Isotherm and heat of adsorption in porous solids with defective pores-adsorption of argon and nitrogen at 77K in Saran activated carbon

The isotherm and isosteric heat of a porous solid are studied in terms of the local isotherms and isosteric heats of individual pores with defective walls, rather than graphitic walls as commonly assumed in the literature. We point out the incorrect formulas that have been used in the literature, and present a correct formula to calculate the isosteric heat for a porous solid. The correct formula is illustrated with a direct Monte Carlo ( MC) simulation of systems of two pores of different sizes, and finally we apply our theory to experimental data of argon and nitrogen adsorption at 77K on S600H and S84 Saran charcoals to derive their pore size distributions ( PSD). We show that the PSD derived from the fitting either the isotherm only or the heat curve only may not be reliable. It is necessary to utilize both the isotherm and heat curves in the derivation of a more reliable PSD. We also show that it is essential to use defected walls of carbon pores to model adsorption in pores as the model using graphitic walls can not describe isotherm and heat of adsorption adequately

Incorporation of impurity anions into DSP: insights into structure and stability from computer modelling

DSP is an important by-product of alumina production via the Bayer process. Under Western Australian processing conditions, the DSP has a sodalite-type structure that can incorporate anions within its framework. This is particularly useful for removal of impurity anions from liquor recycled in the circuit. As a first step to gaining a fundamental understanding of the incorporation process, we have undertaken molecular mechanics calculations to examine the interaction energy between a series of anions and the sodalite framework, as a measure of the affinity of the anions for the sodalite cage. Our calculations predict that the ions have an increased affinity for the cage along the series aluminate, chloride, carbonate, sulfate and hydroxide. These calculations have successfully predicted the trends that we observe from competitive-uptake experiments in our laboratory