Water transfer between solid components

VIII. TRANSFER OF WATER BETWEEN SOLID COMPONENTS VIA THE HEADSPACE... 

Figure 21 Diagram of compartment model for the numerical simulation of calcic soil development. Compartments on left represent solid phases and compartments on right represent aqueous phases. Line A represents precipitation, line B represents dust influx, line C represents the transfer of components due to dissolution and precipitation, hue D represents transfer between aqueous phases, line E represents downward movement of solutes due to gravitational flow of soil water, line F represents evapotranspira-tional water loss, and line G represents leaching losses of solutes (McFadden et al, 1991) (reproduced by permission of Soil Science Society of America from Occurrence, Characteristics, and Genesis of Carbonate, Gypsum and Silica Accumulations in Soils, 1991).

Gas-to-liquid mass transfer is a transport phenomenon that involves the transfer of a component (or multiple components) between gas and liquid phases. Gas-liquid contactors, such as gas-liquid absorption/ stripping columns, gas-liquid-solid fluidized beds, airlift reactors, gas bubble reactors, and trickle-bed reactors (TBRs) are frequently encountered in chemical industry. Gas-to-liquid mass transfer is also applied in environmental control systems, e.g., aeration in wastewater treatment where oxygen is transferred from air to water, trickle-bed filters, and scrubbers for the removal of volatile organic compounds. In addition, gas-to-liquid mass transfer is an important factor in gas-liquid emulsion polymerization, and the rate of polymerization could, thus, be enhanced significantly by mechanical agitation. 

Often the easiest way to set the initial water activity of components of the reaction mixture is by pre-equilibration with a saturated salt solution. The relative humidity or water activity is fixed above a saturated solution of a given salt at a known temperature. As water equilibrates in or out of the solution, solid salt will tend to dissolve or crystallize to maintain saturation and hence the fixed water activity in the headspace. Any other material placed in contact with the headspace will eventually equilibrate to the same water activity. The reaction mixture component can simply be placed inside a closed vessel together with the salt solution, such that water can transfer between the two via the vapour phase. Wide-mouth screw cap jars are convenient, with salt solution over the base and an open vial containing the sample (Fig. 8-3). The rate of equilibration depends on the surface areas exposed and the amount of water that must be transferred. Typically 1-2 days is sufficient for either solid biocatalyst preparations or liquid phases based on relatively non-polar organic solvents. The rate of equilibration may be checked by weighing or Karl Fischer analysis respectively. 

The mass transfer between imdergroimd gas and water in geologic conditions is dominated by gas or volatile organic components. At high pressure and temperature substances can participate in it, which under normal conditions are in liquid or even solid state. Influx of such components in the subsurface gas is called volatilizing or evapouration, and their absorption by water - dissolution. 

Charged atoms or molecules are called ions. If Na and Cl are close together in solution, transfer of electrons between them easily occurs, and because of their opposing charges, they are mutually attracted, combining to form salt, NaCL The bond betwieen them is described as electrovalent. In solution in water, electrovalent compounds such as NaCI tend to separate into their component ions, and to join together again only in the solid material, thus ... 

In the case especially of dipolar liquids or of dipolar liquids adjacent to a liquid or solid metal (electrode case), the electrical properties of the interphase are intimately connected with (a) the structure of the interphase, l.e., the extent of dipole orientation as measured by the component resolved in the normal to the interface, and (b) any degree of charge-transfer that arises from donor/acceptor interaction between the dipoles of the polar liquid or adsorbable components dissolved in it and the metal, e.g., in the case of water, alcohols, amines, heterocyclic bases such as pyridine, etc. 

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