Co-reporter:Michele Galizia, Won Seok Chi, Zachary P. Smith, Timothy C. Merkel, Richard W. Baker, and Benny D. Freeman
Macromolecules October 24, 2017 Volume 50(Issue 20) pp:7809-7809
Publication Date(Web):October 3, 2017
DOI:10.1021/acs.macromol.7b01718
Membrane gas separation is a mature and expanding technology. However, the availability of better membrane materials would promote faster growth. In this Perspective we analyze the state of the art of membrane materials, including polymers and hybrid materials, as well as the current issues and barriers, and finally, we outline future research directions in membrane science. Development of new membrane materials for large scale separations will rely on a multidisciplinary approach that embraces the broad fields of chemical and materials engineering, polymer science, and materials chemistry.
Co-reporter:Zhengwang He, Daniel J. Miller, Sirirat Kasemset, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2017 Volume 525() pp:25-34
Publication Date(Web):1 March 2017
DOI:10.1016/j.memsci.2016.10.002
•Critical and threshold fluxes were determined using the flux-stepping technique.•Fouling tests were performed below and above the critical and threshold fluxes.•Below the threshold flux, resistance was predicted by flux-stepping experiments.•Above the threshold flux, critical pressure is the upper limit of TMP.Critical and threshold flux concepts were recently developed to distinguish no fouling, slow fouling and rapid fouling regimes. Membrane fouling behavior is expected to vary with respect to the imposed flux relative to the critical and threshold flux values. However, crossflow fouling tests are often performed independent of critical and threshold flux determinations. In this study, constant flux fouling experiments were performed in connection with critical and threshold flux determination. Fouling behavior was examined in the context of critical and threshold flux. A poly(vinylidene fluoride) microfiltration membrane was challenged with various oil-in-water emulsions. The critical and threshold flux values were estimated using the flux-stepping technique. Constant flux crossflow fouling tests were performed at selected fluxes below and above the critical and threshold fluxes. Below the critical flux, mass transfer resistance remained constant at the clean membrane value. Above the critical flux but below the threshold flux, mass transfer resistance approached a steady state resistance, RB, which was determined from the linear regression of flux-stepping experiments. Above the threshold flux, a three-stage transmembrane pressure (TMP) was observed, consisting of: (1) an initial gradual increase, (2) a TMP jump stage, and (3) a pseudo-steady state. The pseudo-steady state TMP corresponded to the estimated critical pressure of the oil layer.
Co-reporter:Sirirat Kasemset, Lu Wang, Zhengwang He, Daniel J. Miller, Alon Kirschner, Benny D. Freeman, Mukul M. Sharma
Journal of Membrane Science 2017 Volume 522() pp:100-115
Publication Date(Web):15 January 2017
DOI:10.1016/j.memsci.2016.07.016
•UF membranes were modified with polydopamine at various deposition conditions.•Polydopamine modification decreased membrane molecular weight cutoff.•Membrane pore size distribution was modeled using hindered solute transport model.•Tradeoff between membrane selectivity and hydraulic permeability was observed.Membrane surface modification with polydopamine (PDA) coatings can reduce fouling in oily water filtration due, at least in part, to enhanced surface hydrophilicity. In this study, polysulfone (PSf) UF membranes were coated with PDA. PDA coating conditions (solution concentration and deposition time) were varied, and the effect of coating conditions on membrane molecular weight cutoff (MWCO) and hydraulic permeability was measured. Membrane MWCO decreased and PDA film thickness increased as initial dopamine coating solution concentration or deposition time increased. The MWCO decrease confirmed that PDA restricted the membrane pores. While the PDA coating thickness on membrane surfaces grew progressively with increasing initial dopamine concentration or coating time, coating inside the membrane pores was limited by the finite membrane pore size. A tradeoff between selectivity and hydraulic permeability of unmodified and PDA-modified membranes was noted. This tradeoff is reminiscent of that observed in other separation membranes. Zydney’s hindered solute transport model of flow through porous membranes was used to estimate changes in membrane mean pore size and pore size distribution. Based on the modelling results, membrane mean pore radius increased at low initial dopamine concentrations or short deposition times and decreased at high initial dopamine concentrations or long deposition times with increasing initial dopamine concentration or increasing PDA coating time. The pore size distribution narrowed as the membranes were modified with PDA. The porosity to thickness ratio of PDA-modified membranes remained unchanged or was only slightly higher than that of unmodified membranes.
Co-reporter:Jovan Kamcev, Donald R. Paul, Gerald S. Manning, Benny D. Freeman
Journal of Membrane Science 2017 Volume 537(Volume 537) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.memsci.2017.05.034
•Salt diffusion coefficients in membranes are affected by convection and non-ideal effects.•Convection effects decreased apparent salt diffusion coefficients.•Non-ideal thermodynamic effects increased apparent salt diffusion coefficients.•For the ion exchange membranes considered, these two effects nearly cancel each other.Accurate evaluation of salt diffusion coefficients from transport rate data in ion exchange membranes requires accounting for frame of reference and non-ideal thermodynamic effects. Due to a lack of models and experimental data quantifying membrane ion activity coefficients, it has been impossible to evaluate the impact of non-ideal thermodynamic effects on observed salt diffusion coefficients. Here, a framework is presented that includes both frame of reference (i.e., convection) and non-ideal thermodynamic effects in calculating salt diffusion coefficients in ion exchange membranes. Effective concentration averaged NaCl diffusion coefficients were determined as a function of upstream NaCl concentration in commercial ion exchange membranes from NaCl permeability and sorption measurements via the solution-diffusion model. Frame of reference effects were evaluated using a version of Fick's law that accounts for convection. The factors necessary to account for non-ideal thermodynamic effects were developed using Manning's counter-ion condensation theory. At low upstream NaCl concentrations, frame of reference and non-ideal thermodynamic effects on diffusion coefficients were negligible. However, at higher upstream NaCl concentrations (e.g., >0.1 M), both effects contribute measurably to NaCl diffusion coefficients. Correcting for frame of reference effects increased apparent NaCl diffusion coefficients. However, correcting for thermodynamic non-idealities of the ions sorbed into the membranes reduced apparent NaCl diffusion coefficients. Fortuitously, for the materials considered in this study, frame of reference and non-ideal thermodynamic effects nearly cancel each other.
Co-reporter:Alon Y. Kirschner, Chia-Chih Chang, Sirirat Kasemset, Todd Emrick, Benny D. Freeman
Journal of Membrane Science 2017 Volume 541(Volume 541) pp:
Publication Date(Web):1 November 2017
DOI:10.1016/j.memsci.2017.06.055
•PMPC, a polymer zwitterion, was incorporated into PD coatings.•Fouling studies of various membranes showed that PD-PMPC-modified membranes had the greatest fouling resistance.•The difference in performance is likely due to the strongly hydrophilic surface properties contributed by PMPC.Poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC), a polymer zwitterion, is known to reduce biofouling and impart low friction characteristics to materials surfaces. Using a one-step solution coating process, we report the incorporation of PMPC into polydopamine (PD) coatings on ultrafiltration (UF) membranes for oil-water separations. Polysulfone UF membranes were surface-modified with either pure PD or a mixture of PD and PMPC (PD-PMPC). Unmodified and surface-modified membranes were characterized with respect to pure water permeance, contact angle, coating thickness, threshold flux and molecular weight cutoff (MWCO). Both types of modified membranes showed a significant decrease in contact angle compared to unmodified membranes, indicating an increase in hydrophilicity. PD-PMPC-modified membranes had a slightly lower underwater contact angle than PD-modified membranes, as well as a higher threshold flux. Constant flux crossflow fouling experiments were conducted on unmodified, PD-modified, and PD-PMPC-modified membranes using a soybean oil emulsion as a model foulant at fluxes near and below the measured threshold flux. The fouling profiles of membranes with similar pure water permeance values were compared to assess the effect of different coating materials and coating conditions on fouling. PD-PMPC-modified membranes exhibited the greatest fouling resistance. Zeta potential measurements showed only small differences in surface charge between the membranes. MWCO experiments showed no difference in nominal pore size or pore size distribution for the modified membranes, indicating that the difference in fouling performance is likely due to the strongly hydrophilic surface properties contributed by PMPC. PD-PMPC-modified membranes exhibited stable, low transmembrane pressure operation at fluxes where PD-modified and unmodified membranes suffered from rapid fouling and an unstable transmembrane pressure profile.Download high-res image (228KB)Download full-size image
Co-reporter:Michele Galizia, Kevin A. Stevens, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2017 Volume 537(Volume 537) pp:
Publication Date(Web):1 September 2017
DOI:10.1016/j.memsci.2017.05.015
•Gas permeability in TR polymers was described using a thermodynamic model.•Gas diffusivity was predicted.•Unique separation performance of TR polymers is a manifestation of their size-sieving ability.Gas permeability in HAB-6FDA polyimide and its thermally rearranged analogs was described using a thermodynamic model based on the non-equilibrium lattice fluid (NELF) theory. This study is part of an ongoing effort to describe gas sorption and transport behavior of TR polymers theoretically. Hydrogen, nitrogen and methane permeability over a broad range of pressures (up to 32 atm) and temperatures (−10 to 50 °C) was calculated with one adjustable parameter at each temperature, i.e., the infinite dilution mobility coefficient. For highly soluble, swelling gases, such as CO2, matrix plasticization was accounted for by a second adjustable parameter, the plasticization factor, which describes the dependence of penetrant mobility on concentration. Model parameters correlate with membrane structure and gas properties. At fixed temperature, the infinite dilution mobility correlates with penetrant critical volume and polymer fractional free volume. For each penetrant, the temperature dependence of infinite dilution mobility is described by the Arrhenius law. Based on the modeling results, unique separation performance of TR polymers is a manifestation of their strong size-sieving ability. Finally, diffusion coefficients and ideal selectivities were predicted with no adjustable parameters.Download high-res image (185KB)Download full-size image
Co-reporter:Kevin A. Stevens, Zachary P. Smith, Kristofer L. Gleason, Michele Galizia, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2017 Volume 533(Volume 533) pp:
Publication Date(Web):1 July 2017
DOI:10.1016/j.memsci.2017.03.005
•Solubility of H2, N2, CH4, and CO2 decrease with increasing temperature.•Enthalpies of sorption correlate with TR conversion.•CO2/CH4 solubility selectivity does not change with temperature at 10 atm.Thermally rearranged (TR) polymers have been the subject of many fundamental studies, but the effect of TR conversion on temperature-dependent transport properties is largely unexplored. Sorption isotherms for N2, CH4, and CO2 in HAB-6FDA polyimide and its TR analogs were measured at temperatures ranging from −10 °C to 50 °C and pressures up to 27 atm. Solubilities increase with decreasing temperature for each gas and sample tested. At low TR conversions, the sorption process initially becomes less exothermic. However, enthalpies of sorption do not significantly change with TR conversion after the initial stages of rearrangement. Enthalpies of sorption in TR polymers are qualitatively similar to those of other high free volume materials. Solubility selectivity for CO2/CH4 at 10 atm did not change with temperature due to similar enthalpies of sorption for CO2 and CH4. Sorption data were fit to the dual mode model at different temperatures, and model parameters were correlated with polymer and penetrant properties.Download high-res image (172KB)Download full-size image
Co-reporter:Michele Galizia, Francesco M. Benedetti, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2017 Volume 535(Volume 535) pp:
Publication Date(Web):1 August 2017
DOI:10.1016/j.memsci.2017.04.007
•Membranes in divalent counter-ion form contain more salt and less water than in the monovalent form.•Sorption of monovalent salts is influenced by ambient carbon dioxide, while the sorption of divalent salts is not.•Alkali chloride and alkaline earth chloride sorption in sulfonated polystyrene is well described by the Manning-Donnan model.Many fundamentals of ion sorption in ion exchange membranes (IEMs) are not fully understood, and few modern studies focus on multivalent ion sorption, despite the importance of divalent ion transport properties in water purification applications. Here, MgCl2 and CaCl2 sorption in a commercial cross-linked, styrene-divinylbenzene cation exchange membrane (CEM) with fixed sulfonate groups was measured and compared with NaCl, LiCl and KCl sorption in the same material. The data were correlated with counter-ion size and valence, as well as membrane water content. Divalent salts had higher sorption coefficients than monovalent salts, even though membrane water content significantly decreased in the presence of divalent counter-ions. The Donnan potential is weaker in the presence of multivalent counter-ions, which increases co-ion sorption, contributing to the observed increase in salt sorption coefficients for divalent salts. Ion activity coefficients in the membrane were calculated and compared to predictions of the recently proposed Manning-Donnan model. This model showed much better agreement with the experimental data than the ideal Donnan model, suggesting that ion non-ideality in the membrane is important when analyzing ion sorption and transport in IEMs.Download high-res image (278KB)Download full-size image
Co-reporter:Jovan Kamcev;Donald R. Paul
Journal of Materials Chemistry A 2017 vol. 5(Issue 9) pp:4638-4650
Publication Date(Web):2017/02/28
DOI:10.1039/C6TA07954G
Despite their increasing importance in many energy and water purification applications, few systematic studies of ion sorption in ion exchange membranes exist where fixed charge group concentration and water content are varied independently. Such studies are critical for developing fundamental structure/property relations important for rationally tailoring such materials. Here, cation and anion exchange membranes having different fixed charge group concentrations but similar water content were synthesized to investigate the influence of fixed charge group concentration on equilibrium ion sorption in such materials. Co-ion sorption decreased with increasing membrane fixed charge group concentration, as expected, presumably due to enhanced Donnan exclusion. However, the extent to which co-ion sorption was suppressed was different for the cation and anion exchange membranes, despite similar changes in membrane fixed charge group concentration. A thermodynamic model, based on Donnan theory and Manning's counter-ion condensation theory, was used to interpret the data. The model predicted equilibrium co-ion concentrations in the anion exchange membranes with no adjustable parameters. However, good agreement between the model and experimental data for the cation exchange membranes was only obtained by treating the Manning parameter as an adjustable constant, presumably due to phase separation during polymerization, which produced inhomogeneous membranes.
