Monitoring Transient Sorption of Hexane Isomer Mixtures in a Large ZSM-5 Single Crystal via Infrared Microimaging

Infrared (IR) microimaging is employed for selectively recording two-dimensional plots of the individual distributions of the components n-hexane (nC6) and 3-methylpentane (3MP) over a single crystal of zeolite ZSM-5 during mixture adsorption. At a pressure change from 0 to 0.02 mbar, the scenario of “overshooting” is observed, with the concentration of nC6 temporarily exceeding its equilibrium value. After the next pressure step from 0.02 to 2 mbar, 3MP is progressively driven out of the pores, in parallel with an increase in nC6 concentration. The IR microimaging results are corroborated by grand canonical Monte Carlo simulations, which help explain the peculiarities of mass transfer by providing visual representations of the distribution and packing densities of the guest molecules in the pores.