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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.

In the present paper, the simultaneous removal of CO2 and H2S from their pressurized mixture with CH4 (5% CO2–2% H2S–93% CH4) using custom made membrane contactors equipped with micro-porous polymeric hollow fibers is described. Two types of commercial hollow fibers were employed and compared, i.e., expanded poly(tetrafluoroethylene) (ePTFE) and poly(tetrafluoroethylene-co-perfluorinated alkyl vinyl ether) (PFA). The feed gas mixture composition was 2% H2S, 5% CO2 in balance of CH4 to mimic the typical natural gas composition. Distilled water, aqueous sodium hydroxide and amine solutions of different concentrations were tested as absorption liquids to achieve the selective removal of the acid gases from the pressurized gas streams. The effect of pressure on the simultaneous CO2 and H2S absorption rates was investigated by the simultaneous pressurization of the absorption liquid and the feed gas (up to 50 bar) and monitoring the residual acid gases in the exit stream. The obtained experimental results indicated that the simultaneous CO2 and H2S fluxes were enhanced by increasing the inlet gas pressure for both physical and chemical absorption solvents. Up to the authors’ best knowledge, this is the first report on (i) the experimental simultaneous removal of CO2 and H2S from pressurized gas streams using HFM contactors and absorption solvents up to 50 bar and (ii) the utilization of PFA fibers in custom made high pressure-membrane modules. PFA fibers exhibited impressive higher fluxes (9–10 times) for CO2 and H2S than those obtained with the common ePTFE fibers which could be attributed in part to the associated higher mass transfer coefficient. The anticipated CO2/H2S flux ratio of 2.5 (which matches the ratio of their inlet concentrations in the feed gas) was obtained whenever the co-absorption was unhindered into absorption solvent of sufficient capacity, e.g., 2.0 M NaOH solution. Analysis of the mass transfer coefficients showed that while the overall mass transfer coefficients are determined by the liquid phase mass transfer coefficients at low pressures, gas phase mass transfer resistance contributes considerably to the overall resistance at high pressures.

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.

Seven kinds of asymmetric poly(vinylidene fluoride) (PVDF) hollow fiber membranes with considerable different structures at the outer surfaces were prepared via thermally induced phase separation (TIPS) method and applied for CO 2 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 CO 2 into monoethanolamine (MEA) solutions were performed and the effects of membrane structure and inner diameter on the membrane performance were investigated. The module efficiencies were compared for the two patterns of operation, i.e. case 1 operation where liquid flows in the tube side while gas in the shell side and case 2 operation where liquid flows in the shell side while gas in the tube side. CO 2 absorption fluxes observed in case 1 operation were inversely proportional to the inner diameter of the hollow fiber membrane, and CO 2 absorption rate per fiber was almost the same for all membranes. CO 2 absorption rates observed in case 2 operation were much smaller than those in case 1 operations. The performances of the PVDF membranes were comparable with that of the commercial PTFE membrane. A mathematical model for pure CO 2 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 CO 2 absorption rates. Experimental results in case 1 operation were satisfactorily simulated by the model for all membranes with different structures. Experimental results obtained in case 2 operation were also simulated by the model except for a membrane with a very low surface porosity on its outer surface. CO 2 absorption flux increased with increasing the MEA concentration up to the concentration of 2 mol/dm 3 , however, the CO 2 absorption flux hardly increased with further increase in MEA concentration. This behavior is discussed based on the decrease in the effective gas–liquid contacting area with increasing MEA concentration. A method to estimate CO 2 solubility and diffusivity in MEA solutions, which are essential for calculating CO 2 absorption flux by the model, is also described.

A novel facilitated transport membrane consisting of 2,3-diaminopropionic acid (DAPA) as a selective carrier of CO 2 and PVA/PAA gel as support was developed for the removal of CO 2 from the water gas shift reactor in the hydrogen production plants. The membrane performance was tested by the experiments on the selective separation of CO 2 from a mixture of 3.65% CO 2 , 32.9% N 2 and 63.5% H 2 O at the temperature from 125 to 160 °C and the feed gas pressure from 100 to 650 kPa. Typical observed CO 2 permeances were 3.14 × 10 −4 mol/m 2 s kPa at 125 °C and 300 kPa, 1.71 × 10 −4 at 140 °C and the feed gas pressure of 450 kPa and 1.10 × 10 −4 at 160 °C and 600 kPa, and the CO 2 /H 2 selectivities at the respective conditions were 1070, 561 and 432, respectively. Obtained results showed that the water content in the membrane is one of the key factors, which determines the CO 2 permeance and CO 2 /N 2 selectivity. The CO 2 permeance as well as the CO 2 /N 2 selectivity increased with increasing the pressure, which might be mainly caused by increasing the water content in the membrane. It was also found that increasing the carrier concentration could significantly enhance the membrane performance, especially at elevated temperatures.