Co-reporter:Ho Bum Park;Lloyd M. Robeson;Menachem Elimelech;Jovan Kamcev
Science 2017 Volume 356(Issue 6343) pp:
Publication Date(Web):16 Jun 2017
DOI:10.1126/science.aab0530
Filtering through to what's important
Membranes are widely used for gas and liquid separations. Historical analysis of a range of gas pair separations indicated that there was an upper bound on the trade-off between membrane permeability, which limits flow rates, and the selectivity, which limits the quality of the separation process. Park et al. review the advances that have been made in attempts to break past this upper bound. Some inspiration has come from biological membranes. The authors also highlight cases where the challenges lie in areas other than improved separation performance.
Science, this issue p. eaab0530
Co-reporter:Jovan Kamcev, Donald R. Paul, Gerald S. Manning, and Benny D. Freeman
ACS Applied Materials & Interfaces 2017 Volume 9(Issue 4) pp:
Publication Date(Web):January 10, 2017
DOI:10.1021/acsami.6b14902
This study presents a framework for predicting salt permeability coefficients in ion exchange membranes in contact with an aqueous salt solution. The model, based on the solution–diffusion mechanism, was tested using experimental salt permeability data for a series of commercial ion exchange membranes. Equilibrium salt partition coefficients were calculated using a thermodynamic framework (i.e., Donnan theory), incorporating Manning’s counterion condensation theory to calculate ion activity coefficients in the membrane phase and the Pitzer model to calculate ion activity coefficients in the solution phase. The model predicted NaCl partition coefficients in a cation exchange membrane and two anion exchange membranes, as well as MgCl2 partition coefficients in a cation exchange membrane, remarkably well at higher external salt concentrations (>0.1 M) and reasonably well at lower external salt concentrations (<0.1 M) with no adjustable parameters. Membrane ion diffusion coefficients were calculated using a combination of the Mackie and Meares model, which assumes ion diffusion in water-swollen polymers is affected by a tortuosity factor, and a model developed by Manning to account for electrostatic effects. Agreement between experimental and predicted salt diffusion coefficients was good with no adjustable parameters. Calculated salt partition and diffusion coefficients were combined within the framework of the solution–diffusion model to predict salt permeability coefficients. Agreement between model and experimental data was remarkably good. Additionally, a simplified version of the model was used to elucidate connections between membrane structure (e.g., fixed charge group concentration) and salt transport properties.Keywords: counterion condensation; Donnan theory; ion exchange membrane; salt diffusion; salt permeability; salt sorption; tortuosity;
Co-reporter:Jovan Kamcev, Michele Galizia, Francesco M. Benedetti, Eui-Soung Jang, Donald R. Paul, Benny D. Freeman and Gerald S. Manning
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 8) pp:6021-6031
Publication Date(Web):19 Jan 2016
DOI:10.1039/C5CP06747B
Equilibrium partitioning of ions between a membrane and a contiguous external solution strongly influences transport properties of polymeric membranes used for water purification and energy generation applications. This study presents a theoretical framework to quantitatively predict ion sorption from aqueous electrolytes (e.g., NaCl, MgCl2) into charged (i.e., ion exchange) polymers. The model was compared with experimental NaCl, MgCl2, and CaCl2 sorption data in commercial cation and anion exchange membranes. Ion sorption in charged polymers was modeled using a thermodynamic approach based on Donnan theory coupled with Manning's counter-ion condensation theory to describe non-ideal behavior of ions in the membrane. Ion activity coefficients in solution were calculated using the Pitzer model. The resulting model, with no adjustable parameters, provides remarkably good agreement with experimental values of membrane mobile salt concentration. The generality of the model was further demonstrated using literature data for ion sorption of various electrolytes in charged polymers, including HCl sorption in Nafion.
Co-reporter:Michele Galizia, Kevin A. Stevens, Zachary P. Smith, Donald R. Paul, and Benny D. Freeman
Macromolecules 2016 Volume 49(Issue 22) pp:8768-8779
Publication Date(Web):November 10, 2016
DOI:10.1021/acs.macromol.6b01479
For the first time, a theoretical analysis of gas sorption, based on the nonequilibrium lattice fluid (NELF) model, in chemically imidized HAB-6FDA polyimide and its thermally rearranged analogues is presented. Because of the inaccessibility of pVT data in the rubbery region, the characteristic lattice fluid parameters of the polymers considered in this study were obtained from a collection of infinite dilution solubility data at multiple temperatures. Hydrogen, nitrogen, and methane sorption isotherms at 35 °C were fit to the NELF model using one adjustable parameter, i.e., the polymer–penetrant binary interaction parameter, k12. The optimal value of k12 for each polymer–penetrant pair was used to predict hydrogen, nitrogen, and methane sorption isotherms at other temperatures and at pressures up to 6 MPa. For carbon dioxide, a second adjustable parameter, the swelling coefficient, was introduced to account for sorption-induced matrix dilation. The ideal solubility–selectivity is also predicted for several gas pairs. The increase in gas sorption in thermally rearranged samples relative to their polyimide precursor is essentially due to entropic effects, i.e., to the increase in nonequilibrium fractional free volume during thermal rearrangement.
Co-reporter:Michele Galizia, Donald R. Paul, Benny D. Freeman
Polymer 2016 Volume 102() pp:281-291
Publication Date(Web):12 October 2016
DOI:10.1016/j.polymer.2016.09.010
•Methanol diffusion mechanism in charged and uncharged hydrogels is analyzed.•The role of fixed charges on methanol transport in ion exchange polymers is addressed.•The Flory-Rehner model is used to describe mixed methanol-water solubility in uncharged hydrogels.There are few studies of the impact of membrane charge on ion and organic uncharged solute transport in polymers. This study was aimed at addressing the lack of such fundamental information in the literature. Liquid methanol sorption, diffusion and permeation in water swollen, cross-linked, uncharged poly(ethylene glycol) diacrylate (XLPEGDA) and in charged membranes were investigated. Membrane water content significantly influences methanol solubility, diffusivity and permeability, with more swollen membranes having faster methanol transport rates. The Mackie-Meares model was used to interpret and correlate diffusion data. The Flory-Rehner theory for ternary systems was used to interpret methanol sorption isotherms in XLPEGDA-based polymers. Methanol and sodium chloride transport patterns are similar in neutral hydrogels, while substantial differences are observed in ion exchange polymers. These differences are ascribed to sodium chloride transport in charged polymers being strongly influenced by Donnan exclusion, while methanol sorption and diffusion are not.
Co-reporter:Sirirat Kasemset, Zhengwang He, Daniel J. Miller, Benny D. Freeman, Mukul M. Sharma
Polymer 2016 Volume 97() pp:247-257
Publication Date(Web):5 August 2016
DOI:10.1016/j.polymer.2016.04.064
•Polydopamine (PDA) modification increased membrane surface hydrophilicity.•PDA modification did not change membrane surface roughness or zeta potential.•Threshold flux could be increased by PDA modification at optimum conditions.•Hydrophilicity and permeance changes after PDA coating changed threshold flux.•Threshold flux of PDA-modified membranes increased with increasing permeance.Surface modification of porous membranes for water filtration has been extensively reported in the literature to improve fouling resistance. However, surface modification can significantly change the membrane filtration properties, sometimes resulting in more severe fouling than with the original, unmodified membrane. This study focused on demonstrating surface modification strategies and membrane comparison strategies to better understand the complex, competing phenomena occurring when membranes are surface modified. Polysulfone ultrafiltration membranes were modified with polydopamine (PDA) at different initial dopamine concentrations and deposition times. Membrane properties, including surface hydrophilicity, roughness, and zeta potential, were characterized. PDA coatings significantly increased surface hydrophilicity, but they did not markedly change the surface roughness or zeta potential. The threshold flux during oil/water emulsion filtration was determined and used as a fouling parameter for membranes modified with PDA at various modification conditions. The threshold flux increased when PDA was deposited at low initial dopamine concentrations or short coating times. However, PDA deposition at high initial dopamine concentrations or long coating times decreased the threshold flux, suggesting that a tradeoff exists between increased hydrophilicity and reduced pore size due to surface modification. An increase in membrane surface hydrophilicity was observed at all PDA deposition conditions, which tends to reduce foulant adhesion and increase threshold flux. However, extensive PDA coating significantly decreased membrane pure water permeance, suggesting that some membrane pores may have been narrowed or blocked, increasing local permeate flux through the remaining pores in the PDA-modified membranes. This higher local flux would exacerbate fouling and decrease threshold flux. Comparing unmodified and PDA-modified membranes having similar pure water permeance values, the PDA-modified membranes had higher threshold fluxes than the unmodified membranes.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Qiang Liu, Andrew T. Shaver, Yu Chen, Gregory Miller, Donald R. Paul, J.S. Riffle, James E. McGrath, Benny D. Freeman
Polymer 2016 Volume 87() pp:202-214
Publication Date(Web):22 March 2016
DOI:10.1016/j.polymer.2016.01.075
•Submicron poly(arelene ether ketone) copolymer films were UV irradiated.•Permeability increases and selectivity decreases with increasing UV irradiation time and aging time.•Gas permeation properties depend on UV irradiation environment.•Aging environment influences polymer aging behavior.Modification of membranes to improve gas separation properties has been of considerable interest. Crosslinking is one route to modify membranes, but such studies need to be performed on thin membranes to quantify the impact of such modifications at thicknesses relevant to industrial membranes. In this study, the influences of UV irradiation and physical aging on O2 and N2 gas permeation properties of thin (∼150 nm) glassy, amorphous poly(arylene ether ketone) (PAEK) copolymer films at 35 °C and 2 atm were investigated. Thin PAEK copolymer films, prepared from tetramethyl bisphenol A (TMBPA) and 4,4′-difluorobenzophenone (DFBP), were UV irradiated on both sides in air or N2 at 254 nm or 365 nm, which induced crosslinking and, in some cases, photooxidation. Gas permeability decreased and O2/N2 selectivity increased as UV irradiation and aging time increased. At 254 nm, samples irradiated in air have lower permeability coefficients and higher selectivities than samples irradiated in N2, which was ascribed to additional decreases in free volume due to photooxidation in samples irradiated in air. Additionally, samples irradiated in air at 254 nm exhibit less physical aging than uncrosslinked and samples irradiated in N2 at 254 nm, possibly due to interactions among photooxidative polar products that may restrict polymer chain mobility, thereby lowering the aging rate. The influence of water vapor on physical aging of samples irradiated in air was examined. Finally, irradiation at 254 nm leads to more extensive crosslinking and/or photooxidation than irradiation at 365 nm, possibly due to greater UV absorption by the polymer and the higher probability of radical formation at the lower wavelength.
