Adsorption selection criteria

Selectivity for C02 it represents the C02 uptake ratio to the adsorption of any other gas (typically nitrogen for post-combustion capture, and methane for natural gas). It is an essential evaluation criterion, and affects the purity of the adsorbed gas, which will significantly influence the sequestration of C02. The simplest method to estimate the selectivity factor is to use single-component adsorption isotherms of C02 and nitrogen. 

Reversibility. Apparent irreversibility phenomena of ion exchange in NaX were studied with zinc and cobalt ions using a temperature-variation method described in the experimental section. In view of the high selectivity of NaX for bivalent cations at low zeolite loading, the concentration of bivalent ions in the equilibrium solution is quite sensitive to small changes in the surface composition. In fact, the adsorption removal of bivalent cations at low loading, below 0.2, is quantitative or nearly so (99.5% or better). Consequently the value of the equilibrium concentration is an ideal criterion for assessing either reversibility or equilibrium conditions. 

Different charge-compensating cations in zeolite L have been tested for their promotional effect in n-hexane aromatization. Apparently, high basicity of the alkaline and alkaline earth promoter favors n-hexane aromatization. Basicity and selectivity both increase from Li and Cs 331) and from Mg to Ba (22,25). Bezouhanova et al. studied the FTIR bands of linearly adsorbed CO in the range of 2060-2075 cm . One band at 2075 cm", which is also found on unsupported Pt, is attributed to extrazeolite Pt particles, a second band shifts from 2060 cm" for Li to lower wavenumbers with K and Rb 331). Another criterion, used by Larsen and Haller, is the measured rate of competitive hydrogenation of benzene and toluene, which has been found to correlate with the zeolite basicity (25). As described in a previous section, this method had previously been used by Tri el al. to probe for the electron deficiency of Pt particles in acidic zeolites 332). The rate data are analyzed in terms of a Langmuir-Hinshelwood model and the ratio of the adsorption coefficients of toluene and benzene, A, /b, is determined. It was found to decrease from 8.6 for Pt/Si02, and 5.4 for Pt/MgL, to 4.4 for Pt/BaL. As direct electron transfer from the cations to neutral Pt particles is unlikely, an interaction of Pt with the zeolite framework or with... 

Figures 5(a) and 5(b) show the simulated breakthrough curves of both total protein and HSV-1 respectively. It should be noticed that the dimensionless time scales in these two figures differ by four orders of magnitude. The breakpoint of HSV-1 is the operating endpoint at which the effluent from the adsorption column can no longer meet the desired sterilization criterion. Since the HSV-1 has a much higher affinity to the bead surface, the breakpoint of HSV-1 appears much later than that of the total protein. To optimize the protein recovery, one should improve the design of the bead surface (better selectivity, higher loading capacity), size, and operating parameters of the filter to further delay the breakpoint of the virus elution. A stochastic approach to model the removal process may be more appropriate in low concentrations of viruses.

Finally, Satterfield (p. 185) states that highly mobile" oxygen should result in a highly active, nonselective catalyst. Germain in fact says that for simple metal oxides there is a direct, but limited, correlation between activity and oxygen mobility. Satterfield also points out, however, that oxygen mobility as a sole criterion for catalyst activity and selectivity is somewhat limited. For instance, this concept does not account for the effect of partially oxidized intermediate adsorption on selectivity in series-type reactions nor for the effects of mixed oxide composition and catalyst surface defects on catalytic reactivity, especially in partial oxidation reactions. 

MenU F, Lucat C, Debich A (1994) The thick-film route to selective gas sensors. Sens Actuators B 25 415- 20 Miller JB (2001) Catalytic sensors for monitoring explosive atmospheres. IEEE Sensors J l(l) 88-93 Park J-H, Yang RT (2005) Simple criterion for adsorbent selection for gas purification by pressure swing adsorption processes. Ind Eng Chem Res 44 1914-1921... 

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