Solid water desorption

In this section the distinction between dissolved and sorbed species is introduced into the box model concept in the simplest possible manner, that is, by assuming a reversible linear equilibrium relationship between the dissolved concentration, C (molm 3), and the species sorbed on solids, Cs(mol kg 1). (The units m3 and kgs refer to water volume and solid mass, respectively.) The sorption/ desorption process shall be fast compared to other processes which affect the chemical (e.g., mixing, chemical transformation). As discussed in Chapter 9 (Eq. 9-7), the (observed) solid-water distribution ratio Kd is defined by. 

The secondary drying is governed by two factors the temperature of the product and the binding energy of the water to the solid. The desorption rate DR is the tool to monitor its progress (see Section 1.2.3) ... 

Current multimedia models are inadequate in many respects. Description of intermedia transport across the soil-air and unsaturated soil-saturated soil zones suffers from the absence of a suitable theory for multiphase transport through the multiphase soil matrix. These phenomena are crucial in describing pollutant migration associated with hazardous chemical waste sites. Existing unsaturated-zone soil transport models fail to include mass transfer limitations associated with adsorption and desorption and with absorption and volatilization processes. Rather, most models assume equilibrium among the soil-air, soil-solid, solid-water, and soil-contaminant phases. 

Fig. 9 Water vapor sorption isotherms for a-, P-, and y-CD at 40 C. (Dashed line adsorption, solid line desorption). (Adapted from Ref...

The sublimation step removes the water molecules that were separated from the solids as ice crystals in the freezing step. Sublimation is the process by which solid water is directly transformed into vapour water. When sublimation occurs during the freeze-drying step, it is commonly referred to as the primary drying process . The sublimation step does not affect unfrozen water associated to the solids (sorbed water), which is removed during the desorption step. 

Temperature-programmed desorption was used to monitor water desorption (TPE-temperature programmed evolution) during the solid-state exchange in vacuum as well as for studies of acidity of the samples via adsorption and desorption of ammonia. TPD of ammonia (TPDA) was carried out after NH3 adsorption at 395K for 0.5h on 10 mg discs of samples followed by desorption at the same temperature for Ih. The heating rate was lOK/min. A mass spectrometer (Balzers QMG 311) was applied to determine the desorbed ammonia and water. 

Sorption processes are very effective and include adsorption/desorption (reversible binding at the solid-water interface), absorption (diffusion of pollutants into the solid matrix), precipitation and coprecipitation (incorporation into a freshly formed solid), and occlusion (sequestration of adsorbed pollutants during mineral growth). The most important factors for retention processes are pollutant concentration, the composition of the solid matrix, solution composition (e.g., complexing agents) and E/pH conditions (Brady and Boms 1997). 

Fig. 5. Water desorption from zeolite Linde A in its original cationic form (Na ). Solid lines experimental curves dashed lines calculated elementary curves (see text), a DSC curve b EGA curve (reproduced by permission from [14])...

Figure 3. Computer graphics of (a) changes in the refractive index of the effluent from the adsorption cell filled with the adsorbent, graphitised carbon black, and a non-adsorbing solid (PTFE) and, (b) thermal output of the thermistors measuring heat effects due to interactions at solid-water interface caused by adsorption and desorption of n-butanol from its 10 gf solution in water on 0.0696 g of GRAPHON at 25°C. Flow rate of water carrier - 3 mlh. ...

A new experimental procedure based on the isothermal desorption of vapour is proposed to extend the domain of characterisation of porous solids and powders by capillary condensation until the macropore range. The set-up is based on the use of a Tian-Calvet type microcalorimeter that insures a lull control of temperature gradients around the sample and allows the desorption isotherm to be determined very close to the saturation pressure. The principle of the experiment is described and the first results obtained for water desorption are compared to measurements based on gravimetry as well as to pore size distributions obtained by mercury porosimetry. 

Fig. 2. Water adsorption (solid line) / desorption (dotted Une) isotherms at 295K for (a) PRIOO series and (b) PRSD series carbons...

Homekaer L, Baurichter A, Petrunin W, Luntz AC, Kay BD, Al-Halabi A (2005) Influence of surface morphology on D2 desorption kinetics from amorphous solid water. J Chem Phys 122 124701... 

Diffusion barriers are very hard to measure and are mostly determined by quantum chemical calculations. The quality of these data relies heavily on the potential and substrate used. Experimentally, diffusion barriers can be inferred by detecting reaction products between the mobile species of interest and some immobile, sparse other reactant. Matar et al. [70] were able to determine the diffusion of H on amorphous solid water by reaction of H and O2. In chemical models, often the approximation is made that the diffusion barrier is a constant fraction of the desorption energy values of 0.3, 0.5 or 0.78 are usually taken. 

Fig. XVI-7. Dielectric isotherms of water vapor at 15°C adsorbed on a-FeiOa (solid points indicate desorption). A complete monolayer was present at P/P = 0.1, and by P/P = 0.8 several layers of adsorbed water were present. (From Ref. 110.)...

Fig. 5.10 The adsorption isotherms of n-hexane (A) and of water (B) on graphitized carbon black.Solid symbols denote desorption. (After...

Gas absorption, sembbing desorption, stripping Humidifieation and water eooling Dehumidifieation and air eonditioning Drying of solids, solutions/slumes... 

A. J. H. Eouter, J. van Door-nmalen, J. J. Vreuls and U. A. Th Brinkman, On-line solid-phase extr-action-thermal desorption-gas chr-omatography with ion trap detection tandem mass spectr-ometr-y for the analysis of microcontaminants in water , 7. High Resolut. Chromatogr. 19 679-685(1996). 

We have found that at 60Z R.H. the water concentration In the paint film has increased by l.OZ (m/m) in comparison with that In the wet paint (after correction for the Increase In solid content after spraying). The rate of water absorption by or desorption from the paint layer Is illustrated in Figure 2. 

Gas absorption, scrubbing desorption, stripping Humidification and water cooling Dehumidification and air conditioning Drying of solids, solutions/slurries... 

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