Adsorption and separation of propane/propylene on various ZIF-8 polymorphs: Insights from GCMC simulations and the ideal adsorbed solution theory (IAST)

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Vol. 386; p. 123945
• Main Authors: Li, Libo, Duan, Yifan, Liao, Shouwei, Ke, Qia, Qiao, Zhiwei, Wei, Yanying
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.04.2020
• Subjects: Gas adsorption; Grand Canonical Monte Carlo (GCMC) simulations; Ideal Adsorbed Solution Theory (IAST); Olefin/paraffin separation; Polymorphs; Zeolitic Imidazolate Frameworks (ZIFs); Zeolitic Imidazolate Frameworks (ZIFs); Olefin/paraffin separation; Ideal Adsorbed Solution Theory (IAST); Grand Canonical Monte Carlo (GCMC) simulations; Polymorphs; Gas adsorption
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2019.123945

The adsorption and separation of olefin/paraffin on several ZIF-8 polymorphs, including our newly synthesized ones (Sci. Adv. 2018, 4, eaau1393), were studied herein. The ZIF-8 polymorphs showed distinctly different olefin/paraffin adsorption performance, even though their chemical composition are identical. Various analysis (e.g. porosity, heat of adsorption, distribution density contours, etc.) were carried out to further reveal how the geometrical structure of ZIF polymorphs lead to diverse gas adsorption performance. This work not only yielded scientific insights which could help developing MOFs with better gas adsorption/separation performance, but also validated thoroughly the methodology of combing GCMC with IAST which could be extended to a wide range of further researches. [Display omitted] •ZIF-8 polymorphs, e.g. newly synthesized ones, show distinct adsorption isotherms etc.•GCMC was proven to agree with IAST thoroughly, thus could be used together hereafter.•The adsorption competition of olefin/paraffin was shown at micro/macro-scopic level.•Different gas selective adsorption mechanisms at low/high pressure were unveiled.•The correlation between ZIFs' structure and gas adsorption performance was revealed. Olefin/paraffin separation is critical for modern chemical industry, yet consumes huge amount of energy as these molecules are very similar. ZIF-8 polymorphs brought very promising opportunities to solve such problem by showing unprecedented propane/propylene separation performance in our recent work (S. Zhou, Y. Wei, L. Li, Y. Duan, et al., Sci. Adv., 2018, 4, eaau1393), whereas some relevant scientific questions remain poorly understood: 1. How the geometrical difference among these polymorphs lead to the superior gas separation performance? 2. How to develop polymorphs with even better adsorption/separation performance? Herein, Grand Canonical Monte Carlo (GCMC) simulations and the IAST model were employed to study the adsorption of propane/propylene on several ZIF-8 polymorphs with a large variety of topology, which is critical for understanding and implementing ZIF-based adsorption or membrane separation process. Our simulation results well agree with the experimental data, revealing the adsorption and separation mechanism of olefin/paraffin on the ZIF-8 polymorphs. The ZIFs’ interactions with gas and their porosity were found to well correlate with the gas uptake, and the density distribution contours further revealed the adsorption competition between propane and propylene. The adsorption of propane + propylene mixtures on ZIF-8 polymorphs was further studied via multi-component GCMC and IAST, both yielding similar results, such as propane selectivities and uptakes. This work not only provided with in-depth insights to understand the adsorption and separation of olefin/paraffin on ZIFs, but also validated combining GCMC with IAST as an efficient methodology to study this subject.