Saturation sorptive

FIGURE 5.28 Influencing factors of chamber climate in a trough chamber 1 — evaporation of low volatile components of the mobile phase from the trough bottom until saturation, 2 — sorptive saturation, 3 — evaporation from the layer, 4 — adsorption of the vapor phase. 

Under saturated or very wet conditions, soils tend to have increased amounts of OM. This results in dark colors and dramatically changes the chemical characteristics of a soil. OM increases a soil s sorptive and cation exchange capacities and thus alters the movement and extraction of components present. OM increases ped formation and stability, thus increasing both aeration and percolation, but under saturated conditions, reduction reactions prevail (see Figure 2.12). 

Recently, Bonin and Simpson (2007) showed in their study that polycyclic aromatic hydrocarbons sorptive behavior could not be solely attributed to a specific SOM chemical characteristic (i.e., aliphaticity or aromaticity) and concluded that both structure and OM physical conformation are important in sorption processes. Martin-Neto et al. (1994b) used analysis of microwave power saturation curves (Weil et al., 1994) to obtain information about HA conformation. They observed that at pH > 3.5 a typical curve of homogeneous saturation was obtained for the oxisol HA, whereas at pH 2.3 inhomogeneous saturation occurred. The peat HA showed only homogeneous saturation. However, a similar inhomogeneous trend ... 

Because the density of the adsorbate pj cannot be measured directly, the liquid density at the triple point may be used as an approximation. It should be bom in mind that according to eqs. (5b) moEX and m are practically identical for low densities or at low pressures of the sorptive. At high densities, eg. near saturation pressure remarkable differences may exist. Consequently, the same effects should be taken into account when calculating the inner surface of porous solids fi om higex or m , respectively. 

Pre-loading means, in general terms, i.e. irrespective of the degree of saturation of the chamber and layer, any sorptive uptake of gas molecules from the chamber atmosphere by the imwetted TLC layer (see also Section 3.4 Conditioning ). 

Sorptive saturation means that condition in which the chromatographic layer is in equilibrium with all components of the saturated gas space. This is a special case of pre-loading , namely its upper limit. 

The sorptive saturation of the layer with solvent molecules can also be achieved using the time-controlled conditioning equipment of Baron (Fig. 61). At the end of the selected conditioning time (maximum 60 min), the plate is automatically lowered into the solvent. 

Figure 61. Conditioning device as an aid to the sorptive saturation of the layer by solvent molecules (Baron)...

The equilibrium water saturation of a polymeric system increases with the number of polar groups present in the polymeric matrix. Circumstances like the accessibility of the polar groups, the relative strength of the water-water versus water-polymer bonds and for semi-crystalline polymers the degree of crystallinity, hamper a straightforward correlation between the number of polar groups and the solubility. Van Krevelen [1] presents the amount of water per structural group at equilibrium (expressed as molar ratio), as what he calls the best possible approach to the sorptive capacity of (amorphous) polymers versus water. 

Besides any capillary transport of liquid moisture and vapor diffusion, there is sorptive or bound moisture diffusion within the fibers when they are less than fully saturated [50]. At relative humidities below 0.8, the sorptive transport coefficient diminishes exponentially with decreasing values of relative humidity. 

Sorbent offers many energetically nearly homogenous adsorption sites. Sorptive gas pressure (p) is well below saturation pressure at system temperature ps(T) > p. 

Here the index (c) indicates critical state of the sorptive gas. The pressure (Pr) is known as Riedel pressure, an equivalent for the saturation pressure for supercritical temperatures of the gas [7.17]... 

Figure 7.12. The BET-adsorption isotherm (BET AI), Eq. (7.70) showing for C>2 an inflection point and at the sorptive gas saturation pressure p = Ps(T) a singularity n — 00 indicating pore condensation and the appearance of a bulk liquid phase [7.1-7.5],...

Here po is the density of the sorptive medium in a reference liquid state which may be chosen as the density of the saturated boiling liquid at the chosen temperature, i. e. po = Ps (T), [7.5, 7.3]. The parameter a in the characteristic curve of the sorbent material (7.78) is the reciprocal of a specific energy the exponent N normally is limited to 2 < N < 6 and for zeolites and activated carbons often has numerical values about N = 3. Both parameters are characteristic for a sorbent material and the micropore spectrum included in it. Details of practical applications of (7.79) and a variety of generalizations to real gas adsorptives and multicomponent systems can be found in the (still growing) literature in this field [7.53 7.55, 7.58]. 

Po Pa reference pressure, often chosen as saturation pressure of sorptive gas at temperature T, i. e. po = ps(T)... 

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