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Facilitated diffusion in immobilized liquid membranes: experimental verification of the “jumping” mechanism and percolation threshold in membrane transport
Journal of Membrane Science, 75 (1992) 1-5 Elsevier Science Publishers B.V.. Amsterdam
Facilitated diffusion in immobilized liquid membranes: Experimental verification of the “jumping” mechanism and percolation threshold in membrane transport A.A. Kalachev”, L.M. Kardivarenkob, N.A. Plate and V.V. Bagreevb “A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninski Prospect 29, Moscow B-71 (Russia) b V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin str. 19, Moscow B-333 (Russia) (Received July 26,199l; accepted in revised form May 19,1992)
Abstract Co (II) and Fe (III) transport through a supported liquid membrane consisting of a microporous nitrocellulose film (Synpor) immobilizing a tri-n-octylamine (TOA) as a carrier and n-decane as a liquid membrane matrix, has been investigated. Membrane transport was evaluated by measuring the 6oCoand 5sFe-radioactivity in the strip solution. The conductivity of the extracted compounds through the membrane was also measured. A maximum in the curve of Co (II) flux vs. TOA concentration was found. This maximum in flux was shown to occur at the same (e.g. 1.8 M) TOA concentration as the main maximum in the conductivity. It was shown that this phenomenon can be connected with a changing from the common transport mechanism to so-called “jumping” membrane transport which previously theoretically has been predicted by Cussler et al. [J. Membrane Sci., 43 (1989 ) 1491. Such membrane transport is realized in a relatively narrow interval of the carrier (TOA) concentration and may be more effective than the common facilitated diffusion mechanism. To obtain the described effect one needs to hold such a supported liquid membrane under transfer conditions during a certain period of time, in order for the membrane medium in the “jumping” region to become self-organized and self-fitted for the membrane transport process. Keywords: membrane extraction; supported liquid membranes; tri-n-octylamine;
Introduction One of the most interesting areas in membrane science today is the possibility to realize fast and selective separation by the use of carriers which, being present in the membrane Correspondence to: A.A. Kalachev. Present Address: IMM Institute of Microtechnology GmbH, Ackermannweg 10, P.O. Box 2440, D-6500 Mainz (Germany).
0376-7388/92/$05.00
cobalt
body, can specifically interact with one of the components in the feed mixture [l-3]. The theory developed by Cussler et al. [ 41 predicts that at a certain (relatively high) concentration of carrier in the membrane the common transport mechanism may change to some other form of transport where the ligand (penetrant) moves through the membrane by “jumping” from one carrier molecule to another. The carrier concentration above which such mecha-
0 1992 Elsevier Science Publishers B.V. All rights reserved.
2
nism can be realized, is considered as the percolation threshold [ 41. It is not very easy to verify this prediction with the use of the common solid, e.g. polymeric, membranes, because it is very difficult in such materials to change the concentration of carrier without influencing the morphology and other parameters of the resulting membrane. At higher carrier concentrations a solid membrane has a completely different physical structure than at lower ones. Therefore, earlier attempts described in the literature [ 5-81 are full of uncomparable data and the existence of a percolation threshold is still doubtful [ 41. It is well known, that the polymeric and supported liquid membranes (SLM) have rather different properties. Nevertheless, it can be shown that the SLM systems can operate with a range of carrier concentrations; increasing the carrier concentration results in a sharp flux increase followed by a drop in flux [ 9-12 1. Some authors explane this maximum by the increase of the carrier viscosity. We tried to treat this phenomenon from another point of view. We used the SLM with trin-octylamine in a liquid membrane matrix (ndecane); these compounds are miscible with each other at any composition. The system enables one to prepare membranes having carrier concentration up to 100% and even at this highest carrier content the membrane is still a homogeneous liquid. Experimental Materials All compounds including tri-n-octylamine (TOA) and n-decane (DN ) (analytical purity grade) were supplied by Fluka and used without further purification. The supported liquid membranes used consisted of a microporous nitrocellulose film (Synpor, Czechoslovakia, pore diameter 0.45
A.A. Kalachev et al./J. Membrane Sci. 75 (1992)1-5
