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

Abstract

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.

Magnetic-Induced Swing Adsorption over Iron Oxide/13X: Effects of Particle Size and Oxide Phase on Sorbent Regeneration in Ethylene/Ethane Separation

“…π-bond interactions and dipole and quadrupole moments). In contrast, C 2 H 6 , which has a larger kinetic diameter, is excluded from the smaller pores. , When binary equilibrium adsorption was attainedwhich occurs when C 2 H 4 approaches the end of the columnboth gases returned to their molar feed compositions. Although the uptakes of the C 2 H 6 and C 2 H 4 were lower over Fe 20 (F)/13X than over other sorbents, the shape of the front was roughly similar across the sorbents, with slight differences in the sharpness of the desorption profiles of C 2 H 6 when the particle size of iron oxide was increased ( i.e., it became slightly broader), as in Fe 20 (C–F)/13X sorbents.…”

Kinetic Assessment of Light Hydrocarbons Separation over Fe-Doped 13X Composite Sorbents Under Multicomponent Feed Conditions

“…The introduction of Fe 1 into the 13X framework led to the confinement of the micropore channels, thereby enhancing the molecular sieving effect and favoring C 2 H 4 selectivity. C 2 H 4 , with a smaller kinetic diameter compared to C 2 H 6 (4.163 Å vs 4.443 Å), effectively penetrated into the pores of 13X, whereas C 2 H 6 , with a larger kinetic diameter, was excluded from the smaller pores of 13X. , Additionally, the presence of Fe particles in the Fe 1 (NPs)/13X composite, predominantly in the form of Fe 3+ , promoted stronger interactions between C 2 H 4 and the surface through van der Waals (vdW) forces (i.e., π-bond interactions and dipole/quadrupole moments). On the other hand, in the case of Fe 10 (NPs)/13X, the separation efficiency declined due to the particles agglomeration and pore blockage.…”

“…As a result, further purification is required to purify C 2 H 4 for utilization as a feedstock. Adsorption-based separations offer a great potential to replace the traditional cryogenic distillation and fulfill the energy-efficient separation economy in olefin/paraffin separations. , The separation of C 2 H 4 /C 2 H 6 is especially challenging because of the similarities in their physical properties such as boiling point, molecular weight, and kinetic diameter. − …”

Combination of Low-Polar and Polar Binding Sites in Aliphatic MOFs for the Efficient C2H6/C2H4 Separation

“…Metal–organic frameworks (MOFs), self-assembled by inorganic metal nodes or metal clusters with organic bridging ligands, are well-known for their tailored-to-application tunability of pore structures and pore environment, which have showed huge potential in the construction of C 2 H 6 -preferred adsorbents. − As previous research studies indicated, creating a non-polar/inert pore environment is considered as an effective method to avoid strong interactions between the framework and C 2 H 4 , and some MOFs with this feature have been reported. − However, the paucity of strong binding sites may also lead to poor capture of C 2 H 6 and thus low C 2 H 6 /C 2 H 4 selectivity. It is conceivable that more low-polar binding sites on the pore surface should be beneficial to the selective capture of C 2 H 6 due to multiple van der Waals interactions. , Besides, methyl groups make the C 2 H 6 molecule wider and bulkier than C 2 H 4 (Table S1), which provides more opportunity for C 2 H 6 to get close the pore corners.…”