Effect of Zeolitic Imidazolate Framework Topology on the Purification of Hydrogen from Coke Oven Gas

This work aims to shed light on the performance of zeolitic imidazolate frameworks for hydrogen purification from coke oven gases (COG). Using molecular simulation, we model COG as a mixture of six gases and study the effect of ZIF topology on the separation performance. To do this, we compare similar structures, e.g., ZIF-8 and ZIF-11, and focus on obtaining information that explains why they behave differently while being so similar. Simulation results show that the structure with the smallest pore size best separates hydrogen from carbon monoxide and nonpolar molecules. The adsorption of carbon dioxide is also strongly affected by the polarizability of the structure. However, the adsorption of the other components (methane, carbon monoxide, nitrogen, and oxygen) is strongly dependent on their pore size. We also provide molecular information on the effect of phase transition on hydrogen purification using ZIF-7 as an example, which drastically changes the pore volume of the structure when it changes phase. These findings will help to select high-performance ZIFs for adsorption- or screening-based hydrogen purification.