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Concentration polarization in polyelectrolyte-enhanced ultrafiltration
Colloids and Surfaces, 49 (1990) 259-267 Elsevier Science Publishers B.V., Amsterdam
259
Concentration Polarization in PolyelectrolyteEnhanced Ultrafiltration JOHN F. SCAMEHORN, SHERRIL D. CHRISTIAN, EDWIN E. TUCKER and BERNADETTELTAN Znstitute for Applied Surfactant Research, University of Oklahoma, Norman, OK 73019 (U.S.A.) (Received 7 June 1989; accepted 8 January 1999)
ABSTRACT Polyelectrolyte-enhanced ultrafiltration (PEUF ) is a new method of removing ions from water. In PEUF, a polyelectrolyte of opposite charge to the target ion is added to solution and the target ion binds to the polymer. The polyelectrolyte is then removed from the water by ultrafiltration. The resulting permeate solutions are quite pure, with measured rejections in excess of 99%. In this work, a solution containing copper was treated using PEUF with poly(styrene sulfonate) as the anionic polyelectrolyte over a wide range of polymer concentrations. As the ret&ate becomes more concentrated in polyelectrolyte, the rejection decreases and the flux decreases. However, even with concentrated retentate solutions, the rejections remain high (96% was the lowest rejection observed here). Fluxes only decline sharply when the concentration in the retentate is quite high. Hence, classical concentration polarization behavior is observed in PEUF, but it is not severe in the operating range of practical importance, indicating the promise of PEUF as an industrial separation process.
INTRODUCTION
Colloid-enhanced .ultrafiltration methods can be used to remove dissolved solutes from water very effectively and economically. Micellar-enhanced ultrafiltration (MEUF) involves the addition of surfactants to water. The surfactants form micelles, which are roughly spherical aggregates containing 50-100 surfactant molecules. The micelles have a hydrophobic interior and the hydrophilic portion of the surfactants forms the surface of the micelle. Dissolved organics in solution will tend to solubilize or dissolve in the micelle. If the surfactant has opposite charge to a multivalent ion in solution, this counterion will bind to the micelles. The solution is then treated in an ultrafiltration unit with membrane pore sizes small enough to reject the micelles. The result is that the micelles with their solubilized organics and bound ions become concentrated in the retentate (the solution not passing through membrane) and the permeate (the solution passing through membrane) can be quite pure. 0166.6622/90/$03.50
0 1990 -
Elsevier Science Publishers B.V.
260
MEUF has been shown to be effective at removing dissolved organics [l-8], multivalent cations or anions [ 3-111, or organics and divalent cations simultaneously [ 121. Polyelectrolyte-enhanced ultrafiltration (PEUF) involves the addition of a soluble polyelectrolyte to the water containing a solute having a charge opposite to that of the polyelectrolyte. The target solute binds to the polyelectrolyte by electrostatic attraction and the solution is treated with ultrafiltration using a membrane having pore sizes small enough to filter the polyelectrolyte from solution. We have studied the removal of the divalent cation, Cu2+, using poly (styrene sulfonate) in a PEUF process at fairly low polyelectrolyte concentrations [ 131. An advantage of PEUF over MEUF is that none of the polyelectrolyte will pass into the permeate for an optimum system, in contrast with MEUF, where some of the surfactant will always be present in monomeric or unaggregated form and pass into the permeate. On the other hand, MEUF can be used to remove both nonionic organics and ions, while PEUF can remove only ions of opposite charge to the polyelectrolyte. From an engineering viewpoint, flow rates through the membrane are important, as well as the rejection of designated species by the membrane. MEUF has been shown to follow traditional concentration polarization behavior with fairly high gel concentrations (ca 0.55 M) [ 591. This means that for practical systems, high water recoveries are attainable in MEUF without entering a regime where low fluxes are observed. The purpose of this work is to investigate the concentration polarization behavior and study rejections of heavy metals in PEUF at relatively high colloid concentrations. The results are compared to those for MEUF to help ascertain which novel technology shows greater promise for heavy metal removal from water. EXPERIMENTAL
Materials Sodium poly (styrene sulfonate) or PSS, having an average molecular weight of approximately 35 000, was obtained from Aldrich Chemical Co., and used without further purification. Analytical reagent grade copper chloride (Mallinckrodt Chemicals) was used without further purification. Water was deionized twice and passed through a carbon adsorption column.
