Water-Stable Microporous Bipyrazole-Based Framework for Efficient Separation of MTO Products

Abstract

Recently, methanol-to-olefins (MTO) technology has been widely used. The development of new adsorbents to separate MTO products and obtain highpurity ethylene (C 2 H 4 ) and propylene (C 3 H 6 ) has become an urgent task. Herein, an exceptionally highly water-stable metal−organic framework (MOF), [Cu 3 (OH) 2 (Me 2 BPZ) 2 ]•(solvent) x (1) (H 2 Me 2 BPZ = 3,3′-dimethyl-1H,1′H-4,4′bipyrazole) with hexagonal pores, has been elaborately designed and constructed. After being soaked in water for 7 days, it still maintains its structure, and the uptake of N 2 at 77 K is unchanged. The adsorption capacity of C 3 H 6 can reach 138 cm 3 g −1 , while the uptake of C 2 H 4 is only 52 cm 3 g −1 at 298 K and 1 bar. The dynamic breakthrough experiments show that the mixture of C 3 H 6 /C 2 H 4 (50/50, v/v) can be efficiently separated in one step. High-purity C 2 H 4 and C 3 H 6 can be obtained through an adsorption and desorption cycle and the yields of C 2 H 4 (purity ≥ 99.95%) and C 3 H 6 (purity ≥ 99%) are 84 and 48 L kg −1 , respectively. Surprisingly, when the flow rate is increased, the separation performance has no obvious change. Additionally, humidity has no effect on the separation performance. Finally, theoretical simulations indicate that there are stronger interactions between the C 3 H 6 molecule and the framework, which are beneficial to capturing C 3 H 6 over C 2 H 4 . KEYWORDS: metal−organic frameworks, methanol-to-olefins (MTO), water-stable, C 3 H 6 /C 2 H 4 separation, polymer-grade C 2 H 4

An MOF-Based Single-Molecule Propylene Nanotrap for Benchmark Propylene Capture from Ethylene

“…Particularly, ZJU-74a-Pd exhibits by far the highest C 3 H 6 uptake of 60.5 cm 3 cm –3 at 0.01 bar and 296 K (Figure c), surpassing all the reported MOFs such as Ni-MOF-74 (53.5 cm 3 cm –3 ), MAC-4 (35.2 cm 3 cm –3 ), SIFSIX-1-Cu (28.3 cm 3 cm –3 ), and UTSA-74 (5.4 cm 3 cm –3 ) . The C 3 H 6 uptake can further increase to 103.8 cm 3 cm –3 at 296 K and 0.1 bar, which also exceeds all the top-performing MOFs except Ni-MOF-74 (Figure d and Table S3), , such as MAC-4 (96.8 cm 3 cm –3 ), SIFSIX-1-Cu (91.8 cm 3 cm –3 ), Mn-dtzip (77.4 cm 3 cm –3 ), MIL-101(Cr) (34.9 cm 3 cm –3 ), and spe-MOF (22.4 cm 3 cm –3 ) . In contrast, the low-pressure C 2 H 4 uptake of ZJU-74a-Pd is much lower than that of C 3 H 6 , with a much smaller uptake of 14.2 cm 3 cm –3 at 0.01 bar.…”