Development of dynamic column breakthrough for multicomponent adsorption equilibrium and diffusion
Creators: Wilkins, Nicholas S.
Publisher: name: University of Alberta Library
Year: 2022

<p>Pressure and temperature swing adsorption processes are increasingly being designed and optimized computationally. The reliability of these predictions are highly dependent on the quality of the experimental equilibrium and kinetic data used in these simulations. Consistent experimental methodology is fundamental to obtain accurate data. The main aims of this thesis are to provide multicomponent adsorption equilibrium and kinetic data on various adsorbents, to provide recommendations to improve experimental methodology, and finally to use this data for pressure swing adsorption design and optimization. Dynamic column breakthrough is extensively studied in this thesis. This method involves a column packed with an adsorbent of interest that can measure multicomponent equilibrium and kinetics, as well as column dynamics. This thesis examines all three of these aspects in dynamic column breakthrough. A few highlights are described below.</p>

<p>The equilibrium loading of each species in a multicomponent mixture can be calculated from a dynamic column breakthrough experiment. This is most commonly done with a ternary gas mixture for a binary equilibrium measurement: the column is initialized with an inert gas (such as helium), and then replaced with a binary mixture of adsorbates. After the experiment is finished, a transient mass balance can be solved to yield an equilibrium loading for each species in the mixture. However, a ternary adsorption breakthrough experiment (two adsorbates and one inert) on a highly selectively system, will often yield erroneous equilibrium data for the weaker component. This is in part due to the measurement of effluent flow, and part due to the long experimental times that accumulate error in the transient mass balance. It was found that a desorption breakthrough experiment, performed after a desired multicomponent adsorption experiment, yielded more accurate data with less associated error for the weaker species. This is due to the relatively short experimental time for the weaker component to desorb, minimizing the accumulation of error in the mass balance. The stronger component can be calculated from the adsorption breakthrough experiment. The combined elution profile yields the binary equilibrium data at a given composition, temperature and total pressure. The error associated with the adsorption mass balance of the weaker component can also be bypassed by performing true binary experiments without an inert (only the two adsorbates of interest). These experiments are performed by saturating the column with one adsorbate of interest, and then performing an adsorption breakthrough experiment with a binary mixed-adsorbate system. This methodology still requires two sets of experiments to obtain a single binary pairing, but avoids error due to roll-up.</p>

<p>Dynamic column breakthrough is usually performed with tens to hundreds of grams of adsorbent. This sample size creates a large signal change in the effluent mole flow measurement, reduces loading variation from heterogeneous samples, and minimizes effects due to the extra-column volume. However, nothing in the transient mass balance excludes measurement on milligram sized samples. This thesis provides recommendations to build a milligram-scale dynamic column breakthrough apparatus to obtain accurate and precise unary and binary equilibrium data.  While some aspects of milligram-scale experimentation are complicated, overall the milligram-scale operation offered many more benefits. These included shorter experimental times, near-isothermal operation, a much simpler effluent flow calibration, as well as being able to test as-synthesized and crystalline adsorbents. This apparatus was tested with mixtures of dry gases on various adsorbent materials. This thesis provides quantitative data for unary and binary adsorption equilibrium, and qualitative trends for multicomponent kinetics, from dynamic column breakthrough experiments on milligram quantities of adsorbent.</p>