Adsorption Hysteresis in Open Slit-like Micropores.

Grygorii Dragan,Alexander Iorgov,Volodymyr Kutarov,Eva Schieferstein

doi:10.3390/molecules26165074

Abstract

Adsorption hysteresis in the low-pressure range is only rarely described in the literature. To optimise, for example, heat storage technologies, a deeper understanding of the low-pressure hysteresis (LPH) process is necessary. Here, two thermodynamically based approaches are further developed for analysing the LPH within the framework of thermodynamically irreversible processes and fractal geometry. With both methods developed, it is possible to obtain the description of the adsorption and desorption branches with high accuracy. Within the framework of the two thermodynamic models of the hysteresis loop, generalised equations are obtained with the control parameter in the form of the degree of irreversibility. This is done by taking the adsorption of water on alumina as an example. It is shown that the fractal dimension of the adsorption process is larger than the fractal dimension of the desorption branch, meaning that the phase state of the adsorbate is more symmetric during the adsorption step than in the desorption process.

Highlights

In recent years, it has become apparent that the only way to avoid irreversible climate change and the dramatic effects of global warming on the planet is to reduce carbon dioxide emissions
Two approaches have been proposed for calculating the hysteresis loop, based on: (1) The classical theory of volume filling in micropores [4]; (2) The alternative theory of adsorption in micropores [5]
The determination of the thermodynamic invariant is based on the values of potential barriers to adsorption–desorption and the degree of deviation of the pore size distribution function from the Gaussian distribution

Summary

Introduction

It has become apparent that the only way to avoid irreversible climate change and the dramatic effects of global warming on the planet is to reduce carbon dioxide emissions. This can be achieved through the introduction of more efficient energy systems and the use of energy sources that do not allow CO2 emissions. To solve the problem of global warming, an important role is played by heat storage technologies, which are based on adsorption processes In this case, thermal energy is accumulated in the form of adsorption heat and is released during desorption. Since these adsorption systems often show hysteresis, a theoretical study of adsorption hysteresis is of great interest [1]

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