pm, thickness ca. 100 pm) impregnated with TOA solution in DN or with pure TOA or pure DN. Transport of both investigated metals (cobalt and iron) in the absence of the carrier TOA could not be observed. Equipment and techniques Membrane transport was evaluated by measuring the “‘Co- or 59Fe-radioactivity in the strip solution. The membrane cell consisted of two polytetrafluoroethylene cylindrical chambers (23 ml). The chambers were separated by the SLM and clamped together (the area of each side of the SLM contacted with solution was 4 cm2 ). Both chambers were stirred by peristaltic pumps at a flow rate of 80 ml/min. Initially one chamber was filled with an aqueous feed of 6M HCl solution without Co(I1) or Fe(II1) salts and the other one with an aqueous NHIOH solution (ca. 1 M, pH=11.5); the whole membrane cell was maintained at 23°C for 30 min in a thermostated bath. Subsequently aqueous stock solution of labelled Co (II) or Fe (III) was added to the feed solution in a final concentration of 10e5M and the initial radioactivity of the feed and strip solution was measured at the zero time point. Activity in strip solution samples (2 ml) was measured at 10 min intervals. After measuring the radioactivity the sample was returned to the stripping chamber. All experiments were performed three times. The spread of obtained values was less than 2%. Conductivity (at frequency 1592 Hz) through the membrane was measured in the same apparatus and under the same conditions. Electrodes were placed in the feed and strip solution at 1 cm distance from both sides of the membrane. The conductance measurements were made for ca. 30 min till constant values were found. The values for each TOA concentration are shown in the Fig. 3.
A.A. Kalachev et al/J. Membrane Sci. 75 (1992)1-5
Results and discussion Figure 1 shows a typical metal ion concentration increase for the strip solution as a function of time. These data lead to the conclusion that the overall transfer process can be divided into three time periods: first (7,) where no detectable amount of metal ions is presented in the strip solution [e.g. until ca. 25 min for Co (II ) ] ; second, a linear region (e.g. 0.5-3 hr ) and third, a period where concentration increases again. The first time interval (r,) presents the ion penetration time through the membrane. It is known [ 131, that Fe (III) is not reextracted from the TOA-phase and therefore not transferred through TOA-SLM; so, appearence of Fe (III) in the stripping solution after 3 hr means that the third part of the curves in Fig. 1 is a result of partial degradation of the membrane medium and of the formation of bulk massive non-selective water channels through the membrane; this is due to the leakage of the liquid carrier and filler from the pores. Taking this into consideration the duration of all subsequent experiments was limited to 1 hr (the middle point of the linear part of the Fig. 1, curve 2). The variation of the flux (J) of Co (II) through the SLM with TOA concentration in DN at various times is shown in Fig. 2. At a
Fig. 1. Recovery % Co (II) and Fe (III) from feed solution against the time.
40-
“5 $ 30. a E
l-20min 2-
40min
3-
6Omin
c e x 7 20.
lo-
0.5
1
1.5 Cont. TOA (rn%,1
2.5 )
Fig. 2. The dependence of the Co (II) flux (J) through the membrane in strip solution on the TOA concentration.
relatively low TOA concentration the flux increases and approaches a certain constant value. This is a well-known feature of SLMs containing a membrane carrier [ 31. The carrier concentration in most of the earlier published studies was limited by relatively low values. In our case further increase of the TOA concentration leads to a secondary increase of the flux (curves 2 and 3 in Fig. 2 ) . Subsequent increasing of the TOA concentration leads to flux decrease. The peak in the flux is accompanied by the maximum in conductivity at a TOA concentration of ca. 1.8 M (Fig. 3). More interesting is the influence of TOA concentration on r, (time needed for metal-ion penetration through the membrane, Fig. 1 ), which is shown in Fig. 4. At low TOA concentration r,, decreased with increasing TOA content and then approached some more or less constant value (ca. 12 min). At ca. 1.7-1.8 M TOA 7, sharply drops to almost zero. Thus all these results show that at some threshold carrier concentration some new and much more effective transport mechanism
A.A. Kalachev et al./J. Membrane Sci. 75 (1992)1-5
Feed solution co. 6M Co (II)
HCI
co (II)
presents
as [CoCl_,]‘-H,+
Pore,
containing
solution
of
in
presents
as [cocI,]“(NH,+),
TOA
DN
TOA
or
TOAH+
0
0.4
0.8
1.2 Cont.
1.6 2 TOA (mol/
2.4 I ) A
Fig. 3. The dependence of the conductivity brane on TOA concentration in DN.
of the memLOW TOA
concentration
0.8 -
8 -? 0.65
High TOA
b? 0.4 -
(ca. 1.8M)
concentration
a-
.
