Desorption, temperature

A secondary fan draws the air and forces it through the secondary heat exchanger, where the reduced air volume temperature is raised to the required desorption temperature. The preheated air is then used to desorb the air in one portion of the wheel. As the air exits the desorption section the organic concentration is approximately 10 times the concentration of the original process stream. This low volume, higher concentration stream then enters the induced draft section of a catalytic or thermal recuperative oxidizer, where the organics are destroyed. 

FIG. 9 (a-c) Experimental LEED intensities for (1 x 3) (solid line) and (1x2) (long-short dashed) structures and corresponding TPD rates (dotted lines) as a function of desorption temperature for approximate initial coverages 1 /3, 1 /2, 2/3 ML. Arbitrary units, (d-f) Theoretical LEED intensities, calculated with Eq. (40), and theoretical TPD rates for these initial coverages. Heating rate 1 K/s. (Reprinted from Ref. 39 with permission from Elsevier Science.)... 

Current use of statistical thermodynamics implies that the adsorption system can be effectively separated into the gas phase and the adsorbed phase, which means that the partition function of motions normal to the surface can be represented with sufficient accuracy by that of oscillators confined to the surface. This becomes less valid, the shorter is the mean adsorption time of adatoms, i.e. the higher is the desorption temperature. Thus, near the end of the desorption experiment, especially with high heating rates, another treatment of equilibria should be used, dealing with the whole system as a single phase, the adsorbent being a boundary. This is the approach of the gas-surface virial expansion of adsorption isotherms (51, 53) or of some more general treatment of this kind. 

Figure 5.24. Effect of catalyst potential, Uwr, on oxygen peak desorption temperature, Tp during 02 TPD from Pt/YSZ.4,5 The exact definition of Uwr has been given in Figure 4.45. It is the UWr value at the beginning of the TPD run and differs little (<0.1 V) from the UWR value at Tp.4,7 Reprinted with permission from the American Chemical Society.

H2 TDS was used as the highest H2 desorption temperature (370 K) occurs below the temperature regime of encapsulation. For the reduced sample there was a 70% decrease In H2 chemisorption and a 33 K shift to lower temperatures when the unannealed sample (first H2 TDS) was compared to the sample annealed at 370 K (second H2 TDS). No change In the AES was observed after either the first or second TDS, showing that the Pt overlayer does not Island or encapsulate. We take these low Pt coverage experiments to Indicate an electronic Interaction (preferably bond formation, which does not require significant charge transfer) between Pt and reduced Tl species that Is activated at about 370 K. 

The peak in Ae methane TPD curve occurs at 230 K. The appearance of gas-phase meAane marks Ae temperature at which methane is formed on Ae surface because Ae reaction temperature is well above Ae desorption temperature for meAane. As wiU be Ascussed below, Ae donainant mechanism for meAane fotmation on Ni(lOO) is ... 

Temperature-programmed desorption of mesitylene shows a marked difference to the catalysts prepared on MgCl2 surfaces. The spectrum contains only one desorption peak at aroimd 250 K. Due to the similar desorption temperature to the peak observed for MgCl2-based films, this peak was assigned to desorption from low coordinated or defect sites [118]. 

Figure 2 displays a qualitative correlation between the increase or decrease in CO desorption temperature and relative shifts in surface core-level binding energies (Pd(3d5/2), Ni(2p3/2), or Cu(2p3/2) all measured before adsorbing CO) [66]. In general, a reduction in BE of a core level is accompanied by an enhancement in the strength of the bond between CO and the supported metal monolayer. Likewise, an opposite relationship is observed for an increase in core-level BE. The correlation observed in Figure 2 can be explained in terms of a model based on initial-state effects . The chemisorption bond on metal is dominated by the electron density of the occupied metal orbital to the lowest unoccupied 27t -orbital of CO. A shift towards lower BE decreases the separation of E2 t-Evb thus the back donation increases and vice versa. 

Simulations of the storage have shown that desorption temperatures below the possible 130 °C from the district heat can lead to higher COPcw,/. Experiments with 130 °C, 100 °C and 80 °C were carried out. Figure 256 shows the 100 °C desorption as an example. 

The results for COP. / , ,. COPcoo and pcoo/ for the different desorption temperatures were shown in Table 35. 

The best performance was measured using a desorption temperature of 80 °C. Below that temperature almost no dehumidification can be observed. 

The results of a similar experiment with adsorbed hydrogen is shown in Fig. 2.3b. Only one desorption peak was observed in the temperature range studied [50], The desorption peak temperature lies at 420 K for the experiment with 0.8 L and is shifted to lower temperatures as the H2 concentration increases indicating second order desorption kinetics. Surface states with desorption temperatures at 165 K, 220 K, 280 K and 350 K were reported for the adsorption of H2 and D2 at 120 K [51]. Thermal desorption experiments after H2 adsorption at 350 K show only one desorption state at ca. 450 K [52],... 

---