A new honeycomb MOF for C2H4 purification and C3H6 enrichment by separating methanol to olefin products

Abstract

C₂H₄ and C₃H₆ are the main products of the MTO (methanol to olefins) process and they are also important industrial raw materials. However, it is a great challenge to separate them from MTO products energetically and efficiently. We herein constructed a stable C₃H₆-selective MOF [Mn₂(dtzip)(DMF)₂]·3DMF·H₂O (Mn-dtzip), by the reaction between the Mn²⁺ ions and 4,6-di(1H-tetrazol-5-yl)isophthalic acid (H₄dtzip) ligands containing carboxylic acid and tetrazole bifunctional groups. The activated material with polar honeycomb channels revealed a preferential adsorption of C₃H₆ with high uptake (216.4 cm³ g⁻¹, 298 K and 100 kPa) and significant selectivity of C₃H₆/C₂H₄ (8.6) ascribed to more accessible C₃H₆ adsorption sites including exposed metal centers, uncoordinated tetrazolate N atoms, and carboxylate groups compared to C₂H₄, as uncovered by theoretical simulations. Moreover, breakthrough experiments confirmed large differences in retention times between C₂H₄ and C₃H₆ in the separation column packed with the MOF, thus realizing an effective separation of C₂H₄–C₃H₆ to not only yield ≥99.9% purity of C₂H₄ by a one-step method but also greatly increased the enrichment of C₃H₆, such as from 50% to 90%, in the adsorbed mixtures.