Hybrid super-porous hydrogel composites with high water vapor adsorption capacity – Adsorption isotherm and kinetics studies

Water vapors adsorption capacity of deliquescent salts is very high, but they dissolve in the adsorbed water by forming crystalline hydrates which restricts their use in different water vapor adsorption applications. This limitation can be overcome by incorporating deliquescent salts within a polymer matrix which will keep the salt solution in place. Furthermore, if the polymer matrix used is also capable of adsorbing water vapor, it will further improve the overall performance of desiccant systems. Therefore, in this work, we are proposing the synthesis and use of a highly effective new solid polymer desiccant material, i.e. superporous hydrogel (SPHs) of sodium acrylate and acrylic acid P(SA+AA), and subsequently its composite with deliquescent salt, i.e. calcium chloride (CaCl₂), for the adsorption of water vapors from humid air without the dissolution of deliquescent salt in the adsorbed water. Synthesized SPH composite was characterized using different techniques like scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). Parental P(SA+AA)-SPHs matrix alone exhibited the adsorption capacity of 1.02 g_w/g_ads which increased to 3.35 g_w/g_ads after incorporating CaCl₂ salt in the polymer matrix. For both materials, experimental isotherm data agreed with Guggenheim, Anderson and Boer (GAB) isotherm model and exhibited type-III adsorption isotherm. The adsorption kinetics followed linear driving force model. Furthermore, adsorbents were used successively for ten cycles of adsorption and regeneration. Therefore, the proposed polymer desiccant material overcomes the problem of dissolution of deliquescent salts and purposes a new class of highly effective solid desiccant material.