Highly Propylene-Selective Mixed-Matrix Membranes by in Situ Metal–Organic Framework Formation Using a Polymer-Modification Strategy

Abstract

Despite the potential of C 3 H 6 /C 3 H 8 separation, there have been no industrial applications of zeolitic-imidazole framework-8 (ZIF-8) mixed-matrix membranes (MMMs) because of the moderate separation performances and several challenging processing issues. Herein, we present a new paradigm of MMM fabrication, named polymer-modification-enabled in situ metal−organic framework formation (PMMOF), enabling in situ formation of ZIF-8 fillers inside the 4,4-(hexafluoroisopropylidene)diphthalic anhydride 2,4,6-trimethyl-1,3phenylenediamine polymer. PMMOF consists of four steps including hydrolysis of a polymer, ion-exchange, ligand treatment, and imidization. Each step was thoroughly analyzed and important processing parameters were identified, enabling the structural control of MMMs by PMMOF. The binary C 3 H 6 /C 3 H 8 separation performance of the MMMs showed much higher separation factors than conventionally prepared MMMs at similar filler loadings, satisfying the commercial C 3 H 6 /C 3 H 8 separation performance criteria. PMMOF was successfully applied for other MOFs, demonstrating that the process could be general. Finally, as a proof of concept, asymmetric mixed-matrix hollow fiber membranes (i.d. of 0.45 mm and o.d. of 0.63 mm) with ultrathin selective skin layers were prepared by PMMOF, showing C 3 H 6 permeance of 2.17 GPU and C 3 H 6 /C 3 H 8 separation factor of ∼20.

Mechanochemically synthesized ZIF‐8 nanoparticles blended into 6FDA‐TrMPD membranes for C3H6/C3H8 separation

“…Separation performance comparison of 20 wt% mechano‐synthesized ZIF‐8 MMM (M1) and 20 wt% solvothermal‐synthesized ZIF‐8 MMMs in literatures 3,26,28,29,40–43 . The upper bound line indicates the results obtained by Koros et al 25 …”

“…Figure 8 shows the C 3 H 6 /C 3 H 8 separation performance of 20 wt% ZIF‐8 filled MMMs in literatures 3,26,28,29,40–43 . The detail values were summarized in Table S1 as well as the synthesis condition of ZIF‐8.…”

“…Figure 8 shows the C 3 H 6 /C 3 H 8 separation performance of 20 wt% ZIF-8 filled MMMs in literatures. 3,26,28,29,[40][41][42][43] The detail values were summarized in Table S1 as well as the synthesis condition of ZIF-8. The M1 membrane using mechano-synthesized ZIF-8 provides a medium separation performance among these MMMs.…”

“…A new paradigm of ZIF-8/6FDA-TrMPD MMMs fabrication based on solvothermal synthesis was presented by Jeong et al, named as polymer modificationenabled in-situ MOF formation (PMMOF). 28 The method enhanced the C 3 H 6 /C 3 H 8 ideal selectivity of the neat membrane by 230% with loading 26 wt% ZIF-8. The separation performance of the MMMs was further improved by in-situ linker doping.…”

“…The C 3 H 6 permeability and C 3 H 6 /C 3 H 8 ideal selectivity of a 48 wt% ZIF‐8/6FDA‐TrMPD membrane were 258% and 150% higher than those of the neat 6FDA‐TrMPD membrane. A new paradigm of ZIF‐8/6FDA‐TrMPD MMMs fabrication based on solvothermal synthesis was presented by Jeong et al, named as polymer modification‐enabled in‐situ MOF formation (PMMOF) 28 . The method enhanced the C 3 H 6 /C 3 H 8 ideal selectivity of the neat membrane by 230% with loading 26 wt% ZIF‐8.…”