Energy efficient ethylene purification in a commercially viable ethane-selective MOF

Abstract

• Cu(BDC)(DMF) using BDC as a cheap ligand was prepared using a simple and easy-to-scale up method. • Cu(BDC) simultaneously meets the requirements of high C 2 H 6 uptake and excellent ethane/ethylene separation selectivity. • Cu(BDC) exhibits excellent thermal stability and could be stored at room temperature for>1 year. • Cu(BDC) shows excellent separation ability with superior regeneration capability. Separating ethane (C 2 H 6 ) from ethylene (C 2 H 4 ) using ethane-selective adsorbents to replace energy-intensive cryogenic distillation technology is an important energy-saving method in the petrochemical industry to obtain high purity C 2 H 4 . Limited to the low separation efficiency in current commercial materials, it is very urgent and promising to fabricate such alkane selective adsorbents using cheap ligands and simple synthesis methods, which have characteristics such as stable structure, high C 2 H 6 uptake, and adsorption selectivity. In this work, we have used one of the cheapest ligands (terephthalic acid, H 2 BDC) to prepare Cu(BDC)(DMF) via a simple and easy-to-scale up solvothermal method. The activated Cu(BDC) exposed diamond-shaped one-dimensional pores form a stronger affinity with C 2 H 6 than C 2 H 4 through the double function of C-H∙∙∙π interactions and C-H∙∙∙O hydrogen bonds. Benefiting from the difference in these interactions, Cu(BDC) exhibited a higher adsorption capacity of C 2 H 6 (51.5 cm 3 /g) compared to C 2 H 4 (45.1 cm 3 /g) at 1 bar and 298 K, which resulted in high adsorption selectivity (2.0) for the C 2 H 6 /C 2 H 4 mixture (50/50, v/v). Breakthrough experiments indicated that Cu(BDC) successfully achieved the removal of C 2 H 6 from C 2 H 6 /C 2 H 4 (50/50 and 10/90, v/v) mixtures to obtain high purity C 2 H 4 (> 99.99%) using a one-step separation process. When compared with the benchmark materials, Fe 2 (O 2 )(dobdc) and NIIC-20, Cu(BDC) had the advantages of much lower preparation cost and enhanced structural stability. These comprehensive properties indicated that Cu(BDC) with a commercially viable price and synthesis process, could be potentially used for the C 2 H 6 removal step during the production of high purity C 2 H 4 .