-63
/ 01 Cont.
TOA (n-ml/l
1
Fig. 5. Scheme of the penetration mechanism: (A) common facilitated transport; (B ) “jumping” mechanism.
Fig. 4. The dependence of the time of metal ion penetration through the membrane (T,,) on the TOA concentration.
through membrane is developed. We assume that probably for the first time the previously theoretically predicted [ 41 diffusion mechanism in membrane transport, i.e. “jumping” of the penetrating species from one complexing centre to another through the membrane, is demonstrated. The scheme of such a process is shown in Fig. 5. One may also note that such membrane transport is not found in pure TOA, but is realized in a ca. 1.8 A4 TOA solution. So the system needs some amount of DN. This can be explained by Cussler’s statement [ 41: “It is that of a bucket brigade, in which a solute bucket is passed from one carrier hand to the next”. Obviously, each member of such a bucket
brigade has to have some local mobility otherwise it may hold the bucket but can not pass it on to the next member. A low viscous residual concentration of DN enables the carrier to move (oscillate) and pass a Co(II)-ion to the next carrier molecule. At the highest carrier concentration (100% TOA = 2.3M TOA) the viscosity or steric hindering depress the transport. Initially at low TOA concentration classical facilitated transport takes place. Further increase of the TOA concentration leads to gradual immobilization of TOA molecules in the viscous medium which results in transport hinderance and in shortening of the mean distance between TOA molecules. At a certain threshold TOA concentration the distance between
A.A. Kalachev et al./J. Membrane Sci. 75 (1992)1-5
neighboring TOA molecules becomes short enough to realize the jump of a [CoC1412--anion to the next TOAR+-cation. The resulting process presents a high-effective membrane transport of Co(I1). Taking into account the well-known relationship:
5
known and new combinations liquid filler.
1
1
Conclusions The “jumping” membrane transport, which previously had been theoretically predicted [ 41, was observed for the first time and the approximate percolation threshold distance was determined by using a homogeneous supported liquid membrane system. Such membrane transport is more effective than common facilitated membrane transport and is realized in a relatively narrow interval of carrier concentration. To obtain the effect one needs to hold the SLM under transfer conditions during a certain period of time, so the membrane medium in the “jump” region becomes self-organized and self-fitted for the membrane transport process. Using certain SLMs with sufficiently high concentrations of carrier may result in new highly effective membranes on the basis of
and
References
c=L3N, where C is the molar concentration of molecules, L represents the average distance between molecules and NA is Avogadro’s number, simple calculations reveal that at a concentration of 1.8A4the average threshold distance between the TOA molecules (L) is about 10 A. It is very interesting to note that at short measuring times (up to ca. 20 min) one is unable to observe “jumping” penetration (see Fig. 2 ) . It seems that the system needs some period of time to create a sufficient number of continuous TOA chains from one side of membrane to the other. These chains were formed after ca. 40 min (Fig. 2, curve 2). So under conditions of “jumping” transport the membrane medium should be self-organized in a certain way.
