Diffusion Kinetics of CO2, CH4, and their Binary Mixtures in Porous Organic Cage CC3

The sorption kinetics of single- and binary-component mixtures of CO2 and CH4 in porous organic cage (POC) CC3 was investigated by the zero-length column (ZLC) technique for the purpose of understanding the experimental diffusivity values of light gases through this novel branch of porous molecular solids. The intracrystalline diffusivities were measured at 25 °C, and a binary-gas ratio of 10/90 CO2/CH4 was utilized in order to mirror concentrations of CO2 and CH4 in natural gas. The diffusion time constants were measured and then compared in order to investigate the effects of coadsorption for binary-gas mixtures and were also compared against molecular simulation diffusion values that have been reported in other works. The diffusion time constants measured for CO2 for single- and binary-component trials were found to be 1.05 × 10–3 and 8.70 × 10–4 s–1, respectively, whereas for CH4, these measured values were estimated to be 1.10 × 10–3 and 1.03 × 10–3 s–1, respectively. Moreover, the diffusion of CO2 revealed the presence of surface resistances due to adsorbent pore window size limitations that hinder the transport of CO2 molecules upon diffusion. The findings of this study provide novel experimental kinetic characterizations of the sorption kinetics of CO2 and CH4 through CC3 for the separation of CO2 from natural gas.