Cation membranes

Electrodialysis units are constructed using a plate-and-frame technique similar to filter presses. Alternating sheets of anionic and cationic membranes are placed between two electrodes. The plating or rinse solution to be recovered (electrolyte) circulates past the system s electrodes. Hydrogen and oxygen evolve. Positive ions travel to the negative terminal and negative ions travel to the... 

Test cation Membrane anion — Membrane cation... 

Figure 4.8—Membrane and electrochemically regenerated suppressors. Two types of membrane exist those that allow the permeation of cations (H+ and Na+) and those that allow the permeation of anions (OH and X ). a) The microporous cationic membrane model is adapted to the elution of an anion. Only cations can migrate through the membrane (corresponding to a polyanionic wall that repulses the anion in the solution) b) Anionic membrane suppressor placed after a cationic column and in which ions are regenerated by the electrolysis of water. Note in both cases the counter-current movement between the eluted phase and the solution of the suppressor c) Separation of cations illustrating situation b).

Bipolar Membrane 0 Cation Membrane 0 Anion Membrane... 

In this process, dissolved electrolytes are removed by application of electromotive force across a battery of semipermeable membranes constructed from cation and anion exchange resins. The cation membrane passes only cations and the anion membrane only anions. The two kinds of membranes are stacked alternately and separated about 1mm by sheets of plastic mesh that are still provided with flow passages. When the membranes and spacers are compressed together, holes in the comers form appropriate conduits for inflow and outflow. Membranes are 0.15-0.6 mm thick. A commercial stack may contain several hundred compartments or pairs of membranes in parallel. A schematic of a stack assembly is... 

C CATION MEMBRANE A ANION MEMBRANE 0 COMPARTMENT NUMBER(SEE TE T)... 

Table I lists the typical physical characteristics of the new and old membranes, including a Nepton CR-61 on 9-ounce dynel which was substituted for the 9-ounce glass in production a year or two earlier. Figure 2 shows the electrical resistance of the 4-ounce and 9-ounce membranes. From Table I, it can be seen that the reduction in thickness from 30 mils to 23 mils in both the cation and anion membranes led to reduction in Mullen burst strength to 140 p.s.i. The electrical through resistance (Figure 2) was decreased to approximately two thirds for the cation membranes and about one half for the anion membrane. The Nepton CR-61 9-ounce glass membrane had a much lower resistance than the 9-ounce dynel, because of a difference in the weave pattern in the cloth, so that there was actually little if any difference between the 4-ounce dynel cation and the 9-ounce glass cation in electrical through resistance. However, the superior resistance of the dynel backing to mechanical failures leads to its selection.

A new commercially available cation membrane, Nepton CR-61 on 4-ounce dynel backing, is 23 mils thick and has an electrical through resistance in 0.01A NaCl of 14 ohms per sq. cm., about two thirds that of a similar membrane 30 mils thick on 9-ounce dynel backing. It has the same electrical resistance as a 9-ounce glass-backed CR-61 membrane, also 30 mils thick, but much better chemical stability to acids and alkalies and better mechanical stability to vibrations. The Mullen burst strength of the 4-ounce membranes is 140 p.s.i., about half that for the 9-ounce dynel, but still sufficient to be useful for field operation. Its stiffness and resistance to bowing, for which no standard measurements are yet available, are sufficient to allow its use in membrane stacks with tortuous path spacers operating at pressures of 60 p.s.i. and flow velocities of 60 cm. per second. 

CL-DNA complexes form spontaneously when solutions of cationic liposomes (typically containing both a cationic lipid and a neutral helper lipid) are combined. We have discovered several distinct nanoscale structures of CL-DNA complexes by synchrotron X-ray diffraction, three of which are schematically shown in Fig. 1. These are the prevalent lamellar phase with DNA sandwiched between cationic membranes (Lo,c) [22], the inverted hexagonal phase with DNA encapsulated within inverse lipid tubes (Hnc) [23], and the more recently discovered Hj0 phase with hexagonally arranged rod-like micelles surrounded by DNA chains forming a continuous substructure with honeycomb symmetry [24]. Both the neutral lipid and the cationic lipid can drive the formation of specific structures of CL-DNA complexes. The inverse cone shape of DOPE favors formation of the... 

In summary, our findings suggest that cholesterol and certain analogs are a highly valuable neutral lipid component ( helper lipid ) for CL-DNA complexes because they facilitate endosomal escape by reducing the repulsive hydration and protrusion forces. They are thus able to lower the kinetic barrier for fusion of the cationic membranes of CL-DNA complexes with the anionic membrane of the endosome and increase TE, in addition to their beneficial effect on aM. 

B. Spread a few drops of 0.2% (w/v) solution of methylene blue or erythrocin-B over the entire surface of the anionic or cationic membrane, respectively. 

A. Equilibrate a sample of anionic or cationic membrane in 1 kmol/m3 HC1 or NaOH, respectively, for about 24 hours. 

The ED stack is the unit holding together anionic and cationic membranes assembled in parallel as in a filter press between two electrode-end blocks in such a manner that the stream undergoing ion depletion (i.e., the diluate or diluting stream) is kept separated from the other solution (concentrate or concentrating stream) undergoing ion enrichment. Figure 4 shows an exploded view of it. 

FIG. 8 Schematic diagrams of different arrangements for an ED unit equipped with bipolar membranes (bmp) coupled to anionic (a) and/or cationic (c) membranes (A) three-compartment configuration (B) two-compartment configuration using bipolar and cationic membranes (C) two-compartment configuration using bipolar and anionic... 

The anionic or cationic membrane perm-selectivity (am) for the corresponding counterions can be expressed as the ratio by the differences between the real and theoretical transport numbers in the membrane and solution phases ... 

By referring to Figure 9, in any cell pair the presence of an anionic and a cationic membrane gives rise to four boundary layers and thus to four junction potentials differences ( ja,k ar d jc,k) and two Donnan potential differences ( Da and k )c). their mathematical expressions being given in Table IV. 

OR CATIONIC MEMBRANE RESISTANCES OF THE BOUNDARY LAYERS ADJACENT TO THE ANIONIC (7[Pg.296]

Both the first (ohmic) and second (polarization controlled) regions can be noted in Figure 10, reporting the results of typical limiting current measurements performed on an ED stack composed of only 19 cationic membranes (CMV type, see Table II) and model solutions containing 9 and 28 mol of NaCl per m3 for superficial velocities (vs) ranging from 3.4 to 5.9 cm/s (Fidaleo and Moresi, 2005a). 

Lindstrand et al. (2000) investigated the effect of different organic fou-lants, such as octanoic acid, sodium octonate, and sodium dodecylbenzene sulfonate, on anionic and cationic membranes by monitoring the increase in the membrane resistance (Rm) with time. 

FIG. 12 Schematic layout of a transport depletion ED stack used to demineralize whey c, cationic membrane ERS, electrode-rinsing solution n, neutral membrane. 

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