of carrier
2
3
4
5
6
7
8
9
10
11
12
13
P.R. Danesi and L. Reichley-Vinger, A composite supported liquid membrane for ultraclean cobaltnickel separation, J. Membrane Sci., 27 (1986) 339347. M. Harada, N. Shiomi and F. Yamazaki, Separation of metals by liquid membrane with tri-n-octylamine, J. Chem. Eng. Japan, 17 (1984) 567-572. P.R. Danesi, R. Chiarizia and A. Castagnola, Transfer rate and separation of Cd(I1) and Zn(I1) chloride species by trilaurylammonium chloride-triethylbenzene supported liquid membrane, J. Membrane Sci., 14 (1983) 161-173. E.L. Cussler, R. Aris and A. Bhown, On the limits of facilitated diffusion, J. Membrane Sci., 43 (1989) 149164. N. Ogata, K. Sanui and H. Fujimura, Active transport membrane for cloride ion, J. Appl. Polym. Sci., 25 (1980) 1419-1425. M. Yoshikava, H. Ogata, K. Sanui and N. Ogata, Active and selective transport of anions through poly (Npropenoyl-Q-acrinidylamine-co-acrilonitrile),Polym. J., 15 (1983) 609-612. M Yoshikawa, Y. Imashiro, K. Sanui and N. Ogata Active and selective transport of halogen ions through poly( I-vinylimidazole-co-styrene) membranes, J. Membrane Sci., 20 (1984) 189-199. M. Yoshikawa, S. Shudo, K. Sanui and N. Ogata, Active transport of organic acids through poly(4-vinylpyridine-co-acrylonitrile) membranes, J. Membrane Sci., 26 (1986) 51-61. M.A. Chaudry, M.T. Malik and A. Ah, Transport of MO (VI) ions through tri-n-octylamine-xylene based supported liquid membranes, Sep. Sci. Technol., 25 (1990) 263-291. M.A. Chaudry, M.T. Malik and A. Ali, Transport of Co (II) ions through di (2-ethylhexylphosphoric acid) Ccl, supported liquid membranes, Sep. Sci. Technol., 25 (1990)1161-1174. A.A. Elhassadi ad D.D. Do, Effect of carrier and its diluent on the transport of metals across supported liquid membranes (SLM ) . I. Solubility mechanism, Sep. Sci. Technol., 21 (1986) 267-283. A.A. Elhassadi and D.D. Do, Effect of a carrier and its diluent on the transport of metals across supported liquid membranes (SLM). II. Viscosity effect, Sep. Sci. Technol., 21 (1986) 285-297. Y. Marcus and A.S. Kertes, Exchange and Solvent Extraction of Metal Complexes, Wiley-Interscience, London, 1969.
Facilitated diffusion in immobilized liquid membranes: Experimental verification of the “jumping” mechanism and percolation threshold in membrane transport A.A. Kalachev”, L.M. Kardivarenkob, N.A. Plate and V.V. Bagreevb “A. V. Topchiev Institute of Petrochemical Synthesis, Russian Academy of Sciences, Leninski Prospect 29, Moscow B-71 (Russia) b V.I. Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, Kosygin str. 19, Moscow B-333 (Russia) (Received July 26,199l; accepted in revised form May 19,1992)
Abstract Co (II) and Fe (III) transport through a supported liquid membrane consisting of a microporous nitrocellulose film (Synpor) immobilizing a tri-n-octylamine (TOA) as a carrier and n-decane as a liquid membrane matrix, has been investigated. Membrane transport was evaluated by measuring the 6oCoand 5sFe-radioactivity in the strip solution. The conductivity of the extracted compounds through the membrane was also measured. A maximum in the curve of Co (II) flux vs. TOA concentration was found. This maximum in flux was shown to occur at the same (e.g. 1.8 M) TOA concentration as the main maximum in the conductivity. It was shown that this phenomenon can be connected with a changing from the common transport mechanism to so-called “jumping” membrane transport which previously theoretically has been predicted by Cussler et al. [J. Membrane Sci., 43 (1989 ) 1491. Such membrane transport is realized in a relatively narrow interval of the carrier (TOA) concentration and may be more effective than the common facilitated diffusion mechanism. To obtain the described effect one needs to hold such a supported liquid membrane under transfer conditions during a certain period of time, in order for the membrane medium in the “jumping” region to become self-organized and self-fitted for the membrane transport process. Keywords: membrane extraction; supported liquid membranes; tri-n-octylamine;
Introduction One of the most interesting areas in membrane science today is the possibility to realize fast and selective separation by the use of carriers which, being present in the membrane Correspondence to: A.A. Kalachev. Present Address: IMM Institute of Microtechnology GmbH, Ackermannweg 10, P.O. Box 2440, D-6500 Mainz (Germany).
