three kinds of polyethylene glycols (PEG) with the molecular weight of 200, 400 and 600 were used as polymer and diluents. In all cases, liquid–liquid (L–L) phase separation occurred and asymmetric cellular structures with the smaller pores at the outer surface were obtained. The properties of membranes such as pore size, water permeability, solute rejection and intensity were investigated by changing molecular weight of PEG, concentration of PVB, composition of the bath and air gap distance. The smaller molecular weight of PEG, the more PEG in the bath and the shorter air gap distance resulted in the higher water permeability, the lower solute rejection property and the lower mechanical strength.

Novel hollow fiber facilitated transport membrane modules were used for ethylene/ethane separation using an aqueous silver nitrate solution as a carrier solution. In this membrane system, a feed gas consisting of 80 mol% C 2 H 4 and 20 mol% C 2 H 6 and an aqueous 4 M silver nitrate solution are supplied to the lumen side (high pressure side, feed side) of a hollow fiber ultrafiltration membrane module and flow upward. In the lumen, the solution absorbs C 2 H 4 selectively to become a rich or laden solution. Some part of the rich solution permeates the membrane to the permeate side (low pressure side, shell side) and other part of the solution leaves the module from its top and then it is supplied to the top of the shell side, where the absorbed gas is stripped from the rich solution and recovered as enriched ethylene. The lean solution is circulated to the lumen of the hollow fiber module by a pump. The feed side pressure was from 200 to 500 kPa and the permeate side pressure was atmospheric. Three modules with different liquid permeability and design were used in experiments. The module, in which the carrier solution permeated the membrane at the upper part of the module, had higher performance than the module in which the solution permeated at the lower part. The module, in which the solution did not permeate the membrane, also had high performance although a large gas–liquid separator was needed downstream of the module. The module efficiency, which is defined as the ratio of the experimentally observed ethylene recovery to the recovery calculated by assuming gas–liquid phase equilibria at both sides of the membrane, was from 61 to almost 100%. Ethylene in the feed gas was concentrated from 80 to 99.8 mol%. The maximum C 2 H 4 permeance was 1.1 × 10 −4 mol m −2 s −1 kPa −1 (3.3 × 10 −4 cm 3 cm −2 s −1 cm Hg −1 ) and the selectivity of C 2 H 4 over C 2 H 6 was about 375 at the ethylene partial pressure of 164 kPa. The maximum ethylene recovery was 87% when the mean residence time of the feed gas in the module was 4.9 s. The membrane was confirmed to be stable during a series of experiments.

Experiments on the facilitated transport of Ce(III) from mixed aqueous HNO3/NaNO3 solutions to water through supported liquid membranes (SLM) were performed using a stirred permeation cell. The SLMs consisted of organic solutions of octyl(phenyl)‐N,N‐diisobutyl‐carbamoylmethylphosphine oxide (CMPO) in 2‐nitrophenyl octyl ether (2‐NPOE) absorbed into microporous polypropylene membranes. The effects of the temperature and the carrier concentration on the permeation rate of Ce(III) were investigated. It was shown that the uphill transport of Ce(III) could be achieved without adding masking agents of Ce(III) in the strip solution. A mathematical model for analyzing the facilitated transport of Ce(III) was proposed. The permeation rate of Ce(III) could be simulated by using various physical and chemical parameters that were independently determined or estimated.

Mesoporous silica membranes were prepared by solvent evaporation methods using tetraethyl orthosilicate (TEOS) as a silica source and hexadecyltrimethylammonium chloride (CTAC) as a template and applied to filtration membranes which enable to separate solutes by nano-order size. Effect of the membrane thickness on structure formation was studied. The final membrane thicknesses were controlled from 0.43 μm to 127.7 μm by several deposition methods, such as spin-coating, casting by applicator, and pouring in Petri dish. The mesophase of the membrane changed from a cubic phase to a one-dimensional hexagonal (1d-H) phase with increasing membrane thickness. The membrane thickness was one of the key factors to control the mesostructure formed in the solvent evaporation method. In the monitoring of the structural growth process, it was found that 1d-hexagonal structure was initially obtained on a glass substrate, and this structure was changed to cubic structure. This result can be explained by changing the surfactant concentration, which decides the mesostructures. For filtration application, the silica membrane with the cubic structure was deposited by spin-coating on the porous alumina substrate. The rejection coefficient of Vitamin B 12 with the molecular weight of 1355 was about 0.8.