Co-reporter:Qiang Liu, Donald R. Paul, Benny D. Freeman
Polymer 2016 Volume 82() pp:378-391
Publication Date(Web):15 January 2016
DOI:10.1016/j.polymer.2015.11.051
•A series of HAB- and APAF-based polyimide homopolymers and copolymers was synthesized.•Permeability increases and selectivity decreases with increasing TR conversion and APAF content.•Tensile stress and elongation at break decrease with increasing TR conversion and APAF content.Gas transport and mechanical properties are reported for a series of copolyimides and their corresponding thermally rearranged (TR) analogs. Random copolyimides of APAF/HAB-6FDA with various compositions were synthesized via chemical imidization from 2,2′-bis (3-amino-4-hydroxyphenyl)-hexafluoropropane (APAF), 3,3′-dihydroxy-4,4′-diaminobiphenyl (HAB), and 2,2′-bis-(3,4-dicarboxy-phenyl) hexafluoropropane dianhydride (6FDA). These copolyimides were thermally treated at temperatures between 350 °C and 450 °C to prepare TR polybenzoxazoles (PBOs). Pure gas permeabilities of H2, CH4, N2, O2, and CO2 were measured at 35 °C with upstream pressures ranging from 3 to 17 atm. In general, gas permeability increased and selectivity decreased as TR conversion increased. Gas permeability also increased with increasing APAF content in the polyimides as a result of higher fractional free volume (FFV) imparted by the extra hexafluoroisopropylidene group in APAF. Stress–strain relationships were recorded for the polyimides and their TR analogs. As polyimides underwent thermal rearrangement, samples became more rigid, and tensile stress and elongation at break decreased. A similar trend in mechanical properties was also observed as APAF content increased, which was attributed to the lower molecular weight of APAF-containing polymers, resulting from the lower reactivity of APAF relative to that of HAB.
Co-reporter:Jovan Kamcev, Eui-Soung Jang, Ni Yan, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2015 Volume 479() pp:55-66
Publication Date(Web):1 April 2015
DOI:10.1016/j.memsci.2014.12.031
•Atmospheric CO2 influences NaCl permeability and sorption measurements.•CO2-driven ion exchange interferes with conductivity measurements.•Nitrogen bubbling during permeability experiments reduces CO2 interference.•More counter-ions than co-ions desorb from ion exchange membranes due to CO2.Characterizing ion sorption and transport properties in charged polymers is critical for developing fundamental understanding necessary to prepare high performance membranes. The presence of dissolved CO2CO2 from the atmosphere in aqueous solutions can interfere with measurements of salt permeability and sorption in ion-exchange membranes, frustrating characterization of ion transport properties. In water or aqueous saline solutions, CO2CO2 speciates to form ions such as H+H+ and HCO3−HCO3−. NaCl or other salt permeability experiments are often performed by exposing a membrane to two salt solutions of different concentrations in a conventional diffusion cell and monitoring the conductivity rise with time in the receiving chamber (i.e., the chamber containing the lower salt concentration). H+H+ and HCO3−HCO3− ions in the external solutions on either side of the membrane undergo ion exchange with counter-ions in cation- and anion-exchange membranes, respectively. This CO2CO2-induced ion exchange interferes with conductivity measurements designed to measure receiver salt concentration change with time due to ion permeation through the polymer from the higher salt concentration chamber (i.e., the donor chamber). This phenomenon results in non-linear changes in downstream conductivity with time, which is most pronounced at low donor cell NaCl concentrations, especially for anion-exchange membranes. Furthermore, this effect is absent when an anion-exchange membrane in the HCO3−HCO3− form is tested using NaHCO3NaHCO3 rather than NaCl for permeability measurements. The effect of CO2CO2 on NaCl permeability measurements can be significantly reduced when ultra-high purity N2N2 gas is bubbled through the donor and receiver solutions in the diffusion cell during the experiment, making it possible to obtain true NaCl permeability values. During NaCl sorption experiments, when an ion-exchange membrane was equilibrated with a NaCl solution of 0.1 M or lower, the amount of desorbed mobile counter-ions was significantly greater than the amount of desorbed mobile co-ions. The desorption of unequal amounts of ions can also be attributed to ion exchange between the membrane and solution phase and has implications for determining the mobile NaCl sorption coefficient. Procedures for addressing these issues are described.
Co-reporter:Kristofer L. Gleason, Zachary P. Smith, Qiang Liu, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2015 Volume 475() pp:204-214
Publication Date(Web):1 February 2015
DOI:10.1016/j.memsci.2014.10.014
•Mixed-gas transport was characterized for CO2 and CH4 in HAB–6FDA polyimide and TR polymers.•Mixed-gas selectivity was generally higher than pure-gas selectivity.•CO2-induced plasticization decreased as the degree of TR conversion increased.Permeability coefficients for pure CO2, pure CH4, and CO2/CH4 mixtures containing 50% CO2 are reported for a polyimide synthesized from 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA) and for three thermally-rearranged (TR) derivatives thereof. Permeability measurements were made at 35 °C for fugacities ranging from 4 to 25 atm. The permeability of CO2 and CH4 increased as the degree of TR conversion increased. For example, CO2 permeability at 10 atm increased by a factor of 30 between the unconverted polyimide and its TR analog converted at 450 °C. In pure-gas experiments, CO2 was observed to plasticize the unconverted polyimide, but it did not appear to plasticize the TR polymers. In mixed-gas experiments, dual-mode competitive sorption caused a depression in CH4 permeability, with very little change in CO2 permeability. In addition, plasticization by CO2 was evident in the CH4 mixed-gas permeability trends, but its impact was small in contrast with dual-mode competitive effects. Consequently, CO2/CH4 mixed-gas permeability selectivity was higher than the ideal selectivity, calculated as the ratio of pure gas permeability coefficients. The dual-mode sorption and permeation model was fit to the experimental data. Dual-mode model parameters and model predictions are reported, along with their confidence intervals. By comparing the dual-mode model predictions with the experimental mixed-gas data, the degree of CO2-induced plasticization was observed to decrease as the degree of TR conversion increased and was completely absent (within experimental uncertainty) for the TR polymer converted at 450 °C.
Co-reporter:Jovan Kamcev, Donald R. Paul, and Benny D. Freeman
Macromolecules 2015 Volume 48(Issue 21) pp:8011-8024
Publication Date(Web):October 20, 2015
DOI:10.1021/acs.macromol.5b01654
Manning’s counterion condensation theory, originally developed for polyelectrolyte solutions, was used to predict ion activity coefficients in charged (i.e., ion exchange) membranes with no adjustable parameters. Equilibrium sodium and chloride ion concentrations in negatively and positively charged membranes were determined experimentally as a function of external NaCl concentration, and ion activity coefficients in the membranes were obtained via a thermodynamic treatment. Theoretical values for membrane ion activity coefficients obtained via Manning’s model were compared with those obtained experimentally. Good agreement was observed between the experimental and theoretical values for membrane ion activity coefficients, especially at higher external NaCl concentrations. However, some deviation between experimental and theoretical values was observed in the dilute regime. Manning’s model was also used to obtain activity coefficients for various electrolytes in ion exchange resins using ion sorption data from the literature, and these values were compared to those obtained experimentally.
Co-reporter:Zachary P. Smith, Rajkiran R. Tiwari, Michelle E. Dose, Kristofer L. Gleason, Thomas M. Murphy, David F. Sanders, Gabriella Gunawan, Lloyd M. Robeson, Donald R. Paul, and Benny D. Freeman
Macromolecules 2014 Volume 47(Issue 9) pp:3170-3184
Publication Date(Web):April 28, 2014
DOI:10.1021/ma402521h
The permeability–selectivity upper bounds show that perfluoropolymers have uniquely different separation characteristics than hydrocarbon-based polymers. For separating helium from hydrogen, these differences are particularly dramatic. At a given helium permeability, the upper bound defined by perfluoropolymers has helium/hydrogen selectivities that are 2.5 times higher than that of the upper bound defined by hydrocarbon-based polymers. Robeson hypothesized that these differences in transport properties resulted from the unusual sorption relationships of gases in perfluoropolymers compared to hydrocarbon-based polymers, and this paper seeks to test this hypothesis experimentally. To do so, the gas permeability, sorption, and diffusion coefficients were determined at 35 °C for hydrogen and helium in a series of hydrocarbon-, silicon-, and fluorocarbon-based polymers. Highly or completely fluorinated polymers have separation characteristics above the upper-bound for helium/hydrogen separation because they maintain good diffusivity selectivities for helium over hydrogen and they have helium/hydrogen sorption selectivities much closer to unity than those of hydrocarbon-based samples. The silicon-based polymer had intermediate sorption selectivities between those of hydrocarbon-based polymers and perfluoropolymers. Comparisons of hydrogen and helium sorption data in the literature more broadly extend the conclusion that helium/hydrogen sorption selectivity is rather different in hydrocarbon and fluorocarbon-based media.
Co-reporter:Dr. Zachary P. Smith ; Benny D. Freeman
Angewandte Chemie International Edition 2014 Volume 53( Issue 39) pp:10286-10288
Publication Date(Web):
DOI:10.1002/anie.201404407
Co-reporter:David F. Sanders, Ruilan Guo, Zachary P. Smith, Kevin A. Stevens, Qiang Liu, James E. McGrath, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2014 463() pp: 73-81
Publication Date(Web):
DOI:10.1016/j.memsci.2014.03.032
Co-reporter:David F. Sanders, Ruilan Guo, Zachary P. Smith, Qiang Liu, Kevin A. Stevens, James E. McGrath, Donald R. Paul, Benny D. Freeman
Polymer 2014 Volume 55(Issue 7) pp:1636-1647
Publication Date(Web):1 April 2014
DOI:10.1016/j.polymer.2014.02.001
Thermal rearrangement of polyimides with ortho-position groups to polybenzoxazoles and related structures has been of recent interest for producing gas separation membranes. This study explores the influence of synthesis route and ortho-position functional group on the thermal rearrangement process and the fractional free volume of thermally rearranged (TR) polymers produced from polyimides derived from 3,3′-dihydroxy-4,4′-diamino-biphenyl and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (HAB–6FDA). Acetate, propanoate, and pivalate ortho-position functional groups were considered. Thermogravimetric analysis (TGA) was used to study thermal rearrangement at temperatures between 350 and 450 °C, and evolved gases from TGA were analyzed via mass spectrometry to characterize the byproducts of thermal rearrangement and thermal degradation. CO2 was the major byproduct of thermal rearrangement for all samples, and its evolution began well before the onset of thermal degradation. When non-hydroxyl ortho-position groups were present in the polymers, several byproducts other than CO2 were also observed due to the loss of these ortho-position groups before thermal rearrangement. Free volume generally increased with increasing extent of thermal rearrangement, but precise values of free volume could not be accurately determined for polymers with propanoate and pivalate ortho-position functional groups due to uncertainties in the chemical structure of partially converted materials. For polymers with acetate and hydroxyl ortho-position groups, free volume could be determined within the uncertainty of density measurements. Thermal rearrangement behavior and free volume results for acetate containing polymers synthesized via different routes were very similar. Based on these results, the chemical structure of the ortho-position functional group has a larger impact on TR polymer properties than the polyimide precursor synthesis route.
Co-reporter:Daniel J. Miller, Sirirat Kasemset, Lu Wang, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2014 452() pp: 171-183
Publication Date(Web):
DOI:10.1016/j.memsci.2013.10.037
Co-reporter:Daniel J. Miller, Sirirat Kasemset, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2014 454() pp: 505-515
Publication Date(Web):
DOI:10.1016/j.memsci.2013.12.027
Co-reporter:Dr. Zachary P. Smith ; Benny D. Freeman
Angewandte Chemie 2014 Volume 126( Issue 39) pp:10452-10454
Publication Date(Web):
DOI:10.1002/ange.201404407
Co-reporter:Daniel J. Miller, Xiaofei Huang, Hua Li, Sirirat Kasemset, Albert Lee, Dileep Agnihotri, Thomas Hayes, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2013 Volume 437() pp:265-275
Publication Date(Web):15 June 2013
DOI:10.1016/j.memsci.2013.03.019
•Polydopamine and PEG were used to modify membranes for hydraulic fracturing wastewater.•A modified UF module showed increased flux and decreased TMP relative to an unmodified module.•Modified RO modules did not exhibit an improvement in flux or NDP relative to unmodified modules.•Modified RO modules exhibited higher and more stable salt rejection than unmodified modules.Polyacrylonitrile hollow fiber ultrafiltration (UF) and polyamide spiral wound reverse osmosis (RO) membrane modules were surface-modified by contact with an aqueous solution containing dopamine to deposit polydopamine on the membrane surfaces and other wetted parts inside the modules. UF modules were further modified by grafting poly(ethylene glycol) (PEG) brushes to the polydopamine coating. Polydopamine and polydopamine-g-PEG coatings increase hydrophilicity of the membrane surfaces and have previously been shown to improve fouling resistance towards model oil/water emulsions in laboratory studies. In a pilot-scale test treating hydraulic fracturing flowback water from the Barnett Shale region of Texas, the fouling performance of modified UF and RO membrane modules was compared to that of unmodified analogs. UF modules were used to remove most of the highly fouling organic matter in the feed before desalination by a train of RO elements. Polydopamine-modified UF modules maintained higher flux, lower transmembrane pressure difference, and improved cleaning efficiency relative to unmodified modules. The polydopamine coating did not appear to improve RO fouling behavior, presumably because most of the organic foulants had been removed by UF pretreatment of the feedwater. However, higher and more stable salt rejection was observed in modified RO modules than in unmodified modules.
