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.