Determination of adsorption and desorption isotherms of zeolite LTA(4A) using the gravimetric method

Poós, Tibor (2025) Determination of adsorption and desorption isotherms of zeolite LTA(4A) using the gravimetric method. In: 9th European Drying Conference, EuroDrying 2025, 2025.07.06-2025.07.09, Wageningen.

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Abstract

The moisture adsorption and desorption behavior of porous materials is significantly influenced by the size and shape of their pore structure. A sorption isotherm graphically represents the equilibrium moisture content of a material as a function of the equilibrium relative humidity of the surrounding air (or water activity in the case of food materials) at a constant temperature. In this study, the adsorption and desorption isotherms of Zeolite LTA (4A) granular material were determined at 30°C, 40°C, 50°C, and 60°C using a gravimetric measurement system. The obtained sorption isotherms exhibited S-shaped (sigmoidal) curves, characteristic of multilayer sorption mechanisms. The minor hysteresis loop indicates that the adsorption and desorption processes are governed by different physicochemical mechanisms, which can be attributed to the heterogeneity of the pore structure. Various model equations, including modified BET, mod. Chung-Pfost, mod. GAB, mod. Halsey, mod. Henderson, and mod. Oswin models, were fitted to the experimental data using non-linear regression analysis. The mod. GAB model demonstrated the best fit to the measured data, while all models, except for the mod. BET, provided satisfactory correlations (R²>0.85). Furthermore, the isosteric heat of adsorption and desorption of the investigated material was determined, quantifying the heat absorbed during adsorption equilibrium and the heat released during desorption equilibrium. Our findings contribute to the optimization of zeolite applications in industrial moisture control and drying processes.

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