Co-reporter:Cláudio P. Ribeiro Jr., Benny D. Freeman, Douglass S. Kalika, and Sumod Kalakkunnath
Industrial & Engineering Chemistry Research 2013 Volume 52(Issue 26) pp:8906-8916
Publication Date(Web):November 6, 2012
DOI:10.1021/ie302344z
Aromatic random copolyimides were synthesized and tested as membrane materials for the separation of a mixture of aromatic and aliphatic hydrocarbons by pervaporation. The polymers were synthesized by a two-step polycondensation route with a total of 4 aromatic dianhydrides, 4 aromatic diamines, and 3 diamino-terminated aliphatic oligomers containing either ether or siloxane units. Pervaporation experiments were conducted at two temperatures with toluene/n-heptane and benzene/n-heptane mixtures as feed streams. All polymers were selective toward the aromatic hydrocarbon. Introduction of siloxane units in the polymer generally led to very high hydrocarbon permeability coefficients, but caused a reduction in selectivity relative to that of the aromatic homopolyimide. Incorporation of ether units, on the other hand, did not generally cause such large increases in permeability, nor large decreases in selectivity. The performance of these materials was compared with previous results reported in the literature for other polymers.
Co-reporter:Sirirat Kasemset, Albert Lee, Daniel J. Miller, Benny D. Freeman, Mukul M. Sharma
Journal of Membrane Science 2013 s 425–426() pp: 208-216
Publication Date(Web):
DOI:10.1016/j.memsci.2012.08.049
Co-reporter:David F. Sanders, Zachary P. Smith, Ruilan Guo, Lloyd M. Robeson, James E. McGrath, Donald R. Paul, Benny D. Freeman
Polymer 2013 Volume 54(Issue 18) pp:4729-4761
Publication Date(Web):16 August 2013
DOI:10.1016/j.polymer.2013.05.075
Over the past three decades, polymeric gas separation membranes have become widely used for a variety of industrial gas separations applications. This review presents the fundamental scientific principles underpinning the operation of polymers for gas separations, including the solution-diffusion model and various structure/property relations, describes membrane fabrication technology, describes polymers believed to be used commercially for gas separations, and discusses some challenges associated with membrane materials development. A description of new classes of polymers being considered for gas separations, largely to overcome existing challenges or access applications that are not yet practiced commercially, is also provided. Some classes of polymers discussed in this review that have been the focus of much recent work include thermally rearranged (TR) polymers, polymers of intrinsic microporosity (PIMs), room-temperature ionic liquids (RTILs), perfluoropolymers, and high-performance polyimides.Figure optionsDownload full-size imageDownload as PowerPoint slide
Co-reporter:Zachary P. Smith, Rajkiran R. Tiwari, Thomas M. Murphy, David F. Sanders, Kristofer L. Gleason, Donald R. Paul, Benny D. Freeman
Polymer 2013 Volume 54(Issue 12) pp:3026-3037
Publication Date(Web):24 May 2013
DOI:10.1016/j.polymer.2013.04.006
Hydrogen sorption between −20 °C and 70 °C and at pressures up to 60 bara was determined for a polyimide and corresponding thermally rearranged (TR) polymers prepared from 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). Hydrogen sorption increased by a factor of approximately 2.6 between the polyimide precursor and the most highly converted TR polymer. This relative increase in sorption was similar to that observed for other non-polar light gases such as N2, O2, and CH4, but less than that observed for CO2. Additionally, H2 sorption was measured for other polymers commonly studied in the membrane literature, including AF 2400, Matrimid®, polysulfone, and poly(dimethylsiloxane). Among the glassy polymers tested, polysulfone had the lowest H2 sorption, and the HAB-6FDA TR polymer had the highest H2 sorption. A slight dual-mode curvature was observed for H2 sorption in several of the glassy materials, and it was most pronounced at low temperatures and for the TR polymers. Enthalpies of sorption were also determined. The most exothermic enthalpy of sorption occurred in Matrimid®, and a slightly endothermic enthalpy of sorption was observed in rubbery poly(dimethylsiloxane). Comparisons between gravimetric and volumetric sorption showed similar results.
Co-reporter:Wei Xie, Geoffrey M. Geise, Benny D. Freeman, Hae-Seung Lee, Gwangsu Byun, James E. McGrath
Journal of Membrane Science 2012 Volumes 403–404() pp:152-161
Publication Date(Web):1 June 2012
DOI:10.1016/j.memsci.2012.02.038
The influence of synthesis conditions (e.g., monomer concentration and membrane preparation protocol) on transport properties of polyamide thin-film composite (TFC) membranes prepared using m-phenylenediamine (MPD) and trimesoyl chloride (TMC) via interfacial polymerization is reported. For example, at 25 °C, NaCl rejection and permeate flux combinations of 99.6 ± 0.1% and 42 ± 3 L/(m2 h), respectively, were achieved in crossflow filtration using a 2000 ppm aqueous solution of NaCl and a transmembrane pressure difference of 225 psi (15.5 bar). Additionally, a sulfone diamine, disulfonated bis[4-(3-aminophenoxy)phenyl]sulfone (S-BAPS), was used in place of MPD to prepare TFC membranes. The resulting membranes had low NaCl rejection but somewhat higher permeate flux than MPD/TMC membranes. These membranes had reduced chlorine tolerance compared to those prepared using MPD as the diamine.Graphical abstractHighlights► Polyamide TFCs were prepared from m-phenylenediamine and trimesoyl chloride. ► TFC membranes have 0.4 ± 0.1% NaCl passage and permeate flux of 42 ± 3 L/(m2 h). ► Post-polymerization thermal treatment did not improve rejection or permeate flux. ► TFC membranes were synthesized from S-BAPS, a disulfonated sulfone diamine and TMC. ► S-BAPS based membranes have higher permeate flux and lower rejection than MPD based ones.
Co-reporter:Zachary P. Smith, David F. Sanders, Cláudio P. Ribeiro, Ruilan Guo, Benny D. Freeman, Donald R. Paul, James E. McGrath, Steve Swinnea
Journal of Membrane Science 2012 Volumes 415–416() pp:558-567
Publication Date(Web):1 October 2012
DOI:10.1016/j.memsci.2012.05.050
The solubilities of H2, N2, O2, CH4, and CO2 were determined over a range of pressures at 35 °C in a glassy, amorphous, ortho-functional polyimide prepared from 3,3′-dihydroxy-4,4′-diamino-biphenyl (HAB) and 2,2′-bis-(3,4-dicarboxyphenyl) hexafluoropropane dianhydride (6FDA). The HAB-6FDA polyimide was partially converted to its corresponding thermally rearranged (TR) polymer by thermal treatments at different times and temperatures. At 10 atm, solubility coefficients of H2, N2, O2, CH4, and CO2 increased by a factor of approximately two between the polyimide and the most highly converted TR polymer. Correlations between solubility and penetrant condensability were in good agreement with such correlations in other fluorinated polymers. Dual-mode sorption model parameters were determined from the sorption isotherms. The affinity constant, Henry's law solubility, and Langmuir capacity constant increased with gas condensability, and increases in the Langmuir capacity constant were observed as TR polymer conversion increased. Comparisons were made between the solubility selectivity of CO2/CH4, O2/N2, CH4/N2, and CO2/N2 with HAB-6FDA, its corresponding TR polymers, and with other polymers in the literature. Qualitatively, a decrease in solubility selectivity for gas pairs including CO2 correlates with imide and acetate loss during conversion.Graphical abstractHighlights▸ Solubility of H2, N2, O2, CH4, and CO2 increases as thermal rearrangement proceeds. ▸ Non-equilibrium free volume increases during thermal rearrangement. ▸ Solubility scales with critical temperature of the penetrant gas.
Co-reporter:Bryan D. McCloskey, Ho Bum Park, Hao Ju, Brandon W. Rowe, Daniel J. Miller, Benny D. Freeman
Journal of Membrane Science 2012 Volumes 413–414() pp:82-90
Publication Date(Web):15 September 2012
DOI:10.1016/j.memsci.2012.04.021
Surface deposition of polydopamine, PD, using facile aqueous-based chemistry at mild reaction conditions, was accomplished on reverse osmosis, nanofiltration, ultrafiltration, and microfiltration membranes. This surface treatment not only retained much of the membranes’ intrinsic pure water permeability, but also improved the fouling resistance of polypropylene microfiltration (MF), poly(tetrafluoroethylene) MF, poly(vinylidene fluoride) MF, poly(arylene ether sulfone) ultrafiltration (UF), polysulfone UF, polyamide (PA) nanofiltration, and PA reverse osmosis membranes, as measured using oil/water emulsion filtration. To demonstrate scalability of this approach, PD was applied to, and improved the fouling resistance of, membrane modules. Following PD deposition, membranes could be further modified by grafting fouling-resistant macromolecules, such as poly(ethylene glycol), to further improve fouling resistance of MF membranes.Highlights► Polydopamine was deposited on a variety of water purification membranes. ► The polydopamine modification improved the fouling resistance of all membranes studied. ► Poly(ethylene glycol) was covalently bound to polydopamine-modified membranes to further enhance membrane fouling resistance. ► Polydopamine deposition is easily scalable to membrane modules.
Co-reporter:Hua Li, Kevin K. Tung, D. R. Paul, Benny D. Freeman, Mark E. Stewart, and Jason C. Jenkins
Industrial & Engineering Chemistry Research 2012 Volume 51(Issue 21) pp:7138-7145
Publication Date(Web):April 30, 2012
DOI:10.1021/ie201905j
To better characterize the fundamentals of oxygen scavenging as a means to prepare high oxygen barrier polymer films, the oxidation of 1,4-polybutadiene, in the presence of a transition metal salt catalyst, cobalt neodecanoate, was studied at 30 °C. Oxygen uptake of 1,4-polybutadiene films was measured as a function of cobalt neodecanoate concentration. In these samples, oxygen mass uptake values as high as 15 wt % were observed, and the kinetics of oxidation were of the order of 10 days. Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis suggest that the oxidation was heterogeneous, with the film surface being highly oxidized and the film center being less oxidized. Interestingly, the oxygen uptake exhibited a maximum with catalyst loading, which is believed to be related to the heterogeneous nature of the oxidation process. Since antioxidants are typically added during the industrial scale preparation and the amount of antioxidants would affect the oxygen mass uptake value and oxidation kinetics, the importance of an antioxidant removal method and a normalized purification strategy were determined prior to oxygen uptake experiments.
Co-reporter:Cláudio P. Ribeiro, Benny D. Freeman, Douglass S. Kalika, Sumod Kalakkunnath
Journal of Membrane Science 2012 s 390–391() pp: 182-193
Publication Date(Web):
DOI:10.1016/j.memsci.2011.11.042
Co-reporter:David F. Sanders, Zachary P. Smith, Cláudio P. Ribeiro Jr., Ruilan Guo, James E. McGrath, Donald R. Paul, Benny D. Freeman
Journal of Membrane Science 2012 s 409–410() pp: 232-241
Publication Date(Web):
DOI:10.1016/j.memsci.2012.03.060
Co-reporter:Daniel R. Dreyer, Daniel J. Miller, Benny D. Freeman, Donald R. Paul, and Christopher W. Bielawski
Langmuir 2012 Volume 28(Issue 15) pp:6428-6435
Publication Date(Web):April 4, 2012
DOI:10.1021/la204831b
Herein we propose a new structure for poly(dopamine), a synthetic eumelanin that has found broad utility as an antifouling agent. Commercially available 3-hydroxytyramine hydrochloride (dopamine HCl) was polymerized under aerobic, aqueous conditions using tris(hydroxymethyl)aminomethane (TRIS) as a basic polymerization initiator, affording a darkly colored powder product upon isolation. The polymer was analyzed using a variety of solid state spectroscopic and crystallographic techniques. Collectively, the data showed that in contrast to previously proposed models, poly(dopamine) is not a covalent polymer but instead a supramolecular aggregate of monomers (consisting primarily of 5,6-dihydroxyindoline and its dione derivative) that are held together through a combination of charge transfer, π-stacking, and hydrogen bonding interactions.
