Editorial overview: Separations engineering: advances in adsorption
Résumé
This themed issue of Current Opinion in Chemical Engineering is dedicated to recent advances in adsorption-especially in the context of fields relevant to chemical engineering. On this occasion, a series of 10 outstanding contributions, written by experts from both the academic and industrial worlds, have been gathered around key questions connected to adsorption phenomena in membrane and separation sciences, electrochemistry and energy conversion/storage, poromechanics and civil engineering, etc. All these contributions are short and focused mini-reviews-typically, about 2500 words-on the latest experimental and/or theoretical developments in emerging adsorption topics. About half of these mini-reviews deal with current advances in adsorption in chemical engineering fields: Adsorption in Membrane Science, Coupling adsorption/mechanics; Adsorption and coadsorption processes at the industrial scale; Adsorption effects in electrochemistry; Adsorption-driven heat pumps/chillers. The other half of these mini-reviews focus on advanced techniques to probe adsorption: Spectroscopic tools for adsorption; Imaging techniques to probe adsorption; Probing adsorption using Nuclear Magnetic Resonance; Kinetic approaches for molecular modeling of adsorption; Free energy techniques for simulation of adsorption. Each of these contributions focuses on some of the most important recently published work and emphasizes the significance of these advancements towards the overall progress of the field. The authors were also asked to focus on a few key advances based on the recent literature (within the past 2 to 5 years) rather than survey an entire field and to provide their critical assessment of these developments and future prospects. An additional key feature of the Current Opinion journals is to provide an annotation for each of the most interesting articles within the bibliography of the reviews. Adsorption is a process of adhesion of atoms, molecules or ions in either gas or liquid phase, at the surface of solids or liquids. Most of the papers in this issue focus on physisorption, i.e. the process in which the adsorbed species do not form chemical bonds with the surface but only bind through physical forces (dispersion, electrostatic, etc.). Also the papers focus on adsorption on solid surfaces, and do not discuss adsorption on liquid phases. This however does not mean that chemisorption or adsorption on liquid surface is of lesser interest. The research of various aspects of adsorption is very broad, and this issue could have covered many more topics. We decided to limit them to those which have not been covered in recent review papers. There is a number of fields relevant to chemical engineering in which adsorption has recently emerged as a key ingredient. While in some applications adsorption effects have been recognized for a long time as important, there are over domains where they have been overlooked or only considered in a very effective fashion. This includes applications belonging to membrane science, poromechanics i.e. the field of mechanics of porous media which accounts for the coupling with the thermodynamics of confined fluids, gas or liquid adsorption in soft matter physics, phase transformation such as for heat pumps and chillers, etc. In fact, developments in these fields have often been done without specifically accounting for adsorption effects until recently. The present themed issue on Advances in Adsorption from Current Opinion in Chemical Engineering intends to highlight these recent developments. This is a timely issue as these efforts have been quite impressive in the last 10-20 years with significant breakthroughs reported-with or without direct technological transfer already made. As indicated above, the mini-reviews in this themed issue subdivides into (1) five contributions focusing on advanced techniques to probe adsorption and (2) five contributions dealing with current advances in adsorption relevant to chemical engineering fields. In the two following paragraphs, we list and comment each of these mini-reviews. Advanced techniques to probe adsorption • The paper by Ustinov presents an overview of the recent advances in development of kinetic Monte Carlo (kMC) method for application to modeling equilibrium phenomena [1]. As it is obvious from the name, the kMC method has been used for a number of years for modeling kinetics. However, in the recent years, it was shown to be a viable alternative to conventional (Metropolis) Monte Carlo to predict thermodynamic equilibrium, in particular adsorption equilibrium. This review outlines the main features of the method, and shows examples of application of this method for gas adsorption on solid surfaces. Importantly, the kMC method provides a straightforward way to calculate the Gibbs free energy, while performing simulations in the canonical ensemble • Another review focusing on free energy calculations-in the specific context of the flexibility of compliant MOF materials-is the work by Tanaka and Miyahara [2]. Such
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