Desorption water

Enabhng the use of hard or even sea water for heat rejection e,g, for absorption of gases (CO9, SO9, CIO9, , , ) in chilled water (desorption is provided simultaniously with chilling) when a direct contact barometric condenser is used. 

Figure 2.2 Reactivity of oxygen states chemisorbed at Ni(210) (a) at 295 K and (b) at 77 K to water adsorbed at 77 K. The oxygen concentration ct is calculated from the 0(1 s) spectra. The oxygen state preadsorbed at 295 K is unreactive with water desorption complete at 160K whereas that at 77 K is reactive, resulting in surface hydroxylation.37 (Reproduced from Refs. 37, 42).

That chemisorbed oxygen was active in hydrogen abstraction, resulting in water desorption and the formation of chemisorbed sulfur, was first established by XPS at copper and lead surfaces.42 An STM study of the structural changes when a Cu(110)-O adlayer is exposed (30 L) to hydrogen sulfide at 290 K indicates the formation of c(2 x 2)S strings. 

Nitrogen adsorption isotherms were measured with a sorbtometer Micromeretics Asap 2010 after water desorption at 130°C. The distribution of pore radius was obtained from the adsorption isotherms by the density functional theory. Electron microscopy study was carried out with a scanning electron microscope (SEM) HitachiS800, to image the texture of the fibers and with a transmission electron microscope (TEM) JEOL 2010 to detect and measure metal particle size. The distribution of particles inside the carbon fibers was determined from TEM views taken through ultramicrotome sections across the carbon fiber. 

Coadsorption of HF and water has no effect on the water desorption peaks, but stabilizes part or all of the HF to higher temperatures, as shown by Figure 5. As long as at least 5 molecules of water per HF molecule are added to the surface (up to monolayer coverage, or 8 H-O/HF for subsequent layers) no HF desorbs until water starts to leave the surface around 170 K, peaking at 180 K. As long as at least 1 molecule of water is initially present per HF, no HF desorption will occur until 150 K, peaking at 162 K. If more HF than H 0 molecules are present initially, some HF will desorb in a peak at 136 K, near the temperature at which HF alone desorbs. Coadsorption thus can yield HF desorption at three peaks, one not stabilized vs. HF alone, one stabilized by 30 K, and one stabilized by 50 K, i.e., to the water desorption temperature. 

Electrochemical cells, particularly those with aqueous electrolytes, operate well above the freezing temperature of water. Since water desorbs from Pt below its freezing point ca. 180 K), there is a very low temperature ceiling for which reactions may take place. While the low temperature of water desorption precludes UHV study of many, if not most, electrocatalytic reactions, the surface reaction... 

The number of acid sites on pillared clays was determined by means of temperature programmed desorption (TPD) of ammonia. In each TPD experiment, a sample weighing about 0.5 g was treated in vacuo for 1 h at a given temperature in the range 400 - 600°C. Ammonia was adsorbed at a desired temperature (100-300°C) for 30 min and evacuated for 30 min. This sample was heated to 700°C at a rate of 10°C/min and desorbed ammonia was monitored by thermal conductivity detector. As water was desorbed simultaneously with ammonia, the ammonia TPD spectrum was obtained by point-by-point subtraction of the water desorption spectrum obtained with the sample which had not adsorbed ammonia. 

To investigate the hydration and dehydration processes of H-SAPO-34 and H-SAPO-37, H and Al MAS NMR spectroscopy was applied under CF conditions with the equipment shown in Fig. 12 (217). The chemical behavior and the change of the silicoaluminophosphate framework were monitored as nitrogen loaded with water or dry nitrogen was injected into the MAS NMR rotor filled with the silicoaluminophosphates. By this approach, the primary adsorption sites of water in silicoaluminophosphates and the variation of the aluminum coordination were observed. Furthermore, the formation of framework defects and the conditions of water desorption were characterized. 

The water desorption from Z500 was characterized by a large endotherm appearing at approximately 160°C. With butanediol and water present (Figure 4), this endotherm was shifted slightly to 175 C and a second small endotherm was observed at 240°C. Also, a large exotherm appeared at about 330-400°C. Since the desorption of a physically adsorbed species should produce an endotherm, it is apparent that the exotherm must be associated with some molecular rearrangement. The most likely explanation is the cyclization reaction of butanediol to produce tetrahydrofuran. 

As discussed in Chapter 10, network polymers - as linear polymers - obey the time-temperature equivalence principle in the domain where they are stable, both chemically (no postcure, no thermal degradation), and physically (no orientation relaxation, water desorption, physical aging, etc.). 

This example is to show that the water desorption during applicable measuring times becomes less and less. If the pressure rise of 8 x 10 2 mbar/h in this installation is converted into leak rate, LR = 3.6 X 10 3 mbar L/s, or after 10 h it drops to 1.8 X10 3 mbar L/s. In the LR region of 10 3 mbar L/s one has to expect such variations between different measurements, since desorption depends on the history of the plant before measurements start and variations of this size disturb neither the BTM nor DR measurements. 

To demonstrate the potential available, simulations were carried out for the oxidation of carbon monoxide on a palladium shell catalyst with water desorption from 3A zeolite as a heat sink, based on experimentally validated model parameters for the individual steps (Figure 16). The calculations indicated that the reaction cycle time could be lengthened by a factor of 10, to a total 20 minutes, in comparison to a simple regenerative process with a similar amount of inert material instead of adsorbent in the fixed bed and for the same threshold for temperature deviation from the initial value. 

Figure 5.7. Amount of (a) copper (Cu2+) and (b) calcium (Ca2+) sorbed and subsequently desorbed by peat as a function of time. Sorption involved addition of 0.2 cmol Cu2+ or Ca2+ kg-1 H-saturated peat in 1 liter of water. Desorption involved addition of 0.2 cmol H30+ ions to the samples from the sorption experiments in 1 liter water. The stirring rate was 470 rpm and the temperature of the studies was 298 K. [From Bunzl et al. (1976), with permission.]...

In accordance with these features, the film deposition mechanism presented in Figure 9.7 was suggested. To explain the decrease in the film growth rate and the variation of the composition of chemisorbed MC1X surface groups with temperature, it was assumed that the concentration of surface OH groups is controlled by the dehydroxylation (water desorption) reaction (Figure 9.8). 

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