Inorganic Composite Membranes by Plasma

Teruhiko Kai , Yasunori Suma , Shuichiro Ono , Takeo Yamaguchi , Shin-ichi ... MIKIHIRO NOMURA , YASUYUKI MINETA , NAOKO YAMAGUCHI , EIICHI ...
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Preparation of Organic/Inorganic Composite Membranes by Plasma-Graft Filling Polymerization Technique for Organic-Liquid Separation Teruhiko Kai,*,† Takeo Yamaguchi, and Shin-ichi Nakao Department of Chemical System Engineering, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

Pore-filling-type organic/inorganic composite membranes were prepared by a plasma-graft polymerization technique. Shirasu porous glass (SPG) was used as the inorganic substrate, and methyl acrylate was used as the grafting monomer. Two preparation procedures were employed: direct plasma grafting and two-step plasma grafting. Optical microscope and microFT-IR studies showed that the grafted polymer was formed in the pores of the SPG substrate. The thickness of the grafted layer formed by direct plasma grafting was about 50 µm. With the two-step plasma grafting, the grafted layer formed was thinner. The grafted membranes showed chloroform selectivity in pervaporation and vapor permeation of a chloroform/n-hexane mixture. The separation performance of the grafted membranes was stable throughout the separation experiments. This implies that the grafted polymers are covalently bonded to the inorganic substrate. The grafted membrane prepared by the two-step plasma grafting showed higher selectivity than that of a filling-type membrane with a high-density polyethylene (HDPE) substrate. This result proved that the inorganic substrate can exhibit a high swelling-suppression effect and the filling-type membrane with an inorganic substrate can exhibit high selectivity in pervaporation separation. The membranes were thermally stable at least up to 150 °C. Introduction Recently, a membrane separation process has been considered as a promising way to separate organic-liquid mixtures. A suitable membrane that can separate organic-liquid mixtures efficiently can make the membrane process competitive with conventional separation processes such as distillation. For this it is very important to develop new membranes that show high permeation and selectivity. In addition, durability at high temperature is necessary to successfully apply the membranes to high-temperature separation processes. For application of polymeric membranes to separate organic-liquid mixtures, membrane swelling must be controlled to obtain high separation performances, because the swelling always results in poor selectivity because of its plasticization effect. For this purpose, we have proposed the concept of a filling-polymerized membrane to prevent membrane swelling.1,2 Pores of a porous substrate were filled with grafted polymer. The substrate material must be completely inert to any kinds of organic liquids. The swelling of the grafted polymer is suppressed by the matrix of the substrate. In our previous study, we had used porous high-density polyethylene (HDPE) as the substrate and the fillingpolymerized membrane had been made by a plasmagraft polymerization technique. The membranes showed high permselectivity in pervaporation of organic-liquid mixtures or removal of chlorinated organics from water. Other research groups reported membranes made by the * Corresponding author. Tel: +81-3-5841-7346. Fax: +813-5684-8402. † Present address: Advanced Materials Laboratory, Japan Chemical Innovation Institute, 2-22-13 Yanagibashi, Taitoku, Tokyo 111-0052, Japan. Tel: +81-3-3851-8876. Fax: +813-5822-7220. E-mail: [email protected].

same concept, and the membranes showed good separation performances in organic-liquid separations.3-5 The separation process sometimes must operate at higher temperature, and for this, the membranes need high-temperature durability. The swelling-suppression effect of the polymeric substrate, however, becomes weaker as the operating temperature becomes higher. This is because the elastic energy of the polymer crystals decreases with an increase in temperature.6 On the other hand, a porous inorganic substrate is stable at high temperature, so the composite membrane with a porous inorganic substrate will be more suitable for separation of organic-liquid mixtures at higher temperature. Besides, the composite membrane has the possibility of having high selectivity because of the rigid structure of the inorganic substrate. Some techniques that can form polymers in porous inorganic substrates were reported previously. Sakohara et al. prepared polymeric gel membranes in the pores of a thin ceramic support by polymerization in the pores.7 Liu et al. applied electrochemical synthesis or photochemical synthesis for this purpose.8,9 These techniques need cross-linking to fix the polymer in the pores, because the polymer is not covalently bonded to the inorganic substrate. In another instance, radical polymerization was employed to form grafted polymer onto the modified porous glass substrates.10-13 Cohen et al. reported pervaporation of water/trichloroethylene (TCE) mixtures and organic-liquid mixtures with the membranes prepared by radical polymerization onto inorganic substrates.12,13 This technique can stably fix the polymer without cross-linking because of covalent bonding with the inorganic surface. In this paper, we applied a plasma-graft polymerization technique to prepare filling-type organic/inorganic composite membranes, and porous glass was employed

