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

Recently, methanol-to-olefins (MTO) technology has been
widely
used. The development of new adsorbents to separate MTO products and
obtain high-purity ethylene (C2H4) and propylene
(C3H6) has become an urgent task. Herein, an
exceptionally highly water-stable metal–organic framework (MOF),
[Cu3(OH)2(Me2BPZ)2]·(solvent)x (1) (H2Me2BPZ = 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 N2 at
77 K is unchanged. The adsorption capacity of C3H6 can reach 138 cm3 g–1, while the uptake
of C2H4 is only 52 cm3 g–1 at 298 K and 1 bar. The dynamic breakthrough experiments show that
the mixture of C3H6/C2H4 (50/50, v/v) can be efficiently separated in one step. High-purity
C2H4 and C3H6 can be obtained
through an adsorption and desorption cycle and the yields of C2H4 (purity ≥ 99.95%) and C3H6 (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 C3H6 molecule and the framework, which are
beneficial to capturing C3H6 over C2H4.