Adsorption isotherms on activated carbons

Figure 1 PSDs obtained using grand canonical Monte Carlo (GCMC) molectdar simulation to interpret CH4, CF4 and SFfi adsorption isotherms on activated carbon at 296 K [24].

To satisfy this condition, the Gaussian distribution should be multiplied by the factor 2/[l + erf B/fTg, i2 )] [121] consequently, the isothemi Eq. (54) should be also multiplied by this factor. This factor is negligible for 5/2.3because the erf function is close to unity. Another disadvantage of the truncated Gaussian distribution (i.e., Eq. (53) a 0) is its nonzero value for 5 = 0, which is physically unrealistic 5 = 0 implies that the micropore dimension x = 0 and then the distribution function should be equal to zero [122]. Stoeckli et al. [123-125] and Dubinin [115, 126] showed tliat Eq. (54) gives a good representation of many adsorption isotherms on active carbons. 

This Appendix gives the location of the large amount of data scattered throughout the textbook, abietic acid-heptane-methylcellosolve+10% water Distribution coefficient. Table 13-3 acetic acid Adsorption isotherm on activated carbon, Table 18-2 and Problem 18.D7 acetic acid-benzene-water Distribution coefficients. Table 13-3 acetic acid-l-butanol-water Distribution coefficient. Table 13-3 acetic acid-3-heptanol-water Distribution coefficient. Problems 13.D5 and 13.D6 acetic acid-isopropyl ether-water Equilibrium data. Table 13-5 acetonaphthalene Adsorption isotherm on silica gel. Table 18-2... 

Figure 10.26. Hydrogen adsorption isotherms on activated carbon, CECA AC35 (BET surface area 1000 m /g, from Lamari et ai., 2000, with permission).

Braeuer, P. Salem, M., and Hatting, P Calculation of single adsorption isotherms from gravimetrically measured binary gas mixture adsorption isotherms on activated carbon at high pressures, Sep. Purif Technol., 12(3), 255-263(1997). 

Single-component adsorption equilibria on activated carbon of the n-alkanes Q-C4 and of the odorant tert-butyl mercaptan were measured at the operating conditions expected in a large-scale facility for adsorbed natural gas (ANG) storage. The experimental data were correlated successfully with the Adsorption Potential theory and collapsed into a single temperature-independent characteristic curve. The obtained isotherm model should prove to be very useful for predicting the adsorption capacity of an ANG storage tank and to size and optimize the operation of a carbon-based filter for ANG applications. 

Adsorption isotherms on microcrystalUne carbons, which include charcoals, carbon blacks, and active carbons, from solutions of solids and liquids have been found to be of the forms shown in Figure 3.1. The Freundlich isotherm equation could be applied to isotherm 1(c), which is for solutions of solids of limited solubility. The other three forms of isotherms show a maximum in each case that could not be... 

Ideal adsorbed solution theory (lAST) was used in this study because it is the most common approach used to predict the multicomponent adsorption isotherms onto activated carbon by using only single solute equilibrium data. The lAST is based on the assumption that the adsorbed mixture forms an ideal solution at a constant spreading pressure. The model can be represented by the following Equation 6.4 ... 

Fig. 1. Fquilihrium isotherms for adsorption on activated carbon at 298 K showing the effect of surface modification (2). —, SO2 -...

Isotherm Models for Adsorption of Mixtures. Of the following models, all but the ideal adsorbed solution theory (lAST) and the related heterogeneous ideal adsorbed solution theory (HIAST) have been shown to contain some thermodynamic inconsistencies. References to the limited available Hterature data on the adsorption of gas mixtures on activated carbons and 2eohtes have been compiled, along with a brief summary of approximate percentage differences between data and theory for the various theoretical models (16). In the following the subscripts i and j refer to different adsorbates. 

Typical adsorption isotherms for light hydrocarbons on activated carbon prepared from coconut shells ate shown in Figure 11 (46). The polarizabihties and boiling points of these compounds increase in the order... 

Many simple systems that could be expected to form ideal Hquid mixtures are reasonably predicted by extending pure-species adsorption equiUbrium data to a multicomponent equation. The potential theory has been extended to binary mixtures of several hydrocarbons on activated carbon by assuming an ideal mixture (99) and to hydrocarbons on activated carbon and carbon molecular sieves, and to O2 and N2 on 5A and lOX zeoHtes (100). Mixture isotherms predicted by lAST agree with experimental data for methane + ethane and for ethylene + CO2 on activated carbon, and for CO + O2 and for propane + propylene on siUca gel (36). A statistical thermodynamic model has been successfully appHed to equiUbrium isotherms of several nonpolar species on 5A zeoHte, to predict multicomponent sorption equiUbria from the Henry constants for the pure components (26). A set of equations that incorporate surface heterogeneity into the lAST model provides a means for predicting multicomponent equiUbria, but the agreement is only good up to 50% surface saturation (9). 