10.1021/ie9904100 CCC: $19.00 © 2000 American Chemical Society Published on Web 08/12/2000

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Figure 1. Concepts of membrane preparation procedures by a plasma-graft polymerization technique.

as the substrate. A plasma-graft polymerization technique will have some advantages; the linear grafted polymer will be formed in the pores of the inorganic substrate, and the grafted polymer is covalently bonded to the inorganic substrate. Thus, the grafted polymer in the pores should be more stable. The filling-type membrane having a linear grafted polymer showed high permeability compared with the usual cross-linked membranes because of high diffusivity of the solvent in linear polymers.14 Besides, in plasma-graft polymerization, the polymerization will continue until air (oxygen) is introduced into the reaction tube.15 Hence, it is easy to manipulate the grafting time and hence the graft density of the grafted layer. When the density of the grafted layer in the pores is controlled, it is possible to design membranes showing good separation properties. Although there are previous reports about plasmagraft polymerization with a porous glass substrate, a grafted layer was reportedly formed on the outer surface.16,17 In this paper, we report the formation of grafted polymer in the pores of the porous glass substrate by a plasma-graft polymerization technique. The membrane showed good permselectivity in pervaporation and in vapor permeation. Membrane Preparation Procedures In this research, we examined two kinds of preparation procedures as described in Figure 1. (a) Direct Plasma Grafting. In this procedure, linear grafted polymer was formed on the glass pore surface directly by plasma-graft polymerization. (b) Two-Step Plasma Grafting. To improve the formed radical density on the pore surface by plasma treatment, a thin polymer layer was made on the pore surface, and then plasma grafting was carried out. This preparation procedure consists of two plasma-grafting steps. At the first step, a thin cross-linked polymer is formed on the pore surface of the porous glass substrate by plasma-graft polymerization. At the second step, a linear polymer is formed by plasma-graft polymerization in the substrates previously treated at the first step. The grafted polymer is formed from the cross-linked grafted polymer on the pore surface.

Experimental Section Materials. A tubular-type Shirasu porous glass (SPG, length 10-12 cm, outer diameter 5 mm, inner diameter 4 mm, pore diameter 90 nm, porosity 0.50, specific surface area 19.6 m2‚g-1) received from Industrial Research Institute of Miyazaki Prefecture was used as the porous substrate. SPG is a controlled-pore glass membrane prepared by phase separation of calcium aluminoborosilicate glass.18 The substrate has a symmetric structure. Methyl acrylate (MA) and vinyl acrylate (VA) were purified by distillation under vacuum and were used as the grafting monomer and cross-linking agent, respectively. For direct plasma grafting, a 5 wt % MA aqueous solution was used. For the two-step plasma grafting, a 5 wt % MA/VA (90/10 wt %) aqueous solution with 5 wt % sodium dodecylbenzenesulfonate (SDS) was used in the first step. SDS was added to dissolve the hydrophobic VA in water. In the second step, a 5 wt % MA aqueous solution was used. The monomer solutions were degassed by repeated freezing and thawing under vacuum. Plasma Treatment and Graft Polymerization. The grafting procedure was basically the same as that with the organic substrate reported previously.1 A SPG substrate was placed in a glass tube and was treated by RF-Plasma (power 10 W, pressure 10 Pa) under an argon atmosphere for 1 min. Then, the plasma-treated substrate was contacted with the monomer aqueous solution under an argon atmosphere at 10 Pa. The purpose of the inert atmosphere was to avoid oxygen in air from entering the reaction tube. Graft polymerization was carried out in a shaking bath at 30 °C. The grafted membranes were rinsed in toluene overnight to remove the homopolymer and the nonreacted monomer and were oven-dried at 40 °C. The amount of grafting was calculated as the weight of grafted polymer per unit area of the outer surface of the substrate. In the case of the two-step-prepared membranes, we plugged both edges of the substrate with glass plugs to avoid grafting at the inner side. From now on, the MA-grafted membranes with SPG or HDPE substrate are referred to as SPG-g-MA and HDPE-g-MA, respectively. The membrane with the two-

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Figure 3. Relationship between the grafting time and the amount of grafting (SPG-g-MA).

