Polymeric pseudo-liquid membranes from poly(octadecyl methacrylate)

Polymeric pseudo-liquid membranes from poly(octadecyl methacrylate)

Journal of Membrane Science 445 (2013) 8–14 Contents lists available at SciVerse ScienceDirect Journal of Membrane Science journal homepage: www.els...

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Journal of Membrane Science 445 (2013) 8–14

Contents lists available at SciVerse ScienceDirect

Journal of Membrane Science journal homepage: www.elsevier.com/locate/memsci

Polymeric pseudo-liquid membranes from poly(octadecyl methacrylate) Hiroki Tsujimoto, Masakazu Yoshikawa n Department of Biomolecular Engineering, Kyoto Institute of Technology, Matsugasaki, Kyoto 606–8585, Japan

art ic l e i nf o

a b s t r a c t

Article history: Received 26 March 2013 Received in revised form 9 May 2013 Accepted 21 May 2013 Available online 25 May 2013

The novel liquid membrane system, which is named polymeric pseudo-liquid membrane, was constructed from poly(octadecyl methacrylate) (PC18MA), which showed a rubbery state under operating conditions, as a membrane matrix, and dibenzo-18-crown-6 (DB18C6) for the transport of KCl or O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (AAMC) for that of racemic mixture of phenylglycine (Phegly) as a carrier. The results of KCl transport revealed that KCl transport was attained by carrier-diffusion mechanism even though membrane matrix was composed of polymeric material. The polymeric pseudo-liquid membrane containing chiral carrier AAMC showed optical resolution ability, in other words, the membrane selectively transported L-Phegly and its permselectivity toward L-Phegly reached 1.48 at the operating temperature of 40 1C. Chiral separation ability was greatly dependent on the operating temperature and a wide range of permselectivity from L-isomer to D-isomer permselectivity was attained by adjusting the operating temperature. The present study revealed that the polymeric pseudo-liquid membrane is a promising membrane system in membrane separation. & 2013 Elsevier B.V. All rights reserved.

Keywords: Chiral separation Crown ether Liquid membrane Polymeric pseudo-liquid membrane Poly(octadecyl methacrylate)

1. Introduction Membrane separation is regarded as an environmentally-friendly separation technique, and is ecologically and economically competitive to other separation methods [1–3]. Membranes are divided into two types of category based on their membrane morphologies, such as liquid and solid (polymeric) membranes. In the case of former membrane, carrier or carrier in it works as an important role to express permselectivity. On the other hand, in the latter case, membrane performance of permselectivity is bestowed on a given membrane by the introduction of molecules or functional moieties expressing molecular recognition ability as a fixed carrier. Comparing with the preparation of polymeric membranes with a fixed carrier, the construction of liquid membrane is much easier. A liquid membrane is easily obtained by the dissolution of carrier into solvent, membrane matrix. As described above, liquid membrane can be obtained easily without knowledge and experience of organic synthesis. However, liquid membrane has drawbacks in long-term stability, such as the evaporation of the membrane solution and “wash-out” of the carrier and/or carrier/target molecule complex during operation [4–9]. Overcoming the drawbacks of liquid membrane mentioned above will lead the liquid membrane to a promising and a mighty method to segregate a target substrate from a mixture

n

Corresponding author. Tel.: +81 75 724 7816; fax: +81 75 724 7800. E-mail address: [email protected] (M. Yoshikawa).

0376-7388/$ - see front matter & 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.memsci.2013.05.039

containing compounds with similar or same molecular dimensions and showing similar or same chemical and/or physical properties. There are various approaches that can be found to obtain durable liquid membranes; (1) polymer liquid crystal composite membranes [10,11], (2) polymer inclusion membranes [12–20], (3) organogel membranes [21,22], (4) stabilization of top layer of supported liquid membranes by interfacial polymerization [23– 25], (5) room temperature ionic liquids [26,27], and (6) polymeric pseudo-liquid membranes [28–33]. “Polymeric pseudo-liquid membrane” is defined as a liquid membrane composed of polymeric materials with a rubbery state and carrier for a given target substrate. Even though polymeric pseudo-liquid membrane consisted of rubbery polymer, which was a flowable liquid, as a membrane matrix, diffusivities of carrier and carrier/target molecule complex in it should be lower than those in an usual liquid membrane, which consisted of organic liquid, such as chloroform etc., and carrier. Transport mechanism for polymeric pseudo-liquid membrane was proved to be a carrier-diffusion mechanism by adopting poly(2-ethylhexyl acrylate) (P2EHA), with glass transition temperature of around –60.5 1C, as a membrane matrix [32]. So far, poly(2-ethylhexyl methacrylate) (P2EHMA) with glass transition temperature (Tg) of −14.3 1C [31], poly(2-ethylhexyl acrylate) (P2EHA) with Tg of –60.5 1C [32], and poly(dodecyl methacrylate) (PC12MA) with Tg of –66.3 1C [33] were adopted as membrane matrices for polymeric pseudo-liquid membrane. Normalized fluxes of K+ through polymeric pseudo-liquid membranes with number average molecular weight of around 2.0  104,

