(219f) Measurement of Water Adsorption Kinetics Using the Zero Length Column

In this contribution a zero length column (ZLC) system is adapted to run experiments with water at high relative humidity (>75%) and the results are interpreted to determine the kinetics of adsorption for a mesoporous material.

Results for an SBA-15 sample show that to in order achieve equilibrium conditions very low flowrates are needed in the hysteresis region. As the flowrate is increased progressively kinetic limitations become dominant, but the mass transfer mechanism is complex. In order to interpret the experimental results it is first necessary to correlate the equilibrium curve with an appropriate analytical isotherm. This information allows to determine from the experimental ZLC curves the apparent linear driving force (LDF) constant at different adsorbed phase concentrations. The experimental results, show that this apparent LDF constant is dependent on flowrate and therefore cannot be used to represent the system accurately. A diffusion model is introduced with a concentration dependent diffusivity and this is shown to provide a good match to the observed kinetic responses, without the need to introduce additional parameters.

The kinetic experiments have been carried out with different sample masses, and the talk will also cover how to interpret correctly the response of smaller sample masses, where the correction for the blank becomes increasingly important. A signal deconvolution approach is shown to correctly transform the signal from the detector to the water concentration in the vapor phase.