Polymer blend hollow fiber membranes were prepared via thermally induced phase separation (TIPS). Poly(vinyl butyral) (PVB) and poly(ethylene-co-vinyl alcohol) (EVOH) were used as polymers and diluent was polyethylene glycols (PEG) with the molecular weight of 200. The phase diagrams obtained in the polymer blends system indicated both UCST (upper critical solution temperature) and LCST (lower critical solution temperature) behaviors. For LCST behavior, there were two kinds of phase separations. It was considered that the phase separation occurred at higher temperature was between PVB and EVOH, and that occurred at lower temperature was between polymer and diluent. The addition of EVOH had an eminent effect on the hollow fiber membrane structure and membrane performance. With the increase of EVOH content in the polymer blend system, the membrane became more hydrophilic, and the water permeability became higher due to the enlargement of the pores. The addition of EVOH was also effective to improve the mechanical property of hollow fiber membrane.

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.

Energy consumption for the separation of CO 2 in flue gas by a novel hollow fiber facilitated transport membrane module was evaluated and compared with those by conventional separation processes such as gas absorption and polymeric membrane separation. In the novel facilitated transport membrane system, both a feed gas (CO 2 /N 2 mixture) and a carrier solution (aqueous diethanolamine solution) are supplied to the lumen side (feed side, high pressure side) of the hollow fiber ultrafiltration membrane module and flow upward. 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 become a lean solution and the lean solution is returned to the lumen side by a pump. The feed side pressure was atmospheric and the permeate side pressure was controlled in the range from 10 to 27 kPa. CO 2 in the feed gas consisting of 10% CO 2 and 90% N 2 was concentrated to higher than 99%. The effects of various system parameters, such as permeate side pressure, temperature, gas and liquid flow rates and the inner diameter of hollow fiber membrane, on the energy consumption for CO 2 recovery were investigated. Energy consumption decreased with increasing temperature and had a minimum at an optimum permeate side pressure. The minimum energy consumption was estimated as 0.211 kWh kg-CO 2 −1 when the inner diameter of the hollow fiber was 0.8 mm. The energy consumption increased with feed gas flow rate, however, it was little influenced by liquid flow rate. The energy consumption decreased remarkably with increasing the inner diameter of the hollow fiber, and it was estimated as 0.072 kWh kg-CO 2 −1 when hollow fibers of 1.4 mm in inner diameter were used. This value is the lowest among those reported so far.

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.

天然ガス火力発電所排ガスからの二酸化炭素除去への膜・吸収ハイブリッド法の適用を検討した．膜・吸収ハイブリッド法はCO2の吸収液とCO2/N2混合ガスとを限外ろ過中空糸膜の内部に同時に供給し，膜外部を減圧にして分離推進力を与えCO2を膜外部に分離するCO2の分離方法である．吸収液としてはジエタノールアミン（DEA）と2-ブチルアミノエタノール（BAE）の混合水溶液を選択した．発電所から放出されるCO2を回収し90%以上に濃縮した後，気体で輸送するケース1では，CO2の回収に要する動力は0.10 kWh/kg-CO2であり，エネルギーおよび設備コストを含むCO2分離コストは3.09円/kg-CO2であった．また発電所から放出されるCO2を回収し，分離後液化し液体炭酸として輸送するケース2では，CO2の回収に要する動力は0.22 kWh/kg-CO2，CO2分離コストは5.14円/kg-CO2であった．これらの値はいずれも従来のCO2分離・回収法よりも小さく，膜・吸収ハイブリッド法でCO2を分離・回収するシステムは経済性に優れていることが示唆された．

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.

A novel facilitated transport membrane module for gas separation 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 module and flow upward. Most of the carrier solution which contains dissolved solute gas, CO2 in the present case, permeates the membrane to the permeate side (low-pressure side, shell side), where the solution liberates dissolved gas to become a lean solution, and the lean solution is returned to the lumen of the capillary module by a pump. This type of capillary membrane module was applied to the separation of CO2 from model flue gases consisting of CO2 and N2 using various amines as carriers or absorbents of CO2. The feed side pressure was atmospheric and the permeate side pressure was controlled at 9–27 kPa. CO2 in the feed was successfully concentrated from 1.5–15 to 98.5–99.8 mol%. When the CO2 mole fraction in the feed was 0.1 and the mean residence time of gas in the module was 0.28 s, the CO2 permeance was 3.8×10−4 mol m−2 s−1 kPa−1 (1.1×10−3 cm3 cm−2 s−1 cmHg−1) and the CO2 recovery was 76%. The selectivity of CO2 over N2 was in the range from about 800 to 8000. The membrane was very stable over a discontinuous 4-month testing period. The energy consumption was found to be much smaller than those of conventional chemical absorption and membrane separation processes.

