Th-MOF showing six-fold imide-sealed pockets for middle-size-separation of propane from natural gas

Separation of propane from natural gas is of great importance to industry. However, in light of size-based separation, there still lacks effective method to directly separate propane from natural gas, due to the comparable physical properties for these light alkanes (C1–C4) and the middle size of propane. In this work, we found that a new Th-metal-organic framework (MOF) could be an ideal solution for this issue. The Th-MOF takes UiO-66-type structure, but with the pocket sealed by six-fold imide groups; this not only precisely reduces the size of pocket to exactly match propane, but also enhances the host—guest interactions through multiple (C)H(^δ+)⋯(^δ−)O(C) interactions. As a result, highly selective adsorption of propane over methane, ethane, and butane was observed, implying unique middle-size separation. The actual separation was confirmed by breakthrough experiments of simulated natural gas, confirming its superior application in direct separation of propane from natural gas. The separation mechanism, as unveiled by both theoretical calculation and comparative experiments, is due to the six-fold imide-sealed pocket that could effectively distinguish propane from other light alkanes through both size effect and host—guest interactions.