Diffusion-Gating Enabled Ternary C2H4 Purification and Inverse C2H2/CO2 Separation in an Adaptive Hopf-Link Metal–Organic Framework

Abstract

The simultaneous purification of polymer-grade ethylene (C2H4) and recovery of high-purity acetylene (C2H2) from complex ternary mixtures with carbon dioxide (CO2) represents a critical industrial challenge. Conventional adsorbents employ thermodynamic selectivity to bind C2H2 and CO2 preferentially over C2H4, enabling one-step C2H4 purification but necessitating an energy-intensive desorption step for C2H2 recovery, as C2H2 typically binds more strongly. Here, we report a fundamentally different approach using diffusion-gating in an adaptive Hopf-link metal–organic framework, ZJNU-600, which replaces thermodynamic control. The framework comprises two orthogonal, interpenetrated sql nets mechanically interlocked as Hopf links, with thiocyanate linkers acting as molecular hinges that modulate the pore aperture. This architecture establishes an ideal kinetic diffusion hierarchy of CO2 > C2H2 > C2H4, completely inverting the elution order compared to equilibrium-based separation. Dynamic breakthrough experiments demonstrate that ZJNU-600 achieves one-step production of C2H4 from ternary mixtures while simultaneously enabling the direct recovery of C2H2 via inverse separation, eliminating the need for energy-intensive desorption. The exceptionally low isosteric heat of CO2 adsorption (24.7 kJ mol–1) further suggests minimal regeneration energy. Computational studies reveal that the diffusion barrier hierarchy arises from the differential chemical compatibility of each gas with the hydroxyl-decorated pore walls. This work establishes kinetic pore-aperture engineering as a generalizable and energy-efficient design principle for multicomponent gas separations, effectively inverting the separation hierarchy dictated by thermodynamic affinity.