Investigations into the temperature dependence of the adsorption enthalpy

• Applicant: Dr.-Ing. Christian Bläker
• Subject Area: Chemical and Thermal Process Engineering
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 544961101

Adsorption is an exothermal process in which adsorption heat is released. Fixed-bed adsorbers are quasi-adiabatic systems due to their small surface-to-volume ratio, so that the time of the breakthrough and the shape of the breakthrough curves are strongly influenced by caloric effects. A pronounced temperature dependence of the heat of adsorption is critical, since the temperatures of adsorption and desorption differ significantly, especially in TSA processes (Temperature Swing Adsorption), and the heat of adsorption influences the respective process steps in different ways. In science, instead of the process variable adsorption heat, the state variable adsorption enthalpy is often considered; both can be converted directly into each other. Within the framework of the proposed project, the temperature dependence of the load-dependent adsorption enthalpy for different adsorbent-adsorptive systems will be quantified for the first time. The adsorption enthalpy is measured by adsorption calorimetry for different temperatures and, in addition, it is calculated in analogy to the Clausius-Clapeyron method using the isosteric method, which assumes that the adsorption enthalpy is temperature independent. The systematic comparison of both methods allows for the first time to quantify the influence of a temperature dependence of the adsorption enthalpy on the prediction accuracy of the isosteric method. Since the enthalpy of adsorption is a measure of the strength of interactions, the influence of temperature on the various interaction mechanisms between adsorptive and adsorbent surface will also be analyzed. These findings should lead to a heuristic set of rules that can be used to estimate for which systems or which types of interactions temperature independence exists and the isosteric method is usable, and for which systems calorimetric measurements of the adsorption enthalpy are necessary. For temperature-dependent systems, an empirical model approach based on physical analogies will be developed to estimate the temperature dependence of the load-dependent adsorption enthalpy. Finally, the adsorption entropy will be calculated using the calorimetrically measured adsorption enthalpy and the Gibbs energy. The mutual influence of the order state (entropy) and the strength of the interactions (enthalpy) will be discussed. The comparison makes it possible to check whether the enthalpic or the entropic contribution is more temperature-dependent and whether the temperature dependence of the load dominates. Comparable studies have not yet been found in the literature.

• DFG Programme: Research Grants