Experimental characterization of silica gel adsorption and desorption isotherms under varying temperature and relative humidity in a fixed bed reactor

In the context of energy and the environment and considering the increasing energy demand in industrial processes and for thermal comfort, enhancing system performance and optimizing operations are essential. This paper presents a comprehensive analysis of the adsorption -desorption isotherms of silica gels, which are widely used desiccant materials. Accurate characterization of the adsorption and desorption behaviors is pivotal for assessing their performance across various applications. In this study, we examined multiple isothermal equations describing the interaction between silica gel and water vapor. Our findings highlight the critical importance of the adsorption capacity at low temperatures, as confirmed by experimental results from a climatic wind tunnel. The experimental results indicate that the isosteric heat of adsorption (ΔH_ads) decreases with increasing moisture content, suggesting a progressive reduction in the energy required for water uptake as adsorption progresses. Furthermore, we demonstrate that the adsorption and desorption isotherms follow distinct paths, highlighting a divergence from hypothetical models. Two empirical correlations linking water content to temperature and relative humidity for both adsorption and desorption processes were developed, showing good agreement with experimental results compared to existing correlations in the literature and illustrating the gap between theoretical and experimental findings. This research enhances our understanding of the adsorption properties of silica gel and provides the groundwork for its effective application in areas such as atmospheric water generation and air conditioning systems, among others.