Figure 2. (A) Pervaporation apparatus for organic/inorganic composite membranes: (a) feed solution (constant temperature), (b) membrane, (c) magnetic stirrer, (d) vacuum gauge, (e) stopcock, (f) cold trap, (g) leak to atmosphere, (h) vacuum pump. (B) Vapor permeation apparatus for organic/inorganic composite membranes: (a) feed solution, (b) membrane module, (c) circulation pump, (d) vacuum gauge, (e) stopcock, (f) cold trap, (g) leak to atmosphere, (h) vacuum pump, (i) condenser, (j) oven, (k) thermostat.

step grafting is referred to as SPG-g-MA/VA (amount of grafting [mg‚cm-2])-MA (amount of grafting [mg‚cm-2]). Morphological Analysis. The morphological details of the cross section of the membranes were observed by an optical microscope (Nikon, OPTIPHOT-2). The images of reflectance were observed. The composition of the cross section of the membrane was examined by Micro FT-IR (Nicolet, MAGNA550 with Nic-Plan). The aperture size was 10 × 50 [µm2], and the measurement region was scanned in a 10 µm step. The dispersion-corrected spectra of reflectance were obtained. Pervaporation and Vapor Permeation. Pervaporation and vapor permeation of chloroform/n-hexane were carried out (feed composition 72/28 wt %). The calculated evaporative separation factor was about 1.2 (the value remained almost the same in the temperature range of 25-50 °C). The pervaporation apparatus and the vapor permeation apparatus are shown in parts A and B of Figure 2, respectively. In pervaporation (Figure 2A), both edges of the membrane were connected to stainless steel tubes with a CAJON Ultra-Torr connector. The effective length of the membrane was about 7 cm. The total volume of the feed liquid was about 2 L. The outer surface of the membrane was contacted with a feed solution, and the inside was evacuated. In vapor permeation (Figure 2B), a feed solution was pumped into the thermostat by a magnetic rotary pump. The vaporized feed from the thermostat was introduced into the membrane module kept at the permeation temperature. Because the feed tank of the vapor permeation

apparatus was not sealed completely, the feed pressure of vapor was about 1 atm. The effective length of the measured membrane was 6.0 cm. The outer surface of the membrane was contacted with the vaporized feed solution, and the inside was evacuated. In both cases, the permeate was collected in vacuum trap condensers cooled by liquid nitrogen. The permeation rate and composition were determined by the permeate weight and gas chromatography, respectively. The permeate side pressure was maintained between 0.5 and 0.9 Torr. The separation factor was calculated with the following equation:

R ) y(100 - x)/x(100 - y) where x is the concentration of chloroform in the feed mixture [wt %] and y is the concentration of chloroform in the permeate mixture [wt %]. Results and Discussion Membrane Preparation and Characterization of the Grafted Membrane. 1. Direct Plasma Grafting. The relationship between the grafting time and the amount of grafting for the SPG-g-MA membrane is shown in Figure 3, together with the data of HDPE-gMA. (In the case of HDPE-g-MA, we used the HDPE substrate of thickness 10 µm, porosity value 0.52, and pore diameter 20 nm. A 3.0 vol % MA aqueous solution was used as the grafting monomer solution.1) Without plasma treatment, no weight increase was detected even after 5 h of graft polymerization. So, weight increase should be caused by plasma-graft polymerization. The amount of grafting increased with time. This means that we can control the grafting amount with the grafting time. A comparison of the grafting rate with the HDPEg-MA case, as in Figure 3, showed a lower grafting rate with the SPG substrate than with the HDPE substrate. The rate of grafting was low for the SPG substrate even after considering the differences in the thickness of the grafted layer and the monomer concentration. This difference in the grafting rate might be caused by a radical density difference formed on the pore surface by plasma treatment. Figure 4 shows optical micrographs of the cross section of the substrate (a) and the grafted membrane having 5.1 mg‚cm-2 grafting (b). As shown in Figure 4a, the cross section of the substrate was observed as white colored. For the grafted membrane, a black layer of thickness 50-60 µm was observed at both the outer and inner surface regions.

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Figure 4. Optical micrographs of the cross section of the SPG substrate and the SPG-g-MA membrane: (a) SPG substrate; (b) SPG-g-MA, 5.1 mg‚cm-2.

