Abstract
The isosteric heat of adsorption ( q st ) is a critical parameter to describe the CO 2 adsorption separation system for the determination of energy consumption of regeneration. The q st could be easily determined using the ensemble fluctuation approach as well as indirect approaches, including the isosteric and analytic ones; however the obtained q st values could be affected by the method used to determine them. To date, only a few studies compared these approaches using the same criteria, leading to challenges in identifying the proper approach for calculating q st . In this study, detailed comparisons of the indirect approaches and ensemble fluctuation approach were performed. The adsorption isotherms and q st values of Cu-BTC, MIL-47(V), MIL-100(Cr), and MIL-101(Cr), were obtained using the grand canonical Monte Carlo simulation. Then, q st was calculated using indirect approaches and the effect of the fitting equation was discussed. The results indicated that the ensemble fluctuation approach significantly depended on the force field. The simulated q st values of MIL-100(Cr) and MIL-101(Cr) were consistent with the calorimetric data; however, the simulated q st values of Cu-BTC and MIL-47(V) were not. For the indirect approaches, the Padè equation, combined with the isosteric approach, provided the most accurate q st values, and the relative deviation was approximately 1% under most conditions. This indicated the Padè equation could emerge as a universal fitting equation. Moreover, for the pressure or temperature swing adsorption processes, using excess variables to directly determine q st was not recommended, because the “isoexcess heat” could deviate from the isosteric heat by up to 10%. • Detailed overview of theory on isosteric heat. • Comprehensive comparison of various approaches for determination of isosteric heat. • GCMC simulation study of CO 2 gas adsorption on Cu-BTC, MIL-47(V), MIL-100(Cr), and MIL-101(Cr). • Effect of fitting formula on calculation of isosteric heat. • Effect of use of excess amounts on calculated isosteric heat of TSA and PSA.
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