Polymer inclusion membranes (PIMs) consisting of cellulose triacetate (CTA) as a polymer matrix, 2-nitrophenyl n -octyl ether (NPOE) as a solvent and octyl(phenyl)- N , N -diisobutylcarbamoylmethylphosphine oxide (CMPO) or N , N , N ′, N ′-tetraoctyl-3-oxapentanediamide (TODGA) as a carrier were developed, and the facilitated transport of cerium(III) ions using the PIMs was investigated experimentally. It was observed that the present PIMs were very effective to transport cerium(III) ions from the feed phase to the strip phase. The transport rate was strongly influenced by the experimental conditions such as the solvent/polymer ratio, the operating temperature, the membrane thickness, the carrier concentration and the feed concentration. The experimental results indicated that the transport was controlled by the diffusion of the ion-carrier complex in the membrane.

High-density polyethylene (HDPE) hollow fiber membranes were prepared via thermally induced phase separation (TIPS). The pore size at the outer surface was quite smaller than that at the inner surface and the membrane structure was asymmetric. A membrane module was prepared by the obtained hollow fiber membranes. Experiments on the carrier-mediated transport of Ce(III) through supported liquid membranes (SLMs) were performed using the membrane module. The SLMs consisted of organic solutions of octyl(phenyl)-N,N-diisobutylcarbamoylmethyl phosphine oxide (CMPO) and tributyl phosphate (TBP) in dodecane absorbed into the microporous HDPE hollow fiber membrane. Effect of the aqueous strip solution flow rate on the membrane performance was investigated.

Microporous high-density polyethylene (HDPE) and low-density polyethylene (LDPE) hollow fiber membranes were prepared from polyethylene–diisodecyl phthalate solution via thermally induced phase separation. Effect of the polyethylene density on the membrane structure and performance was investigated. The HDPE membrane showed about five times higher water permeability than the LDPE membrane because it had the larger pore and the higher porosity at the outer membrane surface. The formation of the larger pore was owing to both the initial larger structure formed by spinodal decomposition and the suppression of the diluent evaporation from the outer membrane surface due to the higher solution viscosity. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 471–474, 2004

Honeycomb patterned polystyrene film was prepared from a polystyrene chloroform solution including polyion complexes by solvent evaporation under high atmospheric humidity. Formation of the honeycomb pattern was owing to the hexagonally packed water droplets which condensed onto the polymer solution. The pore diameter and the pore depth of the honeycomb pattern were remarkably influenced by the polystyrene molecular weight. A light scattering experiment was conducted to follow the structure formation process. The change of the lattice constant was explained by the behavior of water droplets.

Poly(ethylene-co-vinyl alcohol) (EVOH) hollow fiber membranes with ultrafiltration performance were prepared from EVOH/glycerol systems via thermally induced phase separation (TIPS). The diluent glycerol was used as bore liquid to make a lumen of the hollow fiber for the purpose of prevention of the diluent evaporation and the larger pores formation at the inner surface of the hollow fiber. The obtained hollow fiber membranes showed asymmetric structures with skin layer near the outer surface, the larger pores just below the skin layer and the smaller pores near the inner surface. The formation of the larger pores near the outer surface was due to the enhanced pore growth by the water penetration. Some primary factors affecting the structure and performance of the membranes such as ethylene content (EC) in EVOH, cooling water bath temperature and take-up speed were studied extensively. The water permeability can be improved by increasing the water bath temperature and the take-up speed and by decreasing the EC. Both the pore size at the outer surface and the connectivity between the pores have to be considered together to understand the experimental result of the water permeability and the solute rejection.

A novel facilitated transport membrane for gas separation using a capillary membrane module is proposed in which a carrier solution is forced to permeate the membrane. Both a feed gas and a carrier solution are supplied to the lumen side (high pressure side, feed side) of the capillary ultrafiltration membrane and flow upward. Most of the carrier solution which contains dissolved solute gas, CO 2 in the present case, permeates the membrane to the permeate side (low pressure side, shell side), where the solution liberates dissolved gas to form a lean solution. The lean solution is circulated to the lumen side. This type of capillary membrane module was applied to the separation of CO 2 from model flue gases consisting of CO 2 and N 2 . Monoethanolamine (MEA), diethanolamine (DEA) and 2-amino-2-methyl-1-propanol (AMP) were used as carriers or absorbents of CO 2 . The feed side pressure was atmospheric and the permeate side was evacuated at about 10 kPa. CO 2 in the feed gas was successfully concentrated from 5–15% to more than 98%. The CO 2 permeance was as high as 2.7×10 −4 mol m −2 s −1 kPa −1 (8.0×10 −4 cm 3 cm −2 s −1 cmHg −1 ) when the CO 2 mole fraction in the feed was 0.1 and temperature was 333 K. The selectivity of CO 2 over N 2 was in the range from 430 to 1790. The membrane was very stable over a discontinuous one-month testing period.

