Modified prescribed diffusion

Modified Gouy-Chapman theory has been applied to soil particles for many years (Sposito, 1984, Chapter 5). It postulates only one adsorption mechanism -the diffuse-ion swarm - and effectively prescribes surface species activity coefficients through the surface charge-inner potential relationship contained implicitly in the Poisson-Boltzmann equation (Carnie and Torrie, 1984). Closed-form... [Pg.250]

Fig. 5 shows the low pressure adsorption isotherms of n-nonane by the micropore entrance modified ACF and the pristine ACF. These adsorption isotherms were determined under the almost equilibrium conditions. A remarkable enhancement of n-nonane adsorption with the micropore entrance modification is observed in the low P/Po region, although the adsorption amounts at high P/Pq region almost coincide with each other. The fractional filling of n-nonane at saturation is almost constant irrespective of the surface modification with TTS the ratios of the saturation n-nonane adsorption Wo(nonane) to the saturation Nj adsorption Wo(N2) for the modified ACF and ACF were 0.72 and 0.70, respectively. Thus, the low pressure uptake depends sensitively on the chemical state of the external surface, while the fractional filling at saturation does not change. Consequently, the slight uptake of the pristine ACF should be caused by the limitation of micropore diffusion. The diffusion limitation can be removed by application of n-nonane pressure of P/Pq >0.1 according to the result shown in Fig. 5. Accordingly, a marked enhancement of low pressure adsorption by the micropore-entrance modification is associated with enrichment of n-nonane molecules at the entrance of the micropore due to favourable interaction of n-nonane with hydrocarbon chains of TTS. The amount of the n-nonane enrichment can be estimated from the comparison of both adsorption isotherms in Fig. 5. With the adsorption amount indicated by the horizontal broken line, the equal amount of adsorption for both samples is obtained at different relative pressures of 0.065 (for ACF) and 0.02 (for TTS-modified ACF). That is, application of P/Pq = 0.065 is necessary for the prescribed adsorption in the case of ACF, whereas the TTS-modified ACF does not need such a high P/Pq. Application of P/Po = 0.02 is sufficient for the adsorption by the TTS-modified ACF. Thus, the TTS-modification increases the concentration...

$Fig. 5 shows the low pressure adsorption isotherms of n-nonane by the micropore entrance modified ACF and the pristine ACF. These adsorption isotherms were determined under the almost equilibrium conditions. A remarkable enhancement of n-nonane adsorption with the micropore entrance modification is observed in the low P/Po region, although the adsorption amounts at high P/Pq region almost coincide with each other. The fractional filling of n-nonane at saturation is almost constant irrespective of the surface modification with TTS the ratios of the saturation n-nonane adsorption Wo(nonane) to the saturation Nj adsorption Wo(N2) for the modified ACF and ACF were 0.72 and 0.70, respectively. Thus, the low pressure uptake depends sensitively on the chemical state of the external surface, while the fractional filling at saturation does not change. Consequently, the slight uptake of the pristine ACF should be caused by the limitation of micropore diffusion. The diffusion limitation can be removed by application of n-nonane pressure of P/Pq >0.1 according to the result shown in Fig. 5. Accordingly, a marked enhancement of low pressure adsorption by the micropore-entrance modification is associated with enrichment of n-nonane molecules at the entrance of the micropore due to favourable interaction of n-nonane with hydrocarbon chains of TTS. The amount of the n-nonane enrichment can be estimated from the comparison of both adsorption isotherms in Fig. 5. With the adsorption amount indicated by the horizontal broken line, the equal amount of adsorption for both samples is obtained at different relative pressures of 0.065 (for ACF) and 0.02 (for TTS-modified ACF). That is, application of P/Pq = 0.065 is necessary for the prescribed adsorption in the case of ACF, whereas the TTS-modified ACF does not need such a high P/Pq. Application of P/Po = 0.02 is sufficient for the adsorption by the TTS-modified ACF. Thus, the TTS-modification increases the concentration...$

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