Phenol adsorption dodecyl benzene sulfonate

Phenol and dodecyl benzene sulfonate are two solutes that have markedly different adsorption characteristics. The surface diffusion coefficient of phenol is about fourteen times greater than that for dodecyl benzene sulfonate. The equilibrium adsorption constants indicate that dodecyl benzene sulfonate has a much higher energy of adsorption than phenol (20,22). The adsorption rates from a mixture of these solutes can be predicted accurately, if (1) an adequate representation is obtained for the mixture equilibria, and (2) the diffusion rates in the solid and fluid phases are not affected by solute-solute interactions. 

Figure 15. Adsorption rates from phenol and dodecyl benzene sulfonate mixtures ...

Diffusion-type models have been used for the adsorption of lead, copper, p-nitrophenol, phenol, p-bromophenol, p-toluene sulfonate and dodecyl benzene sulfonate on activated carbon (Hashimoto etal., 1977 Xiu and Li, 2000 Chen and Wang, 2004 Crittenden and Weber, 1978), and ion exchange of ammonia, lead, and other heavy metals on clinoptilolite (Inglezakis and Grigoropoulou, 2003 Cincotti et al, 2001 Semmens et al, 1978 Cooney et al, 1999). 

Experimental isotherm data for the adsorption of four solutes, phenol, p-bromophenol, p-toluene sulfonate, and dodecyl benzene sulfonate onto activated carbon are shown in Figures 1 to 4. The isotherm constants are estimated using a nonlinear parameter estimation program, and are shown in Table 1. The parameter estimation program uses the principal axis method to obtain the parameters, a, b and 3 that will minimize the sum of the squares of the differences between experimental and computed isotherm data. 

Adsorption equilibria for the systems phenol-p-toluene sulfonate, phenol-p-bromophenol and phenol-dodecyl benzene sulfonate are shown in Figures 5, 6 and 7. In these figures, the ratio of the observed equilibrium values and computed values from equation (14) are plotted against the equilibrium liquid phase concentration of the solute in the mixture. It is seen that most of the data points are well within a deviation of 20%. The results for these diverse solute systems indicate that equation (14) is suitable for correlating binary equilibrium data for use in multicomponent rate models. 

As seen from Table 2, phenol, j>-toluene sulfonate and 2 bromophenol have similar adsorption rate characteristics. The equilibrium data for these solutes indicate that phenol and p-toluene sulfonate have similar energies of adsorption (24), as indicated by the constant b in the component isotherm (qe Qbx,ce/ (1 + bLCe) -bromophenol and dodecyl benzene sulfonate are adsorbed more strongly than phenol (22). 

The experimental and predicted profiles for adsorption from a mixture 5 x 10 H phenol and 5 x 10 H dodecyl benzene sulfonate are shown in Figure 15. The rate of adsorption of dodecyl benezene sulfonate is faster than predicted, and for phenol, the rate is slower than predicted. However, the shape of the predicted profiles for both solutes closely parallel the experimental curves. Similar trends may be noted in Figure 16 for the adsorption rates from a 10 4 H phenol and 10 4 H dodecyl benzene sulfonate mixture. The mixture equilibrium data for these solutes have been correlated satisfactorily. Thus, it would appear that solute-solute interactions are affecting the diffusional flux of each solute. Moreover, from Figure 17 for the total concentrations, it may be seen that the interaction effects are mutually compensating. The total concentration profiles for both... 

Solute-solute Interactions may affect the diffusion rates In the fluid phase, the solid phase, or both. Toor (26) has used the Stefan-Maxwell equations for steady state mass transfer In multicomponent systems to show that, in the extreme, four different types of diffusion may occur (1) diffusion barrier, where the rate of diffusion of a component Is zero even though Its gradient Is not zero (2) osmotic diffusion, where the diffusion rate of a component Is not zero even though the gradient Is zero (3) reverse diffusion, where diffusion occurs against the concentration gradient and, (4) normal diffusion, where diffusion occurs In the direction of the gradient. While such extreme effects are not apparent in this system, it is evident that the adsorption rate of phenol is decreased by dodecyl benzene sulfonate, and that of dodecyl benzene sulfonate increased by phenol. 

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