0376-7388/92/$05.00
cobalt
body, can specifically interact with one of the components in the feed mixture [l-3]. The theory developed by Cussler et al. [ 41 predicts that at a certain (relatively high) concentration of carrier in the membrane the common transport mechanism may change to some other form of transport where the ligand (penetrant) moves through the membrane by “jumping” from one carrier molecule to another. The carrier concentration above which such mecha-
0 1992 Elsevier Science Publishers B.V. All rights reserved.
2
nism can be realized, is considered as the percolation threshold [ 41. It is not very easy to verify this prediction with the use of the common solid, e.g. polymeric, membranes, because it is very difficult in such materials to change the concentration of carrier without influencing the morphology and other parameters of the resulting membrane. At higher carrier concentrations a solid membrane has a completely different physical structure than at lower ones. Therefore, earlier attempts described in the literature [ 5-81 are full of uncomparable data and the existence of a percolation threshold is still doubtful [ 41. It is well known, that the polymeric and supported liquid membranes (SLM) have rather different properties. Nevertheless, it can be shown that the SLM systems can operate with a range of carrier concentrations; increasing the carrier concentration results in a sharp flux increase followed by a drop in flux [ 9-12 1. Some authors explane this maximum by the increase of the carrier viscosity. We tried to treat this phenomenon from another point of view. We used the SLM with trin-octylamine in a liquid membrane matrix (ndecane); these compounds are miscible with each other at any composition. The system enables one to prepare membranes having carrier concentration up to 100% and even at this highest carrier content the membrane is still a homogeneous liquid. Experimental Materials All compounds including tri-n-octylamine (TOA) and n-decane (DN ) (analytical purity grade) were supplied by Fluka and used without further purification. The supported liquid membranes used consisted of a microporous nitrocellulose film (Synpor, Czechoslovakia, pore diameter 0.45
A.A. Kalachev et al./J. Membrane Sci. 75 (1992)1-5
pm, thickness ca. 100 pm) impregnated with TOA solution in DN or with pure TOA or pure DN. Transport of both investigated metals (cobalt and iron) in the absence of the carrier TOA could not be observed. Equipment and techniques Membrane transport was evaluated by measuring the “‘Co- or 59Fe-radioactivity in the strip solution. The membrane cell consisted of two polytetrafluoroethylene cylindrical chambers (23 ml). The chambers were separated by the SLM and clamped together (the area of each side of the SLM contacted with solution was 4 cm2 ). Both chambers were stirred by peristaltic pumps at a flow rate of 80 ml/min. Initially one chamber was filled with an aqueous feed of 6M HCl solution without Co(I1) or Fe(II1) salts and the other one with an aqueous NHIOH solution (ca. 1 M, pH=11.5); the whole membrane cell was maintained at 23°C for 30 min in a thermostated bath. Subsequently aqueous stock solution of labelled Co (II) or Fe (III) was added to the feed solution in a final concentration of 10e5M and the initial radioactivity of the feed and strip solution was measured at the zero time point. Activity in strip solution samples (2 ml) was measured at 10 min intervals. After measuring the radioactivity the sample was returned to the stripping chamber. All experiments were performed three times. The spread of obtained values was less than 2%. Conductivity (at frequency 1592 Hz) through the membrane was measured in the same apparatus and under the same conditions. Electrodes were placed in the feed and strip solution at 1 cm distance from both sides of the membrane. The conductance measurements were made for ca. 30 min till constant values were found. The values for each TOA concentration are shown in the Fig. 3.
