Ultramicroporous material based parallel and extended paraffin nano-trap for benchmark olefin purification

Abstract

Selective paraffin capture from olefin/paraffin mixtures could afford high-purity olefins directly, but suffers from the issues of low separation selectivity and olefin productivity. Herein, we report an ultramicroporous material (PCP-IPA) with parallel-aligned linearly extending isophthalic acid units along the one-dimensional channel, realizing the efficient production of ultra-high purity C₂H₄ and C₃H₆ (99.99%). The periodically expanded and parallel-aligned aromatic-based units served as a paraffin nano-trap to contact with the exposed hydrogen atoms of both C₂H₆ and C₃H₈, as demonstrated by the simulation studies. PCP-IPA exhibits record separation selectivity of 2.48 and separation potential of 1.20 mol/L for C₃H₈/C₃H₆ (50/50) mixture, meanwhile the excellent C₂H₆/C₂H₄ mixture separation performance. Ultra-high purity C₃H₆ (99.99%) and C₂H₄ (99.99%) can be directly obtained through fixed-bed column from C₃H₈/C₃H₆ and C₂H₆/C₂H₄ mixtures, respectively. The record C₃H₆ productivity is up to 15.23 L/kg from the equimolar of C₃H₈/C₃H₆, which is 3.85 times of the previous benchmark material, demonstrating its great potential for those important industrial separations.

Fig. 1. Scheme and structure of PCP-IPA.

a Schematic illustration of the common paraffin-trap channel, b schematic illustration of the parallel and extended paraffin nano-trap channel, (c) the building blocks (Co^II, DPG, and IPA organic ligand) and the 3D network topology of PCP-IPA, d the 1D channel structure of PCP-IPA (C, orange or grey-80%; H, white; N, blue; O, red; Co, light blue).

Fig. 2. The paraffin and olefin sorption in PCP-IPA.

a The C₃H₈, C₃H₆, C₂H₆, and C₂H₄ adsorption isotherms at 298 K; b IAST selectivity (c) comparison plot of C₃H₈/C₃H₆ (50/50 v/v) IAST selectivity among benchmark materials; comparison of PCP-IPA separation potential (ΔQ _IAST) with reported benchmark MOFs based on IAST calculation from d C₃H₈/C₃H₆ (50/50 v/v) mixtures and e C₂H₆/C₂H₄ (50/50 v/v) mixtures. f Time-dependent gas uptake profiles of C₃H₈ at 50 mbar and 298 K.

Fig. 3. DFT-D calculated preferable binding sites for paraffins and olefins in PCP-IPA.

a C₃H₈, b C₃H₆, c C₂H₆, and d C₂H₄ binding sites in PCP-IPA. The closest contacts between framework atoms and the gas molecules are defined by the distances (in Å) and the distances include the Van der Waals radius of atoms. (Framework: C, gray-80%; H, white; N, blue; O, red; Co, light blue; Gas: C, orange; H, white).

Fig. 4. Paraffin/olefin separation.

Dynamic breakthrough curves under 298 K and 1.0 bar of a C₃H₈/C₃H₆ (50/50 v/v) mixture, b C₃H₈/C₃H₆ (5/95 v/v) mixture, and c C₂H₆/C₂H₄ (50/50 v/v) with (hollow) or without water vapor (solid); comparison of high pure olefin productivity on PCP-IPA with reported benchmark materials for d C₃H₈/C₃H₆ (50/50 v/v) mixture and e C₂H₆/C₂H₄ (50/50 v/v) mixture; f recycling breakthrough tests for C₃H₈/C₃H₆ (5/95 v/v, red, 2.20 mL/min), C₃H₈/C₃H₆ (50/50 v/v, blue, 1.10 mL/min), C₃H₈/C₃H₆ (50/50 v/v, cyan, 2.20 mL/min) and C₂H₆/C₂H₄ (50/50 v/v, orange, 3.7 mL/min) separation with PCP-IPA under 298 K and 1.0 bar.