Equilibrium and transient sorption of vapours and gases in the polymer of intrinsic microporosity PIM-1

Abstract

The gravimetric sorption technique was used for the study of equilibrium and transient sorption of various groups of vapours (alcohols, hydrocarbons, water) and gases (methane, nitrogen, oxygen, carbon dioxide) in the polymer of intrinsic microporosity PIM-1 at 25°C. Sorption isotherms of all compounds, except gases and water, exhibited S-shaped character, while the isotherms of gases are linear or concave over the inspected pressure region. Sorption isotherms of vapours were quantitatively parameterized with the Guggenheim, Anderson and de Boer (GAB) layered-adsorption model, which provided a comparable approximation of the data on carbon dioxide as the dual mode sorption model. Abnormally fast kinetics of transient sorption (superdiffusion) was observed in the region of diluted and saturated vapours of all measured compounds, except water, n-butane and carbon dioxide. The anomalous sorption kinetics was well parameterized with the convective–diffusion model. The anomalous nature of the mass transport in PIM-1 is also demonstrated by distinct trends for gases, alkanes and alcohol vapours in the correlations of diffusion coefficients with penetrant molecular volume and solubility coefficients with the square of critical temperature. The results obtained in this work indicate the occurrence of a transport mode that has a different nature than the classically employed solution-diffusion model.