Dialysis membranes solute permeabilities

Membrane symmetric microporous with 0.1 to 10 nm pore diameter. Hydraulic permeability 10 to 8 g/s m MPa. Membrane-solute permeability 0.05 to 9 m/s depending on the solute and the membrane. Dialysis transfer coefficient 1 to 10 pm/s. Hollow fiber. 

In one version of the urea electrode, shown in Figure 11.16, an NH3 electrode is modified by adding a dialysis membrane that physically traps a pH 7.0 buffered solution of urease between the dialysis membrane and the gas-permeable... 

Electrodialysis. In electro dialysis (ED), the saline solution is placed between two membranes, one permeable to cations only and the other to anions only. A direct electrical current is passed across this system by means of two electrodes, causiag the cations ia the saline solution to move toward the cathode, and the anions to the anode. As shown ia Figure 15, the anions can only leave one compartment ia their travel to the anode, because a membrane separating them from the anode is permeable to them. Cations are both excluded from one compartment and concentrated ia the compartment toward the cathode. This reduces the salt concentration ia some compartments, and iacreases it ia others. Tens to hundreds of such compartments are stacked together ia practical ED plants, lea ding to the creation of alternating compartments of fresh and salt-concentrated water. ED is a continuous-flow process, where saline feed is continuously fed iato all compartments and the product water and concentrated brine flow out of alternate compartments. 

H Yasuda, A Peterlin, CK Colton, KA Smith, EW Merrill. Permeability of solutes through hydrated polymer membranes HI. Theoretical background for the selectivity of dialysis membranes. Makromol Chem 126 177-186, 1969. 

At least two different techniques are available to compress an emulsion at a given osmotic pressure H. One technique consists of introducing the emulsion into a semipermeable dialysis bag and to immerse it into a large reservoir filled with a stressing polymer solution. This latter sets the osmotic pressure H. The permeability of the dialysis membrane is such that only solvent molecules from the continuous phase and surfactant are exchanged across the membrane until the osmotic pressure in the emulsion becomes equal to that of the reservoir. The dialysis bag is then removed and the droplet volume fraction at equilibrium is measured. 

Another approach employed to establish the occurrence of a density nversion between the two solutions subsequent to boundary formation involves dialysis between the two solutions s0>. The dialysis membrane is impermeable to the polymer solutes but permeable to the micromolecular solvent, H20. Transfer of water across the membrane occurs until osmotic equilibrium involving equalization of water activity across the membrane is attained. Solutions equilibrated by dialysis would only undergo macroscopic density inversion at dextran concentrations above the critical concentration required for the rapid transport of PVP 36 0 50). The major difference between this type of experiment and that performed in free diffusion is that in the former only the effect of the specific solvent transport is seen which is equivalent to a density inversion occurring with respect to a membrane-fixed or solute-fixed frame of reference. Such restrictions are not imposed on free diffusion where equilibration involves transport of all components in a volume-fixed frame of reference. The solvent flow is governed specifically by the flow of the polymer solutes as described by Eq. (3) which, on rearrangement, gives... 

Reverse osmosis and normal osmosis (dialysis) are directly related processes. In simple terms, if a selective membrane (i.e., a membrane freely permeable to water, but much less permeable to salt) separates a salt solution from pure water, water will pass through the membrane from the pure water side of the membrane into the side less concentrated in water (salt side) as shown in Figure 2.8. This process is called normal osmosis. If a hydrostatic pressure is applied to the salt side of the membrane, the flow of water can be retarded and, when the applied pressure is sufficient, the flow ceases. The hydrostatic pressure required to stop... 

Consider two chambers separated by a dialysis membrane permeable to ions and water. After the chambers are filled with a KC1 solution and allowed to come to equilibrium, the concentration of K+ and CR ions will be the same on each side of the membrane. An RNA with Z negative charges is then added to the left chamber (Fig. 21.1 A). Because the RNA must be added as a neutral salt, Z cations are also added. In the example diagrammed in Fig. 21.1 A, Z = 16 and the K+ salt of the RNA, K RNA,... 

