Sulfonate membranes

Membranes offer a format for interaction of an analyte with a stationary phase alternative to the familiar column. For certain kinds of separations, particularly preparative separations involving strong adsorption, the membrane format is extremely useful. A 5 x 4 mm hollow-fiber membrane layered with the protein bovine serum albumin was used for the chiral separation of the amino acid tryptophan, with a separation factor of up to 6.6.62 Diethey-laminoethyl-derivatized membrane disks were used for high-speed ion exchange separations of oligonucleotides.63 Sulfonated membranes were used for peptide separations, and reversed-phase separations of peptides, steroids, and aromatic hydrocarbons were accomplished on C18-derivatized membranes. 

In an early study, Mauritz et al. investigated anion—cation interactions within Nation sulfonate membranes versus degree of hydration using FTIR/ ATR and solid state NMR (SSNMR) spectroscopies. An understanding of the dynamic ionic—hydrate molecular structures within and between the sulfonate clusters is essential for a fundamental understanding of the action of these membranes in ion transport. This information can be directly related to the equilibrium water swelling that, in turn, influences molecular migration. 

Risen et al. investigated cation—anion interactions using far IR spectroscopy (50—300 cm ) to study Nafion sulfonate membranes that were neutralized by cations in the series Na+, K+, Rb+, and Cs+ and the series Mg +, Ca +, Sr +, and Ba +, as well as the acid form." The spectra in this region for hydrated samples show a broad but well-defined band below 300 cm that is not present for the acid form. For both the monovalent alkali and divalent alkaline earth series, the band monotonically shifts to lower frequencies, f, such that foe where Mis the... 

Miura and Yoshida also investigated the changes in the microstructure of 1100 EW Nafion sulfonate membranes, in alkali, ammonium, and alkylammonium cation forms, that were induced by swelling in ethanol using DSC, dynamic mechanical analysis (DMA), SAXS, and electron probe microanalysis (EPMA). These studies were performed within the context of liquid pervaporation membranes that could potentially be used to separate ethanol from water... 

Earlier, Gavach et al. studied the superselectivity of Nafion 125 sulfonate membranes in contact with aqueous NaCl solutions using the methods of zero-current membrane potential, electrolyte desorption kinetics into pure water, co-ion and counterion selfdiffusion fluxes, co-ion fluxes under a constant current, and membrane electrical conductance. Superselectivity refers to a condition where anion transport is very small relative to cation transport. The exclusion of the anions in these systems is much greater than that as predicted by simple Donnan equilibrium theory that involves the equality of chemical potentials of cations and anions across the membrane—electrolyte interface as well as the principle of electroneutrality. The results showed the importance of membrane swelling there is a loss of superselectivity, in that there is a decrease in the counterion/co-ion mobility, with greater swelling. 

Mauritz and Gray analyzed the IR continuous absorption of hydrated Na OH - and K OH -imbibed Nafion sulfonate membranes for the purpose of correlating this phenomenon to the current efficiency (cation transference number) of chlor-alkali electrochemical cells.In this case, the similar issue of OH ( defect proton ) conductivity is important. A distinct continuous absorption appeared in the spec-... 

Polyallylamine (Mw = 70 000 g/mol) and polystyrene sulfonate (M, = 70 000 g/mol) were obtained from Aldrich. PAH was used as received, while PSS was purified from low molecular weight impurities by dialysis (Polyether-sulfone membranes, MW cut off 10 000 g/mol, Millipore) against ultra pure water and freeze dried. All water used for preparing solutions or for dialysis was purified by a Purelab Plus UV/UF, Elga Lab Water system and had a resistivity smaller than 0.055 xS/cm and a total organic content between 2 and 12 ppb (parts per billion). 

Crosslinked polyether sulfone membranes containing pendant sulfonic acid groups were prepared by Michot [4] and used in electrochemical cells. 

Gierke, T., Hsu, W. (1982). The cluster-network model of ion clustering in perfluoro-sulfonated membranes. In "Perfluorinated lonomer Membranes", American Chemical Society Symp. Series 180, Washington, DC. 

The maximum pore size used to separate phospholipid micelles, in which color pigments and other impurities are physically bound, can be in the range of 10,000-50,000 Da depending on the polymer type. Considerable swelling occurs with poly-sulfone membranes, which, in turn, affects the membrane chemistry drastically and reduces flow rates and in some cases totally closes the pores. Similar results have also been observed with polyamide and fluorinated polymers. 

Membrane bioreactor Asymmetric poly-sulfone membrane Diffusion of carbohydrates in liquid-filled pores Enzymatic hydrolysis of lactose Whole cells of Sutfolobus solfataricus entrapped in the tube wall 65... 