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of which unit being (mol cm cm−2 h−1)/{(mol cm−3)(mol cm−3)2}, were determined to be 5.88  103 for P2EHA [32] and 5.79  104 for PC12MA [33], respectively. From this, it can be expected that polymeric materials of which glass transition temperature is lower than around –67 1C, is adopted as a membrane matrix for a polymeric pseudo-liquid membrane, such a polymeric pseudoliquid membrane would give a higher flux value than those observed previously. To this end, in the present study, poly (octadecyl methacrylate) (PC18MA), of which glass transition temperature was reported to be −100 1C [34,35] was adopted as a candidate membrane matrix for a polymeric pseudo-liquid membrane. If PC18MA works well as a membrane matrix for polymeric pseudo-liquid membrane, any carriers dissolved into PC18MA will express their intrinsic transport ability. In the present study, to this end, transport of KCl through polymeric pseudo-liquid membrane from PC18MA and dibenzo-18-crown-6 (DB18C6) and chiral separation of racemic mixture of phenylglycine (Phegly) through that from PC18MA and O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (AAMC) were investigated.

2. Experimental 2.1. Materials Octadecyl methacrylate (C18MA) was purchased and purified as reported [36]. 2,2′-Azobis(2-methylpropionitrile) (AIBN) [37] and toluene [38] were purified by conventional methods. Dibenzo-18crown-6 (DB18C6), KCl, O-allyl-N-(anthracenylmethyl)cinchonidinium bromide (AAMC) (Scheme 1), D-phenylglycine (D-Phegly), and LPhenylglycine (L-Phegly) were obtained from commercial sources and used without further purification. Tetrahydrofuran (THF) of HPLC grade was purchased and used without purification. Water purified with an ultrapure water system (Simpli Lab, Millipores S. A., Molsheim, France) was used. 2.2. Preparation of poly(octadecyl methacrylate), PC18MA A 8.007 g (2.364  10−2 mol) of C18MA and 19.4 mg (1.181  10−4 mol) of AIBN, and 46.0 cm3 of toluene were degassed by four freeze-pump-thaw cycles and sealed off below 1.3  10−2 Pa (1.0  10−4 mmHg). The sealed ampoule was shaken in the water bath at a constant temperature of 45 1C for 145 h. The polymerization solution was poured into methanol and then the obtained precipitate was dried at ambient temperature for 2 days. 7.524 g (94.0%) of PC18MA was obtained.

Polystyrene standards (Tosoh co.) were used for calibration and THF as eluent at a flow rate of 1.0 cm3 min−1. Differential scanning calorimetry (DSC) measurement was performed with Shimadzu DSC-60. The heating rate was fixed to be 10 1C min−1 and the sample was purged with nitrogen at a flow rate of 50 cm3 min−1. 2.4. Preparation of polymeric pseudo-liquid membrane Polymeric pseudo-liquid membranes (PPLM's) for KCl transport were prepared as follows: a 100.0 mg of PC18MA and the prescribed amount of DB18C6, of which amount was 2.50 mg, 5.00 mg, 6.25 mg, 7.50 mg and 10.00 mg, were dissolved in 1.0 cm3 of CHCl3. The polymer solution thus prepared was poured into a flat-laboratory dish (48 mm diameter), followed by immersing a PTFE membrane filter (Omnipore Membrane Filter (Millipore Corporation); diameter 47 mm; pore radius, 0.10 μm; porosity 0.80; thickness, 80 μm) into the cast solution. And then the flat-laboratory dish was evacuated in a desiccator so that the cast solution could thoroughly penetrate into pores in the PTFE membrane filter. The solvent was allowed to evaporate at 25 1C for 5 h and then additionally at 60 1C for 24 h. Control membrane was prepared as follows: 100.0 mg of PC18MA was dissolved in 1.0 cm3 of CHCl3. Control membrane for PPLM was constructed from the solution thus prepared as described above. PPLM for chiral separation was prepared as described above. Instead of DB18C6, 5.00 mg of O-allyl-N-(9-anthracenylmethyl-) cinchonidinium bromide (AAMC) was adopted as a carrier for chiral separation of racemic mixture of Phegly. 2.5. KCl transport Transport of KCl through the membrane was studied by using apparatus schematically shown in Fig. 1. The PTFE filter membrane impregnated with membrane component, such as PC18MA and carrier or just PC18MA, was secured tightly with Parafilm between two chambers of a permeation cell. The thickness of the PTFE filter, 80 μm, was adopted as a membrane thickness for the present study. In the present study, the membrane area for PTFE filter membrane was 3.0 cm2; the effective membrane area was determined to be 2.4 cm2. The volume of each chamber was 40.0 cm3. A 1.0  10−4 mol cm−3 of KCl aqueous solution was placed in the left-hand side chamber (L-side) and deionized water in the righthand side chamber (R-side). Transport experiments were carried out at 60 1C (333 K), 50 1C (323 K), and 40 1C (313 K), respectively. Aqueous solutions in both chambers were stirred by magnetic

