Needs, status, techniques and problems with binary gas adsorption experiments

• Published in: Advances in colloid and interface science 1998-07, Vol.76, p.227-269
• Main Author: Talu, Orhan
• Format: Article
• Language: English
• Subjects: Adsorption; Binary; Chemistry; Colloidal state and disperse state; Data; Equilibrium; Exact sciences and technology; Experiment; Gas; General and physical chemistry; Porous materials; Solid-gas interface; Surface physical chemistry
• ISSN: 0001-8686; 1873-3727
• DOI: 10.1016/S0001-8686(98)00048-7

Microporous adsorbents are gaining ever increasing importance in industry. “Almost all applications of adsorption involve mixtures.” This statement probably appears in the first paragraph of most papers on the topic. Yet, we cannot reliably predict even the simplest case, binary gas adsorption, from pure component information. Hence the need for data. Recent improvements in instrumentation made available `push-button' systems for measuring pure component isotherms. Such systems do not exist for binary measurements which are at least an order of magnitude more complicated and time consuming. Only a few research groups operate custom-made systems to collect binary gas adsorption data utilizing different techniques. This paper reviews some of the most commonly used techniques. Thermodynamic relations provide an essential framework for the design of experimental techniques, experimental protocols, and for the analysis of data. Similar to other experimental methods, the accuracy of results is proportional to the complexity of measurements. According to some counts, there are more models of multicomponent adsorption than accurate data to test them in literature. If the experiments are not designed and performed carefully, the uncertainties of final results mushroom to unacceptable levels especially for variables such as selectivity. A complete error analysis for a typical system is shown. The results with consideration to error analysis show that most data available in literature cannot be used to scrutinize between models. Lack of good data also hinders our understanding of the microstructure of adsorbents.