Methods Ultrafiltration was studied using 400 ml stirred cells at 30°C and 414 kPa (60 psi). Spectrum cellulose acetate membranes with molecular weight cutoffs (MWCO)of 1000,5 000 and 10 000 were used. A feed solution of 300 ml
261
was used to initiate a run. The run was terminated when 200 ml had passed through the membrane as permeate. Fluxes were determined during the run by timing and weighing samples of permeate. The rejection of copper or polyelectrolyte was determined by measuring the concentration of copper in the permeate. For each run, this rejection is reported at the point in the run where 100 ml of permeate have passed through (the mid-point ) . The retentate composition at any point in the run was calculated from a material balance and a knowledge of permeate concentrations. Therefore, one rejection and numerous flux data are produced in a run. The copper concentrations were measured using a Varian SpectrAAatomic absorption spectrophotometer. The PSS concentration in the permeate was measured using a Bausch and Lomb Speconic 1001 UV spectrophotometer. P RESULTS AND DISCUSSION
The permeate copper concentration is shown as a function of rententate copper concentration in Fig. 1 and Table 1. Since almost all of the PSS and Cu2+ is rejected in the ultrafiltration, the ratio of Cu”‘/PSS in the retentate remains nearly constant throughout a run (in this case, the molar ratio was l/5). All PSS concentrations given here are based on monomer units, hence, 0.1 A4 refers to 0.1 M of styrene sulfonate units (molecular weight 183) in
j
, 1
“, ,,;,;;~gyy,j 10
RETENTATE COPPER CONCENTRATION (mM)
Fig. 1. Copper concentration in permeate for PEUF.
10'
262 TABLE 1 Rejection of PSS and Cu2+ by PEUF Membrane MWCO
1000 1000 1000 5000 5000 5 000 10 000 10 000 10 000
[PSSIR’ wu)
[cu2+]a’ ww
[PSSIP”
[Cl?+]pa
ww
(mw
15 45 150 15 45 150 15 45 150
3 9 30 3 9 30 3 9 30
0.007 0.0536 0.240 0.0244 0.0740 0.351 0.019 0.0843 0.411
0.0336 0.113 1.088 0.0263 0.100 1.513 0.0354 0.198 1.20
Rejection ( ??I)b PSS
cl?+
99.95 99.88
98.88
99.84
96.37
99.84
99.12 98.88 94.96 98.82 97.80 96.00
99.84 99.77 99.87 99.81 99.73
98.74
“Subscripts R and P refer to retentate and permeate, respectively. bRejection (% ) = 100 (1 - [Permeate] / [Retentate] ).
solution, not 0.1 M of poly (styrene sulfonate) (molecular weight approximately 85 000) in solution. The general observation from the data is that copper is rejected very efficiently by PEUF, rejections reaching as high as 99.12% for the conditions used here. As the PSS and Cu2+ concentrations in the retentate increase, rejection of copper decreases somewhat, a result predicted from a theoretical model [ 131 and also observed for heavy metal removal by MEUF [ 8-111. The results are very similar for the three membranes used, indicating that pore size does not have a significant effect on solute rejection, as long as the colloid is being effectively filtered from the permeate, a conclusion previously reached for MEUF
[51.
The PSS in the permeate ranged from 0.047 to 0.27% of that in the retentate, showing the the colloid is being effectively rejected by all the membranes used here. The PSS in the permeate is believed to be low molecular weight components of the polymer.
Flux Figure 2 presents the flux as a function of the retentate polyelectrolyte concentration. Traditional concentration polarization behavior [ 141 is observed, with the flux declining linearly with the logarithm of retentate concentration, at high enough retentate concentrations. At low retentate concentrations, the flux approaches that of pure water for all three membranes. Figure 3 represents relative flux as a function of retentate polyelectrolyte concentration (relative flux is flux/flux of pure water). The data for the three
263
60
MEMBRANE PORE SIZE x 0 0
5000 1 000 10 000
MWCO MWCO
10
10’ 10 a 10’ RETENTATE POLYELECTROLYTECONCENTRATION (mM)
Fig. 2. Absolute flux for PEUF.
