Retention adsorption

To calculate the contributions of all molecular groups to retention (adsorption equilibrium constant) ai, ARmi under some standard conditions, it is necessary to determine the retention volumes Vm (Va) or capacity factor k or Rm values from Rp data for a number of compounds possessing different amounts of such groups and to solve the systems of linear equations (2 or 3 or 5) by the least -squares method. 

The Walborsky mechanism provide.s three possible explanations of partial retention, adsorption of Rv pathway X, and ultrafast [R -MgX] collapse. Deciding among them, or partitioning their effects, is a legitimate problem but not one considered by Walborsky, who has opted recently for a retention pathway X [7.10,20],... 

Cartridge-type hydrophobic membrane Filtration has largely replaced depth filtration as a means of sterilizing gases. Collection of panicles from a gas stream by membrane Filtration is, as with liquid filtration, a function of both sieving and other means of retention. Adsorption and electrostatic attraction are far more important to retention of particles in gas Filtration than in liquid Filtration. Because there are more mechanisms and interactions between pore surfaces and particles, removal of particles is more easily accomplished from gas streams than from liquids. Gases are quite satisfactorily sterilized using 0.45 pm pore size rated membranes. 

The use of microemulsions in the context of washing and cleaning was recently reviewed [1]. There seem to be no reasons to believe that any fundamental new impact is needed in this area from a physicochemical point of view. Large-scale applications in the area of soil remediation can be expected in the near future. In this context it will be essential to estimate microemulsion formation, price, chemical performance, and mechanisms of retention (adsorption) on the solid material when designing these kinds of washing systems. Microemulsions for use in soil remediation have been summarized by Miller and coworkers [12,13] and Schwuger and coworkers [14,15]. 

The transient RF and concentration curves of polysaccharide G2 are illustrated in Figure 8. The transient RF curve reflects some plugging behavior but not to the degree indicated by the high retention factor (321 Ib/acre-foot). The high RRF of 9.3 reflects some polymer retention/adsorption phenomena. The large retention could have resulted from association of polysaccharide molecules with divalent ions such as Mg and Ca to form reversible complexes in the 80/20 connate water at the flood front. Such a... 

Surfactant retention (adsorption plus any other phenomena that might cause retention) was measured by injecting a surfactant solution containing radiolabeled sodium dihexyl sulfosuccinate into a column packed with contaminated Hill field soil. Tritiated water was used as a conservative tracer. Figure 13 shows the effluent concentration from the column for both these labeled molecules as measured by liquid scintillation counting. The almost identical breakthrough and elution of these molecules indicate very low adsorption of the surfactant on this soil. 

Cores. Native-state cores were used to determine polymer retention (adsorption plus trapped material). In each experiment, three cores were mounted in a Hassler sleeve to form a composite core about 10 in. [25 cm] long. Tensleep crude oil was injected into the cores under 300 psi [2070 kPa] backpressure. Then the eores were waterflooded with CBFIB at high injection rates until no more oil could be produced by waterflooding. 

The foregoing is an equilibrium analysis, yet some transient effects are probably important to film resilience. Rayleigh [182] noted that surface freshly formed by some insult to the film would have a greater than equilibrium surface tension (note Fig. 11-15). A recent analysis [222] of the effect of surface elasticity on foam stability relates the nonequilibrium surfactant surface coverage to the foam retention time or time for a bubble to pass through a wet foam. The adsorption process is important in a new means of obtaining a foam by supplying vapor phase surfactants [223]. 

The effect of these factors on the adsorption isotherm may be elucidated by reference to specific examples. In the case of the isotherm of Fig. 5.17(a), the nonporous silica had not been re-heated after preparation, but had been exposed to near-saturated water vapour to ensure complete hydroxylation. The isotherm is of Type II and is completely reversible. On the sample outgassed at 1000°C (Fig. 5.17(h)) the isotherm is quite different the adsorption branch is very close to Type III, and there is extrensive hysteresis extending over the whole isotherm, with considerable retention of adsorbate on outgassing at 25°C at the end of the run. 

In liquid-solid adsorption chromatography (LSC) the column packing also serves as the stationary phase. In Tswett s original work the stationary phase was finely divided CaCOa, but modern columns employ porous 3-10-)J,m particles of silica or alumina. Since the stationary phase is polar, the mobile phase is usually a nonpolar or moderately polar solvent. Typical mobile phases include hexane, isooctane, and methylene chloride. The usual order of elution, from shorter to longer retention times, is... 

Kovat s retention index (p. 575) liquid-solid adsorption chromatography (p. 590) longitudinal diffusion (p. 560) loop injector (p. 584) mass spectrum (p. 571) mass transfer (p. 561) micellar electrokinetic capillary chromatography (p. 606) micelle (p. 606) mobile phase (p. 546) normal-phase chromatography (p. 580) on-column injection (p. 568) open tubular column (p. 564) packed column (p. 564) peak capacity (p. 554)... 

The effect of temperature, pressure, and oil composition on oil recovery efficiency have all been the subjects of intensive study (241). Surfactant propagation is a critical factor in determining the EOR process economics (242). Surfactant retention owing to partitioning into residual cmde oil can be significant compared to adsorption and reduce surfactant propagation rate appreciably (243). 

Other Fiber Evaluation Methods. The extent of fiber separation (fiber openness) is an important evaluation criteria that is commonly measured by several techniques, namely ak permeabiUty, adsorbed gas volume, bulk density, and residence (compression and recovery). The adsorption and retention of kerosene is also used as a measure of fiber openness and fiber adsorption capacity (34). 

Bound moisture in a solia is that hquid which exerts a vapor pressure less than that of the pure hquid at the given temperature. Liquid may become bound by retention in small capillaries, by solution in cell or fiber walls, by homogeneous solution throughout the sohd, and by chemical or physical adsorption on solid surfaces. 

Second, most membrane materials adsorb proteins. Worse, the adsorption is membrane-material specific and is dependent on concentration, pH, ionic strength, temperature, and so on. Adsorption has two consequences it changes the membrane pore size because solutes are adsorbed near and in membrane pores and it removes protein from the permeate by adsorption in addition to that removed by sieving. Porter (op. cit., p. 160) gives an illustrative table for adsorption of Cytochrome C on materials used for UF membranes, with values ranging from 1 to 25 percent. Because of the adsorption effects, membranes are characterized only when clean. Fouling has a dramatic effect on membrane retention, as is explained in its own section below. 

It is seen, from equation (5), that a graph relating the reciprocal of the corrected retention volume to the concentration of the moderator can provide values for the adsorption/desorption coefficient and the surface area of the stationary phase. Scott and Simpson [1] used this technique to measure the surface area of a reversed phase and the curves relating the reciprocal of the corrected retention volume to moderator concentration are those shown in Figure 2. 

From the point of view of solute interaction with the structure of the surface, it is now very complex indeed. In contrast to the less polar or dispersive solvents, the character of the interactive surface will be modified dramatically as the concentration of the polar solvent ranges from 0 to l%w/v. However, above l%w/v, the surface will be modified more subtly, allowing a more controlled adjustment of the interactive nature of the surface It would appear that multi-layer adsorption would also be feasible. For example, the second layer of ethyl acetate might have an absorbed layer of the dispersive solvent n-heptane on it. However, any subsequent solvent layers that may be generated will be situated further and further from the silica surface and are likely to be very weakly held and sparse in nature. Under such circumstances their presence, if in fact real, may have little impact on solute retention. 

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