The composition of the black layer was analyzed by micro-FT-IR. Figure 5 shows micro-FT-IR spectra over

the cross section of the 6.2 mg‚cm-2 grafted membrane from the outer surface (a) and the inner surface (b). Peaks at 1740 cm-1 and 1070 cm-1 are characteristic peaks of poly(MA) and SPG, respectively. Both peaks of poly(MA) and the SPG substrate exist within 50-70 µm thickness; the peak of poly(MA) was not detected in any other part. The results imply that composite layers made of grafted poly(MA) and glass were formed at the outer and inner surface regions of the substrate, and the thickness was about 50-70 µm. This indicates that graft polymerization took place in the substrate pores, and the black layer observed by an optical microscope corresponds to the grafted polymer of poly(MA) formed in the pores of the SPG substrate. The average graft density in the pores was about 1 g‚cm-3 after about 3 h of reaction. Because the density of poly(MA) is only 1.2 g‚cm-3, the graft density in the pores should be high enough to act as a membrane material. In other words, grafted polymer can be formed in the pores of the SPG substrate to high grafting density values by a plasmagraft polymerization technique, and the filling-type organic/inorganic composite membrane can be successfully tailored by this technique. 2. Two-Step Plasma Grafting. At the first step, we prepared the substrate with a thin layer of cross-linked polymer on its pore surface, and the grafting amount was lower than 1 mg‚cm-2. At the second step, we fixed the grafting time as 1 h. Typical optical micrographs and micro-FT-IR spectra of the cross section of SPG-g-

Figure 5. Micro-FT-IR spectra (reflectance) over the cross section of the SPG-g-MA membrane (6.2 mg‚cm-2; aperture size 10 µm × 50 µm, stage step size 10 µm): (a) cross section near the outer surface; (b) cross section near the inner surface.

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Figure 6. Optical micrographs of the cross section of the SPGg-MA/VA-MA membrane: (a) SPG-g-MA/VA (0.046)-MA (1.9); (b) SPG-g-MA/VA (0.73)-MA (1.6).

Figure 7. Micro-FT-IR spectra (reflectance) over the cross section of the SPG-g-MA/VA-MA membrane near the outer surface (aperture size 10 µm × 50 µm, stage step size 10 µm): (a) SPGg-MA/VA (0.046)-MA (1.9); (b) SPG-g-MA/VA (0.73)-MA (1.6).

MA/VA-MA membranes are shown in Figures 6 and 7, respectively. Observation with an optical microscope showed that the cross section of the substrate after the first step had no black layer. Further micro-FT-IR

analyses revealed that the region near the outer surface had the grafted polymer with a low graft density. Black layers in optical micrographs were observed after the second step. This implies that the second-step graft polymerization occurred in the pores of the substrate. In the case of the SPG-g-MA/VA (0.046)-MA (1.9) membrane, two layers of white and black layers were observed by an optical microscope, as shown in Figure 6a. Micro-FT-IR spectra of the cross section of the SPGg-MA/VA (0.046)-MA (1.9) membrane are shown Figure 7a. Analysis of the micro-FT-IR results showed that the grafting density of the grafted polymer is low in the white layer and the grafting density of the grafted polymer is high in the black layer. The thickness of the black layer has not changed significantly by rinse with toluene. On the other hand, in the case of the SPG-g-MA/VA (0.73)-MA (1.6) membrane, only a black layer was formed at the outer surface, as shown in Figure 6b. Micro-FT-IR spectra of the cross section of the SPG-gMA/VA (0.73)-MA (1.6) membrane are shown in Figure 7b. It was confirmed that the grafted layer was formed at the outer surface. In most cases, the grafted layer was formed at the outer surface and the thickness was about 25-30 µm. The differences in the formation of the grafted layer should be related to the amount of the cross-linked polymer layer at the first step. In general, during plasma treatment, etching and activation of the substrate pore surface take place at the same time. We analyzed the outer surface of the MA/VA-grafted SPG substrate before and after plasma treatment with microFT-IR and found that the peak at 1740 cm-1, designating poly(MA), got smaller after plasma treatment. When the amount of the cross-linked polymer layer was low, plasma treatment at the second step etched and removed the cross-linked polymer layer around the outer surface. Because the energy of the plasma was weakened at 20-50 µm depth, only activation of the crosslinked polymer layer occurred inside the substrate. Therefore, grafted layer was not formed at the outer surface, and a two-layer structure was obtained. When the amount of the cross-linked polymer layer was high enough, plasma at the second step did not completely etch the cross-linked polymer layer, and the radicals were formed on the remaining cross-linked polymer layer around the outer surface. Therefore, a grafted layer was also formed around the outer surface at 0-30 µm depth. The amount of the cross-linked polymer should be high enough to remain by plasma treatment. The required amount of cross-linked polymer will be low if the energy of the plasma treatment is controlled low. So, we should optimize conditions of plasma treatment at the second step. It is interesting that the thickness of the grafted layer was 25-30 µm, about half of that of the SPG-g-MA membrane. Several reasons can be considered to explain the thinner structure formed by the two-step reaction. One possible reason is the effect of the reduced pore size by the existence of the cross-linked polymer, and another reason is the difference of the surface material of the substrate that may affect the surface radical density. A thinner grafted layer is preferable for organicliquid separation. With the two-step plasma grafting, the average graft density in the pores was over 1 g‚cm-3 with only 1 h of reaction. This result indicated that the grafting rate