2.3. Characterization of PC18MA Gel permeation chromatography (GPC) was performed on a JASCO liquid chromatography system composed of a PU-2089 HPLC pump and 860-CO column oven (operated at 35 1C) equipped with JASCO 870-UV and Shodex RI-101 RI detector.

Scheme 1

9

Fig. 1. Schematic representation of the setup for KCl transport experiment.

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stirrers. The revolution rate of magnetic stirrer was kept apparently constant as possible, though that could not be specified in the present study. Concentration of KCl in the permeate side (R-side) was determined by conductometric analysis by using Portable Kohlrausch Brideg TYPE BF-62A (Shimadzu Rika Instruments Co., Ltd.) and CO-1305 oscilloscope (KENWOOD), of which schematic diagram is shown in Fig. 1.

Against the authors' motivation for the present study, this led to the conclusion that the operating temperature of membrane transport had to be above 33.4 1C. Otherwise, membrane transport would be hardly observed.

2.6. Chiral separation of Phegly

Dibenzo-18-crown-6 (DB18C6) was adopted as a metal ion carrier and KCl as the model target substrate so that the results obtained in the present study could be compared with previous results [31–33]. Fig. 3 shows time-transport curves of KCl through five types of polymeric pseudo-liquid membrane composed of PC18MA and DB18C6, and the corresponding control membrane at the experimental temperature of 60 1C. Those for other operating temperatures of 50 1C and 40 1C also gave similar time-transport curves. The flux of steady state for each membrane was determined from the straight line of each time-transport curve. As can be seen, KCl was considerably transported through the control membrane. In other words, considerable amount of KCl was transported through the PC18MA liquid membrane by simple diffusion, which composed of the diffusion of free ion and uncomplexed ion pairs. In the case that transport of uni-univalent salt, such as KCl and so forth, is transported through a given membrane simultaneously by simple diffusion and facilitated transport, the flux of uniunivalent salt can be represented by Eq. (2) [39,40].

Aqueous solution of racemic Phegly was placed in the left-hand side chamber (L-side) and aqueous solution in the right-hand side chamber. Each concentration of racemic Phegly was fixed to be 1.0  10−6 mol cm−3. Transport experiment was carried out as described above at 60 1C (333 K), 50 1C (323 K), and 40 1C (313 K). In addition to the above three experimental conditions, the chiral separation was also carried out at 80 1C (353 K). The pH condition of the source phase (L-side) was kept to be 11 by Na2HPO4/NaOH and that of the receiving phase was maintained at pH of 3 by H3PO4/NaH2PO5. The amounts of D- and L-Phegly transported through the membrane were determined by liquid chromatography (LC) [JASCO PU-2080, equipped with a UV detector (JASCO UV-2075)], using a CHIRALPAK MA(+) column [50  4.6 mm (i.d.)] (Daicel Chemical Ind. Ltd.) and aqueous copper sulfate as an eluent. The permselectivity αL/D is defined as the flux ratio, JL/JD divided by the concentration ratio [L-Phegly]/[D-Phegly] αL=D ¼ ðJ L =J D Þ=ð½L−Phegly=½D−PheglyÞ

ð1Þ

3. Results and discussion 3.1. Characterization of PC18MA The number average molecular weight of PC18MA prepared in the present study was determined to be 1.83  105 and its polydispersity index, Mw/Mn, to be 2.47. Fig. 2 shows DSC thermograph of PC18MA obtained in the present study for membrane matrix. The glass transition temperature (Tg), which was reported to be −100 1C [34,35], could not be observed in the present study, since it was too low to be measured. Contrary to this, the endothermic peak corresponds to the melting point is observed at 33.4 1C. The observed endothermic peak might be due to the melting of side chain of PC18MA, octadecyl moiety.

