Reverse permeability effect

Some laboratory experiments may be easier to interpret in terms of quantitative Ap/LQ values instead of a dimensionless capillary number. For example, when experiments with surfactants are carried out at constant rates (and thus a constant v]j/a) on rocks of different permeabilities, it appears that the oil recovery actually increases for those rocks with lower permeabilities. Clearly, the better recovery is not a "reverse permeability effect" but it comes about because the AP/La is much higher in tighter rocks when all experiments are carried out at a constant rate. In general, almost all of the experimental and theoretical... 

Addition of sterol to bilayer membranes dramatically decreased both ionic and non-ionic permeability [212] but interaction of polyenes with membrane sterol did more than simply reverse the effect of sterol incorporation. Polyene addition produced specific permeability alterations [201—205] consistent with the creation of ion-selective channels or pores within the bilayer. 

Membrane Pervaporation Since 1987, membrane pei vapora-tion has become widely accepted in the CPI as an effective means of separation and recovery of liquid-phase process streams. It is most commonly used to dehydrate hquid hydrocarbons to yield a high-purity ethanol, isopropanol, and ethylene glycol product. The method basically consists of a selec tively-permeable membrane layer separating a liquid feed stream and a gas phase permeate stream as shown in Fig. 25-19. The permeation rate and selectivity is governed bv the physicochemical composition of the membrane. Pei vaporation differs From reverse osmosis systems in that the permeate rate is not a function of osmotic pressure, since the permeate is maintained at saturation pressure (Ref. 24). 

In Section 7.7.5.4, we discuss the effects of additives in the acceptor wells that create a sink condition, by strongly binding lipophilic molecules that permeate across the membrane. As a result of the binding in the acceptor compartment, the transported molecule has a reduced active (unbound) concentration in the acceptor compartment, cA(t), denoted by the lowercase letter c. The permeability equations in the preceding section, which describe the nonsink process, are inappropriate for this condition. In the present case, we assume that the reverse transport is effectively nil that is, CA(t) in Eq. (7.1) may be taken as cA(t) 0. As a result, the permeability equation is greatly simplified ... 

A very effective way to improve the pertraction performances in permeability and selectivity is to incorporate extractants into the hydrophobic phase, which react with a given solute reversibly and selectively. 

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