Adsorption. Adsorption (qv) is an effective means of lowering the concentration of dissolved organics in effluent. Activated carbon is the most widely used and effective adsorbent for dyes (4) and, it has been extensively studied in the waste treatment of the different classes of dyes, ie, acid, direct, basic, reactive, disperse, etc (5—22). Commercial activated carbon can be prepared from lignite and bituminous coal, wood, pulp mill residue, coconut shell, and blood and have a surface area ranging from 500—1400 m /g (23). The feasibiUty of adsorption on carbon for the removal of dissolved organic pollutants has been demonstrated by adsorption isotherms (24) (see Carbon, activated carbon). Several pilot-plant and commercial-scale systems using activated carbon adsorption columns have been developed (25—27). 

Once the heel has been established in the carbon bed, the adsorption of the fuel vapor is characterized by the adsorption of the dominant light hydrocarbons composing the majority of the hydrocarbon stream. Thus it is common in the study of evaporative emission adsorption to assume that the fuel vapor behaves as if it were a single light aliphatic hydrocarbon component. The predominant light hydrocarbon found in evaporative emission streams is n-butane [20,33]. Representative isotherms for the adsorption of n-butane on activated carbon pellets, at two different temperatures, are shown in Fig. 8. The pressure range covered in the Fig. 8, zero to 101 kPa, is representative of the partial pressures encountered in vehicle fuel vapor systems, which operate in the ambient pressure range. 

The Freundlich liquid phase isotherm can be used to determine the effect of solubility on the adsorptive capacity of activated carbon over a range of different concentrations. Phenol is highly soluble due to its polar nature whilst, in comparison, tetrachloroethylene (PCE) has a low solubility due to being non-polar. In the isotherms illustrated, the concentration of phenol is low relative to its solubility limit and consequently, the adsorptive capacity peaks at 18% maximum (see Figure 9). In comparison the concentration of tetrachloroethylene is relatively close to its solubility limit and, accordingly, the adsorptive capacity is exceptionally good. 

The adsorption isotherm for H2S on activated carbon is represented by (Valenzuela and Myers, 1989)... 

Nitrogen adsorption experiments showed a typical t)q5e I isotherm for activated carbon catalysts. For iron impregnated catalysts the specific surface area decreased fix>m 1088 m /g (0.5 wt% Fe ) to 1020 m /g (5.0 wt% Fe). No agglomerization of metal tin or tin oxide was observed from the SEM image of 5Fe-0.5Sn/AC catalyst (Fig. 1). In Fig. 2 iron oxides on the catalyst surface can be seen from the X-Ray diffractions. The peaks of tin or tin oxide cannot be investigated because the quantity of loaded tin is very small and the dispersion of tin particle is high on the support surface. 

Dubinin-Raduskevish (DR) Due to the great significance of vapor adsorption on activated carbons, the DR isotherm, which is the most widely used in such cases, will be presented. It has several advantages (Dubinin, 1966) ... 

Equation 3 was verified experimentally (3) over wide ranges of temperature and equilibrium pressure for the adsorption of various vapors on active carbons with different parameters for the microporous structure. For adsorption on zeolites, this equation fitted the experimental results well only in the range of high values of 0 (4, 5, 6, 7). Among other equations proposed for the characteristic curve (4, 5, 8, 9, 10) we chose to use the Cohen (4) and Kisarov s (10) equation, which starts from the following adsorption isotherm equation ... 

Form of protium and deuterium adsorption isotherms on the sample of nanoporous carbon are similar to ones on activated carbon and zeolites. They comparison is shown in figure 3. You can see that adsorption capacity of the NPC samples is larger than one on common sorbents such as zeolites [10-11] and it is close to active carbon [12]. 

Figure 4.2 shows the Langmuir isotherms of (a) phenobarbital and (b) mephobar-bital adsorption on activated carbon. The maximum adsorption capacity (K,/K2) of activated carbon for mephobarbital is lower than that for phenobarbital. The affinity constant (1/K2) for mephobarbital is higher than that for phenobarbital. This is expected because higher solubility gives a lower adsorption affinity. Table 4.1 illustrates the Langmuir constants of various drugs on carbon black. 

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