Fig. 2. DSC thermograph of PC18MA (Heating rate, 10 1C min−1; N2 flow, 50 cm3 min−1).

3.2. Transport of KCl through the PC18MA polymeric pseudo-liquid membrane

J C;obsd ¼ ðDCA k=δÞ½Kþ 2 þ ðDCLA kK½DB18C6=δÞ½Kþ 2

ð2Þ

In Fig. 4, the product of JC,obsd and membrane thickness δ, JC (mol cm cm−2 h−1), which is flux per unit membrane thickness and per unit membrane area, is plotted as a function of carrier concentration. The relationships for the operating temperature of 60 1C, 50 1C, and 40 1C are shown in Fig. 4. At any transport condition, the flux JC gives a straight line, passing through that for each control experiment. The relationship shown in Fig. 4 can be explained by Eq. (2). The relationship in Fig. 4 revealed that the membrane transport was carried out by carrier-diffusion mechanism [39,40] not by fixed-site jumping [15,41,42]. In other words, at the present membrane transport conditions, the membrane

Fig. 3. Time–transport curves of KCl through the PC18MA liquid membranes (Operating temperature, 60 1C (333 K)).

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Fig. 4. Relationship between KCl flux and the DB18C6 concentration through PC18MA liquid membranes.

Fig. 5. Dependence of facilitated KCl and simple diffusion fluxes on KCl feed concentration at the operating temperature of 50 1C (323 K) ([DB18C6] ¼ 1.32  10−4 mol cm−3).

matrix of PC18MA was fluid enough so that carrier and carrier/ substrate complex could diffuse freely within the membrane. As a result, membrane transport of K+ was carried out like usual supported liquid membranes [39,40]. In order to confirm the flux dependence on substrate concentration, which can be derived from Eq. (2), the relationship between K+ flux and the initial concentration of KCl was studied. The K+ flux facilitated by carrier and that of simple diffusion at the operating temperature of 50 1C (323 K) are plotted as a function of initial feed KCl concentration. The relationships are shown in Fig. 5. The plots of logarithm of both K+ fluxes against the logarithm of the initial KCl concentration gave a slope of two. In the present study, transport of K+ was studied at three types of membrane transport temperature, such as 60 1C, 50 1C, and 40 1C. As an example, time-transport curves of K+ with DB18C6 concentration of 6.94  10−5 mol cm−3 (2.5 wt%) at three types of operating temperature are shown in Fig. 6. The slope of timetransport curves increased at a steady state with the raise in the operating temperature. The activation energy of membrane transport would be determined from the fluxes obtained from Fig. 6. As shown in Fig. 7, Arrhenius plot of K+ flux vs. reciprocal of absolute temperature yields an activation energy of membrane transport. From the slope of the straight line, the activation energy of K+ transport was determined to be 39.0 kJ mol−1. In our previous study, poly(2-ethylhexyl methacrylate) (P2EHMA) [31], poly(2-ethylhexyl acrylate) (P2EHA) [32], and poly(dodecyl

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Fig. 6. Dependence of KCl transport through the PC18MA liquid membrane on operating temperature ([DB18C6] ¼6.94  10−5 mol cm−3; [KCl]0 ¼1.00  10−4 mol cm−3).