Polysulfone (PSf) membranes were prepared by the immersion precipitation method from casting solution of PSf and a water-soluble polymer, poly(vinyl pyrrolidone) (PVP), in dimethylacetamide. The effect of the molecular weight of PVP on the phase separation rate during the porous membrane formation was investigated by the light scattering method. The plots of scattered intensity against scattered angle showed maxima, which indicated that the phase separation occurred by spinodal decomposition. The structure growth rate remarkably enhanced by the addition of PVP with the lower molecular weight due to both the deeper quench depth and the lower polymer concentration brought about by the PVP leaching into nonsolvent bath. The increase of PVP molecular weight resulted in a decrease of the structure growth rate. Moreover, with the increase of the molecular weight of PVP, the membrane structures were changed from a macrovoid structure to a sponge structure.

Microporous polypropylene (PP) membranes were prepared by the thermally induced phase separation (TIPS) technique and used as supports of liquid membranes. Several different quenching temperatures were used in the preparation of the microporous membranes. Membranes prepared by air-cooling and quenching in a water bath of 353 K showed higher porosity at the membrane surface compared with those made by quenching in a water bath of 303 K and in ice-water. A simplified one-dimensional heat transfer equation was solved to evaluate the temperature profile within the membrane to demonstrate the effect of quenching temperature on the final pore size distribution. The calculated result suggested that the asymmetric membrane structure formed by quenching in 303 K water and ice-water was not attributable to the temperature gradient.Supported liquid membranes (SLMs) were prepared by impregnating a carrier solution in the prepared porous polypropylene membranes, and uphill transport of Ce(III) was investigated using octyl(phenyl)-N,N-diisobutyl-carbamoyl-methylphosphine oxide (CMPO) as a carrier, tributyl phosphate (TBP) as a modifier, and dodecane as a solvent. The membranes prepared by air-cooling showed higher permeability of Ce(III) than the commercial membrane.

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.

Liquid-liquid thermally induced phase separation of the polymer-diluent system of poly(ethylene-co-vinyl alcohol) (EVOH)-glycerol was examined under light scattering. For EVOH with an ethylene content of 38 mol % (EVOH38), maxima of the scattered light intensity were observed that indicated that phase separation occurred by the spinodal decomposition (SD). The growth of the structures formed by the general liquid-liquid phase separation obeyed a power-law scaling relationship in SD. For EVOH with an ethylene content of 32 mol % (EVOH32), the liquid-liquid phase separation resulted from the polymer crystallization. In this case, the structure growth showed the characteristic behavior in which the crystalline particles were initially formed, and then the droplets formed by the liquid-liquid phase separation induced by the crystallization grew rapidly. Furthermore, the growth of the droplet by the phase separation was followed by an optical microscope measurement at a constant cooling rate. The phase-separated structure formed after the crystallization can grow faster than that formed by the normal liquid-liquid phase separation.

Porous membranes were prepared through the thermally induced phase separation of poly(ethylene-co-vinyl alcohol) (EVOH)/glycerol mixtures. The binodal temperature and dynamic crystallization temperature were determined by optical microscopy and differential scanning calorimetry measurements, respectively. It was determined experimentally that the liquid–liquid phase boundaries were shifted to higher temperatures when the ethylene content in EVOH increased. For EVOHs with ethylene contents of 32–44 mol %, liquid–liquid phase separation occurred before crystallization. Cellular pores were formed in these membranes. However, only polymer crystallization (solid–liquid phase separation) occurred for EVOH with a 27 mol % ethylene content, and the membrane morphology was the particulate structure. Scanning electron microscopy showed that the sizes of the cellular pores and crystalline particles in the membranes depended on the ethylene content in EVOH, the polymer concentration, and the cooling rate. Furthermore, the tendency of the pore and particle sizes was examined in terms of the solution thermodynamics of the binary mixture and the crystallization kinetics. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 853–860, 2003

The phase-separation mechanism during porous membrane formation by the dry-cast process was investigated by the light-scattering method in poly(methyl methacrylate)/ethyl acetate (EA)/2-methyl-2,4-pentanediol system. The evaporation of EA from the cast solution induced the phase separation and thus the porous membrane was obtained. By the light-scattering measurement on the phase-separation kinetics, the phase separation was found to occur by a spinodal decomposition mechanism. As the amount of nonsolvent in the cast solution decreased, the structure growth rate decreased and the growth stopped soon. The obtained porous structure was isotropic rather than asymmetric. The average interpore distances obtained from the SEM observation roughly agreed with the final constant interphase periodic distances measured by the light-scattering method. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 10: 3205–3209, 2002

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.

