A unified kinetic model for adsorption and desorption – Applied to water on zeolite

• A kinetic model for reversible adsorption and desorption processes under non-isothermal conditions is deduced.
• The formulation with partial differential equations is adaptable to the geometry of the adsorbent.
• The model is applied to zeolite 3A.
• A unified sorption model is introduced.

A kinetic model for reversible adsorption and desorption processes under non-isothermal conditions based on reaction kinetics is deduced. This is done by explicit temperature dependence of all equations of the model. However in the performed experiments the coupling with the thermal bath was strong enough to neglect thermal conductivity and set the temperature as a timely-varying and spacial-constant parameter. Furthermore adsorption- and desorption-mechanisms of higher order and diffusion are considered. The formulation with partial differential equations is adaptable to the geometry of the adsorbent. To solve the system of coupled differential equations numerical methods of Wolfram Mathematica® are used. This model is applied to water on zeolite 3A. Beside the non-isothermal thermogravimetric analysis and the differential scanning calorimetry an isothermal experiment for the time-dependent measurement of the adsorption is used to evaluate the model. The sorption isotherms of a commercial zeolite manufacturer serve as a further source of comparison. The parameters are fitted numerically with the χ2χ2 -method to the experimental data. As a result of this paper a unified sorption model is introduced.

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