0.2
MEMBRANE PORE SIZE 1 000 5 000
YWCO MWCO
0.0 10 10’ 10’ 10’ RETENTATE POLYELECTROLYTECONCENTRATION (mM)
Fig. 3. Relative flux for PEUF.
membranes coincide on this plot. An extrapolation for these data would result in a gel concentration (where flux equals 0) of approximately 1 M. In practical applications, a region of low relative flux would be avoided, so the important conclusion from Fig. 3 is that the relative flux remains high until high retentate concentrations are achieved. For example, it requires approximately 250 mM
264
polyelectrolyte in the retentate to reduce the relative flux to 0.5. The relative flux versus retentate colloid concentration plots for MEUF do not exhibit the coincidence of the data for different pore size membranes, although all membranes did yield the same gel concentration [ 51. In order to compare flux from PEUF and MEUF directly, Figs 4-6 present relative flux plots for PEUF and MEUF for the same molecular weight cutoff membrane. From Fig. 4, for a 1000 MWCO membrane, the MEUF and PEUF data coincide. The MEUF used a cationic surfactant, cetylpyridinium chloride or CPC as the colloid [5]. From Fig. 5, for a 5 000 MWCO membrane, the relative flux for PEUF is higher than that for MEUF, but the decline in flux in the concentration polarization region at higher concentrations has the same slope for MEUF and PEUF. In this figure, MEUF data with CPC [ 51, as well as sodium dodecyl sulfate or SDS [9], as the colloid or surfactant, are presented. The data using the cationic and anionic surfactant coincide, indicating the relative insensitivity of MEUF flux to micelle charge or size. Finally, Fig. 6 shows that for a 10 000 MWCO membrane, PEUF exhibits substantially greater relative flux values than MEUF (with CPC as the surfactant). No precipitate was observed in any of the systems discussed here. It should be noted that the water soluble polyelectrolyte or surfactant micelles bind a very large fraction of any oppositely charged multivalent ions present in solution. The resulting reduction in the thermodynamic activity of the ion (e.g., Cu2 + ) can prevent precipitation even under conditions where the ion would precipitate in the absence of the colloid. The general conclusion from the flux data is that PEUF does not demon-
1.0
0.6
C0LL0l0 0 SURFACTANT (CPC) q POLYELECTROLYTE 10
RETENTATE
10 ’ COLLOIO
1
@,
10’ CONCENTRATION
10' (mM)
Fig. 4. Fklative flux for 1000 MWCO membranes for PEUF and MEUF.
265
0.0
10'
10'
10 RETENTATE
COLLOIO
CONCENTRATION
10'
(mM j
Fig. 5. Relative flux for 5 000 MWCO membranes for PEUF and MEUF.
I 1.0
;-@% B
I
I-
10000 MWCO MEMBRANE
-
0
0.8 y%O 5
q
0
dO.6
%
0
5
m %I
3 kO.4
0
0
0 0 0
0.2 :O SIJRFACTANT (CPC) :O POLYELECTROLYTE 0.0 10 RETENTATE
10 1 COLLOIO
10' CONCENTRATION
10'
(mM)
Fig. 6. Relative flux for 10 000 MWCO membranes for PEUF and MEUF.
266
strate severe concentration polarization effects until a fairly high concentration of polyelectrolyte is present in the retentate. In fact, flux values are equal to or greater than for MEUF under comparable conditions. This is an unanticipated result, since one would expect that the intertwining of polymer chains might cause a polyelectrolyte solution to have a higher viscosity and poorer fluxes than an equivalent micellar solution. Micelle-micelle interactions appear to cause extended structures in solution in MEUF which are at least as limiting to water diffusion to the membrane as are water soluble polymers. However, from a practical view, the fact that high concentrations are necessary before concentration polarization becomes substantial (as well as the excellent rejection of multivalent metals) should make both of these technologies quite viable as industrial separations. ACKNOWLEDGEMENTS
Financial support for this work was provided by the Department of Energy Office of Basic Energy Sciences Grant No DE-FG0564ER13678, Department of Energy Grant No DE-FG0137FE61146, National Science Foundation Grant No CBT-6314147, the Oklahoma Mining and Minerals Resources Research Institute, the University of Oklahoma Energy Center, Aqualon Corp., E.I. DuPont de Nemours and Co., Kerr-McGee Corp., Sandoz Chemical Co., Shell Development Co., and Unilever Corp.