Co-reporter:Wei Xie, Geoffrey M. Geise, Benny D. Freeman, Chang Hyun Lee, James E. McGrath
Polymer 2012 Volume 53(Issue 7) pp:1581-1592
Publication Date(Web):22 March 2012
DOI:10.1016/j.polymer.2012.01.046
Disulfonated poly(arylene ether sulfone)s are high glass transition temperature polymers, and their water and salt transport properties depend sensitively on thermal processing history. In this study, films of a 32 mol% disulfonated poly(arylene ether sulfone) random copolymer (BPS-32), polymerized in the potassium counter-ion form, were acidified using solid state and solution routes. The resulting acid counter-ion form materials were then converted to sodium, potassium, and calcium counter-ion forms via ion exchange. Additionally, several films were subjected to various thermal treatments in the solid state. Water uptake as well as water and NaCl permeability of these BPS-32 films were measured. Acidification via immersion of BPS-32 films in boiling sulfuric acid solution increased water uptake, and water and salt permeability increased. Exposure of samples to elevated temperature also influenced transport properties. For example, immersing BPS-32 films in boiling water for 4 h increased water sorption by 50%, water permeability by 2.3 times, and NaCl permeability by 8 times. The counter-ion form of the sulfonated polymer influenced the polymer’s transport properties, but these effects were weaker than the effect of thermal treatment. Generally, the BPS-32 samples prepared with different processing histories followed a trade-off between water/salt permeability selectivity and water permeability. These results suggest that, like many other glassy polymers, thermal processing history influences small molecule transport in these materials.
Co-reporter:Hua Li, Benny D. Freeman, O. Max Ekiner
Journal of Membrane Science 2011 Volume 369(1–2) pp:49-58
Publication Date(Web):1 March 2011
DOI:10.1016/j.memsci.2010.11.024
A series of poly(urethane-urea)s were synthesized using 4,4′-methylenediphenyl diisocyanate (MDI), various polyether diols, and ethylene diamine (EDA). The polyethers were poly(ethylene glycol) (PEG) 2000, poly(propylene glycol) (PPG) 2700, poly(tetramethylene ether glycol) (Terathane®) 2000, Terathane® 2900, and a mixture of PEG 2000 and Terathane® 2000. The polymer based on PEG 2000 is semi-crystalline at room temperature, and the others are amorphous. The fractional free volume (FFV) increases as polyether molecular weight and soft segment content increase. The permeability of these materials to He, H2, O2, N2, CO2 and CH4 was measured at 35 °C, and gas permeability increased with increasing FFV. The physical properties and gas transport characteristics of these poly(urethane-urea)s were compared with those of rubbery networks based on crosslinked PEG and PPG.Research highlights▶ We synthesized a series of poly(urethane-urea)s were using MDI and various polyethers. ▶ Polyether structure influences fractional free volume and gas transport performance. ▶ PPG and Terathane® based polymers have lower water uptake than PEG based polymers.
Co-reporter:Elizabeth M. Van Wagner, Alyson C. Sagle, Mukul M. Sharma, Young-Hye La, Benny D. Freeman
Journal of Membrane Science 2011 Volume 367(1–2) pp:273-287
Publication Date(Web):1 February 2011
DOI:10.1016/j.memsci.2010.11.001
To improve fouling resistance, polyamide reverse osmosis (XLE) and nanofiltration (NF90) membranes were modified by grafting poly(ethylene glycol) (PEG) diglycidyl ether (PEGDE) to their top surfaces from aqueous solution. The effect of PEG molecular weight (200 vs. 1000) and treatment solution concentration (1% (w/w) vs. 15% (w/w)) on water flux and NaCl rejection was measured. PEGDE grafting density as well as surface properties of modified and unmodified membranes, including charge, hydrophilicity and roughness, were measured and compared. The fouling resistance of modified membranes to charged surfactants (i.e., sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (DTAB)) and emulsions of n-decane and these charged surfactants was compared to that of unmodified membranes. In general, modified membranes exhibited improved fouling resistance and an improved ability to be cleaned after fouling compared to unmodified membranes. Fouling resistance increased with increasing PEG molecular weight, but showed little dependence on treatment solution concentration, suggesting that further improvements in membrane fouling resistance might be obtained by using lower concentrations of higher molecular weight PEG for surface modification.Research highlights▶ Top surface of polyamide RO and NF membranes was grafted with PEGDE from aqueous solution. ▶ Studied effect of PEGDE molecular weight and solution concentration on performance and surface properties. ▶ Measured flux, NaCl rejection, grafting density, hydrophilicity, surface roughness and charge. ▶ Measured fouling resistance to charged surfactants (SDS, DTAB) and n-decane/surfactant emulsions. ▶ Fouling resistance increased with increasing PEG MW, but was independent of solution concentration.
Co-reporter:Katrina Kratz;Wei Xie;Albert Lee;Todd Emrick
Macromolecular Materials and Engineering 2011 Volume 296( Issue 12) pp:1142-1148
Publication Date(Web):
DOI:10.1002/mame.201100064
Co-reporter:Wei Xie, Hao Ju, Geoffrey M. Geise, Benny D. Freeman, James I. Mardel, Anita J. Hill, and James E. McGrath
Macromolecules 2011 Volume 44(Issue 11) pp:4428-4438
Publication Date(Web):May 12, 2011
DOI:10.1021/ma102745s
The influence of cation form and degree of sulfonation on free volume, as probed via positron annihilation lifetime spectroscopy (PALS), and water and salt transport properties was determined in a systematic series of directly copolymerized disulfonated poly(arylene ether sulfone) random copolymers. Polymer samples were studied in both the dry and hydrated states. PALS-based estimates of free volume in the dry polymers were compared with those estimated using density and the Bondi group contribution method, and PALS-based free volume data for hydrated polymers were correlated with water and salt transport properties. The transport properties depend strongly on free volume cavity size. Samples with larger free volume elements have higher water and salt solubility, diffusivity, and permeability and lower water/salt diffusivity and permeability selectivity. Sorption of water alters the characteristic free volume of the polymer matrix by two competing mechanisms: water molecules partially occupy the original free volume in the initially dry polymer, thereby reducing free volume cavity size, and water swells the polymer matrix therefore increasing the mean free volume size as a result of increased polymer chain plasticization. The importance of the second effect increases as water uptake and, thus, plasticization increases.
Co-reporter:Cláudio P. Ribeiro Jr., Benny D. Freeman, Donald R. Paul
Journal of Membrane Science 2011 377(1–2) pp: 110-123
Publication Date(Web):
DOI:10.1016/j.memsci.2011.04.032
Co-reporter:Yingying Jiang, Frank T. Willmore, David Sanders, Zachary P. Smith, Claudio P. Ribeiro, Cara M. Doherty, Aaron Thornton, Anita J. Hill, Benny D. Freeman, Isaac C. Sanchez
Polymer 2011 Volume 52(Issue 10) pp:2244-2254
Publication Date(Web):4 May 2011
DOI:10.1016/j.polymer.2011.02.035
Within a polymer thin film, free volume elements have a wide range of size and topology. This broad range of free volume element sizes determines the ability for a polymer to perform molecular separations. Herein, six permeable thermally rearranged (TR) polymers and their precursors were studied. Using atomistic models, cavity size (free volume) distributions determined by a combination of molecular dynamics and Monte Carlo methods were consistent with experimental observation that TR polymers are more permeable than their precursors. The cavity size distributions determined by simulation were also consistent with free volume distributions determined by positron annihilation lifetime spectroscopy. The diffusion, solubility and permeation of gases in TR polymers and their precursors were also simulated at 308 K, with results that agree qualitatively with experimental data.
Co-reporter:Cláudio P. Ribeiro Jr., Benny D. Freeman, Donald R. Paul
Polymer 2011 Volume 52(Issue 18) pp:3970-3983
Publication Date(Web):18 August 2011
DOI:10.1016/j.polymer.2011.06.042
The advantages of the Maxwell–Stefan (MS) formulation over Fick’s law to describe multicomponent mass transfer are well recognized. However, in its original form, the MS equations are written in terms of mole fractions, which are ill-defined if one of the components is a polymer. To overcome this problem, a revised formulation of the MS equations written in terms of volume fractions is proposed. The resulting equations satisfy the Gibbs–Duhem restriction and are fully consistent with the multicomponent Flory–Huggins theory in the sense that we avoid any assumption regarding the size of the penetrants or of the polymer segments. This formulation is combined with the Flory–Huggins model to derive general expressions for modeling steady-state mass transfer across polymer films for both pure components and binary mixtures. The proposed MS formulation is used to analyze the separation of carbon dioxide/ethane mixtures by a cross-linked poly(ethylene oxide) membrane. For this particular system, at T≥o25CT≥25oC, mixed-gas permeability coefficients can be predicted with an average deviation of less than 5% without any input from multicomponent permeation data.
Co-reporter:Wei Xie, Joe Cook, Ho Bum Park, Benny D. Freeman, Chang Hyun Lee, James E. McGrath
Polymer 2011 Volume 52(Issue 9) pp:2032-2043
Publication Date(Web):19 April 2011
DOI:10.1016/j.polymer.2011.02.006
Water and sodium chloride solubility, diffusivity and permeability in disulfonated poly(arylene ether sulfone) (BPS) copolymers were measured for both acid and salt form samples at sulfonation levels from 20 to 40 mol percent. The hydrophilicity of these materials, based on water uptake, increased significantly as sulfonation level increased. The water permeability of BPS materials in both the salt and acid forms increases more than one order of magnitude as sulfonation level increases from 20% to 40%, while NaCl permeability increases by two orders of magnitude. The water and salt diffusivity and permeability were correlated with water uptake, consistent with expectations from free volume theory. In addition, a tradeoff was observed between water/salt solubility, diffusivity, and permeability selectivity and water solubility, diffusivity and permeability, respectively. This finding suggests a water/salt permeability/selectivity tradeoff, similar to that operative in gas separation polymers, in this family of polymers.
Co-reporter:Hua Li, Kevin K. Tung, D.R. Paul, Benny D. Freeman
Polymer 2011 Volume 52(Issue 13) pp:2772-2783
Publication Date(Web):8 June 2011
DOI:10.1016/j.polymer.2011.04.019
Oxygen mass uptake was measured in 1,4-polybutadiene (PB) films undergoing cobalt-catalyzed oxidation in air. Films thicker than approximately 50 μm showed an increase in oxygen uptake per unit polymer mass as film thickness increased, while oxygen uptake per unit film area remained independent of thickness, suggesting that oxidation was heterogeneous and proceeded essentially as an oxidized front penetrating into the film from the surfaces exposed to oxygen. In contrast, oxidation in films thinner than about 28 μm proceeds homogeneously, with oxygen uptake per unit mass being essentially independent of thickness. In oxidized samples, oxygen and nitrogen permeability decreased by more than two orders of magnitude relative to permeability values in unoxidized samples. In thicker films, a two-phase model, based upon high levels of oxidation in a thin skin at the surface of PB and relatively low levels of oxidation in the core of the films, was used to describe gas permeability data and estimate the oxygen and nitrogen permeability in fully oxidized PB.
Co-reporter:Victor A. Kusuma, Benny D. Freeman, Stephan L. Smith, Alexander L. Heilman, Douglass S. Kalika
Journal of Membrane Science 2010 Volume 359(1–2) pp:25-36
Publication Date(Web):1 September 2010
DOI:10.1016/j.memsci.2010.01.049
3-[Tris-(trimethylsiloxy)silyl] propyl acrylate (TRIS-A) was copolymerized with poly(ethylene glycol) diacrylate (PEGDA), and the gas transport and physical properties of the resulting copolymers were characterized. Introduction of TRIS-A led to increased polymer fractional free volume and strong broadening of the glass–rubber relaxation without a significant shift in glass transition temperature in samples containing up to 80 wt% TRIS-A. Gas permeability increased significantly as TRIS-A content increased: for instance, addition of 80 wt% TRIS-A increased CO2 permeability from 110 to 800 barrer. The strongly non-polar character of TRIS-A, however, resulted in progressively lower CO2 affinity for the polymer network, leading to decreased CO2/light gas selectivity with increasing TRIS-A content.