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.

Porous membranes were prepared from a polymer blend system by the thermally induced phase separation (TIPS) process. The polymer blend system was isotactic polypropylene (iPP)/polybutene (PB) and the diluent was diphenyl ether (DPE). Two types of porous membranes were prepared by the extractions of DPE alone and both DPE and PB after the phase separation. The effect of the addition of PB to the iPP solution on the phase diagram was investigated and the phase separation kinetics was measured by the light scattering method. The addition of PB resulted in the higher solute rejection property and lower water permeance. By the further extraction of PB from the porous iPP/PB membrane prepared by the extraction of DPE, the water permeance was approximately doubled, maintaining almost the same rejection property.

The effect of convective flow of a carrier solution through a facilitated transport membrane on the CO 2 permeation behavior was investigated using diethanolamine (DEA) as a carrier of CO 2 . A dead-end type filtration cell, equipped with an ultrafiltration membrane, was used as a gas permeation cell. A carrier solution was supplied to the feed side (high pressure side) of the cell and was allowed to permeate to the receiving side (low pressure side) and was circulated between the receiving and the feed side by a pump. The feed gas was a mixture of CO 2 and CH 4 . The convective flow of the carrier solution through the membrane enhanced the gas permeance. For example, the CO 2 permeance, R CO 2 , increased with increasing the volumetric permeation flux of the carrier solution u and when u was 1.9×10 −5 m s −1 and the CO 2 partial pressure was 4.0 kPa, R CO 2 was 6.23×10 −5 mol m −2 s −1 kPa −1 . This value was about ten times that at u =0 with no convective flow of the carrier solution across the membrane. The selectivity of CO 2 over CH 4 was as high as 1970. This type of membrane was very stable during the experiments for more than 2 months.

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.

The effect of diluents on isotactic polypropylene (iPP) membrane formation via thermally induced phase separation was investigated. The diluents were methyl salicylate (MS), diphenyl ether (DPE), and diphenylmethane (DPM). The cloud-point curve was shifted to a lower temperature in the order iPP–MS, iPP–DPE, and iPP–DPM, whereas the crystallization temperature was not influenced so much by diluent type. Droplet-growth processes were investigated under two conditions: quenching the polymer solution at the desired temperature and cooling at a constant rate. Although droplet sizes were in the order iPP–MS, iPP–DPE, and iPP–DPM in both cases, the difference was more pronounced with the constant cooling rate condition. Scanning electron microscopy indicated that interconnected structures were obtained when the polymer solution was quenched in ice water. The effect of the diluents on these structures was observed. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 169–177, 2001

Poly(acrylic acid) (PAA)/poly(vinyl alcohol) (PVA) membrane was prepared for the facilitated transport of CO2. The carrier of CO2 was monoprotonated ethylenediamine and was introduced in the membrane by ion exchange. The ion-exchange capacity of the membrane was 4.5 meq/g, which was much higher than that of the Nafion 117 membrane. The membrane was highly swollen by the aqueous solution. Much higher selectivity of CO2 over N2 and higher CO2 permeability were obtained in the PAA/PVA membrane than in the Nafion membrane because of the higher ion-exchange capacity and solvent content. The highest selectivity was more than 1900 when the CO2 partial pressure in the feed gas was 0.061 atm. Effects of ion-exchange capacity, membrane thickness, and annealing temperature in conditions of membrane preparation on membrane performance were investigated. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 936–942, 2001

Polypropylene particles were prepared by a thermally induced phase separation. The particle formation occurred by the nucleation and growth mechanism in the metastable region. The particle growth was followed by the dynamic light scattering measurement. Although the growth rates depended on the experimental conditions such as the polymer concentration and temperature, the particle diameter d increased with time t in accordance with the relation of d3∝t in all cases. Detailed consideration on the slope values indicated that the particles grew by the coalescence mechanism. The particle size distribution, which was obtained by SEM observation, became broader when the polymer concentration was higher.

Anisotropic (gradation in pore size) and asymmetric (dense surface skin) polypropylene membranes were produced by the thermally induced phase separation (TIPS) process and solute rejection by these membranes was investigated. Anisotropic membranes were obtained by inducing a polymer concentration gradient in the polymer-diluent solution prior to phase separation. The concentration gradient was established by controlled evaporation of diluent from one side of the solution. The anisotropic membranes showed much higher rejection coefficients for latex particles with diameter of 100 nm than an isotropic polypropylene membrane prepared by the TIPS method without evaporation. Asymmetric structures were achieved by imposing a cooling rate gradient across the membrane. The membrane had a skin layer of about 1 μm thickness at the surface that was rapidly cooled. The solute rejection coefficient reached more than 0.95 for lysozyme of molecular weight of 14 600. This result shows that ultrafiltration polypropylene membranes can be produced by the TIPS process if asymmetry is induced during the membrane formation process.