REFERENCES 1
2 3
8 9
10 11 12
S.D. Christian and J.F. Scamehom, in J.F. Scamehom and J.H. Harwell (Eds), SurfactantBased Separation Processes, Marcel Dekker, New York, 1989, p. 3. G.A. Smith, S.D. Christian, E.E. Tucker and J.F. Scamehom, ACS Symp. Ser., 342 (1987) 184. S.N. Bhat, G.A. Smith, E.E. Tucker, S.D. Christian, W. Smith and J.F. Scamehom, Ind. Eng. Chem. Res., 26 (1987) 1217. L.L. Gibbs, J.F. Scamehom and S.D. Christian, J. Membrane Sci., 30 (1987) 67. R.O. Dunn, J.F. Scamehorn and S.D. Christian, Sep. Sci. Technol., 22 (1987) 763. R.O. Dunn, J.F. Scamehorn and S.D. Christian, Sep. Sci. Technol., 20 (1985) 257. P.S. Leung, in A.R. Cooper (Ed.), Ultrafiltration Membranes and Applications, Plenum Press, New York, 1979, p. 415. J.F. Scamehorn and J.H. Harwell, in D.T. Wasan, D.O. Shah and M.E. Ginn (Eds), Surfactants in Chemical/Process Engineering, Marcel Dekker, New York, 1988, p. 77. J.F. Scamehorn, S.D. Christian and R.T. Ellington, in J.F. Scamehorn and J.H. Harwell (Eds), Surfactant-Based Separation Processes, Marcel Dekker, New York, 1989, p. 29. S.D. Christian, S.N. Bhat, E.E. Tucker, J.F. Scamehom and D.A. El-Sayed, AIChE, J., 34 (1988) 189. J.F. Scamehorn, R.T. Ellington, S.D. Christian, B.W. Penney, R.O. Dunn and S.N. Bhat, AIChE Symp. Ser., 250 (1986) 48. R.O. Dunn, J.F. Scamehorn and S.D. Christian, Colloid Surfaces, 35 (1989) 49.
267 13 14
K.J. Sasaki, S.L. Burnett, S.D. Christian, E.E. Tucker and J.F. Scamehorn, (1989) 363. M.C. Porter, in P.A. Schweitzer (Ed.), Handbook of Separation Techniques Engineers, McGraw-Hill, New York, 1979, Section 2.1.
Langmuir, for Chemical
5
259
Concentration Polarization in PolyelectrolyteEnhanced Ultrafiltration JOHN F. SCAMEHORN, SHERRIL D. CHRISTIAN, EDWIN E. TUCKER and BERNADETTELTAN Znstitute for Applied Surfactant Research, University of Oklahoma, Norman, OK 73019 (U.S.A.) (Received 7 June 1989; accepted 8 January 1999)
ABSTRACT Polyelectrolyte-enhanced ultrafiltration (PEUF ) is a new method of removing ions from water. In PEUF, a polyelectrolyte of opposite charge to the target ion is added to solution and the target ion binds to the polymer. The polyelectrolyte is then removed from the water by ultrafiltration. The resulting permeate solutions are quite pure, with measured rejections in excess of 99%. In this work, a solution containing copper was treated using PEUF with poly(styrene sulfonate) as the anionic polyelectrolyte over a wide range of polymer concentrations. As the ret&ate becomes more concentrated in polyelectrolyte, the rejection decreases and the flux decreases. However, even with concentrated retentate solutions, the rejections remain high (96% was the lowest rejection observed here). Fluxes only decline sharply when the concentration in the retentate is quite high. Hence, classical concentration polarization behavior is observed in PEUF, but it is not severe in the operating range of practical importance, indicating the promise of PEUF as an industrial separation process.
INTRODUCTION
Colloid-enhanced .ultrafiltration methods can be used to remove dissolved solutes from water very effectively and economically. Micellar-enhanced ultrafiltration (MEUF) involves the addition of surfactants to water. The surfactants form micelles, which are roughly spherical aggregates containing 50-100 surfactant molecules. The micelles have a hydrophobic interior and the hydrophilic portion of the surfactants forms the surface of the micelle. Dissolved organics in solution will tend to solubilize or dissolve in the micelle. If the surfactant has opposite charge to a multivalent ion in solution, this counterion will bind to the micelles. The solution is then treated in an ultrafiltration unit with membrane pore sizes small enough to reject the micelles. The result is that the micelles with their solubilized organics and bound ions become concentrated in the retentate (the solution not passing through membrane) and the permeate (the solution passing through membrane) can be quite pure. 0166.6622/90/$03.50
0 1990 -
Elsevier Science Publishers B.V.
