(292d) Diffusion Of Solvent Vapors In Nanoporous Adsorbents: Single Particle Studies Using Concentration Swing Frequency Response

A new frequency response method using concentration variation has been extended to investigate diffusion of solvent vapors in nanoporous adsorbents. The method is based on periodically time-varying species feed concentrations with a constant total molar inlet flow rate. A single particle with a mass of 1 to 4 milligrams is used to study the vapor diffusion rates in the adsorbents. The method requires only a small amount of adsorbent, which is advantageous for new materials development. For analysis, a mathematical model is formulated considering nanopore diffusion, surface barrier resistance, external film resistance, and axial dispersion.

The system was used to examine the diffusion of water in silica gel and hexane in activated carbon. The water vapor diffusion mechanism is described by the linear driving force model, but the hexane vapor is controlled by nanopore diffusion. The diffusion rates for different concentrations have been measured to study the concentration dependence. The examples considered show that the novel concentration-swing frequency response apparatus is capable of accurately measuring mass transfer rates for adsorption of vapors.