A.A. Kalachev et al/J. Membrane Sci. 75 (1992)1-5
Results and discussion Figure 1 shows a typical metal ion concentration increase for the strip solution as a function of time. These data lead to the conclusion that the overall transfer process can be divided into three time periods: first (7,) where no detectable amount of metal ions is presented in the strip solution [e.g. until ca. 25 min for Co (II ) ] ; second, a linear region (e.g. 0.5-3 hr ) and third, a period where concentration increases again. The first time interval (r,) presents the ion penetration time through the membrane. It is known [ 131, that Fe (III) is not reextracted from the TOA-phase and therefore not transferred through TOA-SLM; so, appearence of Fe (III) in the stripping solution after 3 hr means that the third part of the curves in Fig. 1 is a result of partial degradation of the membrane medium and of the formation of bulk massive non-selective water channels through the membrane; this is due to the leakage of the liquid carrier and filler from the pores. Taking this into consideration the duration of all subsequent experiments was limited to 1 hr (the middle point of the linear part of the Fig. 1, curve 2). The variation of the flux (J) of Co (II) through the SLM with TOA concentration in DN at various times is shown in Fig. 2. At a
Fig. 1. Recovery % Co (II) and Fe (III) from feed solution against the time.
40-
“5 $ 30. a E
l-20min 2-
40min
3-
6Omin
c e x 7 20.
lo-
0.5
1
1.5 Cont. TOA (rn%,1
2.5 )
Fig. 2. The dependence of the Co (II) flux (J) through the membrane in strip solution on the TOA concentration.
relatively low TOA concentration the flux increases and approaches a certain constant value. This is a well-known feature of SLMs containing a membrane carrier [ 31. The carrier concentration in most of the earlier published studies was limited by relatively low values. In our case further increase of the TOA concentration leads to a secondary increase of the flux (curves 2 and 3 in Fig. 2 ) . Subsequent increasing of the TOA concentration leads to flux decrease. The peak in the flux is accompanied by the maximum in conductivity at a TOA concentration of ca. 1.8 M (Fig. 3). More interesting is the influence of TOA concentration on r, (time needed for metal-ion penetration through the membrane, Fig. 1 ), which is shown in Fig. 4. At low TOA concentration r,, decreased with increasing TOA content and then approached some more or less constant value (ca. 12 min). At ca. 1.7-1.8 M TOA 7, sharply drops to almost zero. Thus all these results show that at some threshold carrier concentration some new and much more effective transport mechanism
A.A. Kalachev et al./J. Membrane Sci. 75 (1992)1-5
Feed solution co. 6M Co (II)
HCI
co (II)
presents
as [CoCl_,]‘-H,+
Pore,
containing
solution
of
in
presents
as [cocI,]“(NH,+),
TOA
DN
TOA
or
TOAH+
0
0.4
0.8
1.2 Cont.
1.6 2 TOA (mol/
2.4 I ) A
Fig. 3. The dependence of the conductivity brane on TOA concentration in DN.
of the memLOW TOA
concentration
0.8 -
8 -? 0.65
High TOA
b? 0.4 -
(ca. 1.8M)
concentration
a-
.
-63
/ 01 Cont.
TOA (n-ml/l
1
Fig. 5. Scheme of the penetration mechanism: (A) common facilitated transport; (B ) “jumping” mechanism.
Fig. 4. The dependence of the time of metal ion penetration through the membrane (T,,) on the TOA concentration.
through membrane is developed. We assume that probably for the first time the previously theoretically predicted [ 41 diffusion mechanism in membrane transport, i.e. “jumping” of the penetrating species from one complexing centre to another through the membrane, is demonstrated. The scheme of such a process is shown in Fig. 5. One may also note that such membrane transport is not found in pure TOA, but is realized in a ca. 1.8 A4 TOA solution. So the system needs some amount of DN. This can be explained by Cussler’s statement [ 41: “It is that of a bucket brigade, in which a solute bucket is passed from one carrier hand to the next”. Obviously, each member of such a bucket
brigade has to have some local mobility otherwise it may hold the bucket but can not pass it on to the next member. A low viscous residual concentration of DN enables the carrier to move (oscillate) and pass a Co(II)-ion to the next carrier molecule. At the highest carrier concentration (100% TOA = 2.3M TOA) the viscosity or steric hindering depress the transport. Initially at low TOA concentration classical facilitated transport takes place. Further increase of the TOA concentration leads to gradual immobilization of TOA molecules in the viscous medium which results in transport hinderance and in shortening of the mean distance between TOA molecules. At a certain threshold TOA concentration the distance between
A.A. Kalachev et al./J. Membrane Sci. 75 (1992)1-5
neighboring TOA molecules becomes short enough to realize the jump of a [CoC1412--anion to the next TOAR+-cation. The resulting process presents a high-effective membrane transport of Co(I1). Taking into account the well-known relationship:
5
known and new combinations liquid filler.
