(205b) Characterizing Mass Transfer Properties in Porous Materials with Transient Data

Obtaining adsorption equilibria and kinetic data in porous materials is imperative for the proper design of adsorption units. Generating the equilibria information is relatively simple; whereas, kinetic measurements face experimental challenges such as eliminating heat and mass transfer impact. Additionally, these measurements are affected by the accuracy of mathematical model used to obtain the mass transfer parameters. The macroscopic methods used in mass transfer studies consist of measuring either the uptake into or release from the material. Subsequently, the experimental data is matched with an appropriate mass transfer model to extract the kinetic parameters. Consequently, the accuracy of kinetic parameter obtained strongly depends on how well the model resembles the experimental conditions. Gravimetric methods are commonly used and consist of recording the weight gain (or loss) in a sample as a function of time. For such methods, it is typically desirable to have a step change in pressure or concentration. A sudden increase in pressure, however, may cause the weight balance to oscillate. Moreover, the conventional method omits a significant amount of data measured before the pressure stabilizes, and hence is unable to utilize the information during the transient period which can be is critical for materials with complex pore structure.

A new methodology that represents an improved experimental design has been developed. It makes use of the entire dataset including the transient data. The method is based on a mathematical model that mimics the transient experimental conditions. More accurate determination of the kinetic parameters is thus possible. For complex materials, additional insights into the mass transfer behavior can be determined. The new method and its applications to several materials including activated carbon, zeolite, and shale rock are presented.