Co-reporter:Yuan-Hsuan Wu, Ho Bum Park, Teruhiko Kai, Benny D. Freeman, Douglass S. Kalika
Journal of Membrane Science 2010 Volume 347(1–2) pp:197-208
Publication Date(Web):1 February 2010
DOI:10.1016/j.memsci.2009.10.025
Crosslinked poly(ethylene glycol) (PEG) free-standing films were prepared by UV-induced photopolymerization of poly(ethylene glycol) diacrylate (PEGDA) crosslinker in the presence of varying amounts of water or monofunctional poly(ethylene glycol) acrylate (PEGA). The crosslinked PEGDA films exhibited polymerization induced phase separation (PIPS) when the water content of the prepolymerization mixture was greater than 60 wt%. These phase separated films contain pores that scatter visible light, rendering them translucent or opaque. Visible light absorbance measurements, water uptake, water permeability, and salt kinetic desorption experiments were used to characterize the structure of these phase separated, crosslinked hydrogels. The films with PIPS exhibited a porous morphology in CryoSEM studies. Dead-end filtration experiments using deionized water and 1 g/l bovine serum albumin (BSA) solutions were performed to explore the fundamental transport and fouling properties of these materials. The total flux of pure water through the films after prior exposure to BSA solution was nearly equal to that measured for the as-prepared material, indicating that these PEGDA films resist fouling by BSA under the conditions studied.
Co-reporter:Hao Ju, Alyson C. Sagle, Benny D. Freeman, James I. Mardel, Anita J. Hill
Journal of Membrane Science 2010 Volume 358(1–2) pp:131-141
Publication Date(Web):15 August 2010
DOI:10.1016/j.memsci.2010.04.035
Three series of crosslinked poly(ethylene oxide) (XLPEO) hydrogel materials were synthesized via UV-photopolymerization of aqueous solutions containing (1) poly(ethylene glycol) diacrylate (PEGDA) (n = 10), (2) PEGDA (n = 13), and (3) mixtures of PEGDA (n = 13) and poly(ethylene glycol) acrylate (PEGA) (n = 7), where n is the number of ethylene oxide groups. The water content in the prepolymerization mixture was varied from 0 to 80 wt.% and resulted in XLPEO hydrogels having equilibrium water contents ranging from 0.3 to 0.8 (v/v). These hydrophilic XLPEO hydrogels are highly water permeable. The NaCl transport properties of XLPEO were studied using direct permeation and kinetic desorption methods, and good agreement between these two methods was observed. Generally, NaCl permeability in XLPEO increased from less than 0.1–2 (×10−6 cm2/s) as prepolymerization water content increased from 0 to 80 wt.%. NaCl permeability also increased with increasing PEGDA chain length and was higher in samples prepared with PEGA in the prepolymerization solution, presumably due to decreases in effective crosslink density. There is a tradeoff between water permeability and water/salt selectivity: materials with high water permeability typically exhibit low water/salt selectivity, and vice versa. NaCl permeability and diffusivity were strongly correlated with free volume in the hydrogels. Free volume was characterized based on both equilibrium water content and positron annihilation lifetime spectroscopy (PALS). In these samples, the equilibrium water content was proportional to the fractional free volume from the PALS measurements.
Co-reporter:Yuan-Hsuan Wu, Ying-Ling Liu, Yung Chang, Akon Higuchi, Benny D. Freeman
Journal of Membrane Science 2010 Volume 348(1–2) pp:47-55
Publication Date(Web):15 February 2010
DOI:10.1016/j.memsci.2009.10.039
UV photopolymerization was used to prepare films from N-vinyl-2-pyrrolidone (NVP) crosslinked with N,N′-methylenebisacrylamide (MBAA). These samples were crosslinked in the presence of water. Although the initial mixtures of water, NVP and MBAA were optically transparent, the final films were white, indicating that phase separation occurred during photopolymerization. The influence of UV intensity on the crosslinked NVP film structure was characterized using CryoSEM for cross-sectional imaging and Bio-AFM for imaging surface morphology. The influence of UV intensity on transport properties was characterized using dead-end filtration to measure water permeability and molecular weight cutoff (MWCO). Samples polymerized at high UV intensity had 2.7 times higher water permeability than those polymerized at low UV intensity, even though the structure, as probed via SEM and AFM, shows little to no significant changes. Higher UV intensity also led to somewhat higher MWCO values, indicating a tradeoff between water permeability and solute sieving characteristics.
Co-reporter:Bryan D. McCloskey, Hao Ju and Benny D. Freeman
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 1) pp:366-373
Publication Date(Web):November 11, 2009
DOI:10.1021/ie901197u
A series of poly(ethylene glycol) diglycidyl ether−cross-linked chitosan (chi−PEG hybrid) films were prepared to elucidate their potential as fouling-resistant ultrafiltration (UF) membrane coating layers. Water permeability increased as the poly(ethylene glycol) diglycidyl ether to chitosan ratio in the prepolymerization mixture increased due to increased porosity in the polymer matrix resulting from phase separation during polymerization. Composite membranes for oil−water emulsion filtration were prepared by coating an optimized member of the chi−PEG hybrid family onto a commercial polysulfone ultrafiltration membrane. Scanning electron microscopy (SEM), attenuated total reflectance Fourier transform infrared spectroscopy (FTIR), and pure water permeance measurements indicated that, depending on the concentration of chitosan in the coating solution, the coating layer thickness could be controlled, so water permeance could be optimized. These composite membranes exhibited water flux values more than 5 times higher than that of uncoated membranes after 1 day of oily water crossflow filtration, indicating that the hydrophilic polymer coating significantly enhanced the fouling resistance of the underlying polysulfone membrane. The organic rejection of the coated membranes was also slightly higher than that of the uncoated polysulfone membranes.
Co-reporter:David T. Allen and Benny D. Freeman
Industrial & Engineering Chemistry Research 2010 Volume 49(Issue 23) pp:11857-11858
Publication Date(Web):November 24, 2010
DOI:10.1021/ie1021249
Co-reporter:Cláudio P. Ribeiro JR.
Journal of Polymer Science Part B: Polymer Physics 2010 Volume 48( Issue 4) pp:456-468
Publication Date(Web):
DOI:10.1002/polb.21907
Abstract
Experimental solubility and sorptive dilation data are reported for carbon dioxide and ethane in a crosslinked poly(ethylene oxide) (XLPEO) rubbery copolymer. Five different temperatures (253 ≤ T(K) ≤ 308) were considered, with a maximum gas pressure of 2.09 MPa (20.6 atm). The polymer was prepared by photopolymerization of a solution containing 70 wt % poly(ethylene glycol) methyl ether acrylate (PEGMEA) and 30 wt % poly(ethylene glycol) diacrylate (PEGDA). Sorption isotherms were described by the Flory-Huggins model. For each gas, the Flory-Huggins interaction parameter was a decreasing function of temperature and did not show a composition dependence. Dilation and sorption data were combined to calculate the partial molar volume (PMV) of the gases in the polymer, which was an increasing function of temperature. Based on a comparison with literature data for a XLPEO homopolymer prepared from pure PEGDA over the same range of operating conditions, an effect of the network composition on both gas solubility and PMV was found. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 456–468, 2010
Co-reporter:Benny D. Freeman
Polymer 2010 Volume 51(Issue 22) pp:5005-5006
Publication Date(Web):15 October 2010
DOI:10.1016/j.polymer.2010.08.041
Co-reporter:Victor A. Kusuma, Gabriella Gunawan, Zachary P. Smith, Benny D. Freeman
Polymer 2010 Volume 51(Issue 24) pp:5734-5743
Publication Date(Web):12 November 2010
DOI:10.1016/j.polymer.2010.09.069
Pure gas permeability coefficients of a series of copolymers based on polar, hydrophilic poly(ethylene glycol) dimethacrylate, n = 14 (PEGDMA) and siloxane-based co-monomer, [methyl bis(trimethylsiloxy)silyl] propyl glycerol methacrylate (SiGMA) are reported. SiGMA is miscible with PEGDMA and able to form homogeneous films. SiGMA contains a bulky siloxane-based end group, which acts to increase permeability, and an –OH pendant group, which increases miscibility with polar co-monomers, such as PEGDMA. As the SiGMA content in these copolymers increases to 53 vol%, CO2 permeability increases from 95 to 255 barrer, while CO2/N2 and CO2/H2 pure gas selectivities decrease from 58 to 20 and 6.4 to 3.2, respectively. At the same time, fractional free volume of the copolymer increases from 0.118 to 0.140. Comparisons to a similar copolymer system are made to rationalize the permeability and selectivity trends of this series of copolymers.
Co-reporter:Cláudio P. Ribeiro Jr., Benny D. Freeman
Polymer 2010 Volume 51(Issue 5) pp:1156-1168
Publication Date(Web):2 March 2010
DOI:10.1016/j.polymer.2010.01.012
Mixed-gas CO2/C2H6 sorption and dilation in a cross-linked poly(ethylene oxide) copolymer were studied at temperatures ranging from −20 to 35 °C. The polymer was prepared by photopolymerization of a solution containing 70 wt.% poly(ethylene glycol) methyl ether acrylate (PEGMEA) and 30 wt.% poly(ethylene glycol) diacrylate (PEGDA). Four different gas mixtures (10, 25, 50 and 70 mol% CO2) were considered at operating pressures up to 21 atm. At a given temperature, polymer dilation increased with pressure and CO2 content. Compared to pure-gas values, CO2 solubility was higher in the presence of ethane, an effect whose extent increased with decreasing temperature. Ethane solubility in the polymer also increased in the presence of CO2 compared to the pure-gas value at T ≥ 25 °C. However, at T ≤ 0 °C, the presence of carbon dioxide initially reduced ethane solubility. As the fugacity of CO2 in the mixture increased and the polymer dilated, ethane solubility progressively increased, eventually surpassing the pure-gas value. The multicomponent Flory–Huggins model could describe the pure- and mixed-gas data simultaneously, provided that an empirical composition dependence was included in the interaction parameters for T < 25 °C.
Co-reporter:Bryan D. McCloskey, Ho Bum Park, Hao Ju, Brandon W. Rowe, Daniel J. Miller, Byeong Jae Chun, Katherine Kin, Benny D. Freeman
Polymer 2010 Volume 51(Issue 15) pp:3472-3485
Publication Date(Web):8 July 2010
DOI:10.1016/j.polymer.2010.05.008
The influence of polydopamine (PDOPA) deposition and poly(ethylene glycol) (PEG) grafting on pure water flux and bovine serum albumin (BSA) adhesion of two polysulfone ultrafiltration (UF) membranes, a poly(vinylidene fluoride) microfiltration (MF) membrane, and a polyamide reverse osmosis (RO) membrane is reported. When modified with PDOPA, all membranes exhibited a systematic reduction in protein adhesion. For example, 90 min of PDOPA deposition led to at least 96% reduction in BSA adhesion to these membranes at neutral pH. BSA adhesion was further reduced by subsequent PEG grafting to PDOPA (PDOPA-g-PEG). The membranes’ pure water flux values (i.e., with no foulants present) were influenced to different extents by PDOPA and PDOPA-g-PEG modifications. In the porous membranes (i.e., the UF and MF membranes), the pure water flux reduction due to these modifications correlated with membrane pore size, with the smallest flux reductions observed in the MF membrane (e.g., <1% flux reduction for all PDOPA modification times considered), which have the largest pores, and the largest flux reductions occurring in UF membranes (e.g., a 40% flux reduction after 90 min of PDOPA deposition), which have pore sizes on the order of the PDOPA deposition thickness. The RO membranes, which are essentially non-porous, exhibited a flux reduction of 25% after 90 min of PDOPA deposition.