Ind. Eng. Chem. Res., Vol. 39, No. 9, 2000 3289 Table 1. Separation Performance of the SPG-g-MA and HDPE-g-MA Membranes in Pervaporation of Chloroform/ n-Hexane (72/28 wt %) membrane (amount of grafting [mg‚cm-2]) SPG-g-MA (2.5) HDPE-g-MA (2.3)a a

temp [°C]

permeation rate [kg‚m-2‚h-1]

separation factor

25 50 25

5.3 10.1 5.3

4.3 2.7 10.6

Reference 2.

increased by the existence of the MA/VA layer on the pore surface. Pervaporation and Vapor Permeation. 1. Membrane Prepared by the Direct Plasma-Grafting Procedure. Membranes with more than a 5 mg‚cm-2 grafted layer showed no permeation of n-hexane (single component), chloroform (single component), or a chloroform/n-hexane (72/28 wt %) mixture, unlike membranes with the polymeric substrate. The polymeric substrate has an elastic property, and the filling-type membrane with the polymeric substrate can swell even though the grafted polymer completely fills the pores. However, the inorganic substrate is rigid, and solvent hardly penetrates into the grafted polymer when the grafted polymer completely fills the rigid inorganic pores. For inorganic substrate cases, it is important to control the grafted polymer density in the pores to prepare solvent-permeable membrane. The grafting density can be controlled by the grafting time, as shown in Figure 3. A 2.5 mg‚cm-2 grafted membrane showed chloroform selectivity from a chloroform/n-hexane (72/28 wt %) mixture. The results are shown in Table 1 together with the data of the HDPE-g-MA membrane.2 The comparison of the SPG-g-MA and HDPE-g-MA membranes showed that selectivity obtained with the SPG-g-MA membrane was lower than that of the HDPE-g-MA membrane, while the permeation rate was almost the same. The low selectivity of the SPG-g-MA membrane might be due to pinholes. It should be noted that, even with the presence of such selectivity-deteriorating pinholes, the permeation rate through the thick SPG-g-MA membrane is only comparable to the thinner HDPE-gMA membranes. Though we made membranes by direct plasma grafting with other SPG substrates having different pore sizes and examined pervaporation performance, pervaporation performances were not commendably superior to the data shown in Table 1. 2. Membrane Prepared by the Two-Step PlasmaGrafting Procedure. In the case of SPG-g-MA/VA-MA membranes, the permeation rate was insignificantly low when the total amount of grafting was higher than about 2 mg‚cm-2. The grafting density must be controlled at the second step. The pervaporation data obtained for some SPG-g-MA/VA-MA membranes are shown in Table 2. The pervaporation performance of the SPG-g-MA/VAMA membrane was superior to that of the SPG-g-MA membrane. A high separation factor was obtained by more homogeneous grafting formation in the substrate. With the second-step plasma grafting, the grafting rate became higher than that with direct plasma grafting. This indicated the possibility that the radical density on the pore surface increased compared with the original glass surface case. If this high radical density improves the homogeneity of the radical formation on the pore

