Adsorptive Separation of Geometric Isomers of 2-Butene on Gallate-Based Metal-Organic Frameworks.

The separation of mixed C olefins is a highly energy-intensive operation in the chemical industry due to the close boiling points of the unsaturated C isomers. In particular, the separation of /-2-butene is among the most challenging separation processes for geometric isomers and is of prime importance to increase the added value of C olefins. In this work, we report a series of isostructural gallate-based metal-organic frameworks (MOFs), namely, M-gallate (M = Ni, Mg, Co), featuring oval-shaped pores, that are ideally suitable for shape-selective separation of /-2-butene through their differentiation in minimum molecular cross-section size. Significantly, Mg-gallate displays a record high /-2-butene uptake selectivity of 3.19 at 298 K, 1.0 bar in single-component adsorption isotherms. These gallate-based MOFs not only exhibit the highest selectivity for /-2-butene separation but also accomplish a highly efficient separation of 1,3-butadiene, 1-butene, and -butene. DFT-D study shows that Mg-gallate interacts strongly with -2-butene and 1,3-butadiene along with short distances of C···H-O cooperative supramolecular interaction of 2.57-2.83 and 2.45-2.79 Å, respectively. In breakthrough experiments, Mg-gallate not only displays prominent separation performance for /-2-butene but also realizes the clean separation of a ternary mixture of 1,3-butadiene/1-butene/-butene and a binary mixture of 1-butene/-butene. This work indicates that M-gallate are industrially promising materials for adsorption separation of geometric isomers of C hydrocarbons.