In hemodialysis, blood from the patient flows on one side of a membrane and a specially prepared dialysis solution is fed to the other side. Waste material in the blood such as urea, excess acids, and electrolytes diffuse into the dialysate the blood is then returned to the patient, as shown in Fig. 48. A patient typically undergoes dialysis three times per week in sessions lasting several hours each. Modern dialysis systems combine sophisticated monitoring and control functions to ensure safe operation. Regenerated cellulose was the first material used in hemodialysis membranes because of its biocompatibility and low cost it remains the most popular choice. Subsequently, high-permeability dialysis membranes derived from cellulose esters, modified polysulfone, or polyacrylonitrile copolymers have also gained wide acceptance because of the shorter sessions they make possible. 

Figure 21,1-7 shows membrane permeability and reflection coefficient as a function of molecular weight for a cellulosic dialysis membrane.3 For two solutes, A and B, having molecular weights of 200 and 2000 daltons, respectively, feed-side concentrations at a point on the membmae surface of 0.1 g/cm3, and negligible dialysale-side concentrations, dC = 0.1 g/cm3 and C 0.067 g/cm3. For solute A, PM = 3.6 X 10-J cm/s and 1 - a = 0,8, Substituting these values into Eq, (21.1-2), we obtain... 

Figure 5.28 Change in permeability coefficient (D/6) of urea (neutral molecule) with ion exchange capacity of anion exchange membranes and composite membranes (D diffusion coefficient, cm2 s 6 thickness of the membrane, cm). ( ) Commercial anion exchange membranes (NEOSEPTA AM-1, AM-2 and AM-3, strongly basic anion exchange) ( ) Fe-Py membrane (A) Py-Fe membrane. The permeability coefficient was measured by diffusion dialysis of urea solution using a two-compartment cell (2.0 mol l urea solution/membrane/ pure water) for 48 h at 25.0 °C under vigorous agitation). The ion exchange capacity on the horizontal axis represents values before preparation of the composite membranes.

Donnan dialysis is an ion exchange process in which an ion exchange membrane is placed between two solutions, i.e., the feed (I) and receiver (II) solutions. The membrane is permeable to counter-ions and excludes co-ions. The ionic strength of the feed solution is relatively low compared with that of the receiver electrolyte solution. At equilibrium, if concentrations are used instead of activities, there is the following Donnan relationship,... 

Ultrafiltration A separation process somewhat like dialysis in which a colloidal dispersion is separated from a noncolloidal solution by a semipermeable membrane, that is, a membrane that is permeable to all species except the colloidal-sized ones. Here an applied pressure (rather than osmotic pressure) across the membrane drives the separation. As in dialysis the solution containing the colloidal species is referred to as... 

Figure 6.11 Dialysis Saturated solution of biological macromolecule (e.g. protein) is placed in an environment separated from precipitant solution by semi-permeable membrane. Very slow solute diffusion across the membrane creates precipitant gradient in the macromolecule solution to "seed" crystallisation.

Another example deals with amino acid analysis using immobilized specific microorganisms in combination with selective electrodes (35). Thus, glutamine could be analyzed by an electrode consisting of a potentiometric ammonia gas sensor and a layer of the bacterium Sarcina flava (American type culture collection 147) trapped in the volume between a NHo-permeable membrane on the surface of the electrode and a dialysis membrane in contact with the surrounding solution (Fig. 10). Using this electrode, steady state potentials were reached within 5 minutes. 

Figure 10. (A) Schematic diagram of the bacterial electrode a, bacterial layer b, dialysis membrane c, gas-permeable membrane d, internal sensing element e, internal filling solution and f, plastic electrode body. (B) Detail of the membrane phases (35).

This effect can be observed experimentally in the following way. An aqueous solution containing a chosen ion i is poured into two identical chambers separated by a membrane permeable to water and dissolved solutes but not to suspended solids (i.e., a dialysis membrane). The moles of charge contributed by ion i to one of these chambers is Z, co,F, where Zf is the valence of the ion, Cq, is its concentration, and V is the volume of the chamber. After kilograms of a solid are suspended in one of the chambers and equilibrium with respect to the transport of ion / is established across the membrane, the concentration of ion / in the chamber not containing the suspended solid will rise to q if the surfaces of the solid repel ion i. This increase in concentration is associated quantitatively with a region of depletion of ion i in the chamber containing the suspended solid... 

A cuprophane dialysis membrane separates two compartments with a volume of 100 ml. The left compartment contains a solution of 5.10 M sodiumpoiyacryiate and the right comparnitent a solution of 10 M sodiumcbloride. The membrane is permeable... 

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