Modelling of water adsorption by activated carbons: effects of microporous structure and oxygen content

Abstract

The present paper examines the adsorption of water by microporous carbons containing various amounts of surface oxygen and a smaller proportion of basic centres. The modelling of water adsorption for 293 and 310 K, using variable pore size distributions (PSD), confirms that the overall type IV isotherm is the sum of a type I isotherm associated with the specific interactions, and a type V isotherm reflecting the non-specific interactions. The principle of temperature invariance is followed by these isotherms, which indicates that modelling leads to the Dubinin-Astakhov equation.The present approach allows the prediction of water adsorption near room temperature, on the basis of the PSD and the density of oxygen present on the surface area of the micropores. It is assumed, to a first and good approximation, that the pores are slitshaped and the oxygen distribution is random.

On the determination of surface areas in activated carbons

“…This information is also confirmed by STM [9]. More recently, modelling of CO 2 [11,12] and H 2 O [13] adsorption, based on the hypothesis of slit-shaped micropores, provides an independent confirmation for the PSDs of typical microporous carbons. Fig.…”

“…For example, the analysis of CO 2 adsorption based on model isotherms, leading to PSDs [12,13], the selective adsorption of phenol from aqueous solutions [1,2,15], or the analysis of comparison plots [17,18]. The approaches appear to provide good estimates for the surface areas S mi and S e .…”

“…The study is based on 18 activated carbons and 3 microporous carbon blacks with average micropore widths L o between 0.65 and approximately 2-2.5 nm (Table 1) [1,2,[8][9][10][11][12][13][14][15]20]. The structural properties E o (characteristic energy), W o and S e , were obtained by the classical treatment of various adsorption isotherms of non-specific adsorbates (benzene, nitrogen, CO 2 ) within the framework of DubininÕs theory, as described in detail elsewhere [1][2][3].…”

Analysis of gas adsorption in Kureha active carbon based on the slit–pore model and Monte-Carlo simulations

“…They find that this approach is able to predict co-adsorption of water and ethane on BPL active carbon quite well, and much better than theories based on, for example, ideal adsorbed solution theory (IAST). Unfortunately, they also find that satisfactory accuracy can only be achieved if the density of active surface sites is allowed to depend on pore width, which produces significant additional model complexity and contradicts other work [29] using more empirical methods. In our view, their results for water adsorption are likely to be sensitive to their particular PSD, which in turn is sensitive to their particular choice of ethane and graphitic wall molecular models (Figures 2a to 2c in this work demonstrate the sensitivity of the PSD to molecular model parameters), and they did not analyse this sensitivity.…”

Effect of the temperature in adsorption phenomena of water onto Sub-Bituminous coal

“…Las grandes pilas de carbón, especialmente las almacenadas por largos periodos, pueden desarrollar puntos calientes de auto-calentamiento causado por la adsorción/desorción de agua en carbón [8][9][10]; 2) Los costos industriales por el transporte se incrementan; y 3) Una alta cantidad de energía es requerida para el secado del carbón vía procesos térmicos. En este sentido, muchos autores han estudiado el equilibrio de adsorción y los factores que lo afectan [11][12][13][14]: Se destacan los trabajos de: Salame & Bandosz [12], los cuales estudiaron las propiedades termodinámicas de carbones con diferentes grados de acidez superficial, mediante la construcción de isotermas de sorción de agua a tres temperaturas cercanas al ambiente (283-303K) utilizando el método termogravimétrico dinámico. Los resultados obtenidos indicaron que el calor isostérico solo es afectado por la heterogeneidad energética de la superficie.…”