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.

Recent developments in the facilitated transport membranes (FTMs) for gas separations with high selectivity are described focusing on CO2/N2, 02/N2 and olefin/paraffin separations. There are two types of FTM, i.e., mobile carrier membrane and fixed carrier membrane. For both types of membrane, the rate and equilibrium of the reaction between the carrier and the penetrant gas have decisive effects on the membrane performance. With respect to fixed carrier membranes for O2/N2 separation, a composite membrane with a very thin active layer of Co (II) -porphyrin complex of about 80nm thickness on a porous support exhibits promising O2 permeance and selectivity. Very efficient solid polymer electrolyte membranes containing silver salts have been developed for olefin/paraffin separations, and the threshold carrier concentration behavior has been elucidated from the coordination behavior of silver ion in the membrane. Finally, a novel type of “facilitated transport membrane” accompanied by permeation of a carrier solution, which overcomes the drawback of liquid membranes such as instability and low permeability, is shown to be very effective for CO2/N2 and C2H4/C2H6 separations.

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

燃焼排ガスからの二酸化炭素除去への促進輸送膜の適用を, コンピューターシミュレーションにより検討した. 燃焼排ガス源としては100万kWの天然ガス火力発電所と石炭火力発電所を, 促進輸送膜としては2,3-ジアミノプロピオン酸 (DAPA) をキャリアとしたゲル塗布膜を選択した. 発電所から放出されるCO2の50%を回収し90%に濃縮した後, 気体で輸送するケースでは, CO2の回収に要する電力は天然ガス火力発電所, 石炭火力発電所でそれぞれ発電量の8.39%と10.55%であった. CO2分離コストはそれぞれ359円/kmol-CO2と283円/kmol-CO2であった. また, 発電所から放出されるCO2の50%を回収し, 膜分離後液化し99.9%に濃縮し輸送するケースでは, CO2の回収に要する電力は天然ガス火力発電所, 石炭火力発電所でそれぞれ発電量の11.1%と14.5%であった. CO2分離コストはそれぞれ247円/kmol-CO2と354円/kmol-CO2であった.促進輸送膜によりCO2を分離・回収するシステムが経済性に優れるシステムであることを推定した.

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.

マイクロ流路内での層流や高熱伝導特性の利点を生かす膜型触媒とガス分離膜の両性能を有する炭素膜の開発を試みた. ポリアミド酸膜に3種類の金属イオン(Ni2+, Zn2+, Cu2+)をイオン交換し, 熱処理·炭化して金属担持炭素膜を作製した. 金属イオンは炭化挙動に大きく影響を及ぼし, イオン交換後に炭化して作製した炭素膜ではマクロ孔の発達が認められた. また, 交換する金属イオンの種類を選択することにより炭素膜のミクロ構造は大きく変化することがわかった.炭素膜中の金属形態は金属単体あるいは酸化物であり, 700℃で炭化した膜中においてはCu型で約20nm, Ni型で約25nm, Zn型では約100nmの粒子が高分散で担持されており, 高活性が期待できた. また, メタノール熱分解においては水素選択性に優れていた.

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.

Phase separation rate during porous membrane formation by immersion precipitation was investigated by light scattering in a polyimide/N-Methylpyrrolidone (NMP)/water system. In the light scattering measurement, plots of scattered intensity against scattered angle showed maxima in all cases, which indicated that phase separation occurred by a spinodal decomposition (SD). Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient Dapp and an interphase periodic distance Λ, were obtained. The growth process of Λ was also followed by light scattering. The growth rate had the same tendency as Dapp when water content in the nonsolvent bath and the polymer concentration in the cast solution were changed. The pore size of the final membrane increased with decreasing water content, which was opposite to the tendency of Λ growth rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 292–296, 2003

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

A novel facilitated transport membrane, a bulk flow liquid membrane (BFLM), was applied to ethylene/ethane separation using silver nitrate as a carrier. In this membrane system, a carrier solution is supplied to the feed gas side (high pressure side) of a UF membrane and is allowed to permeate to the permeate side (low pressure side). The transferred carrier solution is recycled to the feed side. The effect of such convective flow of the carrier solution through the membrane on ethylene permeance was investigated using a dead-end type filtration cell equipped with an ultrafiltration membrane. The C2H4 permeance, RC2H4, increased with increasing the volumetric permeation flux of the carrier solution u, and when u was 4×10−5m s−1 and the C2H4 partial pressure was 9 kPa, RC2H4 was 4×10−5 mol m−2 s−1 kPa−1 and the selectivity of C2H4 over C2H6 was 1100. This value was ≈30 times that at u=0. This type of membrane was very stable during intermittently performed experiments for more than 2 months.

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.

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.

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.

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. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 171–178, 1999

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. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 159–170, 1999