260
MEUF has been shown to be effective at removing dissolved organics [l-8], multivalent cations or anions [ 3-111, or organics and divalent cations simultaneously [ 121. Polyelectrolyte-enhanced ultrafiltration (PEUF) involves the addition of a soluble polyelectrolyte to the water containing a solute having a charge opposite to that of the polyelectrolyte. The target solute binds to the polyelectrolyte by electrostatic attraction and the solution is treated with ultrafiltration using a membrane having pore sizes small enough to filter the polyelectrolyte from solution. We have studied the removal of the divalent cation, Cu2+, using poly (styrene sulfonate) in a PEUF process at fairly low polyelectrolyte concentrations [ 131. An advantage of PEUF over MEUF is that none of the polyelectrolyte will pass into the permeate for an optimum system, in contrast with MEUF, where some of the surfactant will always be present in monomeric or unaggregated form and pass into the permeate. On the other hand, MEUF can be used to remove both nonionic organics and ions, while PEUF can remove only ions of opposite charge to the polyelectrolyte. From an engineering viewpoint, flow rates through the membrane are important, as well as the rejection of designated species by the membrane. MEUF has been shown to follow traditional concentration polarization behavior with fairly high gel concentrations (ca 0.55 M) [ 591. This means that for practical systems, high water recoveries are attainable in MEUF without entering a regime where low fluxes are observed. The purpose of this work is to investigate the concentration polarization behavior and study rejections of heavy metals in PEUF at relatively high colloid concentrations. The results are compared to those for MEUF to help ascertain which novel technology shows greater promise for heavy metal removal from water. EXPERIMENTAL
Materials Sodium poly (styrene sulfonate) or PSS, having an average molecular weight of approximately 35 000, was obtained from Aldrich Chemical Co., and used without further purification. Analytical reagent grade copper chloride (Mallinckrodt Chemicals) was used without further purification. Water was deionized twice and passed through a carbon adsorption column.
Methods Ultrafiltration was studied using 400 ml stirred cells at 30°C and 414 kPa (60 psi). Spectrum cellulose acetate membranes with molecular weight cutoffs (MWCO)of 1000,5 000 and 10 000 were used. A feed solution of 300 ml
261
was used to initiate a run. The run was terminated when 200 ml had passed through the membrane as permeate. Fluxes were determined during the run by timing and weighing samples of permeate. The rejection of copper or polyelectrolyte was determined by measuring the concentration of copper in the permeate. For each run, this rejection is reported at the point in the run where 100 ml of permeate have passed through (the mid-point ) . The retentate composition at any point in the run was calculated from a material balance and a knowledge of permeate concentrations. Therefore, one rejection and numerous flux data are produced in a run. The copper concentrations were measured using a Varian SpectrAAatomic absorption spectrophotometer. The PSS concentration in the permeate was measured using a Bausch and Lomb Speconic 1001 UV spectrophotometer. P RESULTS AND DISCUSSION
The permeate copper concentration is shown as a function of rententate copper concentration in Fig. 1 and Table 1. Since almost all of the PSS and Cu2+ is rejected in the ultrafiltration, the ratio of Cu”‘/PSS in the retentate remains nearly constant throughout a run (in this case, the molar ratio was l/5). All PSS concentrations given here are based on monomer units, hence, 0.1 A4 refers to 0.1 M of styrene sulfonate units (molecular weight 183) in
j
, 1
“, ,,;,;;~gyy,j 10
RETENTATE COPPER CONCENTRATION (mM)
Fig. 1. Copper concentration in permeate for PEUF.
