Sorption temperature dependence

Piatt, J.J., Backhus, D.A., Capel, P.D., Eisenreich, SJ. (1996) Temperature-dependent sorption of naphthalene, phenanthrene, and pyrene to low organic carbon aquifer sediments. Environ. Sci. Technol. 30, 751-760. 

Classical characterization methods (gas sorption, TEM, SEM, FTIR, XPS and elemental analysis) were used to describe the resulting porous carbon structures. Temperature-dependent experiments have shown that all the various materials kept the nitrogen content almost unchanged up to 950 °C, while the thermal and oxidation stability was found to be significantly increased with N-doping as compared to all pure carbons. Last but not least, it should be emphasized that the whole material synthesis occurs in a remarkably energy and atom-efficient fashion from cheap and sustainable resources. 

Spurlock, F. C., Estimation of humic-based sorption enthalpies from nonlinear isotherm temperature dependence Theoretical development and applications to substituted phenylureas , J. Environ. Qual., 24,42-49 (1995). 

The results of experimental studies of the sorption and diffusion of light hydrocarbons and some other simple nonpolar molecules in type-A zeolites are summarized and compared with reported data for similar molecules in H-chabazite. Henry s law constants and equilibrium isotherms for both zeolites are interpreted in terms of a simple theoretical model. Zeolitic diffusivitiesy measured over small differential concentration steps, show a pronounced increase with sorbate concentration. This effect can be accounted for by the nonlinearity of the isotherms and the intrinsic mobilities are essentially independent of concentration. Activation energies for diffusion, calculated from the temperature dependence of the intrinsic mobilitieSy show a clear correlation with critical diameter. For the simpler moleculeSy transition state theory gives a quantitative prediction of the experimental diffusivity. 

Table I. Values of Kq and q0 Giving Temperature Dependence of Henry Constants for Sorption in 5A Zeolite and Chabazite according to Equation 2 ...

As a consequence of the assumed temperature dependence of the molecular volume of the sorbate, the isosteric heats of sorption, calculated... 

Figure 8. Temperature dependence of limiting diffusivity for sorption in 5A zeolite data for C02 from Sargent and Whitford (37), X theoretical line from Equations 14 and 16, — data of Garg (31),. ...

This picture fits very well with the tendency of the sorption isotherm curvature (and hence of the site sorption mode) to disappear at T > Tg. On a more quantitative level, the above characterization of the Henry sorption mode is supported by the smooth temperature dependence of K, found in the PET-C02 system 12), which indicates a roughly unchanged enthalpy of sorption AH, above and below Tg. Additional support is provided by the correlation between K, and the Lennard-Jones parameter s/k characteristic of the gaseous penetrant, in accordance with... 

The quantitative formulation of the site sorption mode, on the other hand, has the virtue of simplicity, but is undoubtedly rather highly idealised. Ideally, Eq. (9) refers to a collection of distinct, permanent and independent sites each accomodating one penetrant molecule Sq measures the concentration of these sites in the membrane and K2 their affinity for the penetrant assuming them to be isoenergetic 35,36). On this basis, the temperature dependence of K2 should yield a constant enthalpy for this sorption mode AH2 35,36). Consistency with the physical picture presented above requires moreover that AH2 be more exothermic than AH, U). 

Temperature Dependence Values of K(K have usually been measured at temperatures between 20 and 25°C. Temperature caused changes in are expected to be similar to those of Kow. Werth and Reinhard [8] studied the influence of temperature on TCE sorption by natural sediments soils, and aquifer material. In agreement with theoretical considerations, they found small heat effects under conditions when the soil organic matter was assumed to be the dominant sorbent phase. 

Polymer hydrophilicity can be judged in the cases (a), (c), or (d) of Fig. 14.1. It is defined as the affinity of a polymer for water, which can be quantified by the equilibrium mass gain, W, determined in standard conditions, e.g., in a saturated atmosphere from a sorption experiment. depends on the vapor pressure or activity of water and on the temperature. It varies, typically from 0 to 10% in most networks. 