Co-reporter:Yuan-Hsuan Wu, Benny D. Freeman
Journal of Membrane Science 2009 Volume 344(1–2) pp:182-189
Publication Date(Web):15 November 2009
DOI:10.1016/j.memsci.2009.07.050
Crosslinked N-vinyl-2-pyrrolidone (NVP) free-standing films were prepared by UV-induced photopolymerization in the presence of water using N,N′-methylenebisacrylamide (MBAA) as the crosslinker. A series of crosslinked films were prepared at various prepolymerization water contents and NVP/MBAA ratios. The films underwent phase separation during polymerization. Cryogenic scanning electron microscope (CryoSEM) was used to characterize the morphology of the films. The influence of monomer/crosslinker ratio and prepolymerization water content on morphology and water transport was characterized. Higher water content or higher monomer content in the prepolymerization mixture led to more open structures and, in turn, higher water permeability.
Co-reporter:Victor A. Kusuma, Benny D. Freeman, Matthew A. Borns, Douglass S. Kalika
Journal of Membrane Science 2009 Volume 327(1–2) pp:195-207
Publication Date(Web):5 February 2009
DOI:10.1016/j.memsci.2008.11.022
Three series of amorphous cross-linked poly(ethylene oxide) (XLPEO) rubbers were prepared by photopolymerization of prepolymer solutions containing poly(ethylene glycol) diacrylate (PEGDA) cross-linker and one of three structurally similar short chain acrylate co-monomers: 2-hydroxyethyl acrylate (2-HEA), ethylene glycol methyl ether acrylate (EGMEA) and 2-ethoxyethyl acrylate (2-EEA). Copolymerization with the mono-functional acrylates led to the insertion of short side branches along the network backbone, terminated by either hydroxy, methoxy or ethoxy functional groups. Permeability measurements for the copolymers (35 °C) are presented for CO2, H2, CH4, O2 and N2; corresponding solubility and diffusivity data are presented for CO2 and CH4. The side branches significantly influenced the thermal and gas transport properties of the polymers: methoxy and ethoxy terminated side-branches modestly increased fractional free volume and gas permeability. This effect was more pronounced by the introduction of ethoxy-terminated 2-EEA, while the presence of hydroxy terminated 2-HEA side-branches reduced free volume, resulting in a strong decrease in gas permeability with increasing co-monomer content. In each case, gas diffusivity correlated with polymer fractional free volume, while gas solubility was a function of both free volume characteristics and the corresponding concentration and accessibility of polar groups within the networks. The resulting selectivity ratios reflected variations in penetrant affinity and size discrimination as a function of copolymer composition. This study highlights the significant changes in various XLPEO properties that can be achieved by making small changes to its network structure.
Co-reporter:L.M. Robeson, B.D. Freeman, D.R. Paul, B.W. Rowe
Journal of Membrane Science 2009 Volume 341(1–2) pp:178-185
Publication Date(Web):30 September 2009
DOI:10.1016/j.memsci.2009.06.005
A large database of permeability values for common gases (He, H2, O2, N2, CO2 and CH4) has been employed in the following correlation: Pj=kPin where Pi and Pj are the permeabilities of gases i and j; the indices are chosen such that the value of n is >1.0. The plots of log Pi versus log Pj show linear behavior over nine orders of magnitude implying solution–diffusion behavior persists over the entire range of permeabilities existing in known dense polymeric materials. The scatter of data around the linear correlation for each gas pair was modest over the entire range of permeability. It was found that n correlates with the kinetic diameter of the specific gases of the pair by a relationship: n − 1∼(dj/di)2 − 1 in agreement with theory. Correlations exist between n and k for the noted relationship and nu and ku of the upper bound relationship of Pi=kuαijnu where αij = Pi/Pj. The experimental values of n − 1 enable the determination of a new set of kinetic diameters showing excellent agreement between theory and experimental results. The value of 1/k was found to be virtually an exact fit with the relationship developed by Freeman in predicting the value of ku for the upper bound relationship using the new set of kinetic diameters where the calculations were constrained to minimize the error in (n − 1) = (dj/di)2 − 1. The significance of these results includes a new set of kinetic diameters predicted by theory and agreeing with experimental data with accuracy significantly improved over the zeolite determined diameters previously employed to correlate diffusion selectivity in polymers. One consequence of this analysis is that the kinetic diameter of CO2 is virtually identical to that of O2. Additionally, the theoretical relationship developed by Freeman for the upper bound prediction is further verified by this analysis which correlates the average permeability for polymeric materials as compared to the few optimized polymer structures offering upper bound performance.
Co-reporter:Elizabeth M. Van Wagner, Alyson C. Sagle, Mukul M. Sharma, Benny D. Freeman
Journal of Membrane Science 2009 Volume 345(1–2) pp:97-109
Publication Date(Web):1 December 2009
DOI:10.1016/j.memsci.2009.08.033
Crossflow filtration experiments were performed to characterize the water flux and NaCl rejection of three commercial polyamide reverse osmosis (RO) membranes (LE and XLE from DOW Water Solutions and AG from GE Water and Process Technologies). Thorough cleaning of the crossflow system, combined with following the manufacturer's recommended pretreatment and test conditions (i.e., feed pressure, flowrate, temperature, feed pH, and feed filtration) resulted in measured performance values consistent with manufacturer benchmarks. Correction for the effect of concentration polarization also proved important. The influence of feed pH and continuous feed filtration on water flux and salt rejection was characterized. While rejection was strongly affected by feed pH, water flux was essentially unaffected. Continuous filtration of the feed led to higher water flux and lower salt rejection than that observed in experiments with unfiltered feed, suggesting fouling of the membrane surfaces by unfiltered feed. The flux and rejection of these three membranes obeyed a general tradeoff relation: membranes that exhibited higher flux had lower rejection and vice versa.
Co-reporter:Victor A. Kusuma, Scott Matteucci, Benny D. Freeman, Michael K. Danquah, Douglass S. Kalika
Journal of Membrane Science 2009 Volume 341(1–2) pp:84-95
Publication Date(Web):30 September 2009
DOI:10.1016/j.memsci.2009.05.043
Gas transport properties of rubbery cross-linked poly(ethylene oxide) films containing short phenoxy-terminated pendant chains are reported. Poly(ethylene glycol) diacrylate (PEGDA) was UV-polymerized with poly(ethylene glycol) phenyl ether acrylate co-monomers of two different ethylene oxide repeat unit lengths: n = 2 (DEGPEA) and n = 4 (PEGPEA). Although fractional free volume increased with increasing co-monomer concentration, gas permeability did not rise accordingly. For instance, while FFV increased from 0.120 to 0.135 in both series of copolymers, CO2 permeability went from 110 to 35 barrer (DEGPEA) or to 100 barrer (PEGPEA). At the same time, glass transition temperature increased from −37 to −12 °C (DEGPEA) or to −28 °C (PEGPEA). The observed decrease in chain mobility with phenoxy-terminated co-monomer content indicated by increasing glass–rubber transition temperature apparently had a stronger influence on gas transport properties than the increase in fractional free volume.
Co-reporter:Alyson C. Sagle, Elizabeth M. Van Wagner, Hao Ju, Bryan D. McCloskey, Benny D. Freeman, Mukul M. Sharma
Journal of Membrane Science 2009 340(1–2) pp: 92-108
Publication Date(Web):
DOI:10.1016/j.memsci.2009.05.013
Co-reporter:Hao Ju, Bryan D. McCloskey, Alyson C. Sagle, Victor A. Kusuma, Benny D. Freeman
Journal of Membrane Science 2009 330(1–2) pp: 180-188
Publication Date(Web):
DOI:10.1016/j.memsci.2008.12.054
Co-reporter:Alyson C. Sagle, Hao Ju, Benny D. Freeman, Mukul M. Sharma
Polymer 2009 50(3) pp: 756-766
Publication Date(Web):
DOI:10.1016/j.polymer.2008.12.019
Co-reporter:Hao Ju, Bryan D. McCloskey, Alyson C. Sagle, Yuan-Hsuan Wu, Victor A. Kusuma, Benny D. Freeman
Journal of Membrane Science 2008 Volume 307(Issue 2) pp:260-267
Publication Date(Web):15 January 2008
DOI:10.1016/j.memsci.2007.09.028
Potential fouling reducing coating materials were synthesized via free-radical photopolymerization of aqueous solutions of poly(ethylene glycol) diacrylate (PEGDA). Crosslinked PEGDA (XLPEGDA) exhibited high water permeability and good fouling resistance to oil/water mixtures. Water permeability increased strongly with increasing the water content in the prepolymerization water mixture, going from 10 to 150 L μm/(m2 h bar) as prepolymerization water content increased from 60 to 80 wt.%. However, molecular weight cutoff decreased as water content increased. These materials were applied to polysulfone (PSF) UF membranes to form coatings on the surface of the PSF membranes. Oil/water crossflow filtration experiments showed that the coated PSF membranes had water flux values 400% higher than that of an uncoated PSF membrane after 24 h of operation, and the coated membranes had higher organic rejection than the uncoated membranes.
Co-reporter:Scott Matteucci, Victor A. Kusuma, David Sanders, Steve Swinnea, Benny D. Freeman
Journal of Membrane Science 2008 Volume 307(Issue 2) pp:196-217
Publication Date(Web):15 January 2008
DOI:10.1016/j.memsci.2007.09.035
Titanium dioxide (TiO2) nanoparticles were dispersed via solution processing in poly(1-trimethylsilyl-1-propyne) (PTMSP) to form nanocomposite films. Nanoparticle dispersion was investigated using atomic force microscopy and transmission electron microscopy. At low-particle loadings, nanoparticles were dispersed individually and in nanoscale aggregates. At high-particle loadings, some nanoparticles formed micron-sized aggregates. The gas transport and density exhibited a strong dependence on nanoparticle loading. At low-TiO2 loadings, the composite density was similar to or slightly higher than that predicted by a two-phase additive model. However, at particle loadings exceeding approximately 7 nominal vol.%, the density was markedly lower than predicted, suggesting that the particles induced the creation of void space within the nanocomposite. For example, when the TiO2 nominal volume fraction was 0.35, the polymer/particle composite density was 40% lower than expected based on a two-phase additive model for density. At low-nanoparticle loading, light gas permeability was lower than that of the unfilled polymer. At higher nanoparticle loadings, light gas permeability (i.e., CO2, N2, and CH4) increased to more than four times higher than in unfilled PTMSP. At most, selectivity changed only slightly with particle loading.
Co-reporter:Cláudio P. Ribeiro Jr., and Benny D. Freeman
Macromolecules 2008 Volume 41(Issue 23) pp:9458-9468
Publication Date(Web):November 7, 2008
DOI:10.1021/ma801478c
Experimental gas solubility and sorptive dilation data are reported for carbon dioxide and ethane in a cross-linked poly(ethylene oxide) rubber prepared by photopolymerization of poly(ethlyene glycol)diacrylate. Five different operating temperatures (253 ≤ T (K) ≤ 308) were considered, with a maximum gas pressure of 2.16 MPa (21.3 atm). The importance of taking sorptive dilation into account in the determination of gas solubility in polymers by the pressure−decay method was demonstrated. Sorption isotherms in terms of gas fugacity were described by the Flory−Huggins model. In the case of ethane, the Flory−Huggins interaction parameter was a decreasing function of temperature. In contrast, for carbon dioxide, a single parameter represented all isotherms. Dilation and sorption data were combined to calculate the partial molar volume (PMV) of the gases in the polymer, which was an increasing function of temperature. The PMV data were compared to the available literature data for other rubbery polymers and liquids. The chemical structure of the polymer influenced the PMV of the sorbed gas, and a correlation between matrix (i.e., solvent or polymer) solubility parameter and PMV was found.
Co-reporter:HoBum Park ;BennyD. Freeman ;Zhong-Bio Zhang Dr.;Mehmet Sankir Dr.;JamesE. McGrath
Angewandte Chemie International Edition 2008 Volume 47( Issue 32) pp:6019-6024
Publication Date(Web):
DOI:10.1002/anie.200800454
Co-reporter:Roy D. Raharjo, Benny D. Freeman, Donald R. Paul, Giulio C. Sarti, Edgar S. Sanders
Journal of Membrane Science 2007 Volume 306(1–2) pp:75-92
Publication Date(Web):1 December 2007
DOI:10.1016/j.memsci.2007.08.014
Pure and mixed gas n-C4H10 and CH4 permeability coefficients in poly(dimethylsiloxane) (PDMS) are reported at temperatures from −20 to 50 °C. CH4 partial pressures range from 1.5 to 14.6 atm, and n-C4H10 partial pressures range from 0.09 to 1.8 atm. CH4 permeability increases with increasing n-C4H10 concentration in the polymer. For example, at −20 °C, CH4 permeability increases to approximately twice its pure gas value, from 730 to 1500 Barrer, as n-C4H10 concentration increases from 0 to 75 cm3(STP)/cm3 polymer. In contrast, n-C4H10 permeabilities in the mixtures are essentially unaffected by the presence of CH4. Diffusion coefficients of n-C4H10 and CH4 in mixtures were calculated using mixture permeability data and mixture solubility data. n-C4H10-induced plasticization increases n-C4H10 and CH4 diffusion coefficients in mixtures. Mixed gas n-C4H10/CH4 permeability, solubility, and diffusivity selectivities are lower than those estimated from pure gas measurements due to the higher CH4 permeability, solubility, and diffusion coefficients in mixtures. The mixed gas permeability selectivity increases as n-C4H10 fugacity increases and temperature decreases. In contrast, mixture diffusivity selectivity varies little with temperature or n-C4H10 concentration. The increase in mixed gas permeability selectivity with increasing n-C4H10 activity and decreasing temperature is mainly due to increases in n-C4H10/CH4 solubility selectivity. Based upon a Maxwell–Stefan analysis, the influence of coupling effects on permeation properties were negligible.