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.

Experiments on the removal of phenol by emulsion liquid membrane containing aqueous LiOH or NaOH solution in the inner aqueous phase were performed using a one-stage continuous stirred vessel and a two-stage countercurrent mixer-settler, and the effects of operation conditions such as phenol concentration, feed and emulsion flow rates and stirring speed on the pehnol removal were investigated.When the liquid was withdrawn from the lower position of the stirred vessel, the hold-up (volume fraction of W/O emulsion) in the vessel increased, resulting in high phenol removal compared to the case when the liquid was withdrawn from the higher position of the vessel. The stage efficiency was more than 90% and at favorable conditions, the efficiency was as high as 99%, indicating very effective contact between external aqueous phenol solutions and W/O emulsion drops in the stirred vessel. The two-stage countercurrent mixer-settler was very effective for achieving high phenol removal. The W/O emulsion loaded with phenol could be demulsified by an electrocoalescer.

Facilitated transport of CO 2 through a thin solution-cast perfluorosulfonic acid ionomer membrane has been studied. The CO 2 carrier was monoprotonated ethylenediamine and was immobilized in the ionomer membrane by electrostatic force. The cast membrane with membrane thickness 22 μm showed much higher CO 2 permeance than the commercial Nafion ® 117 membrane of thickness 186 μm. However, selectivity of CO 2 over N 2 was lower in the cast membrane. The effects of the membrane thickness and annealing temperature in the membrane preparation on membrane performance were investigated. CO 2 permeability and the selectivity decreased with decreasing membrane thickness and with increasing annealing temperature. Dynamic mechanical studies were done to study the membrane structures. The cast membrane annealed at 200°C showed two peaks similar to the commercial membrane. In contrast to this, the peak assigned to the polar region was small in the cast membrane annealed at a lower temperature, which suggested that clear clusters do not form in the membrane.

Polyethylenimine (PEI)/poly(vinyl alcohol) (PVA) blend membranes were prepared for the facilitated transport of CO2. The polymeric carrier PEI was retained in the blend membrane by the entanglement with PVA chains. The CO2 permeance decreased with an increase in CO2 partial pressure in feed gas, whereas the N2 permeance was nearly constant. This result clearly showed that only CO2 was transported by the facilitated transport mechanism. The CO2 and N2 permeabilities increased monotonically with the PEI weight percent in the blend membrane, whereas the selectivity of CO2 over N2 showed a maximum. The selectivity increased remarkably with increasing heat-treatment temperature of the membrane. The highest selectivity obtained reached more than 230 when the CO2 partial pressure was 0.065 atm. The prepared membrane was stable.

The kinetics of droplet growth in the metastable region were investigated in cellulose acetate/acetone/nonsolvent system. The results obtained by the dynamic light scattering apparatus indicated that the droplet diameter d increased with time t in the relation of d 3 ∝ t in all cases. From the detailed consideration on the slope values in these relations, it was concluded that the droplet growth mechanism in this system was coalescence mechanism rather than Ostwald ripening mechanism. The direct observation of the freeze-dried polymer solution by SEM was not contradictory to this conclusion. The initial stage of droplet growth was investigated by the stopped-flow apparatus. The experimental results on the turbidities showed that the droplets grew in the relation of d 3 ∝ t as well as the results by the light scattering.

In order to examine the feasibility of treating low level radioactive wastewater by supported liquid membranes (SLMs), experiments were performed using a stirred permeation cell. Aqueous solutions of nitric acid and/or sodium nitrate containing about 550 ppm Ce(III), 490 ppm Fe(III), 320 ppm Cr(III) and 330 ppm Ca(II) were used as a simulated low level radioactive wastewater. The liquid membrane consisted of octyl(phenyl)- N , N -diisobutylcarbamoylmethylphsophine oxide as a carrier of cerium, tributylphosphate as a modifier and dodecane as a solvent. The strip solutions were water and aqueous sodium citrate solutions. The effects of various experimental conditions such as concentrations of cerium, HNO 3 and NaNO 3 in the feed solution, liquid membrane composition and temperature were investigated. Rapid transport and enrichment of cerium were realized by adding sodium citrate to the strip solution as the masking agent of cerium and also using a feed solution of low nitric acid concentration and high sodium nitrate concentration. Increasing the temperature from 298 to 318 K was very effective in enhancing the permeation rate of cerium. The membrane area required for removing 99.9% of cerium from the feed solution containing about 550 ppm Ce was estimated as 3.3 m 2 at 1 m 3 day −1 of the treatment rate.

Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) ethyl esters were effectively separated from oleic acid (OA) and palmitic acid (PA) ethyl esters by oil-in-water (O/W) emulsion liquid membranes containing silver nitrates as a mobile carrier. Since the silver ions in the liquid membrane phase have a high affinity to the carbon-carbon double bonds in polyunsaturated fatty acids (PUFA), DHA and EPA ethyl esters were selectively transported through the complex formation with the silver carrier from the internal material phase to the external recovery phase. The stability of the liquid membranes in the O/W emulsions was the most important factor to achieve a high recovery yield of their PUFA esters with a high purity. Surfactants were limited to nonionic surfactants to obtain a stable emulsion liquid membrane when containing the silver carrier. Concentrations of the surfactant and silver nitrates had a predominant effect to operate the PUFA separation by emulsion liquid membranes effectively. There is an optimal concentration for the silver nitrates and excess dosage of the carrier causes the instability of liquid membranes. Under the best conditions, 86% polyunsaturated fatty acid esters were successfully separated through the silver liquid membrane in a few minutes with a 98% purity.

The various types of porous membranes were prepared by dry-cast process in several cellulose acetate/acetone/nonsolvent systems. The nonsolvents used were 2-methyl-2,4-pentanediol, hexanol and octanol. Because of the high boiling points of the nonsolvents used in this work, only the solvent (acetone) evaporated during the membrane formation. The effects of the nonsolvent weight fraction in the cast solution, the polymer weight fraction, membrane thickness and kinds of the nonsolvents on the membrane structures were studied. As the nonsolvent weight fraction increased, the membrane morphology changed in the order of entirely dense, asymmetric and entirely porous structures. The increase in the polymer weight fraction and the decrease in the membrane thickness suppressed the asymmetric structures. These kinds of nonsolvents significantly influenced the membrane morphology. In order to understand the change of the obtained membrane structures, the phase diagrams for ternary systems were clarified experimentally and theoretically. Moreover, the mass transfer process was analyzed and the changes in the polymer volume fractions during the membrane formation were simulated. Based on both these thermodynamic and kinetic properties, the membrane structures obtained were discussed in detail. The asymmetrc structures obtained in this work were found to be attributable to the kinetic difference in the increase rates of the polymer fractions across the binodal line.

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.

A series of experiments on the facilitated transport of CO2 through supported liquid membranes impregnated with aqueous solutions of various amines as carriers was performed, and the effects of the reaction rate and the chemical equilibrium of the reaction between CO2 and amine on the permeability of CO2 were investigated. Four primary amines (monoethanolarnine (MEA), ethylenediamine (EDA), monoprotonated ethylenediamine (EDAH+), 2-amino-2-methyl-l-propanol (AMP)), one secondary amine (diethanolamine (DEA)) and two tertiary amines (triethanolamine (TEA), methyldiethanolamine (MDEA)) were used as the carrier. The feed gas was a mixture of CO2 and CH4. High CO2 permeabilities were obtained with the EDAH+ membrane due to its moderate chemical equilibrium constant Keq which is favorable for both fast absorption of CO2 at the feed side of the membrane and fast stripping at the sweep side. Low CO2 permeabilities were obtained with the tertiary amine and AMP membranes due to their low reactivity. The CO2 permeability through the MEA membrane, which has too large a Keq value at low temperature, increased with increasing temperature due to the decrease in Keq and also due to the increase in the reaction rate. The experimental results obtained with the MEA, DEA and EDAH+ membranes were simulated on the basis of the theory of facilitated transport.

In order to investigate the percolation behavior for ion transport, copolymers of styrene and methacrylic acid (MAA) were synthesized over a wide range of ion concentrations. The flux of K + through the ionomer membrane was almost independent of the feed K + concentration as far as the ratio of K + concentration to Na + concentration in the feed solution was maintained at constant. This was the characteristic for ionomer membrane. The permeability of K + increased discontinuously at about 14 mol% of MAA, which demonstrated the percolation behavior for K + transport. In the relation between the permeability and a difference of the volume fraction of MAA and water from the threshold volume fraction, a simple power law was confirmed. The critical exponent and the percolation threshold obtained for this system were 1.7 and 0.165, respectively, and these values were nearly in agreement with those expected for the randomly dispersed system. The copolymers of styrene and sodium methacrylate were well-known to form ion clusters. However, since our ionomer membrane was prepared without neutralization of the copolymer of styrene and MAA, it is considered that the carboxyl groups of the copolymer were undissociated at the time of the membrane preparation, and therefore the ion clustered structure was not formed. The result of DSC measurement suggested that the ionomer had no cluster structure.

