Water-Stable Microporous Bipyrazole-Based Framework for Efficient Separation of MTO Products
Guoli Zhen, Yongyao Liu, Yunzhe Zhou, Zhenyu Ji, Hengbo Li, Shuixiang Zou, Wenjing Zhang, Yashuang Li, Yuanzheng Liu, Cheng Chen, Mingyan Wu
Abstract
Recently, methanol-to-olefins (MTO) technology has been widely used. The development of new adsorbents to separate MTO products and obtain high-purity 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-1 H,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 .