Table 2. Separation Performance of the SPG-g-MA/ VA-MA Membranes in Pervaporation and Vapor Permeation of Chloroform/n-Hexane (72/28 wt %) permeation membrane (amount temp rate separation of grafting [mg‚cm-2]) [°C] [kg‚m-2‚h-1] factor process SPG-g-MA/VA (0.46)MA (1.1) SPG-g-MA/VA (0.15)MA (1.2) SPG-g-MA/VA (0.59)MA (1.4) SPG-g-MA/VA (0.32)MA (0.45)

25

0.5

16.3

PV

50 50

2.2 12.0

13.7 4.5

PV PV

50

1.1

6.9

PV

150 50 150

0.39 1.3 0.40

7.5 7.9 8.1

VP PV VP

Figure 8. Relationship between the feed temperature and the permeation rate or the separation factor, R, in pervaporation of chloroform/n-hexane (72/28 wt %).

surface, the two-step plasma grafting is an effective method to make membranes without pinholes. Figure 8 shows the pervaporation results of the SPGg-MA/VA (0.46)-MA (1.1) and HDPE-g-MA (2.4) membranes at 25-50 °C. The separation factor of the SPGg-MA/VA (0.46)-MA (1.1) membrane was higher than that of the HDPE-g-MA membrane. As shown, high separation factor and low permeation rate were obtained by using the rigid pore matrix of the inorganic substrate for grafting. In the case of the polymeric substrate, the pervaporation performance of the membrane is decided by the elastic property of the substrate. On the other hand, in the case of the rigid inorganic substrate, the pervaporation performance of the membrane should vary with the grafting density in the substrate pores, and the membrane with the inorganic substrate should show a high separation factor if the grafting density is controlled high enough. With the pervaporation results, it was proved that the inorganic substrate can show a high swelling-suppression effect and that the filling-type organic/inorganic composite membranes are capable of showing high separation factors. Vapor permeation was carried out for some membranes at 150 °C. The results are included in Table 2. The prepared membranes showed permselectivity at 150 °C. This indicates that the membranes are thermally stable at least up to 150 °C. When the results are compared with those at 50 °C, selectivity values hardly changed, although the permeation rate decreased. The reason for the low permeation rate was considered as

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follows: The vapor pressure of chloroform at 150 °C is 9.3 atm. On the other hand, the total pressure in the membrane module was only 1 atm even at 150 °C, because the feed tank of the vapor permeation apparatus was not completely sealed. This probably caused a low solvent activity (about 0.081 at 150 °C and about 0.72 at 50 °C). This decrease in the driving force might influence the permeation rate. Conclusions The filling-type organic/inorganic composite membranes were prepared with a SPG substrate by a plasma-graft polymerization technique for separating organic-liquid mixtures. Two membrane preparation procedures were employed, and the following conclusions were obtained. 1. With direct plasma grafting, pores of the porous glass substrate could be activated directly by plasma treatment and the grafted layer was formed in the pores of the SPG substrate to high graft density. The prepared membranes showed chloroform selectivity in pervaporation of chloroform/n-hexane. 2. With the two-step plasma grafting, the grafted layer could be formed in the pores of the SPG substrate to high graft density. The obtained pervaporation performance was improved compared with the SPG-gMA membrane. The prepared membranes showed a high separation factor. So, it was proved that the inorganic substrate can show a high swelling-suppression effect and that the filling-type organic/inorganic composite membranes are capable of showing high separation factors. The membranes were thermally stable at least up to 150 °C. Acknowledgment A part of this work has been conducted by the support of the Petroleum Energy Center (PEC) subsidized from Ministry of International Trade and Industry. The authors thank Industrial Research Institute of Miyazaki Prefecture for supplying Shirasu porous glass base membranes. The authors also acknowledge helpful advice and discussions with Mr. Takashi Sugawara. Literature Cited (1) Yamaguchi, T.; Nakao, S.; Kimura, S. Plasma-Graft Filling Polymerization: Preparation of a New Type of Pervaporation Membrane for Organic Liquid Mixtures. Macromolecules 1991, 24, 5522. (2) Yamaguchi, T.; Nakao, S.; Kimura, S. Solubility and Pervaporation Properties of the Filling Polymerized Membrane Prepared by Plasma-Graft Polymerization for Pervaporation of Organic-Liquid Mixtures. Ind. Eng. Chem. Res. 1992, 31, 1914. (3) Wang, H.; Lin, X.; Tanaka, K.; Kita, H.; Okamoto, K. Preparation of Plasma-Grafted Polymer Membranes and Their