Ion exchange membranes were prepared by grafting acrylic acid (AA) and methacrylic acid to the substrates such as microporous polyethylene (PE) and polytetrafluoroethylene (PTFE), and homogeneous poly[1-(trimethylsilyl)-1-propyne] (PTMSP) by the use of the plasma graft polymerization technique. Experiments on the facilitated transport of CO2 through the grafted membrane were carried out by using various diamines, diethylenetriamine and triethylenetetramine as the carrier. Among all the membranes tested, the AA grafted membrane containing ethylenediamine as the carrier showed the highest selectivity of CO2 over N2. For example, when the CO2 partial pressure in the feed phase was 0.047 atm, the selectivity reached more than 4000 with 1.0 × 10−4 cm3/(cm2 s cmHg) of CO2 permeation rate. The use of PTFE and PTMSP substrates were effective for increasing the permeation rate of CO2. The effects of CO2 partial pressure in the sweep gas and temperature on the permeation rates and selectivities were also investigated. The CO2 partial pressure in the sweep gas hardly influenced the membrane efficiencies up to 0.023 atm.

Experiments on the separation of ethyl ester of eicosapentaenoic acid (EPA-Et) and that of docosahexaenoic acid (DHA-Et) contained in ethyl ester of bonito oil (bonito oil-Et) were performed using circulating liquid membranes (CIRLMs) containing sliver nitrate as a carrier. In this liquid membrane system an aqueous silver nitrate solution was circulated between a stirred vessel containing an organic solution of bonito oil-Et and another stirred vessel containing a receiving organic solvent. Using the CIRLM, two types of uphill facilitated transport of EPA-Et and DHA-Et in bonito oil-Et were demonstrated. The first type utilizes the distribution ratio of EPA-Et and DHA-Et, defined as the ratio of the concentration in the aqueous phase to that in the organic phase at equilibrium, which is remarkably dependent on the temperature, and the second uphill transport was based on the fact that the distribution ratio is considerably dependent on the solvent of the organic phase. A model of permeation throu...

The selective separation of rare earth metals by solvent extraction including chelating polymers in the aqueous phase was investigated. The chelating polymers were synthesized in this laboratory by introducing ethylenediaminetetraacetic acid (EDTA) onto water-soluble polyallylamine. The highest selectivity obtained for the Y/Er separation system was 14.7, which was much higher than that in conventional solvent extraction (about 1.4) and also higher than that in extraction including EDTA (about 5.0). This means that the number of extraction stages required can be considerably reduced by the addition of chelating polymers. The effects of several experimental conditions such as pH, extractant concentrations, chelating polymer concentrations, and initial total rare earth metal concentrations on the separation factors and the distribution ratios for the Y/Er system were studied in detail. Furthermore, this extraction method was applied to other separation systems (Y/Dy, Y/Ho, Y/Tm). A remarkably high ...

New hydrophilic chelating polymers were synthesized by introducing ethylene-diaminetetraacetic acid (EDTA) onto water-soluble polyallylamine. The selective separation of rare earth metals by solvent extraction including these chelating polymers in the aqueous phase is the goal of this work. The polymers were characterized by IR analysis, elemental analysis, gel permeation chromatography (GPC) measurement, and pH titration. Two kinds of polymers with different solubilities in water were produced using different solvents. Both polymers were naturally precipitated in the presence of rare earth metals. This Suggests that in the solvent extraction system including these cheiating polymers, the recovery of the polymers is easy. Adsorption properties of Y3+ and Er3+ on these polymers were also investigated. The separation properties by adsorption on the polymers were comparable to those by EDTA. The chelating polymers had the characteristics that their separation factors decreased by adsorption and the ...

It is well known that the selectivity of rare earth metals by solvent extraction is increased by the addition of a chelating agent such as diethylenetriaminepentaacetic acid (DTPA) in the aqueous phase. One of the disadvantages of this method is the decrease in extraction rates due to complexation in the aqueous phase. In this paper, further addition of organic acids to the aqueous phase was examined for the purpose of enhancing the extraction rates in solvent extraction with DTPA. The addition of several kind of organic acids such as formic acid, acetic acid, malonic acid, lactic acid and citric acid was investigated for a Er/Y separation system. A remarkable enhancement in extraction rates was observed with a slight decrease in the selectivity by the addition of citric acid or lactic acid. Extraction rates in the presence of both DTPA and citric acid increased with the increase in citric acid concentration and with the increase in proton concentration. A 150 times enhancement in extraction rates was found in the low proton concentration condition. In order to analyze the extraction rates and selectivities obtained, mass transfer equations were presented by considering both the dissociation reaction of rare earth metal-DTPA complexes and the complex formation between rare earth metal and organic acid in the aqueous phase. The experimental data were analyzed by these equations.

