Ahmet Sirkecioglu

The relationship of the geometric factor in the Dubinin–Astakhov isotherm equation with the fractal dimension

Abstract The parameter n found in the Dubinin–Astakhov (D–A) equation, which may be expressed as θ=exp[−(A/E)n], allows the estimation of the fractal dimensions of microporous adsorbents, such as those investigated in this study. An empirical relationship is shown to exist between n and fractal dimension values when hydrocarbon adsorbates are utilized. The employment of two adsorption isotherms for the same adsorbate, namely those pertaining to the investigated adsorbent and to a reference adsorbent, the fractal dimension of which is known, are sufficient for the evaluation. The values of the fractal dimensions of the zeolites 13X, 5A, 4A, G5 (a faujasite type zeolite), silicalite and two distinct active carbon samples are determined to be possible to be estimated by utilizing the proposed method based on the D–A equation and the results obtained are in accordance with those determined previously by employing the Pfeifer–Avnir and the point-slope methods. The validity of the parameters of D–A isotherm equation in the correlation of full adsorption data is a prerequisite for the evaluation of the fractal dimension values by using the D–A method. The tendency of the n values to become independent of the pressure range above a certain higher pressure value is an indicator of such a validity.

Removal of detergents from water by adsorption on activated carbons obtained from various precursors

AbstractThe adsorption of detergents—sulfonic and phenolic compounds—from aqueous solutions by activated carbons (AC), obtained on the base of different precursors, was studied. The carbon adsorbents used were prepared by water vapor pyrolysis of different raw materials: peach stones, olive stones, natural asphaltite, mixtures from coal tar pitch, and furfural. It was established that all the samples of ACs have close values of high adsorption capacities toward the studied detergents. Some factors affecting the adsorption process—the time of treatment and the amount of the adsorbent—were investigated. It was established that the amount of adsorbent has no significant influence on the adsorption process.

Estimation of the temperature effect on the adsorption capacities of zeolites

Abstract The variations occurring in the ‘so called’ monolayer or saturation capacities with respect to changes in adsorption temperature were investigated for silicalite. The equation, nm=fV1−D, relates the number of moles adsorbed to the molar volume of the adsorbate and the adsorption fractal dimension value of the zeolite. Any change occurring in the capacity not related to the change in the effective size of the adsorbate is expected to be represented by the constant f. No regular pattern in the variation of the f values with respect to temperature could be observed. For the cases investigated, it seems that the effect of any other factor originating from the change in temperature, besides the variation of the effective size of the adsorbate, on the capacity value is negligible. Estimating the temperature effect on the capacity, by taking the adsorption fractal dimension into account, seems to result in capacities that are more consistent with the experimental values, compared to using the conventional linear relationship between the capacity and the temperature dependent liquid density or molar volume.