10'
262 TABLE 1 Rejection of PSS and Cu2+ by PEUF Membrane MWCO
1000 1000 1000 5000 5000 5 000 10 000 10 000 10 000
[PSSIR’ wu)
[cu2+]a’ ww
[PSSIP”
[Cl?+]pa
ww
(mw
15 45 150 15 45 150 15 45 150
3 9 30 3 9 30 3 9 30
0.007 0.0536 0.240 0.0244 0.0740 0.351 0.019 0.0843 0.411
0.0336 0.113 1.088 0.0263 0.100 1.513 0.0354 0.198 1.20
Rejection ( ??I)b PSS
cl?+
99.95 99.88
98.88
99.84
96.37
99.84
99.12 98.88 94.96 98.82 97.80 96.00
99.84 99.77 99.87 99.81 99.73
98.74
“Subscripts R and P refer to retentate and permeate, respectively. bRejection (% ) = 100 (1 - [Permeate] / [Retentate] ).
solution, not 0.1 M of poly (styrene sulfonate) (molecular weight approximately 85 000) in solution. The general observation from the data is that copper is rejected very efficiently by PEUF, rejections reaching as high as 99.12% for the conditions used here. As the PSS and Cu2+ concentrations in the retentate increase, rejection of copper decreases somewhat, a result predicted from a theoretical model [ 131 and also observed for heavy metal removal by MEUF [ 8-111. The results are very similar for the three membranes used, indicating that pore size does not have a significant effect on solute rejection, as long as the colloid is being effectively filtered from the permeate, a conclusion previously reached for MEUF
[51.
The PSS in the permeate ranged from 0.047 to 0.27% of that in the retentate, showing the the colloid is being effectively rejected by all the membranes used here. The PSS in the permeate is believed to be low molecular weight components of the polymer.
Flux Figure 2 presents the flux as a function of the retentate polyelectrolyte concentration. Traditional concentration polarization behavior [ 141 is observed, with the flux declining linearly with the logarithm of retentate concentration, at high enough retentate concentrations. At low retentate concentrations, the flux approaches that of pure water for all three membranes. Figure 3 represents relative flux as a function of retentate polyelectrolyte concentration (relative flux is flux/flux of pure water). The data for the three
263
60
MEMBRANE PORE SIZE x 0 0
5000 1 000 10 000
MWCO MWCO
10
10’ 10 a 10’ RETENTATE POLYELECTROLYTECONCENTRATION (mM)
Fig. 2. Absolute flux for PEUF.
0.2
MEMBRANE PORE SIZE 1 000 5 000
YWCO MWCO
0.0 10 10’ 10’ 10’ RETENTATE POLYELECTROLYTECONCENTRATION (mM)
Fig. 3. Relative flux for PEUF.
membranes coincide on this plot. An extrapolation for these data would result in a gel concentration (where flux equals 0) of approximately 1 M. In practical applications, a region of low relative flux would be avoided, so the important conclusion from Fig. 3 is that the relative flux remains high until high retentate concentrations are achieved. For example, it requires approximately 250 mM
264
polyelectrolyte in the retentate to reduce the relative flux to 0.5. The relative flux versus retentate colloid concentration plots for MEUF do not exhibit the coincidence of the data for different pore size membranes, although all membranes did yield the same gel concentration [ 51. In order to compare flux from PEUF and MEUF directly, Figs 4-6 present relative flux plots for PEUF and MEUF for the same molecular weight cutoff membrane. From Fig. 4, for a 1000 MWCO membrane, the MEUF and PEUF data coincide. The MEUF used a cationic surfactant, cetylpyridinium chloride or CPC as the colloid [5]. From Fig. 5, for a 5 000 MWCO membrane, the relative flux for PEUF is higher than that for MEUF, but the decline in flux in the concentration polarization region at higher concentrations has the same slope for MEUF and PEUF. In this figure, MEUF data with CPC [ 51, as well as sodium dodecyl sulfate or SDS [9], as the colloid or surfactant, are presented. The data using the cationic and anionic surfactant coincide, indicating the relative insensitivity of MEUF flux to micelle charge or size. Finally, Fig. 6 shows that for a 10 000 MWCO membrane, PEUF exhibits substantially greater relative flux values than MEUF (with CPC as the surfactant). No precipitate was observed in any of the systems discussed here. It should be noted that the water soluble polyelectrolyte or surfactant micelles bind a very large fraction of any oppositely charged multivalent ions present in solution. The resulting reduction in the thermodynamic activity of the ion (e.g., Cu2 + ) can prevent precipitation even under conditions where the ion would precipitate in the absence of the colloid. The general conclusion from the flux data is that PEUF does not demon-
1.0
0.6
C0LL0l0 0 SURFACTANT (CPC) q POLYELECTROLYTE 10
RETENTATE
10 ’ COLLOIO
1
@,
10’ CONCENTRATION
10' (mM)
Fig. 4. Fklative flux for 1000 MWCO membranes for PEUF and MEUF.