Morphology and Pervaporation Properties toward Benzene/Cyclohexane Mixtures. J. Polym. Sci., Part A: Polym. Chem. 1998, 36, 2247. (4) Ulbricht, M.; Schwarz, H. Novel High Performance PhotoGraft Composite Membranes for Separation of Organic Liquids by Pervaporation. J. Membr. Sci. 1997, 136, 25. (5) Mika, A. M.; Childs, R. F.; Dickson, J. M.; McCarry, B. E.; Gabnon, D. R. A New Class of Polyelectrolyte-Filled Microfiltration Membranes with Environmentally Controlled Porosity. J. Membr. Sci. 1995, 108, 37. (6) Yamaguchi, T.; Miyazaki, Y.; Nakao, S.; Tsuru, T.; Kimura, S. Membrane Design for Pervaporation or Vapor Permeation Separation Using a Filling-Type Membrane Concept. Ind. Eng. Chem. Res. 1998, 37, 177. (7) Sakohara, S.; Muramoto, F.; Sakata, T.; Asaeda, M. Separation of Acetone/Water Mixture by Thin Acrylamide Gel Membrane Prepared in Pores of Thin Ceramic Membrane. J. Chem. Eng. Jpn. 1990, 23, 40. (8) Liu, C.; Martin, C. R. Composite Membranes from Photochemical Synthesis of Ultrathin Polymer Film. Nature 1991, 352, 50. (9) Liu, C.; Chen, W.-J.; Martin, C. R. Electrochemical Synthesis of Ultrathin-Film Composite Membranes. J. Membr. Sci. 1992, 65, 113. (10) Otake, K.; Tsuji, T.; Konno, M.; Saito, S. Preparation of a New Hydrogel and Porous Glass Composite Membrane. J. Chem. Eng. Jpn. 1988, 21, 443. (11) Castro, R. P.; Cohen, Y.; Monbouquette, H. G. The Permeability Behavior of Poly(vinylpyrrolidone)-Modified Porous Silica Membranes. J. Membr. Sci. 1993, 84, 151. (12) Jou, J.; Yoshida, W.; Cohen, Y. A novel ceramic-supported polymer membrane for pervaporation of dilute volatile organic compounds. J. Membr. Sci. 1999, 162, 269. (13) Cohen, Y.; Yoshida, W.; Jou, J.-D.; Ohya, H.; Bei, N. Ceramic-supported polymer (CSP) membranes for pervaporation separation of organic/aqueous and organic/organic mixtures. Proc. ICOM ‘99 1999, No. 249. (14) Yamaguchi, T.; Tominaga, A.; Nakao, S.; Kimura, S. Chlorinated Organics Removal from Water by Pervaporation with Membranes Made by Plasma-Graft Filling Polymerization. AIChE J. 1996, 42, 892. (15) Osada, Y.; Iriyama, Y.; Ohta, M. Plasma-initiated Graft Polymerization of Water-soluble Vinyl Monomers onto Hydrophobic Films and its Application to Metal Ion Adsorbing Films. Nippon Kagaku Kaishi 1983, No. 6, 831 (Japanese). (16) Nishimiya, K.; Haraguchi, T.; Ide, S.; Hatanaka, C.; Kajiyama, T.; Goto, M. Modification of Solid Surface by PlasmaGraft Polymerization. Kitakyushu Kogyo Koto Senmon Gakko Kenkyu Hokoku 1991, 24, 139 (Japanese). (17) Haraguchi, T.; Nishimiya, K.; Ide, S.; Hatanaka, C.; Isomura, K.; Nakashio, F.; Goto, M.; Kajiyama, T. Application of Hollow Fiber Modified by Plasma-Graft Polymerization to RareEarth Metal Extractor. Kitakyushu Kogyo Koto Senmon Gakko Kenkyu Hokoku 1992, 25, 97 (Japanese). (18) Nakashima, T.; Kuroki, Y. Effects of Composition and Heat Treatment on the Phase Separation of Na2O-B2O3-SiO2-Al2O3CaO Glass Prepared from Volcanic Ashes. Nippon Kagaku Kaishi 1981, 1231 (Japanese).

Received for review June 11, 1999 Revised manuscript received June 12, 2000 Accepted June 13, 2000 IE9904100