Nonlinear 3D Ligand-Based Metal–Organic Framework for Thermodynamic–Kinetic Synergistic Splitting of Mono-/Dibranched Hexane Isomers
Jingyi Zhou, Kuishan Wen, Ke Tian, Jinjian Li, Yuanyuan Jin, Jing Li, Zhiguo Zhang, Zongbi Bao, Qilong Ren, Qiwei Yang
Abstract
The selective splitting of hexane isomers without the use of energy-intensive phase-change processes is essential for the low-carbon production of clean fuels and also very challenging. Here, we demonstrate a strategy to achieve a complete splitting of the high-RON dibranched isomer from the monobranched and linear isomers, by using a nonlinear 3D ligand to form pillar-layered MOFs with delicate pore architecture and chemistry. Compared with its isoreticular MOFs with the same ted pillar but different linear 3D or linear 2D in-layer ligands, the new MOF constructed in this work, Cu(bhdc)(ted) 0.5 (ZUL-C5), exhibited an interesting “channel switch” effect which creates pore space with reduced window size and channel dimensionality together with unevenly distributed alkyl-rich adsorption sites, contributing to a greatly enhanced ability to discriminate between mono- and dibranched isomers. Evidenced by a series of studies including adsorption equilibrium/kinetics/breakthrough tests, guest-loaded single-crystal/powder XRD measurement, and DFT-D modeling, a thermodynamic–kinetic synergistic mechanism in the separation was proposed, resulting in a record production time for high-purity 2,2-dimethylbutane along with a high yield.