265
0.0
10'
10'
10 RETENTATE
COLLOIO
CONCENTRATION
10'
(mM j
Fig. 5. Relative flux for 5 000 MWCO membranes for PEUF and MEUF.
I 1.0
;-@% B
I
I-
10000 MWCO MEMBRANE
-
0
0.8 y%O 5
q
0
dO.6
%
0
5
m %I
3 kO.4
0
0
0 0 0
0.2 :O SIJRFACTANT (CPC) :O POLYELECTROLYTE 0.0 10 RETENTATE
10 1 COLLOIO
10' CONCENTRATION
10'
(mM)
Fig. 6. Relative flux for 10 000 MWCO membranes for PEUF and MEUF.
266
strate severe concentration polarization effects until a fairly high concentration of polyelectrolyte is present in the retentate. In fact, flux values are equal to or greater than for MEUF under comparable conditions. This is an unanticipated result, since one would expect that the intertwining of polymer chains might cause a polyelectrolyte solution to have a higher viscosity and poorer fluxes than an equivalent micellar solution. Micelle-micelle interactions appear to cause extended structures in solution in MEUF which are at least as limiting to water diffusion to the membrane as are water soluble polymers. However, from a practical view, the fact that high concentrations are necessary before concentration polarization becomes substantial (as well as the excellent rejection of multivalent metals) should make both of these technologies quite viable as industrial separations. ACKNOWLEDGEMENTS
Financial support for this work was provided by the Department of Energy Office of Basic Energy Sciences Grant No DE-FG0564ER13678, Department of Energy Grant No DE-FG0137FE61146, National Science Foundation Grant No CBT-6314147, the Oklahoma Mining and Minerals Resources Research Institute, the University of Oklahoma Energy Center, Aqualon Corp., E.I. DuPont de Nemours and Co., Kerr-McGee Corp., Sandoz Chemical Co., Shell Development Co., and Unilever Corp.
REFERENCES 1
2 3
8 9
10 11 12
S.D. Christian and J.F. Scamehom, in J.F. Scamehom and J.H. Harwell (Eds), SurfactantBased Separation Processes, Marcel Dekker, New York, 1989, p. 3. G.A. Smith, S.D. Christian, E.E. Tucker and J.F. Scamehom, ACS Symp. Ser., 342 (1987) 184. S.N. Bhat, G.A. Smith, E.E. Tucker, S.D. Christian, W. Smith and J.F. Scamehom, Ind. Eng. Chem. Res., 26 (1987) 1217. L.L. Gibbs, J.F. Scamehom and S.D. Christian, J. Membrane Sci., 30 (1987) 67. R.O. Dunn, J.F. Scamehorn and S.D. Christian, Sep. Sci. Technol., 22 (1987) 763. R.O. Dunn, J.F. Scamehorn and S.D. Christian, Sep. Sci. Technol., 20 (1985) 257. P.S. Leung, in A.R. Cooper (Ed.), Ultrafiltration Membranes and Applications, Plenum Press, New York, 1979, p. 415. J.F. Scamehorn and J.H. Harwell, in D.T. Wasan, D.O. Shah and M.E. Ginn (Eds), Surfactants in Chemical/Process Engineering, Marcel Dekker, New York, 1988, p. 77. J.F. Scamehorn, S.D. Christian and R.T. Ellington, in J.F. Scamehorn and J.H. Harwell (Eds), Surfactant-Based Separation Processes, Marcel Dekker, New York, 1989, p. 29. S.D. Christian, S.N. Bhat, E.E. Tucker, J.F. Scamehom and D.A. El-Sayed, AIChE, J., 34 (1988) 189. J.F. Scamehorn, R.T. Ellington, S.D. Christian, B.W. Penney, R.O. Dunn and S.N. Bhat, AIChE Symp. Ser., 250 (1986) 48. R.O. Dunn, J.F. Scamehorn and S.D. Christian, Colloid Surfaces, 35 (1989) 49.
267 13 14
K.J. Sasaki, S.L. Burnett, S.D. Christian, E.E. Tucker and J.F. Scamehorn, (1989) 363. M.C. Porter, in P.A. Schweitzer (Ed.), Handbook of Separation Techniques Engineers, McGraw-Hill, New York, 1979, Section 2.1.
Langmuir, for Chemical
5