Fig. 7. Temperature dependence of KCl transport through the PC18MA liquid membrane ([DB18C6] ¼ 6.94  10−5 mol cm−3; [KCl]0 ¼ 1.0  10−4 mol cm−3).

methacrylate) (PC12MA) [33] were investigated as membrane matrices for polymeric pseudo-liquid membranes, of which Tg values were determined to be −14.3 1C [31], −60.5 1C [32], and −66.3 1C [33]. The activation energies of K+ transport for those membranes were determined to be 49.1 kJ mol−1 for P2EHMA, 33.2 kJ mol−1 for P2EHA, and 32.7 kJ mol−1 for PC12MA. The relationship between activation energy of membrane transport and the corresponding glass transition temperature is given in Fig. 8. The previous three types of membrane matrices, such as P2EHMA, P2EHA, and PC12MA, showed tendency that the activation energy of transport is decreased with the fall in the corresponding glass transition temperature, Tg. Contrary to this, the present membrane matrix, PC18MA, gave higher activation energy than those for P2EHA and PC12MA. This is due to the fact that PC18MA consists of a long alkyl moiety of octadecyl group, though the Tg of PC18MA was reported to be −100 1C [34,35]. In Table 1, the flux values obtained in the present study are summarized together with previous results for polymeric pseudoliquid membranes from P2EHMA [31], P2EHA [32], and PC12MA [33], supported liquid membrane [43], and polymer inclusion membrane [14] so that the present results can be compared with those results. The membrane performances for those membranes are given as normalized fluxes, which are fluxes per unit membrane area, per unit membrane thickness, per unit carrier concentration, and per square of unit substrate concentration. From

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Fig. 8. Relationship between activation energy of KCl transport and glass transition temperature of membrane matrix.

Table 1 Comparison of normalized K+ flux values for various membranes. J (normalized flux of K+) (mol cm cm

−2

Flux ratioa

Operating temp/1C

−1

h )

Table 2 Chiral separation of racemic phenylglycine (Phegly).

(mol cm−3)(mol cm−3)2 PC18MA/DB18C6b PC18MA/DB18C6b PC18MA/DB18C6b PC12MA/DB18C6c P2EHA/DB18C6d P2EHMA/DB18C6e CHCl3/DB18C6f PIM/DC18C6g

Fig. 9. Chiral separation of racemix mixture of Phegly through the PC18MA liquid membrane (Operating temperature, 40 1C (313 K); [AAMC] ¼8.26  10−5 mol cm−3; [D-Phegly]0 ¼ [L-Phegly]0 ¼ 1.00  10−6 mol cm−3).

6.89  103 4.98  103 2.80  103 5.79  104 5.88  103 6.20  103 1.67  102 2.37  102

41 30 17 350 35 37 1 1.4

60 50 40 40 40 40 25 25

Operating temp. 1C

JD mol cm cm−2 h−1

JL mol cm cm−2 h−1

αL/D

αD/L

40 50 60 80

9.76  10−11 2.32  10−10 5.80  10−10 2.31  10−9

1.45  10−10 2.97  10−10 6.42  10−10 2.17  10−9

1.48 1.28 1.11 –

– – – 1.06

a Flux ratios are the relative values; the flux value for the supported liquid membrane being set as unity. b Present study; Mn of PC18MA ¼1.83  105, Tg ¼−100 1C. c Cited from Ref. [33]; Mn of PC12MA ¼2.01  104, Tg ¼−66.3 1C. d Cited from Ref. [32]; Mn of 2EHA ¼1,98  104, Tg ¼ −60.5 1C. e Cited from Ref. [31]; Mn of P2EHMA¼ 2.50  103,Tg ¼−14.3 1C. f Cited from Ref. [43]. g Cited from Ref. [14].

the Tg values of membrane matrix for polymeric pseudo-liquid membrane, the normalized flux for the membrane from PC18MA with Tg of −100 1C [34,35] would be expected to show the highest value among those four types of polymeric pseudo-liquid membranes. Against expectation, the normalized flux for PC12MA showed the highest value among polymeric pseudo-liquid membranes. This is also due to the fact that PC18MA is composed of a long alkyl moiety of octadecyl group. As reported previously [32], the normalized flux is greatly dependent on a molecular weight of membrane matrix as well. Polymeric pseudo-liquid membrane from PC18MA, of which molecular weight is lower than that in the present study, would give higher flux values than that in the present study.

Fig. 10. Temperature dependence of Phegly transport through the PC18MA liquid membrane ([AAMC] ¼ 8.26  10-5 mol cm−3; [D-Phegly]0 ¼ [L-Phegly]0 ¼ 1.00  10−6 mol cm−3).

