Simultaneous removal of C2H2 and C2H6 for C2H4 purification by robust MOFs featuring a high density of heteroatoms

Abstract

Simultaneous removal of C₂H₆ and C₂H₂ from C₂H₄ streams is of great importance in the petrochemical industry but remains a challenging task. To address this challenge, we have selected three isoreticular MOFs with high stability, low cost, and desirable scale-up ability, namely, MOF-303, MIL-160, and CAU-23 and assessed their potential in simultaneous removal of acetylene and ethane for ethylene purification. Each MOF exhibits desirable C₂H₂ and C₂H₆ uptake capacity (>5.5 mmol g⁻¹ and >4 mmol g⁻¹, respectively), as well as good C₂H₂/C₂H₄ selectivity (>2) and C₂H₆/C₂H₄ selectivity (>1.5). Notably, MOF-303 takes up 4.96 mmol g⁻¹ C₂H₆ at 298 K and 1 bar, the highest value among the three MOFs, with C₂H₆/C₂H₄ selectivity in the range of 1.55–2.47. MIL-160 possesses a very high C₂H₂ uptake (9.1 mmol g⁻¹) and C₂H₂/C₂H₄ selectivity, 10.6 (1 : 1, v/v), at 298 K, much higher than those of all other MOFs tested to date for simultaneous removal of C₂H₆ and C₂H₂ from C₂H₄. The results from breakthrough experiments confirm that all three MOFs demonstrate excellent performance for C₂H₄ purification in a ternary mixture of C₂H₆/C₂H₄/C₂H₂ (1 : 1 : 1, v/v/v). For MOF-303, MIL-160, and CAU-23, polymer-grade C₂H₄ up to 0.164, 0.21, and 0.181 mmol g⁻¹ can be obtained from the equimolar ternary mixture in a single separation step from the breakthrough experiment. Additionally, DFT calculations have been performed to further investigate the mechanism of adsorption/separation for C₂H₆, C₂H₄, and C₂H₂.