Understanding how pore surface fluorination influences light hydrocarbon separation in metal–organic frameworks

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2021-03, Vol.407, p.127183, Article 127183
• Main Authors: Wu, Xue-Qian, Liu, Jing-Hao, He, Tao, Zhang, Peng-Dan, Yu, Jiamei, Li, Jian-Rong
• Format: Article
• Language: English
• Subjects: Adsorbent modification; Adsorptive separation; Light hydrocarbons; Metal–organic frameworks (MOFs); Structure–property relationship
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2020.127183

A contrastive model has been established through pore surface fluorination in three Cu(II)-MOFs for exploring the structure–property relationship of gas separation in MOFs. Both fluorinated MOFs exhibit notably enhanced separation performances toward alkyne/alkene mixtures confirmed by adsorption and column breakthrough experiments, and the related adsorbate-adsorbent interactions were investigated by molecular simulations. [Display omitted] •A contrastive model has been established ingeniously via structural modification in three Cu(II)-MOFs.•The MOFs can effectively separate C2H2/C2H4 and C3H4/C3H6 confirmed by breakthrough experiments.•The comparison of the separation performances provides useful information to clarify the structure-separation relationship.•Molecular simulations reveal the adsorption sites and adsorbate-adsorbent interactions. The designability and tunability of the pore structure are the advantage of metal–organic frameworks (MOFs) for adsorptive separation applications. However, it is still challenging to design MOF adsorbent rationally according to industrial demands, because of the complexity in the separation processes and the relative lack of structure-separation relationship information. Herein, we established a contrastive model ingeniously via structural modification at the atom level in three Cu(II)-MOFs constructed from isonicotinic acid (HINA) and its fluorinated analogue 3-fluoro-isonicotinic acid (HFINA), targeting on controlling pore surface fluorination for studying light hydrocarbon separation. Both the fluorinated MOFs (Cu-FINA-1 and 2) show notably enhanced C2H2/C2H4 and C3H4/C3H6 selectivity compared with Cu-INA without increasing regeneration energy consumption. Especially, Cu-FINA-2 exhibits a considerable IAST selectivity (6.3–9.3) for C3H4/C3H6, while Cu-FINA-1 achieves a C3H6 process productivity of 31.6 cm3/g in column breakthrough experiments. Molecular simulations reveal that the polar F sites within the confined pores can interact with gas adsorbates through C-H···F hydrogen bonds, and the tailored pore size and optimal diffusion kinetics mainly contribute to the excellent separation selectivity for Cu-FINA-1. This work highlights how pore surface fluorination and related structural evolution can influence light hydrocarbon adsorption/separation properties in MOFs, and thus promotes the rational design and precise optimization of new adsorbents for alkynes/alkenes separations, even at the atom level.