Ballard Advanced Materials (BAM) ionomers are sulfonated copolymers of trifluorostyrene and substimted trifluorostyrene monomers. BAM, a subsidiary of Ballard Power Systems, investigated the conducting polymers based on polyphenylquinoxaline (PPQ). These can be sulfonated in a wide range and were referred to as BAMIG (Ballard first generation) membranes, but these membranes were found to have short durability. To overcome this problem, BAM developed a second generation of advanced membranes based on two distinct material types. The first material type consisted of a series of sulfonated poly(2,6-diphenyl 1,4-phenylene oxide). The second material type consisted of a series of sulfonated poly(arylether sulfone). But the durability of these membranes was also insufficient. Since the durability of previous membranes was limited, Ballard produced a novel family of sulfonated membranes based on a,p,p-ttifluorostyrene monomers and a series of substituted ttifluoro-comonomers... 

S. J. Paddison, G. Bender, K.D. Kreuer, N. Nicoloso, and T.A. Zawodzinski. The microwave region of the dielectric spectrum of hydrated Nafion (R) and other sulfonated membranes. Journal of New Materials for Electrochemical Systems 3, 291-300 2000. 

Self-diffusion coefficients of polyvalent cations in these perfluorinated ionomer membranes have not been reported. It can be inferred from the use of the sulfonate membranes as Donnan dialysis devices that transport of cations such as CuflT), Mg(II), and Al(III) under a concentration gradient is rapid. Also, column chromatographic separation of the alkaline-earth ion is readily accomplished with a powdered Nafion perfluorosulfonate polymer, which is again an indication of facile diffusion of these cations within the polymer phase. 

In 5 M NaOH, the carboxylate now shows slightly lower values of the diffusion coefficients compared to the sulfonate membrane. This pattern is repeated for values measured with 4 M and 5 M NaCl solutions as well. " At higher NaOH solution concentrations, values for the carboxylate become much smaller, averaging... 

Homogeneous or bilayer membranes of only sulfonate functionality can yield reasonably high current efficiencies if a high-EW polymer faces the catholyte. Unfortunately, large electrical resistances also result with such materials. Surface treatment of a sulfonate membrane to yield a layer of sulfonamide exchange sites also produces a membrane with improved current efficiency. However, these sites are slowly hydrolyzed in an operating cell, so that this approach is not commercially viable. 

Some of these features are illustrated in Figures 14-18. A rather typical literature plot of current efficiency vs, sodium hydroxide concentration for perfluorosulfonate membranes is shown in Fig. 14. Nation 427 is a 1200-EW sulfonate membrane with fabric reinforcement. Poor hydroxide rejection occurs at catholyte concentrations above 10 wt % but a minimum is seen at higher concentrations, wtih increasing current efficiency from 28 to 40% caustic (9-14 M). The current efficiency of a 1200-EW homogeneous perfluorosulfonate film is shown in more detail over this concentration region in Fig. 15. Sodium ion transport number niol F ), which is equivalent to caustic current efficiency, is plotted vs. both brine anolyte and caustic catholyte concentration. These values were determined using radiotracer techniques, which have proven to be rapid and accurate methods for the determination of membrane performance. " " " A rather sharp maximum is seen at 14 M NaOH, and the influence of brine con-... 

In this paper, we will report results mainly obtained on perfluorinated sulfonated membranes. First, we will show that the distribution of the ion exchange groups may be quite nonuniform on... 

A similar behavior has also been observed in membranes obtained by copolymerization. Many recent perfluorinated sulfonated membranes have been obtained by copolymerization of tetrafluoroethylene with a sulfonyl fluoride vinyl ether. This high molecular weight polymer has the following formula ... 

The ratio of the permeabilities of two cations in a cation exchange membrane is equal to the product of the ion exchange equilibrium constant and their mobility ratio (1). Therefore it is important to characterize the equilibrium ion exchange selectivity of ion exchange polymers in order to understand their dynamic properties when used in membrane form. Nafion (E.I. du Pont de Nemours and Co.) perfluorinated sulfonate membranes have found wide use in a variety of applications, many of which involve exchange of cations across membranes that separate solutions of different ionic composition. The inherent cationic selectivity of the polymer is an important consideration for such applications. Results of ion exchange selectivity studies of Nafion polymers are reviewed in this chapter, and are compared to those of other sulfonate ion exchange polymers. 

Figure 10. Typical oscilloscope traces showing variations of the ionic SAXS profiles upon stretching the cesium-sulfonate membranes having 1100 EW under dry state in a direction (left) parallel (n = 0°) and (right) perpendicular (V = 90°) to stretching direction X is draw ratio of the membranes. Key 1, X = 1.0 2,1 — 1.1 3, X = 1.2 4, X = 1.3 5, X = 1.5.

---