(454a) Diffusion Measurements Using a Volumetric Differential Pressure Apparatus

In this work we present the first adsorption kinetic experiments carried out on an innovative differential volumetric system we have recently designed and built. The system is equipped with a differential and an absolute pressure transducer as well as thermocouples to measure the temperature of the dosing and the uptake cells, including the direct measurement of the sample temperature. Differently from conventional single-branch volumetric systems, in the case of differential systems, the methodology is based on following the differential pressure between two symmetric branches (namely, sample and reference) as the gas expands from the dosing to the uptake volumes.

Double-branch volumetric systems present some key advantages compared to conventional single-branch ones. The use of the differential pressure (as opposed to absolute) significantly improves the quality of the transient pressure signal allowing high accuracy kinetic measurements over the entire range of absolute pressure available. Despite these advantages, these type of volumetric apparatuses are not very common and limited literature is currently available. This is particularly true regarding the use of volumetric differential apparatuses for the measurements of adsorption kinetics for which, at the knowledge of the authors, no kinetic data are available in the literature.

Here we present the methodology to use the apparatus for accurate kinetic measurements over a wide range of pressures. The kinetic model developed for the conventional volumetric systems has been adapted to the new configuration to take into account the use of the differential pressure and possible asymmetries of the system.

To validate both the system and model we have carried out experiments on commercial adsorbents used for air separation using different gases in a range of experimental conditions to determine the capabilities (and the limits) of the technique for the measurements of adsorption transport kinetics.