Evaluation of a mixed geometry model for the characterization of activated carbons

Abstract

The predictions of the Pure Slit Geometry Model (PSGM) and the Mixed Geometry Model (MGM) for the characterization of activated carbons (AC) are compared and tested against the behavior of the textural properties of series of AC obtained from coconut shells by varying the concentration of the chemical activation agent over a wide range. Through the analysis of results it is concluded that the MGM can be regarded as reliable as the PSGM, with an apparently more consistent description of the behavior as a function of the degree of chemical activation and superior consistency between the results for different adsorbates, like N 2 and CO 2 .

Effect of the pore geometry in the characterization of the pore size distribution of activated carbons

“…In particular, Prasad et al 1999 show experimental differential adsorption enthalpies values of the order of 6 kcal/mol for a very ''pure'' AC (phosphorous and sulfur contents less than 0.005 %) obtained by physical activation, providing evidence of interactions of adsorbate molecules with more than two graphitic walls. These facts support the Mixed Geometry Model (MGM), proposed and tested in the last few years (Azevedo et al 2010;Soares Maia et al 2010;Toso et al 2011), which assumes that the AC porous network is better represented by a mixture of infinitely long slit geometry pores and triangular geometry pores of different sizes. The model isotherm of MGM is given by the following expression.…”

“…Finally, there is an interesting finding for N 2 @ 77 K adsorption using the MGM. Figure 6 shows differential and cumulative PSDs for AC samples obtained from coconut shells by chemical activation (Toso et al 2011). The MGM and SGM N 2 isotherm fits, not shown here, are very similar.…”

Textural Characteristics and Energetic Parameters of Activated Carbon Monoliths: Experiments and Monte Carlo Simulations

“…The PSDs predicted by the adsorption of N 2 and CO 2 in the ultramicropore region were in good agreement for all the samples (considering that the N 2 PSD was biased due to the 1 nm pore-size gap due to the absence of heterogeneity), a behaviour that is not always observed (Débora et al 2010(Débora et al , 2011de Oliveira et al 2011;Toso et al 2010).…”

Effects of potential models on nitrogen adsorption on triangular pore: An improved mixed model for energetic characterization of activated carbon

“…Although there is experimental evidence suggesting that the carbon pores have a slitlike geometry, several works [9][10][11][12][13] suggest that the use of triangular-shaped pores introduces an energetic heterogeneity due to the pore shape, which might produce better agreement to experimental measurements of the isosteric heat of adsorption obtained using slit pores as a model. The mixed model is not better than existing models that consider heterogeneity, such as QSDFT or the Two-Dimensional NLDFT model [14,15].…”