The leak rate becomes critical if the solid content is small, e.g. 1%, then ql-rmx has to be 2 X 10-3 mbar L/s, all other conditions being equal. In such cases, the leak rate of the chamber should be measured before charging the product The secondary dying step depends on only one factor the sorption behavior of the product and its temperature dependence which is shown for one product in Figure... 

Sorption coefficients quantitatively describe the extent to which an organic chemical is distributed at equilibrium between an environmental solid (i.e., soil, sediment, suspended sediment, wastewater solids) and the aqueous phase it is in contact with. Sorption coefficients depend on (1) the variety of interactions occurring between the solute and the solid and aqueous phases and (2) the effects of environmental and/or experimental variables such as organic matter quantity and type, clay mineral content and type, clay to organic matter ratio, particle size distribution and surface area of the sorbent, pH, ionic strength, suspended particulates or colloidal material, temperature, dissolved organic matter (DOM) concentration, solute and solid concentrations, and phase separation technique. 

Additional characteristics typically associated with hydrophobic sorption or partitioning include sorption isotherms that are linear over a relatively wide range of concentrations, sorption coefficients that are not strongly temperature dependent, and a lack of competition between sorbates (Chiou, 1989). 

The remaining vacuum pumps to be discussed in this chapter fall into a group which remove gas particles from systems by sorption effects such as adsorption, chemisorption/gettering and implantation. They tend to be used on systems where any contamination of the vacuum by pump fluids, lubricants, etc. must be avoided. However, those pumps that remove gas particles exclusively by temperature-dependent gas adsorption on molecular sieves or A1203 (adsorption pumps) will not be discussed. 

The ability of palladium to adsorb or absorb large amounts of hydrogen was known before the end of the last century. Much more precise work has been reported in recent years (I, 2, 3, 18). Such studies accurately showed the dependence of the sorption process on pressure and temperature. The isotherms generally indicated a sudden increase in the sorption of hydrogen at a certain pressure, which was very temperature-dependent. This sudden rise in the amounts sorbed at definite pressures suggested a phase shift in the crystalline structure of the palladium from a hydrogen-poor cr-phase to a hydrogen-rich / -phase. Such... 

The sorption data showed that the change proceeded in an isobaric manner which was strongly temperature-dependent, varying from 4 to 5 mm. at 0° C. to 4000 mm. at 200° C. Sievertz and Briinig (18) constructed a critical zone, similar to those found in gas condensations, under which the amount adsorbed was small and above which the pressure increased sharply. Gillespie and Galstaun (1) found the critical point to be 295.3° C. at 19.87-atm. pressure. Here the H/Pd ratio equalled 0.270. Above this temperature the isotherms showed almost normal character. Sievertz and Briinig (18) found that the log P at which the transformation took place varied inversely as the absolute temperature. 

Hansson, J.-A. (1970). Sorption of hemicelluloses on cellulose fibres, Part 3. The temperature dependence on sorption of birch xylan and pine glucomannan at kraft pulping conditions. Sven. Papperstidn. 73,49-53. 

The position of the sorption isotherms depends on temperature the higher the temperature, the lower the position on the graph. 

Almog and hrier (1978) made a direct calorimetric measurement of the dependence of the heat of solution of ribonuclease A on water content (Fig. 2). The heat of solution drops strongly in the low hydration range 90% of the heat change is obtained at about half-hydration. The differential heat for transfer of water from the pure liquid to the protein is estimated from the data of Fig. 2 as 8 kcal/mol of water at the lowest hydration studied (the heat of condensation of water should be added for comparison with isosteric heats), and it decreases monotonically with increased hydration. There is no extremum at low hydration, unlike what has been reported based on the temperature dependence of the sorption isotherm. It is not clear whether this difference reflects inaccuracies in the data used in van t Hoff analyses of the sorption isotherms, or a complex hydration path that is not modeled properly in the van t Hoff analyses. 

For the material with cellular pores the temperature dependence of the lower closure point pressure (plpo)i. was measured over a wide temperature range. It is found that in a hysteresis phase diagram (ptpo vs. 777i) the locus of (p/po)H and of the closure point-pressure p po)h almost coincide. Thus it appears that this locus represents a universal border line between sorption isotherms with and without hysteresis loop. 

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