Feasible ethylene separation from a ternary mixture using zeolite-like metal-organic framework@divinylbenzene composite monolith

Abstract

Ethylene is a vital intermediate in the petrochemical industry, and its purification from a C2 ternary mixture of up to 99.9% is essential to obtain a polymer-grade gas in an energy-demanding process. Adsorption-based separation offers an alternative approach for ethylene purification in a one-step process. Here, we report the fabrication of a monolithic composite from a zeolite-like metal-organic framework with a sodalite topology (sod-ZMOF) incorporated into a divinylbenzene polymer (ZMOF@DVB), to purify ethylene from binary and ternary mixtures of C2 hydrocarbons. The monolithic structure provides the composite with mechanical stability and high permeability, while only 2.31 wt% loading of sod-ZMOF nanoparticles has increased the BET surface area by 2.5 times, focused the pore size at 10.1 Å, and allowed for specific interactions. Gas chromatography was used to investigate the separation performance of the composite, reviling a quite satisfying selectivity of ethane/ethylene (1.89) and acetylene/ethylene (1.28), with comparable values to those of benchmark adsorbents used for similar applications and calculated via the ideal adsorbed solution theory (IAST). It is proposed that the anionic framework boosted the high polarizable ethane molecules' adsorption over ethylene; on the other hand, the Lewis basic nature of the extra-framework imidazolium cations neutralizes the anionic ZMOF structure drives acetylene's preferential adsorption over ethylene. As a proof of concept, imidazolium cations were exchanged in-situ by Na+ cations, and selectivities decreased to 1.37 for ethane/ethylene and 1.15 for acetylene/ethylene. An inverse gas chromatography approach was utilized to evaluate the thermodynamic parameters and showed an enthalpic-entropic motivated separation before cation exchange. However, after removing bulky imidazolium cations, separation became more entropic-driven.