Fixed Feed Temperature-Programmed Modulation—A Quantitative Method To Obtain Thermophysical Parameters: Application to Chemical Warfare Agent Adsorbents

Assessing the interaction between an adsorbate and a surface is essential for optimal engineering and design of adsorbents. For low-vapor-pressure adsorbates, which also exhibit relatively weak adsorption behavior (physisorption), both the sample and the system (manifolding, reactor, etc.) demonstrate similar affinities for the probe molecule. To minimize errors, researchers often use large sample masses, which are not often convenient to obtain, particularly for new lab-generated materials. To circumvent this issue, we demonstrate an approach where we fix the thermodynamic state of the system, and then thermally perturb a small sample under fixed feed conditions, thus eliminating the impact of the system response. By varying the thermal modulation rate, various regimes for analyzing adsorption, desorption, and reactions are possible, which enables the extraction of thermophyiscal parameters. In this paper, we first validate the fixed feed temperature-programmed modulation (FFTPM) method against a common adsorbate/adsorbent (methanol/BPL carbon) and then extend the technique to dimethyl methyl phosphonate (DMMP)/carbon systems. We demonstrate the utility of such an approach for quantitatively assessing adsorption capacities, differential heats of adsorption, isosteric heats of adsorption, and adsorption kinetics parameter estimation for DMMP on carbon adsorbents. The FFTPM method is well-suited for rapidly screening and characterizing adsorbents, reactive sorbents, and other systems which exhibit physisorption phenomena.