Confined facilitated transport within covalent organic frameworks for propylene/propane membrane separation

Energy-efficient membrane technology is sought to replace or integrate with conventional energy- and cost-intensive distillation for precise propylene/propane separation. Covalent organic framework (COF)-based composite membranes (CMs) are promising candidates for the representative difficult propylene/propane separation system. However, the large-size pore of COFs cannot achieve an effective separation of gas pairs with sub-angstrom (0.2 angstrom) size differences. Here, we design confined facilitated transport nanochannels within COFs as productive fillers to construct CMs. The anchored high-density Ag+ carriers facilitate C3H6 monomolecular high-speed transport along the nanochannel surface. Under this confined transport mechanism, the problem of over-sized COF pores can be partially circumvented, and high selectivity obtained. Moreover, the obtained asymmetric configuration of SCOF-Ag/PI CMs results in directional gas transport. As the first work of COF-based membranes for olefin/paraffin separation, SCOF-Ag/PI CMs demonstrate a high propylene permeability of 75.16 barrer and good propylene/propane selectivity of 35.45, out-performing most of the polymer-based membranes and approaching the performance of ZIF-8 membranes. Furthermore, SCOF-Ag/PI CMs exhibit over one-month durability. The excellent separation performance combined with operating stability provides a promising alternative approach toward efficient C3H6/C3H8 separation.

Automated summary

This article explores the application of covalent organic framework (COF)-based composite membranes (CMs) in propylene/propane separation. The study reveals that the design of confined facilitated transport nanochannels within COFs can address the issue of oversized pores and achieve high selectivity separation. Experimental results demonstrate that SCOF-Ag/PI CMs exhibit high propylene permeability, good propylene/propane selectivity, and long durability.