3.3. Chiral separation of racemic Phegly So far, polymeric pseudo-liquid membrane was studied by the membrane transport of metal ions as a model membrane transport system. In the case of liquid membrane, its membrane performance is exclusively dependent on selectivity of the carrier found in it. This led to the expectation that a given membrane matrix of

rubbery polymer has the potential to become a polymeric pseudoliquid membrane showing permselectivity toward any type of substrate. To this end, in the present study, the possibility of the present polymeric pseudo-liquid membrane for chiral separation was investigated. Since optical resolution with membrane is not an urgent problem to be solved like production of pure water, waste

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water treatment, and so forth, but an important one to prepare for forthcoming health problems [44–46]. Cinchona alkaloids were used as resolving agents for chiral binaphthols [47], chiral acids [48], amino acid derivatives [48,49], and oligopeptides [50]. Cinchona alkaloid was also adopted as a carrier for optical resolution [51]. Form this, O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (AAMC) was adopted as a carrier for enantioselective transport and the membrane performance was studied using racemic mixture of phenylglycine (Phegly) as a model racemate. As an example, the time-transport curve of racemic Phegly through PC18MA polymeric pseudo-liquid membrane at 40 1C is shown in Fig. 9. The L-isomer of Phegly was transported through the membrane in preference to the corresponding D-Phegly as reported [51]. The membrane performance of chiral separation ability is summarized in Table 2. As given in Table 2, the permselectivity toward L-Phegly was increased with the fall in the operating temperature. This might be due to the enhancement of intermolecular interaction between Phegly and AAMC, such as Coulombic attraction, hydrogen bonding, and so forth with the fall in the operating temperature. Using results for three different operating temperatures, the activation energy of transport would be determined. Fig. 10 shows the Arrhenius plot of chiral separation. From the obtained straight line in Fig. 10, the activation energy of chiral separation with AAMC/ PC18MA was determined to be 73.0 kJ mol−1 for D-Phegly and 62.5 kJ mol−1 for L-Phegly, respectively. From Fig. 10, the permselectivity toward L-Phegly is anticipated to be raised to be 1.65 at the melting temperature of the membrane matrix of PC18MA, 33.4 1C (306.4 K). Furthermore, chiral separation ability of the present membrane system would be hardly observed at the operating temperature of around 72.3 1C (345.3 K). The mechanism of membrane transport of Phegly through AAMC/PC18MA membrane is still maintained over the operating temperature of 72.3 1C (345.3 K), opposite permselectivity would be attained. This is an interesting subject to study whether any membrane performance, such as permselectivity, can be attained by changing the operating temperature. To this end, the chiarl separation of racemic mixture of Phegly was carried out at the experimental temperature of 80 1C, in addition to those three different operating temperatures. As anticipated from the Arrhenius plot shown in Fig. 10, the D-isomer of Phegly was selectively transported at the operating temperature of 80 1C. The permselectivity toward D-Phegly was determined to be 1.06, which was opposite to that observed at other operating temperatures.

4. Conclusions Novel liquid membrane system, which is named polymeric pseudo-liquid membrane, was constructed from poly(octadecyl methacrylate) (PC18MA), which showed rubbery state under operating conditions, as a membrane matrix, and dibenzo-18crown-6 (DB18C6) for the transport of KCl or O-allyl-N-(9-anthracenylmethyl)cinchonidinium bromide (AAMC) for that of racemic mixture of phenylglycine (Phegly) as a carrier. The results of KCl transport revealed that KCl transport was attained by carrierdiffusion mechanism. The polymeric pseudo-liquid membrane containing chiral carrier showed optical resolution ability, in other words, the membrane selectively transported L-Phegly and its permselectivity toward L-Phegly reached 1.48 at the operating temperature of 40 1C. Chiral separation ability was greatly dependent on the operating temperature and a wide range of permselectivity from L-isomer to D-isomer perm selectivity was attained by adjusting the operating temperature. The present study revealed that polymeric pseudo-liquid membrane is a promising membrane system in membrane separation.

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Nomenclature diffusion coefficient of the free solute [cm2 h−1] dsiffusion coefficient of the complexed solute [cm2 h−1] JC total flux of the diffusing solute, K+, across the membrane per unit membrane thickness (JC ¼δ  JC,obsd)[mol cm cm−2 h−1] JC,obsd observed total flux of the diffusing solute, K+, across the membrane [mol cm−2 h−1] k partition coefficient of the solute between water and the organic membrane [mol−1 cm3] K equilibrium constant for the association [mol−1 cm3] δ membrane thickness [cm] [DB18C6]total concentration of complexed and uncomplexed carrier, DB18C6 in the membrane [mol cm−3] + [K ] concentration of the diffusing solutes. K+, in the source phase [mol cm−3] DCA DCLA

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