(527d) Determination of Optimal Hot Purge Gas Temperature in Regenerating Thermally an Air-Drying Zeolite 13X Column By Equilibrium Theory Analysis

Air-drying TSA processes have been widely commercialized for reducing air humidity down to ppb levels, producing a dry air suitable for production of engineering plastics and food. In designing such a cyclic adsorption process driven by temperature swing, it is crucial to find optimal regeneration temperature, so that the adsorbents can be regenerated fully for the next adsorption run and simultaneously the time taken for regeneration has to be short enough for good bed productivity.

In this study, the regeneration temperature was optimized by Equilibrium Theory. The theoretical breakthrough curves and their temperature profiles were constructed by the hodography in which a Toth isotherm was taken as equilibrium isotherm [1]. Interestingly, the breakthrough curves constructed by Equilibrium Theory exhibited different trends at varying regeneration temperatures. Its initial part always consists of two plateaus connected by a shock. The second plateau is followed by a simple wave at a low regeneration temperature. With increasing regeneration temperature, however, a shock wave appears and evolves in the middle of the trailing wave. This interesting results indicates that the regeneration temperature must be sufficiently high so that the shock wave could be large enough to reach below the targeted dew point of the dry air.

It was also investigated the effect of capillary condensation on the breakthrough curve. To this end, Aranovich-Donohue isotherm [2] was taken for equilibrium isotherm of water vapour on zeolite 13X. Incorporating the Type II isotherm into the governing equations made the second plateau elongated in time, but did not affect much the rest of the trailing curve.

Full numerical simulations of the thermal regeneration breakthroughs were also carried out. Their results were coherent with the experimental data measured earlier by the author at three different regeneration temperatures (423K, 473K and 523K) [3]

[1] Wang, Y. and LeVan, M.D., Adsorption Equilibrium of Binary Mixtures of Carbon Dioxide and Water Vapor on Zeolite 5A and 13X, J. Chem. Eng. Data, 2010, 55, 3189.

[2] Kim, K.-M., Oh, H.-T., Lim, S.-J., Ho., K., Park, Y., Lee, C.-H., Adsorption Equilibria of Water Vapor on Zeolite 3A, Zeolite 13X, and Dealuminated Y Zeolite, J. Chem. Eng. Data, 2016, 61, 1547, 2016

[2] Ahn, H. and Lee, C.-H., Effects of Capillary Condensation on Adsorption and Thermal Desorption Dynamics of Water in Zeolite 13X and Layered Beds, Chem. Eng. Sci., 2004, 59(13), 2727.