The sorption dynamics of propane, i-butane and neopentane in carbon nanotubes

Carbon nanotube (CNT) was prepared by the catalytic vapor deposition (CVD) method. Various procedures were applied to get nanotubes in pure and well-defined form. The sorption kinetics of C-3-C-5 methyl methanes was studied in the CNT samples taking advantage of the unique potentials of the frequency response (FR) technique. Applying a batch-type FR system rate spectra were recorded in the 0.001-10 Hz frequency range. The temperature and the mean pressure of the measurements were varied in the -20 to 100 degrees C and the 60 to 600 Pa range, respectively. Over a CNT sample similar FR spectra were recorded for the sorption of the alkanes, different in molecular size and shape. Results suggested two parallel sorption processes, characterized by different sorption capacities and time constants. The processes were assigned to sorption on the convex and concave surfaces of the carbon tubes. On tube surfaces, having large number of structural defects and oxygen-containing functional groups, the sorption rate was found to be governed by the rate of diffusion.