(84c) A Vacuum Set-up for Fundamental Studies of Self- and Transport Diffusion in Porous Media

Authors: 
Yu, H., University College London
Coppens, M. O., University College London

The diffusion of gas molecules in porous media involves molecular interactions between gas molecules and the collisions between gas molecules and the pore walls [1]. The physics of diffusion in disordered nanoporous media have attracted a lot of attention, due to applications in many industrial processes involving heterogeneous catalysis, separations, and controlled molecular delivery and uptake [2,3]. This project is focusing on the fundamental study of gaseous diffusion in heterogeneous porous media in the Knudsen regime, where the mean free path of the molecules is much larger than the pore diameter, so that molecule-wall collisions dominate molecular transport.

Usual studies of diffusion in disordered porous media obfuscate effects on the pore scale, as pore network effects influence the overall diffusion. To gain more insight into to effects of geometry on diffusion in the Knudsen regime at the level of individual pores, measurements are performed in a high-vacuum system. The experiments emulate what is happening in disordered nanoporous media on a macroscopic scale, by using a high-vacuum system and 3D-printed channels to investigate features of complex porous media, such as fractal pores [4]. This set-up allows us to validate Knudsen diffusion theory in complex geometries more directly than has ever been the case. Some preliminary results will be shared, including features of the set-up itself, and first results from studies on Knudsen diffusion.

REFERENCES

  1. Millington, R., Gas diffusion in porous media. Science, 1959. 130(3367): p. 100-102.
  2. Malek, K. and M.-O. Coppens, Knudsen self- and Fickian diffusion in rough nanoporous media. The Journal of Chemical Physics, 2003. 119(5): p. 2801-2811.
  3. Sahimi, M., G.R. Gavalas, and T.T. Tsotsis, Statistical and continuum models of fluid-solid reactions in porous media. Chemical Engineering Science, 1990. 45(6): p. 1443-1502.
  4. Coppens, M.-O., The effect of fractal surface roughness on diffusion and reaction in porous catalysts – from fundamentals to practical applications. Catalysis Today, 1999. 53(2): p. 225-243.