A series of experiments on the facilitated transport of CO2 through supported liquid membranes containing monoethanolamine (MEA) and diethanolamine (DEA) was performed. The feed gas was a mixture of CO2 and CH4, and the CO2 partial pressure pCO2,F was in the range from 0.05 to 0.97 atm. Compared to the MEA membranes, the DEA membranes showed a little higher permeation rate of CO2 since the equilibrium constant of the reaction between CO2 and MEA is too large for CO2 to be released to the receiving phase rapidly. When pCO2,F and the MEA concentration were 0.05 atm and 4 mol/dm3, respectively, the separation factor α(CO2/CH4) was about 2000. It was found that if the membrane thickness multiplied by the square root of the tortuosity factor of the microporous support membrane is used as the effective pore length, the experimentally observed permeation rates of CO2 can be satisfactorily simulated by the theory of facilitated transport of CO2 through aqueous amine membranes. A method for estimating the solubili...

Plasma polymerized membranes were prepared from octamethyltrisiloxane for the purpose of separation of O2 over N2. The obtained membrane consisted of plasma prepared polymer layer on top of a porous polyproplene substrate. The membrane polymerized under the mild plasma condition (low power input and high monomer flow rate) showed the high permeation rate. Selectivity, however, was hardly affected by the plasma conditions. The selectivity and permeation rate obtained were 2.6 and 2.5 × 10−10 kmol/(m2·s·Pa) (=7.5×10−4 cm3/(cm2·s·cmHg)), respectively. This high permeation rate was attributed to the use of the monomer with the long, flexible siloxane chain and the mild plasma condition. Moreover, the membranes were prepared from a series of monomers with different siloxane chain lenghts (methoxytrimethylsilane, hexamethyldisiloxane, and octamethyltrisiloxane), and from those with different alkyl chain lenghts (methoxytrimethylsilane, propoxytrimethylsilane, and hexyloxytrimethylsilane). As the siloxane chain lenghts of the starting monomers increased and the alkyl chain lengths decreased, the permeation rates of the corresponding polymers increased. The selectivities were nearly constant regardless of the difference in the starting monomer structures. The structures of the plasma prepared polymers were analyzed by XPS and IR measurements, and discussed in relation to the membrane efficiencies. © 1994 John Wiley & Sons, Inc.

A new type of cation-exchange membrane was prepared by grafting acrylic acid onto a microporous polyethylene membrane by use of plasma-grafted polymerization technique. The facilitated transport of CO2 through the plasma-grafted membrane containing ethjylenediamine was studied. The obtained membrane showed remarkably high CO2 permeability and selectivity of CO2 over N2. When the CO2 partial pressure in the feed gas was 0.047 atm, the CO2 permeability and the selectivity obtained were 1.0×10−4 cm3 cm−2 s−1 cmHg−1 and 4700, respectively. These efficiencies were much higher than those of conventional polymer membranes, and were also superior to efficiencies of ion-exchange membranes containing a carrier, reported so far. These excellent results are probably attributable to the high ion-exchange capacity and the high water content. The newly prepared membrane was stable.

The effect of recycling of a feed solution from the outlet to the inlet of the feed channel of a plate-and-frame type supported liquid membrane module on the recovery of zinc was investigated under the condition that the feed side mass transfer resistance is predominant. Di(2-ethylhexyl)phosphoric acid was used as the carrier. It was found that at a given feed flow rate, recycling of the feed solution is effective for improving the recovery of zinc since recycling brings about an increase of the flow rate in the feed channel and also the mass transfer coefficient in the feed side. The experimental data could be satisfactorily simulated by a proposed theoretical model.

Eicosapentaenoic acid ethyl ester (EPA-Et) was successfully transported against its concentration gradient from a n-dodecane solution to a m-xylene solution through a bulk liquid membrane as well as a supported liquid membrane containing silver nitrate as a carrier. The principle of this uphill transport is that the distribution ratio of EPA-Et, which is defined as the ratio of the equilibrium concentration of EPA-Et in an aqueous silver nitrate solution to that in an organic solution, is highly dependent on the solvent of the organic phase, n-Dodecane gives a much higher distribution ratio than m-xylene. This is the first demonstration of uphill transport by use of solvent dependence of the distribution ratio of a permeant solute.