Thermal desorption effectiveness

Figure 4.46. Thermal desorption spectra after electrochemical O2 supply to Ag/YSZ through the electrolyte for 10 min. Each curve corresponds to different adsorption temperature and current in order to achieve nearly constant initial coverage. Desorption was performed with linear heating rate, p=l K/s (Inset) Effect of potential on peak temperature.31 Reprinted with permission from Academic Press.

The variations in the kinetic parameters (E, m,n) with chlorine coverage shown in Fig. 5 are entirely consistent with our studies by thermal desorption spectroscopy, which show the effects of chlorine... 

Then the reduction of stored NO with hydrogen was addressed. The stability/reactivity of the NO adsorbed species was analysed under different atmospheres (inert and reducing) both at constant temperature and under temperature programming. The bulk of data pointed out that in the absence of significant thermal effects in the catalyst bed, the reduction of stored nitrates occurs through a Pt-catalysed surface reaction that does not involve the thermal desorption of the stored nitrates as a preliminary step. A specific role of a Pt-Ba interaction was suggested, which plays a role in the NO storage phase as well. 

Air temperatures in arid zones are generally high and show significant daily variations. Because of the absence of a protective vegetative cover and a specific thermal absorption and desorption effects due to surface or rock colors or slope aspect, air temperatures of 35-45°C may reach peaks up to 50-60°C or more on rock surfaces. 

Pumping capacity is an important consideration in thermal desorption. The pumping speed should be sufficiently high to prevent readsorption of the desorbed species back onto the surface. The effect is that spectra broaden towards higher... 

However, due to the difficulties in calculating ion yields in SIMS, quantitation of the data is not very reliable, and their work was not conclusive. We have determined here that the reaction of chemisorbed ethylene to form ethylidyne is first order in ethylene coverage. A noticeable isotope effect was observed, with activation energies of 15.0 and 16.7 Kcal/mole for C H and 02 respectively. These values are smaller than those calculated from TDS, but the differences can be reconciled by including the recombination of hydrogen atoms on the surface in the interpretation of the thermal desorption experiments. 

We have measured the kinetics of ethylidyne formation from chemisorbed ethylene over Pt(lll) surfaces. The rates of reaction display a first order dependence on the ethylene coverage. There is an isotope effect, since the reaction for CjH is about twice as fast as for CjD. We obtain values for the activation energy of 15.0 and 16.7 Kcal/mole for the normal and deuterated ethylene, respectively. These values are lower than those obtained from TDS experiments, but the differences can be reconciled by taking into account the hydrogen recombination when analyzing the thermal desorption data. 

Thermal design methods, for heat exchangers, 13 248-263 Thermal design parameters, effect of uncertainties in, 13 257-258 Thermal desorption... 

Examination of the effect of temperature (220°C-270°C) and the total heating time (20-45 minutes) on the thermal desorption process led us to adopt 2TO°C for 45 minutes as the optimum conditions for further studies. Assessment of the commercially available desorption systems in which there is flash heating of the sample, have shown that significant losses of some important compounds (p-ciesol, indole) occur on the surfaces of the metal connectors and sample transfer lines. It was to overcome these problems that the all silica system (Figure 2) was developed. 

Thermal desorption technologies have several potential limitations. Inorganic contaminants or metals that are not particularly volatile will not be effectively removed by the process. If chlorine or another chlorinated compound is present, some volatilization of inorganic constituents in the waste may also occur. Caution should also be taken regarding the disposition of the material treated by thermal desorption because the treatment process may alter the physical properties of the material. 

The thermal blanket technology does have several limitations. High soil moisture increases the cost of remediation involving thermal desorption because of the energy required to vaporize the water. In addition, treatment within the saturated zone is not feasible since treatment temperatures would be limited to the boiling point of water (i.e., 100°C). Finally, the technology is only effective to an approximate depth of 0.5 m below ground surface. 

Inorganic contaminants or metals that are not particularly volatile will not be effectively removed by thermal desorption. H chlorine or another chlorinated compound is present, some volatilization of inorganic constituents in the waste may also occur. 

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