Geometry control of adsorption sites in sulfonate-pillared hybrid ultramicroporous materials for efficient C4 olefin separations

Abstract

Efficient isolation of C4 olefins is of paramount importance in petrochemical industry yet a challenging task mainly realized via heat-driven processes owing to their similar physical properties. Herein, sulfonate anion-pillared hybrid ultramicroporous materials (HUMs), namely TMOF-1 and ZU-619 (BDS-1-Cu-i) were reported for the first time for the efficient separation of ternary C4 olefin mixtures (C4H6/n-C4H8/iso-C4H8). The geometry of adsorption sites was judiciously controlled via tuning the interpenetration direction of sulfonate anions through varying the length of anions. Interestingly, ethanedisulfonate anions in TMOF-1 exhibit the vertically interpenetrated direction, leading to TMOF-1 with pore size of 4.5 Å to exclude iso-C4H8. Furthermore, the vertical interpenetration makes the adjacent anions behave as synergetic adsorption sites for n-C4H8 and C4H6 trapping, thus endowing TMOF-1 with strong host–guest interactions and the benchmark Henry coefficient separation selectivities for C4H6/iso-C4H8 (519.2) and n-C4H8/iso-C4H8 (93.2) mixtures. In contrast, ZU-619 with butanedisulfonate anions as pillars exhibits normal interpenetration framework, giving rise to the anion-restricted pore size of 9.4 Å. This large pore size results in ZU-619 with weak host–guest interactions for C4 olefins through one sulfate anion. The specific host–guest interaction modes were unveiled by molecular simulations, presenting the efficiency of binding site geometry control for gas separation. The separation efficiency was confirmed by breakthrough experiments, the results presented that TMOF-1 showed excellent separation performances for C4H6/n-C4H8/iso-C4H8 mixtures and ZU-619 can be a good candidate for C4H6/n-C4H8 separation.