Permeation conditions

The quantitative descriptor of lipophilicity, the partition coefficient P, is defined as the ratio of the concentrations of a neutral compound in organic and aqueous phases of a two-compartment system under equilibrium conditions. It is commonly used in its logarithmic form, logP. Whereas 1-octanol serves as the standard organic phase for experimental determination, other solvents are applied to better mimic special permeation conditions such as the cyclohexane-water system for BBB permeation. Measurement of log P is described in Chapters 12 and 13 as well as in Ref [22]. 

Depending on reaction and permeation conditions, two modes of FC can be defined natural and forced filtration. In the first case, infiltration flow is a consequence of the natural pressure gradient between the atmosphere (typically constant) and the reaction zone. In the second case, forced gas flow is induced by... 

The issues related to containment of reaction components are sometimes underestimated in their importance. Their consequences, however, will surface quickly early in full implementation. Some general material characteristics have been discussed in Chapter 4, but they are mostly limited to the temperature and chemical environment typical of traditional separation applications. The material aspects of the membrane related to high-temperature reactive and permeating conditions will be reviewed in this section. 

As a special case there is pervaporation, in which the feed material is a liquid, but the permeate becomes a gas or vapor. That is, the temperature and pressure of the permeate produced are such that the permeate product will exist in the gaseous or vapor phase. Conceivably and conversely, the feed stream could be a gas but the permeate conditions would be such that the components selectively obtained would constitute a liquid phase. In any event, compositional phase changes (e.g., flash vaporizations) can affect the outcome. 

A water-in-oil emulsion dispersed in an aqueous phase (W/O/W ELM) is generally stabilized by the addition of a surfactant. In the case of type 2 facihtation, a carrier species is also present. The concentration of these additives together with the composition of the internal aqueous phase, external aqueous phases, and the permeation conditions influence the properties of the ELM system. These effects are summarized as follows ... 

Permeate conditions pressure 0.5 to 2 kPa absolute with condenser temperatures -20 to +30°C. 

The receptor phase of any diffusion cell should provide an accurate simulation of the in vivo permeation conditions. The permeant concentration in the receptor fluid should not exceed 10 percent of saturation solubility (Skelly et al. 1987), as excessive receptor phase concentration can lead to a decrease in absorption rate and result in an underestimate of bioavailability. The most common receptor fluid is pH 7.4 phosphate-buffered saline (PBS), although if a compound has a water solubility below 10 p.g/mL, then a wholly aqueous receptor phase is unsuitable, and addition of solubilizers becomes necessary (Bronaugh 1985). 

In order to solve the MDPE in Equation 9.1, it is necessary to understand how y is related to x. There are numerous methods of describing this relationship. Gas separation involves the diffusion of a gaseous mixture through the membrane material. The rate at which a gas, or particular component of a gas mixture, moves through a membrane is known as the flux (total or individual). In order to obtain a general flux model for a gas separation membrane, the fundamental thermodynamic approach incorporating the solution-diffusion model [11] will be used at vacuum permeate conditions (itp 0) ... 

Feed temperature = dose to the normal boiling temperature usually 50-100 °C. Permeate conditions pressure 0.5-2 kPa absolute with condenser temperatures -20 to -t30 °C. 

Membrane type aCOi/Hj CO2 permeability (Barrer) Gas permeation conditions Reference... 

T. Suzuki, Y. Tabuchi, S. Tsushima, S. Elirai, Measurement of water content distribution in catalyst coated membranes under water permeation conditions by magnetic resonance imaging, Int. J. Hydrogen Energy 36 (2011) 5479—5486. 

The enhancement of the barrier provides compensation for the effects of reduced wall thickness in lighter weight packaging and smaller-size containers. The wall surface area per unit of the content is inversely related to container size. Pig. 33.14 shows the effect in terms of yearly oxygen ingress under constant permeation conditions, P, and wall thickness. 

The permeation properties of PMP were also determined as a function of feed gas composition using mixtures of 1 to 8 mol% w-butane in methane. The mixed-gas permeation conditions were the same as those described above. The i-butane and methane permeabilities of PMP as a function of the relative n-butane pressure are shown in Figure 2. The relative -butane pressure, p/psatj is the partial n-butane pressure in the mixture to the n-butane saturation pressure at 25 C (35.2 psia). As the relative n-butane pressure in the feed gas increased from 0 to about 0.1, the permeability of methane decreased about 5-foId, whereas the n-butane permeability was essentially constant. As a result, the n-butane/methane selectivity of PMP increased from 11 at a relative n-butane pressure of 0.05 to 16 at a relative n-butane pressure of 0.38, as shown in Figure 3. 

In these models, the equations governing the flow and species balance in the feed channel are standard and are coupled together via the variation of viscosity with concentration and wall permeation. On the other hand, the wall permeation conditions of solvent and solute permeation need to be identified. If the membrane rejection of the solute is identified via a salt rejection coefficient, Ri, then the following conditions hold at the membrane wall (y = 0) (Figure 7.2.3(b)) for the solute transport ... 

The solvent permeation condition at the wall employs, along with the no-slip condition (i.e. = 0 at y — 0), the... 

Seawater RO desalination plants typically consist of the following key components intake pretreatment system filter effluent transfer pumps high-pressure pumps, piping, and RO membrane system energy recovery system and permeate conditioning (posttieatment) facilities. 

Steps 1 and 5 depend on the following factors permeation conditions (temperature and partial pressures), the nature of the chemical species and the type of crystalline material. Steps 1 and 5 are, generally, assumed to be fast processes. Steps 2, 3 and 4 are usually activated processes (Barrer, 1990). Intra-crystalline zeolite diffusion is described as configurational diffusion. 

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