Co-reporter:Scott Kelman, Haiqing Lin, Edgar S. Sanders, Benny D. Freeman
Journal of Membrane Science 2007 Volume 305(1–2) pp:57-68
Publication Date(Web):15 November 2007
DOI:10.1016/j.memsci.2007.07.035
Ethane can be a major component of natural gas, and it forms a maximum pressure azeotrope with carbon dioxide, which can hinder carbon dioxide removal if distillation is used. This paper describes a solubility selective membrane material for this separation. A crosslinked poly(ethylene oxide) [PEO] material [XLPEO] was prepared from a prepolymer solution containing 71 wt.% poly(ethylene glycol) methyl ether acrylate [PEGMEA] monomer and 29 wt.% poly(ethylene glycol) diacrylate [PEGDA] crosslinker, and it exhibits high carbon dioxide permeability and high carbon dioxide/ethane selectivity. For example, at 253 K and 10 atm total feed fugacity, the CO2/C2H6 selectivity for a 45 mol% CO2 and 55 mol% C2H6 gas mixture is approximately 12, and the CO2 permeability is 83 Barrers. The performance of the membrane material for breaking the CO2/C2H6 azeotrope was simulated using a computer model. XLPEO was found to be effective in breaking the azeotrope. At a feed composition of 45 mol% CO2 and 55 mol% C2H6, 85% ethane recovery could be achieved at an ethane purity of 78% for a single stage membrane separation operating at 253 K and 11.3 atm total pressure. Experimental sorption, pure gas diffusion and permeability, and mixed gas permeation data for CO2 and C2H6 in this polymer are presented at temperatures ranging from 253 to 308 K.
Co-reporter:Leah S. Worrel, Jason A. Morehouse, Leah A. Shimko, Douglas R. Lloyd, Desmond F. Lawler, Benny D. Freeman
Separation and Purification Technology 2007 Volume 53(Issue 1) pp:71-80
Publication Date(Web):15 February 2007
DOI:10.1016/j.seppur.2006.06.017
The objective of this paper is to demonstrate that membrane performance (flux, rejection, and permeate particle size distribution as a function of time) can be influenced by modifying the membrane pore size characteristics. Poly(ethylene teraphthalate) (PET) track-etched (T-E) membranes with nominal pores sizes ranging from 0.2 to 10 μm were uniaxially stretched to increase the major axis, aspect ratio, pore area, and porosity while decreasing the minor axis. Permeation results for pure water feed as well as separate feed suspensions of spherical particles and irregular-shaped particles showed that flux can be increased and flux decline decreased by stretching membranes. Additionally, rejection of both irregular-shaped and spherical particles was increased by stretching membranes.
Co-reporter:Haiqing Lin;Elizabeth Van Wagner;Lora G. Toy;Raghubir P. Gupta
Science 2006 Vol 311(5761) pp:639-642
Publication Date(Web):03 Feb 2006
DOI:10.1126/science.1118079
Abstract
Polymer membranes are attractive for molecular-scale separations such as hydrogen purification because of inherently low energy requirements. However, membrane materials with outstanding hydrogen separation performance in feed streams containing high-pressure carbon dioxide and impurities such as hydrogen sulfide and water are not available. We report highly permeable, reverse-selective membrane materials for hydrogen purification, as exemplified by molecularly engineered, highly branched, cross-linked poly(ethylene oxide). In contrast to the performance of conventional materials, we demonstrate that plasticization can be harnessed to improve separation performance.
Co-reporter:H. Lin;I. Roman;R. Raharjo;E. Van Wagner;B. D. Freeman
Advanced Materials 2006 Volume 18(Issue 1) pp:39-44
Publication Date(Web):21 NOV 2005
DOI:10.1002/adma.200501409
Rubbery membrane materials based on high-solubility selectivity for the removal of CO2 from natural gas are made from highly branched, crosslinked poly(ethylene oxide) (XLPEO) which exhibits high CO2/CH4 selectivity (α) even in the presence of high activities of plasticizing agents (e.g., CO2 and higher hydrocarbons). Decreasing temperature improves the separation performance. Many conventional glassy gas separation materials, including polyimides such as 6FDA-mPD, lose selectivity when strongly plasticized (see Figure).
Co-reporter:Kazukiyo Nagai;Lora G. Toy;Masahiro Teraguchi;Giseop Kwak;Toshio Masuda;Ingo Pinnau
Journal of Polymer Science Part B: Polymer Physics 2002 Volume 40(Issue 19) pp:2228-2236
Publication Date(Web):21 AUG 2002
DOI:10.1002/polb.10276
The gas permeability and n-butane solubility in glassy poly(1-trimethylgermyl-1-propyne) (PTMGP) are reported. As synthesized, the PTMGP product contains two fractions: (1) one that is insoluble in toluene and soluble only in carbon disulfide (the toluene-insoluble polymer) and (2) one that is soluble in both toluene and carbon disulfide (the toluene-soluble polymer). In as-cast films, the gas permeability and n-butane solubility are higher in films prepared from the toluene-soluble polymer (particularly in those films cast from toluene) than in films prepared from the toluene-insoluble polymer and increase to a maximum in both fractions after methanol conditioning. For example, in as-cast films prepared from carbon disulfide, the oxygen permeability at 35 °C is 330 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene-soluble polymer and 73 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene-insoluble polymer. After these films are conditioned in methanol, the oxygen permeability increases to 5200 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene-soluble polymer and 6200 × 10−10 cm3 (STP) cm/(cm2 s cmHg) for the toluene-insoluble polymer. The rankings of the fractional free volume and nonequilibrium excess free volume in the various PTMGP films are consistent with the measured gas permeability and n-butane solubility values. Methanol conditioning increases gas permeability and n-butane solubility of as-cast PTMGP films, regardless of the polymer fraction type and casting solvent used, and minimizes the permeability and solubility differences between the various films (i.e., the permeability and solubility values of all conditioned PTMGP films are similar). © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2228–2236, 2002
Co-reporter:Benny Freeman
Membrane Technology (October 2013) Volume 2013(Issue 10) pp:7
Publication Date(Web):1 October 2013
DOI:10.1016/S0958-2118(13)70207-6
In the USA, chemical engineers at The University of Texas at Austin have developed high-efficiency, durable filters to improve mobile water-recycling systems used in hydraulic fracturing – the oil and gas drilling process known as fracking. According to the researchers, the filters may significantly reduce the amount of water and energy that fracking requires.
Co-reporter:Zhengwang He, Sirirat Kasemset, Alon Y. Kirschner, Yu-Heng Cheng, Donald R. Paul, Benny D. Freeman
Water Research (15 June 2017) Volume 117() pp:230-241
Publication Date(Web):15 June 2017
DOI:10.1016/j.watres.2017.03.051
•Crude oil-in-water emulsions were formulated at various salt concentrations.•Foulant zeta potential decreased with increasing salt concentration.•DLVO model was used to simulate short-range interactions.•Model predictions of fouling propensity matched experimental observations.•Electrostatic interactions dominated van der Waals interactions in this study.The effects of inorganic salts and organic hydrocarbons on membrane fouling are often investigated independently. However, in many cases, these foulants are commonly found together, and such mixtures are rarely the subject of fouling studies. In this study, crude oil-in-water emulsions were formulated at three different added NaCl concentrations, 0, 10-3 and 10−1 M. Surface properties, such as surface tension and surface charge, of these emulsions and a poly(vinylidene fluoride) (PVDF) microfiltration (MF) membrane were characterized. The Derjaguin-Landau-Verwey-Overbeek (DLVO) model was utilized to simulate membrane-oil droplet and oil layer-oil droplet surface interactions. The DLVO model qualitatively predicted increasing fouling propensity with increasing emulsion salt concentration. The PVDF MF membrane was challenged with crude oil-in-water emulsions in constant permeate flux crossflow fouling tests to characterize the fouling propensity of the various emulsions, and the results were consistent with the model predictions.
Co-reporter:Leah S. Worrel, Jason A. Morehouse, Leah A. Shimko, Douglas R. Lloyd, Desmond F. Lawler, Benny D. Freeman
Separation and Purification Technology (15 February 2007) Volume 53(Issue 1) pp:71-80
Publication Date(Web):15 February 2007
DOI:10.1016/j.seppur.2006.06.017
The objective of this paper is to demonstrate that membrane performance (flux, rejection, and permeate particle size distribution as a function of time) can be influenced by modifying the membrane pore size characteristics. Poly(ethylene teraphthalate) (PET) track-etched (T-E) membranes with nominal pores sizes ranging from 0.2 to 10 μm were uniaxially stretched to increase the major axis, aspect ratio, pore area, and porosity while decreasing the minor axis. Permeation results for pure water feed as well as separate feed suspensions of spherical particles and irregular-shaped particles showed that flux can be increased and flux decline decreased by stretching membranes. Additionally, rejection of both irregular-shaped and spherical particles was increased by stretching membranes.
Co-reporter:Jovan Kamcev, Donald R. Paul and Benny D. Freeman
Journal of Materials Chemistry A 2017 - vol. 5(Issue 9) pp:NaN4650-4650
Publication Date(Web):2017/02/06
DOI:10.1039/C6TA07954G
Despite their increasing importance in many energy and water purification applications, few systematic studies of ion sorption in ion exchange membranes exist where fixed charge group concentration and water content are varied independently. Such studies are critical for developing fundamental structure/property relations important for rationally tailoring such materials. Here, cation and anion exchange membranes having different fixed charge group concentrations but similar water content were synthesized to investigate the influence of fixed charge group concentration on equilibrium ion sorption in such materials. Co-ion sorption decreased with increasing membrane fixed charge group concentration, as expected, presumably due to enhanced Donnan exclusion. However, the extent to which co-ion sorption was suppressed was different for the cation and anion exchange membranes, despite similar changes in membrane fixed charge group concentration. A thermodynamic model, based on Donnan theory and Manning's counter-ion condensation theory, was used to interpret the data. The model predicted equilibrium co-ion concentrations in the anion exchange membranes with no adjustable parameters. However, good agreement between the model and experimental data for the cation exchange membranes was only obtained by treating the Manning parameter as an adjustable constant, presumably due to phase separation during polymerization, which produced inhomogeneous membranes.
Co-reporter:Jovan Kamcev, Michele Galizia, Francesco M. Benedetti, Eui-Soung Jang, Donald R. Paul, Benny D. Freeman and Gerald S. Manning
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 8) pp:NaN6031-6031
Publication Date(Web):2016/01/19
DOI:10.1039/C5CP06747B
Equilibrium partitioning of ions between a membrane and a contiguous external solution strongly influences transport properties of polymeric membranes used for water purification and energy generation applications. This study presents a theoretical framework to quantitatively predict ion sorption from aqueous electrolytes (e.g., NaCl, MgCl2) into charged (i.e., ion exchange) polymers. The model was compared with experimental NaCl, MgCl2, and CaCl2 sorption data in commercial cation and anion exchange membranes. Ion sorption in charged polymers was modeled using a thermodynamic approach based on Donnan theory coupled with Manning's counter-ion condensation theory to describe non-ideal behavior of ions in the membrane. Ion activity coefficients in solution were calculated using the Pitzer model. The resulting model, with no adjustable parameters, provides remarkably good agreement with experimental values of membrane mobile salt concentration. The generality of the model was further demonstrated using literature data for ion sorption of various electrolytes in charged polymers, including HCl sorption in Nafion.
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