Selectivity active carbon content dependence

The classifications in Table 16-3 are intended only as a rough guide. For example, a carbon molecular sieve is truly amorphous but has been manufactured to have certain structural, rate-selective properties. Similarly, the extent of hydrophobicity of an activated carbon will depend on its ash content and its level of surface oxidation. 

Effectiveness of selective adsorption of phenanthrene in Triton X-100 solution depends on surface area, pore size distribution, and surface chemical properties of adsorbents. Since the micellar structure is not rigid, the monomer enters the pores and is adsorbed on the internal surfaces. The size of a monomer of Triton X-100 (27 A) is larger than phenanthrene (11.8 A) [4]. Therefore, only phenanthrene enters micropores with width between 11.8 A and 27 A. Table 1 shows that the area only for phenanthrene adsorption is the highest for 20 40 mesh. From XPS results, the carbon content on the surfaces was increased with decreasing particle size. Thus, 20 40 mesh activated carbon is more beneficial for selective adsorption of phenanthrene compared to Triton X-100. 

A pressure swing adsorption process (PSA) has been described with high efficiency for separation and capture of C02 in N2 at content from 16 to 25% (22). High purity C02 (> 99%) was recovered with efficiency ranging from 53% to 70% depending on C02 concentration. The selectivity and sorption capacity of zeolite 13X (FAU type) was much better than those of activated carbon. However, the influence of H20 on process efficiency was not reported. It is clear that H20, always present in flue gases from combustion, should first be separated to prevent inhibition of the zeolite. 

A reference material, or a matrix, is a filter paper with constant absorptivity for the whole range of relative air humidities. In calculations and the diagram presented in Figure 45.22, the authors took the equilibrium moisture content Xy p = 0.01 Xp yy y, where Xp yy y Is thc maxlmum equilibrium moisture content of the matrix at 25°C. From the diagram in Figure 45.22, materials of mean sorptive activity (K = 1-1.5, e.g., maize meal, potato flour, and peat) with an absorptivity K that does not depend on air humidity, q>, and materials of high sorptive activity K > 2, e.g., zeolite, silica gel, and activated carbon) with absorptivity that depends to a large extent on the relative air humidity, cp, can be selected. 

Metals other than A1 have been successfully introduced in numerous zeolite frameworks. Aluminum substitution by other metals, such as Fe, Ga, Zn, Co or Cu in the zeolite framework results in modified acidity, and subsequently modified catalytic activity, for certain reactions such as selective catalytic reduction of NOx by hydrocarbons. For example, a calorimetric and IR spectroscopic study of the adsorption of N2O and CO at 303 K on Cu(II)-exchanged ZSM-5 zeolites with different copper loadings has been performed by Rakic et al. [92]. The active sites for both N2O and CO are Cu (I) ions, which are present on the surface as a result of the pre-treatment in vacuum at 673 K. The amounts of chemisorbed species adsorbed by the investigated systems and the values of the differential heats of adsorption of both nitrous oxide (between 80 and 30 kJ mof ) and carbon monoxide (between 140 and 40 kJ mol ) demonstrate the dependence of the adsorption properties on the copper content. 

---