Selectivity Tuning of Adsorbents for Ethane/Ethylene Separation: A Review

Ethylene is an important feedstock for the production of many key-valued compounds, especially polymers. About 60% of the total ethylene produced is utilized for the production of polyethylene, while ethylene is normally produced by steam cracking of naphtha along with traces of ethane, which is undesirable. Considering the energy-intensive nature of the current technology to obtain ultrapure ethylene, the development of novel materials for separating ethylene from ethane by adsorption is of great significance, yet it remains challenging owing to the close molecular sizes and physical properties of the two compounds. Both ethylene- and ethane-selective adsorbents are reviewed in this work. Yet, as the industrial feed is rich in ethylene with traces of ethane, in order to obtain polymer grade ethylene, multiple adsorption–desorption cycles are required, which is yet again energy-demanding. Thus, ethane-selective adsorbents are energetically favorable; hence, in this Review, we pay particular focus on ethane-selective adsorbents. The rationale behind reverse-selective adsorbents is critically reviewed and discussed. Most of the ethane-selective adsorbents have been reported to exhibit low selectivity compared to ethylene-selective ones, as reverse-selectivity is mostly based on weak van der Waals interactions. In addition, we focused on various reported mechanisms behind the adsorptive separation of ethane/ethylene mixtures, as well as modifications and surface functionalization techniques reported for different types of adsorbents investigated for this separation.