1
1
Conclusions The “jumping” membrane transport, which previously had been theoretically predicted [ 41, was observed for the first time and the approximate percolation threshold distance was determined by using a homogeneous supported liquid membrane system. Such membrane transport is more effective than common facilitated membrane transport and is realized in a relatively narrow interval of carrier concentration. To obtain the effect one needs to hold the SLM under transfer conditions during a certain period of time, so the membrane medium in the “jump” region becomes self-organized and self-fitted for the membrane transport process. Using certain SLMs with sufficiently high concentrations of carrier may result in new highly effective membranes on the basis of
and
References
c=L3N, where C is the molar concentration of molecules, L represents the average distance between molecules and NA is Avogadro’s number, simple calculations reveal that at a concentration of 1.8A4the average threshold distance between the TOA molecules (L) is about 10 A. It is very interesting to note that at short measuring times (up to ca. 20 min) one is unable to observe “jumping” penetration (see Fig. 2 ) . It seems that the system needs some period of time to create a sufficient number of continuous TOA chains from one side of membrane to the other. These chains were formed after ca. 40 min (Fig. 2, curve 2). So under conditions of “jumping” transport the membrane medium should be self-organized in a certain way.
of carrier
2
3
4
5
6
7
8
9
10
11
12
13
P.R. Danesi and L. Reichley-Vinger, A composite supported liquid membrane for ultraclean cobaltnickel separation, J. Membrane Sci., 27 (1986) 339347. M. Harada, N. Shiomi and F. Yamazaki, Separation of metals by liquid membrane with tri-n-octylamine, J. Chem. Eng. Japan, 17 (1984) 567-572. P.R. Danesi, R. Chiarizia and A. Castagnola, Transfer rate and separation of Cd(I1) and Zn(I1) chloride species by trilaurylammonium chloride-triethylbenzene supported liquid membrane, J. Membrane Sci., 14 (1983) 161-173. E.L. Cussler, R. Aris and A. Bhown, On the limits of facilitated diffusion, J. Membrane Sci., 43 (1989) 149164. N. Ogata, K. Sanui and H. Fujimura, Active transport membrane for cloride ion, J. Appl. Polym. Sci., 25 (1980) 1419-1425. M. Yoshikava, H. Ogata, K. Sanui and N. Ogata, Active and selective transport of anions through poly (Npropenoyl-Q-acrinidylamine-co-acrilonitrile),Polym. J., 15 (1983) 609-612. M Yoshikawa, Y. Imashiro, K. Sanui and N. Ogata Active and selective transport of halogen ions through poly( I-vinylimidazole-co-styrene) membranes, J. Membrane Sci., 20 (1984) 189-199. M. Yoshikawa, S. Shudo, K. Sanui and N. Ogata, Active transport of organic acids through poly(4-vinylpyridine-co-acrylonitrile) membranes, J. Membrane Sci., 26 (1986) 51-61. M.A. Chaudry, M.T. Malik and A. Ah, Transport of MO (VI) ions through tri-n-octylamine-xylene based supported liquid membranes, Sep. Sci. Technol., 25 (1990) 263-291. M.A. Chaudry, M.T. Malik and A. Ali, Transport of Co (II) ions through di (2-ethylhexylphosphoric acid) Ccl, supported liquid membranes, Sep. Sci. Technol., 25 (1990)1161-1174. A.A. Elhassadi ad D.D. Do, Effect of carrier and its diluent on the transport of metals across supported liquid membranes (SLM ) . I. Solubility mechanism, Sep. Sci. Technol., 21 (1986) 267-283. A.A. Elhassadi and D.D. Do, Effect of a carrier and its diluent on the transport of metals across supported liquid membranes (SLM). II. Viscosity effect, Sep. Sci. Technol., 21 (1986) 285-297. Y. Marcus and A.S. Kertes, Exchange and Solvent Extraction of Metal Complexes, Wiley-Interscience, London, 1969.