Optimizing Trace Acetylene Removal from Acetylene/Ethylene Mixture in a Flexible Metal–Organic Framework by Crystal Downsizing
Jianyao Zhu, Ke Tian, Yang Liu, Zongbi Bao, Zhiguo Zhang, Baogen Su, Qilong Ren, Qiwei Yang
Abstract
Improving the gas separation performance of metal–organic frameworks (MOFs) by crystal downsizing is an important but often overlooked issue. Here, we report three different-sized flexible ZUL-520 MOFs (according to the crystal size from large to small, the three samples are, respectively, named ZUL-520-0, ZUL-520-1, and ZUL-520-2) with the same chemical structure for optimizing trace acetylene (C 2 H 2 ) removal from acetylene/ethylene (C 2 H 2 /C 2 H 4 ) mixture. The three differently sized activated ZUL-520 (denoted as ZUL-520a) exhibited almost identical C 2 H 2 uptake of 4.8 mmol/g at 100 kPa, while the C 2 H 2 uptake at 1 kPa increased with a downsizing crystal. The C 2 H 2 uptake of activated ZUL-520-2 (denoted as ZUL-520-2a) at 1 kPa was ∼55% higher than that of activated ZUL-520-0 (denoted as ZUL-520-0a). The adsorption isotherms and adsorption kinetics validated that gas adsorptive separation is governed not only by adsorption thermodynamics but also by adsorption kinetics. In addition, all three different-sized ZUL-520a MOFs showed high C 2 H 2 /C 2 H 4 selectivity. Grand canonical Monte Carlo (GCMC) simulations and dispersion-corrected density functional theory (DFT-D) computations illustrated a plausible mechanism of C 2 H 2 adsorption in MOFs. Importantly, breakthrough experiments demonstrated that ZUL-520a can effectively separate the C 2 H 2 /C 2 H 4 (1/99, v/v) mixture and the C 2 H 4 productivity obtained by ZUL-520-2a was much higher than that by ZUL-520-0a. Our work may provide an easy but powerful strategy for upgrading the performance of gas adsorptive separation in MOFs.