Phase desorption

Adsorption from the gas-phase Desorption to the gas-phase Dissociation of molecules at the surface Reactions between adsorbed molecules Reactions between gas and adsorbed molecules. 

Two-Phase Desorption System. The mixed solvent technique has limited use for complex mixtures since it is more difficult to chromatograph, precludes determination of the polar solvent added, and may cause additional interference to other compounds present. A two-phase system has been developed which is capable of measuring both polar and non-polar organic solvents present simultaneously in work environments (19). 

The large number of ionization methods, some of which are highly specialized, precludes complete coverage. The most common ones in the three general areas of gas-phase, desorption, and evaporative ionization are described below. 

Abstract. In the paper we consider the problems with moving bound that model the kinetics of hydrogen desorption from hydrides of metals. Change of phase, desorption processes and size reduction effect are taken into consideration. Equations are derived at various assumptions for the experimental method of thermal desorption spectrometry. As the high-temperature TDS-spectra peaks are considered, the diffusion may be assumed to be fast. Therefore ordinary differential equations are sufficient. We present the results of numerical experiments for the models with bulk and surface desorption. 

We suppose here that the flux balance from the very beginning determines the dynamics of the dissolved hydrogen concentration. Flux balance is determined by the difference of the desorption flux and the flux from the hydride phase. Desorption is bulk. To avoid singularity in the obtained differential equations at t = 0 we should consider an initial skin a thin layer of metal with dissolved hydrogen around the hydride core. Initial cover appears at the preliminary stage of the TDS experiment before the TDS-splash begins. We model the density of the... 

Different expressions relating the reaction probability 7 to other parameters of the system have been proposed in the case of liquid particles (see e.g., Schwartz, 1986 Hanson and Ravishankara, 1994 Hu et al, 1995 Hanson, 1997a, b Seinfeld and Pandis, 1998). Adopting the scheme shown in Figure 2.4 to account for the transfer of molecules from the gas phase to the surface (adsorption with a corresponding transfer coefficient noted ka(js), from the surface to the gas phase (desorption noted kdes), from the surface into the bulk of the particle (solvation noted ksoi), and from the bulk to the surface (kgs), Hanson (1997b) has... 

Geerdink, R. B., Kooistra-Sijpersma, A., Tiesnitsch, J., Kienhuis, P. G. M., and Brinkman, U. A. Th., Determination of polar pesticides with atmospheric pressure chemical ionization mass spectrometry-mass spectrometry using methanol and/or acetonitrile for solid-phase desorption and gradient liquid chromatography, J. Chromatogr. A, 863, 147-155, 1999. 

Operating condition Adsorption phase Desorption phase... 

Langvardt, P. W., Melcher, R. G. Simultaneous Determination of Polar and Non-polar Solvents in Air Using a Two-Phase Desorption from Charcoal, Am. Ind. Hyg. Assoc. J. 40,1006(1979)... 

Hydrogen chemisorption on fidlerenes has been investigated by several authors. Brosha et al. report an irreversible storage capacity of 2.6 wt%, which corresponds to a stoichiometric formula of C6oHig,7, at 673 K and 103 bar H2. While the samples can be directly hydrogenated through exposure to the gas phase, desorption is irreversible and accompanied by coUapse of the fijllerene structure to graphite-like species [44]. 

Other preservatives, propiconazole and tebuconazole, were also screened using IMS, specifically an lONSCAN with direct solid phase desorption inlet to rapidly detect these substances in Scotch pine (Pinus sylvestris) The findings proved that... 

Rasmussen, J.S. Felby, C. Prasad S. Schmidt H. Eiceman, G.A., Rapid detection of propiconazole and tebuconazole in wood by solid phase desorption ion mobility spectrometry, Wood Sci. Technol. 2001, 45(2), 205-214. 

In solvent recovery plants, temperature-swing processes are most frequently used. The loaded adsorbent is direct heated by steam or hot inert gas, which at the same time serves as a transport medium to discharge the desorbed vapor and reduce the partial pressure of the gas-phase desorpt. As complete desorption of the adsorpt cannot be accomplished in a reasonable time in commercial-scale systems, there is always heel remaining which reduces the adsorbent working capacity. 

In the rectification section, below the feed point, the lighter components are stripped from the adsorbed phase while the heavier components are concentrated in the adsorbed phase. Desorption of the heavier components is accomplished by steam stripping in the bottom section of the column in which the temperature is raised to 510°F by a dowtherm heat exchanger and live... 

Supercritical fiuid extraction and chromatography and comparative complimentary phasing desorption mass spectrometry secondary ion mass spectrometry have been used to determine oligomers in polyethylene terephthalate. ... 

Sorption is the process whereby solute species are transferred from the mobile to the stationary phase, desorption being the reverse process. These processes occur continually throughout a chromatographic separation, and the system is therefore described as being in a state of dynamic equilibrium. A solute is repeatedly re-distributed between the phases as the mobile phase advances, in an attempt to maintain an equihbiium corresponding to its distribution ratio, D. 

Figure 1 Desorption profile and two-phase desorption model regression for the three soils after two month aging period.

While we have no accurate data for the molecular weights of the carboxylate-alumoxanes, based upon the gas phase desorption measurements and the SEI micrographs, we can propose that the particle size of the alumoxanes is significantly smaller than the parent boehmite. Furthermore, the alumoxane particles are rod or sheet-like in shape, not linear polymers. This is due to the destruction of hydrogenbonding within the mineral as hydroxide groups are removed and replaced with acid functionalities, as shown in Scheme 1. 

Adsorption can depend upon the configuration of available sites on the strrface. Desorption is a process of evaporating atoms from a strrface into the vapor phase. Desorption depends upon the surface temperatrrre, the ntrmber of atoms... 

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